adhesive sheet

Abstract

To provide an adhesive sheet that has an adhesive layer containing heat-expandable microspheres and yet has excellent pick-up property when the adherend is peeled off.SOLUTION: The adhesive sheet of the present invention has an adhesive layer containing heat-expandable microspheres, and in the adhesive layer, the expansion property of the adhesive when heated to the foaming peak temperature of the heat-expandable microspheres (thickness of the adhesive layer when heated to the foaming peak temperature of the heat-expandable microspheres / thickness of the adhesive layer at 23°C) is 1.1 to 2. In one embodiment, the adhesive layer contains an active energy ray-curable adhesive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] In the process of manufacturing electronic components, pressure-sensitive adhesive sheets used for the purpose of temporarily fixing workpieces (e.g., electronic components) are known to exhibit adhesive properties during temporary fixing and exhibit releasability when fixation is not required. As one such pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet containing heat-expandable microspheres in the pressure-sensitive adhesive layer has been studied (e.g., Patent Document 1). This pressure-sensitive adhesive sheet exhibits a desired adhesive strength to fix the workpiece at relatively low temperatures, such as room temperature. However, when heated, the heat-expandable microspheres expand, creating irregularities on the surface of the pressure-sensitive adhesive layer, reducing the adhesive strength and allowing the workpiece to be easily peeled off.

[0003] After the workpiece is temporarily fixed as described above, the workpiece may be picked up from above and transported (e.g., by suction) during peeling. In this case, the workpiece may tilt due to uneven deformation of the pressure-sensitive adhesive layer surface, resulting in poor pickup. This problem becomes more pronounced as the workpiece (e.g., electronic components) becomes smaller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-131507 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a PSA sheet that has an adhesive layer containing heat-expandable microspheres and yet has excellent pick-up properties when peeled from an adherend. [Means for solving the problem]

[0006] The pressure-sensitive adhesive sheet of the present invention comprises a pressure-sensitive adhesive layer containing heat-expandable microspheres, and the pressure-sensitive adhesive layer has a pressure-sensitive adhesive expansion ratio (thickness of the pressure-sensitive adhesive layer when heated to the peak expansion temperature of the heat-expandable microspheres / thickness of the pressure-sensitive adhesive layer at 23°C) of 1.1 to 2 when heated to the peak expansion temperature of the heat-expandable microspheres. In one embodiment, the pressure-sensitive adhesive layer contains an active energy ray-curable pressure-sensitive adhesive. In one embodiment, the active energy ray-curable pressure-sensitive adhesive contains a polymer and an oligomer as an active energy ray-reactive compound. In one embodiment, the active energy ray-curable pressure-sensitive adhesive contains an active energy ray-reactive polymer. In one embodiment, the active energy ray-curable pressure-sensitive adhesive contains a photopolymerization initiator, and the photopolymerization initiator is at least one selected from the group consisting of alkylphenone-based photopolymerization initiators, hydroxyacetophenone-based photopolymerization initiators, hydroxyketone-based photopolymerization initiators, aminoacetophenone-based photopolymerization initiators, and benzylketanol-based photopolymerization initiators. In one embodiment, the active energy ray-curable pressure-sensitive adhesive contains a tackifier. In one embodiment, the content of the tackifier is 1 part by weight to 100 parts by weight relative to 100 parts by weight of the polymer in the active energy ray-curable pressure-sensitive adhesive. In one embodiment, the pressure-sensitive adhesive layer has an elastic modulus of 3.0 MPa to 400 MPa as measured by nanoindentation at a temperature 10° C. lower than the expansion start temperature of the expandable microspheres. In one embodiment, the heat-expandable microspheres have a volume-cumulative particle diameter D50 of 13 μm to 50 μm. In one embodiment, the heat-expandable microspheres have a particle size distribution peak width of 20 μm or less. In one embodiment, the content of the heat-expandable microspheres is 5 to 50 parts by weight per 100 parts by weight of the polymer in the pressure-sensitive adhesive. In one embodiment, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet has an initial adhesive strength of 0.5 N / 20 mm to 25 N / 25 mm when attached to SUS304BA. In one embodiment, the pressure-sensitive adhesive sheet further comprises a substrate, and the pressure-sensitive adhesive layer is disposed on at least one side of the substrate. According to another aspect of the present invention, there is provided a method for producing an electronic component, comprising the steps of attaching the pressure-sensitive adhesive sheet to a device, irradiating the pressure-sensitive adhesive sheet with ultraviolet light, and heating the pressure-sensitive adhesive sheet to peel the device from the pressure-sensitive adhesive sheet. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet that has an adhesive layer containing heat-expandable microspheres and yet has excellent pick-up properties when peeled off from an adherend. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. Overview of adhesive sheets 1(a) is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. The pressure-sensitive adhesive sheet 100 comprises a pressure-sensitive adhesive layer 10. The pressure-sensitive adhesive sheet of the present invention may consist solely of the pressure-sensitive adhesive layer 10, or may further comprise any appropriate layer in addition to the pressure-sensitive adhesive layer.

[0010] FIG. 1(b) is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to another embodiment of the present invention. Pressure-sensitive adhesive sheet 200 further comprises a substrate 20, with a pressure-sensitive adhesive layer 10 disposed on at least one side of the substrate 20. FIG. 1(c) is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to yet another embodiment of the present invention. Pressure-sensitive adhesive sheet 300 comprises a pressure-sensitive adhesive layer 10 and another pressure-sensitive adhesive layer 30 disposed on at least one side of the pressure-sensitive adhesive layer 10. As shown in the illustrated example, a substrate 20 may be disposed between the pressure-sensitive adhesive layer 10 and the other pressure-sensitive adhesive layer 30. Alternatively, although not shown, the substrate may be omitted and the pressure-sensitive adhesive sheet may be formed from a pressure-sensitive adhesive layer and another pressure-sensitive adhesive layer. Furthermore, although not shown, the pressure-sensitive adhesive sheet may further comprise, as layers other than the pressure-sensitive adhesive layer, an elastic layer (described below in Section E) capable of imparting elasticity to the pressure-sensitive adhesive sheet, a separator (described below in Section F) releasably disposed on the pressure-sensitive adhesive layer, or the like. Pressure-sensitive adhesive layers may also be disposed on both sides of the substrate.

[0011] In one embodiment, the pressure-sensitive adhesive layer may be a pressure-sensitive adhesive layer that can be cured by irradiation with active energy rays. The curable pressure-sensitive adhesive layer may be configured to include an active energy ray-curable pressure-sensitive adhesive.

[0012] The pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present invention contains heat-expandable microspheres. The heat-expandable microspheres can expand at a predetermined temperature. When the pressure-sensitive adhesive layer containing such heat-expandable microspheres is heated, the heat-expandable microspheres expand, causing unevenness on the adhesive surface (i.e., the surface of the pressure-sensitive adhesive layer), resulting in a decrease or loss of adhesive strength. When the pressure-sensitive adhesive sheet of the present invention is used as a sheet for temporarily fixing a workpiece during processing of electronic components (e.g., printed circuit boards), the adhesive strength required for temporary fixing is exhibited when the workpiece is subjected to a predetermined processing (e.g., dicing), and when the workpiece is peeled from the pressure-sensitive adhesive sheet after processing, the adhesive strength is reduced or lost by heating, resulting in good peelability. In one embodiment, if the pressure-sensitive adhesive layer is curable, the pressure-sensitive adhesive layer is cured with active energy rays after processing, and then heated to peel off the workpiece. By performing a bonding operation before curing, the pressure-sensitive adhesive sheet can be attached with good unevenness-following ability. In another embodiment, when the pressure-sensitive adhesive layer is curable, the pressure-sensitive adhesive layer is cured by active energy rays, and then the workpiece is attached.

