Composition for developing an exposed photographic product having improved biodegradability

Abstract

 The present invention concerns a novel composition for developing silver halide photographic products having improved biodegradability.
The composition of the invention comprises at least one metal ions capable of reducing silver ions and at least one organic complexing agent of formula:


wherein R₁ and R₂ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, M is hydrogen or a counter-ion, p and q are 1, and n is greater than or equal to 2, and preferably between 2 and 5.
Such a developing composition makes it possible effectively to process a large number of exposed photographic products and has improved biodegradability.

Description

[0001] The present invention concerns a novel composition for developing silver halide photographic products having improved biodegradability. In particular, the invention concerns a rapid-access developing solution for the development of exposed silver halide grains, which contains an organometallic complex as a developing agent.

[0002] In conventional processing methods, the silver halide grains carrying a latent image formed by exposure are developed by immersing the exposed photographic product in an alkaline solution containing a reducing developing agent. The developing agent is an organic compound selected from the di- and polyhydroxybenzenes, aminophenols and reductones. The dihydroxybenzenes which are used most often are for example hydroquinone and its derivatives, and catechol and its derivatives. Examples of aminophenols comprise 4-amino-1-hydroxybenzene and its derivatives. The most important reductones include ascorbic acid, D-isoascorbic acid and their derivatives and salts. These organic developing agents can in practice be used along with an auxiliary developing agent such as phenidones or Elon®.

[0003] Patent application DE 4 209 347 describes a developer containing a conventional developing agent such as a phenol, aminophenol or pyrazolidone and a biodegradable water- softening agent which acts as a sequestering agent for the magnesium or calcium ions contained in the water. In this patent application, provision is made for replacing EDTA, already known as a complexing agent but which is only slightly biodegradable, with nitrilotriacetic acid, which is biodegradable.

[0004] It is also known that inorganic developers containing as a developing agent, a metal capable of reducing the silver ions into metallic silver can be used.

[0005] The activity of these developing agents can be improved by the presence of a complexing agent able to form complexes with the metallic ion of higher valency. By thus eliminating the oxidised form of the metallic ion as it is formed, the thermodynamic force of the reduction of the silver and the corresponding oxidation of the metallic ions is maintained. According to T H James, Photo. Sci.& Eng., Vol 4, No 5, 1960, pages 271-280, these organometallic complexes can be used to develop different types of silver halides and within a wide pH range. The mechanism of such a development was described by H J Price in Journal of Photographic Science and Engineering, 14(6), 391-396, 1970 and 19(5), 283-287, 1975.

[0006] French patent 1 068 805 describes the use of complexes of iron (II) and titanium (III) with particular aliphatic aminopolycarboxylic acids, and the salts of these acids, in order to develop exposed silver halide photographic products. The described aminopolycarboxylic acids are characterised in that the amino group or groups comprise at most one hydrogen atom bonded directly to the nitrogen atom. The aminopolycarboxylic acids cited are ethylenediamine tetraacetic acid (EDTA), methylenediamine tetraacetic acid, nitrilotriacetic acid (NTA) and diethylenetriamino diacetic acid. These acids are in particular complexed with iron (II) and titanium (III).

[0007] US patent 3 982 945 describes a composition for developing exposed photographic products which contain, as a developing agent, a metallic complex consisting of a metal capable of changing valency. In particular, the developing composition contains a complex of iron (II), and an aliphatic aminocarboxylic acid substituted by at least one hydroxyl group. The presence of a hydroxyl substituent on the aminocarboxylic acid makes it possible to improve the efficiency of the development compared with the same aminocarboxylic acid which is not substituted by a hydroxyl group.

[0008] Japanese patent application JP-55-146448 describes a developer which contains, as a developing agent, a trivalent titanium complex which has reducing properties, either intrinsically or after exposure to light. In this application, the titanium is complexed by means of a hydroxycarboxylic acid having 1 or 2 hydroxyl groups and 1 to 3 carboxylic groups. The titanium complexed by means of such an acid appears much more stable than the titanium complex obtained from ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine pentacetic acid (DTPA).

