JP2010242029A - Acrylic foamed sheet with anisotropic cell structure and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic foamed sheet which, when compressed, is excellent in recovery properties, heat resistance, cushioning properties, heat insulating properties, lightweight properties, and soundproof properties and a method for producing the acrylic foamed sheet. <P>SOLUTION: The acrylic foamed sheet is composed of an acrylic resin. In the cells composing the foamed sheet, the ratio of cells having cell major axis of 500 &mu;m or smaller is 80% or higher; the expansion magnification ratio is three times or higher; the thickness is 0.5-5 mm; and there is a vertically long anisotropic cell structure in the sheet thickness direction. In the acrylic foamed sheet, the anisotropic cell structure is an independent bubble structure. Preferably, the ratio (L/S) of the average cell major axis L of the anisotropic cell structure at the cut surface in the thickness direction to the average cell minor axis S is 1.1-3.0. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an acrylic foam sheet having an anisotropic cell structure and a method for producing the same.

  Conventionally, acrylic resin foam sheets are widely used in applications such as building materials because they are excellent in light weight and heat insulation.

  As such an acrylic resin foam sheet, in a state where a swelling agent such as water is added to one or more monomers selected from the group consisting of acrylamide, methacrylamide, acrylic acid and methacrylic acid, A method for producing an acrylic resin foam sheet is disclosed in which a polymer is produced by polymerizing the monomer, and the polymer is heated to foam (see Patent Document 1). However, the acrylic resin foam sheet obtained by the above-mentioned method for producing an acrylic resin foam sheet has a very large cell size and a large variation in cell size, so that a buffer required for the foam sheet is required. There are problems such as insufficient properties such as property, soundproofing and heat insulation, and unevenness in the sheet.

  Also, heating / cooling containing one or more additives selected from the group consisting of a rubber component and an inorganic filler, the additive being contained in an amount of 0.1 to 200 parts by weight with respect to 100 parts by weight of the acrylic resin. Accordingly, a method for producing an acrylic resin foam sheet that does not cause warping or uneven thickness has been disclosed (see Patent Document 2). Acrylic resin foams generally have cushioning and cushioning properties, heat insulating properties, light weight, sound insulation, heat resistance, weather resistance, chemical resistance, etc. It is expected to be used in a wide variety of industrial and consumer applications, including soundproofing materials, lightweight moldings, interior materials (floor materials, etc.), civil engineering and building materials, pipe covers, containers, and toys. When the acrylic resin foam sheet obtained by the method for producing a resin foam sheet has a large amount of a rubber component, there is a concern about a decrease in oil resistance and chemical resistance. In addition, when a large amount of an inorganic filler is added for the purpose of improving heat resistance and shape stability, the foamed sheet may have reduced flexibility and mechanical strength. In addition, none of the above patent documents describes an acrylic resin-based foamed sheet excellent in heat resistance and shape stability due to the introduction of a specific shape of a cell or a cross-linked structure.

Japanese Patent Publication No. 40-29020 Japanese Patent Laid-Open No. 2006-335926

  Accordingly, an object of the present invention is to provide an acrylic foam sheet that is excellent in recoverability when compressed, heat resistance, buffer properties, heat insulation, light weight, and soundproofing, and a method for producing the acrylic foam sheet. It is to provide.

  Further, in the conventional foam molding method, when a desired foam thickness is to be obtained, processing such as slicing is supported.

  Therefore, the other object of this invention is to provide the manufacturing method of the acrylic foam sheet which can manufacture the acrylic foam sheet which has desired thickness continuously with high precision.

  Furthermore, from the viewpoint of environment and energy, there is also a need for a foam molding method that does not substantially contain environmentally hazardous substances such as organic solvents and does not require heating the monomer composition during polymerization.

  Accordingly, another object of the present invention is to provide a method for producing an acrylic foam sheet that is substantially free from environmentally hazardous substances such as organic solvents and does not require heating of the monomer composition during polymerization. .

  As a result of intensive studies to solve the above problems, the inventors of the present invention have a specific acrylic monomer mixture or a partial polymer thereof having an isocyanate group protected by a protective group and regenerating the isocyanate group by heating. Irradiating a photopolymerizable acrylic resin composition obtained by adding a photopolymerization initiator and a thermal foaming agent with active energy rays to produce a foamable acrylic resin sheet (i); If the method of obtaining an acrylic foam sheet through the step (ii) of heating and foaming the foamable acrylic resin sheet is used, the recoverability when compressed, heat resistance, buffering property, heat insulation, light weight, soundproofing The present inventors have found that an acrylic foam sheet having excellent properties can be obtained and completed the present invention.

  That is, the present invention is a foam sheet composed of an acrylic resin, and in the cells constituting the cell, the proportion of cells having a cell major axis of 500 μm or less accounts for 80% or more, and the expansion ratio is 3 times or more. The acrylic foam sheet is characterized by having a thickness of 0.5 to 5 mm and having a vertically long anisotropic cell structure in the thickness direction of the sheet.

  Further, according to the present invention, the anisotropic cell structure is a closed cell structure, and the ratio of the average cell major axis L and the average cell minor axis S (L / S) of the anisotropic cell structure at the cut surface in the thickness direction. The acrylic foamed sheet is provided wherein is 1.1 to 3.0.

  Further, according to the present invention, 70 to 99% by weight of (a) an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms (a) as a monomer component constituting the acrylic resin, (b ) The above acrylic foamed sheet containing a vinyl monomer having an active hydrogen group that reacts with an isocyanate group in an amount of 1 to 30% by weight.

  Furthermore, this invention provides the said acrylic foam sheet in which acrylic resin has a crosslinked structure.

  Furthermore, the present invention provides the acrylic foamed sheet, wherein the crosslinked structure is formed of an isocyanate compound in which at least one or more (c) isocyanate groups are protected by a protective group and the isocyanate group is regenerated by heating. provide.

  Furthermore, the present invention provides at least one (a) 70 to 99% by weight of an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms, and (b) an active hydrogen group that reacts with an isocyanate group. Isocyanate compound which regenerates an isocyanate group by heating at least 1 or more sorts of (c) isocyanate groups by a protective group in the acrylic monomer mixture containing 1-30 weight of the vinyl monomer which has this, or its partial polymer , (D) a photopolymerization initiator, and (e) a photopolymerizable acrylic resin composition obtained by adding a thermal foaming agent is irradiated with active energy rays to produce a foamable acrylic resin sheet. The acrylic foam sheet is obtained through the step (i) and the step (ii) of heating and foaming the foamable acrylic resin sheet. To provide a method of manufacturing an acrylic foam sheet characterized by.

  Furthermore, this invention provides the manufacturing method of the said acrylic foam sheet which heats and foams in the state which laminated | stacked the release film on both surfaces of the foamable acrylic resin sheet in process (ii).

According to this invention, since it has the said structure, it is excellent in the recoverability at the time of compressing, heat resistance, buffer property, heat insulation, lightweight property, and soundproofing property.
Further, according to the method for producing an acrylic foam sheet of the present invention, an acrylic foam sheet excellent in recoverability, heat resistance, buffering property, heat insulating property, light weight, and soundproofing property when compressed is continuously desired. Can be produced with high accuracy, and is substantially free from environmentally hazardous substances such as organic solvents, and it is not necessary to heat the monomer composition during polymerization.

2 is an electron micrograph (magnification: 80 times) of a cross section of Example 1. FIG. 4 is an electron micrograph (magnification: 80 times) of a cross section of Example 2. FIG. 2 is an electron micrograph (magnification: 1200 times) of a cross section of Comparative Example 1. 6 is an electron micrograph (magnification: 1200 times) of a cross section of Comparative Example 3.

