Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
lZ1~2t;
MULTICOLOR PHOTOGRAPHIC ELEMENTS CONTAINI~G
SILVER IODIDE GRAINS
Field of thD Invention
The invention relates to silver halide
photographic elements capable of producing multi-
color images and to processes for their use.
Background of the Invention
Kofron et al Canadian Patent 1,175,698,
titled SENSITIZED HIGH ASPECT RATIO SILVER HALIDE
EMULSIONS AN~ PHOTOGRAPHIC ELEMENTS, commonly
assigned, discloses multicolor photographic elements
in which at least one of the blue, green, and red
recording emulsion layers is comprised of a dispers-
ing medium and silver halide grains, wherein at
least 50 percent of the total projected area of the
silver halide grains is provided by chemically and
spectrally sensitized tabular silver halide grains
having a thickness of less than 0.3 micron, a
diameter of at least ~.6 micron, and an average
aspect ratio of greater than ~:1. Kofron et al
specifically discloses the use of high aspect ratio
tabular grain emulsions in which the tPbular grains
are comprised of silver bromoiodide (iodide being
limited by its solubility in silver bromide to about
40 mole percent), silver bromide, silver chloride,
silver chloride containing minor amounts of bromide
and/or iodide, and silver chlorobromide. (Except as
otherwise indicated, all references to halide
percentages are based on silver present in the
corresponding emulsion, grain, or grain region being
discussed; e.g., a grain consisting of silver
bromoiodide containing 40 mole percent iodide also
contains 60 mole percent bromide.) Kofron et al
; contains no disclosure of high aspect ratio tabular
grain silver iodide emulsions, and, because of the
rarity with which silver iodide emulsions are
employed in muiticolor photographic elements,
~2~6Z6
bases its teachings on the properties of the silver
halides more commonly employed in multicolor
photography. For example, Kofron et al teaches
increasing the permissible maximum thickness of the
tabular grains from 0.3 micron to 0.5 micron to
increase blue light absorption, recognizing that the
thicker tabular grains are better able to assist the
blue spectral sensitizing dyes in absorbing blue
light. Further, Kofron et al discusses multicolor
photographic elements in which high aspect ratio
tabular grain blue recording emulsion layers overlie
minus blue (green and/or red) recording emulsion
layers and discuæses the effects of blue light
reaching these minus blue recording emulsion
layers. Jones and Hill Canadian Patent 1,174,885,
titled PHOTOGRAPHIC IMAGE TRANSFER FILM UNIT,
commonly assigned, is essentially cumulative in its
teachings, but is directed specifically to image
transfer film units. Maskasky Canadian Patent
1,175,278, titled CONTROLLED SITE EPITAXI~L SENS~TI-
ZATION, commonly assigned is essentially cumulPtive
; in its teachlngs, but is directed specifically to
the sensitization of high aspect ratio tabular
grains by silver salt epitaxy.
Radiation-sensitive silver iodide emul-
sion~, though infrequently employed in photography,
are known in the art. Silver halide emulsions which
employ grains containing silver iodide as a separate
and distinct phase are illustrated by Steigmann
German Patent 505,012, issued August 12, 1930;
Steigmann, Photographische Industrie, "Green- and
Brown-Developing Emulsions", Vol. 34, pp. 764, 766,
and 872, published July 8 and August 5, 1938;
Maskasky U.S. Patents 4,094,6~4 and 4,142,900; and
Koitabashi et al U.K. Patent Application 2,063,499A.
Maskasky Research Disclosure, Vol. 18153, May 1974,
12i~Z6
Item 18153~ reports silver iodide phosphate photo-
graphic emulsions in which silver i~ coprecipitated
with iodide and phosphate. A separate silver iodide
phase i6 not reported.
The crystal structure of silver iodide has
been ~tudied by crystallographers, particularly by
those interested in photography. As illustrated by
Byerley and Hirsch, "Dispergions of Metastable High
Temperature Cubic Silver Iodide", Journal of Photo-
10 ~raPhic Science, Vol. 18, 1970, pp. 53-59, it i~
generally recognized that silver iodide is capable
of existing in three different crystal forms. The
most commonly encountered form of silver iodide
crystals is the hexagonal wurtzite type, designated
15 3 phase silver lodide. Silver iodide is also stable
at room temperature in its face centered cubic
crystalline form, designated y phase silver
iodide. A third form of crystalline silver iodide,
stable only at temperatures above about 147C, is
20 the body centered cubic form, designated ~ phase
silver iodide. The B phase is the most stable form
of silver iodide.
James, The Theory of the Photographic
Process, 4th Ed., Macmillan, 1977, pp. 1 and 2,
25 contains the following summary of the knowledge of
the art:
According to the conclusions of Kokmei~er
and Van Hengel, which have been widely accepted,
more nearly cubic AgI is precipitated when
silver ions are in excess and more nearly
hexagonal AgI when iodide ions are in excess.
More recent measurements indicate that the
presence or absence of gelatin and the rate of
addition of the reactants have pronounced
effects on the amounts of cubic and hexagonal
A8I. Entirely hexagonal material was produced
only when gelatin was present and the solutions
~,~
21~Z6
were added slowly without an excess of either
A~ or+I~. No condition was found where
only cubic ma~erial was observed.
Tabular silver iodide crystals have been
observed. Preparations with an excess of iodide
ions, producing hexagonal crystal structures of
predominantly ~ phase silver iodide are reported by
Ozaki and Hachisu, "Photophoresis and Photo-
agglomeration of Plate-like Silver Iodide Parti-
cles", Science of Light, Vol. 19, No. 2, 1970, pp.59-71, and Zharkov, Dobroserdova, and Panfilova,
"Crystallization of Silver Halides in Photographic
Emulsions IV. Study by Electron Microscopy of Silver
Iodide Emulsions", Zh. Nauch. Prikl. Fot. Kine,
March-April, 1957, 2, pp. 102-105.
Daubendiek, "AgI Precipitations: Effects
of pAg on Crystal Growth(PB), III-23", Papers from
the 197~ International Congress of Photo~raphic
Science, Rochester, New York, pp. 140-143, 1~7~,
reports the formation of tabular silver iodide
grains during double-jet precipitations at a pAg of
1.5. Because of the excess of silver ions during
precipitation, it is believed that these tabular
grains were of face centered cubic crystal struc-
ture. However, the average aspect ratio of thegrains was low, being estimated at substantially
less than 5:1.
Maskasky Can. Serial No. 440,119, filed
concurrently herewith and co~monly assigned, titled
GAMMA PHASE SILVER IODIDE EMULSIONS, PHOTOGRAPHIC
ELEMENTS CONTAINING THESE EMULSIONS, AND PROCESSES
FOR THEIR USE, discloses the first high aspect ratio
tabular grain silver iodide emulsions in which the
grsins are of a face centered cubic crystal struc-
ture, as is characteristic of silver iodide.
Z6
Summary of the Invention
In one aspect this invention is directed toa photographic element capable of producing a
multicolor image comprised of a support and, located
5 on the support, superimposed emulsion layers for
facilitating separate recording of blue, green, and
red light, each comprised of a tispersing medium and
silver halide grains. The improvement comprises at
least 50 percent of the total pro~ected area of the
10 silver halide grains in at least one emulsion layer
being provided by thin tabular silver iodide grains
having a thickness of less than 0.3 micron and an
average aspect ratio of greater than 8:1.
In another aspect, the invention iB direct-
15 ed to protucing a visible photographic image byprocessing in an aqueous alkaline solution in the
presence of a developing agent an imagewise exposed
photographic element as described above.
The multicolor photographic elements of
20 this invention exhibit high efficiencies in the
absorption of blue light. They can display reduced
color contamination of minus blue (i.e., red and/or
green) records by blue light. The multicolor
photographic elements of this invention can elimi-
25 nate yellow filter layers without exhibiting color
contamination of the minus blue record. In addition
the multicolor elements of this invention can
exhibit improvements in image sharpness ant in
speed-grain relationships of the minus blue records.
Although the invention has been described
with reference to certain specific advanta~es, other
advantages will become apparent in the course of the
~ detailed description of preferred embodiments.
;~ Brief DescriPtion of the Drawings
Figures 1 through 6 are photomicrographs of high
aspect ratio tabular grain emulsions;
:`
:
, . ~
zla6z6
--6--
Figure 7 is a plot of speed versus ~ranularity;
and
Figures 8 and ~ are schematic diagrams related
to scattering.
Description of Preferred Embodiments
-
This invention is directed to photographic
elements capable of producing multicolor images and
to processes for their use~ The multicolor photo~
graphic elements of this invention each incorporate
at least one silver halide emulsion layer comprised
of u dispersing medium and silver halide grains. At
least 50 percent of the total projected area of the
silver halide grains in the blue recording emulsion
layer ~s provided by thin tabular grain6 having a
thickness of less than 0.3 micron and an average
aspect ratio of greater than 8:1. This emulsion
layer is preferably a blue recording emulsion layer
and is for convenience described below with
reference to this use.
In addition to at least one blue recording
emulsion layer as described above the multicolor
photographic elements additionally include at least
one green recording silver halide emulsion layer and
at least one red recording silver halide emulsion
layer. The multicolor photographic elements can
also optionally include one or more additional blue
recording emulsion layers. All of these additional
emulsion layers can be chosen from among conven-
tional multicolor photographic element emulsion
layers. In a preferred form at least one green
recording emulsion layer and at least one red
recording emulsion layer are also comprised of high
aspect ratio tabular grain emulsions. In certain
preferred forms of the invention all of the emulsion
layers can be comprised of high aspect ratio tabular
12iQ~2~
grain emulsions. Tabular silver iodide grsins
sstisfying the s~me general r~quirement~ as those of
the blue recording emulsion layer described above
can be present in any or all of these ~dditional
emul~ion layers, or high aspect ratio tabular grain
silver halide emulsions of other halide compositions
can be present in any or all of these ~dditional
emulsion layer6.
As appl~ed to the silver halide emulsions
of the present lnvention the texm "high aspect
ratio" i6 herein defined as requiring that the
silver halide grains having a thickness of less than
0.3 micron have an average aspect ratio of greater
than 8:1 and account for at lea6t 50 percent of the
totsl proJected area of the silver halide grsins.
The preferred higH aspect ratio tabular grain eilver
halide emulsions of the presen~ invention are those
wherein the ~ilver halide grains having a thicknes~
of less than 0.3 micron (optimally less than 0.2
micron) have an average aspect ratio of at least
12:1 and optimally at least 20:1.
It is appreciated that the thinner the
tabular grain~ accounting for a given percentage of
the pro~ected area, the higher the average aspect
2~ ratio of the emulgion. Individual tabular silver
iodide grains have been ob~erved having thickne~6es
slightly in excess of 0.005 micron, suggesting that
preparat~ons of tabular silver iodide grains accord-
ing to this invention having average thicknesses
down to that value or at lea~t 0.01 micron are
feasible. It is a di~tinct advantage of h~gh aspect
ratio tabulax silver iodide grains that they can be
prepsred at thicknesses less than high aspect ratlo
tabular grains of other halide compositions.
Minimum tabular 8rain thicknesses of 0.03 micron for
high aspect ratio tabular grain emulsions are
6~6
generally contemplated, these being particularly
readily achieved for silver bromide and ~ilver
bromoiodide tabular grain emulsions.
The grain characteri6tics described above
S of the high aspect ratio tabular grain emulsion6 can
be readily ascertained by procedures well known to
those skilled in the art. As employed herein the
term "aspect ratio" refers to the rstio of the
diameter of the grain to its thickness. The
"diameter" of the gra~n is in turn defined as the
diameter of a circle having an area equal to the
pro~ected area of the grain as viewed in a photo-
micrograph (or an electron microgrsph) of an emul-
sion sample. From shadowed electron microgr~ph~ of
emulsion ssmple6 it i8 possible to determlne the
thickness and diaméter of each grain and to identify
those tabular grain~ having ~ thickness of less than
0.3 micron. From this ~he aspect ratlo of each such
tabular grain can be calculated, ~nd the aspect
2~ ratios of all the tabular grains in the ssmple
meeting the less than 0.3 micron thickness criterion
can be averaged to obtain their average aspect
ratio. By this definitisn the average dspect ratio
is the average of individual tabular grain aspect
ratios. In practice it is usually simpler to obtain
an average thickness and an average diameter of the
tabular grains havlng a thicknesæ of less than 0.3
micron and to calculate the aver~ge aspect ratio as
the ratio of these two averages. Whether the
sveraged individual aspect ratios or the averages of
thlckness and diameter are used to determine the
average aspect ratio, within the tolerances of grain
mea~urements contemplated, the average aspect ratios
obtained do not significantly differ. The pro~ected
areas of the silver iodide grains meeting the
thicknes~ and diameter criteria can be ~ummed, the
~21~Z6
projected areas of the remaining silver iodide
grains in the photomicrogr~ph can be summed sepa-
rately, and from the two sums the percertage of the
total projected area of the silver iodide grains
provided by the grains meeting the thickness and
diameter critera can be calculated.
In the above determinations a reference
tabular grain thickness of less than 0.3 micron was
chosen to distinguish the uniquely thin tabular
grains herein contemplated from thicker tabular
grains which provide inferior photographic proper-
ties. At lower diameters it is not always possible
to distinguish tabular and nontabular grains in
micrographs. The tabular grains for purposes of
this disclosure are those which are less than 0.3
micron in thickness and appear tabular at 2,500
times magnification. The term "projected area" is
used in the same sense as the terms "projection
area" and "projective area" commonly employed in the
art; see, for example, James and ~iggins, ~undamen~
tals of Photo~raphic Theory, Morgan and Morgan, New
York, p. 15.
In a preferred form offering a broad range
of observed advantages the present invention
employs, in addition to high aspect ratio silver
iodide emulsions~ high aspect ratio silver bromo-
iodide emulsions. High aspect ratio silver bromo-
iodide emulsions and their preparation is the
subject of Wilgus and Haefner Canadian Patent
1,175,6~3, commonly assigned, titled HIGH ASPECT
RATIO SILVER BROMOIODIDE EMULSIONS AND PROCESSES FOR
THEIR PREPARATION.
High aspect ratio tabular grain silver
bromoiodide emulsions can be prepared by a precipi-
tation process which forms a part of the Wilgus and
-- 121~626
-10 -
Haefner invention. Into a conventional reaction
vessel for silver halide precipitstion, equipped
with an efficient stirring mechanism, i8 introduced
a dispersing medium. Typically the dispersing
5 medium initially introduced into the reac~ion vessel
is at least about 10 percent, preferably 20 to 80
percent, by weight based on total weight of the
dispersing medium present in the silver bromoiodide
emulsion at the conclusion of grain precipitation.
10 Since dispersing medium can be removed from the
reaction vessel by ultrafiltration during eilver
bromoiodide grain precipitation, as taught by Mignot
U.S. Patent 4,334,012, it is appreciated that the
volume of dispersing medium initially pre~ent in the
15 resction vessel can equal or even exceed the volume
of the silver bromoiodide emulsion present in the
reaction ves~el at the conclusion of grain precip~-
tation. The dispersing medium initially introduced
into the reaction vessel is preferably water or a
20 dispersion of peptizer in water, optionally contain-
ing other ingredients, such as one or more Rilver
halide ripening agents and/or metal dopants, more
specifically described below. Where a peptizer is
initially present, it i8 preferably employed in a
25 concentr~tion of at least 10 percent, most prefer-
ably at least 20 percent, of the total peptizer
present at the completion of silver bromoiodide
precipitation. Additional dispersing medium is
added to the reaction vessel with the silver and
30 halide salts and can also be introduced through a
separate ~e~. It is common practice to ad~ust the
proportion of dispersing medium, particularly to
increase the proportion of peptizer, after the
completion of the salt introductions.
~Z~6Z6
-11 -
A minor portion, typically less than lO
percent, of the bromide salt employed in forming the
silver bromoiodide grains is init~ally present ~n
the resction veRsel to ad~ust the bromide ~on
concentration of the di~persing med~um at the outset
of silver bromoiodide precipitation. Also, the
dispersing medium in the reaction vessel iB initial-
ly æubsthntially free of iodide ions, since the
pre6ence of iodide ions prior to concurrent ~ntro-
ducton of silver and bromlde salts favors theformation of thick and nontabular grains. A~
employed herein, the term "substantially free of
iodide ions" as applied to the contents of the
reaction vessel means that there are insufficient
iodide ions present a~ compared to bromide ions to
precipitate as a separate silver iodide phase. It
i6 preferred to maintain the iodide concentration in
the reaction vessel prior to silver salt introduc-
tion at less than 0.5 mole percent of the total
halide ion concentration present. If the pBr of the
dispersing medium is initially too high, the tabular
silver bromolodide grains produced will be compara-
tively thick and therefore of low aspect ratios. It
is contemplated to maintsin the pBr of the reaction
vessel initially at or below 1.6, preferably below
1.5. On the other hand, lf the pBx is too low, the
formation of nontabular gilver bromoiodide grains is
favored. Therefore, it i8 contemplated to maintain
the pBr of the reaction vessel at or above 0.6. (As
herein employed, pBr is defined as the negative
logarithm of bromide ion concentration. pH, pCl,
pI, and pAg are similarly defined for hydrogen,
chloride, iodide, and silver ion concentration~,
re~pectively.)
During precipitation silver, bromide, and
iodide salts are added to the reaction vessel by
~ZlQG26
-12-
techniques well known in the precipitation of silver
bromoiodlde grains. Typically an aqueous solution
of a soluble silver salt, such aR silver nitrate, i8
introduced into the reaction vessel concurrently
with the introduction of the bromide and iod~de
salt6. The bromide and iodide salts are also
typically introduced as aqueous ~alt solution~, such
as aqueous ~olutions of one or more soluble
ammonium, alkali metal (e.g., sodium or potassium),
or alkaline earth metal (e.g , magnesium or calclum)
halide salts. The silver salt is at least initially
introduced into the reaction vessel separately from
the iodide salt. The iodide and bromlde salts can
be added to the reaction vessel ~eparately or as 8
mixture.
With the introduction of 8i lver salt in~o
the reaction vessel the nucleation stage of grain
formation i8 initiated. A popula~ion of grain
nuclei is formed which i8 capable of serving as
precipitation sltes for silver bromlde and silver
iodide as the introduction of sllver, bromide, and
iodide salts continues. The precipitation of silver
bromide and 6ilver iodide onto existing grain nuclei
constitutes the growth stage of grain formation.
The aspect ratios of the tabular grains formed
according to this invention are less affected by
iodide and bromide concentrations during the growth
stage than during the nucleation stage. It i8
therefore possible during the growth stage to
increase the permi6sible latitude of pBr during
concurrent introduction of silver, bromide, and
iodide salts above 0.6, preferably ln the r~nge of
from about 0.6 to 2.2, most preferably from about
0.8 to about 1.6, the latter being particularly
preferred where a substantial rate of grain nuclei
formation continues throughout the introduction of
` ``` lZ~(~6Z~i
-13-
silver, bromide, and iodide salt~, 6uch a~ in the
preparation of highly polydispersed emulsions.
Raising pBr values above 2.2 dùring tabular grain
growth re~ults in thickening of the grains, but csn
be tolerated in many instances while gtill reali~ing
an average aspect ratio of greater thsn 8:1.
As an alternative to the introduction of
silver, bromide, and iodide ~alts as aqueous solu-
tions, it is specifically contemplated to introduce
the silver, bromide, and iodide galts, inltially or
in the growth stage, in the form of fine silver
halide grains suspended in dispersing medium. The
grain size is such that they are readily Ostwald
ripened onto lsrgex grain nuclei, if any are
present, once introduced into the reaction vessel.
The maximum useful grain ~izes will depend on the
specific conditions within the reaction vessel, such
as temperature and the presence of solubllizing and
ripening agents. Silver bromide, silver iodide,
and/or silver bromoiodide gralns can be introduced.
(Since bromide and/or iodide is precipitated in
preference to chloride, it is also possible to
employ silver chlorobromide and silver chlorobromo-
iodide grains.) The silver halide grains are
preferably very fine--e.g., less than 0.1 micron in
mean diameter.
Sub~ect ~o the pBr requirements set forth
above, the concen~ratlons and rate~ of silver,
bromide, and iodide salt introductions can take any
convenient conventional form. The silver and halide
salts are preferably introduced in concentrations of
from 0.1 to 5 moles per liter, although broades
conventional concentration ranges, such a8 from 0.01
mole per liter to saturation, for example, are
; 35 contemplated. Specifically preferred precipitation
techniques are those which achieve shortened
~,
~2~6Z6
-14-
precipitation times by increa~ing the rate of silver
and halide ~alt introduction during the run. The
rate of silver and halide salt introduction can be
increased either by increasing the rate at which the
dispersing medium and the silver and halide ~alts
are introduced or by increasing the concentrations
of the 6~ lver and halide salts within the dispersing
medium being introduced. It i8 specifically prefer-
red to increase the rate of silver and halide salt
introduction, but to maintain the rate of introduc-
tion below the threshold level at which the forma-
tion of new grsin nuclei is favored--i.e., to avoid
renucleation, as taught by Irie U.S. Patent
3,650,757, Kurz U.S. Pstent 3,672,900, Saito U.S.
Patent 4,242,445, Wilgus German OLS 2,107,118,
Teitscheid et al European Patent Application
80102242, and Wey "Growth Mechanism of AgBr Cry6tal6
in Gelatin Solutlon", Photo~raphic Science and
~ineerin~, Vol. 21, No. 1, January/February 1977
p. 14, et. seq. By svoiding the formation of
additional grain nuclei after pa6sing into the
growth stage of precipitation, relatively monodis-
persed tabular silver bromoiodide grain populations
can be obtained. Emulsions having coefficients of
variation of less than about 30 percent can be
prepared. (As employed herein the coefficient of
variation is defined as 100 times the standsrd
deviation of the grain diameter divided by the
average grain diameter.) By intentionally favoring
renucleation during the growth stage of precipita-
tion, it is, of course, possible to produce polydis-
persed emulsions of substantially higher coeffi-
cient6 of variation.
