JP2015183177A - Adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive having a sufficient pot life, from which such an adhesive layer can be formed that has a low dielectric constant, substantially prevents blisters or peeling when left in a high temperature and high humidity environment, and suppresses odors and yellow discoloration.SOLUTION: The adhesive comprises a polymer (A) having a weight average molecular weight of 600000 to 1500000 and a polymer (B) having a weight average molecular weight of 50000 to 400000. The polymer (A) is obtained by copolymerizing a monomer mixture that comprises an alkyl (meth)acrylate ester (a) and a monomer (b) having a 4-10C aliphatic cyclic substituent and a (meth)acryloyl group; the polymer (B) is obtained by copolymerizing a monomer mixture that comprises an alkyl (meth)acrylate ester (a) and a polar group-containing monomer (c); and the polymer (A) is included by 70 to 95 wt.% in total 100 wt.% of the polymer (A) and the polymer (B). 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, smartphones and tablet-type terminals are becoming more sophisticated without increasing the thickness of the device, so the components to be mounted are made smaller and thinner, but the thickness of the adhesive layer is no exception. . 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. The dielectric constant is a constant specific to the substance that determines the capacitance. The capacitance is proportional to the dielectric constant, and the higher the dielectric constant of the substance, the higher the value of the capacitance. 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.

  In addition, since the adhesive is easily affected by temperature and humidity, the adhesive layer is likely to be whitened when the adhesive sheet is placed in a high temperature and high humidity environment and then returned to a normal room temperature atmosphere. There was a problem.

  Therefore, in Patent Document 1, (meth) acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group is used as the main monomer component, and carboxyl group-containing monomer is used as the monomer component in 3 parts by weight based on 100 parts by weight of the total monomer components. 10 to 10 parts by weight, and the acrylic polymer (a) having a weight average molecular weight of 500,000 to 900,000 and a glass transition temperature when forming a homopolymer are 60 to 190 ° C. and have a cyclic structure An ethylenically unsaturated monomer is used as a main monomer component, and a carboxyl group-containing monomer is contained as a monomer component in an amount of 3 to 10 parts by weight with respect to 100 parts by weight of all monomer components, and the weight average molecular weight is 3000 to 6000. An adhesive containing the oligomer (b) is disclosed.

  Patent Document 2 discloses an alkyl acrylate having a linear or branched alkyl group having 6 to 10 carbon atoms, and an alkyl methacrylate having a linear or branched alkyl group having 1 to 10 carbon atoms. A pressure-sensitive adhesive containing a polymer synthesized from one or more monomer components selected from the group consisting of an ester, a (meth) acrylic acid ester having an alicyclic hydrocarbon group, and a nitrogen-containing monomer is disclosed.

JP 2005-255877 A JP 2012-173354 A

  However, the pressure-sensitive adhesive of Patent Document 1 has a problem that the pressure-sensitive adhesive sheet is lifted or peeled off from the adherend after aging at high temperature and high humidity. Moreover, since the adhesive of patent document 2 uses N-vinyl pyrrolidone according to an Example, the problem of the hygiene which a specific odor remains in an adhesive layer, the problem that an adhesive layer turns yellow, and adhesive There was a problem that the pot life of the agent was short.

  The present invention has good transparency, low dielectric constant, and is less likely to float and peel when placed in a high temperature and high humidity atmosphere, and can form an adhesive layer that suppresses odor and yellowing. An object of the present invention is to provide an adhesive having a pot life and an adhesive sheet.

