Adhesive composition, adhesive tape, and electronic device

Abstract

A purpose of the present invention is to provide an adhesive composition able to exhibit both excellent adhesion to rough surfaces and excellent heat resistance. Another purpose of the present invention is to provide an adhesive tape having an adhesive layer formed using said adhesive composition. A further purpose of the present invention is to provide an electronic device that includes the adhesive tape. The present invention is an adhesive composition which contains an acrylic copolymer. The acrylic copolymer has a constituent unit derived from an alkyl (meth)acrylate ester and a constituent unit derived from an olefin-based polymer having a polymerizable unsaturated double bond at a terminal. The acrylic copolymer has at least one constituent unit selected from the group consisting of 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.

Description

Adhesive composition, adhesive tape, and electronic device

[0001] The present invention relates to an adhesive composition. Furthermore, the present invention relates to an adhesive tape having an adhesive layer formed using the adhesive composition. Moreover, the present 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, there has been an increase in the use of adhesive tapes on substrates with rough surfaces. Adhesive tapes used on rough surfaces require excellent adhesion to rough surfaces, enabling them to firmly fix the substrate to the rough surface. To improve the adhesion to rough surfaces in conventional adhesive tapes, it is necessary to make the adhesive layer of the tape softer. However, such tapes have poor heat resistance. On the other hand, adhesive tapes with high heat resistance have poor adhesion to rough surfaces because the adhesive layer cannot adequately conform to the rough surface. Therefore, it has been difficult to achieve both good adhesion to rough surfaces and good heat resistance.

[0005] The present invention aims to provide an adhesive composition that can achieve both excellent adhesion to rough surfaces and excellent heat resistance. Furthermore, the present invention aims to provide an adhesive tape having an adhesive layer formed using the adhesive composition. Moreover, the present invention aims to provide an electronic device containing the adhesive tape.

[0006] Disclosure 1 is an adhesive composition containing an acrylic copolymer, wherein the acrylic copolymer has constituent units derived from an alkyl (meth)acrylate and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal, 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. Disclosure 2 is the adhesive composition of Disclosure 1, wherein the total content ratio of constituent units derived from n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, and 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 composition of Disclosure 1 or 2, wherein the acrylic copolymer further has constituent units derived from isobornyl (meth)acrylate. Disclosure 4 is an adhesive composition of Disclosure 1, 2, or 3, wherein the content of constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal in the acrylic copolymer is 5% by mass or more and 50% by mass or less. Disclosure 5 is an adhesive composition of Disclosure 1, 2, 3, or 4, wherein the acrylic copolymer has constituent units derived from a monomer having a crosslinkable functional group. Disclosure 6 is an adhesive composition of Disclosure 1, 2, 3, 4, or 5, wherein the acrylic copolymer includes a block copolymer having at least one block A having constituent units derived from an alkyl (meth)acrylate ester and at least one block B having constituent units derived from a vinyl aromatic compound. Disclosure 7 is an adhesive composition of Disclosure 6, 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. Disclosure 8 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, or 7, wherein the acrylic copolymer has a weight-average molecular weight of 700,000 or more and 1,500,000 or less.Disclosure 9 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, or 8, which 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 product of a block having structural units derived from a conjugated diene compound. Disclosure 10 is an adhesive composition of 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 composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, which contains a pigment. Disclosure 12 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, which contains a tackifying resin. Disclosure 13 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 in which the adhesive composition does not contain a tackifying resin. Disclosure 14 is an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 in which the adhesive composition contains a crosslinking agent. Disclosure 15 is an adhesive tape having an adhesive layer formed using an adhesive composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14. Disclosure 16 is an adhesive tape of Disclosure 15 in which the adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less. Disclosure 17 is an adhesive tape of Disclosure 15 or 16 in which 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. Disclosure 18 is an adhesive tape according to Disclosure 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 Disclosure 15, 16, 17, or 18, wherein the adhesive layer has a loss loss tangent of 0.5 or more at 23°C as measured in a dynamic viscoelastic measurement at a measurement frequency of 100 Hz. Disclosure 20 is an adhesive tape according to Disclosure 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 of Disclosure 15, 16, 17, 18, 19 or 20 in which the adhesive layer has a foamed structure. Disclosure 22 is an adhesive tape of Disclosure 15, 16, 17, 18, 19 or 20 in which the adhesive layer has a deemed density of 0.59 g / cm³. ３ 1.15g / cm or more ３ The following is the adhesive tape of Disclosure 21. Disclosure 23 is the adhesive tape of Disclosure 15, 16, 17, 18, 19, 20, 21 or 22 without a base material. Disclosure 24 is the adhesive tape of Disclosure 15, 16, 17, 18, 19, 20, 21 or 22 having a base material. Disclosure 25 is the adhesive tape of Disclosure 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 used to fix electronic equipment components or automotive components. Disclosure 26 is an electronic device including the adhesive tape of Disclosure 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25. The present invention will now be described in detail. Hereinafter, embodiments of the present invention or one thereof will be described as "this embodiment".

[0007] The present inventors investigated an adhesive composition containing an acrylic copolymer, wherein the acrylic copolymer has structural units derived from (meth)acrylate alkyl ester and structural units derived from an olefin polymer having polymerizable unsaturated double bonds at its terminals. Furthermore, they investigated using a specific compound as the monomer used for the structural units derived from the (meth)acrylate alkyl ester. As a result, they found that an adhesive composition that can achieve both excellent adhesion to rough surfaces and excellent heat resistance can be obtained, thus completing the present invention. In this specification, "(meth)acrylic" means acrylic or methacrylic.

[0008] The adhesive composition of this embodiment contains an acrylic copolymer. The acrylic copolymer has constituent units derived from an alkyl (meth)acrylate and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal. Furthermore, 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 (hereinafter sometimes simply referred to as "constituent unit derived from alkyl (meth)acrylate (a)"). By making the acrylic copolymer have constituent units derived from alkyl (meth)acrylate and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal, and having a constituent unit derived from alkyl (meth)acrylate (a) as the constituent unit derived from alkyl (meth)acrylate, the adhesive composition of this embodiment can achieve both excellent rough surface adhesion and excellent heat resistance.

[0009] The above-mentioned acrylic copolymer has a structure in which the main chain consists of structural units derived from (meth)acrylate alkyl ester and the side chains consist of structural units derived from an olefin polymer having polymerizable unsaturated double bonds at the ends. In this structure, the structural units derived from the olefin polymer having polymerizable unsaturated double bonds at the ends, which are present in the side chains of the acrylic copolymer, aggregate through interaction and form pseudo-crosslinks. Therefore, when the strain is small, the cohesive force of the adhesive composition is increased by the above-mentioned pseudo-crosslinks, improving the heat resistance of the adhesive composition of this embodiment. On the other hand, when the strain applied to the adhesive layer becomes large, the above-mentioned pseudo-crosslinks break and the molecules of the acrylic copolymer stretch, so the adhesive composition of this embodiment exhibits high flexibility, and therefore the adhesive composition of this embodiment can sufficiently follow rough surfaces and improve adhesion to rough surfaces.

