Adhesive sheet

Abstract

The present invention provides an adhesive sheet which has an adhesive layer that is easily releasable by heating and is sufficiently reduced in the passing amount of ultraviolet laser light. The adhesive sheet has an adhesive layer. The adhesive layer contains a polymer and a thermal polymerization initiator. The polymer contains an ethylenically unsaturated group. The content of the thermal polymerization initiator in the adhesive layer is 0.01 part by weight or more relative to 100 parts by weight of the polymer. The adhesive layer has a light transmittance of 70% or less at a wavelength of 355 nm.

Description

adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2024-029846, filed on February 29, 2024, the entire contents of which are incorporated herein by reference.

[0002] Generally, adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are soft solids (viscoelastic bodies) at temperatures near room temperature and easily adhere to adherends under pressure. Because of their ease of application to adherends, adhesives are widely used in a variety of fields in the form of supported adhesive sheets having an adhesive layer on a support, or in the form of supportless adhesive sheets without a support. Some such adhesives are used by adhering to an adherend and are removed from the adherend after their adhesive purpose has been fulfilled. Prior art documents disclosing this type of conventional technology include Patent Documents 1 to 4. Patent Documents 1 to 4 disclose thermosetting adhesives. Patent Document 5 also describes a dicing adhesive sheet having an adhesive layer containing an ultraviolet absorber.

[0003] Japanese Patent Application Publication No. 2015-29105 Japanese Patent Application Publication No. 2016-204617 Japanese Patent Application Publication No. 2019-56101 Japanese Patent Application Publication No. 10-209087 Japanese Patent Application Publication No. 2013-21105

[0004] Simone Napolitano, 'Irreversible adsorption of polymer melts and nanoconfinement effects', Soft Matter, 2020, 16, pp. 5348-5365Ben O'Shaughnessy and Dimitrios Vavylonis, 'Non-Equilibrium in Adsorbed Polymer Layers', J. Phys.: Condens. Matter, 17, 2005, pp. R63-99

[0005] PSA used for applications requiring peeling and removal from an adherend is required to exhibit good adhesion while adhering to the adherend and to have the ability to be easily peeled from the adherend after the adhesive has served its purpose. For example, PSA applied to adherends that undergo heat treatment desirably have easy releasability, allowing them to be easily peeled from the adherend after being heated while attached to the adherend. However, when adherends such as glass, metal, and resin are heated at high temperatures while the PSA is attached, the PSA adheres to the adherend surface, increasing the peel strength (heavy peeling), which can lead to problems such as reduced releasability and adhesive residue. Non-Patent Documents 1 and 2 describe how various polymers acquire adsorption properties upon heating. For example, with the thermosetting PSAs described in Patent Documents 1 to 4, it is difficult for the PSA to harden prior to adsorption to the adherend during high-temperature heating. This prevents the adhesive from reducing or suppressing the increase in peel strength due to the adhesive hardening, and the adhesive is unable to maintain stable easy releasability after high-temperature heating.

[0006] Against this background, the present inventors have focused on thermosetting adhesives containing a thermal polymerization initiator in the adhesive and have been conducting research and development, and have succeeded in obtaining an adhesive that remains easily releasable (heat-releasable) even after being attached to an adherend and heated at high temperatures. Such heat-releasable properties can also be referred to as heat-resistant releasability, since they remain easily releasable even after heat treatment, which usually increases the peel strength. Due to their usefulness, adhesive sheets with such heat-releasable properties or heat-resistant releasable properties are expected to be applied to various applications and various adherends. For example, they are expected to be used as processing materials in which a semiconductor wafer is processed while held by an adhesive layer, and then peeled from the semiconductor after processing.

[0007] One example of semiconductor wafer processing involves irradiation with ultraviolet laser light having a wavelength of 355 nm. Ultraviolet laser light with this wavelength can be focused to a narrow beam, enabling high-precision laser processing. However, because the laser light used in such laser processing is highly intense, if the adhesive layer has high laser light transmittance, the laser light irradiated onto the adherend may cut the adherend and further damage the adhesive sheet substrate by passing through the adhesive layer at the exposed portion. If the adhesive sheet substrate absorbs the laser light and breaks, the semiconductor processing process may be disrupted. Furthermore, the laser light may pass through the entire adhesive sheet and damage objects on the opposite side of the adhesive sheet. For example, Patent Document 5 describes that when a dicing adhesive sheet is held on a suction stage at its backside and a semiconductor wafer attached to the adhesive surface of the adhesive sheet is processed by laser dicing, the suction stage may be damaged by the laser light passing through the adhesive sheet.

[0008] In an adhesive sheet having heat-peelability, if it is possible to prevent the occurrence of events such as the above-mentioned laser light rupturing the adhesive sheet substrate without impairing the heat-peelability, the adhesive sheet can be used as a useful adhesive sheet suitable for applications in which laser light is irradiated for processing of adherend materials, such as the above-mentioned laser processing of semiconductors.

[0009] The present invention was created in consideration of the above circumstances, and aims to provide an adhesive sheet having an adhesive layer that is easily peelable by heating and that has a sufficiently reduced amount of ultraviolet laser light passing through it.

[0010] According to this specification, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is provided. The pressure-sensitive adhesive layer includes a polymer and a thermal polymerization initiator. The polymer includes an ethylenically unsaturated group. The content of the thermal polymerization initiator in the pressure-sensitive adhesive layer is 0.01 parts by weight or more per 100 parts by weight of the polymer. The pressure-sensitive adhesive layer has a light transmittance of 70% or less at a wavelength of 355 nm. According to this configuration, the polymer having an ethylenically unsaturated group and the thermal polymerization initiator in the pressure-sensitive adhesive layer react upon heating, reducing the peel strength of the pressure-sensitive adhesive and enabling easy thermal peeling. Furthermore, since the pressure-sensitive adhesive layer has a light transmittance of 70% or less at a wavelength of 355 nm, the amount of ultraviolet laser light passing through can be sufficiently reduced. When a pressure-sensitive adhesive sheet having such a pressure-sensitive adhesive layer is used in applications where laser light is irradiated on the pressure-sensitive adhesive layer side for processing an adherend material, for example, the pressure-sensitive adhesive layer's light transmittance at a wavelength of 355 nm can protect the pressure-sensitive adhesive sheet substrate and objects on the opposite side of the pressure-sensitive adhesive sheet from laser light. As a result, it is possible to prevent the occurrence of an event in which the adhesive sheet substrate is broken by laser light that has passed through the adhesive layer, or an event in which an object located on the opposite side of the adhesive sheet is damaged.

[0011] In some embodiments, the pressure-sensitive adhesive layer comprises an ultraviolet absorber A having an absorbance of 0.01 or more at a wavelength of 355 nm. By using an ultraviolet absorber A having the above absorbance, the transmittance of light at a wavelength of 355 nm of the pressure-sensitive adhesive layer can be reduced.

[0012] In some embodiments, the content of the ultraviolet absorber A in the pressure-sensitive adhesive layer is preferably 0.01 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the polymer. By setting the content of the ultraviolet absorber A within the above range, it is possible to preferably achieve both easy heat peelability and a reduced transmittance of light at a wavelength of 355 nm in the pressure-sensitive adhesive layer.

[0013] In some embodiments, the PSA sheet preferably has a post-heat peel strength of 3 N / 20 mm or less from a silicon wafer after heat treatment for 30 minutes at 180° C. A PSA sheet exhibiting the above post-heat peel strength can be easily removed from the silicon wafer, for example, in a use in which the sheet is attached to a silicon wafer, due to its easy heat peelability.

[0014] 1 is a cross-sectional view schematically showing an example of an adhesive sheet.

[0015] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic to clearly explain the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0016] In this specification, the "base polymer" of a PSA refers to the main rubbery polymer component contained in the PSA. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, unless otherwise specified, the "main component" refers to a component that accounts for more than 50% by weight.

[0017] In this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. In this specification, the acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer.

[0018] Furthermore, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" refers to an acryloyl group and a methacryloyl group in a comprehensive sense. Therefore, the concept of acrylic monomer here can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" refers to acrylic acid and methacrylic acid in a comprehensive sense, and "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense. The same applies to other similar terms.

[0019] In this specification, "weight" may be read as "mass." For example, "% by weight" may be read as "% by mass," and "parts by weight" may be read as "parts by mass."

[0020] <Adhesive Sheet> The adhesive sheet disclosed herein is configured to include an adhesive layer. The adhesive sheet may be a substrate-attached adhesive sheet in a form in which the adhesive layer is provided on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-releasable substrate; typically, an adhesive sheet comprising an adhesive layer) in a form in which the adhesive layer is supported by a release liner. The concept of adhesive sheet here may include what are called adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or sheets. Alternatively, it may be an adhesive sheet in the form of a sheet processed into various shapes.

[0021] The cross-sectional structure of a PSA sheet is shown in Figure 1. As shown in Figure 1, PSA sheet 1 has an adhesive surface 1A and is in the form of a single-sided PSA sheet in which a PSA layer 20 is provided on one surface 10A of a sheet-like base layer (supporting substrate) 10. PSA sheet 1 is used by attaching the surface 20A of the PSA layer 20, which is the adhesive surface 1A, to an adherend. The back surface 10B of the base layer 10 (the surface opposite to one surface 10A) also serves as the back surface 1B of the PSA sheet 1 and constitutes the outer surface of the PSA sheet 1. Before use (i.e., before attachment to an adherend), PSA sheet 1 may be in the form of a release-liner-attached PSA sheet 50 in which the adhesive surface 1A is protected by a release liner 30, the side of which facing at least the PSA layer 20 serves as a release surface. Alternatively, the adhesive sheet may be in a form in which the other surface (back surface) 10B of the base material layer 10 is the release surface, and when the adhesive sheet 1 is rolled up, the adhesive layer 20 abuts against the back surface, thereby protecting its surface (adhesive surface 1A).

[0022] <Adhesive Layer> (Light Transmittance at 355 nm Wavelength) The adhesive layer disclosed herein is characterized by a light transmittance at 355 nm wavelength (light transmittance at 355 nm wavelength) of 70% or less. This allows for sufficient reduction in the amount of ultraviolet laser light passing through. When an adhesive sheet having such an adhesive layer is used in applications where laser light is irradiated on the adhesive layer side for processing of an adherend material, for example, the adhesive sheet substrate and the object on the opposite side of the adhesive sheet can be protected from laser light based on the light transmittance at 355 nm wavelength of the adhesive layer. As a result, it is possible to prevent the occurrence of laser light passing through the adhesive layer causing breakage of the adhesive sheet substrate or damage to the object located on the opposite side of the adhesive sheet. From this viewpoint, in some preferred embodiments, the transmittance of light at a wavelength of 355 nm of the pressure-sensitive adhesive layer is approximately 50% or less (e.g., less than 50%), may be 40% or less, more preferably 30% or less (e.g., less than 30%), even more preferably 20% or less (e.g., less than 20%), still more preferably 15% or less, even more preferably 10% or less (e.g., less than 10%), particularly preferably 5% or less, may be 3% or less, may be 2% or less, or may be 1% or less (e.g., less than 1%).

[0023] The lower limit of the light transmittance at a wavelength of 355 nm of the pressure-sensitive adhesive layer is 0%, but depending on the mode of use, it is possible to protect the pressure-sensitive adhesive sheet substrate or the object on the opposite side without designing the light transmittance at a wavelength of 355 nm to be excessively low. Therefore, in some embodiments, the light transmittance at a wavelength of 355 nm of the pressure-sensitive adhesive layer may be approximately 1% or more, 3% or more, 5% or more, 8% or more, or 10% or more (for example, more than 10%). Increasing the light transmittance at a wavelength of 355 nm to a predetermined value or more can be advantageous from the viewpoint of suppressing a decrease in heat peelability. The light transmittance at a wavelength of 355 nm of the pressure-sensitive adhesive layer can be measured using an ultraviolet-visible-infrared spectrophotometer. More specifically, it can be measured by the method described in the Examples below.

[0024] (Component for Reducing 355 nm Light Transmittance) The component for reducing the 355 nm light transmittance of the pressure-sensitive adhesive layer to 70% or less (component for reducing 355 nm light transmittance) is not particularly limited, and for example, an ultraviolet absorber that absorbs 355 nm light or an ultraviolet scattering agent that reflects and scatters 355 nm light can be used. By incorporating such a component into the pressure-sensitive adhesive layer, the 355 nm light transmittance can be reduced. As the component for reducing 355 nm light transmittance, any of inorganic materials (zinc oxide, titanium oxide, carbon black, etc.), organic materials (such as ultraviolet absorbers described below), and organic-inorganic composites can be used. These can be used alone or in combination of two or more. Alternatively, the polymer described below can be used as the component for reducing 355 nm light transmittance. For example, the 355 nm light transmittance of the pressure-sensitive adhesive layer can be reduced by using a polymer incorporating an ultraviolet-absorbing structural unit (for example, a structural unit containing a benzotriazole structure). In this embodiment, the polymer that is a constituent of the pressure-sensitive adhesive layer can function as a component that reduces the transmittance of light with a wavelength of 355 nm, so the use of the ultraviolet absorber or ultraviolet scattering agent is not essential.

