Adhesive composition, adhesive sheet formed from the adhesive composition, and article using the adhesive sheet.

Abstract

This adhesive composition comprises 100 parts by mass of (a) syrup obtained by mixing a (meth)acrylic copolymer containing alkyl (meth)acrylate and a carboxyl group-containing (meth)acrylate as constituent components, an alkyl (meth)acrylate monomer, a carboxyl group-containing (meth)acrylate monomer, and a hydroxyl group-containing (meth)acrylate monomer, 0.5-10 parts by mass of (b) a tackifying resin, 0.1-3.0 parts by mass of (c) hollow fine particles, 0.1-5 parts by mass of (d) a photopolymerization initiator, and 0.01-5 parts by mass of (e) a crosslinking agent, wherein: the hollow fine particles (c) are resin-based hollow fine particles having a shell part composed of an organic polymer material; the 25% compressive strength of a crosslinked adhesive layer formed of the adhesive composition is 0.06-0.11 MPa; and the tensile strength of the adhesive layer at 23ºC is 0.35-0.65 MPa. The adhesive composition can form an adhesive layer having excellent flexibility and having excellent adhesive strength even at a high temperature.

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition containing hollow fine particles, a pressure-sensitive adhesive sheet formed from the pressure-sensitive adhesive composition, and an article using the pressure-sensitive adhesive sheet. [Background Art]

[0002] In fields such as automotive parts and mechanical parts, pressure-sensitive adhesive tapes (hereinafter referred to as foam pressure-sensitive adhesive tapes) using a foam obtained by foaming a resin material as a base material have been used. Since foam pressure-sensitive adhesive tapes have excellent stress relaxation properties, they also have excellent adhesion to members having steps and irregularities, and can be used for adherends in a wider range of applications compared to double-sided tapes using non-woven fabrics or resin films as base materials.

[0003] However, in foam pressure-sensitive adhesive tapes, since the resin that is the constituent material of the foam softens at high temperatures, there has been a concern that air bubbles present inside collapse and the aforementioned stress relaxation property is lost. In addition, a foam pressure-sensitive adhesive tape usually requires separate lamination of a pressure-sensitive adhesive layer, and the adhesive force of the pressure-sensitive adhesive layer generally decreases at high temperatures. That is, there has been a limitation for use in automotive parts that are expected to be used under high-temperature environments.

[0004] Patent Document 1 discloses a pressure-sensitive adhesive sheet formed from an ultraviolet-curable pressure-sensitive adhesive composition containing hollow microspheres and having a pressure-sensitive adhesive layer excellent in shear strength and adhesive strength (adhesive force) under high-temperature environments. In this document, as hollow microspheres (hollow fine particles), it is preferable to use hollow inorganic fine spherical bodies from the viewpoint of the efficiency and weight of polymerization using ultraviolet reaction, and it is stated that using hollow glass balloons makes it possible to improve high-temperature adhesive force without impairing other properties such as shear force and holding power. However, even when such inorganic hollow fine particles are used, even if holding power and high-temperature adhesive force can be improved, there has been a risk that the flexibility of the pressure-sensitive adhesive layer is impaired because the particles themselves are hard. In addition, the adhesive force at high temperatures may not be sufficient in some cases.

[0005] Patent Document 2 discloses an adhesive sheet comprising an acrylic polymer and hollow fine particles, and having an adhesive layer that does not contain air bubbles. Among the hollow fine particles, it is stated that hollow inorganic fine particles are more preferably used in this adhesive sheet from the viewpoint of the efficiency of polymerization using ultraviolet reaction and weight. The adhesive sheet described in Patent Document 2 is said to combine adhesiveness and reworkability, but its adhesive strength and flexibility at high temperatures are not particularly considered. According to the inventors' findings, the glass balloon content (9-12 parts) disclosed in the examples and reference examples of Patent Document 2 is effective in improving reworkability, but the flexibility of the adhesive sheet is poor, and it is expected that the adhesive strength will decrease at high temperatures. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-88408 (Japanese Patent No. 5408640), paragraph

