Adhesive sheet, structure, method for producing structure, and method

Abstract

Provided is an adhesive sheet that is equipped with a base material, is easy to peel when heated, and suitably maintains adhesion even after heat treatment. The adhesive sheet has a base material layer and an adhesive layer. The adhesive layer contains a polymer and a thermal polymerization initiator. The polymer includes an ethylenically unsaturated group. The adhesive sheet has a post-heating peel force decrease rate of more than 50% and no more than 99.9%. The base material layer has a tensile elongation of 100% or more at 23°C and a tensile elongation of 100% or more even after being subjected to heat treatment at 180°C for 30 minutes.

Description

Pressure-sensitive adhesive sheet, structure, and method for manufacturing the structure

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a structure, and a method and method for manufacturing a structure. This application claims priority to Japanese Patent Application No. 2024-056873, filed on March 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 in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to an adherend by applying pressure. Because of their ease of application to an adherend, adhesives are widely used in a variety of fields, for example, in the form of a supported adhesive sheet having an adhesive layer on 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. Patent documents disclosing this type of conventional technology include Patent Documents 1 to 4. Patent Documents 1 to 4 disclose thermosetting adhesives.

[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

[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 and have been conducting research and development, and have succeeded in obtaining an adhesive that remains easily releasable (heat-peelable) even after being attached to an adherend and heated at high temperatures. Such heat-peelable property can also be referred to as heat-resistant peelability, since it remains easily releasable even after heat treatment, which usually increases the peel strength. A pressure-sensitive adhesive sheet with such heat-peelable property can be designed to maintain a certain level of adhesiveness and maintain its adhesive state with the adherend even after heat treatment, in order to prevent unintentional peeling, such as the pressure-sensitive adhesive sheet naturally peeling off from the adherend after heat treatment and before removal from the adherend.

[0007] In addition, when the pressure-sensitive adhesive sheet having the above-mentioned heat-peelability is configured as a substrate-attached pressure-sensitive adhesive sheet having a substrate (support), the substrate used must have heat resistance so that it can maintain a predetermined performance even after being exposed to high-temperature heat treatment. However, substrates with excellent heat resistance generally tend to have high rigidity, which can sometimes limit the expected performance. Specifically, when a pressure-sensitive adhesive sheet having a heat-resistant substrate is attached to an adherend and subjected to heat treatment, and then a load is applied to a part of the pressure-sensitive adhesive sheet before being removed from the adherend, even if it is static, due to the high rigidity of the heat-resistant substrate, a load is likely to be applied to the adhesive part, and therefore the retention of the adhesive state with the adherend tends to decrease. Thus, there is a technical trade-off between the heat resistance of the substrate and the retention of the adhesive state with the adherend after heat treatment.

[0008] The present invention was made in view of the above circumstances, and has an object to provide a substrate-attached pressure-sensitive adhesive sheet that has easy heat-peelability and maintains a good adhesive state even after heat treatment.

[0009] According to this specification, a pressure-sensitive adhesive sheet is provided that has a substrate layer and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer contains a polymer and a thermal polymerization initiator. The polymer contains an ethylenically unsaturated group. The pressure-sensitive adhesive sheet has a post-heat peel force reduction rate of more than 50% and not more than 99.9%. The post-heat peel force reduction rate is calculated using the formula: Post-heat peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heat peel force F1 [N / 20 mm] measured in an environment at 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heat peel force F0 [N / 20 mm] from the silicon wafer). The substrate layer also has a tensile elongation of 100% or more at 23°C, and maintains a tensile elongation of 100% or more even after heat-treatment at 180°C for 30 minutes. A pressure-sensitive adhesive sheet that satisfies the above-mentioned pressure-sensitive adhesive composition and post-heat peel strength reduction rate is cured by heat treatment, reducing the peel strength and exhibiting heat-sensitive peelability. Specifically, the pressure-sensitive adhesive sheet maintains a good adhesion state with the adherend after heat treatment, while exhibiting the above-mentioned heat-sensitive peelability, allowing it to be easily peeled from the adherend during peeling. Furthermore, the base layer has a tensile elongation of 100% or more at 23°C, and a tensile elongation of 100% or more even after heat treatment at 180°C for 30 minutes, so that the retention of the adhesion state with the adherend after heat treatment can be improved.

[0010] This specification also provides a pressure-sensitive adhesive sheet having a substrate layer and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer contains a polymer and a thermal polymerization initiator. The polymer contains an ethylenically unsaturated group. The pressure-sensitive adhesive sheet has a post-heat peel strength reduction rate of more than 50% and not more than 99.9%. The post-heat peel strength reduction rate is calculated using the formula: Post-heat peel strength reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heat peel strength F1 [N / 20 mm] measured in an environment at 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heat peel strength F0 [N / 20 mm] from the silicon wafer). The substrate layer also has a heat shrinkage rate of less than 1% in a heat shrinkage test in which the sheet is heated at 200°C for 10 minutes. The pressure-sensitive adhesive sheet has a tensile elongation of 80% or more at 23°C. A pressure-sensitive adhesive sheet that satisfies the above-mentioned pressure-sensitive adhesive composition and post-heat peel strength reduction rate is cured by heat treatment, reducing the peel strength and exhibiting heat-sensitive releasability. Specifically, the pressure-sensitive adhesive sheet exhibits the heat-sensitive releasability described above while maintaining a good adhesion state with the adherend after heat treatment, and can be easily peeled from the adherend during peeling. Furthermore, since the pressure-sensitive adhesive sheet includes a substrate layer having heat resistance with a heat shrinkage rate of less than 1% and has a tensile elongation of 80% or more at 23°C, the retention of the adhesion state with the adherend after heat treatment can be improved.

[0011] In some embodiments, the substrate layer is made of a polyimide film, an acrylic resin film, an epoxy resin film, a fluororesin film, or a polyester film. The technology disclosed herein is preferably implemented in an embodiment including a substrate layer made of the above-mentioned resin film. In particular, the substrate layer is preferably made of a polyimide film or a polyester film.

[0012] In some embodiments, the thickness of the substrate layer is 5 μm or more and 130 μm or less. In a configuration including a substrate layer having a thickness within a predetermined range, the effects of the technology disclosed herein are preferably exhibited.

[0013] The pressure-sensitive adhesive sheet disclosed herein has heat-peelability and can be easily peeled from an adherend, and therefore can be preferably used in various methods in which the sheet is attached to an adherend and then peeled and removed from the adherend. For example, the pressure-sensitive adhesive sheet is preferably used in a method including a processing step of processing the adherend as an object to be processed to which the pressure-sensitive adhesive sheet is attached, and a peeling step of peeling the pressure-sensitive adhesive sheet from the adherend after the processing step.

[0014] The present specification also provides a structure comprising any one of the pressure-sensitive adhesive sheets disclosed herein and a substrate to which the pressure-sensitive adhesive sheet is attached. The pressure-sensitive adhesive sheet disclosed herein is used in the form of a structure comprising the pressure-sensitive adhesive sheet and the substrate, for example, after being attached to a substrate as an adherend.

[0015] This specification also provides a method for producing a structure comprising any one of the pressure-sensitive adhesive sheets disclosed herein and a substrate. This production method includes a step of attaching the pressure-sensitive adhesive sheet to the substrate. The pressure-sensitive adhesive sheet disclosed herein is used, for example, in the form of the structure obtained as described above.

[0016] Furthermore, the pressure-sensitive adhesive sheet disclosed herein can be preferably used for processing an adherend using the pressure-sensitive adhesive sheet. Thus, according to this specification, for example, a method is provided that includes a processing step of processing a substrate to which any of the pressure-sensitive adhesive sheets disclosed herein has been attached. Such a method may further include a peeling step of peeling the pressure-sensitive adhesive sheet from the substrate after the processing step. The pressure-sensitive adhesive sheet disclosed herein has heat-peelability and can be easily peeled from the adherend, making it suitable for various methods that include the peeling step described above.

[0017] 1 is a cross-sectional view schematically showing one embodiment of a pressure-sensitive adhesive sheet, and FIGURE 2 is a cross-sectional view schematically showing another embodiment of a pressure-sensitive adhesive sheet.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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."

