Adhesive tape

Abstract

To provide an adhesive tape excellent in adhesion reliability, and transmission visibility when exposed to a high temperature and high humidity environment after bonding adherends together.SOLUTION: An adhesive tape includes an adhesive layer formed with an adhesive composition, wherein the adhesive composition contains a (meth)acrylic copolymer and a tackifier resin, the adhesive tape has a visible light transmittance of 50% or more, and a floating height between an aluminum plate and a polycarbonate resin plate is 10 mm or less when a repulsion resistance test is performed, in which a laminate obtained by bonding an aluminum plate having a width of 25 mm, a length of 150 mm, and a thickness of 0.3 mm and a polycarbonate resin plate having a width of 25 mm, a length of 200 mm, and a thickness of 1 mm via the adhesive tape having a width of 25 mm and a length of 150 mm disposed at a central portion in a lengthwise direction of the polycarbonate resin plate is deformed into an arc shape such that a distance between both ends in the lengthwise direction of the polycarbonate resin plate becomes 180 mm by applying bending stress in the lengthwise direction of the laminate, and thereafter heated for 72 hours under an environment of 60°C and 90% RH.SELECTED DRAWING: None

Description

[Technical Field]

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

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

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

[0004]

[0003] Pressure-sensitive adhesive tapes used for bonding display panel modules and the like are required to have not only good adhesion to adherends but also good transmissive visibility so as to enable visual inspection after lamination of the adherends. In order to improve the adhesion of pressure-sensitive adhesive tapes to adherends, it has been considered to incorporate a tackifier resin into the pressure-sensitive adhesive composition used to form the adhesive layer of the pressure-sensitive adhesive tape. However, incorporating a large amount of tackifier resin has the problem of reducing the transparency of the pressure-sensitive adhesive tape. On the other hand, adjusting the content of the tackifier resin to improve the transparency of the pressure-sensitive adhesive tape has the problem that, even if the transparency of the pressure-sensitive adhesive tape itself is improved, the pressure-sensitive adhesive tape may have poor transmissive visibility when exposed to a high-temperature, high-humidity environment after lamination of the adhesive tape.

[0005] An object of the present invention is to provide a pressure-sensitive adhesive tape that is excellent in adhesive reliability and in see-through visibility when exposed to a high-temperature, high-humidity environment after being attached to an adherend. [Means for solving the problem]

[0006] Disclosure 1 relates to an adhesive tape having an adhesive layer formed using an adhesive composition, the adhesive composition comprising a (meth)acrylic copolymer and a tackifier resin, the adhesive tape having a visible light transmittance of 50% or more, and a laminate obtained by bonding an aluminum plate having a width of 25 mm, a length of 150 mm, and a thickness of 0.3 mm to a polycarbonate resin plate having a width of 25 mm, a length of 200 mm, and a thickness of 1 mm via the adhesive tape having a width of 25 mm and a length of 150 mm positioned at the center of the polycarbonate resin plate in the longitudinal direction, wherein bending stress is applied in the longitudinal direction of the laminate to deform the polycarbonate resin plate into an arc-shaped warp so that the distance between both ends of the polycarbonate resin plate in the longitudinal direction is 180 mm, and the laminate is then heated in an environment of 60°C and 90% RH for 72 hours. When this adhesive tape is subjected to a resilience test, the lift height between the aluminum plate and the polycarbonate resin plate is 10 mm or less. Disclosure 2 is the pressure-sensitive adhesive tape of Disclosure 1, wherein the total content of the tackifier resin in the pressure-sensitive adhesive composition is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the (meth)acrylic copolymer. The present disclosure 3 is the pressure-sensitive adhesive tape of the present disclosure 1 or 2, wherein the tackifier resin comprises a tackifier resin having a softening temperature of 110°C or higher, and the content of the tackifier resin having a softening temperature of 110°C or higher in the pressure-sensitive adhesive composition is 10 parts by mass or more per 100 parts by mass of the (meth)acrylic copolymer. Disclosure 4 is the pressure-sensitive adhesive tape of Disclosure 1, 2, or 3, wherein the tackifier resin comprises at least one selected from the group consisting of rosin ester-based tackifier resins and terpene-based tackifier resins. Disclosure 5 is the pressure-sensitive adhesive tape of Disclosure 1, 2, 3, or 4, wherein the (meth)acrylic copolymer has a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 6 carbon atoms. A sixth aspect of the present disclosure is the pressure-sensitive adhesive tape of the fifth aspect of the present disclosure, wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer having a crosslinkable functional group. Disclosure 7 is the pressure-sensitive adhesive tape of Disclosure 6, wherein the monomer having a crosslinkable functional group includes at least one selected from the group consisting of a carboxy group-containing monomer and a hydroxy group-containing monomer. The present disclosure 8 is the pressure-sensitive adhesive tape of the present disclosure 6 or 7, wherein the (meth)acrylic copolymer contains 0.01 mass % or more and less than 20 mass % of the structural unit derived from the monomer having a crosslinkable functional group. A ninth aspect of the present disclosure is the pressure-sensitive adhesive tape of the fifth, sixth, seventh, or eighth aspect of the present disclosure, wherein the (meth)acrylic copolymer further comprises a structural unit derived from n-heptyl (meth)acrylate. Disclosure 10 is a pressure-sensitive adhesive tape according to Disclosure 5, 6, 7, 8, or 9, wherein the (meth)acrylic copolymer further comprises a structural unit derived from at least one monomer having a non-crosslinkable ether structure selected from the group consisting of a monomer having a cyclic ether structure other than an epoxy group or an oxetanyl group, and a monomer having an acyclic ether structure. Disclosure 11 is the pressure-sensitive adhesive tape of Disclosure 10, wherein the (meth)acrylic copolymer contains more than 0% by mass and 50% by mass or less of the structural unit derived from the monomer having a non-crosslinkable ether structure. A twelfth aspect of the present disclosure is the pressure-sensitive adhesive tape of any one of the first, second, third, fourth, fifth, sixth, seventh, eighth, nineth, tenth, and eleventh aspects of the present disclosure, wherein the (meth)acrylic copolymer has a weight-average molecular weight of 700,000 or more and 1,500,000 or less. Disclosure 13 is the pressure-sensitive adhesive tape of Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the pressure-sensitive adhesive composition further contains a crosslinking agent. Disclosure 14 is the pressure-sensitive adhesive tape of Disclosure 13, wherein the crosslinking agent includes at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. Disclosure 15 is the pressure-sensitive adhesive tape of Disclosure 14, wherein the crosslinking agent includes the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent. Disclosure 16 is a pressure-sensitive adhesive tape according to Disclosures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, used for fixing electronic equipment components or vehicle-mounted components. The present invention will be described in detail below.

