Adhesive tape

Abstract

This adhesive tape contains thermally expandable microspheres, the thermally expandable microspheres are configured from a shell and a volatile substance contained in the shell, and said shell is configured from a resin with a glass transition temperature (Tg) of 120 C° or higher. In one embodiment, the resin configuring the shell contains a constituent unit that has a carboxyl group.

Description

Technical Field

[0001] The present invention relates to an adhesive tape. More specifically, it relates to an adhesive tape capable of exhibiting easy peelability in response to thermal stimulation.

Background Art

[0002] In the process of manufacturing electronic components and the like, as an adhesive tape used for temporarily fixing a workpiece, an easily peelable adhesive tape that exhibits adhesiveness during temporary fixing and peelability in a situation where fixing is not required is known. As one such adhesive tape, an adhesive tape configured to contain thermally expandable microspheres typified by a foaming agent in an adhesive layer has been studied (for example, Patent Document 1). This adhesive tape exhibits a desired adhesive force at a relatively low temperature typified by normal temperature, while when heated to a predetermined temperature (foaming temperature) or higher, the foaming agent expands, unevenness occurs on the surface of the adhesive layer, and the adhesive force decreases. In such an adhesive tape, it is also possible to peel the adherend only by the action of gravity.

[0003] On the other hand, in recent years, the manufacturing processes and usage environments of electronic components have become diversified, and electronic components are assumed to be exposed to a higher temperature environment than before, and it is required to exhibit desired performance even in such an environment. Therefore, when manufacturing electronic components, reliability may be evaluated by a test in which high-temperature conditions and low-temperature conditions such as a thermal shock test are cycled.

[0004] Also in the thermal shock test, an adhesive tape configured to contain a foaming agent can be used for temporarily fixing the test specimen. For the adhesive tape used in this way, a foaming agent that can foam at a temperature equal to or higher than the high-temperature condition of the thermal shock test is used, and it is required to have the characteristic of not showing peelability during the thermal shock test and showing peelability by heating after the test. However, conventional foaming agents have a problem that the foaming temperature decreases due to a thermal history below the foaming temperature, and the adhesive force of the adhesive tape is unnecessarily decreased during the thermal shock test.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide an adhesive tape in which a decrease in foaming temperature due to thermal history is prevented.

Means for Solving the Problems

[0007] The adhesive tape of the present invention contains thermally expandable microspheres, and the thermally expandable microspheres 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 structural unit having a carboxyl group. In one embodiment, the content ratio of the structural unit having a carboxyl group is 5 parts by weight to 97 parts by weight with respect to 100 parts by weight of the resin. In one embodiment, at an environmental temperature of 25°C, the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film is 0.5 N / 20 mm to 20 N / 20 mm. In one embodiment, when the adhesive surface of the adhesive tape heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film, the adhesive force b is 50% or more with respect to the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C. In one embodiment, the adhesive force c when the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film after performing the cycle of heating up to 140 °C and then cooling down to 25 °C twice is 50% or more with respect to the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to the polyethylene terephthalate film under an environmental 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 adhesive tape further includes a base material. In one embodiment, the adhesive tape further includes another adhesive layer, and the base material is disposed between the adhesive layer and the another adhesive layer.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide an adhesive tape in which a decrease in the foaming temperature due to a thermal history is prevented.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] A. Overall structure of the adhesive tape FIG. 1(a) is a schematic cross-sectional view of an adhesive tape according to one embodiment of the present invention. Typically, the adhesive tape 100 includes an adhesive layer 10. The adhesive tape of the present invention may be composed only of the adhesive layer 10, or may further include any appropriate layer in addition to the adhesive layer.

[0011] FIG. 1(b) is a schematic cross-sectional view of an adhesive tape according to another embodiment of the present invention. The adhesive tape 200 includes an adhesive layer 10 and a base material 20 disposed on at least one side of the adhesive layer 10. FIG. 1(c) is a schematic cross-sectional view of an adhesive tape according to still another embodiment of the present invention. The adhesive tape 300 includes an adhesive layer 10 and another adhesive layer 30 disposed on at least one side of the adhesive layer 10. A base material 20 may be disposed between the adhesive layer 10 and the another adhesive layer 30 as shown in the illustrated example. Although not shown, the base material may be omitted and the adhesive tape may be composed of the adhesive layer and the another adhesive layer. Further, although not shown, the adhesive tape may further include, as a layer other than the adhesive layer, an elastic layer (described in item E below) that can impart elasticity to the adhesive tape, a separator (described in item F below) detachably disposed on the adhesive layer, and the like.

[0012] The above-mentioned adhesive tape contains thermally expandable microspheres. In one embodiment, the adhesive layer contains thermally expandable microspheres. The thermally expandable microspheres can expand at a predetermined temperature. When the adhesive layer containing such thermally expandable microspheres is heated to a temperature equal to or higher than the predetermined temperature, the thermally expandable microspheres expand, irregularities are generated on the adhesive surface (i.e., the surface of the adhesive layer), and the adhesive force decreases or disappears. When the adhesive tape of the present invention is used as a temporary fixing sheet for a test object or a workpiece during, for example, the test or processing of an electronic component (e.g., a ceramic capacitor), the necessary adhesiveness is exhibited in a situation where fixing is required. Thereafter, when the adhesive tape is peeled off, the adhesive force decreases or disappears due to heating, and good peelability is exhibited.

[0013] At an environmental temperature of 25°C, the initial adhesive force a when the adhesive surface of the adhesive tape of the present invention is adhered to a polyethylene terephthalate film (for example, with a thickness of 25 μm) 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 such a range, for example, 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 force means the adhesive force in a state that has not undergone a heat history of 50°C or higher. Also, the adhesive force refers to the adhesive force measured by a method according to JIS Z 0237:2000 (laminating condition: 1 reciprocation of a 2 kg roller, peeling speed: 300 mm / min, peeling angle 180°).

[0014] The adhesive force b when the adhesive surface of the adhesive tape of the present invention heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film (for example, with a thickness of 25 μm) 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] The adhesive force b when the adhesive surface of the adhesive tape of the present invention heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film (for example, with a thickness of 25 μm) is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more with respect to the initial adhesive force a.

