GB2345151A - Photographic developing solutions - Google Patents

Abstract

A photographic developing solution is provided which comprises the sulphite or bisulphite salt of N-methyldiethanolamine at a concentration of at least 0.05 moles/dmâ together with at least one silver halide developing agent (eg. hydroquinone or an ascorbic acid-type agent) and at least one superadditive developing agent (eg. 1-phenyl-4-methyl-4-hydroxymethylpyrazolid-3-one). The solution is additionally characterised by a mole ratio of N-methyldiethanolamine to sulphite of at least 1:1 and a pH of at least 8. The solution may also contain a metal complexing agent (eg. diethylenetriamine penta acetic acid). A concentrated developing solution which may be used to prepare the above solution on dilution is also provided. The developing solution of the invention is particularly useful for developing conventional monochrome silver halide camera films.

Description

Photographic Developing Solutions Field of the Invention This invention relates to developing solutions for silver halide photographic materials.

Background Developing solutions useful in silver halide photography are well known, and are described, for example, in the books Photographic Processing Chemistry by L F A Mason, second edition published by the Focal Press in 1974, and Modem Photographic Processing by Grant Haist, published by Wiley Interscience in 1979. These solutions are used to reduce exposed silver halide crystals to silver metal and in so doing form the silver image in monochrome photographic materials.

It is a fundamental requirement that the development process must distinguish between those grains that have been exposed to light and those that have not.

Silver halide grains that have been exposed to light contain latent image centres and one mechanistic explanation of the ability of developers to distinguish between exposed and unexposed grains is that the reduction of Ag+ in exposed grains is an autocatalytic process. In this process the latent image centre (a small cluster of silver atoms) provides the focus of the catalytic process. In unexposed grains there are no silver clusters and thus these fail to develop.

The distribution of silver clusters between grains in silver halide photographic materials is not solely determined by exposure history. Grains might be exposed, but the silver cluster may fail to reach the critical size at which it becomes a viable focus for the chemical reduction process, while on the other hand silver clusters may form in unexposed grains. The ability of a developing solution to discriminate between exposed and unexposed grains is thus a fundamentally important property of the developer. Commercial developer solutions are formulated to ensure as high a yield as is possible of development of exposed grains with as few as possible of unexposed grains contributing to the image. When unexposed grains develop, they give rise to fog. This ability of a developer solution to discriminate between exposed and unexposed grains may be measured in terms of the speed to fog ratio that is obtained when photosensitive materials are developed.

A second and commercially important aspect of the development process is that for monochrome camera films, in which the developed silver is itself the visible image, the morphology of the developed silver can directly influence the appearance of the image, and in particular it can influence the perceived graininess of the image. Grain is the term used to describe the optical effect in which randomly distributed clumps of developed silver appear to come together into groups. It is a subjective property, most easily seen as non-uniform distribution of density in a image area where density is expected to be constant. By using a scanning microdensitometer, this non-uniformity can be objectively measured, and the objective scale upon which graininess is measured is called granularity. Since the granularity of an image is determined by the form of the developed silver, the chemical composition and properties of the developer can strongly affect this property. It is well known that developing solutions which have high concentrations of dissolved sulphite are favoured for producing low grain images, and it is commonly held that the reason for this is that the high developer sulphite ion concentration favours a high contribution from the so-called solution physical development process rather than the chemical development process.

As well as moderating the form of the developed silver by facilitating solution physical development, sulphite fulfils another key role in the developing solution. It is an antioxidant that can reduce loss of the developing agents to aerial oxidation, and in so doing preserve the appearance and clean working properties of the developing solution. It is also, by virtue of being a silver halide solvent capable of conferring a degree of protection from'sludging', in which dissolved Ag+ is reduced to produce deposits of metallic silver over the processing equipment.

