Method for separating member, and pressure-sensitive adhesive sheet

Abstract

Provided is a method in which from a structure comprising a first member, a second member, and an adhesive part interposed between the first member and the second member and adherent to both the first member and the second member, the first member and / or the second member is separated after a heat treatment. The adhesive part includes a curable pressure-sensitive adhesive layer. The separation method includes a step (fluid supply step) in which a fluid is supplied to the adhesive part from the first-member side or the second-member side.

Description

Component separation method and adhesive sheet

[0001] The present invention relates to a method for separating members and a pressure-sensitive adhesive sheet. This application claims priority to Japanese Patent Application No. 2023-122024, filed on July 26, 2023, the entire contents of which are incorporated herein by reference.

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

[0003] Incidentally, a method is known in which a substrate is held by suction using a holding table having a plurality of flow holes connected to a vacuum device and a gas supply device, and then gas is supplied after circulation using the gas supply device to eliminate the reduced pressure state between the substrate and the holding table, thereby removing the substrate from the holding table (for example, Patent Document 5).

[0004] Japanese Patent Application Publication No. 2015-29105 Japanese Patent Application Publication No. 2016-204617 Japanese Patent Application Publication No. 2019-56101 Japanese Patent Application Publication No. 10-209087 Japanese Patent No. 6990038

[0005] PSA used for applications requiring peeling and removal from an adherend is required to exhibit good adhesion while adhering to the adherend and to have the ability to be easily peeled from the adherend after the adhesive has served its purpose. For example, a PSA applied to an adherend to be heat-treated should desirably have easy peelability, allowing it to be easily peeled from the adherend after being heated while attached to the adherend. PSA with such properties can be used that maintain a certain adhesive strength during adhesion and fixation while reducing the peel strength at an appropriate time. Known examples of PSA capable of reducing the peel strength include ultraviolet-irradiation peelable PSAs that reduce the peel strength by irradiating ultraviolet light. Furthermore, the present inventors have been conducting research and development of thermosetting PSAs based on a design concept different from conventional ones, and have succeeded in obtaining PSAs that reduce the peel strength and have easy peelability (heat-peelability) when attached to an adherend and heated at high temperatures.

[0006] However, for example, when the adherend is a brittle material such as a semiconductor wafer or thin glass, even after the peel strength of the adhesive is reduced, the peeling force may be biased toward a portion of the adherend, potentially damaging the adherend. Furthermore, when joining rigid bodies together, even after the adhesive strength to the adherend is reduced, it is not possible to deform the rigid adherend and use it to peel the adhesive, so a considerable amount of force is required to release the adhesion of the entire adhesive surface, and it may be difficult to manually release the bonded adherends.

[0007] On the other hand, if the peel strength of the adhesive is excessively reduced by ultraviolet irradiation treatment or heat treatment, the adhesive may separate from the adherend at an unintended time due to a slight external force such as vibration, or even without any external force, and may be damaged by being dropped, etc. For example, a known technology for heat-releasable adhesives is one in which a foaming agent or heat-expandable microspheres is contained in the adhesive, and the adhesive is foamed or expanded by heating to a predetermined temperature to cause peeling. However, such heat-releasable adhesives may spontaneously peel from the adherend when heated, making it difficult to separate the adhesive from the adherend at a desired time after heat treatment.

[0008] It would be useful if a method could be realized that could separate adherends that have limitations or difficulties in peeling operations, such as the above-mentioned brittle materials and rigid bodies, from an adhesive sheet at a desired time without damaging the adherend, or that could easily release the adhesion between rigid bodies.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a method for separating members using a curable adhesive and a fluid. Another related object of the present invention is to provide a pressure-sensitive adhesive sheet that can be used in the above separation method.

[0010] This specification provides a method for separating at least one of a first member and a second member from a structure including a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhering the first member and the second member after a heat treatment. The adhesive portion has a curable adhesive layer. The separation method also includes a step of supplying a fluid to the adhesive portion from the first member side or the second member side (a fluid supply step).

[0011] In the above method, the adhesive joint having the curable adhesive layer is cured by the heat treatment or by applying an appropriate adhesive curing treatment such as irradiation with active energy rays after the heat treatment, thereby reducing the adhesive strength to the first and second members while maintaining the first and second members without separation. By supplying a fluid from one of the members, the fluid acts on the adhesive bond between the members, separating at least one of the first and second members from the adhesive joint. In this way, the members are separated by the curing of the adhesive and the action of the fluid, so that even if the members are made of brittle materials, the members are unlikely to be damaged during separation. Furthermore, even if the first and second members are rigid, they can be easily separated by simply applying a force perpendicular to the adhesive surface, for example.

[0012] In some preferred embodiments, the pressure-sensitive adhesive layer is in contact with the first member. The adhesive portion has a hole communicating with the first member and the second member. The separation method includes, as the fluid supplying step, a step of supplying the fluid from the second member side to the hole in the adhesive portion. According to this configuration and method, the fluid is supplied from the second member side and acts through the hole in the adhesive portion to separate the first member from the pressure-sensitive adhesive layer. Based on this action, the first member is separated from the pressure-sensitive adhesive layer.

[0013] In some preferred embodiments, the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator. The pressure-sensitive adhesive layer containing an ethylenically unsaturated group and a radical polymerization initiator can be effectively cured by heat treatment, irradiation with active energy rays, or the like.

[0014] In some preferred embodiments, the pressure-sensitive adhesive layer is a thermosetting pressure-sensitive adhesive layer, which can be cured by utilizing a heat treatment.

[0015] In some preferred embodiments, the radical polymerization initiator is a thermal polymerization initiator. When the pressure-sensitive adhesive layer contains a thermal polymerization initiator as the radical polymerization initiator, the adhesive strength to a member can be reduced by utilizing a heat treatment.

[0016] In some embodiments, the first member and the second member are optically opaque. The technology disclosed herein is applicable to the separation of optically opaque members as described above, since the technology disclosed herein uses a thermosetting adhesive that can be cured by heat treatment and the adhesive strength can be reduced.

[0017] In some embodiments, the adhesive portion comprises the pressure-sensitive adhesive layer. Alternatively, in some other embodiments, the adhesive portion has a laminated structure including, in this order, a first pressure-sensitive adhesive layer as the pressure-sensitive adhesive layer, a base layer, and a second pressure-sensitive adhesive layer. The technology disclosed herein can be preferably implemented in embodiments having an adhesive portion having any of the above configurations.

[0018] In some embodiments, the pressure-sensitive adhesive layer has a gel fraction increase of 10% or more after heat treatment at 180° C. for 30 minutes. The pressure-sensitive adhesive layer (thermosetting pressure-sensitive adhesive) that increases the gel fraction after heating can reduce the adhesive strength to a member by utilizing heat treatment.

[0019] In some embodiments, the pressure-sensitive adhesive layer preferably has a Young's modulus Y1 [MPa] after heat treatment at 180°C for 30 minutes that is 100 times or more the Young's modulus Y0 [MPa] before heating, i.e., a Young's modulus change ratio after heating (Y1 / Y0) of 100 or more. The higher the Young's modulus change ratio after heating, the higher the degree of curing of the pressure-sensitive adhesive layer during heating, and the more likely it is that heat-peelable properties will be obtained. A pressure-sensitive adhesive layer that satisfies the above characteristics can effectively reduce its adhesive strength to a member by utilizing heat treatment.

[0020] This specification also provides a pressure-sensitive adhesive sheet for use as a joining part in any of the separation methods disclosed herein. This pressure-sensitive adhesive sheet has a curable pressure-sensitive adhesive layer. The separation method disclosed herein is preferably carried out by using a pressure-sensitive adhesive sheet having a curable pressure-sensitive adhesive layer as an adhesive part.

[0021] This specification also provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet has holes formed therein. The pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator. With a pressure-sensitive adhesive sheet having the above configuration, the adherend can be easily peeled off with little stress by supplying a fluid to the holes after heat treatment. A pressure-sensitive adhesive sheet having the above configuration can be preferably applied to the separation method disclosed herein.

[0022] 10A and 10B are cross-sectional views schematically showing an example of a structure used in a separation method, and FIG. 10C are cross-sectional views schematically showing another example of a structure used in a separation method.

[0023] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic to clearly explain the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0024] In this specification, the "base polymer" of a PSA refers to the main rubbery polymer component contained in the PSA. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, unless otherwise specified, the "main component" refers to a component that accounts for more than 50% by weight.

[0025] In this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. In this specification, the acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer.

[0026] Furthermore, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" refers to an acryloyl group and a methacryloyl group in a comprehensive sense. Therefore, the concept of acrylic monomer here can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" refers to acrylic acid and methacrylic acid in a comprehensive sense, and "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense. The same applies to other similar terms.

[0027] In this specification, "weight" may be read as "mass." For example, "% by weight" may be read as "% by mass," and "parts by weight" may be read as "parts by mass."

[0028] <Method for Separating Members> The method for separating members disclosed herein is a method for separating at least one of a first member and a second member from a structure having the first member and the second member after heat treatment.

[0029] (Structure) The structure used in the separation method has, for example, the cross-sectional structure shown schematically in FIG. 1 . The structure 100 shown in FIG. 1 has a first member 10, an adhesive portion 30, and a second member 20, in this order. The adhesive portion 30 is disposed between the first member 10 and the second member 20 and adheres to the first member 10 and the second member 20. In the embodiment shown in FIG. 1 , the first member 10 and the second member 20 are sheet-shaped or plate-shaped, and the adhesive portion 30 is a layered body. The adhesive portion 30 is composed of a curable adhesive layer 31 and bonds the first member 10 and the second member 20. In other words, the first member 10 and the second member 20 are bonded via the adhesive portion 30 including the curable adhesive layer 31. In this embodiment, the first member 10 is a semiconductor wafer, and the second member 20 is a metal member. Furthermore, a substrate-less adhesive sheet 30 made of a curable adhesive layer 31 is used as the adhesive portion 30. More specifically, a first adhesive surface (first adhesive surface) which is one surface 30A of the adhesive portion (adhesive sheet) 30 is adhered to a first member 10 as an adherend, and a second adhesive surface (second adhesive surface) which is the other surface 30B (the surface opposite to the one surface) of the adhesive portion (adhesive sheet) 30 is adhered to a second member 20 as an adherend.

[0030] Furthermore, a communication hole 25 is formed in the second member 20, and a hole (through hole) 35 is also formed in the adhesive portion 30, with the hole 35 communicating with the first member 10 and the second member 20. In the structure 100, the second member 20 and the adhesive portion 30 are arranged so that the communication hole 25 and the opening of the hole 35 coincide with each other, and the first member 10 is arranged on the hole 35 and is in contact with the curable pressure-sensitive adhesive layer 31.

[0031] (Heat Treatment) In the member separation method disclosed herein, first, the structure 100 is subjected to heat treatment. The heat treatment may be a heat treatment on at least one of the first member 10 and the second member 20. In this embodiment, heating for processing the semiconductor wafer serving as the first member 10 corresponds to the heat treatment. Alternatively, the heat treatment may be a heat treatment on the adhesive portion 30. When the curable adhesive layer 31 is a thermosetting adhesive, the heat treatment on the adhesive portion 30 may correspond to a heat curing treatment or an adhesive strength reducing treatment step.

[0032] The temperature of the heat treatment is appropriately set depending on the purpose of the heat treatment. The heat resistance of the member is also taken into consideration when setting the heat treatment temperature. Although not particularly limited, the heat treatment temperature may be, for example, above 100°C, above 120°C, above 150°C (e.g., above 150°C), above 160°C, or above 170°C. The upper limit of the heat treatment temperature is generally below 250°C, and may be below 230°C or below 200°C. The heat treatment time is not particularly limited, but may be, for example, 3 minutes or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 60 minutes or more, more than 1 hour, more than 3 hours, more than 4 hours, or more than 5 hours. There is no particular upper limit to the heat treatment time, but it may be, for example, within 10 hours, within 5 hours, or within 3 hours, and from the viewpoint of the efficiency of the heating process, it may be, for example, within 1 hour or within 30 minutes. The heating means is not particularly limited, and means such as placing the material in a high-temperature chamber such as an oven or blowing hot air can be used.

[0033] In an embodiment in which the curable adhesive layer 31 of the adhesive portion 30 is a thermosetting adhesive, the heat treatment as described above may harden the curable adhesive layer 31 and reduce the adhesive strength of the adhesive portion 30. In an embodiment in which the curable adhesive layer 31 is a curable adhesive other than a thermosetting adhesive, for example, in an embodiment in which the curable adhesive layer 31 is an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, the curable adhesive layer 31 may be irradiated with active energy rays such as ultraviolet rays before or after the heat treatment to harden the curable adhesive layer 31 and reduce the adhesive strength.

[0034] After the heat treatment or adhesive curing treatment, the adhesive strength of the adhesive portion 30, which had previously firmly bonded the first member 10 and the second member 20, decreases, but the first member 10 and the second member 20 are held together without separation. Specifically, the curable adhesive layer 31 can hold the first member 10 and the second member 20 together to the extent that they do not peel off from each other. This reduction in adhesive strength and holding state is preferably achieved, for example, by using an adhesive containing an ethylenically unsaturated group and a radical polymerization initiator, as described below. This prevents the members 10 and 20 from unintended separation from the adhesive portion 30.

[0035] (Fluid Supplying Step) Next, a fluid is supplied to the adhesive bond 30 from the second member 20 side. Specifically, air A is supplied to the flow holes 25 of the second member 20. The supplied air A passes through the flow holes 25 and then through the holes 35 of the adhesive bond 20 to reach the first member 10. The air A presses the surface 10A of the first member 10 (the surface in contact with the adhesive bond 30) so as to separate the first member 10 from the adhesive bond 30. This action creates a gap at the adhesive surface between the first member 10 and the adhesive bond 30, centered on the opening of the hole 35. The air A moves along the surface direction between the surface 10A of the first member 10 and the first adhesive surface 30A of the adhesive bond 30, widening the gap, thereby separating the first member 10 from the adhesive bond 30. With this separation method, the load during separation is substantially only the air supply, so the semiconductor wafer, which is the first member 10, is less likely to be damaged during separation. Furthermore, the first member 10 can be easily separated simply by applying a force (air pressure) in a direction perpendicular to the adhesive surface between the first member 10 and the adhesive portion 30 .

[0036] The fluid is not limited to air, and various gases such as nitrogen gas can be used. The fluid is also not limited to gas, and liquids such as water, ethanol, and other organic solvents can be used. The fluid supply means is not particularly limited, and known or commonly used gas or liquid supply devices can be used. The amount of fluid supplied (supply rate) is appropriately set depending on the purpose, the type and size of the member and adhesive sheet, etc.

[0037] Another exemplary structure of a structure used in the separation method is shown schematically in Figure 2. Structure 200 shown in Figure 2 differs from structure 100 shown in Figure 1 in that adhesive portion 30 has a laminated structure including a first pressure-sensitive adhesive layer 31, a base layer 34, and a second pressure-sensitive adhesive layer 32, in this order. Pressure-sensitive adhesive sheet 30 used as adhesive portion 30 is configured as a substrate-attached double-sided pressure-sensitive adhesive sheet in which first pressure-sensitive adhesive layer 31 and second pressure-sensitive adhesive layer 32 are provided on a first surface 34A and a second surface 34B of base layer 34 (e.g., a resin film), respectively. In this embodiment, first pressure-sensitive adhesive layer 31 and second pressure-sensitive adhesive layer 32 are both curable pressure-sensitive adhesive layers. Other aspects of structure 200 are basically the same as those of the structure shown in Figure 1, and therefore description thereof will not be repeated. 2 , for example, by differentiating the compositions or properties of the first pressure-sensitive adhesive layer 31 and the second pressure-sensitive adhesive layer 32, the separability of the first member 10 and the second member 20 can be differentiated, enabling reliable separation of only the members to be separated or different timing for separation of the members. It is also possible to separate only one of the first member 10 and the second member 20 at a desired timing, while leaving the other member unseparated from the adhesive portion 30, or to separate the other member using a different method or at a different timing. For example, after separating the first member 10 and the second member 20 from the structure 200, the adhesive portion (pressure-sensitive adhesive sheet) 30 remaining on the separated member can be easily peeled off from the member.

