This invention relates to a method for forming a positive color image by use of an inner latent image type light-sensitive silver halide color photographic material for formation of direct positive color image, more particularly to novel processing method which is little in dependence on the concentration change in bromide ion caused by the change in amount replenished and the influence by evaporation and also in dependence on processing time and yet is not impaired in rapidity, and also small in developing fog, especially a processing method with small amount to be replenished and high processing stability.
Methods for obtaining direct positive images known in the prior art can be classified mainly into the two types. One type employs a silver halide emulsion having previously fogged nucleus and positive image is obtained after development by destroying the fogged nucleus or the latent image at the exposed portion by utilizing solarization or Hershel effect, etc. The other type employs an inner latent image type silver halide emulsion not previously subjected to fogging, fogging treatment (treatment for forming developing nucleus) is applied after image exposure and then surface development is performed or alternatively surface treatment is performed while applying fogging treatment (treatment for forming developing nucleus) after image exposure, whereby a positive image can be obtained.
The above fogging treatment (treatment for forming developing nucleus) may be conducted by way of giving the whole surface exposure, chemically by use of a fogging agent, or by use of a strong developing solution, or further by heat treatment, etc.
Of the above two methods for formation of positive images, the methods of the latter type are generally higher in sensitivity than the methods of the former type and therefore suitable for uses in which high sensitivity is required.
In this field of the art, various techniques have been hitherto known. For example, there have been known the methods disclosed in U.S. Pat. Nos. 2,592,250, 2,466,957, 2,497,875, 2,588,982, 3,761,266, 3,761,276 and 3,796,577 and U.K. Pat. No. 1,151,363.
In the case of processing of an inner latent image type light-sensitive silver halide color photographic material (hereinafter referred to as inner latent image type light-sensitive material), the process comprises basically the two steps of color development and desilverization which are performed after application of the fogging treatment and/or while applying fogging treatment, desilverization comprising bleaching and fixing steps or bleach-fixing step. Otherwise, as additive processing steps, rinsing processing, stabilizing processing, etc., are added.
In the color development performed after application of fogging treatment and/or while applying fogging treatment, the silver halide at the unexposed portion is reduced to silver, and at the same time the oxidized aromatic primary amine developing agent reacts with a coupler to form a dye. In this process, the halide ions formed by reduction of silver halide are dissolved out into the developing solution to be accumulated therein. Separately, the components such as inhibitors contained in the inner latent image type light-sensitive material are dissolved in the color developing solution to be accumulated therein. In the desilverization step, the silver formed by development is bleached with an oxidizing agent and then all the silver salts are removed from within the inner latent image light-sensitive material as soluble silver salts with a fixing agent. It is also known to perform one bath bleach-fixing processing method, in which the bleaching step and the fixing step are carried out at the same time.
In the color developing solution, developing inhibiting substances are accumulated by developing processing of the inner latent image type light-sensitive material as described above. On the other hand, the color developing agent or benzyl alcohol are consumed or brought out as accumulated within the inner latent image type light-sensitive materials, and the concentrations of those components become lowered. Accordingly, in the developing processing method in which a large amount of inner latent image type light-sensitive materials are continuously processed by means of an automatic developing machine, etc., it is necessary to have a means for maintaining the components of the color developing solution within the constant levels in order to avoid changes in characteristic after finishing of development due to the changes in component concentration. As such a means, it has been generally employed to replenish the components in shortage and replenishing a replenisher for diluting unnecessary increased components. Due to replenishing of such a replenisher, a large amount of overflow of the solution is necessarily formed and discarded, and therefore this method involves great problems in economy and environmental pollution. For this reason, in recent years, in order to reduce the above overflow solution there has been proposed and practically employed the so-called low flow replenishment system in which these replenishers are concentrated and replenished in a small amount.
However, if the amount replenished is extremely reduced, the organic inhibitors or halide ion concentration dissolved out into the developing solution will suffer from great concentration changes even by slight errors in the amount replenished and will be susceptible to the influence by concentration through evaporation whereby the above spent accumulated products are generally increased in concentration. For example, by increase of halide ion concentration, the developing reaction is inhibited, particularly more inhibited at the higher density portion of the characteristic curve, whereby there ensues the problem such that no satisfactory density can be obtained even by elongation of the processing time. For avoiding this, for example, one may consider to remove the halide ions by ion exchange resin or electrodialisis from the overflow solution and use it as the replenisher again by regeneration with addition of a regenarating agent for replenishing the defficient components which became in shortage during development or lost during regeneration treatment, as proposed in processing of the surface latent image type light-sensitive silver halide color photographic material (hereinafter referred to as surface latent image type light-sensitive material) for formation of negative image.
