Adhesive sheet

Abstract

Provided is an adhesive sheet having double-sided adhesiveness. The pressure-sensitive adhesive sheet includes a first pressure-sensitive adhesive layer constituting a first pressure-sensitive adhesive surface and a second pressure-sensitive adhesive layer constituting a second pressure-sensitive adhesive surface. The first 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. The post-heating peeling force Fa1 [N / 20 mm] of the first adhesive layer of the adhesive sheet is different from the post-heating peeling force Fb1 [N / 20 mm] of the second adhesive layer.

Description

Technical Field

[0001] This invention relates to adhesive sheets, and more particularly to adhesive sheets with double-sided adhesive properties.

[0002] This application claims priority based on Japanese Patent Application No. 2023-122023, filed on July 26, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Generally, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) have the following properties: they exhibit a soft, solid (viscoelastic) state in a temperature range near room temperature and adhere easily to the substrates by means of pressure. Considering the excellent operability of bonding to substrates, adhesives are widely used in various fields in the form of adhesive sheets with an adhesive layer on a support, or in the form of adhesive sheets without a support. Among such adhesives, there are those used to bond to substrates and removed from substrates after the bonding purpose is completed.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6587811 Summary of the Invention

[0005] The problem that the invention aims to solve For adhesives used in applications involving peeling off from adhered objects, it is required that they exhibit good adhesion during bonding to the adhered object and can be easily peeled off after the bonding purpose is completed. To achieve such properties, techniques are known to include thermally expandable microspheres in the adhesive that expand upon heating to a specified temperature (e.g., Patent Document 1). However, such heat-peelable adhesive sheets achieve their heat-peeling function by reducing the bonding area between the adhesive surface and the adhered object through the expansion of the thermally expandable microspheres upon heating. Therefore, there is a tendency for the peeling force after heating to be difficult to control, and they are sometimes unsuitable for fixed applications involving heating processes. For example, they may sometimes separate from the adhered object unintended due to treatment methods such as the configuration of the heated adhered object or the application of vibration.

[0006] Therefore, the object of the present invention is to provide an adhesive sheet that can be easily peeled off by heating and is also suitable for fixing applications accompanied by heating processes.

[0007] Methods for solving problems According to this specification, a double-sided adhesive sheet (double-sided adhesive sheet) is provided. The adhesive sheet comprises a first adhesive layer and a second adhesive layer. The first adhesive layer constitutes a first adhesive surface, which is a first side of the adhesive sheet. The second adhesive layer constitutes a second adhesive surface, which is a second side of the adhesive sheet. The second side of the adhesive sheet is the surface opposite to the first side. The first adhesive layer comprises at least one of a polyfunctional monomer having two or more olefinic unsaturated groups in one molecule and a polymer having olefinic unsaturated groups, and further comprises a thermal polymerization initiator. Furthermore, for the adhesive sheet, the peel strength Fa1 [N / 20mm] after heating, measured after the first adhesive layer is bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, is different from the peel strength Fb1 [N / 20mm] after heating after the second adhesive layer is bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH.

[0008] For adhesive sheets with the above-described configuration, the desired heat-peelability function can be achieved by including a first adhesive layer containing a thermal polymerization initiator and thermally curing it by thermally polymerizing olefinic unsaturated groups. By utilizing the aforementioned thermal polymerization, the peel force after heating can be easily controlled, making it preferably suitable for fixing applications accompanying heating processes. Furthermore, since the peel forces of the first and second adhesive layers are designed to differ after heating, the disassembly operability and reusability (recyclability, reuse, etc.) of the joint formed by joining the first and second components with the adhesive sheet as a barrier are excellent when disassembled after heating.

[0009] In some preferred embodiments of the adhesive sheet, the difference in peel force after heating (|Fb1-Fa1|) calculated from the peel force after heating Fa1 [N / 20mm] and the peel force after heating Fb1 [N / 20mm] is 0.5N / 20mm or more. With this design, for example, when the joint formed by joining the first component and the second component with the adhesive sheet in between is disassembled after heating, it is possible to improve the predictability of which component, the first or the second component, the adhesive sheet will remain on.

[0010] In some methods, it is appropriate that the peel force Fa0 [N / 20mm] of the first adhesive layer before heating, measured when it is bonded to a glass plate at 23°C and 50%RH, and the peel force Fa1 [N / 20mm] after heating, measured when it is bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, and the reduction rate A [%] of the peel force after heating, calculated using the following formula, is greater than 20% and less than 99.9%.

[0011] Peel force reduction rate A[%] after heating = (1 - Fa1 / Fa0) × 100 According to the adhesive sheet that satisfies the above characteristics, it can perform sufficient heat-peeling function on the first adhesive surface and can appropriately suppress the phenomenon of unintended separation from the heated adhered material.

[0012] In some types of adhesive sheets, the first adhesive layer and the second adhesive layer are laminated with a substrate in between. That is, a double-sided adhesive sheet (double-sided adhesive sheet with substrate) is formed by sequentially laminating the first adhesive layer, the substrate, and the second adhesive layer. For this type of double-sided adhesive sheet, since the substrate imparts strength (e.g., tensile strength), when disassembling a joint formed by joining the first and second components with the adhesive sheet in between, it is easy to peel off the remaining double-sided adhesive sheet from the separated components after separating the first and second components. Furthermore, from the viewpoint of reworkability (re-adhesion) when the adhesive sheet is pasted onto an adhered object, it is also advantageous for the adhesive sheet to be reinforced with a substrate.

[0013] In some types of adhesive sheets, the second adhesive layer comprises at least one of a polyfunctional monomer having two or more olefinically unsaturated groups and a polymer having olefinically unsaturated groups, and further comprises a thermal polymerization initiator. According to the adhesive sheet having the second adhesive layer, a stable heat-peelable function can be achieved even on the second adhesive surface.

[0014] In some embodiments, it is appropriate that the peel force Fb0 [N / 20mm] of the second adhesive layer before heating, measured when bonded to a glass plate at 23°C and 50%RH, and the peel force Fb1 [N / 20mm] after heating, measured when bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, and the reduction rate B [%] of the peel force after heating calculated using the following formula, is greater than 20% and less than 99.9%.

[0015] Peel strength reduction rate B[%] after heating = (1 - Fb1 / Fb0) × 100 According to the adhesive sheet that meets the above characteristics, it can exert a moderate heat-peeling function even on the second adhesive surface, and can appropriately suppress the phenomenon of unintended separation from the adherend after heat curing.

[0016] In some types of adhesive sheets, it is preferable that the peel strength Fa0 [N / 20mm] before heating, measured when the first adhesive layer is bonded to a glass plate at 23°C and 50%RH, and the peel strength Fb0 [N / 20mm] before heating, measured when the second adhesive layer is bonded to a glass plate at 23°C and 50%RH, are both 4.0 N / 20mm or higher. Adhesive sheets that satisfy the above characteristics exhibit excellent adhesion performance to the adhered objects before heating (before thermosetting). Furthermore, in some types of adhesive sheets, it is preferable that the peel strength Fa1 [N / 20mm] after heating of the first adhesive layer and the peel strength Fb1 [N / 20mm] after heating of the second adhesive layer are both less than 3.0 N / 20mm. For adhesive sheets that satisfy the above characteristics, for example, in applications where a joint formed by bonding the first and second components with the adhesive sheet is disassembled after heating, the disassembly operability of the joint and the reusability of the disassembled material are good. Adhesive sheets that meet the above characteristics can provide good fixation performance during use and can be easily separated from the adhered objects after use by utilizing the heat-peeling function.

[0017] The adhesive sheet disclosed herein can preferably be used as a component of a joint having a first component bonded to a first adhesive surface of the adhesive sheet and a second component bonded to a second adhesive surface of the adhesive sheet. The joint can be easily disassembled, for example, by a disassembly method comprising a step of heat-treating the joint, leaving the adhesive sheet on the second component, and separating the first component from the first adhesive surface. Therefore, it is preferred from the viewpoint of disassembly operability and the reusability (recyclability, reuse, etc.) of the disassembled material.

[0018] It should be noted that appropriate combinations of the elements described in this specification are also included within the scope of the invention for which patent protection is sought through this patent application. Attached Figure Description

[0019] [ Figure 1 This is a schematic cross-sectional view illustrating the structure of an adhesive sheet according to one embodiment.

[0020] [ Figure 2 [A cross-sectional view illustrating the configuration of a joint according to one embodiment is shown schematically.] Detailed Implementation

[0021] The following describes suitable embodiments of the present invention. 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 on carrying out the invention as set forth in this specification and the technical common sense at the time of filing. The present invention can be carried out based on the disclosures in this specification and the technical common sense in the field.

[0022] It should be noted that in the following figures, the same reference numerals are sometimes used to describe components or parts that perform the same function, and repeated descriptions are sometimes omitted or simplified. Furthermore, the embodiments described in the figures are schematic for the purpose of clearly illustrating the invention and do not necessarily represent the exact dimensions or scale of the actual product provided.

[0023] In this specification, the term "base polymer" in the adhesive refers to the main component of the rubber-like polymer contained in the adhesive. The aforementioned rubber-like polymer refers to a polymer that exhibits rubber-like elasticity in a temperature range near room temperature. Furthermore, in this specification, the term "main component," unless otherwise specified, refers to the component contained in a proportion exceeding 50% by weight.

[0024] In this specification, "acrylic polymer" refers to a polymer comprising monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Acrylic polymers in this specification are defined as polymers comprising monomer units derived from acrylic monomers.

[0025] Furthermore, in this specification, the term "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" generally refers to both acryloyl and methacryloyl groups. Therefore, the concept of acrylic monomers as used herein can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" generally refers to both acrylic acid and methacrylic acid, and "(meth)acrylate" generally refers to both acrylate and methacrylate. Other similar terms are used in the same way.

[0026] Furthermore, in this specification, "weight" can be replaced with "mass". For example, "weight%" can be replaced with "mass%", and "parts by weight" can be replaced with "parts by mass".

[0027] <Adhesive sheet> The adhesive sheet disclosed herein is a double-sided adhesive sheet (double-sided adhesive sheet), having a first adhesive layer constituting a first adhesive surface and a second adhesive layer constituting a second adhesive surface. The adhesive sheet can be a substrate-supported double-sided adhesive sheet in which the first adhesive layer and the second adhesive layer are laminated with a substrate between them, or it can be a substrate-free double-sided adhesive sheet without a substrate. The concept of adhesive sheet as used herein may include objects referred to as adhesive tape, adhesive label, adhesive film, etc. The adhesive sheet disclosed herein can be in roll form or in single sheet form. Alternatively, it can be an adhesive sheet further processed into various shapes.

[0028] The structure of an adhesive sheet according to one embodiment is schematically shown. Figure 1 The adhesive sheet 1 is configured as a double-sided adhesive sheet with a substrate, comprising: a substrate 20 having a first side and a second side; a first adhesive layer 21 disposed on the first side of the substrate 20; and a second adhesive layer 22 disposed on the second side, which is a surface of the substrate 20 opposite to the first side. The adhesive sheet 1 has a first side and a second side, which is a surface opposite to the first side. The surface of the first adhesive layer 21 is configured as a first adhesive surface 1A, which also serves as the first side of the adhesive sheet 1, and the surface of the second adhesive layer 22 is configured as a second adhesive surface 1B, which also serves as the second side of the adhesive sheet 1. Alternatively, the adhesive sheet disclosed herein may also be configured, for example, to consist of a substrate 20 having a first side and a second side; a first adhesive layer 21 disposed on the first side of the substrate 20; and a second adhesive layer 22 disposed on the second side, which is a surface of the substrate 20 opposite to the first side. Figure 1 The structure shown omits the structure of the substrate 20, that is, the structure in which the first adhesive layer 21 and the second adhesive layer 22 are directly (without the substrate) stacked together, forming a substrate-free double-sided adhesive sheet.

[0029] Adhesive sheet 1 is used, for example, to adhere the first adhesive surface 1A and the second adhesive surface 1B to different parts of an object. The locations where adhesive surfaces 1A and 1B are adhered can be individual parts of different components, or different parts within a single component. For example... Figure 1 As shown, the adhesive sheet 1 before use (i.e., before being adhered to the object) can be an adhesive sheet 50 with release liner, in which the first adhesive surface 1A and the second adhesive surface 1B are protected by release liner 31 and 32, respectively, which are at least the sides opposite to the adhesive layers 21 and 22 that become the release surfaces. As the release liner 31 and 32, for example, it is preferable to use a release liner configured such that a release layer formed by a release agent is provided on one side of the sheet substrate (liner substrate), making that side the release surface. Alternatively, the release liner 32 can be omitted, and a release liner 31 with two sides as release surfaces can be used, overlapped with the adhesive sheet 1 and wound into a spiral shape, thereby forming an adhesive sheet with release liner in which the second adhesive surface 1B is protected by contact with the back of the release liner 31 (roll shape).

[0030] <Peeling force> (Poor peeling force after heating (Fb1-Fa1)) The adhesive sheet disclosed herein has a first adhesive surface composed of a first adhesive layer and a second adhesive surface composed of a second adhesive layer. The peel strength Fa1 [N / 20mm] after heating, measured at 23°C and 50%RH after the first adhesive layer is bonded to a glass plate and heated at 180°C for 30 minutes, differs from the peel strength Fb1 [N / 20mm] after heating, measured at 23°C and 50%RH after the second adhesive layer is bonded to a glass plate and heated at 180°C for 30 minutes. That is, the difference in peel strength after heating (|Fb1-Fa1|), calculated as the absolute value of the difference between Fa1 and Fb1, is greater than 0 N / 20mm. With this adhesive sheet design, for example, when a joint consisting of a first component and a second component joined together with the adhesive sheet is disassembled after heating, it is possible to predetermine which component (the first or the second component) the adhesive sheet will remain on, or to improve its predictability. This improves the disassembly operability of the aforementioned joint and the reusability (recyclability, reuse, etc.) of the disassembled materials.

[0031] The peel force difference (|Fb1-Fa1|) after heating can be, for example, 0.03 N / 20 mm or more, 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. If the peel force difference (|Fb1-Fa1|) after heating increases, there is a tendency to increase the predictability of whether the two parts separate in the form of adhesive residue on the first or second part. In some embodiments, the peel force difference (|Fb1-Fa1|) after heating can 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. There is no particular upper limit to the peel force difference (|Fb1-Fa1|) after heating. In some methods, the difference in peel strength after heating (|Fb1 - Fa1|) can be, for example, less than 30 N / 20 mm, less than 25 N / 20 mm, less than 15 N / 20 mm, less than 10 N / 20 mm, less than 5.0 N / 20 mm, less than 3.0 N / 20 mm, or less than 2.5 N / 20 mm. It should be noted that, typically, both Fa1 and Fb1 after heating are greater than 0 N / 20 mm.

[0032] For the adhesive sheet disclosed herein, since it has a first adhesive layer configured to be easily peeled by heat polymerization, it is preferably carried out in such a manner that the peeling force Fa1 after heating is less than the peeling force Fb1 after heating, that is, Fa1 [N / 20 mm] < Fb1 [N / 20 mm]. According to this method, for the adhesive surface of the adhesive sheet after heating, while the easy peeling property can be exhibited on the first adhesive surface, a relatively large peeling force can be maintained on the second adhesive surface. The adhesive sheet designed in this way, for example, when the joined body formed by joining the first member and the second member through the above-mentioned adhesive sheet is disassembled after heating, it is easy to leave the above-mentioned adhesive sheet on the above-mentioned second member and separate the above-mentioned first member from the above-mentioned first adhesive surface. Therefore, it is preferable from the viewpoints of the disassembly operability of the above-mentioned joined body and the reusability (recyclability, reusability, etc.) of the disassembled product.

[0033] (Peeling force Fa1 of the first adhesive layer after heating) In the adhesive sheet disclosed herein, the peel force Fa1 of the first adhesive layer after heating is not particularly limited, and can be appropriately set such that it exhibits the desired ease of peeling after heating and the peel force difference (|Fb1-Fa1|) after heating exceeds 0. In some embodiments, from the viewpoint of the aforementioned ease of peeling, it is appropriate for the peel force Fa1 of the first adhesive layer after heating to be less than 3.0 N / 20 mm, it is advantageous to be less than 2.0 N / 20 mm, and preferably less than 1.0 N / 20 mm. In some embodiments where a higher level of ease of peeling after heating is required, the peel force Fa1 of the first adhesive layer after heating may be less than 1.0 N / 20 mm, preferably less than 0.8 N / 20 mm, more preferably less than 0.6 N / 20 mm, further preferably less than 0.5 N / 20 mm, and may also be less than 0.4 N / 20 mm, less than 0.3 N / 20 mm, less than 0.2 N / 20 mm, or even less than 0.2 N / 20 mm. In this way, an adhesive sheet with a low peel strength Fa1 after heating can easily peel the adherend from the heated first adhesive layer (first adhesive surface) while suppressing the load applied to the adherend. Therefore, it is also preferable to use in the case of adhering the first adhesive surface to an adherend made of brittle materials such as glass or semiconductor materials (typically hard and brittle materials). The peel strength Fa1 after heating is typically greater than 0 N / 20 mm, and from the viewpoint of the adherend retention after heating, it is appropriate to be 0.01 N / 20 mm or more. For example, the peel strength Fa1 after heating can be 0.05 N / 20 mm or more, or 0.1 N / 20 mm or more, or 0.2 N / 20 mm or more, or 0.3 N / 20 mm or more, or 0.4 N / 20 mm or more. In some methods, the peeling force Fa1 after heating can be above 0.5N / 20mm, above 0.8N / 20mm, above 1.0N / 20mm, above 1.5N / 20mm, or above 2.0N / 20mm.