The concentration of iodide in the ~ilver
bromoiodide emulsions can be controlled by the
introduction of iodide salts. Any conventional
.~
626
-15-
iodide concentration can be employed. Even very
small amounts of iodide--e.g., as low as 0.05 mole
percent--are recognized in the art to be benef~-
cial, In their preferred form the emulsions of the
present invention incorporate at least about 0.1
mole percent iodlde. Silver iodide can be incorpo-
rated into the tabular silver bromoiodide grains up
to its solubility limit in silver bromide at the
temp~rature of grain formation. Thus, silver iodide
concentrations of up to about 40 mole percent in the
tabular silver bromoiodide grains can be achieved at
precipitation temperatures of 90C. In practice
precipitation temperatures can range down to near
ambient room temperatures--e.g., about 30C. It is
generally preferred that precipitation be undertaken
at temperatures in the range of from 40 to 80C.
The relative proportion of iodide and
bromide salts introduced into the reaction vessel
during precipitation can be maintained ~n a fixed
ratio to form a substantially uniform iodide profile
in the tabular silver bromoiodide grains or varied
to achieve differing photographic effects. Solberg
et al Canadian Patent 1,175,697~ commonly assigned,
titled RADIATION-SENSITIVE SILVER BROMOIODID~
EMULSlO~S, PHOTOGRAPHIC ELE~JENTS, AND PROCESSES FOR
THEIR USE, has recognized specific photographic
advantages to result from increasing the proportion
of iodide 1n annular or otherwise laterally
displaced regions of high aspect ratio tabular grain
silver bromoiodide emulsions as compared to central
regions of the tabular grains. Solberg et al
teaches iodide concentrations in the central regions
of from 0 to 5 mole percent, with at least one mole
percent higher iodide concentrations
626
-16-
in the laterally surrounding annular regions up to
the solubility limit of silver io~ide in silver
bromide, preferably up to about 20 mole percent and
optimally up to about 15 mole percent. Solberg et
al constitutes a preferred species of high aspect
ratio tabular grain silver bromoiodide emulsions.
In a variant form it is specifically contemplated to
terminate iodide or bromide and iodide salt addition
to the reaction vessel prior to the termination of
silver salt addition so that excess halide reacts
with the silver salt. This results in a shell of
silver bromide being formed on the tabular silver
bromoiodide grains. Thus, it is apparent that the
tabular silver bromoiodide grains can exhibit
substantially uniform or graded iodide concentration
profiles and that the gradation can be controlled,
as desired, to favor higher iodide concentrations
internally or at or near the surfaces of the ~abular
silver brsmoiodide grains.
; 20 Although the preparation of the high aspect
ratio tabular grain silver bromoiodide emulsions has
been described by reference to the process of Wilgus
and Haefner, which produces neutral or nonammoniacal
emulsions, these emulsions and their utility are not
limited by any particular process for their prepara-
tion. A process of preparing high aspect ratio
tabular grain silver bromoiodide ~mulsions
discovered subsequent to that of Wilgus and Haefner
is described by Daubendiek and Strong Canadian
Patent 1,175,701a commonly assigned, titled METHOD
OF PREPARING HIGH ASPECT RATIO GRAINS. Daubendiek
and Strong teaches an improvement over the processes
of Maternaghan, U.S. Patents 4,150,994, 4,184,877,
and 4,184,878, wherein
26
-17 -
in a preferred form the silver iodide concentration
in the reaction vessel is reduced below 0.05 mole
per liter and the maximum size of the silver iodide
grains initially present in the reaction vessel is
reduced below 0.05 micron.
High aspect ratio tabular grain silver
bromide emulsions lacking iodide are also useful in
th~ multicolor photographic elements of this
invention and can be prepared by the process
described by Wilgus and Haefner modified to exclude
iodide. High aspect ratio tabular grain silver
bromide emulsions can alternatively be prepared
following a procedure similar to that employed by
deCugnac and Chateau, "Evolution of the Morphology
of Silver Bromide Crystals During Physical Ripen-
ing", Science et Industries Photographiques, Vol.
33, No. 2 ~lg62), pp. 121-125. High aspect ratio
silver bromide emulsions containing square and
rectangular grains can be prepared as taught by
Mignot Canadian Patent 1,175,699, commonly assigned,
titled SILVER BROMIDE EMULSIONS OF NARROW GRAIN SIZE
DISTRIBUTION AND PROCESSES ~OR THEIR PREPARATION.
In this process cubic seed grains having an edge
length of less than 0.15 micron are employed. While
maintaining the pAg of the seed grain emulsion in
the range of from 5.0 to 8.0, the emulsion is
ripened in the substantial absence of nonhalide
silver icn complexing agents to produce tabular
silver bromide grains having an average aspect ratio
of at least 8.5:1. Still other preparations of high
aspect ratio tabular grain silver bromide emulsions
lacking iodide are illustrated in the examples.
To illustrate the diversity of high aspect
ratio tabular grain silver halide emulsions which
, ~
2~6~6
can be employed in addition to the high aspect ratio
tabular grain silver iodide emulsions in the
multicolor photographic elements of this invention,
attention is directed to Wey Canadian Patent
1,175,691, commonly assigned~ titled IMPROVED
DOUBLE-JET PRECIPITATION PROCESSES AN~ PRODUCTS
THEREOF, which discloses a process of preparing
tabular ~ilver chloride grains which are substan-
tially internally free of both silver bromide and
silver iodide. Wey employs a double-jet precipita-
tion process wherein chloride and silver salts are
concurrently introduced into a reaction vessel
containing dispersing medium in the presence of
ammonia. During chloride salt introduction the pAg
within the dispersing medium is in the range of from
6.5 to 10 and the pH in the range of from 8 to 10.
The presence of ammonia at h~gher temperatures tends
to cause thick grains to form, therefore precipita-
tion temperatures are limited to up to 60C. The
process can be optimized to produce high aspect
ratio tabular grain silver chloride emulsions.
Maskasky Canadian Patent 1,175,693,
commonly assigned, titled SILVER CHLORI~E EMULSIONS
OF MODIFIED C~YSTAL HABIT AND PROCESSES FOP~ T~EIR
PREPARATION, discloses a process of preparing
tabular grains of at least 50 mole percent chloride
having opposed crystal faces lying in {111}
cry~tal planes and, in one preferred form, at least
one peripheral ed~e lying parallel to a <Zll>
crystallographic vector in the plane of one of the
major surfaces. Such tabular grain emulsions can be
prepared by reacting aqueous silver and chloride-
containing halide salt solutions in the presence of
a crystsl habit modifying amount of an amino-substi-
tuted azaindene and a peptizer having a thioetherlinkage.
'~
lZ1~626
-19-
Wey and Wilgus Canadian Patent 1,175,698,
commonly assigned, titled NOVEL SILVER CH~OROBROMIDE
~MULSIONS AND PROCESS~S FOR THEIR PREPARATION,
discloses tabular grain emulsions wherein the silver
halide grains contain chloride and bromide in at
least annular grain regions and preferably through-
out. The tabular grain regions containing silver,
chloride, and bromide are formed by maintainin8 a
molar ratio of chloride aDd bromide ions of from
1.6:1 to about 260:1 and the total concentration of
halide ions in the reaction vessel in the range of
from 0.10 to 0.90 normal during introduction of
silver, chloride, bromide, and, optionally, iodide
salts into the reaction vessel. The molar ratio of
silver chloride to silver bromide in the ~abular
gr~ins can range from 1:99 to 2:3.
Silver halide emulsions containing high
aspect ratio silver iodide tabular grains of face
centered cubic crystal structure are disclosed by
Maskasky Can. Serial No. 44~,019, filed concurrently
herewith, titled GAMMA PHASE SILVER IODIDE EMUL-
SIONS, PHOTOGRAPHIC ELEMENTS CONTAINING THESE
EMULSIONS, AND PROCESSES FOR THEIR USE, cited
above. Such emulsions can be prepared by modifying
conventional double-jet silver halide precipitation
procedures. As noted by James, The Theory of the
Photographic Proces6, cited above, precipitation on
the silver side of the equivalence point (the point
at which æilver and iodide ion concentrations are
equal) is important to achievin~ face centered cubic
crystal structures. For example, it is preferred to
precipitate at a pAg in the vicinity of 1.5, as
undertaken by Daubendiek, cited above. (As employed
herein pAg is the negative logarithm of silver ion
concentration.) Second, in comparing the processes
`` 12~626
-20
employed in preparing the high aspect ratio tabular
grain silver iodide emulsions with the unpublished
details of the process employed by ~aubendiek, 'IAgI
Precipitations: Effects of pAg on Crystal Growth
(PB)", cited above, to achieve relatively low aspect
ratio silver iodide grains, the flow rates for
silver and iodide salt introductions in relation to
the final reaction veæsel volume are approximately
an order of magnitude lower than those of Daubendiek
(<0.003 mole/minute/liter as compared to <0.02
mole/minute/liter employed by Daubendiek).
Silver halide emulsions containing high
aspect ratio silver iodide tabular grains of a
hexagonal cry6tal structure, as exhibited by B phase
silver iodide, can be prepared by double-jet
precipitation procedures on the halide side of the
equivalence pointO Useful parameters for precipita-
tion are illustrsted in the Examples below. Zharkov
et al, cited above, discloses the preparation of
silver iodide emulsions containing tabular gralns of
~ phase crystal structure by ripening in the
presence of a ammonia and an excess of potassium
iodide~
High aspect ratio tabular grain emulsions
u~eful in the practice of this invention can have
extremely high average aspect ratios. Tabular grain
average aspect ratios can be increased by increaæing
average grain diameters. This can produce ~harpness
advantageæ, but maximum average grain diameteræ are
generally limited by granularity requirements for a
specific photographic application. Tabular grain
average aæpect ratios can also or alternatively be
increased by decreasing average grain thicknesses.
`~ ~Z1~62~
-21-
When silver coverages are held con~tant, decreasing
~he thickness of tabular grains generally improves
granularity as a direct function of increasing
aspect ratio. Hence the maximum average aspect
ratios of the tabular grain emulsions employed in
the multicolor photographic elements of this
invention are a function of the maxlmum average
grain diameters acceptable for the specific photo-
graphic application and the minimum attainable
tabular grain thicknesses which can be produced.
Maximum average aspect ratios have been observed to
vary, depending upon the precipitation technique
employed and the tabular grain halide composition.
The highest observed average aspect ratios, 500:1,
for tabular grains with photographically useful
average grain diameters, have been achieved by
Ostwald ripening preparations of silver bro~ide
grains, with aspect ratios of 100:1, 200:1, or even
higher being obtainable by double-jet precipitation
procedures. The presence of iodide generally
decreases the maximum average aspect ratios realized
in silver bromoiodide tabular grains, but the
preparation of silver bromoiodide tabular grain
emulsions having average aspect ratios of 100:1 or
even 200:1 or more is feasible. Average aspect
ratios as high as 50:1 or even 100:1 for silver
chloride tabular grains, optionally containing
bromide and/or iodide, can be prepared as taught by
Maskasky Can. Patent 1,175,6~3, cited above.
Because of the exceptionally thin silver iodide
tabular grains which can be obtained, high average
aspect ratios ranging up to 100:1 can be readily
achieved, regardless of whether the silver iodide is
in a face centered cubic (y phase) or hexagonal
(~ phase) crystal structure. Emulsions containing
silver iodide tabular grains of hexagonal crystal
structure of even higher average
``` lZ~26
-22-
aspect ratios, ranging up to 200:1, or even 500:1,
are contemplated.
Modifying compounds can be present during
tabular grain precipitation. Such compounds can be
5 initially in the reaction vessel or can be added
along with one or more of the salts according to
conventional procedures. Modifying compounds, such
as compounds of copper, thallium, lead 9 biRmuth
cadmium, zinc, middle chalcogens (i.e., sulfur9
10 selenium, and tellurium), gold, and Group VIII noble
metals, can be present during silver halide precipi-
tation, as illu~trated by Arnold et al U.S. Patent
1,195,432, Hochstetter U.S. Patent 1,951,933,
Trivelli et al U.S. Patent 2,448,060, Overman U.S.
15 Patent 2,628,167, Mueller et al UOS. Patent
2,950,972, Sidebotham U.S. Patent 3,488,709,
Rosecrants et al U.S. Patent 3,737,313, Berry et al
U.S. Patent 3,772,0319 Atwell U.S. Patent No.
4,269,927, and Research Disclosure, Vol. 134, June
20 1975, Item 13452. Research Disclosure and its
predecessor, Product Licensing Index, are publica-
t~ons of Kenneth Ma~on Publications Limited;
Emsworth; Hampshire P010 7DD; United Kingdom. The
tabular grain emulsions can be internally reduction
25 gensitized during precipitation, as illustrated by
Moisar et al, Journal of PhotograPh~c Science, Vol.
25, lg77, pp. 19-27.
The individual silver and halide salts can
be added to the reaction vessel through surface or
3~ subsurface delivery tubes by gr~vi~y feed or by
delivery apparatus for maintaining control of the
rate of delivery and the pH9 pBr, and/or pAg of the
reaction vessel contents, as illustrated by Culhane
et al U.S. Patent 3,821,002, Oliver U.S. Patent
35 3,031,304 and Claes et al, Photographische Korres-
pondenz, Band 102, Number 10, 1967, p. 162. In
.;
~` 121~6Z~
-23-
order to obta~n rapid distribution of the reactants
within the reaction vessel, specially constructed
mixing devices can be employed, as illustrated by
Audran U.S. Patent 2,996,287, McCros6en et al U.S.
Patent 3,342,605, Frame et al U.S. Patent 3,415,650,
Porter et al U.S. Patent 3,785,777, Finnicum et al
U.S. Patent 4,147,551, Verhille et al U.S. Patent
4,171,224, Calamur U.K. Patent Application
2,022,431A, Saito et al German OLS 2,5i5,364 and
2,556,885, and Research Disclosure, Volume 166,
February 1978, Item 16662.
In forming the tabular grain emulsions a
dispersing medium is initially contained in the
reaction vessel. In a preferred form the dispersing
medium is comprised on an aqueous peptizer suspen-
sion. Peptizer concentrations of from 0.2 to about
10 percent by weight, based on the total weight of
emulsion components in the reaction vessel, can be
employed. It is common practice to maintain the
concentration of the peptizer in the reaction vessel
in the range of below about 6 percent, based on the
total weight, prior to and during silver halide
formation and to ad3ust the emulsion vehicle concen-
tration upwardly for optimum coating characteristics
by delayed, supplemental vehicle additions. I~ is
contemplated that the emulsion as initially formed
will contain from about 5 to 50 grams of peptizer
per mole of æilver hal~de, preferably about 10 to 30
grams of peptizer per mole of silver halide.
Additional vehicle can be added later to bring the
concentratlon up to as high as 1000 grams per mole
of silver halide. Preferably the concentration of
vehicle in the finished emulsion is above 50 grams
per mole of silver halide. When coated and dried in
forming a photographic element the vehicle prefer-
ably forms about 30 to 70 percent by weight of the
emulsion layer.
~2~6Z6
-24 -
Vehicles (which include both binders and
peptizer 8 ) can be chosen from among those conven-
tionally employed in silver halide emulsions.
Preferred peptizer~ are hydrophilic colloids, which
can be employed alone or in comb~nation wlth hydro-
phobic materialsO Suitable hydrophilic materials
include substances such as protein~, protein deriva-
tives, cellulose derivative6--e.g~, cellulose
esters, gelatin--e.g., alkali-tseated gelatin
(cattle bone or hide gelatin) or acid-treated
gelatin (pigskin gelat~n), gelatin derivative~--
e.g., acetylated gelatin, phthalated gelatin and the
like, polysaccharides such as dextran, gum arabic,
zeinS casein, pectin, collagen derivative6, agar-
agar, arrowroot, albumin and the like as describedin Yutzy et al U.S. Patents 2,614,928 and '929, Lowe
et al U.S. Patents 2,691,582, 2,614,930, '931,
2,327,808 and 2,448,534, Gates et al U.S. Patents
2,787,545 and 2 9 956,880, Himmelmann e~ al U.S.
Patent 3,061,436, Farrell et al U.S. Patent
2,816,027, Ryan U.S. Patents 3,132,945, 3,138,461
and 3,186,846, Dersch et al U.R. Patent 1,167,159
and U.S. Patent 8 2,960,405 and 3,436,220, Geary V.S.
Patent 3,486,896, Gazzard U.K. Patent 793,549, Gates
et al U.S. Patents 2,992,213, 3,157,506, 3,184,312
and 3,539,353, M~ller et al U.S. Patent 3,227,571,
Boyer et al U.S. Patent 3,532,502, Malan U.S. Patent
3,551,151, Lohmer et al U.S. Patent 4,018,609,
Luciani et 81 U.K. Patent 1,186,790, Hori et al U.R.
Patent 1,489,080 and Belgian Patent 856,631, U.K.
Patent 1,490~644, V.K. Patent 1,483,551, Arase et al
U.K. Patent 1,459,906, Salo U.S. Patents 2,110,491
and 2,311,086, Fallesen U.S. Patent 2,343,650, Yutzy
U.S. Patent 2,322,085, Lowe U.S. Patent 2,563,791,
Talbot et al U.S. Patent 2,725,293, Hilborn U.S.
Patent 2,748,022, DePauw et al U.S. Patent
~.Z~ ~26
-25-
2,956,883, Ritchie U.K. Patent 2,095, DeStubner U.S.
Patent 1,752,069, Sheppard et al U.S. Patent
2,127,573, Lierg U.S. Patent 2,256,720~ Ga~par U.S.
Patent 2,361,936, Farmer U.K. Patent 15,727, Stevens
U.K. Patent 1,062,116 and Yamamoto et al U.S. Patent
3,~23,517.
Other materials commonly employed in
combination wlth hydrophilic colloid peptizers as
vehicles (including vehicle extenders--e.g., mater-
ials in the fo~m of latices) include synthetic
polymeric peptizers, carriers and/or binders such es
poly(vinyl lactams~, acrylamide polymers, polyvinyl
alcohol and its derivatives, polyvinyl acetal6,
polymer B of alkyl and sulfoalkyl acrylate6 and
meth~cryl~tes, hydrolyzed polyvinyl acetate6,
polyamides, polyvinyl pyridine, acrylic acid poly-
mers, maleic anhydride copolymer6, polyalkylene
oxides, methacryl~mide copolymers, polyvinyl
oxazolidinone6, maleic acid copolymers, vlnylamine
copolymers, methacrylic acid copolymers, acryloyl-
oxyalkylsulfonic acid copolymers, sulfoalkylacryl-
amide copolymers, polyalkyleneimine copolymers,
polyamines, N,N-dialkylaminoalkyl acrylates, vinyl
imidazole copolymer~, vinyl sulfide copolymers,
halogenated styrene polymers, amineacrylamide
polymers, polypeptldes and the like as deRcribed in
Hollister et al U.S. Patents 3,679,425, 3,706,564
and 3,813,251, Lowe U.S. Patents 2,253,078,
2,276,322, '323, 2,281,703, 2,311,058 and 2,414,207,
Lowe et al U.S. Patents 2,484,456, 2,541,474 and
2,632,704, Perry et al U.S. Patent 3,425,836, Smith
et al U.S. Patents 3,415,653 and 3,615,624, Smith
U.S. Patent 3,488,708, Whiteley et al U.S. Patents
3,392,025 and 3,511,818, Fitzgerald U.S. Patents
3,681,079, 3,721,565, 3,852,073, 3,861,918 and
3,925,083, Fitzgerald et al U.S. Patent 3,879,205,
2~
-26-
Nottorf U.S. Patent 3,142,568, Houck et al U.S.
Patents 3,062,674 and 3,220,844, Dann et al U.S.
Patent 2,882,161, Schupp U.S. Patent 2,579,016,
Weaver U.S. Patent 2,829,053, Alles et al U.S.
Patent 2,698,240, Priest et al U.~. Patent
3,003,879, Merrill et al U.S. Patent 3,~19,397,
Stonham U.S. Patent 3,284,207, Lohmer et al U.S.
Patent 3,167,430, Williams U.S. Pstent ~,957,767,
Dawson et al U.S. Patent 2,893,867, Smith et al U.S.
Patents 2,860,986 and 2,904,539, Ponticello et al
U.S. Patentæ 3,929,482 and 39860,428, Ponticello
U.S. Patent 3,939,130, Dykstra U.S. Patent 3,411,911
and Dykstra et al Canadian Patent 774,054, Ream et
al U.S. Patent 3,287,289, Smith U.K. Patent
1~466,600~ Stevens U.K. Patent 1,062,116, Fordyce
U.S. Patent 2,211,323, Martinez U.S. Patent
2,284,877, Watkins U.S. Patent 2,420,455, Jones U.S.
Patent 2,533,166, Bolton U.S Patent 2,495,918,
Graves U.S. Patent 2,289,775, Yackel U.S. Patent
27565,418, Unruh et al U.S~ Patents 2,865,893 and
2,875,059, Rees et al U.S. Patent 3,536,491,
Broadhead et al U.K. Patent 1,348,815, Taylor et al
U.S. Patent 3,479,186, Merrill ~t al U.S. Patent
3,520,857, Bacon et al U.S. Patent 3,690,888, Bowman
U.S. Patent 3,748~143, Dickinson et al U.K. Patents
808,227 and '228, Wood U.K. Patent 822,192 and
Iguchi et al U.K. Patent 1,398,055. These addi~
tional materials need not be present in the ~eaction
vessel during silver halide precipitation, but
rather are conventionally added to the emulsion
prior to coating. The vehicle materials, including
particularly the hydrophilic colloids, as we~l as
the hydrophobic materials useful in combination
therewith can be employed not only in the emulsion
layers of the photographic elements of this inven-
tion, but also in other layers, such as overcoat
626
layers, interlayers and layers positioned beneath
the emulsion layers.
