 |
Description  |
|
|
This invention relates to image formation. In one aspect, it relates to
image-formation processes which utilize a redox reaction. In certain other
aspects, it relates to image amplification or image replacement.
A variety of image-forming systems have been described in the prior art
which utilize redox reactions. Belgian Patent 742,768 of June 8, 1970,
describes an image amplification procedure which features the use of
peroxy compounds and reducing agents, such as photographic
color-developing agents However, such redox systems are highly unstable;
photographic color-developing agents are oxidized merely in the presence
of air and peroxy compounds react extremely rapidly with such reducing
agents. Hence, it would be desirable to provide image-forming redox
systems in which the oxidizing and reducing agents are more stable.
U.S. Pat. No. 3,152,903 by Sheppard et al issued October 17, 1964, suggests
various redox systems which have a physical barrier, (e.g., phase
separation) to prevent redox reaction. The oxidizing and reducing agents
proposed undergo substantially immediate redox reaction in the absence of
external catalyst when they are incorporated in an inert solvent solution.
There appears to be no disclosure in this patent of a redox system which
is stable in the absence of some physical barrier.
British Patent 777,635 published June 26, 1957, suggests photographic
bleach baths which contain a cobalt (III) complex and which may contain a
reducing agent, However, photographic bleach baths contain a silver halide
solvent. In the presence of silver halide solvent, the cobalt complex
reacts directly with the silver and does not undergo, to any significant
degree, redox reaction with the reducing agent.
Photographic physical-developer solutions are well known in the art. For
example, Dippel et al in U.S. Pat. No. 2,750,292 issued June 12, 1956,
describe the formation of dyes simultaneously and in situ with the
formation of a metal image during physical development of a photographic
element containing a metal image and a photographic coupler, with a
solution containing photographic color-developing agent and a reducible
metal salt. However, a serious disadvantage with physical developers is
that they do not have a high degree of stability. One reason for this
instability is that the reaction products of the redox reaction are
catalysts for further redox reaction, i.e., the reaction is autocatalytic.
It would, accordingly, be desirable to provide a nonautocatalytic
oxidizing-reducing agent combination.
Christensen, U.S. Pat. No. 2,517,541 issued Aug. 8, 1950, describes
photographic silver halide emulsions containing amounts less than about
0.1% by weight of the wet emulsion of an alkali metal cobalticyanide. The
exposed elements containing this addendum are developed in typical
photographic developer solutions. The low concentrations of cobalticyanide
proposed probably are necessary to avoid fogging the emulsion. Such low
amounts of potassium cobalticyanide would not contribute substantially to
image formation via redox reaction, even if there is a redox reaction
between the cobalticyanide and the developer in areas where silver is
developed. However, it is unlikely that even limited redox reaction occurs
because potassium cobalticyanide does not undergo redox reaction with
typical color-developing agents in the presence of predeveloped silver.
It is well-known that polymerization of photopolymers can be initiated by a
radical which an be liberated through a light-catalyzed redox reaction.
See Rust, "Fast Imaging Systems Using Photopolymers", Optical Spectra,
March/April, 1968, pp. 41-45 at p. 42. There does not, however, appear to
by any suggestion in the art relative to providing a stable reducing
agent-oxidizing agent combination which can be catalyzed into a redox
reaction with a catalytic material.
British Patent 1,194,581 published June 10, 1970, describes an imaging
process in which a photosensitive composition, upon exposure to light,
generates nuclei of a metal which is more noble than silver and is
catalytic to the electroless deposition of a nonnoble metal. An image is
formed by an electroless deposition of nonnoble free metal on the nuclei.
There appears to be no disclosure in this patent of a stable redox system
which is nonautocatalytic.
In the photographic dye bleach system, such as described by Gasper, U.S.
Pat. No. 2,270,118 issued Jan. 13, 1942, dyes are produced imagewise by
treating diffusely dyed layers containing silver images with an acid
solution which destroys the dye imagewise in areas where silver is
present. The destruction of the dye can be accelerated with various
"catalysts", such as phenazine. The reactions in the dye bleach system
appear to proceed on a stoichiometric basis. See Mayer et al, U.S. Pat.
No. 3,340,060 issued Sept. 5, 1967, col. 1, lines 18-21, noting that 4
silver atoms are required to destroy 1 azo dye group. It would be
desirable to provide a photographic system which would make more efficient
use of silver than in the silver dye bleach process.
