Note: Descriptions are shown in the official language in which they were submitted.
2~ 315g 44215CAN8A
Liqht-Sensitive Elements For Radio~raPhic Use And
Process For the Formation of an X-Ra~y Image
FIELD OF THE INVENTION
The present invention refers to light-sensitive sil-
ver halide elements to be used in radiography and, more in
particular, to light-sensitive silver halide elements to
be used with intensifying screens to obtain improved X-ray
images.
BACKGROUND OF THE INVENTION
In radiography, and particularly in medical radiogra-
phy, light-sensitive elements having silver halide emul-
sion layers coated on one side of a transparent base are
used. It is known to be more preferable to use silver
halide emulsions on both sides to obtain better develo-
pability as compared to single-side coated elements.
Light-sensitive elements having silver halide emulsion
layers coated on one side and, more preferably, on both
sides of the base are generally used in association with
intensifying screens in order to reduce the ~-ray exposure
necessary to obtain the required image. Generally, one
intensifying screen is used on each side of the light-sen-
sitive element. The silver halides used in the light-sen-
sitive elements are sensitive or sensitized to a region of
the electromagnetic spectrum corresponding to the wave-
length of the light emitted by the luminescent materials
used in the intensifying screens, thus providing signifi-
cant amplification factors.
The quality of the image obtained upon exposure and
development of said radiographic elements is negatively
affected by light scattering and crossover exposure. Light
scattering occurs both in single and double-side emulsion
layer coated radiographic materials. It is caused when
light emitted by one screen is diffused (scattered) by
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silver halide grains causing a reduction in image sharp-
ness.
Crossover exposure, which also causes a reduction in
image sharpness, occurs in double emulsion layer coated
radiographic materials when light emitted by one screen
passes through the adjacent emulsion layer and the support
and, the light having been spread by the support, image-
wise exposes the emulsion layer on the opposite side of
the support.
The crossover exposure causes poor definition even
if light-sensitive elements are used which employ reduced
silver halide coverages to lower the costs or increase
the processing speed of the element. In fact, the de-
crease of the emulsion turbidity increases the amount of
light available for crossover and therefore worsens the
image.
To reduce the crossover phenomenon, dyes or pigments
can be used within the photographic element. The absorp-
tion of said dyes or pigments is in a region of the elec-
tromagnetic spectrum corresponding to the wavelength of
the light emitted by the intensifying screens. The dyes or
pigments absorb some of the light emitted by the intensi~
fying screen so that imaging of the rear emulsion by the
forward screen is reduced by absorbance of the light from
the forward screen by the anticrossover layer. These dyes
or pigments are eliminated during the photographic devel-
oping, fixing and/or washing process of the exposed mate-
rial; they can be for instance washed away or, more pref-
erably, bleached while processing the radiographic ele-
ment.
The dyes can be incorporated in any layer of the
light-sensitive element: in the emulsion layer, in an in-
termediate layer between the emulsion and the base, or in
the subbing layer of the support base. It is preferred to
incorporate the dyes in a layer different from that con-
taining the emulsion to avoid possible desensitization
phenomena. Since 1978, Minnesota Mining and Manufacturing
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Company has sold a radiographic element under the name of
3M TrimaxTM Type XUD X-Ray Film to be used in combination
with 3M TrimaxTM Intensifying Screens. That radiographic
element comprises a transparent polyester base, each sur-
face of which has a silver halide emulsion layer sensi-
tized to the light emitted by the screens. Between the
emulsion and the base is a gelatin layer containing
water-soluble acid dyes, which dyes can be decolorized
during processing and have an absorption in a region of
the electromagnetic spectrum corresponding to the wave-
length of the light emitted by the screens and of the
spectral sensitivity of the emulsion. The dyes are an-
chored in the layer by means of a basic mordant consisting
of polyvinylpyridine.
In the practical solution of reducing the crossover
exposure by using a mordanted dye layer (as described for
instance in the European Patent Application 101,295), some
problems are created which up to now have not yet been
solved properly. In fact, the improvement of image defini-
tion involves not only a natural decrease in the sensitiv-
ity of the light-sensitive element caused by the absorp-
tion of the transmitted and diffused light which otherwise
would take part in the formation of a part of the image,
but also the possibility of desensitization phenomena due
to the migration of dye, not firmly mordanted, into the
silver halide emulsion layer. There is also a problem with
residual stain even after processing, the retention of
significant ~uantities of thiosulfate from the fixing bath
which causes image yellowing upon long-time shelf storage,
and lengthening of the drying times after processing be-
cause of element thickening.
Other approaches have been suggested to reduce cross-
over, as reported hereinbelow.
US Patent 3,923,515 discloses a relatively lower
speed silver halide emulsion between the support and a
higher speed silver halide emulsion layer to reduce cross-
over.
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US Patent 4,639,411 discloses a photographic element,
to be used with blue emitting intensifying screens,having
reduced crossover, said element comprising coated on both
sides of a transparent support a blue sensitive silver
halide emulsion layer and, interposed between the support
and the emulsion layer, a blue absorbing layer comprising
bright yellow silver iodide grains of a specific crystal
structure.
Japanese Patent Application 62-52546 discloses a ra-
diographic element of improved image quality comprising
coated on both sides of a transparent support a light sen-
sitive silver halide emulsion layer and, interposed be-
tween the support and the emulsion layer, a layer contain-
ing water insoluble metal salt particles having adsorbed
on their surface a dye. Said dye has a maximum absorption
within the range of + 20 nm of the maximum absorption of
said silver halide and corresponds to the light emitted by
intensifying screens. Silver halides are disclosed as pre-
ferred metal salt particles.
