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Publication numberUS3515556 A
Publication typeGrant
Publication dateJun 2, 1970
Filing dateAug 1, 1967
Priority dateAug 1, 1967
Publication numberUS 3515556 A, US 3515556A, US-A-3515556, US3515556 A, US3515556A
InventorsAmering Charles F, Russell Harold D
Original AssigneeEastman Kodak Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Photographic developing process utilizing hemlock tannin polymer
US 3515556 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,515,556 PHOTOGRAPHIC DEVELOPING PROCESS UTILIZ- IN G HEMLOCK TANNIN POLYMER Harold D. Russell and Charles F. Amering, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Aug. 1, 1967, Ser. No. 657,540 Int. Cl. G03c 5/24 US. CI. 96-63 14 Claims ABSTRACT OF THE DISCLOSURE Processing of photographic silver halide emulsions with processing compositions containing a dispersing agent which is a hemlock tannin polymer, such as a mixture of copolymers of catechin with leucocyanidin extracted from certain tree bark.

This invention relates todispersing agents in photographic processes and compositions. One aspect of the invention relates to photographic processing with photographic compositions, especially photographic aqueous processing solutions, containing a member of a class of polyphenolic compounds which are hemlock tannin polymers. Another aspect relates to a continuous process employing such processing compositions in continuous transport processing apparatus.

Many image-recording systems use image-formlng materials comprising a support with one or more layers comprising hydrophilic colloid materials such as gelatin. Since the advent of film processing by film transport machines, as described for example in US. Pat. 3,023,779, the processing of such image recording systems has encountered particular problems in the form of unwanted markings on the processed elements. These markings occur in a definite line pattern at a fixed distance from the leading edge of a photographic element or sheet undergoing processing. When processing film, for example, in a roller transport machine having many rollers of the same diameter, this effect from each roller will occur at the same point on the film and will be cumulative.

These markings have been shown to be of two types. One type results due to simple dirt deposition, herein referred to as a simple pi line, and the other type has been found to be due to density variations in the developed silver. This latter type of marking is herein referred to as a chemical pi line. The simple pi lines can be removed by buffing, but no process or composition heretofore has been satisfactory for preventing formation of chemical pi lines resulting from the density variation of silver. Attempts up to the present time have not been satisfactory for removing these markings either.

The efforts to prevent formation of chemical pi lines have included addition of coating aids or surfactants to the hydrophilic colloid layers of a photographic element. The surfactants used, however, often influence characteristics other than the coating performance of such layers, such as surface roughness, permeability of processing solutions, and the like. As an example, saponin has been employed as a coating aid for photographic elements; but, when such elements are processed through continuous transport processing machines, such as a roller transport processor, as illustrated in US. Pat. 3,023,779, objectionable foaming occurs in the washing section of the machine. This foam tends to adhere to the surface of the processed photographic element causing objectionable marks.

Attempts have also been made to eliminate markings,

such as pi lines, by modifying the roller surface and roller composition of the machine or by varying the hardness of the emulsion. In addition, changing the composition of the various processing solutions has also been attempted.

Various types of dispersing agents and surfactants have been added to processing solutions, but, as demon strated in following Example 6, have not been satisfactory for removing the undesired markings. Moreover, increasing the amounts of such dispersing agents or surfactants used does not provide the desired results. This is also demonstrated in Example 6.

It has also been observed that after prolonged use of processing solutions in continuous processing machines, such as in roller transport processors, that colloidal silver produced as a byproduct of development tends to nucleate surface development on photographic elements being processed. This results in undesirable increased fog level of the resulting image. For example, when processing photographic elements containing a silver halide emulsion layer, such as X-ray films, it is observed that after many sheets have been processed, a processing solution containing a silver halide developing agent can cause an undesired significant increase in minimum density of the emulsion.

The processes and compositions of the invention surprisingly have been found to overcome these effects, e.g., undesired pi lines and significant increases in minimum density resulting from the presence of colloidal silver in processing solutions.

It is an object of the invention to provide photographic processes, especially continuous processes, and compositions for processing exposed photographic elements whereby undesired markings, such as pi lines, are avoided.

It is also an object of the invention to provide photographic processes and compositions for processing exposed photographic elements which avoid coagulation of colloidal silver in processing solutions and undesired markings.