[0007] The present inventors have considered that even if the transparency of an adhesive tape itself is improved by adjusting the content of a tackifier resin, the adhesive tape may still have poor transmissive visibility when exposed to a high-temperature, high-humidity environment after being bonded to an adherend because the adhesive tape's adhesive reliability is insufficient, resulting in partial peeling of the adherend or the formation of air bubbles between the adhesive tape and the adherend. Therefore, the present inventors have investigated ways to ensure that the visible light transmittance of the adhesive tape is at or above a specific value, while ensuring that the floating height between the aluminum plate and the polycarbonate resin plate when a laminate formed by bonding an aluminum plate and a polycarbonate resin plate via the adhesive tape is at or below a specific value when subjected to a repulsion resistance test under specific conditions. As a result, they have found that an adhesive tape can be obtained that has excellent adhesive reliability and excellent transmissive visibility when exposed to a high-temperature, high-humidity environment after being bonded to an adherend, thereby completing the present invention.

[0008] The pressure-sensitive adhesive tape of the present invention has a visible light transmittance lower limit of 50%. When the visible light transmittance is 50% or more and the lift height after the repulsion resistance test described below is 10 mm or less, the pressure-sensitive adhesive tape of the present invention exhibits excellent transmittance visibility when exposed to a high-temperature, high-humidity environment after being attached to an adherend. The visible light transmittance lower limit is preferably 70%, and more preferably 90%. Furthermore, the higher the visible light transmittance of the pressure-sensitive adhesive tape of the present invention, the more preferable it is, and although there is no particular preferred upper limit, the practical upper limit is 99.99%. The visible light transmittance of the pressure-sensitive adhesive tape can be measured by the following method. That is, first, a glass plate measuring 52 mm in width, 76 mm in length, and 1.0 mm in thickness is prepared, and the glass plate is attached to adhesive tape cut to the same width and length as the glass plate to prepare a test piece. Note that the test piece is not laminated with a release film for protecting the adhesive layer. Next, the visible light transmittance of the obtained test piece is measured at room temperature (20°C or higher and 25°C or lower) using a haze meter in accordance with JIS K 7375:2008. Examples of the haze meter include the NDH 4000 (manufactured by Nippon Denshoku Industries Co., Ltd.).

[0009] The adhesive tape of the present invention is a laminate obtained by bonding an aluminum plate 25 mm wide, 150 mm long, and 0.3 mm thick to a polycarbonate resin plate 25 mm wide, 200 mm long, and 1 mm thick via the 25 mm wide, 150 mm long adhesive tape placed in the longitudinal center of the polycarbonate resin plate. A bending stress is applied to the laminate in the longitudinal direction to deform the polycarbonate resin plate into an arc-shaped warp so that the distance between both ends in the longitudinal direction is 180 mm. After a repulsion resistance test was performed, the laminate was heated at 60°C and 90% RH for 72 hours. The upper limit of the lift height between the aluminum plate and the polycarbonate resin plate (hereinafter also referred to as "lift height after repulsion resistance test") was 10 mm. By having a lift height of 10 mm or less after the repulsion resistance test, the adhesive tape of the present invention has excellent adhesive reliability. Furthermore, by having a lift height of 10 mm or less after the repulsion resistance test and the above-mentioned visible light transmittance of 50% or more, the pressure-sensitive adhesive tape of the present invention exhibits excellent transmissive visibility when exposed to a high-temperature, high-humidity environment after being bonded to an adherend. The preferred upper limit of the lift height after the repulsion resistance test is 8 mm, and more preferably 2 mm. It is most preferred that the lift height after the repulsion resistance test is 0 mm, i.e., no lift occurs after the repulsion resistance test. Specifically, the repulsion resistance test can be carried out by the following method: Figure 1 is a schematic diagram showing a method for testing the repulsion resistance of a pressure-sensitive adhesive tape. Specifically, adhesive tape 1 was first cut into a flat rectangular shape measuring 25 mm wide and 150 mm long. An aluminum plate 2 measuring 25 mm wide, 150 mm long, and 0.3 mm thick was then bonded to a polycarbonate resin plate 3 measuring 25 mm wide, 200 mm long, and 1 mm thick using the adhesive tape 1. The adhesive tape 1 was then adjusted to be positioned at the longitudinal center of the polycarbonate resin plate 3. A 2 kg rubber roller was run back and forth over the polycarbonate resin plate 3 at a speed of 300 mm / min, bonding the polycarbonate resin plate 3 and the aluminum plate 2 together via the adhesive tape 1. The resulting laminate was then left to stand at 23°C for 24 hours to produce a laminate 4. The laminate 4 was attached to a jig 5 as shown in FIG. 1 , and bending stress was applied in the longitudinal direction of the laminate 4, deforming the laminate 4 into an arc-shaped warp so that the distance between both ends of the polycarbonate resin plate 3 in the longitudinal direction was 180 mm. In this state, the laminate 4 is placed in a constant temperature and humidity oven at 60°C and 90% RH and left to stand for 72 hours. The laminate 4 is taken out of the oven while still warped in an arc shape, and the floating height H (mm) between the aluminum plate 2 and the polycarbonate resin plate 3 is measured with a vernier caliper.

[0010] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition. The visible light transmittance and the floating height after the repulsion resistance test can be adjusted to the above-mentioned values ​​by adjusting the type and content of each component constituting the pressure-sensitive adhesive composition. Examples of a method for forming the pressure-sensitive adhesive layer using the pressure-sensitive adhesive composition include a method in which the pressure-sensitive adhesive composition is applied to a release film or the like, and then the pressure-sensitive adhesive composition is dried by heating. The pressure-sensitive adhesive layer may contain the uncrosslinked pressure-sensitive adhesive composition, or may contain a crosslinked product of the pressure-sensitive adhesive composition.

