Adhesive tape

Abstract

To provide an adhesive tape having excellent initial reworkability, and capable of favorably using for fixing an adherend having a bent part.SOLUTION: An adhesive tape includes an adhesive layer formed using an adhesive composition, where the adhesive composition includes a (meth)acrylic copolymer, the (meth)acrylic copolymer has a constitutional unit derived from alkyl (meth)acrylate, a shear storage modulus at 23°C of the adhesive layer is 0.25 MPa or higher, and a loss tangent at 65°C of the adhesive layer is 0.50 or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive tape. [Background technology]

[0002] Conventionally, pressure-sensitive adhesive tapes having a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition have been widely used to fix components in electronic devices, vehicles, houses, and building materials (e.g., Patent Documents 1 to 3). Specifically, for example, pressure-sensitive adhesive tapes are used to adhere a cover panel for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or to adhere a touch panel module to a display panel module. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-052050 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-021067 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-120876 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, acrylic adhesives containing acrylic copolymers have been widely used as adhesives with excellent adhesive strength. Examples of acrylic monomers that constitute the acrylic copolymer contained in acrylic pressure-sensitive adhesives include alkyl (meth)acrylates such as n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. However, pressure-sensitive adhesives that use alkyl (meth)acrylates such as n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate as the main component have high tack, making them difficult to peel off when accidentally touching an adherend, and presenting a problem with initial reworkability.

[0005] Furthermore, in recent years, in order to improve the design of electronic devices, components such as displays have become more flexible and curved. Pressure-sensitive adhesive tapes used to fix adherends having bent portions, such as flexible or curved display components, are subjected to a repulsive force that attempts to return to a flat surface, and therefore, in order to withstand this repulsive force, they are required to have not only adhesive strength but also excellent stress relaxation properties.

[0006] An object of the present invention is to provide a pressure-sensitive adhesive tape that has excellent initial reworkability and can be suitably used for fixing an adherend having a curved portion. [Means for solving the problem]

[0007] Disclosure 1 relates to an adhesive tape having an adhesive layer formed using an adhesive composition, the adhesive composition containing a (meth)acrylic copolymer, the (meth)acrylic copolymer having a structural unit derived from alkyl (meth)acrylate, the adhesive layer having a shear storage modulus at 23°C of 0.25 MPa or more and a loss tangent at 65°C of 0.50 or more. Disclosure 2 is the pressure-sensitive adhesive tape of Disclosure 1, wherein the pressure-sensitive adhesive layer has a glass transition temperature of 0°C or higher as measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz and a measurement temperature range of -40°C or higher and 200°C or lower. Disclosure 3 is the pressure-sensitive adhesive tape of Disclosure 1 or 2, wherein the alkyl(meth)acrylate includes 1-methylheptyl(meth)acrylate. Disclosure 4 is the pressure-sensitive adhesive tape of Disclosure 3, wherein the (meth)acrylic copolymer contains 50 mass % or more of structural units derived from 1-methylheptyl (meth)acrylate. Disclosure 5 is a pressure-sensitive adhesive tape according to Disclosure 1, 2, 3, or 4, wherein the (meth)acrylic copolymer has a content of structural units derived from a (meth)acrylate having a linear alkyl group having 4 to 8 carbon atoms in an amount of less than 50%, or does not have any structural units derived from a (meth)acrylate having a linear alkyl group having 4 to 8 carbon atoms. The present disclosure 6 is the pressure-sensitive adhesive tape of the present disclosure 1, 2, 3, 4, or 5, wherein the (meth)acrylic copolymer further has a structural unit derived from n-heptyl (meth)acrylate. The present disclosure 7 is the pressure-sensitive adhesive tape of the present disclosure 1, 2, 3, 4, 5, or 6, wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer having a crosslinkable functional group. Disclosure 8 is the pressure-sensitive adhesive tape of Disclosure 7, wherein the monomer having a crosslinkable functional group includes a hydroxyl group-containing monomer. Disclosure 9 is the pressure-sensitive adhesive tape of Disclosure 7 or 8, wherein the (meth)acrylic copolymer contains 1.0 mass % or more and 20 mass % or less of the structural unit derived from the monomer having a crosslinkable functional group. Disclosure 10 is a pressure-sensitive adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, or 9, wherein the (meth)acrylic copolymer has at least one structural unit selected from the group consisting of structural units derived from a monomer having a cyclic ether structure free of an epoxy group or an oxetanyl group, and a non-cyclic ether structure. Disclosure 11 is the pressure-sensitive adhesive tape of Disclosure 10, in which the content of structural units derived from the cyclic ether structure free of the epoxy group and the oxetanyl group and the monomer having the acyclic ether structure is 0.01% by mass or more and 50% by mass or less. Disclosure 12 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the (meth)acrylic copolymer further has a structural unit derived from a monomer that does not have a crosslinkable functional group and has a glass transition temperature of 0°C or higher when made into a homopolymer. Disclosure 13 is the pressure-sensitive adhesive tape of Disclosure 12, in which the content of structural units derived from monomers that do not have the crosslinkable functional groups and have a glass transition temperature of 0°C or higher when made into a homopolymer is 0.1% by mass or more and 70% by mass or less. A fourteenth aspect of the present disclosure is the pressure-sensitive adhesive tape of the first, second, third, fourth, fifth, sixth, seventh, eighth, nineth, tenth, eleventh, twenty-two, or thirteenth aspect of the present disclosure, wherein the (meth)acrylic copolymer has a weight-average molecular weight of 800,000 or more. Disclosure 15 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the pressure-sensitive adhesive composition further contains a tackifier. The present disclosure 16 is the pressure-sensitive adhesive tape of the present disclosure 15, wherein the tackifier includes at least one selected from the group consisting of a rosin ester-based tackifier, a terpene-based tackifier, and a (meth)acrylic tackifier. Disclosure 17 is the pressure-sensitive adhesive tape of Disclosure 16, wherein the tackifier comprises the rosin ester-based tackifier and the terpene-based tackifier. Disclosure 18 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, wherein the pressure-sensitive adhesive composition further contains a crosslinking agent. Disclosure 19 is the pressure-sensitive adhesive tape of Disclosure 18, wherein the crosslinking agent includes at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. Disclosure 20 is the pressure-sensitive adhesive tape of Disclosure 19, wherein the crosslinking agent includes the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent. Present Disclosure 21 is the pressure-sensitive adhesive tape of Present Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the pressure-sensitive adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less. Disclosure 22 is an adhesive tape according to Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, having a substrate layer. Disclosure 23 is a pressure-sensitive adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22 used for fixing electronic equipment components or vehicle-mounted components. The present invention will be described in detail below.

[0008] The present inventors have investigated adjusting the shear storage modulus and loss tangent of a pressure-sensitive adhesive layer of a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer to fall within specific ranges, and as a result have found that a pressure-sensitive adhesive tape having excellent initial reworkability and suitable for use in fixing an adherend having a curved portion can be obtained, thereby completing the present invention. The pressure-sensitive adhesive tape of the present invention has excellent initial reworkability, and therefore can be more easily attached to an adherend.

[0009] In this specification, the type of each structural unit in the (meth)acrylic copolymer described below and the type of each component in the pressure-sensitive adhesive composition may be one type or two or more types, unless otherwise specified. Furthermore, in this specification, unless otherwise specified, "content ratio" and "content amount" refer to the type of structural unit that defines the "content ratio," or, when two or more types of components that define the "content amount" are included, the total content ratio of all types of said structural units and the total content amount of all types of said components.

[0010] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition. The shear storage modulus at 23°C of the pressure-sensitive adhesive layer described below, the loss tangent at 65°C of the pressure-sensitive adhesive layer described below, the gel fraction of the pressure-sensitive adhesive layer described below, and the content of bio-derived carbon of the pressure-sensitive adhesive layer described below can be adjusted to the values ​​described below by adjusting the type and content of each component constituting the pressure-sensitive adhesive composition. Examples of methods for forming the pressure-sensitive adhesive layer using the pressure-sensitive adhesive composition include a method in which the pressure-sensitive adhesive composition is applied to a release film or the like, and then the pressure-sensitive adhesive composition is dried by heating, etc. The pressure-sensitive adhesive layer may contain the uncrosslinked pressure-sensitive adhesive composition, or may contain a crosslinked product of the pressure-sensitive adhesive composition.

[0011] The lower limit of the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is 0.25 MPa. When the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is 0.25 MPa or more, tackiness of the pressure-sensitive adhesive layer can be suppressed, and the pressure-sensitive adhesive tape of the present invention exhibits excellent initial reworkability. The lower limit of the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is preferably 0.35 MPa, and more preferably 0.45 MPa. Furthermore, the upper limit of the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is preferably 1.00 MPa. When the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is 1.00 MPa or less, the pressure-sensitive adhesive layer does not become too hard, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, and the pressure-sensitive adhesive tape can be more suitably used for fixing an adherend having a curved portion. The upper limit of the shear storage modulus of the pressure-sensitive adhesive layer at 23°C is more preferably 0.80 MPa, and even more preferably 0.70 MPa.

