US 3137574 A
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United States Patent O 3,137,574 STABHJITY OF RAPID-PROCESSED PHOTOGRAPI-HC PTS Eric Thomas Smith and Leslie Alfred Williams, Harrow,
England, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Sept. 29, 1960, Ser. No. 59,195 Claims priority, application Great Britain Nov. 12, 1959 3 Claims. (Cl. 96-61) This invention relates to photography and more particularly to a method for improving the silver image stability of rapid-processed photographic prints.
The rapid processing of photographic prints is known in the art and has been described, for example in Broughton et al., US. Patent 2,614,927, issued October 21, 1952. In the rapid-processing technique the conventionally required fixing and washing steps are eliminated and the developed silver image is stabilized by treatment with a solution which does not react with metallic silver and which forms a light-inert silver complex by reaction with undeveloped silver halide. The stabilization bath is used only until the silver halide has been converted to a complex with the stabilizing compound and the complex is left in the emulsion layer, the layer being dried without any further treatment such as Washing. This produces a photographic print and materially shortens the time necessary for processing exposed emulsion. While the rapid-processing methods known in the art are satisfactory for the stabilization of silver images which are not to be stored under adverse conditions, there is the disadvantage that such images tend to fade when stored under conditions of high temperature and humidity. The propensity of rapid-processed prints to fade has seriously limited the use of the process particularly in producing copies for office files.
It is, therefore, a principal object of the present invention to provide a rapid-processing method for silver halide layers which produces prints having improved stability to high temperature and humidity.
These objects are accomplished by the method described herein which includes treatment of the photographic prints obtained thereby with a compound of the general formula:
wherein X represents -CH=CH, S, O, NH or CR'=N (R' representing a hydrogen atom or an alkyl group, such as methyl, carboxymethyl, ethyl, propyl, butyl, etc., especially an alkyl group containing from 1 to 4 carbon atoms), Y and Z represent hydrogen atoms or monovalent substitutents such as alkyl groups (e.g., methyl, ethyl, etc.) or hydroxyl groups and may be the same or different, or Y and Z together represent the atoms necessary to complete a benzene ring. When Y and Z represent a benzene ring, this ring can bear substituents such as methyl, ethyl, chlorine, methoxyl, ethoxyl, hydroxyl, amino, etc. Included within the method described, the silver image preserving compounds of our invention can be incorporated in the developing solution, in the stabilizing solution, or in a special treating bath, or the compounds can be incorporated in the lightsensitive silver halide layer directly. In any event, the compounds of our invention are effective in preventing fading on storage of rapidly-processed photographic prints in a humid, high-temperature environment.
Representative compounds of the general formula given above which can be used in the present invention are: (1) 2',3' dihydrobenzothiazolo-Z',3',5,4-triazole(1,2,4)-
(2) l',2' dihydroquinolino l,2',4,5-triazole(1,2,4)-3- thiol:
(3) 1,2' dihydropyridino 2',l',5,4 triazole(1,2,4)-
(4) 2',3' dihydrobenzimidazolo 2,3',5,4 triazole In rapid processing, a silver halide photographic emulsion, preferably a gelatin-silver halide emulsion is exposed in the usual way and developed with a suitable silver halide developing solution. After development, the excess developing solution present on the surface of the print is removed by any convenient means such as squeegee, and the print is then treated with a stabilizing solution. The purpose of the stabilizing agent is to make the undeveloped silver halide substantially incapable of change on further light exposure. The stabilizing agent must be a compound which does not react with metallic silver and which forms a light-stable, silver complex by reacting with the undeveloped silver halide in the emulsion layer. Stabilizing agents suitable for this purpose are compounds containing double-bonded sulfur or an SH linkage, such as alkali metal and ammonium thiocyanates, alkali metal and ammonium thiosulfates,
processed silver images; accordingly, the present invention is primarily directed to improvements and further silver image preservation in thiocyanate rapidly-processed prints.
