Adhesive composition and adhesive tape

Abstract

The purpose of the present invention is to provide an adhesive composition capable of exhibiting high shear adhesive strength and excellent adhesion to an adherend. The purpose of the present invention is also to provide an adhesive tape having an adhesive layer formed using the adhesive composition. The present invention is an adhesive composition containing a (meth)acrylic copolymer, wherein the (meth)acrylic copolymer has a constituent unit derived from an alkyl (meth)acrylate having a branched alkyl group, and the alkyl (meth)acrylate having a branched alkyl group contains a branched alkyl group-containing alkyl (meth)acrylate exhibiting a glass transition temperature of -55°C to -15°C when formed into a homopolymer.

Description

Adhesive composition and adhesive tape

[0001] The present invention relates to a pressure-sensitive adhesive composition. The present invention also relates to a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition.

[0002] Conventionally, pressure-sensitive adhesive tapes having a pressure-sensitive adhesive layer containing 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.

[0003] JP 2015-052050 A JP 2015-021067 A JP 2015-120876 A

[0004] Acrylic adhesives containing acrylic copolymers are widely used as adhesives with excellent adhesive strength. Examples of acrylic monomers that constitute the acrylic copolymers contained in acrylic adhesives include alkyl (meth)acrylates such as n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. When an n-butyl (meth)acrylate-based adhesive, whose main component is n-butyl (meth)acrylate, is used, the adhesive's cohesive strength is high and its shear adhesive strength is high, but the surface energy of such an adhesive is high, resulting in poor adhesion to adherends (especially adherends with low surface energy). On the other hand, when a 2-ethylhexyl (meth)acrylate-based adhesive, whose main component is 2-ethylhexyl (meth)acrylate, is used, the surface energy of the adhesive is low because 2-ethylhexyl (meth)acrylate contains many methyl groups with low polarity, resulting in good adhesion to adherends. However, such an adhesive has low cohesive strength.

[0005] An object of the present invention is to provide a pressure-sensitive adhesive composition that can exhibit high shear adhesive strength and excellent adhesion to an adherend, and a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition.

[0006] Disclosure 1 is a pressure-sensitive adhesive composition comprising a (meth)acrylic copolymer, the (meth)acrylic copolymer having structural units derived from an alkyl (meth)acrylate having a branched alkyl group, the alkyl (meth)acrylate having a branched alkyl group comprising a branched alkyl group-containing alkyl (meth)acrylate having a glass transition temperature of −55° C. or higher and −15° C. or lower when made into a homopolymer. Disclosure 2 is a pressure-sensitive adhesive composition according to Disclosure 1, wherein the branched alkyl group-containing alkyl (meth)acrylate having a glass transition temperature of −55° C. or higher and −15° C. or lower when made into a homopolymer comprises structural units derived from 1-methylheptyl (meth)acrylate. Disclosure 3 is a pressure-sensitive adhesive composition according to Disclosure 2, wherein the (meth)acrylic copolymer contains 60 mass% or more of structural units derived from 1-methylheptyl (meth)acrylate. Disclosure 4 is the pressure-sensitive adhesive composition of Disclosure 1, 2, or 3, wherein the branched-chain alkyl group-containing alkyl (meth)acrylate, which has a glass transition temperature of -55°C or higher and -15°C or lower when made into a homopolymer, is synthesized from a biologically derived alcohol and (meth)acrylic acid. Disclosure 5 is the pressure-sensitive adhesive composition of Disclosure 1, 2, 3, or 4, wherein the (meth)acrylic copolymer contains 60 mass% or more of structural units derived from a branched-chain alkyl group-containing alkyl (meth)acrylate, which has a glass transition temperature of -55°C or higher and -15°C or lower when made into the homopolymer. Disclosure 6 is the pressure-sensitive adhesive composition of Disclosure 1, 2, 3, 4, or 5, wherein the (meth)acrylic copolymer contains 35 mass% or less of structural units derived from an alkyl (meth)acrylate having a linear alkyl group, or does not contain any structural units derived from an alkyl (meth)acrylate having a linear alkyl group. The present disclosure 7 is the pressure-sensitive adhesive composition of the present disclosure 1, 2, 3, 4, 5, or 6, wherein the (meth)acrylic copolymer has a structural unit derived from an alkyl(meth)acrylate having a linear alkyl group, and the alkyl(meth)acrylate having a linear alkyl group includes n-heptyl(meth)acrylate.Disclosure 8 is the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, or 7, wherein the (meth)acrylic copolymer further has a structural unit derived from a monomer having a crosslinkable functional group. Disclosure 9 is the pressure-sensitive adhesive composition of Disclosure 8, wherein the monomer having a crosslinkable functional group includes a hydroxyl group-containing monomer. Disclosure 10 is the pressure-sensitive adhesive composition of Disclosures 8 or 9, wherein the (meth)acrylic copolymer contains 0.01% by mass or more and 20% by mass or less of a structural unit derived from a monomer having a crosslinkable functional group. Disclosure 11 is the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the (meth)acrylic copolymer has at least one structural unit selected from the group consisting of a structural unit derived from a monomer having a cyclic ether structure other than an epoxy structure or an oxetane structure, and a structural unit derived from a monomer having an acyclic ether structure. Disclosure 12 is the pressure-sensitive adhesive composition of Disclosure 11, wherein the (meth)acrylic copolymer contains 0.01% by mass or more and 50% by mass or less of structural units derived from a monomer having a cyclic ether structure other than an epoxy structure or an oxetane structure, and structural units derived from a monomer having an acyclic ether structure. Disclosure 13 is the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the (meth)acrylic copolymer contains structural units derived from a monomer having no crosslinkable functional group and a glass transition temperature of 0° C. or higher when made into a homopolymer. Disclosure 14 is the pressure-sensitive adhesive composition of Disclosure 13, wherein the (meth)acrylic copolymer contains 0.1% by mass or more and 70% by mass or less of structural units derived from a monomer having no crosslinkable functional group and a glass transition temperature of 0° C. or higher when made into a homopolymer. The present disclosure 15 is a pressure-sensitive adhesive composition according to the present disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the weight-average molecular weight of the (meth)acrylic copolymer is 800,000 or more and 1,500,000 or less. The present disclosure 16 is a pressure-sensitive adhesive composition according to the present disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, further comprising a tackifier.Disclosure 17 is the pressure-sensitive adhesive composition of Disclosure 16, wherein the tackifier comprises at least one selected from the group consisting of a rosin ester tackifier, a terpene tackifier, and an acrylic tackifier. Disclosure 18 is the pressure-sensitive adhesive composition of Disclosure 17, wherein the tackifier comprises the rosin ester tackifier and the terpene tackifier. Disclosure 19 is the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, further comprising a crosslinking agent. Disclosure 20 is the pressure-sensitive adhesive composition of Disclosure 19, wherein the crosslinking agent comprises at least one selected from the group consisting of an isocyanate crosslinking agent and an epoxy crosslinking agent. Disclosure 21 is the pressure-sensitive adhesive composition of Disclosure 20, wherein the crosslinking agent comprises the isocyanate crosslinking agent and the epoxy crosslinking agent. Disclosure 22 is the PSA composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, which does not contain a surfactant. Disclosure 23 is the PSA composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22, which further contains a pigment. Disclosure 24 is the PSA composition of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, in which the content of bio-derived carbon in the PSA composition is 10% or more. Disclosure 25 is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24. Disclosure 26 is the pressure-sensitive adhesive tape of Disclosure 25, wherein the pressure-sensitive adhesive layer has a gel fraction of 10% by mass or more and 70% by mass or less. Disclosure 27 is the pressure-sensitive adhesive tape of Disclosure 25 or 26, having a substrate layer. Disclosure 28 is the pressure-sensitive adhesive tape of Disclosures 25, 26, or 27, used for fixing electronic device components or vehicle-mounted components. The present invention will be described in detail below.

[0007] The present inventors discovered that, in a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer, by using an acrylic monomer that is an alkyl (meth)acrylate having a branched alkyl group and has a glass transition temperature within a specific range, among the various acrylic monomers that constitute the (meth)acrylic copolymer, a pressure-sensitive adhesive composition that can exhibit high shear adhesive strength and excellent adhesion to an adherend can be obtained, leading to the completion of the present invention. The pressure-sensitive adhesive composition of the present invention can exhibit superior adhesion to an adherend (particularly an adherend with low polarity) compared to n-butyl (meth)acrylate-based pressure-sensitive adhesive compositions, and can exhibit higher shear adhesive strength compared to 2-ethylhexyl (meth)acrylate-based pressure-sensitive adhesive compositions. Furthermore, because the pressure-sensitive adhesive composition of the present invention can exhibit excellent adhesion to an adherend, even immediately after being laminated to the adherend, it can exhibit adhesive strength equivalent to that observed after a period of time has passed since being laminated to the adherend (after adhesion has been enhanced). In this specification, the term "(meth)acrylic" refers to acrylic or methacrylic, and the term "(meth)acrylate" refers to acrylate or methacrylate.

[0008] In this specification, the type of each structural unit in the (meth)acrylic copolymer described below and each component in the pressure-sensitive adhesive composition may be of only one type or of two or more types, unless otherwise specified. Furthermore, in this specification, unless otherwise specified, the terms "content ratio" and "content amount" refer to the total content ratio of all types of structural units or the total content amount of all types of components, when two or more types of structural units or components that define the "content ratio" are included.

[0009] The pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic copolymer. The (meth)acrylic copolymer has structural units derived from an alkyl (meth)acrylate having a branched alkyl group.

[0010] The alkyl(meth)acrylate having a branched alkyl group includes a branched alkyl group-containing alkyl(meth)acrylate having a glass transition temperature (hereinafter sometimes simply referred to as "homopolymer Tg") of -55°C or more and -15°C or less when made into a homopolymer (hereinafter, the branched alkyl group-containing alkyl(meth)acrylate having a homopolymer Tg of -55°C or more and -15°C or less will be referred to as "branched alkyl group-containing alkyl(meth)acrylate (A)"). When the branched alkyl group-containing alkyl(meth)acrylate contains the branched alkyl group-containing alkyl(meth)acrylate (A) (i.e., the (meth)acrylic copolymer has structural units derived from the branched alkyl group-containing alkyl(meth)acrylate (A), the pressure-sensitive adhesive composition of the present invention can exhibit high shear adhesive strength and excellent adhesion to adherends. In this specification, the term "glass transition temperature when made into a homopolymer" refers to the glass transition temperature measured by differential scanning calorimetry of a homopolymer in which the weight-average molecular weight of the alkyl (meth)acrylate is 100,000 or more and 2,000,000 or less. More specifically, the homopolymer Tg can be measured by, for example, measuring under conditions of a nitrogen atmosphere (nitrogen flow, flow rate 50 mL / min) in accordance with JIS K6240:2011, a measurement temperature of -100°C to 200°C, and a temperature rise rate of 10°C / min. In general, as long as the weight-average molecular weight is 100,000 or more and 2,000,000 or less, the homopolymer Tg does not depend on the weight-average molecular weight.

