Adhesive tape

Abstract

To provide an adhesive tape containing heat-expandable microspheres, which has excellent releasability after heating and leaves little adhesive residue on an adherend. [Solution] The pressure-sensitive adhesive tape of the present invention comprises a substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the substrate, wherein the pressure-sensitive adhesive layer contains heat-expandable microspheres, and wherein, in a thermomechanical analysis of the pressure-sensitive adhesive tape, when heated at a heating rate of 3°C / min, the time required for the tape to reach point B from point A is 45 to 200 seconds, where point A is the point at which the pressure-sensitive adhesive tape starts to deform, point C is the point at which the pressure-sensitive adhesive tape expands after point A and reaches a maximum deformation, and point B is the point at which the deformation between point A and point C is half the amount at point C.

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, 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 configured to contain thermally expandable microspheres 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, the thermally expandable microspheres expand, causing irregularities on the surface of the adhesive layer and reducing the adhesive force. In such an adhesive tape, it is also possible to peel the adherend only by the action of gravity.

[0003] On the other hand, for easily peelable adhesive tapes, reduction of adhesive residue when peeling the adherend is required. Similarly, for adhesive tapes using thermally expandable microspheres, reduction of adhesive residue is an issue. When applying this adhesive tape to a fragile adherend, a micro adherend, an adherend requiring cleanliness, etc., adhesive residue becomes particularly problematic.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention was made to solve the above-mentioned conventional problems, and its objective is to provide an adhesive tape that contains thermally expandable microspheres, exhibits excellent peelability after heating, and leaves little adhesive residue on the adherend. [Means for solving the problem]

[0006] The adhesive tape of the present invention comprises a base material and an adhesive layer disposed on at least one surface of the base material, wherein the adhesive layer contains thermally expandable microspheres, and when the adhesive tape is heated at a heating rate of 3°C / min in thermomechanical analysis, the deformation initiation point is defined as point A, the point where the deformation of the adhesive tape is at its maximum after expanding past point A is defined as point C, and the point between point A and point C where the deformation is half the deformation at point C is defined as point B, the time from point A to point B is between 45 seconds and 200 seconds. In one embodiment, the time taken from point B to point C is 200 seconds or more. In one embodiment, the temperature at point B is between 50°C and 250°C. In one embodiment, the thermally expandable microsphere is composed of a shell formed from a resin and an organic solvent contained within the shell, and the thickness of the shell is 1 μm to 15 μm. In one embodiment, the thermally expandable microsphere is composed of a shell formed from a resin and an organic solvent contained within the shell, wherein the glass transition temperature of the resin is 50°C to 250°C. In one embodiment, the thermally expandable microsphere is composed of a shell formed from a resin and an organic solvent contained within the shell, wherein the resin forming the outer shell includes at least one selected from the group consisting of constituent units derived from isobornyl acrylate, methacrylonitrile, acrylonitrile, methyl (meth)acrylate, vinylidene chloride, and (meth)acrylic acid. In one embodiment, the boiling point of the organic solvent is -50°C to 100°C. In one embodiment, the elastic modulus of the adhesive layer determined by nanoindentation is 0.1 MPa to 500 MPa. In one embodiment, the gel fraction of the adhesive constituting the adhesive layer is 30% to 99% by weight. [Effects of the Invention]

[0007] According to the present invention, by appropriately controlling the deformation behavior during heating, it is possible to provide an adhesive tape that exhibits excellent peelability after heating and leaves minimal adhesive residue on the adherend after peeling. [Brief explanation of the drawing]

[0008]

Figure 1

Figure 2

[0009] A. Overall structure of the adhesive tape Figure 1 is a schematic cross-sectional view of an adhesive tape according to one embodiment of the present invention. This adhesive tape 100 comprises a base material 10 and an adhesive layer 20 disposed on at least one surface (one side in the illustrated example) of the base material 10.

[0010] The adhesive layer provided in the adhesive tape of the present invention contains thermally expandable microspheres. These thermally expandable microspheres can expand at a predetermined temperature. When heated, the thermally expandable microspheres expand in such an adhesive layer, causing irregularities on the adhesive surface (i.e., the surface of the adhesive layer), resulting in a decrease or loss of adhesive strength. When the adhesive tape of the present invention is used, for example, as a temporary fixing sheet for workpieces during the processing of electronic components (e.g., ceramic capacitors), the adhesive strength necessary for temporary fixing is exhibited when the workpiece is subjected to predetermined processing, and when the adhesive tape is peeled off the workpiece after processing, the adhesive strength decreases or disappears due to heating, resulting in good peelability. In one embodiment, the thermally expandable microspheres are composed of a shell and an organic solvent contained within the shell, and expand due to the volatilization of the organic solvent.

[0011] In the adhesive tape of the present invention, when the adhesive tape is heated at a heating rate of 3°C / min in thermomechanical analysis, the time from the point where deformation begins to the point where the amount of deformation during expansion and deformation becomes half of the maximum deformation is 45 seconds to 200 seconds. This will be explained in more detail using Figure 2. Figure 2 is a diagram showing an example of measurement results when an adhesive tape according to one embodiment of the present invention is subjected to thermomechanical analysis, and shows the relationship between temperature and the amount of deformation (displacement) of the adhesive tape in the analysis. When the adhesive tape is heated (heating rate: 3°C / min), it begins to deform (expand) when it reaches a predetermined temperature. This point is the "deformation initiation point" mentioned above. For convenience, this deformation initiation point will be designated as point A. The deformation of the adhesive tape mainly depends on the expansion and contraction of the thermally expandable microspheres contained in the adhesive layer. After point A has passed, if heating continues, the adhesive tape (essentially a thermally expandable microsphere) will continue to expand and then begin to contract. For example, when using a thermally expandable microsphere composed of a shell and an organic solvent contained within the shell, the microsphere expands up to a predetermined temperature due to the evaporation of the organic solvent, and begins to contract when all of the organic solvent has evaporated. The point at which contraction begins is the point at which the deformation of the adhesive tape is at its maximum. For convenience, this point is designated as point C. Furthermore, between the point A and the point C, a point where the amount of deformation becomes half of the amount of deformation X (100 μm in the illustrated example) at the point C (the point where the amount of deformation during expansion and deformation becomes half of the maximum amount of deformation, 50 μm in the illustrated example) is defined as the point B. In the present invention, the time from the point A to the point B is 45 seconds to 200 seconds. The analysis conditions in the above thermomechanical analysis are as follows. <Analysis conditions> Device name: manufactured by Seiko Instruments Inc., product name "TMA / SS150" Measurement mode: expansion method, with the adhesive layer on the probe side Sample size: 5 mm square Probe: 1 mm φ Probe load: 0 N Measurement temperature range: room temperature (25 °C ± 5 °C) to 250 °C Heating rate: 3 °C / min

[0012] In the present invention, by setting the time from the point A to the point B to be 45 seconds to 200 seconds, an adhesive tape with less glue residue when the adherend is peeled off can be obtained. From the point A to the point B, as the thermally expandable microspheres expand, the adhesive layer deforms (expands). However, on the surface of the adhesive layer, no unevenness is formed, or if it is formed, it is minute, and it is considered that almost the entire surface of the adhesive layer is pressed against the adherend. Such a state, combined with the softening of the adhesive due to heating, is considered to be a state that promotes glue residue on the adherend. In the present invention, by setting the time in such a state (that is, the time from the point A to the point B) to 200 seconds or less, an adhesive tape with less glue residue can be obtained. On the other hand, if the time from the point A to the point B is less than 45 seconds, this means that the thermally expandable microspheres expand rapidly. In such a case, there is a risk that problems such as the adherend flying may occur due to the rapid change of the thermally expandable microspheres.

