JP2015147873A - Double-sided adhesive sheet and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided adhesive sheet having an excellent level-difference absorbing property and a method of producing the same.SOLUTION: A double-sided adhesive sheet of the invention is a double-sided adhesive sheet for fixing a member forming a portable electronic device, the double-sided adhesive sheet comprising an acrylic adhesive layer comprising an acrylic polymer comprising a polar monomer-derived constitutional unit by 9-30 mass% as a base polymer, wherein the acrylic adhesive layer has a thickness of 280 μm or more.

Description

  The present invention relates to a double-sided pressure-sensitive adhesive sheet and a method for producing the same.

  Conventionally, double-sided pressure-sensitive adhesive sheets have been used in various technical fields. For example, in the field of portable electronic devices such as mobile phones and portable information terminals, double-sided pressure-sensitive adhesive sheets are used for fixing between various members. As an example, Patent Document 1 discloses that a protective panel (lens) that protects a display unit of a portable electronic device is fixed to a housing using a double-sided adhesive sheet. The double-sided pressure-sensitive adhesive sheet is bonded to these members and fixed to each other while being sandwiched between the protective panel and the housing.

JP 2009-108314 A

  In recent years, an injection molded product made of plastic is sometimes used as a member (for example, a housing or a frame) constituting a portable electronic device. A member made of an injection-molded product (hereinafter referred to as an injection-molded member) is used in a popular portable electronic device or the like for the reason that the cost can be suppressed as compared with a general metal member.

  However, this type of injection-molded member may be distorted to form a stepped portion (for example, a convex portion) due to warpage or sink marks. When a conventional double-sided pressure-sensitive adhesive sheet is attached to such an injection-molded member, a gap is formed between the double-sided pressure-sensitive adhesive sheet and the step portion of the injection-molded member. There was a possibility of causing various defects.

  An object of the present invention is to solve the conventional problems and to solve the following objects. That is, an object of this invention is to provide the double-sided adhesive sheet excellent in level | step difference absorbability, and its manufacturing method.

  As a result of intensive studies to achieve the above object, the present inventor is a double-sided pressure-sensitive adhesive sheet for fixing a member constituting a portable electronic device, and the structural unit derived from a polar monomer is 9 to 30% by mass. It was found that a double-sided pressure-sensitive adhesive sheet comprising an acrylic pressure-sensitive adhesive layer having an acrylic polymer as a base polymer and having a thickness of 280 μm or more has excellent step absorbability, leading to the completion of the present invention. It was.

  In the double-sided PSA sheet, the acrylic polymer may include 50% by mass or more of a structural unit derived from a (meth) acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms. .

  In the double-sided pressure-sensitive adhesive sheet, the acrylic polymer may contain 2% by mass or more of a structural unit derived from a carboxyl group-containing monomer as a structural unit derived from the polar monomer.

  In the double-sided pressure-sensitive adhesive sheet, the acrylic polymer may contain 2% by mass or more of a structural unit derived from a hydroxyl group-containing monomer as a structural unit derived from the polar monomer.

  In the double-sided PSA sheet, the acrylic polymer may include 10% by mass or more of a structural unit derived from a heterocyclic ring-containing vinyl monomer as a structural unit derived from the polar monomer.

  In the double-sided pressure-sensitive adhesive sheet, the acrylic polymer may include a structural unit derived from a polyfunctional monomer having two or more polymerizable functional groups.

  In the double-sided pressure-sensitive adhesive sheet, the acrylic pressure-sensitive adhesive layer may have a transmittance of 5% or less in the thickness direction.

  In the double-sided pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer may contain a colorant, and the content of the colorant may be 0.25% by mass or less.

  In the double-sided pressure-sensitive adhesive sheet, the colorant may be a black colorant.

  In the double-sided PSA sheet, the solvent-insoluble fraction of the PSA layer may be 50% or more.

  In the double-sided PSA sheet, the solvent-insoluble fraction of the PSA layer may be 60% or more.

  In the double-sided pressure-sensitive adhesive sheet, the member constituting the portable electronic device may be made of a plastic injection molded product.

  In the double-sided pressure-sensitive adhesive sheet, the shape in plan view may be any one selected from the group consisting of a tape shape, a strip shape, a U shape, an L shape, and a frame shape. .

  The method for producing a double-sided pressure-sensitive adhesive sheet according to the present invention includes a plurality of types of monomer components for forming an acrylic polymer, a partial polymer obtained by polymerizing a part of the monomer components, a photopolymerization initiator, and coloring. A step of forming a pressure-sensitive adhesive composition comprising a pressure-sensitive adhesive composition on a support to form a coating film comprising the pressure-sensitive adhesive composition; and irradiating the coating film with light to form the monomer component in the coating film And the step of curing the coating film to obtain an acrylic pressure-sensitive adhesive layer, and the amount of the photopolymerization initiator in the pressure-sensitive adhesive composition is: It is 0.3 parts by mass or more with respect to 100 parts by mass of all monomer components for forming the acrylic polymer, and the blending amount of the colorant in the pressure-sensitive adhesive composition is 100 parts by mass of all monomer components. Against Or less 0.25 mass parts.

  ADVANTAGE OF THE INVENTION According to this invention, the double-sided adhesive sheet excellent in level | step difference absorbability, and its manufacturing method can be provided.

Schematic sectional view of the double-sided pressure-sensitive adhesive sheet of Example 1 Schematic plan view showing sample set for evaluation used for evaluation of step absorbency AA line sectional view of FIG.

  The double-sided pressure-sensitive adhesive sheet according to the present embodiment comprises at least one acrylic pressure-sensitive adhesive layer (hereinafter sometimes simply referred to as “pressure-sensitive adhesive layer”) containing an acrylic polymer as a base polymer. In general, “double-sided pressure-sensitive adhesive sheet” is sometimes called with a name different from “double-sided pressure-sensitive adhesive tape”, “double-sided pressure-sensitive adhesive film”, etc., but in this specification, the expression is unified to “double-sided pressure-sensitive adhesive sheet”. . Further, the surface of the pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive sheet may be referred to as “pressure-sensitive adhesive surface”.

  As a form of the double-sided pressure-sensitive adhesive sheet, a so-called substrate-less double-sided pressure-sensitive adhesive sheet not provided with a base material (support) is preferable. This base material-less double-sided pressure-sensitive adhesive sheet is composed of only an acrylic pressure-sensitive adhesive layer. Hereinafter, the acrylic pressure-sensitive adhesive layer provided in the double-sided pressure-sensitive adhesive sheet will be described in detail.

(Acrylic adhesive layer)
The pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer (main component). 50 mass% or more is preferable, as for the content rate (mass%) of the acrylic polymer in an adhesive layer (100 mass%), 60 mass% or more is more preferable, and 75 mass% or more is still more preferable. Further, the upper limit of the content (% by mass) of the acrylic polymer in the pressure-sensitive adhesive layer is not particularly limited, but is preferably 100% by mass or less, more preferably 99.9% by mass or less, and further 99% by mass or less. preferable.

(Acrylic polymer)
The acrylic polymer (100% by mass) contains 9 to 30% by mass of a structural unit derived from a polar monomer.

(Polar monomer)
The polar monomer is composed of a monomer having at least one polar group and containing a polymerizable unsaturated bond. The acrylic polymer (100% by mass) preferably contains 12% by mass or more, more preferably 15% by mass or more, of a structural unit derived from a polar monomer. The acrylic polymer (100% by mass) preferably contains 30% by mass or less, more preferably 26% by mass of a structural unit derived from a polar monomer.