[0013] The adhesive layer exhibits a pressure-sensitive adhesive expansion coefficient of 1.1 to 2 when heated to the peak expansion temperature of the heat-expandable microspheres. In this specification, the pressure-sensitive adhesive expansion coefficient is calculated for a single pressure-sensitive adhesive layer by the formula [thickness at peak expansion / initial thickness], where the thickness at 20°C (initial thickness) and the thickness when heated to the peak expansion temperature of the heat-expandable microspheres (thickness at peak expansion) are taken as the initial thickness. The "peak expansion temperature" refers to the temperature at which the pressure-sensitive adhesive sheet reaches its maximum thickness when heated at a predetermined temperature (20°C to 300°C) for 1 minute. The "temperature at maximum thickness" refers to the temperature at which the thickness reaches its maximum due to the expansion of the heat-expandable microspheres. At temperatures higher than the "temperature at maximum thickness," the pressure-sensitive adhesive tape becomes thinner again due to the contraction of the heat-expandable microspheres. The temperature at which the thickness of the pressure-sensitive adhesive layer reaches 110% of the initial thickness at 20°C is referred to as the "expansion onset temperature," as described below. In addition, when the pressure-sensitive adhesive layer is curable, the heating during measurement of both the "foaming peak temperature" and the "foaming onset temperature" is performed by irradiation with active energy rays (e.g., UV irradiation (1000 mJ / cm 2)) will be held later.

[0014] In the present invention, by specifying the adhesive expansion property as described above, deformation in the thickness direction of the adhesive layer upon heating is suppressed, improving the uniformity of the deformation. Meanwhile, the heat-expandable microspheres can be preferably used to generate minute irregularities. By using the adhesive sheet of the present invention having such characteristics, the workpiece does not tilt when peeled off, thereby preventing pickup failure. The adhesive expansion property when heated to the peak expansion temperature of the heat-expandable microspheres is preferably 1.1 to 1.8, more preferably 1.1 to 1.6, and even more preferably 1.1 to 1.5. Within these ranges, the above-mentioned effects are significant. The adhesive expansion property can be controlled, for example, by the elastic modulus of the adhesive layer (e.g., elastic modulus measured by nanoindentation at a temperature 10°C lower than the expansion onset temperature), the size characteristics of the heat-expandable microspheres (e.g., 50% particle size, particle size distribution), the amount of heat-expandable microspheres added, etc.

[0015] The initial adhesive strength of the adhesive layer of the pressure-sensitive adhesive sheet when applied to SUS304BA is preferably 0.5 to 25 N / 20 mm, more preferably 1 to 20 N / 20 mm, even more preferably 1.5 to 18 N / 20 mm, and particularly preferably 2 to 15 N / 20 mm. Within these ranges, a pressure-sensitive adhesive sheet exhibiting good adhesive properties can be obtained, for example, as a temporary fixing sheet used in the manufacture of electronic components. In this specification, the initial adhesive strength refers to the adhesive strength before the heat-expandable microspheres are expanded (or before the adhesive layer is cured, if curable). The adhesive strength is measured at 23°C according to a method in accordance with JIS Z 0237:2000 (lamination conditions: one reciprocal movement with a 2 kg roller, peel speed: 300 mm / min, peel angle: 180°).

[0016] In one embodiment, when the pressure-sensitive adhesive layer is curable, the pressure-sensitive adhesive sheet is cured by irradiation with active energy rays (for example, an integrated light dose of 1000 mJ / cm 2When the pressure-sensitive adhesive layer is adhered to SUS304BA by ultraviolet light of 1000 mJ / cm 2 at 23°C, the adhesive strength at 23°C when the pressure-sensitive adhesive layer is adhered to SUS304BA is preferably 0.1 N / 20 mm to 25 N / 20 mm, more preferably 0.2 N / 20 mm to 15 N / 20 mm, even more preferably 0.2 N / 20 mm to 10 N / 20 mm, and particularly preferably 0.2 N / 20 mm to 5 N / 20 mm. As a method for irradiating with active energy rays, for example, after adhering the pressure-sensitive adhesive sheet to SUS304BA, an ultraviolet irradiator "UM810 (high-pressure mercury lamp light source)" (manufactured by Nitto Seiki Co., Ltd.) is used to irradiate the pressure-sensitive adhesive sheet from the pressure-sensitive adhesive sheet side with an integrated light amount of 1000 mJ / cm 2 . 2 Examples of the method include irradiating the film with ultraviolet light.

[0017] The thickness of the pressure-sensitive adhesive sheet is preferably 30 μm to 500 μm, more preferably 40 μm to 300 μm, and even more preferably 50 μm to 200 μm.

[0018] In one embodiment, the pressure-sensitive adhesive sheet can be used as a fixing material for temporarily fixing a device when manufacturing an electronic component. In one embodiment, a method for manufacturing an electronic component is provided, comprising the steps of: attaching the pressure-sensitive adhesive sheet to a device; irradiating the pressure-sensitive adhesive sheet with ultraviolet light; and then heating the pressure-sensitive adhesive sheet and peeling the device from the pressure-sensitive adhesive sheet. Preferably, the "expansion property of the pressure-sensitive adhesive when heated to the peak expansion temperature of the heat-expandable microspheres" is controlled by adjusting the ultraviolet light irradiation conditions in the "step of irradiating the pressure-sensitive adhesive sheet with ultraviolet light." The ultraviolet light irradiation dose is, for example, 10 mJ / cm. 2 ~1500mJ / cm 2 is.

[0019] B.Adhesive layer The pressure-sensitive adhesive layer contains a pressure-sensitive adhesive for imparting adhesiveness and heat-expandable microspheres.

[0020] The pressure-sensitive adhesive layer preferably has a normal elastic modulus at 23°C, as measured by nanoindentation, of 1.0 MPa to 20.0 MPa, and more preferably 3.0 MPa to 15.0 MPa. The "normal elastic modulus as measured by nanoindentation" refers to the elastic modulus before irradiation with active energy rays. The method for measuring the normal elastic modulus as measured by nanoindentation will be described later.

[0021] The pressure-sensitive adhesive layer preferably has a modulus of elasticity of 3.0 MPa to 400 MPa, more preferably 3.0 MPa to 320 MPa, even more preferably 3.0 MPa to 280 MPa, and particularly preferably 6.0 MPa to 200 MPa, as measured by nanoindentation at a temperature 10°C lower than the expansion onset temperature of the heat-expandable microspheres. Within these ranges, the expansion of the heat-expandable microspheres can be appropriately restricted, the expansion of the pressure-sensitive adhesive can be favorably controlled, tilting of the adherend during peeling can be prevented, and a pressure-sensitive adhesive sheet exhibiting sufficient heat-peelability can be obtained. The "modulus of elasticity as measured by nanoindentation at a temperature 10°C lower than the expansion onset temperature of the heat-expandable microspheres" can be adjusted by any appropriate method. For example, the modulus of elasticity can be adjusted to an appropriate range depending on the structure of the pressure-sensitive adhesive components. In one embodiment, an adhesive layer is formed using an active energy ray-curable adhesive, and the adhesive layer is irradiated with active energy rays (e.g., ultraviolet rays) to adjust the "elastic modulus as measured by nanoindentation at a temperature 10°C lower than the expansion initiation temperature of the heat-expandable microspheres." In this embodiment, the active energy ray-curable adhesive contains an active energy ray-reactive compound (monomer or oligomer) or an active energy ray-reactive polymer, and the "elastic modulus as measured by nanoindentation at a temperature 10°C lower than the expansion initiation temperature of the heat-expandable microspheres" can be adjusted by adjusting the amount of carbon-carbon multiple bonds in these compounds, the amount of adhesive added, the dose of active energy rays, etc.

[0022] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 200 μm, more preferably 15 μm to 100 μm, still more preferably 20 μm to 60 μm, and particularly preferably 25 μm to 45 μm.

[0023] The surface roughness Ra of the pressure-sensitive adhesive layer before the expansion of the heat-expandable microspheres at an ambient temperature of 25°C is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. Within these ranges, a pressure-sensitive adhesive sheet can be obtained that can reduce the occurrence of irregularities on the adhesion surface of an adherend. The surface roughness Ra can be adjusted to an appropriate value by adjusting the content and average particle size of the heat-expandable microspheres contained in the pressure-sensitive adhesive layer. The surface roughness Ra can be measured in accordance with JIS B 0601:1994.

