A method of stabilizing a light-sensitive silver halide color photographic material

Abstract: A method of stabilizing a light-sensitive silver halide color photographic material is disclosed in which the devel­ oped silver halide color photographic material is treated with a solution of a chelating agent following bleaching and fixing and before subsequent washing, if any, bleaching and fixing involving the use of an iron complex salt such that the con­ centration of said iron complex salt in the said solution does not exceed 1 x 10⁻¹ mols per litre.

Description: The present invention relates to a method of stabilizing a dye image formed in a light-sensitive silver halide color photographic material. It is well known that a light-sensitive silver halide color photographic material produces azomethine and indoaniline dyes by color development to form the color image. It is also well known that these dyes discolor under ultraviolet or visible light. Further, their discoloration also occurs even when they are kept in the dark. Particularly, this discoloration is accelerated by high temperature and humidity. This phenomenon of discoloration of the developed color image is a significant weakness in color photography and an improvement is much needed. Various preventive measures have been disclosed for preventing the discoloration of a developed color image in a silver halide color photographic material in the dark or in the light. For example, US Patent No 2 788 274 discloses a process using a zinc salt solution; US Patent No 2 913 338 a process making use of a calcium, magnesium or cadmium salt; and British Patent Nos 909 824 and 1 001 446 a process using a solution containing a monosaccharide, disaccharide or hexitol and a process using a solution containing formaldehyde and polycarboxylic acid, respectively. However, some of these preventive measures give only a slight improvement and others, though effective in preventing discoloration, make use of compounds which soften the gelatin film thus weakening considerably its mechanical strength. To prevent softening of the gelatin layer, formaldehyde has been used in some cases notwithstanding that this compound has a tendency to soil the white border of the print. To prevent the discoloration of the dye picture, chemicals with which the photographic material has been loaded in processing baths must be removed in a washing step which lasts as long as possible using as large a volume of water as possible. For faster processing and labor saving, therefore, such a stabilizing process has only a minor or insignificant effect and is therefore omitted in some cases. Further, for the same purpose and also for the alleviation of environmental pollution and a reduction in processing costs, it is general practice to perform processes in individual processing solutions at high temperature, reduced washing time, and/or use a reduced volume of water for washing, which makes the stabilization of dye images less effective. A stabilizing process that includes no washing step is disclosed in, for example, US Patent No 3 335 004. This is a silver stabilizing process making use of a thiocyanate salt whose stabilizing bath contains a large quantity of sulfite salts, so that image dyes are readily reduced to their leuco form, influencing the color photographic image significantly as regards its deterioration. Further, at the low pH which is used for such a stabilizing bath, there is a danger of generating sulfurous acid gas. Accordingly, this process is not satisfactory. A conventional stabilizing process of a color image thus fails to achieve the stabilization of a photographic image for a long period of time while simultaneously speeding up the process time, labor saving, alleviating environmental pollution and reducing the volume of washing water. After a variety of investigations to prevent the discoloration of a developed color image in the dark or in the light, we have found a solution. According to the present invention there is provided a method of processing a light-sensitive silver halide color photographic material involving bleaching and fixing wherein an iron complex salt is used as a blending agent characterised in that to stabilise the material against dye image fading in the dark, it is treated with a solution of a chelating agent (hereinafter referred to as the "stabilising solution") directly following bleaching and fixing or bleach-fixing as the final stage of the method prior to drying without intermediate washing such that the iron complex salt is present in the solution in an amount which does not exceed 1 × 10⁻¹ mols per litre and, when a multi-tank stabilising bath is used for the said solution, the iron complex salt is present in the last tank in an amount which does not exceed 1 × 10⁻¹ mols per litre. The soluble iron salts to be used in the present invention are various complex salts of divalent or trivalent iron ions. Compounds supplying these iron ions are, for example, ferric chloride, ferric sulfate, ferric nitrate, ferrous chloride, ferrous sulfate and ferrous nitrate, carboxylic acid iron salts including ferric acetate and ferric citrate, and various iron complex salts. Examples of the compounds that can react with these iron ions to form complex salts are expressed by the following general formulae [I] through [XI]. M m P m O 3m Formula [I] M n+2 P n O 3n+1 Formula [II] In the formulae [I] [II], M: Hydrogen, alkali metal, or ammonium; m: Integer from 3 to 6 n: Integer from 2 to 20 B-A₁-Z-A₂-C Formula [III] In the formulas [III] and [IV], A₁ to A₆ individually represent substituted or unsubstituted alkylene groups, Z an alkylene group, a cyclo alkylene group, a phenylene group, -R-O-R, -ROROR- (R = alkyl group), or >N-A₇ [A₇ = hydrogen, hydrocarbon (preferably C₁-C₁₂ alkyl group), C₁-C₄ aliphatic carboxylate, C₁-C₄ hydroxyalkyl], and B, C, D, E, F, and G individually an -OH group, -COOM group, or -PO₃M₂ (M = hydrogen, alkali metal, or ammonium). where R₁: -COOM, -PO(OM)₂; R₂: Hydrogen, alkyl group (preferably C₁ to C₄ alkyl group), -(CH₂) n COOM, or phenyl group; R 3: Hydrogen, -COOM; M: Hydrogen, alkali metal, or ammonium; m: 0 or 1; and n: from 1 to 4 q: 0 or 1 R₄N(CH₂PO₃M₂)₂ Formula [VI] where R₄: an alkyl, preferably lower alkyl, group, aryl group, aralkyl group, or nitrogen-containing 6-membered heterocyclic group [optionally substituted by, e.g., -OH, -OR₅ (R₅ = alkyl group of C₁ to C₄), -PO₃M₂, -CH₂PO₃M₂, -N(CH₂PO₃M₂)₂, -COOM, and/or -N(CH₂COOM)₂]; and M: Hydrogen, alkali metal or ammonium where R₆, R₇, R₈ independently represent: Hydrogen, an alkyl, preferably lower alkyl, group, -OH, a hydroxyalkyl group, PO₃M₂ or -NJ₂ (J = H, OH, alkyl group (preferably C₁-C₄), or -C₂H₄OH, -PO₃M₂); X, Y, and Z independently represent: -OH, -COOM, -PO₃M₂, or H; M: Hydrogen, alkali metal, or ammonium; and n, q independently represent: 0 or 1 where M, R₉, R₁₀ independently represent: Hydrogen, alkali metal, ammonium, an alkyl group, preferably C₁ to C₁₂, an alkenyl group, or alicyclic group where R₁₁: Alkyl group, preferably C₁ to C₁₂, alkoxy group, preferably C₁ to C₁₂, monoalkylamino group, preferably C₁ to C₁₂, dialkylamino group, preferably C₂ to C₁₂, amino group, aryloxy group, preferably C₆ to C 24, allylamino group or amyloxy group, preferably C₆ to C₂₄; and Q₁ to Q₃ independently represent: -OH, alkoxy group, preferably C₁ to C₂₄, aralkyloxy group, aryloxy group, -OM₃ (M₃ = a cation such as alkali metal or ammonium), amino group, cyclic amino group, e.g. a morpholino group, alkylamino group, dialkylamino group, allylamino group, or alkyloxy group. Beside compounds expressed by the general formulas [I] to [XI], citric acid and glycine, for example, may be cited though the former compounds are generally superior. Specific examples of the compounds as expressed by the formulas [I] through [XI] are: (1) Na₄P₄O₁₂ (2) Na₃P₃O₉ (3) H₄P₂O₇ (4) H₅P₃O₁₀ (5) Na₆P₄O₁₃ (15) (HOC₂H₄)₂NCH₂COOH The concentration of iron salt in the stabilizing bath should not exceed 1 × 10⁻¹ mol/l. For a continuous stabilizing process using a stabilizing bath comprising a number of successive tanks for treatment in countercurrent with a replenishing solution added to the last tank, the maximum amount of the above soluble iron salt is determined with reference to the concentration of the last tank. The stabilizing solution (or stabilizing bath) of the present invention has a pH.of 3.0 to 9.0. Below pH 3.0 or above 9.0, the effect in preventing the discoloration of dyes is reduced. In the present invention, therefore, the pH is preferably adjusted to 4.5 to 8.5 and more preferably to 6.0 to 8.0. To the stabilizing solution are preferably added buffer agents for a buffering action. For such buffer agents, acetic acid, sodium acetate, boric acid, phosphoric acid or sodium hydroxide, for example, are preferably used, though such iron complex forming agents as mentioned above may be used in excess of the iron ions for a buffering action. According to the present invention, the discoloration of the color picture can be avoided without softening the gelatin film. Further, in the present invention, the stabilizing treatment improves the stability of the dye picture substantially even when a foreign chemical or chemicals are retained in trace amounts in the photographic material. In the prior art, a compound such as ethylenediaminetetraacetic acid ferric complex salt used as a bleaching agent in color processing has to be thoroughly washed out in the washing step but we have found, rather unexpectedly, that the presence of soluble iron ions