US3372030A - Method of shortening the processing time of color photography - Google Patents

Description

States Unite This invention relates to color photography and more particularly to methods for the manufacture of multilayer color materials capable of rapid penetration by processing solutions and methods of processing such materials.

The processing of exposed color photographic sensitive materials include the essential steps of development, fixing, bleaching, washing and drying. A recognized major disadvantage of known color films and papers is the relatively long time which is required to elfect complete processing, especially as compared to black and white materials. Thus a total period of up to fifty minutes may be required for the complete processing of conventional color film or paper involving about 6 to minutes to effect development, about 4 minutes in the stop bath, about 10 minutes washing and about 10 minutes in the bleach and fix bath followed by final washing. A desideratum in the field of color photography is to provide a color material which may be completely processed in a period of time comparable to that of black and white. However, as those skilled in the art know, the rapid processing of color materials is a much more diflicult problem than that of black and white for the reason that the three or more color emulsion layers offer more hindrance to rapid penetration of processing solutions than does the single black and white emulsion layer.

A major object of the invention is to provide a rapid method of processing color photographic sensitive material.

Another object of the invention is to provide a novel color photographic material characterized by inherent rapid processing properties.

A further object of the invention is toprovide a novel emulsion for use in the manufacture of color photosensitive material capable of rapid and sharp image formation in all layers.

Yet another object of the invention is to provide a rapid method of processing color photographic sensitive material by elfectively correlating and adapting the physical chemical and physicochemical and thermal characteristics of processing media with the potential rapid processing properties of an improved color photographic material. An additional object of the invention is to provide a novel multi-layer photographic color sensitive material having extremely thin total emulsion thickness and characterized by high contents of silver and couplers and a high ratio of silver and couplers to gelatin.

'Another object of the invention is to provide a novel emulsion for use in the manufacture of color photo-sensitive material incorporating novel functioning hardening agents to provide readily coatable low viscosity emulsions and ultimate thermostable films. These and other important and related objects are accomplished by invoking the concept and utilizing the materials and techniques in the specific correlations hereinafter described.

In achieving the rapid processing of color photographic material according to the invention, materials are selected and a number of steps are so integrated and correlated that each qualifies each other and accumulative effect is to reduce the total processing time to a higher degree 3,37Z,3 Patented Mar. 5, 1968 and gelatin contents of a standard conventional emulsion, a thin emulsion and emulsions of special type produced according to the invention are compared.

TABLE I [Grams per sq. ft.]

Standard Thin Special Silver Nitrate 0. l 0. O3 0. 4 Color Coupler 0.03 0.01 0.1 Gelatine 1. 0 0. 3 O. 3

As the data in Table I shows the thin coating with the conventional type of emulsion would have a lack of coupler density because of the low contents of silver and coupler. It is to be observed also that it would not give the desired result of rapid penetration and processing to its full extent because of the unfavorable ratio of silver to gelatine and coupler to gelatine as shown in the following Table 11.

TABLE II Standard Special Ratio Silver: Gelatine 1:10 1:1 Ratio Coupler: Gelatine 1:30 1:3

As the figures in Table 11 show, the gelatine proportion in conventional emulsion is 10 times higher than that of silver and 30 times higher than that of coupler and it is obvious that this will slow down the penetration of processing solutions. By utilizing the methods of the invention, as hereinafter described, a coating may be produced which is characterized by the figures of column 3, Table I and column 2, of Table II. It is thus to be observed that not only are very high contents of silver and coupler achieved, but at the same time the ratio of silver to gelatine and coupler to gelatine is altered in a very pronounced degree. Thus, as is shown in Table II, in the emulsions of the invention the ratio of silver to gelatine is nearly 1 to 1 and the ratio of coupler to gelatine l to 3, that is, these ratios have been altered in the order of 10' times as compared to conventional emulsions.