[0013] The time from point A to point B is preferably 70 seconds to 180 seconds, more preferably 90 seconds to 170 seconds. Within such a range, the above effects will be prominent.

[0014] The time from point B to point C is preferably 30 seconds or more, more preferably 60 seconds or more, still more preferably 180 seconds or more, and particularly preferably 200 seconds or more. In the stage of approaching point C after passing point B, the thermally expandable microspheres further expand. Along with this, irregularities occur on the surface of the adhesive layer, and the contact surface between the adhesive layer and the adherend gradually becomes smaller. As a result, the adhesive force of the adhesive tape decreases or disappears. On the other hand, when the thermally expandable microspheres start to shrink after passing point C, the contact surface between the adhesive layer and the adherend begins to increase, and the adhesive tape will exhibit adhesiveness again. That is, from point B to point C, the adhesive tape exhibits excellent peelability. By setting the time in this state to be the above-mentioned predetermined time or more, when using the adhesive tape in the manufacturing process of electronic components, etc., it is possible to sufficiently ensure the time required for the peeling process of the adherend. Also, when the time from point B to point C is too short, this means that the thermally expandable microspheres deform rapidly, and components of the adhesive layer (for example, the adhesive) that cannot follow the rapid deformation of the thermally expandable microspheres may be separated into small pieces, and the separated components of the adhesive layer may cause adhesive residue.

[0015] The upper limit of the time from point B to point C is, for example, 3600 seconds or less, preferably 1800 seconds or less, more preferably 1000 seconds or less. Within such a range, thermally expandable microspheres with an appropriate amount of encapsulated organic solvent can be used.

[0016] In the above thermomechanical analysis, the temperature at point A (also referred to as the point A temperature) is preferably 30°C to 200°C, more preferably 40°C to 180°C, and particularly preferably 60°C to 180°C.

[0017] In the thermomechanical analysis described above, the temperature at point B (also called the point B temperature) is preferably 50°C to 250°C, more preferably 70°C to 200°C, and even more preferably 80°C to 150°C. Setting the point B temperature to 50°C or higher prevents the adhesive tape from developing unnecessary peelability (for example, developing peelability under conditions of high ambient temperature, such as in summer). Furthermore, if the point B temperature exceeds 250°C, there is a risk of deterioration or ignition of the adhesive tape before it develops peelability.

[0018] In the thermomechanical analysis described above, the temperature at point C (also called the point C temperature) is preferably 90°C to 350°C, and more preferably 100°C to 200°C.

[0019] Under an ambient temperature of 25°C, before the thermally expandable microspheres foam, the adhesive strength when the adhesive surface of the adhesive tape of the present invention is attached to a polyethylene terephthalate film (e.g., 25 μm thick) is preferably 0.2 N / 20 mm or more, more preferably 0.2 N / 20 mm to 20 N / 20 mm, and even more preferably 2 N / 20 mm to 10 N / 20 mm. Within this range, an adhesive tape useful as a temporary fixing sheet used in the manufacture of electronic components can be obtained, for example. In this specification, adhesive strength refers to the adhesive strength measured by a method in accordance with JIS Z 0237:2000 (bonding conditions: 2 kg roller, 1 reciprocating motion; peeling speed: 300 mm / min; peeling angle: 180°).

[0020] The thickness of the adhesive tape of the present invention is preferably 30 μm to 500 μm, and more preferably 40 μm to 300 μm.

[0021] B. Adhesive layer The above adhesive layer contains thermally expandable microspheres. In practical terms, the adhesive layer further contains an adhesive.

[0022] B-1.Thermally expandable microspheres Any suitable thermally expandable microsphere can be used as the above-mentioned thermally expandable microsphere, as long as it is a microsphere that can expand to the extent that it causes the surface of the adhesive layer to become uneven when heated. For example, a microsphere composed of a shell and a volatile substance (typically an organic solvent) contained within the shell can be used as the above-mentioned thermally expandable microsphere.

[0023] Examples of materials for forming the above-mentioned shells include resins, glass, and metals. Among these, resins are preferred. Using resins makes it possible to obtain thermally expandable microspheres that soften and expand easily when heated. Furthermore, since the shells formed from resins have a density close to that of the adhesive, they are advantageous in that they can be dispersed with high uniformity within the adhesive layer.

[0024] As the resin that forms the above shell, for example, a resin having constituent units derived from radically polymerizable monomers is used. Examples of such monomers include nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. The polymer composed of these monomers may be a monopolymer or a copolymer.

[0025] Furthermore, the resin forming the shell may be a crosslinked material. Crosslinking allows for adjustment of the excluded free volume of the polymer, thereby controlling the diffusivity of the encapsulated volatile substances, the expansion of the shell, and other properties. The crosslinked material may further contain constituent units derived from monomers having two or more polymerizable double bonds in the molecule. In one embodiment, the above-mentioned radically polymerizable monomer and the 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, triacrylic 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, and 1,10-decanediol di(meth)acrylate. PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol Examples include tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol acrylate benzoate, trimethylolpropane acrylate benzoate, 2-hydroxy-3-acryloyloxypropyl(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, phenylglycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer, phenylglycidyl ether acrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, and pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer.

[0026] In one embodiment, the resin forming the shell contains at least one selected from the group consisting of constituent units derived from isobornyl acrylate, methacrylonitrile, acrylonitrile, methyl (meth)acrylate, vinylidene chloride, and (meth)acrylic acid. Using a resin having these constituent units, it is possible to form a shell that has low solubility in the encapsulated organic solvent and is resistant to permeation or infiltration by the organic solvent before heating. Furthermore, using the above resin, it is possible to obtain thermally expandable microspheres with good deformability upon heating. Moreover, using the above monomer, it is possible to easily control the thermal properties of the shell by crosslinking or the like.

[0027] In one embodiment, methacrylonitrile and / or acrylonitrile are preferably used from the viewpoint of improving resistance to the encapsulated organic solvent. When these monomers are used, the total content ratio of constituent units derived from methacrylonitrile and constituent units derived from acrylonitrile is preferably 10% to 99% by weight, more preferably 20% to 99% by weight, and particularly preferably 30% to 95% by weight, based on 100% by weight of the resin forming the shell. Within this range, it is possible to obtain thermally expandable microspheres that have excellent solvent resistance and whose B-point temperature can be easily set appropriately.

[0028] In one embodiment, methyl (meth)acrylate is preferably used from the viewpoint of ease of controlling shell hardness. By using methyl (meth)acrylate, for example, the shell hardness can be easily controlled by crosslinking such as electron beam crosslinking in combination with a crosslinkable monomer (for example, a monomer having two or more polymerizable double bonds in the above molecule). When methyl (meth)acrylate is used, the content of the methyl (meth)acrylate is preferably less than 65% by weight, more preferably 1% to 55% by weight, and particularly preferably 1% to 50% by weight, based on 100% by weight of the resin forming the shell.

[0029] Furthermore, when flexibility is to be imparted to the shell, vinylidene chloride is preferably used. The amount of vinylidene chloride used can be any appropriate amount depending on the glass transition temperature of the desired resin.