[0034] (Peel force Fb1 of the second adhesive layer after heating) In the adhesive sheet disclosed herein, the heat-induced peel strength Fb1 of the second adhesive is not particularly limited and can be appropriately set so that the heat-induced peel strength difference (|Fb1 - Fa1|) exceeds 0. Typically, the heat-induced peel strength Fb1 exceeds 0 N / 20 mm, and from the viewpoint of retention of the adhered material after heating, a value of 0.01 N / 20 mm or more is appropriate. In some embodiments, the heat-induced peel strength Fb1 can 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, or 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. There is no particular upper limit to the heat-induced peel strength Fb1 of the second adhesive layer; for example, it can be less than approximately 30 N / 20 mm, less than 20 N / 20 mm, less than 15 N / 20 mm, less than 10 N / 20 mm, or less than 7.0 N / 20 mm. A relatively low heat-induced peel strength Fb1 of the second adhesive layer is advantageous, for example, when considering methods for removing the adhesive from the substrate bonded to the second adhesive surface after heating. In some methods, the peel force Fb1 after heating can be, for example, less than 5.0 N / 20 mm, less than 4.0 N / 20 mm, less than 3.0 N / 20 mm (e.g., less than 3.0 N / 20 mm), or less than 2.5 N / 20 mm, less than 2.0 N / 20 mm, less than 1.5 N / 20 mm, less than 1.0 N / 20 mm (e.g., less than 1.0 N / 20 mm), less than 0.5 N / 20 mm, less than 0.3 N / 20 mm, or less than 0.2 N / 20 mm or less than 0.2 N / 20 mm.

[0035] (Peel force ratio after heating (Fb1 / Fa1)) In some preferred embodiments of the adhesive sheet disclosed herein, the ratio of the peel force after heating (Fb1 / Fa1), calculated from the peel force after heating Fa1 [N / 20mm] of the first adhesive layer and the peel force after heating Fb1 [N / 20mm] of the second adhesive layer, exceeds 1.0. Therefore, in the adhesive surfaces of the heated adhesive sheet, while the first adhesive surface exhibits easy peeling, a relatively large peel force is maintained on the second adhesive surface. Such an adhesive sheet is preferred, for example, in a usage where a joint formed by joining the first and second components with the aforementioned adhesive sheet is heated and then disassembled, considering the ease of disassembly of the joint and the reusability (recyclability, reuse, etc.) of the disassembled material. From this perspective, in some embodiments, a peel force ratio after heating (Fb1 / Fa1) of 1.5 or more is advantageous, preferably 2.0 or more, more preferably 3.0 or more, and can be 4.0 or more, or even 5.0 or more. There is no particular upper limit to the peel strength ratio (Fb1 / Fa1) after heating, and in some methods, a higher ratio is better. In other methods, the peel strength ratio (Fb1 / Fa1) after heating can be, for example, 1000 or less, or 500 or less. For example, in methods considering the retention of the adherend on the first adhesive surface after heating, or considering the removal of the adherend on the second adhesive surface from the heated adhesive sheet, it is advantageous that the peel strength ratio (Fb1 / Fa1) after heating is not too high. In such methods, the peel strength ratio (Fb1 / Fa1) after heating can 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.

[0036] (Peel force Fa0 of the first adhesive layer before heating) The initial (before heating) peel force Fa0 of the first adhesive layer of the adhesive sheet disclosed herein is suitable, for example, 0.5 N / 20 mm or more, advantageous, 0.8 N / 20 mm or more, and preferably 1.0 N / 20 mm or more or greater. Adhesive sheets exhibiting the aforementioned peel force Fa0 before heating are able to provide good adhesion to the adherend on the first adhesive surface, for example, to properly hold the adherend. From the viewpoint of easily obtaining better adhesion (e.g., the retention performance of the adhered objects), in some embodiments, the aforementioned pre-heating peel force Fa0 can 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 force Fa0 can be appropriately set according to the required adhesion in the first adhesive surface, and is therefore not limited to a specific range. For example, it can be less than about 30 N / 20 mm, less than 20 N / 20 mm, less than 15 N / 20 mm, less than 10 N / 20 mm, less than 5.0 N / 20 mm, or less than 3.0 N / 20 mm. The pre-heating peel force Fa0 of the first adhesive layer refers to the peel strength (peel force) against the glass plate measured at 23°C with a peel angle of 180 degrees and a speed of 300 mm / min. More specifically, the above-mentioned pre-heating peel force Fa0 is measured using the method described in the following examples.

[0037] (Reduction rate A of peel strength after heating of the first adhesive layer) In some embodiments, it is appropriate for the first adhesive layer to have a heat-induced peel force reduction rate A, calculated from the pre-heat peel force Fa0 and the post-heat peel force Fa1 based on the following formula, to be greater than 20% (e.g., greater than 30%), greater than 40% is advantageous, and preferably greater than 50%.

[0038] Peel force reduction rate A[%] after heating = (1-Fa1 / Fa0)×100 The first adhesive surface of the adhesive sheet that meets the above characteristics exhibits good adhesion to the adherend while also demonstrating good peelability (heat-peelability) upon removal after heat treatment. In some preferred embodiments, the reduction rate A after heat treatment can be 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 97% or more. The higher the reduction rate A after heat treatment, the better the heat-peelability. Furthermore, in some embodiments, the reduction rate A after heat treatment is preferably less than 99.9%. Based on an adhesive sheet with a reduction rate A of less than 99.9% after heat treatment, the first adhesive surface maintains adhesion to the adherend while exhibiting the desired peelability. This prevents the adherend bonded to the first adhesive surface from naturally peeling off the adhesive sheet due to heat and / or causing adverse conditions. From this perspective, the reduction rate A of peel force after heating can be less than 99.0% or less than, for example, 95.0%.

[0039] (Peel force Fb0 of the second adhesive layer before heating) In the adhesive sheet disclosed herein, the initial peel force Fb0 of the second adhesive layer before heating is not particularly limited and can be appropriately set according to the purpose. In some embodiments, the initial peel force Fb0 of the second adhesive layer before heating can be, for example, 0.2 N / 20 mm or more, 0.5 N / 20 mm or more is appropriate, and preferably 0.8 N / 20 mm or more. The adhesive sheet exhibiting the above-mentioned initial peel force Fb0 before heating can exert good adhesion to the adhered object on the second adhesive surface, for example, it can properly hold the adhered object. From the viewpoint of easily obtaining better adhesion (e.g., the retention performance of the adhered object), in some embodiments, the initial peel force Fb0 before heating can be, for example, 1.0 N / 20 mm or more, or 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 adhesive layer is not limited to a specific range. For example, it can be less than about 30 N / 20 mm, less than 20 N / 20 mm, less than 15 N / 20 mm, less than 10 N / 20 mm, less than 5.0 N / 20 mm, or less than 3.0 N / 20 mm. The pre-heating peel force Fb0 of the second adhesive layer refers to the peel strength (peel force) against the glass plate measured at 23°C with a peel angle of 180 degrees and a speed of 300 mm / min. More specifically, the pre-heating peel force Fb0 is measured using the method described in the following examples.

[0040] (Reduction rate of peel strength B after heating of the second adhesive layer) In the adhesive sheet disclosed herein, the relationship between the pre-heating peel force Fb0 and the post-heating peel force Fb1 of the second adhesive layer is not particularly limited. For example, the post-heating peel force Fb1 may be greater than, less than, or equal to the pre-heating peel force Fb0. More specifically, the post-heating peel force reduction rate B of the second adhesive layer, calculated from the pre-heating peel force Fb0 and the post-heating peel force Fb1 based on the following formula, may be less than 0% (e.g., less than -300%, less than -500%, etc.), may exceed 0% (e.g., more than 0%, less than 99.0%), or may be approximately 0%.

[0041] Peel strength reduction rate B[%] after heating = (1-Fb1 / Fb0)×100 In some cases, such as considering the removability of the adhesive after heating, the peel force reduction rate B after heating may be greater than 20%, greater than 30%, greater than 40%, or greater than 50%, or greater than 60%, greater than 70%, or greater than 80%, greater than 85%, or greater than 90%.

[0042] In some embodiments of the adhesive sheet disclosed herein, it is appropriate for the peel strengths Fa0 and Fb0 [N / 20mm] before heating to both be 1.0N / 20mm or more, and they can both be 2.0N / 20mm or more. In some preferred embodiments, the peel strengths Fa0 and Fb1 before heating are 3.0N / 20mm or more, more preferably 4.0N / 20mm or more, even more preferably 5.0N / 20mm or more, and can both be 7.0N / 20mm or more, or both 8.0N / 20mm or more. For adhesive sheets where both Fa0 and Fa1 are 4.0N / 20mm or more or higher before heating, the adhesion performance of the adhered objects on the first and second adhesive surfaces is good before heating (initially), making them suitable for applications such as manufacturing a joint to firmly join two components together through the adhesive sheet.

[0043] In some embodiments of the adhesive sheet disclosed herein, the peel forces Fa1 and Fb1 [N / 20mm] after heating are preferably both less than 4.0N / 20mm, and more preferably both less than 3.0N / 20mm. Adhesive sheets that satisfy the above characteristics, for example, in the method of using a joint formed by joining two components with the adhesive sheet in between, to be disassembled after heating, provide good disassembly operability of the joint and good reusability of the disassembled material.

[0044] For adhesive sheets where the peel forces Fa0 and Fb0 before heating are both above or greater than the specified lower limit, and the peel forces Fa1 and Fb1 after heating are both below or less than the specified upper limit, they can exhibit good fixing performance during use and can be easily separated from the adhered object by utilizing the heat-peeling function after use, and are therefore preferred.

[0045] The peel strength of the first and second adhesive layers before heating, the peel strength after heating, and their relative relationship can be achieved and adjusted by appropriately selecting the following based on the contents of this specification: the type of polymer contained in each adhesive layer (monomer composition, etc.), whether it contains other components that may be contained in each adhesive layer (e.g., thermal polymerization initiators, multifunctional monomers, as described later), the type and content of other components, their combination, and whether a crosslinking agent is used in each adhesive layer, the type of crosslinking agent, and the amount used, etc.

[0046] <Gel fraction> (Increase in gel fraction of the first adhesive layer (Ga1-Ga0)) In some embodiments of the adhesive sheet disclosed herein, it is preferable that the increase in gel fraction (Ga1-Ga0) calculated from the gel fraction Ga0 [%] before heating and the gel fraction Ga1 [%] after heating of the first adhesive layer is typically greater than 0%, for example, 5% or more is suitable, and preferably 10% or more. A first adhesive layer satisfying the above-mentioned increase in gel fraction (Ga1-Ga0) tends to exhibit good thermosetting properties and readily exhibits the effect of reduced peel force due to heating (heat-peelability) in the first adhesive surface. From the viewpoint of easily obtaining better heat-peelability, in some embodiments, the increase in gel fraction (Ga1-Ga0) of the first adhesive layer is more preferably 13% or more, for example, 16% or more, 20% or more, 25% or more, 30% or more, 35% or more, or 40% or more. In addition, in some approaches, from the viewpoint of preferably achieving both adhesion before heating and easy peeling after heating simultaneously, it is appropriate for the gel fraction increase (Ga1-Ga0) of the first adhesive layer to be, for example, 70% or less, preferably 60% or less, or possibly 50% or less, or possibly 40% or less.

[0047] Regarding the gel fraction Ga0 of the first adhesive layer before heating, it is determined as the weight ratio of the ethyl acetate insoluble matter in the adhesive sample taken from the initial (before heating) first adhesive layer. Regarding the gel fraction Ga1 of the first adhesive layer after heating, it is determined in the same manner as the gel fraction Ga0 before heating for the adhesive sample taken from the first adhesive layer after heating at 180°C for 30 minutes. More specifically, the gel fraction Ga0 before heating and the gel fraction Ga1 after heating are measured using the method described in the following examples. Furthermore, regarding the gel fraction Gb0 before heating and the gel fraction Gb1 after heating of the second adhesive layer (described later), it is determined in the same manner as the gel fraction Ga0 before heating and the gel fraction Ga1 after heating of the first adhesive layer for the adhesive sample taken from the second adhesive layer or after heating at 180°C for 30 minutes.

[0048] (Gel fraction of the first adhesive layer after heating, Ga1) The first adhesive layer of the adhesive sheet disclosed herein preferably satisfies any increase in gel fraction (Ga1-Ga0) disclosed herein, and the gel fraction Ga1 after heating is 50% or more (more preferably 70% or more, and even more preferably 80% or more). Based on the first adhesive layer exhibiting such thermosetting properties, good heat-release properties are easily achieved. From the viewpoint of improving heat-release properties, in some viewpoints, the aforementioned gel fraction Ga1 after heating is preferably 83% or more, more preferably 85% or more, and may also be 88% or more, 90% or more, 93% or more, 95% or more, or 97% or more. The gel fraction Ga1 of the first adhesive layer after heating is typically less than 100%, and from the viewpoint of retention of the adhered object after heating, it is appropriate to be 99.8% or less (e.g., 99.5% or less), preferably 99% or less, and may also be 98% or less, 95% or less, 92% or less, or 90% or less. In some methods, the gel fraction Ga1 of the first adhesive layer after heating can be less than 85%, less than 80%, or less than 75%.

[0049] (Gel fraction of the first adhesive layer before heating, Ga0) The initial gel fraction Ga0 of the first adhesive layer before heating is not particularly limited. In some embodiments, from the viewpoint of obtaining sufficient adhesion to the adhered object and good heat-removable properties, a gel fraction Ga0 before heating of 85% or less is suitable, preferably 80% or less, more preferably 75% or less, and may also be 70% or less, 65% or less, or 60% or less. Furthermore, from the viewpoint of easily obtaining moderate cohesion and holding power, in some embodiments, an initial gel fraction Ga0 of 20% or more before heating of the first adhesive layer is suitable, preferably 30% or more, more preferably 40% or more, further preferably 50% or more, and may also be 60% or more, or 70% or more.

[0050] (Gel fraction of the second adhesive layer) In the adhesive sheet disclosed herein, the gel fraction Gb0 before heating and the gel fraction Gb1 after heating of the second adhesive layer are not particularly limited.

[0051] In some embodiments, from the viewpoint of the adhesion of the second adhesive surface, it is appropriate for the gel fraction Gb0 of the second adhesive layer before heating to be about 99.8% or less, preferably 99.5% or less (e.g., 99% or less). From the viewpoint of easily obtaining higher adhesion, in some embodiments, the gel fraction Gb0 before heating 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 moderate cohesion and holding power, in some embodiments, the gel fraction Gb0 before heating is suitable to be 20% or more, preferably 30% or more, more preferably 40% or more, further preferably 50% or more, and may also be 60% or more, or 70% or more.

[0052] Furthermore, the gel fraction Gb1 of the second adhesive layer after heating is typically less than 100%. From the viewpoint of retention of the adherend after heating, it is appropriate to be 99.8% or less, preferably 99.5% or less, and may also be 99% or less, or 98.5% or less. In some embodiments, the gel fraction Gb1 after heating may also be 95% or less, 92% or less, or 90% or less. From the viewpoint of easily obtaining moderate cohesion and retention force after heating, in some embodiments, it is appropriate to have a gel fraction Gb1 of 50% or more (e.g., more than 50%) after heating, preferably 60% or more, more preferably 70% or more, and may also be 80% or more, 90% or more, or 95% or more.

[0053] The increase in gel fraction (Gb1-Gb0) calculated from the gel fraction Gb0 [%] before heating and the gel fraction Gb1 [%] after heating of the second adhesive layer is not particularly limited, and can, for example, be in the range of 0% to 80%. More specifically, the range of the increase in gel fraction (Gb1-Gb0) varies depending on the purpose, for example, whether the second adhesive layer is thermosetting. In the case where the second adhesive layer is not thermosetting, the lower limit of the increase in gel fraction (Gb1-Gb0) of the second adhesive layer can be, for example, 0% or more, or more than 0%, and the upper limit can be, for example, less than 50%, less than 40%, less than 30%, less than 20%, or less than 10%. In addition, in the case where the second adhesive layer is thermosetting, the lower limit of the increase in gel fraction (Gb1-Gb0) of the second adhesive layer can be, for example, more than 5%, more than 10%, or more than 15%, and the upper limit can be, for example, less than 80%, less than 70%, less than 60%, less than 50%, or less than 40%.

[0054] The adhesive sheet disclosed herein can be, for example, an adhesive sheet in which the gel fraction of the first adhesive layer is initially (before heating) approximately equal to or lower than the gel fraction of the second adhesive layer, and after heating at 180°C for 30 minutes, the gel fraction of the first adhesive layer becomes higher than the gel fraction of the second adhesive layer. For some types of adhesive sheets, the value of the gel fraction Gb0[%] before heating minus the gel fraction Ga0[%] before heating is, 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 the value of the gel fraction Ga1[%] after heating minus the gel fraction Gb1[%] after heating can, for example, exceed 0%, preferably 5% or more, more preferably 10% or more, 15% or more, 20% or more, or 30% or more. Based on the adhesive sheet where the gel fractions of the first and second adhesive layers before and after heating satisfy the above relative relationship, it is easy to obtain an adhesive sheet where the difference in peel force after heating (|Fb1-Fa1|) is within any upper or lower limit disclosed herein, in the case where the peel force after heating is Fb1>Fa1.

[0055] The gel fractions of the first and second adhesive layers before heating, the gel fractions after heating, and their relative relationships can be achieved and adjusted mainly based on the contents described in this specification by appropriately selecting the following: the type of polymer contained in each adhesive layer (monomer composition, etc.), whether it contains other components that may be contained in each adhesive layer (such as the thermal polymerization initiator and multifunctional monomers described below), the type and content of other components, their combination, and whether a crosslinking agent is used in each adhesive layer, the type of crosslinking agent, and the amount used, etc.

[0056] Young's Modulus (Young's modulus Ya1 after heating the first adhesive layer) After the first adhesive layer constituting the adhesive sheet disclosed herein is heated to 180°C for 30 minutes, a heated Young's modulus Ya1 [MPa] measured at 23°C and 50%RH is suitable to be 5 MPa or more, preferably 10 MPa or more. Based on such a first adhesive layer with a high heated Young's modulus Ya1, there is a tendency for good peelability to be easily obtained in the first adhesive surface of the adhesive surface after heating. From this viewpoint, in some embodiments, the heated Young's modulus Ya1 can be, for example, 15 MPa or more, or 20 MPa or more, or 30 MPa or more, 40 MPa or more, 50 MPa or more, 60 MPa or more, or 70 MPa or more, or 90 MPa or more, or 110 MPa or more. In addition, from the viewpoint of avoiding excessive reduction in peel strength after heating, it is appropriate for the Young's modulus Ya1 after heating to be, for example, 2000 MPa or less, preferably 1000 MPa or less, more preferably 500 MPa or less, or 300 MPa or less, or 200 MPa or less, or 150 MPa or less, 100 MPa or less, or 75 MPa or less.

