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Description  |
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FIELD OF THE INVENTION
The present invention relates to an internal latent image-type silver
halide emulsion forming a direct positive photographic image. More
particularly, it is concerned with an internal latent image-type silver
halide emulsion containing silver halide grains with a mean grain size of
not more than 0.4 .mu.m, forming a direct positive photographic image in
which D.sub.max is high and D.sub.min is low.
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 3,317,322 and 3,761,276 disclose that when chemical
sensitization is applied to the surface of internal latent image-type
silver halide grains comprising a core of silver halide doped with metal
ions, or chemically sensitized, or subjected to both treatments, and a
shell of the silver halide covering at least light-sensitive sites of the
core (hereinafter referred to as "core/shell type grains"), a reversal
image is obtained by development in the presence of foggants, or by a
direct reversal process of the type that an overall light-exposure is
applied at the time of development.
These core/shell type grains, the core of silver halide being at least
chemically sensitized, when employed in a fine grain silver halide
emulsion with a mean grain size of not more than 0.4 .mu.m in order to
obtain a direct positive photographic material which provides good
graininess and high resolution power have the disadvantages that only a
reversal image in which D.sub.max is low and D.sub.min is high is
obtained, and that the light-sensitive material has insufficient stability
with time.
That is, even if an internal latent image-type silver halide emulsion is
prepared by applying chemical sensitization to the core of silver halide
grains with a mean grain size of not more than 0.4 .mu.m to the extent
that when applied to the core of silver halide grains with a relatively
large grain size (e.g., more than 0.4 .mu.m) (for example, to the extent
applied in preparation method of Emulsion A at Example 1 in U.S. Pat. No.
3,761,276) or applying chemical sensitization to the core of silver halide
grains with a mean grain size of not more than 0.4 .mu.m to such an extent
that addition amount of chemical sensitizer is increased in proportion to
the increase of specific surface area of the core of silver halide grains
(i.e., in proportion to becoming small in the core of silver halide
grains) and then applying chemical sensitization to the shell of silver
halide grains, a satisfactory reversal image cannot be obtained, a
satisfactory image cannot be formed; D.sub.max is low or D.sub.min is high
and good reversal performance cannot be obtained.
SUMMARY OF THE INVENTION
An object of the invention is to provide an internal latent image-type
emulsion which even if the mean grain size of the silver halide grains is
not more than 0.4 .mu.m, can produce a satisfactory reversal image in
which D.sub.max is high and D.sub.min is low.
Another object of the invention is to provide an internal latent image-type
silver halide emulsion having satisfactory stability with time.
The present invention provides an internal latent image-type silver halide
emulsion containing core/shell type silver halide grains with a mean grain
size of about 0.4 .mu.m or less, the grains comprising a core of
chemically sensitized silver halide and a shell of silver halide covering
at least the light-sensitive sites of the core, and the surface of the
grains being chemically sensitized, wherein the core is chemically
sensitized to such an extent that the difference between fog density
F.sub.1 and fog density F.sub.2 as defined below is at least 0.10, where
fog density F.sub.1 is the fog density when the internal latent image-type
emulsion is coated in an amount (as silver) of 1.5 g/m.sup.2 and developed
with Developer D as described below at 20.degree. C. for 13 minutes
without application of imagewise exposure (not including base density).
Fog density F.sub.2 is the fog density when the internal latent image-type
emulsion is coated in an amount (as silver) of 1.5 g/m.sup.2 and developed
with Developer E as described below at 20.degree. C. for 13 minutes
without application of imagewise exposure (not including base density).
______________________________________
Composition of Developer D
N--Methyl-p-aminophenol Sulfate
2.5 g
L-Ascorbic Acid 10 g
Sodium Metaborate 35 g
Potassium Bromide 1 g
Sodium Thiosulfate 3 g
Water to make 1,000 ml
Composition of Developer E
N--Methyl-p-aminophenol Sulfate
2.5 g
L-Ascorbic Acid 10 g
Sodium Metaborate 35 g
Potassium Bromide 1 g
Water to make 1,000 ml
______________________________________
That is, it has been found that the objects are attained by carrying out
chemical sensitization of the core to such an extent that the difference
between F.sub.1 (total fog of the negative image) and F.sub.2 (surface fog
of the negative image), i.e., F.sub.1 -F.sub.2 (internal fog of the
negative image), is at least 0.10.
