Note: Descriptions are shown in the official language in which they were submitted.
1~4~17
The invention relates to photographic direct positive sil-
ver halide emulsions which are sensitized with special cyanine
dyesO
Numerous sensitizing dyes are known for the usual negative
silver halide emulsions, e.g. mono- or trimethine cyanines,
merocyanines or rhodacyaninesO
The known sensitizing dyes, however, cannot usually be
used for sensitizing direct positive emùlsions, i.e. emulsions
which are processed to produce positive images after the usual
exposure and development, because they generally cause flatte-
ning of the ~~-value or gradationO On the other hand, compounds
have already been described which are only suitable as sensi-
tizing dyes for direct positive emulsionsO If used in negative
emulsions, these compounds cause fogglng and their sensitizing
effect is unsatisfactory. Indocyanines are examples of sensi-
-tizing dyes which have been used for direct positive emulsions.
Although these have a quite advantageous effect on the sensi- -
tivity of the emulsions to the red region of the spectrum, their - -
sensitizing effect is still not completely satisfactory. This
also applies to the direct positive indole sensitizing dyes for
the green region o* the spectrum and to bis-thiazol and bis-selen-
azolyl compounds which are known as sensitizers for direct posi-
tive emul~ions. -
- ~ ~ ......
It i8 among the ob~ects of the present invention to provide
sensitizing dye~ for direct positive silver halide emulsion~
which havc a ~ufficient~y intense sensltizing effect and do not
adversely affec~ the gradation.
. ' , ".
A-G 854 - 2 -
. ~ ' ,.
. . '
~4~3917
We now have found that cyanine dyes which have a thiazole
nucleus whose carbon atom in the 5 position is connected via a
methine chain to a second nucleus of the type usually present
in known cyanine dyes, are highly effective cyanine dyes,
suitable for the preparation of direct posotive photographic
silver halide emùlsionsO The new cyanine dyes are particularly
suitable as so-called electron acceptors and spectral sensi-
tizers for developable fogged silver halide emulsions. They
produce both excellent general speed and a selective sensitivity
to light from the green and red regions of the visible spectrum.
Images obtained with such silver halide emulsions are except-
ionally clear and sharp and have excellent contrast~ m e
second nucleus which is connected to the thiazole nucleus by a
methine group may be a 5- or 6-membered nitrogen containing
nucleus of the type normally found in known cyanine dyes.
Particular utility is exhibited by cyanine dyes character-
ized by one of the following formulae I or II:
:
- .
I R1 _ N = (CH - CH=)nC - CH = CH ~ ~ R3
Anion 0 R N ~
R6 ' R8
R ~ C - (CH = CH~ 6
R4 ~ Anion ~
.. . .
A-G 854 - 3 -
1~J4~917
wherein
Rl represents ~1) a saturated or unsaturated aliphatic hydrocarbon group
which preferably contains up to 6 carbon atoms and may be substituted, e.g.
with phenyl, hydroxyl, halogen, carboxyl, sulfo, carbonamido, carbalkoxy,
sulfato or thiosulfato, sulfonamido or phosphato, (2) cycloalkyl such as
cyclohexyl, or (3) aryl, particularly phenyl;
R2, R4, R8 stand for (1) hydrogen, (2) saturated or unsaturated aliphstic
groups preferably containing up to 6 carbon atoms, for example methyl or
ethyl, or t3) aryl, for example phenyl which may be substituted, for example
with alkyl, or alkoxy;
R3 represents -SR or -NR OR l;
R5, R6, R represent (1) hydrogen, (2) saturated or unsaturated aliphatic
groups preferably containing up to 3 carbon atoms, for example methyl or
ethyl, t3) aryl, for example phenyl, or t4) carbalkoxy such as carbethoxy, and
R5 and R may also together represent the ring members required for completing -
a condensed benzene or naphthalene ring; ~ --
R9, R10, Rll represent (1) saturated or unsaturated aliphatic groups prefer-
ably containing up to 6 carbon atoms, for example methyl or ethyl, or (2)
aryl, for example phenyl; R10 and Rll may also together represent the ring ; ---
members required for completing a heterocyclic ring, e.g. for completing a
pyrrolidine, piperidine, morpholine or thiomorpholine, indoline or tetra- -
hydroquinoline ring;
n = 0 or 1, -
m ~ 0 or 1, ~
' '
F
.
