JP6572566B2 - Adhesive sheet and electronic device - Google Patents

Description

  The present invention relates to an adhesive sheet that can be used when manufacturing an electronic device such as a portable electronic terminal.

  Adhesive sheets are used in the production scenes of various products including electronic devices and automobiles. For example, in the manufacturing scene of the electronic device, the adhesive sheet is used for fixing two or more casings constituting the electronic device, fixing a rechargeable battery, a circuit board, and the like.

  Examples of the pressure-sensitive adhesive sheet that can be used in the above-described scene include, for example, a polymer obtained by copolymerizing at least an alkyl acrylate ester, a hydroxyl group-containing monomer, vinyl acetate, and a carboxyl group-containing monomer, and the carboxyl group in the polymer. What is obtained using a pressure-sensitive adhesive composition characterized in that the ratio of the group-containing monomer is 0.01 to 1.0 part by mass, contains a crosslinking agent, and has a ball tack of 12 to 30 is known. (For example, refer to Patent Document 1).

  On the other hand, in a wide variety of use cases of electronic devices such as portable electronic terminals, as the pressure-sensitive adhesive sheet, for example, a constant stress due to distortion or the like is applied to a portion joined using a pressure-sensitive adhesive sheet for a long time. Even when it is added over a long period of time, durability (static load holding force) that does not cause floating or peeling, which is a practical problem, is required. Here, the excellent static load holding force means that when an adherend is adhered using an adhesive sheet and a certain load is applied in a direction perpendicular to the adhesion surface, the adherend adheres with time. It means that it is difficult to cause general lifting and peeling.

  In particular, a pressure-sensitive adhesive sheet with excellent static load holding power has been found as the pressure-sensitive adhesive sheet has become smaller and the width of the pressure-sensitive adhesive sheet has become narrower as the mobile electronic terminal and the like have become larger and thinner. Was in a situation that was not.

JP 2011-168658 A

  The problem to be solved by the present invention is to provide an adhesive sheet excellent in static load holding force.

  In the present inventors, the pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a tensile strength obtained from a stress-strain curve (so-called S-S curve) having a predetermined value or more is excellent in static load holding force and exclusively constitutes an electronic device. It has been found that it can be suitably used for fixing parts.

That is, the present invention is an adhesive sheet used for fixing components constituting an electronic device, and has a tensile strength of 6 N / cm ² based on a stress-strain curve at a strain amount of 100% on one side or both sides of a substrate. It is related with the adhesive sheet characterized by having the adhesive layer (A) which is the above.

  Since the pressure-sensitive adhesive sheet of the present invention is excellent in static load holding force, for example, fixing of two or more casings constituting an electronic device such as a portable electronic terminal, fixing of a casing and a lens member, casing and a rechargeable battery, etc. For example, it can be suitably used for fixing.

The stress-strain curve of the adhesive layer which comprises the adhesive tape obtained in Example 9 is represented.

The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet used for fixing components constituting an electronic device, and has a tensile strength of 6 N / cm based on a stress-strain curve at a strain amount of 100% on one side or both sides of a substrate. It has the adhesive layer (A) which is ^two or more.

As the pressure-sensitive adhesive layer (A) constituting the pressure-sensitive adhesive sheet of the present invention, one having a tensile strength based on a stress-strain curve at a strain amount of 100% is 6 N / cm ² or more.

  Here, the tensile strength was obtained by laminating a test piece made of an adhesive layer having a thickness of about 400 μm, a marked line interval of 2 cm, and a width of 1 cm obtained by laminating a 50 μm thick adhesive layer at a temperature of 23 ° C. and humidity. When the amount of strain is 100% in a stress-strain curve (so-called SS curve) measured by a tensile test at a tensile speed of 300 mm / min using a tensile tester in a measurement environment of 50%. Refers to the tensile strength of

Here, the pressure-sensitive adhesive sheet provided with the pressure-sensitive adhesive layer having a tensile strength of less than 6 N / cm ² may not exhibit a practically sufficient static load holding force.

The upper limit of the tensile strength is not particularly limited, is preferably 30 N / cm ² or less, more preferably 25 N / cm ² or less, it is 20 N / cm ² or less, and the peel adhesive strength It is further preferable for expressing the performance of the pressure-sensitive adhesive sheet including the push strength and the static load holding force in a well-balanced manner.

  As the pressure-sensitive adhesive layer (A), one having a thickness of 1 μm to 150 μm is preferably used, and one having a thickness of 5 μm to 100 μm is more preferable.

  The pressure-sensitive adhesive layer (A) can be formed using various pressure-sensitive adhesives. Especially, as said adhesive layer (A), it is an adhesive layer formed using the adhesive containing an acrylic polymer (a1), tackifying resin (a2), and a crosslinking agent (a3), for example. It is preferable for forming a pressure-sensitive adhesive layer having a specific tensile strength.

Moreover, as said adhesive layer (A), it is preferable to use the thing whose tensile strength based on the stress-strain curve in the strain amount of 500% is 12 N / cm < ² > or more, and uses 13 N / cm < ² > or more. it is more preferable to, more preferably the use of 15N / cm ² or more of, more preferably the use of 17N / cm ² or more of, it is particularly preferred to use 19N / cm ² or more of . The upper limit of the tensile strength is preferably at 70N / cm ² or less, it is more preferable to use those 65N / cm ² or less. By using a pressure-sensitive adhesive layer having a tensile strength based on a stress-strain curve at a strain amount of 500% within the above range, it has a well-balanced pressure-sensitive adhesive performance such as peel strength and peel strength as well as push strength. It is preferable in obtaining a pressure-sensitive adhesive sheet.

  As said acrylic polymer (a1) which may be contained in the said adhesive, the tensile strength of an adhesive layer (A) is set to a specific range, As a result, it is equipped with the still more excellent static load holding power. In forming the pressure-sensitive adhesive layer, it is preferable to use one having an acid value in the range of 1 to 50, more preferably one having an acid value in the range of 10 to 50. It is more preferable to use one having an acid value in the range of 40. The acid value is preferably an acid value derived exclusively from a carboxyl group. In addition, the said acid value points out mg of potassium hydroxide required in order to neutralize the acid group which exists in the said acrylic polymer (a1) solution.

  Moreover, as said acrylic polymer (a1), when forming the adhesive layer provided with the still more excellent static load retention force, it is preferable to use what has an aliphatic cyclic structure.

  Examples of the aliphatic cyclic structure include a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a propylcyclohexyl group, a tricyclo [5,2,1,0,2,6] decyl group, and a bicyclo [ 4,3,0] -nonyl group, tricyclo [5,3,1,1] dodecyl group, propyltricyclo [5,3,1,1] dodecyl group, norbornene group, isobornyl group, dicyclopentanyl group, In order to obtain a pressure-sensitive adhesive sheet having both excellent peel strength and excellent push strength, cyclohexyl, norbornene, isobornyl, and adamantyl are among others. preferable.

  Moreover, as said acrylic polymer (a1), it is preferable to use what has a weight average molecular weight of 800,000 or more, in order to obtain the adhesive sheet excellent in the still more excellent static load holding power, 800,000- It is more preferable to use a material having a weight average molecular weight in the range of 3 million, and using a material having a weight average molecular weight in the range of 1,000,000 to 2,200,000 can reduce the tensile strength of the pressure-sensitive adhesive layer (A). It is more preferable when setting to a specific range and, as a result, obtaining an adhesive sheet excellent in static load retention. In addition, the said weight average molecular weight is a weight average molecular weight in standard polystyrene conversion measured with a gel permeation chromatograph (GPC).

  The molecular weight is measured by the GPC method using a Tosoh Corporation GPC apparatus (HLC-8329GPC) and converted to polystyrene.

Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μl
Eluent: THF
Flow rate: 1.0 ml / min Measurement temperature: 40 ° C
This column: TSKgel GMHHR-H (20) 2 Guard column: TSKgel HXL-H
Detector: differential refractometer Standard polystyrene molecular weight: 10,000 to 20 million (manufactured by Tosoh Corporation)

  As said acrylic polymer (a1), it is preferable to use what has a glass transition temperature of -15 degrees C or less, and it is much more preferable to use what has a glass transition temperature of -45 degreeC--20 degreeC. It is more preferable for obtaining a pressure-sensitive adhesive sheet having both excellent static load holding power. The glass transition temperature refers to a calculated value calculated by the FOX equation.