[0009] US patent 5 310 631 describes a composition for developing, after exposure, photographic products consisting of silver halide emulsions sensitised with selenium. The developing composition contains, as a developing agent, a metallic complex consisting of a metal capable of changing valency. In particular, the developing composition contains a complex of iron (II) or titanium (III) with a polyaminocarboxylic acid such as EDTA or DTPA or their salts.

[0010] If the conventional organic developers (derived from hydroquinone) are compared with inorganic developers containing a metallic complex as the developing agent, it appears that the metallic developers may have certain advantages. They may for example be more easily soluble in water, and they may be usable within a wider pH range, which makes it possible to use less alkaline processing baths. In addition, these metallic complexes form completely reversible redox systems, which makes it possible easily to determine and control the redox potential of the developing bath and easily to regenerate the oxidised form of the metallic complex into its initial reducing form simply by reduction of the processing bath.

[0011] The possibility of regenerating this type of developing bath makes it possible to obtain ecological processing by reducing the amount of replenishment of the baths and minimising the volume of effluent.

[0012] However, as is shown by the prior art set out above, metallic developers necessarily contain an organic complexing agent which is, in the majority of cases, EDTA. This complexing agent is particularly effective but has low biodegradability.

[0013] The object of the present invention is an inorganic photographic developing composition. Such a developing composition makes it possible to process effectively a large number of exposed photographic products and has improved biodegradability.

[0014] The inorganic developing composition of the present invention comprises at least one metal ions capable of reducing silver ions and at least one first organic complexing agent of formula:

wherein R₁ and R₂ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, M is hydrogen or a counter-ion, p and q are 1 and n is greater than or equal to 2, and preferably between 2 and 5.

[0015] This invention also provides a method of processing a silver halide photographic product comprising :
   exposing the photographic product to form a latent image, and developing the latent image with the developing composition described above.

[0016] The metal ions capable of reducing silver ions which are useful as a developing agent are for example titanium(III), iron(II), vanadium(II) and chromium(II), and preferably titanium(III), which is the least toxic of the aforesaid metals.

[0017] The quantity of complexing agent is at least equimolar to the quantity of metal ions capable of reducing silver ions contained in the developing composition. In general, it is preferred to work with developing compositions in which the quantity of complexing agent is greater than the quantity of metal ions capable of reducing silver ions.

[0018] In the organometallic developing compositions, the quantity of metal ions capable of reducing silver ions is in general between 0.05 M and the solubility limit of the metal ions in the developing composition (at the temperature of use of the composition), preferably between about 0.1 and 0.5 mol/l.

[0019] According to the invention, the quantity of metal ions capable of reducing silver ions and of complexing agents is such that the molar ratio Metal ions:Complexing agent is between 1:1 and 1:10, and preferably between 1:2 and 1:4.

[0020] According to the present invention, the alkyl groups include straight or branched chain, substituted or not. The counter-ions can be for example lithium, sodium or potassium ions.

[0021] According to one embodiment of the invention, the complexing agent is β-alanine diacetic acid of formula:

[0022] According to the invention, the developing composition may also comprise a second polycarboxylic or aminopolycarboxylic complexing agent different from the first complexing agent.

[0023] The second complexing agent can be nitrilotriacetic acid (NTA), an aminopolycarboxylic acid such as methylene iminodiacetic acid (MIDA), iminodiacetic acid (IDA) or (acetamido)iminodiacetic acid (AIDA), an acid having a heterocyclic ring such as pyridine-2-carboxylic acid (PCA) or pyridine-2,6-carboxylic acid (PDCA), a polycarboxylic acid substituted by one or more hydroxyl groups selected from citric acid, tricarballylic acid, tartaric acid, gluconic acid and finally a dicarboxylic aliphatic acid selected from malonic, succinic and glutaric acids. gluconic acid and finally a dicarboxylic aliphatic acid selected from malonic, succinic and glutaric acids.

HOOC-CHOH-CHOH-COOH

Tartaric acid

HOOC-CH₂-C(OH)(COOH)-CH₂-COOH

Citric acid

HOOC-CH₂-CH₂-CH₂-COOH

Glutaric acid

HOCH₂-(CHOH)₄-COOH

Gluconic acid

HOOC-CH₂-COOH

Malonic acid

HOOC-(CH₂)₂-COOH

Succinic acid

HOOC-CH₂-CH(COOH)-CH₂COOH

Tricarballylic acid

[0024] The useful second complexing agents are preferably at least partly biodegradable, do not pose any problems with regard to environment, do not pose any toxicity or safety problem and do not impair the photographic performance of the developing compositions nor the capacity of the latter for being regenerated. Preferably, they do not form any insoluble salts or precipitates when the developing composition is prepared, stored or exposed to air.