[0038] In the structure 200, both the first pressure-sensitive adhesive layer 31 and the second pressure-sensitive adhesive layer may be curable as described above, or only one of the pressure-sensitive adhesive layers may be curable.

[0039] In the above separation method, the first member does not have a flow hole. However, the first member may have a flow hole and a fluid may be supplied to the adhesive portion from the first member side to separate the second member. In this case, the second member may or may not have a flow hole. The number of flow holes provided in the first member and the second member is not limited to one and can be an appropriate number, for example, from about 1 to 50. Depending on the size of the members, the number of flow holes may be two or more, five or more, or even ten or more to ensure separation with less load. When porous materials are used for the first member and the second member, the porous structure may be used as a fluid passage. In this case, it is not necessary to provide flow holes in the first member and the second member. The size of the flow hole is not particularly limited and can be appropriately set depending on the purpose and the material and size of the members, such as having an opening with a diameter ranging from about 10 microns to several centimeters (more specifically, about 10 μm to 5 cm).

[0040] Although the adhesive portion (adhesive sheet) has one hole, the number is not limited thereto and can be any number within the range of, for example, 1 to 50, depending on the number of flow holes in the first and second members. Depending on the size of the members, the number of holes may be two or more, five or more, or even ten or more to ensure separation with less load. When multiple holes are provided in the adhesive portion (adhesive sheet), it is preferable to arrange the holes at a predetermined interval, such as even intervals, so that the fluid load is not concentrated on one member. Alternatively, the adhesive portion (adhesive sheet) may not have any holes. In this case, the second member can be separated from the adhesive portion by fluid supplied through the flow holes in the second member. When flow holes are provided in the first member and fluid is supplied, the first member can be separated from the adhesive portion. In other words, by devising the hole configuration and fluid supply method, it is possible to separate only one of the first member and the second member from the adhesive portion, or to separate both the first member and the second member from the adhesive portion at the same time or at different times. The size of the holes is not particularly limited and can be set appropriately depending on the purpose, the size of the opening of the communication hole, and the material and size of the member, for example, having an opening with a diameter ranging from about 10 microns to several centimeters (more specifically, for example, about 10 μm to 5 cm). The size of the opening of the hole may be the same as or different from the size of the opening of the communication hole of the member.

[0041] Furthermore, in the above-described separation method, the first member, the second member, and the adhesive portion constituting the structure are all configured in a layered, sheet-like, or plate-like shape, and the structure has the form of a laminated structure (laminate). However, the shapes of the first member, the second member, and the adhesive portion do not have to be layered, sheet-like, or plate-like, and can have various shapes. For example, the first member and the second member only need to have a surface that contacts the adhesive portion, and may have various three-dimensional shapes, such as complex shapes or curved shapes, based on the application and purpose of use. The adhesive portion can also have various shapes to match the surface shapes of the first member and the second member.

[0042] In this specification, the terms "member" and "second member" are used to mean components of a structure, and are not particularly limited other than that meaning. For example, the first member and the second member may be separate, independent articles or parts, or may be members that constitute separate articles.

[0043] Furthermore, the structure may optionally include other members or components in addition to the first and second members. For example, if the first and second members are part of a product, the structure may be composed of multiple members or elements.

[0044] Furthermore, the adhesive sheet disclosed herein (more specifically, the adhesive sheet described below) can be one in which, for example, the high-temperature heat treatment as described above hardens the adhesive, reducing the peel strength or suppressing the increase in peel strength, and even if the heated state continues for a long time, the increase in peel strength (heavy peeling) does not occur or is suppressed. Therefore, it is possible to maintain easy heat peelability even after a long-term heat treatment.

[0045] Hereinafter, details of a pressure-sensitive adhesive sheet that can be used as an adhesive part in the separation method disclosed herein will be described, followed by details of the first member and the second member. Note that the following pressure-sensitive adhesive sheets and structures provided by this specification are suitable for the above-mentioned separation method, but can be used in embodiments that are not limited to the above-mentioned separation method. Therefore, the pressure-sensitive adhesive sheets and structures disclosed herein are not limited to being used in the above-mentioned separation method.

[0046] <Adhesive Sheet> The adhesive sheet disclosed herein is configured to include an adhesive layer. The adhesive sheet may be a substrate-attached adhesive sheet in a form in which the adhesive layer is provided on both sides of a non-releasable substrate (support substrate), or may be a substrate-less adhesive sheet in a form in which the adhesive layer is supported on a release liner (i.e., an adhesive sheet without a non-releasable substrate; typically, an adhesive sheet comprising an adhesive layer). The concept of adhesive sheet here may include what are called adhesive tapes, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or sheets before use. Alternatively, it may be an adhesive sheet in the form of a sheet that has been further processed into various shapes.

[0047] <Adhesive Layer> Various curable adhesive layers can be used as the adhesive layer. This allows the adhesive layer to be cured by heating, irradiation with active energy rays, or the like, thereby reducing the adhesive strength to the adherend. The adhesive constituting such an adhesive layer may be a thermosetting adhesive that is cured by heating, or an active energy ray-curable adhesive (typically an ultraviolet-curable adhesive) that is cured by irradiation with active energy rays such as ultraviolet rays.

[0048] In this specification, the term "curable adhesive (layer)" refers to an adhesive (layer) that, upon undergoing a predetermined curing treatment (e.g., a heat treatment or active energy ray irradiation treatment under predetermined conditions), satisfies at least one of the following conditions: the gel fraction increases by 5% or more compared to the initial value (before the curing treatment), and the Young's modulus increases by 2.0 times or more. For example, in this specification, the term "thermosetting adhesive (layer)" refers to an adhesive (layer) that, upon undergoing a heat treatment at 180°C for 30 minutes, satisfies at least one of the following conditions: the gel fraction increases by 5% or more (preferably 10% or more) compared to the initial value (before the heating treatment), and the Young's modulus increases by 2.0 times or more (preferably 5.0 times or more or 10 times or more). The gel fraction and Young's modulus are measured by the method described in the Examples below.

[0049] Although not particularly limited, in some embodiments, it is preferable to use a thermosetting adhesive layer as the adhesive layer. A thermosetting adhesive layer allows the adhesive layer to be efficiently and effectively cured by heat treatment. As such an adhesive layer, although not particularly limited, various adhesive layers containing an ethylenically unsaturated group and a radical polymerization initiator can be preferably used. This allows the adhesive layer to be favorably cured by heating, active energy ray irradiation, or the like, thereby effectively reducing the adhesive strength to the adherend. The adhesive constituting such an adhesive layer may be a thermosetting adhesive that cures by heating, or an active energy ray-curable adhesive (typically an ultraviolet-curable adhesive) that cures by irradiation with active energy rays such as ultraviolet rays. Although not particularly limited, the ethylenically unsaturated group can be contained in the adhesive layer by using a polymer or monomer (hereinafter, sometimes referred to as a "compound monomer" to distinguish it from the monomer component used in the synthesis of the polymer) that has an ethylenically unsaturated group.

[0050] Hereinafter, a pressure-sensitive adhesive layer containing an ethylenically unsaturated group and a radical polymerization initiator will be mainly described, but it is not intended to limit the pressure-sensitive adhesive layer disclosed herein to the pressure-sensitive adhesive layer having the above-mentioned configuration. For example, as the pressure-sensitive adhesive layer (curable pressure-sensitive adhesive layer) disclosed herein, other curable pressure-sensitive adhesive layers, such as a curable pressure-sensitive adhesive layer (typically a thermosetting pressure-sensitive adhesive layer) that utilizes a curing reaction of an epoxy-acid (e.g., an acid anhydride), can also be used.

[0051] (Polymer) In the technology disclosed herein, the type of adhesive is not particularly limited. The adhesive layer may contain one or more polymers selected from various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, and mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. The above polymers may be used as base polymers in the adhesive and function as structural polymers that shape the adhesive. From the viewpoints of adhesive performance, cost, and the like, adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, adhesives (acrylic adhesives) that use acrylic polymers with excellent heat resistance as the base polymer are preferred.

[0052] The following description will mainly focus on acrylic pressure-sensitive adhesives and pressure-sensitive adhesive layers formed from such pressure-sensitive adhesives, i.e., pressure-sensitive adhesive sheets having acrylic pressure-sensitive adhesive layers, but it is not intended to limit the pressure-sensitive adhesive layers disclosed herein to acrylic pressure-sensitive adhesive layers.

[0053] (Acrylic Polymer) In some embodiments, the acrylic polymer is an acrylic polymer in which more than 50% by weight of the monomer components constituting the polymer is an acrylic monomer. The proportion of the acrylic monomer in the monomer components is suitably 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, and may be, for example, 90% by weight or more. The upper limit of the proportion of the acrylic monomer in the monomer components constituting the acrylic polymer is 100% by weight, and the proportion of the acrylic monomer may be, for example, 98% by weight or less, 95% by weight or less, or 92% by weight or less, from the viewpoint of obtaining the effect of using a non-acrylic monomer. The acrylic monomer may be used alone or in combination of two or more.

[0054] In some preferred embodiments, the monomer component includes an alkoxy group-containing (meth)acrylate. Acrylic polymers containing an alkoxy group-containing (meth)acrylate as a monomer component tend to provide good adhesion and also tend to be compatible with, for example, the monomer contained in the pressure-sensitive adhesive layer described below (hereinafter, sometimes referred to as a "compounded monomer" to distinguish it from the monomer component used in synthesizing the polymer). The alkoxy group-containing (meth)acrylate may be used alone or in combination of two or more.

[0055] Examples of alkoxy group-containing (meth)acrylates include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; and alkoxy(poly)alkylene glycol (meth)acrylates such as methoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, ethoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate. Of these, alkoxyalkyl (meth)acrylates are preferred, and among these, alkoxyalkyl (meth)acrylates having an alkoxy group with 1 to 4 carbon atoms (e.g., 1, 2, or 3 carbon atoms) are more preferred, with methoxyethyl (meth)acrylate being particularly preferred.

[0056] The content of the alkoxy group-containing (meth)acrylate in the monomer component constituting the acrylic polymer is not particularly limited. From the viewpoint of effectively obtaining the effects of using the alkoxy group-containing (meth)acrylate, the content of the alkoxy group-containing (meth)acrylate in the monomer component is usually about 1 wt% or more, for example, 10 wt% or more, or even 30 wt% or more. In some embodiments, from the viewpoint of adhesive properties such as adhesive strength and compatibility with the blended monomer, the content of the alkoxy group-containing (meth)acrylate in the monomer component is, for example, more than 30 wt%, preferably 40 wt% or more, more preferably 50 wt% or more (for example, more than 50 wt%), and even more preferably 55 wt% or more. In some embodiments, the upper limit of the content of the alkoxy group-containing (meth)acrylate in the monomer component is approximately 99% by weight or less, or may be 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight or less, and even more preferably 65% ​​by weight or less, or may be 60% by weight or less, from the viewpoint of introducing an ethylenically unsaturated group into the polymer and obtaining the effects of other copolymerizable monomers such as functional group-containing monomers.

[0057] In some other embodiments, the monomer component constituting the acrylic polymer may include a chain alkyl(meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms at the ester terminal. Hereinafter, a chain alkyl(meth)acrylate having an alkyl group having X to Y carbon atoms at the ester terminal will be referred to as "C Ｘ－Ｙ In this specification, the term "chain alkyl (meth)acrylate" is used to mean both straight chain and branched chain. The chain alkyl (meth)acrylates can be used singly or in combination of two or more.

[0058] C １－２０Non-limiting examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and methyl (meth)acrylate. (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

[0059] C is a monomer component constituting an acrylic polymer. １－２０ In the embodiment using alkyl (meth)acrylate, C １－２０ As the alkyl (meth)acrylate, at least C ４－２０ It is preferable to use alkyl (meth)acrylate, and at least C ４－１８ It is more preferred to use alkyl (meth)acrylates. １－２０ As the alkyl (meth)acrylate, C ４－８ It is preferable to use alkyl (meth)acrylate. ４－８ The use of alkyl acrylates is more preferred. ４－８ The alkyl (meth)acrylates can be used alone or in combination of two or more. ４－８The use of alkyl (meth)acrylate tends to make it easier to obtain good adhesive properties (adhesive strength, etc.). For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as the monomer component is preferred, and an acrylic polymer containing at least 2EHA is particularly preferred. １－２０ In some other embodiments using alkyl (meth)acrylates, C ７－１２ Alkyl (meth)acrylates are preferably used. ７－１２ The alkyl (meth)acrylates can be used alone or in combination of two or more. ７－１２ Examples of alkyl (meth)acrylates include C ７－１０ Alkyl acrylates are preferred, C ７－９ Alkyl acrylate is more preferred, C ８ Alkyl acrylates are more preferred.

[0060] C is a monomer component constituting an acrylic polymer. １－２０ In an embodiment in which alkyl(meth)acrylate is used, C in the above monomer component １－２０ The content of alkyl (meth)acrylate is not particularly limited. １－２０ In order to effectively obtain the effect of using alkyl (meth)acrylate, in some embodiments, C １－２０ The content of alkyl (meth)acrylate is usually about 1% by weight or more, and may be, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more (for example, more than 50% by weight). In some embodiments, from the viewpoint of introducing an ethylenically unsaturated group into the polymer or obtaining the effect of other copolymerizable monomers, the above C １－２０ The content of alkyl (meth)acrylate is approximately 99% by weight or less, may be 90% by weight or less, approximately 70% by weight or less, 50% by weight or less (for example, less than 50% by weight), 30% by weight or less, 10% by weight or less, 1% by weight or less, or 0.1% by weight or less. １－２０It may be one that is substantially free of alkyl (meth)acrylate.

[0061] In some embodiments, the monomer components constituting the acrylic polymer preferably include other monomers besides the alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. Such other monomers may be monomers (copolymerizable monomers) copolymerizable with the alkoxyalkyl (meth)acrylate and linear alkyl (meth)acrylate. The other monomers may be used, for example, to introduce ethylenically unsaturated groups into the polymer. Suitable examples of the other monomers include monomers having polar groups (e.g., carboxy groups, hydroxyl groups, nitrogen-containing rings, etc.). The polar group-containing monomers may be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the PSA. The other monomers may be used alone or in combination of two or more.

[0062] Examples of other monomers include carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, monomers containing a sulfonic acid group or a phosphoric acid group, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, monomers having a succinimide skeleton, maleimides, itaconimides, aminoalkyl (meth)acrylates, alkoxysilyl group-containing monomers, vinyl esters, vinyl ethers, aromatic vinyl compounds, olefins, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, and other heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols.

[0063] When using such other monomers, the amount used is not particularly limited, but is suitably 1 wt% or more of the total monomer components. From the viewpoint of better demonstrating the effects of using the other monomers, the amount used of the other monomers may be 10 wt% or more, 20 wt% or more, or even 30 wt% or more of the total monomer components. Furthermore, from the viewpoint of easily balancing the adhesive properties, the amount used of the other monomers is suitably 60 wt% or less of the total monomer components, preferably 50 wt% or less (e.g., less than 50 wt%), and may be 45 wt% or less.

[0064] In some embodiments, the monomer component constituting the acrylic polymer includes a monomer having a nitrogen atom. The use of a monomer having a nitrogen atom can increase the cohesive strength of the PSA and favorably improve the adhesive strength. As the monomer having a nitrogen atom, for example, an amide group-containing monomer, an amino group-containing monomer, or a monomer having a nitrogen atom-containing ring can be used. The monomer having a nitrogen atom can be used alone or in combination of two or more.

