US3149970A

US3149970A - Production of photographic silver images by physical development

Info

Publication number: US3149970A
Application number: US513A
Authority: US
Inventors: Edith Weyde
Original assignee: Agfa AG
Current assignee: Agfa Gevaert NV
Priority date: 1959-01-10
Filing date: 1960-01-05
Publication date: 1964-09-22
Anticipated expiration: 1981-09-22
Also published as: DE1110519B; BE586348A; GB920277A; CH392256A; FR1244812A

Description

United States Patent 3,149,970 PRDDUQTIQN 0F PHOTQGRAPHKCSILVER EMAGES BY PHYSICAL DEVELOPMENT Edith Weyde, Leverlrusen, Germany, assignor to AGFA Alrtiengeseilsehaft, Leverhusen, Germany, a corporation of Germany No Drawing. Filed Jan. 5, 1966, Ser. No. 513 Claims priority, application Germany Jan. 10, 1959 7 Claims. (Cl. 96-48) The present invention relates to the production of photographic silver images by physical development maliing use of light-sensitive layers having a low content of silver halide or colloidal silver.

It is known that photographic silver images can be pro duced by means of a physical developer. This physical developer contains in principle dissolved silver salts as Well as silver halide developing agents. For producing the silver images ordinary photographic silver halide emulsion layers are used which, after exposure, are first fixed and then developed in said physical developer. This process is seldom used in practice on account of the loss in lightsensitivity connected therewith, the comparatively long processing time required, and the low density of the silver image obtained therewith.

It has now been found that these draw-backs connected with the production of photographic silver images by means of a physical developer can be overcome if silver halide emulsion layers are used which have a very low content of silver halide, and if these layers, after exposure, are subjected to a physical development without previous fixing.

For the production of the aforementioned silver halide emulsion layers there are preferably used silver halide emulsions which contain per liter silver halide in an amount corresponding to about 0.1-1 g. of silver. The process can, however, also be carried out with a silver halide emulsion containing 0.01 to 3 g. of silver in the form of silver halide per liter of emulsion. Even emulsions with only one mg. of silver chloride or silver bromide per liter of 6 percent gelatin solution still produce an image, even though this image is of low quality. The use of emulsions with more than 1 g. of silver per liter, generally does not produce any appreciable improvement in the light-sensitivity. The silver halide of these emulsions may consist of silver chloride, silver bromide, or mixtures of silver chloride and silver bromide in any proportions. Moreover, silver iodide may be present in these emulsions, preferably in an amount up to 10 percent by Weight as calculated on the total amount of silver halide. The binding agent of the silver halide emulsion preferably consists of gelatin which may be present in an amount of about 1 to 10 percent, preferably 4 to 8 percent.

It has, furthermore, been found that such silver halide emulsions are especially effective for the production of which the precipitation of the silver halide is effected without using a large excess of halogen salts so that these emulsions are not consequently subjected to an Ostwald ripening (which refers to enlargement of the silver halide grain or crystal, and is different from chemical or afterripening). Furthermore, it has been found advantageous to so adjust the concentrations of the solutions used for the production of the silver halide emulsions that the emulsions obtained need not be substantially diluted in order to obtain the aforementioned concentrations. For the precipitation of the silver halide there may be used silver nitrate or any other Water-soluble silver salts on the one hand and alkali-metal and halide such as sodium chloride, potassium bromide, potassium iodide on the other hand. The water-soluble silver salts and the alkali-metal halides are preferably used in equivalent amounts. It is, hoW- ever, also possible to use the alkali-metal halides in a stoichiometrical excess up to about percent since in the latter case Ostwald-ripening usually does not occur due to the small concentrations of the halogen salts used. In any case, the concentration of the halogen salts should be so small at the time of precipitation that the solubility .of the silver halide is insignificant so that no or practically no enlargement of the silver halide grain occurs during the production and during the Working-up of the emulsions. For example, if a relatively large excess of sodium chloride is added to an emulsion of the above type, and if the emulsion is allowed to digest for some hours at elevated temperature, and enlargement of the grain occurs, Whereby the production of the image in the manner previously described is less satisfactory.