with the chelating agent contributes to the stabilization of the dye picture. It will be appreciated that the soluble iron salt present in the bleach-fix or fix bath is automatically brought in by the photographic material to the stabilizing solution. It has been found that in the presence of a soluble iron salt other chemical ingredients, for example thiosulfate and sulfite salts, are effectively neutral in the discoloration of the dye picture provided their concentration is below a certain critical level, resulting in higher stability of the dye picture. To reduce the concentration of these chemical ingredients down to a desirable level, it is preferable to perform the stabilisation in a stabilizing bath comprising a plurality of tanks using a replenishing solution in countercurrent. The stabilizing process of the present invention is performed at the final stage of the color processing. The stabilizing bath may comprise a single tank. For the reasons mentioned above, however, the stabilizing bath of the present invention preferably comprises a plurality of tanks for a multi-bath process. Further, the number of tanks used to achieve the desired results is closely dependent on the relation between the amount brought in with the photographic material from the processing bath containing the organic acid ferric complex salt and the volume of replenishing solution added. Namely, the smaller the ratio of the volume of replenishing solution added to the amount brought in, the larger the number of tanks required, and vice versa. Though, generally, the number of tanks also depends on the concentration of the bath containing the organic acid ferric complex salt, if the volume of replenishing solution used is about three to five times as great as the volume brought in, two to eight tanks are preferably used for the stabilization; if, however, the volume ratio is fifty, preferably two to four tanks are used for the stabilization to achieve the desired results. For the stabilizing bath of the present invention, a generally buffered solution whose pH is 3.0 to 9.0 is used; various buffer agents can be used. Specific examples of such buffer agents are borate, metaborate, borax, monocarboxylate, dicarboxylate, polycarboxylate, hydroxycarboxylate, amino acid, aminocarboxylate, monobasic, dibasic and tribasic phosphate, sodium hydroxide and potassium hydroxide. Various chelating agents can be added. Examples of such chelating agents are aminopolycarboxylate, aminopolyphosphonic acid, phosphonocarboxylic acid, alkylidenediphosphonic acid, polyphosphate, pyrophosphoric acid, metaphosphoric acid, and gluconate. The use of 1-hydroxyethylidene-1,1-diphosphonic acid is particularly preferred. Commonly known additives can be included in the stabilizing bath, for example fluorescent whitening dye, surfactant, bactericide, antiseptic, organic sulfur compound, onium salt, formalin, hardening agent such as aluminium or chromium, and various metal salts. These materials can be added in any combination and quantities provided the pH of the stabilizing bath can be maintained in the specified range; the stability of the photographic picture during storage is generally not affected adversely, and there is no precipitation in the bath. Beside the chelating agent, compounds preferably added to the stabilizing bath of the present invention are buffer agents such as acetic acid and sodium acetate, bactericides such as 5-chloro-2-methyl-4-isothiazolin-3-on, 1-2-benzisothiazolin-3-on and thiabenzazole, a trace of formaldehyde, hardening agents such as aluminium salt and magnesium salt, fluorescent whitening dye etc. However, since the processing method of the present invention can achieve efficient stabilization of the dye picture and save the washing step, the above additive compounds are preferably added at a more dilute concentration to avoid environmental pollution and to reduce processing costs, provided they are added in an amount to endow the solution with a satisfactory buffering capacity. The temperature for the stabilization is suitably 15 to 60°C, and preferably 20 to 45°C. The stabilization time is preferably set short from the viewpoint of quick processing, which is normally from 20 s to 10 min, and most preferably 1 to 5 min. In the case of a multi-tank stabilization system, preferably the earlier the position of a tank, the shorter the treatment time therein and vice versa. Specifically, it is preferred for the treatment time in successive tanks to increase 20 to 50% as compared to the previous tank. In this way, the processing method of the present invention can also be applied to color paper, color reversal paper, color positive film, color negative film, color reversal film and color X-ray film, for example. If the stabilizing bath of the present