[0011] The pressure-sensitive adhesive composition contains a (meth)acrylic copolymer. The (meth)acrylic copolymer preferably has a structural unit derived from an alkyl(meth)acrylate having a linear or branched alkyl group having 6 carbon atoms (hereinafter also referred to as "C6 alkyl(meth)acrylate"). By making the (meth)acrylic copolymer have a structural unit derived from the C6 alkyl(meth)acrylate, it is possible to obtain a pressure-sensitive adhesive tape having excellent adhesive reliability without blending a large amount of a tackifier resin into the pressure-sensitive adhesive composition, and as a result, it becomes easier to adjust the visible light transmittance and the lift height after the repulsion resistance test to the respective above-mentioned values. In this specification, the term "(meth)acrylic" means acrylic or methacrylic, and the term "(meth)acrylate" means acrylate or methacrylate.

[0012] Examples of the C6 alkyl (meth)acrylate include n-hexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-methylpentyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, etc. Of these, n-hexyl acrylate is preferred.

[0013] The preferred lower limit of the content of the structural units derived from the C6 alkyl (meth)acrylate in the (meth)acrylic copolymer is 50% by mass, and the preferred upper limit is 99% by mass. When the content of the structural units derived from the C6 alkyl (meth)acrylate is within this range, it becomes easier to adjust the visible light transmittance and the lift height after the repulsion resistance test of the resulting pressure-sensitive adhesive tape to the respective values ​​described above. The more preferred lower limit of the content of the structural units derived from the C6 alkyl (meth)acrylate is 70% by mass, and even more preferred is 75% by mass, with the more preferred upper limit being 97% by mass. Furthermore, as long as the visible light transmittance and the floating height after the repulsion resistance test can be adjusted to the above-mentioned values, the lower limit of the content of the structural unit derived from the C6 alkyl (meth)acrylate in the (meth)acrylic copolymer may be set to a value less than 50% by mass, specifically, for example, 25% by mass, 35% by mass, etc. The content of the structural unit derived from the C6 alkyl (meth)acrylate in the (meth)acrylic copolymer can be determined by measuring the (meth)acrylic copolymer by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR measurement, 13 C-NMR measurement, etc., and calculation can be performed from the integrated intensity ratio of the hydrogen peak derived from the C6 alkyl (meth)acrylate.

[0014] The (meth)acrylic copolymer preferably further contains a structural unit derived from a monomer having a crosslinkable functional group. When the (meth)acrylic copolymer has a structural unit derived from the monomer having a crosslinkable functional group, the cohesive strength of the pressure-sensitive adhesive layer is improved, and the resulting pressure-sensitive adhesive tape has better adhesion to the adherend.

[0015] Examples of the monomer having a crosslinkable functional group include a carboxy group-containing monomer, a hydroxy group-containing monomer, a glycidyl group-containing monomer, an amide group-containing monomer, a nitrile group-containing monomer, etc. Among these, the monomer having a crosslinkable functional group preferably includes at least one selected from the group consisting of a carboxy group-containing monomer and a hydroxy group-containing monomer, since this facilitates adjustment of the gel fraction of the pressure-sensitive adhesive layer, which will be described later. The monomer having a crosslinkable functional group preferably has a (meth)acryloyl group. In this specification, the term "(meth)acryloyl" means acryloyl or methacryloyl.

[0016] The carboxy group-containing monomer may, for example, be (meth)acrylic acid. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 1-methyl-3-hydroxypropyl (meth)acrylate, 1-methyl-2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1-methyl-2-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 1-ethyl-2-hydroxyethyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 9-hydroxynonyl (meth)acrylate, and polypropylene glycol mono(meth)acrylate. The glycidyl group-containing monomer may, for example, be glycidyl (meth)acrylate. Examples of the amide group-containing monomer include isopropyl(meth)acrylamide and dimethylaminopropyl(meth)acrylamide. Examples of the nitrile group-containing monomer include (meth)acrylonitrile.

[0017] The (meth)acrylic copolymer preferably has a lower limit of 0.01% by mass and an upper limit of 20% by mass for the content of the structural unit derived from the monomer having a crosslinkable functional group. When the content of the structural unit derived from the monomer having a crosslinkable functional group is within this range, the resulting pressure-sensitive adhesive tape has superior adhesion to the adherend. The more preferred lower limit of the content of the structural unit derived from the monomer having a crosslinkable functional group is 0.1% by mass and an even more preferred upper limit is 10% by mass. The content of the structural unit derived from the monomer having the crosslinkable functional group in the (meth)acrylic copolymer can be determined by measuring the (meth)acrylic copolymer by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR measurement, 13C-NMR measurement or the like) and calculation can be performed from the integrated intensity ratio of the hydrogen peak derived from the monomer having the crosslinkable functional group.

[0018] The (meth)acrylic copolymer may contain structural units derived from monomers other than the structural units derived from the C6 alkyl (meth)acrylate and the structural units derived from the monomer having a crosslinkable functional group, as long as the object of the present invention is not impaired. Examples of the other monomers include alkyl (meth)acrylates other than the C6 alkyl (meth)acrylates, monomers having a cyclic ether structure other than an epoxy group or an oxetanyl group, and monomers having an acyclic ether structure.

[0019] Examples of the other (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 1-methylheptyl (meth)acrylate, and n-nonyl (meth)acrylate. acrylate, isononyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, esters of 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)-1-octanol and (meth)acrylic acid, esters of (meth)acrylic acid and alcohols having a total of 18 carbon atoms and one or two methyl groups in a linear main chain, behenyl (meth)acrylate, arachidyl (meth)acrylate, etc. In particular, the (meth)acrylic copolymer may have, as a structural unit derived from the other (meth)acrylic acid alkyl esters, a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 7 carbon atoms (hereinafter also referred to as "C7 alkyl (meth)acrylate"), or a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 8 carbon atoms (hereinafter also referred to as "C8 alkyl (meth)acrylate"). Among these, n-heptyl (meth)acrylate is preferred as the other (meth)acrylic acid alkyl ester. That is, when the (meth)acrylic copolymer has a structural unit derived from the other (meth)acrylic acid alkyl ester, the (meth)acrylic copolymer preferably has a structural unit derived from n-heptyl (meth)acrylate as the structural unit derived from the other (meth)acrylic acid alkyl ester.

[0020] When the (meth)acrylic copolymer has, in addition to the structural units derived from the C6 alkyl (meth)acrylate, at least one of structural units derived from the C7 alkyl (meth)acrylate and structural units derived from the C8 alkyl (meth)acrylate, the total content of the structural units derived from the C6 alkyl (meth)acrylate, structural units derived from the C7 alkyl (meth)acrylate, and structural units derived from the C8 alkyl (meth)acrylate in the (meth)acrylic copolymer may be 80% by mass or more, or 85% by mass or more. Furthermore, the total content of the structural units derived from the C6 alkyl (meth)acrylate, structural units derived from the C7 alkyl (meth)acrylate, and structural units derived from the C8 alkyl (meth)acrylate may be 99% by mass or less, or 97% by mass or less.