[0024] After the pressure-sensitive adhesive sheet of the present invention is heated to expand the heat-expandable microspheres, the surface roughness Ra of the pressure-sensitive adhesive layer is preferably 1 μm or more, more preferably 3 μm or more. Within this range, a pressure-sensitive adhesive sheet can be obtained in which the adhesive strength is reduced or eliminated after heating, allowing easy peeling of the adherend. Here, the surface roughness Ra of the pressure-sensitive adhesive layer refers to the surface roughness Ra of the pressure-sensitive adhesive layer after heating in the absence of an adherend.

[0025] B-1. Adhesive Any appropriate adhesive may be used as the adhesive constituting the adhesive layer as long as the effects of the present invention can be obtained. In one embodiment, a curable adhesive is used as the adhesive, and preferably an active energy ray curable adhesive is used. In another embodiment, a pressure-sensitive adhesive is used as the adhesive. Examples of pressure-sensitive adhesives include acrylic adhesives and rubber adhesives. Preferably, a curable adhesive is used. Use of a curable adhesive makes it possible to preferably control the adhesive expansion.

[0026] (Active energy ray curable adhesive) Examples of the active energy ray-curable adhesive include those described in Ultraviolet Curing System (by Kiyomi Kato, published by General Technology Center, (1989)), Photocuring Technology (edited by Technical Information Association, (2000)), JP 2003-292916 A, and Japanese Patent No. 4151850. More specifically, examples include adhesives (R1) containing a polymer as a base material and an active energy ray-reactive compound (monomer or oligomer), and adhesives (R2) containing an active energy ray-reactive polymer. In one embodiment, adhesive (R1) contains a polymer and an oligomer as an active energy ray-reactive compound.

[0027] Examples of the polymer that can be used as the base material include rubber-based polymers such as natural rubber, polyisobutylene rubber, styrene-butadiene rubber, styrene-isoprene-styrene block copolymer rubber, reclaimed rubber, butyl rubber, polyisobutylene rubber, and nitrile rubber (NBR); silicone-based polymers; and acrylic-based polymers. These polymers may be used alone or in combination of two or more.

[0028] Examples of the active energy ray-reactive compound include photoreactive monomers or oligomers having multiple functional groups with carbon-carbon multiple bonds, such as acryloyl groups, methacryloyl groups, vinyl groups, allyl groups, and acetylene groups. Among these, compounds having ethylenically unsaturated functional groups are preferred, and (meth)acrylic compounds having ethylenically unsaturated functional groups are more preferred. Compounds having ethylenically unsaturated functional groups readily generate radicals upon exposure to ultraviolet light, allowing the formation of a pressure-sensitive adhesive layer that can be cured in a short period of time. Furthermore, the use of (meth)acrylic compounds having ethylenically unsaturated functional groups allows the formation of a pressure-sensitive adhesive layer that has an appropriate hardness after curing (specifically, a hardness that allows the heat-expandable microspheres to be foamed well). Specific examples of photoreactive monomers or oligomers include (meth)acryloyl group-containing compounds such as urethane oligomers, urethane (meth)acrylates, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-butanediol di(meth)acrylate, and polyethylene glycol di(meth)acrylate; dimers to pentamers of the (meth)acryloyl group-containing compounds; and the like. These compounds may be used alone or in combination of two or more. The active energy ray-reactive compound may contain one or more functional groups. The presence of two or more functional groups facilitates control of the properties of the pressure-sensitive adhesive layer. In this specification, oligomers are those with a molecular weight of 3.0 × 10 4 The molecular weight of the oligomer is preferably 100 or more, and is preferably 1.0 × 10 4 The molecular weight of the oligomer is preferably the weight average molecular weight (Mw) calculated in terms of standard polystyrene determined by gel permeation chromatography (GPC), or the molecular weight calculated from the chemical formula.

[0029] When an oligomer is used as the active energy ray-reactive compound, the number of functional groups (the number of functional groups having a carbon-carbon multiple bond) per molecule of the oligomer is preferably 7 or more, more preferably 8 or more, even more preferably 9 or more, and particularly preferably 10 or more. Within this range, the elastic modulus can be suitably adjusted, and a pressure-sensitive adhesive layer capable of exhibiting suitable pressure-sensitive adhesive expansion properties can be obtained. The upper limit of the number of functional groups is preferably 20.

[0030] The active energy ray reactive compound may be a monomer such as epoxidized butadiene, glycidyl methacrylate, acrylamide, vinylsiloxane, or an oligomer composed of such a monomer. The pressure-sensitive adhesive (R1) containing such a compound can be cured by high-energy rays such as ultraviolet rays and electron beams.

[0031] Furthermore, the active energy ray-reactive compound may be a mixture of an organic salt such as an onium salt and a compound having multiple heterocycles in the molecule. When the mixture is irradiated with active energy rays (e.g., ultraviolet light or an electron beam), the organic salt is cleaved to generate ions, which act as initiating species to cause a ring-opening reaction of the heterocycles, forming a three-dimensional network structure. Examples of the organic salt include iodonium salts, phosphonium salts, antimonium salts, sulfonium salts, and borate salts. Examples of the heterocycle in the compound having multiple heterocycles in the molecule include oxirane, oxetane, oxolane, thiirane, and aziridine.

[0032] In the pressure-sensitive adhesive (R1) comprising the above-mentioned base polymer and active energy ray-reactive compound, the content of the active energy ray-reactive compound is preferably 5 to 200 parts by weight, more preferably 10 to 150 parts by weight, even more preferably 10 to 100 parts by weight, and particularly preferably 10 to 80 parts by weight, per 100 parts by weight of the base polymer. Within this range, the elastic modulus can be suitably adjusted, and a pressure-sensitive adhesive layer capable of exhibiting favorable pressure-sensitive adhesive expansion properties can be obtained. If the content of the active energy ray-reactive compound is too high, there is a risk of contamination of the adherend.

[0033] As the active energy ray reactive polymer, any appropriate polymer having a carbon-carbon double bond can be used.

[0034] In one embodiment, the polymer having a carbon-carbon double bond is obtained by introducing a carbon-carbon double bond into a polymer not containing a carbon-carbon double bond by a method such as chemical modification. A specific example of a method for introducing a carbon-carbon double bond into a polymer not containing a carbon-carbon double bond is a method in which a monomer having a functional group A is polymerized onto a polymer not containing a carbon-carbon double bond, and then a compound (monomer or oligomer) having a carbon-carbon double bond and a functional group B reactive with the functional group A is reacted (typically by condensation or addition reaction) so as not to lose the carbon-carbon double bond. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among these, a combination of a hydroxyl group and an isocyanate group is preferred from the viewpoint of reaction traceability. Furthermore, as for the combination of the functional groups A and B, as long as it is a combination that can produce a polymer having a carbon-carbon double bond, one of the functional groups in the combination may be functional group A and the other may be functional group B, or one of the functional groups may be functional group B and the other may be functional group A. Among these, a combination in which the polymer has a hydroxyl group and the compound has an isocyanate group is preferred.

[0035] Furthermore, when the polymer not containing a carbon-carbon double bond is a vinyl alcohol-based polymer (e.g., polyvinyl alcohol), a suitable example is a method in which a vinyl alcohol-based polymer is reacted with a vinyl halide such as vinyl bromide or an allyl halide such as allyl bromide. The reaction is carried out under appropriate basic conditions. Alternatively, for example, a method of preparing a polymer having a carbon-carbon double bond using a microorganism capable of producing a polymer, such as that disclosed in Japanese Patent No. 4502363, may be employed. The conditions for this method, such as the microbial species and microbial culture conditions, may be determined by adopting the conditions described in the above patent publication or by appropriately modifying them within the scope of the technical common sense of a person skilled in the art.

