TWI840331B - Adhesive composition and adhesive sheet - Google Patents

Abstract

An adhesive composition is provided, which can form an adhesive layer having blister resistance and whitening resistance under high durability conditions. An adhesive composition comprises: a (meth)acrylic copolymer (A) having a glass transition temperature (Tg) less than 0°C, an olefin polymer (B) and a crosslinking agent (C), wherein the viscosity of the olefin polymer (B) at 25°C is 0.5-30.0 Pa‧s.

Description

Adhesive composition and adhesive sheet

The present invention relates to an adhesive composition and an adhesive sheet.

In recent years, the market for smartphones and tablet computers has been expanding rapidly, and both are equipped with touch panels. The touch panel is a layered body of various materials, and adhesives are used to bond the various materials (for example, refer to patent document 1).

For example, polycarbonate is used as the material of the support and cover parts (surface support) of the touch panel. However, polycarbonate contains moisture due to its manufacturing process. When the adhesive sheet is attached to the polycarbonate plate and a durability test is performed, foaming from the moisture occurs. In this way, foaming caused by outgassing from the laminated material may occur.

In addition, the use of touch panels in automotive applications is also expanding, and in automotive applications, due to the high temperature in summer, etc., high durability is required that exceeds general use. However, conventional adhesives cannot meet the high durability conditions for automotive applications.

[Existing technical literature] 【Patent Literature】

Patent document 1: Patent publication No. 2013-018892

The subject of the present invention is to provide an adhesive composition capable of forming an adhesive layer having excellent blister resistance even under high durability conditions.

The inventors of the present invention have conducted in-depth research to solve the above problems. As a result, they found that the adhesive composition with the following structure can solve the above problems, thus completing the present invention.

The present invention, for example, relates to the following [1] to [4].

[1] An adhesive composition comprising: a (meth)acrylic copolymer (A) having a glass transition temperature (Tg) less than 0°C, an olefin polymer (B) and a crosslinking agent (C), wherein the viscosity of the olefin polymer (B) at 25°C is 0.5-30.0 Pa‧s.

[2] The adhesive composition according to [1] above, wherein the olefinic polymer (B) does not have a cross-linking functional group.

[3] The adhesive composition according to [1] or [2], wherein the (meth)acrylic copolymer (A) is a copolymer containing 50 to 99% by mass of an alkoxyalkyl (meth)acrylate and 0.5 to 20% by mass of a monomer containing a crosslinking functional group.

[4] An adhesive sheet having an adhesive layer formed from the adhesive composition described in any one of [1] to [3] above.

According to the present invention, it is possible to provide an adhesive composition capable of forming an adhesive layer having excellent blister resistance even under high-durability conditions.

The adhesive composition and adhesive sheet of the present invention are described below.

In this specification, acrylic acid and methacrylic acid are collectively referred to as "(meth)acrylic acid", and acrylate and methacrylate are collectively referred to as "(meth)acrylate". In addition, "polymer" is used to include homopolymers and copolymers, and "polymerization" is used to include homopolymerization and copolymerization.

[Adhesive composition]

The adhesive composition of the present invention contains the (meth)acrylic copolymer (A), olefin polymer (B) and crosslinking agent (C) described below. The adhesive composition of the present invention may also contain an additive (D) as needed.

≪(Meth)acrylic acid copolymer (A)≫

The glass transition temperature (Tg) of the (meth)acrylic copolymer (A) is less than 0°C.

For example, the Tg of the (meth)acrylic copolymer (A) can be obtained by the Fox equation.

The Tg of the (meth)acrylic copolymer (A) is less than 0°C, preferably -80 to -10°C, and more preferably -70 to -30°C. When the Tg is within the above range, it is preferred from the perspective of the adhesion of the adhesive layer to the adherend. Furthermore, when the Tg is above the above lower limit, it is preferred from the perspective of improving the cohesion of the adhesive layer and the durability.