[0053] [Patent Document 2] Japanese Patent Publication No. 2013-221073 (Japanese Patent No. 5950669), paragraph

[0042] [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide an adhesive composition capable of forming an adhesive layer that is highly flexible and has excellent adhesive strength even at high temperatures, an adhesive sheet formed from the adhesive composition, and an article using the adhesive sheet. [Means for solving the problem]

[0008] As a result of diligent research to achieve the above objectives, the inventors of this invention have found that an adhesive sheet formed from the following adhesive composition is highly effective in solving the above problems, and have completed the present invention. That is, the adhesive composition according to one aspect of the present invention is (a) A (meth)acrylic copolymer comprising alkyl (meth)acrylate and (meth)acrylate having a carboxyl group as constituent components, and 100 parts by mass of a syrup obtained by mixing alkyl (meth)acrylate monomer, (meth)acrylate monomer having a carboxyl group and (meth)acrylate monomer having a hydroxyl group, (b) 0.5 to 10 parts by mass of tackifying resin, (c) Hollow fine particles in a quantity of 0.1 to 3.0 parts by mass, (d) 0.1 to 5 parts by mass of a photopolymerization initiator, (e) Crosslinking agent in a quantity of 0.01 to 5 parts by mass, An adhesive composition containing, The hollow fine particles (c) are resin-based hollow fine particles having a shell made of an organic polymer material. The 25% compressive strength of the crosslinked adhesive layer formed from the aforementioned adhesive composition is 0.06 to 0.11 MPa. The adhesive layer is characterized by having a tensile strength of 0.35 to 0.65 MPa at 23°C.

[0009] Furthermore, according to one aspect of the present invention, an adhesive sheet comprising an adhesive layer made of the above-mentioned adhesive composition, and an article using the adhesive sheet are provided. [Effects of the Invention]

[0010] The (meth)acrylic syrup (a) used in the adhesive composition of the present invention contains a copolymer in which (meth)acrylate having the two types of functional groups described above is an essential component, and therefore easily forms a crosslinked structure regardless of the type of crosslinking agent (e). For this reason, the adhesive layer formed from the adhesive composition of the present invention can maintain high adhesive strength even at high temperatures. Because the adhesive layer becomes highly polar due to these functional groups, excellent adhesive strength can be obtained, especially to metals. Furthermore, because the tackifying resin (b) is an essential component, the initial adhesive strength to materials with uneven surfaces or steps can be enhanced. Furthermore, since a relatively small amount of resin-based hollow microparticles using an organic polymer material instead of an inorganic material as the shell material is used, the compressive strength and tensile strength of the pressure-sensitive adhesive layer after formation fall within predetermined ranges, making it possible to achieve both step conformability, curved surface adhesion, and adhesive strength under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 3] It is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 4] It is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. [Figure 5] It is a schematic cross-sectional view of an adhesive sheet according to an embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to only these embodiments. The pressure-sensitive adhesive composition according to the present invention is (a) a (meth)acrylic copolymer comprising alkyl (meth)acrylate and (meth)acrylate having a carboxyl group as constituent components; and 100 parts by mass of a syrup obtained by mixing an alkyl (meth)acrylate monomer, a (meth)acrylate monomer having a carboxyl group, and a (meth)acrylate monomer having a hydroxyl group, (b) 0.5 to 10 parts by mass of a tackifier resin, (c) 0.1 to 3.0 parts by mass of hollow microparticles, (d) 0.1 to 5 parts by mass of a photopolymerization initiator, (e) 0.01 to 5 parts by mass of a crosslinking agent, which is a pressure-sensitive adhesive composition comprising: the hollow microparticles (c) are resin-based hollow microparticles having a shell portion composed of an organic polymer material, The pressure-sensitive adhesive layer after crosslinking formed from the pressure-sensitive adhesive composition has a 25% compressive strength of 0.06 to 0.11 MPa, wherein the pressure-sensitive adhesive layer has a tensile strength of 0.35 to 0.65 MPa at 23°C.