[0057] Regarding the Young's modulus Ya1 of the first adhesive layer after heating, it was determined from the stress-strain curve (SS curve) under the condition of a tensile speed of 50 mm / min for the first adhesive layer after heat treatment at 180°C for 30 minutes at 23°C and 50%RH. Regarding the Young's modulus Ya0 of the first adhesive layer before heating (described later), it was determined in the same manner as the Young's modulus Ya1 after heating, except that the first adhesive layer was not subjected to the aforementioned heat treatment. The Young's modulus Yb0 before heating and the Young's modulus Yb1 after heating of the second adhesive layer (described later) were measured in the same manner as the Young's modulus Ya0 before heating and the Young's modulus Ya1 after heating of the first adhesive layer. More specifically, the Young's moduli Ya0, Ya1, Yb0, and Yb1 were measured using the method described in the following examples.

[0058] (Young's modulus increase ratio of the first adhesive layer (Ya1 / Ya0)) The first adhesive layer constituting the adhesive sheet disclosed herein preferably has a thermosetting property where the Young's modulus increase ratio (Ya1 / Ya0) calculated from the Young's modulus Ya0 [MPa] before heating (measured at 23°C and 50%RH) and the Young's modulus Ya1 [MPa] after heating is approximately 2.0 or higher (e.g., 5.0 or higher, 10 or higher, 20 or higher, or 30 or higher). A higher Young's modulus increase ratio tends to result in a higher degree of curing of the adhesive layer after heating, and a greater ease of obtaining excellent heat-peelability in the first adhesive surface. From this viewpoint, in some embodiments, the Young's modulus increase ratio (Ya1 / Ya0) of the first adhesive layer is preferably 50 or higher, more preferably 80 or higher, 100 or higher, or 150 or higher, and even more preferably 200 or higher or 250 or higher. There is no particular upper limit to the Young's modulus increase ratio (Ya1 / Ya0) of the first adhesive layer. In some cases, the Young's modulus increase ratio (Ya1 / Ya0) can be, for example, less than 10,000, less than 5,000, less than 3,000, less than 2,500, less than 2,000, less than 1,500, or less than 1,000.

[0059] (Young's modulus Ya0 of the first adhesive layer before heating) The Young's modulus Ya0 [MPa] of the first adhesive layer constituting the adhesive sheet disclosed herein before heating is not particularly limited. The aforementioned Young's modulus Ya0 before heating can be appropriately selected in a way that achieves the desired adhesion (e.g., peel strength Fa0 before heating) corresponding to the intended use of the adhesive sheet. In some embodiments, from the viewpoint of adhesion in the first adhesive surface, the aforementioned Young's modulus Ya0 before heating is, for example, less than 5.0 MPa, advantageous to be 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 also be 0.4 MPa or less, or 0.3 MPa or less or 0.2 MPa or less. In addition, the Young's modulus Ya0 before heating can be, for example, 0.001 MPa or more. From the viewpoint of easily obtaining moderate cohesion and holding power, it is advantageous to be 0.005 MPa or more, preferably 0.01 MPa or more, more preferably 0.05 MPa or more, or 0.08 MPa or more, or 0.1 MPa or more.

[0060] (Young's modulus of the second adhesive layer) In the adhesive sheet disclosed herein, the Young's modulus Yb0 before heating (initial) and the Young's modulus Yb1 after heating of the second adhesive layer are not particularly limited, for example, they can be in the range of about 0.001 MPa to about 1000 MPa.

[0061] In some embodiments, from the viewpoint of the adhesion of the second adhesive surface, it is appropriate for the Young's modulus Yb0 of the second adhesive layer before heating to be less than 5.0 MPa, preferably 3.0 MPa or less, and also 2.0 MPa or less, 1.0 MPa or less, or 0.8 MPa or less. Alternatively, the aforementioned Young's modulus Yb0 before heating can be, for example, 0.001 MPa or more. From the viewpoint of easily obtaining moderate cohesion and holding power, 0.005 MPa or more is advantageous, preferably 0.01 MPa or more, more preferably 0.05 MPa or more, and also 0.08 MPa or more, 0.1 MPa or more, or 0.3 MPa or more.

[0062] Furthermore, in some embodiments, from the viewpoint of retention of the adherend after heating, it is appropriate for the Young's modulus Yb1 of the second adhesive layer after heating to be 100 MPa or less, preferably 50 MPa or less, and for example, it can be 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. Additionally, the aforementioned Young's modulus Yb1 after heating can be, for example, 0.001 MPa or more. From the viewpoint of easily obtaining moderate cohesion and holding power, it is advantageous to be 0.005 MPa or more, preferably 0.01 MPa or more, and it can also be 0.05 MPa or more, 0.08 MPa or more, 0.1 MPa or more, or 0.3 MPa or more.

[0063] The Young's modulus increase ratio (Yb1 / Yb0) calculated from the Young's modulus Yb0 [MPa] before heating and the Young's modulus Yb1 [MPa] after heating of the second adhesive layer is not particularly limited, and can, for example, be in the range of 0 to 10,000. A more specific range of the Young's modulus increase ratio (Yb1 / Yb0) varies depending on the purpose, for example, whether the second adhesive layer is thermosetting. In the case where the second adhesive layer is not thermosetting, the lower limit of the Young's modulus increase ratio (Yb1 / Yb0) of the second adhesive layer can be 1.0 or higher, and the upper limit can be less than 2.0 or less than 1.5. In addition, the lower limit of the Young's modulus increase ratio (Yb1 / Yb0) in the thermosetting manner of the second adhesive layer can be, for example, 2.0 or more, 5.0 or more, 10 or more, 30 or more, 50 or more, or 100 or more, and the upper limit can be, 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.

[0064] (Young's modulus ratio after heating (Ya1 / Yb1)) In some embodiments, the heated Young's modulus ratio (Ya1 / Yb1), calculated by the ratio of the heated Young's modulus Ya1 of the first adhesive layer to the heated Young's modulus Yb1 of the second adhesive layer, is preferably greater than 1.0, preferably 1.5 or more, and may also be 2.0 or more, 5.0 or more, or 10 or more, 30 or more, 50 or more, 100 or more, 150 or more, or 200 or more. Based on an adhesive sheet satisfying any of the above-mentioned heated Young's modulus ratios (Ya1 / Yb1), in embodiments where the heated peel force is Fb1 > Fa1, it is easy to obtain an adhesive sheet where the heated peel force difference (|Fb1 - Fa1|) is within any of the upper and lower limits disclosed herein. There is no particular limitation on the upper limit of the heated Young's modulus ratio (Ya1 / Yb1), and it may be, for example, less than 10,000, less than 5,000, less than 1,000, less than 500, or less than 100.

[0065] (Young's modulus ratio before heating (Ya0 / Yb0)) The Young's modulus ratio (Ya0 / Yb0), calculated as the ratio of the Young's modulus Ya0 of the first adhesive layer before heating to the Young's modulus Yb0 of the second adhesive layer before heating, is not particularly limited. In some embodiments, the upper limit of the aforementioned Young's modulus ratio (Ya0 / Yb0) before heating may be, for example, 0.001 or more, 0.01 or more, or 0.1 or more. Furthermore, the lower limit of the aforementioned Young's modulus ratio (Ya0 / Yb0) before heating may be, for example, 10000 or less, 1000 or less, 100 or less, or 10 or less.

[0066] The Young's modulus of the first and second adhesive layers before heating, the Young's modulus after heating, and their relative relationships can be achieved and adjusted mainly based on the contents described in this specification by appropriately selecting the following: the type of polymer contained in each adhesive layer (monomer composition, etc.), whether it contains other components that may be contained in each adhesive layer (e.g., thermal polymerization initiators, multifunctional monomers, as described later), the type and content of other components, their combination, and whether a crosslinking agent is used in each adhesive layer, the type of crosslinking agent, and the amount used, etc.

[0067] <First Adhesive Layer> The first adhesive layer of the adhesive sheet disclosed herein is a thermosetting adhesive layer. In this specification, thermosetting adhesive layer (adhesive) means having the property that, upon heating at 180°C for 30 minutes, at least one of the gel fraction and Young's modulus becomes higher than initially (before heating). As a suitable example of a thermosetting adhesive layer, an adhesive layer in which the gel fraction increases by 5% or more or 10% or more based on the aforementioned heating treatment can be cited. As other suitable examples of a thermosetting adhesive layer, an adhesive layer in which the Young's modulus increases by 2.0 times, 5.0 times or more, or 10 times or more based on the aforementioned heating treatment can be cited. It should be noted that the above description of the definition and preferred examples of thermosetting adhesive layers can also be applied to the case where the second adhesive layer is thermosetting.

[0068] Typically, the first adhesive layer described above comprises at least a polymer and may further comprise a monomer. From the viewpoint of easily achieving the desired thermosetting properties and heat-removable properties, the first adhesive layer is preferably one of a multifunctional monomer (hereinafter sometimes abbreviated as "multifunctional monomer") having two or more olefinic unsaturated groups in one molecule and a polymer having olefinic unsaturated groups.

[0069] (polymer) In the disclosed technology, 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, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluoropolymers, which are usable in the field of adhesives. These polymers serve as the base polymer in the adhesive and function as the structural polymer for shaping the adhesive. From the viewpoints of adhesive performance and cost, adhesives containing acrylic polymers or rubber polymers as the base polymer are preferred. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred.

[0070] The following description focuses on adhesive sheets having an adhesive layer made of an acrylic adhesive, i.e., an acrylic adhesive layer as the first adhesive layer, but it is not intended to limit the first adhesive layer of the adhesive sheet disclosed herein to an acrylic adhesive layer.

[0071] (Acrylic polymer) In some embodiments, an acrylic polymer is used where more than 50% by weight of the monomer components constituting the polymer are acrylic monomers. It is suitable for the acrylic monomers to account for 60% by weight or more of the monomer components, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, for example, 90% by weight or more. The maximum allowable percentage of acrylic monomers in the monomer components constituting the acrylic polymer is 100% by weight. From the viewpoint of obtaining the effect of using non-acrylic monomers, the percentage of acrylic monomers can be, for example, 98% by weight or less, 95% by weight or less, or 92% by weight or less. Acrylic monomers can be used alone or in combination of two or more.

[0072] In some preferred embodiments, the monomer component comprises an alkoxy-containing (meth)acrylate. Based on acrylic polymers containing alkoxy-containing (meth)acrylates as monomer components, it is easy to obtain an adhesive layer that preferably simultaneously achieves good initial adhesion and easy peeling after heating. Furthermore, in the case where the first adhesive layer comprises a multifunctional monomer, compatibility with that multifunctional monomer is readily obtained. The acrylic polymers containing alkoxy-containing (meth)acrylates as monomer components can be polymers without olefinic unsaturated groups or polymers with olefinic unsaturated groups.

[0073] Examples of alkoxy-containing (meth)acrylates include: methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate, and other alkoxyalkyl (meth)acrylates; 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, ethoxypolypropylene glycol (meth)acrylate, and other alkoxy(poly)alkylene glycol (meth)acrylates; and so on. Alkoxyalkyl (meth)acrylates are preferred, and more preferably alkoxyalkyl (meth)acrylates having an alkoxy group having 1 to 4 carbon atoms (e.g., 1, 2 or 3 carbon atoms) are preferred, with methoxyethyl (meth)acrylates being particularly preferred.

[0074] There is no particular limitation on the content of alkoxy-containing (meth)acrylates in the monomer components constituting acrylic polymers. From the viewpoint of effectively obtaining the effects brought about by the use of alkoxy-containing (meth)acrylates, the content of alkoxy-containing (meth)acrylates in the aforementioned monomer components is generally about 1% by weight or more, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more. In some embodiments, from the viewpoint of adhesive properties such as adhesion strength and compatibility with multifunctional monomers, the content of alkoxy-containing (meth)acrylates in the aforementioned monomer components 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. The maximum content of the alkoxy-containing (meth)acrylate in the aforementioned monomer components is 100% by weight. For example, from the viewpoint of obtaining other comonomers such as monomers containing functional groups, in some embodiments, it is advantageous for the content of the aforementioned alkoxy-containing (meth)acrylate to be about 99% by weight or less, and it can be 95% by weight or less, 93% by weight or less, or 90% by weight or less. In other embodiments, the content of the aforementioned alkoxy-containing (meth)acrylate can be about 80% by weight or less, 70% by weight or less, 65% by weight or less, or 60% by weight or less.

[0075] In other embodiments, the monomeric component constituting the acrylic polymer may be a chain alkyl (meth)acrylate containing a straight-chain or branched alkyl group having 1 to 20 carbon atoms at the ester terminus. Hereinafter, chain alkyl (meth)acrylates having an alkyl group having X to Y carbon atoms at the ester terminus will sometimes be designated as "C". X-Y "Alkyl (meth)acrylates". It should be noted that in this specification, the term "chain" is used to include both linear and branched chains. The aforementioned chain alkyl (meth)acrylates can be used alone or in combination of two or more.

[0076] As C 1-20Non-limiting specific 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, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecanyl methacrylate, stearyl methacrylate, isostearyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, etc.

[0077] Of these, it is preferable to use at least C. 4-20 Alkyl (meth)acrylates, more preferably using at least C 4-18 Alkyl (meth)acrylates. In some ways, as C 1-20 Alkyl (meth)acrylates, preferably using C 4-8 Alkyl (meth)acrylates. More preferably, C... 4-8 Alkyl acrylate. C 4-8 Alkyl (meth)acrylates can be used alone or in combination of two or more. (C) 4-8 The use of alkyl (meth)acrylates tends to readily yield good adhesive properties (adhesive strength, etc.). For example, as the monomer components mentioned above, acrylic polymers containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) are preferred, and acrylic polymers containing at least 2EHA are particularly preferred. Furthermore, when using C... 1-20 Among other methods of using alkyl (meth)acrylates, C is preferred. 7-12 Alkyl (meth)acrylates. C 7-12 Alkyl (meth)acrylates can be used alone or in combination of two or more. As C 7-12 Alkyl (meth)acrylate, preferably C 7-10 Alkyl acrylate, more preferably C 7-9 Alkyl acrylates, more preferably C8 alkyl acrylates.

[0078] C in the monomer components that constitute acrylic polymers 1-20There are no particular restrictions on the content of alkyl (meth)acrylates. From effectively obtaining C 1-20 Considering the effects of using alkyl (meth)acrylates, the C in the above monomer components 1-20 The content of alkyl (meth)acrylates is typically about 1% by weight or more, for example, it can be 10% by weight or more, 30% by weight or more, or 50% by weight or more. In some cases, from the viewpoint of adhesive properties such as adhesion strength, the C content of the above monomer components is... 1-20 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. The C content in the above monomer components... 1-20 The maximum content of alkyl (meth)acrylate is 100% by weight, for example, considering the effect of obtaining other comonomers such as monomers containing functional groups. In some embodiments, the above C 1-20 It is advantageous for the alkyl (meth)acrylate content to be about 99% by weight or less, but it can be 95% by weight or less, 93% by weight or less, or 90% by weight or less. It should be noted that the above C... 1-20 The content range of alkyl (meth)acrylates can be as follows: 1-20 The C contained in alkyl (meth)acrylates 4-20 Alkyl (meth)acrylates, C 4-18 Alkyl (meth)acrylates, C 4-8 Alkyl (meth)acrylates, C 4-8 Alkyl acrylate, C 7-12 Alkyl (meth)acrylates, C 7-10 Alkyl acrylate, C 7-9 The respective content ranges of alkyl acrylates, C8 alkyl acrylates, BA, and 2EHA.

[0079] In some embodiments, the monomer components constituting the acrylic polymer preferably include monomers other than the aforementioned alkoxyalkyl (meth)acrylates and chain alkyl (meth)acrylates. These other monomers can be monomers capable of copolymerizing with alkoxyalkyl (meth)acrylates and chain alkyl (meth)acrylates (copolymeric monomers). As these other monomers, monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, rings containing nitrogen atoms, etc.) are preferably used. Monomers with polar groups can help introduce crosslinking points into the acrylic polymer and improve the cohesive strength of the adhesive. Other monomers can be used alone or in combination of two or more.

[0080] The following monomers can be cited as specific examples of other monomers without limitation.

[0081] Monomers containing carboxyl groups: for example, acrylic acid, methacrylic acid, carboxyethyl methacrylate, carboxypentyl methacrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc.

[0082] Monomers containing anhydride groups: for example, maleic anhydride and itaconic anhydride.

[0083] Monomers containing hydroxyl groups: for example, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 8-hydroxyoctyl methacrylate, 10-hydroxydecyl methacrylate, 12-hydroxylaurate methacrylate, methyl methacrylate (4-hydroxymethylcyclohexyl) methacrylate, etc., hydroxyalkyl methacrylates, etc.

[0084] Monomers containing sulfonic acid or phosphoric acid groups: for example, styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide propanesulfonic acid, (meth)acrylic acid sulfopropyl ester, (meth)acryloyloxynaphthalene sulfonic acid, 2-hydroxyethylacryloyl phosphate, etc.

[0085] Monomers containing epoxy groups: For example, glycidyl acrylate (meth)acrylate, 2-ethyl glycidyl ether (meth)acrylate, and other epoxy-containing acrylates, allyl glycidyl ether, glycidyl ether (meth)acrylate, etc.

[0086] Monomers containing cyano groups: for example, acrylonitrile, methacrylonitrile, etc.

[0087] Monomers containing isocyanate groups: for example, ethyl 2-isocyanate of (meth)acrylate, etc.

[0088] Monomers containing an amide group: for example, (meth)acrylamide; 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, N,N-di(tert-butyl) (meth)acrylamide, etc.; N-monoalkyl (meth)acrylamides such as N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N-n-butyl (meth)acrylamide; N-vinylcarboxylic amides such as N-vinylacetamide; monomers having both hydroxyl and amide groups, for example, N-(2-hydroxyethyl) (meth)acrylamide. N-hydroxyalkyl (meth)acrylamides, such as N-(2-hydroxypropyl)(meth)acrylamide, 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 alkoxy and amide groups, such as N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; and N,N-dimethylaminopropyl (meth)acrylamide, alkoxydiacetone (meth)acrylamide, vinylformamide, and vinylacetamide.

[0089] Monomers containing amino groups: for example, aminoethyl methacrylate, N,N-dimethylaminoethyl methacrylate, and tert-butylaminoethyl methacrylate.

[0090] Monomers having a ring containing a nitrogen atom: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrrazine, N-vinylpyrrole, N-vinylimidazolium, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisooxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, etc. (e.g., N-vinyl-2-caprolactam and other lactams).

