WO1994010610A1 - Process for forming direct digital colour proofs on print stock material - Google Patents

Abstract

A process for obtaining multicolour images serving as a colour proof is disclosed comprising the steps of exposing information-wise a set of differently coloured photosensitive elements (7) containing silver halide, processing them to differently coloured images (12) and transferring these images by a thermal lamination and delamination successively in register on top of each other to a receptor element, (1) or (1'), bearing an adhesive layer pack, (3) or (3'), and serving as final or as temporary support for the obtained colour proof. In the preferred embodiment this information-wise exposure is a direct laser exposure, e.g. by an Ar+ laser, of digitally stored information corresponding to the four separations made on a scanner of a multicolour original. For the final support of the proof the same material can be chosen as for the actual print run.

Description

DESCRIPTION

PROCESS FOR FORMING DIRECT DIGITAL COLOUR PROOFS ON PRINT STOCK MATERIAL.

1. Field of the invention.

The present invention relates to a process for obtaining multicolour colloid images for colour proofing in graphic arts, and more particularly, for direct digital proofing.

2. Background of the invention.

In the field of pre-press graphic arts there has been a long felt need for a simple and fast technique offering "colour proofs" of high quality and reproducibility.

Photographically produced colour proofs are a simulation for multicolour halftone reproductions as will be produced by successive printing in register with the separate standard inks : magenta, yellow, cyan and black on a conventional printing press.

Press proofing for the production of colour proofs by preparing a printing plate and running the plate on the press to produce only a few copies as proof of the quality of the halftone separation transparencies used in the plate production is a very cumbersome and expensive procedure and therefore photographic processes have been developed to obtain a similar result by means of which the appearance of a print starting from particular colour separation negatives or positives can be judged by the printer and client.

So in US 4,933,258 and US 4,766,053 a method for forming a colour proof based on the successive transfer to a temporary support of several colour images obtained by exposing and developing several photosensitive elements comprising photosensitive resin layers. Finally the complete image is transferred to a permanent support being print paper stock. Products related to these method are marketed as the FUJI COLOR ART system. However this process is too insensitive to allow direct digital proofing by means of laser sources.

A process for producing a multicolour pattern using silver halide emulsion materials is described in European Patent Specification EP 0 185 410. This method comprises the following steps : (1) the scanningwise exposure of a multicolour original attached to a rotating scanner drum in order to obtain separate red light, green light and blue light output signals received by photon-detectors to produce corresponding electrical signals, which are fed into a computer,

(2) the computer controlled exposure, of differently coloured hardening developable photographic materials each comprising on a temporary support one or more hardenable hydrophilic colloid layers at least one of which contains dispersed photosensitive silver halide,

(3) transferring integrally said hydrophilic colloid layer(s) of a first of said exposed photographic materials onto a permanent support, which at its surface is less hydrophobic than the temporary support, by pressing the permanent support in the presence of an aqueous liquid against the hydrophilic colloid layer side of said photographic material and removing the temporary support, thus leaving said hydrophilic colloid layer(s) on said same permanent support, and

(4) developing the transferred exposed photosensitive silver halide with a hardening developing agent to form imagewise hardened coloured hydrophilic colloid portions and removing the non-hardened colloid portions to leave a coloured relief image on the permanent support, and

(5) producing a multicolour pattern on said same permanent support by repeating the steps (3) and (4) with one or more other scanning-wise exposed differently coloured photographic materials, the transfer procedure of step (3) being effected in image register.

Depending on the wavelenght of the scanner output laser the direct exposure by this laser of the different coloured materials requires the presence of special silver halide emulsions spectrally sensitized to the emission wavelenght of the laser. An alternative procedure consists in generating by a scanner colour separation negatives or positives on a scan film and exposing the described coloured colloid materials through these separation negatives or positives in a conventional contact-apparatus provided with an ultraviolet rich radiation source. In this way rather insensitive non-spectrally sensitized emulsions rich in chloride can be used.

Apparatuses and photosensitive materials used in accordance with the process disclosed in EP 0 305 599 are commercialized by Agfa- Gevaert N.V. under the registered trade name AGFAPROOF system. However these processes show the disadvantage that the final multicolour image is formed on a permanent support which is not the real material on which the actual print will be run. This material can consist of e.g. low quality paper stock, e.g. for newspaper printing, or coated paper for higher quality print, e.g. magazines, or a metal carrier (printing on cans, etc.) . In most cases however a paper stock is used. If the proof support and the actual print paper stock differ too much in their physical and optical properties, e.g. paper texture, gloss and dot gain, the judgment of the proof by printer or customer will be hampered because the nature of the paper background will influence the visual effect of the colour proof.

