Photographic processing solutions

Abstract: A photographic aqueous processing solution containing at least one compound which has a maximum solubility therein corresponding to a desired operating level, which solution is kept in equilibrium with the solid compound thus maintaining its concentration at the desired level without the need for a replenishing system.

Description: Field of the Invention This invention relates to photographic processing solutions and in particular to the control of the concentration of components therein. Background of the Invention In photographic processing solutions the concentrations of the various components need to be kept close to certain aim levels. The normal way to maintain chemical levels is to replenish the component at the same rate as it is consumed. Consumption rates vary with exposure (and hence the amount of silver developed) and losses due to aerial oxidation, evaporation, etc., can vary widely for different processes and processing machines. Even in a particular machine and particular process, simply replenishing at a calculated rate can lead to variability. It is normal for processing chemicals to be as soluble as possible to facilitate solution preparation. Problem to be Solved by the Invention The problem to be solved is how to maintain the desired concentration of a processing solution component in a simple but accurate way. Summary of the Invention According to the present invention there is provided a photographic processing solution containing at least one compound which has a maximum solubility therein corresponding to a desired operating level, which solution is kept in equilibrium with the solid compound thus maintaining its concentration at the desired level. Advantageous Effect of the Invention The concentration of the compound in the photographic processing solution is maintained at the desired level regardless of degree of consumption, evaporation, aerial oxidation or other deterioration. A desired level of, for example, an antioxidant can be maintained automatically without any need to take account of the consumption rate if the solubility is limited to, say, 0.06 molar or some other effective level. This means that the system can be used universally regardless of high or low utilisation conditions. In addition another benefit has been found in that lower dissolved levels of antioxidant than those in which a more soluble antioxidant would normally be useable are advantageous because the solid material is oxidised by the air at a lower rate than that in solution. The process does not require replenishment pumps nor any expertise to keep it within control limits. However, other processing solution compounds will, of course, still need replenishment. Detailed Description of the Invention The principle of using a solid which slowly dissolves in a solution in which it is kept is well known, for example a "loo block" in a lavatory cistern. However while it appears similar to that of the invention it employs a completely different principle. In the "loo block" case a solid source is used as a means of replenishment by virtue of an approximately controlled dissolution rate as opposed to a specific limited solubility . This dissolution rate is not related to the final solubility of the agent involved and so the level is not related to the level in solution at any one time. In the invention, the level in solution determines how much more of the agent will dissolve up to the point of maximum solubility, which is set as the operating level or the highest operating level. The solid part of the component may be kept in a filter housing or in some similar containment device through which the solution circulates or it may be located elsewhere, eg, in the processing tank or a supply tank. In order to assist the compound to dissolve in the processing solution a "solvent bridge" material may be employed. Hence the processing solution may contain a solvent for the said compound. The solvents may be water-miscible or non-water-miscible. Examples of such solvents include an organic alcohol, ketone or ester, preferably isopropanol or cyclohexanone. It is envisaged that the components could be colour or black and white developing agents, auxiliary developing agents or electron transfer agents such