Adhesive sheet

Abstract

The present application provides an adhesive sheet having good high-temperature shear holding property and stress relaxation property that makes it difficult for the influence of a convex portion or a height difference present on one side of the adhesive sheet to be shown on the other side. The adhesive sheet has an adhesive layer. In the adhesive sheet, the breaking strength of the above-mentioned adhesive layer in a tensile test conducted at a tensile speed of 10 mm / min is 2 MPa or less. In addition, the 80°C adhesive force retention rate (P RT 80°C / P 80℃ × 100) of the above-mentioned adhesive sheet, which is obtained from the relationship between the 180-degree peeling strength P 80℃ 80°C of the above-mentioned adhesive sheet against a stainless steel plate measured at 23°C and the 180-degree peeling strength P RT 80°C of the above-mentioned adhesive sheet against a stainless steel plate measured at 80°C, is 50% or more.

Description

Technical Field

[0001] This invention relates to adhesive sheets. This application claims priority to Japanese Patent Application No. 2020-153621, filed on September 14, 2020, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Generally, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are soft solids (viscoelastics) in a temperature range near room temperature, and have the property of easily adhering to the substrate under pressure. Utilizing this property, adhesives are widely used, for example, in the form of adhesive sheets with an adhesive layer on a supporting substrate or in the form of substrate-free adhesive sheets without a supporting substrate, for joining, fixing, and protecting components in smartphones and other portable electronic devices. Patent documents 1-2 can be cited as examples of technical documents related to adhesive tapes for fixing components in portable electronic devices.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-70102

[0006] Patent Document 2: Japanese Patent Application Publication No. 2018-28051 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] For adhesive sheets used in environments exposed to high temperatures, good adhesive properties are required even at high temperatures. For example, portable electronic devices are sometimes used in high-temperature environments, and their internal spaces sometimes contain heat due to the generation of electronic components. Therefore, adhesive sheets used for this purpose need to have sufficient adhesive reliability even at high temperatures. Furthermore, the adhesive area for fixing components within portable electronic devices is usually small due to size and weight limitations. Therefore, adhesive sheets used for this purpose need to have good adhesive reliability even with a small area, and the performance requirements are becoming even higher due to the demands for lightweighting and miniaturization. Especially for portable electronic devices with touch panel displays, such as smartphones, while miniaturizing and thinning the product itself, the trend towards larger screens is driven by considerations of visual visibility and operability. For adhesives used in this application, adhesive fixation performance under even more stringent conditions is required. In the fixing of components within portable electronic devices, adhesive sheets with excellent adhesive properties (e.g., high-temperature shear retention) not only in the room temperature range but also in the high-temperature range are desirable.

[0009] However, in adhesive bonding, some objects have uneven surfaces or irregularities on their adhesive side and back side (the side opposite to the adhesive side of the adhesive sheet). Furthermore, even if an object adhered to one adhesive side of the adhesive sheet has a flat shape, if a component or article disposed on the back side of that object has irregularities, pressing it against the adhesive sheet can transmit these protrusions to the adhesive sheet through the object, causing deformation of the sheet surface. Moreover, even other components separated by the adhesive sheet (objects adhered to the other adhesive side of the adhesive sheet, and components disposed on the back side of those objects) can experience deformation due to these protrusions.

[0010] In the fixing of components within the aforementioned portable electronic devices, components such as flexible printed wiring boards (FPCs) can be bent to accommodate the confined space within the device. Such components can form protrusions in a flat assembly of components. Furthermore, due to the combination and arrangement of multiple components, height differences can arise between them. When the aforementioned assembly of components is pressed into the internal space or crimped, these protrusions and height differences within the device can deform the adhesive sheet via other components (the adhered material). This deformation of the sheet surface sometimes results in a scratch-like appearance on the opposite side of the adhesive sheet (the side opposite to the side with the protrusion, etc.). Such deformation of the adhesive sheet surface caused by protrusions, etc., can lead to undesirable effects in the adhered material component and, for example, in the assembly of components disposed on the back side of the adhered material component, causing uneven application of external forces such as impacts to the deformed portion, resulting in breakage points.

[0011] The present invention was made in view of the above circumstances, and its object is to provide an adhesive sheet that has good high-temperature shear retention and stress relaxation properties that make the effects of protrusions and height differences on one side of the adhesive sheet less likely to appear on the other side.

[0012] means for solving problems

[0013] According to this specification, an adhesive sheet having an adhesive layer is provided. In this adhesive sheet, the tensile strength of the adhesive layer in a tensile test performed at a tensile speed of 10 mm / min is 2 MPa or less. Furthermore, the 180-degree peel strength P of the adhesive sheet to a stainless steel sheet, measured at 23°C, is also specified. RT The 180-degree peel strength P of the above-mentioned adhesive sheet to stainless steel plate was measured at 80°C. 80℃ The adhesion retention rate (P) of the above adhesive sheet at 80℃ was obtained by calculating the relationship. 80℃ / P RTThe adhesive strength (×100) is 50% or more. Compared to the adhesive strength of the aforementioned adhesive sheet at 23°C, the adhesive strength of the aforementioned adhesive sheet at 80°C is maintained at 50% or more (adhesive strength retention rate at 80°C is 50% or more), demonstrating good high-temperature adhesive properties compared to room temperature. This adhesive suppresses the reduction in holding force that easily deteriorates at high temperatures, exhibiting excellent high-temperature shear retention. Furthermore, since the tensile strength of the adhesive layer of the adhesive sheet is limited to 2 MPa or less, its stress relaxation properties prevent or reduce the impact of protrusions or height differences existing on one side of the adhesive sheet on the other side. According to the technology disclosed herein, an adhesive sheet that balances high-temperature shear retention and stress relaxation properties in a balanced manner can be provided.

[0014] In some embodiments, the adhesive sheet is a substrate-based double-sided adhesive sheet with a substrate layer, the total thickness of which accounts for more than 50% of the total thickness of the adhesive sheet. According to such a substrate-based double-sided adhesive sheet, while enjoying the advantages of processability and operability due to the substrate, the stress relaxation properties provided by the adhesive layer can be better utilized. In other embodiments, the adhesive sheet is a substrate-free double-sided adhesive sheet composed of the aforementioned adhesive layers. According to the substrate-free adhesive sheet, the adhesive properties and stress relaxation properties based on the adhesive layer can be maximized. Furthermore, the substrate-free double-sided adhesive sheet can be thinned to the extent that it lacks a substrate, which can help in the miniaturization and space-saving of products using the double-sided adhesive sheet.

[0015] In some preferred embodiments, the adhesive layer comprises a tackifying resin with a softening point of less than 145°C. By using a tackifying resin with a softening point of less than 145°C, it is possible to reduce the breaking strength while maintaining high-temperature shear retention, thus exhibiting superior stress relaxation properties.

[0016] The adhesive layer disclosed herein can be an acrylic adhesive layer comprising an acrylic polymer as a base polymer. The technology disclosed herein is preferably implemented in a configuration having an acrylic adhesive layer. In some preferred embodiments, the acrylic polymer contains at least 50% by weight an alkyl (meth)acrylate having an alkyl group having 7 or more carbon atoms at the ester terminus. The acrylic polymer composed of the above monomers tends to have a low glass transition temperature (Tg), and can preferably balance excellent adhesive properties and stress relaxation properties.

[0017] In some embodiments, the adhesive layer comprises acrylic oligomers. By including acrylic oligomers in the adhesive layer, the effects of the technology disclosed herein can preferably be achieved.

[0018] In some embodiments, the adhesive composition used to form the aforementioned adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent. By using both isocyanate and epoxy crosslinking agents as crosslinking agents, it is preferable to achieve both high-temperature shear retention and stress relaxation properties.

[0019] In some preferred embodiments, the total thickness of the adhesive layers is 30 μm or more. Adhesive layers with a thickness exceeding a specified value readily absorb the effects of protrusions and height differences acting on the surface of the adhesive sheet. Furthermore, adhesive layers with sufficient thickness result in superior adhesive properties.

[0020] The adhesive sheet disclosed herein exhibits excellent high-temperature bonding properties (particularly high-temperature shear retention), making it suitable for use as a fixing component within portable electronic devices that are sometimes used in high-temperature environments or whose internal space is sometimes heated by the heat generated by electronic components. Furthermore, sometimes multiple components are disposed within portable electronic devices, some of which have protrusions or height differences. For example, wiring boards, housings, and other components with height differences may be disposed within the portable electronic device. When these multiple components are pressed into the internal space or crimped, the aforementioned protrusions, etc., can directly or indirectly deform other components. In such portable electronic devices, by utilizing the stress relaxation properties of the adhesive sheet disclosed herein, the effects of protrusions, etc., present on one side of the adhesive sheet can be prevented or reduced from manifesting on the other side. The adhesive sheet disclosed herein is particularly suitable for applications involving the fixing of components disposed within portable electronic devices. Attached Figure Description

[0021] Figure 1 A cross-sectional view illustrating an example of the construction of an adhesive sheet.

[0022] Figure 2 A cross-sectional view is shown schematically to illustrate another example of the composition of the adhesive sheet.

[0023] Figure 3 An exploded perspective view illustrating an example of the configuration of a display device. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described. It should be noted that matters necessary for implementing the present invention, other than those specifically mentioned in this specification, can be understood by those skilled in the art based on the teachings on implementation of the invention as described in this specification and common technical knowledge at the time of application. The present invention can be implemented based on the disclosure in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components / parts that perform the same function are sometimes labeled with the same reference numerals, and repeated descriptions may be omitted or simplified. Additionally, for the purpose of clearly illustrating the present invention, the embodiments described in the drawings are schematic and do not necessarily accurately represent the dimensions or scale of the adhesive sheet of the present invention actually provided as a product.

[0025] In this specification, "adhesive" refers to a material that, as described above, is a soft solid (viscoelastic) in a temperature range near room temperature and has the property of easily adhering to the substrate under pressure. The adhesive referred to here, as defined in "CADahlquist, 'Adhesion: Fundamental and Practice', McLaren & Sons, (1966) p. 143," can generally be a material having a complex tensile modulus E. * (1Hz) < 10 7 dyne / cm 2 Materials with the properties described above (typically, materials that have the properties described above at 25°C).

[0026] <Example of adhesive sheet composition>

[0027] The adhesive sheet disclosed herein can be a substrate-supported adhesive sheet having the aforementioned adhesive layer on one or both sides of a non-peelable substrate (supporting substrate), or a substrate-free adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate) in which the aforementioned adhesive layer is held on a release liner. The concept of adhesive sheet herein can include items referred to as adhesive tape, adhesive label, adhesive film, etc. It should be noted that the adhesive sheet disclosed herein can be in roll form or in single sheet form. Alternatively, it can be an adhesive sheet further processed into various shapes.

[0028] The structure of a double-sided adhesive substrate-free adhesive sheet (substrate-free double-sided adhesive sheet) is illustrated in the figure. Figure 1 middle. Figure 1The adhesive sheet 1 shown has a substrate-free adhesive layer 21 on both sides 21A and 21B protected by release liner 31 and 32, which serve as release surfaces at least on the adhesive layer side. Alternatively, the adhesive sheet has a substrate-free adhesive layer on one surface (adhesive surface, first adhesive surface) protected by release liner on both sides, and when wound, the other surface (adhesive surface, second adhesive surface) of the adhesive layer contacts the back of the release liner, thereby enabling the second adhesive surface of the adhesive layer to also be protected by the release liner. From the viewpoint of reducing the thickness of the adhesive sheet, the technology disclosed herein is preferably implemented in such a substrate-free form. Substrate-free adhesive sheets are easy to make thin, and are also advantageous from the viewpoint of maximizing adhesive properties such as adhesive strength and impact resistance.

[0029] The adhesive sheet disclosed herein may, for example, have... Figure 2 The cross-sectional structure of the adhesive sheet is schematically shown in the figure. Figure 2 The adhesive sheet 2 shown has the following configuration: adhesive layers 21 and 22 (also referred to as first adhesive layer 21 and second adhesive layer 22, respectively) are provided on each side (all non-peelable) of a substrate (substrate layer) 10, and these adhesive layers are protected by release liner 31 and 32, which are at least peelable surfaces on the adhesive layer side. Alternatively, the adhesive sheet may also have the following configuration: adhesive layers (first adhesive layer and second adhesive layer) are provided on each side (all non-peelable) of the substrate, and one of the adhesive layers (first adhesive layer) is protected by a release liner with both sides serving as peelable surfaces. Such an adhesive sheet may be configured such that another adhesive layer (second adhesive layer) contacts the back side of the release liner, thereby also being protected by the release liner.

[0030] <80℃ Adhesion retention rate>

[0031] The adhesive sheet disclosed herein has an adhesive force P at 23°C. RT and the adhesive force P at 80℃ 80℃ The 80℃ adhesion retention rate (P) was obtained from the relationship. 80℃ / P RTThe adhesive strength at 80°C is 50% or more (×100). The adhesive sheet satisfying the above characteristics retains 50% or more of its adhesive strength at 80°C compared to its adhesive strength at 23°C (80°C adhesive strength retention rate is 50% or more), exhibiting good high-temperature adhesive properties (especially high-temperature shear retention). From the viewpoint of maintaining high-temperature adhesive properties, the aforementioned 80°C adhesive strength retention rate is preferably 55% or more, more preferably 60% or more, further preferably 65% ​​or more, and can be 70% or more, or 75% or more. There is no particular upper limit to the aforementioned 80°C adhesive strength retention rate; in some cases, it is typically 100% or less, and can be 90% or less, or 80% or less. Adhesives having the aforementioned 80°C adhesive strength retention rate tend to easily achieve a breaking strength below the specified value described later. It should be noted that the adhesive strength P at 23°C... RT Adhesive force P at 80℃ 80℃ The peel strength P of the adhesive sheet to the stainless steel plate at 180 degrees, measured at 23°C, is respectively. RT The 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 80°C. 80℃ Specifically, the determination is performed using the methods described in the embodiments described later.

[0032] <Temperature strength of adhesive layer>

[0033] The adhesive sheet disclosed herein has an adhesive layer with a tensile strength of 2 MPa or less. By limiting the tensile strength of the adhesive layer to 2 MPa or less, the adhesive layer has an excellent tendency for stress relaxation, and the effects of protrusions or height differences present on one side of the adhesive sheet can be prevented or reduced from appearing on the other side. The aforementioned tensile strength is preferably 1.5 MPa or less, more preferably 1.2 MPa or less, even more preferably 1.0 MPa or less, and particularly preferably 0.8 MPa or less (e.g., 0.6 MPa or less). From the viewpoint of maintaining an adhesive force retention rate of 50% or more at 80°C, the aforementioned tensile strength of 0.1 MPa or more is appropriate, and can be 0.3 MPa or more, 0.5 MPa or more, or 0.9 MPa or more (e.g., 1.4 MPa or more). The tensile strength of the adhesive layer is determined by a tensile test performed at a tensile speed of 10 mm / min, specifically by the method described in the embodiments described later. In a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer on each side of the substrate, at least one (preferably two) adhesive layers satisfy the aforementioned tensile strength.