These emulsions precipitated in very dilute form have, as expected, a very low light-sensitivity. It has however been found that such emulsions can be sensitized with sensitizing dyes on a quite unusually high scale, the sensitization being comparatively stronger the smaller the amount of silver that is contained in the emulsions. It was established that all known sensitizing dyes produce the eifect. If there are simultaneously used different dyes which sensitize the emulsion for different spectral regions, then layers can be obtained which have a substantially higher sensitivity than for example that of emulsions for micro-films, which are comparable with these emulsions as regards grain size. Suitable optical sensitizers are for instance those which are disclosed in German Patents Nos. 733,026; 725,825; 737,639; 730,852; 714,764; 757,784; 888,046; 927,527 and 929,080 and US. Patents Nos. 2,226,156; 2,231,659; 2,185,182. and British Patents Nos. 466,244; 493,455; 519,895 and 509,927. Moreover there may be further cited by Way of example eosin, erythrosin, pinacyanol.

The type of gelatin which is used also has a strong influence on the sensitivity of such emulsions. Even extremely small quantities of ripening substances are sufiicicut to improve the sensitivity, while on the other hand inhibiting substances can greatly reduce the sensitivity.

Binding agents other than gelatin, for example polyvinyl alco-hol and its derivatives, carboxymethyl cellulose and the like, also produce layers which are suitable for use.

The layers, after imagewise exposure, can be processed in various ways. For example the exposed silver halide layer may be brought into contact with an unexposed silver chloride layer in the presence of a silver halide developer solution, containing a silver halide solvent, and this can for example take place in an apparatus which is used for the silver salt diffusion process as it is for instance disclosed in French Patent No. 879,995 or in British Patent No. 672,844, U. S. Patent No. 2,657,618 or French Patent No. 1,015,772. In this case the auxiliary silver chloride layer serves as a silver donor, since silver chloride is dissolved by the developer solution containing a silver halide solvent and thereafter is brought into contact with the exposed silver halide layer. Instead of a silver chloride layer there may also be used a silver chlorobromide layer, the silver halide of which con tains up to about 30 percent of silver bromide. A few seconds after the two layers have entered into contact, they can be separated from one another and a negative silver image of the copied original is seen in the exposed layer. This only has to be rinsed for a short time before being dried, fixing being unnecessary.

The processing can however also be carried out With a physical developer which contains silver salts as well as reducing agents, but then a longer time is required for the production of the image. The image is very rapidly obtained if the exposed layer is first treated with an aqueous solution of a silver salt in the form of a complex compound with for example a sulphite or a thiosulphate and then with a silver halide developer solution. The following method has also proved very satisfactory: Silver halide developer substances which are resistant to diffusion, for example those indicated in German Patent No. 954,391, are added to the silver halide layer. After exposure of such layers, they are treated with an alkaline aqueous solution of a silver complex salt, as for instance the complex salt of silver chloride and sodium thiosulfate, and since no developer substances can enter the solution of the silver salts, these solutions remain essentially unchanged in composition and can be reused frequently.

It is, furthermore, possible to use a two-layer system, in which case there is for example employed, as silver donor, a normal silver chloride layer which must not contain any water-soluble silver halide salts and which is only sensitive to blue light. As light-sensitive layer, there is used a silver halide layer with a low silver content as disclosed above, which layer has for example been sensitized for green light. After exposure behind 'a yellow filter, the processing is carried out with a silver halide developer solution which contains the silver halide solvent. The silver chloride of the auxiliary layer is dissolved, diffuses into the layer with a low silver content and is deposited therein on the nuclei which are formed by exposure to light. The silver chloride auxiliary layer can also have added thereto dyes which serve as antihalation layer and which are bleached in the processing. The auxiliary layer is preferably arranged as the outer layer; however, it may also form the inner layer. After processing the auxiliary layer need not be removed from the image layer, since the silver chloride of the auxiliary layer is usually completely dissolved in the developing solution. The layers with low silver content can also be coated with a protective layer, this producing the advantage of better whites.

In order to obtain black silver deposits, it is advisable to add stabilizers or toning agents such as heterocyclic nitrogen-sulphur compounds, for example -phenyl-n1ercapto-tetrazole in ordinary concentrations, either to the processing bath, to the layer having a low silver content, or to the silver chloride auxiliary layer. These substances somewhat delay the silver deposition owing to the sparing solubility of their silver salts in silver halide solvents.

