JP2015183178A - Adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive and an adhesive sheet having high adhesive force to an acrylic plate and a low dielectric constant.SOLUTION: The adhesive contains a polymer (A) obtained by polymerizing a monomer mixture that comprises 2-ethylhexyl acrylate, an alkyl (meth)acrylate ester (a) having 8-12C branched alkyl group other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, and a monomer (b) selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate and n-propyl (meth)acrylate. 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.

The touch panel is composed of a surface glass plate and a liquid crystal module, but there is a demand from the market to replace triacetyl cellulose used for the protective film that protects the polarizer inside the liquid crystal module with acrylic resin to prevent light leakage. . However, there is a problem that it is difficult to obtain an adhesive strength to the acrylic resin.
In addition, in order to reduce the weight of electronic devices and enhance the impact resistance, there is an increasing number of cases where the glass plate of the touch panel is replaced with an acrylic plate. However, the acrylic plate has a problem that it is difficult to obtain an adhesive strength as described above.

  Therefore, Patent Document 1 discloses that 19 to 99.5% by weight of an alkyl (meth) acrylate having a branched alkyl group having 10 to 24 carbon atoms at the terminal of the ester group, and any of a carboxyl group-containing monomer and a hydroxyl group-containing monomer. A pressure-sensitive adhesive containing a (meth) acrylic polymer obtained by polymerizing a monomer component containing is disclosed.

JP 2012-246477 A

  However, the conventional pressure-sensitive adhesive has a certain level of adhesion to the glass plate, but has insufficient adhesion to the acrylic plate.

  An object of this invention is to provide the adhesive and adhesive sheet with low adhesive force with respect to an acrylic board, and a dielectric constant.

The pressure-sensitive adhesive of the present invention comprises 2-ethylhexyl acrylate, (meth) acrylic acid alkyl ester (a) having 8 to 12 branched alkyl groups other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, and methyl (meth) acrylate. A polymer (A) obtained by polymerizing a monomer mixture containing any monomer (b) selected from the group consisting of ethyl (meth) acrylate and n-propyl (meth) acrylate,
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, 2-ethylhexyl acrylate, (meth) acrylic acid alkyl ester (a) having 8 to 12 branched alkyl groups other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, and methyl (meth) A pressure-sensitive adhesive containing a polymer (A) obtained by polymerizing a monomer mixture containing any monomer (b) selected from the group consisting of acrylate, ethyl (meth) acrylate and n-propyl (meth) acrylate is an acrylic plate The adhesive strength was excellent, and a low dielectric constant could be achieved.

  ADVANTAGE OF THE INVENTION By this invention, the adhesive force and adhesive sheet with low adhesive force with respect to an acrylic board and a dielectric constant can be provided.

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, (meth) acrylic acid alkyl ester (a) having 8 to 12 branched alkyl groups other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, and methyl (meth) acrylate. A polymer (A) obtained by polymerizing a monomer mixture containing any monomer (b) selected from the group consisting of ethyl (meth) acrylate and n-propyl (meth) acrylate,
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) comprises 2-ethylhexyl acrylate, (meth) acrylic acid alkyl ester (a) having 8 to 12 branched alkyl groups other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, methyl ( It is formed by polymerizing a monomer mixture containing any monomer (b) selected from the group consisting of (meth) acrylate, ethyl (meth) acrylate and n-propyl (meth) acrylate. Although the polymer (A) and the synergistic effect of each monomer used for the synthesis can provide good adhesion to the acrylic plate and a low dielectric constant, among them, 8 to 12 other than 2-ethylhexyl acrylate and 2-ethylhexyl acrylate The use of (meth) acrylic acid alkyl ester (a) (hereinafter referred to as (meth) acrylic acid alkyl ester (a)) having a branched alkyl group greatly contributes to a low dielectric constant. Further, 2-ethylhexyl acrylate, and any monomer (b) selected from the group consisting of methyl (meth) acrylate, ethyl (meth) acrylate and n-propyl (meth) acrylate (hereinafter referred to as monomer (b)) Use greatly contributes to high adhesion to acrylic plates.