[0030] The thickness of the shell is preferably 15 μm or less, more preferably 7 μm or less, even more preferably 5 μm or less, and particularly preferably 4 μm or less. Within this range, the time from point A to point B can be shortened, making it easy to reduce the time from point A to point B to 200 seconds or less, as described above. The lower limit of the shell thickness is preferably 1 μm or more, more preferably 2 μm or more. Within this range, a thermally expandable microsphere that is resistant to destruction by unexpected external forces can be obtained. Furthermore, if the shell thickness is less than 1 μm, the physical properties of the shell change due to wetting (diffusion) of the organic solvent contained within the shell, and as a result, the time from point B to point C may be significantly shortened. In other words, by setting the upper and lower limits of the shell thickness within the above range, a thermally expandable microsphere that can rapidly expand in the initial stage of heating (point A to point B) and maintain the expanded state for a long time during subsequent heating (point B to point C) can be easily obtained. Furthermore, by setting the upper and lower limits of the shell thickness within the above range, it is possible to reduce temperature variations during foaming.

[0031] The glass transition temperature (Tg) of the resin constituting the above shell is preferably 50°C to 250°C, more preferably 60°C to 200°C, and even more preferably 80°C to 150°C. Within this range, it is possible to obtain appropriately expandable thermal expandable microspheres, and by using these thermal expandable microspheres, it is possible to easily obtain adhesive tape with an appropriately set point B temperature. In this specification, when the resin is a copolymer, the above glass transition temperature is determined by Fox's formula. Fox's formula is as follows: the glass transition temperature Tg (°C) of the copolymer and the glass transition temperature Tg of the homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. iThis is the relationship with (°C). In Fox's equation below, Tg(°C) is the glass transition temperature of the copolymer, and W is the glass transition temperature. i is the weight fraction of monomer i, Tg i (°C) indicates the glass transition temperature of the monopolymer formed from monomer i. 1 / (273+Tg)=Σ(W i / (273+Tg i )) The glass transition temperatures of monopolymers formed from monomers are as follows: acrylonitrile monopolymer (AN): 97°C, methyl methacrylate monopolymer (MMA): 102°C, methacryloylnitrile monopolymer (MAN): 120°C, vinylidene chloride monopolymer: 75°C, and isobornyl acrylate monopolymer: 97°C. For other monopolymers, the values ​​listed in the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) can be used. If multiple Tg values ​​are listed in this document, the "conventional" value should be adopted.

[0032] The glass transition temperature (Tg) of the resin forming the above-mentioned shell is preferably 45°C or less, and more preferably 5°C to 35°C, when the absolute difference (|Tg-B point temperature|) from the desired B point temperature is 45°C or less. Using a resin having such a glass transition temperature makes it easy to set the B point temperature to the desired temperature.

[0033] The volatile substances contained within the above shell are typically organic solvents. Examples of such organic solvents 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 hydrocarbon groups having 2 to 8 carbon atoms, or compounds in which some of the hydrogen atoms of the hydrocarbon group are substituted with fluorine atoms. In one embodiment, the organic solvent used is hydrocarbons composed only of hydrogen 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. These organic solvents may be used individually or in combination of two or more. The above organic solvents have the advantage of having low affinity for the resin and / or adhesive forming the shell, being difficult to dissolve the shell and / or adhesive, and not easily altering physical properties such as thermal properties. Furthermore, hydrocarbons composed solely of hydrogen and carbon atoms are preferred from the viewpoint of industrial application.

[0034] In one embodiment, branched hydrocarbons (e.g., isobutane, isopentane, etc.) are used as hydrocarbons composed only of hydrogen and carbon atoms. Branched hydrocarbons are not easily charged, and using this solvent can prevent accidents such as ignition due to static charge.

[0035] The boiling point of the above organic solvent is preferably -50°C to 100°C, and more preferably -20°C to 100°C. Within this range, it is possible to obtain thermally expandable microspheres in which the shells can expand well without being destroyed. However, if the boiling point of the organic solvent is too low, the operations to suppress volatilization during the production of thermally expandable microspheres may become complicated.

[0036] The absolute value of the difference (|bp-Tg|) between the boiling point (bp) of the above organic solvent and the glass transition temperature (Tg) of the resin constituting the shell is preferably 0°C to 150°C, more preferably greater than 0°C and 150°C or less, and even more preferably 5°C to 125°C. When two or more types of organic solvents (mixed solvents) are used, it is preferable that the difference between the boiling point of the solvent with the largest weight percentage and the glass transition temperature (Tg) of the resin constituting the shell is within the above range. Within such a range, the time from point A to point B, and the time from point B to point C can be appropriately and easily adjusted. It is preferable that the boiling point (bp) of the above organic solvent is lower than the glass transition temperature (Tg) of the resin forming the shell. If an organic solvent with a boiling point higher than the glass transition temperature of the shell is used, the shell may be destroyed by the pressure generated when the organic solvent is heated, or the adhesive may be scattered, which may hinder the functions and effects expected of the present invention.

[0037] Furthermore, thermally expandable microspheres are often exposed to environments that can crush them before heating, such as surrounding adhesives and the application process. Therefore, it is preferable to use a vapor pressure that prevents the thermally expandable microspheres from being crushed even before heating.

[0038] The content of the above organic solvent is preferably 5% to 35% by weight, and more preferably 10% to 30% by weight, relative to the weight of the heat-expandable microspheres before heating. Within this range, an adhesive tape can be obtained in which the heat-expandable microspheres are dispersed with high uniformity in the adhesive layer. If the content is less than 5% by weight, the heat-expandable microspheres tend to be unevenly distributed on the surface of the adhesive layer during manufacturing due to reasons such as low density, and after heating, there is a risk that excessively large bumps and dips will form on the surface of the adhesive layer. If the content exceeds 35% by weight, the density will be high and the microspheres will settle in the adhesive layer, and even after heating, sufficient bumps and dips may not form on the surface of the adhesive layer, potentially resulting in a failure to obtain the desired peelability and the occurrence of adhesive residue.

[0039] Under an ambient temperature of 25°C, the average particle size (number basis) of the thermally expandable microspheres before foaming is preferably 1 μm to 40 μm, more preferably 5 μm to 40 μm, and even more preferably 10 μm to 40 μm. Within this range, thermally expandable microspheres with high dispersibility in the adhesive layer can be obtained. An adhesive layer containing thermally expandable microspheres with high dispersibility exhibits high uniformity of the irregularities created by heating and can exhibit excellent release properties. The average particle size of the thermally expandable microspheres can be controlled, for example, by the conditions when polymerizing the thermally expandable microspheres (details will be described later). In this specification, the average particle size can be measured by observing the thermally expandable microspheres used, or thermally expandable microspheres taken from the adhesive layer before heating, using an optical microscope or an electron microscope. Alternatively, the average particle size can be measured by a particle size distribution measurement method using laser scattering. More specifically, the average particle size can be measured using a particle size distribution analyzer (for example, a Shimadzu Corporation product called "SALD-2000J") after dispersing the thermally expandable microspheres in a predetermined solvent (for example, water).