Light dispersion plays no part in these layers having a low silver content, since these layers are completely clear and transparent, and the resolving power is thus extremely high. Moreover, since the image silver which forms during the processing and which precipitates from the solution is of very fine grain, such images can be very greatly enlarged.

It hasbeen found possible using such layers with a low silver content in combination with the present developing method also to produce direct positive images by using the Herschel effect, for example in accordance with British Patent No. 748,681. It is known that silver halide emulsion layers, especially silver chloride emulsion layers, which are fogged either by light or chemical means, can be so modified by additives such as pinacryptol yellow or those disclosed in British Patents Nos. 748,681 and 667,206 that, when they are exposed to rays of relatively long wave length (yellow or red), they produce a positive image after development, because the light of longer wave length has made the fogging nuclei ineffective. It has now been found that the same effect is produced by using, instead of an ordinary fogged silver halide emulsion, sil ver nuclei which have been prepared from the emulsions of the present invention, especially silver chloride emulsion, or from dilute solutions of water-soluble silver salts such as silver nitrate, which solutions contain gelatin or other suitable binding agents in an amount of about 2 to percent by weight. The last mentioned solutions preferably contain 0.001 to l g. of silver per liter. Here also, the best results are obtained by using layers which contain l 0.001 to 0.1 g. of silver in colloidal form per square meter of surface area, which is equivalent to from 0.0001 to 0.01 milligram per square centimeter.

These materials are provided with the same additives as those used for the direct positive emulsions based on the Herschel effect such as (l) 2-(2,4dinitrostyryl)benzothiazole and similar heterocyclic compounds of the benzothiazole, quinoline, indolenine, benzotriazole, and rhodanine series, the fused phenyl radicals of which are substituted by at least one nitro radical and their alkyl quaternary salts, such as are described in British Patent No. 667,206, and (2) o-nitrobenzylpyridinium chloride and similar six-numbered heterocyclic compounds containing a ring nitrogen atom and a nitrobenzyl substituent radical, such as are described in British Patent No. 748,681, these additives being preferably used in amounts of 0.1 to 10 g. per liter of emulsion. At the exposed areas, the silver nuclei are made ineffective by these substances and a positive silver image is obtained after processing by one of the methods described above.

Example 1 To a 6 percent aqueous gelatin solution at a temperature of 40 C. are added per liter, 1 cc. of a 1 percent sodium chloride solution, 3 cc. of a 1 percent silver nitrate solution and 1 cc. of a 0.01 percent eosin solution, from which a photographic layer is cast onto a paper or film support. The thickness of the dried layer will be between 2 and 10 microns.

After exposure to an original by means of an incandescent lamp this layer is conducted through an apparatus such as that used for the silver salt diffusion process, and an ordinary unexposed silver chloride layer is used as the silver donor. The developer solution applied has the following composition:

1000 cc. of water 15 g. of hydroquinone l g. of 2-phenyl-3-pyrazolidone 10 g. of caustic soda 40 g. of anhydrous sodium sulphite 1 g. of potassium bromide 15 g. of sodium thiosulphate 0.01 g. of 5-phenylmercaptotetrazole Shortly after the two layers have left the apparatus, they are separated (i.e. after being in contact for a few seconds). A negative of the original is seen on the exposed layer. The layer is then rinsed for a short period and dried.

Example 2 The same light-sensitive layer as in Example 1 is used and this is treated with a developer having the following composition:

1000 cc. of water 5 g. of Amidol (diarninophenol hydrochloride) g. of anhydrous sodium sulphite.

The processing is as set out in Example 1.

Example 3 The same light-sensitive layer as in Example 1 is used 0 and the processing is carried out as follows.

The layer is dipped after exposure for a short time into a solution which is prepared as follows.

A solution of 50 g. of sodium thiosulphate in water has added thereto such a quantity of silver chloride that a solution saturated with silver chloride is formed. The layer is thereafter introduced into the following developer:

1000 cc. of water 15 g. of hydroquinone 0.5 g. of l-phenyl-3-pyrazolidone 10 g. of caustic soda 30 g. of anhydrous sodium sulphite 0.5 g. of potassium bromide.

Temperature of developer solution: 22 C. Developing time: /2 to 2 minutes.

