adhesive tape

Abstract

To provide a pressure-sensitive adhesive tape capable of preventing an expansion temperature from lowering due to thermal hysteresis.SOLUTION: A pressure-sensitive adhesive tape includes a thermal expansive microsphere. The thermal expansive microsphere includes a shell and a volatile substance contained inside the shell. The shell is constituted of a resin in which a glass-transition temperature (Tg) is 120°C or higher. In one embodiment, the resin constituting the shell includes a constitutional unit having a carboxyl group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an adhesive tape, and more particularly to an adhesive tape that can exhibit easy peelability in response to a thermal stimulus. [Background technology]

[0002] In the manufacturing process of electronic components and the like, adhesive tapes used for the purpose of temporarily fixing workpieces are known to exhibit adhesive properties during temporary fixing and exhibit releasability when fixation is not required. As one such adhesive tape, an adhesive tape containing heat-expandable microspheres, typically a foaming agent, in the adhesive layer has been studied (see, for example, Patent Document 1). While this adhesive tape exhibits a desired adhesive strength at relatively low temperatures, typically room temperature, when heated above a predetermined temperature (foaming temperature), the foaming agent expands, causing unevenness on the surface of the adhesive layer and reducing the adhesive strength. Such adhesive tapes also enable the adherend to be peeled off simply by the action of gravity.

[0003] On the other hand, in recent years, the manufacturing processes and use environments of electronic components have become more diverse, and electronic components are expected to be exposed to higher temperature environments than before, and are required to exhibit desired performance even in such environments. Therefore, when manufacturing electronic components, reliability is sometimes evaluated by tests such as thermal shock tests in which high temperature and low temperature conditions are cycled.

[0004] In thermal shock tests, adhesive tapes containing a foaming agent can also be used for temporarily fixing test pieces. The adhesive tapes used in this way use a foaming agent that can foam at temperatures equal to or higher than the high-temperature conditions of the thermal shock test, and are required to have the property of not exhibiting releasability during the thermal shock test but exhibiting releasability upon heating after the test. However, conventional foaming agents have a problem in that their foaming temperature decreases due to thermal history below the foaming temperature, which unnecessarily reduces the adhesive strength of the adhesive tape during the thermal shock test. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-131507 Summary of the Invention [Problem to be solved by the invention]

[0006] 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 pressure-sensitive adhesive tape in which a decrease in foaming temperature due to thermal history is prevented. [Means for solving the problem]

[0007] The pressure-sensitive adhesive tape of the present invention contains heat-expandable microspheres, which are composed of a shell and a volatile substance contained in the shell, and the shell is composed of a resin having a glass transition temperature (Tg) of 120°C or higher. In one embodiment, the resin constituting the shell contains a constituent unit having a carboxyl group. In one embodiment, the content of the structural unit having a carboxyl group is 5 parts by weight to 97 parts by weight relative to 100 parts by weight of the resin. In one embodiment, the adhesive surface of the adhesive tape is attached to a polyethylene terephthalate film at an ambient temperature of 25° C., and the initial adhesive strength a is 0.5 N / 20 mm to 20 N / 20 mm. In one embodiment, the adhesive strength b when the adhesive surface of the adhesive tape that has been heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film is 50% or more of the initial adhesive strength a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an ambient temperature of 25°C. In one embodiment, the adhesive strength c when the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film after two cycles of heating to 140°C and then cooling to 25°C is 50% or more of the initial adhesive strength a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an ambient temperature of 25°C. In one embodiment, the volatile substance is an organic solvent, and the difference (Tg-bp) between the boiling point (bp) of the organic solvent and the glass transition temperature (Tg) of the resin constituting the shell is 0°C or more. In one embodiment, the pressure-sensitive adhesive tape further comprises a substrate. In one embodiment, the pressure-sensitive adhesive tape further comprises another pressure-sensitive adhesive layer, and the substrate is disposed between the pressure-sensitive adhesive layer and the another pressure-sensitive adhesive layer. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape in which a decrease in foaming temperature due to thermal history is prevented. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of an adhesive tape according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A. Overall structure of adhesive tape 1(a) is a schematic cross-sectional view of a pressure-sensitive adhesive tape according to one embodiment of the present invention. Typically, the pressure-sensitive adhesive tape 100 comprises a pressure-sensitive adhesive layer 10. The pressure-sensitive adhesive tape of the present invention may consist of only the pressure-sensitive adhesive layer 10, or may further comprise any appropriate layer in addition to the pressure-sensitive adhesive layer.

[0011] FIG. 1(b) is a schematic cross-sectional view of a pressure-sensitive adhesive tape according to another embodiment of the present invention. Pressure-sensitive adhesive tape 200 comprises a pressure-sensitive adhesive layer 10 and a substrate 20 disposed on at least one side of the pressure-sensitive adhesive layer 10. FIG. 1(c) is a schematic cross-sectional view of a pressure-sensitive adhesive tape according to yet another embodiment of the present invention. Pressure-sensitive adhesive tape 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 tape may be composed of a pressure-sensitive adhesive layer and another pressure-sensitive adhesive layer. Furthermore, although not shown, the pressure-sensitive adhesive tape 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 tape, a separator (described below in Section F) releasably disposed on the pressure-sensitive adhesive layer, or the like.

[0012] The pressure-sensitive adhesive tape contains heat-expandable microspheres. In one embodiment, the pressure-sensitive adhesive layer 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 to a predetermined temperature or higher, the heat-expandable microspheres expand, causing unevenness on the adhesive surface (i.e., the surface of the pressure-sensitive adhesive layer), and reducing or eliminating adhesive strength. When the pressure-sensitive adhesive tape of the present invention is used as a temporary fixing sheet for test specimens or workpieces during testing or processing of electronic components (e.g., ceramic capacitors), the necessary adhesive strength is exhibited when fixing is required, and when the pressure-sensitive adhesive tape is subsequently peeled off, the adhesive strength is reduced or eliminated by heating, resulting in good releasability.

