US2139774A - Sensitizing and hardening photographic emulsions - Google Patents

Description

atented Dec. 13, 1938 2,139,774 SENSITIZING AND HARDENING PHOTO- PATENT OFFICE GRAPHIC EMULSIONS Samuel E. Sheppard, Robert C. Houck, and Raymond H. Lambert, Rochester, N. Y., assignors,

by mesne assignments,

pany, Jersey City, N. J.,

Jersey to Eastman Kodak Coma corporation of New i No Drawing. Application July 10, 1936 Serial No. 90,000

4 Claims.

This invention relates to finishing photographic emulsions and particularly, to sensitizing and hardening gelatino-silver halide emulsions.

In practice it has been found necessary to treat 5 photographic gelatin or emulsion solutions or layers with a hardening agent in order to increase the resistance of the gelatin or emulsion layer to swelling or softening, particularly when processed at increased temperatures. Compounds which have been used for this purpose are chrome alum, formaldehyde, and other reagents. In application Serial No. 745,754, filed September 27, 1934 in thenames of S. E. Sheppard and R. C. Houck, there is disclosed the use of hydroxy aldehydes up to and including the pentoses for this purpose.

As is well known, a gelatino-silver halide emulsion when first mixed is quite slow or insensitive, and unsatisfactory for making fast negative emulsions. The emulsion mixture is, therefore, digested or ripened in orderto increase the sensitivity. This ripening is ordinarily accomplished by the action of heat or by digestion with ammonia, either alone or in combination with heating. After treatment in this way the emulsion may be jelled and set and then re-melted and coated on the emulsion support. The hardening agent is added at some period subsequent to the digestion, before coating the emulsion on the support.

In many cases the degree of hardening produced in this way, as indicated by the melting point, swelling, behavior on photographic processing and other ways, is not complete after drying the product, but-a greater or lesser amount of so-called after hardening occurs on storage 5 of the plates or films. This may continue through a period of months'and may equal or surpass in degree the initial hardening on first drying. This after hardening, therefore, gives rise to a product whose properties are variable with time unless an inconvenientiy long period of storage prior to use is involved. One consequence of this is generally reduction of speed of development, but other objectionable changes in photographic properties may ensue. A further objection is that it is necessary to repeatedly subject samples of the plates or films to incubation tests in order to ascertain the amount of hardening that has taken place.'

50 It is, therefore, an object of the present invention to provide a means for eliminating after hardening and for producing a more stable emulsion which will show less change in regard to sensitometric and physical properties, such as hardening and swelling, on storage. A further object is to provide a novel method for hardening photographic emulsions. A still further object is to provide a photographic emulsion which will be resistant to relatively high temperatures without objectionable fogging or de-sensitizing. Other objects will appear hereinafter.

We have discovered that with a considerable number of hardening agents the slow process of after hardening may be eliminated and the emulsion brought to a stable condition by heating the coated, dried plates or films, the emulsion of which has been subjected to little or no wet digestion, for a specified time (period of hours only) at specific temperatures and relative humidities. i

Our process of heat accelerated hardening would have only limited application as carried out on emulsions after ordinary finishing, that is, emulsions which had been subjected to digestion or ripening. Since our process is equivalent to a period of incubation under tropical conditions, photographic emulsions prepared in the usual way and subjected to our process would probably, if not certainly, show rapid deterioration, such as fogging, hypersensitization or desensitization, decrease in contrast, etc., on storage.

On the other hand, it is possible to treat a photographic emulsion to moist incubation at specified temperature and relative humidities, according to our invention, and thereby, to produce an emulsion which is fairly stable over a long period of time and which does not exhibit a tendency. to after hardening on storage. This treatment increases the sensitivity of the emulsion, and avoids the necessity of the usual wet digestion.

In accordance with our process a gelatino-silver halide emulsion prepared in the usual way by precipitating a silver halide in the presence of gelatin had added thereto a hardening agent and it is then coated ontoa suitable support at the usual temperature, for example 40 C. and dried in the usual way. The plate or film is then subjected to the heat treatment described below and the combined sensitizing and hardening action performed in this way.

This dry digestion or moist incubation has a number of advantages over the usual wet digestion in which the emulsions are ripened prior to addition of the hardening agent, in that the progress of the hardening is more conveniently controlled and that there is less tendency to increased fogging with increasing sensitization. This is shown by the following tables indicating the speed of plates, subjected to digestion and obtained by moist incubation (for 3.5 hours) was nearly, twice that obtained by wet digestion (at twenty minutes) for a corresponding amount of fog formation.

emulsions at a specified temperature and relative humidity containing. various hardening agents, where the emulsion was not subjected to digestion prior to adding the hardening agent. In each casethe time required to produce a certain melting point has been comparedwith the proper time that would be required to store the emulsion at room temperature in order toreach a melting point of 80 C. to 90 C.

pH6.2-6.7 (except where otherwise; noted).