[0065] Non-limiting specific examples of the monomer having a nitrogen atom include the following: Amide group-containing monomers: for example, (meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide; N-monoalkyl(meth)acrylamides such as N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-n-butyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having a hydroxyl group and an amide group, for example, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide; N-hydroxyalkyl(meth)acrylamides such as N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, for example, N-alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and others, such as N,N-dimethylaminopropyl(meth)acrylamide, alkoxydiacetone(meth)acrylamide, vinylformamide, and vinylacetamide. Amino group-containing monomers, for example, aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate.Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, and the like (for example, lactams such as N-vinyl-2-caprolactam).

[0066] Suitable examples of the monomer having a nitrogen atom include monomers having a nitrogen atom-containing ring, of which N-vinyl-2-pyrrolidone (NVP) and N-acryloylmorpholine (ACMO) are particularly preferred.

[0067] The amount of the nitrogen-containing monomer (preferably the nitrogen-containing ring-containing monomer) used is not particularly limited. In some embodiments, the amount of the nitrogen-containing monomer used in the monomer component may be 1 wt% or more, or may be 3 wt% or more. In some preferred embodiments, the amount of the nitrogen-containing monomer used in the monomer component is 5 wt% or more, more preferably 7 wt% or more, even more preferably 9 wt% or more, or may be 10 wt% or more, 12 wt% or more, or may be 14 wt% or more. The greater the amount of the nitrogen-containing monomer used, the more the cohesive strength of the PSA tends to improve. In some embodiments, the amount of the nitrogen-containing monomer used is suitably, for example, 40 wt% or less of the total monomer component, and may be 35 wt% or less. In some preferred embodiments, the amount of the nitrogen-containing monomer used in the monomer component is 30 wt% or less, more preferably 25 wt% or less, even more preferably 20 wt% or less, or may be 18 wt% or less.

[0068] In some embodiments, the monomer component includes a hydroxyl group-containing monomer. Use of a hydroxyl group-containing monomer can adjust the cohesive strength and crosslink density of the PSA, thereby improving adhesive strength. Hydroxyl group-containing monomers can also be preferably used as a means of introducing ethylenically unsaturated groups into a polymer. Examples of hydroxyl group-containing monomers that can be used include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. For example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) can be preferably used. The hydroxyl group-containing monomers may be used alone or in combination of two or more.

[0069] When a hydroxyl group-containing monomer is used, the amount used is not particularly limited, and may be, for example, 0.01 wt% or more, 0.1 wt% or more, or 0.5 wt% or more of the total monomer components. In some embodiments, the amount of the hydroxyl group-containing monomer used is 1 wt% or more, more preferably 2 wt% or more, or even 3 wt% or more of the total monomer components. In some preferred embodiments, the amount of the hydroxyl group-containing monomer used is 5 wt% or more, more preferably 7 wt% or more, even more preferably 10 wt% or more, and particularly preferably 12 wt% or more of the total monomer components. Such an amount of the hydroxyl group-containing monomer is suitable when the hydroxyl group-containing monomer is used as a means of introducing an ethylenically unsaturated group into the polymer. In some embodiments, the amount of the hydroxyl group-containing monomer used is, for example, 40 wt% or less of the total monomer components, preferably 30 wt% or less, more preferably 20 wt% or less, and even more preferably 15 wt% or less.

[0070] In some preferred embodiments, the monomer component of the acrylic polymer uses a monomer having a nitrogen atom (for example, an amide group-containing monomer such as (meth)acrylamide, or a monomer having a nitrogen atom-containing ring such as NVP or ACMO) in combination with a hydroxyl group-containing monomer (for example, HEA or 4HBA) as a monomer having a polar group (polar group-containing monomer). This allows for a good balance between adhesive strength and cohesive strength. In an embodiment in which a monomer having a nitrogen atom and a hydroxyl group-containing monomer are used in combination, the amount A of the monomer having a nitrogen atom is Ｎ and the amount A of hydroxyl group-containing monomer ＯＨ Weight ratio (A Ｎ / A ＯＨ ) is not particularly limited, and may be, for example, 0.1 or more, 0.5 or more, 1.0 or more, 1.2 or more, 1.5 or more, or 1.8 or more. Ｎ / A ＯＨ ) may be, for example, 10 or less, 5 or less, 3 or less, or 2.5 or less.

[0071] In some embodiments, the monomer component may include a carboxyl group-containing monomer. Non-limiting examples of carboxyl group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Preferred examples include AA and MAA. The carboxyl group-containing monomer may be used alone or in combination of two or more. For example, AA and MAA may be used in combination.

[0072] The amount of the carboxyl group-containing monomer used may be, for example, 0.01 wt% or more, 0.1 wt% or more, 1 wt% or more, 3 wt% or more, 6 wt% or more, or 8 wt% or more of the total monomer components. The greater the amount of the carboxyl group-containing monomer used, the more the cohesive strength of the PSA tends to improve. The proportion of the carboxyl group-containing monomer may be, for example, 20 wt% or less, 10 wt% or less, 3 wt% or less, 1 wt% or less (e.g., less than 1 wt%), or 0.1 wt% or less. The monomer components may be substantially free of the carboxyl group-containing monomer.

[0073] Furthermore, when an acrylic polymer having an ethylenically unsaturated group, which will be described later, is used as the polymer, it is preferable to use, as the other monomer, a monomer having a functional group (functional group A) capable of reacting with a functional group (functional group B) of a compound having an ethylenically unsaturated group, which will be described later. In this embodiment, the type of the other monomer is determined depending on the type of compound. Examples of other monomers having functional group A include carboxyl group-containing monomers, epoxy group-containing monomers, hydroxyl group-containing monomers, and isocyanate group-containing monomers, and hydroxyl group-containing monomers are particularly preferred. By using a hydroxyl group-containing monomer as the other monomer, the acrylic polymer has a hydroxyl group. On the other hand, by using, for example, an isocyanate group-containing monomer as the compound having an ethylenically unsaturated group, the hydroxyl group of the acrylic polymer reacts with the isocyanate group of the compound, and an ethylenically unsaturated group derived from the compound is introduced into the acrylic polymer.

[0074] Furthermore, when another monomer is used for the purpose of reacting with a compound having an ethylenically unsaturated group, the amount of the other monomer (preferably a hydroxyl group-containing monomer) is suitably about 1 wt% or more of the total monomer components, preferably about 5 wt% or more, more preferably about 10 wt% or more, and may be about 12 wt% or more, from the viewpoint of adhesive properties such as curability and cohesive strength of the adhesive. Furthermore, from the viewpoint of maintaining good adhesive properties such as adhesive strength, the amount of the other monomer is suitably about 40 wt% or less of the total monomer components, preferably about 30 wt% or less, more preferably about 25 wt% or less, and may be about 20 wt% or less (e.g., 15 wt% or less).

[0075] The acrylic polymer may contain, as another monomer component, a polyfunctional monomer having at least two ethylenically unsaturated groups, such as a (meth)acryloyl group or a vinyl group. By using a polyfunctional monomer as a monomer component, the cohesive strength of the pressure-sensitive adhesive can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and, for example, one or more suitable polyfunctional monomers selected from those exemplified as blended monomers contained in the pressure-sensitive adhesive layer described below can be used alone or in combination.

[0076] The amount of polyfunctional monomer used is not particularly limited and can be appropriately set so as to achieve the purpose of using the polyfunctional monomer. The amount of polyfunctional monomer used can be approximately 3% by weight or less of the above-mentioned monomer components, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of polyfunctional monomer used to approximately 0.001% by weight or more (for example, approximately 0.01% by weight or more) of the monomer components.

[0077] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. As a monomer supply method for solution polymerization, a batch charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, or the like can be appropriately employed. The polymerization temperature can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0078] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixed solvent of two or more selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, halogenated alkanes such as 1,2-dichloroethane, lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol, ethers such as tert-butyl methyl ether, and ketones such as methyl ethyl ketone can be used.

[0079] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method.For example, although not particularly limited, for example, azo-based polymerization initiators, peroxide-based polymerization initiators, redox-based polymerization initiators formed by the combination of peroxide and reducing agent, substituted ethane-based polymerization initiators, etc. can be used.As the polymerization initiator, for example, one or more of the radical polymerization initiators (for example, thermal polymerization initiators) exemplified below to be added to the pressure-sensitive adhesive layer can be selected and used.

[0080] The amount of the polymerization initiator used is not particularly limited and may be a normal amount depending on the polymerization method, polymerization mode, etc. For example, about 0.001 to 5 parts by weight (typically about 0.01 to 2 parts by weight, e.g., about 0.01 to 1 part by weight) of the polymerization initiator can be used per 100 parts by weight of all monomer components to be polymerized.

[0081] (Polymer having an ethylenically unsaturated group) In some embodiments, the pressure-sensitive adhesive layer comprises a polymer having an ethylenically unsaturated group such as an acryloyl group, a methacryloyl group, a vinyl group, or an allyl group. When a pressure-sensitive adhesive comprises a polymer having an ethylenically unsaturated group, the ethylenically unsaturated group of the polymer reacts when heated or when irradiated with active energy rays, etc., and the pressure-sensitive adhesive can be cured to a high degree of cure, thereby obtaining excellent peelability (for example, heat peelability or heat-resistant peelability). Furthermore, when a pressure-sensitive adhesive comprises a polymer having an ethylenically unsaturated group, in an embodiment in which a monomer (compounded monomer) is contained in the pressure-sensitive adhesive layer, sufficient peelability (for example, heat peelability or heat-resistant peelability) can be achieved while limiting the amount of the compounded monomer used.

[0082] In some embodiments, the polymer having an ethylenically unsaturated group is a polymer having an ethylenically unsaturated group in a side chain. As the monomer component of the polymer having an ethylenically unsaturated group, one or more of the monomer components exemplified for the polymer above can be used within the above content range.

[0083] The amount of ethylenically unsaturated groups in the polymer having an ethylenically unsaturated group is not particularly limited, and from the viewpoint of curability, etc., it is suitably 0.01 mmol per 1 g of polymer (hereinafter also referred to as mmol / g) or more, and may be 0.1 mmol / g or more, or may be 0.5 mmol / g or more. The amount of ethylenically unsaturated groups in the polymer is suitably 10.0 mmol / g or less, and may be 5.0 mmol / g or less, 3.0 mmol / g or less, 2.5 mmol / g or less, or may be 2.0 mmol / g or less.

[0084] The amount of ethylenically unsaturated groups in a polymer, for example, when the ethylenically unsaturated groups are (meth)acryloyl groups, is measured by the following method. First, 0.25 mg of the polymer to be measured is dissolved in 50 mL of THF (tetrahydrofuran), and 15 mL of methanol is added to obtain a solution. Next, 10 mL of 4N aqueous sodium hydroxide is added to the solution to obtain a mixed solution. Next, the mixed solution is stirred at a liquid temperature of 40°C for 2 hours. Further, 10.2 mL of 4N methanesulfonic acid solution is added to the mixed solution and stirred. 5 mL of demineralized water is added to the mixture, followed by 2 mL of methanol to prepare a measurement solution. The content of (meth)acrylic acid in the measurement solution is measured by HPLC (High Performance Liquid Chromatography) (absolute calibration curve method), and the content of ethylenically unsaturated groups is calculated. (HPLC measurement conditions) Column: Phenomenex Synergi 4μ Polar-RP 80A (4.6 mm × 250 mm) Column temperature: 40°C Flow rate: 1.0 mL / min Detector wavelength: 210 nm Eluent: THF (for HPLC) 55 / buffer water (containing 0.2% phosphoric acid and 0.2% triethylamine) 45 Aqueous solution injection volume: 5 μL

[0085] An example of a method for measuring the content of ethylenically unsaturated groups other than (meth)acryloyl groups is a method for measuring the bromine number in accordance with JIS K2605: 1996. In this measurement method, the content of ethylenically unsaturated groups other than (meth)acryloyl groups is determined by converting the number of grams of bromine (Br) added to 100 g of the polymer to be measured into the number of moles of bromine (Br) added to 1 g of the polymer.

[0086] The method for introducing an ethylenically unsaturated group into a polymer is not particularly limited, and an appropriate method can be selected from methods known to those skilled in the art. From the viewpoint of molecular design, etc., a method of introducing an ethylenically unsaturated group into a side chain of a polymer is preferred. For example, a method of reacting (typically condensation or addition reaction) a compound having an ethylenically unsaturated group with a functional group (functional group B) reactive with a functional group (functional group A) introduced into an acrylic polymer by copolymerization, so as not to lose the ethylenically unsaturated group, can be preferably used. Examples of combinations of functional group A and functional group B include a combination of a carboxy group and an epoxy group, a combination of a carboxy group and an aziridyl group, and a combination of a hydroxyl group and an isocyanate group. Among these, a combination of a hydroxyl group and an isocyanate group is preferred from the viewpoint of reaction traceability. From the viewpoint of polymer design, etc., a combination in which the acrylic polymer has a hydroxyl group and the compound has an isocyanate group is particularly preferred.

[0087] As described above, the compound having an ethylenically unsaturated group may have a functional group B that can react with functional group A. Suitable examples of such compounds include isocyanate group-containing monomers (isocyanate group-containing compounds) such as 2-(meth)acryloyloxyethyl isocyanate. Of these, 2-(meth)acryloyloxyethyl isocyanate is more preferred. An acrylic polymer having an ethylenically unsaturated group can be obtained by reacting the isocyanate group of the isocyanate group-containing compound having an ethylenically unsaturated group with the hydroxyl group of the acrylic polymer to form a bond (specifically, a urethane bond).

[0088] The amount of the compound having an ethylenically unsaturated group (for example, an isocyanate group-containing monomer) to be added is not particularly limited, but from the viewpoint of reactivity with the functional group A (for example, a hydroxyl group) in the polymer, it is preferable to add the compound having an ethylenically unsaturated group in an amount of 100 moles (M Ａ ) and the moles of functional group B (isocyanate group) (M Ｂ ) and the molar ratio (M Ａ / M Ｂ ) can be set to be in the range of about 0.5 to 2 (for example, 1 to 1.5).

[0089] In embodiments in which a polymer having an ethylenically unsaturated group is used as the polymer, the content of the polymer having an ethylenically unsaturated group in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the amount of the polymer having an ethylenically unsaturated group used is suitably approximately 10% by weight or more of the total polymer (specifically, base polymer) contained in the pressure-sensitive adhesive layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the pressure-sensitive adhesive layer may consist essentially of the polymer having an ethylenically unsaturated group.

[0090] In some other embodiments, the polymer may be a polymer substantially free of ethylenically unsaturated groups such as acryloyl groups, methacryloyl groups, vinyl groups, and allyl groups (the amount of ethylenically unsaturated groups is less than 0.01 mmol / g). The amount of such a polymer used is suitably approximately 10% by weight or more of the total polymer (specifically, base polymer) contained in the PSA layer, and may be about 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, 95% by weight or more, or 99 to 100% by weight. In some embodiments, the base polymer contained in the PSA layer may essentially consist of a polymer substantially free of ethylenically unsaturated groups.

[0091] The molecular weight of the polymer (e.g., acrylic polymer) is not particularly limited and can be set within an appropriate range depending on the required performance, etc. The weight average molecular weight (Mw) of the polymer is approximately 1 × 10 ４ It is appropriate that the value is equal to or greater than 10×10. ４ By using a polymer having a Mw of a predetermined value or more, a good balance between cohesive strength and adhesive strength can be achieved. In some embodiments, the Mw is 20 × 10 or more from the viewpoint of obtaining heat resistance and good adhesiveness. ４ It may be 30 × 10 or more. ４ More than that is fine, about 40 x 10 ４ More than that is fine, about 50 x 10 ４or more, for example, about 55×10 ４ The upper limit of the Mw of the polymer is not particularly limited, and may be, for example, about 1000×10 ４ It may be less than or equal to approximately 100×10 ４ Here, Mw refers to a value calculated in terms of standard polystyrene obtained by gel permeation chromatography (GPC). As the GPC apparatus, for example, a model named "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) may be used.