[0040] In one embodiment, the content of thermally expandable microspheres is expressed as the area ratio of thermally expandable microspheres measured from a cross-section. If the cross-sectional area of ​​the adhesive layer at a predetermined cross-section is A, and the cross-sectional area of ​​the thermally expandable microspheres at the same cross-section is B, then the ratio of the cross-sectional area B of the thermally expandable microspheres is preferably 3% to 75%, and more preferably 3.5% to 70%, relative to the cross-sectional area A of the adhesive layer. If the ratio of the cross-sectional area B is less than 3%, even if the thermally expandable microspheres are heated and expanded, the irregularities that occur on the adhesive surface may be insufficient, and the desired peelability may not be obtained. On the other hand, if the ratio of the cross-sectional area B exceeds 75%, the volume change of the adhesive layer may become too large, which may cause lifting and peeling between the substrate and the adhesive layer, and the adhesive content in the adhesive layer may be low, which may not be able to obtain the desired adhesive strength. The ratio of the cross-sectional area B of the thermally expandable microspheres can be determined, for example, by appropriately processing an image obtained by observing the cross-section of the adhesive layer with an electron microscope (for example, Hitachi Technologies' product name "S-3400N Low Vacuum Scanning Electron Microscope"). For example, the image can be printed on paper, and the weight a of the paper containing the adhesive layer (i.e., the entire adhesive layer including the thermally expandable microspheres) and the weight b of the paper cut out only from the thermally expandable microsphere portion can be used to determine the ratio b / a × 100.

[0041] The content of thermally expandable microspheres is preferably 5% to 95% by weight, more preferably 10% to 70% by weight, and even more preferably 10% to 50% by weight, relative to the weight of the adhesive layer. Within this range, it is possible to achieve the above-mentioned ratio of the cross-sectional area B of thermally expandable microspheres. Furthermore, while keeping the content of thermally expandable microspheres within the above range, the cross-sectional area B of the thermally expandable microspheres can be set to a preferred range by performing operations such as stirring the adhesive layer-forming composition until immediately before the coating process, in order to prevent the thermally expandable microspheres from being unevenly distributed in the adhesive layer. The content of 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. Percentage of thermally expandable microspheres (by weight) = Weight of thermally expandable microspheres / Weight of adhesive layer × 100

[0042] The above-mentioned thermally expandable microspheres can be manufactured by any suitable method. In one embodiment, the thermally expandable microspheres are obtained by suspension polymerization. Suspension polymerization is usually carried out by dispersing monomers (shell-forming materials) and an organic solvent in an aqueous dispersion medium containing a dispersant, and polymerizing the monomers in the presence of the organic solvent. A dispersion stabilizer may also be used to stabilize the dispersion. Examples of dispersion stabilizers in the aqueous dispersion medium include inorganic fine particles such as silica, magnesium hydroxide, calcium phosphate, and aluminum hydroxide. In addition, examples of dispersion stabilization auxiliary agents may be used, such as condensation products of diethanolamine and aliphatic dicarboxylic acids, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polyvinyl alcohol, and various emulsifiers.

[0043] The properties of the thermally expandable microspheres, such as particle size and organic solvent content, can be controlled by adjusting the polymerization conditions, the type and amount of mixed components, etc., in the suspension polymerization described above. For example, large-particle thermally expandable microspheres can be obtained by reducing the amount of dispersant added or by slowing down the stirring speed during polymerization. Furthermore, thermally expandable microspheres with thicker shells can be obtained by increasing the amount of monomer blended or by slowing down the stirring speed during polymerization.

[0044] B-2. Adhesive Any suitable adhesive can be used as the adhesive constituting the above-mentioned adhesive layer, as long as the effects of the present invention are obtained. Examples of such adhesives 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 these, acrylic adhesives, rubber adhesives, or silicone adhesives are preferred, and acrylic adhesives are more preferred.

[0045] The gel fraction of the above adhesive is preferably 20% to 100% by weight, more preferably 30% to 99% by weight, and even more preferably 50% to 99% by weight. If the gel fraction is less than 20% by weight, even if the thermally expanding microspheres expand and create irregularities on the surface of the adhesive layer, the adhesive layer may flow and the irregularities may disappear in a short time. Also, the excluded volume of polymer molecules is small, and the organic solvent in the thermally expanding microspheres easily permeates between the polymer molecular chains, which may increase the time it takes to travel from point A to point B. On the other hand, if the gel fraction exceeds 99% by weight, the thermal expansion of the thermally expanding microspheres may be inhibited, resulting in insufficient irregularities, or even if irregularities are created, the thermally expanding microspheres may explode, scattering the shells of the thermally expanding microspheres and the surrounding adhesive layer, which may worsen the adhesive residue. The gel fraction of the adhesive can be controlled by adjusting the composition of the base polymer constituting the adhesive, the type and amount of crosslinking agent added to the adhesive, and the type and amount of tackifier. The method for measuring the gel fraction will be described later.

[0046] The base polymer contained in the above adhesive preferably has OH groups or COOH groups. This is because using such a base polymer makes it possible to adjust the gel fraction using a crosslinking agent. Furthermore, the aggregation of the base polymer by intermolecular forces such as hydrogen bonding can be adjusted by controlling the amount of OH groups or COOH groups that do not react with the crosslinking agent. This makes it possible to control the uneven shape of the adhesive surface caused by the expansion of the thermally expandable microspheres, and the shell permeability of organic solvents contained in the thermally expandable microspheres.

[0047] The hydroxyl value of the base polymer having an OH group is preferably 0 to 50, more preferably 20 to 30. The acid value of the base polymer having a COOH group is preferably 10 to 100, more preferably 20 to 50. The hydroxyl value and acid value of the polymer in the adhesive layer can be measured by extracting the solvent-soluble components from the adhesive layer. Specifically, the solvent-soluble components can be extracted by the following method. (i) Prepare a solution sample by immersing the adhesive layer in a solvent and dissolving the solvent-soluble components in the adhesive layer in the solvent. As a solvent, one solvent selected from chloroform (CHCl3), methylene chloride (CH2Cl2), tetrahydrofuran (THF), acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), methanol, ethanol, toluene, and water, or a mixed solvent containing two or more of these in any ratio, can be used, taking polarity and other factors into consideration. Typically, about 0.2 g of the adhesive layer is mixed with about 30 mL of solvent and stirred for 30 minutes to 12 hours at a temperature ranging from room temperature to the boiling point of the solvent used. If necessary, for example, if the extraction efficiency of the analyte is low, a solution sample may be prepared by adding approximately the same amount of solvent to the sample after the above solution has been separated and stirring, and then separating that solution once or multiple times. (ii) The solvent can be removed from the above solution sample by methods such as evaporation, and the solvent-soluble polymer can be extracted. Note that solvent-soluble polymers may contain solvent-soluble components that are not the target of measurement, such as low molecular weight unreacted crosslinking agents. In such cases, a solvent-soluble polymer consisting only of the target component is prepared by methods such as adding only the polymer component to a solvent insoluble in the solution sample (reprecipitation method) or by molecular weight fractionation using gel filtration chromatography with the solution sample (preparative liquid chromatography method).

[0048] (Acrylic adhesive) Examples of the above acrylic adhesives include acrylic adhesives that use an acrylic polymer (homopolymer or copolymer) as a base polymer, in which one or more alkyl (meth)acrylate esters are used as monomer components. Specific examples of alkyl (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples of C1-20 alkyl esters of (meth)acrylate include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, alkyl esters of (meth)acrylate having a linear or branched alkyl group with 4 to 18 carbon atoms are preferably used.