Thus sulphite is greatly used in the formulation of developing solutions for monochrome films. It is always appropriate to incorporate large amounts of sulphite ion, and as a generalisation, it might be said that a monochrome film developer cannot have too much sulphite. However when developing solutions are formulated the amount of sulphite that can be incorporated is limited by the solubility of the ingredients. Hence industry standard developers like Ilford ID11 and Kodak D76, which are formulated to produce approximately 0.76 mole/dm3 so32-in solution are made using sodium sulphite, and cannot be formulated other than as working strength solutions which are prepared from powder blends because of the limiting solubility of sodium sulphite (approximately 1.0 mole/dm3 at normal temperatures) There is increasing interest in the provision of photographic processing solutions in the form of concentrated liquids, which are easier to handle and much more convenient to use as they only need to be diluted. The limited solubility of inorganic sulphites is a constraint on the formulation of such concentrated developing solutions. It is known according to British Patent specification 958 678 that one way of circumventing the limiting solubility of inorganic sulphites is to formulate developing solutions using addition compounds between sulphur dioxide and hydroxyalkylamines as the source of sulphite in the developing solution. These addition compounds will be referred to as sulphite or bisulphite salts of alkanolamines hereinafter. Alkanolamines are as the name implies, saturated molecules which contain both an hydroxyl (-OH) and an amine (-NR2) functional group. They are common components of liquid concentrate developing solutions, (and other processing solutions), and in these they fulfil a variety of roles : 1. The alkanolamines themselves are normally liquid at room temperature and are readily soluble in water. This means that a high concentration of alkanolamine can be formulated in a liquid concentrate.

2. They facilitate dissolution of the other organic components of the developer. i. e. they are solvents for the developing agents.

3. The basic amine group acts as a pH buffer. The pH buffer capacity of their solutions is at a maximum at the pKa of the alkanolamine ; -NH2 + H+ =-NH3+ pKa > 7 Many alkanolamines have pKas in the range that is relevant for camera film developer formulation, and the high solubility of the alkanolamine ensures that a high concentration of buffer molecules can be attained.

4. The amine group forms a weak complex with sulphur dioxide in the presence of water. These complexes are regarded as the sulphite or bisulphite salts, either of which may be produced, depending upon the stoichiometry: RNH2 + H2SO3 = RNH3+ + HSO3-= RNH2. H2SO3 (bisulphite) 2RNH2 + H2SO3 = 2RNH3+ SO-= (RNH. H. SO (sulphite) In practice, developers, and particularly liquid concentrates, are more likely to be formulated with the sulphite rather than the bisulphite because the bisulphite is acidic, and additional alkali would need to be added to make the solution sufficiently alkaline for development. In fact additional alkanolamine is generally added to that used to form the sulphite salt. In commercial developer solution formulations the ratio of alkanolamine to sulphite is typically between about 2: 1 and about 2.5: 1.

5. The sulphite and bisulphite salts of alkanolamines are normally highly soluble, not only in water but also in other solvents and particularly in excess alkanolamine. This enables high concentrations of sulphite to be obtained in photographic developing solutions and also enables liquid concentrates for such solutions to be prepared which have high concentrations of sulphite ion.

For all of these reasons, alkanolamines are widely used in the formulation of monochrome camera film developers. Although many alkanolamines are known, those used in practice are diethanolamine, ethanolamine, butyldiethanolamine and methylethanolamine.

Problem to be Solved Despite their widespread use, alkanolamines are not without disadvantages.

They are development accelerators and this means that developers formulated with alkanolamines will require shorter development times than would analogous solutions formulated with sodium or potassium salts. In some processing methods this can be disadvantageous, especially if it leads to development times which are too short to be easily controlled. Also, because the induction time for development of exposed grains is statistically distributed not all of the developable grains may start to develop at short development times and this can lead to lower than optimum sensitometric film speeds. Conversely, the alkanolamine may lead to high levels of fog. Finally, the alkanolamine often accounts for a very large part of the bulk weight of a developer composition, and in these cases the hazards associated with the use of the developer concentrate will be greatly influenced by the hazards associated with the alkanolamine.

Thus there is a need to formulate high dilution liquid developer solutions which provide good discrimination of speed against fog and which also give rise to low grain images. We have found that these needs are best served using developing solutions formulated using N-methyldiethanolamine, which is hereinafter just referred to as methyldiethanolamine. Moreover this alkanolamine is of relatively low volatility, thus minimising the hazards of exposure to the vapour.

