Adhesive sheet

Abstract

To provide an adhesive sheet having excellent light-pressure adhesion.SOLUTION: Provided is an adhesive sheet having an adhesive layer. The adhesive layer comprises an acrylic polymer and an acrylic oligomer. The acrylic polymer is a polymer of monomer components including: an alkyl (meth)acrylate having a chain alkyl group having at least 7 carbon atoms; and a monomer having a reactive functional group. Here, the monomer components contain at least 3 wt.% of the monomer having the reactive functional group. The storage modulus of the adhesive layer at -20°C is less than 220 MPa.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of adhering to an adherend when pressure is applied. Taking advantage of such properties, adhesives are widely used in various industrial fields, from portable electronic devices such as smartphones and home appliances to automobiles and office automation equipment, typically in the form of adhesive sheets containing an adhesive layer, for purposes such as joining parts and protecting surfaces. Patent documents 1 and 2 are cited as technical documents related to adhesive sheets. Patent documents 1 and 2 describe adhesives containing acrylic polymers polymerized using heptyl acrylate as a monomer component. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 125247 [Patent Document 2] International Publication No. 2021 / 125278 Summary of the Invention [Problem to be solved by the invention]

[0004] In general, adhesive sheets are designed to exert the desired performance (adhesive strength, etc.) by being pressed against an adherend with sufficient pressure. However, depending on the application location and usage mode of the adhesive sheet, it may be desirable to apply a small pressure during pressing. For example, in the case of an adhesive sheet used to fix components in an electronic device, the components constituting the electronic device may include precision equipment, so it is not desirable to apply the sheet by heavy pressing that would cause a load on the precision equipment. Adhesive sheets used for such purposes may be required to have the performance of exerting sufficient adhesive strength even when applied by light pressing. If an adhesive sheet that can exert adhesive strength (light pressure adhesion) that is comparable to that when pressed against a sufficient pressure even under light pressure conditions can be realized, it can be used as an adhesive sheet suitable for the above-mentioned purposes. In addition, according to the adhesive sheet having excellent light pressure adhesion as described above, there are few restrictions on the pressing conditions, and the range of application of the adhesive sheet is expanded, which is beneficial.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a pressure-sensitive adhesive sheet that is excellent in light pressure-bonding adhesiveness. [Means for solving the problem]

[0006] According to this specification, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer is provided. The pressure-sensitive adhesive layer includes an acrylic polymer and an acrylic oligomer. The acrylic polymer is a polymer of a monomer component including an alkyl(meth)acrylate having a chain alkyl group with 7 or more carbon atoms and a monomer having a reactive functional group. The monomer component includes 3% by weight or more of the monomer having the reactive functional group. The pressure-sensitive adhesive layer has a storage modulus of less than 220 MPa at -20°C. With the pressure-sensitive adhesive sheet having the above configuration, even under light pressure bonding conditions, the same adhesiveness (light pressure bonding adhesiveness) is achieved as compared to when pressure-bonded with sufficient pressure.

[0007] In some embodiments, the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms is an alkyl acrylate having a chain alkyl group having 7 or 8 carbon atoms. A pressure-sensitive adhesive containing a polymer of an alkyl acrylate having a chain alkyl group having 7 or 8 carbon atoms can easily reduce the storage modulus at -20°C, and the effects of the technology disclosed herein can be preferably achieved.

[0008] In some preferred embodiments, the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms comprises heptyl acrylate. By using an acrylic polymer containing heptyl acrylate as a monomer component, it is easy to form a flexible pressure-sensitive adhesive having a storage modulus at -20°C of a predetermined value or less, and it is easy to obtain a pressure-sensitive adhesive having excellent light pressure-bonding adhesion.

[0009] In some preferred embodiments, the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes 2-ethylhexyl acrylate (2EHA). According to the technology disclosed herein, a pressure-sensitive adhesive having excellent light pressure-bonding adhesiveness can be obtained by using an acrylic polymer containing 2EHA as a monomer component.

[0010] In some embodiments, the monomer having the reactive functional group is preferably at least one selected from a carboxyl group-containing monomer and a hydroxyl group-containing monomer. The acrylic polymer in which the carboxyl group-containing monomer or the hydroxyl group-containing monomer is copolymerized has a moderately improved cohesive force, and therefore good adhesion reliability is easily obtained.

[0011] In some embodiments, the weight average molecular weight (Mw) of the acrylic polymer is in the range of 300,000 to 1,500,000. By using an acrylic polymer having the above monomer composition and Mw in the above range, the effects of the technology disclosed herein are preferably realized.

[0012] In some embodiments, the glass transition temperature (Tg) of the acrylic oligomer is 20° C. or more and 200° C. or less. By using an appropriate amount of an acrylic oligomer having an appropriate Tg within the above range, the light compression adhesive strength and normal compression adhesive strength can be improved in a well-balanced manner.

[0013] In some embodiments, the content of the acrylic oligomer in the pressure-sensitive adhesive layer is less than 30 parts by weight relative to 100 parts by weight of the acrylic polymer. By using an appropriate amount of the acrylic oligomer within the above range, a pressure-sensitive adhesive having excellent light pressure-bonding adhesion is easily obtained.

[0014] In some preferred embodiments, the pressure-sensitive adhesive layer further comprises a tackifier resin. By including the tackifier resin, the adhesive strength, including the light pressure adhesive strength, can be preferably improved based on the combined effect of the acrylic oligomer and the tackifier resin.

[0015] The adhesive sheet disclosed herein has excellent light pressure-bonding adhesion, and therefore can be preferably used in applications where it is desirable to limit the pressure during pressure-bonding.For example, it is suitable for fixing members in electronic devices, including home appliances, office automation equipment, and mobile electronic devices such as smartphones.As described above, this specification provides an electronic device using any of the adhesive sheets disclosed herein, in other words, an electronic device including the adhesive sheet. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. [Diagram 2] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Diagram 3] FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 4] 1 is a front view showing a schematic diagram of an example of a portable electronic device including an adhesive sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A preferred embodiment of the present invention will be described below. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood by a person skilled in the art based on the teachings on carrying out the invention described in this specification and the common general knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general knowledge in the field. In addition, in the following drawings, members and parts that perform the same function may be described by using the same reference numerals, and duplicated descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product.

[0018] In this specification, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state at temperatures near room temperature and that has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here is generally a material having a complex tensile modulus E * (1Hz)<10 7 dyne / cm 2 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0019] In this specification, biomass-derived carbon means carbon (renewable carbon) derived from biomass materials, i.e., materials derived from renewable organic resources. The biomass materials typically refer to materials derived from biological resources (typically plants that perform photosynthesis) that can be reproduced sustainably in the presence of sunlight, water, and carbon dioxide. Therefore, materials derived from fossil resources that are depleted through use after mining (fossil resource-based materials) are excluded from the concept of biomass materials here. The biomass carbon ratio of the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, i.e., the proportion of biomass-derived carbon in the total carbon contained in the pressure-sensitive adhesive layer and pressure-sensitive adhesive sheet, can be estimated from the carbon isotope content with mass number 14 measured in accordance with ASTM D6866.

[0020] <Composition of adhesive sheet> The adhesive sheet disclosed herein is configured to include an adhesive layer. The adhesive sheet may be in the form of a substrate-less double-sided adhesive sheet having a first adhesive surface constituted by one surface of the adhesive layer and a second adhesive surface constituted by the other surface of the adhesive layer. Alternatively, the adhesive sheet disclosed herein may be in the form of a substrate-attached adhesive sheet in which the adhesive layer is laminated on one or both surfaces of a supporting substrate. Hereinafter, the supporting substrate may simply be referred to as a "substrate". The concept of the adhesive sheet here may include those referred to as adhesive tapes, adhesive labels, adhesive films, and the like. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be in the form of an adhesive sheet further processed into various shapes.

[0021] The structure of an adhesive sheet according to an embodiment is shown in FIG. 1. The adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet made of an adhesive layer 21. The adhesive sheet 1 is used by attaching a first adhesive surface 21A, which is configured by one surface (first surface) of the adhesive layer 21, and a second adhesive surface 21B, which is configured by the other surface (second surface) of the adhesive layer 21, to different locations on an adherend. The locations to which the adhesive surfaces 21A and 21B are attached may be locations on different members, or may be different locations within a single member. The adhesive sheet 1 before use (i.e., before being attached to an adherend) may be a component of an adhesive sheet 100 with a release liner in which the first adhesive surface 21A and the second adhesive surface 21B are protected by release liners 31 and 32, each of which has a release surface at least on the side facing the adhesive layer 21, as shown in FIG. 1. As the release liners 31 and 32, for example, a sheet-like substrate (liner substrate) configured such that one side serves as a release surface by providing a release layer made of a release treatment agent on the one side can be preferably used. Alternatively, the release liner 32 can be omitted, and a release liner 31 having release surfaces on both sides can be used, which is superimposed on the PSA sheet 1 and rolled up in a spiral shape to form a PSA sheet with a release liner in a form in which the second adhesive surface 21B is protected by contacting the back surface of the release liner 31 (roll form).

[0022] The structure of an adhesive sheet according to another embodiment is shown in FIG. 2. The adhesive sheet 2 is configured as a substrate-attached single-sided adhesive sheet including a sheet-like supporting substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, and an adhesive layer 21 provided on the first surface 10A side. The adhesive layer 21 is fixedly provided on the first surface 10A side of the supporting substrate 10, that is, without the intention of separating the adhesive layer 21 from the supporting substrate 10. As shown in FIG. 2, the adhesive sheet 2 before use may be a component of an adhesive sheet 200 with a release liner in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, at least the side facing the adhesive layer 21 being a release surface. Alternatively, the release liner 31 may be omitted, and a supporting substrate 10 with a second surface 10B being a release surface may be used, and the adhesive sheet 2 may be rolled up so that the adhesive surface 21A is in contact with the second surface (rear surface) 10B of the supporting substrate 10 and protected.

[0023] The structure of a pressure-sensitive adhesive sheet according to yet another embodiment is shown in FIG. 3. The pressure-sensitive adhesive sheet 3 is configured as a substrate-attached double-sided pressure-sensitive adhesive sheet including a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, a first pressure-sensitive adhesive layer 21 fixedly provided on the first surface 10A side, and a second pressure-sensitive adhesive layer 22 fixedly provided on the second surface 10B side. As shown in FIG. 3, the pressure-sensitive adhesive sheet 3 before use may be a component of a release-liner-attached pressure-sensitive adhesive sheet 300 in which the surface (first adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and the surface (second adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 are protected by release liners 31 and 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 having both release surfaces may be used, which is superimposed on the pressure-sensitive adhesive sheet 3 and wound in a spiral shape to configure a release-liner-attached pressure-sensitive adhesive sheet in a form (roll form) in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31. The substrate-attached pressure-sensitive adhesive sheet according to the above-mentioned other embodiment is preferable because of its excellent processability, handleability, and the like.

[0024] In the above-mentioned double-sided pressure-sensitive adhesive sheet with a substrate, at least one of the first and second pressure-sensitive adhesive layers (e.g., the first pressure-sensitive adhesive layer) may be an adhesive layer described below, and the other pressure-sensitive adhesive layer (e.g., the second pressure-sensitive adhesive layer) may be an adhesive layer disclosed herein, or may be an adhesive layer having a composition different from that of the adhesive layer disclosed herein (specifically, the one pressure-sensitive adhesive layer, e.g., the first pressure-sensitive adhesive layer). Such other pressure-sensitive adhesive layer may be formed, for example, from a known or commonly used pressure-sensitive adhesive.

[0025] The technology disclosed herein can be preferably implemented in a form including a substrate-less double-sided adhesive sheet. Substrate-less double-sided adhesive sheets can be made thinner because they do not have a substrate, and can contribute to the miniaturization and space saving of products to which the double-sided adhesive sheet is applied. In addition, substrate-less adhesive sheets can maximize the thickness of the adhesive layer to exhibit light pressure adhesion.