British Patent 239,875 published Nov. 5, 1925, describes a photographic
element useful in the diazo process which includes a cobalt (III) metal
complex and, optionally, silver halide. This diazo image-forming process
is a substitution reaction rather than a redox reaction. Further, the
incorporated cobalt(III) complex fogs the silver halide.
There is a need in the art, therefore, for image-forming systems which
feature a reducing-oxidizing agent combination which is relatively inert
to redox reaction even when in a reactive environment and which do not
form reaction products which catalyze the redox reaction. Further, there
is need in the art for redox reaction systems which can be utilized to
amplify faint images or replace images with other images having a
different color value. In addition, it is desirable to provide a method
whereby the extremely high light sensitivity of photographic silver halide
can be utilized to generate a latent or faint silver image that acts as a
catalyst for a redox system to amplify or replace the silver image.
One object of this invention is to provide a method and composition for
forming images.
Another object of this invention is to provide an image-forming method in
which a redox reaction is utilized to produce a change in light value.
Still another object of this invention is to provide an image-forming
process in which at least one of the reaction products of a redox reaction
is utilized to tan a binder such as a hydrophilic colloid.
A further object of this invention is to provide a method for amplifying
faint or invisible images.
Another object of this invention is to supplement metal images with dye
images and/or hardened hydrophilic colloid images.
Still another object of this invention is to replace metallic images with
dye images and/or hydrophilic colloid images.
Another object of this invention is to provide a method for increasing the
amount of tanning or crosslinking which can be obtained in photographic
elements with a given amount of photosensitive recording material.
Other objects of this invention will be apparent from the disclosure herein
and the appended claims.
In one embodiment of this invention, an improvement is provided in an
image-forming process wherein an oxidation-reduction reaction is utilized
to from a photographic image, which improvement comprises employing an
oxidizing agent and a reducing agent which undergo redox reaction in the
presence of catalytic material and which are essentially inert to
oxidation-reduction reaction in the absence of a catalytic material, the
oxidizing agent and the reducing agent being so chosen that the reaction
products thereof are noncatalytic for the oxidation-reduction reaction. At
least one of the reaction products is then used to harden, tan or
crosslink a hardenable material.
In another embodiment of this invention, an improvement is provided in an
image-forming process wherein a reaction product of an oxidation-reduction
reaction is utilized to form a photographic image, such as a hardened
hydrophilic colloid, which improvement comprises employing an oxidizing
agent and a reducing agent which undergo imagewise redox reaction at a
catalytic surface, the oxidizing agent being complex of a metal ion with
ligands which, when a test sample of the complex is dissolved at 0.1 molar
concentration at 20.degree. C. in an inert solvent solution containing a
0.1 molar concentration of an uncoordinated ligand, exhibit essentially no
exchange of uncoordinated and coordinated ligands for at least 1 min.
In a further embodiment of this invention, an improvement is provided in a
method of forming photographic images wherein a dye is produced in
addition to hardening a binder vehicle. An aromatic primary amino
color-developing agent can be oxidized in the development of an exposed
photographic silver halide emulsion, and the oxidized color-developing
agent reacts with a photographic color coupler to form a dye.
In still another embodiment of this invention, processing compositions are
provided comprising the oxidation-reduction combination featured in this
invention.
The terms "tan", "harden" and "crosslink" are used interchangeably herein
and generally refer to reactions wherein a binder vehicle or colloid is
reacted to increase substantially the melting point, lower the water
solubility, etc.
