JP2022070985A - Pressure-sensitive adhesive sheet and method for producing the same and adhesive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive sheet which hardly causes white turbidity due to deformation.

SOLUTION: There is provided a pressure-sensitive adhesive sheet (5) in which an adhesive containing an acrylic-based polymer and an acrylic oligomer having an average molecular weight of 1000 to 30000 is formed in a sheet form. The base polymer contains an acrylic segment and a urethane-based segment and the content of the urethane-based segment is 3 to 30 pts.wt. based on 100 pts.wt. of the acrylic segment. The urethane-based segment contains one or more urethane chains selected from the group consisting of a polyether urethane and a polyester urethane. The content of the urethane-based segment other than a polyether urethane-based segment is 15 pts.wt. or less based on 100 pts.wt. of the acrylic segment.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to an adhesive sheet and a method for producing the same. Further, the present invention relates to an adhesive film in which a transparent film is fixed to one surface of an adhesive sheet.

Adhesive sheets are used in various aspects such as joining, protecting, and decorating articles. A typical example of the pressure-sensitive adhesive sheet is an acrylic pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive containing an acrylic-based base polymer as a main component. The acrylic adhesive sheet exhibits adhesive properties such as appropriate wettability, cohesiveness and adhesiveness, and is also excellent in weather resistance and heat resistance.

Various characteristics such as the glass transition temperature of the acrylic pressure-sensitive adhesive can be easily adjusted by changing the type of the constituent monomer and the copolymerization ratio. By introducing a crosslinked structure into the base polymer, the acrylic pressure-sensitive adhesive can enhance the cohesive force and adjust the adhesive properties and the like. For example, a crosslinked structure can be introduced into the polymer by reacting a polymer having a reactive functional group such as a hydroxyl group or a carboxy group in the side chain with a crosslinking agent such as isocyanate or epoxy. Further, by using a polyfunctional monomer or oligomer having two or more polymerizable functional groups in one molecule as the copolymerization component, a polymer having a crosslinked structure can be obtained. A polyfunctional (meth) acrylate is generally used as the polyfunctional monomer / oligomer for introducing a crosslinked structure into an acrylic polymer.

By increasing the cohesiveness of the pressure-sensitive adhesive, the shear storage elastic modulus tends to increase, and the adhesive holding power tends to improve. On the other hand, if the cohesiveness of the pressure-sensitive adhesive is increased, the viscosity tends to decrease, and the adhesive strength in a low temperature environment may be insufficient. As a pressure-sensitive adhesive having excellent adhesiveness at low temperatures, a urethane-based pressure-sensitive adhesive obtained by copolymerizing a urethane oligomer and an acrylic-based monomer is known (for example, Patent Document 1).

International Publication No. 2014/0277888

A pressure-sensitive adhesive having a structure derived from a urethane polymer chain (urethane-based segment) in the base polymer may have properties that are difficult to achieve with a pressure-sensitive adhesive using a base polymer composed of only an acrylic-based monomer. However, according to the studies by the present inventors, there is a problem that the pressure-sensitive adhesive sheet composed of the pressure-sensitive adhesive using the base polymer in which the urethane-based segment and the acrylic-based segment are bonded causes cloudiness due to deformation. found.

When such an adhesive sheet is used in an application that requires transparency, it may become cloudy with use and may cause a problem in visibility. For example, in a membrane switch of a home electric appliance or the like, a protective sheet is provided on the surface of the surface sheet via an adhesive sheet for the purpose of protecting the printed portion of the surface sheet. If the adhesive sheet becomes cloudy due to repeated deformation due to repeated pressing of the switch, the characters printed on the surface sheet become difficult to see, and it becomes difficult to identify the switch.

In view of such problems, an object of the present invention is to provide an adhesive sheet that is less likely to cause white turbidity due to deformation.

The present invention relates to a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive containing an acrylic base polymer is formed in the form of a sheet. The base polymer contains an acrylic segment and a urethane segment, and the content of the urethane segment is 3 to 30 parts by weight with respect to 100 parts by weight of the acrylic segment. Urethane-based segments include one or more urethane chains selected from the group consisting of polyether urethane and polyester urethane.

The content of the urethane-based segment other than the polyether urethane-based segment is 15 parts by weight or less with respect to 100 parts by weight of the acrylic-based segment. The content of the polyether urethane segment with respect to 100 parts by weight of the acrylic segment is preferably 3 parts by weight or more. The weight average molecular weight of the urethane-based segment is preferably 3000 to 50,000.

In the acrylic segment, the amount of the (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms with respect to the total amount of the constituent monomer components is preferably 30 to 80% by weight.

In the base polymer, the acrylic segment and the urethane segment are covalently bonded. In one embodiment, the acrylic base polymer has a structure in which the acrylic segment is crosslinked by the urethane segment. The polymer in which the acrylic segment is crosslinked by the urethane segment can be obtained, for example, by copolymerizing a monomer component constituting the acrylic segment with a urethane (meth) acrylate having a (meth) acryloyl group at the terminal.

In the method for producing a pressure-sensitive adhesive sheet according to an embodiment of the present invention, the curable pressure-sensitive adhesive composition is applied in layers on a substrate to cure the pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition contains an acrylic monomer and / or a partial polymer thereof, and a urethane (meth) acrylate. The content of urethane (meth) acrylate with respect to a total of 100 parts by weight of the acrylic monomer and its partial polymer is 3 to 30 parts by weight. The pressure-sensitive adhesive composition may further contain a photopolymerization initiator. The pressure-sensitive adhesive composition preferably contains an acrylic monomer and a partial polymer thereof in a total amount of 50% by weight or more.

The urethane (meth) acrylate contained in the pressure-sensitive adhesive composition contains one or more urethane (meth) acrylates selected from the group consisting of polyether urethane (meth) acrylates and polyester urethane (meth) acrylates, and is an acrylic monomer. The content of the urethane (meth) acrylate other than the polyether urethane (meth) acrylate in a total of 100 parts by weight of the partial polymer thereof is 15 parts by weight or less. The weight average molecular weight of the urethane (meth) acrylate is preferably 3000 to 50,000.

Further, the present invention relates to an adhesive film in which a transparent film is fixed to one surface of the adhesive sheet.

The pressure-sensitive adhesive sheet of the present invention is unlikely to cause white turbidity due to deformation due to tension or the like. Therefore, it is suitable for applications that require transparency, especially applications that involve deformation such as protective films for membrane switches.

It is sectional drawing which shows the structural example of the adhesive sheet with a release film. It is sectional drawing which shows an example of the usage form of an adhesive sheet.

In the pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive is formed in the form of a sheet. The pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet contains an acrylic-based base polymer.

[Base polymer]
Acrylic-based base polymers include acrylic-based segments and urethane-based segments. The content of the urethane-based segment with respect to 100 parts by weight of the acrylic-based segment of the base polymer is 3 to 30 parts by weight.

When the amount of the urethane-based segment is 30 parts by weight or less, white turbidity (tensile white turbidity) at the time of tensile deformation of the pressure-sensitive adhesive sheet is suppressed. From the viewpoint of suppressing tensile white turbidity, the amount of the urethane-based segment in the base polymer is preferably 25 parts by weight or less with respect to 100 parts by weight of the acrylic-based segment.

The acrylic segment and the urethane segment in the base polymer are bonded by a covalent bond. As a polymer in which an acrylic segment and a urethane segment are covalently bonded, a block polymer in which both segments form a main chain, one segment forms a main chain and the other segment is bonded to the main chain to form a side chain. Examples thereof include a graft polymer constituting the above, and a crosslinked polymer in which one segment is crosslinked with the other segment. As the graft polymer and the crosslinked polymer, the acrylic segment is the main chain, and the acrylic segment as the main chain (acrylic polymer chain) is preferably bonded to the side chain or the urethane segment as the crosslinked component.

The range of the amount of the urethane-based segment that can suppress the tensile white turbidity of the pressure-sensitive adhesive sheet also differs depending on the bonding mode between the acrylic-based segment and the urethane-based segment, the composition of the acrylic-based segment and the urethane-based segment, and the like. In the following, after explaining the acrylic segment and the urethane segment, the content of the urethane segment and the like will be described in more detail.

