GB2292813A

GB2292813A - Photographic developer

Info

Publication number: GB2292813A
Application number: GB9417303A
Authority: GB
Inventors: Michael John Parker; Anthony Martin Lannon; William Edward Long
Original assignee: Ilford Ltd
Current assignee: Ilford Imaging UK Ltd
Priority date: 1994-08-27
Filing date: 1994-08-27
Publication date: 1996-03-06
Anticipated expiration: 2014-08-27
Also published as: GB9417303D0; GB2292813B

Abstract

A photographic silver halide developing solution comprises 1 an ascorbic acid developing agent or a salt thereof, at a working strength concentration of 0.01 molar to 0.2 molar, 2 as a colour stabiliser boric acid, a boronic acid or a salt thereof at a concentration of 0.01 to 0.4 molar, 3 a sulphite salt, at a working strength concentration of 0.01 to 0.4 molar, at least 4 one basic buffer selected from a carbonate, an organic alkanolamine, a phosphate, a phenoxide, or a hydroxide, the buffer being present in sufficient amount to keep the solution at required pH of 8.5 or above. The developer may also contain 5 a second developer such as an aminophenol or a hydrazolidone and 6 a metal complexing agent. The developer may be in the form of a concentrate.

Description

Entitled: Photographic Silver Halide Developing Solution This invention relates to photographic processing solutions for monochrome photographic materials. Suitable components and formulations for use in such solutions are well known, and are described for example in the books Photographic Processing Chemistry by LFA Mason, published by the Focal Press in 1975, and Modern Photographic Processing, by Grant Haist, published by Wiley-Interscience in 1979. Dihydroxybenzene compounds, and especially hydroquinone, are in common use as the main developing component in monochrome photographic processing solutions.

Of recent years, there has been increased interest in replacing hydroquinone by more environmentally desirable compounds, and especially by ascorbic acid and related compounds. The use of such compounds is well known, and is described in the two books by Mason and Haist.

Specific formulations comprising ascorbic acid and similar compounds of use for processing monochrome photographic materials are described for example, in European patent Applications 0 603 586, 0 588 408, 0 573 700, 0 552 511, and 0 461 783, United States Patent 5,236,816, WO 93/11456, WO 93/12463, and Research Disclosure 35249, August 1993.

One disadvantage of the known formulations of ascorbic acid and related compounds for the processing of monochrome photographic materials is that they tend to be coloured, and become increasingly so on storage and in use. For instance, the formulations provided in European Patent Application 0 461 783 are yellow when freshly prepared, and become deep orange coloured on storage, even in the absence of air. This is in contrast to known photographic developing compostions containing dihydroxybenzene developing agents which can be prepared to be almost colourless and do not darken appreciably on storage, even in the presence of air.

We have now found formulations for ascorbic acid based developing solutions for black and white photographic materials which do not rapidly discolour.

According to the present invention there is provided a photographic silver halide developing solution which comprises an ascorbic acid developing agent, or a salt thereof, at a concentration of 0.01 molar to 0.2 molar, as a colour stabiliser boric acid or a boronic acid, or salts thereof, at a concentration of 0.01 to 0.4 molar, sulphite salt, at a concentration of 0.01 to 0.4 molar, and at least one basic buffer, selected from a carbonate buffer, a phosphate buffer, a phenoxide type buffer, an organic alkanolamine buffer, or a hydroxide buffer, the buffer being present in sufficient amount to keep the solution at the required pH.

Boric acid, boronic acid or salts thereof are hereinafter referred to as borate.

By an ascorbic acid developing agent is meant a compound of the formula I

in which the group R represents a hydroxylated alkyl group.

Particularly useful compounds of this formula are L-ascorbic acid and D-isoascorbic acid in which the group R is -CHOHCH2OH, and salts thereof. An especially useful compound is sodium L-ascorbate, which is commercially available.

It is to be understood that at the pH values of use for the present invention, the ascorbic acid type compound exists in solution predominantly in the form of ascorbate anion, and this is one reason for sodium ascorbate being preferred for use.

The most suitable buffer for the present invention is determined by the desired pH of the developing solution. The developing solutions of the present invention are useful at a pH of 8.5 and above. Preferably the pH is in the region of 10.0 to 10.5, in which case the most preferred buffer is a carbonate buffer, for example sodium carbonate. Suitable phenoxide buffers include salts of p-hydroxybenzoic acid, p-hydroxybenzene sulphonic acid, and salicylic acid. Suitable organic alkanolamine buffers include diethanolamine and N-methyl-ethanolamine.

Suitable phosphate buffers include inorganic phosphoric acid salts such as mono, di or tri sodium or potassium orthophosphat:es and the like.

For developing solutions of pH greater than 12.0, and sometimes for solutions of lower pH, it is generally necessary to use a hydroxide compound to obtain the desired pH.