The pressure-sensitive adhesive of the present invention comprises a polymer (A) having a weight average molecular weight of 600,000 to 1,500,000 and a polymer (B) having a weight average molecular weight of 50,000 to 400,000,
The polymer (A) is a copolymer of a monomer mixture containing (meth) acrylic acid alkyl ester (a) and a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms and a (meth) acryloyl group. And
The polymer (B) is obtained by copolymerizing a monomer mixture containing a (meth) acrylic acid alkyl ester (a) and a polar group-containing monomer (c),
In a total of 100% by weight of the polymer (A) and the polymer (B), the polymer (A) is contained at 70 to 95% by weight,
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, a high molecular weight polymer (A) using a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms and a low molecular weight using a polar group-containing monomer (c). The pressure-sensitive adhesive using the polymer (B) at a specific ratio obtained excellent stress relaxation properties. As a result, the pressure-sensitive adhesive of the present invention has a low dielectric constant, but is less likely to float or peel even when placed in a high-temperature and high-humidity atmosphere, and can form a pressure-sensitive adhesive layer that suppresses odor and yellowing. In addition, the pressure-sensitive adhesive of the present invention also had an effect of having a sufficient pot life while obtaining the above characteristics.

  Adhesive having a sufficient pot life that can form a pressure-sensitive adhesive layer having a low dielectric constant and less likely to float and peel when placed in a high-temperature and high-humidity atmosphere according to the present invention. An agent and an adhesive sheet can be provided.

A typical sectional view of a dielectric constant measurement sample.

  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 (meth) acryloyl group includes an acryloyl group and a methacryloyl group. The monomer means an ethylenically unsaturated monomer. Further, the adherend is a partner to which the adhesive sheet is attached.

The pressure-sensitive adhesive of the present invention comprises a polymer (A) having a weight average molecular weight of 600,000 to 1,500,000 and a polymer (B) having a weight average molecular weight of 50,000 to 400,000.
The polymer (A) is a copolymer of a monomer mixture containing (meth) acrylic acid alkyl ester (a) and a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms and a (meth) acryloyl group. And
The polymer (B) is obtained by copolymerizing a monomer mixture containing a (meth) acrylic acid alkyl ester (a) and a polar group-containing monomer (c),
In a total of 100% by weight of the polymer (A) and the polymer (B), the polymer (A) is contained at 70 to 95% by weight,
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 pressure-sensitive adhesive of the present invention, the polymer (A) mainly has a function of lowering the dielectric constant of the pressure-sensitive adhesive layer, and the polymer (B) mainly has a pressure-sensitive adhesive when the pressure-sensitive adhesive sheet is placed in a high-temperature and high-humidity environment. It functions to suppress whitening of the layer and to prevent the pressure-sensitive adhesive layer from floating and peeling off from the adherend (for example, a glass plate). The pressure-sensitive adhesive of the present invention can suppress whitening of the pressure-sensitive adhesive layer after being placed in a high-temperature and high-humidity atmosphere without using acryloylmorpholine or N-vinylpyrrolidone. A pot life.

  In the present invention, the polymer (A) is a monomer mixture containing a (meth) acrylic acid alkyl ester (a) and a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms and a (meth) acryloyl group. It is a copolymerized polymer. In addition, (meth) acrylic-acid alkylester (a) does not contain the monomer (b) which has a C4-C10 aliphatic cyclic substituent. The term “having an aliphatic cyclic substituent having 4 to 10 carbon atoms” in the monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms (hereinafter referred to as monomer (b)) means an aliphatic cyclic group. The atoms forming the ring of the substituent means that 4 to 10 carbon atoms are present, and the carbon atom contained in the group bonded to the ring is not included in the number of carbon atoms. Specifically, for example, both “cyclohexyl group” and “3-methylcyclohexyl group” are defined as “aliphatic cyclic substituent having 6 carbon atoms” in the present invention. Further, as the atoms forming the ring, there may be one atom other than the carbon atom (so-called heteroatom) together with the carbon atom, but two heteroatoms are not included in the monomer (b), and A hetero atom is not included in the carbon number.

  The (meth) acrylic acid alkyl ester (a) is preferably a monomer having an alkyl group having 1 to 18 carbon atoms. Specifically, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, (meth ) Octyl acrylate, nonyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, ( Examples include myristyl (meth) acrylate, palmityl (meth) acrylate, and stearyl (meth) acrylate. The (meth) acrylic acid alkyl ester (a) preferably has 4 to 18 carbon atoms in the alkyl group, and (meth) acrylic acid in which the alkyl group other than 2-ethylhexyl acrylate and 2-ethylhexyl acrylate has 4 to 18 carbon atoms. It is more preferable to use an alkyl ester in combination. When using 2-ethylhexyl acrylate, 45-85 weight% is preferable among 100 weight% of monomer mixtures used for a synthesis | combination of a polymer (A), and 50-75 weight% is more preferable.