  The acrylic foam sheet of the present invention is a foam sheet composed of an acrylic resin, and in the cells constituting the cell, the proportion of cells having a cell major axis of 500 μm or less accounts for 80% or more, and the expansion ratio is 3 times or more. And it is 0.5-5 mm in thickness, and has a vertically long anisotropic cell structure in the thickness direction of the sheet. In the present invention, the cell structure is preferably a closed cell structure. In the present application, “tape or sheet” may be simply referred to as “tape” or “sheet”. In addition, when the nature, shape, and distribution of an object do not depend on the direction, the object is isotropic, whereas when the object depends on the direction, the object is anisotropic.

  The acrylic foam sheet of the present invention has a structure in which the cell length varies depending on the measurement direction, and the mechanical and physical properties (for example, compression recovery property, soundproof property, flexibility, etc.) are “thickness direction” of the foam sheet. And “width / length direction (direction perpendicular to thickness direction)”.

  The acrylic foam sheet of the present invention is an acrylic resin foam, and the acrylic resin to be formed is (a) an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms, and (b) an isocyanate group. An acrylic monomer mixture containing at least a vinyl monomer having an active hydrogen group that reacts with or a partially polymerized product thereof, (c) an isocyanate compound in which an isocyanate group is protected by a protective group, and the isocyanate group is regenerated by heating, (d) A photopolymerization type acrylic resin composition containing at least a photopolymerization initiator and (e) a thermal foaming agent (“photopolymerization type acrylic resin composition” may be referred to as “photopolymerizable acrylic resin composition”). ). That is, the acrylic foam sheet of the present invention includes (a) an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms, and (b) a vinyl monomer having an active hydrogen group that reacts with an isocyanate group. A monomer mixture or a partially polymerized product thereof, (c) an isocyanate compound in which an isocyanate group is protected by a protective group, and an isocyanate compound that regenerates the isocyanate group by heating, (d) a photopolymerization initiator, and (e) a thermal foaming agent It consists of the blend.

  The acrylic foam sheet of the present invention is obtained by irradiating the layer of the photopolymerizable acrylic resin composition with active energy rays to obtain a foamable acrylic resin sheet, and then heating and foaming the foamable acrylic resin sheet. It is produced by making it. When the foamable acrylic resin sheet is heated and foamed, an isocyanate group is generated from the isocyanate compound (c) by heating, and the isocyanate group reacts with an active hydrogen group (isocyanate group) of the monomer (b). React with an active hydrogen group) to form a crosslinked structure. For this reason, in the acrylic foam sheet of the present invention, the constituting acrylic resin has a three-dimensional network structure by crosslinking. That is, the acrylic foam sheet of the present invention is a crosslinked foam.

(Photopolymerizable acrylic resin composition)
The photopolymerizable acrylic resin composition includes (a) an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms, and (b) an acrylic containing at least a vinyl monomer having an active hydrogen group that reacts with an isocyanate group. A monomer mixture or a partially polymerized product thereof, (c) an isocyanate compound in which an isocyanate group is protected by a protective group, and an isocyanate compound that regenerates the isocyanate group by heating, (d) a photopolymerization initiator, and (e) a thermal foaming agent It is a composition containing, Comprising: It is a composition which forms the acrylic type foam sheet of this invention.

  Unlike the “foamable composition obtained by kneading a resin and a thermal foaming agent” used in the prior art, the photopolymerizable acrylic resin composition is a liquid composition and can be used in the prior art. The low-temperature decomposable thermal foaming agent (a foaming agent that generates gas at about 90 to 130 ° C.) can be easily blended.

  The acrylic monomer mixture or a partially polymerized product thereof is a main component in the photopolymerizable acrylic resin composition, and the content thereof is 60% by weight or more (for example, 60% with respect to the total amount of the photopolymerizable acrylic resin composition). ˜99 wt%), preferably 70 wt% or more (for example, 70 to 95 wt%).

  The acrylic monomer mixture or a partially polymerized product thereof includes at least an alkyl (meth) acrylate as a main monomer component and (b) a vinyl monomer having an active hydrogen group that reacts with an isocyanate group.

  The alkyl (meth) acrylate is not particularly limited, and includes an ester of acrylic acid or methacrylic acid having a linear or branched alkyl group, an ester of acrylic acid or methacrylic acid having a cyclic alkyl group, and a fluorine-containing alkyl group. Any of acrylic acid and methacrylic acid esters may be used. One or more alkyl (meth) acrylates are used. The alkyl (meth) acrylate means “ester of acrylic acid or methacrylic acid having an alkyl group”.

  Examples of the alkyl (meth) acrylate having a linear or branched alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, an amyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, and an isooctyl group. Group, nonyl group, isononyl group, isodecyl group, dodecyl group, lauryl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicodecyl group and the like. An alkyl (meth) acrylate having a linear or branched alkyl group of preferably 4 to 18, more preferably 4 to 12) is mentioned.

  Examples of the alkyl (meth) acrylate having a cyclic alkyl group include 1-20 (preferably 4) carbon atoms such as a dicyclopentanyl group, a dicyclopentenyloxyethyl group, a cyclohexyl group, an isobornyl group, and an adamantyl group. -18, more preferably 4-12) alkyl (meth) acrylates having a cyclic alkyl group.

  Examples of esters of acrylic acid and methacrylic acid having a fluorine-containing alkyl group include 2,2,2-trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate may be mentioned.

  The ratio of the alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms in the acrylic monomer mixture or its partial polymer is based on the total amount of monomer components constituting the acrylic monomer mixture or its partial polymer. 70 to 99% by weight, preferably 80 to 90% by weight. When the content is less than 70% by weight, (b) a vinyl monomer having an active hydrogen group that reacts with an isocyanate group (particularly a vinyl monomer containing a polar group) in the foamable acrylic resin sheet obtained after irradiation with active energy rays. A microgel in which polar parts are partially agglomerated is produced, and in the foaming process, the part becomes a poorly foamed part, which may cause problems in terms of the quality of the resulting foamed sheet, whereas 99% by weight If it exceeds 1, the amount of the polar monomer that becomes a cross-linking point decreases, and as a result, there may be a problem in terms of compression recovery and heat resistance.

  (B) The vinyl monomer having an active hydrogen group that reacts with an isocyanate group is not particularly limited, but a vinyl monomer containing a polar group is preferably used. For example, (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxy Carboxyl group-containing monomers such as pentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid; acid anhydride monomers such as maleic anhydride and itaconic anhydride; 2-hydroxyethyl (meth) acrylate, (meta ) 2-hydroxypropyl acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, (meth ) 12-hydroxylauryl acrylate Hydroxyl-containing monomers such as (4-hydroxymethylcyclohexyl) methyl (meth) acrylate; styrenesulfonic acid, allylsulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, (meth) acrylamidepropanesulfonic acid, sulfopropyl Sulfonic acid group-containing monomers such as (meth) acrylate and (meth) acryloyloxynaphthalene sulfonic acid; Phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate; Amides such as (meth) acrylamide, N-methylolacrylamide and acryloylmorpholine Monomers: N- (meth) acryloyloxymethylenesuccinimide, N- (meth) acryloyl-6-oxyhexamethylenesuccinimide, N- (meth) acryloyl-8-o Succinimide monomers such as cyoctamethylene succinimide; acrylonitrile, methacrylonitrile, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, fluorine (meth) acrylate , Silicone (meth) acrylate, 2-methoxyethyl acrylate and the like.

  Among them, the vinyl monomer (b) is preferably a carboxyl group-containing monomer or a hydroxyl group-containing monomer from the viewpoint of reactivity with an isocyanate group, and particularly preferably 4-hydroxybutyl (meth) acrylate as the carboxyl group-containing monomer. .