[0026] <Adhesive layer> (Viscoelastic properties) The adhesive layer disclosed herein (in an embodiment comprising a first adhesive layer and a second adhesive layer, at least one of the first adhesive layer and the second adhesive layer; the same applies hereinafter unless otherwise specified) is characterized in that it has a storage modulus at -20°C (-20°C storage modulus) of less than 220 MPa. An adhesive sheet comprising an adhesive layer having a -20°C storage modulus of less than 220 MPa achieves equivalent adhesion (light compression adhesion) even under light compression conditions compared to compression with sufficient pressure. As a result of the inventors' investigations, it has become clear that the storage modulus at -20°C in the low temperature range shows a higher correlation with light compression adhesion than the storage modulus in the normal temperature range (for example, comparison between Comparative Examples 1 and 3 described below, and comparison between Examples 3-4 and Examples 13-14, etc.). As a result of further investigation, it was confirmed that excellent light pressure adhesion can be obtained by making the -20°C storage modulus of the adhesive containing the acrylic polymer and acrylic oligomer having a predetermined monomer composition less than 220MPa, and the present invention was completed. The reason why excellent light pressure adhesion can be obtained by having the above-mentioned -20°C storage modulus is not particularly limited, but it is considered that the adhesive having the above-mentioned -20°C storage modulus is likely to exhibit a good initial adhesion state to the adherend even if the pressure during compression is light, and as a result, the light pressure adhesion is increased, and light pressure adhesion that is comparable to that of normal compression is realized.

[0027] In some embodiments, the -20°C storage modulus may be 200MPa or less, 150MPa or less, 100MPa or less, 80MPa or less, 60MPa or less, or 50MPa or less. From the viewpoint of obtaining better light pressure bonding adhesiveness, in some preferred embodiments, the -20°C storage modulus is 45MPa or less, more preferably 40MPa or less, even more preferably 35MPa or less, particularly preferably 30MPa or less, 25MPa or less, 20MPa or less, 15MPa or less, 10MPa or less, or 5MPa or less. The -20°C storage modulus is usually about 0.1MPa or more, or may be 0.5MPa or more. In some preferred embodiments, the -20°C storage modulus is about 1MPa or more, may be 3MPa or more, 5MPa or more, 8MPa or more, 10MPa or more, or 12MPa or more. The higher the -20°C storage modulus, the more the cohesive strength of the pressure-sensitive adhesive layer tends to improve, for example, the more the processability tends to improve. In addition, by having a moderate cohesive strength, good adhesive properties (adhesive strength, etc.) tend to be easily obtained. In some other preferred embodiments, the -20°C storage modulus is about 15 MPa or more, may be 20 MPa or more, may be 25 MPa or more, may be 30 MPa or more, or may be 35 MPa or more. In still other embodiments, the -20°C storage modulus is about 50 MPa or more, may be 100 MPa or more, may be 150 MPa or more, may be 180 MPa or more, or may be 200 MPa or more.

[0028] Although not particularly limited, in some embodiments, the storage modulus at 23°C (23°C storage modulus) of the pressure-sensitive adhesive layer is about 0.15 MPa or less, preferably 0.13 MPa or less, more preferably 0.12 MPa or less, and even more preferably 0.11 MPa or less, and may be less than 0.10 MPa, from the viewpoint of adhesion to an adherend. Having the above 23°C storage modulus is also preferable in terms of light pressure adhesion. The above 23°C storage modulus may be 0.09 MPa or less, may be 0.08 MPa or less, or may be 0.07 MPa or less. In some embodiments, the above 23°C storage modulus may be about 0.01 MPa or more, or may be about 0.03 MPa or more. In some preferred embodiments, the above 23°C storage modulus may be about 0.05 MPa or more, or may be 0.07 MPa or more. The higher the 23°C storage modulus, the more the cohesive strength of the pressure-sensitive adhesive layer tends to improve, for example, the more the processability tends to improve. In addition, having a moderate cohesive strength tends to easily obtain good adhesive properties.

[0029] In the technology disclosed herein, the storage modulus of the adhesive layer (specifically, the storage modulus at -20°C and the storage modulus at 23°C) can be determined by dynamic viscoelasticity measurement. Specifically, a plurality of adhesive layers to be measured (double-sided adhesive sheets in the case of a substrate-less double-sided adhesive sheet) are stacked to prepare an adhesive layer having a thickness of about 2 mm. A sample obtained by punching out the adhesive layer into a disk shape having a diameter of 7.9 mm is sandwiched and fixed between parallel plates, and dynamic viscoelasticity measurement is performed under the following conditions using a viscoelasticity tester (e.g., ARES manufactured by TA Instruments or its equivalent) to determine the storage modulus (specifically, the storage modulus at -20°C and the storage modulus at 23°C). Measurement mode: Shear mode Temperature range: -70℃~150℃ Heating rate: 5℃ / min ·Measurement frequency: 1Hz The above method is also used in the Examples described later. The pressure-sensitive adhesive layer to be measured may be one formed by applying the corresponding pressure-sensitive adhesive composition in a layer form and drying or curing it.

[0030] (Acrylic polymer) The adhesive layer constituting the adhesive sheet disclosed herein contains an acrylic polymer. The above-mentioned adhesive layer is typically an adhesive layer having an acrylic polymer as a base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of a rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) contained in the adhesive layer. In addition, in this specification, the "main component" refers to a component contained in an amount of more than 50% by weight, unless otherwise specified. In addition, the following explanation of the adhesive and the components that may be contained in the adhesive layer are also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

[0031] In addition, in this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. In this specification, "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0032] The acrylic polymer in the technology disclosed herein is preferably, for example, a polymer of a monomer raw material containing an alkyl (meth)acrylate as a main monomer, where the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

[0033] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH2=C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, this range of carbon atoms will be referred to as "C 1-20 From the viewpoint of the storage modulus of the adhesive, R 2 C 1-14 (For example, C 1-10 , typically C 4-8 It is appropriate to use alkyl (meth)acrylate, which is a chain alkyl group of the formula (I), as the main monomer.

[0034] R 2 C 1-20 Specific examples of the alkyl(meth)acrylate, which is a chain alkyl group, include, but are not limited to, methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, t-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl ... Examples of alkyl (meth)acrylate include isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more.

[0035] The proportion of alkyl (meth)acrylate in the monomer components constituting the acrylic polymer is typically more than 50% by weight, and can be, for example, 70% by weight or more, 85% by weight or more, 90% by weight or more (for example, more than 90% by weight), 92% by weight or more, 94% by weight or more, or more than 95% by weight. The upper limit of the proportion of alkyl (meth)acrylate is 97% by weight or less from the viewpoint of copolymerizing a monomer having a reactive functional group. In some preferred embodiments, the proportion of alkyl (meth)acrylate in the monomer components is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. By limiting the proportion of alkyl (meth)acrylate within the above range, the properties (e.g., cohesive strength, etc.) based on the use of copolymerizable monomers such as monomers having reactive functional groups can be preferably exhibited.

[0036] The monomer component constituting the acrylic polymer used in the technology disclosed herein is an alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms at the ester end (hereinafter, referred to as "C 7+ According to the technology disclosed herein, the monomer component includes C 7+ By using an acrylic polymer containing alkyl (meth)acrylate, it is possible to obtain the desired storage modulus at -20°C and realize light pressure adhesion. 7+ The alkyl (meth)acrylates can be used alone or in combination of two or more.

[0037] Above C 7+ The alkyl (meth)acrylate is typically an alkyl (meth)acrylate having a chain alkyl group having 7 to 20 carbon atoms at the ester end (i.e., C 7-20 Alkyl (meth)acrylate. 7-20The number of carbon atoms in the chain alkyl group of the alkyl (meth)acrylate is suitably 18 or less, may be 14 or less, is preferably 12 or less, more preferably 9 or less, further preferably 8 or less, and particularly preferably 7, from the viewpoints of light pressure bonding adhesiveness, compatibility with other components, and the like. 7+ As the alkyl (meth)acrylate, an alkyl acrylate having a chain alkyl group having 7 or more carbon atoms (for example, 7 or more and 20 or less, 7 or more and 18 or less, 7 or more and 14 or less, 7 or more and 12 or less, 7 or more and 9 or less, 7 or 8) at the ester end is preferably used.

[0038] C in the monomer components that make up acrylic polymers 7+ The proportion of alkyl (meth)acrylate is typically more than 50% by weight, and can be, for example, 70% by weight or more, 85% by weight or more, 90% by weight or more (for example, more than 90% by weight), 92% by weight or more, or 94% by weight or more (for example, more than 95% by weight). 7+ The upper limit of the proportion of alkyl (meth)acrylate is 97% by weight or less from the viewpoint of copolymerizing a monomer having a reactive functional group. 7+ The proportion of alkyl (meth)acrylate is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. 7+ By limiting the proportion of alkyl (meth)acrylate, properties (such as cohesive strength) based on the use of a copolymerizable monomer such as a monomer having a reactive functional group can be favorably exhibited.

[0039] In some embodiments, R in formula (1) 1 is a hydrogen atom and R 2 C 7-8 Alkyl acrylate, which is a chain alkyl group of 7-8 It is preferable to use alkyl acrylate as the main monomer. 7-8The acrylic polymer containing alkyl acrylate as a monomer component is likely to form a pressure-sensitive adhesive layer having a low storage modulus at -20°C. 7-8 When an alkyl acrylate is used, the C contained in the monomer component 7-8 The proportion of alkyl acrylate is, for example, more than 50% by weight, preferably 70% by weight or more, may be 90% by weight or more (e.g., more than 90% by weight), may be 92% by weight or more, or may be 94% by weight or more (e.g., more than 95% by weight). 7-8 The upper limit of the proportion of alkyl acrylate is 97% by weight or less from the viewpoint of copolymerizing a monomer having a reactive functional group. 7-8 The proportion of alkyl acrylate is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. 7-8 By limiting the proportion of alkyl acrylate, properties (e.g., cohesive strength, etc.) based on the use of copolymerizable monomers such as monomers having reactive functional groups can be favorably exhibited. 7-8 The alkyl acrylates may be used alone or in combination of two or more. 7-8 Suitable examples of alkyl acrylates include n-heptyl acrylate (n-HpA) and 2-ethylhexyl acrylate (2EHA).

[0040] In some preferred embodiments, the monomer component constituting the acrylic polymer includes 2EHA. The ratio of 2EHA in the monomer component of the acrylic polymer is, for example, more than 50% by weight, preferably 70% by weight or more, may be 80% by weight or more, 85% by weight or more, 90% by weight or more (for example, more than 90% by weight), 92% by weight or more, 94% by weight or more, or 95% by weight or more (for example, more than 95% by weight). In addition, the ratio of 2EHA in the monomer component is 97% by weight or less from the viewpoint of copolymerizing a monomer having a reactive functional group. In some preferred embodiments, the ratio of 2EHA in the monomer component is 96% by weight or less, and may be 95% by weight or less. In some other preferred embodiments, the ratio of 2EHA in the monomer component is 92% by weight or less, more preferably 90% by weight or less (for example, less than 90% by weight), even more preferably 85% by weight or less (for example, less than 85% by weight), and particularly preferably 80% by weight or less (for example, less than 80% by weight).

[0041] In some preferred embodiments, the monomer component constituting the acrylic polymer contains heptyl acrylate. The acrylic polymer polymerized using a monomer component containing heptyl acrylate has better flexibility than other alkyl acrylate polymers such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA), and therefore the adhesive containing such a polymer is likely to achieve a storage modulus of −20° C. less than a predetermined value. The reason why the heptyl acrylate polymer has better flexibility is not particularly limited, but it is considered that the polymer containing heptyl acrylate as a monomer unit has a low glass transition temperature and a relatively large space between the main chains in the adhesive. Among heptyl acrylates, n-heptyl acrylate is preferred from the viewpoint of flexibility. The acrylic polymer synthesized containing n-heptyl acrylate as a monomer component has a relatively long linear side chain, and therefore it is considered that the space between the main chains is likely to be larger.

[0042] The ratio of heptyl acrylate in the monomer component of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, suitably 70% by weight or more, preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more (e.g., more than 90% by weight), particularly preferably 92% by weight or more, may be 94% by weight or more, may be 95% by weight or more, or may be 96% by weight or more. By increasing the amount of heptyl acrylate used, the effect of its use (e.g., a decrease in the storage modulus of the adhesive at -20°C) can be effectively expressed. On the other hand, the upper limit of the ratio of heptyl acrylate in the monomer component is 97% by weight or less from the viewpoint of copolymerizing a monomer having a reactive functional group. In some preferred embodiments, the ratio of heptyl acrylate in the monomer component is 96% by weight or less, may be 95% by weight or less, or may be 94% by weight or less. It is preferable to limit the ratio of heptyl acrylate within the above range in terms of obtaining a moderate cohesive force.

[0043] In the embodiment in which heptyl acrylate is used as a monomer component, the acrylic polymer may be copolymerized with an alkyl (meth)acrylate other than heptyl acrylate. The alkyl (meth)acrylate other than heptyl acrylate may be, for example, a compound represented by the above formula (1) and an alkyl (meth)acrylate other than heptyl acrylate. The alkyl (meth)acrylate other than heptyl acrylate may be used alone or in combination of two or more.