  Examples of the polar monomer include a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a heterocyclic ring-containing vinyl monomer. These may be used alone or in combination of two or more.

  In addition, as a preferable embodiment of the structural unit derived from the polar monomer, for example, the structural unit derived from the carboxyl group-containing monomer, the structural unit derived from the hydroxyl group-containing monomer, and the structural unit derived from the heterocyclic ring-containing vinyl monomer. And combined use.

(Carboxyl group-containing monomer)
The acrylic polymer (100% by mass) preferably contains 2% by mass or more, more preferably 3% by mass or more of a structural unit derived from a carboxyl group-containing monomer as a structural unit derived from a polar monomer. The acrylic polymer (100% by mass) preferably contains 5% by mass or less, more preferably 4% by mass or less of a structural unit derived from a carboxyl group-containing monomer as a structural unit derived from a polar monomer.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and acid anhydrides thereof (for example, acid anhydrides such as maleic anhydride and itaconic anhydride). Containing monomer) and the like. These may be used alone or in combination of two or more.

  In this specification, “(meth) acryl” represents “acryl” and / or “methacryl” (one or both of “acryl” and “methacryl”).

(Hydroxyl group-containing monomer)
The acrylic polymer (100% by mass) preferably contains 2% by mass or more, more preferably 3% by mass or more of a structural unit derived from a hydroxyl group-containing monomer as a structural unit derived from a polar monomer. Further, the acrylic polymer (100% by mass) preferably contains 5% by mass or less, more preferably 4% by mass or less of a structural unit derived from a hydroxyl group-containing monomer as a structural unit derived from a polar monomer.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxy (meth) acrylate. Examples include hexyl, vinyl alcohol, and allyl alcohol. These may be used alone or in combination of two or more.

(Heterocycle-containing vinyl monomer)
The acrylic polymer (100% by mass) preferably contains 10% by mass or more, more preferably 12% by mass or more of a structural unit derived from a heterocyclic-containing vinyl monomer as a structural unit derived from a polar monomer. Preferably it contains 15 mass% or more. In addition, the acrylic polymer (100% by mass) contains, as a structural unit derived from a polar monomer, a structural unit derived from a heterocyclic ring-containing vinyl monomer, preferably 30% by mass or less, more preferably 25% by mass or less. More preferably, the content is 20% by mass or less.

  Examples of the heterocyclic ring-containing vinyl monomer include N-vinyl-2-pyrrolidone, (meth) acryloylmorpholine, N-vinylpiperidone, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylcaprolactam and the like. Can be mentioned. These may be used alone or in combination of two or more.

((Meth) acrylic acid alkyl ester)
The acrylic polymer (100% by mass) is a (meth) acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms (simply referred to as “(meth) acrylic acid alkyl ester”). In some cases, it is preferable to contain 50% by mass or more of a structural unit derived from.

  The acrylic polymer (100% by mass) is more preferably contained in an amount of 60% by mass or more, more preferably 70% by mass or more, as a structural unit derived from a (meth) acrylic acid alkyl ester. Further, the acrylic polymer (100% by mass) is preferably contained in an amount of 85% by mass or less, more preferably 80% by mass or less as a structural unit derived from the (meth) acrylic acid alkyl ester.

  Examples of the (meth) acrylic acid alkyl ester include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, ( Isobutyl acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, (meth) acrylic acid Heptyl, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, (meth) acrylic Isodecyl acid, undecyl (meth) acrylate, dodecyl (meth) acrylate (Meth) acrylic acid tridecyl, (meth) acrylic acid tetradecyl, (meth) acrylic acid pentadecyl, (meth) acrylic acid hexadecyl, (meth) acrylic acid heptadecyl, (meth) acrylic acid octadecyl, (meth) acrylic acid nonadecyl, ( Examples include (meth) eicosyl acrylate. These may be used alone or in combination of two or more.

  In addition, as a (meth) acrylic-acid alkylester, the (meth) acrylic-acid alkylester which has a C1-C14 linear or branched alkyl group is preferable, and a C1-C8 linear or (Meth) acrylic acid alkyl ester having a branched alkyl group is more preferable, and n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isooctyl acrylate, isononyl acrylate, and the like are more preferable.

(Multifunctional monomer)
The acrylic polymer is a structural unit derived from a polyfunctional monomer having two or more polymerizable functional groups containing an unsaturated double bond (hereinafter sometimes simply referred to as “polyfunctional monomer”). May be included.

  The acrylic polymer (100% by mass) preferably contains a constituent unit derived from a polyfunctional monomer in an amount of 0.01% by mass or more, more preferably 0.02% by mass or more, and further preferably 0.05% by mass. Including above. Further, the acrylic polymer (100% by mass) preferably contains 0.5% by mass or less, more preferably 0.3% by mass or less of a structural unit derived from a polyfunctional monomer.

  Examples of the multifunctional monomer include hexanediol di (meth) acrylate, butanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and neopentyl glycol. Di (meth) acrylate, 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 and the like. These may be used alone or in combination of two or more.

  If the acrylic polymer contains a structural unit derived from a polyfunctional monomer, the acrylic polymer will contain a cross-linked acrylic polymer, and the cohesiveness and adhesive strength of the adhesive layer Etc. are improved.

(Other monomers)
The acrylic polymer may contain a monomer other than the above-described monomer as a structural unit as long as the object of the present invention is not impaired. Examples of such monomers include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, Amide group-containing monomers such as N-hydroxyethyl (meth) acrylamide; Amino group-containing monomers such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and t-butylaminoethyl (meth) acrylate; Epoxy group-containing monomers such as glycidyl (meth) acrylate and methyl glycidyl (meth) acrylate; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; sulfonic acid group-containing monomers such as sodium vinyl sulfonate; 2-hydroxyethylacrylo Phosphoric acid group-containing monomers such as sulfate; Imido group-containing monomers such as cyclohexylmaleimide and isopropylmaleimide; Isocyanate group-containing monomers such as 2-methacryloyloxyethyl isocyanate; Vinyl esters such as vinyl acetate and vinyl propionate; Styrene, Aromatic vinyl compounds such as vinyl toluene; olefins or dienes such as ethylene, butadiene, isoprene and isobutylene; vinyl ethers such as vinyl alkyl ether; vinyl chloride and the like. These may be used alone or in combination of two or more.

(Method for producing acrylic polymer)
The acrylic polymer can be prepared using a known or common polymerization method. Examples of the polymerization method include a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, and a photopolymerization method. Among these, in preparing the acrylic polymer, it is preferable to use a curing reaction by heat or active energy rays (for example, ultraviolet rays) using a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator. In particular, it is preferable to use a curing reaction using a photopolymerization initiator because it has advantages such as shortening the polymerization time and increasing the thickness of the pressure-sensitive adhesive layer.

  For example, an acrylic polymer can be prepared by irradiating a monomer composition containing a photopolymerization initiator with active energy rays (for example, ultraviolet rays) to polymerize the monomer. Moreover, you may mix | blend the other component included in an adhesive layer with a polymerization initiator at the time of preparation of an acrylic polymer. In addition, you may use polymerization initiators, such as a thermal polymerization initiator and a photoinitiator utilized for preparation of an acrylic polymer, individually or in combination of 2 or more types.

  Examples of the thermal polymerization initiator include azo polymerization initiators [for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis ( 2-methylpropionic acid) dimethyl, 4,4′-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2 -(5-Methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis (2-methylpropionamidine) disulfate, 2,2'-azobis (N, N'-dimethylene) Isobutylamidine) dihydrochloride, etc.], peroxide polymerization initiators (for example, dibenzoyl peroxide, t-butylpermaleate, lauroyl peroxide) ), And a redox polymerization initiator and the like. The amount of the thermal polymerization initiator used is not particularly limited as long as it can be conventionally used as a thermal polymerization initiator.

