US2119724A - Reduction of contrast of photographic emulsions - Google Patents

Description

June 7, 1938.

REDUCTION c. J. STAUD 2,119,724

0F CONTRAST OF PHOTbGRAPHIC EMULSIONS Filed July 10, 1935 pwmbzezkummwmrwkmmzm pfif mulially I m ilzlged I 'I I I Patented June 1 938 UNlTE D STATES PATENT OFFICE.

REDUCTION or CONTRAST or micro ammo Emulsions Cyril J. Stand, Rochester, N. Y., assignor, by mesne assignments. to Eastman Kodak Com pany, Jersey City, N. J., a corporation of New Jersey Application July 10, 1935, Serial No. 30,716

2 Claims.

fact that the developer does not difiuse evenly into all portions of theemulsion during development, but acts more rapidly on those layers lying closer to the surface than on the lower layers. Furthermore, the oxidation products resulting from the action of the developer are removed rapidly at the surface, but diifuse much more slowly from the lower layers of the emulsion and consequently accumulate there in such concentration as to exert a marked restraining action on the developer.

This invention has as its principal object to provide a means of reducing the contrast of a photographic emulsion. Another object is to provide a means of' controlling the action of a developer on a light-sensitive photographic emulsion. A further object is to provide an improved photographic film which may be developed without an undesirable degree of contrast in a developed image. Other objects will appear hereinafter.

These objects are accomplished by the following invention, which in its broader aspects, comprises applying over the outer surface of the emulsion a thin, permeable layer comprising a cellulose derivative having. incorporated therein a water-soluble compound readily miscible with the cellulose derivative. I have found that'the application of such a coating results in reducing the contrast of the image obtained on development. This result is rather surprising, especially in view of the'fact that the cellulose derivatives are. in general, impermeable to water and other liquids to an extent which would'lead one to the conclusion that their use in connection with the .overcoating of photographic emulsions would be impractical. I have found, however, that if certain watersoluble ingredients are incorporated with the cellulose derivative, a thin coating may be produced which is suflicientlypermeable t'o permit penetration of the developer and that this coating has the remarkable effect of controlling the action of the developer to such an extent that the contrast 'of the resulting image may be considerably reduced over what would be the case if such layer were'rtot employed.

In the following examples and description I have set forth several of the preferred embodiments of my invention, but it is to be understood This invention relates to photographic matethat they are included merely for purposes of illustration and not as a limitation thereof.

In the accompanying drawing in which like reference characters refer to like parts,

Fig. 1 is a section through a photographic film embodying my invention, .the thickness of the various layers being greatly exaggerated for clearness of illustration;

Fig. 2 is a section through another type of pho tographic product in accordance with the invention illustrating the use of water-permeable layers both over and between the various emulsion. layers of a film comprising a plurality of emulsion layers. A I

The cellulose derivative employed may be a simple cellulose ester-such as cellulose nitrate, cellulose acetate, cellulose propionate, a mixed ester, such as cellulose acetate nitrate, cellulose acetate propiona-te, or a cellulose ether. Many other similar compounds willsuggest themselves to those skilled in the art. In accordance with my invention the cellulose derivative is applied in the form of asolution of rather low concentration, since only an extremely thin layer of the material should be laid down on the emulsion. Otherwise it would require an excessive length of time for the developer to penetrate the coating thus produced. In order to provide for the necessary degree of permeability of the. celluloseQde-v rivative layer, I mix with the cellulose derivative solution a water-soluble material e'asily miscible therewith. This material must conform to certain requirements, namely, it must not-inhibit adhesion of the cellulose derivative to the emulsion, it must be compatible with the cellulose de rivative and with the emulsion and must'besoluble, both in water and in the solvent orsolvent combination employed for dissolving the cellulose derivative.

= materials which I have found useful for the pur- Typical examples of water-soluble 40 poses of my invention are certain water-soluble compounds. including mono-acetin, the compesi tions manufactured and sold by the Glycol Prod ucts Company of New York,.Nw Y0rk, under the trade names; Glycol Bori-Borate and Glyceryl Bori-Borate and certain other compounds suchas sucrose, dextrin, starch acetate and'pyridine ni- I v Example I f 5 grams of cellulose "acetate and 2 grams of m'o'noacetin are-dissolved in '100 cc. of ethylene chloride, 9 parts, and ethanol 1 part, producing a 5% solution. This-solution is applied in any .well known manner to the surface of a moderately derivative coating over the emulsion has marked;

ly reduced the contrast of the original ,e'mulsion.