  The proportion of the vinyl monomer (b) in the acrylic monomer mixture or its partial polymer is 1 to 30% by weight with respect to the total amount of monomer components constituting the acrylic monomer mixture or its partial polymer, preferably 10 to 20% by weight. If it is less than 1% by weight, the heat resistance of the acrylic foam sheet may be lowered. If it exceeds 30% by weight, (b) a vinyl monomer having an active hydrogen group that reacts with an isocyanate group (particularly a vinyl monomer containing a polar group) in the foamable acrylic resin sheet obtained after irradiation with active energy rays. A microgel in which polar parts are partially agglomerated is generated, and in the foaming process, the part becomes a poorly foamed part, which may cause problems in terms of the quality of the obtained foamed sheet.

  Further, a copolymerizable monomer other than the vinyl monomer (b) may be used in the acrylic monomer mixture or a partial polymer thereof. Such copolymerizable monomers can be used alone or in combination of two or more.

  Examples of such copolymerizable monomers include polyfunctional monomers. Examples of multifunctional monomers include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and pentaerythritol. Di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) ) Acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl di (meth) acrylate, hexyl di (meth) acrylate, etc. And the like.

  When a polyfunctional monomer is used as a copolymerizable monomer in an acrylic monomer mixture or a partial polymer thereof, the ratio thereof is not particularly limited as long as the effects of the present invention are not impaired, and the acrylic monomer mixture or a partial polymer thereof. Is 0.01 to 2% by weight, preferably 0.02 to 1% by weight, based on the total amount of the monomer components constituting the. If it exceeds 2% by weight based on the total amount of the monomer components, the cohesive force becomes too high, which may cause foaming failure. In addition, if it is less than 0.01% by weight based on the total amount of the monomer components, the cohesive force is lowered, and there is almost no change in the elastic modulus of the foamable acrylic resin sheet, resulting in a polyfunctional effect on the foaming ratio and cell diameter. There is a possibility that the effect of monomer addition cannot be expected.

  Examples of copolymerizable monomers other than polar group-containing vinyl monomers and multifunctional monomers include vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene and vinyltoluene; ethylene, butadiene, Olefins or dienes such as isoprene and isobutylene; vinyl ethers such as vinyl alkyl ether; vinyl chloride; (meth) acrylic acid alkoxyalkyl monomers such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; vinylsulfone Sulfonic acid group-containing monomers such as sodium acid; Phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate; Imide group-containing monomers such as cyclohexylmaleimide and isopropylmaleimide; Meth) acrylate; and a silicon atom-containing (meth) acrylate.

  (C) The isocyanate compound is protected with a protecting group and is not particularly limited as an isocyanate compound that regenerates the isocyanate group by heating. However, the isocyanate group has at least one isocyanate group in one molecule, and the isocyanate group Protected with blocking agents such as substituted phenols, oximes, acetoacetic acid alkyl esters, malonic acid alkyl esters, phthalimides, imidazoles, hydrogen chloride, hydrogen cyanide or sodium bisulfite and in specific temperature ranges (eg 90-130) A blocked isocyanate compound in which the blocking agent is dissociated to regenerate the isocyanate group when heated at about 0 ° C.). In addition, such a block isocyanate compound can be used individually or in combination of 2 or more types.

  Examples of the blocked isocyanate compound include 2- (0- [1′-methylpropylideneamino] carboxyamino) ethyl methacrylate (trade name “Karenz MOI-BM” manufactured by Showa Denko KK), 2-[(3 5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP” manufactured by Showa Denko KK), block isocyanate compound of hexamethylene diisocyanate [for example, product name “Duranate TM block isocyanate” (manufactured by Asahi Kasei Chemicals), etc. ] Etc. are mentioned.

  Among them, from the viewpoint of the storage stability of the foamable acrylic resin sheet obtained after irradiation with active energy rays and the content of the organic solvent, it has one blocked isocyanate group and at least one (meth) acryloyl group in the same molecule. (Meth) acrylate compounds are preferred. Specifically, 2- (0- [1′-methylpropylideneamino] carboxyamino) ethyl methacrylate (trade name “Karenz MOI-BM” manufactured by Showa Denko KK), 2-[(3,5-dimethylpyrazolyl) ) Carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP”, manufactured by Showa Denko KK).

  The amount of the isocyanate compound (c) used is not particularly limited as long as a crosslinked structure can be formed, and is appropriately adjusted according to the type and amount of the vinyl monomer (b). The molar ratio (b) / (c) between the monomer and the isocyanate compound (c) in a state where the isocyanate group is regenerated by heating is 1.0 / 0.01 to 1.0 / 1.0 (preferably 1.0 / 0.05 to 1.0 / 0.5, more preferably 1.0 / 0.1 to 1.0 / 0.3). If the amount used is small, the foamed shape may not be maintained under high temperature storage conditions. On the other hand, if it is excessively large, unreacted NCO groups may remain in the system in a large amount.

  More specifically, a hydroxyl group-containing monomer (for example, 4-hydroxybutyl acrylate) is used as the vinyl monomer (b), and one blocked isocyanate group is present in the same molecule as the isocyanate compound (c). And a (meth) acrylate compound having at least one (meth) acryloyl group (for example, 2- (0- [1′-methylpropylideneamino] carboxyamino) ethyl methacrylate, etc.), the molar ratio (b) / (C) is 1.0 / 0.01 to 1.0 / 1.0 (preferably 1.0 / 0.05 to 1.0 / 0.5, more preferably 1.0 / 0.1). An amount in the range of ~ 1.0 / 0.3) is preferred.

  (D) The photopolymerization initiator is not particularly limited. For example, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, Photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators, and the like can be used. In addition, a photoinitiator can be used individually or in combination of 2 or more types.

  Specifically, as the ketal photopolymerization initiator, for example, benzyldimethyl ketal, 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name “Irgacure 651” manufactured by Ciba Japan Co., Ltd.), etc. Is mentioned. Examples of the α-hydroxyketone photopolymerization initiator include 1-hydroxy-cyclohexyl-phenylketone (trade name “Irgacure 184” manufactured by Ciba Japan), 2-hydroxy-2-methyl-1-phenyl-propane- 1-one (trade name “Darocur 1173” manufactured by Ciba Japan), 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one (trade name) “Irgacure 2959” manufactured by Ciba Japan Ltd.). Examples of the α-aminoketone photopolymerization initiator include 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one (trade name “Irgacure 907” manufactured by Ciba Japan). 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 (trade name “Irgacure 369” manufactured by Ciba Japan). Examples of the acylphosphine oxide photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide (trade name “Lucirin TPO” manufactured by BASF), bis (2,4,6-trimethylbenzoyl) -phenylphosphine. Examples include fin oxide (trade name “Irgacure 819” manufactured by Ciba Japan). Examples of the benzoin ether photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one, and anisole. Examples include methyl ether. Examples of the acetophenone photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, 4-t-butyl-dichloro. Examples include acetophenone, 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone (trade name “Darocur 2959” manufactured by Ciba Japan). Examples of the aromatic sulfonyl chloride photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime photopolymerization initiator include 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime. Examples of the benzoin photopolymerization initiator include benzoin. Examples of the benzyl photopolymerization initiator include benzyl. Examples of the benzophenone photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3′-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexyl phenyl ketone, and the like. Examples of the ketal photopolymerization initiator include benzyl dimethyl ketal. Examples of the thioxanthone photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4. -Diisopropyl thioxanthone, dodecyl thioxanthone, etc. are mentioned.