[0010] Furthermore, as mentioned above, when the strain is small, the cohesive force of the resulting adhesive composition increases, making it easier to obtain an adhesive composition with higher bending rigidity and thus better bending resistance. Moreover, when the strain is large, the resulting adhesive composition exhibits high flexibility, making it easier to obtain an adhesive composition with higher stress relaxation properties and thus better shock absorption.

[0011] The above acrylic copolymer has a constituent unit derived from the above alkyl (meth)acrylate (a) as a constituent unit derived from the above alkyl (meth)acrylate. By including the constituent unit derived from the above alkyl (meth)acrylate (a) in the constituent unit derived from the above alkyl (meth)acrylate (a), the adhesive composition of this embodiment can exhibit excellent adhesion to rough surfaces. The above acrylic copolymer may have only one type of constituent unit derived from the above alkyl (meth)acrylate (a), or it may have two or more types.

[0012] The reason why the presence of the above-mentioned acrylic copolymer as a constituent unit derived from the above-mentioned alkyl (meth)acrylate (a) improves the adhesion to rough surfaces of the adhesive composition of this embodiment is not clear. However, it is presumed that the presence of the above-mentioned acrylic copolymer as a constituent unit derived from the above-mentioned alkyl (meth)acrylate (a) lowers the glass transition temperature of the acrylic copolymer and lowers the storage modulus at room temperature of the adhesive composition of this embodiment, thereby exhibiting high flexibility and improving the adhesion to rough surfaces.

[0013] The total content of constituent units derived from the above-mentioned alkyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (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. By having a total content of constituent units derived from alkyl (meth)acrylate (a) of 30% by mass or more, the resulting adhesive composition can exhibit better adhesion to rough surfaces. 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 60% 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, 60% by mass or more and 100% by mass or less, etc.

[0014] 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 composition can exhibit even better adhesion to rough surfaces. Furthermore, the resulting adhesive composition can be provided with excellent bending resistance.

[0015] The preferred lower limit for the content of constituent units derived from isobornyl (meth)acrylate to the constituent units derived from alkyl (meth)acrylate is 1% by mass, and the preferred upper limit is 60% by mass. When the content of constituent units derived from isobornyl (meth)acrylate is 1% by mass or more, the resulting adhesive composition can exhibit better adhesion to rough surfaces. Furthermore, the resulting adhesive composition can be given better bending resistance. When the content of constituent units derived from isobornyl (meth)acrylate is 60% by mass or less, the resulting adhesive composition can exhibit better adhesion to rough surfaces. A more preferred lower limit for the content of constituent units derived from isobornyl (meth)acrylate is 5% by mass, a more preferred upper limit is 50% by mass, an even more preferred lower limit is 10% by mass, and an even more preferred upper limit is 40% by mass. Examples of the content ratio of the constituent units derived from isobornyl (meth)acrylate include 1% by mass or more and 60% by mass or less, 5% by mass or more and 50% by mass or less, and 10% by mass or more and 40% by mass or less.

[0016] The above acrylic copolymer may have, as constituent units derived from the above alkyl (meth)acrylate, a constituent unit derived from the above alkyl (meth)acrylate (a) and a constituent unit derived from the above alkyl (meth)acrylate (b), which is a constituent unit other than the constituent unit derived from the above isobornyl (meth)acrylate.

[0017] 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.

[0018] 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.

[0019] 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, which is a bio-derived material, and (meth)acrylic acid.

[0020] In the above acrylic copolymer, the content ratio of the structural unit derived from the above (meth)acrylic acid alkyl ester preferably has a lower limit of 50% by mass and an 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 resulting adhesive composition can exhibit better rough surface adhesiveness. The 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, the more preferable upper limit is 90% by mass, the further preferable lower limit is 65% by mass, the further preferable upper limit is 85% by mass, and the further more preferable upper limit is 80% by mass. 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, and the like.

[0021] The above olefin polymer having a polymerizable unsaturated double bond at the terminal may have a polymerizable unsaturated double bond at one terminal or may have polymerizable unsaturated double bonds at both terminals. Among them, from the viewpoint that intermolecular chemical crosslinking is unlikely to occur, the cohesive force of the resulting adhesive composition is increased, and more excellent heat resistance can be exhibited, an olefin polymer having a polymerizable unsaturated double bond at one terminal is preferable.

[0022] 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.

[0023] 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 that the glass transition temperature of the acrylic copolymer described later is more likely to satisfy a suitable range, and the resulting adhesive composition exhibits better adhesion to rough surfaces. 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.

[0024] In the above acrylic copolymer, the content ratio of the structural unit derived from the olefin polymer having a polymerizable unsaturated double bond at the terminal preferably has a lower limit of 5% by mass and an upper limit of 50% by mass. When the content ratio of the structural unit derived from the olefin polymer having a polymerizable unsaturated double bond at the terminal is 5% by mass or more, an appropriate number of pseudo-crosslinks are formed. As a result, the cohesive force of the obtained adhesive composition is increased, and more excellent heat resistance can be exhibited. When the content ratio of the structural unit derived from the olefin polymer having a polymerizable unsaturated double bond at the terminal is 50% by mass or less, the obtained adhesive composition exhibits appropriate flexibility, so that more excellent rough surface adhesiveness can be exhibited. The more preferable lower limit of the content ratio of the structural unit derived from the olefin polymer having a polymerizable unsaturated double bond at the terminal is 8% by mass, the more preferable upper limit is 45% by mass, the further preferable lower limit is 10% by mass, the further preferable upper limit is 40% by mass, the even more preferable lower limit is 15% by mass, and the even more preferable upper limit is 30% by mass. Examples of the content ratio of the structural unit derived from the olefin polymer having a polymerizable unsaturated double bond at the terminal 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, 15% by mass or more and 30% by mass or less, and the like.

[0025] The above acrylic copolymer preferably has a structural unit derived from a monomer having a crosslinkable functional group. Since the acrylic copolymer has a structural unit derived from a monomer having a crosslinkable functional group, the acrylic copolymer can sufficiently form a crosslinked structure by being chemically crosslinked via a crosslinking agent between molecules, and also, since the polar functional groups in the acrylic copolymer interact with each other, the cohesive force of the obtained adhesive composition is further increased. As a result, the obtained adhesive composition can exhibit more excellent heat resistance. In addition, the obtained adhesive composition can exhibit sufficient adhesive force, and the obtained adhesive composition can exhibit more excellent rough surface adhesiveness.