  Examples of the photopolymerization initiator include a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, and a photoactive oxime photopolymerization initiator. Agents, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, and the like. .

  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 [ BASF, trade name: Irgacure 651], anisole methyl ether, and the like. Examples of the acetophenone photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone [manufactured by BASF, trade name: Irgacure 184], 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one [manufactured by BASF, trade name: Irgacure 2959], 2-hydroxy-2-methyl-1-phenyl-propane Examples include -1-one [manufactured by BASF, trade name: Darocur 1173], methoxyacetophenone, and the like. Examples of the α-ketol photopolymerization initiator include 2-methyl-2-hydroxypropiophenone, 1- [4- (2-hydroxyethyl) -phenyl] -2-hydroxy-2-methylpropane-1 -ON etc. are mentioned.

  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-based 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, isopropylthioxanthone. 2,4-diisopropylthioxanthone, dodecylthioxanthone and the like.

  Examples of the acylphosphine oxide photopolymerization initiator include bis (2,6-dimethoxybenzoyl) phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) (2,4,4-trimethylpentyl) phosphine oxide, Bis (2,6-dimethoxybenzoyl) -n-butylphosphine oxide, bis (2,6-dimethoxybenzoyl)-(2-methylpropan-1-yl) phosphine oxide, bis (2,6-dimethoxybenzoyl)-( 1-methylpropan-1-yl) phosphine oxide, bis (2,6-dimethoxybenzoyl) -t-butylphosphine oxide, bis (2,6-dimethoxybenzoyl) cyclohexylphosphine oxide, bis (2,6-dimethoxybenzoyl) Octylphosphine oxide Bis (2-methoxybenzoyl) (2-methylpropan-1-yl) phosphine oxide, bis (2-methoxybenzoyl) (1-methylpropan-1-yl) phosphine oxide, bis (2,6-diethoxybenzoyl) (2-methylpropan-1-yl) phosphine oxide, bis (2,6-diethoxybenzoyl) (1-methylpropan-1-yl) phosphine oxide, bis (2,6-dibutoxybenzoyl) (2-methyl Propan-1-yl) phosphine oxide, bis (2,4-dimethoxybenzoyl) (2-methylpropan-1-yl) phosphine oxide, bis (2,4,6-trimethylbenzoyl) (2,4-dipentoxy Phenyl) phosphine oxide, bis (2,6-dimethoxybenzoyl) benzylphosphine Sid, bis (2,6-dimethoxybenzoyl) -2-phenylpropylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2-phenylethylphosphine oxide, bis (2,6-dimethoxybenzoyl) benzylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2-phenylpropylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2-phenylethylphosphine oxide, 2,6-dimethoxybenzoylbenzylbutylphosphine oxide, 2,6-dimethoxybenzoyl Benzyloctylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2,5-diisopropylphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2-methylphenylphosphine Oxide, bis (2,4,6-trimethylbenzoyl) -4-methylphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2,5-diethylphenylphosphine oxide, bis (2,4,6- Trimethylbenzoyl) -2,3,5,6-tetramethylphenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethyl Benzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) isobutylphosphine oxide, 2,6-dimethoxyoxybenzoyl-2 , 4,6-Trimethylbenzoyl-n-butylbutyl Fin oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, bis (2,4,6-trimethylbenzoyl) -2,4-dibutoxyphenylphosphine oxide, 1,10-bis [bis (2, 4,6-trimethylbenzoyl) phosphine oxide] decane, tri (2-methylbenzoyl) phosphine oxide and the like.

  The amount of the photopolymerization initiator used is not particularly limited as long as an acrylic polymer can be formed by a photopolymerization reaction. For example, with respect to 100 parts by mass of all monomer components used to form the acrylic polymer. 0.01 to 5 parts by mass, more preferably 0.03 to 3 parts by mass, and still more preferably 0.05 to 2 parts by mass. When the usage-amount of a photoinitiator is such a range, a polymerization reaction can fully be performed and the fall of the molecular weight of the polymer to produce | generate can be suppressed. As a result, the cohesive strength of the formed pressure-sensitive adhesive layer is ensured.

  In activating the photopolymerization initiator, it is important to irradiate the monomer composition containing the photopolymerization initiator with active energy rays. Examples of such active energy rays include ionizing radiation such as α rays, β rays, γ rays, neutron rays, electron rays, and ultraviolet rays, and 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 long as the photopolymerization initiator can be activated to cause the monomer component to react.

  The weight average molecular weight (Mw) of the acrylic polymer is, for example, 100,000 to 5,000,000. The measurement of the weight average molecular weight of an acrylic polymer is calculated | required in polystyrene conversion by GPC (gel permeation chromatography) method. Specifically, TSKgelGMH-H (20) × 2 columns are used in HPLC 8020 manufactured by Tosoh Corporation, and measurement is performed with a tetrahydrofuran solvent under a flow rate of 0.5 ml / min.

(Coloring agent)
The pressure-sensitive adhesive layer may contain a colorant as a component other than the acrylic polymer. By including a colorant, the pressure-sensitive adhesive layer has design properties and optical characteristics (light shielding properties, light reflectivity, etc.). Colorants may be used alone or in combination of two or more.

  The content (%) of the colorant in the pressure-sensitive adhesive layer (100% by mass) is not particularly limited and is appropriately set according to the purpose. For example, the content is preferably 0.25% by mass or less, 0 20 mass% or less is more preferable. Moreover, as for the content rate (%) of the coloring agent in an adhesive layer (100 mass%), 0.1 mass% or more is preferable, for example.

  For example, when the pressure-sensitive adhesive layer is used for light shielding, the visible light transmittance in the thickness direction of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 5.0% or less, more preferably 3.0% or less. . The visible light transmittance is measured by the method described in Examples described later.

  In addition, when using an adhesive layer for the light-shielding use, it is preferable that an adhesive layer is colored black. Examples of the black colorant used in the pressure-sensitive adhesive layer include carbon black (for example, furnace black, channel black, acetylene black, thermal black, lamp black), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium. Black, cyanine black, activated carbon, ferrite (for example, nonmagnetic ferrite, magnetic ferrite), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, complex oxide black pigment, anthraquinone organic black pigment, etc. . Among these, carbon black is preferable from the viewpoint of cost and availability.

  Moreover, when using an adhesive layer for a light reflection use, it is preferable that an adhesive layer is colored white. Examples of the white colorant used in the pressure-sensitive adhesive layer include titanium oxide (for example, titanium dioxide such as rutile titanium dioxide and anatase titanium dioxide), zinc oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, and oxidation. Calcium, tin oxide, barium oxide, cesium oxide, yttrium oxide, magnesium carbonate, calcium carbonate (eg, light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, zinc carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide , Zinc hydroxide, aluminum silicate, magnesium silicate, calcium silicate, barium sulfate, calcium sulfate, barium stearate, zinc white, zinc sulfide, talc, silica, alumina, clay, kaolin, titanium phosphate, mica, gypsum, white car Inorganic white colorants such as zinc, diatomaceous earth, bentonite, lithopone, zeolite, sericite, and hydrous halloysite, acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, silicone Organic white colorants such as resin-based resin particles, urea-formalin-based resin particles, and melamine-based resin particles.