In a preferred embodiment of our invention, we use a thiocyanate stabilizing compound such as ammonium thiocyanate, or an alkali metal thiocyanate, and in addition, we further stabilize using a triazole-thiol compound of this invention so as to give an increased preservation of the silver image. The concentration of the organic thiol compound can vary over a wide range. When the imagepreserving organic thiol compound is used in the developer solution, the preferred range of concentration is from about 0.05 gram to about 3.0 grams per liter of developer solution. The use of higher concentrations than this in the developer solution does not have a detrimental efifect except that development may in some instances be slowed preserving compound is incorporated in the emulsion during manufacture, it can be incorporated in a quantity from about 0.01 to about 0.5 gram per volume of liquid emulsion containing 100 grams of silver.
The photographic emulsions used in the practice of this invention are generally of the developing-out type. Suit able emulsions for use in this invention have been described in Kendall and Wood, US. Patent 2,669,515, issued February 16, 1954; Kendall and Hill, US. Patent 2,541,472, issued February 13, 1951; and Brice, US. Patent 2,448,857, issued September 7, 1948.
The emulsions used in this invention can advantageously be hardened emulsions. The emulsions may be hardened with any suitable hardener for gelatin, such as formaldehyde, a halogen-substituted aliphatic acid such as mucobromic acid as described in White, US. Patent 2,080,019, issued May 11, 1937, or by compounds such as those described in US. Patents 2,725,294; 2,725,295; and 2,725,305, issued November 29, 1955. The emulsions can be coated on paper or other opaque supports or on any of the well-known transparent supports such as cellulose nitrate, cellulose acetate, polyethylene terephthalate, polystyrene, polycarbonate, etc.
The developing agents which can be incorporated into the emulsions according to an embodiment of this invention comprise developing agents such as 3,4-dihydroxydiphenyl, 2,3-dihydroxydiphenyl, hydroquinone compounds,
e.g., hydroquinone, chlorohydroquinone, methyl hydroquinone, etc., and 3-pyrazolidones (e.g., 1-phenyl-3-pyrazolidone, 4-methyl-l-phenol-3-pyrazolidone, 4,4-dimethyl-1-phenyl-3-pyrazolidone, 'etc.). Where developing agents are incorporated into the emulsion directly, development is usually by immersion in an alkaline processing solution such as that disclosed in Broughton, US. Patent- 2,614,927, issued October 21, 1952, in such an event the thiol compounds of our invention can be incorporated in the alkaline processing solution, in the stabilizing bath or in a separate processing bath. Where a separate processing bath is used, it can be employed either before or after the stabilizing treatment.
The organic thiol preserving compounds suitable for use in our invention can be prepared according to the methods described in our co-pending application, Williams, US. application Serial No. 655,472, filed April 29, 1957, and in Knott et 211., US. Patent 2,861,076, patented November 18, 1958.
Our invention will now be described by way of specific examples although it is not intended that we be in any Way limited thereby.
EXAMPLE 1 The following example illustrates a manner of practice r 4 of our invention. A suitable emulsion was prepared as follows:
Solutions were made of (A) 25 grams of gelatin in 1 liter of water at 40 C., (B) grams of silver nitrate in 500 cc. of water at 20 C., and (C) 35 grams of sodium chloride in 500 cc. of water. Solutions (B) and (C) were simultaneously run into Solution (A) at a uniforrnrate while stirring the latter over a period of about 10 minutes. Solution (B) was not allowed to run in faster than (C). Thereafter 150 grams of gelatin in 1450 cc. of Water at 40 C. were added. The emulsion was hardened using a suitable gelatin hardening agent such as formaldehyde. The emulsion was then coated on a paper support over an area of about 500 square feet. Samples of the dry product were then exposed in a number of ways to a subject, including contact with or projection of a negative and by reflex exposure with a subject comprising printed matter on a paper base. Thereafter the exposed samples of the element were processed by surface application of the following solutions in a small processing machine.
Table I Developer Grams Sodium hydroxide 22.5 Sodium sulfite (anhydrous) 80.0 Hydroquinone 36.0 Phenidone developer 2.0 Potassium bromide 0.5 Water to 1000 cc.
Table II Stabilizer:
Ammonium thiocyanate grams 300 Acetic acid (glacial) cc 40 Water to 1000 cc.
The machine was run at 10 feet per minute giving ap proximately 2 seconds treatment in the developer solution followed with about 3 seconds treatment in the stabilizer solution.
