EP0548124B1

EP0548124B1 - Stabilisers for rx developers

Info

Publication number: EP0548124B1
Application number: EP91915628A
Authority: EP
Inventors: Amanda Audrey Kodak Limited Tannahill
Original assignee: Kodak Ltd; Eastman Kodak Co
Current assignee: Kodak Ltd; Eastman Kodak Co
Priority date: 1990-09-13
Filing date: 1991-08-30
Publication date: 1995-02-08
Anticipated expiration: 2011-08-30
Also published as: JPH06500863A; DE69107307T2; GB9020000D0; WO1992005471A1; DE69107307D1; EP0548124A1

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

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 from low silver chloride laydown coatings having a coating weight of less than 21mg/929cm²(sqft), and preferably about 13mg/929cm²(sqft), 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 acid, phosphoric acid photographically effective salts thereof, but excluding nitro-substituted, nitrogen containing, heterocyclic anti-fogging compounds. It is thus possible to dispense with separate anti-fogging agent per se. The functional salt is preferably an alkali metal salt.
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. A preferred concentration of the stabilizer with respect to the developer is 5 to 250mg/l.
According to another aspect of the present invention there is provided a photographic paper suitable for use with a redox amplification colour developer composition, characterised in that the paper incorporates an anti-fogging compound selected from uric acid, phosphoric acid and photographically effective salts thereof; subject to the proviso that the paper does not include nitro-substituted, nitrogen-containing, heterocyclic anti-fogging compounds.
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/929cm²(sqft)., green sensitive layer 4.0mg/929cm² (sqft)., blue sensitive layer 6.4mg/929cm² (sqft), giving a total weight of silver 13.4mg/929cm² (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.

Key:

EDTA: ethylene diamine tetracetic acid
CD3: β-methanesulphonamidoethylaminotoluidine sesquisulphate hydrate

The pH was adjusted to 10.3, with dilute NaOH, or H₂SO₄ 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 H₂O). 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 secs. development, followed by 30 secs. fix, and 90 secs. 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.
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

A redox amplification colour developer composition comprising an oxidising agent and a colour developing component; characterised in that the composition comprises a combined anti-fogging agent and stabiliser for the oxidising agent selected from uric acid, phosphoric acid and photographically effective salts thereof, but excluding nitro-substituted, nitrogen-containing, heterocyclic anti-fogging compounds.
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.
A composition according to claim 3 characterised in that the ratio is 1 ml to 5 - 20 mg of the combined stabiliser.
A composition according to claim 1 characterised in that the oxidising agent is hydrogen peroxide.
A composition according to any preceding claim characterised in that the photographically effective salt is an alkali metal salt.
A method of stabilising a redox amplification colour developer composition comprising an oxidising agent and a colour developing component, characterised by adding to the composition a combined stabiliser and anti-fogging compound selected from uric acid, phosphoric acid and photographically effective salts thereof, but excluding nitro-substituted, nitrogen-containing, heterocyclic anti-fogging compounds.
A method as claimed in claim 6 characterised in that the oxidising agent is hydrogen peroxide.
A method according to claim 6 or 7 characterised in that the concentration of the combined stabilizer with respect to the developer composition is 5 to 250 mg/l.
A photographic paper suitable for use with a redox amplification colour developer composition, characterised in that the paper incorporates an anti-fogging compound selected from uric acid, phosphoric acid and photographically effective salts thereof; thereby to inhibit fogging due to interaction between an oxidizing agent a colour developing component on developing the paper; subject to the proviso that the paper does not include nitro-substituted, nitrogen-containing, hetercyclic anti-fogging compounds.