JP7035729B2 - A photosensitive resin composition for letterpress printing original plate, and a letterpress printing original plate obtained from the photosensitive resin composition. - Google Patents

Description

The present invention relates to a photosensitive resin composition for a letterpress printing original plate and a letterpress printing original plate obtained from the photosensitive resin composition, and in particular, is excellent in gradation printing reproducibility and printing resistance of a highlight portion, and further has plate surface adhesiveness. It relates to a water-developable photosensitive resin composition which can provide a low letterpress printing original plate.

Generally, the photosensitive resin letterpress composition usually used for a printing plate contains a polymer compound, a photopolymerizable unsaturated compound, and a photopolymerization initiator as essential components, and if necessary, a stabilizer and a plasticizer. Additives such as are blended.

Conventionally, this photosensitive resin composition layer is irradiated with active light through a negative film (or positive film) having a transparent image portion to cure the photosensitive layer of the exposed portion, and then the photosensitive layer of the non-exposed portion is suitable. It is widely known to produce a relief plate for printing by a plate-making process of dissolving and removing with a various solvent, drying and post-exposure.

As the above-mentioned photosensitive resin composition, those using polyamide, polyether urea urethane, fully saponified or partially saponified polyvinyl acetate, etc. as a soluble polymer have been proposed, and photosensitive using polyamide or polyether urea urethane has been proposed. The relief composition is particularly preferably used because of its excellent wear resistance. In the original plate for photosensitive resin letterpress using these photosensitive resin letterpress compositions, the original plate for photosensitive resin letterpress with a highly repulsive elasticized photosensitive resin layer improves the high-speed printing suitability as an improvement in printability (patented). See Documents 1 and 2).

Recently, the user's request for the original plate for photosensitive resin letterpress has been moving toward reproducing finer patterns, and 5% or less of 200 lines of the minimum highlight part used for printing photographic materials is continuous. Therefore, it is required to have reproducibility of smoothly changing the brightness (gradation of the highlight portion halftone dots) in the printed matter in which the halftone dots are reduced.

As a conventional technique for meeting the requirement of fine highlight halftone dot printability, the original plate for photosensitive resin letterpress with improved image reproducibility by forming a multilayer structure with different light transmission rates of the photosensitive resin layer (Patent Document). 3), and the original plate for photosensitive resin letterpress (see Patent Document 4) whose relief shape is sharpened by multi-layering the photosensitive resin layer, etc., but the highlight portion of the printed matter is 1 to 5% high in halftone dots. Both the reproducibility of the halftone dot printed matter in the light part and the manufacturing cost of the original plate for the photosensitive resin letterpress could not be satisfied. In particular, regarding the manufacturing cost, when the improvement in reproducibility is achieved by increasing the number of layers, it is unavoidable that the manufacturing cost increases due to the complicated manufacturing process.

On the other hand, with the progress of computers, a method has been proposed in which information processed on a computer is directly output on a printing original plate to obtain a printing original plate without requiring a process of creating an original film. In this method, when exposed to ultraviolet rays in the presence of oxygen, it can be made smaller than the original image due to polymerization failure due to oxygen (see Patent Document 5), and the area of the highlight halftone dots can be easily reduced on the computer screen. There is a feature that can be corrected, and the reproducibility of the highlighted printed matter is improved. However, these methods for producing original printing plates require an expensive laser irradiation device, and it has been desired to improve the reproducibility of printed matter by an inexpensive method.

In addition, there is often a problem in letterpress printing plates that cracks occur in the plate during printing, which causes defective printed matter. In order to improve this printing resistance, a method of using a partially saponified PVA and a polyamide compound in combination (see Patent Document 6) and a method of using a specific cross-linking agent (see Patent Document 7) have been proposed.

Japanese Unexamined Patent Publication No. 04-97154 Japanese Unexamined Patent Publication No. 05-11447 Japanese Unexamined Patent Publication No. 2002-23349 Japanese Unexamined Patent Publication No. 06-313966 Japanese Unexamined Patent Publication No. 09-171247 Japanese Unexamined Patent Publication No. 2001-272767 Japanese Unexamined Patent Publication No. 2014-142622

The present invention has been made in view of the current state of the prior art as described above, and an object thereof is to achieve both gradation printing reproducibility of a highlight portion and printing durability even when printing at a particularly high pressure. Further, an object of the present invention is to provide a photosensitive resin composition for a letterpress printing original plate having low plate adhesiveness, and a letterpress printing original plate using the same.

