Adhesive tape and electronic device

Abstract

The purpose of the present invention is to provide an adhesive tape capable of achieving both excellent step followability and excellent rebound resistance. The purpose of the present invention is also to provide an electronic device comprising the adhesive tape. The present invention is an adhesive tape having an adhesive layer, wherein: the adhesive layer has a foamed structure; the adhesive layer contains an acrylic copolymer having a constituent unit derived from an alkyl (meth)acrylate; and the acrylic copolymer has at least one constituent unit selected from the group consisting of constituent units derived from n-hexyl (meth)acrylate, constituent units derived from n-heptyl (meth)acrylate, and constituent units derived from 1-methylheptyl (meth)acrylate.

Description

Adhesive tape, and electronic devices

[0001] This invention relates to an adhesive tape. Furthermore, this invention relates to an electronic device including the adhesive tape.

[0002] Adhesive tapes having an adhesive layer containing an adhesive have been widely used for fixing components in various industrial applications such as electronic equipment, vehicles, housing, and building materials (for example, Patent Documents 1 to 3). Specifically, for example, adhesive tapes are used to adhere a cover panel for protecting the surface of portable electronic devices to a touch panel module or display panel module, or to adhere a touch panel module to a display panel module.

[0003] Japanese Patent Publication No. 2015-052050, Japanese Patent Publication No. 2015-021067, Japanese Patent Publication No. 2015-120876

[0004] In recent years, the shapes of objects to be bonded with adhesive tape have become more complex, with an increasing number of objects having steps or uneven surfaces. Adhesive tapes used to bond such objects with steps or uneven surfaces are required to have excellent step-following ability (the ability to conform to the steps) and durability against the repulsive force generated during bonding (rebound resistance). In conventional adhesive tapes, methods to improve step-following ability include softening the adhesive layer or creating a foamed structure, but such adhesive tapes have poor rebound resistance. On the other hand, adhesive tapes with high rebound resistance have a hard adhesive layer, resulting in a decrease in step-following ability. Therefore, it has been difficult to achieve both step-following ability and rebound resistance in adhesive tapes.

[0005] The present invention aims to provide an adhesive tape that can achieve both excellent step-following ability and excellent rebound resistance. Furthermore, the present invention aims to provide an electronic device containing the adhesive tape.

[0006] Disclosure 1 is an adhesive tape having an adhesive layer, wherein the adhesive layer has a foamed structure, and the adhesive layer contains an acrylic copolymer having constituent units derived from an alkyl (meth)acrylate, and the acrylic copolymer has at least one constituent unit selected from the group consisting of constituent units derived from n-hexyl (meth)acrylate, constituent units derived from n-heptyl (meth)acrylate, and constituent units derived from 1-methylheptyl (meth)acrylate. Disclosure 2 is the adhesive tape of Disclosure 1, wherein the total content ratio of constituent units derived from n-hexyl (meth)acrylate, constituent units derived from n-heptyl (meth)acrylate, and constituent units derived from 1-methylheptyl (meth)acrylate to the constituent units derived from the alkyl (meth)acrylate is 30% by mass or more. Disclosure 3 is the adhesive tape of Disclosure 1 or 2, wherein the acrylic copolymer further has constituent units derived from isobornyl (meth)acrylate. Disclosure 4 is an adhesive tape according to Disclosure 1, 2, or 3, wherein the acrylic copolymer has structural units derived from monomers having crosslinkable functional groups. Disclosure 5 is an adhesive tape according to Disclosure 1, 2, 3, or 4, wherein the acrylic copolymer has structural units derived from olefin polymers having polymerizable unsaturated double bonds at their ends. Disclosure 6 is an adhesive tape according to Disclosure 5, wherein the content of structural units derived from olefin polymers having polymerizable unsaturated double bonds at their ends in the acrylic copolymer is 5% by mass or more and 50% by mass or less. Disclosure 7 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, or 6, comprising a block copolymer in which the acrylic copolymer has at least one block A having structural units derived from (meth)acrylate ester and at least one block B having structural units derived from vinyl aromatic compounds. Disclosure 8 is an adhesive tape according to Disclosure 7, wherein the content of structural units derived from vinyl aromatic compounds in the acrylic copolymer is 2.5% by mass or more and 20% by mass or less.Disclosure 9 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, or 8, wherein the adhesive layer contains an aromatic block copolymer (X) having at least two blocks having structural units derived from a vinyl aromatic compound, and at least one of a block having structural units derived from a conjugated diene compound and a hydrogenated form of a block having structural units derived from a conjugated diene compound. Disclosure 10 is an adhesive tape according to Disclosure 9, wherein the content of the aromatic block copolymer (X) is 60 parts by mass or less per 100 parts by mass of the acrylic copolymer. Disclosure 11 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the adhesive layer contains a pigment. Disclosure 12 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the adhesive layer contains a tackifying resin. Disclosure 13 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 in which the adhesive layer does not contain a tackifying resin. Disclosure 14 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 in which the adhesive layer has constituent units derived from a crosslinking agent. Disclosure 15 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 in which the adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less. Disclosure 16 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 in which the adhesive layer has a deemed density of 0.59 g / cm³. ３ 1.15g / cm or more ３The following are adhesive tapes according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. Disclosure 17 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the adhesive layer has a shear storage modulus of 0.30 MPa or more at 23°C as measured in a dynamic viscoelastic measurement at a measurement frequency of 1 Hz. Disclosure 18 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, wherein the adhesive layer has a shear storage modulus of 0.02 MPa or more at 65°C as measured in a dynamic viscoelastic measurement at a measurement frequency of 1 Hz. Disclosure 19 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, wherein the adhesive layer has a loss tangent of 0.5 or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 100 Hz. Disclosure 20 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19, wherein the adhesive layer has a bio-derived carbon content of 10% or more. Disclosure 21 is an adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, which does not have a base material. Disclosure 22 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 having a substrate. Disclosure 23 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22 having a 180° peel force of 10 N / 25 mm or more on SUS at 23°C. Disclosure 24 is an adhesive tape of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23 used to fix electronic equipment components or automotive components. Disclosure 25 is an electronic device that includes the adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24. The present invention will be described in detail below.Hereinafter, embodiments of the present invention or one thereof will be described as "this embodiment."

[0007] The present inventors investigated the use of a specific compound as a monomer for an adhesive tape having an adhesive layer containing an acrylic copolymer, wherein the adhesive layer has a foamed structure, and furthermore, the monomer has a constituent unit derived from the alkyl (meth)acrylate ester. As a result, they found that it is possible to obtain an adhesive tape that can achieve both excellent step-following ability and excellent rebound resistance, thus completing the present invention. In this specification, "(meth)acrylic" means acrylic or methacrylic.

[0008] The adhesive tape of this embodiment has an adhesive layer. The adhesive layer has a foamed structure. Because the adhesive layer has a foamed structure, the adhesive layer has excellent flexibility, and the adhesive tape of this embodiment has excellent ability to follow steps. In addition, because the adhesive layer has excellent stress relaxation properties, the resulting adhesive tape can be easily given excellent shock absorption.

[0009] Methods for forming a foamed structure in the adhesive layer include, for example, a method in which foaming particles are incorporated into the adhesive composition that forms the adhesive layer, and then the mixture is applied to a release film or the like and heated and dried to form the foamed structure; a method in which gas is forcibly mixed and dispersed into the adhesive composition that forms the adhesive layer to form the foamed structure; and a method in which liquefied gas is mixed into the adhesive composition that forms the adhesive layer to form the foamed structure. Among these, the method in which foaming particles are incorporated into the adhesive composition, and then the mixture is applied to a release film or the like and heated and dried to form the foamed structure is preferred, from the viewpoint that the bubbles formed in the adhesive layer are easily dispersed when the adhesive composition is dried at a high temperature, and the resulting adhesive tape has better step-following ability.

[0010] Examples of the foaming particles mentioned above include those that foam when heated, and may also be thermally expanded particles. Specifically, examples include thermally decomposed foaming agents and thermally expandable microcapsules, and among these, it is preferable that the foaming particles include thermally expandable microcapsules.

[0011] The above-mentioned heat-expandable microcapsules are particles in which a volatile substance such as a low-boiling point solvent is encapsulated inside an outer resin shell. When heated, the outer resin shell softens, and the encapsulated volatile substance volatilizes or expands. As a result, the outer shell expands due to the resulting pressure, increasing the particle size. Therefore, when heated, the heat-expandable microcapsules become hollow particles with air bubbles inside the outer shell. Consequently, in the adhesive layer, the inclusion of the heat-expandable microcapsules in the foaming particles prevents the gas generated from the foaming particles from escaping to the outside of the adhesive layer, making it easier to maintain an appropriate amount of air bubbles within the adhesive layer and thus improving the foaming ratio of the adhesive layer. As a result, the flexibility of the adhesive layer is further improved, and the resulting adhesive tape has superior ability to follow uneven surfaces.

[0012] The outer shell resin of the above-mentioned heat-expandable microcapsules is preferably a thermoplastic resin. Examples of the above-mentioned thermoplastic resin include one or more resins selected from vinyl polymers and copolymers thereof such as ethylene, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, butadiene, and chloroprene, polyamides such as nylon 6 and nylon 66, and polyesters such as polyethylene terephthalate. Among these, copolymers of acrylonitrile are preferred from the viewpoint that the encapsulated volatile substances do not easily permeate and the average particle size of the foamed particles, described later, can be adjusted to a suitable range.

[0013] Examples of volatile substances encapsulated inside the above-mentioned thermally expandable microcapsules include hydrocarbons with 3 to 7 carbon atoms such as propane, propylene, butene, n-butane, isobutane, isopentane, neopentane, n-pentane, hexane, and heptane; petroleum ethers; methane halogens such as methyl chloride and methylene chloride; and CCl ３ F, CCl ２ F ２ Examples include one or more low-boiling point liquids selected from chlorofluorocarbons, tetramethylsilanes, trimethylethylsilanes, and other tetraalkylsilanes. Among these, hydrocarbons having 3 to 7 carbon atoms are preferred.

[0014] Furthermore, the adhesive resin composition may already contain hollow particles as the foaming particles. By including hollow particles as foaming particles in the adhesive resin composition, it becomes easier to make the average diameter of the bubbles uniform compared to when an adhesive resin composition containing heat-expandable microcapsules is heated to form hollow particles in the adhesive layer. This improves the uniformity of the thickness of the adhesive layer, resulting in an adhesive tape with superior shock absorption.

[0015] Examples of hollow particles to be pre-included in the adhesive resin composition include particles produced by heating and expanding thermally expandable microcapsules, particles produced by the core-shell method, and particles produced by the bubble template method.

[0016] The average particle size of the foamed particles described above has a preferred lower limit of 15 μm and a preferred upper limit of 60 μm. Having the average particle size of the foamed particles within this range makes it easier to adjust the balance between the step-following ability and rebound resistance of the resulting adhesive tape. A more preferred lower limit for the average particle size of the foamed particles is 20 μm, a more preferred upper limit is 55 μm, an even more preferred lower limit is 25 μm, and an even more preferred upper limit is 50 μm. Examples of the average particle size of the foamed particles include 15 μm to 60 μm, 20 μm to 55 μm, 25 μm to 50 μm, etc. In this specification, the "average particle size of the foamed particles" refers to the average particle diameter of the foamed particles in an unfoamed state obtained by observing the adhesive composition containing the foamed particles. The average particle size of the foamed particles can also be obtained by randomly selecting particles using an optical microscope and calculating the average of 10 points.

[0017] Furthermore, the expansion initiation temperature of the foaming particles (also called the "foaming initiation temperature") is not particularly limited, but examples include a temperature range of 95°C to 150°C. The "expansion initiation temperature of foaming particles" refers to the temperature at which the foaming particles begin to expand, and can be measured using a thermomechanical analyzer (TMA) or the like.

[0018] Examples of commercially available foaming particles include Expancel 920DU40 (manufactured by Nippon Philite Co., Ltd., average particle size 40 μm), Expancel 920DU80 (manufactured by Nippon Philite Co., Ltd., average particle size 80 μm), EMC-20(B)R (manufactured by Nippon Philite Co., Ltd., average particle size 20 μm), and Advancel EML101 (manufactured by Sekisui Chemical Co., Ltd., average particle size 50 μm).

[0019] The above adhesive layer contains an acrylic copolymer. The above acrylic copolymer has constituent units derived from alkyl (meth)acrylate.

[0020] The above acrylic copolymer has at least one constituent unit selected from the group consisting of constituent units derived from the above alkyl (meth)acrylate, such as a constituent unit derived from n-hexyl (meth)acrylate, a constituent unit derived from n-heptyl (meth)acrylate, and a constituent unit derived from 1-methylheptyl (meth)acrylate (hereinafter, this may also be simply referred to as "constituent unit derived from alkyl (meth)acrylate (a)"). The presence of the above alkyl (meth)acrylate constituent unit in the above alkyl (meth)acrylate constituent unit gives the adhesive tape of this embodiment excellent rebound resistance. The above acrylic copolymer may have only one type of constituent unit derived from alkyl (meth)acrylate (a), or it may have two or more types.

[0021] The reason why the adhesive layer exhibits excellent step-following properties due to the presence of structural units derived from the (meth)acrylate alkyl ester (a) in the acrylic copolymer is unclear. However, the presence of structural units derived from the (meth)acrylate alkyl ester (a) in the acrylic copolymer allows the storage modulus in the rubbery flat region to remain relatively high even as the glass transition temperature of the acrylic copolymer decreases. As a result, the adhesive layer exhibits high flexibility while the stress generated in response to rebound is small, and it is presumed that the resulting adhesive tape will have excellent rebound resistance.