[0023] <Configuration of Pressure-Sensitive Adhesive Sheet> The pressure-sensitive adhesive sheet disclosed herein is configured to include a pressure-sensitive adhesive layer, and is a substrate-attached pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on one or both sides of a substrate (support substrate). The concept of pressure-sensitive adhesive sheet referred to here may include what are called pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, pressure-sensitive adhesive films, etc. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be a pressure-sensitive adhesive sheet processed into various shapes.

[0024] The cross-sectional structure of a pressure-sensitive adhesive sheet according to one embodiment is shown in Figure 1. As shown in Figure 1, the pressure-sensitive adhesive sheet 1 has an adhesive surface 1A, and is in the form of a single-sided pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer 20 is provided on one surface 10A of a sheet-like base layer (supporting substrate) 10. The pressure-sensitive adhesive sheet 1 is used by attaching the surface 20A of the pressure-sensitive adhesive layer 20, which is the adhesive surface 1A, to an adherend. The back surface 10B of the base layer 10 (the surface opposite to the one surface 10A) also serves as the back surface 1B of the pressure-sensitive adhesive sheet 1, and constitutes the outer surface of the pressure-sensitive adhesive sheet 1. Before use (i.e., before being attached to an adherend), the pressure-sensitive adhesive sheet 1 may be in the form of a release-liner-attached pressure-sensitive adhesive sheet 100 in which the adhesive surface 1A is protected by a release liner 30, the side of which facing at least the pressure-sensitive adhesive 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).

[0025] The pressure-sensitive adhesive sheet may also have a cross-sectional structure shown in Fig. 2, for example. The pressure-sensitive adhesive sheet 2 shown in Fig. 2 is in the form of a single-sided pressure-sensitive adhesive sheet including a sheet-like substrate layer (support substrate) 10, an undercoat layer 15 provided on a first surface 10A of the substrate layer 10, and a pressure-sensitive adhesive layer 20 provided on the first surface 15A of the undercoat layer 15. The pressure-sensitive adhesive sheet 2 is used by attaching the surface 20A of the pressure-sensitive adhesive layer 20, which is its adhesive surface 2A, to an adherend. More specifically, the second surface 15B of the undercoat layer 15 is in contact with the first surface 10A of the substrate layer 10, and the first surface 15A is in contact with the pressure-sensitive adhesive layer 20. The second surface (back surface) 10B of the substrate layer 10 is also the back surface 2B of the pressure-sensitive adhesive sheet 2 and constitutes the outer surface of the pressure-sensitive adhesive sheet 2. The PSA sheet 2 before use (i.e., before attachment to an adherend) may be in the form of a PSA sheet 200 with a release liner, in which the adhesive surface 2A is protected by a release liner 30, the release surface of which is at least the PSA layer 20 side. Alternatively, the PSA sheet may be in the form in which the other surface (back surface) 10B of the base layer 10 is the release surface, and the PSA sheet 2 is wound into a roll so that the PSA layer 20 abuts against the back surface, thereby protecting the surface (adhesive surface 2A).

[0026] <Characteristics of Pressure-Sensitive Adhesive Sheet> (Tensile Elongation at 23°C) In some embodiments, the pressure-sensitive adhesive sheet preferably has a tensile elongation of 80% or more at 23°C. In some embodiments, the pressure-sensitive adhesive sheet preferably includes a substrate layer that has heat-resistance and exhibits a heat shrinkage rate of less than 1% in a heat shrinkage test described below, and has a tensile elongation of 80% or more at 23°C. A pressure-sensitive adhesive sheet that satisfies the above configuration and characteristics can improve the ability to maintain its adhesive state with an adherend after heat treatment by including the heat-resistant substrate layer. With such a pressure-sensitive adhesive sheet, when an external force that deforms the pressure-sensitive adhesive sheet is applied after heat treatment and before peeling, for example, the pressure-sensitive adhesive sheet is less likely to lose its adhesive state with the adherend and to unintentionally peel off. From the viewpoint of improving the ability to maintain the adhesive state, in some preferred embodiments, the tensile elongation at 23°C may be 85% or more, 90% or more, 95% or more, or 100% or more. Furthermore, the upper limit of the tensile elongation at 23°C is not particularly limited, and in some preferred embodiments, from the viewpoint of achieving both the heat resistance of the base layer and the ability to maintain the adhesive state, it may be 200% or less, 150% or less, or 120% or less.

[0027] The tensile elongation of the PSA sheet at 23° C. is specifically measured by the method described in the Examples below. The tensile direction in the measurement of the tensile elongation can be any one direction of the PSA sheet, but is preferably the MD (Machine Direction) or TD (Transverse Direction) of the base layer, and is preferably the MD of the base layer.

[0028] (Post-heat peel force reduction rate) In some embodiments, the PSA sheet preferably has a post-heat peel force reduction rate of more than 50%, as determined by the formula: Post-heat peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (In the above formula, 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 220°C for 30 minutes, and F0 is the pre-heat peel force [N / 20 mm].) A PSA sheet satisfying the above properties can adhere well to an adherend, and can exhibit good heat-peelability and heat-resistant 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 92% or more. The greater the post-heat peel force reduction rate, the more excellent heat-peelability and heat-resistant releasability can be exhibited. 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% can maintain its adhesive state with the adherend before post-heat peeling while retaining easy heat peelability. This can prevent 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, 98.0% or less, 97.0% or less, 96.0% or less, or 95.0% or less.

[0029] (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 3.0 N / 20 mm or more, more preferably 5.0 N / 20 mm or more, even more preferably 7.0 N / 20 mm or more, particularly preferably 10.0 N / 20 mm or more, and may be 12 N / 20 mm or more, or may be 15 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-heating peel force F0 is measured by the method described in the examples below.

[0030] (Post-heat peel force F1) Although not particularly limited, in some embodiments, the PSA sheet preferably has a peel force (post-heat peel force) F1 from an adherend after heat treatment at 220°C for 30 minutes of heating of 5 N / 20 mm or less. A PSA 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, even more 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, or may be 0.01 N / 20 mm or more. A PSA sheet having a post-heat peel force F1 of a predetermined value or more has easy heat peelability and can maintain its adhesion to the adherend before post-heat peeling. This can prevent the PSA sheet from spontaneously peeling off from the adherend due to heating and the resulting defects. From this perspective, in some preferred embodiments, the post-heating peel force F1 may be, for example, 0.1 N / 20 mm or more, 0.2 N / 20 mm or more, 0.3 N / 20 mm or more, 0.5 N / 20 mm or more, 0.7 N / 20 mm or more, or 1.0 N / 20 mm or more. Specifically, the post-heating peel force F1 refers to the peel force measured under conditions of a peel angle of 180 degrees and a peel speed of 300 mm / min in an environment of 23 ° C after heat treatment at 220 ° C for 30 minutes while attached to the adherend. A silicon wafer is used as the adherend. More specifically, the post-heating peel force F1 is measured by the method described in the Examples below.

[0031] <Adhesive Layer> (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 adhesives 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 base polymers are preferably used. Among these, adhesives (acrylic adhesives) that use acrylic polymers with excellent heat resistance as the base polymer are preferred. In this specification, the polymer contained in the adhesive layer is also referred to as polymer A.

[0032] Hereinafter, the following description will be mainly focused 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.

[0033] (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.

[0034] 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 may be included in the pressure-sensitive adhesive layer described below (hereinafter, sometimes referred to as "compound monomers" to distinguish them from the monomer components used in synthesizing the polymer). The alkoxy group-containing (meth)acrylates may be used alone or in combination of two or more.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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)acrylates. 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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).

