WO1996010216A1

WO1996010216A1 - Negative or positive working surprint colour proofing system

Info

Publication number: WO1996010216A1
Application number: PCT/EP1995/003424
Authority: WO
Inventors: Eddie Daems; Luc Leenders; Rudi De Busser
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1994-09-27
Filing date: 1995-08-30
Publication date: 1996-04-04
Anticipated expiration: 1997-03-27

Abstract

A negative or positive working method is disclosed for the formation of a surprint colour proof in pre-press graphic arts. A pigmented photosensitive composition with a specific layer arrangement as described in the specification is subjected image-wise to exposure by actinic radiation thereby undergoing photopolymerisation in the exposed areas. Depending on the monomer/binder ratio either the information-wise exposed areas or the information-wise non-exposed areas are transferred to a receiver base and form there a negative or a positive image respectively. By repeating this procedure with different colorants a full colour proof can be obtained.

Description

NEGATIVE OR POSITIVE WORKING SURPRINT COLOUR PROOFING SYSTEM

1. Field of the invention.

The present invention relates to dry processable negative or positive working surprint colour proofing systems based on

photopolymerization.

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 photoimaging processes and materials 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.

For colour proofing there are two general types of photoimaging methods, namely the overlay type and the single sheet or surprint type.

In the overlay type of colour proofing method, an independent transparent plastic support is used as base for the production of a proof image of each color separation film by applying a

photosensitive solution containing the corresponding colorant and by performing a process for image formation. A plurality of such supports carrying images of the corresponding colours are then superimposed upon each other over a white sheet to produce a colour proofing composite. The primary advantage of the overlay method is that proofs can be made quickly and can serve as a progressive proof by combining any two or three colours in register. However, this type of colour proofing material has the disadvantage that the superimposed polymeric supports tend to darken the background of the final full proof. As a result, the impression of the colour proofing composite thus prepared is vastly different from that of the prints actually obtained with conventional printing presses and with proof presses. Examples of such overlay approaches are contained in U.S. Patents 3,136.637, 3,211,553, and 3,326.682. A commercial overlay colour proofing system is CROMACHECK, marketed by Du Pont Co.

In the single sheet or surprint type of colour proofing method, a colour proof is prepared by successively producing images of different colours from different colour separation films on a single receiver sheet. This can be accomplished by sequentially applying colorants or coloured, photosensitive layers to a single opaque support. This method more closely resembles the actual printing process and eliminates the colour distortion inherent in the overlay system. Examples of such single sheet approaches are contained in U.S. Patents 3,671,236; 4,260,673; 4.366,223; 4,650.738; 4.656,114; and 4,659,642.

Colour proofing systems can also be subdivided in dry processes and in methods involving one or more wet processing steps.

As an example for the latter, in US 4,933,258 and US 4,766,053 a method is disclosed 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.

Another wet process for producing a multicolour pattern using silver halide emulsion materials is described in European Patent Specification EP 0 185 410. This process involves the successive transfer of differently coloured hardening developable silver halide containing hydrophilic layers onto a permanent support. After the transfer and the image-wise exposure a wet processing cyclus is performed cosecutively for each colour, each involving a hardening development step, a bleach-fix step, and a wash-off step of the unhardened parts. Further variations and improvements on this process, which is commercialized by Agfa-Gevaert N.V. under the trade name AGFAPROOF. are disclosed in EP 0 305 599 and European patent application Appl . No. 92203339.

US 4,596,757 provides a method for transferring images or solid colours which are subsequently imaged. The photosensitive material comprises a carrier support having sequentially disposed thereon a release layer, a coloured photopolymerizable layer and an adhesive layer. The material can undergo exposure, lamination to a temporary support, wet development, and then lamination to a receptor sheet. Alternatively, the photosensitive material can be laminated to a receptor sheet, undergo exposure and then wet processing. Both processes require development in an aqueous medium.

In EP 0 339 860 a proofing system is described involving a development step by alkali.

However in recent years, for reason of convenience,

easy-handling, and for ecological reasons, dry photoimaging

processes are preferred.

In U.S. Patent 4,489,154 a process is claimed which produces a single layer colour proof without wet development. The

photosensitive material comprises a stripable cover sheet, a coloured photoadherent layer, a non-photosensitive organic

contiguous layer and a sheet support. The material is exposed and peel developed. The positive or negative image is transferred to a receiver base. A fresh layer of adhesive must be applied to the receptor for each subsequent transfer.

In EP 0 437 343 a dry proofing method is disclosed comprising, in order, (A) providing a photosensitive element comprising (i) a support, (ii) a coloured photopolymerizable layer, (iii) an adhesive layer, (B) in either order, providing a receiver base to which said adhesive layer is laminated, and image-wise exposing this

photosensitive composition to actinic radiation, (C) peeling apart said support and said receiver base, thereby transferring the adhesive layer and the non-exposed parts to the receiver base, while the exposed parts remain on the support, and (D) optionally

repeating steps (A) to (C) with different colorants. This method is only positive working.