(Other additives)
The pressure-sensitive adhesive layer may further contain additives shown below as long as the object of the present invention is not impaired. Examples of additives include metal powders such as copper, nickel, aluminum, chromium, iron, and stainless steel, carbonates such as calcium carbonate (eg, heavy calcium carbonate, light calcium carbonate), magnesium carbonate, sodium carbonate, and potassium carbonate. , Hydroxides such as aluminum hydroxide and magnesium hydroxide, talc, mica, clay, bentonite, silica, alumina, aluminum silicate, titanium oxide, hollow microspheres, thermally expandable microspheres, tackifiers, crosslinking agents ( For example, epoxy crosslinking agent, isocyanate crosslinking agent, silicone crosslinking agent, oxazoline crosslinking agent, aziridine crosslinking agent, silane crosslinking agent, alkyl etherified melamine crosslinking agent, metal chelate crosslinking agent), crosslinking accelerator , Silane coupling agent, anti-aging agent, pigment, dye, UV absorber Antioxidants, chain transfer agents, plasticizers, softeners, antistatic agents, solvents, polymers, adhesives (eg rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamides) Adhesives, urethane adhesives, fluorine adhesives, epoxy adhesives) and the like. These may be used alone or in combination of two or more.

  The pressure-sensitive adhesive layer preferably has a structure that does not substantially contain bubbles. In the present specification, “substantially free of bubbles” means that the bubbles are not actively formed in the pressure-sensitive adhesive layer except when inevitably mixed. The bubble content in such an adhesive layer is ideally zero. In addition, the bubble content rate in the actual pressure-sensitive adhesive layer is preferably 3% by volume or less, more preferably 1% by volume or less, with respect to the total volume (100% by volume) of the pressure-sensitive adhesive layer.

In addition, the content rate (volume%) of the bubble in an adhesive layer can be measured with the following method.
(Measuring method)
(1) The pressure-sensitive adhesive layer is cut in the thickness direction to produce a measurement sample in a state where damage to the cut surface is suppressed as much as possible. In addition, after immersing an adhesive layer in liquid nitrogen, the said adhesive layer may be fractured | ruptured and a measurement sample may be produced.
(2) Next, the cross section (cut surface, fracture surface) of the obtained measurement sample was increased 100 times by a field emission scanning electron microscope (FE-SEM) (manufactured by Hitachi High-Technologies Corporation, model: S-4800). Zoom in.
(3) Then, in the enlarged cross-section, a square portion surrounded by (width 1 mm) × (thickness of the adhesive layer) is defined as a reference area S1, and the total area S2 of the bubble portions included in the S1 Ask for.
(4) The bubble ratio (%) in the cross section is obtained by (S2 / S1) × 100.
(5) By repeating the operations (1) to (4) described above, the pressure-sensitive adhesive layer was sampled at a total of five locations at regular intervals along one direction. Adopted as the bubble content (volume%) in the agent layer.

(Method for producing pressure-sensitive adhesive layer (double-sided pressure-sensitive adhesive sheet))
The pressure-sensitive adhesive layer is formed using, for example, a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition is not particularly limited as long as it can form the above-described pressure-sensitive adhesive layer, and is appropriately selected according to the purpose. As the pressure-sensitive adhesive composition, from the viewpoint of workability and the like, a monomer composition containing a plurality of types of monomer components for forming an acrylic polymer, a polymerization initiator for polymerizing the monomer components, and as necessary It is preferable to use a curable pressure-sensitive adhesive composition containing a mixture with other components such as a colorant to be added. In particular, the pressure-sensitive adhesive composition is preferably a photocurable pressure-sensitive adhesive composition using a photopolymerization initiator as a polymerization initiator. The curable pressure-sensitive adhesive composition is a so-called solventless pressure-sensitive adhesive composition, and is prepared by mixing the polymerization initiator and the like with the monomer composition.

  In addition, the said monomer composition consists of a mixture of monomer components, such as a (meth) acrylic-acid alkylester, an acidic group containing monomer (a hydroxyl group containing monomer, a carboxyl group containing monomer), a heterocyclic ring containing vinyl monomer, etc., for example. Although the said monomer composition changes with the kind of monomer component, a composition ratio, etc., normally it has comprised the liquid state. Therefore, for the purpose of increasing the viscosity of the monomer composition and improving workability (handleability), etc., the monomer component contained in the monomer composition is partially polymerized to obtain a partial weight. A coalescence may be formed. The monomer composition containing the partial polymer is in a syrup state. The unreacted monomer component in the monomer composition is appropriately polymerized after the curable pressure-sensitive adhesive composition is prepared.

  For the polymerization of the partial polymer, a known or conventional polymerization method can be used. For example, the monomer components in the monomer composition may be appropriately polymerized using various polymerization initiators (for example, photopolymerization initiators) exemplified in the above-mentioned “acrylic polymer production method”. . In addition, the polymerization rate of the said partial polymer is adjusted to 5-15 mass%, for example, Preferably it is 7-10 mass%. As for the polymerization rate of the partial polymer, for example, the correlation between the viscosity of the monomer composition and the polymerization rate of the partial polymer is grasped in advance, and the viscosity of the monomer composition is adjusted based on the correlation. Can be adjusted accordingly. In addition, the said partial polymer will be finally contained in an adhesive layer as a part of acrylic polymer.

  In addition, when using a polyfunctional monomer as a monomer component for forming an acrylic polymer, the polyfunctional monomer may be blended in the monomer composition before the partial polymer is formed, You may mix | blend with the said monomer composition after the said partial polymer is formed. However, from the viewpoint of forming a cross-linked acrylic polymer and reliably increasing the cohesiveness of the pressure-sensitive adhesive layer, the polyfunctional monomer is blended in the monomer composition after the partial polymer is formed. It is preferable.

  The curable pressure-sensitive adhesive composition after the preparation is applied by applying it in a layer form on a suitable support such as a substrate or a release liner. Thereafter, a curing step is performed on the layered pressure-sensitive adhesive composition (coating film). Moreover, a drying process is given before and after a hardening process as needed. When the pressure-sensitive adhesive composition contains a thermal polymerization initiator as a polymerization initiator, the pressure-sensitive adhesive composition is cured by starting a polymerization reaction by heating. On the other hand, when the pressure-sensitive adhesive composition contains a photopolymerization initiator as a polymerization initiator, the pressure-sensitive adhesive composition is cured by being irradiated with an active energy ray such as ultraviolet rays, and cured ( Photocured). The active energy ray may be irradiated from one side of the layered pressure-sensitive adhesive composition (coating film) or from both sides. Thus, when the said adhesive composition is hardened | cured, the adhesive layer which can be utilized for the double-sided adhesive sheet of this embodiment is obtained.

  In addition, when performing curing (photocuring) with active energy rays, a known or conventional oxygen blocking method (for example, the layered pressure-sensitive adhesive composition (pressure-sensitive adhesive layer)) is used so that the polymerization reaction is not inhibited by oxygen in the air. An appropriate support such as a release liner or a substrate may be bonded to the top, and a photocuring reaction may be performed in a nitrogen atmosphere).

  In addition, for the application (coating) of the pressure-sensitive adhesive composition, a known or common coating method can be used, and a general coater (for example, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip coater). Roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, direct coaters, etc.) can be used.

  In addition, the pressure-sensitive adhesive layer is a pressure-sensitive adhesive composition other than the above-described curable pressure-sensitive adhesive composition (for example, a solvent-type pressure-sensitive adhesive composition, an emulsion-type pressure-sensitive adhesive composition) unless the object of the present invention is impaired. It may be formed using.

