Pressure-sensitive adhesive sheet

Abstract

Provided is a pressure-sensitive adhesive sheet, both surfaces of which are tacky. The pressure-sensitive adhesive sheet includes a first pressure-sensitive adhesive layer, which forms a first pressure-sensitive adhesive surface, and a second pressure-sensitive adhesive layer, which forms a second pressure-sensitive adhesive surface. The first pressure-sensitive adhesive layer includes a polyfunctional monomer having two or more ethylenically unsaturated groups in the molecule and / or a polymer having an ethylenically unsaturated group and further contains a heat-polymerization initiator. With respect to the pressure-sensitive adhesive sheet, the first pressure-sensitive adhesive layer after heating has a peel force Fa1 [N / 20 mm] which differs from the peel force Fb1 [N / 20 mm] of the second pressure-sensitive adhesive layer after heating.

Description

adhesive sheet

[0001] The present invention relates to a pressure-sensitive adhesive sheet, and more particularly to a double-sided pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2023-122023, filed on July 26, 2023, the entire contents of which are incorporated herein by reference.

[0002] Generally, adhesives (also called 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 in the form of a supported adhesive sheet having an adhesive layer on a support, or in the form of a supportless adhesive sheet having no support. Some such adhesives are used by adhering to an adherend, and are removed from the adherend after their adhesive purpose has been fulfilled.

[0003] Japanese Patent No. 6587811

[0004] Pressure-sensitive adhesives used in applications requiring peeling and removal from an adherend are required to exhibit good adhesion while adhering to the adherend and to be easily peelable from the adherend after the adhesive has served its purpose. To achieve this performance, a technique has been known in which the pressure-sensitive adhesive contains heat-expandable microspheres that expand upon heating to a predetermined temperature (see, for example, Patent Document 1). However, because this type of heat-peelable pressure-sensitive adhesive sheet exhibits its thermal peeling function by expanding the heat-expandable microspheres upon heating, thereby reducing the adhesive area between the adhesive surface and the adherend, it tends to be difficult to control the peel strength after heating, making it unsuitable for fixing applications involving a heating process. For example, depending on the placement of the sheet relative to the adherend after heating or handling, such as when subjected to vibration, the sheet may unintentionally separate from the adherend.

[0005] Therefore, an object of the present invention is to provide a pressure-sensitive adhesive sheet that can be easily peeled by heating and is also suitable for fixing applications that involve a heating process.

[0006] According to this specification, a double-sided adhesive sheet (double-sided adhesive sheet) is provided. The adhesive sheet includes a first adhesive layer and a second adhesive layer. The first adhesive layer constitutes a first adhesive surface, which is the first surface of the adhesive sheet. The second adhesive layer constitutes a second adhesive surface, which is the second surface of the adhesive sheet, where the second surface of the adhesive sheet is the surface opposite to the first surface. The first adhesive layer includes at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule and a polymer having an ethylenically unsaturated group, and further includes a thermal polymerization initiator. The adhesive sheet has a post-heat peel strength Fa1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the first adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes, and a post-heat peel strength Fb1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the second adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes, which are different from each other.

[0007] A pressure-sensitive adhesive sheet having such a configuration can exhibit the desired heat-peelability function by including a first pressure-sensitive adhesive layer that contains a thermal polymerization initiator and is thermally cured by thermally polymerizing ethylenically unsaturated groups. By utilizing the thermal polymerization, the peel strength after heating can be easily controlled, making the sheet suitable for use in fixing applications involving a heating process. Furthermore, since the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are designed to have different peel strengths after heating, the sheet is easy to dismantle and has good reusability (e.g., recyclability) when dismantling a bonded structure formed by bonding a first member and a second member via the pressure-sensitive adhesive sheet after heating.

[0008] In some preferred embodiments, the PSA sheet has a post-heating peel strength difference (|Fb1-Fa1|) calculated from the post-heating peel strength Fa1 [N / 20 mm] and the post-heating peel strength Fb1 [N / 20 mm] of 0.5 N / 20 mm or more. By designing the PSA sheet in this manner, for example, when a bonded body in which a first member and a second member are bonded via the PSA sheet is disassembled after heating, it is possible to improve predictability as to which of the first and second members the PSA sheet will remain on when the two members are separated.

[0009] In some embodiments, the first pressure-sensitive adhesive layer has a post-heat peel strength reduction rate A [%] calculated from the pre-heat peel strength Fa0 [N / 20 mm] measured after attachment to a glass plate at 23°C and 50% RH and the post-heat peel strength Fa1 [N / 20 mm] measured after attachment to a glass plate at 180°C for 30 minutes and then at 23°C and 50% RH using the following formula: Post-heat peel strength reduction rate A [%] = (1 - Fa1 / Fa0) x 100; A pressure-sensitive adhesive sheet satisfying the above characteristics exhibits sufficient heat-removable function on the first pressure-sensitive adhesive surface and can appropriately suppress unintentional separation from the adherend after heating.

[0010] In some embodiments, the PSA sheet has a structure in which the first PSA layer and the second PSA layer are laminated via a substrate. That is, the structure is a double-sided PSA sheet (substrate-attached double-sided PSA sheet) in which the first PSA layer, the substrate, and the second PSA layer are laminated in this order. A double-sided PSA sheet having such a structure is provided with strength (e.g., tensile strength) by the substrate. Therefore, for example, when dismantling a bonded structure in which a first member and a second member are bonded via the PSA sheet, after separating the first and second members, the double-sided PSA sheet remaining on the separated members can be easily peeled from the members. Furthermore, the PSA sheet being reinforced by the substrate is advantageous, for example, from the viewpoint of reworkability (ease of repositioning) when attaching the PSA sheet to an adherend.

[0011] In some embodiments, the second pressure-sensitive adhesive layer contains at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups per molecule and a polymer having an ethylenically unsaturated group, and further contains a thermal polymerization initiator. The pressure-sensitive adhesive sheet having the second pressure-sensitive adhesive layer can also exhibit a stable heat-releasable function on the second pressure-sensitive adhesive surface.

[0012] In some embodiments, the second pressure-sensitive adhesive layer suitably has a post-heat peel strength reduction rate B [%] calculated from the pre-heat peel strength Fb0 [N / 20 mm] measured after attachment to a glass plate at 23°C and 50% RH and the post-heat peel strength Fb1 [N / 20 mm] measured after attachment to a glass plate at 180°C for 30 minutes and then at 23°C and 50% RH using the following formula: Post-heat peel strength reduction rate B [%] = (1 - Fb1 / Fb0) x 100. A pressure-sensitive adhesive sheet satisfying the above properties exhibits an appropriate heat-releasable function on the second pressure-sensitive adhesive surface as well, and can appropriately suppress unintentional separation from the adherend after thermal curing.

[0013] In some embodiments, the pressure-sensitive adhesive sheet preferably has a pre-heat peel strength Fa0 [N / 20 mm] measured by attaching the first pressure-sensitive adhesive layer to a glass plate at 23°C and 50% RH, and a pre-heat peel strength Fb0 [N / 20 mm] measured by attaching the second pressure-sensitive adhesive layer to a glass plate at 23°C and 50% RH, both of which are 4.0 N / 20 mm or greater. Pressure-sensitive adhesive sheets that satisfy these characteristics have excellent adherend fixing performance before heating (before thermal curing). Furthermore, in some embodiments, the post-heat peel strength Fa1 [N / 20 mm] of the first pressure-sensitive adhesive layer and the post-heat peel strength Fb1 [N / 20 mm] of the second pressure-sensitive adhesive layer are both preferably less than 3.0 N / 20 mm. In a use mode in which a bonded structure in which a first member and a second member are bonded via the pressure-sensitive adhesive sheet is heated and then disassembled, the bonded structure has good disassembly workability and reusability. A pressure-sensitive adhesive sheet that satisfies the above-mentioned properties can exhibit good fixing performance during use, and can be easily separated from the adherend after use by utilizing its heat-releasable function.

[0014] The pressure-sensitive adhesive sheet disclosed herein can be preferably used, for example, as a component of a bonded structure including a first member to which a first adhesive surface of the pressure-sensitive adhesive sheet is adhered and a second member to which a second adhesive surface of the pressure-sensitive adhesive sheet is adhered. The bonded structure can be easily disassembled, for example, by a disassembly method including a step of subjecting the bonded structure to a heat treatment and then separating the first member from the first adhesive surface while leaving the pressure-sensitive adhesive sheet on the second member. Therefore, the pressure-sensitive adhesive sheet is preferable from the viewpoint of ease of disassembly and reusability (e.g., recyclability, reusability) of the disassembled product.

[0015] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application.

[0016] 1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to an embodiment; 2 is a cross-sectional view schematically showing the configuration of a bonded body according to an embodiment;

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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."

[0022] <Adhesive Sheet> The adhesive sheet disclosed herein is a double-sided adhesive sheet (double-sided adhesive sheet) having a first adhesive layer constituting the first adhesive surface of the adhesive sheet and a second adhesive layer constituting the second adhesive surface. The adhesive sheet may be a substrate-attached double-sided adhesive sheet in which the first adhesive layer and the second adhesive layer are laminated via a substrate, or a substrateless double-sided adhesive sheet without a substrate. The concept of adhesive sheet here may include what are called adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet processed into various shapes.

[0023] The structure of a pressure-sensitive adhesive sheet according to one embodiment is shown schematically in Figure 1. This pressure-sensitive adhesive sheet 1 is configured as a substrate-attached double-sided pressure-sensitive adhesive sheet including a substrate 20 having a first side and a second side, a first pressure-sensitive adhesive layer 21 disposed on the first side of the substrate 20, and a second pressure-sensitive adhesive layer 22 disposed on the second side of the substrate 20, the side opposite the first side. The pressure-sensitive adhesive sheet 1 has a first side and a second side opposite the first side. The surface of the first pressure-sensitive adhesive layer 21 constitutes a first pressure-sensitive adhesive surface 1A that also serves as the first side of the pressure-sensitive adhesive sheet 1, and the surface of the second pressure-sensitive adhesive layer 22 constitutes a second pressure-sensitive adhesive surface 1B that also serves as the second side of the pressure-sensitive adhesive sheet 1. The pressure-sensitive adhesive sheet disclosed herein may also be configured as a substrate-less double-sided pressure-sensitive adhesive sheet having a structure in which the substrate 20 is omitted from the structure shown in Figure 1, i.e., a pressure-sensitive adhesive layer in which the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 are laminated directly (without a substrate interposed therebetween).

[0024] The PSA sheet 1 is used, for example, by attaching the first adhesive surface 1A and the second adhesive surface 1B to different locations on an adherend. The locations to which the adhesive surfaces 1A and 1B are attached may be locations on different members, or may be different locations on a single member. Before use (i.e., before being attached to an adherend), the PSA sheet 1 may be a component of a release-liner PSA sheet 50 in which the first adhesive surface 1A and the second adhesive surface 1B are protected by release liners 31 and 32, respectively, with at least the sides facing the PSA layers 21 and 22 serving as release surfaces, as shown in FIG. 1 . The release liners 31 and 32 may preferably be, for example, sheet-like substrates (liner substrates) configured such that one side serves as a release surface by providing a release layer made of a release treatment agent on that surface. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, which may be superimposed on the adhesive sheet 1 and rolled up in a spiral shape, thereby forming an adhesive sheet with a release liner in a form (roll form) in which the second adhesive surface 1B is protected by being in contact with the back surface of the release liner 31.

[0025] <Peel Force> (Post-Heating Peel Force Difference (Fb1-Fa1)) The pressure-sensitive adhesive sheet disclosed herein has a first adhesive surface constituted by a first pressure-sensitive adhesive layer and a second adhesive surface constituted by a second pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet has a post-heating peel force Fa1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the first pressure-sensitive adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes, and a post-heating peel force Fb1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the second pressure-sensitive adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes. That is, the post-heating peel force difference (|Fb1-Fa1|), calculated as the absolute value of the difference between the post-heating peel forces Fa1 and Fb1, is greater than 0 N / 20 mm. With such a pressure-sensitive adhesive sheet, when a bonded body in which a first member and a second member are bonded via the pressure-sensitive adhesive sheet is heated and then dismantled, it is possible to specify in advance or to increase the predictability of which of the first and second members the pressure-sensitive adhesive sheet will remain on when the two members are separated, thereby improving the ease of dismantling the bonded body and the reusability (recyclability, reuse, etc.) of the dismantled parts.

[0026] The post-heating peel force difference (|Fb1-Fa1|) may be, for example, 0.03 N / 20 mm or more, suitably 0.05 N / 20 mm or more, preferably 0.1 N / 20 mm or more, and more preferably 0.5 N / 20 mm or more. As the post-heating peel force difference (|Fb1-Fa1|) increases, the predictability of which of the first and second components the PSA sheet will remain on when the two components separate tends to improve. In some embodiments, the post-heating peel force difference (|Fb1-Fa1|) may be, for example, 0.7 N / 20 mm or more, 0.9 N / 20 mm or more, 1.2 N / 20 mm or more, 1.5 N / 20 mm or more, 1.7 N / 20 mm or more, or 2.0 N / 20 mm or more. The upper limit of the post-heating peel force difference (|Fb1-Fa1|) is not particularly limited. In some embodiments, the post-heating peel force difference (|Fb1-Fa1|) may be, for example, approximately 30 N / 20 mm or less, 25 N / 20 mm or less, 15 N / 20 mm or less, 10 N / 20 mm or less, 5.0 N / 20 mm or less, 3.0 N / 20 mm or less, or 2.5 N / 20 mm or less. Note that the post-heating peel forces Fa1 and Fb1 are both typically 0 N / 20 mm or more.

[0027] The pressure-sensitive adhesive sheet disclosed herein includes a first pressure-sensitive adhesive layer configured to be easily peelable by thermal polymerization, and thus can be preferably implemented in an embodiment in which the post-heat peel strength Fa1 is smaller than the post-heat peel strength Fb1, i.e., Fa1 [N / 20 mm] < Fb1 [N / 20 mm]. According to such an embodiment, the adhesive surface of the pressure-sensitive adhesive sheet after heating can exhibit easy peelability on the first adhesive surface while maintaining a relatively large peel strength on the second adhesive surface. A pressure-sensitive adhesive sheet designed in this manner is preferable from the viewpoint of ease of dismantling the assembly and reusability (e.g., recyclability, reusability) of the dismantled product, for example, when a bonded assembly in which a first member and a second member are bonded via the pressure-sensitive adhesive sheet is dismantled after heating.

[0028] (Post-heating peel strength Fa1 of first pressure-sensitive adhesive layer) In the pressure-sensitive adhesive sheet disclosed herein, the post-heating peel strength Fa1 of the first pressure-sensitive adhesive layer is not particularly limited and can be appropriately set so that the desired ease of releasability is exhibited after heating and the post-heating peel strength difference (|Fb1-Fa1|) exceeds 0. In some embodiments, from the viewpoint of the above-mentioned ease of releasability, the post-heating peel strength Fa1 of the first pressure-sensitive adhesive layer is suitably, for example, less than 3.0 N / 20 mm, advantageously 2.0 N / 20 mm or less, and preferably 1.0 N / 20 mm or less. In some embodiments requiring a higher level of easy peelability after heating, the post-heat peel strength Fa1 of the first pressure-sensitive adhesive layer may be, for example, less than 1.0 N / 20 mm, preferably 0.8 N / 20 mm or less, more preferably 0.6 N / 20 mm or less, and even more preferably 0.5 N / 20 mm or less, and may be 0.4 N / 20 mm or less, 0.3 N / 20 mm or less, 0.2 N / 20 mm or less, or less than 0.2 N / 20 mm. A pressure-sensitive adhesive sheet with such a low post-heat peel strength Fa1 can easily peel an adherend from the first pressure-sensitive adhesive layer (first adhesive surface) after heating while reducing the load applied to the adherend. Therefore, it can also be preferably used in embodiments in which the first adhesive surface is attached to an adherend made of a brittle material (typically a hard and brittle material) such as a glass material or a semiconductor material. The post-heating peel force Fa1 is typically greater than 0 N / 20 mm, and from the viewpoint of adherend retention after heating, etc., it is appropriate that it be 0.01 N / 20 mm or greater. The post-heating peel force Fa1 may be, for example, 0.05 N / 20 mm or greater, 0.1 N / 20 mm or greater, 0.2 N / 20 mm or greater, 0.3 N / 20 mm or greater, or 0.4 N / 20 mm or greater. In some embodiments, the post-heating peel force Fa1 may be 0.5 N / 20 mm or greater, 0.8 N / 20 mm or greater, 1.0 N / 20 mm or greater, 1.5 N / 20 mm or greater, or 2.0 N / 20 mm or greater.

