JP2015183179A - Adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive from which an adhesive layer having a low dielectric constant and favorable adhesive force with respect to a member having low polarity such as COP (cycloolefin polymer) can be formed, and an adhesive sheet.SOLUTION: The adhesive contains a polymer (A) obtained by polymerizing a monomer mixture that comprises 2-ethylhexyl acrylate, an alkyl (meth)acrylate (a) having a 4-9C branched alkyl group other than 2-ethylhexyl acrylate, and a monomer (b) having 4-10C aliphatic cyclic substituent. An adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz can be formed from the above adhesive.

Description

  The present invention relates to an adhesive.

  Due to dramatic advances in electronics in recent years, various flat panel displays (FPD) such as liquid crystal displays (LCD), plasma displays (PDP), rear projection displays (RPJ), EL displays, light emitting diode displays, etc. Widely used as a device. Such a display device usually has various films such as an antireflection film for preventing reflection from an external light source and a protective film (protection film) for preventing scratches on the surface of the display device. It is used. For example, a polarizing film or a retardation film is used for a liquid crystal cell member used in an LCD.

In addition to being used as a display device, the FPD is also used as an input device such as a touch panel. Generally, a protective film, an antireflection film, a transparent electrode film, and the like are used for the touch panel. These films are generally bonded together using an adhesive (also referred to as a pressure-sensitive adhesive).
There are various types of operating principles of the touch panel, such as a capacitive method, a resistive film method, an infrared method, etc. Among them, a capacitive touch panel is widely used because of its excellent practicality. This method operates by sensing a change in capacitance between the fingertip and the conductive film at that point when the fingertip touches the display surface.

  In addition, since electronic devices such as smartphones and tablet terminals are becoming more sophisticated without increasing their thickness, the components to be mounted are made smaller and thinner, but the thickness of the adhesive layer is also an exception. is not. However, if the thickness of the adhesive layer is reduced, the capacitive touch panel malfunctions when touching the display because the change in capacitance at the point touched by the fingertip affects the surroundings of the point. There was a problem that was likely to occur. And the malfunction has a tendency to increase in proportion to the dielectric constant height of the pressure-sensitive adhesive layer. Note that the dielectric constant is a constant specific to the substance that determines the capacitance, and the capacitance is proportional to the dielectric constant. The higher the dielectric constant of the substance, the more easily the capacitance value changes. . On the other hand, the lower the dielectric constant, the less the capacitance value changes. Therefore, a pressure-sensitive adhesive that can form a pressure-sensitive adhesive layer having a low dielectric constant and having a capacitance value that hardly depends on the thickness of the pressure-sensitive adhesive layer has been demanded. Moreover, the function which does not corrode the transparent conductive film of a touchscreen is also required.

  A touch panel display is mainly composed of a surface glass plate, a touch panel, and a liquid crystal module. Triacetyl cellulose (hereinafter referred to as TAC) used for a protective film for protecting a polarizer inside the liquid crystal module is optically distorted. In order to prevent and reduce the birefringence, replacement with a cycloolefin polymer (hereinafter referred to as COP) is in progress. However, COP has low adhesion to the pressure-sensitive adhesive sheet as compared with TAC, and good adhesive strength has not been obtained. Moreover, the adhesive force with respect to the transparent conductive film (for example, ITO film | membrane) of a touchscreen is also required naturally.

  Therefore, in Patent Document 1, a cyclic structure-containing monomer (25% by weight to 99.5% by weight), and a branched structure-containing (meth) acrylic monomer having a branched alkyl group having 3 to 18 carbon atoms at the ester terminal is 0.8%. A pressure-sensitive adhesive containing a (meth) acrylic polymer obtained by polymerizing a monomer component containing 5% by weight to 70% by weight is disclosed.

International Publication No. 2013/002184

  However, the conventional pressure-sensitive adhesive has a problem that adhesion to a low-polarity member such as COP is low.

  An object of the present invention is to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that can form a pressure-sensitive adhesive layer having a low dielectric constant and good adhesion to members having low polarity such as COP.

