DESCRIPTION

The present invention relates to tone controlling compounds for use in the light-sensitive image receiving layers of a silver halide diffusion transfer process.

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 co plexing 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 they are converted into silver by the action of the developer on 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 l-phenyl-2-tetrazoline-5-thione.

All these compounds, although efficacious in their way, have drawbacks and accordingly the need exists to improve the performance 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.

The inventors have investigated a number of compounds to ascertain whether improvements in toners for image receiving layers can be achieved. In particular they have sought to accelerate image production.

According therefore to a first aspect of the present invention there is provided 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 a tone controlling compound selected from at least one of;

(1) an alkyl disulphide substituted by a water solubilizing group;

(2) a thiazolidine carboxylic acid;

(3) a substituted or unsubstituted ^ -thiobutyrolactone;

(4) a higher alkyl thioglycolate; or

(5) a substituted rhodanine compound.

In a further aspect of the present invention there is provided a method for controlling the tone transmission density in a non-light-sensitive image receiving element of a silver halide diffusion transfer process, which comprises incorporating in the image receiving layer of said element a compound selected from:

(1) an alkyl disulphide substituted by a water solubilizing group;

(2) a thiazolidine carboxylic acid;

(3) a substituted or unsubstituted ^-thiobutyrolactone;

(4) a higher alkyl thioglycolate, or

(5) a substituted rhodanine compound,

thereby to accelerate image production in use.

The water solubilizing group of the alkyl disulphide compound is preferably a carboxylic group and the alkyl group is preferably propyl. Accordingly the

preferred compound is 3-carboxypropyl disulphide. This last compound has in fact been described in US-A-3,779,757 which relates to carboxyl-alkyl substituted disulphides for use in the stabilization of photographic images in the silver halide diffusion transfer process. There is no disclosure of its use as a tone controller.

The thiazolidine carboxylic acid may optionally be further substituted. A particularly preferred compound of this type is thiazolidine-4-carboxylic acid of the formula:

H

COOH N

\ / \

« *

Compounds of this general type have been described in GB-A-1,190,678 but only for use in light-sensitive photographic emulsions. There is no suggestion of their use as tone controllers in accordance with the present invention.

The substituted or unsubstituted Y-thiobutyrolactones in accordance with the present invention have the formula:

These may be substituted or unsubstituted, but preferably are unsubstituted.

The higher alkyl thioglycolates in accordance with the present invention are preferably those with at least ten carbon atoms in the alkyl group. For example a preferred compound of this type is octadecyl thioglycolate of the general formula:

HS.CH ₂ .COO.(CH ₂ ) ₁₇ .CH ₃

Compounds of this general type have been described in US-A-4,463,082 which reveals the utilization of propyl thioglycolate in admixture with a noble metal stabilizer. There is no disclosure of the use of the higher alkyl thioglycolates per se as tone controllers.

The substituted rhodanine compound of the present invention may have the general formula

wherein R represents a -(CH _^ ) - COOH group wherein n

is 0 to 6, and is most preferably an acetic acid group at the 3-position.

In all the foregoing cases the toner accelerates the physical development of silver in the presence of development nuclei when incorporated in a non-light-sensitive image receiving layer of a silver halide diffusion transfer process. These compounds may be used alone or in combination with other known toners in two or three layer receiver formats on film or on paper base at different levels of swell. They also may be used singularly or in admixture with each other.

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/m 2, preferably from 20 to 150 mg/m2.

The invention will now be described, by way of illustration only, with reference to the following examples:-

EXAMPLE 1

The toner, 3-carboxypropyl disulphide, was coated in a three-layer receiver format on paper base.

i) Samples were processed using PMT III activator in a suitable diffusion transfer processor (e.g. Kodak I agemate 43DT) with an unexposed PMTII projection negative, 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) of the transferred silver was measured for 6 and 12 seconds lamination (Table 1).

Table 1

Toner DT (6s) DT (12s)

3-carboxypropyl disulphide 0.59 0.90

5-methylbenzotriazole (Prior art) 0.41 0.65

2-phenyl-5-mercapto-oxadiazole (Prior art) 0.42 0.72

ii) Samples were processed with a step-wedge exposed PMTII continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured, and the 5-90 contrast index noted (Table 2) .