[0012] The loss tangent (tanδ) of the pressure-sensitive adhesive layer at 65°C has a lower limit of 0.50. When the loss tangent of the pressure-sensitive adhesive layer at 65°C is 0.50 or more, the pressure-sensitive adhesive tape of the present invention has excellent stress relaxation properties and can be suitably used for fixing an adherend having a curved portion. The loss tangent of the pressure-sensitive adhesive layer at 65°C is preferably 0.52, more preferably 0.54. Furthermore, the upper limit of the loss tangent of the pressure-sensitive adhesive layer at 65°C is preferably 0.70. By having the loss tangent of the pressure-sensitive adhesive layer at 65°C of 0.70 or less, the pressure-sensitive adhesive tape of the present invention can be more suitably used for fixing an adherend having a curved portion even in a high-temperature environment without losing its adhesive strength. The upper limit of the loss tangent of the pressure-sensitive adhesive layer at 65°C is more preferably 0.65, and even more preferably 0.60.

[0013] The shear storage modulus of the pressure-sensitive adhesive layer at 23°C and the loss tangent of the pressure-sensitive adhesive layer at 65°C are measured by dynamic viscoelasticity measurement at a frequency of 1.0 Hz. Specifically, the pressure-sensitive adhesive layers alone are first stacked to produce a laminate approximately 1 mm thick, which is then cut into a 6 mm wide and 10 mm long specimen. The specimen is then subjected to dynamic viscoelasticity measurement using a dynamic viscoelasticity measuring device in shear mode under a nitrogen atmosphere at a temperature of -50°C to 150°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.1%. Examples of such dynamic viscoelasticity measuring devices include the DVA-200 (manufactured by IT Instrumentation & Control Co., Ltd.).

[0014] Specific methods for adjusting the shear storage modulus at 23°C of the pressure-sensitive adhesive layer include, for example, a method of adjusting the type and content of a tackifier, and a method of adjusting the type and content ratio of a monomer contained in the (meth)acrylic copolymer.

[0015] Specific methods for adjusting the loss tangent at 65°C of the pressure-sensitive adhesive layer include, for example, a method for adjusting the weight average molecular weight of the (meth)acrylic copolymer, a method for adjusting the type and content ratio of a monomer having a crosslinkable functional group, and a method for adjusting the type and content of a crosslinking agent.

[0016] The pressure-sensitive adhesive layer preferably has a glass transition temperature (hereinafter sometimes simply referred to as "glass transition temperature of the pressure-sensitive adhesive layer") of 0°C, as measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz and a measurement temperature range of -40°C to 200°C. When the pressure-sensitive adhesive layer has a glass transition temperature of 0°C or higher, the pressure-sensitive adhesive tape of the present invention has excellent initial reworkability. Furthermore, the pressure-sensitive adhesive tape of the present invention has improved heat resistance. The lower limit of the glass transition temperature of the pressure-sensitive adhesive layer is more preferably 5°C, even more preferably 10°C, even more preferably 12°C, and particularly preferably 15°C. Furthermore, the upper limit of the glass transition temperature of the pressure-sensitive adhesive layer is preferably 30° C. When the glass transition temperature of the pressure-sensitive adhesive layer is 30° C. or lower, the pressure-sensitive adhesive layer has appropriate flexibility, making it possible to provide a pressure-sensitive adhesive tape that can be more suitably used for fixing an adherend having a curved portion. The upper limit of the glass transition temperature of the pressure-sensitive adhesive layer is more preferably 27° C., and even more preferably 25° C. In this specification, the "glass transition temperature of the pressure-sensitive adhesive layer" refers to the temperature at which a maximum due to micro-Brownian motion appears among the maximum loss tangents (tan δ) obtained by dynamic viscoelasticity measurement. When there are multiple maximum loss tangents, in this specification, the "glass transition temperature of the pressure-sensitive adhesive layer" refers to the temperature at which the lowest loss tangent maximum appears among the maximum loss tangents in the range of -25°C to 50°C.

[0017] The glass transition temperature of the pressure-sensitive adhesive layer is measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz. Specifically, the pressure-sensitive adhesive layers are first stacked to form a laminate approximately 1 mm thick, which is then cut into a 6 mm wide and 10 mm long specimen. The specimen is then subjected to dynamic viscoelasticity measurement using a dynamic viscoelasticity measuring device in shear mode under a nitrogen atmosphere at a temperature range of -40°C to 200°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.08%. Examples of such dynamic viscoelasticity measuring devices include the DVA-200 (manufactured by IT Instrumentation & Control Co., Ltd.).

[0018] Specific methods for adjusting the glass transition temperature of the pressure-sensitive adhesive layer include, for example, a method of using an alkyl (meth)acrylate having a branched alkyl group such as 1-methylheptyl (meth)acrylate as a constituent monomer of the (meth)acrylic copolymer and adjusting its content ratio; a method of adjusting the content of a tackifier; a method of using a tackifier having a softening point within a specific range as a tackifier; and a method of adjusting the content of a crosslinking agent or the content of a monomer having a crosslinkable functional group, thereby adjusting the gel fraction of the pressure-sensitive adhesive layer.

[0019] The pressure-sensitive adhesive composition contains a (meth)acrylic copolymer. The (meth)acrylic copolymer has structural units derived from alkyl (meth)acrylate. In this specification, the term "(meth)acrylic" means acrylic or methacrylic, and the term "(meth)acrylate" means acrylate or methacrylate.

[0020] The alkyl (meth)acrylate in the structural unit derived from the alkyl (meth)acrylate may be composed solely of petroleum-derived materials, but preferably also contains biologically derived materials. In recent years, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products have become a major concern, and efforts have been made to conserve petroleum resources by using bio-derived materials instead of petroleum-derived materials. The alkyl (meth)acrylate contains a bio-derived material, which is preferable from the viewpoint of saving petroleum resources. Furthermore, since the bio-derived material is originally produced by absorbing carbon dioxide from the atmosphere, even if it is burned, it is thought that the total amount of carbon dioxide in the atmosphere will not increase, which is also preferable from the viewpoint of reducing carbon dioxide emissions.

[0021] When the alkyl(meth)acrylate contains a biologically derived material, the alkyl(meth)acrylate is preferably synthesized by esterifying an alcohol, which is a biologically derived material, with (meth)acrylic acid. An example of a method for obtaining alcohol, which is a biological material, is a method in which materials collected from plants and animals (e.g., ricinoleic acid derived from castor oil) are used as raw materials, and an alkali-fused mixture is distilled to obtain 1-methylheptyl alcohol, which is a biological material, inexpensively and easily.

[0022] The alkyl (meth)acrylate preferably contains 1-methylheptyl (meth)acrylate. When the alkyl (meth)acrylate contains 1-methylheptyl (meth)acrylate (i.e., the (meth)acrylic copolymer has a structural unit derived from 1-methylheptyl (meth)acrylate), the shear storage modulus at 23°C and the loss tangent at 65°C of the pressure-sensitive adhesive layer can be more appropriately adjusted. As a result, the pressure-sensitive adhesive tape of the present invention has better initial reworkability and can be more suitably used for fixing an adherend having a curved portion.

[0023] The preferred lower limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer is 50% by mass. When the content of the structural units derived from 1-methylheptyl (meth)acrylate is 50% by mass or more, the shear storage modulus at 23°C and the loss tangent at 65°C of the pressure-sensitive adhesive layer can be more appropriately adjusted. As a result, the pressure-sensitive adhesive tape of the present invention has better initial reworkability and can be more suitably used for fixing an adherend having a curved portion. The more preferred lower limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate is 70% by mass, and even more preferred is 90% by mass. Furthermore, the upper limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate may be 99.99% by mass, but from the viewpoint of the cohesive strength of the bulk of the pressure-sensitive adhesive layer, the upper limit is preferably 99% by mass. The content of the structural unit derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 C-NMR or the like) and the concentration can be calculated from the integrated intensity ratio of the hydrogen peak derived from the 1-methylheptyl (meth)acrylate.

[0024] The (meth)acrylic copolymer may have a structural unit derived from an alkyl (meth)acrylate other than 1-methylheptyl (meth)acrylate.

[0025] The alkyl (meth)acrylate other than the above-mentioned 1-methylheptyl (meth)acrylate is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-methylpentyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and methyl (meth)acrylate. Examples of the acrylic acid ester include methyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)octanol-1 and (meth)acrylic acid, esters of alcohols having a total of 18 carbon atoms and one or two methyl groups in the linear main chain and (meth)acrylic acid, behenyl (meth)acrylate, arachidyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

[0026] In the (meth)acrylic copolymer, the content of structural units derived from an alkyl (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms is preferably less than 50% by mass. When the content of structural units derived from an alkyl (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms is less than 50% by mass, the shear storage modulus at 23°C and the loss tangent at 65°C of the pressure-sensitive adhesive layer can be more appropriately adjusted. As a result, the pressure-sensitive adhesive tape of the present invention has better initial reworkability and can be more suitably used for fixing an adherend having a bent portion. When the alkyl (meth)acrylate has a structural unit derived from an alkyl (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms, the upper limit of the content of the structural unit derived from the (meth)acrylate having the linear alkyl group is more preferably 40 mass%, and even more preferably 25 mass%, and it is most preferable that the (meth)acrylic copolymer does not have a structural unit derived from the alkyl (meth)acrylate having the linear alkyl group having from 4 to 8 carbon atoms. The content of the structural unit derived from alkyl (meth)acrylate having a linear alkyl group having 4 to 8 carbon atoms can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 The degree of carbon monoxide absorption can be calculated from the integrated intensity ratio of the peak of hydrogen derived from the alkyl (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms.

