JP2010023492A - Resin compound for laser engravable original printing plate and laser engravable printing plate obtained therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin compound which is a raw material of a printing original plate for laser engraving which enables production of a printing plate superior in resolution without causing printing defect. <P>SOLUTION: This is a printing original plate for laser engraving, a printing plate which is obtained by irradiating with light a photosensitive resin layer installed on a supporting body and cross-linking-hardening it. The laser engravable printing original plate for flexographic printing is characterized in that a photosensitive resin layer is composed of a photosensitive resin compound containing: (A) a hydrophobic polymer obtained from water dispersive latex having a weight average gelation ≥20%; (B) a photo polymerizing compound; and (C) a photo-polymerization initiator, that at least one of the photo polymerizing compounds of the (B) component is a photo polymerizing oligomer in which ethylenically unsaturated group is bonded with end and/or side chain of a diene polymer, and that the diene polymer in the photo polymerizing oligomer has a number average molecular weight of 1,000-2,500. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a resin composition as a raw material for a laser engraving printing original plate, and a laser engraving printing original plate obtained from such a resin composition.

  Conventionally, a printing plate for flexographic printing used for printing packaging materials, building materials, and the like has been conventionally exposed to a printing original plate made of a photosensitive resin according to an image to crosslink the resin in the exposed portion, and then the unexposed portion in the unexposed portion. In recent years, printing plates by laser engraving that directly form a relief image on a printing original plate using a laser are becoming widespread in order to improve the efficiency of printing plate production. In the printing plate manufacturing process by laser engraving, unevenness is formed on the plate surface by irradiating the printing original plate with a laser beam according to the image to decompose the image forming material in the irradiated portion. At this time, a viscous resin residue is generated due to the decomposition of the image forming material in the laser irradiation portion, and a part thereof is scattered also in the non-laser irradiation portion. Since these resin wastes cause problems when left on the printing plate, they are removed from the printing plate by sucking with a dust collector provided near the laser device during laser irradiation and / or by washing the printing plate after laser irradiation. Removed.

  Conventionally, printing masters for laser engraving are known which comprise a resin composition in which a photopolymerizable compound and a photopolymerization initiator are blended with synthetic rubber or natural rubber (see Patent Documents 1 and 2). However, since this printing original plate is mainly composed of rubber, the original plate itself has high adhesiveness, and the resin residue generated by laser irradiation remains attached to the plate without being removed by suction during laser irradiation or cleaning after laser irradiation. Easy to remain. If the resin residue remains attached to the laser non-irradiated portion (convex portion) of the printing plate, this portion is a portion to which ink is applied at the time of printing, which may cause printing defects. In addition, if the resin residue remains attached to the bottom of the laser-irradiated portion (recessed portion) of the printing plate, the depth of the halftone dot will decrease, and if it remains attached to the side surface of the recessed portion, the reproducibility of the halftone dot will decrease. In either case, the resolution may be lowered.

  In order to cope with this problem, the mechanical properties of the printing original plate can be improved by adding a laser-absorbing colored filler such as carbon black to the resin composition, or by adding a colorless transparent filler such as silica fine powder. There has been proposed a technique for improving and consequently reducing the adhesiveness (see Patent Document 3). However, the method of blending a laser-absorbing filler such as carbon black uses a colored filler, so that there is a problem that the resin composition becomes opaque and cannot be sufficiently cured by light irradiation. there were. In addition, the method of blending a filler such as silica fine powder is colorless and transparent, so that the problem as in the case of blending carbon black does not occur, but in order to sufficiently reduce the adhesiveness of the printing original plate, a large amount There was a problem that a filler was required and the moldability and physical properties of the printing original plate were remarkably impaired. Thus, since the addition of the filler adversely affects the moldability and physical properties of the printing original plate, development of a method capable of reducing the adhesiveness of the printing original plate without adding the filler has been demanded. .