<Acrylic segment>
The acrylic segment contains (meth) acrylic acid alkyl ester as the main constituent monomer component. In addition, in this specification, "(meth) acrylic" means acrylic and / or methacrylic.

As the (meth) acrylic acid alkyl ester, a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferably used. The (meth) acrylic acid alkyl ester may have a branched alkyl group or a cyclic alkyl group.

Specific examples of the (meth) acrylic acid alkyl ester having a chain alkyl group include (meth) methyl acrylate, (meth) ethyl acrylate, (meth) butyl acrylate, (meth) isobutyl acrylate, and (meth). S-butyl acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-Ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate , (Meta) undecyl acrylate, (meth) dodecyl acrylate, (meth) isotridodecyl acrylate, (meth) tetradecyl acrylate, (meth) isotetradecyl acrylate, (meth) pentadecyl acrylate, (meth) Examples thereof include cetyl acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isooctadecyl (meth) acrylate, nonadecil (meth) acrylate, and aralkyl (meth) acrylate.

Specific examples of the (meth) acrylic acid alkyl ester having an alicyclic alkyl group include (meth) acrylic acid cyclopentyl, (meth) acrylic acid cyclohexyl, (meth) acrylic acid cycloheptyl, (meth) acrylic acid cyclooctyl and the like. (Meta) acrylic acid cycloalkyl ester; (meth) acrylic acid ester having a bicyclic aliphatic hydrocarbon ring such as (meth) acrylic acid isobornyl; dicyclopentanyl (meth) acrylate, dicyclopentanyloxy Three rings such as ethyl (meth) acrylate, tricyclopentanyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate Examples thereof include (meth) acrylic acid esters having the above-mentioned aliphatic hydrocarbon rings.

The amount of the (meth) acrylic acid alkyl ester with respect to the total amount of the monomer components constituting the acrylic segment is preferably 30% by weight or more, more preferably 40% by weight or more, still more preferably 50% by weight or more. From the viewpoint of setting the glass transition temperature (Tg) of the segment in an appropriate range, the acrylic segment has the above-mentioned amount of (meth) acrylic acid alkyl ester having a chain alkyl group having 4 to 10 carbon atoms with respect to the total amount of the constituent monomer components. It is preferably in the range.

The constituent components of the urethane-based segment (for example, urethane (meth) acrylate) are not included in the monomer components constituting the acrylic-based segment. In a graft polymer having an acrylic segment as a main chain and having a urethane graft side chain, or a crosslinked polymer in which an acrylic segment is crosslinked from a urethane segment, the main chain structure contains a terminal functional group of the urethane segment. The same applies when there is.

The acrylic segment may contain a hydroxyl group-containing monomer or a carboxy group-containing monomer as a constituent monomer component. When the acrylic segment has a hydroxyl group-containing monomer as a constituent monomer component, the white turbidity of the pressure-sensitive adhesive tends to be suppressed in a high-temperature and high-humidity environment, and a highly transparent pressure-sensitive adhesive can be obtained.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and (meth) acrylic. Examples thereof include (meth) acrylic acid esters such as 8-hydroxyoctyl acid, 10-hydroxydecyl (meth) acrylic acid, 12-hydroxylauryl (meth) acrylic acid and (4-hydroxymethylcyclohexyl) -methylacrylate. Among these, the acrylic segment has a (meth) acrylic acid having a hydroxyalkyl group having 4 to 8 carbon atoms as a constituent monomer component because it has high compatibility with the urethane segment and the adhesive sheet is less likely to become cloudy. It preferably contains an ester.

The amount of the hydroxy group-containing monomer is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, still more preferably 5 to 25% by weight, based on the total amount of the monomer components constituting the acrylic segment.

Examples of the carboxy group-containing (meth) acrylic acid ester include acrylic monomers such as (meth) acrylic acid, (meth) acrylic acid carboxyethyl, and (meth) acrylic acid carboxypentyl, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Examples include acid.

The acrylic segment may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholin, (meth) acryloylmorpholin, and N-vinyl. Examples thereof include vinyl-based monomers such as carboxylic acid amides and N-vinylcaprolactam, and cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile.

When the acrylic segment contains a highly polar monomer such as a hydroxyl group-containing monomer or a carboxy group-containing monomer as a constituent monomer component, the cohesive force of the pressure-sensitive adhesive is enhanced, and the adhesive retention at high temperature tends to be improved. .. The amount of highly polar monomer (total of hydroxyl group-containing monomer, carboxy group-containing monomer, and nitrogen-containing monomer) with respect to the total amount of the monomer components constituting the acrylic segment is preferably 1 to 60% by weight, more preferably 5 to 50% by weight. 10 to 45% by weight is more preferable. The amount of the nitrogen-containing monomer with respect to the total amount of the monomer components constituting the acrylic segment is preferably 1 to 40% by weight, more preferably 3 to 30% by weight, still more preferably 5 to 25% by weight.

Acrylic segments include acid anhydride group-containing monomers, (meth) acrylic acid caprolactone adducts, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, vinyl acetate, vinyl propionate, styrene, and α as monomer components other than the above. -Vinyl-based monomers such as methylstyrene; cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth) acrylate; polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate. Glycol-based acrylic ester monomers such as (meth) methoxyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate; (meth) tetrahydrofurfuryl acrylate, fluorine (meth) acrylate, silicone (meth) acrylate and (meth). Acrylic acid ester-based monomers such as 2-methoxyethyl acrylate may be contained.

Acrylic segments may contain polyfunctional monomers or oligomers. The polyfunctional compound contains two or more polymerizable functional groups having an unsaturated double bond such as a (meth) acryloyl group or a vinyl group in one molecule. Examples of the polyfunctional compound include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, bisphenol A ethylene oxide-modified di (meth) acrylate, and bisphenol A propylene oxide-modified di (meth) acrylate. Meta) acrylate, alcandiol di (meth) acrylate, tricyclodecanedimethanol di (meth) acrylate, ethoxylated isocyanuric acid triacrylate, pentaerythrtri (meth) acrylate, pentaeristol di (meth) acrylate, trimethylol Propanetri (meth) acrylate, ditrimethylol propanetetra (meth) acrylate, ethoxylated pentaeristol tetra (meth) acrylate, pentaeristol tetra (meth) acrylate, dipentaeristol poly (meth) acrylate, dipentaeristol Examples thereof include hexa (meth) acrylate, neopentyl glycol di (meth) acrylate, glycerin di (meth) acrylate, epoxy (meth) acrylate, butadiene (meth) acrylate, and isoprene (meth) acrylate.

When the acrylic segment contains a polyfunctional monomer as a constituent monomer component, a branched structure (crosslinked structure) is introduced into the segment. As will be described later, in one embodiment of the pressure-sensitive adhesive of the present invention, a crosslinked structure with a urethane-based segment is introduced into the acrylic-based segment. In a base polymer having such a crosslinked structure, if the amount of the crosslinked structure introduced by a polyfunctional monomer component other than the urethane-based segment increases, the low-temperature adhesive strength of the pressure-sensitive adhesive may decrease. Therefore, the amount of the polyfunctional compound with respect to the total amount of the monomer components constituting the acrylic segment is preferably 3% by weight or less, more preferably 1% by weight or less, further preferably 0.5% by weight or less, and 0.3% by weight or less. Is particularly preferable.

The acrylic segment preferably has the highest content of (meth) acrylic acid alkyl ester among the above-mentioned monomer components. The thermal properties and transparency of the pressure-sensitive adhesive sheet are likely to be affected by the type of monomer (main monomer) having the highest content among the constituent monomers of the acrylic segment. For example, when the main monomer of the acrylic segment is a (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the compatibility with the urethane segment is high and the tensile white turbidity tends to be suppressed. In particular, when acrylic acid _C4 alkyl ester such as butyl acrylate is the main monomer, tensile cloudiness tends to be suppressed. The amount of the (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms is preferably 30 to 80% by weight, more preferably 35 to 75% by weight, based on the total amount of the monomer components constituting the acrylic segment. 40-70% by weight is more preferable. In particular, the content of butyl acrylate as a constituent monomer component is preferably in the above range.