[0044] In some embodiments, the proportion of heptyl acrylate in the total amount of alkyl (meth)acrylate contained in the monomer component is, for example, 50% by weight or more (specifically, 50 to 100% by weight, for example, more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and may be 99% by weight or more, or may be 100% by weight. By adopting such a monomer composition, the effect of using heptyl acrylate can be effectively exhibited.

[0045] In some embodiments, the monomer component may contain an alkyl (meth)acrylate having an alkyl group derived from biomass at the ester end (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become important, and it is desired to reduce the amount of fossil resource-based materials such as petroleum used. Under these circumstances, it is also desired to reduce the amount of fossil resource-based materials used in the field of adhesives. By using a biomass alkyl (meth)acrylate, it is possible to preferably realize an acrylic adhesive that takes into consideration the reduction of dependency on fossil resource-based materials.

[0046] The biomass alkyl (meth)acrylate is not particularly limited, and is, for example, an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the biomass-derived alkanol has 3 or more carbon atoms, the alkanol may be linear or branched. In some embodiments, an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate used in the synthesis of an acrylic polymer. In such a biomass alkyl (meth)acrylate, the higher the number of carbon atoms of the alkanol, the higher the ratio of the number of biomass-derived carbons to the total number of carbons contained in the biomass alkyl (meth)acrylate, that is, the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the above biomass alkyl (meth)acrylate, it is desirable that the alkyl group derived from biomass has a large number of carbon atoms in terms of reducing the dependency on fossil resource-based materials. On the other hand, if the alkyl group constituting the alkyl (meth)acrylate has too many carbon atoms, it tends to be difficult to obtain adhesive properties such as adhesive strength, and it may also be disadvantageous in terms of productivity such as synthesis, handling, and cost. In an embodiment in which an ester of a biomass-derived alkanol and a non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, it is desirable to use a material that has a good balance between adhesive properties and reduced dependency on fossil resource-based materials (more specifically, the biomass carbon ratio of the above alkyl (meth)acrylate).

[0047] In some preferred embodiments, biomass-derived heptyl acrylate (biomass heptyl acrylate) is used as the heptyl acrylate. By using biomass heptyl acrylate, the effect of the technology disclosed herein can be realized while reducing the dependency on fossil resource-based materials. The biomass heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid, and for example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid can be used. In such a compound, only the heptyl group is biomass-derived. As the biomass-derived heptyl acrylate, it is preferable to use biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate).

[0048] The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components of the acrylic polymer is, for example, 50% by weight or more (e.g., more than 50% by weight) in some embodiments, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, particularly preferably 90% by weight or more, may be 92% by weight or more, may be 94% by weight or more, or may be 96% by weight or more. The proportion of biomass alkyl (meth)acrylate (preferably biomass heptyl acrylate) in the monomer components is 97% by weight or less, and in some embodiments, may be 95% by weight or less, may be 93% by weight or less, or may be 91% by weight or less.

[0049] The monomer components constituting the acrylic polymer in the technology disclosed herein include monomers having reactive functional groups. By copolymerizing a monomer having a reactive functional group with an acrylic polymer, a functional group that can become a crosslinking base point is introduced into the acrylic polymer. In addition, based on the action of the monomer having a reactive functional group, the adhesive strength to the adherend can be improved. Examples of the monomer having such a reactive functional group include a carboxyl group-containing monomer, a hydroxyl group (OH group)-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), an amino group-containing monomer (aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), an epoxy group-containing monomer, a cyano group-containing monomer, a keto group-containing monomer, a monomer having a nitrogen atom-containing ring (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), an alkoxysilyl group-containing monomer, an imide group-containing monomer, etc. The above-mentioned monomers having reactive functional groups can be used alone or in combination of two or more. Among these, carboxyl group-containing monomers and hydroxyl group-containing monomers are preferred. The hydroxyl group-containing monomers are preferably used together with 2EHA as a monomer component.

[0050] The proportion of the monomer having a reactive functional group in the monomer component of the acrylic polymer is 3% by weight or more (e.g., more than 3.0% by weight). By using the monomer having a reactive functional group in the above-mentioned predetermined amount or more, the effect of using the monomer having a reactive functional group is effectively exerted, and it is possible to realize a suitable cohesive force and good adhesive properties. In some preferred embodiments, the proportion of the monomer having the reactive functional group may be 4.0% by weight or more, 4.5% by weight or more, 5.0% by weight or more (e.g., more than 5.0% by weight), 5.5% by weight or more, 6.0% by weight or more, 6.5% by weight or more, or 7.0% by weight or more. In some embodiments, the amount of the monomer having a reactive functional group is, for example, appropriately 20% by weight or less of the total monomer component, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the monomer having the reactive functional group may be 10% by weight or less (e.g., less than 10% by weight), 8% by weight or less, 6% by weight or less, or 5% by weight or less (e.g., less than 5% by weight). In some other preferred embodiments, the ratio of the monomer having the reactive functional group in the monomer component is 8% by weight or more, 10% by weight or more (e.g., more than 10% by weight), 15% by weight or more (e.g., more than 15% by weight), or 20% by weight or more (e.g., more than 20% by weight). In such an embodiment, the ratio of the monomer having the reactive functional group in the monomer component is suitably 40% by weight or less, preferably 35% by weight or less, more preferably 30% by weight or less, and may be 25% by weight or less. By appropriately adjusting the amount of the monomer having the reactive functional group used within the above range, a pressure-sensitive adhesive having excellent light pressure adhesion and good adhesive properties is easily obtained.

[0051] In some embodiments, the monomer component of the acrylic polymer preferably contains a carboxyl group-containing monomer. The carboxyl group-containing monomer can improve the cohesive strength based on its polarity. In addition, when a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used, the carboxyl group can be a crosslinking point of the acrylic polymer. In addition, the use of the carboxyl group-containing monomer can exhibit better adhesion to an adherend such as a highly polar material. From the viewpoint of light pressure adhesion, the carboxyl group-containing monomer is preferably used together with heptyl acrylate.

[0052] Examples of the carboxyl group-containing monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid. The carboxyl group-containing monomer may be a monomer having a metal salt of a carboxyl group (e.g., an alkali metal salt). The carboxyl group-containing monomer may be used alone or in combination of two or more. Among them, preferred carboxyl group-containing monomers include AA and MAA. AA is particularly preferred. When one or more carboxyl group-containing monomers are used, the proportion of AA in the carboxyl group-containing monomer is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. In a particularly preferred embodiment, the carboxyl group-containing monomer is substantially composed of AA alone. AA is considered to be one of the most suitable monomer materials among the carboxy group-containing monomers disclosed herein due to its combined effects such as polarity based on the carboxy group, its role as a crosslinking point, and Tg (106° C.).

[0053] In some embodiments, the ratio of the carboxyl group-containing monomer in the monomer component of the acrylic polymer is 3% by weight or more (e.g., more than 3.0% by weight), preferably 4.0% by weight or more, more preferably 4.5% by weight or more, even more preferably 5.0% by weight or more (e.g., more than 5.0% by weight), particularly preferably 5.5% by weight or more, and may be 6.0% by weight or more, 6.5% by weight or more, or 7.0% by weight or more. By increasing the amount of the carboxyl group-containing monomer used, the cohesive strength of the adhesive layer is improved based on the action of the carboxyl group-containing monomer, and by having a moderate cohesive strength, good adhesive properties (adhesive strength, etc.) are easily obtained. In addition, the amount of the carboxyl group-containing monomer is, for example, appropriately 20% by weight or less of the monomer component, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the carboxyl group-containing monomer may be 10% by weight or less (e.g., less than 10% by weight), 8% by weight or less, 6% by weight or less, or 5% by weight or less (e.g., less than 5% by weight). By appropriately adjusting the amount of the carboxyl group-containing monomer used within the above range, it is easy to obtain excellent light pressure bonding adhesion and a pressure-sensitive adhesive having good adhesive properties.

[0054] In the embodiment in which the monomer component constituting the acrylic polymer contains a carboxyl group-containing monomer, the acrylic polymer may be copolymerized with a functional group-containing monomer other than the carboxyl group-containing monomer. As the functional group-containing monomer other than the carboxyl group-containing monomer, one or more of the monomers exemplified as the monomers having a reactive functional group other than the carboxyl group-containing monomer can be used.

[0055] When the monomer component constituting the acrylic polymer contains a functional group-containing monomer other than the carboxyl group-containing monomer, the content of the functional group-containing monomer other than the carboxyl group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effect of using the functional group-containing monomer other than the carboxyl group-containing monomer, the content of the functional group-containing monomer other than the carboxyl group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, suitably 0.5% by weight or more, and may be 1% by weight or more. Also, for example, in an embodiment in which the monomer component of the acrylic polymer contains heptyl acrylate and a carboxyl group-containing monomer, from the viewpoint of easily balancing the adhesion performance in relation to these monomer components, the content of the functional group-containing monomer other than the carboxyl group-containing monomer in the monomer component is suitably 30% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less). In some embodiments, the content of functional group-containing monomers other than carboxy group-containing monomers in the monomer component is, for example, less than 3 wt%, may be less than 1 wt%, may be less than 0.5 wt%, may be less than 0.3 wt%, or may be less than 0.1 wt%. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component of the acrylic polymer does not substantially contain functional group-containing monomers other than carboxy group-containing monomers.

[0056] In this specification, the monomer component being substantially free of monomer A (e.g., the optional functional group-containing monomer) means that the monomer A is not used at least intentionally, and it is permissible for the monomer A to be unintentionally included in an amount of, for example, about 0.01% by weight or less.

[0057] In addition, a hydroxyl group-containing monomer may be used as a functional group-containing monomer other than the carboxyl group-containing monomer. One or more of the specific examples of hydroxyl group-containing monomers described later may be used. When a hydroxyl group-containing monomer is used, the content of the hydroxyl group-containing monomer in the monomer component is suitably about 10% by weight or less (for example, 0.001 to 10% by weight), preferably about 5% by weight or less, more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl group-containing monomer in the monomer component may be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, or less than 0.01% by weight. The monomer component of the acrylic polymer may not substantially contain a hydroxyl group-containing monomer. In the technology disclosed herein, the desired properties and effects can be preferably realized in a composition in which the amount of the hydroxyl group-containing monomer used is limited or not used.

[0058] In the embodiment in which the monomer component contains a carboxyl group-containing monomer, the proportion of the carboxyl group-containing monomer in the total monomers having a reactive functional group (total functional group-containing monomers including the carboxyl group-containing monomer) used as the copolymerization component of the acrylic polymer is 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the carboxyl group-containing monomer in the total monomers having a reactive functional group is 100% by weight, for example, 95% by weight or less. For example, in the embodiment in which the monomer component of the acrylic polymer contains heptyl acrylate and a carboxyl group-containing monomer, the proportion of the carboxyl group-containing monomer is preferably adopted.

[0059] In some other embodiments, the monomer component of the acrylic polymer preferably contains a hydroxyl group-containing monomer. The hydroxyl group-containing monomer may crosslink with, for example, an isocyanate-based crosslinking agent, and contribute to the formation of a pressure-sensitive adhesive having good cohesive strength. From the viewpoint of light pressure adhesion, the hydroxyl group-containing monomer is preferably used together with 2EHA.

[0060] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; polypropylene glycol mono(meth)acrylate; and the like. The hydroxyl group-containing monomers can be used alone or in combination of two or more. Among them, preferred hydroxyl group-containing monomers include 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA).

[0061] In some other embodiments (embodiments in which the monomer component contains a hydroxyl group-containing monomer), the ratio of the hydroxyl group-containing monomer in the monomer component of the acrylic polymer is 3% by weight or more (e.g., more than 3.0% by weight), preferably 4.0% by weight or more, more preferably 4.5% by weight or more, and may be 5.0% by weight or more. This allows the effect of using the hydroxyl group-containing monomer to be suitably exhibited. In addition, the amount of the hydroxyl group-containing monomer is, for example, appropriately 20% by weight or less of the monomer component, preferably 15% by weight or less, more preferably 12% by weight or less. In some preferred embodiments, the amount of the hydroxyl group-containing monomer may be 10% by weight or less, 8% by weight or less, or 6% by weight or less. In some other preferred embodiments, the ratio of the hydroxyl group-containing monomer in the monomer component is 8% by weight or more, may be 10% by weight or more (e.g., more than 10% by weight), may be 15% by weight or more (e.g., more than 15% by weight), or may be 20% by weight or more (e.g., more than 20% by weight). In this embodiment, the proportion of the hydroxyl group-containing monomer in the monomer components is suitably 40% by weight or less, preferably 35% by weight or less, more preferably 30% by weight or less, and may be 25% by weight or less. By appropriately adjusting the amount of the hydroxyl group-containing monomer used within the above range, it is easy to obtain a pressure-sensitive adhesive having excellent light pressure-bonding adhesion and good adhesive properties.