It is specifically contemplated that grain
ripening can occur during the preparation of high
5 aspect ratio tabular gra~n silver hallde emulsions
u~eful in the practice of the present invention, and
it iB preferred that grain ripening occur within the
reaction vessel during at least silver bromoiodide
grain formation. Known silver halide solvents are
10 u~eful in promoting ripening. For example, an
excess of bromide ions, when present in the reaction
vessel, is known to promote ripening. It ~8 there-
fore app~rent that the bromide salt solution run
into the reaction vessel can itself promote ripen-
15 ing. Other ripening agents can also be employed andcan be e~tirely contained within the dispersing
medium ~n the reaction ves~el before silver and
halide salt addition, or they can be introduced in~o
the reaction ves~el along with one or more of the
20 halide salt, silver ~alt, or peptizer. In ~till
another variant the ripening agent can be introduced
independently during halide and silver salt
additions.
Among preferred ripen~ng agents are those
25 containing ~ulfur. Thiocyanate salts can be used,
such as alkali metal, most commsnly sodium and
pota~s~um, and ammonium thiocyanate salts. While
any conventional quantity of the thiocyanate salts
can be introduced~ preferred concentrations are
30 gener&lly from about 0.1 to 20 grams of thiocyanate
salt per mole of silver halide. Illustrative prior
teachings of employing thiocyanate ripening agents
are found in Nietz et al, U.S. Patent 2,2~2,264,
cited above; Lowe et al U.S. Patent 2,448,534 and
35 Illingsworth U.S. Patent 3,320,069. Alternatively,
-- ~LZ~ 2~i
-28-
conventional thioether ripening agents, such as
those disclosed in McBride U.S. Patent 3,2719157,
Jones U.S. Patent 3,574,628, and Ro~ecrants et al
U.S. Patent 3,737,313~ can be employed.
The high aRpect ratio tabular grsin emul-
sions are preferably washed to remove soluble
salts. The soluble sslts can be removed by decanta-
tion, filtrat~on, and/or chill setting and leaching,
as illustrated by Craft U.S. Patent 2,316,B45 and
10 McFall et al U.S. Patent 3,396,027; by coagulation
washing, a~ illustrated by Hewitæon et al U.S.
Patent 2,618,556, Yutzy et al U.S. Patent 2,614,928,
Yackel U.S. Patent 2,565,418, Hart et al U.S. Patent
3,241,969, Waller et al U.S. Patent 2,489,341,
15 Klinger U.K. Patent 1,305,409 and ~ersch et al U.K.
Patent 1,167,159; by centrifugation and decantation
of a coagulated emulsion, as illustrated by Murray
U.S. Patent 2,463,794, U~ihara et al U.S. Patent
37707,378, Audran U.S. Patent 2,996,287 and Timson
20 U.S. Pa~ent 3,498,454; by employing hydrocyclones
alone or in combination wi~h centrifugeæ, as illus-
trated by U.K. Patent 1,336,692, Claes U.K. Patent
1,356,573 and Ushomirskii et al Soviet Chemical
Industry, Vol. 6, No. 3, 1974, pp. 181-185; by
25 diafiltration with a semipermeable membrane, as
illustrated by Research Disclosure, Vol. 102,
October 1972, Item 10208, Hagemaier et al Research
Disclosure, Vol. 1319 March 1975, Item 13122, Bonnet
Research Disclosure, Vol. 135, July 1975, Item
30 13577, Berg et al German OLS 2,436,461, Bolton U.S.
Patent 2,495,918, and Mignot U.S. Patent 4,334,012,
cited above, or by employing an ion exchange resin,
as illustrated by Maley U.S. Patent 3,782,953 and
Noble U.S. Patent 2,827,428. The emulsions, with or
35 without senæitizers, can be dried and stored prior
~ .,
Z6
-29-
to use as illustrPted by ~esearch Disclosure, Vol.
101, September 1972, Item 10152. Washing is
particularly advantageous in terminating ripening of
the tabular ~rains after the completion of precipi-
tation to avoid increasing their thickness and
reducing their aspect ratio.
Once the high aspect ratio tabular grain
emulsions have been formed they can be shelled to
produce core-shell emulsions by procedures well
known to those skilled in the art. Any photograph-
ically useful silver salt c~n be employed in forming
æhells on the high aspect ratio tabular grain
emulsions prepared by the present process. Tech-
niques for forming silver salt shells are illus-
trated by Berriman U.S. Patent 3,367,778, Porter et
al U.S. Patents 3,2~6,313 and 3,317,322, Morgan U.S.
Patent 3,917,485, and Maternaghan, cited above.
Since conventional techniques for shelling do not
favor the formation of high aspect ratio tabular
grains, as shell growth proceeds the average aspect
ratio of the emulsion declines. If conditions
favorable for tabular grain formation are present in
the reaction vessel during shell formation, shell
growth can occur preferentially on the outer edges
of the grains so that aspect ratio need not
declin~. Wey and Wilgus, cited above, specifically
teach procedures for shelling tabular grains without
necessarily reducing the aspect ratios of the
resulting core-shell grains as compared to the
tabular grains employed as cor~ grains. Evans,
Daubendiek, and Raleigh Canadian Patent 1,175,692,
commonly assigned, titled DIRECT REVERSAL EMULSIONS
AND PHOTOGRAPHIC ELEMENTS USEFUL IN IMAGE TRANSFER
FI~M UNITS, specifically discloses the preparation
of high aspect ratio
~`
-` ~Z~6Z6
-3~
core-shell tabular grain emulsions for use ~n
forming direct reversal imageæ.
Although thé procedures for preparing
tabular silver halide grains described above will
5 produce high sspect ratio tabular grain emulsions in
which tabular grains satisfying the thickness and
diameter criteria for aspect ratio account for at
leaæt 50 percent of the total pro~ected area of the
total silver halide grain population) it is recog-
10 nized that further advantages can be realized byincreasing the proportion of such tabulsr grains
present. Preferably at lea~t 70 percent (optimally
at least 90 percent) of the total pro~ected area is
provided by tabular silver halide grains meeting the
15 thickness and diameter criteria. While minor
amounts of nonta~ular grains are fully compatible
with many pho~ographic applications, to achieve the
full ad~antages of tabular grains the proportion of
tabular grains can be increa~ed. Larger tabular
20 silver halide grains can be mechanically ~eparated
from smaller, nontabular grains in a mixed popula-
tion of grains using conventional separation tech-
niques--e.g., by using a centrifuge or hydro-
cyclone. An illustrative teaching of hydrocyclone
25 separation ig provided by Audran et al U.S. Patent
3,3~6,641.
To the extent that radiation-sensitive
silver halide emulsions other than high aspect ratio
tabular grain emulsions are employed in the multi-
30 color photographic elements of this invention, theycan be chosen from any conventional emulsion hereto-
fore employed in multicolor photographic elements.
Illustrative emulsions, their preparation and
chemical sens~tization are disclosed in Research
35 Disclosure, Vol. 176, December 1978, Item 17643,
Paragraph I, Emulsion preparation and types and
Para~raph III, chemical sensitization.
121~i26
Silver iodide emulsions other than high
aspect ratio tabular grain emulsions to the extent
el~ployed in various forms of the multicolor photo-
graphic elements of this invention can be precipi-
tated by procedures generally similar to those forpreparing the high aspect ratio tabular grain silver
iodide emulsions, described above, but without
taking the precautions indicated to produce high
average aspect ratios. For example, such emulsions
can be prepared by the techniques disclosed by
Byerley and Hirsch, Zharkov et al, and Daubendiek,
"AgI Precipitations: Effects of pAg on Crystal
Growth (PB)", each cited above.
The silver iodide emulsions employed in the
multicolor photographic elements of this invention
can be senæitized by conventional techniques. A
preferred chemical sensitization technique iB to
deposit a silver salt epitaxially onto the tabular
silver iodide grains. The epitaxial deposition of
silver chloride onto silver iodide host grains is
taught by Maskasky ~.S. Patents 4,094,684 and
4,142,900, and the analogous deposition of silver
bromide onto silver iodide host grains is taught by
Koitabashi et al U.K. Patent Application 2,063,499A,
each cited above.
It is specifically preferred to employ the
high aspect ratio tabular ilver iodide grains as
host grains for epitaxial deposition. The terms
"epitaxy" and "epitaxial" are employed in their art
recognized sense to indicate that the silver salt is
in a crystalline form having its orientation
controlled by the host tabular grains. The tech-
niques described in Maskasky Can. Patent 1,175,693,
cited above, are directly applicable to
,
, , ~
, ~^
" lZ~6~6
~32-
epitaxlal deposition on the silver iodide host
grains of this inven~ion. The silver ~alt epitaxy
is substantially excluded in a controlled manner
from at least a portion of the major crystal faces
5 of the tabular hoæt grains. The tabular ho~t grains
direct epitaxial deposition of silver aalt to their
edges and/or corners.
By confin~ng epitaxial deposition to
selected sites on the tabular grains an improvement
10 in sensitivity can be achieved as compared to
allowing the silver salt to be epitaxially deposited
randomly over the major faces of the tabular
grains~ The degree to which the silver salt is
confined to selected sensitization sites, leaving at
15 least a portion of the major crystal faces substan-
tially free of epitaxially deposited silver salt,
can be varied widely without departing from the
invention. In general, larger increases in sen~i-
tivity are realized as the epitaxial coverage of the
20 ma~or crystal faces decreases. It is specifically
contemplated to confine epitaxially deposited silver
salt to less than half the area of the ma~or Grystal
faces of the tabular grains, preferably less than 25
percent, and in certain forms, such as corner
25 epitaxial 6ilver salt deposits, optimally to less
than 10 or even 5 percent of the area of the ma~or
cry~tal faces of the ~abular grains. In some
embodiments epitaxial deposition has been observed
to commence on the edge surfaces of the tabular
30 ~rains. Thus, where epitaxy is limited, it may be
otherwise confined to selected edge sensitization
~ites and effectively excluded from the major
crystal faces.
The epitaxially deposited silver salt can
35 be used to provide sensitization sites on the
,.~
--~ 121~Z6
-33-
tabular host grains. By controlling the sltes of
epitaxial deposition, it is possible to achieve
selective site sensitization of the tabular host
grains. Sensitization can be achieved ~ one or
5 more ordered sites on the tabular host grains. By
ordered it is meant that the sensitization site~
bear a predictable, nonrandom relationship to the
ma~or crystal faces of the tabular gr~ins and,
preferably, to each other. 8y controlling epitaxlal
deposition with respect to the ma~or crystal faces
of the tabular grains it is possible to control both
the number and lateral spacing of sensitization
~ites.
In some instances selective site sen6itiza-
tion can be detected when the silver ~odide 8rain6
are exposed to radiation to which they are ~ensitive
and surface latent image centers are produced at
sensitization sites. If the grAins bearing latent
image centers sre entirely developed, the location
and number of the latent image centers cannot be
determined. However, if development is arrested
before development has spread beyond the immediate
vicinity of the latent image center, and the
partially developed grain is then viewed under
magnification, the partial development 6ites are
clearly visible. They correspond generally to the
sites of the latent image centers which in turn
generally correspond to the sites of sensitizaton.
The sensitizing silver salt that is
deposited onto the host tabular grains at selected
~ites can be generally chosen from among any silver
salt cap*ble of being epitaxially grown on a silver
halide grain and heretofore known to be useful in
photography. The anion content of the silver salt
and the tabular silver halide grains differ suffi-
ciently to permit differences in the re~pective
,
26
-34-
crystMl ~tructures to be detected. It i8 6pecifi-
cally contemplated to choo~e the silver salts from
among those heretofore known to be useful in forming
6hells for core-shell silver halide emul6ion~. In
addition to all the known photographically useful
silver halides, the silver salts can include other
silver salt6 known to be capable of precipitstlng
onto silver halide grains, such a6 silver thio-
cyanate, silver cyanide, ~ilver carbonate, sllver
ferricyanide, silver arsenate or arsenite, and
silver ch~omate. Silver chloride is a specifically
prefer~ed sensitizer. Depending upon the silver
salt chosen and the intended applicat~on, the ~llver
salt can usefully be deposi~ed in the pre~ence of
any of the modifying compounds described above in
connection with the tabular gilver halide gralns.
Some iodide from the host grain~ may enter the
~ilver salt epitaxy. It is also contemplated that
the host grains can contain anions other than iodide
up to their solubility limit in silver iodide, and,
as employed herein, the term "silver iodide grains"
is intended to include such host grains.
Conventional chemical sensitizstion can be
undertaken prior to controlled site epitsxial
deposition of silver salt on the host tabulQr grain
or a8 a following step. When silver chloride and/or
silver th~ocyanate is deposited~ a large increase in
sensitivity i8 realized merely by selective site
depo6ition of the silver ~alt. Thus, further
chemical sensitization steps of a conventional type
need not be undertaken to obtain photographic
speed. On the other hand, an additional increment
ln speed can generally be obtained when further
chemical sensitization is undertaken, and it i8 a
distinct advantage that neither elevated temperature
nor extended holding times are required in finishing
21~62~
the emulsion. The quantity of sensitizers can be
reduced, if desired, where (1) epitaxial deposition
itself improves sensitivity or (2) sen6itization is
directed to epitaxial deposition sites. Sub6tan-
tially optimum sensitization of tabular silveriodide emulsions ha~ been achieved by the epitaxial
deposition of silver chloride without further
chemical sens~tization.
Any conventional technique for chemical
sensitization following controlled g~te epitaxial
deposition can be employed. In general chemical
sensitization should be undereaken based on the
composition of the gilver salt deposited rather than
the composition of the host tabular graing, since
chemical senBitization i8 believed to occur primar-
ily at the silver salt deposition site6 or perhap6
immediately ad~acent thereto. Conventional tech-
niques for achieving noble metal ~e.g., gold) middle
chalcogen (e.g., sulfur, selenium, andJor tellur-
ium), or reduction sensitization as well a~ combina-
tions the~eof are disclosed in Research Disclosure,
Item 17643, Paragraph III, cited above.
High aspect ratio tabular grain emulsions
other ~han the silver iod~de emulsions discussed
above can be chemically sensitized by procedures
similar to those employed in chemically sensitizing
emulsions conventionally employed in multicolor
photographic elements, described above. Extremely
high speeds and highly improved speed-granularity
relationshipR can be achieved when the emul~ions are
substantially optimally sensitized following the
teachings of Kofron et al, cited above. In one
preferred form chemical sensitization is undertaken
after spectral ~ensitization. Similar resultg have
also been achieved in some instances by introducing
other adsorbable materials, such as f~nish modi-
` ~21~626
-36 -
fiers, into the emulsion prior to chemical sensiti-
zation. Independent of the prior incorporation of
adsorbable materials, it is preferred to employ
thiocyanates during chemical sensitization in
concentrations of from about 2 X 1~- 3 to 2 mole
percent, based on silver, as taught by Damschroder
U.S. Patent 2,462,361. Other ripening agents can be
used during chemical sensitization. Still a third
approach, capable of being practiced independently
of, but compatible with, the two approaches
described above, is to deposit silver salts epitax-
ially on the high aspect ratio tabular grains, as is
taught by Maskasky Can. Patent 1,175,278, cited
above.
The silver iodide emulsions intended to
record blue light exposures can, but need not, be
spectrally sensitized in the blue portion of the
spectrum. Silver bromide and silver bromoiodide
emulsions containing nontabular grains and relative-
ly thick tabular grains can be employed to record
blue light without incorporating blue sensitizers,
although their absorption efficiency is much higher
when blue sensitizers are present. The silver
halide emulsion~, regardless of composition,
intended to record minus blue light are spectrally
sensitized to red or green light by the use of
spectral sensitizing dyes.
The silver halide emulsions incorporated in
the multicolor photographic elements of this
invention can be spectrally sensitized with dyes
from a variety of classes, including the polymethine
dye class, which classes include the cyanines,
merocyanines, complex cyanines and merocyanines
(i.e., tri-, tetra-, and poly-nuclear cyanines and
merocyanines), oxonols, hemioxonols, styryls,
; merostyryls, and streptocyanines.
lZl~Z6
-37-
The cyanine spectral sens~tizing dyes
include, ~oined by a methine linkage, two basic
heterocyclic nuclei, such as those derived from
quinolinium, pyridinium, isoquinolinium, 3H-indo-
lium, benzte]lndolium, oxazolium, oxazolinium,thiazolium, thiazolinlum, selenazolium, selenazolin-
ium, imidazolium, imidazolinium, benzoxa~olium,
benzothiazolium, benzoselenazolium, benzimidazolium,
naphthoxazolium, naphthothiazolium, naphtho~elena-
zolium, dihydronaphthothiazolium, pyrylium, andimidazopyrazinium quaternary salts.
The merocyanine spectral sensitizing dyes
include, ~oihed by a double bond or a methine
linkage, 8 basic heterocyclic nucleus of the cyanine
dye type and an acidic nucleus, such 8B can be
derived from barbituric acid, 2-thiobarbituric acid,
rhodanine, hydantoin, 2-thiohydantoin, 4-thiohydan-
toin, 2-pyrazolin-5-one, 2-lsoxazolin-5-one, indan-
1,3-dione, cyclohexane-1,3-dione, 1,3-dioxane-4,6-
dione, pyrazolln-3,5-dione, pentene-2,4-dione,
alkylsulfonylacetonitrile, malononitrile, isoquino-
lin-4-one, and chroman-2,4-dione.
One or more spectral sensi~izing dyes may
be used. Dyes with sensitizing maxima at wave-
lengths throughout the visible spectrum and with agreat variety of spectral sensitivity curve shapes
are known. The choice and relative proportions of
dyes depends upon the region of the spectrum to
which æensitivity is desired and upon the shape of
the spectral sensitivity curve desired. Dyes with
overlapping spectral sensitivity curves will often
yield in combination a curve in which the sensi-
tivity at each wavelength in the area of overlap is
approximately equal to the sum of the sensitivities
of the individual dye~. Thus, it is possi~le to use
combinations of dyes with different maxima to
.,,
.......
~Z~ iZ6
-38 -
achieve a spectral sen6itivity curve with a maximum
intermedi~te to the ~ensitizing maxima of the
individual dye 8 .
Combinations of spectral sen6itizing dyes
can be u~ed which result in supersensitization--that
is, spectral sensitization that i8 greater in some
spectral region than that from any concentration of
one of the dyes alone or that which would re6ult
from the additive effect of the dyes. Supersensiti-
zation can be achieved with selected combinations ofspectral sensitizing dyes and other addenda, such aR
~tabilizers snd antifoggants, development accele-
rators or inhibitors, coating aids, brighteners and
antistatic agents. Any one of several mechanisms a6
well as compounds which can be responsible for
supersensitizatioff sre discussed by Gilman, "Review
of the Mechanisms of Supersensitization", Photo-
graphic Science snd Engineering, Vol. 18, 1974, pp.
418-430.
Spectral gensitizing dyes also affect the
emulsions in other ways. Spectral sensitizing dyes
can also function as antifoggants or stabilizers,
development ~ccelerators or inhibltors, and halogen
acceptors or electron acceptors, as disclosed in
Brooker et al U.S. Patent 2,131,038 and Shiba et al
U.S. Patent 3,930,860.
Sensitizing action can be correlated to the
position of molecular energy levels of a dye with
respect to ground state and conduction band energy
levels of the silver hslide crystals. These energy
levels csn in turn be correlated to polarographic
oxidation snd reduction potentisls~ a8 discussed in
Photographic Science and EngineerinR, Vol. 18, 1974,
pp. 49-53 ~Sturmer et al), pp. 175-178 (Leubner~ and
pp. 475-485 (Gilman). Oxidatlon and reduction
potentisls can be measured as described by R. F.
. ,,
`` ~2~:!6Z6
-39-
Large in Photographic Sensitivity, Academic Press,
1973, Chapter 15.
The chemistry of cyanine and related dyes
is illustrsted by Weisæberger and Taylor,
Topics _ Heterocyclic Chemistry, John Wiley and
Sons, New York, 1977, Chapter VIII; Venkataraman,
The Chemistry of Synthetic Dyes, Acsde~ic Press, New
York, 1971, Chapter V; James, The _ eorv of the
Photographic Process, 4th Ed., Macmillan, 1977~
Chapter 8, and F. M. Hamer, Cyanine Dyes and Related
Compounds, John Wiley and Sons, 1964.
Among useful spectral sensitizing dyes for
sensitizing silver halide emulsions are those found
in U.K. Patent 742,112, Brooker U.S. Patents
1,846,300, '301, '302, '303, '304, 2,078,233 a~d
2,089,729, B~ooker et al U.S. Patents 2,165,338,
2,213,238, 2,231,658, 2,4g3,747, '748, 2,526,632,
2,739,964 (Reissue 24,292), 2,778,823, 2,917,516,
3,352,857, 3,411,916 and 3,431,111, Wilmanns et al
U.S. Patent 2,295,276, Sprague U.S. Patents
2,481,698 and 2,503,776, Carroll et al U.S. Patent6
2,688,545 and 2,704,714~ Larive et al U.S. Patent
2,921,067, Jones U.S. Patent 2,945,763, Nys et al
U.S. Patent 3,282,933, Schwan et al U.S. Patent
3,397,060, Riester U.S. Patent 3,660,102, Kampfer et
al U.S. Patent 3,660,103, Taber et al U.S. Patents
3,335,010, 3,352,680 and 3,384,486, Lincoln et al
U.S. Patent 3,397,981, Fumia et al U.S. Patent~
3,482,978 and 3,623,881, Spence et al U.S. Patent
3,718,470 and Mee U.S. Patent 4,025,349. Example~
of useful dye combinations, including supersensitiz-
ing dye comb~nations, are found in Motter U.S.