From the viewpoint of lowering the glass transition temperature of the base polymer to obtain a pressure-sensitive adhesive having excellent low-temperature adhesiveness, the glass transition temperature of the acrylic segment is preferably 0 ° C. or lower. On the other hand, from the viewpoint of enhancing the adhesive holding power at high temperature, the glass transition temperature of the acrylic segment is preferably −30 ° C. or higher, more preferably −20 ° C. or higher, still more preferably −10 ° C. or higher. The glass transition temperature (Tg) of the acrylic segment is obtained from the peak top temperature of the loss tangent (tan δ) by the dynamic viscoelastic measurement (frequency: 1 Hz) of the polymer obtained by polymerizing the monomer components constituting the acrylic segment.

Since it is difficult to measure the glass transition temperature of the acrylic segment alone in the base polymer in which the acrylic segment and the urethane segment are bonded, the evaluation may be performed based on the theoretical Tg. The theoretical Tg is calculated from the glass transition temperature Tg _i of the homopolymer of the constituent monomer components of the acrylic segment and the weight fraction Wi _i of each monomer component by the following Fox formula.
1 / Tg = Σ ( _{Wi / Tg i )}

Tg is the theoretical glass transition temperature (unit: K) of the polymer chain, Wi is the weight fraction of the monomer component _i constituting the segment (copolymerization ratio based on the weight), and Tg _i is the glass transition of the homopolymer of the monomer component i. Temperature (unit: K). As the glass transition temperature of the homopolymer, the numerical value described in the third edition of the Polymer Handbook (John Wiley & Sons, Inc., 1989) can be adopted. For the Tg of the homopolymer of the monomer not described in the above document, the peak top temperature of the loss tangent (tan δ) by the dynamic viscoelasticity measurement may be adopted.

From the viewpoint of lowering the glass transition temperature of the base polymer to obtain a pressure-sensitive adhesive having excellent low-temperature adhesiveness, the theoretical Tg of the acrylic segment is preferably 10 ° C. or lower, more preferably 0 ° C. or lower. On the other hand, from the viewpoint of enhancing the adhesive holding power at high temperature, the theoretical Tg of the acrylic segment is preferably −60 ° C. or higher, more preferably −50 ° C. or higher, further preferably −40 ° C. or higher, and particularly preferably −30 ° C. or higher. ..

<Urethane segment>
The urethane-based segment is a molecular chain having a urethane bond. Urethane-based segments are typically obtained by reacting a diol with a diisocyanate and contain a polyurethane chain. From the viewpoint of obtaining a pressure-sensitive adhesive capable of achieving both low-temperature adhesiveness and high-temperature holding power, the molecular weight of the polyurethane chain in the urethane-based segment is preferably 3000 to 50,000, more preferably 4000 to 40,000, and even more preferably 5000 to 30,000.

Examples of the diol used for forming the polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol and hexamethylene glycol; polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, epoxy polyols and caprolactone polyols. High molecular weight polyols of.

Among these, from the viewpoint of suppressing tensile cloudiness of the pressure-sensitive adhesive sheet, the polyurethane chain preferably contains a polyether urethane having a polyether polyol as a diol component and / or a polyester urethane having a polyester polyol as a diol component. In particular, when the polyurethane chain contains a polyether polyol, the tensile white turbidity of the pressure-sensitive adhesive sheet tends to be suppressed.

The polyether polyol can be obtained by ring-opening addition polymerization of an alkylene oxide on a polyhydric alcohol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran. Examples of the polyhydric alcohol include the above-mentioned diol, glycerin, trimethylolpropane and the like.

The polyester polyol is a polyester having a hydroxyl group at the terminal, and is obtained by reacting a polybasic acid with a polyhydric alcohol so that the alcohol equivalent is excessive with respect to the carboxylic acid equivalent. As the polybasic acid component and the polyhydric alcohol component constituting the polyester polyol, a combination of dibasic acid and diol is preferable.

Examples of the dibasic acid component include aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, and terephthalic acid; alicyclics such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Formula dicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decandicarboxylic acid, dodecandicarboxylic acid, octadecanedicarboxylic acid; Examples thereof include acid anhydrides of dicarboxylic acids and lower alcohol esters.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, and the like. 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F , Hydrogenated bisphenol A, hydrogenated bisphenol F and the like.

The polycarbonate polyol is a polycarbonate polyol obtained by subjecting a diol component to a phosgene in a polycondensation reaction; the diol component and dimethyl carbonate, diethyl carbonate, diprovyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, carbonic acid Polycarbonate polyol obtained by ester exchange condensation with carbonic acid diesters such as diphenyl and dibenzyl carbonate; copolymerized polycarbonate polyol obtained by using two or more kinds of polyol components in combination; the above-mentioned various polycarbonate polyols and carboxy group-containing compounds are esterified. Polycarbonate polyol obtained by reaction; Polycarbonate polyol obtained by etherifying the various polycarbonate polyols with a hydroxyl group-containing compound; Polycarbonate polyol obtained by performing an ester exchange reaction between the various polycarbonate polyols and an ester compound; Polycarbonate polyol obtained by ester exchange reaction between a polyol and a hydroxyl group-containing compound; Polycarbonate-based polycarbonate polyol obtained by polycondensation of the above-mentioned various polycarbonate polyols and a dicarboxylic acid compound; Examples thereof include the obtained copolymerized polyether-based polycarbonate polyol.

The polyacrylic polyol is obtained by copolymerizing a (meth) acrylic acid ester with a monomer component having a hydroxyl group. Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and (meth). ) Hydroxyalkyl esters of (meth) acrylic acids such as 4-hydroxybutyl acrylate, 2-hydroxypentyl (meth) acrylic acid; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; N- Examples thereof include methylol (meth) acrylamide. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate and the like.

The polyacrylic polyol may contain a monomer component other than the above as a copolymerization component. Examples of the copolymerization monomer component other than the above include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid and their anhydrides and mono or diesters; and unsaturated nitriles such as (meth) acrylonitrile. Classes; unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether; α-olefins such as ethylene and propylene; Examples thereof include halogenated α, β-unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; and α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene.

The diisocyanate used to form the polyurethane chain may be either aromatic diisocyanate or aliphatic. Examples of the aromatic diisocyanate include 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-. Phenylene diisocyanate, 2-chloro-1,4-phenyldiisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, xylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl sulfoxide diisocyanate , 4,4'-diphenylsulfone diisocyanate, 4,4'-biphenyldiisocyanate and the like. Examples of the aliphatic diisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, and isophorone diisocyanate. , Dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane, methylcyclohexanediisocyanate and the like.

As the diisocyanate, a derivative of an isocyanate compound can also be used. Examples of the derivative of the isocyanate compound include a dimer of polyisocyanate, a trimer of isocyanate (isocyanurate), a polypeptide MDI, an adduct with trimethylolpropane, a biuret modified product, an allophanate modified product, and a urea modified product. ..

As the diisocyanate component, a urethane prepolymer having an isocyanate group at the terminal may be used. By reacting the polyhydric alcohol with the polyisocyanate compound so that the polyisocyanate compound becomes excessive, a urethane prepolymer having an isocyanate group at the terminal can be obtained.

By introducing a functional group capable of binding to an acrylic segment at the end of the polyurethane chain, a covalent bond can be formed between the urethane segment and the acrylic segment. For example, by using a polyurethane chain having a functional group that can be bonded to the end of the acrylic segment, a block polymer having an acrylic segment and a urethane segment can be obtained. At one end of the polyurethane chain, a compound having a functional group capable of copolymerizing with the monomer component constituting the acrylic segment or a functional group capable of reacting with a carboxy group, a hydroxyl group, etc. contained in the side chain of the acrylic segment is used. As a result, a graft polymer in which the urethane-based segment is bonded as a side chain to the acrylic-based segment (acrylic polymer chain as the main chain) can be obtained. Both ends of the polyurethane chain (multiple ends if the polyurethane chain has branches) are contained in a functional group copolymerizable with the monomer components constituting the acrylic segment, or in the side chain of the acrylic segment. By using a compound having a functional group capable of reacting with a carboxy group, a hydroxyl group, or the like, a crosslinked structure with a urethane-based segment can be introduced into the acrylic-based segment.