[0025] According to one embodiment, the developing composition contains a mixture of the first and second complexing agents, ADA and NTA in which the ADA/NTA molar ratio is less than or equal to 1:1.

[0026] Within the scope of the present invention, the activity of the developing solution can be maintained by regenerating the used composition by electrolytic reduction, which makes the process of the present invention particularly ecological.

[0027] In addition to the compounds described above, the developing composition may contain development inhibitors such as potassium bromide, organic anti-fogging agents capable of reducing fogging whilst keeping the discrimination equal or increasing it, a solvent for silver halides, a fixing solution, preservatives such as bisulphites, and development accelerators such as ammonium compounds.

[0028] Although the activity of the inorganic developing compositions is relatively independent of the pH conditions, it is preferred to use inorganic developing compositions which have a pH below 7 and preferably between 3 and 6.

[0029] The photographic products which can be processed by means of the inorganic composition of the invention may comprise light-sensitive emulsions consisting of silver bromide, silver chloride, silver bromoiodide, silver chlorobromide, silver chloroiodide or silver chlorobromoiodide.

[0030] These emulsions can be sensitised in accordance with the various methods described in Research Disclosure, December 1989, No 308119, published by Kenneth Mason Publications Ltd, Emsworth, Hampshire PO10 7DQ, England (hereinafter referred to as Research Disclosure), Section IV.

[0031] As used herein, the term "about" refers to a variance of ± 10% of the indicated value.

[0032] The composition of the invention can be used for developing black and white films or photographic papers or for the black and white development stage in the processing of reversal colour films or photographic papers.

[0033] The following examples are used to illustrate the practice of this invention, but not to be limiting in any way.

EXAMPLE 1 (Comparative)

[0034] A film for medical X-ray is exposed using a sensitometer equipped with a lamp having a colour temperature of 2850°K for 1/50 second. The sensitometer is fitted with a Kodak filter simulating the emission of a green screen. The X-ray film exposed in this way is given a processing which comprises a development stage at ambient temperature (3 min), a fixing stage (2 min) and a water washing stage (5 min).

[0035] The developing composition comprises the following compounds:

• Ti(III) (0.20 mol/l) from TiCl₃
• EDTA (0.4 mol/l)
• Anti-fogging agent (35 mg/l)
• KBr (6 g/l).

[0036] The pH of the composition is 5.

[0037] The fixing bath is the RP X-OMAT® fixer.

[0038] The film is evaluated using a Macbeth® TD 903 densitometer.

[0039] For each sample developed, the minimum density (Dmin) and maximum density (Dmax) are measured and the discrimination (Δ), which is equal to (Dmax - Dmin)*100, is determined.

[0040] The sensitometric results are set out in Table 1.

EXAMPLE 2

[0041] The same film for medical X-ray is exposed, developed and evaluated in accordance with the method of Example 1. In this example, the developing composition contains the following compounds:

• Ti(III) (0.15 mol/l) from TiCl₃
• ADA (0.6 mol/l)
• Anti-fogging agent (45 mg/l)
• KBr (6 g/l).

[0042] The pH of the composition is 4.

[0043] The fixing bath is identical to the one described above.

[0044] The sensitometric results are set out in Table 1.

EXAMPLE 3

[0045] The same film for medical X-ray is exposed, developed and evaluated in accordance with the method of Example 1. In this example, the developing composition contains the following compounds:

• Ti(III) (0.20 mol/l) from TiCl₃
• ADA (0.8 mol/l)
• Anti-fogging agent (45 mg/l)
• KBr (6 g/l).

[0046] The pH of the composition is 4.

[0047] The fixing bath is identical to the one described above.

[0048] The sensitometric results are set out in Table 1.

