US3211551A

US3211551A - Diffusion transfer process

Info

Publication number: US3211551A
Application number: US7841A
Authority: US
Inventors: Wendt Rudolf
Original assignee: Lumoprint Zindler KG and Co GmbH
Current assignee: Lumoprint Zindler KG and Co GmbH
Priority date: 1957-12-10
Filing date: 1960-02-10
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12
Also published as: FR1245422A; DE1080854B; GB921370A

Description

United States Patent f 3,211,551 DIFFUSION TRANSFER PROCESS Rudolf Wendt, Hamburg, Germany, assignor to Lumoprint Zindler KG., Hamburg, Germany No Drawing. Filed Feb. 10, 1960, Ser. No. 7,841 11 Claims. (Cl. 96--29) This invention relates to photographic developing and copying processes and is more particularly concerned with a novel contact-copying material and a method for its manufacture for producing correctly sided positive images from exposed photographic emulsion layers. The invention, moreover, provides for a new process for producing such positive images by employing the novel contact-copying material.

The invention is applicable to the production of positive images from all kinds of exposed photographic, silverhalide containing emulsion layers comprising additional developing substances.

In known photographic diffusion processes, generally, a latent image is first produced by exposure of a photographic layer, whereupon this image is developed in contact with a gelatine layer containing reduction nuclei, preferably colloidal silver, by dissolving the unexposed silver-halide in the photographic layer.

It is also known to cause and initiate such a diffusion by the action of heat, in which case substances are added to the. corresponding layers which, upon heating above their melting point, split off water of crystallization. Such a water-yielding substance (i.e. a hydrate) is, for example, crystallized sodium sulphate. The water of crystallization liberated during the heating referred to dissolves the developing substances and fixing agents, so that the development and fixing are caused merely by heating. In prior methods of this kind gelatine was used which is reversible so as to absorb part of the liberated water of crystallization by its own swelling.

Furthermore a method for producing embossed pictures by heating is known in which the heat acts upon the developers having tanning characteristics. This method also uses gelatine for both the negative and positive layers.

It is a primary object of this invention to overcome the drawbacks of known processes of the kind referred to, and to provide a novel contact material which, merely upon being pressed while heated against an exposed photographic layer, will result in the formation of a correctly sided positive image on the material corresponding to the latent image on the exposed photographic layer.

A further object of the invention resides in the provision of a process for producing correctly sided positive images from exposed photographic layers.

It is also an object of this invention generally to improve on photographic contact-copying processes and photographic contact-copying material and methods for their manufacture as presently practiced and used.

Briefly, in accordance with this invention, correctly sided positive images are formed by pressing against the exposed film layer a positive or transfer layer comprising polyvinyl alcohol and a hydrate, such as sodium acetate, capable of yielding water of crystallization. Polyvinyl alcohol upon heatingin contrast to gelatine-is not reversible upon absorption of water.

According to a preferred embodiment of the invention,

the polyvinyl alcohol layer comprises, in addition to the 3,211,551 Patented Oct. 12,1965

ice

water-releasing substances, also bifunctional or trifunctional alcohols which assure a high residual moisture and at the same time act as reducing agents.

It is essential for the successful operation according to the invention that the positive layer is not formed by re-v versible gelatine, but that polyvinyl alcohol isused, and that this transfer layer does not contain colloidal silver.

Polyvinyl alcohol if used as a layer-forming substance will liberate the bound water of crystallization much better than the known layer substances, e.g., gelatine. Advantageously, sodium acetate is added to the polyvinyl layer as a deliquescent thermally activable hydrate. The amount of sodium acetate is chosen in such a manner that, during use and upon heating, an amount of water is liberated which is required to enable the activation of the developing agents in the negative layer and the diffusion of the silver salt from its unexposed areas into the positive layer. Besides sodium acetate, sodium citrate and sodium sulphate can be used. Preferably, glycerol is added as a reducing agent. In a positive layer formed in this way the presence of colloidal silver is superfluous.

The negative layer, from which the image is to be transferred, may comprise any desired silver-halide emulsion, for example, silver-chloride and silver-bromide emulsion in varying mixtures, having a high or low sensitivity with any desired gradations and with a normal, increased or decreased content of silver. The commonly known photographic developing substances are added to the negative emulsion layer. As developing substances can be used: methyl p aminophenol-sulphate, paraphenylenediamine and its derivatives and hydroquinone. The following alkali substances may be used: sodium carbonate and caustic soda.

Advantageously, heating presses, electrically heated high-gloss presses, drum dryers, or the like may 'be used for the developing and the simultaneous transmission of the image to the positive layer. The temperature is chosen so that it remains below the hardening point of the positive layer. Generally, a working temperature of -80 C. is advantageous, but this of course is dependent on the positive-layer composition, hence I wish not to limit myself to this temperature range. Advantageously, the invention includes a temperature range from 70 to 120 for operation. Advantageously, the press has a pressure of 0.5-1.0 kg./m.