  Here, an example of the manufacturing method of an adhesive layer (double-sided adhesive sheet) is demonstrated. This manufacturing method is a method for manufacturing a pressure-sensitive adhesive layer used for light shielding.

  The production method includes a plurality of types of monomer components for forming an acrylic polymer, a partial polymer obtained by polymerizing a part of the monomer components, a photopolymerization initiator, and a colorant (for example, carbon black). A step (first step) of applying a pressure-sensitive adhesive composition having a surface of the pressure-sensitive adhesive composition to the support and irradiating the coating film with light (for example, ultraviolet rays). And the step of photopolymerizing the monomer component in the coating film to form the acrylic polymer and curing the coating film to obtain an acrylic pressure-sensitive adhesive layer (second step).

  And in the said manufacturing method, the compounding quantity of the said photoinitiator in the said adhesive composition is 0.3 mass part or more with respect to 100 mass parts of all the monomer components for forming the said acrylic polymer. And the compounding quantity of the said coloring agent in the said adhesive composition is 1.5 mass parts or less with respect to 100 mass parts of all the said monomer components, Preferably it is 1.0 mass part or less. In the pressure-sensitive adhesive composition, when the blending amount of the photopolymerization initiator and the blending amount of the colorant are within such ranges, the photopolymerization initiator is sufficiently activated by the light irradiated in the second step. The monomer component can be sufficiently polymerized (photopolymerized). Therefore, according to the said manufacturing method, a comparatively large adhesive layer (for example, 280 micrometers or more) can be formed, including a coloring agent. In addition, even if the compounding quantity of a coloring agent is such a range, if the thickness of an adhesive layer is large, the visible light transmittance | permeability in the thickness direction of an adhesive layer can be made low enough.

(Adhesive layer thickness)
The thickness of the pressure-sensitive adhesive layer is 280 μm or more, preferably 300 μm or more, more preferably 350 μm or more. When the thickness (μm) of the pressure-sensitive adhesive layer is in such a range, the pressure-sensitive adhesive layer follows the shape of the stepped portion even if a stepped portion (for example, a convex portion) is formed on the surface of the adherend. Thus, it can be adhered to the adherend so that it is deformed and is in close contact with the stepped portion without a gap.

  The upper limit of the thickness of the pressure-sensitive adhesive layer is not particularly limited and is appropriately set depending on the purpose. For example, it is preferably 1,500 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less.

(Release liner)
The surface (adhesive surface) of the pressure-sensitive adhesive layer in the double-sided pressure-sensitive adhesive sheet may be protected by a release liner until use. In the double-sided pressure-sensitive adhesive sheet, each pressure-sensitive adhesive surface may be protected by a separate release liner, or each pressure-sensitive adhesive surface may be protected by a single release liner in a form wound in a roll. The release liner is used as a protective material for the adhesive surface, and is peeled off when it is attached to an adherend. Moreover, when the double-sided pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet, the release liner also serves as a support. The release liner is not necessarily provided on the double-sided pressure-sensitive adhesive sheet.

  A conventional release paper or the like can be used as the release liner, and is not particularly limited. As the release liner, for example, a substrate having a release treatment layer, a low adhesive substrate made of a fluoropolymer, a low adhesive substrate made of a nonpolar polymer, or the like can be used. As a base material which has the said peeling process layer, the base material surface-treated by peeling processing agents, such as a silicone type, a long-chain alkyl type, a fluorine type, molybdenum sulfide, is mentioned, for example. Examples of the fluorine-based polymer in the low-adhesive substrate made of the fluoropolymer include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chloro Examples include fluoroethylene-vinylidene fluoride copolymer. Examples of the nonpolar polymer include olefinic resins (for example, polyethylene and polypropylene).

  Examples of the substrate to be surface-treated with the release treatment agent include polyester films such as polyethylene terephthalate; olefin resin films such as polyethylene films and polypropylene films; polyvinyl chloride films; polyimide films; polyamide films such as nylon films; Examples thereof include plastic films such as rayon film, and papers such as high-quality paper, Japanese paper, kraft paper, glassine paper, synthetic paper, and top coat paper. Among these, from the viewpoint of processability, a polyester film or paper is preferable, and polyethylene terephthalate is more preferable. The release liner can be formed by a known or conventional method. Further, the thickness of the release liner is not particularly limited.

(Supporting substrate)
The double-sided pressure-sensitive adhesive sheet may include a support base material as necessary. As the support substrate, for example, a plastic film substrate (hereinafter referred to as a plastic film substrate) is used. The material of the plastic film substrate is not particularly limited. For example, a polyester resin such as polyethylene terephthalate, an acrylic resin such as polymethyl methacrylate, polycarbonate, triacetyl cellulose, polysulfone, polyarylate, polyimide, polyvinyl chloride, poly Cyclic olefin polymers such as vinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, trade name “ARTON (cyclic olefin polymer, manufactured by JSR)”, trade name “ZEONOR (cyclic olefin polymer, manufactured by Nippon Zeon)” For example, plastic materials such as In addition, you may use these plastic materials individually or in combination of 2 or more types. The “support base material” is a portion that is affixed to an adherend together with the adhesive layer when a double-sided adhesive sheet is used (attached). The release liner that is peeled off when the double-sided PSA sheet is used (attached) is not included in the “support base material”.

(shape)
There is no restriction | limiting in particular in the shape of a double-sided adhesive sheet, According to a use, it sets suitably. Specific shapes of the double-sided pressure-sensitive adhesive sheet include various shapes such as a tape shape (strip shape), a strip shape, a U shape (a U shape), an L shape, and a frame shape (loop shape) when viewed in plan. The shape is mentioned.

(Step absorbency)
The double-sided pressure-sensitive adhesive sheet of the present embodiment has excellent step absorbability, and the pressure-sensitive adhesive layer has the shape of the step portion even if a step portion (for example, a convex portion) is formed on the surface of the adherend. It can be bonded to the adherend so that it deforms so as to follow and is in close contact with the stepped portion without any gap. Such a pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet has appropriate flexibility and can be deformed so as to absorb the stepped portion on the adherend. Therefore, the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet according to the present embodiment can be adhered to an adherend made of a member having low dimensional accuracy so as to allow the error.

  In the double-sided pressure-sensitive adhesive sheet of the present embodiment, the height of the stepped portion on the adherend that can be absorbed is preferably 35% or less, more preferably relative to the thickness (100%) of the pressure-sensitive adhesive layer. 30% or less.

(Other characteristics)
Although the adhesive force (N / 20mm) of the double-sided adhesive sheet (adhesive layer) of this embodiment is not specifically limited, For example, Preferably it is 20 N / 20mm or more. The adhesive strength can be measured by the method described in Examples described later. Moreover, the double-sided pressure-sensitive adhesive sheet (pressure-sensitive adhesive layer) of the present embodiment has a characteristic (holding force) that does not easily peel off even if it is applied to an adherend for a long time. The holding force can be measured by the method described in Examples described later. Moreover, the double-sided pressure-sensitive adhesive sheet (pressure-sensitive adhesive layer) of the present embodiment has characteristics such as workability (handleability), durability, and drop impact resistance.

(Use of double-sided PSA sheet)
The double-sided pressure-sensitive adhesive sheet of the present embodiment is used, for example, when fixing various members and modules constituting a mobile electronic device. Examples of such portable electronic devices include mobile phones, PHS, smartphones, tablets (tablet computers), mobile computers (mobile PCs), personal digital assistants (PDAs), electronic notebooks, portable televisions, portable radios, and the like. Mobile broadcast receivers, portable game machines, portable audio players, digital camera cameras, camcorder video cameras, and the like.

