TONE CONTROLLING COMPOUNDS

Abstract: This invention provides a non-light-sensitive image receiving element for use in a silver halide diffusion transfer process, characterised in that it contains in a layer thereof an S-thiuronium alkyl sulphonate of the general formula (1): wherein R is a C₁- C₆ linear or branched substituted or unsubstituted alkylene group.

Description: The present invention relates to tone controlling compounds and particularly to tone controlling compounds for use in silver complex diffusion transfer processes. In silver complex diffusion transfer processes a light-sensitive silver halide material is image-wise exposed, processed in a developer or activator containing a silver complexing agent, and then contacted with a non-light-sensitive image receiving layer containing development nuclei (also passed through the processing solution). The image-wise exposed silver halide in the light-sensitive material is developed to silver while the unexposed silver halide portions are transferred by diffusion into the receiving layer whereupon it is converted into silver by the action of the developer on to the nuclei. Thus a positive image of the original appears on the receiving layer after separation of the image receiving material from the light-sensitive silver halide material. This process having been first described in GB-A-614,155, is now well known. Certain compounds are now conventionally used in such non-light-sensitive image receiving layers; for example 2-phenyl-5-mercapto-oxadiazole and 5-methylbenzotriazole. These compounds are utilized to control the density and tone of the positive image. Other toners, such as those described in GB-A-950,668 or in GB-A-1,158,479, can either accelerate the production of a positive image as compared to an image receiving layer having no toners added thereto, or as compared to an image receiving layer with known development retarding toners, for example 1-phenyl-2-tetrazoline-5-thione. All these compounds, although efficacious in their way, have drawbacks and accordingly the need exists to improve the preformance of non-light-sensitive image receiving layers and in particular to improve speed of development which would allow a faster 'strip time' and improve resolution and exposure latitude by decreasing sideways diffusion of complexed silver. From US-A-4,500,632 it is known that S-thiuronium alkyl sulphonates stabilize silver images formed on a photographic light-sensitive material against long term deterioration. We have now found however that these S-thiuronium alkyl sulphonates have the unexpected effect of accelerating the physical development of silver in non-light-sensitive image receiving layers in a silver complex diffusion transfer process. According to one aspect of the present invention there is provided therefore a non-light-sensitive image receiving element for use in a silver complex diffusion transfer process characterised in that it contains in a layer thereof an S-thiuronium alkyl sulphonate of the general formula (1): wherein R is a C₁ - C₆ linear or branched, substituted or unsubstituted, alkylene group. In a second aspect the invention provides a silver complex diffusion transfer process, which process comprises passing a non-light-sensitive image receiving element and an image-wise exposed light-sensitive silver halide element through a processing solution, laminating them in face to face contact, and stripping them apart when processing is over, said non-light-sensitive element including an S-thiuronium alkyl sulphonate as above defined, thereby to accelerate the physical development of silver in the image receiving layer. In a preferred form of the invention R as given above may be selected from -CH₂CH₂CH₂- (I) -CH₂CH₂CH₂CH₂- (III) or -CH₂CH₂- (V) The toners employed herein may be used in conjunction with toners of different types if desired. It has been shown that toners in accordance with the foregoing accelerate the physical development of silver in the presence of development nuclei when incorporated in the non-light-sensitive image receiving layers of a silver complex diffusion transfer process. Thus, when processed with a light-sensitive projection negative donor the faster developing receiver layers give improved resolution and exposure latitude without significant lowering of contrast. Furthermore, the maximum transmission densities obtained after 6, 12 or 30 seconds lamination are found to be increased over that achievable in the compounds of the prior art. Furthermore, when processed with a light-sensitive PMTII Continuous Tone Negative donor, the faster developing receiver layers are able to give improved (i.e.lower) contrast over that achievable with the compounds of the prior art. The toners may be employed at concentrations from 1 to 500 mg/m², preferably from 20 to 150 mg/m². In the following discussion of suitable materials for use in the emulsions and elements used in this invention, reference will be made to Research Disclosure, December 1989, Item 308119, published by Industrial Opportunities Ltd., The old Harbourmaster's, 8 North Street, Emsworth, Hants PO1O 7DD, U.K. This publication will be identified hereafter as "Research Disclosure". The silver halide emulsion employed can be either negative-working or positive-working. Suitable emulsions and their preparation are described in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers are described in Research Disclosure Section IX and the publications cited therein. The photographic elements or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilisers (see Research Disclosure Section VI), antistain agents (see Research Disclosure Section VII, paragraph I), light absorbing and scattering materials (see Research Disclosure Section VIII), hardners (see Research Disclosure Section X), plasticisers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), mating agents (see Research Disclosure Section XVI), and development modifiers (see Research Disclosure Section XXI). The photographic elements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein, for example on a paper or transparent film base. Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed. The invention will now be described, by way of illustration only, in the following examples:- The toners were coated individually in the following format on polyethylene coated paper base (Figure 1). PAPER BASE The nickel sulphide nuclei were formed by precipitation in a 5.2% (w/w) solution of gelatin from sodium sulphide (75 g/l) and nickel nitrate (35 g/l). The dispersion was then stabilised by the addition of silver iodide and other solutions before coating on the aforementioned paper base. i) Samples were processed using PMTII activator in a suitable, diffusion transfer processor (e.g. Kodak Imagemate 43DT) with an unexposed projection negative donor, stripped apart immediately after the trailing edge had left the processor, and development stopped instantly by immersing in a 5% acetic acid solution. The transmission density (DT) from different parts of the transferred silver halide was measured representing 6 and 12 second lamination times (Table 1). The results show that the toners of the invention accelerate the production of positive image, compared to the two * cited toners of the prior art. ii) Samples were processed with a step-wedge exposed continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured and the 5-90 contrast measured (Table 2). (The 5-90 contrast being the gradient of a straight line drawn between 5% and 90% of the density range of the density-log exposure curve.) The results show that the toners of the invention provide lower contrast when processed with a continuous tone donor, compared to the two * cited toners of the prior art.

Claims: A non-light-sensitive image receiving element for use in a silver complex diffusion transfer process, characterised in that it contains in a layer thereof an S-thiuronium alkyl sulphonate of the general formula (1): wherein R is a C₁- C₆ linear or branched, substituted or unsubstituted, alkylene group. An image receiving element according to claim 1 characterised in that R is selected from -CH₂CH₂CH₂- (I) -CH₂CH₂CH₂CH₂- (III) or -CH₂CH₂- (V) An image receiving element according to claims 1 or 2 characterised in that the S-thiuronium compound is present at a concentration of 1 to 500 mg/m². preferably 20 to 150 mg/m². A silver complex diffusion transfer process, which process comprises passing a non-light-sensitive image receiving element and an image-wise exposed light-sensitive silver halide element through a processing solution, laminating them in face to face contact, and stripping them apart when processing is over, said non-light-sensitive element including an S-thiuronium alkyl sulphonate of the general formula (1) as defined in Claim 1.

Inventors: BAKER, JULIE, BARNETT, ANTHONY MALCOLM, GRAY, COLIN JAMES
Applicants: EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1990
Main classification: G03C8
IPC codes: G03C8, G03C1