Stabilised peroxide bleaching solutions and their use for processing of photographic elements

Abstract: Color photographic elements are bleached after exposure and development by using a hydrogen peroxide bleaching solution. This solution comprises a hydrogen peroxide bleaching agent, chloride ions in an amount of at least 0.35 mol/l, a first acidic compound which is an organic phosphonic acid or a salt thereof, and a second acidic compound which is either a 2-pyridinecarboxylic acid or 2,6-pyridinedicarboxylic acid (or a salt thereof), or a polyaminocarboxylic acid having one or more secondary amines at a pH of 8 to 11 (or a salt thereof). The bleaching solution is stabilized by the presence of the two acidic compounds.

Description: The present invention relates generally to the processing of color photographic elements. More particularly, it relates to the use of stabilized peroxide bleaching solutions comprising a certain amount of chloride ion and two distinct sequestering acidic compounds. The compositions and the methods for their use in photography are the subject of this invention. During processing of silver halide photographic elements, the developed silver is oxidized to a silver salt by a suitable bleaching agent. The oxidized silver is then removed from the element in a fixing step. The most common bleaching solutions contain complexes of ferric ion and various organic ligands. One primary desire in this industry is to design bleaching compositions which are more compatible with the environment, and thus it is desirable to reduce or avoid the use of ferric complex bleaching agents. Peracid bleaching solutions, such as those containing peroxide, persulfate, perborate, perphosphate, perhalogen, percarboxylic acid or percarbonate bleaching agents, offer an alternative to the ferric complex bleaching solutions. They are less expensive and present lower chemical and biological demands on the environment since their by-products can be less harmful. While persulfate bleaching agents have low environmental impact, they have the disadvantage that their bleaching activity is slow and thus require the presence of a bleaching accelerator. The most common bleaching accelerators are thiol compounds that have offensive odors. Because hydrogen peroxide reacts and decomposes to form water, a peroxide based bleaching solution offers many environmental advantages over persulfate and ferric complex bleaching solutions. As a result, many publications describe peroxide bleaching solutions, including US-A-4,277,556, US-A-4,301,236, US-A-4,454,224, US-A-4,717,649, and WO-A-92/01972. In addition, WO-A-92/07300 and EP 0 428 101A1 describe hydrogen peroxide compositions for bleaching high chloride emulsions. These compositions comprise up to 0.4 mole of chloride ions per liter of solution and have a pH in the range of 5 to 11. These particular bleaching solutions, however, cause vesiculation in the processed element. WO-A-93/11459 describes hydrogen peroxide bleaching solutions that include two or more water-soluble sequestering agents for complexing with transition metals. These solutions appear suitable for use with low silver paper materials. Despite all of the efforts of researchers in the art, no hydrogen peroxide bleaching composition has been commercialized because of various problems including vesiculation (that is, blistering from evolution of oxygen), poor bleaching efficiency and solution instability. There remains a need, however, for highly efficient hydrogen peroxide bleaching solutions which have improved stability. This invention provides a hydrogen peroxide bleaching solution having a pH of from 7 to 13 and comprising: a hydrogen peroxide bleaching agent, and chloride ions present in an amount of at least 0.35 mol/l, the bleaching solution characterized as further comprising: a) a first acidic compound that is an organic phosphonic acid or a salt thereof, and b) a second acidic compound that is either: a 2-pyridinecarboxylic acid or 2,6-pyridinedicarboxylic acid, or a salt thereof, or an aminopolycarboxylic acid having at least one secondary amine at a pH of from 8 to 11, or a salt thereof. The method of this invention for processing a color photographic element comprises: bleaching an imagewise exposed and developed color photographic element with the hydrogen peroxide bleaching solution as described above. The bleaching solution of this invention provides all of the advantages of no vesiculation and efficient and rapid bleaching. In addition, however, the bleaching solution of this invention has improved stability. That is, the loss in hydrogen peroxide over time is considerably reduced. Thus, the solution has improved shelf life during shipping and storage. These advantages are achieved by including in the solution a combination of two different water-soluble acidic compounds, each of which are known for different purposes (such as chelating with ferric ions). However, they have not been previously used in combination as sequestrants to stabilize hydrogen peroxide bleaching solutions. Thus, the discovery that this combination of acidic materials provides this effect