[0027] Examples of the (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms include n-butyl(meth)acrylate, n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, and n-octyl(meth)acrylate. Among these, from the viewpoint of maintaining the flexibility of the pressure-sensitive adhesive layer while exhibiting excellent cohesive strength, when the (meth)acrylic copolymer has a structural unit derived from a (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms, it is preferred that the structural unit derived from the alkyl(meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms is a structural unit derived from n-heptyl(meth)acrylate.

[0028] The (meth)acrylic copolymer preferably further contains a structural unit derived from a monomer having a crosslinkable functional group. Since the (meth)acrylic copolymer contains structural units derived from the monomer having a crosslinkable functional group, the pressure-sensitive adhesive layer has excellent cohesive strength, which further reduces tackiness of the pressure-sensitive adhesive layer, resulting in the pressure-sensitive adhesive tape of the present invention having excellent initial reworkability. Furthermore, since the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved adhesive strength, making it more suitable for use in fixing an adherend having a curved portion. Furthermore, since the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved heat resistance and excellent retention performance at high temperatures.

[0029] Examples of the monomer having a crosslinkable functional group include a carboxy group-containing monomer, a hydroxy group-containing monomer, a glycidyl group-containing monomer, an amide group-containing monomer, a nitrile group-containing monomer, etc. Among these, the monomer having a crosslinkable functional group preferably includes at least one selected from the group consisting of a carboxy group-containing monomer and a hydroxy group-containing monomer, and more preferably includes a hydroxy group-containing monomer, because this facilitates adjustment of the shear storage modulus at 23°C of the pressure-sensitive adhesive layer, the loss tangent at 65°C of the pressure-sensitive adhesive layer, and the gel fraction of the pressure-sensitive adhesive layer, which will be described later. The monomer having a crosslinkable functional group has a homopolymer Tg, which will be described later, but is not particularly limited, and may be 0° C. or higher. The monomer having a crosslinkable functional group preferably has a (meth)acryloyl group. In this specification, the term "(meth)acryloyl" means acryloyl or methacryloyl.

[0030] Examples of the carboxy group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, (meth)acryloylacetic acid, (meth)acryloylpropionic acid, (meth)acryloylbutyric acid, (meth)acryloylpentanoic acid, and crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 1-methyl-2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1-methyl-2-hydroxypropyl (meth)acrylate, 1-methyl-3-hydroxypropyl (meth)acrylate, 1-ethyl-2-hydroxyethyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate, and polypropylene glycol mono(meth)acrylate. The glycidyl group-containing monomer may, for example, be glycidyl (meth)acrylate. Examples of the amide group-containing monomer include dimethyl(meth)acrylamide, isopropyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Examples of the nitrile group-containing monomer include (meth)acrylonitrile.

[0031] The preferred lower limit of the content of the structural unit derived from the monomer having a crosslinkable functional group in the (meth)acrylic copolymer is 1.0% by mass, and the preferred upper limit is 20% by mass. When the content of the structural unit derived from the monomer having a crosslinkable functional group is 1.0% by mass or more, the pressure-sensitive adhesive layer has excellent cohesive strength, thereby further reducing tackiness of the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive tape of the present invention has excellent initial reworkability. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved adhesive strength, making it more suitable for use in fixing an adherend having a curved portion. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved heat resistance, making it more suitable for use in fixing an adherend having a curved portion. When the content of the structural unit derived from the monomer having a crosslinkable functional group is 20% by mass or less, the pressure-sensitive adhesive layer does not become too hard, and the pressure-sensitive adhesive tape of the present invention has improved adhesive strength, making it more suitable for use in fixing an adherend having a curved portion. The more preferred lower limit of the content of the structural units derived from the monomer having a crosslinkable functional group is 3.0% by mass, the more preferred upper limit is 15% by mass, the even more preferred lower limit is 5.0% by mass, and the even more preferred upper limit is 10% by mass. The content of the structural unit derived from the monomer having a crosslinkable functional group in the (meth)acrylic copolymer can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 C-NMR or the like) and the degree of crosslinking can be calculated from the integrated intensity ratio of the hydrogen peak derived from the monomer having the crosslinkable functional group.

[0032] The preferred lower limit of the content of the structural units derived from the hydroxyl group-containing monomer in the (meth)acrylic copolymer is 0.01% by mass, and the preferred upper limit is 2.0% by mass. When the content of the structural units derived from the hydroxyl group-containing monomer is within the above range, the pressure-sensitive adhesive layer is more likely to form a crosslinked structure, and the pressure-sensitive adhesive layer has appropriate bulk strength, thereby further improving the heat resistance of the pressure-sensitive adhesive tape of the present invention. Furthermore, the pressure-sensitive adhesive tape has further improved retention performance at high temperatures. The more preferred lower limit of the content of the structural units derived from the hydroxyl group-containing monomer is 0.05% by mass, the more preferred upper limit is 1.0% by mass, and the even more preferred lower limit is 0.1% by mass. The content of the structural units derived from the hydroxyl group-containing monomer in the (meth)acrylic copolymer can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 C-NMR or the like) and the ratio of the integrated intensities of the hydrogen peaks derived from the hydroxyl group-containing monomer can be calculated.

[0033] The preferred lower limit of the content of the structural units derived from the carboxyl group-containing monomer in the (meth)acrylic copolymer is 0.1% by mass, and the preferred upper limit is 15% by mass. When the content of the structural units derived from the carboxyl group-containing monomer is within the above range, the pressure-sensitive adhesive layer is more likely to form a crosslinked structure, and the pressure-sensitive adhesive layer has appropriate bulk strength, thereby further improving the heat resistance of the pressure-sensitive adhesive tape of the present invention. Furthermore, the pressure-sensitive adhesive tape has further improved retention performance at high temperatures. The more preferred lower limit of the content of the structural units derived from the carboxyl group-containing monomer is 1.0% by mass, and the more preferred upper limit is 10% by mass, and the even more preferred lower limit is 3.0% by mass, and the even more preferred upper limit is 8.0% by mass. The range of the content of the structural unit derived from the carboxy group-containing monomer may be, for example, 0.1% by mass or more and 15% by mass or less, 0.1% by mass or more and 10% by mass or less, 0.1% by mass or more and 8.0% by mass or less, 1.0% by mass or more and 15% by mass or less, 1.0% by mass or more and 10% by mass or less, 1.0% by mass or more and 8.0% by mass or less, 3.0% by mass or more and 15% by mass or less, 3.0% by mass or more and 10% by mass or less, or 3.0% by mass or more and 8.0% by mass or less. The content of the structural units derived from the carboxyl group-containing monomer in the (meth)acrylic copolymer can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 C-NMR or the like) and the ratio of the integrated intensities of the hydrogen peaks derived from the carboxyl group-containing monomer can be calculated.

[0034] The (meth)acrylic copolymer preferably has at least one constituent unit selected from the group consisting of constituent units derived from monomers having a cyclic ether structure other than the epoxy group and the oxetanyl group, and constituent units derived from monomers having an acyclic ether structure (hereinafter, sometimes simply referred to as "constituent units derived from monomers having a non-crosslinkable ether structure"). When the (meth)acrylic copolymer has the constituent units derived from monomers having a non-crosslinkable ether structure, the resulting pressure-sensitive adhesive layer has improved adhesive strength and can exhibit better adhesion to adherends.

[0035] Examples of the monomer having a cyclic ether structure other than the epoxy group and the oxetanyl group include monomers having a cyclic ether structure such as tetrahydrofurfuryl (meth)acrylate. Examples of the monomer having an acyclic ether structure include monomers having an acyclic ether structure such as 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and ethyl carbitol (meth)acrylate.

[0036] The content of the structural units derived from the monomer having a non-crosslinkable ether structure in the (meth)acrylic copolymer is preferably up to 50% by mass. When the content of the structural units derived from the monomer having a non-crosslinkable ether structure is 50% by mass or less, the resulting pressure-sensitive adhesive layer has improved adhesive strength and can exhibit superior adhesion to the adherend. The content of the structural units derived from the monomer having a non-crosslinkable ether structure is more preferably up to 30% by mass, and even more preferably up to 10% by mass. Furthermore, when the (meth)acrylic copolymer has a constituent unit derived from the monomer having the non-crosslinkable ether structure, the lower limit of the content of the constituent unit derived from the monomer having the non-crosslinkable ether structure in the (meth)acrylic copolymer is not particularly limited as long as it is more than 0 mass%, but a preferred lower limit is 0.01 mass%, a more preferred lower limit is 0.1 mass%, and an even more preferred lower limit is 1.0 mass%. Note that the (meth)acrylic copolymer may not have a constituent unit derived from the monomer having the ether structure, i.e., the content of the constituent unit derived from the monomer having the non-crosslinkable ether structure may be 0 mass%. Examples of the content of the structural unit derived from the monomer having a non-crosslinkable ether structure include ranges of 0% by mass to 50% by mass, 0% by mass to 30% by mass, 0% by mass to 10% by mass, more than 0% by mass to 50% by mass, more than 0% by mass to 30% by mass, more than 0% by mass to 10% by mass, 0.01% by mass to 50% by mass, 0.01% by mass to 30% by mass, 0.01% by mass to 10% by mass, 0.01% by mass to 10% by mass, 0.1% by mass to 50% by mass, 0.1% by mass to 30% by mass, 0.1% by mass to 10% by mass, 1.0% by mass to 50% by mass, 1.0% by mass to 30% by mass, and 1.0% by mass to 10% by mass. The content of the structural unit derived from the monomer having a non-crosslinkable ether structure can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13C-NMR or the like) and calculation can be performed from the integrated intensity ratio of the hydrogen peak derived from the structural unit derived from the monomer having the non-crosslinkable ether structure.