[0022] The total content of constituent units derived from the above-mentioned alkyl (meth)acrylate, n-hexyl (meth)acrylate, and 1-methylheptyl (meth)acrylate in relation to the above-mentioned alkyl (meth)acrylate (hereinafter sometimes simply referred to as "total content of constituent units derived from alkyl (meth)acrylate (a)") is preferably 30% by mass. When the total content of constituent units derived from alkyl (meth)acrylate (a) is 30% by mass or more, the resulting adhesive tape will have better rebound resistance. A more preferable lower limit for the total content of constituent units derived from alkyl (meth)acrylate (a) is 45% by mass, and an even more preferable lower limit is 70% by mass. Furthermore, a higher total content of constituent units derived from alkyl (meth)acrylate (a) is preferable, with 100% by mass being the most preferable. The total content percentage of constituent units derived from the above-mentioned alkyl (meth)acrylate (a) can be, for example, 30% by mass or more and 100% by mass or less, 45% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, etc.

[0023] The above acrylic copolymer preferably further contains a structural unit derived from isobornyl (meth)acrylate as a structural unit derived from the above alkyl (meth)acrylate. By including the structural unit derived from isobornyl (meth)acrylate in the structural unit derived from the above alkyl (meth)acrylate, the resulting adhesive tape will have superior rebound resistance. Furthermore, the resulting adhesive tape can be given superior bending resistance.

[0024] The content ratio of the structural unit derived from the above isobornyl (meth)acrylate in the structural unit derived from the above alkyl (meth)acrylate is preferably at least 1% by mass and preferably at most 60% by mass. When the content ratio of the structural unit derived from the above isobornyl (meth)acrylate is at least 1% by mass, the resulting adhesive tape has more excellent anti-rebound properties. Further, the resulting adhesive tape can impart more excellent bending resistance. When the content ratio of the structural unit derived from the above isobornyl (meth)acrylate is at most 60% by mass, the resulting adhesive tape has more excellent step-following properties. The more preferable lower limit of the content ratio of the structural unit derived from the above isobornyl (meth)acrylate is 5% by mass, the more preferable upper limit is 50% by mass, the further preferable lower limit is 8% by mass, the further preferable upper limit is 40% by mass, the still more preferable lower limit is 10% by mass, and the particularly preferable lower limit is 20% by mass. Note that examples of the content ratio of the structural unit derived from the above isobornyl (meth)acrylate include, for example, at least 1% by mass and at most 60% by mass, at least 5% by mass and at most 50% by mass, at least 8% by mass and at most 40% by mass, at least 10% by mass and at most 40% by mass, at least 20% by mass and at most 40% by mass, and the like.

[0025] The above acrylic copolymer may have, as the structural unit derived from the above alkyl (meth)acrylate, a structural unit derived from the above alkyl (meth)acrylate (a) and a structural unit derived from an alkyl (meth)acrylate (b) which is a structural unit other than the structural unit derived from the above isobornyl (meth)acrylate.

[0026] Examples of constituent units derived from the above alkyl (meth)acrylate (b) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, isohexyl (meth)acrylate, cyclohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ( Examples of constituent units derived from alkyl esters of (meth)acrylate include n-octyl meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, etc. Furthermore, if the above acrylic copolymer has constituent units derived from the above alkyl ester (b), it may have only one type of constituent unit derived from the above alkyl ester (b), or it may have two or more types.

[0027] In recent years, the depletion of petroleum resources and the emission of carbon dioxide from the combustion of petroleum-derived products have become serious concerns. Therefore, attempts are being made to conserve petroleum resources by using bio-derived materials instead of petroleum-derived materials. For this reason, the (meth)acrylate alkyl ester in the constituent unit derived from the above-mentioned alkyl (meth)acrylate ester may consist only of petroleum-derived materials, but it is preferable that it also contains bio-derived materials. The inclusion of bio-derived materials in the above-mentioned alkyl (meth)acrylate ester is preferable from the viewpoint of conserving petroleum resources, and furthermore, since bio-derived materials are originally produced by taking in carbon dioxide from the atmosphere, it is thought that burning them will not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the viewpoint of reducing carbon dioxide emissions.

[0028] When the (meth)acrylic acid alkyl ester in the structural unit derived from the above (meth)acrylic acid alkyl ester contains a bio-derived material, the (meth)acrylic acid alkyl ester is preferably synthesized by esterification of an alcohol that is a bio-derived material and (meth)acrylic acid.

[0029] In the above acrylic copolymer, the content ratio of the structural unit derived from the above (meth)acrylic acid alkyl ester has a preferable lower limit of 50% by mass and a preferable upper limit of 95% by mass. When the content ratio of the structural unit derived from the above (meth)acrylic acid alkyl ester is within the above range, the obtained adhesive tape can exhibit better step-following properties. A more preferable lower limit of the content ratio of the structural unit derived from the above (meth)acrylic acid alkyl ester is 60% by mass, a more preferable upper limit is 90% by mass, a further more preferable lower limit is 65% by mass, a further more preferable upper limit is 85% by mass, and an even more preferable upper limit is 80% by mass. In addition, examples of the content ratio of the structural unit derived from the above (meth)acrylic acid alkyl ester include 50% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, 65% by mass or more and 85% by mass or less, 65% by mass or more and 80% by mass or less, etc.

[0030] The above acrylic copolymer preferably has a structural unit derived from a monomer having a crosslinkable functional group. When the above acrylic copolymer has a structural unit derived from a monomer having a crosslinkable functional group, polar functional groups in the above acrylic copolymer interact with each other. Also, when the adhesive composition forming the above adhesive layer contains a crosslinking agent, the acrylic copolymer is chemically crosslinked via the crosslinking agent between molecules, so that a crosslinked structure can be sufficiently formed. As a result, the cohesive force of the above adhesive layer is further increased, and the above adhesive layer has sufficient adhesive strength and appropriate hardness, so that the obtained adhesive tape has better anti-rebound properties.

[0031] Examples of constituent units derived from monomers having the above-mentioned crosslinkable functional group include constituent units derived from carboxyl group-containing monomers, constituent units derived from hydroxyl group-containing monomers, constituent units derived from amide group-containing monomers, and constituent units derived from amino group-containing monomers. In particular, from the viewpoint of further increasing the cohesive force of the adhesive layer and enabling the resulting adhesive tape to have better rebound resistance, it is preferable that the constituent units derived from monomers having the above-mentioned crosslinkable functional group include at least one selected from the group consisting of constituent units derived from carboxyl group-containing monomers and constituent units derived from hydroxyl group-containing monomers.

[0032] Specific examples of constituent units derived from the above-mentioned carboxyl group-containing monomers include unsaturated monocarboxylic acids such as (meth)acrylic acid, (meth)acryloylacetic acid, (meth)acryloylpropionic acid, (meth)acryloylbutyric acid, (meth)acryloylpentanoic acid, and crotonic acid, as well as constituent units derived from unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Specific examples of constituent units derived from the above-mentioned hydroxyl group-containing monomers include constituent units derived from 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Specific examples of constituent units derived from the above-mentioned amide group-containing monomers include constituent units derived from N-vinyl-2-pyrrolidone, N,N-dimethyl(meth)acrylamide, and N-isopropyl(meth)acrylamide. Specific examples of constituent units derived from the above-mentioned amino group-containing monomers include constituent units derived from (meth)acryloylmorpholine, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. Furthermore, the constituent units derived from monomers having these crosslinkable functional groups may consist of only one type, or two or more types may coexist.

[0033] The monomer having the above-mentioned crosslinkable functional group preferably contains bio-derived materials, but may consist solely of petroleum-derived materials. Theoretically, it is also possible to use monomers that consist entirely of bio-derived materials as constituent units of the above-mentioned acrylic copolymer. From the viewpoint of cost and productivity of the adhesive layer, monomers containing relatively inexpensive and readily available bio-derived materials may be used, and these may be combined with monomers consisting solely of petroleum-derived materials.

[0034] In the above acrylic copolymer, the total content of constituent units derived from the monomer having the crosslinkable functional group is preferably 0.1% by mass at the lower limit and preferably 10% by mass at the upper limit. When the total content of constituent units derived from the monomer having the crosslinkable functional group is 0.1% by mass or more, the cohesive force of the adhesive layer is further increased, and the adhesive layer has sufficient adhesive strength and appropriate hardness, so the resulting adhesive tape has better rebound resistance. When the total content of constituent units derived from the monomer having the crosslinkable functional group is 10% by mass or less, the adhesive layer exhibits appropriate flexibility, so the resulting adhesive tape has better step-following ability. A more preferred lower limit for the total content of constituent units derived from the monomer having the above-mentioned crosslinkable functional group is 0.5% by mass, a more preferred upper limit is 9.0% by mass, an even more preferred lower limit is 1.0% by mass, an even more preferred upper limit is 8.0% by mass, an even more preferred lower limit is 3.0% by mass, a particularly preferred lower limit is 5.0% by mass, and a particularly preferred upper limit is 7.0% by mass. Examples of the total content of constituent units derived from the monomer having the above-mentioned crosslinkable functional group include 0.1% by mass or more and 10% by mass or less, 0.5% by mass or more and 9.0% by mass or less, 1.0% by mass or more and 8.0% by mass or less, 3.0% by mass or more and 8.0% by mass or less, 5.0% by mass or more and 7.0% by mass or less.

[0035] The above acrylic copolymer preferably has structural units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals. By making the above acrylic copolymer have structural units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals, the adhesive layer can achieve both better step-following ability and better rebound resistance.

[0036] The above acrylic copolymer has structural units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals, resulting in a structure in which structural units derived from alkyl (meth)acrylate ester are the main chain and structural units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals are the side chains. In this structure, the structural units derived from the olefin polymer having polymerizable unsaturated double bonds at its terminals, contained in the side chains of the acrylic copolymer, aggregate through interaction, forming a pseudo-crosslink. Therefore, when the strain is small, the cohesive force of the adhesive layer is increased by the above-mentioned pseudo-crosslink, and the adhesive layer has sufficient adhesive strength and appropriate hardness, resulting in an adhesive tape with superior rebound resistance. On the other hand, when the strain applied to the adhesive layer increases, the above-mentioned pseudo-crosslink breaks, and the molecules of the acrylic copolymer stretch, causing the adhesive layer to exhibit greater flexibility. As a result, the adhesive layer can adequately follow rough surfaces, and the adhesive tape with superior step-following ability is achieved.

[0037] Furthermore, as described above, because the acrylic copolymer has the structure described, the cohesive force of the adhesive layer increases when the strain is small, which makes it easier for the adhesive layer to have higher bending rigidity, and thus easier to impart excellent bending resistance to the resulting adhesive tape. Moreover, because the adhesive layer of the acrylic copolymer exhibits higher flexibility when the strain is large, the stress relaxation properties of the adhesive layer increase, and thus easier to impart excellent shock absorption to the resulting adhesive tape.

[0038] The olefin polymer having a polymerizable unsaturated double bond at one end may have a polymerizable unsaturated double bond at one end or at both ends. Among these, the olefin polymer having a polymerizable unsaturated double bond at one end is preferred from the viewpoint that intramolecular chemical crosslinking is less likely to occur, the cohesive force of the adhesive layer is further increased, and the resulting adhesive tape has better rebound resistance.

[0039] Examples of olefin polymers having a polymerizable unsaturated double bond at one or both ends include ethylene-butylene copolymers, ethylene-propylene copolymers, ethylene polymers, propylene polymers, and butene polymers, which have a group containing a polymerizable unsaturated carbon-carbon double bond at one or both ends. Examples of the group containing a polymerizable unsaturated carbon-carbon double bond include (meth)acryloyl groups, vinyl ether groups, and styryl groups. Among these, (meth)acryloyl groups are preferred because they exhibit excellent copolymerization with the alkyl (meth)acrylate esters. In this specification, "(meth)acryloyl" means acryloyl or methacryloyl.

[0040] Examples of olefin polymers having polymerizable unsaturated double bonds at their ends include ethylene macromonomers having a (meth)acryloyl group at one end, propylene macromonomers having a (meth)acryloyl group at one end, ethylene-butylene macromonomers having a (meth)acryloyl group at one end, and ethylene-propylene macromonomers having a (meth)acryloyl group at one end. Among these, ethylene-butylene macromonomers having a (meth)acryloyl group at one end and ethylene-propylene macromonomers having a (meth)acryloyl group at one end are preferred from the viewpoint of obtaining an adhesive tape with better step-following ability. These olefin polymers having polymerizable unsaturated double bonds at their ends may be used individually or in combination of two or more. In this specification, "macromonomer" refers to a monomer having polymerizable functional groups with a weight-average molecular weight of about 1,000 to 100,000.

[0041] In the above acrylic copolymer, the preferred lower limit of the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 5% by mass, and the preferred upper limit is 50% by mass. When the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 5% by mass or more, an appropriate number of pseudo-crosslinks are formed. As a result, the cohesive force of the adhesive layer is increased, and the adhesive layer has sufficient adhesive strength and appropriate hardness, so the resulting adhesive tape has better rebound resistance. When the content of constituent units derived from the olefin polymer having polymerizable unsaturated double bonds at its ends is 50% by mass or less, the adhesive layer exhibits higher flexibility, so the adhesive layer can follow rough surfaces well, and the resulting adhesive tape has better step-following ability. A more preferable lower limit for the content of constituent units derived from olefin polymers having polymerizable unsaturated double bonds at their ends is 8% by mass, a more preferable upper limit is 45% by mass, an even more preferable lower limit is 10% by mass, an even more preferable upper limit is 40% by mass, an even more preferable lower limit is 15% by mass, and an even more preferable upper limit is 30% by mass. Examples of the content of constituent units derived from olefin polymers having polymerizable unsaturated double bonds at their ends include 5% by mass or more and 50% by mass or less, 8% by mass or more and 45% by mass or less, 10% by mass or more and 40% by mass or less, 10% by mass or more and 30% by mass or less, 15% by mass or more and 30% by mass or less, etc.

[0042] The above-mentioned acrylic copolymer preferably has structural units derived from vinyl aromatic compounds. Having structural units derived from vinyl aromatic compounds in the acrylic copolymer results in an adhesive tape with superior rebound resistance.