DETAILED DESCRIPTION OF THE INVENTION
It has been unexpected according to the present invention that in
core/shell type silver halide grains comprising a core of silver halide
chemically sensitized and a shell covering at least the light-sensitive
sites of the core, the surface of the grains being chemically sensitized,
the degree of chemical sensitization necessary for obtaining good reversal
performance remarkably must be varied depending upon the size of silver
halide grains and in fine grain core/shell type silver halide grains with
a mean grain size of not more than 0.4 .mu.m, when according to the above
described processing conditions the chemical sensitization is strongly
applied to the core of silver halide grains to the extent that internal
fog of the negative image (F.sub.1 -F.sub.2) is at least 0.10, a good
reversal image can be obtained. That is because when chemical
sensitization is strongly applied to a core/shell type silver halide
emulsion with a relatively large grain size to the extent that internal
fog of the negative image (F.sub.1 -F.sub.2) is at least 0.10 according to
the present invention D.sub.max is low and reversal performance is
deteriorated good reversal image can be obtained.
Although the exact reason why the degree of chemical sensitization for core
of core/shell type silver halide grains with a fine grain size must be
strengthened is not clear, while not desiring to be bound it is believed
to be due to the fact that the light-sensitive site of inner portion and
surface of the grains are in physically close relation to each other and,
therefore, are difficultly distinguished from each other. For this reason,
these fine silver halide grains cannot become good core/shell internal
latent image-type silver halide grains.
In the present invention, core/shell type silver halide grains having a
mean grain size of 0.05 to 0.4 .mu.m are used. More specifically, those
grains having a mean grain size of about 0.1 to 0.3 .mu.m are effectively
used.
The term "mean grain size" as used herein indicates the mean of the grain
diameters when silver halide grains are spherical or nearly spherical, or
the edge lengths when they are cubic, calculated based on projected areas.
In preparing core/shell type silver halide grains to be used in the
emulsion of the present invention, the core of the silver halide which is
chemically sensitized or is subjected to both treatments of chemical
sensitization and doping with metal ions is first formed, and then the
surface of the core is covered with the shell of silver halide, which is
further chemically sensitized. It is not necessary for the entire surface
of the grains constituting the core to be covered with the shell. It is
sufficient if at least the light-sensitive sites (where chemical
sensitization is made or light-decomposed silver is formed upon light
exposure) of the core are covered with the shell. It is determined with
degree of internal fog of the negative image evaluated in the method
described above whether light-sensitive sites of the core are sufficiently
covered with the shell.
The chemical sensitization of the core of the core/shell type silver halide
grains can be performed using known techniques such as the methods
described in Grafkides, Chimie et Physique Photographique, Paul Montel Co.
(1967), V. L. Zelikman et al., Making and Coating Photographic Emulsions,
The Focal Press Co. (1964), and H. Frieser ed., Die Grundlagen der
Photographischen Prozesse mit Silberhalogeniden, Akademische
Verlagsgesellschaft (1968).
That is, a sulfur sensitization method using compounds containing sulfur
capable of reacting with silver ion, or using active gelatin, a reduction
sensitization method using reducing substances, a noble metal
sensitization method using noble metal (e.g., gold) compounds, and so
forth can be used alone or in combination with each other. Of these
methods, a combination of the gold sensitization method and the sulfur
sensitization method provides the best results. In some cases, the
reduction sensitization method may be used in combination with the gold
sensitization method and the sulfur sensitization method.
Sulfur sensitizers which can be used include thiosulfates, thioureas,
thiazoles, and rhodanines. Representative examples are described in U.S.
Pat. Nos. 1,574,944, 2,410,689, 2,278,947, 2,728,668 and 3,656,955.
Reduction sensitizers which can be used include stannous salts, amines,
hydrazine compounds, formamidinesulfinic acid, and silane compounds.
Representative examples are described in U.S. Pat. Nos. 2,487,850,
2,419,974, 2,518,698, 2,983,609, 2,983,610 and 2,694,637. For noble metal
sensitization, gold complex salts and complex salts of metals belonging to
Group VIII of the Periodic Table such as platinum, iridium and palladium
can be used. Representative examples are described in U.S. Pat. Nos.
2,399,083, 2,448,060 and British Pat. No. 618,061.