in hydrogen peroxide bleaching solutions is unexpected to us. FIG. 1 is a graphical plot of relative hydrogen peroxide concentration versus storage time for two bleaching solutions of this invention and a bleaching solution of the prior art, as discussed in Examples 1-2 below. Hydrogen peroxide bleaching solutions of this invention include a conventional hydrogen peroxide bleaching agent including, but not limited to hydrogen, alkali and alkaline earth salts of peroxide, or a compound which releases or generates hydrogen peroxide. Such hydrogen peroxide precursors are well known in the art, and include for example, perborate, perphosphate, percarbonate, percarboxylate, and hydrogen peroxide urea. In addition, hydrogen peroxide can be generated on site by electrolysis of an aqueous solution. Examples of peroxide bleaching solutions are described, for example, in Research Disclosure, publication 36544, pages 501-541 (September, 1994). Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 10011). This reference will be referred to hereinafter as "Research Disclosure". Hydrogen peroxide is a preferred bleaching agent. The amount of peroxide (or its precursor) is generally at least 0.15 mol/l, and from 0.15 to 5 mol/l is preferred. The optimum amount will depend upon the type of photographic element being processed. For example, for color negative films that contain silver bromoiodide emulsions, more preferred amounts are from 0.9 to 3 mol/l. The most preferred amounts for silver bromoiodide emulsions are from 1.45 to 2.0 mol/l. For motion picture print films, the more preferred amount is from 0.15 to 1 mol/l, and a most preferred amount is from 0.35 to 0.6 mol/l. For photographic color papers, the preferred amounts would be from 0.15 to 3 mol/l. Chloride ions can be supplied to the bleaching solution as part of a simple inorganic salt, for example, sodium chloride, potassium chloride, ammonium chloride and lithium chloride. In addition, they can be supplied as organic complexes such as tetraalkylammonium chlorides. The preferred salts are sodium chloride and potassium chloride. The chloride ion concentration is at least 0.35 mol/l, with from 0.45 to 2 mol/l being preferred, and from 0.45 to 1 mol/l being most preferred. The bleaching solutions of this invention are quite simple, having four essential components: the peroxide bleaching agent, the chloride ions, and two distinct sequestrant acidic compounds, as defined below. An optional but preferred component is a buffer. The bleaching solution of this invention is alkaline, having a pH within the general range of from 7 to 13, with a pH of from 8 to 11 being preferred. The pH can be provided by adding a conventional weak or strong base, and can be maintained by the presence of one or more suitable buffers including, but not limited to, sodium carbonate, potassium carbonate, sodium borate, potassium borate, sodium phosphate, calcium hydroxide, sodium silicate, beta-alaninediacetic acid, arginine, asparagine, ethylenediamine, ethylenediaminetetraacetic acid, glycine, histidine, imidazole, isoleucine, leucine, methyliminodiacetic acid, nicotine, nitrilotriacetic acid, piperidine, proline, purine and pyrrolidine. Sodium or potassium carbonate are preferred. The amount of useful buffer or base would be readily apparent to one skilled in the art. The first acidic compound can be one or more organic phosphonic acids or salts thereof. Generally such compounds are represented by the structure (I): R 1 N(CH 2 PO 3 M 2 ) 2 or (II): R 2 R 3 C(PO 3 M 2 ) 2 wherein R 1 is hydrogen, a substituted or unsubstituted alkyl group of 1 to 12 carbon atoms (such as methyl, hydroxymethyl, ethyl, isopropyl, t-butyl, hexyl, octyl, nonyl, decyl, benzyl, 4-methoxybenzyl, β-phenethyl, o -octamidobenzyl or β-phenethyl), a substituted or unsubstituted alkylaminoalkyl group (wherein the alkyl portion of the group is as defined above, such as methylaminoemethyl or ethylaminoethyl), a substituted or unsubstituted alkoxyalkyl group of 1 to 12 carbon atoms (such as methoxymethyl, methoxyethyl, propoxyethyl, benzyloxy, methoxymethylenemethoxymethyl or t-butoxy), a substituted or unsubstituted cycloalkyl group of 5 to 10 carbon atoms (such as cyclopentyl, cyclohexyl, cyclooctyl or 4-methylcyclohexyl), a substituted or unsubstituted aryl group of 6 to 10 carbon atoms (such as phenyl, xylyl, tolyl, naphthyl, p-methoxyphenyl or 4-hydroxyphenyl), or a substituted or unsubstituted 5- to 10-membered heterocyclic group having one or more nitrogen, oxygen or sulfur atoms in the ring besides carbon atoms [such as pyridyl, primidyl, pyrrolyldimethyl, pyrrolyldibutyl, benzothiazolylmethyl, tetrahydroquinolylmethyl, 2-pyridinylmethyl, 4-(N-pyrrolidino)butyl or 2-(N-morpholino)ethyl]. R 2 is hydrogen, a substituted or unsubstituted alkyl group of 1 to 12 carbon atoms (as defined above), a substituted or unsubstituted aryl group of 6 to 10 carbon atoms (as defined above), a substituted or unsubstituted cycloalkyl group of 5 to 10 carbon atoms (as defined above), a substituted or unsubstituted 5- to 10-membered heterocyclic group (as defined above), -PO 3 M 2 or -CHR 4 PO 3 M 2 . R 