A suitable buffer concentration is at least 0.1 molar, and a preferred concentration is around 0.5 molar.

A preferred concentration of the ascorbic acid type compound is between about 0.01 molar and 0.1 molar, corresponding to around 2 gram/litre of sodium L-ascorbate, as a lower limit.

It is preferred that the borate concentration is at least equal to the concentration of the ascorbate type compound, and most preferred that the concentration of the borate is between about two times and three times that of the ascorbate.

Suitable sulphite salts include alkali metal sulphite salts, such as sodium or potassium sulphite. It is preferred that the alkali metal sulphite molar concentration is approximately equal to that of the ascorbate type compound.

The alkali metal sulphite is present in the developing solution as an antioxidant but as shown in one of the accompanying examples it also has some co-operative action with the boric acid or boronic acid in helping to prevent the build-up on colour in the developing solution. A convenient method of formulating the solutions of the inventions is to incorporate the alkali metal sulphite in the form of potassium sulphite solution.

However in order to obtain the correct desired pH of the solutions of this invention, it is necessary to make a careful choice of the acid and basic forms of the various components. One advantage of the invention is that the desired pH can readily be achieved by choice between, for example, ascorbic acid and sodium ascorbate, boric acid and sodium metaborate, and sodium metabisulphite and sodium sulphite.

Alternatively, it is of course possible to obtain the correct final pH by adjustment of the solution with additional base, such as sodium hydroxide, or with additional acid, such as acetic acid, but this is not preferred.

A suitable boronic acid for the present invention is phenyl boronic acid, of formula III

In order to achieve maximum efficiency when using the developing solution of the present invention it is preferred to carry out development of exposed silver halide material using the developing solution of the present invention in the presence of an electron transfer agent.

Most preferably the electron transfer agent is present in the developing solution of the present invention. However, it may be present in the silver halide material which is to be developed.

By electron transfer agent is meant a compound which acts synergistically with a main developing agent such as ascorbic acid to provide an active relatively long lasting developing combination. A large number are known from the patent literature but in practice the two most commonly used ones are amino-phenols such as p-methylaminophenol which is known commercially as Metol and pyrazolidinone compounds of general formula II:

in which Ar is an aromatic ring, R1 and R2 are hydrogen, lower alkyl, or hydroxy alkyl, and R3 are hydrogen, lower alkyl or phenyl. by lower alkyl is meant an alkyl group with up to 3 carbon atoms.

Preferably Ar is phenyl or a substituted phenyl such as 4-methyl phenyl or 4-chloro-pllenyl.

A particularly preferred pyrazolidinone compound is l-phenyl-4-methyl-4-hydroxymethyl pyrazolid-3-one. A suitable quantity of this compound to be present in a developing solution of the present invention is from 0.1 to 1 g/litre. This compound is hereinafter referred to as compound A.

Preferably at least one metal complexing agent is present in the concentrated developing solution. A particularly suitable compound is diethylenetriaminepentacetic acid hereinafter referred to as DTPA.

Other suitable metal complexing agents include phosphonic acids such as l-hydroxyethylidene l,l-diphosphonic acid, diethylenetriaminepenta (methylenephosphonic acid), ethylenediaminetetra (methylene phosphonic acid) and nitrilotris (methylenephosphonic acid) and alkali metal salts thereof.

A suitable quantity of metal complexing agent to be present in the developing solution is up to 100 millimoles/litre.

An alkali bromide and in particular potassium bromide may be present in the developing solution as a stabiliser or antifoggant. A suitable amount is from 0.1-10 g/litre.

An organic antifoggant may be present in the developing solution of the present invention. A preferred antifoggant is benzotriazole. A suitable amount is from 0.1 to O.5g/litre but preferably about O.lg/litre.

The developing solutions provided by this invention as hereinbefore set forth are so called working strength solutions, and may be made up as such from individual solid components, as in Example 1 which follows.

However, one of the advantages of the present invention is that the formulations may readily be provided in commercially useful forms such as combined powders in packets, bags, or sachets, or in the form of liquid concentrates, which may be diluted with water in a ratio of 1:2, 1:4, 1:9 or more, to give the working strength solutions of the invention. This invention is in fact especially advantageous for developers which are supplied in the form of liquid concentrates, since the desirable property of low colouration and reduced discolouration on storage is retained by such concentrates.

Therefore according to this aspect of the present invention there is provided a concentrated photographic silver halide developing solution which will produce upon dilution a working strength solution which comprises an ascorbic acid developing agent or a salt thereof, at a concentration of 0.01 molar to 1.0 molar, as a colour stabiliser boric acid, a boronic acid or a salt thereof at a concentration of 0.01 to 3.0 molar, a sulphite salt at a concentration of 0.01 to 1.0 molar, at least one basic buffer selected from a carbonate buffer, an organic alkanolamine buffer, a phosphate buffer, a phenoxide type buffer or a hydroxide buffer.