Patent 3,506,443 and Schwan et al U~S. Patent
3,672,898. As examples of supersensitizing combina-
tions of spectral sensitizing dyes and non-light
absorbing addenda, it is specifically contemplated
.~J
12~¢~Z6
-40-
to employ thiocyanates during spectral sensitiza-
tion, as taught by Leermakers U.S. Patent 2,221,805;
bis-triazinylaminostilbenes, as taught by McFall et
al U.S. Patent 2,933,390; sulfona~ed aromatic
compounds, as taught by Jones et al U.S. Paten~
2,937,089j mercapto-~ubstituted heterocycles, a~
taught by Riester U.S. Patent 3,457,078; iodlde, as
taught by U.K. Patent 1,413,826; and still other
compounds, such as those disclosed by Gilman,
"Review of ~he Mechanisms of Supersensitization'~,
cited above.
Conventional amount~ of dyes can be
employed in spectrally sensitizing the emulsion
layers contain~ng nontabular or low aspect ratio
lS tabular silver halide grains. To realize the full
advantages of this invention it is preferred to
adsorb spectral sensitizing dye to the grain
surfaces of the high aspect ratio tabular grain
emulsions in a substantially optimum amount--that
is, in an amount sufficient to realize at least 60
percent of the maximum photographic speed attainable
from the grains under contemplated conditions of
exposure. The quantity of dye employed will vary
with the specific dye or dye combination chosen as
well as the size and aspect ratio of the grains. It
is known in the photographic art that optimum
spectral sensitization is obtained with organic dyes
at about ~5 to 100 percent or more of monolayer
coverage of the total available surface area of
surface sensitive silver halide grains, as
disclosed, for example, in West et al, "The Adsorp-
tion of Sensitizing Dyes in Photographic Emulsions",
Journal of Phys. Chem., Vol 56, p. 1065, 1952;
Spence et al, "Desensitization of Sensitizing Dyes",
Journal of Physical and Colloid Chemistry, Vol. 56,
No. 6, June 1948, pp. 1090-1103; and Gilman et al
`` ~21(~6Z6
--~1--
U.S. Patent 3,979,213. Optimum dye concentration
levels can be chosen by procedure~ taught by Mees,
Theory of the Photographic Process, Macmi}lan, 1942,
pp. 1067-1069.
Although native blue sensitivity of silver
bromide or bromoiodide is usually relied upon in the
art in emulsion layers intended to record expo6ure
to blue light, it i8 gpecifically recognized that
advantages can be realized from ~he use of blue
10 spectral se~sitizing dyes. When the blue recording
emulsion~ in such emulsion layer~ are high aspect
ratio tabular grain silver bromide and silver
bromoiodide emulsions, very large increases in speed
are realized by the use of blue spectral sensitizing
15 dye8.
Useful blue spectr~l ~ensitizing dyes for
high a6p~ct ratio tabular grain silver bromide and
silver bromoiodide emulsions can be selected from
any of the dye classes known to yield spectral
20 sensitizers. Polymethine dyes, ~uch a~ cyanines,
merocyanines, hemicyMnines, hemioxonols, and mero-
styryls, are preferred blue spectral sensitizers
; Generally useful blue spectral sensitizers can be
selected from among these dye classes by their
25 absorption characteristics--i.e., hue. There are,
however, general structural correlations that can
serve as a guide in selecting useful blue sensi-
tizers. Generally the shorter the methine chain,
the shorter the wavelength of the 6ensitizing
30 maximum. Nuclei also influence absorption. The
addition of fused rings to nuclei tends to favor
longer wavelengths of absorption. Substituents ca~
also alter absorption characteristics. In the
formulae which follow, unles~ othewise specified,
alkyl groups and moieties contain from 1 to 2~
carbon atoms, preferably from 1 to 8 carbon atoms.
. ,
.~
~21~6Z6
-42 -
Aryl groups and moieties contain from 6 to 15 carbon
atoms and are preferably phenyl or naphthyl group~
or moieties.
Preferred cyanine blue spectral sensitizers
are monometh~ne cyanines; however, u~eful cyanine
blue spectral sensitizers can be selected from among
those of Formula 1.
1- -Z~- -I R3 R4 Rs 1- _z2_ _ I
10 Rl~N~CH-CH~pC-C~~C~C)m~C~CH~CH~qN~R2
Formula 1 k Q
where
zl and Z2 may be the same or different
and each represents the elements needed to complete
a cyclic nucleus dérived from basic heterocyclic
nitrogen compounds such as oxazoline, oxazole,
benzoxazole, the naphthoxazoles (e.g., naphth-
[2,1-d]oxazole, naphth[2,3-d]oxazole, and naphth-
~1,2-d]oxazole), thiazoline, thiazole, benzothia-
zole, the naphthothiazoles (e.g., naphtho~2,1-d]-
thiazole), the thiazoloquinolines (e.g., thiazolo-
[4,5-b]quinoline), selenazollne, selenazole, benzo-
selenazole, the naphthoselenazoles (e.g., naphtho-
tl,2-d~selenazole), 3H-indole (e.g., 3,3-dimethyl-
3H-indole), the benzindoles (e.g., l,l-dimethylbenz-
[e]indole), imidazoline, imidazole, benzimidazole,
the naphthimidazoles (e.g., naphth~2,3-d]imidazole),
pyridine, and quinoline, which nuclei may be substi-
tuted on the ring by one or mose of a wide varietyof substituents such as hydroxy, the halogens (e.g.,
fluoro, chloro, bromo, and iodo), alkyl groups or
substituted alkyl groups (e.g., methyl, ethyl,
propyl, isopropyl, butyl, octyl, dodecyl, octadecyl,
2-hydroxyethyl, 3-sulfopropyl, carboxymethyl,
2-cyanoethyl, and trifluoromethyl), aryl groups or
` " lZ~626
-43-
substituted aryl groups (e.g., phenyl, l-naphthyl,
2-naphthyl, 4-sulfophenyl, 3-carboxyphenyl, and
4-biphenyl), aralkyl group~ (e.g., benzyl and
phenethyl), alkoxy groups (e.g., methoxy, ethoxy,
and isopropoxy), aryloxy groups (e.g., phenoxy and
l-naphthoxy), alkylthio groups (e.g., methylthio and
ethylthio), arylthio groups (e.g., phenylthio,
~-tolythio, and 2-naphthylthio), methylenedioxy,
cyano, 2-thienyl, styryl, amino or substituted amino
groups (e.g., anilino, dimethylamino, diethylamino,
and morpholino), acyl groups, such as carboxy (e.g.,
acetyl and benzoyl) and sulfo;
Rl and R2 can be the game or different and
reprefient ~lkyl groups, aryl groups, alkenyl groups,
or aralkyl groups, with or without substituents,
(e.g., carboxymethyl, 2-hydroxyethyl, 3-fiulfopropyl,
3-sulfobutyl, 4-sulfobutyl, 4-sulfophenyl, 2-meth-
oxyethyl, 2-sulfatoethyl, 3-thiosulfatopropyl,
2-phosphonoethyl, chlorophenyl, and bromophenyl);
R3 represents hydrogen;
R~ and R5 represents hydrogen or alkyl of
from 1 to 4 carbon atoms;
p and q are 0 or 1, except that both p and q
pre~erably are not l;
m i~ 0 or 1 except that when m is 1 both p and q
are 0 and at leaRt one of Z~ and Z2 represents
imidazoline, oxazoline, thiazoline, or selenazoline;
A is an anionic group;
B is a cstionic group; and
k and ~ may be 0 or 1, depending on whether
ionic substituents are present. Variants are, of
course, possible in which Rl and R3, R2 and
R5, or Rl and R2 (particularly when m, p, and
q are 0) together represent the atoms necessary to
complete an alkylene bridge.
Some representative cyanine dyes useful a~
blue sensitizers are listed in Table I.
. .,J
~Z$~;~iZ6
-44 -
Table I
l. 3,3'-Diethylthiacyanine b~omide
~ CH-- ~+ ;l ;
S
I I Br~
C2Hs C2Hs
2. 1-Ethyl-3'-methyl-4'-phenylnaphtho[1,2-
d]thiazolothiazolinocyanine bromide
~-~ ,S~ ~
CH--~ ~ J
\-~ C2Hs CHa ~-~ B~
lS3. 1',3-Diethyl-4-phenyloxazolo-2'-cyanine
iodlde
\ .~ \./ ~.
. Il / ~CH-l~+/ll\ ~l
20~./ C2Hs C2Hs I-
4. Anhydro 5-chloro-5'-methoxy-3,3'-bi B -
(~-6ulfoethyl)thiacyanine hydroxide,
triethylamine s~lt
~-\ /s\ /s\ /-~
C~!~-/Y\N/ ~ bCH
(CH2) 2 (CHz) 2 (CzH5)3NH+
SOa S03
-45-
5. 3,3'-Bis(2-carboxyethyl3thiazolino-
carbocyanine iodide
\ /s\
CH-CH-CH--~ ~ ~
(CH~)2 (CH2)2
COOH COOH
6. 1,1'-Diethyl-3,3'-ethylenebenzimida-
zolocyanine iodide
C 2H5 C2H5
~ ? \\N+/ \ ~
CH2- CH2 I-
7. 1-(3-E~hyl-2-benzothiazolinylidene)-
1,2,3,4-tetrahydro-2-methylpyrido-
~2,1-b]-benzothiazolinium iodide
/ 5\ /-~
~-/ ~ \ ~ I-
C 2Hs
~ H3
8. Anhydro-5,5'-dimethoxy-3,3'-bl 8 (3-
sulfopropyl)thiscyanine hydroxide, sodium
salt
I 1l \ -CH--/\ + ¦l i
NaS03(CH2) 3 (CH2~3S03- Ns +
Preferred merocyanine blue spectral sensi-
tizers are zero methine merocyanine~; however,
6Z6
-46 ~
u~eful me~ocyanine blue spectral ~ensitizer~ can be
selected from among those of Formula 2.
o
_ _z _ _ R/~ 11
-G
5R-N~cH-cH~rc~(c-cR )n \G2
Formula 2
where
Z represent~ the Rame elements as either Zl or
0 Z2 of Formula 1 above;
R represents the same group~ a~ e~ther Rl or
R2 of Formula 1 above;
R4 and Rs represent hydrogen, an alkyl group
of 1 to 4 carbon fltoms~ or an aryl group (e.g.,
phenyl or naphthyl) 3
Gl repre~ents an slkyl group or 6ub6tituted
alkyl group, an aryl or sub~t~tuted aryl group, an
aralkyl group, ~n alkoxy group, ~n aryloxy group, a
hydroxy group~ an amino group, a subRtituted amino
group wherein ~pecific group~ are of the types in
Formula l;
G2 can represent eny one of the groups listed
for Gl and in addition can repre~ent a cyano
group, an alkyl, or arylsulfonyl group, or a group
represented by -C-Gl, or G2 taken together with
o
can represent the elements needed to complete a
syclic acidic nucleus such a6 those derived from
2,4-oxazolidinone (e.g., 3-ethyl-2,4-oxazolidin-
dione), 2,4-thiazolidindione (e.g., 3-methyl-2,4-
ehiazolidlndione), 2-thio-2~4-oxazolidindione (e.g.,
3-phenyl-2-thio-2,4-oxazolidindione), rhodanine,
Euch as 3-ethylrhodanlne, 3-phenylrhodanine,
3~(3-dimethylaminopropyl)rhodanine, and 3 calboxy-
~LZ1~6Z~-47-
methylrhodanine, hydantoin (e.g., 1,3-diethylhydan-
toin and 3-ethyl-1-phenylhytantoin), 2-thiohydantoin
(e.g., l-ethyl-3-phenyl-2-thiohydantoin, 3-heptyl-
l-phenyl-2-thiohydantoin, and 1,3-diphenyl-2-thio-
hydantoin), 2-pyrazolin-5-one, such as 3-methyl-1-
phenyl-2-pyrazolln-5-one, 3-methyl-1-(4-carboxy-
butyl)-2-pyrazolin-5-one, and 3-methyl-2-(4-sulfo-
phenyl)-2-pyrazolin-5-one, 2-isoxazolin-5-one (e.g.,
3-phenyl-2-isoxazolin-5-one), 3,5-pyrazolidindione
(e.g., 1,2-diethyl-3,5-pyrazolidindione and 1,2-di-
phenyl-3,5-pyrazolidindione), 1,3-indandione,
1,3-dioxane-4,6-dione, 1,3-cyclohexanedione, barbi-
turic acid (e.g., l-ethylbarbituric acid and 1,3-di-
ethylbarbituric acid), and 2-thiobarbiturlc acid
(e.g., 1,3-diethyl-2-thiobarbituric acid and
1,3-bi B (2-methoxyethyl)-2-thiobarbituric BCi d);
r and n each can be 0 or 1 except that when n is
1 then generally either Z is restricted to imidazo-
line, oxazoline, selenazoline, thiazoline, imidazo-
line, oxazole, or benzoxazole, or Gl and G2 donot repre6ent a cyclic sy6tem. Some representative
blue 6ensitizin~ merocyanine dyes are listed below
in Table II.
Table II
1. 5-(3-Ethyl-2-benzoxazolinylidene)-3-
phenylrhodanine
1 ll
~ ~ II-N/ ~.
~ S
C2Hs
~2~ 26
-48-
2. 5-tl-(2-Carboxyethyl) 1,4-dihydro-4-
pyridinyl~dene]-l-ethyl-3-phenyl-2-thio-
. hydantoin
S i i
~ ! -N/ ~.
HOOCCH2CH~ S
'-- \N/
C2Hs
3. 4-(3-Ethyl-2~benzothiazolinylidene)-3-
methyl-l-(~-~ulfophenyl)-2-pyrazolin-5-
one, Pota~ium Salt
. i iI_SO3 K~
.~ ~./S~ ll-N/ ~.
~N
C2Hs ~H3
4. 3-Carboxymethyl-5-(5-chloro-3-ethyl-2-
benzothiflzolinylidene)rhodanine
Cl/ ~-/ ~ \S/
C2Hs
5. 1,3-Diethyl-5-t3,4,4-trimethyloxazoli-
dinylidene)ethylidene]-2-thiobarbituric acid
H C ~ CH-CH.~ S
H3C I ~ \C2Hs
CH3
~Z~ i2~
~49-
Useful blue sensitizing hemicyanine dyes
include those represented by Formul~ 3.
l l G3
R-N~CH-CH~pC~CLI~CL2(~CL3CL4) ~N~ 4
Formula 3 (A)k
where
Z, R, and p repre~ent the same element6 aæ in
Formula 2; G 3 and G4 may be the same or differ-
10 ent and may represent alkyl, substituted alkyl,aryl, substituted aryl, or aralkyl, as illustrated
for ring substituents in Formula 1 or G3 and G4
taken together complete a ring sy~tem derived from a
cycl~c secondary amine, such as pyrrolidine, 3-pyr-
15 roline, p~peridine, piperazine (e.g., 4-methylpiper-
azine and 4-phenylpiperazlne), morpholine, 1,2,3,4-
tetrahydroquinoline, decahydroquinoline, 3~azabi-
cyclo[3,2,2]nonane, indoline, azetidine, and hexa-
hydroazepine;
Ll to L4 repre~ent hydrogen, alkyl of 1 to 4
carbon~, aryl, substituted aryl, or any two of Ll,
L2, L3, L4 can represent the elements needed
to complete an alkylene or carbocyclic bridge;
n is O or l; and
A and k have the same definition as in Formula 1.
Some representative blue Rensitizin~
hemicyanine dyes are ll~ted below in Table III.
~21~2~
-so -
Table III
1. 5,6-Dichloro-2-[4-(diethylamino)-1,3-
butadien-l-yl~-1,3-diethylbenzimidazolium
iodide
C2 ~s
l~C~ N" C2Hs
- CH-CH-CH-CH-N~
C2Hs I-
2. 2-{2-[2-(3-Pyrrolino)-l-cyclopenten-
l-yl~ethenyl}3-ethylthiazolinium
perchlorate
i ~ -CH-CH~-C-C/ ~
I Cl-04
C2Hs
0 3. 2-(S,S-Dimethyl-3-piperidino-2-cyclohexen-
l-yldenemethyl)-3-ethylbenzoxazolium
perchlorate
(CH3 )2
i \~/ \ CH=~ /. Cl-04
C2 Hs
Useful blue sensitiz~ng hemioxonol dyes
30 include those represented by Formula 4.
G~- ~ 0 G3
C'CLl ( -CL2 -CL3 ) -~
Formula 4
where
"` ~Z1~62
-51 -
G~ and G2 represent the same elements as in
Formula 2;
G3, G4, Ll, L2, and L3 represent the
same elements as in Formula 3; and
n is O or 1.
Some representative blue ~ensitizing
hemioxonol dyes are listed in Table IV.
Table IV
1. 5-(3-Anilino-2-propen-1-ylidene)-1,3-
diethyl-2-thiobarbituric acid
C2 Hs
/N-C~ H
S'-~ ,~ ~CH-CH-CH-N-
C2Hs
2. 3-Ethyl-5-(3-piperidino-2-propen-1-
ylidene)rhodanine
o
2 0 ~ /- -CH-CH~=CH-~ /-
g \S/ -
3.3-Allyl ~5-[5,5 -dimethyl-3-(3-pyrrolino)-
2-cyclohexen-1-ylidene]rhodanine
O Hs C\ /CH3
CH2~CH-CH2\~ \ ./ \ ~< \
Useful blue sensitiz~ng merostyryl dyes
~nclude those represented by Formula 5.
G ~--CH-~CH~CH)n--~ ~ ~ G4
Formula 5
~ \
lZ~L~62~ -
-~2 -
where
Gl, G2, G3, G4, and n are as defined in
Formula 4.
Some representative blue sensitizing
5 merostyryl dyes are listed in Table V.
Table V
1. 1-Cyano-1-~4-dimethylaminobenzylidene)-
2-pentanone
~C-CH-~
2. 5-(4-Dimethylaminobenzylidene-2~3-
diphenylthiazolidin-4-one-1-oxide
.\ O
./ ~ \ / \ CH3
CH3
11 11
~./ O
3. 2-(4-Dimethylaminocinnamylidene)thiazolo-
[3,2-a]benzimldazol-3~one
._. O
\N-~ / ZcH-cHzcH-.~
Spectral sensitization can be undertaken at
any stage of emulsion preparation heretofore known
30 to be useful. Most commonly spectral sensitization
is undertaken ln the art subsequent to the comple-
tion of chemical sensitization. However, it is
specifically recognized that spectral sensitization
can be undertaken alternatively concurrently with
35 chemical sensitizat~on, can entirely precede chemi-
cal sensitization, and can even commence prior to
lZ~;6
-s3-
the completion of silver halide grain precipitation,
as taught by Philippaerts et al U.S. Patent
3,628,960, and Lock-r et al U.S. Patent 4,225,666.
As taught by Locker et al, it is specifically
contemplated to distribute introduction of the
spectral sensitizing dye into the emulsion so that a
portion of the spectral sensitizing dye is present
prior to chemical sensitization and a remaining
portion is in~roduced after chemical sensitization.
Unlike Locker et al, it is specifically contemplated
that the spectral sensitizing dye can be added to
the emulsion after 80 percent of the silver halide
has been precipitated. Sensitization can be
enhanced by pAg adjustment, including variation in
pAg which completes one or more cycles, during
chemical and/or spectral sensitization. A specific
example of pAg adjustment is provided by Research
Disclosure, Vol. 181, May 1979, Item 18155.
Multicolor Photographic ~lement and
Processing Features
In addition to the radiation-sensitive
emulsions described above the multicolor photo-
graphic elements of this invention can include a
variety of features which are conventional in
multicolor photographic elements and therefore
require no detailed description. For example, the
multicolor photographic elements of this invention
can employ conventional features, such as disclosed
in Research Disclosure, Item 17643, cited above.
Optical brighteners can be introduced, as disclosed
by Paragraph V. Antifoggants and sensitizers can be
incorporated, as disclosed by Paragraph VI.
Absorbing and scattering materials can be employed
in the emulsions of the invention and in separate
layers of the photographic elements, as described in
Paragraph VIII. Hardeners can be incorporated, as
disclosed in Paragraph X.
lZ~6Z6
-54-
Coating aids, as described in Paragraph XI, and
plasticizers and lubricants, as des~ribed in Para-
graph XII, can be present. Antistatic layers, as
described in Paragraph XIII, can be present.
5 Methods of addition of addenda are described in
Paragraph XIV. Matting agents can be incorporated,
as described in Paragraph XVI. Developing agents
and development modifiers can, if desired, be
incorporated, as described in Paragraphs XX and
10 XXI. Silver halide emulsion layers as well as
interlayers, overcoats, and subbing layer6, if any,
present in the photographic elements can be coated
and dried as described in Paragraph XV.
The layers of the photographic elements can
15 be coated on a variety of supports~ Typical photo-
graphic supports include polymeric film, wood
fiber--e.g., paper, metallic sheet and foil, glass
and ceramic supporting elements provided with one or
more subbing layers to enhance the adhesive, anti-
20 static~ dimensional, abrasive, hardness, frictional,
antihalation and/or other properties of the support
surface. Typical of useful paper and polymeric film
supports are those disclosed in Research Disclosure,
Item 17643, cited above, Paragraph XVII.
The multicolor photographic elements can be
used to form dye images therein through the selec-
tive destruction or formation of dyes. The photo-
graphic elements can be used to form dye images by
emplo~ing developers containing dye image formers,
30 such as color couplers, as illustrated by U.K.
Patent 478,984, Yager et al U.S. Patent 3,113,864,
Vittum et al U.S. Patents 3,002,836, 2,271,238 and
2,362,598, Schwan et al U.S. Patent 2,950,970,
Carroll et al U.S. Patent 2,592,243, Porter et al
35 U.S. Patents 2,343,703, 2,376,380 and 2,369,489,
Spath U.K. Patent 886,723 and U.S. Patent 2,899,306,
Tuite U.S. Patent 3,152,896 and Mannes et al U.S.
~ Z6
Patents 2,115,394, 2,252,718 and 2,108,602, and
Pilato U.S. Patent 3,547,650. In this form the
developer contains a color-developing agent (e.g., a
primary aromatic amine) which in its oxidized form
5 is capable of reacting with the coupler (coupling)
to form the image dye.