[0025] (Ultraviolet Absorber) In some preferred embodiments, the pressure-sensitive adhesive layer contains an ultraviolet absorber. By using an ultraviolet absorber, the transmittance of light at a wavelength of 355 nm through the pressure-sensitive adhesive layer can be preferably reduced while maintaining easy heat peelability. Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. One or more suitable ultraviolet absorbers can be used from the above-mentioned various ultraviolet absorbers. Among them, from the viewpoint of ultraviolet absorption at a wavelength of 355 nm, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers are preferred, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and triazine-based ultraviolet absorbers are more preferred, benzophenone-based ultraviolet absorbers and triazine-based ultraviolet absorbers are even more preferred, and benzophenone-based ultraviolet absorbers are particularly preferred.

[0026] Examples of benzotriazole-based ultraviolet absorbers (benzotriazole-based compounds) include 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole, ester compounds of benzenepropanoic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7 to C9 side chain and linear alkyl), octyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]-4-hydroxy-5-(1,1-dimethylethyl) ... ] propionate and 2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzoloriazol-2-yl)phenyl]propionate, 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol, methyl-3-(3-(2H-benzotriazol-2-yl)phenyl)propionate 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-triazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300 reaction products, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-triazol-2-yl)-4-hydroxyphenyl)propionate / polyethylene glycol 300 reaction products 3-tetramethylbutyl)phenol, 2-2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol], reaction products of methyl-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate with polyethylene glycol 300, 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol, 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole, 2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazole, 2-(2H-benzotriazol-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol, 2-(4-benzoyloxy-2-hydroxyphenyl)-5-chloro-2H-benzotriazole, 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 2-(2H-benzotriazol-2-yl)-p-cellulose, 2-(5-chloro-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol, and the like.

[0027] Commercially available benzotriazole-based ultraviolet absorbers include those manufactured by BASF under the trade names "Tinuvin PS," "Tinuvin 384-2," "Tinuvin 109," "Tinuvin 900," "Tinuvin 928," "Tinuvin 1130," "Tinuvin P," "Tinuvin 234," "Tinuvin 326," "Tinuvin 328," "Tinuvin 329," "Tinuvin 360," "Tinuvin 213," and "Tinuvin 571"; those manufactured by Sumika Chemtex Co., Ltd. under the trade name "Sumisorb 250"; those manufactured by Shipro Chemical Co., Ltd. under the trade names "SEESORB 703," "SEESORB 706," and "SEESORB 7012BA"; and those manufactured by Chemipro Chemical Co., Ltd. under the trade name "KEMISORB 73"; trade names "ADK STAB LA-31", "ADK STAB LA-32", and "ADK STAB LA-36" manufactured by ADEKA Corporation; and the like.

[0028] Examples of benzophenone-based ultraviolet absorbers (benzophenone-based compounds) include 2-hydroxy-4-n-octyloxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoic acid hexyl ester, etc. Commercially available benzophenone-based ultraviolet absorbers include those manufactured by Shipro Chemical Co., Ltd. under the trade name "SEESORB 106," manufactured by Chemipro Chemical Co., Ltd. under the trade name "KEMISORB 111," and those manufactured by BASF under the trade name "Uvinul A Plus."

[0029] Examples of benzoate-based ultraviolet absorbers (benzoate-based compounds) include 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate, etc. Commercially available benzoate-based ultraviolet absorbers include "Tinuvin 120" manufactured by BASF.

[0030] Examples of triazine-based ultraviolet absorbers (triazine-based compounds) include a reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(C10 to C16, mainly C12 to C13 alkyloxy)methyl]oxirane, 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-[3-(dodecyloxy)-2-hydroxypropoxy]phenol, a reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl)-glycidic acid ester, and 2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4 Examples of the triazine-based ultraviolet absorber include hydroxyphenyl triazine-based ultraviolet absorbers (hydroxyphenyl triazine-based compounds), such as 2-(4,6-diphenyl-1,3,5-triazine, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine, and 2,4-bis-[{4-(2-ethylhexyloxy)-2-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine. As the triazine-based ultraviolet absorber, hydroxyphenyl triazine-based ultraviolet absorbers are preferably used.

[0031] Commercially available triazine-based ultraviolet absorbers (for example, hydroxyphenyltriazine-based ultraviolet absorbers) include those manufactured by BASF under the trade names "Tinuvin 400," "Tinuvin 405," "Tinuvin 460," "Tinuvin 1577," "Tinuvin 479," "Tinuvin 477," and "Tinosorb S"; and those manufactured by ADEKA under the trade name "ADEKA STAB LA-46."

[0032] Examples of cyanoacrylate-based ultraviolet absorbers (cyanoacrylate-based compounds) include alkyl-2-cyanoacrylate, cycloalkyl-2-cyanoacrylate, alkoxyalkyl-2-cyanoacrylate, alkenyl-2-cyanoacrylate, alkynyl-2-cyanoacrylate, ethyl-2-cyano-3,3-diphenylacrylate, etc. Commercially available cyanoacrylate-based ultraviolet absorbers include "Uvinul 3035" manufactured by BASF.

[0033] Examples of the ultraviolet absorber that can be used include pigments or dyes such as azo-based, phthalocyanine-based, anthraquinone-based, lake-based, perylene-based, perinone-based, quinacridone-based, thioindigo-based, dioxandine-based, isoindolinone-based, quinophthalone-based, carbonyl-based, indigo-based, quinoneimine-based, methine-based, quinoline-based, and nitro-based pigments.

[0034] Although not particularly limited, the ultraviolet absorber preferably has a maximum absorption wavelength of about 250 nm or more and 450 nm or less (e.g., about 280 nm or more and 400 nm or less). Such an ultraviolet absorber tends to effectively reduce the light transmittance of the pressure-sensitive adhesive layer at a wavelength of 355 nm.

[0035] In some embodiments, an ultraviolet absorber A having an absorbance of 0.01 or more at a wavelength of 355 nm is used as the ultraviolet absorber. The ultraviolet absorber A exhibiting the above absorbance can reduce the light transmittance of the pressure-sensitive adhesive layer at a wavelength of 355 nm. The absorbance of the ultraviolet absorber at a wavelength of 355 nm may be 0.03 or more, or may be 0.05 or more. From the viewpoint of effectively reducing the light transmittance of the pressure-sensitive adhesive layer at a wavelength of 355 nm, the absorbance of the ultraviolet absorber at a wavelength of 355 nm may be preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, even more preferably 0.5 or more, even more preferably 0.7 or more, and particularly preferably 0.9 or more (e.g., 1.0 or more). The absorbance of the ultraviolet absorber at a wavelength of 355 nm may be, for example, 1.5 or less, or may be 1.2 or less.

[0036] In this specification, the absorbance of an ultraviolet absorber at a wavelength of 355 nm is measured by the following method. That is, 0.1 g of the ultraviolet absorber to be measured is diluted with 1000 times tetrahydrofuran (THF) by weight, and added to a quartz cell with an optical path length of 10 mm. Then, using a ultraviolet-visible-infrared spectrophotometer, the absorbance is calculated from transmitted light at a wavelength of 355 nm. As the ultraviolet-visible-infrared spectrophotometer, a product name "V-750" manufactured by JASCO Corporation or an equivalent product can be used.

[0037] Although not particularly limited, ultraviolet absorbers having a molecular weight of approximately 1,000 or less can be preferably used. The molecular weight of the ultraviolet absorber may be approximately 800 or less, or approximately 700 or less. The molecular weight of the ultraviolet absorber may also be approximately 100 or more, or approximately 200 or more. In some preferred embodiments, the molecular weight of the ultraviolet absorber is 300 or more, 400 or more, 500 or more, or 550 or more.

[0038] When an ultraviolet absorber is used, the amount of the ultraviolet absorber used is not particularly limited and can be an amount that allows the pressure-sensitive adhesive layer to have a light transmittance of 355 nm wavelength within a predetermined range. In some embodiments, the content of the ultraviolet absorber contained in the pressure-sensitive adhesive layer may be more than 0 parts by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the pressure-sensitive adhesive layer, and may be, for example, 0.01 parts by weight or more, or 0.05 parts by weight or more. From the viewpoint of effectively reducing the light transmittance of the pressure-sensitive adhesive layer at a wavelength of 355 nm, in some preferred embodiments, the content of the ultraviolet absorber is 0.1 parts by weight or more relative to 100 parts by weight of the polymer, more preferably 0.3 parts by weight or more, even more preferably 0.5 parts by weight or more, even more preferably 0.7 parts by weight or more, particularly preferably 0.9 parts by weight or more, and may be 1 part by weight or more, 1.5 parts by weight or more, 2 parts by weight or more, or 2.5 parts by weight or more. In some embodiments, the content of the ultraviolet absorber may be, for example, 50 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less, relative to 100 parts by weight of the polymer. Limiting the amount of ultraviolet absorber used can be advantageous from the viewpoint of suppressing a decrease in heat peelability. From this viewpoint, in some preferred embodiments, the content of the ultraviolet absorber is 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, even more preferably 1.5 parts by weight or less, and may be 1.0 parts by weight or less (for example, less than 1.0 part by weight), relative to 100 parts by weight of the polymer.

[0039] (Polymer) In the technology disclosed herein, the type of adhesive is not particularly limited. The adhesive layer may contain one or more polymers selected from various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, and mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. The above polymers may be used as base polymers in the adhesive and function as structural polymers that shape the adhesive. From the viewpoints of adhesive performance, cost, and the like, adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, adhesives (acrylic adhesives) that use acrylic polymers with excellent heat resistance as the base polymer are preferred.

[0040] The following description will mainly focus on acrylic pressure-sensitive adhesives and pressure-sensitive adhesive layers formed from such pressure-sensitive adhesives, i.e., pressure-sensitive adhesive sheets having acrylic pressure-sensitive adhesive layers, but it is not intended to limit the pressure-sensitive adhesive layers disclosed herein to acrylic pressure-sensitive adhesive layers.

[0041] (Acrylic Polymer) In some embodiments, the acrylic polymer is an acrylic polymer in which more than 50% by weight of the monomer components constituting the polymer is an acrylic monomer. The proportion of the acrylic monomer in the monomer components is suitably 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, and may be, for example, 90% by weight or more. The upper limit of the proportion of the acrylic monomer in the monomer components constituting the acrylic polymer is 100% by weight, and the proportion of the acrylic monomer may be, for example, 98% by weight or less, 95% by weight or less, or 92% by weight or less, from the viewpoint of obtaining the effect of using a non-acrylic monomer. The acrylic monomer may be used alone or in combination of two or more.

[0042] In some preferred embodiments, the monomer component includes an alkoxy group-containing (meth)acrylate. Acrylic polymers containing an alkoxy group-containing (meth)acrylate as a monomer component tend to provide good adhesion and also tend to be compatible with, for example, the monomers that can be included in the pressure-sensitive adhesive layer (described below, sometimes referred to as "compound monomers" to distinguish them from the monomer components used in synthesizing the polymer). The alkoxy group-containing (meth)acrylates can be used alone or in combination of two or more.

[0043] Examples of alkoxy group-containing (meth)acrylates include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; and alkoxy(poly)alkylene glycol (meth)acrylates such as methoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate. Of these, alkoxyalkyl (meth)acrylates are preferred, and among these, alkoxyalkyl (meth)acrylates having an alkoxy group with 1 to 4 carbon atoms (e.g., 1, 2, or 3 carbon atoms) are more preferred, with methoxyethyl (meth)acrylate being particularly preferred.

[0044] The content of the alkoxy group-containing (meth)acrylate in the monomer component constituting the acrylic polymer is not particularly limited. From the viewpoint of effectively obtaining the effects of using the alkoxy group-containing (meth)acrylate, the content of the alkoxy group-containing (meth)acrylate in the monomer component is usually about 1 wt% or more, for example, 10 wt% or more, or even 30 wt% or more. In some embodiments, from the viewpoint of adhesive properties such as adhesive strength and compatibility with the blended monomer, the content of the alkoxy group-containing (meth)acrylate in the monomer component is, for example, more than 30 wt%, preferably 40 wt% or more, more preferably 50 wt% or more (for example, more than 50 wt%), and even more preferably 55 wt% or more. In some embodiments, the upper limit of the content of the alkoxy group-containing (meth)acrylate in the monomer component is approximately 99% by weight or less, or may be 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight or less, and even more preferably 65% ​​by weight or less, or may be 60% by weight or less, from the viewpoint of introducing an ethylenically unsaturated group into the polymer and obtaining the effects of other copolymerizable monomers such as functional group-containing monomers.