invention contains soluble silver salts, silver can be recovered from the bath by the technique of ion exchange, metal substitution, electrolysis or silver sulfide precipitation, for example. To further illustrate the invention, the following Example is given: Example 1 After picture printing, a roll of Sakura color paper (manufacturer: Konishiroku Photo Industry Co., Ltd.) was processed by an automatic developing machine for color processing with continuous replenishment. The processes and the formulation of the processing solutions used were as follows: Standard processes: Formulation of processing solution: [Color development tank's solution] [Color development replenishing solution] [Bleach-fix tank's solution] [Bleach-fix replenishing solution A] [Bleach-fix replenishing solution B] The automatic developing machine was filled with the color development tank's solution and bleach-fix tank's solution as formulated above, and a stabilizing solution as formulated below. While processing the color paper, the above color development replenishing solution and bleach-fix replenishing solutions A and B, and stabilizing replenishing solution were added at intervals of 3 min using a measuring cup, to conduct a running test. The color development tank was replenished at a rate of 324 ml of replenishing solution/m² of color paper, and the bleach-fix tank at a rate of 25 ml of each replenishing solution/m² of color paper. For stabilization, the stabilizing bath of the automatic developing machine was modified so it might comprise either a single tank or three or six tanks for a continuous process. When the stabilizing bath of the automatic developing machine comprised a plurality of tanks, the first through, say, sixth tanks, in the direction of movement of the photographic material and a multi-tank countercurrent system in which the loss of solution was made up for at the last tank with the overflow from one tank added to the tank before it was used. Stabilization in the solution formulated below was continued after the continuous processing until the volume of bleach-fix replenishing solutions A and B added totalled three times (taken together) the volume of the bleach-fix bath. The first tank of the stabilizing bath was checked for any sign of precipitation, while the red mid-density (D = 1.5) was measured for the test samples obtained by the running processing. The samples were left to stand at 80°C and 80 RH% for sixty days and the measurements for the red mid-density were repeated. Table 5 shows the results. It is noted that 50 ml of bleach-fix solution was brought into the stabilizing bath with each square meter of color paper. Stabilizing solution (and stabilizing solution replenisher) As can be seen from the above table, in washing of the control sample (1), a slight precipitation in the first tank was detected with the appearance of algae at the tank walls, in spite of the very large volume of water used for replenishment, resulting in significant contamination of the color paper in some cases. Further, in the sample storage test, a large drop in red mid-density was detected in this case. By contrast, with the samples (2) through (9) that were stabilized according to the present invention, there was no precipitation in the stabilizing tank and the red mid-density showed a smaller drop in the storage test. Even in the stabilization of the present invention, however, if the volume of replenishing solution used is less than hundred times the volume of bleach-fixing solution brought in with the photographic material, the effect in preventing the red discoloration is limited, to some extent, when using a single tank stabilizing bath bath; this is probably because there is not enough dilution of the ingredients other than the ferric complex salt brought in from the bleach-fix solution. Thus, it is found that when the method of stabilizing the dye picture in the stabilizing solution of the present invention is used and the fixing or bleach-fixing process is directly followed by the stabilizing process, a more remarkable effect in preventing the discoloration of the dye picture can be achieved by using a stabilizing bath comprising a plurality of tanks and by making the solution overflow one tank to the next countercurrent, with the loss of solution made up at the last tank stage in the direction of the photosensitive material. It is noted that for the three tank bath used for the stabilization of samples (7) and (8) of present example, the dip time was set at 20, 40 s and 2 min for the first, second and third tank, respectively, while for the six tank bath used for the stabilization of samples (9) and (10), the time was set to 10 s for the first two tanks, and 20, 30 50 s and 1 min for the third, fourth, fifth and sixth tank, respectively.