Japanese Patent No. 2846954 JP-A-11-338139 Special table 2004-533343

  The present invention has been made in view of the current state of the prior art, and its purpose is that it has less engraving debris generated during laser engraving, can form dots with an ideal shape with high resolution, and is clear. It is providing the resin composition which can be printed, and providing the printing original plate for laser engraving obtained from this resin composition.

  As a result of intensive studies to achieve the above object, the present inventors have found that (A) a hydrophobic polymer obtained from an aqueous dispersion latex having a weight average gelation degree of 20% or more, and (B) a photopolymerizable compound. And (C) a photosensitive resin composition containing a photopolymerization initiator, wherein the photopolymerizable compound of component (B) is an ethylenically unsaturated group at the end and / or side chain of a diene polymer having a specific molecular weight. The present inventors have found that these problems can be overcome by using a photopolymerizable oligomer formed by bonding, and have completed the present invention.

That is, according to the present invention, there is provided a resin composition for a printing original plate capable of laser engraving characterized by the following:
(A) It consists of a photosensitive resin composition containing a hydrophobic polymer obtained from an aqueous dispersion latex having a weight average gelling degree of 20% or more, (B) a photopolymerizable compound, and (C) a photopolymerization initiator. In addition, at least one of the photopolymerizable compounds of the component (B) is a photopolymerizable oligomer in which an ethylenically unsaturated group is bonded to the terminal and / or side chain of the diene polymer, The diene polymer has a number average molecular weight of 1000 to 2500, and is capable of laser engraving.

According to the preferable aspect of this invention, the quantity of the ethylenically unsaturated group in the photopolymerizable oligomer which is (B) component in the photosensitive resin layer is 0.05-0.20 molar equivalent in a photosensitive composition. / 100g.
Further, a laser-engravable original for flexographic printing containing 25 to 50% by weight of the photopolymerizable oligomer as the component (B) in the photosensitive resin layer is preferable.
According to the present invention, there is also provided a laser-engravable printing original plate obtained by molding such a resin composition into a sheet shape or a cylindrical shape and then irradiating the molded product with light to cure by crosslinking. Is done.

  The resin composition for printing plate precursor capable of laser engraving of the present invention comprises a hydrophobic polymer obtained from an aqueous dispersion latex having a weight average gelation degree of 20% or more and a conjugated diene polymer having a number average molecular weight of 1000 to 2500. The photopolymerizable oligomer used is an essential component. It is a feature of the present invention that an oligomer having a specific molecular weight is used as a main component in the photopolymerizable compound. By using a photopolymerizable compound of an oligomer type having a specific molecular weight, it has succeeded in achieving both the basic performance of laser engraving and the rubber elasticity essential for flexographic printing. For this reason, the resin composition of this invention is very suitable as a flexographic printing original plate for laser engraving. When a so-called polymer having a high molecular weight is used as the photopolymerizable compound, the laser engraving performance is deteriorated in terms of adhesion of resin residue and a halftone dot shape. On the other hand, if a so-called monomer having a low molecular weight is used, the rubber elasticity required for flexographic printing becomes poor and printing becomes unclear.

  The resin composition of the present invention is extremely suitable as a raw material for a printing original plate for laser engraving. (A) Latex having a weight average gelation degree of 20% or more, (B) a photopolymerizable compound, (C) A photosensitive resin composition containing a photopolymerization initiator, wherein at least one of the photopolymerizable compounds as the component (B) is light in which an ethylenically unsaturated group is bonded to a terminal and / or a side chain. It is a polymerizable oligomer. The number average molecular weight of the preferred conjugated diene polymer is 1000 to 2500, and the more preferred number average molecular weight is 1000 to 2000.