  (D) Although it does not restrict | limit especially as the usage-amount of a photoinitiator, 0.01-5 weight part is preferable with respect to 100 weight part of all the monomer components which comprise an acryl-type monomer mixture or its partial polymer, Preferably it is 0.05-3 weight part. If it is less than 0.01 part by weight, the polymerization reaction may be insufficient, and if it exceeds 5 parts by weight, the polymer may have a low molecular weight.

  (E) Although an appropriate thing can be used as a thermal foaming agent, from the point of physical property control (flexibility, compressive load, etc.) of the anisotropy provision of a cell structure and the foamed sheet obtained, a chemical foaming agent is used. preferable. In addition, a thermal foaming agent can be used individually or in combination of 2 or more types.

  Examples of the chemical foaming agent include fluorinated alkanes such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarboxylic amide (ADCA), and barium azodicarboxylate; p -Hydrazine compounds such as toluenesulfonyl hydrazide, diphenylsulfone-3,3'-disulfonyl hydrazide, 4,4'-oxybis (benzenesulfonyl hydrazide) (OBSH), allyl bis (sulfonyl hydrazide); p-toluylene sulfonyl semicarbazide, Semicarbazide compounds such as 4,4′-oxybis (benzenesulfonyl semicarbazide); Triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; N, N′-dinitrosopentamethylene Organic foaming agents such as N-nitroso compounds such as tolamine, N, N′-dimethyl-N, N′-dinitrosotephthalamide, azide compounds, and inorganic foaming agents such as ammonium carbonate, sodium bicarbonate, and anhydrous sodium nitrate Etc.

  In addition, in this invention, since (d) photoinitiator is used as a polymerization initiator, it is not heated when a foamable acrylic resin sheet is produced. Moreover, since the photopolymerizable acrylic resin composition is in a liquid state, a foaming agent can be easily blended therein. For this reason, (c) As a foaming agent, a low-temperature foaming type foaming agent (a foaming agent that generates gas at about 90 to 160 ° C.) may be used.

  As a low-temperature foaming type foaming agent, for example, trade name “CELLMIC CAP” manufactured by Sankyo Kasei Co., Ltd. (decomposition temperature: 125 ° C.), product name “CELLMIC EP-50” manufactured by Sankyo Kasei Co., Ltd. (decomposition temperature: 125 ° C.) ADCA-based composite foaming agents (azodicarbonamide-based composite foaming materials) such as azide compounds (decomposition temperature: 110 ° C.); azo compounds such as azobisisobutyronitrile (decomposition temperature: 100-103 ° C.); N, N Nitroso compounds such as' -dimethyl-N, N'-dinitrosotephthalamide (decomposition temperature: 105 ° C); OBSH-based blowing agents such as 4,4'-oxybis (benzenesulfonylhydrazide) (decomposition temperature: 158 ° C); Hydrazine-based blowing agents such as benzenesulfonyl hydrazide (decomposition temperature: 95 ° C.) and p-toluenesulfonyl hydrazide (decomposition temperature: 110 to 115 ° C.) Etc., and the like.

  (E) The use amount of the thermal foaming agent can be appropriately selected according to the type of the thermal foaming agent to be used, the physical properties of the desired foamed material based on the foaming ratio, and the like. For example, in the case of a chemical foaming agent such as an organic foaming agent or an inorganic foaming agent, (a) an alkyl (meta) having an alkyl group having 1 to 20 carbon atoms from the viewpoint of obtaining a foaming ratio exceeding 3 times and a closed cell structure. 5) to 50 parts by weight is preferable, preferably 10 to 40 parts by weight, based on 100 parts by weight of the acrylic monomer mixture or partial polymer thereof containing at least the acrylate) and the vinyl monomer (b). If the blending amount of the thermal foaming agent is too small, the foam to be foam molded may not substantially function as a foam or an anisotropic cell structure may not be obtained. If the amount is too large, the generated gas utilization efficiency may be significantly reduced due to the permeation of the generated gas.

  In the present invention, a foaming aid may be used for the purpose of lowering the decomposition temperature of (e) the thermal foaming agent. Examples of such foaming aids include urea-based, salicylic acid-based, and benzoic acid-based foaming aids. Among these, it is preferable to use a urea-based foaming aid from the viewpoint of foaming efficiency.

  The blending amount of the foaming aid is adjusted as a blending ratio with the foaming agent used, and the foaming agent / foaming aid is about 4/1 to 1/1 (weight ratio).

  The photopolymerizable acrylic resin composition may contain an appropriate additive as long as it does not inhibit the photopolymerizability. Examples of such additives include tackifiers (for example, rosin derivative resins, polyterpene resins, petroleum resins, oil-soluble phenol resins, etc., which are solid, semisolid or liquid at room temperature), fillers (talc, Calcium carbonate, magnesium carbonate, silicic acid and its salts, clay, mica powder, aluminum hydroxide, magnesium hydroxide, zinc white, bentonine, carbon black, silica, alumina, aluminum silicate, acetylene black, aluminum powder), plastic Agent, softener, colorant (pigment, dye, etc.), surfactant (foam stabilizer) (eg, ionic surfactant, silicone surfactant, fluorine surfactant, etc.), anti-aging agent, oxidation Examples include inhibitors.

  The photopolymerizable acrylic resin composition can be prepared by mixing and dispersing the above components uniformly. Since this photopolymerizable acrylic resin composition is usually formed into a sheet by coating on a substrate, it is preferable to have an appropriate viscosity suitable for the coating operation. The viscosity of the photopolymerizable acrylic resin composition is, for example, blended with various polymers such as acrylic rubber, polyurethane, thickening additive, and the monomer component in the photopolymerizable acrylic resin composition is irradiated with light. It can adjust by carrying out partial polymerization by. That is, the photopolymerizable acrylic resin composition may be a partially polymerized composition (partially polymerized product, monomer syrup) in which the monomer component is partially polymerized in advance to increase the viscosity. In addition, a desirable viscosity is a rotor: No. 5 rotors, rotation speed 10 rpm, measurement temperature: As a viscosity set on the conditions of 30 degreeC, it is 5-50 Pa.s, More preferably, it is 10-40 Pa.s. When the viscosity is less than 5 Pa · s, the liquid flows when applied on the substrate, and when it exceeds 50 Pa · s, the viscosity is too high to make application difficult.

(Foaming acrylic resin sheet)
The foamable acrylic resin sheet is obtained by irradiating the photopolymerizable acrylic resin composition with an active energy ray and curing it. More specifically, in the foamable acrylic resin sheet, the photopolymerizable acrylic resin composition layer is formed by applying the photopolymerizable acrylic resin composition on a predetermined surface such as a substrate or a release film. The photopolymerizable acrylic resin composition layer is produced by irradiating an active energy ray and photocuring it. The foamable acrylic resin sheet is foamed by heating to form an acrylic foam sheet.

  In this invention, since the photoinitiator is used as a polymerization initiator, it is not heated when a foamable acrylic resin sheet is produced. For this reason, it is easy to control the temperature at the time of photopolymerization so as not to exceed the boiling point of each monomer component, and an acrylic resin having a desired molecular structure can be obtained with high reliability by photopolymerization. In addition, since the evaporation of the photopolymerizable acrylic resin composition is suppressed during photopolymerization, a change in the thickness of the photopolymerizable acrylic resin composition layer is suppressed, and a foamable acrylic resin having a desired thickness A resin sheet can be obtained with high accuracy.