In order to obtain an acrylic base polymer having a crosslinked structure with urethane-based segments, it is preferable to use a compound having (meth) acryloyl groups at both ends of the urethane chain. For example, by copolymerizing the monomer component constituting the acrylic segment with the urethane di (meth) acrylate having (meth) acryloyl groups at both ends, a crosslinked structure by the urethane segment can be introduced into the acrylic segment. Urethane (meth) acrylate has excellent compatibility with acrylic monomers and acrylic polymer chains, and has an advantage that it is easy to uniformly introduce cross-linking points into acrylic segments.

Urethane di (meth) acrylates having (meth) acryloyl groups at both ends can be obtained, for example, by using a (meth) acrylic compound having a hydroxyl group in addition to the diol component in the polymerization of polyurethane. From the viewpoint of controlling the chain length (molecular weight) of the urethane-based segment, diol and diisocyanate are reacted so as to have an excess of isocyanate to synthesize an isocyanate-terminated polyurethane, and then a (meth) acrylic compound having a hydroxyl group is added. Therefore, it is preferable to react the terminal isocyanate group of polyurethane with the hydroxyl group of the (meth) acrylic compound.

By reacting the polyhydric alcohol with the polyisocyanate compound so that the polyisocyanate compound becomes excessive, a urethane chain having an isocyanate group at the terminal can be obtained. In order to obtain an isocyanate-terminated polyurethane, a diol component and a diisocyanate component are used so that the NCO / OH (equivalent ratio) is preferably 1.1 to 2.0, more preferably 1.15 to 1.5. do it. The diisocyanate component may be added after the diol component and the diisocyanate component are mixed in substantially equal amounts and reacted.

Examples of the (meth) acrylic compound having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyhexyl (meth) acrylate, hydroxymethylacrylamide, and hydroxyethyl. Examples include acrylamide.

As urethane (meth) acrylate, commercially available products sold by Arakawa Chemical Industry, Shin-Nakamura Chemical Industry, Toa Synthetic, Kyoeisha Chemical, Nippon Kayaku, Nippon Synthetic Chemical Industry, Negami Industry, Daicel Ornex, etc. are used. May be good. The weight average molecular weight of the urethane (meth) acrylate is preferably 3000 to 50000, more preferably 4000 to 40,000, still more preferably 5000 to 30000.

The glass transition temperature of the urethane (meth) acrylate is preferably 0 ° C. or lower, more preferably −10 ° C. or lower, further preferably −30 ° C. or lower, and particularly preferably −40 ° C. or lower. By using a low Tg urethane acrylate, a pressure-sensitive adhesive having excellent low-temperature adhesive strength can be obtained even when a crosslinked structure is introduced by a urethane-based segment to enhance the cohesive force of the base polymer. The lower limit of the glass transition temperature of urethane (meth) acrylate is not particularly limited, but from the viewpoint of obtaining a pressure-sensitive adhesive having excellent high-temperature holding power, -100 ° C or higher is preferable, -80 ° C or higher is more preferable, and -60 ° C or higher is preferable. More preferred.

When using a polyfunctional urethane (meth) acrylate such as urethane di (meth) acrylate to introduce a crosslinked structure with a urethane-based segment into an acrylic-based segment, the glass transition temperature of the urethane-based segment of the base polymer is urethane (meth). ) Approximately equal to the glass transition temperature of acrylate.

<Preparation of base polymer>
The polymer having an acrylic segment and a urethane segment can be polymerized by various known methods. Acrylic is used by using a polyfunctional urethane (meth) acrylate such as urethane di (meth) acrylate as a constituent component of the urethane-based segment, and by copolymerizing the monomer component for constituting the acrylic-based segment and the urethane (meth) acrylate. An acrylic polymer having a crosslinked structure formed by a urethane segment introduced into the system segment can be obtained.

As described above, in order to increase the cohesive force by introducing the crosslinked structure and suppress the tensile white turbidity of the pressure-sensitive adhesive sheet, the content of the urethane-based segment in the base polymer is 3 to 3 to 100 parts by weight of the acrylic-based segment. 30 parts by weight is preferable. Therefore, the amount of urethane (meth) acrylate used at the time of preparing the base polymer is preferably 3 to 30 parts by weight with respect to 100 parts by weight of the monomer component for forming the acrylic segment.

As the content of the urethane-based segment increases, the adhesive sheet tends to become turbid in tension. In particular, when the content of urethane components other than polyether urethane is large, tensile cloudiness is likely to occur. Therefore, the content of the urethane component other than the polyether urethane in the base polymer is preferably 7 parts by weight or less, more preferably 5 parts by weight or less, and further preferably 4 parts by weight or less with respect to 100 parts by weight of the acrylic segment. The content of the polyether urethane component in the base polymer is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, based on 100 parts by weight of the acrylic segment.

As described above, the range of the amount of the urethane-based segment that can suppress the tensile white turbidity of the pressure-sensitive adhesive sheet differs depending on the combination of the acrylic-based segment and the urethane-based segment.

When the main monomer of the acrylic segment is a (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms, the compatibility with the urethane segment is high, and tensile white turbidity tends to be suppressed. The content of the urethane-based segment in the base polymer is preferably 3 to 30 parts by weight, more preferably 5 to 25 parts by weight, based on 100 parts by weight of the acrylic segment. The content of the urethane-based segment other than the polyether urethane in the base polymer is preferably 15 parts by weight or less, more preferably 12 parts by weight or less, still more preferably 10 parts by weight or less, based on 100 parts by weight of the acrylic segment. The content of the polyether urethane segment in the base polymer is preferably 3 to 30 parts by weight, more preferably 4 to 25 parts by weight, still more preferably 5 to 20 parts by weight, based on 100 parts by weight of the acrylic segment.

When the main monomer of the acrylic segment is a (meth) acrylic acid alkyl ester having a chain alkyl group having 7 to 10 carbon atoms, the (meth) acrylic acid alkyl ester having a chain alkyl group having 6 or less carbon atoms is used. Tension white turbidity of the pressure-sensitive adhesive sheet is more likely to occur than when it is the main monomer. Therefore, the content of the urethane-based segment in the base polymer is preferably 3 to 20 parts by weight, more preferably 5 to 15 parts by weight, based on 100 parts by weight of the acrylic segment. The content of the urethane-based segment other than the polyether urethane in the base polymer is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, still more preferably 1 part by weight or less, based on 100 parts by weight of the acrylic segment. The content of the polyether urethane segment in the base polymer is preferably 3 to 20 parts by weight, more preferably 4 to 15 parts by weight, still more preferably 5 to 10 parts by weight, based on 100 parts by weight of the acrylic segment.

When urethane (meth) acrylate is used as a constituent component of the urethane-based segment, the type and amount of urethane (meth) acrylate may be adjusted so that the amount of the urethane-based segment is within the above range.

Examples of the polymerization method of the base polymer include solution polymerization, photopolymerization, bulk polymerization, emulsion polymerization and the like. Since the reaction efficiency of radical polymerization is high, the solution polymerization method or photopolymerization is preferable. Ethyl acetate, toluene and the like are used as the solvent for solution polymerization.

Depending on the type of polymerization reaction, a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator may be used. Examples of the photopolymerization initiator include a benzoin ether-based photopolymerization initiator, an acetophenone-based photopolymerization initiator, an α-ketol-based photopolymerization initiator, an aromatic sulfonyl chloride-based photopolymerization initiator, and a photoactive oxime-based photopolymerization initiator. Benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, and the like can be used. .. Examples of the thermal polymerization initiator include an azo-based initiator, a peroxide-based initiator, a redox-based initiator in which a peroxide and a reducing agent are combined (for example, a combination of a persulfate and sodium hydrogen sulfite, and a peroxide). A combination of sodium ascorbate, etc.) can be used.