[0029] (Post-heating peel strength Fb1 of second pressure-sensitive adhesive layer) In the pressure-sensitive adhesive sheet disclosed herein, the post-heating peel strength Fb1 of the second pressure-sensitive adhesive layer is not particularly limited and can be appropriately set so that the post-heating peel strength difference (|Fb1-Fa1|) exceeds 0. The post-heating peel strength Fb1 is typically greater than 0 N / 20 mm, and from the viewpoint of adherend retention after heating, etc., it is suitably 0.01 N / 20 mm or greater. In some embodiments, the post-heating peel strength Fb1 may be, for example, 0.05 N / 20 mm or more, 0.1 N / 20 mm or more, 0.2 N / 20 mm or more, 0.5 N / 20 mm or more, 0.8 N / 20 mm or more, 1.0 N / 20 mm or more, or 1.5 N / 20 mm or more, 2.0 N / 20 mm or more, 2.5 N / 20 mm or more, 3.0 N / 20 mm or more, 3.3 N / 20 mm or more, or 3.5 N / 20 mm or more. The upper limit of the post-heating peel strength Fb1 of the second PSA layer is not particularly limited and may be, for example, approximately 30 N / 20 mm or less, 20 N / 20 mm or less, 15 N / 20 mm or less, 10 N / 20 mm or less, or 7.0 N / 20 mm or less. It can be advantageous, for example, in embodiments where the removability after heating from an adherend attached to the second PSA layer after heating from the adherend is taken into consideration, that the post-heat peel strength Fb1 of the second PSA layer is not too high. In some embodiments, the post-heat peel strength Fb1 may be, for example, 5.0 N / 20 mm or less, 4.0 N / 20 mm or less, 3.0 N / 20 mm or less (e.g., less than 3.0 N / 20 mm), or 2.5 N / 20 mm or less, or may be 2.0 N / 20 mm or less, 1.5 N / 20 mm or less, 1.0 N / 20 mm or less (e.g., less than 1.0 N / 20 mm), 0.5 N / 20 mm or less, 0.3 N / 20 mm or less, or 0.2 N / 20 mm or less.

[0030] (Post-Heating Peel Force Ratio (Fb1 / Fa1)) In some preferred embodiments of the pressure-sensitive adhesive sheet disclosed herein, the post-heating peel force ratio (Fb1 / Fa1), calculated from the post-heating peel force Fa1 [N / 20 mm] of the first pressure-sensitive adhesive layer and the post-heating peel force Fb1 [N / 20 mm] of the second pressure-sensitive adhesive layer, is greater than 1.0. This allows the pressure-sensitive adhesive sheet to exhibit easy peelability on the first pressure-sensitive adhesive surface after heating, while maintaining a relatively high peel force on the second pressure-sensitive adhesive surface. A pressure-sensitive adhesive sheet designed in this manner is preferred, for example, in a use mode in which a bonded body in which a first member and a second member are bonded via the pressure-sensitive adhesive sheet is heated and then disassembled, from the viewpoint of the ease of disassembly of the bonded body and the reusability (recyclability, reusability, etc.) of the disassembled body. From this viewpoint, in some embodiments, the post-heating peel force ratio (Fb1 / Fa1) is advantageously 1.5 or more, preferably 2.0 or more, more preferably 3.0 or more, and may be 4.0 or more, or even 5.0 or more. The upper limit of the post-heating peel force ratio (Fb1 / Fa1) is not particularly limited, and in some embodiments, the higher the better. In other embodiments, the post-heating peel force ratio (Fb1 / Fa1) may be, for example, 1,000 or less, or even 500 or less. For example, in some embodiments, such as embodiments in which the retention of an adherend attached to the first adhesive surface after heating is taken into consideration, or embodiments in which the removability of an adherend attached to the second adhesive surface from the PSA sheet after heating is taken into consideration, it can be advantageous for the post-heating peel force ratio (Fb1 / Fa1) to be not too large. In such embodiments, the post-heating peel force ratio (Fb1 / Fa1) may be, for example, 100 or less, 50 or less, 30 or less, 20 or less, 10 or less, 8.0 or less, 6.0 or less, or 5.0 or less.

[0031] (Pre-heating peel strength Fa0 of first pressure-sensitive adhesive layer) In the pressure-sensitive adhesive sheet disclosed herein, the initial (pre-heating) peel strength Fa0 of the first pressure-sensitive adhesive layer is suitably, for example, 0.5 N / 20 mm or more, advantageously 0.8 N / 20 mm or more, and preferably 1.0 N / 20 mm or more or greater than 1.0 N / 20 mm. A pressure-sensitive adhesive sheet exhibiting the above pre-heating peel strength Fa0 allows the first pressure-sensitive adhesive surface to exhibit good adhesion to an adherend, and is able to, for example, appropriately hold the adherend. From the viewpoint of making it easier to obtain better adhesion (e.g., adherend retention performance), in some embodiments, the pre-heating peel force Fa0 may be, for example, 1.2 N / 20 mm or more, 1.5 N / 20 mm or more, 1.8 N / 20 mm or more, 2.0 N / 20 mm or more, 3.0 N / 20 mm or more, 4.0 N / 20 mm or more, 5.0 N / 20 mm or more, 7.0 N / 20 mm or more, 8.0 N / 20 mm or more, 9.0 N / 20 mm or more, or 10 N / 20 mm or more. The upper limit of the pre-heating peel strength Fa0 is appropriately set depending on the adhesiveness required for the first adhesive surface, and is not limited to a specific range. For example, it may be approximately 30 N / 20 mm or less, 20 N / 20 mm or less, 15 N / 20 mm or less, 10 N / 20 mm or less, 5.0 N / 20 mm or less, or 3.0 N / 20 mm or less. The pre-heating peel strength Fa0 of the first adhesive layer refers to the peel strength (peel force) from a glass plate measured under conditions of a peel angle of 180 degrees and a peel speed of 300 mm / min in an environment of 23°C. More specifically, the pre-heating peel strength Fa0 is measured by the method described in the Examples below.

[0032] (Post-heat peel strength reduction rate A of the first pressure-sensitive adhesive layer) In some embodiments, the post-heat peel strength reduction rate A of the first pressure-sensitive adhesive layer, calculated from the pre-heat peel strength Fa0 and the post-heat peel strength Fa1 using the following formula: Post-heat peel strength reduction rate A [%] = (1 - Fa1 / Fa0) × 100; is suitably greater than 20% (e.g., greater than 30%), advantageously greater than 40%, and preferably greater than 50%. The first pressure-sensitive adhesive surface of a pressure-sensitive adhesive sheet satisfying the above characteristics can exhibit good adhesion to an adherend while exhibiting good releasability (heat-induced releasability) upon peeling after heat treatment. In some preferred embodiments, the post-heat peel strength reduction rate A can be 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or even 97% or more. The greater the post-heat peel strength reduction rate A, the better the heat-induced releasability that can be exhibited. In some embodiments, the post-heat peel strength reduction rate A is preferably less than 99.9%. With a pressure-sensitive adhesive sheet having a post-heat peel strength reduction rate A of less than 99.9%, the first pressure-sensitive adhesive surface after heating maintains its adhesive state with the adherend while exhibiting the desired ease of releasability from the adherend. This prevents the adherend attached to the first pressure-sensitive adhesive surface from spontaneously peeling from the pressure-sensitive adhesive sheet due to heating, and prevents the resulting defects from occurring. From this perspective, the post-heat peel strength reduction rate A may be 99.0% or less, for example, less than 95.0%.

[0033] (Pre-heating peel strength Fb0 of second pressure-sensitive adhesive layer) In the pressure-sensitive adhesive sheet disclosed herein, the pre-heating (initial) peel strength Fb0 of the second pressure-sensitive adhesive layer is not particularly limited and can be appropriately set depending on the purpose. In some embodiments, the pre-heating peel strength Fb0 of the second pressure-sensitive adhesive layer may be, for example, 0.2 N / 20 mm or more, suitably 0.5 N / 20 mm or more, and preferably 0.8 N / 20 mm or more. A pressure-sensitive adhesive sheet exhibiting the above pre-heating peel strength Fb0 allows the second pressure-sensitive adhesive surface to exhibit good adhesion to an adherend, and can, for example, properly hold the adherend. From the viewpoint of making it easier to obtain better adhesion (e.g., adherend retention performance), in some embodiments, the pre-heating peel force Fb0 may be, for example, 1.0 N / 20 mm or more, 1.2 N / 20 mm or more, 1.5 N / 20 mm or more, 2.0 N / 20 mm or more, 3.0 N / 20 mm or more, 4.0 N / 20 mm or more, 5.0 N / 20 mm or more, or 7.0 N / 20 mm or more. The upper limit of the pre-heating peel force Fb0 of the second pressure-sensitive adhesive layer is not limited to a particular range, and may be, for example, approximately 30 N / 20 mm or less, 20 N / 20 mm or less, 15 N / 20 mm or less, 10 N / 20 mm or less, 5.0 N / 20 mm or less, or 3.0 N / 20 mm or less. The pre-heating peel strength Fb0 of the second pressure-sensitive adhesive layer refers to the peel strength (peel strength) from a glass plate measured under conditions of a peel angle of 180° and a peel speed of 300 mm / min in an environment of 23° C. More specifically, the pre-heating peel strength Fb0 is measured by the method described in the examples below.

[0034] (Post-heat peel strength reduction rate B of second pressure-sensitive adhesive layer) In the pressure-sensitive adhesive sheet disclosed herein, the relationship between the pre-heat peel strength Fb0 and the post-heat peel strength Fb1 of the second pressure-sensitive adhesive layer is not particularly limited. For example, the post-heat peel strength Fb1 may be greater than the pre-heat peel strength Fb0, smaller than the pre-heat peel strength Fb0, or approximately the same as the pre-heat peel strength Fb0. More specifically, the post-heat peel strength reduction rate B of the second pressure-sensitive adhesive layer, calculated from the pre-heat peel strength Fb0 and the post-heat peel strength Fb1 using the following formula: Post-heat peel strength reduction rate B [%] = (1 - Fb1 / Fb0) × 100, may be less than 0% (e.g., -300% or less, -500% or less), greater than 0% (e.g., greater than 0% and less than 99.0%), or even approximately 0%. In some embodiments, such as when the removability of the second adhesive surface from the adherend to which it is attached after heating is taken into consideration, the post-heat peel force reduction rate B may be, for example, more than 20%, more than 30%, more than 40%, or more than 50%, or may be 60% or more, 70% or more, or 80% or more, 85% or more, or 90% or more.

[0035] In some embodiments of the PSA sheet disclosed herein, the pre-heating peel forces Fa0 and Fb0 [N / 20 mm] are both suitably 1.0 N / 20 mm or greater, and may both be 2.0 N / 20 mm or greater. In some preferred embodiments of the PSA sheet, the pre-heating peel forces Fa0 and Fb1 are 3.0 N / 20 mm or greater, more preferably 4.0 N / 20 mm or greater, even more preferably 5.0 N / 20 mm or greater, and may both be 7.0 N / 20 mm or greater, or may both be 8.0 N / 20 mm or greater. PSA sheets in which both the pre-heating peel forces Fa0 and Fa1 are 4.0 N / 20 mm or greater or a higher predetermined value have good fixing performance to adherends on the first and second PSA surfaces before heating (initial stage), and are suitable for applications such as producing a bonded body in which two members are firmly bonded via the PSA sheet. In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the post-heat peel strengths Fa1 and Fb1 [N / 20 mm] are, for example, preferably both less than 4.0 N / 20 mm, and preferably both less than 3.0 N / 20 mm. A pressure-sensitive adhesive sheet satisfying the above characteristics provides good dismantling workability for an assembly in which two members are joined via the pressure-sensitive adhesive sheet, and good reusability of the dismantled articles, for example, when the assembly is dismantled after heating. A pressure-sensitive adhesive sheet having pre-heat peel strengths Fa0 and Fb0 both equal to or greater than a predetermined lower limit and post-heat peel strengths Fa1 and Fb1 both equal to or less than a predetermined upper limit is preferred because it can exhibit good fixing performance during use and can be easily separated from an adherend after use by utilizing its easy-to-remove function upon heating.

[0036] The pre-heating peel strength, post-heating peel strength and the relative relationship between them of the first and second pressure-sensitive adhesive layers can be achieved and adjusted based on the contents of this specification by appropriately selecting the type of polymer contained in each pressure-sensitive adhesive layer (monomer composition, etc.), the presence or absence, type and amount of other components that may be contained in each pressure-sensitive adhesive layer (e.g., a thermal polymerization initiator or polyfunctional monomer, as described below), and their combinations, as well as the presence or absence, type and amount of use of a crosslinking agent in each pressure-sensitive adhesive layer.

[0037] <Gel Fraction> (Increase in Gel Fraction (Ga1-Ga0) of First Pressure-Sensitive Adhesive Layer) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the increase in gel fraction (Ga1-Ga0) calculated from the pre-heating (initial) gel fraction Ga0 [%] and the post-heating gel fraction Ga1 [%] of the first pressure-sensitive adhesive layer is typically greater than 0%, suitably 5% or greater, and preferably 10% or greater. A first pressure-sensitive adhesive layer that satisfies the above-mentioned increase in gel fraction (Ga1-Ga0) exhibits good thermosetting properties and tends to be more likely to exhibit a peel force reduction effect due to heating (easy thermal releasability) on the first pressure-sensitive adhesive surface. From the viewpoint of easily obtaining better heat-peelability, in some embodiments, the gel fraction increase (Ga1-Ga0) of the first pressure-sensitive adhesive layer is more preferably 13% or more, and may be, for example, 16% or more, 20% or more, 25% or more, 30% or more, 35% or more, or 40% or more. Also, in some embodiments, from the viewpoint of easily achieving both adhesiveness before heating and easy releasability after heating, the gel fraction increase (Ga1-Ga0) of the first pressure-sensitive adhesive layer is, for example, suitably 70% or less, preferably 60% or less, or may be 50% or less, or may be 40% or less.

[0038] The pre-heat gel fraction Ga0 of the first pressure-sensitive adhesive layer is determined as the weight percentage of the ethyl acetate-insoluble content of a pressure-sensitive adhesive sample taken from the initial (pre-heated) first pressure-sensitive adhesive layer. The post-heat gel fraction Ga1 of the first pressure-sensitive adhesive layer is determined in the same manner as the pre-heat gel fraction Ga0 for a pressure-sensitive adhesive sample taken from the first pressure-sensitive adhesive layer after heat treatment at 180°C for 30 minutes. More specifically, the pre-heat gel fraction Ga0 and post-heat gel fraction Ga1 are measured by the method described in the Examples below. The pre-heat gel fraction Gb0 and post-heat gel fraction Gb1 of the second pressure-sensitive adhesive layer described below are determined in the same manner as the pre-heat gel fraction Ga0 and post-heat gel fraction Ga1 of the first pressure-sensitive adhesive layer for a pressure-sensitive adhesive sample taken from the second pressure-sensitive adhesive layer or the second pressure-sensitive adhesive layer after heat treatment at 180°C for 30 minutes.