Japanese Patent Application 62-99748 discloses a ra-
diographic element of improved image quality comprising
coated on both sides of a transparent support a light-sen-
sitive silver halide emulsion layer and, interposed be-
tween the support and the emulsion layer, a silver halide
emulsion layer having substantially no light-sensitivity.
The approaches of using light-insensitive silver
halide layers as anticrossover layers interposed between
the support and the light-sensitive silver halide emulsion
layers, although preferred to using dyes or pigments, en-
counter some problems such as the increase of silver cov-
erage and bad bleaching characteristics in photographic
processing tresidual stain).
Additionally, FR 2,084,66~ describes a double-side
coated radiographic element comprising between the support
and the silver halide emulsion layer, a light absorbing
layer comprising dispersed particles of manganese dioxide.
GB 2,075,208 describes a silver halide photographic
2~815~
material with improved antistatic properties comprising a
support having in one layer thereon electrically conduc-
tive metal oxide particles dispersed in a binder, and US
4,574,115 describes a silver halide photographic material
comprising a silver halide emulsion layer and a layer con-
taining light-insensitive metal salt grains (such as, for
example, silver halide grains or zinc oxide particles) on
which a dye is adsorbed, wherein the absorption maximum of
said dye is separated by 20 nm or more from the sensitiza-
tion maximum of said emulsion layer located in a position
farther from the light source than the layer containing
said dye.
SUMMARY OF THE INVENTION
This invention is directed to a silver halide X-ray
element to be used with X-ray intensifying screens com-
prising a transparent support base having coated on at
least one of its sides a spectrally sensitized silver
halide emulsion layer and, between the support base and
the silver halide emulsion layer, a hydrophilic colloid
layer aontaining a) substantially light-insensitive low
iodide silver bromciodide grains having an average grain
size in the range of from 0.01 to 0.1 ~m on which a spec-
tral sensitizing dye is adsorbed to form a J-band, said
dye adsorbed on said grains having a significant portion
of its absorption in a region of the electromagnetic spec-
trum corresponding substantially to the spectral sensitiv-
ity of the silver halide emulsion, and b) dispersed zinc
oxide particles.
The combined action of absorption (from the J-band of
the light-insensitive silver bromoiodide grains) and re-
flection (from the zinc oxide particles) of the light
emitted by the X-ray intensifying screens offers advantag-
es in crossover reduction without causing negative ef-
fects, such as significant loss of sensitivity, residual
stain, image instability upon storage and excessive
., ~
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element thickening.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention refers to a silver
halide light-sensitive element to be associated with X-ray
intensifying screens and used in radiography.
Said light-sensitive silver halide element for use in
radiography with X-ray intensifying screens according to
the present invention comprises a transparent support base
having coated on at least one of its sides, preferably on
both of its sides, a spectrally sensitized silver halide
emulsion layer and, between the support base and the sil-
ver halide emulsion layer, a hydrophilic colloid layer
containing a) substantially light-insensitive low iodide
silver bromoiodide grains having an average grain size in
the range of from 0.01 to 0.1 ~m on which a spectral sen-
sitizing dye is adsorbed to form a J-band, said dye
adsorbed on said grains having a significant portion of
its absorption in a region of the electromagnetic spectrum
corresponding substantially to the spectral sensitivity of
the silver halide emulsion, and b) dispersed zinc oxide
particles.
The term "low iodide silver bromo-iodide grains" in
the present invention means a total percentage of halide
in the grains of from 0 mole percent to less than 10 mole
percent iodide. Preferably the silver iodide provided by
the silver bromoiodide grains is limited to less than 5
mole percent of the total silver halide present in the
grains, and more preferably less than 3 mole percent. Sil-
ver iodide grains of at least 1 mole percent are preferred
to produce the desired J-band.
Said silver bromoiodide grains are substantially
light-insensitive, that is they do not form any image upon
conventional exposure (e.g. for an exposure of 10-2 sec-
onds) to radiations of a wavelength in the range from 420
to 700 nanometers and development in standard black and
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white and color developers. Such sensitivity can be gener-
ally described as being of less than 1 ASA. In the case of
the emulsions of the present invention, they preferably
are of a sensitivity lower than 10 1 ASA. The grain size
of said light-insensitive silver bromoiodide grains is
particularly restricted. The grains are 0.1 ~m or less in
mean diameter. The minimum mean diameters of the grains
are limited only by synthetic convenience. Typically,
grains of at least 0.01 ~m in mean diameter are employed.
The light-insensitive silver bromoiodide grains of the
present invention have adsorbed on their surface speçtral
sensitizing dyes that exhibit absorption maxima in the
blue and/or green and/or red portions of the visible spec-
trum. Spectral sensitizing dyes according to this inven-
tion produce J aggregates if adsorbed on the surface of
the silver halide grains and a sharp absorption band
(J-band) with a bathocromic shifting with respect to the
absorption maximum of the free ~ye in aqueous solution.
Spectral sensitizing dyes producing J aggregates are well
known in the art, as illustrated by F. M. Hamer, Cyanine
Dves and Related Com~ounds, John Wiley and Sons, 1964,
Chapter XVII and by T. H. James, The Theor~ of the Photo-
qra~hic Process, 4th edition, Macmillan, 1977, Chapter 8.
In a preferred form, J-band exhibiting dyes are
cyanine dyes. Such dyes comprise two basic heterocyclic
nuclei joined by a linkage of methine groups. The
heterocyclic nuclei preferably include fused benzene rings
to enhance J aggregation. The heterocyclic nuclei are
preferably quinolinium, benzoxazolium, benzothiazolium,
benzoselenazolium, benzimidazolium, naphthoxazolium, naph-
thothiazolium and naphthoselenazolium quaternary salts.