At the time of polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder) or the like may be used for the purpose of adjusting the molecular weight. Examples of the chain transfer agent include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Examples thereof include α-methylstyrene dimer.

In the preparation of the base polymer, the total amount of the monomer components constituting the acrylic segment and the constituent components of the urethane segment (for example, urethane (meth) acrylate) is reacted at once according to the bonding mode of the acrylic segment and the urethane segment. It may be allowed to be allowed to be polymerized, or the polymerization may be carried out in multiple stages. For example, in the case of obtaining a polymer in which a crosslinked structure by a urethane-based segment is introduced into an acrylic-based segment by multi-step polymerization, a monofunctional monomer constituting the acrylic-based segment is polymerized to form a prepolymer composition (). Prepolymerization), a method of adding a polyfunctional compound such as urethane di (meth) acrylate to the syrup of the prepolymer composition to polymerize (post-polymerize) the prepolymer composition and the polyfunctional monomer is preferable. The prepolymer composition is a partial polymer containing a polymer having a low degree of polymerization and an unreacted monomer.

By prepolymerizing the constituent components of the acrylic polymer, branch points (crosslinking points) due to a polyfunctional compound such as urethane di (meth) acrylate can be uniformly introduced into the acrylic segment. Further, after applying a mixture (adhesive composition) of a low molecular weight polymer or a partial polymer and an unpolymerized monomer component on a base material, post-polymerization is performed on the base material to form a pressure-sensitive adhesive sheet. You can also.

Since a low polymerization degree composition such as a prepolymer composition has low viscosity and excellent coatability, a method of applying a pressure-sensitive adhesive composition which is a mixture of a prepolymer composition and a polyfunctional compound and then performing post-polymerization on a substrate. According to the above, the productivity of the pressure-sensitive adhesive sheet can be improved and the thickness of the pressure-sensitive adhesive sheet can be made uniform.

The prepolymer composition is prepared, for example, by partially polymerizing (prepolymerizing) a composition (referred to as "composition for forming a prepolymer") in which a monomer component constituting an acrylic segment and a polymerization initiator are mixed. can. The composition for forming a prepolymer may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, a part of the polyfunctional compound which is a raw material of the polymer may be contained in the composition for forming a prepolymer, and the prepolymer may be subjected to post-polymerization by adding the remainder of the polyfunctional compound after the polymerization.

The composition for forming a prepolymer may contain a chain transfer agent or the like, if necessary, in addition to the monomer and the polymerization initiator. The method for polymerizing the prepolymer is not particularly limited, but photopolymerization is preferable because the molecular weight (polymerization rate) of the prepolymer can be easily adjusted. The polymerization initiator and chain transfer agent used for the prepolymerization are not particularly limited, and for example, the above-mentioned photopolymerization initiator and chain transfer agent can be used.

The polymerization rate of the prepolymer is not particularly limited, but is preferably 3 to 50% by weight, more preferably 5 to 40% by weight, from the viewpoint of obtaining a viscosity suitable for coating on a substrate. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity and irradiation time of active light such as UV light, and the like. The polymerization rate of the prepolymer is calculated by the following formula from the weight before and after heating (drying) when the prepolymer composition is heated at 130 ° C. for 3 hours. When the prepolymerization is carried out by solution polymerization, the polymerization rate is calculated by subtracting the amount of the solvent from the total weight of the prepolymer composition as the weight before drying in the following formula.
Polymerization rate (%) of prepolymer = weight after drying / weight before drying x 100

The prepolymer composition is mixed with polyfunctional urethane (meth) acrylate, and if necessary, the rest of the monomer components constituting the acrylic segment, a polymerization initiator, a chain transfer agent, other additives, and the like, and cured. By performing post-polymerization after preparing the adhesive pressure-sensitive adhesive composition, a base polymer in which a crosslinked structure of a urethane-based segment is introduced into an acrylic-based segment can be obtained.

The polymerization initiator and chain transfer agent used for post-polymerization are not particularly limited, and for example, the above-mentioned photopolymerization initiator and chain transfer agent can be used. If the polymerization initiator during the prepolymerization remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for post-polymerization can be omitted.

The polymerization method of the post-polymerization is not particularly limited, and may be the same as or different from the polymerization method of the prepolymer. When the prepolymer is polymerized by photopolymerization, it is preferable that the post-polymerization is also carried out by photopolymerization. In particular, photopolymerization is suitable for preparing a solvent-free pressure-sensitive adhesive composition that contains substantially no solvent. The polymerization rate of the reaction product after the post-polymerization is preferably 95% or more, more preferably 97% or more, still more preferably 99% or more.

Since the base polymer after post-polymerization has a large molecular weight and a high viscosity, it may be difficult to apply it to a substrate. Therefore, in the formation of the pressure-sensitive adhesive sheet, a curable pressure-sensitive adhesive composition containing a prepolymer composition and a urethane (meth) acrylate is prepared, the pressure-sensitive adhesive composition is applied in a layered manner on a substrate, and then post-polymerization is performed. Is preferable.

As described above, the curable pressure-sensitive adhesive composition contains, in addition to the prepolymer composition and urethane (meth) acrylate, the rest of the monomer components constituting the acrylic segment, the polymerization initiator, the chain transfer agent and the like. May be good. The curable pressure-sensitive adhesive composition may contain a polymer other than the base polymer, an oligomer, various additives and the like.

(Oligomer)
The curable pressure-sensitive adhesive composition and the cured pressure-sensitive adhesive may contain various oligomers for the purpose of adjusting the adhesive strength of the pressure-sensitive adhesive sheet, adjusting the viscosity, and the like. As the oligomer, for example, one having a weight average molecular weight of about 1000 to 30,000 is used. As the oligomer, an acrylic oligomer is preferable because it has excellent compatibility with an acrylic base polymer.

The acrylic oligomer contains a (meth) acrylic acid alkyl ester as a main constituent monomer component. Among them, (meth) acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth) acrylate) and (meth) acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl) as constituent monomer components. Those containing (meth) acrylate) are preferable. Specific examples of the chain alkyl (meth) acrylate and the alicyclic alkyl (meth) acrylate are as exemplified above as the constituent monomers of the acrylic segment.

The glass transition temperature of the acrylic oligomer is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and even more preferably 40 ° C. or higher. By using a low Tg base polymer introduced with a crosslinked structure of urethane-based segments in combination with a high Tg acrylic oligomer, the high-temperature holding power of the pressure-sensitive adhesive tends to be improved. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is generally 200 ° C. or lower, preferably 180 ° C. or lower, and more preferably 160 ° C. or lower. The glass transition temperature of the acrylic oligomer is calculated by the above-mentioned Fox formula.

Among the exemplified (meth) acrylic acid alkyl esters, the chain alkyl (meth) acrylate is preferably methyl methacrylate because it has a high glass transition temperature and is excellent in compatibility with the base polymer. As the alicyclic alkyl (meth) acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer contains one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate as constituent monomer components, and methyl methacrylate. Is preferable.

The amount of the alicyclic alkyl (meth) acrylate is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, still more preferably 30 to 70% by weight, based on the total amount of the monomer components constituting the acrylic oligomer. The amount of the chain alkyl (meth) acrylate with respect to the total amount of the monomer components constituting the acrylic oligomer is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, still more preferably 30 to 70% by weight.

The weight average molecular weight of the acrylic oligomer is preferably 1000 to 30,000, more preferably 1500 to 10000, and even more preferably 2000 to 8000. By using an acrylic oligomer having a molecular weight in the above range, the adhesive strength of the pressure-sensitive adhesive and the holding characteristics at high temperatures tend to be improved.

The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components by various polymerization methods. Various polymerization initiators may be used in the polymerization of the acrylic oligomer. Further, a chain transfer agent may be used for the purpose of adjusting the molecular weight.

When the pressure-sensitive adhesive composition contains an oligomer component such as an acrylic oligomer, the content thereof is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the above base polymer. 2 to 10 parts by weight is more preferable. When the content of the oligomer in the pressure-sensitive adhesive composition is in the above range, the adhesiveness at high temperature and the holding power at high temperature tend to be improved.

