MXPA00012690A - Photo-curable polymer composition and flexographic printing plates containing the same - Google Patents

Abstract

Photo-curable polymer composition comprising:(a) a first block copolymer comprising at least two blocks A of polymerised mono-vinyl aromatic monomer, at least one block B of polymerised conjugated diene monomer, and, optionally, a residue of a di-functional coupling agent, wherein the total polymerised mono-vinyl aromatic monomer content is in the range from 5 to 25 wt.%of the block copolymer, and wherein the residue, if present, is derived from a di-functional coupling agent containing alkoxy or epoxy functional groups;(b) 0 to 70%by weight of a second block copolymer having one block A at least one block B and, optionally, a residue of a di- or multi-functional coupling agent, wherein the total polymerised mono-vinyl aromatic monomer content is in the range from 5 to 50 wt.%of the block copolymer (c) at least 5%by weight of a low molecular weight block copolymer and (d) a photo-initiator. Flexographic printing plate precursor comprising a photo-curable layer sandwiched between two release films or a release film and a support. Cured polymer composition, obtainable by curing the photo-curable composition;flexographic printing plate containing the cured polymer composition, process for printing on a substrate with the flexographic printing plate.

Description

COMPOSITION OF PHOTO-CURABLE POLYMER AND FLEXOGRAPHIC PRINTING PLATES THAT CONTAIN IT p_S3U? -N EE LA B? JENKN The present invention relates to photo-curable polymer compositions. In particular, it relates to photo-curable polymer compositions for use in printing plates, comprising a block copolymer having two or more blocks of polymerized monovinyl aromatic monomer, and one or more blocks of polymerized conjugated diene; a second polymer having a polymerized monovinyl aromatic monomer block and one or more blocks of polymerized conjugated diene, a low molecular weight block copolymer comprising a block of polymerized monovinyl aromatic monomer and one or more blocks of polymerized conjugated diene and a photoinitiator . The invention also relates to flexographic printing plate precursors containing the photo-curable polymer composition, as well as to flexographic printing plates. Flexographic printing plates are well known in the art and are especially useful for commercial printing on various products such as flexible plastic containers, cartons, plastic bags, boxes and envelopes.

Ref: 125693 For purposes of this specification, cured nc plates used to prepare flexographic (cured) printing plates are referred to as flexographic printing plate precursors. Flexographic printing plate precursors typically comprise a photo-curable layer, prepared from a photo-curable polymer composition, and protective layer (s) to protect the photo-curable layer of daylight. Optionally, the precursor of the flexographic printing plate further comprises a support. Often a support is used to give strength to the flexographic printing plate (precursor). Alternatively, the precursor side of the flexographic printing plate opposite the image side (printing) of the printing plate is cured to form a support. Typically, in the absence of a support, a flexographic printing plate is prepared by first curing the side of the photo-curable layer of the FPP precursor (acronym in photo-curable printing plate) removed from the printing side. As a result the cross-linking side of the photo-curable layer becomes a substantially insoluble thermoset layer and acts as a support for the uncured portion of the flexographic printing plate precursor. Subsequently, the side that is used for printing is selectively cured by exposing the sensitive image of the photo-curable layer to light, e.g. UV light. The parts of the layer not exposed (uncured) are then removed in developer baths e.g. with a solvent or water. After drying, the flexographic printing plate is ready to use. It will be appreciated that the curing of the sensitive image of the FPP precursor must be done in a precise manner. Any unintentional curing could lead to an uncured image on the flexographic printing plate, and therefore unclear prints. In order to avoid undesirable scattering of light it is important that the precursor of the flexographic printing plate be as transparent as possible, ie, not dark. In addition, there is a need for further improvement of the total combination of the physical properties of such photo-curable polymer composition for use in a flexographic printing plate (precursor). The printing plates should be soft and elastic after curing. Normally, elasticity is obtained by the presence of an elastomer in the photo-curable polymer composition. Often, the elastomer is a block copolymer having two or more polymerized styrenes and one or more polymerized diene blocks. The FPP precursor must be easy and quick to cure, and the uncured material should be easy to remove, and preferably not sticky. The flexographic printing plate must be dimensionally stable during storage; it must be flexible enough to wrap around a printing cylinder; strong enough to withstand the rigors experienced during a printing process; abrasion resistant; Pretty soft to facilitate the transfer of ink during the printing process; and quite solvent resistant to particular ink to avoid image blur. It will be appreciated that achieving an attractive balance of all these physical properties will be difficult. It would be desirable if a photo-curable polymer composition could be found which has a good abrasion resistance when cured, has a relatively low hardness, allows easy removal of uncured and / or non-dark parts, thus allowing precise curing without dispersion of actinic radiation to unwanted parts. Preferably, the photo-curable polymer composition has an attractive balance of the above and other relevant properties.

