US2376371A

US2376371A - Polyvinyl alcohol emulsion coating

Info

Publication number: US2376371A
Application number: US501990A
Authority: US
Inventors: Wesley G Lowe; Kearney P Griffin
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1943-09-11
Filing date: 1943-09-11
Publication date: 1945-05-22
Anticipated expiration: 1962-05-22
Also published as: FR961819A

Description

Patented May 2;, recs roLYvrNYi. onoL EMULSlON cosrrnvd Wesley G. howe and Kearney 1. Grlilln, Roche ester, N. Y1, assignors to Eastman Kodak Company, Rochester, N. Jersey No Drawing.

Application September 11, Serial No. 501,990

Y., a corporation of New if Mathis. (Cl. 117-34) This invention involves a method of preparing photographic products from polyvinyl alcohol sliver halide emulsions.

that by subjecting emulsion layers to those treat- Polyvinyl' alcohol has beenreierred to as a carrier for the silver halide in photographic emulsions as described, for instances, in U. S. Patents 2,311,058 and 2,311,059 of Wesley G.

Lowe. Up to now, in preparing photographicproducts from those emulsions, no method has been developed which assures a rapid setting thereof, such as is obtained in the coating of gelatin emulsions in which chilling is employed. The use of various gelling agents with polyvinyl alcohol photographic emulsions to form a thermal reversible ge'lhas been suggested and, although setting of the emulsion is obtained by chilling with those compositions, nevertheless, that setting action is notsuihciently rapid to compare with the setting obtained when gelatin emulsions are used in the preparation of photographic products.

One object of our invention is to provide a method for the rapid setting of polyvinyl alcohol emulsion layers so that photographic products may be easily manufactured therefrom with the use of only a reasonable amount of time for that merits a rapid setting of the emulsion layer is obtained resulting in uniformity and ease of preparation of the photographic product.

We have found that by the incorporation of but a small amount of a boron compound in a polyvinyl alcohol photographic emulsion at a pH of not more than 6, the emulsion may be read- 5 ily coated out upon a support such as. paper or iilm base to form a thin layer which is quickly set by fuming with ammonia or the like.

' Anyone interested in the processwhich we have found might consider the use of ammonia on a operation. Another object of our invention is to provide a method for preparing photographic products from polyvinyl alcohol emulsions in which the emulsion may be coated out at ordinary temperature. A further object of our invention is to provide a method forsetting polyw vinyl alcohol photographic emulsions which method is not affected by the presence oi gelatin in the emulsion. Many of the jelling agents previously proposed lose their effectiveness when photographic emulsion as undesirable because it is known to increase the graininess and speed of emulsions and to raise their pH. We have found, however, that by our process in which the ammonia issupplied by fuming, there is no appreciable increase of either graininess or speed in the polyvinylalcohol photographic emulsion and that the drying operation which is "employed to dry the'emulsion layer alsordrives off any ammonia which may be present in the emulsion and a pH of 7' isfinally' obtained.

Various boron compounds have been. found to be' suitable. For instance, borer, sodium borate, boric acid, or the like may be employed providing it is mixed with the polyvinyl alcohol emulsionunder acid conditions. The phi or"; the

emulsion should never beallowed to exceed 7 and it is preferably kept at a pH of not-more than ii.

Although our setting method is not of any particular value forsetting an emulsion en masse,

- it is of very great value in the preparationfof gelatin is employed with polyvinyl alcohol in photographic emulsions. This disadvantage is plates, films or paper involving the coating out of polyvinyl alcohol emulsion thereon. Durin this step in the process of manufacturing light,

' sensitive photographic products, it is'necess'ary to avoided by our invention. A still further object of our invention is to provide a method for costing out polyvinyl alcohol emulsions in which low viscosity polyvinyl alcohols have been employed in their preparation. Due to the nature of our invention, low viscosity or greatly diluted polyvinyl alcohol solutions can be employed without.

being washed away such as in some processes where contact with liquid is involved. Other 0b:- 7

jects will appear herein.

get very rapid setting to avoid flow of the emulsion on the film or paper, the necessity being greater in the caseof film because such coatings fare often appreciably thickerthan coatings on Our invention involves the preparation of photographic products using polyvinyl alcohol emulsions in which setting is accomplished. by

incorporating boron compounds into the emulsion composition and, after coatlngout the emulsion onto its support, fuming of the emulsion layer with a volatile base such as ammonl methylamine or ethylamine. We have" I paper thus tending to causeiiow inspite of the viscosity inherent in the emulsions. r