3 is hydrogen, hydroxyl, a substituted or unsubstituted alkyl group of 1 to 12 carbon atoms (defined above) or -PO 3 M 2 . R 4 is hydrogen, hydroxyl, a substituted or unsubstituted alkyl group of 1 to 12 carbon atoms (as defined above) or -PO 3 M 2 . M is hydrogen or a water-soluble monovalent cation imparting water-solubility such as an alkali metal ion (for example sodium or potassium), or ammonium, pyridinium, triethanolammonium, triethylammonium ion or others readily apparent to one skilled in the art. The two cations in each molecule do not have to be the same. Preferably, M is hydrogen, sodium or potassium. In defining the substituted monovalent groups herein, useful substituents include, but are not limited to, an alkyl group, hydroxy, sulfo, carbonamido, sulfonamido, sulfamoyl, sulfonato, thioalkyl, alkylcarbonamido, alkylcarbamoyl, alkylsulfonamido, alkylsulfamoyl, carboxyl, amino, halo (such as chloro or bromo) sulfono, or sulfoxo, alkoxy of 1 to 5 carbon atoms (linear or branched) . , -PO 3 M 2 , -CH 2 PO 3 M 2 or -N(CH 2 PO 3 M 2 ) 2 wherein the alkyl (linear or branched) for any of these groups has 1 to 5 carbon atoms. Representative phosphonic acids useful in the practice of this invention include, but are not limited to the compounds listed in EP 0 428 101A1. Representative useful compounds are 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriaminepentaphosphonic acid, ethylenediamine-N,N,N',N'-tetramethylenephosphonic acid, nitrilo-N,N,N-trimethylenephosphonic acid, 1,2-cyclohexanediamine-N,N,N',N'-tetramethylenephosphonic acid, o-carboxyaniline-N,N-dimethylenephosphonic acid, propylamine-N,N-dimethylenephosphonic acid, 4-(N-pyrrolidino)butylamine-N,N-bis(methylenephosphonic acid), 1,3-diamine-2-propanol-N,N,N',N'-tetramethylenephosphonic acid, 1,3-propanediamine-N,N,N',N'-tetramethylenephosphonic acid, 1,6-hexanediamine-N,N,N',N' -tetramethylenephosphonic acid, o -acetamidobenzylamine-N,N-dimethylenephosphonic acid, o -toluidine-N,N-dimethylenephosphonic acid, 2-pyridinylmethylamine-N,N-dimethylenephosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, diethylenetriamine-N,N,N',N",N"-penta (methylenephosphonic acid), 1-hydroxy-2-phenylethane-1,1-diphosphonic acid, 2-hydroxyethane-1,1-diphosphonic acid, l-hydroxyethane-1,1,2-triphosphonic acid, 2-hydroxyethane-1,1,2-triphosphonic acid, ethane-l,l-diphosphonic acid, and ethane-1,2-diphosphonic acid, or salts thereof. Particularly useful first acidic compounds are 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilo-N,N,N-trimethylenephosphonic acid, diethylenetriamine-N,N,N',N",N"-penta(methylenephosphonic acid), or salts thereof. The amount of organic phosphonic acid used in the practice of the invention is at least 0.0005 mol/l and generally up to 0.03 mol/l. An amount of from 0.0025 to 0.012 mol/l is preferred. A second acidic compound in the bleaching solution can be any of a number of compounds described below. In one embodiment, it is a compound that is water-soluble and preferably biodegradable, and can be a substituted or unsubstituted 2-pyridinecarboxylic acid or substituted or unsubstituted 2,6-pyridinedicarboxylic acid (or equivalent salt). The substituents which may be on the pyridinyl ring include substituted or substituted alkyl, substituted or unsubstituted cycloalkyl or substituted or unsubstituted aryl groups (as defined above for structures I-II), hydroxy, nitro, sulfo, amino, carboxy, sulfamoyl, sulfonamide, phospho, halo or any other group that does not interfere with ferric ion ternary complex formation, stability, solubility or catalytic activity. The substituents can also be the atoms necessary to form a 5- to 7-membered fused ring between any of the positions of the pyridinyl nucleus. The preferred acidic compounds of this type are represented by the following structures: and wherein R, R', R" and R''' are independently hydrogen, a substituted or unsubstituted alkyl group of 1 to 5 carbon atoms (as defined above), a substituted or unsubstituted aryl group of 6 to 10 carbon atoms (as defined above), a substituted or unsubstituted cycloalkyl group of 5 to 10 carbon atoms (as defined above), hydroxy, nitro, sulfo, amino, carboxy, sulfamoyl, sulfonamido, phospho or halo (such as chloro or bromo), or any two of R, R', R'' and R''' can comprise the carbon atoms necessary to form a substituted or unsubstituted 5 to 7-membered ring fused with the pyridinyl nucleus. The monovalent and divalent radicals defining Structures III and IV can have substituents like those defining the radicals for Structures I-II above. M is as defined above. Preferably, R, R', R'' and R''' are independently hydrogen, hydroxy or carboxy. The most preferred compounds are unsubstituted 2-pyridinecarboxylic acid and 2,6-pyridinedicarboxylic acid or salts thereof. In another embodiment, the second acidic compound is an aminopolycarboxylic acid that has at least one secondary amino group at a pH of from 8 to 11, and at least two carboxyl groups (polydentate), or their corresponding salts. Such acids can be bidendate, tridentate, tetradentate, pentadentate and hexadentate ligands. These acids must be water-soluble