Other objects and advantages of the processes and compositions of the invention will be apparent from the following description.

The invention comprises a method of processing an exposed photographic element having at least one silver halide emulsion layer employing a processing solution containing a dispersing agent comprising, in sulfonated form, a hemlock tannin polymer.

It also comprises a composition, suitable for developing an exposed photographic element having at least one silver halide emulsion layer, containing a silver halide developing agent and a dispersing agent comprising, in sulfonated form, a hemlock tannin polymer.

It further comprises a composition, suitable for processing an exposed photographic element having at least one silver halide emulsion layer, containing a silver halide processing agent, a coagulant for colloidal silver and a dispersing agent comprising, in sulfonated form, a hemlock tannin polymer.

Hemlock tannin polymers as employed herein refers to a class of polyphenolic compounds typically found in coniferous tree barks, such as in the bark of Western hemlock trees (T saga heterophyllw). The class of polymers can be prepared by extraction with hot water (about 97 C.) from such tree barks. Polymers within this class and a suitable method for their preparation are set out, for example, in an article by H. L. Hergert, L. E. Van- Blarican, J. C. Steinberg and K. R. Grasy in Forest Products Journal, vol. XV, No. 11, November 1965, pp. 485-491. Hemlock tannin polymers within the scope of the invention can also be prepared by the method set out in US. Pat. 2,782,241-K. R. Gray and H. L. Crosby, issued Feb. 19, 1957. This method includes extraction of the desired polymeric products with a dilute aqueous alkali metal hydroxide solution at elevated temperature, e.g. about 65 C. to 185 C.

The hemlock tannin polymers of the invention are typically in sulfonated form. That is, they contain at least one sulfonate group, typically an alkali metal sulfonate group, e.g. -SO Na or -SO K. The hemlock tannin polymers can be sulfonatecl using a wide variety of sulfonation processes, such as set out in Noller, Chemistry of Organic Compounds, W. B. Saunders and Co., Philadelphia, 1952, including treating the hemlock tannin polymer with sodium sulfite or sulfuric acid.

Typically, the hemlock tannin polymers can contain at least one sulfonate group for each repeating unit of the polymeric material.

Especially suitable members of the class of hemlock tannin polymers are, in sulfonated form, copolymers of catechin:

with leucocyanidin:

having the repeating structural units:

o g Q 0H l I on OH 1 The average molecular weight and number of repeating structural units is typically sufliciently high that the copolymers are solid; however, the number is not exactly known. The molecular weights of the polymeric products of the invention are usually at least about 3,000 or more.

A useful commercially available dispersing agent within the scope of the invention is sold under the trade name of Rayflo-C, :by Rayonier, Incorporated, New York, NY. This dispersing agent is a water soluble mixture of copolymers of catechin with leucocyanidin in sulfonated form. It is a red-brown, free-flowing powder having the following typical chemical characteristics:

Percent Phenolic hydroxyl 7.8 Methoxy groups 1.4 Sodium 9.0 Calcium 0.3 pH (1% by weight aqueous solution) 8.2 Moisture 4.7

The dispersing agent according to the invention can be suitably admixed, dissolved or incorporated in any suitable manner in an aqueous processing solution. It can be incorporated in the form of a dry powder, aqueous concentrate, dispersion, aqueous solution, or in other suitable forms.

It is often advantageous to provide separate containers, such as packages or bottles of the components or mixtures of the components of the processing compositions of the invention for storage before use. These can be in containers in kit form.

The suitable concentrations of dispersing agent employed in a particular processing solution can vary and will be influenced by the particular ingredients of the processing solution, the temperature employed and other factors which can be determined by those skilled in the art. An effective concentration of dispersing agent found suitable for a typical processing agent such as a developer, stabilizer, or fixer solution comprises about 0.001 to about 10 grams of dispersing agent per liter of solution containing the processing agent. A particularly useful concentration is about 0.1 gram to about 1.0 gram of the dispersing agent per liter of processing solution.

An aqueous processing solution as employed herein refers to a wide range of aqueous solutions which are suitable for processing an exposed photographic emulsion. Such a solution is usually a developing, stabilizing or fixing composition, but, other processing solutions are suitable. Typical processing solutions and their components are disclosed, for example, in Mees, Theory of the Photographic Process, 3rd ed., Macmillan Company, New York, NY. (1966).