.We have found that only very smallrproportions of boric acid or acid solutlon'of borax are necessary in the, emulsion in order to obtain rapid setting of polyvinyl alcohol photographic emulsion layers by fuming the emulsions with ammonia. We have found that ordinarily 1% or even less of boric acid (based on the weight of polyvinyl alcohol) is'suflicient to accomplish the desired result and that any proportion between 1 and 6% based on the weight of the polyvinyl alcohol will accomplishthe purpose desired; Al-

found though the use of a. greater proportion than 6% instance, coatings up to .005"

of boric acid may be employed, it is known that larger proportions of boron compounds exert marked effects on the viscosity of polyvinyl alcohol and too great a proportion of boron compound does increase the difficulties in the coating operations. Where, however, this is not objectionable, such as where the emulsion is warmed immediately prior to applying as an emulsion layer, there is no objection to the use of larger.

such as by passing the film immediately after coating through a fuming box saturated with ammonia gas. If the emulsion layers are too thick, the setting action is not as rapid as with the ordinary thickness of emulsion layer. For are satisfactorily set by a very short fuming operation, whereas coatings much in excess of .005" require a little time of fuming before those coatings are sufiiciently hard to withstand further processing of the emulsion layer,

Our method of setting photographic emulsion layers makes possible the use of very low viscosity polyvinyl alcohols as the carrier for silver halides. Our invention makes possible more dilution of polyvinyl alcohol photographic emulsions than has been considered safe previously to assure a uniform and substantially even coating. A very convenient way to prepare photographic products in accordance with our invention is to first treat the polyvinyl alcohol emulsion with a gelling agent so as to gel the same at a low temperature thereby enabling the operator to cut the emulsion into shreds and wash the same. Thereupon the shreds are washed with cold water to remove everything but the silver halide and the carrier therefor. The washed emulsion may then be worked up and employed by coating it out on photographic film or photographic paper. For instance, a good photographic paper may be prepared by taking an ordinary baryta coated paper,

particularly one which has been coated with a polyvinyl alcohol in baryta as described and claimed in Clark application Serial No. 348,013, and applying a coating thereto of a polyvinyl alcohol emulsion containing borax therein. After the coating operation has been completed, the emulsion layer is at once subjected to the action of ammonia gas which sets the emulsion enabling it to be readily dried without any waviness or other irregularity therein.

The following examples illustrate our invention:

- Example 1 An emulsion of silver halide-polyvinyl alcohol was prepared containing a-naphthol therein in accordance with the directions given in U. S. Patent 2,311,058. The emulsion was set by gelling, shredded and washed in accordance with the description of that patent. The emulsion was then warmed to liquefy it, the pH was adjusted to 5 and 100 cc. thereof was mixed with 2 cc. of

. act as the vehicle for the were free from fog. It is to be understood that the preparation and refining of the emulsion was all carried out under darkened conditions.

Example 2 A portion of the emulsion of Example 1 containing acidified borax was diluted with 5 its weight of water. This lowered its viscosity and made coating easier. The emulsion was then coated out on a glass plate and fumed with ammonia as before. The emulsion set very rapidly and the resulting product gave good sensitometric results.

Example 3 Some of the emulsion, as prepared in Example 1, was coated onto a cellulose acetate film base which was then passed through a chamber filled with ammonia gas. Very rapid setting occurred and the film was readily dried in a stream of air in the usual way. In this case the thickness of the coating was of the order used on commercial photographic film. Examination of the developed image obtained with the film showed that it was not higher in graininess than the developed image from the same emulsion not fumed with ammonia. The photographic speeds were also equal whether or not ammonia was used to set the emulsion.

Example 4 A silver halide emulsion .was prepared by first preparing the silver halide in a solution containing gelatin as the silver halide dispersing agent followed by the addition of polyvinyl alcohol to silver halide as described in U. s, Patent No. 2,276,323 of Wesley G. Lowe. The ratio of gelatin to polyvinyl alcohol in the emulsion was about one to ten. cc. of the emulsion was taken and its pH was adjusted to 5.5 by the addition of acetic acid. 2 cc. of 4% acid boric solution (pH 6) was added thereto and the emulsion was coated on film base. Fuming with ammonia gave rapid setting and the dried and processed film showed no increase in graininess due to the action of the ammonia.