[0011] Since the branched alkyl group-containing alkyl (meth)acrylate (A) contains a branched alkyl group, it can have a large number of low-polarity methyl groups. Therefore, it is presumed that the (meth)acrylic copolymer containing structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) reduces the surface energy of the pressure-sensitive adhesive composition of the present invention, thereby enabling the pressure-sensitive adhesive composition to exhibit excellent adhesion to an adherend. Furthermore, the glass transition temperature of the branched alkyl group-containing alkyl (meth)acrylate (A) when formed into a homopolymer is in a specific range of −55°C or higher and −15°C or lower. It is presumed that the branched alkyl group-containing alkyl (meth)acrylate (A) having a glass transition temperature in the specific range can suppress a decrease in the cohesive strength of the pressure-sensitive adhesive composition when the (meth)acrylic copolymer contains structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A). Furthermore, when the (meth)acrylic copolymer contains a structural unit derived from the branched alkyl group-containing alkyl (meth)acrylate (A), the glass transition temperature of the (meth)acrylic copolymer is appropriately reduced, and the storage modulus exhibited by the pressure-sensitive adhesive composition of the present invention is also appropriately reduced, which is presumably why the pressure-sensitive adhesive composition of the present invention can exhibit sufficient adhesion to an adherend.

[0012] The homopolymer Tg of the branched alkyl group-containing alkyl (meth)acrylate (A) is preferably −50°C in lower limit and −25°C in upper limit. When the homopolymer Tg of the branched alkyl group-containing alkyl (meth)acrylate (A) is within the above range, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The homopolymer Tg of the branched alkyl group-containing alkyl (meth)acrylate (A) is more preferably −45°C in lower limit and −30°C in upper limit. Examples of the homopolymer Tg include −50°C or higher to −25°C or lower, −50°C or higher to −30°C or lower, −45°C or higher to −25°C or lower, and −45°C or higher to −25°C or lower. The homopolymer Tg is measured by differential scanning calorimetry. More specifically, the homopolymer Tg can be measured in a nitrogen atmosphere (nitrogen flow, flow rate 50 mL / min) using a differential scanning calorimeter (manufactured by Seiko Instruments Inc., "220C" or the like) according to a method in accordance with JIS K6240:2011, under conditions of a measurement temperature of -100°C to 200°C and a temperature rise rate of 10°C / min.

[0013] Examples of the branched alkyl group-containing alkyl(meth)acrylate (A) include isobutyl(meth)acrylate (homopolymer Tg: -26°C), isoamyl acrylate (homopolymer Tg: -45°C), 1-methylheptyl acrylate (homopolymer Tg: -45°C), 1-methylheptyl methacrylate (homopolymer Tg: -25°C), isodecyl methacrylate (homopolymer Tg: -41°C), and isostearyl acrylate (homopolymer Tg: -18°C). Among these, the branched alkyl group-containing alkyl(meth)acrylate (A) preferably contains a (meth)acrylate having a branched alkyl group having from 4 to 10 carbon atoms, and more preferably contains 1-methylheptyl(meth)acrylate. When the (meth)acrylic copolymer contains structural units derived from 1-methylheptyl(meth)acrylate, the resulting pressure-sensitive adhesive composition is more likely to achieve both high adhesion to an adherend and high cohesive strength.

[0014] The branched alkyl group-containing alkyl (meth)acrylate (A) may consist solely of petroleum-derived materials, but preferably contains a biologically-derived material. In recent years, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products have become a problem. Therefore, attempts have been made to conserve petroleum resources by using biologically-derived materials instead of petroleum-derived materials. The inclusion of a biologically-derived material in the branched alkyl group-containing alkyl (meth)acrylate (A) is preferable from the viewpoint of conserving petroleum resources. Furthermore, since biologically-derived materials are originally produced by absorbing carbon dioxide from the atmosphere, their combustion is thought to not increase the total amount of carbon dioxide in the atmosphere, which is also preferable from the viewpoint of reducing carbon dioxide emissions.

[0015] When the branched alkyl group-containing alkyl (meth)acrylate (A) contains a biological material, the branched alkyl group-containing alkyl (meth)acrylate (A) is preferably synthesized from a biologically derived alcohol containing a branched alkyl group and (meth)acrylic acid, and more preferably synthesized by esterification of a biologically derived alcohol with (meth)acrylic acid. Examples of methods for obtaining biologically derived alcohol include a method in which a material collected from plants or animals (e.g., ricinoleic acid derived from castor oil) is used as a raw material, and an alkali-fused mixture is distilled to obtain biologically derived 1-methylheptyl alcohol inexpensively and easily.

[0016] The preferred lower limit of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) in the (meth)acrylic copolymer is 60% by mass. When the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) is 60% by mass or more, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The more preferred lower limit of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) is 75% by mass, and the even more preferred lower limit is 90% by mass. Furthermore, the preferred upper limit of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) is 99% by mass. When the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) is within this range, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The upper limit of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) is more preferably 97% by mass, and even more preferably 95% by mass. Examples of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) include 60% by mass or more and 99% by mass or less, 60% by mass or more and 97% by mass or less, 60% by mass or more and 95% by mass or less, 75% by mass or more and 99% by mass or less, 75% by mass or more and 97% by mass or less, 75% by mass or more and 95% by mass or less, 90% by mass or more and 99% by mass or less, 90% by mass or more and 97% by mass or less, and 90% by mass or more and 95% by mass or less. The content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) 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 calculate from the integrated intensity ratio of the peak of hydrogen derived from the branched alkyl group-containing alkyl (meth)acrylate (A).

[0017] The preferred lower limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer is 60% by mass. When the content of the structural units derived from 1-methylheptyl (meth)acrylate is 60% by mass or more, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The more preferred lower limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate is 75% by mass, and the even more preferred lower limit is 90% by mass. Furthermore, the preferred upper limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate is 99% by mass. When the content of the structural units derived from 1-methylheptyl (meth)acrylate is 99% by mass or less, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The upper limit of the content of the structural units derived from 1-methylheptyl (meth)acrylate is more preferably 97% by mass, and even more preferably 95% by mass. Examples of the content of the structural units derived from 1-methylheptyl (meth)acrylate include 60% by mass or more and 99% by mass or less, 60% by mass or more and 97% by mass or less, 60% by mass or more and 95% by mass or less, 75% by mass or more and 99% by mass or less, 75% by mass or more and 97% by mass or less, 75% by mass or more and 95% by mass or less, 90% by mass or more and 99% by mass or less, 90% by mass or more and 97% by mass or less, and 90% by mass or more and 95% by mass or less. The content of the structural units 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 The amount of hydrogen can be calculated from the integrated intensity ratio of the peak of hydrogen derived from the 1-methylheptyl (meth)acrylate by performing spectroscopy (e.g., C-NMR) on the 1-methylheptyl (meth)acrylate.

[0018] The content of the structural units derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer can also be calculated by pyrolysis GC-MS. More specifically, a standard sample having a known content of structural units derived from 1-methylheptyl (meth)acrylate is subjected to pyrolysis GC-MS measurement, a calibration curve is prepared from the measured 2-octene peak area, and the resulting calibration curve can be used to calculate the content of the structural units derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer. More specifically, the calibration curve can be prepared as follows: A (meth)acrylic copolymer (standard sample) having a known content of structural units derived from 1-methylheptyl (meth)acrylate is prepared by adjusting the blending ratio of n-heptyl (meth)acrylate and 1-methylheptyl (meth)acrylate. The standard sample is weighed out and subjected to pyrolysis GC-MS measurement under the conditions below, and a total ion current chromatogram for each sample is obtained. A calibration curve can be created by plotting the content of structural units derived from 1-methylheptyl (meth)acrylate on the horizontal axis and the peak area of ​​2-octene in a total ion current chromatogram on the vertical axis. Next, the same amount of the (meth)acrylic copolymer to be measured as the standard sample used to create the calibration curve is weighed out and pyrolysis GC-MS measurement is performed under the following conditions. The content of structural units derived from 1-methylheptyl (meth)acrylate in the (meth)acrylic copolymer is calculated from the peak area of ​​2-octene in the obtained total ion current chromatogram and the created calibration curve. The content of structural units derived from n-heptyl (meth)acrylate, which will be described later, can also be calculated from the peak area of ​​1-heptene in the (meth)acrylic copolymer using a similar method.<Pyrolysis GC-MS measurement conditions> - Equipment: PY-3030D (manufactured by FRONTIER LAB) - Thermal decomposition temperature: 550°C - GC-MS equipment: Agilent 7890B (manufactured by Agilent Technologies), and JMS-Q1500 (manufactured by JEOL Ltd.)・Inlet temperature: 300℃ ・Sample amount: 0.2mg precision weighing ・Column: Ultra-ALLOY-1 (non-polar) 0.25mmφ x 30m x 0.25μm ・He flow rate: 1.0mL / min (split ratio 1:50)・Column temperature: Starting temperature: 40°C (held for 3 minutes), heating rate: 10°C / min, final temperature: 300°C (held for 5 minutes) ・MS temperature: Ion source: 230°C, interface: 250°C MS measurement range: 35 to 600 Ionization method: EI method Measurement mode: Scan Ionization voltage: 70 eV.

[0019] The (meth)acrylic copolymer preferably further comprises a structural unit derived from a monomer having a crosslinkable functional group. When the (meth)acrylic copolymer comprises a structural unit derived from the monomer having a crosslinkable functional group, the resulting pressure-sensitive adhesive composition can exhibit excellent cohesive strength, thereby exhibiting higher shear adhesive strength. Furthermore, the excellent cohesive strength further improves heat resistance, thereby enabling the composition to exhibit better retention performance at high temperatures.

[0020] 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, and a nitrile group-containing monomer. 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, since this facilitates adjustment of the degree of crosslinking of the resulting pressure-sensitive adhesive composition. The homopolymer Tg of the monomer having a crosslinkable functional group is not particularly limited and may be 0°C or higher. The monomer having a crosslinkable functional group preferably includes a (meth)acryloyl group. In this specification, the term "(meth)acryloyl" refers to acryloyl or methacryloyl.

[0021] 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, polypropylene glycol mono(meth)acrylate, etc. Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate, etc. Examples of the amide group-containing monomer include dimethyl(meth)acrylamide, isopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, etc. Examples of the nitrile group-containing monomer include (meth)acrylonitrile, etc.

[0022] The preferred lower limit of the content of the structural units derived from the monomer having a crosslinkable functional group in the (meth)acrylic copolymer is 0.01% by mass, and the preferred upper limit is 20% by mass. When the content of the structural units derived from the monomer having a crosslinkable functional group is 0.01% by mass or more, the resulting pressure-sensitive adhesive composition can exhibit excellent cohesive strength, thereby achieving higher shear adhesive strength. Furthermore, the excellent cohesive strength improves heat resistance and provides better high-temperature retention. When the content of the structural units derived from the monomer having a crosslinkable functional group is 20% by mass or less, the polarity of the (meth)acrylic copolymer is reduced, thereby reducing the surface energy of the resulting pressure-sensitive adhesive composition, thereby enabling it to exhibit better adhesion to an adherend. The more preferred lower limit of the content of the structural units derived from the monomer having a crosslinkable functional group is 1.0% by mass, and the more preferred upper limit is 10% by mass. Examples of the content of the structural unit derived from the monomer having a crosslinkable functional group include 0.01% by mass or more and 20% by mass or less, 0.01% by mass or more and 10% by mass or less, 1.0% by mass or more and 20% by mass or less, and 1.0% by mass or more and 10% by mass or less. 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 The crosslinking functional group content can be calculated from the integrated intensity ratio of the hydrogen peak derived from the monomer having the crosslinkable functional group by performing spectroscopy (e.g., C-NMR) on the polymer.

[0023] 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 has appropriate bulk strength, thereby further improving the shear storage modulus at 80°C of the pressure-sensitive adhesive layer, and therefore further improving the heat resistance of the pressure-sensitive adhesive layer and the pressure-sensitive adhesive tape. In addition, 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 The amount of hydrogen can be calculated from the integrated intensity ratio of the hydrogen peak derived from the hydroxyl group-containing monomer by performing spectroscopy (e.g., C-NMR) on the hydroxyl group-containing monomer.

