STABILISERS FOR RX DEVELOPERS

Abstract: The invention provides a redox amplification colour development composition comprising an oxidising agent and a colour developing component; the composition comprising a stabiliser for the oxidising component which is also effective as an anti-fogging agent. The oxidising agent may be hydrogen peroxide and the combined stabilising agent may be uric or phosphoric acid, or a functional salt thereof. The invention also provides a photographic paper coated with such a stabiliser for redox amplification colour developer thereby to inhibit fogging.

Description: STABILISERS FOR RX DEVELOPERS DESCRIPTION This invention relates to stabilisers for RX developers. Particularly the invention relates to the processing of photographic materials by redox amplification developer systems in order to ameliorate the inherent instability of such solutions. In photographic colour development processes, and particularly in the RX, redox amplification, process it is desirable to provide colour development materials which degrade only slowly so that they can be used readily in automatic processing. In the RX, redox amplification, process "normal sensitometry", is produced fro:n low silver chloride laydown coatings having a coating weight of less than 21mg/sqft, and preferably about 13mg/sgft, by using a combination of a traditional colour developer with an oxidant. Such developer hybrids are inherently unstable since they contain an intimate admixture of the colour developer with an oxidant which is often hydrogen peroxide. This inherent instability restricts the modes of use of the system and makes maintaining good sensitometry quite difficult. It has been proposed in Organic Chemistry page 867 Sedgewick to use uric or phosphoric acids as stabilisers for hydrogen peroxide per se. Further from Henn & Carpenter, Phot. Sci. Eng. vol 3, page 135, 1959 it is known to use uric acid as a photographic developer. We have now found that these acids and their functional salts will stabilise oxidants such as peroxide even in the presence of the normal components of a redox amplification developer system, and that the presence of such acids and/or their functional salts has not only the effect of inhibiting the interaction between the colour developer and the stabiliser, thereby to increase the useful life of the developer solutions, but also beneficially effects the development process to enhance the developed quality of the image by markedly reducing the tendance of such systems to produce fogged products. In a further aspect of the invention it has been found that uric acid, phosphoric acid or its functional salts may be included in a coating on a photographic paper thereby to give improved fogging levels by inhibiting oxidant/colour developer interaction in situ. ■ In US-A-4,045,225 there is disclosed a colour developer composition comprising an oxidising agent and a colour developing component, wherein the composition additionally comprises a stabiliser such as uric acid for the oxidising agent. However, such composition includes at least one nitro-substituted nitrogen containing hetrocyclic anti-fogging compound. We have now found that the incorporation of a stabiliser such as uric acid into the photographic paper stabilises the development while also acting as an anti-fogging agent thereby enabling said nitrogen containing compound to be dispensed with. According to the present invention therefore there is provided a redox amplification colour developer composition comprising an oxidizing agent and a colour developing component, characterised in that said composition comprises a combined stabiliser and anti-fogging agent selected from uric or phosphoric acids. It is thus possible to dispense with separate anti-fogging agent per se. In a preferred form of the invention the composition has a ratio of oxidizing agent to combine stabiliser in the range of 1 ml to 2 to 50 mg of the combined stabiliser, and preferably 1 ml of the agent to 5 - 20 mg of the acid. According to another aspect of the present invention there is provided a photographic paper having coated thereupon a stabiliser as set forth above for a redox amplification colour developer, thereby to inhibit fogging due to interaction between the stabiliser and the developer. It will thus be seen that an incorporation of the stabilisers in accordance with the present invention inhibit the interaction between the colour developer and the oxidising agent for example hydrogen peroxide thereby increasing the useful lifetimes of solutions for use in automatic processing, while also acting an an anti-fogging agent. The invention will now be described, by way of illustration only, with reference to the accompanying drawing and with reference to the following example; The figure annexed hereto shows the graph of the effect of uric acid in amplifying developers. EXAMPLE A multilayer colour paper, suitable for an "RX" process was prepared. The paper was of a similar construction to current 2001 paper products with respect to the dispersions used, and the gel laydown. "All chloride" emulsions were used and the silver concentrations for each layer were as follows - red sensitive layer 3.0mg/sqft., green sensitive layer 4.0mg/sqft., blue sensitive layer 6.4mg/sqft, giving a total weight of silver 13.4mg/sqft. An initial developer was prepared using a potassium carbonate buffer, to which the required photographic reagents were added. Final developer composition is shown below. Com onent Concentration: Key: EDTA ethylene diamine tetracetic acid CD3 β-methanesulphonamidoethylaminotoluidine sesquisulphate hydrate The pH was adjusted to 10.3, with dilute NaOH, or H-SO. as required. Samples of developer above were then prepared with different concentrations of uric acid. Uric Acid was first dissolved in an alkali solution of KoH, (0.5g K OH plus 0.5g uric acid in 50mls H 2 0) . Subsequently this solution was used to give developers with various concentrations of uric acid: 0, 25, 50, & 100 mg uric acid/litre of developer. Control samples of these developers were then taken, whilst the remaining volume was equilibrated to 35 C in a tank line. Hydrogen Peroxide (100 vol.) was added to each developer, to give an oxidant concentration of 5ml/l of developer. Next, suitably exposed sensitometric strips were processed through each of the four experimental developers at intervals over a period of 2.5 hrs. Processing was 30 sees. development, followed by 30 sees, fix, and 90 sees, wash. After each strip samples of the developers were taken for CD3 analysis. The figure shows a graph of the data from CD3 analysis, clearly the developers with higher uric acid concentrations have more CD3 left than the control sample. The sensitometric effects of incorporating uric acid into amplifying developers is summarised below, whilst relevant data is given in Tables 1 to 4. TABLE ONE : EFFECT OF URI C ACID ON AMPLIFYI NG Developer o MG URIC ACID PER LITRE OF Developer TIME RDHIN GDM N BDMIN DHAX GDMAX BDMAX RCOK SCON BCON TABLE TWO: EFFECT OF URIC ACID ON AMPLIFYING Developer 25 MG URIC ACID PER LITRE OF Developer TIME RDMIK GDMIN BDMIN RDMAX GDMAX BDMAX P.CON GCON BCON TABLE THREE: EFFECT OF URIC ACID ON AMPLIFYING Developer 50 HG URIC ACID PER LITRE OF Developer TIME 0 HRS 0.5 HRS 1.0 HRS 2.0 HRS TABLE FOUR : EFFECT OF URIC ACID OH AMPLIFYING Developer loo MG URIC ACID PER LITRE OF Developer TIME 0 HRS 0.5 HRS 1.0 HRS 2.0 HRS 2.50 HRS Red & Green D mins both show a relative increase compared to the control. The highest uric acid concentration shows the most stabilising effect. Blue D min is improved by the incorporation of uric acid in the amplifying developer, the improvement is best at the higher concentrations and is maintained over the test period. All three D max densities are improved compared to the control by the incorporation of uric acid in the developer and show reduced variations. Contrasts for the layers show variation, but the magnitude of the uric acid containing samples are reduced compared to the control which is an advantage.