The positive layer is applied onto a carrier sheet or strip such as paper, plastic or the like. It is of course within the scope of this invention to coat the carrier material with positive layers on both sides. In this case and during developing by heat the carrier coated on both sides will be placed between two negative layers so that a copy on each side is obtained in a single step. According to a preferred embodiment, substances may be added to the positive layer which will further and enhance the development of the negative layer. Such additives may include, for example, alkali-metal salts such as sodium carbonate and substances which facilitate the conversion of the unexposed silver halide into a soluble complex compound, such as sodium thiosulphate. Preferably, the deliquescent hydrates are added, with reference to the polyvinyl alcohol, in amounts of about -200%. Furthermore, conventional hardening agents as well as additives for preventing yellowing and achieving improved blackening and contrast may be added to the positive layer.

The invention will now be described with reference to the following examples, it being understood, however, that these examples are given by way of illustration and not of limitation and that many alterations may be made in, e.g., quantities, choice of material and operating conditions in general Without departing from the scope and spirit of this invention as described in the appended claims.

Example 1 10 g. of polyvinyl alcohol are stirred with 20 ml. of glycerol in a porcelain dish until a homogeneous paste is formed. A solution of 2 g. of sodium carbonate in 50 ml. of water is added to this paste under constant stirring. The mass thus otbtained is then heated to SO -100 C. and 15 g. of sodium acetate in solid form is added. After the sodium acetate is completely dissolved, the mass is coated onto a carrier such as paper, whereupon the layer is dried.

Example 2 A positive layer is prepared as in Example 1, with the further addition of 1 g. of sodium thiosulphate to induce the unexposed silver halide of the negative layer to form soluble complex salts.

Example 3 A positive layer is prepared as in Example 2 with the further addition of 0.2 g. of benztriazole for increasing the blackening effect of the reduced silver in the positive layer.

Example 4 A positive layer is prepared as in Example 2 with the further addition of 0.2 g. of potassium metabisulphite to increase the dissolving action of the sodium thiosulphate.

Example 5 A positive layer is prepared as in Example 4 with the further addition of 0.2 g. of sodium bicarbonate to minimize yellowing.

In all examples, a sheet of paper or plastic material is used as the carrier. The carrier material should advantageously be water-repelling.

Example 6 A coated carrier sheet obtained according to any one of Examples 1-5 is placed against an exposed photographic emulsion layer, e.g., an exposed film, containing common developing substances. Pressure and heat are applied. The temperature should be about 70-80 C. The image appears on the positive layer after a short time.

However, it is pointed out that the temperature depends on the hardening degree of the negative layer and may thus vary in accordance with the composition of this layer. The duration of the heating depends on the nature and amount of the water-liberating substance used in the layer.

The concept of using polyvinyl alcohol as layer-forming material in positive contact-copying material is entirely novel and the beneficial result obtained thereby is certainly surprising and unexpected.

I claim:

1. A process for producing positive contact copies from an exposed negative provided with a photographic emulsion layer containing a silver halide and a developer therefor, comprising the steps of placing said emulsion layer in contact with a transfer layer of polyvinyl alcohol devoid of colloidal silver and containing a hydrate thermally activable to release bound water, said transfer layer further containing a water-retaining reducing agent and a solvent for silver halide; and heating said layers to a temperature not exceeding 100 C. but sufficient to liberate water from said hydrate with resulting activation of said developer, difiusion of a solution of undeveloped silver halide from unexposed portions of said emulsion layer into said transfer layer and reduction of the diffused silver halide whereby a positive image is produced in said transfer layer.

2. A process for producing positive contact copies from an exposed negative provided with a photographic emulsion layer containing a silver halide and a developer therefor, comprising the steps of placing said emulsion layer in contact with a transfer layer of polyvinyl alcohol devoid of colloidal silver and containing a hydrate thermally activable to release bound water, said transfer layer further containing a water-retaining reducing agent, an alkalimetal salt and a solvent for silver halide; and heating said layers to a temperature not exceeding 100 C. but sutficient to liberate water from said hydrate with resulting activation of said developer, diffusion of a solution of undeveloped silver halide from unexposed portions of said emulsion layer into said transfer layer and reduction of the diffused silver halide whereby a positive image is produced in said transfer layer.