[0026] 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 composition to exhibit even better heat 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.

[0027] 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.

[0028] 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 acrylic monomers that contain bio-derived materials as constituent unit monomers for the above-mentioned acrylic copolymer. From the viewpoint of cost and productivity of the adhesive composition, 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.

[0029] 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 resulting adhesive composition is increased, and the resulting adhesive composition can exhibit better heat resistance. Furthermore, the resulting adhesive composition can exhibit sufficient adhesive strength, and the resulting adhesive composition can exhibit better adhesion to rough surfaces. When the total content of constituent units derived from the monomer having the crosslinkable functional group is 10% by mass or less, the resulting adhesive composition exhibits appropriate flexibility, and thus can exhibit better adhesion to rough surfaces. 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, an even more preferred upper limit is 7.0% by mass, and a particularly preferred lower limit is 5.0% 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 7.0% by mass or less, 5.0% by mass or more and 7.0% by mass or less.

[0030] 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 composition that exhibits superior heat resistance.

[0031] 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 hydrogenated versions thereof. Among these, constituent units derived from styrene are preferred from the viewpoint of achieving a better balance between the rough surface adhesion and heat resistance of the resulting adhesive composition. Note that the composition may contain only one type of constituent unit derived from these vinyl aromatic compounds, or two or more types may coexist.

[0032] 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 above (meth)acrylate alkyl ester and at least one block B having structural units derived from the above vinyl aromatic compound. In particular, from the viewpoint of obtaining an adhesive composition that exhibits better adhesion to rough surfaces and better heat resistance, it is preferable that the above acrylic copolymer contains the above block copolymer.

[0033] The block copolymer may be a diblock copolymer or a triblock copolymer. Among these, a triblock copolymer is preferred from the viewpoint of having an excellent balance between the rough surface adhesion and heat resistance of the resulting adhesive composition, and among triblock copolymers, a triblock copolymer having the structure of block B - block A - block B is more preferred.

[0034] 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 is 20% by mass. By having the content of constituent units derived from the vinyl aromatic compound within the above range, the resulting adhesive composition can exhibit superior heat resistance. 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 very 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.

[0035] 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 results in a higher cohesive force in the resulting adhesive composition, leading to superior heat resistance. A weight-average molecular weight (Mw) of 1,500,000 or less results in a moderately flexible adhesive composition, enabling superior adhesion to rough surfaces. 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) for the above acrylic copolymer include 700,000 to 1,500,000, 800,000 to 1,400,000, and 900,000 to 1,300,000.

[0036] 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 resulting adhesive composition exhibits better heat resistance and better adhesion to rough surfaces. 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) of the above acrylic copolymer include 1.0 to 8.0, 1.5 to 7.5, 2.0 to 7.0, etc.

[0037] 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.

[0038] The preferred lower limit for the content of the acrylic copolymer in the above adhesive composition is 30% by mass. A content of 30% by mass or more of the acrylic copolymer makes it easier to achieve both excellent rough surface adhesion and excellent heat resistance in the resulting adhesive composition. 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Preferably, the above adhesive composition 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 above aromatic block copolymer (X) in the above adhesive composition, the resulting adhesive composition can be provided with superior shock absorption.

[0045] 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.

[0046] 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.

[0047] 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. A content of 7% by mass or more of constituent units derived from the vinyl aromatic compound allows the resulting adhesive composition to exhibit superior 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 ensuring the resulting adhesive composition exhibits 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% by mass or more and 35% by mass or less, and 10% by mass or more and 30% by mass or less.

[0048] 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.

[0049] 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%.

[0050] 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. By having a content of 80% by mass or more of constituent units derived from the conjugated diene compound, the resulting adhesive composition can exhibit superior shock absorption. Furthermore, the resulting adhesive composition can exhibit sufficient adhesive strength, thus enabling superior adhesion to rough surfaces. 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, and 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, 95% by mass or more and 100% by mass or less, etc.

[0051] Examples of the structure of the above aromatic block copolymer (X) include, when the vinyl aromatic polymer block is B and the hydrogenated block having constituent units derived from the conjugated diene polymer block and the hydrogenated conjugated diene polymer block is 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.

[0052] 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.

[0053] 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 composition to exhibit superior 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.

[0054] 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 resulting adhesive composition can exhibit sufficient adhesive strength, thus providing superior adhesion to rough surfaces. Furthermore, the resulting adhesive composition can be given superior bending resistance. 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 composition can exhibit 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.

[0055] The above adhesive composition may be colored. When the adhesive composition is colored, light-shielding properties can be imparted to the resulting adhesive composition. This prevents light from leaking from the adhesive surface, thereby suppressing the irradiation of the adherends with light and ultraviolet rays, and thus reducing degradation of the adherends due to light and ultraviolet rays. Therefore, the resulting adhesive composition can be more suitably used for bonding electronic components.

[0056] If the above adhesive composition is colored, the adhesive composition 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 pigments 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 dyes include azo dyes, anthraquinone dyes, and indigo dyes.

[0057] 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 allows the resulting adhesive composition to exhibit sufficient adhesive strength, thus enabling superior adhesion to rough surfaces. 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 the resulting adhesive composition with sufficient light-shielding properties. 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.

[0058] The above adhesive composition may or may not contain a tackifying resin. When the adhesive composition contains a tackifying resin, the resulting adhesive composition will exhibit sufficient adhesive strength, thus providing superior adhesion to rough surfaces. On the other hand, when the adhesive composition does not contain a tackifying resin, it will provide superior shock absorption.

[0059] When the above adhesive composition contains the above 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 above 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.

[0060] 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.).

[0061] When the above adhesive composition contains the above tackifying resin, it is preferable that the tackifying resin contains a tackifying resin that contains bio-derived carbon. By including a tackifying resin that contains bio-derived carbon, the content of bio-derived carbon in the adhesive layer described later can be increased, and the environmental burden of the resulting adhesive composition can be further reduced. Specific examples of the above tackifying resin containing bio-derived carbon include Pine Crystal KE-100, Pine Crystal KE-359, Pine Crystal KE-604, Pine Crystal KR-140, Super Ester A-75 (all of which are rosin ester resins, manufactured by Arakawa Chemical Industries, Ltd.), Tamanol 803L (terpene phenol resin, manufactured by Arakawa Chemical Industries, Ltd.), and the like.