The present invention relates to a photo-curable polymer composition comprising: (a) a first block copolymer. comprising at least two outer blocks A of polymerized monovinyl aromatic monomer, at least one internal block B of polymerized conjugated diene monomer, and, optionally, a residue of a coupling agent ai or mult i-functional, wherein the total content of the polymerized monovinyl aromatic monomer is in the range of 5 to 25% by weight of the block copolymer, and wherein the residue, if present, is derived from an agent of di- or mult i-functional coupling that contains alkoxy or epoxy functional groups; (b) 0 to 70% by weight, base of the total composition of the block copolymer (a) + (b) + (c), of a second block copolymer, the second block copolymer has a block A of aromatic monomer monovinyl polymerized, at least one block B of a polymerized conjugated diene monomer, and optionally, a residue of a di- or multifunctional coupling agent, wherein the total content of polymerized monovinyl aromatic monomer is in the range of 5 to 50% weight of the block copolymer, and in Sl Sl Sllilililili donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde donde where the residue, if present, is derived from a di- or multi-functional coupling agent containing akoxy or epoxy functional groups; (c) at least 5% by weight, based on the total composition of the block copolymer (a) + (b) + (c), of the low molecular weight block copolymer, where the total of (b) and (c) is from 15% by weight to 80% by weight, based on the total composition of the block copolymer (a) + (b) + (c), the low molecular weight block copolymer has a monomer block A polymerized monovinyl aromatics, and at least one B block of polymerized conjugated diene monomer, and has an average molecular weight in the range of 1,000 to 35,000; and (d) a photo-initiator. For the purposes of this specification, the total composition of the block copolymer is taken to be the block copolymers (a), (c), and, if present, (). Typically, and preferably, the photo-curable polymer composition further comprises an ethylenically unsaturated crosslinking agent that polymerizes upon addition. Such a crosslinking agent is typically a component, such as a monomer or a mixture of monomers, that is compatible with the block copolymer (s). The monomers that can be used in the photo-curable polymer composition are well known in the art. Examples of such monomers can be found in US Patents 4,323,636; 4,753,865; 4, 726, 877 and 4, 894, 315. The term "compatible" means that the captured component can be mixed in a molecularly dispersed manner in the photo-curable composition, or that the component has the same breaking rate, does not substantially cause opacity and does not separate from the photo-curable composition in the course of time, ie it is not separated in 14 days, preferably not in a month. Typically, the ethylenically unsaturated crosslinking agent which polymerizes by addition has a boiling point of at least 100 ° C at atmospheric pressure and a molecular weight of up to 3000, preferably up to 2000. Examples of ethylenically unsaturated crosslinking agents that Suitable polymerization by addition include esters of acrylic acid or methacrylic acid, styrene and derivatives thereof, esters of maleic acid or fumaric acid, acrylamide or methacrylamide and allyl compounds. Preferably, acid esters are used and -4- m & .¿, "-sj ^? *** ^. ^^ - ^ «* ¡^ ^ s ^^^ ^^^^ -. acrylic or methacrylic acid. Especially preferred monomers are 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, and hydroxyethyl methacrylate. Preferably, the first block copolymer is linear, and, if a coupling agent is used, the coupling agent is di-functional. More preferably, non-coupling agent is used. More preferably, the first block copolymer has structure A-B-A. The total average molecular weight of the first block copolymer is preferably in the range of 50,000 to 300,000 g / mol. More preferably, the average molecular weight is in the range of 65,000 to 250,000. The average molecular weight can be determined with gel permeation chromatography (GPC) using polystyrene calibration standards (according to ASTM D 3536). From the measured apparent molecular weight (sometimes referred to as peak molecular weight) the average (true) molecular weight can be calculated. The apparent molecular weight is the molecular weight as if the polymer were 100% polystyrene, as the polystyrene calibration standards are used. The average molecular weight ^^ - ^^^^^^ - j ^^^^^^^^^^^^^^^^^^^^^ g ^^ gM ^ g ^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ - ^^^^^ is a "true" molecular weight that takes into account the chemical composition of the polymer. The total content of poly (monovinyl aromatic) of the first block copolymer is preferably in the range of 10 to 22% by weight, more preferably 15 to 20% by weight. The second block copolymer preferably has structure A-B. The total average molecular weight of the second block copolymer is preferably in the range of more than 35,000 to 150,000. More preferably, the average molecular weight is in the range of 40,000 to 150,000, even more preferably in the range of 45,000 to 120,000. The total poly (aromatic monovinyl) content of the second block copolymer is preferably in the range of 5 to 25% by weight, more preferably 10 to 22% by weight, even more preferably 15 to 20% by weight. The monovinyl aromatic monomer is typically selected from styrene, alkyl styrene Cj-Cj and dialkylstyrene Ci-C4, in particular styrene-methylstyrene, o-methylstyrene or p-methylstyrene, 1,3-dimethylstyrene, p-tert-butylstyrene or mixtures thereof, more preferably styrene.

