US1923764A - Photographic gelatin relief - Google Patents

Description

Aug. 22, 1933. L T TROLAND 1,923,764:

PHOTOGBAPHIC GELATIN RELIEF 'Filed Jan. 50, 1951 Patented Aug. 22, 1933 UNITED STATES PATENT OFFICE `1,923,784 n rno'rocmrnrc GELATIN RELIEF Application January 30, 1931. Serial No. 512,398

12 Claims.

In the photographic art two main processes are known for making photographic gelatin reliefs from silver halide emulsions. One process involves the use of developers which harden the exposed parts of a silver halide emulsion, as for instance the well-known pyrogallic developer. The other process involves the developing of the latent .image with an ordinary non-hardening developer, as for instance a sulphite-containing metol-hydroquinone developer, and the subsequent hardening of the developed image with selectively hardening agents, as for instance an acid solution of bichromate. Although developer hardened reliefs are comparatively rugged, durable and easy to make, the reliefs made by the second method are preferable for certain purposes, especially for making motion picture positives, because they have a nner grain structure and a better photographic characteristic than re- 0 liefs made with hardening developers. However, the method using a separate hardener has two disadvantages which impair its practical application. If the non-hardening developer is not thoroughly washed out before the emulsion has passed into the independent hardener, there is a tendency towards a general hardening of the entire emulsion layer containing the remainder of the developer, so that the unaffected parts of the emulsion, which has been exposed through its support, can not be removed in the subsequent hot water bath, the so-called etch, and no relief can be obtained. On the other hand, if the developing agent is completely rremoved by o Aa thorough washing, the relief tends to disinte- "5 grate in the subsequent hot water bath. It is very diicult to balance these two'actions by adjusting the washing bath, in order to prevent too much hardening and/or disintegration of the relief.

The main object of the present invention is therefore to provide a photographic gelatin relief which has the desirable properties of a relief obtained by independently hardening the developed image, and which can be manufactured as easily as reliefs made with hardening developers. Another object is to provide a photographic process for making gelatin reliefs of a structure, and with characteristics suitable for icertain purposes such as motion pictures, which can be easily carried out on a commercial basis.

Still another object is to provide a development which controls and stabilizes the hardening action of a subsequently applied independent hardening agent. A further object is to provide a new hardening process for gelatin reliefs which combines the advantages, while avoiding the disadvantages, of the two known main processes for making such reliefs. Other objects will be apparent from the following description of the invention which is accompanied by a drawing, in which Fig. 1 shows the structure of a photographic emulsion treated according to the present invention; and

Fig. 2 is a flow sheet of the process according 65 to the invention.

In order to overcome the difficulties ,outlined above, the process according to the present invention combines an ordinary non-hardening development with a hardening development and with separate hardening, thereby obtaining a relief which has the desirable properties of the separately hardened relief without the disadvantages of the process for making such reliefs. Superlicially it might appear that no advantage could be gained by combining these processes, but experiments have shown that a distinct improvement of the gelatin relief can be obtained if the processes are combined. The treatment in a hardening developer hardens the image to a degree which prevents its disintegration during the thorough washing required to remove all the developer which otherwise might result in hardening more than the exposed parts of the emulsion in the subsequent bath in a dierential hardener. Moreover, there is a certain cooperation between the residues of the hardening development and the independent hardener. For the purpose of a better understanding of the invention, the separate actions of hardening developers, for instance pyrogallol, and of independent hardeners, for instance chrornic acid, will first be explained.

After development in a hardening developer each silver grain is surrounded by a hardened zone of considerable size in comparison with the grain. The hardness of this zone depends upon the concentration of the developer and the time allowed for its action. rihe gelatin zone surrounding the emulsion particles may become suiciently hard so that subsequent etching (after the nonhardened gelatin, corresponding to unexposed parts, is dissolved by the warm water), will leave a gelatin relief. If the hardening is carried on far enough all silver grains, which are connected by hardened zones to each other and to the base, contribute to the relief and only those whichhave no connection whatsoever are etched off. However, if the hardening is carried on to such a degree a noticeable grain appears upon the surface of the relief and imparts thereto a pattern in addition to that which forms the picture, which is very undesirable. If the development is not carried on far enough to produce this effect many insufficiently hardened portions are lost and the relief does not truly reproduce the original photographic image. In either case the developed zones contain certain oxidation products of the hardening developer and the size of these zones do not correspond With the concentration of the developer, the concentration controlling the hardness of the zone rather than its size.

