JP2014197078A - Photosensitive resin composition, original printing plate and flexographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photosensitive resin composition which can be stably photocured to a desired thickness while maintaining photocurable property, and to provide an original printing plate and a flexographic printing plate using the above composition in a photosensitive layer.SOLUTION: The photosensitive resin composition comprises (A) a water-dispersion latex, (B) a millable rubber (excluding compounds described in component (C)), (C) a compound having a unit structure represented by formula (1) shown below, (D) a photopolymerizable monomer (excluding compounds described in component (C)), and (E) a photopolymerization initiator. In the formula, R1 represents a hydrogen group or a methyl group; and R2 represents a maleic acid anhydride group or a maleic acid ester group.

Description

  The present invention relates to a photosensitive resin composition, a printing plate precursor, and a flexographic printing plate.

  Conventionally, letterpress printing, intaglio printing, or planographic printing has been performed on printing materials such as packaging materials, labels, and magazines using printing plates. Among these, letterpress printing is performed using letterpress. This relief printing plate includes a flexographic printing plate that can be applied to various types of printing bodies because the material is soft.

  An original plate of a flexographic printing plate includes a photosensitive layer made of a photosensitive resin composition on a substrate such as a PET resin. In a flexographic printing plate, a relief image is formed by irradiating an ultraviolet ray to a photosensitive layer through a negative film adhered to the photosensitive layer and removing an uncured portion.

  In the production of a flexographic printing plate, a base is formed on the photosensitive layer before forming a relief image. The base is formed by irradiating (exposing) ultraviolet rays from the back side (substrate side) of the flexographic printing plate precursor to the entire back side of the photosensitive layer, and photocuring a part of the photosensitive layer with a predetermined thickness. If the base is too thin, it is difficult to form a relief image, and if the base is too thick, the relief image becomes shallow, and the ink fills the concave portion of the relief image and the uneven shape is not reproduced in the printed image. Therefore, in the formation of the base, it is required to stably photocure the photosensitive layer to a desired thickness.

  In this respect, the ultraviolet curing reaction is an effective curing method in the formation of the foundation because the curing can be started and stopped by turning on / off the ultraviolet irradiation, but it is a radical reaction, and the reaction rate is very fast. Therefore, the influence of variations such as the irradiation intensity of the light source (lamp) cannot be ignored, and it is difficult to stably photocure the photosensitive layer to a desired thickness in the formation of the base. Furthermore, recently, a thin photosensitive layer is used for high-definition printing, so that more stable photocuring is required.

  In order to improve this, for example, Patent Documents 1 and 2 disclose a method of suppressing the amount of ultraviolet light transmitted to the photosensitive layer by adding an ultraviolet absorber to the adhesive layer that bonds the substrate and the photosensitive layer. . Also known is a method of suppressing the amount of ultraviolet light transmitted to the photosensitive layer and the reaction by adding an ultraviolet absorber or a photopolymerization inhibitor to the photosensitive layer.

Japanese Patent Laid-Open No. 08-87106 Japanese Patent No. 4304549

  In the method of adding an ultraviolet absorber to the adhesive layer that adheres between the substrate and the photosensitive layer, the adhesive layer is generally as thin as several tens of μm. In addition, it is difficult to develop stable UV absorption.

  In the method of adding an ultraviolet absorber or a polymerization inhibitor to the photosensitive layer, the photocurability of the photosensitive layer is deteriorated due to a decrease in the amount of ultraviolet rays transmitted to the photosensitive layer or a radical reaction during the formation of a relief image. The image cannot be formed sufficiently.

  A problem to be solved by the present invention is a photosensitive resin composition that can be stably photocured to a desired thickness while maintaining photocurability, and a printing plate precursor and a flexographic printing plate using the same. Is to provide.

ただし、Ｒ１は水素基またはメチル基であり、Ｒ２はマレイン酸無水物基またはマレイン酸エステル基である。 In order to solve the above problems, the photosensitive resin composition according to the present invention comprises (A) water-dispersed latex, (B) millable rubber (excluding those described in component (C)), (C) the following formula (1) And (E) a photopolymerization initiator (D), a photopolymerizable monomer (excluding those described in component (C)), and (E) a photopolymerization initiator.

However, R1 is a hydrogen group or a methyl group, and R2 is a maleic anhydride group or a maleic ester group.

  The gist of the printing plate precursor according to the invention is to have a photosensitive layer made of the photosensitive resin composition.

  The gist of the flexographic printing plate according to the present invention is that the printing plate precursor is used.

