US2604397A - Chemical sensitization of photographic emulsions - Google Patents

Description

Patented July 22, 1952 CHEMICAL SENSITIZATION OF PHOTO- GRAPHIC EMULSIONS' Wesley G; Lowe and Jean E. Jones, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application November 18, 1948,

Serial No, 60,816 a 11- Claims. (01. 95-7) This invention relates to photographic emu1 sions and more particularly to chemical sensitizers therefor.

It is Well known that silver halide emulsions may be chemically sensitized with a variety of materials so as to increase the speed and generally the gamma of the emulsion as opposed to :optical sensitization in which the optical 'range of sensitivity is increased' Depending upon the materials and methods employed; it is generally regarded that chemical sensitization results in either the formation of silver sulfide on the surface of the silver halide crystal thus increasing sensitivity or the formation of small amounts of silver from the reduction of silver halide. The

present invention is concerned'with chemical sensitization apparently of the latter type.

We have discovered that when photographic silver halide emulsions are chemically sensitized with water-soluble salts furnishing-the sulfoxalate ion, appreciable increases-inlight sensitivity are obtained. Therefore, one-object ofour invention is to provide novel chemicallysensitized emulsions. Another objectis' to provide silver halide emulsions containing sulfoxalate sensitizing as well as sensitivity due to otherchefnical and optical sensitizers. Other objects will appear from the following description of'o'ur-invention. j "j I The objects of our invention areyaccomplished by incorporating into photographic emulsions a water-soluble formaldehyde sulfoxalate salt such as an alkali metalformaldehydevsulfoxalateparticularly sodium formaldehyde sulfoxalate. The novel sensitizers are incorporated in' the emulsions at any stage in their preparation but'pr-eferably before digestion is complete. Generally in order to obtain the optimum sensitizingefiect we heat the emulsion after addition of the sulfoxalate sensitizer. The sensitizers may be used in conjunction with other cheinical-a'ndoptical sensitizers such as the Well known sulfur sensitizing c'ompoundsy'for example, those disclosed in Sheppard U. S. Patents"1,574,'94l granted March 2, 1926, and 1523,499, granted April 5, 1927, and may be employed before, after or'simultaneously with such sulfur sensitizing and in conjunction with sensitizing dyes. Als o our lnovel sensitizers areuseful with a variety of emulsions producing pronounced speed increases in either negative orpositive typ'e's of emulsions;

a Our invention Will now be illustrated byrefer- .ence to the following specific examples-t Example 1' l I cc. of a promo-iodide positive type of emulsion containing silver halide iobta n drfr grams of silver nitrate and peptized with a gelatin derivative by the process disclosed. in the pending Lowe et a1. SLapplicat'io'n Serial No.

768,478 filed August 13,1947, was adjusted to'a pH of 4.5 then treated at F. with3iQ mg, of sodium formaldehyde sulfoxalalte; and heating continued at this temperature for 20 minutes.

Following this, the emulsion was cooled to 100 F. and the pH raised to 6.0 with sodium hydroxide solution. To samples of the resultant emulsion was added hydrophilicf colloid material such as gelatin or polyvinyl alcohol; respectively, and after addition .of the usual emulsion addenda, the emulsions were coated andfdried in the usual manner. After exposure in an Eastman TXDeiZB Sensitometer (J. Soc. Mot. Pict. Eng. '1??- (1931) p. 536) and processing in a developer solution of the following composition for six minutes, the emulsions were found to have'materially increased in speed, as shown in the table following (samples B and F compared to samples A and Developer Sodium carbonate (dry), do' 19.0

' Potassium bromide do 0.9 Citric acid do- 0.7

Example 2' 100 cc. of the same type of emulsion as'was used in Example 1 but which hadpreviously. been sensitized with arsulfur type of sensitizer e. g. allyl thiourea, .asdescribed in the Lowe et al. in-

vention, was adjusted to pH 4.5 by dilute acetic acid and treated with sodium formaldehyde sulfoxalate as in Example 1 and samples combined with gelatin and polyvinyl alcohol, respectively, to obtain emulsions the sensitivities of which are distinctly higher than obtained by "using either .sensitizer separately as is shown in the table following (samples D and'H compared to samplesB. C;FandG).r

Example 3 100 cc. of emulsion prepared as described in Example 2 (sensitized with: sulfur and sulfoxalate sens'itizersl were precipitated withidilute sulfuric acid and washedtwice with'distilled water. After repeptizing the grains, the pH was adjusted to 6.0, the emulsion heated to 120 F. and 1.0 mg. of potassium auric chloride Was added. After five minutes the temperature was lowered to 100 F., the emulsion was added to gelatin and coated and dried as usual. Thecharacteristics of this emulsion having combined sulfur, sulfoxalate and gold sensitizing, are shown in the table (sample K compared to samples I, J and L).

4 tion is to be taken as limited only by the scope of the appended claims.

