JPH0577067B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a photosensitive elastomer composition. (Prior art) Conventionally, rubber plates used for flexographic printing have been produced by engraving directly on the rubber plate, or by corroding a metal plate to produce an original plate, producing a matrix made of plastic, etc., and applying rubber to this matrix plate. It has been manufactured by pouring and vulcanizing. However, these methods are complex and require skill, involve many steps, and require a lot of money and time. Furthermore, the precision of the obtained rubber plate itself is low, so post-processing such as back-shaving is required before use. It had drawbacks such as the need for In order to solve this drawback, in recent years, methods have been proposed for directly producing flexographic printing plates using photosensitive elastomer compositions. For example, Japanese Patent Publication No. 51-43375 discloses that the elastomeric polymer contains at least two thermoplastic non-elastomeric polymer blocks having a glass transition temperature of 25°C or higher and a 10% bond between the non-elastomeric polymer blocks. It has been shown to be effective to use solvent soluble thermoplastic elastomeric block copolymers with structures bonded by elastomeric blocks having glass transition temperatures below .degree. However, a flexographic printing plate obtained by molding a photosensitive composition using such a block copolymer and irradiating it with light has weaker plate strength than a conventional vulcanized rubber plate, and also requires development during printing plate production. There is a drawback that the plate is swollen by the solvent during the (washing out with solvent) process, resulting in a decrease in image reproducibility, and an improvement is desired. Problems to be Solved by the Invention It is therefore an object of the present invention to provide a photosensitive elastomer composition which is particularly suitable for the production of flexographic printing plates and which does not have the above-mentioned drawbacks. (Means for Solving the Problems) The object of the present invention is to (1) form a linear elastomer A-B in which a terminal group having a polymerizable ethylenic double bond is bonded to at least one end of the molecular chain; type terminal-modified block copolymer (A represents a polymer block of a monovinyl aromatic compound, B represents a polymer block of a conjugated diene monomer), (2) having at least one ethylenic double bond The block copolymer (1) is composed of an addition polymerizable compound and a photopolymerization initiator, and the A-B type living block copolymer obtained by an anionic polymerization method is reacted with a halogen-containing monomer. This is achieved by using a photosensitive elastomer composition characterized in that it is obtained by. The block copolymer used as component (1) in the present invention is a linear one, and is an elastomer in which a terminal group having a radically polymerizable ethylenic double bond is bonded to at least one end of the copolymer chain. A-
It is a type B terminal-modified block copolymer. Block A is a polymer block of a monovinyl aromatic compound such as styrene or α-methylstyrene, and contains one or more polymers of the compound or a copolymer of the compound and a monomer copolymerizable therewith. It is a block of thermoplastic non-elastomeric polymer containing a glass transition temperature of 25°C or higher. Particularly preferred are polystyrene blocks. Block B is a polymer block of conjugated diene monomers such as 1,3-butadiene, isoprene, 1,3-pentadiene, and chloroprene, and is a polymer block of one or more of the monomers or the monomers and This is an elastomeric polymer block containing a copolymer of this and a copolymerizable monomer with a glass transition temperature of 10°C or less. Particularly preferred are polybutadiene blocks or polyisoprene blocks. The A-B type terminal-modified block copolymer used in the present invention has (A-B) as one unit, and about 1 to 10, preferably 1 to 3 units of this unit are repeatedly present in the molecular chain. , which is linear. Block A
The proportion of block B and block B is not particularly limited as long as the terminally modified block copolymer becomes an elastomer, but the preferable proportion of block B in all blocks is 60 to 90% by weight. The weight average molecular weight of block A by GPC is usually in the range of 2,000 to 100,000, and the weight average molecular weight of block B is usually 10,000.