1~4~917
Anion ~ represents any anion, eOg. a halide such as chloride,
bromide or iodide, perchlorate, sulfate, methylsulfate,
p-toluenesulfonate, acetate or oxalate; the anion is
absent in cases where R1 or R4 contains an acid
group in the anionic form so that a betaine is present;
Z represents a radical required for completing a hetero-
cyclic group containing a 5- or 6-membered heterocyclic
ring; the heterocyclic group may contain a condensed
benzene or naphthalene ring a~d other substituents;
the heterocyclic groups are those commonly used in
cyanine chemistry, for example those based on thiazole,
(eOg. thiazole, 4-methylthiazole, 5-methylthiazole, 4,5-di-
methylthiazole, 4-phenylthiazole, 5-phenylthiazolejor 4,5-di-
phenylthiazole), benzothiazole, (eOgObenzothiazole, 4-chloro-
benzothiazole,`~5-chlorobenzothiazole, 6-chlorobenzothiazole,
7-chlorobenzothiazole, 6-bromobenzothiazole, 5-iodobenzothia-
zole, 6-iodobenzothiazole, 4-methylbenzothiazole, 5-methyl-
benzothiazole, 6-methylbenzothiazole, 5,6-dimethylbenzothia-
zole, 4-phenylbenzothiazole, 5-phenylbenzothiazole, 6-phenyl-
benzothiazole, 5-hydroxybenzothiazole, 6-hydroxybenzothiazole,
5-ethoxybenzothiazole, 6-ethoxybenzothiazole, 5,6--dimethoxy-
benzothiazole, 5,6-methylene-dihydroxy-benzothiazole, 5-di-
ethylaminobenzothiazole, 6-diethylaminobenzothiazole, 6-cyano-
benzothiazole, 5-carboxybenzothiazole, 5-sulfobenzothiazole,
tetrahydrobenzothiazole or 7-oxotetrahydrobenzothiazole),
naphthothiazole (e.g. naphto~ 1j2-d_7thiazole, naphtho~ 2,1-d 7
thiazole, 7-methoxynaphtho~ 2,1-d 7thiazole or 8-methoxynaphtho
! 1,2-d 7thiazole), selenazole (eOg. 4-methylselenazole or
4-phenyl-sel~nazole), benzoselenazole (e.g. benzoselenazole,
A-G 854 - 5 -
~4~)9~7
5-chlorobenzoselenazole, 5,6-dlmethyl-benzoselenazole, 5-hydroxy-
benzoselenazole, 5-methoxybenzoselenazole or tetrahydrobenzo-
selenezole), naphthoselenazole (eO~0 naphtho~ 1,2-d_7selenazole
or naphtho-~ 2,1-d 7selenazole), oxazole (eOg. oxazole, 4-meth-
oxyoxazole, 4-phenyloxazole or 4,5-diphenyloxazole), benzoxazole
(benzoxezole, 5-ohlorobenzoxazole, 6-chlorobenzoxazole, 5,6-dl-
methylbenzox~zole, 5-phenylbenzoxazole, 5-hydroxybenzoxazole,
5-methoxybenzoxazole, 5-phenylbenzoxazolè, 5-hydroxybenzoxazole,
5-methoxybenzoxazole, 5-ethoxybenzoxazoie, 6-dlalkylamlnobenz-
oxazole, 5-oarboxybenzoxazole, 5-~ul~obenzoxazole, sulfonamldo-
benzoxazole, or 5-carboxyvinylbenzoxHzole), naphthoxazole (e.g.