Most cited colour proofing systems both dry and wet can exhibit problems with dimensional stability during processing and/or colour transfer steps. Lack of dimensional stability leads to non perfect registering of the different composing colours of the proof. As a result multicolour images with blurred edges are obtained giving the final proof an unsatisfactory outlook.

The present invention extends the teachings on dry surprint (or single sheet) colour proofing systems based on photopolymerisation.

It is an object of the present invention to provide a surprint colour proofing system which involves only dry treatment steps.

It is a further object of the present invention to provide a method for colour proofing which can be both negative or positive working.

It is still a further object of the present invention to provide a colour proofing system improved for dimensional stability so that well registered multicolour images can be obtained.

3. Summary of the invention.

The objects of the present invention are realized by providing a method, and corresponding photosensitive compositions, said method comprising, in one embodiment, the following steps, in order :

(A) providing a photosensitive composition comprising following elements, in order :

(1) a transparent temporary support,

(2) a subbing layer,

(3) a photosensitive layer comprising a polymeric binder, a colorant, a photoinitiating system, and a photopolymerisable ethylenically unsaturated monomer,

(4) an adhesion promoting layer comprising a thermoplastic polymer having a T_g between 20 °C and 110 °C,

(5) a thin polymeric foil having a thickness between 5 and 20 μm.

(6) a permanent or thermal adhesive layer,

(B) either,

(i) providing a receiver base and laminating or adhering it to said adhesive layer (6) . and then information-wise exposing this composite to actinic radiation, or,

(ii) information-wise exposing said photosensitive composition to actinic radiation, and then providing a receiver base and laminating it or adhering it to said adhesive layer (6),

(C) peeling apart said transparent support and said receiver base whereby, depending on the monomer / binder ratio, either (i) the elements (4) to (6) together with the information-wise exposed areas of said photosensitive layer adhere to the receiver base while the information-wise non-exposed areas adhere to said subbing layer (2) on top of said transparent temporary support (negative working), or (ii) whereby the elements (4) to (6) together with the information-wise

non-exposed areas of said photosensitive layer adhere to the receiver base while the information-wise exposed areas adhere to said subbing layer (b) on top of said transparent temporary support (positive working),

(D) optionally repeating steps (A) through (C) at least once with another photosensitive composition containing a different colorant thus forming a multicolour negative or positive image on the receiver base.

The system is negative pr positive working depending on the ratio amount monomer / amount binder in the photosensitive layer. When the monomer / binder ratio is at least 4:1 by weight a negative coloured image is retained on the receiver base. If however the monomer / binder ratio is less than 2:1 by weight a positive image is formed on the receiver base.

In a preferred embodiment titanium dioxide is incorporated in the photosensitive composition, preferably in the polymeric foil (5), in order to regulate the apparent dot size in the final proof.

In an alternative embodiment of the present invention the position of the subbing layer and of the adhesion promoting layer in the final photosensitive composition are interchanged. In this embodiment always a negative coloured image is formed on the receiver base independent of the monomer / binder ratio.

4. Detailed description of the invention.

The particular features and ingredients of the photosensitive element for use in the method of the present invention will now be explained in detail hereinafter.

Suitable transparent supports include e.g. cellulose nitrate film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film. poly(ethylene terephthalate) film, polycarbonate film, polyvinylchloride film or poly-α-olefin films such as polyethylene or polypropylene film. The thickness of such organic resin film is preferably comprised between 0.02 and 0.20 mm.

In a most preferred embodiment the support is a polyethylene terephthalate support.

An example of a suitable subbing layer is a layer containing a polymer containing covalently bound chlorine. Suitable chlorine containing polymers are e.g. polyvinyl chloride, polyvinylidene chloride, a copolymer of vinylidene chloride, an acrylic ester and itaconic acid, a copolymer of vinyl chloride and vinylidene

chloride, a copolymer of vinyl chloride and vinyl acetate, a copolymer of butylacrylate, vinyl acetate and vinyl chloride or vinylidene chloride, a copolymer of vinyl chloride, vinylidene chloride and itaconic acid, a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, chlorinated polyethylene, polychloroprene and copolymers therof, chlorosulfonated polyethylene,

polychlorotrifluoroethylene, polymethyl-alpha-chloroacrylate etc. A preferred chlorine containing polymer is co(vinylidenechloride- methylacrylate-itaconic acid ; 88 % / 10 % : 2 %).

Suitable polymers not containing chlorine include co(styrene- butadiene-carbonic acid), polyvinyl acetate, and

co (methylmethacrylate-butadiene-itaconic acid). In the latter case the amount of the itaconic acid part is preferably comprised between 2 and 15 %. The T„ of the polymer can be adjusted by varying the relative amounts of the methylmethacrylate and the butadiene parts while keeping the itaconic acid part constant at about 5 %. In a most preferred embodiment the copolymer is composed of 47.5 % of methylmethacrylate, 47.5 % of butadiene and 5 % of itaconic acid.

The essential ingredients of the photosensitive layer are a binder, a monomer, a colorant and a photoinitiator.