[0062] In some other embodiments (embodiments in which the monomer component contains a hydroxyl group-containing monomer), the proportion of the hydroxyl group-containing monomer in the total monomers having a reactive functional group (total functional group-containing monomers including the hydroxyl group-containing monomer) used as the copolymerization component of the acrylic polymer is, from the viewpoint of effectively exerting the effect of copolymerizing the hydroxyl group-containing monomer, appropriate to be 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the hydroxyl group-containing monomer in the total monomers having the reactive functional group is 100% by weight, and may be, for example, 95% by weight or less. For example, in an embodiment in which the monomer component of the acrylic polymer contains 2EHA and a hydroxyl group-containing monomer, the above-mentioned proportion of the hydroxyl group-containing monomer is preferably adopted.

[0063] The monomer components constituting the acrylic polymer may contain other copolymerization components other than the monomers having the reactive functional groups described above for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components may be used alone or in combination of two or more.

[0064] The amount of such other copolymerization components is not particularly limited and may be appropriately selected according to the purpose and use, but from the viewpoint of appropriately exerting the effect of use, it is appropriate to set it to 0.05 wt% or more, and it may be 0.5 wt% or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymerization components in the monomer component is appropriate to be 20 wt% or less, and from the viewpoint of appropriately exerting the adhesive properties based on the essential monomer components, it is preferably 10 wt% or less, more preferably 8 wt% or less, and even more preferably less than 5 wt%, for example, it may be less than 3 wt%, or it may be less than 1 wt%. The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer component does not substantially contain other copolymerization components.

[0065] The acrylic polymer may contain a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, as another monomer component. By using a polyfunctional monomer as a monomer component, the cohesive force of the adhesive layer can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and examples thereof include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, and the like. The polyfunctional monomer can be used alone or in combination of two or more kinds.

[0066] The amount of the polyfunctional monomer used is not particularly limited, and can be appropriately set so that the purpose of using the polyfunctional monomer is achieved. The amount of the polyfunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (for example, about 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component.

[0067] In a particularly preferred embodiment, an acrylic polymer synthesized using a monomer component consisting essentially of heptyl acrylate (preferably n-heptyl acrylate) and a carboxyl group-containing monomer (preferably acrylic acid) is used as the acrylic polymer. According to the above monomer composition, the action of heptyl acrylate and the carboxyl group-containing monomer is effectively exerted, and a pressure-sensitive adhesive having a low storage modulus at -20°C and excellent light pressure adhesion can be preferably realized. From this viewpoint, the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component is suitably 90% by weight or more (90 to 100% by weight), preferably 95% by weight or more, more preferably 99% by weight or more, even more preferably more than 99.5% by weight, and particularly preferably more than 99.9% by weight (for example, more than 99.99% by weight), and the total ratio of heptyl acrylate and the carboxyl group-containing monomer in the above monomer component may be 100% by weight.

[0068] The biomass carbon ratio of the monomer components constituting the acrylic polymer (the biomass carbon ratio of the acrylic polymer) may be, for example, 1% or more, suitably 10% or more, preferably 30% or more, more preferably 50% or more (e.g., more than 50%), may be 70% or more, may be 80% or more, or may be 90% to 100%. By designing in this way, an acrylic pressure-sensitive adhesive that takes into consideration the reduction of dependency on fossil resource-based materials can be obtained.

[0069] Although not particularly limited, it is appropriate that the copolymer composition of the acrylic polymer is designed so that the glass transition temperature (Tg) of the polymer is about -15°C or less (for example, about -70°C or more and -15°C or less). Here, the Tg of the acrylic polymer refers to the Tg calculated by the Fox formula based on the composition of the monomer components used in the synthesis of the polymer. The Fox formula, as shown below, is a relational expression between the Tg of the copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0070] The glass transition temperature of the homopolymer used to calculate Tg is determined from known materials, specifically, from the value described in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are described in this document, the highest value is used. If the value is not described in the Polymer Handbook, the value obtained by the measurement method described in JP-A-2007-51271 is used.

[0071] Although not particularly limited, from the viewpoint of impact resistance and adhesion to the adherend, the Tg of the acrylic polymer is advantageously about -25 ° C or less, preferably about -35 ° C or less, more preferably about -40 ° C or less, even more preferably about -50 ° C or less, and may be -55 ° C or less, or may be -60 ° C or less. By appropriately designing the monomer composition so that the Tg is low, there is a tendency to easily obtain excellent light pressure adhesion. In some embodiments, from the viewpoint of cohesive force, the Tg of the acrylic polymer is, for example, about -70 ° C or more, may be about -65 ° C or more, or may be about -60 ° C or more.

[0072] The method for obtaining an acrylic polymer is not particularly limited, and various polymerization methods known as a synthesis method for an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be appropriately adopted. For example, a solution polymerization method can be preferably adopted. As a monomer supply method when carrying out solution polymerization, a lump-sum charging method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. can be appropriately adopted. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0073] The solvent (polymerization solvent) used in the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one of the following solvents or a mixture of two or more of them can be used: aromatic compounds (typically aromatic hydrocarbons) such as toluene; acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as tert-butyl methyl ether; and ketones such as methyl ethyl ketone.

[0074] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and the like. Still other examples of polymerization initiators include redox-based initiators obtained by combining peroxides with reducing agents. Such polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used may be a normal amount, and can be selected, for example, from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the total monomer components.

[0075] The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and an acrylic polymer having an appropriate Mw that can realize the above-mentioned −20° C. storage modulus characteristic is used. For example, the Mw of the acrylic polymer is about 10×10 4 ~500×10 4 From the viewpoint of adhesive performance, the Mw of the base polymer may be in the range of approximately 20×10 4 It may be more than 30×10 4 More than 40 x 10 is fine. 4 More than 50 x 10 is fine. 4or more. In some embodiments, the Mw of the acrylic polymer is greater than 600,000, may be greater than 650,000, is suitably greater than 700,000, and may be greater than 750,000. The greater the Mw of the acrylic polymer, the easier it is to obtain a pressure-sensitive adhesive that exhibits good cohesive strength. In some preferred embodiments, the Mw of the acrylic polymer is greater than 800,000, may be greater than 850,000, may be greater than 900,000, may be greater than 1 million (e.g., greater than 1 million), or may be greater than 1.2 million. For example, a monomer composition containing heptyl acrylate is easy to maintain a low viscosity, so that the synthesis of a high molecular weight substance is good, and an acrylic polymer having the above Mw is easy to obtain. In addition, by using an acrylic polymer that contains heptyl acrylate as a monomer unit and has a Mw of a predetermined value or more, the flexibility based on the chemical structure of the polymer and the cohesive strength based on the molecular weight make it easy to satisfy the above viscoelastic properties (specifically, -20°C storage modulus), and light pressure adhesion can be preferably realized. On the other hand, from the viewpoint of adhesive strength, ease of synthesis, etc., the Mw of the acrylic polymer is usually about 3 million or less, preferably 2.5 million or less, more preferably 2 million or less, even more preferably 1.8 million or less, and may be 1.5 million or less, or may be 1.3 million or less. In some preferred embodiments, the Mw of the acrylic polymer may be 1.1 million or less, 1 million or less, 950,000 or less, or 900,000 or less. By appropriately limiting the Mw of the acrylic polymer, a lower -20 ° C storage modulus is easily obtained. In some other preferred embodiments, the Mw of the acrylic polymer is 800,000 or less, may be 600,000 or less, may be less than 500,000, or may be 450,000 or less.

[0076] The Mw of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated as a standard polystyrene equivalent. Specifically, it can be measured under the following conditions using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation). The same applies to the examples described below. [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0077] (Acrylic Oligomer) The pressure-sensitive adhesive layer contains an acrylic oligomer. By containing the acrylic oligomer, the light pressure adhesion and the normal pressure adhesion can be improved in a well-balanced manner, and excellent light pressure adhesion can be realized. The acrylic oligomer can be used alone or in combination of two or more kinds.

[0078] The acrylic oligomer has a Tg of about 0°C or more and about 300°C or less, preferably about 20°C or more and about 300°C or less, more preferably about 40°C or more and about 300°C or less. By having a Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the adhesive, the Tg of the acrylic oligomer is about 30°C or more, more preferably about 50°C or more (e.g. about 60°C or more), and from the viewpoint of adhesiveness, it is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (e.g. about 80°C or less). By using an acrylic oligomer having an appropriate Tg within the above range, the light pressure adhesive strength and the normal pressure adhesive strength can be improved in a well-balanced manner. In this specification, the Tg of the acrylic oligomer refers to the Tg calculated by the Fox formula based on the composition of the monomer components, similar to the Tg of the above-mentioned acrylic polymer.

[0079] The weight average molecular weight (Mw) of the acrylic oligomer can typically be about 1000 or more and less than about 30000, preferably about 1500 or more and less than about 20000, and more preferably about 2000 or more and less than about 10000. When Mw is within the above range, good adhesive strength is likely to be obtained. In some preferred embodiments, the Mw of the acrylic oligomer is about 2500 or more (e.g., about 3000 or more), and from the viewpoint of adhesiveness, it is preferably about 7000 or less, more preferably about 5000 or less (e.g., about 4500 or less, typically about 4000 or less). The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value in terms of standard polystyrene. Specifically, it is measured using 2 columns of TSKgel GMH-H (20) on a Tosoh HPLC 8020 at a flow rate of about 0.5 mL / min with tetrahydrofuran solvent.

[0080] Examples of monomers constituting acrylic oligomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, Examples of the (meth)acrylate include alkyl (meth)acrylates such as butyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from alcohols derived from terpene compounds. These (meth)acrylates may be used alone or in combination of two or more.

[0081] The acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, typified by alkyl (meth)acrylates in which the alkyl group has a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and (meth)acrylates having a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer. In addition, when ultraviolet light is used in synthesizing an acrylic oligomer or preparing an adhesive layer, those having saturated bonds are preferred in that they are less likely to cause polymerization inhibition, and alkyl (meth)acrylates in which the alkyl group has a branched structure, or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting the acrylic oligomer. The above-mentioned branched alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates all fall under the category of (meth)acrylate monomers in the technology disclosed herein. The alicyclic hydrocarbon group may be a saturated or unsaturated alicyclic hydrocarbon group.

[0082] The proportion of (meth)acrylate monomers (e.g., alicyclic hydrocarbon group-containing (meth)acrylates) in the monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more (e.g., 80% by weight or more, or even 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting essentially of (meth)acrylate monomers.

[0083] In addition to the above (meth)acrylate monomer, functional group-containing monomers can be used as the constituent monomer components of the acrylic oligomer. Suitable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; and hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used alone or in combination of two or more. Among them, carboxy group-containing monomers are preferred, and AA is particularly preferred. For example, by using a carboxy group-containing monomer as the functional group-containing monomer, the adhesive strength to a highly polar adherend can be improved, and excellent light pressure adhesion to such an adherend can be preferably realized.

[0084] When the monomer components constituting the acrylic oligomer contain a functional group-containing monomer, the proportion of the functional group-containing monomer (e.g., a carboxy group-containing monomer such as AA) in the monomer components is suitably about 1 wt % or more, preferably 2 wt % or more, more preferably 3 wt % or more, and is suitably about 15 wt % or less, preferably 10 wt % or less, more preferably 7 wt % or less.

[0085] The acrylic oligomer can be formed by polymerizing its constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be used in an appropriate mode. The type of polymerization initiator (e.g., azo-based polymerization initiator such as AIBN) that can be used as necessary is generally as exemplified in the synthesis of the acrylic polymer, and the amount of the polymerization initiator and the amount of the chain transfer agent, such as n-dodecyl mercaptan, that is optionally used, are appropriately set based on technical common sense so as to obtain a desired molecular weight, so detailed explanations are omitted here.

[0086] From the above viewpoint, suitable acrylic oligomers include, for example, homopolymers of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), as well as copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), copolymers of CHMA and AA, copolymers of ADA and methyl methacrylate (MMA), copolymers of DCPMA and IBXMA, and copolymers of DCPMA and MMA.

