CA1070545A

CA1070545A - Laminates with layer containing styrene-diene block copolymer for flexographic printing plates

Info

Publication number: CA1070545A
Application number: CA240,553A
Authority: CA
Inventors: Peter Richter; August Wigger; Gerhard Fahrbach; Erhard Seiler; Helmut Barzynski
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1974-11-29
Filing date: 1975-11-26
Publication date: 1980-01-29
Also published as: SE7513246L; CH602986A5; FR2292997A1; FR2292997B1; AU8702775A; DK144344B; GB1525965A; DK144344C; NO144121B; SE410058B; DE2456439A1; NO753936L; JPS5174703A; ATA908775A; AT342090B; NO144121C; DK539075A; BE836070A

Abstract

ABSTRACT OF THE DISCLOSURE: Laminates for the manufacture of flexographic printing plates and containing a) a layer con-sisting essentially of a photocrosslinkable mixture of a two-block copolymer of from 30 to 95% w/w of a diene hydrocarbon and from 5 to 70% w/w of a styrene monomer or a partially hydrogenated product thereof with a compatible monomer having at least one C-C double bond, said mixture containing a photo-initiator, b) a non-photocrosslinkable elastomeric underlayer having a Shore A hardness of from 15 to 70 and c) a non-photo-crosslinkable stabilizing layer preferably between layers a) and b)

Description

10'70545 LAMINATES FOR THE MANUFACTURE OF FLEXOGRAPHIC PRINTING PLATES
This invention relates to novel advantageous laminates for the manufacture of flexographic printing plates and containing a photocrosslinkable layer based on a polymer-monomer mixtùre, an elastomeric underlayer and a stabilizing layer. The invention also relates to the manufacture of - flexographic printing plates by imagewise exposure of the photocrosslinkable layer of said laminates followed by removal or washout of the unexposed and non-crosslinked portions of said layer.
Photopolymerizable laminates for the manufacture of relief printing plates for flexographic printing are known per se and are described, for example, in German Published Applications Nos. 2,062,653; 2,138,582, 2,215,090; and 2,223,808, and in U.S. Patents 2,948,611 3,02~,180, 3,658,531, and 3,674,486. However, the prior art materials are not satisfactory in practice in some respects. For example, some of the prior art relief printing plates exhibit insufficient flexibility and elasticity, whilst others tend to undergo plastic deformation :`

~ .

when sub~ected to high shear stresses and elevated printing pressures and are thus inferior to vulcanized rubber used in conventional rubber plates. Poor resis~nce to solvents con-tained in printing inks often leads to premature destruction of the prlnting relief layer. A high degree of swelling of the printing plate during washout necessitates undesirably long drying times be~ore use. British Patent 1,366,769 discloses the use of block copolymers of the type A-B-A as polymers for the relief layer based on a photocrosslinkable mixture of po-lymers and monomers, which block copolymers consist of an elastomeric polymer block between two thermoplastic non-elasto-meric polymer blocks, examples of such systems being styrene-lsoprene-styrene and styrene-butadiene-styrene three-block copolymers. These block copolymers have the disadvantage that they are difficult to manufacture with exactly reproducible properties and that their hlghly concentrated solutlons are difficult to process, for example, in the productlon of unl-form photopolymerizable layers. Furthermore, they often cause haze in the photopolymerizable layer.
It ls an ob~ect of the present invention to provlde la-mlnates for the manufscture of flexographic prlntlng plates which are slmple and economical to manufacture with readily reproducible propertles and in which the photopolymerizable layer may be produced by a conventional casting method using highly concentrated solutions and is readily soluble, in the uncrosslinked state, in conventional developer solutions, the relief printlng plates made therefrom by exposure and develop-ment being highly suitable for printing and showing good re-sistance to conventlonal ink diluents.