The pressure-sensitive adhesive of the present invention comprises 2-ethylhexyl acrylate, a (meth) acrylic acid alkyl ester (a) having a branched alkyl group having 4 to 9 carbon atoms other than 2-ethylhexyl acrylate, and an aliphatic group having 4 to 10 carbon atoms. Containing a polymer (A) obtained by polymerizing a monomer mixture containing a monomer (b) having a cyclic substituent,
An adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz can be formed.

  According to the present invention, when the monomer (b) having an aliphatic cyclic substituent is used to lower the dielectric constant, Tg is high and the adhesive strength tends to be suppressed. The combined use of an acrylate and an alkyl (meth) acrylate (a) having a branched alkyl group having 4 to 9 carbon atoms improved the wetting of the low-polarity member, and achieved both a low dielectric constant and good adhesive strength.

  The present invention can provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that can form a pressure-sensitive adhesive layer having a low dielectric constant and good adhesion to members having low polarity such as COP.

The typical sectional view of the sample for dielectric constant measurement.

  Before describing the present invention, the following terms will be explained. First, an adhesive sheet, an adhesive tape, and an adhesive film are synonymous. Next, the (meth) acrylic acid alkyl ester includes an acrylic acid alkyl ester and a methacrylic acid alkyl ester. The monomer means an ethylenically unsaturated monomer. Moreover, an adherend says the other party which affixes an adhesive sheet.

The pressure-sensitive adhesive of the present invention comprises 2-ethylhexyl acrylate, a (meth) acrylic acid alkyl ester (a) having a branched alkyl group having 4 to 9 carbon atoms other than 2-ethylhexyl acrylate, and an aliphatic group having 4 to 10 carbon atoms. Containing a polymer (A) obtained by polymerizing a monomer mixture containing a monomer (b) having a cyclic substituent,
An adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz can be formed.
The pressure-sensitive adhesive of the present invention is preferably used as a pressure-sensitive adhesive sheet by forming a pressure-sensitive adhesive layer by coating on a substrate or a peelable sheet.

In the present invention, the polymer (A) is composed of 2-ethylhexyl acrylate and (meth) acrylic acid alkyl ester (a) (hereinafter referred to as (meth) acrylic) having a branched alkyl group having 4 to 9 carbon atoms other than 2-ethylhexyl acrylate. And an acid alkyl ester (a)) and a monomer mixture containing a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms (hereinafter referred to as monomer (b)).
The use of 2-ethylhexyl acrylate and (meth) acrylic acid alkyl ester (a) improves the wetting of low-polarity members (low-polar adherends) by lowering the Tg while suppressing the increase in dielectric constant, and the adhesive strength is improved. In addition to the improvement, the steric hindrance effect due to the branched alkyl group suppresses the molecular motion of the polymer chain, and the adhesive layer is less likely to be electrically polarized. Yes.

Specifically, (meth) acrylic acid alkyl ester (a) is isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, 3-pentyl (meth) acrylate, 2-ethyl- 1-butyl (meth) acrylate, 2-heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, s-octyl (meth) acrylate, t-octyl (meth) acrylate, isononyl (meth) Examples include acrylate, s-nonyl (meth) acrylate, t-nonyl (meth) acrylate, and the like.
Of these, isooctyl acrylate and the like are preferable.

  The monomer (b) has an effect of lowering the dielectric constant of the pressure-sensitive adhesive layer. The reason is presumed to be due to the aliphatic cyclic substituent having large steric hindrance. The effect of lowering the dielectric constant is greater for the monomer (b) than 2-ethylhexyl acrylate and (meth) acrylic acid alkyl ester (a).

In the monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms, “having an aliphatic cyclic substituent having 4 to 10 carbon atoms” means carbon as an atom forming the ring of the aliphatic cyclic substituent. This means that 4 to 10 atoms are present. That is, the carbon atom contained in the group couple | bonded with the ring is excluded from the said count.
Specifically, for example, both “cyclohexyl group” and “3-methylcyclohexyl group” are defined as “aliphatic cyclic substituent having 6 carbon atoms” in the present invention.
In addition, atoms other than carbon atoms (so-called heteroatoms) may be present together with carbon atoms as atoms forming the ring, but these are of course excluded from the above counting.