  The foamable acrylic resin sheet can be obtained by photocuring the photopolymerizable acrylic resin composition. The amount of radicals generated by the photopolymerization initiator depends on the type and intensity of irradiated light (active energy rays), Since it varies depending on the time, monomer, and amount of dissolved oxygen in the photopolymerizable acrylic resin composition, when there is a large amount of dissolved oxygen, the amount of radicals generated is suppressed, polymerization does not proceed sufficiently, and unreacted materials. And may adversely affect the polymerization rate, molecular weight and molecular weight distribution of the resulting polymer. Therefore, when producing a foamable acrylic resin sheet, it is preferable to blow an inert gas such as nitrogen into the photopolymerizable acrylic resin composition and replace the oxygen with nitrogen before light irradiation. For example, when photocuring the photopolymerizable acrylic resin composition using an active energy ray in an inert gas atmosphere such as nitrogen gas, it is desirable that oxygen is not present as much as possible in the inert gas atmosphere. The oxygen concentration is preferably 5000 ppm or less.

  In addition, when the photopolymerizable acrylic resin composition layer is photocured by irradiating active energy rays, it is covered with an inert gas atmosphere (for example, under a nitrogen gas atmosphere) or a release film (separator) and oxygenated. Is preferably blocked.

  In applying the photopolymerizable acrylic resin composition, for example, a conventional coater (for example, a comma roll coater, a die roll coater, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, A knife coater, a spray coater, etc.) can be used.

  The release film is not particularly limited as long as it is a thin leaf body that does not easily transmit oxygen, but a transparent film is preferable because a photopolymerization reaction is used. As such a release film, for example, a substrate having a release treatment layer (release treatment layer) with a release treatment agent (release treatment agent) on at least one surface, or a fluorine-based polymer (eg, polytetrafluoroethylene). , Polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene / hexafluoropropylene copolymer, chlorofluoroethylene / vinylidene fluoride copolymer, etc.) A low-adhesive substrate made of (for example, an olefin resin such as polyethylene or polypropylene) can be used. In the case of a low-adhesive substrate, both surfaces can be used as a release surface, while in a substrate having a release treatment layer, the release treatment layer surface is used as a release surface (release treatment surface). can do.

  As the release film, for example, a release film (base material having a release treatment layer) in which a release treatment layer is formed on at least one surface of the release film substrate may be used. The material may be used as it is.

  Such release film substrates include polyester films (polyethylene terephthalate film, etc.), olefin resin films (polyethylene film, polypropylene film, etc.), polyvinyl chloride films, polyimide films, polyamide films (nylon films), rayon films. And a plastic base film (synthetic resin film) such as those obtained by laminating or co-extruding them (2 to 3 layer composite). In particular, a highly transparent polyethylene terephthalate film can be suitably used as the release film substrate.

  The release treatment agent is not particularly limited, and for example, a silicone release treatment agent, a fluorine release treatment agent, a long-chain alkyl release treatment agent, or the like can be used. You may use a mold release processing agent individually or in combination of 2 or more types. The release film that has been subjected to the release treatment with the release treatment agent is formed by, for example, a known formation method.

  The thickness of the release film is not particularly limited, but can be selected from the range of, for example, 12 to 250 μm (preferably 20 to 200 μm) from the viewpoint of ease of handling and economy. The release film may have either a single layer or a laminated form.

  Examples of the active energy rays include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron rays, and ultraviolet rays. Ultraviolet rays are particularly preferable. The irradiation energy, irradiation time, irradiation method, and the like of the active energy ray are not particularly limited.

As a specific example of irradiation with active energy rays, for example, irradiation with ultraviolet rays can be mentioned. The intensity | strength of such an ultraviolet-ray is 1-30 mW / cm < ² > by intensity | strength in wavelength 300-400 nm, More preferably, it is 3-10 mW / cm < ² >. When the intensity of the ultraviolet rays exceeds 30 mW / cm ² , the amount of starting radicals generated per short time becomes excessive, and as a result, the molecular weight of the generated polymer may be reduced and sufficient viscoelasticity may not be obtained. When it is less than 1 mW / cm ^2, it is not preferable because the ultraviolet irradiation time until a foamable acrylic resin sheet is obtained is significantly increased.

  As a light source used for ultraviolet irradiation, a light source having a spectral distribution in a wavelength range of 180 to 460 nm (preferably 300 to 400 nm) is used. For example, a chemical lamp, black light (manufactured by Toshiba Lighting & Technology Co., Ltd.), mercury arc, Common irradiation devices such as a carbon arc, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a metal halide lamp, etc. are used. Note that an irradiation apparatus capable of generating electromagnetic radiation having a wavelength longer or shorter than the above wavelength may be used.

  The illuminance of ultraviolet rays can be set to a desired illuminance by adjusting the distance from the irradiation device serving as a light source to the photopolymerizable acrylic resin composition layer and the voltage, for example.

  The curing time of the foamable acrylic resin sheet can be adjusted by appropriately selecting the components of the photopolymerizable acrylic resin composition, the irradiation method of active energy rays, and the like.

As a specific example of adjusting the curing time by appropriately selecting the active energy ray irradiation method, for example, the method disclosed in JP-A-2003-13015 can be mentioned. Japanese Patent Application Laid-Open No. 2003-13015 discloses a method in which the irradiation of active energy rays is performed in a plurality of stages and thereby the curing time is adjusted more precisely. Specifically, for example, when ultraviolet rays are used as the active energy rays, the ultraviolet irradiation is substantially performed by firstly irradiating light having an illuminance of 30 mW / cm ² or more and irradiating light having an illuminance lower than the first step. The method is divided into the second stage for completing the polymerization reaction; the ultraviolet irradiation is performed with the first stage for irradiating light with an illuminance of 30 mW / cm ² or more, and then with the light irradiation with lower illuminance than the first stage. Examples include a second stage in which the polymerization rate is at least 70% and then a third stage in which light irradiation with an illuminance of 30 mW / cm ² or more is performed to substantially complete the polymerization reaction.

  As the ultraviolet irradiation device used in the first stage, for example, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp or the like is used. In the second stage, for example, a chemical lamp, a black light or the like Is used.

  The thickness of the foamable acrylic resin sheet is not particularly limited, but is preferably 15 to 1500 μm, and preferably about 20 to 1000 μm, from the viewpoint of easy adjustment of the thickness of the obtained foamed sheet and curability. The foamable acrylic resin sheet may have a single layer structure or a laminated structure.

(Acrylic foam sheet)
The acrylic foam sheet of the present invention has at least one (a) 70 to 99% by weight of an alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms and (b) an activity to react with an isocyanate group. At least one (c) isocyanate group is protected with a protective group in an acrylic monomer mixture containing 1 to 30 weights of a vinyl monomer having a hydrogen group or a partial polymer thereof, and the isocyanate group is regenerated by heating. An active energy ray is irradiated to the photopolymerizable acrylic resin composition obtained by adding an isocyanate compound, (d) a photopolymerization initiator, and (e) a thermal foaming agent, and a foamable acrylic resin sheet is obtained. Acrylic foam sheet through step (i) of manufacturing and step (ii) of heating and foaming the foamable acrylic resin sheet By obtaining, it is produced. That is, the acrylic foam sheet of the present invention is produced by heating and foaming the foamable acrylic resin sheet. Furthermore, in the present invention, the photopolymerizable acrylic resin composition is in a liquid state and can be easily blended with a low-temperature decomposable thermal foaming agent. Obtainable.

  In the present invention, since a photopolymerization initiator is used as a polymerization initiator, it does not substantially contain environmental substances such as organic solvents, and it is not necessary to heat the photopolymerizable acrylic resin composition at the time of polymerization. A foaming agent that foams can also be used, and an acrylic resin having a desired molecular structure can be obtained during photopolymerization.

  In the present invention, since the photopolymerization method is used as described above, it is not necessary to heat the photopolymerizable acrylic resin composition during polymerization. For this reason, gas is not generated from the thermal foaming agent in the step (i). In the step (i), the isocyanate group is not regenerated from the isocyanate compound (c), but is formed by the reaction between the isocyanate group and the active hydrogen group of the monomer (b). No structure is formed. Furthermore, evaporation of the photopolymerizable acrylic resin composition is suppressed in the step (i). From these things, the foamable acrylic resin sheet which consists of acrylic resin which has a desired molecular structure is obtained by said process (i).