[0039] (Post-heat gel fraction Ga1 of first pressure-sensitive adhesive layer) The first pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein preferably satisfies any of the gel fraction increase amounts (Ga1-Ga0) disclosed herein and has a post-heat gel fraction Ga1 of 50% or more (more preferably 70% or more, and even more preferably 80% or more). A first pressure-sensitive adhesive layer exhibiting such thermosetting properties is likely to exhibit good heat-peelability. From the viewpoint of improving the post-heat peelability, in some respects, the post-heat gel fraction Ga1 is preferably 83% or more, more preferably 85% or more, and may be 88% or more, 90% or more, 93% or more, 95% or more, or 97% or more. The post-heating gel fraction Ga1 of the first pressure-sensitive adhesive layer is typically less than 100%, and is suitably 99.8% or less (e.g., 99.5% or less) from the viewpoint of adherend retention after heating, etc., and is preferably 99% or less, and may be 98% or less, 95% or less, 92% or less, or 90% or less. In some embodiments, the post-heating gel fraction Ga1 of the first pressure-sensitive adhesive layer may be 85% or less, 80% or less, or 75% or less.

[0040] (Pre-heating gel fraction Ga0 of first pressure-sensitive adhesive layer) The pre-heating (initial) gel fraction Ga0 of the first pressure-sensitive adhesive layer is not particularly limited. In some embodiments, from the viewpoint of obtaining sufficient adhesion to an adherend and good thermal peelability, the pre-heating gel fraction Ga0 is suitably, for example, 85% or less, preferably 80% or less, more preferably 75% or less, and may be 70% or less, 65% or less, or even 60% or less. Furthermore, from the viewpoint of easily obtaining appropriate cohesiveness and holding power, in some embodiments, the pre-heating (initial) gel fraction Ga0 of the first pressure-sensitive adhesive layer is suitably 20% or more, preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and may be 60% or more, or may be 70% or more.

[0041] (Gel Fraction of Second Pressure-Sensitive Adhesive Layer) In the pressure-sensitive adhesive sheet disclosed herein, the pre-heating (initial) gel fraction Gb0 and post-heating gel fraction Gb1 of the second pressure-sensitive adhesive layer are not particularly limited. In some embodiments, the pre-heating gel fraction Gb0 of the second pressure-sensitive adhesive layer is suitably approximately 99.8% or less, and preferably 99.5% or less (e.g., 99% or less), from the viewpoint of the adhesiveness of the second pressure-sensitive adhesive surface, etc. In some embodiments, from the viewpoint of easily obtaining higher adhesiveness, the pre-heating gel fraction Gb0 may be, for example, 98% or less, 95% or less, 90% or less, 85% or less, 80% or less, 70% or less, 65% or less, or 60% or less. Furthermore, from the viewpoint of easily obtaining appropriate cohesion and holding power, in some embodiments, the pre-heating gel fraction Gb0 is suitably 20% or more, preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and may be 60% or more, or may be 70% or more. The post-heat gel fraction Gb1 of the second pressure-sensitive adhesive layer is typically less than 100%. From the viewpoint of adherend retention after heating, it is suitably 99.8% or less, for example, preferably 99.5% or less, and may be 99% or less, or may be 98.5% or less. In some embodiments, the post-heat gel fraction Gb1 may be 95% or less, 92% or less, or 90% or less. From the viewpoint of easily achieving appropriate cohesiveness and retention after heating, in some embodiments, the post-heat gel fraction Gb1 is suitably 50% or more (e.g., more than 50%), preferably 60% or more, more preferably 70% or more, and may be 80% or more, 90% or more, or 95% or more. The gel fraction increase (Gb1 - Gb0) calculated from the pre-heat gel fraction Gb0 [%] and the post-heat gel fraction Gb1 [%] of the second pressure-sensitive adhesive layer is not particularly limited and may be, for example, within the range of 0% to 80%. A more specific range of the gel fraction increase (Gb1-Gb0) can vary depending on the purpose, for example, whether the second pressure-sensitive adhesive layer is thermosetting. In an embodiment in which the second pressure-sensitive adhesive layer is not thermosetting, the lower limit of the gel fraction increase (Gb1-Gb0) of the second pressure-sensitive adhesive layer can be, for example, 0% or more or more than 0%, and the upper limit can be, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less.Furthermore, in an embodiment in which the second pressure-sensitive adhesive layer is thermosetting, the lower limit of the increase in gel fraction (Gb1-Gb0) of the second pressure-sensitive adhesive layer may be, for example, 5% or more, 10% or more, or 15% or more, and the upper limit may be, for example, 80% or less, 70% or less, 60% or less, 50% or less, or 40% or less.

[0042] The PSA sheet disclosed herein may be, for example, a PSA sheet in which the gel fraction of the first PSA layer is approximately equal to or lower than the gel fraction of the second PSA layer initially (before heating), and the gel fraction of the first PSA layer is higher than the gel fraction of the second PSA layer after heat treatment for 30 minutes at 180° C. In some embodiments, the PSA sheet may have a value of (pre-heating gel fraction Gb0 [%] - pre-heating gel fraction Ga0 [%]) of, for example, -5% or more, preferably 0% or more, more preferably 5% or more, 10% or more, 20% or more, or 30% or more, and a value of (post-heating gel fraction Ga1 [%] - post-heating gel fraction Gb1 [%]) of, for example, more than 0%, preferably 5% or more, more preferably 10% or more, 15% or more, 20% or more, or 30% or more. With a PSA sheet in which the gel fractions of the first and second PSA layers satisfy the above relative relationship before and after heating, in an embodiment in which the peel strength after heating is Fb1 > Fa1, it is easy to obtain a PSA sheet in which the difference in peel strength after heating (|Fb1 - Fa1|) is within any of the upper and lower limits disclosed herein.

[0043] The pre-heating gel fractions and post-heating gel fractions of the first and second pressure-sensitive adhesive layers, and the relative relationship therebetween, can be realized and adjusted mainly based on the contents of this specification by appropriately selecting the type of polymer contained in each pressure-sensitive adhesive layer (monomer composition, etc.), the presence or absence, type and amount of other components that may be contained in each pressure-sensitive adhesive layer (e.g., a thermal polymerization initiator, a polyfunctional monomer, as described below), and their combinations, as well as the presence or absence, type and amount of use of a crosslinking agent in each pressure-sensitive adhesive layer.

[0044] <Young's Modulus> (Young's Modulus Ya1 of First Pressure-Sensitive Adhesive Layer after Heating) The first pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein suitably has a Young's modulus Ya1 [MPa] of 5 MPa or more, preferably 10 MPa or more, measured under an environment of 23°C and 50% RH after heating at 180°C for 30 minutes. A first pressure-sensitive adhesive layer with a high Young's modulus Ya1 after heating tends to provide good easy peelability after heating on the first pressure-sensitive adhesive surface. From this perspective, in some embodiments, the Young's modulus Ya1 after heating may be, for example, 15 MPa or more, 20 MPa or more, 30 MPa or more, 40 MPa or more, 50 MPa or more, 60 MPa or more, or 70 MPa or more, or even 90 MPa or more, or 110 MPa or more. Furthermore, from the viewpoint of avoiding an excessive decrease in peel strength after heating, the Young's modulus Ya1 after heating is suitably, for example, 2000 MPa or less, preferably 1000 MPa or less, more preferably 500 MPa or less, and may be 300 MPa or less, 200 MPa or less, 150 MPa or less, 100 MPa or less, or 75 MPa or less.

[0045] The post-heating Young's modulus Ya1 of the first pressure-sensitive adhesive layer is determined from a stress-strain curve (S-S curve) of the first pressure-sensitive adhesive layer that has been heat-treated at 180°C for 30 minutes, under conditions of 23°C, 50% RH, and a tensile speed of 50 mm / min. The pre-heating (initial) Young's modulus Ya0 of the first pressure-sensitive adhesive layer, described below, is determined in the same manner as the post-heating Young's modulus Ya1, except that the first pressure-sensitive adhesive layer is not subjected to the heat treatment. The pre-heating (initial) Young's modulus Yb0 and post-heating Young's modulus Yb1 of the second pressure-sensitive adhesive layer, described below, are measured in the same manner as the pre-heating Young's modulus Ya0 and post-heating Young's modulus Ya1 of the first pressure-sensitive adhesive layer, respectively. More specifically, the above Young's moduli Ya0, Ya1, Yb0, and Yb1 are measured by the method described in the Examples, described below.

[0046] (Young's Modulus Increase Ratio (Ya1 / Ya0) of First Pressure-Sensitive Adhesive Layer) The first pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein suitably has thermosetting properties such that the Young's modulus increase ratio (Ya1 / Ya0), calculated from the pre-heating Young's modulus Ya0 [MPa] measured under an environment of 23°C and 50% RH and the post-heating Young's modulus Ya1 [MPa], is 2.0 or more (e.g., 5.0 or more, 10 or more, 20 or more, or 30 or more). The higher the Young's modulus increase ratio, the higher the degree of curing of the pressure-sensitive adhesive layer upon heating, and the easier it is to obtain excellent heat-peelability on the first pressure-sensitive adhesive surface. From this perspective, in some embodiments, the Young's modulus increase ratio (Ya1 / Ya0) of the first pressure-sensitive adhesive layer is preferably 50 or more, more preferably 80 or more, 100 or more, or 150 or more, and even more preferably 200 or more, or 250 or more. There is no particular upper limit for the Young's modulus increase ratio (Ya1 / Ya0) of the first pressure-sensitive adhesive layer. In some embodiments, the Young's modulus increase ratio (Ya1 / Ya0) may be, for example, approximately 10,000 or less, 5,000 or less, 3,000 or less, 2,500 or less, 2,000 or less, 1,500 or less, or 1,000 or less.

[0047] (Young's modulus Ya0 of the first pressure-sensitive adhesive layer before heating) The Young's modulus Ya0 [MPa] of the first pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein is not particularly limited. The Young's modulus Ya0 before heating can be appropriately selected so as to obtain the desired adhesiveness (e.g., pre-heating peel strength Fa0) depending on the intended use of the pressure-sensitive adhesive sheet. In some embodiments, the Young's modulus Ya0 before heating is, for example, suitably less than 5.0 MPa, advantageously 3.0 MPa or less, preferably 1.0 MPa or less or 0.7 MPa or less, more preferably 0.5 MPa or less (e.g., less than 0.5 MPa), and may be 0.4 MPa or less, 0.3 MPa or less, or 0.2 MPa or less, from the viewpoint of the adhesiveness of the first adhesive surface. Furthermore, the Young's modulus Ya0 before heating may be, for example, 0.001 MPa or more, and from the viewpoint of making it easier to obtain appropriate cohesion and holding power, it is advantageous to have it be 0.005 MPa or more, preferably 0.01 MPa or more, more preferably 0.05 MPa or more, and may be 0.08 MPa or more, or may be 0.1 MPa or more.

[0048] (Young's Modulus of Second Pressure-Sensitive Adhesive Layer) In the pressure-sensitive adhesive sheet disclosed herein, the pre-heating (initial) Young's modulus Yb0 and post-heating Young's modulus Yb1 of the second pressure-sensitive adhesive layer are not particularly limited and may be, for example, within the range of approximately 0.001 MPa to approximately 1000 MPa. In some embodiments, the pre-heating Young's modulus Yb0 of the second pressure-sensitive adhesive layer is, for example, suitably less than 5.0 MPa from the viewpoint of the adhesiveness of the second pressure-sensitive adhesive surface, and is preferably 3.0 MPa or less, and may be 2.0 MPa or less, 1.0 MPa or less, or may be 0.8 MPa or less. Furthermore, the pre-heating Young's modulus Yb0 may be, for example, 0.001 MPa or more, and from the viewpoint of easily achieving appropriate cohesion and holding power, is advantageously 0.005 MPa or more, preferably 0.01 MPa or more, more preferably 0.05 MPa or more, and may be 0.08 MPa or more, 0.1 MPa or more, or may be 0.3 MPa or more. In some embodiments, the post-heating Young's modulus Yb1 of the second pressure-sensitive adhesive layer is suitably 100 MPa or less, preferably 50 MPa or less, from the viewpoint of adherend retention after heating, etc., and may be, for example, 30 MPa or less, 20 MPa or less, 10 MPa or less, 5.0 MPa or less, 1.0 MPa or less, or 0.8 MPa or less. The post-heating Young's modulus Yb1 may be, for example, 0.001 MPa or more, and from the viewpoint of easily achieving appropriate cohesion and retention, it is advantageous to be 0.005 MPa or more, preferably 0.01 MPa or more, and may be 0.05 MPa or more, 0.08 MPa or more, 0.1 MPa or more, or 0.3 MPa or more. The Young's modulus increase ratio (Yb1 / Yb0) calculated from the pre-heating Young's modulus Yb0 [MPa] and the post-heating Young's modulus Yb1 [MPa] of the second pressure-sensitive adhesive layer is not particularly limited, and may be, for example, in the range of 0 to 10,000. A more specific range of the Young's modulus increase ratio (Yb1 / Yb0) may vary depending on the purpose, for example, whether the second pressure-sensitive adhesive layer is thermosetting. In an embodiment in which the second pressure-sensitive adhesive layer is not thermosetting, the Young's modulus increase ratio (Yb1 / Yb0) of the second pressure-sensitive adhesive layer may have a lower limit of 1.0 or more or greater than 1.0, and an upper limit of less than 2.0 or less than 1.5.Furthermore, in an embodiment in which the second pressure-sensitive adhesive layer has thermosetting properties, the Young's modulus increase ratio (Yb1 / Yb0) may have a lower limit of, for example, 2.0 or more, 5.0 or more, 10 or more, 30 or more, 50 or more, or 100 or more, and an upper limit of, for example, 10,000 or less, 5,000 or less, 3,000 or less, 2,500 or less, 2,000 or less, 1,500 or less, or 1,000 or less.

[0049] (Post-heating Young's modulus ratio (Ya1 / Yb1)) In some embodiments, the post-heating Young's modulus ratio (Ya1 / Yb1), calculated as the ratio of the post-heating Young's modulus Ya1 of the first PSA layer to the post-heating Young's modulus Yb1 of the second PSA layer, is suitably, for example, greater than 1.0, preferably 1.5 or greater, and may be 2.0 or greater, 5.0 or greater, 10 or greater, 30 or greater, 50 or greater, 100 or greater, 150 or greater, or 200 or greater. With a PSA sheet that satisfies any of the above-mentioned post-heating Young's modulus ratios (Ya1 / Yb1), in an embodiment in which the post-heating peel strength is Fb1>Fa1, a PSA sheet in which the post-heating peel strength difference (|Fb1-Fa1|) is within any of the upper and lower limits disclosed herein is likely to be obtained. The upper limit of the Young's modulus ratio after heating (Ya1 / Yb1) is not particularly limited, and can be, for example, 10,000 or less, 5,000 or less, 1,000 or less, 500 or less, or 100 or less.

[0050] (Young's modulus ratio before heating (Ya0 / Yb0)) The Young's modulus ratio before heating (Ya0 / Yb0), calculated as the ratio of the Young's modulus before heating Ya0 of the first PSA layer to the Young's modulus before heating Yb0 of the second PSA layer, is not particularly limited. In some embodiments, the upper limit of the Young's modulus ratio before heating (Ya0 / Yb0) may be, for example, 0.001 or more, 0.01 or more, or 0.1 or more. The lower limit of the Young's modulus ratio before heating (Ya0 / Yb0) may be, for example, 10,000 or less, 1,000 or less, 100 or less, or 10 or less.