[0036] The molar ratio (MA / MB) of the moles of functional group A (MA) to the moles of functional group B (MB) is preferably 0.2 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and particularly preferably 1 or more. Within this range, a polymer having a carbon-carbon double bond can be obtained with good reactivity. Furthermore, the molar ratio (MA / MB) is preferably 2 or less, more preferably 1.5 or less, even more preferably 1.3 or less, and particularly preferably 1.1 or less. To increase the contact opportunity between functional group A and functional group B, a larger amount of the compound containing functional group B having a carbon-carbon double bond may be blended. In this case, the molar ratio (MA / MB) is preferably less than 1 (preferably less than 0.99, more preferably less than 0.95). Alternatively, when functional group A is used in other reactions (such as a crosslinking reaction with a crosslinking agent), the molar ratio (MA / MB) is preferably greater than 1. The amount of the compound having functional group B is preferably 1 part by weight or more, more preferably 5 parts by weight or more, even more preferably 10 parts by weight or more, even more preferably 12 parts by weight or more, even more preferably 15 parts by weight or more, even more preferably 18 parts by weight or more, particularly preferably 21 parts by weight or more, and most preferably 23 parts by weight or more, relative to 100 parts by weight of the polymer having functional group A, so long as the molar ratio (MA / MB) is satisfied. The amount of the compound having functional group B is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, and particularly preferably 25 parts by weight or less, relative to 100 parts by weight of the polymer having functional group A.

[0037] Furthermore, the polymer having a carbon-carbon double bond may be, for example, a diene polymer (e.g., a conjugated diene polymer). The diene polymer may be a polymer obtained by polymerizing or copolymerizing a diene (e.g., a conjugated diene). Examples of the diene polymer include butadiene polymers such as polybutadiene and styrene-butadiene copolymer; isoprene polymers such as polyisoprene and styrene-isoprene copolymer; and chloroprene polymers such as polychloroprene.

[0038] Furthermore, from the viewpoint of ease of reactivity, external double bonds are preferable to internal double bonds regarding carbon-carbon double bonds. Here, an internal double bond refers to a double bond that exists in a state where it is incorporated into the main chain of a polymer or oligomer. Both carbon atoms of this carbon-carbon double bond constitute the main chain. Furthermore, an external double bond refers to a double bond that exists outside the molecular chain (e.g., the main chain) of a polymer or oligomer. Note that when a carbon-carbon double bond exists at the end of the main chain of a polymer or oligomer, the double bond is an external double bond.

[0039] The content of the active energy ray reactive polymer (preferably a polymer having a carbon-carbon double bond) is preferably 10 parts by weight or more, more preferably 50 parts by weight or more, even more preferably 70 parts by weight or more, even more preferably 90 parts by weight or more, even more preferably 95 parts by weight or more, even more preferably 97 parts by weight or more, particularly preferably 99 parts by weight or more, and most preferably 99 to 100 parts by weight, relative to 100 parts by weight of the pressure-sensitive adhesive layer. Within such a range, a pressure-sensitive adhesive layer with a suitably adjusted elastic modulus can be obtained.

[0040] In one embodiment, the active energy ray-reactive polymer may be a polymer having an active energy ray-reactive functional group having a carbon-carbon multiple bond, such as an acryloyl group, a methacryloyl group, a vinyl group, an allyl group, or an acetylene group. Preferably, a compound (polymer) having an ethylenically unsaturated functional group is used, and more preferably, a (meth)acrylic polymer having an acryloyl group or a methacryloyl group is used. Specific examples of polymers having an active energy ray-reactive functional group include polymers composed of polyfunctional (meth)acrylates. The polymer composed of the polyfunctional (meth)acrylate preferably has an alkyl ester having 4 or more carbon atoms in its side chain, more preferably an alkyl ester having 6 or more carbon atoms, even more preferably an alkyl ester having 8 or more carbon atoms, particularly preferably an alkyl ester having 8 to 20 carbon atoms, and most preferably an alkyl ester having 8 to 18 carbon atoms. In the above polymer, the content of structural units having an alkyl ester having 4 or more carbon atoms as a side chain is preferably 30% by weight or more, and more preferably 50 to 80% by weight, based on all structural units constituting the polymer.

[0041] The pressure-sensitive adhesive (R2) containing the active energy ray-reactive polymer may further contain the active energy ray-reactive compound (monomer or oligomer).

[0042] The active energy ray-curable adhesive can be cured by irradiation with active energy rays. In the adhesive sheet of the present invention, an adherend is attached before the adhesive is cured, and then the adhesive is cured by irradiation with active energy rays, thereby allowing the adherend to adhere tightly. Examples of active energy rays include gamma rays, ultraviolet rays, visible light, infrared rays (heat rays), radio waves, alpha rays, beta rays, electron beams, plasma flow, ionizing rays, and particle beams. Conditions such as the wavelength and dose of the active energy rays can be set as appropriate depending on the composition of the adhesive, etc. For example, an exposure dose of 10 to 1,000 mJ / cm is used. 2 The adhesive can be cured by irradiating it with ultraviolet light.

[0043] (additives) The PSA may contain any suitable additives as needed, such as photopolymerization initiators, crosslinking agents, tackifiers, plasticizers, pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release agents, softeners, surfactants, flame retardants, and antioxidants.

[0044] In one embodiment, the PSA contains a tackifier. By incorporating a tackifier into the PSA, a PSA layer can be formed in which the heat-expandable microspheres can easily expand. Furthermore, the PSA expansion properties can be adjusted to a suitable level, thereby providing a PSA sheet that can prevent tilting of the adherend during peeling.

[0045] Any appropriate tackifier can be used as the tackifier, for example, a tackifying resin. Specific examples of tackifying resins include rosin-based tackifying resins (e.g., unmodified rosin, modified rosin, rosin phenolic resins, rosin ester resins, etc.), terpene-based tackifying resins (e.g., terpene resins, terpene phenolic resins, styrene-modified terpene resins, aromatic-modified terpene resins, hydrogenated terpene resins), hydrocarbon-based tackifying resins (e.g., aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic / aromatic petroleum resins, aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, coumarone-indene resins, etc.), phenol-based tackifying resins (e.g., alkylphenol-based resins, xylene-formaldehyde-based resins, resols, novolacs, etc.), ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins. Among these, rosin-based tackifying resins, terpene-based tackifying resins, and hydrocarbon-based tackifying resins (such as styrene-based resins) are preferred.The tackifiers may be used alone or in combination of two or more.

[0046] In one embodiment, a rosin-based tackifying resin and / or a terpene-based tackifying resin is used. These tackifying resins are particularly useful when used in combination with a pressure-sensitive adhesive containing a (meth)acrylic compound (such as the above-mentioned active energy ray-curable pressure-sensitive adhesive composed of a (meth)acrylic active energy ray-reactive compound or active energy ray-reactive polymer; the above-mentioned acrylic pressure-sensitive adhesive, etc.). More specifically, since the above-mentioned tackifying resin has good compatibility with pressure-sensitive adhesives containing a (meth)acrylic compound, the use of such a tackifying resin makes it possible to obtain a pressure-sensitive adhesive sheet that is less likely to produce differences in adhesive strength between minute regions on the pressure-sensitive adhesive layer surface and is therefore suitable for handling small adherends (workpieces).

[0047] The amount of the tackifier added is preferably 1 to 100 parts by weight, more preferably 1 to 80 parts by weight, even more preferably 1 to 50 parts by weight, still more preferably 5 to 30 parts by weight, particularly preferably 5 to 20 parts by weight, and most preferably 10 to 20 parts by weight, relative to 100 parts by weight of the polymer in the adhesive.

[0048] The softening point of the tackifier is preferably 200° C. or lower, more preferably 60 to 150° C. Within this range, a pressure-sensitive adhesive layer can be formed that is hard when processed onto an adherend and softens when heated to expand the heat-expandable microspheres.