[0043] Examples of constituent units derived from the vinyl aromatic compounds mentioned above include constituent units derived from styrene, constituent units derived from α-methylstyrene, and constituent units derived from their hydrogenated products. Among these, constituent units derived from styrene are preferred from the viewpoint of providing a superior balance between the ability to follow steps and the rebound resistance of the resulting adhesive tape. Note that the constituent units derived from these vinyl aromatic compounds may consist of only one type, or two or more types may coexist.

[0044] When the above acrylic copolymer has structural units derived from a vinyl aromatic compound, the above acrylic copolymer may be a random copolymer, or it may be a block copolymer having at least one block A having structural units derived from the (meth)acrylate alkyl ester and at least one block B having structural units derived from the vinyl aromatic compound. In particular, from the viewpoint of obtaining an adhesive tape with better rebound resistance, it is preferable that the above acrylic copolymer includes a block copolymer.

[0045] The block copolymer may be a diblock copolymer or a triblock copolymer. Among these, a triblock copolymer is preferred from the viewpoint of having a better balance between the step-following ability and rebound resistance of the resulting adhesive tape, and among triblock copolymers, a triblock copolymer having the structure of block B - block A - block B is more preferred.

[0046] In the above acrylic copolymer, the preferred lower limit for the content of constituent units derived from the vinyl aromatic compound is 2.5% by mass, and the preferred upper limit for the content of constituent units derived from the vinyl aromatic compound is 20% by mass. When the content of constituent units derived from the vinyl aromatic compound is 2.5% by mass or more, the resulting adhesive tape will have better rebound resistance. When the content of constituent units derived from the vinyl aromatic compound is 20% by mass or less, the resulting adhesive tape will have better step-following ability. A more preferred lower limit for the content of constituent units derived from the vinyl aromatic compound is 3.0% by mass, a more preferred upper limit is 18% by mass, an even more preferred lower limit is 3.5% by mass, an even more preferred upper limit is 15% by mass, an even more preferred lower limit is 4.5% by mass, an even more preferred upper limit is 12% by mass, a particularly preferred lower limit is 6.0% by mass, a particularly preferred upper limit is 10% by mass, and a particularly preferred upper limit is 8.0% by mass. Examples of the content ratio of constituent units derived from the vinyl aromatic compound in the above-mentioned acrylic copolymer include 2.5% by mass or more and 20% by mass or less, 3.0% by mass or more and 18% by mass or less, 3.5% by mass or more and 15% by mass or less, 4.5% by mass or more and 12% by mass or less, 6.0% by mass or more and 10% by mass or less, 6.0% by mass or more and 8.0% by mass or less, and so on.

[0047] The weight-average molecular weight (Mw) of the above acrylic copolymer has a preferred lower limit of 700,000 and a preferred upper limit of 1,500,000. A weight-average molecular weight (Mw) of 700,000 or more increases the cohesive force of the adhesive layer, resulting in a more superior rebound resistance of the resulting adhesive tape. A weight-average molecular weight (Mw) of 1,500,000 or less allows the adhesive layer to exhibit moderate flexibility, resulting in a more superior step-following ability of the resulting adhesive tape. A more preferred lower limit for the weight-average molecular weight (Mw) of the above acrylic copolymer is 800,000, a more preferred upper limit is 1,400,000, an even more preferred lower limit is 900,000, and an even more preferred upper limit is 1,300,000. Examples of weight-average molecular weight (Mw) of the above acrylic copolymer include 700,000 to 1,500,000, 800,000 to 1,400,000, and 900,000 to 1,300,000.

[0048] The polydispersity (weight-average molecular weight / number-average molecular weight, Mw / Mn) of the above acrylic copolymer has a preferred lower limit of 1.0 and a preferred upper limit of 8.0. When the polydispersity (Mw / Mn) of the above acrylic copolymer is within the above range, the adhesive layer has better rebound resistance and better step-following ability. A more preferred lower limit for the polydispersity (Mw / Mn) of the above acrylic copolymer is 1.5, a more preferred upper limit is 7.5, an even more preferred lower limit is 2.0, and an even more preferred upper limit is 7.0. Examples of polydispersity (Mw / Mn) values ​​for the above acrylic copolymer include 1.0 to 8.0, 1.5 to 7.5, and 2.0 to 7.0.

[0049] In this specification, "weight-average molecular weight" and "number-average molecular weight" refer to the weight-average molecular weight and number-average molecular weight measured as polystyrene-equivalent molecular weight by gel permeation chromatography (GPC). Specifically, the weight-average molecular weight, number-average molecular weight, and polydispersity of the above-mentioned acrylic copolymer can be measured using, for example, a Waters 2690 Separations Module as the measuring instrument, a Showa Denko GPC KF-806L as the column, and ethyl acetate as the solvent, under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0050] The preferred lower limit for the content of the acrylic copolymer in the adhesive layer is 30% by mass. A content of 30% by mass or more of the acrylic copolymer allows the resulting adhesive tape to achieve both superior step-following ability and superior rebound resistance. A more preferred lower limit for the content of the acrylic copolymer is 40% by mass, and an even more preferred lower limit is 45% by mass. Furthermore, the upper limit for the content of the acrylic copolymer is not particularly limited and may be 100% by mass. However, in order to further improve the step-following ability of the resulting adhesive tape, it is preferable that the adhesive layer has bubbles formed by foaming foamed particles; therefore, the preferred upper limit for the content of the acrylic copolymer is 99.5% by mass. Examples of the acrylic copolymer content include 30% by mass or more and 100% by mass or less, 40% by mass or more and 99.5% by mass or less, and 45% by mass or more and 99.5% by mass or less.

[0051] The polymerization method for synthesizing the above-mentioned acrylic copolymer can be a conventionally known method in which a mixture of monomer raw materials is subjected to a radical reaction in the presence of a polymerization initiator. Examples include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization is preferred because it is easy to synthesize.

[0052] When solution polymerization is used as the polymerization method described above, examples of reaction solvents include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, and diethyl ether. These reaction solvents may be used individually or in combination of two or more.

[0053] Examples of polymerization initiators include organic peroxides and azo compounds. Examples of organic peroxides include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of azo compounds include azobisisobutyronitrile and azobiscyclohexanecarbonilonitrile. These polymerization initiators may be used alone or in combination of two or more.

[0054] Furthermore, even when the acrylic copolymer is a block copolymer, the method for producing the block copolymer is not particularly limited, and conventionally known methods can be used. Specifically, for example, a vinyl aromatic compound may be added to block A, which has been synthesized in the same manner as the acrylic copolymer described above, and copolymerized. Alternatively, the previously synthesized block B and block A may be copolymerized.

[0055] Furthermore, if the block copolymer is a triblock copolymer having the structure of block B - block A - block B, the block copolymer can be obtained, for example, by living polymerization. Examples of living polymerization include living anionic polymerization and RAFT polymerization, but RAFT polymerization is particularly preferred. When producing the A-B-A type block copolymer by RAFT polymerization, block B is obtained using a chain transfer agent (RAFT agent), and then the constituent unit monomers of block A are polymerized or copolymerized in the presence of the obtained block B to produce the triblock copolymer.

[0056] Preferably, the adhesive layer contains an aromatic block copolymer (X) having at least two blocks having structural units derived from vinyl aromatic compounds (hereinafter sometimes simply referred to as "vinyl aromatic polymer blocks"), and at least one of a block having structural units derived from a conjugated diene compound (hereinafter sometimes simply referred to as "conjugated diene polymer blocks") and a hydrogenated product of a block having structural units derived from a conjugated diene compound (hereinafter sometimes simply referred to as "hydrogenated product of conjugated diene polymer blocks"). By containing the aromatic block copolymer (X) in the adhesive layer, the resulting adhesive tape can be provided with superior shock absorption.

[0057] The vinyl aromatic polymer block described above may be any block having 5% by mass or more of constituent units derived from a vinyl aromatic compound, and may also contain constituent units derived from other compounds such as ethylene and 1,3-butadiene (which is converted to an ethylene-butylene structure by hydrogenation). Examples of the vinyl aromatic compound described above include alkylstyrene, halogenated styrene, halogen-substituted alkylstyrene, alkoxystyrene, carboxyalkylstyrene, alkyl ether styrene, alkylsilyl styrene, vinyl benzyl dimethoxy phosphide, vinyl naphthalene, vinyl anthracene, N,N-diethyl-p-aminoethylstyrene, and vinylpyridine.

[0058] Examples of alkylstyrenes include styrene, methylstyrene, dimethylstyrene, and t-butylstyrene. Examples of halogenated styrenes include chlorostyrene, bromostyrene, and fluorostyrene. Examples of halogen-substituted alkylstyrenes include chloromethylstyrene. Examples of alkoxystyrenes include methoxystyrene and ethoxystyrene. Examples of carboxyalkylstyrenes include carboxymethylstyrene. Examples of alkyl ether styrenes include vinyl benzylpropyl ether. Examples of alkylsilyl styrenes include trimethylsilylstyrene. These vinyl aromatic compounds may be used individually or in combination of two or more. Among them, styrene, methylstyrene, and dimethylstyrene are preferred, and styrene is more preferred because it is readily available industrially.

[0059] The preferred lower limit for the content of constituent units derived from the vinyl aromatic compound in the vinyl aromatic polymer block is 7% by mass. Having 7% or more of constituent units derived from the vinyl aromatic compound provides the resulting adhesive tape with excellent bending resistance. A more preferred lower limit for the constituent units derived from the vinyl aromatic compound is 10% by mass. Furthermore, from the viewpoint of the adhesive layer having sufficient adhesive strength, the preferred upper limit for the constituent units derived from the vinyl aromatic compound in the vinyl aromatic polymer block is 35% by mass, and a more preferred upper limit is 30% by mass. Examples of the content of constituent units derived from the vinyl aromatic compound in the vinyl aromatic polymer block include 7% to 35% by mass, 10% to 30% by mass, and so on.

[0060] Examples of the above-mentioned conjugated diene compounds include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-octadiene, 1,3-hexadiene, 1,3-cyclohexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, myrcene, and chloroprene. These conjugated diene compounds may be used individually or in combination of two or more. Among these, 1,3-butadiene and isoprene are preferred due to their high polymerization reactivity and ease of industrial availability. In addition to the above-mentioned conjugated diene compounds, other usable compounds include, for example, 2,5-dihydrofuran-2,5-dione.

[0061] The hydrogenated product of the above-mentioned conjugated diene polymer block refers to a block in which the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound are converted to saturated bonds by hydrogenation. From the viewpoint of preventing degradation due to heat, ultraviolet rays, etc., it is preferable that 80% or more of the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound of the aromatic block copolymer (X) are converted to saturated bonds by hydrogenation, more preferably 90% or more, even more preferably 95% or more, and even more preferably 96% or more. Furthermore, it is most preferable that 100% are converted to saturated bonds by hydrogenation (i.e., a fully hydrogenated product). That is, it is preferable that 80% to 100% of the carbon-carbon double bonds (unsaturated bonds) in the constituent units derived from the above-mentioned conjugated diene compound are converted to saturated bonds by hydrogenation, more preferably 90% to 100%, even more preferably 95% to 100%, and even more preferably 96% to 100%.

[0062] The preferred lower limit for the content of constituent units derived from the conjugated diene compound in the above-mentioned conjugated diene polymer block is 80% by mass. A content of 80% by mass or more of constituent units derived from the conjugated diene compound ensures that the adhesive layer has sufficient adhesive strength, resulting in an adhesive tape with superior rebound resistance. Furthermore, the resulting adhesive tape will have superior step-following ability. A more preferred lower limit for the constituent units derived from the conjugated diene compound is 90% by mass, and an even more preferred lower limit is 95% by mass. There is no particular upper limit for the constituent units derived from the conjugated diene compound, but it may be 100% by mass. Examples of the content of constituent units derived from the conjugated diene compound in the above-mentioned conjugated diene polymer block include 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, and 95% by mass or more and 100% by mass or less.

[0063] Examples of the structure of the above aromatic block copolymer (X) include, when the vinyl aromatic polymer block is B and the conjugated diene polymer block and the hydrogenated product of the conjugated diene polymer block are C, a triblock copolymer represented by formula B-C-B, a diblock copolymer represented by formula B-C, a pentablock copolymer represented by formula C-B-C-B-C, and the like.

[0064] Examples of aromatic block copolymers (X) having the structure represented by the above formula B-C-B include styrene-isoprene-styrene (SIS) block copolymer, styrene-butylene-styrene (SBS) block copolymer, styrene-ethylene-butylene-styrene (SEBS) block copolymer, styrene-ethylene-propylene-styrene (SEPS) block copolymer, styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymer, styrene-isobutylene-styrene (SIBS) block copolymer, and ethylene-styrene-butylene block copolymer. Among these, SIS block copolymer and SEBS block copolymer are preferred from the viewpoint of compatibility with acrylic copolymers.

[0065] The preferred lower limit for the weight-average molecular weight (Mw) of the aromatic block copolymer (X) is 50,000. A weight-average molecular weight (Mw) of 50,000 or more allows the resulting adhesive tape to exhibit excellent shock absorption. A more preferred lower limit for the weight-average molecular weight of the aromatic block copolymer (X) is 100,000, and an even more preferred lower limit is 150,000. While there is no particular preferred upper limit for the weight-average molecular weight of the aromatic block copolymer (X), from the viewpoint of compatibility with acrylic copolymers, it is practically limited to around 500,000. Examples of weight-average molecular weight (Mw) of the aromatic block copolymer (X) include 50,000 to 500,000, 100,000 to 500,000, and 150,000 to 500,000.