[0049] In one embodiment, the acrylic polymer contains monomer-derived structural units whose homopolymer glass transition temperature (Tg) is 80°C or higher (preferably 90°C or higher, and more preferably 100°C or higher). Using such a polymer, an adhesive layer with an appropriate elastic modulus can be formed. Examples of such monomers include cyclohexyl methacrylate (Tg: 83°C), dicyclopentanyl acrylate (Tg: 120°C), dicyclopentanyl methacrylate (Tg: 175°C), isobornyl acrylate (Tg: 94°C), isobornyl methacrylate (Tg: 150°C), t-butyl methacrylate (Tg: 118°C), methyl methacrylate (Tg: 105°C), trimethylolpropane triacrylate (Tg: >250°C), styrene (Tg: 80°C), acrylonitrile (Tg: 97°C), and N-acryloylmorpholine (Tg: 145°C). Among these, methyl methacrylate is preferred. The content of monomer-derived structural units that result in a glass transition temperature (Tg) of 80°C or higher for the homopolymer is preferably 1 to 20 parts by weight, and more preferably 1 to 10 parts by weight, per 100 parts by weight of the base polymer (acrylic polymer).

[0050] The above acrylic polymer may, if necessary, contain units corresponding to other monomers copolymerizable with the above alkyl (meth)acrylate for the purpose of modifying properties such as cohesiveness, heat resistance, and crosslinkability. Examples of such monomers include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride monomers such as maleic anhydride and eicotanoic anhydride; hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate; sulfonic acid group-containing monomers such as styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; (meth (N-substituted)amide monomers such as acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide; (meth)acrylate aminoalkyl monomers such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate; (meth)acrylate alkoxyalkyl monomers such as methoxyethyl (meth)acrylate and 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 monomers such as N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyoctamethylenesuccinimide; vinyl monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinyl carboxylic acid amides, styrene, α-methylstyrene, and N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and (meth)acrylic acid Examples include glycol-based acrylic ester monomers such as methoxypolypropylene glycol phosphate; acrylic acid ester monomers having heterocyclic rings, halogen atoms, silicon atoms, etc., such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; polyfunctional monomers such as hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene; and vinyl ether-based monomers such as vinyl ether. These monomers may be used individually or in combination of two or more.

[0051] (Additives) The above adhesive may contain any suitable additives as needed. Examples of such additives include crosslinking agents, tackifiers, plasticizers, pigments, dyes, fillers, anti-aging agents, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, antioxidants, and the like.

[0052] Any suitable tackifier can be used as the tackifier. For example, a tackifying resin can be used as the tackifier. Specific examples of tackifying resins 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, resol, novolac, etc.), ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins.

[0053] The amount of the tackifier added is preferably 5 to 100 parts by weight, and more preferably 10 to 50 parts by weight, per 100 parts by weight of the base polymer.

[0054] Examples of the above-mentioned crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, as well as urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Among these, isocyanate-based crosslinking agents or epoxy-based crosslinking agents are preferred.

[0055] Specific examples of the above-mentioned isocyanate-based crosslinking agents 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 derivative 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 depending on 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, per 100 parts by weight of the base polymer.

[0056] Examples of the epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediline, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd., 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 Recall diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., product name "Epolite 40E"), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., product name "Epolite 70P"), polyethylene glycol diglycidyl ether (manufactured by Nippon Oil & Fats Co., Ltd., product name "Epiol E-400"), polypropylene glycol diglycidyl ether (manufactured by Nippon Oil & Fats Co., Ltd., product name "Epiol P-200"), sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, product name "Denacol") Examples include EX-611), glycerol polyglycidyl ether (manufactured by Nagase ChemteX, trade name "Denacol EX-314"), pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether (manufactured by Nagase ChemteX, trade name "Denacol EX-512"), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipic acid ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. The content of the epoxy crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, elasticity of the adhesive layer, etc., and is typically 0.01 to 10 parts by weight, more preferably 0.03 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0057] Any suitable plasticizer can be used as the plasticizer described above. Specific examples of plasticizers include trimette acid ester plasticizers, pyromellitic acid ester plasticizers, polyester plasticizers, adipic acid plasticizers, etc. Particularly preferred are trimellitic acid ester plasticizers (e.g., tri(n-octyl) trimellitic acid, tri(2-ethylhexyl) trimellitic acid, etc.) or pyromellitic acid ester plasticizers (e.g., tetra(n-octyl) pyromellitic acid, tetra(2-ethylhexyl) pyromellitic acid, etc.). The plasticizer may be used alone or in combination of two or more types. The plasticizer content is preferably 1 to 20 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0058] B-3. ​​Characteristics of the adhesive layer The elastic modulus of the adhesive layer at 23°C, as determined by nanoindentation, is preferably 0.1 MPa to 500 MPa, and more preferably 0.5 MPa to 400 MPa. In one embodiment, an adhesive layer with an external elastic modulus of 0.8 MPa to 50 MPa is used. If the elastic modulus of the adhesive layer is less than 0.1 MPa, the organic solvent diffused outside the thermally expandable microspheres during heating may quickly permeate the adhesive layer, potentially shortening the time from point B to point C. On the other hand, if the elastic modulus exceeds 500 MPa, it may inhibit the expansion of the thermally expandable microspheres, or the adhesive layer may break when the thermally expandable microspheres expand. The elastic modulus of the adhesive layer can be controlled by introducing monomer-derived structural units whose homopolymer glass transition temperature (Tg) is 80°C or higher, adjusting the degree of crosslinking, etc. The elastic modulus obtained by the nanoindentation method is determined by continuously measuring the load applied to the indenter and the indentation depth during loading and unloading, at a location approximately 3 μm inside the surface of the adhesive layer and where no thermally expanded microspheres exist (a location at least 1 μm away from the shell surface of the thermally expanded microspheres), and then obtaining the load-indentation depth curve. In this specification, the elastic modulus obtained by the nanoindentation method refers to the elastic modulus measured as described above, with the measurement conditions being a loading / unloading rate of 1000 nm / s and an indentation depth of 800 nm.

[0059] The anchoring force between the adhesive layer and the substrate is preferably 4N / 20mm or more, and more preferably 5N / 20mm or more. Within this range, the adhesion between the substrate and the adhesive layer is maintained even after the thermally expandable microspheres have expanded, making it possible to obtain an adhesive tape with minimal adhesive residue. The method for measuring the anchoring force will be described later.

[0060] Under an ambient temperature of 25°C, the arithmetic mean height Sa of the adhesive layer before the thermally expandable microspheres are foamed is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. Within this range, an adhesive tape can be obtained that can reduce the unevenness that occurs on the adhesive surface of the adherend. The arithmetic mean height Sa can be measured in accordance with JIS B 0601:1994 using a laser microscope (Olympus LEXT OLS-4000, image magnification 432x, measurement area 640 × 640 μm (sampling rate 0.625 μm)).

[0061] The arithmetic mean height Sa of the adhesive layer when the adhesive tape of the present invention is heated to point C is preferably 10 μm to 50 μm, and more preferably 3 μm to 30 μm. Within this range, an adhesive tape can be obtained in which the adhesive strength decreases or disappears after heating, allowing the adherend to be easily peeled off. If the arithmetic mean surface height Sa exceeds 50 μm, the foaming stress during the formation of unevenness is too large, and the adherend may be blown off even without any external force applied, potentially adversely affecting subsequent adherend retrieval. The "arithmetic mean height Sa of the adhesive layer when the adhesive tape is heated to point C" is the arithmetic mean height Sa of the adhesive layer of an adhesive tape (5 cm square) heated for 60 ± 5 seconds on a hot plate set to the point C temperature, and can be measured using the laser microscope described above. Here, the arithmetic mean surface height Sa of the adhesive layer refers to the arithmetic mean surface height Sa after heating without an adherend.

[0062] The thickness of the adhesive layer is preferably 5 μm to 300 μm, more preferably 15 μm to 250 μm, even more preferably 30 μm to 100 μm, and particularly preferably 30 μm to 60 μm.