[0021] When the (meth)acrylic copolymer has structural units derived from the C6 alkyl (meth)acrylate and structural units derived from the other (meth)acrylic acid alkyl ester, the content of the structural units derived from the C6 alkyl (meth)acrylate in the total of the structural units derived from the C6 alkyl (meth)acrylate and the structural units derived from the other (meth)acrylic acid alkyl ester may be 25% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more. Furthermore, the content of the structural units derived from the C6 alkyl (meth)acrylate in the total of the structural units derived from the C6 alkyl (meth)acrylate and the structural units derived from the other (meth)acrylic acid alkyl ester may be 99% by mass or less, 97% by mass or less, 95% by mass or less, or 92% by mass or less.

[0022] The (meth)acrylic copolymer has a structural unit derived from at least one monomer having a non-crosslinkable ether structure (hereinafter also simply referred to as "monomer having a non-crosslinkable ether structure") selected from the group consisting of the monomer having a cyclic ether structure other than the epoxy group and the oxetanyl group, and the monomer having an acyclic ether structure, and the resulting pressure-sensitive adhesive tape has superior adhesion to an adherend.

[0023] Examples of the monomer having a cyclic ether structure other than the epoxy group and the oxetanyl group include tetrahydrofurfuryl (meth)acrylate. Examples of the monomer having an acyclic ether structure include 2-methoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and ethyl carbitol (meth)acrylate. Among these, 2-methoxyethyl (meth)acrylate is preferred. That is, when the (meth)acrylic copolymer has a structural unit derived from the monomer having an acyclic ether structure, the structural unit derived from the monomer having an acyclic ether structure is preferably a structural unit derived from 2-methoxyethyl (meth)acrylate.

[0024] When the (meth)acrylic copolymer has structural units derived from the C6 alkyl (meth)acrylate and structural units derived from the 2-methoxyethyl (meth)acrylate, the content of the structural units derived from the C6 alkyl (meth)acrylate in the total of the structural units derived from the C6 alkyl (meth)acrylate and the structural units derived from the 2-methoxyethyl (meth)acrylate may be 25% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more. Furthermore, the content of the structural units derived from the C6 alkyl (meth)acrylate in the total of the structural units derived from the C6 alkyl (meth)acrylate and the structural units derived from the 2-methoxyethyl (meth)acrylate may be 99% by mass or less, 97% by mass or less, 95% by mass or less, or 92% by mass or less.

[0025] When the content of the structural units derived from the monomer having a non-crosslinkable ether structure in the (meth)acrylic copolymer exceeds 0% by mass, the preferred upper limit of the content of the structural units derived from the monomer having a non-crosslinkable ether structure is 50% by mass. By having the content of the structural units derived from the monomer having a non-crosslinkable ether structure exceed 0% by mass and not more than 50% by mass, the resulting pressure-sensitive adhesive tape will have superior adhesiveness. The preferred lower limit of the content of the structural units derived from the monomer having a non-crosslinkable ether structure is 0.01% by mass, and more preferably 0.1% by mass. Furthermore, the more preferred upper limit of the content of the structural units derived from the monomer having a non-crosslinkable ether structure is 30% by mass, and even more preferably 10% by mass. The content of the structural unit derived from the monomer having a non-crosslinkable ether structure in the (meth)acrylic copolymer can be determined by measuring the (meth)acrylic copolymer by mass spectrometry and / or nuclear magnetic resonance spectroscopy ( 1 H-NMR measurement, 13C-NMR measurement or the like) and calculation can be performed from the integrated intensity ratio of the hydrogen peak derived from the monomer having the non-crosslinkable ether structure.

[0026] Examples of the other monomers include cyclohexyl (meth)acrylate, benzyl (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.

[0027] The weight-average molecular weight of the (meth)acrylic copolymer preferably has a lower limit of 700,000 and an upper limit of 1,500,000. When the weight-average molecular weight of the (meth)acrylic copolymer is within this range, the resulting pressure-sensitive adhesive tape has better adhesion to the adherend and transparency. The weight-average molecular weight of the (meth)acrylic copolymer is more preferably 800,000 and more preferably 1,200,000. In this specification, the weight-average molecular weight is a weight-average molecular weight measured by GPC (gel permeation chromatography) in terms of standard polystyrene. Specifically, a (meth)acrylic copolymer is diluted 50 times with tetrahydrofuran (THF) and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm) to prepare a measurement sample. Next, this measurement sample is supplied to a gel permeation chromatograph, and GPC measurement is performed under conditions of a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the (meth)acrylic copolymer is measured, and this value is taken as the weight-average molecular weight of the (meth)acrylic copolymer. An example of the gel permeation chromatograph is the 2690 Separations Module (manufactured by Waters). 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 reaction solvent to control chain transfer to the solvent, and a method of changing the temperature and time during the reaction.

[0028] The (meth)acrylic copolymer can be obtained by polymerizing a mixture of raw material monomers through a radical reaction in the presence of a polymerization initiator. Examples of the radical reaction method include living radical polymerization, free radical polymerization, etc. Living radical polymerization can provide a copolymer having a more uniform molecular weight and composition compared to free radical polymerization, and can suppress the generation of low molecular weight components, etc., thereby increasing the cohesive strength of the resulting pressure-sensitive adhesive layer and providing a pressure-sensitive adhesive tape with superior adhesion to an adherend. The method for polymerizing the monomer mixture can be a conventionally known method, such as solution polymerization (boiling point polymerization or constant temperature polymerization), UV polymerization, emulsion polymerization, suspension polymerization, bulk polymerization, etc. Among these, solution polymerization and UV polymerization are preferred because the resulting pressure-sensitive adhesive tape has better adhesion to the adherend. When solution polymerization is used as the method for polymerizing the monomer mixture, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, dimethyl sulfoxide, ethanol, acetone, and diethyl ether.

[0029] Examples of the polymerization initiator include organic peroxides and azo compounds. Examples of the organic peroxides include 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. Furthermore, when the radical reaction method is the living radical polymerization, the polymerization initiator may be, for example, an organic tellurium polymerization initiator. The organic tellurium polymerization initiator is not particularly limited as long as it is one that is generally used in living radical polymerization, and examples thereof include organic tellurium compounds, organic telluride compounds, etc. Note that, in the living radical polymerization, in addition to the organic tellurium polymerization initiator, an azo compound may also be used as the polymerization initiator for the purpose of accelerating the polymerization rate.

