Photopolymerisable printing plate for the manufacture of printing formes.

0001The present invention relates to photopolymerizable printing plates suitable for the production of printing forms, in particular flexographic printing forms, which have at least one intermediate layer on a dimensionally stable support and thereon a relief-forming photopolymerizable layer which essentially consists of a mixture of polymeric binder and at least one ethylenically unsaturated polymerizable compound. Photoinitiator and thermal polymerization inhibitor and contains certain water-soluble copolymers and certain ethylenically unsaturated polymerizable compounds.

0002Photosensitive polymer compositions which contain partially saponified polyvinyl acetate and a polyfunctional acrylate or methacrylate in combination with the compatibility-improving polyhydric alcohols and can be used for the production of printing plates are known, for example, from EP-A-00 81 964.

0003EP-A-224 164 describes light-sensitive recording materials which contain saponified or partially saponified graft copolymers of vinyl esters on polyalkylene oxides as polymeric binders. In many cases, however, the compatibility of the monomers listed here with the binder is not sufficient to meet increased requirements with regard to image reproduction quality and the elasticity of printing forms produced therefrom.

0004EP-A-00 36 301 describes a photosensitive polyamide resin mixture of alcohol-soluble polyamide, a non-polymeric compound which has both vinyl and epoxy groups in one and the same molecule and can react with the polymeric binder to form copolymerizable polymers, and a polyfunctional one Vinyl monomers, the -O-CH₂-<img file="EP0332983A2_D0001.tif" />-CH₂-O-CO-CR = CH₂ groupings has been described.

0005Accordingly, the use of phenylglycidyl ether acrylate as a softening component, combined with polyfunctional acrylates, in photopolymerizable printing plates which contain alcohol-soluble modified polyamide as a polymeric binder had already been known.

0006However, because of the necessary proportion of polyfunctional acrylates and the resulting high crosslinking density, compositions of this type are not suitable for producing flexible, flexographic printing forms. In addition, the use of alcohol as a developer medium for the production of the printing form for many applications is undesirable.

0007The object of the present invention is to show photopolymerizable printing plates which are suitable for the production of flexible printing forms which do not have the disadvantages mentioned above and are distinguished by excellent compatibility of monomeric and polymeric binders, water developability and high elasticity with low hardness without the use of extractable plasticizers.

0008This object can surprisingly be achieved by combining phenylglycidyl ether (meth) acrylates or similar compounds, ie special monofunctional (meth) acrylates, with modified polyvinyl alcohol as the polymeric binder in the photopolymerizable relief-forming layers, without polyfunctional (meth) acrylates or with ethylenically unsaturated Groups of functionalized binders must also be used.

0009The present invention relates to a photopolymerizable printing plate which is suitable for producing soft-elastic printing forms and which bears at least one intermediate layer on a dimensionally stable support and thereon a photopolymerizable layer which essentially consists of a mixture of polymeric binder, at least one ethylenically unsaturated polymerizable compound, photoinitiator and thermal Polymerization inhibitor, which is characterized in that that in the relief-forming photopolymerizable layer as a polymeric binder, a water-soluble copolymer or derivative of polyvinyl alcohol and as an ethylenically unsaturated polymerizable compound, a compound of the general formula (I)<chemistry id="chem0001" num="0001"><img file="EP0332983A2_D0002.tif" /></chemistry> in which R¹ is hydrogen, an alkyl radical having 1 to 10 carbon atoms or an aryl radical having 6 to 10 carbon atoms, R² represents hydrogen or a methyl radical, and X for - (CH₂-CH₂-O)_n-C₂H₄-, -C₂H₄-, - (CHCH₃-CH₂-O)_n-CHCH₃-CH₂-,<chemistry id="chem0002" num="0002"><img file="EP0332983A2_D0003.tif" /></chemistry> and n = 0 to 8, contains.

0010In addition to hydrogen, the R 1 is, for example, an alkyl radical having 1 to 10 carbon atoms, such as, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, , n-octyl, isooctyl or an aryl radical, such as a phenyl or naphthyl radical in question.

0011An intermediate layer of the printing plate may also contain a compound of the general formula (I) in the polymerized state or there may be a thin layer of a conventional adhesion promoter on the dimensionally stable support as the first intermediate layer and a second intermediate layer thereon, which comprises a compound of the general formula ( I) in a mixture with polymeric binder in the polymerized state.