The conjugated diene monomer is typically a conjugated diene monomer containing from 4 to 8 carbon atoms, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimetyl- 1,3-butadiene, preferably butadiene or isoprene or mixtures thereof, more preferably isoprene. If 1, 3-butadiene is used as the conjugated diene monomer, it may be preferred that a substantial part of 1,3-butadiene is polymerized via the 1,2-addition rather than the 1,4-addition pathway. That is, according to one embodiment, the 1,2-vinyl content of the butadiene block is preferably at least 25% by weight, more preferably from 30 to 60% by weight. The block copolymers are typically prepared by means of anionic polymerization. The preparation of block copolymers is well known to those skilled in the art and has been described in e.g. US Patent 3,265,765; 3,231,635; 3,149,182; 3,238,173; 3,239,478; 3,431,323; Re. 27,145, and many manuals including "Thermoplastic Elastomers, comprehensive review", (1987), edited by N.R. Legge, G. Holden, H.E. Schroeder, Hanser publishers. The composition of the block copolymer comprising both the first block copolymer (a) and the second block copolymer (b) that is used Optionally, the photo-curable composition of the present invention can be conveniently prepared by three different methods. (a) Polymerization of a monovinyl aromatic monomer block with a monofunctional initiator, such as sec-butyl lithium or tert-butyl lithium; adding a conjugated diene to form an "active" diblock copolymer and coupling these active diblock copolymers with a di- or multi-functional (preferably di-functional) coupling agent, containing alkoxy or epoxy groups, preferably methoxy or ethoxy groups . The coupling efficiency of such coupling agents is not 100%, and the desired coupling efficiency can be adapted to some degree. Therefore, the product is typically a blend of coupled multiblock copolymer and uncoupled diblock copolymer. (b) A sequential synthesis of a linear triblock copolymer using a monofunctional or difunctional initiator; separate polymerization of a diblock copolymer and a physical mixture of the two block copolymers. (c) the process described in European Patent Specification No. 691991, which is incorporated herein by reference. The process involves (1) polymerizing the monovinyl aromatic monomer in an inert hydrocarbon solvent, in the presence of an organolithium initiator until substantially complete conversion; (2) adding the conjugated diene monomer to the polymerization mixture and allowing the conjugated diene monomer to polymerize to substantially complete conversion; (3) adding a second portion of organolithium initiator, followed by the addition of a second portion of conjugated diene monomer to polymerize to substantially complete conversion; (4) adding a second portion of a monovinyl aromatic monomer and allowing the monovinyl aromatic monomer to polymerize to substantially complete conversion; and (5) add a terminating agent. By "substantially complete conversion" it is indicated that the polymerization is allowed to proceed to at least 90%, preferably at least 95%, more preferably at least 98% of the charged monomer that has been polymerized. In the above methods the terminating agents are used to terminate any "active" polymer following the polymerization and any coupling with a suitable coupling agent. The terminating agent is a compound that donates protons, preferably an alkanol, more preferably a C: -C4 alkanol, in particular methanol. Method (c) is preferred for the purposes of preparing the block copolymer composition comprising first and second block copolymers. If the block copolymer composition to be used in the composition of the present invention contains a first block copolymer but not a second block copolymer, then the first block copolymer is typically linear and is prepared by sequential polymerization complete The low molecular weight block copolymer is typically prepared separately by anionic polymerization and mixed with the first block copolymer or the first and second block copolymer. The average molecular weight of the low molecular weight block copolymer is preferably from 5,000 to 32,000, more preferably from 10,000 to 30,000. The total polyvinyl aromatic content of the low molecular weight block copolymer is preferably in the range of 5 to 25% by weight, more preferably 10 to 22% by weight, even more preferably 12 to 20% by weight .