(Silane coupling agent)
A silane coupling agent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the adhesive strength. When a silane coupling agent is added to the pressure-sensitive adhesive composition, the amount of the silane coupling agent added is usually about 0.01 to 5.0 parts by weight with respect to 100 parts by weight of the base polymer, and 0.03 to 2.0 parts by weight. It is preferably about.

(Crosslinking agent)
The base polymer may have a crosslinked structure other than the above-mentioned polyfunctional compound, if necessary. By including a cross-linking agent in the pressure-sensitive adhesive composition, a cross-linked structure can be introduced into the base polymer. Examples of the cross-linking agent include compounds that react with functional groups such as hydroxyl groups and carboxy groups contained in the polymer. Specific examples of the cross-linking agent include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, carbodiimide-based cross-linking agents, metal chelate-based cross-linking agents and the like.

As described above, if the amount of the crosslinked structure introduced by other than the urethane-based segment increases, the low-temperature adhesive force of the adhesive may decrease. Therefore, the amount of the crosslinked agent used is 3% by weight based on 100 parts by weight of the base polymer. It is preferably parts or less, more preferably 2 parts by weight or less, and even more preferably 1 part by weight or less.

(Other additives)
In addition to the above-exemplified components, the pressure-sensitive adhesive composition includes a pressure-sensitive adhesive, a plasticizer, a softening agent, a deterioration inhibitor, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, an antistatic agent, and the like. May contain the additive of.

<Preparation of adhesive composition>
A pressure-sensitive adhesive composition can be prepared by mixing each of the above components and, if necessary, a solvent. When forming a pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition preferably has a viscosity suitable for coating on a substrate (for example, about 0.5 to 20 Pa · s). When the pressure-sensitive adhesive composition is a solution, the viscosity of the composition can be adjusted within an appropriate range by adjusting the molecular weight of the polymer, the solid content concentration of the solution, and the like.

As described above, in the formation of the pressure-sensitive adhesive sheet, a curable pressure-sensitive adhesive composition containing a prepolymer composition and a urethane (meth) acrylate is prepared, and the pressure-sensitive adhesive composition is applied in a layer on the substrate, and then afterwards. It is preferable to carry out polymerization. By adjusting the polymerization rate of the prepolymer, the amount of urethane (meth) acrylate added, the amount of oligomer added, and the like, the viscosity of the pressure-sensitive adhesive composition can be adjusted within an appropriate range. As the pressure-sensitive adhesive composition, a thickening additive or the like may be used for the purpose of adjusting the viscosity or the like.

[Adhesive sheet]
A pressure-sensitive adhesive sheet is formed by molding the above-mentioned pressure-sensitive adhesive composition into a sheet shape. When a curable pressure-sensitive adhesive composition is used, the pressure-sensitive adhesive composition is applied onto the base material, and then post-polymerization is performed on the base material by heating, irradiation with active light, or the like, thereby forming a urethane-based segment into an acrylic-based segment. A pressure-sensitive adhesive sheet made of a pressure-sensitive adhesive having a cross-linked structure introduced by the above can be obtained.

The thickness of the adhesive sheet is not particularly limited and may be appropriately set according to the type of adherend and the like. The thickness of the pressure-sensitive adhesive sheet is, for example, about 5 to 500 μm. From the viewpoint of achieving both adhesiveness to the adherend and uniformity of thickness, the thickness of the pressure-sensitive adhesive sheet is preferably 10 to 400 μm, more preferably 15 to 350 μm.

As a method of applying the pressure-sensitive adhesive composition on the substrate, roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat , Lip coat, die coater and the like are used.

When the pressure-sensitive adhesive composition is a solution, it is preferable to dry the solution after applying the pressure-sensitive adhesive composition. As a drying method, heat drying is preferable. The heating and drying temperature is preferably 40 ° C. to 200 ° C., more preferably 50 ° C. to 180 ° C., and particularly preferably 70 ° C. to 170 ° C. As the drying time, an appropriate time may be adopted as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

When the pressure-sensitive adhesive composition is photo-curable, the pressure-sensitive adhesive composition after being applied onto the substrate is photo-cured by irradiating the pressure-sensitive adhesive composition with an active light beam. When photo-curing, a cover sheet may be attached to the surface of the coating layer, and the pressure-sensitive adhesive composition may be sandwiched between the two sheets and irradiated with active light to prevent polymerization inhibition due to oxygen. preferable.

The active light may be selected according to the type of the polymerizable component such as a monomer or urethane (meth) acrylate, the type of the photopolymerization initiator, and the like, and generally, ultraviolet light and / or visible light having a short wavelength is used. .. The integrated light amount of the irradiation light is preferably about 100 to 5000 mJ / cm ² . The light source for light irradiation is not particularly limited as long as the photopolymerization initiator contained in the pressure-sensitive adhesive composition can irradiate light in a sensitive wavelength range, and is an LED light source, a high-pressure mercury lamp, and ultra-high pressure mercury. Lamps, metal halide lamps, xenon lamps and the like are preferably used.

Any suitable base material is used as the base material and the cover sheet used for forming the pressure-sensitive adhesive sheet. The base material and the cover sheet may be a release film having a release layer on the contact surface with the adhesive sheet.

FIG. 1 is a cross-sectional view showing a configuration example of a pressure-sensitive adhesive sheet with a release film, in which release films 1 and 2 are temporarily attached to both sides of the pressure-sensitive adhesive sheet 5. The release films 1 and 2 are used for the purpose of protecting the surface of the adhesive sheet until the adhesive sheet 5 is used for bonding to the adherend. As the release films 1 and 2, those having the release layers 11 and 21 on the surface of the film base materials 10 and 20 (the adhesive surface of the adhesive sheet 5) are preferably used.

As the film base material of the release film, a film made of various resin materials is used. Examples of the resin material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and (meth) acrylic resins. Examples thereof include polyvinyl chloride-based resin, polyvinylidene chloride-based resin, polystyrene-based resin, polyvinyl alcohol-based resin, polyarylate-based resin, and polyphenylene sulfide-based resin. Among these, polyester resins such as polyethylene terephthalate are particularly preferable.

The thickness of the film substrate is preferably 10 to 200 μm, more preferably 25 to 150 μm. When the release films 1 and 2 are provided on both sides of the pressure-sensitive adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. When the pressure-sensitive adhesive composition is applied using the release film as a base material and then the pressure-sensitive adhesive composition is irradiated with active light through the release film for photocuring, the release film provided on the light-irradiated surface is used. It is preferably transparent.

Examples of the material of the release layer include a silicone-based release agent, a fluorine-based release agent, a long-chain alkyl-based release agent, a fatty acid amide-based release agent, and the like. The thickness of the release layer is generally about 10 to 2000 nm. By changing the type of release agent and the thickness of the release layer, the peeling force of the release films 1 and 2 from the pressure-sensitive adhesive layer 5 can be adjusted.

The peeling force when peeling the first release film 1 from the pressure-sensitive adhesive sheet 5 and the peeling force when peeling the second release film 2 from the pressure-sensitive adhesive sheet 5 may be the same or different. When the peeling force of both is different, the release film 2 having a relatively small peeling force is peeled off from the adhesive sheet 5 first and bonded to the first adherend, and the peeling force is relatively large. It is excellent in workability when the release film 1 is peeled off and bonded to the second adherend.

As the release films 1 and 2, the base material or cover sheet used for forming the pressure-sensitive adhesive sheet (application of the pressure-sensitive adhesive composition) may be used as it is, and after the pressure-sensitive adhesive sheet is formed, it is replaced with another release film. May be done.

<Physical characteristics of adhesive sheet>
Since the pressure-sensitive adhesive sheet of the present invention contains a polymer containing an acrylic segment and a urethane-based segment as a base polymer constituting the pressure-sensitive adhesive, it is possible to achieve both adhesiveness at low temperature and adhesive holding power at high temperature. Further, by adjusting the type and content of the urethane-based segment, the white turbidity of the pressure-sensitive adhesive sheet due to deformation such as tension is suppressed.