[0062] When the above adhesive composition contains the above tackifying resin, it is preferable that the tackifying resin has a softening point of 70°C or more and 170°C or less. By including a tackifying resin with a softening point of 70°C or higher, the resulting adhesive composition will exhibit better heat resistance. By including a tackifying resin with a softening point of 170°C or lower, the resulting adhesive composition will have improved interfacial wettability and exhibit better adhesion to rough surfaces. It is more preferable that the tackifying resin includes a tackifying resin with a softening point of 100°C or more and 160°C or less, more preferable that it includes a tackifying resin with a softening point of 120°C or more and 150°C or less, and even more preferable that it includes a tackifying resin with a softening point of 130°C or more and 140°C or less. In this specification, "softening point of tackifying resin" means the softening temperature measured by JIS K2207 (ring-ball method).

[0063] If the above adhesive composition contains the above tackifying resin, it is preferable that the tackifying resin has a hydroxyl value of 25 mg KOH / g or more. By including the tackifying resin with a hydroxyl value of 25 mg KOH / g or more, the resulting adhesive composition will have improved interfacial wettability and exhibit better adhesion to rough surfaces. It is more preferable that the tackifying resin includes a hydroxyl value of 30 mg KOH / g or more, and even more preferable that it includes a hydroxyl value of 35 mg KOH / g or more. The upper limit of the hydroxyl value of the above tackifying resin is not particularly limited, but from the viewpoint of compatibility with the above aromatic block copolymer (X), a preferred upper limit is 200 mg KOH / g. Examples of the hydroxyl value of the above tackifying resin include 25 mg KOH / g or more and 200 mg KOH / g or less, 30 mg KOH / g or more and 200 mg KOH / g or less, 35 mg KOH / g or more and 200 mg KOH / g or less, etc. Furthermore, within this specification, the hydroxyl value of the tackifying resin can be measured by JIS K1557 (phthalic anhydride method).

[0064] When the above adhesive composition contains the above tackifying resin, the preferred upper limit of the content of the tackifying resin per 100 parts by mass of the acrylic copolymer is 60 parts by mass. By having a content of 60 parts by mass or less of the tackifying resin, the resulting adhesive composition does not become too hard and exhibits sufficient adhesive strength, thereby enabling it to exhibit superior adhesion to rough surfaces. A more preferred upper limit for the content of the tackifying resin is 50 parts by mass, an even more preferred upper limit 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 above adhesive composition contains the above tackifying resin, from the viewpoint of enabling the resulting adhesive composition to exhibit superior adhesion to rough surfaces, a preferred lower limit for the content of the tackifying resin is 0.1 parts by mass, and a more preferred lower limit is 1.0 part by mass. As stated above, the above adhesive composition does not need to contain the tackifying resin, and from the viewpoint of providing the resulting adhesive composition with superior shock absorption, it is preferable that the above adhesive composition does not contain the tackifying resin. Furthermore, examples of the content of the tackifying resin include 0 parts by mass or more and 60 parts by mass or less, 0.1 parts by mass or more and 60 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, 1.0 part 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.

[0065] The above adhesive composition preferably contains a crosslinking agent. The inclusion of a crosslinking agent in the adhesive composition results in the acrylic copolymer having a crosslinked structure. Therefore, the resulting adhesive composition exhibits increased cohesive strength and superior heat resistance. Furthermore, the resulting adhesive composition exhibits sufficient adhesive strength and superior adhesion to rough surfaces. From the viewpoint of storage stability, the crosslinking agent may be added to the adhesive composition immediately before forming the adhesive layer described later.

[0066] Examples of the crosslinking agents mentioned above 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 enabling the resulting adhesive composition to exhibit sufficient adhesive strength.

[0067] 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. By having the crosslinking agent content within the above range, the resulting adhesive composition will exhibit better heat resistance and better adhesion to rough surfaces. 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.

[0068] From the viewpoint of preventing aging of the adhesive composition, it is preferable that the above adhesive composition contains an antioxidant (anti-aging agent).

[0069] 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.

[0070] 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.

[0071] The adhesive composition of this embodiment may optionally contain conventionally known additives such as antioxidants, thickeners, softeners, organic fillers, and inorganic fillers, as long as they do not impair the effects of the present invention.

[0072] The method for producing the adhesive composition of this embodiment is not particularly limited and can be produced by conventionally known production methods. For example, it can be produced 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.

[0073] An adhesive tape having an adhesive layer formed using the adhesive composition of this embodiment is also one of the embodiments. The adhesive tape of this embodiment can achieve both excellent adhesion to rough surfaces and excellent heat resistance.

[0074] A method for forming an adhesive layer using the adhesive composition of this embodiment includes, for example, applying the adhesive composition of this embodiment to a release film or the like, and then heating and drying the adhesive composition. The adhesive layer may contain the uncrosslinked adhesive composition, or it may contain the crosslinked product of the adhesive composition.

[0075] 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 and adhesive force of the adhesive layer are further improved, and the rough surface adhesion and heat resistance of the resulting adhesive tape are further improved. When the gel fraction of the adhesive layer is 70% by mass or less, the flexibility of the adhesive layer is further improved, and the rough surface adhesion of the resulting adhesive tape is further improved. 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.

[0076] 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 without a substrate, the measurement is performed using a test piece obtained by cutting after pasting on the substrate, 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 substrate, W ０ : mass of the test piece before immersion, W １ : mass of the test piece after immersion and drying) ２

[0077] 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 constituent units derived from the monomer having the above crosslinkable functional group, a method of adjusting the type and content of the crosslinking agent contained in the above adhesive composition, 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, but it is not limited to these methods.

[0078] 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 at 23°C for the above adhesive layer provides superior bending resistance to the resulting adhesive tape. 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 at 23°C for the above adhesive layer further improves the flexibility of the adhesive layer, thus improving the rough surface adhesion 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, and 0.90 MPa to 3.50 MPa.

[0079] 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 allows the resulting adhesive tape to exhibit superior heat resistance. A more preferred lower limit for the shear storage modulus of the above adhesive layer at 65°C is 0.03 MPa, and an even more preferred lower limit is 0.04 MPa. Furthermore, a preferred upper limit for the shear storage modulus of 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 at 65°C further improves the rough surface adhesion of the resulting adhesive tape. A more preferred upper limit for the shear storage modulus of 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.

[0080] 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"), has a preferred 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 exhibit superior shock absorption. A more preferred lower limit for the loss tangent of the adhesive layer at 23°C is 0.7, and an even more preferred 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, thus improving the rough surface adhesion of the resulting adhesive tape. A more preferred upper limit for the loss tangent of the adhesive layer at 23°C is 2.0, and an even more preferred 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.

[0081] 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 (DVA-200, manufactured by IT Measurement Control Co., Ltd.) under the conditions of shear mode, measurement temperature -50 to 300°C, heating rate 10°C / min, and measurement frequency 1 Hz.