[0037] The (meth)acrylic copolymer may contain structural units derived from other monomers other than the structural units derived from alkyl (meth)acrylate, the structural units derived from the monomer having a crosslinkable functional group, and the structural units derived from the monomer having a non-crosslinkable ether structure, within the scope of not impairing the object of the present invention.

[0038] Examples of the other monomers include benzyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. Furthermore, examples of the other monomers that can be used include various monomers that are commonly used as raw materials for (meth)acrylic copolymers, such as vinyl acetate and styrene.

[0039] It is preferable to use acrylate monomers as the alkyl (meth)acrylates such as the 1-methylheptyl (meth)acrylate, the monomers having a crosslinkable functional group, the monomers having a non-crosslinkable ether structure, and the other monomers. By using acrylate monomers as the 1-methylheptyl (meth)acrylate, the monomers having a crosslinkable functional group, the monomers having a non-crosslinkable ether structure, and the other monomers, the pressure-sensitive adhesive layer does not become too hard compared to when a methacrylate monomer is used, and the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion.

[0040] The (meth)acrylic copolymer preferably has a structural unit derived from a monomer that does not have a crosslinkable functional group and that, when made into a homopolymer, has a glass transition temperature (hereinafter sometimes simply referred to as "homopolymer Tg") of 0° C. or higher. When the (meth)acrylic copolymer has a structural unit derived from a monomer that does not have a crosslinkable functional group and has a homopolymer Tg of 0° C. or higher, it can exhibit higher shear adhesive strength. The monomer having no crosslinkable functional group and having a glass transition temperature of 0°C or higher when made into a homopolymer may be one included in the other alkyl(meth)acrylates or a monomer other than the alkyl(meth)acrylates. The monomer having no crosslinkable functional group and having a glass transition temperature of 0°C or higher when made into a homopolymer may be one included in the non-crosslinkable ether structure monomer.

[0041] Examples of the crosslinkable functional group in the monomer that does not have the above crosslinkable functional group and has a homopolymer Tg of 0° C. or higher include a carboxy group, a hydroxyl group, a glycidyl group, an amide group, and a nitrile group.

[0042] Specific examples of the monomer that does not have a crosslinkable functional group and has a homopolymer Tg of 0°C or higher include n-hexyl methacrylate (homopolymer Tg: 0°C), t-butyl acrylate (homopolymer Tg: 14°C), t-butyl methacrylate (homopolymer Tg: 107°C), cyclohexyl acrylate (homopolymer Tg: 15°C), isobornyl acrylate (homopolymer Tg: 97°C), isobornyl methacrylate (homopolymer Tg: 110°C), tetrahydrofurfuryl methacrylate (homopolymer Tg: 35°C), vinyl acetate (homopolymer Tg: 29°C), and styrene (homopolymer Tg: 100°C).

[0043] The content of the structural units derived from a monomer having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher in the (meth)acrylic copolymer is preferably 0.1% by mass at the lower limit and 70% by mass at the upper limit. When the content of the structural units derived from a monomer having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher is 0.1% by mass or higher, higher shear adhesive strength can be exhibited. When the content of the structural units derived from a monomer having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher is 70% by mass or lower, higher adhesive strength can be exhibited. The content of the structural units derived from a monomer having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher is more preferably 1% by mass at the lower limit and 50% by mass at the upper limit, and even more preferably 3% by mass at the lower limit and 30% by mass at the upper limit. Examples of the content of structural units derived from monomers that do not have the above-mentioned crosslinkable functional groups and have a homopolymer Tg of 0°C or higher include 0.1% by mass to 70% by mass, 0.1% by mass to 50% by mass, 0.1% by mass to 30% by mass, 1% by mass to 70% by mass, 1% by mass to 50% by mass, 1% by mass to 30% by mass, 3% by mass to 70% by mass, 3% by mass to 50% by mass, and 3% by mass to 30% by mass. The content of the structural unit derived from a monomer having no crosslinkable functional group and a homopolymer Tg of 0°C or higher can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR, 13 C-NMR or the like) and the degree of crosslinking can be calculated from the integrated intensity ratio of the hydrogen peak derived from the monomer that does not have the above-mentioned crosslinkable functional group and has a homopolymer Tg of 0° C. or higher.

[0044] The monomer having a crosslinkable functional group, the monomer having a non-crosslinkable ether structure, and the other monomers preferably contain biologically derived materials, but may also consist solely of petroleum-derived materials. Theoretically, all of the acrylic monomers constituting the (meth)acrylic copolymer may be monomers containing biologically-derived materials. From the viewpoint of cost and productivity of the pressure-sensitive adhesive composition, it is also possible to adopt a monomer containing a relatively inexpensive and easily available biologically-derived material and combine this with a monomer consisting solely of a petroleum-derived material.

[0045] The weight average molecular weight of the (meth)acrylic copolymer may be, for example, in the range of 30,000 to 2,000,000. The (meth)acrylic copolymer preferably has a lower limit of 800,000 weight-average molecular weight. When the (meth)acrylic copolymer has a weight-average molecular weight of 800,000 or more, the pressure-sensitive adhesive layer has excellent cohesive strength, which further reduces tackiness of the pressure-sensitive adhesive layer, resulting in the pressure-sensitive adhesive tape of the present invention having excellent initial reworkability. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved adhesive strength, making it more suitable for use in fixing an adherend having a curved portion. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the pressure-sensitive adhesive tape of the present invention has improved heat resistance, resulting in excellent high-temperature retention performance. A more preferred lower limit of the weight-average molecular weight of the (meth)acrylic copolymer is 1,000,000. Furthermore, the preferred upper limit of the weight-average molecular weight of the (meth)acrylic copolymer is 1.5 million. When the weight-average molecular weight of the (meth)acrylic copolymer is 1.5 million or less, the pressure-sensitive adhesive layer does not become too hard, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, and it can be more suitably used for fixing an adherend having a curved portion. The more preferred upper limit of the weight-average molecular weight of the (meth)acrylic copolymer is 1.2 million. In this specification, the weight-average molecular weight is a weight-average molecular weight measured by GPC (gel permeation chromatography) in terms of standard polystyrene. Specifically, a (meth)acrylic copolymer is diluted 50 times with tetrahydrofuran (THF) and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. Next, this measurement sample is supplied to a gel permeation chromatograph, and GPC measurement is performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the (meth)acrylic copolymer is measured, and this value is taken as the weight-average molecular weight of the (meth)acrylic copolymer. An example of the gel permeation chromatograph is the 2690 Separations Module (manufactured by Waters).

[0046] Examples of methods for adjusting the weight average molecular weight of the (meth)acrylic copolymer include a method of changing the type or amount of a polymerization initiator or the monomer concentration during the polymerization reaction, a method of adding a small amount of a chain transfer agent such as dodecyl mercaptan, a method of changing the type of polymerization solvent to control chain transfer to the solvent, and a method of changing the temperature and time during polymerization.

[0047] The (meth)acrylic copolymer can be obtained by polymerizing a mixture of constituent monomers as raw materials through a radical reaction in the presence of a polymerization initiator. Examples of the radical reaction method include living radical polymerization, free radical polymerization, etc. Living radical polymerization can provide a copolymer having a more uniform molecular weight and composition compared to free radical polymerization, and can suppress the generation of low molecular weight components, etc., so that the resulting pressure-sensitive adhesive layer can exhibit stronger cohesive strength and therefore can exhibit better adhesion to the adherend. The method for polymerizing the monomer mixture can be a conventionally known method, such as solution polymerization (boiling point polymerization or constant temperature polymerization), UV polymerization, emulsion polymerization, suspension polymerization, bulk polymerization, etc. Among these, solution polymerization and UV polymerization are preferred because the resulting pressure-sensitive adhesive layer can exhibit superior adhesion to the adherend. When solution polymerization is used as the method for polymerizing the monomer mixture, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, and diethyl ether.

[0048] Examples of the polymerization initiator include organic peroxides and azo compounds. Examples of the 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 the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. Furthermore, when the radical reaction method is the living radical polymerization, the polymerization initiator may be, for example, an organic tellurium polymerization initiator. The organic tellurium polymerization initiator is not particularly limited as long as it is one that is generally used in living radical polymerization, and examples thereof include organic tellurium compounds, organic telluride compounds, etc. Note that, in the living radical polymerization, in addition to the organic tellurium polymerization initiator, the azo compound may also be used for the purpose of accelerating the polymerization rate.

