US1678832A - Photographic light-sensitive material and process of making the same - Google Patents

Description

Patented July 31, 1928.

UNITED STATES 1,678,832 PATENT OFFICE.

SAMUEL E. SHEPPARD, OF ROCHESTER, NEW YORK, ASSIGNOR T EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A. CORPORATION OF NEW YORK.

PHOTOGRAPHIC LIGHT-SENSITIVE MATERIAL AND PROCESS OF MAKING THE SAME.

No Drawing.

This invention relates to the art of photographic light-sensitive materials and to processes of preparing such materials. One object of the invention is to provide photographic emulsions having improved properties because of the presence therein of certain sensitizing substances which I have discovered. Another object of the invention is to provide processes in which such sensltlzing substances are used to improve the hghtsensitiveness of photographic emulsions, articularly developing-out ones. A still urther object of the inventon is to provide colloid products, such as gelatins, the ability of which to form light-sensitive photographic emulsions is greatly increased by said sensitizing substances. Another object of the invention is to provide processes for preparing said colloid products. Other objects will hereinafter appear.

In my U. S. Patent No. 1,574,944, March 2nd, 1926 for photographic light-sensitive material and process of making the same, I have disclosed, among other things, a class of sensitizing materials by means of which the light-sensitiveness of photographic emulsions can be greatly increased, and by means of which colloids, such as gelatins, can be put into the best condition for manufacturing such emulsions. Such materials are effective even when used in very minute quantities relative to the other ingredients of the emulsion.

I have now found another class of sensitizing substances which are similarly effective in the production of light-sensitive emulsions and in the preparation of colloidal intermediates for the manufacture of such emulsions. This new class includes all of the disulfids indicated by the formula,

Application filed June 6, 1927. Serial No. 196.992.

One example of such a substance is the salt of ethyl dioxythiocarbonate as prepared by Debus (Liebigs Anualendcr Ohemie, Vol. 72, page 1 and Vol. 75, page 121) Other examples are the compounds obtained by the action of bromine on mustard oils, or isothiocyanates. These are sometimes called mustard oil oxides. (See Freund, Liebigs Annalender Ohemie, Vol. 235, page 14.)

Still other examples are the thiurets having the following formula,-

s-s RN==C d=NH Another illustration is benzoyldisulfide:

OqHg-C-S-S-C-CBHE a a The proportions in which these compounds are incorporated in the emulsions, or in the colloids for the emulsions, are important. Too much of them will cause fog. The, maximum proportions which can be used practically vary slightly with the particular sensitizing compound which is selected, with the ratio of gelatin to silver halide in the emulsion, with the type of emulslon, as regards grain size, and alkalinlty, with the amount of natural sensitizer also present in the gelatin when the latter is manufactured, with the particular silver halide or halides employed, and with the fog standards which are set by the emulsion maker. The maximum proportion in any case is readily found by routine test.

In all cases the proportion of the sensitizmg compound relative to the other ingredients of the emulsion is remarkably minute. With gelatino-silver-halide developing-out emulsions it is generally less than about ten grains of active sensitizing compound in 130 7 pounds of emulsion (the latter being computd as the weight of its non-equeous ingredients in the dry state); or less than about ten grains in 100 pounds of gelatin (computed as dry gelatin). Smaller proportions are very useful, such as two to three grains of the sensitizing, compound to 100 pounds of dry gelatin or 130 pounds of emulsion.

It will be noted that the quantities of sensitizing compounds are so small in the gelatins or emulsions, that they do not appreciably dilute them, nor have any effect upon their physical properties. The photographic colloids, such as gelatins, can be selected so as to have the right physical properties, such as setting ability, viscosity and proper melting point, without worrying about whether they have also suflicient lightsensitizing power. The latter can be brought up to the normally useful degree by adding my sensitizing compounds. This enables me to cstablish'a ratio of sensitizing compounds to the silver halide in the emulsions which is independent of the ratio of the gelatin to said silver halides.

Like the sensitizing compounds described in my above mentioned patent, the present sensitizing compounds are chemical sensitizers whlch increase the general sensitiveness of the photographic emulsions unlike the effects of dyes which optically sensitize the emulsions to increase their sensitiveness to some particular narrow group of wave lengths. My present sensitizing compounds are effective in all, kinds of emulsions ordinarily met with, such as orthochromatic, panchromatic, X-ray, as well as the ordinary non-color-sensitized ones. They can be added without or with sensitizing dyes or before or after them.

My present sensitizing substances may be, in general, incorporated in the emulsions or in the colloids for the emulsions in the same way as those set forth in my above cited patent. For example, a mixed silver bromide and iodide emulsion in gelatin may be prepared, as set forth in page 3 of said Patent No. 1,574,944. After the emulsion is prepared it may be melted and the proper amount of sensitizing compound thoroughly mixed into it. This mixing is conveniently elfected by dissolving the sensitizing substance in ethyl alcohol or water or a mixture of them, and then stirring such solution into the emulsion. I find it good practice to keep the volume of the solution of sensitizcr below about 2% of the volume of the emulsion into which it is mixed. Where, for instance, one part of benzoyldisulfide by weight is to be incorporated into about 300,000 parts by weight of such emulsion (computed as the weight of its non-aqueous ingredients), the benzoyldisulfide is dissolved in a slightly aqueous ethyl alcohol, equal in volume to 1.5% of the emulsion, and is then stirred into the latter while melted.