The need for wet transfer steps is another disadvantage of this AGFAPROOF system.

It is an object of the present invention to provide a colour proofing process in which the final multicolour image is formed on a permanent support, identical to the real material on wich the actual print will be run.

It is a further object of the present invention to provide a colour proofing process especially suited for so-called direct digital colour proofing comprising information-wise exposure by a scanner output laser of digitally stored information.

It is a still further object of the present invention to provide a colour proofing process which does not require wet transfer steps.

3. Summary of the invention.

The objects of the present invention are realized by providing a process for the production of a multicolour image serving as a colour proof, the process comprising the following steps :

(1) exposing information-wise each of a set of differently coloured photosensitive elements each comprising a temporary support, a stripping layer pack, and a photosensitive layer containing a silver halide, substantially non-hardened gelatin, and a coloured pigment ;

(2) forming differently coloured images by subjecting each of said exposed photosensitive elements to a processing comprising a hardening development step, a bleach-fix step, and a wash-off step of unhardened parts ;

(3) laminating by a dry thermal treatment one of said processed photosensitive elements bearing a coloured image to a receptor element comprising a support and an adhesive layer pack and peeling-off said temporary support of the thus transferred coloured image ; (4) repeating the lamination and peeling-off procedure of (3) successively with each processed photosensitive element bearing a different coloured image, each element being applied in register on top of the previous one.

The receptor element itself can be prepared by trans-laminating the adhesive layer pack from a temporary support, e.g. a polyterephtalate support, on which it is initially present, to the support of the receptor element. This procedure can easily be performed by the user to which a stock of sheets is delivered, each sheet comprising the temporary support, the adhesive layer pack and preferably an easily removable protective foil. Since the adhesive layer pack will adhere to any common print stock material, the customer has the possibility to choose as support for the finished proof that particular material on which the actual print will be run. In this way the proof can be judged visually on the same background as the actual print.

In the preferred embodiment of the present invention each information-wise exposure is a laser exposure controlled by digitally stored information corresponding respectively to the red, green, blue and black separations, produced on a scanner, of a multicolour original. In this embodiment the differently coloured photosensitive elements respectively contain a cyan, a magenta, a yellow and a black pigment. In this way direct digital colour proofs can be produced.

In a direct way of working the support of the receptor element serves as final permanent support of the colour proof, and can consist of e.g. low quality paper stock or a coated paper for higher quality print, or a metal foil, e.g. aluminium. In a more indirect way of doing the receptor element serves as a temporary support for the transferred colour image. In this embodiment the receptor element has a more complex structure. In this case the support has to be a transparent organic resin support, e.g. polyethylene terephtalate. On the side of this support, opposite to the side of the adhesive layer pack, an extra layer pack is applied comprising in successive order following layers (a) a permanent adhesive layer, (b) a siliconised base, which can be a paper base or a transparent organic resin. After transfer of the last exposed and processed relief image the thus formed composite material is splitted in two parts by delamination at the interface of said permanent adhesive layer and said silicone containing layer. Finally the separated part containing the colour proof image is adhered to any final support, chosen by the user, by means of the permanent adhesive layer.

4. Brief description of the drawings.

Fig. 1 illustrates the preparation of a receptor element (1) .

Fig. 2 illustrates the composition of a temporary receptor element (1' ) .

Fig. 3 illustrates the composition of a photosensitive element (7) and the formation of a partial image (12) in this photosensitive element by exposure and processing.

Fig. 4 illustrates the transfer of a partial image (12) formed in a photosensitive element (7) to a receptor element (1) by lamination and delamination.

5.Detailed description of the invention.