  According to the photosensitive resin composition of the present invention, (A) water-dispersed latex, (B) millable rubber (excluding those described in component (C)), (D) photopolymerizable monomer (component (C)) And (E) a photopolymerization initiator, and (C) a compound having a unit structure represented by formula (1) in a material containing a photopolymerization initiator, In comparison, the photocuring speed can be slowed while maintaining photocurability. Thereby, the influence of variation, such as irradiation intensity of a light source (lamp), can be relieved and photocuring can be stably performed to a desired thickness. That is, according to the photosensitive resin composition according to the present invention, the photocuring speed is slower than the case where the component (C) is not included, but the photocuring is insufficient for the formation of a base or a relief image. However, photocurability is maintained.

  And since the printing plate precursor concerning this invention has a photosensitive layer which consists of the said photosensitive resin composition, it can be photocured stably to desired thickness, maintaining photocurability. Thereby, a flexographic printing plate having excellent image reproducibility can be obtained.

It is sectional drawing which shows an example of a structure of the printing plate precursor used for preparation of a flexographic printing plate. It is a figure explaining the evaluation method of a cure rate.

  Next, an embodiment of the present invention will be described in detail.

  The photosensitive resin composition according to the present invention includes (A) water-dispersed latex, (B) millable rubber, (C) a compound having a specific unit structure, (D) a photopolymerizable monomer, (E) a photopolymerization initiator, It contains what contains. The photosensitive resin composition according to the present invention can be suitably used for a photosensitive layer of a printing plate precursor that can be developed with water and an aqueous developer.

  The component (A) water-dispersed latex is a polymer particle dispersed in water as a dispersoid. A polymer is obtained by removing water from the water-dispersed latex. The water-dispersed latex can impart water developability to the photosensitive resin composition.

  Specific examples of the water-dispersed latex include polybutadiene latex, natural rubber latex, styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex, polychloroprene latex, polyisoprene latex, polyurethane latex, and methyl methacrylate-butadiene copolymer. Water-dispersed latex polymers such as polymer latex, vinylpyridine polymer latex, butyl polymer latex, thiocol polymer latex, and acrylate polymer latex, and other components such as acrylic acid and methacrylic acid are copolymerized with these polymers. And the resulting polymer. These may be used alone or in combination of two or more.

  Among these, an aqueous dispersion latex polymer containing a butadiene skeleton or an isoprene skeleton in the molecular chain is preferable from the viewpoint of hardness. Specifically, polybutadiene latex, styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, acrylic acid-methyl methacrylate-butadiene copolymer latex, and polyisoprene latex are preferable. .

  The millable rubber of component (B) can increase the rubber elasticity of the photosensitive resin composition. Thereby, for example, it is possible to expect effects such as easy printing on various substrates. Specific examples of the millable rubber include butadiene rubber (BR), nitrile rubber (NBR), acrylic rubber, epichlorohydrin rubber, urethane rubber, isoprene rubber, styrene isoprene rubber, styrene butadiene rubber, ethylene-propylene copolymer, chlorination. Examples thereof include polyethylene. These may be used alone or in combination of two or more. However, the millable rubber of component (B) excludes those described in component (C).

  Among these, butadiene rubber (BR) and nitrile rubber (NBR) are preferable from the viewpoint of improving the water developability, drying property, and image reproducibility of the photosensitive resin composition. Furthermore, the butadiene rubber (BR) is particularly easy to finely disperse in the photosensitive resin composition, thereby improving the reproducibility of the fine shape and further improving the image reproducibility. preferable.

ただし、Ｒ１は水素基またはメチル基であり、Ｒ２はマレイン酸無水物基または、マレイン酸エステル基である。 Component (C) is a compound having a unit structure represented by the following formula (1). Component (C) is a polymer having a butadiene skeleton or an isoprene skeleton, which may be a solid polymer at room temperature or a liquid polymer, but is a liquid polymer from the viewpoint of excellent kneadability. It is preferable that

However, R1 is a hydrogen group or a methyl group, and R2 is a maleic anhydride group or a maleic ester group.

  Examples of R2 of component (C) include a maleic anhydride group and a maleic ester group. Examples of maleic acid ester groups include maleic acid monoester groups and maleic acid diester groups.

  The component (C) may be a polymer composed only of the unit structure represented by the formula (1), or a block copolymer composed of a combination of the unit structure represented by the formula (1) and another unit structure or It may be a random copolymer. Preferably, from the standpoint of superior compatibility with the butadiene rubber in the component (B), the other unit structure is a block copolymer or random copolymer composed of butadiene or isoprene.

