Receiving Sheet For Diffusion Transfer Processes

Abstract

A receiving sheet for diffusion transfer processes wherein the image-receiving layer contains as the binding agent a mixture of an alkali metal salt of carboxymethyl cellulose and a propylene glycol ether-substituted methyl ether of cellulose and a process for using the receiving sheet. The novel mixture of binders provides an improved positive which effects more rapid image-transfer, better tone and combines ease of sandwich separation with immediate dry feel. 10 Claims, No Drawings

Description

This invention relates to an improved reception sheet for the direct production of positive photographic images by silver and color diffusion transfer process and a method of using the reception sheet.

In the silver salt diffusion transfer process a positive image is transferred by chemical means from an exposed silver halide layer carried by a binding medium such as gelatin to an image-receiving layer comprised of a binding medium usually carrying a silver-precipitating agent. Both the silver halide layer and image-receiving layer are usually supported and are commonly referred to in the diffusion transfer art as the negative sheet and positive sheet, respectively. Transfer of the image is effected by bringing the silver halide layer into contact with the reception layer while both layers are moistened with a processing solution which develops the exposed silver halide and at the same time dissolves the nonexposed silver halide. The dissolved silver halide diffuses the reception layer where it is reduced to a positive image under the activity of the precipitating agent present in the reception layer.

In color diffusion transfer processes, a photosensitive element including a silver halide emulsion layer is exposed to create therein a latent image which is developed and concurrent with and under the control of this development an imagewise distribution of mobile color-providing substances is formed. At least a portion of these color-providing substances is transferred through the processing solution to the image-receiving layer to form a colored image thereon.

The photosensitive and reception layers contacted in these transfer processes must be left together for a short period of time to complete transfer of the image-forming components through the processing solution to the reception layer. It has been found that contact of the two layers for too great a time period frequently presents separation difficulties.

Attempts have been made to alleviate this difficulty as, for instance, by the process described in British Pat. No. 687,751 wherein an improvement in separation is obtained by using in the layers brought together a nongelatin binding agent in one of the layers and a gelatin binding agent in the other layer. Other ways of facilitating separation of the sheets is by the use of silica in or on the reception layer and by use of cellulose ethers as the binding agents as disclosed, for instance, in British Pat. No. 703,312. Unfortunately, certain cellulose ethers such as sodium carboxymethyl cellulose, when used as the sole binder in the layers do not produce a stable receiving layer. Consequently, when these materials are employed, they are usually used in admixture with another binder such as gelatin. Even with this combination, however, separation of the layers becomes difficult at times in excess of approximately 1 minute after sandwiching. More often than not, substitution of binding agents known for their easy release, although performing this function satisfactorily, adversely effect other desirable properties of the reception layer.

It is an object of the present invention, therefore, to provide a diffusion transfer receiving sheet improved in the length of time in which it can be readily separated from a silver-halide containing layer with which it is sandwiched.

Another object of the invention is to provide a reception sheet which when separated from a negative sheet with which it has been sandwiched exhibits excellent dry feel when separated and which may be written on with a ballpoint pen immediately after sandwich separation.

A further object is to provide an economical receiving sheet which can be readily separated after 1 minute of sandwich of the positive and negative sheets and a process of using the receiving sheet.

Another object of the invention is to provide a receiving sheet which when used in conjunction with a negative yields a more rapid image-transfer, better tone and combines ease of sandwich separation with immediate dry feel.

These and other objects of the invention are obtained by a diffusion transfer receiving sheet comprised of a support, and image-receiving layer on said support, the image-receiving layer being comprised of a colloid binding agent composition comprising about 20 to 50 percent by weight of an alkali metal salt of carboxymethyl cellulose and 50 to 80 percent by weight of a propylene glycol ether-substituted methyl ether of cellulose containing about 28 to 30 percent of methoxyl groups and about 7 to 12 percent of propylene glycol ether substitution by weight. The percentages of the cellulose ether components in the binding agent composition are on a solids basis while the percentages of the methoxy and propylene glycol ether-substituted groups are based on the weight of the substituted methyl ether of cellulose.

DETAILED DESCRIPTION OF THE INVENTION

The alkali metal carboxymethyl cellulose component of the mixed colloid binder of the invention is a water-soluble material which may be prepared, for instance, by the procedure described in U.S. Pat. Nos. 2,618,609; 2,607,772 or 2,667,480. The preferred alkali metal carboxymethyl cellulose is sodium carboxymethyl cellulose but other alkali metal derivatives such as potassium, lithium and the like may be used.