The receptor element (1) (see fig. 1) comprises a support (4) and an adhesive layer pack (3) . This adhesive layer pack is initially present on a temporary support (2), e.g. a polyethylene terephtalate resin, and preferably covered by a thin protective foil (not shown) . After removal of this protective foil by the user the adhesive layer pack can be easily trans—laminated by means of a roller laminator from that temporary support to the support of the receptor, being the real print stock material chosen by the user. Before the trans-lamination the adhesive layer pack (3) preferably comprises in successive order starting from the temporary support (2) a thin stripping layer (3-1) , optionally one or more primer layer(s) (3-2), a subbing layer (3-3) and an adhesive layer (3-4) . Due to the trans-lamination process onto the receptor the layer order is reversed and the adhesive layer comes into contact with the receptor support (4) securing effective adhesion to it. Then the delamination of the temporary support is effected at the interface temporary support / stripping layer. This procedure is illustrated in fig. 1. Is is clear that for a good delamination at the exact interface the adhesion of the stripping layer (3-1) to the underlying layers has to be stronger than the adhesion of this stripping layer to the temporary support (2) , and that the adhesion of the adhesive layer (3-4) to the support (4) has to be stronger than the adhesion of the stripping layer to the temporary support (2) . In order to assure effective adhesion the adhesion layer (3-4) contains one or more thermoadhesive polymers chosen from e.g. Co (styrene-butylacrylate-methacrylic acid), Co(styrene- butylmethacrylate-methacrylic acid) , Co(styrene-i.butylmethacrylate- methacrylic acid-metastyrene) , Co(vinylidenechloride-methylacrylate- itaconic acid) , Co(methylmethacrylate-butadiene-itaconic acid) , polyvinylacetate, Co (vinylacetate-ethylene) , Co (n.butylmethaσrylate- i.butylmethacrylate) , poly-n.butylmethacrylate, poly- .butylmethacrylate, Co(methylmethacrylate-ethylacrylate) , Co (vinylacetate-vinyllaurate) , Co(vinylacetate-vinyllaurate-itaconic acid) . A preferred thermoadhesive polymer is Co(vinylacetate- vinyllaurate) . It is preferably present in a concentration ranging from 5 to 50 g/m , and most preferably from 20 to 30 g/π . The relative ratio of vinylacetate / vinyllaurate is preferably between 100 % / 0 % and 70 % / 30 %^•; most preferably this ratio is situated around 80 % / 20 %.

An example of a suitable subbing layer (3-3) contains colloidal silica having an average particle size of 10 nm, α-quartz as matting agent, gelatin and a wetting agent.

Optionally one or more primer layer(s) (3-2) can be present between the subbing layer and stripping layer. An example of a suitable primer layer contains Co (terephtalic acid-isophtalic acid-sulphoisophtalic acid) , Co (methylmethacrylate-butadiene- itaconic acid) , and colloidal silica.

The stripping layer (3-1) is a rather thin layer with a dry tickness preferably comprised between 0.2 and 1 micron. This layer is thermoadhesive and preferably contains a mixture of polyamide and polyhydroxystyrene, in a relative ratio preferably ranging from 100 % / 0% to 70 % / 30 % ; most preferably this ratio is situated around 80 % / 20 %.

In another embodiment of the present invention (see fig. 2) the receptor element (1') shows a more complex structure. On the one side of its support, which has to be a transparent organic resin in this case, a similar adhesive layer pack (3') as decribed above is applied by a similar trans-lamination procedure. On the other side an extra layer pack is present comprising following elements : (a) a permanent adhesive layer (5) and (b) a siliconised base (6), comprising a base (6-1) which can be a paper base or a transparent organic resin, e.g. again polyethylene terephtalate, and a thin silicone layer (6-2) . In this case the receptor element serves as an intermediate temporary support for the colour proof. After transfer of the last processed pigmented image the composite material is split in two parts by delamination at the interface of the silicone containing layer and the permanent adhesive layer. The part containing the colour proof can then be applied by means of its permanent adhesive to any final support chosen by the user. The photosensitive element (7) , illustrated in fig. 3, essentially comprises a temporary support (8) , a stripping layer pack (9) , and at least one hydrophylic photosensitive layer (11) comprising substantially unhardened gelatin as binder, a silver halide emulsion, and a dye pigment providing the desired colour. A silver halide hardening developing agent and/or auxiliary developing agent can be incorporated in the layer but most preferably they are provided during processing in the developing solution. In a preferred embodiment a gelatinous undercoat (10) is present between silver halide layer and stripping layer pack. This undercoat too preferably contains some silver halide in order to assure selective hardening on the appopriate parts.