0012The relief-forming photopolymerizable layer of the printing plate according to the invention can also be covered with a removable protective film.

0013Preferred compounds of formula (I) are those in which R¹ is methyl or hydrogen and X is the rest -CH₂-<img file="EP0332983A2_D0004.tif" />-CH₂- or -CH₂-CH₂- stand.

0014An at least partially saponified graft polymer of vinyl esters, in particular of vinyl acetate, on polyethylene oxide can preferably be used as the water-soluble copolymer of the polyvinyl alcohol. A polyvinyl alcohol partially esterified with methacrylic anhydride and / or a partially acetalized polyvinyl alcohol can preferably be used as the water-soluble derivative of the polyvinyl alcohol.

0015The present invention also relates to a printing plate of the above type, which additionally contains a so-called "sensitometric control system", the relief-forming photopolymerizable layer preferably having at least one photoinitiator which triggers rapid photopolymerization in the layer when exposed to actinic light, and, in a known manner, a combination of a soluble dye with a reducing agent for this dye, which does not cause any noticeable photopolymerization in the layer when exposed to actinic light, the reducing agent not reducing the dye in the absence of actinic light, but when exposed, the dye in the excited electron state can reduce, as described for example in EP-A-114 341.

0016With the photopolymerizable printing plates according to the invention, it is possible in a simple and advantageous manner to produce printing forms with the cliché hardness and elasticity customary in flexographic printing, which are also particularly suitable for printing on rough substrates.

0017The following is to be stated in detail regarding the structural components of the printing plates according to the invention.

0018The usual dimensionally stable, rigid or preferably flexible layer supports are known as dimensionally stable supports, the type of layer support also being determined by the intended use. For example, metallic substrates are suitable, for example made of aluminum, magnesium, copper, zinc, steel or multi-metal plates, which can be used as such or in a form pretreated mechanically, chemically, electrochemically and / or by providing an adhesive lacquer. Polymer films with a metallized surface, such as aluminum-coated polyethylene terephthalate films, are also suitable as supports. Aluminum sheets or foils and dimensionally stable plastic foils, in particular polyester foils, such as polyethylene terephthalate foils, are preferred as supports. These dimensionally stable supports generally have thicknesses of approximately 0.08 to 0.3 mm.

0019One or more intermediate layers are present between the support and the relief-forming photopolymerizable layer.

0020For example, an adhesion promoter or adhesive lacquer layer which is thermally crosslinked can be applied to the carrier. Suitable layers of adhesive lacquer are, for example, those based on a mixture of polyol and polyisocyanate, which generally have a layer thickness of 1 to 100, preferably 5 to 50 μm. Such adhesive lacquer layers are described for example in DE-A-1 597 515, DE-A-2 202 357, EP-A-53 259 and EP-A-53 258.

0021Instead of such conventional adhesive lacquer layers, the qualitative and quantitative composition of which is generally adapted to the type of carrier material and the composition of the relief-forming layer or a further intermediate layer, the carrier can also be coated with a thin layer of a compound of the formula (I), preferably phenylglycidyl ether (meth ) coated with acrylate, to which some (photo) polymerization initiator is added, and then thermally or by exposure or Irradiation are polymerized, whereby generally adhesive layers of 1 to 100 microns are formed on the carrier.

0022Mixtures of polymeric binder and polymerisable ethylenically unsaturated compounds, preferably a compound of general formula (I), the polymerisation initiators and / or polymerisation initiators are suitable as a further intermediate layer arranged between the adhesive layer applied to the support and the relief-forming photopolymerizable layer. Contain photopolymerization initiators and, if appropriate, further conventional additives, such as dyes, plasticizers, regulators and thermal inhibitors, and be polymerized thermally or by irradiation before application of the photopolymerizable relief-forming layer. Such intermediate layers can be 1 to 200, preferably 5 to 100 microns thick. For such intermediate layers come as polymeric binders, for example the water-soluble polymers used in the relief layer, but also, for example, polyvinyl acetates or polyvinyl acetals and as polymerizable ethylenically unsaturated compounds, for example arylglycidyl ether acrylates or methacrylates or phenoxyethyl acrylate or mixtures of these monomers with other polymerizable monomers, such as, for example, mono- or polyfunctional (meth) acrylic acid esters.