  In the present invention, in the step (i), the photopolymerizable acrylic resin composition is applied onto a suitable support, and the photopolymerizable acrylic resin composition coating layer (photopolymerizable acrylic type) is applied. The resin composition layer) is formed, and this sheet-like photopolymerizable acrylic resin composition (photopolymerizable acrylic resin composition layer) is photopolymerized. Further, since the evaporation of the photopolymerizable acrylic resin composition is suppressed during the photopolymerization, a sheet-like photopolymerizable acrylic resin composition (photopolymerizable acrylic resin composition layer) during the photopolymerization is used. The foamable acrylic resin sheet having a desired thickness can be efficiently manufactured with high accuracy. Furthermore, by foaming the foamable acrylic resin sheet in the step (ii), an acrylic foam sheet having excellent thickness accuracy can be obtained even though the thickness is small.

  Further, in the present invention, by heating the foamable acrylic resin sheet in the step (ii), (e) gas is generated from the thermal foaming agent to form bubbles, and the isocyanate of (c) is further formed. An isocyanate group is generated from the compound, and the isocyanate group reacts with an active hydrogen group (active hydrogen group that reacts with the isocyanate group) of the monomer (b) to form a crosslinked structure.

  Thus, in the present invention, (1) a foamable acrylic resin sheet is obtained from a specific photopolymerizable acrylic resin composition, and (2) a foamable acrylic resin having a desired thickness with high accuracy. Forming a sheet and heating and foaming the foamable acrylic resin sheet; and (3) forming a crosslinked structure and forming a cell structure in the step (ii) of heating the foamable acrylic resin sheet. Therefore, in the cell composed of acrylic resin, the proportion of the cell having a cell major axis of 500 μm or less accounts for 90% or more, the expansion ratio is 3 times or more, and the thickness is 0 An acrylic foam sheet having a lengthwise anisotropic cell structure in the thickness direction of the sheet is obtained.

  In the step (ii), when the foamable acrylic resin sheet is foamed, it is preferably heated and foamed in a state where a release film or the like is laminated on both surfaces of the sheet. This is because a vertically long anisotropic cell structure in the sheet thickness direction can be formed more uniformly and with good shape controllability.

  In step (ii), the timing of foaming and crosslinking reaction can be controlled by adjusting the heating temperature, or by selecting the composition of the photopolymerizable acrylic resin composition and the type of the isocyanate compound (c). it can. That is, it is possible to control (e) the timing at which gas is generated by the thermal foaming agent and the timing at which a crosslinked structure is formed by thermal crosslinking. For example, it is possible to form a crosslinked structure after first generating a gas from a thermal foaming agent, and vice versa, and at the same time, generate gas and form a crosslinked structure. For this reason, in this invention, the shape etc. of a vertically long anisotropic cell structure can be controlled in the thickness direction of a sheet | seat.

  Thus, since the acrylic foam sheet of the present invention has a vertically long anisotropic cell structure in the thickness direction of the sheet, when compressing in the thickness direction (foaming direction), it is perpendicular to the thickness direction. Compared with the case of compressing in the direction, the compressive elastic modulus and compressive stress are increased, and excellent recoverability can be expected.

  The anisotropic cell structure of the acrylic foam sheet is a closed cell structure in terms of mechanical strength, shock absorption, compression recovery, compression set, thermal insulation, soundproofing, waterproofing, waterstop, and processability. Preferably there is. The closed cell structure is a single cell structure in which each cell is completely independent.

  The average cell long diameter of the cells of the acrylic foam sheet is 500 μm or less (10 μm to 500 μm), preferably 300 μm or less (10 μm to 300 μm). When the average cell major axis exceeds 500 μm or less, there is a possibility that in the acrylic foamed sheet, there is a problem that through holes are formed in the thickness direction, or that the compression recovery property and workability are deteriorated. In addition, the thickness direction means a direction orthogonal to the surface of the foamed sheet.

  In the acrylic foam sheet, the ratio (L / S) between the average cell major axis (L) and the average cell minor axis (S) of the anisotropic cell structure at the cut surface in the thickness direction is the compression recovery property and compression From 1.1 to 3.0 in terms of permanent distortion, heat insulation in the thickness direction, compression as well as buffering against shear shear such as polishing pad use, and high elasticity without high specific gravity. Preferably, it is 1.5-3.0, More preferably, it is 2.0-3.0.

  In the acrylic foam sheet, the average cell major axis (L) and the average cell minor axis (S) of the anisotropic cell structure at the cut surface in the thickness direction are determined as follows. The acrylic foam sheet is cut in the thickness direction at an arbitrary portion, and electron microscope photographs at several appropriate magnifications (for example, about 10 to 80 times) are obtained using an electron microscope. Next, from this electron micrograph, 10 bubbles are selected in descending order of the cross-sectional area from the bubbles appearing on the cut surface (bubbles appearing in the field of view), and for each bubble, an ellipse with the smallest diameter that can surround the bubble. , The major axis of the ellipse is defined as the cell major axis, and the average is defined as the average cell major axis (L). The minor axis of the ellipse is defined as the cell minor axis, and the average is defined as the average cell minor axis (S). Define. In addition, in the point which measures the above-mentioned bubble diameter, a bubble diameter is judged only based on the bubble cross section which appeared on the photograph.

  In particular, in an acrylic foam sheet, the anisotropic cell structure is a closed cell structure, and the ratio of the average cell major axis L to the average cell minor axis S (L / When S) is 1.1 to 3.0, compression recovery, compression set, heat insulation in the thickness direction, not only compression, but also buffering against shear shear such as polishing pad use, and high specific gravity are achieved. This is useful in terms of achieving high elasticity without any problems.

  In the acrylic foam sheet, bubbles having a cell major axis of 500 μm or less are 80% or more (for example, 80 to 100%) [preferably 90% or more (for example, 90 to 100%)] with respect to all the cells constituting the foam sheet. Has a cell structure. If it is less than 80%, there is a risk that defects (pinholes) due to the formation of through-holes in the thickness direction, defects in compression recovery, and workability will be deteriorated.

The ratio of bubbles having a cell major axis of 500 μm or less among all the cells constituting the acrylic foam sheet is determined as follows. Three electron micrographs having an appropriate magnification (for example, about 10 to 80 times) are obtained using an electron microscope on an arbitrary cut surface of the acrylic foam sheet. For each photograph, 10 bubbles having a large cross-sectional area are selected in order from the largest cross-sectional area, and the selected 30 cell major diameters are measured. In addition, the measuring method of a cell long diameter is the same as the method used when calculating | requiring said average cell long diameter (L). Next, the number N ₁ of bubbles having a cell major axis of 500 μm or less among all the bubbles is counted. And it calculates from a following formula.
Ratio of cell diameter is less bubble _{500μm (%) = (N 1} /30) × 100

  In the acrylic foam sheet according to the present invention, the ratio of bubbles having a cell major axis of 500 μm or less occupies 90% or more of the constituent cells. Therefore, the occurrence of defects (pinholes) due to the formation of through holes in the thickness direction In addition, the possibility of the occurrence of problems such as a decrease in compression recoverability and a decrease in workability is reduced.

  The expansion ratio of the acrylic foam sheet of the present invention is 3 times or more (for example, about 3 to 30 times), preferably 5 times or more (for example, about 5 to 20 times). If it is less than 3 times, there may be a problem in terms of imparting functions such as contribution of low specific gravity, low compression resilience, step following ability, heat insulation, soundproofing, etc. In some cases, defects may occur due to the occurrence of defects (pinholes) due to the formation of through-holes and the reduction in compression recovery.