The gelation degree of the latex (A) used in the present invention needs to be 20% or more on average. (A) The degree of gelation of the latex is preferably 45% or more, and more preferably 65% or more. The degree of gelation is the weight average degree of gelation, and it is possible to satisfy the degree of gelation with a single latex. However, the desired average degree of gelation can be achieved by mixing with a latex having a degree of gelation of 0% or a different degree of gelation. Degree can be achieved.
When the gelation degree of the latex is less than the above value, aggregation and integration of latex fine particles during molding on the printing original plate cannot be sufficiently prevented, and the adhesiveness of the printing original plate may not be maintained low. On the other hand, there is no limit to the upper limit of the gelation degree of latex, and the larger the gelation degree, the better the aggregation and integration preventing effect of latex particles. In addition, the value of the gelation degree of latex is prescribed | regulated by the insolubility in toluene. Specifically, the gelation degree of the latex was measured by accurately weighing 3 g of the latex solution on a 100 μm thick PET film, dried at 100 ° C. for 1 hour, and then immersed in a toluene solution at 25 ° C. for 48 hours. It is measured by drying at 110 ° C. for 2 hours and calculating the weight percentage of insoluble matter.

  The latex (A) used in the present invention may be appropriately selected from conventionally known latexes having a certain level of gelation degree. Specific examples include polybutadiene latex and styrene-butadiene copolymer. Polymer latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, polyisoprene latex, etc. are mentioned, among them polybutadiene latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer. Latex is preferred. These latexes may be modified with (meth) acrylic or carboxy as desired. In addition, since many various synthetic | combination or natural latex is marketed as a gelatinized latex, what is necessary is just to select an appropriate thing from there. Moreover, latex may be used independently or may use 2 or more types together. When two or more kinds of latexes are used, the gelation degree indicates the weight average of these.

  The photopolymerizable compound (B) constituting the resin composition of the present invention has a role of polymerizing and crosslinking by light irradiation to form a dense network for maintaining the shape on the printing original plate. The photopolymerizable compound (B) used in the present invention is a photopolymerizable oligomer in which an ethylenically unsaturated group is bonded to the terminal and / or side chain, and the conjugated diene polymer has a number average molecular weight. It is essential that it is 1000-2500.

  It is a feature of the present invention that an oligomer type photopolymerizable oligomer using a conjugated diene polymer having a number average molecular weight of 1000 to 2500 is used. By using an oligomer type photopolymerizable compound, removal of laser engraving residue can be facilitated and rubber elasticity essential for flexographic printing can be provided. If a high molecular weight having a number average molecular weight exceeding 2500 is used, it is very difficult to remove the residue of the laser engraving. On the other hand, if a so-called monomer having a number average molecular weight of less than 1000 is used, the rubber elasticity required for flexographic printing is poor, printing becomes unclear and the number of printable sheets is small.

  The conjugated diene polymer constituting the photopolymerizable oligomer is constituted by a homopolymer of a conjugated diene unsaturated compound or a copolymer of a conjugated diene unsaturated compound and a monoethylenically unsaturated compound. Examples of such a conjugated diene unsaturated compound homopolymer or a copolymer of a conjugated diene unsaturated compound and a monoethylenically unsaturated compound include a butadiene polymer, an isoprene polymer, a chloroprene polymer, a styrene-chloroprene copolymer, Acrylonitrile-butadiene copolymer, acrylonitrile-isoprene copolymer, methyl methacrylate-isoprene copolymer, methyl methacrylate-chloroprene copolymer, methyl acrylate-butadiene copolymer, methyl acrylate-isoprene copolymer, Examples thereof include methyl acrylate-chloroprene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-chloroprene-styrene copolymer, and the like. Of these, butadiene polymers, isoprene polymers, and acrylonitrile-butadiene copolymers are preferable, and butadiene polymers and isoprene polymers are particularly preferable in terms of rubber elasticity and photocurability.

  The method for introducing an ethylenically unsaturated group into the terminal and / or side chain of the photopolymerizable oligomer is not particularly limited. For example, (1) a hydroxyl group-terminated conjugated diene polymer obtained using hydrogen peroxide as a polymerization initiator Monoethylenically unsaturated carboxylic acid such as (meth) acrylic acid is ester-bonded to the hydroxyl group at the terminal by dehydration or monoethylenically unsaturated such as methyl (meth) acrylate or ethyl (meth) acrylate (2) Conjugated diene system obtained by copolymerizing conjugated diene compound and ethylenically unsaturated compound containing unsaturated carboxylic acid (ester) at least partially Examples include a method of reacting an ethylenically unsaturated alcohol such as allyl alcohol or vinyl alcohol .