From the viewpoint of increasing the high temperature holding power, the shear storage elastic modulus G'25 ° C. at a temperature of ₂₅ ° C. of the pressure-sensitive adhesive sheet is preferably 0.05 MPa or more, more preferably 0.10 MPa or more, further preferably 0.13 MPa or more, and 0. 15 MPa or more is particularly preferable. The shear storage elastic modulus G'80 ° C. at a temperature of the pressure-sensitive adhesive sheet at 80 ° _C. is preferably 0.01 MPa or more, more preferably 0.03 MPa or more, still more preferably 0.05 MPa or more.

From the viewpoint of adhesive holding power, the upper limits of _{G'25 ° C} and G'80 ° C are not particularly limited. In order to give the pressure-sensitive adhesive sheet an appropriate viscosity and wettability, G'25 _{° C.} is preferably 3 MPa or less, more preferably 1 MPa or less, still more preferably 0.5 MPa or less. From the same viewpoint, G'80 _{° C.} is preferably 0.3 MPa or less, more preferably 0.25 MPa or less.

From the viewpoint of achieving both high-temperature holding power and low-temperature adhesiveness, the product of the glass transition temperature Tg (° C) of the pressure-sensitive adhesive sheet and the shear storage elastic modulus G'25 _{° C} (MPa) at a temperature of 25 ° C is -1 or less. It is preferable, -3 or less is more preferable, and -4 or less is further preferable.

<Use of adhesive sheet>
The adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The type of the adherend is not particularly limited, and examples thereof include various resin materials, glass, and metal. In particular, the pressure-sensitive adhesive sheet of the present invention is suitable for applications where transparency is required because tensile cloudiness is suppressed. That is, the pressure-sensitive adhesive sheet of the present invention can be suitably used for bonding transparent members to each other or for bonding transparent members and opaque members.

FIG. 2 is a cross-sectional view of the adhesive film in which the transparent film 3 is fixed to one surface of the adhesive sheet 5. In the adhesive film 101 shown in FIG. 2, the release film 1 is temporarily attached to the other surface of the adhesive sheet 5.

The visible light transmittance of the transparent film 3 is preferably 80% or more, more preferably 90% or more. The thickness of the transparent film 3 is not particularly limited, but is preferably about 5 to 300 μm, more preferably 10 to 250 μm, and even more preferably 20 to 200 μm from the viewpoint of workability such as strength and handleability, and thin layer property.

Examples of the resin material constituting the transparent film 3 include a thermoplastic resin having excellent transparency, mechanical strength, and thermal stability. Specific examples of such thermoplastic resins include cellulose-based resins such as triacetyl cellulose, polyester-based resins, polyether sulfone-based resins, polysulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, and polyolefin-based resins. , (Meta) acrylic resin, cyclic polyolefin resin (norbornen resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, and mixtures thereof.

In the formation of the adhesive sheet with a substrate shown in FIG. 2, for example, one of the release films 2 is peeled off from the adhesive sheet with a release film shown in FIG. 1, and the exposed surface of the adhesive sheet 5 is attached to the transparent film 3. You just have to match. The transparent film 3 may be used as either the base material or the cover sheet used when forming (applying) the adhesive sheet.

After peeling off the release film 1 temporarily attached to the surface of the adhesive sheet 5, the adhesive film can be attached to the surface of the adherend by attaching the exposed surface of the adhesive sheet 5 to the adherend. can.

The adhesive film is used to protect the surface of a member that is deformed during use. For example, adhesive films can be used to protect the surface of membrane switches. The membrane switch has characters or the like printed on the surface sheet for the purpose of identifying the switch. If the printed surface of the front sheet is exposed, the printing may become lighter with use and it may be difficult to identify characters and the like. Therefore, a protective sheet is provided on the surface of the printed surface.

When the switch from the top of the adhesive film provided as the protective sheet is pressed, the adhesive sheet is deformed. Since the adhesive sheet of the present invention is unlikely to cause white turbidity due to deformation, transparency is maintained even when the switch is repeatedly pressed, and the visibility of printed characters on the surface sheet can be maintained.

Since the pressure-sensitive adhesive sheet of the present invention has excellent transparency, low-temperature adhesiveness, and high-temperature holding power, it can be applied not only to membrane switches but also to bonding various members.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Preparation of acrylic oligomer]
60 parts by weight of dicyclopentanyl methacrylate (DCPMA), 40 parts by weight of methyl methacrylate (MMA), 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent are mixed and nitrogen is mixed. The mixture was stirred at 70 ° C. for 1 hour in an atmosphere. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, and the mixture was reacted at 70 ° C. for 2 hours and then heated to 80 ° C. for 2 hours. It was reacted. Then, the reaction solution was heated to 130 ° C., and toluene, the chain transfer agent and the unreacted monomer were dried and removed to obtain a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer was 5100.

[Example 1]
(Polymerization of prepolymer)
As a monomer component for prepolymer formation, 52.8 parts by weight of butyl acrylate (BA), 10.9 parts by weight of cyclohexyl acrylate (CHA), 9.7 parts by weight of N-vinyl-2-pyrrolidone (NVP), acrylic acid. 14.8 parts by weight of 4-hydroxybutyl (4HBA) and 11.8 parts by weight of isostearyl acrylate (ISTA), and a photopolymerization initiator (BASF "Irgacure 184": 0.035 parts by weight, and BASF " Irgacure 651 ”: After compounding 0.035 parts by weight, polymerize by irradiating with ultraviolet rays until the viscosity (BH viscosity meter No. 5 rotor, 10 rpm, measurement temperature 30 ° C.) reaches about 20 Pa · s, and prepolymer. A composition (polymerization rate; about 9%) was obtained.

(Preparation of photocurable pressure-sensitive adhesive composition)
In the above prepolymer composition, as urethane (meth) acrylate, terminal acrylic modified polyether urethane ("UV-3300B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.): 7 parts by weight, and terminal acrylic modified polyester urethane (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) "UV-3010B"): 3 parts by weight, the above acrylic oligomer: 5 parts by weight, as a photopolymerization initiator, Irgacure 184: 0.05 parts by weight, and Irgacure 651: 0.57 parts by weight, as a chain transfer agent. After adding α-methylstyrene dimer (“Nofmer MSD” manufactured by Nichiyu): 0.2 parts by weight and “KBM403” manufactured by Shin-Etsu Chemical Co., Ltd. as a silane coupling agent): 0.3 parts by weight, these are uniformly added. To prepare a pressure-sensitive adhesive composition.

(Making an adhesive sheet)
The above photocurable pressure-sensitive adhesive composition is applied onto a polyethylene terephthalate (PET) film ("MRF50" manufactured by Mitsubishi Chemical Corporation) having a thickness of 50 μm provided with a silicone-based release layer on the surface so as to have a thickness of 150 μm. A coating layer was formed, and a PET film having a thickness of 38 μm (“MRF38” manufactured by Mitsubishi Chemical Corporation) having one side treated with silicone peeling was bonded onto the coating layer. The laminated body was photocured by irradiating this laminate with ultraviolet rays for 300 seconds from the PET film side having a thickness of 38 μm with a black light whose position was adjusted so that the irradiation intensity on the irradiation surface directly under the lamp was 5 mW / cm ² . Then, it was dried in a dryer at 90 ° C. for 2 minutes to volatilize the residual monomer, and a pressure-sensitive adhesive sheet having a thickness of 150 μm was obtained.

[Examples 2 to 6, Comparative Examples 1 to 5]
Table shows the types and amounts of the charged monomer composition in the polymerization of the prepolymer, the polyfunctional compound (urethane acrylate and / or the polyfunctional acrylate) to be added to the pressure-sensitive adhesive composition, the acrylic oligomer, the photopolymerization initiator, and the chain transfer agent. It was changed as shown in 1. Other than that, a photocurable pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and coating on a substrate, photo-curing and removal of residual monomers were carried out to obtain a pressure-sensitive adhesive sheet.

