GB2081920A - Photographic colour reversal process - Google Patents

Abstract

A photographic colour reversal process of reproduction is provided in which, after black and white development of the imagewise exposed photographic element, some or all of the unused developing agent is left in the element and in which the photographic element contains additional silver halide over and above that required to produce Dmax in the colour image such that on development in the reversal stage using a colour-forming developing agent the additional silver halide is sufficient to ensure that the residual black and white developing agent is oxidised. The colour image may be a retained image or a transfer image. The amount of residual black and white developing agent can be reduced by draining the developed element. When the colour image is a transferred image, the amount of residual black and white developing agent is reduced on lamination of the photographic element to an image-receiving material or cover sheet. The process can be carried out using only one processing solution, i.e. the black and white developer. The colour- forming developing agent can be introduced by unblocking and/or from the image-receiving material or cover sheet. The black and white developing agent may be incorporated in the photographic element.

Description

SPECIFICATION Photographic colour reversal process This invention relates to photographic colour reversal processes of reproduction and to materials useful therefor.

The usual practice in carrying out a reversal process, whether to produce a transferred or a retained image, is to remove the residual black-and-white developing agent(s) from the photographic element when the first silver image has been developed by washing.

Thus, in the Example described in U.K. Specification 1,505,566 a negative working silver bromide emulsion containing a sulphonamidonaphthol dye-releasing redox reagent (compound XLII of U.K. Specification 1,405,662) is exposed and developed in 'Kodak' (registered trade mark) developer DK-50 (which is a non-cross-oxidising developer solution) and is then washed and dried to remove the processing solution while being fogged in room-light preparatory to processing with a cross-oxidising developing agent to produce a positive transferred dye image.

We have now found that it is not necessary to remove some or even any of such residual developing agent provided that enough developable silver halide is present during the second stage of the process to oxidise all the residual developing agent and to oxidise sufficient colour-providing developing agent to form a colour image.

According to the present invention there is provided a method of producing a positive colour image utilising a photographic element comprising a support and a photosensitive silver halide layer which layer contains an excess of silver halide over the amount of silver halide required to produce said colour image, said silver halide having associated therewith either a compound which on reaction with oxidised electron transfer agent in an alkaline developer releases a diffusible dye or dye precursor or a compound which on reaction with oxidised colour developing agent in alkaline developer forms a non-diffusible dye, said method comprising the steps of:: (i) imagewise exposing said photosensitive silver halide layer, (ii) developing said layer using a developer containing a black and white developing agent the oxidation product of which does not react with said compound, (iii) allowing unused developing agent to remain in said photographic element, (iv) rendering developable and developing the remaining photosensitive silver halide using (v)a(1) either said electron transfer agent to form an imagewise distribution of said diffusible dye or dye precursor and (v)a(2) allowing at least a portion thereof to diffuse in register into a dye image-receiving layer or (v)(b) using said colour developing agent to form an imagewise distribution of said non-diffusible dye in said material, said excess of photosensitive halide being sufficient, on being rendered developable, to oxidise the black and white developing agent present in the photographic element after step (iii).

To carry out a colour reversal process of the invention wherein some or all of the residual developing agent from the first stage of development is allowed to remain in the photographic element, the element as manufactured for use must contain more silver halide than is required to produce Dmax in the colour image.

This excess silver halide may be incorporated in the usual emulsion layers, i.e. the emulsion layers sensitised to the required bands of the spectrum and containing the compounds necessary to provide the required colours, or may be incorporated in the element as an extra layer, which is preferred for some embodiments of the invention described below. In the latter case the excess silver halide should have a sensitivity such that it is not rendered developable by the first, imagewise, exposure of the photographic element. To meet this requirement a slow, fine grain, emulsion is preferred. Such an emulsion may be coated as the extra layer providing the excess silver halide over or between the usual emulsion or other layers since it will not scatter the exposing light appreciably.Such an extra emulsion layer should be separated from the other emulsion layers by a layer containing a scavenger for oxidised developing agent so as to avoid unwanted colour formation by the action of the oxidised developing agent originating in this extra emulsion layer. Such a scavenger is di-octyl hydroquinone. The amount of scavenger should be equivalent to the amount of developable silver halide in the extra layer. The extra silver halide may be prefogged provided it is separated from the usual layers by a timing layer.