Examples of useful binders include organic solvent-soluble polymers, e.g. polymers derived from α,β-ethylenically unsaturated compounds such as e.g. polyvinyl acetate, a vinyl acetate-vinyl chloride copolymer, a styrene-butadiene copolymer, polyethylene, and polypropylene. Other suitable binders for the photosensitive layer are styrene/maleic anhydride copolymers and their half esters, acrylic polymers and copolymers, polyamides, polyvinyl pyrrolidones, cellulose and its derivatives and phenolic resins. Especially preferred binders are polyvinyl acetals, such as polyvinyl butyral and polyvinyl propional. Still other preferred binders are polyvinyl formals which are commercially available from Monsanto as FORMVAR. The formal content of the polyvinyl formals is approximately 65 % to 86 % expressed as percent polyvinyl formal. The acetate content is approximately 9 % to 30 % expressed as percent polyvinyl acetate. The hydroxyl content is approximately 5 % to 7 % as expressed as percent polyvinyl alcohol. The average molecular weight is between 10.000 and 40.000.

A wide variety of photopolymerisable and photocrosslinkable compounds can be used in the present invention. Suitable monomers include e.g. the monomers disclosed in DE-OS Nos. 4005231. 3516256, 3516257. 3632657 and US 4,629,676. unsaturated esters of polyols. particularly such esters of the alpha-methylene carboxylic acids, e.g. ethylene diacrylate, glycerol tri(meth)acrylate, ethylene dimethacrylate, 1,3-propanediol di(meth)acrylate 1 ,2,4-butanetriol tri(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate,

1,4-benzenediol di(meth)acrylate, pentaerythritol

tetra(meth) acrylate, pentaerythritol triacrylate, dipentaerythritol pentacrylate, trimethylolpropane triacrylate, 1,5-pentanediol di(meth) acrylate. the bis acrylates and methacrylates of

polyethylene glycols of molecular weight 200-500, and the like : unsaturated amides, particularly those of the alphamethylene carboxylic acids, and especially those of Alpha-Omega-diamines and oxygen- interrupted omega-diamines, such as methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide, diethylene triamine tris-methacrylamide,

bis(gamma-methacrylamidopropoxy)ethane, beta-methacrylamidoethyl methacrylate, N-(beta-hydroxyethyl)-beta-(methacrylamido)ethyl acrylate and N,N-bis(beta-methacrylolyoxyethyl)acrylamide, vinyl esters e.g. divinyl succinate, divinyl adipate, divinyl phthalate, divinyl butane-1,4-disulphonate; and unsaturated aldehydes, e.g. sorbaldehyde (hexadienal). The photopolymerizable composition may also comprise polymers and/or oligomers comprising 2 or more polymerizable functions e.g. acrylated epoxies, polyester acrylates, urethane acrylates etc.. It will be clear that these monomers and/or polymers and/or oligomers can be used in admixture.

It is also possible to use monofunctional (meth) acrylic acid esters as monomer provided they are not to volatile and do not spread an unwanted odour. Suitable compounds include n- octylacrylate. n-octylmethacrylate. decylacrylate,

decylmethacrylate, stearylacrylate. stearylmethacrylate.

cyclohexylacrylate, cyclohexylmethacrylate, phenylethylacrylate. phenylethylmethacrylate.

The most preferred polymerizable compounds comprise one or more (meth) acrylate functional groups.

Particular preferred classes of photopolymerizable compounds containing (a) (meth) acrylate group (s) are reactive multifunctional monomers disclosed in EP 0 502 562 and represented by general formula (I) or (II) :

A[-NHCO-X-L¹(-(L²)_u-OCO-CR¹-CH₂)_n]_m (I) wherein n represents an integer from 1 to 3, m equals an integer of 3 to 6 when n equals 1. and 2 to 6 when n equals 2 or 3, and u equals 0 or 1 ;

A represents an organic group of the following nature being 3 to 6 valent when n equals 1 and being 2 to 6 valent when n equals 2 or 3 a) a hydrocarbon residue containing 5 to 25 carbon atoms which may be interrupted by one or more ether, ester or amide functions; b) A¹[-(OCH-CH) -OCONH-A²-]_p-

R³ R⁴

with A¹ representing a linear or branched aliphatic residue that may contain 0 to 3 0-atoms and 2 to 20 C-atoms, an aromatic residue containing 6 to 24 carbon atoms, an aromatic aliphatic residue containing 7 to 28 C-atoms or an cycloaliphatic residue containing 6 to 26 C-atoms, R³ and R⁴ each independently representing a hydrogen or a methyl group. A² representing a hydrocarbon residue containing 5 to 25 carbon atoms, o

represents an integer of 0 to 5 and p represents an integer of 2 to 6 when n equals 2 or 3 and represents an integer of 3 to 6 when n equals 1 ;

c) A¹[-(OCH-CH)_o-OCO-A²-]_p -

R³ R⁴

wherein A¹, A², R³ , R⁴, o and p have the same meaning as defined above

d) A¹[-(OCH-CH)_o-(G-Q)_r-]_p-

R³ R⁴

wherein A¹, A², R³ , R⁴, O and p have the same meaning as defined above ;

G represents -O-CO-NH-Y(-COO-)_q- ;

wherein Y represents a divalent (cyclo) aliphatic residue containing 2 to 15 C-atoms and that may contain an ester, ether or urethane function, and q represents 0 or 1

Q represents a linear or branched aliphatic hydrocarbon residue containing 3 to 15 carbon atoms and which may comprise 1 to 3 oxygen bridges and r equals 0 or 1.