The weight average molecular weight (Mw) of the (meth)acrylic copolymer (A) measured by gel permeation chromatography (GPC method) is preferably 200,000 to 1,000,000, more preferably 250,000 to 800,000, and further preferably 300,000 to 700,000 in terms of polystyrene conversion. When Mw is within the above range, sufficient cohesion is imparted to the adhesive layer obtained from the adhesive composition, and therefore, it is preferred from the viewpoint of improving durability under high temperature conditions or high temperature and high humidity conditions.

Furthermore, the molecular weight distribution (Mw/Mn) of the (meth)acrylic copolymer (A) measured by the GPC method is preferably 2.0 to 15.0, more preferably 2.5 to 13.0, and further preferably 2.8 to 10.0. When Mw/Mn is within the above range, it is preferred to obtain an adhesive layer with excellent durability.

In 100% by mass of the solid content of the adhesive composition, the total content of the (meth)acrylic copolymer (A), the olefin polymer (B) described below, and the crosslinking agent (C) in the adhesive composition is usually 60% by mass or more, preferably 65% by mass or more, and more preferably 70% by mass or more. The solid content refers to the component excluding the solvent.

As the monomer components forming the (meth)acrylic copolymer (A), there can be cited at least one monomer (a1) selected from the (meth)acrylic acid alkyl esters, (meth)acrylic acid alkoxyalkyl esters and alkoxypolyalkylene glycol mono(meth)acrylates described below, a crosslinking functional group-containing monomer (a2), and other monomers (a3). Hereinafter, these may also be referred to as "monomers (a1) to (a3)".

<Single body (a1)>

As the monomer (a1), at least one monomer selected from (meth)acrylate alkyl esters, (meth)acrylate alkoxyalkyl esters, and alkoxypolyalkylene glycol mono(meth)acrylates can be cited.

As the (meth)acrylate alkyl ester, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate.

As the alkoxyalkyl (meth)acrylate, for example, methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate can be cited.

As alkoxypolyalkylene glycol mono(meth)acrylate, for example, methoxydiethylene glycol mono(meth)acrylate, methoxydipropylene glycol mono(meth)acrylate, ethoxytriethylene glycol mono(meth)acrylate, ethoxydiethylene glycol mono(meth)acrylate, and methoxytriethylene glycol mono(meth)acrylate can be cited.

The monomer (a1) may be used alone or in combination of two or more.

In 100% by mass of the monomer component used to form the (meth)acrylic copolymer (A), the content of monomer (a1) is usually 50-99% by mass, preferably 60-98% by mass, and more preferably 65-95% by mass. If it is such a form, the adhesive layer obtained has excellent adhesive strength and cohesive force, so it is preferred. For example, the above content can be controlled by the amount of monomer components.

In particular, when the content of the (meth)acrylic acid alkoxyalkyl ester as the monomer (a1) is 50% by mass or more in 100% by mass of the monomer components used to form the (meth)acrylic copolymer (A), the moisture intruding into the obtained adhesive layer can be effectively dispersed, and an adhesive layer having not only excellent blistering resistance but also excellent whitening resistance can be obtained.

<Monomer (a2)>

Monomer (a2) is a monomer containing a cross-linking functional group, for example, a hydroxyl group-containing monomer and an acid group-containing monomer.

Examples of hydroxyl-containing monomers include hydroxyl-containing (meth)acrylates such as hydroxyl alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate.

As acid groups, for example, carboxyl groups, acid anhydride groups, phosphoric acid groups, and sulfuric acid groups can be cited. As carboxyl group-containing monomers, for example, (meth)acrylic acid, β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, succinic acid mono(meth)acryloyloxyethyl ester, ω-carboxypolycaprolactone mono(meth)acrylate, itaconic acid, crotonic acid, fumaric acid, maleic acid, etc. can be cited. As monomers containing acid groups other than carboxyl groups, for example, phthalic anhydride, maleic anhydride, phosphoric acid group-containing monomers, and sulfuric acid group-containing monomers can be cited.