[0092] (Monomer) In some embodiments, the pressure-sensitive adhesive layer preferably contains a monomer (a compounded monomer) in addition to the polymer. The monomer has an ethylenically unsaturated group. The ethylenically unsaturated group of the monomer functions as a polymerizable functional group (typically a radically polymerizable functional group). By incorporating the monomer into the pressure-sensitive adhesive layer, the monomer is contained in the pressure-sensitive adhesive layer in a pre-reacted (unreacted) state. As a result, after the pressure-sensitive adhesive layer is formed, the monomer contained in the pressure-sensitive adhesive layer reacts during heat treatment under predetermined conditions or upon irradiation with active energy rays, thereby reducing the adhesive strength and achieving easy peelability (e.g., easy heat peelability). For example, when the pressure-sensitive adhesive layer is designed as a thermosetting pressure-sensitive adhesive, incorporating the monomer can form a thermosetting pressure-sensitive adhesive that retains heat-resistant easy peelability even after heat treatment. More specifically, pressure-sensitive adhesives typically adsorb to the surface of the adherend when heated, for example, at high temperatures while attached to the adherend. As a result, the adhesive strength of the pressure-sensitive adhesive to the adherend increases, resulting in heavy peelability. For example, in an embodiment in which a monomer is contained in a pressure-sensitive adhesive together with a thermal polymerization initiator (e.g., a peroxide-based polymerization initiator), the reaction (radical polymerization reaction) between the monomer and the thermal polymerization initiator proceeds rapidly upon heating, allowing the pressure-sensitive adhesive to harden prior to adsorption of the pressure-sensitive adhesive to the adherend. This reduces the adhesive strength to the adherend. Furthermore, even if heating is continued thereafter, the adhesive strength of the pressure-sensitive adhesive to the adherend does not increase but is maintained within a predetermined range, allowing the pressure-sensitive adhesive to exhibit excellent heat-peelability. Note that the technology disclosed herein is not limited to the above considerations. The above-mentioned monomers can be used alone or in combination of two or more.

[0093] Examples of the ethylenically unsaturated group contained in the above-mentioned monomer include, but are not limited to, an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group. Preferred examples of the ethylenically unsaturated group include an acryloyl group and a methacryloyl group. Of these, an acryloyl group is preferred. Hereinafter, a compound having an acryloyl group and / or a methacryloyl group may be referred to as an acrylic monomer. Furthermore, a compound having a vinyl group may be referred to as a vinyl monomer.

[0094] Although not particularly limited, it is appropriate to use a monomer having a molecular weight of 100 or more. In some preferred embodiments, the molecular weight of the monomer may be, for example, 150 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more. The molecular weight of the monomer is usually approximately 100,000 or less, for example, approximately 10,000 or less (e.g., less than 10,000) is appropriate, and 5,000 or less (e.g., less than 5,000) is preferable, and may be 1,500 or less, 1,000 or less (e.g., less than 1,000), 800 or less, or 600 or less. The use of a monomer having a molecular weight within the above range can be advantageous, for example, in terms of the preparation and coatability of the pressure-sensitive adhesive composition. The above molecular weight is the manufacturer's nominal value or a molecular weight calculated from the molecular structure. For the above-mentioned monomers having a molecular weight equal to or greater than a predetermined value, the value of the weight average molecular weight (Mw) calculated in terms of standard polystyrene obtained by GPC may be used.

[0095] In some preferred embodiments, the monomer used has a weight loss rate of 1% or less (specifically, 1.0% or less) at 180°C in TGA (thermogravimetric analysis) at a temperature increase of 10°C / min. By using a heat-resistant monomer (hereinafter also referred to as a "heat-resistant monomer") having a weight loss rate of 1% or less at 180°C, the pressure-sensitive adhesive layer has easy peelability (e.g., easy peelability by heating) due to the inclusion of the monomer, while suppressing outgassing during heating. By using the heat-resistant monomer, for example, it is possible to achieve both easy peelability by heating and reduced outgassing. From the viewpoint of reducing outgassing, in some preferred embodiments, the weight loss rate of the heat-resistant monomer at 180°C is 0.9% or less, more preferably 0.8% or less, even more preferably 0.7% or less, particularly preferably 0.6% or less, and may be 0.5% or less. The lower limit of the weight loss rate of the heat-resistant monomer when heated to 180°C is theoretically 0%, and in practice may be 0.1% or more, 0.2% or more, or 0.3% or more. As the heat-resistant monomer, trimethylolpropane triacrylate (TMPTA, weight loss rate when reaching 180°C: 1%) and dipentaerythritol hexaacrylate (DPHA, weight loss rate when reaching 180°C: 0.5%) are preferably used. The heat-resistant monomer may be used alone or in combination of two or more.

[0096] Specifically, the weight loss rate of the monomer upon heating at 180°C can be measured using a differential thermal analyzer (manufactured by TA Instruments, trade name "Discovery TGA") under measurement conditions of a temperature increase rate of 10°C / min, an air atmosphere, and a flow rate of 25 mL / min.

[0097] In some preferred embodiments, a polyfunctional monomer is used as the monomer. In this specification, the term "polyfunctional monomer" refers to a polymerizable compound having two or more ethylenically unsaturated groups in one molecule, including those referred to as oligomers. Hereinafter, a compound having two or more acryloyl groups and / or methacryloyl groups may be referred to as a polyfunctional acrylic monomer. Furthermore, a compound having two or more vinyl groups may be referred to as a polyfunctional vinyl monomer.

[0098] In some preferred embodiments, the number of ethylenically unsaturated groups contained in one molecule of the polyfunctional monomer may be 3 or more, preferably 4 or more, more preferably 5 or more, and may even be 6 or more. The greater the number of ethylenically unsaturated groups in the polyfunctional monomer, the easier it tends to be to obtain releasability. For example, when the pressure-sensitive adhesive layer is designed as a thermosetting pressure-sensitive adhesive, it tends to have good curing properties upon heating and to easily obtain releasability upon heating. Furthermore, a polyfunctional monomer having a greater number of ethylenically unsaturated groups (functional groups) can obtain releasability (e.g., releasability upon heating) with a relatively small amount of use. This is advantageous because it also reduces the amount of outgassing derived from the polyfunctional monomer. The upper limit of the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer is not limited to a specific range and may be, for example, 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of ethylenically unsaturated groups in one molecule of the polyfunctional monomer may be, for example, 10 or less, 8 or less, or 6 or less. Polyfunctional monomers having the above number of ethylenically unsaturated groups tend to easily achieve both good adhesion and easy releasability (e.g., easy releasability upon heating), and also tend to have excellent storage stability.

[0099] As the polyfunctional monomer, various polyfunctional acrylate monomers or polyfunctional vinyl monomers having two or more ethylenically unsaturated groups can be used. Among them, polyfunctional acrylate monomers can be preferably used. Although not particularly limited, when used in combination with an acrylic polymer, polyfunctional acrylate monomers tend to be compatible and easily exhibit desired properties. The polyfunctional acrylate monomers and polyfunctional vinyl monomers can each be used alone or in combination of two or more.

[0100] Examples of polyfunctional monomers include 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, allyl (meth)acrylate, alkylene oxide-modified bisphenol A di(meth)acrylate, alkylene oxide-modified neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, dimethylol dicyclopentadi(meth)acrylate, vinyl (meth)acrylate, and divinylbenzene. Bifunctional monomers: trifunctional monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxy tri(meth)acrylate, glycerin propoxy triacrylate, tetramethylolmethane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; and tetrafunctional monomers such as pentaerythritol alkoxy tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and pentaerythritol tetra(meth)acrylate. pentafunctional monomers such as sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate; hexafunctional monomers such as dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate; and di- or higher functional monomers such as epoxy acrylate, polyester acrylate and urethane acrylate. Of these, preferred examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate and dipentaerythritol hexa(meth)acrylate.Among these, dipentaerythritol hexa(meth)acrylate is particularly preferred.

[0101] In embodiments in which the pressure-sensitive adhesive layer contains a polyfunctional monomer, the content of the polyfunctional monomer in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the polyfunctional monomer may be approximately 1 part by weight or more, or may be 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the pressure-sensitive adhesive layer. The appropriate amount of the polyfunctional monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, from the viewpoint of improving easy peelability (e.g., improving easy peelability under heat), the content of the polyfunctional monomer is 5 parts by weight or more, may be 7 parts by weight or more, may be 8 parts by weight or more, or may be 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 15 parts by weight or more, even more preferably 20 parts by weight or more, and even more preferably 25 parts by weight or more. By incorporating a sufficient amount of polyfunctional monomer into the adhesive layer, for example, when the adhesive layer is designed as a thermosetting adhesive layer, the polyfunctional monomer contained in the adhesive layer reacts rapidly upon heating, causing the adhesive layer to thermally cure, thereby achieving easy thermal peelability. The upper limit of the content of the polyfunctional monomer in the adhesive layer is not particularly limited and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of polyfunctional monomer per 100 parts by weight of the polymer is suitably approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the polyfunctional monomer per 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less (e.g., less than 20 parts by weight), 18 parts by weight or less, 15 parts by weight or less, or 12 parts by weight or less.According to the technology disclosed herein, the desired easy peelability (e.g., easy peelability by heating) can be preferably achieved with a composition in which the amount of monomer in the pressure-sensitive adhesive layer is limited as described above. Furthermore, by limiting the amount of polyfunctional monomer used, the generation of low molecular weight components derived from the polyfunctional monomer after the reaction of the polyfunctional monomer can be suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

[0102] In embodiments in which a polyfunctional monomer is used as the monomer, the amount of the polyfunctional monomer relative to the total amount of the monomers is not particularly limited. In some embodiments, from the viewpoint of effectively exerting the effect of containing the polyfunctional monomer, the amount of the polyfunctional monomer is suitably approximately 10 wt% or more of the total amount of the monomers, preferably 30 wt% or more, more preferably about 50 wt% or more (e.g., more than 50 wt%), even more preferably 70 wt% or more, even more preferably 90 wt% or more, particularly preferably 95 wt% or more, and may be 99 to 100 wt%. In some embodiments, the monomer contained in the pressure-sensitive adhesive composition may essentially consist of the polyfunctional monomer.

[0103] Furthermore, one or more monofunctional monomers containing one ethylenically unsaturated group per molecule may be used as the monomer. Known monofunctional acrylate monomers and vinyl monomers may be used as the monofunctional monomer. For example, one or more of the acrylate monomers (alkoxy group-containing (meth)acrylates, linear alkyl (meth)acrylates, etc.) exemplified as the monomer components of the polymer may be used.

[0104] In embodiments in which the pressure-sensitive adhesive layer contains the monomer, the content of the monomer in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the monomer may be approximately 1 part by weight or more, or may be 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, preferably an acrylic polymer) contained in the pressure-sensitive adhesive layer. The appropriate amount of the monomer may vary depending on its molecular weight, the number of functional groups, etc., but in some preferred embodiments, from the viewpoint of improving easy peelability (e.g., improving easy peelability under heat), the content of the monomer is 5 parts by weight or more, or may be 7 parts by weight or more, or may be 8 parts by weight or more, or may be 9 parts by weight or more, more preferably 10 parts by weight or more (e.g., more than 10 parts by weight), more preferably 15 parts by weight or more, even more preferably 20 parts by weight or more, and even more preferably 25 parts by weight or more. By incorporating a sufficient amount of the monomer into the pressure-sensitive adhesive layer, for example, when the pressure-sensitive adhesive layer is designed as a thermosetting pressure-sensitive adhesive layer, the monomer contained in the pressure-sensitive adhesive layer reacts rapidly upon heating, causing the pressure-sensitive adhesive layer to thermally cure, thereby achieving easy peelability upon heating. The upper limit of the content of the monomer in the pressure-sensitive adhesive layer is not particularly limited and can be set to achieve the desired adhesive properties. In some embodiments, from the viewpoint of compatibility with the polymer (specifically, the base polymer, for example, an acrylic polymer), the amount of the monomer per 100 parts by weight of the polymer is suitably approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, even more preferably 140 parts by weight or less, and may be 120 parts by weight or less, or may be 90 parts by weight or less. In some preferred embodiments, the amount of the monomer relative to 100 parts by weight of the polymer may be 70 parts by weight or less, 50 parts by weight or less (e.g., less than 50 parts by weight), 45 parts by weight or less (e.g., less than 45 parts by weight), 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less (e.g., less than 20 parts by weight), 18 parts by weight or less, 15 parts by weight or less, or 12 parts by weight or less. According to the technology disclosed herein, a composition in which the amount of monomer in the pressure-sensitive adhesive layer is limited as described above can preferably achieve a desired improvement in easy peelability (e.g., easy peelability upon heating).Furthermore, by limiting the amount of the monomer used, the generation of low molecular weight components derived from the monomer after the reaction of the monomer can be suppressed, and contamination of the adherend surface caused by such low molecular weight components can be prevented.

[0105] (Radical Polymerization Initiator) In some embodiments, the pressure-sensitive adhesive layer preferably contains a radical polymerization initiator. In embodiments in which the pressure-sensitive adhesive layer contains an ethylenically unsaturated group, the radical polymerization initiator can react with the ethylenically unsaturated group contained in the pressure-sensitive adhesive layer to cure the pressure-sensitive adhesive. This can reduce the adhesive strength to the adherend. Suitable examples of radical polymerization initiators include thermal polymerization initiators and photopolymerization initiators. By incorporating a thermal polymerization initiator into the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer can be designed as a thermosetting pressure-sensitive adhesive layer. Furthermore, by incorporating a photopolymerization initiator into the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer can be designed as an active energy ray-curable pressure-sensitive adhesive layer. The radical polymerization initiators can be used alone or in combination of two or more. For example, a thermal polymerization initiator and a photopolymerization initiator may be used in combination. Although not particularly limited, the technology disclosed herein can be preferably implemented with a pressure-sensitive adhesive layer containing a thermal polymerization initiator suitable for a process including a heat treatment.

[0106] (Thermal Polymerization Initiator) In some embodiments, the pressure-sensitive adhesive layer contains a thermal polymerization initiator. Here, the thermal polymerization initiator refers to a polymerization initiator that generates radicals upon heating. By including a thermal polymerization initiator in the pressure-sensitive adhesive layer, the thermal polymerization initiator reacts with the ethylenically unsaturated group in the pressure-sensitive adhesive layer during heat treatment under predetermined conditions, for example, in embodiments in which the pressure-sensitive adhesive layer contains an ethylenically unsaturated group, thereby reducing the adhesive strength and achieving heat-peelability. By including a thermal polymerization initiator, a thermosetting pressure-sensitive adhesive that retains heat-resistant easy-peelability even after heat treatment can be formed.

[0107] As the thermal polymerization initiator, one or more suitable types may be selected and used from various thermal polymerization initiators such as peroxide-based polymerization initiators, azo-based polymerization initiators, redox-based polymerization initiators formed by combining peroxides with reducing agents, and substituted ethane-based polymerization initiators.

[0108] In some embodiments, the thermal polymerization initiator preferably includes at least a peroxide-based polymerization initiator. By incorporating a peroxide-based polymerization initiator into the PSA layer as a thermal polymerization initiator, for example, in embodiments in which the PSA layer contains ethylenically unsaturated groups, the reaction of the ethylenically unsaturated groups in the PSA layer upon heating, i.e., the curing reaction of the PSA layer, proceeds rapidly, ensuring the PSA layer exhibits easy heat-peelability on a variety of adherends, including those that readily adhere to the PSA layer upon heating. One possible reason for this is the high initiation efficiency of peroxide-based polymerization initiators (particularly organic peroxide-based polymerization initiators). Furthermore, peroxide-based polymerization initiators generate a radical (-O.) by cleavage of the -O-O- moiety contained in the compound. However, because this cleavage reaction is reversible, it is believed that if the radical does not collide with the ethylenically unsaturated groups of the compounded monomers or polymer, recombination of -O-O- will occur. This recombined initiator can undergo another cleavage reaction during the specified heating period, colliding with and reacting with the compounded monomers, etc. Therefore, when a peroxide-based polymerization initiator is used, the thermal curing of the pressure-sensitive adhesive layer proceeds rapidly at a reaction rate significantly faster than that of other initiators (e.g., azo-based initiators). Furthermore, since the thermal curing rate is faster than the rate at which the pressure-sensitive adhesive layer and the adherend are firmly adhered together due to heating, it is believed that the peel force after heating is reliably reduced, resulting in heat-sensitive releasability and heat-resistant releasability. The technology disclosed herein is not limited to the above considerations.