nephthol 1,2-d_70xazole, naphtho~ 2,1-d_70xazole or naphtho
~ 2,3-d_70xazolo), imid~zole (o.g, 1-methyllmldazole, 1-ethyl-
4-phenylimld~zole or 1-butyl-4,5-dlmethyllmldazole), benzlmld-
1.5 azole (e.g, 1-methylb0nzlmldazole, 1-butyl-4-methylbenzlmld-
azole, 1-ethyl-5,6-dlchlorobenzlmldazole or 1-ethyl-5-trl~luoro-
mothylbonz~mldazole), n~phthlmldazole (o.g. 1-methylnaphtho-
1~2-~_71mldazolc or 1-ethylnaphtho/~2,3-d_7imidazolo),
3,3-dlalkylindolonlne (~.g. 3,3-dlmethyllndolenlne, 3,3,5-trl-
methylindolenlne or 3,3-dlmethyl-5-methoxylndolenlne),
2-pyrldlno (e,g. pyrldlne, 3-methylpyrldine, 4-methylpyrldlne,
5-methylpyrldlne, 6-methylpyridlne, 3,4-dimethylpyridine,
3,5-dlmothylpyrldine, 3,6-dlmethylpyridlne, 4,5-dimethylpyridlne,
4,6-dlmothylpyrldine, 4-ohloropyrldine, 5-chloropyridlne,
6-chloropyrldlne, 3-hydroxypyrldlne, 4-hydroxypyridlne,
5-hydroxypyridlne, 3-phenylpyrldlne, 4-phenylpyridine or
6-phonylpyridine), 4-pyrldlne (e.g. 2-methylpyrldlne, 3-methyl- :.-.
pyrldlno, 2,3-dlmethylpyrldlne, 2,5-dimethylpyrldine, 2,6-dl-
mothylpyrltlno, 2-¢hloropyrldine, 3-ohloropyrldine, 2-hydroxy- ....
A-a 854 - 6 -
~5~41~9~7
pyridine, or 3-hydroxypyridine), 2-quinoline (eOg. quinoline,
3-methylquinoline, 5-methylquinoline, 7-methylquinoline, 8-methyl-
quinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquino-
line, 6-ethoxyquinoline, 6-hydroxyquinoline, 8-hydroxyquinoline
or 5-oxo-5,6,7,8-tetrahydroquinoline), 4-quinoline (eOgO quino-
line, 6-methoxyq~inoline, 7-methylquinoline or 8-methylquino-
line), isoquinoline (eOg. isoquinoline or 3,4-dihydroisoquino-
line), thiazoline (e.g. thiazoline or 4-methylthiazoline), and
those based on pyrroline, tetrahydropyridine, thiadiazole,
oxadiazole, pyrimidine, triazine or benzothiazine and pyrimi-
done or thiopyrimidoneO The aryl groups and heterocyclic groups
may carry any other additional substituents, eOgO alkyI,
. preferably with up to 3 carbon atoms such as methyl or ethyl,
h~logen such as chlorine or bromine, hydroxyl, alkoxy preferab-
ly with up to 3 carbon atoms such as methoxy or ethoxy, hydroxy-
alkyl, alkylthio, aryl such as phenyl, aralkyl such as benzyl,
amino, substituted amino or nitroO
The following are examples of suitable compounds. The
absorption maxima are measured in methanolic solution unless
otherwise indicatedO In the following table, DMS0 represents
dimethylsulfoxide.
-- : -
No. Dye ~: ~ Absorp- Sensiti-
tion zation
maximum maximum
(nm) (nm)
~ ~ N ~ ; 5~3
A-G 854 . - 7 -
~()4(~917
No. Dye Absorp- Sensiti-
tion zation
maximum maximum
(nm) (nm)
2 02N ~ ~ -CH = CH- ~ b~ SCH 471 550
3 ~ ~ -CH = OH- ~ S~ SCH
4 H3C~N~ 478 540
S~ CH = CH~ SCH
3 3
` C104 ~
H3C.~N 466 540
CH ~ SCH3~DMS0) :~
,
6 02~ G~ ~ 476 550
A-G 854. - 8 -
~ . .