[0024] The preferred lower limit of the content of the structural unit 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 unit 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 has appropriate bulk strength, thereby further improving the shear storage modulus at 80°C of the pressure-sensitive adhesive layer, thereby further improving the heat resistance of the pressure-sensitive adhesive layer and the pressure-sensitive adhesive tape. 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 unit derived from the carboxyl group-containing monomer is 1.0% by mass, and the more preferred upper limit is 10% by mass, and even more preferred lower limit is 3.0% by mass, and 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, 3.0% by mass or more and 8.0% by mass or less. The content of the structural unit derived from the carboxy group-containing monomer in the (meth)acrylic copolymer can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( １ H-NMR, １３ The carbon number can be calculated from the integrated intensity ratio of the hydrogen peak derived from the carboxy group-containing monomer by performing spectroscopy (e.g., C-NMR) on the carbonyl group.

[0025] The (meth)acrylic copolymer may contain structural units derived from other monomers other than the structural units derived from the branched alkyl group-containing alkyl(meth)acrylate (A) and the structural units derived from the monomer having a crosslinkable functional group, provided that the object of the present invention is not impaired. Examples of the other monomers include alkyl(meth)acrylates having a linear alkyl group, branched alkyl group-containing alkyl(meth)acrylates other than the branched alkyl group-containing alkyl(meth)acrylate (A) (hereinafter sometimes referred to as "branched alkyl group-containing alkyl(meth)acrylate (B)"), monomers having a cyclic ether structure other than an epoxy structure or an oxetane structure, and monomers having an acyclic ether structure.

[0026] Examples of the alkyl(meth)acrylate having a linear alkyl group include methyl acrylate (homopolymer Tg: 8°C), methyl methacrylate (homopolymer Tg: 105°C), ethyl acrylate (homopolymer Tg: -20°C), ethyl methacrylate (homopolymer Tg: 50°C), n-butyl acrylate (homopolymer Tg: -54°C), n-butyl methacrylate (homopolymer Tg: 20°C), n-hexyl acrylate (homopolymer Tg: Examples of such alkyl (meth)acrylates include n-hexyl methacrylate (homopolymer Tg: 0°C), n-heptyl acrylate (homopolymer Tg: -68°C), n-heptyl methacrylate (homopolymer Tg: -10°C), n-octyl acrylate (homopolymer Tg: -65°C), n-octyl methacrylate (homopolymer Tg: -18°C), n-lauryl acrylate (homopolymer Tg: -3°C), and n-lauryl methacrylate (homopolymer Tg: -35°C). Among these, from the viewpoint of improving adhesive strength, the alkyl (meth)acrylate having a linear alkyl group preferably contains a (meth)acrylate having a linear alkyl group having from 4 to 8 carbon atoms, and more preferably contains n-heptyl (meth)acrylate.

[0027] The upper limit of the content of the structural units derived from the alkyl (meth)acrylate having a linear alkyl group in the (meth)acrylic copolymer is preferably 35% by mass. When the content of the structural units derived from the (meth)acrylate having a linear alkyl group is 35% by mass or less, the surface energy of the resulting pressure-sensitive adhesive composition is reduced, thereby enabling the composition to exhibit better adhesion to an adherend. The upper limit of the content of the structural units derived from the (meth)acrylate having a linear alkyl group is more preferably 20% by mass, and even more preferably 10% by mass. Furthermore, when the (meth)acrylic copolymer contains structural units derived from the alkyl (meth)acrylate having a linear alkyl group, the lower limit of the content of the structural units derived from the alkyl (meth)acrylate having a linear alkyl group in the (meth)acrylic copolymer is not particularly limited, as long as it is greater than 0% by mass. However, the lower limit is preferably 1% by mass, and more preferably 3% by mass. The (meth)acrylic copolymer may not have any structural units derived from the alkyl (meth)acrylate having a linear alkyl group, i.e., the content of the structural units derived from the alkyl (meth)acrylate having a linear alkyl group may be 0% by mass. Examples of the content of the structural units derived from the alkyl (meth)acrylate having a linear alkyl group include 0% by mass or more and 35% by mass or less, 0% by mass or more and 20% by mass or less, 0% by mass or more and 10% by mass or less, more than 0% by mass or more and 35% by mass or less, more than 0% by mass or more and 20% by mass or less, more than 0% by mass or more and 10% by mass or less, 1% by mass or more and 35% by mass or less, 1% by mass or more and 20% by mass or less, 1% by mass or more and 10% by mass or less, 3% by mass or more and 35% by mass or less, 3% by mass or more and 20% by mass or less, and 3% by mass or more and 10% by mass or less. The content of the structural units derived from the alkyl (meth)acrylate having a linear alkyl group can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( １ H-NMR, １３ The carbon number can be calculated from the integrated intensity ratio of the peak of hydrogen derived from the alkyl (meth)acrylate having the linear alkyl group by performing spectroscopy (e.g., C-NMR) on the carbon number.

[0028] Examples of the branched alkyl group-containing alkyl (meth)acrylate (B) include t-butyl acrylate (homopolymer Tg: 14°C), t-butyl methacrylate (homopolymer Tg: 107°C), and 2-ethylhexyl acrylate (homopolymer Tg: -70°C).

[0029] The content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (B) in the (meth)acrylic copolymer is preferably 35% by mass or less. When the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (B) is 35% by mass or less, the resulting pressure-sensitive adhesive composition can exhibit excellent cohesive strength, thereby achieving higher shear adhesive strength. Furthermore, the excellent cohesive strength further improves heat resistance, resulting in better retention performance at high temperatures. The upper limit of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (B) is more preferably 20% by mass, and even more preferably 10% by mass. Furthermore, when the (meth)acrylic copolymer has a structural unit derived from the branched alkyl group-containing alkyl (meth)acrylate (B), the lower limit of the content of the structural unit derived from the branched alkyl group-containing alkyl (meth)acrylate (B) in the (meth)acrylic copolymer is not particularly limited as long as it is more than 0 mass%, but a preferred lower limit is 1 mass%, more preferably 3 mass%. Note that the (meth)acrylic copolymer does not have a structural unit derived from the branched alkyl group-containing alkyl (meth)acrylate (B), i.e., the content of the structural unit derived from the branched alkyl group-containing alkyl (meth)acrylate (B) may be 0 mass%. In the pressure-sensitive adhesive composition, examples of the content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (B) include 0% by mass or more and 35% by mass or less, 0% by mass or more and 20% by mass or less, 0% by mass or more and 10% by mass or less, more than 0% by mass or more and 35% by mass or less, more than 0% by mass or more and 20% by mass or less, more than 0% by mass or more and 10% by mass or less, 1% by mass or more and 35% by mass or less, 1% by mass or more and 20% by mass or less, 1% by mass or more and 10% by mass or less, 3% by mass or more and 35% by mass or less, 3% by mass or more and 20% by mass or less, and 3% by mass or more and 10% by mass or less. The content of the structural units derived from the branched alkyl group-containing alkyl (meth)acrylate (B) can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( １ H-NMR, １３C-NMR or the like) and calculate from the integrated intensity ratio of the peak of hydrogen derived from the branched alkyl group-containing alkyl (meth)acrylate (B).

[0030] When the (meth)acrylic copolymer has at least one structural unit selected from the group consisting of structural units derived from monomers having a cyclic ether structure other than the epoxy structure and the oxetane structure, and structural units derived from monomers having a non-cyclic ether structure (hereinafter, sometimes simply referred to as "structural units derived from monomers having an ether structure"), the adhesive strength of the resulting pressure-sensitive adhesive composition is further improved, and the pressure-sensitive adhesive composition can exhibit better adhesion to adherends.

[0031] Examples of the monomer having a cyclic ether structure other than the epoxy structure and the oxetane structure include a monomer having a cyclic ether structure such as tetrahydrofurfuryl (meth)acrylate, etc. Examples of the monomer having an acyclic ether structure include a monomer having an acyclic ether structure such as 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and ethyl carbitol (meth)acrylate.

[0032] The content of the structural units derived from the monomer having an ether structure in the (meth)acrylic copolymer is preferably 50% by mass or less. When the content of the structural units derived from the monomer having an ether structure is 50% by mass or less, the resulting pressure-sensitive adhesive composition has improved adhesive strength and can exhibit superior adhesion to an adherend. The content of the structural units derived from the monomer having an ether structure is more preferably 30% by mass, and even more preferably 10% by mass. Furthermore, when the (meth)acrylic copolymer contains structural units derived from the monomer having an ether structure, the lower limit of the content of the structural units derived from the monomer having an ether structure in the (meth)acrylic copolymer is not particularly limited, and may be greater than 0% by mass. The lower limit is preferably 0.01% by mass, more preferably 0.1% by mass, and even more preferably 1.0% by mass. The (meth)acrylic copolymer may not contain structural units derived from the monomer having an ether structure, i.e., the content of the structural units derived from the monomer having an ether structure may be 0% by mass. The content of the structural units derived from the monomer having an ether structure can be, for example, in the ranges of 0% by mass or more and 50% by mass or less, 0% by mass or more and 30% by mass or less, 0% by mass or more and 10% by mass or less, more than 0% by mass or more and 50% by mass or less, more than 0% by mass or more and 30% by mass or less, more than 0% by mass or more and 10% by mass or less, 0.01% by mass or more and 50% by mass or less, 0.01% by mass or more and 30% by mass or less, 0.01% by mass or more and 10% by mass or less, 0.1% by mass or more and 50% by mass or less, 0.1% by mass or more and 30% by mass or less, 0.1% by mass or more and 10% by mass or less, 1.0% by mass or more and 50% by mass or less, 1.0% by mass or more and 30% by mass or less, and 1.0% by mass or more and 10% by mass or less. The content of the structural units derived from the monomer having an ether structure can be determined by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( １ H-NMR, １３ C-NMR, etc.) 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 ether structure.

[0033] 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.

[0034] The branched alkyl group-containing alkyl(meth)acrylate (A), the monomer having a crosslinkable functional group, and the other monomers are preferably acrylate monomers. By using acrylate monomers as the branched alkyl group-containing alkyl(meth)acrylate (A), the monomer having a crosslinkable functional group, and the other monomers, the weight-average molecular weight of the (meth)acrylic copolymer contained in the resulting pressure-sensitive adhesive composition can be easily increased, compared to when a methacrylate monomer is used, and higher shear adhesive strength can be achieved.

[0035] The (meth)acrylic copolymer preferably 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. 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, thereby enabling the copolymer to exhibit higher shear adhesive strength. The 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 may be one of the other alkyl (meth)acrylates or a monomer other than the alkyl (meth)acrylates. The monomer that has a glass transition temperature of 0°C or higher when made into a homopolymer may be one of the monomers having an acyclic ether structure or a cyclic ether structure other than an epoxy structure or an oxetane structure.

[0036] Examples of the crosslinkable functional group in the monomer having no crosslinkable functional group and 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.

[0037] Specific examples of the monomer having no crosslinkable functional group and 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).

[0038] The content of the structural units derived from monomers 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. By having the content of the structural units derived from monomers having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher be 0.1% by mass or higher, higher shear adhesive strength can be exhibited. By having the content of the structural units derived from monomers having no crosslinkable functional groups and a homopolymer Tg of 0°C or higher be 70% by mass or lower, higher adhesive strength can be exhibited. The content of the structural units derived from monomers 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 the structural unit derived from a monomer having no crosslinkable functional group and 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, １３C-NMR, etc.) and calculation can be made from the integrated intensity ratio of hydrogen peaks derived from a monomer that does not have the above-mentioned crosslinkable functional group and has a homopolymer Tg of 0° C. or higher.