[0013] The initial adhesive strength a when the adhesive surface of the adhesive tape of the present invention is attached to a polyethylene terephthalate film (e.g., 25 μm thick) at an ambient temperature of 25°C is preferably 0.5 N / 20 mm to 20 N / 20 mm, more preferably 0.5 N / 20 mm to 18 N / 20 mm, and even more preferably 1 N / 20 mm to 12 N / 20 mm. Within these ranges, an adhesive tape useful as a temporary fixing sheet used in the manufacture of electronic components can be obtained. In this specification, the initial adhesive strength refers to the adhesive strength in a state that has not been subjected to a heat history of 50°C or higher. Furthermore, the adhesive strength refers to the adhesive strength measured according to a method in accordance with JIS Z 0237:2000 (lamination conditions: one reciprocal movement of a 2 kg roller, peel speed: 300 mm / min, peel angle: 180°).

[0014] The adhesive strength b when the adhesive surface of the adhesive tape of the present invention, which has been heated to 140°C and then cooled to 25°C, is adhered to a polyethylene terephthalate film (e.g., 25 μm thick), is 0.4 N / 20 mm to 20 N / 20 mm, more preferably 0.4 N / 20 mm to 17 N / 20 mm, even more preferably 0.8 N / 20 mm to 16 N / 20 mm, particularly preferably 0.8 N / 20 mm to 14 N / 20 mm, and most preferably 0.8 N / 20 mm to 12 N / 20 mm.

[0015] When the adhesive surface of the adhesive tape of the present invention is heated to 140°C and then cooled to 25°C and adhered to a polyethylene terephthalate film (e.g., 25 μm thick), the adhesive strength b is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more of the initial adhesive strength a.

[0016] After two cycles of heating to 140°C and then cooling to 25°C, the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film (e.g., 25 μm thick) and the adhesive strength c is 0.4 N / 20 mm to 20 N / 20 mm, more preferably 0.4 N / 20 mm to 17 N / 20 mm, even more preferably 0.8 N / 20 mm to 16 N / 20 mm, particularly preferably 0.8 N / 20 mm to 14 N / 20 mm, and most preferably 0.8 N / 20 mm to 12 N / 20 mm.

[0017] After two cycles of heating to 140°C and then cooling to 25°C, the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film (e.g., 25 μm thick). The adhesive strength c of the adhesive tape is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more of the initial adhesive strength a.

[0018] The thickness of the pressure-sensitive adhesive tape of the present invention is preferably 30 μm to 500 μm, and more preferably 40 μm to 300 μm.

[0019] B.Adhesive layer As described above, in one embodiment, the pressure-sensitive adhesive layer contains heat-expandable microspheres. In practice, the pressure-sensitive adhesive layer further contains a pressure-sensitive adhesive.

[0020] B-1. Thermally expandable microspheres Heat-expandable microspheres are composed of a shell and a volatile substance (typically an organic solvent) contained within the shell. In the present invention, the shell is composed of a resin having a glass transition temperature (Tg) of 120°C or higher. In the present invention, the use of heat-expandable microspheres containing such a shell makes it possible to obtain an adhesive tape in which the expansion temperature of the heat-expandable microspheres is less likely to fluctuate. More specifically, when conventional blowing agents are heated below their expansion temperature, the expansion temperature tends to decrease due to the thermal history. However, in the present invention, the use of heat-expandable microspheres containing the shell prevents the decrease in expansion temperature due to the thermal history.

[0021] The glass transition temperature (Tg) of the resin constituting the shell is preferably 125°C or higher, more preferably 130°C or higher, and even more preferably 135°C or higher. Within such a range, the effects of the present invention become more pronounced. The upper limit of the glass transition temperature (Tg) of the resin constituting the shell is, for example, 260°C. The glass transition temperature is calculated by the Fox formula. The Fox formula, as shown below, is the ratio of the glass transition temperature Tg (°C) of the copolymer to the glass transition temperature Tg of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. i In the Fox equation below, Tg (°C) is the glass transition temperature of the copolymer, W i is the weight fraction of monomer i, Tg i (°C) indicates the glass transition temperature of the homopolymer formed from monomer i. 1 / (273+Tg)=Σ(W i / (273+Tg i )) The glass transition temperatures of homopolymers formed from the monomers are as follows: methacrylic acid homopolymer: 228°C, acrylonitrile homopolymer: 97°C, methyl methacrylate homopolymer: 102°C, methacryloylnitrile homopolymer: 120°C, vinylidene chloride homopolymer: 75°C, and isobornyl acrylate homopolymer: 97°C. For the glass transition temperatures of homopolymers other than these, values ​​listed in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) can be used. When multiple Tg values ​​are listed in this document, the "conventional" value is used.

[0022] The resin forming the shell may be, for example, a resin having a structural unit derived from a radically polymerizable monomer. Examples of the monomer include nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxyl group-containing 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. The polymer composed of these monomers may be a homopolymer or a copolymer.

[0023] In one embodiment, the resin constituting the shell contains a structural unit having a carboxyl group. When the shell is formed from a resin having a carboxyl group, the molecular state can be maintained even when subjected to thermal history due to the interaction between the carboxyl groups, resulting in a significant effect of preventing a decrease in foaming temperature due to thermal history. The structural unit having a carboxyl group can be, for example, a structural unit derived from the carboxyl group-containing monomer. In one embodiment, the resin constituting the shell contains a structural unit having a carboxyl group and at least one selected from the group consisting of a structural unit derived from isobornyl acrylate, a structural unit derived from methacrylonitrile, a structural unit derived from acrylonitrile, a structural unit derived from methyl (meth)acrylate, and a structural unit derived from vinylidene chloride. Preferably, the resin constituting the shell contains a structural unit having a carboxyl group and a structural unit derived from methacrylonitrile and / or acrylonitrile.

[0024] In the resin constituting the shell, the content of the structural unit having a carboxyl group is preferably 5 to 97 parts by weight, more preferably 5 to 90 parts by weight, even more preferably 5 to 85 parts by weight, particularly preferably 5 to 80 parts by weight, and most preferably 10 to 75 parts by weight, relative to 100 parts by weight of the resin. Within such a range, the effect of preventing a decrease in foaming temperature due to thermal history can be effectively obtained, and a shell having excellent solvent resistance can be formed.