The expansion ratio of the acrylic foam sheet is obtained from the following formula.
Expansion ratio (times) = [specific gravity of foamable acrylic resin sheet (apparent density)] / [specific gravity of acrylic foam sheet (apparent density)]

  In the acrylic foam sheet of the present invention, since the acrylic resin to be formed has a three-dimensional network structure by crosslinking, it is excellent in heat resistance and shape stability.

  The insoluble component ratio (gel fraction) of the acrylic foam sheet of the present invention is preferably 70% by weight or more (for example, 70 to 100% by weight), preferably 80 from the viewpoint of obtaining good heat resistance and shape stability. % By weight or more (for example, 80 to 100% by weight).

The insoluble component ratio (gel fraction) of the acrylic foam sheet is determined as follows. First, a porous fluororesin film (trade name “Nitoflon” manufactured by Nitto Denko Corporation) is cut into 120 mm × 120 mm, and an octopus thread (thickness: 1.5 mm) is cut into about 100 mm, and their weight (The total weight of the fluororesin film and the octopus yarn is defined as “weight (A)”). Next, a predetermined amount (about 100 mg) of an acrylic foam sheet is wrapped in the fluororesin film, the wrapped mouth is tied with an octopus thread, and the acrylic foam sheet is wrapped (“acrylic foam sheet” May be referred to as a “containing packet”). The weight of the acrylic foamed sheet-containing package is measured, and the total weight (A) of the fluororesin film and the octopus yarn is subtracted from the weight of the acrylic foamed sheet-containing package to determine the weight of the acrylic foamed sheet. The weight of the acrylic foam sheet is defined as weight (B). Next, the acrylic foamed sheet-containing package is immersed in 50 mL of ethyl acetate for 7 days, and only the sol component in the acrylic foamed sheet is eluted out of the fluororesin film. And after immersion, the acrylic foam sheet containing package immersed in ethyl acetate for 7 days is taken out, the ethyl acetate attached to the fluororesin film is wiped off, and dried at 130 ° C. for 2 hours. After drying, the weight of the acrylic foam sheet-containing package was measured. The acrylic foam sheet-containing wrapping after drying is defined as weight (C).
And the insoluble component rate (gel fraction) (weight%) of an acrylic foam sheet is computed by following Formula.
Insoluble component ratio (% by weight) = [(C−A) / B × 100]

  The thickness of the acrylic foam sheet of the present invention is not particularly limited, but is preferably from 0.5 to 5 mm, preferably from 0.7 to 3 mm, from the viewpoint of obtaining good step followability, heat insulation, soundproofing, and the like. is there.

  Shape of anisotropic cell structure of acrylic foam sheet, average cell long diameter, average cell short diameter, ratio of cell structure (for example, ratio of cells having a cell long diameter of 500 μm or less with respect to all constituting cells) foaming ratio, Thickness, gel fraction, etc., adjustment of heating temperature, composition of photopolymerizable acrylic resin composition, selection of isocyanate compound (c), selection of foaming agent, control of timing of foaming and crosslinking reaction, etc. Can be adjusted.

  The acrylic foam sheet of the present invention can exhibit excellent recoverability when compressed, and further has excellent heat resistance. Moreover, the acrylic foam sheet of the present invention is excellent in buffering properties, heat insulating properties, light weight properties, soundproofing properties, and the like.

  The acrylic foam sheet of the present invention focuses on properties such as cushioning properties, heat insulation properties, light weight properties, and soundproofing properties. In addition to materials, it is used as a polishing pad used in the manufacture of semiconductor devices using a polishing pad.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Syrup Preparation Example 1)
2-ethylhexyl acrylate (2EHA) (manufactured by Toa Gosei Co., Ltd.) 50 parts by weight, isobornyl acrylate (IBXA) (manufactured by Osaka Organic Chemical Industry Co., Ltd.) 50 parts by weight, having an active hydrogen group having reactivity with an isocyanate group For 100 parts by weight of a mixed monomer solution consisting of 2 parts by weight of 4-hydroxybutyl acrylate (4HBA) as a vinyl monomer, 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name “Irgacure 651” Ciba (Japan Co., Ltd.) 0.05 parts by weight, 1-hydroxy-cyclohexyl-phenyl-ketone (trade name “Irgacure 184” manufactured by Ciba Japan Co., Ltd.) 0.05 parts by weight was added to a four-necked flask, Monomer silo with a polymerization rate of 7% by partial photopolymerization by exposure to ultraviolet light in a nitrogen atmosphere It was obtained flop (partially polymerized product).
Next, 17.7 parts by weight of 4-hydroxybutyl acrylate (4HBA) is added to 100 parts by weight of the syrup, and the mixture is stirred and mixed until uniform, and may be referred to as a target syrup (hereinafter referred to as “syrup (A)”). Got).

Example 1
To 100 parts by weight of the syrup (A), 3.5 parts by weight of 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP”, Showa Denko KK), diphenyl (2, 4,6-trimethylbenzoyl) phosphine oxide (trade name “Lucirin TPO” manufactured by BASF) 0.5 parts by weight, 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH) (trade name “Neoselbon N # 5000” 20 parts by weight of Eiwa Kasei Kogyo Co., Ltd.) and 10 parts by weight of urea-based foaming aid (trade name “Cell Paste k5” manufactured by Eiwa Kasei Kogyo Co., Ltd.) are uniformly mixed, defoamed, and photopolymerizable composition. Was prepared.
The photopolymerizable composition is applied onto the release-treated surface of the release-treated substrate so that the thickness after light irradiation is 300 μm to obtain a coating layer. A laminated body was obtained by covering a polyethylene terephthalate film having a thickness of 38 μm which had been subjected to a release treatment.
The laminated body was irradiated with ultraviolet rays having a light intensity of 5 mW / cm ² (measured with a UV intensity meter having a maximum peak sensitivity of 350 nm (trade name “UVR-T1” manufactured by Topcon Technohouse)) using a black light. Irradiation was performed only for the time necessary to reach 99% to obtain a foamable acrylic resin sheet having a thickness of 300 μm.
Next, with the base material and film laminated on both sides, this foamable acrylic resin sheet is heated and foamed at 130 ° C. for 10 minutes to give an acrylic resin having a thickness of about 1.3 mm. A foam sheet was obtained.

(Example 2)
After obtaining the foamable acrylic resin sheet, the base material and the film were peeled off, and heated and foamed in the absence of the base material and the film on both sides in the same manner as in Example 1 to obtain a thickness of about A 900 μm acrylic resin foam sheet was obtained.

(Comparative Example 1)
Instead of 3.5 parts by weight of 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP” manufactured by Showa Denko KK), 2-methacryloyloxyethyl isocyanate (trade name “Karenz A foamable acrylic resin sheet having a thickness of 300 μm was obtained in the same manner as in Example 1 except that the MOI (made by Showa Denko) was 2.2 parts by weight.
Next, this foamable acrylic resin sheet was heated by the same operation as in Example 1 with the base material and the film laminated on both sides, but formation of a cell structure was not confirmed.
Then, a foamable acrylic resin sheet having a thickness of 300 μm was obtained.

(Comparative Example 3)
1,6-hexanediol diacrylate (trade name) instead of 3.5 parts by weight of 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP” manufactured by Showa Denko KK) A foamable acrylic resin sheet having a thickness of 300 μm was obtained in the same manner as in Example 1, except that “NK ester A-HD” (manufactured by Shin-Nakamura Chemical Co., Ltd.) was 0.2 parts by weight.
Next, the foamable acrylic resin sheet was heated by the same operation as in Example 1 with the base material and the film laminated on both sides, but the generated gas escaped from the resin, thereby causing the acrylic resin Although the phenomenon that the substrate or film spontaneously peeled was observed at the interface between the substrate and the substrate and the interface between the acrylic resin and the film, the formation of the cell structure was not confirmed.
And the acrylic resin sheet was obtained.