[0066] A preferred upper limit for the content of the aromatic block copolymer (X) per 100 parts by mass of the acrylic copolymer is 60 parts by mass. When the content of the aromatic block copolymer (X) is 60 parts by mass or less, the adhesive layer will have sufficient adhesive strength, resulting in an adhesive tape with superior rebound resistance. Furthermore, the resulting adhesive tape will have superior step-following ability. A more preferred upper limit for the content of the aromatic block copolymer (X) is 55 parts by mass, an even more preferred upper limit is 50 parts by mass, and an even more preferred upper limit is 45 parts by mass. A preferred lower limit for the content of the aromatic block copolymer (X) is 10 parts by mass. When the content of the aromatic block copolymer (X) is 10 parts by mass or more, the resulting adhesive tape will have superior step-following ability. Furthermore, the resulting adhesive tape can be given superior shock absorption. A more preferred lower limit for the content of the aromatic block copolymer (X) is 15 parts by mass, an even more preferred lower limit is 20 parts by mass, and an even more preferred lower limit is 30 parts by mass. Examples of the content of the aromatic block copolymer (X) include 10 parts by mass or more and 60 parts by mass or less, 15 parts by mass or more and 55 parts by mass or less, 20 parts by mass or more and 50 parts by mass or less, 30 parts by mass or more and 45 parts by mass or less.

[0067] The adhesive layer may be colored. When the adhesive layer is colored, it can be given light-shielding properties, which prevents light from leaking from the adhesive interface and thus prevents light and ultraviolet rays from irradiating the adherends to be bonded using the adhesive layer, thereby suppressing degradation of the adherends due to light and ultraviolet rays. Therefore, the adhesive layer can be used more suitably for bonding electronic components.

[0068] If the adhesive layer is colored, the adhesive layer contains a coloring agent. Examples of the coloring agent include pigments and dyes. Among these, pigments are preferred from the viewpoint of superior heat resistance. Examples of the pigment include carbon black, aniline black, and titanium dioxide. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable. Examples of the dye include azo dyes, anthraquinone dyes, and indigo dyes.

[0069] The preferred upper limit of the coloring agent content per 100 parts by mass of the acrylic copolymer is 5.0 parts by mass. A coloring agent content of 5.0 parts by mass or less ensures that the adhesive layer has sufficient adhesive strength, resulting in a more superior rebound resistance for the resulting adhesive tape. A more preferred upper limit for the coloring agent content is 4.0 parts by mass, an even more preferred upper limit is 3.5 parts by mass, and an even more preferred upper limit is 3.0 parts by mass. Furthermore, a preferred lower limit for the coloring agent content is 0.2 parts by mass. A coloring agent content of 0.2 parts by mass or more provides sufficient light-shielding properties to the resulting adhesive tape. A more preferred lower limit for the coloring agent content is 0.5 parts by mass, an even more preferred lower limit is 0.8 parts by mass, and an even more preferred lower limit is 1.0 part by mass. Examples of the coloring agent content include 0.2 parts by mass or more and 5.0 parts by mass or less, 0.5 parts by mass or more and 4.0 parts by mass or less, 0.8 parts by mass or more and 3.5 parts by mass or less, 1.0 part by mass or more and 3.0 parts by mass or less.

[0070] The adhesive layer may or may not contain a tackifying resin. When the adhesive layer contains a tackifying resin, it will have sufficient adhesive strength, resulting in a more resilient adhesive tape. On the other hand, when the adhesive layer does not contain a tackifying resin, the resulting adhesive tape will have superior shock absorption.

[0071] When the adhesive layer contains the tackifying resin, examples of the tackifying resin include rosin resins, rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5-C9 copolymer petroleum resins. Among these, rosin ester resins or terpene phenol resins are preferred from the viewpoint of compatibility with the acrylic copolymer, and among these, rosin ester resins or terpene phenol resins having hydroxyl groups are more preferred. These tackifying resins may be used alone or in combination of two or more.

[0072] Examples of rosin ester resins having the hydroxyl group mentioned above include Pencel D-135 and Super Ester A-75 (both manufactured by Arakawa Chemical Industries, Ltd.). Examples of terpene phenol resins include YS Polystar G150 and YS Polystar T160 (both manufactured by Yasuhara Chemical Co., Ltd.).

[0073] If the adhesive layer contains the tackifying resin, it is preferable that the tackifying resin contains bio-derived carbon. By including a bio-derived carbon in the tackifying resin, the content of bio-derived carbon in the adhesive layer described later can be increased, and the environmental burden of the adhesive tape can be further reduced. Specific examples of bio-derived carbon-containing tackifying resins include Pine Crystal KE-100, Pine Crystal KE-359, Pine Crystal KE-604, Pine Crystal KR-140, Super Ester A-75 (all rosin ester resins, manufactured by Arakawa Chemical Industries, Ltd.), Tamanol 803L (terpene phenol resin, manufactured by Arakawa Chemical Industries, Ltd.), and the like.

[0074] If the adhesive layer contains the tackifying resin, it is preferable that the tackifying resin has a softening point of 70°C or higher and 170°C or lower. By including a tackifying resin with a softening point of 70°C or higher, the resulting adhesive tape will have better rebound resistance. By including a tackifying resin with a softening point of 170°C or lower, the wettability of the interface of the adhesive layer is improved, and sufficient adhesive strength is obtained, resulting in an adhesive tape with better rebound resistance. It is more preferable that the tackifying resin contains a tackifying resin with a softening point of 100°C or higher and 160°C or lower, even more preferable that it contains a tackifying resin with a softening point of 120°C or higher and 150°C or lower, and even more preferable that it contains a tackifying resin with a softening point of 130°C or higher and 140°C or lower. In this specification, "softening point of tackifying resin" means the softening temperature measured by JIS K2207 (ring-ball method).

[0075] If the adhesive layer contains the tackifying resin, it is preferable that the tackifying resin has a hydroxyl value of 25 mg KOH / g or more. By including a tackifying resin with a hydroxyl value of 25 mg KOH / g or more, the wettability of the interface of the adhesive layer is improved, and sufficient adhesive strength is achieved, resulting in an adhesive tape with superior rebound resistance. It is more preferable that the tackifying resin includes a tackifying resin with a hydroxyl value of 30 mg KOH / g or more, and even more preferable that it includes a tackifying resin with a hydroxyl value of 35 mg KOH / g or more. There is no particular upper limit to the hydroxyl value of the tackifying resin, but from the viewpoint of compatibility with the aromatic block copolymer (X), a preferred upper limit is 200 mg KOH / g. Examples of hydroxyl values ​​for the tackifying resin include 25 mg KOH / g to 200 mg KOH / g, 30 mg KOH / g to 200 mg KOH / g, and 35 mg KOH / g to 200 mg KOH / g. In this specification, the hydroxyl value of the tackifying resin can be measured by JIS K1557 (phthalic anhydride method).

[0076] When the adhesive layer contains the tackifying resin, the preferred upper limit of the tackifying resin content per 100 parts by mass of the acrylic copolymer is 50 parts by mass. By having a tackifying resin content of 50 parts by mass or less, the adhesive layer does not become too hard, and the adhesive layer has sufficient adhesive strength, resulting in an adhesive tape with superior rebound resistance. A more preferred upper limit for the tackifying resin content is 40 parts by mass, an even more preferred upper limit is 30 parts by mass, an even more preferred upper limit is 20 parts by mass, and a particularly preferred upper limit is 10 parts by mass. When the adhesive layer contains the tackifying resin, from the viewpoint of the resulting adhesive tape having superior rebound resistance, a preferred lower limit for the tackifying resin content is 0.1 parts by mass, and a more preferred lower limit is 1.0 part by mass. As stated above, the adhesive layer does not necessarily have to contain the tackifying resin, and from the viewpoint of providing the resulting adhesive tape with superior shock absorption, it is preferable that the adhesive layer does not contain the tackifying resin. Furthermore, examples of the content of the tackifying resin include 0 parts by mass or more and 50 parts by mass or less, 0.1 parts by mass or more and 50 parts by mass or less, 0.1 parts by mass or more and 40 parts by mass or less, 0.1 parts by mass or more and 30 parts by mass or less, 0.1 parts by mass or more and 20 parts by mass or less, 1.0 part by mass or more and 10 parts by mass or less, and so on.

[0077] Preferably, the adhesive layer has a structure derived from a crosslinking agent. Having a structure derived from a crosslinking agent in the adhesive layer increases its cohesive force, resulting in an adhesive layer with sufficient adhesive strength and appropriate hardness, thus providing the resulting adhesive tape with superior rebound resistance. A method for providing an adhesive layer with a structure derived from a crosslinking agent includes, for example, applying an adhesive composition containing a crosslinking agent to a release film, and then heating and drying the adhesive composition.

[0078] The above adhesive composition preferably contains a crosslinking agent. The inclusion of a crosslinking agent in the adhesive composition results in the adhesive layer having a structure derived from the crosslinking agent. Therefore, the cohesive force of the adhesive layer is increased, and this increased cohesive force results in the adhesive layer having sufficient adhesive strength and appropriate hardness, thus the resulting adhesive tape having superior rebound resistance. From the viewpoint of storage stability, the crosslinking agent may be added to the adhesive composition immediately before forming the adhesive layer described later.

[0079] Examples of the crosslinking agents include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred from the viewpoint of ensuring that the adhesive layer has sufficient adhesive strength.

[0080] The preferred lower limit of the crosslinking agent content per 100 parts by mass of the acrylic copolymer is 0.05 parts by mass, and the preferred upper limit is 5.0 parts by mass. When the crosslinking agent content is within this range, the resulting adhesive tape will have superior rebound resistance and superior step-following ability. A more preferred lower limit for the crosslinking agent content is 0.10 parts by mass, a more preferred upper limit is 3.0 parts by mass, an even more preferred lower limit is 0.15 parts by mass, an even more preferred upper limit is 2.0 parts by mass, an even more preferred upper limit is 1.0 part by mass, and a particularly preferred upper limit is 0.5 parts by mass. Examples of crosslinking agent content include 0.05 parts by mass or more and 5.0 parts by mass or less, 0.10 parts by mass or more and 3.0 parts by mass or less, 0.15 parts by mass or more and 2.0 parts by mass or less, 0.15 parts by mass or more and 1.0 part by mass or less, 0.15 parts by mass or more and 0.5 parts by mass or less.

[0081] From the viewpoint of preventing aging of the adhesive composition, it is preferable that the above adhesive composition contains an antioxidant (anti-aging agent).

[0082] Examples of the above-mentioned antioxidants include phenolic antioxidants, amine antioxidants, benzotriazole antioxidants, benzophenone antioxidants, and HALS (hindered amine light stabilizers). Among these, phenolic antioxidants and amine antioxidants are preferred from the viewpoint of being able to better prevent the oxidation of polymerizable unsaturated hydrocarbons contained in the above-mentioned acrylic copolymers, etc.

[0083] The preferred lower limit of the antioxidant content per 100 parts by mass of the acrylic copolymer is 0.01 parts by mass, and the preferred upper limit is 5 parts by mass. By keeping the antioxidant content within the above range, the adhesive layer can maintain its adhesive strength without deterioration even when stored for a long period of time. A more preferred lower limit for the antioxidant content is 0.1 parts by mass, a more preferred upper limit is 3 parts by mass, an even more preferred lower limit is 0.5 parts by mass, and an even more preferred upper limit is 1 part by mass. Examples of antioxidant content include 0.01 parts by mass or more and 5 parts by mass or less, 0.1 parts by mass or more and 3 parts by mass or less, 0.5 parts by mass or more and 1 part by mass or less, etc.

[0084] The adhesive layer described above may, if necessary, contain conventionally known additives such as thickeners, softeners, organic fillers, and inorganic fillers, as long as they do not impair the effects of the present invention.

[0085] The preferred lower limit for the gel fraction of the adhesive layer is 10% by mass, and the preferred upper limit is 70% by mass. When the gel fraction of the adhesive layer is 10% by mass or more, the cohesive force of the adhesive layer is increased, resulting in the adhesive layer having sufficient adhesive strength and appropriate hardness, and thus the resulting adhesive tape having better rebound resistance. When the gel fraction of the adhesive layer is 70% by mass or less, the flexibility of the adhesive layer is further improved, resulting in improved step-following ability of the resulting adhesive tape. A more preferred lower limit for the gel fraction of the adhesive layer is 20% by mass, a more preferred upper limit is 60% by mass, an even more preferred lower limit is 30% by mass, and an even more preferred upper limit is 50% by mass. Examples of the gel fraction of the adhesive layer include 10% by mass or more and 70% by mass or less, 20% by mass or more and 60% by mass or less, 30% by mass or more and 50% by mass or less, etc.

[0086] The gel fraction of the above adhesive layer is measured by the following method. That is, first, an adhesive tape having the above adhesive layer is cut into a flat rectangular shape with a width of 20 mm and a length of 40 mm to prepare a test piece. After immersing the test piece in ethyl acetate at 23 °C for 24 hours, it is taken out from ethyl acetate and dried at 110 °C for 1 hour. The mass of the dried test piece is measured, and the gel fraction is calculated using the following formula (I). Note that the release film for protecting the above adhesive layer is not laminated on the test piece. Also, when the above adhesive tape is a non-support type adhesive tape having no base material, the measurement is performed using a test piece obtained by cutting after pasting on the base material, or W in the following formula (I) is set to 0 for calculation. Gel fraction (mass%) = 100×(W ０ −W ２ ) / (W ０ −W １ ) (I) (W ０ : mass of the base material, W ０ : mass of the test piece before immersion, W １ : mass of the test piece after immersion and drying) ２

[0087] As a method for adjusting the gel fraction of the above adhesive layer, for example, a method of adjusting the type and content ratio of the structural units derived from the monomers having crosslinkable functional groups contained in the acrylic copolymer in the above adhesive layer, a method of adjusting the type and content of the crosslinking agent contained in the above adhesive layer, a method of adjusting the illuminance and irradiation time of the electron beam or ultraviolet ray used when performing electron beam irradiation or ultraviolet ray irradiation to form the above adhesive layer, etc. can be mentioned.

[0088] The foam structure in the adhesive layer may be an open-cell structure or a closed-cell structure, but a closed-cell structure is preferred. Having a closed-cell structure in the adhesive layer makes it less susceptible to cohesive failure and improves adhesive strength, resulting in a more repulsive adhesive tape. In this specification, an open-cell structure is defined as one where the air layers between cells are partially continuous when the tape cross-section is randomly observed, and a closed-cell structure is defined as one where the air layers between cells are not continuous. The cell structure in the adhesive layer can be confirmed, for example, by observing it at a magnification of 150 to 200 times using an optical microscope (e.g., Keyence's "VHX-6000").