In order to strengthen the degree of chemical sensitization, it is
effective that an addition amount of chemical sensitizer is increased, the
chemical sensitization is applied at high temperature for a long time and
conditions such as pH, pAg or etc. are controlled. It is generally known
that fog is increased as the degree of chemical sensitization is
strengthened and fog formed due to chemical sensitization of core of
core/shell type silver halide grains can be shown as internal fog (F.sub.1
-F.sub.2) in the case of processing the core/shell type silver halide
grains under the condition as described above. The object of the present
invention can be achieved when the degree of chemical sensitization of
core is strengthened and the internal fog (F.sub.1 -F.sub.2) is at least
0.10.
Conditions under which the chemical sensitization is performed can be
determined appropriately. In general, preferred results are obtained when
the chemical sensitization is conducted under conditions so that the pH is
9 or less, the pAg is 10 or less, and the temperature is 40.degree. C. or
higher. In some cases, however, conditions not falling within the
above-defined ranges may be employed.
The core may be doped with metal ions simultaneously with the chemical
sensitization. For this doping of the core with metal ions, a method in
which a metal ion source, such as cadmium salts, zinc salts, lead salts,
thallium salts, iridium salts or its complex salts, rhodium salts or its
complex salts, and iron salts or its complex salts, is present during the
formation of silver halide grains constituting the core or physical
ripening can be used. Metal ions are usually used in a proportion of at
least 10.sup.-6 mol per mol of silver halide.
The above-described treatment of the silver halide of the core and a
technique to cover the surface of silver halide grains constituting the
core with silver halide constituting the shell are known. For example, the
methods described in U.S. Pat. Nos. 3,206,316, 3,317,322, 3,367,778
(excluding a step of fogging the surface of grains), and 3,761,276 can be
employed advantageously.
The ratio of the amount of silver halide used in the core to the amount of
silver halide used in the shell is not critical and can be determined
appropriately. Usually the amount in the shell is employed in a proportion
of from 2 to 10 mols per mol of the amount in the core.
The silver halide of the core and that of the shell preferably have the
same composition, but they may have different compositions. Suitable
silver halides which can be used herein include silver bromide, silver
iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver
chlorobromoiodide, etc. The silver halide emulsion of the present
invention is preferably composed of at least 50 mol% of silver bromide.
Most preferred is a silver bromoiodide emulsion, especially containing
about 10 mol% or less of silver iodide.
These core/shell type silver halide grains may have a regular crystal form
such as a cubic or octahedral form, or may have an irregular crystal form
such as a spherical form and a tabular form or a composite form thereof.
Furthermore, a mixture of grains having different crystal forms may be
used.
In the present invention, the core is chemically sensitized so that the
internal fog density of the negative image as determined under the
above-described conditions is at least 0.10 and preferably at least 0.15.
If, however, the chemical sensitization is performed to an excessive
extent, problems such as a reduction in sensitivity arise. Thus, it is
preferred for the chemical sensitization to be performed to the necessary
extent. Although this upper limit varies depending on the halogen
composition and so forth and cannot be set forth unequivocally, the
chemical sensitization is preferably carried out so that the internal fog
density of the negative image as determined under the above-described
conditions is not more than 0.50.
The surface of the core/shell type silver halide grains as prepared above
is then chemically sensitized. For this chemical sensitization, the
methods described for the chemical sensitization of the core can be
employed. The chemical sensitization of the core/shell type silver halide
grain surface is performed to such an extent that the characteristics as
an internal latent image type emulsion are not degraded. The term
"characteristics as an internal latent image type emulsion" is used herein
to mean that the maximum density of a light-sensitive material, the
material comprising a transparent support and a given emulsion coated
thereon, when exposed to light for a predetermined time of from 0.01 to 10
seconds and developed with Developer A (an internal type developer) as
described below at 20.degree. C. for 3 minutes (the density is determined
by the usual photographic density measuring method) is at least 5 times
greater than that of the same material as described above when exposed to
light in the same manner as above and developed with Developer B (a
surface type developer) also as described below at 20.degree. C. for 4
minutes.
______________________________________
Developer A
Hydroquinone 15 g
Monomethyl-p-aminophenol Sesquisulfate
15 g
Sodium Sulfite 50 g
Potassium Bromide 10 g
Sodium Hydroxide 25 g
Sodium Thiosulfate 20 g
Water to make 1,000 ml
Developer B
p-Oxyphenolglycine 10 g
Sodium Carbonate 100 g
Water to make 1,000 ml
______________________________________
The core/shell type silver halide grains are dispersed in a binder.