Among monomers (a2), hydroxyl-containing monomers and carboxyl-containing monomers are also preferred. At least a portion of the crosslinking functional groups from monomer (a2) become crosslinking points in the (meth)acrylic copolymer (A), and react with the crosslinking agent (C) described later to form a crosslinking structure.

The monomer (a2) may be used alone or in combination of two or more.

In 100% by mass of the monomer component used to form the (meth)acrylic copolymer (A), the content of monomer (a2) is usually 0.5-20% by mass, preferably 0.8-18% by mass, and more preferably 1-15% by mass. With such a form, the cross-linked structure of the (meth)acrylic copolymer (A) can be appropriately formed, and an adhesive layer with appropriate flexibility can be obtained. For example, the above content can be controlled by the amount of monomer components.

<Single body (a3)>

As monomer (a3), monomers other than the above-mentioned monomers (a1) and (a2) can be cited, for example, (meth)acrylates containing alicyclic hydrocarbon groups or aromatic hydrocarbon groups, styrene-based monomers, amide-containing monomers, amino-containing monomers, cyano-containing monomers, vinyl acetate, and polymerizable macromolecular monomers.

Examples of (meth)acrylates of alicyclic hydrocarbons or aromatic hydrocarbons include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

Examples of styrene monomers include styrene; alkyl styrenes such as methyl styrene, dimethyl styrene, trimethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, and octyl styrene; halogenated styrenes such as fluorostyrene, chlorostyrene, bromostyrene, and dibromostyrene; and functionalized styrenes such as nitrostyrene, acetylstyrene, and methoxystyrene.

As the amide group-containing monomer, for example, there can be cited N-alkyl (meth)acrylamide such as (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-hexyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide; and nitrogen-containing heterocyclic monomers such as N-vinylpyrrolidone, N-vinylcaprolactam, (meth)acryloyl morpholine.

As the amino group-containing monomer, for example, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate and the like N,N-dialkylaminoalkyl (meth)acrylate can be cited.

As cyano group-containing monomers, for example, cyano (meth)acrylate and (meth)acrylonitrile can be cited.

Examples of monomers constituting the polymer chain (main chain) portion of the polymerizable macromolecular monomer include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and tert-butyl (meth)acrylate, wherein the carbon number of the alkyl group is preferably 1 to 20, and styrene monomers such as (meth)acrylonitrile, styrene, and α-methylstyrene.

The above-mentioned macromonomers are preferably (meth)acrylic acid macromonomers, (meth)acrylonitrile macromonomers and styrene macromonomers, and can be produced according to various known methods, for example, by the method described in paragraph [0039] of Japanese Patent Publication No. 2013-018227.

As the above-mentioned macromonomer, commercially available products can be used, for example, a macromonomer whose main chain constituent monomer is methyl methacrylate (product name: 45% AA-6 (AA-6S), AA-6; manufactured by Toagosei), a macromonomer whose main chain constituent monomer is a copolymer of styrene/acrylonitrile (product name: AN-6S; manufactured by Toagosei), and a macromonomer whose main chain constituent monomer is butyl acrylate (product name: AB-6; manufactured by Toagosei), and these macromonomers have methacryloyl groups at their terminals.

The monomer (a3) may be used alone or in combination of two or more.

The content of monomer (a3) in 100% by mass of the monomer components used to form the (meth)acrylic copolymer (A) is 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less.

<Method for producing (meth)acrylic acid copolymer (A)>

The (meth)acrylic acid copolymer (A) can be produced by a known method, but is preferably produced by solution polymerization. Specifically, monomer components and polymerization solvents are mixed in a reaction container, and a polymerization initiator is added in an inert gas atmosphere such as nitrogen, and the reaction temperature is heated to about 50-90°C, and the reaction is carried out for 4-20 hours. In addition, during the polymerization reaction, polymerization initiators, chain transfer agents, monomer components, and polymerization solvents can be appropriately added.