Instead of incorporating -n1y sensitized compounds into the melted emulsion, they may be premixed with the emulsion-forming colloid, such as gelatin. In general there is added to the gelatin enough of my sensitizing compounds to make up for any deficiency of natural sensitizing compounds in said gelatin. I may even employ gelatin which is free from natural sensitizing substances, and

depend upon my added sensitized compounds to give it the power to form highly lightsensitive photographic emulsions. In this way I prepare the colloid in a form which serves as a valuable intermediate in the reparation of photographic emulsions. *or example, I may dissolve two or three grains of benzoyldisulfide in slightly aqueous alcohol, and carefully stir the solution into 100 parts of melted gelatin (calculated as dry gelatin). The volume of the alcoholic solution should be only about 1.5% of the volume of the gelatin, thus avoiding anyv appreciable dilution of the colloid.

lVhere it is desired, for simplicity in manufacture, to render gelatin inert and then add known amounts of sensitizing compounds to it, the gelatin may be treated with oxidizing agents, as set forth in page 5 of my Patent No. 1,574,944. This destroys the natural sensitizing compounds present in the gelatin. Then, after proper washing of the gelatin, the right proportions of my sensitizing compounds may be added, as indicated above.

When my new sensitizing compounds are added either to the emulsion, or to colloids for making the emulsion, as hereinabove described, there is an advantage in maintaining a slightly acid condition until a thorough mixture has been obtained, my new substances having less tendency to prematurel split oif sulfur, under such conditions. f course, the alkalinity of the emulsion is immediately restored, as will be understood by those skilled in this art.

While my novel sensitizing compounds are preferably used with gelatin, they, nevertheless, have utility with emulsions made in other colloids, such as albumens, agar-agar, gums, like gum arabic, and cellulosic derivatives. My compounds likewise have utility in emulsions in which different kinds of silver salts are present, such as silver bromide, silver iodide, silver chlorid, or mixtures of any of these with one or more of the others. In place of the above described disulfids, there may be substituted the corresponding diselenids or ditellurids which function as sensitizing compounds in the same way. When I refer hereinafter to disulfids it will be understood that I include such equivalents.

Having thus described my invention, what I claim asnew and desire to secure by LettersPatent is: I

1. A photographic emulsion comprising a colloid, particles of photographic silver salts suspended therein, and an added compound therein upon which at least part of the light-sensitiveness of the emulsion depends, said compound being a disulfide of the type R-o-s-s-o-R a in which R is any organic radical and X and Y are selected from the group of oxygen, imid-nitrogen, sulfur, double bonded carbon.

2. A photographic developing-out gelatino-silver halide emulsion of the alkaline type of relatively high light-sensitiveness, comprising a mixture of the constituents of a gelatino-silver-halide emulsion of lower light-sensitiveness, and an added sensitizing compound upon which depends the difference between said lower and said high lightsensitiveness, said compound being a disulfide of the type in which R is any organic radical and X and Y are selected from the group of oxygen, imid-nitrogen, sulfur, double bonded carbon;

3. A photographic emulsion comprising a colloid, particles of photographic silver salt suspended therein and an added compound therein upon which at least part sensitiveness of the emulsion depends, said compound being less than the order of ten grains per 130 pounds of emulsion, being insufficient to cause immediate fogging tendency, and. being a disulfide of the type RCS-SO R ll ll X Y in which R-is any organic radical and X and Y are selected from the group of oxygen, imid-nitrogen, sulfur, double bonded carbon.

4. In" the process of ing-out colloid sensitive-silver salt emulsion, increasing the light-sensitiveness thereof by incorporating with the other constituents thereof a disulfide of the type in which R is any organic radical and X and Y are selected from the group of oxygen, imid-nitrogen, sulfur, double bonded carbon. r

5. In the process of preparing :1 developing-out colloid-sensitive-silver-salt emulsion, increasing the light-sensitiveness thereof by incorporating with the other constituents thereof an independent sensitizing compound in proportions less than the order of ten grains of compound per 130 pounds of emulsion,

' photographic of the lightpreparing a developbeing a disulfide of the type I R-C-S-S-C-R I I x Y emulsion.

7. An intermediate for use in making emulsions, emulsion-forming colloid having incorporated therein, a disufide of the type R-c-s-s-o-R I U x Y in which R is any and .Y are selected gen, imid-nitrogen, carbon.

8. The process of making an intermediate for use in the preparation of photographic emulsions, which comprises incorporating in an emulsion-forming colloid a disulfide of the type organic radical and X from the group of oxysulfur, double bonded ll X Y in which R is any organic radical and X- and Y are selected from the i group of oxygen, lmld-nitrogen, sulfur, double bonded carbon.

Signed at Rochester, New York, this 28th day of May, 1927.

SAMUEL E. SHEPPARD.

comprising an said compound being insuflicient to cause immediate fogging tendency, and