Summarv of the Invention This invention provides a photographic developing solution formulation comprising the following constituents: 1) methyldiethanolamine sulphite or bisulphite salt 2) at least one silver halide developing agent 3) at least one superadditive developing agent The amount of methyldiethanolamine in the developing solution is not less than 0.05 moles/dm3. The amount of sulphite that is associated with methyldiethanolamine is not less than 0.025 moles/dm3 and not greater than the concentration of the methyldiethanolamine. In practice the amount of sulphite associated with methyldiethanolamine will be limited by the fact that to achieve the correct working strength developer solution pH the mole ratio methyldiethanolamine to sulphite is unlikely to be less than 1 : 1. The mole ratio methyldiethanolamine to sulphite may especially be greater than 1 : 1, and is preferably greater than 2: 1, and most preferably between 2: 1 and about 2.5: 1.

The most suitable silver halide developing agents are dihydroxybenzene compounds, and particularly hydroquinone, or ascorbic acid compounds such as L-ascorbic acid, D-isoascorbic acid, and salts thereof. A preferred concentration of this developing agent is between about 0.01 to 0.10 moles/dm3, as a lower limit and 0.10 to 1.50 moles/dm3 as a higher limit.

By superadditive developing agent is meant a compound which acts synergistically with the main developing agent such as hydroquinone to provide a more active, relatively longer lasting developing combination. A large number of such compounds are known from the patent literature but in practice the two most commonly used classes are amino-phenols such as p-methylaminophenol which is known commercially as Metol and pyrazolidinone compounds such as those provided in United States Patent Specification 2 289 367.

A particularly preferred pyrazolidinone compound is 1-phenyl-4-methyl-4-hydroxymethyl pyrazolid-3-one which is hereinafter referred to as compound A. A suitable quantity of this compound to be present in a developing solution of the present invention is from 0.0005 to 0.05 moles/dm3.

The pH of the developing solution is at least 8, preferably between 8 and 12, and most preferably between 8 and about 11.

Preferably at least one metal complexing agent is also present in the developing solution. A particularly suitable compound is diethylenetriaminepentacetic acid hereinafter referred to as DTPA. Other suitable metal complexing agents include phosphonic acids such as 1-hydroxyethylidene 1,1-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 0.10 moles/dm3.

The developing solution formulations of the invention may be used in processing machines in which the development activity is maintained during exhaustion by replenishment. When used like this, the developing solution may be inocculated with bromide from a so called starter solution, or it may have bromide incorporated during manufacture as part of a kit for machine processing. In these processes constant developer bromide ion concentration is sought to be achieved by replenishing the working strength developing solution with a developing solution that is formulated to be free of bromide, or at least to have a lower concentration of bromide than is associate with the developer in the machine.

Thus an alkali bromide, in particular sodium or potassium bromide may be present in the developing solution as a starter. A suitable amount is from 0.0005 to 0.05 moles/dm3.

An organic antifoggant may also be present in the developing solution of the present invention but this is not preferred.

Other components commonly used in photographic developing solutions may also be present in the solutions of the present invention, in particular other alkanolamines in addition to the methyldiethanolamine.

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 or liquid components, or solutions of these, as in the examples which follow.

However a second aspect of the present invention provides a concentrated developing solution which may be used to prepare the working strength solutions as hereinbefore set forth. Indeed one of the advantages of the present invention is that the formulations may readily be provided in commercially useful forms in the form of such 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, because of the aforementioned desirable properties of alkanolamines.

Therefore according to this aspect of the present invention there is provided a concentrated photographic silver halide developing solution which comprises as the main component methyldiethanolamine at a concentration greater than 1.0 moles/dm3 ; sulphite in association with methyldiethanolamine in the mole ratio (methyldiethanolamine to sulphite) 1: 1 or greater; a developing agent at a concentration greater than 0.20 moles/dm3 ; and a second superadditive developing agent at a concentration greater than 0.01 moles/dm3 and a sequestering agent and which will produce upon dilution a working strength solution.

There is no upper limit on the concentration of methyldiethanolamine because concentrated developing solutions can be formulated which contain no added water and in which the methyldiethanolamine is the medium in which all the other ingredients are dissolved. In this case the upper limit can approach the specific molar volume of methyldiethanolamine. There is no preferred upper limit for sulphite insofar as it is generally accepted that developer solutions cannot be formulated with too much sulphite.

The following example compares the photographic properties of the inventive developer solutions formulated using methyldiethanolamine with those formulated using a variety of alternative alkanolamines at the same molar concentration.

