COLOUR NEGATIVE DEVELOPERS

This invention relates to a method of processing photographic silver halide colour materials and in particular to the replenishment of colour developer for colour negative film.

Colour negative films are processed in an industry standard process called C—41. Most C—41 systems are run on the basis that a replenisher solution is added to the developer and excess developer is removed by letting it overflow. The developer solution thus achieves a stable condition in which chemicals used up during processing are replenished to maintain a working concentration and seasoning products e.g. bromide and iodide ions and antifoggant fragments from DIR couplers entering the developer solution from the film are kept at an acceptable level. Recent C—41 systems are run on a developer replenishment rate of from 500 to 1800 2 ml/m of film processed.

Colour paper is also processed in a replenished system but current colour paper is based on silver chloride emulsions containing very little bromide or iodide. This permits a replenishment regime in which there is little or no need to remove bromide and iodide hence the developer can be replenished with a more than usually concentrated replenisher which does not cause overflow. Such a system is described in European Speci ication 0,173,203. Using such a concentrated source of replenishment can result in zero—overflow from the developer tank and a build—up of seasoning products which is not sign fi antly detrimental to sensitometry. This could involve rebalancing the sensitized coating to match aim sensitometry in the

presence of higher levels of seasoning products. This is a major operation and is best avoided if a simpler option as is described in our invention is available. Another special case is where even though seasoning products do build-up with use, they do not affect sensitometry because the developer used already contains a more powerful inhibitor. For example, if a sensitized material containing a high silver chloride content is processed in a developer containing soluble sodium bromide (0.7 g/1), then the increase in chloride level during use would only have a small effect on sensitometry. This is similar to the method employed in EP—A—0,173 203 for a colour paper developer. To some extent this is an artificial case because high silver chloride coatings are best processed with much lower levels of bromide (about 20 mg/1) to allow for rapid processing (e.g. the RA—4 process). If seasoning products such as chloride are allowed to build—up in the RA—4 process, then sensitometry and processing rapidity are detrimentally a ected.

While is is known to remove seasoning products from developers using ion-exchange resins, such resins have never been used in a system having such low replenishment rates as are achieved by the present invention. For example, in "Developer Recycling — A New Generation" Meckl, Journal of Imaging Technology, 1_3, (1987), 3, 85-89 there is described a system in which the overflow from the colour developer tank is passed to a holding tank and then through ion—exchange resin to remove bromide ions. The so treated solution is then passed to a mixing tank where replenisher components are added and the newly formed solution is then passed to the replenisher tank ready for use. The replenishment

2 rate for a paper process is said to be 325 ml/m .

Japanese application 62/019842 describes a method of reducing the bromide ion concentration of colour developer for silver bromide colour paper by coating an ion—exchange resin on the back of the colour paper. This then takes up bromide ions as it passes through the developer solution. Clearly this process is undesirable because a special and more costly photographic paper has to be used thus rendering the paper more expensive and the process non—universal. The process wastes otherwise regeneratable ion—exchange resin. A coating of such a material on film (having a transparent base) is likely to result in an unacceptably degraded image.

While comparatively low replenishment rates have been proposed for developers for colour papers, no practical system has ever been proposed achieving similar rates for the C—41 process.

According to the present invention there is provided a method of processing a photographic silver halide colour negative film in which the colour developing solution is:

(i) treated with an in-line ion exchange resin to remove developer seasoning products, and (ii) replenished with a sufficiently small volume of replenisher components that substantially no overflow is produced. In the present invention the combination of very low replenishment rates and the use of in-line ion-exchange resin has a cooperative or synergistic effect in that the more effective the removal of seasoning products by the ion—exchange resin, the less is the replenisher that is needed. Hence the theoretical minimum chemical additions can be used while still maintaining standard tank chemistry. This

result indicates that the ion-exchange resin not only removes bromide ions but also undesirable levels of other seasoning products such as antifoggants released from DIR couplers in the film being processed. Unlike the process described by Meckl referred to above, in the present process there is no holding tank for developer overflow and no mixing tank for the addition of replenisher chemicals to the treated developer overflow. The combined features of the present invention yield a film process having exceptionally low replenishment rates.