~409~7
NoO . Dye Absorp- Sensiti-
tion zation
maximum maximum
(nm) (nm)
H C
7 3 \N~ 483 555
i N I-CH = CH ~ (DMS0) (brelt)
CH3~ ~ ~ N~ 3
H3C~ CH 548 580
3 ~ ~ ~CH3 (D~30)
C10
CH3 CH3
3 H3C ~ ~ ~
.
CH
~P~ e===CH S / 3
~ N ~ 539 610
N' ~ ~ N ~ Aceto~) (breit)
C~
010
,
H
3C~ ~ CH3 ` 542 585
o~ CH~C~ -
A-G 854 - C104 ~
_ 9 _
.. .
.. .. ", .....
~C~4Q917
NoO Dye Absorp- Sensiti-
tion zation
maximum maximum
(nm) (nm)
12 02N ~ N~ N / ~ 557 605
3 4
13 H3C`N ~ CH S f 3 556 600
CH3 ~ ~ -N
. . ........................................................ ..
` CH2-CH=CH
14 ~ ~ -CN ~ ~-N ~ 548 600
CH2-CH=CH2
H3C- ~ S03
CH
J
"
3 ':
16 ~ ~ -N ~ ~ 541 590
.
A-G 854 . J ~
- 10 - . .
....
1~4~7
~ e Absorp- Sensiti-
NOL ~ tion zation
maximum. maximu~
(nm) (nm)
CH
~CH ~ ~ ~ 493 535
S / 3 523 560
N~ CH ~ ~ -N
J ~
H3C~N ~ /CH3 529 580
l9~ N~ -$ = CN- ~ -R ~
Cl04 ~
0zN ~ 'NC H ~ H C ~ N~ ~ :
H C
~:C104 ~ -
A-0 854 - 11 -
,,
~, . . . . . . . . . . . .. .
~)4~917
No. Dye Absrop- Sensiti-
tion zation
maximum maximum
(nm) (nm)
fH2-CH=CH2
~N ~ N ~ ~ ~ SCH3 468 530
CH2 -CH=CH2
H3C ~ 3 ;.
, :,,,
CH2-CH=CH2 ; ,
N ~ N ~ ~ ~ N 605
CH2-CH=CH2
H3C ~ so~3
N ~~ ~ N / 485 530
CH3 ~3 ~ (Aceton)
C104 :'
......
- 12 ~
,' ~" ,
~ ` '. .:
,
1~409~7
NoO . Dye Absorp- Sensiti-
tion zation
maximum. maximum
(nm) (nm)
;
31~ > -CH ~ ~-N ~ 476 S15
C2H5 J ~
32~ ~ -CH - CN- ~ S\ ~ ~ ( 449 ) 490
~ .
33~ ~ - CH = CH - ~ ~ -N~CH 653 720
C ~ ~ C 04
02N ~ ' CN ~ ON 559 610
H~C CH3 ~D5So) 600
CH3 ~ ~ ~ - ~ CH3
C104 ~
. -. . .
F /3
A-G 854
1~)4~9~7
No, Dye Ab~orp- Senslti-
tion zatlon
maximum maxlmum
(nm) (nm)
O ~N~-CH ~ CH- ~ ~ N ~ 3 517 575
C104 ~
9 ~ X~ -CH OH ~ ~ ~ N~ 3 ~ 334 ) 590
- 0104-~
02N ~ ~ -ON ~ CH- ~ g~ -N/ ~ ~ 54
~2~5
';
.'.~
. .
;~ ' , ' ,'
F ~
A-G 854 - 4!~- . -
.. . .. . . .. ... . . . . .. ... .. .. .. .. . .. . . . . .. ... . ..
9~7
The new cyanine dyes of the above formula I can easily be
obtained by reacting a heterocyclic compound of the following
formula III:
III R1 _ N = (CH - CH =)nC - R'
'~9
Anion
wherein
R , n, Z and anion have the meaning already indicated and R'
represents a methyl group,
with a thiazolealdehyde of the structural formula IV
OHC S
IV R2 ~ N
.