As polymerization initiators, for example, conventional organic polymerization initiators can be cited, specifically, peroxides such as benzoyl peroxide and lauryl peroxide, and azo compounds such as 2,2'-azobisisobutyronitrile can be cited. Among them, azo compounds are also preferred.

Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(aminoformylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(aminoformylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis(isobutylamide) dihydrate, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-cyanopropanol), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide].

The polymerization initiator may be used alone or in combination of two or more.

The amount of the polymerization initiator used is usually 0.01 to 5 parts by mass relative to 100 parts by mass of the monomer component. In this form, the Mw of the (meth)acrylic copolymer (A) can be adjusted to an appropriate range.

In the solution polymerization, examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, and diphenyl ether; Halides such as oxalic acid, carbon tetrachloride, 1,2-dichloroethane, and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; sulfoxides such as dimethyl sulfoxide and cyclobutane sulfone. The polymerization solvent may be used alone or in combination of two or more.

≪Olefin polymer (B)≫

When an adhesive sheet is manufactured from an adhesive composition and attached to an adherend, the olefin polymer (B) is concentratedly distributed on the interface with the adherend. Since the olefin polymer (B) is concentratedly distributed on the interface with the adherend, it is possible to suppress outgassing from the adherend from entering the adhesive layer, and an adhesive sheet with excellent blister resistance can be obtained.

The viscosity of the olefin polymer (B) at 25°C measured by the method described in the examples is 0.5 to 30.0 Pa‧s, preferably 0.8 to 28.0 Pa‧s, and more preferably 1.0 to 25.0 Pa‧s. When the viscosity is within the above range, it is easy to concentrate on the interface of the adherend when the adhesive sheet is adhered to the adherend, which is preferred from the perspective of blister resistance.

The weight average molecular weight (Mw) of the olefin polymer (B) measured by gel permeation chromatography (GPC method) is 1000-15000 in terms of polystyrene conversion, preferably 2000-13000, and more preferably 2500-12000. When Mw is within the above range, it is easy to migrate to the interface between the adhesive layer and the adherend, which is preferred from the perspective of anti-foaming properties.

Furthermore, the olefinic polymer (B) may or may not have a crosslinking functional group. However, when it has a crosslinking functional group, it will undergo a crosslinking reaction with the (meth)acrylic copolymer (A) described later or the olefinic polymers (B) will undergo a crosslinking reaction with each other, and it will be difficult for the olefinic polymer (B) to migrate to the interface between the adhesive layer and the adherend. Therefore, it is preferred that the olefinic polymer (B) does not have a crosslinking functional group.

In the adhesive composition of the present invention, the content of the olefin polymer (B) is preferably 0.5 to 15 parts by mass, more preferably 0.7 to 12 parts by mass, and further preferably 1.0 to 10 parts by mass relative to 100 parts by mass of the (meth) acrylic copolymer (A). When the content of the olefin polymer (B) is above the lower limit, the adhesive layer can be provided with anti-foaming properties, and when it is below the upper limit, the adhesive layer is less likely to suffer from adverse conditions such as whitening.

As olefin polymers (B), for example, there can be cited LUCANT LX004 (1.0Pa‧s), LUCANT LX010 (2.9Pa‧s), LUCANT LX020 (4.0Pa‧s), LUCANT LX100 (24.2Pa‧s) (all manufactured by Mitsui Chemicals), B-1000 (1.0Pa‧s), B-2000 (7.0Pa‧s) (all manufactured by Nippon Soda), etc. Among the above olefin polymers, LUCANT LX010 and LUCANT LX100 are preferably used from the viewpoint of the presence or absence of functional groups and viscosity.

≪Crosslinking agent (C)≫

The crosslinking agent (C) is not particularly limited as long as it is a component that can undergo a crosslinking reaction with the (meth)acrylic copolymer (A). For example, there can be cited isocyanate crosslinking agents (C1), epoxy crosslinking agents (C2), and metal chelate crosslinking agents (C3).

