Adhesive tape

Abstract

This adhesive tape comprises a base material and an adhesive layer disposed on at least one side of the base material. The adhesive layer contains thermally expanding microspheres and an adhesive. The thermally expanding microspheres are each constituted from a shell and a volatile substance contained in the interior of the shell. The resin constituting the shell contains a constitutive unit having a carboxyl group. In one embodiment, the glass transition temperature (Tg) of the resin constituting the shell is 120°C or higher.

Description

Technical Field

[0001] The present invention relates to an adhesive tape. More specifically, it relates to an adhesive tape that can exhibit 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 situations where fixing is not required is known. As one such adhesive tape, an adhesive tape having a base material and an adhesive layer, and the adhesive layer is composed of an adhesive and thermally expandable microspheres typified by a foaming agent 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 in a situation where it is 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, that is, heat peeling becomes possible. In such an adhesive tape, it is also possible to peel the adherend only by the action of gravity.

[0003] The above-mentioned adhesive tape has a problem that the adhesive layer may float from the base material and may even peel off in some cases. This is considered to be because when the deformation of the adhesive layer becomes large, the movement of the adhesive layer cannot be restricted by the base material. As the temperature rises, the elastic modulus of the adhesive layer decreases and the amount of deformation of the adhesive layer increases, so the floating and peeling of the adhesive layer during heat peeling become a problem.

[0004] The above-mentioned adhesive tape can be used as a temporary fixing tape in a heat treatment process (for example, a heating process, a curing process, etc.). The foaming temperature of the temporary fixing adhesive tape in the heating process is set to be higher than the process temperature. In recent years, due to the demand for improving the tact of the heat treatment process, the heat treatment temperature of the process tends to be high, so the foaming temperature of the adhesive tape is set high, and as a result, the floating and peeling of the adhesive layer during heat peeling are likely to occur.

[0005] As methods for preventing the lifting and peeling of the adhesive layer during heat peeling, there are methods such as providing an undercoat layer between the base material and the adhesive layer, a method of suppressing the deformation of the adhesive layer using a crosslinked adhesive, and a method of reducing the content of thermally expandable microspheres. However, the effect of the method of providing an undercoat layer between the base material and the adhesive layer is limited, and there is selectivity depending on the type of adhesive, so it cannot be a fundamental solution. Further, in the method of suppressing the deformation of the adhesive layer using a crosslinked adhesive, there is a problem of a decrease in the adherend holding property due to a decrease in the initial adhesiveness, and in the method of reducing the content of thermally expandable microspheres, there is a problem of inhibiting the heat peelability.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made to solve the above conventional problems, and an object thereof is to provide an adhesive tape in which the lifting of the adhesive layer from the base material is prevented.

Means for Solving the Problems

[0008] The adhesive tape of the present invention includes a base material and an adhesive layer disposed on at least one side of the base material, the adhesive layer contains thermally expandable microspheres and an adhesive, the thermally expandable microspheres are composed of a shell and a volatile substance contained in the shell, and the resin constituting the shell contains a structural unit having a carboxyl group. In one embodiment, the glass transition temperature (Tg) of the resin constituting the shell is 120° C. or higher. 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, 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 higher. In one embodiment, the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive. In one embodiment, the pressure-sensitive adhesive material contains an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent. 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 1.5 N / 20 mm to 20 N / 20 mm. In one embodiment, the adhesive force b when the adhesive surface of the adhesive tape heated to 130°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. In one embodiment, the adhesive force c when the adhesive surface of the adhesive tape of the present invention after performing the cycle of heating to 130°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. In one embodiment, the adhesive tape includes the adhesive layers on both sides of the base material. In one embodiment, the adhesive layer is provided on one side of the base material, and another adhesive layer is provided on the other side of the base material.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an adhesive tape in which the adhesive layer is prevented from peeling off from the base material.