[0091] Monomers having a succinimide skeleton: for example, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyhexamethylenesuccinimide, etc.

[0092] Maleimides: For example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc.

[0093] Itaconimides: For example, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, etc.

[0094] Aminoalkyl esters of (meth)acrylate: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate.

[0095] Monomers containing alkoxysilyl groups: for example, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, and 3-(meth)acryloyloxypropylmethyldiethoxysilane.

[0096] Vinyl esters: such as vinyl acetate, vinyl propionate, etc.

[0097] Vinyl ethers: For example, vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether.

[0098] Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc.

[0099] Olefins: such as ethylene, butadiene, isoprene, isobutene, etc.

[0100] (Meth)acrylates having alicyclic hydrocarbon groups: for example, cyclopentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentyl methacrylate, adamantane methacrylate, etc.

[0101] (Meth)acrylates having aromatic hydrocarbon groups: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, etc.

[0102] In addition, there are heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogenated (meth)acrylates such as those containing vinyl chloride or fluorine atoms, silicon-containing (meth)acrylates such as organosilicon (meth)acrylates, and (meth)acrylates obtained from terpene compound derivative alcohols.

[0103] When using other monomers, there is no particular limitation on their usage, but it is appropriate to use 0.01% by weight or more of the total monomer component. From the viewpoint of better utilizing the effects of other monomers, the usage of other monomers can be set to 0.1% by weight or more of the total monomer component, and can be 0.5% by weight or more. Furthermore, from the viewpoint of easily obtaining a balanced adhesive property, it is appropriate to use 50% by weight or less of the total monomer component, and preferably 40% by weight or less.

[0104] In some embodiments, the monomeric components constituting the acrylic polymer may include monomers having nitrogen atoms. The use of monomers having nitrogen atoms can improve the cohesive strength of the adhesive and ideally enhance the adhesive force. Monomers having nitrogen atoms can be used alone or in combination of two or more. As a suitable example of a monomer having nitrogen atoms, a monomer having a ring containing nitrogen atoms can be cited. Monomers having nitrogen atoms or a ring containing nitrogen atoms can be used, such as N-vinylcyclic amides represented by general formula (1): [Chemical Formula 1] Here, in general formula (1), R 1 It is a divalent organic group, specifically -(CH2). n - n is an integer from 2 to 7 (preferably 2, 3, or 4). N-vinyl-2-pyrrolidone (NVP) is preferably used. Other suitable examples of monomers having a nitrogen atom include: (meth)acrylamide, N,N-dimethyl(meth)acrylamide, and other N,N-dialkyl(meth)acrylamides; N-monoalkyl(meth)acrylamides such as N-isopropyl(meth)acrylamide; N-hydroxyalkyl(meth)acrylamide such as N-(2-hydroxyethyl)acrylamide (HEAA); N-acryloylmorpholine (ACMO); alkoxydiacetone(meth)acrylamide; vinylformamide, vinylacetamide; etc. NVP, HEAA, and ACMO are more preferred.

[0105] The amount of nitrogen-containing monomer (preferably a monomer with a ring containing a nitrogen atom) used is not particularly limited, and can be, for example, 1% or more by weight of the total monomer component, or 3% or more by weight. In some embodiments, the amount of nitrogen-containing monomer in the above-mentioned monomer component is preferably 5% or more by weight, more preferably 7% or more by weight, and even more preferably 9% or more by weight. In other embodiments, the amount of nitrogen-containing monomer in the above-mentioned monomer component can be 10% or more by weight, 12% or more by weight, or 15% or more by weight. Furthermore, it is appropriate for the amount of nitrogen-containing monomer to be, for example, 40% or less by weight of the total monomer component, or 35% or less by weight, 30% or less by weight, or 25% or less by weight. In some embodiments, the amount of nitrogen-containing monomer can be, for example, 20% or less by weight of the total monomer component, 15% or less by weight, or 12% or less by weight.

[0106] In some embodiments, the monomer component may include monomers containing hydroxyl groups. The use of hydroxyl-containing monomers can adjust the cohesive strength and crosslinking density of the adhesive, and improve its adhesive strength. As hydroxyl-containing monomers, monomers exemplified above can be used, such as preferably 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA). One hydroxyl-containing monomer can be used alone, or two or more can be used in combination.

[0107] There is no particular limitation on the amount of hydroxyl-containing monomers used; for example, it can be 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more of the total monomer component. In some preferred embodiments, the amount of hydroxyl-containing monomers used is 1% by weight or more of the total monomer component, more preferably 2% by weight or more, even more preferably 3% by weight or more, for example, 5% by weight or more. In other embodiments, it is appropriate for the amount of hydroxyl-containing monomers used to be, for example, 40% by weight or less of the total monomer component, preferably 30% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and also 7% by weight or less.

[0108] In some preferred embodiments, for the monomer component of the acrylic polymer, monomers with polar groups (monomers containing polar groups) are combined using monomers with nitrogen atoms (e.g., monomers containing amide groups such as (meth)acrylamide, monomers with rings containing nitrogen atoms such as NVP) and monomers containing hydroxyl groups (e.g., HEA, 4HBA). This allows for a good balance between adhesive and cohesive strength. In the method of combining monomers with nitrogen atoms and monomers containing hydroxyl groups, the amount A of the monomer with nitrogen atoms is... N Amount A of monomers containing hydroxyl groups OH weight ratio (A)N / A OH There are no specific limitations; for example, it can be 0.1 or higher, 0.5 or higher, 1.0 or higher, 1.2 or higher, 1.5 or higher, or 1.8 or higher. Additionally, the above weight ratio (A) N / A OH For example, it can be below 10, below 5, below 3, or below 2.5.

[0109] In some methods, the monomer component includes a monomer containing a carboxyl group. Suitable examples of carboxyl-containing monomers include acrylic acid (AA) and methacrylic acid (MAA). A single carboxyl-containing monomer can be used alone, or two or more can be used in combination. For example, AA and MAA can also be used together.

[0110] The amount of carboxyl-containing monomers used can 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 component. The proportion of the aforementioned carboxyl-containing monomers can be, for example, less than 15% by weight, less than 10% by weight, less than 5% by weight, less than 3% by weight, less than 2% by weight, or less than 1% by weight (e.g., less than 1% by weight).

[0111] Furthermore, when using acrylic polymers with olefinic unsaturated groups as described later as the polymer, monomers having functional groups (functional group A) that can react with functional groups (functional group B) of compounds with olefinic unsaturated groups as described later are preferably used as other monomers. In this manner, the type of other monomer is determined according to the type of compound described above. As other monomers having functional group A, for example, monomers containing carboxyl groups, monomers containing epoxy groups, monomers containing hydroxyl groups, and monomers containing isocyanate groups are preferred, with monomers containing hydroxyl groups being particularly preferred. By using monomers containing hydroxyl groups as other monomers, the acrylic polymer has hydroxyl groups. In contrast, as compounds with olefinic unsaturated groups, for example, by using monomers containing isocyanate groups, the hydroxyl groups of the acrylic polymer react with the isocyanate groups of the compound, and the olefinic unsaturated groups derived from the compound are introduced into the acrylic polymer.

[0112] Furthermore, when other monomers are used for the purpose of reacting with compounds having olefinic unsaturated groups, from the viewpoint of adhesive properties such as thermosetting properties and cohesive strength, it is appropriate for the amount of the aforementioned other monomers (preferably monomers containing hydroxyl groups) to be about 1% by weight or more of the total monomer composition, preferably about 5% by weight or more, more preferably about 10% by weight or more, and also about 12% by weight or more. Additionally, from the viewpoint of maintaining adhesive properties such as good adhesion strength, it is appropriate for the amount of the aforementioned other monomers to be about 40% by weight or less of the total monomer composition, preferably about 30% by weight or less, more preferably about 25% by weight or less, and also about 20% by weight or less (e.g., 15% by weight or less).

[0113] In acrylic polymers, as other monomer components, polyfunctional monomers may be included that have at least two (meth)acryloyl groups, vinyl groups, or other polymerizable functional groups with unsaturated double bonds (typically free radical polymerizable functional groups). By using polyfunctional monomers as monomer components, the cohesive strength of the adhesive can be improved. Polyfunctional monomers can also be used as crosslinking agents. There are no particular limitations on the polyfunctional monomers used; for example, suitable substances from the following list of polyfunctional monomers that can be included in the first adhesive layer can be used alone or in combination of two or more.

[0114] There is no particular limitation on the amount of multifunctional monomer used, and it can be appropriately set in a manner that achieves the intended use of the multifunctional monomer. The amount of multifunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (e.g., about 0.5% by weight or less). The lower limit of the amount used when using multifunctional monomer is greater than 0% by weight, and there is no particular limitation. Generally, by setting the amount of multifunctional monomer used to about 0.001% by weight or more of the monomer component (e.g., about 0.01% by weight or more), the effect of the multifunctional monomer can be appropriately exerted.

[0115] There are no particular limitations on the method for obtaining acrylic polymers. Various known polymerization methods, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization is preferred. As for the monomer supply method during solution polymerization, appropriate methods include one-time feeding of all monomer raw materials, continuous feeding (dropwise addition), and batch feeding (dropwise addition). The polymerization temperature can be appropriately selected based on the type of monomer and solvent used, as well as the type of polymerization initiator; for example, it can be around 20°C to 170°C (typically around 40°C to 140°C).

[0116] The solvent used in solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, any one or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane or cyclohexane; haloalkanes such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone.

[0117] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators, depending on the type of polymerization method. For example, although there is no particular limitation, azo polymerization initiators, peroxide polymerization initiators, redox polymerization initiators based on the combination of peroxide and reducing agent, and substituted ethane polymerization initiators can be used. As a polymerization initiator, one or more of the thermal polymerization initiators exemplified below as added to the adhesive composition can be selected, for example.

[0118] The amount of polymerization initiator used is the usual amount corresponding to the polymerization method or polymerization mode, and there is no particular limitation. For example, about 0.001 to 5 parts by weight of polymerization initiator can be used relative to 100 parts by weight of the total monomer content of the polymerized object (typically about 0.01 to 2 parts by weight, for example about 0.01 to 1 part by weight).

[0119] There are no particular limitations on the molecular weight of the polymer (e.g., acrylic polymers), and it can be set to an appropriate range to suit required properties. The weight-average molecular weight (Mw) of the above polymers is approximately 1 × 10⁻⁶. 4 The above is appropriate; for example, it could be approximately 10 × 10. 4 The above. By using polymers with a Mw value greater than or equal to the specified value, a good balance between cohesive and adhesive strength can be achieved. In some cases, considering both heat resistance and good adhesion, the aforementioned Mw may also be 20 × 10. 4 The above can also be 30×10 4 The above can also be approximately 40 × 10 4 The above can also be approximately 50 × 10 4 The above can also be, for example, approximately 55 × 10 4 That's all. There is no particular upper limit to the Mw of the aforementioned polymers; for example, it could be approximately 1000 × 10⁻⁶. 4 The following can also be approximately 100×10 4 Below. Here, Mw refers to the value converted from standard polystyrene obtained based on gel permeation chromatography (GPC). For example, a GPC apparatus named "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used.

[0120] (Polymers with olefinic unsaturated groups) In some embodiments, polymers having olefinic unsaturated groups such as acryloyl, methacryl, vinyl, and allyl are preferably used as polymers. According to an adhesive containing a polymer having olefinic unsaturated groups, the adhesive is thermo-cured by reacting the olefinic unsaturated groups of the polymer upon heating, thereby achieving the desired heat-resistant peelability. Furthermore, in embodiments where the first adhesive layer contains a multifunctional monomer (described later), by including a polymer having olefinic unsaturated groups, the rate of reduction in peel force after heating can be increased with a smaller amount of multifunctional monomer used, achieving the desired heat-resistant peelability. For example, polymers having olefinic unsaturated groups in their side chains can be used as polymers having olefinic unsaturated groups. As monomer components of the polymer having olefinic unsaturated groups, one or more examples of monomer components of the polymer described above can be used within the aforementioned content range.

[0121] The amount of olefinic unsaturated groups in polymers containing olefinic unsaturated groups is not particularly limited. From the viewpoint of thermosetting properties, it is appropriate to have 0.01 mmol (or less, also referred to as mmol / g) or more per 1g of polymer, which can be 0.1 mmol / g or more, or 0.5 mmol / g or more. Furthermore, it is appropriate for the amount of olefinic unsaturated groups in the above-mentioned polymers to be 10.0 mmol / g or less, which can be 5.0 mmol / g or less, 3.0 mmol / g or less, 2.5 mmol / g or less, or 2.0 mmol / g or less.

[0122] The amount of olefinic unsaturated groups in the polymer, for example, in the case where the olefinic unsaturated group is (meth)acryloyl, is determined by the following method.

[0123] First, 0.25 mg of the polymer to be tested was dissolved in 50 mL of THF (tetrahydrofuran), and then 15 mL of methanol was added to obtain a solution. Next, 10 mL of 4N sodium hydroxide aqueous solution was added to the above solution to obtain a mixture. Then, the mixture was stirred at 40°C for 2 hours. Further, 10.2 mL of 4N methanesulfonic acid solution was added to the mixture, and the mixture was stirred. Then, 5 mL of deionized water was added, followed by 2 mL of methanol, to prepare the test solution.

[0124] The content of (meth)acrylic acid in the test solution was determined by HPLC (High Performance Liquid Chromatography) (absolute standard curve method), and the content of olefinic unsaturated groups was calculated.

[0125] (HPLC determination conditions) Column: Phenomenex Synergi 4μ Polar-RP 80A (4.6mm × 250mm) Column temperature: 40℃ Flow rate: 1.0 mL / min Detector wavelength: 210nm Eluent: THF (for HPLC) 55 / Buffer (containing 0.2% phosphate, 0.2% triethylamine) 45 Aqueous solution injection volume: 5 μL As a method for determining the content of olefinic unsaturated groups other than (meth)acryloyl groups, one example is the method for determining the bromine value according to JIS K2605:1996. In this method, the content of olefinic unsaturated groups other than (meth)acryloyl groups can be determined by converting the number of grams of bromine (Br2) added to 100g of the polymer being measured into the number of moles of bromine (Br2) added to 1g of the polymer.

[0126] There are no particular limitations on the method of introducing olefinically unsaturated groups into polymers. For example, it is preferable to use a method in which a compound having a functional group (functional group B) that can react with a functional group (functional group A) introduced into an acrylic polymer through copolymerization and an olefinically unsaturated group reacts in a manner that the olefinically unsaturated group does not disappear (typically condensation or addition reactions). Examples of combinations of functional group A and functional group B include combinations of carboxyl and epoxy groups, combinations of carboxyl and aziridinyl groups, and combinations of hydroxyl and isocyanate groups. Among these, the combination of hydroxyl and isocyanate groups is preferred from the viewpoint of reaction traceability. From the viewpoint of polymer design, combinations in which the acrylic polymer has hydroxyl groups and the above-mentioned compounds have isocyanate groups are particularly preferred.

[0127] The compounds having olefinic unsaturated groups described above may, as explained above, have a functional group B that can react with functional group A. Suitable examples of such compounds include, for instance, monomers containing isocyanate groups (compounds containing isocyanate groups) that can be used as other monomers for the polymerization of acrylic polymers. More preferably, 2-(meth)acryloyloxyethyl isocyanate. By reacting the isocyanate group of the compound having olefinic unsaturated groups with the hydroxyl groups of the acrylic polymer to form a bond (specifically, a urethane bond), an acrylic polymer having olefinic unsaturated groups can be obtained.

[0128] The amount of the compound having an olefinic unsaturated group (e.g., a monomer containing an isocyanate group) added is not particularly limited. From the viewpoint of reactivity with functional group A (e.g., hydroxyl group) in the polymer, the amount of the compound can be determined by the molar ratio (M) of the aforementioned functional group A. A The molar ratio of ) to functional group B (isocyanate group) (M) B molar ratio (M) A / M B The value is set to a range of approximately 0.5 to 2 (e.g., 1 to 1.5).

[0129] In methods using polymers with olefinically unsaturated groups as the polymer, the content of the polymer with olefinically unsaturated groups in the adhesive layer is not particularly limited. In some methods, it is appropriate for the amount of polymer with olefinically unsaturated groups to be about 10% by weight or more of the total polymer contained in the adhesive layer (specifically the base polymer), and it can 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 methods, the base polymer contained in the adhesive layer may be substantially formed from a polymer with olefinically unsaturated groups.

[0130] In some embodiments, the polymer used may be a polymer that substantially lacks olefinic unsaturated groups such as acryloyl, methacryl, vinyl, or allyl groups (the amount of olefinic unsaturated groups is less than 0.01 mmol / g). It is appropriate for such a polymer to be used in an amount of approximately 10% by weight or more of the total polymer contained in the adhesive layer (specifically, the base polymer), and it may be approximately 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 99–100% by weight. In some embodiments, the base polymer contained in the adhesive layer may be formed substantially from a polymer that substantially lacks olefinic unsaturated groups.

[0131] (Multifunctional monomer) In some embodiments of the adhesive sheet disclosed herein, the first adhesive layer preferably contains a multifunctional monomer in addition to the aforementioned polymer. By including the multifunctional monomer in the adhesive in a pre-reaction (unreacted) state, the multifunctional monomer can react upon high-temperature heating, thereby reducing adhesive strength or suppressing the increase in peel strength and achieving heat-resistant peelability. More specifically, generally, if the adhesive is heated at high temperature while still adhered to the substrate, it will adhere to the surface of the substrate. Therefore, the adhesive strength to the substrate increases, leading to re-peeling. In some embodiments, by including a multifunctional monomer in the adhesive, the reaction of the multifunctional monomer occurs rapidly upon heating, allowing the adhesive to adhere to the substrate before the adhesive itself, thus curing the adhesive. This reduces the adhesive strength to the substrate. Furthermore, even if heating continues thereafter, the adhesive strength to the substrate does not increase but remains within a specified range, thus the adhesive exhibits excellent heat-resistant peelability. It should be noted that the technology disclosed herein is not limited to the above explanation. One multifunctional monomer can be used alone or in combination of two or more.