[0049] Any appropriate photopolymerization initiator can be used as the photopolymerization initiator. Preferably, the photopolymerization initiator is at least one selected from the group consisting of alkylphenone-based photopolymerization initiators, hydroxyacetophenone-based photopolymerization initiators, hydroxyketone-based photopolymerization initiators, aminoacetophenone-based photopolymerization initiators, and benzylketanol-based photopolymerization initiators. The use of such a photopolymerization initiator facilitates control of the curing reaction. More specifically, the use of such a photopolymerization initiator makes it possible to obtain a pressure-sensitive adhesive layer that does not unexpectedly cure under commonly used light such as lighting, but only cures when irradiated with ultraviolet light, which is found only in specialized lighting. This facilitates control of the curing reaction of the pressure-sensitive adhesive layer. Furthermore, the use of such a photopolymerization initiator allows for the formation of a pressure-sensitive adhesive layer that can be rapidly and uniformly cured. The formation of such a pressure-sensitive adhesive layer allows for uniform expansion of the heat-expandable microspheres at the desired timing, preventing tilting of the adherend (chip) during heating.

[0050] B-2.Thermally expandable microspheres Heat-expandable microspheres are microspheres that can expand or foam upon heating. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing such heat-expandable microspheres exhibits sufficient adhesive strength when adhesive strength is required and excellent releasability when releasability is required, because heating causes unevenness on the adhesive surface, reducing adhesive strength.

[0051] The content of the heat-expandable microspheres can be appropriately set depending on the desired adhesive strength reduction, etc. The content of the heat-expandable microspheres is preferably 5 to 50 parts by weight, more preferably 10 to 50 parts by weight, even more preferably 10 to 40 parts by weight, and particularly preferably 10 to 30 parts by weight, per 100 parts by weight of the polymer in the adhesive. Within this range, a smooth adhesive layer can be formed before the heat-expandable microspheres are expanded, and a pressure-sensitive adhesive layer with a favorable uneven surface can be formed after the heat-expandable microspheres are expanded. Furthermore, a pressure-sensitive adhesive sheet can be obtained in which the adhesive expansion property is favorably adjusted, preventing tilting of the adherend during peeling.

[0052] Any suitable heat-expandable microspheres can be used as the heat-expandable microspheres. For example, microspheres having a substance that expands easily upon heating encapsulated in an elastic shell can be used. Such heat-expandable microspheres can be produced by any suitable method, such as coacervation or interfacial polymerization.

[0053] Examples of substances that expand easily when heated include low-boiling liquids such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, normal hexane, isohexane, heptane, octane, petroleum ether, methane halides, and tetraalkylsilanes; and azodicarbonamide, which gasifies by thermal decomposition.

[0054] Examples of materials constituting the shell include polymers composed of nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. Polymers composed of these monomers may be homopolymers or copolymers. Examples of such copolymers include vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate-acrylonitrile copolymer, and acrylonitrile-methacrylonitrile-itaconic acid copolymer.

[0055] The heat-expandable microspheres may be formed using inorganic or organic blowing agents, such as ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium boron hydroxide, and various azides. Examples of organic blowing agents include fluorinated alkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide, and barium azodicarboxylate; hydrazine compounds such as paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis(benzenesulfonylhydrazide), and allylbis(sulfonylhydrazide); semicarbazide compounds such as p-toluylenesulfonylsemicarbazide and 4,4'-oxybis(benzenesulfonylsemicarbazide); triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide.

[0056] The heat-expandable microspheres may be commercially available. Specific examples of commercially available heat-expandable microspheres include "Matsumoto Microsphere" (product name: F-30, F-30D, F-36D, F-36LV, F-50, F-50D, F-65, F-65D, FN-100SS, FN-100SSD, FN-180SS, FN-180SSD, F-190D, F260D, F-2800D) manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., and "Expancel" (product name: 053) manufactured by Nippon Phillite Co., Ltd. -40, 031-40, 920-40, 909-80, 930-120), "Dieform" manufactured by Kureha Chemical Industry Co., Ltd. (grades: H750, H850, H1100, S2320D, S2640D, M330, M430, M520), and "Advancell" manufactured by Sekisui Chemical Co., Ltd. (grades: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501).

[0057] The volume-cumulative particle diameter D50 (particle diameter at 50% of the cumulative volume) of the heat-expandable microspheres is preferably 13 μm to 50 μm, more preferably 13 μm to 40 μm, even more preferably 13 μm to 30 μm, and particularly preferably 15 μm to 30 μm. Within this range, the pressure-sensitive adhesive expansion property can be suitably adjusted to obtain a pressure-sensitive adhesive sheet that can prevent tilting of the adherend during peeling.

[0058] The peak width of the particle size distribution of the heat-expandable microspheres is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 16 μm or less. A uniform particle size also leads to a high degree of uniformity in expansion upon heating. Therefore, the use of heat-expandable microspheres exhibiting such a peak width in the particle size distribution allows for a pressure-sensitive adhesive sheet with favorably controlled expansion properties that prevents tilting of the adherend during peeling. The lower limit of the peak width in the particle size distribution of heat-expandable microspheres is, for example, 10 μm (preferably 8 μm, more preferably 6 μm). In this specification, the "peak width of the particle size distribution" is an index indicating the distribution width of the peak, and is calculated as follows using D84% and D16% when the cumulative frequency of the peak is taken as 100%. Peak width (μm) = D84% (μm) - D16% (μm) The above formula is applied only to the peak having the largest area among the group of peaks represented by a continuous curve.

[0059] The heat-expandable microspheres preferably have an appropriate strength so that they do not burst until their volumetric expansion rate reaches at least 5 times, more preferably at least 7 times, and even more preferably at least 10 times. When such heat-expandable microspheres are used, their adhesive strength can be efficiently reduced by heat treatment.

[0060] C. Base material Examples of the substrate include resin sheets, nonwoven fabrics, paper, metal foils, woven fabrics, rubber sheets, foam sheets, and laminates thereof (particularly laminates containing resin sheets). Examples of resins constituting resin sheets include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymers, ethylene-vinyl acetate copolymers (EVA), polyamides (nylons), wholly aromatic polyamides (aramids), polyimides (PI), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), fluorine-based resins, and polyether ether ketones (PEEK). Examples of nonwoven fabrics include heat-resistant natural fiber nonwoven fabrics such as Manila hemp nonwoven fabrics; and synthetic resin nonwoven fabrics such as polypropylene resin nonwoven fabrics, polyethylene resin nonwoven fabrics, and ester resin nonwoven fabrics. Examples of metal foils include copper foils, stainless steel foils, and aluminum foils. Examples of paper include Japanese paper and kraft paper.

[0061] The thickness of the substrate can be set to any appropriate thickness depending on the desired strength or flexibility, the intended use, etc. The thickness of the substrate is preferably 1000 μm or less, more preferably 1 μm to 1000 μm, even more preferably 1 μm to 500 μm, particularly preferably 3 μm to 300 μm, and most preferably 5 μm to 250 μm.

[0062] The substrate may be subjected to a surface treatment, such as corona treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage shock exposure, ionizing radiation treatment, or coating with a primer.

[0063] Examples of the organic coating material include those described in Plastic Hard Coat Materials II (CMC Publishing, 2004). Urethane-based polymers are preferred, and polyacrylic urethane, polyester urethane, or their precursors are more preferred. These materials are easy to apply to substrates, and are available in a wide variety of industrially available materials at low cost. The urethane-based polymer is, for example, a polymer formed from a reaction mixture of an isocyanate monomer and an alcoholic hydroxyl group-containing monomer (e.g., a hydroxyl group-containing acrylic compound or a hydroxyl group-containing ester compound). The organic coating material may contain optional additives such as a chain extender such as polyamine, an antioxidant, or an oxidation stabilizer. The thickness of the organic coating layer is not particularly limited, but is preferably about 0.1 μm to 10 μm, more preferably about 0.1 μm to 5 μm, and even more preferably about 0.5 μm to 5 μm.