[0055] 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. The use of a polyfunctional monomer as a monomer component can enhance the cohesive strength of the pressure-sensitive adhesive. 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 the polyfunctional monomers exemplified as blending monomers that can be contained in the pressure-sensitive adhesive layer described below can be used alone or in combination.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] (Polymer Having an Ethylenically Unsaturated Group) The adhesive layer disclosed herein contains a polymer having an ethylenically unsaturated group. The ethylenically unsaturated group functions as a polymerizable functional group (typically a radically polymerizable functional group). As the polymer having an ethylenically unsaturated group, for example, one or more suitable polymers can be selected from the various polymers (e.g., acrylic polymers) exemplified above and having an ethylenically unsaturated group. The polymer having an ethylenically unsaturated group can be used as a base polymer in an adhesive. When an adhesive containing the polymer having an ethylenically unsaturated group reacts with the ethylenically unsaturated group during heat treatment, the adhesive can be thermally cured to a high degree, resulting in easy heat peelability. More specifically, when an adhesive is heated, for example, at a high temperature while attached to an adherend, it usually adsorbs to the surface of the adherend. As a result, the adhesive strength of the adhesive to the adherend increases, resulting in heavy peelability. According to the technology disclosed herein, by incorporating a polymer having an ethylenically unsaturated group and a thermal polymerization initiator into the adhesive, the ethylenically unsaturated groups in the adhesive react (radical polymerization reaction) upon heating, allowing the adhesive to harden prior to adsorption to the adherend. This reduces the peel strength from the adherend. Furthermore, even if heating is continued thereafter, the peel strength of the adhesive from the adherend does not increase but is maintained within a predetermined range, allowing the adhesive to exhibit good heat-peelability. However, the technology disclosed herein is not limited to the above considerations. A pressure-sensitive adhesive containing a polymer having an ethylenically unsaturated group can achieve sufficient heat-peelability and heat-resistant heat-peelability without relying on the use of the compounded monomer described below, or while limiting the amount of compounded monomer used.

[0062] Examples of the ethylenically unsaturated group contained in the polymer 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.

[0063] 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.

[0064] 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.

[0065] 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

[0066] 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.

[0067] 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.

[0068] 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).

[0069] 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).

[0070] 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.

[0071] 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. ４ More 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 ４Here, 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 "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) may be used.

[0072] (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.

[0073] 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.

[0074] 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 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 during heat treatment and the easier it is to obtain heat-peelable properties. Furthermore, polyfunctional monomers 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. Polyfunctional monomers having the above number of ethylenically unsaturated groups tend to easily achieve both good adhesion and heat-peelable properties and also tend to have excellent storage stability.

[0079] 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.

[0080] 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.

[0081] 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 even 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. 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 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. It may be 120 parts by weight or less, or even 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 the 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.

[0082] 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.

[0083] 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.

[0084] 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. 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 relative to 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 relative to 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.

[0085] 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.

[0086] (Thermal Polymerization Initiator) The pressure-sensitive 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 the thermal polymerization initiator in the pressure-sensitive adhesive layer, the thermal polymerization initiator reacts with ethylenically unsaturated groups in the pressure-sensitive adhesive layer during heat treatment at a predetermined temperature or higher, thereby reducing the peel force and achieving heat-peelability. By including the thermal polymerization initiator, a thermosetting pressure-sensitive adhesive that retains heat-resistant easy peelability even after heat treatment can be formed.

[0087] 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.

[0088] 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 as the thermal polymerization initiator, the curing reaction of the pressure-sensitive adhesive layer during heat treatment proceeds rapidly, making it easier to achieve excellent 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 the -O-O- moiety occurs. This recombined initiator can undergo another cleavage reaction during the specified heat treatment, 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 faster reaction rate 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 thought that the peel force after heating is effectively reduced, making it easier to obtain excellent heat-peelability and heat-resistant peelability. Note that the technology disclosed herein is not limited to the above considerations.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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).

[0098] (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.

[0099] 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.

[0100] 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").

[0101] 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.

[0102] As the oxazoline-based crosslinking agent, any agent having one or more oxazoline groups in one 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.

[0103] 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 good balance of adhesive properties 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, ethylenically unsaturated groups 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.

[0104] 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 well-balanced adhesive property such as adhesive strength and cohesive strength, and may be, for example, 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, and at such a crosslinking density, ethylenically unsaturated groups in the adhesive layer frequently collide with the thermal polymerization initiator during heat treatment, causing thermal curing to proceed, and the desired heat-peelability and heat-peelability resistance tend to be easily obtained. 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.

[0105] 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.

[0106] 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.

[0107] (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.

[0108] (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.

[0109] (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.

[0110] For example, a method can be employed 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 such an embodiment, a PSA sheet with a substrate can be produced by transferring the PSA layer formed on the release surface to a substrate (or the surface of the undercoat layer in an embodiment in which a primer layer is formed on the substrate; the same applies hereinafter unless otherwise specified). Alternatively, a method (direct method) can be employed in which a PSA composition is directly applied (typically coated) to a substrate and cured to form a PSA layer. 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.

[0111] 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 further 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.

[0112] (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.

[0113] <Substrate Layer> The pressure-sensitive adhesive sheet disclosed herein has a substrate layer. In the pressure-sensitive adhesive sheet, the substrate layer is used as a substrate supporting (backing) the pressure-sensitive adhesive layer. In some embodiments, it is preferable to use a heat-resistant substrate (layer). A substrate (layer) with a predetermined heat resistance does not undergo deformation such as shrinkage or only undergoes a small degree of deformation, and performance can be maintained even after high-temperature heat treatment such as 200°C or higher. For example, the anchoring properties of the pressure-sensitive adhesive layer can be well maintained during peeling after heat treatment. Although not particularly limited, the heat-resistant substrate (layer) preferably has a heat shrinkage rate of less than 1% in a heat shrinkage test performed at 200°C for 10 minutes based on Clause 25 of JIS C2151:2019. From the viewpoint of obtaining better heat resistance, the heat shrinkage rate of the substrate (layer) may be 0.7% or less, 0.5% or less, 0.3% or less, or 0.1% or less (e.g., 0 to 0.1%). The heat shrinkage test is a test in which a test piece obtained by cutting a substrate material to a size of 100 mm x 100 mm is hung in a hot air circulating thermostatic chamber set to 200°C without applying force for 10 minutes, and then cooled to room temperature. The heat shrinkage rate is determined from the dimensional change before and after heating in the test. The heat shrinkage rate obtained in the heat shrinkage test is also used in the examples described below. Hereinafter, a substrate (layer) having the above-described heat resistance may be referred to as a heat-resistant substrate (layer).

[0114] Furthermore, it is preferable to use a substrate (layer) having extensibility such that the pressure-sensitive adhesive sheet has a tensile elongation of 80% or more at 23° C. For example, a substrate having both such mechanical properties and heat resistance can preferably achieve both excellent heat resistance and the ability to maintain the adhesive state with the adherend after heat treatment.

[0115] In some embodiments, the tensile elongation of the substrate (layer) at 23 ° C. is approximately 80% or more, may be approximately 85% or more, may be approximately 90% or more, or may be approximately 95% or more. From the viewpoint of obtaining a pressure-sensitive adhesive sheet having good mechanical properties and good adhesion state retention with an adherend, in some preferred embodiments, the tensile elongation of the substrate (layer) at 23 ° C. is approximately 100% or more, more preferably 110% or more, even more preferably 120% or more, and particularly preferably 130% or more. Furthermore, the upper limit of the tensile elongation at 23 ° C. is not particularly limited, and may be, for example, 1000% or less, 800% or less, 600% or less, or 500% or less. From the viewpoint of achieving both heat resistance and adhesion state retention, in some embodiments, the tensile elongation of the substrate (layer) at 23 ° C. may be approximately 300% or less, may be approximately 200% or less, may be approximately 150% or less, or may be approximately 120% or less. The tensile elongation of the substrate (layer) at 23° C. can be measured by the method described in the Examples below. The tensile direction in the measurement of the tensile elongation can be any one direction, but is preferably the MD or TD of the substrate (layer), and more preferably the MD of the substrate layer.