  The acrylic polymer (a1) is preferably contained in an amount of 5% by mass to 80% by mass and preferably 10% by mass to 50% by mass with respect to the total amount of the adhesive that can be used for forming the adhesive layer (A). It is more preferable to maintain good coating workability.

  As said acrylic polymer (a1), it is preferable to use what is obtained by superposing | polymerizing the vinyl monomer component containing a (meth) acryl monomer.

  As the vinyl monomer component, a vinyl monomer content other than a (meth) acrylic monomer such as vinyl acetate or styrene is 5 mass for forming an adhesive layer having a predetermined tensile strength. % Or less, preferably 3% by mass or less, more preferably 1% by mass or less, and a mixture of (meth) acrylic monomers is preferable.

  As the vinyl monomer component, in forming an adhesive layer having a predetermined tensile strength, a vinyl monomer having a nitrogen atom such as N-vinyl-2-pyrrolidone, vinyl acetate, styrene, etc. The content of vinyl monomers other than (meth) acrylic monomers is 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, based on the total amount of the vinyl monomer components. Some can be used.

  The vinyl monomer component may be an alkyl having a homopolymer glass transition temperature of 100 ° C. or higher with respect to the total amount of the vinyl monomer component in forming an adhesive layer having a predetermined tensile strength. The total content of (meth) acrylate is preferably 1% by mass or less, more preferably 0.5% by mass or less, and 0.1% by mass or less. It is particularly preferred to use it. Specific examples of the alkyl (meth) acrylate having a glass transition temperature of 100 ° C. or higher include methyl methacrylate.

  As the vinyl monomer, for example, a vinyl monomer having a hydroxyl group, a vinyl monomer having an acid group, an alkyl (meth) acrylate, or the like can be used.

  Examples of the vinyl monomer having a hydroxyl group that can be used in producing the acrylic polymer (a1) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-hydroxypropyl (meth). Acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyhexyl (meth) acrylate, 6-hydroxyhexyl (meth) acryl, 8-hydroxyoctyl (meth) acrylate, 10-hydroxy (Meth) acrylic monomers having a hydroxyl group such as decyl (meth) acrylate and 12-hydroxylauryl (meth) acrylate can be used.

  Among these, as the vinyl monomer having a hydroxyl group, 4-hydroxybutyl (meth) acrylate is preferably used, and 4-hydroxybutyl acrylate is preferably used as 2-hydroxyethyl (meth) acrylate or the like. Compared with the case where it uses, it is more preferable when obtaining the adhesive sheet provided with the still more excellent static load holding power.

  The vinyl monomer having a hydroxyl group is preferably used in a range of 0.01% by mass to 0.2% by mass with respect to the total amount of the vinyl monomer component, and 0.01% by mass or more and 0.1% by mass. It is more preferable to use in the range of less than mass%, and use in the range of 0.02 mass% to 0.08 mass% sets the tensile strength of the pressure-sensitive adhesive layer (A) to a specific range, and more It is more preferable for obtaining a pressure-sensitive adhesive sheet having a more excellent static load holding force.

  Examples of the vinyl monomer having an acid group that can be used for producing the acrylic polymer (a1) include acrylic acid, methacrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, and (anhydrous). (Meth) acrylic monomers having carboxyl groups such as itaconic acid, (anhydrous) maleic acid, fumaric acid, crotonic acid, (meth) acrylamide propanesulfonic acid, sulfopropyl (meth) acrylate, (meth) acryloyloxynaphthalene sulfone Vinyl monomers having a sulfonic acid group such as acid, sodium vinyl sulfonate, styrene sulfonic acid, allyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acrylamide propane sulfonic acid, 2- Hydroxyethyl acryloy Having a phosphoric acid group such as a phosphate (meth) can be used acrylic monomers and the like. Among them, it is preferable to use a (meth) acrylic monomer having a carboxyl group, and it is more preferable to use acrylic acid or methacrylic acid in order to obtain a pressure-sensitive adhesive sheet having a still better static load holding force. .

  The vinyl monomer having an acid group is not particularly limited as long as the acid value of the acrylic polymer (a1) is within a predetermined preferable range, but 1 mass with respect to the total amount of the vinyl monomer component. % To 30% by weight, more preferably 1% to 15% by weight, and more preferably 1% to 7% by weight. It is further preferable for obtaining a pressure-sensitive adhesive sheet having a load holding force.

  Moreover, when manufacturing the said acrylic polymer (a1), when introducing an aliphatic cyclic structure into an acrylic polymer (a1), it has an aliphatic cyclic structure as said vinyl monomer component (meta). ) It is preferable to use an acrylic monomer.

  As the vinyl monomer having an aliphatic cyclic structure, cyclohexyl (meth) acrylate or the like is preferably used, and cyclohexyl acrylate is more preferably used.

  The vinyl monomer having an aliphatic cyclic structure can be used in a range of 0.5% by mass to 30% by mass with respect to the total amount of the vinyl monomer component, thereby further maintaining a static load. It is preferable for obtaining a pressure-sensitive adhesive sheet having a force, and more preferably used in the range of 4% by mass to 25% by mass.

  As a vinyl monomer component that can be used in the production of the acrylic polymer (a1), other single vinyl monomers can be used as necessary in addition to the above-described ones.

  Examples of the other vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, and isobutyl (meth) ) Acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) ) Acrylate, isodecyl (meth) acrylate, n-undecyl (meth) acrylate, n-dodecyl (meth) acrylate, n-tridecyl (meth) acrylate, n-tetradecyl (meth) acrylate and other alkyl (meth) acrylates It is possible to use.

  Among the above-mentioned other vinyl monomers, it is preferable to use alkyl (meth) acrylates having 4 to 12 carbon atoms in the alkyl group, and n-butyl acrylate and 2-ethylhexyl acrylate are used. It is preferable to obtain a pressure-sensitive adhesive sheet having a still more excellent static load holding force.

  Among the alkyl (meth) acrylates usable as the other vinyl monomers, alkyl (meth) acrylates having an alkyl group having 4 to 12 carbon atoms are used for the production of the acrylic polymer (a1). It is preferably used in the range of 50% by mass to 8% by mass, more preferably in the range of 60% by mass to 98% by mass, and more preferably in the range of 70% by mass to 96% by mass with respect to the total amount of the vinyl monomer component. % Is preferably used in order to obtain a pressure-sensitive adhesive sheet having a still more excellent static load holding force.

  Examples of other vinyl monomers that can be used in the production of the acrylic polymer (a1) include (meth) acrylic monomers having an amide group, (meth) acrylic monomers having an amino group, and imides. An acrylic monomer having a nitrogen atom such as a (meth) acrylic monomer having a group can be used.

  Examples of the (meth) acrylic monomer having an amide group include acrylamide, methacrylamide, diethylacrylamide, N-vinylpyrrolidone, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-diethylacrylamide. N, N-diethylmethacrylamide, N, N′-methylenebisacrylamide, N, N-dimethylaminopropylacrylamide, N, N-dimethylaminopropylmethacrylamide, diacetoneacrylamide, acryloylmorpholine and the like can be used. .

  As the (meth) acrylic monomer having an amino group, for example, aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate or the like is used. be able to.

  As the (meth) acrylic monomer having an imide group, for example, cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, itaconimide and the like can be used.

  As the other vinyl monomers, in addition to the above, for example, cyano group-containing vinyl monomers such as acrylonitrile and methacrylonitrile, glycidyl such as glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, and allyl glycidyl ether Impairs the effectiveness of group-containing acrylic monomers, vinyl acetate, vinyl propionate, vinyl laurate, styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, other substituted styrenes, methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, etc. You may use in the range which is not.

  The acrylic polymer (a1) can be produced, for example, by supplying the vinyl monomer component and radically polymerizing them in the presence of an organic solvent. Specifically, the acrylic polymer (a1) is radically polymerized by mixing and stirring the vinyl monomer component, the polymerization initiator, and the organic solvent, preferably at a temperature of 40 ° C. to 90 ° C. Can be manufactured. The vinyl monomer component may be supplied all at once or dividedly supplied.