[0025] The resin forming the shell may be a crosslinked product. Crosslinking can adjust the excluded free volume of the polymer, thereby controlling the diffusibility of the encapsulated volatile substance, the expandability of the shell, and the like. The crosslinked product may further contain a structural unit derived from a monomer having two or more polymerizable double bonds in the molecule. In one embodiment, the radically polymerizable monomer and a monomer having two or more polymerizable double bonds in the molecule are used in combination.Examples of the monomer having two or more polymerizable double bonds in the molecule include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacrylformal, triallyl isocyanate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, and 1,10-decanediol di(meth)acrylate. , PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol Examples of the acrylic acid benzoate include phenyl tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol acrylic acid benzoate, trimethylolpropane acrylic acid benzoate, 2-hydroxy-3-acryloyloxypropyl(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, phenyl glycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer, phenyl glycidyl ether acrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, and pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer.

[0026] The thickness of the shell is preferably 1 μm to 15 μm, more preferably 1 μm to 7 μm, and even more preferably 1 μm to 5 μm.

[0027] The volatile substance contained in the shell is typically an organic solvent, such as a linear aliphatic hydrocarbon having 3 to 8 carbon atoms and a fluorinated product thereof, a branched aliphatic hydrocarbon having 3 to 8 carbon atoms and a fluorinated product thereof, a linear alicyclic hydrocarbon having 3 to 8 carbon atoms and a fluorinated product thereof, an ether compound having a hydrocarbon group having 2 to 8 carbon atoms, or a compound in which some of the hydrogen atoms of the hydrocarbon group have been substituted with fluorine atoms. In one embodiment, the organic solvent may be a hydrocarbon composed solely of hydrogen and carbon atoms, such as propane, cyclopropane, butane, cyclobutane, isobutane, pentane, cyclopentane, neopentane, isopentane, hexane, cyclohexane, dimethylhexane, 2-methylpentane, 2,2-dimethylbutane, heptane, cycloheptane, octane, cyclooctane, isooctane, methylheptanes, or trimethylpentanes; or a hydrofluoroether, such as C3F7OCH3, C4F9OCH3, or C4F9OC2H5. These organic solvents may be used alone or in combination. The above organic solvents have the advantages of having low affinity with the shell-forming resin and / or adhesive, making them less likely to dissolve the shell and / or adhesive, and less likely to change physical properties such as thermal properties. Furthermore, hydrocarbons composed solely of hydrogen and carbon atoms are preferred from the perspective of industrial use.

[0028] In one embodiment, branched hydrocarbons (e.g., isobutane, isopentane, etc.) are used as hydrocarbons composed only of hydrogen atoms and carbon atoms. Branched hydrocarbons are difficult to charge, and the use of such solvents can prevent accidents such as fires due to charging.

[0029] The boiling point of the organic solvent is preferably -50°C to 100°C, more preferably -20°C to 100°C. Within this range, heat-expandable microspheres can be obtained whose shells can be expanded well without being destroyed. However, if the boiling point of the organic solvent is too low, the procedure for suppressing volatilization during the production of heat-expandable microspheres may become complicated.

[0030] The difference (Tg-bp) between the boiling point (bp) of the organic solvent and the glass transition temperature (Tg) of the resin constituting the shell is preferably 0°C or higher, more preferably 0°C to 200°C, and even more preferably 50°C to 150°C. If an organic solvent with a boiling point higher than the glass transition temperature of the shell is used, the shell may be destroyed by the pressure generated when the organic solvent is heated, or the adhesive may be scattered, which may impair the functions and effects expected of the present invention. When two or more organic solvents (mixed solvents) are used, the "boiling point (bp) of the organic solvent" is a value calculated by (the sum of the boiling points of the individual organic solvents) / (the number of organic solvents).

[0031] The content of the organic solvent is preferably 5 to 35% by weight, more preferably 10 to 30% by weight, based on the weight of the heat-expandable microspheres before heating. Within this range, a pressure-sensitive adhesive tape can be obtained in which the heat-expandable microspheres are dispersed with high uniformity in the pressure-sensitive adhesive layer. If the content is less than 5% by weight, the heat-expandable microspheres tend to be unevenly distributed on the surface of the pressure-sensitive adhesive layer during production due to low density, etc., and excessively large irregularities may occur on the surface of the pressure-sensitive adhesive layer after heating. If the content exceeds 35% by weight, the density is high and the microspheres settle within the pressure-sensitive adhesive layer, and sufficient irregularities may not be formed on the surface of the pressure-sensitive adhesive layer even after heating, which may result in the desired peelability being impaired and adhesive residue remaining.

[0032] The average particle size (by number) of the heat-expandable microspheres before expansion at an ambient temperature of 25°C is preferably 5 μm to 30 μm, more preferably 5 μm to 28 μm, and even more preferably 10 μm to 25 μm. This range allows for the production of heat-expandable microspheres with high dispersibility in the pressure-sensitive adhesive layer. A pressure-sensitive adhesive layer containing heat-expandable microspheres in a highly dispersed state exhibits high uniformity of unevenness caused by heating and exhibits excellent releasability. The average particle size of the heat-expandable microspheres can be controlled, for example, by the conditions for polymerizing the heat-expandable microspheres (details will be described later). The average particle size can be measured by a particle size distribution measurement method using a laser scattering method. More specifically, the average particle size can be measured by dispersing the heat-expandable microspheres in a predetermined solvent (e.g., water) and then using a particle size distribution measurement device (e.g., Shimadzu Corporation's "SALD-2000J").

[0033] In one embodiment, the content of heat-expandable microspheres is expressed as the area ratio of the heat-expandable microspheres measured from a cross section. If the cross-sectional area of ​​the pressure-sensitive adhesive layer in a given cross section is A and the cross-sectional area of ​​the heat-expandable microspheres in that cross section is B, the proportion of the cross-sectional area B of the heat-expandable microspheres to the cross-sectional area A of the pressure-sensitive adhesive layer is preferably 3% to 75%, more preferably 3.5% to 70%. If the proportion of the cross-sectional area B is less than 3%, the pressure-sensitive adhesive surface may not be sufficiently uneven even when the heat-expandable microspheres are expanded by heating, and the desired releasability may not be achieved. On the other hand, if the proportion of the cross-sectional area B exceeds 75%, the volume change of the pressure-sensitive adhesive layer may be too great, which may cause lifting or peeling between the substrate and the pressure-sensitive adhesive layer. Furthermore, the pressure-sensitive adhesive content in the pressure-sensitive adhesive layer may be so low that the desired adhesive strength may not be achieved. The cross-sectional area B of the heat-expandable microspheres can be determined by, for example, appropriately processing an image obtained by observing the cross section of the pressure-sensitive adhesive layer using an electron microscope (e.g., Hitachi Technologies, trade name "S-3400N Low-Vacuum Scanning Electron Microscope"), and then printing the image onto paper. The cross-sectional area B can be calculated from the weight of the pressure-sensitive adhesive layer (i.e., the entire pressure-sensitive adhesive layer including the heat-expandable microspheres) and the weight of the paper from which only the heat-expandable microspheres are cut out, expressed as b / a × 100.