as pyrazolidinones. Other components could be antioxidants comprising substituted hydroxylamines. In the field of colour image formation by a redox amplification (RX) process, sparingly soluble sources of RX oxidants such as peroxy or other compounds as well as antioxidants such as substituted hydroxylamines could be used as the component. Of the substituted hydroxylamines, the commonly used ones have a relatively high solubility. Diethyl hydroxylamine, for example, is essentially miscible in all proportions with water and is used from concentrated solutions of 85% or 97%. This material and all other photographic antioxidants used commercially are much too soluble to be used for the present invention. Less soluble derivatives of hydroxylamine that are commercially available such as mono-t-butyl-hydroxylamine are also too soluble. On the other hand, dibenzyl-hydroxylamine is commercially available but is almost entirely insoluble in water even with the assistance of surfactants. A preferred group of substituted hydroxylamines is the alkyl and cycloalkyl substituted hydroxylamines with straight or branched chain alkyl groups having from 5 to 8 carbon atoms to give a solubility of up to 0.06 molar for example: n-pentyl-hydroxylamine iso-pentyl-hydroxylamine N-ethyl-N-propyl hydroxylamine hexyl-hydroxylamine cyclohexyl-hydroxylamine N,N-dipropyl-hydroxylamine heptyl-hydroxylamine octyl-hydroxylamine hydroxyoctyl-hydroxylamine hydroxynonyl-hydroxylamine hydroxy-decylhydroxylamine carboxydecyl-hydroxylamine. The above hydroxylamine compounds may be further substituted with hydrophilic and/or hydrophobic groups such that the desired solubility is obtained. Mono-N-Cyclohexyl-hydroxylamine(MCH) has a solubility of about 3.9 to 4 g/l at developer pH(10.0) or about 0.026 molar and is at a level needed for effective use. Another compound which may be used is 4,5-dihydroxylamino-2-propylamino-1,3,5-triazine (CSD). Diethyl hydroxylamine and its sulphonated derivatives such as disulpho diethyl hydroxylamine are used in current commercial formulations from close to zero up to some 0.06 molar. It is estimated that mono alkyl substituents comprising between 5 and 8 carbon atoms would cover the range from almost zero solubility up to 0.06 molar as the maximum solubility of the antioxidant. It is clear that a maximum solubility of about 0.06 molar could be achieved by a multitude of combinations of substituents comprising hydrophobic and hydrophilic groups. This is a highly desirable practical range. The cyclic derivative of hydroxylamine (3) referred to above as CSD with lower solubility (between 0.5 and 1g/l or about 0.005 molar) than cyclohexyl-hydroxylamine was synthesised and its method of synthesis is described below. Preparation of 4,6-dichloro-2-propylamino-1,3,5-triazine (2) Cyanuric chloride (1) (36.9g, 0.2 mole) was dissolved in acetone (600ml) and cooled in an ice/acetone bath. Potassium hydrogen carbonate (25.03g, 0.25 mole) was dissolved in water (150ml) with propylamine (11.82g, 0.2 mole) and added dropwise to the solution of (1) whilst maintaining the temperature below 0°C. The mixture was stirred for 1 hour at 0°C and then stirred for 1 hour at room temperature. The acetone was evaporated off under reduced pressure and the residue (300ml) was poured into water (11). The resulting white solid was filtered, washed with water and dried under vacuum. Yield = 38.2g (92%). The product had nmr, mass and ir spectra which were consistent with the proposed structure. Preparation of 4,5-dihydroxylamino-2-propylamino-1,3,5-triazine (3) Hydroxylamine hydrochloride (120.0g, 1.73 mole) was dissolved in water (250ml). Sodium hydroxide (62.5g, 1.563 mole) was dissolved in water (175ml) and slowly added to the first solution whilst maintaining the temperature below 20°C by means of an ice/acetone bath. Compound (2) (38.1g, 0.184 mole) was dissolved in 1,4-dioxane (250ml) and the aqueous mixture was added dropwise to this whilst maintaining the temperature below 15°C. On completion of the addition a pale purple-coloured waxy precipitate was formed. The mixture was heated to 60°C for 1 hour then to reflux for a further 3 hours. The mixture was cooled and poured into water (11) and left overnight. The mixture was extracted with diethyl ether (total of 31 which