US1844716A

US1844716A - Process of making photographic emulsions

Info

Publication number: US1844716A
Application number: US356607A
Authority: US
Inventors: Raymond H Lambert
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1929-04-19
Filing date: 1929-04-19
Publication date: 1932-02-09
Anticipated expiration: 1949-02-09

Description

Patented Feb. 9, 1932 UNITED STATES PATENT entice RAYMQNID H. LAMBERT, OF ROCHESTER; NEW YORK, ASSIGNUR T0 EASTMAN KGDAK GOMIPAINY, OF ROCHESTER, NEW YORK, A GORPDJBLATION Old" NEW YORK PROCESS OF MAKING PHOTOGJR-APHIC EMULSION$ lt'o Drawing.

This invention relates to a process for the manufacture of photographic emulsion and particularly to a method of Washing the emulsion.

In the preparation of a photographic light-sensitive emulsion the sensitive substance is usually silver halide. This material is prepared by addition of a soluble silver salt to a soluble halide such as potassium or ammonium halide. In the resulting double decomposition or chemical interchange, one product is the insoluble silver halide. Its stability and sensitivity are largely controlled by the presence oi. some protective colloid, usually gelatine, during the precipitation of the insoluble silver halide. A stable suspension is-thus formed.

There are likewise formed in this reaction soluble inorganic salts that must 'be removed from the gelatine prior to further treatment and coating it upon photographic plates or film. Many methods for washing out these superfluous salts have been developed since the processes of King and Johnson developed in 1873. In some processes the set gelatine suspension is extruded or cut into fine shreds and then subjected to a washing treatment which may last from 2% to IE5 hours. The prior methods have been eumhersome, slow and therefore ineflieient.

It is the object ot the present invention to provide a method which will overcome many of the disadvantages of the former processes for washing and purifying the gelatine suspension.

I have found that it suitable inorganic salts be added to the photographic emulsion,

the gelatine may be coagulated therefrom and will settle to thebottom of the container.

- In settling the gelatine will carry with it substantially all of the silver halide which has been formed in the emulsion, and of coursesome ot' the soluble salts which are formed by the interaction of the silver salt With the alkaline halide. The gelatine is in such a form that it may be readily andeasily washed free from the soluble salts without the necessity of shredding or extruding that has hitherto been used.

The inorganic salts which I have tound 7 Application filed April 19,

to the increase 1929. Serial No. 356,607.

suitable for this purpose are the salt-forming elements of the IV group ot the Periodic Tfable, such for example as tin, lead, titan um, cerium, thorium, zirconium, germanium, etc. I have found that the nitrates of these elements are most suitable for my purpose. patihle with the emulsion without in any.

Other salts, however, that are comway afiecting the sensitivity ot the coating thatmay result may be used.

It is essential that the salt be used in the correct concentration. Too small an amount of the salt results in the coagulation oft e gelatine in a slimy relatively non-viscous mass; while too great a concentration of the salt results in a rubbery, tough material trom wllich it is very difficult to wash the soluble sa s.

' tion or settling of the-gelatine requires from two to 7 four hours. Temperatures much above room temperatures should be avoided, as the settling of the gelatine therefrom is considerably retarded in direct proportion in temperature of the emulsion.

sired form it carries down with it substantially all of the silver halide whichhas been formed in the gelatine solution or emulsion.

Two or three trials will be sufficient to determine the most desirable concentra tion. In the use of thorium nitrate, rm: eX-

When the gelatine has eoagulated in the de- I The liquid above the coagulated gelatine contains a large proportion of the soluble salt which liquid can be readily decanted. The gelatine material remaining may he very easily washed, as Water difiuses very readily throughout the mass. In case any fiocculent gelatine remains above the settled gelatine layer, it can be readily separated from the supernatent liquid by simple filtration and can be as readily washed as the main gelatine layer. 1

The concentration of the gelatine in the solution is not critical, but I have found that gelatine solutions containingv as little as from 0.51% of elatine may be readilycoagulated by my method. In fact, the gelatine coagulated fromsuch a solution washes more easily and water difi'uses more readily through it than it does through a 5% gelatine which has been allowed to set and has been shredded into fine noodles.

The supernatant liquid contains a. large proportion of the soluble salts and in a con-' centration sufliciently great to permit their recovery therefrom to be economically effected. Heretofore there has been little or no recovery of the salts which have been washed from the emulsion due to the cost of concentrating and recrystallizing from the dilute liquors. My procedure makes this operation economically practical due to the high percentage of salts found especially in the decanted layer.

After a thorough washing of the gelatine a slight addition of water may be made to the jelly-like mass, and by heating to 60 or 70 C. the material will readily deflocculate.

' The temperature of defiocculation depends volume of the emulsion is 800-900 cc., when,

upon the concentration of the coagulating salt used. At this point more gelatine ma be added and the emulsion digested as wil be well known to those expert in the art.