[0013] (a) Syrup The syrup of component (a) is a mixture of a (meth)acrylic copolymer (a1) comprising, as constituent components, monomer units derived from an alkyl (meth)acrylate and a carboxyl group-containing (meth)acrylate, an alkyl (meth)acrylate monomer (a2), a carboxyl group-containing (meth)acrylate monomer (a3), and a hydroxyl group-containing (meth)acrylate monomer (a4).

[0014] (Meth)acrylic copolymer (a1) The copolymer (a1) comprises, as constituent components, monomer units derived from an alkyl (meth)acrylate and a carboxyl group-containing (meth)acrylate. Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, isohexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, isobornyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among these, it is preferable to introduce a unit derived from a monomer having a relatively long alkyl chain. One of these may be used alone, or two or more thereof may be used in combination. The proportion of the alkyl (meth)acrylate-derived monomer units relative to 100% by mass of all monomer units constituting the copolymer (a1) is preferably 80 to 99% by mass, more preferably 85 to 95% by mass.

[0015] Examples of (meth)acrylates having a carboxyl group include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, and fumaric acid. Among these, (meth)acrylic acid is preferred from the viewpoint of achieving higher strength in the acrylic resin composition. These may be used individually or in combination of two or more. The ratio of monomer units derived from (meth)acrylate having a carboxyl group to 100% by mass of all monomer units constituting copolymer (a1) is preferably 1 to 20% by mass, and more preferably 5 to 15% by mass.

[0016] The copolymer (a1) may contain other (meth)acrylic monomer units as long as the effects of the present invention are not impaired. Examples include nitrogen-containing acrylic monomer units such as (meth)acrylamide, which will be described later, and units derived from (meth)acrylate monomers (a4) having hydroxyl groups.

[0017] Copolymer (a1) is obtained by copolymerizing the above monomer components, and the polymerization method is not particularly limited. For example, it can be carried out using various polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization, using means such as photopolymerization or thermal polymerization. Furthermore, polymerization by radiation such as gamma rays and electron beam polymerization can also be used. Photopolymerization can be carried out, for example, by irradiating the monomer composition with UV rays in the presence of a photopolymerization initiator. Thermal polymerization can be carried out, for example, by heating the monomer composition to 50 to 200°C in the presence of a thermal polymerization initiator. It is also preferable to adjust the molecular weight by using a chain transfer agent such as a thiol compound in combination with polymerization. In addition, unreacted monomers may remain, but since they can be used as a component of syrup (a) as is, there is no particular need to isolate the copolymer. By stopping the polymerization when copolymer (a1) reaches 5 to 50% by mass to form a partial copolymer, it can be handled as a viscous liquid. In this specification, copolymer (a1) means a copolymer with a weight-average molecular weight (Mw) of 100,000 or more. The Mw of copolymer (a1) is preferably between 100,000 and 2,000,000, and more preferably between 500,000 and 1,500,000.

[0018] As the alkyl (meth)acrylate monomer (a2), the alkyl (meth)acrylate listed as a monomer component constituting copolymer (a1) can be used. Similarly, as the (meth)acrylate monomer (a3) ​​having a carboxyl group, the (meth)acrylate having a carboxyl group listed as a monomer component constituting copolymer (a1) can be used. Each of these may be used individually or in combination of two or more.

[0019] Examples of (meth)acrylate monomers (a4) having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyhexyl (meth)acrylate, and monoesters of (meth)acrylic acid with polyethylene glycol or polypropylene glycol. These may be used individually or in combination of two or more.

[0020] Furthermore, other monomers may also include nitrogen-containing acrylic monomers. Specific examples of nitrogen-containing acrylic monomers include (meth)acrylamide, N-alkyl-substituted (meth)acrylamides such as N-isopropyl(meth)acrylamide, N,N-dialkyl-substituted (meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide, acryloylmorpholine, vinylpyridine, N-vinylpyrrolidone, (meth)acrylate aminoethyl, (meth)acrylate dimethylaminoethyl, and (meth)acrylate dimethylaminopropyl. Among these, (meth)acrylamide, N-alkyl-substituted (meth)acrylamide, N,N-dialkyl-substituted (meth)acrylamide, and acryloylmorpholine are preferred from the viewpoint of versatility and industrialization. These may be used individually or in combination of two or more.