Brief Description of the Drawings

[0010]

Figure 1

Best Mode for Carrying Out the Invention

[0011] A. Overall structure of the adhesive tape FIGS. 1(a) and (b) are schematic cross-sectional views of an adhesive tape according to one embodiment of the present invention. The adhesive tape 100 includes a base material 10 and an adhesive layer 20 disposed on at least one side of the base material 10. FIG. 1(c) 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 another adhesive layer 30 disposed on at least one side of the adhesive layer 10. Although not shown, the adhesive tape may further include, as layers other than the adhesive layer, an elastic layer (described in section E below) that can impart elasticity to the adhesive tape, a separator (described in section F below) detachably disposed on the adhesive layer, and the like.

[0012] The adhesive layer contains thermally expandable microspheres. The thermally expandable microspheres can expand at a predetermined temperature. The adhesive layer containing such thermally expandable microspheres expands the thermally expandable microspheres by heating to a predetermined temperature or higher, causing irregularities on the adhesive surface (i.e., the surface of the adhesive layer), and reducing or eliminating the adhesive force. 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 testing 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 peeling the adhesive tape, the adhesive force is reduced or eliminated by 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 1.5 N / 20 mm to 20 N / 20 mm, more preferably 1.5 N / 20 mm to 18 N / 20 mm, and even more preferably 2.0 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. Further, the adhesive force refers to the adhesive force measured by a method in accordance with JIS Z 0237:2000 (laminating condition: 1 reciprocation of a 2 kg roller, tensile 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 130°C and then cooled to 25°C is adhered to a polyethylene terephthalate film (for example, with a thickness of 25 μm) is 0.75 N / 20 mm to 20 N / 20 mm, more preferably 0.75 N / 20 mm to 18 N / 20 mm, and even more preferably 1.0 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 130°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] The adhesive force c when the adhesive surface of the adhesive tape of the present invention after performing the cycle of heating to 130°C and then cooling to 25°C twice is adhered to a polyethylene terephthalate film (for example, with a thickness of 25 μm) is 0.75 N / 20 mm to 20 N / 20 mm, more preferably 0.75 N / 20 mm to 18 N / 20 mm, and even more preferably 1.0 N / 20 mm to 12 N / 20 mm.

[0017] After heating to 130°C and then cooling to 25°C, when the adhesive surface of the pressure-sensitive adhesive tape of the present invention is adhered to a polyethylene terephthalate film (for example, having a thickness of 25 μm), the adhesive strength c is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more with respect to 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, 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 within the shell.

[0021] The resin constituting the shell contains a structural unit having a carboxyl group. If the shell is constituted by a resin having a carboxyl group, the carboxyl group and the base polymer constituting the adhesive in the adhesive layer interact with each other, and cohesiveness is imparted to the adhesive. As a result, in the pressure-sensitive adhesive tape of the present invention, deformation of the adhesive layer is suppressed, and problems such as the adhesive layer floating or peeling off from the base material even at high temperatures can be prevented. By using such a pressure-sensitive adhesive tape of the present invention, adhesive residue on the adherend during heat peeling can be prevented. The structural unit having a carboxyl group can be, for example, a structural unit derived from a carboxyl group-containing monomer such as a carboxyl group-containing monomer such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid.

[0022] The resin constituting the shell may further contain a structural unit derived from a radically polymerizable monomer other than the structural unit having a carboxyl group. Examples of the monomer include nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; 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. In one embodiment, the resin constituting the shell contains at least one selected from the group consisting of a structural unit having a carboxyl group and 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.

[0023] In the resin constituting the above shell, the content ratio of the structural unit having a carboxyl group is preferably 5 parts by weight to 97 parts by weight, more preferably 5 parts by weight to 90 parts by weight, still more preferably 5 parts by weight to 85 parts by weight, particularly preferably 5 parts by weight to 80 parts by weight, and most preferably 10 parts by weight to 75 parts by weight, based on 100 parts by weight of the resin. Within such a range, while controlling the productivity and particle size of the thermally expandable microspheres, deformation of the adhesive layer is suppressed, and problems such as the adhesive layer floating or peeling off from the base material at high temperatures can be prevented. If the content ratio of the structural unit having a carboxyl group is less than the above range, the ratio of the carboxyl groups possessed by the thermally expandable microspheres decreases, the interaction with the base polymer in the adhesive is not sufficient, and there is a risk that the above effects cannot be obtained. If the content ratio of the structural unit having a carboxyl group is more than the above range, it becomes difficult to control the reactivity and particle size during the production of the thermally expandable microspheres, and there is a risk that the productivity decreases.