  Examples of the polymerization initiator include peroxides such as hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, benzoyl peroxide, cumene hydroxy peroxide, and 2,2′-azobis (2-methylbutyro Nitrile), 2,2′-azobis- (2-aminodipropane) dihydrochloride, 2,2′-azobis- (N, N′-dimethyleneisobutylamidine) dihydrochloride, 2,2′-azobis { An azo compound such as 2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide} or the like can be used. The amount of the polymerization initiator used is preferably in the range of 0.01% by mass to 5% by mass with respect to the total amount of the vinyl monomer component.

  As the pressure-sensitive adhesive that can be used in the present invention, it is preferable to use a pressure-sensitive adhesive containing a tackifying resin (a2) in order to obtain a pressure-sensitive adhesive sheet having a still more excellent static load holding force.

  Examples of the tackifying resin (a2) include a rosin-based tackifying resin, a polymerized rosin-based tackifying resin, a polymerized rosin ester-based tackifying resin, a rosin phenol-based tackifying resin, a stabilized rosin ester-based tackifying resin, Use of rosin ester-based tackifier resin, hydrogenated rosin ester-based tackifier resin, terpene-based tackifier resin, terpene phenol-based tackifier resin, petroleum resin-based tackifier resin, (meth) acrylate-based tackifier resin, etc. Can do.

  Among them, the tackifier resin (a2) is selected from the group consisting of a polymerized rosin ester tackifier resin, a disproportionated rosin ester tackifier resin, a petroleum tackifier resin, and a terpene phenol tackifier resin. It is preferable to use a combination of two or more species in order to obtain a pressure-sensitive adhesive sheet that is excellent in compatibility with the acrylic polymer (a1) and has an even better static load retention force, and more preferably three or more types.

  The softening point of the tackifying resin (a2) is preferably 100 ° C. or higher, and it is more preferable to use a resin having a temperature in the range of 120 ° C. to 170 ° C. It is more preferable for obtaining a pressure-sensitive adhesive sheet having a sufficient static load holding force.

  The tackifying resin (a2) is preferably used in an amount of 5 to 60 parts by mass, preferably 10 to 60 parts by mass with respect to 100 parts by mass of the acrylic polymer (a1). Preferably, when used in the range of 20 parts by mass to 50 parts by mass, it is more preferable to obtain a pressure-sensitive adhesive sheet having an even better peel adhesive force, an even better push strength, and an even better static load holding force. preferable.

  Moreover, as said adhesive, when forming the adhesive layer provided with the further outstanding cohesion force, it is preferable to use what contains a crosslinking agent (a3).

  As said crosslinking agent (a3), an isocyanate type crosslinking agent, an epoxy-type crosslinking agent, a metal chelate type crosslinking agent, an aziridine type crosslinking agent etc. can be used, for example. Especially, as said crosslinking agent, it is easy to mix and use the said acrylic polymer (a1) or its solution manufactured previously, and it is possible to use the crosslinking agent which can advance a crosslinking reaction rapidly. Specifically, it is more preferable to use an isocyanate crosslinking agent or an epoxy crosslinking agent.

  Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, naphthylene-1,5-diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, tolylene diisocyanate and their trimethylolpropane adducts, triphenylmethane isocyanate, and the like. Can be used. Especially, as said isocyanate type crosslinking agent, it is preferable to use tolylene diisocyanate, these trimethylol propane adducts, triphenylmethane isocyanate, etc.

  As an index of the degree of crosslinking of the pressure-sensitive adhesive layer (A) formed using the pressure-sensitive adhesive containing the cross-linking agent (a3), the insoluble content after the pressure-sensitive adhesive layer (A) was immersed in toluene for 24 hours was measured. The value of the gel fraction to do is mentioned. As said gel fraction, it is preferable that it is the range of 20 mass%-70 mass%, It is more preferable that it is the range of 30 mass%-60 mass%, It is the range of 35 mass%-55 mass% However, it is more preferable for obtaining a pressure-sensitive adhesive sheet having a still more excellent static load holding force.

  In addition, the said gel fraction can be measured by the method shown below.

  The pressure-sensitive adhesive is applied to one side of an arbitrary release liner so that the thickness after drying is 50 μm, dried at 100 ° C. for 3 minutes, and aged at 40 ° C. for 2 days to form a pressure-sensitive adhesive layer To do. A sample cut into a 50 mm square is used as a sample.

  Next, after measuring the mass (G1) of the sample, the sample is immersed in a toluene solution at 23 ° C. for 24 hours. The toluene-insoluble part of the sample after the immersion is separated by filtration through a 300 mesh wire net, and the mass (G2) of the residue after drying at 110 ° C. for 1 hour is measured, and the gel fraction is determined according to the following formula: .

    Gel fraction (mass%) = (G2 / G1) × 100

  As said adhesive, what contains the other component other than what was mentioned above as needed can be used.

  Examples of the other components include plasticizers, softeners, antioxidants, flame retardants, glass and plastic fibers, balloons and beads, fillers such as metals, metal oxides, and metal nitrides, pigments and dyes, and the like. Additives such as colorants, leveling agents, thickeners, water repellents and antifoaming agents can be used.

  Moreover, as the pressure-sensitive adhesive, it is preferable to use a material containing a solvent as required in addition to the acrylic polymer in order to impart good coating workability. As said solvent, aqueous media, such as an organic solvent and water, etc. are mentioned, for example.

  Examples of the organic solvent include toluene, ethyl acetate, butyl acetate, methyl ethyl ketone, hexane, acetone, cyclohexanone, 3-pentanone, acetonitrile, propionitrile, isobutyronitrile, valeronitrile, dimethyl sulfoxide, dimethylformamide, and the like. be able to.

  As the pressure-sensitive adhesive sheet of the present invention, for example, a pressure-sensitive adhesive sheet provided with the pressure-sensitive adhesive layer (A) on one side or both sides of a nonwoven fabric base material, a foam base material, a resin film base material, etc., only from the pressure-sensitive adhesive layer (A) A so-called base material-less pressure-sensitive adhesive sheet is mentioned.

  The pressure-sensitive adhesive sheet of the present invention can be produced, for example, by applying the pressure-sensitive adhesive to one side or both sides of the base material using a roll coater or a die coater and drying it. In addition, the pressure-sensitive adhesive sheet previously forms the pressure-sensitive adhesive layer (A) by applying the pressure-sensitive adhesive on the surface of the release liner in advance using a roll coater and the like, and then drying the pressure-sensitive adhesive layer (A). Can be produced by a transfer method in which the substrate is bonded to one or both sides of the substrate.

  Moreover, the said base material-less adhesive sheet can be manufactured by apply | coating the said adhesive to the surface of a release liner previously using a roll coater etc., and drying.

  As a base material which comprises the said adhesive sheet, a resin base material, a foam base material, a nonwoven fabric base material, cloth, paper etc. can be used, for example. Especially, it is preferable to use a foam base material as the base material.

  As said foam base material, it is preferable to use the thing whose 25% compressive strength is 20 kPa or more, for example, It is more preferable to use what is 30 kPa-1000 kPa, Use 120-700 kPa thing is used. It is more preferable to use a material having a viscosity of 200 to 600 kPa in order to develop a suitable adhesive force to an adherend having an uneven shape or a rough surface.

  The 25% compressive strength was measured according to JISK6767. The samples cut into 25 corners are overlapped to a thickness of about 10 mm. The sample is sandwiched with a stainless plate having a larger area than the sample, and the strength is measured when the sample is compressed by approximately 2.5 mm (25% of the original thickness) at a rate of 10 mm / min at 23 ° C.

  The foam base material has an interlayer strength of 4 N / cm or more, preferably 6 N / cm to 150 N / cm, more preferably 10 N / cm to 100 N / cm, more preferably 20 N / cm to 60 N / cm. A body substrate can be used.

  By using a foam having an interlayer strength within the above range, it is possible to achieve good followability to the adherend and excellent impact resistance. Furthermore, in order to improve the yield when manufacturing portable electronic devices, when peeling adhesive sheets or parts from work-in-progress (rework), or separating the casing and parts to repair or recycle or reuse the finished product, Even when the substrate is cracked and disassembled, the adhesive sheet can be easily peeled off.