Oxidants preferred in the practice of this invention are the metal
complexes, such as a transition metal complex, e.g., a Group VIII metal
complex, or a complex of a metal of Series 4 of the periodic table
appearing on pp. 54-55 of Lange's Handbook of Chemistry, 8th Edition,
published by Handbook Publisher, Inc., Sandusky, Ohio, 1952. Such
complexes feature a molecule having a metallic atom or ion. This metallic
ion is surrounded by a group of atoms, ions or other molecules which are
generically referred to as ligands. The metallic atom or ion in the center
of these complexes is a Lewis acid; the ligands are Lewis bases. Werner
complexes are well-known examples of such complexes. The useful metal
salts are typically capable of existing in at least two valent states. In
a preferred aspect of the invention, the metal complexes are those
referred to by American chemists as "inert" and by European chemists as
"robust". Particularly useful are complexes of a metal ion with a ligand
which, when a test sample thereof is dissolved at 0.1 molar concentration
at 20.degree. C. in an inert solvent solution also containing 0.1 molar
concentration of a tagged ligand of the same species which is
uncoordinated, exhibits essentially no exchange of uncoordinated and
coordinated ligands for at least 1 min., and preferably for at least
several hours, such as up to 5 hr. or more. This test is advantageously
conducted under the pH conditions which will be utilized in the practice
of the invention. In silver halide photography, this generally will be a
pH of over about 8. Many metal complexes useful in this invention show
essentially no exchange of uncoordinated and coordinated ligands for
several days. The definition of inert metal complexes and the method of
measuring ligand exchange using radioactive isotopes to tag ligands are
well-known in the art; see, for example, Taube, Chem. Rev., Vol. 50, p. 69
(1952), and Basolo and Pearson, Mechanisms of Inorganic Reactions, A Study
of Metal Complexes and Solutions, 2nd Edition, 1967, published by John
Wiley and Sons, p. 141. Further details on measurement of ligand exchange
appear in articles by Adamson et al, J. Am. Chem. Soc., Vol. 73, p. 4789
(1951). The inert metal complexes should be contrasted with labile
complexes which, when tested by the method described above, have a
reaction half-life generally less than 1 min. Metal chelates are a special
type of metal complex in which the same ligand (or molecule) is attached
to the central metal ion at two or more different points. The metal
chelates generally exhibit somewhat slower ligand exchange than
nonchelated complexes. Labile-type chelates may have a half-life of
several seconds, or perhaps slightly longer. Generally, the oxidizing
agents employed are not reduced to a zero valent metal during the redox
reaction of the invention.
Preferred metal complexes in accordance with this invention have
coordination numbers of 6 and are known as octahedral complexes. Cobalt
complexes are especially useful in the practice of this invention. Most
square planar complexes (which have a coordination number of 4) are rather
labile, although some Group VIII metal square planar complexes,
particularly platinum and palladium square planar complexes, exhibit
inertness to rapid ligand exchange.
A wide variety of ligands can be used with a metal ion to form suitable
metal complexes. Nearly all Lewis bases (i.e., substances having an
unshared pair of electrons) can be ligands in metal complexes. Some
typical useful ligands include the halides, e.g., chloride, bromide,
fluoride, nitrite, water, amino, etc., as well as such common ligands as
those referred to on p. 44 of Basolo et al, supra. The lability of a
complex is influenced by the nature of the ligands selected in forming
said complex.
Particularly useful cobalt complexes have a coordination number of 6 and
have a ligand selected from the group consisting of ethylenediamine(en),
diethylenetriamine(dien), triethylenetetraamine(trien), amine (NH.sub.3),
nitrate, nitrite, azide, water, carbonate and propylenediamine(tn).
Especially useful are the cobalt complexes containing ammine ligands such
as the cobalt hexammine salts. Some specific highly useful cobalt
complexes include those having one of the following formulas:
[Co(NH.sub.3).sub.5 H.sub.2 O]X, [Co(NH.sub.3).sub.5 CO.sub.3 ]X,
[Co(NH.sub.3).sub.5 Cl]X, and [Co(NH.sub.3).sub.4 CO.sub.3]X, wherein X
represents one or more anions determined by the charge neutralization
rule, and X preferably represents polyatomic organic anions.
Complexes containing oxidized noble metals or ferramagnetic metals, such as
complexes of CoIII, FeIII, RhIII, PtIV, PdIV and IrIII, which have
reactivities similar to the complexes listed above, could be used in the
practice of this invention. The redox equilibria published in Stability
Constants of Metal-Ion Complexes, Sillen and Martell, published by The
Chemical Society, Burlington House, London, England (1964), indicate that
other complexes have reactivities generally similar to the cobalt
complexes mentioned above.
In one preferred embodiment according to this invention where the
cobalt(III) ion complexes are incorporated in the photographic element,
the anions of the complexes are polyatomic anions, and in some highly
preferred embodiments are polyatomic organic anions. The anions are
associated with the cobalt(III) ion complex in what may be a salt, an
outer sphere complex of an ion pair; see, for example, p. 34 of Basolo et
al, supra. Typical useful polyatomic anions include sulfato groups,
nitrate, and the like. Typical polyatomic organic anions include acetato,
propionato, methanesulfonato, benzenesulfonato, hexanesulfonate, and the
like.