[0016] After heating to 140°C and then cooling to 25°C, when the adhesive surface of the pressure-sensitive adhesive tape of the present invention after performing the cycle twice is adhered to a polyethylene terephthalate film (for example, having a thickness of 25 μm), the adhesive force c is 0.4 N / 20 mm to 20 N / 20 mm, more preferably 0.4 N / 20 mm to 17 N / 20 mm, still 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 heating to 140°C and then cooling to 25°C, when the adhesive surface of the pressure-sensitive adhesive tape of the present invention after performing the cycle twice is adhered to a polyethylene terephthalate film (for example, having a thickness of 25 μm), the adhesive force c is preferably 50% or more, more preferably 80% or more, and still more preferably 90% or more with respect to the initial adhesive force 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 adhesive layer contains thermally expandable microspheres. Practically, the adhesive layer further contains an adhesive.

[0020] B-1. Thermally Expandable Microspheres The thermally expandable microspheres are composed of a shell and a volatile substance (typically an organic solvent) contained in 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, by using such thermally expandable microspheres containing the shell, a pressure-sensitive adhesive tape in which the foaming temperature of the thermally expandable microspheres is less likely to fluctuate can be obtained. More specifically, conventional foaming agents tend to have a decrease in the foaming temperature due to this heat history when heated below the foaming temperature, but in the present invention, by using the thermally expandable microspheres containing the shell, a decrease in the foaming temperature due to the heat history is prevented.

[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 still more preferably 135°C or higher. If it is within such a range, the effects of the present invention become more remarkable. The upper limit of the glass transition temperature (Tg) of the resin constituting the shell is, for example, 260°C. The above glass transition temperature is obtained by Fox's calculation formula. Fox's calculation formula is, as shown below, the relationship between the glass transition temperature Tg (°C) of the copolymer and the glass transition temperature Tg i (°C) of the homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. In the following Fox's formula, Tg (°C) is the glass transition temperature of the copolymer, and W i is the weight fraction of monomer i, and Tg i (°C) represents the glass transition temperature of the homopolymer formed from monomer i. 1 / (273 + Tg) = Σ(W i / (273 + Tg i )) Examples of the glass transition temperature of the homopolymer formed from the monomer are: methacrylic acid homopolymer: 228°C, acrylonitrile homopolymer: 97°C, methyl methacrylate homopolymer: 102°C, methacryloyl nitrile homopolymer: 120°C, vinylidene chloride homopolymer: 75°C, isobornyl acrylate homopolymer: 97°C. In addition, as the glass transition temperature of homopolymers other than these, the values described in "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) can be used. In this document, when multiple Tg values are described, the "conventional" value is adopted.

[0022] As the resin forming the above shell, for example, a resin having a structural unit derived from a radically polymerizable monomer is used. 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; 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 above shell contains a structural unit having a carboxyl group. If the shell is composed of a resin having a carboxyl group, the state of the molecules can be maintained even under a thermal history due to the interaction between carboxyl groups. As a result, the effect of preventing the decrease in the foaming temperature due to the thermal history becomes remarkable. The structural unit having a carboxyl group can be, for example, a structural unit derived from the above carboxyl group-containing monomer. In one embodiment, the resin constituting the above 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 above 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 above shell, the content ratio of the structural unit having a carboxyl group is preferably 5 to 97 parts by weight, more preferably 5 to 90 parts by weight, still 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 with respect to 100 parts by weight of the resin. Within such a range, the effect of preventing the decrease in the foaming temperature due to the heat history can be effectively obtained, and a shell excellent in solvent resistance can be formed.

[0025] The resin forming the above shell may be a crosslinked body. By crosslinking, the free volume of the polymer can be adjusted, whereby the diffusibility of the encapsulated volatile substance, the expansibility of the shell, etc. can be controlled. The crosslinked body may further contain a structural unit derived from a monomer having two or more polymerizable double bonds in the molecule. In one embodiment, the above radically polymerizable monomer and a monomer having two or more polymerizable double bonds in the molecule are used in combination.Examples of monomers having two or more polymerizable double bonds in the molecule include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacryl formal, 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, 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 tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol acrylate benzoate, trimethylolpropane acrylate 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, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, etc.

[0026] The thickness of the above 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 above shell is typically an organic solvent. Examples of the organic solvent include linear aliphatic hydrocarbons having 3 to 8 carbon atoms and their fluorides, branched aliphatic hydrocarbons having 3 to 8 carbon atoms and their fluorides, linear alicyclic hydrocarbons having 3 to 8 carbon atoms and their fluorides, ether compounds having a hydrocarbon group with 2 to 8 carbon atoms, or compounds in which a part of the hydrogen atoms of the hydrocarbon group is substituted by fluorine atoms. In one embodiment, as the organic solvent, hydrocarbons composed only of hydrogen atoms 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, trimethylpentanes, etc.; hydrofluoroethers such as C3F7OCH3, C4F9OCH3, C4F9OC2H5, etc. are used. These organic solvents may be used alone or in combination of two or more. The above organic solvents have the advantages of low affinity with the resin and / or adhesive forming the shell, being difficult to dissolve the shell and / or adhesive, and being difficult to change physical properties such as thermal properties. Also, hydrocarbons composed only of hydrogen atoms and carbon atoms are preferable from the viewpoint of industrial utilization.

[0028] In one embodiment, branched hydrocarbons (e.g., isobutane, isopentane, etc.) are used as the hydrocarbons composed only of hydrogen atoms and carbon atoms. Branched hydrocarbons are difficult to be charged, and using this solvent can prevent accidents such as ignition due to charging.

[0029] The boiling point of the above organic solvent is preferably -50°C to 100°C, more preferably -20°C to 100°C. Within such a range, it is possible to obtain thermally expandable microspheres in which the shell can expand well without being destroyed. In addition, if the boiling point of the organic solvent is too low, the operations for suppressing volatilization during the production of the thermally expandable microspheres may become complicated.

[0030] The difference (Tg - bp) between the boiling point (bp) of the above organic solvent and the glass transition temperature (Tg) of the resin constituting the above shell is preferably 0°C or higher, more preferably 0°C to 200°C, and even more preferably 50°C to 150°C. When using an organic solvent with a boiling point higher than the glass transition temperature of the shell, there is a risk of inhibiting the functions and effects expected in the present invention, such as the shell being destroyed by the pressure generated when the organic solvent is heated, or the adhesive scattering. In addition, 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 each organic solvent) / (the number of types of organic solvents).