[0109] As the peroxide polymerization initiator, for example, organic peroxides such as diacyl peroxide, peroxy ester, peroxydicarbonate, monoperoxycarbonate, peroxyketal, dialkyl peroxide, hydroperoxide, ketone peroxide, etc. are preferably used. Suitable examples of the peroxide polymerization initiator include benzoyl peroxide compounds (typically dibenzoyl peroxide (BPO)) having a benzoyl group which may have a substituent. The peroxide polymerization initiators can be used alone or in combination of two or more.

[0110] Specific examples of peroxide polymerization initiators include BPO, 1,1-di(t-hexylperoxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, and 1,3-bis(t-butylperoxy)-m-isopropyl diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, diisopropylbenzene hydroperoxide, t-butylcumyl peroxide, didecanoyl peroxide, dilauroyl peroxide, 2,4-dichlorobenzoyl peroxide, di(4-t-butylcyclohexyl)peroxydicarbonate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl hydroperoxide, and di-t-butyl peroxide.

[0111] In embodiments in which the pressure-sensitive adhesive layer contains a peroxide-based polymerization initiator, the content of the peroxide-based polymerization initiator in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the peroxide-based polymerization initiator in the pressure-sensitive adhesive layer is suitably 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer, 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, particularly preferably 0.5 parts by weight or more, and may be 0.6 parts by weight or more, or even 0.7 parts by weight or more. The higher the content of the peroxide-based polymerization initiator, for example, in a pressure-sensitive adhesive layer containing ethylenically unsaturated groups, the higher the collision frequency between the peroxide-based polymerization initiator and the ethylenically unsaturated groups, and the more likely the curing reaction will proceed. In addition, in some embodiments, the amount of the 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 may be approximately 5 parts by weight or less. In some preferred embodiments, the amount of the peroxide polymerization initiator relative to 100 parts by weight of the polymer is suitably 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., 1.1 parts by weight or less), and may be 1.0 part by weight or less (e.g., less than 1.0 part by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By setting the content of the peroxide polymerization initiator within the specified range, it is possible to preferably realize a pressure-sensitive adhesive that has efficient thermosetting and easy heat-peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0112] In embodiments in which the pressure-sensitive adhesive layer contains a monomer (a blended monomer) and a peroxide polymerization initiator, the content of the peroxide polymerization initiator in the pressure-sensitive adhesive layer can also be determined by its relative relationship to the blended monomer in the pressure-sensitive adhesive layer. In some embodiments, the amount of the peroxide polymerization initiator per 100 parts by weight of the monomer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, even more preferably 1.0 parts by weight or more, even more preferably 1.2 parts by weight or more, particularly preferably 1.5 parts by weight or more, and may even be 2.0 parts by weight or more, or may even be 2.5 parts by weight or more. In some embodiments, the amount of the peroxide polymerization initiator per 100 parts by weight of the monomer is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and may even be 7 parts by weight or more. The amount of the peroxide polymerization initiator used can be preferably adopted, for example, in a composition in which the monomer content is limited. In some embodiments, the amount of the peroxide polymerization initiator relative to 100 parts by weight of the monomer may be, for example, about 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, or 10 parts by weight or less. In some embodiments, the amount of the peroxide polymerization initiator relative to 100 parts by weight of the monomer may be, for example, 7 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less.

[0113] In some other embodiments, the pressure-sensitive adhesive layer may contain, as a thermal polymerization initiator, persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as azonitrile compounds, azoamide compounds, azoester compounds, alkylazo compounds, azoamidine compounds, azoimidazoline compounds, and polymeric azo compounds, more specifically, 2,2'-azobisisobutyronitrile (AIBN), 1,1'-azobis(cyclohexane-1-carbonitrile), 4,4-azobis(4-cyanovaleric acid), 2,2'-azobis(N- The initiator may contain one or more of the following: butyl-2-methylpropionamide, 2,2'-azobis(2,4,4-trimethylpentane); substituted ethane initiators such as phenyl-substituted ethane; and redox initiators formed by combining a peroxide with a reducing agent, such as a combination of a persulfate with sodium hydrogen sulfite or a combination of a peroxide with sodium ascorbate. Thermal polymerization initiators other than these peroxide-based polymerization initiators are also called non-peroxide-based polymerization initiators. Non-peroxide-based polymerization initiators may be used in addition to peroxide-based polymerization initiators.

[0114] Although not particularly limited, from the viewpoint of effectively exerting the effects of the peroxide polymerization initiator, in some embodiments, the proportion of the peroxide polymerization initiator in the total thermal polymerization initiator contained in the pressure-sensitive adhesive layer is suitably approximately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95 to 100% by weight. The thermal polymerization initiator contained in the pressure-sensitive adhesive layer may consist of a peroxide polymerization initiator.

[0115] In some embodiments, it is preferable to use a thermal polymerization initiator whose self-accelerating decomposition temperature (SADT) [°C] satisfies the formula: SADT + 10 ≥ 60. Here, the SADT of a thermal polymerization initiator is defined as the lowest temperature at which a certain amount of the initiator in a container generates heat of 6°C or more or causes self-accelerating decomposition within seven days. SADT indicates the environmental temperature at which the thermal polymerization initiator decomposes. Based on the fact that the maximum temperature to which a pressure-sensitive adhesive can be exposed during storage is 60°C, the present inventors have experimentally confirmed that if a thermal polymerization initiator has an SADT that is 10°C below the maximum storage temperature or higher, self-accelerating decomposition of the thermal polymerization initiator in the pressure-sensitive adhesive is suppressed, resulting in storage stability that allows the adhesive to maintain good heat-peelability after storage. This is thought to be because heat is relatively less transmitted within the pressure-sensitive adhesive (solid) than when the thermal polymerization initiator is used alone. Based on this discovery, adhesives designed with a thermal polymerization initiator having an SADT that satisfies the above formula (hereinafter also referred to as a high SADT initiator) suppress decomposition of the thermal polymerization initiator in the adhesive, allowing the adhesive to maintain the desired heat-peelability even when the adhesive is exposed to temperatures of approximately 60°C before use. Adhesives containing a thermal polymerization initiator consisting of a high SADT initiator have good storage stability and can maintain good heat-peelability after storage, even when stored for long periods of time or when there are temperature changes during storage. In this specification, the nominal value listed in manufacturer catalogs, etc., is used for the SADT of the thermal polymerization initiator.

[0116] The amount of the thermal polymerization initiator contained in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the content of the thermal polymerization initiator in the pressure-sensitive adhesive layer is suitably 0.1 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the pressure-sensitive adhesive layer, 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, particularly preferably 0.5 parts by weight or more, and may be 0.6 parts by weight or more, or even 0.7 parts by weight or more. The higher the content of the thermal polymerization initiator, for example, in a pressure-sensitive adhesive layer containing an ethylenically unsaturated group, the higher the collision frequency between the thermal polymerization initiator and the ethylenically unsaturated group, and the more likely the curing reaction will proceed. In addition, in some embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer may be, for example, about 10 parts by weight or less, or may be approximately 5 parts by weight or less. In some preferred embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the polymer is suitably 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, particularly preferably less than 1.2 parts by weight (e.g., 1.1 parts by weight or less), and may be 1.0 part by weight or less (e.g., less than 1.0 part by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By setting the total amount of the thermal polymerization initiator within the specified range, it is possible to preferably realize a pressure-sensitive adhesive that has efficient thermosetting and easy heat-peelability while obtaining adhesive properties such as adhesive strength and storage stability.

[0117] Although not particularly limited, in some preferred embodiments, the total proportion of the above-mentioned polymer (specifically, base polymer, for example, acrylic polymer), the above-mentioned monomer (for example, polyfunctional acrylic monomer) and thermal polymerization initiator (peroxide-based polymerization initiator, etc.) in the entire pressure-sensitive adhesive layer is, from the viewpoint of effectively exhibiting a reduction in peel strength upon heating, suitably 50% by weight or more (for example, more than 50% by weight and 100% by weight or less), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and may be 95% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99 to 100% by weight).

[0118] (Photopolymerization initiator) In some embodiments, the pressure-sensitive adhesive layer contains a photopolymerization initiator. Here, the photopolymerization initiator refers to a polymerization initiator that generates radicals by, for example, decomposing itself when irradiated with active energy rays such as ultraviolet rays. By including the photopolymerization initiator in the pressure-sensitive adhesive layer, when the pressure-sensitive adhesive layer is irradiated with active energy rays, for example, in embodiments in which the pressure-sensitive adhesive layer contains ethylenically unsaturated groups, the photopolymerization initiator reacts with the ethylenically unsaturated groups in the pressure-sensitive adhesive layer to harden, thereby reducing the adhesive strength and achieving easy peelability. The photopolymerization initiator may be suitably selected from, for example, ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, oxime ester-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, alkylphenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like, and one or more of these may be used.

[0119] In an embodiment in which the pressure-sensitive adhesive layer contains a photopolymerization initiator, the amount of the photopolymerization initiator contained in the pressure-sensitive adhesive layer is not particularly limited and can be, for example, within the same range as the content of the thermal polymerization initiator. That is, the range of the content of the thermal polymerization initiator relative to 100 parts by weight of the polymer can be applied as the range of the content of the photopolymerization initiator.

[0120] (Crosslinking Agent) The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a crosslinking agent as needed, mainly for the purpose of crosslinking within the pressure-sensitive adhesive layer or between the pressure-sensitive adhesive layer and its adjacent surface. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer in a form after crosslinking reaction. The use of a crosslinking agent allows the cohesive strength of the pressure-sensitive adhesive layer to be appropriately adjusted.

[0121] The type of crosslinking agent is not particularly limited, and can be selected from conventionally known crosslinking agents so that the crosslinking agent exerts an appropriate crosslinking function within the pressure-sensitive adhesive layer, for example, depending on the composition of the pressure-sensitive adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. These crosslinking agents can be used alone or in combination of two or more. From the viewpoint of achieving a good balance between adhesiveness and cohesive strength, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and carbodiimide-based crosslinking agents are preferred, with isocyanate-based crosslinking agents being particularly preferred.

[0122] The isocyanate crosslinking agent may be a polyfunctional isocyanate compound having two or more functionalities, such as aromatic isocyanates such as tolylene diisocyanate, xylene diisocyanate, polymethylene polyphenyl diisocyanate, tris(p-isocyanatophenyl)thiophosphate, and diphenylmethane diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. Examples of commercially available products include isocyanate adducts such as a trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate L"), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Coronate HL"), an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX"), and a trimethylolpropane / xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, Inc., trade name "Takenate D-110N").

[0123] As the epoxy-based crosslinking agent, those having two or more epoxy groups per molecule can be used without particular limitation. Epoxy-based crosslinking agents having three to five epoxy groups per molecule are preferred. Specific examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy-based crosslinking agents include "TETRAD-X" and "TETRAD-C" manufactured by Mitsubishi Gas Chemical Company, Inc., "Epicron CR-5L" manufactured by DIC Corporation, "Denacol EX-512" manufactured by Nagase ChemteX Corporation, and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

[0124] As the oxazoline-based crosslinking agent, any agent having one or more oxazoline groups per molecule can be used without particular limitation. Examples of aziridine-based crosslinking agents include trimethylolpropane tris[3-(1-aziridinyl)propionate] and trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)]. As the carbodiimide-based crosslinking agent, a low molecular weight compound or a high molecular weight compound having two or more carbodiimide groups can be used.

[0125] In some embodiments, an isocyanate-based crosslinking agent is used as the crosslinking agent. The isocyanate-based crosslinking agent facilitates the formation of a pressure-sensitive adhesive having good peelability while exhibiting a well-balanced adhesive property, such as adhesive strength and cohesive strength. The isocyanate-based crosslinking agents can be used alone or in combination of two or more. Although not particularly limited, when an isocyanate-based crosslinking agent is used, the amount used is preferably less than 3 parts by weight per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. By limiting the amount of the isocyanate-based crosslinking agent used, the crosslinking density is appropriately suppressed. At such a crosslinking density, for example, in embodiments in which the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator, the ethylenically unsaturated group in the pressure-sensitive adhesive layer frequently collides with the radical polymerization initiator during heat treatment or irradiation with active energy rays, thereby promoting curing and enhancing peelability. For example, when the pressure-sensitive adhesive layer is designed as a thermosetting pressure-sensitive adhesive, the desired heat-peelability and heat-resistant peelability can be exhibited. The technology disclosed herein is not limited to the above considerations. From this perspective, in some preferred embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the polymer is 2 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 parts by weight or less, even more preferably 0.8 parts by weight or less, and particularly preferably 0.6 parts by weight or less. By limiting the amount of isocyanate-based crosslinking agent used, sufficient adhesive strength tends to be easily obtained. Furthermore, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the polymer can be, for example, 0.01 parts by weight or more. In some preferred embodiments, it may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of isocyanate-based crosslinking agent used within the above range, it is possible to preferably obtain a pressure-sensitive adhesive that preferably achieves the effects of the technology disclosed herein while exhibiting well-balanced adhesive properties such as adhesive strength and cohesive strength.

[0126] When a crosslinking agent is used, the amount of crosslinking agent used may be more than 0 parts by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the adhesive layer, from the viewpoint of realizing a pressure-sensitive adhesive that exhibits a good balance of adhesive properties such as adhesive strength and cohesive strength, and may be, for example, 0.001 parts by weight or more, or even 0.01 parts by weight or more. In some preferred embodiments, the amount of crosslinking agent used relative to 100 parts by weight of the polymer may be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or even 0.5 parts by weight or more. Furthermore, the upper limit of the amount of crosslinking agent used may vary depending on the type of crosslinking agent used, so is not limited to a specific range, but is preferably limited to a predetermined amount or less. By limiting the amount of crosslinking agent used, the crosslinking density can be appropriately suppressed. At such a crosslinking density, for example, in an embodiment in which the pressure-sensitive adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator, the ethylenically unsaturated group in the pressure-sensitive adhesive layer frequently collides with the radical polymerization initiator, thereby promoting curing and improving peelability. For example, when the pressure-sensitive adhesive layer is designed as a thermosetting pressure-sensitive adhesive, the desired heat-peelability and heat-resistance can be achieved. However, the technology disclosed herein is not limited to the above considerations. For example, the amount of crosslinking agent used is suitably less than 10 parts by weight per 100 parts by weight of the polymer, and in some embodiments, it is preferably less than 5 parts by weight, and may be less than 3 parts by weight. In some embodiments, the amount of crosslinking agent used is suitably less than 1 part by weight per 100 parts by weight of the polymer, and is preferably 0.9 parts by weight or less, and may be 0.8 parts by weight or less, 0.7 parts by weight or less, 0.6 parts by weight or less, or 0.5 parts by weight or less. By limiting the amount of crosslinking agent used, sufficient adhesive strength tends to be obtained.

[0127] A crosslinking catalyst may be used to more effectively promote the crosslinking reaction. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used may be, for example, approximately 0.0001 parts by weight or more, approximately 0.001 parts by weight or more, or approximately 0.005 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer, and may be approximately 1 part by weight or less, approximately 0.1 parts by weight or less, or approximately 0.05 parts by weight or less.