[0082] 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 conditions of shear mode, measurement temperature -50 to 300°C, heating rate 10°C / min, and measurement frequency 100 Hz.

[0083] 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 (for example, adjusting the type and content of constituent units derived from alkyl (meth)acrylate, constituent units derived from monomers having crosslinkable functional groups, 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, and adjusting the type and content of the tackifying resin, crosslinking agent, and aromatic block copolymer (X) contained in the adhesive composition.

[0084] 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 adhesive layer include 10% to 100%, 15% to 100%, 18% to 100%, and 20% to 100%.

[0085] 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.

[0086] 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.

[0087] 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 rough surface adhesion of the resulting adhesive tape is further improved. When the thickness of the adhesive layer is 500 μm or less, the adhesive layer has appropriate flexibility, so the rough surface adhesion of the resulting adhesive tape is further improved, and the resulting adhesive tape can be given better 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.

[0088] In this specification, thickness can be measured using a dial thickness gauge (for example, Mitutoyo's "ABS Digimatic Indicator").

[0089] The adhesive layer preferably has a foamed structure. Having a foamed structure in the adhesive layer improves its stress relaxation properties, and the resulting adhesive tape can be provided with superior shock absorption.

[0090] 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, and then applied to a release film or the like and heated and dried to form a foamed structure; a method in which gas is forcibly mixed and dispersed into the adhesive composition to form a foamed structure; and a method in which liquefied gas is mixed into the adhesive composition to form a foamed structure. Among these, the method in which foaming particles are incorporated into the adhesive composition, and then applied to a release film or the like and heated and dried to form a 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 that the resulting adhesive tape can be given excellent shock absorption properties.

[0091] 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.

[0092] The above-mentioned thermally 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 pressure, increasing the particle size. Therefore, when heated, the thermally expandable microcapsules become hollow particles with air bubbles inside the outer shell. Consequently, in the above-mentioned adhesive composition, the inclusion of thermally 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 adhesive layer exhibits superior stress relaxation properties, and the resulting adhesive tape can be provided with excellent shock absorption.

[0093] 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 because they are less permeable to encapsulated volatile substances and allow for easy adjustment of the average particle size of the foamed particles, as described later, within a suitable range.

[0094] 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 ３F, 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.

[0095] 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. This improves the uniformity of the thickness of the adhesive layer, resulting in an adhesive tape with superior shock absorption.

[0096] 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.

[0097] 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. By having the average particle size of the foamed particles within this range, the resulting adhesive tape can be provided with excellent shock absorption. 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.

[0098] 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.

[0099] 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).

[0100] If the adhesive layer has a foamed structure, the foamed structure may be an open-cell structure or an closed-cell structure, but an 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, thus improving the rough surface adhesion of the resulting adhesive tape. In this specification, when observing a tape cross-section randomly, a structure where the air layers between cells are partially continuous is defined as an open-cell structure, and a structure where the air layers between cells are not continuous is defined as an closed-cell structure. The cell structure 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").

[0101] If the adhesive layer has a foamed structure, the deemed density of the 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 its adhesive strength is improved, thus improving the rough surface adhesion of the resulting adhesive tape. The deemed density of the adhesive layer is 1.15 g / cm³. ３The 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 1.12 g / cm³. ３ A more preferable lower limit is 0.70 g / cm³. ３ A more preferable upper limit is 1.10 g / cm³. ３ A more preferable lower limit is 0.75 g / cm³. ３ A more preferable upper limit is 1.05 g / cm³. ３ A particularly preferred lower limit is 0.80 g / cm³. ３ A particularly preferred upper limit is 1.00 g / cm³. ３ A particularly preferable upper limit is 0.90 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 1.12g / cm or more ３ Below, 0.70g / cm ３ 1.10g / cm or more ３ Below, 0.80g / cm ３ 1.00g / cm or more ３ Below, 0.80g / cm ３ 0.90g / cm or more ３ The following are some examples.

[0102] 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.

[0103] When the adhesive layer has a foamed structure, the preferred lower limit for the average major diameter of the bubbles in the adhesive layer is 10 μm, and the preferred upper limit is 80 μm. A maximum average major diameter of 10 μm or more for the bubbles in the adhesive layer improves the stress relaxation properties of the adhesive layer, thus providing superior shock absorption to the resulting adhesive tape. A minimum average major diameter of 80 μm for the bubbles in the adhesive layer makes the adhesive layer less susceptible to cohesive failure and improves its adhesive strength, thus improving the rough surface adhesion of the resulting adhesive tape. 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 foam 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.

[0104] When the adhesive layer has a foamed structure, the preferred lower limit for the average short diameter of the bubbles in the adhesive layer is 10 μm, and the preferred upper limit is 75 μm. A more preferable lower limit for the average short 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 short diameter of the bubbles in the adhesive layer is 75 μm or less, which makes the adhesive layer less susceptible to cohesive failure and further improves its adhesive strength, thus improving the rough surface adhesion of the resulting 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 short 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 foam 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.

[0105] When the adhesive layer has a foamed structure, the aspect ratio of the bubbles in the adhesive layer 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 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 better shock absorption. When the aspect ratio of the bubbles in the adhesive layer is 3.50 or lower, the adhesive layer is less prone to cohesive failure, and the adhesive strength is further improved, so that the rough surface adhesion of the resulting adhesive tape is further improved. A more preferred lower limit for the aspect ratio of the bubbles in the adhesive layer 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 bubbles in the adhesive layer include 1.00 to 3.50, 1.25 to 3.00, 1.50 to 2.50, etc. In this specification, "aspect ratio of bubbles" means the value obtained by dividing the average major diameter of the bubbles by the average minor diameter of the bubbles (average major diameter of bubbles / average minor diameter of bubbles).

[0106] If the adhesive layer has a foamed structure, it is preferable that the average major diameter of the bubbles is 0.80 times or less the thickness of the adhesive layer. By having an average major diameter of bubbles of 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 improved adhesion to rough surfaces of the resulting adhesive tape. It is more preferable that the average major diameter of the bubbles 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. Furthermore, it is preferable that the average major diameter of the bubbles is 0.05 times or more the thickness of the adhesive layer. By having an average major diameter of bubbles of 0.05 times or more the thickness of the adhesive layer, the stress relaxation properties of the adhesive layer are further improved, resulting in the resulting adhesive tape having superior shock absorption. It is more preferable that the average major diameter of the bubbles is 0.10 times or more the thickness of the adhesive layer. That is, it is preferable that the average major diameter of the above-mentioned bubbles is 0.05 times or more and 0.8 times or less the thickness of the above-mentioned adhesive layer, more preferably 0.10 times or more and 0.7 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.