  The (meth) acrylic acid alkyl ester (a) is preferably 10 to 45% by weight, more preferably 20 to 35% by weight, out of 100% by weight of the monomer mixture. Use of 10 to 45% by weight makes it easy to obtain a low dielectric constant and good adhesive properties.

Examples of the monomer (b) include cyclohexyl (meth) acrylate which is a monomer having a cyclohexyl ring, t-butylcyclohexyl (meth) acrylate and trimethylcyclohexyl (meth) acrylate which are derivatives thereof, and isobornyl having an isobornyl skeleton. (Meth) acrylate;
As monomers having a heterocycle, N- (meth) acryloyloxyethylhexahydrophthalimide having a phthalimide skeleton, N- (meth) acryloyloxyethyl-3-methylhexahydrophthalimide, tetrahydrofurfuryl having a tetrahydrofurfuryl ring (meta ) Acrylate and the like.
Of these, cyclohexyl (meth) acrylate having a 6-membered ring structure is preferred.

  The monomer (b) is preferably used in an amount of 10 to 40% by weight, more preferably 15 to 30% by weight, out of 100% by weight of the monomer mixture. It becomes easy to obtain a low dielectric constant by using 10 to 40% by weight.

  In the synthesis of the polymer (A), other monomers can be used in combination with the (meth) acrylic acid alkyl ester (a) and the monomer (b). Other monomers are preferably reactive functional group-containing monomers and other vinyl monomers. The reactive functional group is preferably a hydroxyl group, a carboxyl group, a phosphate group, an amino group, an amide group, an epoxy group, an isocyanato group or a nitrile group.

  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). Examples thereof include polyalkylene glycol (meth) acrylates such as acrylate, polyethylene glycol (meth) acrylate, and polypropylene glycol (meth) acrylate.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, β-carboxyethyl (meth) acrylate, and acid anhydrides thereof.

  Examples of the phosphorus group-containing monomer include 2- (meth) acryloyloxyethyl acid phosphate.

  Examples of the amino group-containing monomer include aminomethyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, and the like.

  Examples of the amide group-containing monomer include (meth) acrylamide, N-methylolacrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, and N-vinylacetamide.

  Examples of the epoxy group-containing monomer include glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, and allyl glycidyl ether.

  Examples of the nitrile group-containing monomer include (meth) acrylonitrile.

  Examples of the isocyanato group-containing monomer include (meth) acryloyloxyethyl isocyanate.

  The reactive functional group-containing monomer is preferably about 0.01 to 10% by weight in 100% by weight of the monomer mixture.

  The other vinyl monomer is a heterocycle-containing monomer, the fluorine-containing monomer is an alkoxyalkyl (meth) acrylate, aryloxyalkyl (meth) acrylate, aromatic (meth) acrylate, vinyl acetate, propyl acetate, vinyl ether compound, α-olefin For example, (meth) acrylonitrile etc. are mentioned.

  Examples of the heterocyclic ring-containing monomer include 2,2,2-trifluoroethyl (meth) acrylate.

  Examples of the fluorine-containing monomer include tetrahydrofurfuryl (meth) acrylate.

  Examples of the alkoxyalkyl (meth) acrylate include methoxyethyl (meth) acrylate and the like, and alkylene oxide adducts thereof.

  Examples of the aryloxyalkyl (meth) acrylate include phenoxyethyl (meth) acrylate, and alkylene oxide adducts thereof.

  Examples of the aromatic (meth) acrylate include styrene and α-methylstyrene.

  The other vinyl monomer is preferably about 0.01 to 10% by weight in 100% by weight of the monomer mixture.

  Monomers can be used alone or in combination of two or more.