[0039] The monomer having a crosslinkable functional group and the other monomers preferably contain biologically derived materials, but may also be composed solely of petroleum-derived materials. In theory, all of the acrylic monomers constituting the (meth)acrylic copolymer may be monomers containing biologically derived materials. From the standpoint of cost and productivity of the pressure-sensitive adhesive composition, a monomer containing a relatively inexpensive and easily available biologically derived material may be used, and this may be combined with a monomer consisting solely of petroleum-derived materials.

[0040] 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 preferred lower limit of the weight-average molecular weight of the (meth)acrylic copolymer is 300,000, and the preferred upper limit is 1,500,000. When the weight-average molecular weight of the (meth)acrylic copolymer is 500,000 or more, the resulting pressure-sensitive adhesive composition can exhibit excellent cohesive strength, thereby exhibiting higher shear adhesive strength. Furthermore, the excellent cohesive strength further improves heat resistance, thereby enabling the pressure-sensitive adhesive composition to exhibit better retention performance at high temperatures. When the weight-average molecular weight of the (meth)acrylic copolymer is 1,500,000 or less, the resulting pressure-sensitive adhesive composition can exhibit reduced surface energy, thereby enabling the pressure-sensitive adhesive composition to exhibit better adhesion to the adherend. The more preferred lower limit of the weight-average molecular weight of the (meth)acrylic copolymer is 500,000, the more preferred upper limit is 1,400,000, the even more preferred lower limit is 700,000, the even more preferred upper limit is 1,300,000, the even more preferred lower limit is 800,000, and the particularly preferred lower limit is 900,000. The weight average molecular weight of the (meth)acrylic copolymer may be, for example, 300,000 to 1,500,000, 300,000 to 1,400,000, 300,000 to 1,300,000, 500,000 to 1,500,000, 500,000 to 1,400,000, 500,000 to 1,300,000, 700,000 to 1,500,000, 700,000 to 1,400,000, 700,000 to 1,300,000, 800,000 to 1,500,000, 800,000 to 1,400,000, 800,000 to 1,300,000, 900,000 to 1,500,000, 900,000 to 1,400,000, 900,000 to 1,300,000, etc. In this specification, the weight average molecular weight is the weight average molecular weight in terms of standard polystyrene measured by GPC (Gel Permeation Chromatography). 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.The gel permeation chromatograph may be, for example, 2690 Separations Module (manufactured by Waters Corporation).

[0041] 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.

[0042] 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 include living radical polymerization and free radical polymerization. Living radical polymerization produces copolymers with more uniform molecular weight and composition than free radical polymerization, and can suppress the generation of low-molecular-weight components, etc., resulting in a pressure-sensitive adhesive composition that exhibits stronger cohesive strength and therefore better adhesion to the adherend. Conventional methods can be used to polymerize the monomer mixture, including solution polymerization (boiling point polymerization or constant temperature polymerization), UV polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization and UV polymerization are preferred because they result in a pressure-sensitive adhesive composition that exhibits better adhesion to the adherend. When solution polymerization is used to polymerize the monomer mixture, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, and diethyl ether.

[0043] 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 compounds include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. Furthermore, when the radical reaction is carried out by living radical polymerization, examples of the polymerization initiator include organotellurium polymerization initiators. The organotellurium polymerization initiator is not particularly limited as long as it is one that is generally used in living radical polymerization, and examples thereof include organotellurium compounds, organotelluride compounds, etc. In addition to the organotellurium polymerization initiator, the azo compound may also be used in the living radical polymerization in order to accelerate the polymerization rate.

[0044] The glass transition temperature of the (meth)acrylic copolymer preferably has a lower limit of −55° C. and a higher limit of −15° C. When the glass transition temperature of the (meth)acrylic copolymer is within the above range, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to adherends. The lower limit of the glass transition temperature of the (meth)acrylic copolymer is more preferably −45° C., and the upper limit is more preferably −25° C. Examples of the glass transition temperature of the (meth)acrylic copolymer include −55° C. or higher and −15° C. or lower, −55° C. or higher and −25° C. or lower, −45° C. or higher and −15° C. or lower, and −45° C. or higher and −25° C. or lower. The glass transition temperature of the (meth)acrylic copolymer can be measured by the same method as for the homopolymer Tg described above.

[0045] The preferred lower limit of the content of the (meth)acrylic copolymer in the pressure-sensitive adhesive composition is 50% by mass, and the preferred upper limit is 99.5% by mass. When the content of the (meth)acrylic copolymer is within this range, the resulting pressure-sensitive adhesive composition can exhibit higher shear adhesive strength and better adhesion to the adherend. The more preferred lower limit of the content of the (meth)acrylic copolymer is 55% by mass, and the more preferred upper limit is 95% by mass, and even more preferred lower limit is 70% by mass, and even more preferred upper limit is 90% by mass, and even more preferred upper limit is 80% by mass. Examples of the content of the (meth)acrylic copolymer include 50% by mass or more and 99.5% by mass or less, 50% by mass or more and 95% by mass or less, 50% by mass or more and 90% by mass or less, 50% by mass or more and 80% by mass or less, 55% by mass or more and 99.5% by mass or less, 55% by mass or more and 95% by mass or less, 55% by mass or more and 90% by mass or less, 55% by mass or more and 80% by mass or less, 70% by mass or more and 99.5% by mass or less, 70% by mass or more and 95% by mass, 70% by mass or more and 90% by mass or less, and 70% by mass or more and 80% by mass or less.

[0046] The pressure-sensitive adhesive composition preferably further contains a tackifier. When the pressure-sensitive adhesive composition contains a tackifier, it is able to exhibit even better adhesive strength.

[0047] The tackifier is not particularly limited, and examples thereof include rosin-based tackifiers, rosin ester-based tackifiers, terpene-based tackifiers, coumarone-indene-based tackifiers, alicyclic saturated hydrocarbon-based tackifiers, C5-based petroleum tackifiers, C9-based petroleum tackifiers, C5-C9 copolymer-based petroleum tackifiers, and acrylic tackifiers. These tackifiers may be used alone or in combination of two or more. Among these, it is preferable to include at least one selected from the group consisting of rosin ester-based tackifiers, terpene-based tackifiers, and acrylic tackifiers, and it is more preferable to include a rosin ester-based tackifier and a terpene-based tackifier.

[0048] Examples of the rosin-based tackifier include rosin-based resins and rosin polyol-based resins. Examples of the rosin ester-based tackifier include rosin ester-based resins, polymerized rosin ester-based resins, and hydrogenated rosin ester-based resins. Examples of the terpene-based tackifier include terpene-based resins and terpene phenol-based resins. The rosin ester-based tackifier and the terpene-based tackifier are preferably derived from living organisms. Examples of the rosin ester-based tackifier derived from living organisms include rosin ester-based tackifiers derived from natural resins such as pine resin. Examples of the terpene-based tackifier derived from living organisms include terpene-based tackifiers derived from plant essential oils.

[0049] 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 tackifier include YS Resin PX1250 and YS Polystar G150 (all manufactured by Yasuhara Chemical Co., Ltd.).

[0050] The acrylic tackifier is composed of a (meth)acrylic compound having a weight-average molecular weight of less than 30,000, and examples of the (meth)acrylic compound having a weight-average molecular weight of less than 30,000 include an acrylic oligomer having a weight-average molecular weight of less than 30,000 and an acrylic monomer having a weight-average molecular weight of less than 30,000, and among these, an acrylic oligomer having a weight-average molecular weight of less than 30,000 is preferred. Note that, in this specification, "acrylic tackifier" does not include the "acrylic isocyanate prepolymer" described below.

[0051] The weight-average molecular weight of the acrylic oligomer used as the acrylic tackifier is less than 30,000. The weight-average molecular weight of the acrylic oligomer is preferably 1,000 or more and less than 30,000. When the weight-average molecular weight of the acrylic oligomer is within the above range, the adhesive strength of the resulting pressure-sensitive adhesive composition is further improved. The weight-average molecular weight of the acrylic oligomer 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 acrylic oligomer can be measured by the same method as the method for measuring the weight-average molecular weight of the (meth)acrylic copolymer described above.

[0052] The glass transition temperature of the acrylic oligomer used as the acrylic tackifier preferably has a lower limit of 0°C and an upper limit of 300°C. When the glass transition temperature of the acrylic oligomer is within the above range, the adhesive strength of the resulting pressure-sensitive adhesive composition is further improved. The lower limit of the glass transition temperature of the acrylic oligomer is more preferably 20°C, and even more preferably 40°C. Examples of the glass transition temperature of the acrylic oligomer include 0°C or higher and 300°C or lower, 20°C or higher and 300°C or lower, and 40°C or higher and 300°C or lower. The glass transition temperature of the acrylic oligomer can be measured, for example, by differential scanning calorimetry under a nitrogen atmosphere (nitrogen flow, flow rate 50 mL / min) according to JIS K6240:2011, under conditions of a measurement temperature of -100°C to 200°C and a heating rate of 10°C / min.

[0053] Examples of the constituent monomers of the acrylic oligomer and the acrylic monomer include the same monomers as those used in the constituent units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) in the (meth)acrylic copolymer, the constituent units derived from the monomers having a crosslinkable functional group, and the constituent units derived from the other monomers.

[0054] Examples of the constituent monomers of the acrylic oligomer and the acrylic monomer 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, nonyl (meth)acrylate, and isopropyl (meth)acrylate. Preferred examples include alkyl (meth)acrylates such as sononyl (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 acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, such as an alkyl (meth)acrylate having a branched alkyl group, such as isobutyl (meth)acrylate or t-butyl (meth)acrylate; an ester of (meth)acrylic acid and an alicyclic alcohol, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, or dicyclopentanyl (meth)acrylate (an alicyclic hydrocarbon group-containing (meth)acrylate); or a (meth)acrylate having a cyclic structure, such as an aryl (meth)acrylate, such as phenyl (meth)acrylate or benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive composition. In addition to the (meth)acrylate monomer, a monomer having a crosslinkable functional group can be used as a constituent monomer component of the acrylic oligomer.Suitable examples of the monomer having a crosslinkable functional group 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 AA and MAA; and hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These monomers having a crosslinkable functional group can be used alone or in combination of two or more. Among these, carboxy group-containing monomers are preferred, and AA is particularly preferred. For example, by using a carboxy group-containing monomer as the monomer having a crosslinkable functional group, the adhesive strength to highly polar adherends can be improved.

[0055] The acrylic oligomer can be synthesized, for example, by the same method as that for the (meth)acrylic copolymer described above. Alternatively, a commercially available acrylic tackifier may be used.

[0056] 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 is more preferably 90°C in lower limit, more preferably 160°C in upper limit, even more preferably 100°C in lower limit, and even more preferably 150°C in upper limit. Examples of the softening point range of the tackifier include 80°C in higher and 170°C in lower, 80°C in higher and 160°C in lower, 80°C in higher and 150°C in lower, 90°C in higher and 170°C in lower, 90°C in higher and 160°C in lower, 90°C in higher and 150°C in lower, 100°C in higher and 170°C in lower, 100°C in higher and 160°C in lower, and 100°C in higher and 150°C in 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).