In order to obtain transferred images with a good resolution, relatively thin hardenable coloured gelatin containing coatings are used. Preferably coatings having a thickness in the range of 1 micron and 15 micron are used, and good results are obtained with pigment coloured layers containing 1 to 10 g of gelatin/πr.

•The temporary support (8) of the photosensitive element preferably is a transparent organic resin, e.g. an unsubbed cellulose triacetate sheet or an unsubbed polyethylene terephtalate sheet. This base can carry an antihalation layer or can contain itself a black pigment giving rise to a density between 0.3 and 0.8.

In the coloured photosensitive layer (11) the dye pigments are preferably used in diffusion-resistant form and can have all kinds of colour, e.g. are cyan, light-cyan, magenta, warm magenta, black, yellow, green, brown, orange, red, white or blue. Considered are likewise metallic colours such as pale gold, rich gold, copper, and silver. In other words the term "colour" in the present invention encompasses the use of all pure and mixed colours as well as black and white. In the standard procedure of making colour proofs simulating conventional four-colour printing photosensitive compositions containing respectively cyan, magenta, yellow and black pigments are used. In the production of superposed multicolour colloid patterns these standard pigments have to match with the spectral properties of the standard process inks as close as possible. Information about standard colour inks can be found in H.M.Cartwright - Ilford Graphic Arts Manual (1962) Vol. I - pages 502 to 504. For letterpress printing these standard colour inks have colour tones as defined in DIN 16538 and for offset printing the colour tones defined in DIN 16539. Further information about colour tones can be found for the USA in the GATF-Colour Charts.

It has been found experimentally that pigments, which are insoluble or very poorly soluble in water and in organic liquids of the alcohol or polyhydric alcohol type, e.g. glycerol, fulfil the requirements of resistance to diffusion. For colour proofing purposes a hardenable colloid layer in the present photographic material should preferably contain said pigments in a concentration sufficiently high for obtaining an optical density of at least 0.35 in the wavelength range of maximum absorption.

Pigments particularly suitable for use in the present invention are known organic non-migratory pigment type dyes, e.g. obtainable under the Trade Marks "HELIO-ECHT", "PIGMOSOL" and "COLANYL" dyes. " "HELIO-ECHT", "PIGMOSOL" and "COLANYL" are diffusion resistant organic pigments that can be dispersed in aqueous medium with the aid of a dispersing agent. These pigments excel in resistance to light, heat, acids, bases, oxidizing agents, and solvents. They are insoluble in hydrophilic colloids such as gelatin.

When in addition to cyan, magenta and yellow relief patterns a black relief pattern is formed in colour proofing, preferably carbon black is used. Apart from carbon black mixtures of coloured pigments may be applied as described e.g. in US 4,427,757.

The photosensitive silver halide used in the silver halide emulsion layers of the photographic material used according to the present invention is e.g. silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or mixtures thereof. The silver halide emulsions may be coarse or fine-grained and can be prepared by any of the well known procedures, e.g. as single jet or double jet precipitation technique.

In a preferred embodiment of this invention the different photosensitive elements are exposed scanningwise by laser radiation, provided by the output laser of a scanner, and controlled by digital information derived from the four colour separations, made on a scanner, of a multicolour original. If the format allows it the scanningwise exposure can be performed simultaneously on four different photosensitive elements without stopping the rotation of the scanner drum. In this preferred embodiment rather sensitive emulsions must be used containing substantial amounts of bromide and/or iodide anions. All kind of output lasers can be used, e.g. an Argon ion laser, a Helium-Neon laser or a semiconductor laser emitting in the infra-red region. For a proper spectral sensitization with respect to a particular laser beam wavelength the usual mono- or polymethine dyes such as acidic or basic cyanines, hemicyanines, oxonols, hemioxonols, styryl dyes or others, also tri- or polynuclear methine dyes, e.g. rhodacyanines or neocyanines may be used. Such spectral sensitizers are described, e.g., by F.M. HAMER in "The Cyanine Dyes and Related Compounds" (1964) Interscience Publishers, John Wiley & Sons, New York. In a particularly preferred embodiment an Argon ion laser is used as exposure source. In this case a sensitizer for the blue spectral region is advantageously used.