  Specific usage modes of the double-sided pressure-sensitive adhesive sheet are not particularly limited. For example, a lens (especially a glass lens) is fixed to a casing, a display panel is fixed to the casing, an input device such as a sheet keyboard or a touch panel To the housing, bonding the protective panel of the information display unit to the housing, bonding of the housings, bonding of the housing to the decorative sheet, various members and modules that make up the portable electronic device Fixing and the like.

  In addition, the “lens” in the present specification is a concept including both a transparent body showing a light refraction action and a transparent body having no light refraction action. In other words, the “lens” in the present specification includes a simple window panel having no refractive action.

  Moreover, as a preferable member for portable electronic devices fixed using a double-sided pressure-sensitive adhesive sheet, for example, a plastic member formed by injection molding or the like can be given. For example, the double-sided pressure-sensitive adhesive sheet is preferably used for fixing an optical member constituting a portable electronic device and a plastic housing.

  Although it does not specifically limit as a raw material which comprises the said plastic member, For example, well-known plastic materials, such as an acrylic resin, a polycarbonate resin, and a polyethylene terephthalate, are mentioned. In addition, a double-sided adhesive sheet can be used suitably also to adherends other than plastics, such as glass and a metal (a metal oxide is included).

  Moreover, the double-sided pressure-sensitive adhesive sheet of this embodiment may be used for fixing various components and various modules in apparatuses other than the above-described portable electronic device. Examples of devices other than the portable electronic device include a display device (image display device) and an input device. Examples of the display device include a liquid crystal display device, an organic EL (electroluminescence) display device, and a PDP ( Plasma display panel) and electronic paper. Examples of the input device include a touch panel.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited at all by these Examples.

[Example 1]
(Production of syrup)
A liquid monomer mixture in which 78 parts by mass of 2-ethylhexyl acrylate (2EHA), 18 parts by mass of N-vinyl-2-pyrrolidone (NVP) and 4 parts by mass of 2-hydroxyethyl acrylate (HEA) are mixed as a monomer component ( Monomer composition) as a photopolymerization initiator, trade name “Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)” (manufactured by BASF Japan Ltd.) 0.05 parts by mass and product After blending 0.05 part by mass of the name “Irgacure 184 (1-hydroxycyclohexyl phenyl ketone)” (manufactured by BASF Japan Ltd.), the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature: 30 ° C.) is about A portion formed by polymerizing a part of the monomer component by irradiating with ultraviolet rays until reaching 15 Pa · s. Polymer (polymerization ratio: 10 wt%) was obtained syrup (2EHA / NVP / HEA = 78/18/4) containing.

(Preparation of adhesive composition A)
4 parts by mass of acrylic acid (AA) and 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA) were added to 100 parts by mass of the syrup to obtain a mixture of the syrup. Further, as an additional photopolymerization initiator, the product name “Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)” (manufactured by BASF Japan Ltd.) 0.7 mass Parts were added. Thereafter, 0.21 parts by mass of carbon black was further added to the mixture as a black pigment (black colorant). By fully mixing these, the pressure-sensitive adhesive composition A was obtained.

  The pressure-sensitive adhesive composition A contains 104.12 parts by mass of all monomer components for forming the acrylic polymer. Among all the monomer components, the acidic group-containing monomer is 8.7 parts by mass (carboxyl group-containing monomer is 4 parts by mass, hydroxyl group-containing monomer is 4.7 parts by mass), and the heterocyclic ring-containing vinyl monomer is 18 parts by mass. Part included.

(Production of double-sided PSA sheet)
The pressure-sensitive adhesive composition A was applied on one surface of the release liner 30 on which the release treatment was performed so that the thickness after curing was 400 μm to obtain a coating layer. And the other release liner 40 was bonded together on the said coating layer from the single side | surface side by which the peeling process was carried out. In addition, as the release liners 30 and 40, a polyethylene terephthalate base material (trade name “MRF”, manufactured by Mitsubishi Polyester Film Co., Ltd., or trade name “MRN”, manufactured by Mitsubishi Polyester Film Co., Ltd.), one side of which is subjected to a release treatment. It was used.

Next, the coating layer was irradiated with ultraviolet rays having an illuminance of 5 mW / cm ² from both sides through release liners 30 and 40 for 3 minutes to cure the coating layer, thereby obtaining a pressure-sensitive adhesive layer 20 having a thickness of 400 μm. In addition, “Black Light” manufactured by Toshiba Corporation was used as a source of ultraviolet rays. The illuminance of ultraviolet rays was adjusted using a UV checker (trade name “UVR-T1”, manufactured by Topcon Corporation, maximum sensitivity: 350 n).

  As described above, a double-sided PSA sheet (baseless double-sided PSA sheet) 10 of Example 1 was obtained (see FIG. 1).

[Example 2]
(Production of double-sided PSA sheet)
Using the same pressure-sensitive adhesive composition A as in Example 1, a double-sided pressure-sensitive adhesive sheet (baseless double-sided pressure-sensitive adhesive sheet) of Example 2 having a pressure-sensitive adhesive layer having a thickness of 350 μm was produced. Specifically, in the same manner as in Example 1, except that the pressure-sensitive adhesive composition A is applied on one surface of the release liner that has been subjected to the release treatment so that the thickness after curing is 350 μm. 2 double-sided PSA sheet was prepared.

Example 3
(Preparation of adhesive composition B)
To 100 parts by mass of the syrup (the same syrup as in Example 1), 4 parts by mass of acrylic acid (AA) and 0.12 parts by mass of 1,6-hexanediol diacrylate (HDDA) are added, and the syrup is added. A mixture of was obtained. Furthermore, as a photopolymerization initiator for an additional amount, a trade name “Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)” (manufactured by BASF Japan Ltd.) 0.5 mass Parts were added. Thereafter, 0.5 parts by mass of carbon black was further added to the mixture as a black pigment (black colorant). By fully mixing these, the pressure-sensitive adhesive composition B was obtained.

  In addition, the adhesive composition B contains 104.12 parts by mass of all monomer components for forming the acrylic polymer. Among all the monomer components, the acidic group-containing monomer is 8.7 parts by mass (carboxyl group-containing monomer is 4 parts by mass, hydroxyl group-containing monomer is 4.7 parts by mass), and the heterocyclic ring-containing vinyl monomer is 18 parts by mass. Part included.

(Production of double-sided PSA sheet)
Using the pressure-sensitive adhesive composition B, a double-sided pressure-sensitive adhesive sheet (baseless double-sided pressure-sensitive adhesive sheet) of Example 3 having a pressure-sensitive adhesive layer having a thickness of 300 μm was produced. Specifically, the pressure-sensitive adhesive composition B is used in place of the pressure-sensitive adhesive composition A, and the pressure-sensitive adhesive composition B is formed on one surface of the release liner that has been subjected to the release treatment so that the thickness after curing is 300 μm. A double-sided pressure-sensitive adhesive sheet of Example 3 was produced in the same manner as in Example 1 except that the coating was applied.

[Comparative Example 1]
(Production of double-sided PSA sheet)
Using the same adhesive composition B as in Example 3, a double-sided pressure-sensitive adhesive sheet (baseless double-sided pressure-sensitive adhesive sheet) of Comparative Example 1 having a pressure-sensitive adhesive layer having a thickness of 250 μm was produced. Specifically, Comparative Example is the same as Example 3 except that the pressure-sensitive adhesive composition B is applied on one surface of the release liner that has been subjected to the release treatment so that the thickness after curing is 250 μm. 1 double-sided PSA sheet was prepared.