Considering now the independent hardening, a chromic hardener is reduced by the silver image and produces hardened zones surrounding the grains. In the commonly used and commercially feasible chromium hardening process these zones are substantially confined to gelatin parts immediately surrounding the grains, are therefore considerably smaller than the corresponding zones produced by a hardening developer, and the. subsequent etching in warm water will remove quite a considerable number of gelatin particles which have no connection with each other nor with the base. On the other hand, the surface pattern of a gelatin relief made in this manner is very much less pronounced than that of a developed relief and such a relief is therefore much better suited for certain purposes (as e. g. for imbibition printing from the relief) than a developer hardened relief.

My improved process permits the making of a relief having these desirable properties without incurring the aforesaid disadvantages of the separate hardening method. This new process will first be decribed in connection with an explanation of its beneficial action, based upon a theory of the process which appears to be the most plausible one in the light of investigations available at the present time. Directions for carrying out the process will then be given as one of the possible practical embodiments of the invention.

The exposed emulsion consists of grains of various sizes, as shown in the drawing. This emulsion is first treated in an ordinary nonhardening developer. As known in the art the reducing action of a developer starts'at points near the surface of the larger particles of exposed silver and spreads from there gradually over the whole particle. Considering the particle 1 (Fig. l) for example, the non-hardening developer starts to reduce the particle at 2 and from there the action continues until the stippled part 3 of the grain is reduced to metallic silver. The development with the non-hardening developer is interrupted at this stage of the process, and continued with a hardening developer. This will now finish the developmenty of the larger particles, but also reduce the small particles 4, which have not yet been attached by the first developer, and zones surrounding both the remainder of the larger particles, of about the size of the smaller grains, and the smaller grains themselves will be thoroughly hardened by the second developer. At this stage of the process there are larger zones of unhardened gelatin containing metallic silver,

and smaller Zones of hardened gelatin, also con-l taining metallic silver, which surround the unhardened zones thereby protecting them and cementing them together so that the emulsion will not disintegrate during the now following step of removing the developer thoroughly from the emulsion by washing. An initial development in a hardening developer followed'by a bath in a non-hardening developer has practically the same effect, as will be obvious to anyone skilled in the then treated in warm water, which dissolves all vunhardened parts of the gelatin.

During the etching process, practically the whole emulsion as far as it was influenced by light will be preserved because the chromate hardened parts, which would normally not extend beyond the zones of reduced silver and therefore tend to disintegrate, are cemented together by the developer hardened zones corresponding to the small exposed silver halide particles and because the action of the independent hardener is extended due to the oxidation products of the hardening developer which penetrate beyond the developer hardened zones. Accordingly, the surface of the relief Will substantially have the character of a chromium hardened relief, since its larger part consists of gelatin hardened with chromium, whereas the developer hardened zones of the surface are too small to cause undesirable irregularities of the relief surface. It is of course understood that the final product will not contain metallic silver, because the customary chromic hardeners are also bleaching agents. The remaining silver bromide is removed in a customary thiosulphate fixing bath.

The following exact directions for carrying out my new process in one of its preferred embodiments are given by way of example.

The exposed emulsion is first developed in a developer made according to the following formula:

Metol (monomethyl paraminophenol sulphate) 3.1 grams Sodium sulphite 45.0 grams Hydroquinone 12.2 grams Sodium carbonate '67.5 grams Potassium bromide 1.9 grams Water to 1 liter This developer should have a temperature of approximately 68 F., and the film should remain therein for about three minutes and twenty seconds. After a washing sufficient to remove any constituents of the first developer not desired in the second bath, the film is removed into the hardening developer of the following composition:

Pyrogallic acid 8.2 grams Citric acid 0.2 grams Potassium bromide .40 grams Sodium hydroxide 3.4 grams Ammonium chloride 1.7 grams Water to 1 liter This formula corresponds to the developer formula as disclosed in my United States Patent No. 1,535,700 of April 28, 1925, and was found to give satisfactory results also if used in the process according to the present invention. The lm is then washed for approximately five minutes and forty seconds in Water of approximately 68 F.

