Adhesive sheet

Abstract

Provided is an adhesive sheet having an adhesive layer containing a polymer, a monomer, and a thermal polymerization initiator. The polymer contains an ethylenically unsaturated group, and the monomer also contains an ethylenically unsaturated group. The thermal polymerization initiator contains a peroxide-based polymerization initiator.

Description

Technical Field

[0001] The present invention relates to adhesive sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2023-011970 filed on January 30, 2023, and Japanese Patent Application No. 2023-122021 filed on July 26, 2023, the entire contents of which are incorporated herein by reference. Background Art

[0003] Generally, adhesives (also called pressure-sensitive adhesives. The same applies hereinafter) have the following properties: they are in a soft solid (viscoelastic) state in a temperature range near room temperature and are easily adhered to an adherend by pressure. In view of the excellent operability of pasting to an adherend, adhesives are widely used in various fields in the form of adhesive sheets with a support having an adhesive layer on a support, or in the form of adhesive sheets without a support. Among such adhesives, there are adhesives that are used by adhering to an adherend and are removed from the adherend after the purpose of the adhesion is completed. As prior art documents disclosing such prior art, Patent Documents 1 to 4 can be cited. Patent Documents 1 to 4 disclose thermosetting adhesives.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-29105

[0007] Patent Document 2: Japanese Patent Application Publication No. 2016-204617

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-56101

[0009] Patent Document 4: Japanese Patent Application Publication No. 1998-209087

[0010] Non-patent literature

[0011] Non-Patent Literature 1: Simone Napolitano, 'Irreversible adsorption of polymer melts and nanoconfinement effects', SoftMatter, 2020, 16, pp. 5348-5365

[0012] Non-Patent Document 2: Ben O'Shaughnessy and Dimitrios Vavylonis, 'No n-Equilibrium in Adsorbed Polymer Layers', J. Phys.: Condens. Matter, 17, 2005, pp. R63-99 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] For adhesives used for peeling and removing from adherends, it is required to have good adhesion during the adhesion to the adherend and to be able to be easily peeled from the adherend after the adhesion purpose is completed. For example, for adhesives suitable for adherends to be treated by heat, it is expected to have easy peelability that allows easy peeling from the adherend after being heated in a state of being adhered to the adherend. However, if adherends such as glass, metal, and resin are heated at high temperatures while being adhered to the adhesive, there is a risk of adverse conditions such as the adhesive being adsorbed on the surface of the adherend, thereby increasing the peeling force (heavy peeling), reducing the peeling property, or generating residual adhesive. In this regard, see the various polymers described in non-patent documents 1 to 2 that have adsorption force by heating. For example, in the case of thermosetting adhesives such as those described in patent documents 1 to 4, it is difficult to make the curing of the adhesive during high-temperature heating appear before the adsorption of the adhesive to the adherend, and the reduction in peeling force and the suppression of the increase in peeling force based on the curing of the adhesive cannot be obtained, and stable easy peelability cannot be obtained after high-temperature heating.

[0015] Based on this background, the inventors of this application have conducted research and development with an eye on thermosetting adhesives containing a thermal polymerization initiator in the adhesive. As a result, they have successfully obtained an adhesive that is easy to peel (heat-peelable) after being attached to an adherend and heated at a high temperature. The above-mentioned heat-peelable property usually also has easy peelability after a heat treatment in which the peeling force increases, and therefore can also be referred to as heat-resistant peelable property. Such adhesive sheets with heat-peelable and heat-resistant peelable properties are expected to be applied to various applications and various adherends due to their usefulness. However, the results of the inventors' research found that, depending on the adherend material, there is a situation where the peeling force does not decrease when heated and the heat-peelable property cannot be obtained. Specifically, for example, the following phenomenon was confirmed: even if an adhesive that exhibits good heat-peelable property is applied to a glass adherend, it becomes difficult to peel off the adherend itself after heating when the surface is composed of an organic material such as an epoxy resin. Therefore, they conducted in-depth research and successfully created an adhesive that can also exhibit heat-peelable property on the surface of an organic material, and can exhibit heat-peelable property regardless of the adherend material, thereby completing the present invention. That is, the present invention provides a pressure-sensitive adhesive sheet that can exhibit heat-peelability with respect to various adherends, such as adherends made of organic materials.

[0016] Means for solving problems

[0017] According to this specification, an adhesive sheet having an adhesive layer comprising a polymer, a monomer, and a thermal polymerization initiator is provided. The polymer comprises an ethylenically unsaturated group, and the monomer also comprises an ethylenically unsaturated group. In addition, the thermal polymerization initiator comprises a peroxide-based polymerization initiator. According to the above configuration, since both the polymer and the monomer contained in the adhesive layer comprise ethylenically unsaturated groups, and a peroxide-based polymerization initiator is used as the thermal polymerization initiator, the curing reaction of the adhesive layer proceeds rapidly upon heating. Therefore, for example, heat-peelable properties can be exhibited even on the surface of organic materials, and heat-peelable properties can be reliably demonstrated. According to the above adhesive sheet, heat-peelable properties can be exhibited on various adherends, such as adherends comprising organic materials. Such adhesive sheets have a wide range of applications and are useful.

[0018] In some preferred embodiments, the adhesive layer includes a multifunctional acrylate monomer as the monomer. The effects of the technology disclosed herein can be ideally achieved by using a multifunctional acrylate monomer as the monomer.

[0019] In some preferred embodiments, the content of the monomer in the adhesive layer is less than 50 parts by weight relative to 100 parts by weight of the polymer. According to the technology disclosed herein, by ensuring that the monomer content in the adhesive layer is within the above range, the desired heat-peelable properties can be ideally achieved.

[0020] In some embodiments, the adhesive layer has a gel fraction of 50% or more before heating. The technology disclosed herein is preferably implemented with a configuration having an adhesive layer having a gel fraction of a predetermined value or more.

[0021] In some preferred embodiments, the Young's modulus Y1 [MPa] of the adhesive layer after heat treatment at 180°C for 30 minutes is 200 times or more the Young's modulus Y0 [MPa] before heating, that is, the Young's modulus change ratio after heating (Y1 / Y0) is 200 or more. A higher Young's modulus change ratio after heating indicates a higher degree of curing of the adhesive layer during heating, and thus tends to facilitate excellent heat-peelability.

[0022] The adhesive sheet disclosed herein exhibits heat-peelability from various adherends, including adherends comprising organic materials. Therefore, for example, it can be advantageously applied to and subsequently peeled from a substrate having an organic surface. The adhesive sheet disclosed herein exhibits excellent heat-peelability (heat-resistant peelability), allowing it to be easily peeled from organic material surfaces even after exposure to temperatures exceeding 150°C, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] [ Figure 1 ] is a cross-sectional view schematically showing an example of a form of an adhesive sheet. DETAILED DESCRIPTION

[0024] The following describes preferred embodiments of the present invention. Except for matters specifically mentioned in this specification, matters necessary for implementing the present invention can be understood by those skilled in the art based on the teachings regarding the implementation of the invention described in this specification and the common technical knowledge at the time of filing the application. The present invention can be implemented based on the disclosure in this specification and the common technical knowledge in the field.

[0025] It should be noted that in the following drawings, components and parts that perform the same function may be described with the same reference numerals, and repeated descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic for the purpose of clearly explaining the present invention and do not necessarily accurately represent the dimensions or reduction ratios of the actual product provided.

[0026] In this specification, the "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive. This rubbery polymer is a polymer that exhibits rubber elasticity in a temperature range near room temperature. Furthermore, in this specification, the term "main component," unless otherwise specified, refers to a component contained in an amount exceeding 50% by weight.

[0027] In this specification, the term "acrylic polymer" refers to a polymer comprising monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule. The term "acrylic polymer" is defined as a polymer comprising monomer units derived from an acrylic monomer.

[0028] In addition, in this specification, the so-called "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, the so-called "(meth)acryloyl group" is a general term for both acryloyl and methacryloyl groups. Therefore, the concept of acrylic monomers mentioned here can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers). Similarly, in this specification, the so-called "(meth)acrylic acid" is a general term for both acrylic acid and methacrylic acid, and the so-called "(meth)acrylate" is a general term for both acrylate and methacrylate. The same applies to other similar terms.

[0029] In this specification, "weight" can be replaced by "mass." For example, "weight %" can be replaced by "mass %" and "parts by weight" can be replaced by "parts by mass."

[0030] <Adhesive Sheet>

[0031] The adhesive sheet disclosed herein comprises an adhesive layer and is constituted. The adhesive sheet can be an adhesive sheet with a substrate having the form of the above-mentioned adhesive layer on one or both sides of a non-peelable substrate (supporting substrate), or an adhesive sheet without a substrate such as the form in which the above-mentioned adhesive layer is retained in a release liner (that is, an adhesive sheet without a non-peelable substrate. Typically, the adhesive sheet is formed by an adhesive layer). In the concept of the adhesive sheet mentioned herein, materials referred to as adhesive tapes, adhesive labels, adhesive films, etc. can be included. The adhesive sheet disclosed herein can be in roll form or in monolithic form. Alternatively, it can be an adhesive sheet further processed into a form of various shapes.

[0032] The cross-sectional structure of the adhesive sheet is shown in Figure 1 .like Figure 1As shown, the adhesive sheet 1 has an adhesive surface 1A, which is a single-sided adhesive sheet having an adhesive layer 20 on the surface 10A on one side of a sheet-like substrate layer (support substrate) 10. The adhesive sheet 1 is used in such a way that the surface 20A of the adhesive layer 20 serving as its adhesive surface 1A is pasted on an adherend. The back surface 10B of the substrate layer 10 (the surface on the opposite side to the surface 10A on one side) is also the back surface 1B of the adhesive sheet 1 and constitutes the outer surface of the adhesive sheet 1. The adhesive sheet 1 before use (i.e., before adhering to an adherend) can be a form of an adhesive sheet 50 with a release liner protected by a release liner 30 in which the adhesive surface 1A is at least protected by the release liner 30 on the adhesive layer 20 side. Alternatively, the surface (back surface) 10B on the other side of the substrate layer 10 can be a release surface, and the adhesive layer 20 can be wound into a roll so that the adhesive layer 20 is in contact with the back surface so that its surface (adhesive surface 1A) is protected.

[0033] <Adhesive Layer>

[0034] (polymer)

[0035] In the technology disclosed herein, the type of adhesive is not particularly limited. The adhesive layer may comprise one or more polymers in various rubber-like polymers such as acrylic polymers, rubber polymers (such as natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers that can be used in the field of adhesives. The above polymers are used as base polymers in the adhesive and can function as structural polymers of the molding adhesive. From the viewpoints of adhesive performance, cost, etc., it is preferred to adopt an adhesive comprising an acrylic polymer or a rubber polymer as the base polymer. Among them, it is preferred to use an adhesive (acrylic adhesive) having excellent heat resistance as the base polymer.

[0036] The following description will focus mainly on acrylic pressure-sensitive adhesives and pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive, ie, an acrylic pressure-sensitive adhesive layer. However, the pressure-sensitive adhesive layer disclosed herein is not intended to be limited to acrylic pressure-sensitive adhesive layers.

[0037] (Acrylic polymer)

[0038] In some embodiments, an acrylic polymer is used in which more than 50% by weight of the monomer components constituting the polymer are acrylic monomers. The proportion of acrylic monomers in the above-mentioned monomer components is suitably 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 85% by weight or more, and for example, 90% by weight or more. The upper limit of the proportion of acrylic monomers in the monomer components constituting the acrylic polymer is 100% by weight. From the perspective of obtaining the effect of using non-acrylic monomers, the proportion of the above-mentioned acrylic monomers can be, for example, 98% by weight or less, 95% by weight or less, or 92% by weight or less. The acrylic monomers can be used alone or in combination of two or more.

[0039] In some preferred embodiments, the monomer component includes an alkoxy-containing (meth)acrylate. Acrylic polymers containing an alkoxy-containing (meth)acrylate as a monomer component tend to exhibit good adhesion and, for example, are more compatible with monomers contained in the adhesive layer described below (hereinafter sometimes referred to as "combining monomers" to distinguish them from monomer components used in the synthesis of the polymer). Alkoxy-containing (meth)acrylates can be used alone or in combination of two or more.

[0040] Examples of (meth)acrylates containing an alkoxy group 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. The like can be cited. Among them, alkoxyalkyl (meth)acrylates are preferred, and among them, alkoxyalkyl (meth)acrylates having an alkoxy group having 1 to 4 carbon atoms (eg, 1, 2, or 3 carbon atoms) are more preferred, and methoxyethyl (meth)acrylate is particularly preferred.