Gelatin can be used advantageously as a binder. Other hydrophilic colloids
can also be used. Examples of suitable hydrophilic colloids are proteins
such as gelatin derivatives, graft polymers of gelatin and other polymers,
albumin and casein, cellulose derivatives such as hydroxyethyl cellulose,
carboxymethyl cellulose and cellulose sulfuric acid esters, and sugar
derivatives such as sodium alginate and starch derivatives.
Lime-processed gelatin, acid-processed gelatin and enzyme-processed gelatin
as described in Bull. Soc. Sci. Photo., Japan, No. 16, page 30 (1966) can
be used as the gelatin. In addition, hydrolyzates and enzyme decomposition
products of gelatin can be used.
The internal latent image-type silver halide emulsion of the present
invention may be spectrally sensitized with methine dyes and so forth.
Dyes which can be used include cyanine dyes, merocyanine dyes, complex
cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes,
hemicyanine dyes, styryl dyes, and hemioxonol dyes. Particularly useful
dyes are cyanine, merocyanine and complex merocyanine dyes. In these dyes,
any of the nuclei commonly used as hetrocyclic nuclei is cyanine dyes can
be employed. That is, a pyrroline nucleus, an oxazoline nucleus, a
thiazoline nucleus, a pyrrole nucleus, an oxazole nucleus, a thiazole
nucleus, a selenazole nucleus, an imidazole nucleus, a tetrazole nucleus,
and a pyridine nucleus; nuclei resulting from the fusion of alicyclic
hydrocarbon rings to the foregoing nuclei; and nuclei resulting from the
fusion of aromatic hydrocarbon rings to the foregoing nuclei, such as an
indolenine nucleus, a benzindolenine nucleus, an indole nucleus, a
benzoxazole nucleus, a naphthoxazole nucleus, a benzothiazole nucleus, a
naphthothiazole nucleus, a benzoselenazole nucleus, a benzimidazole
nucleus, and a quinoline nucleus can be employed. These nuclei may contain
substitutents on the carbon atom thereof.
The merocyanine or complex merocyanine dyes may contain nuclei having a
ketomethylene structure, 5- or 6-membered heterocyclic nuclei such as a
pyrazolin-5-one nucleus, a thiohydantoin nucleus, a
2-thiooxazolidin-2,4-dione nucleus, a thiazolidin-2,4-dione nucleus, a
rhodamine nucleus, and a thiobarbituric acid nucleus.
Useful sensitizing dyes are described in, for example, West German Pat. No.
929,080, U.S. Pat. Nos. 2,231,658, 2,493,748, 2,503,776, 2,519,001,
2,912,329, 3,655,394, 3,656,959, 3,672,897, 3,694,217, British Pat. No.
1,242,588 and Japanese Patent Publication No. 14030/69.
These sensitizing dyes can be used alone or as a combination with each
other. Combinations of sensitizing dyes are often used for the purpose of
supersensitization. Typical examples of such combinations are described
in, for example, U.S. Pat. Nos. 2,688,545, 2,977,229, 3,397,060,
3,522,052, 3,527,641, 3,617,293, 3,628,964, 3,666,480, 3,679,428,
3,703,377, 3,769,301, 3,814,609, 3,837,862, British Pat. No. 1,344,281,
and Japanese Patent Publication No. 4936/68.
In preparing a light-sensitive material using the internal latent
image-type silver halide emulsion of the present invention, the emulsion
is coated on a support together with other photographic layers. The amount
of the emulsion coated is not critical in the present invention. Usually,
when the emulsion is coated in an amount such that the amount of silver is
from about 40 to about 800 mg per square feet of the support, a desirable
reversal image can be obtained.
Suitable supports are those as described in Research Disclosure, Vol. 176,
RD-17643, clause XVII (1978).
The internal latent image-type silver halide photographic emulsion of the
present invention may contain compounds such as polyalkylene oxides or the
ether, ester, amine or like derivatives thereof, thioether compounds,
thiomorpholines, quaternary ammonium salts, urethane derivatives, urea
derivatives, imidazole derivatives and 3-pyrazolidones for the purpose of
increase in sensitivity and in contrast or of acceleration in development.
For example, the compounds described in U.S. Pat. Nos. 2,400,532,
2,423,549, 2,716,062, 3,617,280, 3,772,021, and 3,808,003 can be used.
The internal latent image-type silver halide photographic emulsion of the
present invention may contain antifoggants and stabilizers. For example,
the compounds as described in Research Disclosure, Vol. 176, RD-17643
(1978), clause VI can be used.