  The interlayer strength is measured by the following method. A pressure-sensitive adhesive layer having a thickness of 50 μm (which does not peel off from the adherend and the foam substrate during the following high-speed peel test) was bonded to both surfaces of the foam base material for evaluating the interlayer strength one by one. Thereafter, aging is carried out at 40 ° C. for 48 hours to prepare a double-sided pressure-sensitive adhesive sheet for measuring interlayer strength. Next, a double-sided pressure-sensitive adhesive sheet having a width of 1 cm and a length of 15 cm (in the flow direction and width direction of the foam base material) lined with a polyester film having a thickness of 25 μm on one side is thickened at 23 ° C. and 50% RH. A polyester film having a thickness of 50 μm, a width of 3 cm, and a length of 20 cm is pressure-applied with one reciprocation of a 2 kg roller and allowed to stand at 60 ° C. for 48 hours. After standing at 23 ° C. for 24 hours, the side bonded to the 50 μm-thick polyester film at 23 ° C. and 50% RH is fixed to an attachment jig of a high-speed peel tester, and a 25 μm-thick polyester film is pulled to 15 m The maximum strength is measured when the foam is torn in the direction of 90 degrees per minute.

The tensile elastic modulus in the flow direction and the width direction of the foam base material is not particularly limited, but is preferably 200 N / cm ² or more, more preferably 300 to 1800 N / cm ² . Also preferably the tensile modulus of the flow direction and the ones of the widthwise tensile low elasticity modulus direction is 500~1400N / cm ^2, more preferably 600~1200N / cm ^2. Preferably high direction tensile modulus when this is 700~1800N / cm ^2, more preferably 800~1600N / cm ^2. Further, the tensile elongation at the time of cutting in the tensile test is not particularly limited, but the tensile elongation in the flow direction is preferably 200 to 1500%, more preferably 400 to 1000%, and still more preferably 450 to 800. . A foam base material having a tensile modulus and tensile elongation in the above range can suppress deterioration in workability of the pressure-sensitive adhesive sheet and deterioration in workability of application even if the foamed flexible base material is used. Moreover, when peeling an adhesive sheet, it is hard to generate | occur | produce the interlayer destruction of a foam, and a tear, and even when an interlayer crack generate | occur | produces, the ease of peeling of an adhesive sheet can be provided.

  The tensile elastic modulus in the flow direction and the width direction of the foam base material was measured according to JISK6767. This is the maximum strength of a sample with a marked line length of 2 cm and a width of 1 cm, measured using a Tensilon tensile tester in a temperature of 23 ° C. and a relative humidity of 50% RH under measurement conditions of a tensile speed of 300 mm / min.

  The cell structure of the foam base material is preferable because it is possible to effectively prevent water from entering from the cut surface of the foam base material by adopting a closed cell structure. The shape of the bubbles forming the closed cell structure is moderate following by using closed cells with a longer average bubble size in the flow direction, width direction, or both than the average bubble size in the thickness direction of the foam. It is preferable because it has a good cushioning property.

  The average cell diameter in the flow direction and the width direction of the foam substrate is 1.2 to 700 μm, preferably 10 to 500 μm, more preferably 30 to 300 μm, and still more preferably 50 to 200 μm. By setting the average cell diameter in the flow direction and the width direction in this range, even if the width of the adhesive sheet is narrowed, the number of closed cells per unit width increases, so the water immersion path from the cross section of the foam substrate is suitable. Can be blocked.

  The average cell diameter in the thickness direction of the foam base material depends on the thickness of the foam base material, but is preferably 1 to 150 μm, more preferably 5 to 100 μm, and more preferably 10 to 60 μm.

  The ratio of the average cell diameter in the flow direction of the foam substrate to the average cell diameter in the thickness direction of the foam substrate of the foam substrate (average cell diameter in the flow direction / average cell diameter in the thickness direction), The ratio of the average cell diameter in the width direction of the foam substrate to the average cell diameter in the thickness direction of the foam substrate (average cell diameter in the width direction / average cell diameter in the thickness direction) is 1. 2 to 15 is preferable, 1.2 to 10 is more preferable, and 2 to 8 is still more preferable. By using the foam base material having a ratio of 1.2 or more, the flexibility in the thickness direction of the foam base material can be improved, and as a result, the followability to the surface of the adherend is improved. be able to. The pressure-sensitive adhesive sheet excellent in followability is less expensive to extrude air that tends to remain between the adherend and the pressure-sensitive adhesive sheet (adhesion surface) when the adherends are bonded to each other. For example, even when the pressure-sensitive adhesive sheet is used for bonding between rigid bodies, it is difficult to cause a gap for water to enter the bonding surface, thereby providing excellent waterproofness. be able to.

  In addition, when obtaining a pressure-sensitive adhesive sheet that maintains excellent peel adhesive strength, push strength, static load holding force, and has extremely excellent impact resistance, the foam base material has its [flow direction] The ratio of the average bubble diameter / average bubble diameter in the thickness direction] and the ratio of [average bubble diameter in the width direction / average bubble diameter in the thickness direction] are preferably 6 or less, It is more preferable to use 1.2 to 5.5, and it is more preferable to use 1.2 to 4. By using a foam base material having a ratio in the above range, in addition to excellent peel adhesion, push strength, static load retention, and excellent impact resistance, it has excellent flexibility in the thickness direction. It is also possible to improve the followability to the surface irregularities of the wearing body, waterproofness, and the like.

  Moreover, as said foam base material, ratio of the average bubble diameter of the width direction with respect to the average bubble diameter of the flow direction of a foam base material (average bubble diameter of the width direction / average bubble diameter of the flow direction) is 0.25-0.25. 4 is preferable, 0.33 to 3 is more preferable, 0.6 to 1.5 is further preferable, and 0.7 to 1.3 is preferable. It is particularly preferable because the foam base material is less likely to vary in flexibility and tensile strength in the flow direction and width direction.

  First, a foam base material is cut into a square having a width direction of 1 cm and a flow direction of 1 cm.

  Next, after expanding the cut surface of the cut foam base material 200 times using a digital microscope (trade name “KH-7700”, manufactured by HiROX), the width direction and the flow direction of the foam base material The cut surface of was photographed.

  Next, among the cut surfaces in the width direction of the foam base material, the bubble diameters of all the bubbles existing in an arbitrary range of thickness × width direction distance (2 mm) were measured, and the average value was calculated. . Moreover, what averaged ten average values calculated by performing the said measurement with respect to arbitrary 10 places of the said cut surface was made into the average bubble diameter of the width direction.

  Moreover, the bubble diameter of all the bubbles which exist in the range of arbitrary thickness x flow direction distance (2 mm) among the cut surfaces of the flow direction of the said foam base material was measured, and the average value was computed. Moreover, what averaged ten average values calculated by performing the said measurement with respect to arbitrary 10 places of the said cut surface was made into the average bubble diameter of a flow direction.

The apparent density of the foam substrate is not particularly limited, but it is easy to achieve both impact resistance and excellent adhesion to the adherend by adjusting the interlayer strength, compressive strength, average cell diameter, etc. to the above ranges. To 0.08 to 0.7 g / cm ³ , preferably 0.1 to 0.65 g / cm ³ , more preferably 0.2 to 0.65 g / cm ³ , and particularly preferably 0.3 to 0.6 g. / Cm ³ . The apparent density was measured according to JISK6767. A foam base material cut into a 4 cm × 5 cm rectangle is prepared for about 15 cm ³ minutes, and its mass is measured to determine the apparent density.

  The interlayer strength, compressive strength, tensile elastic modulus and the like of the foam base material can be appropriately adjusted depending on the material of the base material used and the foam structure. The type of the foam substrate used in the present invention is not particularly limited as long as it has the above-mentioned interlayer strength, 25% compressive strength, tensile elastic modulus, etc., but polyethylene, polypropylene, ethylene-propylene copolymer, ethylene- Polyolefin foam made of vinyl acetate copolymer, polyurethane foam, rubber foam made of acrylic rubber, other elastomers, etc. can be used. Since it is easy to produce a foam substrate having a thin closed-cell structure excellent in buffer absorbability and the like, a polyolefin-based foam can be preferably used.