  The amount of the ethylenically unsaturated group in the photopolymerizable oligomer is preferably 0.05 to 0.20 mole equivalent / 100 g in the photosensitive resin composition, particularly preferably 0.05 to 0.15 mole equivalent. / 100g. When the amount is more than 0.20 molar equivalent / g, the hardness becomes too high and it becomes difficult to obtain sufficient elasticity, and the ink carrying property of the solid part at the time of printing is lowered. If it is less than 0.05 molar equivalent / 100 g, the hardness becomes too low and it becomes difficult to obtain a sufficient hardness, and the dot gain in printing increases and the printing accuracy decreases.

  As a method for adjusting the molecular weight of the photopolymerizable oligomer, a method for adjusting the polymerization conditions (initiator amount, amount of chain transfer agent, reaction time, temperature, etc.) in the polymerization reaction of the conjugated diene polymer that is a raw material, It adjusts by the method etc. which control the reaction conditions at the time of reaction which introduce | transduces an ethylenically unsaturated group into a conjugated diene type polymer. Moreover, the method of melt | dissolving the product of the conjugated diene type polymer obtained by superposing | polymerizing on arbitrary reaction conditions in a suitable solvent, and isolate | separating and collecting the specific molecular weight component etc. can be mentioned.

  The content of the photopolymerizable oligomer in the photosensitive resin composition is preferably 15 to 50% by weight. More preferably, it is 25 to 50% by weight. If it is less than 15% by weight, the rubber elasticity of the resin plate is poor, vivid printing is impossible, and the number of printable sheets is small. On the other hand, if it exceeds 50% by weight, the hardness becomes too high and sufficient elasticity is difficult to obtain, and the ink carrying property of the solid part at the time of printing decreases.

  In the photopolymerizable compound (B) of the present invention, in addition to the photopolymerizable oligomer exemplified above, it is possible to use a photopolymerizable compound such as a commonly used monofunctional monomer type acrylate or methacrylate. From the viewpoint of sex. A preferable blending ratio is 5 to 15% by weight in the photosensitive resin composition. If it is less than 5% by weight, there is no effect, and if it exceeds 15% by weight, it becomes fragile, which is not preferable. Specific examples include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl ( Alkyl (meth) acrylates such as meth) acrylate, isoamyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and cycloalkyl (meth) acrylates such as cyclohexyl (meth) acrylate , Halogenated alkyl (meth) acrylates such as chloroethyl (meth) acrylate and chloropropyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate Alkoxyalkyl (meth) acrylates such as phenoxyethyl (meth) acrylate, phenoxyalkyl (meth) acrylates such as nonylphenoxyethyl (meth) acrylate, and the like. Methacrylate.

  The (C) photopolymerization initiator constituting the resin composition of the present invention has a role as an initiator for the photopolymerization / crosslinking reaction of the (B) photopolymerizable compound. As the photopolymerization initiator (C) used in the present invention, any photopolymerization initiator can be used as long as it can polymerize a polymerizable carbon-carbon unsaturated group by light irradiation. Those having a function of generating radicals by autolysis or hydrogen abstraction are preferably used. Specifically, for example, benzoin alkyl ethers, benzophenones, anthraquinones, benzyls, acetophenones, diacetyls and the like can be used.

    In the resin composition of the present invention, optional components such as a hydrophilic polymer, a plasticizer, and / or a polymerization inhibitor can be blended as desired in addition to the above-mentioned three components (A) to (C).