J-band type dyes preferably used in the present invention
have the following general formula (I):
'-------Zl-- , IR3 l4R5 I Z2 '+
Rl~N~(-CH=CH-)p~C=C~(~C=C)m~C=(=CH-CH=)q=N -R2
(A-)k (B )1 (I)
2~i8~S~
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wherein Zl and Z2 may be the same or different and
each represents the elements necessary to complete a cy-
clic nucleus derived from basic heterocyclic nitrogen com-
pounds 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, benzothiazole, the naphthothiazoles (e g.,
naphtho{2,1-d}thiazole), the thiazoloquinolines (e.g.,
thiazolo{4,5-b}quinoline), selenazoline, selenazole,
benzoselenazole, the naphthoselenazoles (e.g., naphtho-
{1,2- d}selenazole, 3H-indole (e.g., 3,3-dimethyl-3H-
indole), the benzindoles (e.g., 1,1-dimethylbenzindole),
imidazoline, imidazole, benzimidazole, the naphth-
imidazoles (e.g., naphth{2,3-d}imidazole), pyridine, and
quinoline, which nuclei may be substituetd on the ring by
one or more of a wide variety of substituents such as
hydroxy, the halogens (e.g., fluoro, bromo, chloro, and
iodo), alkyl groups or substituted alkyl groups (e.g.,
methyl, ethyl, propyl, isopropyl, butyl, octyl, dodecyl,
2-hydroxyethyl, 3-sulfopropyl, carboxymethyl, 2-cyano-
ethyl, and trifluoromethyl), aryl groups or substituted
aryl groups ~e.g., phenyl, 1-naphthyl, 2-naphthyl, 4-
sulfophenyl, 3-carboxyphenyl, and 4-biphenyl), aralkyl
groups (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., ethyl-
thio and methylthio), arylthio groups (e.g., phenylthio,
p-tolythio, and 2-naphthylthio), methylenedioxy, cyano,
2-thienyl, styryl, amino or substituted amino groups
(e.g., anilino, dimethylanilino, diethylanilino, and
morpholino), acyl groups (e.g., acetyl and benzoyl), and
sulfo groups,
R1 and R2 can be the same or different and represent
alkyl groups, aryl groups, alkenyl groups, or aralkyl
groups, with or without substituents, (e.g., carboxy-
methyl, 2-hydroxyethyl, 3-sulfopropyl, 3-sulfobutyl, 4-
sulfobutyl, 2-methoxyethyl, 2-sulfatoethyl,
2~81S5~
3-thiosulfatoethyl, 2-phosphonoethyl, chlorophenyl, and
bromophenyl),
R3 represents a hydrogen atom,
R4 and R5 can be the same or different and represent
a hydrogen atom or a lower alkyl group of from 1 to 4 car-
bon atoms,
p and g are O or 1, except that both p and q prefera-
bly are not 1,
m is O or 1 except that when m is 1 both p and q are
O and at least one of Zl and Z2 represents imidazoline,
oxazoline, thiazoline, or selenazoline,
A is an anionic group, B is a cationic group, and k
and 1 may be O or 1, depending on whether ionic
substituents are present. Variants are, of course, possi-
ble in which R1 and R3, R2 and R5, or R1 and R2 together
represent the atoms necessary to complete an alkylene
bridge.
More preferably said dye adsorbed on said substan-
tially light~insensitive sil~er bromoiodide grains is rep-
resented by the following general formula (II):
~ ~ -CH=C-CH= \ ~ (IIj
R7 N N Rg
R11 R12 (X )n-1
wherein
R1o represents a hydrogen atom or a lower alkyl group
of from 1 to 4 carbon atoms (e.g. methyl, and ethyl),
R6, R7, R8 and Rg each represents a hydrogen atom, a
halogen atom (e.g. chloro, bromo, iodo, and fluoro), a
hydroxy group, an alkoxy group (e.g. methoxy and ethoxy),
an amino group (e.g. amino, methylamino, and dimethyl-
amino~, an acylamino group (e.g. acetamido and propion-
amido), an acyloxy group (e.g. acetoxy group), an alkoxy-
carbonyl group (e.g. methoxycarbonyl, ethoxycarbonyl, and
2~ 1 59
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butoxycarbonyl), an alkyl group (e.g. methyl~ ethyl, and
isopropyl), an alkoxycarbonylamino group (e.g. ethoxy-
carbonylamino) or an aryl group (e.g. phenyl and tolyl),
or, together, R6 and R7 and, respectively, R8 and Rg can
be the atoms necessary to complete a benzene ring (so that
the heterocyclic nucleus results to be, for example, an
a-naphthoxazole nucleus, a ~-naphthoxazole or a
naphthoxazole),
R11 and R12 each represents an alkyl group (e.g.
methyl, propyl, and butyl), a hydroxyalkyl group (e.g. 2-
hydroxyethyl, 3-hydroxypropyl, and 4-hydroxybutyl)j àn
acetoxyalkyl group (e.g. 2-acetoxyethyl and 4-acetoxy-
butyl), an alkoxyalkyl group (e.g. 2-methoxyethyl and 3-
methoxypropyl), a carboxyl group containing alkyl group
(e.g. carboxymethyl, 2-carboxyethyl, 4-carboxybutyl, and
2-(2-carboxyethoxy)-ethyl), a sulfo group containing alkyl
group (e.g. 2-sulfoethyl, 3-sulfopropyl, 4-sulfobutyl,
2-hydroxy-3- sulfopropyl, 2-(3-sulfopropoxy)-propyl, p-
sulfobenzyl, and p-sulfophenethyl), a benzyl group, a
phenethyl group, a vinylmethyl group, and the like,
X represents an acid anion (e.g. a chloride, bro-
mide, iodide, thiocyanate, methylsulfate, ethylsulfate,
perchlorate, and p-toluensulfonate ion), and
n represents 1 or 2.