The amount of low molecular weight block copolymer is preferably not more than 55% by weight, more preferably not more than 50% by weight of the total composition of the block copolymer. If a second block copolymer is present, the amount of low molecular weight block copolymer is preferably at least 10% by weight, more preferably at least 15% by weight of the total composition of the block copolymer. If a second block copolymer is not present, the amount of low molecular weight block copolymer is preferably at least 20% by weight of the total composition of the block copolymer. The second block copolymer, if present, typically comprises at least 5% by weight of the total composition of the block copolymer, preferably at least 10% by weight. Preferably, the second block copolymer comprises at most 60% by weight of the total composition of the block copolymer, more preferably at most 50% by weight, more preferably at most 40% by weight. Photo-initiators are known to those skilled in the art and examples of suitable photo-initiators have been described in European Patent Specification No. 0 696 761 of the European Patent and US Pat. 4,894,315; 4,460,675 and 4,234,676. Typically, the photoinitiator is optionally selected from substituted polynuclear quinones, aromatic ketones, benzoin and benzoin ethers and 2,4,4-triaryl imidazolyl dimers. Preferred photo-initiators are selected from the group consisting of: (1) a benzophenone of the general formula (I) where R1 to R6 independently represent Hydrogen or an alkyl group having from 1 to 4 carbon atoms, preferably methyl, and wherein R7 and / or R & they have the same meaning as R1 to R6 or further represent alkoxy or 1 to 4 carbon atoms, and wherein n has a value of 0, 1, or 2, optionally in combination with at least one tertiary amine, (2) a carbonyl compound containing sulfur, wherein the carbonyl group directly binds to at least one aromatic ring and is preferably the "•" - * - zMi m¿¿ííí ^ ^ MÉMÍa fi ^ í ^ M É | M ^ ^^^ dtMUM |. formula generates l I I wherein R9, R10, and R11 could each represent hydrogen, alkyl of 1 to 4 carbon atoms, and (3) mixtures of (1) and (2). Examples of suitable compounds of category (1) are benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, and eutectic mixtures of 2,4,6-trimethylbenzophenone and 4-methybenzophenone (ESACURE TZT), or 2, 2- dimethoxy-1, 2-diphenyletan-1-one (IRGACURE 651) (ESACURE and IRGACURE are registered trademarks). These compounds could be used in combination with tertiary amines, such as e.g. UVECRYL 7100 (UVECRYL is a registered trademark). Category (2) comprises compounds such as, eg, 2-methyl-l- [4- (met il-t io) f in i 1] -2 -mor fo 1 i nop r opanone-1, commercially available as IRGACURE 907. An example of suitable mixtures (category (3)) is a mixture of 15 weight percent of a mixture of 2-isopropyl ioxanthone and 4-isopropylthioxanthone, and 85 weight percent of a mixture of 2, 4, 6- tr ime ti lben zofenone and 4-methylbenzophenone. This mixture is commercially available under the trade name of ESACURE X15. The photo-initiators of any of the above categories (1), (2), and (3) could also be used in combination with other photo-initiators, such as e.g. UVECRYL P115 (one diamine). Particularly useful is a combination of benzophenone or IRGACURE 651 and UVECRYL P115. In a more preferred embodiment of the present invention the photoinitiator is selected from the group consisting of (i) benzophenone, or 2, 2-dimethoxy-1,2-diphenyletan-1-one (IRGACURE 651), (ii) a mixture of benzophenone or IRGACURE 651, and a tertiary amine, and (iii) 2-methyl-l- [4- (methylthio) phenyl] -2 -mor fol ino-propanone-1. Of these 2-met il-1- [4- (methylthio) phenyl] -2-morpholinopropanone-1 or 2, 2-dimethoxy-1, 2-diphenyl-ethan-1-one are most preferred. Preferably, the photo-curable polymer composition comprises 0.01 to 5% by weight photo-initiator, based on the total composition, preferably 0.1 to 2.5% by weight. The amount of ethylenically unsaturated crosslinking agent which polymerizes by addition is preferably from 0 to 40% by weight, based on the total composition, more preferably from 1 to 40% by weight, in particular 5 to 35% by weight. The photo-curable composition could further comprise plasticizers, and / or one or more stabilizers such as antioxidants, UV stabilizers and radical expellers, as well as other additives known to those skilled in the art which are desirable in photo-curable compositions. The plasticizers are well known to those skilled in the art. Typically, the hardness of a printing plate is decreased by adding a plasticizer to the photo-curable polymer composition. The plasticizer must be substantially compatible with at least the elastomer diene blocks. Examples of commonly used plasticizers include oil and liquid polyolefins such as polyisopropene. Examples of alternative plasticizers that could be used in the composition of the invention are randomly polymerized styrene and conjugated diene oligomers, polybutylene, polybutadiene, polybutene-1, and ethylene-propylene-diene rubber, all have an average molecular weight in the range of 300 to 35,000, Preferably from 300 to 25,000, more preferably from ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ g ^^^^^^^ ** ^^^^^^ 500 to 10, 000. The plasticizer, if present, typically contains up to 40% by weight of the total photo-curable composition, preferably, if present, at least 5% by weight to 35% by weight. It has been found that the low molecular