70 C.60% relative humidity.

P 'ri me oft f ercentea ing a o me of incubation at room Hardening agent gfi ggf gi 3 2252? M l ing 1 1 11 tempere ture to reach gelatin tive hu- 80 midity Hours 0. 0 45 Formaldehyde 10 2 months. 0: 0 e2 0.18 1.0 90 3-4 days. 2. 0 97 0. 0 34 1. 0 34 1 '8 it 0 Months. Arabmose- 4' o 40 5. 5 51 6. 0 64 0.0 sees Z 0 8 22 Months. 3. 0 89 0. 0 e4 Questionable. Several DIBCBtYLL'. 4044 anontbs, perhaps a yea -s1 Acetonyl acetone 4- 2g 4 weeks 23. 0 45-55 0. 0 35-82 Acetonyl acetone 0 3:8 2 34 weeks.

23.0 70 0. 0 55 Acetoxime pH 10.0 aged 10 mos 6.0 m 0 90+ }Quesfionable.

(Very slowly) 'Ierephthalic aldehyde 6- 0 32 Chloral pH 8.0 aged 11 mos 14. 0 2:8 3? (Slowly melting) Methylal pH 8.0 aged 17 mos 14. 0 8:3 1 }Years. Hexamethylene tetramine 1. 0 8:8

a. o 2-8 }e-12 months (estimated). 6.0 g g }e-12 months (estimated).

Wet digestion at 60 C.

Fog 4 min- Time, Speed, H. minutes and D. 3255 Moist incubation at 60 C.

. Fog 4 min- Tune, Speed, H.

utes develophours and D. men;

The following examples illustrate the increased 7 hardening achieved by heating gelatin or gelatin By melting point is meant the temperature at which the emulsion or gelatin dissolves in water on heating the water.

In the above examples we have referred to the use of a pI-l of 6.2 to 6.7 with a temperature of 70 C. and relative humidity of 60%. These limits are for the purposes of example only and-do not exhaust the possibilities of our invention. It

. is known that during digestion of a photographic emulsion the sensitivity varies with the pH but there are practical pH limits above. which it is not desirable to go. In a similar manner the temperature of our treatment may be greater or less than 70 C. and may vary from about 40 C. to

90 C. The relative humidity may also vary somewhat within the range of about 50% to 80%, depending upon the amount and nature of the hardening agent used.

Where the emulsion is subjected to moist incubation without the usual wet digestion, before or after coating it on the support, the temperature of treatment is preferably 60 C. to 70 0., and the relative humidity therefor between 50% and 80%.

Efiect of heat on hardening of gelatin emulsion by various hardening agents 10 Although we have disclosed the use of a number of hardening agents together with a preferred method of carrying out our invention it is to be understood that we are not limited to the compounds and methods of procedure described herein, but that our invention is limited only by the scope of the appended claims.

What we claim is:

1. The process of hardening gelatino silver halide emulsions and substantially eliminating after-hardening, which comprises adding a hardening agent to the emulsion, coating the emulsion on a support and drying it, and subjecting the emulsion to moist incubation at a relative humidity of between 50% and 80% and a temperature of between 40 C. and 90 C. conjointly with ripening, for such length of time as will bring the emulsion to substantially uniform hardness.

2. The process of sensitizing and. hardening photographic emulsions which comprises precipitating a silver halide in the presence of gelatin to form an emulsion, adding a hardening agent to the emulsion, coating the emulsion on a support, drying and then subjecting the emulsion to moist incubation at a relative humidity between about and about 80%, and a. temperature of about C. to C. for such length of time as will bring the emulsion to substantially uniform hardness.

3. The process of sensitizing and hardening photographic emulsions which comprises precipitating a silver halide in the presence of gelatin to form an emulsion, adding a hardening agent to the emulsion, coating the emulsion on a support, drying and then subjecting the emulsion to incubation in air at about 60% relative humidity and 60 C. to 70 C. for such length of time as will bring the emulsion to substantially uniform hardness.

4. The process of sensitizing and hardening photographic emulsions which comprises precipiq tating a silver halidein the presence of gelatin to form an emulsion, adding a hardening agent to the emulsion, coating the emulsion on a support, drying and then subjecting the emulsion to incubation in air at 50% to relative humidity and 60 C. to 70 C. for such length of time as will bring'the emulsion to substantially uniform hardness. 4

SAMUEL E. SHEPPARD. ROBERT C. HOUCK. RAYMOND H. LAMBERT.