The dye-forming couplers can be incorpo-
rated in the photographic elements, as illu~trated
by Schneider et al, Die Chemie, Vol. 57, 1944, p.
10 113, Mannes et al U.S. Patent 2,304,940, Martinez
U.S. Patent 2,269,158, Jelley et al U.S. Patent
2,322,027, Frolich et al U.S. Patent 2,376,679,
Fierke et al U.S. Patent 2,801,171, Smith U.S.
Patent 3,748,141, Tong U.S. Patent 2,772,163,
15 Thirtle et al U.S. Patent 2,835,579, Sawdey et al
U.S. Patent 2,533,514, Peterson U.S. Patent
2,353,754, Seidel U.S. Patent 3,409,435 and Chen
Research Disclosure, Vol. 159, July 1977, Item
15930. The dye-forming couplers can be incorporated
20 in different amounts to achieve differing photo-
graphic effects. For example, U.K. Patent 923,045
and Kumai et al U.S. Patent 3,843,369 teach limiting
the concentration of coupler in relation to ~he
silver coverage to less than normally employed
25 amounts in faster and intermediate speed emulsion
layers.
The dye-forming couplers are commonly
chosen to form sub~ractive primary (i.e., yellow,
magenta and cyan) ~mage dyes and are nondiffusible,
30 colorles6 couplers, such as two and four equivalent
couplers of the open chain ketomethylene, pyra-
zolone, pyrazolotriazole, pyrazolobenzlmidazole,
phenol and naphthol type hydrophobically ballasted
for incorporation in high-boiling organic (coupler)
35 solvents. Such couplers are illustrated by Salminen
et al U.S. Patents 2,423,730, 2,772,162, 2,895,826,
2,710,803, 2,407,207, 3,737,316 and 2,367,531, Loria
-
lZ~6Z6
~56 -
et al U.S. Patents 2,772,161, 2,600,788, 3,006,759,
3,214,437 and 3,253,924, McCrossen et al U.S. Patent
2,875,057, Bush et al U.S. Patent 2,908,573,
Gledhill et al U.S. Patent 3,034,892, Weissberger et
5 al U.S. Patents 2,474,293, 2,407,210, 3,062,653,
3,265,506 and 3,384,657p Porter et al U.S. Patent
2,343,703, Greenhalgh et al U.S. Patent 3,127,269,
Feniak et al U.S. Patents 2,865,748, 2,933,391 and
2,865,751, Bailey et al U.S. Patent 3,725,067,
10 Beavers et al U.S. Patent 3,758,308, Lau U.S. Patent
3,779,763, Fernandez U.S. Patent 3,785,829, U.K.
Patent 969,921, U.K. Patent 1,241,069, U.K. Patent
1,011,940, Vanden Eynde et al U.S. Patent 3,762,921,
Beavers U.S. Patent 2,983,608, Loria U.S. Patent~
15 3,311,476, 3 9 408,194, 3,458,315, 3,447,928,
3,476,563, Cressman et al U.S. Patent 3,419,390,
Young U.S. Patent 3,419,391, Lestina U.S. Patent
3,519,429, U.K. Patent 975,928, U.K. Patent
1,111,554, Jaeken U.S. Patent 3,222,176 and Canadian
20 Patent 726,651, Schulte et al U.K. Patent 1,248,924
and Whitmore et al U.S. Patent 3,227,550. Dye-form-
ing couplers of differing reaction rates in single
or separate layers can be employed to achieve
desired effect~ for specific photographic
25 aPPlications.
The dye-forming couplers upon coupl~ng can
release photographically useful fragments, such as
development inhibitors or accelerators, bleach
accelerators, developing agents, silver halide
30 solvents, toners, hardeners, fogging agents, anti-
foggants, competing couplers, chemical or spectral
sensitlzers and desensitizers. Development inhibi-
tor-releasing (DIR) couplers are illu~trated by
Whitmore et al U.S. Patent 3,143,062, Barr et al
35 U.S. Patent 3,227,554, Barr U.S. Patent 3,733,201,
Sawdey U.S. Patent 3,617,291, Groet et al U.S.
Patent 3,703,375~ Abbott et al U.S. Patent
-- lZlr~Z6
-57-
3,615,506, Weissberger et al U.S. Patent 3,265,506,
Seymour U.S. Patent 3,620,745, Marx et ~1 U.SO
Patent 3,632,345, Mader et al U.S. Patent 3,869,291,
U.K. Patent 1,201,110, Oishi et al U.S. Patent
5 3,642,485, Verbrugghe U.K. Patent 1,236,767,
Fu~iwhara et al U.S. Patent 3,770,436 and Matsuo et
al U.S. Patent 3,808,945. Dye-forming couplers and
nondye-forming compounds which upon coupling release
a variety of photographically useful groups &re
described by Lau U.S. Patent 4,248,962. DIR
compounds which do not form dye upon reaction with
oxidized color-developing ~gents can be employed, a~
illustrated by Fujiwhara et al German OLS 2,529,350
and U.S. Patents 3,928,041, 3,958,993 and 3,961,959,
15 Odenwalder et al German OLS 2,448,063, Tanaka et al
German OLS 2,610,546, Kikuchi et al U.S. Patent
4,049,455 and Credner et al U.S. Patent 4,052,213.
DIR compounds which oxidatively cleave can be
employed, as illu~trated by Porter et al U.S. Patent
20 3,379,529, Green et al U.S. Patent 3,043,690, Barr
U.S. Patent 3,364,022, Duennebier et al U.S. Patent
3,297,445 and Rees et al U.S. Patent 3,287,129.
Silver halide emulsions which are relatively light
insensitive, such ~s Lippmann emulsions, have been
25 utili~ed as interlayer6 and overcoat layer~ to
prevent or control the migration of development
inhibitor fragments as described in Shiba et al U.S.
Patent 3,892,572.
The photographic elements can incorporate
30 colored dye-forming couplers, such as those employed
to form integral masks for negative color images, as
illustrated by Hanson U.S. Patent 2,449,966, Glass
et al U.S. Patent 2,521,908, Gledhill et al U.S.
Patent 3,034,892, Loria U.S. Patent 3,476,563,
35 Lestina U.S. Patent 3,519,429, Friedman U.S. Patent
2,543,691, Puschel et al U.S. Patent 3,028,238,
Menzel et al U.S. Patent 3,061,432 and Greenhalgh
. ..-
~ 6Z~
-5~-
U.K. Patent 1,035,959, and/or competing couplers, as
illustrated by Murin et al U.S. Patent 3,876,428,
Sakamoto et al U.S. Patent 3,580,722, Puschel U.S.
Patent 2,998,314, Whitmore U.S. Patent 2, 808,329,
5 Salminen U.S. Patent 2,742,832 and Weller et al U.S.
Patent 2, 689, 793.
The photographic element6 can include image
dye stabilizers. Such image dye stabilizers are
illustrated by U.K. Patent 1,326,889, Lestina et al
10 U.S. P~tents 3,432,300 and 3,69~,909, Stern et al
U.S. Patent 3,574,627, Brannock et al U.S. Patent
3,573,050, Arai et al U.S. Patent 3,764,337 and
Smith et al U.S. Patent 4,042, 394.
Dye images can be formed or ~mplified by
15 proce~ses which employ in combination with a dye~
image-generating reducing agent an inert transition
metal ion complex oxidizing agent, as illustrated by
Bissonette U.S. Patents 3,748,13~, 3,826,652,
3,862,842 and 3,989,526 and Travis U.S. Patent
20 3,765,891, and/or a peroxide oxidizing agent, as
illu~trated by Mate~ec U.S. Patent 3,674,490,
Research Disclosure, ~ol. 116, December 1973, I~em
11660, and Bissonette Research Disclo~ure, Vol. 148,
August 1976, Items 14836, 14846 and 14847.
The photographic elements can produce dye
images through the selective destruction of dyes or
dye precursors, such as silver-dye-bleach processes,
as illustr~ted by A. Meyer, The Journal of Photo-
graphic Science, Vol. 13, 1965, pp. 90-97. Bleach-
30 able azo, azoxy, xanthene, azine, phenylmethane,
nitroso complex, indigo, quinone~ nitro-substituted,
phthalocyanine and formazan dyes, as illustrated by
Stauner et al U.S. Patent 3,754,923, Piller et al
U.S. Patent 3,749,576, Yoshida et al U.S. Patent
35 3,738,839, Froelich et al U.S. Patent 3,716,368,
Piller U.S. Patent 3,655,388, Williams et al U.S.
Patent 3,642,482, Gilman U.S. Patent 3,567,448,
~Z~J62~
-59-
Loeffel U.S. Patent 3,443,953, Ander~u U.S. Pstents
3,443,952 and 3,211,556, Mory et al U.S. Patents
3,202,511 and 3,178,291 and Anderau et ~1 U.S.
Patents 3,178,285 and 3,178,290, as well as their
5 hydrazo, diazonium and tetrazolium precursors and
leuco and shifted derivative6, ns ~llu6trated by
U.K. Patents 923,265, 999,996 and 1,042,300, Pelz et
al U.S. Patent 3,684,513, Watanabe et al U.S. Patent
3,615,493, Wilson et al U.S. Patent 3,503,741, Boes
10 et al U.S. Patent 3,340,059, Gompf et al U.S. Patent
3,493,372 snd Puschel et al U.S. Patent 3~561,970,
can be employed.
It is common practice in forming dye images
in silver halide photographic elements to remove the
15 developed silver by bleaching. Such removal can be
enhanced by incorporation of a bleach accelerator or
a precursor thereof in a proce6sing solution or in a
layer of the element. In some instances the amount
of silver formed by development is small in relation
20 to the amount of dye produced, particularly in dye
image amplification, as described above, and silver
bleaching is omitted without substantial visual
effect.
The photographic el~ments can be processed
25 to form dye images which correspond to or are
reversals of the silver halide rendered selectively
developable by imagewise exposure. Reversal dye
images can be formed in photographic elements having
differentlally spectrally sensitized silver halide
30 layers by black-and-white development followed by i)
where the elements lack incorporated dye image
formers, sequential reversal color development with
developers containing dye image former~, such as
color couplers, as illustr~ted by Mannes et al U.S.
35 Patent 2,252,718~ Schwan et al U.S. Patent 2,950,970
and Pilato U.S. Patent 3,547,650; ii) where the
elements contain incorporated dye image formers,
:;
z~
-60-
such as color couplers, a single color development
step, as illustrated by the Kodak Ektachrome~ E4
and E6 and Agfa processes described in British
Journal of Pho~ography Annual, 1977, pp. 194-197,
and British Journal of Photography, August 2, 1974,
pp. 668-669; and iii) where the photographic
elements contain bleachable dyes, silver-dye-bleach
processing, as illustrated by the Cibachrome P-10
and P-18 processes described in the British Journal
of Photography Annual, 1977, pp. 204-212.
The photographic elements can be adapted
for direct color reversal processing (i.e., produc-
tion of reversal color images without prior black-
and-white development), as illustrated by U.K.
Patent 1,075,385, Barr U.S. Patent 3,243,294,
Hendess et al ~.S. Patent 3,647,452, Puschel et al
German Patent 1,257,570 and U.S. Patents 3,457,077
and 3,467,520, Accary-Vene~ et al U.K. Patent
1,132,736, Schranz et al German Patent 1,259,700,
Marx et al German Patent 1,259,701 and Muller-Bore
German OLS 2,005,091.
Dye images which correspond to the silver
halide rendered selectively developable by imagewise
exposure, typically negative dye images, can be
produced by processing, as illustrated by the
Kodacolor~ C-22, the Kodak Flexicolor'~ C-41 and
the Agfacolor processes described in British Journal
of PhotogrPphy Annual, 1977, pp. 201~205. The
photographic elements can also be processed by the
Kodak Ekt~print-3 and -300 processes as described in
Kodak Color Dataguide, 5th Ed., 1975, pp. 18-19, and
the Agfa color process as described in British
Journal of Photography Annual, 1977, pp. 205-206,
such processes being particularly suited to process-
ing color print materials, such as resin-coated
photographic papers, to form positive dye images.
The multicolor photographic elements of
this invention produce multicolor images from
Z6
--61
combinations of subtractive primary imaging dyes.
Such photographic elements are comprised of a
support and typically at least a triad of super-
impo~ed silver halide emul~ion layers ~or separately
5 recording blue, green, and red exposures as yellow,
magenta, and cyan dye images, respectively. (Expo-
6ure~ can be of any conventional nature and are
illustrated by Research Disclosure, 17643, cited
above, Paragraph XVIII.) Although the present
10 invention generally embraces any mul~icolor photo-
graphic eleme~t of this type including at least one
silver halide emulsion layer containing high aspect
ratio silver iodide tabular grains, additional
advantages can be realized when additional high
15 aspect ratio tabular grain emulsion layer6 are
employed.
Multicolor photographic elements are often
described in terms of color-forming layer units.
Most commonly multicolor photographic element~
20 contain three superimposed color-forming layer units
each containing at least one silver halide emulsion
layer capable of recording expogure to a different
third of the spectrum and capable of producing a
complementary subtractive primary dye image. Thus,
25 blue, green) and red recording color-forming layer
units are used to produce yellow, magenta, and cyan
dye image~, respectively. Dye imaging materials
need not be present in any color-forming layer unit,
but can be entirely supplied from processing
30 solutions~ When dye imaging materials are
incorporated in the photographic element, they can
be located in an emulsion layer or in a layer
located to receive oxidized developing or electron
transfer agent from an ad~acent emulsion layer of
35 the same color-forming layer unit.
To prevent migration of oxidized developing
or electron transfer agents between color-forming
' .i
~Z~i2~i
layer units with resultant color degradation, it is
common practice to employ scavengers. The scaven-
gers can be located in the emulsion layer~ them-
selves ~ as taught by Yutzy et al U-S- Pstent
5 2,937,086 and/or in interlayers between adjacent
color-formin~ layer units, as illustrated by
Weissberger et al U.S. Patent 2,336,327. It is also
contemplated to employ Lippmann emulRions, particu-
larly silver chloride and silver bromide emulsions
1~ of grain diameters of less than 0.1 micron, blended
with the silver iodide emulsions or in separate
interlayers separating the silver iodide emulsion
layers from the silver halide emulsion layers ~o act
as scavengers for iodide ion6 released on develop-
15 ment. Suitable Lippmann emulsions are disclosed byShiba et al U.S. Patent 3,892,572, cited above, and
Nicholas et al U.S. Patent 3,737~317.
Although each color-forming layer unit can
contain a single emulsion layer, two, three, or more
20 emulsion layers differing in photographic speed are
often incorporated in a single color-forming layer
unit. Where thP desired layer order arrangement
does not permit multiple emulsion layers differing
in speed to occur in a single color-forming layer
25 unit, it i~ common practice to provide multiple
(usually two or three) blue, green, and/or red
recording color-forming layer units in a single
photographic element.
The multicolor photographic elements of
this invention can take any convenient form consis-
tent with the requirements indicated above. Any of
the six possible layer arrangements of Table 27a, p.
211, disclosed by Gorokhovskii, Spectral Studies of
Ib-_lh~55~0~ Y ~ ec~, Focal Press, New York, can
35 be employed. To provide a simple, specific illus-
tration, it is contemplated to add to a conventional
multicolor silver halide photographic element during
lZl~Z~i
-63 -
its preparation one or more blue recording emulsion
layers containing high aspect ratio tabular silver
iodide grains positioned to receive e~po~ing radia-
tion prior to the remaining emul~ion layers.
5 However, in most instances it is preferrred to
sub6titute one or more blue recording emulsion
layers containing high aspect ratio tabular silver
iodide grain~ for con~entional blue recording
emul~ion layers, optionally in combination with
10 layer order srrangement modifications.
The invention can be better appreciated by
reference to the following di6cus~ion of distinctive
features exhibited by the multicolor photographic
elements of thi6 invention, particularly those
15 contributed by th presence of 8 ilver iodide and/or
high average aspect ratio tabular grain~.
a. ~lue light ab60rbing capabilitie6
The multicolor photographic elements of
this invention u6e at least one emul6ion layer
20 containing high aspect ratio tabular ~ilver iodide
grain6 to record imagewise exposures to the blue
portion of the visible spectrum. Since silver
iodide possesses a very high level of absorption of
blue light in the 6pectral region of les6 than about
25 430 nanometer6, in one application of this invention
the 6ilver iodide grains can be relied upon to
absorb blue light of 430 nanometers or less in
wavelength without the use of a blue spectral
sensitizing dye. A silver iodide tabular grain is
30 capable of absorbing mo t of the less than 430
nanometer blue light incident upon it when it is at
least about 0.1 ~icron in thicknes6 and 6ubstan-
tially all of such light when it is at lea~t about
0.15 micron in thickness. (In coating emulsion
35 layers containing high aspect ratio tabular grains
the grains spontaneously align themselves so that
thPir ma~or crystal faces are parallel to the
26
-64-
support ~urface and hence perpendicular to the
direction of exposing radi~tion. Hence exposing
radiation seeks to tr~verse the thickness of the
t~bular grains.)
The blue light abgorbing capability of
tabular silver iodide grains i~ in direct contra~t
to the light absorbing capability of the high sspect
ratio tabular grain emulsion~ of other silver hslide
compositions, such as those disclosed by Kofron et
10 al, cited above. The latter exhibit markedly lower
levels of blue light absorption even at thicknesses
up to 0.3 micron. Kofron et al, for instance,
specifically teaches ~o increase tabular grain
thicknesses up to 0.5 micron to increase blue light
15 absorption. Further, it should be noted that the
tabular grain thicknesses taught by Kofron et al
take into account that the emulgion layer will
normally be coated with a conventional silver
coverage, which i~ sufficient to prov~de many layers
20 of superimposed tabular grains, whereas the 0.1 and
0.15 micron thicknesses above are for a single
grain. It is therefore apparent that not only can
tabular silver iodide grainæ be used without blue
spectral sensitizers, but they permit blue recording
25 emulsion layers to be reduced in thickness (thereby
increasing sharpness) and reduced in silver cover-
age. In considering this application of the inven-
tion further it can be appreciated that tabular
gra~n silver iodide emulsions, provided minimal
30 grain thicknesses are satisfied, absorb blue light
as a function of the pro~ected area which they
present to exposing radiation. Thi~ is a funda-
mental distinction over other silver halides, such
as silver bromide and silver bromoiodide, which,
35 without the assi~tance of spectral sensitizers,
absorb blue light as a function of their volume.
Not only are the high aspect ratio tabular
grain silver iodide emulsions more efficient in
-
~Zl~Z6
-65 -
absorbing blue light than high aspect ratio tabular
grains of differing halide composition, they are
more efficient than conventional silver iodide
emulsion~ containing nontabular gr~ins or lower
5 average aspect ratio tabular grains. At a 8 ilver
coverage chosen to employ the blue light absorbing
capability of the high a~pect ratio tabular silver
iodide grain~ efficiently conventional silver iodide
emulsions present lower pro~ected areas and hence
10 are capable of reduced blue light absorption. They
also capture fewer photons per grain and are of
lower photographic speed than the high aspect ratio
tabular silver iodide grain emulsions, other parame-
ters being comparable. If the average diameters of
15 the conventional silver ~odide grains are increased
to match the pro~ected area6 presented by the high
aspect ratio tabular grain silver iodide emulions,
the conventional grains become much thicker than the
high aspect ratio tabular silver iodide grains,
20 require higher silver coverages to achieve compar-
able blue absorption, and are in general less
efficient.
Although high aspect ratio tabular silver
iodide grain emulsions can be used to record blue
25 light exposures without the use of spectral ~enstiz-
ing dyes, it is appreciated that the native blue
absorption of silver iodide is not high over the
entire blue region of the ~pectrum. To achieve a
photographic respon6e over the entlre blue region of
30 the spectrum it is specifically contemplated to
employ in combinat~on with such emulsion6 one or
more blue sensitizing dyes. The dye preferably
exhibits an absorption peak of a wavelength longer
than 430 nanometers so that the absorption of the
35 silver iodide forming the tabular grains and the
blue sensitizing dye together extend over a larger
wavelength range of the blue spectrum.
-
~ZlQ6Z~
-66 -
While silver iodide and a blue sensitizing
dye can be employed in combination to provide a
photographic response over the entire blue portion
of the spectrum, lf the ~lver iodide grains are
5 cho~en as described above for recording blue light
efficiently in the absence of spectral æens~tizing
dye, the result is a highly unbalanced sensitivity.
The silver iodide grains absorb substantially all of
the blue light of a wavelength of less than 430
10 nanometers while the blue sensitizing dye absorbs
only a fractlon of the blue light of a wavelength
longer than 430. To obtain a balanced sensitivity
over the entire blue portion of the spectrum it is
contemplated to reduce the effic~ency of the silver
15 iodide grains in absorbing light of less than 430
nanometers in wavelength. This can be accomplished
by reducing the average thicknes~ of the tabular
grains 8 o that they are less than 0.1 micron in
thickness. The optimum thicknes6 of the tabular
20 grains for a specific ~pplication is selected 80
that absorption above and below 430 nanometers iB
substantlally matched. This will vary as a function
of the spectral sensitizing dye or dyes employed.
b. CaPabili~ies related to epitaxy
~s indicated above, there are distinct
advantages to be realized by epitax~ally depositing
silver chloride onto the silver halide host grains.
~nce the silver chloride is epitaxially deposited,
however, it can be altered in halide content by
30 substituting le~s soluble halide ions in the silver
chloride crystal la~tice. Using a conventional
halide conversion process bromide and/or halide ions
can be introduced into the orig~nal silver chloride
cry~tal lattice. Halide conversion can be achieved
merely by bringing the emulsion comprised of silver
halide host grains bearing silver chloride epitaxy
into contact with an aqueous solution of bromide
' :
lZiQ626
-67-
and/or iodide salts. An advantage is achieved in
extending the halide compositions available for use
while retaining the advantages of silver chloride
epitaxial deposition. Additionally, the converted
5 halide epitaxy forms an internal latent image. This
permits the emulsions to be applied to photographic
applications requiring the formation of an internsl
latent image, such as direct positive imaBing.