[0045] In some other embodiments, the monomer component constituting the acrylic polymer may include a chain alkyl(meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms at the ester terminal. Hereinafter, a chain alkyl(meth)acrylate having an alkyl group having X to Y carbon atoms at the ester terminal will be referred to as "C Ｘ－Ｙ In this specification, the term "chain alkyl (meth)acrylate" is used to mean both straight chain and branched chain. The chain alkyl (meth)acrylates can be used singly or in combination of two or more.

[0046] C １－２０Non-limiting examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and methyl (meth)acrylate. (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

[0047] C is a monomer component constituting an acrylic polymer. １－２０ In the embodiment using alkyl (meth)acrylate, C １－２０ As the alkyl (meth)acrylate, at least C ４－２０ It is preferable to use alkyl (meth)acrylate, and at least C ４－１８ It is more preferred to use alkyl (meth)acrylate. １－２０ As the alkyl (meth)acrylate, C ４－８ It is preferable to use alkyl (meth)acrylate. ４－８ The use of alkyl acrylates is more preferred. ４－８ The alkyl (meth)acrylates can be used alone or in combination of two or more. ４－８The use of alkyl (meth)acrylate tends to make it easier to obtain good adhesive properties (adhesive strength, etc.). For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as the monomer component is preferred, and an acrylic polymer containing at least 2EHA is particularly preferred. １－２０ In some other embodiments using alkyl (meth)acrylates, C ７－１２ Alkyl (meth)acrylates are preferably used. ７－１２ The alkyl (meth)acrylates can be used alone or in combination of two or more. ７－１２ Examples of alkyl (meth)acrylates include C ７－１０ Alkyl acrylates are preferred, C ７－９ Alkyl acrylate is more preferred, C ８ Alkyl acrylates are more preferred.

[0048] C is a monomer component constituting an acrylic polymer. １－２０ In an embodiment in which alkyl(meth)acrylate is used, C in the above monomer component １－２０ The content of alkyl (meth)acrylate is not particularly limited. １－２０ In order to effectively obtain the effect of using alkyl (meth)acrylate, in some embodiments, C １－２０ The content of alkyl (meth)acrylate is usually about 1% by weight or more, and may be, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more (for example, more than 50% by weight). In some embodiments, from the viewpoint of introducing an ethylenically unsaturated group into the polymer or obtaining the effect of other copolymerizable monomers, the above C １－２０ The content of alkyl (meth)acrylate is approximately 99% by weight or less, may be 90% by weight or less, approximately 70% by weight or less, 50% by weight or less (for example, less than 50% by weight), 30% by weight or less, 10% by weight or less, 1% by weight or less, or 0.1% by weight or less. １－２０It may be one that is substantially free of alkyl (meth)acrylate.

[0049] In some embodiments, the monomer components constituting the acrylic polymer preferably include other monomers besides the alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. Such other monomers may be monomers (copolymerizable monomers) copolymerizable with the alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. The other monomers may be used, for example, to introduce ethylenically unsaturated groups into the polymer. Suitable examples of the other monomers include monomers having polar groups (e.g., carboxy groups, hydroxyl groups, nitrogen-containing rings, etc.). The polar group-containing monomers may be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the PSA. The other monomers may be used alone or in combination of two or more.

[0050] Examples of other monomers include carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, monomers containing a sulfonic acid group or a phosphoric acid group, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, monomers having a succinimide skeleton, maleimides, itaconimides, aminoalkyl (meth)acrylates, alkoxysilyl group-containing monomers, vinyl esters, vinyl ethers, aromatic vinyl compounds, olefins, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, and other heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols.

[0051] When using such other monomers, the amount used is not particularly limited, but is suitably 1 wt% or more of the total monomer components. From the viewpoint of better demonstrating the effects of using the other monomers, the amount used of the other monomers may be 10 wt% or more, 20 wt% or more, or even 30 wt% or more of the total monomer components. Furthermore, from the viewpoint of easily balancing the adhesive properties, the amount used of the other monomers is suitably 60 wt% or less of the total monomer components, preferably 50 wt% or less (e.g., less than 50 wt%), and may be 45 wt% or less.

[0052] In some embodiments, the monomer component constituting the acrylic polymer includes a monomer having a nitrogen atom. The use of a monomer having a nitrogen atom can increase the cohesive strength of the PSA and favorably improve the adhesive strength. As the monomer having a nitrogen atom, for example, an amide group-containing monomer, an amino group-containing monomer, or a monomer having a nitrogen atom-containing ring can be used. The monomer having a nitrogen atom can be used alone or in combination of two or more.

[0053] Non-limiting specific examples of the monomer having a nitrogen atom include the following: Amide group-containing monomers: for example, (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide; N-monoalkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and others, such as N,N-dimethylaminopropyl(meth)acrylamide, alkoxydiacetone(meth)acrylamide, vinylformamide, and vinylacetamide. Amino group-containing monomers, for example, aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate.Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, and the like (for example, lactams such as N-vinyl-2-caprolactam).

[0054] Suitable examples of the monomer having a nitrogen atom include monomers having a nitrogen atom-containing ring, of which N-vinyl-2-pyrrolidone (NVP) and N-acryloylmorpholine (ACMO) are particularly preferred.

[0055] The amount of the nitrogen-containing monomer (preferably the nitrogen-containing ring-containing monomer) used is not particularly limited. In some embodiments, the amount of the nitrogen-containing monomer used in the monomer component may be 1 wt% or more, or may be 3 wt% or more. In some preferred embodiments, the amount of the nitrogen-containing monomer used in the monomer component is 5 wt% or more, more preferably 7 wt% or more, even more preferably 9 wt% or more, or may be 10 wt% or more, 12 wt% or more, or may be 14 wt% or more. The greater the amount of the nitrogen-containing monomer used, the more the cohesive strength of the PSA tends to improve. In some embodiments, the amount of the nitrogen-containing monomer used is suitably, for example, 40 wt% or less of the total monomer component, and may be 35 wt% or less. In some preferred embodiments, the amount of the nitrogen-containing monomer used in the monomer component is 30 wt% or less, more preferably 25 wt% or less, even more preferably 20 wt% or less, or may be 18 wt% or less.

[0056] In some embodiments, the monomer component includes a hydroxyl group-containing monomer. Use of a hydroxyl group-containing monomer can adjust the cohesive strength and crosslink density of the PSA, thereby improving adhesive strength. Hydroxyl group-containing monomers are also preferably used as a means of introducing ethylenically unsaturated groups into polymers. Examples of hydroxyl group-containing monomers that can be used include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. For example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) are preferably used. Hydroxyl group-containing monomers can be used alone or in combination of two or more.

[0057] When a hydroxyl group-containing monomer is used, the amount used is not particularly limited, and may be, for example, 0.01 wt% or more, 0.1 wt% or more, or 0.5 wt% or more of the total monomer components. In some embodiments, the amount of the hydroxyl group-containing monomer used is 1 wt% or more, more preferably 2 wt% or more, or even 3 wt% or more of the total monomer components. In some preferred embodiments, the amount of the hydroxyl group-containing monomer used is 5 wt% or more, more preferably 7 wt% or more, even more preferably 10 wt% or more, and particularly preferably 12 wt% or more of the total monomer components. Such an amount of the hydroxyl group-containing monomer is suitable when the hydroxyl group-containing monomer is used as a means of introducing an ethylenically unsaturated group into the polymer. In some embodiments, the amount of the hydroxyl group-containing monomer used is, for example, 40 wt% or less of the total monomer components, preferably 30 wt% or less, more preferably 20 wt% or less, and even more preferably 15 wt% or less.

[0058] In some preferred embodiments, the monomer component of the acrylic polymer uses a monomer having a nitrogen atom (for example, an amide group-containing monomer such as (meth)acrylamide, or a monomer having a nitrogen atom-containing ring such as NVP or ACMO) in combination with a hydroxyl group-containing monomer (for example, HEA or 4HBA) as a monomer having a polar group (polar group-containing monomer). This allows for a good balance between adhesive strength and cohesive strength. In an embodiment in which a monomer having a nitrogen atom and a hydroxyl group-containing monomer are used in combination, the amount A of the monomer having a nitrogen atom is Ｎ and the amount A of hydroxyl group-containing monomer ＯＨ Weight ratio (A Ｎ / A ＯＨ ) is not particularly limited, and may be, for example, 0.1 or more, 0.5 or more, 1.0 or more, 1.2 or more, 1.5 or more, or 1.8 or more. Ｎ / A ＯＨ ) may be, for example, 10 or less, 5 or less, 3 or less, or 2.5 or less.

[0059] In some embodiments, the monomer component may include a carboxyl group-containing monomer. Non-limiting examples of carboxyl group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Preferred examples include AA and MAA. The carboxyl group-containing monomer may be used alone or in combination of two or more. For example, AA and MAA may be used in combination.

[0060] The amount of the carboxyl group-containing monomer used may be, for example, 0.01 wt% or more, 0.1 wt% or more, 1 wt% or more, 3 wt% or more, 6 wt% or more, or 8 wt% or more of the total monomer components. The greater the amount of the carboxyl group-containing monomer used, the more the cohesive strength of the PSA tends to improve. The proportion of the carboxyl group-containing monomer may be, for example, 20 wt% or less, 10 wt% or less, 3 wt% or less, 1 wt% or less (e.g., less than 1 wt%), or 0.1 wt% or less. The monomer components may be substantially free of the carboxyl group-containing monomer.

[0061] Furthermore, it is preferable to use, as the other monomer, a monomer having a functional group (functional group A) capable of reacting with a functional group (functional group B) of a compound having an ethylenically unsaturated group, which will be described later. In this embodiment, the type of the other monomer is determined depending on the type of the compound. Examples of other monomers having functional group A include carboxy group-containing monomers, epoxy group-containing monomers, hydroxyl group-containing monomers, and isocyanate group-containing monomers, with hydroxyl group-containing monomers being particularly preferred. By using a hydroxyl group-containing monomer as the other monomer, the acrylic polymer has a hydroxyl group. On the other hand, by using, for example, an isocyanate group-containing monomer as the compound having an ethylenically unsaturated group, the hydroxyl group of the acrylic polymer reacts with the isocyanate group of the compound, and an ethylenically unsaturated group derived from the compound is introduced into the acrylic polymer.

[0062] Furthermore, when another monomer is used for the purpose of reacting with a compound having an ethylenically unsaturated group, the amount of the other monomer (preferably a hydroxyl group-containing monomer) is suitably about 1 wt% or more of the total monomer components, preferably about 5 wt% or more, more preferably about 10 wt% or more, and may be about 12 wt% or more, from the viewpoint of the thermosetting property of the adhesive and adhesive properties such as cohesive strength, etc. Furthermore, from the viewpoint of maintaining good adhesive properties such as adhesive strength, the amount of the other monomer is suitably about 40 wt% or less of the total monomer components, preferably about 30 wt% or less, more preferably about 25 wt% or less, and may be about 20 wt% or less (e.g., 15 wt% or less).

[0063] The acrylic polymer may contain, as another monomer component, a polyfunctional monomer having at least two ethylenically unsaturated groups, such as a (meth)acryloyl group or a vinyl group. By using a polyfunctional monomer as a monomer component, the cohesive strength of the pressure-sensitive adhesive can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and, for example, one or more suitable polyfunctional monomers selected from those exemplified as blending monomers that can be contained in the pressure-sensitive adhesive layer described below can be used alone or in combination.

[0064] The amount of polyfunctional monomer used is not particularly limited and can be appropriately set so as to achieve the purpose of using the polyfunctional monomer. The amount of polyfunctional monomer used can be approximately 3% by weight or less of the above-mentioned monomer components, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of polyfunctional monomer used to approximately 0.001% by weight or more (for example, approximately 0.01% by weight or more) of the monomer components.

[0065] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. As a monomer supply method for solution polymerization, a batch charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, or the like can be appropriately employed. The polymerization temperature can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0066] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixed solvent of two or more selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, halogenated alkanes such as 1,2-dichloroethane, lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol, ethers such as tert-butyl methyl ether, and ketones such as methyl ethyl ketone can be used.

[0067] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method.For example, although not particularly limited, for example, azo-based polymerization initiators, peroxide-based polymerization initiators, redox-based polymerization initiators formed by the combination of peroxide and reducing agent, substituted ethane-based polymerization initiators, etc. can be used.As the polymerization initiator, for example, one or more can be selected from those exemplified as the thermal polymerization initiators added to the pressure-sensitive adhesive layer described below.

[0068] The amount of the polymerization initiator used is not particularly limited and may be a normal amount depending on the polymerization method, polymerization mode, etc. For example, about 0.001 to 5 parts by weight (typically about 0.01 to 2 parts by weight, e.g., about 0.01 to 1 part by weight) of the polymerization initiator can be used per 100 parts by weight of all monomer components to be polymerized.