According to these regeneration by ion exchange resin or electrodialisis and the thickened reduced replenish system, processing is affected by evaporation or regeneration operation, and also susceptible to the change in bromide ion concentration, and also affected by the difference in the amount processed as well as the difference in the amount of replenishers, whereby there is involved the drawback that the processing solutions differ in composition to a great extent.
For such reasons, in the low flow replenishment processing or the regeneration method, it is necessary to make efforts to quantitate the components for every cycle of regeneration to maintain the composition at a constant level, and therefore these regeneration processing and low flow replenishment processing can be practiced with difficulty in a developing station or mini-laboratory, etc., having no special skill.
Such problems are caused primarily by the change in bromide ion which is the developing inhibitor. For example, the problem may be estimated to be solved by improving the developing characteristic by making smaller the mean grain size of the silver halide in the inner latent image type light-sensitive material. However, in a color developing solution using 3-methyl-4-amino-N-ethyl-N-.beta.-methanesulfoneamidoethylaniline which is the developing agent of the prior art, if the developing characteristic is improved, processing will become rather more susceptible to the change in bromide ion concentration in the developing solution to result impairment of processing stability as contrary to the expected result.
However, it is an important task to enhance processing stability simultaneously with shortening of the processing time. That is, the strong demand of the era is the above-mentioned low flow replenishment in the economical sense, but short time processing is also strongly demanded in aspect of shortening the time limit of delivery.
Whereas, as mentioned above, rapid processing and stabilization of processing or low flow replenishment are issues which are antagonistic to each other, which may be criticized as a relationship of trade-off.
That is, if low flow replenishment is aimed at, the concentration of the bromide ion which is the inhibiting substance or the concentration of a sulfur compound or a mercapto compound which is the emulsion stabilizer will be increased to impair rapidity, and processing stability is impaired.
Nevertheless, various countermeasures have been taken to expedite color development in the prior art. Particularly, since the above developing agent which have been used in the prior art as the most suitable developing agent for the silver chlorobromide emulsion of the inner latent image type is low in hydrophilic property, it can be slowly penetrated into the light-sensitive material, and therefore various penetrating agents for acceleration of penetration have been investigated. For example, there have been widely employed the method in which color development is accelerated by addition of benzyl alcohol into the color developing solution. However, according to this method no satisfactory color development can be effected unless processing is performed at 33.degree. C. for 3 minutes or longer. Besides, there is also involved the drawback of being susceptible to the subtle influence by the bromide ion concentration. There is also known the method of increasing the pH of the color developing solution, but when the pH becomes 10.5 or higher, the color developing agent will be oxidized at a remarkably higher rate, changes in pH have great effect on processing due to absence of an appropriate buffer to give no stable photographic characteristic, and also dependency on the processing time becomes greater.
It is also known to increase the activity of the color developing solution by increasing the amount of the color developing agent contained therein. However, since the color developing agent is very expensive, the cost of the processing solution becomes higher and at the same time there is the problem of instability that the above agent is difficultly soluble in water and will be readily precipitated. Thus, this method is not useful in practical application.
On the other hand, for accomplishing a rapid color development of the surface latent image type light-sensitive material, it has been known to have the color developing agent previously built in the light-sensitive material. For example, there has been known the method in which the color developing agent is built in as a metal complex (U.S. Pat. No. 3,719,492). However, according to this method, the light-sensitive material is poor in raw storability, and drawbacks such as fogging before use and further tendency to be fogged during development are known to be involved.
Further, for inactivation of the amine portion of the color develping agent, there has been known the method, for example, in which the color developing agent is built in as Schiff salt (U.S. Pat. No. 3,342,559, Research Disclosure, No. 15159, 1976). However, according to these methods, color development cannot be initiated after alkali hydrolysis of the color developing agent (thus involving rather the drawback that color development is delayed).
Further, in the case of having a color developing agent directly built in, in addition to the drawback of fogging of the emulsion during storage due to instability of the color developing agent, various kinds of troubles are known to be generated in processing because the emulsion film quality becomes weaker.
It has been found that the same drawbacks are involved also in the case when the techniques known in the surface latent image type light-sensitive material as described above are applied for the inner latent image type light-sensitive material.
Also, as the accelerators known in the surface latent image type light-sensitive materials in the prior art, investigations have been made about the compounds disclosed in U.S. Pat. Nos. 2,950,970, 2,515,147, 2,496,903, 4,038,075 and 4,119,462; U.K. Pat. Nos. 1,430,998 and 1,455,413; Japanese Unexamined Patent Publications Nos. 15831/1978, 62450/1980, 62451/1980, 62452/1980 and 62453/1980; Japanese Patent Publications Nos. 12322/1976 and 49728/1980; etc. As the result, most of the compounds have insufficient acceleration effect on the inner latent image type light-sensitive materials, and the compounds having high acceleration effect not only have the drawback of forming developing fog but also unsuitable for improvement of processing stability.