[0051] The pre-heating Young's modulus, post-heating Young's modulus and relative relationship therebetween of the first and second pressure-sensitive adhesive layers can be realized and adjusted mainly based on the contents of this specification by appropriately selecting the type of polymer contained in each pressure-sensitive adhesive layer (monomer composition, etc.), the presence or absence, type and amount of other components that may be contained in each pressure-sensitive adhesive layer (e.g., a thermal polymerization initiator, a polyfunctional monomer, as described below), and their combinations, as well as the presence or absence, type and amount of use of a crosslinking agent in each pressure-sensitive adhesive layer.

[0052] <First Pressure-Sensitive Adhesive Layer> The first pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein is a thermosetting pressure-sensitive adhesive layer. Herein, the term "thermosetting pressure-sensitive adhesive layer (pressure-sensitive adhesive)" refers to the property that, upon heat treatment at 180°C for 30 minutes, at least one of the gel fraction and Young's modulus is increased compared to the initial value (before heating). A preferred example of a thermosetting pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer whose gel fraction increases by 5% or more or 10% or more upon the heat treatment. Another preferred example of a thermosetting pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer whose Young's modulus increases by 2.0 times or more, 5.0 times or more, or 10 times or more upon the heat treatment. The above definition and preferred examples of a thermosetting pressure-sensitive adhesive layer can also be applied to a second pressure-sensitive adhesive layer when the second pressure-sensitive adhesive layer is thermosetting.

[0053] The first pressure-sensitive adhesive layer typically contains at least a polymer and may further contain a monomer. From the viewpoint of easily exhibiting the desired thermosetting properties and heat-peelability, the first pressure-sensitive adhesive layer preferably contains at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule (hereinafter sometimes simply abbreviated as "polyfunctional monomer") and a polymer having an ethylenically unsaturated group.

[0054] (Polymer) In the technology disclosed herein, the type of adhesive constituting the first adhesive layer is not particularly limited. The first adhesive layer may contain one or more of 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, mixtures thereof, etc.), 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, etc., adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred.

[0055] The following description will mainly focus on pressure-sensitive adhesive layers made of acrylic pressure-sensitive adhesive, i.e., pressure-sensitive adhesive sheets having an acrylic pressure-sensitive adhesive layer as the first pressure-sensitive adhesive layer, but it is not intended to limit the first pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheets disclosed herein to an acrylic pressure-sensitive adhesive layer.

[0056] (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.

[0057] In some preferred embodiments, the monomer component includes an alkoxy group-containing (meth)acrylate. An acrylic polymer containing an alkoxy group-containing (meth)acrylate as a monomer component is likely to produce a pressure-sensitive adhesive layer that favorably combines good initial adhesion with easy peelability after heating. Furthermore, in embodiments in which the first pressure-sensitive adhesive layer contains a polyfunctional monomer, compatibility with the polyfunctional monomer is likely to be achieved. The acrylic polymer containing an alkoxy group-containing (meth)acrylate as a monomer component may be a polymer that does not contain an ethylenically unsaturated group, or may be a polymer that contains an ethylenically unsaturated group.

[0058] 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.

[0059] 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 effect 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, 30 wt% or more, or 50 wt% or more. In some embodiments, the content of the alkoxy group-containing (meth)acrylate in the monomer component is, for example, more than 50 wt%, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more, from the viewpoint of adhesive properties such as adhesive strength and compatibility with polyfunctional monomers. The upper limit of the content of the alkoxy group-containing (meth)acrylate in the monomer component is 100% by weight, and in some embodiments, from the viewpoint of obtaining the effects of other copolymerizable monomers such as functional group-containing monomers, the content of the alkoxy group-containing (meth)acrylate is advantageously about 99% by weight or less, and may be 95% by weight or less, 93% by weight or less, or 90% by weight or less. In other embodiments, the content of the alkoxy group-containing (meth)acrylate may be about 80% by weight or less, 70% by weight or less, 65% by weight or less, or 60% by weight or less.

[0060] 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.

[0061] 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.

[0062] Of these, at least C ４－２０ It is preferable to use alkyl (meth)acrylate, and at least C ４－１８ It is more preferred to use alkyl (meth)acrylate. １－２０ As the alkyl (meth)acrylate, C ４－８ It is preferable to use alkyl (meth)acrylate. ４－８ The use of alkyl acrylates is more preferred. ４－８ The alkyl (meth)acrylates can be used alone or in combination of two or more. ４－８ The 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.

[0063] C in the monomer components constituting the acrylic polymer １－２０ The content of alkyl (meth)acrylate is not particularly limited. １－２０ From the viewpoint of effectively obtaining the effect of using alkyl (meth)acrylate, C in the above monomer component １－２０ The content of alkyl (meth)acrylate is usually about 1% by weight or more, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more. １－２０ From the viewpoint of adhesive properties such as adhesive strength, the content of alkyl (meth)acrylate is, for example, more than 50% by weight, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more. １－２０ The upper limit of the content of alkyl (meth)acrylate is 100% by weight. In some embodiments, in order to obtain the effect of other copolymerizable monomers such as functional group-containing monomers, １－２０ The content of alkyl (meth)acrylate is advantageously about 99% by weight or less, and may be 95% by weight or less, 93% by weight or less, or 90% by weight or less. １－２０ The range of the content of alkyl (meth)acrylate is １－２０ The above C included in alkyl (meth)acrylate ４－２０ Alkyl (meth)acrylate, C ４－１８ Alkyl (meth)acrylate, C４－８ Alkyl (meth)acrylate, C ４－８ Alkyl acrylate, C ７－１２ Alkyl (meth)acrylate, C ７－１０ Alkyl acrylate, C ７－９ Alkyl acrylate, C ８ The content of each of the alkyl acrylate, BA, and 2EHA may be within a range.

[0064] 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. Suitable examples of the other monomers include monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, nitrogen-containing rings, etc.). The polar group-containing monomers can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the adhesive. The other monomers may be used alone or in combination of two or more.

[0065] Non-limiting specific examples of the other monomers include: Carboxy group-containing monomers: for example, acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Acid anhydride group-containing monomers: for example, maleic anhydride, itaconic anhydride, etc. Hydroxyl group-containing monomers: for example, 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. Monomers containing a sulfonic acid group or a phosphoric acid group: for example, styrenesulfonic acid, allylsulfonic acid, sodium vinylsulfonate, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, 2-hydroxyethyl acryloyl phosphate, etc. Epoxy group-containing monomers: for example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl (meth)acrylate glycidyl ether, allyl glycidyl ether, (meth)acrylic acid glycidyl ether, etc. Cyano group-containing monomers: for example, acrylonitrile, methacrylonitrile, etc. Isocyanate group-containing monomers: for example, 2-isocyanatoethyl (meth)acrylate, etc.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 Examples of suitable monomers include N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine (e.g., lactams such as N-vinyl-2-caprolactam). Monomers having a succinimide skeleton include N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyhexamethylenesuccinimide. Maleimides include N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide. Itaconimides: for example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, etc. Aminoalkyl (meth)acrylates: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate. Alkoxysilyl group-containing monomers: for example, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane. Vinyl esters: for example, vinyl acetate, vinyl propionate, etc.Vinyl ethers: for example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether. Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc. Olefins: for example, ethylene, butadiene, isoprene, isobutylene, etc. (Meth)acrylic acid esters having an alicyclic hydrocarbon group: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, etc. (Meth)acrylic acid esters having an aromatic hydrocarbon group: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc. Other examples include 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.

[0066] When such other monomers are used, the amount used is not particularly limited, but is suitably 0.01 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 0.1 wt% or more, or even 0.5 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 50 wt% or less of the total monomer components, and preferably 40 wt% or less.

[0067] In some embodiments, the monomer component constituting the acrylic polymer may contain 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. The monomer having a nitrogen atom can be used alone or in combination of two or more. A suitable example of the monomer having a nitrogen atom is a monomer having a nitrogen atom-containing ring. The monomer having a nitrogen atom and the monomer having a nitrogen atom-containing ring can be those exemplified above, and for example, a monomer represented by the general formula (1): In the general formula (1), N-vinyl cyclic amides represented by the formula: 1 is a divalent organic group, specifically -(CH2) ｎ n is an integer of 2 to 7 (preferably 2, 3, or 4). Of these, N-vinyl-2-pyrrolidone (NVP) can be preferably used. Other suitable examples of the monomer having a nitrogen atom include N,N-dialkyl(meth)acrylamides such as (meth)acrylamide and N,N-dimethyl(meth)acrylamide; N-monoalkyl(meth)acrylamides such as N-isopropyl(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-(2-hydroxyethyl)acrylamide (HEAA); N-acryloylmorpholine (ACMO); alkoxydiacetone(meth)acrylamide; vinylformamide; vinylacetamide; and the like. Of these, NVP, HEAA, and ACMO are more preferred.

[0068] The amount of the nitrogen-containing monomer (preferably the nitrogen-containing ring-containing monomer) used is not particularly limited and may be, for example, 1% by weight or more, or 3% by weight or more, of the total monomer components. In some embodiments, the amount of the nitrogen-containing monomer used in the monomer components is preferably 5% by weight or more, more preferably 7% by weight or more, and even more preferably 9% by weight or more. In other embodiments, the amount of the nitrogen-containing monomer used in the monomer components may be 10% by weight or more, 12% by weight or more, or 15% by weight or more. Furthermore, the amount of the nitrogen-containing monomer used is suitably, for example, 40% by weight or less, or may be 35% by weight or less, 30% by weight or less, or 25% by weight or less, of the total monomer components. In some embodiments, the amount of the nitrogen-containing monomer used may be, for example, 20% by weight or less, 15% by weight or less, or 12% by weight or less, of the total monomer components.

[0069] In some embodiments, the monomer component may contain 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. Examples of the hydroxyl group-containing monomer that can be used include those exemplified above, and for example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) can be preferably used. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0070] 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 preferred embodiments, the amount of the hydroxyl group-containing monomer used is 1 wt% or more of the total monomer components, more preferably 2 wt% or more, even more preferably 3 wt% or more, for example, 5 wt% or more. In some embodiments, the amount of the hydroxyl group-containing monomer used is suitably, for example, 40 wt% or less of the total monomer components, preferably 30 wt% or less, more preferably 20 wt% or less, even more preferably 10 wt% or less, or may be 7 wt% or less.

[0071] 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) in combination with a hydroxyl group-containing monomer (for example, HEA, 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.

[0072] In some embodiments, the monomer component includes a carboxyl group-containing monomer. Suitable examples of the carboxyl group-containing monomer include acrylic acid (AA) and methacrylic acid (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.

[0073] The amount of the carboxyl group-containing monomer used may be, for example, 0.01% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.3% by weight or more, or 0.5% by weight or more of the total monomer components. The proportion of the carboxyl group-containing monomer may be, for example, 15% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less (e.g., less than 1% by weight).

[0074] Furthermore, when an acrylic polymer having an ethylenically unsaturated group, which will be described later, is used as the polymer, 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 compound. Examples of other monomers having functional group A include carboxyl group-containing monomers, epoxy group-containing monomers, hydroxyl group-containing monomers, and isocyanate group-containing monomers, and hydroxyl group-containing monomers are 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.

[0075] 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).

[0076] The acrylic polymer may contain, as another monomer component, a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group. Using 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, suitable polyfunctional monomers from those described below as polyfunctional monomers that can be contained in the first pressure-sensitive adhesive layer can be used alone or in combination of two or more.

[0077] 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.

[0078] 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).

[0079] 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.

[0080] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to 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 of the examples of the thermal polymerization initiators added to the pressure-sensitive adhesive layer described below can be selected and used.

[0081] 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.

[0082] 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 ４More than that is fine, about 50 x 10 ４ or more, for example, about 55×10 ４ The upper limit of the Mw of the polymer is not particularly limited, and may be, for example, about 1000×10 ４ It may be less than or equal to approximately 100×10 ４ Here, Mw refers to a value calculated in terms of standard polystyrene obtained by gel permeation chromatography (GPC). As the GPC apparatus, for example, a model named "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) may be used.

[0083] (Polymer Having an Ethylenically Unsaturated Group) In some embodiments, a polymer having an ethylenically unsaturated group such as an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group is preferably used as the polymer. When a pressure-sensitive adhesive containing a polymer having an ethylenically unsaturated group is used, the ethylenically unsaturated group of the polymer is reacted upon heating, thereby thermosetting the pressure-sensitive adhesive and achieving the desired heat-peelability. Furthermore, in an embodiment in which the first pressure-sensitive adhesive layer contains a polyfunctional monomer as described below, the inclusion of a polymer having an ethylenically unsaturated group can increase the post-heat peel force reduction rate with the use of a smaller amount of polyfunctional monomer, thereby achieving the desired heat-peelability. As the polymer having an ethylenically unsaturated group, for example, a polymer having an ethylenically unsaturated group in a side chain can be used. As the monomer component of the polymer having an ethylenically unsaturated group, one or more of the monomer components exemplified for the polymer can be used within the above-mentioned content range.

[0084] 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.

[0085] 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: Phenomenex Synergi 4μ Polar-RP 80A (4.6 mm × 250 mm) 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

[0086] 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.

[0087] The method for introducing an ethylenically unsaturated group into a polymer is not particularly limited. For example, a method can be preferably adopted in which a compound having an ethylenically unsaturated group and a functional group (functional group B) capable of reacting with the functional group (functional group A) introduced into the acrylic polymer by copolymerization is reacted (typically by condensation or addition reaction) so as not to lose the ethylenically unsaturated group. 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, from the viewpoint of reaction traceability, a combination of a hydroxyl group and an isocyanate group is preferred. 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.

[0088] 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 the isocyanate group-containing monomers (isocyanate group-containing compounds) exemplified as other monomers that can be used in the polymerization of acrylic polymers. 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).

[0089] 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).

[0090] In embodiments in which a polymer having an ethylenically unsaturated group is used as the polymer, the content of the polymer having an ethylenically unsaturated group in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the amount of the polymer having an ethylenically unsaturated group used is suitably approximately 10% by weight or more of the total polymer (specifically, base polymer) contained in the pressure-sensitive adhesive layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the pressure-sensitive adhesive layer may consist essentially of the polymer having an ethylenically unsaturated group.

[0091] In some embodiments, the polymer used is a polymer substantially free of ethylenically unsaturated groups such as acryloyl groups, methacryloyl groups, vinyl groups, and allyl groups (the amount of ethylenically unsaturated groups is less than 0.01 mmol / g). The amount of such a polymer used is suitably approximately 10% by weight or more of the total polymer (specifically, base polymer) contained in the pressure-sensitive adhesive layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the pressure-sensitive adhesive layer may essentially consist of a polymer substantially free of ethylenically unsaturated groups.

[0092] (Multifunctional Monomer) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the first pressure-sensitive adhesive layer preferably contains a multifunctional monomer in addition to the polymer. By incorporating a multifunctional monomer into the pressure-sensitive adhesive in a pre-reacted (unreacted) state, the multifunctional monomer reacts upon high-temperature heating, reducing adhesive strength or suppressing an increase in peel strength, thereby achieving heat-peelability. More specifically, when a pressure-sensitive adhesive is heated at high temperatures while attached to an adherend, it typically adsorbs to the surface of the adherend. This increases the adhesive strength of the pressure-sensitive adhesive to the adherend, resulting in heavy peeling. In some embodiments, incorporating a multifunctional monomer into the pressure-sensitive adhesive allows the reaction of the multifunctional monomer to proceed rapidly upon heating, allowing the pressure-sensitive adhesive to harden prior to adsorption to the adherend. This reduces adhesive strength to the adherend. Furthermore, even if heating is continued thereafter, the adhesive strength of the pressure-sensitive adhesive to the adherend does not increase but remains within a predetermined range, allowing the pressure-sensitive adhesive to exhibit excellent heat-peelability. Note that the technology disclosed herein is not limited to the above interpretation. The polyfunctional monomers can be used alone or in combination of two or more.