As a suitable thing of a component (C), the polymer shown by the following formula | equation (2)-(3) is mentioned. However, m and n are positive integers.

  The photopolymerizable monomer of component (D) can cure or crosslink the photosensitive resin composition. Examples of the photopolymerizable monomer include ethylenically unsaturated compounds. Examples of the ethylenically unsaturated compound include (meth) acrylic monomers, (meth) acrylic oligomers, and (meth) acrylic modified polymers. Examples of the (meth) acryl-modified polymer include (meth) acryl-modified butadiene rubber and (meth) acryl-modified nitrile rubber. However, the photopolymerizable monomer of component (D) excludes those described in component (C).

  The ethylenically unsaturated compound may be a compound having only one ethylenically unsaturated bond or a compound having two or more ethylenically unsaturated bonds.

  Specific examples of the ethylenically unsaturated compound having only one ethylenically unsaturated bond include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, β-hydroxy-β ′-(meth) acryloyloxyethyl phthalate and other hydroxyl group-containing (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl Alkyl (meth) acrylates such as (meth) acrylate, butyl (meth) acrylate, isoamyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meta ) Cycloalkyl (meth) acrylates such as acrylate, halogenated alkyl (meth) acrylates such as chloroethyl (meth) acrylate and chloropropyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl ( Alkoxyalkyl (meth) acrylates such as meth) acrylate, Phenoxyalkyl (meth) acrylates such as phenoxyethyl acrylate / nonylphenoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, methoxydi Alkoxyalkylene glycol (meth) acrylate such as propylene glycol (meth) acrylate, 2,2-dimethylaminoethyl (Meth) may be mentioned acrylate 2,2 diethylaminoethyl (meth) acrylate 2-hydroxyethyl (meth) acrylate 3-chloro-2-hydroxypropyl (meth) acrylate.

  Specific examples of the ethylenically unsaturated compound having two or more ethylenically unsaturated bonds include alkyldiol di (meth) acrylates such as 1,9-nonanediol di (meth) acrylate, and diethylene glycol di (meth) acrylate. Polyethylene glycol di (meth) acrylate such as polypropylene glycol di (meth) acrylate such as dipropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) ) Acrylates, glycerol tri (meth) acrylates, ethylene glycol diglycidyl ethers with compounds with ethylenically unsaturated bonds such as unsaturated carboxylic acids and unsaturated alcohols and active hydrogen Polyvalent (meth) acrylates obtained by addition reaction of unsaturated epoxy compounds such as polyvalent (meth) acrylates and glycidyl (meth) acrylates obtained by reaction with compounds having active hydrogen such as carboxylic acids and amines, Examples thereof include polyvalent (meth) acrylamides such as methylenebis (meth) acrylamide and polyvalent vinyl compounds such as divinylbenzene.

  The photopolymerization initiator of component (E) is not particularly limited as long as it initiates photopolymerization of the photopolymerizable monomer. For example, alkylphenones, acetophenones, benzoin ethers, benzophenones, thioxanthones, anthraquinones And photopolymerization initiators such as benzyls and biacetyls. Specific examples include benzyl dimethyl ketal, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, methyl-O-benzoylbenzoate, 1-hydroxycyclohexyl phenyl ketone, and the like.

  The photosensitive resin composition according to the present invention includes (A) a water-dispersed latex, (B) a rubber, (D) a photopolymerizable monomer, and (E) a photopolymerization initiator. By adding the compound having the unit structure shown in (2), the photocuring rate can be slowed while maintaining the photocuring property as compared with the case where the component (C) is not included. Thereby, the influence of variation, such as irradiation intensity of a light source (lamp), can be relieved and photocuring can be stably performed to a desired thickness. That is, according to the photosensitive resin composition according to the present invention, the photocuring speed is slower than the case where the component (C) is not included, but the photocuring is insufficient for the formation of a base or a relief image. However, photocurability is maintained.

  In the photosensitive resin composition according to the present invention, (A) water-dispersed latex and (B) rubber are required as matrix polymers. The effect of slowing the photocuring speed while maintaining the photocurability as compared with the case where the component (C) is not included is exhibited when the (A) water-dispersed latex is included together with the (B) rubber. When (A) water-dispersed latex is included together with (B) rubber, the mixture of (A) water-dispersed latex and (B) rubber is phase-separated, and the component (B) around the rubber phase of component (B) ( It is assumed that the water-dispersed latex phase of A) is arranged. In such a sea-island structure, the photopolymerizable monomer of component (D) and the photopolymerization initiator of component (E) are dispersed in one of the phases (for example, the rubber phase of component (B)). It is presumed that the radical polymerization reaction of the photopolymerizable monomer is delayed.