In order to provide data upon the sensitometric effect of each alkanolamine independently of other aspects of the developer in which it is formulated, the developer solutions have to be formulated differing only in the chemical structure of the alkanolamine used. In fact this is not strictly possible. Because of the different pKas of the various alkanolamines, developers differing only in the identity of alkanolamine (in equimolar amonts) would have different pHs and this difference would affect the sensitometric properties of the developers, (possibly greatly). This difficulty was overcome by formulating the developers with constant alkanolamine and sulphite ion concentrations, and the solution pH was then adjusted with NaOH to 8.5 for all the developers. The small amount of inorganic base needed for this adjustment has no sensitometric affect.

Preparation of alkanolamine bisulphites Each alkanolamine that was investigated was converted into the bisulphite by bubbling sulphur dioxide into an aqueous solution of 2.5 gmole of the alkanolamine until the stoichiometric weight increase for a 50% w/w solution of the relevant compound had been reached.

Developer solution formulation The model developer formulation used was: alkanolamine = 460 mM S0-= 460 mM hydroquinone = 80 mM Compound A = 1.2 mM DAPTA = 3.0 mM pH = 8. 50 @ 25 C In this composition the alkanolamine: sulphite stoichiometry is exactly 1: 1.

This ratio was chosen to keep the formulation simple.

Fourteen variants on the above working strength developer formula were produced. The inventive solution using methyldiethanolamine was thus compared with eleven alternative alkanolamines, and also with solutions formulated using potassium and sodium sulphites. Because these two inorganic developers have no intrinsic pH buffer capacity, 0.05 mole/dm3 boric acid was added to mimic the buffering action of the organic alkanolamines. All the developers were formulated as working strength solutions by taking 2.3gmoles of alkanolamine bisulphite, diluting this to 4dm3 with distilled water prior to adding the remaining ingredients, further diluting to 5dm3 and finally pH adjustment with NaOH. The developers were stored in ldm3 bottles, and 350 cm3 removed from this stock as required for each experiment.

Sensitometric evaluation of example developers Strips of HP5+ film were exposed through a continuous wedge to a D552 source at 250 Lux for 1/30 second and a development time range (4,6,8 and 10 minutes) was processed for each developer. This was repeated 4 more times for each developer (i. e. 5 replicates of each time range), with the order of developer choice randomised.

The responses for analysis were the time required for each film to reach a contrast of G, 5=0. 62; and the fog (shown as DMin), foot speed and granularity at this contrast. The granularity reported is the RMS granularity at D=1 (above DMin). The speed to grain efficiency index (SGI) was also calculated: SGI = 10# x G#/granularity2 The mean and 95% confidence limits for each response in each developer were also calculated: 95% CL = mean tcr/4n These results are presented in Table 1.

The raw data in Table 1 is plotted in the following two figures. These figures include the data for developers formulated with either all sodium or all potassium salts. In Figure 1 the mean value for foot speed at G, 5=0. 62 is shown plotted against DMin for each developer. In Figure 2 the mean speed value is shown plotted against the granularity for each developer.

Table I-Summary of Sensitometric Test Data

Counter lon Dev. Time DMin Foot Speed Gran SGI dimethylethanolamine 4. 0 0. 3 0. 30 0. 02 5. 73 ~0.04 40~5 210~40 diisopropanolamine 4. 6 ~0.3 0. 28 ~0.02 5. 76 ~0.02 33~3 340~60 ethanolamine 3. 9 ~0.1 0. 30 ~0.01 5. 78 ~0.04 36~2 300~40 methylethanolamine 6.1~0.2 0. 31 ~0.01 5. 77 ~0.03 43~6 210~60 ethylethanolamine 6.3~0.5 0. 34 ~0.03 5. 82 0. 04 40 3 240 30 dimethylisopropanolamine 4.3 ~0.2 0. 30 ~0.01 5. 80 ~0.04 36~1 295~10 diethanolamine 4. 8 ~0.2 0. 29 ~0.01 5. 76 ~0.04 35~1 290~15 methyldiethanolamine 6. 1 0. 2 0. 29 t 0. 02 5. 83 ~0.01 37~1 310~20 ethyldiethanolamine 5. 5 ~0.1 0. 28 ~0.01 5. 71 ~0.03 47~2 145~15 butyldiethanolamine 4.8~0.1 0. 30 ~0.01 5. 80 0. 03 34 1 350 20 triethanolamine 4.1~0.3 0.30~0.02 5. 72 ~0.04 35~2 260~30 isopropanolamine 4. 2 0.4 0.31 0.01 5.80 0.05 38 2 270 35 sodium 6.3~0.6 0.30~0.01 5.80~0.02 36~2 310~20 potassium 5. 8 0.3 028 t 0.01 5.78 0. 02 33~1 350~35 These two figures clearly show that the sensitometric responses of each developer are determined by the identity of the alkanolamine and that developers comprising the inventive compound methyldiethanolamine have superior image forming properties to any of the other developers. This finding is very significant and was unexpected.

