US 3057721 A
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States Patent 3,@57,7Z1 Fatented Oct. 9, 1962 This invention relates to photography and more particularly to a colloid stratum transfer process thereof.
In the Yutzy and Yackel US. Patent 2,716,059, granted August 23, 1955, is described a colloid stratum transfer process in which a substantially unhardened exposed silver halide emulsion layer is developed in the presence of a gelatin tanning silver halide developing agent and also in the presence of a substantially non-tanning silver halide developing agent so as to obtain a hardened gelatin and silver image in the more exposed regions of the emulsion layer and substantially unhardened gelatin, silver and silver halide in the less exposed regions. Thereafter, the moist emulsion layer is pressed into contact with an absorbent reception sheet to cause the emulsion in the less exposed areas to adhere to the sheet and a stratum thereof to remain on the sheet when the emulsion and sheet are separated.
Substantially non-tanning silver halide developing agents particularly useful in the process are e.g. 4-methoxy-l-naphthol and 8-hydroxy-a-naphthol which, in addition to functioning as a non-tanning silver halide developing agent, have the desirable property of self-coupling (coupling with themselves) in the regions of development and thus forming a dye which adds to the density of the silver image obtained on the reception sheet.
However, when these self-coupling substantially nontanning developing agents are employed in an emulsion layer in conjunction with a tanning developing agent such as 3,4-dihydroxydiphenyl and the emulsion is aged, they undergo oxidation and self-coupling which results in the formation of an undesirable blue coloration throughout the emulsion layer which effectively reduces the speed of the emulsion layer and which coloration detracts from the appearance of the emulsion, the blue coloration being suggestive of emulsion deterioration.
We have discovered that the formation of the blue coloration upon aging of the emulsions containing the mentioned developing agents can be prevented by adding a quantity of an organo-phosphite compound to the emulsion. The preferred organo-phosphite compounds are the oily trialkyl phosphites and triaryl phosphites of the benzene series such as tricresyl phosphite and triisooctyl phosphite. These phosphites possess the additional properties that they are water-insoluble and make excellent solvents for the mentioned silver halide developing agents and therefore may be used in making colloidal dispersions of the developing agent for addition to the aqueous gelatin silver halide emulsions in the manner described in the examples below. The alkyl phosphites and aryl phosphites should, of course, be free of desensitizing action on the silver halide emulsion and this is generally assured by careful synthesis of the compounds.
Representative trialkyl phosphites and triaryl phosphites useful in the emulsions are as follows:
T rimethylpho sphite (CH O P Tri-n-propylphosphite (CH CH CH O P Tri-is opropylphosphite 2 Tri-n-butylphosphite (CH CH CH CH O) P Tri-n-hexylphosphite [CH (CH CH O] P Tri-iso-octylphosphite Tris (Z-ethylhexyl) pho sphite 3 2) 3 z s) 2 3 Z-ethylhexyloctylphenylpho sphite 0OHzCH(CtE5) (CH2)2CH3 P-O-OH2(CH2) r911 43 Triphenylphosphite e s 3 Tricresylphosphite Tri- Z-methoxyphenyl phosphite Organo Phosphorous Compounds, by Gennady M. Kosolapofi, published by John Wiley & Sons, New York, edition, may be referred to for a more detailed description of the compounds and their methods of preparation.
In using the organo phosphite compounds in our invention, we preferably dissolve the tanning developing agent such as 3,4-dihydroxydiphenyl, the self-coupling developing agent such as 4-methoxy-l-naphthol, and the phosphite compound in a suitable solvent such as a lower alcohol or tricresyl phosphate and add this solution with rapid stirring to an aqueous gelatin solution and then add the resulting dispersion to a substantially unhardened gelatino silver halide emulsion for coating on a suitable support such as paper. The resulting emulsion coating can then be stored away for long periods of time without danger of any appreciable amount of the blue coloration appearing. Thereafter the paper is processed as described in the above patent by exposure to a line or halftone subject followed by treatment with alkaline solution to effect tanning development of the exposed areas of the emulsion layer leaving the less exposed portions of the emulsion substantially unhardened. Thereafter the emulsion is pressed against an absorbent sheet, such as paper, to transfer a stratum of the unhardened areas to the sheet and provide a positive reproduction of the original subject. The transferred image on the reception sheet is readily visible since it is composed of both silver and the dye resulting from the self-coupling of 4-metho-xy-1- naphthol.