[0116] Furthermore, it is preferable to use a substrate (layer) having a tensile elongation of 80% or more after heat treatment at 180°C for 30 minutes (tensile elongation after heating at 180°C). A substrate satisfying these characteristics allows the substrate to have predetermined mechanical properties and easily maintain its performance even after heat treatment. The tensile elongation of the substrate (layer) after heating at 180°C may be approximately 85% or more, approximately 90% or more, or approximately 95% or more. In some preferred embodiments, the tensile elongation of the substrate (layer) after heating at 180°C is approximately 100% or more, more preferably 110% or more, even more preferably 120% or more, and particularly preferably 130% or more. For example, it is preferable to use a substrate (layer) having a tensile elongation of 100% or more at 23°C and a tensile elongation of 100% or more after heating at 180°C. A pressure-sensitive adhesive sheet having such a substrate can maintain a good adhesive state with the adherend even after heat treatment. The upper limit of the tensile elongation after heating at 180 ° C is not particularly limited, and may be, for example, 1000% or less, 800% or less, 600% or less, or 500% or less. From the viewpoint of achieving both heat resistance and retention of the adhesive state, in some embodiments, the tensile elongation of the substrate (layer) after heating at 180 ° C may be approximately 300% or less, approximately 200% or less, approximately 150% or less, approximately 140% or less, or approximately 130% or less. The tensile elongation of the substrate (layer) after heating at 180 ° C can be specifically measured by the method described in the Examples below. Note that the tensile direction in measuring the tensile elongation can be any one direction, but it is preferably the MD or TD of the substrate (layer), and preferably the MD of the substrate layer.

[0117] Although not particularly limited, it is preferable that the difference (|E(23°C)-E(180°C)|) between the tensile elongation at 23°C (E(23°C)) [%] and the tensile elongation after heating at 180°C (E(180°C)) [%] of the substrate (layer) is 100 or less. By using a substrate (layer) having such properties, it is easy to obtain a pressure-sensitive adhesive sheet with little change in performance, such as adhesion state retention, before and after heat treatment. The above |E(23°C)-E(180°C)| is more preferably 50 or less, even more preferably 30 or less, particularly preferably 20 or less, and may be 15 or less. The lower limit of the above |E(23°C)-E(180°C)| is usually 0 or more, and may be approximately 5 or more.

[0118] As the substrate (layer), various sheet-like substrates having predetermined properties (for example, heat resistance, tensile elongation, etc.) can be used. In some embodiments, a resin film is preferably used as the substrate (layer). A resin film substrate (layer) is useful because of its excellent processability and handling properties. 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 resin film is a concept that is distinguished from foam films and nonwoven fabrics. The density of the resin film that can be used as the substrate is, for example, approximately 0.85 to 1.80 g / cm ３ It is about 1.00 g / cm ３ or more, 1.10 g / cm ３ or more (for example, 1.20 g / cm ３ or more), and ３ or less, 1.50 g / cm ３ For example, the density may be about 1.10 g / cm ３ ~1.60 g / cm ３ The substrate layer (for example, a resin film) may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0119] As the resin film, for example, polyester film, polyamide resin film, or engineering plastic film having predetermined properties (e.g., heat resistance, tensile elongation, etc.) is preferably used. Specific examples of the engineering plastic film include resin films formed from one or more engineering plastics (which may be super engineering plastics) such as polyethylene naphthalate (PEN), polyphenylene sulfide resin, polyether sulfone resin, polyether ether ketone resin, polyether ketone resin, polyphthalamide resin, polyarylate resin, polyamide imide resin, polyimide (PI) resin, polyether imide resin, fluororesin such as polytetrafluoroethylene (PTFE), acrylic resin, and epoxy resin. The use of engineering plastics is preferred from the viewpoint of heat resistance. From the viewpoint of achieving a better balance between heat resistance and elongation, resin films formed from polyester film or PI resin film are preferred, and PEN film or PI film is more preferred.

[0120] 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.

[0121] The method for producing the substrate layer (e.g., a resin film) is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately employed. Alternatively, a commercially available resin film may be obtained and used as the substrate layer (e.g., a resin film). Examples of commercially available products for the substrate layer include the "UPILEX-RN" series manufactured by UBE, the "GV" series manufactured by PI Advanced Materials, and the "TEONEX" series manufactured by Toyobo Co., Ltd.

[0122] 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), preferably 5 μm or more, and may be approximately 7 μm or more, or may be 10 μm or more. A substrate layer having a thickness of a predetermined value or more tends to have good extensibility. In some embodiments, the thickness of the substrate layer may be 20 μm or more, 30 μm or more, or may be 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 130 μm or less, more preferably approximately 100 μm or less, even more preferably approximately 80 μm or less, and may be 60 μm or less. When the thickness of the substrate layer is reduced, the flexibility of the PSA sheet and its ability to conform to the surface shape of the adherend are improved, and the adhesive state with the adherend tends to be more easily maintained. In some preferred embodiments, the thickness of the substrate layer may be approximately 50 μm or less (e.g., less than 50 μm), 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, or 25 μm or less.

[0123] The surface of the base layer facing the pressure-sensitive adhesive layer may be subjected to a conventionally known surface treatment, such as a corona treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, etc. Such a surface treatment may be a treatment for improving the adhesion between the base layer and the pressure-sensitive adhesive layer, and thus a treatment for improving the anchoring property of the pressure-sensitive adhesive layer.

[0124] An auxiliary layer may be formed on the back surface of the substrate layer, for example, an optical property adjusting layer (e.g., a coloring layer or an antireflection layer), a printed layer or a laminate layer for imparting a desired appearance, an antistatic layer, a release layer, or other surface treatment layer.

[0125] <Undercoat Layer> In some embodiments, the PSA sheet has an undercoat layer between the substrate layer and the PSA layer. By providing an undercoat layer, the anchoring property of the PSA layer to the substrate can be improved. Examples of the undercoat layer include a layer containing one or more resins selected from urethane-based resins, polyester-based resins, acrylic-based resins, acrylic urethane-based resins, acrylic styrene-based resins, polyester urethane-based resins, polyamide-based resins, polyethyleneimine-based resins, melamine-based resins, olefin-based resins, polystyrene-based resins, epoxy-based resins, phenol-based resins, isocyanurate-based resins, cellulose-based resins, polyvinyl acetate-based resins, etc. For example, from the viewpoint of adhesion to the substrate and / or the pressure-sensitive adhesive layer, it is preferable to use one or more resins selected from urethane-based resins, polyester-based resins, acrylic-based resins, acrylic urethane-based resins, acrylic styrene-based resins, polyester urethane-based resins, polyamide-based resins, polyethyleneimine-based resins, melamine-based resins, epoxy-based resins, and isocyanurate-based resins, and it is more preferable to use one or more resins selected from urethane-based resins, acrylic-based resins, acrylic urethane-based resins, polyethyleneimine-based resins, epoxy-based resins, and isocyanurate-based resins.

[0126] The undercoat layer composed of the above-mentioned various resins may contain, as a main component, various polymers such as polyurethane, polyester, acrylic polymer, acrylic-urethane polymer, acrylic-styrene polymer, polyester-urethane polymer, polyamide, polyethyleneimine, polyolefin, polystyrenes, epoxy polymer, phenolic polymer, polyisocyanurate, cellulose polymer, and polyvinyl acetate. The above polymers can be used alone or in combination of two or more. In this specification, the polymer contained in the undercoat layer is also referred to as polymer B.

[0127] In some embodiments, a polymer having an amine group (amine group-containing polymer) is used as the polymer. An undercoat layer containing an amine group-containing polymer facilitates the formation of a resin layer with good heat resistance and cohesiveness. Furthermore, although not particularly limited, the amine group-containing polymer, for example, in an embodiment in which the pressure-sensitive adhesive layer contains an isocyanate group, facilitates excellent anchoring properties. Furthermore, for example, in an embodiment in which an epoxy compound is used to form the undercoat layer, the use of the amine group-containing polymer facilitates the attainment of high cohesive strength. Examples of the amine group-containing polymer include the various polymers exemplified above that contain amine groups. Suitable examples of such polymers include amine group-containing acrylic polymers. Other examples of amine group-containing polymers include polyallylamine, polyethyleneimine, polyvinylamine, etc. The amine group-containing polymers can be used alone or in combination of two or more.