  The blending ratio of component (A) (water-dispersed latex) and component (B) (rubber) in the photosensitive resin composition is the mass of component (A) with respect to the total mass of component (A) and component (B). The ratio (A / (A + B) mass ratio) is preferably in the range of 20 to 90%. More preferably, it is in the range of 30 to 80%, and further preferably in the range of 50 to 70%. When this mass ratio is 20% or more, water development can be performed at high speed. This is presumably because the permeability of the aqueous developer to the photosensitive resin composition is increased. On the other hand, when the mass ratio is 90% or less, the image reproducibility is excellent.

  The content of the component (C) in the photosensitive resin composition is preferably in the range of 1 to 50% by mass, more preferably in the range of 1 to 20% by mass, and still more preferably in the range of 1 to 10% by mass. It is. If content of a component (C) is 1 mass% or more, it is excellent in the said effect. If content of a component (C) is 50 mass% or less, it is excellent in image reproducibility.

  The content of component (D) (photopolymerizable monomer) in the photosensitive resin composition is preferably in the range of 10 to 80% by mass, more preferably in the range of 20 to 50% by mass. When the content of the component (D) is 10% by mass or more, there is no shortage of crosslinking density, and good image reproducibility and ink resistance can be obtained. On the other hand, when the content of the component (D) is 80% by mass or less, the relief is not brittle and the flexibility that is a characteristic of the flexographic printing plate can be ensured.

  Moreover, content of (E) component (photoinitiator) in the photosensitive resin composition becomes like this. Preferably it exists in the range of 0.3-10 mass%, More preferably, it exists in the range of 0.5-5 mass%. It is. If content of (E) component is 0.3 mass% or more, the photopolymerization reaction of component (D) will fully occur and a good image can be formed. On the other hand, if the content of the component (D) is 5% by mass or less, the sensitivity is not too high, and thus the exposure time can be easily adjusted.

  The photosensitive resin composition according to the present invention can contain a surfactant for the purpose of improving water developability. Examples of the surfactant include a cationic surfactant, an anionic surfactant, and a nonionic surfactant. Of the surfactants, an anionic surfactant is particularly preferable.

  Specific examples of anionic surfactants include aliphatic carboxylates such as sodium laurate and sodium oleate, higher alcohol sulfates such as sodium lauryl sulfate, sodium cetyl sulfate, and sodium oleyl sulfate, Polyoxyethylene alkyl allyl ether sulfate such as sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene alkyl allyl ether sulfate such as sodium polyoxyethylene octylphenyl ether sulfate and sodium polyoxyethylene nonylphenyl ether sulfate, Alkyl diphenyl ether disulfonates, alkyl sulfonates such as sodium dodecyl sulfonate, sodium dialkyl sulfosuccinate, Alkyl allyl sulfonates such as killed disulfonate, sodium dodecylbenzenesulfonate, sodium dibutylnaphthalenesulfonate, sodium triisopropylnaphthalenesulfonate, higher alcohol phosphates such as disodium lauryl phosphate monoester, sodium lauryl phosphate diester Examples thereof include ester salts and polyoxyethylene alkyl ether phosphate salts such as polyoxyethylene lauryl ether phosphate monoester disodium / polyoxyethylene lauryl ether phosphate diester sodium. These may be used alone or in combination of two or more. In addition, although the sodium salt was mentioned as a specific example, it is not specifically limited to a sodium salt, The same effect can be acquired also with calcium salt, ammonia salt, etc.

  Of these, sulfonic acid surfactants such as alkyl sulfonates and alkyl allyl sulfonates are preferred from the viewpoint of further improving the water developability of the photosensitive resin composition.

  The content of the surfactant in the photosensitive resin composition is the ratio of the mass of the surfactant to the total mass of the component (A) (water-dispersed latex), the component (B) (rubber), and the surfactant (surfactant). Agent / (A + B + surfactant) mass ratio) is preferably in the range of 0.1 to 20%. More preferably, it is in the range of 0.1 to 15%, and further preferably in the range of 0.1 to 10%. By making this mass ratio 0.1% or more, water development can be performed in a short time. This is presumably because the permeability of the aqueous developer to the photosensitive resin composition is increased. Moreover, drying property improves by making this mass ratio into 20% or less.