[0107] The average major diameter, average minor diameter, and aspect ratio of the bubbles in the adhesive layer can be determined as follows. Specifically, the adhesive layer is sliced ​​using a razor (Feather Corporation) on a plane parallel to the MD (Machine Direction) direction and the thickness direction to obtain an MD cut sample. The obtained MD cut sample is photographed using a digital microscope (for example, Keyence Corporation's "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 photographed image, the bubble with the largest major diameter and the bubble with the second largest major diameter are selected, and the major and minor diameters of these bubbles are measured to calculate the aspect ratio. Perform this operation for three captured images. 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. If the above MD direction is unknown, slice the adhesive layer with a plane parallel to the thickness direction to obtain a cut sample. Slice the sample so that the cutting direction is shifted by 30° from the direction from which the previous cut sample was cut, and measure the aspect ratio in the same manner as above. Repeat the above measurement until returning to the cutting direction of the first measurement. The average of the major axes of the twelve bubbles measured is taken as the average major axis of the bubbles in the adhesive layer, the average of the minor axes of the twelve bubbles is taken as the average minor axis of the bubbles in the adhesive layer, and the average of the aspect ratios of the twelve bubbles is taken as the aspect ratio of the bubbles in the adhesive layer.

[0108] If the adhesive layer has a foamed structure, it is preferable that 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 surface between the adhesive layer and the adherend is increased, which further improves the adhesive strength of the adhesive layer and further improves the rough surface adhesion of the resulting adhesive tape.

[0109] 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.

[0110] When the adhesive layer has a foamed structure, the preferred lower limit of the 180° peel force of the adhesive layer against SUS (stainless steel) at 23°C is 10 N / 25 mm. By having a 180° peel force of 10 N / 25 mm or more against SUS at 23°C, the adhesive layer has a foamed structure while possessing superior adhesion. Therefore, the adhesive tape of this embodiment has superior rough surface adhesion as well as superior shock absorption. A more preferred lower limit of the 180° peel force of the adhesive layer 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 adhesive layer against SUS at 23°C, but approximately 50 N / 25 mm is a practical upper limit. Examples of the 180° peel force of the adhesive layer on SUS at 23°C include 10 N / 25 mm to 50 N / 25 mm, 12 N / 25 mm to 50 N / 25 mm, 15 N / 25 mm to 50 N / 25 mm, and so on.

[0111] The 180° peel force of the above adhesive layer against SUS at 23°C can be measured by the following method. First, if necessary, one side of the obtained adhesive layer (the side not to be measured) is pressed 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. After that, it is cut to a width of 25 mm and a length of 75 mm to prepare a test piece. Next, the prepared test piece is attached to a SUS304 plate (a SUS304 plate that has been washed with ethanol and then wiped dry), pressed onto it by running a 2 kg rubber roller back and forth once at a speed of 300 mm / min, and then 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°.

[0112] Methods for adjusting the 180° peel force of the adhesive layer on 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 and polydispersity of the acrylic copolymer, including the type and content of tackifying resin contained in the adhesive composition, adjusting the thickness of the adhesive layer, and forming a foamed structure in the adhesive layer.

[0113] The above adhesive tape may have other layers besides the adhesive layer as needed, but from the viewpoint of reducing the thickness of the 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 conforms more easily to rough surfaces, and the adhesion to rough surfaces is further improved. Furthermore, it can be used more suitably for bonding and fixing electronic components.

[0114] 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 excellent reworkability. If the adhesive tape does not have a base material, the resulting adhesive tape will conform more easily to rough surfaces, and its adhesion to rough surfaces 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] If the adhesive tape has a base material, examples of the base material include films and nonwoven fabrics. Among these, films are preferred as the base material because they have excellent stiffness and the resulting adhesive tape can be given excellent reworkability. 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.

[0119] If the adhesive layer does not have a foamed structure, a foamed substrate may be used as the substrate type for the base material. By using a foamed substrate, the resulting adhesive tape can be provided with superior shock absorption. The foamed substrate is preferably one containing at least one selected from the group consisting of PE, PP, and PU, and a foamed substrate containing PE is more preferable from the viewpoint of having a better balance between flexibility and rigidity of the substrate. Examples of components of the foamed substrate containing PE include PE made from sugarcane.

[0120] A preferred method for producing the foamed substrate containing PE made from sugarcane is to prepare a foamed resin composition containing a PE resin containing PE made from sugarcane and a foaming agent, and to foam the foaming agent when extruding the foamed resin composition into a sheet using an extruder, thereby crosslinking the resulting polyolefin foam as needed.

[0121] 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 resulting adhesive tape can maintain better rough surface adhesion while having better reworkability. 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, a particularly preferred lower limit is 30 μm, and an even more 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, 30 μm to 100 μm, etc.

[0122] 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: The solution of the adhesive composition prepared by the method described above is applied to the release treatment 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 treatment surface of a 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 a release PET film.

[0123] 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 the 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 of this embodiment can be supplied to an extruder, melt-mixed, and then a sheet-like raw material of the adhesive layer can be extruded.

[0124] 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.

[0125] 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 adhesion to rough surfaces. A total thickness of 500 μm or less allows the adhesive tape to be more suitably used for bonding and fixing internal components of electronic devices (especially internal components of thin electronic devices). 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.

[0126] 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).

[0127] The adhesive composition and adhesive tape of this embodiment are not particularly limited in their use and can be used to fix parts in various industrial applications such as electronic equipment components, vehicles, housing, and building materials. In particular, the adhesive composition and adhesive tape of this embodiment have excellent rough surface adhesion and can therefore be suitably used to fix parts with rough surfaces. Furthermore, the adhesive composition and adhesive tape of this embodiment have excellent heat resistance and can therefore 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 using 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.

[0128] Furthermore, it is preferable that the adhesive composition and adhesive tape of this embodiment be further provided with bending resistance, shock absorption, light shielding, etc., by various methods. Adhesive compositions and adhesive tapes with excellent bending resistance can prevent damage to the adherend due to deformation of the adhesive tape accompanying bending of the adherend, and are therefore 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 them to fix the surface cover panel of a display device to a housing with uneven surfaces. Adhesive compositions and adhesive tapes with excellent shock absorption can prevent damage to components due to impacts such as dropping, and are therefore more suitable for fixing components in portable electronic devices. Adhesive compositions and adhesive tapes with excellent light shielding can further suppress light leakage from the adhesive surface, and are therefore more suitable for fixing electronic device components or automotive components.

[0129] 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.

[0130] According to the present invention, it is possible to provide an adhesive composition that can achieve both excellent adhesion to rough surfaces and excellent heat resistance. Furthermore, according to the present invention, it is possible to provide an adhesive tape having an adhesive layer formed using the adhesive composition. Moreover, according to the present invention, it is possible to provide an electronic device containing the adhesive tape.