[0069] (Polymer Having Ethylenically Unsaturated Groups) The adhesive layer disclosed herein contains a polymer having an ethylenically unsaturated group, such as an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group. When a pressure-sensitive adhesive containing a polymer having an ethylenically unsaturated group is heated, the ethylenically unsaturated group in the polymer reacts, allowing the pressure-sensitive adhesive to be thermally cured to a high degree of hardness, resulting in easy thermal peelability. More specifically, when a pressure-sensitive adhesive is heated, for example at a high temperature, while attached to an adherend, it typically adsorbs to the surface of the adherend. This increases the adhesive strength of the pressure-sensitive adhesive to the adherend, resulting in difficult peeling. According to the technology disclosed herein, by incorporating a polymer having an ethylenically unsaturated group and a thermal polymerization initiator into the pressure-sensitive adhesive, the ethylenically unsaturated group reacts (radical polymerization reaction) upon heating, allowing the pressure-sensitive adhesive to harden prior to adsorption to the adherend. This reduces the adhesive strength to the adherend. Furthermore, even if heating is continued thereafter, the adhesive strength of the PSA to the adherend does not increase but is maintained within a predetermined range, so the PSA can exhibit good heat-peelability. Note that the technology disclosed herein is not limited to the above considerations. A PSA containing a polymer having an ethylenically unsaturated group can achieve sufficient heat-peelability and heat-resistant heat-peelability without relying on the use of a blended monomer described below or while limiting the amount of blended monomer used.

[0070] In some embodiments, the polymer having an ethylenically unsaturated group is a polymer having an ethylenically unsaturated group in a side chain. As the monomer component of the polymer having an ethylenically unsaturated group, one or more of the monomer components exemplified for the polymer above can be used within the above content range.

[0071] The amount of ethylenically unsaturated groups in the polymer having ethylenically unsaturated groups is not particularly limited, and is suitably 0.01 mmol per gram of polymer (hereinafter also referred to as mmol / g) or more, and may be 0.1 mmol / g or more, or may be 0.5 mmol / g or more, from the viewpoint of thermosetting properties, etc. The amount of ethylenically unsaturated groups in the polymer is suitably 10.0 mmol / g or less, and may be 5.0 mmol / g or less, 3.0 mmol / g or less, 2.5 mmol / g or less, or may be 2.0 mmol / g or less.

[0072] The amount of ethylenically unsaturated groups in a polymer, for example, when the ethylenically unsaturated groups are (meth)acryloyl groups, is measured by the following method. First, 0.25 mg of the polymer to be measured is dissolved in 50 mL of THF (tetrahydrofuran), and 15 mL of methanol is added to obtain a solution. Next, 10 mL of 4N aqueous sodium hydroxide is added to the solution to obtain a mixed solution. Next, the mixed solution is stirred at a liquid temperature of 40°C for 2 hours. Further, 10.2 mL of 4N methanesulfonic acid solution is added to the mixed solution and stirred. 5 mL of demineralized water is added to the mixture, followed by 2 mL of methanol to prepare a measurement solution. The content of (meth)acrylic acid in the measurement solution is measured by HPLC (High Performance Liquid Chromatography) (absolute calibration curve method), and the content of ethylenically unsaturated groups is calculated. (HPLC measurement conditions) Column: Synergi 4μ Polar-RP 80A (4.6 mm×250 mm) manufactured by Phenomenex Column temperature: 40° C. Flow rate: 1.0 mL / min Detector wavelength: 210 nm Eluent: THF (for HPLC) 55 / buffer water (containing 0.2% phosphoric acid and 0.2% triethylamine) 45 Aqueous solution injection volume: 5 μL

[0073] An example of a method for measuring the content of ethylenically unsaturated groups other than (meth)acryloyl groups is a method for measuring the bromine number in accordance with JIS K2605: 1996. In this measurement method, the content of ethylenically unsaturated groups other than (meth)acryloyl groups is determined by converting the number of grams of bromine (Br) added to 100 g of the polymer to be measured into the number of moles of bromine (Br) added to 1 g of the polymer.

[0074] The method for introducing an ethylenically unsaturated group into a polymer is not particularly limited, and an appropriate method can be selected from methods known to those skilled in the art. From the viewpoint of molecular design, etc., a method of introducing an ethylenically unsaturated group into a side chain of a polymer is preferred. For example, a method of reacting (typically condensation or addition reaction) a compound having an ethylenically unsaturated group with a functional group (functional group B) reactive with a functional group (functional group A) introduced into an acrylic polymer by copolymerization, so as not to lose the ethylenically unsaturated group, can be preferably used. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among these, a combination of a hydroxyl group and an isocyanate group is preferred from the viewpoint of reaction traceability. From the viewpoint of polymer design, etc., a combination in which the acrylic polymer has a hydroxyl group and the compound has an isocyanate group is particularly preferred.

[0075] As described above, the compound having an ethylenically unsaturated group may have a functional group B that can react with functional group A. Suitable examples of such compounds include isocyanate group-containing monomers (isocyanate group-containing compounds) such as 2-(meth)acryloyloxyethyl isocyanate. Of these, 2-(meth)acryloyloxyethyl isocyanate is more preferred. An acrylic polymer having an ethylenically unsaturated group can be obtained by reacting the isocyanate group of the isocyanate group-containing compound having an ethylenically unsaturated group with the hydroxyl group of the acrylic polymer to form a bond (specifically, a urethane bond).

[0076] The amount of the compound having an ethylenically unsaturated group (for example, an isocyanate group-containing monomer) to be added is not particularly limited, but from the viewpoint of reactivity with the functional group A (for example, a hydroxyl group) in the polymer, it is preferable to add the compound having an ethylenically unsaturated group in an amount of 100 moles (M Ａ ) and the moles of functional group B (isocyanate group) (M Ｂ ) and the molar ratio (M Ａ / M Ｂ ) can be set to be in the range of about 0.5 to 2 (for example, 1 to 1.5).

[0077] The pressure-sensitive adhesive layer may contain a polymer that is substantially free of ethylenically unsaturated groups (a polymer having an ethylenically unsaturated group content of less than 0.01 mmol / g) within a range that does not impair the effects of the technology disclosed herein. The amount of such a polymer that is substantially free of ethylenically unsaturated groups is suitably less than 50% by weight of the total polymer (specifically, base polymer) contained in the pressure-sensitive adhesive layer, and may be less than 30% by weight, less than 10% by weight, less than 3% by weight, or less than 1% by weight. The pressure-sensitive adhesive layer may be substantially free of the above-mentioned polymer that is substantially free of ethylenically unsaturated groups.

[0078] (Ultraviolet-Absorbing Polymer) In some embodiments, a polymer incorporating an ultraviolet-absorbing structural unit (e.g., a structural unit containing a benzotriazole structure) may be used. This allows the transmittance of the pressure-sensitive adhesive layer to be reduced based on the 355 nm wavelength light absorption of the polymer itself, without requiring an additive such as an ultraviolet absorber as an essential component.

[0079] The molecular weight of the polymer (e.g., acrylic polymer) is not particularly limited and can be set within an appropriate range depending on the required performance, etc. The weight average molecular weight (Mw) of the polymer is approximately 1 × 10 ４ It is appropriate that the value is equal to or greater than 10×10. ４ By using a polymer having a Mw of a predetermined value or more, a good balance between cohesive strength and adhesive strength can be achieved. In some embodiments, the Mw is 20 × 10 or more from the viewpoint of obtaining heat resistance and good adhesiveness. ４ It may be 30 × 10 or more. ４More than that is fine, about 40 x 10 ４ More than that is fine, about 50 x 10 ４ or more, for example, about 55×10 ４ The upper limit of the Mw of the polymer is not particularly limited, and may be, for example, about 1000×10 ４ It may be less than or equal to approximately 100×10 ４ Here, Mw refers to a value calculated in terms of standard polystyrene obtained by gel permeation chromatography (GPC). As the GPC apparatus, for example, a model named "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) may be used.

[0080] (Monomer) In some embodiments, the pressure-sensitive adhesive layer preferably contains a monomer (compounded monomer) in addition to the polymer. The monomer has an ethylenically unsaturated group. The ethylenically unsaturated group of the monomer functions as a polymerizable functional group (typically a radically polymerizable functional group). By incorporating the monomer into the pressure-sensitive adhesive layer, the monomer is contained in the pressure-sensitive adhesive layer in a pre-reacted (unreacted) state. As a result, after the pressure-sensitive adhesive layer is formed, the monomer contained in the pressure-sensitive adhesive layer reacts quickly with the ethylenically unsaturated group of the polymer during heat treatment under specified conditions, and the pressure-sensitive adhesive is heat-cured to a high degree of cure, thereby exhibiting excellent heat-peelability. By incorporating the monomer, a thermosetting pressure-sensitive adhesive that retains heat-resistant easy-peelability even after heat treatment can be preferably obtained. The above monomers can be used alone or in combination of two or more.

[0081] Examples of the ethylenically unsaturated group contained in the above-mentioned monomer include, but are not limited to, an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group. Preferred examples of the ethylenically unsaturated group include an acryloyl group and a methacryloyl group. Of these, an acryloyl group is preferred. Hereinafter, a compound having an acryloyl group and / or a methacryloyl group may be referred to as an acrylic monomer. Furthermore, a compound having a vinyl group may be referred to as a vinyl monomer.

[0082] Although not particularly limited, it is appropriate to use a monomer having a molecular weight of 100 or more. In some preferred embodiments, the molecular weight of the monomer may be, for example, 150 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more. The molecular weight of the monomer is usually approximately 100,000 or less, for example, approximately 10,000 or less (e.g., less than 10,000) is appropriate, and 5,000 or less (e.g., less than 5,000) is preferable, and may be 1,500 or less, 1,000 or less (e.g., less than 1,000), 800 or less, or 600 or less. The use of a monomer having a molecular weight within the above range can be advantageous, for example, in terms of the preparation and coatability of the pressure-sensitive adhesive composition. The above molecular weight is the manufacturer's nominal value or a molecular weight calculated from the molecular structure. For the above-mentioned monomers having a molecular weight equal to or greater than a predetermined value, the value of the weight average molecular weight (Mw) calculated in terms of standard polystyrene obtained by GPC may be used.

[0083] In some preferred embodiments, the monomer used has a weight loss rate of 1% or less (specifically, 1.0% or less) at 180°C in TGA (thermogravimetric analysis) at a temperature increase of 10°C / min. By using a heat-resistant monomer (hereinafter also referred to as a "heat-resistant monomer") having a weight loss rate of 1% or less at 180°C, the pressure-sensitive adhesive layer has easy thermal peelability due to the inclusion of the monomer, while suppressing outgassing during heating. By using the heat-resistant monomer, both easy thermal peelability and reduced outgassing can be achieved. From the viewpoint of reducing outgassing, in some preferred embodiments, the weight loss rate of the heat-resistant monomer at 180°C is 0.9% or less, more preferably 0.8% or less, even more preferably 0.7% or less, particularly preferably 0.6% or less, and may even be 0.5% or less. The lower limit of the weight loss rate at 180°C of the heat-resistant monomer is theoretically 0%, and in practice may be 0.1% or more, 0.2% or more, or 0.3% or more. As the heat-resistant monomer, trimethylolpropane triacrylate (TMPTA, weight loss rate at 180°C: 1%) and dipentaerythritol hexaacrylate (DPHA, weight loss rate at 180°C: 0.5%) are preferably used. The heat-resistant monomers can be used alone or in combination of two or more.

[0084] Specifically, the weight loss rate of the monomer upon heating at 180°C can be measured using a differential thermal analyzer (manufactured by TA Instruments, trade name "Discovery TGA") under measurement conditions of a temperature increase of 10°C / min, an air atmosphere, and a flow rate of 25 mL / min.

[0085] In some preferred embodiments, a polyfunctional monomer is used as the monomer. In this specification, the term "polyfunctional monomer" refers to a polymerizable compound having two or more ethylenically unsaturated groups in one molecule, including those referred to as oligomers. Hereinafter, a compound having two or more acryloyl groups and / or methacryloyl groups may be referred to as a polyfunctional acrylic monomer. Furthermore, a compound having two or more vinyl groups may be referred to as a polyfunctional vinyl monomer.

[0086] In some preferred embodiments, the number of ethylenically unsaturated groups contained in one molecule of the polyfunctional monomer may be 3 or more, preferably 4 or more, more preferably 5 or more, and may even be 6 or more. The greater the number of ethylenically unsaturated groups in the polyfunctional monomer, the better the curing property upon heating and the easier it is to obtain heat-peelable properties. Furthermore, a polyfunctional monomer with a greater number of ethylenically unsaturated groups (functional groups) can obtain heat-peelable properties with a relatively small amount of use. This is advantageous because it also reduces the amount of outgassing derived from the polyfunctional monomer. The upper limit of the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer is not limited to a specific range and may be, for example, 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer may be, for example, 10 or less, 8 or less, or 6 or less. A polyfunctional monomer having the above number of ethylenically unsaturated groups tends to easily achieve both good adhesion and heat-peelable properties and also tends to have excellent storage stability.