Table 2

Toner 5-90 contrast

3-carboxypropyl disulphide 0.94 5-methylbenzotriazole (Prior art) 1.53

2-phenyl-5-mercapto-oxadiazole (Prior art) 2.60

The results show that the toner of the invention accelerates the production of positive image, compared to the two cited toners of the prior art.

EXAMPLE 2

The toner, thiazolidine-4-carboxylic acid, was coated in a three-layer receiver format on paper base, in a conventional manner.

i) Samples were processed with unexposed PMTII projection negative, 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) of the transferred silver was measured for 6 and 12 seconds lamination (Table 3) .

Table 3

Toner DT (6s) DT (12s)

thiazolidine-4-carboxylic acid 0.56 0.90 5-methylbenzotriazole (Prior art) 0.41 0.65

2-phenyl-5-mercapto-oxadiazole 0.42 0.72 (Prior art)

ii) Samples were processed with a step-wedge exposed PMTII continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured, and the 5-90 contrast index noted (Table 4) .

Table 4

Toner 5-90 contrast

thiazolidine-4-carboxylic acid 1.07

5-methylbenzotriazole (prior art) 1.53

2-phenyl-5-mercapto-oxadiazole (prior art) 2.60

The results show that the toner of the invention accelerates the production of positive image, compared to the two cited toners of the prior art.

EXAMPLE 3

The toner, ^ -thiobutyrolactone, was coated in a three-layer receiver format on paper base, in the conventional manner.

i) Samples were processed with unexposed PMTII projection negative, 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) of the transferred silver was measured for 6 and 12 seconds lamination (Table 5).

Table 5

Toner DT (6s) DT (12s)

"3"-thiobutyrolactone 5-methylbenzotriazole (Prior art) 2-phenyl-5-mercapto-oxadiazole

(Prior c_rt)

ii) Samples were processed with a step-wedge exposed PMTII continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured, and the 5-90 contrast index noted (Table 6) .

Table 6

Toner 5-90 contrast

)$-thiobutyrolactone 1.17

5-methylbenzotriazole (Prior art) 1.53

2-ρhenyl-5-mercapto-oxadiazole (Prior art) 2.60

The results show that the toner of the invention accelerates the production of positive image, compared to the two cited toners of the prior art.

EXAMPLE 4

The toner, octadecyl thioglycolate, was coated in a three-layer receiver format on paper base, in the conventional manner.

i) Samples were processed with unexposed PMTII projection negative, 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) of the transferred silver was measured for 6 and 12 seconds lamination (Table 7).

Table 7

Toner DT ( 6s ) DT ( 12s )

octadecyl thioglycolate 0 .64 0. 94

5-methylbenzotriazole (Prior art) 0 .41 0.65

2-phenyl-5-mercapto-oxadiazole 0 .42 0.72

(Prior art)

ii) Samples were processed with a step-wedge exposed PMTII continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured, and the 5-90 contrast index noted (Table 8) .

Table 8

Toner 5-90 contrast

octadecyl thioglycolate 0.97

5-methylbenzotriazole 1.53

2-phenyl-5-mercapto-oxadiazole 2.60

The results show that the toner of the invention accelerates the production of positive image, compared to the two cited toners of the prior art.

EXAMPLE 5

The toner, rhodanine-3-acetic acid, was coated in a three-layer receiver format on paper base, in a conventional manner.

i) Samples were processed using PMTII activator in a suitable diffusion transfer processor (e.g. Kodak Imagemate 43DT) with unexposed PMTII projection negative, 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) of the transferred silver was measured for 6 and 12 seconds lamination (Table 9).

Table 9

Toner DT 6s DT 12s

rhodanine-3-acetic acid

5-methylbenzotriazole

2-phenyl-5-mercapto-oxadiazole

ii) Samples were processed with a step-wedge exposed PMTII continuous tone donor, stripped apart after 60 seconds lamination, the reflection density-log exposure curve measured, and the 5-90 contrast index noted (Table 10) .

Table 10

Toner 5-90 contrast

rhodanine-3-acetic acid 5-methylbenzotriazole 2-phenyl-5-mercapto-oxadiazole

The results show that the toner of the invention accelerates the production of positive image, compared to the two cited toners of the prior art.