[0041] The content of the alkoxy-containing (meth)acrylate in the monomer components constituting the acrylic polymer is not particularly limited. From the perspective of effectively obtaining the effects brought about by the use of the alkoxy-containing (meth)acrylate, the content of the alkoxy-containing (meth)acrylate in the above-mentioned monomer components is generally about 1% by weight or more, for example, it can be 10% by weight or more, or it can be 30% by weight or more. In some embodiments, from the perspective of adhesive properties such as adhesion and compatibility with the matching monomers, the content of the alkoxy-containing (meth)acrylate in the above-mentioned monomer components is, for example, greater than 30% by weight, preferably greater than 40% by weight, more preferably greater than 50% by weight (for example, greater than 50% by weight), and further preferably greater than 55% by weight. From the perspective of introducing ethylenically unsaturated groups into the polymer, for example, obtaining the effect of other copolymerizable monomers such as monomers containing functional groups, in some embodiments, the upper limit of the content of the alkoxy-containing (meth)acrylate in the above-mentioned monomer component is approximately 99% by weight or less, and can be 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight or less, further preferably 65% by weight or less, and can also be 60% by weight or less.

[0042] In some other embodiments, the monomer component constituting the acrylic polymer may be a component containing a linear alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms at the ester terminal. Hereinafter, a linear alkyl (meth)acrylate having an alkyl group with X to Y carbon atoms at the ester terminal may be referred to as “C X-Y Alkyl (meth) acrylate". It should be noted that in this specification, the so-called "chain" is used to include linear and branched. The above-mentioned chain alkyl (meth) acrylate can be used alone or in combination of two or more.

[0043] As C 1-20Specific non-limiting examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (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.

[0044] When using C 1-20 In the embodiment in which the alkyl (meth)acrylate is a monomer component constituting the acrylic polymer, 1-20 Alkyl (meth) acrylate, preferably at least C 4-20 Alkyl (meth) acrylate, more preferably at least C 4-18 In some embodiments, as C 1-20 Alkyl (meth) acrylate, preferably C 4-8 Among them, it is more preferable to use C 4-8 Alkyl acrylate. C 4-8 Alkyl (meth)acrylate can be used alone or in combination of two or more. 4-8 The use of alkyl (meth)acrylates tends to easily obtain good adhesive properties (adhesive strength, etc.). For example, as the above-mentioned monomer components, acrylic polymers containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) are preferred, and acrylic polymers containing at least 2EHA are particularly preferred. 1-20 In some other aspects of alkyl (meth) acrylate, C 7-12 Alkyl (meth) acrylate. C 7-12 Alkyl (meth)acrylate can be used alone or in combination of two or more. 7-12 Alkyl (meth) acrylate, preferably C 7-10 Alkyl acrylate, more preferably C 7-9 Alkyl acrylate, more preferably C8 alkyl acrylate.

[0045] When using C 1-20 In the embodiment in which the alkyl (meth)acrylate is used as a monomer component constituting the acrylic polymer, the C 1-20 The content of alkyl (meth) acrylate is not particularly limited. 1-20 Considering the effect of using alkyl (meth)acrylate, in some embodiments, C 1-20 The content of the alkyl (meth)acrylate is generally about 1% by weight or more, for example, 10% by weight or more, 30% by weight or more, or 50% by weight or more (for example, greater than 50% by weight). In addition, in some embodiments, from the perspective of introducing ethylenically unsaturated groups into the polymer and obtaining the effects of other copolymerizable monomers, the above-mentioned C 1-20 The content of the alkyl (meth)acrylate is about 99 wt% or less, 90 wt% or less, about 70 wt% or less, 50 wt% or less (e.g., less than 50 wt%), 30 wt% or less, 10 wt% or less, 1 wt% or less, or 0.1 wt% or less. The above monomer component may also be substantially free of C 1-20 A monomer component of alkyl (meth)acrylate.

[0046] In some embodiments, the monomer components constituting the acrylic polymer preferably include other monomers other than the above-mentioned alkoxyalkyl (meth) acrylate and chain alkyl (meth) acrylate. Such other monomers may be monomers (copolymerizable monomers) that can be copolymerized with alkoxyalkyl (meth) acrylate and chain alkyl (meth) acrylate. For example, the above-mentioned other monomers can be used to introduce ethylenically unsaturated groups into the polymer. As the above-mentioned other monomers, monomers having polar groups (for example, carboxyl groups, hydroxyl groups, rings containing nitrogen atoms, etc.) can be preferably used. Monomers having polar groups can help introduce crosslinking points into acrylic polymers and improve the cohesive force of the adhesive. The other monomers can be used alone or in combination of two or more.

[0047] As other monomers, for example, carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a ring containing a nitrogen atom, 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)acrylates having an alicyclic hydrocarbon group, (meth)acrylates having an aromatic hydrocarbon group, heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, vinyl chloride, halogen atom-containing (meth)acrylates such as fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylates, (meth)acrylates obtained from terpene compound derivative alcohols, etc. can be used.

[0048] When using other monomers such as above, its usage amount is not particularly limited, and it is appropriate to be set as more than 1 % by weight of the overall monomer component. Consider from the viewpoint of the use effect of bringing into play other monomers more well, the usage amount of other monomers can be set as more than 10 % by weight of the overall monomer component, can be set as more than 20 % by weight, also can be set as more than 30 % by weight. In addition, consider from the viewpoint of the equilibrium that easily obtains adhesion properties, it is appropriate to be set as less than 60 % by weight of the overall monomer component in the usage amount of other monomers, preferably be set as less than 50 % by weight (for example, less than 50 % by weight), also can be less than 45 % by weight.

[0049] In some embodiments, the monomer components constituting the acrylic polymer include monomers containing nitrogen atoms. The use of nitrogen-containing monomers enhances the cohesive strength of the adhesive and, ideally, improves adhesion. Examples of nitrogen-containing monomers include monomers containing amide groups, monomers containing amino groups, and monomers containing rings containing nitrogen atoms. Nitrogen-containing monomers can be used alone or in combination of two or more.

[0050] Specific non-limiting examples of the monomer having a nitrogen atom include the following monomers.

[0051] Monomers containing amide groups: for example, (meth)acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(tert-butyl)(meth)acrylamide and the like N,N-dialkyl(meth)acrylamide; N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, N-n-butyl(meth)acrylamide and the like N-monoalkyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylacetamide; monomers having hydroxyl groups and amide groups, for example, N-(2-hydroxyethyl)(meth)acrylamide , N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide and other N-hydroxyalkyl(meth)acrylamide; monomers having alkoxy groups and amide groups, for example, N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide and other N-alkoxyalkyl(meth)acrylamide; and N,N-dimethylaminopropyl(meth)acrylamide, alkoxydiacetone(meth)acrylamide, vinylformamide, vinylacetamide, etc.

[0052] Monomers containing amino groups: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate.

[0053] Monomers having a ring containing a nitrogen atom: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, etc. (for example, lactams such as N-vinyl-2-caprolactam).

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

[0055] There is no particular restriction on the amount of monomers with nitrogen atoms (preferably monomers with rings containing nitrogen atoms). In some embodiments, the amount of monomers with nitrogen atoms in the above-mentioned monomer components can be 1% by weight or more, or 3% by weight or more. In some preferred embodiments, the amount of monomers with nitrogen atoms in the above-mentioned monomer components is 5% by weight or more, more preferably 7% by weight or more, further preferably 9% by weight or more, can be 10% by weight or more, can be 12% by weight or more, or can be 14% by weight or more. The more monomers with nitrogen atoms are used, the more the cohesive force of the adhesive tends to be improved. In addition, in some embodiments, it is appropriate to set the amount of monomers with nitrogen atoms to, for example, 40% by weight or less of the overall monomer component, or it can be set to 35% by weight or less. In some preferred embodiments, the amount of monomers with nitrogen atoms in the above-mentioned monomer components is 30% by weight or less, more preferably 25% by weight or less, further preferably 20% by weight or less, or it can be 18% by weight or less.

[0056] In some embodiments, the monomer component includes a monomer containing a hydroxyl group. By using a monomer containing a hydroxyl group, the cohesion and cross-linking density of the adhesive can be adjusted, and the bonding strength can be improved. In addition, the monomer containing a hydroxyl group is also preferably used as a means for introducing an ethylenically unsaturated group into a polymer. As a monomer containing a hydroxyl group, for example, 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, (meth) acrylate (4-hydroxymethylcyclohexyl) methyl ester and other (meth) acrylate hydroxyalkyl esters can be used. For example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) can be preferably used. The monomer containing a hydroxyl group can be used alone or in combination of two or more.

[0057] The amount used when using a monomer containing a hydroxyl group is not particularly limited, for example, it can be more than 0.01% by weight of the overall monomer component, can be more than 0.1% by weight, or can be more than 0.5% by weight. In some embodiments, the amount of the monomer containing a hydroxyl group is more than 1% by weight of the overall monomer component, more preferably more than 2% by weight, or more than 3% by weight. In some preferred embodiments, the amount of the monomer containing a hydroxyl group is more than 5% by weight of the overall monomer component, more preferably more than 7% by weight, further preferably more than 10% by weight, and particularly preferably more than 12% by weight. Such an amount of monomer containing a hydroxyl group is suitable when using a monomer containing a hydroxyl group as a means of introducing an ethylenically unsaturated group into a polymer. In addition, in some embodiments, it is appropriate to set the amount of the monomer containing a hydroxyl group to, for example, less than 40% by weight of the overall monomer component, preferably less than 30% by weight, more preferably less than 20% by weight, and more preferably less than 15% by weight.

[0058] In some preferred embodiments, as monomer components of acrylic polymers, as monomers having polar groups (monomers containing polar groups), monomers having nitrogen atoms (e.g., monomers containing amide groups such as (meth)acrylamide, monomers containing rings containing nitrogen atoms such as NVP and ACMO) and monomers containing hydroxyl groups (e.g., HEA and 4HBA) are used in combination. This allows for well-balanced adhesion and cohesion. In the embodiment in which monomers having nitrogen atoms and monomers containing hydroxyl groups are used in combination, the amount of monomers having nitrogen atoms is A N The amount of monomer containing hydroxyl group A OH The weight ratio (A N / A OH ) is not particularly limited, and can 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 ) For example, it can be less than 10, less than 5, less than 3, or less than 2.5.

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

[0060] The usage amount of the monomer that contains carboxyl can for example be more than the 0.01 % by weight of monomer component as a whole, can be more than 0.1 % by weight, can be more than 1 % by weight, can be more than 3 % by weight, can be more than 6 % by weight, can also be more than 8 % by weight.The more the usage amount of the monomer that contains carboxyl is, the more the cohesive force of the adhesive is improved.The ratio of the above-mentioned monomer that contains carboxyl can for example be below 20 % by weight, can be below 10 % by weight, can be below 3 % by weight, can be below 1 % by weight (for example, less than 1 % by weight), can also be below 0.1 % by weight.The above-mentioned monomer component can also be the composition that does not actually comprise the monomer that contains carboxyl.

[0061] In addition, as other monomers, it is preferred to use monomers having a functional group (functional group A) that can react with the functional group (functional group B) of the compound having an ethylenically unsaturated group described later. In this manner, the type of other monomers is determined according to the type of the above-mentioned compound. As other monomers with functional group A, for example, preferably a monomer containing a carboxyl group, a monomer containing an epoxy group, a monomer containing a hydroxyl group, a monomer containing an isocyanate group, and particularly preferably a monomer containing a hydroxyl group. By using a monomer containing a hydroxyl group as other monomers, the acrylic polymer has a hydroxyl group. In contrast, as a compound having an ethylenically unsaturated group, for example, by using a monomer containing an isocyanate group, the hydroxyl group of the above-mentioned acrylic polymer reacts with the isocyanate group of the above-mentioned compound, and the ethylenically unsaturated group derived from the above-mentioned compound is introduced into the acrylic polymer.

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

[0063] In the acrylic polymer, as other monomer components, a polyfunctional monomer having at least two ethylenically unsaturated groups such as (meth)acryloyl groups and vinyl groups may be included. By using a polyfunctional monomer as a monomer component, the cohesive force of the adhesive can be increased. The polyfunctional monomer can be used as a cross-linking agent. There are no particular limitations on the polyfunctional monomer. For example, one suitable substance among the substances exemplified as the coordination monomers contained in the adhesive layer described later can be used alone or in combination of two or more.

[0064] The usage amount of multifunctional monomer is not particularly limited, and can be suitably set in a manner to achieve the purpose of use of the multifunctional monomer. The usage amount of multifunctional monomer can be set to less than about 3 wt % of the above-mentioned monomer component, preferably less than about 2 wt %, more preferably less than about 1 wt % (e.g., less than about 0.5 wt %). The lower limit of the usage amount in the case of using multifunctional monomer is greater than 0 wt %, and is not particularly limited. Typically, by setting the usage amount of multifunctional monomer to more than about 0.001 wt % (e.g., more than about 0.01 wt %) of the monomer component, the use effect of the multifunctional monomer can be suitably exerted.