~1000000 range. The terminal-modified block copolymer used in the present invention is characterized by the above structure and a terminal group having a radically polymerizable ethylenic double bond bonded to at least one end of the block copolymer chain. . The terminally modified block copolymer used in the present invention can be obtained by an anionic polymerization method using a common alkali metal base material as an initiator. That is,
An A-B type living block copolymer such as polystyrene-polyisoprene is produced by sequential polymerization, and after adding ethylene oxide or propylene oxide to make the active end of the copolymer block a stable anion, methacrylic acid halide is produced. A terminally modified block copolymer in which a radically polymerizable ethylenic double bond-containing terminal group is bonded to the terminal end of the block polymer chain is produced by reacting with a halogen-containing monomer such as the following. An example is the method disclosed in US Pat. No. 3,786,116. Compounds that react with a block copolymer having a stable anion at the end to form a radically polymerizable end group having an ethylenic double bond include monomers containing halogens such as chlorine, bromine, and fluorine. is used. Such monomers include haloalkyl vinyl ethers such as 1-chloroethyl vinyl ether and 3-chloropropyl vinyl ether, vinyl chloroacetate, vinyl 3-chloropropionate,
Halogen-containing vinyl ethers such as vinyl 2-bromoundecanoate, 2-chloromethyl-1,3
-butadiene, 2-chloromethyl-3-methyl-
Examples include diene halides such as 1,3-butadiene, (meth)acrylic halides such as acrylic acid chloride and methacrylic acid chloride, vinylbenzyl chloride bromennorbornene, and bromomethylnorbornene. These compounds are bonded to one end of the copolymer chain if a monofunctional polymerization initiator is used during the production of the block copolymer, and to both ends of the copolymer chain if a difunctional polymerization initiator is used. Since the terminal-modified block copolymer used in the present invention has a radically polymerizable terminal group introduced by the above method, the copolymer is mixed with an addition polymerizable compound and a photopolymerization initiator. By producing a photosensitive elastomer composition and a flexographic plate and exposing them to light, crosslinking occurs between the molecular chains of the terminally modified block copolymer. As a result, the strength of the flexographic plate after exposure is improved and the reproducibility of the relief image is also significantly improved. The content of the terminal-modified block copolymer is usually 30
% by weight or more, and in consideration of rubber elasticity and ease of molding, it is preferably used in a range of 60 to 95% by weight. If necessary, other elastomeric polymers may be used in combination as long as the gist of the present invention is not impaired. In the photosensitive elastomer composition of the present invention, in addition to the above-mentioned terminal-modified block copolymer, at least one of
An addition polymerizable compound having ethylenic double bonds and a photopolymerization initiator can be used, and these are not particularly limited. Examples of addition polymerizable compounds having at least one ethylenic double bond include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, 1,4 butanediol, 1,6 hexanediol, and the like. Acrylates and dimethacrylates, or trimethylolpropane triacrylates and trimethacrylates, pentaerythritate tetraacrylates and tetramethacrylates, etc.
Examples include NN'-hexamethylene bisacrylamide and methacrylamide, diacetone acrylamide and methacrylamide, styrene, vinyltoluene, divinylbenzene, diallyl phthalate, and triallyl cyanurate, which may be used singly or in combination of two or more. The amount of the compound used is usually 5 to 30% by weight in the photosensitive composition (the same applies hereinafter). As photoinitiators, benzophenone, benzoin, alkyl ethers of benzoin, such as methyl, ethyl, isopropyl and isobutyl ethers of benzoin, α-methylbenzoin, α
-Methylbenzoin methyl ether, α-methoxybenzoin methyl ether, benzoin phenyl ether, α-t-butylbenzoin, anthraquinone, benzanthraquinone, 2-ethylanthraquinone, 2-chloroanthraquinone, 2-
2'dimethoxydiphenylacetophenone, 2,2-