0023According to the invention, the photopolymerizable relief-forming layer consists of a mixture of a polymeric binder, at least one ethylenically unsaturated polymerizable compound, at least one photoinitiator and a polymerization inhibitor, where the polymeric binder can be a water-soluble vinyl alcohol copolymer or a derivative of polyvinyl alcohol and a compound as an ethylenically unsaturated polymerizable compound of the general formula (I), preferably an arylglycidyl (meth) acrylate is used. The use of further ethylenically unsaturated copolymerizable, in particular also polyfunctional, compounds is not necessary to achieve satisfactory results. The use of further, also polyfunctional, copolymerizable compounds can be advantageous for setting certain properties, for example graded plate hardness. Other such copolymerizable ethylenically unsaturated compounds are one or more compounds with at least one photopolymerizable olefinically unsaturated double bond. The known monomers, oligomers and unsaturated polymers used for the production of relief molds and photopolymer high, low and offset printing plates, the type of which depends on the intended use of the mixtures, but also on the type of the other mixture components . Monomers with two or more olefinically unsaturated photopolymerizable double bonds are suitable alone or in a mixture with monomers with only one olefinically unsaturated photopolymerizable double bond. Polymers with several side or terminal olefinically unsaturated double bonds can also be used instead of or in a mixture with the monomers. Examples of suitable monomers are the di- and polyacrylates and methacrylates, as can be prepared by esterifying diols or polyols with acrylic acid or methacrylic acid; such as the di- and tri (meth) acrylates of ethylene glycol, diethylene glycol, triethylene glycol or polyethylene glycols with a molecular weight of up to about 500, 1,2-propanediol, 1,3-propanediol, neopentylglycol, (2,2-dimethylpropanediol), 1.4 -Butanediol, 1,1,1-trimethylolpropane, glycerol or pentaerythritol, furthermore the monoacrylates and monomethacrylates of such diols and polyols, such as, for example Ethylene glycol, di-, tri- or tetraethylene glycol monoacrylate, monomers with two or more olefinically unsaturated bonds which contain urethane groups and / or amide groups, such as the low molecular weight compounds prepared from aliphatic diols of the type mentioned above, organic diisocyanates and hydroxyalkyl (meth) acrylates . Also mentioned are acrylic acid, methacrylic acid and their derivatives such as (meth) acrylamide, N-hydroxymethyl (meth) acrylamide or the (meth) acrylates of monoalcohols with 1 to 6 carbon atoms.

0024Suitable monomers are also reaction products of glycidyl ethers with acrylic acid or methacrylic acid, such as reaction products of bisphenol A diglycidyl ether or butanediol diglycidyl ether with acrylic acid or methacrylic acid.

0025The ethylenically unsaturated copolymerizable compound of the general formula (I) or the mixture of this compound with one or more further ethylenically unsaturated compounds of the type mentioned above are generally in amounts of 10 to 70, preferably 30 to 60,% by weight, based on the total amount polymeric binder and photopolymerizable monomers used in the relief-forming layer.

0026According to the invention, water-soluble vinyl alcohol copolymers and / or water-soluble derivatives of polyvinyl alcohol are suitable as the polymeric binder. Examples of such suitable polymeric binders are elastomeric graft polymers which are soluble or dispersible in aqueous solvents and which are obtained by polymerizing vinyl esters in the presence of polyalkylene oxides and an initiator of free-radical polymerization, Saponification or partial saponification of the resulting graft copolymer and optionally subsequent esterification or transesterification of vinyl alcohol units of the saponified or partially saponified graft copolymer are prepared and essentially consist of structural units of the composition<chemistry id="chem0003" num="0003"><img file="EP0332983A2_D0005.tif" /></chemistry> where Z: grafted on side branches with structural units<chemistry id="chem0004" num="0004"><img file="EP0332983A2_D0006.tif" /></chemistry> R¹ is hydrogen and / or alkyl radicals with 1 or 2 carbon atoms, R² represents alkyl and / or alkenyl radicals, optionally with carboxyl substituents, and x> y, n> m, m at least 2, n + m = 20-2000, and<maths id="math0001" num=""><img file="EP0332983A2_D0007.tif" /></maths> as described in EP-A-224 164.

0027Likewise suitable are polyvinyl alcohols partially esterified with methacrylic acid, as described in EP-A-220 507, and partially acetalized polyvinyl alcohol.