[0132] In this specification, a multifunctional monomer refers to a polymeric compound having two or more olefinic unsaturated groups in one molecule, and also includes substances referred to as oligomers. The aforementioned olefinic unsaturated groups function as polymeric functional groups (typically free radical polymeric functional groups). Examples of olefinic unsaturated groups in multifunctional monomers include acryloyl, methacryloyl, vinyl, and allyl groups, but are not limited to these. Suitable examples of olefinic unsaturated groups include acryloyl and methacryloyl. Acryloyl is preferred. Hereinafter, compounds having two or more acryloyl groups and / or methacryloyl groups are sometimes referred to as multifunctional acrylic monomers. Additionally, compounds having two or more vinyl groups are sometimes referred to as multifunctional vinyl monomers.

[0133] In some embodiments, it is appropriate for the number of olefinic unsaturated groups in the polyfunctional monomer 1 molecule to be 3 or more, preferably 4 or more, more preferably 5 or more, and possibly 6 or more. The more olefinic unsaturated groups the polyfunctional monomer contains, the better the curability upon heating and the easier it is to achieve heat-exfoliation properties. Furthermore, using a polyfunctional monomer with a higher number of olefinic unsaturated groups (functional groups) allows for heat-exfoliation properties to be achieved with a relatively small amount of material. This also reduces the amount of gas escaping from the polyfunctional monomer, which is advantageous. The upper limit for the number of olefinic unsaturated groups in the polyfunctional monomer 1 molecule is not limited to a specific range; for example, it can be 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of olefinic unsaturated groups in the polyfunctional monomer 1 molecule can be, for example, 10 or less, 8 or less, 6 or less, or less than 5. Multifunctional monomers with the above-mentioned number of olefinic unsaturated groups tend to simultaneously achieve good adhesion and easy peeling upon heating, as well as excellent storage stability.

[0134] As multifunctional monomers, various multifunctional acrylate monomers and multifunctional vinyl monomers with two or more olefinic unsaturated groups can be used. Among them, multifunctional acrylate monomers are preferred. Although not particularly limited, multifunctional acrylate monomers tend to exhibit the desired properties by readily exhibiting good compatibility when used in combination with acrylic polymers. One type of multifunctional acrylate monomer and one type of multifunctional vinyl monomer can be used alone or in combination of two or more.

[0135] Examples of multifunctional 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 methacrylate, epoxide-modified bisphenol A di(meth)acrylate, epoxide-modified neopentyl glycol di(meth)acrylate, tricyclodecanediethanol di(meth)acrylate, dihydroxymethyldicyclopentane di(meth)acrylate, vinyl methacrylate, diethyl... Alkenylbenzene and other difunctional monomers; trifunctional monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxytri(meth)acrylate, glycerol propoxytriacrylate, tetramethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate; quadrufunctional monomers such as pentaerythritol alkoxytetra(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate; pentafunctional monomers such as sorbitol penta(meth)acrylate, dipentaerythritol penta(meth)acrylate; hexafunctional monomers such as dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, epoxy alkyl modified hexa(meth)acrylate, caprolactone modified dipentaerythritol hexa(meth)acrylate; and epoxy acrylates, polyester acrylates, urethane acrylates, etc., which have more than two functionalities. Among preferred examples are 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0136] While not specifically limited, it is suitable to use multifunctional monomers with a molecular weight of 100 or higher. In some preferred embodiments, the molecular weight of the multifunctional monomer can be, for example, 150 or higher, 250 or higher, 300 or higher, 350 or higher, 400 or higher, 450 or higher, or 500 or higher. Furthermore, the molecular weight of the multifunctional monomer is generally about 100,000 or less, for example, about 10,000 or less (e.g., less than 10,000) is suitable, preferably 5,000 or less (e.g., less than 5,000), can be 1,500 or less, can be 1,000 or less (e.g., less than 1,000), can be 800 or less, or can be 600 or less. The use of multifunctional monomers with molecular weights within the above ranges is advantageous, for example, in terms of the preparability and coatability of the adhesive composition. It should be noted that the above molecular weights are manufacturer-specified values ​​or molecular weights calculated based on the molecular structure. For multifunctional monomers with a molecular weight above a specified value, the weight-average molecular weight (Mw) calculated from standard polystyrene using GPC can also be used.

[0137] In some preferred embodiments, a multifunctional monomer with a weight reduction rate of 1% or less (specifically 1.0% or less) at 180°C in a TGA (thermogravimetric analysis) under heating conditions of 10°C / min can be used as the multifunctional monomer. By using a multifunctional monomer with the aforementioned heat resistance of less than 1% at 180°C (hereinafter also referred to as "heat-resistant multifunctional monomer"), the adhesive layer exhibits heat-removable properties based on the multifunctional monomer used, and the generation of gas during heating is suppressed. By using the aforementioned heat-resistant multifunctional monomer, both heat-removable properties and reduced gas generation can be achieved simultaneously. From the viewpoint of reducing gas generation, in some preferred embodiments, the weight reduction rate of the heat-resistant multifunctional monomer at 180°C is 0.9% or less, more preferably 0.8% or less, further preferably 0.7% or less, particularly preferably 0.6% or less, and may also be 0.5% or less. Theoretically, the lower limit of the weight loss rate at 180°C for heat-resistant multifunctional monomers is 0%, but practically it can be above 0.1%, 0.2%, or 0.3%. Preferred heat-resistant multifunctional monomers are trimethylolpropane triacrylate (TMPTA, with a weight loss rate of 1% at 180°C) and dipentaerythritol hexaacrylate (DPHA, with a weight loss rate of 0.5% at 180°C). One type of heat-resistant multifunctional monomer can be used alone, or two or more can be used in combination.

[0138] Specifically, the weight loss rate of multifunctional monomers upon heating to 180°C can be measured using a differential thermal analysis apparatus (TA Instruments, trade name "Discovery TGA") under the following conditions: heating rate of 10°C / min, air atmosphere, and flow rate of 25 mL / min.

[0139] The content of the multifunctional monomer in the first adhesive layer is not particularly limited. In some embodiments, the content of the multifunctional monomer is about 1 part by weight or more, or even 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the first adhesive layer. The suitable amount of the multifunctional monomer varies depending on its molecular weight, number of functional groups, etc. In some preferred embodiments, from the viewpoint of heat-peelability, the amount of multifunctional monomer relative to 100 parts by weight of the polymer is appropriate to be 5 parts by weight or more, preferably 10 parts by weight or more, or 20 parts by weight or more, or 30 parts by weight or more, or 40 parts by weight or more, or 50 parts by weight or more, or 60 parts by weight or more, or 70 parts by weight or more, or 80 parts by weight or more, or 90 parts by weight or more, or 100 parts by weight or more. By including a sufficient amount of multifunctional monomer in the adhesive layer, the multifunctional monomer contained in the adhesive layer reacts rapidly upon heating, and the adhesive layer is thermocured, thereby achieving heat-peelability. There is no particular upper limit to the content of the multifunctional monomer in the adhesive layer, and it can be set in a way that achieves the desired adhesive properties. In some cases, from the viewpoint of compatibility with the polymer (specifically the base polymer, such as an acrylic polymer), it is appropriate for the amount of multifunctional monomer to be about 200 parts by weight or less relative to 100 parts by weight of the polymer, 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 can be 120 parts by weight or less, 90 parts by weight or less, or 70 parts by weight or less.

[0140] In some embodiments, the content of the polyfunctional monomer in the first adhesive layer may be less than 50% by weight of the first adhesive layer, but this is not particularly limited. According to the technology disclosed herein, even with such limitation of the amount of polyfunctional monomer in the adhesive, a first adhesive layer with sufficient heat-peelability can be achieved. In some preferred embodiments, the content of the aforementioned polyfunctional monomer is less than 45% by weight of the first adhesive layer, or less than 40% by weight, or less than 35% by weight, or less than 30% by weight, or less than 25% by weight, or less than 20% by weight, or less than 15% by weight, or less than 10% by weight. Furthermore, in some embodiments, from the viewpoint of effectively utilizing the heat-peelability derived from the presence of polyfunctional monomers, the content of the aforementioned polyfunctional monomer may be 1% by weight or more, or 5% by weight or more, or 10% by weight or more, or 15% by weight or more, or 20% by weight or more, or 25% by weight or more of the first adhesive layer. The range of the aforementioned polyfunctional monomer content is preferably adopted when using polymers having olefinically unsaturated groups, but this is not particularly limited.

[0141] (Thermal polymerization initiator) In some embodiments, the first adhesive layer preferably contains a thermal polymerization initiator. Here, a thermal polymerization initiator refers to a polymerization initiator that generates free radicals upon heating. By including the thermal polymerization initiator in the adhesive in a pre-reaction (unreacted) state, the thermal polymerization initiator can react upon high-temperature heating, thereby reducing adhesive strength or suppressing an increase in adhesive strength, preferably achieving heat-resistant peelability.

[0142] There are no particular limitations on the thermal polymerization initiator used. For example, peroxide-based polymerization initiators, azo-based polymerization initiators, redox-based polymerization initiators based on combinations of peroxides and reducing agents, and substituted ethane-based polymerization initiators can be used. Specifically, examples include: persulfates such as potassium persulfate and ammonium persulfate; peroxide compounds such as benzoyl peroxide (BPO) and tert-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; redox initiators based on combinations of peroxides and reducing agents, such as combinations of persulfates and sodium bisulfite, or combinations of peroxides and sodium ascorbate; and so on. These thermal polymerization initiators can be used alone or in combination of two or more. Peroxide-based polymerization initiators and azo-based polymerization initiators are preferred thermal polymerization initiators for use in the technology disclosed herein. Peroxide-based polymerization initiators can also be used in combination with azo-based polymerization initiators.

[0143] As peroxide-based polymerization initiators, organic peroxides such as acyl peroxides, peroxide esters, peroxide dicarbonates, monoperoxide carbonates, peroxide ketals, dialkyl peroxides, hydroperoxides, and ketone peroxides are preferred. Suitable examples of peroxide-based polymerization initiators include benzoyl peroxide compounds having substituted benzoyl groups (typically dibenzoyl peroxide (BPO)). One or more peroxide-based polymerization initiators can be used alone or in combination.

[0144] Specific examples of peroxide-based polymerization initiators include BPO, 1,1-di(tert-hexylperoxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 4,4-bis(tert-butylperoxy)valerate, cumene hydroperoxide, and 2,5-dimethyl-2,5-dihydrohexane peroxide. 1,3-bis(tert-butylperoxy)m-isopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, didecyl peroxide, dilauryl peroxide, 2,4-dichlorobenzoyl peroxide, di(4-tert-butylcyclohexyl) percarbonate, tert-butyl peroxide, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butyl hydrogen peroxide, ditert-butyl peroxide, etc.

[0145] There are no particular limitations on the azo polymerization initiator, and any of the following can be used: azonitrile compounds, azoamide compounds, azo ester compounds, alkyl azo compounds, azomididine compounds, azoimidazoline compounds, and polymeric azo compounds. Non-limiting specific examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexane-1-carboxylonitrile), 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile), 2,2'-azobis(2,4-dimethylpentanitrile), 2,2'-azobis(2-methylbutyronitrile), 4,4-azobis(4-cyanopentanoic acid), 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(2-methylpropionic acid) dimethyl ester, 1,1'-azobis(1-cyclohexanecarboxylic acid) dimethyl ester, 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-triN,N'-dimethyleneisobutylamidine), 2,2'-azobis(2-methylpropane) disulfate, 2,2'-azobis(2-amidinepropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropane] hydrate, 2,2'-azobis[2-(5-methyl-2-imidazoline-2-yl)propane] dihydrochloride, azoisopropylbenzene, etc. Suitable examples of azo polymerization initiators include AIBN, 1,1'-azobis(cyclohexane-1-carboxynitrile), 4,4-azobis(4-cyanopentanoic acid), 2,2'-azobis(N-butyl-2-methylpropionamide), and 2,2'-azobis(2,4,4-trimethylpentane).

[0146] In some methods, it is preferable to use at least a peroxide-based polymerization initiator as the thermal polymerization initiator. Using a peroxide-based initiator as the thermal polymerization initiator tends to easily achieve heat-resistant and heat-resistant peelability. One reason for this is the high initiation efficiency of peroxide-based polymerization initiators (especially organic peroxide-based initiators). Furthermore, peroxide-based polymerization initiators generate free radicals (-O·) through the cleavage of the -OO- group in the compound. However, this cleavage reaction is reversible; therefore, it is believed that -OO- can be re-bonded if the free radical does not collide with the polyfunctional monomer or the olefinic unsaturated group of the polymer. This re-bonded initiator can undergo another cleavage reaction within a specified heating time and collide and react with the polyfunctional monomer, etc. Therefore, it is believed that if a peroxide-based polymerization initiator is used, the thermal curing of the adhesive layer proceeds efficiently, and heat-resistant and heat-resistant peelability can be obtained. It should be noted that the technology disclosed herein is not limited to the above considerations.

[0147] When the first adhesive layer contains a peroxide-based polymerization initiator, the content of the peroxide-based polymerization initiator in the adhesive layer is not particularly limited. In some embodiments, it is appropriate to have 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer, 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 also be 0.5 parts by weight or more (e.g., more than 0.5 parts by weight), or 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 collision frequency between the peroxide-based polymerization initiator and the olefinic unsaturated groups of polyfunctional monomers, etc., and the easier it is to carry out the curing reaction. In addition, in some embodiments, the amount of peroxide-based polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, it is appropriate for the amount of peroxide-based polymerization initiator relative to 100 parts by weight of the polymer to be 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, further preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., less than 1.1 parts by weight), and can be 1.0 parts by weight or less (e.g., less than 1.0 parts 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 keeping the total amount of peroxide-based polymerization initiator within a specified range, it is possible to ideally achieve an adhesive with highly efficient thermosetting properties and heat-resistant peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0148] In embodiments where the first adhesive layer comprises a multifunctional monomer, the content of the peroxide-based polymerization initiator in the first adhesive layer can also be determined based on its relative relationship with the content of the multifunctional monomer. In some embodiments, from the viewpoint of the collision frequency with the olefinic unsaturated groups of the multifunctional monomer, it is appropriate that the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the multifunctional monomer is 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, further preferably 0.4 parts by weight or more, and may also be 0.5 parts by weight or more. In some embodiments, it is appropriate that the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the multifunctional monomer is, for example, 1.0 parts by weight or more, preferably 1.5 parts by weight or more, and may also be 2.0 parts by weight or more, or may also be 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 peroxide-based polymerization initiator relative to 100 parts by weight of the aforementioned multifunctional monomer is, for example, about 25 parts by weight or less, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, or 10 parts by weight or less, or 8.0 parts by weight or less (e.g., less than 8.0 parts by weight), or 6.0 parts by weight or less, or 4.0 parts by weight or less.

[0149] The above description concerning the amount of peroxide-based polymerization initiator used (the content of peroxide-based polymerization initiator in the first adhesive layer, the amount of peroxide-based polymerization initiator relative to 100 parts by weight of the multifunctional monomer) can also be applied to the amount of azo-based polymerization initiator used in a manner in which an azo-based polymerization initiator is used as a thermal polymerization initiator contained in the first adhesive layer.

[0150] In some embodiments, the first adhesive layer may consist only of a peroxide-based polymerization initiator as a thermal polymerization initiator, or it may consist of a peroxide-based polymerization initiator and a thermal polymerization initiator different from the peroxide-based polymerization initiator (a non-peroxide-based polymerization initiator). In the combination of a peroxide-based polymerization initiator and a non-peroxide-based polymerization initiator, the effects and characteristics based on the non-peroxide-based polymerization initiator can be utilized. In some embodiments, it is appropriate for the peroxide-based polymerization initiator to account for about 10% by weight or more of the total thermal polymerization initiator contained in the first adhesive layer. From the viewpoint of effectively utilizing the effect of the peroxide-based polymerization initiator, it is preferable to have 30% by weight or more, more preferably 40% by weight or more, further preferably 50% by weight or more (e.g., more than 50% by weight), and can be 55% by weight or more, or 60% by weight or more. In some preferred embodiments, the peroxide-based polymerization initiator accounts for, for example, about 65% by weight or more of the total thermal polymerization initiator, 75% by weight or more, 85% by weight or more, 95% by weight or more, or 99% by weight or more. In addition, the maximum percentage of peroxide-based polymerization initiators in the total of the above-mentioned thermal polymerization initiators is 100% by weight. In some cases, it can be less than 90% by weight, less than 80% by weight, less than 70% by weight, or less than 60% by weight.

[0151] Regarding non-peroxide-based polymerization initiators used as thermal polymerization initiators in conjunction with peroxide-based polymerization initiators, examples include azo-based polymerization initiators, redox-based polymerization initiators based on combinations of peroxides and reducing agents, and substituted ethane-based polymerization initiators. Specifically, 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; redox initiators based on combinations of peroxides and reducing agents, such as combinations of persulfates and sodium bisulfite, or combinations of peroxides and sodium ascorbate; and so on. These non-peroxide-based polymerization initiators can be used alone or in combination of two or more.

[0152] The amount of thermal polymerization initiator contained in the first adhesive layer (the total amount of the two or more in the case of two or more) is not particularly limited. In some embodiments, it is appropriate to have 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the first adhesive layer, 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 also be 0.5 parts by weight or more (e.g., more than 0.5 parts by weight), or 0.6 parts by weight or more, or 0.7 parts by weight or more. The higher the content of thermal polymerization initiator, the higher the collision frequency between the thermal polymerization initiator and the olefinic unsaturated groups of polyfunctional monomers, etc., and the easier it is to carry out the curing reaction. In addition, in some embodiments, the content of thermal polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, it is appropriate for the amount of peroxide-based polymerization initiator relative to 100 parts by weight of the polymer to be 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, further preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., less than 1.1 parts by weight), and can be 1.0 parts by weight or less (e.g., less than 1.0 parts 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 keeping the content of the thermal polymerization initiator within a specified range, it is possible to ideally achieve an adhesive with highly efficient thermosetting properties and easy peeling upon heating, while obtaining adhesive properties such as adhesion strength and storage stability.