The silver halide emulsions can be of the conventional negative working surface-sensitive type, in particular when separation negatives are used as originals. In this case they can be chemically sensitized, e.g. by adding sulphur-containing compounds, e.g. allyl isothiocyanate, allyl thiourea, sodium thiosulphate and the like, during the chemical ripening stage. Also reducing agents, e.g. the tin compounds described in the Belgian Patent Specifications 493,464 and 568,687, and polyamines such as diethylenetriamine or derivatives of aminomethane-sulphonic acid, e.g. according to the Belgian Patent Specification 547,323, can be used as chemical sensitizers. Other suitable chemical sensitizers are noble metals and noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium. This method of chemical sensitization has been described in the article of R.KOSLOWSKY, Z. Wiss. Photogr. Photophys. Photoσhem. 46, 65-72 (1951) .

Alternatively the silver halide emulsions can be of the direct positive type, in particular when separation positives are used as originals. These direct positive emulsions can be externally prefogged and containing an electron acceptor, or they can be of the unfogged type containing internal electron traps and working with nucleating agents and fogging development ; in the latter case a nucleating agent can be present in at least one of the layers of the photosensitive composition or in the developing solution.

The silver halide emulsions may contain the usual stabilizers, e.g. homopolar or salt-like compounds of mercury with aromatic or heterocyclic rings such as mercaptotriazoles, simple mercury salts, sulphonium mercury double salts and other mercury compounds. Other suitable stabilizers are azaindenes, preferably tetra- or penta-azaindenes, especially those substituted with hydroxyl or amino groups. Compounds of this kind are described by BIRR in Z. Wiss. Photogr. Photophys. Photochem. 47,, 2-27 (1952) . Still other suitable stabilizers are amongst others heteroσyclic mercapto compounds, e.g. phenylmercaptotetrazole, quaternary benzothiazole derivatives and benzotriazole.

The pigmented emulsion layer further preferably contains a polymer latex improving the wet adhesion of the hardened image parts during the wash-off step. A preferred latex is Co(styrene- butadiene) . Other useful latices include polymethylacrylate, polyethylacrylate, Co(methylmethacrylate-butadiene) , Co(styrene- butadiene-acrylamide-acrylic acid) , polyurethaan and poly- vinylisobutylether.

In the photosensitive element there is preferably a thin gelatinous undercoat (10) containing a.o. spacing agents, matting agents, plasticizers and anti-halo compounds. Suitable anti-halo dyes are described in i.a. US 4,092,168, US 4,311,787, DE 2,453,217, and GB 7,907,440. As stated above some silver halide is preferably present in thios gelatinous undercoat.

The stripping layer pack (9) , positioned on the temporary support of the photosensitive element, comprises in successive order starting from the temporary support (8) (see again fig. 3) a stripping layer (9-1), optionally one or more primer layer(s) (9—2) and a subbing layer (9-3) . The dry thickness of the stripping layer preferably ranges from 1 to 6 micron and is most preferably about 2 micron. So this stripping layer (9-1) of the stripping layer pack is considerably thicker than the stripping layer (3-1) of the adhesive layer pack of the receptor element. As it is the case with stripping layer (3-1) the stripping layer (9-1) is thermoadhesive and preferably contains a mixture of polyamide and polyhydroxystyrene in a preferred ratio analogous to layer (3-1) . The subbing and optional primer layers are preferably similar to the corresponding layers of the adhesive layer pack of the receptor element.

Any of the layers of the photosensitive element may further comprise various kinds of surface-active agents in the photographic emulsion layer or in at least one other hydrophilic colloid layer. Suitable surface-active agents include non-ionic agents such as saponins, alkylene oxides e.g. polyethylene glycol, polyethylene glycol/polypropylene glycol condensation products, polyethylene glycol alkyl ethers or polyethylene glycol alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or alkylamides, silicone-polyethylene oxide adducts, glycidol derivatives, fatty acid esters of polyhydric alcohols and alkyl esters of saccharides; anionic agents comprising an acid group such as a carboxy, sulpho, phospho, sulphuric or phosphoric ester group; ampholytic agents such as aminoacids, aminoalkyl sulphonic acids, aminoalkyl sulphates or phosphates, alkyl betaines, and amine-N-oxides; and cationic agents such as alkylamine salts, aliphatic, aromatic, or heterocyclic quaternary ammonium salts, aliphatic or heterocyclic ring-containing phosphonium or sulphonium salts. Preferred surface-active agents are compounds containing perfluorinated alkyl groups.