  The synthesis of the polymer (A) can be obtained by a known synthesis method such as bulk polymerization, solution polymerization, emulsion polymerization, or active energy ray polymerization. Among these, solution polymerization that allows easy molecular weight adjustment is preferred. The synthesis preferably uses a polymerization initiator. As the polymerization initiator, a peroxide and an azo compound can be appropriately selected and used. In the synthesis of the polymer (A), a solvent such as an organic solvent and water can be appropriately selected and used.

  The weight average molecular weight of the polymer (A) is 600,000 to 1,500,000, more preferably 800,000 to 1,200,000. If the weight average molecular weight is 600,000 or more, the dielectric constant can be further reduced. Moreover, if it is 1.5 million or less, the viscosity adjustment of an adhesive will become easy. The weight average molecular weight is a value in terms of polystyrene obtained by GPC (gel permeation chromatography).

  The polymer (B) is a polymer obtained by copolymerizing a monomer mixture containing a (meth) acrylic acid alkyl ester (a) and a polar group-containing monomer (c).

  As the (meth) acrylic acid alkyl ester (a), the monomers exemplified for the (meth) acrylic acid alkyl ester (a) described in the polymer (A) can be used. And 2-ethylhexyl acrylate, n-octyl acrylate, isodecyl acrylate and the like are preferable. Further, it is more preferable to use methyl (meth) acrylate or ethyl (meth) acrylate because the cohesive force is further improved.

  The polar group-containing monomer (c) is preferably, for example, a hydroxyl group, a carboxyl group, a phosphate group, an amino group, an amide group, an epoxy group, an isocyanato group, or a nitrile group as a polar functional group. Specifically, the reactive functional group-containing monomer described in the polymer (A) can be used.

  The polar group of the polar group-containing monomer (c) is more preferably a hydroxyl group, and more preferably 2-hydroxyethyl (meth) acrylate.

  The polar group-containing monomer (c) is preferably used in an amount of 10 to 50% by weight, more preferably 20 to 40% by weight, out of 100% by weight of the monomer mixture used for the synthesis of the polymer (B). The whitening resistance is further improved by using 10 to 50% by weight.

  The synthesis of the polymer (B) can be obtained by a known synthesis method such as bulk polymerization, solution polymerization, emulsion polymerization, or active energy ray polymerization. Among these, solution polymerization that allows easy molecular weight adjustment is preferred. The synthesis preferably uses a polymerization initiator. As the polymerization initiator, a peroxide and an azo compound can be appropriately selected and used. In the synthesis of the polymer (B), a solvent such as an organic solvent and water can be appropriately selected and used.

  It is important that the weight average molecular weight of the polymer (B) is 50,000 to 400,000, and preferably 100,000 to 250,000. When the weight average molecular weight is 50,000 or more, the low molecular weight component of the resin constituting the pressure-sensitive adhesive layer moves to the surface of the adherend and contaminates the adherend, so-called adherend contamination is difficult to occur. On the other hand, if it is 400,000 or less, the whitening resistance of the pressure-sensitive adhesive layer when placed in a high-temperature and high-humidity environment is excellent. In addition, the measuring method of a weight average molecular weight is the same as that of a polymer (A).

The proportion of the polymer (A) and the polymer (B) is 70 to 95% by weight of the polymer (A) in a total of 100% by weight of the polymer (A) and the polymer (B). When the proportion of the polymer (A) is within the above range, the dielectric constant of the pressure-sensitive adhesive layer can be easily lowered.

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 a compound having a reactive functional group having two or more functional groups, and is preferably an isocyanate curing agent, an epoxy curing agent, a metal chelate curing agent, an aziridine curing agent or a carbodiimide curing agent. Moreover, when not containing the said hardening | curing agent, it is preferable to contain a photoinitiator.

  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.

  As the curing catalyst, either a tin-based compound or a non-tin-based compound can be used.

  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.

  The curing agent is preferably an isocyanate curing agent, more preferably an isocyanate curing agent having a triazine ring, and an isocyanurate body of hexamethylene diisocyanate (hereinafter referred to as an HDI nurate body) can be used. A hardening | curing agent can also be used individually or in combination of 2 or more types.