[0034] The aforementioned 80°C adhesion retention rate and tensile strength can be achieved by adjusting the composition of the adhesive sheet according to the description in this manual, by selecting the type of adhesive, the type of adhesive components (base polymer, tackifying resin, crosslinking agent, other additives, etc.), and the amount used.

[0035] <Adhesive layer>

[0036] (Basic Polymer)

[0037] In the technology disclosed herein, there are no particular limitations on the type of adhesive constituting the adhesive layer. The adhesive may contain one or more of the following rubber-like polymers that are usable in the field of adhesives: acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, polysiloxane polymers, polyamide polymers, fluoropolymers, etc., as the adhesive polymer (referring to the structural polymer that forms the adhesive, hereinafter also referred to as the "base polymer"). From the viewpoint of adhesive performance and cost, adhesives containing acrylic polymers or rubber polymers as the base polymer are preferably used. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is preferably implemented using acrylic adhesives.

[0038] The following description mainly focuses on adhesive sheets having an adhesive layer made of acrylic adhesive, i.e., an acrylic adhesive layer, but it is not intended to limit the adhesive layer of the adhesive sheets disclosed herein to an adhesive layer made of acrylic adhesive.

[0039] It should be noted that the "base polymer" of the adhesive refers to the main component of the rubber-like polymer contained in the adhesive, and is not interpreted in any other limiting way. The aforementioned rubber-like polymer refers to a polymer that exhibits rubber-like elasticity in a temperature range near room temperature. Furthermore, in this specification, "main component" refers to a component with a content greater than 50% by weight unless otherwise specified.

[0040] Furthermore, "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer." Therefore, the acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. As a typical example of an acrylic polymer, an acrylic polymer in which the proportion of acrylic monomers in all monomer components used in the synthesis of such an acrylic polymer is greater than 50% by weight can be listed.

[0041] In addition, "(meth)acryloyl" refers to both acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers to both acrylate and methacrylate, and "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid.

[0042] (Acrylic polymers)

[0043] As for the acrylic polymers disclosed herein, polymers containing, for example, alkyl (meth)acrylates as the main monomer and potentially further comprising copolymerizable by secondary monomers that have copolymerization properties with the main monomer are preferred. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition of the aforementioned monomeric raw material.

[0044] As an alkyl methacrylate, a compound represented by, for example, the following formula (1) can be used.

[0045] CH2=C(R 1 COOR 2 (1)

[0046] Wherein, R in equation (1) above 1 It can be a hydrogen atom or a methyl group. Additionally, R... 2 It is a chain alkyl group having 1 to 20 carbon atoms. This range of carbon atoms is sometimes referred to below as "C". 1-20 "From the perspective of the storage modulus of adhesives, etc., with R..." 2 C 1-14 (e.g., C) 1-10 Typically C 4-8 Alkyl (meth)acrylates with chain-like alkyl groups are suitable as the main monomer. From the viewpoint of adhesive properties, R is preferred. 1 It is a hydrogen atom and R 2 C 4-8 Alkyl acrylates with chain-like alkyl groups (hereinafter also referred to as C acrylates) 4-8 Alkyl esters are used as the main monomers.

[0047] As R 2 C 1-20Specific examples of alkyl (meth)acrylates with chain-like alkyl groups are not particularly limited, and examples include: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and octyl (meth)acrylate. Alkyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecanyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecanyl methacrylate, octadecyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, etc. These alkyl methacrylates can be used alone or in combination of two or more. Preferred examples of alkyl methacrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0048] The proportion of alkyl (meth)acrylates in the monomer components constituting acrylic polymers is typically greater than 50% by weight, for example, it can be set to 70% by weight or more, 85% by weight or more, or 90% by weight or more. There is no particular upper limit to the proportion of alkyl (meth)acrylates, but it is preferably set to 99.5% by weight or less (e.g., 99% by weight or less), or, from the viewpoint of preferably utilizing the properties (e.g., cohesiveness) of secondary monomers such as carboxyl-containing monomers, it can be set to 98% by weight or less (e.g., less than 97% by weight). Alternatively, the acrylic polymer may also be a polymer obtained by substantially polymerizing only alkyl (meth)acrylates.

[0049] In addition, using acrylic C 4-8 When alkyl esters are used as monomer components, in the (meth)acrylate alkyl esters contained in these monomer components, acrylic acid C 4-8 The proportion of alkyl esters is preferably 70% by weight or more, and more preferably 90% by weight or more.

[0050] In some embodiments, the monomer components constituting the aforementioned acrylic polymers contain more than 50% by weight of (meth)acrylic acid C. 1-6 Alkyl esters. In other words, the (meth)acrylic acid C in the above-mentioned acrylic polymers. 1-6 The polymerization ratio of alkyl esters can be 50% by weight or more. This is achieved by using (meth)acrylic acid C in this way.1-6 Alkyl esters, as the main monomers, tend to readily exhibit high-temperature shear retention. In this approach, (meth)acrylic acid C 1-6 The proportion of alkyl esters in the monomer component (in other words, the polymerization ratio) is preferably 80% by weight or more, more preferably 90% by weight or more (e.g., 92% by weight or more). (Meth)acrylic acid C 1-6 There is no particular upper limit to the proportion of alkyl esters in the monomer composition, typically below 99% by weight. Considering the relationship with the proportions used in other comonomers, below 97% by weight is appropriate, and preferably below 95% by weight. (Meth)acrylic acid C 1-6 Alkyl esters can be used alone or in combination of two or more. As (meth)acrylic acid C 1-6 Alkyl ester, preferably C14 acrylic acid 1-6 Alkyl esters, more preferably acrylic C 2-6 Alkyl esters, more preferably acrylic C 4-6 Alkyl esters. In some other ways, (meth)acrylic acid C 1-6 Alkyl esters are preferably C14 acrylic acid. 1-4 Alkyl ester, more preferably acrylic acid C 2-4 Alkyl ester. As a (meth)acrylic acid C 1-6 Preferred examples of alkyl esters include BA.

[0051] In some preferred embodiments, the monomer components constituting the above-mentioned acrylic polymer contain more than 50% by weight of (meth)acrylic acid C. 7-10 Alkyl esters. In other words, the (meth)acrylic acid C in the above-mentioned acrylic polymers. 7-10 The copolymerization ratio of alkyl esters is preferably 50% by weight or more. This is achieved by using (meth)acrylic acid C in this way. 7-10 Alkyl esters, as the main monomers, can preferably be used to design acrylic polymers in a way that better balances adhesive strength retention above a specified value at 80°C and tensile strength below a specified value. (Meth)acrylic acid C 7-10 The proportion of alkyl esters in the monomer composition (in other words, the copolymerization proportion) can be greater than 60% by weight, greater than 70% by weight, more preferably greater than 80% by weight, further preferably 90% by weight or more, and particularly preferably 92% by weight or more (e.g., 95% by weight or more). (Meth)acrylic acid C 7-10 There is no particular upper limit to the proportion of alkyl esters in the monomer composition, typically below 99% by weight. Considering the relationship with the proportion used in other comonomers (e.g., monomers containing acidic groups), below 97% by weight is appropriate, and preferably below 96% by weight. (Meth)acrylic acid C 7-10 Alkyl esters can be used alone or in combination of two or more. As (meth)acrylic acid C7-10 Preferred examples of alkyl esters include: 2EHA, isooctyl acrylate, isononyl acrylate, etc. (C-acrylate) 7-10 Alkyl esters. Among them, 2EHA is preferred.

[0052] In the acrylic polymers disclosed herein, secondary monomers can be copolymerized. Examples of secondary monomers that introduce functional groups into the acrylic polymers, which can serve as crosslinking sites or contribute to improved adhesive strength, include: carboxyl-containing monomers, hydroxyl (OH)-containing monomers (e.g., 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate), anhydride-containing monomers, amide-containing monomers (e.g., methacrylamide, N,N-dimethyl(meth)acrylamide), amino-containing monomers (e.g., aminoethyl methacrylate, N,N-dimethylaminoethyl methacrylate), epoxy-containing monomers, cyano-containing monomers, ketone-containing monomers, monomers with a nitrogen-containing ring (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine), alkoxysilyl monomers, and imide-containing monomers. One of these secondary monomers can be used alone, or two or more can be used in combination.

[0053] When the monomer component constituting the acrylic polymer contains the aforementioned functionalized monomer, there is no particular limitation on the content of the functionalized monomer in the monomer component. From the viewpoint of appropriately maximizing the effects of using the functionalized monomer, the content of the functionalized monomer in the monomer component can be set to, for example, 0.1% by weight or more, 0.5% by weight or more is appropriate, and 1% by weight or more is possible. Furthermore, from the viewpoint of easily achieving a balance of adhesive properties in relation to the main monomer, the content of the functionalized monomer in the monomer component is appropriate to be set to 40% by weight or less, preferably 20% by weight or less, and can also be set to 10% by weight or less (e.g., 5% by weight or less).

[0054] In some preferred embodiments, monomers containing acidic groups are used as copolymerizable monomers with alkyl (meth)acrylates, which are the main monomers. The acidic groups can enhance cohesion and provide good adhesion to polar substrates due to their polarity. Furthermore, when using crosslinking agents such as isocyanates or epoxy crosslinkers, the acidic group (typically a carboxyl group) becomes a crosslinking point for the acrylic polymer. Through their action, it is possible to achieve appropriate high-temperature shear retention while maintaining stress relaxation properties.

[0055] As the monomer containing an acidic group, a monomer containing a carboxyl group is preferred. Examples of monomers containing a carboxyl group include: acrylic acid (AA), methacrylic acid (MAA), carboxyethyl methacrylate, crotonic acid, isocrotonic acid, and other olefinically unsaturated monocarboxylic acids; maleic acid, itaconic acid, citraconic acid, and other olefinically unsaturated dicarboxylic acids and their anhydrides (maleic anhydride, itaconic anhydride, etc.). Additionally, the monomer containing an acidic group can be a metal salt (e.g., an alkali metal salt) with a carboxyl group. AA and MAA are preferred, with AA being particularly preferred. One or more monomers containing an acidic group can be used alone or in combination.

[0056] In the disclosed technology, it is appropriate to set the content of acid-containing monomers (typically carboxyl-containing monomers) in the monomer composition (in other words, the copolymerization ratio of acid-containing monomers in the acrylic polymer) to 1.0% by weight or more. By using a specified amount or more of acid-containing monomers, there is a tendency to improve the cohesiveness of the adhesive layer. The copolymerization ratio of acid-containing monomers in the acrylic polymer is preferably greater than 3.0% by weight, more preferably greater than 3.5% by weight, further preferably greater than 4.0% by weight, and particularly preferably greater than 4.5% by weight. It is generally appropriate to set the copolymerization ratio of acid-containing monomers in the acrylic polymer to 20% by weight or less, and from the viewpoint of improving stress relaxation, it is preferably less than 10% by weight, more preferably less than 8.0% by weight, further preferably less than 7.0% by weight, and particularly preferably less than 6.0% by weight (e.g., less than 5.5% by weight).

[0057] The acrylic polymers preferably used in the disclosed technology are copolymers formed by copolymerizing alkyl (meth)acrylate as the main monomer and an acid-containing monomer as a secondary monomer. In such acrylic polymers, the proportion of copolymer components other than the aforementioned alkyl (meth)acrylate and acid-containing monomer can be less than 10% by weight, less than 3% by weight, less than 1% by weight, less than 0.1% by weight, or less than 0.03% by weight (e.g., less than 0.01% by weight). The monomer components constituting the acrylic polymer can substantially not contain functionalized monomers other than the aforementioned acid-containing monomer. Based on acrylic polymers substantially composed of alkyl (meth)acrylate and acid-containing monomer, the effects of the alkyl (meth)acrylate and acid-containing monomer can be maximized. The aforementioned alkyl (meth)acrylate is preferably (meth)acrylate C. 7-10 Alkyl esters (more preferably 2EHA). The above-mentioned monomers containing acidic groups are preferably monomers containing carboxyl groups (more preferably AA).

[0058] For purposes such as improving cohesiveness, the monomer components constituting acrylic polymers may contain other copolymer components besides the aforementioned secondary monomers. Examples of other copolymer components include: vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl methacrylates such as cyclohexyl methacrylate, cyclopentyl methacrylate, and isobornyl methacrylate; aryl methacrylates (e.g., phenyl methacrylate), aryloxyalkyl methacrylates (e.g., phenoxyethyl methacrylate), and arylalkyl methacrylates (e.g., benzyl methacrylate); olefin monomers; chlorinated monomers; isocyanate-containing monomers such as 2-(methacryloyloxyethyl isocyanate); alkoxy-containing monomers such as methoxyethyl methacrylate and ethoxyethyl methacrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; etc. The aforementioned other copolymer components may be used alone or in combination of two or more.

[0059] The amount of the other copolymer components can be appropriately selected according to the purpose and use, and there is no particular limitation. However, from the viewpoint of properly maximizing the effects brought about by the use of other copolymer components, it is appropriate to set it to 0.05% by weight or more, and it can also be set to 0.5% by weight or more. Furthermore, from the viewpoint of easily obtaining a balance of adhesive properties, it is appropriate to set the content of other copolymer components in the monomer component to 20% by weight or less, and it can also be set to 10% by weight or less (e.g., 5% by weight or less). The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain other copolymer components. Here, "the monomer component substantially does not contain other copolymer components" means at least that other copolymer components are not intentionally used, and it is permissible to unintentionally contain, for example, about 0.01% by weight or less of other copolymer components.

[0060] Acrylic polymers may contain polyfunctional monomers as other monomer components, which are polymerizable functional groups (typically free radical polymerizable functional groups) having at least two (meth)acryloyl or vinyl groups with unsaturated double bonds. Using polyfunctional monomers as monomer components can improve the cohesiveness of the adhesive layer. Polyfunctional monomers can also be used as crosslinking agents. There are no particular limitations on polyfunctional monomers; examples include: 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, etc. Polyfunctional monomers can be used alone or in combination of two or more.

[0061] There is no particular limitation on the amount of multifunctional monomer used, and it can be appropriately set in a manner that achieves the intended use of the multifunctional monomer. The amount of multifunctional monomer used can be set to about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (for example, about 0.5% by weight or less). The lower limit of the amount used when using multifunctional monomer is greater than 0% by weight, and there is no particular limitation. Generally, by setting the amount of multifunctional monomer used to about 0.001% by weight or more of the monomer component (for example, about 0.01% by weight or more), the effect of the multifunctional monomer can be appropriately exerted.