[0089] The deemed density of the above adhesive layer has a preferred lower limit of 0.59 g / cm³. ３ Therefore, a preferred upper limit is 1.15 g / cm³. ３ The assumed density of the adhesive layer is 0.59 g / cm³. ３ As a result of the above, the adhesive layer is less prone to cohesive failure, and the adhesive strength is improved, so the resulting adhesive tape has superior resistance to rebound. The deemed density of the above adhesive layer is 1.15 g / cm³. ３ The following conditions improve the stress relaxation properties of the adhesive layer, resulting in a more superior shock absorption property for the resulting adhesive tape. A more preferable lower limit for the deemed density of the adhesive layer is 0.65 g / cm³. ３ A more preferable upper limit is 1.05 g / cm³. ３ A more preferable lower limit is 0.70 g / cm³. ３ A more preferable upper limit is 1.00 g / cm³. ３ A more preferable lower limit is 0.80 g / cm³. ３ The deemed density of the adhesive layer is, for example, 0.59 g / cm³. ３ 1.15g / cm or more ３ Below, 0.65g / cm ３ 1.05g / cm or more ３ Below, 0.70g / cm ３ 1.00g / cm or more ３ Below, 0.80g / cm ３ 1.00g / cm or more３ The following are some examples.

[0090] The deemed density of the adhesive layer described above can be measured using an electronic hydrometer (for example, Mirage's "ED120T") in accordance with JIS K 7222 or similar standards.

[0091] The average major diameter of the bubbles in the adhesive layer has a preferred lower limit of 10 μm and a preferred upper limit of 80 μm. When the average major diameter of the bubbles in the adhesive layer is 10 μm or more, the stress relaxation properties of the adhesive layer are further improved, and the resulting adhesive tape can be given superior shock absorption. When the average major diameter of the bubbles in the adhesive layer is 80 μm or less, the adhesive layer is less prone to cohesive failure and the adhesive strength is further improved, resulting in an adhesive tape with superior rebound resistance. A more preferred lower limit for the average major diameter of the bubbles in the adhesive layer is 15 μm, a more preferred upper limit is 70 μm, an even more preferred lower limit is 20 μm, an even more preferred upper limit is 65 μm, an even more preferred upper limit is 60 μm, a particularly preferred upper limit is 55 μm, and a very preferred upper limit is 50 μm. The average major diameter of the bubbles in the adhesive layer can be, for example, 10 μm to 80 μm, 15 μm to 70 μm, 20 μm to 65 μm, 20 μm to 60 μm, 20 μm to 55 μm, 20 μm to 50 μm, etc.

[0092] The average minor diameter of the bubbles in the adhesive layer has a preferred lower limit of 10 μm and a preferred upper limit of 75 μm. A more preferable lower limit for the average minor diameter of the bubbles in the adhesive layer is 10 μm or more, which further improves the stress relaxation properties of the adhesive layer, thus providing superior shock absorption to the resulting adhesive tape. A more preferable upper limit for the average minor diameter of the bubbles in the adhesive layer is 75 μm or less, which makes the adhesive layer less susceptible to cohesive failure and improves its adhesive strength, resulting in a more resilient adhesive tape. Furthermore, an increase in the tensile strength of the adhesive layer further suppresses cohesive failure, resulting in improved adhesive strength in the resulting adhesive tape. A more preferable lower limit for the average minor diameter of the bubbles in the adhesive layer is 15 μm, a more preferable upper limit is 70 μm, an even more preferable lower limit is 20 μm, an even more preferable upper limit is 65 μm, an even more preferable upper limit is 60 μm, a particularly preferable upper limit is 55 μm, and a very preferable upper limit is 50 μm. The average short diameter of the bubbles in the adhesive layer can be, for example, 10 μm to 75 μm, 15 μm to 70 μm, 20 μm to 65 μm, 20 μm to 60 μm, 20 μm to 55 μm, 20 μm to 50 μm, etc.

[0093] The aspect ratio of the bubbles in the adhesive layer described above has a preferred lower limit of 1.00 and a preferred upper limit of 3.50. When the aspect ratio of the bubbles in the adhesive layer described above is 1.00 or higher, the structure of the bubbles in the adhesive layer becomes flattened, and the stress relaxation properties of the adhesive layer are further improved, so that the resulting adhesive tape can be given superior shock absorption. When the aspect ratio of the bubbles in the adhesive layer described above is 3.50 or lower, the adhesive layer is less prone to cohesive failure and the adhesive strength is further improved, so the resulting adhesive tape has superior rebound resistance. A more preferred lower limit for the aspect ratio of the bubbles in the adhesive layer described above is 1.25, a more preferred upper limit is 3.00, an even more preferred lower limit is 1.50, and an even more preferred upper limit is 2.50. Examples of aspect ratios for the bubbles in the adhesive layer described above include 1.00 to 3.50, 1.25 to 3.00, 1.50 to 2.50, etc. Furthermore, in this specification, "bubble aspect ratio" means the value obtained by dividing the average major diameter of the bubble by the average minor diameter of the bubble (average major diameter of bubble / average minor diameter of bubble).

[0094] It is preferable that the average major diameter of the bubbles in the adhesive layer is 0.80 times or less the thickness of the adhesive layer. When the average major diameter of the bubbles in the adhesive layer is 0.80 times or less the thickness of the adhesive layer, the adhesive layer is less prone to cohesive failure and the adhesive strength is further improved, resulting in an adhesive tape with superior rebound resistance. It is more preferable that the average major diameter of the bubbles in the adhesive layer is 0.70 times or less the thickness of the adhesive layer, even more preferable that it is 0.60 times or less, and even more preferable that it is 0.30 times or less. It is also preferable that the average major diameter of the bubbles in the adhesive layer is 0.05 times or more the thickness of the adhesive layer. When the average major diameter of the bubbles in the adhesive layer is 0.05 times or more the thickness of the adhesive layer, the adhesive layer is less prone to cohesive failure and the adhesive strength is further improved, resulting in an adhesive tape with superior rebound resistance. It is more preferable that the average major diameter of the bubbles in the adhesive layer is 0.10 times or more the thickness of the adhesive layer. That is, it is preferable that the average major diameter of the bubbles is 0.05 times or more and 0.80 times or less the thickness of the foam layer, more preferably 0.10 times or more and 0.70 times or less, even more preferably 0.10 times or more and 0.60 times or less, and even more preferably 0.10 times or more and 0.30 times or less.

[0095] The aspect ratio of a bubble can be determined as follows: Using a razor (Feather Corporation), slice the adhesive layer with a plane parallel to the MD (Machine Direction) direction and the thickness direction to obtain an MD cut sample. Take an image of the obtained MD cut sample using a digital microscope (e.g., Keyence Corporation, "VHX-6000") under conditions such as a magnification of 200x and a measurement screen size of 1.8 mm x 1.3 mm. In the obtained image, select the bubble with the largest major axis and the bubble with the second largest major axis, measure the major and minor axes of these bubbles, and calculate the aspect ratio. Perform this operation for three images, and the average of the major axes of the six bubbles is taken as the average major axis of the bubbles in the adhesive layer, the average of the minor axes of the six bubbles is taken as the average minor axis of the bubbles in the adhesive layer, and the average of the aspect ratios of the six bubbles is taken as the aspect ratio of the bubbles in the adhesive layer. Furthermore, if the MD direction is unknown, the adhesive layer is sliced ​​on a plane parallel to the thickness direction to obtain a cut sample. The slice is made so that the cutting direction is shifted by 30° from the direction from which the previous cut sample was made, and the aspect ratio is measured in the same manner as above. The above measurement is repeated until it returns to the cutting direction of the first measurement, and the average of the major axes of the 12 bubbles measured is taken as the average major axis of the bubbles in the adhesive layer, the average of the minor axes of the 12 bubbles is taken as the average minor axis of the bubbles in the adhesive layer, and the average of the aspect ratios of the 12 bubbles is taken as the aspect ratio of the bubbles in the adhesive layer.

[0096] Preferably, the adhesive layer has a structure in which no air bubbles are exposed on the surface in the thickness direction. Because the adhesive layer does not have air bubbles exposed on the surface in the thickness direction, the area of ​​the adhesive interface between the adhesive layer and the adherend is increased, which improves the adhesive strength of the adhesive layer and results in an adhesive tape with superior rebound resistance.

[0097] One method for creating a structure in which no air bubbles are exposed on the surface in the thickness direction of the adhesive layer is to use the adhesive composition containing large foaming particles, thereby suppressing the floating of foaming particles to the liquid surface during the solution coating of the adhesive composition in the adhesive layer formation process.

[0098] The shear storage modulus of the above adhesive layer at 23°C, measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz (hereinafter sometimes simply referred to as "shear storage modulus at 23°C"), has a preferred lower limit of 0.30 MPa. A shear storage modulus of 0.30 MPa or higher for the above adhesive layer at 23°C allows the resulting adhesive tape to exhibit superior bending resistance. A more preferred lower limit for the shear storage modulus of the above adhesive layer at 23°C is 0.60 MPa, and an even more preferred lower limit is 0.90 MPa. Furthermore, a preferred upper limit for the shear storage modulus of the above adhesive layer at 23°C is 5.00 MPa. A shear storage modulus of 5.00 MPa or lower for the above adhesive layer at 23°C further improves the flexibility of the adhesive layer, resulting in a more superior step-following ability of the resulting adhesive tape. A more preferred upper limit for the shear storage modulus of the above adhesive layer at 23°C is 4.00 MPa, and an even more preferred upper limit is 3.50 MPa. Examples of the shear storage modulus of the adhesive layer at 23°C include 0.30 MPa to 5.00 MPa, 0.60 MPa to 4.00 MPa, 0.90 MPa to 3.50 MPa, and so on.

[0099] The shear storage modulus of the above adhesive layer at 65°C, measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz (hereinafter sometimes simply referred to as "shear storage modulus at 65°C"), has a preferred lower limit of 0.02 MPa. A shear storage modulus of 0.02 MPa or higher for the above adhesive layer at 65°C results in a more superior rebound resistance of the resulting adhesive tape. A more preferred lower limit for the shear storage modulus of 0.03 MPa for the above adhesive layer at 65°C is 0.04 MPa, and an even more preferred lower limit is 0.04 MPa. Furthermore, a preferred upper limit for the shear storage modulus of 0.60 MPa for the above adhesive layer at 65°C is 0.60 MPa. A shear storage modulus of 0.60 MPa or lower for the above adhesive layer results in improved step-following ability of the resulting adhesive tape. A more preferred upper limit for the shear storage modulus of 0.45 MPa for the above adhesive layer at 65°C is 0.45 MPa, and an even more preferred upper limit is 0.30 MPa. Examples of the shear storage modulus of the adhesive layer at 65°C include 0.02 MPa to 0.60 MPa, 0.03 MPa to 0.45 MPa, 0.04 MPa to 0.30 MPa, and so on.

[0100] The loss tangent (tanδ) of the adhesive layer at 23°C, measured in a dynamic viscoelasticity measurement at a measurement frequency of 100 Hz (hereinafter sometimes simply referred to as "loss tangent of the adhesive layer at 23°C"), preferably has a lower limit of 0.5. A loss tangent of the adhesive layer at 23°C of 0.5 or higher allows the resulting adhesive tape to be given superior shock absorption. A more preferable lower limit for the loss tangent of the adhesive layer at 23°C is 0.7, and an even more preferable lower limit is 1.0. Furthermore, a preferred upper limit for the loss tangent of the adhesive layer at 23°C is 2.5. A loss tangent of the adhesive layer at 23°C of 2.5 or lower further improves the adhesive strength of the adhesive layer, resulting in a more repulsion-resistant adhesive tape. A more preferable upper limit for the loss tangent of the adhesive layer at 23°C is 2.0, and an even more preferable upper limit is 1.8. The loss loss tangent of the adhesive layer at 23°C can be, for example, 0.5 to 2.5, 0.7 to 2.0, 1.0 to 1.8, etc.

[0101] The shear storage modulus of the adhesive layer at 23°C and the shear storage modulus of the adhesive layer at 65°C can be measured by dynamic viscoelastic measurement using a viscoelastic spectrometer (IT Measurement Control Co., Ltd., "DVA-200") under the conditions of shear mode, measurement temperature -50°C to 300°C, heating rate 10°C / min, and measurement frequency 1 Hz.

[0102] The loss tangent of the above adhesive layer at 23°C can be measured by dynamic viscoelastic measurement using a viscoelastic spectrometer (DVA-200, manufactured by IT Measurement Control Co., Ltd.) under the following conditions: shear mode, measurement temperature -50°C to 300°C, heating rate 10°C / min, and measurement frequency 100 Hz.

[0103] Methods for adjusting the shear storage modulus of the adhesive layer at 23°C, the shear storage modulus of the adhesive layer at 65°C, and the loss tangent of the adhesive layer at 23°C include, for example, adjusting the thickness of the adhesive layer, adjusting the composition of the acrylic copolymer contained in the adhesive layer (for example, adjusting the type and content of constituent units derived from alkyl (meth)acrylate, constituent units derived from monomers having crosslinkable functional groups, constituent units derived from olefin polymers having polymerizable unsaturated double bonds at their terminals, and constituent units derived from vinyl aromatic compounds, introducing blocks having constituent units derived from vinyl aromatic compounds, copolymerizing constituent units derived from isobornyl (meth)acrylate, etc.), adjusting the weight-average molecular weight, polydispersity, etc. of the acrylic copolymer, adjusting the type and content of the tackifying resin and constituent units derived from vinyl aromatic compounds contained in the adhesive layer, and adjusting the type and content of the crosslinking agent contained in the resin composition forming the adhesive layer.