While these measures lead to a very appreciable speeding up of the penetration of processing solution, it was observed that there is still another factor which is of salient importance. It was found that even in these thin and highly concentrated layers the rate of processing can be slow due to an unsuitable dispersion of color coupler. As a result of research and experiment, it was found that, in order to insure optimum results, the dispersion of color coupler should be as fine as possible and the coupler shouldbe incorporated in such a way to insure concentrated localized reaction in very close juxtaposition to the silver halide particles. The quinone amine cation can then react at high speed and concentration to produce the dyestuff image. By precipitating the coupler under controlled conditions and using in each emulsion layer a wetting agent to control also the charge of diffused double layer of the coupler particles, dispersions of determined particle size and charge are obtained forming with the silver halide a system which is capable of rapid reaction within shortest possible path of diffusion of processing solutions between all of the components concerned and processing time is of commensurately reduced. The use of 3 this technique produces color emulsions capable not only of rapid processing but also characterized by very sharp images with brilliant contrasts.

Another important factor of the invention deals with the production of color emulsions capable of being processed at high temperatures which, of course, accelerates the processing. In respect of color emulsions, this problem of insuring adequate hardness in the emulsion is not a simple problem because the conventional hardening agents have an adverse effect on such emulsions, such as the production of color stains and uncontrollable changes in the viscosity while coating.

A preferred class of hardeners which provide the desired ultimate hardness while insuring the desired necessary low viscosity for application of uniform thin coatings comprises N-hydroxymethyl derivatives of heterocyclic compounds containing an amino group. These compounds contain the group NOH OH and slowly evolve formaldehyde on drying and storage according to the equation Such compounds have a restrained hardening effect in that they do not convert the gelatin into an irreversible coagulum but merely raise the melting point of the gelatin. Thus, they do not effect the viscosity of the emulsion during the coating procedure. An especially preferred compound of this class is that derived from benzirnidazole and having the structure This compound yields formaldehyde and benzimidazole which is in itself a photographic stabilizer and thus the compound also has an anti-fogging action on the emulsion. This compound is preferably used in an amount of the order of 45 mg. per litre of emulsion and is added just prior to final pH adjustment.

Other hardeners which may be used include the methylol derivatives of melamine. These derivatives may have a wide range of stability depending upon their complexity. Relatively simple derivatives having a short life of about seven days may be used for the emulsions but if they are to be incorporated in paper or baryta coating the derivatives should be of a more complex type having greater stability.

The emulsion layers may also contain a sensitizer, and any of the color sensitizers conventionally employed in the preparation of color photographic emulsions may be employed. The emulsion may also contain other additives such as stabilizers, anti-stain agents, etc.

The novel color sensitive material of the invention may be prepared in any desired manner, it is, however, prefer-red to prepare the emulsions using the principle of the reversible coagulation of gelatin, but re-dispersing the precipitated silver halide directly in a color coupler dispersion instead of plain gelatin.

in one preferred method of preparing emulsions according to invention, a warm (50 C.) concentrated dispersion of a suitable gelatin in water is adjusted to an alkaline pH of between about pH 9-9.5, and a reversible coagulant, preferably phthalic anhydride in an amount of about of the weight of the gelatin is added thereto. The dispersion is then allowed to stand until peptisation is completed, and then cooled to about 40 C. and the pH adjusted to pH 7-7.5, for example, by the addition of dilute sulphuric acid. The resulting peptised dispersion is then added to an emulsion of silver chloride or silver bromide in gelatin, preferably one in which only the first digestion has been effected, and the mixture is digested for a suitable period of time. The resultant emulsion is then acidified to pH 2.9-3.0, e.g. by the addition of dilute acid such as sulphuric acid whereupon the emulsion is precipitated and the mother liquors are then decanted off.

The coagulated dispersion may then be re-dispersed at 4852 C. in a dispersion of the desired color coupler such, for example, as a dispersion described in co-pending application Ser. No. 182,097, and the resulting emulsion is further digested, if desired, and finally stabilized. Alternatively, in place of the dispersion of pure gelatin in water, a dispersion of the desired color coupler, such as those described in application Ser. No. 182,097, now US. Patent 3,335,011, may be employed. It is also possible to add the color coupler, in the form of an aqueous or aqueous alcohol solution in caustic alkali solution, or a solution of an organic base, e.g. triethanolamine, directly to the finished emulsion.