It is well known that boric acid and borates form complexes with dihydroxy organic compounds, and various borate/ascorbate complexes have been described in the literature, albeit at concentrations and pH values different from those useful in the present invention. US Patent 2 967 772 describes a complex of ascorbate and borate which is useful as an antioxidant for hydroquinone in developing compositions. It is therefore surprising that complexes between borate and ascorbate do not seem to be involved in the developing solutions of the present invention, and have not been detected analytically.

The following examples will serve to illustrate the invention: Example 1 Ascorbate based developing solutions were prepared to the following formula, designated developer 1 Developer 1 Potassium sulphite (65% w/v soln.) 15cm3 DTPA Na5 (37% w/v soln.) 6.8cm3 Compound A 0.4g Sodium-L-Ascorbate 8g Potassium bromide lg Benzotriazole O.lg Potassium carbonate 20g Water - > 1L pH adjusted to 10.30 Four variants of this formula were prepared in 1L portions: Sample a) Developer 1 as above Sample b) Developer 1 without potassium sulphite Sample c) Developer 1 + 11.2gl 1 sodium metaborate Sample d) Developer 1 without potassium sulphite -l + 11.2gl sodium metaborate Developer c) is according to the invention, samples a), b), and d) are for comparison.The pH was adjusted to 10.30 for each sample.

Each sample of developer was left standing for 13 days in an open 1 litre beaker. The colour of the solutions was measured initially and then at periodic intervals. The change in light absorbance at 400nm was determined. Results obtained are plotted in figure A.

FIGURE A ABSORBANCE &commat;400nm

STANDING TIME (DAYS) Sample a-#-DEVELOPER Sample b -#- DEVELOPER 1 NO SULPHITE Sample c-#-DEVELOPER 1 + SODIOK MELABORATE Sample d ## DEVELOPER 1 NO SULPHITE + SODIUM METABORATE These results clearly show that the colouration of developer l is improved dramatically by the addition of sodium metaborate, and that the most beneficial effect is obtained when sodium metaborate is used in conjunction with potassium sulphite as in sample c; in sample (b) developer 1 formulated without either potassium sulphite or sodium metaborate became unacceptably dark in colour very quickly.

Example 2 Ascorbate based developing solutions were prepared to the following formulae, designated developer 2 and developer 3.

Developer 2 Potassium sulphite (65% w/v soln.) 75cm3 Sodium-L-Ascorbate 5g Compound A 0.15g DTPA Na5 (37% w/v soln.) 4cm3 Potassium bromide 0.5g Diethanolamine 40g Water - > 1 L pH Adjusted to 8.50 Developer 3 DTPA Na5 (37% w/v soln.) 6.8cm3 Sodium Sulphite 13g Sodium-L-Ascorbate 20g Compound A 0.5g Potassium Bromide 5g Potassium Dihydrogen orthophosphate 20g Water - > 1 L pH adjusted to 12.30 A second sample of developer 2 was prepared in 1L portions as above but with the addition of 7g1 sodium metaborate.

A second sample of developer 3 was prepared in 1L portions as above but -l with 28gl sodium metaborate.

Each portion of developer was left standing for 13 days in an open 1L beaker. The colour of the solutions was measured initially ard then at periodic intervals. The change in light absorbance at 400nm was determined. Results obtained are plotted in figure B.

FIGURE B ABSORBANCE &commat;400nm

STANDING TILDE (DAYS) @ DEVELOPER 2 -#- DEVELOPER 2 + SODIUM METABORATE -#- DEVELOPER 3 ## DEVELOPER 3 + SODIUM METABORATE These results show that the colour of developer 2 is improved by the addition of sodium metaborate, whilst the colour of developer 3 is greatly improved by the addition of sodium metaborate but the effect is relatively short lived Consideration of the results presented in examples 1 and 2 shows that the addition of sodium metaborate has a useful effect in developers formulated over the pH range 8.50 to 12.30, but the effect is both long lasting and most apparent in ascorbate based developers formulated at a pH of around 10.30.

Example 3 Developer concentrates based on ascorbate with a dilution factor of (1+9) were prepared to the following formulae, designated developer 4 and developer 5.