  It is preferable to mix | blend 0.01-5 weight part with respect to a total of 100 weight part of a polymer (A) and a polymer (B), and, as for a hardening | curing agent, 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. By including the silane coupling agent, floating and peeling can be further suppressed when placed in a high temperature and high humidity environment.

  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 blended in an amount of 0.001 to 1 part by weight, based on a total of 100 parts by weight of the polymer (A) and the polymer (B), and 0.005 to 0.8 parts by weight. Is more preferable. By adding 0.001 to 1 part by weight of the silane coupling agent, it is possible to further suppress floating and peeling when placed in a high temperature and high humidity environment.

  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. Needless to say, the peelable sheet is bonded to the surface of the pressure-sensitive adhesive layer that is not in contact with the base material.

  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.

  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. It is particularly suitable for an optical member constituting a touch panel display.

  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 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 layer of the pressure-sensitive adhesive sheet of the present invention has a permeation amount of water of 200 g / m ² or more after standing in a 40 ° C. atmosphere for 24 hours. Therefore, the touch panel using the pressure sensitive adhesive sheet of the present invention has high moisture permeability.

  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, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping tube, 37.5 parts of 2-ethylhexyl acrylate, 12.5 parts of cyclohexyl acrylate, and 0.25 of 4-hydroxybutyl acrylate in a nitrogen atmosphere A suitable amount of azobisisobutyronitrile as a polymerization initiator and ethyl acetate as a solvent were charged.
Next, 37.5 parts of 2-ethylhexyl acrylate, 12.5 parts of cyclohexyl acrylate, 0.25 part of 4-hydroxybutyl acrylate, an appropriate amount of azobisisobutyronitrile as a polymerization initiator are added to the dropping tube, and ethyl acetate is used as a solvent. Was charged.
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. Furthermore, it diluted with ethyl acetate and adjusted to 40% of non volatile matter density | concentration. As a result, a polymer (A1) solution having a weight average molecular weight of 900,000 was obtained.

Production Examples (A2) to (A15), (B1) to (B12) [Production of Polymers (A) and (B)]
The polymer (A2) to (A15) solution and the polymer (B1) are the same as in Production Example (A1) except that the monomer type and amount (parts) are changed as described in Table 1. -(B12) solution was obtained.

Abbreviations in Table 1 and Table 2 are as follows.
2EHA: 2-ethylhexyl acrylate n-LA: n-lauryl acrylate SA: stearyl acrylate CHA: cyclohexyl acrylate HHA: hydroxyhexyl acrylate TMCHA: trimethylcyclohexyl acrylate IBOA: isobornyl acrylate PIEA: N-acryloyloxyethyl hexahydrophthalimide NVP: N-vinylpyrrolidone HBA: 4-hydroxybutyl acrylate HEA: 2-hydroxyethyl acrylate MMA: methyl methacrylate MA: methyl acrylate n-BA: n-butyl acrylate

<Example 1>
The polymer (A1) solution and the polymer (B1) were mixed so that the weight ratio of the polymer (A1) to the polymer (B1) was (A1) / (B1) = 80/20. Next, 1 part of HDI nurate as an isocyanate curing agent and KBM which is a silane coupling agent with respect to a total of 250 parts of the polymer (A1) solution and the polymer (B1) solution (corresponding to a nonvolatile content of 100 parts) An adhesive was obtained by blending 0.5 part of -303 (manufactured by Shin-Etsu Chemical).
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 21 and Comparative Examples 1 to 9>
A cast adhesive sheet was obtained in the same manner as in Example 1 except that the formulation of Example 1 was changed to the formulation shown in Table 3 and Table 4.

<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 polymer carbonate plate (hereinafter referred to as PC) and an 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 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)

<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>
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 corrosion resistance.
X: The change rate of the resistance value is 150% or more. Corrosion resistance is poor.