[0153] In embodiments where the first adhesive layer comprises a multifunctional monomer, the content of the thermal polymerization initiator in the first adhesive layer can also be determined based on its relative relationship with the content of the multifunctional monomer. In some embodiments, from the viewpoint of the collision frequency with the olefinic unsaturated groups of the multifunctional monomer, the amount of thermal polymerization initiator relative to 100 parts by weight of the multifunctional monomer is appropriate to be 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, further preferably 0.4 parts by weight or more, and may also be 0.5 parts by weight or more. In some embodiments, the amount of peroxide-based polymerization initiator relative to 100 parts by weight of the multifunctional monomer is, for example, appropriate to be 1.0 parts by weight or more, preferably 1.5 parts by weight or more, and may also be 2.0 parts by weight or more, or may be 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 thermal polymerization initiator relative to 100 parts by weight of the multifunctional monomer may be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, the amount of thermal polymerization initiator relative to 100 parts by weight of the multifunctional monomer is, for example, about 25 parts by weight or less, preferably 20 parts by weight or less, more preferably 15 parts by weight or less, or 10 parts by weight or less, or 8.0 parts by weight or less (e.g., less than 8.0 parts by weight), or 6.0 parts by weight or less, or 4.0 parts by weight or less.

[0154] While not particularly limited, in some preferred embodiments, from the viewpoint of effectively utilizing the reduction in peel strength caused by heating and achieving the desired rate of reduction in peel strength after heating, it is appropriate for the total proportion of the polymer (specifically the base polymer, such as an acrylic polymer), the multifunctional monomer (such as a multifunctional acrylic monomer), and the thermal polymerization initiator (preferably a peroxide-based polymerization initiator) in the total adhesive layer to be 50% by weight or more (e.g., more than 50% by weight and less than 100% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, further 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 (e.g., 99 to 100% by weight).

[0155] (Cross-linking agent) In the adhesive composition used to form the first adhesive layer, a crosslinking agent may be included as needed, primarily for crosslinking within the first adhesive layer or for crosslinking the first adhesive layer with its adjacent surfaces. The crosslinking agent is typically contained in the first adhesive layer in the form of a crosslinked layer after the crosslinking reaction. By using the crosslinking agent, the cohesive strength of the first adhesive layer can be appropriately adjusted.

[0156] There are no particular limitations on the type of crosslinking agent; it can be selected from conventionally known crosslinking agents, for example, based on the composition of the adhesive, in a manner that allows the crosslinking agent to perform an appropriate crosslinking function within the first adhesive layer. Examples of usable crosslinking agents 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. They can be used alone or in combination of two or more. From the viewpoint of achieving a good balance between adhesion and cohesion, 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.

[0157] As isocyanate-based crosslinking agents, multifunctional isocyanate compounds with two or more functions can be used. Examples include aromatic isocyanates such as toluene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; aliphatic isocyanates such as hexamethylene diisocyanate; and so on. Examples of commercially available products include trimethylolpropane / toluene diisocyanate trimer adducts (manufactured by Tosoh Corporation, trade name "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (manufactured by Tosoh Corporation, trade name "Coronate HL"), isocyanurate derivatives of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), trimethylolpropane / xylene diisocyanate adducts (manufactured by Mitsui Chemicals, trade name "Takenate D-110N"), and other isocyanate adducts.

[0158] As epoxy crosslinking agents, substances having two or more epoxy groups per molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups per molecule are preferred. Specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-phenylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include those manufactured by Mitsubishi Gas Chemical Co., Ltd. under the trade names "TETRAD-X" and "TETRAD-C", manufactured by DIC under the trade name "EPICLON CR-5L", manufactured by Nagase Chemtex under the trade name "Denacol EX-512", and manufactured by Nissan Chemical Industries, Ltd. under the trade name "TEPIC-G".

[0159] As an oxazoline crosslinking agent, oxazoline crosslinking agents having more than one oxazoline group per molecule can be used without particular restrictions.

[0160] Examples of aziridine-based crosslinking agents include trimethylolpropane tris[3-(1-acrididinyl)propionate] and trimethylolpropane tris[3-(1-(2-methyl)acrididinylpropionate)].

[0161] As a carbodiimide-based crosslinking agent, it is possible to use low-molecular-weight compounds or high-molecular-weight compounds having two or more carbodiimide groups.

[0162] In some methods, isocyanate-based crosslinking agents are used as crosslinking agents. Isocyanate-based crosslinking agents readily form adhesives that exhibit well-balanced adhesive strength, cohesive strength, and other bonding properties, and possess good heat-relief properties. One type of isocyanate-based crosslinking agent can be used alone, or two or more can be used in combination. While not particularly limited, the amount of isocyanate-based crosslinking agent used is preferably less than 1 part by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer. It is believed that by limiting the amount of isocyanate-based crosslinking agent used, the crosslinking density can be moderately suppressed. At this crosslinking density, during heat treatment, polyfunctional monomers and the like frequently collide with the thermal polymerization initiator, resulting in thermosetting, exhibiting heat-relief properties and heat-resistant peelability, thereby achieving the desired reduction in peel force after heating. It should be noted that the technology disclosed herein is not limited to the above considerations. From the above perspective, in some preferred embodiments, the amount of isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer is 0.9 parts by weight or less, which can 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 isocyanate-based crosslinking agent used, it is easier to obtain high adhesive strength. Furthermore, relative to 100 parts by weight of the polymer, the amount of isocyanate-based crosslinking agent used can be, for example, 0.01 parts by weight or more, which in some preferred embodiments can be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of isocyanate-based crosslinking agent used within the above range, the effects brought about by the technology disclosed herein can be preferably achieved, and an adhesive that exhibits well-balanced adhesive strength, cohesive strength, and other bonding properties can be obtained.

[0163] Regarding the amount of crosslinking agent used (or the total amount when using two or more crosslinking agents), from the viewpoint of achieving a well-balanced adhesive with good adhesive properties such as bonding strength and cohesion, it is acceptable to use an amount more than 0 parts by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer. For example, it can be set to 0.001 parts by weight or more, or 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 aforementioned polymer can be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. Furthermore, the upper limit of the amount of crosslinking agent used may vary depending on the type of crosslinking agent used, and is therefore not limited to a specific range. However, from the viewpoint of achieving good heat-resistant peelability, heat-resistant peelability, and thus the desired reduction rate of peel force after heating, it is preferable to limit it to a specified amount or less. It is believed that by limiting the amount of crosslinking agent used, the crosslinking density can be moderately suppressed. At this crosslinking density, during heat treatment, multifunctional monomers and the like frequently collide with the thermal polymerization initiator and undergo thermosetting, exhibiting heat-resistant peelability and heat-resistant peelability, thereby achieving the desired reduction rate of peel force after heating. It should be noted that the technology disclosed herein is not limited to the above-described considerations. For example, it is appropriate to use less than 10 parts by weight of the crosslinking agent relative to 100 parts by weight of the polymer; in some embodiments, less than 5 parts by weight is preferred, and less than 3 parts by weight is also acceptable. In some embodiments, it is appropriate to use less than 1 part by weight of the crosslinking agent relative to 100 parts by weight of the polymer; preferably less than 0.9 parts by weight, less than 0.8 parts by weight, less than 0.7 parts by weight, less than 0.6 parts by weight, less than 0.5 parts by weight, less than 0.4 parts by weight, less than 0.3 parts by weight, less than 0.2 parts by weight, or less than 0.1 parts by weight. By limiting the amount of crosslinking agent used, it is easier to obtain high adhesion.

[0164] To facilitate a more efficient crosslinking reaction, a crosslinking catalyst may be used. Examples of crosslinking catalysts include tetrabutyl titanate, tetraisopropyl titanate, NACEM iron, butyltin oxide, and dioctyltin dilaurate, among other metal-based crosslinking catalysts. There is no particular limitation on the amount of crosslinking catalyst used. The amount of crosslinking catalyst used, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the binder layer, can be, for example, about 0.0001 parts by weight or more, about 0.001 parts by weight or more, or about 0.005 parts by weight or more; furthermore, it can be about 1 part by weight or less, about 0.1 parts by weight or less, or about 0.05 parts by weight or less.

[0165] In adhesive compositions used to form the first adhesive layer, it is desirable to include compounds that generate keto-enol tautomers as crosslinking inhibitors. For example, compounds that generate keto-enol tautomers are preferably used in adhesive compositions containing isocyanate-based crosslinking agents or adhesive compositions that can be used in conjunction with isocyanate-based crosslinking agents. This can extend the pot life of the adhesive composition.

[0166] Various β-dicarbonyl compounds can be used as compounds that generate keto-enol tautomerism. Specific examples include: β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionylacetate esters such as ethyl propionyl; isobutyrylacetate esters such as ethyl isobutyryl; malonates such as methyl malonate and ethyl malonate; and so on. Among these, acetylacetone and acetoacetate esters are suitable compounds. One or more compounds can be used alone or in combination to generate keto-enol tautomerism.

[0167] The amount of the compound that produces the ketone-enol tautomerism can be, for example, 0.1 to 20 parts by weight or 0.5 to 15 parts by weight relative to 100 parts by weight of the polymer contained in the adhesive layer (specifically, the base polymer, for example, an acrylic polymer). It is also appropriate to set it to 1 to 10 parts by weight or 1 to 5 parts by weight.

[0168] (Monofunctional monomer) Furthermore, the first adhesive layer may, as desired, contain one or more monofunctional monomers comprising one olefinic unsaturated group per molecule. The monofunctional monomers may be used without impairing the effects of the technology disclosed herein. Known monofunctional acrylate monomers and vinyl monomers may be used as monofunctional monomers. While not particularly limited, it is suitable for the content of the monofunctional monomer in the adhesive layer to be about 100 parts by weight or less (0 to 100 parts by weight, e.g., less than 100 parts by weight) relative to 100 parts by weight of the polyfunctional monomer; it may 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 a manner where the adhesive layer is substantially free of monofunctional monomers.

[0169] (Other ingredients) The first adhesive layer may, as needed, contain various additives commonly found in the adhesive field, such as adhesive-improving agents, silane coupling agents, peel strength modifiers (surfactants, etc.), viscosity modifiers (e.g., tackifiers), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, and anti-aging agents. Given these various additives, conventionally known additives can be used by conventional methods; therefore, detailed descriptions are omitted as they do not specifically characterize the present invention.

[0170] It should be noted that the first adhesive layer in the disclosed technology can achieve the desired adhesive properties, such as adhesive strength, without using an adhesive additive. In some embodiments, the content of the adhesive additive in the first adhesive layer can be less than 10 parts by weight, and more particularly less than 5 parts by weight, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the first adhesive layer. The content of the aforementioned adhesive additive can be less than 1 part by weight (e.g., less than 0.5 parts by weight) or less than 0.1 parts by weight (more than 0 parts by weight and less than 0.1 parts by weight). The first adhesive layer can be a substance without an adhesive additive.

[0171] Furthermore, the first adhesive layer in the disclosed technology can achieve the desired heat-peelability without using thermally expandable microspheres, foaming agents, etc. In some embodiments, the content of thermally expandable microspheres in the first adhesive layer may be less than 1 part by weight, and more particularly, less than 0.1 parts by weight, relative to 100 parts by weight of the polymer (specifically, the base polymer, such as an acrylic polymer) contained in the first adhesive layer. Similarly, the content of foaming agent in the first adhesive layer may be less than 1 part by weight, and more particularly, less than 0.1 parts by weight, relative to 100 parts by weight of the polymer (specifically, the base polymer, such as an acrylic polymer) contained in the first adhesive layer. The first adhesive layer may not contain any of the thermally expandable microspheres or foaming agents.

[0172] <Second Adhesive Layer> Typically, the second adhesive layer of the adhesive sheet disclosed herein comprises at least a polymer and may further comprise monomers. The second adhesive layer may be a thermosetting adhesive layer or an adhesive layer where thermosetting is not essential. There is no particular limitation on the type of adhesive constituting the second adhesive layer. The second adhesive layer may comprise one or more of various rubber-like polymers, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluoropolymers, which are usable in the field of adhesives. These polymers can be used as base polymers in the adhesive and function as structural polymers that shape the adhesive. From the viewpoint of adhesive performance and cost, adhesives containing acrylic polymers or rubber polymers as base polymers are preferred. Among these, adhesives using acrylic polymers as base polymers (acrylic adhesives) are preferred.

[0173] The following description mainly focuses on adhesive sheets having an adhesive layer made of acrylic adhesive, i.e., an acrylic adhesive layer as a second adhesive layer, but it is not intended to limit the second adhesive layer of the adhesive sheet disclosed herein to acrylic adhesive layers.

[0174] Furthermore, in the case where the second adhesive layer is thermosetting, from the viewpoint of easily achieving the desired thermosetting properties and heat-resistant peelability, the second adhesive layer preferably comprises at least one of a multifunctional monomer (polyfunctional monomer) having two or more olefinically unsaturated groups per molecule and a polymer having olefinically unsaturated groups, and preferably further comprises a thermal polymerization initiator as needed. The thermosetting second adhesive layer can be manufactured in a manner that achieves the desired initial (before heating) properties and / or post-heating properties, referring to the above description relating to the first adhesive layer, and therefore repeated descriptions are omitted.

[0175] Furthermore, in cases where the second adhesive layer is a thermosetting adhesive layer and is not essential, the adhesive constituting the second adhesive layer (the second adhesive) preferably comprises a polymer without olefinically unsaturated groups. The aforementioned second adhesive layer may, for example, contain the following polymer as the polymer (preferably the base polymer): [polymer containing C...] 1-20 A polymer of monomeric raw materials, with alkyl (meth)acrylates as the main monomer and which may further contain secondary monomers that have copolymerizability with the main monomer. C 1-20 Specific and suitable examples of alkyl (meth)acrylates may be related to the monomer components constituting the acrylic polymer in the relevant first adhesive layer containing C. 1-20The same applies to alkyl (meth)acrylates. For example, acrylic polymers containing one or both of BA and 2EHA as monomer components are preferred, and acrylic polymers containing at least BA are particularly preferred.

[0176] As the aforementioned secondary monomers, examples include various monomers listed as "other monomers" in the description of the first adhesive layer, alkoxyalkyl (meth)acrylates, etc. For example, monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, nitrogen-containing rings, etc.) can be suitably used as the aforementioned secondary monomers. Monomers having polar groups can help introduce crosslinking points into the acrylic polymer or improve the cohesive strength of the adhesive. Secondary monomers can be used alone or in combination of two or more. When using secondary monomers, there is no particular limitation on their usage amount, but 0.01% by weight or more of the total monomer component is appropriate. From the viewpoint of better utilizing the effect of the secondary monomer, the usage amount can be set to 0.1% by weight or more of the total monomer component, or even 0.5% by weight or more. Furthermore, from the viewpoint of easily obtaining a balance of adhesive properties, the usage amount of the secondary monomer is appropriate to be 50% by weight or less of the total monomer component, preferably 40% by weight or less.

[0177] In some embodiments, the monomeric component includes a carboxyl-containing monomer as the aforementioned secondary monomer. Suitable examples of carboxyl-containing monomers include AA and MAA. The carboxyl-containing monomer can be used alone or in combination of two or more. For example, AA and MAA can be used together. The amount of the carboxyl-containing monomer used can 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, 0.5% by weight or more, 1.0% by weight or more, 2.0% by weight or more, or 2.5% by weight or more of the total monomeric component. The amount of the aforementioned carboxyl-containing monomer used can be, for example, less than 15% by weight, less than 10% by weight, less than 5% by weight, or less than 3% by weight of the total monomeric component. In some embodiments, the amount of the aforementioned carboxyl-containing monomer used can be less than 2% by weight or less than 1% by weight of the total monomeric component (e.g., less than 1% by weight).

[0178] In some embodiments, the monomer component includes an alkoxy-containing (meth)acrylate as the aforementioned comonomer. Since specific examples of alkoxy-containing (meth)acrylates are the same as those described in the description concerning the first adhesive layer, repeated descriptions are omitted. The content of the alkoxy-containing (meth)acrylate in the monomer component is not particularly limited; for example, it can be 1% by weight or more, 5% by weight or more, 10% by weight or more, 20% by weight or more, or 30% by weight or more. The upper limit of the content of the alkoxy-containing (meth)acrylate is set such that the total amount with other monomers does not exceed 100% by weight; for example, it can be 45% by weight or less, or 35% by weight or less, 25% by weight or less, 15% by weight or less, 5% by weight or less, 3% by weight or less, or less than 1% by weight.

[0179] It should be noted that other matters related to the polymer that can be used in the second adhesive layer, and other components of the crosslinking agent that can be used to form the second adhesive layer as needed, can be referred to the corresponding descriptions related to the first adhesive layer, and therefore, repeated descriptions are omitted. In some embodiments, the second adhesive layer, like the first adhesive layer, is preferably free of thermally expandable microspheres, foaming agents, etc., or the content of thermally expandable microspheres, foaming agents, etc., is limited to less than 1 part by weight or less than 0.1 parts by weight relative to 100 parts by weight of the polymer.

[0180] <Substrate> The 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; fluoropolymer films; celluloid; and so on. Other examples of resin films include resin films formed from one or more engineering plastics (which may be super engineering plastics) selected from polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamide-imide 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, cellophane, woodfree paper, synthetic paper, and coated paper. Examples of fabrics include woven or nonwoven fabrics obtained by spinning or blending various fibrous materials, either alone or in combination. Examples of such fibrous materials include cotton, synthetic staple fibers, Manila hemp, pulp, rayon, acetate fibers, polyester fibers, polyvinyl alcohol fibers, polyamide fibers, and polyolefin fibers. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foamed sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

[0181] In some preferred embodiments, a resin film with specified rigidity (strength) and excellent processability and operability is used as the substrate. Suitable examples of such resin films include polyester films (e.g., PET films) and polyimide (PI) films. It should be noted that, in this specification, the term "resin film" typically refers to a non-porous film, specifically a resin film that is substantially free of air bubbles (pore-free). Therefore, the above-mentioned resin film is a concept distinct from foamed films and nonwoven fabrics. The density of the resin film that can be used as the substrate can be approximately 0.85 to 1.50 g / cm³. 3 (e.g., 0.90 g / cm) 3 ~1.20g / cm 3 Typically, it is 0.92 g / cm³. 3 ~1.05g / cm 3 The resin film can be a single-layer structure or a multi-layer structure with two or more layers (e.g., a three-layer structure).

[0182] In the substrate (e.g., resin film), known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents can be added as needed. There are no particular limitations on the amount of additives used; they can be appropriately set according to the intended application.

[0183] There are no particular limitations on the manufacturing method of the resin film. For example, conventional resin film forming methods known in the past, such as extrusion molding, blow molding, T-die casting, and calendering roll forming, can be appropriately used.