also, and are preferably biodegradable (defined below). More specifically, these compounds include, but are not limited to, alkylenediaminetetracarboxylic acids having at least one secondary nitrogen atom, and alkylenediaminepolycarboxylic acids having at least one secondary nitrogen atom. Representative useful classes of such acidic compounds are defined below in reference to structures (V)-(IX), although it should be recognized that the invention is not limited in practice to these compounds. Thus, the compounds can have any of the following structures: wherein R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are independently hydrogen, hydroxy, a linear or branched substituted or unsubstituted alkyl group of 1 to 5 carbon atoms (such as methyl, ethyl, propyl, isopropyl, n-pentyl, t-butyl and 2-ethylpropyl), a substituted or unsubstituted cycloalkyl group of 5 to 10 carbon atoms in the ring (such as cyclopentyl, cyclohexyl, cycloheptyl and 2,6-dimethylcyclohexyl), or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms in the aromatic nucleus (such as phenyl, naphthyl, tolyl and xylyl), M is as defined above, W is a covalent bond or a divalent substituted or unsubstituted aliphatic linking group (defined below), wherein at least two of R 11 , R 12 and R 13 are carboxymethyl groups (or equivalent salts), and the third group is hydrogen, wherein one of R 14 and R 15 is hydrogen and the other is substituted or unsubstituted carboxymethyl group (or equivalent salts) or 2-carboxyethyl group (or equivalent salts), and R 16 , R 17 , R 18 and R 19 are independently hydrogen, a substituted or unsubstituted alkyl group of 1 to 5 carbon atoms (as defined above), hydroxy, carboxy, carboxymethylamino, or a substituted or unsubstituted carboxymethyl group (or equivalent salts), provided that one and only one of R 16 , R 17 , R 18 and R 19 is carboxy, carboxymethylamino, or a substituted or unsubstituted carboxymethyl group (or equivalent salts), wherein one of R 20 and R 21 is hydrogen and the other is a substituted or unsubstituted alkyl group of 1 to 5 carbon atoms (as defined above), substituted or unsubstituted hydroxyethyl group, substituted or unsubstituted carboxymethyl or 2-carboxyethyl group (or equivalent salts), M is as defined above, and p and q are independently 0, 1 or 2 provided that the sum of p and q does not exceed 2, or wherein Z represents a substituted or unsubstituted aryl group of 6 to 10 carbon atoms in the nucleus (as defined above) or a substituted or unsubstituted heterocyclic group having 5 to 7 carbon, nitrogen, sulfur and oxygen atoms in the nucleus (such as furanyl, thiofuranyl, pyrrolyl, pyrazolyl, triazolyl, dithiolyl, thiazolyl, oxazoyl, pyranyl, pyridyl, piperidinyl, pyrazinyl, triazinyl, oxazinyl, azepinyl, oxepinyl and thiapinyl), L is a divalent substituted or unsubstituted aliphatic linking group (defined below), one of R 22 and R 23 is hydrogen and the other is a substituted or unsubstituted carboxyalkyl group of 2 to 4 carbon atoms (such as substituted or unsubstituted carboxymethyl or carboxyethyl or equivalent salts) or a hydroxy-substituted carboxyalkyl group of 2 to 4 carbon atoms (or equivalent salts), and r is 0 or 1, provided that there are at least two carboxy groups in the molecule. The "divalent substituted or unsubstituted aliphatic linking group" in the definition of "W" and "L" noted above includes any nonaromatic linking group comprised of one or more alkylene, cycloalkylene, oxy, thio, amino or carbonyl groups that form a chain of from 1 to 6 atoms. Examples of such groups include, but are not limited to, alkylene, alkyleneoxyalkylene, alkylenecycloalkylene, alkylenethioalkylene, alkyleneaminoalkylene, alkylenecarbonyloxyalkylene, all of which can be substituted or unsubstituted, linear or branched, and others that would be readily apparent to one skilled in the art. In defining the "substituted or unsubstituted" monovalent and divalent groups for the structures noted above, by "substituted" is meant the presence of one or more substituents on the group, such as an alkyl group of 1 to 5 carbon atoms (linear or branched), hydroxy, carboxy, sulfo, sulfonato, thioalkyl, alkylcarbonamido, alkylcarbamoyl, alkylsulfonamido, alkylsulfamoyl, carbonamido, sulfonamido, sulfamoyl, amino, halo (such as chloro or bromo), sulfono (-SO 2 R) or sulfoxo [-S(O)R] wherein R is a branched or linear alkyl group of 1 to 5 carbon atoms. In reference to the foregoing structures (V)-(IX), preferred definitions of groups are as follows: M is hydrogen, ammonium, lithium, sodium or potassium, R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are independently hydrogen, hydroxy or methyl, W is a covalent bond or a substituted or unsubstituted alkylene group of 1 to 3 carbon atoms, one of R 14 and R 15 is carboxymethyl, R 16 , R 17 , R 18 and R 19 are independently hydrogen, carboxymethyl or carboxy, one of R 20 and R 21 is methyl or carboxymethyl, Z represents 2-pyridyl or 2-imidazolyl, L is substituted or unsubstituted alkylene of 1 to 3 carbon atoms, one of R 22 and R 23 is 2-carboxyethyl or carboxymethyl, and r is 1. More preferred second acidic