In order to achieve the above object, the present inventors have diligently studied water-soluble or water-dispersible polyurethane of the photosensitive resin composition used for the letterpress printing original plate, and as a result, the oil ring having a concentration in a specific range is contained in the polyurethane. It has been found that the inclusion of the group structural unit makes it possible to achieve both gradation print reproducibility and print resistance of the highlight portion, and the present invention has been completed.

That is, the present invention has the following configurations (1) to (5).
( 1 ) A photosensitive resin composition for a letterpress printing original plate containing a water-soluble or water-dispersible polyurethane, a photopolymerizable unsaturated compound, and a photopolymerization initiator, wherein the polyurethane is obtained from a diol and a diisocyanate. For letterpress printing original plate characterized by containing 45 to 90 mol% of the alicyclic structural unit in the molecule and having a Tg of 50 to 100 ° C. measured by a dynamic viscoelasticity measuring device. Photosensitive resin composition.
( 2 ) The alicyclic diol to be the alicyclic structural unit is at least one selected from the group consisting of 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol and tricyclodecanedimethanol. The photosensitive resin composition for letterpress printing original plate according to ( 1 ), which is the above-mentioned alicyclic diol.
( 3 ) The alicyclic diisocyanate to be the alicyclic structural unit is isophorone diisocyanate, 1,4-diisocyanatocyclohexane, cyclohexane-1,2-diylbis (methylene) diisocyanate, and 4,4'-dicyclohexyl. The photosensitive resin composition for a letterpress printing original plate according to (1) or (2) , which is at least one alicyclic diisocyanate selected from the group consisting of methane diisocyanate.
( 4 ) A letterpress printing original plate provided with a photosensitive resin layer made of the photosensitive resin composition for a letterpress printing original plate according to any one of (1) to (3) .
( 5 ) The letterpress printing original plate according to ( 4 ), which is used for laser engraving.

According to the present invention, it is possible to achieve both gradation printing reproducibility of 1 to 5% of highlights and printing durability without using expensive equipment, and photosensitive for letterpress printing original plates having low plate adhesiveness. A resin composition can be provided.

The photosensitive resin composition for a letterpress printing original plate of the present invention contains a water-soluble or water-dispersible polyurethane, a photopolymerizable unsaturated compound, and a photopolymerization initiator as essential components, and the polyurethane is contained in the molecule. It is characterized by containing 45 to 90 mol% of alicyclic structural units. The mol% contained in the alicyclic structural unit in the molecule of the present invention represents the mol% contained in the alicyclic structural unit when the total number of moles of the diol and the diisocyanate constituting the raw material is 100%.

The polyurethane used in the present invention is a polyurethane containing 45 to 90 mol% of alicyclic structural units in the molecule. If the content ratio of the alicyclic structural unit obtained from the diol and the diisocyanate compound in the polyurethane is less than the above range, there is a problem that the gradation printing reproducibility of the highlight portion is inferior and the plate surface adhesiveness is inferior. On the other hand, if it exceeds the above range, the printing resistance of the polymer, particularly the chipping resistance of the highlight halftone dots, is inferior. Further, when the content ratio of the alicyclic structural unit obtained from the dicarboxylic acid is less than the above range, there is a problem that the gradation printing reproducibility of the highlight portion is inferior and the plate surface adhesiveness is inferior. The printing resistance, especially the chipping resistance of the highlight halftone dots, is inferior.

The alicyclic diol comprises 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanediol, 1,3-cyclohexanediol and tricyclodecanedimethanol. At least one alicyclic alicyclic diol selected from the group. Among these, 1,4-cyclohexanedimethanol is preferable from the viewpoint of reproducibility of gradation printability of the highlight portion.

The alicyclic diisocyanate compound is at least selected from the group consisting of isophorone diisocyanate, 1,4-diisocyanatocyclohexane, cyclohexane-1,2-diylbis (methylene) diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. It is a kind of alicyclic diisocyanate. Among these, 1,4-diisocyanatocyclohexane is preferable from the viewpoint of reproducibility of gradation printability of the highlight portion.

The polyurethane of the present invention preferably contains a cationic group, an anionic group or a nonionic group in order to impart water solubility or water dispersibility. Among these, a cationic group is preferable in order to obtain stable water developability.

As the diol having a cationic group, a diol having a tertiary nitrogen atom is preferable, and a diol having an N-alkyldiethanolamine or a piberazine ring is preferable. As the N-alkyldiethanolamine, N-methyldiethanolamine is preferable. Further, as the diol having a piperazine ring, N, N'-bis (3-hydroxypropyl) piperazine is preferable.