[0087] When the adhesive layer disclosed herein contains an acrylic oligomer, the content is suitably, for example, 0.1 parts by weight or more (for example, 1 part by weight or more) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of better exerting the effect of the acrylic oligomer, the content of the acrylic oligomer is preferably about 3 parts by weight or more, more preferably about 5 parts by weight or more, and may be about 8 parts by weight or more, about 10 parts by weight or more, about 12 parts by weight or more, about 15 parts by weight or more, or about 18 parts by weight or more. In addition, from the viewpoint of compatibility with the acrylic polymer, etc., in some embodiments, the content of the acrylic oligomer is suitably less than 50 parts by weight (for example, less than 40 parts by weight) relative to 100 parts by weight of the acrylic polymer, and from the viewpoint of maintaining a low -20 ° C storage modulus, it is preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, and even more preferably about 20 parts by weight or less. In some embodiments, the content of the acrylic oligomer is less than 20 parts by weight, may be 15 parts by weight or less, may be 12 parts by weight or less, may be 10 parts by weight or less, may be 8 parts by weight or less, or may be 6 parts by weight or less, based on 100 parts by weight of the acrylic polymer. By limiting the amount of the acrylic oligomer used in this manner, the effects of the technology disclosed herein can be preferably exhibited.

[0088] (tackifier resin) In some preferred embodiments, the adhesive layer contains a tackifier resin. By using a tackifier resin, high adhesive strength can be obtained. More specifically, based on the combined use of an acrylic oligomer and a tackifier resin, adhesive strength including light pressure adhesive strength can be preferably improved. The tackifier resin is not particularly limited, and various tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins can be used. Such tackifier resins can be used alone or in combination of two or more.

[0089] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.; the same applies below); and various other rosin derivatives. Examples of the rosin derivative include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., esterified products of rosin) and those obtained by esterifying modified rosin with alcohols (i.e., esterified products of modified rosin); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acid; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acid; rosin alcohols obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid modified rosins, or unsaturated fatty acid modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and thermally polymerizing the mixture; and the like. Among these, rosin esters are preferred.

[0090] Although not particularly limited, specific examples of rosin esters include esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, etc.

[0091] Examples of terpene-based tackifier resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; modified terpene resins obtained by modifying these terpene resins (phenol-modified, aromatic-modified, hydrogen-modified, hydrocarbon-modified, etc.); etc. An example of the modified terpene resin is a terpene phenol resin.

[0092] Terpene phenolic resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept that includes both a copolymer of a terpene and a phenolic compound (terpene-phenol copolymer resin) and a homopolymer or copolymer of a terpene modified with phenol (phenol-modified terpene resin). Specific examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l-forms (dipentene)). Hydrogenated terpene phenolic resin refers to a hydrogenated terpene phenolic resin having a structure obtained by hydrogenating such a terpene phenolic resin. It is also called hydrogenated terpene phenolic resin.

[0093] Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, hydrogenated products thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified products thereof (for example, maleic anhydride modified products), coumarone resins, and coumarone-indene resins.

[0094] In some embodiments, it is preferable to use at least one selected from rosin-based tackifier resins and terpene-based tackifier resins as the tackifier resin. By incorporating rosin-based tackifier resins and / or terpene-based tackifier resins into the acrylic adhesive, the adhesive strength can be improved and excellent light pressure adhesion can be easily obtained. In some preferred embodiments, the total ratio of the rosin-based tackifier resin and the terpene-based tackifier resin to the entire tackifier resin contained in the adhesive layer can be, for example, more than about 50% by weight (more than 50% by weight and 100% by weight or less), and may be more than about 70% by weight, more than about 80% by weight, more than about 90% by weight, more than 95% by weight, or more than 99% by weight.

[0095] Some preferred embodiments include an embodiment in which the tackifier resin contains one or more terpene phenol resins. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the total amount of the tackifier resin is about 25% by weight or more (more preferably about 30% by weight or more). The proportion of the terpene phenol resin in the total amount of the tackifier resin may be about 50% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (for example, about 95% by weight or more and 100% by weight or less, or even about 99% by weight or more and 100% by weight or less) may be a terpene phenol resin.

[0096] The content of the terpene phenol resin in the adhesive layer is not particularly limited as long as the desired viscoelastic properties are satisfied. In some embodiments, the content of the terpene phenol resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer from the viewpoint of improving adhesive strength. In some embodiments, the content of the terpene phenol resin in the adhesive layer is, for example, 70 parts by weight or less, 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the terpene phenol resin is less than 30 parts by weight, more preferably 25 parts by weight or less, and even more preferably 22 parts by weight or less, and may be 20 parts by weight or less.

[0097] The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, a tackifier resin having a softening point (softening temperature) of about 80°C or higher may be preferably used. The softening point of the tackifier resin may be about 100°C or higher, or about 110°C or higher. In addition, from the viewpoint of adhesion to an adherend, a tackifier resin having a softening point of about 200°C or lower (more preferably about 180°C or lower) may be preferably used. In some embodiments, the softening point of the tackifier resin may be lower than 160°C, or may be lower than 150°C.

[0098] The softening point of the tackifier resin in this specification is defined as a value measured based on the softening point test method (ring and ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at a low temperature, and is carefully filled into a ring placed on a flat metal plate so as not to create bubbles. After cooling, the part that protrudes from the flat surface including the top end of the ring is cut off with a slightly heated knife. Next, a holder (ring stand) is placed in a glass container (heating bath) with a diameter of 85 mm or more and a height of 127 mm or more, and glycerin is poured to a depth of 90 mm or more. Next, a steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in glycerin without touching each other, and the temperature of the glycerin is kept at 20°C ± 5°C for 15 minutes. Next, a steel ball is placed in the center of the surface of the sample in the ring, and this is placed in a fixed position on the holder. Next, keeping the distance from the top of the ring to the glycerin surface at 50 mm, place a thermometer and align the center of the thermometer's mercury bulb to the same height as the center of the ring, then heat the container. The flame of the Bunsen burner used for heating should be midway between the center of the bottom of the container and its edge, and heating should be uniform. After heating begins and the temperature of the bath reaches 40°C, the rate of increase must be 5.0 ± 0.5°C per minute. The sample gradually softens and flows down the ring, and the temperature is read when it finally touches the bottom plate, and this is the softening point. The softening point is measured for two or more samples at the same time, and the average value is used.

[0099] In some embodiments, the tackifier resin is a tackifier resin T having a softening point of less than 150° C. L Tackifying resin T is used.L By using the tackifier resin T, a higher adhesive strength can be obtained. L The softening point of Tackifier Resin T is less than 140°C, more preferably less than 130°C, and even more preferably less than 120°C, and may be 110°C or less, 100°C or less, or 90°C or less. By using a tackifier resin having a softening point equal to or less than the above-mentioned predetermined value, it tends to be easier to maintain a low -20°C storage modulus. L The lower limit of the softening point of the tackifier resin T is not particularly limited. L From the viewpoint of exerting an appropriate cohesive force, the softening point of the polyurethane foam may be, for example, about 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, or 110°C or higher.

[0100] Tackifying resin T L As the tackifier resin, one type selected from the tackifier resins exemplified above having a softening point of less than 150° C. can be used alone or in combination of two or more types. L It is preferable that the tackifier resin T contains at least one selected from the group consisting of rosin-based tackifier resins and terpene-based tackifier resins. L may contain one type of rosin-based tackifier resin alone, or may contain two or more types of rosin-based tackifiers in combination. L may contain one terpene-based tackifying resin (eg, a terpene phenolic resin) alone, or may contain two or more terpene-based tackifying resins in combination.

[0101] In some embodiments, tackifier resin T L The proportion of the terpene-based tackifier resin (e.g., terpene phenol resin) in the total can be, for example, more than about 50% by weight, or may be about 65% by weight or more, about 75% by weight or more, 85% by weight or more, or 95% by weight or more. LThe composition can be preferably implemented in an embodiment in which substantially all of (for example, approximately 97% by weight or more, or 99% by weight or more, or may be 100% by weight) is a terpene-based tackifying resin.

[0102] Although not particularly limited, tackifier resin T L Examples of rosin-based tackifying resins that can be preferably used as the tackifying resin include rosin esters such as unmodified rosin ester and modified rosin ester. A preferred example of a modified rosin ester is hydrogenated rosin ester. For example, esters of unmodified rosin or modified rosin (e.g. hydrogenated rosin), such as rosin esters such as methyl ester and glycerin ester, can be used as tackifying resin T. L It can be used as:

[0103] In some embodiments, tackifier resin T L may contain hydrogenated rosin ester. L may contain a non-hydrogenated rosin ester. The term "non-hydrogenated rosin ester" as used herein is a general concept that refers to the above-mentioned rosin esters other than the hydrogenated rosin ester. Examples of the non-hydrogenated rosin ester include unmodified rosin ester, disproportionated rosin ester, and polymerized rosin ester. Tackifier resin T L The rosin esters may include a combination of a hydrogenated rosin ester and a non-hydrogenated rosin ester, may include only one or more hydrogenated rosin esters, or may include only one or more non-hydrogenated rosin esters. L The rosin esters contained in the composition include only one or more hydrogenated rosin esters.

[0104] In some embodiments, tackifier resin T LThe proportion of the rosin-based tackifier resin (e.g., rosin esters) in the total can be, for example, more than about 50% by weight, or may be about 65% by weight or more, about 75% by weight or more, 85% by weight or more, or 95% by weight or more. L The present invention can be preferably implemented in an embodiment in which substantially all of the above (for example, approximately 97% by weight or more, or 99% by weight or more, or may be 100% by weight) is a rosin-based tackifier resin.

[0105] In addition, tackifier resin T L The tackifier resin may or may not contain a tackifier resin having a softening point of less than 50° C., more preferably about 40° C. or less (typically a rosin-based, terpene-based, or hydrocarbon-based tackifier resin, for example, hydrogenated rosin methyl ester). Such a low-softening-point tackifier resin may be a liquid tackifier resin that is liquid at 30° C. The liquid tackifier resin may be used alone or in combination of two or more. The content of the liquid tackifier resin is determined based on the tackifier resin T from the viewpoint of cohesive strength, etc. L It can be about 30% by weight or less of the total, suitably about 10% by weight or less (for example, 0 to 10% by weight), may be about 2% by weight or less (0.5 to 2% by weight), or may be less than 1% by weight.

[0106] Tackifying resin T L The content of is not particularly limited, but in some embodiments, it is appropriate to make it about 70 parts by weight or less relative to 100 parts by weight of the acrylic polymer, and it may be 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less. L By limiting the amount of tackifier resin T to a predetermined amount or less, it is easy to form a PSA having a storage modulus at −20° C. of a predetermined value or less. LThe content of the tackifier resin T is less than 30 parts by weight, more preferably 25 parts by weight or less, further preferably 22 parts by weight or less, and may be 20 parts by weight or less, based on 100 parts by weight of the acrylic polymer. L The content of the tackifier resin T is, for example, 1 part by weight or more, suitably 5 parts by weight or more, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 12 parts by weight or more, and may be 15 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. L The content may be about 20 parts by weight or more, about 25 parts by weight or more, about 30 parts by weight or more, or about 35 parts by weight or more. Such a content is preferably applied, for example, in an embodiment in which an acrylic polymer having a relatively small molecular weight is used.

[0107] In some embodiments, the pressure-sensitive adhesive layer contains a tackifier resin T L and a tackifier resin T having a softening point of 150°C or higher (e.g., 150°C to 200°C). H The tackifier resin T may be used in combination with the above. H As the tackifier resin, one type may be used alone or two or more types may be used in combination from among the tackifier resins exemplified above that have a softening point of 150° C. or higher.

[0108] In some embodiments, tackifier resin T L It is preferable that the tackifier resin T accounts for more than 50% by weight of the total amount of the tackifier resin contained in the pressure-sensitive adhesive layer. L The effect of the inclusion of the tackifier resin T in the total amount of the tackifier resin contained in the adhesive layer is easily manifested. L The ratio of tackifier resin T LFrom the viewpoint of more effectively exerting the effect of use, the content of the tackifier resin in the pressure-sensitive adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, and may be 95% by weight or more, or may be 98% by weight or more. In some preferred embodiments, the tackifier resin contained in the pressure-sensitive adhesive layer is substantially tackifier resin T L In this embodiment, the tackifier resin T L The proportion is in the range of 99 to 100% by weight.