A typical developer solution within the scope of the invention comprises an aqueous solution of a silver halide developing agent, an activator, e.g. an alkali metal hydroxide, and a minor proportion, e.g. about .001 to about 10 grams per liter of solution, of a hemlock tannin polymer in sulfonated form.

A typical fixing or stabilizing solution within the scope of the invention comprises an aqueous solution of a silver halide fixing agent or a silver halide stabilizing agent, and a minor proportion, e.g. about .001 to about 10 grams per liter of solution, of a hemlock tannin polymer in sulfonated form.

Such processing compositions, typically aqueous solutions, are especially suitable for processing a photographic element having at least one silver halide emulsion layer wherein the element is processed in one continuous motion by transporting it into and out of at least one of such processing solutions containing the described hemlock tannin polymers. Suitable apparatus and processing steps are set out, for example, in US. Pats. 3,025,779- Russell et al., issued Mar. 20, 1962; 3,078,024-Sardeson, issued Feb. 19, 1963; 3,122,086Fitch, issued Feb. 24, 1964; 3,149,551-Cramer, issued Sept. 22, 1964; 3,156,- 173--Meyer, issued Nov. 10, 1964; and 3,224,356- Fleisher et a1., issued Dec. 21, 1965.-

As described above, it has been observed that the presence of colloidal silver in processing solutions after a period of use has caused undesired increases in the fog level of photographic emulsions. The presence of a coagulant for colloidal silver in the compositions of the invention has been found to overcome such results. Coagulant as employed herein is intended to refer to compounds which cause the colloidal silver particles in a photographic processing solution to agglomerate or otherwise form larger particles which can be filtered. Examples of suitable coagulants are coagulant thiol compounds, that is, coagulant compounds represented by the structure R-fiSH, wherein R is a hydrocarbon radical such as an alkyl, e.g. a lower alkyl radical, or aryl radical, such as phenyl, xylyl or benzyl radical. Typical coagulants include cysteine and o-mercaptobenzoic acid; coagulant quaternary salts; and high molecular weight polyethylene resins.

The effectiveness of this action caused by the dispersing agent of the invention, and especially by the combination of the dispersing agent with a coagulant, extends for a significant period of use, e.g. several weeks, and is particularly long-lasting when solutions are filtered to remove particles which adversely affect the processed film.

The amount of coagulant employed can vary depending upon components of the processing solution, temperature, and the like. Typically, about .01 to about 1.0% by weight of coagulant of the total processing solution is suitable.

Processing agent or photographic processing agents as employed herein is intended to refer to agents which are normally employed in photographic compositions, elements and processes to develop, stabilize, fix or otherwise treat photographic elements. Suitable processing agents include, for example, developers, stabilizers, fixing agents, compositions which aid in preventing water spotting and the like. Suitable processing agents are set out for example, in Mees, Theory of the Photographic Process, 3rd ed., Macmillan Company, New York, NY. (1966).

The developing agents useful in composition of the invention include any silver halide developing agents. Suitable developing agents include polyhydroxybenzene developing agents, e.g. hydroquinone developing agents such as hydroquinone, alkyl substituted hydroquinones as exemplified by t-butylhydroquinone, methylhydroquinone, dimethylhydroquinone; catechol and pyrogallol; chloro substituted hydroquinones such as chlorohydroquinone or dichlorohydroquinone; alkoxy substituted hydroquinones such as methoxy or ethoxy hydroquinone; aminophenol developing agents such as 2,4-diaminophenols and methylaminophenols; ascorbic acid; pyrazolidone developing agents such as 1-phenyl-3-pyrazolidone, including those described in British Pat. 930,572; and acyl derivatives of p-aminophenol such as disclosed in British Pat. 1,045,303. Such developing agents can be used alone or in combination.

Concentrations of the silver halide developing agent can vary over a wide range. Suitable concentrations in a developer composition will be determined based on other components present, the desired image and other factors which can be determined by those skilled in the art.

Such developing agents can be present in one or more layers of the photographic elements processed.

Developer compositions of the invention typically contain an activator. Any suitable development activator can be employed with the compositions of the invention, such as alkali metal hydroxides, e.g. sodium hydroxide, potassium hydroxide or lithium hydroxide, or other suitable alkaline materials such as organic amines. These can be used in any concentration which is effective for achieving the desired alkalinity.