Examples of the diol having an anionic group include a sulfonic acid group-containing diol and a carboxylic acid group-containing diol. Specific examples of the diol include dimethylolalkanoic acid such as 2,2-dimethylolpropionic acid (DMPA) and 2,2-dimethylolbutanoic acid, and N, N-bishydroxyethylglycine and N, N-bishydroxyethyl. Examples thereof include alanine, 3,4-dihydroxybutane sulfonic acid, 3,6-dihydroxy-2-toluene sulfonic acid and the like. Of these, dimethylol alkanoic acid is preferable, and 2,2-dimethylol propionic acid is more preferable, and 2,2-dimethylol propionic acid is more preferable, from the viewpoint of easy availability.

Examples of the nonionic group include diols containing an ether bond, and specific examples thereof include diethylene glycol and triethylene glycol. Further, when the molecular weight is increased, the Tg of polyurethane is lowered, which is not preferable.

The printing plate obtained from the letterpress printing original plate of the present invention uses polyurethane containing an alicyclic diol and / or an alicyclic diisocyanate obtained from an alicyclic diol, thereby achieving print reproducibility and high resistance to highlights. It is possible to achieve both printability. In polyurethane having many urea bonds, deformation of the plate due to pressure during printing is suppressed, and the print reproducibility of the highlight portion is excellent. However, polyurethane with many urea bonds cannot disperse the repeated stress in printing because the deformation of the plate is suppressed, and cracks occur in the plate in very short printing (low printing durability). ). Further, in polyurethane having alkylene glycol in polyurethane, the stress applied to the plate can be absorbed by the deformation of the portion of the alkylene glycol chain, but the glass transition point (Tg) is lowered, so that the highlight printability is lowered. Have a problem. However, the polyurethane of the present invention maintains a high glass transition point, and it is possible to improve the printing resistance by urethane bonding.

Polyurethane preferably has a glass transition point (Tg) of 30 to 100 ° C. as measured by a dynamic viscoelasticity measuring device. A more preferable range is 50 to 100 ° C. As a method for setting Tg in the above range, control may be performed by the amount of the ring structure of the alicyclic ring introduced into the molecular chain and the amount of urethane bond other than that.

By using polyurethane having a Tg of 30 to 100 ° C. measured by a dynamic viscoelasticity measuring device, the adhesiveness of the plate surface can be reduced. When the Tg is less than 30 ° C., the adhesiveness of the plate is high, so that the adhesion of paper dust generated from the printing paper to the surface of the printing plate during printing increases, and as a result, the ink transfer unevenness caused by the paper dust adhering to the solid portion occurs. Sometimes. On the other hand, when Tg exceeds 100 ° C., the degree of freedom of the molecular chain is lost and the printing durability is impaired. It is considered that the reason why the adhesiveness is reduced when the Tg of polyurethane is 30 ° C. or higher is that the molecular chain of polyurethane is frozen at around room temperature and free movement is suppressed when Tg is 30 ° C. or higher.

The polyurethane used in the present invention needs to have a specific amount of alicyclic structural units in the molecule and to be water-soluble or water-dispersible (water-developable). In order to satisfy the above conditions, the diol may be selected from aliphatic diols, aromatic diols, alicyclic diols and heterocyclic diols, but from the viewpoint of water developability, some diols having a piperazine ring may be used. It is preferable to use it for all. Further, in order to increase the Tg of polyurethane, it is preferable to select an alicyclic diol, and more preferably an alicyclic diol.

Further, the Tg of polyurethane used in the present invention can also be adjusted by increasing or decreasing the amount of polyurethane binding. As the aliphatic diol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 3-butanediol having 5 or less carbon atoms are used in order to increase the amount of polyurethane bond. Examples thereof include methyl-2,4-pentanediol, 2,4-pentanediol, and 1,5-pentanediol. On the other hand, in order to reduce the amount of polyurethane bond, a diol having 6 or more carbon atoms may be used, specifically, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol and the like. Examples thereof include 1,9-nonanediol. Further, the Tg of polyurethane can be lowered by blending a diol having a branched structure such as 2,2-dimethyl-1,3-propanediol.

As the other raw material for synthesizing the polyurethane of the present invention, known aliphatic, alicyclic, or aromatic diisocyanates can be used. For example, examples of the aliphatic diisocyanate include 1,6-hexamethylene diisocyanate, and examples of the alicyclic diisocyanate include isophorone diisocyanate, cyclohexane-1, 2-diylbis (methylene) diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. Can be mentioned. Examples of the aromatic diisocyanate include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and 4,4'-diphenylmethane diisocyanate. In particular, it is preferable to contain 45 to 90% by mass of the above alicyclic diol and / or alicyclic diisocyanate in polyurethane.