The monomer (b) is, for example, cyclohexyl (meth) acrylate which is a monomer having a cyclohexyl ring, t-butylcyclohexyl (meth) acrylate, or trimethylcyclohexyl (meth) acrylate which is a derivative thereof;
Isobornyl (meth) acrylate having an isobornyl skeleton;
As a monomer having a heterocyclic ring, N- (meth) acryloyloxyethyl hexahydrophthalimide having a phthalimide skeleton, N- (meth) acryloyloxyethyl-3-methylhexahydrophthalimide, and (meth) acryloyl having a morpholine ring Examples include morpholine and tetrahydrofurfuryl (meth) acrylate having a tetrahydrofurfuryl ring.
Among these, isobornyl (meth) acrylate, (meth) acryloylmorpholine and N- (meth) acryloyloxyethylhexahydrophthalimide are preferable.

In addition to 2-ethylhexyl acrylate, (meth) acrylic acid alkyl ester (a), and monomer (b), other monomers can be used for the synthesis of polymer (A).
The other monomers include (meth) acrylic acid alkyl ester having an alkyl group having 1 to 3 carbon atoms, (meth) acrylic acid alkyl ester having an alkyl group having 10 or more carbon atoms, and linear alkyl having 4 to 9 carbon atoms. A (meth) acrylic acid alkyl ester having a group and a vinyl monomer are preferred.

Examples of the (meth) acrylic acid alkyl ester having an alkyl group having 1 to 3 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and the like.
Examples of the (meth) acrylic acid alkyl ester having an alkyl group having 10 or more carbon atoms include decyl (meth) acrylate, lauryl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate, (meth) Examples include stearyl acrylate.
Examples of the (meth) acrylic acid alkyl ester having a linear alkyl group having 4 to 9 carbon atoms include butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, Non- (meth) acrylic acid etc. are mentioned.

Examples of the vinyl monomer include amide group-containing monomers such as (meth) acrylamide, N-methylolacrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, N-vinylacetamide, N-vinylpyrrolidone;
Epoxy group-containing monomers such as glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, and allyl glycidyl ether;
Amino group-containing monomers such as aminomethyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate;
Nitrile group-containing monomers such as (meth) acrylonitrile;
Phosphate group-containing monomers such as 2- (meth) acryloyloxyethyl acid phosphate;
Hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate;
Polyalkylene glycol (meth) acrylates such as polyethylene glycol (meth) acrylate and polypropylene glycol (meth) acrylate;
Carboxyl group-containing monomers such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, β-carboxyethyl (meth) acrylate, and anhydrides thereof;
Isocyanate group-containing ethylenically unsaturated monomers such as (meth) acryloyloxyethyl isocyanate;
Fluorine-containing ethylenically unsaturated monomers such as 2,2,2-trifluoroethyl (meth) acrylate;
Alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and their alkylene oxide adducts;
Aryloxyalkyl (meth) acrylates such as phenoxyethyl (meth) acrylate and their alkylene oxide adducts;
Aromatic (meth) acrylates such as benzyl (meth) acrylate;
Aromatic vinyl monomers such as styrene and α-methylstyrene;
Vinyl ester monomers such as vinyl acetate and propyl acetate;
Examples include vinyl ether compounds and α-olefins.
Two or more kinds of other vinyl monomers can be used as appropriate as long as they are within the scope of solving the problems of the present invention.

  Of 100% by weight of the monomer mixture used for the synthesis of the polymer (A), it is preferable to use 40 to 70 parts by weight of 2-ethylhexyl acrylate, and more preferably 50 to 60 parts by weight.

  Of 100% by weight of the monomer mixture used for the synthesis of the polymer (A), the alkyl (meth) acrylate (a) is preferably used in an amount of 10 to 40 parts by weight, more preferably 20 to 30 parts by weight. If it exists in the range of 10-40 weight part, the adhesive force with respect to a low dielectric constant and a low-polarity adherend will improve.

  Of 100% by weight of the monomer mixture used for the synthesis of the polymer (A), the monomer (b) is preferably used in an amount of 5 to 30% by weight, more preferably 10 to 20% by weight. If it is in the range of 5 to 30% by weight, a low dielectric constant can be obtained.