[0065] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthetic methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately adopted. For example, solution polymerization can be preferably adopted. As a monomer supply method when performing solution polymerization, a one-time feeding method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a batch supply (dropping) method, etc. can be appropriately adopted. The polymerization temperature can be appropriately selected according to the types of monomers and solvents used, the type of polymerization initiator, etc., and can be set to, for example, about 20°C to 170°C (typically about 40°C to 140°C).

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

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

[0068] The amount of the polymerization initiator used is not particularly limited and can be a typical 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, for example, about 0.01 to 1 part by weight) of the polymerization initiator can be used per 100 parts by weight of all monomer components to be polymerized.

[0069] (Polymer having ethylenically unsaturated groups)

[0070] The adhesive layer disclosed herein comprises a polymer having ethylenically unsaturated groups such as acryloyl, methacryloyl, vinyl, and allyl. According to the adhesive comprising the polymer having ethylenically unsaturated groups, the ethylenically unsaturated groups possessed by the polymer react when heated, enabling the adhesive to be heat-cured with a high degree of cure, thereby obtaining excellent heat-peelable properties. Furthermore, according to the adhesive comprising the polymer having ethylenically unsaturated groups, the amount of the coordinating monomers can be limited, and sufficient heat-peelable properties, heat-resistant peelable properties, and peel force reduction rate after heating can be achieved.

[0071] In some embodiments, as the polymer having an ethylenically unsaturated group, a polymer having an ethylenically unsaturated group in a side chain can be used. As the monomer component of the polymer having an ethylenically unsaturated group, one or more of the monomer components exemplified as the monomer components of the above-mentioned polymer can be used within the above-mentioned content range.

[0072] The amount of the ethylenically unsaturated group in the polymer with ethylenically unsaturated groups is not particularly limited. From the viewpoints of thermosetting properties, it is appropriate to be set to 0.01mmol (hereinafter, also referred to as mmol / g) or more relative to every 1g of polymer, and can be more than 0.1mmol / g or more than 0.5mmol / g. In addition, it is appropriate to set the amount of the ethylenically unsaturated group in the above-mentioned polymer to be less than 10.0mmol / g, can be less than 5.0mmol / g, can be less than 3.0mmol / g, can be less than 2.5mmol / g or less than 2.0mmol / g.

[0073] The amount of the ethylenically unsaturated group in the polymer can be measured by the following method when the ethylenically unsaturated group is a (meth)acryloyl group, for example.

[0074] First, 0.25 mg of the polymer to be measured was dissolved in 50 mL of THF (tetrahydrofuran), and 15 mL of methanol was added to obtain a solution. Next, 10 mL of 4N sodium hydroxide aqueous solution was added to the solution to obtain a mixed solution. The mixed solution was then stirred at 40°C for 2 hours. Furthermore, 10.2 mL of 4N methanesulfonic acid solution was added to the mixed solution and stirred. To this solution, 5 mL of desalted water was added, followed by 2 mL of methanol to prepare the measurement solution.

[0075] The (meth)acrylic acid content in the measurement solution was measured by HPLC (High Performance Liquid Chromatography) (absolute standard curve method), and the ethylenically unsaturated group content was calculated.

[0076] (HPLC measurement conditions)

[0077] Chromatographic column: Synergi 4μ Polar-RP 80A (4.6 mm × 250 mm) manufactured by Phenomenex

[0078] Column temperature: 40°C

[0079] Flow rate: 1.0 mL / min

[0080] Detector wavelength: 210nm

[0081] Eluent: THF (for HPLC) 55 / buffer (containing 0.2% phosphoric acid, 0.2% triethylamine) 45

[0082] Aqueous solution injection volume: 5μL

[0083] As a method for measuring the content of ethylenically unsaturated groups other than (meth)acryloyl groups, there is exemplified the method of measuring the bromine value in accordance with JIS K2605:1996. In this measurement method, the content of ethylenically unsaturated groups other than (meth)acryloyl groups can be determined by converting the number of grams of bromine (Br2) added to 100 g of the polymer being measured into the number of moles of bromine (Br2) added to 1 g of the polymer.

[0084] The method for introducing ethylenically unsaturated groups into polymers is not particularly limited, and an appropriate method among the methods known to those skilled in the art can be selected. From the viewpoints of molecular design, it is preferably a method for introducing ethylenically unsaturated groups into the side chains of polymers. For example, it is possible to preferably adopt a method in which a compound having a functional group (functional group B) and an ethylenically unsaturated group that can react with the functional group (functional group A) introduced into the acrylic polymer by copolymerization and reacts in a manner such that the ethylenically unsaturated group does not disappear (typically a condensation reaction, an addition reaction). As examples of the combination of functional group A and functional group B, the combination of a carboxyl group and an epoxy group, the combination of a carboxyl group and an aziridine group, the combination of a hydroxyl group and an isocyanate group, etc. can be enumerated. Among them, from the viewpoint of reaction tracking, the combination of a hydroxyl group and an isocyanate group is preferred. From the viewpoints of polymer design, it is particularly preferred that an acrylic polymer has a hydroxyl group and the above-mentioned compound has an isocyanate group.

[0085] As described above, the compound having an ethylenically unsaturated group may have a functional group B that can react with the functional group A. Suitable examples of such compounds include monomers containing an isocyanate group (compounds containing an isocyanate group) such as 2-(meth)acryloyloxyethyl isocyanate. Among them, 2-(meth)acryloyloxyethyl isocyanate is more preferred. 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), an acrylic polymer having an ethylenically unsaturated group can be obtained.

[0086] The amount of the compound having an ethylenically unsaturated group (e.g., an isocyanate group-containing monomer) added is not particularly limited. From the perspective of reactivity with the functional group A (e.g., a hydroxyl group) in the polymer, the amount of the compound having an ethylenically unsaturated group (e.g., an isocyanate group-containing monomer) added can be 1:1 to 2:1 molar amount of the functional group A (M A ) and the molar ratio of functional group B (isocyanate group) (M B ) molar ratio (M A / M B ) is set so as to be in the range of about 0.5 to 2 (for example, 1 to 1.5).

[0087] It should be noted that the adhesive layer may include a polymer having substantially no ethylenically unsaturated groups (a polymer having an amount of ethylenically unsaturated groups less than 0.01 mmol / g) within the scope of the effect brought about by the technology disclosed herein. It is appropriate that the usage amount of the polymer having substantially no ethylenically unsaturated groups is set to be less than 50 wt % of the overall polymer (specifically, base polymer) contained in the adhesive layer, and may be less than 30 wt %, less than 10 wt %, less than 3 wt %, or less than 1 wt %. The adhesive layer may also be a layer that substantially does not include the above-mentioned polymer having substantially no ethylenically unsaturated groups.

[0088] The molecular weight of the polymer (for example, an 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 above polymer is approximately 1×10 4 The above is appropriate, for example, it can be about 10×10 4 By using a polymer having an Mw greater than a predetermined value, cohesion and adhesion can be achieved in a well-balanced manner. In some embodiments, the Mw may be 20×10 4 Above, it can be 30×10 4 Above, it can be about 40×10 4 Above, it can be about 50×10 4 For example, it can be about 55×10 4 The upper limit of the Mw of the above polymer is not particularly limited, and can be, for example, approximately 1000×10 4 Below, it can also be about 100×10 4 Here, Mw refers to a value obtained by gel permeation chromatography (GPC) in terms of standard polystyrene. As a GPC apparatus, for example, the model "HLC-8320GPC" (chromatographic column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used.

[0089] (monomer)

[0090] In addition to the above-mentioned polymer, the adhesive layer also contains a monomer (matching monomer). The above-mentioned monomer has an ethylenically unsaturated group. The ethylenically unsaturated group of the above-mentioned monomer functions as a polymerizable functional group (typically a free radical polymerizable functional group). By making the adhesive layer contain the above-mentioned monomer, the above-mentioned monomer is contained in the adhesive layer in a state before reaction (unreacted). Thus, after the adhesive layer is formed, the above-mentioned monomer contained in the adhesive layer reacts with the ethylenically unsaturated group of the polymer during heat treatment under specified conditions, and the adhesive is heat-cured with a high degree of curing, which can exert excellent heat-resistant and easy-to-peel properties. By including the above-mentioned monomer, a thermosetting adhesive having heat-resistant and easy-to-peel properties can be formed after heat treatment. More specifically, usually, when being attached to an adherend, for example, when heated at a high temperature, the adhesive will be adsorbed on the adherend surface. Therefore, the adhesive strength of the adhesive to the adherend is enhanced, and heavy peeling will occur. According to the technology disclosed herein, by including a polymer and a monomer having an ethylenically unsaturated group together with a thermal polymerization initiator (specifically a peroxide-based polymerization initiator) in the adhesive, the reaction (free radical polymerization reaction) between the monomer and the thermal polymerization initiator is rapidly carried out during heating, and the adhesive can be cured before the adhesive is adsorbed to the adherend. Thus, the adhesion to the adherend can be reduced. Furthermore, even if heating is continued thereafter, the adhesion of the adhesive to the adherend will not increase, but will be maintained within a specified range, so that the adhesive can exhibit excellent heat-resistance. It should be noted that the technology disclosed herein is not limited to the above-mentioned investigation. The above-mentioned monomers can be used alone or in combination of two or more.

[0091] Examples of ethylenically unsaturated groups in the monomers include, but are not limited to, acryloyl, methacryloyl, vinyl, and allyl groups. Suitable examples of ethylenically unsaturated groups include acryloyl and methacryloyl groups. Of these, acryloyl is preferred. Hereinafter, compounds having acryloyl and / or methacryloyl groups may be referred to as acrylic monomers. Furthermore, compounds having vinyl groups may be referred to as vinyl monomers.

[0092] Although not particularly limited, it is appropriate to use a monomer with a molecular weight of 100 or more as the above-mentioned monomer. In some preferred embodiments, the molecular weight of the above-mentioned monomer can be, for example, more than 150, more than 250, more than 300, more than 350, more than 400, more than 450, or more than 500. In addition, the molecular weight of the above-mentioned monomer is generally about 100,000 or less, for example, about 10,000 or less (for example, less than 10,000) is appropriate, preferably 5,000 or less (for example, less than 5,000), less than 1,500, less than 1,000 (for example, less than 1,000), less than 800, or less than 600. The use of the above-mentioned monomer with a molecular weight in the above-mentioned range will become advantageous from the perspective of, for example, the preparation and coating properties of the adhesive composition. It should be noted that the above-mentioned molecular weight is the manufacturer's nominal value or the molecular weight calculated based on the molecular structure. For the above-mentioned monomer with a molecular weight above the specified value, the value of the weight average molecular weight (Mw) converted by standard polystyrene obtained by GPC can also be used.

[0093] In some preferred embodiments, the monomer used herein has a weight loss rate of 1% or less (specifically, 1.0% or less) when reaching 180°C in TGA (thermogravimetric analysis) under a heating condition of 10°C / minute. By using a heat-resistant monomer having a weight loss rate of 1% or less when heated at 180°C (hereinafter referred to as a "heat-resistant monomer"), the adhesive layer exhibits heat-peelability due to the inclusion of the monomer, while suppressing the generation of outgassing during heating. By using such a heat-resistant monomer, both heat-peelability and reduced outgassing can be achieved. From the perspective of reducing outgassing, in some preferred embodiments, the weight loss rate of the heat-resistant monomer when heated 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 at 180°C is theoretically 0%, but in practice, it can be 0.1% or more, 0.2% or more, or 0.3% or more. Preferred heat-resistant monomers include trimethylolpropane triacrylate (TMPTA, weight loss rate of 1% at 180° C.) and dipentaerythritol hexaacrylate (DPHA, weight loss rate of 0.5% at 180° C.). These heat-resistant monomers can be used alone or in combination of two or more.

[0094] Specifically, the 180°C heating weight loss rate of the monomer can be measured using a differential thermal analyzer (manufactured by TA Instruments, trade name "Discovery TGA") under measurement conditions of a temperature increase of 10°C / min, an air atmosphere, and a flow rate of 25 mL / min.

[0095] In some preferred embodiments, a multifunctional monomer can be used as the monomer. It should be noted that, in this specification, the term "multifunctional monomer" refers to a polymerizable compound having two or more ethylenically unsaturated groups in one molecule, including substances known as oligomers. Hereinafter, compounds having two or more acryloyl and / or methacryloyl groups may sometimes be referred to as multifunctional acrylic monomers. Furthermore, compounds having two or more vinyl groups may sometimes be referred to as multifunctional vinyl monomers.