Examples include diethoxyphenylacetophenone, 2,2-diethoxyacetophenone, benzyl, vivaloin, and the like. These photopolymerization initiators may be used alone or in combination of two or more. The amount of the initiator used is usually 0.01 to 5% by weight. In the present invention, components other than those mentioned above may also be included in the photosensitive composition as required. Examples of such components include plasticizers, thermal polymerization inhibitors, and antiaging agents. The plasticizer assists in the production and molding of the photosensitive elastomer composition, promotes the removal of unexposed areas of the photosensitive elastomer composition, and further adjusts the hardness of exposed and cured areas. Depending on these targeted properties, plasticizers are added in amounts ranging from 2 to 40% by weight. Useful substances include hydrocarbon oils such as naphthenic oil and paraffin oil, low molecular weight polystyrene (molecular weight below 3000), α-methylstyrene-vinyltoluene copolymer, petroleum resin, polyacrylate, polyethylene, polyester resin, polyterpene resin. , liquid 1,2- and 1,4-polybutadiene, hydroxides and carboxylated products thereof, liquid acrylonitrile-butadiene copolymers, carboxylated products thereof, and liquid styrene-butadiene copolymers. Examples of thermal polymerization inhibitors include 2,6-di-t
-butyl-4-methylphenol, methoxyphenol, 2,6-di-t-butyl-p-cresol, t-butylcatechol, pyrogallol, naphthylamine, β-naphthol, t-butylhydroxyanisole, hydroquinone, etc. can. The amount used is usually 0.001 to 2% by weight. The photosensitive elastomer compositions of this invention can be prepared in many ways. For example, the mixture is mixed and kneaded using a kneader or roll mill, which are ordinary rubber kneading machines, and then formed into a sheet of desired thickness (hereinafter referred to as a photosensitive layer) using a molding machine such as an extruder, press, or calendar. It can be prepared as: If desired, the photosensitive elastomer compositions of the present invention can also be treated with a solvent, e.g.
A frame is prepared by dissolving a mixture in an appropriate solvent such as chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichlorethylene, tetrachlorethylene, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, benzene, toluene, tetrahydrofuran, etc. A sheet with good thickness accuracy can be obtained by injecting the resin into a liquid and evaporating the solvent to prepare a sheet, or by subjecting this sheet to hot pressing, extrusion, or calendering. The sheet-formed photosensitive elastomer composition of the present invention has a peelable material such as polyethylene, polypropylene, polyester, polystyrene, etc. on the surface of the photosensitive layer to prevent the photosensitive layer from being contaminated or damaged during storage or handling. A thin transparent film layer can be provided. In addition, when the photosensitive elastomer composition of the present invention is exposed to light, the original image is superimposed on the photosensitive layer and irradiated with actinic rays. Additionally, a thin, solvent-soluble, flexible layer may be provided on the surface of the photosensitive layer. In this case, it is desirable that this layer be removed at the same time when the unexposed portions are eluted with a solvent after exposure of the photosensitive layer is completed. By using the photosensitive elastomer composition of the present invention, it is not only possible to produce a flexographic plate with improved strength after exposure, but also a relief image with high resolution can be obtained. The photosensitive elastomer composition of the present invention has high photosensitivity and has excellent properties as a printing plate for flexographic printing, but it can also be used for photoresists, screen printing screens, paints, coating materials, and adhesives. , films, sheet materials, impregnated materials, and other molded products. (Example) The present invention will be described in more detail with reference to Examples below. In addition, the number of copies and percentages in Examples and Comparative Examples
Unless otherwise specified, data are based on weight. Example 1 (A) Synthesis of terminal-modified block copolymer Using the pressure-resistant reactor No. 5, 1.875 kg of a mixed solvent of n-butane/cyclohexane = 30/70, 20 mmol of dibutyl ether, and n-butyl lithium initiator. First, 112.5 g of styrene was polymerized in the presence of 10 mmol at 30°C for 1 hour, followed by isoprene.
687.5g was added and the temperature was controlled by reflux cooling so that the reaction temperature was between 50℃ and 60℃.