The present invention can be configured to remove halide ions at the rate at which they are generated. Tn addition, antifoggant fragments are similarly removed. This invention, therefore, uses both in—line ion-exchange and concentrated-replenisher addition to enable the theoretical minimum chemical input for a C—41 developer solution in a single developer tank configuration. One of the main advantages of this invention is the significant reduction in effluent that arises from its use. The normal developer replenishment rate for Kodak VR400 film in C-41 is 1675 ml/m ² for 35 mm film although this has now been lowered to about 841 2 ml/m with the new C-41 LORR (Low Replenishment

Rate) process. The present invention lowers this

2 rate to between 56.0 and 117 ml/m for 35 mm film.

Since the volume added is very much reduced so is the volume that is expelled. In fact, no overflow is generated and the only effluent comes from that volume of developer carried over into the bleach tank. This is about 18.7 to 56.0 ml/m ² for 35 mm film. The chemical effluent is the same concentration as in a normally replenished process but its volume has been reduced from about 841 ml/m 2 to about 56.0 ml/m?.

A further advantage of the present invention is the reduced chemical input that is necessary by virtue of the reduced effluent and the greater proportion of the chemicals being used to generate image. Based on CD4 (4-(N-ethyl-N-2-hydroxyethyl)~2 —methylphenylenediamine sulphate) the chemical input is 70% less than the current C-41 LORR replenisher. This offers advantages in terms of the cost of the photofinishing operation and in manufacturing cost. An additional advantage of this invention is the ability of this system to cope with a wide range of utilisation conditions. A low utilisation condition can be tolerated more readily because colour developing agent can be added independently of the other components and does not depend for its level in the working tank on the level of the anti—oxidant. Because the bromide level, CD4 level and anti-oxidant level can be controlled independently of each other, the correct tank chemistry can be maintained for any utilisation condition. This is not possible with the conventional method which has all these components in the same replenisher solution. Because of these reasons a process that is replenished with the system described in this invention need never suffer from process collapse.

The system in the present invention is also ideally suited to be controlled by a replenisher management unit that could adjust the chemical input to account for different film types and utilisation conditions.

In the accompanying drawings:

Fig 1 represents the developer tank with its inlets and outlets and

Fig 2 is a control chart for the process described in the Example.

Fig 1 shows a developer tank to which additions of activator solution and solid CD4 colour

developing agent are made. There is a carry—out of developer solution on the film and, should the volume drop, due to evaporation, the level is made up with water. The ion-exchange cartridge is attached to the tank as shown and developer is circulated through it, eg with a pump, preferably only when there is film being processed.

The ion—exchange resin may comprise anionic (for the exchange of anions) or amphoteric types or mixtures thereof. A preferred type of anionic resin is based on a polystyrene matrix cross-linked, for example, with 3% to 5% of divinylbenzene. Its strongly basic character is derived from quaternary ammonium groups. Examples of suitable anionic exchange resins are:

IRA 400 Rohm and Haas

Dowex 1—X8 Dow Chemical, and

Duolite A113 Diamond Shamrock.

The ion—exchange resin is preferably located in a cartridge through which the contents of the colour developer tank are pumped either continuously or when required. When it has been exhausted it may be discarded or regenerated as will be well understood.

The replenisher may be in the form of a solution or a solid. However, its exact form must be such that at normal replenishment rates under normal working conditions substantially no overflow is caused.