What we claim is: 1. A light-sensitive photographic emulsion comprising silver halide and from about 0.03 to 0.75 gram per kilogram of-silver nitrate used in .making the emulsion and converted to silver halide, of a water-soluble formaldehyde sulfoxalate salt as a sensitizing agent.

. lot/E Speed :2. ens.=- Sample Chemical sensitizer Vehicle Gamma Fog 02 above I log None Gelatiin 76 02 .39 Sulioxalate 1 d 1. 58 02 80 72 .02 35 1. l3 02 45 2. 52 03 3. 55 2. 51 05 4. 70 Sulfur type 2. 6 02 4. 3 Sulfur and Sulfoxalate 3. 1 07 7. 3 Sulfur and Sulioxalate and Gold.-- 3. 2 .09 14.0 Sulfur and Gold 3. 5 04 6. 5

It is apparent from the above data that the new sulfoxalate sensitizer used in conjunction with a sulphur sensitizer has effected a speed increase greater than that expected from the activity of the individual sensitizers when used alone. However, the speed increases obtained in absence of sulfur sensitizing are appreciable and valuable.

In the manner of the above examples, other types of silver halide emulsions may be treated with our novel sensitizers alone or in conjunction with other chemical or optical sensitizers. The amount of the sulfoxalate sensitizer incorporated into an emulsion may, depending upon the type of emulsion used, vary somewhat from the optimum amount employed in the above examples, one-fifth to five times as much sensitizer producing emulsion of useful sensitivity that is, from about 0.03 to 0.75 gram of the sensitizer per kilogram of silver nitrate used in making the emulsion and converted to silver halide. Less V heating is usually required when the larger amounts are employed and conversely, when using the smaller quantities of sensitizer.

The novel sensitizers may, in general, be employed i emulsions containing hydrophilic colloid vehicles; for example, gelatin, polyvinyl alcohol, partially hydrolized cellulose esters and co-polymers of polyvinyl alcohol. The ratio of colloid to silver halide present during digestion is not critical in this type of sensitizing since the digestion conditions can be readily adjusted as is well known in the art of sulfur sensitizing. The sensitizers are suitable for the well known types of silver chloride, silver bromide and silver iodide emulsions and emulsions containing mixtures of these halides. Also the emulsions may contain the usual addenda including antifoggants, spreading agents, coupler compounds, etc. Such emulsions are adaptable to use informing single as well as multi-layer films useful in color photography which customarily include two or more emulsion layers on a support sensitized to different regions of the visible spectrum and may or may not contain coupler compounds. According to our invention such color films carry at least one emulsion layer containing a sulfoxalate salt sensitizing agent.

Our invention having been described, we would have it understood that the preceding description is by way of example'only and that our inven- 2. A light-sensitive photographic emulsion comprising silver halide and from about 0.03 to 0.75 gram per kilogram of silver nitrate used in making the emulsion and converted to silver halide, of sodium formaldehyde sulfoxalate as a sensitizing agent.

3. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and from about 0.03 to 0.75 gram per kilogram of silver nitrate used in making the emulsion and converted to silver halide, of sodium formaldehyde sulfoxalate as an additional sensitizing agent.

4. A light-sensitive photographic emulsion comprising silver halide sensitized with a sulfur sensitizing compound, a gold salt sensitizer and sodium formaldehyde sulfoxalate.

5. A light-sensitive photographic emulsion comprising silver halide uniformly dispersed in a hydrophilic colloid vehicle and sensitized with from about 0.03 to 0.75 gram per kilogram of silver nitrate used in making the emulsion and converted to silver halide, of a water-soluble formaldehyde sulfoxalate salt.

6. A light-sensitive photographic emulsion comprising silver halide uniformly dispersed in gelatin and sensitized with from about 0.03 to 0.75 gram per kilogram of silver nitrate used in making the emulsion and converted to silver halide, of sodium formaldehyde sulfoxalate.

7. A light-sensitive photographic emulsion comprising silver halide uniformly dispersed in polyvinyl alcohol and sensitized with from about 0.03 to 0.75 gram per kilogram of silver nitrate used in making the emulsion and converted to silver halide, of sodium formaldehyde sulfoxalate.

8. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion, adjusting the pH of said emulsion to below neutrality, and effecting a further increase in sensitivity by digesting said emulsion in the presence of a water-soluble formaldehyde sulfoxalate salt.

9. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur, sensitivity to said emulsion, adjusting the pH of said emulsion to below neutrality and effecting a further increase in 6 REFERENCES CITED The following references are of record in th file of this patent: I

Number Number UNITED STATES PATENTS Name Date Miller June 10, 1930 Sheppard et a1. Nov. 3, 1936 FOREIGN PATENTS Country Date Great Britain Nov. 21, 1938

Claims (1)

1. A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSION COMPRISING SILVER HALIDE AND FROM ABOUT 0.03 TO 0.75 GRAM PER KILOGRAM OF SILVER NITRATE USED IN MAKING THE EMULSION AND CONVERTED TO SILVER HALIDE, OF A WATER-SOLUBLE FORMALDEHYDE SULFOXALATE SALT AS A SENSITIZING AGENT.