.
wherein
R' and R~ have the meanings mentioned herein before~
The reaction is preferably carried out at temperatures of between
15C.and the reflux temperature of the mixture, preferably using
equimolar or approximately equimolar ratios. The reaction may be
carried out in the presence or absence of a condensing agent,
for example a trialkylamine, in an inert solvent, for example
an alkanol, e.gO ethanol, or acetic acid anhydrideO
The dyes of Formula II are obtained by condensation of a
pyrrole or indole of Formula V:
A-G 854 ~
.
~)46)917
R6 R8
V ~ (C=CH-)mH
R5 N R7
R4
wherein
R4, R5, R6, R7, R8 and m ha~e the meanings already indicated
with an aldehyde of formula IV with the addition of at lea~t
1 mol of an acid, e.g. acetic acidO The condensation may advan-
tageously also be carried out in glacial acetic acid with the -
addition of a condensing agent such as pho~phorus oxychloride.
The thiazole aldehydes of formula IV are easily obtained from
the correspond1ng thlazole~ by the Vilsmeier reaction as
described in German Patent SpecificationsNo. 1,137,024 and
1,147,584.
The preparation~ of dyes 1, 8 and 10 are described in
detail below:
Dre 1
~3 g ~ 2-methyl-3-ethyl-Oenzothiazolium-tosylate and
1.4 g of 2-methylmercapto-4-phenyl-thiazolealdehyde-5 in
20 ml of acetic acid anhydride are heated under reflux for
-
10 minute` The solution i8 cooled and the dye~ i8 ~precipitated
, . ~ .
with potas~ium lodide ~olution, filtered under suotion and
recry~tallized twice,~each time from 100 ml of methanol, with
th~ addition o~ active oharcoal. 1.4 g of dye of ~elting
polnt 228C (decompo~ition~ 18 obtained.
-
, F' ,,~ ~ ~ ,
A~G 854 ~7-
,'
..-
1~)4~917
Dye 8
2.4 g of 1,3,6-trimethyl-2-oxo-pyrimidinium perchlorate and
203 g of 2-dimethylamino-4-phenyl-thiazole-aldehyde-5 in 20 ml
of acetic acid anhydride are heated under reflux for 15 minutesO
The dye precipitates after heating for a short time. The mixture
is cooled and the dye is filtered under suction and recrystall-
ized from 250 ml of glacial acetic acidO
Yield = 4.2 g, m.pO: 277C (decomposition)O
Dye 10
2.0 g of 1-methyl-2-phenyl-indole and 3.0 g of 2-methyl-
phenylamino-4-phenyl-thiazole-aldehyde-5 in 10 ml of glacial
acetic acid with the addition of 2 ml of phosphorus oxychloride
are heated under reflux for one hour. The dye solution is cooled
and the dye is precipitated with sodium perchlorate solution,
filtered under suction and recrystallized from 150 ml of alcoholO
Yield = 1.6 g, mOp. 160 ~ 162Co
The dyes used according to the invention generally have no
sensitizing effect in conventional negative emulsions but on
the contrary reduce the overall sensitivity and reinforce the
unwanted uniform grey fogO In direct positive emulsions, on the
other hand, these dyes have a spectral sensitizing effect
resulting in exceptionally high sensitivity and excellent
steepness of the gradation.
According to a particularly preferred embodiment of the
invention,-the new cyanine dyes are used for the preparation
direct positive photographic silver halide emulsions, in
partlcular developable fogged silver halide emulsionsO
F ,7
A-G 854 _ ~
lg~4~9~7
The emulsions may be fogged by the usual methods, for example
by the action of light or so-called chemical fogging agents,
for example stannous chloride, formaldehyde, thiourea dioxideO
Another advantageous method of fogging the emulsions consists
in adding a reducing compound, for example thiourea dioxide,
and the compound of a metal which is more electropositive than
silver, for example a gold salt, e.g. potassium chloroaurate,
as described in British Patent Specificàtion NoO 723,019.