- 2 -We have found that the above object can be substan-tially achieved with laminates for the manufacture of flexogra-phic printing plates and consisting of a) a layer RS consisting essentially of.a photocrosslinkable mixture of at least one soluble polymer P with at least one monomer M which is compatible with said polymer P and con-tains at least one photocrosslinkable C-C double bond, which mixture contains a photoinitiator and, if desired, conven-tional additives and is soluble in developer solutions used to form the relief in the imagewise-exposed layer RS, b) a non-photocrosslinkable elastomeric underlayer U which is not soluble in said developer solutions and which has a Shore A hardness of from 15 to 70, c) a non-photocrosslinkable stabilizing layer ST which is not soluble in said developer solutions and which is located below the elastomeric underlayer U in the order RS - U -ST, which laminates are characterized in that the photocrosslinkable layer RS contains, as polymer P, a soluble two-block copolymer consisting essentially of from 30 to 95~ w/w of a diene hydro-carbon having 4 or 5 carbon atoms and from 5 to 70% w/w of a monomer of the formula CH2- CHR, where R denotes hydrogen or R' CH3 and R' denotes phenyl or Cl 4 alkyl-substituted phenyl, which ha, a viscosity (measured on a 0.5~ w/w solution in toluene at 25C) of from 60 to 350 ml/g, or a partially hydro-~: genated product thereof and which has either a sudden or gradual transition between the diene hydrocarbon bloc~ and the CH2= CHR
R' block.
Suitable diene hydrocarbons

3 -having 4 or 5 carbon atoms are, in particular, butadiene and isoprene and suitable comonomers of the formula CH2 = CHR, R' ln which R is hydrogen or CH~ and R' is a Cl 4 alkyl-substi-tuted or non-substituted phenyl radical, are styrene, ~-methyl styrene, vinyl toluene, t-butyl styrene; o~ these, styrene is preferred. The content o~ units o~ the last-named styrene-type monomers in the two-block copolymer ls from 5 to 70% and preferably rrom 10 to 40%, by weight, and that of the polymerized units Or the diene hydrocarbon is thus from ~0 to 95% and preferably from 60 to 90%, by weight. Manufac-ture o~ the two-block copolymers of the above kind is known and may be e~fected, in partlcular, ln the manner described in U.S. Patent 3,149,182~ Rererence is also made to I. Kuntz, J. Polymer Sci. 54 (1961), pages 569 to 586, and to Y. U.
Spirin et al, J. Polymer Sci. 58 (1962), pages 1181 to 1189.
The copolymers may be manuractured by a batch or continuous process. When producing copolymers having sudden transitions between the block segments by step-wise copolymerizat~cn it i8 ¢onvenient to begin with the polymerizatlon of that mono-mer whlch ls to be present in the largest amount. It is ad-vantageous to carry out the preparatlon o~ the two-block co-polymers by solutlon polymerlzation, partlcularly suitable solvents being hydrocarbons or mixtures thereo~ and polar sol-vents such as tetrahydro~uran. The type Or solvent used has an influence on the microstructure of the two-block copolymer and on the con~iguration of the diene polymer segments. We prefer to use hydrocarbons as solvent. It ls particularly ad-vantageous to use the solut~ons of the block copolymers pre-pared by solution polymerization either d~rectly or ln a more