[0030] 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 95% by mass. When the content of the (meth)acrylic copolymer is within this range, the resulting pressure-sensitive adhesive tape exhibits an excellent effect of achieving both adhesive reliability and transparency. The more preferred lower limit of the content of the (meth)acrylic copolymer is 65% by mass, and the more preferred upper limit is 90% by mass.

[0031] The pressure-sensitive adhesive composition contains a tackifier resin. By containing the tackifier resin, the pressure-sensitive adhesive tape of the present invention has excellent adhesive reliability.

[0032] The tackifier resin preferably contains at least one selected from the group consisting of rosin ester resins and terpene resins. By containing at least one selected from the group consisting of rosin ester resins and terpene resins as the tackifier resin, the resulting pressure-sensitive adhesive tape has even more excellent adhesion reliability. The tackifier resin more preferably contains a rosin ester resin and a terpene resin. The terpene resin includes a terpene phenol resin.

[0033] Examples of the rosin ester resin include Pencel D-135, Pine Crystal KE-359, Ester Gum AA-V, and Ester Gum H (all manufactured by Arakawa Chemical Industries, Ltd.). Examples of the terpene resin include YS Resin PX1250 (manufactured by Yasuhara Chemical Co., Ltd.) and YS Polystar G150 (manufactured by Yasuhara Chemical Co., Ltd.).

[0034] The tackifier resin preferably contains a tackifier resin having a softening temperature of 110°C or higher. By containing the tackifier resin having a softening temperature of 110°C or higher, the PSA layer does not become too soft, and a decrease in the adhesive strength of the resulting PSA tape can be suppressed. The softening temperature of the tackifier resin having a softening temperature of 110°C or higher is preferably 120°C or higher, and more preferably 130°C or higher. Furthermore, from the viewpoint of improving the wettability of the interface of the pressure-sensitive adhesive layer, the softening temperature of the tackifier resin having a softening temperature of 110°C or higher is preferably 170°C or lower, and more preferably 160°C or lower. In this specification, the "softening temperature" refers to the softening temperature measured by a method in accordance with JIS K 2207 (ring and ball method).

[0035] In the pressure-sensitive adhesive composition, a preferred lower limit for the content of the tackifier resin having a softening temperature of 110°C or higher relative to 100 parts by mass of the (meth)acrylic copolymer is 10 parts by mass or more. When the content of the tackifier resin having a softening temperature of 110°C or higher is 10 parts by mass or more, the resulting pressure-sensitive adhesive tape is more effectively prevented from decreasing in adhesive strength. A more preferred lower limit for the content of the tackifier resin having a softening temperature of 110°C or higher is 20 parts by mass. Furthermore, from the viewpoint of the transparency of the resulting pressure-sensitive adhesive tape, the upper limit of the content of the tackifier resin having a softening temperature of 110°C or higher relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 50 parts by mass, and more preferably 40 parts by mass.

[0036] In the pressure-sensitive adhesive composition, the preferred lower limit of the total tackifier resin 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 total tackifier resin content is within this range, the resulting pressure-sensitive adhesive tape exhibits an excellent effect of achieving both adhesive reliability and transparency. A more preferred lower limit of the total tackifier resin content is 20 parts by mass, and a more preferred upper limit is 40 parts by mass. Furthermore, as long as the visible light transmittance and the floating height after the repulsion resistance test can be adjusted to the above-described values, the lower limit of the total tackifier resin content may be set to a value less than 10 parts by mass, specifically 5 parts by mass, and the upper limit of the total tackifier resin content may be set to a value greater than 50 parts by mass, specifically 110 parts by mass, 100 parts by mass, 90 parts by mass, 80 parts by mass, 70 parts by mass, 60 parts by mass, and the like.

[0037] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a metal chelate-based crosslinking agent, etc. Among these, since the resulting pressure-sensitive adhesive tape will have better adhesion to an adherend and transparency, the crosslinking agent preferably contains at least one selected from the group consisting of the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent, more preferably contains the isocyanate-based crosslinking agent, and even more preferably contains the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent.

[0038] 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 0.1 parts by mass at the lower limit and 10 parts by mass at the upper limit. By ensuring that the content of the crosslinking agent is within this range, the resulting pressure-sensitive adhesive tape will have superior adhesion to the adherend and transparency. The content of the crosslinking agent is more preferably 0.2 parts by mass at the lower limit and 5 parts by mass at the upper limit. In this specification, the "content of crosslinking agent" means the content of the solid content of the crosslinking agent.

[0039] The pressure-sensitive adhesive composition may further contain a crosslinking catalyst for accelerating crosslinking by the crosslinking agent. Examples of the crosslinking catalyst include dibutyltin dilaurate, dibutyltin diacetate, and dioctyltin dilaurate as crosslinking catalysts for the isocyanate-based crosslinking agents.

[0040] The pressure-sensitive adhesive composition may contain additives such as a silane coupling agent, a plasticizer, a softener, a filler, a pigment, a dye, etc., as needed, within the scope of not impairing the object of the present invention.

[0041] The preferred lower limit of the content of bio-derived carbon in the pressure-sensitive adhesive layer is 10%. When the content of bio-derived carbon in the pressure-sensitive adhesive layer is 10% or more, the pressure-sensitive adhesive tape of the present invention is excellent in terms of saving petroleum resources and reducing carbon dioxide emissions, and can reduce the environmental load. The content of bio-derived carbon in the pressure-sensitive adhesive layer is preferably 40% or more, and more preferably 60% or more. The upper limit of the content of the biologically derived carbon is not particularly limited and may be 100%. Furthermore, the content of the biologically derived carbon may be 95% or less, or 90% or less. While carbon derived from living organisms contains a certain percentage of the radioactive isotope (C-14), petroleum-derived carbon contains almost no C-14. Therefore, the content of carbon derived from living organisms can be calculated by measuring the concentration of C-14 contained in the adhesive layer. Specifically, this can be measured in accordance with ASTM D6866-22, a standard used in many bioplastic industries.