[0057] In the pressure-sensitive adhesive composition, the preferred lower limit of the tackifier content 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 tackifier content is 10 parts by mass or more, the resulting pressure-sensitive adhesive composition can exhibit superior adhesive strength. When the tackifier content is 50 parts by mass or less, the pressure-sensitive adhesive composition can exhibit superior adhesion to the adherend. A more preferred lower limit of the tackifier content is 15 parts by mass, a more preferred upper limit is 45 parts by mass, an even more preferred lower limit is 20 parts by mass, an even more preferred upper limit is 40 parts by mass, and an even more preferred lower limit is 30 parts by mass. The content of the tackifier is, for example, 10 parts by mass or more and 50 parts by mass or less, 10 parts by mass or more and 45 parts by mass or less, 10 parts by mass or more and 40 parts by mass or less, 15 parts by mass or more and 50 parts by mass or less, 15 parts by mass or more and 45 parts by mass or less, and 15 parts by mass or more and 45 parts by mass or less. Examples include 0 parts by mass or less, 20 parts by mass or more and 50 parts by mass or less, 20 parts by mass or more and 45 parts by mass or less, 20 parts by mass or more and 40 parts by mass or less, 30 parts by mass or more and 50 parts by mass or less, 30 parts by mass or more and 45 parts by mass or less, 30 parts by mass or more and 40 parts by mass or less.

[0058] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent, from the viewpoint of being able to appropriately adjust the degree of crosslinking. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, and a metal chelate-based crosslinking agent. 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, and more preferably an isocyanate-based crosslinking agent, so that the resulting pressure-sensitive adhesive composition can exhibit superior adhesion to the adherend. It is also more preferable that the crosslinking agent contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. The crosslinking agent may be a single agent, or two or more types may be used in combination. When two or more types of crosslinking agents are used in combination, two or more types of the same type of crosslinking agent may be used (e.g., two or more types of isocyanate-based crosslinking agents may be used), or one or more types of different crosslinking agents may be used in combination (e.g., one or more types of isocyanate-based crosslinking agents and one or more types of epoxy-based crosslinking agents may be used).

[0059] Furthermore, an acrylic isocyanate prepolymer having a weight-average molecular weight of less than 30,000 may be used as the isocyanate crosslinking agent. The acrylic isocyanate prepolymer is a compound obtained by synthesizing an acrylic oligomer having a weight-average molecular weight of less than 30,000 with a diisocyanate compound. The acrylic oligomer in the acrylic isocyanate prepolymer can be synthesized, for example, using the same method as the (meth)acrylic copolymer described above. Furthermore, a commercially available product may be used as the acrylic isocyanate prepolymer.

[0060]

[0043] In the acrylic isocyanate prepolymer, examples of the constituent monomer of the acrylic oligomer include the same monomers as those used in the constituent units derived from the branched alkyl group-containing alkyl (meth)acrylate (A) in the (meth)acrylic copolymer described above, the constituent units derived from the monomers having a crosslinkable functional group, and the constituent units derived from the other monomers.

[0061] Examples of the diisocyanate compound include 4,4-diphenylmethane diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-cyclohexylmethane diisocyanate, toluylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, and 4,4'-isopropylidenedincyclohexyl isocyanate.

[0062] In the pressure-sensitive adhesive composition, the content of the crosslinking agent relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 0.01 parts by mass at the lower limit and 10 parts by mass at the upper limit. By setting the content of the crosslinking agent within this range, the degree of crosslinking of the resulting pressure-sensitive adhesive composition can be appropriately adjusted, allowing it to exhibit better adhesive strength and better adhesion to the adherend. The content of the crosslinking agent is more preferably 0.1 parts by mass at the lower limit and 8.0 parts by mass at the upper limit, still more preferably 0.2 parts by mass at the lower limit and 7.5 parts by mass at the upper limit. Examples of the content of the crosslinking agent include 0.01 parts by mass or more and 10 parts by mass or less, 0.01 parts by mass or more and 8.0 parts by mass or less, 0.01 parts by mass or more and 7.5 parts by mass or less, 0.1 parts by mass or more and 10 parts by mass or less, 0.1 parts by mass or more and 8.0 parts by mass or less, 0.1 parts by mass or more and 7.5 parts by mass or less, 0.2 parts by mass or more and 10 parts by mass or less, 0.2 parts by mass or more and 8.0 parts by mass or less, and 0.2 parts by mass or more and 7.5 parts by mass or less. In this specification, the "content of crosslinking agent" means the content of the solid content of the crosslinking agent.

[0063] The pressure-sensitive adhesive composition may further contain a crosslinking catalyst for accelerating crosslinking by the crosslinking agent. Examples of the crosslinking catalyst include crosslinking catalysts for the isocyanate-based crosslinking agents, such as dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate.

[0064] The pressure-sensitive adhesive composition preferably does not contain a surfactant. The absence of a surfactant in the pressure-sensitive adhesive composition allows the resulting pressure-sensitive adhesive composition to exhibit superior adhesive strength. Furthermore, the absence of a surfactant in the pressure-sensitive adhesive composition further improves heat resistance and allows the pressure-sensitive adhesive composition to exhibit better retention performance at high temperatures. In order for the pressure-sensitive adhesive composition to be surfactant-free, it is preferable not to use the surfactant when obtaining the (meth)acrylic copolymer. For this purpose, for example, solution polymerization, UV polymerization, or the like may be employed as the polymerization method for obtaining the (meth)acrylic copolymer. The absence of a surfactant in the pressure-sensitive adhesive composition means that the content of the surfactant in the pressure-sensitive adhesive composition is 3.0% by mass or less, preferably 1.0% by mass or less.

[0065] The surfactant content can be determined, for example, by measuring the pressure-sensitive adhesive composition using a liquid chromatography mass spectrometer (such as Shimadzu Corporation's "NEXCERA" or Thermo Fisher Scientific's "Exactive"). More specifically, an ethyl acetate solution of the pressure-sensitive adhesive composition is filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm). Approximately 10 μL of the resulting filtrate is injected into a liquid chromatography mass spectrometer and analyzed under the following conditions. The surfactant content can be determined from the area ratio of the peak corresponding to the surfactant in the pressure-sensitive adhesive composition. Preferably, samples with known surfactant content in the pressure-sensitive adhesive composition are prepared for each surfactant type, and a calibration curve showing the relationship between the surfactant content and the peak area ratio is prepared and analyzed. <Analysis conditions> Column: Hypersil GOLD (2.1 x 150 mm) manufactured by Thermo Fisher Scientific Mobile phase: acetonitrile Column temperature: 40°C Flow rate: 1.0 mL / min Ionization method: ESI (electrospray ionization) Capillary temperature: 350°C

[0066] The pressure-sensitive adhesive composition preferably further contains a colorant. By containing the colorant, the pressure-sensitive adhesive composition obtained can exhibit light-blocking properties, making it more suitable for use in fixing electronic device parts or vehicle-mounted parts.

[0067] Examples of the colorant include pigments and dyes. Among these, pigments are preferred from the viewpoint of superior durability.

[0068] Examples of the pigment include color pigments such as black fillers, titanium oxide, etc. Specific examples of the black filler include carbon black, titanium black, etc. Examples of the dye include azo dyes, anthraquinone dyes, indigo dyes, etc.

[0069] The average particle size of the black filler preferably has a lower limit of 0.01 μm and an upper limit of 1.0 μm. When the average particle size of the black filler is within the above range, the resulting pressure-sensitive adhesive composition can exhibit better light-blocking properties. A more preferred lower limit of the average particle size of the black filler is 0.1 μm, and a more preferred upper limit is 0.8 μm. Examples of the average particle size of the black filler include 0.01 μm or more and 1.0 μm or less, 0.01 μm or more and 0.8 μm or less, 0.1 μm or more and 1.0 μm or less, and 0.1 μm or more and 0.8 μm or less. The average particle size can be determined, for example, by observing 50 random black fillers with an electron microscope or an optical microscope and calculating the average particle size of each black filler, or by performing laser diffraction particle size distribution measurement.

[0070] In the pressure-sensitive adhesive composition, the preferred lower limit of the content of the colorant relative to 100 parts by mass of the (meth)acrylic copolymer is 0.1 parts by mass, and the preferred upper limit is 5.0 parts by mass. When the content of the colorant is within this range, the resulting pressure-sensitive adhesive composition can exhibit better light-blocking properties. A more preferred lower limit of the content of the colorant is 0.5 parts by mass, and a more preferred upper limit is 3.0 parts by mass. Examples of the content of the pigment include 0.1 parts by mass or more and 5.0 parts by mass or less, 0.1 parts by mass or more and 3.0 parts by mass or less, 0.5 parts by mass or more and 5.0 parts by mass or less, and 0.5 parts by mass or more and 3.0 parts by mass or less.

[0071] The pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a plasticizer, a softener, a filler, etc., as needed, within the scope of not impairing the object of the present invention.

[0072] The method for producing the pressure-sensitive adhesive composition is not particularly limited, and the composition can be produced by a conventionally known production method, for example, by adding a solvent to the (meth)acrylic copolymer and, if necessary, a tackifier, a crosslinking agent, etc.

[0073] The preferred lower limit of the bio-derived carbon content in the PSA composition is 10%. When the bio-derived carbon content in the PSA composition is 10% or more, the resulting PSA composition is excellent in terms of saving petroleum resources and reducing carbon dioxide emissions, and can reduce the environmental impact. The preferred lower limit of the bio-derived carbon content in the PSA composition is 40%, and the even more preferred lower limit is 60%. The upper limit of the bio-derived carbon content in the PSA composition is not particularly limited and may be 100%, but is, for example, 95% or 90%. Examples of the bio-derived carbon content in the PSA composition include 10% to 100%, 10% to 95%, 10% to 90%, 40% to 100%, 40% to 95%, 40% to 90%, 60% to 100%, 60% to 95%, and 60% to 90%. Note that while carbon derived from living organisms contains a certain proportion of the radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the "content of biologically derived carbon" in this specification can be calculated by measuring the concentration of C-14 contained in the PSA composition or PSA layer. Specifically, it can be measured in accordance with ASTM D6866-24, a standard widely used in the bioplastics industry.

[0074] The content of biologically derived carbon in the pressure-sensitive adhesive composition can be adjusted by changing each component constituting the pressure-sensitive adhesive composition to a biologically derived material and by changing the content of the biologically derived material.

[0075] The pressure-sensitive adhesive composition can be suitably used as a pressure-sensitive adhesive in a pressure-sensitive adhesive layer of a pressure-sensitive adhesive tape or as a liquid pressure-sensitive adhesive.

[0076] The present disclosure also provides a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition. The gel fraction of the pressure-sensitive adhesive layer, the content of bio-derived carbon in the pressure-sensitive adhesive layer, and the glass transition temperature of the pressure-sensitive adhesive layer, which will be described later, can be adjusted to the values ​​described later by adjusting the type and content of each component constituting the pressure-sensitive adhesive composition. Examples of methods for forming a 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. The pressure-sensitive adhesive layer may contain either an uncrosslinked pressure-sensitive adhesive composition or a crosslinked product of the pressure-sensitive adhesive composition.