[0104] The preferred lower limit for the bio-derived carbon content in the adhesive layer is 10%. A bio-derived carbon content of 10% or more in the adhesive layer results in an adhesive tape that is superior in terms of conserving petroleum resources and reducing carbon dioxide emissions, thereby reducing environmental impact. A more preferred lower limit for the bio-derived carbon content in the adhesive layer is 15%, an even more preferred lower limit is 18%, and an even more preferred lower limit is 20%. Furthermore, there is no particular upper limit for the bio-derived carbon content in the adhesive layer, and it may be 100%. Examples of bio-derived carbon content in the foam layer include 10% to 100%, 15% to 100%, 18% to 100%, and 20% to 100%.

[0105] While bio-derived carbon contains a certain percentage of the radioactive isotope C-14, petroleum-derived carbon contains almost no C-14. Therefore, the "biologically derived carbon content" as used herein can be calculated by measuring the concentration of C-14 contained in the adhesive layer. Specifically, it can be measured in accordance with ASTM D6866-24, a standard widely used in the bioplastics industry.

[0106] The content of bio-derived carbon in the adhesive layer can be adjusted by changing the composition of the adhesive layer. Specifically, examples include synthesizing the acrylic copolymer using an alkyl (meth)acrylate containing bio-derived carbon or a monomer having a crosslinkable functional group, incorporating a tackifying resin containing bio-derived carbon into the adhesive layer, or changing the content of the bio-derived material.

[0107] The thickness of the adhesive layer described above has a preferred lower limit of 50 μm and a preferred upper limit of 500 μm. When the thickness of the adhesive layer is 50 μm or more, the adhesive strength of the adhesive layer is further improved, and the resulting adhesive tape has superior rebound resistance. When the thickness of the adhesive layer is 500 μm or less, the adhesive layer has appropriate flexibility, so the resulting adhesive tape has superior step-following ability, and the resulting adhesive tape can be given superior shock absorption. A more preferred lower limit for the thickness of the adhesive layer is 80 μm, a more preferred upper limit is 400 μm, an even more preferred lower limit is 100 μm, an even more preferred upper limit is 300 μm, an even more preferred upper limit is 250 μm, and a particularly preferred upper limit is 200 μm. Examples of the thickness of the adhesive layer include 50 μm to 500 μm, 80 μm to 400 μm, 100 μm to 300 μm, 100 μm to 250 μm, 100 μm to 200 μm, and so on.

[0108] In this specification, thickness can be measured using a dial thickness gauge (for example, Mitutoyo's "ABS Digimatic Indicator").

[0109] The adhesive tape of this embodiment may have other layers besides the adhesive layer as needed, but from the viewpoint of reducing the thickness of the resulting adhesive tape, it is preferable that the adhesive tape has only the adhesive layer. When the adhesive tape has only the adhesive layer, the resulting adhesive tape becomes easier to follow steps, and the step-following ability is further improved. Furthermore, it can be used more suitably for bonding and fixing electronic equipment components.

[0110] The above adhesive tape may or may not have a base material. If the adhesive tape has a base material, the resulting adhesive tape can be given superior reworkability. If the adhesive tape does not have a base material, the resulting adhesive tape will be able to follow steps more easily, and the step-following ability will be further improved. In addition, since the resulting adhesive tape will be thinner, it can be used more suitably for bonding and fixing electronic components.

[0111] If the adhesive tape has a base material, it may be a single-sided adhesive tape having the adhesive layer on one side of the base material, or a double-sided adhesive tape having adhesive layers on both sides of the base material. Furthermore, if the adhesive tape is a double-sided adhesive tape, as long as at least one of the adhesive layers is the adhesive layer, the other adhesive layer is not particularly limited, and the other adhesive layer may be the adhesive layer, or any adhesive layer as long as it does not impair the effects of the present invention.

[0112] If the adhesive tape has a base material, the type of base material used is preferably a base material made from a bio-derived material, from the viewpoint of increasing the bio-derived carbon content of the adhesive tape as a whole. Examples of bio-derived materials include polyesters (PES) such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polylactic acid (PLA), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polybutylene succinate (PBS), as well as polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetylcellulose (TAC), cellulose, and polyamide (PA), all of which are derived from plants.

[0113] Furthermore, from the perspective of reducing environmental impact by decreasing the use of new petroleum resources and suppressing carbon dioxide emissions, base materials made from recycled resources may be used. Methods for recycling resources include, for example, recovering waste from packaging containers, home appliances, automobiles, construction materials, food, etc., or waste generated in the manufacturing process, and using the extracted materials again as raw materials by washing, decontamination, or decomposition by heating or fermentation. Examples of base materials using the above recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., using recovered plastics that have been re-resinated as raw materials. Alternatively, the recovered waste may be burned and used as thermal energy for the manufacture of base materials and their raw materials, or the oils and fats contained in the recovered waste may be mixed with petroleum, fractionally distilled, and refined to be used as raw materials.

[0114] If the adhesive tape has a base material, examples of the base material include films and nonwoven fabrics. In particular, from the viewpoint of the base material having excellent stiffness and further improving the step-following ability of the resulting adhesive tape, films are preferred as the base material, and films containing PES and films containing PA are preferred. Examples of PA include nylon 11, nylon 1010, nylon 610, nylon 510, nylon 410, etc., which are made from castor oil, and nylon 56, etc., which are made from cellulose.

[0115] The preferred lower limit for the thickness of the above-mentioned substrate is 3.5 μm, and the preferred upper limit is 1000 μm. When the thickness of the above-mentioned substrate is within the above range, the substrate has a better balance of flexibility and rigidity, and the step-following ability of the resulting adhesive tape is further improved. A more preferred lower limit for the thickness of the above-mentioned substrate is 5.0 μm, a more preferred upper limit is 500 μm, an even more preferred lower limit is 6.5 μm, an even more preferred upper limit is 300 μm, an even more preferred lower limit is 10 μm, an even more preferred upper limit is 200 μm, and a particularly preferred upper limit is 100 μm. Examples of the thickness of the above-mentioned substrate include 3.5 μm to 1000 μm, 5.0 μm to 500 μm, 6.5 μm to 300 μm, 10 μm to 200 μm, 10 μm to 100 μm, etc.

[0116] The method for manufacturing the adhesive tape of this embodiment is not particularly limited, and conventionally known methods can be used. For example, the method for manufacturing an adhesive tape having only the adhesive layer described above is as follows. Specifically, a solution of the adhesive composition prepared by adding a solvent to a mixture of the acrylic copolymer and, if necessary, the aromatic block copolymer (X), pigment, tackifying resin, crosslinking agent, etc., is applied to the release surface of a release PET film, and the solvent in the solution is dried and removed to form an adhesive layer. Then, by placing the release surface of the release PET film on top of the formed adhesive layer, an adhesive tape can be obtained in which the surface of the adhesive layer is covered with the release PET film.

[0117] Furthermore, in cases where the adhesive layer has a foamed structure, an adhesive layer having a foamed structure can be produced by performing the method for forming the foamed structure and the method for forming the adhesive layer described above, using the method described above. Specifically, for example, after preparing a solution of an adhesive composition containing foamed particles using the method described above, it can be applied to the release surface of a release PET film, and a foamed structure can be formed by heating it for a certain period of time at a temperature exceeding the expansion start temperature of the foamed particles (also called the "foaming start temperature") to form a foamed structure and then drying it, thereby forming an adhesive layer having a foamed structure. It is also possible to produce an adhesive tape using an extruder for extrusion molding. Specifically, for example, the adhesive composition for forming the adhesive layer can be supplied to an extruder, melt-mixed, and then a sheet-like raw material of the adhesive layer can be extruded.

[0118] Furthermore, the following are examples of methods for manufacturing an adhesive tape having the above-mentioned substrate and having the adhesive layer on at least one side of the substrate. Specifically, an adhesive layer formed in the same manner as the method for manufacturing an adhesive tape having only the above-mentioned adhesive layer is bonded to the substrate, pressed together using a rubber roller to create a laminated and integrated structure, and then cured in a 40°C environment for 72 hours to obtain an adhesive tape having an adhesive layer on one side of the substrate. Alternatively, the adhesive composition may be directly applied to the substrate, dried to form an adhesive layer, and then the release treatment surface of a release film is placed on top of the formed adhesive layer. Alternatively, an adhesive tape having adhesive layers on both sides of the substrate can be obtained by placing an arbitrary adhesive layer prepared on the other side of the substrate and then laminating and integrating it.

[0119] The preferred lower limit for the 180° peel force of the above adhesive tape against SUS (stainless steel) at 23°C is 10 N / 25 mm. A 180° peel force of 10 N / 25 mm or more on SUS at 23°C allows the adhesive layer to have a foamed structure while maintaining excellent adhesion. Therefore, the resulting adhesive tape exhibits superior step-following ability and superior shock absorption. A more preferred lower limit for the 180° peel force of the above adhesive tape against SUS at 23°C is 12 N / 25 mm, an even more preferred lower limit is 15 N / 25 mm, and an even more preferred lower limit is 20 N / 25 mm. Furthermore, there is no particular upper limit for the 180° peel force of the above adhesive tape against SUS at 23°C, but approximately 50 N / 25 mm is a practical upper limit. Examples of the 180° peel force of the above adhesive tape on SUS at 23°C include 10N / 25mm to 50N / 25mm, 12N / 25mm to 50N / 25mm, 15N / 25mm to 50N / 25mm, 20N / 25mm to 50N / 25mm, etc.

[0120] The 180° peel force of the above adhesive tape against SUS at 23°C is measured by the following method. First, if necessary, one side of the adhesive tape (the side not to be measured) is pressed against a 23 μm thick polyethylene terephthalate film by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min to create a test piece. Then, it is cut to a width of 25 mm and a length of 75 mm. Next, the adhesive layer of the other side of the prepared test piece is attached to a SUS304 plate (a SUS304 plate that has been cleaned with ethanol and then wiped dry), and pressed against it by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Finally, it is cured at 23°C and 50% RH for 20 minutes to prepare a test sample. The obtained test samples can be measured by allowing them to stand for 20 minutes in an environment of 23°C and 50% RH, and then peeling the adhesive layer from the SUS304 plate in accordance with JIS Z 0237:2009, under conditions of 23°C and 50% RH, a tensile speed of 300 mm / min, and a peeling angle of 180°.

[0121] Methods for adjusting the 180° peel force of the above adhesive tape against SUS at 23°C include, for example, changing the composition of the acrylic copolymer contained in the adhesive layer (for example, increasing the content of monomers having crosslinkable functional groups), adjusting the weight-average molecular weight, polydispersity, etc., of the acrylic copolymer, including a tackifying resin in the adhesive layer, adjusting the thickness of the adhesive layer, and adjusting the content of the crosslinking agent contained in the adhesive composition.

[0122] The total thickness of the above adhesive tape has a preferred lower limit of 50 μm and a preferred upper limit of 500 μm. A total thickness of 50 μm or more allows the resulting adhesive tape to exhibit superior step-following properties. A total thickness of 500 μm or less allows the adhesive tape to be more suitably used for bonding and fixing electronic components (especially thin electronic components). A more preferred lower limit for the resulting adhesive tape is 80 μm, a more preferred upper limit is 400 μm, an even more preferred lower limit is 100 μm, and an even more preferred upper limit is 300 μm. Examples of the total thickness of the adhesive tape include 50 μm to 500 μm, 80 μm to 400 μm, 100 μm to 300 μm, etc. Furthermore, in this specification, "total thickness of the adhesive tape" does not include the thickness of the separator, such as a release film, that protects the outermost adhesive layer of the adhesive tape.

[0123] The adhesive tape of this embodiment has a preferred upper limit of 70% for light transmittance at a wavelength of 550 nm. By having a light transmittance of 70% or less at a wavelength of 550 nm, the adhesive tape of this embodiment can be more suitably used for fixing internal components of electrical and electronic equipment. A more preferred upper limit for the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm is 60%, an even more preferred upper limit is 50%, an even more preferred upper limit is 40%, a particularly preferred upper limit is 30%, and a very preferred upper limit is 10%. There is no particular lower limit for the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm, with 0% being the most preferred. Examples of the light transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm include 0% to 70%, 0% to 60%, 0% to 50%, 0% to 40%, 0% to 30%, and 0% to 10%. Furthermore, the transmittance of the adhesive tape of this embodiment at a wavelength of 550 nm can be measured using a spectrophotometer (such as the "V-670" manufactured by JASCO Corporation).

[0124] The adhesive tape of this embodiment is not particularly limited in its use and can be used to fix parts in various industrial applications such as electronic components, vehicles, housing, and building materials. In particular, because the adhesive tape of this embodiment has excellent step-following ability and excellent rebound resistance, it can be suitably used to fix parts with steps. Specifically, it can be more suitably used to fix electronic equipment components or in-vehicle components. Examples of the electronic equipment components include components in electronic devices such as televisions, monitors, and portable electronic devices, and examples of in-vehicle components include in-vehicle panels. When using the adhesive tape of this embodiment to fix parts, a primer treatment may be performed by applying a primer (undercoat) to the surface of the parts to be bonded, and then the parts may be bonded and fixed with the adhesive tape of this embodiment. The primer is not particularly limited and conventionally known primers can be used, such as epoxy primers, urethane primers, and acrylic primers.

[0125] Furthermore, it is preferable that the adhesive tape of this embodiment be further provided with bending resistance, shock absorption, light shielding properties, etc., by various methods. An adhesive tape with excellent bending resistance can prevent damage to the adherend due to deformation of the adhesive tape when the adherend is bent, making it more suitable for bonding and fixing components of thin electronic devices. Specifically, examples include fixing components in foldable display devices such as thin televisions and thin monitors, and more specifically, using it to fix the surface cover panel of a display device to a housing with uneven surfaces. An adhesive tape with excellent shock absorption can prevent damage to components due to impacts such as drops, making it more suitable for fixing components in portable electronic devices. An adhesive tape with excellent light shielding properties can further suppress light leakage from the adhesive interface, making it more suitable for fixing electronic device components or automotive components.

[0126] An electronic device including the adhesive tape of this embodiment is also one of these embodiments. The electronic device of this embodiment is not particularly limited as long as it includes the adhesive tape, but examples include electronic devices in which electronic components are bonded and fixed together with the adhesive tape, and specifically, for example, a display device in which a cover panel and a housing having irregularities are bonded and fixed together with the adhesive tape.