[0093] In this specification, a polyfunctional monomer refers to a polymerizable compound having two or more ethylenically unsaturated groups in one molecule, including those referred to as oligomers. The ethylenically unsaturated group functions as a polymerizable functional group (typically a radically polymerizable functional group). Examples of ethylenically unsaturated groups possessed by polyfunctional monomers include, but are not limited to, acryloyl groups, methacryloyl groups, vinyl groups, and allyl groups. Suitable examples of ethylenically unsaturated groups include acryloyl groups and methacryloyl groups. Of these, acryloyl groups are preferred. 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.

[0094] In some embodiments, the number of ethylenically unsaturated groups contained in one molecule of the polyfunctional monomer is suitably 3 or more, preferably 4 or more, more preferably 5 or more, and may be 6 or more. The greater the number of ethylenically unsaturated groups in the polyfunctional monomer, the better the curing property upon heating and the easier it is to obtain heat-peelable properties. Furthermore, a polyfunctional monomer with a greater number of ethylenically unsaturated groups (functional groups) can obtain heat-peelable properties with a relatively small amount of use. This is advantageous because it also reduces the amount of outgassing derived from the polyfunctional monomer. The upper limit of the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer is not limited to a specific range and may be, for example, 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer may be, for example, 10 or less, 8 or less, 6 or less, or less than 5. A polyfunctional monomer having the above number of ethylenically unsaturated groups tends to easily achieve both good adhesion and heat-peelable properties and also tends to have excellent storage stability.

[0095] 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.

[0096] 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.

[0097] Although not particularly limited, it is appropriate to use a polyfunctional monomer having a molecular weight of 100 or more. In some preferred embodiments, the molecular weight of the polyfunctional 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 polyfunctional 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 polyfunctional monomer having a molecular weight within the above range can be advantageous, for example, in terms of the preparation and coatability of the pressure-sensitive adhesive composition. The above molecular weight is the manufacturer's nominal value or a molecular weight calculated from the molecular structure. For polyfunctional monomers having a molecular weight equal to or greater than a predetermined value, the weight average molecular weight (Mw) calculated in terms of standard polystyrene obtained by GPC may be used.

[0098] In some preferred embodiments, the polyfunctional 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 polyfunctional monomer having a weight loss rate of 1% or less at 180°C (hereinafter also referred to as a "heat-resistant polyfunctional monomer"), the pressure-sensitive adhesive layer has the heat-peelability due to the use of the polyfunctional monomer, while suppressing outgassing during heating. By using the heat-resistant polyfunctional monomer, both heat-peelability and reduced outgassing can be achieved. From the viewpoint of reducing outgassing, in some preferred embodiments, the heat-resistant polyfunctional monomer has a weight loss rate of 0.9% or less at 180°C, 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 polyfunctional 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 polyfunctional monomer, trimethylolpropane triacrylate (TMPTA, weight loss rate at 180°C is 1%) and dipentaerythritol hexaacrylate (DPHA, weight loss rate at 180°C is 0.5%) are preferably used. The heat-resistant polyfunctional monomer may be used alone or in combination of two or more.

[0099] Specifically, the weight loss rate of a polyfunctional monomer when heated to 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.

[0100] The content of the polyfunctional monomer in the first pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the polyfunctional monomer relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the first pressure-sensitive adhesive layer may be approximately 1 part by weight or more, or may be 3 parts by weight or more. 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 easy heat peelability, the amount of the polyfunctional monomer relative to 100 parts by weight of the polymer is appropriately 5 parts by weight or more, preferably 10 parts by weight or more, may be 20 parts by weight or more, may be 30 parts by weight or more, may be 40 parts by weight or more, may be 50 parts by weight or more, may be 60 parts by weight or more, may be 70 parts by weight or more, may be 80 parts by weight or more, may be 90 parts by weight or more, or may be 100 parts by weight or more. By incorporating a sufficient amount of polyfunctional monomer into the pressure-sensitive adhesive layer, the polyfunctional monomer contained in the pressure-sensitive adhesive layer reacts rapidly upon heating, causing the pressure-sensitive adhesive layer to thermally cure, thereby achieving easy thermal peelability. The upper limit of the content of the polyfunctional monomer in the pressure-sensitive adhesive layer is not particularly limited and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of 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, even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, 90 parts by weight or less, or 70 parts by weight or less.

[0101] Although not particularly limited, in some embodiments, the content of the polyfunctional monomer in the first pressure-sensitive adhesive layer may be less than 50 wt% of the weight of the first pressure-sensitive adhesive layer. According to the technology disclosed herein, even in such embodiments in which the amount of polyfunctional monomer in the pressure-sensitive adhesive is limited, a first pressure-sensitive adhesive layer having sufficient heat-peelability can be achieved. In some preferred embodiments, the content of the polyfunctional monomer is less than 45 wt% of the weight of the first pressure-sensitive adhesive layer, and may be less than 40 wt%, less than 35 wt%, less than 30 wt%, less than 25 wt%, less than 20 wt%, less than 15 wt%, or less than 10 wt%. Furthermore, in some embodiments, the content of the polyfunctional monomer may be 1 wt% or more, 5 wt% or more, 10 wt% or more, 15 wt% or more, 20 wt% or more, or 25 wt% or more of the weight of the first pressure-sensitive adhesive layer, from the viewpoint of effectively exhibiting the heat-peelability due to the inclusion of the polyfunctional monomer. Although not particularly limited, the above range of the content of the polyfunctional monomer can be preferably adopted in an embodiment in which a polymer having an ethylenically unsaturated group is used.

[0102] (Thermal Polymerization Initiator) In some embodiments, the first pressure-sensitive adhesive layer preferably contains a thermal polymerization initiator. Here, the thermal polymerization initiator refers to a polymerization initiator that generates radicals upon heating. By including the thermal polymerization initiator in the pressure-sensitive adhesive in a pre-reacted (unreacted) state, the thermal polymerization initiator reacts upon heating at high temperatures, reducing the adhesive strength or suppressing an increase in the adhesive strength, thereby preferably achieving easy peelability upon heating.

[0103] The thermal polymerization initiator is not particularly limited, and for example, a peroxide-based polymerization initiator, an azo-based polymerization initiator, a redox-based polymerization initiator formed by combining a peroxide and a reducing agent, a substituted ethane-based polymerization initiator, etc. can be used. Specific examples include persulfates such as potassium persulfate and ammonium persulfate; peroxide compounds such as benzoyl peroxide (BPO) and t-butyl hydroperoxide; azo compounds such as 2,2'-azobisisobutyronitrile (AIBN) and 2,2'-azobis(N-butyl-2-methylpropionamide); 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 and sodium hydrogen sulfite, or a combination of a peroxide and sodium ascorbate. These thermal polymerization initiators can be used alone or in combination of two or more. Thermal polymerization initiators that can be preferably used in the technology disclosed herein include peroxide polymerization initiators and azo polymerization initiators. A peroxide polymerization initiator and an azo polymerization initiator may be used in combination.

[0104] 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.

[0105] Specific examples of peroxide-based 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, 1,3-bis(t- Examples of the peroxybenzoate include di(4-t-butylcyclohexyl)peroxydicarbonate, di(4-t-butylperoxy)m-isopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 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.

[0106] The azo polymerization initiator is not particularly limited, and any of azonitrile compounds, azoamide compounds, azoester compounds, alkylazo compounds, azoamidine compounds, azoimidazoline compounds, and polymeric azo compounds can be used. Non-limiting specific examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 4,4-azobis(4-cyanovaleric acid), 2,2'-azobis(4-methylbutyronitrile ... , 2'-azobis(N-butyl-2-methylpropionamide), dimethyl 2,2'-azobis(2-methylpropionate), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis(2-methylpropane), 2,2'-azobis(2,4,4-trimethylpentane), 2-tert-butylazo-2-cyanopropane, 4,4'-azobis(3,3,4,4,5,5,6 ,6,7,7,8,8,8-tri-N,N'-dimethyleneisobutylamidine), 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2'-azobis Examples of the azo polymerization initiator include [2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride and azocumene. Suitable examples of the azo polymerization initiator include AIBN, 1,1'-azobis(cyclohexane-1-carbonitrile), 4,4-azobis(4-cyanovaleric acid), 2,2'-azobis(N-butyl-2-methylpropionamide), and 2,2'-azobis(2,4,4-trimethylpentane).

[0107] In some embodiments, it is preferable to use at least a peroxide-based polymerization initiator as the thermal polymerization initiator. The use of a peroxide-based initiator as the thermal polymerization initiator tends to facilitate the attainment of heat-peelability and heat-resistant peelability. One reason 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. Because this cleavage reaction is reversible, if the radical does not collide with an ethylenically unsaturated group in a polyfunctional monomer or polymer, it is thought that the -O-O- moiety recombines. This recombined initiator can undergo a cleavage reaction again during the specified heating period, colliding with and reacting with the polyfunctional monomer, etc. Therefore, it is thought that the use of a peroxide-based polymerization initiator efficiently promotes thermal curing of the pressure-sensitive adhesive layer, resulting in heat-peelability and heat-resistant peelability. The technology disclosed herein is not limited to the above discussion.

[0108] When a peroxide-based polymerization initiator is contained in the first pressure-sensitive adhesive layer, the content of the peroxide-based polymerization initiator in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, it is appropriate to set the content to 0.1 parts by weight or more per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.4 parts by weight or more. It may also be 0.5 parts by weight or more (e.g., more than 0.5 parts by weight), 0.6 parts by weight or more, or 0.7 parts by weight or more. 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 such as polyfunctional monomers, and the more likely the curing reaction will proceed. In some embodiments, the amount of the peroxide-based polymerization initiator per 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 peroxide-based polymerization initiator relative to 100 parts by weight of the polymer is suitably 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 (e.g., 1.1 parts by weight or less), and may be 1.0 part by weight or less (e.g., less than 1.0 part by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By setting the total amount of peroxide-based polymerization initiator within the specified range, a PSA having efficient thermosetting properties and easy heat-peelability can be preferably realized while obtaining adhesive properties such as adhesive strength and storage stability.

[0109] In embodiments in which the first pressure-sensitive adhesive layer contains a polyfunctional monomer, the content of the peroxide polymerization initiator in the first pressure-sensitive adhesive layer can also be determined by its relative relationship to the content of the polyfunctional monomer. In some embodiments, the amount of the peroxide polymerization initiator per 100 parts by weight of the polyfunctional monomer is, from the viewpoint of the frequency of collision with the ethylenically unsaturated group of the polyfunctional monomer, 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, and may even be 0.5 parts by weight or more. In some embodiments, the amount of the peroxide polymerization initiator per 100 parts by weight of the polyfunctional monomer is, for example, suitably 1.0 parts by weight or more, preferably 1.5 parts by weight or more, and may even be 2.0 parts by weight or more, 2.5 parts by weight or more, 3.0 parts by weight or more, 4.0 parts by weight or more, or 5.0 parts by weight or more. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the polyfunctional monomer is, for example, suitably about 25 parts by weight or less, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, or may be 10 parts by weight or less, 8.0 parts by weight or less (e.g., less than 8.0 parts by weight), 6.0 parts by weight or less, or 4.0 parts by weight or less.

[0110] The above description regarding the amount of the peroxide-based polymerization initiator used (the content of the peroxide-based polymerization initiator in the first pressure-sensitive adhesive layer and the amount of the peroxide-based polymerization initiator per 100 parts by weight of the polyfunctional monomer) can also be applied to the amount of the azo-based polymerization initiator used in an embodiment in which the azo-based polymerization initiator is used as the thermal polymerization initiator to be contained in the first pressure-sensitive adhesive layer.

[0111] In some embodiments, the first pressure-sensitive adhesive layer may contain only a peroxide polymerization initiator as the thermal polymerization initiator, or may contain a peroxide polymerization initiator and a thermal polymerization initiator other than the peroxide polymerization initiator (a non-peroxide polymerization initiator). In embodiments in which a peroxide polymerization initiator and a non-peroxide polymerization initiator are used in combination, the effects and properties of the non-peroxide polymerization initiator can be utilized. In some embodiments, the proportion of the peroxide polymerization initiator in the total thermal polymerization initiator contained in the first pressure-sensitive adhesive layer is suitably approximately 10% by weight or more. From the viewpoint of effectively exerting the effects of the peroxide polymerization initiator, the proportion is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more (e.g., more than 50% by weight), and may be 55% by weight or more, or even 60% by weight or more. In some preferred embodiments, the proportion of the peroxide polymerization initiator in the entire thermal polymerization initiator is, for example, approximately 65% ​​by weight or more, or may be 75% by weight or more, 85% by weight or more, 95% by weight or more, or 99% by weight or more. The upper limit of the proportion of the peroxide polymerization initiator in the entire thermal polymerization initiator is 100% by weight, and in some embodiments, it may be, for example, 90% by weight or less, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

[0112] Examples of non-peroxide polymerization initiators that can be used together with peroxide polymerization initiators as thermal polymerization initiators include azo polymerization initiators, redox polymerization initiators formed by a combination of a peroxide and a reducing agent, and substituted ethane polymerization initiators. Specific examples 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 a combination of a peroxide and a reducing agent, such as a combination of a persulfate and sodium hydrogen sulfite or a combination of a peroxide and sodium ascorbate. These non-peroxide polymerization initiators can be used alone or in combination of two or more.

[0113] The amount of thermal polymerization initiator contained in the first pressure-sensitive adhesive layer (when two or more types are contained, the total content of the two or more types) is not particularly limited. In some embodiments, it is appropriate to set it to 0.1 parts by weight or more per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the first pressure-sensitive adhesive layer, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.4 parts by weight or more. It may also be 0.5 parts by weight or more (e.g., more than 0.5 parts by weight), 0.6 parts by weight or more, or 0.7 parts by weight or more. The higher the content of the thermal polymerization initiator, the higher the frequency of collisions between the thermal polymerization initiator and ethylenically unsaturated groups such as polyfunctional monomers, and the more likely the curing reaction will proceed. Furthermore, in some embodiments, the content of the thermal polymerization initiator per 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 peroxide polymerization initiator relative to 100 parts by weight of the polymer is suitably 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 (e.g., 1.1 parts by weight or less), and may be 1.0 part by weight or less (e.g., less than 1.0 part by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By setting the content of the thermal polymerization initiator within the specified range, it is possible to preferably realize a pressure-sensitive adhesive that has efficient thermosetting and easy heat-peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0114] In embodiments in which the first pressure-sensitive adhesive layer contains a polyfunctional monomer, the content of the thermal polymerization initiator in the first pressure-sensitive adhesive layer can also be determined by its relative relationship to the content of the polyfunctional monomer. In some embodiments, the amount of the thermal polymerization initiator per 100 parts by weight of the polyfunctional monomer is, from the viewpoint of the frequency of collision with the ethylenically unsaturated group of the polyfunctional monomer, 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, and may even be 0.5 parts by weight or more. In some embodiments, the amount of the peroxide-based polymerization initiator per 100 parts by weight of the polyfunctional monomer is, for example, suitably 1.0 parts by weight or more, preferably 1.5 parts by weight or more, and may even be 2.0 parts by weight or more, 2.5 parts by weight or more, 3.0 parts by weight or more, 4.0 parts by weight or more, or 5.0 parts by weight or more. In some embodiments, the amount of the thermal polymerization initiator per 100 parts by weight of the polyfunctional monomer may, for example, be about 10 parts by weight or less, or may even 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 polyfunctional monomer is, for example, suitably about 25 parts by weight or less, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, or may be 10 parts by weight or less, 8.0 parts by weight or less (e.g., less than 8.0 parts by weight), 6.0 parts by weight or less, or 4.0 parts by weight or less.