[0042] 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 in this range, the resulting pressure-sensitive adhesive tape has better adhesion to the adherend. The more preferred lower limit of the gel fraction of the pressure-sensitive adhesive layer is 20% by mass, and the more preferred upper limit is 50% by mass. The gel fraction of the pressure-sensitive adhesive layer is measured by the following method. That is, first, a pressure-sensitive adhesive tape having the pressure-sensitive adhesive layer is cut into a flat rectangular shape of 20 mm wide and 40 mm long to prepare a test piece, and the test piece is immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The mass of the test piece after drying is measured, and the gel fraction is calculated using the following formula (I). Note that no release film for protecting the pressure-sensitive adhesive layer is laminated on the test piece. If the pressure-sensitive adhesive tape is a non-support tape without a substrate, the measurement is performed using a test piece obtained by adhering the tape to a substrate and cutting it, or the calculation is performed without using a substrate, with W0 in the following formula (I) set to 0. Gel fraction (mass%) = 100 × (W2 - W0) / (W1 - W0) (I) (W0: Mass of the substrate, W1: Mass of the test piece before immersion, W2: Mass of the test piece after immersion and drying)

[0043] The pressure-sensitive adhesive layer in the pressure-sensitive adhesive tape of the present invention preferably has a lower limit of 3 μm and an upper limit of 300 μm. By ensuring that the pressure-sensitive adhesive layer has a thickness within this range, the resulting pressure-sensitive adhesive tape will have superior adhesion to the adherend and transparency. The pressure-sensitive adhesive layer more preferably has a lower limit of 5 μm and an upper limit of 200 μm.

[0044] The pressure-sensitive adhesive tape of the present invention may be a non-support type tape having no substrate, or may be a supported type double-sided pressure-sensitive adhesive tape having the above-mentioned pressure-sensitive adhesive layers on both sides of a substrate.

[0045] Examples of the substrate include films and nonwoven fabrics. Furthermore, from the viewpoint of increasing the content of bio-derived carbon in the entire pressure-sensitive adhesive tape, the substrate is preferably a substrate made of a bio-derived material. Examples of the above-mentioned biologically-derived materials include polyesters (PES) such as polyethylene terephthalate (PET), polyethylene furanoate (PEF), polylactic acid (PLA), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polybutylene succinate (PBS), polyethylene (PE), polypropylene (PP), polyurethane (PU), triacetyl cellulose (TAC), cellulose, and polyamide (PA), which are derived from plants.

[0046] The substrate is preferably a film containing PES or a film containing PA from the viewpoint of substrate strength, and is preferably a film containing PA from the viewpoint of heat resistance and oil resistance. Examples of the PA include nylon 11, nylon 1010, nylon 610, nylon 510, nylon 410, etc., which are made from castor oil, and nylon 56, etc., which are made from cellulose.

[0047] Furthermore, from the perspective of reducing the use of new petroleum resources and reducing the environmental burden by suppressing carbon dioxide emissions, substrates made from recycled resources may be used. Examples of resource recycling methods include collecting waste materials such as packaging containers, home appliances, automobiles, construction materials, and food, as well as waste generated during manufacturing processes, and then cleaning, decontaminating, or decomposing the extracted materials by heating or fermentation to reuse them as raw materials. Examples of substrates made from recycled resources include films and nonwoven fabrics made from PET, PBT, PE, PP, PA, etc., which are made from recycled plastics that have been re-resinized. Furthermore, collected waste materials may be burned and used as thermal energy for the production of substrates and their raw materials, or the oils and fats contained in the collected waste materials may be mixed with petroleum, fractionated, and purified, and then used as raw materials.

[0048] The substrate may be a foam substrate from the viewpoint of improving compression characteristics. The foam substrate is preferably a foam substrate containing at least one selected from the group consisting of PE, PP, and PU, and from the viewpoint of achieving a high degree of both flexibility and strength, a foam substrate containing PE is more preferred. Examples of the constituents of the foam substrate containing PE include PE made from sugarcane.

[0049] 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.

[0050] The preferred lower limit of the thickness of the foam substrate is 50 μm, and the preferred upper limit is 5000 μm. By having the thickness of the foam substrate within this range, it is possible to exhibit high impact resistance while also exhibiting high flexibility that allows it to be adhered to the shape of the adherend. The more preferred upper limit of the thickness of the foam substrate is 1000 μm, and even more preferred upper limit is 300 μm.

[0051] The adhesive tape of the present invention has a total thickness (total thickness of the substrate and adhesive layer) of preferably 3 μm at the lower limit and 6000 μm at the upper limit. Having a total thickness within this range of the adhesive tape enhances adhesive strength. The adhesive tape's total thickness is more preferably 1200 μm at the upper limit and even more preferably 500 μm at the upper limit.

[0052] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and the tape can be produced by a conventionally known production method. For example, in the case of a double-sided pressure-sensitive adhesive tape, the following method can be mentioned. First, a solvent is added to a (meth)acrylic copolymer, a tackifying resin, and an optional crosslinking agent, etc. to prepare a pressure-sensitive adhesive composition A. The resulting pressure-sensitive adhesive composition A is applied to the surface of a substrate, and the solvent in the composition is completely dried and removed by heating to form a pressure-sensitive adhesive layer A. Next, a release film is superimposed on the formed pressure-sensitive adhesive layer A with its release-treated surface facing the pressure-sensitive adhesive layer A. Next, a release film separate from the above release film is prepared, and PSA composition B, prepared in the same manner as PSA composition A, is applied to the release-treated surface of this release film. The solvent in the composition is then completely dried and removed to produce a laminate film in which PSA layer B is formed on the surface of the release film. The obtained laminate film is overlaid on the back surface of the substrate on which PSA layer A is formed, with PSA layer B facing the back surface of the substrate to produce a laminate. The laminate is then pressed with a rubber roller or the like to produce a double-sided PSA tape in which PSA layers are on both sides of the substrate and the surfaces of the PSA layers are covered with release films.

[0053] Alternatively, two sets of laminate films may be prepared in a similar manner, and these laminate films may be superimposed on each of both surfaces of a substrate with the pressure-sensitive adhesive layer of the laminate film facing the substrate to prepare a laminate. This laminate may then be pressed with a rubber roller or the like to obtain a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both surfaces of the substrate, the surfaces of the pressure-sensitive adhesive layers being covered with release films.

[0054] The use of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but it is preferably used for fixing electronic device components or vehicle-mounted components. Specifically, the pressure-sensitive adhesive tape of the present invention can be suitably used for adhesively fixing electronic device components in large portable electronic devices, adhesively fixing vehicle-mounted components (for example, vehicle-mounted panels), etc. [Effects of the Invention]

[0055] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that is excellent in adhesive reliability and in see-through visibility when exposed to a high-temperature, high-humidity environment after being attached to an adherend. [Brief explanation of the drawings]

[0056] [Figure 1] FIG. 1 is a schematic diagram showing a method for testing the repulsion resistance of an adhesive tape. DETAILED DESCRIPTION OF THE INVENTION

[0057] 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.