    The polymer (A) can be obtained by a known method such as bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, or active energy ray polymerization. Among these, solution polymerization is preferred because the adjustment of the weight average molecular weight and the adhesion performance is easy. In the synthesis of the polymer (A), a solvent such as an organic solvent and water can be appropriately selected and used.

  For the synthesis of the polymer (A), a polymerization initiator is usually used. As the polymerization initiator, a known peroxide and a known azo compound can be appropriately selected.

  The weight average molecular weight of the polymer (A) is preferably 600,000 to 1,500,000, more preferably 800,000 to 1,200,000. When the weight average molecular weight is 600,000 or more, a low dielectric constant is easily obtained. Moreover, if the weight average molecular weight is 1,500,000 or less, the viscosity of the pressure-sensitive adhesive can be easily adjusted during coating. The weight average molecular weight is a value in terms of polystyrene obtained by GPC (gel permeation chromatography).

  The pressure-sensitive adhesive of the present invention preferably contains a curing agent. By including the curing agent, cohesive force can be easily obtained in the pressure-sensitive adhesive layer. The curing agent is preferably an isocyanate curing agent, an epoxy curing agent, a metal chelate curing agent, an aziridine curing agent, a carbodiimide curing agent, or the like.

  Examples of the isocyanate curing agent include aromatic diisocyanates, aliphatic diisocyanates, araliphatic diisocyanates, and alicyclic diisocyanates, and compounds having bifunctional or higher isocyanate groups such as burettes, nurate bodies, and adduct bodies. Can be mentioned.

  Examples of the epoxy curing agent include compounds having a glycidyl ether group or an alicyclic epoxy group.

  Examples of the metal chelate curing agent include various titanium chelates manufactured by Nippon Soda Co., Ltd., various zirconium chelates manufactured by Matsumoto Fine Chemical Co., Ltd., and various aluminum chelates manufactured by Kawaken Fine Chemical Co., Ltd.

  Examples of the aziridine curing agent include Chemitite PZ-33 and DZ-22E manufactured by Nippon Shokubai Co., Ltd.

  Examples of the carbodiimide curing agent include Nisshinbo Chemical Co., Ltd. Carbodilite V-05 and V-07.

  In the present invention, the curing agent is preferably an isocyanate curing agent. Two or more kinds of curing agents can be used in combination.

  It is preferable to use 0.01-5 weight part of hardening | curing agents with respect to 100 weight part of polymers (A), and 0.1-2 weight part is more preferable. If it is in the range of 0.01 to 5 parts by weight, an appropriate cohesive force and adhesive force can be easily obtained.

  The pressure-sensitive adhesive of the present invention can also contain a silane coupling agent. Heat-and-moisture resistance can be further improved by including a silane coupling agent.

  In addition to the alkoxysilyl group, the silane coupling agent has any substituent such as an epoxy group, a (meth) acryloxy group, an aminoalkyl group, a mercapto group, an alkyl group, and a phenyl group. The substituent is preferably an epoxy group. Examples thereof include KBM303 and KBM402 manufactured by Shin-Etsu Chemical Co., Ltd.

  The silane coupling agent is preferably added in an amount of 0.001 to 1 part by weight, more preferably 0.005 to 0.8 part by weight, based on 100 parts by weight of the polymer (A). Heat-and-moisture resistance can be further improved by blending 0.001 to 1 part by weight of the silane coupling agent.

  The pressure-sensitive adhesive of the present invention may be prepared from other resins, silane coupling agents, tackifiers, fillers, colorants, softeners, ultraviolet absorbers, antioxidants, antifoaming agents, light stabilizers, and weather resistance as necessary. You may mix | blend additives, such as a stabilizer, a hardening accelerator, and a hardening retarder.

  Examples of the other resin include an acrylic resin, a polyester resin, an amino resin, an epoxy resin, and a polyurethane resin. Examples of the filler include talc, calcium carbonate, titanium oxide and the like.

  The pressure-sensitive adhesive sheet of the present invention includes a base material and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive of the present invention. The pressure-sensitive adhesive sheet can be obtained, for example, by forming a pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive to a substrate and drying it. Moreover, an adhesive is applied to the peelable sheet and dried to form an adhesive layer, and the substrate is bonded. The said adhesive layer should just be provided in the at least one surface of the base material. In addition, in order to prevent that a foreign material adheres to an adhesive layer, a peelable sheet is normally bonded on the surface which is not in contact with the base material of an adhesive layer.