[0034] The content of heat-expandable microspheres is preferably 20 to 80 parts by weight, more preferably 20 to 60 parts by weight, and even more preferably 20 to 50 parts by weight, per 100 parts by weight of the pressure-sensitive adhesive layer. Within this range, the cross-sectional area B of the heat-expandable microspheres can be achieved as described above. Furthermore, while maintaining the content of heat-expandable microspheres within the above range, the cross-sectional area B of the heat-expandable microspheres can be controlled within a preferred range by, for example, stirring the pressure-sensitive adhesive layer-forming composition until just before the coating step to prevent uneven distribution of the heat-expandable microspheres in the pressure-sensitive adhesive layer. The content of heat-expandable microspheres can be calculated using the following formula. The weight of the heat-expandable microspheres can be determined by measuring the weight of the heat-expandable microspheres extracted from the pressure-sensitive adhesive layer. Content of heat-expandable microspheres (wt%) = weight of heat-expandable microspheres / weight of adhesive layer × 100

[0035] The heat-expandable microspheres can be produced by any suitable method. In one embodiment, the heat-expandable microspheres are obtained by suspension polymerization. Suspension polymerization is typically carried out by dispersing a monomer (shell-forming material) and an organic solvent in an aqueous dispersion medium containing a dispersant, and polymerizing the monomer in the presence of the organic solvent. A dispersion stabilizer may also be used to stabilize the dispersion. Examples of the dispersion stabilizer in the aqueous dispersion medium include inorganic fine particles such as silica, magnesium hydroxide, calcium phosphate, and aluminum hydroxide. Examples of dispersion stabilizing aids that may be used include condensation products of diethanolamine and aliphatic dicarboxylic acids, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polyvinyl alcohol, and various emulsifiers.

[0036] The properties of heat-expandable microspheres, such as particle size and organic solvent content, can be controlled by adjusting the polymerization conditions for the suspension polymerization and the types and amounts of the mixed components. For example, heat-expandable microspheres with large particle sizes can be obtained by reducing the amount of dispersant added or slowing the stirring speed during polymerization. Heat-expandable microspheres with thick shells can also be obtained by increasing the amount of monomers added or slowing the stirring speed during polymerization.

[0037] B-2. Adhesive Any suitable adhesive may be used as the adhesive constituting the adhesive layer as long as the effects of the present invention can be obtained. Examples of the adhesive include acrylic adhesives, silicone adhesives, vinyl alkyl ether adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine-based adhesives, styrene-diene block copolymer adhesives, and active energy ray-curable adhesives. Among these, acrylic adhesives, rubber adhesives, and silicone adhesives are preferred, and acrylic adhesives are more preferred.

[0038] The gel fraction of the PSA is preferably 20% to 100% by weight, more preferably 30% to 99% by weight, and even more preferably 50% to 99% by weight. If the gel fraction is less than 20% by weight, even if the expansion of heat-expandable microspheres causes unevenness on the surface of the PSA layer, the PSA layer may flow, causing the unevenness to disappear within a short period of time. On the other hand, if the gel fraction exceeds 99% by weight, the thermal expansion of the heat-expandable microspheres may be hindered, resulting in insufficient unevenness. Even if unevenness does occur, the heat-expandable microspheres may explode, scattering the shells of the heat-expandable microspheres and the surrounding PSA layer, resulting in poor adhesive residue. The gel fraction of the PSA can be controlled by adjusting the composition of the base polymer constituting the PSA, the type and content of the crosslinking agent added to the PSA, and the type and content of the tackifier. The gel fraction can be measured as follows. Approximately 0.1 g of adhesive was sampled and precisely weighed (sample weight), and the sample was wrapped in a mesh sheet (trade name "NTF-1122", manufactured by Nitto Denko Corporation) and then immersed in approximately 50 ml of toluene at room temperature for one week. Thereafter, the solvent-insoluble portion (contents of the mesh sheet) was removed from the toluene and dried at 70°C for approximately two hours. The dried solvent-insoluble portion was weighed (weight after immersion and drying), and the gel fraction (wt%) was calculated using the following formula (a): Gel fraction (wt%) = [(weight after immersion and drying) / (weight of sample)] × 100 (a)

[0039] The base polymer contained in the pressure-sensitive adhesive preferably contains OH or COOH groups. This is because the use of such a base polymer allows the gel fraction to be adjusted using a crosslinking agent. Furthermore, the cohesion of the base polymer due to intermolecular forces such as hydrogen bonding can be adjusted by adjusting the amount of OH or COOH groups that do not react with the crosslinking agent. This allows for control of the unevenness of the pressure-sensitive adhesive surface caused by the expansion of heat-expandable microspheres and the shell permeability of the organic solvent contained in the heat-expandable microspheres.

[0040] The acid value of the base polymer is preferably 0 to 100, more preferably 0 to 75, and even more preferably 0 to 50. The acid value of the polymer in the pressure-sensitive adhesive layer can be measured by extracting the solvent-soluble components in the pressure-sensitive adhesive layer. Specifically, the solvent-soluble components can be extracted by the following method. (i) A solution sample is prepared by placing the pressure-sensitive adhesive layer in a solvent and dissolving the solvent-soluble components in the pressure-sensitive adhesive layer in the solvent. As the solvent, taking into consideration polarity and the like, any one solvent selected from chloroform (CHCl3), methylene chloride (CH2Cl2), tetrahydrofuran (THF), acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), methanol, ethanol, toluene, water, etc., or a mixed solvent containing two or more solvents in any ratio can be used. Typically, about 30 mL of solvent is added to about 0.2 g of the adhesive layer, and the mixture is stirred for about 30 minutes to 12 hours at a temperature ranging from room temperature to the boiling point of the solvent used. If necessary, for example, when the extraction efficiency of the target component is low, a solution sample may be prepared by adding a new solvent in roughly the same amount as the separated solution to the sample after separating the solution, stirring the mixture, and separating the solution, and repeating this procedure once or multiple times. (ii) The solvent can be removed from the solution sample by evaporation or other methods, and the solvent-soluble polymer can be extracted. The solvent-soluble polymer may contain solvent-soluble components that are not the target of measurement, such as low-molecular-weight components of unreacted crosslinking agent. In such cases, a solvent-soluble polymer consisting only of the target of measurement can be prepared by, for example, adding the solution sample to a solvent in which only the polymer component is insoluble (reprecipitation method), or by molecular weight fractionation using gel filtration chromatography (preparative liquid chromatography) using the solution sample.