The data clearly identifies methyldiethanolamine as the alkanolamine of choice for formulating a developer for monochrome films. Developers formulated with methyldiethanolamine would be expected to give high speed/grain and speed/fog responses at reasonable development times (methyldiethanolamine does not much accelerate development). Also the hazards associated with this substance are low compared to the other substances in the list.

Figures 1 and 2 are additionally characterised according to the chemical structures of the alkanolamines concerned, and it can be seen that the results do not correlate with these structures.

Thus while the advantages of high silver solvent capacity and sulphite ion concentration may be achieved with any alkanolamine, the objects of the present invention are realised by formulating the developer with methyldiethanolamine because this gives rise to a developer solution formulation that is clearly and unexpectedly superior in terms of the speed/fog and speed/grain responses compared to the other alkanolamines investigated.

Claims (8)

1. Claims 1. A photographic silver halide developing solution containing N-methyldiethanolamine.
2. 2. A photographic silver halide developing solution according to Claim 1 in which the concentration of N-methyldiethanolamine is not less than 0.05 moles/dm3.
3. 3. A photographic silver halide developing solution according to Claim 1 comprising at least one main developing agent selected from hydroquinone or an ascorbic acid type developing agent, or a salt thereof, at a concentration 0.01 to 1.50 moles/dm3.
4. 4. A photographic silver halide developing solution according to Claim 3 where the ascorbic acid developing agent is L-ascorbic acid or D-isoscorbic acid or a salt of either.
5. 5. A photographic silver halide developing solution according to any of Claims 1 to 4 which also comprises at least one superadditive developing agent.
6. 6. A concentrated photographic silver halide developing solution which upon dilution produces a working strength solution according to Claim 1.
7. 7. A concentrated developing solution according to Claim 6 which comprises as the main component N-methyldiethanolamine at a concentration greater than 1.0 moles/dm3 ; sulphite in association with methyldiethanolamine in the mole ratio (methyldiethanolamine to sulphite) 1: 1 or greater; a developing agent at a concentration greater than 0.20 moles/dm3 ; and a second superadditive developing agent at a concentration greater than 0.01 moles/dm3.
8. 8. A photographic silver halide developing solution according to any of Claims 1 to 7 which also contains a sequestering agent.

   8. A photographic silver halide developing solution according to any of Claims 1 to 7 which also contains a sequestering agent. Amendments to the claims have been filed as follows Claims 1. A photographic silver halide developing solution for monochrome camera films containing N-methyldiethanolamine.

   2. A photographic silver halide developing solution according to Claim 1 in which the concentration of N-methyldiethanolamine is not less than 0.05 moles/dm3.

   3. A photographic silver halide developing solution according to Claim 1 comprising at least one main developing agent selected from hydroquinone or an ascorbic acid type developing agent, or a salt thereof, at a concentration 0.01 to 1.50 moles/dm3.

   4. A photographic silver halide developing solution according to Claim 3 where the ascorbic acid developing agent is L-ascorbic acid or D-isoscorbic acid or a salt of either.

   5. A photographic silver halide developing solution according to any of Claims 1 to 4 which also comprises at least one superadditive developing agent.

   6. A concentrated photographic silver halide developing solution which upon dilution produces a working strength solution according to Claim 1.

   7. A concentrated developing solution according to Claim 6 which comprises as the main component N-methyldiethanolamine at a concentration greater than 1.0 moles/dm3 ; sulphite in association with methyldiethanolamine in the mole ratio (methyldiethanolamine to sulphite) 1: 1 or greater; a developing agent at a concentration greater than 0.20 moles/dm3 ; and a second superadditive developing agent at a concentration greater than 0.01 moles/dm3.