[0062] It is appropriate to design the composition of the monomer components constituting the acrylic polymer in such a way that the glass transition temperature (Tg) of the acrylic polymer is about -15°C or lower (for example, about -70°C or higher and -15°C or lower). Here, the Tg of the acrylic polymer refers to the Tg calculated using the Fox formula based on the composition of the monomer components described above. The Fox formula is shown below as a relationship between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer formed by homopolymerizing the monomers constituting the copolymer.

[0063] 1 / Tg=Σ(Wi / Tgi)

[0064] It should be noted that in the above Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K).

[0065] The glass transition temperature of the homopolymer used in the Tg calculation is the value recorded in known sources. For example, for the monomers listed below, the following values ​​are used as the glass transition temperature of the homopolymer of that monomer.

[0066]

[0067] For the glass transition temperature of homopolymers of monomers other than those illustrated above, the values ​​described in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) are used. For monomers for which multiple values ​​are described in that document, the highest value is used. In cases not described in the aforementioned Polymer Handbook, the values ​​obtained by the determination method described in Japanese Patent Application Publication No. 2007-51271 are used.

[0068] While there are no particular limitations, from the viewpoints of stress relaxation, adhesiveness, and impact resistance, a Tg of about -45°C or lower for acrylic polymers is advantageous, preferably about -50°C or lower, more preferably about -55°C or lower, further preferably about -60°C or lower, and particularly preferably about -62°C or lower (e.g., about -64°C or lower). Furthermore, from the viewpoint of the cohesiveness of the adhesive layer, a Tg of acrylic polymers is typically about -70°C or higher, preferably about -68°C or higher, and can be about -65°C or higher, or about -60°C or higher (e.g., about -55°C or higher). The Tg of acrylic polymers can be adjusted by appropriately changing the monomer composition (i.e., the types and proportions of monomers used in the synthesis of the polymer).

[0069] The weight-average molecular weight (Mw) of the base polymer (preferably an acrylic polymer) in the disclosed technology is not particularly limited, and can be, for example, about 10 × 10⁻⁶. 4 ~500×10 4 The range. From a cohesive point of view, the aforementioned Mw is typically approximately 30 × 10⁴. 4 The above is set to approximately 45×10 4 The above (for example, approximately 65 × 10) 4 The above is appropriate. In some preferred embodiments, from the viewpoint of improving high-temperature shear retention, the Mw of the acrylic polymer is greater than 70 × 10⁻⁶. 4 More preferably, approximately 90×10 4 The above is further preferred to be approximately 100 × 10 4 The above is particularly preferred, approximately 110 × 10 4 That's all. Additionally, the aforementioned Mw is typically 300×10 4 The following (more preferably about 200×10) 4 Below, for example, approximately 150×10 4 The following is appropriate.

[0070] The dispersion (Mw / Mn) of the base polymer (preferably an acrylic polymer) disclosed herein is not particularly limited. The dispersion (Mw / Mn) referred to herein is the dispersion expressed as the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn). In some preferred embodiments, the dispersion (Mw / Mn) of the base polymer is 40 or less, and may be less than 20, less than 15 (e.g., less than 12), less than 10, or less than 7.0. By limiting the molecular weight distribution within an appropriate range, stable properties are easily obtained. The lower limit of the aforementioned Mw / Mn is not particularly limited, and may be, for example, 3.0 or more, 5.0 or more, or 9.0 or more. Having a certain degree of molecular weight distribution tends to exhibit a balanced effect between low-molecular-weight and high-molecular-weight components. Such polymers tend to have excellent productivity.

[0071] Mw, Mn, and Mw / Mn can be adjusted by polymerization conditions (time, temperature, etc.), the concentration of non-volatile components (monomer components) during polymerization, the amount of polymerization initiator used, the use of chain transfer agents, and the selection of polymerization solvents based on the chain transfer constant. Mw and Mn are calculated from the values ​​of standard polystyrene obtained by GPC (gel permeation chromatography). For example, a GPC apparatus such as the "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used.

[0072] There are no particular limitations on the method for obtaining the basic polymer (e.g., acrylic polymers), and various known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately employed. For example, solution polymerization is preferred. The polymerization temperature during solution polymerization can be appropriately selected based on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be set, for example, from about 20°C to about 170°C (typically from about 40°C to about 140°C).

[0073] The solvent used in solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). The initiator used in polymerization can be appropriately selected from conventionally known polymerization initiators (e.g., azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN), peroxide initiators, etc.) depending on the type of polymerization method. The amount of polymerization initiator used is the usual amount; for example, it can be selected from about 0.005 parts by weight to about 1 part by weight (typically about 0.01 parts by weight to about 1 part by weight) relative to 100 parts by weight of monomer.

[0074] (Tackifying resin)

[0075] The adhesive layer in the disclosed technology may contain a tackifying resin. This improves the peel strength of the adhesive sheet. As the tackifying resin, one or more selected from phenolic tackifying resins, terpene tackifying resins, modified terpene tackifying resins, rosin tackifying resins, hydrocarbon tackifying resins, epoxy tackifying resins, polyamide tackifying resins, elastomer tackifying resins, ketone tackifying resins, etc., may be used. Phenolic tackifying resins, terpene tackifying resins, and modified terpene tackifying resins are preferred, and phenolic tackifying resins (preferably terpene phenolic resins) are more preferred.

[0076] Examples of phenolic tackifying resins include terpene phenol resins, hydrogenated terpene phenol resins, alkylphenol resins, and rosin phenol resins.

[0077] Terpene phenol resins refer to polymers containing terpene and phenol residues. This concept encompasses both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and resins obtained by modifying homopolymers or copolymers of terpenes with phenol (phenol-modified terpene resins). Preferred examples of terpenes constituting such terpene phenol resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-form, l-form, and d / l-form (terpinene)). Hydrogenated terpene phenol resins refer to hydrogenated terpene phenol resins having a structure obtained by hydrogenating such terpene phenol resins. They are sometimes also called hydrogenated terpene phenol resins.

[0078] Alkylphenol resins are resins obtained from alkylphenols and formaldehyde (oil-based phenolic resins). Examples of alkylphenol resins include phenolic varnish type and methyl phenolic type.

[0079] Rosin phenol resins are typically phenol-modified products of rosin or various rosin derivatives (including rosin esters, unsaturated fatty acid-modified rosin, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenol resins include those obtained by methods such as adding phenol to rosin or various rosin derivatives with an acid catalyst and then thermally polymerizing them.

[0080] Examples of terpene-based tackifying resins include polymers of terpenes (typically monoterpenes), such as α-pinene, β-pinene, d-limonene, l-limonene, and terpinene. These can be homopolymers of a single terpene or copolymers of two or more terpenes. Examples of terpene homopolymers include α-pinene polymers, β-pinene polymers, and terpinene polymers. Examples of modified terpene resins include resins obtained by modifying the aforementioned terpene resins. Specifically, examples include styrene-modified terpene resins and hydrogenated terpene resins.

[0081] The concept of rosin-based tackifying resins here includes both rosin-based resins and rosin derivative resins. Examples of rosin-based resins include: unmodified rosin such as resin rosin, wood rosin, and top-oil rosin (raw rosin); and modified rosin obtained by modifying these unmodified rosin through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosin, etc.).

[0082] Rosin derivative resins are typically derivatives of rosin as described above. The concept of rosin resins here includes derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). Examples include: rosin esters such as unmodified rosin esters (esters of unmodified rosin and alcohols) and modified rosin esters (esters of modified rosin and alcohols); unsaturated fatty acid-modified rosin obtained by modifying rosin with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing the carboxyl groups of rosin or the various rosin derivatives mentioned above (including rosin esters, unsaturated fatty acid-modified rosin, and unsaturated fatty acid-modified rosin esters); metal salts of rosin or the various rosin derivatives mentioned above; etc. Specific examples of rosin esters include: methyl esters, triethylene glycol esters, glycerides, pentaerythritol esters, etc. of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.).

[0083] Examples of hydrocarbon tackifying resins include: aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, and other hydrocarbon resins.

[0084] There is no particular limitation on the softening point of the tackifying resin. From the viewpoint of improving cohesion, a tackifying resin with a softening point (softening temperature) of about 80°C or higher (preferably about 100°C or higher) is preferred. For example, phenolic tackifying resins (such as terpene phenol resins) having such a softening point are preferred. In some embodiments, terpene phenol resins with a softening point of about 135°C or higher (further, about 140°C or higher) can be used. There is no particular limitation on the upper limit of the softening point of the tackifying resin. From the viewpoint of adhesion to the adhered object or substrate, a tackifying resin with a softening point of about 200°C or lower (more preferably about 180°C or lower) is preferred. It should be noted that the softening point of the tackifying resin can be determined according to the softening point test method (ring and ball method) specified in JIS K2207.

[0085] In some preferred embodiments, a tackifying resin T with a softening point of less than 145°C can be used as the tackifying resin.L By using tackifying resin T with a softening point less than 145℃ L This allows for the formation of adhesives that better balance high-temperature shear retention and stress relaxation properties. Tackifying resin T L The softening point is preferably less than 135°C, more preferably less than 125°C, and can also be below 120°C. Tackifying resin T L There is no particular limitation on the lower limit of the softening point; for example, it is above 60°C (thus it is solid at 30°C), and above 80°C is appropriate. From the viewpoint of balancing stress relaxation and high-temperature adhesive properties (e.g., high-temperature shear retention), it is preferably above 90°C, more preferably above 100°C, and may also be above 110°C. As a tackifying resin T... L Appropriate types of tackifying resins can be selected from the above-mentioned tackifying resins, with terpene phenol resins being preferred. Tackifying resin T L One type can be used alone, or two or more types can be used in combination.

[0086] The adhesive layer contains tackifying resin T. L In the case of appropriate performance, the use of tackifying resin T L From the perspective of effectiveness, in the adhesive layer, relative to 100 parts by weight of the base polymer (e.g., acrylic polymer), the tackifying resin T L Setting the content of [the substance] to 1 part by weight or more is appropriate, preferably 5 parts by weight or more, more preferably 10 parts by weight or more, further preferably 15 parts by weight or more (e.g., more than 15 parts by weight), and particularly preferably 18 parts by weight or more. Furthermore, from the viewpoint of cohesion, relative to 100 parts by weight of the base polymer, the tackifying resin T […]. L Setting the amount to less than 50 parts by weight is appropriate. From the viewpoint of high-temperature shear retention, less than 40 parts by weight is preferred, more preferably less than 30 parts by weight, and also less than 25 parts by weight.

[0087] In addition, a liquid tackifying resin that is liquid at 30°C can be used as the tackifying resin. By using a liquid tackifying resin, the breaking strength of the adhesive layer can be preferably reduced. The aforementioned liquid tackifying resin can be, for example, a tackifying resin with a softening point of about 50°C or less, more preferably about 40°C or less (typically tackifying resins such as rosin, terpenes, hydrocarbons, etc., such as hydrogenated rosin methyl ester). One liquid tackifying resin can be used alone or two or more can be used in combination. There is no particular limitation on the content of the liquid tackifying resin, but from the viewpoint of suppressing the influence on adhesive properties (e.g., reduction of cohesiveness), it is preferable to set it to about 0.1% to about 10% by weight of the total adhesive layer, and it is appropriate to set it to about 5% by weight or less (e.g., 0.5% to 2% by weight).

[0088] Using tackifying resin T with a softening point of less than 145℃L In this method, the adhesive layer may or may not include a tackifying resin T that does not have a softening point of less than 145°C. L High softening point tackifying resins (typically tackifying resins with a softening point above 145°C) T H In addition to containing tackifying resin T, the adhesive layer also contains... L In addition, it also contains tackifying resin T H In the case of tackifying resin T L 100 parts by weight, tackifying resin T H Setting the content to less than 100 parts by weight is appropriate, preferably less than 50 parts by weight, more preferably less than 30 parts by weight, and even more preferably less than 10 parts by weight. It can be less than 1 part by weight or less than 0.1 parts by weight. This is achieved by adjusting the content relative to the tackifying resin T... L Quantity limitation of tackifying resin T H The amount of adhesive layer tends to increase stress relaxation.

[0089] As some preferred embodiments, examples can be listed where the aforementioned tackifying resin comprises one or more phenolic tackifying resins (typically terpene phenolic resins). The techniques disclosed herein are preferably implemented, for example, in a manner where, when the total amount of the tackifying resin is set to 100% by weight, about 25% by weight or more (more preferably about 30% by weight or more) is terpene phenolic resin. It is also possible that about 50% by weight or more of the total amount of the tackifying resin is terpene phenolic resin, or about 80% by weight or more (e.g., about 90% by weight or more) is terpene phenolic resin. Alternatively, substantially all of the tackifying resin (e.g., about 95% to 100% by weight, further about 99% to 100% by weight) may be terpene phenolic resin.

[0090] While there are no particular limitations, in some embodiments, the aforementioned tackifying resin may contain a tackifying resin with a hydroxyl value higher than 20 mg KOH / g. Preferably, the tackifying resin has a hydroxyl value of 30 mg KOH / g or higher. Hereinafter, tackifying resins with a hydroxyl value of 30 mg KOH / g or higher are sometimes referred to as "high hydroxyl value resins." Based on tackifying resins containing such high hydroxyl value resins, an adhesive layer with excellent adhesion to the adhered objects and high cohesive strength can be achieved. There is no particular upper limit to the hydroxyl value of the high hydroxyl value resin. From the viewpoint of compatibility with the base polymer, a hydroxyl value of about 200 mg KOH / g or less is appropriate for the high hydroxyl value resin, preferably about 100 mg KOH / g or less, and can be about 70 mg KOH / g or less, or even about 65 mg KOH / g or less. One high hydroxyl value resin may be used alone or in combination of two or more. The technology disclosed herein can preferably be implemented using a high hydroxyl value resin (e.g., phenolic tackifying resin, preferably terpene phenolic resin) containing a hydroxyl value greater than 20 mg KOH / g (e.g., 30 mg KOH / g to 65 mg KOH / g). In some preferred embodiments, the aforementioned high hydroxyl value resin can be a tackifying resin T with a softening point less than 145°C. L .

[0091] Here, the hydroxyl value mentioned above can be determined by potentiometric titration as specified in JIS K0070:1992. The specific determination method is shown below.

[0092] [Method for determining hydroxyl value]

[0093] 1. Reagents

[0094] (1) As an acetylation reagent, the following substance is used: about 12.5 g (about 11.8 mL) of acetic anhydride is added to pyridine to make the total volume 50 mL, and the mixture is stirred thoroughly. Or the following substance is used: about 25 g (about 23.5 mL) of acetic anhydride is added to pyridine to make the total volume 100 mL, and the mixture is stirred thoroughly.

[0095] (2) Use 0.5 mol / L potassium hydroxide ethanol solution as the assay reagent.

[0096] (3) In addition, prepare toluene, pyridine, ethanol and distilled water.