- 4 -concentrated ~orm, after the addition of the other layer com-ponents, for preparing the photocrosslinkable layer RS by castlng. Also suitable are partial hydrogenation products of said two-block copolymers, by which we mean those in which the diene segmer.ts Or the copolymer are entirely or, prerer-ably, partially hydrogenated. Highly suitable are hydrogena-tion products such as are prepared by the process described in &erman Published Application No. 2,013,263.
Suitable two-block copolymers of the above kind have a viscosity number (measured on a 0.5% w/w solution in toluene) o~ from about 60 to 350 ml/g and in partlcular from 90 to 250 ml/g, these values correspondlng to a range of molecular weights ~ o~ rrom about 75,000 to 200,000. It is Or course also possible to use mixtures o~ two-block copolymers of the a~ove kind or, ~or special applications, to mix two-block ¢opolymers wlth minor quantities of other compatible polymers and, in particular, elastomers.
Hlghly sultable mixtures o~ polymers P with monomers M
~or the photocrosslinkable layer RS contain ~rom 60 to 95%
and in particular from 70 to 95%, by weight, o~ polymers P
and ~rom 5 to 40% and in particular ~rom 5 to ~0~, by weight, o~ monomers M. Particularly suita~le examples of monomers M
ha~ing at least one photocrosslinkable, i.e. photopolymeriz-able, C-C double bond which are substantially compatlble with ~ the polymer P are the esters of acrylic and/or methacrylic ; acids with monohydric or polyhydric alcohols, ~or example n-butyl acrylate, n-~utyl methacrylate, 2-ethylhexyl acrylate, lauryl ~crylate, 2-hydroxypropyl acrylate, hexanediol-1,6-dimethacrylate, hexanediol-1,6-diacrylate, 1,1,1-trimethylol-propane triacrylate, pentaerythritol tetraacrylate and di-_ ~, _ ethylene glycol dimethacrylate. Also suitable, in smallamounts, are amides of methacrylic or acrylic acid, for ex-ample N-methylol-methacrylamide butyl ether. Also suitable are N-vinyl compounds such as N-vinylpyrrolidone, vinyl es-ters o~ aliphatic monocarboxylic acids such as vinyl oleate, vinyl ethers of diols such as butanediol-1,4-divinyl ether, and allyl ethers and allyl esters. Monomers which have also been ~ound to be particularly suitable are isocyanate-~ree reaction products o~ organic polyisocyanates such as hexa-methylene diisocyanate, isophorone diisocyanate and toluylenediisocyanate and hydroxyl-containing acrylates or methacryl-ates such as ethylene glycol monoacrylate, hydroxypropyl meth-acrylate and 1,4-butanediol monoacrylate, provided they are suf~iciently compatible with the polymer P. The same applies to the reaction products of diepoxides or polyepoxides, ~or example butanedlol-1,4-dl~lycldyl ether and blsphenol A dl-glycldyl ether wlth methacrylic or acrylic acid. The proper-tles of the photopolymerlzable layers RS can be modi~led for speclal purposes by appropriate choice of the ~onomers or mixtures thereo~. The layer RS also contains, as usual, a photoinltiator, generally ln an amount Or ~rom O.Dl to 10%
and in partlcular ~rom 0.01 to 5%, by weight, examples bein~
ben~oin or benzoin derivatives such as benzoin methyl ether and benzoin isopropyl ether. The layer RS may also contain other conventional additives such as thermal polymerization inhibitors, e,g. p-methoxyphenol, hydroquinone or salts of ~-nitrosocyclohexylhydroxylamine, dyes, photochromic substan-ces, antioxidants and plasticizers (to improve the process-ability when mixin~ the layer).

The thickness o~ the layer RS ls advantageously rrOm 200 to 3000/um and in particular rrom 300 to 2000/um. Pre-ferred layers RS have, after photocrosslinking by overall ex-posure to actinic light, a Shore A hardness ~measured accord-ing to DIN 53~505) of from ~0 to 90 and in particular from 40 to 70 and are as hard or harder, in their photocrosslinked state, than the underlayer U used therewith.
The photocrosslinkable layers ~S are particularly advan-tageously prepared ~rom solutions thereo~ in suitable sol-vents such as cyclohexane, toluene, xylene and tetrahydro-~uran, by casting, which is easy to carry out due to the ract that the two-block copolymers used ln the present invention are distinguished by low solution vlscosities and enable a homogeneous solution of the layer components to be produced.
The use of elevated temperatures is thus unnecessary. The base for layer RS may be the stabillzing layer ST or the un-derlayer U or a protective sheet provided with a coating S
as desaribed below. Ir neoessary, a permanent bond between the layers may be achieved by the use of suitable adhesives or adhesive interlayers.
It ls Orten advantageous to apply a thln, ~lrmly ad-herlng, non-tacky coatlng S to the photocrossllnkable layer RS o~ the laminates, whlch coating S pre~erably consists o~
a polymer capable Or forming hard, non-tacky, transpar~nt and tear-reslstant ~ilms, for axample a polyamide or copolyamlde which ls soluble ln the developer or a mlxture Or such a poly-mer wlth a small amount (10~ by wel~ht or less) o~ a photo-polymer~zable monomer, a photolnitiator and, 1~ necessary, an inhibitor. The thickness o~ thls coating S is adYantageous-~0 ly from about 0.5 to 20/um.