I will now describe a specific example of carrying out my method of coagulation and washing of the gelatine emulsion, but it will be understood that I shall not be restricted thereby except as indicated in the appended claims. Two liters of a prepared emulsion containing 20 grams of gelatine and the pre-- cipitated silver halide in suspension are added with constant stirring to two liters of a solution containing 2 grams of thorium nis trate. The gelatine containing substantially all the silver halide or other suspended insoluble matter settles to the bottom of the container in about 2 to 4 hours at a temperature of 10-20 C. The mother liquor is decanted and the gelatine layer washed with distilled water until substantially all the soluble salts are removed from it. This subsequent washing is carried out at room tem perature or lower. After washing the coagulum is heated to 60 or C. then 30 grams of gelatine in about 200 cc. of water are added while stirring. An emulsion will slowly reform. Water is then added until the final the material is obtained which coats smoothly on a support such as glass or film base.

Such material, when coated on a plate, dries without staining, bumps, or checking, so often found on photographic plates. I have also noted that plates so obtained have more speed, fix more rapidly, and wash more quickl than ordinary plates. Plates unexposure and development an image is obtained which is remarkably clear and with good detail. The presence of these salts likewise acts as a hardener, and the usual hardeners such as alum, formalin, or alcohol need not be used with an emulsion prepared in this way.

Various changes and modifications may be made in the manner of carrying out this process and equivalents of the coagulating salt used without in any way departing from this invention or sacrificing any of the advantages derived therefrom.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver halide, the step which comprises coagulating the gelatine,

2. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver halide, the

step which comprises coagulating gelatine,

with occluded silver halide, with a soluble salt of thorium.

3. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver halide, the step which comprises coagulating gelatine, with occluded silver halide, with thorium nitrate.

4. In the process of reparing. gelatino silver halide emulsions, t e step which comprises coagulating a dilute aqueous gelatinosilver halide-containing emulsion with a soluble salt of an element of the IV group of the Periodic Table.

5. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver halide, the step which comprises coagulating the gelatine, with occluded silver halide, with approximately 5 to 20 parts of thorium nitrate for every 100 parts of gelatine present.

-6. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver halide, the step which comprises coagulating the gelatine, with occluded silver halide, at a temperature of 10 to 20 C. with approximately 5 to 20 parts of thorium nitrate.

7. In the process of preparin a light-sensitive gelatino silver halide emu sion, the step which comprises adding a soluble salt of an element of the IV group of the Periodic Table to the emulsion thereby coagulating the gelatine and occluding therewith substantially all the silver halide contained in the emulsion. I

8. In the process of preparing a gelatine silver halide emulsion, the step which comprises adding a soluble salt of an element of the IV group of the Periodic Table to the emulsion, allowing the gelatine, with occluded silver halide, to settle and washing itfree from soluble salts.

9. In the process of preparing a gelatino silver halide emulsion, the step which comprises adding a soluble salt of an element or the IV group of the Periodic Table to the emulsion, allowing the gelatine, with oceluded silver halide, to settle and decanting V the mother liquor. v

10. In the process of preparing a gelatino silver halide emulsion, the step which comprises adding a soluble salt of an element of the IV group of the Periodic Table to the emulsion, allowin the gelatine, with oceluded silver halide, to settle and decanting the mother liquor, and finallyrecovering the soluble salts from the mother liquor.

11. In the process of preparing a lightsensitive gelatino silver halide emulsion from an emulsion containing gelatine and a silver halide, the step which comprises adding'to the emulsion 5% to 20% (by weight of the gelatine present) of thorium nitrate at a temperature of 10 C. to 20 0., allowing the gelatine, with occluded silverhalide, to settle,

decanting the mother liquor and washing the coagulated gelatine substantially free from soluble salts.

12. In the process of preparing gelatino silver halide emulsions from an emulsion containing gelatine and a silver .halide, the step which comprises coagulating the gelatine,

with occluded silver halide, with a soluble salt of an element of the IV group of the Periodic Table, washing the gelatlne, adding a small amount of water and the required addition of gelatine, and heating to reform an emulsion.

13. In the process of preparing gelatine emulsions from an emulsion containing gelatine and insoluble suspended matter, the step which comprises, coagulating the gelatine,

with occluded insoluble suspended matter, with a soluble salt of an element of the IV group of the Periodic Table. j

14. In the process of preparing gelatine light sensitive emulsions from an emulsion containing gelatine and insoluble suspended light-sensitive matter, the step which comprises coagulating the gelatine, with 0ccluded light-sensitive matter, with a soluble salt of an element of the IV group of the Periodic Table.

Signed at Rochester, New York, this 16th day of April, 1929.

RAYMOND H. LAMBERT.