compounds are N,N-ethylenediaminedisuccinic acid, N,N-ethylenediaminediacetic acid, and N-(2-carboxyethyl)aspartic acid, or salts thereof. Besides those acids specifically defined in the foregoing description, there is considerable literature that describes additional useful second acidic compounds, such as EPA 0 567 126, US-A-5,250,401 and US-A-5,250,402, as long as the compounds have a secondary amino group at a pH of from 8 to 11. The amount of the second acidic compound used in the practice of this invention is at least 0.0005 to 0.05 mol/l. Preferred amounts are from 0.001 to 0.05, mol/l. Mixtures of each type of first or second acidic compound can be used if desired. As used herein, the terms "biodegradable" or "biodegradability" refer to at least 80% decomposition in the standard test protocol specified in by the Organization for Economic Cooperation and Development (OECD), Test Guideline 302B (Paris, 1981), also known as the "Modified Zahn-Wellens Test". The color photographic elements to be processed using the present invention can contain any of the conventional silver halide emulsions. They can be "high chloride" or "low chloride" emulsions, but preferably they are "high chloride" emulsidns. Thus, other emulsions are also useful, including but not limited to, silver bromide, silver iodide, silver bromoiodide, silver chloroiodide, silver chlorobromide, silver bromochloroiodide and silver chlorobromoiodide. By "high chloride" emulsions is meant those having at least 50 mol % of chloride as the halide component of the emulsion grains. More preferably, they contain at least 90 mol % of chloride. "Low chloride" emulsions mean those having less than 30 mol % of chloride, and preferably less than 10 mol % of chloride. The high chloride emulsions contain less than 5 mol % of iodide, and preferably no iodide. In the elements processed according to this invention, the silver coverage can be any suitable amount known in the art, for example, 10 g/m 2 or less. Preferably, the amount is less than 2 g/m 2 , and more preferably, it is less than 0.8 g/m 2 (such as from 0.3 to 0.8 g/m 2 ), especially when "high" silver chloride emulsions are used. The photographic elements processed in the practice of this invention can be single or multilayer color elements. Multilayer color elements typically contain dye image-forming units sensitive to each of the three primary regions of the visible spectrum. Each unit can be comprised of a single emulsion layer or multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element can be arranged in any of the various orders known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer. The elements can also contain other conventional layers such as filter layers, interlayers, subbing layers, overcoats and other layers readily apparent to one skilled in the art. A magnetic backing can be used as well as conventional supports. Considerably more details of the element structure and components, and suitable methods of processing various types of elements are described in Research Disclosure, noted above. All types of emulsions can be used in the elements, including but not limited to, thin tabular grain emulsions, and either positive-working or negative-working emulsions. The elements can be either photographic film or paper elements. The elements are typically exposed to suitable radiation to form a latent image and then processed to form a visible dye image. Processing includes the step of color development in the presence of a color developing agent to reduce developable silver halide and to oxidize the color developing agent. Oxidized color developing agent in turn reacts with a color-forming coupler to yield a dye. Color developers are well known and described in many publications including the Research Disclosure noted above. In addition to color developing agents, the color developer generally contains a buffer (such as potassium carbonate), a sulfite, chelating agents, halides, and one or more antioxidants as preservatives. There are many classes of useful antioxidants including, but not limited to, hydrazines and substituted or unsubstituted hydroxylamines. By substituted hydroxylamines is meant, for example, those having one or more alkyl or aryl groups connected to the nitrogen atom. These alkyl or aryl groups can be further substituted with one or more groups such as sulfo, carboxy, hydroxy, alkoxy, and other groups known in the art which provide solubilizing effects. Examples of such hydroxylamines are described, for example, in US-A-4,876,174, US-A-4,892,804, US-A-5,178,992 and US-A-5,354,646. One particularly useful hydroxylamine is N-isopropyl-N-ethylsulfonic acid hydroxylamine, or a salt thereof. Development can also be carried out using what is known in the art as a "developer/amplifier" solution, as described in US-A-5,324,624. Development is then followed by the use of a bleaching solution as described herein. The bleaching and fixing steps can be carried out in any suitable fashion, as is known in the art. Subsequent to bleaching and fixing, a final washing or stabilizing step may be employed. Color prints and films can be