0028Such suitable polyvinyl alcohols generally have molecular weights <o ostyle="single">M</o>_n between about 4,000 and 100,000, preferably 10,000 and 70,000. The polymeric binder is generally present in the photopolymerizable relief-forming layers according to the invention in amounts of 30 to 90, preferably 40 to 70,% by weight, based on the total amount of polymeric binder and photopolymerizable monomers.

0029The photopolymerizable relief-forming layers according to the invention additionally contain in the usual way at least one photoinitiator, generally in amounts of 0.01 to 10 and in particular 0.01 to 3% by weight, based on the total amount of the photopolymerizable layer. Compounds suitable as photoinitiators are those which are capable of forming free radicals when exposed to actinic light and which trigger rapid photopolymerization in the layer. Examples of suitable photoinitiators are acyloins and acyloin ethers, aromatic diketones and their derivatives and polynuclear quinones. Benzoin and α-hydroxymethylbenzoin and especially their alkyl ethers with 1 to 8 carbon atoms such as benzoin isopropyl ether, α-hydroxymethyl benzoin methyl ether or benzoin methyl ether, benzil monoketals such as benzil dimethyl ketal, benzil methyl ethyl ketal, benzil methyl benzyl ketal are very suitable , Benzil-neopentyl ketal or diarylphosphine oxides, as described in DE-OS 29 09 992, preferably 2,6-dimethoxybenzoyldiphenylphosphine oxide and in particular 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Preferred are type and quantity of photoinitiators that they require only short minimum exposure times, preferably not more than a few minutes, to trigger the photopolymerization when exposed imagewise with actinic light, in particular UV light.

0030The photopolymerizable relief-forming layers according to the invention also expediently also contain inhibitors against thermal polymerization, such as hydroquinone, p-methoxyphenol, dinitrobenzene, p-quinone, methylene blue, β-naphthol, N-nitrosamines such as N-nitrosodiphenylamine, phenothiazine, phosphoric acid esters such as triphenylphosphite or diephosphate and especially the alkali and aluminum salts of N-nitroso-cyclohexyl-hydroxylamine. The inhibitors are generally added to the photopolymerizable mixtures of the relief-forming polymerizable layer in an amount of 0.001 to 3% by weight and in particular in an amount of 0.003 to 1% by weight, based on the total amount of the polymerizable layer.

0031In a known manner, other conventional additives can of course also be used, such as plasticizers, saturated low-molecular compounds with amide or alcohol groups, waxes, pigments, etc.

0032According to a particularly advantageous embodiment of the present invention, the photopolymerizable layer can also contain a regulator system, as described, for example, in EP-A-114 341.

0033These are mixtures of certain dyes (1) with mild reducing agents (2) for the respective dye (1) used (cf. also EP-A-0 114 341). The mixture (1) + (2) should not cause any noticeable photopolymerization in the layer of the photopolymerizable mixture in the imagewise exposure to actinic light, which can be determined with a few experiments. For example, If the exposure time for layers of the photopolymerizable mixture containing the photoinitiator according to the invention, preferably essentially solvent-free, is X hours or minutes, then the corresponding layer which does not contain the photoinitiator should advantageously also be used ten times the exposure time during subsequent development of the relief shape by washing have no noticeable proportions of photopolymerized layer, generally less than 20% by weight of the exposed amounts of monomers should be photopolymerized.

0034Suitable dyes (1) for the photopolymerizable mixtures are, in particular, those from the series of phenoxazine dyes, such as, for example

0035Capri Blue GN (CI 51000), Zapo Real Blue 3 G (CI 51005), Gallo Blue E (CI 51040), Real New Blue 3 R (CI 51175), Nile Blue A (CI 51180), Real Green M (CI 51210), Real Black L (CI 51215) , as well as rhodanil blue, the salt or amide from rhodamine B (Basic Violet 10, CI 45170) and Nile blue (Basic Blue 12, CI 51180), compounds from the range of phenazinium dyes, such as neutral red (CI 50040), neutral violet (CI 50030 ), Azine scarlet G (CI 50045), rhodulin heliotrope 3 B (CI 50055), neutral blue C (CI 50150), azine green GB (CI 50155), safranin B (CI 50200), indamine blue B (CI 50204), rhodulin red G (CI 50215), rhodulin blue GG extra (CI 50220), indazine GB (CI 50221), safranin T (CI 50240), mauvein (CI 50245), naphthyl red (CI 50370) and nigroin black T (CI 50415), acridinium dyes, such as acriflavine (CI 46000), acridine orange (CI 46005), acridine scarlet J (CI 46015 ), Acridine yellow G (CI 46025), Aurazin G (CI 46030), diamond phosphine GG (CI 46035), phosphine E (CI 46045), flaveosin (CI 46060), benzoflavin (CI 46065) and rheonin A (CI 46075), and also phenothiazinium dyes, such as methylene blue or thionine. (Isobutylthio) anthraquinone is also suitable as a dye (1).