weight block copolymer (c) in the photo-curable composition of the present invention acts as a plasticizer, in the sense that hardness decreases. Therefore, according to a preferred embodiment, the photo-curable composition of the present invention does not contain plasticizer. For the purposes of this specification, the low molecular weight block copolymer (c) is not included in the term plasticizer. Stabilizers such as antioxidants / UV stabilizers / radical expellers are also well known to those skilled in the art. Especially, clogged phenols, organometallic compounds, aromatic amines, aromatic phosphites and sulfur compounds are used for this purpose. Preferred stabilizers include phenolic antioxidants, thio compounds and tris (alkyl phenyl) phosphites. Examples of antioxidants / radical expellers - '* - - ^ - - - ^ •• - ^^^^' • ^^ - ^^^ - * - - ** commercially available are pentaerit ritol-tetracis (3, 5-di-ter -butyl-4-hydroxy-hydrocinnamate) (IRGANOX 1010); octadecyl ester of 3,5-bis acid (1,1-d? -methyl-ethyl) -4-hydroxy-benzene propanoic acid (IRGANOX 1076); 2,4-bis (n-octyl-thio) -6- (4-hydroxy? -3,5-di-tert-butylanilino) -l, 3,5-triazine (IRGANOX 565); acrylate 2-tert-butyl-6- (3-tert-butyl-2'-hydroxy-5-methyl-Ibenzyl) -4-methylphenyl (SUMILIZER GM); tris (nonylphenyl) phosphite; tris (mixed mono- and di-phenyl) phosphite; diphosphite of bis (2,4-di-tert-butylphenyl) -pentaerythritol (ULTRANOX 626); dipterethyl pentaerythritol diphosphite (WESTON 618); diphenylamine styrene (NAUGARD 445); N-1, 3-dimethylbutyl-N '-phenyl-paraphenylenediamine (SUMILIZER 116 PPD); tris (2,4-di-tert-butylphenyl) phosphite (IRGAFOS 168); 4, 4-but il iden-bis- (3-met i 1- 6 -er-but-il-phenol) (SUMILIZER BBMS) (IRGANOX, SUMILIZER, ULTRANOX, WESTON, NAUGARD and IRGAFOS are registered trademarks). The stabilizer (s) are typically present in the photo-curable composition in a total amount of 0.01 to 5% by weight, based on the total photo-curable composition, preferably 0.2 to 3% by weight . Other well known components that could be present include polymerization inhibitors, antiozonants, colorants, fillers or z ^ ^ Sm? tiu ^. z ^, .. -.... *. ..., -4 * ¿^ Sfaa3 reinforcers. It is the practice of the expert to select the appropriate additional components in the appropriate quantities. According to a further aspect, the invention relates to a precursor of the flexographic printing plate comprising a photo-curable layer placed between two release films or a release film and a support, wherein the film (s) s) of release and any support substantially prevent the actinic radiation reaching the photo-curable layer, and wherein the photo-curable layer contains the photo-curable polymer composition as described herein. According to still another aspect, the invention relates to a cured polymer composition obtainable by curing a photo-curable composition as described herein with actinic radiation. Curing is typically carried out by subjecting the photo-curable composition to actinic radiation. Usually, the photo-initiator used is more sensitive in the ultra violet range. Therefore, preferably, the radiation source should provide an effective amount of this radiation, more preferably having an output spectrum in the range of 200 to 500 nm, even more preferably in the range of 230 to 450 nm. Particularly suitable UV sources are FUSION bulb lamps having maximum output at 260-270 nm, 320 nm and 360 nm (bulb "H"), at 350-390 nm (bulb "D") or at 400-430 nm ( bulb "V") (FUSIÓN is a registered trademark). Combinations of these FUSION bulb lamps could also be used. The bulb lamps H and D are particularly useful, while a combination of bulb D and bulb H can also be applied properly. A further example of an adequate source of UV radiation is a mercury vapor lamp, such as a 300 W / 2.5 cm (300 W / inch) mercury medium pressure UV lamp from the American UV Company. The invention further relates to a flexographic printing plate containing the cured polymer composition as described herein. Uncured portions of the flexographic printing plate are typically removed with a solvent, followed by drying of the plates, according to procedures known to those skilled in the art as e.g. it is described in EP-A-0 474 178. Primarily for environmental reasons, the uncured portions of the flexographic printing plate could also be removed by means of water. However, water is a poor solvent for the block copolymer composition (hydrophobic), as described herein. Therefore, typically hydrophilic polymers are added to the photo-curable composition, the polymers having an acid or amine value of from 2 to 200, preferably from 5 to 120, more preferably from 20 to 80, as described in EP. -A-0 513 493. Most flexographic printing plates are uniformly post-exposed to ensure that the photo cross-linking process is completed, and optionally subjected to a treatment to remove stickiness according to procedures known to the art. art experts like eg it is described in EP-A-0 474 178. Furthermore, the invention relates to a process for printing on a substrate comprising adding ink to the elevated portion of the image side of the flexographic printing plate as described herein, and contacting the flexographic printing plate containing ink with the substrate, thereby transferring ink from the flexographic printing plate to the substrate, and removing the flexographic printing plate from the substrate. The invention will now be described in more detail with reference to the Examples.