[0087] As the polyfunctional monomer, various polyfunctional acrylate monomers or polyfunctional vinyl monomers having two or more ethylenically unsaturated groups can be used. Among them, polyfunctional acrylate monomers can be preferably used. Although not particularly limited, when used in combination with an acrylic polymer, polyfunctional acrylate monomers tend to be compatible and easily exhibit desired properties. The polyfunctional acrylate monomers and polyfunctional vinyl monomers can each be used alone or in combination of two or more.

[0088] Examples of polyfunctional monomers include 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, allyl (meth)acrylate, alkylene oxide-modified bisphenol A di(meth)acrylate, alkylene oxide-modified neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, dimethylol dicyclopentadi(meth)acrylate, vinyl (meth)acrylate, and divinylbenzene. Bifunctional monomers: trifunctional monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxy tri(meth)acrylate, glycerin propoxy triacrylate, tetramethylolmethane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; and tetrafunctional monomers such as pentaerythritol alkoxy tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate. pentafunctional monomers such as sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate; hexafunctional monomers such as dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate; and di- or higher functional monomers such as epoxy acrylate, polyester acrylate and urethane acrylate. Of these, preferred examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate and dipentaerythritol hexa(meth)acrylate.Among these, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0089] In embodiments in which the pressure-sensitive adhesive layer contains a polyfunctional monomer, the content of the polyfunctional monomer in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the polyfunctional monomer may be approximately 1 part by weight or more, or may be 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the pressure-sensitive adhesive layer. The appropriate amount of the polyfunctional monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, from the viewpoint of improving heat-peelability, the content of the polyfunctional monomer is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 12 parts by weight or more, even more preferably 15 parts by weight or more, and even more preferably 18 parts by weight or more, relative to 100 parts by weight of the polymer contained in the pressure-sensitive adhesive layer. By incorporating the above amount of polyfunctional monomer into the pressure-sensitive adhesive layer, the polyfunctional monomer contained in the pressure-sensitive adhesive layer reacts quickly when heated, and the pressure-sensitive adhesive layer is thermally cured, thereby achieving better heat-peelability. The upper limit of the content of the polyfunctional monomer in the pressure-sensitive adhesive layer is not particularly limited and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of the polyfunctional monomer per 100 parts by weight of the polymer is approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, and even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the polyfunctional monomer per 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less. According to the technology disclosed herein, the desired heat-peelability can be preferably achieved with a composition in which the amount of polyfunctional monomer in the pressure-sensitive adhesive layer is limited as described above.Furthermore, by limiting the amount of polyfunctional monomer used, the generation of low molecular weight components derived from the polyfunctional monomer after heating can be suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

[0090] In embodiments in which a polyfunctional monomer is used as the monomer, the amount of the polyfunctional monomer relative to the total amount of the monomers is not particularly limited. In some embodiments, from the viewpoint of effectively exerting the effect of containing the polyfunctional monomer, the amount of the polyfunctional monomer is suitably approximately 10 wt% or more of the total amount of the monomers, preferably 30 wt% or more, more preferably about 50 wt% or more (e.g., more than 50 wt%), even more preferably 70 wt% or more, even more preferably 90 wt% or more, particularly preferably 95 wt% or more, and may be 99 to 100 wt%. In some embodiments, the monomer contained in the pressure-sensitive adhesive composition may essentially consist of the polyfunctional monomer.

[0091] Furthermore, one or more monofunctional monomers containing one ethylenically unsaturated group per molecule may be used as the monomer. Known monofunctional acrylate monomers and vinyl monomers may be used as the monofunctional monomer. For example, one or more of the acrylate monomers (alkoxy group-containing (meth)acrylates, linear alkyl (meth)acrylates, etc.) exemplified as the monomer components of the polymer may be used.

[0092] In embodiments in which the pressure-sensitive adhesive layer contains a blended monomer, the content of the monomer in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the monomer may be approximately 1 part by weight or more, or may be 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the pressure-sensitive adhesive layer. The appropriate amount of the monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, from the viewpoint of improving heat-peelability, the content of the monomer is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 12 parts by weight or more, even more preferably 15 parts by weight or more, and even more preferably 18 parts by weight or more, relative to 100 parts by weight of the polymer contained in the pressure-sensitive adhesive layer. By incorporating the above amount of the monomer into the pressure-sensitive adhesive layer, the monomer contained in the pressure-sensitive adhesive layer reacts rapidly upon heating, and the pressure-sensitive adhesive layer is thermally cured, thereby achieving better heat-peelability. The upper limit of the content of the monomer in the pressure-sensitive adhesive layer is not particularly limited and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of the monomer per 100 parts by weight of the polymer is suitably approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, and even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the monomer per 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less. According to the technology disclosed herein, the desired heat-peelability can be preferably achieved with a composition in which the amount of monomer in the pressure-sensitive adhesive layer is limited as described above.Furthermore, by limiting the amount of the monomer used, the generation of low molecular weight components derived from the monomer after heating can be suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

[0093] In some other embodiments, the content of the blended monomer (e.g., polyfunctional monomer) in the pressure-sensitive adhesive layer may be less than 10 parts by weight, less than 3 parts by weight, less than 1 part by weight, or less than 0.1 parts by weight, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer may be substantially free of the above-mentioned monomer. According to the technology disclosed herein, since the polymer contained in the pressure-sensitive adhesive layer contains an ethylenically unsaturated group, it is possible to design a pressure-sensitive adhesive having easy heat-peelability without relying on the above-mentioned monomer.

[0094] (Thermal Polymerization Initiator) The adhesive layer contains a thermal polymerization initiator in addition to the polymer. Here, the thermal polymerization initiator refers to a polymerization initiator that generates radicals when heated. By including a thermal polymerization initiator in the adhesive layer, the thermal polymerization initiator reacts with a polymer having an ethylenically unsaturated group during heat treatment under specified conditions, and also reacts with a compounded monomer, if any, to reduce adhesive strength and achieve heat-peelability. By including a thermal polymerization initiator, a thermosetting adhesive that retains heat-resistant easy-peelability even after heat treatment can be formed.

[0095] As the thermal polymerization initiator, one or more suitable types may be selected and used from various thermal polymerization initiators such as peroxide-based polymerization initiators, azo-based polymerization initiators, redox-based polymerization initiators formed by combining peroxides with reducing agents, and substituted ethane-based polymerization initiators.

[0096] In some embodiments, it is preferable to use a peroxide-based polymerization initiator as the thermal polymerization initiator. By incorporating a peroxide-based polymerization initiator into the pressure-sensitive adhesive layer, the reaction of ethylenically unsaturated groups in the pressure-sensitive adhesive layer during heating, i.e., the curing reaction of the pressure-sensitive adhesive layer, proceeds rapidly, resulting in heat-peelability and heat-resistant peelability. One of the reasons for this is thought to be the high initiation efficiency of peroxide-based polymerization initiators (particularly organic peroxide-based polymerization initiators). Furthermore, peroxide-based polymerization initiators generate radicals (-O.) by cleavage of the -O-O- moiety contained in the compound. However, since this cleavage reaction is reversible, it is thought that if the radical does not collide with an ethylenically unsaturated group such as a polymer, recombination of -O-O- occurs. This recombined initiator can undergo another cleavage reaction during the specified heating period, colliding with and reacting with the polymer, etc. Therefore, with peroxide-based polymerization initiators, the thermal curing of the pressure-sensitive adhesive layer proceeds rapidly at a reaction rate significantly faster than with other initiators (e.g., azo-based initiators). Furthermore, since the thermal curing rate is faster than the rate at which the pressure-sensitive adhesive layer and the adherend are firmly adhered together due to heating, it is believed that the peel force after heating is reliably reduced, and heat-peelability and heat-resistant peelability are obtained. Note that the technology disclosed herein is not limited to the above considerations.

[0097] As the peroxide polymerization initiator, for example, organic peroxides such as diacyl peroxide, peroxy ester, peroxydicarbonate, monoperoxycarbonate, peroxyketal, dialkyl peroxide, hydroperoxide, ketone peroxide, etc. are preferably used. Suitable examples of the peroxide polymerization initiator include benzoyl peroxide compounds (typically dibenzoyl peroxide (BPO)) having a benzoyl group which may have a substituent. The peroxide polymerization initiators can be used alone or in combination of two or more.

[0098] Specific examples of peroxide polymerization initiators include BPO, 1,1-di(t-hexylperoxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, and 1,3-bis(t-butylperoxy)-m-isopropyl diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, diisopropylbenzene hydroperoxide, t-butylcumyl peroxide, didecanoyl peroxide, dilauroyl peroxide, 2,4-dichlorobenzoyl peroxide, di(4-t-butylcyclohexyl)peroxydicarbonate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl hydroperoxide, and di-t-butyl peroxide.

[0099] When a peroxide-based polymerization initiator is contained in the pressure-sensitive adhesive layer, the content of the peroxide-based polymerization initiator in the pressure-sensitive adhesive layer is not particularly limited, and may be, for example, 0.01 parts by weight or more, or 0.05 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. In some embodiments, the content of the peroxide-based polymerization initiator is suitably 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, even more preferably 0.5 parts by weight or more, even more preferably 0.6 parts by weight or more, particularly preferably 0.7 parts by weight or more, and may even be 0.8 parts by weight or more, relative to 100 parts by weight of the polymer contained in the pressure-sensitive adhesive layer. The higher the content of the peroxide-based polymerization initiator, the higher the frequency of collisions between the peroxide-based polymerization initiator and ethylenically unsaturated groups in the pressure-sensitive adhesive layer, and the more likely the curing reaction will proceed. In some embodiments, the amount of the peroxide polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or may be approximately 5 parts by weight or less. In some preferred embodiments, the amount of the peroxide polymerization initiator relative to 100 parts by weight of the polymer is appropriately 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (for example, 1.1 parts by weight or less), and may even be 1.0 parts by weight or less (for example, less than 1.0 part by weight). By setting the content of the peroxide polymerization initiator within a predetermined range, it is possible to preferably realize a pressure-sensitive adhesive having efficient thermosetting and easy heat-peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0100] In embodiments in which the pressure-sensitive adhesive layer contains a compounded monomer and a peroxide-based polymerization initiator, the content of the peroxide-based polymerization initiator in the pressure-sensitive adhesive layer can also be determined by its relative relationship to the compounded monomer in the pressure-sensitive adhesive layer. In some embodiments, the amount of the peroxide-based polymerization initiator per 100 parts by weight of the monomer is suitably 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 1.0 parts by weight or more, even more preferably 2.0 parts by weight or more, even more preferably 2.5 parts by weight or more, particularly preferably 3.0 parts by weight or more, and may even be 3.5 parts by weight or more, from the viewpoint of increasing the frequency of collisions with the ethylenically unsaturated groups of the monomer to rapidly progress thermal curing and from the viewpoint of thermally curing the pressure-sensitive adhesive layer to a high degree of cure. The amount of the peroxide-based polymerization initiator used can be preferably employed, for example, in a composition in which the monomer content is limited. In some embodiments, the amount of the peroxide-based polymerization initiator per 100 parts by weight of the monomer can be, for example, about 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, or 10 parts by weight or less. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomer may be 7 parts by weight or less, or may be 5 parts by weight or less.

[0101] Other examples of usable thermal polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(N-butyl-2-methylpropionamide), and 2,2'-azobis(2,4,4-trimethylpentane); substituted ethane initiators such as phenyl-substituted ethane; and redox initiators formed by combining a peroxide with a reducing agent, such as a combination of a persulfate with sodium hydrogen sulfite or a combination of a peroxide with sodium ascorbate. These can be used alone or in combination of two or more.

[0102] Although not particularly limited, from the viewpoint of effectively exerting the effects of the peroxide polymerization initiator, in some embodiments, the proportion of the peroxide polymerization initiator in the total thermal polymerization initiator contained in the pressure-sensitive adhesive layer may be approximately 10% by weight or more, suitably approximately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95 to 100% by weight. The thermal polymerization initiator contained in the pressure-sensitive adhesive layer may consist of a peroxide polymerization initiator.

[0103] In some embodiments, it is preferable to use a thermal polymerization initiator whose self-accelerating decomposition temperature (SADT) [°C] satisfies the formula: SADT + 10 ≥ 60. Here, the SADT of a thermal polymerization initiator is defined as the lowest temperature at which a certain amount of the initiator in a container generates heat of 6°C or more or causes self-accelerating decomposition within seven days. SADT indicates the environmental temperature at which the thermal polymerization initiator decomposes. Based on the fact that the maximum temperature to which a pressure-sensitive adhesive can be exposed during storage is 60°C, the present inventors have experimentally confirmed that if a thermal polymerization initiator has an SADT that is 10°C below the maximum storage temperature or higher, self-accelerating decomposition of the thermal polymerization initiator in the pressure-sensitive adhesive is suppressed, resulting in storage stability that allows the adhesive to maintain good heat-peelability after storage. This is thought to be because heat is relatively less transmitted within the pressure-sensitive adhesive (solid) than when the thermal polymerization initiator is used alone. Based on this discovery, adhesives designed with a thermal polymerization initiator having an SADT that satisfies the above formula (hereinafter also referred to as a high SADT initiator) suppress decomposition of the thermal polymerization initiator in the adhesive, allowing the adhesive to maintain the desired heat-peelability even when the adhesive is exposed to temperatures of approximately 60°C before use. Adhesives containing a thermal polymerization initiator consisting of a high SADT initiator have good storage stability and can maintain good heat-peelability after storage, even when stored for long periods of time or when there are temperature changes during storage. In this specification, the nominal value listed in manufacturer catalogs, etc., is used for the SADT of the thermal polymerization initiator.