To develop the developable silver halide in the second stage of the process a colour-forming developer must be provided. This may be an electron transfer agent when it is desired to cross-oxidise a dye image-providing compound to form the image dye, e.g. a redox dye releaser, or may be a colour developing agent which on oxidation couples with a colour coupler to form a dye, e.g. an immobile dye. The colour-forming developer may be introduced into the processing composition for the second stage of the process by unblocking of blocked colour-forming developers, e.g. a blocked electron transfer agent and/or from a sheet containing the colour-forming developer which is laminated to the photographic element for the second stage.

In the present invention the quantity of residual non-colour-forming developing agent in the photographic element is lowered by steps which do not include washing. Such steps are removal of the element from the first processing bath, draining and lamination of the element with a receiving sheet or a cover sheet which normally absorbs some of the liquid in the element. Such receiving sheets or cover sheets are used in colour transfer processes which constitute the preferred embodiments of the invention.

In a preferred embodiment of the invention the colour image formed in the second stage of the process is a colour transfer image, for example, an image formed by imagewise transfer of a dye or dyes from a negative-working light-sensitive material containing redox dye releasers.

Instead of the redox dye releasers cited above, dye-providing compounds such as are described in U.S.

Patent 3,227,550 or in U.K. Specification 1489695 or German Specification 2613005 may be used. It is preferable to use a mordant skim between the image-forming and image-receiving layer as described in U.K.

Specification 1,537,079.

In one form of colour transfer process of the invention the colour transfer image is obtained from an integral system such as a photographic assemblage comprising the usual emulsion layers, an opaque layer, a background layer for viewing the dye image, a dye image-receiving layer, and, in an additional layer, the extra silver halide required to oxidise the residual developing agent. In addition, a cover sheet and a rupturable pod of processing liquid is included in the assemblage. In this material the extra, or sacrificial, silver halide layer may be coated within the opaque layers as an alternative to coating it under or over the usual emulsion layers or in the cover sheet - the latter location further obviating the formation of unwanted colour.

As indicated above, this excess silver halide layer should be so designed that it does not develop into fog during the first (negative) stage of development but does develop during the second (positive) stage.

In another embodiment of the invention the colour transfer image is formed in a layer which is separated from the light-sensitive photographic element after formation of the image, i.e. a peel apart system.

In peel apart systems, timing of the introduction of the colour-forming developing agent, usually an electron transfer agent, from the receiving sheet can be achieved by delaying lamination until negative development is substantially complete. For integral systems some other delaying mechanism must be introduced. Physical blocking by coating the colour-forming developer or ETA in another layer remote from the emulsion coats and protected, if desired, by a timing layer, may be used. Alternatively, chemical blocking by incorporating the colour-forming developer as e.g. a derivative which is released by alkaline hydrolysis may be used.

The silver halide remaining after the first (negative) stage of development has been completed may be rendered developable for the second (positive) stage to proceed by a variety of means. In laminate and peel apart systems, where the cover/receiver sheet is applied and subsequently removed, conventional light fogging by conducting the second stage in normal room light is a convenient method. But it may be sufficient merely to leave the system to develop into fog, particularly where, e.g. high pH processes and chloride emulsions are involved. This reaction can be accelerated by applying heat after the lamination, giving a simple and convenient process.Developability may also be induced by means of a fogging agent, and this will be the most appropriate means for an integral in-camera process; in that case it must be incorporated in a blocked form to ensure the requisite time delay so that it does not react during the first stage of development. Suitable blocking mechanisms are chemical - e.g. a derivative that is hydrolysed by the alkali of the developer to release the foggant, or physical, e.g. by coating it in a layer remote from the emulsion layers and separated by a timing layer from them.

With dye transfer chemistries, after peeling apart the receiver from the emulsion donor sheet it may be desirable to give a wash to remove deleterious chemicals and to reduce the pH to improve the keeping quality of the image. In the case of integral sytems, however, it will be necessary, and in other cases it may be preferable, to reduce the pH by the use of conventional polymeric acid and timing layers. These may be coated on either base in positions obvious to those skilled in the art, where they will not interfere with image formation. Since the process has gone to completion, the time at which the pH reduction occurs is not critical.