Example 4 0.5 g. of citric acid, 0.3 of sodium chloride and 0.8 g. of silver nitrate, dissolved in water, are added to 1 liter of a 6 percent aqueous gelatin solution. The emulsion is left to stand for about 1 hour at 40 C., and then there are added about mg. of l,1'-diethylbenzthiomesoethyl carbocyanine iodide (optical sensitizer) as well as 10 g. of 1,2-dihydroxy-3-cyclohexyl benzene (silver halide developer substance), dissolved in water.

After casting, the layer obtained is developed in the following solution:

A 5 percent sodium thiosulphate solution saturated with silver chloride is prepared as indicated in Example 3 and this solution has added thereto, per liter, 20 g. of anhydrous sodium sulphite and 10 g. of caustic soda.

Example 5 0.3 g. of silver nitrate is added to 1 liter of 6 percent gelatin solution and the solution is left to stand in a thin layer exposed to light for several days. Photolytic silver is formed. 3 g. of o-nitrobenzyl pyridinium chloride are added to this solution in the dark and the solution is cast. When exposed behind a yellow filter and processed as set out in Example 1, these layers produce a direct positive of the copied original.

What is claimed is:

1. A process for producing a negative photographic silver image which consists essentially of exposing to an object to be reproduced a photosensitive silver halide emulsion layer of essentially uniform thickness which contains uniformly distributed throughout the layer a silver halide in an amount equivalent at most to 0.1 gram of silver per square meter of the emulsion layer that had been cast from an emulsion containing a silver halide in an amount equivalent to between 0.01 and 1.0 gram of silver per liter which had been prepared by adding to a solution of a Water-soluble silver salt a solution of an alkali-metal halide in an amount between one and two stoichiometrical equivalents of the silver salt, so that no Ostwald ripening occurs, and subsequently subjecting the exposed silver halide emulsion layer to physical development without prior fixation of the exposed silver halide emulsion layer.

2. A process for producing a negative photographic silver image which consists essentially of exposing to an object to be reproduced a photosensitive silver halide emulsion layer of essentially uniform thickness which contains uniformly distributed throughout the layer a silver halide in an amount equivalent at most to 0.1 gram. of silver per square meter of the emulsion layer that had been cast from an emulsion containing a silver halide in an amount equivalent to between 0.01 and 1.0 gram of silver per liter which had been prepared by adding to a solution of a water-soluble silver salt a solution of an alkali-metal halide in an amount between one and two stoichiometrical equivalents of the silver salt, so that no Ostwald ripening occurs, and subsequently without prior fixation of the exposed silver halide emulsion layer physically developing the exposed silver halide emulsion layer in contact with an unexposed silver halide emulsion layer containing a silver halide of the group consisting of silver chloride and silver chlorobromide in a solution containing a silver halide solvent which is capable of forming a soluble complex with silver halides, in which physical development treatment silver halide from the unexposed silver halide layer is dissolved in the solution containing the silver halide solvent and is deposited onto the exposed silver halide emulsion layer.

3. A process as defined in claim 2 in which the silver halide solvent is a substance of the group consisting of sodium thiosulfate and sodium sulfite.

4. A process for producing a negative photographic silver image which consists essentially of exposing to an object to be reproduced a photosensitive silver halide emulsion layer of essentially uniform thickness which contains uniformly distributed throughout the layer a silver halide in an amount equivalent at most to 0.1 gram of silver per square meter of the emulsion layer that had been cast from an emulsion containing a conventional silver halide developing substance and a silver halide in an amount equivalent to between 0.01 and 1.0 gram of silver per liter which had been prepared by adding to a solution of a water-soluble silver salt a solution of an alkali-metal halide in an amount between one and two stoichiometrical equivalents of the silver salt, so that no Ostwald ripening occurs, and subsequently without prior fixation of the exposed silver halide emulsion layer subjecting the exposed silver halide emulsion layer to a physical development treatment in an aqueous alkaline solution of a silver halide in a silver halide solvent which is capable of forming a soluble complex with silver halides.

5. A process for producing a negative photographic silver image which consists essentially of exposing through a yellow filter to an object to be reproduced that is illuminated with light rays which include the green region of the visible spectrum a photosensitive photographic material comprising (a) a silver halide emulsion as defined in claim 1 that is sensitive to green light, and

(b) a silver chloride emulsion layer that is essentially sensitive only to blue light,

and subjecting the thus exposed photographic material without prior fixation to physical development in a solution containing a silver halide solvent which is capable of forming a soluble complex with silver halides, in which physical development treatment silver halide from the silver chloride emulsion layer that was unaffected in the original exposure is dissolved in the solution containing the silver halide solvent and is deposited onto the exposed silver halide emulsion layer.