Temperatures employed with the compositions and processes of the invention can vary over a wide range. Typically processing with compositions or elements containing dispersing agents described, such as a copolymer of catechin with leucocyanidin in sulfonated form, is carried out at ambient temperatures; but often it is advantageous to employ elevated temperatures, such as temperatures above about 30 C., e.g. about 30 C. to about 90 C.

The photographic emulsions useful according to the invention include a wide variety of silver halide emulsions. They can be non-spectrally sensitized emulsions,

such as X-ray type emulsions, or they can be orthochromatic, panchromatic, infrared sensitive and the like emulsions containing spectral sensitizing dyes, such as described in US. Pats. 2,526,632 and 2,503,776. Spectral sensitizers which can be used include cyanines, merocyanines, styryls and hemicyanines.

The photographic emulsions employed in the practice of the invention can be sensitized using any of the well known techniques in emulsion making, for example, by digesting with naturally active gelatin or various sulfur, selenium, noble metal and/or gold compounds.

The photographic emulsions processed according to the invention, and the compositions employed for processing, can contain various photographic addenda, especially those known to be beneficial in photographic compositions. The types of addenda and concentrations to be employed can be determined by those skilled in the art. Suitable photographic addenda include, for example, hardeners, e.g. alum, or those set out in British Pat. 974,- 317; buffers which maintain the desired pH level including various sulfonamides and boraxes; coating aides, coating aids, plasticizers; speed increasing addenda, such as quaternary ammonium salts and alkylene oxide polymers, e.g. polyethylene glycols; and stabilizing agents such as sodium sulfite.

The silver halides employed in the practice of the invention include any of the photographic silver halides, such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide, silver bromoiodide and the like. Particularly good results are obtained with so-called high contrast photographic emulsions in which the halide comprises at least about 50 mole percent chloride. The silver halides can be those which form latent images predominantly on the surface of the silver halide grains or those which form latent images inside the silver halide crystals, such as described in US. Pat. 2,592,250 Davey and Knott, issued Apr. 8, 1952.

The photographic emulsions processed according to the invention can be coated on a wide variety of supports. Typical supports include films, such as cellulose acetate films, polyethylene terephthalate or other polyester films, polyvinyl acetal films, polystyrene films, polycarbonate films and related materials, papers, such as paper supports which are coated with resinous materials, e.g. coated with polyethylene, polypropylene and/ or ethylene-butene copolymers, glass, metal and the like.

The photographic elements processed according to the invention typically contain a layer comprising any of the known hydrophilic water permeable binding materials suitable for photographic purposes. These include, for example, gelatin, cellulose derivatives, polymerized vinyl compounds as well as mixtures of such binding agents. The binding agents can also contain water insoluble polymers, such as polymerized ethylenically unsaturated compounds, e.g. polymers of acrylates and methacrylate.

The compositions of the invention can have a wide range of pH values. The developer compositions are typically employed at a pH above about 7, e.g. about 7 to about 14. However, the appropriate pH value will be determined by the purpose of the processing composition, the desired degree of action, and the like.

The time for processing, such as development, fixing or stabilizing, employing the processes and compositions of the invention can vary between about a second up to about an hour or more, depending on the desired image, process ing conditions and the like.

The invention is further illustrated in the following examples:

' EXAMPLE 1 This example illustrates the use of a developer composition containing a dispersing agent according to the invention.

Exposed sheets of film containing a silver halide gelatino emulsion of the type normally used in radiography are fed into a roller transport processor, as described in U.S. Pat. 3,023,779, wherein the transport of the sheets of film through the processing stages is accomplished by means of rollers which contact both sides of the film.

The developing solution which is employed in the processor consists of:

. Grams Methyl-p-aminopheno] 2.0 Sodium sulfite, desiccated 90.0 Hydroquinone 8.0 Sodium carbonate-H O 52.5 Potassium bromide 5.0

Water to make 1.0 liter.

In processing, the film transported by the rollers is passed through a tank containing the developer solution, a fixing tank containing ammonium thiosulfate fixer, a water wash tank and then a drier section where the film is hot-air dried.