The following examples will serve to illustrate our invention.
Example 1 A high-contrast silver chloride emulsion containing one mole of silver chloride and 340 grams of gelatin was melted at 40 C. and the following additions made: 200 grams of 15 percent aqueous saponin and 900 grams of a dispersion made by dissolving 45 grams of 3,4-dihydroxydiphenyl, 10 grams triisooctyl phosphite and 19.3 grams of 4-methoxy-1-naphthol in 129 grams of tricresyl phosphate at about 80 C. and pouring it into a rapidly stirring solution of 64.3 grams of gelatin and 64 grams of 8 percent aqueous saponin solution in 579 cc. of water at 55 C. This mixture was coated over 500 square feet of an unhardened gelatin-sized paper base. The product resulting was processed as described in the above patent by first exposing to a line or halftone (two-tone) subject, then developing with a solution of sodium carbonate after which the developed paper was pressed against a paper receiving sheet to leave a stratum of the unhardened image areas adhered to the receiving sheet when the two sheets were separated.
When a sample of the unexposed coated paper containing the phosphite compound was incubated for 28 days at 120 F. and 42 percent relative humidity, it Was found that the paper had remained white in color and produced good copies at approximately the same exposure Whereas when fresh, a similar paper containing none of the phosphite compounds which had been incubated under the same conditions turned dark blue in color and required a prolonged exposure to obtain a copy.
Example 2 The process of Example 1 was carried out except replacing the triisoctyl phosphite by grams of tricresyl phosphite.
The incubated paper exhibited the same photographic characteristics of remaining white and produced copies at approximately the same exposure after incubation as when the paper was freshly coated.
The other trialkyl and triaryl phosphite compounds may be used in the process of the invention in a similar manner. The optimum quantity of phosphite compound to use depends in part upon the stabilizing activity of the particular phosphite under consideration; however, useful results are obtained by using from about 2 to about 20 grams of the phosphite per mole of silver in the emulsion.
The gelatin tanning silver halide developing agents contained in the silver halide emulsion together with the selfcoupling developing agent such as 4-methoxy-1-naphthol, and the phosphite compound, include hydroquinone and pyrocatechol but preferably the gelatin tanning silver halide developing agents which are substantially nondiffusing in the gelatin emulsion layers are used e.g. 3,4- dihydroxydiphenyl, 2,5-dihydroxydiphenyl, 2,3-dihydroxydiphenyl and 5,6,7,8 tetrahydronaphthohydroquinone. The developing agents are used in the quantity required to obtain adequate tanning of the gelatin emulsion in the exposed regions. About 250 to about 350 grams of the developing agent per kilogram of silver nitrate converted to silver halide and used in making the emulsion may be used. The self-coupling non-tanning developing agent, 4- methoxy-l-naphthol, in the emulsion layer serves to develop silver in the less exposed regions of the emulsion layer without hardening these regions so that upon transfer of these regions to the receiving sheet they will be readily visible. This function of the non-tanning developing agent is explained more fully in the above patent of Yutzy and Yackel. The amount of this developing agent used depends in part upon the developing activity of the tanning developing agent present since the two developing agents are in competition for the development of the exposed silver halide. However, the proportions shown in the above example may be varied appreciably to still obtain useful results.