  The photosensitive resin composition according to the present invention may contain a plasticizer for the purpose of imparting flexibility. Moreover, since the hardness of the photosensitive resin composition can be suppressed by containing a plasticizer, content of a component (D) (photopolymerizable monomer) can be increased. Thereby, ink resistance can be improved.

  Examples of the plasticizer include liquid rubber, oil, polyester, and phosphoric acid compounds. In particular, those having good compatibility with the component (A) or the component (B) are preferable. Examples of the liquid rubber include liquid polybutadiene, liquid polyisoprene, and those modified with maleic acid or an epoxy group. Examples of the oil include paraffin, naphthene, and aroma. Examples of polyester include adipic acid-based polyester. Examples of phosphoric acid compounds include phosphate esters.

  The plasticizer content in the photosensitive resin composition is preferably in the range of 0.1 to 30% by mass. More preferably, it exists in the range of 5-20 mass%. If the content of the plasticizer is 0.1% by mass or more, flexibility can be imparted to the photosensitive resin composition, so that swelling of the photosensitive resin composition by the solvent ink can be suppressed. That is, resistance to solvent ink (solvent ink swelling property) is improved. On the other hand, if content of a plasticizer is 30 mass% or less, the intensity | strength of the photosensitive resin composition is securable.

  Furthermore, in the photosensitive resin composition according to the present invention, a thermal polymerization inhibitor (stabilizer) can be added from the viewpoints of increasing thermal stability during kneading and enhancing storage stability. Examples of the thermal polymerization inhibitor include phenols, hydroquinones, and catechols. The content of the thermal polymerization inhibitor in the photosensitive resin composition is generally in the range of 0.001 to 5 mass%.

  In addition, in the photosensitive resin composition according to the present invention, in order to improve various properties, other ultraviolet absorbers, dyes, pigments, antifoaming agents, fragrances and the like are added within the range not impairing the effects of the present invention. Components can be added as appropriate.

  The photosensitive resin composition according to the present invention can be prepared by, for example, dehydrating while kneading the components (A) to (E). Alternatively, it can be prepared by previously dehydrating the component (A) and then kneading the polymer obtained from the component (A) with the components (B) to (E). Examples of the kneader used at the time of kneading include a twin screw extruder, a single screw extruder, a kneader, and a Banbury mixer.

  Next, the printing plate precursor according to the present invention will be described.

  The printing plate precursor according to the present invention comprises a photosensitive layer comprising the photosensitive resin composition according to the present invention. FIG. 1 shows an example of the configuration of the printing plate precursor. As shown in FIG. 1, in the printing plate precursor 10, the photosensitive layer 16 is laminated on the substrate 12 via the adhesive layer 14.

  The printing plate precursor according to the present invention may be a so-called analog printing plate precursor in which a negative film (one on which an image has already been formed) is brought into close contact with the photosensitive layer at the time of use. It may be a printing plate precursor of a LAM (Laser Ablative Mask) method included in a so-called CTP (Computer to Plate) method in which an infrared ablation layer is in close contact therewith.

  The analog printing plate precursor has an adhesive layer made of an adhesive or the like for bonding the substrate and the photosensitive layer, a photosensitive layer made of the photosensitive resin composition according to the present invention, and the photosensitive layer surface not sticking on the substrate. The adhesive prevention layer for making it and the protective film which prevents the damage | wound of the photosensitive resin composition before use consists of what was laminated | stacked in this order. Examples of the substrate include a plastic film (or plastic sheet) such as a PET film, a metal sheet such as stainless steel and aluminum, and a rubber sheet such as butadiene rubber. Note that when the analog printing plate precursor is used, the protective film is peeled off, and a negative film on which an image has been formed in advance is adhered onto the exposed anti-adhesion layer.

  For example, an analog printing plate precursor is pre-applied with an adhesive on one side of the substrate, an anti-sticking agent is applied on one side of the protective film, and the photosensitive resin composition according to the present invention is pre-applied with the adhesive. It can manufacture by pinching between the board | substrate and the protective film which apply | coated the antiblocking agent previously, and pressing so that the thickness of the photosensitive resin composition may become predetermined thickness.

  The LAM printing plate precursor is different from the analog printing plate precursor in that it has an infrared ablation layer between the photosensitive layer and the protective film, and the other configurations are the same as the analog printing plate precursor. It is the composition. That is, an adhesive layer, a photosensitive layer, an infrared ablation layer, and a protective film are laminated on the substrate in this order. When the LAM printing plate precursor is used, the protective film is peeled off and the infrared ablation layer is exposed.