  Among polyolefin-based foams, the use of a polyethylene-based resin is preferable because it can be easily produced with a uniform thickness and suitable flexibility can be easily imparted.

  The polyylene-based resin is preferably 40% by mass or more, more preferably 50% by mass or more, and more preferably 60% by mass or more based on the total amount of the polyolefin resin used for the production of the foam. Is more preferable, and 100% by mass is particularly preferable.

  As the polyethylene resin, a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst has a narrow molecular weight distribution, and in the case of a copolymer, any molecular weight component is a copolymer component. Are introduced at substantially equal ratios, the polyolefin foam can be uniformly crosslinked. For this reason, since the foamed sheet is uniformly cross-linked, the foamed sheet can be easily stretched uniformly as necessary, and the thickness of the resulting polyolefin-based resin foam is easily uniformed, which is preferable.

  The polyolefin resin may contain a polyolefin resin other than a polyethylene resin obtained using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. Examples of such polyolefin resins include polyethylene resins and polypropylene resins other than those described above. In addition, polyolefin resin may be used independently or 2 or more types may be used together.

  Examples of such polyethylene resins include linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, an ethylene-α-olefin copolymer containing 50% by mass or more of ethylene, and 50% of ethylene. Examples thereof include ethylene-vinyl acetate copolymers containing at least mass%, and these may be used alone or in combination of two or more. Examples of the α-olefin constituting the ethylene-α-olefin copolymer include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Can be mentioned.

  In addition, the polypropylene resin is not particularly limited, and examples thereof include polypropylene and a propylene-α-olefin copolymer containing 50% by mass or more of propylene. The above may be used in combination. Examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. Can be mentioned.

  The polyolefin-based foam may be cross-linked, but is preferably cross-linked when the foamable polyolefin-based resin sheet is foamed with a thermally decomposable foaming agent.

  Next, a method for producing a polyolefin resin foam will be described. The method for producing the polyolefin resin foam is not particularly limited. For example, a polyolefin resin containing 40% by mass or more of a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, and A foamable polyolefin resin composition containing a heat decomposable foaming agent, a foaming aid, and a colorant for coloring the foam in black or white is supplied to an extruder and melt-kneaded. A step of producing a foamable polyolefin resin sheet by extruding the foamed polyolefin resin sheet, a step of crosslinking the foamable polyolefin resin sheet, a step of foaming the foamable polyolefin resin sheet, and melting or A process to stretch the foamed sheet by softening and stretching in either or both of the flow direction or width direction And a method of containing. In addition, the process of extending | stretching a foam sheet should just be performed as needed, and may be performed in multiple times.

  The step of crosslinking the expandable polyolefin resin sheet is, for example, a method of irradiating the expandable polyolefin resin sheet with ionizing radiation, an organic peroxide previously blended in the expandable polyolefin resin composition, Examples include a method of heating the obtained expandable polyolefin resin sheet to decompose the organic peroxide, and these methods may be used in combination.

Examples of ionizing radiation include electron beams, α rays, β rays, and γ rays. The dose of ionizing radiation is such that the gel fraction of the polyolefin resin foam substrate is preferably 5% by mass to 70% by mass, more preferably 20% by mass to 60% by mass, and even more preferably 25% by mass to 55% by mass.
Although it adjusts suitably so that it may become, the range of 5-200 kGy is preferable. Further, the irradiation with ionizing radiation forms a uniform cross-linked structure, and as a result, in order to form a relatively uniform foamed structure, it is preferable to irradiate from both sides of the foamable polyolefin resin sheet. Are preferably the same.

  Examples of the organic peroxide include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis ( t-butylperoxy) octane, n-butyl-4,4-bis (t-butylperoxy) valerate, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α ′ -Bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butyl) Peroxy) hexyne-3, benzoyl peroxide, cumyl peroxyneodecanate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di (ben (Zoylperoxy) hexane, t-butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate and the like may be mentioned, and these may be used alone or in combination of two or more.

  0.01 mass part-5 mass parts are preferable with respect to 100 mass parts of polyolefin resin, and, as for the addition amount of an organic peroxide, 0.1 mass part-3 mass parts are more preferable.

  The amount of the thermally decomposable foaming agent in the foamable polyolefin resin composition may be appropriately determined according to the expansion ratio of the polyolefin resin foam base material, but 1 mass with respect to 100 parts by mass of the polyolefin resin. Part-40 mass parts is preferable, and 1 mass part-30 mass parts is more preferable.

  Further, the method for foaming the expandable polyolefin resin sheet is not particularly limited, and examples thereof include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, and a method using an oil bath. May be used in combination. Among them, the method of heating with hot air or the method of heating with infrared rays is preferable because there is little difference between the front and back surfaces of the polyolefin resin foam substrate surface.

  The stretching of the foam base material may be performed after foaming the foamable polyolefin resin sheet to obtain the foam base material, or may be performed while foaming the foamable polyolefin resin sheet. . In addition, after foaming the foamable polyolefin resin sheet to obtain a foam base material, when the foam base material is stretched, the molten state at the time of foaming is maintained without cooling the foam base material. Subsequently, the foam base material may be stretched, or after the foam base material is cooled, the foam base material may be stretched again by heating the foamed sheet to a molten or softened state.

  Here, the molten state of the foam base material means a state in which the foam base material is heated to a temperature equal to or higher than the melting point of the polyolefin resin constituting the foam base material. The softening of the foam base means a state where the foam base is heated to a temperature not lower than the melting point and lower than the melting point of the polyolefin resin constituting the foam base. By stretching the foam base material, the foam of the foam base material can be produced by stretching the foam base material in a predetermined direction and deforming the foam base material so that the aspect ratio of the foam is within a predetermined range.

  Furthermore, in the extending | stretching direction of a foam base material, it extends | stretches toward the flow direction or the width direction of a elongate foamable polyolefin resin sheet, or toward a flow direction and the width direction. When the foam base material is stretched in the flow direction and the width direction, the foam base material may be stretched simultaneously in the flow direction and the width direction, or may be stretched separately one by one. .

  As a method of stretching the foam base material in the flow direction, for example, a long foam sheet after foaming is used rather than a speed (supply speed) at which a long foamable polyolefin resin sheet is supplied to the foaming process. A method of stretching the foam base material in the flow direction by increasing the winding speed (winding speed) while cooling, foaming rather than the speed (supply speed) of supplying the obtained foam base material to the stretching process Examples include a method of stretching the foam base material in the flow direction by increasing the speed of winding the body base material (winding speed).

  In the former method, the foamable polyolefin resin sheet expands in the flow direction by its own foaming. Therefore, when the foam base material is stretched in the flow direction, the foamable polyolefin resin sheet is foamed. In consideration of the amount of expansion in the flow direction, it is necessary to adjust the supply speed and the winding speed of the foam base so that the foam base is stretched in the flow direction more than the expansion.

  Further, as a method of stretching the foam base material in the width direction, both ends of the foam base material in the width direction are gripped by a pair of gripping members, and the pair of gripping members are gradually moved away from each other. A method of stretching the foam base material in the width direction is preferable. In addition, since the foamable polyolefin resin sheet expands in the width direction by its own foaming, when the foam base material is stretched in the width direction, expansion in the width direction due to foaming of the foamable polyolefin resin sheet. In consideration of the amount, it is necessary to adjust so that the foam base material is stretched in the width direction more than the expansion amount.

  Here, the draw ratio in the flow direction of the polyolefin-based foam is preferably 1.1 to 2.0 times, and more preferably 1.2 to 1.5 times.

  Moreover, 1.2 times-4.5 times are preferable and, as for the draw ratio in the width direction of a polyolefin-type foam base material, 1.5 times-3.5 times are more preferable.

  The foam base material may be colored in order to develop design properties, light shielding properties, concealing properties, light reflectivity, and light resistance in the pressure-sensitive adhesive sheet. The colorants can be used alone or in combination of two or more.

  When the light-shielding property, the concealing property, and the light resistance are imparted to the pressure-sensitive adhesive sheet, the foam base material is colored black. Black colorants include carbon black, graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, complex oxidation Physical black pigments and anthraquinone organic black pigments can be used. Of these, carbon black is preferred from the viewpoint of cost, availability, insulation, and heat resistance that can withstand the temperatures of the process of extruding the foamable polyolefin resin composition and the heating foaming process.