It is particularly to be observed that the preparation of the color coupler dispersion has a considerable influence on the ability of the final emulsion for equal penetration by processing solutions. In carrying out the invention color couplers are employed which are themselves nonditfusible in the emulsion layer, but form fine dispersion in the emulsion and which, therefore, offer the least resistance to the penetration or permeation of processing solutions and couple very rapidly. In general, it is preferred that the color couplers used should contain an acidic, e.g. carboxyl group and further that they should have an anti-diffusion fatty acid side chain. Where they contain an acidic group, such groups should be salted with an organic base, e.g. triethanolamine. It has been found that in the case of color couplers containing an amino group, other than that resulting from acylation by fatty acid chloride of an amino group, the solubility is considerably increased by glycylation of this amino group with chloroacetic acid in aqueous pyridine. It has been observed that such glyclated couplers provides dispersion in gelatin at slightly acid pH in which the particle size of the coupler is substantially less than the particle size of the original color coupler. It is also possible to add color coupler in the form of an oil in water emulsion, the coupler having been dissolved in a suitable water insoluble solvent and the resulting solution finely emulsified in water or aqueous gelatin under the action of a suitable surfactant.

Cyan couplers, that is to say, the couplers which produce during development a Cyan indophenol dyestuffs, which preferably are used are those which are characterized by substitution of such a nature as to give spatial protection of the indophenol grouping against temporary reduction (with consequent decolorization) during processing. Such substitution involves the introduction, in the course of synthesis, of large coplanar group in the 2 or 5 positions in the naphthaline nucleus. Examples of suitable substituted Cyan couplers are (2 N ethyl M stearyl 5 sulphenyl) 2 amido 1 naphthol and 5 phenoxy acetamino l-naphthol. A marked advantage of using Cyan couplers of this type lies in the fact that the color balance of the print can be observed immediately after bleach-fixing without waiting for restoration of the Cyan component during final washing, and furthermore in the fact that a more acid bleach-fix bath has a higher freedom from stain therefore makes coating thickness less critical.

The following is an illustrative example for the preparation of color coupler dispersion.

The siX grams of the color coupler are dissolved in 45 cos. of a 20% solution of triethanolamine and then ccs. of water are added. This solution is then poured at a temperature of 50 C. into a 10-0 ccs. of a 20% gelatin solution forming a fine dispersion. In order to control he formation of this dispersion and its incorporation with the silver halide in the final emulsion it may be advantageous for reasons pointed out heretofore to use anionic, cationic, or non-ionic surfactants, in a concentration amount to about 10% of the quantity of color coupler.

It is often necessary to choose a different surfactant for the various layers of the multi-layer color material according to the type of color coupler employed to improve dispersion and thus the rapidity of coupling and at the same time the adhesiveness of one emulsion layer to another. For instance, it has been found that for use with Cyan coupler 1.2-hydroxy-naphthoic N-stearylamide, an anionic dispersion agent such as cyclohexylamine lauryl sulfate functions effectively, for Magenta coupler 3- stearylacetyl-p-sulphonyl-phenyl-5- pyrazololine, a nonanionic surfactant such as Nonex and for a yellow coupler lauroylamine benzoylacetyl-amine 3.5 isophthalic acid, a cationic dispersion agent such as cetyl pyridinium bromide, may be employed. The coupler dispersions prepared in this way are then used for the dispersion of the precipitated silver halide as described above, or are mixed with a silver halide of the necessary concentration indicated in Tables I and II.

The emulsion layer is coated on to the film or paper base, preferably by an air knife technique.

In order to insure rapid penetration in processing, a developing agent i required which is easily soluble in sufiiciently high concentrations in strongly alkyline solutions such as the di-alkyl P-phenylene diamine having solubility imparting substitutent groups, such as those described in co-pending application Ser. No. 216,072 filed Aug. 10, 1962, now abandoned.