[0104] The amount of the thermal polymerization initiator contained in the pressure-sensitive adhesive layer is not particularly limited. The content of the thermal polymerization initiator in the pressure-sensitive adhesive layer may be, for example, 0.01 parts by weight or more, or may be 0.05 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the pressure-sensitive adhesive layer. In some embodiments, the content of the thermal polymerization initiator in the pressure-sensitive adhesive layer is suitably 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, even more preferably 0.5 parts by weight or more, even more preferably 0.6 parts by weight or more, particularly preferably 0.7 parts by weight or more, and may even be 0.8 parts by weight or more, relative to 100 parts by weight of the polymer contained in the pressure-sensitive adhesive layer. The higher the content of the thermal polymerization initiator, the higher the frequency of collision between the thermal polymerization initiator and the ethylenically unsaturated group in the pressure-sensitive adhesive layer, and the more likely the curing reaction will proceed. In some embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or may be approximately 5 parts by weight or less. In some preferred embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer is appropriately 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (for example, 1.1 parts by weight or less), and may even be 1.0 parts by weight or less (for example, less than 1.0 part by weight). By setting the total amount of the thermal polymerization initiator within a predetermined range, it is possible to preferably realize a pressure-sensitive adhesive having efficient thermosetting and easy heat-peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0105] Although not particularly limited, in some preferred embodiments, the total proportion of the above-mentioned polymer (specifically, base polymer, for example, acrylic polymer), the above-mentioned monomer (for example, polyfunctional acrylic monomer) and thermal polymerization initiator (for example, peroxide-based polymerization initiator) in the entire pressure-sensitive adhesive layer is, from the viewpoint of effectively exhibiting a reduction in peel strength upon heating, suitably 50% by weight or more (for example, more than 50% by weight and 100% by weight or less), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and may be 95% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99 to 100% by weight).

[0106] (Crosslinking Agent) The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a crosslinking agent as needed, mainly for the purpose of crosslinking within the pressure-sensitive adhesive layer or between the pressure-sensitive adhesive layer and its adjacent surface. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer in a form after crosslinking reaction. The use of a crosslinking agent allows the cohesive strength of the pressure-sensitive adhesive layer to be appropriately adjusted.

[0107] The type of crosslinking agent is not particularly limited, and can be selected from conventionally known crosslinking agents so that the crosslinking agent exerts an appropriate crosslinking function within the pressure-sensitive adhesive layer, for example, depending on the composition of the pressure-sensitive adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. These crosslinking agents can be used alone or in combination of two or more. From the viewpoint of achieving a good balance between adhesiveness and cohesive strength, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and carbodiimide-based crosslinking agents are preferred, with isocyanate-based crosslinking agents being particularly preferred.

[0108] The isocyanate crosslinking agent may be a polyfunctional isocyanate compound having two or more functionalities, such as aromatic isocyanates such as tolylene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Examples of commercially available products include isocyanate adducts such as a trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate HL"), an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), and a trimethylolpropane / xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-110N").

[0109] As the epoxy-based crosslinking agent, those having two or more epoxy groups per molecule can be used without particular limitation. Epoxy-based crosslinking agents having three to five epoxy groups per molecule are preferred. Specific examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy-based crosslinking agents include "TETRAD-X" and "TETRAD-C" manufactured by Mitsubishi Gas Chemical Company, Inc., "Epicron CR-5L" manufactured by DIC Corporation, "Denacol EX-512" manufactured by Nagase ChemteX Corporation, and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

[0110] As the oxazoline-based crosslinking agent, any agent having one or more oxazoline groups per molecule can be used without particular limitation. Examples of aziridine-based crosslinking agents include trimethylolpropane tris[3-(1-aziridinyl)propionate] and trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)]. As the carbodiimide-based crosslinking agent, a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups can be used.

[0111] In some embodiments, an isocyanate-based crosslinking agent is used as the crosslinking agent. The isocyanate-based crosslinking agent can easily form a pressure-sensitive adhesive having good heat-peelability while exhibiting a well-balanced adhesive property such as adhesive strength and cohesive strength. The isocyanate-based crosslinking agents can be used alone or in combination of two or more. Although not particularly limited, the amount of isocyanate-based crosslinking agent used is preferably less than 3 parts by weight per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. By limiting the amount of isocyanate-based crosslinking agent used, the crosslinking density is appropriately suppressed. At such a crosslinking density, the polymer and the thermal polymerization initiator frequently collide with each other in the pressure-sensitive adhesive layer during heat treatment, promoting thermal curing, and tending to easily obtain the desired heat-peelability and heat-resistant peelability. From this viewpoint, in some preferred embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the polymer is 2 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 parts by weight or less, even more preferably 0.8 parts by weight or less, and particularly preferably 0.6 parts by weight or less. Limiting the amount of the isocyanate-based crosslinking agent used tends to make it easier to obtain sufficient adhesive strength. Furthermore, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the polymer can be, for example, 0.01 parts by weight or more. In some preferred embodiments, it may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of the isocyanate-based crosslinking agent used within the above range, it is possible to preferably obtain a pressure-sensitive adhesive that exhibits well-balanced adhesive properties such as adhesive strength and cohesive strength while preferably achieving the effects of the technology disclosed herein.

[0112] When a crosslinking agent is used, the amount of the crosslinking agent used may be more than 0 parts by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the adhesive layer, from the viewpoint of realizing a pressure-sensitive adhesive that exhibits a good balance of adhesive properties such as adhesive strength and cohesive strength. For example, the amount may be 0.001 parts by weight or more, or even 0.01 parts by weight or more. In some preferred embodiments, the amount of the crosslinking agent used relative to 100 parts by weight of the polymer may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or even 0.5 parts by weight or more. The upper limit of the amount of the crosslinking agent used may vary depending on the type of crosslinking agent used, and is not limited to a specific range, but is preferably limited to a predetermined amount or less. By limiting the amount of the crosslinking agent used, the crosslinking density is appropriately suppressed. At such a crosslinking density, the polymer in the adhesive layer and the thermal polymerization initiator frequently collide with each other during heat treatment, promoting thermal curing, and tending to easily obtain the desired heat-peelability and heat-peelability resistance. From this viewpoint, for example, the amount of crosslinking agent used is suitably less than 10 parts by weight relative to 100 parts by weight of the polymer, and in some embodiments, it is preferably less than 5 parts by weight, and may be less than 3 parts by weight. In some embodiments, the amount of crosslinking agent used is suitably less than 1 part by weight relative to 100 parts by weight of the polymer, and is preferably 0.9 parts by weight or less, and may be 0.8 parts by weight or less, 0.7 parts by weight or less, 0.6 parts by weight or less, or 0.5 parts by weight or less. By limiting the amount of crosslinking agent used, sufficient adhesive strength tends to be easily obtained.

[0113] A crosslinking catalyst may be used to more effectively promote the crosslinking reaction. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used may be, for example, approximately 0.0001 parts by weight or more, approximately 0.001 parts by weight or more, or approximately 0.005 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer, and may be approximately 1 part by weight or less, approximately 0.1 parts by weight or less, or approximately 0.05 parts by weight or less.

[0114] The PSA composition used to form the PSA layer may optionally contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. For example, a compound that undergoes keto-enol tautomerization may be preferably used in a PSA composition containing an isocyanate-based crosslinking agent or a PSA composition that can be used with an isocyanate-based crosslinking agent. This can have the effect of extending the pot life of the PSA composition. Various β-dicarbonyl compounds can be used as the compound that undergoes keto-enol tautomerization. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionyl acetate esters such as ethyl propionyl acetate; isobutyryl acetate esters such as ethyl isobutyryl acetate; and malonate esters such as methyl malonate and ethyl malonate. Among these, acetylacetone and acetoacetate esters are particularly preferred. The compounds that undergo keto-enol tautomerization may be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerization used may be, for example, 0.1 parts by weight or more and 20 parts by weight or less, and suitably 0.5 parts by weight or more and 15 parts by weight or less, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the pressure-sensitive adhesive layer, and can be, for example, 1 part by weight or more and 10 parts by weight or less, or may be 1 part by weight or more and 5 parts by weight or less.

[0115] (Other Components) The pressure-sensitive adhesive layer may optionally contain various additives commonly used in the field of pressure-sensitive adhesives, such as tackifiers, silane coupling agents, release force modifiers (such as surfactants), viscosity modifiers (e.g., thickeners), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, and antioxidants. These various additives can be conventionally used and do not particularly characterize the present invention, so detailed description is omitted. The technology disclosed herein can achieve desired adhesive properties, such as adhesive strength, without the use of a tackifier. In some embodiments, the content of the tackifier in the pressure-sensitive adhesive layer can be, for example, less than 10 parts by weight, or even less than 5 parts by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. The content of the tackifier may be less than 1 part by weight (e.g., less than 0.5 parts by weight) or less than 0.1 parts by weight (0 parts by weight or more but less than 0.1 parts by weight). The pressure-sensitive adhesive layer may not contain a tackifier.

[0116] (Form of Pressure-Sensitive Adhesive Composition) Although not particularly limited, the pressure-sensitive adhesive layer disclosed herein can be preferably formed using a solvent-based pressure-sensitive adhesive composition. The solvent-based pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition in a form containing pressure-sensitive adhesive-forming components in an organic solvent. The solvent-based pressure-sensitive adhesive composition typically contains a solution polymer of a monomer component, a thermal polymerization initiator (specifically, a peroxide-based polymerization initiator), and optionally other additives. The effects of the technology disclosed herein can be effectively exhibited in a form including a solvent-based pressure-sensitive adhesive (layer). The solvent contained in the solvent-based pressure-sensitive adhesive composition can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixture of two or more solvents selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene; esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; and ketones such as methyl ethyl ketone can be used.

[0117] As described above, this specification provides a pressure-sensitive adhesive composition containing components that can be included in the pressure-sensitive adhesive layer disclosed herein. Specifically, a pressure-sensitive adhesive composition containing a polymer and a thermal polymerization initiator is provided. This pressure-sensitive adhesive composition can form a pressure-sensitive adhesive layer that has easy heat peelability and a sufficiently reduced amount of ultraviolet laser light passing through it. The pressure-sensitive adhesive composition can typically be characterized by a light transmittance of 70% or less at a wavelength of 355 nm when molded into a 30 μm-thick sheet. In some preferred embodiments, the pressure-sensitive adhesive composition contains an ultraviolet absorber. In some preferred embodiments, the pressure-sensitive adhesive composition contains a monomer. The pressure-sensitive adhesive composition may also contain other components that can be included in the pressure-sensitive adhesive layer (e.g., a crosslinking agent, etc.). The content (by weight) of each component that can be included in the pressure-sensitive adhesive layer can be rephrased as the content (by weight) of the solids content (also referred to as the non-volatile content) of the pressure-sensitive adhesive composition. Other details of the pressure-sensitive adhesive composition are as described above for the pressure-sensitive adhesive layer, so a redundant description will be omitted.

[0118] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive layer disclosed herein can be formed by a conventionally known method. After applying (e.g., coating) the pressure-sensitive adhesive composition to a suitable surface, a curing treatment can be appropriately performed to form the pressure-sensitive adhesive in the form of a layer (pressure-sensitive adhesive layer). The pressure-sensitive adhesive composition can be cured by one method (e.g., drying, crosslinking, polymerization, cooling, etc.), or by two or more methods simultaneously or in multiple stages. In the case of a solvent-based pressure-sensitive adhesive composition, the pressure-sensitive adhesive can typically be formed by drying (preferably further crosslinking) the composition.

[0119] For example, in the case of a substrateless double-sided PSA sheet, a method can be used in which a PSA composition is applied to a surface (release surface) having releasability and then cured to form a PSA layer on the surface. In the case of a PSA sheet with a substrate, a method (direct method) can be used in which a PSA composition is directly applied (typically coated) to the substrate and cured to form a PSA layer (transfer method). Alternatively, a method can be used in which a PSA composition is applied to a surface (release surface) having releasability and cured to form a PSA layer on the surface, and then the PSA layer is transferred to the substrate. The release surface can be the surface of a release liner, the back surface of a release-treated substrate, or the like. While the PSA layer disclosed herein is typically formed continuously, it is not limited to this form and may be formed in a regular or random pattern, such as dots or stripes.