X represents 0 or NR²,

L¹ represents an aliphatic hydrocarbon residue that is at least divalent and that may comprise 1 to 3 0-atoms,

L² represents a lower alkylene of 1 to 6 C-atoms which may be branched or linear,

R! represents hydrogen or a methyl group.

R² represents hydrogen or a lower alkyl group of 1 to 6 C-atoms;

wherein

Ur represents a divalent or trivalent condensed urea residue ;

Z represents 0 or NR¹⁰ with R¹⁰ representing alkyl containing 1 to

12 C-atoms ;

R⁷ represents a divalent hydrocarbon residue containing 2 to 25 C- atoms ;

R⁸ represents a hydrocarbon residue with a valence between 2 and 6, and containing 2 to 18 C-atoms, which can be linear or branched and which can be interrupted by upto 3 0 atoms ;

R⁹ represents hydrogen or methyl ;

α represents an integer from 1 to 5 , and

β equals 2 or 3.

Preferably used monomers comprise one of the following residues as hydrocarbon residue A and/or A² of general formula (I) :

wherein R⁵ and R⁶ each independently represent hydrogen or a lower alkyl of 1 to 6 C-atoms, s and t independently represent an integer from 1 to 6 and wherein the aliphatic hydrocarbon residues la, Ic and Id comprise 2 to 6 free valences.

Examples of monomers according to formula (I) suitable for use in accordance with the present invention are shown in table 1.

i and j are respectively 3.5 and 0.5 indicating that compound 6 is a mixture of compounds obtained by reacting i equivalents of glycerine- dimethacrylate and j equivalents of hydroxyethyl methacrylate as disclosed in DE 3.703.130.

i and j are respectively 2.5 and 1.5 indicating that compound 7 is a mixture of compounds obtained by reacting i equivalents of glycerine- dimethacrylate and j equivalents of hydroxyethyl methacrylate as disclosed in DE 3.703.130.

The fractal indexes in the formulas 1, 2 and 10 indicate that these formulas represent a mixture of compounds having a different length of the ethylene-oxide piece in said formulas the indexes thus representing an average of said ethylene-oxide piece. The formulas 14 to 23 represent a mixture of structural isomers and can be used in accordance with the present invention without separation of the isomers. The monomers corresponding to general formula (I) are known and can be prepared according to the German patent application numbers 3,522,005, 3.703,080. 3.643,216. 3.703,130. 3.917.320 and 3.743.728.

In general monomer formula (II) preferred condensed urea residues represented by Ur are following structural units :

Examples of preferred useful monomers according to general formula (II) are listed below in table 2 :

The photoinitiator system, present in the photosensitive layer, comprises one or more compounds which directly furnish free-radicals when activated by actinic radiation. It can also comprise a

plurality of other compounds, e.g. spectral sensitizers, hydrogen donors.

Numerous conventional photoinitiators systems may be used provided they are compatible with the other ingredients of the element-.-Useful photoinitiators are ketoxime-esters. Preferred photoinitiator systems are 2 ,4,5-triphenylimidazolyl dimers in combination with chain transfer agents, or hydrogen donors, such as are disclosed in US 3.479.185, US 3,784.557. US 4,311.783 and

US 4,622.286. Preferred hexaarylbisimidazoles (HABI) are 2-o-chloro- substituted hexaphenylbisimidazoles in which the other positions on the phenyl radicals are unsubstituted or substituted with chloro, methyl or methoxy. The most preferred initiator is o.-Cl-HABI, i.e. 2,2'-bis-(o-chloro-phenyl)-4,4,5,5',tetraphenyl-1,1'-bisimidazole (or simply "bisimidazole") corresponding to following chemical formula

Hydrogen donor compounds useful as chain tranfer agents in the photopolymer layer include : 2-mercaptobenzoxazole, 2- mercaptobenzothiazole, 4-methyl-4H-1,2,4,-triazole-3-thiol, and the like. A preferred hydrogen donor is 2-mercaptobenzoxazole with following formula :

Although the HABI initiating systems described above are preferred, other initiating systems may be used in practicing this invention. Useful photoinitiators described in US 2,760,863 include vicinal ketaldonyl alcohols, such as benzoin, pivaloin, acyloin ethers, e.g. benzoin methyl and ethyl ethers, and α-hydrocarbon- substituted aromatic acyloins. such as α-methylbenzoin. Further useful photoinitiators include quinoxaline compounds as described in U.S. Patent 3,765,898, the vicinal pαlyketaldonyl compounds in U.S. Patent 2,367,660, the α-carbonyls in U.S. Patent 2,367,661 and 2,367,670, the acyloin ethers in U.S. Patent 2,448,828, the

triarylimidazolyl dimers in U.S. Patent 3,479,185, the α-hydrocarbon substituted aromatic acyloins in U.S. Patent 2,722,512. polynuclear quinones in U.S. Patents 2,951,758 and 3,046,127. and s-triazines in U.S. Patent 4.656.272.