The internal latent image-type silver halide photographic emulsion of the
present invention may contain developing agents. For example, the
developing agents as described in Research Disclosure, Vol. 176, RD-17643
(1978), clause XX can be used.
The internal latent image-type silver halide photographic emulsion of the
present invention can be dispersed in colloids hardenable with various
organic or inorganic hardeners. For example, the hardeners as described in
Research Disclosure, Vol. 176, RD-17643 (1978), Section X can be used.
The internal latent image-type silver halide photographic emulsion of the
present invention may contain coating aids. Those compounds as described
in Research Disclosure, Vol. 176, RD-17643 (1978), Section XI can be used
as these coating aids.
The internal latent image-type silver halide photographic emulsion of the
present invention may contain the so-called color couplers. Those
compounds as described in Research Disclosure, Vol. 176, RD-17643 (1978),
clause VII can be used as these color couplers.
The internal latent image-type silver halide photographic emulsion of the
present invention may further contain additives such as antistatic agents,
plasticizers, matting agents, lubricants, ultraviolet absorbers,
brightening agents, and anti-air oxidants.
Dyes may be incorporated into the photographic emulsion layers and other
hydrophilic colloid layers of the light-sensitive materials prepared using
the internal latent image-type silver halide photographic emulsion of the
present invention as filter dyes or for various purposes such as
prevention of irradiation. For example, the dyes as described in Research
Disclosure, Vol. 176, RD-17643 (1978), clause VIII can be used.
The internal latent image-type silver halide photographic emulsion of the
present invention is developed in the presence of fogging agents
(nucleating agents) or with an overall exposure to light. Typical examples
of fogging agents which can be used include hydrazines as described in
U.S. Pat. Nos. 2,588,982 and 2,563,785; hydrazines and hydrazones as
described in U.S. Pat. No. 3,277,552; acylhydrazines as described in
British Pat. No. 2,089,057; quaternary salt compounds as described in U.S.
Pat. No. 1,283,835, Japanese Patent Publication No. 38164/74, U.S. Pat.
Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122; sensitizing
dyes containing a nucleating substituent as described in U.S. Pat. No.
3,718,470; and acylhydrazinophenylthiourea compounds as described in U.S.
Pat. Nos. 4,030,925 and 4,031,127. In addition, the compounds as described
in U.S. Pat. No. 4,139,387 and Japanese Patent Application (OPI) Nos.
133126/79 and 74729/79 can be used (the term "OPI" as used herein refers
to a "published unexamined Japanese patent application").
It is desirable for the fogging agent to be employed in an amount such that
the resulting internal latent image-type silver halide emulsion, when
developed with a surface developer, provides a maximum density which is
sufficiently satisfactory. Preferably the fogging agent is incorporated
into the photographic emulsion layers or their adjacent layers.
The internal latent image-type silver halide photographic emulsion of the
present invention can be used in various applications. In particular, it
is useful as an emulsion for direct positive photographic light-sensitive
materials, as an emulsion for multilayer reversal color light-sensitive
materials, and as an emulsion for use in the color diffusion transfer
process of multilayer light-sensitive materials.
The internal latent image-type silver halide photographic emulsion of the
present invention can be used in combination with diffusion transfer color
image-providing substances releasing a diffusible dye as development
progresses, so that after a suitable developing treatment the desired
transferred image can be obtained in an image-receiving layer. A number of
diffusion transfer dye image-providing substances are known. For example,
the compounds as described in U.S. Pat. Nos. 3,227,551, 3,227,554,
3,443,939, 3,443,940, 3,658,524, 3,698,897, 3,725,062, 3,728,113,
3,751,406, 3,929,760, 3,931,144, 3,932,381, 3,928,312, 4,013,633,
3,932,380, 3,954,476, 3,942,987, 4,013,635, U.S. Pat. No. 351,673, British
Pat. Nos. 840,731, 904,364, 1,038,331, West German Patent Application
(OLS) Nos. 1,930,215, 2,214,381, 2,228,361, 2,317,134, 2,402,900 French
Pat. No. 2,284,140, Japanese Patent Application (OPI) Nos. 113624/76
(corresponding to U.S. Pat. No. 4,055,428), 104343/76, 149328/78 and
143323/78 can be used. It is preferred to use dye image-providing
substances of the type that is originally non-diffusible but undergoes
cleavage after a redox reaction with the oxidized product of a developing
agent, releasing a diffusible dye. These compounds are hereinafter
referred to as "DRR compounds".
