GB2303220A - Photographic developing and fixing process - Google Patents

Abstract

A process for the development and fixing of an exposed photographic material comprising a silver halide emulsion in which at least 60 mole % and less than 90 mole % of the silver halide is silver chloride comprises developing the exposed photographic material in an aqueous solution of a developing agent and passing the film to a bath of fixing solution. To reduce the deterioration in the fixing rate the potassium ion content of the fixing solution is maintained below 5 mole % of the total cation content of the fixing solution, preferably below 1%. Preferably at least 70 mole% of the cations in the developer solution are sodium and less than 5 mole % of the cations are potassium. The concentration of silver in the fixing solution may be from 10g/litre to 25g/litre.

Description

PHOTOGRAPHIC DEVELOPING AND FIXING PROCESS Field of the Invention This invention relates to the processing of photographic materials and particularly to developer solutions and to a developing and fixing process in which they are employed.

Background of the Invention In the processing of imagewise exposed photographic materials the first step is usually the treatment of the exposed material with a developer to reduce the silver halide to metallic silver. In black and white photography the metallic silver usually comprises the desired image. To obtain useful black and white images it is usually desirable to remove the undeveloped silver halide and this is usually accomplished by dissolving it in a silver halide solvent, commonly referred to as a fixing agent. In colour photography the removal of the silver is generally accomplished by oxidising the metallic silver, and dissolving the oxidised metallic silver and undeveloped silver halide with a fixing agent.

The two stages of developing and fixing have therefore become well established in the processing of exposed photographic materials.

Problem to be solved by the Invention It has been known previously that when the fixing stage follows the development without any intervening stage, that small quantities developer solution are carried over into the fixing solution (for example in the gelatin or on the film surface), and that the performance of the fixing stage can be adversely affected.

United States Patent No 5,298,372 describes a methpd for the processing of black and white transmission type film in an automatic processor which has as its object the reduction of the volumes of developer and fixing replenisher solutions used per square metre of photographic material processed. The photographic material comprises a support having a silver halide emulsion layer in which the silver halide is silver chlorobromide, silver chloroiodide or silver chloroiodobromide having a silver chloride content of at least 90 mole and a mean grain size of 0.1 to 0.4 micrometres or silver chloride having the same mean grain size. This patent discloses that the fixing property, measured in terms of the amount of residual silver, deteriorates over a three week period but that the performance can be maintained by using developer solution containing a higher moles of sodium ions.The difference in performance is said to be due to the developing solution being carried over into the fixing solution and proposes that the developing bath should contain sodium ions in an amount comprising at least 70mole of the entire cation content.

Contrary to expectation, it has now been found that, in the processing of photographic materials in which the silver chloride content of the silver halide is less than 90 moles, there is a benefit in using developer solutions which are of high sodium ion and/or low potassium ion concentration. The benefit is particularly noticeable when there is a high concentration of silver in the fixing solution which may occur, for example, when replenishment is reduced.

The present invention therefore provides a solution to the problem of the deterioration in the fixing rate caused by carry over of ions from the developing stage in the case of photographic materials in which the silver chloride content of the silver halide is less than 90mole. The present invention provides a process in which the potassium ion concentration in the fixing solution is controlled.

Summary of the Invention According to the present invention there is provided a process for the development and fixing of an exposed photographic material comprising a silver halide emulsion in which at least 60 mole % and less than 90 mole % of the silver halide is silver chloride, which process comprises developing the exposed photographic material in an aqueous solution of a developing agent and passing the material to a bath of fixing solution in which process there is contamination of the fixing solution with ions carried over from the developing solution and wherein the concentration of potassium ions in the fixing solution is maintained below 5 mole .

Advantageous Effect of the Invention The use of the present invention enables faster rates of fixing to be achieved.

Although the invention is of particular advantage when the fixing stage follows the development without any intervening stage such as a washing step, the invention will nevertheless provide an advantage under any series of process steps where cations from the developer solution contaminate the fixing solution.

Detailed Description of the Invention Preferably the concentration of potassium ions in the fixing solution is less than 3 mole , more preferably below 1 mole W. In terms of gram ions/litre the concentration of potassium ions is preferably less than 0.2 g ions/l, more preferably less than 0.lg ions/l.