Example 1 (comparative) A photo-curable polymer composition was prepared by mixing 100 parts of block copolymer KRATON D1107 with 12 parts by weight of 1,6- hexanediol diacrylate (HDODA), 0.5 parts by weight of antioxidant IRGANOX 1010 ( tetra-cis-ethylene- (3, 5-di-tertiary-but-il-4-hydroxy-hydrocinnamate) methane), and 1.5 parts by weight of photo-initiator IRGACURE 651 (2, 2-dimethoxy-1,2) - diphenylethan-1-one) in a 25% toluene solution (KRATON is a registered trademark). KRATON D1107 is a blend of coupled poly (styrene) -poly (isoprene) -poly (styrene) triblock copolymer and uncoupled poly (styrene) -poly (isoprene) diblock copolymer. A halide containing coupling agent was used (dibromoethane). The coupling efficiency was 83% by weight. Therefore, the content of the diblock copolymer was 17% by weight. The total polystyrene content was 15% by weight. The solution was poured into a plate and the solvent evaporated at room temperature. Subsequently, the composition was heated to 140 ° C and maintained at that temperature for 5 minutes, followed by 5 minutes at 140 ° C, applying while a pressure of 1 MPa on a Schwabenthan press. The photo-curable plate thus obtained 5 was approximately 2mm thick. The plate is - ^^^^^^^^^^^^^^^^^^ s ^^^^^^^^^^^^^^^^^^^^^^ j ^^ ^^^^^^ j ^^^^^ kept in the dark, since the presence of HDODA makes sensitive plates to curing with daylight, and in this case had not been applied protective layers in daylight . The plate was cured with a 300 W / 2.5 cm (300 W / inch) mercury medium pressure UV lamp from the American UV Company. The samples were passed three times under the lamp at a speed of 10 m / min. The following tests were carried out.