[0058] <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.

[0059] <n-heptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was cracked to obtain a mixture containing undecylenic acid and n-heptyl alcohol. The undecylenic acid was then separated from the resulting mixture by distillation to obtain n-heptyl alcohol containing bio-derived carbon. The resulting n-heptyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare n-heptyl acrylate containing bio-derived carbon.

[0060] <1-Methylheptyl acrylate containing bio-derived carbon> Ricinoleic acid derived from castor oil was fused in an alkali to obtain a mixture containing sepacic acid and 1-methylheptyl alcohol. The sepacic acid was then separated from the resulting mixture by distillation to obtain 1-methylheptyl alcohol containing bio-derived carbon. The resulting 1-methylheptyl alcohol containing bio-derived carbon was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare 1-methylheptyl acrylate containing bio-derived carbon.

[0061] <2-hydroxyethyl acrylate containing bio-derived carbon> Ethanol containing bio-derived carbon was obtained by fermenting sugars contained in sugarcane. The obtained bio-derived ethanol was dehydrated to obtain ethylene, which was then oxidized to obtain ethylene oxide, and water was added to obtain ethylene glycol containing bio-derived carbon. The obtained bio-derived ethylene glycol was esterified with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.) to prepare 2-hydroxyethyl acrylate containing bio-derived carbon.

[0062] <Bio-derived carbon-free monomer> n-Butyl acrylate (Tokyo Chemical Industry Co., Ltd.) 2-Ethylhexyl acrylate (Nippon Shokubai Co., Ltd.) 2-Methoxyethyl acrylate (Tokyo Chemical Industry Co., Ltd.) Acrylic acid (manufactured by Nippon Shokubai Co., Ltd.)

[0063] <Tackifying resin> Tackifying resin A: Rosin ester tackifying resin (Arakawa Chemical Industries, Ltd., "Pensel D-135", softening temperature: 130°C to 140°C) Tackifying resin B: Rosin ester tackifying resin (Arakawa Chemical Industries, Ltd., "Pine Crystal KE-359", softening temperature: 94°C to 104°C) Tackifying resin C: Terpene-based tackifying resin (terpene phenol resin) (Yasuhara Chemical Co., Ltd., "YS Polystar G150", softening temperature: 145°C to 155°C)

[0064] <Crosslinking agent> Isocyanate crosslinking agent (Covestro, "Desmodur L-75")

[0065] Example 1 (1) Production of acrylic copolymer Ethyl acetate was added to the reaction vessel as a polymerization solvent, and after bubbling with nitrogen, the reaction vessel was heated while nitrogen was flowing in to initiate reflux. Subsequently, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile 10 times with ethyl acetate was added to the reaction vessel, and 94.9 parts by mass of n-hexyl acrylate containing bio-derived carbon, 0.1 parts by mass of 2-hydroxyethyl acrylate containing bio-derived carbon, and 5.0 parts by mass of acrylic acid were added dropwise over 2 hours. After the dropwise addition was completed, a polymerization initiator solution prepared by diluting 0.1 parts by mass of azobisisobutyronitrile 10 times with ethyl acetate was added again to the reaction vessel, and the polymerization reaction was carried out for 4 hours to obtain an acrylic copolymer-containing solution. The resulting acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm) to prepare a measurement sample. This measurement sample was fed to a gel permeation chromatograph (Waters, "2690 Separations Module") and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the acrylic copolymer was measured, and the weight-average molecular weight was calculated. The results are shown in Table 1.

[0066] (2) Manufacturing of adhesive tapes An isocyanate-based crosslinking agent was added to the obtained acrylic copolymer-containing solution so that the solid content was 1.0 part by mass per 100 parts by mass of the acrylic copolymer in the 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 obtain 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).

[0067] (3) Measurement of gel fraction of adhesive layer The release PET film on one side of the resulting adhesive tape was peeled off, and the tape was laminated to a 23 μm thick base PET film ("FE2002" manufactured by Futamura Chemical Co., Ltd.) and cut into a flat rectangular shape 20 mm wide and 40 mm long. The release PET film on the other side of the adhesive tape was then peeled off to prepare a test piece, and its mass was measured. The test piece was immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The mass of the dried test piece was measured, and the gel fraction was calculated using the following formula (I). The results are shown in Table 1. Gel fraction (mass%) = 100 × (W2 - W0) / (W1 - W0) (I) (W0: Mass of the substrate, W1: Mass of the test piece before immersion, W2: Mass of the test piece after immersion and drying)

[0068] (Examples 2 to 4, 6 to 34, Comparative Examples 1 to 4) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the types and amounts of monomers constituting the acrylic copolymer and the types and amounts of each component contained in the pressure-sensitive adhesive composition were as shown in Tables 1 to 4, and the amount of polymerization initiator added was appropriately changed. The weight-average molecular weight of the 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 4.

[0069] Example 5 A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the types and amounts of each component contained in the pressure-sensitive adhesive composition were as shown in Table 1. The resulting pressure-sensitive adhesive composition was applied to the release-treated surface of a 75-μm-thick release PET film so that the thickness of the pressure-sensitive adhesive layer after drying would be 19 μm, and then dried at 110°C for 5 minutes to obtain a pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive layer was bonded to one side of a 12-μm-thick base PET film (manufactured by Toyobo Co., Ltd., "FE2002"). Furthermore, a pressure-sensitive adhesive layer having the same composition and thickness was prepared on the release-treated surface of another 75-μm-thick release PET film, which was then bonded to the other side of the base PET film and aged at 40°C for 48 hours to obtain a pressure-sensitive adhesive tape (support type, total thickness 50 μm excluding the release PET film) having a pressure-sensitive adhesive layer and a release PET film on both sides of the substrate. The weight-average molecular weight of the 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 adhesive layer was measured using test pieces obtained by cutting the adhesive tape into a flat rectangular shape 20 mm wide and 40 mm long and then peeling off the release PET films on both sides. The results are shown in Table 1.