The polyurethane of the present invention can be obtained by reacting a diol compound with a diisocyanate compound. The reaction between the diol compound and the diisocyanate compound can be synthesized by reacting the diol and the diisocyanate with stirring. If necessary, a reaction catalyst or an organic solvent that does not affect the synthesis of polyurethane may be added for synthesis. Further, the reaction may be a one-step reaction, or may be a two-step synthesis method in which a prepolymer is synthesized and then polymerized.

The molar reaction ratio (amino group / isocyanate group) between the diol and the diisocyanate compound for synthesizing the polyurethane of the present invention is 1.0 or more, preferably 1.02 or more. In this case, even if the excess terminal hydroxyl group remains unreacted, it does not matter as long as it does not adversely affect the performance, physical properties, etc. of the composition using the excess hydroxyl group. Further, when the hydroxyl group / isocyanate group (equivalent ratio) is less than 1.0, an inconvenient reaction such as gelation is likely to occur, which is not preferable.

The polyurethane of the present invention may have a photopolymerizable unsaturated group introduced at the terminal from the photopolymerizable aspect. As a method for introducing a photopolymerizable unsaturated group at the terminal, polyurethane may be synthesized using a photopolymerizable unsaturated compound containing one hydroxyl group in the molecule as a raw material. The photopolymerizable unsaturated compound containing one hydroxyl group in the molecule is a photopolymerizable unsaturated compound containing one hydroxyl group and a (meth) acryloyl group, and specifically, 2-hydroxyethyl (meth). ) Acrylate, 2-hydroxypropyl (meth) acrylate, glycerin mono (meth) acrylate and the like.

The polyurethane of the present invention may contain a urea bond in the molecule as long as the performance is not deteriorated. The strength can be improved by containing a urea bond. The preferred urea bond content is in the range of 0.5-10 mol%.

The polyurethane used in the present invention preferably contains a basic tertiary nitrogen atom. In that case, it is preferable to react with a quaternizing agent to obtain a soluble polyurethane having an ammonium salt-type nitrogen atom from the viewpoint of water solubility. As the quaternizing agent, known organic acids can be used, and aliphatic organic acids and aromatic organic acids can be used. Specific examples of the organic acid include methacrylic acid, acrylic acid, succinic acid, adipic acid, sebacic acid, glycolic acid, lactic acid and the like as the aliphatic organic acid, and benzoic acid and isophthalic acid as the aromatic organic acid. However, an aliphatic organic acid is preferable from the viewpoint of water solubility. Further, the quaternizing agent is preferably used in combination with the organic acid used when reacting the polyurethane, and a part of the amount of the quaternizing agent added is used during the reaction of the polyurethane.

The amount of polyurethane used in the present invention is preferably 45 to 65% by weight in the total photosensitive resin composition. If the amount used is less than 45% by weight, sufficient physical properties cannot be obtained, and if it exceeds 65% by weight, the photocurability may be deteriorated and the image reproducibility may be deteriorated. In order to satisfy both the physical properties and the image reproducibility, it is more preferably 50 to 65% by weight.