The alkyl groups included in said substituents R6,
R7, R8, Rg, R1o, and R11 and, more particularly, the alkyl
portions of said alkoxy, alkoxycarbonyl, alkoxycarbonyl-
amino, hydroxyalkyl, acetoxyalkyl groups and of the alkyl
groups associated with a carboxy or sulfo group each pref-
erably contain from 1 to 12, more preferably from 1 to 4
carbon atoms, the total number of carbon atoms included in
said groups preferably being no more than 20.
The aryl groups included in said substituents R6, R7,
R8 and Rg each preferably contain from 6 to 18, more pref-
erably from 6 to 10 carbon atoms, the total number of car-
bon atoms included in said groups arriving up to 20 carbon
atoms.
2~}~81S9
The following are specific examples of J-band sensi-
tizing dyes belonging to those represented by the general
formula (II) above:
Dye Rlo R6 R7 R8 R3 Rll R12 X n
__________________________________________________________
*
A C2H5 H 5-C1~ 5'-Cl (CH2)3S03 (CH2)3so3H - 1
B C2H5 HC6H5 (C~2)3so3 (cH2)2cHso3E - 1
C CH3 H 5-OCH H 5'-OCH C H (CH2)3S03 - 1
D C2H5 6-CH3 5-Cl H 5'-Cl (CH2)4S03 (CH2)3S03H . - 1
E C2H5 H 5-Cl H 5'-Cl C2H5 C2H5 I 2
* Triethylamine salt
** Sodium salt
____________________________________________________~_____
According to the present invention, it has been found
that the intensity of the sharp absorption band (J-band)
shown by the spectral sensitizing dye adsorbed on the sur-
face of the light-insensitive silver halide grains will
vary with the quantity of the specific dye chosen as well
as the size and chemical composition of the grains. The
maximum intensity of J-band has been obtalned with silver
halide grains having the hereinbefore described sizes and
the chemical compositions adsorbed with J-band spectral
sensitizing dyes in a concentration of from 25 to 100 per-
cent or more of monolayer coverage of the total available
surface area of said silver halide grains. Optimum dye
concentration levels can be chosen in the range of 0.5 to
20 millimoles per mole of silver bromoiodide, preferably
in the range of 2 to 10 millimoles.
The J-band spectral sensitizing dyes are preferably
added to the fine grain low iodide silver bromoiodide
emulsions in the presence of a water soluble iodide or
bromide salt. The J-band exhibited by said dyes adsorbed
on said grains has been found to be increased by the pres-
ence of said salts. Said salts are more advantageously
.... . .
. ~ .
2~?181S9
added to the silver halide emulsion before dye digestion,
that is the pause following dye addition; said pause is
preferably made at a temperature o~ 40 to 60C for a time
of about 50 to 150 minutes. Typical water soluble salts
include alkali metal, alkali earth metal and ammonium
iodide and bromide such as ammonium, potassium, lithium,
sodium, cadmium and strontium iodides and bromides. The
amount of said water soluble iodide and bromide salts is
advantageously in a range of from 50 to 5,000 mg per mole
of silver, and preferably from 100 to 1,000 mg per mole of
silver.
The fine grain low iodide silver bromoiodide substan-
tially light-insensitive emulsions of the present inven-
tion can be prepared by any of well-known procedures. Very
fine grain emulsions known in the art as "Lippmann" emul-
sions are useful herein. According to a preferred proce-
dure these emulsions can be formed by a double jet precip-
itation process wherein water soluble bromide and iodide
salt are added concurrently with water soluble silver salt
to a reaction vessel containing a dispersing medium.
The dispersing medium for said silver bromoiodide
grains can be chosen among those conventionally`employed
in the silver halide emulsions. Preferred dispersion media
include hydrophilic colloids, such as proteins, protein
derivatives, cellulose derivatives (e.g. cellulose
esters), gelatin (e.g. acid or alkali treated gelatin),
gelatin derivatives (e.g. acetylated gelatin, phthalated
gelatin and the like), polysaccarides (e.g. dextran), gum
arabic, casein and the like. It is also common to employ
said hydrophilic colloids in combination with synthetic
polymeric binders and peptizers such as acrylamide and
methacrylamide polymers, polymers of alkyl and sulfoalkyl
acrylates and methacrylates, polyvinyl alcohol and its
derivatives, polyvinyl lactams, polyamides, polyamines,
polyvinyl acetates, and the like. At the end of grain
precipitation, water soluble salts are removed from the
emulsion with procedures known in the art, such as
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ultrafiltration. Such substantially light-insensitive sil-
ver bromiodide grains are not chemically sensitized nor
substantially physically ripened.
In the present invention, the hydrophilic colloid
layer coated between the support base and the silver
halide emulsion layer comprises, in combination with the
light-insensitive very fine low iodide silver bromoiodide
grains having adsorbed on their surface J-band forming
spectral sensitizing dyes, dispersed metal oxide parti-
cles. These are preferably metal oxides which are removed
during development processing steps (development, fixing,
etc.). From the point of view of the dye being removed and
decolored during the processing, zinc oxide is particular-
ly preferred. The particle size of the zinc oxide parti-
cles used in the present invention is not particularly
restricted, but it is generally in the range of from 0.05
to 5 ~m (average diameter), preferably from 0.1 to 1 ~m.
