US2346095A

US2346095A - Chemical sensitizing of photographic emulsions

Info

Publication number: US2346095A
Application number: US435666A
Authority: US
Inventors: Weissberger Arnold; Burt H Carroll
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1942-03-21
Filing date: 1942-03-21
Publication date: 1944-04-04
Anticipated expiration: 1961-04-04
Also published as: FR956682A

Description

Patented Apr. 4, 1944 CHEMICAL SENSITIZING F rno'ro- GRAPHIC EMULSIONS Arnold Weissberger and Burt H. Carroll, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y.,

Jersey a corporation of New No Drawing. Application March 21, 1942,

Serial No. 435,666

Claims.

, This invention relates to photographic emulsions and particularly to materials used in the preparation of such emulsions.

sensitizing of photographic emulsions is of two general types; chemical sensitizing, in which the sensitivity of the emulsion is increased in the spectral region to which the silver halide is originally sensitive, and optical sensitizing, in

which the sensitivity is increased in a spectral region to which the silver halide is not originally sensitive. The present invention relates to the former type of sensitizing.

In the chemical sensitizing of photographic emulsions many compounds have been proposed for the purpose of increasing the sensitivity of the silver halide grains. Compounds such as sulfur bodies have been proposed and in most cases there is thought to be an interaction of the silver halide and the sensitizer to form small specks of silver sulfide on the silver halide grains. These specks are thought to act as nuclei for silver deposition and thereby to increase the sensitivity of the emulsion.

It is an object of the present invention to provide photographic emulsions having new or improved properties because of the use or presence therein of materials, the sensitizing properties of which we have discovered. A further object is to provide a method in which such materials are used to improve photographic emulsions, especially developing out emulsions, with respect to light sensitivity, by which term we include their ability to give the earliest visible impression or image with the minimum exposure or their ability to produce the maximum density after a given exposure or both. A still further object is to provide colloid products such as gelatins, the usefulness of which for forming light-sensitive photographic emulsions is'greatly increased and controlled by the use of our sensitizing materials. A still further object is to provide a method for enhancing the light sensitivity of photographic emulsions immediately after the addition of the sensitizing compounds. Other objects are to increase the general light sensitivity of such photographic emulsions throughout the spectral ranges to which they are normally sensitive and to obtain more stable emulsions through the use of our sensitizingagents. Other objects will appear from the following description of our invention.

These objects are accomplished according to the present invention by incorporating in a silver halide photographic emulsion a non-sulfurcontaining sensitizing body consisting of an alkoxymethylene-fi-diketone.

Our sensitizing material may be used in many Ways. It may be incorporated in emulsions or in colloids used in the preparation of the emulsions. It can also enter the emulsion mixed with other ingredients, organic or inorganic. It increases the light-sensitivity of various emulsions having different speeds or other distinctive characteristics. While it may be added at different stages of emulsion manufacture, nevertheless it can be very conveniently mixed with the emulsion when the latter is otherwise complete and ready for coating. Since its action is immediate when incorporated, the coating need be delayed only long enough to mix the sensitizing material with it.

The alkoxymethylene-fi-diketones which we have found suitable for the purpose of sensitizing and stabilizing photographic emulsions include ethoxymethyleneacetyl acetone and butoxymethyleneacetyl acetone as well a other compounds of this general class.

As will be clear to those skilled in the art, the proportion of sensitizing material added to the emulsions will vary according to the concentrations of the sensitizing material and according to the increase in light sensitivity desired. We have found that the addition of the alkoxymethylene-c-diketones to photographic emulsions in amounts to the order of 10 mg. to 50 mg. Per liter of emulsion tends to increase the threshold speed by .as much as in some cases. Larger amounts of sensitizing agent can be used and smaller amounts can also be used if only slight increase in sensitivity is desired.

Where different batches of emulsion fall below a required manufacturing standard of light sensitivity, although they may otherwise be satisfactory, sensitivity canreadily be brought up to standard by mixing our sensitizing material with them, the proportion varying with the increase necessary to produce a uniform product. The increase in sensitivity can be effected in one step by thoroughly stirring all of the sensitizing material into the emulsion at one time or it may be incorporated in successive steps.

It is convenient to add our sensitizing mate- 25 milligrams of our sensitizing material for each liter of emulsion.

With its light sensitivity increased by the use of our material, the emulsion is melted to the desired degree and is coated on the support, such as suitably subbed glass, film or paper, in the usual way.

The different types of gelatin used for photographic emulsion making may be used in the example above, hard ones being very useful. The temperatures given are, of course, readjusted if the particular gelatin employed has melting and setting point which deviate considerably from the usual ones, this adjustment being a matter of routine control. Our sensitizers can be used to increase the general light-sensitivity of ordinary blue-sensitive photographic emulsions or they can be used for increasing the sensitivity of orthochromatic, panchromatic, X-ray and other pecial emulsions. It is evident, therefore, that they can be used in conjunction with optical sensitizers although they do not act as optical sensitizers for the emulsion. Our sensitizers act to increase the light sensitivity independently of ripening.

In place of gelatin, ot er colloids may be used in the preparation of the photographic emulsion such as collodion, agar, synthetic resins and cellulose esters. Moreover, the principle of the invention is applicable to silver chloride and chlorobromide emulsions as well as to silver bromide and silver bromoiodide emulsions and to mixtures of any two or more of them.

It will be understood that their invention is to be taken as limited only by the scope of the appended claims.

We claim:

1. A photographic emulsion comprising a colloidal material having particles of silver halide dispersed therein, and an added sensitizing compound upon which at least a part of the light sensitivity of the emulsion depends, the sensitizing compound being an alkoxy methylene-fi-diketone.

2. A photographic developing-out gelatino-si'lver halide emulsion of high light sensitivity containing as a sensitizing compound from about 10 milligrams to about 50 milligrams per liter of emulsion of an alkoxy methylene acetyl acetone.

3. A photographic developing-out gelatino-silver halide emulsion of high light sensitivity containing as a seinsitizing compound from about 10 milligrams to about 50 milligrams per liter of emulsion of ethoxymethylene acetyl acetone.

4. A photographic developing-out gelatino-silver halide emulsion of high light sensitivity containing as a sensitizing compound from about 10 milligrams to about 50 milligrams per liter of emulsion of butoxymethylene acetyl acetone.

5. The process of preparing a gelatino-silver halide emulsion of increased light sensitivity which comprises incorporating in said emulsion an alkoxymethylene fl diketone in sensitizing amount which effects an immediate increase in sensitivity.

6. In the process of preparing a developingout gelatino-silver halide emulsion, the method of increasing the light sensitivity of said emulsion by incorporating in it a sensitizing amount of an alkoxy methylene acetyl acetone.

'7. In the process of preparing a developingoutgelatino-silver halide emulsion, the method of increasing the light sensitivity of said emulsion by incorporating in it a sensitizing amount of ethoxymethylene acetyl acetone.

8. In the process of preparing a developingout gelatino-silver halide emulsion, the method of increasing the light sensitivity of said emulsion by incorporating in it a sensitizing amount of butoxymethylene acetyl acetone.

9. In the process of preparing a developingout gelatino-silver halide emulsion, the method of increasing the light sensitivity of said emulsion by incorporating in it from about 10 milligrams to about 50 milligrams per liter of emulsion of ethoxymethylene acetyl acetone.

10. In the process of preparing a developingout gelatino-silver halide emulsion, the method of increasing the light-sensitivity which comprises incorporating therein from about 10 milligrams to about 50 milligrams per liter of emul- 45 sion of butoxymethylene acetyl acetone.

ARNOLD WEISSBERGER. BURT H. CARROLL.