[0031] The content ratio of the above organic solvent is preferably 5% by weight to 35% by weight, more preferably 10% by weight to 30% by weight, based on the weight of the thermally expandable microspheres before heating. Within such a range, it is possible to obtain an adhesive tape in which the thermally expandable microspheres are dispersed with high uniformity in the adhesive layer. If the content ratio is less than 5% by weight, due to reasons such as low density, the thermally expandable microspheres tend to be unevenly distributed on the surface of the adhesive layer during the production of the adhesive layer, and there is a risk of excessive unevenness on the surface of the adhesive layer after heating. If the content ratio exceeds 35% by weight, the density is high and it settles within the adhesive layer, and even after heating, sufficient unevenness cannot be formed on the surface of the adhesive layer, and there is a risk of not obtaining the desired peelability, and there is also a risk of adhesive residue.

[0032] At an environmental temperature of 25°C, before foaming the above-mentioned thermally expandable microspheres, the average particle diameter (number-based) of the thermally expandable microspheres is preferably 5 μm to 30 μm, more preferably 5 μm to 28 μm, and even more preferably 10 μm to 25 μm. If it is within such a range, thermally expandable microspheres with high dispersibility in the adhesive layer can be obtained. An adhesive layer containing thermally expandable microspheres in a highly dispersed state has high uniformity of unevenness generated by heating and can exhibit excellent peelability. The average particle diameter of the above-mentioned thermally expandable microspheres can be controlled, for example, by the conditions when polymerizing the thermally expandable microspheres (details will be described later). The average particle diameter can be measured by a particle size distribution measurement method in the laser scattering method. More specifically, the average particle diameter can be measured using a particle size distribution measuring device (for example, the product name "SALD-2000J" manufactured by Shimadzu Corporation) after dispersing the thermally expandable microspheres to be used in a predetermined solvent (for example, water).

[0033] In one embodiment, the content ratio of the thermally expandable microspheres is represented by the area ratio of the thermally expandable microspheres measured from the cross-section. When the cross-sectional area of the adhesive layer in a predetermined cross-section is A and the cross-sectional area of the thermally expandable microspheres in the cross-section is B, the ratio of the cross-sectional area B of the thermally expandable microspheres is preferably 3% to 75% with respect to the cross-sectional area A of the adhesive layer, and more preferably 3.5% to 70%. When the ratio of the cross-sectional area B is less than 3%, even if the thermally expandable microspheres are expanded by heating, the unevenness generated on the adhesive surface may be insufficient, and there is a possibility that the desired peelability cannot be obtained. On the other hand, when the ratio of the cross-sectional area B exceeds 75%, the volume change of the adhesive layer becomes too large, and there is a possibility of floating and peeling between the base material and the adhesive layer. In addition, the adhesive content ratio in the adhesive layer is low, and there is a possibility that the desired adhesive force cannot be obtained. The ratio of the cross-sectional area B of the thermally expandable microspheres can be obtained, for example, by appropriately processing an image obtained by observing the cross-section of the adhesive layer with an electron microscope (for example, the product name "S-3400N low-vacuum scanning electron microscope" manufactured by Hitachi Technologies). For example, the image can be printed on paper, and from the paper weight a of the adhesive layer portion (that is, the entire adhesive layer containing thermally expandable microspheres) and the paper weight b of the paper with only the thermally expandable microsphere portion cut out, it can be obtained by the formula of b / a×100.

[0034] The content ratio of the thermally expandable microspheres is preferably 20 to 80 parts by weight, more preferably 20 to 60 parts by weight, and still more preferably 20 to 50 parts by weight with respect to 100 parts by weight of the adhesive layer. If it is within such a range, it becomes possible to realize the ratio of the cross-sectional area B of the thermally expandable microspheres as described above. Further, in order to prevent the thermally expandable microspheres from being unevenly distributed in the adhesive layer while the content ratio of the thermally expandable microspheres is within the above range, operations such as stirring the composition for forming the adhesive layer until immediately before the coating step are performed, whereby the cross-sectional area B of the thermally expandable microspheres can be made within a preferable range. The content ratio of the thermally expandable microspheres is determined by the following formula. The weight of the thermally expandable microspheres is determined by measuring the weight of the thermally expandable microspheres extracted from the adhesive layer. Content ratio (weight %) of thermally expandable microspheres = Weight of thermally expandable microspheres / Weight of adhesive layer × 100

[0035] The above thermally expandable microspheres can be produced by any suitable method. In one embodiment, the above thermally expandable microspheres are obtained by suspension polymerization. Suspension polymerization is usually 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. Also, a dispersion stabilizer for stabilizing the dispersion may be used. Examples of the dispersion stabilizer in the aqueous dispersion medium include inorganic fine particles such as silica, magnesium hydroxide, calcium phosphate, and aluminum hydroxide. Further, as the dispersion stability auxiliary agent, for example, a condensation product of diethanolamine and aliphatic dicarboxylic acid, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polyvinyl alcohol, various emulsifiers, etc. may be used.

[0036] By adjusting the polymerization conditions of the suspension polymerization, the types and addition amounts of the mixed components, etc., it is possible to control the characteristics of the thermally expandable microspheres, such as the particle size and the content of the organic solvent. For example, by reducing the addition amount of the dispersant or slowing down the stirring speed during polymerization, thermally expandable microspheres with a large particle size can be obtained. Also, by increasing the blending amount of the monomer or slowing down the stirring speed during polymerization, thermally expandable microspheres with a thick shell can be obtained.

[0037] B-2. Adhesive As the adhesive constituting the adhesive layer, any suitable adhesive can be used 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 adhesives, styrene-diene block copolymer adhesives, and active energy ray-curable adhesives. Among them, acrylic adhesives, rubber adhesives, or silicone adhesives are preferably used, and acrylic adhesives are more preferably used.