For comparison, a second print was processed in a similar manner except that 1 gram per liter of 2,3-dihydrobenzothiazolo-2',3 '-5,4-triazole( 1,2,4 -3 -thiol was added to the developer solution. Both prints were tested by being subjected to moist incubation for 7 days at F. and 75 percent relative humidity.
After the 7-day incubation period the prints processed with a developer solution containing said (thiol compound showed little change in image density while the prints processed in the control developer solution showed a marked fall in maximum image density. The reflection density of the control print after incubation was 0.95 whereas the print processed according to this invention had a reflection density of 1.4. The reflection densities refer to the relative densities of the respective prints as measured on a conventional reflection densitometer.
EXAMPLE 2 The tests of Example 1 were repeated except that a direct-positive emulsion, such as that described in Kendall et al., US. Patent 2,541,472, issued February 13, 1951, was used. After exposure the test print was processed in a developer solution of Example 1 which contained the organic-thiol compound, 2',3-dihydrobenzothiazolo-2'3'- 5,4-triazole(1,2,4)-3-thiol. A control print was handled in a similar manner except that the developing solution for development thereof did not contain said organic compound. Both test and control prints were stabilized in the thiocyanate stabilizer of Example 1. After a 7-day 120 F., 75 percent relative humidity (RH) incubation period, the test print showed areflection density of 1.1 whereas the control print had a reflection density of 0.9.
EXAMPLE 3 A sheet of direct-positive film as used in Example 2 was exposed and processed as in Example 1, except that in this example 0.5 gram per liter of the following com- EXAMPLE 4 A direct-positive emulsion was prepared as in Example 2 except that in this example development was in a developer of Table I except that 0.5 gram per liter of the following compound was added to the developer, namely, 1',2 dihydropyridino-2,l'-5,4-triazole(1,2,4)-3- thiol. After 7 days moist incubation (100 F., 75 percent RH) the print showed only slight loss of maximum density as measured by reflection density, as in Example 1, when compared to the control print which was developed in a developer solution not containing a preserving thiol compound according to the present invention.
EXAMPLE 5 The following example illustrates a manner of practice of our invention wherein a developer compound was incorporated into the emulsion directly. A suitable silver halide emulsion was prepared as follows:
Solutions were made of (A) 25 grams of gelatin in 1 liter of water at 40 C., (B) 100 grams of silver nitrate in 500 cc. of water at 20 C., and (C) 35 grams of sodium chloride in 500 cc. of water. Solutions (B) and (C) were simultaneously run into solution (A) at a uniform rate while stirring the latter over a period of about 10 minutes. Solution (B) was not allowed to run in faster than (C). Thereafter, 150 grams of gelatin in 1200 cc. of water at 40 C. were added. 25 grams of 3,4-dihydroxydiphenyl were then dissolved in 250 cc. of methyl alcohol. This solution was slowly added to the above mixture. The emulsion was hardened using a formaldehyde gelatin hardening agent. The emulsion was then coated on a paper support over an area of about 500 square feet. Samples of the dried product were then exposed by contact with a negative which comprised the subject matter to be printed. Thereafter, the exposed samples of the element were processed by surface application of the following solutions in a small processing machine:
Water to 1000 cc.
The machine was run at 10 feet per minute giving approximately 2 seconds treatment in the developer solution followed with about 3 to 4 seconds treatment in the stabilizer-preservation solution of Table IV.
For comparison, a second set of prints was processed in a similar manner except that the organic-thiol compound was omitted from the stabilizer solution of Table IV. Both sets are prints were tested by being subjected to moist incubation for 7 days at 120 F. and 75 percent relative humidity. The results of the moist incubation test showed that the set of prints which was treated with a thiol compound according to this invention was considerably more resistant to silver image fading during storage in a humid-high-temperature environment than were the control prints not so treated.
EXAMPLE 6 A sheet of photographic film prepared as in Example 5 was exposed and processed as in Example 5 except that according to the present example the organic-thiol compound was incorporated into the emulsion directly. In this example, therefore, a stabilizer solution as shown in Table II was used in the stabilization step. The results of the trial showed similar improved silver image preservation in the rapid-processed photographic prints of this example.