[0096] In some preferred embodiments, the number of ethylenically unsaturated groups contained in one molecule of a multifunctional monomer can be 3 or more, preferably 4 or more, more preferably 5 or more, or 6 or more. The more ethylenically unsaturated groups a multifunctional monomer has, the better the curing property during heating, and the easier it is to obtain a tendency to be easily peeled off by heating. In addition, by using a multifunctional monomer with more ethylenically unsaturated groups (functional groups), it is possible to obtain easily peeled off by heating with a relatively small amount of use. This also reduces the amount of released gas from the multifunctional monomer, which is advantageous. The upper limit of the number of ethylenically unsaturated groups in one molecule of a multifunctional monomer is not limited to a specific range, for example, it can be 50 or less, 40 or less, 30 or less, 20 or less, or 15 or less. In some embodiments, the number of ethylenically unsaturated groups in one molecule of a multifunctional monomer can be, for example, 10 or less, 8 or less, or 6 or less. The polyfunctional monomer having the above number of ethylenically unsaturated groups tends to easily achieve both good adhesiveness and heat-peelability, and also tends to be excellent in storage stability.

[0097] As the multifunctional monomer, various multifunctional acrylate monomers and multifunctional vinyl monomers having two or more ethylenically unsaturated groups can be used. Among these, multifunctional acrylate monomers are preferably used. Although not particularly limited, multifunctional acrylate monomers tend to exhibit desired properties through good compatibility when used in combination with acrylic polymers. Each of the multifunctional acrylate monomers and the multifunctional vinyl monomers can be used alone or in combination of two or more.

[0098] Examples of the polyfunctional monomer 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 dicyclopentane di(meth)acrylate, vinyl (meth)acrylate, diethylene glycol di(meth)acrylate, and the like. Bifunctional monomers such as alkenylbenzene; trifunctional monomers such as trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxy tri(meth)acrylate, glycerol propoxy triacrylate, tetramethylolmethane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate; quadrifunctional 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 epoxy acrylates, polyester acrylates, and urethane acrylates having two or more functional groups. Among 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.

[0099] The content of the multifunctional monomer in the adhesive layer is not particularly limited. In some embodiments, the content of the multifunctional monomer can be about 1 part by weight or more, or 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer. Suitably an acrylic polymer) contained in the adhesive layer. The appropriate amount of the multifunctional monomer can be different according to its molecular weight, number of functional groups, etc. In some preferred embodiments, from the viewpoint of improving the easy peeling property when heated, the content of the multifunctional monomer is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (for example, greater than 10 parts by weight), more preferably 15 parts by weight or more, further preferably 20 parts by weight or more, and further preferably 25 parts by weight or more, by including a sufficient amount of the multifunctional monomer in the adhesive layer, so that when heated, the multifunctional monomer contained in the adhesive layer reacts rapidly, and the adhesive layer is thermally cured, thereby achieving easy peeling property when heated. The upper limit of the content of the multifunctional monomer in the adhesive layer is not particularly limited and can be set in a manner to achieve desired adhesive properties. In some ways, from the viewpoint of the compatibility with polymer (specifically, base polymer. For example, acrylic acid-based polymer), it is appropriate to set the amount of the multifunctional monomer relative to 100 parts by weight of the above-mentioned polymer to be approximately 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, further preferably 140 parts by weight or less, and can be 120 parts by weight or less, or can be 90 parts by weight or less. In some preferred embodiments, the amount of the multifunctional monomer relative to 100 parts by weight of the above-mentioned polymer can be 70 parts by weight or less, can be 50 parts by weight or less (for example, less than 50 parts by weight), can be 45 parts by weight or less (for example, less than 45 parts by weight), can be 40 parts by weight or less, can be 35 parts by weight or less, can be 30 parts by weight or less, can be 25 parts by weight or less, can be 20 parts by weight or less (for example, less than 20 parts by weight), can be 18 parts by weight or less, can be 15 parts by weight or less, or can be 12 parts by weight or less. According to the technology disclosed herein, the desired heat-peelability can be ideally achieved by limiting the amount of multifunctional monomers in the adhesive layer as described above. Furthermore, by limiting the amount of multifunctional monomers used, the generation of low-molecular-weight components derived from the multifunctional monomers after heating is suppressed, thereby preventing contamination of the adherend surface by such low-molecular-weight components.

[0100] In the method of using a multifunctional monomer as the above-mentioned monomer, the amount of the multifunctional monomer in the above-mentioned monomer as a whole is not particularly limited. In some methods, from the viewpoint of effectively exerting the effect of containing a multifunctional monomer, it is appropriate that the amount of the multifunctional monomer is set to about 10% by weight or more of the above-mentioned monomer as a whole, preferably 30% by weight or more, more preferably 50% by weight or more (for example, greater than 50% by weight), further preferably 70% by weight or more, further preferably 90% by weight or more, particularly preferably 95% by weight or more, and also 99 to 100% by weight. In some methods, the above-mentioned monomer contained in the adhesive composition can be substantially composed of a multifunctional monomer.

[0101] In addition, as the above-mentioned monomer, one or more monofunctional monomers containing one ethylenically unsaturated group in one molecule can be used. As the monofunctional monomer, known monofunctional acrylate monomers and vinyl monomers can be used. For example, one or more acrylate monomers (such as alkoxy-containing (meth)acrylates and chain alkyl (meth)acrylates) exemplified as monomer components of the above-mentioned polymer can be used.

[0102] The content of the above-mentioned monomers in the adhesive layer is not particularly limited. In some embodiments, the content of the above-mentioned monomers can be about 1 part by weight or more, or 3 parts by weight or more, relative to 100 parts by weight of the polymer (specifically, the base polymer. Suitable acrylic polymers) contained in the adhesive layer. The appropriate amount of the above-mentioned monomers can be different according to their molecular weight, number of functional groups, etc. In some preferred embodiments, from the viewpoint of improving the easy peeling property when heated, the content of the above-mentioned monomers is 5 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, or 9 parts by weight or more, more preferably 10 parts by weight or more (for example, greater than 10 parts by weight), more preferably 15 parts by weight or more, further preferably 20 parts by weight or more, and further preferably 25 parts by weight or more. By including a sufficient amount of the above-mentioned monomers in the adhesive layer, the above-mentioned monomers contained in the adhesive layer react rapidly when heated, and the adhesive layer is thermally cured, thereby achieving easy peeling property when heated. The upper limit of the content of the above-mentioned monomers in the adhesive layer is not particularly limited and can be set in a manner to achieve the desired adhesive properties. In some embodiments, from the perspective of compatibility with the polymer (specifically, the base polymer, such as an acrylic polymer), the amount of the above-mentioned monomer relative to 100 parts by weight of the above-mentioned polymer is appropriately set to about 200 parts by weight or less, preferably 160 parts by weight or less, more preferably 150 parts by weight or less, further preferably 140 parts by weight or less, and can be 120 parts by weight or less, or 90 parts by weight or less. In some preferred embodiments, the amount of the above-mentioned monomer relative to 100 parts by weight of the above-mentioned polymer can 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 disclosed technology, the desired heat-peelability can be ideally achieved by limiting the amount of monomers in the adhesive layer as described above. Furthermore, by limiting the amount of the monomers used, the generation of low-molecular-weight components derived from the monomers after heating is suppressed, thereby preventing contamination of the adherend surface by such low-molecular-weight components.

[0103] (Thermal polymerization initiator)

[0104] In the adhesive layer, in addition to the above-mentioned polymer and the above-mentioned monomer, a thermal polymerization initiator is also contained. Here, the so-called thermal polymerization initiator refers to a polymerization initiator that generates free radicals by heating. The above-mentioned thermal polymerization initiator at least includes a peroxide-based polymerization initiator. By including a peroxide-based polymerization initiator as a thermal polymerization initiator in the adhesive layer, the reaction of the ethylenically unsaturated groups in the adhesive layer during heating, i.e., the curing reaction of the adhesive layer, is carried out rapidly, and it is possible to reliably demonstrate heating easy peelability for various adherends that contain materials (typically organic materials) that are easily adhered to the adhesive layer due to heating. As one of the reasons, it is believed that the high initiation efficiency of peroxide-based polymerization initiators (especially organic peroxide-based polymerization initiators) is. In addition, peroxide-based polymerization initiators generate free radicals (-O·) by cleavage of the -OO- possessed by the compound, but the cleavage reaction is reversible, so it is believed that when the free radicals do not collide with the ethylenically unsaturated groups of the coordinating monomers and polymers, rebonding of -OO- will occur. The initiator formed by this rebonding can undergo a cracking reaction again within the prescribed heating time, and collides with the coordination monomers and reacts. Therefore, according to the peroxide-based polymerization initiator, the thermal curing of the adhesive layer is carried out rapidly with a reaction speed that is particularly fast compared with other initiators (such as azo-based initiators). Moreover, it is believed that its thermal curing speed is faster than the speed at which the adhesive layer based on heating and the adherend are firmly fitted, so the peeling force is reliably reduced after heating, and heating easy peeling property and heat-resistant easy peeling property can be obtained. It should be noted that the technology disclosed herein is not limited to the above-mentioned investigation.

[0105] As the peroxide-based polymerization initiator, for example, organic peroxides such as diacyl peroxides, peroxyesters, peroxydicarbonates, monoperoxycarbonates, peroxyketals, dialkyl peroxides, hydroperoxides, and ketone peroxides are preferably used. Suitable examples of peroxide-based polymerization initiators include benzoyl peroxide compounds (typically dibenzoyl peroxide (BPO)) having a benzoyl group which may have a substituent. The peroxide-based polymerization initiators can be used alone or in combination of two or more.

[0106] Specific examples of the peroxide-based polymerization initiator include BPO, 1,1-di(tert-hexylperoxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 4,4-bis(tert-butylperoxy)butyl valerate, cumene hydroperoxide, 2,5-dimethyl-2,5-dihydroperoxyhexane, 1,3-bis(tert-butylperoxy) m-Isopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, diisopropylbenzene hydroperoxide, tert-butylcumyl peroxide, didecanoyl peroxide, dilauroyl peroxide, 2,4-dichlorobenzoyl peroxide, di(4-tert-butylcyclohexyl) peroxydicarbonate, tert-butyl perbenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butyl hydroperoxide, di-tert-butyl peroxide, etc.

[0107] The content of the peroxide-based polymerization initiator in the adhesive layer is not particularly limited. In some embodiments, relative to 100 parts by weight of the polymer (specifically, the base polymer. For example, an acrylic polymer) contained in the adhesive layer, it is appropriate that the content of the peroxide-based polymerization initiator in the adhesive layer is set to 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, further preferably 0.4 parts by weight or more, particularly preferably 0.5 parts by weight or more, can be 0.6 parts by weight or more, and can also be 0.7 parts by weight or more. The more the content of the peroxide-based polymerization initiator, the higher the collision frequency of the peroxide-based polymerization initiator and the ethylenically unsaturated group in the adhesive layer, and the easier it is to perform a curing reaction. In addition, in some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the above-mentioned polymer can be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, the amount of the peroxide-based polymerization initiator per 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, further 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 can be 1.0 parts by weight or less (e.g., less than 1.0 parts by weight), 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, or 0.6 parts by weight or less. By ensuring that the content of the peroxide-based polymerization initiator is within the specified range, it is possible to achieve adhesive properties such as adhesive strength and storage stability while ideally achieving an adhesive having high-efficiency thermosetting properties and heat-peelable properties.

[0108] The content of the peroxide-based polymerization initiator in the adhesive layer can also be determined by its relative relationship to the monomers in the adhesive layer. In some embodiments, from the perspective of increasing the frequency of collisions with the ethylenically unsaturated groups of the above-mentioned monomers, thereby rapidly performing thermal curing, and from the perspective of allowing the adhesive layer to thermally cure with a high degree of cure, the amount of the peroxide-based polymerization initiator per 100 parts by weight of the above-mentioned monomers is preferably set to 0.1 parts by weight or more, preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, further preferably 1.0 parts by weight or more, further preferably 1.2 parts by weight or more, particularly preferably 1.5 parts by weight or more, and can be 2.0 parts by weight or more, or even 2.5 parts by weight or more. In addition, in some embodiments, the amount of the peroxide-based polymerization initiator per 100 parts by weight of the above-mentioned monomers is preferably 3 parts by weight or more, more preferably 5 parts by weight or more, and even 7 parts by weight or more. For example, in compositions where the content of the above-mentioned monomers is limited, the usage amount of the above-mentioned peroxide-based polymerization initiator can be preferably adopted. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomers may be, for example, 20 parts by weight or less, 15 parts by weight or less, 12 parts by weight or less, or 10 parts by weight or less. In some embodiments, the amount of the peroxide-based polymerization initiator relative to 100 parts by weight of the monomers may be 7 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less.

[0109] In some embodiments, the adhesive layer may include, as a thermal polymerization initiator, a thermal polymerization initiator different from the peroxide-based polymerization initiator (non-peroxide-based polymerization initiator) in addition to the peroxide-based polymerization initiator. Non-peroxide-based polymerization initiators that can be used together with the peroxide-based polymerization initiator include, for example, azo-based polymerization initiators, redox-based polymerization initiators based on a combination of a peroxide and a reducing agent, and substituted ethane-based polymerization initiators. Specifically, examples include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(N-butyl-2-methylpropionamide), and 2,2'-azobis(2,4,4-trimethylpentane); substituted ethane-based initiators such as phenyl-substituted ethane; and redox-based initiators based on a combination of a peroxide and a reducing agent such as a combination of a persulfate and sodium bisulfite or a combination of a peroxide and sodium ascorbate. These non-peroxide polymerization initiators can be used alone or in combination of two or more.