[0097] 2. Operation

[0098] (1) Weigh approximately 2g of the sample into a flat-bottomed flask, add 5mL of acetylation reagent and 10mL of pyridine, and install an air cooling tube.

[0099] (2) Heat the above flask in a bath at 100°C for 70 minutes, then cool it. Add 35 mL of toluene as a solvent through the top of the cooling tube and stir. Then add 1 mL of distilled water and stir to decompose the acetic anhydride. To ensure complete decomposition, heat it again in the bath for 10 minutes and then cool it.

[0100] (3) Clean the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir.

[0101] (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a pipette.

[0102] (5) Perform potentiometric titration using 0.5 mol / L potassium hydroxide ethanol solution. Take the inflection point of the obtained titration curve as the endpoint.

[0103] (6) Blank test: The above (1) to (5) are performed without adding the sample.

[0104] 3. Calculation

[0105] The hydroxyl value is calculated using the following formula.

[0106] Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D

[0107] Here,

[0108] B: The volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test.

[0109] C: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample.

[0110] f: Factor of 0.5 mol / L potassium hydroxide ethanol solution

[0111] S: Weight of the sample (g)

[0112] D: Acid value

[0113] 28.05: Half of the molecular weight of potassium hydroxide, which is 56.11.

[0114] When the adhesive layer contains a tackifying resin, there is no particular limitation on the amount (total amount) of the tackifying resin used. For example, it can be appropriately set in the range of about 1 part by weight to about 100 parts by weight relative to 100 parts by weight of the base polymer. From the viewpoint of properly exerting the effect of improving peel strength, it is appropriate to set the amount of tackifying resin to 5 parts by weight or more relative to 100 parts by weight of the base polymer (e.g., acrylic polymer), preferably 10 parts by weight or more, and it can also be set to 15 parts by weight or more. In addition, from the viewpoint of impact resistance and cohesion, it is appropriate to set the amount of tackifying resin to 50 parts by weight or less relative to 100 parts by weight of the base polymer (e.g., acrylic polymer), and it can be set to 40 parts by weight or less, or it can be set to 30 parts by weight or less.

[0115] (Acrylic oligomers)

[0116] In some preferred embodiments, the adhesive layer comprises an acrylic oligomer. By including an acrylic oligomer in the adhesive layer, in addition to improved adhesive properties such as increased adhesive strength, it is preferable to also achieve good high-temperature shear retention and stress relaxation properties. As the acrylic oligomer, a polymer with a higher Tg than the Tg of the copolymer corresponding to the composition of the aforementioned monomer components (typically substantially corresponding to the Tg of the acrylic polymer contained in the adhesive formed from the adhesive composition) is preferred. The inclusion of an acrylic oligomer improves the adhesive strength. One acrylic oligomer may be used alone, or two or more may be used in combination.

[0117] The acrylic oligomers described above preferably have a Tg of about 0°C or higher and about 300°C or lower, more preferably about 20°C or higher and about 300°C or lower, and even more preferably about 40°C or higher and about 300°C or lower. With a Tg within the above range, the adhesive strength can be appropriately improved. In some preferred embodiments, from the viewpoint of adhesive cohesiveness, the Tg of the acrylic oligomers is about 30°C or higher, more preferably about 50°C or higher (e.g., about 60°C or higher), and from the viewpoint of adhesiveness, it is preferably about 200°C or lower, more preferably about 150°C or lower, and even more preferably about 100°C or lower (e.g., about 80°C or lower). It should be noted that the Tg of the acrylic oligomers is the same as the Tg of the copolymer corresponding to the composition of the monomer components described above, and is a value calculated based on the Fox formula.

[0118] The weight-average molecular weight (Mw) of acrylic oligomers is typically greater than or equal to about 1,000 and less than about 30,000, preferably greater than or equal to about 1,500 and less than about 20,000, and more preferably greater than or equal to about 2,000 and less than about 10,000. Good adhesive strength and retention properties can be obtained within the above range of Mw, and therefore it is preferred. In some preferred embodiments, from the viewpoint of high-temperature shear retention, the Mw of the acrylic oligomer is about 2,500 or more (e.g., about 3,000 or more). Furthermore, from the viewpoint of adhesiveness, the Mw of the acrylic oligomer is preferably about 7,000 or less, more preferably about 5,000 or less (e.g., about 4,500 or less, typically about 4,000 or less). The Mw of the acrylic oligomer can be determined by gel permeation chromatography (GPC) and calculated as a value converted from standard polystyrene. Specifically, in the HPLC8020 manufactured by Tosoh Corporation, TSKgelGMH-H(20)×2 columns were used as columns, and the determination was performed with tetrahydrofuran solvent at a flow rate of about 0.5 mL / min.

[0119] Monomers constituting acrylic oligomers include, for example: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, heptyl methacrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, etc. Alkyl methacrylates such as isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, and dodecyl methacrylate; esters of methacrylic acid with alicyclic alcohols such as cyclohexyl methacrylate, isobornyl methacrylate, and tetrahydrodicyclopentadienyl methacrylate (methacrylic esters containing alicyclic hydrocarbon groups); aryl methacrylates such as phenyl methacrylate and benzyl methacrylate; methacrylic esters obtained from terpene compound derivative alcohols; etc. Such methacrylic esters can be used alone or in combination of two or more.

[0120] From the viewpoint of further improving the adhesiveness of the adhesive layer, acrylic monomers with a large volumetric structure, such as isobutyl methacrylate or tert-butyl methacrylate, are preferred monomer units. These include alkyl methacrylates with branched alkyl groups, such as cyclohexyl methacrylate, isobornyl methacrylate, tetrahydrodicyclopentadienyl methacrylate, etc., which are esters of methacrylate and alicyclic alcohols (meth acrylates containing alicyclic hydrocarbon groups); and aryl methacrylates with cyclic structures, such as phenyl methacrylate or benzyl methacrylate. Furthermore, when ultraviolet light is used during the synthesis of the acrylic oligomer and the preparation of the adhesive layer, from the viewpoint of minimizing polymerization hindrance, substances with saturated bonds are preferred. Alkyl methacrylates with branched alkyl groups, or esters of methacrylate and alicyclic alcohols (meth acrylates containing alicyclic hydrocarbon groups), can be appropriately used as monomers constituting the acrylic oligomer. It should be noted that the aforementioned branched alkyl esters, alicyclic hydrocarbon esters, and aryl esters of (meth)acrylate are all (meth)acrylate monomers disclosed herein. The alicyclic hydrocarbon group can be a saturated alicyclic hydrocarbon group or an unsaturated alicyclic hydrocarbon group.

[0121] The proportion of (meth)acrylate monomers (e.g., (meth)acrylates containing alicyclic hydrocarbon groups) in the total monomer composition of the acrylic oligomer is typically greater than 50% by weight, preferably 60% by weight or more, more preferably 70% by weight or more (e.g., 80% by weight or more, further 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting substantially only of (meth)acrylate monomers.

[0122] In addition to the aforementioned (meth)acrylate monomers, functionalized monomers can also be used as constituent monomers of acrylic oligomers. Preferred examples of these functionalized monomers include: monomers with nitrogen-containing rings (typically nitrogen-containing heterocycles), such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino-containing monomers, such as N,N-dimethylaminoethyl (meth)acrylate; amide-containing monomers, such as N,N-diethyl(meth)acrylamide; carboxyl-containing monomers, such as AA and MAA; and hydroxyl-containing monomers, such as 2-hydroxyethyl (meth)acrylate. These functionalized monomers can be used alone or in combination of two or more. Carboxyl-containing monomers are preferred, and AA is particularly preferred.

[0123] When all monomer components constituting acrylic oligomers include functionalized monomers, it is appropriate to set the proportion of functionalized monomers (e.g., carboxyl-containing monomers such as AA) in all monomer components to be about 1% by weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and it is appropriate to set it to about 15% by weight or less, preferably 10% by weight or less, more preferably 7% by weight or less.

[0124] Acrylic oligomers can be formed by polymerizing their constituent monomer components. There are no particular limitations on the polymerization method or mode; various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be used in an appropriate manner. The types of polymerization initiators that can be used (e.g., azo initiators such as AIBN) are basically as illustrated in the synthesis of acrylic polymers. Based on common technical knowledge, the amount of polymerization initiator and, optionally, the amount of chain transfer agent such as n-dodecyl mercaptan are appropriately set to achieve the desired molecular weight; detailed descriptions are omitted here.

[0125] From the above perspective, preferred acrylic oligomers include, for example, various homopolymers of tetrahydrodicyclopentadienyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isoborneol methacrylate (IBXMA), isoborneol acrylate (IBXA), tetrahydrodicyclopentadienyl methacrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA). In addition, copolymers of CHMA with isobutyl methacrylate (IBMA), CHMA with IBXMA, CHMA with acrylamide (ACMO), CHMA with diethylacrylamide (DEAA), CHMA with AA, ADA with methyl methacrylate (MMA), DCPMA with IBXMA, and DCPMA with MMA are also listed.

[0126] When the adhesive layer disclosed herein contains acrylic oligomers, it is appropriate that their content is set to 0.1 parts by weight or more (e.g., 1 part by weight or more) relative to 100 parts by weight of the base polymer (typically an acrylic polymer). From the viewpoint of better utilizing the effect of the acrylic oligomers, the aforementioned content of the acrylic oligomers is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more. Furthermore, from the viewpoint of compatibility with the base polymer (typically an acrylic polymer), it is appropriate that the aforementioned content of the acrylic oligomers is set to less than 50 parts by weight, preferably less than 30 parts by weight, more preferably less than 20 parts by weight, and even more preferably less than 15 parts by weight (e.g., less than 12 parts by weight).

[0127] In some preferred embodiments, the adhesive layer contains one or more of the aforementioned tackifying resins (typically tackifying resin T with a softening point less than 145°C). L The tackifying resin and one or more acrylic oligomers are used. By combining the above-mentioned tackifying resin and acrylic oligomers, it is possible to achieve the desired adhesive properties while preferably also considering high-temperature shear retention and stress relaxation. The tackifying resin (typically a tackifying resin T with a softening point less than 145°C) L The content of C) T With respect to the content of acrylic oligomers C O There are no particular restrictions on the ratio, for example, C T / C O A value of about 0.2 or more is appropriate, preferably about 1 or more (e.g., greater than 1), more preferably 1.5 or more, and may also be 1.8 or more. Furthermore, the above-mentioned C... T / C O A ratio of about 20 or less is suitable, preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less. Within the above-mentioned range, the combined effect of the tackifying resin and the acrylic oligomer can preferably be achieved.

[0128] From the viewpoint of preferably maximizing the effects of the technology disclosed herein, it is appropriate for the total amount (total quantity) of the tackifying resin and acrylic oligomer contained in the adhesive layer of some preferred embodiments to be set to about 1 part by weight or more relative to 100 parts by weight of the base polymer (preferably an acrylic polymer), preferably about 10 parts by weight or more, more preferably about 16 parts by weight or more, further preferably about 20 parts by weight or more, particularly preferably about 25 parts by weight or more. In addition, it is appropriate to set it to less than 120 parts by weight (for example, about 80 parts by weight or less), preferably less than 60 parts by weight, more preferably about 50 parts by weight or less, and further preferably about 40 parts by weight or less.

[0129] (Cross-linking agent)

[0130] In the disclosed technology, the adhesive composition used in the formation of the adhesive layer may contain a crosslinking agent as needed. There are no particular limitations on the type of crosslinking agent, and it can be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include, for instance, isocyanate crosslinking agents, epoxy crosslinking agents, etc. Crosslinking agents include zopyridine, melamine, peroxide, urea, metal alkoxide, metal chelate, metal salt, carbodiimide, hydrazine, amine, and silane coupling agents. Among these, isocyanate and epoxy crosslinking agents are preferred. Azoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, with isocyanate-based crosslinking agents and epoxy-based crosslinking agents being particularly preferred. By appropriately selecting and using crosslinking agents, the cohesiveness of the adhesive layer can be obtained, improving stress relaxation and adhesive strength while maintaining high-temperature shear retention. It should be noted that the adhesive layer in the disclosed technology may contain the aforementioned crosslinking agents in the form after the crosslinking reaction, in the form before the crosslinking reaction, in a partially crosslinked form, or in an intermediate or composite form. Typically, the aforementioned crosslinking agents are mainly contained in the adhesive layer in the form after the crosslinking reaction.

[0131] As isocyanate crosslinking agents, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including substances with isocyanurate structures) are preferred. Isocyanate crosslinking agents can be used alone or in combination of two or more.

[0132] Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

[0133] Specific examples of aliphatic polyisocyanates include: 1,2-ethylidene diisocyanate; 1,2-butylidene diisocyanate, 1,3-butylidene diisocyanate, 1,4-tetramethylene diisocyanate, and other butylidene diisocyanates; 1,2-hexylidene diisocyanate, 1,3-hexylidene diisocyanate, 1,4-hexylidene diisocyanate, 1,5-hexylidene diisocyanate, 1,6-hexylidene diisocyanate, 2,5-hexylidene diisocyanate, and other hexylidene diisocyanates; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, etc.

[0134] Specific examples of alicyclic polyisocyanates include: isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated diphenylmethylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0135] Specific examples of aromatic polyisocyanates include: 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Isocyanates, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, terephthalene diisocyanate, naphthyl-1,4-diisocyanate, naphthyl-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, phenylenedimethyl-1,4-diisocyanate, phenylenedimethyl-1,3-diisocyanate, etc.

[0136] Preferred polyfunctional isocyanates include those having an average of three or more isocyanate groups per molecule. These trifunctional or higher isocyanates can be polymers (typically dimers or trimers) of difunctional or trifunctional or higher isocyanates, derivatives (e.g., addition reaction products of polyols with two or more molecules of polyfunctional isocyanates), polymers, etc. Examples include: dimers or trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts of isocyanurate structures), reaction products of trimethylolpropane and toluene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanates, polyether polyisocyanates, polyester polyisocyanates, and other polyfunctional isocyanates. Commercially available products of this polyfunctional isocyanate include: "DURANATETPA-100" manufactured by Asahi Kasei Chemicals, "CORONATE L" manufactured by Tosoh Corporation, "CORONATE HL" manufactured by Tosoh Corporation, "CORONATE HK" manufactured by Tosoh Corporation, "CORONATE HX" manufactured by Tosoh Corporation, and "CORONATE 2096" manufactured by Tosoh Corporation.