Further advantages and features of this form of the
10 invention can be appreciated by reference to
Maskasky U.S. Patent 4,142,900.
When the silver salt epitaxy is much more
readily developed than the host grains, it i~
possible to control whether the 8 ilver salt epitaxy
15 alone or the entire composite grain develops merely
by controlling the choice of developing a8ents and
the conditions of development. With vigorous
developing agents, such as hydroquinone, catechol,
halohydroquinone, N-methylaminophenol 6ul fate,
20 3-pyrazolidinone, and mixtures thereof, complete
development of the composite silver halide grains
can be schieved. Maskasky U.S. Patent 4,094,684,
cited above, illustrates that under certain mild
development conditions it is possible to selectively
25 develop silver chloride epitaxy while not developing
silver iodide host grains. Development can be
specifically optimized for maximum silver develop-
ment or for selective development of epitaxy, which
can re6ult in reduced graininess of the photographic
30 image. Further, the degree of silver iodide devel-
opment can control the release of iodide ions, which
can be used to inhibit development.
c. CaPabilities imparted by iodide ion release
In a 6pecific application of this invention
a multicolor photographic element can be constructed
incorporating a uniform distribution of a redox
catalyst in addition to at least one layer contain-
~-- ~2~ Z6
ing high aspect ratio tabular 6ilver iodide grains.When the silver iodide grains are imagewise devel-
oped, iodide ion iB released which locally poisons
the redox catalyst. Thereafter a redox reaction can
5 be catalyzed by the unpoisoned catalyst remaining.
Bissonette U.S. Patent 4,089,685, specifically
illustrate~ a useful redox system in which a perox-
ide oxidizing agent and a dye-image-generating
reducing agent, such as a color developing agent or
10 redox dye-releasor, react imagewise at available,
unpoisoned catalyst sites within a photographic
element. Maskasky U.S. Patent 4,158,565, di~closes
the use of silver iodide host grains bearing silver
chloride epitaxy in such a redox amplification
15 system.
d. Speed-granularity capabilitieR
An important advantage of the multicolor
photographic elements of this invention is their
improved speed-granularity relationship. As taught
20 by Kofron et al, cited above, substantially opti-
mally chemically and spectrally sensitized high
aspect ratio tabular grain silver halide emul~ions
can exhibit unexpected improvements in the speed-
granularity relationships of multicolor photographic
25 elements.
Within the range of silver halide grain
sizes normally encountered in photographic element~
the maximum speed obtained at optimum sensitization
incresses linearly with increasing grain size. The
30 number of absorbed quanta necessary to render a
grain developable is ~ubstantially independent of
grain size, but the density that a given number of
grains will produce upon development is directly
related to their size. If the aim is to produce a
maximum den~ity of 2, for example, fewer grains of
0.4 micron as compared to 0.2 micron in average
diameter are required to produce that density. Less
. . .
ZS
-69-
radiation is required to render fewer grains
developable.
Unfortunately, because the density produced
with the larger grains is concentrated at fewer
5 sites, there are greater point-to-point fluctuations
in density. The viewer's perception of point-to-
point fluctuations in densi~y is termed "graini-
ness". The objective measuremen~ of point-~o-point
fluctuations in density iB termed "granularity".
10 While quantitative measurements of granularity have
taken different forms, granularity is most commonly
measured as rms (root mean square) granularity,
which is defined as the standard deviation of
density within a viewing microaperture (e g~, 24 to
15 48 microns). Once the maximum permissible granu-
larity (also commonly referred to as grain, but not
to be confused w~th silver halide gra~ns) for a
specific emulsion layer iB identified, the maximum
speed which can be realized for that emulsion layer
20 is also effectively limited.
From the foregoing it can be appreciated
that over the years intensive investigat~on in the
photographic art has rarely been directed toward
ob~aining maximum photographic speed in an absolute
25 sense, but, rather, has been directed toward obtain-
ing maximum fipeed at optlmum sensitization while
satisfying practical granularity or grain criteria.
~rue improvements in silver halide emulsion sensi-
tivity allow speed to be increased without increas-
30 ing granularity, granularity to be reduced withoutdecreasing speed 9 or both speed and granularity to
be simultaneously improved. Such sensitivity
improvement is commonly and succinctly referred to
in the art as improvement in the speed-granularity
35 relationship of an emulsion.
In Figure 7 a schematic plot of speed
versus granularity is shown for five silver halide
` 12~z~
--7U--
emulsion6 1 ~ 2, 3, 4, and 5 of the æame composition,
but differing in grain size, each similarly sens~-
tized, identically coated, and identically
processed. While the indiv~dual emulsions differ in
5 maximum speed and granularity, there is a predict-
able linear relationship between the emulsions, as
indicated by the speed-granularity line A. All
emulsions which can be ~oined along the line A
exhibit the same speed-granularity relationship.
10 Emulsions which exhibit true improvements in sensi-
tivity lie above the speed-granularity line A. For
example, emulsions 6 and 7, which lie on the common
speed-granularity l~ne B, are superior in their
6peed-granularity relationship6 to any one of the
15 emulsions 1 through 5. Emulsion 6 exhibits a higher
speed than emulsion 1, but no higher granularity.
Emulsion 6 exhibits the same speed as emulsion 2,
but at a much lower granularity. Emulsion 7 is of
higher speed than emulsion 2, but is of a lower
20 granularity than emulsion 3, which is of lower speed
than emulsion 7. Emulsion 8, which falls below the
speed-granularity line ~, exhibits the poorest
speed-grunularity relationship shown in Figure 7.
Although emulsion 8 exhibits the highest photo-
25 graphic speed of any of the emulsions, its speed isrealized only at a disproportionate increase in
granularity.
The importance of speed-granularity rela-
tionship in photography has led to extensive efforts
30 to quantify and generalize speed-granularity deter-
minations. It is normally a simple matter to
compare precisely the speed-granularity relation-
ships of an emulsion series differing by a single
characterist~c, such as silver halide grain size.
35 The speed-granularity relationships of photographic
products which produce similar characteristic curves
are often compared. For elaboration of granularity
.,
~6Z~;
measurement~ in dye imaging attention is directed to
"Understanding Grainines~ and Granularity", Kodak
Publication No. F-20, Revised 11-79 (a~ailable from
Eastman Kodak Company, Rochester, New York 14650);
5 Zwick, "Quantitative Studie6 of Factors Affecting
Granularity", PhotograPhic Science and Engineering,
Vol. 9, No. 3, May-June, 1965; Eric60n and Marchant,
"RMS Granularity of Monodisperse Photo~raphic
Emulsions", Photographic Science and Engineering,
10 Vol- 16, No. 4, July-August 1972, pp. 253-257; and
Trabka, "A Random-Sphere Model for ~ye ~louds",
Photographic Science and Engineering, Vol. 21, No.
4, July-August 1977, pp. 183-192.
To achieve the highest attainable speed-
15 granularity relationships in the multicolor photo-
graphic elements 4f this invention lt is specifi-
cally preferred that the emulsions contained in the
multicolor elements be sub6tantially op~imally
chemically and spectrally sensitized, although,
20 sub~ect to the con6iderations discussed above, the
silver iod~de emulsion6 need not be 6pectrally
6en6itized. By "6ub6tantially optimally" it is
meant that the emulsions preferably achieve speed6
of at least 60 percent of the maximum log speed
25 attainable from the grains in the spectral region of
6ensitization under the contemplated conditions of
use and processing. Log speed is herein defined as
lOOtl-log E), where E is measured in meter-candle-
seconds at a density of 0.1 above fog. Sub6tan-
30 tially optimum chemical and spectral ~ensitizationof high aspect ratio tabular grain silver halide
emulsion6, particularly silver bromoiodide emul-
sions, is generally taught by Kofron et al. Such
emulsion6 can exhibit 6peed-granularity relation-
35 ship6 superior to conventional (low aspect ratiotabular grain or nontabular grain) emulsion~. It is
generally preferred to employ silver bromoiodide
/
~Zl~ 26
-7Z-
emulsions in com~ination with the high aspect ratio
tabular grain silver iodide emulsions to achieve the
highest attainable speed-granularity relationship6.
Illingsworth U.S. Patent 3,320,069 particularly
5 illustrates conventional silver bromoiodide emul-
sions of outstanding speed-granularity relat~onship
contemplated for use in the multicolor photographic
elements of ~his invention.
e. Sharpness capabilities
While granularity, because of its relation-
ship to speed, is often a focal point of discussion
relating to image quality, image sharpneRs can be
addressed independently. Some factors which influ-
ence image sharpness, such a8 lateral diffusion of
15 imaging materials during processing (~ometimes
termed "image smearing'l), are more closely related
to imaging and processing materials ~han the silver
halide grains. On the other hand, because of their
light scattering properties, 6ilver halide grains
20 themselves primarily affect sharpne~s during image-
wise exposure. It is known in the ~rt that silver
halide grains having diameters in the range o~ from
0.2 to 0.6 micron exhibit maximum scattering of
visible light.
Loss of image ~harpness resulting from
light scattering generally increaseg with increasing
~hickness of a silver halide emulsion layer. The
reason for this can be appreciated by reference to
Figure 8. If a photon of light 1 i8 deflected by a
30 silver halide grain at a point 2 by an angle r
measured as a declination from its original path and
is thereafter absorbed by a second silver halide
grain at a point 3 after traversing a thickness t_
of the emulsion layer, the photographic record of
35 the photon is di6placed laterally by a distance x.
~f, instead of being absorbed within a thickness
t=, the photon traverses a second equal thickness
~æ~a~626
-73-
t3 and is absorbed at a point 4, the photographic
record of the photon is displaced laterally ~y twice
the distance x. It i8 therefore apparent that the
greater the thickne~s displacement of the silver
5 halide grains in a photographic element, the greater
the risk of reduction in image sharpness attribut-
able to light scatter~ng. (Although Figure 8
illustrates the principle in a very 6imple situa-
tion, it is appreciated that in actual practice a
10 photon is typically reflected from ~everal grains
before actually being absorbed and statistical
methods are requ~red to predict it~ probable ulti-
mate point of sbsorption.)
In multicolor photographic elementg
15 containing three or more superimposed silver halide
emulsion layer6 an lncreased risk of reduction in
image sharpness can be presented, since the ~ilver
halide grains are distributed over at least three
layer thlcknesses. In some applications thickness
20 displacement of the 6ilver halide grains ~8 further
increased by the presence of additional materials
that either (1) increAse the thicknesses of the
emulsion layers themselves--a~ where dye-image-pro-
viding materials, for example, are incorporated in
25 the emulsion layers or (~) form additional layers
separating the silver halide emulsion layers,
thereby increasing their thickness displacement--as
where separate scavenger and dye-image-providing
material layers separate ad~acent emulsion layers.
30 Further, in multicolor photographic elements there
are st least three superimposed layer units, each
containing at least one silver halide emulsion
layer. Thus, there is a substantial opportunity ~or
loss of image shsrpness attributable to scattering.
35 Because of the cumulative scattering of overlying
silver halide emulsion layers, the emulsion layer~
farther removed from the exposing radiation source
- can exhibit very significant reductions in sharpness.
~2~ L16Z~
-74-
The high aspect ratio tabular grain silver
halide emul~ions employed in the multicolor photo-
graphic elements of the p~esent invention a~e
advantageous becnuse of their reduced high angle
5 light scattering as compared to nontabular and lower
aspect ratio tabular grain emulsions. As discussed
above with reference to Figure 8, the art has long
recognized that image sharpness decreases with
increasing thickness of one or more silver halide
10 emulsion layers. ~owever from Figure 8 it i8 al80
apparent that the lateral component of light scat-
tering (x and 2x) increases directly with the angle
. To the extent that the angle y remains
small, the lateral displacement of scattered light
15 remains ~mall and image sharpnes~ remains high.
Advantageous sharpness characterlstics
obtainable with high aspect ratio tabular grain
emulsions of the present invention are attributable
to the reduction of high angle scattering. This can
20 be quantitatively demonstrated. Referring to Figure
~, a sample of an emulsion 1 according to the
present invention is coated on a transparent (spec-
ularly transmissive3 support 3 at a silver coverage
of 1.08 g/m3. Although not shown, the emulsion
25 and support are preferably immersed in a liquid
having a substantially matched refractive index to
minimize Fresnel reflections at the surfaces of the
support and the emulsion. The emulsion coating is
exposed perpendicular to the support plane by a
30 collimated light source 5. Light from the source
following a path indicated by the dashed line 7,
which forms an optical axis, strikes the emulsion
coating at point A. Light which passes through the
support and emulsion can be sensed at a constant
35 distance from the emulsion at a hemispherical
detection surface 9. At a point B, which lies at
the intersection of the extension of the initial
6 Z ~ -
-75-
light path and the detection surface, light of a
maximum intensity level is detected.
An arbitrarily selected point C is shown in
Figure 9 on the detection surface. The dashed line
5 between A and ~ forms an angle ~ with the emulsion
coating. By moving point C on the detection surface
it is possible to vary ~ from 0 to 90. By
measuring the intensity of the light scattered 8~ a
function of the angle ~ it i~ possible (because of
10 the rotational symmetry of light scattering about
the optical axis 7) to determine the cumulative
light distribution as a function of the angle ~.
(For a background description of the cumulMtive
light distribution see DePalma and Gasper, "Deter-
15 mlning the Optical Properties of PhotographicEmulsions by the Monte Carlo Method", Photo~raphic
Sclence and Engineering, Vol. 16, No. 3, May-June
1971, pp. 181-191.)
After determining the cumulative light
20 distribution as a function of the angle ~ at
values from 0 to 90 for the emulsion 1 according to
the present invention, the same procedure is
repeated, but with a conventional emul~ion of the
same average grain volume coated at the same silver
25 coverage on another portion of support 3. In
comparing the cumulative light distribution as a
function of the angle ~ for the two emulsions, for
values of ~ up to 70 (and in some instances up to
80 and higher) the amount of scattered light is
30 lower with the emulsions according to the present
invention. In Figure 9 the angle y is shown as
the complement of the angle ~. The angle of
scattering is herein discussed by reference to the
angle y. Thus, the high aspect ratio tabular
35 grain emulsions of this invention exhibit less
high-angle scattering. Since it is high-angle
scattering of light that contributes dispropor-
z~
-76-
tionately to reduction in image ~harpness, it
follows that ~he high a6pect r~tio tabular grain
emul~lons of the pre~ent invention are in each
instance capable of producing sharper images.
As herein defined the term "collection
angle" i~ the value of the angle ~ at which half
of the light striking he detection ~urface lies
within an area subtended by a cone formed by rota-
tion of line AC about the polar axis at the angle
lO Y while half of the light strikes the detection
surface within the remaining area.
While not wi6hing to be bound by any
particular theory to account for the reduced high
angle scattering properties of high aspect ratio
15 tabular 8rain emulsions according to the present
invention, it is bel~eved that the large flat ma~or
crystal faces presented by the high aspect r&tio
tabular grains as well as the orientation o$ the
grains in the coating account for the improvements
20 in 6harpness observed. Specifically 3 it has been
observed that the tabular grains present in a silver
halide emulsion coating are substantially aligned
with the planar support ~urface on which they lie.
Thus, light directed perpendicular to the photo-
25 graphic element striking the emulGion layer tends tostrike the tabular grains substantlally perpen~
dicular to one ma~or crystal face. The thinness of
tabular grains as well as their orientation when
coated permits the high aspect ratio tabular grain
30 emulsion layers of this invention to be substan-
tially thinner than conventional emulsion coatings,
which can also contribute to sharpness. The tabular
silver iodide grains can be even thinner th~n
tabular grains of other silver halide compositions
35 and be coated at lower silver coverages while still
exhibiting efficient blue absorption. Thus high
aspect ratio tabular grain silver iodide elements
~,'
~L21~6Z6
-77-
often are capable of permitting significant improve-
ments in sh~rpness in the multi~olor elements of
this invention.
In a specific preferred form of the inven-
5 tion the high aspect ratio tabular grain emulsionlayers exhibit a minimum average grain diameter of
at least 1.0 micron, most preferably at least 2
microns. Both improved 6peed and sharpnes~ are
attainable as average grain diameters are
10 increased. While maximum useful average grain
diameters will vary with the graininess that can be
tolerated for a specific imaging application, the
maximum average grain diameters of high aspect ratio
tabular grain emulsions according to the present
15 invention are in all in6tances les6 than 30 microns,
preferably less than 15 microns, and optimally no
greater than 10 microns.
Although it i8 possible to obtain reduced
high angle scattering with ~ingle layer coatings of
20 high aspect ratio tabular grain emulsions according
to the present invention, it does not follow that
reduced high angle scattering is necessarily real-
ized in multicolor coatings. In certain multicolor
coating formats enhanced sharpne6s can be achieved
25 with the high aspect ratio tabular grain emulsions
of this invention, but in other multicolor coating
formats the high a6pect ratio tabular grain emul-
sions of this invention can actually degrade the
sharpne~s of underlying emulsion layers. If the
30 emulsion layer of the multicolor photographic
element lying nearest the exposing radiation source
contains grains having an average diameter in the
range of from 0.2 to 0.6 micron, as is typical of
many nontabular emulsions, it will exhibit maximum
35 scattering of light passing through it to reach the
underlying emulsion layers. Unfortunately, if light
has already been scattered before it reaches a high
6~Ç;
`, ~
aspect ratio tabular grain emulsion layer, the
tabular gr~ins can scatter the light pa~sing through
to one or more underlying emul~ion layer~ to an even
greater degree than a conventional emulsion. Thufi,
5 this particular choice of emulsions and layer
arrangement results in the sharpness of the emulsion
layer or layer~ underlying the high aspect ratio
tabular grain emulsion layer being ~ignlficantly
degraded to an extent greater than would be the case
10 if no high aspect ratio tabular grain emulsion~ were
pre6ent in the layer order arrangement.
In order to realize fully the sharpness
advantages in an emulsion layer that underlies a
high aspect ratio tabular grain emulsion layer it is
15 preferred that the the tabular grain emulsion layer
be positioned ~o receive light that is free of
significant scattering (preferably positioned to
receive substantially specularly transmitted
light). Stated another way, in the multicolor
20 photographic elements of this invention improvements
in sharpnes B in emulsion layers underlying tabular
grain emulsion layers are best realized only when
the tabular grain emulsion layer doe6 not itself
underlie a ~urbid layer. For example, if a high
25 aspect ratio tabular grain green recording emulsion
layer overlie6 a red recording emulsion layer and
underlies a Lippmann emulsion layer and/or a high
aspect ratio tabular grain blue recording emulsion
layer according to this invention, the sharpness of
30 the red recording emulsion layer w~ll be improved by
the presence of the overlying tabular grain emulsion
layer or layers. Stated in quantitative terms, if
the collection angle of the layer or layers over-
lying the high aspect ratio tabular grain green
35 recording emulsion layer is less than about 10~, an
improvement in the sharpness of the red recording
emulsion layer can be realized. It is, of cour~e,
."~'
$
-79-
immaterial whether the red recording emulsion layer
is itself a high aspect ratio tabular grain emulsion
layer insofar as the effect o~ the overlying layers
on its sharpness is concerned.
In a multicolor photographic element
containing superimposed color-forming units it is
preferred that at least the emulsion layer lying
nearest the source of exposing radiation be a high
aspect ratio tabulsr grain emulsion in order to
10 obtain the advantages of sharpnesR offerred by this
invention. In a specifically preferred form of the
invention each emulsion layer which lies nearer the
expo~ing radiation ~ource than another image record-
ing emulsion layer iB a high aspect ratio tabular
15 grain emulsion layer.
f. Blue and minus-blue speed separation
Silver bromide and silver bromoiodide
emulsions possess sufficient native sensitivity to
the blue portion of the spectrum to record blue
20 radiation without blue spectral ~ensitization. When
these emulsions are employed to record green and/or
red ~minus blue) light exposures, ~hey are corre-
spondingly spectrally sensitized. In multicolor
photography, the native sensitivity of silver
25 bromide and silver bromoiodide in emulsions intended
to record blue light iB advantageous. However, when
these silver halides are employed in emulsion layers
intended to record exposure~ in ~he green or red
portion of the spectrum, the native blue sensitivity
30 iB an inconvenience, since response to both blue and
green light or both blue and red light in the
emulsion layers will falsify the hue of the multi-
color image sought to be reproduced.
In constructing multicolor photographic
35 elements using silver bromide or silver bromoiodide
emulsions the color falsification can be analyzed as
two distinct concerns. The first concern is the
~2~
--~u--
difference between ~he blue ~peed of the green or
red recording emulsion layer and its green or red
speed. The second concern is the difference between
the blue speed of each blue recording emulsion layer
5 and the blue speed of the corresponding green or red
recording emulsion layer. Generally in preparing a
multicolor photographic element intended to record
accurately image colors under daylight exposure
conditions (e.g., 5500K) the aim is to achieve a
10 difference of about an order of magnitude between
the blue speed of each blue recor~ing emulsion layer
and the blue speed of the corresponding green or red
recording emulsion layer. The art has recognized
that ~uch aim speed differences are not realized
15 using silver bromide or silver bromoiodide emul~ions
unless employed in combination with one or more
approachés known to ameliorate color falsification.
Even then, full order of magnitude speed differences
have not always been realized in product. However,
20 even when such aim speed differences are realized,
further increasing the separation between blue and
minus blue ~peeds will further reduce the recording
of blue exposures by layers intended to record minus
blue exposures.