processed using a wide variety of processing protocols, as described for example, in Research Disclosure, noted above, and thus can include various combinations of one or more bleaching, fixing, washing or stabilizing steps in various orders, and lastly, drying. Additionally, reversal processes include additional steps of black and white development, chemical fogging, re-exposure and washing prior to color development. Processing according to the present invention can be carried out using conventional deep tanks holding processing solutions. Alternatively, it can be carried out using what is known in the art as "low volume thin tank" processing systems having either rack and tank or automatic tray designs. Such processing methods and equipment are described, for example, in US-A-5,436,118 and publications noted therein. The following examples are presented to illustrate the practice of this invention, and are not intended to be limiting in any way. Unless otherwise indicated, all percentages are by weight. Examples 1-2: Processing of Color Paper Using Stabilized Bleaching Solutions Two bleaching solutions of this invention were evaluated for bleaching effectiveness according to the present invention. They were also evaluated for storage stability. Several comparison bleaching solutions were similarly evaluated. Samples of EKTACOLOR EDGE™ photographic color paper were subjected to a step wedge test object for 1/10 second with HA-50 and NP-11 filters, a 0.3 Inconel and a 3000K color temperature lamp on a conventional lB-sensitometer. They were then processed using the following protocol (under nitrogen) wherein the bleaching time was varied to determine bleaching effectiveness. 45 seconds Development 30 seconds Stop solution (1% v/v H 2 SO 4 ) 30 seconds Water wash 0-2 minutes Bleaching 30 seconds Water wash 1 minute Fixing 2 minutes Water wash 5 minutes Dry. A Control A bleaching solution contained hydrogen peroxide (0.98 mol/l. 3% w/w), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l) and 1-hydroxyethylidene-1,1-diphosphonic acid (0.004 mol/l), and was adjusted to pH 10 using potassium hydroxide. A Control B bleaching solution contained hydrogen peroxide (0.98 mol/l, 3% w/w), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l) and 2-pyridinecarboxylic acid (0.035 mol/l), and was adjusted to pH 10 using potassium hydroxide. A Control C bleaching solution contained hydrogen peroxide (0.98 mol/l, 3% w/w), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l) and 2,6-pyridinedicarboxylic acid (0.035 mol/l), and was adjusted to pH 10 using potassium hydroxide. A Control D bleaching solution was like Control A except that the phosphonic acid was omitted. An Example 1 bleaching solution contained hydrogen peroxide (0.98 mol/l, 3% w/w), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l), 1-hydroxyethylidene-1,1-diphosphonic acid (0.004 mol/l) and 2-pyridinecarboxylic acid (0.035 mol/l), and was adjusted to pH 10 using potassium hydroxide. An Example 2 bleaching solution contained hydrogen peroxide (0.98 mol/l, 3% w/w), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l), 1-hydroxyethylidene-1,1-diphosphonic acid (0.004 mol/l) and 2,6-pyridinedicarboxylic acid (0.035 mol/l), and was adjusted to pH 10 using potassium hydroxide. FIG. 1 shows stability data for the Controls, Example 1 and Example 2 bleaching solutions. These solutions were stored at room temperature for a number of days. After certain number of days, samples of the solutions were evaluated for the amount of hydrogen peroxide remaining. This evaluation was achieved electroanalytically by cyclic voltammetry using a mercury drop electrode. The electroanalytical data were recorded using a conventional EG&G Princeton Applied Research Potentiostat/Galvanostat, Model 273A. The results were plotted as Relative Peroxide Concentration (%) versus time (days). The data for Controls B, C and D were the same, as shown in FIG. 1. From these data, it is clear that the Control B, C and D bleaching solutions decomposed with a day, and the Control A solution decomposed with a halflife of about 7 days. The Example 1 and 2 solutions of this invention had much improved stability. Example 1 decomposed with a halflife of about 21 days, and Example 2 showed very little decomposition after 50 days at room temperature. Thus, it is clear that the combination of a phosphonic acid with a pyridine-carboxylate provides a synergistic improvement in bleaching solution stability over the use of each compound individually. Residual silver (g/m 2 ) was determined by X-ray fluorescence using conventional procedures. The results are tabulated below in Table I for certain density exposures after 45 seconds. Results are also presented for the use of the conventional KODAK EKTACOLOR™ RA bleach-fixing solution. Step Number RA (g/m 2 ) Control A (g/m 2 ) Control B (g/m 2 ) Control C (g/m 2 ) Example 1 (g/m 2 ) Example 2 (g/m 2 ) 1 0.04 0.03 0.67 0.67 0.01 0.02 3 0.05 0 0.62 0.61 0.03 0.02 5 0.05 0.02 0.60 0.56 0.05 0.02 7 0.03 0 0.49 0.44 0.01 0.01 9 0.03 0 0.26 0.2 0.02 0 11 0 0 0.06 0.04 0.02 0.01 13 0 0.01 0.01 0 0 0 15 0 0 0.01 0 0 0 17 0 0 0.01 0 