  The hydrophilic polymer has an effect of improving the printing property by improving the affinity between the printing plate and the water-based ink when the flexographic printing is performed using the produced printing plate. The hydrophilic polymer that can be used in the resin composition of the present invention is -COOH, -COOM (M is a monovalent, divalent, or trivalent metal ion or a substituted or unsubstituted ammonium ion), -OH , —NH 2, —SO 3 H, and those having a hydrophilic group such as a phosphate ester group are preferred. Specifically, a polymer of (meth) acrylic acid or a salt thereof, (meth) acrylic acid or a salt thereof and an alkyl (meta ) A copolymer of acrylate, a copolymer of (meth) acrylic acid or a salt thereof and styrene, a copolymer of (meth) acrylic acid or a salt thereof and vinyl acetate, a (meth) acrylic acid or a salt thereof Copolymer with acrylonitrile, polyvinyl alcohol, carboxymethyl cellulose, polyacrylamide, hydroxyethyl cellulose, polyethylene Side, polyethyleneimine, polyurethane having -COOM group, polyureaurethane having -COOM group, include the polyamic acid and their salts or derivatives having a -COOM group. These may be used alone or in combination of two or more. The blending ratio of the hydrophilic polymer in the resin composition of the present invention is preferably 20% by weight or less, and more preferably 15% by weight or less. If the blending ratio of the hydrophilic polymer exceeds the above upper limit, the water resistance of the produced printing plate is lowered, and the water-based ink resistance may be lowered.

  The plasticizer has an effect of improving the fluidity of the resin composition and an effect of adjusting the hardness of the produced printing original plate. The plasticizer that can be used in the resin composition of the present invention is preferably a compound having good compatibility with (A) latex, and more preferably a polyene compound that is liquid at room temperature or a compound having an ester bond. Examples of the polyene compound that is liquid at room temperature include liquid polybutadiene, polyisoprene, and maleated products and epoxidized products having their end groups or side chains modified. The blending ratio of the plasticizer in the resin composition of the present invention is preferably 20% by weight or less, and more preferably 15% by weight or less. When the blending ratio of the plasticizer exceeds the above upper limit, the mechanical properties and solvent resistance of the printing plate are remarkably lowered, and the printing durability may be lowered.

  The polymerization inhibitor has an effect of increasing the thermal stability of the resin composition. The polymerization inhibitor that can be used in the resin composition of the present invention can be a conventionally known one, and examples thereof include phenols, hydroquinones, and catechols. The blending ratio of the polymerization inhibitor in the resin composition of the present invention is preferably 0.001 to 3% by weight, and more preferably 0.001 to 2% by weight.

  Further, as optional components other than these, a colorant, an antioxidant and the like can be added within a range not impairing the effects of the present invention.

  The resin composition of the present invention is prepared by mixing the above-described three essential components (A) to (C) and optionally an optional component. At that time, an organic solvent such as toluene may be added as desired to facilitate mixing. Further, in order to complete the mixing, it is desirable to sufficiently knead under a heating condition using a kneader. It is preferable that heating conditions are about 50-110 degreeC. Moreover, it is preferable that the organic solvent added at the time of mixing and the water contained in the components are removed under reduced pressure after kneading.

  Next, the printing original plate capable of laser engraving of the present invention will be described. The printing original plate of the present invention is obtained by molding the resin composition of the present invention prepared as described above into a sheet shape or a cylindrical shape, and then irradiating the molded product with light to crosslink and cure. is there.

The photo-curing of the present invention is a synthetic rubber-based photosensitive resin composition formed into a sheet shape, and the sheet-shaped molded product is exposed to an ultraviolet light exposure machine (light source: manufactured by Philips Co., Ltd.) at a distance of 5 cm from the surface to 8 mW / cm ² . 10R), the front and back surfaces are exposed for 10 minutes to be crosslinked and cured.