In one embodiment of the invention, the replenisher components are added as an activator solution and a solution of colour developing agent; in another, the colour developer is added as a solid. In a further embodiment, the replenisher components may be added as three separate solutions having the following compositions:

PART A

Potassium carbonate 470 g/1

Potassium hydroxide 11 g/1

Diethylenetriamine-pentaacetic acid pentasodium salt 106 g/1

Sodium metabisulphite 43 g/1

PART B

Hydroxylamine sulphate 272 g/1

PART C

Sodium metabisulphite 16.5 g/1 CD4 472 g/1

Approximate replenishment rates for the above 3 part replenisher would be: Part A 16.8 to 49.5 ml/m ² of film Part B 1.87 to 6.5 "

Part C 3.5 to 6.5 "

The present invention can also be used to deliberately control tank chemical levels to some values other than those in normal working tank chemistry. This might be desirable for special uses where non-standard sensitometry, e.g. higher speed is needed. The film to be processed may be any camera-speed colour negative film such as those commercially available or as described in Research Disclosure Item 17643 December 1978 pages 22-31 published by Kenneth Mason Publications of Emsworth, Hampshire, United Kingdom.

The following example is included for a better understanding of the invention. The word 'Kodak' is a trade mark. EXAMPLE A seasoning run was carried out for several months to establish the basic operating procedure and the chemical addition and ion—exchange rates. The three elements of the replenishment system are: (i) the activator (ϋ) the addition of solid or concentrated

CD4 (iii) in—line ion—exchange on the developer tank

(i) The activator

This has the composition shown in Table 1.

Table 1 — Film Activator Composition

K ₂ S0 ₃ (anhydrous) 24.0 g/1

Hydroxylamine sulphate 13.4 g/1 Diethylenetriamine—pentaacetic acid pentasodium salt (41% soln. ) 6.5 ml/1

K ₂ C0 ₃ 37.5 g/1 pH 11.6

This solution was kept in a closed container namely a 'bag-in-the-box' collapsible plastic vessel often used for wine and other fluids sensitive to degradation by the atmosphere. A conventional replenisher tank is acceptable for short times (days) but for longer times (weeks) it was found that carbon dioxide absorption from the air caused the pH of the activator to drop so that it was then unable to maintain developer tank pH. These problems were prevented by the use of a collapsible container. This

activator was added at a rate of between 37.4 and 117

2 ml/m of 35 mm film processed depending on the average throughput rate of film on a weekly basis.

The overall average film throughput was about 62 linear metres per day of VR400 which was exposed to average customer density.

(ii) Solid CD4 addition

The rate of addition of solid CD4 was estimated from a computer model of the replenishment system. In practice this was modified slightly to account for some losses of CD4 on the ion—exchange resin. The addition rates were:

1.4 - 1.9 g/m ² VR400

0.65 - 0.94 g/m ² VR100 Solid CD4 was added at the above rates in proportion to the amount of film processed. In practice this was done by removing some developer solution, adding a weighed amount of solid CD4 to this and replacing the same into the developer tank. Although the seasoning run described above was carried out by using the addition of solid CD4, a

CD4 concentrate may equally be used with closely similar results.

(iϋ) In-line ion—exchange IRA400, a strong anion resin available from

Rohm and Haas was used. The ion—exchange rate was

2 196 ml/m for VR400 film. The resin was regenerated with 5% potassium carbonate, washed with demineralised water and then connected in-line with the developer tank. Approximately 400g of resin was contained in a simple flow through cell of about 500 ml volume. The flow through the resin cell was controlled by a conventional replenishment pump which is switched on along with the replenishment pump for the activator when film passes through the processor. The flow of

solution from the developer tank through the cartridge occurs only when film is passing through the processor. The treated solution is then returned directly back to the developer tank. This ensures a controlled rate of removal of bromide ions and other seasoning products. Film was put through the processor at approximately 62 metres of 35 mm film per day. A resin cell of the size described here lasts about one week or for 300 to 385 linear metres of 35 mm VR400 seasoning film.

Analytical samples were taken from the developer tank to monitor chemical levels and assess whether the chemistry was under control. Sensitometric control strips were put through the process throughout the seasoning run of 3 months and a plot of control parameters is shown in Figure 2. It can be seen that the process is in control for the entire run even though this run was also a learning exercise to establish the correct addition and ion—exchange rates.