Polymerized for half an hour. Subsequently, 11 mmol of ethylene oxide was added to make the active end of the isoprene block a stable anion, and 12 mmol of acrylic acid chloride was added to react with the active polymer end. Methanol 5 was added to the reaction mixture as a reaction terminator.
ml, 4-methyl-2,6-di- as oxidative stabilizer
After adding 4 g of t-butylphenol, this mixed solution was dropped little by little into water heated to 85 to 95°C to evaporate the solvent. The obtained polymer was cut into strips and dried with hot air at 85°C. In this way, a terminally modified block copolymer was obtained in which a terminal group having a radically polymerizable ethylenic double bond was bonded. (B) Preparation of photosensitive composition Terminal-modified block copolymer obtained as above
0.6g of benzoin methyl ether to 100g, 1,4
-butanediol dimethacrylate 5g, 2,6
-di-t-butyl-4-methylphenol 0.01g
was added and thoroughly mixed to prepare a photosensitive composition. (C) Physical properties 1 of cured product The above photosensitive composition was exposed to light for 5 minutes using a 300W high-pressure mercury lamp to obtain a cured product. The obtained cured product has a hardness of 40 (measured according to JIS K6301),
The rebound elasticity was 49% (measured at 25°C with a Dunlop trypsometer). Furthermore, changes in strength, elongation, and hardness at room temperature (25°C) (the difference between immediately after and 10 seconds after applying pressure, expressed as ΔHs) were measured.
It was determined according to JIS K6301, and the results shown in Table 1 were obtained.

[Table] Used.
2 The above photosensitive composition was sandwiched between 0.1 mm thick polyester films and formed into a 3 mm thick sheet using a vacuum press machine. The film was peeled off, a negative film was applied, and the film surface was irradiated with the ultraviolet lamp for 3 to 6 minutes. After exposure, the photosensitive original plate was washed and developed with a trichloroethane solution to obtain a relief image (relief height 1.4 mm). The resolution of the obtained plate was determined by visually observing and photographing the obtained relief image, and evaluating the reproducibility limits of convex and concave ruled lines (thin lines) and halftone dots with halftone density of 3% and 95%. The results are shown in Table 2.

[Table] The relief image obtained using the composition of the present invention has a halftone dot reproduction limit of 150 lines/inch, and a ruled line
The reproducibility of fine lines up to 100 μm was much better than that of the commercially available comparative example, and the relief images were sharp and highly accurate. In addition, the relief height of the commercial product of the comparative example was higher than that of the product of the present invention, the swelling due to the solvent during development was large, and the convex ruled lines were twisted (wavy distortion). Corrugated board printing was carried out continuously at a temperature of 45°C using the flexographic plate obtained with the composition of the present invention, and the printing durability was more than 500,000 copies. ' was not accepted. Example 2 In the same manner as in Example 1, terminal-modified blocks and copolymers to which the terminal groups listed in Table 3 were bonded were prepared, and photosensitive compositions were prepared in the same formulation as in Example 1. The strength characteristics of the cured product and the resolution (reproducibility limit) of the flexo plate were evaluated. The results are shown in Table 3.

[Table] Example 3 A-B bonded with an end group having a radically polymerizable ethylenic double bond (acrylic acid chloride was used as the end group source) having the composition shown in Table 4
A type-end modified block copolymer was prepared in the same manner as in Example 1. Using each of these, a cured product and a flexo plate were obtained using the same recipe and method as in Example 1. The strength characteristics and resolution were evaluated, and the results shown in Table 4 were obtained.

【table】

Claims (1)

[Claims] 1 (1) Linear elastomeric A-B type terminal modified block copolymer in which a terminal group having a polymerizable ethylenic double bond is bonded to at least one end of the molecular chain (A is a monovinyl aromatic polymer) block,
(B represents a polymer block of a conjugated diene monomer), (2) an addition polymerizable compound having at least one ethylenic double bond, and (3) a photopolymerization initiator; A photosensitive elastomer composition characterized in that the polymer (1) is obtained by reacting an A-B type living block copolymer obtained by an anionic polymerization method with a halogen-containing monomer. thing.