By far the most common approach to reducing
exposure of red and green spectrally sensitized
silver bromide and silver bromoiodide emulsion
layers to blue light, thereby effectlvely reducing
their blue speed, i8 to locate these emulsion layers
30 behind a yellow (blue absorbing) filter layer. Both
yellow filter dye~ and yellow colloidal silver are
commonly employed for this purpose. In a common
multicolor layer format all of the emulsion layers
are silver bromide or bromoiodide. The emulsion
35 layers intended to record green and red exposures
are located behind a yellow filter while the emul-
sion layer or layers intended to record blue l~ght
' are located in front of the filter layer.
~2~626
-81 -
This arrangement has a number of art-recog-
nized disadvantages. Wh~le blue light expo~ure of
green and red recording emulsion layer~ i~ reduced
to tolerable level~, a less than ideal layer order
5 arrangement is imposed by the use of a yellow
filter. The green and red emulsion layer~ receive
light that haR already pa~sed through both the blue
emulsion layer or layers and the yellow filter.
This light hAs been scattered to Rome extent, and
10 image sharpness can therefore be degraded. Further,
the yellow filter is it~elf imperfect and actually
absorbs to a slight extent in the green por~ion of
the spectrum, which results in a 10R~ of green
speed. The yellow filter material, particularly
15 where it is yellow colloidal silver, increaseR
materials cost and accelerates required replacement
of processing solutions, 6uch as bleaching and
bleach-fixing solutions.
Still another disadvantage associated with
20 separating the blue emulsion layer or layer6 of a
photographic element from the red and green emulsion
lsyers by interposing a yellow filter ls that the
speed of the blue emulsion layer is decreased. This
is because the yellow filter layer absorbs blue
25 light passing through the blue emulsion layer or
layers that might otherwise be reflected to enhance
exposure .
A number of approaches have been suggested
for avoiding the disadvantages of yellow filters in
30 multicolor photographic elements, as illustrated by
Lohmann U.K. Patent 1,560,963, which teache6 relo-
cating the yellow filter layer; Gaspar U.S. Patent
2,344,084, which teaches using silver chloride and
silver chlorobromide emulsions; and Mannes et al
35 U-S- Patent 2,388,859, and Knott et al U.S. Patent
2,456,954~ which teach introducing an order of
magnitude difference between the blue and minus blue,
~z~
-82-
speeds of the blue and minus blue recording emulsion
layers; but each has introduced other significant
disadvantages. For example, Lohmann incur6 blue
light contamination of the minus blue recording
5 emulsions lying above the yellow filter; Gaspar
incurs the reduced speeds and lower speed-granu-
larity rel~tionships of silver chloride and silver
chlorobromide emulsions; and Mannes et al and Knott
et al require large grain size differences to obtain
10 an order of magnitude speed difference in the blue
and minus blue recording emulsion layers, which
requires either increasing granularity or signifi-
cantly reducing ~peed in at least one emulsion layer.
Kofron et al, cited above~ has recognized
15 that the blue light absorption of high aspect ratio
tabular grain silver bromide and silver bromoiodide
emulsions can be sufficiently reduced so that yellow
filter l~yers can be eliminated. However, the
multicolor photographic elements of Kofron et al
20 show significantly larger increases in the separa-
tion of blue and minus blue speeds when yellow
filter layers are incorporated in the multicolor
photograph~c elements to receive blue light prior to
minus blue recording emulsion layers. Fur~her, when
25 Kofron et al employs high aspect ratio tabular
grains of increased thickness ~up to 0.5 micron) or
higher iodide concentrations, significant color
falsification of minus blue recording emul6ion
layers is possible in the absence of yellow filter
30 protection.
In the practice of the present invention
locating at least one high aspect ratio tabular
grain silver iodide blue recording emulsion layer
between the source of exposing radiation and the
35 minus blue recording emulsion layers of the multi-
color photographic element protects the minus blue
recording emulsion layers from blue light exposure
-83-
even more efficiently than most conventional yellow
filter layers incorporated in multicolor photo-
graph~c elements. Thus, conventional yellow filter
layers can be entirely eliminated from multicolor
5 photographic elements according to the present
invention while avoiding color falsiflcation by t~e
minus blue recording emulsion layers. Further, this
can be accomplished while employing any sil~er
halide composition or grain configuration in the
10 minus blue recording emulsion layers 3 while employ-
ing color forming layer units which are substan-
tially matched in speed and contrast, and/or while
exposing the multicolor photographic element to
substantially neutral (5500K) light. Still
15 further, achieving multicolor photographic elements
of such capabilities are in no way incompatible with
achieving the highest levels of sharpness and the
highest speed-granularity capabilities of the
multicolor photographic elements of this invention.
20 Rather, the use of a blue recording high aspect
ratio tabular grain silver ioidide emulsion in the
multicolor photographic elements according to the
present invention both avoids color falsification by
~lue light exposure of the minus blue recording
25 emulsion layers and allows addit~onal improvements
in sharpness and speed-granularity relationships to
be realized.
g. Examples of ~pecific layer order arrange-
ments
Layer Order Arrangement I
Exposure
TB (AgI)
IL
35 G (AgX)
__IL
R (AgX)
lZ~ Z6
-84 -
Layer Order Arran~ment II
Expo~ure
TG (AgX)
IL
IL (AgX)
_ _ TB _ (A~I)
Layer Order Arrangement III
Expo~ure
TB (~gI)
IL
TG (Agl)
_ TR (AgI)
Layer Order Arrangeme~t IV
Exposure
TFB (A~X)
IS
IL (AgI3
_
G (AgX)
IL
R
.,.~,
-85-
Layer Order Arran~ement V
Exposure
TFG_ (AgX)
IL
TFR (AgX)
IL
FB (AgX)
TB (AgI) ~ IS
IL
FG _~gX)
FR (AgX)
IL
SG (AgX)
IL
SR
20 where
B, G, and R designate blue, green, and red
recording color-forming layer units, respectively;
T appearing before the color-forming layer unit
B, G, or R indicates that the emul6ion layer or
25 layers contain a high aspect ratio tabular grain
emulsion, as more 6pec~fically described above,
F appearing before the color-forming layer unit
B, G, or R indica~es that the color-forming layer
unit is faster in photographic speed than at least
30 one other color-forming layer unit which records
light exposure in the same third of the spectrum in
the same Layer Order Arrangement;
S appearing before the color-forming layer unit
B~ G, or R indicates that the color-forming layer
35 unit is slower in photographic speed than at least
one other color-forming layer unit which records
light exposure in the same third of the spectrum in
the same Layer Order Arrangement;
lZR~6Z6
-86 -
AgI indicates that the emul~ion layer or layers
of the color-forming layer unit con~ains ~ silver
iodide emulsion;
AgX indicates that the emul~ion layer or layer6
5 of the color-forming layer unit contains a ~ilver
halide emulsion which permits most of the blue light
striking it to pass through unabsorbed--e.g., silver
chloride, silver bromide, or silver bromoiodide;
IL designates an interlayer containing an
oxidized developing agent or electron transfer agent
scavenger and, where the interlayer ~eparates AgI
and AgX containing color-forming layer units,
preferably also an iodide ion scavenger; and
IS designates an interlayer containing an iodide
15 ion scavenger without necessarily including any
additional scavenger.
Each faster or slower color-forming layer
unit can differ in photographic speed from another
color-forming layer unit which records light expo-
20 sure in the same third of the spectrum as a resultof its position in the Layer Order Arrangement, its
inherent speed properties, or a combination of both.
In Layer Order Arrangements I through V,
the location of the support is not shown. Following
25 customary practice, the ~upport will in most
instances be positioned ~arthest from the Rource of
exposing radiation--that is, beneath the layers as
shown. If the support is colorless and 6pecularly
transmissive--i.e., transparent, it can be located
30 between the exposure source and the indicated
layers. Stated more generally, the support can be
located between the exposure source and any color-
forming layer unit intended to record light to which
the support i8 transparent.
Turning first to Layer Order Arrangement I,
the blue recording color-forming layer unit is
. positioned to receive exposing radiation first.
~ .~
~2~6Z6
-87 -
This color-forming layer unit contains one or more
silver halide emulsions comprised of high average
aspect ratio silver iodide grains. This emulsion
very efficiently absorbs the blue light and 6ubstan-
S tially none of the minus blue light inciden~ uponit. As diseussed above, the tabular silver iodide
grain6 can be relied upon to absorb most or substan-
tially all of the blue light of a wavelength less
than 430 nm even in the absence of a blue spectral
10 sen~itizing dye. When a blue spectral sensitizing
dye iB present, blue light ab60rption by the color-
forming layer unit can be extended to longer blue
wavelengths. If desired to obtain a more nearly
balanced blue absorption over portions of the blue
15 spectrum longer and shorter than 430 nm in wave-
length, the ~hickness of the tabular silver iodide
grains can be reduced below about ~.1 micron down to
the minimum grain thicknesses attainable.
Since the silver iodide tabular grains in
20 the blue recording color-forming layer unit can be
quite thin (0.01 micron or les~) and the halide
composition and pro~ected area of the tabular silver
iodide grains render them quite efficient in absorb-
ing blue light, the blue-recording color-forming
25 layer unit can be thinner than conventional emulsion
layers or even high aspect ratio tabular grain
emulsion layers of differing silver halide content,
such as silver bromide or silver bromoiodide emul-
sion layers. The fact that the blue recording
30 color-forming layer unit contains high aspect ratio
tabular gralns allows a sharper image to be produced
in this color-forming layer unit. Further, the fact
that the blue recording color-forming layer unit is
positioned to receive imaging radiation that is
35 substantially specular, contributes to improving the
sharpnes6 of the minus blue recording color forming
. layer units.
....
626
-88 -
Another unexpected advantage of Layer Order
Arrangement I attributsble to the presence and
location of the ta~ular grain 6ilver iodide emul6ion
layer i6 the increased speed and ~peed-granularity
5 relationship of each underlying radiation-6en6itive
emulsion layer. Since the tabular grain fiilver
iodide emulsion layer requires less silver halide to
absorb blue light efficiently, there iB le~s reflec-
tion of minus blue (green and/or red) light by the
10 6ilver iodide grains than would be the case if
comparable blue ab~orption were achieved uging a
non-tabular emul~ion or a high a~pect ratio tabular
grain emulsion of another halide composition. ThUB,
a higher percentage of minu6 blue light reaches the
15 minus blue recording emulsion l~yers, thereby
enhancing their photographic efficiency.
In any of the varied forms described above
blue light, if any, contained in the light emerging
from the blue-recording color-forming layer unit can
20 be sufficiently attenuated that it i8 unnece~sary to
employ a yellow filter layer in the multicolor
photographic element to protect the underlying green
and red-recording color-forming layer unit~ from
blue light exposure. Hence the green and red-
25 recording color-forming layer unit6 can contain
emulsions of any silver halide composition, includ-
ing silver bromide and/or silver bromoiodide emul-
sions, without exhibiting color fal~ification. The
green and red recording color-forming layer units
30 can be of any conventional silver halide composition
(including silver iodide) or grain configuration
(includlng high aspect ratio tabular grain configu-
ration).
In developing imagewise exposed Layer Order
35 Arrangement I iodide ion can, but need not be
released by the blue recording color-forming layer
unit. Where the tabular silver iodide grains are
-89-
sensitized by epitaxial deposition of a silver
halide other than iodide, 6uch as silver chloride,
it is possible to develop the ~ er chloride
selectively, as described above. In this case few,
5 if any, iodide ions are released by development.
Where the tabular 6ilver iodide grain6 are
developed, at least to some extent, iodide ion6 can
be allowed to migrate to the adjacent color-forming
unit to produce useful interimage effects. It is
10 known in the art that useful lnterimage effects can
be realized by the migration of iodide ions to
adjacent color-forming layer units. Attention i6
drawn to Groet U.S. Patent 4,082,553 for an illus-
trative upplication. However, it is generally
15 preferred to reduce the iodide ions released to an
adjacent color-forming layer unit. This can be
accomplished by incorporating an iodide sc~venger,
such as a silver chloride or s~lver bromide Lippmann
emulsion, in the blue recording color-forming layer
20 unit and/or in the interlayer separating the adja-
cent color-forming layer unit. Because of it small
grain size the Lippmann emulsion is sub~tantially
light insensitive in relation to the blue recording
emulsion layer or layer6.
To avoid repetition, only features that
distinguish subsequent Layer Order Arrangements from
previous Layer Order Arrangement6 are 6pecifically
discu66ed. In Layer Order ~rrangement II the green
and red recording color-forming layer units are
30 comprised of high average aspect ratio tabular
silver halide grains which permit most of the blue
light striking the grains to pass through
unabsorbed. This can be permitted by the composi-
tion of the grains (i.e., the absence of or low
35 concentrations of iodide) and/or diminished thick-
nes6es of the grains. In a particularly preferred
`f form of Layer Order Arrangement II the blue record-
` -
~ Z~ 26
-so -
ing color-forming layer unit is coated on a reflec-
tive support, such as a white support. It is well
appreciated that both initially incident radiation
and initially unabsorbed reflected radiation
5 contribute to exposure of emulsion layers coated on
white reflective supports. In Layer Order Arrange-
ment II the tabular silver iodide grains absorb blue
light initially incident upon them and, if any blue
light is not initially absorbed, these grains also
10 absorb blue light reflected by the support. Thus
the green and red recording color-forming layer
units are protected from blue light exposure by
reflection. The ùse of the silver iodide tabular
grains in the blue recording color-forming layer
15 unit signlficantly reduces the blue exposure of the
minus blue recording emulsion layers even though the
blue recording color-forming layer unit is not
interposed between the radiation source and the
minus blue recording color-forming layer units.
Since each of the color-forming layer units
in Layer Order Arrangement II are compri6ed of high
average aspect ratio silver halide grains, very high
levels of sharpness are possible. Further, Layer
Order Arrangement II offers a significant advantage
25 in that the green recording color-forming layer unit
is positioned nearest the source of exposing radia-
tion. This allows a sharper image to be produced in
the green color-forming layer unit as well as
permitting its speed-granularity relationship to be
30 improved. Since the human eye i8 more sensitive to
the green recording color-forming layer unit image
than the images produced in the remaining color-
forming layer units, the advantages realized in the
green recording color-forming layer unit are highly
35 advantageous in achieving the best overall multi-
color photographic image.
Layer Order Arrangment III differs from
Layer Order Arrangement I in that the green and red
~.2~(~626
-91 -
recording color-forming layer units both contain
high aspect ratio tabular grain silver iodide
emulsions. In view of the capability of producing
extremely thin tabular silver iodide grains, this
5 allows the color-forming layer units to be sub~tan-
tially reduced in th~ckness. This in turn allows
sharper photographic image~ to be produced, particu-
larly in the red recording color-forming layer unit~
although where a white reflective ~upport i8
1~ employed, significant improvements in sharpne~R may
be realized in each of the color-forming layer
units. Although the minus blue color-forming layer
units are highly efficient in recordlng blue light,
they are protected from blue light exposure by the
15 overlying tabular silver iodide grains in the blue
recording color-forming lsyer unit.
L~yer Order Arrangement IV dif~ers from
Layer Order Arrangement I by the addition of an
additional blue recording color forming leyer unit
2~ containing a fast high aspect ratio tabular grain
6ilver halide emulsion the halide of which need not
be silver iodide. By containing high aspect ratio
tabular gra~ns the additional blue color-forming
layer unit avoids ~cattering incident radiation
25 which would degrade the sharpness of imaging records
in underlying emul~on layers. The fast blue-
recording layer unit i8 relied upon to achieve a
blue speed which matches the green and red speeds of
the underlying emulsion layers. The high aspect
30 ratio tabular silver iodide emulsion can be used ~o
extend the exposure latitude of the fast blue
recording color-forming layer unit while at the same
time more efficiently protecting the underlying
color-forming layer units from blue light exposure.
35 Since the two blue recording color-forming layer
units are ad;acent each other, there is no need to
provide an interlayer for oxidized developing agent
626
-92 -
scavenger. However, since the blue recording
color-forming layer units are of differing halide
composition, the inclusion of an iodide 6cavenger in
an interlayer between the color-forming layer units
5 i~ shown, although ne~ther the u~e of an interlayer
or an iodide scavenger is essential. The iodide
scavenger can be incorporated in either or both blue
recording color-forming layer unit~, but iB prefer-
ably incorporated in the one con~aining tabular
10 silver iodide grains. Iodide scavenger can also be
present in the interlayer separating the tabular
silver iodide grain containing blue recording
color-forming layer unit from the green recording
color-forming layer unit.
Layer Order Arrangement V illustrates the
application of the invention to a multicolor photo-
graphic element containing multiple blue, green, and
red color-forming layer units. Incident radiation
initially strikes a green recording color-forming
20 layer unit comprised of a substantially optimally
6ensitized high Aspect ratio tabular grain 6ilver
halide emulsion, preferably a silver bromoiodide
emulsion. The light then passes through to an
underlying red recording color-forming layer unit,
25 which can be identical to the green recording
color-forming layer unit above, except that the
silver halide emulsion is sensitized to red light.
These two minus blue recording color-forming layer
units by reason of their favored location for
30 receiving exposing radiation and because of the
exceptional speed-granularity relationships of
substantially optimally sen6itized high aspect ratlo
tabular grain emulsions can exhibit exceptionally
high speeds. Since speed is normally measured near
35 the toe of a negative-working emulsion character-
i~tic curve, typically at a density of about 0.1
above fog, it is not necessary that the two upper
-` lZ~26
-93-
minus blue recording color-forming layer units be
capable of producing by themselves high dye
densities in order to increase the minus blue speed
of the photographic element. Therefore it i8
5 specifically contemplated that these minus blue
recording color-forming layer units can be excep-
tionally thin. The use of thin coatings i8, 0~
course, compatible with the use of tabular grain
emulsions.
After paæsing through the upper two minus
blue recording color-forming layer units, light is
received by a fast blue recording color-forming
layer unit. Although the fast blue recording
color-forming layer unit can coDtain one or more
15 silver halide emulsion layers of any conventional
type, this color-forming layer unit is preferably
identical to the fast blue color-forming layer unit
described in connection with Layer Order Arrangement
IV. To protect the underlying minus blue recording
20 color-forming layer units from blue light exposure,
a second blue recording color-forming layer unit is
~hown co~taining a high aspect rat~o tabular grain
silver iodide emulsion. An iodide scavenger is also
shown in this color-forming layer unit. It is
25 appreciated that the blue recording silver halide
emulsions can be present, if desired, in the same
color-forming layer unit, either blended or, prefer-
ably, coated as separate layers.
Immediately beneath the blue recording
30 color-forming layer units are two fast minus blue
recording color-forming layer units, a green and a
red color-forming layer unit in that order. Since
the emulsions of these color-forming layer units are
protected from blue light exposure by the high
35 aspect ratio tabular silver iodide grains in the
overlying blue recording color-forming layer unit,
the silver halide emulsions in these two fast minus
~Z~6Z4
-94 -
blue recording color-forming layer units can be from
among any green or red sensitized emulsions hereto-
fore described. In a preferred form the green snd
red sen~itized ~ilver halide emulsions are identical
S to those of the outermo~t two color-forming layer
units. That is, these minu~ blue record~ng color-
forming layer units preferably also contain sub~tan-
tially optimally sensitized high aspect ratio
tabular grain emulsions, most preferably silver
10 bromoiod~de emulsion~.
The two minus blue recording color-forming
layer units farthest from the expo~ing radiation
source are labeled slow color-forming green and red
recording color-formin~ layer unit~. Their unction
5 i8 to extend the exposure latitude of the photo-
graphic element and to contribute additional den~ity
for achieving maximum dye densities ~n ~he case of a
negatlve-working photographic element. The emul-
sions employed can be of any conventional type.
20 They can be identical to the silver halide emulsions
employed in the other minus blue-recording color-
forming layer units, relying on their less favored
layer order arrangement to reduce their effective
speed. Speed-granularity advantages are realized by
25 coating faster and slower emulsions in geparate
layers a~ opposed to blending the emulsions.
The multicolor photographic elements of the
present invention can, if desired, be applied to
image transfer applications. For example, a multi-
30 color photographic element~ can form a part of amulticolor image transfer film unit. When the
photographic elements are employed in image transfer
film units they incorporate dye image providing
material~ which undergo an alteration of mobil~ty as
35 a function of silver halide development. An image
dye receiver can form a part of the image transfer
film unit or be separate therefrom. Useful image
lz~a6z6
-95-
transfer film unit features are disclosed in
Research Disclosure~ Item 17643, cited above,
Paragraph XXIII; Research Disclosure, Vol. 152,
November 1976, Item 15162; and Jones and Hill Can.
Patent 1,175,278, cited above. The image transfer
film units disclosed by Jones and Hill are particu-
larly preferred for image transfer applications of
the photographic elementæ of this invention.
Examples
The preparation and sensitization of high
aspect ratio tabular grain silver iodide emulsions
is illustrated by the following specific examples:
Emulsion Preparation and Sensitization Examples
In each of the examples the contents of the
reaction vessel were stirred vigorously throughout
silver and iodide salt introductions; the term
"percent" means percent by weight, unless otherwise
indicated; and the term "M" stands for a molar
concentration, unless otherwise stated. All
solutions, unless otherwise stated, are aqueous
emulsions.
Example Emulsions 1 through 4 relate to
silver halide emulsions in which the tabular silver
iodide grains are of a face centered cubic crystal
structure.
Example Emulsion 1 Tabular Grain Silver lodide
Emulsion
6.0 liters of a 5 percent deionized bone
gelatin aqueous solution were placed in a precipita-
tion vessel and stirred at pH 4.0 and pAg calculatedat 1.6 at 40C. A 2.5 molar potassium iodide
solution and a 2.5 molar silver nitrate solution
were added for 5 minutes by double-jet addition at a
constant flow rate consuming 0.13 percent of the
silver used. Then the solutions were added for 175
minutes by accelerated flow (44X from start to
,~
lZ1~6Z6
-96 -
f~nish) consuming 99.87 percent of the silver used.
Silver iodide in the amount of 5 moles WAS
precipitated.