[0024] 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, and the like.

[0025] The glass transition temperature (Tg) of the resin constituting the above shell is preferably 120 °C or higher, more preferably 125 °C or higher, still more preferably 130 °C or higher, and particularly preferably 135 °C or higher. By using the thermally expandable microspheres containing a shell having such a glass transition temperature, an adhesive tape with a thermally expandable microsphere whose foaming temperature is less likely to fluctuate can be obtained. More specifically, when a conventional foaming agent is heated below the foaming temperature, the foaming temperature tends to decrease due to this heat history. However, by using the thermally expandable microspheres containing the above shell, a decrease in the foaming temperature due to the heat history is prevented. 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 )) The glass transition temperatures of the homopolymers formed from the monomers are as follows: 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 temperatures 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.

[0026] The thickness of the above shell is preferably 1 μm to 15 μm, more preferably 1 μm to 7 μm, and still 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, etc. 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, 2-methylpentane, 2,2-dimethylbutane, heptane, cycloheptane, octane, cyclooctane, 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 solvent has 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. In addition, hydrocarbons composed only of hydrogen atoms and carbon atoms are preferable from the viewpoint of industrial utilization.

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

[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, thermally expandable microspheres in which the shell can expand well without being destroyed can be obtained. If the boiling point of the organic solvent is too low, the operation 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 still more preferably 50°C to 150°C. When an organic solvent with a boiling point higher than the glass transition temperature of the shell is used, there is a risk of damaging the shell due to the pressure generated when heating the organic solvent, or even causing the adhesive to scatter, which may inhibit the functions and effects expected in the present invention. When two or more types of organic solvents (mixed solvents) are used, the "boiling point (bp) of the organic solvent" is a value calculated by (sum of the boiling points of each organic solvent) / (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, a thermally expandable property that can expand stably can be obtained. When the content ratio is less than 5% by weight, the expansion during heating becomes insufficient, making it difficult to form adhesive irregularities, and there is a risk of poor heat peeling and adhesive residue. When the content ratio exceeds 35% by weight, the expansion during heating becomes excessive, and there is a risk of the adhesive layer peeling off from the base material.

[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 state of high dispersibility 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 during the polymerization of 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] The foaming temperature of the above-mentioned thermally expandable microspheres is preferably 150°C to 280°C, more preferably 155°C to 260°C. In this specification, the foaming temperature of the thermally expandable microspheres can correspond to the temperature at which the adhesive strength of the adhesive tape becomes 1.0 N / 20 mm or less and is 50% or less of the initial adhesive strength.

[0034] 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%, more preferably 3.5% to 70% with respect to the cross-sectional area A of the adhesive layer. 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, manufactured by Hitachi Technologies, trade name "S-3400N Low-Vacuum Scanning Electron Microscope"). For example, the image is printed on paper, and it can be obtained by the formula of b / a×100 from the paper weight a of the adhesive layer portion (that is, the entire adhesive layer including the thermally expandable microspheres) and the weight b of the paper obtained by cutting out only the thermally expandable microsphere portion.

[0035] The content ratio of the thermally expandable microspheres is preferably 5 parts by weight to 80 parts by weight, more preferably 5 parts by weight to 60 parts by weight, and still more preferably 10 parts by weight to 50 parts by weight with respect to 100 parts by weight of the adhesive layer. If it is in 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 in 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 obtained by the following formula. The weight of the thermally expandable microspheres is obtained 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

[0036] The above-mentioned thermally expandable microspheres can be produced by any suitable method. In one embodiment, the 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 a dispersion stability auxiliary agent, for example, a condensation product of diethanolamine and an aliphatic dicarboxylic acid, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polyvinyl alcohol, various emulsifiers, etc. may be used.

[0037] The properties of the thermally expandable microspheres such as the particle size and the content of the organic solvent can be controlled by the polymerization conditions of the above suspension polymerization, the types and addition amounts of the mixed components, etc. For example, by operations such as reducing the addition amount of the dispersant and slowing down the stirring speed during polymerization, thermally expandable microspheres with a large particle size can be obtained. Also, if the blending amount of the monomer is increased or the stirring speed during polymerization is slowed down, thermally expandable microspheres with a thick shell can be obtained.

