US2563791A - Photographic emulsions peptized with zein - Google Patents

Description

Patented Aug. 7, 1951 2,563,791 euorocasrmcmmnsrons PERTIZED I 'M'IIHZEIN Wesley G. Lowe, Rochester; N. Y., 'assignor to Eastman KodakrGnmpa corporation*ofiNewJersey "No Drawing. Application'scptonibet'fl 7 Serial-No. 4737-53 a a Qlaims. (ClnBfi-m?) This invention relates to "the preparation of photographic emulsions characterized' by the of zeinas the peptizirlg agentfor the silver halide employed therein.

:Inthe preparation of silver halide type photographic emulsions it-is desirable to prepare-the silver ghalide in a finely divided form; accomplished ordinarily "by a double decomposition reaction in an aqueous solution .of a "colloid (known as a peptizer). Gelatin-msbeen found to be themost useful for {this purpose but other colloidal substances have "been mentioned as being suitable. When dispersions ,ofisilver halide are desired having a different susceptibility to water than gelatinya problem arisesas mosttofthe water-insoluble colloids donothave good peptizing properties.

'Qne ,object of my invention is to provide a peptizer ior silver halide which is vwater'insoluble. Another object of my invention is fto pr'ovide a method vwherebymixed grain emulsions which are separately .developahle may be prepared. gOther vobjects will appear herein.

I have "found that zein when'in solution in a lower alcohol or acetone and water acts as a peptizer for silver halide upon its jformationand that the resulting dispersion maybe employed in the preparation of photographic emulsions. I

have found that zein-peptized dispersions of silver halide which are differentially developable from gelatin-peptized silver halide {dispersions may be prepared and employed in making photographic emulsions having unique characteristics. zein has characteristics whichespeciady adapt it for mixed grain type remulsions; Some 413i these characteristics are: 1. :Unlike the "majority of vva'i'er'einsoluble c01- loids,-zein is-avery good p'eptizer of silver halide. 2. Unlike many water-insoluble colloids it tolerates the presence "of enough 'water in some of its solvent mixtures to make emulsion making convenient by 'conventional methods. 3. Zein is soluble in benzyl alcohol, which solvent has characteristics making it 'a good medium for dispersion in "gelatin solutions. Some Of these characteristics of benzyl alcohcil are:

a. 'Benzyl alcohol is a good solvent for zein, for many sensitizing dyes andrmany couplers. i). It is sufficiently --water-insoluble *to make convenient formation of a fine-grained, uniform dispersion in gelatin solutions by means-of a colloidmill. Y i c, It is soluble enoug'hin water to be remolied :2 from a-photog-raphic iemulsion 'by watenwashin thei emulsion whlle ininoodle rorm.

1 d. ,Benzyl alcohol *lsva readily available nonfog ging :solverit.

4. Zein-peptized emulsions are satisfaotory in the fineness er dispersion of the silver "halide, photographic stability and ireedom 'from "fog.

5; Drdinarydevelopersgnd"fixing'baths can be used for processing the emulsion, audit develops readily in conplerdevelopers.

6."The envelope -or zein "around the silver halide :graii'ns acts as a ba irrier-to the passage of sensitizing dyes, so 'that contamination of neighboring qgrains 'by transfer oi the optical-sensitizer can' -be a solution of'rein in *isopropyl alcohol-water is particularly useful asfa peptizer for silver halide. 'lI-he silver halide dispersion. may be prepared "by introducing a stream of silver nitrate solution and a stream of an alkali metal halide :solution into the zein solution simultaneously wit'h stirring or byladding the alkali metal halide ftp the solution ofaein and introducing a stream of silver nitrate solution :withstirring. Thereresultsa'nnely divided silver, halide in suspension in the zein "solution. "This dispersion may then be'incorporatedina solution of acompatlble "emulsion" vehicle or preferably is first washed and dispersed in benzyl alcohol, which dispersion may then be dispersed in gelatin or some other vehicle by means of a colloid mill or similar dispersing "mechanism. Such a zein emulsion dispersed .in :geflatin can be developed and 11nd idemirinfll gpr'ocessing solutions.