The crosslinking agent (C) may be used alone or in combination of two or more.

In the adhesive composition of the present invention, the total content of the crosslinking agent (C) is 0.01 to 8 parts by mass, preferably 0.05 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A). In such a form, the crosslinking structure is fully and appropriately formed, and an adhesive with high cohesion, excellent balance of adhesive properties, and excellent durability can be obtained.

<Isocyanate crosslinking agent (C1)>

The isocyanate crosslinking agent (C1) is, for example, an isocyanate compound having two or more isocyanate groups in one molecule. The number of isocyanate groups in one molecule of the isocyanate crosslinking agent (C1) is preferably 2 to 8, more preferably 2 to 5. The number of isocyanate groups within the above range is preferred in terms of crosslinking reaction efficiency and ease of availability.

Examples of diisocyanate compounds having two isocyanate groups in one molecule include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. Examples of aliphatic diisocyanates include aliphatic diisocyanates having 4 to 30 carbon atoms, such as methylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Examples of alicyclic diisocyanates include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate. Examples of aromatic diisocyanates include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate.

As isocyanate compounds having 3 or more isocyanate groups in one molecule, for example, aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates can be cited. Specifically, 2,4,6-toluene triisocyanate, 1,3,5-phenyl triisocyanate, and 4,4',4"-triphenylmethane triisocyanate can be cited.

Furthermore, as isocyanate compounds, for example, the above-mentioned isocyanate compounds having 2 or more isocyanate groups, polymers (for example, dimers or trimers, biuret bodies, isocyanurate bodies), derivatives (for example, addition reaction products of polyols and more than 2 molecules of diisocyanate compounds), and polymers can be cited. As polyols in the above-mentioned derivatives, as low molecular weight polyols, for example, trihydroxymethylpropane, glycerol, pentaerythritol and other trivalent or higher alcohols can be cited; as high molecular weight polyols, for example, polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols can be cited.

As such isocyanate compounds, for example, trimers of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, biuret or isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate, reaction products of trihydroxymethylpropane with tolylene diisocyanate or xylene diisocyanate (e.g., 3-molecule adduct of tolylene diisocyanate or xylene diisocyanate), reaction products of trihydroxymethylpropane with hexamethylene diisocyanate (e.g., 3-molecule adduct of hexamethylene diisocyanate), polyether polyisocyanate, polyester polyisocyanate.

The isocyanate crosslinking agent (C1) may be used alone or in combination of two or more.

<Epoxy crosslinking agent (C2)>

As the epoxy crosslinking agent (C2), an epoxy compound having two or more epoxy groups in one molecule is generally used. For example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N,N-diglycidylaminophenylglycidyl ether, N,N-diglycidyltoluidine, and N,N-diglycidylaniline can be cited.

The epoxy-based crosslinking agent (C2) may be used alone or in combination of two or more.

<Metal chelate crosslinker (C3)>

Metal chelate crosslinking agents (C3) include, for example, polyvalent metal coordination alcohol salts of aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, zirconium, etc., acetylacetone, ethyl acetylacetate, etc. Specifically, aluminum isopropoxide, aluminum sec-butoxide, ethyl aluminum diisopropyl acetylacetate, tris(ethylacetylacetoxy)aluminum, aluminum triacetylacetonate.

The metal chelate crosslinking agent (C3) may be used alone or in combination of two or more.

≪Additives (D)≫

In addition to the above-mentioned components, the adhesive composition of the present invention may also contain at least one selected from organic solvents, antistatic agents, silane coupling agents, ultraviolet absorbers, antioxidants, tackifying resins, plasticizers, defoaming agents, fillers, stabilizers, softeners and wetting agents within a range that does not impair the effects of the present invention.

As an organic solvent, for example, a polymerization solvent described in the description of the method for producing a (meth)acrylic copolymer (A) can be cited. For example, an adhesive composition can be prepared by mixing a polymer solution containing a (meth)acrylic copolymer (A) and a polymerization solvent, an olefin polymer (B) and a crosslinking agent (C). In the adhesive composition of the present invention, the content of the organic solvent is usually 0 to 90% by mass, preferably 10 to 80% by mass.