[0049] The content of the (meth)acrylic copolymer in the pressure-sensitive adhesive composition is not particularly limited, but a preferred lower limit is 50% by mass. When the content of the (meth)acrylic copolymer is 50% by mass or more, the pressure-sensitive adhesive tape of the present invention has better initial reworkability and can be more suitably used for fixing an adherend having a curved portion. A more preferred lower limit of the content of the (meth)acrylic copolymer is 70% by mass. The content of the (meth)acrylic copolymer in the pressure-sensitive adhesive composition may be 100% by mass, that is, the pressure-sensitive adhesive composition may contain only the (meth)acrylic copolymer.

[0050] The pressure-sensitive adhesive composition preferably further contains a tackifier. By containing a tackifier in the pressure-sensitive adhesive composition, the storage modulus at 23°C and the glass transition temperature of the pressure-sensitive adhesive layer are appropriately improved, thereby further suppressing tackiness, thereby further improving the initial reworkability of the pressure-sensitive adhesive tape of the present invention. In addition, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion.

[0051] The tackifier is not particularly limited, and examples thereof include rosin ester tackifiers, terpene tackifiers, coumarone-indene tackifiers, alicyclic saturated hydrocarbon tackifiers, C5 petroleum tackifiers, C9 petroleum tackifiers, C5-C9 copolymer petroleum tackifiers, and (meth)acrylic tackifiers. These tackifiers may be used alone or in combination of two or more. Among these, from the viewpoint of compatibility with the (meth)acrylic copolymer, it is preferable to include at least one selected from the group consisting of rosin ester tackifiers, terpene tackifiers, and (meth)acrylic tackifiers, and it is more preferable to include a rosin ester tackifier and a terpene tackifier.

[0052] Examples of the rosin ester tackifier include polymerized rosin ester resins, hydrogenated rosin ester resins, etc. Examples of the terpene tackifier include terpene resins, terpene phenol resins, etc. The rosin ester tackifier and the terpene tackifier are preferably derived from a living organism. Examples of the rosin ester tackifier derived from a living organism include a rosin ester tackifier derived from a natural resin such as pine resin. Examples of the terpene tackifier derived from a living organism include a terpene tackifier derived from plant essential oils.

[0053] Specific examples of the rosin ester tackifier include Pencel D-135, Pine Crystal KE-359, Ester Gum AA-V, and Ester Gum H (all manufactured by Arakawa Chemical Industries, Ltd.). Specific examples of the terpene-based tackifier include YS Resin PX1250 and YS Polystar G150 (both manufactured by Yasuhara Chemical Co., Ltd.).

[0054] The (meth)acrylic tackifier is made of a (meth)acrylic compound having a weight average molecular weight of less than 30,000. Examples of the (meth)acrylic compound having a weight-average molecular weight of less than 30,000 include a (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 and a (meth)acrylic monomer having a weight-average molecular weight of less than 30,000, and among these, a (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 is preferred.

[0055] The weight average molecular weight of the (meth)acrylic oligomer used as the (meth)acrylic tackifier is less than 30,000. Furthermore, the weight-average molecular weight of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 is preferably 1,000 or more and less than 30,000. When the weight-average molecular weight of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 is within the above range, the adhesive strength of the obtained pressure-sensitive adhesive layer is further improved. The weight-average molecular weight of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 is more preferably 1,500 or more and less than 20,000, and even more preferably 2,000 or more and less than 10,000. The weight average molecular weight of the (meth)acrylic oligomer having a weight average molecular weight of less than 30,000 can be measured by the same method as the method for measuring the weight average molecular weight of the (meth)acrylic copolymer described above.

[0056] The (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 used as the (meth)acrylic tackifier has a glass transition temperature of preferably 0°C at its lower limit and 300°C at its upper limit. When the glass transition temperature of the acrylic oligomer having a weight-average molecular weight of less than 30,000 is within the above range, the adhesive strength of the resulting pressure-sensitive adhesive layer is further improved. The glass transition temperature of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 is more preferably 20°C at its lower limit, and even more preferably 40°C at its upper limit. The glass transition temperature of the (meth)acrylic oligomer having a weight average molecular weight of less than 30,000 may be, for example, 0°C or higher and 300°C or lower, 20°C or higher and 300°C or lower, or 40°C or higher and 300°C or lower. The glass transition temperature of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 can be measured, for example, by differential scanning calorimetry under a nitrogen atmosphere (nitrogen flow, flow rate 50 mL / min) in accordance with JIS K6240:2011, at a measurement temperature of -100°C to 200°C and a heating rate of 10°C / min.

[0057] Examples of the constituent monomer of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 and the (meth)acrylic monomer having a weight-average molecular weight of less than 30,000 include the same monomers as those used in the constituent units derived from the alkyl (meth)acrylate, the constituent units derived from the monomer having a crosslinkable functional group, the constituent units derived from the monomer having a non-crosslinkable ether structure, and the constituent units derived from the other monomers in the (meth)acrylic copolymer described above.

[0058] Specific examples of the constituent monomer of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000 and the (meth)acrylic monomer having a weight-average molecular weight of less than 30,000 include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, alkyl (meth)acrylates such as acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols. The (meth)acrylic oligomer having a weight average molecular weight of less than 30,000 preferably contains, as a monomer unit, a (meth)acrylic monomer having a relatively bulky structure, typified by alkyl (meth)acrylates in which the alkyl group is branched, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and (meth)acrylates having a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer. In addition to the (meth)acrylate monomers, monomers having crosslinkable functional groups can be used as constituent monomer components of the (meth)acrylic oligomer having a weight-average molecular weight of less than 30,000. Suitable examples of the monomers having crosslinkable functional groups include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as acrylic acid and methacrylic acid; and hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These monomers having crosslinkable functional groups can be used alone or in combination of two or more. Among these, carboxy group-containing monomers are preferred, with acrylic acid being particularly preferred. For example, using a carboxy group-containing monomer as the monomer having a crosslinkable functional group can improve adhesion to highly polar adherends.

[0059] The (meth)acrylic oligomer can be synthesized, for example, by the same method as that for the (meth)acrylic copolymer described above. Furthermore, a commercially available product may be used as the (meth)acrylic tackifier.

[0060] The tackifier preferably contains a tackifier having a softening point of 80°C or higher and 170°C or lower. By containing a tackifier having a softening point of 80°C or higher and 170°C or lower, it becomes easier to adjust the glass transition temperature of the pressure-sensitive adhesive layer to within the above-mentioned range, and the obtained pressure-sensitive adhesive tape has better heat resistance. The softening point of the tackifier more preferably has a lower limit of 90°C, a more preferred upper limit of 160°C, an even more preferred lower limit of 100°C, and an even more preferred upper limit of 150°C. The softening point range of the tackifier may be, for example, 80°C or higher and 170°C or lower, 80°C or higher and 160°C or lower, 80°C or higher and 150°C or lower, 90°C or higher and 170°C or lower, 90°C or higher and 160°C or lower, 90°C or higher and 150°C or lower, 100°C or higher and 170°C or lower, 100°C or higher and 160°C or lower, or 100°C or higher and 150°C or lower. In this specification, the "softening point" refers to a softening point measured by a method in accordance with JIS K 2207 (ring and ball method).

[0061] The preferred lower limit of the content of the tackifier relative to 100 parts by mass of the (meth)acrylic copolymer is 10 parts by mass, and the preferred upper limit is 50 parts by mass. When the content of the tackifier is 10 parts by mass or more, tackiness of the pressure-sensitive adhesive layer can be further suppressed, thereby further improving the initial reworkability of the pressure-sensitive adhesive tape of the present invention. Furthermore, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion. When the content of the tackifier is 50 parts by mass or less, the pressure-sensitive adhesive layer does not become too hard, and the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion. The more preferred lower limit of the content of the tackifier is 20 parts by mass, and the more preferred upper limit is 40 parts by mass.

[0062] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent, from the viewpoint of being able to appropriately adjust the gel fraction of the pressure-sensitive adhesive layer, which will be described later. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a metal chelate-based crosslinking agent, etc. Among these, the crosslinking agent preferably contains at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, more preferably an isocyanate-based crosslinking agent, and even more preferably contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, because this provides the pressure-sensitive adhesive layer with better adhesion to the adherend, further improves the stress relaxation property of the pressure-sensitive adhesive tape of the present invention, and makes it more suitable for use in fixing an adherend having a curved portion.

[0063] The content of the crosslinking agent relative to 100 parts by mass of the (meth)acrylic copolymer is not particularly limited, but a preferred lower limit is 0.5 parts by mass and a preferred upper limit is 10 parts by mass. By ensuring that the content of the crosslinking agent is within this range, the gel fraction of the pressure-sensitive adhesive layer (described below) can be appropriately adjusted, and the pressure-sensitive adhesive layer will have superior adhesive strength and superior adhesion to the adherend. As a result, the pressure-sensitive adhesive tape of the present invention will have superior initial reworkability and superior stress relaxation properties. A more preferred lower limit of the content of the crosslinking agent is 2.0 parts by mass and a more preferred upper limit is 5.0 parts by mass. In this specification, the "content of crosslinking agent" means the content of the solid content of the crosslinking agent.

[0064] The pressure-sensitive adhesive composition may further contain a crosslinking catalyst for accelerating crosslinking by the crosslinking agent. Examples of the crosslinking catalyst include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate as crosslinking catalysts for the isocyanate-based crosslinking agents.