Sodium chloride The film is then removed to a bathof the following composition:

Chromic acid 5 grams 25 grams Water to 1 liter After having been removed from this harden- -ing bath, the unhardened parts of the emulsion are brought into a water bath of about 130 F., in which the film remains for about four minutes. After this the nlm is fixed for about two minutes in the customary fixing bath of about 69 F., and then in alcohol of 68 F., also for one minute, and then dried for about twelve minutes at 100 F.

It is of course understood that other hardening and non-hardening developers and various independent hardeners can be used and that the proportions of the ingredients and the exact directions for the steps of the process may be varied in accordance with the properties of different agents acting generally in the same manner as the agents expressly mentioned above. For instance, a pyrogallol developer containing suiiicient sulphide to prevent any hardening action can be used instead of the metol developer or another inherently non-hardening developer, a pyrocatechol developer may be used instead of pyrogallol and acidic bichromate can be used instead of chromic acid.

It should also be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. The method of making photographic gela tin reliefs which comprises partly developing an exposed silver halide emulsion in a solution containing substantially non-hardening reducing agents, partly developing said emulsion with a gelatin hardening reducing agent and subsequently selectively hardening the developed silver image.

2. The method of making photographic gelatin reliefs which comprises partly developing an exposed silver halide emulsion in a non-hardening developer containing hydroquinone, partly developing said emulsion in a pyrogallol developer and then bleaching and hardening the developed image in a chromic acid solution.

3. The method of making photographic gelatin reliefs which comprises partly developing an exposed silver halide emulsion in a solution containing approximately 3 grams metol and 45 grams sodium sulphite in 1 liter of water, partly developing said emulsion in a solution containing approximately 3.2 grams pyrogallic acid and 3.4 grams sodium hydroxide in 1 liter of water, washing the emulsion, hardening the emulsion in a solution containing approximately 5 grams chromic acid and 25 grams sodium chloride in 1 liter of water, and removing the unhardened portions of the emulsion.

4. The method of making photographic gelatin reliefs which comprises developing and partially hardening an exposed silver halide emulsion in consecutive baths of non-tanning and tanning reducing agents, and subsequently hardening the developed silver image in a separate hardening solution.

5. The method of making photographic gelatin reliefs which comprises partly developing the latent image of an exposed silver halide emulsion in a solution containing substantially non-hardening reducing agents, partly deevloping said emulsion with reducing agents hardening the gelatin suiiiciently to prevent disintegration of the exposed portions of the emulsion but not suicient to harden said portions completely and subsequently forming a relief image by completely hardening said portions with a differentially hardening bath and removing the unhardened portions.

6. The method of making photographic gelatin reliefs which comprises partly developing an exposed silver halide emulsion in a non-hardening developer, partly developing in a developer containing agents restraining subsequent disintegration of the gelatin forming the image and selectively hardening the developed image in a separate hardening solution.

'7. The method of making photographic gelatin reliefs by developing the latent image of an exposed silver halide emulsion in baths of non-hardening and hardening developers but confining the hardening to developed portions, which comprises preliminary hardening of said portions together with completely developing them and total hardening of said portions in a differentially hardening solution.

8. 'Ihe method of making gelatin reliefs which 'comprises partly developing an exposed silver developer, further developing said emulsion in a hardening developer producing oxidation products incidentally to development, and subsequently treating the emulsion in a hardening bath selectively controlled by the developed silver as well as said oxidation products.

9. The method of making gelatin reliefs ccmprising partly developing an exposed photographic emulsion in a solution containing substantially non-hardening reducing agents in combination with a subsequent complete development with reducing agents suiiiciently hardening to preserve the exposed emulsion during subsequent treatment and completely hardening said emulsion with a subsequently applied independent hardener. v

10. The method of making photographic gelatin reliefs which comprisespartly developing the larger grains of the emulsion in a non-hardening developer, developing the smaller grains and the previously undeveloped portions of the larger grains in a hardening developer, and subsequently hardening in an independent hardening agent.

11. The method of making photographic gelatin reliefs which comprises partly developing the larger grains of the emulsion in a hardening developer, developing the smaller grains and the previously undeveloped portions of the larger grains in a non-hardening developer, and subsequenly hardening in an independent hardening agen 12. The method of making photographic gelatin reliefs which comprises developing comparatively large portions of the larger grains of the exposed parts of a photographic emulsion in a non-hardening developer, developing and tanning the remainder of the larger grains and the smaller grains in a hardening developer. and hardening said large portions in an independent hardening agent.

LEONARD T. TROLAND.

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