0.02 0 19 0 0.02 0.02 0.01 0 0.02 21 0 0 0.01 0.02 0.01 0.01 The results indicate that the Control B and C bleaching solutions, containing only a "second" acid did not provide effective bleaching after 45 seconds. The Control A bleaching solution, containing only a "first" acid did provide acceptable bleaching. However, as shown in FIGURE 1, the Control A bleaching solution was not acceptably stable after storage for 14 days at room temperature. The Example 1 and 2 bleaching solutions demonstrated considerably better storage stability over the test period. No vesiculation was observed with use of the present invention. The results also show that use of the present invention provided comparable bleaching to the conventional KODAK EKTACOLOR™ RA bleach-fixing solution after storage for 21 days. Examples 3-5: Processing of Color Paper Using Stabilized Bleaching Solutions Three bleaching solutions of this invention were evaluated for bleaching effectiveness according to the present invention. They were also evaluated for stability. Several comparison bleaching solutions were also evaluated. The bleaching solutions contained hydrogen peroxide (0.98 mol/l), potassium chloride (0.35 mol/l), potassium carbonate (0.025 mol/l), potassium bicarbonate (0.025 mol/l) and the sequestering agents and amounts listed in Table II below, and were adjusted to pH 10 using potassium hydroxide. Sequestering Agent Control E Control F Control G Control H Example 3 Example 4 Example 5 1-hydroxyethylidene-1,1-diphosphonic acid 0.004 mol/l 0.0 0.0 0.0 0.004 mol/l 0.004 mol/l 0.004 mol/l N,N-ethylenediamine disuccinic acid 0.0 0.002 mol/l 0.0 0.0 0.002 mol/l 0.0 0.0 N,N-ethylenediamine diacetic acid 0.0 0.0 0.002 mol/l 0.0 0.0 0.002 mol/l 0.0 N-(2-carboxyethyl)-aspartic acid 0.0 0.0 0.0 0.002 mol/l 0.0 0.0 0.002 mol/l The bleaching solutions described above were evaluated for stability over time. The molar concentration (mol/l) of the peroxide bleaching agent was measured electroanalytically by cyclic voltammetry using a mercury drop electrode. The electroanalytical data were recorded using a conventional EG&G Princeton Applied Research Potentiostat/Galvanostat, Model 273A. The results of these measurements over time are provided in Table III below. Each solution was normalized to 0.98 mol of hydrogen peroxide per liter of solution prior to the first measurement. Bleaching Solution Time (days) Fresh 7 14 21 28 35 Control E 0.98 0.88 0.52 0.16 0 0 Control F 0.98 0 0 0 0 0 Control G 0.98 0 0 0 0 0 Control H 0.98 0 0 0 0 0 Example 3 0.98 0.80 0.76 0.68 0.67 0.58 Example 4 0.98 0.82 0.80 0.59 0.57 0.58 Example 5 0.98 0.79 0.76 0.63 0.59 0.53 It can be seen from the data shown in Table III that the three bleaching solutions of this invention retained considerable bleaching activity after 35 days of storage at room temperature. Controls F-H, containing only a polycarboxylic acid, decomposed within a few hours. Control E having a phosphonic acid only, was more stable than the other controls, but decomposed within 21 days. The bleaching compositions of this invention were also evaluated for bleaching activity after 21 days of storage at room temperature. Samples of KODAK EKTACOLOR EDGE™ photographic color paper were subjected to a step wedge test object for 1/10 second with HA-50 and NP-11 filters, a 0.3 Inconel and a 3000K color temperature lamp on a conventional lB-sensitometer. They were then processed using the following protocol (under nitrogen). 45 seconds Development 30 seconds Stop solution (1% v/v H 2 SO 4 ) 30 seconds Water wash 45 seconds Bleaching 30 seconds Water wash 1 minute Fixing 2 minutes Water wash 5 minutes Dry. Residual silver (g/m 2 ) at maximum density was determined by X-ray fluorescence using conventional procedures. The results are tabulated below in Table IV after 45 seconds for certain exposure densities. Results are also presented for the use of the conventional KODAK EKTACOLOR™ RA bleach-fixing solution, and for the Control E solution, both freshly prepared. Of course, in the use of the KODAK EKTACOLOR™ RA bleach-fixing solution, the noted fixing and preceding wash steps were omitted from the processing protocol. Step Number RA-4 (g/m 2 ) Control E (g/m 2 ) Example 3 (g/m 2 ) Example 4 (g/m 2 ) Example 5 (g/m 2 ) 1 0.05 0 0.02 0.01 0 2 0.03 0.01 0 0.01 0.01 3 0.04 0 0.02 0 0.01 11 0.01 0.01 0.02 0.02 0 18 0.01 0 0.02 0 0 19 0.01 0.04 0.01 0.01 0 20 0 0.01 0.01 0 0 The results indicate that the no decline in bleaching performance was observed with the bleaching compositions of this invention after three weeks of storage. In addition, those compositions also provided more complete bleaching of the noted photographic element than the conventional RA-4 bleach-fixing solution that was used freshly prepared. No vesiculation was observed with any of these bleaching compositions. The results of these experiments indicate that the combination of the two specific acids, a phosphonic acid and a polyaminocarboxylic acid (having at least one secondary amine), in the bleaching composition, provided improved stability and no loss in bleaching performance over the use of the individual acids alone.