[0038] The gel fraction of the adhesive is preferably 20% by weight to 100% by weight, more preferably 30% by weight to 99% by weight, and even more preferably 50% by weight to 99% by weight. When the gel fraction is less than 20% by weight, even if the thermally expandable microspheres expand and cause unevenness on the surface of the adhesive layer, the adhesive layer may flow and the unevenness may disappear in a short time. On the other hand, when the gel fraction exceeds 99% by weight, it may inhibit the thermal expansion of the thermally expandable microspheres and not cause sufficient unevenness, or even if unevenness occurs, phenomena such as the thermally expandable microspheres exploding and scattering the shell of the thermally expandable microspheres and the surrounding adhesive layer may occur, and the residue property of the glue may deteriorate. The gel fraction of the adhesive can be controlled by adjusting the composition of the base polymer constituting the adhesive, the type and content of the cross-linking agent added to the adhesive, the type and content of the tackifier, etc. The method for measuring the gel fraction is as follows. Sampling and accurately weighing approximately 0.1 g of the adhesive (weight of the sample), wrapping the sample with a mesh sheet (product name "NTF-1122", manufactured by Nitto Denko Corporation), and then immersing it in approximately 50 ml of toluene at room temperature for 1 week. Thereafter, the solvent-insoluble matter (contents of the mesh sheet) is taken out from toluene, dried at 70 °C for approximately 2 hours, the solvent-insoluble matter after drying is weighed (weight after immersion and drying), and the gel fraction (weight %) is calculated from the following formula (a). Gel fraction (weight %) = [(weight after immersion and drying) / (weight of the sample)] × 100 (a)

[0039] The base polymer contained in the above adhesive preferably has an OH group or a COOH group. This is because by using such a base polymer, it becomes possible to adjust the above gel fraction using a crosslinking agent. Further, the cohesiveness of the base polymer due to intermolecular forces such as hydrogen bonds can be adjusted by the amount of OH groups or COOH groups that do not react with the crosslinking agent. Thereby, the uneven shape of the adhesive surface caused by the expansion of the thermally expandable microspheres and the shell permeability of the organic solvent contained in the thermally expandable microspheres can be controlled.

[0040] The acid value of the above base polymer is preferably 0 to 100, more preferably 0 to 75, and still more preferably 0 to 50. The acid value of the polymer in the adhesive layer can be measured by extracting the solvent-soluble matter in the adhesive layer. Specifically, the solvent-soluble matter can be extracted by the following method. (i) The adhesive layer is put into a solvent to prepare a solution sample in which the solvent-soluble matter in the adhesive layer is dissolved in the above solvent. As the solvent, considering 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 of them in an arbitrary ratio can be used. Typically, about 30 mL of a solvent is added to about 0.2 g of the adhesive layer, and the mixture is stirred for about 30 minutes to about 12 hours in a temperature range from room temperature to about the boiling point of the solvent used. If necessary, for example, when the extraction efficiency of the component to be analyzed is low, after separating the above solution, an operation of adding and stirring approximately the same amount of the solvent as the separated solution to the sample and then separating the solution may be repeated once or multiple times to prepare a solution sample. (ii) The solvent can be removed from the above solution sample by methods such as evaporation to extract the solvent-soluble polymer. Note that the solvent-soluble polymer may contain solvent-soluble components that are not the measurement targets, such as low-molecular-weight components of unreacted crosslinking agents. In that case, a method of adding the above solution sample to a solvent in which only the polymer component is insoluble (reprecipitation method), or molecular weight fractionation (fractional liquid chromatography method) by gel filtration chromatography using the above solution sample is performed to adjust the solvent-soluble polymer consisting only of the measurement targets.

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

[0042] The above acrylic polymer may contain units corresponding to other monomers copolymerizable with the above alkyl (meth)acrylate, as necessary, for the purpose of modifying cohesion, heat resistance, crosslinkability, etc. 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, crotonic acid; acid anhydride monomers such as maleic anhydride, itaconic 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, (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, (meth)acryloyloxynaphthalenesulfonic acid; (N-substituted) amide monomers such as (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N-butyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylolpropane (meth)acrylamide; (meth)acrylic acid aminoalkyl monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate; (meth)acrylic acid alkoxyalkyl monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate; maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide; itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide;Succinimide-based monomers such as N-(meth)acryloyloxymethylene succinimide, N-(meth)acryloyl-6-oxyhexamethylene succinimide, N-(meth)acryloyl-8-oxyoctamethylene succinimide; Vinyl-based monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methyl vinylpyrrolidone, vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazole, vinyl oxazole, vinyl morpholine, N-vinyl carboxylic acid amides, styrene, α-methylstyrene, N-vinyl caprolactam; Cyanoacrylate monomers such as acrylonitrile, methacrylonitrile; Epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; Glycol-based acrylic ester monomers such as (meth)acrylic acid polyethylene glycol, (meth)acrylic acid polypropylene glycol, (meth)acrylic acid methoxyethylene glycol, (meth)acrylic acid methoxypolypropylene glycol; Acrylic acid ester monomers having a heterocyclic ring, halogen atom, silicon atom, etc. such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, 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, urethane acrylate; Olefin-based monomers such as isoprene, butadiene, isobutylene; Vinyl ether-based monomers such as vinyl ether, etc. These monomers may be used alone or in combination of two or more.;

[0043] (Silicone-based adhesive) As the silicone-based adhesive, any suitable adhesive may be used as long as the effect of the present invention can be obtained. As the silicone-based adhesive, for example, a silicone-based adhesive having a base polymer of silicone rubber or silicone resin containing organopolysiloxane is preferably used. As the base polymer constituting the silicone-based adhesive, a base polymer obtained by crosslinking the silicone rubber or silicone resin may be used. In this specification, "silicone rubber" means a polymer (for example, viscosity 1000 Pa·s) in which diorganosiloxane (D unit) as the main component is linked in a linear chain, and "silicone resin" means a polymer composed of triorganosylhemioxane (M unit) and silicate (Q unit) as the main components ("Material Design and Functionalization of Adhesives (Films and Tapes)", Technical Information Association, published on September 30, 2009).

[0044] The silicone rubber may be, for example, an organopolysiloxane containing dimethylsiloxane as a constituent unit. A functional group (for example, a vinyl group) may be introduced into the organopolysiloxane as necessary. The weight average molecular weight of the organopolysiloxane is preferably 100,000 to 1,000,000, more preferably 150,000 to 500,000. The weight average molecular weight can be measured by GPC (solvent: THF).

[0045] The silicone resin is, for example, RSiO 1 / 2 Building block, SiO2 building block, RSiO 3 / 2 and R2SiO structural units (wherein R is a monovalent hydrocarbon group or a hydroxyl group).

[0046] The above silicone rubber and silicone resin can be used in combination. The weight ratio of silicone rubber to silicone resin in the silicone adhesive (rubber: resin) is preferably from 100:0 to 100:220, more preferably from 100:0 to 100:180, and still more preferably from 100:10 to 100:100. The silicone rubber and silicone resin may be contained in the silicone-based adhesive as a mere mixture, or may be contained in the silicone-based adhesive in a form in which the silicone rubber and silicone resin are partially condensed. The rubber: resin ratio depends on the composition of the silicone adhesive 29 can also be determined from the ratio of the Q unit (resin) to the D unit (rubber) obtained by measurement by Si-NMR.