When the compounds of this invention are employed in a thiocyanate-stabilizer solution in amanner of practice of this invention to further stabilize and preserve the silver images produced by a rapid-processing technique, it is preferred to make the stabilization bath acid to counteract alkali present in the developing solution. The alkali of the developing solution is not especially critical since carbonate, caustic alkali and borates all give useful results, although, as is apparent, strong alkali is preferred in those cases where theemulsions incorporate a developing solution since a strong alkaline treating solution will increase the speedof development of the emulsion layers containing the somewhat weaker developing agents, such .as the dihydroxydiphenyl compounds.
In those cases where it is preferred to use a surface application development method, a. precaution should be taken to use well-hardened emulsions so as to prevent the emulsion from adhering to the surface of the applicator such as a pad. In case the emulsion has not been hardened sufficiently prior to processing, this can be done with a formaldehyde hardening bath before or after the development step or in any other suitable way.
It is permitted in the processing of the photographic materials, according to this invention, that the emulsion be immersed in the developer and stabilizing solutions, or as in the case of the developer incorporated emulsions, the alkaline and stabilizing solutions. It may be preferred, however, merely to moisten the surface of the exposed emulsion with the required solutions. In those cases where paper supports are used, the support may become wet on immersion such that the drying time is greatly ex tended.
It will be apparent from the foregoing description of our invention that a substantial proportion of the silver compound remains in the emulsion after the stabilization treatment. This diflfers from the customary fixing and washing in which the intent is to remove the residual silver halide from the emulsion. In this regard, therefore, it is those photographic materials which are customan'ly referred to as rapid-processing materials that this invention primarily pertains.
The advantages which accrue as a result of our process are immediately apparent. The improved stability of the rapidly-devoleped silver images to adverse conditions of temperature and humidity extends considerably the safe use to which prints produced by this process can be put. By the methods of the present invention, the full use of rapid processing photographic materials can now be realized; By eliminating the conventional fixing and washing steps, the total processing time has been decreased from an hour or more to a matter of 2 or 3 minutes, and now by way of the present invention, the prints produced thereby have a stability to fading such that the process can be safely employed in producing oflice file copies. Where safe storage periods are possible with rapid-processing photographic materials, it is immediately apparent that such materials will find a greater appeal in the trade.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope and spirit of the invention,
as described hereinabove and as defined in the appended claims.
- We claim: 7
1. A rapid process for producing a stable visible image in a photographic silver halide emulsion layer containing a latent image consisting in (A) processing said silver halide emulsion layer by developing said layer in a photographic silver halide developing solution and thereafter stabilizing said silver halide emulsion layer by applying an aqueous solution containing at least one stabilizing compound selected from the group consisting of alkali metal thiocyanates, alkali metal thiosulfates, ammonium thiocyanate, and ammonium thiosulfate to form a lightinert complex with resulting undeveloped silver halide, said complex being left in the emulsion layer, said emulsion layer being imbibed during said processing with an aqueous solution containing at least 0.05 gram of a thiol compound having the general formula:
X Y-o Z t N 11541:, wherein X represents a member selected from the group consisting of a vinylene group, a sulfur atom, an oxygen atom, an ,NH group, and a CR=N group wherein R represents a member selected from the group consisting of a hydrogen atom and an alkyl group containing from 1 to 4 carbon atoms, Y and Z each represent a per liter resulting processed layer Without further treatment.
2. A rapid process according to claim 1 wherein said thiol compound is contained in said developing solution.
3; A rapid process according to claim 1 wherein said thiol compound is contained in said stabilizing solution.
References 'Cited in the file of this patent UNITED STATES PATENTS 2,403,927 Kendall et al July 16, 1946 2,887,378 Williams ,May 19, 1959 2,933,388 Knott Apr. 19, 1960 2,956,876 Spath Oct. 18, 1960 2,928,735 Barbier Mar. 15, 1960 3,093,479 Olivares et a1 June 11, 1963 OTHER REFERENCES Meesi The Theory of the Photographic Process, 2nd Ed., 1954, Macmillan Company, pp. 670685.
Crabtree: Rapid Processing of Films and Papers, PSA Journal, February 1949, vol. 15, pages l'30135.