[0064] D. Another adhesive layer Any suitable pressure-sensitive adhesive layer can be formed as the other pressure-sensitive adhesive layer. Examples of pressure-sensitive adhesives that form the other pressure-sensitive adhesive layer include rubber-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, polyester-based pressure-sensitive adhesives, polyamide-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, fluorine-based pressure-sensitive adhesives, and styrene-diene block copolymer-based pressure-sensitive adhesives. The pressure-sensitive adhesive may contain known or commonly used additives such as plasticizers, fillers, surfactants, antioxidants, and tackifiers.

[0065] The thickness of the other pressure-sensitive adhesive layer is preferably 300 μm or less, more preferably 1 μm to 300 μm, and even more preferably 5 μm to 100 μm.

[0066] E. Elastic layer The pressure-sensitive adhesive sheet of the present invention may further include an elastic layer. The elastic layer has a normal elastic modulus of 10.0 MPa or less at 23°C as measured by a nanoindentation method, and is resistant to actinic energy rays (for example, an integrated light dose of 1000 mJ / cm2). 2The elastic layer has a modulus of elasticity of more than 10 MPa as measured by nanoindentation after irradiation with ultraviolet light (ultraviolet rays). The normal modulus of elasticity of the elastic layer as measured by nanoindentation at 23°C is preferably 8 MPa or less, more preferably 5 MPa or less, and even more preferably 3 MPa or less. The elastic layer may be disposed on one side of the pressure-sensitive adhesive layer. When the pressure-sensitive adhesive sheet includes a substrate, the elastic layer may be disposed between the pressure-sensitive adhesive layer and the substrate. The presence of an elastic layer improves conformability to the adherend. Furthermore, the proportion of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet can be reduced, resulting in a pressure-sensitive adhesive sheet that can deform favorably when heated.

[0067] The elastic layer contains a base polymer, and the base polymer may be any of the polymers exemplified as the base polymer constituting the pressure-sensitive adhesive layer. In one embodiment, the elastic layer may contain natural rubber, synthetic rubber, synthetic resin, etc. Examples of such synthetic rubbers and synthetic resins include nitrile-based, diene-based, and acrylic-based synthetic rubbers; thermoplastic elastomers such as polyolefin-based and polyester-based; ethylene-vinyl acetate copolymers; polyurethane; polybutadiene; and soft polyvinyl chloride. The base polymer constituting the elastic layer may be the same as or different from the base polymer constituting the pressure-sensitive adhesive layer. The elastic layer and the pressure-sensitive adhesive layer can be distinguished by the difference in base polymer and / or the presence or absence of a foaming agent (the elastic layer does not contain a foaming agent). More specifically, when the elastic layer and the pressure-sensitive adhesive layer are formed from different base polymers, and the interface between the elastic layer and the pressure-sensitive adhesive layer can be identified by cross-sectional observation, the boundary between the elastic layer and the pressure-sensitive adhesive layer is defined by the interface. Furthermore, when the interface between the elastic layer and the pressure-sensitive adhesive layer cannot be identified by cross-sectional observation, the region in which the foaming agent is observed by cross-sectional observation is the pressure-sensitive adhesive layer.

[0068] The elastic layer may contain any appropriate additives as needed. Examples of such additives include crosslinking agents, vulcanizing agents, tackifying resins, plasticizers, softeners, fillers, antioxidants, etc. When a hard resin such as polyvinyl chloride is used as the base polymer, it is preferable to use a plasticizer and / or softener in combination to form an elastic layer with the desired elasticity.

[0069] The thickness of the elastic layer is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and even more preferably 25 μm to 100 μm. Within this range, the elastic layer can fully exhibit the above functions.

[0070] When the pressure-sensitive adhesive sheet includes an elastic layer, the thickness of the pressure-sensitive adhesive layer is preferably 60% or less, more preferably 50% or less, even more preferably 45% or less, and particularly preferably 40% or less, of the total thickness of the laminate including the pressure-sensitive adhesive layer and the elastic layer. Within this range, the thickness of the pressure-sensitive adhesive layer, which has a significant effect on the deformation of the pressure-sensitive adhesive sheet, can be reduced, resulting in a pressure-sensitive adhesive sheet that has an excellent balance between conformability, suppression of deformation of the pressure-sensitive adhesive layer, and heat-peelability. Furthermore, the thickness of the pressure-sensitive adhesive layer is preferably 10% or more, more preferably 12% or more, even more preferably 15% or more, and particularly preferably 20% or more, of the total thickness of the laminate including the pressure-sensitive adhesive layer and the elastic layer. The "total thickness of the laminate including the pressure-sensitive adhesive layer and the elastic layer" refers to the sum of the thickness of a single pressure-sensitive adhesive layer and the thickness of a single elastic layer. When the pressure-sensitive adhesive sheet includes a substrate, the "laminate including the pressure-sensitive adhesive layer and the elastic layer" refers to a laminate including the pressure-sensitive adhesive layer and the elastic layer that are arranged on the same side of the substrate.

[0071] F. Separator The pressure-sensitive adhesive sheet of the present invention may further include a separator, if necessary. The separator has at least one surface serving as a release surface and may be provided to protect the pressure-sensitive adhesive layer. The separator may be made of any appropriate material.

[0072] G. Manufacturing method of adhesive sheet The pressure-sensitive adhesive sheet of the present invention can be produced by any appropriate method. Examples of methods include a method in which a pressure-sensitive adhesive layer-forming composition containing a pressure-sensitive adhesive and heat-expandable microspheres is directly applied to a substrate, or a method in which the pressure-sensitive adhesive layer-forming composition is applied to any appropriate substrate and the resulting coating layer is transferred to the substrate. The pressure-sensitive adhesive layer-forming composition may contain any appropriate solvent. Alternatively, a pressure-sensitive adhesive layer containing heat-expandable microspheres may be formed by forming a pressure-sensitive adhesive coating layer using a composition containing a pressure-sensitive adhesive, sprinkling heat-expandable microspheres on the pressure-sensitive adhesive coating layer, and then embedding the heat-expandable microspheres in the coating layer using a laminator or the like.

[0073] The content of the heat-expandable microspheres in the composition for forming a pressure-sensitive adhesive layer is preferably 5 to 95% by weight, more preferably 10 to 70% by weight, and even more preferably 10 to 50% by weight, based on the weight of the solid content of the composition for forming a pressure-sensitive adhesive layer.

[0074] When the pressure-sensitive adhesive layer has the above-mentioned elastic layer, the elastic layer can be formed, for example, by applying a composition for forming an elastic layer onto the substrate or the pressure-sensitive adhesive layer.

[0075] Any appropriate coating method can be used to apply each of the compositions. For example, each layer can be formed by coating and then drying. Examples of the coating method include coating methods using a multi-coater, die coater, gravure coater, applicator, etc. Examples of the drying method include natural drying and heat drying. The heating temperature when heat drying is performed can be set to any appropriate temperature depending on the properties of the substance to be dried. [Example]

[0076] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Evaluation methods in the examples are as follows. In the following evaluations, pressure-sensitive adhesive sheets from which the separator had been peeled off were used. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0077] (1)Initial adhesive strength The adhesive sheet was cut to a size of 20 mm wide and 140 mm long, and the adhesive surface was attached to a SUS304BA plate adherend in accordance with JIS Z 0237:2009 by rolling a 2 kg roller back and forth once to obtain a measurement sample. The measurement sample was placed in a thermostatic tensile tester (Shimadzu Corporation, product name "Shimadzu Autograph AG-120kN") equipped with a thermostatic chamber. The adherend was then peeled from the adhesive sheet in the longitudinal direction at a peel angle of 180° and a tensile speed of 300 mm / min, and the load measured was the maximum load (the maximum load excluding the peak top at the beginning of the measurement). This maximum load was then divided by the tape width to obtain the adhesive strength (N / 20 mm width). The above procedure was carried out in an atmosphere of 23°C temperature and 65% RH humidity.