[0137] There is no particular limitation on the amount of isocyanate crosslinking agent used. For example, it can be set to about 0.5 parts by weight or more relative to 100 parts by weight of the base polymer. From the viewpoint of balancing cohesion, adhesion, and impact resistance, the amount of isocyanate crosslinking agent used relative to 100 parts by weight of the base polymer can be set to, for example, greater than 1.0 parts by weight, greater than 1.5 parts by weight, preferably greater than 2.0 parts by weight, and more preferably greater than 2.5 parts by weight (for example, 2.8 parts by weight or more). By using an isocyanate crosslinking agent dosage within the above range, it is preferable to balance high-temperature shear retention and stress relaxation. On the other hand, from the viewpoint of improving stress relaxation and increasing adhesion to the adhered material, the amount of isocyanate crosslinking agent used relative to 100 parts by weight of the base polymer is appropriate to be less than 10 parts by weight, preferably less than 5 parts by weight, more preferably less than 4.5 parts by weight, further preferably less than 4.0 parts by weight, and particularly preferably less than 3.5 parts by weight (for example, 3.0 parts by weight or less).

[0138] In some preferred embodiments, as a crosslinking agent, an isocyanate crosslinking agent and at least one crosslinking agent whose type of crosslinking functional group is different from that of the isocyanate crosslinking agent can be used in combination. According to the technology disclosed herein, by combining a crosslinking agent other than an isocyanate crosslinking agent (i.e., a crosslinking agent whose type of crosslinking reactive group is different from that of the isocyanate crosslinking agent; hereinafter also referred to as "non-isocyanate crosslinking agent") and an isocyanate crosslinking agent, it is possible to appropriately balance high-temperature shear retention and stress relaxation properties.

[0139] There are no particular restrictions on the types of non-isocyanate crosslinking agents that can be used in combination with isocyanate crosslinking agents; appropriate selections can be made from the aforementioned crosslinking agents. Non-isocyanate crosslinking agents can be used alone or in combination of two or more.

[0140] In some preferred embodiments, epoxy crosslinking agents can be used as non-isocyanate crosslinking agents. For example, by using both isocyanate and epoxy crosslinking agents in combination, it is easy to balance cohesiveness and impact resistance. As epoxy crosslinking agents, compounds having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups in one molecule are preferred. Epoxy crosslinking agents can be used alone or in combination of two or more.

[0141] While there are no specific restrictions, specific examples of epoxy crosslinking agents include: N,N,N',N'-tetraglycidyl-m-phenylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include: Mitsubishi Gas Chemical Co., Ltd.'s "TETRAD-C" and "TETRAD-X", DIC Corporation's "EPICLON CR-5L", Nagase Chemte X Co., Ltd.'s "Denacol EX-512", and Nissan Chemical Industries Co., Ltd.'s "TEPIC-G".

[0142] There is no particular limitation on the amount of epoxy crosslinking agent used. For example, the amount of epoxy crosslinking agent used can be set to be greater than 0 parts by weight and less than or equal to about 1 part by weight (typically about 0.001 to about 0.5 parts by weight) relative to 100 parts by weight of the base polymer. From the viewpoint of appropriately improving cohesion, it is appropriate to set the amount of epoxy crosslinking agent used to be about 0.005 parts by weight or more relative to 100 parts by weight of the base polymer, preferably about 0.01 parts by weight or more, and more preferably about 0.02 parts by weight or more. Furthermore, from the viewpoint of improving adhesion to the adhered material, it is appropriate to set the amount of epoxy crosslinking agent used to be about 0.2 parts by weight or less relative to 100 parts by weight of the base polymer, preferably about 0.1 parts by weight or less, and more preferably less than about 0.05 parts by weight. By reducing the amount of epoxy crosslinking agent used, there is a tendency to improve stress relaxation and impact resistance.

[0143] In the disclosed technology, there are no particular limitations on the relationship between the content of isocyanate crosslinking agents and the content of non-isocyanate crosslinking agents (e.g., epoxy crosslinking agents). The content of non-isocyanate crosslinking agents can, for example, be set to about 1 / 50 or less of the content of isocyanate crosslinking agents. From the viewpoint of more appropriately balancing adhesion and cohesion of the adhered material, it is appropriate to set the content of non-isocyanate crosslinking agents, on a weight basis, to be about 1 / 70 or less of the content of isocyanate crosslinking agents, and preferably to be about 1 / 90 or less. Furthermore, from the viewpoint of appropriately leveraging the effects of combining isocyanate crosslinking agents and non-isocyanate crosslinking agents (e.g., epoxy crosslinking agents), it is appropriate to set the content of non-isocyanate crosslinking agents to be about 1 / 1000 or more, for example, about 1 / 500 or more, preferably 1 / 300 or more, and more preferably 1 / 150 or more of the content of isocyanate crosslinking agents.

[0144] There is no particular limitation on the total amount (total amount) of crosslinking agent used. For example, it can be set to about 10 parts by weight or less relative to 100 parts by weight of the base polymer (preferably an acrylic polymer), and can be selected from a range of about 0.005 parts by weight to 10 parts by weight, more preferably from about 0.01 parts by weight to 5 parts by weight.

[0145] (Rust inhibitor)

[0146] Some preferred adhesive layers may contain rust inhibitors. There are no particular limitations on rust inhibitors, but examples include: azole rust inhibitors, amine compounds, nitrites, ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, hexamethylenetetramine, thiourea, phenyl carbamate, and N-cyclohexylcarbamate (CHC), etc. Rust inhibitors can be used alone or in combination of two or more.

[0147] As a rust inhibitor, azole-based rust inhibitors are preferred. Among azole-based rust inhibitors, substances whose active ingredient is an azole compound containing two or more heteroatoms in a five-membered ring aromatic compound, at least one of which is a nitrogen atom, are preferred. Preferred examples of compounds that can be used as azole-based rust inhibitors include benzotriazole-based rust inhibitors whose active ingredient is a benzotriazole compound. Preferred examples of benzotriazole compounds include 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, and carboxybenzotriazole.

[0148] There are no particular limitations on the content of the rust inhibitor; for example, it can be set to 0.01 parts by weight or more (typically 0.05 parts by weight or more) relative to 100 parts by weight of the base polymer. From the viewpoint of obtaining better protection against metal corrosion, the above content can be 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. On the other hand, from the viewpoint of improving the cohesiveness of the adhesive, it is appropriate to set the content of the rust inhibitor to less than 8 parts by weight relative to 100 parts by weight of the base polymer, and it can be 5 parts by weight or less, or 2 parts by weight or less.

[0149] (Coloring agent)

[0150] The adhesive layer may or may not contain a colorant. This allows for adjustment of the light transmittance (light blocking properties) of the adhesive layer. Adjusting the light transmittance of the adhesive layer also helps to adjust the light transmittance of the adhesive sheet containing the adhesive layer. As the aforementioned colorant, various materials capable of attenuating light traveling within the adhesive layer by reflecting and / or absorbing it can be used. The color of the colorant is not particularly limited, and can be, for example, black, gray, white, red, blue, yellow, green, yellowish-green, orange, purple, gold, silver, pearl, etc. The aforementioned colorant can typically be included in the adhesive layer in a state dispersed within the constituent materials of the adhesive layer (which may be in a dissolved state).

[0151] Various pigments and dyes can be used as colorants. Examples of pigments include: zinc carbonate, zinc oxide, zinc sulfide, talc, kaolin, calcium carbonate, titanium dioxide, silicon dioxide, lithium fluoride, calcium fluoride, barium sulfate, aluminum oxide, zirconium oxide, iron oxides, iron hydroxides, chromium oxides, spinel-type calcined pigments, chromic acids, molybdenum chromium red, deep blue pigments, aluminum powder, bronze powder, silver powder, inorganic pigments such as calcium phosphate, phthalocyanines, azo dyes, condensed azo dyes, azo lakes, anthraquinones, perylene / violet ketones, indigo, thioindolinones, isoindolinones, methylimines, etc. Organic pigments include azine, quinacridone, aniline black, triphenylmethane, and carbon black. As dyes, examples include: azo dyes, anthraquinones, quinoline ketones, styryl dyes, diphenylmethane, and triphenylmethane. Azides, triazines, xanthan gum, methane, azobenzene, acridine, diazine. Colorants can be used alone or in appropriate combinations of two or more.

[0152] Black colorants are preferred because light-blocking properties can be efficiently adjusted with a small amount of colorant. Specific examples of black colorants include: carbon black (furnace black, channel black, acetylene black, thermal cracking black, lampblack, pine soot, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, anthocyanin black, hematite, activated carbon, ferrites (non-magnetic ferrites, magnetic ferrites, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complexes, anthraquinone colorants, etc. They can be used alone or in appropriate combinations of two or more. Carbon black is preferred. It should be noted that surface-modified carbon black particles with functional groups such as carboxyl or amino, sulfonic acid, or silicon-containing groups (e.g., alkoxysilyl, alkylsilyl) can also be used as carbon black particles. Such surface-modified carbon black particles are also called self-dispersing carbon black, which do not require the addition of dispersants or can reduce their amount. The above-mentioned carbon black particles can be used alone or in combinations of two or more.

[0153] Particulate colorants (pigments) are preferred because the light-blocking properties of the adhesive layer can be efficiently adjusted using a small amount of colorant. In some preferred embodiments, colorants with an average particle size of about 10 nm or more (e.g., about 30 nm or more) (e.g., particulate black colorants such as carbon black) can be used. The aforementioned average particle size can be, for example, about 50 nm or more, about 100 nm or more, or about 150 nm or more. There is no particular upper limit to the average particle size of the aforementioned colorant; the average particle size of the aforementioned colorant can be, for example, about 3000 nm or less, or about 1000 nm or less. From the viewpoint of improving light-blocking properties, an average particle size of about 500 nm or less for the aforementioned colorant is appropriate.

[0154] It should be noted that the average particle size of the colorant in this specification refers to the volume average particle size. Specifically, it refers to the particle size at which the cumulative value of the particle size distribution reaches 50% (50% volume average particle size; sometimes abbreviated as D below) as measured by a particle size distribution measuring device based on laser scattering / diffraction. 50 As a measuring device, for example, the product manufactured by Microtrac Bell under the name "Microtrac MT3000II" or its equivalent can be used.

[0155] The content of the colorant is not limited to a specific range. From the viewpoint of achieving the desired effect of adding the colorant, the colorant content in the adhesive layer can be set to about 0.1% by weight or more, and setting it to about 0.5% by weight or more is appropriate. From the viewpoint of light blocking properties, it is preferably about 1% by weight or more, more preferably about 2% by weight or more, and even more preferably about 3% by weight or more (e.g., about 5% by weight or more). Furthermore, the upper limit of the colorant content in the adhesive layer can be set to, for example, less than 15% by weight, and setting it to less than 10% by weight is appropriate. It is preferably set to less than 8% by weight, and more preferably less than 7% by weight. From the viewpoint of suppressing the reduction of adhesive properties and maintaining the target performance, it is preferable to limit the amount of colorant used in the adhesive layer.

[0156] (Other additives)

[0157] The adhesive composition may contain, as needed, various additives commonly used in the field of adhesives, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, and light stabilizers. These various additives can be used with conventional methods and are not a feature of this invention; therefore, detailed descriptions are omitted.

[0158] The adhesive layer (a layer composed of adhesive) disclosed herein can be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot-melt adhesive composition, or an active energy ray-cured adhesive composition that is cured by irradiation with active energy rays such as ultraviolet light or electron beams. An aqueous adhesive composition refers to an adhesive composition in which the adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) with water as the main component; typically, it includes what is called a water-dispersible adhesive composition (a composition in which at least a portion of the adhesive is dispersed in water). A solvent-based adhesive composition refers to an adhesive composition in which the adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more examples of organic solvents (such as toluene, ethyl acetate, etc.) that can be used in the above-described solution polymerization can be used without particular limitation. From the viewpoint of adhesive properties, the technology disclosed herein is preferably implemented in a manner having an adhesive layer formed from a solvent-based adhesive composition. In the manner of having a solvent-based adhesive layer formed from a solvent-based adhesive composition, the effects of the technology disclosed herein can preferably be achieved.

[0159] The adhesive layer disclosed herein can be formed using methods known in the art. For example, it can be formed by applying an adhesive composition to a peelable surface (release surface) and allowing it to dry. For adhesive sheets having a substrate, for example, it can be formed by directly applying (typically coating) an adhesive composition to the substrate and allowing it to dry (direct method). Alternatively, it can be formed by applying an adhesive composition to a peelable surface (release surface) and allowing it to dry, thus forming an adhesive layer on that surface, and then transferring the adhesive layer to the substrate (transfer method). As the release surface described above, the surface of the release liner described later is preferably used, for example. It should be noted that the adhesive layer disclosed herein is typically formed continuously, but is not limited to this manner; for example, it can be an adhesive layer formed as a regular or irregular pattern such as dots or stripes.

[0160] The adhesive composition can be coated using conventionally known coating machines such as gravure roller coaters, die coaters, and bar coaters. Alternatively, the adhesive composition can be coated using methods such as dip coating or curtain coating.

[0161] From the viewpoint of promoting cross-linking reactions and improving manufacturing efficiency, the drying of the adhesive composition is preferably carried out under heating. The drying temperature can be set, for example, from about 40°C to about 150°C, and preferably from about 60°C to about 130°C. After the adhesive composition is dried, it can be further cured for purposes such as adjusting the transfer of components within the adhesive layer, proceeding with the cross-linking reaction, and relaxing any strain that may exist within the adhesive layer.

[0162] The adhesive layer disclosed herein can be a single-layer structure or a multi-layer structure with two or more layers. From a productivity point of view, a single-layer structure is preferred for the adhesive layer.

[0163] There is no particular limitation on the thickness of the adhesive layer. The thickness of the adhesive layer is typically about 300 μm or less, preferably about 100 μm or less, more preferably about 70 μm or less, and even more preferably about 50 μm or less. The thickness of the adhesive layer can be set to about 35 μm or less, for example, about 25 μm or less. An adhesive layer with a limited thickness can well meet the requirements for thickness reduction and weight reduction. The lower limit of the adhesive layer thickness is, for example, about 3 μm or more, and about 10 μm or more is appropriate. In some preferred embodiments, the thickness of the adhesive layer is about 20 μm or more, more preferably about 30 μm or more, and can also be about 40 μm or more. By increasing the thickness of the adhesive layer, it is easy to obtain superior adhesive properties. Furthermore, a sufficiently thick adhesive layer easily absorbs the effects of protrusions and height differences acting on the surface of the adhesive sheet. In adhesive sheets where each side of the substrate has an adhesive layer (a first adhesive layer and a second adhesive layer), the thickness of each adhesive layer can be the same or different.