The processing of the different exposed photosensitive elements each giving rise to a partial coloured image involves a hardening development step, a bleach-fix step, a wash-off step and drying.

The hardening development of a latent silver image proceeds with commonly used hardening developing agents, also called tanning developing agents for effecting the development of the silver halide and producing oxidized developing agent acting as hardening agent for gelatin. Suitable hardening developing agents are : 1,4-dihydroxy benzene compounds such as hydroquinone, chlorohydroquinone, bromohydroquinone, toluhydroquinone, morpholinemethyl hydroquinone and sulfohydroquinone. Apart from the main hardening developing agent an auxiliary non-tanning developing agent can be used. Typical auxiliary developing agents include 3—pyrazolidinone developing agents, e.g. 1—phenyl-3-pyrazolidinone, l-phenyl-4,4-dimethyl-3-pyrazolidinone, l-phenyl-4-methyl-4'-hydroxymethyl-3-pyrazolidinone and N-methyl-p-aminophenol sulphate.

As stated above the developing agent (s) can be incorporated in the photosensitive silver halide material and/or in a developing bath. When incorporated in the photographic material it or they may be present in the silver halide emulsion layer or in the optionally present gelatinous undercoat. In case the developing agent (s) are present in the photosensitive element itself the development is carried out with a so-called activator liquid being an aqueous alkaline solution substantially free from developing agents.

Other adjuvants well known to those skilled in the art may be added to the developer or activator liquid used in accordance with the present invention. A survey of conventional developer addenda is given by Grant Haist in "Modern Photographic Processing" - John Wiley ans Sons - New York (1979) p. 220-224. Examples of such addenda include complexing agents for calcium and magnesium ions, present in hard water, e.g. ethylene diamine tetraacetic acid and analogues compounds. Further can be present anti-foaming agents, surface-active agents, biocides, thickening agents like polystyrene sulphonate and antioxidants like benzoate and cyclodextrine. The developing liquid can contain so-called anti-sludge agents in order to reduce dirt streaks on developed material.

In order to obtain pure colours the development step is followed by a bleach-fix step wherein the developed metallic silver is bleached and removed together with residual undeveloped silver halide. The bleach-fixing bath preferably contains conventional fixing agents like sodium or ammonium thiosulphate, and conventional bleaching agents like complexes of iron(III) and polyaminocarboxylic acids, e.g. iron(III)—ethylenediamine-tetraacetic acid mono sodium salt.

The wash-off step for removal of the non-hardened parts is preferably performed by means of warm water.

The structure of a partial image (12) after exposure and processing is illustrated in the right part of fig. 3.

The successive transfer of each differently coloured partial image (12) , the first to the receptor element and the following ones successively in register on top of each other occurs preferably by conveying the two elements together in dry state through a roller laminator to which heat is applied. After each transfer the temporary support is peeled-off at the interface support (8) / stripping layer (9-1) . This is illustrated in fig. 4. In the right part of this figure the adhesive layer pack (3) and and the stripping layer pack (9) are drawn as one layer for sake of simplicity. It is clear that in order to perform a good delamination at the desired interface the adhesion of the temporary support (8) to the stripping layer pack (9) should be the weakest of all the adhesive forces in the total composite pack.

In a preferred procedure a multicolour printing proof is made according to the principles of subtractive colour photography starting with the transfer a first relief image being a cyan image, produced from the red selection of the multicolour original. In successive order a magenta, yellow and black relief image is transferred to the same support. However, the order wherein the colour relief images are made can be chosen arbitrarily.

The finished proof can be given a matted appearance by laminating and delaminating a material with a rough surface to it, e.g. a paper or a draft film. A smooth appearance can be restored by laminating and delaminating a material with a smooth surface to it, e.g. a polyethylene terephtlate foil.

The obtained multicolour relief image can be protected by a transparent resin topcoat, which according to a preferred embodiment is applied by spraying a solution of film forming resin onto the relief image and drying. A suitable "spray-cover" consists of polyisobutyl- methacrylate.

The following examples illustrate the present invention without however limiting it thereto.

EXAMPLES

EXAMPLE 1

- Preparation of the receptor element.

Onto an unsubbed polyethylene terephtalate support having a thickness of 100 micron and serving as temporary support was coated an adhesive layer pack comprising successively a stripping layer, a subbing layer and an adhesive layer.