[0128] The PSA composition used to form the PSA layer may optionally contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. For example, a compound that undergoes keto-enol tautomerization may be preferably used in a PSA composition containing an isocyanate-based crosslinking agent or a PSA composition that can be used with an isocyanate-based crosslinking agent. This can have the effect of extending the pot life of the PSA composition. Various β-dicarbonyl compounds can be used as the compound that undergoes keto-enol tautomerization. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetate esters such as methyl acetoacetate and ethyl acetoacetate; propionyl acetate esters such as ethyl propionyl acetate; isobutyryl acetate esters such as ethyl isobutyryl acetate; and malonate esters such as methyl malonate and ethyl malonate. Among these, acetylacetone and acetoacetate esters are particularly preferred. The compounds that undergo keto-enol tautomerization may be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerization used may be, for example, 0.1 parts by weight or more and 20 parts by weight or less, and suitably 0.5 parts by weight or more and 15 parts by weight or less, relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the pressure-sensitive adhesive layer, and can be, for example, 1 part by weight or more and 10 parts by weight or less, or may be 1 part by weight or more and 5 parts by weight or less.

[0129] (Other Components) The pressure-sensitive adhesive layer may optionally contain various additives commonly used in the field of pressure-sensitive adhesives, such as tackifiers, silane coupling agents, release force modifiers (such as surfactants), viscosity modifiers (e.g., thickeners), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, and antioxidants. These various additives can be conventionally used and do not particularly characterize the present invention, so detailed description is omitted. The technology disclosed herein can achieve desired adhesive properties, such as adhesive strength, without the use of a tackifier. In some embodiments, the content of the tackifier in the pressure-sensitive adhesive layer can be, for example, less than 10 parts by weight, or even less than 5 parts by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. The content of the tackifier may be less than 1 part by weight (e.g., less than 0.5 parts by weight) or less than 0.1 parts by weight (0 parts by weight or more but less than 0.1 parts by weight). The pressure-sensitive adhesive layer may not contain a tackifier.

[0130] The pressure-sensitive adhesive layer may exhibit the desired heat-peelability without using heat-expandable microspheres, a blowing agent, or the like. In some embodiments, the content of heat-expandable microspheres in the pressure-sensitive adhesive layer may be, for example, less than 1 part by weight, or even less than 0.1 part by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. The content of the blowing agent in the pressure-sensitive adhesive layer may be, for example, less than 1 part by weight, or even less than 0.1 part by weight, per 100 parts by weight of the polymer (specifically, the base polymer, e.g., an acrylic polymer) contained in the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may contain neither heat-expandable microspheres nor a blowing agent.

[0131] (Form of Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive layer disclosed herein may be a pressure-sensitive adhesive layer formed from an aqueous pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition. The aqueous pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in a solvent (aqueous solvent) primarily composed of water. The concept of the aqueous pressure-sensitive adhesive composition referred to here may include those referred to as water-dispersed pressure-sensitive adhesive compositions (compositions in which the pressure-sensitive adhesive is dispersed in water), water-soluble pressure-sensitive adhesive compositions (compositions in which the pressure-sensitive adhesive is dissolved in water), etc. Furthermore, the solvent-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive in an organic solvent.

[0132] Although not particularly limited, the PSA layer disclosed herein can be preferably formed using a solvent-based PSA composition. The solvent-based PSA composition is a PSA composition in a form containing PSA-forming components in an organic solvent. The solvent-based PSA composition typically contains a solution polymer of a monomer component and, optionally, other additives. The effects of the technology disclosed herein can be effectively achieved in a form including a solvent-based PSA (layer). The solvent contained in the solvent-based PSA composition can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixture of two or more solvents selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene; esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; and ketones such as methyl ethyl ketone can be used.

[0133] (Formation of Pressure-Sensitive Adhesive Layer) The pressure-sensitive adhesive layer disclosed herein can be formed by a conventionally known method. After applying (e.g., coating) the pressure-sensitive adhesive composition to a suitable surface, a curing treatment can be appropriately performed to form the pressure-sensitive adhesive in the form of a layer (pressure-sensitive adhesive layer). The pressure-sensitive adhesive composition can be cured by one method (e.g., drying, crosslinking, polymerization, cooling, etc.), or by two or more methods simultaneously or in multiple stages. In the case of a solvent-based pressure-sensitive adhesive composition, the pressure-sensitive adhesive can typically be formed by drying (preferably further crosslinking) the composition.

[0134] For example, in the case of a substrateless double-sided PSA sheet, a method can be used in which a PSA composition is applied to a surface (release surface) having releasability and then cured to form a PSA layer on the surface. In the case of a PSA sheet with a substrate, a method (direct method) can be used in which a PSA composition is directly applied (typically coated) to the substrate and cured to form a PSA layer (transfer method). Alternatively, a method can be used in which a PSA composition is applied to a surface (release surface) having releasability and cured to form a PSA layer on the surface, and then the PSA layer is transferred to the substrate. The release surface can be the surface of a release liner, the back surface of a release-treated substrate, or the like. While the PSA layer disclosed herein is typically formed continuously, it is not limited to this form and may be formed in a regular or random pattern, such as dots or stripes.

[0135] The pressure-sensitive adhesive composition can be applied using a known or conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, die coater, bar coater, knife coater, or spray coater. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. From the viewpoints of promoting the crosslinking reaction and improving production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature is not particularly limited, but can be, for example, about 40 to 100°C, and is usually preferably about 60 to 80°C. For example, drying at the above temperatures (e.g., about 1 to 10 minutes, more specifically, about 3 to 7 minutes) involves a low heating temperature and the progress of solvent volatilization, so that in pressure-sensitive adhesive compositions containing a monomer and a thermal polymerization initiator, the reaction of the monomer and the deactivation of the thermal polymerization initiator are negligible. After drying the pressure-sensitive adhesive composition, aging may be carried out for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the substrate or pressure-sensitive adhesive layer.

[0136] (Thickness) The thickness of the pressure-sensitive adhesive layer is not particularly limited. The thickness of the pressure-sensitive adhesive layer is usually 1 μm or more, and may be 2 μm or more, or 3 μm or more. The thicker the pressure-sensitive adhesive layer, the more the adhesive strength to the adherend tends to improve. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is 5 μm or more, may be 10 μm or more, may be 15 μm or more, may be 20 μm or more, or may be 25 μm or more. The upper limit of the thickness of the pressure-sensitive adhesive layer is suitably, for example, about 200 μm or less, may be 100 μm or less (e.g., less than 100 μm), or may be 50 μm or less. Limiting the thickness of the pressure-sensitive adhesive layer within a predetermined range tends to prevent the occurrence of adhesive residue due to cohesive failure and to easily obtain peelability. In addition, a thin pressure-sensitive adhesive layer is advantageous in terms of thinning the pressure-sensitive adhesive sheet, and also tends to have excellent conformability to the adherend. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is 40 μm or less, and may be 30 μm or less.

[0137] (Gel Fraction) The gel fraction of the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, from the viewpoint of obtaining sufficient adhesion to the adherend and good releasability (e.g., easy releasability upon heating), the initial (before heating) gel fraction (by weight) of the pressure-sensitive adhesive layer is, for example, suitably 85% or less, preferably 80% or less, more preferably 75% or less, and may be 70% or less, 65% or less, or even 60% or less. The lower the initial gel fraction, the more likely it is that high releasability (e.g., easy releasability upon heating) will be obtained. Furthermore, from the viewpoint of obtaining pressure-sensitive adhesive layer formability and appropriate cohesiveness and holding power, in some embodiments, the initial gel fraction of the pressure-sensitive adhesive layer is suitably 20% or more, preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and may be 60% or more, or may be 65% or more. Pressure-sensitive adhesives having an appropriate initial gel fraction within the above range tend to have good curing reactivity (e.g., heat-curing reactivity).

[0138] In some embodiments, the gel fraction of the pressure-sensitive adhesive layer after heating is preferably higher than the gel fraction before heating. For example, the pressure-sensitive adhesive layer preferably has a gel fraction increase after heating calculated by the formula: Post-heat gel fraction increase [%] = (G1 / G0 - 1) × 100 (where G1 is the gel fraction [%] of the pressure-sensitive adhesive layer after heat treatment at 180°C for 30 minutes, and G0 is the gel fraction [%] of the pressure-sensitive adhesive layer before heating). The gel fraction increase after heating is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and may be 40% or more, 50% or more, 60% or more, or even 70% or more. A pressure-sensitive adhesive having the above-mentioned post-heat gel fraction increase is easily cured by heating and tends to easily obtain a high post-heat peel force reduction rate, and therefore excellent heat-peelability and heat-resistant easy-peelability. In some embodiments, the upper limit of the increase in gel fraction after heating is appropriately set depending on the desired thermosetting properties, and may be, for example, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less.

[0139] Although not particularly limited, in some embodiments, the gel fraction (by weight) of the pressure-sensitive adhesive layer after heating is, from the viewpoint of exhibiting easy heat-peelability, suitably 50% or more (e.g., more than 50%), preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, particularly preferably 90% or more, and may even be 95% or more. In some embodiments, the gel fraction of the pressure-sensitive adhesive layer after heating may be, for example, 99% or less, 95% or less, or 90% or less.

[0140] The gel fraction of the pressure-sensitive adhesive layer can be adjusted mainly by the monomer composition and Mw of the polymer, the presence or absence and amount of blended monomers, the type and amount of crosslinking agent, etc. The gel fraction after heating can be adjusted mainly by the polymer design (e.g., the amount of ethylenically unsaturated groups introduced), the blend, type and amount of blended monomers, and the use, type and amount of thermal polymerization initiator. Specifically, each of the above gel fractions is measured by the method described in the Examples below.

[0141] (Young's Modulus) Although not particularly limited, in some embodiments, the Young's modulus Y1 [MPa] of the pressure-sensitive adhesive layer after 30 minutes of heat treatment at 180°C is preferably 100 times or more the Young's modulus Y0 [MPa] before heating, i.e., the Young's modulus change ratio after heating (Y1 / Y0) is preferably 100 or more. The higher the Young's modulus change ratio after heating (Y1 / Y0), the higher the degree of curing of the pressure-sensitive adhesive layer upon heating, and the more likely it is that excellent heat-peelability will be obtained. In some preferred embodiments, the Young's modulus change ratio after heating (Y1 / Y0) may be 200 or more, 300 or more, 500 or more, 800 or more, 1000 or more, 1200 or more, 1500 or more, 1800 or more, or 2000 or more. Furthermore, from the viewpoint of providing the pressure-sensitive adhesive layer with an appropriate elastic modulus before heating, in some embodiments, the Young's modulus change ratio after heating (Y1 / Y0) is suitably about 10,000 or less, preferably 5,000 or less, more preferably 2,500 or less, and may be 1,500 or less, 1,000 or less, or 500 or less.

[0142] Although not particularly limited, in some embodiments, the Young's modulus (initial Young's modulus) Y0 of the pressure-sensitive adhesive layer before heating is suitably, for example, approximately 10 MPa or less, preferably 1 MPa or less, more preferably 0.5 MPa or less, even more preferably 0.3 MPa or less, and may be 0.2 MPa or less. A pressure-sensitive adhesive layer having the above-mentioned Young's modulus Y0 before heating tends to easily obtain sufficient adhesion to the adherend and good easy peelability (e.g., easy peelability under heat). Furthermore, from the viewpoint of obtaining pressure-sensitive adhesive layer formability, moderate cohesion, and holding power, in some embodiments, the Young's modulus Y0 of the pressure-sensitive adhesive layer before heating is suitably 0.01 MPa or more, preferably 0.03 MPa or more, more preferably 0.05 MPa or more, even more preferably 0.08 MPa or more, and may be 0.10 MPa or more, 0.12 MPa or more, or 0.15 MPa or more.

[0143] Although not particularly limited, in some embodiments, the Young's modulus Y1 after heating of the pressure-sensitive adhesive layer is suitably 10 MPa or more, preferably 30 MPa or more, more preferably 50 MPa or more, and even more preferably 70 MPa or more. In some preferred embodiments, the Young's modulus Y1 after heating may be 100 MPa or more, 150 MPa or more, or 200 MPa or more. A pressure-sensitive adhesive layer having a Young's modulus after heating of a predetermined value or more tends to have a high degree of curing after heating and excellent heat-peelability. In some embodiments, the Young's modulus Y1 after heating may be, for example, approximately 500 MPa or less, 300 MPa or less, 150 MPa or less, 100 MPa or less, 70 MPa or less, or 50 MPa or less.

[0144] The Young's modulus of the pressure-sensitive adhesive layer can be adjusted mainly by the monomer composition and Mw of the polymer, the presence or absence and amount of blended monomers, the type and amount of crosslinking agent, etc. The Young's modulus Y1 after heating can be adjusted mainly by the design of the polymer (e.g., the amount of ethylenically unsaturated groups introduced), the blend, type and amount of blended monomers, and the use, type and amount of thermal polymerization initiator. The Young's moduli Y0 and Y1 are specifically measured by the method described in the Examples below.

[0145] <First Pressure-Sensitive Adhesive Layer and Second Pressure-Sensitive Adhesive Layer> In an embodiment in which a substrate-attached double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on each side of the substrate is used as the pressure-sensitive adhesive sheet, the details described above regarding the pressure-sensitive adhesive layer apply to the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer provided on each side of the substrate. Furthermore, one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be designed within the scope of the details described above regarding the pressure-sensitive adhesive layer, while the other pressure-sensitive adhesive layer may be designed to be non-curable. For example, the other pressure-sensitive adhesive layer may be designed to be substantially free of at least one (e.g., both) of an ethylenically unsaturated group and a radical polymerization initiator. In this case, the details described above regarding the pressure-sensitive adhesive layer apply, except for the details regarding the ethylenically unsaturated group and the radical polymerization initiator. Alternatively, the other of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be a pressure-sensitive adhesive layer formed from a known or commonly used pressure-sensitive adhesive.

[0146] In embodiments in which a substrate-attached double-sided pressure-sensitive adhesive sheet is used as the pressure-sensitive adhesive sheet, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be the same or different in type, composition, formation method, etc. Furthermore, the properties (gel fraction characteristics, Young's modulus characteristics, etc.) of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be the same or different. Furthermore, the thicknesses of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be the same or different. Although not particularly limited, in some embodiments, the first pressure-sensitive adhesive layer may have a composition containing a blended monomer and a radical polymerization initiator, and the second pressure-sensitive adhesive layer may have a composition that does not contain at least one of the blended monomer and a radical polymerization initiator (e.g., a thermal polymerization initiator such as a peroxide-based polymerization initiator). Furthermore, although not particularly limited, one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be designed so that the Young's modulus change ratio after heating (Y1 / Y0) is 100 or greater, and the other may be designed so that the Young's modulus change ratio after heating (Y1 / Y0) is less than 100 (e.g., 50 or less, 30 or less, 10 or less, or 3 or less). In this case, the Young's modulus of the other pressure-sensitive adhesive layer before and after the heat treatment at 180° C. for 30 minutes is determined as described above for the pre-heat Young's modulus (initial Young's modulus) Y0.

[0147] <Substrate Layer> The pressure-sensitive adhesive sheet disclosed herein may include a substrate layer. Various sheet-like substrates can be used as the substrate (layer) supporting (backing) the pressure-sensitive adhesive layer. Examples of the substrate include resin films, paper, cloth (woven fabric, nonwoven fabric, etc.), rubber sheets, foam sheets, metal foils, and composites thereof. Examples of resin films include polyolefin films; polyester films; vinyl chloride resin films; vinyl acetate resin films; polyamide resin films; fluororesin films; cellophane; and the like. Non-limiting examples of polyester films include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Other examples of resin films include resin films formed from one or more engineering plastics (which may be super engineering plastics) such as polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, and polyimide resins. The use of engineering plastics is preferred from the standpoint of heat resistance.