The photopolymerizable unsaturated compound used in the present invention is a compound containing one or more photopolymerizable unsaturated groups in the molecule, and known compounds can be used. Examples of the compound containing one photopolymerizable unsaturated group in the molecule include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-chloro-2-hydroxypropyl (meth) acrylate. Cyclohexyl (meth) acrylate, benzyl (meth) acrylate, N, N'-dimethylaminoethyl (meth) acrylate, glycidyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, N-methylol (meth) One of acrylamide-n-butyl ether, diacetacrylamide, N-tert-butyl (meth) acrylamide, ring-opening addition reaction product of glycidyl (meth) acrylate and monoalcolate, 2-acrylamide-2-methylpropanesulfonic acid, etc. Examples thereof include compounds having an unsaturated bond of. Examples of the compound containing two or more photopolymerizable unsaturated groups in the molecule include ethylene glycol di (meth) acrylate, 1,3-propanediol di (meth) acrylate, and 1,4-butane diol di (meth). Acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolethanedi (meth) acrylate, trimethylolethanetri (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Tetramethylolmethane di (meth) acrylate, tetramethylolmethanetri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, tri (meth) acryloyloxyethyl phosphate, tris (2-hydroxyethyl) isocyanuric acid and (meth) Triesters with acrylates, ring-opening addition reaction products of polyhydric alcohol polyglycidyl ethers with (meth) acrylic acids, such as reaction products of (poly) ethylene glycol digusidyl ethers with (meth) acrylic acids, Reaction products of (poly) propylene glycol diglycidyl ether and (meth) acrylic acid, reaction products of 1,6-hexamethylene glycol diglycidyl ether and (meth) acrylic acid, glycerin diglycidyl ether and ( Reaction product with meth) acrylic acid, reaction product with trimethylolethane triglycidyl ether and (meth) acrylic acid, reaction product with trimethylolpropane triglycidyl ether and (meth) acrylic acid, diglycidyl isophthalate Reaction product of ether and (meth) acrylic acid, reaction product of diglycidyl ether of dicarboxylic acid of isoprene oligomer and (meth) acrylic acid, ring-opening addition of other active hydrogen compound and glycidyl (meth) acrylate Reaction products such as reaction products of (poly) ethylene glycol and glycidyl (meth) acrylate, reaction products of (poly) propylene glycol and glycidyl (meth) acrylate, reaction production of glycerin and glycidyl (meth) acrylate. Product, reaction product of 2-hydroxyethyl (meth) acrylate and glycidyl (meth) acrylate, reaction product of trimethylolethane and glycidyl (meth) acrylate, reaction production of trimethylolpropane and glycidyl (meth) acrylate Things, (meth) acrylic acid and glycidyl (meth) acrylice Reaction products of aliphatic polyvalent carboxylic acids and glycidyl (meth) acrylates, reaction products of aromatic polyvalent carboxylic acids and glycidyl (meth) acrylates, primary or secondary. N, N'-methylenebis (meth) acrylamide, N, N'-ethylenebis (meth) acrylamide, compounds having two or more unsaturated groups obtained by the reaction of a compound having an amino group with glycidyl (meth) acrylate. , N, N'-propylene bis (meth) acrylamide, N, N'-hexamethylene bis (meth) acrylamide, N, N'-m-phenylene bis (meth) acrylamide, N, N'-m-xylylene bis (meth) ) Acrylate, di (meth) acrylamide-N-methyl ether, 1,3-bis [(meth) acryloylaminomethyl] urea, and its derivatives, 1,3- [bis (meth) acryloylaminomethyl] -1,3 -Dimethylurea and its derivatives, 1,3- [bis (meth) acryloylaminomethyl] ethylene urea and its derivatives, 1,3- [bis (meth) acryloylaminomethyl] trimethylene urea and its derivatives, triacrylicformal, tris Examples thereof include compounds having two or more unsaturated bonds such as tri (meth) acrylate of (2-hydroxyethyl) isocyanuric acid, 1,3-diglycidyl, 5-methyl, and 5-ethylhydantin.

The photopolymerizable unsaturated compound may be used alone, or two or more thereof may be used in combination. The amount of the photopolymerizable unsaturated compound used is preferably 25 to 50% by weight in the total photosensitive resin composition. If the amount of the photopolymerizable unsaturated compound used exceeds 50% by weight, sufficient mechanical strength cannot be obtained, and if it is less than 25% by weight, the photocurability may deteriorate and the image reproducibility may deteriorate. ..

As the photopolymerization initiator used in the present invention, known photopolymerization initiators can be used, and specifically, benzophenones, benzoins, acetophenones, benzyls, benzoin alkyl ethers, benzylalkyl ketals, anthraquinones and the like can be used. , Thioxanthons and the like. Suitable specific examples include benzophenone, benzoin, acetophenone, benzoin methyl ether, benzoin ethyl ether, benzyldimethyl ketal, anthraquinone, 2-chloroanthraquinone, thioxanthone, 2-chlorothioxanthone and the like. The amount of the photopolymerization initiator used is preferably 0.05 to 5% by weight in the total photosensitive resin composition. If it is less than 0.05% by weight, the photopolymerization initiation ability is hindered, and if it exceeds 5% by weight, the photocurability in the thickness direction of the photosensitive resin layer of the printing original plate is lowered when producing a relief for printing, and the image is imaged. Is more likely to be chipped.

Further, a known thermal polymerization inhibitor may be added if necessary. The thermal polymerization inhibitor is added to prevent unplanned thermal polymerization due to heating during preparation, production, molding, etc. of the photosensitive resin composition, or a dark reaction during storage of the composition. Examples of the thermal polymerization inhibitor include hydroquinones such as hydroquinone, mono-tert-butylhydroquinone, 2,5-di-tert-butylhydroquinone and hydroquinone monomethyl ether, and benzoquinones such as benzoquinone and 2,5-diphenyl-p-benzoquinone. , Phenols, catechols, catechols such as p-tert-butylcatechols, aromatic amine compounds, biclinic acids, phenothiazines, α-naphthoquinones, anthraquinones, nitro compounds, sulfur compounds and the like. The amount of the thermal polymerization inhibitor used is preferably 0.001 to 2% by weight, particularly preferably 0.005 to 1% by weight, based on the total photosensitive resin composition. Two or more of these compounds may be used in combination.