  The infrared ablation layer is a layer that can remove a portion irradiated with an infrared laser, and is a layer that itself has a function of blocking the transmission of ultraviolet rays at a practical level, and forms an image on the layer. Therefore, it can serve as a negative (or positive).

  The infrared ablation layer is mainly composed of resin or rubber as a binder, an infrared absorbing material, an ultraviolet absorbing material, a plasticizer, and the like. The infrared ablation layer can be produced, for example, by dissolving the above-described material in a solvent, applying it to a base material, and drying to remove the solvent.

  In the LAM printing plate precursor, for example, an adhesive is applied in advance to one side of the substrate, an infrared ablation layer is applied in advance to one side of the protective film, and the photosensitive resin composition according to the present invention is applied in advance to the adhesive. It can be produced by sandwiching between the substrate and a protective film previously coated with an infrared ablation layer, and pressing the photosensitive resin composition to a predetermined thickness.

  In any printing plate precursor, the thickness of the photosensitive layer is preferably in the range of 0.5 to 5 mm. If the thickness of the photosensitive layer is 0.5 mm or more, the relief depth can be sufficiently secured. On the other hand, if the thickness of the photosensitive layer is 5 mm or less, the weight of the printing plate precursor can be suppressed and practically used as a printing plate.

  Next, the flexographic printing plate according to the present invention will be described.

  The flexographic printing plate according to the present invention comprises a printing plate precursor according to the present invention provided with a photosensitive layer comprising the photosensitive resin composition according to the present invention. That is, the flexographic printing plate according to the present invention comprises a relief image formed on the photosensitive layer of the printing plate precursor according to the present invention.

  In order to form a relief image on the photosensitive layer of the printing plate precursor, first, ultraviolet light irradiation (back exposure) is performed from the back side (substrate side) of the printing plate precursor to the entire back side of the photosensitive layer to form a photosensitive layer having a predetermined thickness. A base is formed on the back side of the photosensitive layer by photocuring the part. If the base is too thin, it is difficult to form a relief image, and if the base is too thick, the relief image becomes shallow, and the ink fills the concave portion of the relief image and the uneven shape is not reproduced in the printed image. Therefore, in the formation of the base, it is required to stably photocure the photosensitive layer to a desired thickness.

The ultraviolet irradiation is usually performed by a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp, or the like that can irradiate light having a wavelength of 300 to 400 nm (UV-A). The irradiation time of ultraviolet rays for forming the base is usually very short, from several seconds to several tens of seconds. Also, the UV-A integrated light quantity in the formation of the base is as small as several tens to several hundreds mJ / cm ² especially when the photosensitive layer is thin. For this reason, the formation of the base performed by the ultraviolet curing reaction cannot ignore the influence of variations such as the irradiation intensity of the light source (lamp), and it is difficult to stably photocure the photosensitive layer to a desired thickness in the formation of the base. .

  In the present invention, since the photosensitive resin composition of the photosensitive layer is composed of the photosensitive resin composition according to the present invention, the irradiation intensity of the light source (lamp) is reduced by slowing the photocuring speed while maintaining the photocurability. The effect of variations such as the above can be mitigated, and photocuring can be stably performed at a desired thickness.

  The thickness of the base to be formed can be determined as appropriate according to the thickness of the photosensitive layer. From the viewpoint of ease of forming a relief image and image reproducibility, the thickness is preferably 1/5 to 4/5 of the thickness of the photosensitive layer. More preferably, it is 2/5 to 3/5.

  Next, when using an analog printing plate precursor, the protective film is peeled off, and a negative film on which an image has been previously formed is brought into close contact with the exposed anti-adhesion layer. On the other hand, when a LAM printing plate precursor is used, the protective film is peeled off, and an infrared laser is irradiated to the exposed infrared ablation layer to form a desired image.

  Next, the photosensitive layer is cured by irradiating ultraviolet rays from above the negative film or the infrared ablation layer (main exposure). The irradiated portion of the photosensitive resin composition is cured by ultraviolet irradiation. In the photosensitive layer covered with the negative film or the infrared ablation layer, a cured portion irradiated with ultraviolet rays and an uncured portion not irradiated with ultraviolet rays are generated.