It, howeverpanpmul'sion is desired which is deveiop'able at a-=pH,greater than 9, the zein emu s ndispsrsed se s may be gelled and handled and thernoodles washed with water to "remove-the benzyl alcohol. The resulting emulsionisicomposed of small particles of :ze-in enclosing :silver vfhalide crystals and dispersed in :gelatin. ilt' is :less 'developahle-at ra' low pH than a similar emulsion prepared in gelatin and .polyviny l .alcohol. M .a rhigh cpl-I, such as above *9 and up to 12, it is readily developed. 'These emulsions are diflicult to sensitize ii the sensitizer is added to the final emulsion due to the zein barrier surrounding-"the grains, *butthey are readily sensitized if the 'sensitizer is added *to the benzyl alcohol solution before dispersing it in gelatin.

To prepare amixed grainyphotographic emulsion the zein-peptiaed emulsion as described herein y be mixed -wlth the conventional type high pH developerpwhereby- 'the zein-peptized emulsion- .developedi. Such an emulsion may be used in a mixed grain process for color photography in which the couplers are added during development. In the second development V another coupler can be introduced and the pH.

emulsion. Y e

If the couplers are dissolved along'with the desired sensitizers in the benzyl alcohol solution of the zein-peptized emulsion before it isdispersed into the gelatin, removal of the benzyl alcoholby washing will leave silver halide, sensitizer and coupler in the small dispersed particles of the zein peptized emulsion. Development in a color developer then develops each particle'as a unit and in View of the highde'gree of dispersion of such an emulsion, gives colorseparation with good photographic quality. To obtain good color separation the following factors are necessary: r

(l) Non-diffusibility ofthe sensitizing dye.

(2) Non-diffusibilityof the couplers.

(3 Limited diffusibility of the oxidized-form of the coupling developer.

If desired, three zeinpeptized emulsions may be prepared and dispersed in gelatin, each containing a suitable sensitizing dye and coupler. The emulsions may then be mixed with. orwithout extra gelatin and coated in a single operation. This procedure would be a simple operation as compared to the coating of, multi-layer color products.1 i In the preparing of zein dispersions in accord ance with my invention, the silver halide is,pre-. pared in a solution of zein in a mixture of .a lower alcohol or acetone and water. The dispersion may be prepared either by runningsolutions of silver: nitrate and alkali metal halide into the zein solution with stirring or by incorporating one of the reagents in the Zein solution and running 1 ma solution of the other reagents.

: .Isopropyl alcohol is preferred for the lower ali- 10 raised so as to develop the zein-peptized patible therewith, such as shellac, rosin, ester resins before dispersing in the gelatin solution. As only a small quantity of zein is required to peptize the silver halide grain, the adding of extra min to. the emulsion in ,benzyl alcohol modifies thefs'ize and properties of the dispersed particles. I have found that concentrations of zein of the order of -12% are quite satisfactory in the preparation of silver halide dispersions in which the. amount of silver halide may be 2-8 times or more the amount of zein employed. I have found that-zein has a good peptizing action on silver halide,and my invention is not limited as to concentrations or proportions. v The following examples illustrate my inven tionz.

Example 1.6% g. of zein were dissolved in a mixture of 225 cc. of water and 250 cc. of isopropyl alcohol, and .55 g. of potassium iodide and 37.25 tg. of potassium bromide were dissolved therein. Another solution was prepared by dissolving 48.5 g. of silver nitrate in a mixture of 225 cc. of water and 250 cc. of isopropyl alcohol. The

. zein solution was raised to a temperature of 57 C.

The silver nitrate solution was allowed to run into the zein solution in seven minutes with good stirring, and the emulsion was stirred for ten minutes at 57 C. The emulsion was then cooled to C. and poured into water. The mass precipitated and was washed in cold water. The emulsion was then stirred with 500 cc. of acetone which removed the water from the emulsion. 100 cc. of benz'yl alcohol were added. The .emulsion was heated to C. and stirred for fifteen minutes. 35

100 cc. of a20% solution of zein were added, and the emulsion dispersed in' a colloid mill with 300 cc. of a 10% solution of gelatin. The emulsion was allowed to set by chilling, was noodled, and

It was then melted and coated onto film base. It Was fou'nd that the emulsion readily developed in normal developers and fixed in normal fixing baths, A comparison of the development characteristics of this emulsion at several different pI-Is with a similar silver bromide emulsion prepared in gelatin is as follows DeveloplO/z T ment pH i 'y Time speed F. -Mz'n. 1 Zein emulsion 30 8.0 0 0 No development.