In Table 1, each component is described by the following abbreviations.
<Acrylic monomer>
BA: Butyl acrylate 2HEA: 2-Ethylhexyl acrylate CHA: Cyclohexyl acrylate NVP: N-vinyl-2-pyrrolidone 4HBA: 4-Hydroxybutyl acrylate 2HEA: 2-Hydroxyethyl acrylate ISTA: Isostearyl acrylate 2MEA: 2-methoxyethyl acrylate

<Urethane acrylate>
UN-350: "Art Resin UN-350" manufactured by Negami Kogyo (polyester urethane diacrylate with a weight average molecular weight of about 12500 and a glass transition temperature of -57 ° C).
UV-3300B: "UV-3300B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (polyether urethane diacrylate with a weight average molecular weight of about 12000 and a glass transition temperature of -30 ° C).
UV-3010B: "UV-3010B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (polyester urethane diacrylate with a weight average molecular weight of about 11000)
UV-3000B: "UV-3000B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (polyester urethane diacrylate with a weight average molecular weight of about 18,000 and a glass transition temperature of -39 ° C)
<Polyfunctional acrylate>
HDDA: Hexanediol diacrylate <photopolymerization initiator>
Irg6511: Irgacure 651 (2,2-dimethoxy-1,2-diphenylethane-1-one)
Irg184: Irgacure 184 (1-hydroxy-cyclohexyl-phenyl-ketone)

[evaluation]
<Weight average molecular weight>
The weight average molecular weight (Mw) of the acrylic oligomer and the urethane (meth) acrylate was measured by a GPC (gel permeation chromatography) apparatus (product name "HLC-8120 GPC") manufactured by Tosoh. As the measurement sample, a filtrate obtained by dissolving the base polymer in tetrahydrofuran to prepare a 0.1% by weight solution and filtering it with a 0.45 μm membrane filter was used. The measurement conditions of GPC are as follows.
(Measurement condition)
Column: Made by Tosoh, G7000HXL + GMHXL + GMHXL
Column size: 7.8 mmφ x 30 cm each (total column length: 90 cm)
Column temperature: 40 ° C, flow rate: 0.8 mL / min
Injection volume: 100 μL
Eluent: Tetrahydrofuran Detector: Differential Refractometer (RI)
Standard sample: Polystyrene

<Storage modulus of adhesive sheet and glass transition temperature>
A measurement sample was obtained by laminating 10 adhesive sheets to a thickness of about 1.5 mm. Dynamic viscoelasticity measurement was performed under the following conditions using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific.
(Measurement condition)
Deformation mode: Torsion measurement frequency: 1Hz
Temperature rise rate: 5 ° C / min Shape: Parallel plate 7.9 mmφ

The shear storage modulus was determined by reading the storage modulus G'at each temperature from the measurement results. The temperature at which the loss tangent (tan δ) was maximized (peak top temperature) was defined as the glass transition temperature of the pressure-sensitive adhesive sheet.

<Tension cloudiness>
The adhesive sheet is cut into a width of 20 mm and a length of 50 mm, one of the release films is peeled off, and a PET film having a thickness of 75 μm is applied to both ends in the length direction so as to have a contact area of 20 mm in width and 15 mm in length. I pasted them together. After peeling off the other release film of the pressure-sensitive adhesive sheet, the PET films bonded to both ends were pulled, and the pressure-sensitive adhesive sheet was stretched so as to be doubled in the length direction (the distance between the PET films at both ends was 60 mm). The adhesive sheet after tension was visually confirmed, and the transparent one was OK, and the white turbidity was NG.
[Evaluation results]
Table 1 shows the composition and evaluation results of each pressure-sensitive adhesive sheet.

None of the pressure-sensitive adhesive sheets of Examples 1 to 6 became cloudy even after the tensile test. In Comparative Examples 1 to 4, which contained only polyester urethane chains as urethane-based segments, cloudiness was observed. Further, white turbidity was also observed in Comparative Example 5 containing 40 parts by weight of urethane-based segment with respect to 100 parts by weight of acrylic-based segment.

White turbidity was observed in Comparative Examples 2 to 4 containing 20 parts by weight of the urethane-based segment with respect to 100 parts by weight of the acrylic-based segment, whereas no cloudiness was observed in Example 3. Comparing Example 3 and Comparative Example 1, both have a urethane-based segment (polyester urethane segment) containing 10 parts by weight other than the polyether urethane-based segment, and Example 3 has a urethane-based segment. Although the content of the urethane was high, no cloudiness was observed in Example 3 and cloudiness was observed in Comparative Example 1. It is considered that this is because the acrylic segment has excellent compatibility with the urethane segment in Example 3 in which the main monomer is butyl acrylate.

From the above results, it can be seen that a pressure-sensitive adhesive sheet in which tensile white turbidity is suppressed can be obtained by adjusting the composition of the acrylic segment and the type and amount of the urethane segment bonded to the acrylic segment.

5 Adhesive sheet 1, 2, Release film 10, 20 Film base material 11, 21, Release layer 3 Transparent film

Claims (11)

An adhesive sheet in which an adhesive containing an acrylic base polymer is formed in the form of a sheet.
The base polymer contains an acrylic segment and a urethane segment, and the content of the urethane segment with respect to 100 parts by weight of the acrylic segment is 3 to 30 parts by weight.
The urethane-based segment contains one or more urethane chains selected from the group consisting of polyether urethane and polyester urethane, and the content of urethane-based segments other than the polyether urethane-based segment with respect to 100 parts by weight of the acrylic-based segment. Is less than 15 parts by weight,
Further, it contains an acrylic oligomer having a weight average molecular weight of 1000 to 30,000, and contains
An adhesive sheet having an acrylic oligomer content of 0.5 to 20 parts by weight with respect to 100 parts by weight of the acrylic base polymer. The pressure-sensitive adhesive sheet according to claim 1, wherein the urethane-based segment has a weight average molecular weight of 3000 to 50,000. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the content of the polyether urethane-based segment is 3 parts by weight or more with respect to 100 parts by weight of the acrylic-based segment. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the acrylic-based base polymer is a cross-linked acrylic segment from the urethane-based segment. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, which contains 50% by weight or more of the acrylic base polymer. An adhesive film in which a transparent film is adhered to one surface of the adhesive sheet according to any one of claims 1 to 5. A method for producing a pressure-sensitive adhesive sheet, wherein a curable pressure-sensitive adhesive composition is applied in a layer on a substrate and the pressure-sensitive adhesive composition is cured.
The pressure-sensitive adhesive composition contains an acrylic monomer and / or a partial polymer thereof, a urethane (meth) acrylate, and an acrylic oligomer having a weight average molecular weight of 1000 to 30,000.
The content of the urethane (meth) acrylate in a total of 100 parts by weight of the acrylic monomer and its partial polymer is 3 to 30 parts by weight.
The urethane (meth) acrylate contains one or more urethane (meth) acrylates selected from the group consisting of polyether urethane (meth) acrylates and polyester urethane (meth) acrylates, and the acrylic monomer and its partial polymerization. The content of urethane (meth) acrylate other than polyether urethane (meth) acrylate in a total of 100 parts by weight of the product is 7 parts by weight or less.
Production of an adhesive sheet in which the content of the acrylic oligomer is 0.5 to 20 parts by weight based on 100 parts by weight of the total of the acrylic monomer and / or a partial polymer thereof and the urethane (meth) acrylate. Method. The method for producing an adhesive sheet according to claim 7, wherein the urethane (meth) acrylate has a weight average molecular weight of 3000 to 50,000. The pressure-sensitive adhesive composition contains a polyether urethane (meth) acrylate as the urethane (meth) acrylate.
The method for producing a pressure-sensitive adhesive sheet according to claim 7 or 8, wherein the pressure-sensitive adhesive sheet is contained in an amount of 3 parts by weight or more based on 100 parts by weight of a total of the acrylic monomer and its partial polymer. The method for producing a pressure-sensitive adhesive sheet according to any one of claims 7 to 9, wherein the pressure-sensitive adhesive composition further contains a photopolymerization initiator. The method for producing a pressure-sensitive adhesive sheet according to any one of claims 7 to 10, wherein the pressure-sensitive adhesive composition contains an acrylic monomer and a partial polymer thereof in a total amount of 50% by weight or more.

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