[0077] 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 cohesive strength of the pressure-sensitive adhesive layer is further improved, and the resulting pressure-sensitive adhesive tape exhibits higher shear adhesive strength. Furthermore, the adhesive strength and high-temperature retention performance of the resulting pressure-sensitive adhesive tape are further improved. When the gel fraction of the pressure-sensitive adhesive layer is 70% by mass or less, the resulting pressure-sensitive adhesive tape has further improved adhesion to the adherend. The more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 20% by mass, the more preferred upper limit is 60% by mass, the even more preferred lower limit is 30% by mass, and the even more preferred upper limit is 50% by mass. Examples of the gel fraction of the pressure-sensitive adhesive layer include 10% by mass or more and 70% by mass or less, 10% by mass or more and 60% by mass or less, 10% by mass or more and 50% by mass or less, 20% by mass or more and 70% by mass or less, 20% by mass or more and 60% by mass or less, 20% by mass or more and 50% by mass or less, 30% by mass or more and 70% by mass or less, 30% by mass or more and 60% by mass or less, and 30% by mass or more and 50% by mass or less. 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 with a width of 20 mm and a length of 40 mm to prepare a test piece. 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 dried test piece is measured, and the gel fraction is calculated using the following formula (I). Note that no separator such as a release film for protecting the pressure-sensitive adhesive layer is laminated on the test piece. In addition, when the pressure-sensitive adhesive tape is a non-support type tape that does not have a base layer, the measurement is carried out using a test piece having a base layer obtained by adhering the tape to a base and cutting the tape, or the measurement is carried out using a test piece having a base layer obtained by adhering the tape to a base layer and cutting the tape, or ０ The calculation is performed assuming that the gel fraction is 0. Gel fraction (mass%) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (I) (W ０ : Mass of the base material layer, W １ : mass of test piece before immersion, W ２ : Mass of test piece after immersion and drying)

[0078] 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 resulting pressure-sensitive adhesive tape 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%. The upper limit of the bio-derived carbon content in the pressure-sensitive adhesive layer is not particularly limited and may be 100%, but is, for example, 95% or 90%. Examples of the bio-derived carbon content in the pressure-sensitive adhesive layer include 10% or more and 100% or less, 10% or more and 95% or less, 10% or more and 90% or less, 40% or more and 100% or less, 40% or more and 95% or less, 40% or more and 90% or less, 60% or more and 100% or less, 60% or more and 95% or less, and 60% or more and 90% or less.

[0079] The glass transition temperature of the pressure-sensitive adhesive layer measured by dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter sometimes simply referred to as the "glass transition temperature of the pressure-sensitive adhesive layer") preferably has a lower limit of -20°C and an upper limit of 35°C. When the glass transition temperature of the pressure-sensitive adhesive layer is within the above range, the resulting pressure-sensitive adhesive tape can exhibit higher shear adhesive strength and better adhesion to the adherend. The glass transition temperature of the pressure-sensitive adhesive layer more preferably has a lower limit of -10°C and an upper limit of 25°C. In this specification, the "glass transition temperature of the pressure-sensitive adhesive layer" refers to the temperature at which the maximum due to micro-Brownian motion appears among the maximums of the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement. For example, the following method can be used for dynamic viscoelasticity measurement to measure the glass transition temperature of the pressure-sensitive adhesive layer. That is, first, the pressure-sensitive adhesive layers are stacked to prepare a laminate having a thickness of about 1 mm, and this is cut into a width of 6 mm and a length of 10 mm to obtain a test piece. Next, the obtained test piece is subjected to dynamic viscoelasticity measurement in a shear mode using a dynamic viscoelasticity measuring device under the conditions of a measurement temperature of −150° C. to 200° C., a temperature rise rate of 5° C. / min, a frequency of 10 Hz, and a strain of 0.08% in a nitrogen atmosphere. Examples of the dynamic viscoelasticity measuring device include DVA-200 (manufactured by IT Measurement & Control Co., Ltd.).

[0080] 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 resulting pressure-sensitive adhesive tape has sufficient adhesive strength. When the thickness of the pressure-sensitive adhesive layer is 300 μm or less, the resulting pressure-sensitive adhesive tape is easily removable. A more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 5 μm, and a more preferred upper limit is 200 μm. Examples of the thickness of the pressure-sensitive adhesive layer include 3 μm or more and 300 μm or less, 3 μm or more and 200 μm or less, 5 μm or more and 300 μm or less, and 5 μm or more and 200 μm or less.

[0081] The pressure-sensitive adhesive tape according to one embodiment of the present invention may have a layer other than the pressure-sensitive adhesive layer.

[0082] The pressure-sensitive adhesive tape may be a non-support type tape that does not have a base layer, or a support type tape that has a base layer. In particular, it is preferable that the pressure-sensitive adhesive tape has a base layer. Since the pressure-sensitive adhesive layer also has excellent adhesion to the base layer, the pressure-sensitive adhesive tape having a base layer can exhibit sufficient adhesive strength immediately after lamination. When the pressure-sensitive adhesive tape is a support type tape having a base layer, it may be a single-sided pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on one side of the base layer, or a double-sided pressure-sensitive adhesive tape having the pressure-sensitive adhesive layers on both sides of the base layer.

[0083] When the pressure-sensitive adhesive tape of one embodiment of the present invention is a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of a base layer, at least one of the pressure-sensitive adhesive layers may be a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of one embodiment of the present invention. In this case, the pressure-sensitive adhesive tape may have a pressure-sensitive adhesive layer not formed from the pressure-sensitive adhesive composition, but from the viewpoint of increasing the content of bio-derived carbon in the pressure-sensitive adhesive tape as a whole, it is preferred that the pressure-sensitive adhesive layers on both sides are pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive composition of one embodiment of the present invention.

[0084] Examples of the substrate used for the substrate layer include a film, a nonwoven fabric, and a foam substrate. 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 biologically-derived material include plant-derived 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).

[0085] 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, the collected waste materials may be burned and used as thermal energy for the production of substrates and their raw materials. The oils and fats contained in the collected waste materials may be mixed with petroleum, fractionated, and purified, and then used as raw materials.

[0086] The substrate used in the substrate layer preferably contains a foam substrate from the viewpoint of further improving conformability to unevenness. The foam substrate is preferably a foam substrate containing at least one selected from the group consisting of PE, PP, and PU, and a foam substrate containing PE is more preferred from the viewpoint of achieving a high degree of both flexibility and strength. Examples of the constituents of the foam substrate containing PE include PE made from sugarcane.

[0087] 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.

[0088] 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 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. Examples of the thickness of the foam substrate include 50 μm or more and 5000 μm or less, 50 μm or more and 1000 μm or less, and 50 μm or more and 300 μm or less.

[0089] The substrate used for the substrate layer is preferably a film containing PES or a film containing PA from the viewpoint of substrate strength. Furthermore, from the viewpoint of heat resistance and oil resistance, a film containing PA is preferred. Examples of PA include nylon 11, nylon 1010, nylon 610, nylon 510, and nylon 410, which are made from castor oil, and nylon 56, which is made from cellulose.

[0090] The preferred lower limit of the thickness of the substrate is 1 μm, and the preferred upper limit is 5000 μm. By having the thickness of the substrate within this range, it is possible to exhibit high impact resistance while exhibiting high flexibility that allows it to be adhered to the shape of the adherend. The more preferred lower limit of the thickness of the substrate is 4 μm, the more preferred upper limit is 1000 μm, the even more preferred lower limit is 10 μm, the even more preferred upper limit is 300 μm, and the even more preferred lower limit is 50 μm. Examples of the thickness of the substrate include 1 μm or more and 5000 μm or less, 1 μm or more and 1000 μm or less, 1 μm or more and 300 μm or less, 4 μm or more and 5000 μm or less, 4 μm or more and 1000 μm or less, 4 μm or more and 300 μm or less, 10 μm or more and 5000 μm or less, 10 μm or more and 1000 μm or less, 10 μm or more and 300 μm or less, 50 μm or more and 5000 μm or less, 50 μm or more and 1000 μm or less, and 50 μm or more and 300 μm or less.

[0091] The total thickness of the pressure-sensitive adhesive tape (for example, the thickness of the pressure-sensitive adhesive layer when the pressure-sensitive adhesive tape has only a pressure-sensitive adhesive layer, or the sum of the thickness of the pressure-sensitive adhesive layer and the thickness of the base layer when the pressure-sensitive adhesive tape has a pressure-sensitive adhesive layer and a base layer) preferably has a lower limit of 3 μm and an upper limit of 6000 μm. When the total thickness of the pressure-sensitive adhesive tape is in this range, the adhesive strength of the resulting pressure-sensitive adhesive tape is further increased. The upper limit of the total thickness of the pressure-sensitive adhesive tape is more preferably 1200 μm, and even more preferably 500 μm. The total thickness of the pressure-sensitive adhesive tape is, for example, 3 μm or more and 6000 μm or less, 3 μm or more and 1200 μm or less, or 3 μm or more and 500 μm or less.

[0092] The method for producing the pressure-sensitive adhesive tape is not particularly limited, and it can be produced by a conventionally known production method. For example, in the case of a double-sided pressure-sensitive adhesive tape having a substrate layer, the following method can be mentioned. First, a pressure-sensitive adhesive composition A is prepared by the method described above. The obtained pressure-sensitive adhesive composition A is applied to the surface of the 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-mentioned release film is prepared, and a pressure-sensitive adhesive composition B prepared in the same manner as the pressure-sensitive adhesive composition A is applied to the release-treated surface of this release film, and the solvent in the composition is completely dried and removed to produce a laminate film in which the pressure-sensitive adhesive layer B is formed on the surface of the release film. The obtained laminate film is superimposed on the back surface of the substrate on which the pressure-sensitive adhesive layer A has been formed, with the pressure-sensitive adhesive layer B facing the back surface of the substrate to produce a laminate. Then, by pressing the laminate with a rubber roller or the like, a double-sided adhesive tape can be obtained which has adhesive layers on both sides of the substrate and in which the surfaces of the adhesive layers are covered with release films.

[0093] 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 and in which the surfaces of the pressure-sensitive adhesive layers are covered with release films.

[0094] The pressure-sensitive adhesive tape may be colored. The color of the pressure-sensitive adhesive tape is not particularly limited, and examples thereof include white, black, gray, etc. Among these, black and gray are preferred from the viewpoint of further improving the light-shielding properties of the resulting pressure-sensitive adhesive tape.

[0095] The pressure-sensitive adhesive tape can be colored, for example, by incorporating a pigment (dye) into the pressure-sensitive adhesive composition. Examples of the pigment include carbon black ("Multilac A903 Black" manufactured by Toyocolor Co., Ltd.).

[0096] The application of the pressure-sensitive adhesive tape is not particularly limited, but it is preferably used for fixing electronic components or vehicle-mounted components. Specifically, the obtained pressure-sensitive adhesive tape can be suitably used for adhesively fixing electronic components in large portable electronic devices, adhesively fixing vehicle-mounted components (e.g., vehicle panels), etc. Furthermore, since the pressure-sensitive adhesive tape can exhibit excellent adhesion to the adherend, it can exhibit adhesive strength immediately after being attached to the adherend that is equivalent to the adhesive strength after time has passed since being attached to the adherend (after adhesion has been enhanced). In other words, since the pressure-sensitive adhesive tape can suppress adhesion enhancement to the adherend over time after being attached to the adherend, it can be suitably used for protecting the adherend, etc.

[0097] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that exhibits high shear adhesive strength and excellent adhesion to an adherend, and also to provide a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition.

[0098] 1A and 1B are diagrams showing a shear adhesive strength test and a high temperature retention test, respectively.

[0099] 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.

[0100] <1-Methylheptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was alkali-fused to obtain a mixture containing sepacic acid and 1-methylheptyl alcohol. Next, sepacic acid was separated from the obtained mixture by distillation to obtain 1-methylheptyl alcohol containing bio-derived carbon. 1-Methylheptyl acrylate containing bio-derived carbon was prepared by esterifying the obtained 1-methylheptyl alcohol containing bio-derived carbon with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.).

[0101] <Isostearyl acrylate containing bio-derived carbon> After isomerization of oleic acid obtained from rapeseed oil, the resulting monomer acid was hydrogenated and purified by solvent fractionation to obtain isostearyl alcohol containing bio-derived carbon. The resulting isostearyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare isostearyl acrylate containing bio-derived carbon.

[0102] <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.

[0103] <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. Next, undecylenic acid was separated from the obtained mixture by distillation to obtain n-heptyl alcohol containing bio-derived carbon. The obtained 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.

[0104] <Isobornyl acrylate containing bio-derived carbon> Camphene containing bio-derived carbon was obtained by isomerizing pinene extracted from pine resin. Camphene containing bio-derived carbon was reacted with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare isobornyl acrylate containing bio-derived carbon.