The polyatomic anions are preferably those which in the sodium salt form
are not silver halide solvents, i.e., the sodium salt of the polyatomic
anion when employed in an aqueous solution (60.degree. C.) at a 0.02 molar
concentration does not dissolve more than 5 times the amount by weight of
silver chloride which can be dissolved in distilled water at 60.degree. C.
The sodium salts of anions such as thiocyanate and thiosulfate in a 0.02
molar concentration dissolve more than 5 times the amount by weight of
silver chloride which is dissolved by distilled water at 60.degree. C.
In another embodiment where cobalt(III) ion complexes are incorporated in
the photographic element, they are incorporated as water-insoluble ion
pairs. The use of water-insoluble ion pairs of cobalt(III) ion complexes
is described in more detail in Bissonette et al, U.S. Ser. No. 307,894
entitled "Ion-Paired Cobaltic Complexes and Photographic Elements
Containing Same", filed Nov. 20, 1972, issued as U.S. Pat. No. 3,847,619
on Nov. 12, 1974, which is incorporated herein by reference. Generally,
these ion pairs comprise a cobalt(III) ion complex ion-paired with an
anionic organic acid having an equivalent weight of at least 70 based on
acid groups. Preferably, the acid groups are sulfonic acid groups.
In certain highly preferred embodiments, cobalt(III) ion complexes are used
in this invention which contain ammine (NH.sub.3) ligands or have a net
positive charge which is preferably a net charge of +3. A cobalt(III) ion
with six (NH.sub.3) ligands has a net charge of +3. A cobalt(III) ion with
five (NH.sub.3) ligands and one chloro ligand has a net charge of +2. A
cobalt (III) ion with two ethylenediamine(en) ligands and two (N.sub.3)
azide ligands has a net charge of +1. Generally, the best tanning results
have occurred where the cobalt(III) complex has a net charge of +3 and/or
the cobalt complex contains at least three ammine ligands.
When the cobalt(III) ion complexes are used in a liquid solution to obtain
tanning, the liquid composition can contain from about 10 mg. to about 50
g./l. of solution, and preferably it contains from about 100 mg. to about
10 g./l. based on cobalt. Where the cobalt(III) ion complex is
incorporated in the photographic element, good tanning can be achieved
when the element contains the cobalt(III) ion complex in a concentration
at least 0.5% by weight of unhardened hydrophilic colloid in said element
based on cobalt and preferably at least 1.0%.
The redox reaction which takes place in the practice of this invention
occurs at a catalytic surface, i.e., the reaction environment is a
heterogeneous medium wherein the catalyst is in one phase, the oxidant and
reductant are in another phase, and the reaction takes place on the
interface between the phases. Generally, the catalyst will be a solid
material and the oxidant and the reductant will be in a liquid phase. Any
catalytic material can be utilized which initiates and promotes redox
reaction between the oxidizing agents and reducing agents selected. While
the reaction mechanism is not completely understood, it appears that the
catalyst appears to allow electron transfer between the oxidizing agent
and the reducing agent. In a preferred embodiment, the catalysts are the
metals or chalcogens of Group VIII or 1B elements. In another embodiment,
the catalyst can be an activated carbon or activated charcoal. Many useful
catalysts are the zero valent metals or metal nuclei. Specific useful
catalysts include metals such as platinum, copper, silver, gold and
chalcogens such as silver sulfides, silver oxides, nickel sulfide, cuprous
sulfide, cobalt sulfide, aurous sulfide and cupric oxide. While several of
the catalysts are referred to as chalcogens, it is understood that, in
some instances, an equilibrium mixture may be present in the product, such
as a mixture of silver hydroxide and silver oxide.
In accordance with this invention, the catalyst appears to provide redox
reaction in a true catalytic fashion. The amount of redox reaction is not
limited by the amount of catalyst present, since the redox reaction of
this invention does not proceed on a stoichiometric basis with respect to
the catalyst. Generally, in the absence of the catalyst the oxidant and
the reductant can be described as being in a state where they are
substantially kinetically stable; i.e., the kinetic reaction is so slow or
practically nonexistent as to be not noticeable in the process. The
catalyst appears to interact with the oxidant and/or reductant in such a
fashion as to overcome the kinetic barrier. Where the oxidant and
reductant are thermodynamically stable in the reaction medium, the
catalyst can lower the kinetic barrier by converting either the oxidant or
reductant to another form which will provide a thermodynamically unstable
combination which is also kinetically unstable. Where the oxidant and
reductant are thermodynamically unstable but substantially kinetically
stable, the catalyst can function to lower the kinetic barrier, allowing
the reaction to proceed at a substantially faster rate.