Developer 4 (comparison) Potassium sulphite (65% w/v soln.) 50cm3 DTPA Na5 (37% w/v soln.) 68cm3 Compound A 4g Sodium-L-Ascorbate 80g Sodium Metabisulphite 39g Potassium Bromide 10g Benzotriazole lg Potassium Carbonate 200g Water - > 1 L Diluted (1+9) gives a solution of pH 10.30 Developer 5 (invention) DTPA Na5 (37% w/v soln.) 68cm3 Boric acid 54g Potassium hydroxide 38g Potassium sulphite (65% w/v soln.) 150cm3 Compound A 4g Sodium-L-Ascorbate 80g Potassium bromide lOg Benzotriazole lg Potassium carbonate 200g Water - > 1 L Diluted (1+9) gives a solution of pH 10.30 The colour of developers 4 and 5, as concentrates, and then as working strength solutions diluted (1+9), was determined by measuring light absorbance at 400nm, when prepared.Developers 4 and 5 were stored for 20 weeks in tightly capped bottles and the colour of both concentrates and each solution diluted (1+9) was measured as before.

Results obtained are presented in figure C.

Figure C Absorbance &commat; 400nm

Fresh After 20 weeks storage Developer 4 : concentrate 0.153 2.962 diluted (1+9) 0.112 1.130 Developer 5 : concentrate 0.098 0.714 diluted (1+9) 0.062 0.007 These results show that ascorbate based developers outside the scope of this invention become dark on storage when stored as a concentrate. It is also shown that a working strength solution prepared from such a stored concentrate is very much darker than a working strength solution prepared from the same concentrate when fresh. These conclusions are illustrated by the results for developer 4.

The results for developer 5 show that the addition of borate improves the colouration of both fresh concentrate developer and the resultant working strength solution. It is also shown, most importantly, that this advantageous effect is maintained after 20 weeks storage for both the concentrate and the resultant working strength solution.

Example 4 One part of developer concentrate 4 was diluted with 9 parts of water to produce a working strength developer with a pH of 10.30, and this solution was used to process a silver chlorobromide photographic paper which had been exposed through a sensitometric wedge. Comparison was made with developer concentrate 5, which was diluted to the same degree, resulting in the same solution pH, and was used to process the same photographic paper.

The sensitometric results obtained are set out in Table D.

In this table: Dmin is minimum density Ds is 90% of Dmax (maximum density) Contrast is the difference between logE values at Dmin + 0.04 and Ds.

Speed is measured at a density of 0.6 + Dmin Shoulder contrast is the difference between logE values at 80% of Dmax and 95% of Dmax IT(s) is induction time in seconds, which is the time elapsing before the photographic image begins to appear.

Table D Dmin Ds Contrast Speed Shoulder IT(s) Contrast Working strength Developer 4 0.01 1.89 0.89 2.27 0.15 10.0 (comparison) Working strength Developer 5 0.01 1.88 0.89 2.28 0.15 10.5 (invention) Thus whilst working strength developer 5 gives a significant advantage in colour over working strength developer 4 (as illustrated in example 3) this has not impaired the sensitometric performance of this developer.

Claims

Claims:

1. A photographic silver halide developing solution which comprises an ascorbic acid developing agent or a salt thereof, at a working strength concentration of 0.01 molar to 0.2 molar, as a colour stabiliser boric acid, a boronic acid or a salt thereof at a concentration of 0.01 to 0.4 molar, a sulphite salt, at a working strength concentration of 0.01 to 0.4 molar, at least one basic buffer selected from a carbonate buffer, an organic alkanolamine buffer, a phosphate buffer, a phenoxide type buffer or a hydroxide buffer, the buffer being present in sufficient amount to keep the solution at the required pH.

2. A photographic silver halide developing solution according to claim 1 where the ascorbic acid developing agent is L.-ascorbic acid or D-isoscorbic acid or a salt of either.

3. A photographic silver halide developing solution according to claim 1 which has a pH in the range of 10 to 10.5 and which comprises as a buffer a carbonate buffer.

4. A photographic silver halide developing solution which has a pH greater than 12 and which comprises as a buffer a hydroxide compound.

5. A photographic silver halide developing solution according to claim 1 wherein the concentration of boric acid, borDnic acid or salt thereof is at least equal to the concentration of ascorbic acid developing agent.

6. A photographic silver halide developing solution according to claim 5 wherein the concentration of boric acid, boronic acid or salt thereof present in the solution is two to three times the concentration of ascorbic acid developing agent.

7. A photographic silver halide developing solution according to claim 1 wherein the concentration of alkali metal sulphite in the developing solution is equal to the concentration of ascorbic acid developing agent.

8. A photographic silver halide developing solution according to claim 1 which also comprises an electron transfer agent.

9. A concentrated photographic silver halide developing solution which upon dilution produces a working strength solution which comprises an ascorbic acid developing agent or a salt thereof, at a concentration of 0.1 molar to 1.0 molar, as a colour stabiliser boric acid, a boronic acid or a salt thereof at a concentration of 0.01 to 3.0 molar, an alkali metal sulphite at a concentration of 0.01 to 1.0 molar, at least one basic buffer selected from a carbonate buffer, an organic alkanolamine buffer, a phosphate buffer, a phenoxide type buffer or a hydroxide buffer.