[0063] B-4. Other ingredients The adhesive layer described above may further contain any other suitable components, insofar as the effects of the present invention are obtained. Examples of other components include beads. Examples of such beads include glass beads and resin beads. By adding such beads to the adhesive layer, the elastic modulus of the adhesive layer can be improved, and an adhesive tape that can process workpieces with greater precision can be obtained. The average particle size of the beads is, for example, 0.01 μm to 50 μm. The amount of beads added is, for example, 10 to 200 parts by weight, preferably 20 to 100 parts by weight, per 100 parts by weight of the adhesive layer.

[0064] C. Substrate Examples of the above-mentioned substrates include resin sheets, nonwoven fabrics, paper, metal foils, woven fabrics, rubber sheets, foamed sheets, and laminates thereof (especially laminates including resin sheets). Examples of resins that make up resin sheets include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), polyamide (nylon), fully aromatic polyamide (aramid), polyimide (PI), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), fluororesins, and polyether ether ketone (PEEK). Examples of nonwoven fabrics include nonwoven fabrics made from heat-resistant natural fibers such as nonwoven fabrics containing Manila hemp; and synthetic resin nonwoven fabrics such as polypropylene resin nonwoven fabrics, polyethylene resin nonwoven fabrics, and ester resin nonwoven fabrics. Examples of metal foils include copper foil, stainless steel foil, and aluminum foil. Examples of paper include Japanese paper (washi) and kraft paper.

[0065] The thickness of the above-mentioned substrate can be set to any appropriate thickness depending on the desired strength or flexibility, as well as the intended use. The thickness of the substrate is preferably 1000 μm or less, more preferably 1 μm to 1000 μm, even more preferably 1 μm to 500 μm, particularly preferably 3 μm to 300 μm, and most preferably 5 μm to 250 μm.

[0066] The above-mentioned substrate may be subjected to surface treatment. Examples of surface treatments include corona treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage electric shock exposure, ionizing radiation treatment, and coating treatment with a primer.

[0067] Examples of the above-mentioned organic coating materials include those described in Plastic Hard Coat Materials II (CMC Publishing, (2004)). Preferably, urethane polymers, more preferably polyacrylic urethane, polyester urethane, or precursors thereof are used. This is because coating and application to the substrate is simple, and a wide variety of types can be selected industrially and are readily available at low cost. The urethane polymer is, for example, a polymer consisting of a reaction mixture of isocyanate monomer and alcoholic hydroxyl group-containing monomer (e.g., hydroxyl group-containing acrylic compound or hydroxyl group-containing ester compound). The organic coating material may contain optional additives such as chain extenders such as polyamines, antioxidants, and oxidation stabilizers. 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 preferred, and about 0.5 μm to 5 μm is more preferred.

[0068] F. Manufacturing method of the adhesive tape The adhesive tape of the present invention can be manufactured by any suitable method. Examples of methods for manufacturing the adhesive tape of the present invention include directly coating a substrate with an adhesive layer-forming composition containing an adhesive and thermally expandable microspheres, or coating an adhesive layer-forming composition onto any suitable substrate and transferring the formed coating layer to the substrate. The adhesive layer-forming composition may contain any suitable solvent. Alternatively, after forming an adhesive coating layer with an adhesive-containing composition, thermally expandable microspheres may be sprinkled onto the adhesive coating layer, and then the thermally expandable microspheres may be embedded in the coating layer using a laminator or the like to form an adhesive layer containing thermally expandable microspheres.

[0069] The content of thermally expandable microspheres in the adhesive layer forming composition is preferably 5% to 95% by weight, more preferably 10% to 70% by weight, and even more preferably 10% to 50% by weight, relative to the solid content weight of the adhesive layer forming composition.

[0070] Any suitable coating method can be used for each of the above compositions. For example, the coating can be applied and then dried to form each layer. Examples of coating methods include coating using a multi-coater, die coater, gravure coater, applicator, etc. Examples of drying methods include natural drying and heat drying. In the case of heat drying, the heating temperature can be set to any suitable temperature depending on the properties of the substance to be dried.

[0071] G. Applications The adhesive tape of the present invention can be suitably used as a sheet for temporarily fixing electronic component materials when manufacturing electronic components. In one embodiment, the adhesive tape of the present invention is used as a temporary fixing sheet when cutting electronic component materials. Examples of such electronic component materials include ceramic capacitor materials. By temporarily fixing electronic component materials such as ceramic capacitor materials on the adhesive tape of the present invention, displacement of the material can be prevented, and as a result, the material can be cut with excellent precision. Any suitable cutting method can be used as the cutting method in the above cutting process. [Examples]

[0072] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods in the examples are as follows. In the evaluation below, adhesive tape with the separator removed was used. Also, in the examples, unless otherwise specified, "parts" and "%" are based on weight.

[0073] [evaluation] (1) Measurement of the hydroxyl value of the base polymer of the adhesive (Pre-processing) (i) 2 g of the adhesive in the adhesive layer was added to 300 ml of chloroform, and reflux was carried out for 1 day. Impurities such as dust were filtered out and removed from the resulting solution, and the filtrate was collected. (ii) The chloroform solution prepared in (i) above was added dropwise to 10 L of methanol over 1 hour, and the resulting precipitate was collected. (iii) The precipitate obtained by the operation in (ii) above was dissolved in 300 ml of chloroform. This solution was added dropwise to 10 L of methanol over 1 hour, and the resulting precipitate was collected. (iv) The precipitate obtained by the operation in (iii) above was dissolved again in 300 ml of chloroform. This solution was added dropwise to 10 L of methanol over 1 hour, and the resulting precipitate was collected. (v) The precipitate obtained in (iv) was measured by GPC, and it was confirmed that there was no low molecular weight fraction with a weight average molecular weight of 2000 or less. The precipitate (base polymer) was used as a sample for measuring the hydroxyl value. (v’) In the case where the precipitate contains a low molecular weight compound with a weight average molecular weight of 2000 or less, the operation in (iv) above was repeated until the low molecular weight compound was no longer contained. The above GPC measurement was carried out under the following conditions using "HLC-8120GPC" manufactured by Tosoh Corporation and polystyrene as a molecular weight standard substance. <Measurement conditions for GPC> · Sample concentration: 0.2 wt% (tetrahydrofuran solution) · Sample injection volume: 10 μl · Eluent: Tetrahydrofuran (THF) · Flow rate: 0.6 mL / min · Column temperature (measurement temperature): 40 °C · Column: Trade name "TSKgel Super HM-H / H4000 / H3000 / H2000" (manufactured by Tosoh Corporation) · Detector: Differential refractometer (RI) · Standard polystyrene: Tsk gel standard polystyrene F-288, F-40, F-4, A-5000, A-500 manufactured by Tosoh Corporation (Measurement of hydroxyl value) The hydroxyl value was evaluated according to JIS K 0070-1992 (acetylation method). Approximately 25 g of acetic anhydride was taken, pyridine was added, and the total volume was increased to 100 mL. The mixture was thoroughly stirred to prepare the acetylation reagent. Approximately 2 g of the base polymer was accurately weighed and placed in a flat-bottom flask. 5 mL of acetylation reagent and 10 mL of pyridine were added, and an air condenser was attached. After heating at 100°C for 70 minutes, the mixture was allowed to cool. 35 mL of toluene (or tetrahydrofuran if the adhesive is poorly soluble in toluene) was added from the top of the condenser and stirred. Then, 1 mL of water was added and stirred to decompose the acetic anhydride. To complete the decomposition, the mixture was heated again for 10 minutes and then allowed to cool. The condenser was washed with 5 mL of ethanol and removed, and 50 mL of pyridine was added as a solvent and stirred. 25 mL of 0.5 mol / L potassium hydroxide ethanol solution was added to this solution using a volumetric pipette, and potentiometric titration was performed with the 0.5 mol / L potassium hydroxide ethanol solution to calculate the hydroxyl value using the following formula. Hydroxyl value (mgKOH / g) = (BC) × f × 28.05 / S + D B: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample. f: Factor of 0.5 mol / L potassium hydroxide ethanol solution S: Sample volume (g) D: Acid value