[0041] (acrylic adhesive) Examples of the acrylic adhesive include an acrylic adhesive having as a base polymer an acrylic polymer (homopolymer or copolymer) using one or more (meth)acrylic acid alkyl esters as a monomer component. Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and methyl (meth)acrylate. Examples of (meth)acrylic acid C1-20 alkyl esters include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 4 to 18 carbon atoms can be preferably used.

[0042] The acrylic polymer may contain units corresponding to other monomers copolymerizable with the alkyl (meth)acrylate, if necessary, for the purpose of modifying properties such as cohesive strength, heat resistance, and crosslinkability. Examples of such monomers include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride monomers such as maleic anhydride and itanoic anhydride; hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; (N-substituted) amide monomers such as methylol (meth) acrylamide, N,N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, N-methylol (meth) acrylamide, and N-methylol propane (meth) acrylamide; aminoalkyl (meth) acrylate monomers such as aminoethyl (meth) acrylate, N,N-dimethylaminoethyl (meth) acrylate, and t-butylaminoethyl (meth) acrylate; alkoxyalkyl (meth) acrylate monomers such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate; maleimide monomers such as N-cyclohexyl maleimide, N-isopropyl maleimide, N-lauryl maleimide, and N-phenyl maleimide; itaconimide monomers such as N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide, and N-lauryl itaconimide;succinimide-based monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, and N-(meth)acryloyl-8-oxyoctamethylene succinimide; vinyl-based monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinylcarboxylic acid amides, styrene, α-methylstyrene, and N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and (meth)acrylate. Examples of suitable monomers include glycol-based acrylic ester monomers such as methoxypolypropylene glycol acrylate; acrylic ester monomers having heterocycles, halogen atoms, silicon atoms, etc., such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; polyfunctional monomers such as hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene; and vinyl ether-based monomers such as vinyl ether. These monomers may be used alone or in combination of two or more.

[0043] (Silicone adhesive) Any suitable silicone-based pressure-sensitive adhesive may be used as long as it can achieve the effects of the present invention. Preferred examples of the silicone-based pressure-sensitive adhesive include silicone rubber or silicone resin containing organopolysiloxane as a base polymer. The base polymer constituting the silicone-based pressure-sensitive adhesive may be a base polymer obtained by crosslinking the silicone rubber or silicone resin. In this specification, "silicone rubber" refers to a polymer (e.g., viscosity 1000 Pa·s) composed of a linear chain of diorganosiloxane (D units) as the main component, and "silicone resin" refers to a polymer composed of triorganosylhemioxane (M units) and silicate (Q units) as the main components ("Material Design and Functionalization of Pressure-Sensitive Adhesives (Films and Tapes)," Technical Information Association, published September 30, 2009).

[0044] Examples of the silicone rubber include organopolysiloxanes containing dimethylsiloxane as a constituent unit. A functional group (e.g., a vinyl group) may be introduced into the organopolysiloxane as needed. The weight-average molecular weight of the organopolysiloxane is preferably 100,000 to 1,000,000, and more preferably 150,000 to 500,000. The weight-average molecular weight can be measured by GPC (solvent: THF).

[0045] Examples of the silicone resin include RSiO 1 / 2 Building block, SiO2 building block, RSiO 3 / 2 and R2SiO structural units (where R is a monovalent hydrocarbon group or a hydroxyl group).

[0046] The silicone rubber and silicone resin may be used in combination. The weight ratio of silicone rubber to silicone resin (rubber:resin) in the silicone pressure-sensitive adhesive is preferably 100:0 to 100:220, more preferably 100:0 to 100:180, and even more preferably 100:10 to 100:100. The silicone rubber and silicone resin may be contained in the silicone pressure-sensitive adhesive as a simple mixture, or may be contained in the silicone pressure-sensitive adhesive in a partially condensed form. The rubber:resin ratio is determined by the composition of the silicone pressure-sensitive adhesive. 29 It can also be determined from the ratio of Q units (resin) to D units (rubber) measured by Si-NMR.

[0047] (rubber adhesive) Any suitable adhesive can be used as the rubber-based adhesive as long as the effects of the present invention can be obtained. Examples of the rubber-based adhesive that can be used include, for example, natural rubber; polyisoprene rubber, butadiene rubber, styrene-butadiene (SB) rubber, styrene-isoprene (SI) rubber, styrene-isoprene-styrene block copolymer (SIS) rubber, styrene-butadiene-styrene block copolymer (SBS) rubber, styrene-ethylene-butylene-styrene block copolymer (SEBS) rubber, styrene-ethylene-propylene-styrene block copolymer (SEPS) rubber, styrene-ethylene-propylene block copolymer (SEP) rubber, reclaimed rubber, butyl rubber, polyisobutylene rubber, and synthetic rubbers such as modified versions of these rubbers.

[0048] (additives) The PSA may contain any suitable additives as needed, such as crosslinkers, tackifiers, plasticizers, pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, and antioxidants.

[0049] 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.

[0050] The amount of the tackifier added is preferably 5 to 100 parts by weight, and more preferably 10 to 50 parts by weight, relative to 100 parts by weight of the base polymer.

[0051] Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, as well as urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Of these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred.

[0052] Specific examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and xylylene diisocyanate; and isocyanate adducts such as trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HL"), and hexamethylene diisocyanate isocyanurate (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HX"). The content of the isocyanate-based crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, elasticity of the adhesive layer, etc., and is typically 0.1 to 20 parts by weight, and more preferably 0.5 to 10 parts by weight, per 100 parts by weight of the base polymer.