The amount of zinc oxide particles used in the present
invention is not particularly limited, but is selected
depending upon the desired reflecting action and the de-
sired transparency of the developed radiographic element;
it is generally in a range of from 0.1 to 10 g/m2, and
preferably from 0.5 to 3 g/m2.
The light-sensitive element comprises a polymeric
base of the type commonly used in radiography, for in-
stance a polyester base, in particular a polyethylene
terephthalate base.
On at least one surface, preferably on both surfaces
of the base there is coated a silver halide emulsion layer
in a hydrophilic colloid. The emulsions coated on the two
surfaces may also be different and comprise emulsions
commonly used in photographic elements, such as silver
chloride, silver iodide, silver chloro-bromide, silver
chloro-bromo-iodide, silver bromide and silver bromo-io-
dide emulsions, the silver bromo-iodide emulsions being
particularly useful for the X-ray elements. The silver
halide crystals may have different shapes, for instance
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cubic, octahedral, spherical, tabular shapes, and may have
epitaxial growth; they generally have mean sizes ranging
from O.2 to 3 ~m, more preferably from O.4 to 1.5 ~m. The
emulsions are coated on the base at a total silver cover-
age comprised in the range from about 3 to 6 grams per
s~uare meter. The silver halide binding material used is a
water-permeable hydrophilic colloid, which is preferably
gelatin, but other hydrophilic colloids, such as gelatin
derivatives, albumin, polyvinyl alcohol, alginates, cellu-
lose hydrolized esters, hydrophilic polyvinyl polymers,
dextrans, polyacrylamides, acrylamide hydrophilic
copolymers and alkylacrylates can also be used alone or in
combination with gelatin.
The light-sensitive element according to the present
invention is associated with the intensifying screens so
as to be exposed to the radiations emitted by said
screens. The screens are made of relatively thick phosphor
layers which transform the x-rays into light radiation (e.
g., visible light). The screens absorb a portion of x-rays
much larger than the light-sensitive element and are used
to reduce the radiation doses necessary to obtain a useful
image. According to their chemical composition, the phos-
phors can emit radiations in the blue, green or red region
of the visible spectrum and the silver halide emulsions
are sensitized to the wavelength region of the light emit-
ted by the screens. Sensitization is performed by using
spectral sensitizers well-known in the art. The x-ray in-
tensifying screens used in the practice of the present
invention are phosphor screens well-known in the art. Par-
ticularly useful phosphors are the rare earth oxysulfides
doped to control the wavelength of the emitted light and
their own efficiency. Preferably are lanthanum, gadolinium
and lutetium oxysulfides doped with trivalent terbium as
described in US patent 3,725,704. Among these phosphors,
the preferred ones are gadolinium oxysulfides wherein from
about 0.005% to about 8% by weight of the gadolinium ions
are substituted with trivalent terbium ions, which upon
2~ 18159
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excitation by w radiations, x-rays, cathodic rays emit in
the blue-green region of the spectrum with a main emission
line around 544 nm. The silver halide emulsions are spec-
trally sensitized to the spectral region of the light
emitted by the screens, preferably to a spectral region of
an interval comprised within 25 nm from the wavelength of
maximum emission of the screen, more preferably within 15
nm, and most preferably within 10 nm. Many types and com-
binations of spectral sensitizers can be used. In a pre
ferred form of the present invention particularly useful
spectral sensitizing dyes are those which exhibit an ab-
sorption peak (J-band) in their aggregated state. In a
preferred form of the present invention, particularly use-
ful spectral sensitizing dyes are those represented by the
general formula (I) above. In the most preferred form of
the present invention, wherein the phosphors of the
screens are the gadolinium oxysulfides doped with
trivalent terbium ions which emit light radiation com-
prised in the blue-green region of the visible spectrum,
particularly useful dyes are those represented by formula
(II) above and specific examples of dyes which absorb in
the spectral region of emission of the gadolinium
oxysulfides doped with trivalent terbium ions are those
reported hereinabove. Preferably, the spectral sensitizing
dye adsorbed on the light-sensitive silver halide grains
has the same formula of the spectral sensitizing dye
adsorbed on the substantially light-insensitive very fine
grain low iodide silver bromoiodide grains as hereinbefore
described.
The hydrophilic colloid layer containing the substan-
tially light-insensitive very fine grain low iodide silver
bromoiodide emulsions and the dispersed zinc oxide parti-
cles is a layer coated between the base and the silver
halide emulsion layer. It is apparent that in a radio-
graphic element having both surfaces of the support coated
with light-sensitive emulsion layers either of the
light-insensitive layers according to the present
Z~18159
- 16 -
invention employed alone can effectively reduce crossover
from both screens. Thus, only one light--insensitive layer
is required, although for manufacture convenience double
coated radiographic elements most commonly employ identi-
cal light-insensitive layers on opposite surfaces of the
support. The hydrophilic colloid may be any colloid of the
type generally used in the photographic elements as said
above for the emulsion layer, the preferred colloid being
gelatin. The layer may be either an intermediate auxiliary
layer coated between the subbing layer of the base and the
emulsion layer or the same subbing layer of the base. As
known, in fact, the photographic base is per se hydroph~-
bic and needs a hydrophilic layer, viz. the subbing layer,
to assure sufficient adhesion of the light-sensitive
hydrophilic layers. The use of the subbing layer, which
normally consists of gelatin, to contain the substantially
light-insensitive very fine grain low iodide silver
bromoiodide emulsions and the dispersed zinc oxide parti-
cles according to the subject invention has the advantage
of eliminating one layer, thus allowing a lower thickness
of the photographic material and shorter drying times dur-
ing the photographic processing. The thickness of the lay-
er containLng the substantially light-insensitive very
fine grain low iodide silver bromoiodide emulsions and the
dispersed zinc oxide particles according to the present
invention is the normal thickness of layers used in the
photographic elements as non light-sensitive layers (such
as intermediate auxiliary layers or sublayers). Generally,
said thickness ranges from 0.05 to 2 ~m. Within such a
range, as known in the art, a lower thickness, e.g. be-
tween O.05 to O.5 ~m, is used when the layer works as a
sublayer and a higher thickness, e.g. between 1 and 2 ~m,
is used when the layer works as a intermediate auxiliary
layer. Besides, as known to the skilled in the art, the
coating techniques used to coat the sublayer, i.e. the air
knife coating technigue, allow thinner layers than the
coating techniques used to coat the auxiliary layers, e.g.