[0021] The amount of components in the syrup is preferably such that, with the total mass being 100%, the copolymer (a1) is 5 to 50% by mass and the other monomer components (a2) to (a4) total 50 to 95% by mass, and more preferably the copolymer (a1) is 8 to 40% by mass and the other monomer components (a2) to (a4) total 60 to 92% by mass. The proportion of the other monomer components (a2) to (a4) is preferably such that (a2) > (a3) ​​> (a4).

[0022] (b) Tackifying resin Various tackifying resins can be used, such as hydrogenated petroleum resins, rosin-based resins, terpene-based resins, hydrocarbon-based resins, and phenol-based resins. One of these can be used alone or in combination of two or more.

[0023] The tackifying resin (b) is blended in an amount of 0.5 to 10 parts by mass per 100 parts by mass of syrup (a), preferably 1 to 10 parts by mass per 100 parts by mass of syrup (a), and more preferably 2 to 8 parts by mass per 100 parts by mass of syrup (a).

[0024] (c) Hollow fine particles The hollow fine particles constituting the adhesive composition according to the present invention are resin-based hollow fine particles having a shell made of an organic polymer material. The organic polymer material constituting the shell is preferably a resin containing acrylonitrile as a constituent unit. The average particle diameter of the hollow fine particles is preferably 1 to 150 μm, and more preferably 10 to 130 μm. Here, the average particle diameter refers to the volume-based median diameter (D50). In the case of commercially available products, selection may be based on catalog values. The thickness of the shell is preferably 0.1 to 20 μm, more preferably 2 to 15 μm. Hydrocarbons are preferably encapsulated within the hollow portion of the hollow microparticles, allowing them to function as thermally expandable balloons. When heated, the organic polymer material (thermoplastic resin) constituting the shell begins to soften, the encapsulated hydrocarbons begin to gasify, the internal pressure increases, and the balloon expands. However, above a certain temperature, gas permeates and escapes from the shell, causing it to contract.

[0025] The content of hollow fine particles in the acrylic resin composition is 0.1 to 3.0 parts by mass, preferably 0.5 to 2 parts by mass, per 100 parts by mass of the syrup (a). Furthermore, in order to improve dispersion within the adhesive composition, surface treatments such as coupling treatment and stearic acid treatment may be appropriately performed on the hollow fine particles.

[0026] (d) Photopolymerization initiator As photopolymerization initiators, photoradical polymerization initiators can be used, including known polymerization initiators such as alkylphenone-based, acylphoscin oxide-based, and oxyphenyl acetate-based initiators. Alkylphenone-based initiators are further subdivided into benzyl ketal, α-hydroxyalkylphenone, α-hydroxyacetophenone, α-aminoalkylphenone, etc. The photopolymerization initiator (d) is blended in an amount of 0.1 to 5 parts by mass per 100 parts by mass of syrup (a), preferably 0.2 to 2 parts by mass, and more preferably 0.3 to 1 part by mass per 100 parts by mass of syrup (a).

[0027] (e) Crosslinking agent The adhesive composition according to the present invention is preferably characterized by containing a crosslinking agent, from the viewpoint of being able to form a crosslinked structure. As the crosslinking agent, at least one crosslinking agent selected from the group consisting of polyfunctional (meth)acrylic monomers, polyfunctional (meth)acrylic oligomers, difunctional or more glycidyl group-containing compounds, and difunctional or more isocyanate group-containing compounds is preferred from the viewpoint of reactivity with acrylic syrup (a).

[0028] Specific examples of polyfunctional (meth)acrylic monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

[0029] Specific examples of polyfunctional (meth)acrylic oligomers include urethane (meth)acrylates and epoxy (meth)acrylates, which are oligomerized by reacting compounds having multiple isocyanate groups or glycidyl groups with (meth)acrylic acid or hydroxyl group-containing (meth)acrylates.