[0184] The aforementioned substrate may be substantially composed of a resin film. Alternatively, in addition to the resin film, the aforementioned substrate may also include auxiliary layers. Examples of such auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers for imparting a desired appearance, laminated layers, antistatic layers, primer layers, release layers, and other surface treatment layers.

[0185] The thickness of the substrate is not particularly limited and can be appropriately selected according to the purpose, typically ranging from 1 to 500 μm. From the viewpoints of processability, usability, and operability, a substrate thickness of 2 μm or more (e.g., 3 μm or more, typically 5 μm or more) is suitable, and can be approximately 7 μm or more, or 10 μm or more. Furthermore, a substrate thickness of approximately 200 μm or less is suitable; from the viewpoints of lightweighting and thinness, approximately 100 μm or less is preferred, more preferably approximately 50 μm or less, and can be 30 μm or less, 20 μm or less, or 15 μm or less. When the substrate thickness decreases, there is a tendency for improved flexibility of the adhesive sheet and increased conformability to the surface shape of the adhered object. The aforementioned substrate thickness can also preferably be applied to the thickness of the resin film used as a substrate or its constituent element.

[0186] Alternatively, the substrate surface can be subjected to conventional surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation, acid treatment, alkali treatment, and primer application, as needed. Such surface treatments can improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring effect of the adhesive layer on the substrate. The composition of the primer is not particularly limited and can be appropriately selected from known sources. The thickness of the primer layer is not particularly limited; for example, approximately 0.01 μm to 1 μm is suitable, and preferably approximately 0.1 μm to 1 μm. Furthermore, the above-mentioned surface treatments, antistatic treatments, and other surface treatments can also be applied to the substrate surface. Such surface treatments can be applied to one or both sides of the substrate.

[0187] <Making Adhesive Sheets> The adhesive layer of the adhesive sheet disclosed herein can be formed using methods known in the art. For example, the first adhesive layer and the second adhesive layer can each be applied (e.g., coated) to a suitable surface with their respective adhesive compositions and then subjected to appropriate curing treatment, thereby forming each adhesive in a layered (adhesive layer) form. The curing method for the adhesive composition (e.g., drying, crosslinking, polymerization, cooling, etc.) can be applied individually, or two or more can be applied simultaneously or in stages. Regarding solvent-based adhesive compositions, typically, the composition can be dried (preferably further crosslinked) to form an adhesive. The surface to which the adhesive composition is applied can be a peelable surface (peel surface) or a non-peelable surface. The non-peelable surface can be a non-peelable substrate surface, the surface of a pre-formed second adhesive layer or the surface of the first adhesive layer, etc.

[0188] While not specifically limited, the technology disclosed herein is preferably implemented using solvent-based adhesive compositions. These solvent-based adhesive compositions are adhesive compositions in the form of containing adhesive-forming components in an organic solvent. Typically, solvent-based adhesive compositions contain a solution polymer of monomeric components, a multifunctional monomer, a thermal polymerization initiator, and optionally other additives. In the form of a solvent-based adhesive (layer), the effects of the technology disclosed herein can be effectively achieved. The solvent contained in the solvent-based 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 the following can be used: aromatic compounds such as toluene (typically aromatic hydrocarbons); esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; haloalkanes such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; and so on.

[0189] The coating of the adhesive composition can be performed using known or conventional coating machines such as gravure roller coaters, reverse roller coaters, kiss roller coaters, dip roller coaters, die coaters, bar coaters, air knife coaters, and spray coaters. Alternatively, the adhesive composition can be coated by impregnation, curtain coating, or other similar methods.

[0190] From the viewpoint of promoting crosslinking reactions and improving manufacturing efficiency, drying the adhesive composition is preferably carried out under heating. The drying temperature is not particularly limited, but can be set to around 40–100°C, and is generally preferred to be around 60–80°C. For example, regarding drying at the above temperatures (e.g., drying for about 1–10 minutes, more specifically about 3–7 minutes), the heating temperature is low, and solvent evaporation sometimes occurs. In cases where the adhesive composition supplied for drying contains polyfunctional monomers and thermal polymerization initiators, the reaction of the polyfunctional monomers and the deactivation of the thermal polymerization initiator are negligible. Furthermore, after drying the adhesive composition, aging treatment can be performed to adjust component transfer within the adhesive layer, facilitate crosslinking reactions, and relax strain present in the substrate and adhesive layer.

[0191] <Thickness of adhesive layer> The thickness of the first adhesive layer and the second adhesive layer is not particularly limited. The thickness of each adhesive layer can be, for example, 1 μm or more, 2 μm or more, or 3 μm or more. There is a tendency that the greater the thickness of the adhesive layer, the higher the adhesive strength to the adhered object. In some preferred embodiments, the thickness of each adhesive layer is 5 μm or more, or it can be 7 μm or more, 9 μm or more, 10 μm or more, or more than 10 μm, or it can be 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. Furthermore, the thickness of each adhesive layer is, for example, suitable to be around 200 μm or less, or it can be 100 μm or less (e.g., less than 100 μm), or it can be 50 μm or less. For example, by limiting the thickness of the first adhesive layer to a specified range, there is a tendency to prevent the formation of residual adhesive due to cohesive failure and to easily obtain easy peelability. In some preferred embodiments, the thickness of each adhesive layer may be, for example, less than 40 μm, less than 30 μm (e.g., less than 30 μm), less than 20 μm, or less than 15 μm. The thickness of the first adhesive layer and the thickness of the second adhesive layer may be the same or different. For example, the thickness of the first adhesive layer may be greater than the thickness of the second adhesive layer, or vice versa.

[0192] Furthermore, the combined thickness of the first adhesive layer and the second adhesive layer can be, for example, 3 μm or more, 5 μm or more is suitable, preferably 8 μm or more, and more preferably 10 μm or more. In some embodiments, the combined thickness of the first and second adhesive layers can 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. Additionally, the combined thickness of the first and second adhesive layers is preferably about 250 μm or less, can be 150 μm or less, 100 μm or less, or 80 μm or less. Furthermore, a smaller combined thickness of the first and second adhesive layers is advantageous in terms of thinner adhesive sheets and tends to have excellent conformability to the adhered object. In some preferred embodiments, the combined thickness of the first and second adhesive layers can be, for example, 60 μm or less, 50 μm or less, 45 μm or less, or 40 μm or less. It should be noted that when the adhesive sheet disclosed herein is in the form of a substrate-free double-sided adhesive sheet formed from the first adhesive layer and the second adhesive layer, the total thickness of the adhesive sheet is consistent with the combined thickness of the first and second adhesive layers.

[0193] <Total Thickness> The total thickness of the adhesive sheet disclosed herein (which may include a first and a second adhesive layer, and further may include a substrate, but does not include a release liner) is not particularly limited, and a range of approximately 5 to 1000 μm is appropriate. From the viewpoint of adhesive properties and usability, the total thickness of the adhesive sheet can be 10 μm or more, 15 μm or more, or 20 μm or more. In some embodiments, the total thickness of the adhesive sheet can be 30 μm or more, 40 μm or more, or 50 μm or more. Furthermore, from the viewpoint of lightweighting and thinning, in some embodiments, the total thickness of the adhesive sheet is 500 μm or less, or 300 μm or less. In some preferred embodiments, the total thickness of the adhesive sheet is 100 μm or less (e.g., less than 100 μm), more preferably 80 μm or less, or 70 μm or less. Reducing the thickness of the adhesive sheet is also advantageous in terms of thinning, miniaturization, lightweighting, and resource conservation.

[0194] <Removing the liner> The release liner used for the adhesive sheet disclosed herein is not particularly limited. For example, a release liner whose surface has been peeled off from a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can be used. In the aforementioned peeling treatment, for example, silicone-based or long-chain alkyl-based release agents can be used. In some embodiments, a peeled resin film is preferably used as the release liner.

[0195] <Joint> The adhesive sheet disclosed herein can be used in a joint body that is disposed between two components (adhesives) and joins the two components. In the aforementioned joint body, the adhesive sheet disclosed herein serves as a joint portion for joining the two components. The aforementioned joint body may, for example, include a first component bonded to a first adhesive surface of the adhesive sheet and a second component bonded to a second adhesive surface of the adhesive sheet.

[0196] The joint disclosed herein may, for example, have Figure 2 The cross-sectional structure is schematically shown. The joint 100 includes a first component 71, a second component 72, and a joint portion 80 disposed between the first component 71 and the second component 72. The joint 100 has a structure comprising a stacked body sequentially including the first component 71, the joint portion 80, and the second component 72. Figure 2 In the illustrated embodiment, the first component 71 and the second component 72 are sheet-like or plate-like, and the joining portion 80 is a layered body. At least one of the first component 71 and the second component 72 may be made of a brittle material (e.g., glass, semiconductor wafers, or other hard and brittle materials). The joining portion 80 is constructed by including any of the adhesive sheets 90 disclosed herein, joining the first component 71 and the second component 72. In other words, the first component 71 and the second component 72 are joined via the joining portion 80 including the adhesive sheet 90. One adhesive surface (first adhesive surface) 80A of the adhesive sheet 90 is bonded to the first component 71 as the adherend, and the other adhesive surface (second adhesive surface, opposite to the first adhesive surface) 80B is bonded to the second component 72 as the adherend. The adhesive sheet 90 includes a first adhesive layer and a second adhesive layer (…). Figure 2 (Illustrations omitted.) The first adhesive surface 80A is composed of a first adhesive layer, and the second adhesive surface 80B is composed of a second adhesive layer. The adhesive sheet 90 may further have a substrate disposed between the first adhesive layer and the second adhesive layer. As the adhesive sheet 90, a substrate-free adhesive sheet formed only of adhesive layers including the first adhesive layer and the second adhesive layer may be used, or a substrate-supported double-sided adhesive sheet may also be used.

[0197] It should be noted that in the above embodiments, the first component, the second component, and the joint portion constituting the joint body are all configured as layers, sheets, or plates, and the joint body has the form of a stacked structure (laminated body). However, the shapes of the first component, the second component, and the joint portion do not have to be layered, sheet-like, or plate-like; they can have various shapes. For example, the first component and the second component only need to have surfaces that contact the joint portion, but they can also have complex shapes, curved shapes, or various three-dimensional component shapes based on their uses and purposes. The joint portion can also have various shapes corresponding to the surface shapes of the first component and the second component.

[0198] In addition, in this specification, the term "component" in the first component and the second component is used in the sense of a constituent element of an assembly, and is not particularly limited other than this meaning. For example, each of the first component and the second component may be a separately independent article or part, or may each be a component constituting another article.

[0199] In addition, the assembly may optionally further include other components and constituent elements on the basis of the first and second components. For example, when the first component and the second component are part of a product such as an electronic device, the assembly may be composed of multiple components and elements.

[0200] <Disassembly method> According to this specification, a disassembly method for the above-mentioned assembly is also provided. This disassembly method includes a step of, after performing a heat treatment on the above-mentioned assembly, leaving the above-mentioned adhesive sheet on the above-mentioned second component and separating the above-mentioned first component from the above-mentioned first adhesive surface. The adhesive sheet disclosed herein is designed to include a first adhesive layer suitable for exhibiting heat-peelability (heat-resistant peelability), and the peel strengths Fa1 and Fb1 of the first and second adhesive layers after heating are different (typically Fa1 < Fb1). Therefore, it is suitable for performing the step of leaving the adhesive sheet on the above-mentioned second component and separating the above-mentioned first component from the above-mentioned first adhesive surface after the above-mentioned heat treatment.

[0201] The temperature for the aforementioned heat treatment is not particularly limited; for example, it can be a temperature above 100°C. In some embodiments, the heat treatment temperature can be approximately 110°C or above, or 120°C or above, or 130°C or above, or 140°C or above, or 150°C or above, or 160°C or above, or 170°C or above. The upper limit of the heat treatment temperature varies depending on the purpose of the heat treatment, the heat resistance of the adhered materials, etc., and is generally below 260°C, or below 250°C, or below 230°C, or below 200°C, or below 180°C. In some preferred embodiments, the heat treatment temperature can be below 180°C, or below 170°C, or below 160°C, or below 150°C, or below 140°C, or below 130°C, or below 120°C. The heat treatment time is not particularly limited and can be within 10 hours, 5 hours, or 3 hours. From the viewpoint of heating process efficiency, in some preferred embodiments, it can be within 1 hour, 30 minutes, 15 minutes, 10 minutes, or 5 minutes. The adhesive sheet disclosed herein can achieve thermal curing of the first adhesive layer through the aforementioned short heat treatment, thereby exhibiting heat-resistant peelability. Furthermore, the heat treatment time can be more than 1 minute, more than 3 minutes, more than 5 minutes, more than 7 minutes, or more than 9 minutes. In some embodiments, the heat treatment time can be more than 10 minutes, more than 30 minutes, more than 60 minutes, more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. The adhesive sheet disclosed herein achieves thermal curing of the first adhesive layer and reduces peel force through heat treatment based on the aforementioned heating temperature. Even if the heating state continues for a long time, an increase in peel force (re-peeling) will not occur or will be suppressed. Therefore, it can maintain heat-resistant peelability even after prolonged heat treatment. There is no specific upper limit to the heat treatment time, but from the perspective of efficiency of the heating process, it can be within 10 hours, within 5 hours, or within 3 hours.

[0202] <Uses> The uses of the adhesive sheet disclosed herein are not particularly limited. Since at least the first adhesive layer exhibits heat-removable peelability, the adhesive sheet disclosed herein can be used for various purposes, including bonding the first adhesive layer (first adhesive surface) to an object and removing it from the object after the bonding purpose is completed. For example, it can be used as an adhesive sheet for fixing (temporary fixing), shielding, and protecting the object during processing. For example, the adhesive sheet disclosed herein is preferably used when the object being bonded is opaque or when ultraviolet-irradiated release adhesives cannot be applied, but there are no particular limitations.

[0203] Furthermore, the adhesive sheet disclosed herein can also be preferably used as a process material for fixing and peeling off objects in the manufacturing process of electronic devices and electronic components. Additionally, suitable applications for the adhesive sheet disclosed herein include semiconductor device manufacturing. For example, in semiconductor wafer processing (typically silicon wafer processing), it can preferably be used as a wafer fixing sheet to fix the wafer to a mounting plate (processing table). Furthermore, the adhesive sheet disclosed herein can also preferably be used as a protective sheet to protect the wafer during the aforementioned wafer processing. In particular, during the manufacturing of semiconductor devices, the components are exposed to heat during processing steps, etc., so an adhesive sheet with heat resistance and easy peeling is preferred. Furthermore, the adhesive sheet disclosed herein is also suitable for optical applications requiring heat resistance. More specifically, for example, the adhesive sheet disclosed herein can be used for optical applications such as bonding optical components (optical component bonding) and manufacturing articles using the aforementioned optical components (optical articles). It should be noted that the aforementioned optical components refer to components that possess optical characteristics (such as polarization, refraction, scattering, reflection, transmission, absorption, diffraction, rotation, and visual recognition).

[0204] The types of adhesive materials (adhesive materials) disclosed herein are not particularly limited. The adhesive sheets disclosed herein can be used for fixing and protecting various components and materials. Examples of adhesive materials include: alkaline glass, alkali-free glass, and other glass; stainless steel (SUS), aluminum, and other metal materials; alumina, silicon dioxide, and other ceramic materials; polyester resins such as PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, transparent polyimide resins, and other resin materials; and so on. Suitable examples of adhesive materials include, for example, glass materials such as alkaline glass, semiconductor wafers, etc. The aforementioned glass materials can be, for example, glass plates with surfaces locally covered with transparent conductive films (e.g., ITO (indium tin oxide) films) or FPC (flexible printed circuit boards) that can be used in tablet PCs, mobile phones, organic LEDs (light-emitting diodes), etc.

[0205] The matters disclosed in this specification include the following.

[0206] [1] An adhesive sheet, which is a double-sided adhesive sheet, wherein, The aforementioned adhesive sheet comprises a first adhesive layer and a second adhesive layer. The first adhesive layer constitutes a first adhesive surface as a first side of the adhesive sheet, and the second adhesive layer constitutes a second adhesive surface as a second side of the adhesive sheet, wherein the second surface is the surface opposite to the first surface. The first adhesive layer comprises at least one of a polyfunctional monomer having two or more olefinic unsaturated groups and a polymer having olefinic unsaturated groups, and further comprises a thermal polymerization initiator. The peel strength Fa1 [N / 20mm] after the first adhesive layer was bonded to the glass plate and heated at 180°C for 30 minutes, measured at 23°C and 50%RH, is different from the peel strength Fb1 [N / 20mm] after the second adhesive layer was bonded to the glass plate and heated at 180°C for 30 minutes, measured at 23°C and 50%RH.

[0207] [2] The adhesive sheet as described in [1] above, wherein the difference in peel force after heating (|Fb1-Fa1|) calculated from the peel force after heating Fa1 [N / 20mm] and the peel force after heating Fb1 [N / 20mm] is 0.5N / 20mm or more.

[0208] [3] The adhesive sheet as described in [1] or [2] above, wherein the peel strength Fa0 [N / 20mm] of the first adhesive layer before heating, measured when bonded to a glass plate at 23°C and 50%RH, and the peel strength Fa1 [N / 20mm] after heating, measured when bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, and the peel strength reduction rate A [%) after heating, calculated using the following formula, is greater than 20% and less than 99.9%. The rate of decrease in peel force after heating, A[%] = (1 - Fa1 / Fa0) × 100.

[0209] [4] An adhesive sheet as described in any one of [1] to [3] above, wherein the first adhesive layer and the second adhesive layer are laminated with respect to a substrate.

[0210] [5] The adhesive sheet as described in any one of [1] to [4] above, wherein the second adhesive layer comprises at least one of a polyfunctional monomer having two or more olefinic unsaturated groups in one molecule and a polymer having olefinic unsaturated groups, and further comprises a thermal polymerization initiator.

[0211] [6] The adhesive sheet as described in any one of [1] to [5] above, wherein the peel strength reduction rate B [%) of the second adhesive layer after heating, calculated using the following formula, is greater than 20% and less than 99.9%, based on the peel strength Fb0 [N / 20mm] before heating, measured when the second adhesive layer is bonded to a glass plate and subjected to an environment of 23°C and 50%RH, and the peel strength Fb1 [N / 20mm] after heating when the second adhesive layer is bonded to a glass plate and subjected to a heat treatment at 180°C for 30 minutes and then subjected to a heat treatment at 23°C and 50%RH. The rate of decrease in peel force after heating is B[%] = (1 - Fb1 / Fb0) × 100.