[0038] 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, active energy ray curable adhesives, etc. Among them, acrylic adhesives, rubber adhesives or silicone adhesives are preferable, and acrylic adhesives are more preferable.

[0039] The gel fraction of the above-mentioned adhesive is preferably 20% by weight to 100% by weight, more preferably 30% by weight to 99% by weight, and still 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 the surface of the adhesive layer becomes uneven, 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, the heating expansion of the thermally expandable microspheres may be inhibited and sufficient unevenness may not occur, or even when unevenness occurs, phenomena such as the thermally expandable microspheres exploding and the shells of the thermally expandable microspheres and the surrounding adhesive layer flying off 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. About 0.1 g of the adhesive was sampled and precisely weighed (weight of the sample), and after wrapping the sample with a mesh sheet (trade name "NTF-1122", manufactured by Nitto Denko Corporation), it was immersed in about 50 ml of toluene at room temperature for 1 week. Then, the solvent-insoluble matter (the content of the mesh sheet) was taken out from toluene, dried at 70 °C for about 5 hours, the solvent-insoluble matter after drying was weighed (weight after immersion and drying), and the gel fraction (% by weight) was calculated from the following formula (a). Gel fraction (% by weight) = [(weight after immersion and drying) / (weight of the sample)] × 100 (a)

[0040] The base polymer contained in the above-mentioned adhesive preferably has an OH group or a COOH group. By using such a base polymer, the effect of the present invention becomes more remarkable. In addition, by using the above-mentioned base polymer, it becomes possible to adjust the above gel fraction using a cross-linking agent. In addition, 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 cross-linking agent. Thereby, the uneven shape on the surface of the adhesive caused by the expansion of the thermally expandable microspheres can be controlled.

[0041] The acid value of the above base polymer is preferably from 0 to 100, more preferably from 10 to 80, and even more preferably from 20 to 50. The acid value of the polymer in the pressure-sensitive adhesive layer can be measured by extracting the solvent-soluble component in the pressure-sensitive adhesive layer. Specifically, the solvent-soluble component can be extracted by the following method. (i) The pressure-sensitive adhesive layer is put into a solvent to prepare a solution sample in which the solvent-soluble component in the pressure-sensitive adhesive layer is dissolved in the above solvent. As the solvent, in consideration of 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 the solvent is added to about 0.2 g of the pressure-sensitive adhesive layer, and the mixture is stirred for about 30 minutes to about 12 hours in a temperature range from room temperature to 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 amount of solvent approximately equal to the separated solution is newly added to the sample and stirred, and the operation of separating the solution is repeated once or more times to prepare a solution sample. (ii) The solvent can be removed from the above solution sample by a method such as evaporation to take out 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 putting the above solution sample into a solvent insoluble only in the polymer component (reprecipitation method), or molecular weight fractionation (fractional liquid chromatography method) by gel filtration chromatography using the above solution sample is used to adjust the solvent-soluble polymer consisting only of the measurement target.

[0042] (Acrylic pressure-sensitive adhesive) Examples of the acrylic pressure-sensitive adhesive include an acrylic pressure-sensitive adhesive based on an acrylic polymer (homo-polymer or co-polymer) 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., i.e., (meth)acrylic acid C1-20 alkyl esters. Among them, (meth)acrylic acid alkyl esters having a linear or branched alkyl group with 4 to 18 carbon atoms can be preferably used.

[0043] The above acrylic polymer may, if necessary, contain units corresponding to other monomers copolymerizable with the above (meth)acrylic acid alkyl ester for the purpose of modifying cohesion, heat resistance, crosslinkability, etc. Such monomers include, for example, 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-based 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-based monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate; (meth)acrylic acid alkoxyalkyl-based monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate; maleimide-based monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide; itaconimide-based 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 carboxamides, styrene, α-methylstyrene, N-vinyl caprolactam; cyanoacrylate monomers such as acrylonitrile, methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; glycol-based acrylate 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.;

[0044] (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).

[0045] 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, and more preferably 150,000 to 500,000. The weight average molecular weight can be measured by GPC (solvent: THF).