[0053] Examples of the epoxy crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc., trade name "Tetrad C"), 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 1600"), neopentyl glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 1500NP"), ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 1500NP"), and ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 1500NP"). Licor diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 40E"), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolight 70P"), polyethylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name "Epiol E-400"), polypropylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name "Epiol P-200"), sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol") EX-611), glycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-314"), pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-512"), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. The content of the epoxy-based crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, elasticity of the adhesive layer, etc., and is typically 0.01 to 10 parts by weight, and more preferably 0.03 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0054] Any appropriate plasticizer can be used as the plasticizer. Specific examples of plasticizers include trimellitic acid ester-based plasticizers, pyromellitic acid ester-based plasticizers, polyester-based plasticizers, and adipic acid-based plasticizers. Among these, trimellitic acid ester-based plasticizers (e.g., tri(n-octyl) trimellitate, tri(2-ethylhexyl) trimellitate, etc.) or pyromellitic acid ester-based plasticizers (e.g., tetra(n-octyl) pyromellitate, tetra(2-ethylhexyl) pyromellitate, etc.) are preferred. The plasticizers may be used alone or in combination of two or more. The content of the plasticizer is preferably 1 to 20 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0055] B-3. ​​Characteristics of the adhesive layer The modulus of elasticity of the pressure-sensitive adhesive layer at 23°C as measured by nanoindentation is preferably 0.1 MPa to 500 MPa, and more preferably 0.5 MPa to 400 MPa. The modulus of elasticity as measured by nanoindentation is determined by continuously measuring the load and indentation depth of an indenter pressed into the pressure-sensitive adhesive layer, during loading and unloading, at a location approximately 3 μm inward from the surface of the pressure-sensitive adhesive layer and not containing heat-expandable microspheres (a location 1 μm or more away from the shell surface of the heat-expandable microspheres). The modulus of elasticity as measured by nanoindentation is determined from the load-indentation depth curve obtained. In this specification, the modulus of elasticity as measured by nanoindentation is determined as described above under the following measurement conditions: loading / unloading rate: 1000 nm / s, indentation depth: 800 nm.

[0056] The arithmetic mean height Sa 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. A pressure-sensitive adhesive tape in this range can be obtained that can reduce the occurrence of irregularities on the adhesion surface of an adherend. The arithmetic mean height Sa can be measured in accordance with JIS B 0601:1994 using a laser microscope (Olympus LEXT OLS-4000, image magnification 432x, measurement area 640 × 640 μm (sampling rate 0.625 μm)).

[0057] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 300 μm, more preferably 5 μm to 250 μm, even more preferably 5 μm to 100 μm, and particularly preferably 5 μm to 60 μm.

[0058] B-4. Other ingredients The pressure-sensitive adhesive layer may further contain any appropriate other component as long as the effects of the present invention are obtained. Examples of other components include beads. Examples of such beads include glass beads and resin beads. Adding such beads to the pressure-sensitive adhesive layer can improve the elastic modulus of the pressure-sensitive adhesive layer, thereby obtaining a pressure-sensitive adhesive tape that can process workpieces with greater precision. The average particle diameter of the beads is, for example, 0.01 μm to 50 μm. The amount of beads added is, for example, 10 parts by weight to 200 parts by weight, preferably 20 parts by weight to 100 parts by weight, per 100 parts by weight of the pressure-sensitive adhesive layer.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] D. Another adhesive layer Any suitable pressure-sensitive adhesive layer may be formed as the other pressure-sensitive adhesive layer. Examples of pressure-sensitive adhesives that may 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. The other pressure-sensitive adhesive layer may also have the configuration described in Section B above.

[0064] 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.

[0065] E. Elastic layer The pressure-sensitive adhesive tape of the present invention may further comprise an elastic layer. The elastic layer may be disposed on one side of the pressure-sensitive adhesive layer. When the pressure-sensitive adhesive tape comprises a substrate, the elastic layer may be disposed between the pressure-sensitive adhesive layer and the substrate. By providing the elastic layer, the conformability to the adherend is improved. Furthermore, when the pressure-sensitive adhesive tape comprising the elastic layer is heated during peeling, deformation (expansion) of the pressure-sensitive adhesive layer in the plane direction is restricted, and deformation in the thickness direction is prioritized. As a result, peelability is improved.

[0066] 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 may be a foamed film formed from the base polymer. The foamed film can be obtained by any appropriate method. 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 distinguished 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.

[0067] 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.

[0068] The thickness of the elastic layer is preferably 3 μm to 200 μm, and more preferably 5 μm to 100 μm.Within this range, the elastic layer can fully exhibit the above functions.

[0069] The tensile modulus of the elastic layer at 25°C is preferably 0.2 MPa to 500 MPa, more preferably 0.3 MPa to 500 MPa, and even more preferably 0.5 MPa to 500 MPa. Within this range, the elastic layer can fully exhibit the above-mentioned functions. The tensile modulus can be measured in accordance with JIS K 7161:2008.

[0070] F. Separator The pressure-sensitive adhesive tape 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.

[0071] G. Adhesive Tape Manufacturing Method The pressure-sensitive adhesive tape 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] H.Usage The pressure-sensitive adhesive tape of the present invention can be suitably used as a sheet for temporarily fixing electronic component materials when manufacturing and evaluating electronic components. In one embodiment, the pressure-sensitive adhesive tape of the present invention can be used as a pressure-sensitive adhesive tape for temporarily fixing a test subject in a thermal shock test. In another embodiment, the pressure-sensitive adhesive tape of the present invention can be used as a pressure-sensitive adhesive tape for temporarily fixing a workpiece in a molding process (e.g., a molding process involving heating). [Example]

[0076] The present invention will be described in more 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 examples, "parts" and "%" are by weight unless otherwise specified.

[0077] [evaluation] (1)Initial adhesive strength The adhesive tape was cut to a size of 20 mm wide and 140 mm long, and a polyethylene terephthalate film (trade name "Lumirror S-10" manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) was attached to the adhesive layer as an adherend by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237 (2000) at a temperature of 25°C and a humidity of 65%RH. The adhesive tape with the adherend was then placed in a tensile tester with a thermostatic chamber (manufactured by Shimadzu Corporation, trade name "Shimadzu Autograph AG-120kN") set to 25°C and left for 30 minutes. Thereafter, the load when the adherend was peeled from the adhesive tape was measured at a peel angle of 180° and a peel rate (tensile rate) of 300 mm / min. The maximum load (maximum load excluding the peak top at the beginning of the measurement) was determined, and this maximum load was defined as the adhesive strength (N / 20 mm).