[0127] According to the present invention, it is possible to provide an adhesive tape that can achieve both excellent step-following ability and excellent rebound resistance. Furthermore, according to the present invention, it is possible to provide an electronic device that includes the adhesive tape.

[0128] This is a schematic diagram illustrating the method for evaluating bending resistance. This is a schematic diagram of a test specimen used for evaluating impact absorption. This is a schematic diagram illustrating the method for evaluating impact absorption.

[0129] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The materials used in the examples and comparative examples are as follows.

[0130] <Monomers containing bio-derived carbon> (1) Linoleic acid derived from castor oil was converted to linoleic acid hydroperoxide by lipoxygenase, and then a mixture containing n-hexylaldehyde was obtained by isomerase. By distillation of the obtained mixture, bio-derived carbon-containing n-hexylaldehyde was obtained. Furthermore, by hydrogenation of the obtained bio-derived carbon-containing n-hexylaldehyde, bio-derived carbon-containing n-hexyl alcohol was obtained. By esterifying the obtained bio-derived carbon-containing n-hexyl alcohol with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), bio-derived carbon-containing n-hexyl acrylic acid was synthesized.

[0131] (2) Ricinoleic acid derived from n-heptyl acrylate castor oil was cracked to obtain a mixture containing undecylenic acid and n-heptyl alcohol. Then, undecylenic acid was separated from the obtained mixture by distillation to obtain n-heptyl alcohol containing bio-derived carbon. By esterifying the obtained n-heptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), n-heptyl acrylate containing bio-derived carbon was synthesized.

[0132] (3) Ricinoleic acid derived from 1-methylheptyl acrylate castor oil was dissolved in alkali to obtain a mixture containing sebacic acid and 1-methylheptyl alcohol. Then, sebacic acid was separated from the obtained mixture by distillation to obtain 1-methylheptyl alcohol containing bio-derived carbon. 1-methylheptyl acrylate containing bio-derived carbon was synthesized by esterifying the obtained 1-methylheptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0133] (4) Pinene extracted from pine resin was isomerized to obtain camphene containing bio-derived carbon. By reacting camphene containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), isobornyl acrylate containing bio-derived carbon was synthesized.

[0134] (5) Pinene extracted from pine resin was isomerized to obtain camphene containing bio-derived carbon. By reacting camphene containing bio-derived carbon with methacrylic acid (manufactured by Mitsubishi Chemical Corporation), isobornyl methacrylate containing bio-derived carbon was synthesized.

[0135] <Biologically derived, carbon-free monomers> ・Methyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Methyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・n-butyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・2-ethylhexyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) ・Ethylene-butylene macromonomer (ethylene-butylene macromonomer with a (meth)acryloyl group at one end, manufactured by Kraton Polymers, "HPVM-L1253") ・Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) ・2-hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) ・Styrene (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0136] <Expandable Particles> - Expandable particle A: Expancel 920DU40 (thermal expandable microcapsule, manufactured by Nippon Philite Co., Ltd., average particle size 40 μm) - Expandable particle B: Expancel 920DU80 (thermal expandable microcapsule, manufactured by Nippon Philite Co., Ltd., average particle size 80 μm) - Expandable particle C: EMC-20 (hollow particle, manufactured by Nippon Philite Co., Ltd., average particle size 20 μm) - Expandable particle D: EMC-40 (hollow particle, manufactured by Nippon Philite Co., Ltd., average particle size 53 μm)

[0137] <Aromatic Block Copolymer (X)> ・SIS Block Copolymer: Quintac 3620 (manufactured by Zeon Corporation, styrene ratio 14%) ・SEBS Block Copolymer: DYNARON 8300P (manufactured by ENEOS Materials Corporation, styrene ratio 9%)

[0138] <Pigments> ・Carbon Black: Multi-Lac A903 Black (manufactured by Toyo Color Co., Ltd.)

[0139] <Tackifying Resins> ・Terpene phenol resin: YS Polystar G150 (manufactured by Yasuhara Chemical Co., Ltd., softening point: 145-155°C, hydroxyl value: 120-140 mg KOH / g) ・Rosin ester resin: Pine Crystal KE-359 (manufactured by Arakawa Chemical Industries, Ltd., softening point: 94-104°C, hydroxyl value: 38-47 mg KOH / g, tackifying resin containing bio-derived carbon)

[0140] <Crosslinking agents> - Isocyanate-based crosslinking agent: Desmodulo L-75 (manufactured by Covestro) - Epoxy-based crosslinking agent: Tetrad E-5C (manufactured by Mitsubishi Gas Chemical Company)

[0141] (Synthesis of Acrylic Copolymers) (Acrylic Copolymers A-K, O-R, U-Z, AA) A reactor equipped with a thermometer, stirrer, and condenser was prepared. A mixture of the constituent unit monomers shown in Tables 1-2 and 80 parts by mass of ethyl acetate were added to the reactor, and the reactor was heated to start reflux. Subsequently, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane was added to the reactor as a polymerization initiator, and polymerization was started under reflux. Next, 0.01 parts by mass of 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane was added 1 hour and 2 hours after the start of polymerization, and further, 0.05 parts by mass of t-hexylperoxypivalate was added 4 hours after the start of polymerization to continue the polymerization reaction. Eight hours after the start of polymerization, an ethyl acetate solution of the acrylic copolymer was obtained. The weight-average molecular weight of the obtained acrylic copolymer was measured using a 2690 Separations Module (Waters Inc.) as the measuring instrument, a GPC KF-806L column (Showa Denko Corporation), and ethyl acetate as the solvent, under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The results are shown in Tables 1 and 2.

[0142] (Acrylic copolymers L-N, S-T) (1) Synthesis of RAFT agent 0.902 g of 1,6-hexanedithiol, 1.83 g of carbon disulfide, and 11 mL of dimethylformamide were placed in a two-necked flask and stirred at 25°C. 2.49 g of triethylammonium was added dropwise over 15 minutes and stirred at 25°C for 3 hours. Next, 2.75 g of methyl-α-bromophenylacetic acid was added dropwise over 15 minutes and stirred at 25°C for 4 hours. Then, 100 mL of extraction solvent (n-hexane:ethyl acetate = 50:50) and 50 mL of water were added to the reaction mixture and liquid-liquid extraction was performed. The organic layers obtained from the first and second liquid-liquid extractions were mixed and washed sequentially with 50 mL of 1 M hydrochloric acid, 50 mL of water, and 50 mL of saturated brine. Sodium sulfate was added to the organic layer after washing and dried, then the sodium sulfate was filtered off, and the filtrate was concentrated using an evaporator to remove the organic solvent. The obtained concentrate was purified by silica gel column chromatography to obtain the RAFT agent.

[0143] (2) Synthesis of a block having structural units derived from styrene 0.19 g of the obtained RAFT agent, 0.035 g of styrene and 2,2'-azobis(2-methylbutyronitrile) (ABN-E) as a polymerization initiator, and 80 g of ethyl acetate as a solvent were placed in a two-necked flask, and the temperature was raised to 85°C while purging the flask with nitrogen gas. The amount of styrene added was such that the content ratio in the acrylic copolymer is as shown in Tables 1 and 2. Then, the polymerization reaction was carried out by stirring at 85°C for 6 hours (first stage reaction). After the completion of the first stage reaction, 400 g of n-hexane was added to the flask, and the reactants were stirred to precipitate the product. Unreacted monomers (St) and the RAFT agent were filtered off, and the reactants were dried under reduced pressure at 70°C to obtain a block having structural units derived from styrene (block B).

[0144] (3) Synthesis of Acrylic Copolymers Furthermore, a mixture of constituent unit monomers other than styrene shown in Tables 1-2, 0.0027 g of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) as a polymerization initiator, and 5 g of ethyl acetate as a solvent, along with the previously obtained block having constituent units derived from styrene, was placed in a two-necked flask, and the flask was heated to 85°C while purging the inside with nitrogen gas. The polymerization reaction was then carried out by stirring at 85°C for 6 hours (second-stage reaction), and a reaction solution containing a block copolymer consisting of a block having constituent units derived from styrene (block B) and a block derived from constituent unit monomers other than styrene shown in Tables 1-2 (block A) was obtained. A portion of the reaction solution was taken, 400 g of n-hexane was added thereto, and the reaction products were stirred to precipitate. After that, the unreacted monomers and solvent were filtered off, and the reaction products were dried under reduced pressure at 70°C to remove the block copolymer from the reaction solution. By the above method, an acrylic copolymer having a triblock copolymer structure with blocks having constituent units derived from styrene was synthesized. Subsequently, ethyl acetate solutions of the synthesized acrylic copolymers were prepared. The weight-average molecular weight was measured using the same method as for acrylic copolymers A-K, O-R, U-Z, and AA. The results are shown in Tables 1-2.

[0145]

[0146]

[0147] (Example 1) (1) Preparation of adhesive tape To the solution of acrylic copolymer A obtained in "(Synthesis of acrylic copolymer)" described above, 0.4 parts by mass of thermally expandable microcapsules as foaming particles, 0.2 parts by mass of an isocyanate-based crosslinking agent as a crosslinking agent, and 30 parts by mass of ethyl acetate as a solvent were added to 100 parts by mass of the solid content of acrylic copolymer A, and the mixture was thoroughly stirred to prepare a solution containing an adhesive composition. The solution containing the prepared adhesive composition was applied to the release surface of a 50 μm thick release PET film, dried at 110°C for 5 minutes, and then heated at 155°C for 1 hour to form a foamed structure, thereby forming an adhesive layer with a foamed structure and a thickness of 200 μm. The release surface of a 50 μm thick release PET film was bonded to the obtained adhesive layer, and then cured at 40°C for 48 hours to obtain an adhesive tape.

[0148] (2) Measurement of Gel Fraction of Adhesive Layer The release PET film was peeled off one side of the obtained adhesive tape and bonded to a 23 μm thick base PET film (Futamura Chemical Co., Ltd., "FE2002"), and cut into a flat rectangular shape with a width of 20 mm and a length of 40 mm. The release PET film was then peeled off the other side of the adhesive tape to prepare a test specimen, and its mass was measured. The test specimen was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The mass of the dried test specimen was measured, and the gel fraction (mass %) was calculated using the following formula (I). Note that the test specimen was assumed not to have a release film laminated to protect the adhesive layer. The results are shown in Table 3. Gel fraction (mass %) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (I) (W ０ : Mass of the base material, W １ : Mass of the test specimen before immersion, W ２ (Mass of the test specimen after immersion and drying)

[0149] (3) Measurement of the deemed density of the adhesive layer The release PET film on both sides is peeled off from the obtained adhesive tape, and the deemed density of the adhesive layer (g / cm³) is determined in accordance with JIS K 7222.３ The following was measured. The results are shown in Table 3.

[0150] (4) Measurement of the shear storage modulus of the adhesive layer at 23°C and the shear storage modulus of the adhesive layer at 65°C A test specimen was prepared by layering multiple adhesive layers, each prepared by peeling off the release PET film from both sides of the obtained adhesive tape, to a thickness of 500 μm. Dynamic viscoelasticity measurements were performed on the prepared test specimen using a viscoelastic spectrometer (IT Measurement Control Co., Ltd., "DVA-200") under the conditions of simple heating mode with a heating rate of 10°C / min, shear mode, measurement frequency of 1 Hz, and temperature range from -50°C to 300°C. The shear storage modulus (MPa) of the adhesive layer at 23°C and the shear storage modulus (MPa) of the adhesive layer at 65°C were measured. The results are shown in Table 3.

[0151] (5) Measurement of the loss tangent of the adhesive layer at 23°C A test specimen was prepared by layering multiple adhesive layers, each prepared by peeling off the release PET film from both sides of the obtained adhesive tape, to a thickness of 500 μm. Dynamic viscoelasticity measurements were performed on the prepared test specimen using a viscoelastic spectrometer (DVA-200, manufactured by IT Measurement Control Co., Ltd.) under the conditions of simple heating mode with a heating rate of 10°C / min, shear mode, measurement frequency of 100 Hz, and temperature range from -50°C to 300°C. The loss tangent of the adhesive layer at 23°C was measured using this method. The results are shown in Table 3.

[0152] (6) Measurement of 180° peel force of adhesive tape against SUS at 23°C After peeling off the release PET film from one side (the side not to be measured) of the obtained adhesive tape, the exposed adhesive layer was pressed and backed onto a 23 μm thick polyethylene terephthalate film by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Then, the piece was cut to a width of 25 mm and a length of 75 mm to prepare a test piece. Next, the adhesive layer of the other side (the side to be measured) of the prepared test piece was attached to a SUS304 plate (a SUS304 plate that had been washed with ethanol and then wiped dry), and pressed by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. After that, it was cured at 23°C and 50% RH for 20 minutes to prepare a test sample. The obtained test samples were left to stand for 20 minutes at 23°C and 50% RH. Then, in accordance with JIS Z 0237:2009, the 180° peel force (N / 25 mm) against SUS at 23°C was measured using a tensile testing machine (A&D Corporation, "RTI") to peel the adhesive tape from the SUS304 plate at a tensile speed of 300 mm / min and a peel angle of 180° under the conditions of 23°C and 50% RH. The results are shown in Table 3.

[0153] (Examples 2-34, 36-37, Comparative Examples 4-6) In the above-described "(1) Preparation of adhesive tape," the adhesive tape was prepared and various measurements were performed in the same manner as in Example 1, except that the composition of the adhesive composition and the thickness of the adhesive layer were as shown in Tables 3-6. The results are shown in Tables 3-6.

[0154] (Example 35) An adhesive layer having a foamed structure was formed in the same manner as in Example 1, except that the composition of the adhesive composition and the thickness of the adhesive layer were as shown in Table 5. The obtained adhesive layer was attached to one side of the substrate shown in Table 5, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Furthermore, an adhesive layer having a foamed structure with the same composition and thickness was prepared and attached to the other side of the substrate, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min to laminate and integrate it, and then cured in an environment of 23°C for 1 hour to obtain an adhesive tape having adhesive layers on both sides of the substrate. Note that "PET film" in Table 5 is Lumirror (thickness: 38 μm) manufactured by Toray Industries, Inc.