. . .
.
'.
2~18159
an extrusion coating technique.
$he sharp absorption band (J-band) shown by the spec-
tral sensitizing dye adsorbed on the light-insensitive
silver bromoioide grains of the layer coated between the
base and the light-sensitive silver halide emulsion layer
according to the present invention has the aim of absorb-
ing the light emitted by the intensifying screens and
therefore of avoiding or reducing the cross-over phenome-
non. The presence of-the zinc oxide particles has the aim
of reflecting the light emitted by the intensifying
screens and therefore of avoiding or reducing the decrease
of sensitivity of the material. Of course, the higher the
optical absorbance of the light-insensitive layer measured
at the wavelength corresponding to the main emission peak
of the phosphors, the better the image quality of the ma-
terial, but at the same time the lower the sensitivity.
Therefore, the man skilled in the art can choose the
J-band absorbance by properly selecting the type and
amount of spectral sensitizing dye adsorbed on the light-
insensitive silver bromoiodide grains, the amount of water
soluble iodide or bromide salts as hereinbefore described
as well as the silver coating coverage and the amount of
zinc oxide particles according to the desired ratio be-
tween image guality (crossover) and sensitivity. Particu-
larly useful optical absorbances are in the range from 0.3
to 2.0, read at the wavelength corresponding to the spec-
tral emission maximum of the screens. The crossover reduc-
~ion attained with the light-insensitive layer according
to this invention is preferably at least 10%, more prefer-
ably at least 20% and most preferably at least 30% lower
than the cross-over which can be obtained without said
light-insensitive layer. Within such absorbance range,
lower values of absorbance provide X-ray elements having a
high sensitivity and good image qualities. Higher values
of absorbance provide X-ray materials having a good sensi-
tivity and high image quality. The absorbance above does
not consider the possible optical density of the base. The
zn~is~
- 18 -
base may contain a dye, as previously described.
It is known in the photographic art that photographic
speed obtainable from the silver halide grains increases
with the increasing concentration of the sensitizing dye
until maximum speed is obtained with an optimum dye con-
centration, after that, further increases in dye concen-
tration cause a decrease in the obtainable speed. The op-
timum amount of dye employed can vary depending upon the
specific dye, as well as upon the size and aspect of the
grains. Surprisingly, the amount of dye adsorbed on the
surface of the low aspect ratio cubic grain silver halide
emulsions of the light-sensitive layer can be increased
beyond the optimum dye concentration to obtain in combina-
tion with the substantially light-insensitive J-band form-
ing silver bromoiodide grains of the light-insensitive
layer the full advantages of this invention, i.e. a re-
duced light scattering and cross-over exposure without a
significant loss in speed.
The J-band sensitization dyes are preferably added to
the low aspect ratio cubic grain silver halide emulsions
in the presence of a water soluble iodide or bromide salt.
The J-band sensitization is increased by the presence of
said salts, increasing the strong coloration of the ele-
ment before processing and consequently reducing the
cross-over of exposing radiations by adding a smaller
amount of dye. The residual stain after processing of the
radiographic element also is lower. Said salts are more
advantageously added to the silver halide emulsion before
dye digestion, that is the pause following dye addition;
said pause is preferably made at a temperature of 40 to
60C for a time of about 50 to 150 minutes.
Typical water soluble salts include alkali metal,
alkali earth metal and ammonium iodide and bromide such as
ammonium, potassium, lithium, sodium, cadmium and stron-
tium iodides and bromides. The amount of said water solu-
ble iodide and bromide salts is advantageously lower than
100 mg per mole of silver, and preferably ranges from
Z~ 5g
-- 19 -
about 40 to about 70 mg per mole of silver.
Other radiographic elements according to this inven-
tion having highly desirable imaging characteristics are
those which employ one or more light-sensitive high aspect
ratio tabular grain emulsions or intermediate aspect ratio
tabular grain emulsions, as disclosed in US Patents
4,425,425 and 4,425,426. Preferred tabular grain emulsions
for use in the radiographic elements of this invention are
those in which tabular silver halide grains having a
thickness of less than 0.5 ~m, preferably less than 0.3 ~m
and optimally less than 0.2 ~m, have an average aspect
ratio of greater than 5:1, preferably greater than 8:i and
optimally greater than 12:1 and account for greater than
50 percent, preferably greater than 70 percent and opti-
mally greater than 90 percent of the total projected area
of the silver halide grains present in the emulsion. It is
specifically contemplated to provide double coated radio-
graphic elements according to this invention in which tab-
ular grain emulsion layers are coated nearer the support
than nontabular grain silver halide emulsion layers to
reduce crossover, as illustrated in European Patent Appli-
cation 84,637.