The propylene glycol ether-substituted methyl ether of cellulose which constitutes the second essential ingredient of the mixed colloid binding agent of the invention likewise may be prepared by a variety of methods known to the art. It is commercially available as Methocel 60 H.G.

Precipitating agents are preferably included in the image-receiving layer of the receiving sheet used in silver halide diffusion transfer processes. Suitable precipitating agents include metallic sulfides and selenides, these terms being understood to include the selenosulfides, the polysulfides and the polyselenides. The preferred precipitating agents are the heavy metal sulfides, e.g., of zinc, chromium, gallium, iron, cadmium, cobalt, nickel, lead, antimony, bismuth, silver, cerium, arsenic, copper; and the heavy metal selenides, e.g., of lead, zinc, antimony, and nickel. Also suitable as precipitating agents are heavy metals such as silver, gold, platinum, palladium and mercury. The silver precipitating agents are provided in the receiving layer in a highly dispersed condition, preferably as colloidal particles. The silver precipitating agent is employed in the receiving sheet in small concentrations. Concentrations of about 2 .+-. 10.sup..sup.-5 gram-moles for each square foot of the surface area of the receiving sheet have proved adequate.

Advantageously, particles of silica, preferably in colloidal form, are also present in the image-receiving layer along with the precipitating agent. Although the essentially pure forms of silica such as silica aerogel give best results, it is possible to use particles of less pure silicas such as, for instance, silicas derived from kieselguhr, diatomaceous earth, infusorial earth, etc. The amount of silica employed is generally substantially greater than the silver precipitating agent used.

If desired, other ingredients commonly provided in the image-receiving layers such as antifoaming agents, coatability improvers, etc. may be added as is well known in the art. Also, in addition to the alkali metal carboxymethyl cellulose and the propylene glycol ether-substituted methyl ether of cellulose components, there may be included in the binding agent composition other known binding agents of the art, as long as they are used in concentrations that do not have a deleterious effect upon the advantageous results obtained by the novel colloid binding agent mixture of the invention. Illustrative of such binding agents are polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, partially hydrolyzed polyvinyl acetate, polyvinyl pyrrolidone and the like.

The image-receiving layer of the invention containing the novel binder composition can be prepared and applied to suitable supports by any of the known procedures and techniques of the art. A particularly desirable method involves preparing an aqueous dispersion of the silica particles to which there is added effective quantity of one or more of a suitable sulfide ion-capturing salt such as a nitrate, borate, chloride, sulfate, acetate, etc., of any of the following metals: nickel, lead, iron cobalt, and the like. Thereafter, an equimolar quantity of a soluble sulfide is added. The anions of sulfide and the cations of the ion-capturing salt combine to precipitate from the solution as insoluble crystals of the metal sulfide thereby producing a dispersion of the insoluble sulfide in the silica. The mixed colloid binding agent of the invention in water is then added to the silica-metal sulfide dispersion and the resulting mixture then coated on a suitable sheet support by any of the conventional methods of the art.

Supports upon which the image-receiving layer may be disposed include by way of example, paper, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethyleneterephthalate film, polyethylene film, polypropylene film, polyethylene-coated paper, polypropylene-coated paper, and the like.

The silver halide layer utilized in conjunction with novel receiving sheets of the invention can be any of the conventional negative-type developing emulsions. Typical silver halides include silver chloride, silver bromide, silver bromoiodide, silver chloroiodide, silver chlorobromoiodide, and the like. Mixtures of more than one of such silver halides can be utilized. In accordance with the usual practice, such silver halide emulsions can contain, for instance, spectral sensitizers, speed-increasing addenda, hardeners, coating aids, plasticizers, antifoggants, and similar conventional emulsion addenda. Developing agents may be incorporated into the silver halide emulsion, if desired, or can be contained in a contiguous layer. The silver halide layers may be coated on a variety of supports of the type described above for the image-receiving sheets.

Typically, the photographic processing liquid layer in the silver salt diffusion transfer systems, through which the image-forming component is transferred, is a viscous, aqueous alkaline solution of a silver halide developer, a silver halide solvent for reaction with the unexposed portions of a photosensitive layer and, if desired, a thickening agent.