[0115] Although not particularly limited, in some preferred embodiments, the total proportion of the above-mentioned polymer (specifically, a base polymer, for example, an acrylic polymer), polyfunctional monomer (for example, a polyfunctional acrylic monomer) and thermal polymerization initiator (preferably a peroxide-based polymerization initiator) in the entire pressure-sensitive adhesive layer is 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), from the viewpoint of effectively exerting a reduction in peel strength due to heating and realizing a desired rate of reduction in peel strength after heating.

[0116] (Crosslinking Agent) The pressure-sensitive adhesive composition used to form the first pressure-sensitive adhesive layer may contain a crosslinking agent as needed, mainly for the purpose of crosslinking within the first pressure-sensitive adhesive layer or between the first pressure-sensitive adhesive layer and its adjacent surface. The crosslinking agent is typically contained in the first pressure-sensitive adhesive layer in a form after a crosslinking reaction. Use of the crosslinking agent allows the cohesive strength of the first pressure-sensitive adhesive layer to be appropriately adjusted.

[0117] The type of crosslinking agent is not particularly limited, and can be selected from conventionally known crosslinking agents so that the crosslinking agent exhibits an appropriate crosslinking function within the first 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.

[0118] 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").

[0119] 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.

[0120] As the oxazoline-based crosslinking agent, any agent having one or more oxazoline groups per molecule can be used without particular limitation. Examples of aziridine-based crosslinking agents include trimethylolpropane tris[3-(1-aziridinyl)propionate] and trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)]. As the carbodiimide-based crosslinking agent, a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups can be used.

[0121] 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 with good heat-peelability while exhibiting a balanced adhesive property, such as adhesive strength and cohesive strength. The isocyanate-based crosslinking agent can be used alone or in combination with two or more. Although not particularly limited, when an isocyanate-based crosslinking agent is used, the amount used is preferably less than 1 part 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 the isocyanate-based crosslinking agent used, the crosslinking density is appropriately suppressed. At such a crosslinking density, frequent collisions between the polyfunctional monomer and the thermal polymerization initiator during heat treatment promote thermal curing, resulting in heat-peelability and heat-resistant peelability, and ultimately achieving the desired post-heat peel strength reduction rate. It is believed that the technology disclosed herein is not limited to the above discussion. From this viewpoint, in some preferred embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer is 0.9 parts by weight or less, or may be 0.8 parts by weight or less, or 0.7 parts by weight or less, or 0.6 parts by weight or less, or 0.5 parts by weight or less, or 0.4 parts by weight or less, or 0.3 parts by weight or less, or 0.2 parts by weight or less, or 0.1 parts by weight or less. By limiting the amount of the isocyanate-based crosslinking agent used, high adhesive strength tends to be easily obtained. Furthermore, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer can be, for example, 0.01 parts by weight or more, and in some preferred embodiments, it may be 0.05 parts by weight or more, or 0.1 parts by weight or more, or 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of isocyanate-based crosslinking agent used within the above range, it is possible to preferably obtain a pressure-sensitive adhesive that exhibits a good balance of adhesive properties such as adhesive strength and cohesive strength while preferably realizing the effects of the technology disclosed herein.

[0122] When a crosslinking agent is used, the amount used (when two or more crosslinking agents are used, the total amount thereof) 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 well-balanced adhesive properties 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 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 crosslinking agent used may vary depending on the type of crosslinking agent used, and is not limited to a specific range. However, from the viewpoint of realizing good heat-peelability and heat-peelability resistance, and thus the desired rate of decrease in peel strength after heating, it is preferably limited to a predetermined amount or less. By limiting the amount of crosslinking agent used, the crosslink density is appropriately suppressed. At such a crosslink density, the polyfunctional monomer and the thermal polymerization initiator frequently collide with each other during heat treatment, causing thermal curing, resulting in the development of heat-peelability and heat-resistant peelability, and ultimately achieving the desired post-heat peel force reduction rate. The technology disclosed herein is not limited to the above considerations. For example, the amount of crosslinking agent used is suitably less than 10 parts by weight per 100 parts by weight of the polymer. In some embodiments, it is preferable that the amount is 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 per 100 parts by weight of the polymer. It is preferable that the amount is 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, 0.5 parts by weight or less, 0.4 parts by weight or less, 0.3 parts by weight or less, 0.2 parts by weight or less, or 0.1 parts by weight or less. By limiting the amount of crosslinking agent used, high adhesive strength tends to be easily obtained.

[0123] 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.

[0124] The PSA composition used to form the first 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 may result in an effect of extending the pot life of the PSA composition. Various β-dicarbonyl compounds may 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.

[0125] (Monofunctional Monomer) If desired, the first pressure-sensitive adhesive layer may contain one or more monofunctional monomers containing one ethylenically unsaturated group per molecule. The monofunctional monomer is used within a range that does not impair the effects of the technology disclosed herein. Known monofunctional acrylate monomers and vinyl monomers may be used as the monofunctional monomer. While not particularly limited, the content of the monofunctional monomer in the pressure-sensitive adhesive layer is suitably approximately 100 parts by weight or less (0 parts by weight or more and 100 parts by weight or less, for example, less than 100 parts by weight) per 100 parts by weight of the polyfunctional monomer. It may also be less than 50 parts by weight, less than 30 parts by weight, less than 10 parts by weight, or less than 1 part by weight. The technology disclosed herein can be implemented in an embodiment in which the pressure-sensitive adhesive layer is substantially free of monofunctional monomers.

[0126] (Other Components) The first 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 first pressure-sensitive adhesive layer in the technology disclosed herein may achieve desired adhesive properties, such as adhesive strength, without the use of a tackifier. In some embodiments, the content of the tackifier in the first pressure-sensitive adhesive layer may 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 first 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 first PSA layer may not contain a tackifier. Furthermore, the first PSA layer in the technology disclosed herein may exhibit the desired heat-peelability without using heat-expandable microspheres, a blowing agent, or the like. In some embodiments, the content of heat-expandable microspheres in the first PSA layer may be, for example, less than 1 part by weight, or even less than 0.1 parts by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the first PSA layer. The content of the blowing agent in the first PSA layer may be, for example, less than 1 part by weight, or even less than 0.1 parts by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the first PSA layer. The first PSA layer may contain neither heat-expandable microspheres nor a blowing agent.

[0127] <Second Pressure-Sensitive Adhesive Layer> The second pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein typically contains at least a polymer and may further contain a monomer. The second pressure-sensitive adhesive layer may be a thermosetting pressure-sensitive adhesive layer or may not necessarily be a thermosetting pressure-sensitive adhesive layer. The type of pressure-sensitive adhesive constituting the second pressure-sensitive adhesive layer is not particularly limited. The second pressure-sensitive adhesive layer may contain one or more of various rubber-like polymers that can be used in the field of pressure-sensitive adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. The above polymers may be used as base polymers in pressure-sensitive adhesives and function as structural polymers that shape the pressure-sensitive adhesive. From the standpoints of adhesive performance, cost, etc., pressure-sensitive adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, pressure-sensitive adhesives using acrylic polymers as the base polymer (acrylic pressure-sensitive adhesives) are preferred.

[0128] The following description will mainly focus on pressure-sensitive adhesive layers made of acrylic pressure-sensitive adhesive, i.e., pressure-sensitive adhesive sheets having an acrylic pressure-sensitive adhesive layer as the second pressure-sensitive adhesive layer, but it is not intended to limit the second pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheets disclosed herein to an acrylic pressure-sensitive adhesive layer.

[0129] In an embodiment in which the second pressure-sensitive adhesive layer is thermosetting, the second pressure-sensitive adhesive layer preferably contains at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule (polyfunctional monomer) and a polymer having an ethylenically unsaturated group, from the viewpoint of easily exhibiting the desired thermosetting properties and easy heat-peelability, and preferably further contains a thermal polymerization initiator as necessary. The thermosetting second pressure-sensitive adhesive layer can be prepared so as to exhibit the desired initial (before heating) performance and / or post-heat performance by referring to the above description regarding the first pressure-sensitive adhesive layer, and therefore redundant explanations will be omitted.

[0130] In addition, in an embodiment in which the second pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer that does not necessarily require thermosetting properties, the pressure-sensitive adhesive (second pressure-sensitive adhesive) constituting the second pressure-sensitive adhesive layer preferably contains a polymer having no ethylenically unsaturated group. １－２０ The polymer (preferably the base polymer) may be a polymer of a monomer raw material that contains an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer. １－２０ Specific examples and preferred examples of alkyl (meth)acrylate include those in which the monomer component constituting the acrylic polymer in the first pressure-sensitive adhesive layer is C １－２０ The same applies as in the case of containing an alkyl (meth)acrylate. For example, an acrylic polymer containing one or both of BA and 2EHA as the monomer component is preferred, and an acrylic polymer containing at least BA is particularly preferred.

[0131] Examples of the secondary monomer include the various monomers listed as "other monomers" in the description of the first pressure-sensitive adhesive layer, alkoxyalkyl (meth)acrylates, etc. For example, a monomer having a polar group (e.g., a carboxy group, a hydroxyl group, a nitrogen-containing ring, etc.) can be suitably used as the secondary monomer. Monomers having a polar group can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the pressure-sensitive adhesive. The secondary monomers can be used alone or in combination of two or more. When a secondary monomer is used, its amount is not particularly limited, but is suitably 0.01 wt% or more of the total monomer components. From the viewpoint of better demonstrating the effects of using the secondary monomer, the amount of the secondary monomer may be 0.1 wt% or more, or even 0.5 wt% or more of the total monomer components. Furthermore, from the viewpoint of easily balancing the adhesive properties, the amount of the secondary monomer used is suitably 50 wt% or less of the total monomer components, and preferably 40 wt% or less.

[0132] In some embodiments, the monomer component includes a carboxyl group-containing monomer as the secondary monomer. Suitable examples of the carboxyl group-containing monomer include AA and MAA. The carboxyl group-containing monomer can be used alone or in combination of two or more. For example, AA and MAA can be used in combination. The amount of the carboxyl group-containing monomer used may be, for example, 0.01 wt% or more, 0.05 wt% or more, 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 1.0 wt% or more, 2.0 wt% or more, or 2.5 wt% or more of the total monomer component. The amount of the carboxyl group-containing monomer used may be, for example, 15 wt% or less, 10 wt% or less, 5 wt% or less, or 3 wt% or less of the total monomer component. In some embodiments, the amount of the carboxyl group-containing monomer used may be 2 wt% or less, 1 wt% or less (e.g., less than 1 wt%) of the total monomer component.

[0133] In some embodiments, the monomer component includes an alkoxy group-containing (meth)acrylate as the secondary monomer. Specific examples of the alkoxy group-containing (meth)acrylate are the same as those described for the first pressure-sensitive adhesive layer, so redundant description will be omitted. The content of the alkoxy group-containing (meth)acrylate in the monomer component is not particularly limited and may be, for example, 1 wt% or more, 5 wt% or more, 10 wt% or more, 20 wt% or more, or 30 wt% or more. The upper limit of the content of the alkoxy group-containing (meth)acrylate is set so that the total amount with other monomers does not exceed 100 wt%, and may be, for example, 45 wt% or less, 35 wt% or less, 25 wt% or less, 15 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less, or even less than 1 wt%.

[0134] For other matters regarding the polymer that can be used in the second PSA layer, and for crosslinking agents and other components that can be used in forming the second PSA layer as needed, reference can be made to the corresponding descriptions regarding the first PSA layer, and duplicate descriptions will be omitted. In some embodiments, like the first PSA layer, the second PSA layer preferably does not contain heat-expandable microspheres, a blowing agent, etc., or the content of heat-expandable microspheres, a blowing agent, etc., per 100 parts by weight of the polymer is preferably limited to less than 1 part by weight or less than 0.1 parts by weight.

[0135] <Substrate> The pressure-sensitive adhesive sheet disclosed herein may include a substrate. Various sheet-like substrates can be used as the substrate, such as resin films, paper, cloth, rubber sheets, foam sheets, metal foils, and composites thereof. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyamide resin films; fluororesin films; cellophane; and the like. Other examples of resin films include resin films formed from one or more engineering plastics (which may be super engineering plastics) such as polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, and polyimide resins. The use of engineering plastics is preferred from the viewpoint of heat resistance. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, and top-coated paper. Examples of fabrics include woven fabrics and nonwoven fabrics made from various fibrous materials, either alone or in combination. Examples of the fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

[0136] In some preferred embodiments, a resin film having a predetermined rigidity (strength) and excellent processability and handling properties is used as the substrate. Suitable examples of such resin films include polyester films (e.g., PET films), polyimide (PI) films, etc. 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 distinct from foam films and nonwoven fabrics. The density of the resin film that can be used as the substrate is approximately 0.85 to 1.50 g / cm. ３ (For example, 0.90 g / cm ３ ~1.20 g / cm ３ , typically 0.92 g / cm ３ ~1.05g / cm ３ The resin film may have a single layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0137] The substrate (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., as needed. The amount of additives to be added is not particularly limited and can be appropriately determined depending on the application, etc.

[0138] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately employed.

[0139] The substrate may be substantially composed of a resin film. Alternatively, the substrate may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer or an anti-reflection layer), a printing layer or a laminating layer for imparting a desired appearance, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0140] The thickness of the substrate 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 is suitably 2 μm or more (e.g., 3 μm or more, typically 5 μm or more), and may be approximately 7 μm or more, or may be 10 μm or more. Furthermore, the thickness of the substrate is suitably approximately 200 μm or less. From the viewpoint of weight reduction and thinning, it is preferably approximately 100 μm or less, more preferably approximately 50 μm or less, and may be 30 μm or less, 20 μm or less, or 15 μm or less. As the thickness of the substrate decreases, the flexibility of the PSA sheet and its ability to conform to the surface shape of the adherend tend to improve. The above substrate thickness can also be preferably applied to the thickness of the resin film used as the substrate or a component thereof.

[0141] The surface of the substrate may be subjected to conventional surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer, as necessary. Such surface treatments may be intended to improve the adhesion between the substrate and the pressure-sensitive adhesive layer, in other words, the anchoring ability of the pressure-sensitive adhesive layer to the substrate. The composition of the primer is not particularly limited and can be appropriately selected from known primers. The thickness of the primer layer is not particularly limited, but is suitably about 0.01 μm to 1 μm, and preferably about 0.1 μm to 1 μm. The surface of the substrate may also be subjected to the various surface treatments described above or to a surface treatment such as an antistatic treatment. Such surface treatments may be applied to one or both sides of the substrate.

[0142] <Preparation of Pressure-Sensitive Adhesive Sheet> The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein can be formed by a conventionally known method. For example, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer can each be formed in the form of a layer (pressure-sensitive adhesive layer) by applying (e.g., coating) the corresponding pressure-sensitive adhesive composition to an appropriate surface and then appropriately performing a curing treatment. A single method (e.g., drying, crosslinking, polymerization, cooling, etc.) for curing the pressure-sensitive adhesive composition may be used, or two or more methods may be used simultaneously or in multiple stages. Solvent-based pressure-sensitive adhesive compositions are typically formed by drying (preferably further crosslinking) the composition. The surface to which the pressure-sensitive adhesive composition is applied may be a surface having releasability (a release surface) or a non-releasable surface. The non-releasable surface may be a non-releasable substrate surface, the surface of a pre-formed second pressure-sensitive adhesive layer or the surface of a pre-formed first pressure-sensitive adhesive layer, etc.