By employing light-sensitive low aspect ratio cubic
grain silver halide or tabular grain silver halide emul-
sion layers as above described, which themselves reduce
crossover, in combination with the light-insensitive low
iodide silver bromoiodide emulsion layer according to this
invention, radiographic elements exhibiting extremely low
crossover levels can be achieved while also achieving high
photographic speed and low residual stain.
The spectral sensitizing dyes can be used in the
light-sensitive silver halide emulsion layers of the ra-
diographic elements of this invention in combination among
them or with other addenda, such as stabilizers,
antifoggants, development modifiers, coating agents,
brighteners and antistatic agents, which combination re-
sults in a supersensitization (that is, into a spectral
2~ 159
- 20 -
sensitization higher than that which could be obtained
with any dye or addendum used alone or would result from
the additive effect of the dyes and addenda). Mechanisms
and compounds responsible for supersensitization are de-
scribed for example in Photographic Science and Engineer-
ing, 18, 418-430, (1974). In particular advantageous re-
sults are obtained according to this invention by combin-
ing the spectral sensitizing dyes with a supersensitizing
amount of a polymeric compound having amino-allilydene-
malononitrile moieties, as described in US Pat. No.
4,307,183, such as copolymers of a vinyl addition monomers
and 3-diallyl-amino-allylidene-malononitrile monomer.
In addition to the features specifically described
above, the photographic elements of this invention, in the
light-sensitive silver halide emulsion layers or in other
layers, can include additional addenda of conventional
nature, such as stabilizers, antifoggants, brighteners,
absorbing materials, hardeners, coating aids,
plasticizers, lubricants, matting agents, antikinking
agents, antistatic agents, and the like, as described in
Research Disclosure, Item 17643, December 1978 and in Re-
search Disclosure, Item 18431, August 1979.
Preferred radiographic elements are of the type de-
scribed in BE Patent 757,815 and in US Patent 3,705,858,
i.e. elements whPrein at least one light-sensitive silver
halide emulsion layer is coated on both surfaces of a
transparent support, the total silver coverage per surface
unit for both layers being lower than about 6 g/m2, pref-
erably than 5 g/m2. Such supports are preferably polyester
film supports, such as polyethylene terephthalate films.
Generally said supports for use in medical radiography are
blue tinted. Preferred dyes are anthraquinone dyes, such
as those described in US Patents 3,488,195; 3,849,139;
3,918,976; 3,933,502; 3,948,664 and in UK Patents
1,250,983 and 1,372,668.
The exposed radiographic elements can be processed by
any of the conventional processing techniques. Such
.
2~ 159
processing techni~ues are illustrated for example in Re-
search Disclosure, I~em 17643, cited above. Roller trans-
port processing is particularly preferred, as illustrated
in US Patents 3,025,779; 3,515,556; 3,545,971 and
3,647,459 and in UK Patent 1,269,268. Hardening develop-
ment can be undertaken, as illustrated in US Patent
3,232,761.
As regards the processes for the silver halide emul-
sion preparation and the use of particular ingredients inthe emulsion and in the light-sensitive element, reference
is made to Research Disclosure 18,431 published in August
1979, wherein the following chapters are dealt with in
deeper details:
IA. Preparation, purification and concentration methods
for silver halide emulsions.
IB. Emulsion types.
IC. Crystal chemical sensitization and doping.
II. Stabilizers, antifogging and antifoldins agents.
IIA. Stabilizers and/or antifoggants.
IIB. Stabilization or emulsions chemically sensitized
with gold compounds.
IIC. Stabilization of emulsions containing polyalkylene
oxides or plasticizers.
IID. Fog caused by metal contaminants.
IIE. Stabilization of materials comprising agents to in-
crease the covering power.
I~F. Antifoggants for dichroic fog.
IIG. Antifoggants for hardeners and developers comprising
hardeners.
IIH. Additions to minimize desensitization due to fold-
ing.
III. Antifoggants for emulsions coated on polyester bas-
es.
IIJ. Methods to stabilize emulsions at safety lights.
IIK. Methods to stabilize x-ray materials used for high
temperature. Rapid Access, roller processor trans-
port processing.
2~ 159
- 22 -
III. Compounds and antistatic layers.
IV. Protective layers.
V. Direct positive materials.
VI. Materials for processing at room light.
VII. X-ray color materials.
VIII. Phosphors and intensifying screens.
IX. Spectral sensitization.
X. W -sensitive materials
XII. Bases
EXAMPLE 1
A light-sensitive cubic grain silver bromo iodide
gelatin emulsion (having 2.3% mole iodide) was prepared.
Said emulsion comprised cubic grains having an average
diameter of about 0.7 ~m and an average aspect ratio of
about 1:1. The emulsion was chemically sensitized with a
sulfur compound and a gold compound, spectrally sensitized
with 0.750 g/mole of silver of the green spectral sensi-
tizing dye A and added with KI in an amount of 60 mg/mole
of silver. The emulsion, added with stabilizing and
antifogging agents, surface active agents and gelatin
hardeners, was coated on both sides of a subbed polyeth-
ylene terephthalate support base (blue tinted with an
anthraquinone dye and having an optical density in green
light of 0.13). The emulsion was coated at 2.2 g/m2 silver
and 1.6 g/m2 gelatin per side. Each emulsion layer was
finally covered with a protective gelatin layer at a gela-
tin coverage of 1.1 g/m2. (Film lA).
A light-insensitive fine grain silver bromo-iodide
gelatin emulsion (having 2% iodide mole) was prepared.