[Evaluation]
(Total light transmittance)
About each double-sided adhesive sheet (only adhesive layer) of Examples 1-3 and Comparative Example 1, total light transmittance (%) was measured by the method shown below. The measurement results are shown in Table 1.

  The double-sided pressure-sensitive adhesive sheet with one release liner peeled off was attached to a slide glass (trade name “S-1112”, manufactured by Matsunami Glass Industrial Co., Ltd., total light transmittance 91.8%, haze 0.4%). Then, what peeled off the other release liner was used as the test piece. And the total light transmittance of this test piece was measured using the haze meter (Brand name "HM-150", Murakami Color Research Laboratory make).

(Solvent insoluble fraction)
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the solvent insoluble content rate (mass%) was measured by the method shown below (only an adhesive layer). The measurement results are shown in Table 1.

  A predetermined amount of the pressure-sensitive adhesive layer (initial mass W1) was immersed in an ethyl acetate solution in a predetermined container and left at room temperature for 1 week. Thereafter, the insoluble matter was taken out from the container, and the mass (W2) after drying it was measured, and (W2 / W1) × 100 was defined as the solvent insoluble fraction (mass%).

(Step absorbency)
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the level | step difference absorptivity was evaluated by the method shown below.
FIG. 2 is a plan view of a sample set for evaluation used when evaluating step absorbability, and FIG. 3 is a cross-sectional view taken along line AA of FIG. 2 and 3, 41 is a polycarbonate plate, 42 is a step tape, 43 is a window frame-shaped double-sided pressure-sensitive adhesive sheet, 44 is an acrylic plate (acrylic lens), and 45 is a non-woven fabric. Hereinafter, the procedure for evaluating the step absorbability will be specifically described.

  First, the double-sided pressure-sensitive adhesive sheets of Examples and Comparative Examples are cut into a window frame shape (frame shape) having a width of 1 mm (width: 60 mm, length: 40 mm), and then a window frame-shaped double-sided pressure-sensitive adhesive sheet (hereinafter referred to as window frame shape). A double-sided pressure-sensitive adhesive sheet) was obtained. Four window frame-shaped double-sided PSA sheets are prepared for one evaluation sample set. Next, the window frame-shaped double-sided pressure-sensitive adhesive sheet was bonded to four acrylic plates (acrylic lens, horizontal: 60 mm, vertical: 40 mm, thickness: 1 mm) so as to border the acrylic plate.

  Apart from the acrylic plate, a single polycarbonate plate (PC plate) was prepared in which two step tapes (width: 5 mm, thickness: 100 μm) were affixed in parallel with each other. Then, four pieces of the acrylic plate are placed on the polycarbonate plate so that the window frame-shaped double-sided pressure-sensitive adhesive sheet overlaps the step tape, and the inside of the window frame-shaped double-sided pressure-sensitive adhesive sheet (width: 35 mm, long The sample sets for evaluation were obtained by integrating the four samples for evaluation (see FIGS. 2 and 3). Each acrylic plate was pressure-bonded to the polycarbonate plate under the condition of one reciprocating 2 kg roller. Each sample for evaluation has a convex step portion having a height of 100 μm, and a window frame-shaped double-sided pressure-sensitive adhesive sheet is overlapped on the step portion. The non-woven fabric piece is confined inside each evaluation sample. Since the nonwoven fabric piece has the property of changing color when it absorbs water, the presence or absence of water in each sample for evaluation can be visually confirmed by the presence or absence of the color change of the nonwoven fabric piece.

  Such an evaluation sample set was aged for 30 minutes in a standard state (temperature: 23 ° C., humidity: 50% RH). Thereafter, the evaluation sample set is submerged in a 1 m water tank for 30 minutes in a standard state (temperature: 23 ° C., humidity: 50% RH) based on the IPX7 standard (JIS C0920 / IEC60529). The level difference absorbability of the double-sided pressure-sensitive adhesive sheet (window frame-shaped double-sided pressure-sensitive adhesive sheet) was evaluated by confirming the presence or absence of water immersion.

  For each example and comparative example, two sample sets for evaluation were prepared, and the presence or absence of water immersion was confirmed for a total of eight evaluation samples. Based on the result of the presence or absence of water immersion, the step absorbability of the double-sided PSA sheet in each example and comparative example was evaluated. As the evaluation results, Table 1 shows the number of evaluation samples that were not submerged among the total of eight evaluation samples.

  In addition, about each Example and the comparative example, the sample for evaluation which is not provided with the level | step-difference part was produced in the procedure similar to the sample for evaluation mentioned above except omitting two level | step difference tapes. And also about the sample for evaluation which is not provided with this level | step-difference part, the presence or absence of water immersion was evaluated similarly to the case where the level | step-difference part is provided. As the evaluation results, Table 1 shows the number of evaluation samples that were not submerged among the total of eight evaluation samples.

(Adhesive strength (to PC board))
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the adhesive force (N / 20mm) with respect to a polycarbonate board was measured by the method shown below. The measurement results are shown in Table 1.

  One release liner was peeled from the double-sided pressure-sensitive adhesive sheet to expose one pressure-sensitive adhesive surface of the pressure-sensitive adhesive layer. The double-sided PSA sheet was lined with a 50 μm thick PET film that had not been subjected to a peeling treatment on the exposed PSA surface. What was cut out from the backed double-sided PSA sheet to a width of 20 mm was used as a test piece. As the adherend, a clean polycarbonate plate (PC plate) cleaned by rubbing 10 reciprocations with a clean waste impregnated with isopropyl alcohol was used. The other release liner was peeled off from the test piece, and the test piece was pressure-bonded to the adherend by a method in which a 2 kg roller was rolled back and forth once. The test piece in a state of being bonded to the adherend is left in a measurement environment of 23 ° C. and 50% RH for 30 minutes, and then, using a tensile tester, at a tensile speed of 300 mm / min and a peeling angle of 180 °, The peel strength (N / 20 mm) of the test piece was measured.

(Adhesive strength (vs. SUS board))
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the adhesive force (N / 20mm) with respect to a stainless steel (SUS304B) board was measured. The measurement method is the same as that described above except that a stainless steel (SUS304B) plate is used instead of the polycarbonate plate (PC plate). The results are shown in Table 1.

(Retention force (60 ° C))
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the retention strength in a 60 degreeC environment was evaluated with the method shown below. The evaluation results are shown in Table 1.

  One release liner was removed from the double-sided pressure-sensitive adhesive sheet to expose one pressure-sensitive adhesive surface of the pressure-sensitive adhesive layer. The double-sided PSA sheet was lined with a 50 μm thick PET film that had not been subjected to a peeling treatment on the exposed PSA surface. What was cut out from the backed double-sided PSA sheet to a size of 10 mm in width and 50 mm in length was used as a test piece. As the adherend, a clean bakelite plate washed by rubbing 10 times with clean waste impregnated with toluene was used. The other release liner was peeled off from the test piece, and the test piece was pressure-bonded to the adherend so that one end protruded outside by a method of rolling a 2 kg roller once. After the test piece in a state of being bonded to the adherend (bakelite body) is left at 40 ° C. for 30 minutes, the bakelite plate is suspended in an environment of 40 ° C., and the free end of the test piece (extends from the bakelite plate). A load of 500 g was applied to the portion and left in an environment of 60 ° C. for 2 hours. When the test piece dropped from the adherend before the lapse of 2 hours from the application of the load, the holding force was determined to be “defective”. Further, when the test piece was held on the adherend even after 2 hours from the application of the load, it was determined that the holding force was “good”. Table 1 also shows the distance (mm) by which the test piece was displaced after 2 hours.