Thls coatin~ S makes lt possible to apply a negative to the laminate for the preparation of relie~ printing plates without the negative sticking to ~he laminate or bubbles rorm-ing, as would in some cases occur if the coating S were omit-ted on account of the surface tack of the layer RS. During development Or the exposed areas of the layer RS to rorm the relief layer, the coating S is generally washed away together with the non-crosslinked areas.
It ls also orten advanta~eous to provide the coating S
with a strippable protective sheet such as a polyester sheet, which sheet may, if desired, be applied to the layer RS at the same time as the coating S~ In general, the protective sheet is removed ~rom the layer RS berore exposure, whilst the coating S generally remains on said layer RS during ex-posure.
The elastomeric underlayer U has a Shore A hardness Or from 15 to 70 and prererably rrom 25 to 60 and its thlckness i8 generally ~rom 0.5 to 6 mm and ln particular rrom about 1 to 4 mm. The hardness Or the underlayer U is, in the prererred embodiment o~ the laminates, equal to or less than the hard-ness o~ the layer RS in the photocrosslinked state.
Sultable elastomerlc materials ~or the underlayer U are ~or example natural rubber, polybutadiene, butadiene-acrylo-nitrile copolymers, butadiene-styrene copolymers, slllcone ; rubber, polysulfide rubber, vlnylidene chloride-hexa~luoro-propylene copolymers, isoprene-styrene and butadiene-styrene block copolymers and, in pPrticular, polyurethane e~astomers whlch may be prepared in known manner ~rom relatively hlgh molecular we1ght polyhydroxyl compounds such as polyesters .i , .-, or polyethers, and optionally low molecular weight polyols and polyisocyanates, in particular diisocyanates. Reference is made in this connection, for example, to Saunders-Frisch, "Polyuretha-nes", Part II, Chapter IX, Interscience Publishers Inc., New York, 1964. The materials used in layer U should conveniently be such as can be processed into layers having a low tolerance on thickness, for example by casting and hardening in molds or heatable centrifuges or, in the case of thermoplastic materials, for example by calandering. The base may, if desired , be of the same material as the layer RS if this is processed to the required dry layer thickness and then photocrosslinked by overall exposure.
Alternatively, the layer U may be prepared from foam-like mate-rials or foams themselves may be used, provided they exhibit a suitable degree of elasticity and do not absorb the printing inks or developer solutions. Preferably, the materials used in layer U are not soluble or only sparingly soluble in the solvents used for developing layer P.
The stabilizing layer ST is intended to impart absolute dimentional stability to the laminate and to prevent deformation of the printing plate when it is fitted to the cylinder of the printing press so as to enable a high degree of register to be achieved for multicolor printing. In the preferred embodiment of the laminates of the invention, the stabilizing layer ST is firmly bonded between the photopolymerizable layer RS and the elastomeric underlayer U. This embodiment has the added advan-tage that the underlayer U is not affected by the solvent liquid during de--_ 9 _ velopment o~ the rellef, thus a~oiding swelling o~ the layer U and the need ~or increased subsequent drying. In the pre-ferred position of layer ST, it generally has a thickness of ~rom about 5 to 500/um and in particular from 10 to 200/um.
The hardness of the stabilizing layer ST should be distinctly higher than that of the other layers. Advantageously, it has a modulus of elasticlty ~measured accordlng to DIN 53,457) Or ~rom 1 x 10~ to 2.1 x 106 and prererably rrom 5 x 103 to 2.1 x 106 kg/cm2. Suitable materials for the stabilizing layer ST
are for example plastics sheeting, metal layers or layers of crosslinked sur~ace coat1ng materials which may, if desired, be rein~orced by ~abrics such as glass fiber or textile fab-rics. We prerer to use plastlcs sheeting such as polyester sheeting. The layers U, ST and ~S, i.e. the relief layer, are ~irmly bonded to3ether. Where suitable polymer materials hav-lng an appropriate chemical structure are used, such a bond may be readlly achieved by, say, oalandering under the action Or suitable organic solvents ~or sortening the surraces Or the layers. However, it ls o~ten necessary to provide a ~irm bond between the layers by applying to one or both sides thereo~ thin layers o~ adhesion promoters or adhesives ~ollow-ed by bonding o~ the layers, in whlch case thin layers o~ ad-hesive are ~ormed between the layers, these having a thickness, however, o~ less than 100/um and prererably less than 30/um.
Such adhesive layers may be prepared using conventional sin~le ^ component and two-component adhesives, the type used depend-ing on the types o~ materials and polymers used in the layers U, ST and ~S. Frequently used, suitable adhesives are, ~or example, the conventional two-¢omponent adhesives based on .