The photosensitive resin composition of the present invention is formed by molding into a desired laminated body by any known method such as hot pressing, casting, melt extrusion, solution casting, etc., in addition to the melt molding method. , A letterpress printing original plate provided with a photosensitive resin layer can be obtained.

The letterpress printing original plate can be used by laminating a molded product (unexposed resin) molded into a sheet shape on a support with or without a known adhesive. As the support, any one such as a plastic film such as steel, aluminum, glass, and polyester film can be used, and a film having a thickness in the range of 50 to 500 μm is used. When the sheet-shaped molded product (unexposed resin) is supplied as a laminated body laminated on the support, it is preferable that the protective film is further laminated in contact with the sheet-shaped molded product (unexposed resin). As the protective film, a film-shaped plastic can be used, and for example, a polyester film having a thickness of 125 μm is used. Further, an anti-adhesion layer may be provided between the photosensitive resin layer and the protective film, which is transparent and has no adhesiveness and is coated with a polymer dispersed or dissolved in a developing solution to a thickness of 0.5 to 3 μm. By providing the adhesive prevention layer on the surface of the photosensitive resin layer, it is possible to easily peel off the protective layer during the next exposure operation even when the surface adhesiveness is strong.

In the letterpress printing original plate of the present invention, a cap layer having a thickness of 1 to 30 μm may be provided between the photosensitive resin layer and the adhesive prevention layer. Since the cap layer is not removed in the developing process and remains on the printing plate, the surface characteristics and durability of the printing plate can be adjusted by providing the cap layer. As the cap layer, a known cap layer can be used.

The letterpress printing original plate of the present invention can produce a CTP (Computer to Plate) plate that does not use a negative film by providing a heat-sensitive mask layer on the surface of the photosensitive resin layer. As the heat-sensitive mask layer, a known heat-sensitive mask layer can be used.

The original plate for letterpress printing obtained from the photosensitive resin composition of the present invention is exposed by closely superimposing a negative film or a positive film having a transparent image portion on a photosensitive resin layer and irradiating it with active light from above. To create an original plate in which only the exposed part through which the active light has passed is insolubilized. As the active light beam, a light source such as a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, or a chemical lamp having a wavelength of usually 300 to 450 nm is used. On the other hand, in the case of the CTP plate, the heat-sensitive mask layer is irradiated like an image with an IR laser to form a mask (same function as a negative film) on the photosensitive resin layer. After the image information is written on the heat-sensitive mask layer, the photosensitive printing original plate is irradiated with the active light on the entire surface through the mask to create an original plate in which only the exposed portion through which the active light is transmitted is insolubilized.

Next, the unexposed portion is dissolved and removed with a suitable solvent, particularly neutral water in the present invention, but the unexposed portion can be dissolved and removed by a developing method such as a spray-type developing device or a brush-type developing device. After that, the printing plate from which the unexposed portion is melted and removed is subjected to draining, drying, and post-exposure steps to obtain the final printing plate.

When the original plate for letterpress printing obtained from the photosensitive resin composition of the present invention is used, it is found that both the gradation printability and the print resistance of the highlight portion are excellent, and the adhesiveness of the plate surface is very low. It was issued. Therefore, by using the letterpress printing original plate of the present invention, it is possible to print a large number of copies with one plate for high-quality printing. Further, since the adhesiveness on the plate surface is reduced, the adhesion of dust and paper dust is reduced before and during printing, and the number of times the plate is washed can be significantly reduced.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. The number of copies in the embodiment represents a mass part. The evaluation of the characteristic values in the examples was based on the following method.