For the preparation of the stripping layer eight parts of a 10 % solution of polyamide (trade name AMILAN CM-8000, TORAY ind. Ldt. ) in warm methanol and two parts of a 10 % solution of polyhydroxystyrene( trade name MARUZEN Resin M) in methylcellosolve were mixed together and coated onto the support as to obtain a dry thickness of 0.45 micron. No primer layer was present. The subbing layer contained gelatin at a coverage of 233 mg/m , colloidal silica having an average particle size of 10 n at 520 mg/m , α-quartz as matting agent and saponin as wetting agent. The adhesive layer was coated from a 20 % solution of Co(vinylacetate-vinyllaurate) (trade name VINNAPAS B100, WACKER CHEMIE) as to obtain a dry thickness of 30 micron.

By conveying the temporary support carrying the adhesive layer pack and a sheet of print stock paper through a roller laminator at a speed of 60 cm/min and a temperature of 75 °C the adhesive layer pack was trans-laminated to the paper and the polyethylene terephtalate foil was peeled-off. - Preparation of the photosensitive elements.

Onto an unsubbed polyethylene terephtalate layer having a thickness of 100 micron a stripping layer, a subbing layer, a gelatinous undercoat and a pigmented silver halide layer were coated in that order. Like the stripping layer of the receptor this stripping layer contained a mixture of polyamide and polyhydroxyethylene but was coated as to obtain a dry thickness of 2 micron. The subbing layer was identical to the one of the receptor element. The gelatinous undercoat was a non-pigmented gelatin binder layer containing 0.7 g/m of gelatin and 0.095 gAir^* of a matting agent on the basis of silica particles covered at the outside with urea-formaldehyde resin. A silver halide emulsion consisting of 83.6 mole % of chloride, 16 mole % of bromide and 0.4 mole % of iodide was coted on top at silver coverage of 0.25 g/m , expressed as AgNθ3, and at a gelatin coverage of 1.8 g/m . The emulsion was sensitized to the blue spectral region. The layer further contained the cyan coloured pigment FLEXONYL BLUE Paste (C.I. Index No 74,160) at a concentration of 6.3 g per liter coating composition corresponding to a coverage of 0.126 g/m'^** of solid pigment.

Three other photosensitive elements were prepared with similar compositions but different pigment pastes. The magenta pigment was HELIOECHTCARMIN BB TEIG (Colour Index Nr. 12,485) and the yellow pigment was HELIOECHTGELB GRN 7476 Feinteig (Colour Index Nr. 21,100) . Said pigment pastes were used in an amount of 14.5 g and 17.6 g respectively per liter of coating composition. In the black pigment paste carbon black was used in admixture with the above mentioned FLEXONYL BLUE respectively in an amount of 15.75 g and 1.26 g per liter of coating composition.

- The scanningwise exposure.

The scanningwise exposure proceeded on a commercial scanner operating with an argon ion laser source emitting at 488 nm.

The four photographic materials containing the differently pigmented coatings, said materials having DIN A4 format, were arranged adjacently on the scanner drum, so that in a single step all the pigmented coatings were exposed without stopping the rotation of the drum. - The processing.

The first of the exposed photosensitive elements was hardening developed by dipping it for 30 s in a developing solution, having following composition : hydroquinone 3.0 g potassium hydroxide 25 g potassium carbonate 150 g potassium bromide 0.5 g sodium sulphite 2.0 g

1-phenyl—3-pyrazolidinone 4.0 g mono sodium salt of ethylenediamine- tetra-acetic acid 1.0 g

Thereupon the developed material was led through a bleach-fix bath containing sodium thiosulphate and the mono sodium salt of iron(III)-ethylenediamine tetra—acetic acid.

To obtain a cyan coloured relief image the hardening developed and bleach—fix processed material was wash—off processed with a warm (35 °C) water spray. The relief image was dried.

The processing was repeated with the other photosensitive elements containing different pigments. In this way four different relief images were obtained.

- Transfer of the relief images.

The photosensitive element containing the exposed and processed cyan image was laminated while applying heat to the adhesive side of the receptor element by conveying the elements through a CODOR LAMIPACKER LP650 roller laminator at a speed of 50 cm/min. The upper roller guiding the image element was heated to about 95 °C and the under roller guiding the receptor was heated to about 110 °C. Then the temporary polyethylene terephtalate support was peeled-off. The procedure was repeated with the other exposed and processed images which were transferred in register on top of each other.