polyurethane and on polychloroprene, which may be applied to the layers to be bonded, for example, by casting in a suit-able thickness. In some cases, where the layer ST is between the layers RS and U, it has proved advantageous to provide the elastomeric underlayer U, on the side remote from the layer ST, with an overlayer ~' based on a non-tacky polymer and having a thic~ness of from 0.1 to 20/um and particularly ~rom 0.2 to lO/um. Suitable polymers ~or this layer are often the same as those used in the preparation of the coating S.
Again, the coating S~ should preferably transmit actinic light.
The lamlnates of the invention may be used ror the pre-paration of relief printing plates, particularly flexographic printing plates, in known manner by imagewise exposure Or the layer RS and then removing the unexposed, i.e. non-oross-llnked, area~ Or sald layer RS, partioularly by a washout proaess. Exposure, whloh may be erreated ln flat-plate expo-sure equlpment or a rotary exposure unit, ls suitably aarried out usln~ conventional light sources emittlng aatinic light, for example conventional ultraviolet fluorescent tubes or hlgh-pressure mercury lamps. The emitted wavelength should ; pre~erably be ~rom ~00 to 400 ~u and should be correlated to the absorptlon aharacteristlcs of the photoinitlator aontalnsd ln the layer RS. Examples of suitable developer solutions for washin~ out the non-crosslinked areas o~ layer RS to effeat relief development are ahlorinated hydrocarbons such as tri-chloroethane, symmetrlcal tetrachloroethane, tctraahloroethyl-ene, hydroaarbons such as hexane, toluene and other or~anic solvents such as N-methylpyrrolidone or mixtures thereo~ wlth lower alcohols rOr controlling the washout process.
The laminates of the invention and the relie~ printing plates made therefrom have a number of advantages. The use o~ the two-block copolymer in the layer RS is superior to the use of three-block copolymers A-B-A as proposed in Bri-tish Patent 1,~66,769, in that it is simpler and more econo-mical to manuracture. Furthermore, three-block copolymers are much more di~ficult to produce wlth uni~orm, reproducible characteristics. Another advantage o~ the use Or two-block copolymers is their much lower viscosity even at high concen-trations, which means that even solutions with a high solids content show good pourability and thus make preparation of the layers more economical. The good solubility is also ad-vantage~us for de~elopment of the relief printing plates. An-other advantage o~ the layers RS o~ the invention over those o~ ~ritish Patent 1,366,769 is that they exhibit no haze even when stored for relatlvely long periods ln the unexposed state but remaln glass clear and are thererore oapable Or glvlng distlnct demarcations between exposed and unexposed ~, 20 segments of the layer, which is not the case with cloudy layers. The two-block copolymers in admixture with the mono-mers show9 after exposure, a surprisingly big improvement in their elastic properties, their ~low resistance and their swelling resistance when contacted by the printing ink sol-vents most commonly used in flexographic printing. Layers ~S
containing partially hydrogenated two-block copolymers exhibit a particularly low tendency to oxidation. The laminat~s o~
the invention are distinguished not only by their simplicity o~ manu~acture but also by the rapidity and ease with which they can be converted into relie~ prlnting plates and also by the good printing properties Or the latter. The printing layer, when in use, readily conforms to irregularities in the surface of the material to be printed. Moreover, the re-lie~ image is not stretched when the plate is mounted on cy-linders of dirferent diameter, this being particularly impor-tant in multicolor printing.
In the ~ollowing Examples the parts and percentages are by weight unless otherwise stated. Parts by volume bear the same relatlon to parts by weight as the liter to the kllogram.