[0110] Although not particularly limited, in order to effectively exert the effect of the peroxide-based polymerization initiator, in some embodiments, the ratio of the peroxide-based polymerization initiator contained in the adhesive layer to the total thermal polymerization initiator is preferably about 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, further preferably 90% by weight or more, and particularly preferably 95 to 100% by weight. The thermal polymerization initiator contained in the adhesive layer may also be composed of a peroxide-based polymerization initiator.

[0111] In some embodiments, as a thermal polymerization initiator, it is preferred to use a thermal polymerization initiator having a self-accelerating decomposition temperature (SADT) [°C] that satisfies the following formula: SADT+10≥60. Here, the SADT of the so-called thermal polymerization initiator is defined as the lowest temperature at which heat of 6°C or above or self-accelerating decomposition is caused within 7 days when placed in a certain amount of a container. SADT represents the ambient temperature at the boundary of whether the thermal polymerization initiator causes decomposition. Based on the fact that the maximum temperature to which the adhesive is exposed during storage is 60°C, the inventors of the present application have experimentally confirmed that if the thermal polymerization initiator has a SADT of -10°C or a temperature higher than the above-mentioned maximum storage temperature, the self-decomposition of the thermal polymerization initiator in the adhesive can be suppressed, and storage stability that can maintain good heat-peelable properties after storage can be obtained. This is believed to be because it is more difficult to conduct heat in the adhesive (in the solid) compared to the case of a single thermal polymerization initiator. Based on this discovery, an adhesive designed using a thermal polymerization initiator having a SADT that satisfies the above formula (hereinafter also referred to as a high SADT initiator) can suppress the decomposition of the thermal polymerization initiator in the adhesive even when the adhesive is exposed to a temperature of approximately 60°C before use, and the adhesive can maintain the desired heat-peelable properties. Adhesives containing a thermal polymerization initiator containing a high SADT initiator have excellent storage stability even in the case of long-term storage or temperature changes during storage, and can maintain good heat-peelable properties after storage. It should be noted that in this specification, the SADT used as the thermal polymerization initiator is the nominal value recorded in the manufacturer's catalog, etc.

[0112] The amount of the thermal polymerization initiator contained in the adhesive layer is not particularly limited. In some embodiments, relative to 100 parts by weight of the polymer (specifically, the base polymer. For example, an acrylic polymer) contained in the adhesive layer, it is appropriate that the content of the thermal polymerization initiator in the adhesive layer is set to 0.1 parts by weight or more, preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, further preferably 0.4 parts by weight or more, particularly preferably 0.5 parts by weight or more, can be 0.6 parts by weight or more, and can also be 0.7 parts by weight or more. The more the content of the thermal polymerization initiator, the higher the collision frequency of the thermal polymerization initiator and the ethylenically unsaturated group in the adhesive layer, and the easier it is to carry out the curing reaction. In addition, in some embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the above-mentioned polymer can be, for example, about 10 parts by weight or less, or about 5 parts by weight or less. In some preferred embodiments, the amount of the thermal polymerization initiator relative to 100 parts by weight of the above-mentioned polymer is appropriately 3 parts by weight or less (less than 3 parts by weight), preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less, further 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), can be 1.0 parts by weight or less (e.g., less than 1.0 parts by weight), can be 0.9 parts by weight or less, can be 0.8 parts by weight or less, can be 0.7 parts by weight or less, and can also be 0.6 parts by weight or less. By making the total amount of the thermal polymerization initiator within the specified range, it is possible to achieve adhesive properties such as adhesive strength and storage stability while ideally realizing an adhesive having efficient thermosetting properties and heat-removable properties.

[0113] Although not particularly limited, in some preferred embodiments, from the viewpoint of effectively showing the reduction in peel force during heating and achieving the desired peel force reduction rate after heating, the total proportion of the above-mentioned polymer (specifically, the base polymer, such as an acrylic polymer), the above-mentioned monomer (such as a multifunctional acrylic monomer) and the thermal polymerization initiator (such as a peroxide polymerization initiator) in the entire adhesive layer is appropriately 50 weight % or more (for example, greater than 50 weight % and less than 100 weight %), preferably 70 weight % or more, more preferably 80 weight % or more, further preferably 90 weight % or more, can be 95 weight % or more, can be 98 weight % or more, and can also be 99 weight % or more (for example, 99 to 100 weight %).

[0114] (cross-linking agent)

[0115] In the adhesive composition for forming the adhesive layer, a crosslinking agent can be contained as needed, mainly for the purpose of crosslinking within the adhesive layer or crosslinking the adhesive layer with its adjacent surface. The crosslinking agent is typically contained in the adhesive layer in the form after the crosslinking reaction. By using a crosslinking agent, the cohesive force of the adhesive layer can be appropriately adjusted.

[0116] The kind of cross-linking agent is not particularly limited, and can be selected from among the cross-linking agents known in the past, for example, according to the composition of adhesive, in adhesive layer, bring into play the mode of suitable cross-linking function with this cross-linking agent.As spendable cross-linking agent, can exemplify isocyanate cross-linking agent, epoxy cross-linking agent, oxazoline cross-linking agent, aziridine cross-linking agent, carbodiimide cross-linking agent, melamine cross-linking agent, urea cross-linking agent, metal alkoxide cross-linking agent, metal chelate cross-linking agent, metal salt cross-linking agent, hydrazine cross-linking agent, amine cross-linking agent etc..They can be used alone or in combination of two or more.From the viewpoint of realizing adhesiveness and cohesion well simultaneously from balanced property, preferably isocyanate cross-linking agent, epoxy cross-linking agent, oxazoline cross-linking agent, aziridine cross-linking agent, carbodiimide cross-linking agent, particularly preferably isocyanate cross-linking agent.

[0117] As the isocyanate crosslinking agent, a polyfunctional isocyanate compound having two or more functional groups can be used. Examples thereof include 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 trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name “Coronate L”), trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name “Coronate HL”), isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name “Coronate HX”), and trimethylolpropane / xylene diisocyanate adduct (manufactured by Mitsui Chemicals, Inc., trade name “Takenate D-110N”).

[0118] As epoxy crosslinking agents, those having two or more epoxy groups per molecule can be used without particular limitation. Epoxy crosslinking agents having 3 to 5 epoxy groups per molecule are preferred. Specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include "TETRAD-X" and "TETRAD-C" manufactured by Mitsubishi Gas Chemical, "EPICLON CR-5L" manufactured by DIC, "Denacol EX-512" manufactured by Nagase Chemtex, and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd.

[0119] As the oxazoline-based crosslinking agent, any oxazoline-based crosslinking agent having one or more oxazoline groups in one molecule can be used without particular limitation.

[0120] Examples of the aziridine-based crosslinking agent include trimethylolpropane tris[3-(1-aziridinyl)propionate] and trimethylolpropane tris[3-(1-(2-methyl)aziridinylpropionate)].

[0121] As the carbodiimide-based crosslinking agent, a low-molecular compound or a high-molecular compound having two or more carbodiimide groups can be used.

[0122] In some embodiments, an isocyanate cross-linking agent is used as a cross-linking agent. By using an isocyanate cross-linking agent, it is easy to form an adhesive that exerts adhesive properties such as adhesion and cohesion in a well-balanced manner and has good heat-resistance. An isocyanate cross-linking agent can be used alone or in combination of two or more. Although not particularly limited, the amount used when using an isocyanate cross-linking agent is preferably less than 3 parts by weight relative to 100 parts by weight of the polymer (specifically, a base polymer. For example, an acrylic polymer) contained in the adhesive layer. It is believed that by limiting the amount of isocyanate cross-linking agent used, the cross-linking density is appropriately suppressed. At this cross-linking density, during heat treatment, in the adhesive layer, the coordinating monomer and the like frequently collide with the thermal polymerization initiator and are thermally cured, which can increase the rate of reduction in peeling force after heating and exhibit the desired heat-resistance and heat-resistant peelability. It should be noted that the technology disclosed herein is not limited to the above-mentioned investigations. From the above viewpoint, in some preferred embodiments, the amount of the isocyanate cross-linking agent used relative to 100 parts by weight of the above-mentioned polymer is 2 parts by weight or less, more preferably 1.5 parts by weight or less, further preferably 1.0 parts by weight or less, further preferably 0.8 parts by weight or less, and particularly preferably 0.6 parts by weight or less. By limiting the amount of the isocyanate cross-linking agent used, there is a tendency to easily obtain sufficient bonding strength. In addition, the amount of the isocyanate cross-linking agent used relative to 100 parts by weight of the above-mentioned polymer can be, for example, set to 0.01 parts by weight or more, in some preferred embodiments, it can be 0.05 parts by weight or more, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. By appropriately setting the amount of the isocyanate cross-linking agent within the above-mentioned range, it is possible to ideally achieve the effects brought about by the technology disclosed herein, and ideally obtain an adhesive that exhibits bonding properties such as bonding strength and cohesive force in a well-balanced manner.

[0123] About the usage amount of the cross-linking agent when using a cross-linking agent, from the viewpoint of realizing that the adhesive having good balance gives play to the adhesive properties such as bonding force, cohesive force, the amount more than 0 weight part is obtained relative to 100 weight parts of polymer (specifically, base polymer. For example, acrylic acid polymer), for example, it can be set to more than 0.001 weight part, or it can be set to more than 0.01 weight part. In some preferred embodiments, the usage amount of the cross-linking agent relative to 100 weight parts of above-mentioned polymer can be more than 0.05 weight part, can be more than 0.1 weight part, can be more than 0.3 weight part, or it can be more than 0.5 weight part. In addition, the upper limit of the usage amount of the cross-linking agent can be different according to the cross-linking agent kind used, so it is not limited to specific scope, but is preferably limited to below the specified amount. It is believed that by limiting the usage amount of cross-linking agent, cross-linking density is appropriately suppressed. Under this cross-linking density, when heat treated, the coordination monomer in the adhesive layer etc. frequently collides with the thermal polymerization initiator and is thermally cured. It is possible to improve the peeling force reduction rate after heating, and show desired heating easy peelability, heat-resistant easy peelability. It should be noted that technology disclosed herein is not limited to the above-mentioned investigation. For example, relative to 100 parts by weight of the above-mentioned polymer, it is appropriate that the usage amount of the cross-linking agent is set to be less than 10 parts by weight. In some ways, it is preferably less than 5 parts by weight, and it is also possible to be less than 3 parts by weight. In some ways, relative to 100 parts by weight of the above-mentioned polymer, it is appropriate that the usage amount of the cross-linking agent is set to be less than 1 part by weight. It is preferably set to below 0.9 part by weight, can be below 0.8 part by weight, can be below 0.7 part by weight, can be below 0.6 part by weight, and it is also possible to be below 0.5 part by weight. By limiting the usage amount of the cross-linking agent, there is a tendency to easily obtain sufficient bonding force.

[0124] In order to carry out the cross-linking reaction more effectively, a cross-linking catalyst can be used. As a cross-linking catalyst, metal cross-linking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, triacetylacetonate iron, butyl tin oxide, and dioctyltin dilaurate are exemplified. The amount of the cross-linking catalyst used is not particularly limited. The amount of the cross-linking catalyst used can be set to, for example, about 0.0001 parts by weight or more, about 0.001 parts by weight or more, or about 0.005 parts by weight or more relative to 100 parts by weight of the polymer (specifically, the base polymer. For example, an acrylic polymer) contained in the adhesive layer. In addition, it can be set to about 1 part by weight or less, about 0.1 part by weight or less, or about 0.05 part by weight or less.

[0125] The adhesive composition used to form the adhesive layer may, if desired, contain a compound that undergoes keto-enol tautomerism as a crosslinking retardant. For example, in an adhesive composition containing an isocyanate crosslinking agent or an adhesive composition that can be used in combination with an isocyanate crosslinking agent, a compound that undergoes keto-enol tautomerism is preferably used. This can extend the pot life of the adhesive composition.

[0126] Various β-dicarbonyl compounds can be used as compounds that produce keto-enol tautomerism. Specific examples include β-diketones such as acetylacetone and 2,4-hexanedione; acetoacetic esters such as methyl acetoacetate and ethyl acetoacetate; propionylacetic esters such as ethyl propionylacetate; isobutyrylacetic esters such as ethyl isobutyrylacetate; and malonic esters such as methyl malonate and ethyl malonate. Suitable compounds include acetylacetone and acetoacetic esters. Compounds that produce keto-enol tautomerism can be used alone or in combination of two or more.