〔 Adhesive sheet 〕

The adhesive sheet of the present invention has an adhesive layer formed by the above-mentioned adhesive composition. The adhesive layer can be obtained by crosslinking the above-mentioned adhesive composition, specifically, crosslinking the (meth)acrylic copolymer (A) with a crosslinking agent (C).

As adhesive sheets, for example, there can be cited a double-sided adhesive sheet having only the above-mentioned adhesive layer; a double-sided adhesive sheet having a substrate and the above-mentioned adhesive layer formed on both sides of the substrate; a single-sided adhesive sheet having a substrate and the above-mentioned adhesive layer formed on one side of the substrate; and an adhesive sheet having a release sheet subjected to a peeling treatment attached to the surface of the adhesive layer of these adhesive sheets that is not in contact with other layers.

The conditions for forming the adhesive layer are as follows. The above composition is applied to a release sheet or a substrate, and dried at usually 60 to 120°C, preferably 70 to 110°C, usually for 1 to 5 minutes, preferably 2 to 4 minutes to form a coating. Then, if applied to a release sheet, the substrate or release sheet is bonded to the coating on the side without the release sheet, and if applied on a substrate, the release sheet is bonded to the coating. Then, the curing (aging) is performed in an environment of usually 1 day or more, preferably 3 to 10 days, usually 5 to 60°C, preferably 15 to 40°C, usually 30 to 70% RH, preferably 40 to 70% RH. If crosslinking is performed under the above-mentioned aging conditions, a crosslinked body (network polymer) can be efficiently formed. If the coating is sandwiched by a separator, the separator on one side is peeled off after aging, and the exposed adhesive layer is bonded to the substrate.

As the substrate and the separator, for example, there can be cited plastic films such as polyester (e.g., polyethylene terephthalate, polyethylene naphthalate), polyethylene, polypropylene, polycarbonate, polymethyl methacrylate, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, polyamide, polyurethane, polyvinyl chloride, etc.; fabrics, non-woven fabrics; paper, glass, etc. The substrate and the separator may have their respective surfaces subjected to a release treatment.

The thickness of the adhesive layer is usually 3~1000μm, preferably 5~500μm. The thickness of the substrate and the separator is usually 10~1000μm.

From the perspective of improving cohesion, adhesion and re-peelability, the gelation rate of the adhesive layer is preferably 40~90% by mass, more preferably 50~80% by mass, and further preferably 60~70% by mass.

The gelation rate of the adhesive layer can be obtained as follows. About 0.1 g of the adhesive is sampled from the adhesive layer and placed in a sampling bottle. 30 mL of ethyl acetate is added and shaken for 4 hours. The contents of the sampling bottle are filtered through a 200-mesh stainless steel mesh. The residue on the mesh is dried at 100°C for 2 hours and the dry mass is measured. Then, the gelation rate of the adhesive layer is obtained by the following formula.

Gel rate (mass %) = (dry mass/adhesive sampling mass) × 100 (%)

The adhesive sheet of the present invention has a highly durable adhesive layer. In particular, when tested under harsh conditions such as 90°C/95%RH, it exhibits excellent blister resistance, whitening resistance, and substrate adhesion. The adhesive sheet of the present invention, which is highly durable under high temperature and high humidity conditions suitable for automotive use, can be used as a wide range of industrial adhesive sheets or can be used for bonding various resin films.

〔use〕

The adhesive sheet of the present invention can be bonded to various components, and is particularly suitable for bonding touch panel components that bond different types of parts. The touch panel can be mounted on, for example, smartphones and tablet computers, and can also be mounted on vehicle-mounted devices such as car navigation devices.