[0030] Examples of compounds containing two or more functional glycidyl groups include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylenediamine, N,N,N',N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, mN,N-diglycidylaminophenylglycidyl ether, N,N-diglycidyltoluidine, N,N-diglycidylaniline, pentaerythritol polyglycidyl ether, and 1,6-hexanediol diglycidyl ether.

[0031] Examples of isocyanate group-containing compounds with two or more functionalities include isocyanate monomers such as tolylene diisocyanate (TDI), chlorphenyl diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate, as well as isocyanate compounds, isocyanurates, and biuret-type compounds obtained by adding these isocyanate monomers to trimethylolpropane or the like, and urethane prepolymer-type isocyanates obtained by adding them to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols. These crosslinking agents can be used individually or in combination of two or more.

[0032] The amount of crosslinking agent in the acrylic resin composition is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the polymer (total monomers before polymerization).

[0033] The adhesive composition according to the present invention is characterized in that the crosslinked adhesive layer formed from it has a 25% compressive strength of 0.06 to 0.11 MPa, and the tensile strength of the adhesive layer at 23°C is 0.35 to 0.65 MPa. The 25% compressive strength is the value measured by the method described in the examples below. If the compressive strength is less than 0.06 MPa, it becomes difficult to maintain the shape of the sheet, and if it exceeds 0.11 MPa, the ability to conform to steps and curved surfaces decreases. A compressive strength of 0.06 to 0.10 MPa is more preferable. Furthermore, the tensile strength of the adhesive layer at 23°C is the value measured by the method described in the examples below. If the tensile strength is less than 0.35 MPa, the cohesive force of the adhesive layer is weak, resulting in reduced holding power. If it exceeds 0.65 MPa, the cohesive force is too strong, resulting in reduced peel strength. A tensile strength of 0.38 to 0.56 MPa is more preferable. The peel strength of the adhesive layer is not particularly limited as long as it has the appropriate peel strength for the purpose. However, it is preferable that the peel strength of the crosslinked adhesive layer formed from the adhesive composition according to the present invention shows little change in peel strength between room temperature (23°C) and high temperature (90°C).

[0034] The adhesive composition of the present invention may contain various additives known in the art of the present invention, to the extent that they do not affect the compressive strength and tensile strength described above. Examples of such additives include flame retardants, pigments, antioxidants, lubricants, etc., and one or more of these may be included in combination.

[0035] The adhesive composition according to the present invention can be used as an adhesive layer formed by molding the adhesive composition into a sheet and crosslinking it. The adhesive layer may be molded into a sheet on its own, or it may be used as a tape-like material with an adhesive layer formed on a substrate. Particularly preferred is its use as a double-sided adhesive sheet for bonding articles together, as described later. In this specification, such sheet-like materials and tape-like materials are collectively referred to as adhesive sheets.

[0036] Figures 1 to 5 are schematic cross-sectional views illustrating the layer structure of the adhesive sheet of the present invention. Figure 1 shows a sheet composed solely of an adhesive layer using the adhesive composition of the present invention, in which hollow fine particles 2 are dispersed within the crosslinked adhesive layer 1. The top and bottom surfaces of the sheet are adhesive surfaces, forming a double-sided adhesive sheet. In terms of handling before use, a release film is provided on the adhesive surface, and when bonding articles, the release film is peeled off and the adhesive surface is attached to the surface of the article to be bonded.