(Retention force (80 ° C))
About each double-sided adhesive sheet of Examples 1-3 and the comparative example 1, the retention strength in an 80 degreeC environment was evaluated. The evaluation method is the same as that described above except that an environment of 80 ° C. is used instead of the environment of 60 ° C. The results are shown in Table 1.

  The double-sided pressure-sensitive adhesive sheet of Example 1 includes a pressure-sensitive adhesive layer having a thickness of 400 μm. The acrylic polymer in the pressure-sensitive adhesive layer contains 74.9% by mass (= 78 / 104.12 × 100) of a structural unit derived from 2EHA (an example of an alkyl (meth) acrylate). The acrylic polymer contains 17.3% by mass (= 18 / 104.12 × 100) of a structural unit derived from NVP (an example of a heterocyclic ring-containing vinyl monomer). The acrylic polymer contains 3.84% by mass (= 4 / 104.12 × 100) of a structural unit derived from HEA (an example of an acidic group-containing monomer and a hydroxyl group-containing monomer). The acrylic polymer contains 3.84% by mass (= 4 / 104.12 × 100) of a structural unit derived from AA (an example of an acidic group-containing monomer and a carboxyl group-containing monomer). The acrylic polymer contains 0.12% by mass (= 0.12 / 104.12 × 100) of a structural unit derived from HDDA (an example of a multifunctional monomer). The acrylic polymer contains 25% by mass of a structural unit derived from a polar monomer. The solvent insoluble fraction (%) of the pressure-sensitive adhesive layer of Example 1 was 73% by mass.

  As shown in Table 1, the double-sided PSA sheet of Example 1 was not immersed in all the evaluation samples among the total of eight evaluation samples. From this, it was confirmed that the adhesive layer of the double-sided pressure-sensitive adhesive sheet of Example 1 was excellent in step absorbability.

  The double-sided pressure-sensitive adhesive sheet of Example 2 includes a pressure-sensitive adhesive layer having a thickness of 350 μm. As in Example 1, the acrylic polymer in the pressure-sensitive adhesive layer contains 74.9% by mass of a structural unit derived from 2EHA, 17.3% by mass of a structural unit derived from NVP, and is derived from HEA. It contains 3.84% by mass of units, 3.84% by mass of structural units derived from AA, and 0.12% by mass of structural units derived from HDDA. The acrylic polymer contains 25% by mass of a structural unit derived from a polar monomer. However, the solvent-insoluble fraction (%) of the pressure-sensitive adhesive layer of Example 2 was lower than that of Example 1 and was 72% by mass.

  As for the double-sided pressure-sensitive adhesive sheet of Example 2, as shown in Table 1, all of the evaluation samples out of the total of eight evaluation samples were not submerged. From this, it was confirmed that the adhesive layer of the double-sided pressure-sensitive adhesive sheet of Example 2 is excellent in step absorbability.

  The double-sided pressure-sensitive adhesive sheet of Example 3 includes a pressure-sensitive adhesive layer having a thickness of 300 μm. As in Example 1, the acrylic polymer in the pressure-sensitive adhesive layer contains 74.9% by mass of a structural unit derived from 2EHA, 17.3% by mass of a structural unit derived from NVP, and is derived from HEA. It contains 3.84% by mass of units, 3.84% by mass of structural units derived from AA, and 0.12% by mass of structural units derived from HDDA. The acrylic polymer contains 25% by mass of a structural unit derived from a polar monomer. However, the solvent-insoluble fraction (%) of the pressure-sensitive adhesive layer of Example 3 was 68% by mass, which was lower than that of Example 1 and Example 2.

  As shown in Table 1, the double-sided pressure-sensitive adhesive sheet of Example 3 was not submerged for four evaluation samples out of a total of eight evaluation samples, but the remaining four were submerged. . From this, although the adhesive layer of the double-sided adhesive sheet of Example 3 is inferior compared with Example 1 and Example 2, it can be said that it is excellent in level | step difference absorbability compared with Comparative Example 1 mentioned later.

  The double-sided pressure-sensitive adhesive sheet of Comparative Example 1 includes a pressure-sensitive adhesive layer having a thickness of 250 μm. As in Example 1, the acrylic polymer in the pressure-sensitive adhesive layer contains 74.9% by mass of a structural unit derived from 2EHA, 17.3% by mass of a structural unit derived from NVP, and is derived from HEA. It contains 3.84% by mass of units, 3.84% by mass of structural units derived from AA, and 0.12% by mass of structural units derived from HDDA. The acrylic polymer contains 25% by mass of a structural unit derived from a polar monomer. However, the solvent-insoluble fraction (%) of the pressure-sensitive adhesive layer of Comparative Example 1 was 68% by mass, which was lower than that of Example 1 and Example 2.

  As shown in Table 1, the double-sided pressure-sensitive adhesive sheet of Comparative Example 1 resulted in all of the evaluation samples being immersed in a total of eight evaluation samples. From this, it was confirmed that the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet of Comparative Example 1 does not have step absorbability.

  In addition, about the waterproofing test without adhesive force, holding force, and a level | step-difference part, any result of the double-sided adhesive sheet of Examples 1-3 and Comparative Example 1 was a favorable result.

  10 ... Double-sided pressure-sensitive adhesive sheet, 20 ... Acrylic adhesive layer, 30, 40 ... Release liner

Claims (8)

A double-sided pressure-sensitive adhesive sheet for fixing a member constituting a portable electronic device,
An acrylic pressure-sensitive adhesive layer having an acrylic polymer containing 9 to 30% by mass of a structural unit derived from a polar monomer as a base polymer,
The double-sided adhesive sheet whose thickness of the said acrylic adhesive layer is 280 micrometers or more.   The double-sided pressure-sensitive adhesive according to claim 1, wherein the acrylic polymer contains 50 mass% or more of a structural unit derived from a (meth) acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms. Sheet.   The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the acrylic polymer contains 2% by mass or more of a structural unit derived from a carboxyl group-containing monomer as a structural unit derived from the polar monomer.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the acrylic polymer contains 2% by mass or more of a structural unit derived from a hydroxyl group-containing monomer as a structural unit derived from the polar monomer.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the acrylic polymer contains 10 mass% or more of a structural unit derived from a heterocyclic ring-containing vinyl monomer as a structural unit derived from the polar monomer.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the acrylic polymer includes a structural unit derived from a polyfunctional monomer having two or more polymerizable functional groups.   The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the acrylic pressure-sensitive adhesive layer has a transmittance of 5% or less in the thickness direction. A method for producing a double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 7,
A support comprising a pressure-sensitive adhesive composition comprising a plurality of types of monomer components for forming an acrylic polymer, a partial polymer obtained by polymerizing a part of the monomer components, a photopolymerization initiator, and a colorant. A step of forming a coating film comprising the above-mentioned pressure-sensitive adhesive composition by applying on the top,
Irradiating the coating film with light to photopolymerize the monomer component in the coating film to form the acrylic polymer, and curing the coating film to obtain an acrylic pressure-sensitive adhesive layer. Prepared,
The compounding amount of the photopolymerization initiator in the pressure-sensitive adhesive composition is 0.3 parts by mass or more with respect to 100 parts by mass of all monomer components for forming the acrylic polymer, and the pressure-sensitive adhesive composition. In the method for producing a double-sided pressure-sensitive adhesive sheet, the blending amount of the colorant is not more than 0.25 parts by mass with respect to 100 parts by mass of all the monomer components.

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