Some care is needed in selecting the particular oxidant-reductant-catalyst
combination employed in the practice of the invention, bearing in mind the
circumstances governing any particular embodiment of the invention. The
oxidizing-reducing agent combination should undergo essentially no redox
reaction except in the presence of external catalyst material. Also, the
catalyst should be so selected that it is essentially unreactive under the
conditions employed with either the oxidizing agent alone or reducing
agent alone. In the environment in which the reaction takes place, the
catalyst should promote the redox reaction, but should not itself undergo
a redox reaction directly with either the reducing agent or oxidizing
agent to any substantial degree. Preferably, the oxidizing agent and the
reducing agent are so chosen that, when test samples thereof are each
dissolved at a 0.01 molar concentration in an inert solvent at 20.degree.
C., essentially no redox reaction occurs for at least 15 minutes and
preferably for several hours, such as 12 hours, or several days, such as a
month or more.
Combinations of oxidant and reductant which undergo a more rapid redox
reaction in the absence of catalyst are, however, useful in embodiments of
the invention where the oxidizing agent and reducing agent are in reactive
condition for brief periods of time. In one such embodiment, separate
solutions of oxidizing agent and reducing agent can be sprayed on a
support carrying an imagewise distribution of catalyst. An imagewise redox
reaction takes place in the presence of the catalyst. After sufficient
redox reaction occurs, the unreacted reducing agent and oxidizing agent
are removed in any convenient manner, for example, using an air jet, a
stream of liquid or a chemical neutralizer. In other embodiments of the
invention, an imagewise pattern of catalyst, together with a nonimagewise
distribution of oxidant (or reductant), can be contacted with reductant
(or oxidant) for a time sufficient to permit imagewise redox reaction.
Thereafter, the reductant (or oxidant) can be removed. In these and other
embodiments of the invention, the oxidant and reductant need not possess a
high degree of inertness to redox reaction in the absence of catalyst.
In preferred embodiments of the invention, an imagewise pattern of catalyst
is contracted with the combination of oxidizing and reducing agent in
accordance with the invention. However, a nonimagewise distribution of
oxidizing agent and catalyst can be contacted with an imagewise pattern of
reducing agent, or an imagewise pattern of oxidizing agent can be
contacted with the combination of reducing agent and catalyst to form
images in accordance with the invention. Also, an imagewise pattern of
catalyst, together with a nonimagewise distribution of oxidizing agent,
can be contacted with reducing agent or an imagewise pattern of catalyst,
together with a nonimagewise distribution of reducing agent, can be
contacted with oxidizing agent to initiate redox reaction in accordance
with the invention.
Any suitable means can be utilized to contact the oxidizing agent, reducing
agent and catalyst. For example, an imagewise pattern of catalyst can be
contacted with a solution containing oxidant and reductant. In one
convenient embodiment of the invention, a hydrophilic colloid layer coated
on a suitable support contains a pattern of catalyst and is contacted with
an aqueous solution containing oxidant and reductant. The concentration of
reductant and oxidant in such solutions can vary over a wide range.
Optimum concentrations depend on such variables as time of contact, amount
of catalyst present and reactivity of the particular oxidizing
agent-reducing agent-catalyst combination chosen. Typical useful
concentrations of oxidant and reductant, each, range from about 0.1 to 50,
and preferably 1 to 15, g./liter of solution, using contact or residence
times of about 30 sec. up to 2 hr. or longer. The oxidizing agent and
reducing agent can also be contained in and released from rupturable pods
or pressure-sensitive capsules. An alternative method for initiating redox
reaction in accordance with the invention involves incorporating the
oxidant and reductant in a hydrophilic colloid layer, coated on a suitable
support, and contacting the layer with a plate bearing a metal catalyst
relief image. The metal relief image initiates and promotes the redox
reaction between the oxidant and reductant contained in the hydrophilic
colloid layer. If desired, portions of the oxidant or reductant can be
incorporated both in processing solutions and hydrophilic colloid layers,
which can also contain a suitable source of catalyst such as
light-sensitive silver halide.