[0074] (2) Measurement of gel fraction of adhesive Approximately 0.1 g of adhesive from the adhesive layer was sampled and accurately weighed (sample weight). The sample was then wrapped in a mesh sheet (product name "NTF-1122", manufactured by Nitto Denko Corporation) and immersed in approximately 50 ml of toluene at room temperature for one week. After that, the solvent-insoluble matter (contents of the mesh sheet) was removed from the toluene and dried at 70°C for approximately 2 hours. The solvent-insoluble matter after drying was weighed (weight after immersion and drying), and the gel fraction (weight %) was calculated using the following formula (a). In Comparative Example 4, before the measurement, ultraviolet light of 500 mJ / cm² was used. 2The adhesive was cured by irradiating it with ultraviolet light. For the ultraviolet irradiation, we used the "UM810" manufactured by Nitto Seiki Co., Ltd. Gel fraction (weight %) = [(weight after immersion and drying) / (weight of sample)] × 100 (a)

[0075] (3) Thermomechanical analysis of adhesive tape A 5mm x 5mm piece of adhesive tape was cut to obtain a measurement sample. The measurement sample was attached to the measuring device so that it was in contact with the probe side of the measuring device. Next, the sample was heated from room temperature at a predetermined heating rate to obtain a temperature-displacement (length) curve. Based on the temperature-displacement curve, we determined the time from the deformation initiation point (point A) to the point where the deformation during expansion is half of the maximum deformation (point B), the time from point B to the point where the deformation of the adhesive tape is maximum (point C), the temperature at point A, the temperature at point B, and the temperature at point C. <Analysis conditions> Device name: Seiko Instruments Inc., product name "TMA / SS150" Measurement mode: Expansion method, with the adhesive layer facing the probe. Sample size: 5mm square Probe: 1mmφ Probe load: 0N Measurement temperature range: Room temperature (25℃±5℃) to 250℃ Heating rate: 3℃ / min

[0076] (4) The arithmetic mean height Sa of the adhesive layer when point C is reached. A 5cm x 5cm piece of adhesive tape was cut to obtain a measurement sample. The measurement sample was heated for 60 ± 5 seconds on a hot plate set to point C temperature. After heating, the arithmetic mean height Sa of the adhesive layer was measured using a laser microscope (Olympus LEXT OLS-4000, image magnification 432x, measurement area 640 x 640 μm (sampling rate 0.625 μm)).

[0077] (5) Elastic modulus of the adhesive layer by nanoindentation method The adhesive tape was cut in the thickness direction using a microtome, and the elastic modulus of the cut surface was measured using a nanoindenter. More specifically, the measurement target was the cross-sectional surface of the adhesive layer, approximately 3 μm away from the surface of the adhesive layer, and in a location where thermal expansion microspheres were absent (adhesive at least 1 μm away from the shell surface of the thermal expansion microspheres). The displacement-load hysteresis curve obtained by pressing a probe (indenter) against the object to be measured was numerically processed using the software (triboscan) attached to the measuring device to obtain the modulus of elasticity (average value of 10 measurements). The nanoindenter apparatus and measurement conditions are as follows. <Equipment and measurement conditions> Equipment: Nanoindenter; Triboindenter manufactured by Hysitron Inc. Measurement method: Single indentation method Measurement temperature: 23℃ Pressing speed: Approximately 1000 nm / sec Indentation depth: Approximately 800 nm Probe: Made of diamond, Berkovich type (triangular pyramidal shape)

[0078] (6) Anchor force of the substrate-adhesive layer The adhesive side of adhesive tape (manufactured by Nitto Denko Corporation, No. 315) was attached to the adhesive layer side of the adhesive tape described in the example using a hand roller. Next, double-sided tape (manufactured by Nitto Denko Corporation, No. 5000N) was attached to the base material side of the adhesive tape described in the example to create a 10mm x 70mm strip. After that, a 2mm thick SUS plate was attached to the other side of the double-sided tape to create a test specimen. The adhesive tape on the obtained test specimens was peeled off at a 180° angle, 50 mm / mm. As a result, if only the adhesive tape peeled off, i.e., the anchor was not damaged, it was considered a pass (indicated by ○ in the table). If the adhesive layer was peeled off along with the adhesive tape, or if the anchor was damaged, the peeling force at that time was measured. Furthermore, since the adhesive strength when adhesive tape is directly attached to a SUS plate is 5N / 10mm, it can be said that products that pass the above test have an anchoring force of 5N / 10mm or more.

[0079] (7) Adhesive residue evaluation 1 (Relationship between time from point A to point B and adhesive residue) Adhesive tape was applied to the entire mirror surface of a 4-inch silicon mirror wafer (bare wafer with orientation flat) using a hand roller, and left at room temperature for 1 hour. A wafer with the adhesive tapes attached was placed on a hot plate whose B-point temperature was set to ±5°C for each adhesive tape (the wafer surface without the adhesive tape was in contact with the hot plate surface), and heated for 10 seconds ± 1 second. After removing the wafer with adhesive tape from the hot plate, the wafer was positioned so that the adhesive tape would peel off naturally (the wafer was flipped over with the adhesive tape side facing down) and the adhesive tape was removed. If the adhesive tape did not fall off naturally and could not be removed from the wafer, it was removed by picking it up with tweezers. In Comparative Example 4, before this operation, ultraviolet light of 500 mJ / cm² was applied. 2 The adhesive was cured by UV irradiation. A "UM810" UV irradiator manufactured by Nitto Seiki Co., Ltd. was used for the UV irradiation. The central 1x1mm area of ​​the mirror surface after the adhesive tape was removed was observed with an optical microscope (Olympus Optical Co., Ltd., 5x objective lens, 10x eyepiece), and the number of adhesive residues on the wafer surface (approximately dot-like (granular) or irregularly shaped images not observed on new wafers before the adhesive tape was applied) was counted. In the table, the number of remaining glue pieces is indicated as follows: ◎ for 0-500 pieces, ○ for 500-1000 pieces, △ for 1000-5000 pieces, and × for 5000 pieces or more.