As a method for molding the resin composition of the present invention into a sheet or cylinder, a conventionally known resin molding method can be used. For example, the resin composition of the present invention can be used on a suitable support or in a printing machine. The method of apply | coating on a cylinder and pressing with a heat press machine etc. can be mentioned. As the support, a material having flexibility and excellent dimensional stability is preferably used, and examples thereof include polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, and polycarbonate. The thickness of the support is from 50 to 250 μm, preferably from 100 to 200 μm, from the viewpoints of mechanical properties and shape stability of the printing original plate. Further, if necessary, a known adhesive conventionally used for this type of purpose may be provided on the surface in order to improve the adhesion between the support and the resin layer. The pressing condition is preferably about ²⁰ to 200 kg / cm ² , and the temperature condition during pressing is preferably about room temperature to about 150 ° C. The thickness of the formed product may be appropriately determined depending on the size and properties of the printing original plate to be produced, and is not particularly limited, but is usually about 0.1 to 10 mm.

  Next, the molded resin composition is irradiated with light to polymerize and crosslink the (B) photopolymerizable compound in the resin composition, thereby curing the molded product to obtain a printing original plate. Examples of the light source used for curing include a high-pressure mercury lamp, an ultra-high pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, and a xenon lamp, and the curing can be performed by other known methods. Although the light source used for curing may be one type, the curability of the resin may be improved by curing using two or more types of light sources having different wavelengths, so two or more types of light sources may be used. There is no problem.

  The printing original plate thus obtained is attached to the surface of the plate mounting drum of the laser engraving apparatus, and the irradiated portion of the original plate is decomposed by laser irradiation according to the image to form a concave portion, whereby a printing plate is manufactured. Since the printing original plate obtained from the resin composition of the present invention is composed of a hydrophobic polymer obtained from latex and an oligomer type photopolymerizable compound of a specific molecular weight, the resin residue generated by laser irradiation is less likely to adhere to the plate surface. It is possible to effectively prevent printing defects and reduction in resolution due to residue adhesion.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

The characteristics were measured by the following method.
(1) Crosslinking degree of latex 3 g of a latex solution was accurately calculated on a PET film having a thickness of 100 μm, dried at 100 ° C. for 1 hour, then immersed in a toluene solution at 25 ° C. for 48 hours, and at 110 ° C. for 2 hours. It was dried and measured by calculating the weight percent insolubles.
(2) Measurement of the number average molecular weight of the photopolymerizable oligomer The measurement was performed by size exclusion chromatography (GPC). The measurement apparatus was SYSTEM-21 (Shodex), and the column was GMH _XL- GMH _XL- G2000H _XL (manufactured by TOSOH). A sample dissolved in chloroform at a concentration of about 0.5% (W / V) was used as a measurement solution, and measurement was performed under the conditions of an injection amount of 200 μl, a flow rate of 0.7 ml, and a column temperature of 40 ° C. The average molecular weight was calculated in terms of polystyrene using standard polystyrene (manufactured by TOSHO).

(Synthesis of photopolymerizable oligomer)
(Synthesis example 1): Photopolymerizable oligomer (I)
Hydroxyl group-containing polybutadiene (molecular weight: number average molecular weight 1200, hydroxyl group content: 1.83 meq / kg) 900 parts by weight and acrylic acid 131 parts by weight in the presence of 900 parts by weight of cyclohexane and 10 parts by weight of toluenesulfonic acid, 70 After reacting at 5 ° C. for 5 hours, cyclohexane was distilled off to obtain a photopolymerizable oligomer I. The number average molecular weight of the obtained photopolymerizable oligomer was 1300.
(Synthesis Example 3): Photopolymerizable oligomer (II)
Hydroxyl group-containing polyisoprene (molecular weight: number average molecular weight 2000, hydroxyl group content: 1.30 meq / kg) 900 parts by weight and acrylic acid 93 parts by weight in the presence of 900 parts by weight of cyclohexane and 10 parts by weight of toluenesulfonic acid, After reacting at 70 ° C. for 5 hours, cyclohexane was distilled off to obtain photopolymerizable oligomer (II). The number average molecular weight of the obtained photopolymerizable oligomer was 2100.
(Comparative Synthesis Example 1): Photopolymerizable oligomer (III)
Hydroxyl group-containing polybutadiene (molecular weight: number average molecular weight 300, hydroxyl group content: 5.0 meq / kg) 900 parts by weight of acrylic acid weight 357 parts in the presence of 900 parts by weight of cyclohexane and 10 parts by weight of toluenesulfonic acid, 70 After reacting at 0 ° C. for 2 hours, cyclohexane was distilled off to obtain a photopolymerizable oligomer (III). The number average molecular weight of the obtained photopolymerizable oligomer was 400.
(Comparative Synthesis Example 2): Photopolymerizable oligomer (IV)
Hydroxyl group-containing polybutadiene (molecular weight: number average molecular weight 2800, hydroxyl group content: 0.83 meq / kg) 900 parts by weight and acrylic acid 60 parts by weight in the presence of 900 parts by weight of cyclohexane and 10 parts by weight of toluenesulfonic acid, After reacting at 5 ° C. for 5 hours, cyclohexane was distilled off to obtain a photopolymerizable oligomer (IV). The number average molecular weight of the obtained photopolymerizable oligomer was 2900.