[0047] (rubber-based adhesive) As the above rubber-based adhesive, any suitable adhesive can be used as long as the effects of the present invention can be obtained. Examples of the above rubber-based adhesive include 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, recycled rubber, butyl rubber, polyisobutylene rubber, or rubber-based adhesives having these modified products, etc. as base polymers are preferably used.

[0048] (Additive) The above adhesive may contain any suitable additive as required. Examples of the additive include crosslinking agents, tackifiers, plasticizers, pigments, dyes, fillers, anti-aging agents, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, peel adjustment agents, softeners, surfactants, flame retardants, antioxidants, etc.

[0049] As the above-mentioned tackifier, any suitable tackifier can be used. As the tackifier, for example, a tackifying resin is used. Specific examples of the tackifying resin include rosin-based tackifying resins (e.g., unmodified rosin, modified rosin, rosin-phenol resins, rosin ester resins, etc.), terpene-based tackifying resins (e.g., terpene resins, terpene-phenol 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 resins, xylene resins, etc.), aliphatic-aromatic petroleum resins, aliphatic-alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, etc.), phenol-based tackifying resins (e.g., alkylphenol resins, xylene formaldehyde resins, resols, novolacs, etc.), ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, elastomer-based tackifying resins, etc.

[0050] The addition amount of the above-mentioned tackifier is preferably 5 to 100 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the base polymer.

[0051] As the above-mentioned crosslinking agent, for example, in addition to isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, 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, amine-based crosslinking agents, etc. can be mentioned. Among them, preferably, it is an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent.

[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; 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 isocyanurate form of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HX"); etc. The content of the isocyanate-based crosslinking agent can be set to any appropriate amount according to the desired adhesive strength, elasticity of the adhesive layer, etc., and is typically 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the base polymer.

[0053] Examples of the epoxy crosslinking agent include N,N,N’,N’-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, trade name “Tetrad C”), 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name “Epolite 1600”), neopentyl glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name “Epolite 1500NP”), ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name “Epolite 40E”), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name “Epolite 70P”), polyethylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name “Epole E-400”), polypropylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name “Epole 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, resorcin diglycidyl ether, bisphenol-S-diglycidyl ether, epoxy resins having two or more epoxy groups in the molecule, and the like. The content of the epoxy crosslinking agent can be set to any appropriate amount according to the desired adhesive strength, elasticity of the adhesive layer, etc., and is typically 0.01 parts by weight to 10 parts by weight, more preferably 0.03 parts by weight to 5 parts by weight, based on 100 parts by weight of the base polymer.

[0054] As the above plasticizer, any suitable plasticizer can be used. Specific examples of the plasticizer include, for example, trimellitic acid ester plasticizers, pyromellitic acid ester plasticizers, polyester plasticizers, adipic acid plasticizers, and the like. Among them, preferably, trimellitic acid ester plasticizers (for example, tri(n-octyl) trimellitate, tri(2-ethylhexyl) trimellitate, etc.) or pyromellitic acid ester plasticizers (for example, tetra(n-octyl) pyromellitate, tetra(2-ethylhexyl) pyromellitate, etc.). The plasticizer may be used alone or in combination of two or more. The content of the plasticizer is preferably 1 part by weight to 20 parts by weight, more preferably 1 part by weight to 5 parts by weight, based on 100 parts by weight of the base polymer.

[0055] B-3. Characteristics of the Adhesive Layer The elastic modulus of the above adhesive layer by nanoindentation method at 23°C is preferably 0.1 MPa to 500 MPa, more preferably 0.5 MPa to 400 MPa. The elastic modulus by nanoindentation method refers to the elastic modulus measured as follows: within about 3 μm from the surface of the adhesive layer and at a location where there are no thermally expanded microspheres (a location more than 1 μm away from the shell surface of the thermally expanded microspheres), the load on the indenter and the indentation depth are continuously measured during loading and unloading when the indenter is pressed into the adhesive layer, and it is obtained from the obtained load - indentation depth curve. In this specification, the elastic modulus by nanoindentation method refers to the elastic modulus measured as described above with the measurement conditions of load / unload rate: 1000 nm / s and indentation depth: 800 nm.

[0056] At an environmental temperature of 25°C, before foaming the above-mentioned thermally expandable microspheres, the arithmetic mean height Sa of the above-mentioned adhesive layer is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. If it is within such a range, an adhesive tape can be obtained that can reduce the unevenness generated on the adherend's adhering surface. 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 432 times, measurement area 640×640 μm (sampling rate 0.625 μm).

[0057] The thickness of the above-mentioned 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 components The above-mentioned adhesive layer may further contain any appropriate other components as long as the effects of the present invention can be obtained. Examples of other components include beads. Examples of the beads include glass beads, resin beads, etc. If such beads are added to the adhesive layer, the elastic modulus of the adhesive layer can be improved, and an adhesive tape that can process the workpiece more accurately can be obtained. The average particle diameter of the beads is, for example, 0.01 μm to 50 μm. The addition amount of the beads is, for example, 10 parts by weight to 200 parts by weight, preferably 20 parts by weight to 100 parts by weight, based on 100 parts by weight of the adhesive layer.

[0059] C. Substrate Examples of the base material include a resin sheet, non-woven fabric, paper, metal foil, woven fabric, rubber sheet, foamed sheet, and laminates thereof (particularly, laminates containing a resin sheet). Examples of the resin constituting the resin sheet include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), polyamide (nylon), wholly aromatic polyamide (aramid), polyimide (PI), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), fluororesin, polyetheretherketone (PEEK), and the like. Examples of the non-woven fabric include non-woven fabrics made of heat-resistant natural fibers such as non-woven fabrics containing Manila hemp; synthetic resin non-woven fabrics such as polypropylene resin non-woven fabrics, polyethylene resin non-woven fabrics, and ester-based resin non-woven fabrics. Examples of the metal foil include copper foil, stainless steel foil, and aluminum foil. Examples of the paper include Japanese paper and kraft paper.

[0060] The thickness of the base material can be set to any appropriate thickness according to the desired strength or flexibility, as well as the purpose of use and the like. The thickness of the base material is preferably 1000 μm or less, more preferably 1 μm to 1000 μm, still more preferably 1 μm to 500 μm, particularly preferably 3 μm to 300 μm, and most preferably 5 μm to 250 μm.

[0061] The base material may be subjected to surface treatment. Examples of the surface treatment include corona treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, ionization radiation treatment, coating treatment with an undercoat agent, and the like.