[0080] (8) Adhesive residue evaluation 2 (Relationship between time from B point to C point and adhesive residue) Adhesive tape was applied to the entire mirror surface of a 4-inch silicon mirror wafer (bare wafer with orientation flat) using a hand roller, and left at room temperature for 1 hour. A wafer with the adhesive tapes attached was placed on a hot plate heated to the B temperature ±5°C of each adhesive tape (so that the wafer surface without adhesive tape was in contact with the hot plate surface), and heated for 210 ± 10 seconds. After removing the wafer with adhesive tape from the hot plate, the wafer was positioned so that the adhesive tape would peel off naturally (the wafer was flipped over with the adhesive tape side facing the ground) and the adhesive tape was removed. If the adhesive tape did not fall off naturally and could not be removed from the wafer, it was removed by picking it up with tweezers. In Comparative Example 4, before this operation, ultraviolet light of 500 mJ / cm² was applied. 2 The adhesive was cured by irradiating it with ultraviolet light. For the ultraviolet irradiation, we used the "UM810" manufactured by Nitto Seiki Co., Ltd. The central 1x1mm area of ​​the mirror surface after the adhesive tape was removed was observed with an optical microscope (Olympus Optical Co., Ltd., objective lens 5x magnification, eyepiece lens 10x magnification), and the number of adhesive residues on the wafer surface (approximately dot-like (granular) or irregularly shaped images not seen on new wafers before the adhesive tape was applied) was counted. In the table, the number of remaining glue pieces is indicated as follows: ◎ for 0-500 pieces, ○ for 500-1000 pieces, △ for 1000-5000 pieces, and × for 5000 pieces or more.

[0081] [Manufacturing Example 1] Fabrication of thermally expandable microspheres A 150 g of sodium chloride, 70 g of colloidal silica (manufactured by Nissan Chemical Corporation, trade name "Snowtex") containing 20% ​​by weight of silica as the active ingredient, 1 g of polyvinylpyrrolidone, and 0.5 g of a condensate of diethanolamine and adipic acid were added to 600 g of distilled water. The pH of the resulting mixture was then adjusted to 2.8-3.2 to obtain an aqueous solution. To the above aqueous solution, 80 g of acrylonitrile, 40 g of methyl methacrylate, and 130 g of vinylidene chloride were added as oil-based additives to form the shell. Furthermore, 1 g of ethylene glycol dimethacrylate was added as a crosslinking agent to obtain the 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., product name "TK Homomixer"). Furthermore, 70 g of isobutane (boiling point: -11.7°C) and 5 g of an initiator (diisopropyl oxydicarbonate) were added to the pressure-resistant reaction vessel as organic solvents intended to be encapsulated within the shell. The mixture was stirred by rotating a homomixer under predetermined initial stirring conditions (stirring speed: 6000 rpm, stirring time: 2 minutes), and then the reaction was carried out for 24 hours while stirring at 80 rpm and heating to 60°C. The solid obtained by filtering the reaction solution after the reaction was left at room temperature under a nitrogen atmosphere for one week to obtain thermally expandable microspheres. The obtained thermally expandable microspheres were measured using a Shimadzu Corporation product name "SALD-2000J" and found to have an average particle size of 12.5 μm. Furthermore, X-ray CT (ZEISS Xradia520versa (measurement conditions: tube voltage 60KV, tube current 83μA, pixel size 0.20μm / pixel)) revealed that the solvent within the thermally expandable microspheres was isobutane, present at 13% by weight relative to the weight of the thermally expandable microspheres. The same X-ray CT measurement also revealed that the shell thickness of the thermally expandable microspheres was 2.8 μm.

[0082] [Production examples 2-11] Thermally expandable microspheres B-K Except for the amounts of colloidal silica, oil-based additives (acrylonitrile, methacryloylnitrile, isovonyl methacrylate, methyl methacrylate, vinylidene chloride), organic solvents intended to be encapsulated in the shell (isobutane, isopentane (boiling point: 27.7°C), petroleum ether, isooctane (boiling point: 99°C)), and initial stirring conditions during polymerization, the thermally expandable microspheres B to K were prepared in the same manner as in Production Example 1. The average particle size, amount of organic solvent contained, and shell thickness of the thermally expandable microspheres were also measured in the same manner as in Production Example 1. The results are shown in Table 1.

[0083] [Table 1]

[0084] [Example 1] A composition for forming an adhesive layer was prepared by mixing 100 parts by weight of an acrylic copolymer (a copolymer of ethyl acrylate (EA), methyl methacrylate (MMA), 2-ethylhexyl acrylate (2EHA), and 2-hydroxyethyl acrylate (HEA), where EA, MMA, 2EHA, and HEA components are in a ratio of 60:5:30:5 (weight ratio); weight-average molecular weight: 350,000; hydroxyl value: 24), 20 parts by weight of a tackifier (manufactured by Yasuhara Chemical Co., Ltd., trade name "YS Polysta S145"), 3 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 210 parts by weight of toluene. The weight-average molecular weight of the acrylic copolymer was measured by the method described in evaluation (1) above. The above adhesive layer-forming composition was applied to a PET film (thickness: 50 μm) used as a base material, and dried to obtain an adhesive tape (adhesive layer (thickness: 30 μm) / base material). The gel fraction of the adhesive was 85%. The obtained adhesive tapes were subjected to the evaluations (3) to (8) described above. The results are shown in Table 2.

[0085] [Examples 2-5, Comparative Examples 1-4] An adhesive tape was obtained in the same manner as in Example 1, except that the composition of the acrylic copolymer and the composition of the adhesive layer forming composition were as shown in Table 2. The obtained adhesive tape was subjected to the evaluations (3) to (8) described above. The results are shown in Table 2. In Table 2, "crosslinking agent Tetrad C" is an epoxy crosslinking agent manufactured by Mitsubishi Gas Chemical Company (trade name "Tetrad C"), "DPHA" is dipentaerythritol hexaacrylate (manufactured by Shin Nakamura Kogyo Kagaku Co., Ltd.), and "Irgacure 184" is a photoinitiator manufactured by BASF Japan Ltd. (trade name "Irgacure 184").

[0086] [Table 2] [Explanation of Symbols]

[0087] 10 Adhesive layer 20 Base material 100 Adhesive Tapes

Claims

1. An adhesive tape comprising a base material and an adhesive layer disposed on at least one surface of the base material, The adhesive layer comprises an acrylic adhesive and thermally expandable microspheres. The elastic modulus of the adhesive layer, determined by nanoindentation, is 0.8 MPa to 50 MPa. The thermally expandable microsphere is composed of a shell formed from resin and an organic solvent contained within the shell. The thickness of the shell is 1 μm to 15 μm. The resin forming the shell contains at least one selected from the group consisting of constituent units derived from isobornyl (meth)acrylate, methacrylonitrile, acrylonitrile, methyl (meth)acrylate, vinylidene chloride, and (meth)acrylic acid. In a thermomechanical analysis of the adhesive tape, when heated at a heating rate of 3°C / min, the point where deformation begins is defined as point A, the point where the deformation of the adhesive tape is at its maximum after passing point A is defined as point C, and the point between point A and C where the deformation is half the deformation at point C is defined as point B. The time it takes to travel from point A to point B is between 45 seconds and 200 seconds. Adhesive tape.

2. The adhesive tape according to claim 1, wherein the time taken from point B to point C is 200 seconds or more.

3. The adhesive tape according to claim 1 or 2, wherein the temperature at point B is 50°C to 250°C.

4. The adhesive tape according to any one of claims 1 to 3, wherein the glass transition temperature of the resin is 50°C to 250°C.

5. The adhesive tape according to any one of claims 1 to 4, wherein the boiling point of the organic solvent is -50°C to 100°C.

6. The adhesive tape according to any one of claims 1 to 5, wherein the gel fraction of the adhesive constituting the adhesive layer is 30% by weight to 99% by weight.

7. The adhesive tape according to any one of claims 1 to 6, wherein the absolute value of the difference between the boiling point (bp) of the organic solvent and the glass transition temperature (Tg) of the resin constituting the shell is 0°C to 150°C.

8. The adhesive tape according to any one of claims 1 to 7, wherein the thickness of the adhesive layer is 5 μm to 300 μm.

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