[0128] In this specification, the amine group is defined as -NH ２ , —NHR, or —NR １ R ２ and may take the form of any of primary amine, secondary amine, and tertiary amine. １ and R ２ is an aliphatic group, an alicyclic group, or an aromatic group which may have a substituent. １ and R ２ may be, for example, a carbon chain such as an aliphatic group (e.g., an alkyl group) which may have a substituent. The amine group is a concept which encompasses amino groups and substituted amino groups.

[0129] In some embodiments, the undercoat layer contains an acrylic polymer. A undercoat layer containing an acrylic polymer can provide good adhesion to various substrates. Furthermore, a undercoat layer containing an acrylic polymer can provide better anchoring properties, for example, in embodiments in which the PSA layer contains an acrylic polymer as a base polymer. While not particularly limited, the glass transition temperature (Tg) of the acrylic polymer used in the undercoat layer is suitably about 0°C or higher (e.g., above 0°C) from the viewpoint of providing good anchoring properties even after heat treatment. It is preferably about 30°C or higher, and may be about 50°C or higher, about 70°C or higher, or about 90°C or higher. From the viewpoint of providing good anchoring properties, the upper limit of the Tg of the acrylic polymer is, for example, about 200°C or lower, about 150°C or lower, about 120°C or lower, about 100°C or lower, about 80°C or lower, or about 60°C or lower. For commercially available products, the Tg of the acrylic polymer can be the manufacturer's nominal value. When the manufacturer's nominal value is unknown or when the polymer is synthesized, the Tg can be determined from the temperature of the inflection point of the obtained calorimetric curve by analysis using a differential scanning calorimeter (DSC). As the DSC, a product name "Q2000" manufactured by TA Instruments or an equivalent product can be used.

[0130] In some preferred embodiments, an amine group-containing acrylic polymer is used as the acrylic polymer. In the amine group-containing acrylic polymer, the amine group may be contained in the polymer in the form of an amino group or an aminoalkyl group. An acrylic polymer having an aminoalkyl group is sometimes referred to as an aminoalkylated acrylic polymer. The amine group preferably has, for example, a primary amine structure. The aminoalkyl group may have, for example, about 1 to 8 carbon atoms, such as 1 to 4 or even 1 or 2 carbon atoms. A preferred example is a polymer having an aminoethyl group as the aminoalkyl group, i.e., an aminoethylated acrylic polymer. The amine group-containing acrylic polymer may have, in addition to the amine group (e.g., amino group or aminoalkyl group), a substituent such as an alkyl group or alkoxy group having about 1 to 18 carbon atoms. Commercially available aminoethylated acrylic polymers include, for example, the "Polyment" series manufactured by Nippon Shokubai Co., Ltd.

[0131] The molecular weight of the acrylic polymer that can be contained in the undercoat layer is not particularly limited. In some embodiments, the weight average molecular weight (Mw) of the acrylic polymer may be about 10,000 or more, about 30,000 or more, about 50,000 or more, or about 70,000 or more. In some embodiments, the Mw may be, for example, about 1,000,000 or less, about 300,000 or less, or about 150,000 or less.

[0132] In some other embodiments, the primer layer contains polyethyleneimine. A primer layer containing polyethyleneimine can provide good adhesion to various substrates and excellent anchoring properties. The polyethyleneimine may be any polyethyleneimine having a polyethyleneimine structure, such as an acrylic polymer ethyleneimine adduct or a polyethyleneimine adduct. While not particularly limited, in some embodiments, the Mw of the polyethyleneimine may be approximately 1,000 or more, approximately 3,000 or more, approximately 5,000 or more, or approximately 7,000 or more. Furthermore, in some embodiments, the Mw may be, for example, approximately 100,000 or less, approximately 50,000 or less, or approximately 30,000 or less. Commercially available polyethyleneimines include the "Epomin" series manufactured by Nippon Shokubai Co., Ltd.

[0133] For commercially available products, the Mw of the polymer can be the manufacturer's nominal value. When the nominal value is unknown or for polymers obtained by synthesis, a value measured by GPC under known appropriate conditions can be used. For example, the GPC measurement conditions for acrylic polymers can be the Mw measurement conditions for the polymer contained in the pressure-sensitive adhesive layer.

[0134] The content of the polymer (e.g., an acrylic polymer such as an aminoethylated acrylic polymer, or polyethyleneimine) in the undercoat layer is suitably, for example, about 50% by weight or more (e.g., more than 50% by weight), and may be about 70% by weight or more, about 80% by weight or more, about 85% by weight or more, about 90% by weight or more, or about 95% by weight or more. When other components are added, the content of the polymer may be, for example, less than 100% by weight, for example, 99.9% by weight or less, 99% by weight or less, or 98% by weight or less.

[0135] In some embodiments, the undercoat layer may contain one or more compounds such as isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, carbodiimide compounds, melamine compounds, and metal chelates. These compounds may function as curing agents. Epoxy compounds are preferably used from the viewpoints of heat resistance and cohesive strength. For example, in embodiments in which the undercoat layer contains an amine group-containing polymer, the cohesive strength of the undercoat layer can be preferably improved by using an epoxy compound.

[0136] The epoxy compound preferably has two or more epoxy groups in one molecule. The epoxy compound may be a bifunctional epoxy compound having two epoxy groups in one molecule, or a polyfunctional epoxy compound having three or more epoxy groups in one molecule. The epoxy compounds may be used alone or in combination of two or more.

[0137] Examples of bifunctional epoxy compounds include, but are not limited to, bisphenol A epoxy resins, bisphenol F epoxy resins, hydrogenated bisphenol A epoxy resins (i.e., epoxy compounds corresponding to a structure in which the aromatic rings of bisphenol A epoxy resins are converted to cycloalkyl rings by hydrogenation), hydrogenated bisphenol F epoxy resins, biphenyl epoxy resins, aliphatic epoxy resins (e.g., polypropylene glycol epoxy resins), 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, etc. Commercially available bifunctional epoxy compounds include the "jER" series manufactured by Mitsubishi Chemical Corporation.

[0138] Examples of polyfunctional epoxy compounds include, but are not limited to, novolac-type epoxy resins, glycidylamine-type epoxy resins, biphenyl-type epoxy resins, triphenylmethane-type epoxy resins, dicyclopentadiene-type epoxy resins, glycerin-type epoxy resins, trimethylolpropane-type epoxy resins, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and polyglycerol polyglycidyl ether. The number of epoxy groups contained in one molecule of the polyfunctional epoxy compound is at least 3 or more, and may be 4 or more, or 5 or more. The number of epoxy groups contained in one molecule of the polyfunctional epoxy compound is typically 10 or less, and may be 8 or less, or 6 or less. Commercially available products of the polyfunctional epoxy compound include "Tetrad-X" and "Tetrad-C" manufactured by Mitsubishi Gas Chemical Company, Inc., "Epiclon CR-5L" manufactured by DIC Corporation, "Denacol EX-512" manufactured by Nagase ChemteX Corporation, and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

[0139] Although not particularly limited, the molecular weight of the epoxy compound is, for example, about 100 to 3000, and may be about 200 or more, or about 300 or more, or may be about 1000 or less, or may be about 500 or less. The molecular weight is a value calculated from the molecular structure.

[0140] In embodiments in which the undercoat layer contains an epoxy compound as a curing agent, the proportion of the epoxy compound in the entire curing agent may be, for example, 1 wt % or more, 3 wt % or more, or 5 wt % or more. From the viewpoint of effectively obtaining the effect of adding the epoxy compound, in some embodiments, the proportion of the epoxy compound in the entire curing agent is preferably about 10 wt % or more, more preferably about 30 wt % or more, even more preferably about 50 wt % or more (e.g., more than 50 wt %), even more preferably about 70 wt % or more, and particularly preferably about 90 wt % or more, for example, about 95 to 100 wt %.