  As another aspect of the pressure-sensitive adhesive sheet of the present invention, a pressure-sensitive adhesive sheet is formed by applying a pressure-sensitive adhesive to a peelable sheet and drying it, and further bonding the peelable sheet (referred to as a cast pressure-sensitive adhesive sheet). Is also preferable.

  The thickness of the pressure-sensitive adhesive layer is usually about 10 to 175 μm.

  For the coating, for example, a known coating apparatus such as a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater or the like can be used. During coating, the solvent can be removed by heating or the like.

  The substrate is preferably, for example, paper, cellophane, plastic, rubber, foam, cloth, rubber cloth, resin-impregnated cloth, glass plate, wood or the like. The substrate may be plate-shaped or film-shaped. Moreover, the structure which laminated | stacked the base material independently or several base materials is also preferable.

  Examples of the plastic include polyolefin resins such as polyvinyl alcohol, triacetyl cellulose, polypropylene, polyethylene, polycycloolefin, and ethylene-vinyl acetate copolymer, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Polycarbonate resin, polynorbornene resin, polyarylate resin (PAR: copolymer resin of bisphenol A and phthalic acid), polyacrylic resin, polyphenylene sulfide resin, polystyrene resin, polyamide resin, polyimide resin, epoxy resin (Resin obtained by reacting an epoxy group-containing resin with polyamine or carboxylic anhydride).

The base material may be an optical member such as an antireflection (AR) film, a polarizing plate, or a retardation plate, which is an optical function added to a plastic film.
The adhesive sheet of this invention can be used as a member which comprises a liquid crystal display (especially touchscreen use) by using an optical member.

  The dielectric constant of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present invention at a frequency of 100 kHz is 3.5 or less. The lower the dielectric constant, the better. However, the lower limit in the current technical level is about 2.5. The adhesive of the present invention can form an adhesive layer having a low dielectric constant as described above. For this reason, the touch panel using the pressure-sensitive adhesive sheet of the present invention is unlikely to malfunction even if the pressure-sensitive adhesive layer is thin.

  The pressure-sensitive adhesive sheet of the present invention can be preferably used for optical display applications, but the application is not particularly limited, and is used for general labels, and light-transmitting adherends such as window glass and vehicle glass. Is preferred.

Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, “parts” represents “parts by weight” and “%” represents “% by weight” unless otherwise specified.
“Mn” represents the number average molecular weight, and “Mw” represents the weight average molecular weight.

(Measurement conditions for weight average molecular weight)
・ Device: LC-GPC system “Prominence” manufactured by Shimadzu Corporation
Column: 4 GMHXL manufactured by Tosoh Corp. and 1 HXL-H manufactured by Tosoh Corp. are connected in series. Mobile phase solvent: Tetrahydrofuran Column temperature: 40 ° C
・ Flow rate: 1.0ml / min

Production Example (A1) [Production of Polymer (A)]:
In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, under a nitrogen atmosphere, 40 parts of 2-ethylhexyl acrylate, 10 parts of cyclohexyl acrylate, 0.25 part of 4-hydroxybutyl acrylate, polymerization start An appropriate amount of azobisisobutyronitrile as an agent was added, and ethyl acetate was charged as a solvent. Heated until the solution temperature reached 80 ° C.
Next, 40 parts of 2-ethylhexyl acrylate, 10 parts of cyclohexyl acrylate, 0.25 part of 4-hydroxybutyl acrylate, an appropriate amount of azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as a solvent were added to the dropping tube.
The reactor was heated until the solution temperature reached 80 ° C., and after confirming that the reaction had started in the reactor, the solution was dropped from the dropping tube over 2 hours. After completion of dropping, the reaction temperature was kept at about 80 ° C. and the reaction was continued for 5 hours, and then cooling was started. Subsequently, it diluted with ethyl acetate and the non volatile matter was adjusted to 40%. As a result, a polymer (A1) solution having a weight average molecular weight of 900,000 was obtained.