Various known developing agents can be used for developing light-sensitive
materials prepared using the emulsion of the present invention. For
example, polyhydroxybenzenes such as hydroquinone, 2-chlorohydroquinone,
2-methylhydroquinone, catechol, and pyrogallol; aminophenols such as
p-aminophenol, N-methyl-p-aminophenol, and 2,4-diaminophenol;
3-pyrazolidones such as 1-phenyl-3-pyrazolidones,
1-phenyl-4,4-dimethyl-3-pyrazolidone,
1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone, and
5,5-dimethyl-1-phenyl-3-pyrazolidone; and ascorbic acids can be used alone
or in combination with each other. More specifically, for example, the
developers described in Japanese Patent Application (OPI) No. 55928/83 can
be used.
In forming dye images in the presence of dye-forming couplers, aromatic
primary amine developing agents, preferably p-phenylenediamine-based
developing agents, can be used. Typical examples are
4-amino-3-methyl-N,N-diethylaniline hydrochloride,
N,N-diethyl-p-phenylenediamine,
3-methyl-4-amino-N-ethyl-N-.beta.-(methanesulfoamido)ethylaniline,
3-methyl-4-amino-N-ethyl-N-(.beta.-sulfoethyl)aniline,
3-ethoxy-4-amino-N-ethyl-N-(.beta.-sulfoethyl)aniline, and
4-amino-N-ethyl-N-(.beta.-hydroxyethyl)aniline. These developing agents
may be incorporated into an alkaline processing composition (processing
element) or into a suitable layer of the light-sensitive element.
Where DRR compounds are used, if they are cross-oxidizable, any silver
halide developers can be used.
The developer may contain compounds such as sodium sulfite, potassium
sulfite, ascorbic acid and reductones (e.g., piperidinohexose reductone)
as preservatives.
A direct positive image can be obtained by developing the light-sensitive
material of the present invention with surface developers. These surface
developers are such that the process of development is induced
substantially by latent images or fog nuclei present on the surface of the
silver halide grains. Although it is preferred for the developer not to
contain silver halide solvents, it may contain silver halide solvents
(e.g., sulfites) as long as the internal latent image does not
substantially contribute until the development with the surface
development centers of silver halide grains is complete.
The developer may contain compounds such as sodium hydroxide, potassium
hydroxide, sodium carbonate, potassium carbonate, trisodium phosphate, and
sodium metaborate as alkalis or buffers. These agents are employed in an
amount so as to control the pH of the developer within the range of from
10 to 13 and preferably from 11 to 12.5.
The developer may contain color development accelerators such as benzyl
alcohol. In order to further lower the minimum density of the direct
positive image, it is advantageous for the developer to contain compounds
commonly used as antifoggants, such as benzimidazoles (e.g.,
5-nitrobenzimidazole), and benzotriazoles (e.g., benzotriazole and
5-methylbenzotriazole).
The light-sensitive material of the present invention can be processed with
viscous developers. A viscous developer is a liquid composition containing
the components necessary for developing the silver halide emulsion and for
forming the diffusion transfer dye image. The solvent is composed mainly
of water and sometimes contains hydrophilic solvents such as methanol and
methyl Cellosolve. The processing composition contains a sufficient amount
of alkali to maintain the pH necessary for causing development of the
emulsion layer and further to neutralize acids (e.g., hydrohalic acids
such as hydrobromic acid, and carboxylic acids such as acetic acid) formed
during the steps of development and color image formation. Alkalis which
can be used include alkali metal or alkaline earth metal salts, such as
lithium hydroxide, sodium hydroxide, potassium hydroxide, a calcium
hydroxide dispersion, tetramethyl ammonium hydroxide, sodium carbonate,
trisodium phosphate, and the like, and amines such as diethylamine.
Preferably sodium hydroxide is employed in a concentration such that the
pH at room temperature is at least about 12 and particularly 14 or more.
When the light-sensitive material of the present invention is used in the
diffusion transfer photographic process, it is preferably in the form of a
film unit. This film unit, which is designed so that a light-sensitive
element is processed by passing through a pair of pressure applying
members arranged in a parallel relationship, is basically composed of the
following three elements:
(1) A light-sensitive element containing an antifoggant;
(2) An image-receiving element: and
(3) A processing element containing a means to release an alkaline
processing composition in the film unit, such as a rupturable container,
and further containing a silver halide developer.
The present invention is described in greater detail by reference to the
following examples, but the present invention is not limited to the
examples. Unless otherwise indicated, all parts, percents, ratios and the
like are by weight.