' Example II grams of Glyceryl Bori-Borate are dissolved in 100 cc. of acetone solution. This solution is applied in any well known manner to the surface of a moderately high contrast emulsion previously coated on a suitable film support. A' second emullayers maybe of differential sensitivity characteristics. Upon exposing, developing, fixing and washing the film itis found that a negative of a highly satisfactory degree of contrast is produced, the permeable cellulose derivative layers over the emulsion layers providing a means of controlling contrast the action of the developer thereon similarly to the single emulsion layer film of Extains about.50% by weight of the cellulose derivative material, the remaining 50% consisting of the water-soluble material. I have also found that the most satisfactory results are obtained when this 50- 50 mixture is dissolved in the solvent to produce a .5 to solution. As previously indicated, it is necessary to use relatively dilute solutions in order that the cellulose derivative layer laid down on the. emulsion shall not be too thick, as this would undoubtedly increase the time of "development and subsequent processing. As will be readily appreciated the thickness of this layer. is a matter which can vary widely, but in any event the layer will probably not be more than 20 to 50 microns in depth.

Although I do not restrict-myself to the use of any particular solvent, water-soluble component or cellulose derivative, nor to any particular concentration of the coating solution, I find that the more satisfactory results are obtained with the relatively volatile solvents and the use of concentrations of dissolved components of not over 5%.

My invention will be more clearly understood by reference to the accompanying drawing in which the numeral I (Fig. 1) represents a support such as a glass plate, a cellulose derivative film, or the like. The numeral 2 designates a itable light-sensitive gelatino-silver halide emulsion, while the numeral .3 designates a thin, permeable cellulose ester layer having incorporated therewith in accordance with my inventiona .water-soluble component, such as monoacetin.

result is that all of the exposed grains of the sensitive silver halide are acted upon more uniformly throughout the various strata of the emulsion and 'for a more nearly equal period. It follows that, since the oxidation products of development are more uniformly distributed, the tendency toward accumulation ofsuch prodnets in rather hi h concentrations in the, upper layers of the emulsion (as is thecase with emulsions which are not provided with such coatings) Y is reduced. or eliminated. This makes possible a 5 grams of cellulose acetate propionate and 2.5

fairly uniform removal of such products throughout the" emulsion in the fixing and subsequent operations, and results in a fairly marked reduction of contrast as compared to emulsions which are not treated as described herein.

In the film structure illustrated in Figure 2, the numeral I designates any suitable .cellulose derivative film support, such as one composed of cellulose nitrate or cellulose acetate. The m1- merals 2 and 4 designate moderately high contrast emulsion layers of differential sensitivity, while the numerals 3 and 5 designate, respectively, a layer of cellulose derivative material containing a miscible, water-soluble component, such as monoacetin, Glycol Bori-Borate, sucrose, dextrin or other compatible water-soluble material, and a similar cellulose derivative layer containing these componentssuperimposed on the'upper emulsion layer. As in the product of Figure 1, the permeable cellulose derivative layers provide a means of controlling the eflect of the developer on the different light sensitive emulsion layers, reducing the contrast of the original emulsion.

It will be evident from the above examples that the percentage of the water-soluble material in the permeable layers may be varied to, conform to varying emulsion requirements. For example, if a more permeable layer is required the percentage of water-soluble component will be'increased, and vice versa.

Although I have referred herein principally to the effect of the cellulose derivative coating in reducing the contrast of the emulsion, such coating has the additional advantage that it serves to some degree as a protective coating and reduces the possibility of damage-to the film be-' cause of scratches, abrasions and the like. y- What I claim is:

1. In the process of developing the latent image '.by subjecting the exposed film to the action of a developer, the step which comprises controlling the contrast of the image by controlling the rate and uniformity of diifusion of the developer into the emulsion layer by coating the surface of the emulsion layer with an extremely thin, permeable, permanently adherent, sistant, cellulose derivative layer which is insoluble in the presence of alkaline developing solutions and'containing a water-soluble and ,displaceable compound in sumcient amount to permit penetration of the layer by the developer by displacement of the water-soluble compound, whereby the action of the' developer on the lightsensitive emulsion is rendered substantially uniform throughout.

2. A photographic film comprising a support layer, a light-sensitive gelatino-silver halide emulsion coated on the support and means for Y controlling the contrast of a latent image in the emulsion layer upon development by controlling the rate and uniformity of diffusion of the developer into the emulsion layer, said means comabrasion-reprising an extremely thin, permeable, permanent- 1y adherent, abrasion-resistant, cellulose derivative layer which is insoluble in the presence of alkaline developing solutionsand containing a water-soluble and displaceable compound in sufficient amount to permit penetration of the layer by the developer by displacement of the watersoluble compound, whereby the action of the developer on the light-sensitive emulsion is rendered

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