The reducing agent and the oxidizing agent employed herein advantageously
have good solubility in water; preferably, they are soluble in amounts of
at least 0.1 g. and preferably at least 10 g./liter of water. However,
other solvents, preferably a polar solvent such as methanol or ethanol,
can be employed. In certain embodiments of the invention, reducing agents
and oxidizing agents having very low water solubility can be employed.
The processes of the invention are admirably suited to amplify faint or
even invisible quantities of catalyst. The invention is highly effective
with light-sensitive silver halide materials wherein latent image silver
or a low-density silver image can be utilized to generate an image record.
In addition, the processes of the invention are useful in supplementing an
image, for example, a silver or other zero valent metal image, or an image
composed of other catalysts, oxidants or reductants utilized in accordance
with the invention. It is also possible to replace preformed images with
other images in accordance with the processes of the invention.
The improvements obtained in tanning processes in accordance with this
invention can generally be obtained in any photographic element which
contains a crosslinkable colloid or crosslinkable material. The
photographic element can be a receiver element comprising a support having
thereon at least one layer containing a crosslinkable material such as a
binder vehicle; the receiver element can be placed in interfacial contact
with another element during the tanning step to crosslink the material.
The element can contain a support having thereon at least one layer
containing a photographic recording material, such as silver halide, and
at lest one layer containing a crosslinkable material. The imagewise
tanning can be accomplished by means wherein at least one of the essential
ingredients which are the oxidant, the reducing agent and the catalyst is
provided during said process in an imagewise distribution, and the
crosslinkable colloid is one which can be effectively crosslinked or
hardened by the reaction products of the redox reaction.
In accordance with certain embodiments of this invention, an improvement is
provided in photograhic processes wherein imagewise-exposed photographic
elements comprising a support having coated thereon silver halide grains
dispersed in a crosslinkable colloid are developed to produce a silver
image, and the colloid is crosslinked imagewise in areas where a metallic
silver develops. The improvement is obtained by contacting such
photographic elements with the combination of an oxidant and reductant
which undergo imagewise redox reaction in the presence of metallic silver,
the reduced form of said oxidant being a crosslinking agent for the
colloid. The process of this aspect of the invention can be conducted with
a photographic developer as reducing agent. The oxidized form of the
developing agent can also function as a crosslinking agent. The metallic
silver produced by the action of a photographic developer on exposed
silver halide catalyzes an oxidation-reduction reaction in accordance with
the invention.
If desired, subsequent to developing a silver image in a cross-linkable
colloid, the photographic element is contacted with the combination of
oxidizing agent and reducing agent in accordance with the invention to
generate the cross-linking agent. Using the latter procedure, it is not
necessary that the reducing agent be a selective photograhic silver halide
developing agent. When metal complexes are employed as oxidants, it is
preferable that the ligands released on redox reaction should not
interfere with the cross-linking.
This invention is useful in conventional tanning development where any
suitable colloid, preferably gelatin, is cross-linked or hardened.
Advantageously, the silver halide emulsion is an unhardened or partially
hardened gelatin silver halide emulsion.
The practice of this aspect of the invention results in tanning with
developers which have not been considered tanning developers, and
increases the tanning obtained with conventional tanning developers. The
invention is, accordingly, useful with any of the known tanning developing
agents, e.g., pyrogallol and catechols such as 4-phenylpyrocatechol, or
photographic developing agents which normally tan or cross-link colloids,
such as the hydroquinones, pyrazolidones such as 1-phenyl-3-pyrazolidone,
the p-phenylenediamines, the p-aminophenols and the diaminophenols. This
embodiment of the invention is useful in dye imbibition and colloid
transfer processes and in the preparation of photoresists, planographic
printing plates and lithographic printing plates.
This invention permits the incorporation of substantial amounts of sulfite
(e.g., sodium sulfite) in the tanning developer solutions, while retaining
effective tanning. The amount of sulfite which could be added to
conventional tanning developing agents was limited because of the
inhibiting effect sulfite has on tanning development. Hence, using the
practice of this invention, more stable tanning developer solutions are
possible because of the higher tolerance for sulfite stabilizer in
accordance with this invention.