was discarded) and the aqueous layer left standing for 72 hours. The resulting precipitate was filtered, washed with water and dried under vacuum. Yield = 12.1g (33%). The product had nmr, mass and ir spectra which were consistent with the proposed structure. Examples of other types of the compound having limited solubility are colour and black-and-white developing agents. Specific examples are listed below: (a) Colour developing agents These need to be in the solubility range of 0 to about 0.015 molar or 6.5g/l of a commonly used colour developing agent such as CD3 (methyl sulphonamidoethyl ethylamino toluidine sesquisulphate hydrate). This agent is however soluble to about 12g/l or 0.028 molar which is about twice its normal upper operating limit and so does not fall within the scope of the present invention. The following colour developing agents have suitably lower solubilities: N,N-diethyl-p-phenylene diamine N,N-diethyl-3-methyl-p-phenylenediamine N,N-dipropyl-p-phenylene diamine N,N-dipropyl-3-methyl-p-phenylenediamine N,N-dihydoxypropyl-3-methyl-p-phenylenediamine (b) Black and White developing agents These are used usually within the range 0 to 0.01 molar or about 2 g/l of a commonly used auxiliary developing agent such as 4,4-dimethyl-1-phenyl-3-pyrazolidone which would come within the scope of the present invention but at the higher solubility limit. The following compounds have suitable lower solubilities: 4-ethyl-1-phenyl-3-pyrazolidone 4,4-dimethyl-1-phenyl-3-pyrazolidone 4,4-diethyl-1-phenyl-3-pyrazolidone 4-n-pentyl-1-phenyl-3-pyrazolidone 4-hydroxypentyl-1-phenyl-3-pyrazolidone 4,4-dimethyl-1-phenyl-4'-methyl-3-pyrazolidone 4-n-pentyl-1-phenyl-4'-methoxy-3-pyrazolidone. The present processing solutions may be any of those described in Research Disclosure Item 36544, September 1994, Sections XVII to XX, published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom. The following Examples are included for a better understanding of the invention. EXAMPLE 1 A circulation system of about 500ml capacity was set up in which solid N-monocyclohexyl hydroxylamine(MCH) was retained behind a removable filter paper filter. The solution circulated was potassium carbonate at pH=10.5. The solution was left to circulate for 30 minutes and the amount of MCH in solution was determined by removing the paper filter which retained the MCH drying it and weighing it. This gave the amount of solid not in solution and hence, by difference from that on the filter initially, the amount in solution. An extra volume of potassium carbonate solution which did not contain MCH was added to the system and after 30 minutes the amount of MCH in solution was determined. The volume was increased by increments of 10%. In a second part of the experiment most of the solution was removed from the system and evaporated to reduce its volume, again in increments of 10%. Solid MCH came out of solution and was collected on the filter and weighed as before. The amount of MCH in solution during this dilution or evaporation procedure is shown in Table 1. Equilibrium Levels of N-cyclohexyl hydroxylamine Volume % Relative to initial MCH in Solution 150 3.96g/l 140 4.05g/l 130 4.11g/l 120 3.87g/l 110 3.81g/l 100 3.80g/l 90 3.88g/l 80 3.92g/l 70 4.03g/l This shows that regardless of any dilution that might occur by addition of a replenisher solution which did not contain MCH or loss of volume by evaporation, the level of MCH automatically adjusted itself to the initial level within 30 minutes. EXAMPLE 2 The compounds CSD and MCH were compared with diethyl hydroxylamine at equimolar levels in a developer of the composition shown in Table 2. Developer Composition Component Concentration AC5 0.6g/l K 2 CO 3 25g/l KBr 28mg/l KCl 6.0g/l TEA (85%) 5.5ml/l REU 1.0g/l Antioxidant see below. CD3 4.35g/l pH 10.05 where AC5 is a 60% W/W solution of 1-hydroxyethylidene-1,1-diphosphonic acid; TEA is an 85% solution of triethanolamine in water; REU is a commercially available optical brightener called Phorwite™ REU and CD3 is N-[2-(4-amino-N-ethyl-m-toluidino)ethyl]-methanesulphonamide sesquisulphate hydrate. The antioxidant level was equivalent to 3.0ml/l diethyl hydroxylamine(85%); which is about 0.029 molar. The three developers were as follows; Developer Antioxidant Amount Dev 