The photoinitiator is preferably present in the photosensitive layer in an amount ranging from 2 to 30 % by weight.

Many of the well known photoinitiator systems have limited applicability because they are activated only by UV radiation. For exposure in the visible region, e.g. by lasers, the use of so-called sensitizers is indispensable. A large number of free-radical generating systems have been used as sensitizers for the visible region for photopolymerizable compositions. US-P 3,652.275 discloses selected bis (p-dialkylaminobenzylidene)ketones as sensitizers for HABI initiator systems. US-P 4.162,162 discloses selected

sensitizers derived from aryl ketones and p-dialkylaminoaldehydes. US-P 4.987.230 and US-P 4.987,230 also disclose sensitizers for HABI systems.

A preferred sensitizer is 7-diethylamino-4-methylcoxιmarin.

Dyes and/or pigments are included in the photosensitive layer. Preferred colorants for this invention are pigments rather than dyes. Light fast colorants are preferred. The pigments are typically dispersed with an organic binder in an organic solvent or mixture of organic solvents. The pigments may be organic or inorganic. They are ground to a small enough particle size to duplicate the particle size and color of equivalent inks. The median diameter is generally less than 1 μm.

Non-exclusive examples of colorants usable in the present invention are as follows : Permanent Yellow G (C.I. 21095);

Permanent Yellow GR (C.I. 21100), Permanent Yellow DHG (C.I. 21090), Permanent Rubine L6B (C.I. 15850:1). Permanent Pink F3B (C.I.

12433). Hostaperm Pink E (73915). Hostaperm Red Violet ER (C.I.

46500), Permanent Carmine FBB (12485). Hostaperm Blue B2G (C.I.

74160), Hostaperm Blue A2R (C.I. 74160), and Carbon Printex 25. Most of these pigments are products of Hoechst AG. They can be used separately or blended for a desired colour. The colorant is present in the photosensitive layer in an amount preferably ranging from 10 % to 50 % by weight.

Other ingredients which may be present in the photosensitive layer include thermal polymerization inhibitors, plasticizers, residual solvents, surfactants, inert fillers, antihalation

compounds and optical brightening agents.

The photosensitive layer is preferably coated at a dry coverage ranging from 0.25 g/m² to 10 g/ m².

The procedure for the application of the next layers (4) and (6), and foil (5) onto the photosensitive layer (3) is preferably as follows. A composite is prepared comprising a thin polymeric foil (5) which is coated on one side with an adhesion promoting layer (4) containing a thermoplastic polymer, and on the other side with a permanent or thermal adhesive layer (6). On this latter side also a release foil is provided. Examples of such composites which are commercially available are KT8 or KT10H (Kimoto Co., Tokyo, Japan), and MECROTAPE (Mecron Electrotechnik. Nixdorf Gmbh, Liederbach, Germany). Then this composite is laminated at elevated temperature to the photosensitive element (1) + (2) + (3), the photosensitive layer (3) and the adhesion promoting layer (4) facing each other. Then the release foil being preferably a polyethylene coated paper or a polyethylene terephthalate sheet coated with a silicone release layer, is peeled off and disposed of.

The photosensitive composition with on top layer (6) is then adhered to a receiver base at room temperature in case of a

permanent adhesive polymer in layer (6), or laminated to a receiver base at elevated temperature in case of a thermal adhesive polymer in layer (6).

The thermoadhesive polymers of layer (4) are preferably coated from aqueous solutions for ecological reasons. Therefore the polymers are preferably incorporated as latices. They must show a T_g between 20 and 110 °C. Useful latices include styrene-butadiene latices. These latices can contain other comonomers which improve the stablitity of the latex, such as acrylic acid, methacrylic acid and acrylamide. Other possible polymer latices include

polyvinyiacetate, copoly(ethylene-vinylacetate).

copoly(acrylonitrile-butadiene-acrylic acid). copoly(styrene- butylacrylate), copoly(methylmethacrylate-butadiene),

copoly(methylmethacrylate-butylmethacrylate).

copoly(methylmethacrylate-ethylacrylate), copolyester(terephtalic acid-sulphoisophtalic acid-ethyleneglycol), copolyester(terephtalic acid-sulphoisophtalic acid-hexanediol-ethyleneglycol). Other suitable polymers for use in the thermoadhesive layer are the

BAYSTAL polymer types, marketed by Bayer AG, which are on the basis of styrene-butadiene copolymers. still other useful polymers are the EUDERM polymers, also from Bayer AG, which are copolymers comprising n. -butylacrylate. methylmethacrylate, acrylonitrile and small amounts of methacrylic acid.