0036The choice of the dye (1) used in the photopolymerizable mixture is primarily determined by the aesthetic impression. For example, a visual assessment of the printing plates is particularly easy with the compounds neutral red (CI 50040), safranin T (CI 50240) and rhodanil blue, which are preferably used in the photopolymerizable mixture.

0037In combination with the dye (1), the layers according to the invention can therefore contain a sufficient amount of a reducing agent (2) for the dye (1) which does not reduce the dye (1) used in the absence of actinic light, and the dye when exposed can reduce in the excited electron state, especially to the semiquinone. Examples of such mild reducing agents are ascorbic acid, anethole, thiourea, diethylallylthiourea, hydroxylamine derivatives, especially N-allylthiourea and preferably salts of N-nitrosocyclohexyl-hydroxylamine, especially the potassium and aluminum salts. The latter are also known as inhibitors against thermal polymerization in photopolymerizable mixtures. The amount of the reducing agent added is generally about 0.005 to 5 and in particular 0.01 to 1% by weight, based on the total amount of the photopolymerizable layer, but should not be less than the reduction equivalent of the amount of the dye (1) used. In many cases, the addition of 3 to 10 times the amount of dye (1) used has proven successful.

0038The photopolymerizable printing plates are generally produced by applying a homogeneous mixture of the components of the photopolymerizable relief layer, optionally with the addition of solvents or solvent mixtures, to a dimensionally stable support which has expediently been provided beforehand with one or more adhesion-promoting layers.

0039The homogeneous photopolymerizable mixture can be prepared in the usual way by mixing the individual components in conventional mixing units, for example in kneaders, extruders or stirred kettles. The homogeneous mixture is then generally applied in a thickness of 25 to 6000, preferably 200 to 1000 .mu.m to the dimensionally stable support provided with the adhesive layer or with one or more intermediate layers.

0040It may also be advantageous to apply a cover or protective layer to the photopolymerizable relief-forming layer, for example a thin layer of polymers soluble in the developer medium, such as polyvinyl alcohol or polyvinyl alcohol-polyethylene oxide copolymers.

0041The photopolymerizable printing plates according to the invention can be processed in a known manner to give relief forms, in particular printing forms. For this purpose, the layer of the photosensitive material is generally exposed imagewise with actinic light from light sources, such as UV fluorescent tubes, high, medium or low pressure mercury lamps, fluorescent tubes, etc., the emitted wavelength preferably being between 300 and 420 nm. The unexposed and uncrosslinked layer portions can be removed by spraying, washing, brushing, etc. with aqueous solvents or water. It is an advantage of the printing plates according to the invention that they allow the unexposed layer parts to be washed out with pure water without the addition of organic solvents. Developed relief and printing forms are expediently dried at temperatures of up to 120 ° C. and, if necessary, after-exposed simultaneously or thereafter with actinic light.

0042The printing forms produced from recording materials according to the invention are particularly suitable for flexographic printing, newspaper flexographic printing and similar types of printing.

0043The printing plates according to the invention which contain a compound of the general formula (I), in particular phenylglycidyl ether (meth) acrylate as a photopolymerizable ethylenically unsaturated compound in the relief-forming layer, can be produced very advantageously and can be processed into printing forms which have high elasticity and low hardness.

0044The invention is illustrated by the following examples. Unless stated otherwise, the parts and percentages therein relate to the weight. Parts by volume behave in parts like liters to kilograms.

0045The cliché hardness was measured using an apparatus for determining the Brinell hardness (according to DIN 53 456) under load (film hardness determination apparatus according to Pfund) by measuring the depth of penetration of a quartz ball with a diameter of 5.926 mm.

example 1

0046A graft copolymer is obtained by thermal polymerization of 3 parts of vinyl acetate in the presence of 2 parts of polyethylene oxide with an average molar mass of 35,000 g / mol and subsequent transesterification in methanolic sodium hydroxide solution, as described in EP-A-224 164. From 55 parts of this graft copolymer, 45 parts of phenylglycidyl ether acrylate (= reaction product of phenylglycidyl ether and acrylic acid), 1.5 parts of benzyldimethylketal, 0.5 part of potassium salt of N-nitrosocyclohexylhydroxylamine, 0.05 part of safranin T (CI 50 240), 50 parts of water and 50 parts of methanol is prepared by stirring at 60 ° C a solution.