[0070] (Visible light transmittance) The resulting adhesive tape was cut to a width of 52 mm and a length of 76 mm, the release PET film on one side was peeled off, and the tape was adhered to a glass plate (manufactured by Matsunami Glass Industry Co., Ltd., "S9112") having a thickness of 1.0 mm, a width of 52 mm, and a length of 76 mm. The release PET film on the other side of the adhesive tape was peeled off from the obtained test piece, and the visible light transmittance was measured at room temperature (20°C or higher and 25°C or lower) in accordance with JIS K 7375: 2008 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "NDH 4000"), using the glass plate before the adhesive tape was attached as a reference. The results are shown in Tables 1 to 4.

[0071] (Rebound resistance test) The resulting adhesive tape was cut into a flat rectangular shape measuring 25 mm wide and 150 mm long. An aluminum plate measuring 25 mm wide, 150 mm long, and 0.3 mm thick was bonded to a polycarbonate resin plate measuring 25 mm wide, 200 mm long, and 1 mm thick using the adhesive tape. The adhesive tape was adjusted so that it was positioned at the longitudinal center of the polycarbonate resin plate. A 2 kg rubber roller was rolled back and forth over the polycarbonate resin plate at a speed of 300 mm / min, bonding the polycarbonate resin plate and aluminum plate together via the adhesive tape. The laminate was then left at 23°C for 24 hours to produce a laminate. The resulting laminate was attached to a jig as shown in Figure 1, and bending stress was applied in the longitudinal direction of the laminate, deforming the laminate into an arc-shaped warp so that the distance between both ends of the polycarbonate resin plate in the longitudinal direction was 180 mm. The laminate was then placed in a constant temperature and humidity oven at 60°C and 90% RH and left to stand for 72 hours. The laminate was taken out of the oven while still warped in an arc shape, and the floating height H (mm) between the aluminum plate and the polycarbonate resin plate was measured with a vernier caliper. The results are shown in Tables 1 to 4.

[0072] <Evaluation> The pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated by the following methods, and the results are shown in Tables 1 to 4.

[0073] (Adhesion reliability) From the results of the above "(Rebound Resistance Test)", the adhesive reliability was evaluated according to the following criteria. ◎: When the floating height H is 2 mm or less ○: When the floating height H is more than 2 mm and less than 10 mm ×: When the floating height H exceeds 10 mm

[0074] (Transmission visibility when exposed to high temperature and humidity environments) A test piece obtained in the same manner as in the above "(Visible light transmittance)" was placed in a constant temperature and humidity oven at 60°C and 90% RH and left to stand for 72 hours. Thereafter, the test piece was removed from the oven, and a black plate was placed on one of the glass plate sides of the test piece. The test piece was visually observed from the glass plate side where the black plate was not placed, and the transmittance visibility was evaluated according to the following criteria. ◎: When the black color is not lost and can be seen ○: No cloudiness, but the black color has faded ×: If cloudiness is observed

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] [Table 4] [Industrial Applicability]

[0079] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that is excellent in adhesive reliability and in see-through visibility when exposed to a high-temperature, high-humidity environment after being attached to an adherend. [Explanation of symbols]

[0080] 1 adhesive tape 2 aluminum plates 3 Polycarbonate resin plate 4 Laminate 5 Jig

Claims

1. A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition, The pressure-sensitive adhesive composition contains a (meth)acrylic copolymer and a tackifying resin, The adhesive tape has a visible light transmittance of 50% or more, A laminate obtained by bonding an aluminum plate having a width of 25 mm, a length of 150 mm, and a thickness of 0.3 mm to a polycarbonate resin plate having a width of 25 mm, a length of 200 mm, and a thickness of 1 mm via the adhesive tape having a width of 25 mm and a length of 150 mm, which is placed in the center of the longitudinal direction of the polycarbonate resin plate, is subjected to a bending stress in the longitudinal direction of the laminate to deform the polycarbonate resin plate into an arc-shaped warp so that the distance between both ends in the longitudinal direction is 180 mm, and then subjected to a repulsion resistance test in which the laminate is heated in an environment of 60°C and 90% RH for 72 hours, and the floating height between the aluminum plate and the polycarbonate resin plate is 10 mm or less. An adhesive tape characterized by:

2. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the total content of the tackifier resin in the pressure-sensitive adhesive composition is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the (meth)acrylic copolymer.

3. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the tackifier resin comprises a tackifier resin having a softening temperature of 110°C or higher, and the content of the tackifier resin having a softening temperature of 110°C or higher in the pressure-sensitive adhesive composition is 10 parts by mass or higher per 100 parts by mass of the (meth)acrylic copolymer.

4. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the tackifier resin comprises at least one selected from the group consisting of rosin ester-based tackifier resins and terpene-based tackifier resins.

5. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer comprises a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 6 carbon atoms.

6. The pressure-sensitive adhesive tape according to claim 5 , wherein the (meth)acrylic copolymer further comprises a structural unit derived from a monomer having a crosslinkable functional group.

7. The pressure-sensitive adhesive tape according to claim 6 , wherein the monomer having a crosslinkable functional group comprises at least one selected from the group consisting of a carboxyl group-containing monomer and a hydroxyl group-containing monomer.

8. The pressure-sensitive adhesive tape according to claim 6 , wherein the (meth)acrylic copolymer contains structural units derived from the monomer having a crosslinkable functional group in an amount of 0.01% by mass or more and less than 20% by mass.

9. The pressure-sensitive adhesive tape according to claim 5, wherein the (meth)acrylic copolymer further comprises a structural unit derived from n-heptyl (meth)acrylate.

10. The pressure-sensitive adhesive tape according to claim 5, wherein the (meth)acrylic copolymer further comprises a structural unit derived from at least one monomer having a non-crosslinkable ether structure selected from the group consisting of a monomer having a cyclic ether structure other than an epoxy group or an oxetanyl group, and a monomer having an acyclic ether structure.

11. The pressure-sensitive adhesive tape according to claim 10 , wherein the (meth)acrylic copolymer contains more than 0% by mass and not more than 50% by mass of the structural unit derived from the monomer having a non-crosslinkable ether structure.

12. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the (meth)acrylic copolymer has a weight average molecular weight of 700,000 or more and 1,500,000 or less.

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

14. The pressure-sensitive adhesive tape according to claim 13, wherein the crosslinking agent comprises at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

15. The pressure-sensitive adhesive tape according to claim 14 , wherein the crosslinking agent comprises the isocyanate-based crosslinking agent and the epoxy-based crosslinking agent.

16. The adhesive tape according to claim 1 or 2, which is used for fixing electronic equipment parts or vehicle-mounted parts.

Images