An especially preferred class of thermoadhesive polymers for use in layer (4) are acrylic polymers and copolymers. Vinyl acetate polymers and copolymers are most preferred. Polyvinyl acetates are available from Hoechst AG as Mowilith. These resins have a average molecular weight between 35,000 and 2,000,000. In the preferred embodiment, the polyvinyl acetate is present in the adhesive layer in an amount of greater than 60 percent by weight. In this case organic solvents can also be used for coating the adhesion promoting (4) layer to the thin polymeric foil. The thickness of the adhesion promoting layer is preferably comprised between 0.2 and 3 μm.

The thin polymeric foil having a thickness between 5 and 20 μm can be chosen from the same list of polymeric resins enumerated for the transparent temporary support. In a preferred embodiment a thin polyethylene terephthalate foil is used.

Adhesive layer (6) can contain a permanent adhesive, also called pressure-sensitive polymer, or a thermal adhesive, also called heat- sensitive polymer. Preferably a pressure sensitive adhesive is used. A survey of pressure and/or thermal adhesives is given by J. Shields in "Adhesives Handbook", 3rd. ed. (1984), Butterworths - London. Boston, and by Ernest W. Flick in "Handbook of Adhesive Raw

Materials" (1982). Noyens Publications, Park Ridge. New Jersey - USA.

Examples of pressure- sensitive adhesive resins are described in US-P 4,033,770 for use in the production of adhesive transfers (decalcomanias) by the silver complex diffusion transfer process, in the Canadian Patent 728,607 and in the United States Patent

3,131,106. Pressure-sensitive adhesives are usually composed of (a) thermoplastic polymer (s) having some elasticity and tackiness at room temperature (about 20°C), which is controlled optionally with a plasticizer and/or tackifying resin. A thermoplastic polymer is completely plastic if there is no recovery on removal of stress and completely elastic if recovery is instantaneous and complete.

Particularly suitable pressure-sensitive adhesives are selected from the group of polyterpene resins, low density polyethylene, a copoly(ethylene/vinyl acetate), a poly(C₁-C₁₆) alkyl acrylate, a mixture of poly (C₁-C₁₆) alkyl acrylate with polyvinyl acetate, and copoly(vinylacetate-acrylate) being tacky at 20°C.

In the production of a pressure-adhesive layer an intrinsically non-tacky polymer may be tackified by the adding of a tackifying substance, e.g. plasticizer or other tackifying resin.

Examples of suitable tackifying resins are the terpene

tackifying resins described in the periodical "Adhesives Age", Vol. 31, No. 12, November 1988, p. 28-29.

When the polymer of layer (6) is thermal adhesive it can be chosen from the same group of polymers as listed for the adhesion promoting layer (4). In this case preferably a polymer with a T_g lower than 50 °C is used.

The thickness of the adhesive layer (6) is preferably comprised between 0.5 and 20 μm.

Receiver bases may comprise virtually any material which can withstand the laminating and dry development processes. Plastic sheets such as polyethylene terephthalate are useful for this purpose. Preferably the plastic sheet serving as receiver base is thicker than the transparent support of the original photosensitive element ; its thickness is preferably comprised between 50 and 400 μm. Resin coated paper sheets, such as polyethylene coated paper, may also be used. Still other bases may include wood, glass, metal, cardboard and the like. Preferably, the receiver sheet in usual printing paper.

Information-wise exposure can be performed before or after the photosensitive composition is adhered or laminated to the receiver base. Preferebly it is done after, so when the whole composite is complete. Such exposure may be performed by actinic radiation from a light source through a conventional halftone negative or positive colour separation under vacuum frame conditions. Mecury vapor discharge lamps are preferred over metal halide lamps. Other radiation sources, such as carbon arc and pulsed xenon may also be used. Light absorbing filters may be used to reduce light scattering in the materials. When the photosensitive element has been

sensitized to the visible spectral region as explained above electronically stored information can be recorded directly on the photosensitive element by a laser source, e.g. an Ar ion laser (so- called Direct Digital Colour proofing, DDCP).

Finally the photosensitive composition is dry developed by peeling apart the support and the receiver base from each other at room temperature with a steady, continuous motion. No devices are necessary to hold down the receiver base during peeling because only moderate manual peeling forces are needed to separate the materials. The preferred peel angle relative to the peel direction is greater than 90°.

Depending on the monomer / binder ratio a different result can be obtained. When this ratio is greater than 4:1 by weight then the elements (4) to (6) together with the information-wise exposed areas of said photosensitive layer adhere to the receiver base while the information-wise non-exposed areas adhere to said subbing layer (2) on top of said transparent temporary support. In this way a negative colour proof image is obtained. On the other hand when the monomer / binder ratio is smaller than 2:1 then the elements (4) to (6) together with the information-wise non-exposed areas of said photosensitive layer adhere to the receiver base while the

information-wise exposed areas adhere to said subbing layer (2) on top of said transparent temporary support. In this way a positive colour proof image is obtained.