The hardenable hydrophilic colloids useful in certain embodiments of this
invention are those generally known in the photographic art which can be
hardened by photographic hardeners such as formaldehyde. In certain
preferred embodiments, the hardenable hydrophilic colloid is a material,
such as gelatin, which has a melting point of less than 150.degree. F. and
preferably less than 120.degree. F., and it preferbly has a melting point
above about 80.degree. F. In another embodiment, the hydrophilic colloid
is a material which can be hardened by a photographic hardening agent to
provide at least 100% lower water solubility of the hardened material at a
temperature of 90.degree. F.
The terms "unhardened hydrophilic colloid" and "cross-linkable colloid" as
used herein refer to those materials which are capable of substantial
further hardening. These materials may possess a small amount of
crosslinking or may have been hardened or tanned slightly. However, these
terms generally refer to those materials which are capable of being
further hardened to provide a melting point differential between hardened
and unhardened hydrophilic colloid of at least 20.degree. F. and
preferably at least 40.degree. F. wherein the unhardened hydrophilic
colloid has a melting point of less than 150.degree. F.
Typical useful hydrophilic colloids include proteinaceous materials such as
gelatin and similar materials which can be hardened by photographic
hardeners, for example, such as other proteinaceous photographic vehicles.
The unhardened hydrophilic colloid is generally coated on the support at a
coverage of from about 5 to about 3000 mg./ft..sup.2 and preferably from
10 to about 2000 mg./ft..sup.2.
Generally, it is preferred to use gelatin as the unhardened hydrophilic
colloid but other vehicles, and especially those which contain groups
which are ligands as described above, can also be used. Moreover, other
photographic binding agents can be used as substituted in whole or in part
for gelatin. Suitable photographic binders include colloidal albumin,
cellulose derivatives, synthetic resins such as polyvinyl compounds and
the like, and peferably the water-soluble and latex polyvinyl compounds.
In certain instances, it is desirable to use latex polymers to improve
dimensional stability such as, for example, the alkyl acrylates and alkyl
methacrylate polymers. Where the binding agents are used as substitutes
for all or part of the gelatin, the layer must still have the properties
as defined for the unhardened hydrophilic colloid layer as set forth
herein.
In certain embodiments, the photographic elements used in accordance with
this invention have supports which have a hydrophobic surface. Elements of
this type are desirable to provide a lithographic plate wherein the
hardened gelatin will provide a hydrophilic surface and the areas where
the colloid is removed will provide a hydrophobic or oleophilic surface.
Typical useful hydrophobic supports include materials such as
polyethylene, polystyrene, cellulose esters such as cellulose acetate,
polyesters, polytetrafluoroethylene, polystyrenebutadiene, etc.
The hydrophobic surface can be treated to obtain adhesion to the unhardened
hydrophilic colloid layer by methods known for improving the adhesion of
hydrophilic materials to hydrophobic supports such as electron
bombardment, flame-treating, oxidation with sulfuric acid-dichromatic
solution, treatment with chlorine gas, hydrogen peroxide, nitric acid,
etc.
The photographic elements of this invention may comprise incorporated
developers such as black-and-white-developing agents or color-developing
agents. Since the hardening of the hydrophilic colloid does not depend on
a tanning developer such as 4-phenyl catechol, etc., generally any
developing agent can be used to develop the silver halide. Likewise, where
other photographic metal salts are used the reducing agent can be
incorporated in the photographic element.
If the developing agent is incorporated in the silver halide emulsion or in
a contiguous layer, development can be attained by using an alkaline
activator.
Typical activator baths for the photographic element containing a
developing agent include, for example, an aqueous solution of an alkaline
material such as sodium carbonate, sodium hydroxide, potassium carbonate,
potassium hydroxide, etc. Suitable baths can comprise, for example, an
aqueous solution containing about 1% sodium hydroxide.
The developer solution or activator solution may also contain gelatin
softeners such as citric acid or urea to aid in removal of the soft
hydrophilic colloid during the wash-off step.
Typical of the activator solutions which can be used in my process are
those disclosed in U.S. Pat. Nos. 2,596,754, 2,596,756, 2,725,298,
2,739,890, 2,763,553, 2,835,575, 2,852,371 and 2,865,745.
The development and/or tanning processes as referred to herein can be
effected by bathing the photographic element in an activator solution or
developing solution. Alternatively, a viscous processing solution can be
placed between the photographic element and a spreading sheet for
spreading in a predetermined amount across and in contact with the
emulsion side of the photographic element so as to provide all of the
solution required for processing. The viscous proces | | |