[0065] The pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a plasticizer, a softener, a filler, a dye, or a pigment, as needed, within the scope of not impairing the object of the present invention.

[0066] The preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 10% by mass, and the preferred upper limit is 70% by mass. When the gel fraction of the pressure-sensitive adhesive layer is 10% by mass or more, the pressure-sensitive adhesive layer has excellent cohesive strength, thereby further reducing tackiness of the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive tape of the present invention has excellent initial reworkability. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion. Furthermore, when the pressure-sensitive adhesive layer has excellent cohesive strength, the heat resistance of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion. When the gel fraction of the pressure-sensitive adhesive layer is 70% by mass, the pressure-sensitive adhesive layer has excellent adhesion to the adherend, and the stress relaxation of the pressure-sensitive adhesive tape of the present invention is further improved, making it more suitable for use in fixing an adherend having a curved portion. The more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 20% by mass, and the more preferred upper limit is 50% by mass. The gel fraction of the pressure-sensitive adhesive layer is measured by the following method. That is, first, a pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer is cut into a flat rectangular shape of 20 mm wide and 40 mm long to prepare a test piece, and the test piece is 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 test piece after drying is measured, and the gel fraction is calculated using the following formula (I). Note that no release film for protecting the pressure-sensitive adhesive layer is laminated on the test piece. Furthermore, when the pressure-sensitive adhesive tape of the present invention is a non-support type tape that does not have a substrate layer, the measurement is performed using a test piece obtained by adhering it to a substrate and cutting it, or the calculation is performed without using a substrate layer, assuming W0 in the following formula (I) to be 0. Gel fraction (mass%) = 100 × (W2 - W0) / (W1 - W0) (I) (W0: Mass of the base layer, W1: Mass of the test piece before immersion, W2: Mass of the test piece after immersion and drying)

[0067] The preferred lower limit of the bio-derived carbon content in the pressure-sensitive adhesive layer is 10%. When the bio-derived carbon content in the pressure-sensitive adhesive layer is 10% or more, the pressure-sensitive adhesive tape of the present invention is excellent in terms of saving petroleum resources and reducing carbon dioxide emissions, and can reduce the environmental burden. The more preferred lower limit of the bio-derived carbon content in the pressure-sensitive adhesive layer is 40%, and the even more preferred lower limit is 60%. Furthermore, the upper limit of the content of bio-derived carbon in the pressure-sensitive adhesive layer is not particularly limited, and may be 100%. Biologically derived carbon contains a certain percentage of the radioactive isotope (C-14), whereas petroleum-derived carbon contains almost no C-14. Therefore, the "biologically derived carbon content" in this specification can be calculated by measuring the concentration of C-14 contained in the PSA layer. Specifically, this can be measured in accordance with ASTM D6866-22, a standard widely used in the bioplastics industry.

[0068] The preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 3 μm, and the preferred upper limit is 300 μm. When the thickness of the pressure-sensitive adhesive layer is 3 μm or more, the pressure-sensitive adhesive tape of the present invention has sufficient adhesive strength. When the thickness of the pressure-sensitive adhesive layer is 300 μm or less, the pressure-sensitive adhesive layer has improved adhesion to the adherend, and the stress relaxation properties of the pressure-sensitive adhesive tape of the present invention are further improved, making it more suitable for use in fixing an adherend having a curved portion. The more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm, and the more preferred upper limit is 200 μm.

[0069] The pressure-sensitive adhesive tape of the present invention may have a layer other than the pressure-sensitive adhesive layer.

[0070] The pressure-sensitive adhesive tape of the present invention may be a non-support type tape that does not have a base layer, or may be a supported type tape that has a base layer. In particular, from the viewpoint of providing a pressure-sensitive adhesive tape with good stiffness and superior stress relaxation properties, it is preferable that the pressure-sensitive adhesive tape of the present invention has a base layer. When the adhesive tape of the present invention is a support-type tape having a base layer, it may be a single-sided adhesive tape having an adhesive layer on one side of the base layer, or a double-sided adhesive tape having adhesive layers on both sides of the base layer.

[0071] When the pressure-sensitive adhesive tape is a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of a base layer, it is sufficient that at least one of the pressure-sensitive adhesive layers contains a (meth)acrylic copolymer having a structural unit derived from the alkyl (meth)acrylate, and that the shear storage modulus at 23°C and the loss tangent at 65°C of the pressure-sensitive adhesive layer satisfy the above-mentioned ranges, but it is preferable that the pressure-sensitive adhesive layers on both sides satisfy the above-mentioned configuration.

[0072] Examples of the substrate used for the substrate layer include a film, a nonwoven fabric, a foam substrate, etc. The substrate used for the substrate layer is preferably a substrate made of a biologically derived material, from the viewpoint of increasing the content of biologically derived carbon in the entire pressure-sensitive adhesive tape. Examples of the above-mentioned biologically-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), polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetyl cellulose (TAC), cellulose, and polyamide (PA), which are derived from plants.

[0073] Furthermore, from the perspective of reducing the use of new petroleum resources and reducing the environmental burden by suppressing carbon dioxide emissions, substrates made from recycled resources may be used. Examples of resource recycling methods include collecting waste materials such as packaging containers, home appliances, automobiles, construction materials, and food, as well as waste generated during manufacturing processes, and then cleaning, decontaminating, or decomposing the extracted materials by heating or fermentation to reuse them as raw materials. Examples of substrates made from recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., which are made from recycled plastics that have been re-resinized. Furthermore, collected waste materials may be burned and used as thermal energy for the production of substrates and their raw materials, or the oils and fats contained in the collected waste materials may be mixed with petroleum, fractionated, and purified, and then used as raw materials.

[0074] From the viewpoint of excellent stress relaxation properties, the substrate used in the substrate layer preferably includes a foam substrate. The foam substrate is preferably a foam substrate containing at least one selected from the group consisting of PE, PP, and PU, and from the viewpoint of achieving a high degree of both flexibility and strength, a foam substrate containing PE is more preferred. Examples of the constituents of the foam substrate containing PE include PE made from sugarcane.

[0075] A preferred method for producing the foam base material is, for example, to prepare a foamable resin composition containing a PE resin containing sugarcane-derived PE and a foaming agent, and then foam the foaming agent when extruding the foamable resin composition into a sheet using an extruder, and optionally crosslink the resulting polyolefin foam.

[0076] The preferred lower limit of the thickness of the foam substrate is 50 μm, and the preferred upper limit is 5000 μm. By having the thickness of the foam substrate within this range, it is possible to exhibit high impact resistance while also exhibiting high flexibility that allows it to be adhered to the shape of the adherend. The more preferred upper limit of the thickness of the foam substrate is 1000 μm, and even more preferred upper limit is 300 μm.

[0077] The substrate used in the substrate layer is preferably a film containing PES or a film containing PA from the viewpoint of substrate strength, and is preferably a film containing PA from the viewpoint of heat resistance and oil resistance. Examples of the 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.

[0078] The preferred lower limit of the thickness of the substrate is 50 μm, and the preferred upper limit is 5000 μm. By having the thickness of the substrate within this range, high flexibility can be achieved, allowing the substrate to be bonded in close contact with the shape of the adherend. The more preferred upper limit of the thickness of the substrate is 1000 μm, and the even more preferred upper limit is 300 μm.

[0079] The pressure-sensitive adhesive tape of the present invention has a total thickness (the sum of the thickness of the base layer and the thickness of the pressure-sensitive adhesive layer) of preferably 3 μm at its lower limit and 6000 μm at its upper limit. When the total thickness of the pressure-sensitive adhesive tape of the present invention is within this range, the adhesive strength of the pressure-sensitive adhesive tape of the present invention is further increased. The upper limit of the total thickness of the pressure-sensitive adhesive tape of the present invention is more preferably 1200 μm, and even more preferably 500 μm.

[0080] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and the tape can be produced by a conventionally known production method. For example, in the case of a double-sided pressure-sensitive adhesive tape, the following method can be mentioned. First, a pressure-sensitive adhesive composition A is prepared by adding a solvent to the (meth)acrylic copolymer and, if necessary, a tackifier, a crosslinking agent, etc. The obtained pressure-sensitive adhesive composition A is applied to the surface of a substrate, and the solvent in the composition is completely dried and removed by heating to form a pressure-sensitive adhesive layer A. Next, a release film is superimposed on the formed pressure-sensitive adhesive layer A with its release-treated surface facing the pressure-sensitive adhesive layer A. Next, a release film separate from the above release film is prepared, and PSA composition B, prepared in the same manner as PSA composition A, is applied to the release-treated surface of this release film. The solvent in the composition is then completely dried and removed to produce a laminate film in which PSA layer B is formed on the surface of the release film. The obtained laminate film is overlaid on the back surface of the substrate on which PSA layer A is formed, with PSA layer B facing the back surface of the substrate to produce a laminate. The laminate is then pressed with a rubber roller or the like to produce a double-sided PSA tape in which PSA layers are on both sides of the substrate and the surfaces of the PSA layers are covered with release films.

[0081] Alternatively, two sets of laminate films may be prepared in a similar manner, and these laminate films may be superimposed on each of both surfaces of a substrate with the pressure-sensitive adhesive layer of the laminate film facing the substrate to prepare a laminate. This laminate may then be pressed with a rubber roller or the like to obtain a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both surfaces of the substrate, the surfaces of the pressure-sensitive adhesive layers being covered with release films.