[0105] <Isobornyl methacrylate containing bio-derived carbon> Camphene containing bio-derived carbon was obtained by isomerizing pinene extracted from pine resin. Camphene containing bio-derived carbon was reacted with methacrylic acid (manufactured by Mitsubishi Chemical Corporation) to prepare isobornyl methacrylate containing bio-derived carbon.

[0106] <2-hydroxyethyl acrylate containing bio-derived carbon> Ethanol containing bio-derived carbon was obtained by fermenting sugar contained in sugarcane. The obtained ethanol containing bio-derived carbon was dehydrated to obtain ethylene, which was then oxidized to obtain ethylene oxide, to which water was added to obtain ethylene glycol containing bio-derived carbon. The obtained ethylene glycol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare 2-hydroxyethyl acrylate containing bio-derived carbon.

[0107] <Tetrahydrofurfuryl acrylate containing bio-derived carbon> Tetrahydrofurfuryl alcohol containing bio-derived carbon was obtained by hydrogenating furfural contained in sugarcane. Tetrahydrofurfuryl alcohol containing bio-derived carbon was reacted with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare tetrahydrofurfuryl acrylate containing bio-derived carbon.

[0108] <Bio-derived carbon-free monomers> ・Isobutyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Isoamyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Isodecyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Methyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Ethyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・n-Butyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・t-Butyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・2-Ethylhexyl acrylate (manufactured by Nippon Shokubai Co., Ltd.) ・Cyclohexyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) ・4-Hydroxybutyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・2-Hydroxypropyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Acrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) ・Dimethylacrylamide (manufactured by Tokyo Chemical Industry Co., Ltd.) ・2-Methoxyethyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0109] <Tackifiers> Tackifier A: terpene-based tackifier (terpene phenol-based resin) (manufactured by Yasuhara Chemical Co., Ltd., "YS Polystar G150", softening temperature: 145°C to 155°C) Tackifier B: rosin ester-based tackifier (polymerized rosin ester-based resin, manufactured by Arakawa Chemical Industries, Ltd., "Pensel D-135", softening temperature: 130 to 140°C) Tackifier C: rosin ester-based tackifier (manufactured by Arakawa Chemical Industries, Ltd., "Pine Crystal KE-359", softening temperature: 94 to 104°C) Tackifier D: rosin-based tackifier (rosin polyol-based resin) (manufactured by Arakawa Chemical Industries, Ltd., "Pine Crystal D-6021", softening temperature: 95°C to 105°C) Tackifier E: acrylic tackifier It should be noted that, as the acrylic tackifier, an acrylic oligomer obtained by synthesis by the following method was used. That is, a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel was charged with 95 parts by mass of cyclohexyl methacrylate (CHMA) and 5 parts by mass of acrylic acid (Aa), azobisisobutyronitrile (AIBN 10 parts by mass) as a polymerization initiator, and ethyl acetate as a polymerization solvent, and stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, then heated to 85 ° C. and reacted for 5 hours to obtain an acrylic oligomer with a solids concentration of 50%. The obtained acrylic oligomer was diluted 50 times with tetrahydrofuran (THF) and the resulting diluted solution was filtered with a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. This measurement sample was supplied to a gel permeation chromatograph (manufactured by Waters Corporation, "2690 Separations Module"), and GPC measurement was 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 acrylic oligomer was measured to determine the weight-average molecular weight, which was found to be 3,600.

[0110] <Crosslinking Agents> Isocyanate-based crosslinking agent (manufactured by Covestro, "Desmodur L-75") Epoxy-based crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc., "Tetrad X") Acrylic isocyanate prepolymer Metal chelate-based crosslinking agent (manufactured by Soken Chemical & Engineering Co., Ltd., aluminum chelate "M-A5DT") The acrylic isocyanate prepolymer used was an acrylic isocyanate prepolymer synthesized by the following method. That is, 30 parts by mass of n-butyl acrylate, 70 parts by mass of methyl methacrylate, 14.1 parts by mass of N-1-butylaminoethyl methacrylate, and 2.8 parts by mass of 2-aminoethanethiol were mixed, and 30% by mass of this mixture and 50 parts by mass of toluene were placed in a 30 cc four-necked flask and heated to 70°C with stirring while circulating nitrogen. The atmosphere in the flask was replaced with nitrogen for 60 minutes, and then 0.1 parts by mass of azobisisobutyronitrile was added. After the heat generated by the polymerization had subsided somewhat, the remaining 70% by weight of the mixture plus 0.2 parts by weight of azobisisobutyronitrile was slowly added dropwise to the flask using a dropping funnel. The dropping time was 2 hours, and the polymerization was terminated when no further heat generation was observed. The conversion rate (weighed after heating and drying at 150°C for 30 minutes) was 98.8%, and the weight-average molecular weight of the resulting acrylic oligomer (measured by vapor pressure osmometry) was 4800. The number of amino groups per molecule (calculated using the Microkjeldahl method and molecular weight) was 31. The copolymer solution after the reaction was then heated and azeotropically dehydrated, after which 25.2 parts by weight of 4,4'-diphenylmethane diisocyanate and 0.1 parts by weight of tin octoate were added and reacted at 80°C for 4 hours to synthesize an acrylic isocyanate prepolymer, which was used as a crosslinking agent. The isocyanate content after the reaction (quantitatively determined by dibutylamine) was 3% by weight in terms of solids content.

[0111] <Surfactant> Sodium polyoxyethylene nonylphenyl ether sulfate (Kao Corporation, "Levenol WZ")

[0112] <Pigment> Carbon black (Toyo Color Co., Ltd., "Multilac A903 Black")

[0113] Example 1 (1) Production 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. Subsequently, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile as a polymerization initiator 10 times with ethyl acetate was added to the reaction vessel, and 94.9 parts by mass of isobutyl acrylate, 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 completion of the dropwise addition, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile as a polymerization initiator 10 times with ethyl acetate was added again to the reaction vessel, and a 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 times with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. The measurement sample was supplied to a gel permeation chromatograph (Waters Corporation, "2690 Separations Module") and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C to measure the polystyrene-equivalent molecular weight of the (meth)acrylic copolymer and determine the weight-average molecular weight. The results are shown in Table 1.

[0114] (2) Production of Pressure-Sensitive Adhesive Tape An isocyanate-based crosslinking agent was added to the obtained (meth)acrylic copolymer-containing solution so that its solid content was 0.5 parts by mass per 100 parts by mass of the acrylic copolymer in the (meth)acrylic copolymer-containing solution, thereby preparing a pressure-sensitive adhesive composition. 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 to form a pressure-sensitive adhesive layer. The obtained pressure-sensitive adhesive layer was 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).

[0115] (3) Measurement of gel fraction of adhesive layer The release PET film on one side of the obtained adhesive tape was peeled off, and the tape was attached to a 23 μm thick base PET film (manufactured by Futamura Chemical Co., Ltd., "FE2002"), and cut into a flat rectangular shape with a width of 20 mm and a length of 40 mm. The release PET film 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 (mass%) was calculated using the following formula (I). The results are shown in Table 1. Gel fraction (mass%) = 100 × (W ２ -W ０ ) / (W １ -W ０ ) (I) (W ０ : Mass of the base material layer, W １ : mass of test piece before immersion, W ２ : Mass of test piece after immersion and drying)

[0116] (Examples 2 to 20, 22 to 23, 28 to 61, 67 to 75, 77 to 81, Comparative Examples 1 to 5) 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 each component of the pressure-sensitive adhesive composition were changed to those shown in Tables 1 to 8. Furthermore, the weight-average molecular weight of the (meth)acrylic copolymer 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 8. Note that for Examples 14 to 16, 29 to 31, 55 to 56, 70 to 71, 77 to 81 and Comparative Examples 1 to 5, pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types and amounts of each component of the pressure-sensitive adhesive composition were changed as shown in Tables 2, 3, 5, 7 and 8, and the amount of polymerization initiator added, etc. were changed as appropriate.

[0117] Example 21 (1) Preparation of (meth)acrylic copolymer To 100 parts by mass of the acrylic monomer mixture shown in Table 2 constituting the (meth)acrylic copolymer, which had been placed in a separate container, 5.8 parts by mass of polyoxyethylene nonylphenyl ether sodium sulfate and 57 parts by mass of deionized water were added and stirred to prepare an emulsion of the monomer mixture. 40 parts by mass of deionized water and 0.2 parts by mass of polyoxyethylene nonylphenyl ether sodium sulfate were added to a reaction vessel, and nitrogen was introduced, raising the internal temperature to 80°C. Subsequently, 4.0 parts by mass of a 5% aqueous solution of potassium persulfate was added to the reaction vessel. The previously prepared emulsion of the monomer mixture was added dropwise to the reaction vessel over 3 hours, and in parallel, 4.0 parts by mass of a 5% aqueous solution of potassium persulfate was added dropwise, and emulsion polymerization was carried out at an internal temperature of 80-83°C. After the dropwise addition was completed, the mixture was maintained at the same temperature for 3 hours, then cooled to room temperature, and 25% aqueous ammonia was added to adjust the pH of the reaction solution to 7.5, yielding an emulsion copolymer having an average particle size of 210 nm. To the resulting emulsion copolymer-containing solution was added an alkali-thickening acrylic thickener (Saibinol AZ-1, manufactured by Saiden Chemical Co., Ltd.), 25% aqueous ammonia, and deionized water to obtain an acrylic copolymer-containing solution with a solids concentration of 50%, a viscosity of 3500 mPa s, and a pH of 8.0.

[0118] (2) Production of Pressure-Sensitive Adhesive Tape Except for using the obtained acrylic copolymer, a pressure-sensitive adhesive tape was obtained in the same manner as in Example 1. The surfactant content was determined using the prepared pressure-sensitive adhesive composition, and the weight-average molecular weight and gel fraction of the acrylic copolymer were determined in the same manner as in Example 1. The results are shown in Table 2.

[0119] Examples 24 to 27, 62 to 66, and 76: Pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1, except that the type and amount of the monomer constituting the (meth)acrylic copolymer and the type and amount of each component of the pressure-sensitive adhesive composition were changed as shown in Tables 3, 6 to 7. 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 3, 6 to 7. 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 pressure-sensitive adhesive layers on both sides of the substrate, with the pressure-sensitive adhesive layers on both sides covered with release PET films. The weight-average molecular weight of the (meth)acrylic copolymer and the gel fraction of the pressure-sensitive adhesive layer were measured in the same manner as in Example 1. The gel fraction of the pressure-sensitive adhesive layer was measured using test pieces obtained by cutting the pressure-sensitive adhesive tape into a flat rectangular shape with a width of 20 mm and a length of 40 mm and then peeling off the release PET films on both sides. The results are shown in Tables 3, 6 to 7.

[0120] The substrates used as the substrate layer in Examples 24 to 27, 62 to 66, and 76 are as follows: PET film (manufactured by Futamura Chemical Co., Ltd., "FE2002", thickness 50 μm) PE foam (manufactured by Sekisui Chemical Co., Ltd., "WL02", thickness 150 μm) Nonwoven fabric (manufactured by Toray International Inc., "G2260-1S", thickness 610 μm) PI film (manufactured by PI Advanced Materials, "GF", thickness 12 μm) PEN film (manufactured by Toyobo Co., Ltd., "Teonex Q5100", thickness 12 μm) Colored substrate (manufactured by Toray Industries, Inc., "Lumirror #25-X30", thickness 23 μm)

[0121] <Evaluation> The pressure-sensitive adhesive tapes obtained in the Examples and Comparative Examples were evaluated by the following methods. The results are shown in Tables 1 to 8.