EXAMPLE 4

[0049] The same film for medical X-ray is exposed, developed and evaluated in accordance with the method of Example 1. In this example, the developing composition contains:

• Ti(III) (0.15 mol/l) from TiCl₃
• ADA (0.3 mol/l)
• NTA (0.3 mol/l)
• Anti-fogging agent (45 mg/l)
• KBr (6 g/l).

[0050] The pH of the composition is 4.

[0051] The fixing bath is identical to the one described above.

[0052] The sensitometric results are set out in Table 1.

EXAMPLE 5

[0053] The same film for medical X-ray is exposed, developed and evaluated in accordance with the method of Example 1. In this example, the development composition contains:

• Ti(III) (0.15 mol/l) from TiCl₃
• NTA (0.6 mol/l)
• Anti-fogging agent (35 mg/l)
• KBr (6 g/l).

[0054] The pH of the composition is 4.

[0055] The fixing bath is identical to the one described above. In this example, the appearance of a white precipitate was observed when the development bath was put in an open tank.

[0056] The sensitometric results are set out in Table 1.

TABLE 1

	Δ
EX. 1	332
EX. 2	348
EX. 3	383
EX. 4	371
EX. 5	327

[0057] The sensitometric results which are expressed by means of Δ show that the composition of the present invention makes it possible to obtain a discrimination which is greater than that of the development composition containing EDTA.

EXAMPLE 6

[0058] In this example, the Dmin, Dmax and discrimination obtained with a developing composition as described in Example 4 are determined, before and after subjecting this composition to bubbling through with oxygen.

[0059] Within the scope of the present invention, electrolysis was carried out, using 4 dm² stainless steel electrodes and an ESC7000® (Electrosynthesis Company) selective membrane with an intensity of 5 A. The nature of the electrodes and of the selective membrane is not limited to that of Example 6. The electrolysis conditions are also open to many variants, accessible to a person skilled in the art, depending on the application envisaged and without departing from the spirit of the invention.

[0060] The sensitometric results are set out in the Table below.

TABLE 2

	Δ
EX. 6A	339	After bubbling
EX. 6B	358	After 2 hours of regeneration

[0061] The treatment by electrolysis of the developing composition makes it possible to restore a satisfactory discrimination, preferably equal to or greater than that produced by the freshly prepared composition.

Claims

1. An inorganic photographic developing composition comprising at least one metal ions capable of reducing silver ions and a first organic complexing agent of formula:

wherein R₁ and R₂ are each independently a hydrogen atom or a C₁-C₁₀ alkyl group, M is hydrogen or a counter-ion , p and q are 1, and n is greater than or equal to 2.

2. The composition according to Claim 1, wherein said complexing agent is

3. The composition of Claim 1 wherein said metal ions capable of reducing silver ions is titanium(III), iron(II), vanadium(II) or chromium(II).

4. The composition of Claim 1, further comprising a second complexing agent selected from nitrilotriacetic acid (NTA), an aminopolycarboxylic acid such as methylene iminodiacetic acid (MIDA), iminodiacetic acid (IDA) or (acetamido)iminodiacetic acid (AIDA), and acid having a heterocyclic ring such as pyridine-2-carboxylic acid (PCA) or pyridine-2,6-carboxylic acid (PDCA), a polycarboxylic acid substituted by one or more hydroxyl groups selected from citric acid, tricarballylic acid, tartaric acid, gluconic acid, or a dicarboxylic aliphatic acid selected from malonic, succinic and glutaric acids.

5. The composition of Claim 1 wherein the molar ratio of metal ions capable of reducing silver ions to complexing agents is between about 1:2 and 1:4.

6. The composition of Claim 4 wherein the molar ratio of said first complexing agent to said second complexing agent is less than or equal to about 1:1.

7. The composition of claim 1 wherein said metal ions capable of reducing silver ions is titanium (III) present at from about 0.05 to about 0.5 mol/l.

8. The composition of claim 4 wherein said first complexing agent is ADA and said second complexing agent is NTA at a molar ratio of less than or equal to about 1:1.

9. The composition of claim 1 wherein pH of the composition is below 7.

10. The composition of claim 1 wherein n is 2 to 5.

11. A method of processing a silver halide photographic product comprising :
exposing a photographic product to form a latent image, and developing the latent image with an inorganic developing composition, said inorganic developing composition being such as defined in any of claims 1 to 10.