[0155] In Example 35, regarding the "(2) Measurement of the gel fraction of the adhesive layer" described above, the obtained adhesive tape was cut into a flat rectangular shape with a width of 20 mm and a length of 40 mm, and the release PET film on both sides was peeled off to make a test piece, and in the calculation of the gel fraction, W in the above formula (I) ０ The measurements were performed in the same manner as in Example 1, except that the calculation was performed using the mass of the base material. The results are shown in Table 5. Furthermore, for the above-mentioned "(3) Measurement of the deemed density of the adhesive layer," "(4) Shear storage modulus of the adhesive layer at 23°C and shear storage modulus of the adhesive layer at 65°C," and "(5) Measurement of the loss tangent of the adhesive layer at 23°C," the adhesive layer was removed from the obtained adhesive tape using a cutter knife, and the measurements were performed in the same manner as in Example 1. The results are shown in Table 5. For the above-mentioned "(6) Measurement of the 180° peel force of the adhesive tape against SUS at 23°C," the measurement was performed in the same manner as in Example 1. The results are shown in Table 5.

[0156] (Examples 38-39) The composition and thickness of the adhesive layer were as shown in Table 5. In the drying process of the adhesive composition, instead of drying at 110°C for 5 minutes and then heating at 155°C for 1 hour, heating at 110°C for 3 minutes was performed to form an adhesive layer having a foamed structure in the same manner as in Example 1. Otherwise, the adhesive tape was prepared and various measurements were performed in the same manner as in Example 1. The results are shown in Table 5.

[0157] (Comparative Example 1) (1) Preparation of Adhesive Tape To the solution of acrylic copolymer V obtained in "(Synthesis of Acrylic Copolymer)" described above, 0.2 parts by mass of an isocyanate-based crosslinking agent and 30 parts by mass of ethyl acetate as a solvent were added to 100 parts by mass of the solid content of acrylic copolymer V, and the mixture was thoroughly stirred to prepare a solution containing the adhesive composition. The prepared solution containing the adhesive composition was applied to the release surface of a 50 μm thick release PET film, and then dried at 110°C for 5 minutes to form an adhesive layer with a thickness of 100 μm that does not have a foamed structure. The obtained adhesive layer was bonded to the release surface of a 50 μm thick release PET film, and then cured at 40°C for 48 hours to obtain an adhesive tape. Various measurements were performed in the same manner as in Example 1, except that "(3) Measurement of the deemed density of the adhesive layer" described above was not performed. The results are shown in Table 6.

[0158] (Comparative Examples 2-3) In the above-described "(1) Preparation of adhesive tape," the adhesive tape was prepared and various measurements were performed in the same manner as in Comparative Example 1, except that the composition of the adhesive composition and the thickness of the adhesive layer were as shown in Table 6. The results are shown in Table 6.

[0159] (Comparative Example 7) An adhesive layer without a foamed structure was formed in the same manner as in Comparative Example 1, except that the composition of the adhesive composition and the thickness of the adhesive layer were as shown in Table 6. The obtained adhesive layer was attached to one side of the substrate shown in Table 6, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min. Furthermore, an adhesive layer without a foamed structure of the same composition and thickness was prepared and attached to the other side of the substrate, and then pressed down by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min to laminate and integrate it, and then cured in an environment of 23°C for 1 hour to obtain an adhesive tape having adhesive layers on both sides of the substrate. Note that "polyethylene foam" in Table 6 is Volara (thickness: 100 μm) manufactured by Sekisui Chemical Co., Ltd. In addition, various measurements were performed in the same manner as in Example 35, except that "(3) Measurement of deemed density of the adhesive layer" described above was not performed. The results are shown in Table 6.

[0160] <Evaluation> The adhesive tapes obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 3 to 6.

[0161] (Step-following ability) A single-sided tape (125 mm x 20 mm, 50 μm thick) with a PET film base was attached to the center of a glass plate (125 mm x 50 mm, 1.5 mm thick) so that the length of the adhesive tape coincided with the transverse direction of the glass plate, creating a step of 50 μm in height. In the above-mentioned "(1) Preparation of adhesive tape", the obtained adhesive tape was cut to a size of 25 mm x 50 mm, and one side was backed with a polyethylene terephthalate (PET) sheet with a thickness of 23 μm. The other side of the adhesive tape backed with the PET sheet was attached to the surface of the glass plate where the step was created, and a laminate was created by pressing it from the glass plate side with a 2 kg rubber roller at a speed of 300 mm / min for one back-and-forth motion. The obtained laminate was visually observed for the presence or absence of air trapped from the step at the adhesive interface between the adhesive tape and the step of the glass plate, and the step-following ability of the adhesive tape was evaluated according to the following criteria. A: No air trapped inside was present. B: Air trapped inside was present.

[0162] (Rebound Resistance) A single-sided tape (125 mm x 20 mm, 50 μm thick) with a PET film substrate was attached to the center of a glass plate (125 mm x 50 mm, 1.5 mm thick) so that the center and short side of the adhesive tape coincided with the center and short side of the glass plate, respectively, creating a step of 50 μm in height. In the above-mentioned "(1) Preparation of Adhesive Tape", the obtained adhesive tape was cut to a size of 25 mm x 50 mm, and one side was backed with a polyethylene terephthalate (PET) sheet with a thickness of 23 μm. The other side of the adhesive tape backed with the PET sheet was attached to the stepped surface of the glass plate, and a 2 kg rubber roller was pressed from the glass plate side at a speed of 300 mm / min for one back-and-forth motion to create a laminate. Of the obtained laminates, those in which no air was trapped from the stepped portion at the adhesive interface between the adhesive tape and the stepped portion of the glass plate were selected as test specimens. Specifically, this evaluation was performed only on samples that received a "○" rating for "(Step Followability)" as described above, and was not performed on Comparative Examples 1 to 4 and 7, where the "(Step Followability)" rating was "×". The obtained test pieces were placed in an 80°C oven, and the presence or absence of air trapped from the stepped portion was visually observed after a predetermined time had elapsed. The rebound resistance of the adhesive tape was evaluated according to the following criteria: A: No air trapped occurred in less than 24 hours. B: Air trapped occurred between 6 hours and less than 24 hours. C: Air trapped occurred between 1 hour and less than 6 hours. D: Air trapped occurred in less than 1 hour. -: Air trapped was present at the time of application.

[0163] (Bending Resistance) Figure 1 shows a schematic diagram illustrating the evaluation method for bending resistance. Aluminum alloy plates (SHAANXI SHWEW-E STEEL PIPE, "Aluminum 6061-T6", 1.6 mm thick, 25.4 mm wide, 203.2 mm long) were attached to both sides of the obtained adhesive tape by applying a load of 1 MPa for 20 seconds at 65°C to laminate them together, and then cured by leaving them undisturbed at 23°C for 24 hours to produce laminate 1. The produced laminate 1 was set up in a Tensilon (manufactured by A&D Company, Limited) used as a measuring instrument in accordance with JIS K 7171 as shown in Figure 1 (distance between compression jigs: 57.15 mm, distance between fixing jigs: 177.8 mm). Subsequently, the laminate 1 was compressed at a constant speed of 0.05 mm / s in an environment with a temperature of 23 ± 1°C and a humidity of 50 ± 5%, until the load reached 50 N. In the obtained stress-deformation curve, the slope of the line (stress / deformation) was calculated from two points on the stress-deformation curve: one with a stress of 20 N and another with a stress of 50 N. Based on the obtained slope of the line, the bending resistance of the adhesive tape was evaluated according to the following criteria: A: The slope of the line was 17.0 N / mm or greater. B: The slope of the line was 15.5 N / mm or greater and less than 17.0 N / mm. C: The slope of the line was less than 15.5 N / mm. Even if the evaluation was "C", the adhesive tape of this embodiment can be used without problems depending on the application.

[0164] (Impact Absorption) The obtained adhesive tape 4 was cut to a size of 30 mm x 30 mm, and two SUS plates 5 measuring 125 mm x 50 mm and 2 mm thick were stacked as shown in Figure 2 to create a test specimen 6. The obtained test specimen 6 was set up as shown in Figure 3 so that when the pendulum 7 passed its lowest point, it would collide with only one of the SUS plates 5 on the test specimen. Then, a pendulum 7 with a mass of 1.0 kg was allowed to free-fall from a height of 0.20 m (H in Figure 3) and collided with the test specimen 9, after which the highest height h reached was measured. Using the obtained height h, the impact absorption energy was calculated from the following formula. Note that the lowest point reached by the pendulum 7 is defined as 0. Impact absorption energy (J) = mg(0.2 - h) (m: mass of the pendulum (kg), g: acceleration due to gravity (9.80 m / s) ２ (h: measured height) Based on the calculated shock absorption energy, the shock absorption performance of the adhesive tape was evaluated according to the following criteria: A: Shock absorption energy was 0.50 J or more. B: Shock absorption energy was 0.30 J or more and less than 0.50 J. C: Shock absorption energy was 0.15 J or more and less than 0.30 J. D: Shock absorption energy was less than 0.15 J. Even if the evaluation is "D", the adhesive tape of this embodiment can be used without problems depending on the application.

[0165] (Light-shielding properties) The obtained adhesive tape was cut to a width of 2 mm x length of 75 mm. Next, one adhesive layer of the cut adhesive tape was placed facing the polishing surface of waterproof abrasive paper (Noritake Coated Abrasives, "C947H", grit size 360, surface roughness Ra = 10.8 μm), and then bonded to the test piece by passing a 2 kg rubber roller back and forth at a speed of 300 mm / min. After that, the other adhesive layer of the adhesive tape was placed facing the polishing surface of waterproof abrasive paper, and then bonded to the test piece by passing a 2 kg rubber roller back and forth at a speed of 300 mm / min. After that, it was cured at 23°C and 50% RH for 20 minutes to prepare a test sample. Using a floodlight, the luminous intensity of 3.0 × 10⁻¹⁶ was set on the surface of the adhesive tape bonded to the prepared test sample. ５The light-blocking properties of the adhesive tape were evaluated by irradiating it with light from a CD and visually checking for light leakage, according to the following criteria: A: No light leakage was observed visually. B: Light leakage was observed visually. Even if the evaluation is "B", the adhesive tape of this embodiment can be used without problems depending on the application.

[0166]

[0167]

[0168]

[0169]

[0170] According to the present invention, it is possible to provide an adhesive tape that can achieve both excellent step-following ability and excellent rebound resistance. Furthermore, according to the present invention, it is possible to provide an electronic device that includes the adhesive tape.

[0171] 1. Laminate 2. Compression jig 3. Fixing jig 4. Adhesive tape 5. SUS plate 6. Test piece 7. Pendulum

Claims

1. An adhesive tape having an adhesive layer, wherein the adhesive layer has a foamed structure, the adhesive layer contains an acrylic copolymer having constituent units derived from an alkyl (meth)acrylate, and the acrylic copolymer has at least one constituent unit selected from the group consisting of constituent units derived from n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, and 1-methylheptyl (meth)acrylate.

2. The adhesive tape according to claim 1, wherein the total content ratio of the constituent units derived from the (meth)acrylate, the constituent units derived from the (meth)acrylate, and the constituent units derived from the (meth)acrylate, in relation to the alkyl (meth)acrylate, is 30% by mass or more.

3. The adhesive tape according to claim 1 or 2, wherein the acrylic copolymer further comprises a constituent unit derived from isobornyl (meth)acrylate.

4. The adhesive tape according to claim 1, 2, or 3, wherein the acrylic copolymer has constituent units derived from monomers having crosslinkable functional groups.

5. The adhesive tape according to claim 1, 2, 3, or 4, wherein the acrylic copolymer has constituent units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals.

6. The adhesive tape according to claim 5, wherein the content of constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminals in the acrylic copolymer is 5% by mass or more and 50% by mass or less.

7. The adhesive tape according to claim 1, 2, 3, 4, 5, or 6, wherein the acrylic copolymer comprises a block copolymer having at least one block A having a structural unit derived from an alkyl (meth)acrylate ester and at least one block B having a structural unit derived from a vinyl aromatic compound.

8. The adhesive tape according to claim 7, wherein the content of constituent units derived from the vinyl aromatic compound in the acrylic copolymer is 2.5% by mass or more and 20% by mass or less.

9. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the adhesive layer contains an aromatic block copolymer (X) having at least two blocks having structural units derived from a vinyl aromatic compound, and at least one of a block having structural units derived from a conjugated diene compound and a hydrogenated form of a block having structural units derived from a conjugated diene compound.

10. The adhesive tape according to claim 9, wherein the content of the aromatic block copolymer (X) is 60 parts by mass or less per 100 parts by mass of the acrylic copolymer.

11. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the adhesive layer contains a pigment.

12. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the adhesive layer contains a tackifying resin.

13. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the adhesive layer does not contain a tackifying resin.

14. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the adhesive layer has constituent units derived from a crosslinking agent.

15. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less.

16. The adhesive layer has an assumed density of 0.59 g / cm³. ３ 1.15g / cm or more ３ The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15.

17. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the adhesive layer has a shear storage modulus of 0.30 MPa or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 1 Hz.

18. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, wherein the adhesive layer has a shear storage modulus of 0.02 MPa or more at 65°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 1 Hz.

19. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, wherein the adhesive layer has a loss tangent of 0.5 or more at 23°C as measured in a dynamic viscoelasticity measurement at a measurement frequency of 100 Hz.

20. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19, wherein the adhesive layer has a bio-derived carbon content of 10% or more.

21. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, which does not have a base material.

22. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, having a base material.

23. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22, wherein the 180° peel force against SUS at 23°C is 10 N / 25 mm or more.

24. The adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, used for fixing electronic equipment components or in-vehicle components.

25. Electronic device comprising the adhesive tape according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24.

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