[0143] Although not particularly limited, the technology disclosed herein can be preferably implemented 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 polyfunctional monomer, a thermal polymerization initiator, and optionally other additives. The effects of the technology disclosed herein can be effectively achieved 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.

[0144] 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 viewpoints 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 evaporation. Therefore, when the pressure-sensitive adhesive composition to be dried contains a polyfunctional monomer or a thermal polymerization initiator, the reaction of the polyfunctional monomer and the deactivation of the thermal polymerization initiator are negligible. After drying the pressure-sensitive adhesive composition, aging may be carried out for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the substrate or pressure-sensitive adhesive layer.

[0145] <Thickness of Pressure-Sensitive Adhesive Layer> The thickness of each of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is not particularly limited. The thickness of each pressure-sensitive adhesive layer may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more. The greater the thickness of the pressure-sensitive adhesive layer, the greater the adhesive strength to the adherend tends to be. In some preferred embodiments, the thickness of each pressure-sensitive adhesive layer is 5 μm or more, 7 μm or more, 9 μm or more, 10 μm or more, more than 10 μm, 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. Furthermore, the thickness of each pressure-sensitive adhesive layer is suitably, for example, approximately 200 μm or less, and may be 100 μm or less (e.g., less than 100 μm), or 50 μm or less. For example, by limiting the thickness of the first pressure-sensitive adhesive layer within a predetermined range, the occurrence of adhesive residue due to cohesive failure is prevented, and easy peelability tends to be obtained. In some preferred embodiments, the thickness of each pressure-sensitive adhesive layer may be, for example, 40 μm or less, 30 μm or less (e.g., less than 30 μm), 20 μm or less, or 15 μm or less. The thickness of the first pressure-sensitive adhesive layer and the thickness of the second pressure-sensitive adhesive layer may be approximately the same or different. For example, the thickness of the first pressure-sensitive adhesive layer may be greater than the thickness of the second pressure-sensitive adhesive layer, or vice versa.

[0146] The total thickness of the first and second pressure-sensitive adhesive layers may be, for example, 3 μm or more, suitably 5 μm or more, preferably 8 μm or more, and more preferably 10 μm or more. In some embodiments, the total thickness of the first and second pressure-sensitive adhesive layers may be, for example, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, or 40 μm or more. The total thickness of the first and second pressure-sensitive adhesive layers is suitably, for example, about 250 μm or less, and may be 150 μm or less, 100 μm or less, or 80 μm or less. A small total thickness of the first and second pressure-sensitive adhesive layers is advantageous in terms of reducing the thickness of the pressure-sensitive adhesive sheet, and tends to provide excellent conformability to the adherend. In some preferred embodiments, the total thickness of the first and second PSA layers may be, for example, 60 μm or less, 50 μm or less, 45 μm or less, or 40 μm or less. When the PSA sheet disclosed herein is in the form of a substrateless double-sided PSA sheet consisting of a first PSA layer and a second PSA layer, the total thickness of the PSA sheet described below will be the same as the total thickness of the first and second PSA layers.

[0147] <Total Thickness> The total thickness of the PSA sheet disclosed herein (comprising first and second PSA layers, and optionally further comprising a substrate, but excluding 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, 15 μm or more, or 20 μm or more, from the viewpoints of adhesive properties, handleability, etc. In some embodiments, the total thickness of the PSA sheet may be 30 μm or more, 40 μm or more, or 50 μm or more. 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 even 300 μm or less. In some preferred embodiments, the total thickness of the PSA sheet is 100 μm or less (e.g., less than 100 μm), more preferably 80 μm or less, or even 70 μm or less. Reducing the thickness of the PSA sheet is advantageous in terms of thinning, miniaturization, weight reduction, resource conservation, etc.

[0148] <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.

[0149] <Conjugate> The pressure-sensitive adhesive sheet disclosed herein can be used in a conjugate disposed between two members (adherends) to join the two members. In the conjugate, the pressure-sensitive adhesive sheet disclosed herein is used in the joint that joins the two members. The conjugate can include, for example, a first member to which a first adhesive surface of the pressure-sensitive adhesive sheet is adhered, and a second member to which a second adhesive surface of the pressure-sensitive adhesive sheet is adhered.

[0150] The bonded structure disclosed herein may have, for example, a cross-sectional structure schematically shown in FIG. 2 . The bonded structure 100 includes a first member 71, a second member 72, and a bonding portion 80 disposed between the first member 71 and the second member 72. The bonded structure 100 has a laminate configuration including the first member 71, the bonding portion 80, and the second member 72, in this order. In the embodiment shown in FIG. 2 , the first member 71 and the second member 72 are sheet-shaped or plate-shaped, and the bonding portion 80 is a layered body. At least one of the first member 71 and the second member 72 may be made of a brittle material (e.g., a hard-brittle material such as glass or a semiconductor wafer). The bonding portion 80 includes any one of the pressure-sensitive adhesive sheets 90 disclosed herein and bonds the first member 71 and the second member 72 together. In other words, the first member 71 and the second member 72 are bonded together via the bonding portion 80 including the pressure-sensitive adhesive sheet 90. The adhesive sheet 90 has one adhesive surface (first adhesive surface) 80A adhered to a first member 71 as an adherend, and the other adhesive surface (second adhesive surface; the surface opposite the first adhesive surface) 80B adhered to a second member 72 as an adherend. The adhesive sheet 90 includes a first adhesive layer and a second adhesive layer (not shown in FIG. 2 ), with the first adhesive surface 80A being composed of the first adhesive layer and the second adhesive surface 80B being composed of the second adhesive layer. The adhesive sheet 90 may further include a substrate disposed between the first adhesive layer and the second adhesive layer. The adhesive sheet 90 may be a substrateless adhesive sheet composed only of adhesive layers including the first adhesive layer and the second adhesive layer, or a double-sided adhesive sheet with a substrate.

[0151] In the above embodiment, the first member, the second member, and the joint portion constituting the joined body are all configured in a layered, sheet-like, or plate-like shape, and the joined body has the form of a laminated structure (laminate). However, the shapes of the first member, the second member, and the joint portion do not have to be layered, sheet-like, or plate-like, and can have various shapes. For example, the first member and the second member only need to have a surface that contacts the joint portion, and may have various three-dimensional member shapes, such as complex shapes or curved shapes, based on the application and purpose of use. The joint portion can also have various shapes to match the surface shapes of the first member and the second member.

[0152] In this specification, the terms "member" and "members" in the terms "first member" and "second member" are used to mean constituent elements of a joined body, and are not particularly limited other than that meaning. For example, the first member and the second member may each be an independent article or part, or each may be a member constituting a different article.

[0153] Furthermore, the bonded structure may include other members or components in addition to the first and second members. For example, if the first and second members are part of a product such as an electronic device, the bonded structure may be composed of multiple members or elements.

[0154] <Disassembly Method> This specification also provides a method for disassembling the above-described joined body. The disassembly method includes the steps of: subjecting the joined body to a heat treatment; and then separating the first member from the first adhesive surface while leaving the pressure-sensitive adhesive sheet on the second member. The pressure-sensitive adhesive sheet disclosed herein includes a first pressure-sensitive adhesive layer suitable for exhibiting heat-peelability (heat-resistant peelability); and is designed so that the post-heat peel strengths Fa1, Fb1 of the first and second pressure-sensitive adhesive layers are different (typically, Fa1 < Fb1). Therefore, the pressure-sensitive adhesive sheet is suitable for carrying out the step of separating the first member from the first adhesive surface while leaving the pressure-sensitive adhesive sheet on the second member after the heat treatment.

[0155] The temperature of the heat treatment is not particularly limited and may be, for example, a temperature higher than 100°C. In some embodiments, the heat treatment temperature may be, for example, about 110°C or higher, about 120°C or higher, about 130°C or higher, about 140°C or higher, about 150°C or higher, about 160°C or higher, or 170°C or higher. The upper limit of the heat treatment temperature may vary depending on the purpose of the heat treatment, the heat resistance of the adherend, etc., but is generally about 260°C or lower, about 250°C or lower, 230°C or lower, 200°C or lower, or 180°C or lower. In some preferred embodiments, the heat treatment temperature may be less than 180°C, 170°C or lower, 160°C or lower, 150°C or lower, 140°C or lower, 130°C or lower, or 120°C or lower. The heat treatment time is not particularly limited and may be within 10 hours, within 5 hours, or within 3 hours. However, in some preferred embodiments, from the viewpoint of the efficiency of the heating process, the heat treatment time may be within 1 hour, within 30 minutes, within 15 minutes, within 10 minutes, or within 5 minutes. The pressure-sensitive adhesive sheet disclosed herein may be one in which the first pressure-sensitive adhesive layer is thermally cured by the above-mentioned short-term heat treatment, thereby exhibiting heat-peelability. Furthermore, the heat treatment time may be 1 minute or more, 3 minutes or more, 5 minutes or more, 7 minutes or more, or 9 minutes or more. In some embodiments, the heat treatment time may be 10 minutes or more, 30 minutes or more, 60 minutes or more, or more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. The adhesive sheet disclosed herein can be one in which the first adhesive is thermally cured by heat treatment at the above-mentioned heating temperature, the peel strength is reduced, and an increase in the peel strength (heavy peeling) does not occur or is suppressed even when the heated state continues for a long time. Therefore, it is possible to maintain heat-peelability (heat-resistant peelability) even after a long-term heat treatment. There is no particular upper limit to the heat treatment time, but from the viewpoint of the efficiency of the heating process, it may be within 10 hours, within 5 hours, or within 3 hours.

[0156] <Uses> The uses of the pressure-sensitive adhesive sheet disclosed herein are not particularly limited. Since at least the first pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein can exhibit heat-peelability, the pressure-sensitive adhesive sheet can be used in a variety of applications, such as by adhering the first pressure-sensitive adhesive layer (first pressure-sensitive adhesive surface) to an adherend and then removing it from the adherend after its intended purpose has been achieved. For example, the pressure-sensitive adhesive sheet can be used as a pressure-sensitive adhesive sheet for fixing (temporarily fixing), masking, or protecting the adherend during processing. While not particularly limited, the pressure-sensitive adhesive sheet disclosed herein can be preferably used in situations where an ultraviolet irradiation-peelable pressure-sensitive adhesive cannot be used, such as when the adherend is non-transparent to light.

[0157] The pressure-sensitive adhesive sheet disclosed herein can also be preferably used as a process material that is fixed to and peeled from an adherend in the manufacturing process of electronic devices and electronic components, for example. A suitable application of the pressure-sensitive adhesive sheet disclosed herein is the manufacturing of semiconductor elements. For example, it can be preferably used as a wafer fixing sheet that fixes the wafer to a fixing plate (processing table) in semiconductor wafer processing (typically silicon wafer processing). 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 wafer 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 requiring heat resistance. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be used as an optical pressure-sensitive adhesive sheet used, for example, for bonding optical components (for bonding optical components) or for manufacturing products using the optical components (optical products). The optical member refers to a member having optical properties (for example, polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.).

[0158] The type of material (adherend material) to be attached as disclosed herein is not particularly limited. The pressure-sensitive adhesive sheet disclosed herein can be used for fixing or protecting various members or materials. 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 PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, and transparent polyimide resins. 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 partially provided with a transparent conductive film (e.g., an ITO (indium tin oxide) film) or an FPC (flexible printed circuit board), such as those used in tablet computers, mobile phones, organic LEDs (light-emitting diodes), etc.

[0159] The matters disclosed by this specification include the following: [1] A double-sided adhesive sheet, the adhesive sheet comprising a first adhesive layer and a second adhesive layer, the first adhesive layer constituting a first adhesive surface that is a first side of the adhesive sheet, and the second adhesive layer constituting a second adhesive surface that is a second side of the adhesive sheet, wherein the second surface is the surface opposite to the first surface, the first adhesive layer comprising at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule and a polymer having an ethylenically unsaturated group, and further comprising a thermal polymerization initiator, the adhesive sheet having a post-heat peel strength Fa1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the first adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes, and a post-heat peel strength Fb1 [N / 20 mm] measured in an environment of 23°C and 50% RH after the second adhesive layer is attached to a glass plate and heat-treated at 180°C for 30 minutes, which is different from the adhesive sheet. [2] [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the post-heat peel strength difference (|Fb1-Fa1|) calculated from the post-heat peel strength Fa1 [N / 20 mm] and the post-heat peel strength Fb1 [N / 20 mm] is 0.5 N / 20 mm or more. [3] The pressure-sensitive adhesive sheet according to [1] above, wherein the first pressure-sensitive adhesive layer has a post-heat peel strength reduction rate A [%] calculated by the following formula from the pre-heat peel strength Fa0 [N / 20 mm] measured after being attached to a glass plate and under an environment of 23°C and 50% RH, and the post-heat peel strength Fa1 [N / 20 mm] measured after being attached to a glass plate and under heat treatment at 180°C for 30 minutes, and then under an environment of 23°C and 50% RH, of which A [%] is more than 20% and less than 99.9%.

[0023] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are laminated via a substrate.

[0024] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the second pressure-sensitive adhesive layer contains at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule and a polymer having an ethylenically unsaturated group, and further contains a thermal polymerization initiator.[6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, wherein the second pressure-sensitive adhesive layer has a post-heat peel strength reduction rate B [%] calculated by the following formula from a pre-heat peel strength Fb0 [N / 20 mm] measured after being attached to a glass plate and under an environment of 23°C and 50% RH, and a post-heat peel strength Fb1 [N / 20 mm] measured after being attached to a glass plate and under heat treatment at 180°C for 30 minutes, and then under an environment of 23°C and 50% RH, which is higher than 20% and lower than 99.9%: post-heating peel strength reduction rate B [%] = (1 - Fb1 / Fb0) x 100 [7] The pressure-sensitive adhesive sheet according to any one of the above [1] to [6], wherein the pre-heating peel strength Fa0 [N / 20 mm], measured after the first pressure-sensitive adhesive layer is attached to a glass plate and under an environment of 23°C and 50% RH, and the pre-heating peel strength Fb0 [N / 20 mm], measured after the second pressure-sensitive adhesive layer is attached to a glass plate and under an environment of 23°C and 50% RH, are both 4.0 N / 20 mm or more, and the post-heating peel strength Fa1 [N / 20 mm] of the first pressure-sensitive adhesive layer and the post-heating peel strength Fb1 [N / 20 mm] of the second pressure-sensitive adhesive layer are both less than 3.0 N / 20 mm. [8] A bonded structure comprising: the adhesive sheet according to any one of [1] to [7] above; a first member to which a first adhesive surface of the adhesive sheet is attached; and a second member to which a second adhesive surface of the adhesive sheet is attached. [9] A method for dismantling the bonded structure according to [8] above, comprising the steps of: subjecting the bonded structure to a heat treatment; and separating the first member from the first adhesive surface while leaving the adhesive sheet on the second member.