[0141] In embodiments in which the undercoat layer contains a polymer and a curing agent, the content of the curing agent (e.g., an epoxy compound) relative to 100 parts by weight of the polymer (e.g., an acrylic polymer such as an aminoethylated acrylic polymer, or an amine group-containing polymer such as polyethyleneimine) is not particularly limited and may be, for example, 0.01 parts by weight or more, or may be 0.1 parts by weight or more. From the viewpoint of improving the cohesive strength of the undercoat layer, in some embodiments, the content of the curing agent relative to 100 parts by weight of the polymer is preferably 0.5 parts by weight or more, more preferably 1.0 parts by weight or more (e.g., more than 1.0 part by weight), even more preferably 2 parts by weight or more, or may be 3 parts by weight or more. Furthermore, from the viewpoint of maintaining good anchoring properties even after heat treatment, the content of the curing agent relative to 100 parts by weight of the polymer is, for example, approximately 25 parts by weight or less, suitably less than approximately 20 parts by weight, preferably approximately 15 parts by weight or less, more preferably approximately 10 parts by weight or less, may be approximately 7 parts by weight or less, or may be approximately 5 parts by weight or less.

[0142] The undercoat layer may contain various additives, such as thickeners, stabilizers, fillers, antifoaming agents, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, and ultraviolet absorbers, as needed.

[0143] The undercoat layer can be formed by applying a composition for forming an undercoat layer (e.g., a solution containing undercoat layer-forming components) directly to the surface of the substrate using an applicator such as a wire bar, spray coater, fountain die coater, lip coater, closed-edge die coater, gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, or knife coater, followed by drying. The drying temperature is not particularly limited, but can be, for example, about 40 to 200°C, and typically about 100 to 180°C is preferred. The drying time is, for example, about 1 to 10 minutes, and preferably about 1 to 5 minutes. The undercoat layer is typically formed continuously, but is not limited thereto. For example, the undercoat layer may be formed in a regular or random pattern such as dots or stripes. Furthermore, from the viewpoint of accelerating the curing of the undercoat layer and improving production efficiency, drying by heating under appropriate conditions (temperature and time) may be performed during the formation of the undercoat layer.

[0144] The thickness of the primer layer (after drying) is not particularly limited. In some embodiments, it may be 0.01 μm or more, or may be 0.1 μm or more. From the viewpoint of improving anchoring properties, in some preferred embodiments, the thickness of the primer layer is approximately 0.5 μm or more, more preferably approximately 1 μm or more, and may be approximately 2 μm or more. Furthermore, in some embodiments, the thickness of the primer layer may be, for example, approximately 20 μm or less, approximately 15 μm or less, approximately 10 μm or less, approximately 7 μm or less, approximately 5 μm or less, or approximately 3 μm or less. By setting the thickness of the primer layer within the above range, the effect of improving anchoring properties due to the placement of the primer layer can be preferably exerted.

[0145] <Total Thickness> The total thickness of the PSA sheet disclosed herein (which may include a PSA layer, an undercoat 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, 100 μm or less (e.g., less than 100 μm), 80 μm or less, or 60 μm or less. Reducing the thickness of the PSA sheet is advantageous in terms of thinning, miniaturization, weight reduction, resource conservation, etc.

[0146] <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.

[0147] <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.

[0148] In some embodiments, the temperature of the heat treatment of the adherend to which the PSA sheet is attached is, for example, above 100°C, and may be about 110°C or higher, about 120°C or higher, about 130°C or higher, about 150°C or higher (e.g., above 150°C), 160°C or higher, or 170°C or higher. In some preferred embodiments, the temperature of the heat treatment of the adherend to which the PSA sheet is attached may be 180°C or higher, 200°C or higher (e.g., above 200°C), 220°C or higher, or around 250°C. 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 280°C or lower, about 260°C or lower, about 250°C or lower, 230°C or lower, 200°C or lower, or 180°C or lower. The heat treatment time is not particularly limited and may be within 10 hours, within 5 hours, or 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, within 30 minutes, within 15 minutes, within 10 minutes, or within 5 minutes. In the PSA sheet disclosed herein, the PSA can be thermally cured by the above-mentioned short-term heat treatment, thereby exhibiting easy heat-peelability. 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, more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. In the PSA sheet disclosed herein, the PSA can be thermally cured by the heat treatment at the above-mentioned heating temperature, reducing the release force, and even if the heated state continues for a long period of time, an increase in the release force (heavy release) can be prevented or suppressed. Therefore, it is possible to maintain heat peelability (heat-resistant peelability) even after a long-term heat treatment.

[0149] <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 from an adherend using heat. For example, it can be used in applications in which the sheet may be exposed to temperatures above 100°C (e.g., about 120°C to 260°C) while attached to an adherend. It can also be preferably used in applications in which the sheet may be exposed to temperatures above 150°C (e.g., about 160°C to 260°C), or even 200°C or higher (e.g., about 200°C to 280°C) while attached to an adherend.

[0150] Examples of applications for the pressure-sensitive adhesive sheet disclosed herein include masking applications, temporary fixing applications, and protective applications, which require heat resistance from the pressure-sensitive adhesive sheet. Furthermore, for example, the pressure-sensitive adhesive sheet can be preferably used as a process material that is fixed to an adherend and then peeled off during the manufacturing process of electronic devices and electronic components. Another suitable application for the pressure-sensitive adhesive sheet disclosed herein is semiconductor element manufacturing. For example, the pressure-sensitive adhesive sheet can be preferably used as a wafer fixing sheet that fixes the wafer to a fixing plate during semiconductor wafer processing (typically silicon wafer processing). For example, the pressure-sensitive adhesive sheet can be preferably used as a process material that is peeled off from the semiconductor wafer after processing while the semiconductor wafer is held by the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet disclosed herein can also be preferably used as a protective sheet that protects the wafer during the wafer processing. In particular, during the manufacturing of semiconductor elements, the semiconductor element may be exposed to heat during processing steps, etc., so a heat-resistant, easily peelable pressure-sensitive adhesive sheet is preferably used. The pressure-sensitive adhesive sheet disclosed herein can also be used for optical applications that require heat resistance. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be used, for example, as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members. The optical members refer to members having optical properties (for example, polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.).

[0151] The following further describes an example of the use of the heat-peelable and heat-resistant adhesive sheets disclosed herein, specifically, their use in semiconductor device manufacturing. In this use, a semiconductor wafer is fixed to a fixing plate (e.g., a hard substrate such as a glass plate or an acrylic plate) via an adhesive sheet, i.e., attached to the adhesive sheet, and then subjected to various processes such as dicing (e.g., laser dicing). The semiconductor chips diced by the dicing process can be separated from the adhesive sheet and picked up, for example, through an expanding process. In this way, the adhesive sheet is removed from the semiconductor wafer, which is the adherend (also referred to as a peeling process). In addition to the dicing process, optional processing steps that can be performed between the attachment of the adhesive sheet to the adherend and its removal include, but are not limited to, backgrinding, etching, photolithography, ion implantation, die bonding, wire bonding, and packaging. In the processing steps, the adhesive sheet can be exposed to heating at 100°C or higher (e.g., high-temperature heating at around 200°C). Through the above-described processes, semiconductor devices are manufactured.

[0152] Furthermore, since the PSA sheet disclosed herein can exhibit good heat-peelability even on organic material surfaces, it can be preferably used in applications in which it is attached to the surface of a substrate (adherend) whose surface is made of an organic material and then peeled from the surface. Examples of such substrate materials include circuit boards (e.g., printed circuit boards (PCBs) and flexible circuit boards (FPCs)). The PSA sheet can be preferably used as a temporary fixing sheet for such circuit boards.

[0153] 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 or protecting various components or materials. The adherend material can be made of an organic material, an inorganic material, or a composite thereof. Examples of adherend materials 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 polyethylene terephthalate (PET), acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, transparent polyimide resins, epoxy resins, and phenolic resins. Suitable examples of adherend materials include circuit boards whose surfaces are made of epoxy resin (e.g., glass cloth-based epoxy resin copper-clad laminates). Other suitable examples of adherend materials include glass materials such as alkali glass and semiconductor wafers. The glass material may be, for example, a glass plate having a surface on which a transparent conductive film (e.g., an ITO (indium tin oxide) film) or an FPC (flexible circuit board) is partially provided, such as a glass plate used in tablet computers, mobile phones, organic LEDs (light-emitting diodes), etc.