<Water vapor permeability>
Two cast pressure-sensitive adhesive sheets were prepared, one release liner was peeled off, the exposed pressure-sensitive adhesive layers were bonded together, and a measurement sample in which a 50 μm-thick pressure-sensitive adhesive layer was sandwiched between the two release liners was prepared. One release liner was peeled from this sample, and the exposed pressure-sensitive adhesive layer was bonded to gauze. Next, the other release liner was peeled off and attached to the mouth (1 inch in diameter) of a 200 ml Erlenmeyer flask containing 50 ml of water, and the total weight was weighed.
This Erlenmeyer flask with gauze was left in an oven set at 40 ° C. (no humidity adjustment) for 24 hours, then cooled to room temperature, and the total weight was weighed again to reduce the amount of water in the Erlenmeyer flask (units). : G / m ² ) was calculated and evaluated according to the following criteria.
○: Reduced amount of water is 300 g / m ² or more (good)
Δ: Water reduction amount is 200 g / m ² or more and less than 300 g / m ² (practical)
X: The amount of water reduction is less than 200 g / m ² (not practical)

<Odor>
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 bonded to the exposed pressure-sensitive adhesive layer on gauze. Next, the other peelable sheet was peeled off and bonded to gauze in the same manner. The test pressure-sensitive adhesive sheet was cut to a width of 10 mm, put in a 225 ml mayonnaise bottle, tightly sealed, and left in a constant temperature bath at 40 ° C. for 1 hour. Sensory evaluation was performed.
○: One person or less felt a strange odor (good)
Δ: 2 to 3 people felt a strange odor (practical)
X: Four or more people felt a strange odor (not practical)

<Yellowing>
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 to obtain a laminate, and then a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., measuring device: SE6000) was used. Used to measure L, a, and b before the measurement test. The laminate 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, L, a, and b after the test were measured using a color difference meter. And yellowing was evaluated by the difference (Δb) in the b value before and after the test.
○: Δb is less than 1. (Good)
Δ: Δb is 1 or more and 2 or less. (Practical acceptable)
X: Δb exceeds 2 (not practical)

<Pot life>
The viscosity of the adhesive immediately after blending the curing agent in an atmosphere of 25 ° C. was measured with a B-type viscometer (rotor: 3, rotation speed: 12 rpm, measurement time: 1 minute, unit: mPa · s). The pressure-sensitive adhesive was left in an atmosphere at 25 ° C. for 12 hours, and the viscosity was measured in the same manner as described above. The change rate of the viscosity before and after leaving the adhesive was calculated, and the pot life was evaluated according to the following criteria.
○: Viscosity change is less than 30%. (Good)
Δ: Viscosity change of 30% or more and less than 100%. (Practical acceptable)
X: Viscosity change 100% or more. (Not practical)

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 (6)

A polymer (A) having a weight average molecular weight of 600,000 to 1,500,000 and a polymer (B) having a weight average molecular weight of 50,000 to 400,000,
The polymer (A) is a copolymer of a monomer mixture containing (meth) acrylic acid alkyl ester (a) and a monomer (b) having an aliphatic cyclic substituent having 4 to 10 carbon atoms and a (meth) acryloyl group. And
The polymer (B) is obtained by copolymerizing a monomer mixture containing a (meth) acrylic acid alkyl ester (a) and a polar group-containing monomer (c),
In a total of 100% by weight of the polymer (A) and the polymer (B), the polymer (A) is contained at 70 to 95% by weight,
An adhesive capable of forming an adhesive layer having a dielectric constant of 3.5 or less at a frequency of 100 kHz. Furthermore, the adhesive of Claim 1 which can form the adhesive layer whose water-vapor permeability is 200 g / m < ² > / day or more.   The pressure-sensitive adhesive according to claim 1 or 2, wherein the polar group contained in the polar group-containing monomer (c) is a hydroxyl group.   Furthermore, the adhesive of any one of Claims 1-3 containing an isocyanate hardening | curing agent.   The pressure-sensitive adhesive according to claim 4, wherein the isocyanate curing agent has a triazine ring.   The adhesive sheet provided with the base material and the adhesive layer formed from the adhesive of any one of Claims 1-5.

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