This whole procedure can now optionally be repeated at least once with a photosensitive composition having a different colorant in its photosensitive layer. In the usual case, the whole procedure will be performed four times with four different colours in order to obtain a full colour proof. These four colours are cyan, magenta, yellow and black. Thanks to the excellent dimensional stability of the photosensitive compositions of the present invention the different colours are superimposed on top of each other in perfect register so that sharp multicolour image edges are obtained.

In order to regulate the apparent dot size (so-called "dot gain") in the final print appropriate amounts of titanium dioxide can be incorporated in the thin polymeric foil (5) or in the adhesive layer (6) or in the adhesion promoting layer (4) of the photosensitive composition transferred as first to the receiver base. Preferably the titanium dioxide is incorporated in the thin polymeric foil (5). In the latter case the relative amount of titanium dioxide is preferably comprised between 5 and 50 % by weight.

In an alternative embodiment of the present invention the layers (2) and (4) are interchanged in position. Thus a photosensitive composition with following arrangement is obtained, in order :

temporary transparent support / adhesion promoting layer /

photosensitive layer / subbing layer / thin polymeric foil / permanent or thermal adhesive layer. The whole procedure is further identical to the one described above. However with this arrangement of elements always a negative coloured image is obtained independent of the monomer / binder ratio.

The present invention will now be illustrated by the following examples without however being limited thereto.

EXAMPLES

Example 1

To a polyethylene terephthalate support of 63 μm thickness a subbing layer was applied containing copoly (methylmethacrylate- butadiene-itaconic acid : 47.5 % / 47.5 % / 5 %) at a coverage of 50 mg/m . For the photosensitive layer a coating composition was prepared containing following ingredients :

HOSTAPERM BLUE was incorporated as a 10 % dispersion containing also 5 % of FORMVAR from a 1:1 solvent mixture of l-methoxy-2- propanol and γ-butyrolactone.

This coating solution was applied to the subbed support by means of a BRAIVE coating knife giving rise to a wet coating thickness of 50 μm.

The coating solution for the adhesion promoting layer contained 82 g of butyl acetate and 18 g of vinyl acetate copolymer (MOWILITH 30. Hoechst AG). This solution was coated at a dry coverage of 1.5 g/m² onto a 10 μm thick polyethylene terephtalate foil, which was already coated at the other side with a 4 μm thick permanent adhesive layer consisting of co (vinyl acetate - butyl acrylate), for instance DICRYLAM AL of Ciba-Geygy Co., and which was further provided with a release foil, being a 36 μm thick polyethylene terephthalate sheet coated with a silicone release layer, over this adhesive layer. This composition was contacted at the side of the adhesion promoting layer with the pigmented photosensitive layer and laminated to it at 80 °C.

After removal of the release foil to set free the permanent adhesive layer the whole composite was applied to polyethylene coated paper, serving as receiver base, by lamination at room temperature. Then this composite material was image-wise exposed with UV light in a contact apparatus through the original temporary support. Then the temporary support and the receiver base were peeled apart whereby the information-wise exposed areas were removed with the temporary support plus subbing layer while the information- wise unexposed areas together with the adhesion promoting layer, the thin polyethylene terephthalate foil and the adhesive layer all adhered to the paper receiver. The delamination took place under an angle of 180 ° at a low constant speed of 250 cm/min. In this way a positive coloured image was formed on the paper base.

Example 2

The photosensitive composition and the procedure were identical to those of example 1 with the exception that the coating solution of layer (3) was composed as follows :

(*) ketoxime ester is represented by following formula :

Carbon printex 25 was incorporated as a 10 % dispersion

containing also 5 % of FORMVAR from a 1:1 solvent mixture of l-methoxy-2-propanol and γ-butyrolactone.

Due to the fact that the monomer / binder ratio was higher than 4:1 a negative coloured image was finally obtained contrary to example 1.

Example 3

A similar photosensitive composition was built up as in example 1 with the exception that the subbing layer and the adhesion promoting layer were interchanged in position. So the layer sequence of the complete composite before exposure was as follows :

polyethylene temporary support / adhesion promoting layer /

photosensitive layer / subbing layer / 10 μm thick polyethylene terephthalate foil / permanent adhesive layer / paper receiver base. Then this composite material was information-wise exposed with UV light in a contact apparatus through the original temporary support. Then the temporary support and the receiver base were peeled apart whereby the image-wise unexposed areas were removed with the temporary support plus adhesion promoting layer while the image-wise exposed areas together with the subbing layer, the thin polyethylene terephthalate foil and the adhesive layer all adhered to the paper receiver. The delamination took place under an angle of 180° at a low constant speed of 250 cm/min. In this way a negative coloured image was formed on the permanent paper base.

Claims

CLAIMS 1. Method for the formation of a negative or positive coloured

image comprising, in order, the following steps :

(1) a transparent temporary support,

(2) a subbing layer,

(5) a thin polymeric foil having a thickness between 5 and 20 μm.

(6) a permanent or thermal adhesive layer,

(B) either,

(i) providing a receiver base and laminating or adhering it to said adhesive layer (6), and then information-wise exposing this composite to actinic radiation, or,

(ii) information-wise exposing said photosensitive composition to actinic radiation, and then providing a receiver base and laminating it or adhering it to said adhesive layer (6) .