[0148] In some preferred embodiments, a resin film having a predetermined rigidity (strength) and excellent processability and handling properties is used as the substrate (layer). Among these, from the viewpoint of heat resistance, polyester films, polyamide resin films, and engineering plastic films (e.g., polyimide resin films, etc.) are preferred as the resin film substrate. In this specification, the term "resin film" typically refers to a non-porous film, and typically refers to a resin film that is substantially bubble-free (void-free). Therefore, the above-mentioned resin film is a concept that is distinct from foam films and nonwoven fabrics. The density of the resin film that can be used as the substrate is approximately 0.85 to 1.50 g / cm. ３ (e.g., 0.90 g / cm ３ ~1.20 g / cm ３ , typically 0.92 g / cm ３ ~1.05g / cm ３The resin film may have a single layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0149] The substrate layer (e.g., a resin film) may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc. The amount of additives to be added is not particularly limited and can be set appropriately depending on the application, etc.

[0150] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately employed.

[0151] The substrate layer may be substantially composed of a resin film. Alternatively, the substrate layer may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer or an anti-reflection layer), a printing layer or a laminating layer for imparting a desired appearance, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0152] The thickness of the base layer is not particularly limited and can be selected appropriately depending on the purpose, but generally can be 1 to 500 μm. From the viewpoints of processability, handleability, workability, etc., the thickness of the base layer is suitably 2 μm or more (for example, 3 μm or more, typically 5 μm or more), and may be approximately 7 μm or more, or may be 10 μm or more. Furthermore, the thickness of the base layer is suitably approximately 200 μm or less, and from the viewpoint of weight reduction and thinning, it is preferably approximately 100 μm or less, more preferably approximately 50 μm or less, and may be 30 μm or less, 20 μm or less, or 15 μm or less. As the thickness of the base layer decreases, the flexibility of the PSA sheet and its ability to follow the surface shape of the adherend tend to improve.

[0153] The surface of the substrate layer facing the pressure-sensitive adhesive layer may be subjected to conventional surface treatments such as corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer, as necessary. Such surface treatments may be intended to improve the adhesion between the substrate layer and the pressure-sensitive adhesive layer, in other words, the anchoring ability of the pressure-sensitive adhesive layer to the substrate layer. The composition of the primer is not particularly limited and can be appropriately selected from known primers. The thickness of the primer layer is not particularly limited, but is suitably about 0.01 μm to 1 μm, and preferably about 0.1 μm to 1 μm. The back surface of the substrate layer may be subjected to the various surface treatments described above or to an antistatic treatment, etc.

[0154] <Total Thickness> The total thickness of the PSA sheet disclosed herein (which may include a PSA layer and a substrate layer, but does not include a release liner) is not particularly limited, and is suitably in the range of approximately 5 to 1000 μm. The total thickness of the PSA sheet may be 10 μm or more, 15 μm or more, or 20 μm or more, from the viewpoints of adhesive properties, handleability, etc. In some embodiments, the total thickness of the PSA sheet may be 30 μm or more, 40 μm or more, or 50 μm or more. Furthermore, from the viewpoint of weight reduction and thinning, in some embodiments, the total thickness of the PSA sheet is 500 μm or less, or may be 300 μm or less. In some preferred embodiments, the total thickness of the PSA sheet is 100 μm or less (e.g., less than 100 μm), more preferably 80 μm or less, or may be 70 μm or less. Reducing the thickness of the PSA sheet is advantageous in terms of thinning, miniaturization, weight reduction, resource conservation, etc.

[0155] <Release Liner> The release liner used in the PSA sheet (PSA sheet before use) disclosed herein is not particularly limited, and examples that can be used include release liners in which the surface of a liner substrate such as a resin film or paper has been release-treated, and release liners made of low-adhesion materials such as fluorine-based polymers (polytetrafluoroethylene, etc.) and polyolefin-based resins (polyethylene, polypropylene, etc.). For example, silicone-based or long-chain alkyl-based release treating agents can be used for the release treatment. In some embodiments, a release-treated resin film can be preferably used as the release liner.

[0156] <Characteristics of Pressure-Sensitive Adhesive Sheet> (Post-Heating Peel Force F1) Although not particularly limited, in some embodiments, the post-heating peel force F1 of the pressure-sensitive adhesive sheet is not particularly limited and can be appropriately set so as to exhibit the desired ease of removability after heating. In some embodiments, from the viewpoint of the ease of removability, the post-heating peel force F1 is suitably, for example, less than 3.0 N / 20 mm, advantageously 2.0 N / 20 mm or less, and preferably 1.0 N / 20 mm or less. In some embodiments where a higher level of ease of removability after heating is required, the post-heating peel force F1 may, for example, be less than 1.0 N / 20 mm, preferably 0.8 N / 20 mm or less, more preferably 0.6 N / 20 mm or less, even more preferably 0.5 N / 20 mm or less, and may be 0.4 N / 20 mm or less, 0.3 N / 20 mm or less, 0.2 N / 20 mm or less, or less than 0.2 N / 20 mm. Such a pressure-sensitive adhesive sheet with a low post-heat peel force F1 can easily peel off the adherend while reducing the load applied to the adherend. Therefore, it can be preferably used in an embodiment in which it is attached to an adherend made of a brittle material (typically a hard and brittle material), such as a glass material or a semiconductor material. The post-heat peel force F1 is typically greater than 0 N / 20 mm, and from the viewpoint of adherend retention after heating, it is appropriate that it be 0.01 N / 20 mm or more. The post-heat peel force F1 may be, for example, 0.05 N / 20 mm or more, 0.1 N / 20 mm or more, 0.2 N / 20 mm or more, 0.3 N / 20 mm or more, or 0.4 N / 20 mm or more. In some embodiments, the post-heat peel force F1 may be 0.5 N / 20 mm or more, 0.8 N / 20 mm or more, 1.0 N / 20 mm or more, 1.5 N / 20 mm or more, or 2.0 N / 20 mm or more. The post-heat peel strength F1 refers to the peel strength (peel force) measured in an environment of 23°C and 50% RH after being attached to a glass plate and heat-treated at 180°C for 30 minutes.

[0157] (Pre-heating peel force F0) Although not particularly limited, in some embodiments, the initial (pre-heating) peel force F0 of the PSA sheet is suitably, for example, 0.5 N / 20 mm or more, advantageously 0.8 N / 20 mm or more, and preferably 1.0 N / 20 mm or more, or more than 1.0 N / 20 mm. A PSA sheet exhibiting the above pre-heating peel force F0 can exhibit good adhesion to an adherend, and can, for example, properly hold the adherend. From the viewpoint of making it easier to obtain better adhesion (e.g., adherend retention performance), in some embodiments, the pre-heating peel force F0 may be, for example, 1.2 N / 20 mm or more, 1.5 N / 20 mm or more, 1.8 N / 20 mm or more, 2.0 N / 20 mm or more, 3.0 N / 20 mm or more, 4.0 N / 20 mm or more, 5.0 N / 20 mm or more, 7.0 N / 20 mm or more, 8.0 N / 20 mm or more, 9.0 N / 20 mm or more, or 10 N / 20 mm or more. The upper limit of the pre-heating peel force F0 is appropriately set depending on the required adhesiveness, and is not limited to a specific range, and may be, for example, approximately 30 N / 20 mm or less, 20 N / 20 mm or less, 15 N / 20 mm or less, 10 N / 20 mm or less, 5.0 N / 20 mm or less, or 3.0 N / 20 mm or less. Note that the pre-heating peel force F0 refers to the peel strength (peel force) against a glass plate measured under conditions of a peel angle of 180 degrees and a speed of 300 mm / min in an environment of 23°C.

[0158] (Post-heat peel strength reduction rate A) Although not particularly limited, in some embodiments, the post-heat peel strength reduction rate A of the PSA sheet, calculated from the pre-heat peel strength F0 and the post-heat peel strength F1 using the following formula: Post-heat peel strength reduction rate A [%] = (1 - F1 / F0) x ​​100; is suitably higher than 20% (e.g., higher than 30%), advantageously higher than 40%, and preferably higher than 50%. A PSA sheet satisfying the above characteristics can exhibit good adhesion to an adherend while exhibiting good releasability (heat-induced releasability) upon peeling after heat treatment. In some preferred embodiments, the post-heat peel strength reduction rate A may 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 post-heat peel strength reduction rate A, the better the heat-induced releasability that can be exhibited. In some embodiments, the post-heat peel strength reduction rate A is preferably less than 99.9%. A PSA sheet having a post-heat peel strength reduction rate A of less than 99.9% maintains its adhesive state with the adherend after heating while exhibiting the desired ease of releasability from the adherend. This prevents the adherend from spontaneously peeling from the PSA sheet due to heating and the resulting defects. From this perspective, the post-heat peel strength reduction rate A may be 99.0% or less, for example, less than 95.0%.

[0159] The pre-heating peel force, post-heating peel force, and the relative relationship therebetween can be achieved and adjusted based on the contents of this specification by appropriately selecting the type of polymer contained in the pressure-sensitive adhesive layer (monomer composition, etc.), the presence or absence, type and amount of other components that may be contained in the pressure-sensitive adhesive layer (e.g., a thermal polymerization initiator or polyfunctional monomer, as described below), and their combinations, as well as the presence or absence, type and amount of use of a crosslinking agent in each pressure-sensitive adhesive layer.

[0160] Furthermore, in an embodiment in which a substrate-attached double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on each side of the substrate is used as the pressure-sensitive adhesive sheet, the pre-heating peel strength and post-heating peel strength of the first pressure-sensitive adhesive layer surface and the second pressure-sensitive adhesive layer surface may be the same or different.

[0161] The pre-heating peel force F0 and the post-heating peel force F1 are specifically measured by the following method. (Pre-heating Peel Force F0) A pressure-sensitive adhesive sheet is cut to a size of 20 mm wide and 100 mm long, and the adhesive surface of the pressure-sensitive adhesive sheet is bonded to an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate with polished edges) as an adherend under an environment of 23°C and 50% RH by rolling a 2 kg roller back and forth once. The adherend with the pressure-sensitive adhesive sheet attached is left to stand for 6 hours under the same environment, and this is used as an evaluation sample. The evaluation sample is set in a tensile tester under an environment of 23°C and 50% RH, and the pressure-sensitive adhesive sheet is peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min, and the peel strength (pre-heating peel force) F0 [N / 20 mm width] is measured. The tensile tester may be a Shimadzu EZ-S 500N or equivalent. If the PSA sheet used to prepare the evaluation sample is a double-sided PSA sheet, the non-measurement side may be lined with a PET film before the measurement.

[0162] (Post-heat peel force F1) Using a pressure-sensitive adhesive sheet, an evaluation sample is prepared using the method described above for measuring the pre-heat peel force F0. The obtained evaluation sample is heated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand in an environment of 23°C and 50% RH for 30 minutes. The evaluation sample is then placed in a tensile tester under the same conditions, and the peel strength (post-heat peel force) F1 [N / 20 mm width] is measured when the pressure-sensitive adhesive sheet is peeled from the adherend at a peel angle of 180° and a speed of 300 mm / min. The adherend, tensile tester, and other factors are the same as those for measuring the pre-heat peel force F0.

[0163] <First Member and Second Member> The materials of the first member and the second member are not particularly limited, and various materials exemplified as adherend materials described below can be used. For example, a material containing one or more of glass, semiconductor material (e.g., silicon wafer), metal material, ceramic material, and resin material can be used. In the technology disclosed herein, glass, semiconductor material, metal material, and ceramic material can be used as the first member and the second member. These materials have a predetermined heat resistance, so the heat-separation technology disclosed herein can be applied. Furthermore, the above materials are typical examples of rigid materials. When the first member and the second member are both rigid, deformation of the members cannot be used to separate the members, but by applying the separation method disclosed herein, the bond between the rigid members can be easily released. Furthermore, thin glass and semiconductor material are typical examples of brittle materials and hard-brittle materials. By applying the separation method disclosed herein to a structure in which members made of such materials are bonded, the members can be separated without damaging the members. The materials of the first and second members may be the same or different.

[0164] The term "rigid body" refers to an object having a rigidity and size that is not substantially deformed by human force. Although not particularly limited, the term "rigid body" in this specification refers to an object having a tensile modulus of elasticity of 1×10 １０ Pa or more; and bending rigidity is 0.01 Pa m ３ or more;

[0165] The tensile modulus refers to the tensile modulus measured in accordance with JIS K7161. More specifically, it is measured by the following method. [Tensile Test] A test specimen is prepared by cutting a measurement object into a strip of 10 mm width. This test specimen is stretched in accordance with JIS K7161 under the following conditions to obtain a stress-strain curve. (Stretching Conditions) Measurement temperature: 25°C Tensile speed: 300 mm / min Chuck distance: 50 mm As the tensile tester, a universal tension-compression tester (device name "Tension-Compression Tester, TCM-1kNB", manufactured by Minebea Co., Ltd.) or an equivalent can be used. The tensile modulus can be determined from the linear regression of the stress-strain curve. In addition, the bending rigidity value D [Pa m ３ ] is expressed by the formula: D = Eh, where h [m] is the thickness of the material, ν is the Poisson's ratio of the material, and E [Pa] is the tensile modulus of elasticity. ３ / 12(1-ν ２ ) ;

[0166] In some embodiments, the first member and the second member may be non-transparent to light (typically non-transparent to ultraviolet light). Examples of such non-transparent member materials include semiconductor materials such as silicon wafers and metal materials. According to the technology disclosed herein, the adhesive strength of a thermosetting adhesive can be reduced by heat treatment, making it possible to separate the non-transparent member in situations where a non-transparent member, such as a non-transparent member, cannot be used with a UV-release adhesive.

[0167] In some embodiments, for example, when the first member is a glass plate or a semiconductor wafer, the second member may be a plate (also referred to as a support stand) that supports the first member. For example, a combination of the first member and the second member described above may be used in the processing of optical components including glass plates or semiconductor wafers. Examples of the support stand include those having one or more flow hole openings on the surface that adheres to the adhesive portion (i.e., the surface on which the pressure-sensitive adhesive sheet is placed). The support stand is typically made of metal, but may also be made of a ceramic material or a resin material.

[0168] The thickness of the first member and / or the second member is not particularly limited, and in some embodiments, may be, for example, approximately 0.05 mm or more, approximately 0.1 mm or more, 0.2 mm or more, 0.3 mm or more, or approximately 0.5 mm or more. Glass (e.g., a glass plate), semiconductor material (e.g., a silicon wafer), metal material (e.g., a metal plate), or ceramic material (e.g., a ceramic plate) having a thickness greater than a certain level may have rigid properties, and therefore the application of the technology disclosed herein is advantageous. In some embodiments, the thickness may be approximately 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, or 5 mm or more. The maximum thickness of the first member and / or the second member is not particularly limited, and may be approximately 30 cm or less, approximately 10 cm or less, approximately 1 cm or less, approximately 5 mm or less, or approximately 2 mm or less. In some embodiments, the thickness of the first member and / or the second member may be approximately 1 mm or less (e.g., less than 1 mm), 0.7 mm or less, 0.5 mm or less (e.g., less than 0.5 mm), or 0.3 mm or less. Glass (e.g., a glass plate) and semiconductor materials (e.g., silicon wafers) having a thickness of a certain amount or less may have the properties of brittle materials (typically hard and brittle materials), and therefore, there are great advantages to applying the technology disclosed herein.

[0169] <Applications> The applications to which the separation method and pressure-sensitive adhesive sheet disclosed herein can be applied are not particularly limited. They can be used in a variety of applications requiring the separation of components bonded with a pressure-sensitive adhesive. Examples of such applications include masking applications requiring heat resistance from the pressure-sensitive adhesive sheet, temporary fixation applications, and protective applications. Pressure-sensitive adhesive sheets can also be preferably used as process materials that are fixed to and peeled from adherends in the manufacturing process of electronic devices and electronic components. Suitable applications for the separation method and pressure-sensitive adhesive sheet disclosed herein include semiconductor device manufacturing applications. For example, pressure-sensitive adhesive sheets can be preferably used as wafer-fixing sheets that fix semiconductor wafers to fixing plates in semiconductor wafer processing (typically silicon wafer processing). Pressure-sensitive adhesive sheets disclosed herein can also be preferably used as protective sheets that protect wafers during the wafer processing. In particular, pressure-sensitive adhesive sheets with heat resistance and easy peelability are preferably used during the manufacturing of semiconductor devices, as they may be exposed to heat during processing steps, etc.