[0122] (Shear Adhesion Strength) A shear adhesive strength test was conducted in accordance with JIS K6850 to measure the shear adhesive strength of an adhesive tape. Figure 1 shows a schematic diagram of the shear adhesive strength test. Specifically, an adhesive tape 1 was first cut into a size of 25 mm x 25 mm, and two SUS304 plates 2 (SUS304 plates washed with ethanol and then wiped dry) each having a size of 125 mm x 50 mm and a thickness of 2 mm were laminated as shown in Figure 1. The laminate was then pressed with a 5 kg weight for 10 seconds to bond the plates together, and then allowed to stand at 23°C and 50% RH for 24 hours to prepare a test sample in which the two SUS304 plates 2 were bonded together via the adhesive tape 1. After fixing one SUS304 plate 2 of the obtained test sample, the upper part of the other SUS304 plate 2 was pulled at a rate of 50 mm / min in a direction perpendicular to the lamination direction of the SUS304 plate 2 (the direction of the arrow in Figure 1) using a tensile tester (Shimadzu Corporation, "Precision Universal Testing Machine AUTOGRAPH AGS-X"). The stress (MPa) at which the adhesive tape 1 broke was measured, and this value was taken as the shear adhesive strength. The shear adhesive strength of the adhesive tape was evaluated by rating it as "○" when the obtained shear adhesive strength was 1.0 MPa or more, "△" when it was 0.7 MPa or more and less than 1.0 MPa, and "×" when it was less than 0.7 MPa.

[0123] (Adhesion to Adherend) (1) Adhesion Strength Immediately After Adhesion of the Adhesive Tape The 180° peel force was measured immediately after adhering the adhesive tape to the glass. Specifically, first, one release PET film of the adhesive tape was peeled off, and the tape was backed with a 23 μm thick PET film (manufactured by Futamura Chemical Co., Ltd., "FE2002"), then cut into a width of 25 mm and a length of 75 mm. The other release PET film was peeled off to prepare a test piece. This test piece was placed on a 1 mm thick glass plate (manufactured by Matsunami Glass Industry Co., Ltd., "Large Slide Glass, White Edge Polished No. 2") with the adhesive layer (the side to be measured) facing the glass plate, and then bonded to the test piece by rolling a 2 kg rubber roller back and forth once at a speed of 300 mm / min. The test piece was then aged at 23 ° C. and 50% RH for 20 minutes to prepare a test sample. The obtained test samples were peeled in a 180° direction under conditions of 23°C, 50% RH, and a pulling rate of 300 mm / min, and the 180° peel strength (N / 25 mm) immediately after lamination of the pressure-sensitive adhesive tape was measured. The adhesion of the pressure-sensitive adhesive tape to the adherend was evaluated as follows: a 180° peel strength of 12 N / 25 mm or more was marked "◎", a 10 N / 25 mm or more but less than 12 N / 25 mm was marked "◯", a 9 N / 25 mm or more but less than 10 N / 25 mm was marked "△", and a 180° peel strength of less than 9 N / 25 mm was marked "X".

[0124] (2) Development of adhesive strength immediately after application of adhesive tape The 180° peel force was measured one day after application of the adhesive tape to the glass, and the development of adhesive strength immediately after application of the adhesive tape was calculated using the 180° peel force immediately after application of the adhesive tape to the glass measured by the method described above in "(1) Adhesive strength immediately after application of the adhesive tape" and the 180° peel force one day after application of the adhesive tape to the glass. Specifically, a test piece was first prepared by the method described above in "(1) Adhesive strength immediately after application of the adhesive tape," and the test piece was then applied to a glass plate, followed by aging at 23°C and 50% RH for one day to prepare a test sample. The obtained test sample was peeled in the 180° direction under conditions of 23°C, 50% RH, and a pulling speed of 300 mm / min, and the 180° peel force (N / 25 mm) one day after application of the adhesive tape was measured. Using the 180° peel force immediately after laminating the adhesive tape to the glass, measured by the above-mentioned method of "(1) Adhesive strength immediately after laminating the adhesive tape," and the 180° peel force one day after laminating the adhesive tape to the glass, the adhesive strength development rate (%) immediately after laminating the adhesive tape was calculated according to the following formula (II): Adhesive strength development rate (%) = {(180° peel force immediately after laminating the adhesive tape) / (180° peel force one day after laminating the adhesive tape)} × 100 (II) The adhesion of the adhesive tape to the adherend was evaluated by rating a value of "○" when the resulting adhesive strength development rate was 85% or higher, "△" when it was 70% or higher but less than 85%, and "×" when it was less than 70%.

[0125] (High-Temperature Retention Performance) A high-temperature retention test was conducted in accordance with JIS Z 0237:2009. FIG. 2 shows a schematic diagram of the high-temperature retention test. Specifically, first, one side (the side not being measured) of the pressure-sensitive adhesive tape 1 was lined with a 23 μm-thick polyethylene terephthalate film 3 (manufactured by Futamura Chemical Co., Ltd., "FE2002"), and then cut into a width of 25 mm and a length of 75 mm to prepare a test piece. This test piece was placed so that its adhesive layer (the side being measured) faced a 2 mm-thick, 50 mm-wide, and 80 mm-long SUS304 plate 2 (SUS304 plate washed with ethanol and then wiped dry), and then a 2 kg rubber roller was reciprocated on the test piece at a speed of 300 mm / min, so that a portion of the test piece protruded from the SUS304 plate 2 (adhesion area: width 25 mm, length 25 mm). The test sample was then aged at 23°C and 50% RH for 20 minutes to prepare a test sample. The test sample was placed in an environment of 80°C and 50% RH and allowed to stand for 15 minutes. Under this environment, a 1 kg weight 4 was attached to the polyethylene terephthalate film 3 of the test sample so that a load in the shear direction (lengthwise direction) was applied in accordance with JIS Z 0237:2009. One hour after attaching the weight 4, the amount of displacement in the shear direction from the position where the pressure-sensitive adhesive layer was attached to the SUS304 plate 2 was measured. The high-temperature retention performance of the pressure-sensitive adhesive tape was evaluated as follows: "○" if the amount of displacement was 0.5 mm or less; "△" if the amount of displacement was more than 0.5 mm but the test piece did not fall; and "×" if the test piece fell. Even if the evaluation was "×," the pressure-sensitive adhesive tape of the present invention can still be used without any problems depending on its intended use.

[0126]

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that exhibits high shear adhesive strength and excellent adhesion to an adherend, and also to provide a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition.

[0135] 1. Adhesive tape 2. SUS304 plate 3. Polyethylene terephthalate (PET) film 4. Weight (1 kg)

Claims

1. It contains (meth)acrylic copolymer, The (meth)acrylic copolymer has constituent units derived from alkyl (meth)acrylate having branched alkyl groups, The aforementioned alkyl (meth)acrylate having a branched alkyl group includes a branched alkyl group-containing alkyl (meth)acrylate whose glass transition temperature when it is a homopolymer is between -55°C and -15°C. An adhesive composition characterized by the following features.

2. The adhesive composition according to claim 1, wherein the branched alkyl group-containing alkyl (meth)acrylate, when used as a homopolymer, has a glass transition temperature of -55°C or higher and -15°C or lower, comprises a constituent unit derived from 1-methylheptyl (meth)acrylate.

3. The adhesive composition according to claim 2, wherein the (meth)acrylic copolymer contains 60% by mass or more of constituent units derived from 1-methylheptyl (meth)acrylate.

4. The adhesive composition according to claim 1, 2, or 3, wherein the branched alkyl group-containing alkyl (meth)acrylate, when used as the homopolymer, has a glass transition temperature of -55°C or higher and -15°C or lower, is synthesized from an alcohol and (meth)acrylic acid, which are bio-derived materials.

5. The adhesive composition according to claim 1, 2, or 3, wherein the (meth)acrylic copolymer contains 60% by mass or more of constituent units derived from branched alkyl group-containing alkyl (meth)acrylate, which has a glass transition temperature of -55°C or higher and -15°C or lower when used as the homopolymer.

6. The adhesive composition according to claim 1, 2, or 3, wherein the (meth)acrylic copolymer contains 35% by mass or less of structural units derived from alkyl (meth)acrylate having a linear alkyl group, or does not contain structural units derived from alkyl (meth)acrylate having a linear alkyl group.

7. The (meth)acrylic copolymer has constituent units derived from alkyl (meth)acrylate having a linear alkyl group, The adhesive composition according to claim 1, 2, or 3, wherein the alkyl (meth)acrylate having the linear alkyl group comprises n-heptyl (meth)acrylate.

8. The adhesive composition according to claim 1, 2, or 3, wherein the (meth)acrylic copolymer further comprises structural units derived from monomers having crosslinkable functional groups.

9. The adhesive composition according to claim 8, wherein the monomer having the crosslinkable functional group includes a monomer containing a hydroxyl group.

10. The adhesive composition according to claim 8, wherein the (meth)acrylic copolymer has a content of 0.01% by mass or more and 20% by mass or less of constituent units derived from monomers having crosslinkable functional groups.

11. The adhesive composition according to claim 1, 2, or 3, wherein the (meth)acrylic copolymer has at least one constituent unit selected from the group consisting of constituent units derived from monomers having a cyclic ether structure other than an epoxy structure and an oxetane structure, and constituent units derived from monomers having an acyclic ether structure.

12. The adhesive composition according to claim 11, wherein the (meth)acrylic copolymer contains 0.01% by mass or more and 50% by mass or less constituent units derived from monomers having a cyclic ether structure other than the epoxy structure and the oxetane structure, and constituent units derived from monomers having the acyclic ether structure.

13. The adhesive composition according to claim 1, 2, or 3, wherein the (meth)acrylic copolymer does not have a crosslinkable functional group and has constituent units derived from a monomer whose glass transition temperature is 0°C or higher when it is a homopolymer.

14. The adhesive composition according to claim 13, wherein the (meth)acrylic copolymer does not have the crosslinkable functional group, and the content of constituent units derived from monomers having a glass transition temperature of 0°C or higher when homopolymerized is 0.1% by mass or more and 70% by mass or less.

15. The adhesive composition according to claim 1, 2, or 3, wherein the weight-average molecular weight of the (meth)acrylic copolymer is 800,000 or more and 1,500,000 or less.

16. Furthermore, the adhesive composition according to claim 1, 2, or 3, further containing a tackifier.

17. The adhesive composition according to claim 16, wherein the tackifier comprises at least one selected from the group consisting of rosin ester tackifiers, terpene tackifiers, and acrylic tackifiers.

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

19. Furthermore, the adhesive composition according to claim 1, 2, or 3, further containing a crosslinking agent.

20. The adhesive composition according to claim 19, wherein the crosslinking agent comprises at least one selected from the group consisting of isocyanate-based crosslinking agents and epoxy-based crosslinking agents.

21. The adhesive composition according to claim 20, wherein the crosslinking agent comprises the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent.

22. The adhesive composition according to claim 1, 2, or 3, which does not contain a surfactant.

23. Furthermore, the adhesive composition according to claim 1, 2, or 3, further containing a pigment.

24. The adhesive composition according to claim 1, 2, or 3, wherein the content of bio-derived carbon in the adhesive composition is 10% or more.

25. An adhesive tape having an adhesive layer formed using the adhesive composition according to claim 1, 2, or 3.

26. The adhesive tape according to claim 25, wherein the gel fraction of the adhesive layer is 10% by mass or more and 70% by mass or less.

27. The adhesive tape according to claim 25, having a base layer.

28. The adhesive tape according to claim 25, used for fixing electronic equipment components or in-vehicle components.