[0127] The amount of the compound that produces keto-enol tautomerism used can be, for example, 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of the polymer (specifically, the base polymer, for example, an acrylic polymer) contained in the adhesive layer, and it is appropriate to set it to 0.5 parts by weight to 15 parts by weight. For example, it can be set to 1 part by weight to 10 parts by weight, or it can be set to 1 part by weight to 5 parts by weight.

[0128] (Other ingredients)

[0129] The adhesive layer may contain various additives commonly used in the adhesive field, such as adhesion-imparting agents, silane coupling agents, release force modifiers (surfactants, etc.), viscosity modifiers (e.g., tackifiers), leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, and anti-aging agents, as needed. For such various additives, conventionally known additives can be used by conventional methods, and since they do not particularly characterize the present invention, detailed descriptions are omitted.

[0130] It should be noted that the technology disclosed herein can achieve desired adhesive properties such as adhesion without using an adhesion-imparting agent. In some embodiments, the content of the adhesion-imparting agent in the adhesive layer can be, for example, less than 10 parts by weight, and further can be less than 5 parts by weight relative to 100 parts by weight of the polymer (specifically, a base polymer, such as an acrylic polymer) contained in the adhesive layer. The content of the above-mentioned adhesion-imparting agent can be less than 1 part by weight (for example, less than 0.5 parts by weight), or less than 0.1 parts by weight (more than 0 parts by weight and less than 0.1 parts by weight). The adhesive layer can be a substance that does not contain an adhesion-imparting agent.

[0131] (Form of Adhesive Composition)

[0132] Although not particularly limited, the adhesive layer disclosed herein can be preferably formed using a solvent-based adhesive composition. The above-mentioned solvent-based adhesive composition is an adhesive composition in the form of an adhesive-forming component contained in an organic solvent. The solvent-based adhesive composition typically contains a solution polymer of a monomer component, a compounding monomer and a thermal polymerization initiator (specifically, a peroxide-based polymerization initiator), and optionally other additives. In the form of a solvent-based adhesive (layer), the effects brought about by the technology disclosed herein can be effectively exerted. The solvent contained in the solvent-based adhesive composition can be appropriately selected from conventionally known organic solvents. For example, any one solvent selected from the following, or a mixed solvent of two or more solvents, can be used, namely: aromatic compounds such as toluene (typically aromatic hydrocarbons); esters such as ethyl acetate and butyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; and the like.

[0133] (Formation of Adhesive Layer)

[0134] Adhesive layer disclosed herein can be formed by known methods in the past. After adhesive composition is given (such as applied) to suitable surface, by suitably implementing curing treatment, adhesive can be formed with the form of stratiform (adhesive layer). The curing means (such as drying, crosslinking, polymerization, cooling etc.) of adhesive composition can only be applicable to 1 kind, also can be applicable to 2 kinds or more simultaneously or in multiple stages. In the case of solvent-based adhesive composition, typically, said composition can be made to dry (preferably further crosslinked) and form adhesive.

[0135] For example, under the situation of the two-sided adhesive sheet of no base material, can adopt following method: after giving adhesive composition to the surface (peeling surface) with peelability, by making this adhesive composition solidify and on this surface, form adhesive layer.Under the situation of the adhesive sheet with base material, can adopt by this base material directly giving (typically coating) adhesive composition and making it solidify and form the method (direct method) of adhesive layer.In addition, also can adopt by giving adhesive composition to the surface (peeling surface) with peelability and making it solidify and on this surface, form adhesive layer, and this adhesive layer is transferred to the method (transfer method) of base material.As above-mentioned peeling surface, can utilize the surface of release liner, through peeling the base material back side etc. of processing.It should be noted that, adhesive layer disclosed here typically forms continuously, but is not limited to such form, for example, can also be formed as the adhesive layer of the regular or random pattern such as dot-shaped, strip.

[0136] The adhesive composition can be applied using a known or customary coating machine such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a die coater, a rod coater, an air knife coater, or a spray coater. Alternatively, the adhesive composition can be applied by impregnation or curtain coating.

[0137] From the viewpoints of promoting the cross-linking reaction and improving the manufacturing efficiency, the drying of the adhesive composition is preferably carried out under heating. The drying temperature is not particularly limited, and can be set to about 40 to 100°C, and is generally preferably set to about 60 to 80°C. For example, the heating temperature of the drying at the above temperature (for example, about 1 to 10 minutes, more specifically about 3 to 7 minutes) is low, and sometimes the volatilization of the solvent is also in progress. In the adhesive composition containing monomers and thermal polymerization initiators, the reaction of the monomers and the deactivation of the thermal polymerization initiator are negligible. In addition, after the adhesive composition is dried, it can be aged for the purpose of adjusting the component transfer in the adhesive layer, carrying out the cross-linking reaction, and relaxing the strain that may exist in the substrate and the adhesive layer.

[0138] (thickness)

[0139] The thickness of the adhesive layer is not particularly limited. The thickness of the adhesive layer is generally 1 μm or more, can be 2 μm or more, or can be 3 μm or more. There is a tendency that the greater the thickness of the adhesive layer, the higher the adhesion to the adherend. In some preferred embodiments, the thickness of the adhesive layer is 5 μm or more, can be 10 μm or more, can be 15 μm or more, can be 20 μm or more, or can be 25 μm or more. It is appropriate to set the upper limit of the thickness of the adhesive layer to be about 200 μm or less, for example, can be 100 μm or less (for example, less than 100 μm), or can be 50 μm or less. By limiting the thickness of the adhesive layer to a specified range, the generation of residual adhesive caused by cohesive failure is prevented, and there is a tendency to easily obtain easy peelability. In addition, a thin adhesive layer is advantageous in terms of thinning the adhesive sheet, and there is a tendency to have excellent followability to the adherend. In some preferred embodiments, the thickness of the adhesive layer is 40 μm or less, or can be 30 μm or less.

[0140] (Gel fraction)

[0141] The gel fraction of the adhesive layer is not particularly limited. In some embodiments, from the perspective of obtaining sufficient adhesion to the adherend and good heat-peelability, the initial (before heating) gel fraction (weight basis) of the adhesive layer is, for example, 85% or less, preferably 80% or less, more preferably 75% or less, can be 70% or less, can be 65% or less, or can be 60% or less. Those with a lower initial gel fraction tend to easily obtain a higher rate of reduction in peel force after heating. In addition, from the perspective of obtaining adhesive layer formability, moderate cohesion, and holding power, in some embodiments, the initial gel fraction of the adhesive layer is appropriate to be 20% or more, preferably 30% or more, more preferably 40% or more, further preferably 50% or more, can be 60% or more, or can be 70% or more. Adhesives having an appropriate initial gel fraction within the above range tend to have good heat-curing reactivity.

[0142] Furthermore, the gel fraction of the adhesive layer after heating is preferably higher than the gel fraction before heating. In some embodiments, the increase in gel fraction of the adhesive layer after heating, as determined by the following formula, is preferably 10% or greater, more preferably 20% or greater, even more preferably 30% or greater, and may be 40% or greater, 50% or greater, 60% or greater, or 70% or greater.

[0143] Gel fraction increase rate after heating [%] = (G1 / G0-1) × 100

[0144] (In the above formula, G1 is the gel fraction [%] of the adhesive layer after heat treatment at 180°C for 30 minutes, and G0 is the gel fraction [%] of the adhesive layer before heating.)

[0145] Adhesives having such a high rate of increase in gel fraction after heating tend to be easily cured by heating, easily achieving a high rate of reduction in peel force after heating, and thus, easily achieving excellent heat-peelability and heat-resistant peelability. In some embodiments, the upper limit of the rate of 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.

[0146] Although not particularly limited, in some embodiments, from the perspective of achieving easy heat-peelability, the post-heating gel fraction (weight basis) of the adhesive layer is suitably 50% or greater (e.g., greater than 50%), preferably 70% or greater, more preferably 80% or greater, even more preferably 85% or greater, particularly preferably 90% or greater, and may be 95% or greater. Furthermore, in some embodiments, the post-heating gel fraction of the adhesive layer may be, for example, 99% or less, 95% or less, or 90% or less.

[0147] The gel fraction of the adhesive layer can be adjusted primarily by the polymer's monomer composition, Mw, the amount of added monomers, and the type and amount of the crosslinking agent. Furthermore, the post-heat gel fraction can be adjusted primarily by the polymer's design (e.g., the amount of ethylenically unsaturated groups introduced), the type and amount of added monomers, and the type and amount of the thermal polymerization initiator. Specifically, the aforementioned gel fractions were measured using the methods described in the Examples below.

[0148] (Young's modulus)

[0149] In some embodiments, with respect to the adhesive layer, it is preferred that the Young's modulus Y1 [MPa] after heat treatment at 180°C for 30 minutes is 200 times or more of the Young's modulus Y0 [MPa] before heating, that is, the Young's modulus change ratio (Y1 / Y0) after heating is 200 or more. The higher the Young's modulus change ratio (Y1 / Y0) after heating, the higher the degree of curing of the adhesive layer during heating, and the easier it is to obtain excellent heat-peelable properties. In some preferred embodiments, the Young's modulus change ratio (Y1 / Y0) after heating can be 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. In addition, from the perspective of making the adhesive layer before heating have an appropriate elastic modulus, in some embodiments, it is appropriate to set the Young's modulus change ratio (Y1 / Y0) after heating to about 10,000 or less, preferably 5,000 or less, more preferably 2,500 or less, and can be 1,500 or less, 1,000 or less, or 500 or less.

[0150] Although not particularly limited, in some ways, the Young's modulus Y0 before heating of the adhesive layer (initial Young's modulus) is, for example, about 10MPa or less, preferably 1MPa or less, more preferably 0.5MPa or less, further preferably 0.3MPa or less, or 0.2MPa or less. According to the adhesive layer with the above-mentioned Young's modulus Y0 before heating, there is a tendency to easily obtain sufficient adhesion to adherend and good heating easy peelability. In addition, from the viewpoint of obtaining adhesive layer formation, appropriate cohesion, holding power, in some ways, the Young's modulus Y0 before heating of the adhesive layer is suitable for more than 0.01MPa, preferably 0.03MPa or more, more preferably 0.05MPa or more, further preferably 0.08MPa or more, or more than 0.10MPa, or more than 0.12MPa, or more than 0.15MPa.

[0151] Although not particularly limited, in some embodiments, it is appropriate that the Young's modulus Y1 of the adhesive layer after heating is 10 MPa or more, preferably 30 MPa or more, more preferably 50 MPa or more, and further preferably 70 MPa or more. In some preferred embodiments, the Young's modulus Y1 after heating can be 100 MPa or more, 150 MPa or more, or 200 MPa or more. According to the adhesive layer having a Young's modulus after heating of more than a specified value, there is a tendency that the degree of curing after heating is high and excellent heat-peelability is easily obtained. In addition, in some embodiments, the Young's modulus Y1 after heating can be, for example, about 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.

[0152] The Young's modulus of the adhesive layer can be adjusted primarily by the polymer's monomer composition, Mw, the amount of added monomers, and the type and amount of the crosslinking agent. Furthermore, the Young's modulus after heating, Y1, can be adjusted primarily by the polymer's design (e.g., the amount of ethylenically unsaturated groups introduced), the type and amount of added monomers, and the type and amount of the thermal polymerization initiator. Specifically, the Young's moduli Y0 and Y1 are measured using the methods described in the Examples below.

[0153] <Base Material Layer>

[0154] The adhesive sheet disclosed herein may include a substrate layer. As a substrate (layer) supporting (lining) the adhesive layer, various sheet-like substrates can be used. As the above-mentioned substrate, resin film, paper, cloth (woven fabric, non-woven fabric, etc.), rubber sheet, foam sheet, metal foil, their composites, etc. can be used. Examples of resin films include polyolefin films; polyester films; vinyl chloride resin films; vinyl acetate resin films; polyamide resin films; fluororesin films; cellophane; etc. As non-limiting examples of polyester films, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc. can be mentioned. As other examples of resin films, resin films formed of one or more engineering plastics (which may be super engineering plastics) selected from polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylate resins, polyamideimide resins, polyimide resins, etc. can be mentioned. The use of engineering plastics is preferred from the viewpoint of heat resistance.

[0155] In some preferred embodiments, a resin film having a specified rigidity (strength) and excellent processability and operability is used as a substrate (layer). Among them, from the viewpoint of heat resistance, the resin film substrate is preferably a polyester film, a polyamide resin film, an engineering plastic film (such as a polyimide resin film, etc.). It should be noted that in this specification, the so-called "resin film" is typically a non-porous film, typically referring to a resin film that does not substantially contain bubbles (no voids). Therefore, the above-mentioned resin film is a concept that is distinguished from foam films and non-woven fabrics. The density of the resin film that can be used as a substrate can be about 0.85 to 1.50 g / cm 3 (e.g. 0.90 g / cm 3 ~1.20g / cm 3 , typically 0.92 g / cm 3 ~1.05g / cm 3 The resin film may have a single-layer structure or a multi-layer structure of two or more layers (eg, a three-layer structure).