The emulsion was centrifuged, resuspended
5 in distilled water, centrifuged, re6uspended in 1.0
liters of a 3 percent gelatin solution and adju~ted
to pAg 7.2 measured at 40C. The resul~cant tabular
grain silver iodide emulsion had an average grain
diameter of 0.84 l~m, an average grain thickness of
10 0.0661lm, an aspect ratio of 12.7:1, and greater
than 80 percent of the grains were tabular based on
projected area. Using x-ray powder diffraction
analysis greater than 90 percent of the silver
iodide was estimated to be present in the y
15 phase. See Figure 1 for a carbon replica electron
micrograph of a sample of the emul~ion.
Example Emulsion 2 Epitaxial AgCl on Tabular
Grain AgI Emulsion
29.8 g of the tabular grain AgI emulsion
20 (0.04 mole) prepared in Example 1 was brought to a
final weight of 40.0 g with distilled water and
placed in a reaction vessel. The pAg was measured
as 7.2 at 40C. Then 10 mole percent silver
chloride was precipitated onto the AgI host emulsion
25 by double-,~et addition for approximately 16 minutes
of 0.5 molar NaCl solution and a 0.5 molar AgN03
solution at 0.5 ml/minute. The pAg was maintained
at 7.2 throughout the run. See Figure 2 for a
carbon replica photomicrograph of a sample of the
30 emulsion-
Example Emulsion 3 Epitaxial AgCl plu8 Iridiumon Tabular Grain AgI Emulsion
Emulsion 3 was prepared similarly to the
epitaxial AgCl tabular grain AgI emulsion of Example
35 2 with the exception that 15 seconds after the start
of the silver salt and halide salt solutions 1.44 mg
of an iridium compound/Ag mole was added to the
- reaction vessel.
~Z1~26
-97-
Example Emulsions 1, 2 and 3 were each
coated on a polyester film support at 1.73 g
sil~er/m2 and 3.58 g gelatin/m2. The coatings
were overcoated with 0.54 g gelatin/m2 snd
5 contained 1.0 percent bis(vinylsulfonylmethyl)ether
hardener based on tot~l gelatin content. The
coatings were expoged for 1/2 second to a 600W
2850K tungsten light 60urce through a 0-6.0 den~ity
~tep tablet (0.30 step6) and processed for 6 minutes
10 at 20C in a total (surface + internal) developer of
the type described by Weiss et al U.S. Pstent
3,826,654.
Sensitometric results reveal that for the
tabular grain AgI host emulsion (Emulsion 1) no
15 discernible image was obtained. However, for the
epitaxial AgCl (10 mole percent)/tabular grain AgI
emulsion (Emulsion 2), a significant negative image
was obtained with a D-min of 0.17, a D-max of 1.40,
and a contrast of 1.7. For the iridium sensitized
20 epitaxial AgCl (10 mole percent)/tabular grain AgI
emulsion (Emulsion 3) a negative image was obtained
with a D-min of 0.19, a D-max of 1.40, a contrast of
1.2, and approximately 0.5 log E faster in threshold
speed than Emulsion 2.5 Example Emulsion 4 The Use of Phosphate to
Increase the Size of AgI
Tabular Grains
This emulsion was prepared similar to
Example Emulsion 1 except that it contained 0.011
30 molar R2HP04 in the precipitation vessel and
0.023 molar K2HP04 in the 2.5 molar potas-
sium iodide solution.
The resultant tabular grain emulsion was
found to consist of silver iodide. No phosphorus
35 was detectable using x-ray microanalysis. The AgI
tabular grain emulsion had an average grain diameter
of 1.65~m compared to 0.84~m found for Example
lZ~626
-98 -
Emulsion 1, an average grain thicknes6 of 0.20~m,
an aspect ratio of 8.3:1, and ~reater than 70
percent of the grains were tabular based on
projected area. Greater than 90 percent of the
5 silver iodide was present in the ~ phase as
determined by x-ray powder diffraction analysis.
Example Emul~ions 5 through X relate to
silver halide emulsions in which the tabular silver
iodide grains are of a hexagonal crystal structure,
10 indicat~ng the silver iodide to be present predomi-
nantly in the ~3 phase.
~:xample Emulsion 5 Tabular Grain AgI Emulsion
4.0 liters of a 2.0 percent deionized
phthalated gelatin aqueous solution containil g 0.08
15 molar potassium iodide were placed in a precipita-
tion vessel with stirring. The pH was adju~ted to
5.8 et 40C. The temperature was increased to 80C
and the pI was determined to be 1.2. Then a 1.0
molar potassium iodide solution a'c 45C and a 0.06
20 molar silver nitrate solution at 45C were run
concurrently into the precipitation vesRel by
double-jet addition. The silver salt solution was
added for 138.9 minutes by accelerated flow (3.5X
from start to finish) utilizing 0.3 mole of silver.
25 The iodide salt solution was added at a rate suffi-
cient to maintain the pI at 1.2 at 80C throughout
the run. The emul~ion was cooled to 30C, washed by
the coagulation method of Yutzy and Frame, U.S.
Patent 2,614,928, and stored at pH 5.8 and pAg 9.5
30 measured at 40C. The resultant tabular grain
6ilver iodide emulsion had an average grain diameter
of 2.5 llm, an average thickne~s of 0.30 llm, an
average aspect ratio of 8.3:1, and greater than 75
percent of the pro~ected area was provided by
35 tabulsr grains. See Figure 3 for a photomicrograph
of Emulsion S.
~Z~6Z6
99
Example Emulsion 6 Tabular Grain AgI Host
Emulsion
5.0 liters of a 2.0 percent deionized
phthalated gelatin aqueous solution (Solution A)
5 containing 0.04 molar potassium iodide were placed
in a precipitation ves~el with 6tirring and the pH
wss ad~usted to 5.8 at 409C. The temperature was
increased to 90C and the pI Wa8 de~erm~ned to be
1.6. Then a 1.0 molar potass~wm iodide solution at
10 70C (Solution B) and a 6.95 x 10- 2 molar
AgN03 solution at 70C (Solution C) were run
concurrently into Solution A by double-~et addi-
tion. Solution C was added for 125 minute by
accelerated flow (2.23X from start to finish consum-
15 ing 6.4 percent of the total silver used. SolutionC wa~ then added at accelerated flow rate6 in five
intervals of 125 minutes, 150 minute~, 150 minutes,
150 minutes, and 20 minutes each consuming 13.7
percent, 20.8 percent, 25.3 percent, 29.7 percent,
20 and 4.0 percent, re~pectively, of the total silver
used. Solution B was added concurrently throughout
at flow rates sufficient to maintain the pI at 1.6
at 90C. The emulsion was cooled to 30C, washed by
the coagulation method of Yutzy and Frame U.S.
25 Patent 2,614,928, and stored at pH 6.0 and pAg 9.5
measured at 40C. Approximately 7.6 x 10-1 mole
of silver was used to prepare this emulsion. The
resul~ant tabular grain sllver iodide emulsion had
an average grain diameter of 7.7~m, an average
30 thlckness of 0.35~m, an aspect ratio of 22:1, and
greater than 75 percent of the pro~ected area was
provided by the tabular gra~ns.
Example Emuls~on 7 Silver Bromide (10 mole
percent) Deposition on
Tabular Grain AgI Emul~ion
A total of 2.03 liters of a 0.98 percent
deionized phthalated gelatin aqueous solution
lZ1~6Z6
-100 -
containing 444.0 g (0.44 mole) of Emulsion 6 were
placed in a precipitation vessel with stirring. The
pH wa~ ad~usted to approximately 6.2. The pAg was
ad~usted to approximately 7.6 at 40C using a 1 x
5 10-3 molar potassium bromide solution. Then a 0.1
molar potassium bromide solution at 40C and a 0.1
molar silver nitrate solution at 40C were run
concurrently into the precipitation vessel by
double-~et addition. The silver 6alt solution was
10 added for 30 minutes at 14.8 ml/minute while the
bromide salt solution was added at a rate ~ufficient
to maintain the pAg at 7.6 at 40C. Approximately
10 mole percent silver bromide was added to the
tabular 8rain silver iodide host emulsion. The
15 emulsion was cooled to 30C, washed by the coagula-
tion method of Yutzy and Frame U.S. Patent
2,614,928, and stored at pH 5.8 and pAg 8.2 measured
at 40C.
The silver bromide epitaxially deposited
20 was almost exclusively along the edges of the
tabular silver iodide host crystals.
ExamPle Emulsion 8 Silver Chloride (10 mole
percent) Deposition on
Tabular Grain AgI Emulsion
A total of 1.98 liters of a 1.26 percent
deionized phthalated gelatin aqueous solution
containing 486.0 g (0.44 mole) of an Emulsion 6
repeat were placed in a precipitation vessel with
stirring. The pH was ad~usted to approximately
30 6Ø The pAg was ad~usted to approximately 6.9 at
40C using a 1.0 molar potassium chloride solution.
Then a 9.25 x 10- 2 molar potassium chloride
solution at 40C and a 9.25 x 10- 2 molar silver
nitrate solution at 40C were run concurrently into
35 the precipitation vessel by double-~et addition.
The silver salt solution was added for 60 minute~ at
8.0 ml/minute while the chloride salt solution was
26
-101 -
added at a rate such that the pAg changed from 6~9
to 6.7 at 40C throughout the run. Approximately 10
mole percent æilver chloride was added to the
tabular grain silver iodide hoæt emulsion. The
5 emulsion was cooled to 30C, washed by the coagula-
tion method of Yutzy and Frame U.S. Patent
2,614,928, and ~tored at pH 5.0 and p~g 7.2 measured
at 40C.
The silver chloride epitaxially deposited
10 was almost exclusively along the edges of the
tabular silver iodide host crystals.
Example Emulsion6 6, 7, and 8 were sepa-
rately coated on polyester film support at 1.61 g
silver/m2 and 5.38 g gelatin/m2. The coating
15 elements also contained 1.61 g yellow coupler
~-pivalyl-~4-(4-hydroxybenzenesulfonyl)-
phenoxy]-2-chloro-5-(n-hexadecanesulfonamido)~
acetanilide/m2, 3.29 g 2-(2-octadecyl)-5-sulfo-
hydroquinone, sodium salt/Ag mole and 1.75 g 4-hy-
20 droxy-6-methyl-1,3,3a,7-tetraazaindene/Ag mole. The
coating elements were overcoated with a 0.89 g
gelatin/m2 layer that contained 1.75 percent by
weight hardener bi6(vinylsul0nylmethylaether based
on total gelatin content. Emulsion 8 was also
25 spectrally sensitized with 0.25 millimole anhydro-
5,5'-dichloro-3,3'-bis(3-gulfopropyl)thiacyanine
hydroxide trimethylamine salt/Ag mole and then
chemically sensitized with 15 mg gold sulfide/Ag
mole for 5 minutes at 55C and coated as described
30 above-
The coatings were exposed for 1/10 secondto A 600 watt 3000K tungsten light source through a
0-6.0 density step tablet (0.30 steps) and processed
for either 3 or 6 minutes at 37.7C in a color
35 developer of the type described in The British
Journal of Photography Annual, 1979, pages 204-206.
Blue sensitometry was obtained. Sensito-
metric results revealed that for Emulsion 6, the
2~ @
-102-
tabular grain AgI host emulsion, no d~scernible
image was obtained at either 3 minutes or 6 minutes
development time. Emulsion 7, the AgBr deposited on
AgI host emulsion, resulted in a significant nega-
5 tive image at 6 minutes development with a D-min of
0.13, a D-max of 0.74, and a contrast of 0.42.
Unsensitized Emulsion 8, the AgCl deposited on AgI
host emulsion, resulted in a substantial negative
image a~ 3 minutes development with a D-min of 0.13,
10 a D-max of 0.74, and a contrast of 0.80. Further-
more, the chemically and spectrally sensitized
Emulsion 8 which had a D-min of 0.13, D-max of 0.80,
and contrast of 0.65, was approximately 0.60 log E
faster in speed than unsensitized Emulsion 8.5 Example Emulsion 9 Tabular Grain Agl Host
Emulsion
5.0 liters of a 2.0 percent deionized
gelatin aqueous solution containing 0.04 molar
potassium iodide were placed in a precipitation
20 ves~el with stirring. The pH was ad~usted to 5.8 at
40C. The temperature was increased to 90C and the
pI was determined to be 1.4. Then a 0.5 molar
potassium ioodide solution and a 0.07 molar silver
nitrate solution were run concurrently into the
25 precipitation vessel by double-jet addition. The
silver salt solution was added in six increments
according to the followlng flow profile.
Silver Salt Addition Profile
Accelerated flow Percent of
30 Run Time (Start to Finish) Total S~lver
. _
125' 2.23x 6.1
125' 1.55x 10.8
150' 1.43x 19.2
150' 1.3 x 26.1
3515~' 1.23x 32.9
20' 1.03x 4.9
A total of approximately 0.8 mole of silver
was utilized. The iodide salt solution was added at
2 6
-103-
a rate sufficient to maintain the pI at approxi-
mately 1.4 at 90C throughout the precipitation.
The emulsion was cooled to 30C and washed by the
coagulation method of Yutzy and Frame U.S. Patent
5 2,614,928. The resultant tabular grain 6ilver
iodide emulsion had an average grain diameter of
11.4 ~m, an average grain thickness cf 0.32 ~m,
an average aspect r~tio of 35.6:1, and greater than
75 percent of the projected surface area was
10 contributed by the tabular silver iodide gr~ins.
See Figure 4 for a photomicrogr~phic of Emulsion 9.
Example Emulsion 10 Silver Chloride (10 mole
percent) Deposition on
Tabular Grain AgI Emul~ion
A sample of Emulsion 9 in the amount of
1048 grams (1.3 mole AgI) prepared above wa6 placed
in a precipitation vessel. Next 1.3 liters of
di~tilled water were added and the emulsion wa~
ad~usted to pAg 7.0 at 40C using a 1.0 molar KCl
20 solution. Then a 1.0 molar KCl solut~on and a 0.46
molar AgNO3 solution were added over two hours
by double-jet utilizing accelerated flow (2x from
start to finish) at controlled pAg 7.0 at 40C. A
total of 10 mole percent silver chloride was
25 precipitated onto the silver iodide host Emulsion
9. Following precipitation the emulsion was cooled
to 30C and washed by the coagulation method of
Yutzy and Frame U.S. Patent 2,614,928. See Figure 5
for a photomicrogrsph of Emulsion 10.
30 Example Emulsion ll Silver Bromide (5 mole
percent) Deposition on
Tabular Grain AgI Emulsion
A tabular grain AgI emulsion was prepared
by a double-~et precipitation technique. The
r 35 emulsion had an average grain diameter of 6.0 ~m,
an average grain thickness of 0.23 ~m, an average
aspect ratio of 26:1, and greater than 75 percent
121~6~6
-104-
of the pro~ected surface area was contributed by the
tabular silver iodide grains.
The tabular grain ~ilver iodide emulsion in
the amount of 600 grams (1.0 mole AgI) w~s plAced in
5 a precipitation vessel. Next 1.6 liters of distil-
led water were added and the emul~ion was ad~usted
to pAg 8.0 at 40C using a 1.0 molar KBr solution.
Then a l.0 molar KBr solution and a 0.037 molar
AgNO3 solution were added over elght hours by
10 double-jet utilizing accelera~ed flow (Sx from start
to finish) at controlled pAg 8.0 a~ 40C. A to$al
of 5 mole percent silver bromide was precipitated
onto the silver iodide host emulsion. Following
precipitation the emulsion was cooled to 30C and
15 washed by the coagulation method o$ Yutzy and Frame
~.S. Patent 2,614,928. See Figure 6 for a photo-
micrograph of Emulsion 11.
Multicolor Photographic Element Example
Three silver halide emulsions of near
20 equivalent grain volumes were prepared by double-~et
precipitation techniques. The emulsions were
separately coated in the blue layer of multilayer
elements and compared for the blue light absorption
in the green recording layer. Emulsion A was a
25 three-dimensional grain silver iodide with an
average grain size of 0.75~m and an average grain
volume of 0.22(~m)3. Emulsion B was a tabular
grain silver bromoiodide (97:3) emulsion with an
average grain diameter of 1.8~m, an average grain
30 thickness of O.O99~m, an aspect ratio of 18:1, an
average pro;ected area of greater than 80%, and an
average grain volume of 0.25(~m)3. Emulsion C,
satisfying the requirements of this invention, was a
tabular grain silver iodide emulsion with an average
35 grain diameter of 1.7~m, an average grain thick-
ness of 0.095~m, an average aspect ratio of
12~ Z6
-105-
17.9:1, a tabular grain projected area of greater
than 50% of the total grain projected area, and an
average grain volume of 0.21(~m)3.
Each emulsion was coated in the blue layer
(Layer 9) at 0.97 g. silver/m2 and 1.51g.
gelatin/m2. Layer 9 also contained 2-(2-octa-
decyl)-5-sulfohydro-quinone, sodium ~alt at 0.30
glm2 and 4-hydroxy-6-methyl-1,3,3~,7-tetraazain-
dene at 2.27 g¦m2. No yellow filter layer was
10 present in the multilayer element.
The remaining film tructure coated on
cellulose triacetate support is described b~low.
Layer 1: A slow cyan imaging component containing a
blend of a red sensitized tabular grain
(0.16~m thick x 5.3~m diameter) oeilver
bromoiodide (97:3) emulsion and a red
sensitized 0.55~m three-dimensional grain
silver bromo~odide (97:3) emulsion in a
1.7:1 ratio coated at 2.48 g. ~ilver/m2
and 2.56 g. gelatin/m2. Also present
were cyan dye-forming coupler at 0.94
g/m2, 2-(2-octadecyl)-5 -8ul fohydro-
quinone, sodium salt at 0.08 g/m2 And
4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene
at 0.80 g/m2.
Layer 2: Gelatin lnterlayer at 0.61 g/m2.
Layer 3: A slow magenta imaging component containing
a blend of a green sensitized tabulsr grain
(0.16~m thick x 5.3~m diameter) silver
bromoiodide (97:3) emulsion, A green
sensitized 0.5S ~m three-dimensional
gr in silver bromoiodide (97:3) emulsion,
and a green sensitized 0.21~m three-
dimensional green silver bromoiodide
(95.2:4.8) emulsion in a ratio of 4.2:3.2:1
coated at 2.73 g. silver/m2 and 2.70 g.
~2~``626
-106 -
gelatin/m2. Alæo present were magenta
coupler at 0.82 g/m2, 2-(2-octadecyl)-S-
sulfohydro-quinone, sodium salt at 0.11
g/m2, and 4-hydroxy-6-methyl-1,3,3a~7-
tetraazaindene at 0.44 g/m2.
Layer 4: Gelatin interlayer at 0.61 g/m2 .
Layer 5: A fast cyan imaging component containing a
red sensitized tabular grain (0.16~m
thick x 5.3~m diameter) sllver bromo-
iodide (97:3) emulsion coated at 1.83 g.
silver/m2 snd 1.83 g. gela~in/m2. Also
present were cyan coupler 0.22 g/m2,
2-(2-octadecyl)-5-sulfohydroquinone, sodium
salt at 0.06 g/m2 a and 4-hydroxy-6-
methyl-1,3,3a,7-tetraazaindene at 1.25
g/m2 .
Layer 6: Gelat~n interlayer at 0.61 g/mZ.
Layer 7: A fast magenta imaging component con~aining
a green sensit~zed tabular grain (0.16~m
thick x 5.3~m diameter) silver bromo-
iodide (97:3) emulsion coated at 1.83 g.
silver/m2 and2.09 g. gelatin/m2. Also
present were magenta coupler at 0.16
g/m2, 2-(2-octadecyl)-5-sulfohydro-
quinone, sodium ~alt at 0.06 g/m2, and
4-hydroxy-6-methyl-1,3,3a,7~tetraazaindene
at 1025 g/m2.
Layer 8: Gelatin interlayer at 0.81 g/m2.
The multilayer element was overcoated with
30 1.36 g. gelatin/m2 and hardened with 2.0% bis-
(vinylsulfonyl-methyl) ether based on the total
gelatin content.
A control coating was also prepared with
the exception that the silver halide emuls~on was
35 omitted from Layer 9. Gelatin was coated at 1.51
g/m2 in that layer. The remaining layers were the
same as described above.
~Z~6Z6
-107 -
Each coating was exposed for 1/10 second to
a 600W 5500K tungsten light ~ource through a 0-6.0
density step tablet (0.30 steps) plus Wratten 36 +
38A filter (permitting only 350 to 460 nm wavelength
5 light to be transmitted) and processed for-2 1/2
minutes in a color developer of the type described
in the British Journal of Photography Annual, 1979,
pages 204-206.
To provide a measure of the blue light
10 transmitted through Layer 9> a characteristic curve
of the magenta record was plotted for each multi-
color element, and the ~peed of the magenta record
was measured. Layer magenta ~peed~ indicate lower
levels of blue light transmi~sion.
TABLE VI
Coating Relative Blue Speed
Control 100
Emulsion A (three-dimensional 61
grain AgI)
Emulsion B (tabular grain AgBrI) 92
Emul~ion C (tabular grain AgI) 51
30 relative speed units - 0.30 log E, where E is
exposure measured in meter-candle-seconds.
As shown in Table VI the multicolor element
25 containing Emulsion C provided the lowest relative
blue speed in the magenta record layer. This
indicated that of the three emulsions of near
equivalent grain volumes, the tabular grain silver
iodide emul~ion ab~orbed the greatest amount of blue
30 light. The improvement of Emulsion C over Emulsion
A demonstrated that blue light absorption by silver
iodide occurred due to projected surface area rather
than grain volume. These results show that by
coating a high aspect ratio silver iodide emulsion
35 in a blue recording layer less unwanted blue light
is transmitted to the underlying emulsion layers.
,
~21~6~6
-108-
The invention has been described in detail
with particular reference to preferred embodiments
thereof, but it will be under~tood that variations
and modifications can be effected within the spirit
5 and scope of the invention.