[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-heat peeling force F0) A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer to be evaluated on a resin film is cut into a size of 20 mm wide and 100 mm long, and under an environment of 23 ° C and 50% RH, the adhesive surface of the pressure-sensitive adhesive layer is pressed against an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35 mm, blue plate edge polished) as an adherend by rolling a 2 kg roller back and forth once. Under the same environment, the adherend with the pressure-sensitive adhesive sheet attached is left standing for 6 hours, and used as an evaluation sample. The evaluation sample is set in a tensile tester under an environment of 23 ° C and 50% RH, and the peel strength (pre-heat peeling force) F0 [N / 20 mm width] is measured when the pressure-sensitive adhesive sheet is peeled off from the adherend under the conditions of a peel angle of 180 ° and a speed of 300 mm / min. This pre-heating peel force F0 is referred to as pre-heating peel force Fa0 when the pressure-sensitive adhesive layer to be evaluated is the first pressure-sensitive adhesive layer, and as pre-heating peel force Fb0 when the pressure-sensitive adhesive layer to be evaluated is the second pressure-sensitive adhesive layer. The resin film can be any of the various resin films that can be used as the substrate for the pressure-sensitive adhesive sheets disclosed herein, with suitable examples including polyimide (PI) film and polyethylene terephthalate (PET) film. The thickness of the resin film is preferably approximately 10 μm to 100 μm, and preferably approximately 10 μm to 75 μm (e.g., approximately 25 μm to 75 μm). A tensile tester such as the Shimadzu EZ-S 500N or an equivalent can be used. Furthermore, when the pressure-sensitive adhesive sheet used to prepare the evaluation sample is a double-sided pressure-sensitive adhesive sheet, the non-measurement side can be backed with a PET film before measurement. The pre-heat peel forces Fa0 and Fb0 shown in Tables 1 and 2 below were measured using an evaluation sample prepared using an adhesive sheet having an adhesive layer to be evaluated on one side of a 50 μm thick polyimide film (manufactured by Toray DuPont Co., Ltd., product name "Kapton 200H").

[0162] (Post-heat peel force F1) An evaluation sample is prepared using a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer to be evaluated on a resin film, using the method described above for measuring the pre-heat peel force F0. The obtained evaluation sample is heated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand 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 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. This post-heat peel force F1 is referred to as post-heat peel force Fa1 when the pressure-sensitive adhesive layer to be evaluated is the first pressure-sensitive adhesive layer, and as post-heat peel force Fb1 when the pressure-sensitive adhesive layer to be evaluated is the second pressure-sensitive adhesive layer. The adherend, tensile tester, and other factors are the same as those used for measuring the pre-heat peel force F0.

[0163] (Release Force Reduction Rate After Heating) The release forces Fa0 and Fb0 [N / 20 mm] before heating and the release forces Fa1 and Fb1 [N / 20 mm] after heating are substituted into the following formula to calculate the release force reduction rates A and B [%]: Release force reduction rate A [%] after heating = (1 - Fa1 / Fa0) x 100 Release force reduction rate B [%] = (1 - Fb1 / Fb0) x 100

[0164] (Difference in peel strength after heating) The difference in peel strength after heating (|Fb1-Fa1|) was calculated from the peel strength after heating Fa1 [N / 20 mm] of the first pressure-sensitive adhesive layer and the peel strength after heating Fb1 [N / 20 mm] of the second pressure-sensitive adhesive layer. In all of Examples 1 to 17, Fb1 > Fa1, so Tables 1 and 2 show the value of Fb1-Fa1 as the difference in peel strength after heating.

[0165] (Gel Fraction) The gel fraction of the PSA layer (weight ratio of ethyl acetate insoluble matter) is measured by the following method. Approximately 0.1 g of a PSA sample (weight Wg1) is wrapped in a purse-shaped porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane is available from Nitto Denko Corporation under the trade name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent. The wrapper is immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23° C.) for 7 days to elute only the sol component in the PSA layer out of the membrane. The wrapper is then removed, the ethyl acetate adhering to the outer surface is wiped off, and the wrapper is dried at 130° C. for 2 hours, and the weight of the wrapper (Wg4) is measured. The gel fraction of the PSA layer can be determined by substituting each value into the following formula: Gel fraction [%] = [(Wg4 - Wg2 - Wg3) / Wg1] x 100 The gel fraction of the PSA layer is measured initially (gel fraction before heating) and after the PSA layer is heat-treated 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 (gel fraction after heating).

[0166] (Young's Modulus) A pressure-sensitive adhesive layer to be evaluated is prepared in a state where both sides are covered with release liners, and the pressure-sensitive adhesive layer is cut together with the release liners to a size of 80 mm wide (when the pressure-sensitive adhesive layer is 30 μm thick) and 30 mm long. One release liner is removed from the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is wound up in the longitudinal direction on the other release liner while taking care not to trap air bubbles, thereby preparing a 30 mm long rod-shaped sample. The rod-shaped sample is placed in a tensile tester (manufactured by ORIENTEC, product name "RTC-1150A") and pulled under conditions of a measurement temperature of 23°C, a chuck distance of 10 mm, and a pulling speed of 50 mm / min. The initial elastic modulus is determined from the rise of the obtained stress-strain curve (S-S curve), and this is taken as the Young's modulus [MPa] of the pressure-sensitive adhesive layer. The Young's modulus of the pressure-sensitive adhesive layer is measured initially (Young's modulus before heating) and after the pressure-sensitive adhesive layer 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 (Young's modulus after heating). The reason why the cut width of the pressure-sensitive adhesive layer is set to 80 mm is that the cross-sectional area of ​​the pressure-sensitive adhesive layer in the cross section along the width direction is 2 to 2.5 mm. ２ It is desirable to adjust the cutting width depending on the thickness of the adhesive layer so that the cross-sectional area is approximately the same.

[0167] Example 1 (Preparation of First 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 mixture 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) was added in an amount equivalent to 16 moles per 20 moles of HEA used as a raw material for the acrylic polymer a, 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, 30 parts of dipentaerythritol hexaacrylate (DPHA) as a polyfunctional monomer, 0.5 parts of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-101E"; hereinafter referred to as "crosslinking agent CL1"), and 0.5 parts of benzoyl peroxide (manufactured by NOF Corporation, product name "Niper BW"; hereinafter referred to as "thermal polymerization initiator TO1") as a thermal polymerization initiator were added and mixed uniformly to prepare a pressure-sensitive adhesive composition for forming a first pressure-sensitive adhesive layer (first pressure-sensitive adhesive composition) according to this example.

[0168] (Preparation of second pressure-sensitive adhesive composition) To the solution of the acrylic polymer A, 0.3 parts of crosslinking agent CL1 and 0.8 parts of thermal polymerization initiator TO1 were added relative to 100 parts of the acrylic polymer A, and the mixture was mixed uniformly to prepare a pressure-sensitive adhesive composition for forming a second pressure-sensitive adhesive layer (second pressure-sensitive adhesive composition) according to this example.

[0169] (Preparation of Pressure-Sensitive Adhesive Sheet) The first 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 first pressure-sensitive adhesive layer with a thickness of 30 μm. The second 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 second pressure-sensitive adhesive layer with a thickness of 30 μm. The second pressure-sensitive adhesive layer was laminated by bonding to the second surface of a 12.5 μm thick polyimide (PI) film (product name "Kapton 50H", manufactured by DuPont-Toray Co., Ltd.) as a substrate, and then the first pressure-sensitive adhesive layer was laminated by bonding to the first surface of the PI film. Aging was then performed at 50°C for 3 days. In this way, a pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with substrate) according to this example was prepared. The first and second pressure-sensitive adhesive surfaces of the pressure-sensitive adhesive sheet were protected by the release liners used to form the first and second pressure-sensitive adhesive layers, respectively.

[0170] Examples 2 to 14 A first PSA composition according to each example was prepared in the same manner as in Example 1, except that the type and amount of crosslinking agent, type and amount of thermal polymerization initiator, and type and amount of polyfunctional monomer were changed as shown in Tables 1 and 2. A substrate-attached double-sided PSA sheet according to each example was produced in the same manner as in Example 1, using the obtained first PSA composition and the same second PSA composition as in Example 1. In Tables 1 and 2, the thermal polymerization initiator TO2 is the product name "Niper BMT" (a benzoyl peroxide-based thermal polymerization initiator manufactured by NOF Corporation), the thermal polymerization initiator TA1 is AIBN, the polymerization initiator TA2 is 2,2'-azobis(2,4,4-trimethylpentane) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "VR-110"), HDDA is 1,6-hexanediol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), and the crosslinking agent CL2 is an epoxy-based crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Tetrad C").

[0171] Examples 15 to 17 A PSA sheet (double-sided PSA sheet with substrate) according to each Example was produced in the same manner as in Example 9, except that a 25 μm thick polyimide (PI) film (product name "Kapton 100H" manufactured by DuPont-Toray Co., Ltd.), a 50 μm thick polyimide (PI) film (product name "Kapton 200H" manufactured by DuPont-Toray Co., Ltd.), or a 25 μm thick PET film (product "Lumirror S10" manufactured by Toray Industries, Inc.) was used as the substrate.

[0172] Comparative Example 1 A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer was charged with 97 parts of n-butyl acrylate (BA), 3 parts of acrylic acid (AA), and 43 parts of ethyl acetate as a polymerization solvent. 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was then added as a thermal polymerization initiator, and a polymerization reaction (solution polymerization) was carried out at 61°C for 6 hours under a nitrogen atmosphere to obtain a solution containing acrylic polymer B. 0.5 parts of crosslinker CL2 per 100 parts of acrylic polymer B was added to the solution of acrylic polymer B, and the mixture was mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example. A pressure-sensitive adhesive sheet (substrate-attached double-sided pressure-sensitive adhesive sheet) according to this example was produced in the same manner as in Example 1, except that first and second pressure-sensitive adhesive layers having the thicknesses shown in Table 2 were produced using this pressure-sensitive adhesive composition.

[0173] The outline of each example and the evaluation results are shown in Tables 1 and 2.

[0174]

[0175]

[0176] As shown in Tables 1 and 2, in all of the pressure-sensitive adhesive sheets of Examples 1 to 17, the post-heat peel strength Fa1 of the first pressure-sensitive adhesive layer was smaller than the post-heat peel strength Fb1 of the second pressure-sensitive adhesive layer. More specifically, in all of the pressure-sensitive adhesive sheets of Examples 1 to 17, Fb1 - Fa1 was 0.5 N / 20 mm or greater. In the pressure-sensitive adhesive sheets of these Examples, the first pressure-sensitive adhesive layer exhibited a high ease-of-removal effect upon heat treatment, while the second pressure-sensitive adhesive layer exhibited a relatively mild ease-of-removal effect compared to the first pressure-sensitive adhesive layer. On the other hand, in the pressure-sensitive adhesive sheet of Comparative Example 1, the post-heat peel strengths of the first and second pressure-sensitive adhesive layers were equivalent.

[0177] The adhesive sheet of Example 9 was cut to a size of 165 mm x 65 mm, and the second adhesive surface was bonded to an alkali glass plate B (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate edge polished) as the second member. The first adhesive surface was then bonded to an alkali glass plate A (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate edge polished) as the first member. This assembly was then placed in an autoclave and autoclaved at 50°C, 5 atmospheres, and for 15 minutes. The assembly was then removed from the autoclave and allowed to stand for 30 minutes at room temperature and normal pressure (23°C, 1 atmosphere). The resulting assembly of alkali glass plate A / adhesive sheet / alkali glass plate B was then heat-treated in an oven at 180°C for 30 minutes, removed from the oven, and allowed to stand for 30 minutes at 23°C and 50% RH. An attempt was then made to manually disassemble the assembly (all evaluations were performed by the same adult female). Specifically, a ruler (or a metal plate) was inserted between the layers at the end of the bonded structure, and after inserting it about 10 mm, force was applied in the vertical direction (thickness direction of the evaluation sample) to attempt disassembly. As a result, the bonded structure was successfully disassembled in such a manner that the alkali glass plate A was peeled off from the first adhesive layer, leaving the entire adhesive sheet on the alkali glass plate B. Furthermore, the adhesive sheet remaining on the alkali glass plate B was peeled off from the alkali glass plate B by first peeling off a region of about 10 mm from one end of the adhesive sheet from the alkali glass plate B, and then grasping that portion with a human hand and pulling it in a direction of about 150 to 180 degrees, thereby successfully peeling it off from the alkali glass plate B without tearing.

[0178] 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.

[0179] REFERENCE SIGNS LIST 1 Pressure-sensitive adhesive sheet 1A First pressure-sensitive adhesive surface 1B Second pressure-sensitive adhesive surface 2 Pressure-sensitive adhesive sheet 20 Substrate 21 First pressure-sensitive adhesive layer 22 Second pressure-sensitive adhesive layer 31, 32 Release liner 50 Pressure-sensitive adhesive sheet with release liner 71 First member 72 Second member 80 Bonding portion 90 Pressure-sensitive adhesive sheet 100 Bonded body

Claims

1. A double-sided adhesive sheet, the adhesive sheet comprising a first adhesive layer and a second adhesive layer, the first adhesive layer constituting a first adhesive surface which is a first surface of the adhesive sheet, the second adhesive layer constituting a second adhesive surface which is a second surface of the adhesive sheet, the second surface being a surface opposite to the first surface, the first adhesive layer comprising at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule and a polymer having an ethylenically unsaturated group, and further comprising a thermal polymerization initiator, the first adhesive layer being attached to a glass plate and heat-treated at 180°C for 30 minutes, and thereafter a post-heat peel strength Fa1 [N / 20 mm] measured in an environment of 23°C and 50% RH is different from a post-heat peel strength Fb1 [N / 20 mm] measured in an environment of 23°C and 50% RH, the second adhesive layer being attached to a glass plate and heat-treated at 180°C for 30 minutes.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the post-heating peel strength difference (|Fb1-Fa1|) calculated from the post-heating peel strength Fa1 [N / 20 mm] and the post-heating peel strength Fb1 [N / 20 mm] is 0.5 N / 20 mm or more.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the first pressure-sensitive adhesive layer has a post-heat peel strength reduction rate A [%] calculated from the pre-heat peel strength Fa0 [N / 20 mm] measured in an environment of 23°C and 50% RH after being attached to a glass plate and heat-treated at 180°C for 30 minutes, and the post-heat peel strength Fa1 [N / 20 mm] measured in an environment of 23°C and 50% RH according to the following formula, which is higher than 20% and lower than 99.9%. Post-heat peel strength reduction rate A [%] = (1-Fa1 / Fa0) x 100 4. The adhesive sheet according to claim 1 or 2, wherein the first adhesive layer and the second adhesive layer are laminated via a substrate.

5. An adhesive sheet as described in claim 1 or 2, wherein the second adhesive layer contains at least one of a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule and a polymer having an ethylenically unsaturated group, and further contains a thermal polymerization initiator.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the second pressure-sensitive adhesive layer has a post-heat peel strength reduction rate B [%] calculated from the pre-heat peel strength Fb0 [N / 20 mm] measured in an environment of 23°C and 50% RH after being attached to a glass plate and heat-treated at 180°C for 30 minutes, and the post-heat peel strength Fb1 [N / 20 mm] measured in an environment of 23°C and 50% RH according to the following formula: Post-heat peel strength reduction rate B [%] = (1-Fb1 / Fb0) x 100 7. The adhesive sheet according to claim 1 or 2, wherein a pre-heating peel strength Fa0 [N / 20 mm] measured when the first adhesive layer is attached to a glass plate and under an environment of 23°C and 50% RH, and a pre-heating peel strength Fb0 [N / 20 mm] measured when the second adhesive layer is attached to a glass plate and under an environment of 23°C and 50% RH, are both 4.0 N / 20 mm or more, and a post-heating peel strength Fa1 [N / 20 mm] of the first adhesive layer and a post-heating peel strength Fb1 [N / 20 mm] of the second adhesive layer are both less than 3.0 N / 20 mm.

8. A joint comprising: an adhesive sheet according to claim 1 or 2; a first member to which a first adhesive surface of the adhesive sheet is adhered; and a second member to which a second adhesive surface of the adhesive sheet is adhered.

9. A method for dismantling the joined body according to claim 8, comprising the steps of: subjecting the joined body to a heat treatment; and then separating the first member from the first adhesive surface while leaving the adhesive sheet on the second member.

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