  When imparting designability or light reflectivity to the pressure-sensitive adhesive sheet, the foam base is colored white. White colorants include titanium oxide, zinc oxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, yttrium oxide, magnesium carbonate, calcium carbonate, barium carbonate, zinc carbonate , Aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, aluminum silicate, calcium silicate, barium sulfate, calcium sulfate, barium stearate, zinc white, talc, silica, alumina, clay, kaolin, phosphoric acid Organic white colorants such as titanium, mica, gypsum, white carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, etc., and organics such as silicone resin particles, acrylic resin particles, urethane resin particles, melamine resin particles And the like can be used white colorant. Of these, aluminum oxide and zinc oxide are preferable from the viewpoint of cost, availability, color tone, and heat resistance that can withstand the temperature of the step of extruding the foamable polyolefin resin composition and the heating and foaming step.

  In addition, the foamable polyolefin-based resin composition includes a foaming aid such as a plasticizer, an antioxidant, and zinc oxide, and a cell core modifier as long as the physical properties of the polyolefin-based resin foam substrate are not impaired. , Heat stabilizers, flame retardants such as aluminum hydroxide and magnesium hydroxide, antistatic agents, glass and plastic hollow balloon beads, metal powder, fillers such as metal compounds, conductive fillers, thermal conductive fillers A known material such as may be optionally contained in the resin. The polyolefin resin foam base material used in the pressure-sensitive adhesive sheet of the present invention is preferably 0.1% by mass to 10% by mass, preferably 1% by mass, based on the polyolefin resin, in order to maintain appropriate followability and cushioning properties. % To 7% by mass is preferable.

  In addition, when blending the colorant, the thermally decomposable foaming agent, the foaming aid, and the like into the foamable polyolefin resin composition, it is supplied to the extruder from the viewpoint of preventing color unevenness, partial excessive foaming, and insufficient foaming. It is preferable to prepare a masterbatch with a thermoplastic resin having high compatibility with the expandable polyolefin resin composition or the expandable polyolefin resin composition in advance.

  In order to improve the adhesion of the foam substrate to the pressure-sensitive adhesive layer and other layers, surface treatment such as corona treatment, flame treatment, plasma treatment, hot air treatment, ozone / ultraviolet treatment, easy-adhesive treatment agent application, etc. May have been made. In the surface treatment, when the wetting index by the wetting reagent is 36 mN / m or more, preferably 40 mN / m, more preferably 48 mN / m, good adhesion to the adhesive can be obtained. The foam base material having improved adhesion may be bonded to the pressure-sensitive adhesive layer in a continuous process. Further, the foam base material with improved adhesion may be temporarily wound up and stored, and then bonded to the pressure-sensitive adhesive layer in a separate process at a later date.

  In addition, when winding up the foam base material having improved adhesion, it is preferable to wind it through a film made of paper, polyethylene, polypropylene, polyester, or the like in order to prevent blocking of the foam base material. . The film is preferably a polypropylene film or a polyester film having a thickness of 25 μm or less.

  Moreover, as a resin base material which can be used for the said base material, plastic films, such as a polyester film, a polyethylene film, a polypropylene film, a polyvinyl chloride film, etc. can be used, for example. As the resin base material, one subjected to corona treatment, anchor coat treatment, or the like can be used for improving the anchoring property of the pressure-sensitive adhesive layer.

  As the substrate, it is preferable to use a substrate having a thickness of 1 μm to 1500 μm. When using a resin substrate as the substrate, it is preferable to use a resin substrate having a thickness of 1 μm to 150 μm, and using a resin substrate having a thickness of 1 to 100 μm is an excellent tape. It is more preferable for producing the effect of imparting excellent workability and excellent followability to the adherend. Moreover, when using the said foam base material as said base material, it is preferable to use a thing with a thickness of 1500 micrometers or less as said foam base material, and it is more preferable to use a thing with a thickness of 1200 micrometers or less. It is preferable to use one having a thickness of 500 μm or less in order to provide excellent tape workability and excellent followability to the adherend. The lower limit of the thickness is preferably 50 μm.

  Moreover, the said adhesive sheet may have another layer as needed other than the said base material and an adhesive layer.

  Examples of the other layers include a laminate layer such as a polyester film, a light shielding layer, a light reflection layer, a metal layer, and the like in order to provide, for example, dimensional stability of the pressure-sensitive adhesive sheet and good tensile strength and reworkability. Can be mentioned.

  The pressure-sensitive adhesive sheet of the present invention has a still more excellent static load holding force. Therefore, the pressure-sensitive adhesive sheet of the present invention has a width of the narrowest portion of the pressure-sensitive adhesive sheet of 5 mm or less, preferably 0.1 mm to 3 mm, more preferably 0.5 mm to 2.5 mm, for example, due to restrictions such as the application site and shape It can be used for fixing a restricted member.

  The narrow member is often used as a member in industrial applications such as portable electronic devices such as mobile phones, automobiles, building materials, OA, and home appliance industries.

  Specific examples of the member include two or more casings and lens members that constitute an electronic terminal.

  An article such as an electronic device in which two or more cases and lens members are fixed using the pressure-sensitive adhesive sheet of the present invention does not easily fall off due to an impact such as dropping, and has excellent waterproof properties.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

[Preparation Example 1] Method for Producing Acrylic Polymer (A-1) In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 80.94 parts by mass of n-butyl acrylate, 2-ethylhexyl acrylate 5 Mass parts, 10 parts by mass of cyclohexyl acrylate, 4 parts by mass of acrylic acid, 0.06 parts by mass of 4-hydroxybutyl acrylate, and 200 parts by mass of ethyl acetate were charged, and the temperature was raised to 72 ° C. while blowing nitrogen under stirring. .

  Next, 2 parts by mass of a 2,2′-azobis (2-methylbutyronitrile) solution previously dissolved in ethyl acetate (solid content: 0.1% by mass) was added to the mixture, and the mixture was stirred at 72 ° C. After holding for 4 hours, it was held at 75 ° C. for 5 hours.

  Next, the mixture was diluted with 98 parts by mass of ethyl acetate and filtered through a 200 mesh wire mesh to obtain an acrylic polymer (A-1) solution (nonvolatile content: 40% by mass) having a weight average molecular weight of 1,600,000.

In addition, the said weight average molecular weight is a weight average molecular weight in standard polystyrene conversion measured by a gel permeation chromatograph (GPC), and was measured with the following method.
The measurement of the molecular weight by GPC method is a standard polystyrene conversion value measured using a GPC apparatus (HLC-8329GPC) manufactured by Tosoh Corporation.

Sample concentration: 0.5% by mass (tetrahydrofuran solution)
Sample injection volume: 100 μl
Eluent: THF (tetrahydrofuran)
Flow rate: 1.0 ml / min Measurement temperature: 40 ° C
This column: TSKgel GMHHR-H (20) 2 Guard column: TSKgel HXL-H
Detector: differential refractometer Standard polystyrene molecular weight: 10,000 to 20 million (manufactured by Tosoh Corporation)

[Preparation Example 2] Production method of acrylic polymer (A-2) The amount of 4-hydroxybutyl acrylate used was changed from 0.06 parts by mass to 0.02 parts by mass, and the amount of n-butyl acrylate used The acrylic polymer (A-2) solution (non-volatile content: 40% by mass) having a weight average molecular weight of 1,640,000 was prepared in the same manner as in Preparation Example 1, except that 80.94 parts by mass was changed from 80.94 parts by mass to 80.98 parts by mass. Obtained.

[Preparation Example 3] Production method of acrylic polymer (A-3) The amount of 4-hydroxybutyl acrylate used was changed from 0.06 parts by weight to 0.1 parts by weight, and the amount of n-butyl acrylate used. The acrylic polymer (A-3) solution having a weight average molecular weight of 16.2 million (nonvolatile content: 40% by mass) was prepared in the same manner as in Preparation Example 1 except that 80.94 parts by mass was changed from 80.94 parts by mass to 80.9 parts by mass. Obtained.