Said emulsion comprised grains having an average diameter
of 0.06 ~m. The emulsion was added with 5.5 g/ mole of
silver of the green spectral sensitizing dye A and 400
mg/mole of silver of potassium iodide. The emulsion was
added with a dispersion of fine particles of zinc oxide
having a mean diameter of 0.5 ~m, prepared by dispersing
2l~ 5~
- 23 -
zinc oxide in gelatin in the presence of anionic dispers-
ing agents with the aid of a high speed stirrer, in an
amount such as to have 1,080 g of zinc oxide per mole of
silver. The emulsion was coated on both sides of the sup-
port base above at 0.1 g/m2 silver, 1 g/m2 zinc oxide and
1.5 g/m2 gelatin per side. Both surfaces of the film thus
obtained were coated with silver halide emulsion layPrs
and protective layers as Film lA above. (Film lB).
Each film was interposed between two green emitting
3M TrimaxTM T8 intensifying screens, then exposed through
a laminated aluminium step wedge to X-rays of 300 mA and
80 kV for 0.15 seconds. After the exposure, the films were
p-rocessed in a 3M TrimaticTM XP 507 roller transport pro-
cessor. Processing consisted of 3M XAD/2 Developer for 24
seconds at 35C, followed by fixing in 3M XAF/2 Fixer for
24 seconds at 30C, washing in tap water for 22 seconds at
35C and drying for 22 seconds at 35C.
The sensitometric and image quality results are tabu-
lated in the following table. Percent cross-over has been
calculated by using the following equation:
ercent Cross-over = x 100
antilog (olog E)
wherein ~log E is the difference in sensitivity between
the two emulsion layers of the same film when exposed with
a single screen (the lower the percent of cross-over, the
better the image quality). The measurement of the J-band
was made referring to the spectrophotometric curve of the
unexposed film in the region of 400 to 700 nm by measuring
the absorbance st 549 nm, which corresponds to the dye
absorbance J-band peak near to the main emission peak of
the phosphor of the screen.
59
- 24 -
Table 1
Film Total Ag J-band Speed Percent
g/m~ Crossover
lA 4.4 1.35 3.0934
lB 4.6 1.76 3.1017
**
lC 7.1 1.70 2.7517
) J-band of the double side coated light-insensitive
silver bromoiodide layers.
) 3M XUD Film: anticross-over film having an emulsion
layer coated on both sides of the support base and a
. mordanted dye layer between each emulsion layer and
the support, the total silver coverage of the film
being 7.1 g/m2.
EXAMPLE 2
A radiographic film (Film 2A) was prepared similar to
Film lA of Example 1 having a total silver coverage of
4.24 g/m2.
~ adiographic films (Films 2B, 2C and 2D) according to
the present invention were prepared similar to Film lB of
Example 1 respectively having a total silver coverage of
4.61 g/m2, 0.1 g/m2 of light-insensitive silver
bromo-iodide grains per side and 0.5 g/m2 of zinc oxide
per side (Film 2B), a total silver coverage of 4.57 g/m2,
0.1 g/m2 of light-insensitive silver bromo-iodide grains
and 1 g/m2 of zinc oxide per side (Film 2C), a total sil-
ver coverage of 4.54 g/m2, 0.1 g/mZ of light-insensitive
silver bromo-iodide grains per side and 1.5 g/m2 of zinc
oxide per side (Film 2D).
Radiographic films (Films 2E, 2F and 2G) according to
the present invention were prepared similar to Film lB of
Example 1 respectively having a total silver coverage of
4.80 g/m2, 0.2 g/m2 of light-insensitive silver
bromo-iodide grains per side and 0.5 g/m2 of zinc oxide
Z~ llS9
per side (Film 2E), a total silver coverage of 4.76 g/m2,
0.2 g/m2 of light-insensitive silver bromo-iodide grains
per side and 1 g/m2 of zinc oxide per side (Film 2F), a
total silver coverage of 4.7 g/m2, 0.2 g/m2 of
light-insensitive silver bromo-iodide grains per side and
1.5 g/m2 of zinc oxide per side (Film 2G).
Radiographic films (Films 2H and 2I) were prepared
similar to Film lB of Example 1 respectively having a to-
tal silver coverage of 4.59 g/m2, 0.1 g/m2 of
light-insensitive silver bromo-iodide grains per side and
no zinc oxide (Film 2H), a total silver coverage of 4.85
g/m2, 0.2 g/m2 of light-insensitive silver bromo-iodide
grains per side and no zinc oxide (Film 2I).
Radiographic films (Films 2L, 2M and 2N) were pre-
pared similar to Film lB of Example 1 respectively having
a total silver coverage of 4.38 g/m2, 0.5 g/m2 of zinc
oxide per side and no light-insensitive silver
bromo-iodide grains (Film 2L), a total silver coverage of
4.33 g/m2, 1 g/m2 of zinc oxide per side and no
light-insensitive silver bromo-iodide grains (Film 2M), a
total silver coverage of 4.33 g/m2, 1.5 g/m2 of zinc oxide
per side and no light-insensitive silver bromo-iodide
grains (Film 2N).
Samples of the films above, after storage at 50C for
15 hours, were exposed and processed as described in Exam-
ple 1.
The following Table reports the results of speed and
percent crossover.
21~ lS~
- 26 -
Table 2
Film Total Ag (g/m2) Speed Percent Crossover
__________ ____________________________________
2A 4.24 2.59 39
2B 4.61 2.62 21
2C 4.57 2.62 20
2D 4.54 2.68 17
2E 4.80 2.53 15
2F 4.76 2.57 14
2G 4.71 2.61 13
2H 4.59 2.52 24
2I 4.85 2.49 15
2L 4 38 2.71 33
.
2M 4.33 2.77 29
2N 4.33 2.78 26
The result show how the radiographic films of the
present invention offer advantages in cross-over reduction
without loss of sensitivity.