0047The solution is poured onto a steel sheet provided with an adhesive varnish and scraped off in such a way that a layer of the photopolymerizable mixture of 500 μm thickness is formed after drying. The printing plate thus obtained is exposed to actinic light through a negative for 4 minutes and developed for 2 minutes at 20 ° C. in a commercially available spray washer with water. After drying, an elastic printing form is obtained with a smooth, tack-free surface, a very well-developed relief and a Brinell hardness (according to DIN 53 456) of 10 cN / mm².

Example 2

0048From a solution of 10 parts of a partially hydrolyzed polyvinyl acetate (degree of polymerization 400, degree of saponification 80 mol%), the free hydroxyl groups of which were esterified with 5 mol% acrylic acid, 50 parts of a polyethylene oxide-polyvinyl alcohol graft copolymer (e.g. Mowiol® 04-M1 from Hoechst), 40 parts of phenylglycidyl ether acrylate, 1.2 parts of benzil dimethyl ketal, 0.5 part of potassium salt of N-nitrosocyclohexylhydroxylamine and 0.05 part of safranin T in 50 parts of water and 50 parts of methanol, as in Example 1 described, made a printing plate.

0049After imagewise exposure, development in water and drying, an elastic printing form with a smooth surface, a very well-developed relief and a Brinell hardness of 35 cN / mm² is obtained.

Example 3

0050From a solution of 10 parts of a partially hydrolyzed polyvinyl acetate (degree of polymerization 400, degree of saponification 80 mol%), the free hydroxyl groups of which were esterified with 5 mol% acrylic acid, 50 parts of the polyethylene oxide-polyvinyl alcohol graft copolymer described in Example 1, 40 parts phenylglycidyl ether acrylate, 1.2 parts of benzil dimethyl ketal, 0.5 parts of potassium salt of N-nitrocyclohexylhydroxylamine and 0.05 parts of Safranin T in 50 parts of water and 50 parts of methanol, as described in Example 1, a printing plate is prepared.

0051After imagewise exposure, development in water and drying, a rubber-elastic printing form with a well-developed relief and a Brinell hardness of 14 cN / mm² is obtained.

Example 4

0052A solution of a photopolymerizable mixture as described in Example 1 is poured onto a polyester film provided with a 2 μm thick layer of polyvinyl alcohol and knife-coated so that a 500 μm thick photopolymerizable layer is formed after drying. Phenylglycidyl ether acrylate, which contains 2% dissolved benzil dimethyl ketal, is applied to an aluminum sheet degreased by washing with acetone in such a way that, after exposure to actinic light, a 50 μm thick layer of the polymerized acrylate is formed.

0053By laminating the photopolymeric layer with the carrier prepared in this way, using a mixture of ethanol and water in a ratio of 1: 1, and peeling off the polyester film, a printing plate is produced, from which printing plates with excellent adhesion between the relief layer and carrier are produced by the process described above be preserved.

Example 5

0054The procedure is as described in Example 3, but a 0.2 mm thick polyethylene terephthalate film is used as the support instead of the aluminum sheet. Here too, printing forms with excellent adhesion to the carrier are obtained.

Comparative Example 1

0055From a solution of 25 parts of a polyethylene oxide-polyvinyl alcohol graft copolymer (e.g. Mowiol 04-M1 from Hoechst AG), the free hydroxyl groups of which were esterified with 4 mol% acrylic acid, 45 parts of a graft copolymer prepared as described in Example 1, 30 parts of ethylene glycol dimethacrylate, 1.2 parts of benzil dimethyl ketal, 0.5 part of potassium salt of the N-nitrosocyclohexylhydroxylamine and 0.05 part of Safranin T in 50 parts of water and 50 parts of methanol, a printing plate is prepared as described in Example 1.

0056An exposure time of more than 25 minutes is necessary to produce a printing form from the raw plate produced in this way.

0057You get hard, brittle clichés with a rough surface and poorly formed relief layer.