[0082] The use of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but it is preferably used for fixing electronic device components or vehicle-mounted components. Specifically, the pressure-sensitive adhesive tape of the present invention can be suitably used for adhesively fixing electronic device components in large portable electronic devices, adhesively fixing vehicle-mounted components (e.g., vehicle-mounted panels), etc. In particular, the pressure-sensitive adhesive tape of the present invention can be suitably used for fixing adherends having bent portions. Examples of adherends having bent portions include bendable electronic device components and electronic device components having curved shapes, and specific examples include flexible displays. [Effects of the Invention]

[0083] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent initial reworkability and can be suitably used for fixing an adherend having a curved portion. [Brief explanation of the drawings]

[0084] [Figure 1] FIG. 1 is a diagram schematically illustrating a flip-up test. [Figure 2] FIG. 1 is a diagram schematically illustrating an example of a measurement sample in which a floating height occurred after a flip-up test. DETAILED DESCRIPTION OF THE INVENTION

[0085] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples. The materials used in the examples and comparative examples are as follows.

[0086] <n-Hexyl acrylate containing bio-derived carbon> Linoleic acid derived from castor oil was converted to linoleic acid hydroperoxide using lipoxygenase, and then a mixture containing n-hexylaldehyde was obtained using isomerase. The resulting mixture was distilled to obtain n-hexylaldehyde containing bio-derived carbon. The obtained n-hexylaldehyde containing bio-derived carbon was then hydrogenated to obtain n-hexyl alcohol containing bio-derived carbon. The obtained n-hexyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare n-hexyl acrylate containing bio-derived carbon.

[0087] <n-heptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was cracked to obtain a mixture containing undecylenic acid and n-heptyl alcohol. The undecylenic acid was then separated from the resulting mixture by distillation to obtain n-heptyl alcohol containing bio-derived carbon. The resulting n-heptyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare n-heptyl acrylate containing bio-derived carbon.

[0088] <1-Methylheptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was fused in an alkali to obtain a mixture containing sepacic acid and 1-methylheptyl alcohol. The sepacic acid was then separated from the resulting mixture by distillation to obtain 1-methylheptyl alcohol containing bio-derived carbon. The resulting 1-methylheptyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare 1-methylheptyl acrylate containing bio-derived carbon.

[0089] <Isobornyl methacrylate containing bio-derived carbon> Camphene, which contains bio-derived carbon, was obtained by isomerizing pinene extracted from pine resin. Camphene, which contains bio-derived carbon, was reacted with methacrylic acid (manufactured by Mitsubishi Chemical Corporation) to prepare isobornyl methacrylate, which contains bio-derived carbon.

[0090] <2-hydroxyethyl acrylate containing bio-derived carbon> Ethanol containing bio-derived carbon was obtained by fermenting sugars contained in sugarcane. The obtained bio-derived ethanol was dehydrated to obtain ethylene, which was then oxidized to obtain ethylene oxide, to which water was added to obtain 2-hydroxyethyl alcohol containing bio-derived carbon. The obtained bio-derived 2-hydroxyethyl alcohol was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare 2-hydroxyethyl acrylate containing bio-derived carbon.

[0091] <Bio-derived carbon-free monomer> Methyl acrylate (Tokyo Chemical Industry Co., Ltd.) Ethyl acrylate (Tokyo Chemical Industry Co., Ltd.) n-Butyl acrylate (Tokyo Chemical Industry Co., Ltd.) 2-Ethylhexyl acrylate (Nippon Shokubai Co., Ltd.) Cyclohexyl acrylate (Tokyo Chemical Industry Co., Ltd.) Acrylic acid (Nippon Shokubai Co., Ltd.) Dimethylacrylamide (Tokyo Chemical Industry Co., Ltd.)

[0092] <Tackifier> Tackifier A: Terpene-based tackifier (terpene phenol-based resin) (Yasuhara Chemical Co., Ltd., "YS Polystar G150", softening temperature: 145°C to 150°C) Tackifier B: Rosin ester tackifier (Arakawa Chemical Industries, Ltd., "Pine Crystal KE-359", softening temperature: 94°C to 104°C) Tackifier C: Rosin ester tackifier (Arakawa Chemical Industries, Ltd., "Super Ester A-75", softening temperature: 70°C to 80°C) Tackifier D: Rosin ester tackifier (polymerized rosin ester resin, manufactured by Arakawa Chemical Industries, Ltd., "Pensel D-135", softening temperature: 130-140°C)

[0093] <Crosslinking agent> Isocyanate crosslinking agent (Tosoh Corporation, "Coronate HX") Epoxy crosslinking agent (Mitsubishi Gas Chemical Company, Inc., "Tetrad X")

[0094] Example 1 (1) Preparation of (meth)acrylic copolymer Ethyl acetate was added as a polymerization solvent to a reaction vessel, and nitrogen was bubbled through. The reaction vessel was then heated while nitrogen was flowing in to initiate reflux. Next, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile 10 times with ethyl acetate was added to the reaction vessel, and 94.9 parts by mass of 1-methylheptyl acrylate containing biocarbon, 0.1 parts by mass of 2-hydroxyethyl acrylate containing biocarbon, and 5.0 parts by mass of acrylic acid were added dropwise over two hours. After the dropwise addition, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile 10 times with ethyl acetate was added again to the reaction vessel, and the polymerization reaction was carried out for four hours to obtain a (meth)acrylic copolymer-containing solution. The resulting (meth)acrylic copolymer-containing solution was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm) to prepare a measurement sample. This measurement sample was fed to a gel permeation chromatograph (Waters, "2690 Separations Module") and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the (meth)acrylic copolymer was measured, and the weight-average molecular weight was calculated. The results are shown in Table 1.

[0095] (2) Manufacture of adhesive tapes To the resulting (meth)acrylic copolymer-containing solution, 20.0 parts by mass of tackifier A and an isocyanate-based crosslinking agent were added so that the solids content was 1.5 parts by mass per 100 parts by mass of the (meth)acrylic copolymer in the (meth)acrylic copolymer-containing solution, thereby preparing a pressure-sensitive adhesive composition. The resulting pressure-sensitive adhesive composition was applied to the release-treated surface of a 75 μm-thick release PET film so that the thickness of the pressure-sensitive adhesive layer after drying would be 50 μm, and then dried at 110°C for 5 minutes to form a pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive layer was then placed on the release-treated surface of a 75 μm-thick release PET film and aged at 40°C for 48 hours to obtain a pressure-sensitive adhesive tape (non-support type).

[0096] (3) Measurement of shear storage modulus of adhesive layer at 23°C Both release PET films of the resulting adhesive tape were peeled off, and the adhesive layers were stacked to form a 1 mm thick laminate, which was then cut into a 6 mm wide and 10 mm long specimen. Dynamic viscoelasticity measurements were performed on the resulting specimen using a dynamic viscoelasticity measuring device (IT Measurement & Control Co., Ltd., "DVA-200") in shear mode under a nitrogen atmosphere at temperatures ranging from -50°C to 150°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.1%, to measure the shear storage modulus (MPa) of the adhesive layer at 23°C. The results are shown in Table 1.

[0097] (4) Measurement of the loss tangent of the adhesive layer at 65°C The loss tangent of the pressure-sensitive adhesive layer at 65° C. was obtained by the dynamic viscoelasticity measurement in the above-mentioned “(3) Measurement of shear storage modulus of pressure-sensitive adhesive layer at 23° C..” The results are shown in Table 1.

[0098] (5) Measurement of the glass transition temperature of the adhesive layer The release PET films on both sides of the resulting adhesive tape were peeled off, and the adhesive layers were stacked to form a 1 mm thick laminate. This was then cut into a 6 mm wide, 10 mm long specimen. The resulting specimen was then subjected to dynamic viscoelasticity measurements in shear mode under a nitrogen atmosphere at a temperature range of -40°C to 200°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.08%, to determine the glass transition temperature of the adhesive layer. The results are shown in Table 1.

[0099] (6) Measurement of gel fraction of adhesive layer The release PET film on one side of the resulting adhesive tape was peeled off, and the tape was laminated to a 23 μm thick base PET film (Futamura Chemical Co., Ltd., "FE2002") and cut into a flat rectangular shape 20 mm wide and 40 mm long. The release PET film on the other side of the adhesive tape was then peeled off to prepare a test piece, and its mass was measured. The test piece 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 piece was measured, and the gel fraction (% by mass) was calculated using the following formula (I). The results are shown in Table 1. Gel fraction (mass%) = 100 × (W2 - W0) / (W1 - W0) (I) (W0: Mass of the substrate, W1: Mass of the test piece before immersion, W2: Mass of the test piece after immersion and drying)

[0100] (Examples 2 to 19, 26 to 42, Comparative Examples 1 to 8) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types and amounts of the monomers constituting the (meth)acrylic copolymer and the types and amounts of the components of the pressure-sensitive adhesive composition were changed to those shown in Tables 1 to 5. Furthermore, the weight-average molecular weight of the (meth)acrylic copolymer, the shear storage modulus of the pressure-sensitive adhesive layer at 23°C, the loss tangent of the pressure-sensitive adhesive layer at 65°C, the glass transition temperature of the pressure-sensitive adhesive layer, and the gel fraction of the pressure-sensitive adhesive layer were measured in the same manner as in Example 1. The results are shown in Tables 1 to 5. In Examples 32 to 34, the types and amounts of each component of the pressure-sensitive adhesive composition were changed as shown in Tables 3 and 4, and further, in "(1) Production of (meth)acrylic copolymer", the amount of polymerization initiator added, etc. were appropriately changed, and pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1.