[0037] Figure 2 shows an adhesive sheet in which an adhesive layer 1 is placed on one side of a base material 3, and a design can be applied to the non-adhesive side of the base material 3 by printing or other means. Therefore, a printable receiving layer (not shown) can also be provided on the non-adhesive side of the base material 3. Figure 3 shows an adhesive sheet in which an adhesive layer 1 is placed on both sides of the base material 3. Any material can be used as the base material, as long as it is a base material used in the field and exhibits excellent adhesive strength with the adhesive layer according to the present invention. For example, known films, nonwoven fabrics, foams, cloths, paper, and combinations thereof can be used. The thickness of the substrate is not particularly limited, but can be selected from a range of, for example, 1 μm to 200 μm. The surface of the substrate to which the adhesive layer is to be applied may be subjected to an easy-adhesion treatment as needed. Examples of easy-adhesion treatments include primer treatment, corona treatment, etching treatment, plasma treatment, and sandblasting treatment. One or more combinations of these can be selected. The substrate may be subjected to surface treatment such as antistatic treatment as needed. Examples of antistatic treatment include treatment with antistatic agents such as cationic surfactants, anionic surfactants, and nonionic surfactants. In addition, the substrate may be colored as needed by printing or kneading.

[0038] Figure 4 shows an adhesive sheet in which one adhesive surface is an adhesive layer 1 containing hollow fine particles 2 according to the present invention, and the other surface is an adhesive layer 4 that does not contain hollow fine particles 2. Figure 5 shows an adhesive sheet in which a substrate 3 is inserted between adhesive layer 1 and adhesive layer 4. Although the adhesive layer 4 that does not contain hollow fine particles 2 may have inferior step-following ability compared to the adhesive layer 1 containing hollow fine particles 2, this is not a problem as long as the surface to be bonded by adhesive layer 4 is flat. As the adhesive layer 4, conventionally known adhesive layers or adhesive layers obtained by removing hollow fine particles from adhesive layer 1 can be used.

[0039] The method for manufacturing the adhesive layer is not particularly limited, and conventionally known methods can be used.

[0040] Articles using the adhesive sheet according to the present invention are articles used in fields such as automobile parts and machine parts, and can be used for joining and bonding articles that are exposed to temperatures of 50°C or higher during their manufacturing and usage processes. [Examples]

[0041] The present invention will be described in more detail below with reference to examples. In the following description, "parts" means "parts by mass".

[0042] Preparation of partial copolymer A The compositions shown in Table 1 were placed in a flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen gas inlet. Under a nitrogen atmosphere, the mixture was irradiated using an ultraviolet irradiation device (Panasonic: Aicure UP50 (product name)) at an irradiation intensity of 800-1,200 mW / cm². 2 Partial copolymer A containing approximately 15% by mass of copolymer A1 of 2-ethylhexyl acrylate and acrylic acid was produced by photopolymerization by irradiation with ultraviolet light (measured using a UVM-100 light meter manufactured by ITEC Systems Co., Ltd.) for 8 to 12 minutes. The weight-average molecular weight of copolymer A1 was approximately 1 million.

[0043] [Table 1]

[0044] [Method for making adhesive sheets] Using this partial copolymer A, syrups were prepared with the compositions shown in Tables 2-1 to 2-4. Other materials were then added and uniformly mixed to obtain an adhesive composition. The numbers in the tables indicate quantities. An adhesive composition was applied between the release surfaces of two silicone-release-treated 50 μm thick PET films (manufactured by Fujimori Kogyo Co., Ltd., product name "Film Vina KF#50"), and the irradiation intensity was 3.0~5.0 mW / cm². 2 A fluorescent lamp (Toshiba FL20S W) was irradiated from both sides for 2 minutes to obtain an adhesive sheet. The thickness of the adhesive sheet was adjusted to 800 μm.

[0045] [Table 2-1]

[0046] [Table 2-2]

[0047] [Table 2-3]

[0048] [Table 2-4]

[0049] The details of the material names in Tables 2-1 to 2-4 are as follows: (Material details) (Syrup (a)) Partial copolymer A: Approximately 15% by mass and approximately 85% by mass of unreacted monomers of copolymer A1 2-EHA: 2-ethylhexyl acrylate, manufactured by Mitsubishi Chemical Corporation. NOAA: n-octyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. β-CEA: β-carboxyethyl acrylate, manufactured by Daicel Ornex Co., Ltd. 4HBA: 4-hydroxybutyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. HEA: Hydroxyethyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. AM-90G: Methoxypolyethylene glycol acrylate (product name: NK ester AM-90G), manufactured by Shin-Nakamura Chemical Co., Ltd. IBOA: Isobornyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. ACMO: Acryloylmorpholin, manufactured by KJ Chemicals.