  Subsequently, a relief image is formed by removing the uncured portion of the photosensitive layer in the developer. An aqueous developer is used as the developer. The water-based developer is composed of water to which a surfactant or a pH adjuster is added as necessary. The uncured portion of the photosensitive layer can be removed by washing out the uncured portion using, for example, a spray developing device or a brush type washing machine.

  Next, the printing plate material is taken out from the developer and dried. Next, the entire printing plate material dried as necessary is irradiated with ultraviolet rays (post-exposure). Thereby, a flexographic printing plate is obtained.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

The components used in this example are specifically shown below.
・ Ingredient (A)
A polymer obtained from water-dispersed latex (Nipol LX111NF, manufactured by Zeon Corporation).
・ Ingredient (B)
BR: [Nippon BR1220, manufactured by Nippon Zeon Co., Ltd.]
・ Ingredient (C)
Compound of Formula (2) [“LIR-410” manufactured by Kuraray Co., Ltd.]
・ Ingredient (D)
Acrylic modified liquid BR: [Osaka Organic Chemical Co., Ltd., BAC-45]
Acrylic monomer: [manufactured by NOF Corporation, 1,9-nonanediol dimethacrylate]
・ Ingredient (E)
Photopolymerization initiator: [Ciba Japan Co., Ltd., Irgacure 651]
・ (Other ingredients)
Surfactant: [manufactured by NOF Corporation, Newlex R]
Plasticizer: [Esso Oil Co., Ltd., Christol 70]
Thermal polymerization inhibitor: [MEHQ (hydroquinone monomethyl ether) manufactured by Seiko Chemical Co., Ltd.]

Example 1
<Preparation of photosensitive resin composition>
54.6 parts by weight of water-dispersed latex (30 parts by weight of polymer as solid content), 10 parts by weight of acrylic-modified liquid BR, and 10 parts by weight of acrylic monomer are mixed and heated in a dryer heated to 120 ° C. for 2 hours. Water was evaporated to obtain a mixture of a polymer obtained from the water-dispersed latex and a photopolymerizable monomer. In a kneader, this mixture, 25 parts by weight of BR, 8 parts by weight of a surfactant (4 parts by weight of a polymer as a solid content), 3 parts by weight of a compound of the formula (2), and 10 parts by weight of a plasticizer Kneaded for 45 minutes. Thereafter, 0.2 parts by mass of a thermal polymerization inhibitor and 1 part by mass of a photopolymerization initiator were put into a kneader and kneaded for 5 minutes to obtain a photosensitive resin composition of Example 1.

<Preparation of printing plate precursor>
The photosensitive resin composition thus obtained was coated with an adhesive on one side of a 125 μm-thick PET film, and a protective film with an anti-blocking agent applied on one side of a 100 μm-thick PET film. And the adhesive layer, the photosensitive layer made of the photosensitive resin composition, on the substrate by pressing with a press machine heated to 120 ° C. so that the thickness of the photosensitive resin composition is 1 mm, A printing plate precursor of Example 1 in which an anti-sticking agent layer and a protective film were laminated in this order was produced.

(Example 2)
In the same manner as in Example 1, except that the compound of the formula (3) [“UC-203” manufactured by Kuraray Co., Ltd.] was used as the compound corresponding to the component (C) instead of the compound of the formula (2). A resin composition and a printing plate precursor were obtained.

(Comparative Example 1)
A photosensitive resin composition of Comparative Example 1 was obtained in the same manner as in Example 1 except that the compound corresponding to Component (C) was not added. A printing plate precursor of Comparative Example 1 was produced in the same manner as Example 1 using this photosensitive resin composition.

(Comparative Example 2)
A photosensitive resin composition of Comparative Example 2 was obtained in the same manner as in Example 1 except that BR 55 parts by mass was used without using water-dispersed latex. A printing plate precursor of Comparative Example 2 was produced in the same manner as Example 1 using this photosensitive resin composition.

(Comparative Example 3)
A photosensitive resin composition and a printing plate precursor were obtained in the same manner as in Example 1 except that unmodified liquid isoprene rubber [“LIR-30” manufactured by Kuraray Co., Ltd.] was used instead of the compound of formula (2). .

  About each obtained printing plate precursor, the hardening rate at the time of forming a base was evaluated. Further, image reproducibility was evaluated using a negative film for image reproducibility evaluation. The results are shown in Table 1.