Claims: A hydrogen peroxide bleaching solution having a pH of from 7 to 13 and comprising: a hydrogen peroxide bleaching agent, and chloride ions present in an amount of at least 0.35 mol/l, the bleaching solution characterized as further comprising: a) a first acidic compound that is an organic phosphonic acid or a salt thereof, and b) a second acidic compound that is either: a 2-pyridinecarboxylic acid or 2,6-pyridinedicarboxylic acid, or a salt thereof, or an aminopolycarboxylic acid having at least one secondary amine at a pH of from 8 to 11, or a salt thereof. The solution as claimed in claim 1 having a pH of from 8 to 11, and wherein the bleaching agent is hydrogen peroxide. The solution as claimed in either claim 1 or 2 wherein the chloride ion is present in an amount of from 0.45 to 2 mol/l, the first acidic compound is present in an amount of from 0.0005 to 0.03 mol/l, and the second acidic compound is present in an amount of from 0.0005 to 0.05 mol/l. The solution as claimed in any of claims 1 to 3 wherein the organic phosphonic acid or salt thereof has the structure (I): R 1 N(CH 2 PO 3 M 2 ) 2 or the structure (II): R 2 R 3 C(PO 3 M 2 ) 2 wherein R 1 is hydrogen, an alkyl group of 1 to 12 carbon atoms, an alkylaminoalkyl group, an alkoxyalkyl group of 1 to 12 carbon atoms, a cycloalkyl of 5 to 10 carbon atoms, an aryl group of 6 to 10 carbon atoms, or a 5-to 10-membered heterocyclic group, R 2 is hydrogen, an alkyl group of 1 to 12 carbon atoms, an aryl group of 6 to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbon atoms, a 5- to 10-membered heterocyclic group, or -PO 3 M 2 , or -CHR 4 PO 3 M 2 , R 3 is hydrogen, hydroxyl, an alkyl group of 1 to 12 carbon atoms or -PO 3 M 2 , R 4 is hydrogen, hydroxyl, an alkyl group of 1 to 12 carbon atoms or -PO 3 M 2 , and M is hydrogen or a water-soluble monovalent cation. The solution as claimed in any of claims 1 to 4 wherein the second acidic compound has any of the structures: wherein R, R', R" and R''' are independently hydrogen, an alkyl group of 1 to 5 carbon atoms, an aryl group of 6 to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbon atoms, hydroxy, nitro, sulfo, amino, phospho, carboxy, sulfamoyl, sulfonamido or halo, or any two of R, R', R'' and R''' can comprise the carbon atoms necessary to form a 5 to 7-membered ring fused with the pyridinyl nucleus, and M is hydrogen or a monovalent cation, or wherein R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are independently hydrogen, hydroxy, an alkyl group of 1 to 5 carbon atoms, an cycloalkyl group of 5 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms in the aromatic nucleus, M is as defined above, and W is a covalent bond or a divalent aliphatic linking group, wherein at least two of R 11 , R 12 and R 13 are carboxymethyl groups or equivalent salts, and the third group is hydrogen, wherein one of R 14 and R 15 is a carboxymethyl or 2-carboxyethyl group or equivalent salt, and the other is hydrogen, and R 16 , R 17 , R 18 and R 19 are independently hydrogen, an alkyl group of 1 to 5 carbon atoms, hydroxy, carboxymethylamino, carboxy or carboxymethyl, or equivalent salt, provided that one and only one of R 16 , R 17 , R 18 and R 19 is carboxy, carboxymethylamino or carboxymethyl, or equivalent salt, wherein one of R 20 and R 21 is hydrogen, and the other is an alkyl group of 1 to 5 carbon atoms, a hydroxyethyl group, a carboxymethyl group or a 2-carboxyethyl group, or equivalent salt, M is as defined above, and p and q are independently 0, 1 or 2 provided that the sum of p and q does not exceed 2, or wherein Z represents an aryl group of 6 to 10 carbon atoms in the nucleus or a heterocyclic group having 5 to 7 carbon, nitrogen, sulfur and oxygen atoms in the 5 nucleus, L is a divalent aliphatic linking group, one of R 22 and R 23 is hydrogen, and the other is a carboxyalkyl group of 2 to 4 carbon atoms or a hydroxy-substituted carboxyalkyl group of 2 to 4 carbon atoms, or equivalent salt, and r is 0 or 1, provided that there are at least two carboxy groups in the molecule. The solution as claimed in any of claims 1 to 5 wherein the first acidic compound is 1-hydroxyethylidene-1,1-diphosphonic acid, nitrilo-N,N,N-trimethylenephosphonic acid, diethylenetriamine-N,N,N',N",N"-penta(methylenephosphonic acid), or salts thereof, and the second acidic compound is 2-pyridinecarboxylic acid, 2,6-pyridinedicarboxylic acid, N,N-ethylenediaminedisuccinic acid, N,N-ethylenediaminediacetic acid, N-(2-carboxyethyl)aspartic acid, or a salt thereof. A method for processing a color photographic element comprising: bleaching an imagewise exposed and developed color photographic element with a hydrogen bleaching solution as claimed in any of claims 1 to 6. The method as claimed in claim 7 wherein the bleaching solution comprises the chloride ions in an amount of from 0.45 to 1 mol/l. The method as claimed in either claim 7 or 8 wherein the organic phosphonic acid or salt thereof is present in an amount of from 0.0025 to 0.012 mol/l and the second acidic compound is present in an amount of from 0.001 to 0.05 mol/l. The method as claimed in any of claims 7 to 9 wherein the bleaching agent is present in an amount of from 0.15 to 5 mol/l. The method as claimed in any of claims 7 to 10 wherein the photographic element comprises a silver halide emulsion having more than 50 mol % silver chloride and less than 5 mol % of silver iodide. The method as claimed in any of claims 7 to 10 wherein the photographic element comprises a silver halide emulsion having more than 90% silver chloride. The method as claimed in any of claims 7 to 12 carried out in a low volume thin tank processing system. The method as claimed in any of claims 7 to 13 wherein the processing photographic element has less than 0.8 g of silver per m 2 . The method as claimed in any of claims 7 to 14 wherein bleaching with said peroxide bleaching solution is preceded with color development with a developer/amplifier solution. The method as claimed in any of claims 7 to 15 wherein bleaching with said bleaching solution is preceded by color development with a color developer solution comprising N-isopropyl-N-ethylsulfonic acid hydroxylamine or a salt thereof.

Inventors: HAYE SHIRLEYANNE ELIZABETH, REYES MAYRA BEATRIZ, HAYE, SHIRLEYANNE ELIZABETH, REYES, MAYRA BEATRIZ
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1996
Main classification: G03C7
IPC codes: G03C7, C11D7