Sheets of film processed in this manner have horizontal lines of higher than background density a few inches in from the leading edge of the film and parallel to the leading edge.

A group of the same films identically exposed are processed employing the above developer solution with the exception that 0.5 gram per liter of solution of a hemlock tannin polymer, i.e., a mixture of copolymers of catechin with leucocyanidin in sulfonated form is added. The unsulfonated form of this copolymer mixture is represented by the Structures III and IV. After processing in the roller transport processor, the resulting developed film shows no horizontal lines. Even the very first sheets of film processed in the roller transport processor employing the solution containing the polyphenolic dispersing agent of the invention are free of horizontal lines or pi markings.

EXAMPLE 2 This example demonstrates the use of a dispersing agent of the invention in another developer composition.

Exposed sheets of film containing a silver halide gelatino emulsion of the type normally used in radiography are processed in a roller transport processor as set out in Example 1. The developer solution employed in the processor consists of:

Grams l-phenyl-S-pyrazolidone 3.0 Hydroquinone 20.0 Sodium sulfite, desiccated 75.0 Sodium metaborate, crystalline 48.0 Sodium hydroxide 7.5 Potassium bromide 5.0 S-rnethyl benzotriazole 0.3

13-Methylgluteraldehyde bis-sodium bisulfite 15.0 Water to make 1.0 liter.

It is found that pi markings appear on the leading edges of the sheets processed through the processor employing this developer composition.

When 0.25 gram per liter of a dispersing agent of the invention consisting of a mixture of copolymers of catechin with leucocyanidin in sulfonated form are thoroughly mixed in this processing solution and two sheets of film are then processed through the processor, the sheets processed thereafter are free of any pi line markings.

EXAMPLE 3 The process set out in Example 2 is repeated employing 0.001 gram per liter of the dispersing agent in the developing solution. Exposed film processed with this concentration in the developer solution is free of any pi line markings.

EXAMPLE 4 The process set out in Example 2 is repeated employing 10.0 grams per liter of the dispersing agent in the developer solution. Exposed film processed with this concentration of dispersing agent in the developer solution is free of pi line markings.

8 EXAMPLE 5 This example demonstrates the use of a dispersing agent of the invention in both a developer and fixing solution.

The procedure set out in Example 2 is repeated. However, besides adding 0.25 gram of the dispersing agent per liter of developing solution, 0.25 gram of the dispersing agent per liter of solution is added to the ammonium thiosulfate fixing solution also employed during processing. The resulting processed film is free of any pi line markings.

Processing is carried out in the same manner employing a copolymer of catechin with leucocyanidin in a range of concentrations of 0.001 to 10.0 grams of copolymer per liter of solution in the fixing solution. The resulting processed film is also free of pi line markings. This indicates that the copolymer can be incorporated in both a developing solution and a fixing solution over a range of concentrations.

EXAMPLE 6 This is a comparative example demonstrating that the dispersing agent of the invention provides unexpected properties and results over other wetting agents or surface active agents.

Two identical developing solutions as described in EX- ample 2 are prepared, one with and one without the addition of a surface active agent. Identical exposed films are processed with each solution through a roller transport machine as described in Example 2. The surface active agent in the first solution is an anionic wetting agent added to the developer solution at the rate of 2 grams of wetting agent per liter of solution. The anionic wetting agent employed is the sodium salt of mononaphthalene sulfonic acid. Both resulting processed films contain pi line markmgs.

Even increasing concentrations does not improve pi line markings. Thus, when the concentration of anionic wetting agent is increased to 20 grams per liter of developing solution, the processed film still shows pi line markings.

In another comparative run, a developer solution as described in Example 2 is prepared with the addition of other dispersant emulsifiers. Employing 2 grams per liter of processing solution of sulfonated and partially desulfonated lignosulfates results in the processed films having pi line markings.

Employing alkanolamide dispersing agents in a similar manner produces unsatisfactory results due to their effect on the sensitometric characteristics or fogging of the light sensitive films.

EXAMPLE 7 This example illustrates the use of a dispersing agent of the invention in combination with a colloidal silver coagulant in processing solutions.

The procedure set out in Example 1 is repeated using the same developer solution with the exception that 1 part by volume of the dispersing agent and 1 part by volume cysteine are added per 1000 parts by volume of developer solution. This causes the suspended matter in the developer solution to form particles which are filterable from the developer solution. The minimum density of the photographic emulsion processed through this solution is significantly reduced.