[0120] The pressure-sensitive adhesive composition can be applied using a known or conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, die coater, bar coater, knife coater, or spray coater. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. From the viewpoint of promoting the crosslinking reaction and improving production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature is not particularly limited, but can be, for example, about 40 to 100°C, and is usually preferably about 60 to 80°C. For example, drying at the above temperatures (e.g., about 1 to 10 minutes, more specifically, about 3 to 7 minutes) involves a low heating temperature and the progress of solvent volatilization, so that, for example, in a pressure-sensitive adhesive composition containing a monomer or a thermal polymerization initiator, the reaction of the monomer or the deactivation of the thermal polymerization initiator is negligible. After drying the pressure-sensitive adhesive composition, aging may be carried out for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the substrate or pressure-sensitive adhesive layer.

[0121] (Thickness) The thickness of the pressure-sensitive adhesive layer is not particularly limited. The thickness of the pressure-sensitive adhesive layer is usually 1 μm or more, and may be 2 μm or more, or 3 μm or more. The thicker the pressure-sensitive adhesive layer, the more the adhesive strength to the adherend tends to improve. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is 5 μm or more, may be 10 μm or more, may be 15 μm or more, may be 20 μm or more, or may be 25 μm or more. The upper limit of the thickness of the pressure-sensitive adhesive layer is suitably, for example, about 200 μm or less, may be 100 μm or less (e.g., less than 100 μm), or may be 50 μm or less. Limiting the thickness of the pressure-sensitive adhesive layer within a predetermined range tends to prevent the occurrence of adhesive residue due to cohesive failure and to easily obtain peelability. In addition, a thin pressure-sensitive adhesive layer is advantageous in terms of thinning the pressure-sensitive adhesive sheet, and also tends to have excellent conformability to the adherend. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is 40 μm or less, and may be 30 μm or less.

[0122] <Substrate Layer> The pressure-sensitive adhesive sheet disclosed herein may include a substrate layer. Various sheet-like substrates can be used as the substrate (layer) supporting (backing) the pressure-sensitive adhesive layer. Examples of the substrate include resin films, paper, cloth (woven fabric, nonwoven fabric, etc.), rubber sheets, foam sheets, metal foils, and composites thereof. Examples of resin films include polyolefin films; polyester films; vinyl chloride resin films; vinyl acetate resin films; polyamide resin films; fluororesin films; cellophane; and the like. Non-limiting examples of polyester films include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Other examples of resin films include resin films formed from one or more engineering plastics (which may be super engineering plastics) such as polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, and polyimide resins. The use of engineering plastics is preferred from the standpoint of heat resistance.

[0123] In some preferred embodiments, a resin film having a predetermined rigidity (strength) and excellent processability and handling properties is used as the substrate (layer). Among these, from the viewpoint of heat resistance, polyester films, polyamide resin films, and engineering plastic films (e.g., polyimide resin films, etc.) are preferred as the resin film substrate. In this specification, the term "resin film" typically refers to a non-porous film, and typically refers to a resin film that is substantially bubble-free (void-free). Therefore, the above-mentioned resin film is a concept that is distinct from foam films and nonwoven fabrics. The density of the resin film that can be used as the substrate is approximately 0.85 to 1.50 g / cm. ３ (For example, 0.90 g / cm ３ ~1.20 g / cm ３ , typically 0.92 g / cm ３ ~1.05g / cm ３The resin film may have a single layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0124] Although not particularly limited, in some embodiments, the substrate layer has a light transmittance of less than 70% at a wavelength of 355 nm. In some preferred embodiments, the substrate layer's light transmittance at a wavelength of 355 nm may be less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 3%, less than 1%, or less than 0.1%. A substrate layer having the above-mentioned light transmittance at a wavelength of 355 nm may absorb the laser light and break when irradiated with laser light. Therefore, it is particularly meaningful to provide a pressure-sensitive adhesive layer having a light transmittance of 70% or less at a wavelength of 355 nm as disclosed herein to sufficiently reduce the amount of laser light passing through the pressure-sensitive adhesive layer side and protect the substrate layer from the laser light. In some embodiments, the substrate layer's light transmittance at a wavelength of 355 nm may be 0.01% or more, 1% or more, or 10% or more. The light transmittance at a wavelength of 355 nm of the substrate layer can be measured using an ultraviolet-visible-infrared spectrophotometer. More specifically, it can be measured by the method described in the Examples below.

[0125] The substrate layer (e.g., a resin film) may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc. The amount of additives to be added is not particularly limited and can be set appropriately depending on the application, etc.

[0126] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately employed.

[0127] The substrate layer may be substantially composed of a resin film. Alternatively, the substrate layer may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer or an anti-reflection layer), a printing layer or a laminating layer for imparting a desired appearance, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0128] The thickness of the substrate layer is not particularly limited and can be selected appropriately depending on the purpose, but generally can be 1 to 500 μm. From the viewpoints of processability, handleability, workability, etc., the thickness of the substrate layer is suitably 2 μm or more (e.g., 3 μm or more, typically 5 μm or more), and may be approximately 7 μm or more, or 10 μm or more. In some embodiments, the thickness of the substrate layer may be 20 μm or more, 30 μm or more, or 40 μm or more. Furthermore, the thickness of the substrate layer is suitably approximately 200 μm or less, and from the viewpoint of weight reduction and thinning, it is preferably approximately 100 μm or less, more preferably approximately 80 μm or less, and may be 60 μm or less. As the thickness of the substrate layer decreases, the flexibility of the PSA sheet and its ability to conform to the surface shape of the adherend tend to improve.

[0129] The surface of the substrate layer facing the pressure-sensitive adhesive layer may be subjected to conventional surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer, as necessary. Such surface treatments may be intended to improve the adhesion between the substrate layer and the pressure-sensitive adhesive layer, in other words, the anchoring ability of the pressure-sensitive adhesive layer to the substrate layer. The composition of the primer is not particularly limited and can be appropriately selected from known primers. The thickness of the primer layer is not particularly limited, but is suitably about 0.01 μm to 1 μm, and preferably about 0.1 μm to 1 μm. The back surface of the substrate layer may be subjected to the various surface treatments described above or to an antistatic treatment, etc.

[0130] <Total Thickness> The total thickness of the PSA sheet disclosed herein (which may include a PSA layer and a substrate layer, but does not include a release liner) is not particularly limited, and is suitably in the range of approximately 5 to 1000 μm. The total thickness of the PSA sheet may be 10 μm or more, 30 μm or more, or 50 μm or more, from the viewpoints of adhesive properties, handleability, etc. Furthermore, from the viewpoints of weight reduction and thinning, in some embodiments, the total thickness of the PSA sheet is 500 μm or less, or may be 300 μm or less. In some preferred embodiments, the total thickness of the PSA sheet is 150 μm or less, 120 μm or less, or 100 μm or less (e.g., less than 100 μm). Reducing the thickness of the PSA sheet is advantageous in terms of thinning, miniaturization, weight reduction, resource conservation, etc.

[0131] <Release Liner> The release liner used in the PSA sheet disclosed herein is not particularly limited, and examples thereof include release liners in which the surface of a liner substrate such as a resin film or paper has been release-treated, and release liners made of low-adhesion materials such as fluorine-based polymers (polytetrafluoroethylene, etc.) and polyolefin-based resins (polyethylene, polypropylene, etc.). For example, silicone-based or long-chain alkyl-based release treating agents can be used for the release treatment. In some embodiments, a release-treated resin film can be preferably used as the release liner.

[0132] <Characteristics of Pressure-Sensitive Adhesive Sheet> (Post-heat Peel Force Reduction Rate) In some embodiments, the pressure-sensitive adhesive sheet preferably has a post-heat peel force reduction rate of more than 50%, as calculated by the formula: Post-heat peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heat peel force [N / 20 mm] measured in an environment of 23°C after being attached to an adherend and heat-treated at 180°C for 30 minutes, and F0 is the pre-heat peel force [N / 20 mm]). A pressure-sensitive adhesive sheet that satisfies the above properties can adhere well to an adherend, and exhibit good heat-peelability and heat-resistant easy releasability when peeled after heat treatment. In some preferred embodiments, the post-heat peel force reduction rate may be 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, or 95% or more. The greater the post-heat peel strength reduction rate, the better the heat releasability and heat resistance of the adhesive. Furthermore, the post-heat peel strength reduction rate is preferably less than 99.9%. A pressure-sensitive adhesive sheet having a post-heat peel strength reduction rate of less than 99.9% maintains its adhesive state with the adherend after heating while exhibiting the desired releasability from the adherend. This prevents the pressure-sensitive adhesive sheet from spontaneously peeling from the adherend due to heating and the resulting defects. From this perspective, the post-heat peel strength reduction rate may be 99.0% or less, for example, less than 95.0%.

[0133] (Pre-heating peel force F0) Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet suitably has a pre-heating peel force F0 of 1.0 N / 20 mm or more, preferably 2.0 N / 20 mm or more, more preferably 3.0 N / 20 mm or more, even more preferably 4.0 N / 20 mm or more, and particularly preferably 5.0 N / 20 mm or more. A pressure-sensitive adhesive sheet exhibiting the above pre-heating peel force F0 can exhibit good adhesion to an adherend such as a silicon wafer. The upper limit of the pre-heating peel force F0 is appropriately set depending on the required adhesiveness, and is not limited to a specific range, and may be, for example, approximately 30 N / 20 mm or less, or approximately 20 N / 20 mm or less. The pre-heating peel force F0 specifically refers to the peel force against a silicon wafer measured under conditions of a peel angle of 180 degrees and a speed of 300 mm / min in an environment of 23°C. The pre-heating peel force F0 is also referred to as the initial peel force. More specifically, the pre-heat peel force F0 is measured by the method described in the Examples section below.

[0134] (Post-heat peel force F1) Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet preferably has a peel force (post-heat peel force) F1 from an adherend after heat treatment at 180°C for 30 minutes of 5 N / 20 mm or less. A pressure-sensitive adhesive sheet exhibiting the above post-heat peel force F1 has easy heat peelability and may further have heat-resistant easy peelability after heat treatment. From the viewpoint of releasability, in some preferred embodiments, the post-heat peel force F1 is 3 N / 20 mm or less, more preferably 2 N / 20 mm or less, even more preferably 1.5 N / 20 mm or less, particularly preferably 1.2 N / 20 mm or less, and may even be 1.0 N / 20 mm or less. The lower limit of the post-heat peel force F1 may be 0.0 N / 20 mm or more (e.g., 0.1 N / 20 mm or more). Specifically, the post-heat peel force F1 is the peel force measured under conditions of a peel angle of 180° and a peel speed of 300 mm / min in an environment of 23°C after heating the tape attached to an adherend at 180°C for 30 minutes. The adherend used is a silicon wafer. More specifically, the post-heat peel force F1 is measured by the method described in the Examples below.

[0135] <Removal Method> This specification provides a method for removing a pressure-sensitive adhesive sheet attached to an adherend from the adherend. The removal method includes a step of subjecting the adherend to a heat treatment at a predetermined temperature or higher, and then removing the pressure-sensitive adhesive sheet from the adherend. The pressure-sensitive adhesive sheet disclosed herein has heat-removal properties (heat-resistant removability), and therefore can be easily removed from the adherend even after being exposed to heat under predetermined conditions.

[0136] In some embodiments, the temperature of the heat treatment of the adherend to which the PSA sheet is attached is suitably 120°C or higher, and may be about 130°C or higher, or may be about 150°C or higher. In some preferred embodiments, the temperature of the heat treatment of the adherend to which the PSA sheet is attached is higher than 150°C, may be 160°C or higher, or may be 170°C or higher. The upper limit of the heat treatment temperature may vary depending on the purpose of the heat treatment, the heat resistance of the adherend, etc., but is generally about 260°C or lower, may be about 250°C or lower, may be 230°C or lower, may be 200°C or lower, or may be 180°C or lower. The heat treatment time is not particularly limited, and may be within 10 hours, may be within 5 hours, or may be within 3 hours. From the viewpoint of the efficiency of the heating process, etc., in some preferred embodiments, the heat treatment time may be within 1 hour, may be within 30 minutes, may be within 15 minutes, may be within 10 minutes, or may be within 5 minutes. The pressure-sensitive adhesive sheet disclosed herein can exhibit heat-peelability by the short-term heat treatment described above. The heat treatment time may be 1 minute or more, 3 minutes or more, 5 minutes or more, 7 minutes or more, or 9 minutes or more. In some embodiments, the heat treatment time may be 10 minutes or more, 30 minutes or more, 60 minutes or more, or more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. The pressure-sensitive adhesive sheet disclosed herein can be heat-cured by heat treatment at the above-mentioned heating temperature, reducing the release force, and even if the heated state continues for a long time, an increase in the release force (heavy release) can be prevented or suppressed. Therefore, it is possible to maintain heat-peelability (heat-resistant easy peelability) even after long-term heat treatment.