[Example 1]
(A) Component latex is BR latex (manufactured by Nippon Zeon, LX111NF: gelation degree 8
6%, non-volatile content: non-volatile content 55%) 80 parts by weight (44 parts by weight as solid content), NBR latex (manufactured by Nippon Zeon, SX1503A: gelation degree 0%, non-volatile content non-volatile content 42%) 14 parts by weight (solid 6 parts by weight), (B) as a photopolymerizable compound, 30 parts by weight of a photopolymerizable oligomer (I), 9 parts by weight of lauryl methacrylate, (C) 1.0 part by weight of benzyldimethyl ketal as a photopolymerization initiator, In addition, PFT-3 (a compound having a urethane urea structure and a molecular weight of about 20,000, a non-volatile content of 25%) 20 parts by weight (5 parts by weight as a solid content) as a hydrophilic polymer, and hydroquinone as a polymerization inhibitor 0.1 parts by weight of monomethyl ether and 5 parts by weight of liquid butadiene rubber (molecular weight of about 2,000) as a plasticizer are mixed in a container together with 5 parts by weight of toluene. And the mixture was kneaded at 105 ° C. with a pressure kneader, followed give toluene and water was removed under reduced pressure photosensitive resin composition.

[Examples 2 to 12]
Based on the composition ratio in Table 1, a photosensitive resin composition (total 100 parts by weight) was prepared in the same manner as in the production method of Example 1. In addition, about (A) component and the hydrophilic polymer, it calculated and mix | blended so that the weight ratio of solid might be united from a non volatile matter.

[Comparative Examples 1-7]
Based on the composition ratio in Table 1, a photosensitive resin composition (total 100 parts by weight) was prepared in the same manner as in the production method of Example 1. In addition, about (A) component and the hydrophilic polymer, it calculated and mix | blended so that the weight ratio of solid might be united from a non volatile matter.

  Next, the printing original plate produced in Examples 1-12 and Comparative Examples 1-7 was wound around the plate mounting drum of the laser engraving apparatus with a double-sided tape, and laser engraving was performed under the following conditions. Simultaneously with the start of laser engraving, the dust collector installed in the vicinity of the laser gun was operated, and the continuously engraved resin debris was discharged out of the apparatus. After laser engraving, the plate removed from the mounting drum was washed with water for 3 minutes with a water-developing plate-only washing machine (Toyobo CRS600, 1% washing soap aqueous solution, water temperature 40 ° C.) and adhered to the plate surface. A small amount of resin residue was removed and dried to obtain a printing plate.