[0154] <Structure, Manufacturing Method Thereof, and Method> As described above, this specification provides a structure comprising the adhesive sheet disclosed herein and an adherend to which the adhesive sheet is attached, and a method for manufacturing a structure including a step of attaching the adhesive sheet to an adherend. Adherends used in such structures and methods for manufacturing a structure include the various adherends exemplified above, as well as workpieces and components made of various adherend materials. Suitable examples of adherends include the semiconductor wafers, optical components, circuit boards, and other various substrates. The manufacturing method may include a step of preparing the adherend and the adhesive sheet.

[0155] Furthermore, since the pressure-sensitive adhesive sheet disclosed herein can be preferably used for processing an adherend using the pressure-sensitive adhesive sheet, this specification provides, for example, a method including a processing step of processing an adherend to which the pressure-sensitive adhesive sheet disclosed herein is attached. Such a method can be referred to as a method for processing an adherend, and can be a method of using a pressure-sensitive adhesive sheet in processing the adherend. Examples of the adherends used include the various adherends exemplified above, as well as workpieces and components composed of various adherend materials. These are also referred to as objects to be processed before the processing step and as processed products after the processing step. Suitable examples of adherends include various substrates such as the semiconductor wafers, optical components, and circuit boards mentioned above. Furthermore, for example, in an embodiment in which the adherend is a semiconductor wafer, the method can be a method for manufacturing semiconductor elements. The processing step is not particularly limited and can be various processing steps performed on various adherends. For example, in an embodiment in which the adherend is a semiconductor wafer or a circuit board such as a PCB or FPC, processing steps performed on the adherend may include, for example, a dicing step such as laser dicing, a backgrinding step, an etching step, a photolithography step, an ion implantation step, a die bonding step, a wire bonding step, a molding step, a packaging step, etc. The above processing step may be a step involving heating, i.e., a heat treatment step.

[0156] In one embodiment, the above-mentioned method (e.g., a method for processing an adherend, a method for using a pressure-sensitive adhesive sheet in processing the adherend, etc.) may further include a peeling step of peeling the pressure-sensitive adhesive sheet from the adherend after the above-mentioned processing step. The pressure-sensitive adhesive sheet disclosed herein has heat-releasability and can be easily peeled from the adherend, making it suitable for various methods including the above-mentioned peeling step. Note that the above-mentioned method may include, before the above-mentioned processing step, a step of preparing the pressure-sensitive adhesive sheet and the adherend, or a step of attaching the pressure-sensitive adhesive sheet to the adherend.

[0157] In one embodiment, a heat treatment is performed on the adherend to which the pressure-sensitive adhesive sheet is attached, before, after, or during the processing step. Such a heat treatment may be a processing step involving heating. For example, among the above processing steps, laser dicing may be a process involving heat generation, i.e., heating. Furthermore, the molding step is, for example, a process of sealing chips on a PCB with a resin such as an epoxy resin, and may include a process involving heating at around 175°C. Furthermore, processing of circuit boards such as FPCs may usually include a bonding step using reflow at 250°C or higher. Note that the conditions for the heat treatment, such as the heating temperature, are as described above, and therefore will not be described again. By undergoing the above-mentioned heat treatment, the pressure-sensitive adhesive sheet can be easily peeled from the adherend based on the heat-peelability of the pressure-sensitive adhesive sheet.

[0158] As described above, the PSA sheet disclosed herein can be preferably used in various methods for being attached to an adherend and then peeled off and removed from the adherend. For example, it is preferably used in a method including a processing step of processing the adherend as an object to be processed to which the PSA sheet is attached, and a peeling step of peeling the PSA sheet from the adherend after the processing step.

[0159] The matters disclosed by this specification include the following: [1] A pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises a polymer and a thermal polymerization initiator, and the polymer comprises an ethylenically unsaturated group, and wherein the post-heat peel force reduction rate is greater than 50% and not greater than 99.9%, and wherein the post-heat peel force reduction rate is determined by the formula: Post-heat peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heat peel force F1 [N / 20 mm] measured in an environment of 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heat peel force F0 [N / 20 mm] from the silicon wafer), and wherein the base layer has a tensile elongation of 100% or more at 23°C, and the tensile elongation is still 100% or more even after heat-treatment at 180°C for 30 minutes. [2] A pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer comprises a polymer and a thermal polymerization initiator, and the polymer comprises an ethylenically unsaturated group, and wherein the post-heating peel force reduction rate is greater than 50% and not more than 99.9%, and wherein the post-heating peel force reduction rate is calculated using the formula: Post-heating peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heating peel force F1 [N / 20 mm] measured in an environment of 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heating peel force F0 [N / 20 mm] from the silicon wafer); and wherein the base layer has a heat shrinkage rate of less than 1% in a heat shrinkage test in which the sheet is heated at 200°C for 10 minutes, and the pressure-sensitive adhesive sheet has a tensile elongation at 23°C of 80% or more. [3] A pressure-sensitive adhesive sheet having a base layer and a pressure-sensitive adhesive layer, wherein the pressure-sensitive 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 pressure-sensitive adhesive layer is 0.01 parts by weight or more per 100 parts by weight of the polymer, and the base layer has a tensile elongation of 100% or more at 23°C and maintains a tensile elongation of 100% or more even after heat treatment at 180°C for 30 minutes.[4] A pressure-sensitive adhesive sheet having a base layer and 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, the base layer has a heat shrinkage rate of less than 1% in a heat shrinkage test in which the base layer is heated at 200°C for 10 minutes, and the pressure-sensitive adhesive sheet has a tensile elongation of 80% or more at 23°C. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the base layer is composed of a polyimide film, an acrylic resin film, an epoxy resin film, a fluororesin film, or a polyester film. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the base layer is composed of a polyimide film or a polyester film. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6] above, wherein the thickness of the base layer is 5 μm or more and 130 μm or less. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7] above, wherein an undercoat layer is provided on the surface of the base layer facing the pressure-sensitive adhesive layer. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] above, which is used in a method comprising: a processing step of processing an adherend as an object to be processed to which the pressure-sensitive adhesive sheet is attached; and a peeling step of peeling the pressure-sensitive adhesive sheet from the adherend after the processing step.

[10] A structure comprising the pressure-sensitive adhesive sheet according to any one of [1] to [9] above, and a substrate to which the pressure-sensitive adhesive sheet is attached.

[11] A method for producing a structure comprising the pressure-sensitive adhesive sheet according to any one of [1] to [8] above, and a substrate, the method comprising a step of attaching the pressure-sensitive adhesive sheet to the substrate.

[12] A method comprising a processing step of processing a substrate to which the pressure-sensitive adhesive sheet according to any one of [1] to [8] above is attached.

[13] The method according to

[12] above, further comprising a peeling step of peeling the pressure-sensitive adhesive sheet from the substrate after the processing step.

[0160] 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.

[0161] <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 the adherend with 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 pressure-sensitive adhesive sheet is peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min, and the peel strength (pre-heating peel force) F0 [N / 20 mm width] is measured. A silicon wafer (manufactured by Shin-Etsu Chemical Co., Ltd., 6 inch N<100>-100) 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.

[0162] (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 220°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.

[0163] (Reduction rate of peeling force after heating) The reduction rate of peeling force after heating is calculated from the above-mentioned peeling force before heating F0 and peeling force after heating F1 according to the following formula: Reduction rate of peeling force after heating [%]=(1−F1 / F0)×100

[0164] (Tensile elongation of base layer (23°C)) A dumbbell-shaped No. 3 test piece was prepared using the material used for the base layer and used as an evaluation sample. The evaluation sample was set in a tensile tester under an environment of 23°C and 50% RH, and a tensile test was performed at a speed of 50 mm / min to measure the breaking elongation, which was taken as the tensile elongation of the base layer at 23°C. The tensile elongation at 23°C is also referred to as the tensile elongation before heating to distinguish it from the tensile elongation after heating at 180°C described below. The tensile elongation [%] is the elongation [%] at break and is calculated from the formula: tensile elongation [%] = (gauge line distance at break [mm] - gauge line distance before tensile test [mm]) / gauge line distance before tensile test [mm] × 100. As a tensile tester, a Shimadzu product named "EZ-S 500N" or an equivalent product can be used.