a. A solution of 167.5 parts o~ a gradual-transition poly-styrene-polybutadiene two-block copolymer having a content of 20% of polymerized units o~ styrene and a viscosity num-ber Or 14~.4 ml/g and 0.2 part of 2,6-di-t-butyl-4-methyl-phenol in 220 parts by volume o~ tetrahydro~uran ls pre-pared w~th stirring at 65C. Following homo~enlzatlon, lO
parts of hexanediol-1,6-diacrylate and 20 parts o~ lauryl acrylate are added. 2 parts Or ~-methylol benzoin methyl ether, 0.2 part o~ hydroquinone monomethyl ether and 0.06 part o~ a commercially available black dye are dissolved ; in some tetrahydro~uran wlth a little methanol, and the resultin~ solution is mlxed into the polymer solution. A
125/um thick polyethylene terephthalate sheet (protectlve sheet) provided with an approximately l/um thick layer S
o~ a soluble copolyam~de is knlfe-coated with the result-ing solut~on such that, a~ter dry~ng, a 670Jum thlck lRyer RS is producedO
A~ter exposure in a flat-plate exposure un~t provided - 1~ -wlth 60 watt ultraviolet fluorescent lamps, a photocross-linked sample o~ the layer RS has a Shore A hardness o~ 60 and a resilience, as measured by DIN 53,512, Or 55~.
b. An unexposed specimen as prepared under la above is bonded to a transparent polyethylene terephthalate sheet having a thickness of 75/um by means of a commercial two-component polyurethane adhesive applled in a thickness o~ 20/um, the bond being between the said polyethylene terephthalate sheet and the side o~ said specimen remote from the pro-tective layerc The other slde of said polyethylene tereph-~ thalate sheet is bondedJ using the same adhesive, to a ; 2 mm thick elastomeric underlayer U prepared ~rom a poly-ester glycol, toluylene diisocyanate and an activator and cured at 1~0C. The underlayer U has a Shore A hardness o~
~7 and a resilience Or 45%~
c. When the 125/um thlck polyester protective sheet orlginally serving as base for the application o~ the relief layer RS
ls stripped o~, the polyamide rilm remains on the unex-i posed relief layer RS due to better adhesion and thus makesit possible to place a negative in contact therewith with-out it stloking thereto or bubbles being ~ormed, ~or the purpose o~ exposure through a photographic negatlYe. Fol-lowing preliminary exposure rrom the rear side Or the la-minate ~or 30 seconds over the entire area o~ the relie~
layer RS through the underlayer U (underlayer U ~acing the llght source), the relle~ layer RS is exposed through a combined llne/halftone ne~ative ~or about 15 minutes. ~he relie~ is then developed ~or 4 minutes ln a spray wssher using a mixture of trichloroethylene and isopropanol (ratlo by volume 70~0)~ Following brier drying and post-exposure Or the entire plate ror lO minutes, a rellef printing plate is obtained which is distinguished by very good reproduc-tion of all details contained in the negative and whlch shows excellent printing properties.
: EXAMPLE 2 As described in Example 1, a solution Or 35 parts of a polyisoprene-polystyrene two-block copolymer showing a sharp transition between the blocks and having a viscosity number o~ 158 and a content Or 25~ of polymerized units of styrene in 65 parts of toluene is prepared, to which solution 7 parts of butanediol-194-dimethacrylate, 000~ part o~ toluhydro-~uinone, 004 part of a-methylol benzoin methyl ether and 0.05 part of di-2,6-t-butyl-4-methylphenol are added. As in Ex-ample 1, a layer RS is made from the resulting solution and f thls ls then used to prepare a laminate ln the manner des-cribed aboveO The photocrosslinked rellef layer RS has a Shore A hardness Or 58 and a resilience Or 55%. Relief print-. ing plates made from the laminate in the manner described : above showed very good printing propertiesO
EXAMPLE ~
Example 2 is repeated except that 40 parts Or a sharp-transitlon polyisoprene-polystyrene two-blo¢k copolym~r hav-lng a V'ff scosity number o~ 82 and a content Or 20% of poly-merlzed unlts of styrene are used for the preparation Or the solution for the formation of layer RS. The Shore A hardness o~ the relie~ layer RS9 in the photocrosslinked state, o~ the resultin~ laminate ls 480 Example 2 is repeated except that 12 parts of hexane-diol-1,6-dimethacrylate are used in place of 7 parts of bu-tanediol-1,4-dimethacrylate. The photocrosslinked relief layer has a Shore A hardness of 44 and a resilience of 53%.

