US3404981A - Process for preventing image destruction in thiocyanate-stabilized photographic prints - Google Patents

Description

United States Patent PROCESS FORPREVENTING IMAGE DESTRUC- TION IN THIOCYANATE-STABILIZED PHOTO- GRAPHIC PRINTS Albert Edward Harris and Edward Cyril Dodd, Ilford, England, assignors to 'Ilford Limited, Ilford, England, a British company N0 Drawing. Filed June 21, 1965, Ser. No. 465,747 Claims priority, application Great Britain, June 24, 1964,

6 Claims. (CI. 96-50) ABSTRACT OF THE DISCLOSURE I There is provided a process for producing a photographic print -by imagewise exposing a photographic material comprising an absorbent base carying on one side thereof a layer of silver halide emulsion containing a photographic developer therein. An image is developed in the emulsion of the photographic material and stabilized with a"thiocyanate stabilizer solution. The improvement comprises preventing the image destruction resulting from residual thiocyanate contained in the absorben't base by applying a water-vapor impermeable layer to the said base on the side thereof which does not carry the said emulsion. The Water vapor impermeable layer can be applied either before or after the developing and stabilizing steps.

This invention relates to the production of photographic prints and to photographic material.

A known process of producing photographic prints is to employ as printmaterial a base material which carries a layer of a photographic silver halide emulsion which contains a photographic developing agent, imagewise expose the material, treat it with an alkaline bath in order toactivate the development (a so-called activator bath), thereby producing a silver image in the material, and then to treat the material with a bath (aso-called stabiliser bath), containing a substance which by complexing with the residualsilver'halide in the material inhibits its light sensitivity, thus stabilising the photographic print obtained.

Thepresent invention relates to an improvement in the materials used for the said process and in the prints obtained by the said process, which for convenience is hereinafter referredto as a process of the type defined. -It is possible to carry out a process of the type defined by feeding the exposed print material through a series of rollers, or a system of troughs followed by squeegee rollers, which apply to it, successively, the activator solution andthe stabilizer solution, thus rendering possible the production of prints in a rapid and reliable manner. The print material usually has a paper base.

However, it has been discovered that when the materialfor use in ;a process of-the type defined has a paper or other absorbent base and the stabilizing agent used is a thiocyanate such as ammonium, sodium or potassium thiocyanate,;there tends-to occur on storage some fading of the image, i.e. image destruction in the photographic print. The tendency for image destruction to occur is aggravated when. the. printis stored in conditions of high humidity;

. It is an object of the present invention to provide a photographic printwwhich has been processed by a process of the type defined and which has a reduced tendency for the image to become destroyed on keeping.

According to the present invention there is provided a process for the production of photographic prints which 3,404,981 Patented Oct. 8, 1968 ice comprises processing exposed print material of the type which comprises developer-containing silver-halide emulsion coated on to an absorbent base, firstly with an alkaline activator solution and then with a thiocyanate stabiliser solution, the process being characterised in that there is applied to the print material on its side remote from the emulsion, either before or after processing, a water-vapour impermeable layer (herein called, for brevity, a waterproof layer).

In general it is most convenient to apply the waterproof layer to the print material before the material is coated with the emulsion and therefore, according to another feature of the present invention, there is provided a process for the production of print material which comprises applying a waterproof layer to one side of an absorbent base and thereafter coating the base material on its non-waterproofed side with a developer-containing silver-halide emulsion.

In another embodiment of the invention, the absorbent base is coated with a developer-containing silver-halide emulsion and subsequently has a waterproof layer applied to its side remote from the emulsion, before the material is exposed or processed.

In yet another embodiment of the invention, the print material which consists of an absorbed base on to which is coated a developer-containing silver-halide emulsion, is exposed and processed firstly with an alkaline activator solution and secondly with a thiocyanate stabilising solution and subsequently has applied to its side remote from the exp'osedand developed emulsion a waterproof layer.

The following examples will serve to illustrate the invention. In each of them'the following activator and stabilizer solutions were employed:

Activator solution:

Sodium hydroxide G. per litre 60 Sodium sulphite do 50 Stabiliser solution:

Ammonium thiocyanate G. per litre 280 Sodium sulphite anhydrous do 5 Sodium metabisulphite do 32 1-phenyl-S-mercaptetrazole do 5 Industrial ethyl alcohol ml. per litre 200 Example 1 Paper base was coated on one side with a thin layer of polyethylene and a developer-containing gelatino silverhalide emulsion was then coated on to the opposite side of the base. This material was then exposed, developed in an alkaline activator solution and the material was then treated with the stabiliser solution. After several weeks storage the resultant image on the material was found to be completely intact and not at all etched compared to the image on material which has been exposed and processed at the same time, but the base of which had not been coated with polyethylene.

Example 2 Paper base was coated on one side with a thin layer of Butakon, a styrene-butadiene copolymer. (Butakon is a registered trademark.) This material was coated with a developer-containing gelatino-silver-halide emulsion on its opposite side, and exposed and processed as in Example l. After several weeks storage, the photographic image on the material was found to be completely intact and not at all etched.

Example 3 Paper base was coated with a developer-containing gelatino-silver-halide emulsion. After the emulsion was completely dry, the material was coated on its side remote from the emulsion with a thin layer of the styrene-butadiene used in Example 2. After exposure and Example 4 A developer-containing gelatino-silver-halide emulsion coated on to paper base was exposed and processed using the method of Example 1 to produce a photographic image. After the material had dried off, a waterproofing film was applied to the material on the side remote from the image by means of a pressure-sensitive adhesive tape. After several weeks storage the photographic image was found to be completely intact and not at all etched.

In all these examples a gelatino-silver-halide emulsion is used, but it is within the scope of the invention to use other binders for the silver halide such as polyvinyl alcohol.

In our Belgian Patent No. 639,140, the use of a 5- mercapto-tetrazole added to the stabilising solution was described and it is within the scope of the present invention to add such a S-mercapto-tetrazole to the stabilising solution used in the processes described. It is so added in the specific stabiliser solution used in the examples, though its presence is not essential.

The invention accordingly records the methods of making prints of improved stability, the print materials and the prints obtained, all as hereinbefore described.

We claim as our invention:

1. In a process for producing a photographic print by imagewise exposing a photographic material comprising an absorbent base carrying on one side thereof a layer of silver-halide emulsion containing a photographic developer therein, developing an image in said emulsion,

a thiocyanate stabilizer solution, the improvement comprising preventing the mage destruct resulting fr m residual thiocyanate contained in. the. absorbent -.base by applying a water-vapor impermeable layer to the said base on the side thereof which does not carry the said emulsion.

2. A method according toclaim 1 wherein the watervapour impermeable layer is'applied to the absorbent base before it is coated with the photographic 'ernulsio'ri' 3. A method according to claim ZIwh'er einIthe watervapour impermeablelayer is;polyethy1ene. 3

4. A method according to claim 1- wherein the watervapour impermeable layer is applied'to-the-absorbent base after it has been coated with thephotographidemulsion but before imagewise exposure of the emulsion and processing thereof 5. A method according to claim 4 wherein the watervapour impermeable layer is a copolymer of butadiene and styrene. i

6. A method according to claim 1 wherein the watervapour impermeable layer is applied to the absorbent base after the photographic material has been imagewise exposed and processed. v a v v v,

References Cited OTHER REFERENCES Milton, James: Photographic Base Materials Brit. J. Photog., Sept. 21, 1956, pp. 462-463.

NORMAN G. TORCHIN, Primary Examiner.

c. E. DAVIS, Assistant Examiner. a