Example 5 A silver halide emulsion was prepared by preparing the silver halide as in the preceding exampreceding example and in the same quantity. The emulsion was coated onto film base and fumed with ammonia. It was found that rapid setting occurred and that the film dried and could be processed in the usual manner.

It is to be understood that in each of the exthe polyvinyl alcohol predominates. For instance, even the ordinary commercial polyvinyl alcohol has only been hydrolyzed to a point where it still contains approximately 1 to 5% of polyvinyl acetate. If, however, the hydrolysis has beencarried out to a point sufiicient to give the material the characteristics of polyvinyl alcohol that hydrolyzed material comes under the polyvinyl alcohol designation which is employed herein. Ordinarily this would mean at least 50% of polyvinyl alcohol present in the material employed as the carrier for the silver halide in the photographic emulsion.

Our invention is directed to a process of setting photographic emulsion coatings, and admits of reversing the setting characteristics if, for any reason, the operator desires to again liquefy the emulsion. For instance, after a photographic product has been prepared, if testing of that product does not show the desired properties, the emulsion may be recovered by treatment with, aqueous acid such as by soaking the photographic product in a dilute solution of acetic acid for a time. After recovering the emulsion from its support in liquid form, it may be further treated and again coated out on a support such as a glass plate, photographic paper or film base and fumed with a volatile base to again cause setting.

We claim:

1. A method of preparing photographic products from polyvinyl alcohol-silver halide emulsions which comprises incorporating a small proportion of boric acid in the emulsion at a pH of not more than 6, coating out the emulsion upon a support, fuming with a volatile base to set the emulsion, coating and drying the same, all under conditions whereby the light sensitiveness of the emulsion is not detrimentally affected.

2. A method of preparing photographic products which comprises incorporating in a polyvinyl alcohol photographic emulsion a small amount of a gelling agent and gelling the emulsion at low temperature, cutting the emulsion into shreds and washing the same, incorporating in the emulsion a small proportion of an aqueous solution of borax having a pH of 6 imparted thereto by acetic acid, coating out the emulsion upon a support, fuming with a volatile base to set the emulsion coating and then drying the same all under conditions whereby the lightsensitiveness of the emulsion is not detrimentally affected.

3. A method of preparing photographic products from polyvinyl alcohol-silver halide emulsions, which comprises incorporating a small proportion of a boron compound which forms boric acid under aqueous acid conditions, in the emulsion at a pH of not more than 6, coating out the emulsion upon a support, fuming the emulsion coating with a volatile base to set the same, and then drying the emulsion coating, all under conditions whereby the light-sensitiveness of the emulsion is not detrimentally affected.

4. A method of preparing photographic products which comprises incorporating into a silver halide-polyvinyl alcohol photographic emulsion in aqueous form a small proportion of a boron compound which forms boric acid under aqueous acid conditions, at a pH of not more than 6, coating out the emulsion upon a support therefor, setting the emulsion coating by subjecting to the action of ammonia gas, and drying the emulsion coating upon the support, all under conditions whereby the light sensitiveness of the emulsion is not detrimentally affected.

5'. A method of preparing photographic products from polyvinyl alcohol-silver halide emulsions, which comprises incorporating therein a small proportion of a boron compound, which forms boric acid under aqueous acid conditions, at a pH of not more than 6, coating out the emulsion upon paper, setting the emulsion by fuming with a volatile base, and then drying the same, all under conditions whereby the light-sensitiveness of the emulsion is not detrimentally affected.

6. A method of preparing photographic products from polyvinyl alcohol-silver halide emulsions which comprises incorporating a small proportion of borax in the emulsion at a pH of? not more than 6, coating out the emulsion upon a support, fuming the emulsion coating with a volatile base to set the same and then drying the emulsion coating, all under conditions whereby the light-sensitiveness of the emulsion is not detrimentally affected.

'7. A method of preparing ucts from polyvinyl alcohol-silver halide emulsions, which comprises incorporating in the emulsion a small proportion of borax having a pH of 6 imparted thereto by acetic acid, coating out the emulsion upon a support, fuming the emulsion coating with a volatile base to set the same and then drying the emulsion coating, all under conditions whereby the light-sensitiveness of the emulsion is not detrimentally affected.

WESLEY G. LOWE. KEARNEY P. GRIFFIN.

photographic prod-