Examples of (meth) acrylic acid alkyl ester (a) include 2-ethylhexyl methacrylate, isooctyl (meth) acrylate, s-octyl (meth) acrylate, t-octyl (meth) acrylate, isononyl (meth) acrylate, and s-nonyl. (Meth) acrylate, t-nonyl (meth) acrylate, isodecyl (meth) acrylate, s-decyl (meth) acrylate, t-decyl (meth) acrylate, isoundecyl (meth) acrylate, s-undecyl (meth) acrylate, t -Undecyl (meth) acrylate, isolauryl (meth) acrylate, s-lauryl (meth) acrylate, t-lauryl (meth) acrylate, etc. are mentioned.
Of these, isodecyl acrylate and the like are preferable.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate. And the like, and the like. Among these, 4-hydroxybutyl acrylate is more preferable.

For the synthesis of the polymer (A), another monomer (c) can be used.
Other monomers (c) are, for example, isopropyl (meth) acrylate, (meth) acrylic acid alkyl ester having an alkyl group having 4 to 7 carbon atoms, (meth) acrylic acid having a linear alkyl group having 8 to 12 carbon atoms Alkyl esters, (meth) acrylic acid alkyl esters having an alkyl group having 13 or more carbon atoms, (meth) acrylic acid alkyl esters having a cyclic substituent;
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;
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 monomers such as (meth) acryloyloxyethyl isocyanate;
Heterocycle-containing monomers such as tetrahydrofurfuryl (meth) acrylate and (meth) acryloylmorpholine;
Fluorine atom-containing monomers such as 2,2,2-trifluoroethyl (meth) acrylate;
Alkylene oxide structure-containing monomers such as polyethylene glycol (meth) acrylate and polypropylene glycol (meth) acrylate;
Alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and its alkylene oxide structure-containing monomers;
Aryloxyalkyl (meth) acrylates such as phenoxyethyl (meth) acrylate and its alkylene oxide structure-containing monomers;
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.
The other monomer (c) can be used alone or in combination of two or more.

  Of 100% by weight of the monomer mixture used for the synthesis of the polymer (A), 20 to 80 parts by weight of 2-ethylhexyl acrylate is preferably used, and more preferably 30 to 70 parts by weight.

  The (meth) acrylic acid alkyl ester (a) is preferably used in an amount of 10 to 70% by weight, more preferably 15 to 60% by weight, out of 100% by weight of the monomer mixture. When about 10 to 70% by weight of (meth) acrylic acid alkyl ester (a) is used, a low dielectric constant is easily obtained.

  The hydroxyl group-containing monomer is preferably used so that the hydroxyl value of the polymer (A) is about 0.01 to 3 mgKOH / g, more preferably 0.01 to 2.5 mgKOH / g, and 0.01 to 2 mgKOH. / G is more preferable.

  The monomer (b) is preferably used in an amount of 1 to 15% by weight, more preferably 8 to 15% by weight, out of 100% by weight of the monomer mixture. When the monomer (b) is used in an amount of about 1 to 15% by weight, it becomes easy to obtain a high adhesive force with respect to the acrylic plate, and the moisture and heat resistance is further improved.

  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 about 600,000 to 1,500,000, more preferably 800,000 to 1,200,000. If the weight average molecular weight is in the range of about 600,000 to 1,500,000, the low dielectric constant and the applicability of the adhesive can be further improved. 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.

  As for the usage-amount of a hardening | curing agent, it is preferable to mix | blend 0.01-5 weight part with respect to 100 weight part of polymers (A), and 0.1-2 weight part is more preferable. By blending 0.01 to 5 parts by weight of the curing agent, the cohesive strength and adhesive strength can be further improved.

  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.