[0050] (Tackifying resin (b)) P-125: Hydrogenated petroleum resin (softening point 125±5℃, product name: Alcon P-125), manufactured by Arakawa Chemical Industries, Ltd. P-140: Hydrogenated petroleum resin (softening point 140±5℃, product name: Alcon P-140), manufactured by Arakawa Chemical Industries, Ltd. P-90: Hydrogenated petroleum resin (softening point 90±5℃, product name: Alcon P-90), manufactured by Arakawa Chemical Industries, Ltd. G125: Terpene phenol resin (softening point 125±5℃, product name: YS Polystar G125), manufactured by Yasuhara Chemical Co., Ltd. KE-100: Hydrogenated rosin ester (softening point 100±5℃, product name: Pine Crystal KE-100), manufactured by Arakawa Chemical Industries, Ltd.

[0051] (Hollow fine particles (c)) F-80DE: Acrylonitrile copolymer hollow microparticles (average particle size 90-130 μm), manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd. F-80SDE: Acrylonitrile copolymer hollow microparticles (average particle size 20-40 μm), manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd. 30P70T: Inorganic hollow microparticles, manufactured by Potters Barotini. (Photopolymerization initiator (d)) HAP: α-hydroxyacetophenone (trade name: Omnirad1173), manufactured by IGM Resins.

[0052] (Crosslinking agent (e)) Tetrad X: N,N,N',N'-Tetraglycidyl-m-Xylenediamine, manufactured by Mitsubishi Gas Chemical Company. HDDA: 1,6-Hexanediol diacrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. A-1000: Polyethylene glycol diacrylate (product name: NK ester A-1000), manufactured by Shin Nakamura Chemical Industry Co., Ltd. A-DPH: Dipentaerythritol hexaacrylate (product name: NK Ester A-DPH, manufactured by Shin Nakamura Chemical Industry Co., Ltd.) MR-200: Polymeric MDI (Product name: Millionate MR-200), manufactured by Tosoh Corporation.

[0053] Physical property evaluation The adhesive sheets prepared as described above were subjected to the following evaluations. The results are shown in Tables 3-1 to 3-4. (Tensile test of adhesive sheet) In accordance with JIS Z 0237, an adhesive sheet with a thickness of 800 μm, a width of 25 mm, and a length of 100 mm was subjected to tensile testing using a tensile testing machine (Toyo Seiki Co., Ltd.: Strograph V-1C) under the conditions of 23°C, 50% RH, a grip distance of 30 mm, and a test speed of 300 mm / min, and the maximum tensile strength was measured. The maximum tensile strength was also measured under the same conditions after changing the temperature to 90°C.

[0054] (Compression strength of adhesive sheet) A 12mm thick laminate was formed by stacking 30mm square adhesive sheets. This laminate was compressed using a compression tester (Shimadzu Corporation: AG-50kNX Plus) at 23°C, 50% RH, and a test speed of 10mm / min, and the compressive strength at 25% deformation was measured.

[0055] (Peel strength) Two types of SUS 304 steel plates were prepared: one with a thickness of 1.5 mm, a length of 50 mm, and a surface finish of BA (cold-rolled and then brightly heat-treated), which was cleaned with acetone; and another with a thickness of 2.0 mm, a length of 50 mm, and a polypropylene (PP) plate, which was cleaned with isopropyl alcohol. The prepared adhesive sheet was cut to 10 mm x 130 mm, one side of the release film on both sides of the adhesive sheet was peeled off, and a polyester film with a thickness of 50 μm, a width of 15 mm, and a length of 300 mm was laminated to it. Next, the release film on the opposite side was peeled off, and after lightly attaching it to the substrate, a 5 kg roller was used to press it back and forth over the test piece at a speed of approximately 300 mm per minute. After crimping, the adhesive sheet was left at room temperature for 24 hours. Then, the edges of the adhesive sheet were folded back 180 degrees, and the sheet was continuously peeled off at a speed of 50 ± 5 mm per minute under a 23°C, 50% RH atmosphere. The average test force (unit: N / 10 mm) was read. The results are shown as SUS (23°C) and PP (23°C). Similarly, the bonded and pressed test specimens were left at room temperature for 24 hours. After that, the edges of the adhesive sheets were folded back 180 degrees, and the specimens were placed in a 90±3°C hot air circulating constant temperature chamber for 1 hour. Then, under a 90°C atmosphere, they were continuously peeled off at a speed of 50±5 mm per minute, and the average test force was read. The results are shown as SUS(90°C) and PP(90°C). Furthermore, as a percentage change in peel strength, the difference in peel strength between 23°C and 90°C divided by the peel strength at 23°C is shown in Tables 3-1 to 3-4.