[0078] (2) Adhesive strength after UV irradiation The adhesive sheet was cut to a size of 20 mm wide and 140 mm long, and the adhesive surface was bonded to the SUS304BA plate as the adherend in accordance with JIS Z 0237:2009 by rolling a 2 kg roller back and forth once. After leaving it for 30 minutes, it was exposed to ultraviolet light (irradiation dose 1000 mJ / cm 2 ) was irradiated. The measurement sample was set in a tensile tester equipped with a thermostatic chamber (Shimadzu Corporation, product name "Shimadzu Autograph AG-120kN"). Thereafter, the adherend was peeled from the adhesive sheet in the lengthwise direction under the conditions of a peel angle of 180° and a tensile speed of 300 mm / min, and the load was measured. The maximum load (the maximum value of the load excluding the peak top at the beginning of the measurement) was determined, and this maximum load was divided by the tape width to obtain the adhesive strength (N / 20 mm width). The above operation was carried out in an atmosphere of temperature: 23°C and humidity: 65% RH.

[0079] (3) Adhesive expansion The adhesive sheet was cut into a test piece having a width of 20 mm and a length of 140 mm. A 10 mm thick heat-resistant glass (140 mm x 140 mm) was placed on a hot plate (Shamal Hot Plate "HHP-411") and preheated to a specified temperature. A test piece was placed on this hot plate, and a 10 mm thick heat-resistant glass was placed to cover the test piece. After leaving the test piece as is for 1 minute, the thickness of the test piece was measured with a dial gauge to determine the thickness of the adhesive layer (thickness of the test piece (adhesive sheet) - thickness of the substrate). The predetermined temperature was varied from 20°C to 300°C in 10°C increments, and the above procedure was repeated for each predetermined temperature. Specifically, a new test piece was used at each predetermined temperature (without continuous use of the same test piece), and the thickness of the pressure-sensitive adhesive layer after heating was measured. The temperature at which the pressure-sensitive adhesive layer reached its maximum thickness as a result of these procedures was defined as the peak foaming temperature. The temperature at which the pressure-sensitive adhesive layer reached 110% of the thickness (initial thickness) of the pressure-sensitive adhesive layer at 20°C was defined as the foaming start temperature of the heat-expandable microspheres. The thickness of the adhesive layer was taken as the thickness at 20°C (initial thickness), and the thickness when heated to the peak foaming temperature (thickness at peak foaming) was used to calculate the adhesive expansion using the formula [thickness at peak foaming / initial thickness]. In the examples and comparative examples in which the adhesive layer was an adhesive that was curable with active energy rays (ultraviolet rays), UV irradiation was performed using an ultraviolet irradiator ("UM810 (high-pressure mercury lamp light source)" (manufactured by Nitto Seiki Co., Ltd.), cumulative light intensity 1000 mJ / cm 2 ) A test piece was prepared using the pressure sensitive adhesive sheet after the test.

[0080] (4) Elastic modulus of the pressure-sensitive adhesive layer measured by nanoindentation at a temperature 10°C lower than the expansion temperature of the heat-expandable microspheres The elastic modulus measured by nanoindentation is determined by continuously measuring the load and indentation depth of an indenter applied to a sample (e.g., an adhesive surface) during loading and unloading, and then calculating the elastic modulus from the applied load-indentation depth curve. The elastic modulus measured by nanoindentation is determined by pressing a diamond Berkovich-type (triangular pyramidal) probe perpendicularly against a cut-out cross-section of the layer to be measured, and then numerically processing the resulting displacement-load hysteresis curve using software (triboscan) provided with the measurement device. In this specification, the elastic modulus is measured using a nanoindenter (Triboindenter TI-950, manufactured by Hysitron Inc.) at a specified temperature using a single indentation method with an indentation speed of approximately 500 nm / sec, an extraction speed of approximately 500 nm / sec, and an indentation depth of approximately 3000 nm.

[0081] (5) Chip flying A QFN lead frame (size: 125 mm x 65 mm; the surface that faces the adhesive sheet is the resin side) sealed with epoxy resin (Hitachi Chemical Co., Ltd., product name "CEL-9200HF9") was attached to the adhesive layer of each adhesive sheet. This was then attached to a 6-inch dicing ring and fully cut into 5 mm x 5 mm chips using a dicer (dicing cutting process was performed). The number of chips that flew off during this cutting was counted. The dicing blade used was a ZH05-SD2000-N1-110-DD manufactured by DISCO. The dicing blade feed speed was 70 mm / s and the dicing blade rotation speed was 50,000 rpm. The percentage of chips that peeled off from the adhesive tape (chip skipping) during the cutting process (chip skipping rate) was calculated and used to evaluate the cutting processability. If all chips were attached to the adhesive tape and not peeled off, the chip skipping rate was 0% (i.e., the chip skipping rate was 0%). The number of diced chips was A0, and the number of chip skipping was A, and the chip skipping rate X was calculated according to formula (1). X = (A / A0) × 100 (1) The smaller the rate at which chips peel off (chip fly rate), the better the chip fly prevention performance.

[0082] (6) Heat peeling failure After the cutting, the sheet was heated for 5 minutes at the peak foaming temperature using a programmable temperature controller (hot air dryer) (manufactured by Isuzu Manufacturing Co., Ltd., "EP-K-300"). After the heat treatment, the adhesive tape was turned upside down in the air (with the chips facing downwards), and the chips were allowed to fall freely from the adhesive tape. The percentage of chips remaining on the sheet (chip residue) was calculated. Note that if all chips were removed and none remained on the adhesive tape, the chip residue was calculated as 0%. Therefore, a small amount of chips remaining after heat treatment (small chip residue) indicates good heat peelability. The number of chips before peeling was defined as B0, and the number of chips remaining on the sheet after the heat peeling treatment was defined as B. The chip residue Y was calculated according to formula (2). Y = (B / B0) × 100 (2)

[0083] (7) Chip tilt After cutting in (5) above, the sheet was heat-treated for 5 minutes at the peak foaming temperature using a programmable temperature controller (hot air dryer) (manufactured by Isuzu Manufacturing Co., Ltd., "EP-K-300"). After the heat treatment, the tilt of the chips was visually checked before carrying out (6) above, and the percentage of tilted chips (chip tilt) (%) after heat peeling was confirmed. Note that if all chips are neat and untilted, the chip tilt is 0%. Therefore, a small number of tilted chips after heat treatment (low chip tilt) indicates good chip tilt. The number of chips before peeling was defined as C0, and the number of tilted chips on the sheet after heat peeling was defined as C, and the chip tilt Z was calculated according to formula (3). Z = (C / C0) × 100 (3)

[0084] (8) Chip collection failure (number) The total number of defective chips in (6) above and (7) above was determined as the number of defective chips that were not collected.

[0085] (9) Particle size distribution peak width and particle size (D50) of heat-expandable microspheres The adhesive sheet was fixed to a holder, and serial transmission images (1601 images from 0° to 360°) were taken using an X-ray CT (Zeiss, Xradia 520 Versa, pixel size 0.3 μm / pixel, analysis software ImageJ). Next, a tomographic image was created by reconstructing the total transmission image, and a three-dimensional reconstruction image (TIF stack image) and a reconstructed cross-sectional image (three-view image) were created. Foams were identified from the obtained three-dimensional reconstruction image (TIF stack image), and the volume-cumulative particle diameter D50 and peak width were calculated.

[0086] [Production Example 1] Production of Polymer 1 30 parts by weight of 2-ethylhexyl acrylate, 70 parts by weight of ethyl acrylate, 5 parts by weight of methyl methacrylate, 5 parts by weight of hydroxyethyl acrylate, and 0.15 parts by weight of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated at 60°C to obtain a toluene solution of an acrylic copolymer (polymer 1).