Typical reducing compounds which are suitable for preparing :
such fogged silver halide emulsions are, for example stannous
salts, such as stannous chloride, hydrazine, sulfur compounds
such as thiourea dioxide, phosphonium salts, e O g O tetra-
(hydroxymethyl)-phosphonium chloride. Typical compounds of
metals which are more electropositive than silver are, for
example compounds of gold, rhodium, platinum, palladium and
iridium. It is preferred to use soluble salts of the said noble
metals, e.gO potassium chloroauràte, auric chloride and
(NH4)2-PdCl6.
The concentration of the reducing agents or the compounds
of the metal which is more electropositive than silver, used
for fogging can vary within wide limitsO In general, concen-
trationA of .0005 to about .06 milli-equivalent~ of reducing
agent and about .001 to about .01 milli-mols of the noble
metal salt per mol silver halide have proved suffic~ent.
Fogging can be also accomplished with the method of æilver halide
dlgestion described by W00D in "J.phot.Science 1 (1963) page
163, at pAg valueA between 2 and 5 and pH values of a~out 6.5.
F 1~
A-G 854
1~4~917
Any type of direct positive photographic emulsions can be
spectrally sensitized by the sensitizing dyes of the present
inventionO Suitable direct positive emulsions include silver
halide emulsions the grains of which have high internal sensi-
tivity in particular silver halide emulsions containing internalelectron trapsO`Particular utility is exhibited by direct posi-
tive silver halide grains comprising a central core of a sllver
halide which contains centres which act as electron traps and
an outer shell covering said core comprising a fogged silver
halide that develops to silver without exposure. ~mulsions of
that type are disclosed by Eo MOISAR and Fo WAGNER in "Berichte
der Bunsengesellschaft f~r physikalische Chemie" 67 (1963),
pages 365 - 359. We furthermore refer to British patent peci-
fications 1,027,146 and 1,151,781 or to French patent specifi-
-cation 1,585,791. m e formations of the centres or specks in
the inside of the grains particularly on the core of the
composite grain are produced as known per se by chemical sensi-
tizing the emulsions with compounds of noble metals in particu-
lar gold or iridium salts are sulfur compounds such as thio-
~ulfates. In particular u8eful is a treatment with noble metal
salts and sulfur compoundsO
.
The spectral sensitizers of the present invention can also
be applied to direct positive emulsions which are fogged on
- the surface so that they can be developed to silver without
exposure and which contain at the surface electron acceptors
auch as desensitizing dyes. Suitable dyes for this purpose are
well-known. Referen¢e i8 made eOg. to pinacryptol yellow or
~9
A-G 854 - 2~-
i~4~9~7
nitro-substituted polymethine dyes. m e technic of desensiti-
zation and the chemical structure of suitable desensitizing
dyes are described e.gO by 0. RI~ST~R in "Mitteilungen aus den
Forschungslaboratorien der Agfa", Volume 1 (1955), page 44 or
5 in the handbook '!Grundlagen der photographischen Prozesse mit
Silberhalogeniden", Volume 3, page 10770 The direct positive
sensitizing dyes of the present invention can be used in
combination with further sensitizing dyes capable of sensitizing
direct positive emulsions and desensitizing negative silver
halide emulsions as described for example in US patent speci-
fications 3,31~, 796 or 3, 505,070. Further suitable direct
positive emulsion are described in German patent specifications
606,392 or 642,222 or in UK patent specifications 581,773 or
655,0090
The direct positive emulsions may also contain mercury
salts and thallium salts as described in British patent speci-
fication 1,203,744 or US patent specification 3,620,7500
The silver halide of the silver halide emulsions to which
the new.cyanine dyes may be added may consist of one of the
u~ual silver halides used for preparing photographic silver
halide emulsions, i.eO for example silver bromide, silver iodide,
silver chloride, silver chlorobromide, silver bromoiodide and
silver chlorobromoiodide.