[0131] This is a schematic diagram illustrating a heat resistance test. This is a schematic diagram illustrating a 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 a method for evaluating impact absorption.

[0132] 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.

[0133] <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.

[0134] (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 resulting 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.

[0135] (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 resulting 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.).

[0136] (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.

[0137] (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.

[0138] <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.)

[0139] <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)

[0140] <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%)

[0141] <Pigments> ・Carbon Black: Multi-Lac A903 Black (manufactured by Toyo Color Co., Ltd.)

[0142] <Tackifying Resins> ・Rosin ester resin: Pine Crystal KE-359 (manufactured by Arakawa Chemical Industries, Ltd., softening point: 94-104°C, hydroxyl value: 38-47 mgKOH / g, tackifying resin containing bio-derived carbon) ・Terpene phenol resin: YS Polystar G150 (manufactured by Yasuhara Chemical Co., Ltd., softening point: 145-155°C, hydroxyl value: less than 120-140 mgKOH / g)

[0143] <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)

[0144] (Synthesis of Acrylic Copolymers) (Acrylic Copolymers A-K, O-Q, X-Y, AA, Z, a-d) A reactor equipped with a thermometer, stirrer, and condenser was prepared. A mixture of the constituent unit monomers shown in Tables 1-3 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 Co., Ltd.) 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 to 3.

[0145] (Acrylic copolymers R to U) Except for changing the solvent used in the polymerization reaction from 80 parts by mass of ethyl acetate to the solvent shown below, the synthesis was carried out in the same manner as for acrylic copolymers A to K, O to Q, X to Y, AA, Z, and a to d, and the weight-average molecular weight was measured. The results are shown in Table 2. <Solvent used in polymerization reaction> Acrylic copolymer R: 100 parts by mass of ethyl acetate Acrylic copolymer S: 90 parts by mass of ethyl acetate Acrylic copolymer T: 70 parts by mass of ethyl acetate Acrylic copolymer U: 60 parts by mass of ethyl acetate

[0146] (Acrylic copolymers L-N, V-W) (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 in an evaporator to remove the organic solvent. The resulting concentrate was purified by silica gel column chromatography to obtain the RAFT agent.

[0147] (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 polymerization initiators, and 80 g of ethyl acetate as a solvent were placed in a two-necked flask, and the flask was heated to 85°C while purging the inside of 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).

[0148] (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, 5 g of ethyl acetate as a solvent, and the previously obtained block having constituent units derived from styrene were placed in a two-necked flask, and the flask was heated to 85°C while purging the inside of the flask with nitrogen gas. Then, the polymerization reaction was 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-Q, X-Y, AA, Z, and a-d. The results are shown in Tables 1-2.

[0149]

[0150]

[0151]

[0152] (Example 1) (1) Preparation of adhesive tape To the solution of acrylic copolymer A 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 A, 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. The release surface of a 50 μm thick release PET film was bonded to the resulting adhesive layer, and then cured at 40°C for 48 hours to obtain an adhesive tape.

[0153] (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 4. 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)

[0154] (3) Measurement of the shear storage modulus of the adhesive layer at 23°C and 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 at 65°C were measured. The results are shown in Table 4.

[0155] (4) 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 (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 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 4.

[0156] (Examples 2-23, Comparative Examples 1-5) 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 and thickness of the adhesive layer were as shown in Tables 4-5 and 8. The results are shown in Tables 4-5 and 8.

[0157] (Examples 24-25) The adhesive layer was formed in the same manner as in Example 1, except that the composition and 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 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., and "polyethylene foam" is Volara (thickness: 100 μm) manufactured by Sekisui Chemical Co., Ltd.

[0158] In Examples 24-25, for 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 following 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 "(3) 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" and "(4) 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.

[0159] (Example 26) (1) Preparation of adhesive tape To the solution of acrylic copolymer Q obtained in "(Synthesis of acrylic copolymer)" described above, 0.4 parts by mass of thermally expandable microcapsules as foaming particles and 30 parts by mass of ethyl acetate as a solvent were added to 100 parts by mass of solids of acrylic copolymer Q, 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 by heating at 155°C for 1 hour to form a foamed structure, thereby forming a 200 μm thick adhesive layer having a foamed structure. The resulting 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.

[0160] (2) Measurement of the gel fraction of the adhesive layer The gel fraction of the adhesive layer was measured using the same method as in Example 1. The results are shown in Table 6.

[0161] (3) 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 The shear storage modulus of the adhesive layer at 23°C and the shear storage modulus of the adhesive layer at 65°C were measured using the same method as in Example 1. The results are shown in Table 6.

[0162] (4) Measurement of the loss tangent of the adhesive layer at 23°C The loss tangent of the adhesive layer at 23°C was measured using the same method as in Example 1. The results are shown in Table 6.

[0163] (5) Measurement of the deemed density of the adhesive layer The release PET film on both sides is peeled off from the adhesive tape, and the deemed density of the adhesive layer is determined in accordance with JIS K 7222 (g / cm³). ３ The following was measured. The results are shown in Table 6.

[0164] (Examples 27-47, 49-50) In the above-described "(1) Preparation of adhesive tape," the adhesive tape was prepared and various measurements were taken in the same manner as in Example 26, except that the composition and thickness of the adhesive layer were as shown in Tables 6-7. The results are shown in Tables 6-7.

[0165] (Example 48) An adhesive layer having a foamed structure was formed in the same manner as in Example 1, except that the composition and thickness of the adhesive layer were as shown in Table 7. The obtained adhesive layer was attached to one side of the substrate shown in Table 7, 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 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 for 1 hour in an environment of 23°C to obtain an adhesive tape having adhesive layers on both sides of the substrate. Note that "PET film" in Table 7 is Lumirror (thickness: 38 μm) manufactured by Toray Industries, Inc.

[0166] Furthermore, the measurements described above for "(2) Measurement of the gel fraction of the adhesive layer," "(3) 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," and "(4) Measurement of the loss tangent of the adhesive layer at 23°C" were performed using the same methods as in Examples 24 and 25. The results are shown in Table 7. In addition, for "(5) Measurement of the deemed density of the adhesive layer" described above, the adhesive layer was removed from the obtained adhesive tape using a cutter knife, and the measurement was performed using the same method as in Example 26. The results are shown in Table 7.

[0167] (Examples 51-52) The composition and thickness of the adhesive layer were as shown in Table 7, and instead of heating at 155°C for 1 hour during the drying process, 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 26. The results are shown in Table 7.

[0168] <Evaluation> The adhesive tapes obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 4 to 8.