[0046] 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).

[0047] 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 even 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 is 29 It can also be determined from the ratio of the Q unit (resin) to the D unit (rubber) obtained by measurement by Si-NMR.

[0048] (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 a synthetic rubber such as a modified product thereof; etc. A rubber-based adhesive having such a base polymer is preferably used.

[0049] (Additive) The above adhesive may contain any suitable additive as necessary. Examples of the additive include a crosslinking agent, tackifier, plasticizer, pigment, dye, filler, anti-aging agent, conductive material, antistatic agent, ultraviolet absorber, light stabilizer, peel adjustment agent, softening agent, surfactant, flame retardant, antioxidant, etc.

[0050] 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 (for example, unmodified rosin, modified rosin, rosin-phenol resins, rosin ester resins, etc.), terpene-based tackifying resins (for example, terpene resins, terpene-phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, hydrogenated terpene resins), hydrocarbon-based tackifying resins (for example, aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (for example, 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 (for example, 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.

[0051] The addition amount of the above-mentioned tackifier is preferably 5 to 100 parts by weight, more preferably 5 to 50 parts by weight, based on 100 parts by weight of the base polymer.

[0052] 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, there are also 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. Among them, preferably, it is an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent.

[0053] 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"); and the like. 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.

[0054] 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 “Epicol E-400”), polypropylene glycol diglycidyl ether (manufactured by NOF Corporation, trade name “Epicol 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 to 10 parts by weight, more preferably 0.03 to 5 parts by weight, based on 100 parts by weight of the base polymer.

[0055] 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.) are used. 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.

[0056] 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: inside about 3 μm from the surface of the adhesive layer and at a location where there are no thermally expandable microspheres (a location more than 1 μm away from the shell surface of the thermally expandable microspheres). When the indenter is pressed into the adhesive layer, the load on the indenter and the indentation depth are continuously measured during loading and unloading, 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.

[0057] The thickness of the above adhesive layer is preferably 5 μm to 300 μm, more preferably 5 μm to 250 μm, still more preferably 5 μm to 100 μm, and particularly preferably 5 μm to 60 μm.

[0058] B-4. Other Components As long as the effects of the present invention can be obtained, the above adhesive layer may further contain any appropriate other components. Examples of the other components include beads. Examples of the beads include glass beads, resin beads, and the like. If such beads are added to the adhesive layer, the elastic modulus of the adhesive layer can be improved, and an adhesive tape capable of processing a workpiece with higher accuracy 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 above base material include resin sheets, non-woven fabrics, papers, metal foils, woven fabrics, rubber sheets, foamed sheets, laminates thereof (particularly laminates containing resin sheets), and the like. 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, polyether ether ketone (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, aluminum foil, and the like. Examples of the paper include Japanese paper, kraft paper, and the like.

[0060] The thickness of the above base material can be set to any appropriate thickness according to the desired strength or flexibility, 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 above-mentioned substrate may be surface-treated. 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 a primer, etc.

[0062] Examples of the above-mentioned organic coating material include materials described in Plastic Hard Coat Material II (published by CMC, (2004)). Preferably, a urethane-based polymer is 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 of them 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 (for example, a hydroxyl group-containing acrylic compound or a hydroxyl group-containing ester compound). The organic coating material may contain, as optional additives, a chain extender such as polyamine, an antioxidant, an oxidation stabilizer, 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. The adhesive may be blended with known or conventional additives such as plasticizers, fillers, surfactants, antioxidants, tackifiers, etc.