(1) Highlight printability (highlight gradation print reproducibility)
First, on a photosensitive resin letterpress original plate with a photosensitive layer thickness of 685 μm, net dots 175 lines-1% to 95%, minimum independent point diameter 50 to 600 μm, minimum independent line width 10 to 150 μm, and solid image (width 1 cm). Using a print evaluation negative including (x length 5 cm), the minimum exposure time that 175 lines-1% can be reproduced is set as the optimum exposure time, and a 25 W / m ² chemical lamp is used to reach a height of 5 cm from the surface of the photosensitive resin. Exposed from. Next, it was developed with a brush type washer (120 μmφ nylon brush, JW-A2-PD type produced by Nippon Denshi Seiki Co., Ltd.) in tap water at 25 ° C. to obtain a relief image. Further, the mixture was dried with warm air at 70 ° C. for 10 minutes and then exposed with an ultra-high pressure mercury lamp for 30 seconds to obtain a printing plate. Image reproducibility of 175 lines-1% was determined with the naked eye using a 10x loupe. The highlight printability was evaluated using the obtained printing plate. A rotary printing press P-20 (manufactured by Sanjo Machinery Co., Ltd.) was used as the printing machine, Best Cure Indigo (manufactured by T & K TOKA) was used as the ink, and Gloss PW-8K (manufactured by Lintec) was used as the printed matter. The printing pressure (pressure between the plate and the printed matter) was gradually increased, and the printing was evaluated by setting the part where the solid part disappeared as the appropriate pressure. In addition, the ink feed amount was adjusted so that the ink density at the solid portion was 1.7 abs. The halftone dot concentration of 175 lines 1% to 5% at an appropriate pressure was measured using CCDOT4 (manufactured by SDG Co., Ltd.), and the results are expressed in% and summarized in Table 1. The measured halftone dot density of the printed matter should be close to the halftone dot density of the negative film, and further, the halftone dot density of the printed matter smoothly decreases as the halftone dot density of the negative film decreases from 5% to 1%. It is preferable to continue. When the halftone dot density of the printed matter is smoothly reduced in this way, it is evaluated that the gradation of highlights is excellent.

(2) Adhesiveness on the plate surface The printing plate was manufactured by the same method as when the relief for evaluating the highlight part of (1) was created, and the adhesiveness of the surface of the printing plate was evaluated using the obtained printing plate. .. The adhesiveness was evaluated by pressing a coated paper (gloss PW-8K, manufactured by Lintec Corporation), which is a printed matter, against a plate and using the following criteria based on the degree of slippage of the coated paper.
◯: The coated paper slips without resistance.
Δ: The coated paper and the plate stick to each other, but slip when force is applied.
X: The coated paper and the plate adhere to each other and do not slip.

(3) Printing durability The highlight part of (1) The printing plate is manufactured by the same method as when the relief for evaluation of printability was created, and the printing plate is pressurized by 100 μm from the appropriate printing pressure (high pressure printing condition) 5,000 shots. After printing 5,000 shots, the printed matter and the plate were observed with a microscope magnified 200 times, and evaluated according to the following criteria.
⊚: No cracks on printed matter and plate.
◯: There is no defect in the printed matter, but there is a slight crack in the plate. Δ: The defect cannot be visually confirmed in the printed matter, but a defect is seen in the observation at 200 times.
X: Defects can be visually confirmed in the printed matter.

(4) Content of alicyclic building blocks in polyurethane (mol%)
The reaction of polyurethane is an addition reaction, and the molar ratio is determined by the amount of raw material charged. Therefore, for the content of the alicyclic constituent unit in polyurethane, the molar content was calculated from the amount of the raw material containing the alicyclic constituent unit. When the amount to be charged was unknown, it was determined by ^{1 1} H-NMR.

(6) Glass transition point (Tg)
The glass transition point (Tg) was measured using a dynamic viscoelasticity measuring device. Measurement was performed in a tensile mode using a dynamic viscoelastic device DVA220 manufactured by IT Measurement Control Co., Ltd. The measurement was performed in an air atmosphere at a heating rate of 4 ° C./min, a frequency of 10 Hz, and a sample shape of 15 mm × 4 mm. The peak temperature of Tan δ was defined as the glass transition temperature (Tg).

The raw materials used in the examples are as follows.
BD: 1,4-butanediol NPG: Neopentyl glycol CHDM: 1,4-Cyclohexanedimethanol TCDM: Tricyclodecanedimethanol NMDA: N-methyldiethanolamine BHPP: N, N'-bis (3-hydroxypropyl) ) Piperazin HDI: 1,6-hexamethylene diisocyanate IPDI: Isophorone diisocyanate Hydrogenated MDI: 4,4'-dicyclohexylmethane diisocyanate

Example 1
In a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen blowing tube, 23.5 parts by mass of 1,4-cyclohexanedimethanol and 13.0 parts by mass of N-methyldiethanolamine were added to 50 parts by mass of methyl ethyl ketone. Dissolved in the part. Next, 14.6 parts by mass of hexamethylene diisocyanate and 48.9 parts by mass of isophorone diisocyanate were gradually added under stirring. The solution was reacted at 75-80 ° C for 120 minutes. Then, 50 parts by mass of methyl ethyl ketone was further added and reacted at 75 to 80 ° C. for 180 minutes to obtain a polyurethane solution having a solid content concentration of 50% by mass. A part of this solution was taken in a Teflon (registered trademark) coated petri dish, methyl ethyl ketone was evaporated and removed, and then dried under reduced pressure to obtain polyurethane. The obtained polyurethane contained 64 mol% of alicyclic structural units calculated from the charged amount, and had a glass transition point (Tg) of 69 ° C.