In addition, it has been found that the solubility of the less soluble derivatives of N-diethyl-P-phenylene diamine or this compound itself may be effectively employed by adding to the developer solution certain water miscible solvents which are photographically inert or may be even development promoting. Such solvents are generally characterized by the property or ability of taking into solution at least an equal weight of the desired developing substance. Illustrative preferred solvents of this type are dialkyl sulfoxides, formdialkyl amides and morpholene. It has been established for example, that a developer solution of basically the conventional or usual composition can be employed effectively in the present invention by adding a suificient quantity, of the order of 510%, of one of the above solvents to dissolve 6 grams of N- diethyl-P-toluylene diamine and obtain complete development in about one fifth of the time that is required if the same developing agent is used at its normal concentration of 3 grams per litre.

It has also been found unexpectedly that developer solutions of similar high efficiency can be prepared by dispersing a quantity of the developing substance as a collodial dispersion by means of anionic or non-ionic surfactants. For example, a developer solution may be made up containing 6 grams per litre of N-diethyl-P- toluylene diamine, partly in true solutions and partly in collodial suspension by the use of about 5 grams of calsolene oil or Teepol or Nonex per litre.

Again, a mixture of solvent and surfactant such as a mixture of formdimethyl amide and calsolene oil may be employed to produce developers with at least twice the standard contents of developing agent. Preferably such developer baths are adjusted to a high pH of the order of 11-13 and are operated at temperatures of between about 26 to 35 C. to insure complete development in a matter of from about 1 /2 to 3 minutes.

The next processing step of the improved method is treatment either'in a short acid stop-bath or the immediate application of a bleach-fix solution as described and claimed in co-pending application Ser. No. 154,333.

Similarly, effective bleach-fix bath operable at low pH may be employed utilizing the ferric complex of N- hydroxyethyl ethylene diamine tri-acetic acid or homologues thereof of the following type:

An example for formula for such a bleach-fix solution is as follows:

6 Ferric N-hydroxyethylethylene diamine-triacetic acid grams 90 Ammonium thiosulfate do 90 Thiourea do 1 Sodium sulphite (anhydrous) do 10 Sodium metabisulphite do 10 Distilled water to make 1 litre.

To this solution is added acetic acid until the desired low pH is reached which can lie between pH 4 and pH 6.5. Iron chelate compounds of the above type will stand pH values as low as pH 2.

The following is an example of an illustrative procedure for very rapid processing of exposed photographic sensitive material according to the invention. An exposed film of the type described is immersed in an agitated bath, at a temperature of about 35 C., of a developing solution of the following composition:

Sodium N-ethyl-N-hydroxyethyl N sulpho alkyl P- phenelene diamine grams 3.25 Potassium hydroxide do 15.0 Trisodium phosphate do 50.0 Potassium bromide do 1.0 Sodium sulphite do 5.0

Water to 1 litre (pH 12.8).

A fully developed image is obtained in 1 /2 to 3 minutes according to the make of the film used.

Without any washing or treatment in a stop bath the developed photographic material is passed immediately to and agitated in a stop-bleach-fix bath maintained at a temperature of about 27 C. and having the following composition:

With such a treatment film is usually completely fixed and bleached in a matter of five minutes or less and paper in usually one or two minutes. The processed film is then washed for a few minutes and then dried.

If desired after development the color photographic material may be treated in a stop-bleach stablizler bath to arrest development and remove the silver image, and the residual silver halide may be dissolved subsequently in a separate fixing bath. For such stop-bleach stabilizer baths it is preferred to use alkali metal persalts in conjunction with amine sulphur compounds capable of imino-sulphydryl tantomerization e.g. thio amides such as thiourea. Such baths may give complete bleaching in only a few seconds. A preferred bath of this type may comprise the following:

Ammonium persulphate .gms 50 Thiourea gms 5 Water, 1 litre.

The pH of this bath is within the range 5.5-6.5. If other persalts are used, the pH may require adjustment as by the addition of a suitable acid buffer.

In experimentation with bleach-fix baths it has been observed that at the low pH i.e. of the order of pH 4 to 5 of the solutions employed the speed of penetration into the film is considerably increased. This may have some relation to the properties of the iron chelate compounds themselves or with the solubility of the reaction influence of acid such structure is transformed into a more grainy and easily penetrable substance.