  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 of 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

<Measurement of hydroxyl value (OHV)>
About 1 g of a sample (polymer solution) is accurately weighed in a stoppered Erlenmeyer flask and dissolved by adding 100 ml of a toluene / ethanol (volume ratio: toluene / ethanol = 2/1) mixture. Further, exactly 5 ml of an acetylating agent (a solution in which 25 g of acetic anhydride was dissolved in pyridine to make a volume of 100 ml) was added and stirred for about 1 hour. To this, phenolphthalein reagent is added as an indicator and lasts for 30 seconds. Thereafter, the solution is titrated with a 0.1N alcoholic potassium hydroxide solution until the solution becomes light red.
The hydroxyl value was determined by the following formula. The hydroxyl value was a numerical value in the dry state of the resin (unit: mgKOH / g).
Hydroxyl value (mgKOH / g) = [{(ba) × F × 28.25} / S] / (nonvolatile content / 100) + D
Where S: Amount of sample collected (g)
a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)
b: Consumption of 0.1N alcoholic potassium hydroxide solution in the empty experiment (ml)
F: Potency of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

Production Example (A1) [Production of Polymer (A)]:
In a nitrogen atmosphere, a reactor equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, 15 parts 2-ethylhexyl acrylate, 30 parts isooctyl acrylate, 5 parts methyl acrylate, 4-hydroxybutyl acrylate 0 .25 parts, an appropriate amount of azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as a solvent were charged. Heated until the solution temperature reached 80 ° C.
Subsequently, 15 parts of 2-ethylhexyl acrylate, 30 parts of isooctyl acrylate, 4.75 parts of methyl acrylate, 0.25 part of 4-hydroxybutyl acrylate, and azobisisobutyronitrile in appropriate amounts and ethyl acetate were charged into 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 (A17) [Production of polymer (A)]:
Except having changed the kind and compounding quantity (part) of the monomer as having described in Table 1, it carried out similarly to a manufacture example (A1), and obtained the polymer (A2)-(A17) solution.

Abbreviations in Table 1 are as follows.
2EHA: 2-ethylhexyl acrylate i-OA: isooctyl acrylate i-DA: isodecyl acrylate t-DA: t-decyl acrylate i-LA: isolauryl acrylate i-TDMA: isotetradecyl methacrylate MA: methyl acrylate MMA: methyl Methacrylate EA: ethyl acrylate n-PA: n-propyl acrylate n-BA: n-butyl acrylate 4HBA: 4-hydroxybutyl acrylate

<Example 1>
With respect to 250 parts of polymer (A1) solution (nonvolatile content: equivalent to 100 parts), 0.7 part of hexamethylene diisocyanate (HDI) nurate (in terms of nonvolatile content) as an isocyanate curing agent, and silane coupling agent 0.5 parts of KBM-303 (manufactured by Shin-Etsu Chemical Co., Ltd.) (non-volatile content conversion) was blended to obtain an adhesive.
The obtained pressure-sensitive adhesive was coated on a peelable sheet (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 13 and Comparative Examples 1 to 4>
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 an acrylic plate and an ITO / PET film, respectively, 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 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)

<Floating / peeling>
In order to evaluate the heat and moisture resistance, the following tests were conducted to evaluate the float and peeling. 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 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 attached to a glass plate, and then left in an environment of 85 ° C.-90% RH for 240 hours. Then, after cooling in an atmosphere of 23 ° C.-50% RH for 24 hours, whether or not bubbles were generated in the pressure-sensitive adhesive layer and whether the pressure-sensitive adhesive sheet was lifted or peeled off were visually evaluated according to the following evaluation criteria.
○: No bubbles, no floats, and no peeling. Are better.
(Triangle | delta): The bubble, the float, and peeling were seen slightly. Practical use x: Many bubbles, floating and peeling were observed. Impractical

<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 8 to 12 carbon atoms other than 2-ethylhexyl acrylate, a hydroxyl group-containing monomer, methyl (meth) acrylate, ethyl (meth) Containing a polymer (A) formed by polymerizing a monomer mixture containing any monomer (b) selected from the group consisting of acrylate and n-propyl (meth) acrylate,
An adhesive capable of forming an adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz.   The pressure-sensitive adhesive according to claim 1, wherein the polymer (A) has a hydroxyl value of 0.01 to 3 mgKOH / g or less.   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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