(Comparative Example 4)
Thickness was obtained in the same manner as in Example 1 except that 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate (trade name “Karenz MOI-BP”, manufactured by Showa Denko KK) was not blended. A 300 μm foamable acrylic resin sheet was obtained.
Got.

(Evaluation)
About an Example and a comparative example, foamability was evaluated by observing a section with an electron microscope. Moreover, the ratio of the insoluble component ratio, the expansion ratio, the cell diameter (average cell major axis (L), average cell minor axis (S)), L / S, and cell structure having a cell major axis of 500 μm or less were measured. The results are shown in Table 1.

(Evaluation of foamability)
About an Example and a comparative example, arbitrary parts are cut | disconnected by the microtome cutter in thickness direction, The cut surface is used for the bubble structure using a scanning electron microscope (device name "S-4800" manufactured by Hitachi High-Technologies Corporation). Was observed. Examples of electron micrographs of cross sections in Examples and Comparative Examples are shown in FIGS. 1 to 4, the vertical direction of the drawings is the thickness direction of the sheet.
FIG. 1 is an electron micrograph of the cross section of Example 1, and the magnification is 80 times. FIG. 2 is an electron micrograph of the cross section of Example 2, and the magnification is 80 times. FIG. 3 is an electron micrograph of the cross section of Comparative Example 1, and the magnification is 1200 times. FIG. 4 is an electron micrograph of the cross section of Comparative Example 3, and the magnification is 1200 times.

(Measurement of average cell major axis (L) and average cell minor axis (S))
A sample for measurement was prepared by cutting the produced sheet with a microtome cutter in the thickness direction. The cut surface of the sample for measurement was photographed at a magnification of 80 using a scanning electron microscope (device name “S-4800” manufactured by Hitachi High-Technologies Corporation).
Next, from this electron micrograph, 10 bubbles appearing on the cut surface are selected in descending order of the cross-sectional area, and for each bubble, an ellipse with the smallest diameter that can surround the bubble is drawn, and the major axis of this ellipse is drawn. Is the cell major axis, the average is the average cell major axis (L), the minor axis of this ellipse is the cell minor axis, and the average is the average cell minor axis (S).

(Measurement of the ratio of bubbles having a cell major axis of 500 μm or less)
A sample for measurement was prepared by cutting the produced sheet with a microtome cutter in the thickness direction. The cut surface of the measurement sample was photographed at a magnification of 80 using a scanning electron microscope (device name “S-4800” manufactured by Hitachi High-Technologies Corporation), and three electron micrographs of the cut surface were obtained. For each photograph, 10 bubbles were selected in descending order of the cross-sectional area, and the selected 30 cell long diameters were measured. The cell major axis was measured in the same manner as described above (measurement of average cell major axis (L) and average cell minor axis (S)). Next, the number N ₁ of bubbles having a cell major axis of 500 μm or less was counted and calculated from the following formula.
Ratio of cell diameter is less bubble _{500μm (%) = (N 1} /30) × 100

(Insoluble component ratio)
The insoluble component ratio (gel fraction) was determined as follows. First, a porous fluororesin film (trade name “Nitoflon” manufactured by Nitto Denko Corporation) is cut into 120 mm × 120 mm, and an octopus thread (thickness: 1.5 mm) is cut into about 100 mm, and their weight (The total weight of the fluororesin film and the octopus yarn is defined as “weight (A)”). Next, a predetermined amount (about 100 mg) of the sample is wrapped in the fluororesin film, and the wrapped mouth is tied with an octopus thread to wrap the sample (sometimes referred to as “sample-containing package”). Was made. The weight of the sample-containing package was measured, and the total weight (A) of the fluororesin film and the octopus yarn was subtracted from the weight of the sample-containing package to determine the weight of the sample. In addition, let the weight of a sample be a weight (B). Next, the sample-containing package was immersed in 50 mL of ethyl acetate for 7 days, and only the sol component in the sample was eluted out of the fluororesin film. Then, after immersion, the sample-containing package immersed in ethyl acetate for 7 days was taken out, and the ethyl acetate on the fluororesin film was wiped off and dried at 130 ° C. for 2 hours with a dryer. After drying, the weight of the sample-containing package was measured. The sample-containing package after drying was defined as weight (C).
And the insoluble component rate (gel fraction) (weight%) was computed by following Formula.
Insoluble component ratio (% by weight) = [(C−A) / B × 100]

(Foaming ratio)
In accordance with JIS K 7112, the specific gravity of the foamable acrylic resin sheet before heat treatment, the acrylic resin foam sheet (acrylic resin sheet) after heat treatment was measured, and based on the value of the obtained specific gravity, It calculated from the following formula.
The sample for measuring the specific gravity was a sample that was allowed to stand for 16 hours in an environment of temperature: 23 ± 2 ° C. and humidity: 50 ± 5%, and the specific gravity meter was an electronic specific gravity meter (device name “MD-2005” manufactured by Alpha Mirage). ) Was used.
Expansion ratio (times) = (specific gravity of foamable acrylic resin sheet before heat treatment) / (specific gravity of acrylic resin foam sheet (acrylic resin sheet) after heat treatment)

  In Table 1, “Presence / absence of double-sided lamination” indicates whether or not a base material and a film were laminated on both sides when heat-treating the foamable acrylic resin sheet. “-” Indicates that measurement was impossible.

Claims (7)

  A foam sheet composed of an acrylic resin, and in the cell to be constructed, the proportion of cells having a cell major axis of 500 μm or less occupies 80% or more, the expansion ratio is 3 times or more, and the thickness is 0.5 An acrylic foam sheet having a longitudinally long anisotropic cell structure in the sheet thickness direction of ˜5 mm.   The anisotropic cell structure is a closed cell structure, and the ratio (L / S) between the average cell major axis L and the average cell minor axis S of the anisotropic cell structure at the cut surface in the thickness direction is 1.1 to 3. The acrylic foam sheet according to claim 1, which is 0.0.   The acrylic resin reacts with at least one or more (a) alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms in an amount of 70 to 99% by weight and (b) an isocyanate group as a constituent monomer component. The acrylic foam sheet according to claim 1 or 2, comprising a vinyl monomer having an active hydrogen group in a proportion of 1 to 30% by weight.   The acrylic foam sheet according to any one of claims 1 to 3, wherein the acrylic resin has a crosslinked structure.   The acrylic foamed sheet according to claim 4, wherein the crosslinked structure is formed of an isocyanate compound in which at least one or more (c) isocyanate groups are protected with a protective group and the isocyanate group is regenerated by heating.   70 to 99% by weight of at least one or more (a) alkyl (meth) acrylate having an alkyl group having 1 to 20 carbon atoms, and (b) 1 to 1 vinyl monomer having an active hydrogen group that reacts with an isocyanate group. An isocyanate compound containing at least one (c) isocyanate group that is protected by a protecting group in an acrylic monomer mixture containing 30 wt. And (e) a step (i) of producing a foamable acrylic resin sheet by irradiating active energy rays to a photopolymerizable acrylic resin composition obtained by adding a thermal foaming agent; The acrylic foam sheet according to any one of claims 1 to 5, through a step (ii) of heating and foaming the foamable acrylic resin sheet. Acrylic foam sheet manufacturing method, characterized in that to obtain.   The method for producing an acrylic foam sheet according to claim 6, wherein in the step (ii), the foam is heated and foamed in a state where release films are laminated on both surfaces of the foamable acrylic resin sheet.