[0062] Examples of the above-mentioned organic coating material include materials described in Plastic Hard Coat Material II (CMC Publishing, (2004)). Preferably, urethane-based polymers are used, more preferably polyacrylic urethane, polyester urethane, or their precursors. This is because coating and application to the substrate are simple, and industrially, a wide variety can be selected and obtained at low cost. The urethane-based polymer is, for example, a polymer composed of a reaction mixture of an isocyanate monomer and an alcohol group-containing monomer (e.g., a hydroxyl group-containing acrylic compound or a hydroxyl group-containing ester compound). The organic coating material may contain, as optional additives, chain extenders such as polyamines, anti-aging agents, oxidation stabilizers, etc. The thickness of the organic coating layer is not particularly limited, but for example, about 0.1 μm to 10 μm is suitable, about 0.1 μm to 5 μm is preferable, and about 0.5 μm to 5 μm is more preferable.

[0063] D. Another adhesive layer As the above-mentioned another adhesive layer, any appropriate adhesive layer can be formed. Examples of the adhesive for forming another adhesive layer include rubber-based adhesives, acrylic-based adhesives, vinyl alkyl ether-based adhesives, silicone-based adhesives, polyester-based adhesives, polyamide-based adhesives, urethane-based adhesives, fluorine-based adhesives, styrene-diene block copolymer-based adhesives, etc. Known or conventional additives such as plasticizers, fillers, surfactants, anti-aging agents, and tackifiers may be blended in the adhesive. Also, another adhesive layer may have the same configuration as described in item B above.

[0064] The thickness of another 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 include an elastic layer. The elastic layer can be disposed on one side of the pressure-sensitive adhesive layer. When the pressure-sensitive adhesive tape includes a base material, the elastic layer can be disposed between the pressure-sensitive adhesive layer and the base material. By providing the elastic layer, the followability to the adherend is improved. Further, when the pressure-sensitive adhesive tape including the elastic layer is heated during peeling, the deformation (expansion) in the plane direction of the pressure-sensitive adhesive layer is restricted, and the deformation in the thickness direction is prioritized. As a result, the peelability is improved.

[0066] The elastic layer contains a base polymer, and as the base polymer, the polymers exemplified as the base polymer constituting the pressure-sensitive adhesive layer can be used. In one embodiment, the elastic layer may contain natural rubber, synthetic rubber, synthetic resin, etc. Examples of the synthetic rubber and synthetic resin include nitrile-based, diene-based, and acrylic-based synthetic rubbers; thermoplastic elastomers such as polyolefin-based and polyester-based; ethylene-vinyl acetate copolymer; polyurethane; polybutadiene; soft polyvinyl chloride, etc. The base polymer constituting the elastic layer may be the same as or different from the base polymer forming 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 suitable method. Note that the elastic layer and the pressure-sensitive adhesive layer can be distinguished by the difference in the 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, etc., when 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. Also, when the interface between the elastic layer and the pressure-sensitive adhesive layer cannot be identified by cross-sectional observation, the region where the foaming agent is observed by cross-sectional observation is the pressure-sensitive adhesive layer.

[0067] The above elastic layer may contain any suitable additive as required. Examples of the additive include a crosslinking agent, a vulcanizing agent, a tackifier resin, a plasticizer, a softening agent, a filler, an antioxidant, and the like. When a hard resin such as polyvinyl chloride is used as the base polymer, it is preferable to use a plasticizer and / or a softening agent in combination to form an elastic layer having a desired elasticity.

[0068] The thickness of the above elastic layer is preferably 3 μm to 200 μm, more preferably 5 μm to 100 μm. If it is within such a range, the above functions of the elastic layer can be fully exerted.

[0069] The tensile elastic modulus of the above 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. If it is within such a range, the above functions of the elastic layer can be fully exerted. The tensile elastic modulus can be measured according to JIS K 7161:2008.

[0070] F. Separator The pressure-sensitive adhesive tape of the present invention may further include a separator as required. At least one surface of the separator serves as a release surface and can be provided to protect the above pressure-sensitive adhesive layer. The separator can be composed of any suitable material.

[0071] G. Manufacturing method of the adhesive tape The pressure-sensitive adhesive tape of the present invention can be manufactured by any suitable method. For example, the pressure-sensitive adhesive tape of the present invention can be manufactured by a method of directly coating a composition for forming a pressure-sensitive adhesive layer containing a pressure-sensitive adhesive and thermally expandable microspheres on a substrate, or a method of transferring a coating layer formed by coating a composition for forming a pressure-sensitive adhesive layer on an arbitrary suitable substrate to the substrate. The composition for forming a pressure-sensitive adhesive layer may contain any suitable solvent. Further, after forming a pressure-sensitive adhesive coating layer with a composition containing a pressure-sensitive adhesive, thermally expandable microspheres may be sprinkled on the pressure-sensitive adhesive coating layer, and then the thermally expandable microspheres may be embedded in the coating layer using a laminator or the like to form a pressure-sensitive adhesive layer containing thermally expandable microspheres.

[0072] The content ratio of the thermally expandable microspheres in the composition for forming the adhesive layer is preferably 5% by weight to 95% by weight, more preferably 10% by weight to 70% by weight, and even more preferably 10% by weight to 50% by weight based on the solid content weight of the composition for forming the adhesive layer.

[0073] When the adhesive layer has the above elastic layer, the elastic layer can be formed, for example, by coating a composition for forming the elastic layer on a substrate or on the adhesive layer.

[0074] As the coating method for each of the above compositions, any suitable coating method can be adopted. For example, after coating, it can be dried to form each layer. Examples of the coating method include coating methods using a multi-coater, a die coater, a gravure coater, an applicator, etc. Examples of the drying method include natural drying, heat drying, etc. When heat drying, the heating temperature can be set to any suitable temperature according to the characteristics of the substance to be dried.

[0075] H. Applications The adhesive tape of the present invention can be suitably used as a sheet for temporarily fixing an electronic component material when manufacturing and evaluating an electronic component. In one embodiment, the adhesive tape of the present invention can be used as an adhesive tape for temporarily fixing a test specimen in a thermal shock test. In another embodiment, the adhesive tape of the present invention can be used as an adhesive tape for temporarily fixing a workpiece in a molding process (for example, a molding process involving heating).

Examples

[0076] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples. The evaluation methods in the examples are as follows. Also, in the examples, unless otherwise specified, "parts" and "%" are based on weight.