The invention may be embodied in other specific forms in which the concept of potentiating the inherent amenability of the improved color photographic material to rapid processing may be achieved by specific correlation and sequential coaction with selected processing media to accelerate the total processing procedure. The present embodiments are to be considered illustrative and not restrictive; the scope of the invention being indicated by the appended claim rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claim are therefore intended to be embraced thereby.

I claim:

1. A method of shortening the processing time of color photographic sensitive material which comprises, providing a multi-layer emulsion-coated photographic material in which each layer incorporates closely spaced finely dispersed coupler and silver halide particles in a photographic dispersion medium, each emulsion layer being of the order of 2 microns in thickness, the ratio of silver to dispersion medium is substantially 1:1, the ratio of coupler to dispersion medium being substantially 1:3; exposing the material to form a latent image; converting the latent image to a visible image by subjecting the exposed material for a brief period at a temperature of between about 20 C. and 35 C. to the action of a highly alkaline aqueous solution of a developer selected from the group consisting of N-diethyl-p-phenylene diamine and substituted, more soluble derivatives thereof; immediately immersing the developed material for a brief period in a bleach-fix bath comprising an acid solution of a silver halide solvent and an acid-stable ferric salt of an alkylene amine polyacetic acid and then washing and drying the thus processed material.

References Cited 3 OTHER REFERENCES 7 Baker: Photographic Emulsion Technique, page 156,

20 second edition, American Photographic Publishing Co,

Boston (1948).

Carroll et al.: Bureau of Standards Journal of Research, vol. 7, pages 811 825, (1931).

Yoshida: Chemical Abstracts, vol. 53, page 8900, (1959).

Baker: Photographic Emulsion Technique, pages 157-162, second edition, American Photographic Publishing Co., Boston, (1948).

Glafkides: Photographic Chemistry, vol. 1, pages 55, 56 and 108, Fountain Press, London, (1958).

NORMAN G. TORCHIN, Primary Examiner.

J. T. BROWN, Assistant Examiner.

Claims (1)

1. A METHOD OF SHORTENING THE PROCESSING TIME OF COLOR PHOTOGRAPHIC SENSITIVE MATERIAL WHICH COMPRISES, PROVIDING A MULTI-LAYER EMULSION-COATED PHOTOGRAPHIC MATERIAL IN WHICH EACH LAYER INCORPORATES CLOSESLY SPACED FINELY DISPERSED COUPLER ANC SILVER HALIDE PARTICLES IN A PHOTOGRAPHIC DISPERSION MEDIUM, EACH EMULSION LAYER BEING OF THE ORDER OF 2 MICRONS IN THICKNESS, THE RATIO OF SILVER TO DISPERSION MEDIUM IS SUBSTANTIALLY 1:1, THE RATIO OF COUPLER TO DISPERSION MEDIUM BEING SUBSTANTIALLY 1:3; EXPOSING THE MATERIAL TO FORM A LATENT IMAGE; CONVERTING THE LATENT IMAGE TO A VISIBLE IMAGE BY SUBJECTING THE EXPOSED MATERIAL FOR A BRIEF PERIOD AT A TEMPERATURE OF BETWEEN ABOUT 20*C. AND 35*C. TO THE ACTION OF A HIGHLY ALKALIE AQUEOUS SOLUTION OF A DEVELOPER SELECTED FROM THE GROUP CONSISTING OF NIDIETHYL-P-PHENYLENE DIAMINE AND SUBSTITUTED, MORE SOLUBLE DERIVATIVES THEREOF; IMMEDIATELY IMMERSING THE DEVELOPED MATERIAL FOR A BRIEF PERIOD IN A BLEACH-FIX BATH COMPRISING AN ACID SOLUTION OF A SILVER HALIDE SOLVENT AND AN ACID-STABLE FERRIC SALT OF AN ALKYLENE AMINE POLYACETIC ACID AND THEN WASHING AND DRYING THE THUS PROCESSED MATERIAL.