Preferably the fixing solution contains thiosulphate and preferably the concentration of thiosulphate is at least 0.8 molar, and can be greater eg above 1.5 molar.

Desirably the concentration of sodium ions in the developing solution is at least 70 mole %, more preferably at least 85 mole %, most preferably at least 90 mole W.

Preferably less than 20 mole % of the cations in the developer solution are potassium, more preferably less than 5 mole %. The content of potassium ions can be less than 1 mole% and the solution may be substantially free of potassium ions. By substantially free we do not mean to exclude potassium completely since potassium compounds may be present as impurities in the commercially available forms of other components.

During the course of the process the concentration of silver in solution builds up in the fixing solution and the benefit of the present invention is particularly significant at relatively high concentrations of silver in the fixing solution, for example above 5g/litre measured as metallic silver.

At higher concentrations of silver, for example in the range 10 to 25g/litre the benefit from the present invention is greater. Concentrations of silver above 25g/litre should preferably be avoided.

The silver chloride content of the silver halide in the photographic material is, as stated above less than 90mole% and is preferably less than 80mole W and can be less than 75mole%.

Preferably the amount is at least 65 mole% and preferred ranges are from 60 to 85 and 65 to 80mole%.

Preferably the other halide ion is bromide and will normally make up the balance, so that for example, where the silver chloride content is 85 mole% the amount of silver bromide will be 15 mole%. In some cases there can be a very minor amount of iodide ie less than 0.5molest probably less than 0.lmole%.

The invention is illustrated by the following Examples.

Three developer solutions were made up according to the formulae in Table 1.

Developer solution 1 contained mixed cation salts, Developer solution 2 contained cations that were almost entirely potassium and Developer solution 3 contained only sodium cations.

Table 1 Developer 1 2 3 potassium hydroxide 18g 35.2g sodium hydroxide 12.3g - 25.2g sodium metabisulphite 45g - 45g potassium metabisulphite - 52.6g sodium bromide 3.8g - 3.8g potassium bromide - 4.4g pentectic acid(40%) 10mls 10mls lOmIs benzotriazole 0.21g 0.21g 0.21g phenylmercaptotetrazole 0.03g 0.03g 0.03g hydroquinone 25g 25g 25g hydroxymethyl methyl phenidone 0.8g 0.8g 0.8g potassium carbonate 38.6g 38.6g sodium carbonate - - 29.6g diethylene glycol 36mls 36mls 36mls pH 10.4 10.4 10.4 The above quantities when diluted with water made up 1 litre of developer.

A concentrated fixer was made up with the following composition: ammonium thiosulphate 730g sodium sulphite 12g acetic acid 23mls water to 1 litre pH adjusted to 5.0 with sodium hydroxide This concentrated fixer was diluted with different amounts of demineralized water as set out in Tables 2 and 3 before use.

To the diluted fixer was added 21.6g/l silver chloride and 13g/l silver bromide to simulate the silver that might be seasoned from film passing through the process.

The fixing rates of two films were measured in these fixers and also in fixer to which different amounts of the different developers had been added. These were compared to developers that had been diluted with demineralized water. The films used were "Kodak" IMAGESET LD Scanner Film, and "Kodak" IMAGELITE ESY Scanner Film. The fixing time was measured by continuously monitoring the infra-red density of the film until there was no change in density. The film was agitated by a burst of nitrogen of 0.4s every 4s.

The fixing times of the different films in the different contaminated fixers are shown in Tables 2 and 3. From the results it can be seen that for all fixer dilutions and all films, the presence of developer 1 and developer 2 increases the fixing time, ie reduces the fixing rate compared to fixer diluted with water. However the developer made with all sodium salts ie Developer 3 did not retard fixing significantly over the fresh fixer position and in some cases accelerated fixing, in particular those fixers that were more concentrated, as was seen by the dilution with water.

In order to check the sensitometric effect of the three developers, strips of "Kodak" IMAGESET LD Scanner Film were exposed to a sensitometric wedge illuminated with red light. Each strip was processed using different developers in the following process: develop 30s 350C fixer (as above diluted 1+3 ) 30s 350C wash 30s 350C The process was carried out in a small upright processing tank with the agitation used in the fixing experiments described above.