[0169] (Rough Surface Adhesion) In accordance with JIS Z 0237:2009, the 180° peel strength of the adhesive tape was measured on water-resistant abrasive paper (Noritake Coated Abrasives, "C947H", grit size 360, surface roughness Ra = 10.8 μm) as a rough surface. The surface roughness Ra of the water-resistant abrasive paper was measured using a laser microscope (KEYENCE, color 3D laser microscope, "VK-8710"). Specifically, first, the back side of the water-resistant abrasive paper was bonded to a SUS304 plate using adhesive tape (Sekisui Chemical Co., Ltd., "#560"). Next, one side (the side not measured) of the adhesive tape obtained in the examples and comparative examples was backed with a 23 μm thick polyethylene terephthalate film (Futamura Chemical Co., Ltd., "FE2002"), and then cut to a width of 25 mm x length of 75 mm to prepare test specimens. The test specimen was placed on the abrasive surface of water-resistant abrasive paper, which was attached to a SUS304 plate, with the adhesive layer (the side to be measured) facing the abrasive surface. Then, a 2 kg rubber roller was passed back and forth once at a speed of 300 mm / min to bond the specimen. After that, it was cured at 23°C and 50% RH for 20 minutes to prepare the test sample. In accordance with JIS Z 0237:2009, the test sample was peeled in the 180° direction at a tensile speed of 300 mm / min under conditions of 23°C and 50% RH, and the peel force (N / 25 mm) was measured. The adhesion to rough surfaces was evaluated according to the following criteria: A: Peel force was 15.0 N / 25 mm or more. B: Peel force was 12.0 N / 25 mm or more and less than 15.0 N / 25 mm. C: Peel force was 10.0 N / 25 mm or more and less than 12.0 N / 25 mm. D: The peeling force was less than 10.0 N / 25 mm.

[0170] (Heat Resistance) The heat resistance of the adhesive tape was evaluated by conducting the heat resistance test described below. Figure 1 shows a schematic representation of the heat resistance test. Specifically, first, one side of the adhesive tape 2 (the side not measured) was backed with a 23 μm thick polyethylene terephthalate film 1 (Futamura Chemical Co., Ltd., "FE2002"), and then cut to a width of 25 mm x length of 75 mm to prepare a test piece. This test piece was placed opposite a SUS304 plate 3 (a SUS304 plate that had been washed with ethanol and then wiped dry) with an adhesive layer (the side to be measured) that was 2 mm thick, 50 mm wide, and 80 mm long, so that the adhesive area was 25 mm x 25 mm. Then, a 2 kg rubber roller was passed back and forth once at a speed of 300 mm / min to bond the test piece. After that, it was cured at 23°C and 50% RH for 20 minutes to prepare a test sample. The test sample was placed in an environment of 80°C and 50% RH and left to stand for 15 minutes. Then, in this environment, a 1 kg weight 4 was attached to the polyethylene terephthalate film 1 of the test sample in accordance with JIS Z 0237:2009 so that a shear load was applied. One hour after attaching the weight 4, the amount of shear displacement from the position where the adhesive layer SUS304 plate 3 was bonded was measured, and the heat resistance of the adhesive tape was evaluated according to the following criteria: A: The amount of displacement was 0.5 mm or less. B: The amount of displacement was greater than 0.5 mm and 10 mm or less. C: The amount of displacement was greater than 10 mm, but the test piece did not fall. D: The test piece fell.

[0171] (Bending Resistance) Figure 2 shows a schematic diagram illustrating the evaluation method for bending resistance. Aluminum alloy plates (SHAANXI SHEEW-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 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 a laminate 5. The produced laminate 5 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 2 (distance between compression jigs: 57.15 mm, distance between fixing jigs: 177.8 mm). Subsequently, the laminate 5 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 more. B: The slope of the line was 15.5 N / mm or more 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.

[0172] (Impact Absorption) The resulting adhesive tape 2 was cut to a size of 30 mm x 30 mm, and two SUS plates 8 measuring 125 mm x 50 mm and 2 mm thick were stacked as shown in Figure 3 to create a test specimen 9. For the resulting test specimen 9, as shown in Figure 4, the test specimen 9 was set up so that when the pendulum 10 passed its lowest point, it would collide with only one of the SUS plates 8 on the test specimen 9. Then, a pendulum 10 with a mass of 1.0 kg was free-falled from a height of 0.20 m (H in Figure 4) and collided with the test specimen, and 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 10 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.

[0173] (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, 50% RH for 20 minutes to prepare the 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.

[0174]

[0175]

[0176]

[0177]

[0178]

[0179] According to the present invention, it is possible to provide an adhesive composition that can achieve both excellent adhesion to rough surfaces and excellent heat resistance. Furthermore, according to the present invention, it is possible to provide an adhesive tape having an adhesive layer formed using the adhesive composition. Moreover, according to the present invention, it is possible to provide an electronic device containing the adhesive tape.

[0180] 1. Polyethylene terephthalate (PET) film 2. Adhesive tape 3. SUS304 plate 4. Weight (1 kg) 5. Laminate 6. Compression jig 7. Fixing jig 8. SUS plate 9. Test piece 10. Pendulum

Claims

1. An adhesive composition comprising an acrylic copolymer, wherein the acrylic copolymer has constituent units derived from alkyl (meth)acrylate and constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminus, 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.

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

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

4. The adhesive composition according to claim 1, 2, or 3, wherein the content of constituent units derived from an olefin polymer having a polymerizable unsaturated double bond at its terminal in the acrylic copolymer is 5% by mass or more and 50% by mass or less.

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

6. The adhesive composition according to claim 1, 2, 3, 4, or 5, 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.

7. The adhesive composition according to claim 6, 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.

8. The adhesive composition according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the acrylic copolymer has a weight-average molecular weight of 700,000 or more and 1,500,000 or less.

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

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

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

14. The adhesive composition according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the adhesive composition contains a crosslinking agent.

15. An adhesive tape having an adhesive layer formed using the adhesive composition according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14.

16. The adhesive tape according to claim 15, wherein the adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less.

17. The adhesive tape according to claim 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 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 15, 16, 17, or 18, wherein the adhesive layer has a loss 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 15, 16, 17, 18, or 19, wherein the adhesive layer contains 10% or more of bio-derived carbon.

21. The adhesive tape according to claim 15, 16, 17, 18, 19, or 20, wherein the adhesive layer has a foamed structure.

22. 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 21, which is as follows:

23. The adhesive tape according to claim 15, 16, 17, 18, 19, 20, 21, or 22, which does not have a base material.

24. The adhesive tape according to claim 15, 16, 17, 18, 19, 20, 21, or 22, having a base material.

25. The adhesive tape according to claim 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24, used for fixing electronic equipment components or in-vehicle components.

26. Electronic device comprising the adhesive tape according to claim 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25.

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