[0156] The base layer (e.g., resin film) may be mixed with known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents as needed. The amount of the additives is not particularly limited and can be appropriately set according to the intended use.

[0157] The method for producing the resin film is not particularly limited, and for example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting, and calendar roll molding can be appropriately adopted.

[0158] 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 optical property adjustment layers (e.g., coloring layers, antireflection layers), printed layers for imparting a desired appearance, laminate layers, antistatic layers, primer layers, release layers, and other surface treatment layers.

[0159] The thickness of the substrate layer is not particularly limited and can be appropriately selected according to the purpose, and can generally be 1 to 500 μm. From the viewpoints of processability, usability, operability, etc., it is appropriate that the thickness of the substrate layer is 2 μm or more (for example, 3 μm or more, typically 5 μm or more), can be about 7 μm or more, or can be 10 μm or more. In some embodiments, the thickness of the substrate layer can be 20 μm or more, can be 30 μm or more, or can be 40 μm or more. In addition, it is appropriate that the thickness of the substrate layer is about 200 μm or less. From the viewpoint of lightweight and thin thickness, it is preferably about 100 μm or less, more preferably about 80 μm or less, or can be 60 μm or less. When the thickness of the substrate layer becomes smaller, there is a tendency for the softness of the adhesive sheet and the followability to the surface shape of the adherend to be improved.

[0160] The adhesive layer side surface of the substrate layer can be subjected to corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, coating of primer (primer) and other known surface treatments as needed. Such surface treatment can be used to improve the adhesion of the substrate layer and the adhesive layer. In other words, it can be used to improve the anchoring property of the adhesive layer to the substrate layer. The composition of the primer is not particularly limited and can be appropriately selected from known substances. The thickness of the primer layer is not particularly limited, and for example, about 0.01 μm to 1 μm is appropriate, preferably about 0.1 μm to 1 μm. In addition, the back of the substrate layer can be subjected to surface treatments such as the above-mentioned various surface treatments, antistatic treatment, etc.

[0161] <Total Thickness>

[0162] The total thickness of the adhesive sheet disclosed herein (which may include an adhesive layer and a substrate layer, but does not contain a release liner) is not particularly limited, and it is appropriate to set it in the range of about 5 to 1000 μm. From the viewpoints of adhesive properties, usability, etc., the total thickness of the adhesive sheet can be 10 μm or more, 30 μm or more, or 50 μm or more. In addition, from the viewpoint of lightweight and thin thickness, in some embodiments, the total thickness of the adhesive sheet is 500 μm or less, or 300 μm or less. In some preferred embodiments, the total thickness of the adhesive sheet is 150 μm or less, 120 μm or less, or 100 μm or less (for example, less than 100 μm). Reducing the thickness of the adhesive sheet is also advantageous in terms of filmization, miniaturization, lightweighting, and resource saving.

[0163] <Release liner>

[0164] The release liner used in the adhesive sheet disclosed herein is not particularly limited. For example, release liners having a release-treated surface of a liner substrate such as a resin film or paper, or release liners formed from low-adhesion materials such as fluorine-based polymers (polytetrafluoroethylene, etc.) or polyolefin-based resins (polyethylene, polypropylene, etc.) can be used. For example, silicone-based or long-chain alkyl-based release agents can be used. In some embodiments, a release liner using a release-treated resin film is preferably used.

[0165] <Properties of Adhesive Sheet>

[0166] (Peel force reduction rate after heating)

[0167] In some embodiments, the pressure-sensitive adhesive sheet preferably has a peel strength reduction rate A after heating calculated by the following formula of greater than 50%:

[0168] Peel force reduction rate after heating A[%] = (1-F1 / F0) × 100

[0169] (In the above formula, F1 is the peel force after heating [N / 20mm] measured at 23°C after being attached to an adherend and heated at 180°C for 30 minutes. F0 is the peel force before heating [N / 20mm].)

[0170] Adhesive sheets meeting the above characteristics can adhere well to adherends and exhibit excellent heat-peelability and heat-resistant peelability when peeled after heat treatment. In some preferred embodiments, the peel force reduction rate A after heating can be 60% or greater, 70% or greater, 80% or greater, 85% or greater, 90% or greater, or 95% or greater. The greater the peel force reduction rate A after heating, the better the heat-peelability and heat-resistant peelability. Furthermore, the peel force reduction rate A after heating is preferably less than 99.9%. Adhesive sheets with a peel force reduction rate A after heating of less than 99.9% maintain their bond to the adherend after heating and exhibit the desired peelability from the adherend. This prevents the adhesive sheet from naturally peeling from the adherend due to heating, and the resulting undesirable effects. Considering this, the peel force reduction rate A after heating can be 99.0% or less, for example, less than 95.0%.

[0171] (Peel force F0 before heating)

[0172] Although not particularly limited, in some embodiments, the peel force F0 before heating of the adhesive sheet is suitably 1.0 N / 20 mm or greater, preferably 2.0 N / 20 mm or greater, more preferably 3.0 N / 20 mm or greater, further preferably 4.0 N / 20 mm or greater, and particularly preferably 5.0 N / 20 mm or greater. Adhesive sheets exhibiting the above peel force F0 before heating can exhibit good adhesion to various adherends, such as organic materials. The upper limit of the peel force F0 before heating is appropriately set according to the required adhesion and is therefore not limited to a specific range. For example, it can be approximately 20 N / 20 mm or less, or approximately 10 N / 20 mm or less. Specifically, the peel force F0 before heating refers to the peel force measured at a peel angle of 180 degrees and a speed of 300 mm / min against an FR-4 glass cloth-based epoxy resin copper-clad laminate at 23°C. The peel force F0 before heating is also referred to as the initial peel force. More specifically, the peel force F0 before heating is measured by the method described in Examples below.

[0173] (Peel force after heating F1)

[0174] Although not particularly limited, in some embodiments, it is appropriate that the peeling force (peeling force after heating) F1 of the adhesive sheet to the adherend after heat treatment at 180°C for 30 minutes is less than 3N / 20mm, preferably 1.0N / 20mm or less. The adhesive sheet showing the above-mentioned peeling force F1 after heating can become an adhesive sheet having easy peeling by heating and further having heat-resistant easy peeling after heat treatment. From the perspective of peelability, in some preferred embodiments, the above-mentioned peeling force F1 after heating is less than 1.0N / 20mm, more preferably 0.8N / 20mm or less, further preferably 0.6N / 20mm or less, particularly preferably 0.5N / 20mm or less, can be 0.4N / 20mm or less, or can be 0.3N / 20mm or less. The lower limit of the above-mentioned peeling force F1 after heating can be 0.0N / 20mm, or can be 0.01N / 20mm or more (for example, 0.1N / 20mm or more). Specifically, the post-heat peel force F1 refers to the peel force measured at a peel angle of 180 degrees and a peel speed of 300 mm / min at 23°C after the sheet is attached to an adherend and subjected to a heat treatment at 180°C for 30 minutes. An FR-4 glass cloth-based epoxy resin copper-clad laminate can be used as the adherend. More specifically, the post-heat peel force F1 is measured using the method described in the Examples below.

[0175] <Peeling method>

[0176] According to this specification, a method for peeling an adhesive sheet adhered to an adherend from the adherend is provided. The peeling method comprises the steps of heating the adherend to which the adhesive sheet is adhered at a temperature above a predetermined temperature, and then peeling the adhesive sheet from the adherend. The adhesive sheet disclosed herein exhibits heat-peelability (heat-resistant peelability), and thus can be easily peeled from the adherend even after exposure to heat under predetermined conditions.

[0177] In some embodiments, the temperature for heat treatment of the adherend to which the adhesive sheet is attached is suitably 120°C or higher, and may be approximately 130°C or higher, or may be approximately 150°C or higher. In some preferred embodiments, the temperature for heat treatment of the adherend to which the adhesive sheet is attached is higher than 150°C, and may be 160°C or higher, or may be 170°C or higher. The upper limit of the heat treatment temperature may vary depending on the purpose of the heat treatment, the heat resistance of the adherend, etc., but is generally approximately 260°C or lower, approximately 250°C or lower, 230°C or lower, 200°C or lower, or 180°C or lower. The time for heat treatment is not particularly limited and may be within 10 hours, within 5 hours, or within 3 hours. From the perspective of the efficiency of the heating process, in some preferred embodiments, the time for heat treatment may be within 1 hour, within 30 minutes, within 15 minutes, within 10 minutes, or within 5 minutes. The adhesive sheet disclosed herein is subjected to the above-mentioned short-time heat treatment to thermally cure the adhesive, and can exhibit heat-resistance. In addition, the heat treatment time can be more than 1 minute, can be more than 3 minutes, can be more than 5 minutes, can be more than 7 minutes, or can be more than 9 minutes. In some embodiments, the heat treatment time can be more than 10 minutes, can be more than 30 minutes, can be more than 60 minutes, can exceed 1 hour, can exceed 3 hours, can exceed 4 hours, or can exceed 5 hours. The adhesive sheet disclosed herein is subjected to the above-mentioned heating temperature-based heat treatment to thermally cure the adhesive, and the peeling force is reduced. Even if the heated state continues for a long time, the increase in peeling force (heavy peeling) will not occur or can be suppressed. Therefore, heat-resistance (heat-resistant peeling) can be maintained even after a long period of heat treatment.

[0178] <Purpose>

[0179] The use of the adhesive sheet disclosed herein is not particularly limited. The adhesive sheet disclosed herein effectively demonstrates the characteristic of being easily peelable by heating for various adherends such as adherends containing organic materials based on rapid heat curing, and can be used as an adhesive sheet for various uses that require easy peelability by heating, such as uses in which the adhesive sheet is peeled off from the adherend by heating. For example, when it is attached to an adherend, it can be used for uses that are exposed to heating exceeding 100°C (for example, about 120°C to 260°C). In addition, when it is attached to an adherend, it can be preferably used for uses that are exposed to heating exceeding 150°C (for example, about 160°C to 260°C).

[0180] As the applications to which the adhesive sheet disclosed herein is applicable, for example, masking applications, temporary fixing applications, and protective applications that require heat resistance for the adhesive sheet can be cited. In addition, for example, it can also be preferably used as a process material that is fixed to an adherend and peeled off in the manufacturing process of electronic equipment or electronic components. In addition, as suitable applications of the adhesive sheet disclosed herein, semiconductor element manufacturing applications can be cited. For example, in semiconductor wafer processing (typically silicon wafer processing), it can be preferably used as a wafer fixing sheet that fixes the wafer to a fixed plate. In addition, the adhesive sheet disclosed herein can also be preferably used as a protective sheet that protects the wafer in the above-mentioned wafer processing. In particular, when semiconductor elements are manufactured, they are exposed to heating during the processing steps, etc., so it is preferred to utilize an adhesive sheet with heat-resistant and easily peelable properties. In addition, the adhesive sheet disclosed herein can also be applied to optical applications that require heat resistance. More specifically, for example, as an optical adhesive sheet for bonding optical components (optical component bonding), the manufacturing application of products (optical products) using the above-mentioned optical components, etc., the adhesive sheet disclosed herein can be used. The optical member is a member having optical properties (for example, polarization, light refraction, light scattering, light reflection, light transmittance, light absorption, light diffraction, optical rotation, and visibility).

[0181] In addition, the adhesive sheet disclosed herein can also exhibit good heat-peelable properties even on organic material surfaces. Therefore, it can be preferably used in a manner of sticking to the surface of a substrate (adherend) whose surface is composed of an organic material and then peeling it from the surface. As such a substrate material, for example, a circuit substrate (e.g., a printed wiring board (PCB), a flexible circuit substrate (FPC)) can be cited. As a sheet for temporarily fixing such a circuit substrate, an adhesive sheet can be preferably used.

[0182] The type of material (adherend material) disclosed herein for pasting is not particularly limited. The adhesive sheet disclosed herein can be used for fixing and protecting various components and materials. As the adherend material, a material composed of any one of an organic material, an inorganic material, or a composite thereof can be used. Examples of adherend materials include: glasses such as alkaline glass and alkali-free glass; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; resin materials such as polyester resins such as PET, acrylic resins, ABS resins, polycarbonate resins, polystyrene resins, transparent polyimide resins, epoxy resins, and phenolic resins; and so on. As suitable examples of adherend materials, for example, a circuit substrate (for example, a glass cloth substrate epoxy resin copper-clad laminate) having a surface composed of epoxy resin can be cited. In addition, as other suitable examples of adherend materials, for example, glass materials such as alkaline glass, semiconductor wafers, etc. can be cited. The glass material may be a glass plate having a surface partially provided with a transparent conductive film (such as an ITO (indium tin oxide) film) or an FPC (flexible circuit board), which can be used in tablet personal computers, mobile phones, organic LEDs (light emitting diodes), etc.