EXAMPLE 1
The following emulsions were prepared.
Emulsions A-1 to A-18
An aqueous solution of potassium bromide and an aqueous solution of silver
nitrate were added simultaneously to an aqueous gelatin solution at
40.degree. C. over a 20 minute period with vigorous agitation to prepare a
silver bromide emulsion with a mean grain size of 0.08 .mu.m. This
emulsion was divided into five equal portions. To each portion were added
sodium thiosulfate and chloroauric acid (tetrahydrate) in the amounts
shown in Table 1 below, and the resulting mixture was heated at 75.degree.
C. for 80 minutes to achieve chemical sensitization (chemical
sensitization of the grain core). With the thus-obtained silver bromide
grains as the core, silver bromide was allowed to grow under the same
conditions as described above, and finally a core/shell type silver
bromide emulsion with a mean grain size of 0.18 .mu.m was obtained. This
emulsion was further divided into three equal portions. To each portion
were added sodium thiosulfate and chloroauric acid (tetrahydrate) in the
amounts shown in Table 1 below, and the resulting mixture was chemically
sensitized by heating at 65.degree. C. for 60 minutes (surface chemical
sensitization) to prepare an internal latent image-type silver halide
emulsion. In this way, Emulsions A-1 to A-18 were prepared.
TABLE 1
______________________________________
Grain Core Chemical Grain Surface Chemical
Sensitization.sup.(1)
Sensitization.sup.(2)
Sodium Chloroauric
Sodium Chloroauric
Emulsion
Thiosulfate
Acid Thiosulfate
Acid
______________________________________
A-1 20 20 0 0
2 20 20 2.0 2.0
3 20 20 6.2 6.2
4 20 20 12.4 12.4
5 40 40 2.0 2.0
6 40 40 6.2 6.2
7 40 40 12.4 12.4
8 130 130 2.0 2.0
9 130 130 6.2 6.2
10 130 130 12.4 12.4
11 580 580 2.0 2.0
12 580 580 6.2 6.2
13 580 580 12.4 12.4
14 860 860 2.0 2.0
15 860 860 6.2 6.2
16 860 860 12.4 12.4
17 130 130 24.8 24.8
18 580 580 24.8 24.8
______________________________________
.sup.(1) mg/core Ag/mol
.sup.(2) mg/core/shell Ag/mol
Emulsions B-1 to B-3
An aqueous solution of potassium bromide and an aqueous solution of silver
nitrate were added simultaneously to an aqueous gelatin solution to
prepare a silver bromide emulsion with a mean grain size of 0.25 .mu.m.
This emulsion was divided into two equal portions. To each portion was
added sodium thiosulfate and chloroauric acid (tetrahydrate) in the
amounts shown in Table 2 below, and the resulting mixture was heated at
75.degree. C. for 80 minutes to achieve chemical sensitization (chemical
sensitization of core). With the thus-obtained silver bromide grains as
the core, silver bromide was allowed to grow under the same conditions as
described above, and finally a core/shell type silver bromide emulsion
with a mean grain size of 0.4 .mu.m was prepared. This emulsion was
further divided into two equal portions. To each portion were added sodium
thiosulfate and chloroauric acid (tetrahydrate) in the amounts shown in
Table 2 below, and the resulting mixture was chemically sensitized by
heating at 65.degree. C. for 60 minutes (surface chemical sensitization)
to prepare an internal latent image-type silver halide emulsion. In this
way, Emulsions B-1 to B-3 were prepared.
TABLE 2
______________________________________
Grain Core Chemical Grain Surface Chemical
Sensitization.sup.(1)
Sensitization.sup.(2)
Sodium Chloroauric
Sodium Chloroauric
Emulsion
Thiosulfate
Acid Thiosulfate
Acid
______________________________________
B-1 7 7 0.7 0.7
B-2 7 7 2.1 2.1
B-3 190 190 0.7 0.7
______________________________________
.sup.(1) mg/core Ag/mol
.sup.(2) mg/core/shell Ag/mol
Emulsions C-1 to C-4 (Control Group)
An aqueous solution of potassium bromide and an aqueous solution of silver
nitrate were added simultaneously to an aqueous gelatin solution at
75.degree. C. over a 40 minute period with vigorous agitation to prepare a
silver bromide emulsion with a mean grain size of 0.4 .mu.m. This emulsion
was divided into two equal portions. To each portion were added sodium
thiosulfate and chloroauric acid (tetrahydrate) in the amounts shown in
Table 3 below, and the resulting mixture was heated at 75.degree. C. for
80 minutes to achieve chemical sensitization (chemical sensitization of
core). With the thus-obtained silver bromide grains as the core, silver
bromide was allowed to grow under the same conditions as described above,
and finally a core/shell type silver bromide emulsion with a mean grain
size of 0.6 .mu.m was prepared. This emulsion was further divided into two
equal portions. To each portion were added sodium thiosulfate and
chloroauric acid (tetrahydrate) in the amounts shown in Table 3 below, and
the resulting mixture was heated at 65.degree. C. for 60 minutes to
achieve chemical sensitization (surface chemical sensitization), whereupon
an internal latent image-type silver halide emulsion was obtained. In this
way, Emulsions C-1 to C-4 were prepared.