In other embodiments of the invention the colour image is a retained image formed by reaction of the oxidised developing agent formed in the second stage of the process after the residual developing agent from the first stage has been consumed. The retained image may be formed by the reaction of oxidised colour developing agent with a colour coupler. The oxidised colour developing agent may be formed from a blocked colour-coupling developer contained in an emulsion layerwhich is unblocked by the alkaline processing composition after an appropriate period. In this embodiment the colour coupler may be incorporated in the photosensitive element and the colour developer in a cover sheet so that when the cover sheet is laminated to the element in the second stage of processing the colour developer diffuses into the element The colour coupling developing agent may be of the p-phenylene diamine type and may be coated in a gelatin layer on the cover sheet. This system necessitates peeling apart and bleaching and fixing the silver.

The process of the invention is illustrated by the following Examples: 1. Negative, donor sheet, coating (All coating weight figures are expressed in mg per sq.m.) Layer 9 Gelatin 1075 Scavenger 700 BVSME 8 8 Gelatin 1200 Blue Sens. Emulsion Ag 500 Antifoggant 0.05 g/mole Ag Scavenger 29 BVSME 9 7 Gelatin 1200 Yellow RDR (a) 550 BVSME 9 6 Gelatin 1075 Scavenger 700 Carey Lea Silver Ag 180 BVSME 8 5 Gelatin 1200 Green Sons. Emulsion Ag 530 Antifoggant 0.1 g/moleAg BVSME 9 4 Gelatin 1200 Magenta RDR (b) 550 BVSME 9 3 Gelatin 1075 Scavenger 700 BVSME 8 2 Gelatin 1200 Red Sons.Emulsion Ag 230 Antifoggant 0.4 g/mole Ag Cyan RDR (c) 400 BVSME 9 1 Gelatin 1075 BVSME 8 Anti-halo 'Estar' Support The compounds used were the following: Yellow RDR (a)

Magenta RDR (b)

Cyan RDR (c)

Silver chlorobromide emulsions, suitably sensitized were used. The RDRs were incorporated as conventional dispersions in the water-immiscible solvent, 1 ,4-cyclohexane dimethylene-bis-2-ethyl hexanoate.

The scavenger was di-dodecyl hydroquinone.

The antifoggant was 3'-(Tetrazo-5-thioi-yl)acetanilide sodium salt.

BVSME is bis(vinylsulphonylmethyl)ether.

2. Positive, receiver sheet, coating Pigskin Gelatin 5000 Mordant 5000 BVSME 75 Formaldehyde 35 ETA 430 Coated on antistatic'Estar' base.

ETA is 1-phenyl-4-hydroxymethyl-4-methyl pyrazolidone Mordant X is terpoly (styrene- [ N-vinylbenzyl-N-benzyl-N,N-dimethyli ammonium chloride) divinyl benzyl.

Example 1 A sheet of the negative material was exposed using a colour step wedge giving neutral, red, green, blue, cyan, magenta and yellow exposures. A dry mordant sheet was hinged to the negative at one end using a small strip of PVC tape, and the exposed negative only was soaked in the developer solution for 321 minutes at 82.5 F using a little agitation, the mordant sheet being left dry.

The developer solution comprised: Distilled water 100 ml Sodium Hydroxide 2.5 g Potassium Bromide 0.5 g 5-Methyl Benzotriazole 0.05 g Sodium Sulphite 5.0 g Glycin 0.7 g 11 -Amino undecanoic acid 0.15 g On completion of this first stage of development the negative was removed from the solution, drained (approx.5 seconds) and sandwiched with the attached dry mordant sheet by passing the two sheets in register between a pair of stainless steel nip rollers. Light fogging was started 10 seconds after lamination and was carried out by moving the laminate over a 'Photoflood' lamp at a distance of approximately six inches for 15 seconds. After a further 4 minutes the sandwich was peeled apart to reveal a good positive image.

Example 2 Example 1 was repeated except that the glycin in the developer solution was replaced by 0.35 g of t-butylhydroquinone. A similar positive was obtained.

Example 3 A cover sheet was prepared by coating 'Estar' base with gelatin at 10.76 g/sq.m containing the colour developer N-ethyl-N-hydroxyethyl-p-phenylenediamine sulphate at 2.69 g/sq.m, with 624 mg sodium carbonate, 269 mg sodium sulphite and 161 mg BVSME persq.m.