110.0 parts by mass (55 parts by mass as a solid content) of the polyurethane solution having a solid content concentration of 50% by mass thus obtained was added to 100 parts of methanol and heated and mixed at 65 ° C. to obtain N-ethyltoluene. 5.0 parts of sulfonic acid amide, 0.03 part of 1,4-naphthoquinone and 0.1 part of hydroquinone monomethyl ether were added and dissolved by stirring for another 30 minutes. After that, 2.5 parts of glycidyl methacrylate (GMA), 18 parts of water, 0.3 part of ammonium sulfate, 0.1 part of oxalic acid, 1.0 part of benzyldimethylketal as a photopolymerization initiator, and 2-hydroxy-3-acryloyl. 32.5 parts of oxypropyl methacrylate (branchant Blemmer GAM manufactured by Nippon Oil & Fats Co., Ltd.) was added and dissolved by stirring for 30 minutes. Then, the temperature was gradually raised to distill off methanol and water, and the temperature in the kettle was concentrated to 110 ° C. At this stage, a fluid and viscous photosensitive resin letterpress composition was obtained.

Next, using a support having an adhesive layer having a coating film of 20 μm, which is obtained by coating an adhesive composition containing an ultraviolet absorber on a polyester film having a thickness of 250 μm, the above-mentioned photosensitive resin composition is brought into contact with the coating film of the support. A material was cast, and the film side of a polyester film having a thickness of 125 μm coated with a film of polyvinyl alcohol (AH-24, manufactured by Nippon Synthetic Chemical Co., Ltd.) having a thickness of 2 μm was brought into contact with the photosensitive resin letterpress composition. A raw plate of a sheet-like laminated body having a total thickness of 1080 μm was formed using a laminator.

After storing the raw plate for 7 days or more, the highlight part printability, plate surface adhesiveness, and printing resistance were evaluated. These evaluation results are shown in Table 1 together with the details of the polyurethane of Example 1.

Examples 2-9, Comparative Examples 1-3
Based on the composition of polyurethane in Table 1, polyurethane was synthesized in the same manner as in Example 1. The glass transition point (Tg) of polyurethane was measured in the same manner as in Example 1. Using the obtained polyurethane, a photosensitive resin composition was prepared in the same manner as in Example 1 to obtain a printing original plate. The obtained printing plate was evaluated in the same manner as in Example 1. These evaluation results are shown in Table 1 together with the details of the polyurethanes of Examples 2 to 9 and Comparative Examples 1 to 3.

As can be seen from Table 1, as shown in Examples 1 to 9, when polyurethane having an alicyclic structural unit amount of 45 to 90 mol% in polyurethane was used, highlight halftone dots of 1 to 5% were used. Both gradation and printing durability are compatible. In addition, it is also excellent in plate surface adhesiveness due to the effect of improving the glass transition point.

According to the photosensitive resin composition of the present invention, it is possible to obtain a letterpress printing original plate which is excellent in gradation printing reproducibility and printing resistance of 1 to 5% highlight portion and has low plate surface adhesiveness.

Claims (5)

A photosensitive resin composition for a letterpress printing original plate containing a water-soluble or water-dispersible polyurethane, a photopolymerizable unsaturated compound, and a photopolymerization initiator, wherein the polyurethane is an alicyclic group obtained from a diol and a diisocyanate. A photosensitive resin for a letterpress printing original plate, characterized in that the structural unit contains 45 to 90 mol% of an alicyclic structural unit in the molecule and the Tg measured by a dynamic viscoelasticity measuring device is 50 to 100 ° C. Composition. The alicyclic diol as the alicyclic structural unit is at least one fat selected from the group consisting of 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol and tricyclodecanedimethanol. The photosensitive resin composition for letterpress printing original plate according to claim 1 , which is a cyclic diol. The alicyclic diisocyanate to be the alicyclic structural unit is derived from isophorone diisocyanate, 1,4-diisocyanatocyclohexane, cyclohexane-1,2-diylbis (methylene) diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. The photosensitive resin composition for a letterpress printing original plate according to claim 1 or 2, wherein the alicyclic diisocyanate is at least one selected from the group. A letterpress printing original plate provided with a photosensitive resin layer made of the photosensitive resin composition for a letterpress printing original plate according to any one of claims 1 to 3 . The letterpress printing original plate according to claim 4 , which is used for laser engraving.