Finally a multicolour proof of excellent quality was obtained. EXAMPLE 2

The previous example was repeated with the exception that the receptor element was replaced by a more complex structure. The support was a transparent polyethylene support. On one side the same adhesive layer pack was applied as in example 1. On the other side an extra layer pack was applied comprising in successive order following layers (a) a permanent adhesive layer containing polyvinylacetate, (b) a commercial siliconised polyethylene coated paper base, known as "MAC TAC REMOVABLE ADHESIVE". After transfer of the last colour relief image the thus formed composite material was split in two parts by delamination at the interface of the permanent adhesive layer and the silicone containing layer. Finally the separated part containing the colour proof image was adhered to print paper stock.

An excellent multicolour proof was obtained.

Claims

1. Process for the production of a multicolour image for colour proofing comprising the following steps :

(1) exposing information-wise each of a set of differently coloured photosensitive elements each comprising a temporary support, a stripping layer pack, and a photosensitive layer containing a silver halide, substantially non-hardened gelatin, and a coloured pigment ;

(2) forming differently coloured images by subjecting each of said exposed photosensitive elements to a processing comprising a hardening development step, a bleach-fix step, and a wash-off step of unhardened parts ;

(3) laminating by a dry thermal treatment one of said processed photosensitive elements bearing a coloured image to a receptor element comprising a support and an adhesive layer pack and peeling-off said temporary support of the thus transferred coloured image ;

(4) repeating the lamination and peeling-off procedure of (3) successively with each processed photosensitive element bearing a different coloured image, each element being applied in register on top of the previous one.

2. Process according to claim 1 wherein each information-wise exposure of each differently coloured photosensitive element is a laser exposure controlled by digitally stored information corresponding respectively to a blue, a green, a red and a black separation of a multicolour original produced on a scanner.

3. Process according to claim 2 wherein said laser exposure is performed by an Argon ion laser.

4. Process according to any of claims 1 to 3 wherein said receptor element is itself prepared by trans-laminating said adhesive layer pack, initially present on a temporary support, to said support of said receptor element.

5. Process according to any of claims 1 to 4 wherein said adhesive layer pack of said receptor element comprises, in successive order starting from the support, an adhesive layer, optionally one or more primer layer(s), a subbing layer and a stripping layer.

6. Process according to claim 5 wherein said adhesive layer of said receptor element contains a vinylacetate-vinyllaurate copolymer.

7. Process according to claim 6 wherein the relative ratio of vinylacetate / vinyllaurate of said copolymer is comprised between 100 % / 0 % and 60 % / 40 %.

8. Process according to any of claims 1 to 7 wherein said stripping layer pack of the photosensitive element comprises, in successive order starting from said temporary support, a stripping layer, optionally one or more primer layer(s), and a subbing layer.

9. Process according to any of claims 5 to 8 wherein said stripping layer of said adhesive layer pack of said receptor element and/or said stripping layer of said stripping layer pack of said photosensitive element contain(s) a mixture of polyamide and polyhydroxystyrene.

10. Process according to claim 9 wherein the relative ratio of polyamide to polyhydroxystyrene in said mixture is comprised between 100 % / 0 % and 70 % / 30 %.

11. Process according to any of claims 1 to 10 wherein said support of said receptor element is the final support of the colour proof and consists of print stock paper.

12. Process according to claim 11 wherein said print stock paper is coated paper.

13. Process according to any of claims 1 to 11 wherein said support of said receptor element is the final support of the colour proof and consists of a metal foil.

14. Process according to claim 13 wherein said metal foil is an aluminium foil.

15. Process according to any of claims 1 to 10 wherein said receptor element serves as a temporary carrier of the transferred image, its support is a subbed transparent organic resin and it contains, opposite to the side of the adhesive layer pack, an additional layer pack comprising in successive order following elements :

(a) a permanent adhesive layer,

(b) a siliconised base.

16. Process according to claim 15 comprising the following additional steps :

(5) splitting the thus formed composite material in two parts by delamination at the interface of said permanent adhesive layer and said siliconised base ;

(6) adhering the separated part containing the transferred coloured image to a final support by means of said permanent adhesive layer.