Suitable silver halide developing agents include hydroquinone, substituted-hydroquinones, etc., such as those substituted in the 2, 3, 5 or 6 position carbon atoms or any combinations of these with lower alkyl groups such as methyl, ethyl, propyl, butyl, etc., lower alkoxy groups, halogen groups such as chlorine, bromine, fluorine and other groups commonly used as substituents; resorcinol, catechol, ascorbic and isoascorbic acid, preferably in the form of its alkaline metal salt; the 3-pyrazolidones such as are described in U.S. Pat. No. 2,875,048 Haist et al.; the aminophenols such as p-aminophenol, N-methylaminophenol, etc.; developing agents containing an amino group usually in the form of the hydrochloride or the sulfate, and the like.

Illustrative of typical silver halide solvents are the water-soluble thiosulfates such as sodium, potassium, and ammonium thiosulfates; the alkali thiocyanates, alkyl selenocyanates, thioglycerol, aminoethanediols, p,p'-di-thia-suberic acid, etc. The preferred silver halide solvents are the thiosulfates. Other addenda commonly employed in alkaline processing compositions for diffusion transfer processes may be included in the processing liquid, if desired. The addenda include, for instance, restrainers such as potassium bromide, stain preventives such as alkaline metal sulfites, sequestering agents such as ethylenediaminetetraacetic acid, 1,3-diamino- 2 -propanoltetraacetic acid, etc.

Thickening agents commonly employed in the processing compositions include, for instance, hydroxyethyl cellulose or carboxymethyl cellulose. Thickened processing compositions usually have a viscosity of at least 5,000 c.p.s. to 100,000 or even 200,00 c.p.s.

As examples of color diffusion transfer processes may be mentioned the processes disclosed in U.S. Pat. No. 2,983,606 wherein dye developers (i.e., compounds which contain in the same molecule both the chromophoric system of a dye and also a silver halide developing function) are the color-providing substances, the processes disclosed in U.S. Pat. No. 2,674,049 wherein color developers are employed to develop the latent image and color couplers are the color-providing substances and the processes disclosed in U.S. Pat. No. 2,774,668 and U.S. Pat. No. 3,087,817 wherein complete, preformed dyes are used as color-providing substances.

The following examples are included to further illustrate the present invention.

EXAMPLE I

Precipitating nuclei are made in the presence of colloidal silica by adding mixture B to mixture A, both identified below, with vigorous agitation. ##SPC1##

The resulting solution is then coated onto paper which has been clay- or baryta-coated in the normal way with an applicator roller and air-knife in an amount of 0.3 liter per square meter of paper whereupon the layer is dried rapidly with hot air. The image-receiving sheet obtained is laid upon a silver halide emulsion layer of an imagewise-exposed, light-sensitive material prepared by coating a gelatin silver chloride emulsion containing hydroquinone and 1-phenyl-3 -pyrazolidone on a paper support. Both materials are then passed through a developing solution and immediately thereafter the image-receiving layer and the light-sensitive layer are squeezed into close contact to form a sandwich. The resulting sandwich is found to be readily separable at times up to 2 minutes. Moreover, the separated positive image-receiving sheet exhibits an excellent dry feel and may be written upon with a ballpoint pen directly after sandwich separation. The density of the transfer image is found to be very good. Upon rapid separation, that is, separation under ten seconds, a dark-gray tone is obtained, and separation after 10or more seconds provides good black image.

EXAMPLE II

Example I is repeated substituting gelatin for the Methocel 60 H.G. The results are as follows: Separation of the sandwich is very difficult after 1 minute of sandwiching. On rapid separation, that is, under 10 seconds, a brown tone rather than a dark-gray tone is obtained. The dry feel of the separated positive sheet is inferior to that exhibited by that of example I at similar sandwich times.

The invention has been described in detail with particular reference to preferred embodiments thereof, but, it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

1. A diffusion transfer receiving sheet comprised of a support, an image-receiving layer on said support, said image-receiving layer being comprised of a colloid binding agent composition comprised of about 20 to about 50 percent by weight of an alkali metal salt of carboxymethyl cellulose and about 80 to about 50 percent by weight of a propylene glycol ether-substituted methyl ether of cellulose containing about 28 to 30 percent methoxyl groups and about 7 to 12 percent propylene glycol ether

2. The receiving sheet of claim 1 wherein the image-receiving layer

3. The receiving sheet of claim 2 wherein the silver precipitating agent is

4. The receiving sheet of claim 3 wherein the heavy metal sulfide is nickel

5. The receiving sheet of claim 1 wherein the alkali metal salt of

6. The receiving sheet of claim 1 wherein said image-receiving layer