[0109] Although not particularly limited, in some embodiments, the tackifier resin may contain a tackifier resin having a hydroxyl value of more than 20 mgKOH / g. Among them, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more is preferable. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more may be referred to as a "high hydroxyl value resin". By using a tackifier resin containing such a high hydroxyl value resin, a pressure-sensitive adhesive layer having excellent adhesion to an adherend and high cohesive strength can be realized. In some embodiments, the tackifier resin may contain a high hydroxyl value resin having a hydroxyl value of 50 mgKOH / g or more (e.g., 70 mgKOH / g or more). Although not particularly limited, such a high hydroxyl value resin (e.g., terpene phenol resin) is preferably used in combination with an acrylic polymer containing heptyl acrylate as a monomer component, for example, to achieve both adhesive strength and cohesive strength.

[0110] The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with acrylic polymers, the hydroxyl value of the high hydroxyl value resin is usually about 300 mgKOH / g or less, and is preferably about 200 mgKOH / g or less, and is preferably about 180 mgKOH / g or less, more preferably about 160 mgKOH / g or less, and even more preferably about 140 mgKOH / g or less, and may be 120 mgKOH / g or less, 100 mgKOH / g or less, or 80 mgKOH / g or less (for example, 65 mgKOH / g or less). The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin contains a high hydroxyl value resin with a hydroxyl value of 30 to 160 mgKOH / g (for example, a terpene tackifier resin, preferably a terpene phenol resin). In some embodiments, a high hydroxyl value resin having a hydroxyl value of 30 to 80 mgKOH / g (eg, 30 to 65 mgKOH / g) can be preferably used.

[0111] Here, the hydroxyl value may be a value measured by potentiometric titration as specified in JIS K0070: 1992. The specific measurement method is as follows. [Method for measuring hydroxyl value] 1. Reagents (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make the total volume 50 mL, and stir thoroughly before use. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make the total volume 100 mL, and stir thoroughly before use. (2) Use a 0.5 mol / L potassium hydroxide ethanol solution as the measurement reagent. (3) In addition, prepare toluene, pyridine, ethanol and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) Heat the flask in a 100°C bath for 70 minutes, then allow it to cool, add 35 mL of toluene as a solvent from the top of the cooling tube and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. Heat again in the bath for 10 minutes to complete the decomposition, then allow it to cool. (3) Wash the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir. (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a volumetric pipette. (5) Perform potentiometric titration with 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the endpoint. (6) A blank test is carried out by carrying out steps (1) to (5) above without adding any sample. 3.Calculation The hydroxyl value is calculated according to the following formula. Hydroxyl value (mgKOH / g) = [(BC) x f x 28.05] / S + D Where: B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Amount of 0.5 mol / L potassium hydroxide ethanol solution used for the sample (mL), f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: sample weight (g), D: acid number, 28.05: 1 / 2 the molecular weight of potassium hydroxide, 56.11. It is.

[0112] As the high hydroxyl value resin, those having a hydroxyl value of a predetermined value or more among the above-mentioned various tackifier resins can be used. The high hydroxyl value resin can be used alone or in combination of two or more. For example, a terpene phenol resin having a hydroxyl value of 50 mgKOH / g or more can be preferably used as the high hydroxyl value resin. The terpene phenol resin is advantageous because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

[0113] Although not particularly limited, when a high hydroxyl value resin is used, the ratio of the high hydroxyl value resin (e.g., terpene phenol resin) to the entire tackifier resin contained in the adhesive layer may be about 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. In some embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is preferably, for example, about 30% by weight or more. This allows the effect of using the high hydroxyl value resin to be preferably exhibited. In some preferred embodiments, the ratio of the high hydroxyl value resin to the entire tackifier resin is about 40% by weight or more, about 50% by weight or more (e.g., more than 50% by weight), about 60% by weight or more, about 70% by weight or more, about 80% by weight or more, or about 90% by weight or more. Substantially all of the tackifier resin (e.g., about 95 to 100% by weight, or even about 99 to 100% by weight) may be a high hydroxyl value resin.

[0114] The softening point of the high hydroxyl value resin is not particularly limited. The softening point of the high hydroxyl value resin may be, for example, about 50°C or more, and from the viewpoint of improving the cohesive force, a high hydroxyl value resin having a softening point (softening temperature) of about 80°C or more may be preferably used. For example, a terpene phenol resin having such a softening point may be preferably used. The softening point of the high hydroxyl value resin may be about 100°C or more, or about 110°C or more. The upper limit of the softening point of the high hydroxyl value resin is not particularly limited. From the viewpoint of adhesion to the adherend, a high hydroxyl value resin having a softening point of about 200°C or less (more preferably about 180°C or less) may be preferably used. In some embodiments, the softening point of the high hydroxyl value resin may be less than 160°C, less than 150°C, less than 145°C, less than 140°C, less than 130°C, or less than 120°C.

[0115] The content of the high hydroxyl value resin in the adhesive layer is not particularly limited as long as the desired viscoelastic properties are satisfied. In some embodiments, the content of the high hydroxyl value resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, and is preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength. In some embodiments, the content of the high hydroxyl value resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the high hydroxyl value resin is less than 30 parts by weight, more preferably 25 parts by weight or less, and even more preferably 22 parts by weight or less, and may be 20 parts by weight or less.

[0116] When the adhesive layer disclosed herein contains a tackifier resin, a tackifier resin derived from a plant (vegetable tackifier resin) may preferably act as the tackifier resin from the viewpoint of improving the biomass carbon ratio of the adhesive layer. Examples of vegetable tackifier resins include the above-mentioned rosin-based tackifier resin and terpene-based tackifier resin. The vegetable tackifier resin may be used alone or in combination of two or more. When the adhesive layer disclosed herein contains a tackifier resin, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is preferably 30% by weight or more (e.g., 50% by weight or more, typically 80% by weight or more). In some embodiments, the proportion of the vegetable tackifier resin in the total amount of tackifier resins is 90% by weight or more (e.g., 95% by weight or more, typically 99 to 100% by weight). The technology disclosed herein may be preferably implemented in an embodiment that does not substantially contain tackifier resins other than vegetable tackifier resins.

[0117] The content of the tackifier resin in the pressure-sensitive adhesive layer is not particularly limited as long as it satisfies the desired viscoelastic properties. In some embodiments, the content of the tackifier resin is usually about 1 part by weight or more, and is preferably about 5 parts by weight or more, preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (for example, 15 parts by weight or more) relative to 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength including light pressure adhesion. In some other embodiments, the content of the tackifier resin relative to 100 parts by weight of the acrylic polymer may be about 20 parts by weight or more, about 25 parts by weight or more, about 30 parts by weight or more, or about 35 parts by weight or more. Such a content can be preferably applied, for example, in an embodiment in which an acrylic polymer with a relatively small molecular weight is used. In some embodiments, the content of the tackifier resin in the pressure-sensitive adhesive layer is, for example, 70 parts by weight or less, 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, or 30 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the tackifier resin is less than 30 parts by weight, more preferably 25 parts by weight or less, even more preferably 22 parts by weight or less, or may be 20 parts by weight or less. By limiting the content of the tackifier resin, it is easy to maintain a low -20°C storage modulus.

[0118] In some preferred embodiments, the adhesive layer contains one or more of the above-mentioned tackifier resins and one or more of the acrylic oligomers. By using a tackifier resin and an acrylic oligomer in combination, higher adhesive strength (e.g., light pressure adhesive strength, etc.) can be obtained. The content C of the acrylic oligomer in the adhesive layer O [wt%] Tackifier resin content C T [weight%] ratio (C T / C O ) is not particularly limited, and is suitably set to, for example, 0.1 or more and 10 or less. In some embodiments, the above ratio (C T / C OThe ratio (C) is 0.25 or more, may be 0.4 or more, may be 0.7 or more, or may be 0.8 or more. T / C O The higher the ratio (C T / C O ) is about 1 or more (for example, more than 1.0), more preferably 1.5 or more, even more preferably 2.0 or more, and may be 2.5 or more, 3.0 or more, or 3.5 or more. From the viewpoint of obtaining the effect of adding the acrylic oligomer, in some embodiments, the above ratio (C T / C O ) is about 9 or less, suitably 7 or less, may be 5 or less, or may be 3 or less. In some other embodiments, the ratio (C T / C O ) may be 2 or less, 1.5 or less, or 1.2 or less.

[0119] In some preferred embodiments, the total amount (total amount) of the acrylic oligomer and tackifier resin contained in the adhesive layer is about 1 part by weight or more relative to 100 parts by weight of the acrylic polymer, preferably about 10 parts by weight or more, more preferably about 16 parts by weight or more, even more preferably about 20 parts by weight or more, and particularly preferably about 25 parts by weight or more, from the viewpoint of favorably exerting the effects of the technology disclosed herein. In some other embodiments, the total amount of the acrylic oligomer and tackifier resin is about 30 parts by weight or more, preferably about 35 parts by weight or more, may be about 40 parts by weight or more, may be about 45 parts by weight or more, or may be about 50 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. Such a total amount can be preferably applied in an embodiment in which an acrylic polymer with a relatively small molecular weight is used. In addition, the total amount of the acrylic oligomer and tackifier resin is preferably less than 120 parts by weight (for example, about 80 parts by weight or less) relative to 100 parts by weight of the acrylic polymer, and may be about 70 parts by weight or less. In some preferred embodiments, the total amount of the acrylic oligomer and tackifier resin is less than 60 parts by weight, more preferably about 50 parts by weight or less, even more preferably about 40 parts by weight or less, and particularly preferably 35 parts by weight or less, or may be 30 parts by weight or less, 28 parts by weight or less, or 26 parts by weight or less, based on 100 parts by weight of the acrylic polymer.

[0120] In the technology disclosed herein, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer in the adhesive layer is appropriately set so that the effects of the technology disclosed herein are exerted, and is not limited to a specific range. In some preferred embodiments, the total amount (total amount) of the acrylic polymer, tackifier resin and acrylic oligomer in the entire adhesive layer is suitable to be more than 50% by weight, preferably about 70% by weight or more, more preferably about 90% by weight or more, even more preferably 95% by weight or more (for example, 95% by weight or more and 100% by weight or less, or less than 100% by weight), and may be 98% by weight or more, from the viewpoint of preferably exerting the effects of the technology disclosed herein.

[0121] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. The crosslinking agents may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, and isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain a moderate cohesive force, and an adhesive having a good balance between adhesive force and cohesive force can be formed. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form partially crosslinked, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

[0122] As the isocyanate-based crosslinking agent, a polyfunctional isocyanate (which refers to a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agent can be used alone or in combination of two or more kinds.

[0123] Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0124] 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 xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0125] Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, Examples of the diisocyanate include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0126] A preferred polyfunctional isocyanate is one having an average of three or more isocyanate groups per molecule. Such a trifunctional or higher isocyanate may be a multimer (typically a dimer or trimer) of a bifunctional or trifunctional or higher isocyanate, a derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of a polyfunctional isocyanate), a polymer, etc. For example, a dimer or trimer of diphenylmethane diisocyanate, an isocyanurate of hexamethylene diisocyanate (a trimer adduct of an isocyanurate structure), a reaction product of trimethylolpropane and tolylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other polyfunctional isocyanates may be mentioned. Commercially available examples of such polyfunctional isocyanates include those manufactured by Asahi Kasei Chemicals Corporation under the trade names "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0127] The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. The amount of the isocyanate-based crosslinking agent used is not particularly limited. In some embodiments, the amount of the isocyanate-based crosslinking agent used can be, for example, about 0.1 parts by weight or more relative to 100 parts by weight of the acrylic polymer. From the viewpoint of achieving both cohesive strength and adhesion, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the acrylic polymer is usually preferably about 0.3 parts by weight or more (for example, 0.5 parts by weight or more). In some preferred embodiments, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the acrylic polymer is about 1.0 parts by weight or more, more preferably about 1.5 parts by weight or more, even more preferably about 2.0 parts by weight or more, particularly preferably about 2.5 parts by weight or more, and may be about 2.8 parts by weight or more. From the viewpoint of improving adhesion to an adherend, the amount of the isocyanate crosslinking agent used is suitably 10 parts by weight or less, preferably 8 parts by weight or less, more preferably 6 parts by weight or less, even more preferably 5 parts by weight or less, particularly preferably 4 parts by weight or less, and may be 3.5 parts by weight or less, or may be 3.2 parts by weight or less, based on 100 parts by weight of the acrylic polymer. Although not particularly limited, the above isocyanate crosslinking agent content can be preferably applied to an acrylic polymer containing a carboxyl group-containing monomer as a monomer component.