[0164] In some preferred embodiments, the total thickness of the adhesive layers constituting the adhesive sheet is 20 μm or more. An adhesive layer with this thickness readily absorbs the effects of protrusions and height differences acting on the surface of the adhesive sheet. Furthermore, with a thickness exceeding a specified value, the adhesive layer tends to exhibit superior adhesive properties (e.g., adhesive strength, impact resistance). In a substrate-free adhesive sheet consisting only of adhesive layers, the total thickness of the adhesive layers is the same as the thickness of the adhesive sheet. In a double-sided adhesive sheet with a substrate, the total thickness of the adhesive layers is the total thickness of the adhesive layers (first adhesive layer and second adhesive layer) disposed on each side of the substrate. The total thickness of the adhesive layers is more preferably 30 μm or more, and can be 35 μm or more, 45 μm or more, or 55 μm or more. An upper limit for the total thickness of the adhesive layers is, for example, about 200 μm or less. From the viewpoint of thickness reduction and weight reduction, it is preferably about 100 μm or less, and can be about 75 μm or less, or about 60 μm or less. The above-mentioned range of total thickness is preferably applied to adhesive sheets with substrates.

[0165] While there are no particular limitations, in some embodiments the light transmittance of the adhesive layer constituting the adhesive sheet can be limited. In some embodiments, the light transmittance of the adhesive layer is 30% or less. Adhesive sheets with such adhesive layers can have light-blocking properties. The light transmittance of the adhesive layer can be 20% or less, or less than 10%. The lower limit of the aforementioned light transmittance is not particularly limited; it can be substantially 0%, i.e., below the detection limit, or it can be 1% or more, 5% or more, or 15% or more. In other embodiments, the light transmittance of the adhesive layer is greater than 30%. The light transmittance of the adhesive layer can, for example, be greater than 50%, or 70% or more (e.g., 85% or more). Adhesive layers with light transmittance (and thus transparency) are preferably used for optical applications and various other applications with suitable light transmittance.

[0166] The transmittance [%] of the adhesive layer is the transmittance along the thickness direction of the adhesive layer (transmittance at a wavelength of 550 nm), measured using a commercially available transmittance meter according to JIS K 7136:2000. A spectrophotometer manufactured by Hitachi, Ltd. (device name "U4150 type spectrophotometer") or its equivalent can be used as the transmittance meter. The transmittance of the adhesive sheet is also measured using the same method.

[0167] <Substrate (Substrate Layer)>

[0168] In the form of adhesive sheets disclosed herein, which are single-sided or double-sided adhesive sheets with a substrate, the substrate used as the supporting (backing) adhesive layer can be resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or composites thereof. Examples of resin films include: polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluorinated resin films; and cellophane. Examples of paper include: Japanese paper, kraft paper, cellophane, high-quality paper, synthetic paper, and surface-coated paper. Examples of cloth include woven fabrics and non-woven fabrics obtained by weaving various fibrous materials alone or in blends. Examples of the aforementioned fibrous materials include: cotton, synthetic staple fibers, Manila hemp, pulp, rayon, cellulose acetate, polyester fibers, polyvinyl alcohol fibers, polyamide fibers, and polyolefin fibers. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyurethane sheets and foamed neoprene sheets. Examples of metal foils include aluminum foil and copper foil.

[0169] It should be noted that the term "nonwoven fabric" here primarily refers to the concept of nonwoven fabric for adhesive sheets used in the field of adhesive tapes and other adhesive sheets, typically referring to nonwoven fabric (sometimes also called "paper") produced using conventional papermaking machines. Furthermore, the term "resin film" here typically refers to a non-porous resin sheet, a concept distinct from nonwoven fabric (i.e., not containing nonwoven fabric). The aforementioned resin film can be any of the following: non-stretch film, uniaxial stretch film, or biaxial stretch film.

[0170] As the substrate constituting the adhesive sheet with a substrate, a substrate containing a resin film as the base film is preferably used. The base film is typically a (non-dependent) component that can independently maintain its shape. The substrate in the disclosed technology can be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include a coloring layer, a reflective layer, a primer layer, an antistatic layer, etc., disposed on the surface of the base film.

[0171] The aforementioned resin film is a film in which a resin material is the main component (e.g., a component with a content greater than 50% by weight in the resin film). Examples of resin films include: polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluorinated resin films; cellophane; etc. The resin film can also be a rubber film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoint of operability and processability, and PET films are particularly preferred.

[0172] The substrate can be transparent or light-blocking. In some cases, a colorant can be contained in the substrate (e.g., a resin film). This allows adjustment of the substrate's light transmittance (light blocking property). Adjusting the substrate's light transmittance (e.g., vertical transmittance) can help adjust the light transmittance of the substrate, and consequently, the light transmittance of the adhesive sheet containing the substrate.

[0173] As a colorant, the same pigments and dyes known in the prior art can be used, as can be found in the adhesive layer. There are no particular limitations on the colorant; for example, it can be black, gray, white, red, blue, yellow, green, yellowish-green, orange, purple, gold, silver, pearl, etc.

[0174] The aforementioned substrate (e.g., resin film) may contain various additives as needed, such as fillers (inorganic fillers, organic fillers, etc.), dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, and plasticizers. The proportion of each additive is approximately less than 30% by weight (e.g., approximately less than 20% by weight, typically approximately less than 10% by weight).

[0175] The aforementioned substrate (e.g., a resin film) can be a single-layer structure or a multi-layer structure with two, three, or more layers. From the viewpoint of shape stability, a single-layer structure is preferred. In the case of a multi-layer structure, it is preferable that at least one layer (preferably all layers) is a layer having a continuous structure of the aforementioned resin (e.g., a polyester resin). The manufacturing method of the substrate (typically a resin film) can appropriately employ conventionally known methods without particular limitation. For example, conventionally known film forming methods such as extrusion molding, blow molding, T-die casting, and calendering roll forming can be appropriately employed.

[0176] The substrate can be colored by a coloring layer disposed on the surface of a base film (preferably a resin film). In a substrate comprising a base film and a coloring layer, the base film may or may not contain a colorant. The coloring layer may be disposed on either surface of the base film or on both surfaces. In a configuration where coloring layers are disposed on both surfaces of the base film, the composition of these coloring layers may be the same or different.

[0177] For the surface of the substrate, conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of primer can be performed. Such surface treatments can be used to improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring effect of the adhesive layer on the substrate.

[0178] Furthermore, when the disclosed technology is implemented in the form of a single-sided adhesive sheet with a substrate, a peeling process can be performed on the back side of the substrate as needed. The peeling process can be, for example, applying a typical polysiloxane, long-chain alkyl, or fluorinated peeling agent in the form of a thin film typically about 0.01 μm to about 1 μm (e.g., about 0.01 μm to about 0.1 μm). By performing this peeling process, effects such as easy unwinding of the adhesive sheet into a roll can be achieved.

[0179] There is no particular limitation on the thickness of the substrate. The thickness of the substrate can be set to, for example, about 200 μm or less (e.g., about 100 μm or less). Depending on the intended use and application of the adhesive sheet, the thickness of the substrate can be about 70 μm or less, about 30 μm or less, about 15 μm or less, about 8 μm or less, or about 5 μm or less (e.g., 3 μm or less). Limiting the thickness of the substrate can meet the requirements for thinning and weight reduction. Furthermore, adhesive sheets with a substrate having a limited thickness tend to better utilize the stress relaxation properties introduced by the adhesive layer. There is no particular limitation on the lower limit of the substrate thickness, for example, 0.5 μm or more. From the viewpoint of operability (handleability) and processability of the adhesive sheet, a substrate thickness of about 1 μm or more is appropriate, and can be about 2 μm or more, about 5 μm or more, for example, about 10 μm or more.

[0180] In adhesive sheets with a substrate layer and single or double-sided adhesive adhesion, it is appropriate that the total thickness of the adhesive layer accounts for more than 50% of the total thickness of the adhesive sheet. With such an adhesive sheet with a substrate, the advantages of processability and operability provided by the substrate can be enjoyed while better utilizing the stress relaxation properties of the adhesive layer. The proportion of the total thickness of the adhesive layer to the total thickness of the adhesive sheet is preferably 70% or more, more preferably 80% or more, further preferably 90% or more, and particularly preferably 95% or more. From the viewpoint of obtaining the effects provided by the substrate, it is appropriate that the proportion of the total thickness of the adhesive layer to the total thickness of the adhesive sheet is 99% or less, and can be less than 95% or less than 90%.

[0181] <Removing the liner>

[0182] In the technology disclosed herein, release liner can be used in the formation of the adhesive layer, the fabrication of the adhesive sheet, the storage of the adhesive sheet before use, its distribution, and shape processing. There are no particular limitations on the release liner; for example, a release liner with a release treatment layer on the surface of the liner substrate such as a resin film or paper can be used; a release liner containing a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can also be used. The release treatment layer can be formed, for example, by surface treatment of the liner substrate with release agents such as silicone, long-chain alkyl, fluorinated, or molybdenum sulfide.

[0183] <Properties of adhesive sheets, etc.>

[0184] (Adhesion strength at 23℃)

[0185] The adhesive strength (180-degree peel strength to stainless steel sheet measured at 23°C) of the adhesive sheet disclosed herein can vary depending on the intended use and application location, and is therefore not limited to a specific range. For example, the adhesive strength at 23°C can be set to approximately 1 N / 25 mm or more, and approximately 5 N / 25 mm or more is suitable. From the viewpoint of adhesive reliability, the adhesive strength at 23°C is preferably 10 N / 25 mm or more, more preferably 15 N / 25 mm or more, further preferably 18 N / 25 mm or more, and particularly preferably 20 N / 25 mm or more. The adhesive sheet having the above-mentioned adhesive strength at 23°C has adhesive strength suitable for bonding and fixing, for example, suitable for bonding and fixing in portable electronic devices where high adhesive reliability is required when the adhesive area is limited. There is no particular upper limit to the adhesive strength at 23°C, and it can be approximately 30 N / 25 mm or less (e.g., 25 N / 25 mm or less). The adhesive strength at 23°C can be measured by the method described in the examples described later. In the case of double-sided adhesive sheets with adhesive surfaces on both sides, the adhesive force on each side at 23°C can be the same or different.

[0186] (Adhesion strength at 80℃)

[0187] The adhesive strength of the adhesive sheet disclosed herein at 80°C (180-degree peel strength to stainless steel sheet measured at 80°C) can vary depending on the intended use and application location, and is therefore not limited to a specific range. For example, the adhesive strength of the adhesive sheet at 80°C can be set to approximately 1 N / 25 mm or more, and approximately 5 N / 25 mm or more is suitable. From the viewpoint of adhesive reliability at high temperatures, the adhesive strength at 80°C is preferably 8 N / 25 mm or more, more preferably 10 N / 25 mm or more, further preferably 12 N / 25 mm or more, and may also be 15 N / 25 mm or more. The adhesive sheet having the above-mentioned adhesive strength at 80°C has adhesive strength suitable for bonding and fixing in applications exposed to high temperatures, such as in portable electronic devices where heat is sometimes present and high adhesive reliability is required when the adhesive area is limited. There is no particular upper limit to the adhesive strength at 80°C, and it can be approximately 30 N / 25 mm or less (e.g., 20 N / 25 mm or less). The adhesive strength at 80°C can be measured by the method described in the examples described later. In the case of double-sided adhesive sheets with adhesive surfaces on both sides, the adhesive force on each side at 80°C can be the same or different.

[0188] (Stress relaxation time)

[0189] The adhesive sheet disclosed herein exhibits a stress half-life (stress relaxation time) of less than 40 seconds in stress relaxation tests performed by the method described in the embodiments described later. Adhesive sheets satisfying this characteristic tend to have excellent stress relaxation properties and can be adhesive sheets that make it difficult for the effects of protrusions or height differences present on one side of the adhesive sheet to manifest on the other side. The aforementioned stress relaxation time is preferably less than 30 seconds, more preferably less than 20 seconds, further preferably less than 15 seconds, and particularly preferably less than 10 seconds (e.g., less than 7 seconds). From the viewpoint of also considering high-temperature shear retention, the aforementioned stress relaxation time can be more than 1 second, more than 3 seconds, or more than 8 seconds.

[0190] (High-temperature shear holding force)

[0191] The adhesive sheet disclosed herein can withstand a high-temperature shear retention test performed by the method described in the embodiments described later, without falling off the adherend after one hour from the start of the test. Such an adhesive sheet exhibits excellent high-temperature shear retention properties.

[0192] (Light transmittance)

[0193] While not particularly limited, in some embodiments, the adhesive sheet preferably has a light transmittance of 30% or less. Such an adhesive sheet can have light-blocking properties. The light transmittance of the adhesive sheet can be 20% or less, or less than 10%. There is no particular limitation on the lower limit of the aforementioned light transmittance; it can be substantially 0%, i.e., below the detection limit, or it can be 1% or more, 5% or more, or 15% or more. In other embodiments, the light transmittance of the adhesive sheet is greater than 30%. The light transmittance of the adhesive sheet can, for example, be greater than 50%, or 70% or more (e.g., 85% or more). Adhesive sheets with light transmittance (and thus transparency) are preferably used for optical applications and various other applications with suitable light transmittance.

[0194] (Total thickness)

[0195] The total thickness of the adhesive sheet (including an adhesive layer and a substrate, but excluding a release liner) disclosed herein is not particularly limited. The total thickness of the adhesive sheet can be set to, for example, about 300 μm or less; from a thinning perspective, about 200 μm or less is suitable, and it can be about 150 μm or less (e.g., about 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be set to about 50 μm or less, for example, about 35 μm or less. There is no particular limitation on the lower limit of the adhesive sheet thickness; for example, setting it to about 10 μm or more is suitable, preferably about 20 μm or more, more preferably about 30 μm or more, and it can be about 40 μm or more, or about 80 μm or more. Adhesive sheets with a thickness of a specified value or more tend to readily absorb the effects of protrusions and height differences acting on the surface of the adhesive sheet. Furthermore, they tend to have good operability, excellent adhesion, and excellent impact resistance. It should be noted that in adhesive sheets without a substrate, the thickness of the adhesive layer is the total thickness of the adhesive sheet.

[0196] <Uses>

[0197] The adhesive sheet disclosed herein exhibits excellent high-temperature shear retention and stress relaxation properties that prevent the effects of protrusions or height differences on one side of the adhesive sheet from manifesting on the other side. Utilizing these characteristics, the adhesive sheet can be used for a variety of applications. For example, it is preferably used for fixing various components in environments exposed to high temperatures. The adhesive sheet disclosed herein is suitable for applications such as fixing components in various portable electronic devices. Portable electronic devices sometimes have internal heat, making the use of adhesive sheets with excellent high-temperature adhesive properties desirable. The aforementioned examples of portable electronic devices, without limitation, include: mobile phones, smartphones, tablet PCs, laptop PCs, various wearable devices (such as wristwatches, modular devices worn on the wrist, modular devices worn on the body with clips, straps, etc., including eyewear (monocular, binocular, and helmet-type), clothing devices worn as accessories on shirts, socks, hats, etc., and earwear such as headphones), digital cameras, digital camcorders, audio equipment (portable music players, voice recorders, etc.), calculators (desktop calculators, etc.), portable gaming devices, electronic dictionaries, electronic notebooks, e-books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. It should be noted that in this specification, "portable" is not adequately interpreted as merely being able to carry; it essentially refers to a level of portability that is relatively easy for an individual (standard adult) to move.