[0165] (Tensile elongation of substrate layer after heating at 180°C) Using the material used for the substrate layer, an evaluation sample is prepared using the method described above for measuring the tensile elongation of the substrate layer. The obtained evaluation sample is heated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand in an environment of 23°C and 50% RH for 30 minutes. The evaluation sample is then placed in a tensile tester under the same environment, and a tensile test is performed at a speed of 50 mm / min to measure the breaking elongation, which is the tensile elongation of the substrate layer after 30 minutes of heat treatment at 180°C. This tensile elongation after heating is also referred to as the tensile elongation after heating at 180°C. The tensile tester and other details are the same as those for measuring the tensile elongation of the substrate layer.

[0166] (Tensile elongation of pressure-sensitive adhesive sheet) A pressure-sensitive adhesive sheet with a release liner was cut into 20 mm wide strips, the release liner was peeled off, and the strips were placed in a tensile tester with a chuck distance of 50 mm. A tensile test was conducted under conditions of 23°C and 50% RH, with a tensile speed of 300 mm / min, and the breaking elongation [%] was measured, which was defined as the tensile elongation of the pressure-sensitive adhesive sheet at 23°C. The tensile elongation [%] is the elongation [%] at break of the pressure-sensitive adhesive sheet, and is calculated from the formula: tensile elongation [%] = (gauge line distance at break [mm] - gauge line distance before tensile test [mm]) / gauge line distance before tensile test [mm] x 100. The tensile tester may be a universal tension-compression tester (apparatus name "Tension-Compression Tester, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent. In the following examples, the tensile direction was the MD (machine direction) of the substrate layer.

[0167] (Post-heat retention test) A stainless steel (SUS) ring (annular structure with an outer diameter of 8 inches and a width of 1.2 mm; the adhesive sheet attachment surface is flat) is prepared as an adherend, and an adhesive sheet cut to a predetermined shape and size is placed over the ring so that it covers the entire ring in an environment of 23°C and 50% RH. The adhesive surface of the adhesive sheet is pressed onto the ring using a hand roller to bond them together. The obtained evaluation sample is heat-treated in an oven at 180°C for 30 minutes, removed from the oven, and allowed to stand in an environment of 23°C and 50% RH for 30 minutes. In the same environment, the evaluation sample is fixed with a jig so that the adhesive sheet side of the evaluation sample is facing downward and the adhesive sheet is horizontal, and a 3 kg weight is gently placed on the center of the adhesive sheet from the SUS ring side (upper side) of the evaluation sample. After leaving it in this state for 60 minutes, the adhesion state between the SUS ring and the adhesive sheet is visually observed, and if the adhesion between the SUS ring and the adhesive sheet is completely maintained, it is judged as O (pass), and if at least part of the SUS ring and the adhesive sheet are peeled off, it is judged as × (fail).

[0168] 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"), and 0.8 parts of benzoyl peroxide (manufactured by NOF Corporation, trade name "Niper BW", SADT: 75°C) as a thermal polymerization initiator were added and mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example.

[0169] (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 polymer solution containing, on a solids basis, 100 parts of an aminoethylated acrylic polymer (manufactured by Nippon Shokubai Co., Ltd., product name "Polyment NK-350", weight average molecular weight (Mw) 100,000, glass transition temperature (Tg) 40°C) and 3 parts of an epoxy compound (manufactured by Mitsubishi Chemical Corporation, product name "jER828") was applied using a wire bar to one side of a 50 μm-thick polyimide (PI) film (product name "Upilex-RN50", manufactured by UBE) serving as a substrate layer. The solution was then dried in an oven at 150°C for 3 minutes to form a primer layer with a dry thickness of 2 μm. The primer layer-forming surface of the PI film was then bonded to the pressure-sensitive adhesive layer obtained above, and the resulting layer was then aged at 50°C for 3 days. In this way, a PSA sheet (a single-sided PSA sheet with a substrate) according to this example was produced. The adhesive surface of the PSA sheet was protected by a release liner.

[0170] Examples 2 to 5 and Comparative Examples 1 to 3 Substrate-attached single-sided PSA sheets for each example were prepared in the same manner as in Example 1, except that the composition of the PSA layer and the type and thickness of the substrate layer were changed as shown in Table 1. The materials shown in Table 1 are as follows. PI(A): PI film (trade name "Upilex-RN50", manufactured by UBE, thickness 50 μm) PI(B): PI film (trade name "Upilex-RN25", manufactured by UBE, thickness 25 μm) PI(C): PI film (trade name "GV", manufactured by PI Advanced Materials, thickness 25 μm) PI(D): PI film (trade name "Kapton 200H", manufactured by Toray DuPont, thickness 50 μm) PI(E): PI film (trade name "Kapton 100H", manufactured by Toray DuPont, thickness 25 μm) PEN: polyethylene naphthalate (PEN) film (trade name "Teonex Q51", manufactured by Toyobo, thickness 50 μm) PET: PET film (product name "Lumirror S10", manufactured by Toray Industries, Inc., thickness 50 μm)

[0171] The outline of each example and the evaluation results are shown in Table 1.

[0172]

[0173] 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.

[0174] REFERENCE SIGNS LIST 1, 2 Pressure-sensitive adhesive sheet 1A, 2A Adhesive surface 1B, 2B Back surface 10 Base material layer 10A First surface 10B Second surface 15 Primer layer 15A First surface 15B Second surface 20 Pressure-sensitive adhesive layer 20A Surface of pressure-sensitive adhesive layer 30 Release liner 100, 200 Pressure-sensitive adhesive sheet with release liner

Claims

1. A pressure-sensitive adhesive sheet having a base layer and 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, and wherein the post-heat peel force reduction rate is greater than 50% and not greater than 99.9%, and wherein the post-heat peel force reduction rate is calculated using the following formula: Post-heat peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heat peel force F1 [N / 20 mm] measured in an environment of 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heat peel force F0 [N / 20 mm] from the silicon wafer). ）； 　 wherein the base layer has a tensile elongation of 100% or more at 23°C and a tensile elongation of 100% or more even after heat treatment at 180°C for 30 minutes.

2. A pressure-sensitive adhesive sheet having a base layer and 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, and the post-heating peel force reduction rate is greater than 50% and not more than 99.9%, wherein the post-heating peel force reduction rate is calculated using the following formula: Post-heating peel force reduction rate [%] = (1 - F1 / F0) x ​​100 (where F1 is the post-heating peel force F1 [N / 20 mm] measured in an environment of 23°C after being attached to a silicon wafer and heat-treated at 220°C for 30 minutes, and F0 is the pre-heating peel force F0 [N / 20 mm] from the silicon wafer). ）； 　 wherein the base layer has a heat shrinkage rate of less than 1% in a heat shrinkage test in which the base layer is heated at 200°C for 10 minutes, and the pressure-sensitive adhesive sheet has a tensile elongation of 80% or more at 23°C.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the substrate layer is made of a polyimide film, an acrylic resin film, an epoxy resin film, a fluororesin film, or a polyester film.

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the substrate layer is made of a polyimide film or a polyester film.

5. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the thickness of the substrate layer is 5 μm or more and 130 μm or less.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein an undercoat layer is provided on the surface of the substrate layer facing the pressure-sensitive adhesive layer.

7. The adhesive sheet according to claim 1 or 2, which is used in a method comprising a processing step of processing an adherend as an object to be processed to which the adhesive sheet is affixed, and a peeling step of peeling the adhesive sheet from the adherend after the processing step.

8. A structure comprising the adhesive sheet according to claim 1 or 2 and a substrate to which the adhesive sheet is attached.

9. A method for manufacturing a structure comprising the adhesive sheet according to claim 1 or 2 and a substrate, the method comprising the step of attaching the adhesive sheet to the substrate.

10. A method comprising a processing step of processing a substrate to which the adhesive sheet according to claim 1 or 2 has been attached.

11. The method according to claim 10, further comprising a peeling step of peeling the adhesive sheet from the substrate after the processing step.

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