The material used in Example la for the layer RS i9 poured onto a 50~um thick polyethylene terephthalate sheet acting as layer ST so as to form a layer thereon having a thickness of 1.5 mm when dry. The layer is then exposed over its entire surface for 30 minutes under a bank of 60 watt ultraviolet fluorescent tubes, i.e. it is completely photo-crosslinked to form an underlayer U. The other, free side of the polyester sheet (layer ST) iS then bonded, by means of a commercial chloroprene adhesive, to the unexposed layer RS
prepared as in Example la, the bond being between said free 3, side of the polyester sheet and the free side of the layer RS. There i8 obtained a laminate in which, after exposure and photocrosslinking of the relief layer RS, the layer RS
(photocrosslinked) and the underlayer U have the same mechanical properties. ~"

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Laminates for the production of relief printing plates and comprising a) a layer RS consisting essentially of a photocrosslinkable mixture of at least one soluble polymer P and at least one monomer M which is compatible with polymer P and has at least one photocrosslinkable C-C double bond, which mixture con-tains a photoinitiator and is soluble in developer solutions used to form the relief in the imagewise-exposed layer RS, b) a non-photocrosslinkable elastomeric underlayer U which has a Shore A hardness of from 15 to 70 and is insoluble in said developer solutions, c) a non-photocrosslinkable stabilizing layer ST which is inso-luble in said developer solutions, and which is located below the elastomeric underlayer U in the order RS-U-ST, wherein the photocrosslinkable layer RS contains, as polymer P, a soluble two-block copolymer consisting essentially, of from 30 to 95% by weight of a diene hydrocarbon having 4 or 5 carbon atoms and from 5 to 70% by weight of a monomer of the formula CH2 = , where R is hydrogen or CH3; R' is phenyl or C1-4 alkyl substituted phenyl, which two-block copolymer has a visco-sity (measured on a 0.5% w/w solution in toluene at 25°C) of from 60 to 350 ml/g, or a partially hydrogenated product thereof and which has either a sudden or gradual transition between the diene hydrocarbon block and the CH2= block.

2. Laminates as claimed in claim 1, wherein the layer RS consists essentially of a mixture of from 60 to 95% by weight of the two-block copolymer P and from 5 to 40% by weight of a compatible monomer M having at least one photocrosslinkable C-C

double bond, which mixture contains from 0.01 to 10% by weight of a photoinitiator, the percentages of P and M totalling 100.

3. Laminates as claimed in claim 1 or 2, wherein said mixture further contains conventional additives.

4. Laminates as claimed in claim 1, wherein the pho-tocrosslinkable layer RS has a thickness of from 200 to 3000 µm and the elastomeric underlayer U has a thickness of from 0.5 to 6 mm.

5. Laminates as claimed in claim 1, wherein the sta-bilizing layer ST has a thickness of from 5 to 500 µm and is firmly bonded between the photocrosslinkable layer RS and the elastomeric underlayer U.

6. Laminates as claimed in claim 1, wherein the Shore A hardness of the relief-forming layer RS following photocross-linking by overall exposure to actinic light is from 30 to 90.

7. Laminates as claimed in claim 1, wherein the pho-tocrosslinkable layer RS has a non-tacky coating S which trans-mits actinic light.

8. Laminates as claimed in claim 7, wherein said non-tacky coating S is further covered by a protective sheet.

9. Laminates as claimed in claim 1, wherein partial hydrogenation products of the two-block copolymer P are used in which the diene segments are partially or completely hydro-genated.