Opacity Opacity was measured according to ASTM D1003 on a Colorquest II apparatus in uncured samples without support. The results are given in Table 1.

Example 2 (comparative) A photo-curable composition was prepared as in Example 1, but a block copolymer composition A was used. The block copolymer composition A is a mixture of 83% by weight of a triblock copolymer of poly (styrene) -poly (isoprene) -poly (styrene) and 17% by weight of a copolymer of poly (styrene) diblock. ) -poli (isoprene). The triblock copolymer does not contain a coupling agent. The total polystyrene content is 15% by weight and the total apparent molecular weight of the triblock copolymer is 210,000. The total average molecular weight is 144,000. The average molecular weight of the diblock copolymer is 72,000. The composition A of the block copolymer is prepared by rebooting according to the procedure described in the European patent specification No. 0691991. For this photo-curable composition the hardness and gel content was also determined using the following procedures.

Hardness Shore A hardness was determined after penetration of 24s of the needle into the sample and according to ASTM D 2240.

Sel content The gel content is a measure of the degree of reclosement after curing. To measure the gel content, a known amount of the cured plate is soaked in toluene overnight. The undissolved mass is dried at 70 ° C in a vacuum until no more weight loss occurs. The gel content is calculated by: gel content (%) = weight (dry) / weight (initial) * 100 with weight (initial) which is the weight of the cured plate before dissolving in toluene, and weight ( dry) which is the weight of the cured plate after dissolving in toluene and drying. In addition, the opacity was also measured in the 2 mm thick flexographic printing plate samples cured and developed, without support. The results are given in Table 1.

Example 3 (comparative) A photo-curable composition was prepared as in Example 1, but a block copolymer composition B was used. Composition B of block copolymer is a mixture of 44% by weight of a triblock copolymer of poly (styrene) -poly (isoprene) -poly (styrene) and 56% by weight of a poly (diblock copolymer) copolymer. styrene) -poli (isoprene). The triblock copolymer does not contain a coupling agent. The total polystyrene content is 16% by weight and the total average molecular weight of the triblock copolymer is 160., 000 The average molecular weight of the diblock copolymer is about 80,000. The composition B of the block copolymer is prepared by reinitiation according to the procedure described in the specification i j > eg | ^^^^^^^ European patent fcp No. 0691991.

Example 4 A photo-curable composition was prepared as in Example 3 but in the formulation, 10% by weight of the block copolymer composition B was replaced by a low molecular weight styrene-isoprene block copolymer, which had a polystyrene content of 13% by weight and an average molecular weight of 30,000.

Example 5 A photo-curable composition was prepared as in Example 3 but in the formulation, 20% by weight of the block copolymer composition B was replaced by a low molecular weight styrene-isoprene block copolymer having a polystyrene content of 13% by weight and a weight average molecular weight of 30,000.

Examples 6-8 Example 5 was repeated, but with 30, 40 and 50% by weight respectively of the block copolymer composition which was replaced with the low molecular weight styrene-isoprene block copolymer.

Table 1 E i emplo 2 3 4 5 6 7 8 1 1 1 1 No.: 1 1 UV9 = cured by 9 steps under the UV lamp (Sh A) = Shore A hardness [24] = uncertain data formality (41) = double Comparative Example 1 as compared to the other examples, demonstrates that a copolymer composition of block containing a residue of a dibromoethane coupling agent is much more opaque. The introduction of low molecular weight block copolymer into the block copolymer composition does not significantly affect the amount of opacity. Comparative Examples 2 and 3 demonstrate that an increase in the high molecular weight diblock copolymer in the block copolymer composition does not significantly reduce the hardness. The introduction of low molecular weight block copolymer into the block copolymer composition does not advantageously reduce the hardness.

EXAMPLE 9 A block copolymer composition C was prepared by mixing 79% by weight of the block copolymer composition A of Example 2 with 21% by weight of a low molecular weight styrene-isoprene block copolymer, which had a polystyrene content of 13% by weight and an average molecular weight of 30,000. Composition C of block copolymer was tested in a composition for flexographic printing plate jS? ß ^ a ííi ^ suitable for development in water. The water development capacity was estimated as very good. The abrasion resistance of this flexographic printing plate was significantly better than a flexographic printing plate composition containing KRATON D1112. KRATON D1112 is comparable to KRATON D1107 of Example 1, but contains 40% by weight of uncoupled diblock copolymer.

EXAMPLE 10 A block copolymer composition D was prepared by mixing 81% by weight of a triblock copolymer is complete sequential tireno-isoprene-styrene, having a polystyrene content of 19% by weight and an average molecular weight of about 116,000 with 19% by weight of a low molecular weight styrene-isoprene block copolymer, having a polystyrene content of 13% by weight and an average molecular weight of 30,000.

Composition D of block copolymer was tested in a flexographic printing plate composition suitable for water development. The development capacity of the printing plate with water was considered reasonable.

Examples 11 and 12 Example 10 was repeated, but using 23% by weight and 26% by weight respectively of the low molecular weight styrene-isoprene block copolymer. The block copolymer compositions were tested in a flexographic printing plate composition suitable for water development. For both block copolymer compositions, the developing ability of the flexographic printing plate with water was estimated as very good.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (12)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A photo-curable polymer composition, characterized in that it comprises: (a) a first block copolymer comprising at least two outer blocks A of polymerized monovinyl aromatic monomer, at least one internal block B of polymerized conjugated diene monomer, and, optionally , a residue of a di- or multi-functional coupling agent, wherein the total content of the polymerized monovinyl aromatic monomer is in the range of 5 to 25% by weight of the block copolymer, and wherein the waste, if present, is derived from a di- or mult i-functional coupling agent containing alkoxy or epoxy functional groups; (b) 0 to 70% by weight of a second block copolymer, the second block copolymer has a block A of polymerized monovinyl aromatic monomer, at least one block B of a polymerized conjugated diene monomer, and optionally, a residue of a di-or multi-functional coupling agent, wherein the