[0137] <Applications> The pressure-sensitive adhesive sheet disclosed herein has heat-peelability, and can therefore be used as a pressure-sensitive adhesive sheet for various applications requiring heat-peelability, such as applications in which the sheet is peeled off and removed from an adherend by heating. For example, the pressure-sensitive adhesive sheet can be used in applications in which the sheet may be exposed to heat above 100°C (e.g., about 120°C or higher and 260°C or lower) while attached to an adherend. The pressure-sensitive adhesive sheet can also be preferably used in applications in which the sheet may be exposed to heat above 150°C (e.g., about 160°C or higher and 260°C or lower) while attached to an adherend.

[0138] The pressure-sensitive adhesive sheet disclosed herein is also suitable for applications in which laser light irradiation is performed for processing, etc., of an adherend material. The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer capable of sufficiently reducing ultraviolet laser light. Therefore, for example, when processing, etc., of an adherend material by laser light irradiation while holding the adherend on the adhesive surface of the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive sheet substrate and the object on the opposite side of the pressure-sensitive adhesive sheet can be protected from the laser light. The wavelength of the laser light is not limited to a specific wavelength, and it is preferable to use a laser with an oscillation wavelength in the ultraviolet range (wavelength 10 to 400 nm). For example, a KrF excimer laser with an oscillation wavelength of 248 nm, a XeCI excimer laser with an oscillation wavelength of 308 nm, or a YAG laser with a third harmonic (355 nm) or fourth harmonic (266 nm) can be used. Alternatively, even in the case of lasers with wavelengths of 400 nm or more, it is possible to absorb light in the ultraviolet region via the multiphoton absorption process, and cutting widths of 20 μm or less can be achieved by multiphoton absorption ablation using titanium sapphire lasers with wavelengths of around 750 to 800 nm and a pulse width of 1 e －９ Lasers with a wavelength of 355 nm or less can be used. In particular, the pressure-sensitive adhesive sheet disclosed herein is preferably used for applications using ultraviolet laser light with a wavelength of 355 nm, which can be focused into a narrow beam and can perform high-precision laser processing.

[0139] Examples of applications for the pressure-sensitive adhesive sheet disclosed herein include temporary fixing applications requiring heat resistance from the pressure-sensitive adhesive sheet. For example, it can be preferably used as a process material that is fixed to an adherend and then peeled off in the manufacturing process of electronic devices and electronic components. Another suitable application for the pressure-sensitive adhesive sheet disclosed herein is the manufacturing of semiconductor elements. For example, it can be preferably used as a wafer fixing sheet that fixes the wafer to a fixing plate in semiconductor wafer processing (typically silicon wafer processing). For example, it can be preferably used as a process material that is peeled off from the semiconductor after processing while the semiconductor wafer is held by the pressure-sensitive adhesive layer. Since laser light can be used to process the semiconductor wafer, it is meaningful to use the pressure-sensitive adhesive sheet disclosed herein. Furthermore, during the manufacturing of semiconductor elements, the sheet may be exposed to heat during processing steps, etc., so a heat-resistant, easily peelable pressure-sensitive adhesive sheet is preferably used.

[0140] The type of material (adherend material) to which the pressure-sensitive adhesive sheet disclosed herein is attached is not particularly limited. The pressure-sensitive adhesive sheet disclosed herein can be used for fixing various members and materials. The adherend material can be made of an organic material, an inorganic material, or a composite thereof. Examples of the adherend material include glass such as alkali glass or alkali-free glass; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; and resin materials such as polyester resins such as PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, transparent polyimide resins, epoxy resins, and phenolic resins. Suitable examples of the adherend material include glass materials such as alkali glass and semiconductor wafers.

[0141] The matters disclosed in this specification include the following. [1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises a polymer and a thermal polymerization initiator, the polymer comprises an ethylenically unsaturated group, the content of the thermal polymerization initiator in the pressure-sensitive adhesive layer is 0.01 parts by weight or more relative to 100 parts by weight of the polymer, and the pressure-sensitive adhesive layer has a light transmittance of 70% or less at a wavelength of 355 nm. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the pressure-sensitive adhesive layer comprises an ultraviolet absorber A having an absorbance of 0.01 or more at a wavelength of 355 nm. [3] The pressure-sensitive adhesive sheet according to [1] above, wherein the content of the ultraviolet absorber A in the pressure-sensitive adhesive layer is 0.01 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the polymer. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the post-heat peel strength from a silicon wafer after heat treatment at 180°C for 30 minutes is 3 N / 20 mm or less.

[0142] [5] A pressure-sensitive adhesive composition comprising a polymer and a thermal polymerization initiator, the polymer containing an ethylenically unsaturated group, the content of the thermal polymerization initiator being 0.01 parts by weight or more relative to 100 parts by weight of the polymer, and having a light transmittance of 70% or less at a wavelength of 355 nm when molded into a sheet having a thickness of 30 μm. [6] The pressure-sensitive adhesive composition according to [5] above, comprising an ultraviolet absorber A having an absorbance of 0.01 or more at a wavelength of 355 nm. [7] The pressure-sensitive adhesive composition according to [6] above, wherein the content of the ultraviolet absorber A is 0.01 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the polymer.

[0143] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0144] <Evaluation Method> (Pre-heating Peel Force F0) A pressure-sensitive adhesive sheet is cut to a size of 20 mm wide and 100 mm long, and the adhesive surface of the pressure-sensitive adhesive sheet is pressed against an adherend using a hand roller under an environment of 23°C and 50% RH. The adherend with the pressure-sensitive adhesive sheet attached is left to stand for 2 hours under the same environment, and this is used as an evaluation sample. The evaluation sample is placed in a tensile tester under an environment of 23°C and 50% RH, and the peel strength (pre-heating peel force) F0 [N / 20 mm width] is measured when the pressure-sensitive adhesive sheet is peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min. A silicon wafer (6 inch N<100>-100, manufactured by Shin-Etsu Chemical Co., Ltd.) is used as the adherend, and the adhesive surface of the pressure-sensitive adhesive sheet is attached to the mirror surface of the silicon wafer for measurement. The tensile tester may be a Shimadzu product named "EZ-S 500N" or an equivalent product. When the evaluation object is a double-sided PSA sheet, the measurement may be performed with the non-measurement side lined with a PET film.

[0145] (Post-heat peel force F1) Using a pressure-sensitive adhesive sheet, an evaluation sample is prepared using the method described above for measuring the pre-heat peel force F0. The obtained evaluation sample is heated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand for 30 minutes in an environment of 23°C and 50% RH. The evaluation sample is then placed in a tensile tester under the same conditions, and the peel strength (post-heat peel force) F1 [N / 20 mm width] is measured when the pressure-sensitive adhesive sheet is peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min. The adherend, tensile tester, and other factors are the same as those for measuring the pre-heat peel force F0.

[0146] (Reduction rate of peeling force after heating) The reduction rate of peeling force after heating is calculated from the above-mentioned pre-heating peeling force F0 and post-heating peeling force F1 according to the following formula: Reduction rate of peeling force after heating [%] = (1 - F1 / F0) x ​​100

[0147] (Light transmittance at a wavelength of 355 nm) A pressure-sensitive adhesive composition was applied to the release surface of a commercially available PET release liner (light transmittance at a wavelength of 355 nm of 85%), and the resulting pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) of a predetermined thickness (30 μm in the example below) was cut into a size of 50 mm x 50 mm to prepare an evaluation sample (pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) with a release liner). The prepared evaluation sample was placed in a UV-Vis-IR spectrophotometer, and the absorbance A1 at a wavelength of 355 nm was measured. The absorbance A of the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) alone was calculated from the difference (A1 - A0) between the absorbance A0 of the release liner alone, which had been measured in advance using the UV-Vis-IR spectrophotometer, and the above absorbance A1. The light transmittance [%] of the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) at a wavelength of 355 nm was then determined from the obtained absorbance A. The relationship between absorbance A and light transmittance T is A = 2 - log (%T). If the light transmittance of the PSA layer at a wavelength of 355 nm is 70% or less, it is determined that the amount of ultraviolet laser light passing through is sufficiently reduced. A Hitachi High-Technologies Corporation product, model UH4150, or an equivalent can be used as the UV-Vis-IR spectrophotometer. Alternatively, the PSA layer (pressure-sensitive adhesive sheet) with a release liner and the corresponding release liner alone may be obtained, and the light transmittance [%] of the PSA layer (pressure-sensitive adhesive sheet) at a wavelength of 355 nm may be determined by the method described above. The light transmittance of the substrate (layer) and the PSA sheet with the substrate at a wavelength of 355 nm can be measured using the substrate (layer) and the PSA sheet with the substrate as evaluation samples using the UV-Vis-IR spectrophotometer described above.

[0148] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer was charged with 100 parts of a monomer component containing methoxyethyl acrylate (MEA), acryloylmorpholine (ACMO), and hydroxyethyl acrylate (HEA) in a molar ratio of 80:20:20, and 65 parts of toluene as a polymerization solvent. 0.2 parts of benzoyl peroxide was added as a thermal polymerization initiator, and a polymerization reaction (solution polymerization) was carried out for 6 hours at 61°C under a nitrogen atmosphere to obtain a solution containing an acrylic polymer a. To this solution of acrylic polymer a, methacryloyloxyethyl isocyanate (MOI) in an amount equivalent to 16 moles relative to 20 moles of HEA used as a raw material for the acrylic polymer a was added, and an addition reaction treatment was carried out in an air stream at 50°C for 48 hours to obtain a solution of an acrylic polymer A having a methacryloyl group at the side chain end. To 100 parts of acrylic polymer A, 20 parts of dipentaerythritol hexaacrylate (DPHA) as a monomer, 0.5 parts of an isocyanate crosslinking agent (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-101E"), 0.8 parts of benzoyl peroxide (manufactured by NOF Corporation, trade name "Niper BW", SADT: 75°C) as a thermal polymerization initiator, and 0.5 parts of an ultraviolet absorber (manufactured by BASF, trade name "Tinuvin 326", absorbance at 355 nm: 0.95) were added and mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example.

[0149] (Preparation of Pressure-Sensitive Adhesive Sheet) The pressure-sensitive adhesive composition obtained above was applied to the release surface of a commercially available PET release liner and dried at 80°C for 5 minutes to form a 30 μm thick pressure-sensitive adhesive layer. A 50 μm thick polyimide (PI) film (trade name "Kapton 200H", manufactured by DuPont-Toray Co., Ltd., light transmittance at a wavelength of 355 nm: 0.01%) was laminated to this pressure-sensitive adhesive layer, and then aging was carried out at 50°C for 3 days. In this way, a pressure-sensitive adhesive sheet (single-sided pressure-sensitive adhesive sheet with a substrate) according to this example was prepared. The adhesive surface of the pressure-sensitive adhesive sheet was protected by the release liner.

[0150] Examples 2 to 9 and Comparative Example 1 A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 1, except that the type and amount of UV absorber and the amount of monomer (DHPA) were changed as shown in Table 1, and the resulting pressure-sensitive adhesive composition was used to produce a substrate-attached single-sided PSA sheet according to each example in the same manner as in Example 1. In Table 1, Tinosorb S represents a UV absorber manufactured by BASF (trade name "Tinosorb S", absorbance at 355 nm: 0.93), Uvinul A Plus represents a UV absorber manufactured by BASF (trade name "Uvinul A Plus", absorbance at 355 nm: 1.0), and Uvinul 3035 represents a UV absorber manufactured by BASF (trade name "Uvinul 3035", absorbance at 355 nm: 0.04).

[0151] The outline of each example and the evaluation results are shown in Table 1.

[0152]

[0153] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0154] REFERENCE SIGNS LIST 1 Pressure-sensitive adhesive sheet 1A Adhesive surface 1B Back surface 10 Base material layer 10A One surface 10B Other surface 20 Pressure-sensitive adhesive layer 20A Surface of pressure-sensitive adhesive layer 30 Release liner 50 Pressure-sensitive adhesive sheet with release liner

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises a polymer and a thermal polymerization initiator, the polymer comprises an ethylenically unsaturated group, the content of the thermal polymerization initiator in the pressure-sensitive adhesive layer is 0.01 parts by weight or more per 100 parts by weight of the polymer, and the pressure-sensitive adhesive layer has a light transmittance of 70% or less at a wavelength of 355 nm.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer contains an ultraviolet absorber A having an absorbance of 0.01 or more at a wavelength of 355 nm.

3. The pressure-sensitive adhesive sheet according to claim 2, wherein the content of said ultraviolet absorber A in said pressure-sensitive adhesive layer is 0.01 parts by weight or more and 50 parts by weight or less per 100 parts by weight of said polymer.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which has a post-heat peel strength of 3 N / 20 mm or less from a silicon wafer after heat treatment at 180°C for 30 minutes.

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