[0056] (Retention strength test) For the substrate, a polished stainless steel plate was used, which had been polished 30 times back and forth with #280 abrasive paper and then cleaned with acetone. A 25mm x 25mm piece of adhesive sheet had its release liner peeled off from one side and attached to the edge of the polished stainless steel plate. A 5kg roller was then used to press the sheet back and forth over the test piece at a speed of approximately 300mm per minute. After that, the release liner on the opposite side was peeled off, and an aluminum foil with a thickness of 130±20μm was similarly bonded to it. After bonding and pressing, the samples were left for 24 hours. Then, a weight of 1 ± 0.01 kg was placed on the aluminum foil side, and the samples were left in a 90 ± 3°C hot air circulating constant temperature chamber for 1 hour to check for any drops (A: none, B: dropped).

[0057] [Table 3-1]

[0058] [Table 3-2] [Industrial applicability]

[0059] The adhesive composition according to the present invention is capable of forming an adhesive layer that is highly flexible and has excellent adhesive strength even at high temperatures, and can maintain the desired adhesive strength even in the manufacture of articles that have an uneven surface and are subjected to high-temperature processing. [Explanation of symbols]

[0060] 1. Adhesive layer 2 Hollow particles 3 Base material 4 Other adhesive layers

Claims

1. (a) A (meth)acrylic copolymer comprising alkyl (meth)acrylate and (meth)acrylate having a carboxyl group as constituent components, and 100 parts by mass of a syrup obtained by mixing alkyl (meth)acrylate monomer, (meth)acrylate monomer having a carboxyl group and (meth)acrylate monomer having a hydroxyl group, (b) 0.5 to 10 parts by mass of tackifying resin, (c) Hollow fine particles in a quantity of 0.1 to 3.0 parts by mass, (d) 0.1 to 5 parts by mass of a photopolymerization initiator, (e) Crosslinking agent in a quantity of 0.01 to 5 parts by mass, An adhesive composition containing, The hollow fine particles (c) are resin-based hollow fine particles having a shell made of an organic polymer material. The 25% compressive strength of the crosslinked adhesive layer formed from the adhesive composition is 0.06 to 0.11 MPa. The adhesive layer is characterized by having a tensile strength of 0.35 to 0.65 MPa at 23°C. Adhesive composition.

2. The adhesive composition according to claim 1, wherein the organic polymer material is at least one polymer material containing acrylonitrile as a constituent unit.

3. The adhesive composition according to claim 1, wherein the volume average particle diameter D50 of the resin-based hollow fine particles is in the range of 1 to 150 μm.

4. An adhesive sheet comprising an adhesive layer formed from the adhesive composition according to any one of claims 1 to 3.

5. The adhesive sheet according to claim 4, comprising a single layer of the aforementioned adhesive layer.

6. The adhesive sheet according to claim 4, wherein the adhesive layer is provided on at least one surface of a substrate supporting the adhesive layer.

7. The adhesive sheet according to claim 4, wherein at least a portion of the surface of the adhesive layer has a substrate and / or another adhesive layer.

8. An article to which at least a portion is covered with an adhesive layer formed from the adhesive composition described in any one of items 1 to 3.

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