[0198] Furthermore, the adhesive sheet possesses stress relaxation properties that prevent the effects of protrusions or height differences existing on one side from manifesting on the other side. Therefore, it is suitable for fixing various components with unevenness or height differences, such as adhered objects, components disposed on the back side of the adhered object, and articles. Even when unevenness or height differences are pressed against the adhesive sheet side as described above, the adhesive sheet disclosed herein can prevent or reduce the influence of such protrusions. For example, in the fixing of components within the aforementioned portable electronic device, due to the limited space within the device, components such as FPCs are sometimes accommodated in a bent form, and such components can form protrusions in a flat component group. Additionally, due to the combination and arrangement of multiple components, height differences can arise between these components. By using the adhesive sheet disclosed herein, the influence of such protrusions or height differences within the aforementioned device can be prevented or reduced.

[0199] The adhesive sheet disclosed herein can be used for various applications requiring light blocking properties. For example, in electronic devices such as portable electronic devices, light-emitting elements are included for purposes such as image display. Therefore, for adhesive sheets, limited light transmittance (e.g., light blocking properties) is required to prevent light leakage. For such electronic devices, adhesive sheets with a specified light blocking property can be used. For example, the above-mentioned adhesive sheet can be used in electronic devices that include various light sources such as LEDs (light-emitting diodes) and self-emissive organic EL (electroluminescent) elements. The above-mentioned electronic devices may be electronic devices having organic EL display devices or liquid crystal display devices (typically portable electronic devices). For example, the adhesive sheet disclosed herein is suitable for use on the back of a display screen (display unit) such as a touch panel display in a portable electronic device.

[0200] The materials (adhesive materials) to which the adhesive sheets disclosed herein are pasted are not particularly limited, and examples include: metallic materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, or alloys containing two or more of these; polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called aromatic polyamide resins, etc.), polyarylate resins, polycarbonate resins, liquid crystal polymers, and various other resin materials (typically plastic materials); alumina, zirconium oxide, soda-lime glass, quartz glass, carbon, and other inorganic materials. Among these, metallic materials such as copper, aluminum, and stainless steel, and resin materials such as polyester resins like PET, polyimide resins, aromatic polyamide resins, and polyphenylene sulfide resins (typically plastic materials) are widely used. These materials can be used to construct components of electronic devices and other products. The adhesive sheet disclosed herein can be used to adhere to components made of the aforementioned materials. Furthermore, the aforementioned materials can be materials constituting the mounting objects (e.g., electromagnetic wave shielding materials, reinforcing plates, etc.) of the aforementioned pressure-sensitive sensor, display unit, etc. It should be noted that the mounting object refers to the object to which the adhesive sheet is adhered, i.e., the object to be adhered. Additionally, the back component refers to a component disposed on the opposite side of the surface (visual recognition side) of the aforementioned pressure-sensitive sensor or display unit, for example, in a portable electronic device; for example, it can be a component disposed as described later. Figure 3 The components of the support portion 240 on the back side of the display device 200 shown. Furthermore, the aforementioned fixing object can be any form of single-layer or multi-layer structure, and various surface treatments can be applied to the surface (adhesive surface) of the adhesive sheet. While there are no particular limitations, as an example of a fixing object, a back panel component with a thickness of approximately 1 μm or more (typically approximately 5 μm or more, for example, approximately 60 μm or more, and further approximately 120 μm or more) and approximately 1500 μm or less (for example, approximately 800 μm or less) can be cited.

[0201] Figure 3 This is an exploded perspective view schematically illustrating an example of the configuration of a display device that can be used as an application object for the adhesive sheet disclosed herein. Figure 3 As shown, the portable electronic device 100 includes a display device 200 comprising a display section 220 and a support section 240, which are composed of a protective member or an organic EL unit, etc. The display device 200 also includes an adhesive sheet 230. In this configuration example, the adhesive sheet 230 is a double-sided adhesive sheet (double-sided adhesive sheet) used to fix the components constituting the display section 220 and the support section 240. It should be noted that the support section 240 is composed of a substrate (a metal plate such as a stainless steel plate or an aluminum plate). The adhesive sheet disclosed herein is preferably used as a constituent element of the display device as described above.

[0202] The matters disclosed in this specification include the following.

[0203] [1] A portable electronic device, wherein the portable electronic device is a portable electronic device having a display device, the display device comprising a display section and a support section, the display section comprising a protective member and an organic EL unit, wherein...

[0204] The adhesive sheet engages with the support portion.

[0205] The adhesive sheet has an adhesive layer.

[0206] The tensile strength of the adhesive layer in a tensile test at a tensile speed of 10 mm / min is less than 2 MPa.

[0207] The 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 23°C. RT and the 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 80°C. 80℃ The adhesion retention rate (P) of the adhesive sheet at 80°C was obtained by calculating the relationship. 80℃ / P RT (×100) is over 50%.

[0208] [2] The portable electronic device described in [1] above, wherein the display unit has a touch panel that functions as an input unit.

[0209] [3] The portable electronic device as described in [1] or [2] above, wherein the adhesive sheet is a double-sided adhesive sheet with a substrate layer, and the total thickness of the adhesive layer accounts for more than 50% of the total thickness of the adhesive sheet.

[0210] [4] The portable electronic device as described in [1] or [2] above, wherein the adhesive sheet is a substrate-free double-sided adhesive sheet composed of the adhesive layer.

[0211] [5] The portable electronic device as described in any one of [1] to [4] above, wherein the adhesive layer comprises a tackifying resin with a softening point of less than 145°C.

[0212] [6] The portable electronic device as described in any one of [1] to [5] above, wherein the adhesive layer is an acrylic adhesive layer containing an acrylic polymer as the base polymer.

[0213] [7] The portable electronic device as described in [6] above, wherein in the acrylic polymer, an alkyl (meth)acrylate having an alkyl group having 7 or more and 10 or less carbon atoms at the ester end is polymerized in a proportion of 50% by weight or more.

[0214] [8] The portable electronic device as described in [6] or [7] above, wherein the adhesive layer comprises an acrylic oligomer.

[0215] [9] The portable electronic device as described in any one of [1] to [8] above, wherein the adhesive composition for forming the adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent.

[0216]

[10] The portable electronic device as described in any one of [1] to [9] above, wherein the total thickness of the adhesive layer is 30 μm or more.

[0217]

[11] An adhesive sheet, wherein the adhesive sheet is an adhesive sheet having an adhesive layer, wherein...

[0218] The tensile strength of the adhesive layer in a tensile test at a tensile speed of 10 mm / min is less than 2 MPa.

[0219] The 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 23°C. RT and the 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 80°C. 80℃ The 80℃ adhesion retention rate (P) was obtained from the relationship. 80℃ / P RT (×100) is over 50%.

[0220]

[12] As described in

[11] above, wherein the adhesive sheet is a double-sided adhesive sheet with a substrate layer, and the total thickness of the adhesive layer accounts for more than 50% of the total thickness of the adhesive sheet.

[0221]

[13] The adhesive sheet as described in

[11] above, wherein the adhesive sheet is a substrate-free double-sided adhesive sheet composed of the adhesive layer.

[0222]

[14] An adhesive sheet as described in any one of

[11] to

[13] above, wherein the adhesive layer comprises a tackifying resin with a softening point of less than 145°C.

[0223]

[15] The adhesive sheet as described in any one of

[11] to

[14] above, wherein the adhesive layer is an acrylic adhesive layer containing an acrylic polymer as the base polymer.

[0224]

[16] The adhesive sheet as described in

[15] above, wherein in the acrylic polymer, an alkyl (meth)acrylate having an alkyl group having 7 or more and 10 or less carbon atoms at the ester end is polymerized in a proportion of 50% by weight or more.

[0225]

[17] An adhesive sheet as described in

[15] or

[16] above, wherein the adhesive layer comprises an acrylic oligomer.

[0226]

[18] The adhesive sheet as described in any one of

[11] to

[17] above, wherein the adhesive composition for forming the adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent.

[0227]

[19] The adhesive sheet as described in any one of

[11] to

[18] above, wherein the total thickness of the adhesive layer is 30 μm or more.

[0228]

[20] An adhesive sheet as described in any one of

[11] to

[19] above, wherein the adhesive sheet is used for fixing components within a portable electronic device.

[0229] Example

[0230] The following describes some embodiments of the present invention, but it is not intended to limit the present invention to the contents shown in these embodiments. It should be noted that, unless otherwise specified, "parts" and "%" in the following description are based on weight.

[0231] <Example 1>

[0232] (Preparation of acrylic polymers)

[0233] In a reaction vessel equipped with a stirrer, thermometer, nitrogen inlet pipe, reflux condenser, and dropping funnel, 95 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA) as monomer components, and 233 parts of ethyl acetate as polymerization solvent were added. The mixture was stirred for 2 hours while nitrogen was introduced. This removed oxygen from the polymerization system. Then, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator were added, and solution polymerization was carried out at 60°C for 8 hours to obtain a solution of an acrylic polymer (A1). The Mw of this acrylic polymer (A1) was approximately 70 × 10⁻⁶. 4 .

[0234] (Preparation of the adhesive composition)

[0235] In the aforementioned acrylic polymer solution, relative to 100 parts of the acrylic polymer (A1) contained in the solution, 20 parts of tackifying resin (B1), 3 parts of isocyanate crosslinking agent, and 0.01 parts of epoxy crosslinking agent were added and stirred to prepare an adhesive composition. As the tackifying resin (B1), a terpene phenolic resin (trade name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., with a softening point of approximately 115°C and a hydroxyl value of 30 mg KOH / g to 60 mg KOH / g) was used. As the isocyanate crosslinking agent, a 75% ethyl acetate solution of trimethylolpropane / toluene diisocyanate trimer adduct (manufactured by Tosoh Co., Ltd.) was used. As the epoxy crosslinking agent, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used.

[0236] (Making the adhesive sheet)

[0237] The adhesive composition obtained was coated onto one surface (first side) of a 2 μm thick polyethylene terephthalate (PET) film (trade name "Lumirror", manufactured by Toray Industries, Inc.) as the substrate layer, and dried at 100°C for 2 minutes to form a first adhesive layer with a thickness of 24 μm. Additionally, a polyester release film (trade name "DIAFOIL MRF", thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) with double-sided release treatment as the release liner was prepared. The prepared adhesive composition was coated onto one release surface of the release liner and dried at 100°C for 2 minutes to form a second adhesive layer with a thickness of 24 μm. This second adhesive layer was transferred onto the non-adhesive layer surface of the substrate layer on which the first adhesive layer was formed, thereby producing the double-sided adhesive sheet with a substrate in this example.

[0238] <Example 2>

[0239] As the substrate layer, a 12μm thick PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) was used. The thickness of each adhesive layer (first adhesive layer and second adhesive layer) was changed to 44μm. Otherwise, the process was the same as in Example 1, thereby producing the double-sided adhesive sheet with substrate in this example.

[0240] <Example 3>

[0241] (Preparation of the adhesive composition)

[0242] The monomer composition was changed to 95 parts of 2-ethylhexyl acrylate (2EHA) and 5 parts of AA. The concentration of the non-volatile component (monomer component) was adjusted by increasing the amount of polymerization solvent. Otherwise, acrylic polymer (A2) was synthesized by a method essentially the same as that used for the synthesis of acrylic polymer (A1), thus obtaining a solution of acrylic polymer (A2). The Mw of this acrylic polymer (A2) is approximately 120 × 10⁻⁶. 4 In this acrylic polymer solution, relative to 100 parts of acrylic polymer (A2) contained in the solution, 20 parts of tackifying resin (B1), 10 parts of acrylic oligomer, 6.58 parts of black colorant, and 3 parts of isocyanate crosslinking agent and 0.03 parts of epoxy crosslinking agent were added and stirred to prepare an adhesive composition. The tackifying resin, isocyanate crosslinking agent, and epoxy crosslinking agent were the same substances used in Example 1. The black colorant was "ATDN101 BLACK" (containing carbon black particles with an average particle size of 350 nm), manufactured by Daihisei Chemical Co., Ltd. It should be noted that the adhesive composition in this example contains a small amount (approximately 1% to 1.5% by weight based on solid content) of liquid tackifying resin.

[0243] As an acrylic oligomer, a substance prepared by the following method was used. Specifically, in a reaction vessel equipped with a stirrer, thermometer, nitrogen inlet pipe, reflux condenser, and dropping funnel, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and toluene as a polymerization solvent were added. After stirring in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, the temperature was raised to 85°C and the reaction was allowed to proceed for 5 hours, thereby obtaining an acrylic oligomer with a solid content concentration of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0244] (Making the adhesive sheet)

[0245] The adhesive composition described above was applied to the release surface of a 38 μm thick polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Corporation), and dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 35 μm. The release surface of a 25 μm thick polyester release liner (trade name "DIAFOIL MRF", manufactured by Mitsubishi Polyester Corporation) was then bonded onto this adhesive layer. This resulted in a substrate-free double-sided adhesive sheet with a thickness of 35 μm, protected on both sides by the two polyester release liners described above.

[0246] <Example 4>

[0247] Using the adhesive composition of Example 3, and otherwise in the same manner as in Example 1, a double-sided adhesive sheet with a substrate having an adhesive layer (first adhesive layer and second adhesive layer) with a thickness of 24 μm on each side of a PET film substrate with a thickness of 2 μm was produced.

[0248] <Example 5>

[0249] The monomer composition was changed to 70 parts BA, 30 parts 2EHA, 3 parts AA, and 0.05 parts 4-hydroxybutyl acrylate (4HBA). Otherwise, acrylic polymer (A3) was synthesized using a method substantially the same as that used for synthesizing acrylic polymer (A1), thus obtaining a solution of acrylic polymer (A3). To this acrylic polymer solution, 30 parts of tackifying resin (B2) and 2 parts of isocyanate crosslinking agent were added relative to 100 parts of acrylic polymer (A3) contained in the solution, and the mixture was stirred to prepare an adhesive composition. As the tackifying resin (B2), a polymeric rosin ester (manufactured by Arakawa Chemical Industry Co., Ltd., trade name "Pensel D125") with a softening point of 125°C was used. As the isocyanate crosslinking agent, the same substance used in Example 1 was used.

[0250] An adhesive composition was coated onto one surface (first side) of a 12 μm thick PET film substrate (trade name "Lumirror", manufactured by Toray Industries, Inc.) and dried at 100°C for 2 minutes to form a first adhesive layer with a thickness of 19 μm. Additionally, a polyester release film (trade name "DIAFOIL MRF", thickness 38 μm, manufactured by Mitsubishi Polyester Co., Ltd.) with double-sided release treatment as the release liner was prepared. The prepared adhesive composition was coated onto one release surface of the release liner and dried at 100°C for 2 minutes to form a second adhesive layer with a thickness of 19 μm. This second adhesive layer was transferred to the non-adhesive layer surface of the substrate on which the first adhesive layer was formed, thereby producing the double-sided adhesive sheet with substrate in this example.