TABLE 3
______________________________________
Grain Core Chemical Grain Surface Chemical
Sensitization.sup.(1)
Sensitization.sup.(2)
Sodium Chloroauric
Sodium Chloroauric
Emulsion
Thiosulfate
Acid Thiosulfate
Acid
______________________________________
C-1 4 4 0.5 0.5
C-2 4 4 1.5 1.5
C-3 150 150 0.5 0.5
C-4 200 200 0.5 0.5
______________________________________
.sup.(1) mg/core Ag/mol
.sup.(2) mg/core/shell Ag/mol
To each emulsion was added a fogging agent,
anhydro-2-[3-(phenylhydrazo)butyl]-3-(3-sulfopropyl)benzothiazolium
hydroxide, in an amount of 1,000 mg per mol of silver. The resulting
emulsion was coated on a polyethylene terephthalate support in an amount
(as silver) of 1,500 mg/m.sup.2 and a gelatin protective layer was further
coated thereon to prepare a light-sensitive sample. Two samples were
prepared for each emulsion.
Each sample was exposed for 1 second through a step wedge to a 1 kw
tungsten lamp at a color temperature of 2,854.degree. K. One of the two
samples for each emulsion was developed with Developer C having the
formulation shown in Table 4 at 37.degree. C. for 1 minute and then
stopped, fixed and rinsed in the usual manner to obtain a positive image.
The other sample was developed with Developer D or Developer E having the
formulation shown in Table 5 below at 20.degree. C. for 13 minutes and
then stopped, fixed and rinsed in the usual manner to obtain a negative
image. The solutions used for the stops and the fixations as described
above are as follows.
Stop Solution
Aqueous Acetic Acid Solution
______________________________________
Fixing Solution
______________________________________
H.sub.2 O 600 ml
Ammonium Thiosulfate (70%)
320 ml
Na.sub.2 SO.sub.3 20 g
KI 0.5 g
CH.sub.3 COOH (90%) 3 ml
H.sub.2 O to make 1 l
______________________________________
The total fog, surface fog and internal fog (difference between the total
fog and surface fog) of the negative image were measured. The results
obtained are shown in Table 6 below.
TABLE 4
______________________________________
Developer C
______________________________________
Hydroquinone 35 g
Sodium Sulfite 80 g
Potassium Carbonate 40 g
Sodium Bromide 3 g
1-Phenyl-4-methyl-4-hydroxymethyl-3-
3 g
pyrazolidone
5-Methylbenzotriazole 20 mg
Water to make 1,000 ml
The pH was adjusted to 11.6 with potassium hydroxide
______________________________________
TABLE 5
______________________________________
Developer D
N--Methyl-p-aminophenol Sulfate
2.5 g
L-Ascorbic Acid 10 g
Sodium Metaborate 35 g
Potassium Bromide 1 g
Sodium Thiosulfate 3 g
Water to make 1,000 ml
Developer E
N--Methyl-p-aminophenol Sulfate
2.5 g
L-Ascorbic Acid 10 g
Sodium Metaborate 35 g
Potassium Borate 1 g
Water to make 1,000 ml
______________________________________
Table 6 shows D.sub.max, D.sub.min and D.sub.max /D.sub.min of the positive
image formed in each sample prepared using Emulsions A-1 to A-18, and the
total fog, surface fog, and internal fog (not including base density) of
the negative image.
TABLE 6
______________________________________
Negative Image
Positive Image Total Surface Internal
Emulsion
D.sub.max
D.sub.min
D.sub.max /D.sub.min
Fog Fog Fog
________________________ | | |