[0087] [Production Example 2] Production of Polymer 2 100 parts by weight of 2-ethylhexyl acrylate, 25 parts by weight of acryloylmorpholine, 18 parts by weight of hydroxyethyl acrylate, and 0.25 parts by weight of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated at 60°C to obtain a toluene solution of an acrylic copolymer. 12 parts by weight of methacryloyloxyethyl isocyanate was added to this and an addition reaction was carried out to obtain a toluene solution of an acrylic copolymer (polymer 2) having a carbon-carbon double bond.

[0088] [Production Example 3] Production of Polymer 3 100 parts by weight of butyl acrylate, 5 parts by weight of acrylic acid, and 0.15 parts by weight of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated at 60°C to obtain a toluene solution of an acrylic copolymer (polymer 3).

[0089] [Production Example 4] Production of Polymer 4 100 parts by weight of 2-ethylhexyl acrylate, 5 parts by weight of acrylic acid, and 0.15 parts by weight of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated at 60°C to obtain a toluene solution of an acrylic copolymer (polymer 4).

[0090] [Production Example 5] Production of Polymer 5 100 parts by weight of butyl acrylate, 5 parts by weight of hydroxyethyl acrylate, and 0.15 parts by weight of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated at 60°C to obtain a toluene solution of an acrylic copolymer (polymer 5).

[0091] [Example 1] (Preparation of Elastic Layer-Forming Composition) A composition for forming an elastic layer was prepared by mixing a toluene solution of polymer 1 (100 parts by weight), 1 part by weight of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), 30 parts by weight of an active energy ray-reactive compound (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "Shikou UV1700B"), 3 parts by weight of a photopolymerization initiator (manufactured by BASF, product name "Omnirad127D"), and toluene. (Preparation of Composition for Forming Pressure-Sensitive Adhesive Layer) A composition for forming a pressure-sensitive adhesive layer was prepared by mixing a toluene solution of polymer 1 (100 parts by weight), 0.5 parts by weight of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), 30 parts by weight of an active energy ray-reactive compound (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Shikou UV1700B"), 3 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "Omnirad127D"), 15 parts by weight of a tackifier (manufactured by Yasuhara Chemical Co., Ltd., trade name "Mighty Ace G125"), 35 parts by weight of heat-expandable microspheres (manufactured by AkzoNobel, trade name "092-40DU"), and toluene. (Preparation of adhesive tape) A PET film (manufactured by Toray Industries, Inc., product name "Lumirror S10", thickness: 25 μm) as a substrate was subjected to corona treatment, and the above-mentioned composition for forming an elastic layer was applied and dried to form an elastic layer (thickness: 50 μm) on the substrate. The above-mentioned adhesive layer-forming composition was applied to a polyethylene terephthalate film with a silicone release agent-treated surface (manufactured by Mitsubishi Chemical Polyester Film Corporation, product name "MRF38") and dried to form an adhesive layer (30 μm) on the polyethylene terephthalate film. The pressure-sensitive adhesive layer formed on the polyethylene terephthalate film was transferred to the elastic layer to obtain a pressure-sensitive adhesive tape having a substrate, an elastic layer, and a pressure-sensitive adhesive layer in this order. The obtained pressure-sensitive adhesive tape was subjected to the above evaluations (1) to (9). The results are shown in the table.

[0092] [Examples 2 to 13, Comparative Examples 1 and 2] Pressure-sensitive adhesive sheets were obtained in the same manner as in Example 1, except that the polymers, crosslinking agents, heat-expandable microspheres, active energy ray-reactive compounds, and photopolymerization initiators shown in Table 1 were used in the amounts shown in Table 1, and that the substrates shown in Table 1 were used. The pressure-sensitive adhesive sheets obtained were subjected to the above-mentioned evaluations. The results are shown in Table 1. The components used were as follows: (Crosslinking agent) Coronate L: Manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L" Tetrad C: Manufactured by Mitsubishi Gas Corporation, product name "Tetrad C" (thermal expandable microspheres) 092-40DU: Manufactured by AkzoNobel, product name "092-40DU" H-750D: Manufactured by Kureha Corporation, product name "H-750D" EML101: Sekisui Chemical Co., Ltd., product name "EML101" F-50D: Matsumoto Yushi Pharmaceutical Co., Ltd., product name "F-50D" (active energy ray reactive compound) ·UV1700B: Manufactured by Nippon Gosei Kagaku Co., Ltd., product name "Shikou UV1700B", molecular weight: 2000, C=C10 pieces / 1 molecule) ·UV3000B Manufactured by Nippon Gosei Kagaku Co., Ltd., product name "Shikou UV3000B", molecular weight 18000, C=C2 pieces / 1 molecule)) ·UV7605B Manufactured by Nippon Gosei Co., Ltd., product name "Shikou UV7605B", molecular weight 1100, C=C6 pieces / 1 molecule) (Photopolymerization initiator) ·Omnirad 127D: Manufactured by BASF, product name “Omnirad 127D” Omnirad 651: BASF, product name "Omnirad 651"

[0093] [Table 1] [Explanation of symbols]

[0094] 10 adhesive layer 20 Base material 30 Another adhesive layer 100, 200, 300 adhesive sheets

Claims

1. The adhesive layer comprises heat-expandable microspheres and a pressure-sensitive adhesive layer. the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive, the adhesive layer has an adhesive expansion property when heated to the peak expansion temperature of the heat-expandable microspheres (thickness of the adhesive layer when heated to the peak expansion temperature of the heat-expandable microspheres / thickness of the adhesive layer at 20°C) of 1.1 to 2; the pressure-sensitive adhesive layer has an elastic modulus of 3.0 MPa to 400 MPa as measured by nanoindentation at a temperature 10°C lower than the expansion initiation temperature of the heat-expandable microspheres; The heat-expandable microspheres have a volume-cumulative particle diameter D50 of 13 μm to 50 μm. Adhesive sheet.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the acrylic pressure-sensitive adhesive is an active energy ray-curable pressure-sensitive adhesive.

3. The pressure-sensitive adhesive sheet according to claim 2 , wherein the active energy ray-curable pressure-sensitive adhesive comprises a polymer and an oligomer as an active energy ray-reactive compound.

4. The pressure-sensitive adhesive sheet according to claim 2 , wherein the active energy ray-curable pressure-sensitive adhesive comprises an active energy ray-reactive polymer.

5. the active energy ray-curable pressure-sensitive adhesive contains a photopolymerization initiator, the photopolymerization initiator is at least one selected from the group consisting of alkylphenone-based photopolymerization initiators, hydroxyacetophenone-based photopolymerization initiators, hydroxyketone-based photopolymerization initiators, aminoacetophenone-based photopolymerization initiators, and benzylketanol-based photopolymerization initiators; The pressure-sensitive adhesive sheet according to claim 2 .

6. The pressure-sensitive adhesive sheet according to claim 2 , wherein the active energy ray-curable pressure-sensitive adhesive contains a tackifier.

7. 7. The pressure-sensitive adhesive sheet according to claim 6, wherein the content of the tackifier is 1 part by weight to 100 parts by weight per 100 parts by weight of the polymer in the active energy ray-curable pressure-sensitive adhesive.

8. 8. The pressure-sensitive adhesive sheet according to claim 1, wherein the heat-expandable microspheres have a particle size distribution peak width of 20 μm or less.

9. 9. The pressure-sensitive adhesive sheet according to claim 1, wherein the content of the heat-expandable microspheres is 5 to 50 parts by weight per 100 parts by weight of the polymer in the pressure-sensitive adhesive.

10. The pressure-sensitive adhesive sheet according to any one of claims 1 to 9, wherein the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet has an initial adhesive strength of 0.5 N / 20 mm to 25 N / 25 mm when attached to SUS304BA.

11. further comprising a substrate; The pressure-sensitive adhesive layer is disposed on at least one side of the substrate. The pressure-sensitive adhesive sheet according to claim 1 .

12. A step of attaching the pressure-sensitive adhesive sheet according to any one of claims 1 to 11 to a device; irradiating the pressure-sensitive adhesive sheet with ultraviolet light; and heating the adhesive sheet and peeling the device from the adhesive sheet. Manufacturing methods for electronic components.

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