Claims: CLAIMS 1. A redox amplification colour developer composition comprising an oxidising agent and a colour developing component; characterised in that the composition comprises a combined stabiliser and anti-fogging agent for the oxidising agent selected from uric and phosphoric acids or a functional salt thereof. 2. A composition according to claim 1 characterised in that the ratio of the oxidising agent to the combined stabiliser is 1 ml to 2 - 50 mg of the stabiliser. 3. A composition according to claim 3 characterised in that the ratio is 1 ml to 5 - 20 mg of the stabiliser. 4. A composition according to claim 1 characterised in that the oxidising agent is hydrogen peroxide. 5. A composition according to any preceding claim characterised in that the functional salt is an alkali metal salt. 6. A method of stabilising a redox amplification colour developer comprising an oxidising agent, which comprises adding to said oxidising agent a stabiliser characterised in that the oxidising agent is hydrogen peroxide, and the stabilising agent is selected from uric acid, phosphoric acid, or a functional salt thereof. 7. A method according to claim 5 characterised in that the concentration of the stabilizer with respect to the developer is 5 to 250 mg/1. 8. A photographic paper having coated thereupon a composition according to any of claims 1 to 5 including a stabiliser for a redox amplification colour developer, thereby to inhibit fogging due to interaction between the stabiliser and the developer. 9. A photographic paper according to claim 8 characterised in that the stabiliser is selected from uric acid, phosphoric acid, or a photographically effective salt thereof. 10. A redox amplification colour developer composition substantially as hereinbefore set forth with reference to, and as illustrated in, the accompanying drawing and/or the foregoing example. 11. A method of stabilising a redox amplification colour developer system comprising an oxidising agent substantially as hereinbefore set forth with reference to, and/or as illustrated in the accompanying drawing or in the foregoing Example. 12. A photographic paper comprising a stabiliser substantially as hereinbefore set forth with reference to, and as illustrated in, the accompanying drawing and/or as show in the foregoing Example.

Inventors: TANNAHILL AMANDA AUDREY, TANNAHILL, AMANDA, AUDREY
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1991
Main classification: G03C7
IPC codes: G03C7