As a touch panel unit, for example, a resistive film touch panel unit and an electrostatic capacitive touch panel unit can be cited, which are all laminates of various materials, and the adhesive composition of the present invention can be used in the bonding of the above-mentioned various materials. As the use of the adhesive layer formed by the above-mentioned adhesive composition, for example, an adhesive layer for bonding between transparent parts and an adhesive layer for bonding a transparent part to a transparent conductive film can be cited.

Since the touch panel unit is placed on the outermost surface of the screen, the adhesive used is required to have high transparency, high heat resistance, and moisture and heat resistance.

The touch panel unit has, for example, a surface support, an adhesive layer, a transparent conductive film formed of a metal or a metal oxide, or a transparent conductive film formed of a metal with a support or a metal oxide with a support. Examples of metals and metal oxides include indium tin oxide (ITO), antimony tin oxide (ATO), and tin oxide.

The adhesive sheet of the present invention has good adhesion to polyolefin adherends such as polypropylene and polyethylene, and has high heat resistance. In addition, it also has good adhesion to adherends such as resins and glass other than polyolefins.

The adhesive sheet of the present invention is not limited to touch panel components, but can be used for various screen components, automotive components, aircraft components, ship components, electrical product components, building material components, and other components.

Implementation example

The present invention is described in detail below based on the embodiments, but the present invention is not limited to these embodiments. In the following embodiments, "parts" means "parts by mass" unless otherwise specified.

Each measured value in the embodiment is obtained by the following method.

[Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn)]

For the (meth)acrylic copolymer (A), Mw and Mw/Mn based on standard polystyrene conversion were obtained by gel permeation chromatography (GPC) under the following conditions.

‧Measurement device: HLC-8120GPC (manufactured by TOSOH CORPORATION)

‧GPC column structure: The following 5-column combination (all made by TOSOH CORPORATION)

(1)TSK-GEL HXL-H (guard column)

(2)TSK-GEL G7000HXL

(3)TSK-GEL GMHXL

(4)TSK-GEL GMHXL

(5)TSK-GEL G2500HXL

‧Sample concentration: Dilute with tetrahydrofuran to 1.0 mg/cm ³

‧Mobile phase solvent: tetrahydrofuran

‧Flow rate: 1.0cm ³ /min

‧Column temperature: 40℃

〔Manufacturing Example 1〕

In a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet pipe, 85 parts of 2-methoxyethyl acrylate (MEA), 10 parts of n-butyl acrylate (BA), 5 parts of 2-hydroxyethyl acrylate (HEA), 80 parts of ethyl acetate, and 50 parts of methyl ethyl ketone were mixed, and the temperature was raised to 75°C while introducing nitrogen. Then, 0.1 parts of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was carried out for 4 hours at 75-76°C in a nitrogen atmosphere. After the reaction was completed, the reaction solution was diluted with ethyl acetate to prepare a polymer solution. The obtained (meth)acrylic copolymer (A-1) had a Tg of -49°C, a Mw of 300,000, and a Mw/Mn of 3.8.

〔Manufacturing Example 2〕

In a reaction apparatus equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet pipe, 95 parts of n-butyl acrylate (BA), 4 parts of acrylic acid (AA), 1 part of 2-hydroxyethyl acrylate (HEA) and 130 parts of ethyl acetate were mixed, and the temperature was raised to 75°C while introducing nitrogen. Then, 0.1 parts of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was carried out for 4 hours at 75~76°C in a nitrogen atmosphere. After the reaction was completed, the reaction solution was diluted with ethyl acetate to prepare a polymer solution. The obtained (meth)acrylic copolymer (A-2) had a Tg of -46°C, a Mw of 600,000, and a Mw/Mn of 4.0.

[Example 1]

With respect to 100 parts of the solid content of the (meth)acrylic acid copolymer (A-1), 1 part of the olefin polymer LUCANT LX004 (Mitsui Chemicals, viscosity (25°C) 1 Pa‧s, weight average molecular weight 3000: active ingredient 100%) and 0.6 parts of the isocyanate crosslinking agent Y-75 (Shoken Chemicals, isocyanurate of hexamethylene diisocyanate: ethyl acetate solution with a solid content of 75%) were added to the above solution to obtain an adhesive composition.