[0128] In some other embodiments, the amount of the isocyanate crosslinking agent used can be, for example, about 0.01 parts by weight or more relative to 100 parts by weight of the acrylic polymer, and from the viewpoint of achieving both cohesive strength and adhesion, it is appropriate to use about 0.02 parts by weight or more, preferably about 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more. In such an embodiment, the amount of the isocyanate crosslinking agent used is appropriate to use 5 parts by weight or less relative to 100 parts by weight of the acrylic polymer, preferably 2 parts by weight or less, more preferably 1 part by weight or less (for example, less than 1.0 part by weight), even more preferably 0.7 parts by weight or less, particularly preferably 0.4 parts by weight or less, and may be 0.3 parts by weight or less. Although not particularly limited, the above isocyanate crosslinking agent content can be preferably applied to an acrylic polymer containing a hydroxyl group-containing monomer as a monomer component.

[0129] As the epoxy crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without any particular limitation. An epoxy crosslinking agent having 3 to 5 epoxy groups in one molecule is preferred. The epoxy crosslinking agent can be used alone or in combination of two or more kinds.

[0130] Non-limiting specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's product names "TETRAD-C" and "TETRAD-X," DIC Corporation's product name "Epicron CR-5L," Nagase ChemteX Corporation's product name "Denacol EX-512," Nissan Chemical Industries' product name "TEPIC-G," etc.

[0131] The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used can be, for example, more than 0 part by weight and about 1 part by weight or less (typically about 0.001 to 1 part by weight) relative to 100 parts by weight of the acrylic polymer. From the viewpoint of suitably exerting the effect of improving the cohesive force, the amount of the epoxy crosslinking agent used is usually about 0.002 parts by weight or more relative to 100 parts by weight of the acrylic polymer, preferably about 0.005 parts by weight or more, for example, about 0.01 parts by weight or more, or about 0.02 parts by weight or more. From the viewpoint of improving adhesion to the adherend, the amount of the epoxy crosslinking agent used can be about 0.7 parts by weight or less, appropriately about 0.5 parts by weight or less, preferably about 0.2 parts by weight or less, more preferably about 0.1 parts by weight or less (for example, less than 0.1 parts by weight), and may be 0.07 parts by weight or less, 0.04 parts by weight or less, or 0.03 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. By limiting the amount of the epoxy crosslinking agent used within a predetermined range, it is easy to maintain sufficient adhesive strength.

[0132] In some preferred embodiments, the crosslinking agent is a combination of an isocyanate-based crosslinking agent and at least one crosslinking agent having a different type of crosslinkable functional group from that of the isocyanate-based crosslinking agent. The technology disclosed herein can be preferably implemented in an embodiment in which a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent having a different type of crosslinkable reactive group from that of an isocyanate-based crosslinking agent. Hereinafter, also referred to as a "non-isocyanate-based crosslinking agent") is used in combination with an isocyanate-based crosslinking agent.

[0133] The type of non-isocyanate crosslinking agent that can be used in combination with the isocyanate crosslinking agent is not particularly limited, and can be appropriately selected from the above-mentioned crosslinking agents. The non-isocyanate crosslinking agent can be used alone or in combination of two or more. In some preferred embodiments, an epoxy crosslinking agent can be used as the non-isocyanate crosslinking agent. For example, by using an isocyanate crosslinking agent and an epoxy crosslinking agent in combination, better adhesion properties can be achieved.

[0134] The relationship between the content of the isocyanate crosslinking agent and the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent) is not particularly limited, and is appropriately set within a range that satisfies a predetermined viscoelasticity characteristic. The content of the isocyanate crosslinking agent is, for example, more than 1 time, preferably about 10 times or more, more preferably about 50 times or more, more preferably about 80 times or more, even more preferably about 100 times or more (for example, more than 100 times), and particularly preferably about 120 times or more (for example, about 140 times or more) relative to the content of the nonisocyanate crosslinking agent (preferably an epoxy crosslinking agent). Furthermore, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent), the content of the isocyanate-based crosslinking agent relative to the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is usually, for example, approximately 1000 times or less, appropriately approximately 500 times or less, preferably approximately 300 times or less, more preferably approximately 200 times or less, and even more preferably approximately 180 times or less (for example, approximately 160 times or less).

[0135] The content of the crosslinking agent in the adhesive composition disclosed herein (total amount of crosslinking agent) is not particularly limited. From the viewpoint of cohesion, the content of the crosslinking agent is usually about 0.001 parts by weight or more, preferably about 0.01 parts by weight or more, and may be about 1 part by weight or more, or may be about 2 parts by weight or more, or may be about 2.5 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. The content of the crosslinking agent in the adhesive composition is usually about 20 parts by weight or less, preferably about 15 parts by weight or less, and preferably about 10 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, the content of the crosslinking agent relative to 100 parts by weight of the acrylic polymer is 5.0 parts by weight or less, may be 4.0 parts by weight or less, or may be 3.5 parts by weight or less.

[0136] (Other additives) In addition to the above-mentioned components, the adhesive composition may contain various additives, as necessary, that are common in the field of adhesives, such as leveling agents, crosslinking assistants, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, antiaging agents, UV absorbers, antioxidants, rust inhibitors, light stabilizers, etc. As for such various additives, conventionally known ones can be used in the usual manner, and they do not particularly characterize the present invention, so detailed explanations will be omitted.

[0137] The adhesive layer (layer made of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive (adhesive layer forming component) in a solvent (aqueous solvent) mainly composed of water, and typically includes those called water-dispersed adhesive compositions (compositions in a form in which at least a part of the adhesive is dispersed in water). The solvent-based adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more of the organic solvents exemplified as those usable in the above-mentioned solution polymerization (toluene, ethyl acetate, etc.) can be used without particular limitation. The technology disclosed herein can be preferably implemented in an embodiment having an adhesive layer formed from a solvent-based adhesive composition from the viewpoint of adhesion properties, etc.

[0138] The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) or a non-release surface and dried to form an adhesive layer. In the case of an adhesive sheet having a substrate, for example, a method (direct method) can be adopted in which an adhesive composition is directly applied (typically coated) to the substrate and dried to form an adhesive layer. In addition, a method (transfer method) can be adopted in which an adhesive composition is applied to a surface having releasability (release surface) and dried to form an adhesive layer on the surface, and the adhesive layer is transferred to a substrate. From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of a release liner, the back surface of a substrate treated for release, etc. can be used. The adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

[0139] The pressure-sensitive adhesive composition can be applied using a conventionally known coater such as a gravure roll coater, a die coater, a bar coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. From the viewpoints of promoting the crosslinking reaction, improving production efficiency, etc., the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150° C., and is usually preferably about 60 to 130° C. After drying the pressure-sensitive adhesive composition, aging may be further performed for the purpose of adjusting the component migration in the pressure-sensitive adhesive layer, advancing the crosslinking reaction, relaxing distortion that may exist in the pressure-sensitive adhesive layer, etc.

[0140] (Thickness) The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer having an appropriate thickness, for example, in the range of 0.1 to 500 μm, can be adopted depending on the application and purpose of use. In some embodiments, from the viewpoint of avoiding excessive thickness of the adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, and even more preferably about 50 μm or less. The thickness of the adhesive layer can be about 35 μm or less, for example, about 30 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less. An adhesive layer with a limited thickness can well meet the demand for thinning and weight reduction. In addition, generally, when the thickness of the adhesive layer is small, the adhesion to the adherend tends to be easily reduced, but according to the technology disclosed herein, a configuration having an adhesive layer with a limited thickness can realize sufficient adhesive strength, such as light pressure adhesion. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the pressure-sensitive adhesive layer is, in some embodiments, appropriately about 0.5 μm or more, may be about 1 μm or more, and is advantageously about 3 μm or more. From the viewpoint of improving adhesive strength including light pressure bonding strength, it is preferably about 10 μm or more, more preferably about 12 μm or more (e.g., more than 12 μm), even more preferably about 15 μm or more, for example, may be about 18 μm or more. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is more than 20 μm, may be 24 μm or more, may be 27 μm or more, may be about 30 μm or more, may be about 35 μm or more, or may be about 40 μm or more. In a substrate-attached double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on each side of the substrate, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may have the same thickness or may have different thicknesses.

[0141] (Biomass carbon ratio) In some embodiments, the pressure-sensitive adhesive layer contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive layer is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive layer may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive layer may be, for example, 90% or less, 85% or less, or 80% or less.

[0142] <Base material> In an embodiment in which the adhesive sheet disclosed herein is in the form of a single-sided or double-sided adhesive type adhesive sheet with a substrate, the substrate supporting the adhesive layer may be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or a composite thereof. Examples of paper include Japanese paper, craft paper, glassine paper, wood-free paper, synthetic paper, and top-coated paper. Examples of cloth include woven fabrics and nonwoven fabrics made by spinning various fibrous materials alone or in combination. Examples of the fibrous material include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil. The substrate supporting the adhesive layer is also called the substrate layer in the adhesive sheet.

[0143] The substrate may be formed from a material derived from biomass or a material derived from non-biomass. From the viewpoint of producing a PSA sheet that takes into consideration the reduction of dependency on fossil resource-based materials, a substrate material derived from biomass (typically a resin film) is preferably used.

[0144] The substrate may be formed using a recyclable material or a recycled material (also called a recycled material). A resin film is preferably used as such a recycled material. Since a resin film (for example, a polyester film such as a PET film) is recyclable, it is possible to continuously reproduce the resin film after use, regardless of whether or not a plant-derived material is used, and the environmental load can be reduced by reusing the resin film after use. Such a recyclable resin film or recycled resin film is also called a recycled film. The recycled material (for example, a recycled film) may be formed from a biomass-derived material or a non-biomass-derived material.

[0145] As the substrate constituting the substrate-attached pressure-sensitive adhesive sheet, a substrate containing a resin film as the base film can be preferably used. The above-mentioned base film is typically a member capable of independently maintaining its shape (independent). The substrate in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the above-mentioned base film. Examples of the above-mentioned auxiliary layer include a colored layer, a reflective layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the above-mentioned base film.

[0146] The resin film is a film containing a resin material as a main component (for example, a component contained in the resin film in an amount of more than 50% by weight). Examples of the resin film 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; fluororesin films; cellophane; and the like. The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Among them, from the viewpoint of handling and processability, polyester films are preferred, and PET films are particularly preferred.

[0147] In this specification, the term "resin film" refers to a typically non-porous sheet, and is a concept that is distinguished from so-called nonwoven fabric or woven fabric (in other words, a concept that excludes nonwoven fabric or woven fabric). The resin film may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. In addition, such a resin film may be non-foamed. Here, a non-foamed resin film refers to a resin film that has not been intentionally treated to form a foam. Specifically, a non-foamed resin film may be a resin film with an expansion ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

[0148] The above-mentioned substrate (e.g., resin film) may contain various additives such as fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, etc. The blending ratio of various additives is about less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0149] The substrate (e.g., resin film) may have a single-layer structure, or may have a multi-layer structure of two, three or more layers. From the viewpoint of shape stability, the substrate preferably has a single-layer structure. In the case of a multi-layer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (e.g., polyester resin). The method for producing the substrate (typically a resin film) is not particularly limited and may be any conventionally known method. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calendar roll molding may be appropriately used.

[0150] The surface of the substrate may be subjected to a conventionally known surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment, an acid treatment, an alkali treatment, application of a primer, etc. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the pressure-sensitive adhesive layer, in other words, the anchoring property of the pressure-sensitive adhesive layer to the substrate.

[0151] In addition, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a substrate, the back surface of the substrate may be subjected to a release treatment as necessary. The release treatment may be, for example, a treatment in which a general silicone-based, long-chain alkyl-based, fluorine-based or other release treating agent is applied in the form of a thin film typically of about 0.01 μm to 1 μm (for example, 0.01 μm to 0.1 μm). By carrying out such a release treatment, it is possible to obtain an effect such as facilitating unwinding of a roll of the pressure-sensitive adhesive sheet.

[0152] In the pressure-sensitive adhesive sheet of an embodiment including a substrate, the thickness of the substrate is not particularly limited. In order to prevent the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the substrate can be, for example, about 200 μm or less, preferably about 150 μm or less, and more preferably about 100 μm or less. Depending on the purpose and mode of use of the pressure-sensitive adhesive sheet, the thickness of the substrate may be about 70 μm or less, about 50 μm or less, or about 30 μm or less (for example, about 25 μm or less). In some embodiments, the thickness of the substrate may be about 20 μm or less, about 15 μm or less, or about 10 μm or less (for example, about 5 μm or less). By reducing the thickness of the substrate, the thickness of the pressure-sensitive adhesive layer can be made larger even if the total thickness of the pressure-sensitive adhesive sheet is the same. This can be advantageous in terms of improving adhesion to the adherend or substrate. In addition, a substrate with a limited thickness can be one that satisfies the demand for thinning and weight reduction. The lower limit of the substrate is not particularly limited. From the viewpoint of the handling property and processability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (e.g., 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more. In some embodiments, the thickness of the substrate can be about 15 μm or more, and may be about 25 μm or more.