The total content of polymerized monovinyl aromatic monomer is in the range of 5 to 50% by weight of the block copolymer, and wherein the residue, if present, is derived from an agent Di- or multifunctional coupling 5 containing alkoxy or epoxy functional groups; (c) at least 5% by weight of a low molecular weight block copolymer, wherein the total of (b) and (c) is from 15% by weight to 80% by weight, the block copolymer 10 of low molecular weight having an A block of polymerized monovinyl aromatic monomer, and at least one B block of polymerized conjugated diene monomer, and has an average molecular weight in the range of 1,000 to 35,000; and 15 (d) a photo-initiator. 2. A photo-curable polymer composition as claimed in claim 1, characterized in that it further comprises an ethylenically unsaturated crosslinking agent that polymerizes upon addition.

3. A photo-curable polymer composition as claimed in claim 1 or 2, characterized in that the first block copolymer has the structure A-B-A, and has a total average molecular weight in the range of 50,000 to 300,000.

4. A photo-curable polymer composition as _r_L__lI I ¡LJ ^^ _ - ^ a ^? t? 1fc ^ * ^. .... claimed in any of the preceding claims, characterized in that the second block copolymer has structure A-B.

5. A photo-curable polymer composition as claimed in claim 4, characterized in that the second block copolymer has a total average molecular weight in the range of 40,000 to 150,000 g / mol.

6. A photo-curable polymer composition as claimed in any of the preceding claims, characterized in that the total of (b) and (c) is at least 20% by weight.

7. A photo-curable polymer composition as claimed in any of the preceding claims, characterized in that it comprises from 0.01 to 5% by weight of photo-initiator.

8. A photo-curable polymer composition as claimed in any of the preceding claims, characterized in that it comprises from 5 to 35% by weight of the ethylenically unsaturated crosslinking agent which polymerizes by addition.

9. A precursor of the flexographic printing plate, characterized in that it comprises a photo-curable layer between two release films or a release film and a support, wherein the (s) release film (s) and any support substantially prevent the actinic radiation reaching the photo-curable layer, and wherein the photo-curable layer contains the photo-curable polymer composition as claimed in any of the preceding claims.

10. A cured polymer composition, characterized in that it is obtained by curing a photo-curable composition as claimed in any of claims 1-8 with actinic radiation.

11. A flexographic printing plate, characterized in that it contains the cured polymer composition of claim 10.

12. A process for printing on a substrate, characterized in that it comprises putting ink on the elevated portion of the image side of the flexographic printing plate according to claim 11. , and contacting the flexographic printing plate containing ink with the substrate, thereby transferring ink from the flexographic printing plate to the substrate, and removing the flexographic printing plate from the substrate. .l¿ ^ & £ - # ac% & ¿®¿ # ^ 's,. ~ ^ .. ¿& £ SUMMARY OF THE INVENTION A photo-curable polymer composition comprising: (a) a first block copolymer comprising at least two blocks A of polymerized monovinyl aromatic monomer, at least one block B of polymerized conjugated diene monomer, and, optionally, a residue of a di-functional coupling agent, wherein the total content of the polymerized monovinyl aromatic monomer is in the range of 5 to 25% by weight of the block copolymer, and wherein the residue, if present, is derived from a coupling agent di-functional containing alkoxy or epoxy functional groups; (b) 0 to 70% by weight of a second block copolymer having a block A, at least one block B, and optionally, a residue of a di- or multi-functional coupling agent, wherein the total content of polymerized monovinyl aromatic monomer is in the range of 5 to 50% by weight of the block copolymer, (c) at least 5% by weight of a low molecular weight block copolymer and (d) a photoinitiator. The precursor of the flexographic printing plate comprises a photo-curable layer placed between two release films or a release film and a support. The cured polymer composition is obtained by curing the photo-curable composition; the flexographic printing plate contains the cured polymer composition, process for printing on a substrate with the flexographic printing plate. M? UibAzuiy -z- z, ". mmß & \ ^^ ¿-.---, --M .- ^ zi '---.' -.-. . .. ~ -, "-,"? To "t¡ &a .. a ..