[0077] [Evaluation] (1) Initial Adhesion Force The adhesive tape was cut into a size of width: 20 mm and length: 140 mm. On the adhesive layer, a polyethylene terephthalate film (trade name "Lumirror S-10", manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) as the adherend was pressure-bonded and laminated by reciprocating a 2 kg roller once under an atmosphere of temperature: 25°C and humidity: 65%RH in accordance with JIS Z 0237 (2000). Next, the adhesive tape with the adherend was set in a tensile testing machine with a thermostatic chamber set at 25°C (manufactured by Shimadzu Corporation, trade name "Shimadzu Autograph AG-120kN") and left for 30 minutes. Then, the adherend was peeled off from the adhesive tape under the conditions of peeling angle: 180° and peeling speed (tensile speed): 300 mm / min, and the load at the time of peeling was measured. The maximum load at that time (the maximum value of the load excluding the peak top at the initial stage of measurement) was determined, and this maximum load was taken as the adhesion force (N / 20 mm).

[0078] (2) Adhesion Force after Heating at 140°C The adhesive tape was cut into a size of width: 20 mm and length: 140 mm. On the adhesive layer, a polyethylene terephthalate film (trade name "Lumirror S-10", manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) as the adherend was pressure-bonded and laminated by reciprocating a 2 kg roller once under an atmosphere of temperature: 25°C and humidity: 65%RH in accordance with JIS Z 0237 (2000). Next, the adhesive tape with the adherend was placed in an environment at 140°C for 30 minutes, and then placed in an environment at 25°C for 30 minutes. Thereafter, the adhesion force was measured in the same manner as in (1) above.

[0079] (3) Adhesion Force after Heat Cycle The adhesive tape was cut into a size of width: 20 mm and length: 140 mm, and a polyethylene terephthalate film (trade name "Lumirror S-10", manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 20 mm) as an adherend was laminated on the adhesive layer under an atmosphere of temperature: 25 °C and humidity: 65% RH in accordance with JIS Z 0237 (2000) by reciprocating a 2 kg roller once for pressure bonding. Next, the adhesive tape with the adherend was placed in an environment of 140 °C for 30 minutes, then placed in an environment of 25 °C for 30 minutes, again placed in an environment of 140 °C for 30 minutes, and then placed 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 at 140 °C The adhesive tape was placed in an environment of 140 °C for 30 minutes, and then placed in an environment of 25 °C for 30 minutes. Thereafter, the appearance of the adhesive layer was visually confirmed. A case where the appearance was good without foaming was judged as qualified (○ in Table 1), and a case where foaming occurred and the appearance was poor was judged as unqualified (× in Table 1).

[0081] (5) Appearance after heat cycle The adhesive tape was placed in an environment of 140 °C for 30 minutes, then placed in an environment of 25 °C for 30 minutes, again placed in an environment of 140 °C for 30 minutes, and then placed in an environment of 25 °C for 30 minutes. Thereafter, the appearance of the adhesive layer was visually confirmed. A case where the appearance was good without foaming was judged as qualified (○ in Table 1), and a case where foaming occurred and the appearance was poor was judged as unqualified (× in Table 1).

[0082] (6) Package retention rate A QFN lead frame (size: 125 mm × 65 mm; the bonding surface with the adhesive sheet is a resin surface (surface roughness Ra: 3 μm)) sealed with an epoxy resin (manufactured by Hitachi Chemical Co., Ltd., trade name "CEL-9200HF9") was adhered onto the adhesive layer of the adhesive tape, and it was mounted and fixed on a 6-inch dicing ring. Then, it was fully cut into 250 chips with a size of 5 mm × 5 mm (cutting process by dicing). Next, it was placed in an environment at 140°C for 30 minutes with the adherend bonding surface facing up, then placed in an environment at 25°C for 30 minutes, again placed in an environment at 140°C for 30 minutes, and then placed in an environment at 25°C for 30 minutes. Next, the adhesive tape with the adherend was inverted, and the retention rate of the packages was evaluated from the number of packages remaining in the adhesive layer.

[0083] [Production Example 1] Preparation of Thermally Expandable Microspheres A 150 parts by weight of sodium chloride, 70 parts by weight of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name "Snowtex") with a silica active ingredient of 20% by weight, 1 part by weight of polyvinylpyrrolidone, and 0.5 part by weight of a condensate of diethanolamine and adipic acid were added to 600 parts by weight of distilled water, and then the pH of the resulting mixture was adjusted to 2.8 - 3.2 to obtain an aqueous solution. To the above 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. Further, 1 part by weight of ethylene glycol dimethacrylate as a crosslinking agent was added to obtain a reaction solution. The above 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"). Further, 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 (diisopropyl oxydicarbonate) were added to the pressure-resistant reaction vessel. The homomixer was rotated under predetermined initial stirring conditions (stirring speed: 6000 rpm, stirring time: 2 minutes) to stir the above mixture, and then heated to 60 °C while stirring at 80 rpm for 24 hours for reaction. The solid content obtained by filtering the reaction solution after the reaction was left at room temperature for one week under a nitrogen stream to obtain thermally expandable microspheres. In addition, the obtained thermally expandable microspheres had an average particle size of 30 μm when measured under the trade name "SALD-2000J" manufactured by Shimadzu Corporation. Also, by X-ray CT (Xradia520versa manufactured by ZEISS (measurement conditions: tube voltage 60 KV, tube current 83 μA, pixel size 0.20 μm / pixel)), it was found that the solvents encapsulated in the thermally expandable microspheres were isopentane and isooctane, and they contained 15% by weight based on the weight of the thermally expandable microspheres. Further, when measured by the above X-ray CT, the thickness of the shell of the thermally expandable microspheres was 2.5 μm.

[0084] [Production Example 2 to 10] Thermally Expandable Microspheres B to J Thermally 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, methyl methacrylate) were as described in Table 1. Also, in the same manner as in Production Example 1, the average particle size, the amount of the contained organic solvent, and the thickness of the shell of the thermally expandable microspheres were measured. The results are shown in Table 1.