Gelatin emulsion 70 30 8.0 319 0. 80, Partial development. 2 'Zein emulsion 70 9 8.6 0 0 N 0 development.

Gelatin emulsion 70 9 8.0 5.0 0.85 Partial development. 3 Zeinemulsion 70 6 9.5 1. l 0.27 Partial development. Gelatinemulsion 70 6 9.5 4.25 2.6 Maximum development. 4 Zein emulsion 70 '2 10.8 3.8 0. 64 Maximum development. Gelatin emulsionnnn 70 2 10.8 5.5 L43 Partial development.

phatic alcohol as theam'ount ofwater which can be-tolerated is approximately 50%, this being an advantage in dissolving the silver: nitrate and metal ha1ides;'-Other. lower, alcohols, such as ethyl or methyLor acetone, may beemployed if desired, it being desirable that the maximum water which will not render the zein insoluble be employed ordinarily. Instead of incorporating the silver halide dispersion in gelatin, it may be desired to incorporate it in a solution of afarm It was found that the image quality of this emul sion was very good, the developed graininess was low, and the emulsion was free of fog.

Example 2.A'small amount of a solutionof the sensitizing .dye 2,3-diethyl-4-methyloxathiazolo carbocyanine iodide was added to a sample of the emulsion of Example 1. Exposure behind filters indicated that the emulsion had acquired almost no color sensitivity. in the green, indicating that the silver halide protected by the zein was resistant to sensitizing by this dye in the external phase- V Example 3.-- Part. of the emulsion of Example 1 was mixed with a solution of the sensitizing dye, 3-ethyl-5-(2-ethyl 1 -,benzothiazylidene-isopropylidene)-2-thio-'2,4 (3,5) -oxazoledione, the dye being dissolved in benzyl alcohol and added to a benzyl alcohol solution of the emulsion before its dispersal in gelatin solution. The emulsion was then added to gelatin solution, the mass was chilled, noodled, thoroughly washed with water, melted and. coated on film base. This emulsion showed satisfactory sensitivity in the green, indicating that sensitization of this type of emulsion can be carried out satisfactorily if the sensitizing is done before dispersing in gelatin solution.

Example 4.-Part of the emulsion of Example 1 in its final form (dispersed in gelatin and washed free of benzyl alcohol) was mixed with a silver chloride emulsion dispersed in gelatin. The mixed grain emulsion thus obtained was coated out on film base and developed with 11-16, with the pH adjusted to 8.6. In a time of nine minutes good development of the chloride emulsion was obtained but no develops-lent of the zein peptized emulsion occurred.

Example 5.Part of the emulsion of Example 1 was coated on plates and dried down without washing out benzyl alcohol. This emulsion processed readily but it was found that the develop ment restraint at low p'Hs which is typical of the washed emulsion was absent in this unwashed emulsion. This indicates that removal of the benzyl alcohol is desirable for protection of the silver halide grain against penetration by developer having low pH.

Example 6.-An emulsion was prepared as in Example 1 but when the emulsion was dissolved in benzyl alcohol no additional zein was added to the grains. The zein emulsion was dispersed in gelatin solution, chilled, noodled, washed, melted and coated onto film base. It was found that the development restraint of the emulsion when subjected to developers having a low pH was inferior to that obtained in the emulsion containing extra zein. This indicates that the development resistance of an emulsion can be regulated by controlling the amount of zein used in the emulsion.

I claim:

1. A method of preparing an optically sensitized emulsion which comprises forming zeinpeptized silver halide grains, dispersing the zeinsilver halide mass in benzyl alcohol, adding optical sensitizer thereto and incorporating the dispersion into aqueous gelatin,

2. The product of the process of claim 1.

WESLEY G. LOWE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number

Claims (1)

1. A METHOD OF PREPARING AN OPTICALLY SENSITIZED EMULSION WHICH COMPRISES FORMING ZEINPEPTIZED SILVER HALIDE GRAINS, DISPERSING THE ZEINSILVER HALIDE MASS IN BENZYL ALCOHOL, ADDING OTPICAL SENSITIZER THERETO AND INCORPORATING THE DISPERSION INTO AQUEOUS GELATIN.