The new dyes may be incorporated with silver halLde
emulsions at the usual concentrations, for example concentrations
of about 50 to 2.000 mg, preferably about 400 to 800 mg/mol
of sllyer halide.
o
A-G 854
~4~7
The ne~ cyanine dyes are preferably added to the washed,
prepared silver halide emulsions and dispersed in them as uni-
formly as possible. The incorporation of the dyes in the
emulsions may be carried out by the usual known methods, for
example the dyes may be added to the emulsions from solutions
in suitable solvents. The solvent must, of course, be selected
so that they have no adverse effect on the light-sensitive
photographic material which is to be produced. Suitable
solvents are, for example, methanol, isopropanol, acetone and
water, either separately or mixed with each otherO
me binder of the silver halide emulsions to which the
cyanine dyes according to the invention may be added may be
any of the hydrophilic colloids commonly used for the prepa-
ration of photographic silver halide emulsions, for example -
naturally substances such as proteins, in particular gelatin,
albumin, agar-agar, gum arabic or alginic acid or synthetic
hydrophilic resins such as polyvinyl alcohol, polyvinyl
pyrrolidone, cellulose ethers or partly hydrolyzed cellulose
acetate.
- The emulsions containing one or more cyanine dyes accor-
dlng to the invention may be applied to the usual opaque or
transparent photographlc supports used for the preparation
Or photographic materials, ~or example supports of glass,
cellulose acetate, cellulose acetobutyrates or polyesters,
e.g. polyethylene terephthalate, or supports of baryta-coated
paper or paper coated with polyole~ines such as polyethylene. --
F z~
A-G 854
1~4~917
The photographic silver halide emulsions to which the new
cyanine dyes are added, as well as the other layers of a photo-
graphic material which is prepared using these emulsions may be
hardened by the addition of the usual hardeners such as
aldehyde hardeners, eOgO formaldehyde or mucochloric acid.
The good sensitizing effect is preserved even in the
presence of water-soluble and emulsified color couplers. The
emulsion may also contain the usual wetting agents, stabilizers,
brightening agents and other additivesO
10 li xamPle
45 mg of Dye 3 in the form of a 1:1000 solution in methanol
are added with stirring to 1 kg of a direct positive emulsion
which has been fogged by chemical fogging with ammonia and
excess silver nitrate and which contains 004 mol of silver
halide per kilogram of casting solution with an iodine content
of 205 mol percent, based on the amount of silver, and the
mixture i8 left to digest for 10 minutesO 10 ml of a 4 % solution
of saponin as wetting agent and 25 ml of a 5 % solution of
mucochloric acid are then addedO
The emulsion is then cast on a cellulose acetate support in the
usual mannerO When dry, the layer is exposed to white light in
a sensltometer and developed for 5 minutes at 20C with a
de~eloper of the following composition:
F ~ z~
A-G 854 _ 2, _ -
917
p-methylaminophenol 305 g
anhydrous sodium sulfite60.0 g
hydroquinone 900 g
anhydrous sodium carbonate40.0 g
potassium bromide 3.5 g
made up to 1 litre with waterO
The emulsion is then fixed in the usual mannerO A positive
image of the step wedge with exceptional clear whites and
excellent gradation is obtained. The spectral sensitization
curve is shown in Figure 20 Figure 1 shows for comparison the
sensitivity curve obtained without a sensitizer.
If Dye 3 is replaced by an equal quantity of Dye 11, the
~ensitiza~ion curve shown in Figure 3 is obtained, and if with
... .
an equal quantity of Dye 12, the sensitization curve shown in
Figure 4 is obtained. Using the same photographic process,
the 8ensitization curves shown in Figures 5, 6 and 7 are
obtained using Dyes 13, 31 and 340
,- ,
.:' .
.,
,
" , - '
`.
A-G 854
,
, , . , , , . , , , ,. ".. ,,; " , "; " , ... .