[0078] (2) Adhesive strength after heating to 140°C The adhesive tape was cut to a size of 20 mm wide and 140 mm long, and a polyethylene terephthalate film (trade name "Lumirror S-10" manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) was attached as an adherend to the adhesive layer by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237 (2000) in an atmosphere of temperature: 25°C and humidity: 65% RH. The adhesive tape with the adherend was then placed in an environment of 140°C for 30 minutes, and then in an environment of 25°C for 30 minutes. Thereafter, the adhesive strength was measured in the same manner as in (1) above.

[0079] (3) Adhesion after heat cycle The adhesive tape was cut to a size of 20 mm wide and 140 mm long, and a polyethylene terephthalate film (trade name "Lumirror S-10" manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) was attached to the adhesive layer as an adherend by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237 (2000) in an atmosphere of temperature: 25°C and humidity: 65% RH. The adhesive tape with the adherend was then placed in an environment of 140°C for 30 minutes, then in an environment of 25°C for 30 minutes, then again in an environment of 140°C for 30 minutes, and then in an environment of 25°C for 30 minutes. Thereafter, the adhesive strength was measured in the same manner as in (1) above.

[0080] (4) Appearance after heating to 140℃ The adhesive tape was placed in an environment at 140°C for 30 minutes, and then in an environment at 25°C for 30 minutes. The appearance of the adhesive layer was then visually inspected. A tape with no foaming and a good appearance was rated as passed (○ in Table 1), and a tape with foaming and a poor appearance was rated as failed (× in Table 1).

[0081] (5) Appearance after heat cycle The adhesive tape was placed in an environment at 140°C for 30 minutes, then in an environment at 25°C for 30 minutes, then again in an environment at 140°C for 30 minutes, and then again in an environment at 25°C for 30 minutes. The appearance of the adhesive layer was then visually inspected. A tape with no foaming and a good appearance was rated as passed (○ in Table 1), and a tape with foaming and a poor appearance was rated as failed (× in Table 1).

[0082] (6) Package retention rate A QFN lead frame (size: 125 mm x 65 mm; the adhesive surface bonded to the adhesive sheet was the resin surface (surface roughness Ra: 3 μm)) sealed with epoxy resin (Hitachi Chemical Co., Ltd., product name "CEL-9200HF9") was attached to the adhesive layer of the adhesive tape. This was then attached to a 6-inch dicing ring and cut into 250 5 mm x 5 mm chips using a dicer (a cutting process was performed by dicing). The tape was then placed with the adherend side facing up in an environment at 140°C for 30 minutes, then in an environment at 25°C for 30 minutes, then again in an environment at 140°C for 30 minutes, and then in an environment at 25°C for 30 minutes. The adhesive tape with the adherend was then inverted, and the package retention rate was evaluated based on the number of packages remaining on the adhesive layer.

[0083] [Production Example 1] Preparation of heat-expandable microspheres A 150 parts by weight of sodium chloride, 70 parts by weight of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., product name "Snowtex") containing 20% ​​by weight of active silica, 1 part by weight of polyvinylpyrrolidone, and 0.5 parts by weight of a condensate of diethanolamine and adipic acid were added to 600 parts by weight of distilled water, and the pH of the resulting mixture was adjusted to 2.8 to 3.2 to obtain an aqueous solution. To the aqueous solution, 70 parts by weight of acrylonitrile and 180 parts by weight of methacrylic acid were added as oil-based additives for the shell material, and 1 part by weight of ethylene glycol dimethacrylate was added as a crosslinking agent to obtain a reaction solution. The reaction solution was added to a pressure-resistant reaction vessel equipped with a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd., trade name "TK Homomixer"), and then 20 parts by weight of isopentane (boiling point: 27.7°C) and 55 parts by weight of isooctane (boiling point: 99°C) as organic solvents intended to be encapsulated in the shell, and 5 parts by weight of an initiator (diisopropyloxydicarbonate) were added to the pressure-resistant reaction vessel. The mixture was stirred using a homomixer under the specified initial stirring conditions (stirring speed: 6000 rpm, stirring time: 2 minutes), and then heated to 60°C while stirring at 80 rpm to carry out a reaction for 24 hours. The reaction solution was filtered after the reaction, and the obtained solid content was allowed to stand at room temperature under a nitrogen stream for 1 week to obtain heat-expandable microspheres. The resulting heat-expandable microspheres had an average particle size of 30 μm, as measured using a Shimadzu SALD-2000J instrument. X-ray CT (ZEISS Xradia 520versa, measurement conditions: tube voltage 60 kV, tube current 83 μA, pixel size 0.20 μm / pixel) revealed that the solvent in the heat-expandable microspheres was isopentane and isooctane, accounting for 15 wt% of the heat-expandable microspheres. The shell thickness of the heat-expandable microspheres was measured using the X-ray CT and was 2.5 μm.

[0084] [Production examples 2-10] Thermally expandable microspheres B-J Heat-expandable microspheres B to J were prepared in the same manner as in Production Example 1, except that the type of organic solvent intended to be encapsulated in the shell and the composition of the oil-based additives (acrylonitrile, methacrylic acid, methacrylonitrile, and methyl methacrylate) were as shown in Table 1. The average particle size, amount of organic solvent contained, and shell thickness of the heat-expandable microspheres were measured in the same manner as in Production Example 1. The results are shown in Table 1.

[0085] [Table 1]

[0086] [Example 1] (Preparation of Elastic Layer-Forming Composition) A composition for forming an elastic layer was prepared by mixing 100 parts by weight of an acrylic copolymer (a copolymer of 2-ethylhexyl acrylate (2EHA), ethyl acrylate (EA), methyl methacrylate (MMA), and 2-hydroxyethyl acrylate (HEA), with a weight ratio of 2EHA structural units:EA structural units:MMA structural units:HEA structural units = 30:70:5:5), 1 part by weight of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), and toluene. (Preparation of Composition for Forming Pressure-Sensitive Adhesive Layer) A composition for forming a pressure-sensitive adhesive layer was prepared by mixing 100 parts by weight of an acrylic copolymer (a copolymer of 2-ethylhexyl acrylate (2EHA), ethyl acrylate (EA), methyl methacrylate (MMA), and 2-hydroxyethyl acrylate (HEA), with a weight ratio of 2EHA structural units:EA structural units:MMA structural units:HEA structural units=30:70:5:5), 10 parts by weight of a tackifier (manufactured by Yasuhara Chemical Co., Ltd., trade name "Mighty Ace G125"), 2 parts by weight of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), 30 parts by weight of heat-expandable microspheres A, and toluene. (Preparation of adhesive tape) The composition for forming an elastic layer was applied to a PET film (manufactured by Toray Industries, Inc., product name "Lumirror S10", thickness: 100 μm) as a substrate and dried to form an elastic layer (thickness: 15 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 (35 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-mentioned evaluations (1) to (6). The results are shown in Table 5.