[0064] The thickness of the 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 with respect to the adherend is improved. Further, when the pressure-sensitive adhesive tape including the elastic layer is heated at the time of 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. Further, 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. 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 0.01 MPa to 500 MPa, more preferably 0.05 MPa to 500 MPa, and even more preferably 0.1 MPa to 500 MPa. Within such a range, the above functions of the elastic layer can be fully exerted. The tensile elastic 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 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. The pressure-sensitive adhesive tape of the present invention includes, for example, 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 base material, or a method of transferring a coating layer formed by coating a composition for forming a pressure-sensitive adhesive layer on any suitable substrate to a base material. 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 still 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 appropriate coating method can be adopted. For example, each layer can be formed by drying after coating. 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 appropriate 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 electronic component materials when manufacturing and evaluating electronic components. 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 resin sealing process during the manufacture of a substrate-less semiconductor package. Here, the semiconductor package refers to a form of a package of a semiconductor component that enables surface mounting of a single high-integration semiconductor on a printed circuit board. Specifically, it refers to a wafer-level chip scale package (WLCSP), a fan-out wafer-level package (FOWLP), a fan-in wafer-level package (FIWLP), etc. In the resin sealing process in the manufacture of these packages, heating for resin curing and resin injection pressure occur, and the adhesive tape needs to function to hold the bare chip in place without moving against these, and after the sealing process, it needs to be easily peeled off from the bare chip. That is, the adhesive tape disclosed in the present application can be suitably used in the manufacture of the aforementioned packages, and can particularly exert its function without fail in the resin sealing process. In yet another embodiment, the adhesive tape of the present invention can be used as an adhesive tape for temporarily fixing a workpiece in a patternning process of a wiring circuit. In yet another embodiment, the adhesive tape of the present invention can be used as an adhesive tape for temporarily fixing a workpiece in an electrode coating and drying process of an electronic component. In yet another embodiment, the adhesive tape of the present invention can be used as an adhesive tape for temporarily fixing an adherend in order to consistently process the dicing process and the heat treatment process of an electronic component on the same tape. Thus, the adhesive tape of the present invention can be suitably used in processes involving heating.

Example

[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 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: 25 mm) as an adherend was pressure-bonded and laminated by reciprocating a 2 kg roller once under the 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 bath 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 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 obtained, and this maximum load was taken as the adhesive force (N / 20 mm).

[0078] (2) Chip Flying and Chip Remaining (Chip Flying) On the adhesive layer of each adhesive tape, a QFN lead frame (size: 125 mm × 65 mm; the bonding surface with the adhesive sheet is the resin surface) encapsulated with an epoxy resin (manufactured by Hitachi Chemical Co., Ltd., trade name "CEL-9200HF9") was adhered, and it was mounted and fixed on a 6-inch dicing ring and fully cut into chips with a size of 5 mm × 5 mm through a dicing machine (subjected to a cutting process by dicing). During this cutting, the number of occurrences of chip flying was calculated. At this time, a DISCO ZH05-SD2000-N1-110-DD blade was used as the dicing blade. The feed rate of the dicing blade was 70 mm / S, and the rotational speed of the dicing blade was 50000 / s. The ratio (chip flying rate) (%) of the number of chips peeled off from the adhesive tape (chips flew off) during cutting was determined and used as an evaluation of the cutting processability. When all the chips are attached to the adhesive tape and not peeled off, the chip flying rate is 0% (i.e., the chip flying rate is 0%). Let the number of diced chips be A0 and the number of chips that flew off be A. The chip flying rate X was determined according to formula (1). X=(A / A0)×100 ···(1) The smaller the ratio of chips peeled off (chip flying rate), the better the chip flying prevention property. (Chip remaining) After the cutting, using a program temperature controller (hot air dryer) (manufactured by Isuzu Motors Ltd., "EP-K-300"), heat treatment was performed at the foaming temperature for 5 minutes. After the heat treatment, the adhesive tape was turned over in the air so that the top and bottom were reversed (so that the chips were on the bottom), and the chips were peeled off from the adhesive tape by natural fall, and the ratio (chip remaining) (%) of the chips remaining on the sheet was determined. When all the chips are peeled off and do not remain on the adhesive tape, the chip remaining is 0%. Therefore, the fact that the amount of processed chips remaining after the heat treatment is small (the chip remaining is small) means that the heat peelability is good. Let the number of chips before peeling be B0 and the number of chips remaining on the sheet after the heat peeling treatment be B. The chip remaining Y was determined according to formula (2). Y=(B / B0)×100 ···(2)

[0079] (3) Appearance (adhesive layer peeling) Each adhesive tape was cut into a size of width: 50 mm and length: 100 mm. After peeling off the separator, a cutter was used to make grid-like cuts (5 cuts in the X-Y direction at 5 mm intervals) on the adhesive surface containing the thermally expandable microspheres, and the separator was bonded again with a hand roller. At this time, the adhesive layer part was fully cut and the substrate was also cut into it. With a 10-mm-thick heat-resistant glass placed on the top plate of the heat source, a test piece with the grid-like cuts (the heated part is 50 mm × 50 mm) was heated for 5 minutes using a hot plate (Shamal hot plate "HHP-411") preheated to the foaming temperature + 20°C, and the number of floating adhesive layers in the taken-out sample was counted.