[Preparation Example 4] Production method of acrylic polymer (A-4) Preparation example, except that the cyclohexyl acrylate is not used and the amount of 2-ethylhexyl acrylate is changed from 5 parts by mass to 15 parts by mass 1 was used to obtain an acrylic polymer (A-4) solution (nonvolatile content: 40% by mass) having a weight average molecular weight of 1.32 million.

[Preparation Example 5] Method for Producing Acrylic Polymer (A-5) The amount of acrylic acid used is changed from 4 parts by mass to 2 parts by mass, and the amount of n-butyl acrylate used is from 80.94 parts by mass. An acrylic polymer (A-5) solution having a weight average molecular weight of 1,640,000 (nonvolatile content: 40 mass) in the same manner as in Preparation Example 1 except that the content is changed to 97.94 parts by mass and 2-ethylhexyl acrylate is not used. %).

[Preparation Example 6] Method for Producing Acrylic Polymer (A-6) The amount of acrylic acid used is changed from 4 parts by mass to 6 parts by mass, and the amount of n-butyl acrylate used is from 80.94 parts by mass. An acrylic polymer (A-6) solution having a weight average molecular weight of 1,640,000 (nonvolatile content: 40 mass) in the same manner as in Preparation Example 1 except that the content is changed to 93.94 parts by mass and 2-ethylhexyl acrylate is not used. %).

[Preparation Example 7] Production method of acrylic polymer (A-7) The amount of 2,2′-azobis (2-methylbutyronitrile) solution used is from 2 parts by mass (solid content: 0.1% by mass) to 1 mass. An acrylic polymer (A-7) solution (non-volatile content 40% by mass) having a weight average molecular weight of 1.780,000 was obtained in the same manner as in Preparation Example 1, except that the content was changed to parts (solid content 0.05% by mass). .

[Preparation Example 8] Production method of acrylic polymer (A-8) The amount of 2,2′-azobis (2-methylbutyronitrile) solution used is from 2 parts by mass (solid content: 0.1% by mass) to 10 masses. An acrylic polymer (A-8) solution (nonvolatile content 40% by mass) having a weight average molecular weight of 810,000 was obtained in the same manner as in Preparation Example 1, except that the content was changed to parts (solid content 0.5% by mass). .

[Comparative Preparation Example 1] Production method of acrylic polymer (B-1) In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube and a thermometer, 95.9 parts by mass of n-butyl acrylate and 4 parts by mass of acrylic acid Part, 0.1 part by mass of 2-hydroxyethyl acrylate, and 200 parts by mass of ethyl acetate were added and the temperature was raised to 72 ° C. while blowing nitrogen under stirring.

  Next, 2 parts by mass of a 2,2′-azobis (2-methylbutyronitrile) solution previously dissolved in ethyl acetate (solid content: 0.1% by mass) was added to the mixture, and the mixture was stirred at 72 ° C. After holding for 4 hours, it was held at 75 ° C. for 5 hours.

  Next, the mixture was diluted with 98 parts by mass of ethyl acetate and filtered through a 200 mesh wire mesh to obtain an acrylic polymer (B-1) solution (nonvolatile content: 40% by mass) having a weight average molecular weight of 1,860,000.

[Comparative Preparation Example 2] Production method of acrylic polymer (B-2) In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet, and a thermometer, 63.9 parts by mass of n-butyl acrylate, 2-ethylhexyl acrylate 32 parts by mass, 4 parts by mass of acrylic acid, 0.1 part by mass of 4-hydroxybutyl acrylate, and 200 parts by mass of ethyl acetate were charged, and the temperature was raised to 72 ° C. while blowing nitrogen under stirring.

  Next, 2 parts by mass of a 2,2′-azobis (2-methylbutyronitrile) solution previously dissolved in ethyl acetate (solid content: 0.1% by mass) was added to the mixture, and the mixture was stirred at 72 ° C. After holding for 4 hours, it was held at 75 ° C. for 5 hours.

  Next, the mixture was diluted with 98 parts by mass of ethyl acetate and filtered through a 200 mesh wire mesh to obtain an acrylic polymer (B-2) solution (nonvolatile content: 40% by mass) having a weight average molecular weight of 750,000.

[Example 1]
In a container, with respect to 100 parts by mass of the acrylic polymer (A-1), 15 parts by mass of polymerized rosin ester-based tackifier resin D-125 (Arakawa Chemical Industries, Ltd.) and disproportionated rosin ester-based tackifier resin After mixing and stirring 10 parts by mass of A-125 (manufactured by Arakawa Chemical Industries, Ltd.), ethyl acetate was added to obtain an adhesive solution having a solid content of 31% by mass.

  Next, Vernock D-40 (manufactured by DIC Corporation, trimethylolpropane adduct of tolylene diisocyanate, isocyanate group content 7% by mass, nonvolatile content 40% by mass with respect to 100 parts by mass of the pressure-sensitive adhesive solution. ) After adding 1.4 parts by mass, stirring and mixing so as to be uniform, an adhesive (p-1) was obtained by filtering through a 100 mesh wire net.

  Next, the pressure-sensitive adhesive is coated on the surface of the release liner using a bar coater so that the thickness of the pressure-sensitive adhesive layer after drying is 65 μm, and dried at 80 ° C. for 3 minutes. A layer was made.

Next, the pressure-sensitive adhesive layer was made of a polyolefin-based foam substrate having a thickness of 170 μm (apparent density of 0.45 g / cm ³ , with the surface wetting index adjusted to 54 mN / m by corona treatment on both sides). The pressure-sensitive adhesive sheet (P-1) was prepared by sticking to both surfaces and curing for 48 hours in an environment of 40 ° C. In addition, the tensile strength measured by the method mentioned later of the adhesive layer which the said adhesive sheet (P-1) has was 11.3 N / cm < ² >.

[Example 2]
Instead of the acrylic polymer (A-1) solution, the acrylic polymer (A-2) solution is used, and the compounding amount of Bernock D-40 is changed from 1.4 parts by mass to 1.6 parts by mass. Except for this, a pressure-sensitive adhesive (p-2) and a pressure-sensitive adhesive sheet (P-2) were obtained in the same manner as in Example 1.

[Example 3]
Instead of the acrylic polymer (A-1) solution, the acrylic polymer (A-3) solution is used, and the compounding amount of Bernock D-40 is changed from 1.4 parts by mass to 1.2 parts by mass. Except for this, a pressure-sensitive adhesive (p-3) and a pressure-sensitive adhesive sheet (P-3) were obtained in the same manner as in Example 1.

[Example 4]
Instead of the acrylic polymer (A-1) solution, the pressure-sensitive adhesive (p-4) and pressure-sensitive adhesive sheet (P-4) and pressure-sensitive adhesive sheet (P-4) were prepared in the same manner as in Example 1 except that the acrylic polymer (A-4) solution was used. P-4) was obtained.

[Example 5]
Instead of the acrylic polymer (A-1) solution, the pressure-sensitive adhesive (p-5) and pressure-sensitive adhesive sheet (P-5) and pressure-sensitive adhesive sheet (P-5) were used in the same manner as in Example 1 except that the acrylic polymer (A-5) solution was used. P-5) was obtained.

[Example 6]
Instead of the acrylic polymer (A-1) solution, the pressure-sensitive adhesive (p-6) and pressure-sensitive adhesive sheet (p-6) and pressure-sensitive adhesive sheet (P-6) were used in the same manner as in Example 1 except that the acrylic polymer (A-6) solution was used. P-6) was obtained.

[Example 7]
A pressure-sensitive adhesive (p-7) and a pressure-sensitive adhesive sheet (p-7) and pressure-sensitive adhesive sheet (p-7) were prepared in the same manner as in Example 1 except that the acrylic polymer (A-7) solution was used instead of the acrylic polymer (A-1) solution. P-7) was obtained.

[Example 8]
Instead of the acrylic polymer (A-1) solution, the pressure-sensitive adhesive (p-8) and pressure-sensitive adhesive sheet (p-8) and pressure-sensitive adhesive sheet (P-8) were prepared in the same manner as in Example 1 except that the acrylic polymer (A-8) solution was used. P-8) was obtained.