Table 4 shows a comparison of the sensitometry. The difference in the results is less than the noise in the experiment suggesting that the cation differences were not having a sensitometric effect.

Table 2 "Kodak" IMAGESET LD Scanner Film Fixing Rates- Effect of Developer and Fixer Dilution.

Developer W Dev Fixing Times (seconds) Type in Fixer dil.1+2 dil.1+3 dil.1+4 dil.1+5 0 14 11 14 18 water 10 12 10 13 10 (as 20 7 10 15 23 diluent) 30 6 10 16 26 Developer 1 10 11 16 15 20 (control) 20 18 21 36 41 30 24 31 49 220 Developer 2 10 17 18 40 71 (all 20 24 26 80 125 potassium) 30 31 50 78 256 Developer 3 10 10 10 16 21 (all 20 8 12 18 23 sodium) 30 6 11 22 28 The silver halide in the film comprised 70% chloride and 30% bromide.

Kodak and IMAGESET are Registered Trade Marks.

Table 3 "Kodak'1 IMAGELITE ESY Scanner Film Fixing Rates Effect of Developer and Fixer Dilution.

Developer % Dev Fixing Times (seconds) Type in Fixer dil.1+2 dil.1+3 dil.1+4 dil.1+5 0 11 7 13 16 water 10 9 9 13 18 20 6 10 13 18 30 6 10 13 26 Developer 1 10 11 10 16 20 (control) 20 14 16 27 28 30 16 24 39 68 Developer 2 10 21 16 35 54 (all 20 20 26 55 86 potassium) 30 22 44 68 290 Developer 3 10 10 10 13 20 (all 20 7 10 14 20 sodium) 30 6 12 15 24 The silver halide content of the film comprised 70% chloride and 30% bromide.

IMAGELITE is a Registered Trade Mark Table 4 Sensitometry of "Kodak" IMAGESET LD Scanner Film: effect of cation Developer 1 Developer 2 Developer 3 all potassium all sodium Dmin 0.030 0.033 0.021 Dmax 5.69 5.39 5.39 PDM 4.48 4.48 4.45 PrD 5.50 5 07 5.44 S0.6 0.84 0.90 0.84 Sp2 0.77 0.83 0.75 Sp4 0.71 0.73 0.66 USC 19.49 18.78 19.26 EC 16.51 16.58 15.11 The abbreviations used in the above table are known to those in the art but for the avoidance of doubt the following explanation is given.

Dmin and Dmax are well known in the art.

PDM and PrD stand for two recognised measurements of practical Dmax.

S0.6, Sp2 and Sp4 refer to relative speeds at 0.6, 2 and 4 density units above Dmin.

USC stands for upper scale contrast and EC is a measure of average contrast.

Claims (8)

Claims:

1. A process for the development and fixing of an exposed photographic material comprising a silver halide emulsion in which at least 60 mole % and less than 90 mole W of the silver halide is silver chloride, which process comprises developing the exposed photographic material in an aqueous solution of a developing agent and passing the film to a bath of fixing solution in which process there is contamination of the fixing solution with ions carried over from the developing solution and wherein the concentration of potassium ions in the fixing solution is maintained below 5 moles of the total cation content.

2. A process as claimed in claim 1 wherein the concentration of potassium ions in the fixing solution is maintained below 1 mole t.

3. A process as claimed in any one of the preceding claims wherein the concentration of silver in the fixing solution is at least 5g/litre.

4. A process as claimed in claim 3 wherein the concentration of silver is from 10 to 25 g/l.

5. A process as claimed in any one of the preceding claims wherein the concentration of sodium ions in the developer solution is at least 70 mole W of the total cation content.

6. A process as claimed in claim 5 wherein at least 85 mole% of the cations in the developer solution are sodium ions.

7. A process as claimed in any one of the preceding claims wherein less than 5 mole % of the cations in the developer solution are potassium.

8. A process as claimed in any one of the preceding claims wherein the photographic material is a black and white photographic material.