[0080] (4) Adhesive attachment After cutting in the above (2), using a program temperature controller (hot air dryer) (manufactured by Isuzu Manufacturing Co., Ltd., "EP-K-300"), a heat treatment was performed at the foaming temperature for 5 minutes. After the heat treatment, the adhesive tape was turned over in the air so that the top and bottom were reversed (so that the chip was at the bottom), and the chip was peeled off from the adhesive tape by natural fall, and the ratio (%) of the adhesive foreign matter adhering to the recovered chip (adhesive attachment) was visually confirmed. In addition, when no adhesive foreign matter adheres to all the chips, the adhesive attachment is 0%. Therefore, the fact that the amount of adhesive attachment to the processed chip after heat treatment is small (less adhesive attachment) means that the adhesive attachment property is good. Arbitrarily 100 chips were recovered from the heat-peeled chips and used as the denominator of formula (3) (when the number of heat-peeled chips is less than 100, let that number be C0). Let the number of chips with adhesive attachment among them be C, and the adhesive attachment Z was obtained according to formula (3). Z = (C / C0) × 100 ···(3)

[0081] [Production Example 1] Preparation of thermally expandable microspheres A 150 g of sodium chloride, 70 g of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name "Snowtex") with a silica active ingredient of 20% by weight, 1 g of polyvinylpyrrolidone, and 0.5 g of a condensate of diethanolamine and adipic acid were added to 600 g of distilled water, and then the pH of the obtained mixture was adjusted to 2.8 - 3.2 to obtain an aqueous solution. To the above aqueous solution, 125 g of acrylonitrile and 120 g of methacrylic acid were added as oil-based additives for the shell material. Further, 1 g 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"), and further, 20 g of isopentane (boiling point: 27.7 °C) and 55 g of isooctane (boiling point: 99 °C), which were intended to be encapsulated in the shell, and 5 g of an initiator (diisopropyl oxydicarbonate) were added to the pressure-resistant reaction vessel. 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"), and further, 70 g of isobutane (boiling point: -11.7 °C), which was intended to be encapsulated in the shell, and 5 g of an initiator (diisopropyl oxydicarbonate) were added to the pressure-resistant reaction vessel. The homomixer was rotated under predetermined initial stirring conditions (stirring speed: 8000 rpm, stirring time: 2 minutes) to stir the above mixture, and then the mixture was heated to 60 °C while stirring at 80 rpm and reacted for 24 hours. The solid content obtained by filtering the reaction solution after the reaction was left at room temperature for 1 week under a nitrogen stream to obtain thermally expandable microspheres. The obtained thermally expandable microspheres had an average particle size of 25 μm when measured with 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 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.

[0082] [Production Examples 2 to 7] Thermally Expandable Microspheres B to K Thermally expandable microspheres B to K were prepared in the same manner as in Production Example 1, except that the composition of the oil-based additives (acrylonitrile, methacrylic acid, methacrylonitrile, methyl methacrylate, acrylic acid) was as shown in Table 1. Also, the average particle size of the thermally expandable microspheres was measured in the same manner as in Production Example 1. The results are shown in Table 3.

[0083] [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 an elastic layer-forming composition. (Preparation of the composition for forming the 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)), 20 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 the adhesive layer. (Production of the adhesive tape) The above elastic layer-forming composition 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 adhesive layer-forming composition 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 (4). The results are shown in Table 3.

[0084] [Examples 2 to 14, Comparative Examples 1 to 2] 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 the compositions shown in Table 1 or Table 2. The obtained adhesive tape was subjected to the above evaluations (1) to (4). The results are shown in Table 3. In Table 1 or Table 2, "Crosslinking agent tetrad C" is an epoxy-based crosslinking agent (trade name "Tetrad C") manufactured by Mitsubishi Gas Chemical Company.