[0085]

Table 1

[0086] [Example 1] (Preparation of Composition for Forming Elastic Layer) 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), 2EHA structural unit:EA structural unit:MMA structural unit:HEA structural unit = 30:70:5:5 (weight ratio)), 1 part by weight of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), and toluene were mixed to prepare a composition for forming an elastic layer. (Preparation of Composition for Forming Adhesive Layer) 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), 2EHA structural unit:EA structural unit:MMA structural unit:HEA structural unit = 30:70:5:5 (weight ratio)), 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 crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate L"), 30 parts by weight of thermally expandable microspheres A, and toluene were mixed to prepare a composition for forming an adhesive layer. (Production of Adhesive Tape) The above composition for forming an elastic layer was applied to a PET film (manufactured by Toray Industries, Inc., trade name "Lumirror S10", thickness: 100 μm) as a base material, and dried to form an elastic layer (thickness: 15 μm) on the base material. The above composition for forming an adhesive layer was applied to a polyethylene terephthalate film with a silicone release agent-treated surface (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38"), and dried to form an adhesive layer (35 μm) on the polyethylene terephthalate film. The adhesive layer formed on the polyethylene terephthalate film was transferred to the elastic layer to obtain an adhesive tape having a base material, an elastic layer and an 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.

[0087] [Examples 2 to 8, Example 11, Comparative Examples 1 to 3] An adhesive tape was obtained in the same manner as in Example 1, except that the compositions of the composition for forming the elastic layer (composition of the base polymer, amount of crosslinking agent) and the composition for forming the adhesive layer (composition of the base polymer, type of crosslinking agent, amount of crosslinking agent, type of thermally expandable microspheres) were those shown in Tables 2 to 4. The obtained adhesive tape was subjected to the above evaluations (1) to (6). The results are shown in Table 5. In the table, "Crosslinking agent tetrad C" is an epoxy-based crosslinking agent (trade name "Tetrad C") manufactured by Mitsubishi Gas Chemical Company, Inc. In Example 11, although there was no foaming and the appearance was good for "Appearance after heating at 140 °C" and "Appearance after heat cycle", minute irregularities were observed on the surface to such an extent that it did not significantly affect the adhesive strength from the stage before the evaluation (therefore, the evaluation result is indicated as Δ).

[0088] [Example 9] In the same manner as in Example 1, a composition for forming an elastic layer and a composition for forming an adhesive layer were prepared. Furthermore, 100 parts by weight of an acrylic copolymer (copolymer of 2-ethylhexyl acrylate (2EHA), ethyl acrylate (EA), methyl methacrylate (MMA) and 2-hydroxyethyl acrylate (HEA), 2EHA structural unit: EA structural unit: MMA structural unit: HEA structural unit = 30:70:5:5 (weight ratio)), 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 were mixed to prepare another composition for forming an adhesive layer. The above composition for forming an elastic layer was applied to a PET film (manufactured by Toray Industries, Inc., trade name "Lumirror S10", thickness: 100 μm) as a base material, and dried to form an elastic layer (thickness: 15 μm) on the base material. The above composition for forming an adhesive layer was applied to a polyethylene terephthalate film with a silicone release agent-treated surface (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38"), and dried to form an adhesive layer (35 μm) on the polyethylene terephthalate film. Further, the above composition for forming another pressure-sensitive adhesive layer was applied to a polyethylene terephthalate film with a silicone release agent-treated surface (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38"), and dried to form another pressure-sensitive adhesive layer (10 μm) on the polyethylene terephthalate film. The pressure-sensitive adhesive layer formed on the polyethylene terephthalate film was transferred to the elastic layer, and another pressure-sensitive adhesive layer was transferred to the surface of the substrate where the elastic layer was not formed, to obtain a pressure-sensitive adhesive tape comprising another pressure-sensitive adhesive layer, 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 (6). The results are shown in Table 5.

[0089] [Example 10] (Preparation of Composition for Forming Silicone Pressure-Sensitive Adhesive Layer) 100 parts by weight of an addition-reaction type silicone-based pressure-sensitive adhesive (manufactured by Toray Industries, Inc., trade name "Silicone Rubber SD-4580L", silicone rubber: silicone resin = 60:40 (weight ratio)), 0.5 parts by weight of a platinum-based catalyst (manufactured by Toray Industries, Inc., trade name "SRX-212"), 30 parts by weight of thermally expandable microspheres A, and 100 parts by weight of toluene were mixed to prepare a composition for forming a pressure-sensitive adhesive layer. (Production of Pressure-Sensitive Adhesive Tape) The above composition for forming a silicone pressure-sensitive adhesive layer was applied to a polyimide film (manufactured by Toray DuPont Co., Ltd., trade name "Kapton 200H", thickness 50 μm) as a substrate layer, and dried to form a pressure-sensitive adhesive layer (thickness: 30 μm) on the substrate, to obtain a pressure-sensitive adhesive tape. The obtained pressure-sensitive 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 Substrate 100 Adhesive tape

Claims

1. An adhesive tape comprising an adhesive layer containing thermally expandable microspheres and a substrate disposed on at least one side of the adhesive layer, wherein the thermally expandable microspheres are composed of a shell and a volatile substance contained within the shell, the shell is composed 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 substrate includes 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, fluororesin, or polyether ether ketone. Adhesive tape.

2. The adhesive tape according to claim 1, wherein the resin constituting the shell contains a structural unit having a carboxyl group.

3. The adhesive tape according to claim 2, wherein the content ratio of the structural unit having a carboxyl group is 5 parts by weight to 97 parts by weight with respect to 100 parts by weight of the resin.

4. The adhesive tape according to any one of claims 1 to 3, wherein the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C is 0.5 N / 20 mm to 20 N / 20 mm.

5. The adhesive tape according to any one of claims 1 to 4, wherein the adhesive force b when the adhesive surface of the adhesive tape heated to 140°C and then cooled to 25°C is adhered to a polyethylene terephthalate film is 50% or more with respect to the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C.

6. The adhesive tape according to any one of claims 1 to 5, wherein the adhesive force c when the adhesive surface of the adhesive tape of the present invention after performing the cycle of heating to 140°C and then cooling to 25°C twice is adhered to a polyethylene terephthalate film is 50% or more with respect to the initial adhesive force a when the adhesive surface of the adhesive tape is adhered to a polyethylene terephthalate film at an environmental temperature of 25°C.

7. The pressure-sensitive adhesive tape according to any one of claims 1 to 6, wherein the elastic modulus of the pressure-sensitive adhesive layer at 23°C by nanoindentation is from 0.1 MPa to 500 MPa.

8. Further comprising another pressure-sensitive adhesive layer, wherein the base material is disposed between the pressure-sensitive adhesive layer and the another pressure-sensitive adhesive layer, The pressure-sensitive adhesive tape according to claim 1.

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