[0212] [7] The adhesive sheet as described in any one of [1] to [6] above, wherein the peel force Fa0 [N / 20mm] before heating, measured when the first adhesive layer is bonded to the glass plate at 23°C and 50%RH, and the peel force Fb0 [N / 20mm] before heating, measured when the second adhesive layer is bonded to the glass plate at 23°C and 50%RH, are both 4.0N / 20mm or more, and the peel force Fa1 [N / 20mm] after heating of the first adhesive layer and the peel force Fb1 [N / 20mm] after heating of the second adhesive layer are both less than 3.0N / 20mm.

[0213] [8] A joint comprising: The adhesive sheet described in any one of [1] to [7] above; The first component with the first adhesive surface of the aforementioned adhesive sheet attached; and The second component has the second adhesive surface to which the aforementioned adhesive sheet is pasted.

[0214] [9] A disassembly method, which is a method for disassembling the joint described in [8] above, wherein the disassembly method includes: The process of heat-treating the above-mentioned joint to leave the adhesive sheet on the second component and separating the first component from the first adhesive surface.

[0215] Example The following describes some embodiments of the present invention, but it is not intended to limit the invention to the contents shown in these embodiments. It should be noted that, unless otherwise stated, in the following description, "parts" and "%" are based on weight.

[0216] <Evaluation Methods> (Peeling force F0 before heating) An adhesive sheet with the adhesive layer of the evaluation object on a resin film was cut to a size of 20 mm wide and 100 mm long. Under conditions of 23°C and 50%RH, a 2 kg roller was used to press the adhesive surface of the adhesive layer together once, thus bonding it to an alkaline glass plate (Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue-edged polished) as the substrate. Under the same conditions, the substrate with the adhesive sheet attached was left to stand for 6 hours and used as an evaluation sample. The evaluation sample was placed in a tensile testing machine at 23°C and 50%RH, and the peel strength (peel force before heating) F0 [N / 20 mm width] was measured when the adhesive sheet was peeled from the substrate at a peel angle of 180 degrees and a speed of 300 mm / min. This peel force before heating F0 is referred to as the peel force before heating Fa0 when the adhesive layer of the evaluation object is the first adhesive layer, and as the peel force before heating Fb0 when the adhesive layer is the second adhesive layer.

[0217] As the aforementioned resin film, various resin films suitable as the substrate for the adhesive sheets disclosed herein can be used. Suitable examples include polyimide (PI) films and polyethylene terephthalate (PET) films. A thickness of approximately 10 μm to 100 μm is appropriate, and preferably approximately 10 μm to 75 μm (e.g., approximately 25 μm to 75 μm). As the tensile testing machine, the product name "EZ-S500N" or its equivalent manufactured by Shimadzu Corporation can be used. Furthermore, when the adhesive sheet used to prepare the evaluation sample is a double-sided adhesive sheet, the measurement can be performed simply by lining the non-testing side with a PET film.

[0218] It should be noted that the peel forces Fa0 and Fb0 before heating shown in Tables 1 and 2 below were measured using the following evaluation samples. These evaluation samples were made using an adhesive sheet with an adhesive layer on one side of a 50 μm thick polyimide film (manufactured by Toray DuPont, trade name "KAPTON200H"), which is the object of evaluation.

[0219] (Peeling force F1 after heating) An evaluation sample was prepared using an adhesive sheet having an adhesive layer for the evaluation object on a resin film, prepared according to the method described in the above-described determination of peel strength F0 before heating. The obtained evaluation sample was heated 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. Next, the evaluation sample was placed in a tensile testing machine under the same conditions, and the peel strength (peel strength after heating) F1 [N / 20mm width] was measured when the adhesive sheet was peeled from the adherend at a peel angle of 180 degrees and a speed of 300 mm / min. This peel strength after heating F1 is referred to as peel strength after heating Fa1 when the adhesive layer of the evaluation object is the first adhesive layer, and as peel strength after heating Fb1 when the second adhesive layer is present. The adherend, tensile testing machine, and other matters are the same as those for the determination of peel strength F0 before heating.

[0220] (Reduction rate of peel force after heating) Substitute the peel forces Fa0 and Fb0 [N / 20mm] before heating and the peel forces Fa1 and Fb1 [N / 20mm] after heating into the following formula to calculate the reduction rate of peel force A and B [%] after heating.

[0221] Peel force reduction rate A[%] after heating = (1 - Fa1 / Fa0) × 100 Peel strength reduction rate B[%] after heating = (1 - Fb1 / Fb0) × 100 (Poor peeling force after heating) The difference in peel strength after heating (|Fb1-Fa1|) is calculated from the peel strength after heating of the first adhesive layer, Fa1 [N / 20mm], and the peel strength after heating of the second adhesive layer, Fb1 [N / 20mm]. In Examples 1 to 17, Fb1 > Fa1, therefore, the value of Fb1-Fa1 is shown as the difference in peel strength after heating in Tables 1 and 2.

[0222] (Gel fraction) The gel fraction (weight percentage of ethyl acetate insolubles) of the adhesive layer was determined by the following method.

[0223] Approximately 0.1 g of adhesive sample (weight Wg1) was wrapped in a purse-shaped container using a porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening was tied tightly with kite string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane used was the product "NITOFLON (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product available from Nitto Denko Corporation.

[0224] The packaging bag was immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23°C) for 7 days to allow only the sol component in the adhesive layer to dissolve to the outside of the membrane. The packaging bag was then removed, and the ethyl acetate adhering to its outer surface was wiped off. The packaging bag was then dried at 130°C for 2 hours, and its weight (Wg) was measured. Next, the values ​​were substituted into the following formula to determine the gel fraction of the adhesive layer.

[0225] Gel fraction [%] = [(Wg4 - Wg2 - Wg3) / Wg1] × 100 The gel fraction of the adhesive layer was measured as follows: the initial gel fraction (gel fraction before heating) and the gel fraction after heating the adhesive layer by heating it in an oven at 180°C for 30 minutes and then letting it stand at 23°C and 50%RH for 30 minutes.

[0226] (Young's modulus) The adhesive layer of the evaluation object was prepared with release liner covering both sides. It was cut together with the release liner into a size of 80 mm wide (for an adhesive layer thickness of 30 μm) and 30 mm long. One release liner was removed from the adhesive layer, and the adhesive layer was wound along its length on the other release liner in a manner that prevented air bubbles from entering, thus producing a 30 mm long rod-shaped specimen. The rod-shaped specimen was placed in a tensile testing machine (ORIENTEC, trade name "RTC-1150A") and subjected to tension at a measurement temperature of 23°C, a clamping distance of 10 mm, and a tensile speed of 50 mm / min. The initial elastic modulus was determined from the rise in the obtained stress-strain curve (SS curve) and used as the Young's modulus [MPa] of the adhesive layer.

[0227] The Young's modulus of the adhesive layer was measured as follows: the initial Young's modulus (Young's modulus before heating) and the Young's modulus after heating the adhesive layer in an oven at 180°C for 30 minutes and then allowing it to stand at 23°C and 50%RH for 30 minutes (Young's modulus after heating).

[0228] It should be noted that setting the cut width of the adhesive layer to 80mm is to ensure that the cross-sectional area of ​​the adhesive layer along this width is 2 to 2.5mm². 2 Within the left and right range, the cutting width is preferably adjusted according to the thickness of the adhesive layer to achieve the same cross-sectional area.

[0229] <Example 1> (Preparation of the first adhesive composition) 100 parts of a monomer mixture containing methoxyethyl acrylate (MEA), acrylamide (ACMO), and hydroxyethyl acrylate (HEA) in a molar ratio of 80:20:20, and 65 parts of toluene as a polymerization solvent were added to a reaction vessel equipped with a condenser, a nitrogen inlet, a thermometer, and a stirrer. 0.2 parts of benzoyl peroxide as a thermal polymerization initiator were also added. The polymerization reaction (solution polymerization) was carried out at 61°C for 6 hours under a nitrogen atmosphere, thereby obtaining a solution containing acrylic polymer a. Methacryloxyethyl isocyanate (MOI) was added to this acrylic polymer a solution in an amount equivalent to 16 moles relative to 20 moles of HEA used as a raw material for acrylic polymer a. An addition reaction was carried out at 50°C for 48 hours in an air stream, thereby obtaining a solution of acrylic polymer A with methacryl groups at the end of its side chains.

[0230] To a solution of the aforementioned acrylic polymer A, relative 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, product name "Takenate D-101E"; hereinafter referred to as "crosslinking agent CL1"), and 0.5 parts of benzoyl peroxide (manufactured by Nippon Oil Co., Ltd., product name "NYPER BW"; hereinafter referred to as "thermal polymerization initiator TO1") were added and uniformly mixed to prepare the adhesive composition for forming the first adhesive layer in this example (the first adhesive composition).

[0231] (Preparation of the second adhesive composition) To the solution of the acrylic polymer A described above, 0.3 parts of crosslinking agent CL1 and 0.8 parts of thermal polymerization initiator TO1 were added relative to 100 parts of acrylic polymer A, and the mixture was homogeneous to prepare the adhesive composition for forming the second adhesive layer in this example (the second adhesive composition).

[0232] (Making of adhesive sheets) The first 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 adhesive layer with a thickness of 30 μm. The second adhesive composition obtained above was also applied to the release surface of a commercially available PET release liner, and dried at 80°C for 5 minutes to form a second adhesive layer with a thickness of 30 μm. The second adhesive layer was then laminated onto the second surface of a 12.5 μm thick polyimide (PI) film (product name "KAPTON 50H", manufactured by Toray DuPont) as a substrate, and then the first adhesive layer was laminated onto the first surface of the PI film. The film was then subjected to an aging treatment at 50°C for 3 days. This process produced the adhesive sheet (double-sided adhesive sheet with substrate) of this example. The first and second adhesive surfaces of the adhesive sheet were protected by release liners used to form the first and second adhesive layers, respectively.

[0233] <Examples 2-14> The types and amounts of crosslinking agents, thermal polymerization initiators, and multifunctional monomers were varied as shown in Tables 1 and 2. Otherwise, the first adhesive compositions for each example were prepared in the same manner as in Example 1. Using the obtained first adhesive compositions and the same second adhesive compositions as in Example 1, double-sided adhesive sheets with substrates were produced in the same manner as in Example 1. It should be noted that in Tables 1 and 2, thermal polymerization initiator TO2 represents the product name "NYPER BMT" (manufactured by Nippon Oil Co., Ltd., benzoyl peroxide-based thermal polymerization initiator), thermal polymerization initiator TA1 represents AIBN, polymerization initiator TA2 represents 2,2'-azobis(2,4,4-trimethylpentane) (manufactured by Fujifilm and Wako Pure Chemical Industries Co., Ltd., product name "VR-110"), HDDA represents 1,6-hexanediol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), and crosslinking agent CL2 represents an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "TETRAD C").

[0234] <Examples 15-17> Except for using a 25μm thick polyimide (PI) film (product name "KAPTON 100H", manufactured by Toray DuPont), a 50μm thick polyimide (PI) film (product name "KAPTON 200H", manufactured by Toray DuPont), or a 25μm thick PET film (product name "Lumirror S10", manufactured by Toray) as the substrate, the adhesive sheets (double-sided adhesive sheets with substrates) of each embodiment were prepared in the same manner as in Example 9.

[0235] <Comparative Example 1> 97 parts of n-butyl acrylate (BA), 3 parts of acrylic acid (AA), and 43 parts of ethyl acetate as a polymerization solvent were added to a reaction vessel equipped with a condenser, a nitrogen inlet pipe, a thermometer, and a stirring device. 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were added. The polymerization reaction (solution polymerization) was carried out at 61°C for 6 hours under a nitrogen atmosphere, thereby obtaining a solution containing acrylic polymer B.

[0236] To the solution of the acrylic polymer B described above, 0.5 parts of crosslinking agent CL2 were added relative to 100 parts of acrylic polymer B, and the mixture was homogeneously mixed to prepare the adhesive composition of this example. Except for using this adhesive composition to prepare the first and second adhesive layers of the thickness shown in Table 2, the adhesive sheet (double-sided adhesive sheet with substrate) of this example was prepared in the same manner as in Example 1.

[0237] The summaries and evaluation results of each case are shown in Tables 1-2.

[0238] [Table 1] [Table 2] As shown in Tables 1 and 2, for the adhesive sheets of Examples 1 to 17, the peel force Fa1 of the first adhesive layer after heating is less than the peel force Fb1 of the second adhesive layer after heating. More specifically, the Fb1-Fa1 of the adhesive sheets of Examples 1 to 17 are all 0.5 N / 20 mm or more. For the adhesive sheets of these examples, the first adhesive layer exhibits a high peelability effect due to heating, while the second adhesive layer shows a relatively mild peelability effect compared to the first adhesive layer. On the other hand, in the adhesive sheet of Comparative Example 1, the peel forces of the first and second adhesive layers after heating are equal.

[0239] It should be noted that the adhesive sheet of Example 9 was cut to a size of 165mm × 65mm, and its second adhesive surface was attached to the alkaline glass plate B (manufactured by Matsunami Glass Industry Co., Ltd., 1.35mm thick, with a polished blue rim) which served as the second component. Then, the first adhesive surface was attached to the alkaline glass plate A (manufactured by Matsunami Glass Industry Co., Ltd., 1.35mm thick, with a polished blue rim) which served as the first component. The resulting article was then placed in an autoclave and subjected to autoclaving treatment at 50°C and 5 atmospheres for 15 minutes. After being removed from the autoclave, it was allowed to stand at room temperature and pressure (23°C, 1 atmosphere) for 30 minutes. The resulting joint of alkaline glass plate A / adhesive sheet / alkaline glass plate B was then heated in an oven at 180°C for 30 minutes. After being removed from the oven, it was allowed to stand at 23°C and 50%RH for 30 minutes. The disassembly of the joint was then attempted by hand (all evaluations of adult females were performed by the same person). Specifically, a ruler (or metal plate) is inserted into the interlayer portion at the end of the aforementioned joint, penetrating approximately 10 mm. Force is then applied in the vertical direction (the thickness direction of the evaluation sample) to attempt disassembly. As a result, the joint is disassembled such that the adhesive sheet remains entirely on the alkaline glass plate B, and the alkaline glass plate A is peeled off from the first adhesive layer. Furthermore, for the adhesive sheet remaining on the alkaline glass plate B, a portion approximately 10 mm from one end of the adhesive sheet is first peeled off from the alkaline glass plate B. This portion is then held by hand and stretched at approximately 150–180 degrees, allowing it to be peeled off from the alkaline glass plate B without tearing.

[0240] The specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes examples obtained by various modifications and alterations to the specific examples described above.

[0241] Explanation of reference numerals in the attached figures 1. Adhesive sheet 1A First adhesive surface 1B Second adhesive surface 2 Adhesive sheet 20 Substrate 21 First adhesive layer 22 Second adhesive layer 31, 32 Peeling off the gasket 50 Adhesive sheets with release liner 71 Part 1 72 Part 2 80 Joint 90 Adhesive Sheets 100 joint

Claims

1. An adhesive sheet, which is a double-sided adhesive sheet, wherein, The adhesive sheet comprises a first adhesive layer and a second adhesive layer. The first adhesive layer forms a first adhesive surface, which is a first side of the adhesive sheet, and the second adhesive layer forms a second adhesive surface, which is a second side of the adhesive sheet, wherein the second surface is the surface opposite to the first surface. The first adhesive layer comprises at least one of a polyfunctional monomer having two or more olefinic unsaturated groups in one molecule and a polymer having olefinic unsaturated groups, and further comprises a thermal polymerization initiator. The peel strength Fa1 [N / 20mm] after the first adhesive layer was bonded to the glass plate and heated at 180°C for 30 minutes, measured at 23°C and 50%RH, is different from the peel strength Fb1 [N / 20mm] after the second adhesive layer was bonded to the glass plate and heated at 180°C for 30 minutes, measured at 23°C and 50%RH.

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

3. The adhesive sheet according to claim 1 or 2, wherein The peel strength Fa0 [N / 20mm] of the first adhesive layer before heating, measured when it was bonded to a glass plate at 23°C and 50%RH, and the peel strength Fa1 [N / 20mm] after heating, measured when it was bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, and the reduction rate A [%] of the peel strength after heating, calculated using the following formula, is higher than 20% and lower than 99.9%. The rate of decrease in peel force after heating, A[%] = (1 - Fa1 / Fa0) × 100.

4. The adhesive sheet according to claim 1 or 2, wherein The first adhesive layer and the second adhesive layer are laminated together with the substrate in between.

5. The adhesive sheet according to claim 1 or 2, wherein The second adhesive layer comprises at least one of a multifunctional monomer having two or more olefinic unsaturated groups in one molecule and a polymer having olefinic unsaturated groups, and further comprises a thermal polymerization initiator.

6. The adhesive sheet as claimed in claim 1 or 2, wherein, The peel strength Fb0 [N / 20mm] of the second adhesive layer before heating, measured when bonded to a glass plate at 23°C and 50%RH, and the peel strength Fb1 [N / 20mm] after heating, measured when bonded to a glass plate and heated at 180°C for 30 minutes at 23°C and 50%RH, and the reduction rate B [%] of the peel strength after heating, calculated using the following formula, are both higher than 20% and lower than 99.9%. The rate of decrease in peel force after heating is B[%] = (1 - Fb1 / Fb0) × 100.

7. The adhesive sheet as claimed in claim 1 or 2, wherein, The peel force Fa0 [N / 20mm] of the first adhesive layer before heating, measured at 23°C and 50%RH, and the peel force Fb0 [N / 20mm] of the second adhesive layer before heating, measured at 23°C and 50%RH, are both greater than 4.0 N / 20mm. Furthermore, the peel force Fa1 [N / 20mm] of the first adhesive layer after heating and the peel force Fb1 [N / 20mm] of the second adhesive layer after heating are both less than 3.0 N / 20mm.

8. A joint comprising: The adhesive sheet according to claim 1 or 2; The first component is adhered to the first adhesive surface of the adhesive sheet; and The second component is bonded to the second adhesive surface of the adhesive sheet.

9. A disassembly method, comprising a method for disassembling the joint as described in claim 8, wherein, The dismantling method includes: The process of leaving the adhesive sheet on the second component and separating the first component from the first adhesive surface after heat treatment of the joint.

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