2. Method according to claim 1 wherein the ratio monomer / binder in said photosensitive layer (3) is at least 4:1 by weight, and wherein in step (C) the elements (4) to (6) together with the information-wise exposed areas of said photosensitive layer adhere to the receiver base while the information-wise

non-exposed areas adhere to said subbing layer (2) on top of said transparent temporary support, so that after optional step (D) a negative multicolour image is obtained on said receiver base.

3. Method according to claim 1 wherein the ratio monomer / binder in said photosensitive layer (3) is smaller than 2:1 by weight, and wherein in step (C) the elements (4) to (6) together with the information-wise non-exposed areas of said photosensitive layer adhere to the receiver base while the information-wise exposed areas adhere to said subbing layer (2) on top of said transparent temporary support, so that after optional step (D) a positive multicolour image is obtained on said receiver base.

4. Method for the formation of a negative coloured image

comprising, in order, the following steps :

(1') a transparent temporary support,

(2') an adhesion promoting layer comprising a thermoplastic polymer having a T_g between 10 °C and 100 °C.

(3') a photosensitive layer ccmprising a polymeric binder, a colorant, a photoinitiating system, and a photopolymerisable ethylenically unsaturated monomer,

(4') a subbing layer,

(5') a thin polymeric foil having a thickness between 5 and 20 μm,

(6') a permanent or thermal adhesive layer,

(B) either,

(ii) information-wise exposing said photosensitive composition to actinic radiation, and then providing a receiver base and laminating it or adhering it to said adhesive layer (6) ,

(C) peeling apart said transparent temporary support and said receiver base whereby the elements (4) to (6) together with the information-wise exposed areas of said photosensitive layer adhere to the receiver base while the information-wise

non-exposed areas adhere to said adhesion promoting layer on top of said transparent temporary support (negative working),

(D) optionally repeating steps (A) through (C) at least once with another photosensitive element containing a different colorant thus forming a multicolour negative image on said receiver base.

5. Method according to any of claims 1 to 4 wherein said thin

polymeric foil (5) contains titanium dioxide.

6. Method according to claim 5 wherein the relative amount of

titanium dioxide contained in said foil (5) is comprised between 5 and 50 % by weight.

7. Method according to any of claims 1 to 6 wherein said

photosensitive layer is coated at a dry coverage between 0.25 g/m² and 10 g/m².

8. Method according to any of claims 1 to 7 wherein said

photoinitiating system comprises 2,2'-bis-(o-chloro-phenyl)- 4,4,5,5',tetraphenyl-1,1'-bisimidazole as photoinitiator.

9. Method according to any of claims 1 to 8 wherein said

transparent temporary support (1) is a polyethylene

terephthalate support.

10. Method according to any of claims 1 to 9 wherein said thin

polymeric foil (5) is a polyethylene terephtalate foil.

11. Method according to any of claims 1 to 9 wherein said receiver base is printing paper.

12. Photosensitive composition comprising following elements, in order :

(1) a transparent temporary support,

(2) a subbing layer,

(3) a photosensitive layer comprising a polymeric binder, a colorant, a photoinitiating system, and a photopolymerisable ethylenically unsaturated monomer, (4) an adhesion promoting layer comprising a thermoplastic polymer having a T_g between 10 °C and 100 °C,

(5) a thin polymeric foil having a thickness between 5 and 20 μm,

(6) a permanent or thermal adhesive layer.

13. Photosensitive composition comprising following elements, in order :

(1') a transparent temporary support,

(2') an adhesion promoting layer comprising a thermoplastic polymer having a T_g between 10 °C and 100 °C,

(3') a photosensitive layer comprising a polymeric binder, a colorant, a photoinitiating system, and a photopolymerisable ethylenically unsaturated monomer,

(4') a subbing layer,

(5') a thin polymeric foil having a thickness between 5 and 20 μm,

(6') a permanent or thermal adhesive layer.

14. Photosensitive composition according to claim 12 or 13 wherein said thin polymeric foil (5) contains titanium dioxide.

15. Photosensitive composition according to claim 14 wherein the amount of titanium dioxide contained in said foil (5) is comprised between 5 and 50 % by weight.

16. Photosensitive composition according to any of claims 12 to 15 wherein said photosensitive layer is coated at a dry coverage between 0.25 g/m² and 10 g/m².

17. Photosensitive composition according to any of claims 12 to 16 wherein said photoinitiating system comprises 2,2' bis-(o- chloro-phenyl)-4.4,5.5',tetraphenyl-1,1'-bisimidazole as photoinitiator.

18. Photosensitive composition according to any of claims 12 to 17 wherein said transparent temporary support (1) or (1') is a polyethylene terephthalate support.

19. Photosensitive composition according to any of claims 12 to 18 wherein said thin polymeric foil (5) is a polyethylene terephtalate support.

20. Method according to any of claims 12 to 19 wherein said receiver base is printing paper.