[0183] The matters disclosed in this specification include the following.

[0184] [1] An adhesive sheet having an adhesive layer comprising a polymer, a monomer and a thermal polymerization initiator,

[0185] The aforementioned polymer contains ethylenically unsaturated groups,

[0186] The aforementioned monomer contains an ethylenically unsaturated group,

[0187] The thermal polymerization initiator includes a peroxide-based polymerization initiator.

[0188] [2] The adhesive sheet according to [1] above, wherein the adhesive layer contains a multifunctional acrylate monomer as the monomer.

[0189] [3] The adhesive sheet according to [1] or [2] above, wherein the content of the monomer in the adhesive layer is less than 50 parts by weight relative to 100 parts by weight of the polymer.

[0190] [4] The adhesive sheet according to any one of [1] to [3] above, wherein the content of the thermal polymerization initiator in the adhesive layer is 0.1 part by weight or more and 1 part by weight or less per 100 parts by weight of the polymer.

[0191] [5] The adhesive sheet according to any one of [1] to [4] above, wherein the adhesive layer has a gel fraction of 50% or more before heating.

[0192] [6] The adhesive sheet according to any one of [1] to [5] above, wherein the Young's modulus Y1 [MPa] of the adhesive layer after heat treatment at 180°C for 30 minutes is 200 times or more the Young's modulus Y0 [MPa] before heating.

[0193] [7] The adhesive sheet according to any one of [1] to [6] above, which is used by being adhered to the surface of a substrate having a surface made of an organic material and then peeled from the surface.

[0194] Example

[0195] Hereinafter, some embodiments of the present invention will be described, but it is not intended that the present invention be limited to the contents shown in these embodiments. It should be noted that, unless otherwise specified, in the following description, "parts" and "%" are based on weight.

[0196] <Evaluation Method>

[0197] (Peel force F0 before heating)

[0198] Adhesive sheet is cut into the size of width 20mm, length 100mm, under the environment of 23 ℃, 50%RH, 2kg roller is reciprocated 1 time and the adhesive surface of adhesive sheet is pressed and is applied to adherend.Under the same environment, the adherend of the above-mentioned adhesive sheet is left to stand for 6 hours, used as evaluation sample. The above-mentioned evaluation sample is arranged in tensile testing machine under the environment of 23 ℃, 50%RH, measures the peel strength (peeling force before heating) F0 [N / 20mm width) when the adhesive sheet is peeled off from adherend under the conditions of peeling angle 180 degrees, speed 300mm / minute. As adherend, FR-4 glass cloth substrate epoxy resin copper clad laminate (Nikkan Industrial Co., Ltd. system, product number " L6504C1 ") is used. As tensile testing machine, product name " EZ-S 500N " or its equivalent product of Shimadzu company system can be used. When the object to be evaluated is a double-sided PSA sheet, the non-measurement surface may be lined with a PET film before measurement.

[0199] (Peel force after heating F1)

[0200] Using an adhesive sheet, an evaluation sample was prepared by the method described in the determination of the peeling force F0 before heating. The obtained evaluation sample was heat-treated in an oven at 180°C for 30 minutes, removed from the oven, and allowed to stand for 30 minutes under an environment of 23°C and 50% RH. Then, the evaluation sample was placed in a tensile testing machine under the same environment to measure the peel strength (peeling force after heating) F1 [N / 20mm width) when the adhesive sheet was peeled off from the adherend at a peeling angle of 180 degrees and a speed of 300mm / min. Regarding the adherend, tensile testing machine, and other matters, the same procedures were used as for the determination of the peeling force F0 before heating.

[0201] (Gel fraction)

[0202] The gel fraction (weight ratio of the ethyl acetate-insoluble component) of the pressure-sensitive adhesive layer can be measured by the following method.

[0203] Approximately 0.1 g of an adhesive sample (weight Wg1) was wrapped in a purse-shaped porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm and tied with kite string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane used was Nitoflon (registered trademark) NTF1122 (average pore size 0.2 μm, porosity 75%, thickness 85 μm), available from Nitto Denko Corporation, or an equivalent.

[0204] The package was immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23°C) for 7 days to allow only the sol component in the adhesive layer to elute to the outside of the film. The package was then removed and the ethyl acetate adhering to the outer surface was wiped off. The package was then dried at 130°C for 2 hours, and the weight of the package (Wg4) was measured. The values were then substituted into the following formula to determine the gel fraction of the adhesive layer.

[0205] Gel fraction [%] = [(Wg4-Wg2-Wg3) / Wg1] × 100

[0206] The gel fraction of the adhesive layer was measured initially (gel fraction before heating), after the adhesive layer was heated in an oven at 180°C for 30 minutes, and after being removed from the oven and allowed to stand for 30 minutes in an environment of 23°C and 50% RH (gel fraction after heating).

[0207] (Young's modulus)

[0208] Prepare the adhesive layer in a state where both sides are covered with release liners, cut it into a size of 80 mm in width and 30 mm in length for each release liner, remove the release liner on one side from the above-mentioned adhesive layer, and on the release liner on the other side, roll up the above-mentioned adhesive layer along its length direction in a manner not to introduce bubbles, thereby making a rod-shaped sample with a length of 30 mm. The above-mentioned rod-shaped sample is set in a tensile testing machine (manufactured by ORIENTEC, trade name "RTC-1150A"), and stretched under the conditions of a measuring temperature of 23°C, a distance between chucks of 10 mm, and a tensile speed of 50 mm / min. The initial elastic modulus is determined based on the rise of the obtained stress (Stress)-strain (Strain) curve (SS curve), and is used as the Young's modulus [MPa] of the adhesive layer. It should be noted that the cutting width of the adhesive layer is set to 80 mm in order to make the cross-sectional area of the adhesive layer in the cross section along the width direction between 2 and 2.5 mm. 2 It is desirable to adjust the cutting width in accordance with the thickness of the adhesive layer so as to obtain a similar cross-sectional area within the range of .

[0209] The Young's modulus of the adhesive layer was measured initially (Young's modulus before heating), and after the adhesive layer was heated in an oven at 180°C for 30 minutes, removed from the oven, and allowed to stand for 30 minutes in an environment of 23°C and 50% RH (Young's modulus after heating).

[0210] <Example 1>

[0211] (Preparation of Adhesive Composition)

[0212] A reaction vessel equipped with a condenser, a nitrogen inlet, a thermometer, and a stirrer was charged with 100 parts of monomer components consisting of methoxyethyl acrylate (MEA), acryloylmorpholine (ACMO), and hydroxyethyl acrylate (HEA) at a molar ratio of 80:20:20, 65 parts of toluene as a polymerization solvent, and 0.2 parts of benzoyl peroxide as a thermal polymerization initiator. A polymerization reaction (solution polymerization) was carried out at 61°C under a nitrogen atmosphere for 6 hours to obtain a solution containing acrylic polymer A. To this solution of acrylic polymer A, an amount of methacryloyloxyethyl isocyanate (MOI) equivalent to 16 mol relative to 20 mol of HEA, a raw material for acrylic polymer A, was added, and an addition reaction was carried out at 50°C in an air stream for 48 hours to obtain a solution of acrylic polymer A having a methacryloyl group at the end of the side chain.

[0213] To the solution of the acrylic polymer A, 30 parts of dipentaerythritol hexaacrylate (DPHA) as a monomer, 0.5 parts of an isocyanate crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D-101E"), and 0.5 parts of benzoyl peroxide (manufactured by NOF Corporation, product name "NYPER BW", SADT: 75°C) as a thermal polymerization initiator were added based on 100 parts of the acrylic polymer A, and the mixture was uniformly mixed to prepare the adhesive composition involved in this example.

[0214] (Production of Adhesive Sheet)

[0215] The adhesive composition obtained in the above manner 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 adhesive layer. A 50 μm thick polyimide (PI) film (product name "Kapton 200H", manufactured by Du Pont-Toray Co., Ltd.) was attached to the adhesive layer and aged at 50°C for 3 days. Thus, the adhesive sheet (single-sided adhesive sheet with a substrate) involved in this example was produced. The adhesive surface of the adhesive sheet was protected by a release liner.

[0216] <Examples 2 to 12 and Comparative Examples 1 to 3>

[0217] A PSA composition for each example was prepared in the same manner as in Example 1, except that the type and amount of monomers, the type and amount of thermal polymerization initiator, and the amount of crosslinking agent were changed as shown in Table 1. Using the resulting PSA composition, a single-sided PSA sheet with a substrate for each example was produced in the same manner as in Example 1. In Table 1, HDDA represents 1,6-hexanediol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), NYPERBMT represents "NYPER BMT" (manufactured by NOF Corporation, benzoyl peroxide-based, SADT: 45°C), AIBN represents 2,2'-azobisisobutyronitrile, and VR-110 represents 2,2'-azobis(2,4,4-trimethylpentane) (manufactured by FUJIFILM Wako Pure Chemical Corporation, product name "VR-110").

[0218] <Comparative Example 4>

[0219] Into a reaction vessel equipped with a condenser, a nitrogen inlet tube, a thermometer, and a stirrer, 85 parts of MEA, 10 parts of N-vinyl-2-pyrrolidone (NVP), and 5 parts of 4-hydroxybutyl acrylate (4HBA) as monomer components, and 300 parts of ethyl acetate as a polymerization solvent were placed. 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added, 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.

[0220] To the solution of the acrylic polymer B, 100 parts of DPHA as a monomer, 0.5 parts of the isocyanate crosslinking agent, and 0.5 parts of benzoyl peroxide (manufactured by NOF Corporation, product name "NYPER BW", SADT: 75°C) as a thermal polymerization initiator were added based on 100 parts of the acrylic polymer B, and the mixture was uniformly mixed to prepare the adhesive composition involved in this example.

[0221] A single-sided pressure-sensitive adhesive sheet with a substrate according to this example was produced in the same manner as in Example 1 except that the pressure-sensitive adhesive composition was used.

[0222] The summary and evaluation results of each example are shown in Table 1. In the measurement of the peel strength after heating, when the pressure-sensitive adhesive layer was firmly bonded to the adherend by heating and the peel strength could not be measured, the evaluation was "X".

[0223] [Table 1]

[0224]

[0225] As shown in Table 1, in Examples 1-12, which used adhesives whose polymers and monomers contained ethylenically unsaturated groups and contained a peroxide-based polymerization initiator as a thermal polymerization initiator, it was confirmed that the peel force was sufficiently reduced after heating when attached to the surface of an organic material (epoxy resin of an FR-4 glass cloth-based epoxy copper-clad laminate). On the other hand, in Comparative Examples 1-2, which used an azo-based polymerization initiator (rather than a peroxide-based one) as a thermal polymerization initiator, Comparative Example 3, which did not use a monomer, and Comparative Example 4, which used a polymer without ethylenically unsaturated groups, all failed to peel from the adherend after heating, and the post-heating peel force could not be measured. While the adhesive sheets of Comparative Examples 1-4 all exhibited good heat-peelability from alkaline glass plates, it is believed that due to differences in the surface smoothness of the adherend and the adhesion between the organic material and the adhesive during high-temperature heating, they adhered to the adherend to an impervious degree after heating. For example, in Comparative Examples 1 and 2, the reaction rate of the azo polymerization initiator is slower than that of the peroxide polymerization initiator. Therefore, it is believed that the adhesive and the adherend adhere more quickly than the curing during heating. It should be noted that in Comparative Example 4, a larger amount of monomer was added to increase the curing degree after heating (Young's modulus after heating), but even so, peeling after heating was difficult.

[0226] While the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the claims. The technology described in the claims includes various modifications and variations of the specific examples described above.

[0227] Description of Reference Numerals

[0228] 1 Adhesive sheet

[0229] 1A bonding surface

[0230] 1B Back

[0231] 10 base material layer

[0232] 10A side surface

[0233] 10B The other side of the face

[0234] 20 adhesive layers

[0235] 20A bonding surface

[0236] 30 release liners

[0237] 50 Adhesive sheet with release liner

Claims

1. An adhesive sheet having an adhesive layer comprising a polymer, a monomer and a thermal polymerization initiator, The polymer comprises ethylenically unsaturated groups, The monomer contains an ethylenically unsaturated group, The thermal polymerization initiator includes a peroxide-based polymerization initiator.

2. The adhesive sheet according to claim 1, wherein The adhesive layer includes a multifunctional acrylate-based monomer as the monomer.

3. The adhesive sheet according to claim 1 or 2, wherein The content of the monomer in the adhesive layer is less than 50 parts by weight based on 100 parts by weight of the polymer.

4. The adhesive sheet according to claim 1 or 2, wherein The adhesive layer has a gel fraction of 50% or more before heating.

5. The adhesive sheet 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 200 times or more the Young's modulus Y0 [MPa] before heating. 6 . The adhesive sheet according to claim 1 , which is used by being adhered to a surface of a substrate having a surface composed of an organic material and then peeled from the surface.

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