As the laser engraving apparatus, a FlexPose! Direct equipped with a 300 W carbon dioxide laser manufactured by Luescher Flexo was used. The specification of this equipment is laser wavelength 1
The diameter of the plate mounting drum was 300 mm, and the processing speed was 1.5 hours / 0.5 m 2. The conditions for laser engraving are as follows. Note that (1) to (3) are conditions specific to the apparatus. Conditions can be arbitrarily set for (4) to (7), and the standard conditions of this apparatus are adopted for each condition.
(1) Resolution: 2540 dpi
(2) Laser pitch: 10 μm
(3) Drum rotation speed: 982 cm / sec (4) Top power: 9%
(5) Bottom power: 100%
(6) Shoulder width: 0.30mm
(7) Relief depth: 0.60 mm
(8) Evaluation image: 175 lpi, halftone dots in 1% increments from 1 to 100%

The following evaluation items were investigated for the obtained printing plate.
(1) Using an magnifying magnifying glass 10 times the degree of resin residue adhesion, the amount of resin residue adhesion to the printing plate surface was visually inspected and shown in the following four stages.
◎: Almost no adhesion ○: Some adhesion △: Quite adhesion ×: Extreme adhesion (2) Shape of halftone dots The shape of halftone dots (area ratio 10% at 150 lpi) was observed with a microscope. . A halftone dot having a conical shape is excellent in printing suitability and printing durability.
○: Conical △: Partially unclear ×: Unclear (3) Rebound resilience modulus A steel ball with a diameter of 10mm (weight 4.16g) is dropped from the height of 20cm, and the rebounding height (a) is read. a / 20) × 100 was used for the percentage display. The determination was made according to the following criteria.
(Circle): 55% or more (triangle | delta): 54-45% x: Less than 45% (4) Printability evaluation The ink paste property of the printed matter was visually observed using the flexographic printing machine. Further, the microscopic image reproducibility (150 lpi, 1 to 5% halftone dot) of the obtained printed matter was visually confirmed using a 100 × microscope. Regarding printing durability, 1 million copies were printed, and the occurrence of cracks on the surface of the subsequent printing plate was confirmed with a 30-fold magnifier.
Ink paste property: ○: Good △: Some color unevenness ×: Whole color unevenness Micro image printability; ○: Good △: Some dot unevenness ×: Large halftone dot unevenness
Printing durability: ○: No cracks △: Some parts ×: All parts

  Photopolymerization using a hydrophobic polymer obtained from an aqueous dispersion latex having a weight average gelation degree of 20% or more, particularly 45% or more, and a conjugated diene polymer having a number average molecular weight of 1000 to 2500 from the evaluation results of Table 1. It is clear that the combination with the functional oligomer has succeeded in achieving both the basic performance of laser engraving and the rubber elasticity essential for flexographic printing.

  The resin composition of the present invention is compatible with both the basic performance of laser engraving and the elasticity of rubber essential for flexographic printing, and the resin residue generated by laser irradiation during printing plate preparation remains attached to the plate surface. Since it hardly remains, it can be suitably used for producing a printing original plate for laser engraving, particularly in the field of flexographic printing.

Claims (3)

  A printing original plate for laser engraving obtained by irradiating a photosensitive resin layer provided on a support with light and crosslinking and curing the photosensitive resin layer, wherein the photosensitive resin layer (A) has a weight average gelation degree of 20% or more. A photosensitive polymer composition containing a hydrophobic polymer obtained from an aqueous dispersion latex, (B) a photopolymerizable compound, and (C) a photopolymerization initiator, and at least one of the photopolymerizable compounds of the component (B). One is a photopolymerizable oligomer in which an ethylenically unsaturated group is bonded to the terminal and / or side chain of a diene polymer, and the number average molecular weight of the diene polymer in the photopolymerizable oligomer is 1000 to 2500. An original for flexographic printing capable of laser engraving, characterized by being.   2. The laser-engravable original for flexographic printing according to claim 1, wherein the photopolymerizable oligomer (B) in the photosensitive resin layer is contained in an amount of 25 to 50% by weight.   The amount of ethylenically unsaturated groups in the photopolymerizable oligomer that is the component (B) in the photosensitive resin layer is 0.05 to 0.20 molar equivalent / 100 g in the photosensitive composition. The flexographic printing original plate capable of laser engraving according to claim 1 or 2.