[0101] (Examples 20 to 25, 43 to 44) Pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1, except that the types and amounts of the monomers constituting the (meth)acrylic copolymer and the types and amounts of each component of the pressure-sensitive adhesive composition were changed as shown in Tables 2 to 4. The obtained pressure-sensitive adhesive composition was applied to the release-treated surface of a 75 μm-thick release PET film so that the thickness of the pressure-sensitive adhesive layer after drying would be 50 μm, and then dried at 110°C for 5 minutes. The obtained pressure-sensitive adhesive layer was bonded to one side of the substrate shown in Tables 2 to 4. Furthermore, a pressure-sensitive adhesive layer having the same composition and thickness was formed on the release-treated surface of another 75 μm-thick release PET film, which was then bonded to the other side of the substrate and aged at 40°C for 48 hours, to obtain a pressure-sensitive adhesive tape (support type) having a pressure-sensitive adhesive layer and a release PET film on both sides of the substrate. In addition, the weight-average molecular weight of the (meth)acrylic copolymer, the shear storage modulus of the pressure-sensitive adhesive layer at 23°C, the loss tangent of the pressure-sensitive adhesive layer at 65°C, and the gel fraction of the pressure-sensitive adhesive layer were measured in the same manner as in Example 1. The shear storage modulus of the pressure-sensitive adhesive layer at 23°C, the loss tangent of the pressure-sensitive adhesive layer at 65°C, and the glass transition temperature of the pressure-sensitive adhesive layer were measured on the pressure-sensitive adhesive layer before being attached to a substrate. The gel fraction of the pressure-sensitive adhesive layer was measured using a test piece obtained by cutting the pressure-sensitive adhesive tape into a flat rectangular shape 20 mm wide and 40 mm long and then peeling off the release PET films on both sides. The results are shown in Tables 2 to 4.

[0102] The substrates used as the substrate layers in Examples 20 to 25 and 43 to 44 are as follows. PET film (Futamura Chemical Co., Ltd., "FE2002", thickness 50 μm) PI film (PI Advanced Materials, "GF", thickness 12 μm) PEN film (Toyobo Co., Ltd., "Teonex Q5100", thickness 12 μm) PE foam (manufactured by Sekisui Chemical Co., Ltd., "WL02", thickness 150 μm) Nonwoven fabric (Toray Industries, "Acstar G2260-1S", thickness 610 μm) Colored substrate (Toray Industries, "Lumirror #25-X30", thickness 23 μm)

[0103] <Evaluation> The pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated by the following methods, and the results are shown in Tables 1 to 5.

[0104] (Initial reworkability) A probe tack test was carried out in accordance with JIS Z3284 to measure the probe tack value of the pressure-sensitive adhesive layer. Specifically, the obtained adhesive tape was cut into a size of 30 mm wide x 30 mm long to prepare a test piece, and then a probe tack test was performed on the adhesive layer of the prepared test piece using a probe tack tester (manufactured by RHESCA, "TAC-2") under conditions of 23°C, pressure of 98 gf, pressure rate of 100 mm / sec, pressure time of 3 seconds, and peel rate of 5 mm / sec, and the probe tack value (N / 5 mmφ) of the adhesive layer was measured. The initial reworkability of the adhesive tape was evaluated by rating it as follows: if the probe tack value of the obtained adhesive layer was 7.5 N / 5 mmφ or less, it was marked as "○", if it was more than 7.5 N / 5 mmφ but not more than 12.5 N / 5 mmφ, it was marked as "△", and if it was more than 12.5 N / 5 mmφ, it was marked as "×".

[0105] (Suitability for fixing an adherend having a curved portion) A flip-up test was conducted to evaluate the suitability of adhesive tapes for fixing bent adherends. Figure 1 shows a schematic diagram of the flip-up test. Specifically, a 50 mm wide, 100 mm long, and 6 mm thick polycarbonate (PC) plate 1 (TAKIRON C.I., "PC-1600") was bonded to a 10 mm wide, 70 mm long, and 188 μm thick PET film (Toray Industries, Inc., "Lumirror #188") using double-sided tape (Sekisui Chemical Co., Ltd., "Double Tack Tape #570E"). A 2 kg rubber roller was then run back and forth across the polycarbonate plate 1 at a speed of 300 mm / min to produce a laminate in which the polycarbonate plate 1 and the PET film 3 were integrated via the double-sided tape. The adhesive tape obtained in the Examples or Comparative Examples was cut into a 10 mm wide, 3 mm long piece of adhesive tape 2, which was then bonded to the polycarbonate plate 1 of the resulting laminate. The portion of the PET film 3 in the laminate where the polycarbonate plate 1 was not laminated was bent and then overlaid on the adhesive tape 2 to produce a measurement sample. This measurement sample was placed in a constant humidity oven at 65°C and 90% RH in this state and left to stand for 72 hours to perform a flip-up test. The measurement sample was removed from the oven, and the floating height H (mm) between the adhesive tape 2 and the PET film 3 (see Figure 2) was measured with a vernier caliper. The suitability of the adhesive tape for fixing an adherend having a curved portion was evaluated as follows: if the lift height H was 1 mm or less, it was marked as "○"; if the lift height was greater than 1 mm but the adhesive tape 2 did not peel off, it was marked as "△"; and if the adhesive tape 2 peeled off, it was marked as "×".

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] [Table 4]

[0110] [Table 5] [Industrial Applicability]

[0111] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent initial reworkability and can be suitably used for fixing an adherend having a curved portion. [Explanation of symbols]

[0112] 1 polycarbonate plate 2 adhesive tapes 3 PET film

Claims

1. A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition contains a (meth)acrylic copolymer, The (meth)acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate, the pressure-sensitive adhesive layer has a shear storage modulus at 23°C of 0.25 MPa or more; The pressure-sensitive adhesive layer has a loss tangent of 0.50 or more at 65°C. An adhesive tape characterized by:

2. the pressure-sensitive adhesive layer has a glass transition temperature of 0°C or higher, as measured by dynamic viscoelasticity measurement at a measurement frequency of 1 Hz and a measurement temperature range of -40°C or higher and 200°C or lower; The adhesive tape according to claim 1.

3. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the alkyl (meth)acrylate comprises 1-methylheptyl (meth)acrylate.

4. The pressure-sensitive adhesive tape according to claim 3, wherein the (meth)acrylic copolymer contains 50% by mass or more of structural units derived from 1-methylheptyl (meth)acrylate.

5. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer contains less than 50% of structural units derived from a (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms, or the (meth)acrylic copolymer does not contain any structural units derived from a (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms.

6. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer further comprises a structural unit derived from n-heptyl (meth)acrylate.

7. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer having a crosslinkable functional group.

8. The pressure-sensitive adhesive tape according to claim 7 , wherein the monomer having a crosslinkable functional group includes a hydroxyl group-containing monomer.

9. The pressure-sensitive adhesive tape according to claim 7 , wherein the (meth)acrylic copolymer contains the structural unit derived from the monomer having a crosslinkable functional group in an amount of 1.0% by mass or more and 20% by mass or less.

10. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer has at least one structural unit selected from the group consisting of structural units derived from a monomer having a cyclic ether structure free of an epoxy group and an oxetanyl group, and a non-cyclic ether structure.

11. The pressure-sensitive adhesive tape according to claim 10, wherein the content of structural units derived from the cyclic ether structure having no epoxy group or no oxetanyl group and the monomer having the acyclic ether structure is 0.01% by mass or more and 50% by mass or less.

12. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer that does not have a crosslinkable functional group and has a glass transition temperature of 0°C or higher when made into a homopolymer.

13. The pressure-sensitive adhesive tape according to claim 12, wherein the content of structural units derived from a monomer that does not have a crosslinkable functional group and has a glass transition temperature of 0°C or higher when made into a homopolymer is 0.1% by mass or more and 70% by mass or less.

14. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer has a weight average molecular weight of 800,000 or more.

15. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive composition further contains a tackifier.

16. The pressure-sensitive adhesive tape according to claim 15, wherein the tackifier comprises at least one selected from the group consisting of a rosin ester tackifier, a terpene tackifier, and a (meth)acrylic tackifier.

17. The adhesive tape according to claim 16, wherein the tackifier comprises the rosin ester-based tackifier and the terpene-based tackifier.

18. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive composition further contains a crosslinking agent.

19. The pressure-sensitive adhesive tape according to claim 18, wherein the crosslinking agent comprises at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

20. The pressure-sensitive adhesive tape according to claim 19, wherein the crosslinking agent comprises the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent.

21. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less.

22. The adhesive tape according to claim 1 or 2, which comprises a substrate layer.

23. 3. The adhesive tape according to claim 1, which is used for fixing electronic equipment parts or vehicle-mounted parts.

Images