[Example 9]
As the tackifier resin, 10 parts by mass of the polymerized rosin ester tackifier resin D-125 (Arakawa Chemical Industries, Ltd.) and disproportionated rosin ester tackifier resin A-125 (Arakawa Chemical Industries, Ltd.) 5 A pressure-sensitive adhesive (p-9) and pressure-sensitive adhesive sheet (P-9) in the same manner as in Example 1 except that 15 parts by weight of petroleum-based tackifying resin FTR6125 (Mitsui Chemicals, Inc.) are used. Got.

[Example 10]
Instead of the polyolefin foam substrate having a thickness of 170 μm, a polyolefin foam substrate having a thickness of 140 μm (apparent density 0.40 g / cm ³ ) was used, and the thickness of the pressure-sensitive adhesive layer after drying The pressure-sensitive adhesive (p-10) and the pressure-sensitive adhesive sheet (P-10) were obtained in the same manner as in Example 1 except that the thickness was changed from 65 μm to 80 μm.

[Comparative Example 1]
Other than using the acrylic polymer (B-1) solution instead of the acrylic polymer (A-1) solution and changing the amount of Vernock D-40 from 1.4 parts by mass to 1.2 parts by mass Obtained the adhesive (q-1) and the adhesive sheet (Q-1) by the same method as Example 1.

[Comparative Example 2]
Other than using the acrylic polymer (B-2) solution instead of the acrylic polymer (A-1) solution and changing the amount of Vernock D-40 from 1.4 parts by mass to 1.6 parts by mass Obtained the adhesive (q-2) and the adhesive sheet (Q-2) by the same method as Example 1.

[Measurement Method of Tensile Strength Based on Stress-Strain Curve at 100% and 500% Strain]
The pressure-sensitive adhesive is applied to one side of an arbitrary release liner so that the thickness after drying is 50 μm, dried at 80 ° C. for 3 minutes, and aged at 40 ° C. for 48 hours to form a pressure-sensitive adhesive layer. did. Next, this pressure-sensitive adhesive layer was laminated to a thickness of about 400 μm to prepare a test piece having a marked line interval of 2 cm and a width of 1 cm.

  From the stress-strain curve (so-called SS curve) measured at a tensile speed of 300 mm / min using a tensile tester in a measurement environment at a temperature of 23 ° C. and a humidity of 50%, the amount of strain was measured. Tensile strength was determined at 100% and 500%.

[Measurement method of gel fraction]
The pressure-sensitive adhesive composition is coated on one side of an arbitrary release liner so that the thickness after drying is 50 μm, dried at 80 ° C. for 3 minutes, and aged at 40 ° C. for 2 days. Form. A sample cut into a 50 mm square was used as a sample.

  Next, after measuring the mass (G1) of the sample, the sample is immersed in a toluene solution at 23 ° C. for 24 hours. The toluene-insoluble matter of the sample after the immersion is separated by filtering through a 300 mesh wire mesh, and the mass (G2) of the residue after drying at 110 ° C. for 1 hour is measured, and the gel fraction is obtained according to the following formula. It was.

    Gel fraction (mass%) = (G2 / G1) × 100

[Evaluation method of static load holding force]
In an atmosphere of a temperature of 23 ° C. and a relative humidity of 50%, one pressure-sensitive adhesive layer of a frame-shaped pressure-sensitive adhesive sheet having an outer shape of 14 mm × 14 mm and a width of 2 mm is applied to an acrylic plate (Mitsubishi Rayon, 2 mm thick and 15 mm × 15 mm in outer diameter). Acrylite MR200 “trademark”, hue: transparent).

Next, an acrylic plate with an adhesive sheet is attached to a rectangular stainless steel plate having a diameter of 8 mm in the center and a thickness of 2 mm and an outer shape of 65 mm × 30 mm, and then the hole is closed, and then 50 N / cm ² The test piece was pressed for 10 seconds.

  In an atmosphere of a temperature of 40 ° C. and a relative humidity of 50%, the test piece was leveled so that the acrylic plate side was down, and both ends on the short side of the stainless steel plate were fixed. Next, a weight of 400 g was attached to the center of the acrylic plate, and the acrylic plate was left in a state of being loaded downward.

  Next, in an atmosphere at a temperature of 40 ° C. and a relative humidity of 50%, the time (minutes) until the distance between the acrylic plate attached with the weight and the stainless steel plate is 0.2 mm apart from before the start of the test is measured. did. In addition, even if 24 hours passed from the start of measurement, an increase in the distance between the acrylic plate and the stainless steel plate was less than 0.2 mm was described as “1440 minutes or more” in the table described later.

[Push strength]
A rectangular acrylic plate (Mitsubishi Rayon Co., Ltd. Acrylite MR200 “trademark”, hue: transparent) having a thickness of 2 mm and an outer diameter of 65 mm × 45 mm in an environment of a temperature of 23 ° C. and a relative humidity of 50% RH. A frame-shaped pressure-sensitive adhesive sheet having a rectangular width of 2 mm and a width of the pressure-sensitive adhesive sheet was pasted.

  Next, affix the adhesive sheet to a rectangular ABS plate (Sumitomo Bakelite Co., Ltd. Toughace REAR003, hue: natural, no wrinkles) with a 10 mm diameter hole in the center and a thickness of 2 mm, 100 × 150 mm The acrylic plate thus attached is pasted so that the center of the acrylic plate and the center of the ABS plate coincide with each other, and is pressed once by a 2 kg roller, and then 1 in an environment of temperature 23 ° C. and relative humidity 50% RH. The test piece was left standing for a period of time.

  From the ABS side of the test piece, the acrylic plate was pushed at 10 mm / min with a tensile tester equipped with a 8 mm diameter stainless steel probe through a hole in the ABS plate, and the strength at which the acrylic plate was peeled was measured.

Claims (8)

A pressure-sensitive adhesive sheet for use in fixing the components constituting the electronic device, on one or both sides of the substrate, stress at the strain amount 100% - stress based on the distortion curve is 6N / cm ² or more 30 N / cm ² or less pressure-sensitive adhesive layer (a) possess, the pressure-sensitive adhesive layer (a) are those containing acrylic polymer (a1), tackifier (a2) and the crosslinking agent (a3), the acrylic polymer (a1 ) Is a polymer of a vinyl monomer component, and uses a vinyl monomer having an acid group in a range of 1% by mass to 30% by mass with respect to the total amount of the vinyl monomer component, and has a hydroxyl group. An alkyl (meth) acrylate in which a vinyl monomer is used in the range of 0.01% by mass to 0.2% by mass with respect to the total amount of the vinyl monomer component, and the alkyl group has 4 to 12 carbon atoms. In the range of 50% to 98% by weight The average mass molecular weight is 800,000 or more, and the tackifier (a2) is a polymerized rosin ester tackifier resin, disproportionated rosin ester tackifier resin, petroleum tackifier resin, and terpene phenol tackifier It is 1 or more types chosen from the group which consists of provision resin, 5-60 mass parts is used with respect to 100 mass parts of said acrylic polymers (a1), The adhesive sheet characterized by the above-mentioned. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer (A) has a thickness in the range of 1 µm to 100 µm. The pressure-sensitive adhesive sheet according to claim 1, wherein the base material is a foam base material. The pressure-sensitive adhesive sheet according to claim 3, wherein the foam base material has a thickness of 1500 μm or less. The acrylic polymer (a1), the with respect to the total amount of the vinyl monomer component, (meth) content of the vinyl monomer other than the acrylic monomer is a total of 5 wt% or less, and a glass transition temperature of the homopolymer There pressure-sensitive adhesive sheet according to claim 3 or 4 content of 100 ° C. or more alkyl (meth) acrylate is less than or equal to the total 1% by weight. The tackifier resin (a2) contains two or more selected from the group consisting of a polymerized rosin ester tackifier resin, a disproportionated rosin ester tackifier resin, a petroleum tackifier resin, and a terpene phenol tackifier resin. The pressure-sensitive adhesive sheet according to any one of claims 3 to 5 . The pressure-sensitive adhesive sheet according to any one of claims 1 to 6 , which is used for fixing a casing or a lens constituting a portable electronic device. Electronic device obtained by two or more components of the electronic device is fixed using an adhesive sheet according to any one of claims 1-7.

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