3. A process for producing positive contact copies from an exposed negative provided with a photographic emulsion layer containing a silver halide and a developer therefor, comprising the steps of placing said emulsion layer in contact with a transfer layer of polyvinyl alcohol devoid of colloidal silver and containing a hydrate thermally activable to release bound water, said transfer layer further containing a water-retaining reducing agent selected from the group which consists of difunctional and trifunctional alcohols and a solvent for silver halide; and heating said layers to a temperature not exceeding 100 C. but sufficient to liberate Water from said hydrate with resulting activation of said developer, diffusion of silver halide from unexposed portions of said emulsion layer into said transfer layer and reduction of the diffused silver halide whereby a positive image is produced in said transfer layer.

4. A process for producing positive contact copies from an exposed negative provided with a photographic emulsion layer containing a silver halide and a developer therefor, comprising the steps of placing said emulsion layer in contact with a transfer layer of polyvinyl alcohol devoid of colloidal silver and containing a hydrate thermally activable to release bound water, said transfer layer further containing a water-retaining reducing agent selected from the group which consists of difunctional and trifunctional alcohols, an alkali-metal salt and a solvent for silver halide; and heating said layers to a temperature not exceeding 100 C. but sutficient to liberate water from said hydrate with resulting activation of said developer, diffusion of a solution of undeveloped silver halide from unexposed portions of said emulsion layer into said transfer layer and reduction of the diffused silver halide whereby a positive image is produced in said transfer layer.

5. A process as defined in claim 4 wherein said hydrate is selected from the group which consists of sodium acetate, sodium citrate and sodium sulphate.

6. A process as defined in claim 4 wherein said reducing agent is glycerol.

7. A process as defined in claim 4 wherein said solvent is sodium thiosulphate.

8. A process as defined in claim 4 wherein said alkalimetal salt is sodium carbonate.

9. A process for producing positive contact copies from an exposed negative provided with a photographic emulsion layer containing a silver halide and a developer therefor, comprising the steps of placing said emulsion layer in contact with a transfer layer of polyvinyl alcohol devoid of colloidal silver and containing sodium acetate, glycerol, sodium thiosulphate and sodium carbonate, and heating said layers to a temperature ranging substantially between 70 and C. to liberate water from said sodium acetate with resulting activation of said developer, diffusion of silver halide from unexposed portions of said emulsion layer into said transfer layer and reduction of the diifused silver halide whereby a positive image is produced in said transfer layer.

10. A process as defined in claim 9 wherein the proportion of sodium acetate ranges substantially between 100% and 200%, by weight, of the polyvinyl alcohol.

11. A process as defined in claim 10 wherein the sodium carbonate and the sodium thiosulphate are present in quantities of the order of one-tenth the weight of the sodium acetate.

References Cited by the Examiner UNITED STATES PATENTS 2,352,014 6/44 Rott 96-29 2,412,200 12/46 Blum 26029.6 2,747,999 5/ 56 Yutzy et a1. 96-29 2,878,121 3/59 Gray 96-29 2,971,840 2/61 Haydn et a1. 9629 6 FOREIGN PATENTS 555,103 8/57 Belgium. 1,003,578 2/57 Germany.

614,155 10/48 Great Britain. 5 790,811 2/ 58 Great Britain. 801,053 9/58 Great Britain.

OTHER REFERENCES Glafkides, Photographic Chemistry, Fountain Press, 10 London, 1958, pages 150-154.

NORMAN G. TORCIHN, Primary Examiner.

MILTON STERMAN, PHILIP E. MANGAN, l5 Examiners.

Claims

1. A PROCESS FOR PRODUCING POSITIVE CONTACT COPIES FROM AN EXPOSED NEGATVE PROVIDED WITH A PHOTOGRAPHIC EMULSION LAYER CONTAINING A SILVER HALIDE AND A DEVELOPER THEREFOR, COMPRISING THE STEPS OF PLACING SAID EMULSION LAYER IN CONTACT WITH A TRANSFER LAYER OF POLYVINYL ALCOHOL DEVOID OF COLLOIDAL SILVER AND CONTAINING A HYDRATE THERMALLY ACTIVABLE TO RELEASE BOUND WATER, SAID TRANSFER LAYER FURTHER CONTAINING A WATER-RETAINING REDUCING AGENT AND A SOLVENT FOR SILVER HALIDE; AND HEATING SAID LAYERS TO A TEMPERATURE NOT EXCEEDING 100*C. BUT SUFFICIENT TO LIBERATE WATER FROM SAID HYDRATE WITH RESULTING ACTIVATION OF SAID DEVELOPER, DIFFUSION OF A SOLUTION OF UNDEVELOPED SILVER HALIDE FROM UNEXPOSED PORTIONS OF SAID EMULSION LAYER INTO SAID TRANSFER LAYER AND REDUCTION OF THE DIFFUSED SILVER HALIDE WHEREBY A POSITIVE IMAGE IS PRODUCED IN SAID TRANSFER LAYER.