The gelatino silver halide emulsions containing the developing agents are substantially unhardened, as defined in the above patent. That is, the emulsion should be no harder than would be the case with gelatin containing about 0.25 ounce of formaldehyde solution (40 percent diluted 1:3 with Water) or 0.7 gram dry formaldehyde per pound dry gelatin freshly coated or 0.1 ounce of the solution per pound dry gelatin for a sample aged three to six months under average room conditions.
When using the unhardened emulsions containing the developing agents and phosphite compounds in the colloid stratum transfer process illustrated above, any of the techniques disclosed in Yutzy et al. patent may be employed for improving the optical density of the print. For example, the print while still moist from the transfer operation may be exposed to light of suitable intensity and duration with the result that added silver density will become apparent. Another method is to perform the transfer from the developed emulsion layer to a receiving sheet having an absorbent surface of the type disclosed in the Chan et al. US. Patent 2,865,745, granted December 23, 1958.
The alkaline solution used for activating the exposed emulsion layer in the process is not especially critical and may comprise aqueous sodium carbonate solution. However, alkaline solutions containing amines, for example, B-diethylaminoethanol described by Weyerts et al. US. patent application Ser. No. 814,378, filed May 20, 1959, and potassium carbonate-acetamide solutions described by Linge, US. patent application Ser. No. 810,575, filed May 4, 1959, are very useful.
In the process of the invention as Well as in the processes of the mentioned Yutzy et al. patent, it may be desirable to add a quantity of fogged silver halide to the emulsion containing developing agent. As a result the density of the print is improved. Useful results are obtained using from about 3 to 30% fogged silver halide.
1. A photographic emulsion comprising a mixture of substantially unhardened gelatin silver halide, a gelatin tanning silver halide developing agent, a substantially non-tanning self-coupling silver halide developing agent of the class consisting of 4-methoxy-1-naphthol and 8- hydroxy-l-naphthol and a member of the class consisting of a trialkyl phosphite and a monocyclic triaryl phosphite of the benzene series.
2. A photographic emulsion comprising a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy-lnaphthol and a member of the class consisting of a trialkyl phosphite and a monocyclic triaryl phosphite of the benzene series.
3. A photographic emulsion comprising a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy-lnaphthol and a trialkyl phosphite.
4. A photographic emulsion comprising a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy1- naphthol and a monocyclic triarylphosphite of the henzene series.
5. -A photographic emulsion comprising a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy-1- naphthol and tricresyl phosphite.
6. A photographic emulsion comprising a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy-1- naphthol and triisooctyl phosphite.
7. A method of photographic reproduction which comprises exposing to a line or half-tone subject a gelatinosilver halide emulsion layer containing a mixture of substantially unhardened gelatin, silver halide, a gelatin tanning silver halide developing agent, 4-methoxy-l-naphthol and a member of the class consisting of a trialkyl phosphite and a monocyclic triaryl phosphite of the benzene series, so as to obtain some exposure in the areas of the emulsion layer corresponding to the shadow areas of the subject and appreciably more exposure in the areas of the emulsion layer corresponding to the highlight areas of the subject, said emulsion being not harder than a gelatin layer containing 0.7 gram of formaldehyde per pound of gelatin freshly coated, developing said exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the areas of the emulsion layer corresponding to the highlights of the subject, and substantially unhardened gelatin, silver and silver halide in the areas of the emulsion layer corresponding to the shadows of the subject, said development being such as to prevent any substantial tanning of the emulsion layer in said areas corresponding to the shadows of the subject, pressing a sheet having an absorbent surface against said emulsion layer while said emulsion layer is moist, to cause only the shadow areas of the emulsion to adhere to the sheet, and separating said sheet and emulsion layer to leave only a stratum of said shadow areas of the emulsion layer adhered to said sheet.
8. The process of claim 7 wherein the phosphite compound is triisooctyl phosphite.
9. The process of claim 7 wherein the phosphite com pound is tricresyl phosphite.
References Cited in the file of this patent UNITED STATES PATENTS Teal et al. Oct. 21, 1952