[0085] [Example 15] In the same manner as in Example 1, a composition for forming an adhesive layer was prepared. The above composition for forming an adhesive layer was applied to a PET film (manufactured by Toray Industries, Inc., trade name "Lumirror ES-10", thickness: 100 μm) as a base material, dried, and an adhesive layer was formed on the base material to obtain an adhesive tape. The obtained adhesive tape was subjected to the above evaluations (1) to (4). The results are shown in Table 3.

[0086] [Example 16] 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 an adhesion promoter (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, dried, and an elastic layer (thickness: 15 μm) was formed on the base material. A silicone release agent-treated polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38") was coated with the above composition for forming an adhesive layer and dried to form an adhesive layer (35 μm) on the polyethylene terephthalate film. Also, a silicone release agent-treated polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38") was coated with the above another composition for forming an adhesive layer 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 base material where the elastic layer was not formed, to obtain an adhesive tape comprising another adhesive layer, 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 (4). The results are shown in Table 3.

[0087] [Example 17] An adhesive tape was obtained in the same manner as in Example 1, except that a PI film (manufactured by Toray DuPont Co., Ltd., trade name "Kapton 100H", thickness: 25 μm) was used instead of the PET film (manufactured by Toray Industries, Inc., trade name "Lumirror S10", thickness: 100 μm) as the base material. The obtained adhesive tape was subjected to the above evaluations (1) to (4). The results are shown in Table 3.

[0088] [Example 18] An adhesive tape was obtained in the same manner as in Example 17, except that the thermally expandable microspheres C prepared in Production Example 3 were used instead of the thermally expandable microspheres A prepared in Production Example 1. The obtained adhesive tape was subjected to the above evaluations (1) to (4). The results are shown in Table 3.

[0089] [Comparative Example 3] An adhesive tape was obtained in the same manner as in Example 15, except that the thermally expandable microspheres K prepared in Production Example 11 were used instead of the thermally expandable microspheres A prepared in Production Example 1. The obtained adhesive tape was subjected to the above evaluations (1) to (4). The results are shown in Table 3.

[0090]

Table 1

[0091]

Table 2

[0092]

Table 3

Explanation of Symbols

[0093] 10 Adhesive layer 20 Substrate 100 Adhesive tape

Claims

1. A base material and an adhesive layer disposed on at least one side of the base material, wherein the adhesive layer contains thermally expandable microspheres and an adhesive, the thermally expandable microspheres are composed of a shell and a volatile substance contained within the shell, the resin constituting the shell contains a structural unit having a carboxyl group, in the resin constituting the shell, the content ratio of the structural unit having a carboxyl group is 10 parts by weight or more with respect to 100 parts by weight of the resin, 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 adhesive contains a base polymer having an OH group or a COOH group, the acid value of the base polymer is 0 to 100, the base material contains 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, an adhesive tape.

2. The adhesive tape according to claim 1, wherein the glass transition temperature (Tg) of the resin constituting the shell is 120°C or higher.

3. The adhesive tape according to claim 1 or 2, wherein the elastic modulus of the adhesive layer at 23°C by nanoindentation is 0.1 MPa to 500 MPa.

4. The adhesive tape according to any one of claims 1 to 3, wherein the adhesive is an acrylic adhesive.

5. The adhesive tape according to any one of claims 1 to 4, wherein the adhesive contains an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent.

6. The adhesive tape according to any one of claims 1 to 5, 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 1.5 N / 20 mm to 20 N / 20 mm.

7. The adhesive force b when the adhesive surface of the adhesive tape heated to 130°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. The adhesive tape according to any one of claims 1 to 6.

8. The adhesive force c when the adhesive surface of the adhesive tape of the present invention after performing the cycle of heating to 130°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. The adhesive tape according to any one of claims 1 to 7.

9. The adhesive tape according to any one of claims 1 to 8, comprising the adhesive layer on both sides of the base material.

10. The adhesive tape according to any one of claims 1 to 8, comprising the adhesive layer on one side of the base material and another adhesive layer on the other side of the base material.

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