It is also known to accelerate development by providing a silver halide emulsion layer which is substantially non-light-sensitive in a surface latent image type light-sensitive material as disclosed in Japanese Unexamined Patent Publications Nos. 23225/1975, 14236/1981; U.K. Pat. No. 1,378,577, German Laid-open Patent Publication No. (OLS) 26 22 922; etc., but its function is to absorb unnecessary halogens released during development and developing inhibiting substances such as unnecessary eliminated groups of DIR couplers or DAR couplers, and it is not to accelerate positively development. Particularly, even when applied for an inner latent image type light-sensitive material, its development accelerating effect is not only small, but no processing stabilizing effect can be obtained with respect to fluctuation in bromide ion concentration, although it may have an effect with respect to fluctuation in iodide ion concentration.
On the other hand, in the case of the surface latent image type light-sensitive material, the speed of color development is said to differ depending on the kind of the para-phenylenediamine derivative employed and depend on the redox potential. Of these color developing agents, N-alkyl substituted color developing agents having low water solubility such as N,N-diethyl-p-phenylenediamine sulfate or 3-methyl-4-amino-N,N-diethylaniline hydrochloride, while having high developing activity and enabling rapid processing, are known to be low in dark fading characteristic of the color formed dye after processing. When applied for the inner latent image type light-sensitive material, substantially similar results were obtained and no stability could be obtained with respect to the bromide ion concentration. On the other hand, when 3-methyl-4-amino-N-ethyl-N-.beta.-methoxyethylaniline-di-toluenesulfonate which is said to be preferable with high developing activity in the surface latent image type light-sensitive material (see U.S. Pat. Nos. 3,656,950 and 3,658,525) is applied for the inner latent image type light-sensitive material, rapid processing can be surely effected but no stability with respect to the bromide ion concentration can be obtained and yellow stain was also found to be generated markedly in the unexposed portion of the inner latent image type light-sensitive material after processing. Particularly, when processed within a short time, the color developing solution remains to cause disadvantageously generation of coarse stains. Thus, this compound was found to be unuseful in rapid processing.
On the other hand, 3-methyl-4-amino-N-ethyl-.beta.-methanesulfoneamidoethylanilinesesquisulfa te monohydrade or 3-methyl-4-amino-N-.beta.-hydroxyethylaniline sulfate in which alkyl sulfoneamide group or hydroxyalkyl group which is a water-soluble group is introduced into the N-alkyl group has been said to exhibit little difference in half-wave potential exhibiting the redox potential and both to be weak in developing activity, as can be seen from Photographic Science and Engineering Vol. 8, No. 3, May to June, 1964, pp. 125-137. Thus, it has been generally admitted that there is substantially no color developing agent which is high in developing activity for the inner latent image type silver chlorobromide emulsion and also excellent in processing stability, and 3-methyl-4-amino-N-ethyl-N-.beta.-methanesulfoneamidoethylaniline sulfate has been generally used together with benzyl alcohol. However, in this case, as described above, the processing is susceptible to the influence by the change in the bromide ion concentration.
On the other hand, in the thickened reduced replenish processing in which the replenisher is reduced, there is another problem of increased entrainment of processing solution components. This is because the ratio of the tank solution renewed with the replenisher is lowered due to reduction in the amount replenished, and also because the term for use of the solution is prolonged. Entrainment of other processing solution is caused by the so-called back contamination in which the processing solution components immediately after development are brought into the color developing solution by splash or delivering leader or hangers for hanging belts or films in the adjacent processing solutions in the processing machine. Of these entrained components accumulated, thiosulfate ions which is the fixing agent dissolve silver halides and promote physical development, whereby the exposed portion having internally a latent image is developed to generate marked developing fogging. Thus, this problem occurs strongly particularly when direct bleach-fixing processing is applied after color development. Also, increased entrainment of a metal salt which is the bleaching agent, particularly, a ferric salt will promote decomposition of hydroxylamine which is a preservative to generate ammonia ions. This decomposition reaction is greatly acceletated at 30.degree. C. or higher. Generation of the ammonia ions will accelerate physical development similarly as thiosulfate ions whereby involving the problem of generation of development fogging.
Accordingly, under the state of the art, even an amount to be replenished may be lowered for economical improvement and lowering in environmental polution, it would be strongly desirable to have a color developing solution which can be processed rapidly, and can maintain photographic performance constantly, and can be processed stably without decomposition of the effective components or change in photographic processing performance even when the processing solution may be used for a long term.