Claims: A method of processing a light-sensitive silver halide color photographic material involving bleaching and fixing, wherein an iron complex salt is used as a bleaching agent characterised in that, to stabilise the material against dye image fading in the dark, it is treated with a solution of a chelating agent directly following bleaching and fixing, or bleach-fixing, as the final stage of the method prior to drying without intermediate washing such that the iron complex salt is present in the solution in an amount which does not exceed 1 x 10⁻¹ mols per litre and, when a multi-tank stabilising bath is used for the said solution, the iron complex salt is present in the last tank in an amount which does not exceed 1 x 10⁻¹ mols per litre. A method according to claim 1 which is carried out continuously and in which following bleaching and fixing, or bleach-fixing, the developed silver halide color photographic material is brought into contact with a stabilizing solution, the chelating agent being added to said solution with replenisher therefor. A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formula: M m P m O 3m (I) or M n+2 P n O 3n+1 (II) wherein M represents a hydrogen atom, an alkali metal or an ammonium ion; m represents an integer from 3 to 6; and n represents an integer from 2 to 20. A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formulae: B-A₁-Z-A₂-C (III) or wherein A₁ to A₆ each independently represent a substituted or unsubstituted alkyl group; Z represents an alkylene group, a cycloalkylene group or phenylene group, -R-O-R or -ROROR- (wherein R represents an alkyl group) or >N-A₇ (wherein A₇ represents a hydrogen atom or a hydrocarbon, carboxy C₁-C₄ aliphatic or C₁-C₄ hydroxy alkyl radical); and B, C, D, E, F and G each independently represents an -OH group, -COOM group, or -PO₃M₂ (wherein M represents a hydrogen atom, an alkali metal or an ammonium ion). A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formula: wherein R₁ represents -COOM or -PO(OM)₂; R₂ represents a hydrogen atom, an alkyl group, -(CH₂) n COOM or a phenyl group; R₃ represents a hydrogen atom or -COOM; M represents a hydrogen atom, an alkali metal, or an ammonium ion; m and q are independently 0 or 1; and n represents an integer from 1 to 4. A method according to claim 1 or 2 in which the soluble iron salt is a complex salt of an iron ion and a compound represented by the formula: R₄N(CH₂PO₃M₂)₂ (VI) wherein R₄ represents an alkyl group, an aryl group, an aralkyl group or a nitrogen-containing 6-membered heterocyclic group optionally substituted by -OH, -OR₅, -PO₃M₂, -CH₂PO₃M₂, -N(CH₂PO₃M₂)₂, -COOM and/or -N(CH₂COOM)₂ wherein R₅ is a C₁-C₄ alkyl group; and M represents a hydrogen atom, an alkali metal or an ammonium ion. A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formula: wherein R₆, R₇ and R₈ each independently represents a hydrogen atom, an alkyl group, -OH, a hydroxyalkyl group, PO₃M₂, -NJ₂ (wherein J represents a hydrogen atom, -OH, an alkyl group,-C₂H₄OH or -PO₃M₂); X, Y and Z each independently represents -OH, -COOM, -PO₃M₂ or a hydrogen atom; M represents a hydrogen atom, an alkali metal or an ammonium ion; and n and q are independently 0 or 1. A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formula: wherein M, R₉ and R₁₀ each independently represents a hydrogen atom, an alkali metal, an ammonium ion, an alkyl group, an alkenyl group, or an alicyclic group. A method according to claim 1 or 2 in which the soluble iron complex salt is a complex salt of an iron ion and a compound represented by the formula: wherein R₁₁ represents an alkyl group, an alkoxy group, a monoalkylamino group, a dialkylamino group, an amino group, an aryloxy group, an allylamino group or an amyloxy group; and Q₁ through Q₃ each independently represents -OH, an alkoxy group, an aralkyloxy group, an aryloxy group, -OM₃ wherein M₃ represents a cation, an amino group, a cyclic amino group, an alkylamino group, a dialkylamino group, an allylamino group or an alkoxy group. A method according to any one of the preceding claims in which the chelating agent is an aminopoly carboxylate, aminopoly phosphonic acid, phosphono carboxylic acid, alkylidenediphosphonic acid, polyphosphate, pyrophosphoric acid, metaphosphoric acid or gluconate. A method according to claim 10 in which the chelating agent is 1-hydroxyethylidene-1,1-diphosphonic acid. A method according to any one of the preceding claims in which the iron complex salt is present in a bleach fix bath. A method according to any one of the preceding claims in which thiosulfate is also present in the said solution.

Inventors: KOBOSHI SHIGEHARU, KUREMATSU MASAYUKI, KOBOSHI, SHIGEHARU, KUREMATSU, MASAYUKI
Applicants: KONISHIROKU PHOTO IND, KONICA CORPORATION
Application year: 1985
Main classification: G03C11
IPC codes: G03C7, G03C11