(Evaluation of curing speed)
Using an exposure apparatus in which 15 80 W chemical lamps are arranged, 15 cm from the substrate 2 side of the printing plate precursor 1 in which the photosensitive layer 4 is laminated on the substrate 2 via the adhesive layer 3 as shown in FIG. As shown in FIG. 2B, ultraviolet rays were irradiated from the substrate 2 side of the printing plate precursor 1 for 3 seconds or 5 seconds (back exposure). Thereby, a part of the photosensitive layer 4 was cured to form a cured layer 4a. Integrated light quantity of UV-A at this time was, respectively ^{85mJ / cm 2, 160mJ / cm} 2. Next, it was washed out for 10 minutes using an aqueous developer containing a surfactant, and the uncured layer 4b of the photosensitive layer was removed as shown in FIG. 2 (c). Since Comparative Example 2 cannot be developed with an aqueous developer, washing out was similarly performed using a solvent developer. Next, after sufficiently drying with hot air of 50 ° C., the thickness of the cured layer 4 a was measured together with the thickness of the substrate 2 and the adhesive layer 3. The combined thickness d was taken as the relief thickness. When the photosensitive layer thickness is 1 mm, the range of thickness d suitable for printing is about 400 to 700 μm, and the curing speed is slow until the thickness reaches 400 μm and / or in the range of 400 to 700 μm. The influence of variations such as irradiation intensity can be mitigated. In this embodiment, the effect is that the base thickness d is reduced in the irradiation for 3 seconds or 5 seconds. The results are shown in Table 1.

(Evaluation of image reproducibility)
Using an exposure apparatus in which 15 80 W chemical lamps are arranged, the base is formed by irradiating ultraviolet rays from the substrate side of the printing plate precursor so that the base thickness becomes 500 to 550 μm, and then the protective film is peeled off. A negative film for evaluation of image reproducibility (having halftone dots “150 Lpi / 2%” and “independent point φ120 μm”) is vacuum-contacted, and exposed for 6 minutes from a distance of 15 cm from the negative film on the negative film (main exposure) )did. Thereafter, the negative film was removed, and as described above, the film was developed for 10 minutes using an aqueous developer or solvent developer containing a surfactant, and then sufficiently dried with hot air at 50 ° C. Thus, a flexographic printing plate was produced. The surface of the prepared flexographic printing plate was observed with a microscope to evaluate image reproducibility. The case where the image was reproduced was “◯”, and the case where the image was not reproduced was “x”.

  Compared with Comparative Example 1 in which the compound corresponding to Component (C) is not added to the photosensitive resin composition forming the photosensitive layer, and Comparative Example 2 in which the water-dispersed latex corresponding to Component (A) is not blended In Example 1 in which both the component (C) and the component (A) are blended, it can be seen that the base thickness is thin and the curing rate is slow. Moreover, in Example 1, even if it mix | blends a component (C), only a cure rate will become slow, and as shown by evaluation of image reproducibility, hardening is not inhibited in main exposure, and it fully hardens | cures. The image can be reproduced.

  That is, according to the embodiment, the photocuring speed can be slowed while maintaining the photocuring property as compared with the case where the component (C) is not included, and thereby, the variation of the irradiation intensity of the light source (lamp) is reduced. Since the influence can be mitigated, it can be stably photocured to a desired thickness. And in order to acquire such an effect, it turns out that both a component (C) and a component (A) are required, and even if any one lacks, an effect is not acquired.

  Further, according to Table 1, it can be seen that in Comparative Example 3 in which R2 is a hydrogen group in the structure of Formula (1), the initial curing rate is relatively fast, and the base thickness is increased to nearly 700 μm after 5 seconds of exposure. . On the other hand, in Example 2 using the compound contained in component (C), the initial curing rate was clearly slower than that in Comparative Example 3, and curing was achieved by using a compound modified with a maleate group or the like. It can be seen that the effect of reducing the speed can be obtained. And in the irradiation time of 3 seconds at the initial stage of curing, the foundation thickness is about ½ of the foundation thickness when the irradiation time is 5 seconds. The effect of variations such as the irradiation intensity can be mitigated, and photocuring can be stably performed to a desired thickness.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

Claims (3)

(A) water-dispersed latex, (B) millable rubber (excluding those described in component (C)), (C) a compound having a unit structure represented by the following formula (1), (D) photopolymerizable monomer ( A photosensitive resin composition comprising (E) a photopolymerization initiator, excluding those described in the component (C).

However, R1 is a hydrogen group or a methyl group, and R2 is a maleic anhydride group or a maleic ester group.   A printing plate precursor having a photosensitive layer comprising the photosensitive resin composition according to claim 1.   A flexographic printing plate using the printing plate precursor according to claim 2.

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