[0087] [Examples 2 to 8, Example 11, Comparative Examples 1 to 3] Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the compositions for forming the elastic layer (composition of base polymer, amount of crosslinking agent) and the compositions for forming the pressure-sensitive adhesive layer (composition of base polymer, type of crosslinking agent, amount of crosslinking agent, type of heat-expandable microspheres) were as shown in Tables 2 to 4. The pressure-sensitive adhesive tapes obtained were subjected to the above-mentioned evaluations (1) to (6). The results are shown in Table 5. In the table, "Crosslinking agent Tetrad C" is an epoxy-based crosslinking agent manufactured by Mitsubishi Gas Chemical Company, Inc. (trade name "Tetrad C"). In Example 11, the "appearance after heating to 140°C" and "appearance after heat cycling" were good with no foaming, but even before the evaluation, small irregularities were observed on the surface to the extent that they did not significantly affect the adhesive strength (therefore, the evaluation result was rated as △).

[0088] [Example 9] In the same manner as in Example 1, a composition for forming an elastic layer and a composition for forming a pressure-sensitive adhesive layer were prepared. Furthermore, another composition for forming an adhesive layer was prepared by mixing 100 parts by weight of an acrylic copolymer (a copolymer of 2-ethylhexyl acrylate (2EHA), ethyl acrylate (EA), methyl methacrylate (MMA), and 2-hydroxyethyl acrylate (HEA), with a weight ratio of 2EHA structural units:EA structural units:MMA structural units:HEA structural units = 30:70:5:5), 10 parts by weight of a tackifier (manufactured by Yasuhara Chemical Co., Ltd., trade name "Mighty Ace G125"), 3 parts by weight of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), and toluene. The composition for forming an elastic layer was applied to a PET film (manufactured by Toray Industries, Inc., product name "Lumirror S10", thickness: 100 μm) as a substrate and dried to form an elastic layer (thickness: 15 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 (35 μm) on the polyethylene terephthalate film. In addition, the above-mentioned composition for forming another adhesive layer 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 another adhesive layer (10 μm) on the polyethylene terephthalate film. The adhesive layer formed on the polyethylene terephthalate film was transferred to the elastic layer, and another adhesive layer was transferred to the surface of the substrate on which the elastic layer was not formed, thereby obtaining an adhesive tape having another adhesive layer, substrate, elastic layer and adhesive layer in this order. The obtained adhesive tape was subjected to the above evaluations (1) to (6). The results are shown in Table 5.

[0089] [Example 10] (Preparation of silicone pressure-sensitive adhesive layer-forming composition) A composition for forming a pressure-sensitive adhesive layer was prepared by mixing 100 parts by weight of an addition reaction type silicone pressure-sensitive adhesive (manufactured by Toray Industries, Inc., product name "Silicone Rubber SD-4580L," silicone rubber:silicone resin = 60:40 (weight ratio)), 0.5 parts by weight of a platinum catalyst (manufactured by Toray Industries, Inc., product name "SRX-212"), 30 parts by weight of heat-expandable microspheres A, and 100 parts by weight of toluene. (Preparation of adhesive tape) The silicone adhesive layer-forming composition was applied to a polyimide film (manufactured by Toray DuPont Co., Ltd., product name "Kapton 200H", thickness 50 μm) as a substrate layer, and dried to form an adhesive layer (thickness: 30 μm) on the substrate, thereby obtaining an adhesive tape. The obtained adhesive tape was subjected to the above evaluations (1) to (6). The results are shown in Table 5.

[0090] [Table 2]

[0091] [Table 3]

[0092] [Table 4]

[0093] [Table 5] [Explanation of symbols]

[0094] 10 adhesive layer 20 Base material 100 adhesive tape

Claims

1. a pressure-sensitive adhesive layer containing heat-expandable microspheres, a substrate disposed on at least one side of the pressure-sensitive adhesive layer, and an elastic layer disposed on one side of the pressure-sensitive adhesive layer; The heat-expandable microspheres are composed of a shell and a volatile substance contained in the shell, the shell is made of a resin having a glass transition temperature (Tg) of 120°C or higher, the volatile substance is an organic solvent, and the difference (Tg-bp) between the boiling point (bp) of the organic solvent and the glass transition temperature (Tg) of the resin constituting the shell is 50°C to 150°C; the resin constituting the shell contains a structural unit having a carboxyl group, the content of the structural unit having a carboxyl group is 5 parts by weight to 97 parts by weight relative to 100 parts by weight of the resin constituting the shell, the substrate comprises a resin sheet, The resin constituting the resin sheet is polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyamide, wholly aromatic polyamide, polyimide, polyvinyl chloride, polyphenylene sulfide, fluorine-based resin, or polyether ether ketone; Adhesive tape.

2. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the pressure-sensitive adhesive tape has an initial adhesive strength a of 0.5 N / 20 mm to 20 N / 20 mm when the adhesive surface of the pressure-sensitive adhesive tape is attached to a polyethylene terephthalate film at an ambient temperature of 25°C.

3. 3. The adhesive tape according to claim 1, wherein an adhesive strength b when the adhesive surface of the adhesive tape that has been heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film is 50% or more of an initial adhesive strength a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C.

4. 4. The adhesive tape according to claim 1, wherein the adhesive strength c when the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film after two cycles of heating to 140°C and then cooling to 25°C is 50% or more of the initial adhesive strength a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C.

5. 5. The pressure-sensitive adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer has a modulus of elasticity at 23° C. measured by a nanoindentation method of 0.1 MPa to 500 MPa.

6. Further provided with another adhesive layer, The substrate is disposed between the pressure-sensitive adhesive layer and the other pressure-sensitive adhesive layer. The adhesive tape according to claim 1 .

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