6. In a process for producing a direct positive silver image which comprises exposing an ordinary fogged photosensitive silver halide emulsion layer containing a substance that is capable of promoting the Herschel efiect to an object to be reproduced that is illuminated by light rays within the yellow to red regions of the spectrum and subsequently developing the said exposed fogged silver halide emulsion layer in a silver halide developing composition, the improvement which consists in using, in place of such an ordinary fogged silver halide emulsion layer, a photosensitive emulsion layer of essentially uniform thickness containing uniformly distributed therethrough colloidal silver that was produced by casting an emulsion of the group consisting of (i) photosensitive silver halide emulsions containing a silver halide in an amount equivalent to between 0.01 and 1.0 gram of silver per liter which had been prepared by adding to a solution of a water-soluble silver salt a solution of an alkali-rnetal halide in an amount between one and two stoichiometrical equivalents of the silver salt, so that no Ostwald ripening occurs, and

(ii) photosensitive emulsions containing between 2 and 10% by weight of gelatin and an amount of a watersoluble silver salt equivalent to between 0.001 and 1.0 gram of silver per liter, each of which emulsions contains a substance that is capable of promoting the Herschel effect and has been fogged by exposure to light, and, after exposure of the emulsion layer to the object to be reproduced, subjecting without prior fixation the thus exposed emulsion layer to physical development.

7. A process as defined in claim 6 in which the substance that is capable of promoting the Herschel effect is a substance of the group consisting of (i) heterocyclic compounds of the benzothiazole,

quinoline, indolenine, benzotriazole, and rhodanine series, the fused phenyl radicals of Which are substituted by at least one nitro radical, and their alkyl quaternary ammonium salts, and

(ii) six-membered heterocyclic compounds containing a ring nitrogen atom and a nitrobenzyl substituent radical, that are capable of promoting the Herschel effect.

References Cited in the file of this patent UNITED STATES PATENTS ..2,712,995 Weyde July 12, 1955 2,751,295 Salminen et al June 19, 1956 2,937,945 Weyde May 24, 1960 OTHER REFERENCES Wall et al.: Photographic Facts and Formulas, Am. Photo. Publ. Co. (Boston), 1947, pp. 95 and 96.

Henney and Dudley: Handbook of Photography, pages 373-374, McGraW-Hill, New York (1939).

The Photographic Journal, Section A, January 1950,

James 'et a1 June 19, 1956

Claims

1. A PROCESS FOR PRODUCING A NEGATIVE PHOTOGRAPHIC SILVER IMAGE WHICH CONSISTS ESSENTIALLY OF EXPOSING TO AN OBJECT TO BE REPRODUCED A PHOTOSENSITIVE SILVER HALIDE EMULSION LAYER OF ESSENTIALLY UNIFORM THICKNESS WHICH CONTAINS UNIFORMLY DISTRUBUTED THROUGHOUT THE LAYER A SILVER HALIDE IN AN AMOUNT EQUIVALENT AT MOST TO 0.1 GRAM OF SILVER PER SQUARE METER OF THE EMULSION LAYER THAT HAD BEEN CAST FROM AN EMULSION CONTAINING A SILVER HALIDE IN AN AMOUNT EQUIVALENT TO BETWEEN 0.01 AND 1.0 GRAM OF SILVER PER LITER WHICH HAD BEEN PREPARED BY ADDING TO A SOLUTION OF A WATER-SOLUBLE SILVER SALT A SOLUTION OF AN ALKALI-METAL HALIDE IN AN AMOUNT BETWEEN ONE AND TWO STOICHIOMETRICAL EQUIVALENTS OF THE SILVER SALT, SO THAT NO OSTWALD RIPENING OCCURS, AND SUBSEQUENTLY SUBJECTING THE EXPOSED SILVER HALIDE EMULSION LAYER TO PHYSICAL DEVELOPMENT WITHOUT PRIOR FIXATION OF THE EXPOSED SILVER HALIDE EMULSION LAYER.