[0251] <Example 6>

[0252] A solution of acrylic polymer (A1) was prepared using the same method as in Example 1. In this acrylic polymer solution, 25 parts of acrylic oligomer and 1 part of isocyanate crosslinking agent were added relative to 100 parts of acrylic polymer (A1) contained in the solution.

[0253] An adhesive composition was prepared by mixing 0.075 parts of an epoxy crosslinking agent with the mixture. The same types of substances as those used in Example 3 were used as the acrylic oligomer, isocyanate crosslinking agent, and epoxy crosslinking agent.

[0254] In addition to using the obtained adhesive composition, a double-sided adhesive sheet with a substrate having an adhesive layer (first adhesive layer and second adhesive layer) with a thickness of 19 μm on each side of a PET film substrate with a thickness of 12 μm was produced in the same manner as in Example 5.

[0255] <Example 7>

[0256] (Preparation of the adhesive composition)

[0257] The monomer composition was changed to 93 parts BA, 7 parts AA, and 0.04 parts 4HBA. Otherwise, acrylic polymer (A4) was synthesized using a method substantially the same as that used for synthesizing acrylic polymer (A1), thus obtaining a solution of acrylic polymer (A4). To this acrylic polymer solution, relative to 100 parts of acrylic polymer (A4) contained in the solution, 15 parts of tackifying resin (B3), 15 parts of acrylic oligomer, and 1.2 parts of isocyanate crosslinking agent and 0.01 parts of epoxy crosslinking agent were added, and the mixture was stirred to prepare an adhesive composition. The acrylic oligomer, isocyanate crosslinking agent, and epoxy crosslinking agent were the same substances used in Example 3. As the tackifying resin (B3), a terpene phenol resin (trade name "Tamanol 803L", manufactured by Arakawa Chemical Industry Co., Ltd., with a softening point of about 145°C to 160°C and a hydroxyl value of 1 mgKOH / g to 20 mgKOH / g) was used.

[0258] Using the obtained adhesive composition, an adhesive layer with a thickness of 50 μm was formed, otherwise the same procedure as in Example 3 was performed, thereby obtaining a substrate-free double-sided adhesive sheet with a thickness of 50 μm that was protected on both sides by the two polyester release liner sheets mentioned above.

[0259] <Evaluation>

[0260] Fracture strength in tensile tests

[0261] The adhesive layers were stacked to obtain an adhesive layer laminate with a thickness of approximately 0.4 mm. Only the upper and lower surfaces of this laminate were covered by release liner. The laminate was then autoclaved for 20 minutes (50°C, 0.5 MPa) to prevent air bubbles from remaining between layers, and then cut into pieces 10 mm wide and 100 mm long to obtain test pieces. At 23°C and 50% RH, the two release films covering the upper and lower surfaces were peeled off to expose the adhesive layer laminate. Tensile tests were performed on the test pieces using a tensile testing machine (Minebea Corporation, universal tensile and compression testing machine, device name "Tensile and Compression Testing Machine, TCM-1kNB") with a clamping distance of 10 mm and a tensile speed of 10 mm / min. The SS curve was calculated, and the strength at break (breaking strength) [MPa] of the test piece was determined. It should be noted that for substrate-free adhesive sheets, an adhesive layer laminate with a thickness of approximately 0.4 mm can be obtained by peeling and stacking release liner. For adhesive sheets with a substrate, an adhesive composition for forming the adhesive used in the test is used to form an adhesive layer on a release support under the same conditions as when the adhesive sheet is formed, and then the layers are stacked to obtain an adhesive layer laminate with a thickness of about 0.4 mm. Furthermore, it is preferable to apply powder to the adhesive surface at the clamping location during the test to eliminate the influence of adhesive stickiness.

[0262] [Adhesive strength at 23°C]

[0263] Under a testing environment of 23°C and 50% RH, a 50 μm thick PET film was backed onto one adhesive side of a double-sided adhesive sheet and cut into pieces 25 mm wide and 100 mm long to prepare test samples. For the prepared test samples, a 2 kg roller was used to press the adhesive side of the test sample against the surface of a stainless steel plate (SUS304BA plate) once under the same conditions of 23°C and 50% RH. After being placed under the same conditions for 30 minutes, the 180° peel strength (adhesive force at 23°C) [N / 25 mm] was measured using a universal tensile and compression testing machine according to JIS Z 0237:2000, at a tensile speed of 300 mm / min and a peel angle of 180°. The universal tensile and compression testing machine used was the Minebea TG-1kN or an equivalent. It should be noted that in the case of a single-sided adhesive sheet, the aforementioned PET film backing is not required.

[0264] [Adhesive strength at 80℃]

[0265] The test sample was prepared in the same manner as the 23°C adhesion strength test. A 2kg roller was used to press the adhesive side of the test sample against the surface of a stainless steel sheet (SUS304BA sheet). After being placed in the same environment for 30 minutes, and then further placed at 80°C for 30 minutes, the 180° peel strength (80°C adhesion strength) [N / 25mm] was measured using a universal tensile and compression testing machine according to JIS Z 0237:2000, at a tensile speed of 300 mm / min and a peel angle of 180 degrees. The universal tensile and compression testing machine used was the Minebea TG-1kN or an equivalent. It should be noted that in the case of single-sided adhesive sheets, the aforementioned PET film backing is not required.

[0266] [Stress relaxation test]

[0267] The adhesive sheets were stacked to obtain an adhesive sheet laminate with a thickness of 1 mm. Only the upper and lower surfaces of this laminate were protected by release liner. The laminate was cured at 50°C for one day to prevent air bubbles from remaining between the layers, and then cut into 10 mm × 10 mm pieces to obtain test pieces. The two release films covering the upper and lower surfaces were peeled off to expose the adhesive sheets. Using a commercially available micro-autograph, the laminate was compressed in the vertical direction (thickness direction) at a speed of 50 mm / min under a testing environment of 23°C and 50% RH, stopping the compression at a stress of 50 N. This state was maintained, and the stress reduction was measured over time. The time it took for the stress to reach 25 N was recorded as the stress relaxation time (stress half-life). The shorter the stress relaxation time, the better the stress relaxation properties of the adhesive sheet. A stress relaxation time of 40 seconds or less is considered to indicate stress relaxation properties that make the effects of protrusions or height differences on one side of the adhesive sheet less apparent on the other side. As a micro strength evaluation testing machine, the product name "MST-200NX" or its equivalent manufactured by Shimadzu Corporation is used.

[0268] [High-Temperature Shear Holding Test]

[0269] According to JIS Z0237:2009, a high-temperature holding force test is conducted at 80°C to evaluate high-temperature shear retention. Specifically, a 50μm thick PET film is backed onto one adhesive side of a double-sided adhesive sheet at 23°C and 50% RH, and cut into 10mm wide pieces to create the test sample. A 2kg roller is used to reciprocate once, and the other adhesive side of the test sample is then adhered to a bakelite board, serving as the substrate. The adhesive area between the test sample and the substrate is 10mm wide and 20mm long. The test sample, thus adhered to the substrate, is hung suspending at 80°C for 30 minutes. A 500g load is then applied to the free end of the test sample, and it is placed at 80°C for 1 hour under this load. A test sample that remains attached to the substrate after 1 hour is considered "qualified," while a test sample that peels off from the substrate within 1 hour is considered "unqualified." It should be noted that for single-sided adhesive sheets, the PET film backing is not required.

[0270] The composition of each adhesive sheet and the adhesive summary, the tensile strength [MPa] based on the tensile test, and the adhesive force P at 23°C are described. RT [N / 25mm], Adhesion strength P at 80℃ 80℃ [N / 25mm], Adhesion retention rate at 80℃ (P) 80℃ / P RT The evaluation results of (×100) [%), stress relaxation time [seconds], and high-temperature shear retention are shown in Table 1.

[0271] Table 1

[0272]

[0273] As shown in Table 1, for the adhesive sheets in Examples 1 to 4, the tensile strength of the adhesive layer is less than 2 MPa. Furthermore, the adhesion retention rate at 80°C (P0.05) is... 80℃ / P RT The stress relaxation time of these adhesive sheets was less than 40 seconds, and the results of the high-temperature shear retention test were also satisfactory. Among them, the adhesive sheets of Examples 3 and 4 not only maintained high-temperature shear retention but also had short stress relaxation times and excellent stress relaxation properties. On the other hand, the adhesion retention rate at 80°C (P0.05) was over 50%. 80℃ / P RT The high-temperature shear retention test result of the adhesive sheet in Example 5, whose ×100) was less than 50%, was unqualified. In addition, the stress relaxation time of the adhesive sheets in Examples 6 and 7, whose adhesive layer tensile strength was greater than 2 MPa, was greater than 40 seconds, or the stress was not halved when observed over time.

[0274] Based on the above results, the tensile strength of the adhesive layer is below 2 MPa, and the adhesion retention rate at 80℃ is (P0.05).80℃ / P RT The adhesive sheet with a cross-sectional area of ​​50% or more (×100) exhibits good high-temperature shear retention and a tendency for excellent stress relaxation, which can prevent or reduce the influence of protrusions and height differences on one side of the adhesive sheet on the other side.

[0275] The specific examples of the present invention have been described in detail above, but they are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes the contents obtained by various modifications and alterations to the specific examples described above.

[0276] Label Explanation

[0277] 1, 2 adhesive sheets

[0278] 10. Substrate (Substrate Layer)

[0279] 21 Adhesive layer (first adhesive layer)

[0280] 22 Adhesive layer (second adhesive layer)

[0281] 31, 32 Peeling gaskets

Claims

1. An adhesive sheet, wherein the adhesive sheet is an adhesive sheet having an adhesive layer, wherein, The adhesive layer is an acrylic adhesive layer containing an acrylic polymer as the base polymer, wherein the weight-average molecular weight of the acrylic polymer is greater than 70 × 10⁻⁶. 4 And it is 500×10 4 the following, In the acrylic polymers, alkyl acrylates having an alkyl group having 7 or more but less than 10 carbon atoms at the ester terminus are polymerized in a proportion greater than 70% by weight. In the acrylic polymer, an acid-containing monomer is copolymerized, and the monomer component constituting the acrylic polymer contains 1.0% by weight or more and 20% by weight of the acid-containing monomer. The adhesive layer further comprises a tackifying resin T with a softening point of 100°C or higher and less than 135°C. L The tackifying resin T L The tackifying resin T comprises a terpene phenolic resin with a softening point of less than 135°C, in proportion to 100 parts by weight of the acrylic polymer. L The content is 5 parts by weight or more and less than 40 parts by weight. The adhesive layer further comprises a liquid tackifying resin, the content of which is 0.1% to 10% by weight of the total adhesive layer. The adhesive layer further comprises an acrylic oligomer containing an alicyclic hydrocarbon-containing (meth)acrylate as a monomer. The alicyclic hydrocarbon-containing (meth)acrylate accounts for 70% by weight or more of all monomer components constituting the acrylic oligomer, and the content of the acrylic oligomer is 5 parts by weight or more and less than 20 parts by weight relative to 100 parts by weight of the acrylic polymer. The adhesive composition used to form the adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent. The amount of the isocyanate crosslinking agent used is greater than 1.0 part by weight and less than 5 parts by weight relative to 100 parts by weight of the acrylic polymer, and the amount of the epoxy crosslinking agent used is greater than 0.01 parts by weight and less than 0.1 parts by weight. The tensile strength of the adhesive layer in a tensile test at a tensile speed of 10 mm / min is less than 2 MPa. The 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 23°C. RT and the 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 80°C. 80℃ The adhesive strength retention rate P of the adhesive sheet at 80°C was obtained by calculating the relationship. 80℃ / P RT ×100 is over 50%. The tensile strength at break and the 180-degree peel strength P of the adhesive sheet to the stainless steel plate measured at 23°C. RT The 180-degree peel strength P of the adhesive sheet to the stainless steel plate, measured at 80°C. 80℃ The determination methods are described below. Methods for determining fracture strength in tensile tests: The adhesive layers were stacked to obtain an adhesive layer laminate with a thickness of approximately 0.4 mm. Only the upper and lower surfaces of the laminate were covered by release liner. The laminate was autoclaved at 50°C and 0.5 MPa for 20 minutes to prevent air bubbles from remaining between the layers. It was then cut into pieces with a width of 10 mm and a length of 100 mm to obtain test pieces. The two release films covering the upper and lower surfaces were peeled off at 23°C and 50% RH to expose the adhesive layer laminate. Tensile tests were performed on the test pieces using a tensile testing machine with a clamping distance of 10 mm and a tensile speed of 10 mm / min. The SS curve was obtained, and the strength at break, i.e., the breaking strength, was determined. The 180-degree peel strength P of the adhesive sheet to the stainless steel plate was measured at 23°C. RT Method for determining adhesive strength at 23℃: Under a testing environment of 23℃ and 50%RH, a 50μm thick PET film was backed onto one adhesive side of a double-sided adhesive sheet and cut into pieces 25mm wide and 100mm long to prepare the test sample. For the prepared test sample, under the same conditions of 23℃ and 50%RH, a 2kg roller was applied once to press the adhesive side of the test sample against the surface of a SUS304BA stainless steel plate. After being placed under the same conditions for 30 minutes, the 180° peel strength P was measured using a universal tensile and compression testing machine according to JISZ 0237:2000, at a tensile speed of 300mm / min and a peel angle of 180°. RT ; The 180-degree peel strength P of the adhesive sheet to the stainless steel plate was measured at 80°C. 80℃ Determination method: The test sample was prepared in the same manner as the test for adhesion at 23°C. A 2kg roller was used to press the adhesive surface of the test sample against the surface of a SUS304BA stainless steel sheet. After being placed in the same environment for 30 minutes, and then further placed at 80°C for 30 minutes, the 180° peel strength P was measured using a universal tensile and compression testing machine according to JIS Z 0237:2000, at a tensile speed of 300 mm / min and a peel angle of 180 degrees. 80℃ .

2. The adhesive sheet as claimed in claim 1, wherein, The adhesive sheet is a double-sided adhesive sheet with a substrate layer, and the total thickness of the adhesive layer accounts for more than 50% of the total thickness of the adhesive sheet.

3. The adhesive sheet as described in claim 1, wherein, The adhesive sheet is a substrate-free double-sided adhesive sheet composed of the adhesive layer.

4. The adhesive sheet according to any one of claims 1 to 3, wherein, The total thickness of the adhesive layer is 30 μm or more.

5. The adhesive sheet according to any one of claims 1 to 3, wherein, The adhesive pad is used to secure components within portable electronic devices.

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