Production Examples (A2) to (A13) [Production of Polymer (A)]:
Except having changed the kind and compounding quantity (part) of a monomer as having described in Table 1, it carried out similarly to a manufacture example (A1), and obtained the polymer (A2)-(A13) solution.

Abbreviations in Table 1 are as follows.
2EHA: 2-ethylhexyl acrylate i-NA: isononyl acrylate i-OA: isooctyl acrylate i-BA: isobutyl acrylate n-BA: n-butyl acrylate i-DA: isodecyl acrylate CHA: cyclohexyl acrylate ACMO: acryloyl morpholine IBOA: Isobornyl acrylate PIEA: N-acryloyloxyethyl hexahydrophthalimide

<Example 1>
0.7 part of isocyanurate of hexamethylene diisocyanate (hereinafter also referred to as HDI) as an isocyanate curing agent with respect to 250 parts of polymer (A1) solution (nonvolatile content: equivalent to 100 parts), and silane coupling 0.5 parts of KBM-303 (manufactured by Shin-Etsu Chemical Co., Ltd.) as an agent was blended to obtain an adhesive.
The obtained pressure-sensitive adhesive was coated on a release liner (thickness 38 μm) using a comma coater and dried at 100 ° C. for 2 minutes to form a pressure-sensitive adhesive layer having a thickness of 25 μm. Another release liner was bonded to this pressure-sensitive adhesive layer and aged at room temperature for 7 days to obtain a cast pressure-sensitive adhesive sheet.

<Examples 2 to 11 and Comparative Examples 1 and 2>
Cast adhesive sheets were obtained in the same manner as in Example 1 except that the formulation of Example 1 was changed to the formulations shown in Table 2 and Table 3.

  The following physical property evaluation was performed using the obtained cast adhesive sheet. The results are shown in Table 2 and Table 3.

<Adhesiveness>
The obtained cast adhesive sheet was prepared in a size of 25 mm wide × 100 mm long to prepare a test adhesive sheet. One peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to a 100 μm thick polyethylene terephthalate film (hereinafter referred to as PET film, product name: A-4300, manufactured by Toyobo Co., Ltd.). . Next, the other peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the pressure-sensitive adhesive layer was attached to a glass plate in an atmosphere of 23 ° C.-50% RH, and pressure-bonded with a roll according to JIS Z-0237. After 24 hours from the press bonding, the adhesive strength (peeling angle 180 °, peeling speed 300 mm / min; unit N / 25 mm width) was measured with a universal tensile tester.
Separately, the adherend was changed from a glass plate to a COP or ITO / PET film, and the adhesive strength was measured in the same manner as described above. The ITO / PET film was a PET film on which indium tin oxide (ITO) was vapor-deposited, and a test adhesive sheet was attached to the ITO vapor-deposited surface. Evaluation was made on adhesiveness based on adhesive strength as follows.
A: Adhesive strength is 5.0 N / 25 mm or more. (Good)
Δ: Adhesive strength is 1.0 N / 25 mm or more and less than 5.0 N / 25 mm. (Practical acceptable)
X: Adhesive strength is less than 1.0 N / 25mm. (Bad)

<Transparency>
A cast adhesive sheet was prepared in a size of 25 mm wide × 100 mm long to prepare a test adhesive sheet. One peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to a PET film having a thickness of 100 μm. Next, the other peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, adhered to a glass plate using a laminator in an atmosphere of 23 ° C.-50% RH, and left in an environment of 85 ° C.-90% RH for 240 hours. Then, after cooling for 24 hours in an atmosphere of 23 ° C.-50% RH, HAZE (haze) was measured using Turbidimeter NDH5000W (manufactured by Nippon Denshoku Industries Co., Ltd.). The evaluation criteria are as follows.
○: HAZE is less than 1.0 (good transparency).
Δ: HAZE is 1.0 or more and less than 3.0 (transparency is slightly good).
X: HAZE is 3.0 or more (poor transparency).