1(Control) diethyl hydroxylamine (85%) 3ml/l Dev 2(Inv.) CSD (Mwt 200.2) 5.73g/l Dev 3(Inv.) mono-N-cyclohexyl-hydroxylamine hydrochloride 4.34g/l These developers were placed in 500ml measuring cylinders and stirred continuously with magnetic stirrers to create a vortex depth of about 5mm in each case in order to ensure continuous aeration. The diethyl hydroxylamine was completely in solution, CSD was about 10 to 15% in solution the rest was a solid swirling in the solution. About 90% of the N-cyclohexyl hydroxylamine was in solution with the rest as a solid swirling in solution. Samples were taken each day and analysed for CD3 content. The result are shown in Table 3 below. Limited Solubility Antioxidants Age (weeks) CD3 concentration (g/l) Dev 1 Dev 2 Dev 3 0 4.5 4.4 4.3 1 3.4 4.3 3.9 2 2.1 3.7 2.8 3 0.8 3.2 2.0 4 0 2.8 1.5 5 0 2.3 1.2 It can be seen that the control developer has lost all its CD3 in just over 3 weeks whereas Dev 2 has lost only 30% and Dev 3 about 60%. It is interesting that the developer which had the least concentration of antioxidant at any one time, Dev 2, was the best preserved. This is an unexpected and additional benefit of the invention. It appears that while the antioxidant is in its solid form it is not itself oxidised by the air and so is able to maintain a reservoir of potentially active material. The control developer which contains the same molar amount of antioxidant will be prone to loss of antioxidant not only in preserving the colour developing agent but also by direct aerial oxidation. Developer 3 shows behaviour intermediate between the other two as reflects its intermediate solubility. Thus it appears that limited solubility antioxidants are not only capable of maintaining a desired level automatically independent of usage rate (since this level is equal to the maximum solubility) but also they can be used at lower dissolved levels because they are continuously replaced from the solid source and while in the solid phase are oxidised by the air at a lower rate.

Claims: A photographic aqueous processing solution containing at least one compound which has a maximum solubility therein corresponding to a desired operating level, which solution is kept in equilibrium with the solid compound thus maintaining its concentration at the desired level. A processing solution as claimed in claim 1 which contains a solvent for the said compound. A processing solution as claimed in claim 2 in which the solvent is an organic alcohol, ketone or ester, preferably isopropanol or cyclohexanone. A processing solution as claimed in any of claims 1-3 in which the processing solution contains a silver halide colour developing agent. A processing solution as claimed in any of claims 1-4 which contains a peroxide oxidising agent. A processing solution as claimed in any of claims 1-5 which contains a hydroxylamine antioxidant having one or more N-substituents which are an alkyl or cycloalkyl group of 5-8 carbon atoms which may be further substituted with hydrophilic and/or hydrophobic groups. A processing solution as claimed in claim 6 in which the hydroxylamine compound is pentyl-hydroxylamine, hexyl-hydroxylamine, heptyl-hydroxylamine, octyl-hydroxylamine, mono-N-cyclohexyl-hydroxylamine or 4,5-dihydroxylamino-2-propylamino-1,3,5-triazine. A processing solution as claimed in any of claims 1-5 in which said at least one compound is a colour developing agent, black-and-white developing agent, antioxidant, antifoggant or pH buffer. A processing solution as claimed in any of claims 1-8 in which the solubility of the said compound in the photographic processing solution is from 0.001 to 0.2, preferably from 0.01 to 0.06 molar. A method of processing an imagewise exposed photographic material which includes the step of treating it with a processing solution according to any of claims 1-9. A method as claimed in claim 10 in which the processing solution is recirculated through a containment device containing the solid compound. A method as claimed in claim 9 or 10 in which the containment device is a filter housing containing a filter.

Inventors: GODDARD JOHN DEMITA, TWIST PETER JEFFERY, GODDARD, JOHN DEMITA, TWIST, PETER JEFFERY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1997
Main classification: G03C7
IPC codes: G03C7