EXAMPLE 8 The same processing steps with the same solutions as in Example 7 are carried out with the exception that the cysteine is replaced with o-mercaptobenzoic acid as the coagulant. This produces similar results as obtained in Example 7.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A method comprising processing an exposed photographic element having at least one silver halide emulsion layer in a processing solution containing a dispersing agent comprising, in sulfonated form, a hemlock tannin polymer.

2. A process as in claim 1 wherein said hemlock tannin polymer is a mixture of copolymers of catechin with leucocyanidin.

3. A process as in claim 1 wherein said mixture of hemlock tannin polymers is a mixture of copolymers of catechin with leucocyanidin having the following properties:

Percent by weight Phenolic hydroxyl 7.8 Methoxy groups 1.4 Sodium 9.0 Calcium 0.3 pH in 1% by weight aqueous solution 8.2

4. A process as in claim 1 wherein said dispersing agent comprises about 0.001 to about grams per liter of said processing solution.

5. A process as in claim 1 wherein said processing solution comprises a silver halide developer solution.

6. A process as in claim 1 wherein said processing solution comprises a silver halide fixing solution.

7. A process as in claim 1 wherein said processing is carried out by transporting by means of roller said element in a continuous motion into and out of said processing solution.

8. A composition comprising a silver halide developing agent and a dispersing agent comprising in sulfonated form a hemlock tannin polymer.

9. A composition as in claim 8 wherein said hemlock tannin polymer is a copolymer of catechin with leucocyanidin.

10. A composition as in claim 8 wherein said dispersing agent comprises a mixture of copolymers of catechin with leucocyanidin having the following properties:

Percent by weight Phenolic hydroxyl 7.8 Methoxy groups 1.4 Sodium 9.0 Calcium 0.3 pH in 1% by weight aqueous solution 8.2

11. A composition as in claim 8 comprising an aqueous solution of about 0.001 to about 10 grams per liter of solution of hemlock tannin polymers.

12. A composition comprising a silver halide processing agent, a coagulant for colloidal silver and a dispersing agent comprising, in sulfonated form, a hemlock tannin polymer.

13. A composition as in claim 12 comprising an aqueous solution of a silver halide developing agent, a coagulant for colloidal silver, and a dispersing agent comprising in sulfonated form a copolymer of catechin with leucocyanidin.

14. A composition as in claim 12 wherein said coagulant is cysteine, o-mercaptobenzoic acid or di-isobutyl phenoxyethoxy ethyl dimethyl ammonium chloride.

References Cited UNITED STATES PATENTS 3,007,971 11/1961 Creighton 260-619 2,782,241 2/1957 Gray et a1 2606l9 2,533,990 12/ 1950 Blake 9666.3 3,026,264 3/1962 Rocklin et al. 252-52 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, Assistant Examiner US. Cl. X.R. 9666

Patent Citations
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US2533990 *Jun 10, 1947Dec 12, 1950Du PontSilver halide developer compositions containing polyoxyalkylene ethers of hexitol ring dehydration products
US2782241 *Mar 2, 1955Feb 19, 1957Rayonier IncBark treatment process and product
US3007971 *Apr 10, 1959Nov 7, 1961Macmillan & Bloedel LtdProcess for recovering polyphenols
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3928042 *Jul 22, 1974Dec 23, 1975IttPreservatives for photographic developers
US4323642 *Mar 9, 1981Apr 6, 1982Eastman Kodak CompanyStable photographic developers containing an indazole antifoggant and a lignosulfonate
US5830315 *Jul 6, 1995Nov 3, 1998Betzdearborn Inc.Treatment of Aqueous systems using a chemically modified tannin
US5843337 *Aug 4, 1997Dec 1, 1998Betzdearborn Inc.Treatment of aqueous systems using a chemically modified tannin
US5977287 *Jul 16, 1998Nov 2, 1999Betzdearborn Inc.Treatment of aqueous systems using a chemically modified tannin
Classifications
U.S. Classification430/404, 430/428, 430/434, 430/466
International ClassificationG03C5/305
Cooperative ClassificationG03C5/305, G03C5/3053
European ClassificationG03C5/305B, G03C5/305