<Dielectric constant>
A method for measuring the dielectric constant will be described with reference to FIG. The obtained cast adhesive sheet was prepared in a size of width 100 mm × length 100 mm to prepare a test adhesive sheet. One peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the exposed pressure-sensitive adhesive layer 4 was bonded to the aluminum vapor deposition layer 3 </ b> C formed on the glass plate 6. Next, the other peelable sheet of the test pressure-sensitive adhesive sheet is peeled off, and a dielectric constant measurement sample 1 is obtained by forming the aluminum vapor-deposited layers 3A and 3B on the surface of the exposed pressure-sensitive adhesive layer 4 that is not in contact with the aluminum vapor-deposited layer 3C. It was. Next, the connection terminal 2A of the measurement device 7 was connected to the measurement terminal connection part 5 of the dielectric constant measurement sample 1, and the connection terminal 2B was connected to the aluminum vapor deposition layer 3A. The dielectric constant was measured under the following conditions. The evaluation criteria are as follows.

Measuring apparatus: British Solartron 1260 impedance measuring instrument Amplifier: British Solartron 1296 type dielectric constant measurement interface electrode configuration: 21 mmΦ, 40 nm thick aluminum deposited layer Counter electrode: 21 mmΦ, 40 nm thick aluminum deposited layer AC current: 100 mV
Terminal: Pin probe Frequency: 100 kHz
Measurement environment: 23 ° C-50% RH
Sample thickness: 25 μm
(Evaluation criteria)
○: Dielectric constant is 3.0 or less. (Good)
(Triangle | delta): A dielectric constant is larger than 3.0 and is 3.5 or less. (Practical acceptable)
X: Dielectric constant is larger than 3.5. (Bad)

<Heat and heat resistance>
The measurement sample prepared in the above <Transparency> section was left in an environment of 85 ° C.-90% RH for 240 hours. Then, after cooling for 24 hours in an atmosphere of 23 ° C.-50% RH, the presence or absence of bubbles in the pressure-sensitive adhesive layer and the presence or absence of lifting or peeling of the pressure-sensitive adhesive sheet were visually evaluated under the following conditions.
○: No bubbles, floats, and peeling are observed Δ: Slight bubbles, lifts, and peeling are observed ×: Many bubbles, lifts, and peelings are seen

<Corrosion resistance>
The obtained cast pressure-sensitive adhesive sheet was prepared in a size of 40 mm wide × 100 mm long to prepare a test pressure-sensitive adhesive sheet. One peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the exposed pressure-sensitive adhesive layer was bonded to a PET film having a thickness of 100 μm. Next, the other peelable sheet of the test pressure-sensitive adhesive sheet was peeled off, and the exposed pressure-sensitive adhesive layer was transparent in a PET film having a width of 40 mm × a length of 160 mm in which a transparent conductive film was formed of ITO in a 23 ° C.-50% RH atmosphere. A laminated body was obtained by sticking on the conductive film using a laminator, and the resistance value was measured using a Lorester GP (model number MCP-T600, manufactured by Mitsubishi Chemical Corporation).
Next, the laminate was left in an environment of 85 ° C.-90% RH for 1000 hours, and then the resistance value was measured again. The corrosion resistance of the transparent conductive film was evaluated by calculating the change rate of the resistance value before and after the standing. The evaluation criteria are as follows.
○: Resistance change rate is less than 150%. Good.
X: The change rate of the resistance value is 150% or more. Impractical

DESCRIPTION OF SYMBOLS 1 Dielectric constant measurement sample 2A Measurement terminal 2B Measurement terminal 3A Aluminum vapor deposition layer 3B Aluminum vapor deposition layer 3C Aluminum vapor deposition layer 4 Adhesive layer 5 Measurement terminal junction part 6 Glass plate 7 Measuring apparatus

Claims (3)

2-ethylhexyl acrylate, (meth) acrylic acid alkyl ester (a) having a branched alkyl group having 4 to 9 carbon atoms other than 2-ethylhexyl acrylate, and a monomer having an aliphatic cyclic substituent having 4 to 10 carbon atoms ( a polymer (A) obtained by polymerizing a monomer mixture containing b),
An adhesive capable of forming an adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz.   The monomer (b) is any one selected from the group consisting of isobornyl (meth) acrylate, (meth) acryloylmorpholine, N- (meth) acryloyloxyethylhexahydrophthalimide and cyclohexyl (meth) acrylate. Adhesive.   The adhesive sheet provided with the base material and the adhesive layer formed from the adhesive of Claim 1 or 2.

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