[0170] The separation method and pressure-sensitive adhesive sheet disclosed herein can also be applied to optical applications. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be used as an optical pressure-sensitive adhesive sheet used, for example, for bonding optical components (for bonding optical components) or for manufacturing products (optical products) using the optical components. The optical component refers to a component having optical properties (for example, polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical component is not particularly limited as long as it has optical properties, but examples include components constituting devices (optical devices) such as display devices (image display devices) and input devices, or components used in these devices. Examples of the display device include liquid crystal display devices, organic EL (electroluminescence) display devices, PDPs (plasma display panels), electronic paper, etc. Examples of the input device include touch panels, etc.

[0171] The separation method and pressure-sensitive adhesive sheet disclosed herein are also suitable for applications in which brittle materials (typically hard and brittle materials) such as glass and semiconductor materials are bonded together and then separated. For example, the separation method and pressure-sensitive adhesive sheet disclosed herein can be preferably used in applications in which two adherends are fixed together, at least one of which is made of a brittle material such as glass or semiconductor material.

[0172] The type of material (adherend material) to be attached as disclosed herein is not particularly limited. The pressure-sensitive adhesive sheet disclosed herein can be used for fixing or protecting various members or materials. Examples of adherend materials include glass such as alkali glass or alkali-free glass; semiconductor materials such as silicon wafers; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; and resin materials such as polyester resins such as PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, and transparent polyimide resins. Suitable examples of adherend materials include glass materials such as alkali glass and semiconductor wafers. The glass material may be, for example, a glass plate having a surface partially provided with a transparent conductive film (e.g., an ITO (indium tin oxide) film) or an FPC (flexible printed circuit board), as used in tablet computers, mobile phones, organic LEDs (light-emitting diodes), etc.

[0173] The present specification discloses the following: [1] A method for separating at least one of a first member and a second member from a structure including a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhering the first member and the second member after a heat treatment, wherein the adhesive portion has a curable adhesive layer, and the separation method includes a step of supplying a fluid to the adhesive portion from the first member side or the second member side (a fluid supplying step). [2] The separation method according to [1] above, wherein the adhesive layer is in contact with the first member, the adhesive portion has a hole communicating with the first member and the second member, and the fluid supplying step is a step of supplying the fluid to the hole in the adhesive portion from the second member side. [3] The separation method according to [1] above or [2] above, wherein the adhesive layer includes an ethylenically unsaturated group and a radical polymerization initiator. [4] The separation method according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer is a thermosetting pressure-sensitive adhesive layer. [5] The separation method according to any one of [1] to [4] above, wherein the radical polymerization initiator is a thermal polymerization initiator. [6] The separation method according to any one of [1] to [5] above, wherein the first member and the second member are optically non-transparent. [7] The separation method according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive layer has a gel fraction increase of 10% or more after heat treatment at 180°C for 30 minutes. [8] The separation method according to any one of [1] to [7] above, wherein the pressure-sensitive adhesive layer has a Young's modulus Y1 [MPa] after heat treatment at 180°C for 30 minutes that is 100 times or more the Young's modulus Y0 [MPa] before heating. [9] The separation method according to any one of [1] to [8] above, wherein the adhesive portion consists of the pressure-sensitive adhesive layer, or has a laminated structure including a first pressure-sensitive adhesive layer as the pressure-sensitive adhesive layer, a base layer, and a second pressure-sensitive adhesive layer in this order.

[10] A pressure-sensitive adhesive sheet used as the adhesive portion in the separation method according to any one of [1] to [9] above, the pressure-sensitive adhesive sheet having a curable pressure-sensitive adhesive layer.

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer having holes formed therein, the pressure-sensitive adhesive layer including an ethylenically unsaturated group and a radical polymerization initiator.

[0174] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0175] <Evaluation Method> (Gel Fraction) The gel fraction of the PSA layer (weight ratio of ethyl acetate insoluble matter) is measured by the following method. Approximately 0.1 g of a PSA sample (weight Wg1) is wrapped in a purse-shaped porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane used is available from Nitto Denko Corporation under the trade name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent. The wrapper is immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23° C.) for 7 days to elute only the sol component in the PSA layer out of the membrane. The wrapper is then removed, the ethyl acetate adhering to the outer surface is wiped off, and the wrapper is dried at 130° C. for 2 hours, and the weight of the wrapper (Wg4) is measured. The gel fraction of the PSA layer can be determined by substituting each value into the following formula: Gel fraction [%] = [(Wg4 - Wg2 - Wg3) / Wg1] x 100 The gel fraction of the PSA layer is measured initially (gel fraction before heating) and after the PSA layer is heat-treated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand in an environment of 23°C and 50% RH for 30 minutes (gel fraction after heating).

[0176] (Young's Modulus) A pressure-sensitive adhesive layer is prepared with both sides covered with release liners, and cut together with the release liners to a size of 80 mm wide (when the thickness of the pressure-sensitive adhesive layer is 30 μm) and 30 mm long. One release liner is removed from the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is wound up on the other release liner in the longitudinal direction, taking care not to trap air bubbles, to prepare a 30 mm long rod-shaped sample. The rod-shaped sample is placed in a tensile tester (manufactured by ORIENTEC, product name "RTC-1150A") and pulled under conditions of a measurement temperature of 23°C, a chuck distance of 10 mm, and a pulling speed of 50 mm / min. The initial modulus is determined from the rise of the resulting stress-strain curve (S-S curve), and this is taken as the Young's modulus [MPa] of the pressure-sensitive adhesive layer. The reason for cutting the pressure-sensitive adhesive layer to a width of 80 mm is that the cross-sectional area of ​​the pressure-sensitive adhesive layer in the cross section along the width direction is 2 to 2.5 mm. ２ For example, when the adhesive layer thickness is not 30 μm as in Comparative Example 1 (adhesive layer thickness 10 μm), it is desirable to adjust the cutting width depending on the thickness of the adhesive layer so that the cross-sectional area is approximately the same. The Young's modulus of the adhesive layer is measured initially (Young's modulus before heating) and after the adhesive layer is heat-treated in an oven at 180° C. for 30 minutes, removed from the oven, and left to stand in an environment of 23° C. and 50% RH for 30 minutes (Young's modulus after heating).

[0177] Example 1 (Preparation of Pressure-Sensitive Adhesive Composition) A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer was charged with 100 parts of a monomer component containing methoxyethyl acrylate (MEA), acryloylmorpholine (ACMO), and hydroxyethyl acrylate (HEA) in a molar ratio of 80:20:20, and 65 parts of toluene as a polymerization solvent. 0.2 parts of benzoyl peroxide was added as a thermal polymerization initiator, and a polymerization reaction (solution polymerization) was carried out for 6 hours at 61°C under a nitrogen atmosphere to obtain a solution containing an acrylic polymer a. To this solution of acrylic polymer a, methacryloyloxyethyl isocyanate (MOI) in an amount equivalent to 16 moles relative to 20 moles of HEA used as a raw material for the acrylic polymer a was added, and an addition reaction treatment was carried out in an air stream at 50°C for 48 hours to obtain a solution of an acrylic polymer A having a methacryloyl group at the side chain end. To 100 parts of acrylic polymer A, 10 parts of dipentaerythritol hexaacrylate (DPHA) as a polyfunctional monomer, 0.3 parts of an isocyanate crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name "Takenate D-101E"), and 0.8 parts of benzoyl peroxide (manufactured by NOF Corporation, product name "Niper BW", SADT: 75°C) as a thermal polymerization initiator were added and mixed uniformly to prepare a pressure-sensitive adhesive composition according to this example.

[0178] (Preparation of Pressure-Sensitive Adhesive Sheet) The pressure-sensitive adhesive composition obtained above was applied to the release surface of a commercially available PET release liner and dried at 80°C for 5 minutes to form a 30 μm thick pressure-sensitive adhesive layer. The release surface of another commercially available PET release liner was then bonded to this pressure-sensitive adhesive layer. This was then subjected to aging at 50°C for 3 days. In this way, a substrate-less double-sided pressure-sensitive adhesive sheet having a thickness of 30 μm and both sides protected by the two PET release liners was obtained.

[0179] (Fabrication of Structure) The double-sided PSA sheet with release liner was cut to a size of 16 cm square, and one release liner was peeled off from the double-sided PSA sheet to expose the second adhesive surface, which was then bonded to a stainless steel (SUS) plate (5 mm thick, approximately 20 cm square) serving as a second member. This SUS plate had a through hole (opening diameter approximately 1 cm) near the center. Then, using a drill, a through hole with a diameter similar to that of the opening in the SUS plate was formed in the double-sided PSA sheet to match the opening of the through hole in the SUS plate. Next, the other release liner was peeled off from the double-sided PSA sheet to expose the first adhesive surface, which was then bonded to a silicon wafer (300 μm thick, 6-inch mirror wafer manufactured by Shin-Etsu Chemical Co., Ltd.) serving as a first member. In this way, a structure having the cross section shown schematically in FIG. 1 was obtained. This structure had, in this order, a silicon wafer (first member), a PSA sheet (adhesive portion), and a SUS plate (second member).

[0180] Example 2 A pressure-sensitive adhesive composition was prepared using the same method as in Example 1. The pressure-sensitive adhesive composition was applied to the release surface of a commercially available PET release liner and dried at 80°C for 5 minutes to form a 30 μm-thick pressure-sensitive adhesive layer. Two of these pressure-sensitive adhesive layers were prepared and bonded to each side of a 12.5 μm-thick polyimide (PI) film (product name "Kapton 50H", manufactured by DuPont-Toray Co., Ltd.). Aging was then performed at 50°C for 3 days. In this manner, a substrate-attached double-sided pressure-sensitive adhesive sheet having a 30 μm-thick pressure-sensitive adhesive layer was obtained. This pressure-sensitive adhesive sheet had a first pressure-sensitive adhesive layer, a PI film (substrate layer), and a second pressure-sensitive adhesive layer, in that order, with the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer having the same composition. Each adhesive surface of the pressure-sensitive adhesive sheet was protected by a PET release liner. Except for using the double-sided PSA sheet with the substrate, a structure having a silicon wafer (first member), a PSA sheet (adhesive portion), and a SUS plate (second member) in this order was obtained in the same manner as in Example 1. This structure has a cross section as shown schematically in Figure 2.

[0181] Example 3 A pressure-sensitive adhesive composition was prepared using the same method as in Example 1, except that the polyfunctional monomer and thermal polymerization initiator were not added. A substrate-attached double-sided pressure-sensitive adhesive sheet having, in this order, a first pressure-sensitive adhesive layer, a PI film (substrate layer), and a second pressure-sensitive adhesive layer was obtained using the same method as in Example 2, except that a pressure-sensitive adhesive layer formed using the resulting pressure-sensitive adhesive composition was used as the second pressure-sensitive adhesive layer. The first pressure-sensitive adhesive layer of this pressure-sensitive adhesive sheet was the same as the first pressure-sensitive adhesive layer of Example 2. A structure having, in this order, a silicon wafer (first member), a pressure-sensitive adhesive sheet (adhesive portion), and a SUS plate (second member) was obtained using the same method as in Example 2, except that the substrate-attached double-sided pressure-sensitive adhesive sheet was used. This structure has a cross-section as schematically shown in FIG. 2 .

[0182] Examples 4 and 5 A structure having a cross section as schematically shown in FIG. 1 was obtained in the same manner as in Example 1, except that the first member was changed to a stainless steel plate having a thickness of 5 mm (Example 4) or a glass plate having a thickness of 300 μm (Example 5).

[0183] Comparative Example 1 A reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer was charged with 97 parts of n-butyl acrylate (BA), 3 parts of acrylic acid (AA), and 43 parts of ethyl acetate as a polymerization solvent. 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was then added as a thermal polymerization initiator, and a polymerization reaction (solution polymerization) was carried out at 61°C for 6 hours under a nitrogen atmosphere to obtain a solution containing acrylic polymer B. 0.5 parts of an epoxy-based crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "Tetrad C") per 100 parts of acrylic polymer B was added to the solution of acrylic polymer B, and the mixture was mixed uniformly to prepare a pressure-sensitive adhesive composition. A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that a 10 μm-thick pressure-sensitive adhesive layer was formed using the pressure-sensitive adhesive composition obtained above. A structure was obtained using the pressure-sensitive adhesive sheet.

[0184] <Separation test> The structure according to each example was heat-treated in an oven at 180°C for 30 minutes, removed from the oven, and left to stand in an environment of 23°C and 50% RH for 30 minutes. Air was then supplied at a predetermined pressure to the flow holes of the second member to attempt separation of the first member. If the members could be separated without damage, the result was judged as "Good" (passed). If the members could not be separated, the result was recorded as "impossible to separate."

[0185] The outline of each example and the evaluation results are shown in Table 1.

[0186]

[0187] As shown in Table 1, the structures according to Examples 1 to 5, in which the adhesive sheet serving as the adhesive portion had a curable adhesive layer, passed the separation test. In Examples 1 to 3, a thin silicon wafer could be separated without damage, and in Example 5, a thin glass plate could be separated without damage. In addition, in Example 4, 5 mm thick SUS plates bonded together could be easily separated in the vertical direction. On the other hand, in Comparative Example 1, in which a non-curable adhesive was used, the members could not be separated in the separation test. In the separation test, the first and second members of the structures according to Examples 1 to 5 were held together without peeling from the adhesive portion after the heat treatment and before the air supply.

[0188] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0189] DESCRIPTION OF SYMBOLS 10 First member 10A Surface (surface in contact with adhesive portion) 20 Second member 25 Flow hole 30 Adhesive portion (adhesive sheet) 30A First adhesive surface 30B Second adhesive surface 31 Curable adhesive layer (first adhesive layer) 32 Second adhesive layer 34 Base layer 35 Hole 100, 200 Structure A Air

Claims

1. A method for separating at least one of a first member and a second member from a structure comprising a first member, a second member, and an adhesive portion disposed between the first member and the second member and adhering to the first member and the second member after a heat treatment, wherein the adhesive portion has a curable adhesive layer, and the separation method includes a step of supplying a fluid to the adhesive portion from the first member side or the second member side (fluid supply step).

2. The separation method according to claim 1, wherein the adhesive layer is in contact with the first member, the adhesive portion has a hole communicating with the first member and the second member, and the fluid supplying step is a step of supplying the fluid to the hole in the adhesive portion from the second member side.

3. The separation method according to claim 1 or 2, wherein the adhesive layer contains an ethylenically unsaturated group and a radical polymerization initiator.

4. The separation method according to claim 1 or 2, wherein the adhesive layer is a thermosetting adhesive layer.

5. The method of claim 3, wherein the radical polymerization initiator is a thermal polymerization initiator.

6. The separation method according to claim 1 or 2, wherein the first member and the second member are non-transmissive to light.

7. The separation method according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has an increase in gel fraction of 10% or more after heat treatment at 180°C for 30 minutes.

8. The separation method according to claim 1 or 2, wherein the Young's modulus Y1 [MPa] of the adhesive layer after heat treatment at 180° C. for 30 minutes is 100 times or more greater than the Young's modulus Y0 [MPa] before heating.

9. A separation method as described in claim 1 or 2, wherein the adhesive portion is composed of the adhesive layer, or has a laminated structure including a first adhesive layer as the adhesive layer, a base layer, and a second adhesive layer in this order.

10. An adhesive sheet used as an adhesive part in the separation method according to claim 1 or 2, comprising a curable adhesive layer.

11. An adhesive sheet having an adhesive layer, the adhesive layer having holes formed therein, the adhesive layer containing an ethylenically unsaturated group and a radical polymerization initiator.

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