A sheet of a conventional colour coupler-containing print material with negative emulsions - 'Ektacolor' 74 paper - was exposed and processed as in Example 1 using the same solution but without the 11-amino undecanoic acid. The development was continued for 10 minutes at 82.5 F, before laminating with the cover sheet and fogging as in Example 1. The sheets were peeled apart 4 minutes after lamination and the 'Ektacolor' paper sheet rinsed, followed by the normal 'Ektaprint' 2 chemistry bleach/fix and washing steps.

Colour coupling was found to have taken place only where required to give a reversal image showing that the invention may be performed with colour coupling reactions as well as with dye releasers.

This Example shows also that the invention may be extended to chemistries in which oxidative coupling forms a mobile dye or releases a preformed dye. The colour coupling developer would be contained in a receiving layer structure of the type used in the other examples in this invention; bleaching, fixing, etc.

would obviously then be unnecessary. Such chemistries are described in U.S. Patents 3,227,550, 3,227,552 and 3,227,554.

In the present invention the presence of an ETA (electron transfer agent) is unnecessary during the first, negative, stage of development. It is only necessary to introduce the ETA for the second, positive stage. This may most conveniently be done by incorporating it in the receiver/cover sheet. As an extension of the present invention, chemically or physically blocked ETA's could be introduced at any convenient position, providing that their release was so timed as to coincide approximately with the lamination step. Clearly the use of blocked ETA's is essential for the practice of this invention in the integral mode, where donor and receiver layer are preregistered, and hence lamination effectively occurs at the start of the processing cycle.

The process of the invention can be carried out using only one processing solution, i.e. the black and white developer. The colour-forming developing agent can b,e introduced by unblocking and/or from the image-receiving material or cover sheet The black and white developing agent may be incorporated in the photographic element.

Claims (10)

1. A method of producing a positive colour image utilising a photographic element comprising a support and a photosensitive silver halide layer which layer contains an excess of silver halide over the amount of silver halide required to produce said colour image, said silver halide having associated therewith either a compound which on reaction with oxidised electron transfer agent in an alkaline developer releases a diffusible dye or dye precursor or a compound which on reaction with oxidised colour developing agent in alkaline developer forms a non-diffusible dye, said method comprising the steps of;; (i) imagewise exposing said photosensitive silver halide layer, (ii) developing said layer using a developer containing a black and white developing agent the oxidation product of which does not react with said compound, (iii) allowing unused developing agent to remain in said photographic element, (iv) rendering developable and developing the remaining photosensitive silver halide using (v)a(1) either said electron transfer agent to form an imagewise distribution of said diffusible dye or dye precursor and (v)a(2) allowing at least a portion thereof to diffuse in register into a dye image-receiving layer or (v)(b) using said colour developing agent to form an imagewise distribution of said non-diffusible dye in said material, said excess of photosensitive halide being sufficient, on being rendered developable, to oxidise the black and white developing agent present in the photographic element after step (iii).

2. A method according to claim 1 wherein the agent used in step (iv) is formed by release from a precursor therefor.

3. A method according to claim 1 wherein the electron transfer agent used in said step (v)a(l) is formed by release from a blocked electron transfer agent.

4. A method according to any of the preceding claims wherein the agent used in step (iv) diffuses into said silver halide layer from a layer which is separable from said photographic element or which is coated on said support as an additional layer.

5. A method according to any of claims 1 to 4 wherein the unused developing agent remaining in the photographic element is the residue left after allowing the element to drain after step (ii).

6. A method according to any of claims 1 to 5 wherein the unused developing agent remaining in the photographic element is the residue left after laminating the element with an image-receiving sheet or a cover sheet after step (ii).

7. A method according to any of the preceding claims wherein step (iv) is accelerated by heating the photographic element.

8. A method according to claim 1 substantially as described in Example 1,2 or 3.

9. A photographic element which comprises a support, a negative-working silver halide emulsion layer and an image-providing compound associated with said layer and also which comprises additional silver halide contained in said layer or in a distinct layer and a black and white developing agent, the amount of additional silver halide being sufficient to oxidise all or nearly all of said black and white developing agent.

10. A photographic element according to claim 9 wherein said additional silver halide is in a distinct layer which layer is separated from said silver halide emulsion layer by a layer containing a scavenger for oxidised developing agent produced by said additional silver halide.