The obtained adhesive composition was applied to a polyethylene terephthalate (PET) film subjected to a peeling treatment in such a way that the thickness after drying became 50 μm, and the solvent was removed by drying at 80°C for 3 minutes to form an adhesive layer. The peeling-treated PET film was attached to the surface of the adhesive layer opposite to the contact surface with the PET film. Then, the adhesive sheet having an adhesive layer with a thickness of 50 μm was obtained by aging at 23°C and 65% RH for 7 days.

[Examples 2 to 7, Comparative Examples 1 to 5]

Except for preparing the adhesive composition using the components listed in Table 1, the adhesive sheet was obtained by processing in the same manner as in Example 1.

<Evaluation>

[Blistering resistance test]

The peeled PET film was peeled off from the adhesive sheet, and the exposed adhesive layer was attached to a 100μm thick PET film (substrate), cut into 60mm×50mm size, and then the peeled PET film on the other side was peeled off, and the exposed adhesive layer was attached to a polycarbonate plate (PC plate, adherend), and then kept in an autoclave set at 50℃ and 5 atmospheres for 20 minutes to prepare a test plate. After the test plate was placed at 90℃/95%RH for 72 hours, the blister resistance was evaluated using the following criteria.

◎: No appearance defects such as foaming and floating were observed

○: Slightly poor appearance such as foaming and floating was observed, but there is no problem in practical use

△: Appearance defects such as foaming and floating were observed

×: Appearance defects such as foaming and floating were observed over a wide area

〔Whitening resistance test〕

The PET film treated with peeling treatment was peeled off from the adhesive sheet, and the exposed adhesive layer was attached to a 100μm thick PET film (substrate), and then cut into a size of 60mm×50mm. The PET film treated with peeling treatment on the other side was peeled off, and the exposed adhesive layer was attached to a polycarbonate plate (PC plate, adherend). Then, the test plate was kept in an autoclave set at 50℃ and 5 atmospheres for 20 minutes to prepare a test plate. After the test plate was placed at 90℃/95%RH for 100 hours, the presence or absence of whitening was confirmed by visual inspection according to the following criteria.

○: No whitening or appearance defects were observed

△: A slight whitening is observed, which is a poor appearance, but it is a range that does not cause any practical problems.

×: Whitening is observed over a wide area, resulting in poor appearance

LUCANT LX004 (Made by Mitsui Chemicals, viscosity 1.0Pa‧s, Mw3000)

LUCANT LX010 (Made by Mitsui Chemicals, viscosity 2.9Pa‧s, Mw5000)

LUCANT LX100 (Made by Mitsui Chemicals, viscosity 24.2Pa‧s, Mw 10000)

LUCANT LX200 (Made by Mitsui Chemicals, viscosity 57.0Pa‧s, Mw 12000)

B-1000 (made by Japan Soda, viscosity 1.0Pa‧s, Mw4000)

G-1000 (made by Japan Soda, viscosity 77.2Pa‧s, Mw5600)

IR2200 (Made by JSR, solid state)

※The viscosity of olefin polymers is the value at 25℃, and the active ingredient is 100%.

Claims (2)

An adhesive composition comprises: a (meth)acrylic copolymer A having a glass transition temperature Tg less than 0°C, wherein the (meth)acrylic copolymer A is a copolymer containing 50-99% by mass of alkoxyalkyl (meth)acrylate and 0.5-20% by mass of a monomer component containing a crosslinking functional group; an olefin polymer B; and a crosslinking agent C, wherein the olefin polymer B does not have a crosslinking functional group, the viscosity of the olefin polymer B at 25°C is 0.5-25.0 Pa‧s, and its weight average molecular weight (Mw) is 3000-10000. An adhesive sheet having an adhesive layer formed from the adhesive composition described in claim 1.