[0153] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and for example, a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a fluorine-based polymer (polytetrafluoroethylene, etc.) can be used. The release treatment layer can be formed by surface treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As the liner substrate, a substrate formed using a biomass-derived material or a recycled material (recycled film, etc.) can be preferably used, similar to the substrate of the above-mentioned adhesive sheet.

[0154] <Total thickness of adhesive sheet> The total thickness of the adhesive sheet disclosed herein (including the adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, about 1 mm or less, may be about 500 μm or less, or may be about 300 μm or less, and from the viewpoint of thinning, is appropriately about 200 μm or less, and may be about 150 μm or less (for example, about 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be about 50 μm or less, and may be, for example, about 35 μm or less. The lower limit of the thickness of the adhesive sheet is, for example, 0.1 μm or more (for example, 0.5 μm or more), is appropriately about 3 μm or more, preferably about 10 μm or more, more preferably about 15 μm or more, even more preferably about 20 μm or more, may be about 30 μm or more, or may be about 50 μm or more. A pressure-sensitive adhesive sheet having a thickness equal to or greater than a certain value is likely to be able to adhere to an adherend and also tends to be easy to handle. In a substrate-less pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is the total thickness of the pressure-sensitive adhesive sheet.

[0155] <Characteristics of adhesive sheet> (Light pressure bonding strength) In some embodiments, the adhesive sheet is pressure-bonded to a stainless steel plate (SUS plate) as an adherend using a 0.5 kg roller in an environment of 23°C and 50% RH, and then left in the same environment for 30 minutes, and the peel strength (light pressure adhesive strength) measured under conditions of a pulling speed of 300 mm / min and a peel angle of 180 degrees is preferably about 3 N / 25 mm or more. An adhesive sheet exhibiting such light pressure adhesive strength can exhibit good adhesive strength even under light pressure conditions. The light pressure adhesive strength may be about 5 N / 25 mm or more, or about 10 N / 25 mm or more. In some preferred embodiments, the light pressure adhesive strength is about 15 N / 25 mm or more (e.g., 17 N / 25 mm or more), about 20 N / 25 mm or more, 23 N / 25 mm or more, or 25 N / 25 mm or more (e.g., 26 N / 25 mm or more). The upper limit of the light pressure adhesive strength is not particularly limited, but may be, for example, about 50 N / 25 mm or less. More specifically, the light pressure adhesive strength is measured by the method described in the Examples below.

[0156] (Normal pressure bonding strength) Although not particularly limited, in some embodiments, the adhesive sheet is pressure-bonded to a stainless steel plate (SUS plate) as an adherend using a 2 kg roller in an environment of 23°C and 50% RH, and then left in the same environment for 30 minutes, and the peel strength (normal pressure-bonding adhesive strength) measured under the conditions of a pulling speed of 300 mm / min and a peel angle of 180 degrees is preferably about 3 N / 25 mm or more. An adhesive sheet exhibiting the above adhesive strength can exhibit good adhesive strength. The normal pressure-bonding adhesive strength may be about 5 N / 25 mm or more, or about 10 N / 25 mm or more. In some preferred embodiments, the normal pressure-bonding adhesive strength is about 15 N / 25 mm or more (e.g., 17 N / 25 mm or more), about 20 N / 25 mm or more, 23 N / 25 mm or more, or 25 N / 25 mm or more (e.g., 26 N / 25 mm or more). The upper limit of the normal pressure-bonding adhesive strength is not particularly limited, but may be, for example, about 50 N / 25 mm or less. More specifically, the normal pressure-bonding adhesive strength is measured by the method described in the Examples below.

[0157] (Adhesive strength ratio (light crimping / normal crimping)) The adhesive sheet disclosed herein preferably has a ratio (P2 / P1) of the light pressure adhesive strength P2 [N / 25 mm] to the normal pressure adhesive strength P1 [N / 25 mm] greater than 85% in percentage. An adhesive sheet satisfying such characteristics can exhibit an adhesive strength (light pressure adhesiveness) equivalent to that when compressed with sufficient pressure even under light pressure bonding conditions. The ratio (P2 / P1) is preferably 90% or more, more preferably 92% or more, and even more preferably 94% or more. In some preferred embodiments, the ratio (P2 / P1) is greater than 95%, and may be 97% or more, 98% or more, 99% or more, or 100%.

[0158] (Biomass carbon ratio) In some embodiments, the pressure-sensitive adhesive sheet contains a biomass-derived material, and the biomass carbon ratio thereof may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive sheet is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive sheet means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive sheet, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of material availability, it may be 95% or less, or 90% or less. From the viewpoint of easily exerting good adhesive performance, in some embodiments, the biomass carbon ratio of the pressure-sensitive adhesive sheet may be, for example, 90% or less, 85% or less, or 80% or less.

[0159] <Application> The use of the adhesive sheet disclosed herein is not particularly limited, and can be used in various applications.The adhesive sheet disclosed herein has excellent light pressure adhesion, so it can be preferably used, for example, for adhesion and fixing of members in applications where it is desirable to limit the pressure during pressure bonding.For example, it is suitable for fixing members in electronic devices including home appliances, OA devices, and mobile electronic devices such as smartphones.

[0160] Non-limiting examples of the portable electronic device include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear type devices worn on the wrist like a wristwatch, modular type devices worn on a part of the body with a clip or strap, eyewear type devices including glasses (monocular type and binocular type devices, including head-mounted type devices), clothing type devices attached to shirts, socks, hats, etc. in the form of accessories, earwear type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not mean that it is sufficient to simply be portable, but rather that it has a level of portability that allows an individual (average adult) to carry it relatively easily. Examples of the electronic device include personal computers (desktop type, notebook type, tablet type, etc.), televisions, etc. These may include a built-in display device such as a liquid crystal or organic electroluminescence display device.

[0161] Although not particularly limited, the pressure-sensitive adhesive sheet disclosed herein can exhibit high adhesive strength to highly polar materials.The material that constitutes such highly polar surfaces can include, for example, metal materials such as stainless steel, glass materials, and polyester resin members such as PET.Such highly polar materials can be, for example, members that constitute electronic devices such as portable electronic devices.

[0162] Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet is preferably used in electronic devices that include various light sources such as LEDs (light emitting diodes) and light-emitting elements such as self-emitting organic ELs. For example, it is preferably used in electronic devices (typically mobile electronic devices) equipped with organic EL displays or liquid crystal displays.

[0163] FIG. 4 is a schematic example of a portable electronic device (smartphone) using the adhesive sheet disclosed herein. As shown in FIG. 4, a battery (heat generating element) 540 is built into a housing 520 of the portable electronic device 500. The portable electronic device 500 is also configured to include an adhesive sheet 550. In this configuration example, the adhesive sheet 550 has the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members that constitute the portable electronic device 500. The portable electronic device 500 is provided with a touch panel 570 whose display unit also functions as an input unit. The adhesive sheet disclosed herein is preferably used as a component (member joining means) of the portable electronic device described above.

[0164] In addition, in some embodiments, the PSA sheet disclosed herein may have a PSA layer containing an acrylic polymer with a high biomass carbon ratio, and therefore may be used as a substitute for a conventional acrylic PSA in various applications in which the acrylic PSA (i.e., an acrylic PSA with a low biomass carbon ratio) is used, thereby contributing to reducing dependency on fossil resource-based materials. The PSA sheet disclosed herein may be preferably used as a PSA sheet with reduced dependency on fossil resource-based materials.

[0165] The matters disclosed by this specification include the following: [1] A portable electronic device, an adhesive sheet is bonded to a member constituting the portable electronic device, The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer and an acrylic oligomer, The acrylic polymer is an alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms; A monomer having a reactive functional group; A polymer of a monomer component comprising: the monomer component contains 3% by weight or more of the monomer having the reactive functional group, The portable electronic device, wherein the pressure-sensitive adhesive layer has a storage modulus at -20°C of less than 220 MPa. [2] The portable electronic device according to the above [1], wherein the alkyl (meth)acrylate having a chain alkyl group with 7 or more carbon atoms is an alkyl acrylate having a chain alkyl group with 7 or 8 carbon atoms. [3] The mobile electronic device according to the above [1] or [2], wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes heptyl acrylate. [4] The mobile electronic device according to any one of the above [1] to [3], wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes 2-ethylhexyl acrylate. [5] The portable electronic device according to any one of the above [1] to [4], wherein the monomer having a reactive functional group is at least one selected from a carboxy group-containing monomer and a hydroxyl group-containing monomer. [6] The portable electronic device according to any one of the above [1] to [5], wherein the weight average molecular weight of the acrylic polymer is within the range of 300,000 or more and 1,500,000 or less. [7] The portable electronic device according to any one of the above [1] to [6], wherein the acrylic oligomer has a glass transition temperature of 20° C. or higher and 200° C. or lower. [8] The portable electronic device according to any one of the above [1] to [7], wherein the content of the acrylic oligomer in the pressure-sensitive adhesive layer is less than 30 parts by weight per 100 parts by weight of the acrylic polymer. [9] The portable electronic device according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive layer further contains a tackifier resin.

[0166]

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer contains an acrylic polymer and an acrylic oligomer, The acrylic polymer is an alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms; A monomer having a reactive functional group; A polymer of a monomer component comprising: the monomer component contains 3% by weight or more of the monomer having the reactive functional group, The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a storage modulus at -20°C of less than 220 MPa.

[12] The pressure-sensitive adhesive sheet according to the above-mentioned

[11] , wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms is an alkyl acrylate having a chain alkyl group having 7 or 8 carbon atoms.

[13] The pressure-sensitive adhesive sheet according to the above-mentioned

[11] or

[12] , wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes heptyl acrylate.

[14] The pressure-sensitive adhesive sheet according to any one of the above-mentioned

[11] to

[13] , wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes 2-ethylhexyl acrylate.

[15] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[14] , wherein the monomer having a reactive functional group is at least one selected from a carboxy group-containing monomer and a hydroxyl group-containing monomer.

[16] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[15] , wherein the weight average molecular weight of the acrylic polymer is within the range of 300,000 or more and 1,500,000 or less.

[17] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[16] , wherein the acrylic oligomer has a glass transition temperature of 20° C. or higher and 200° C. or lower.

[18] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[17] , wherein the content of the acrylic oligomer in the pressure-sensitive adhesive layer is less than 30 parts by weight per 100 parts by weight of the acrylic polymer.

[19] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[18] , wherein the pressure-sensitive adhesive layer further contains a tackifier resin.

[20] The pressure-sensitive adhesive sheet according to any one of

[11] to

[19] above, which is used for fixing components in an electronic device.

[21] An electronic device comprising the pressure-sensitive adhesive sheet according to any one of

[11] to

[20] above. EXAMPLES

[0167] Some examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0168] <Example 1> (Synthesis of acrylic polymers) In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, 93 parts of n-heptyl acrylate (n-HpA) and 7 parts of acrylic acid (AA) as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was performed at 60°C to 70°C for 8 hours to obtain a solution of an acrylic polymer. The weight average molecular weight (Mw) of this acrylic polymer was 900,000. The Mw was adjusted by adjusting the concentration of the monomer components during polymerization. The above n-HpA is a compound synthesized using heptyl alcohol derived from biomass and having a heptyl group derived from biomass at the ester end.

[0169] (Preparation of Pressure-Sensitive Adhesive Composition) To the acrylic polymer solution obtained above, 20 parts of terpene phenol resin A (trade name "YS Polystar T-115", terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd., softening point about 115 ° C., hydroxyl value 30 to 60 mg KOH / g) as a tackifier resin, 5 parts of acrylic oligomer, 3 parts (solid content basis) of isocyanate crosslinking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), and 0.02 parts of epoxy crosslinking agent (trade name "TETRAD-C", 1,3-bis (N, N-diglycidyl aminomethyl) cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Ltd.) were added per 100 parts of the acrylic polymer contained in the solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition according to this example. The acrylic oligomer used was prepared by the following method. Specifically, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and ethyl acetate as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, and the mixture was stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, and then heated to 85°C and reacted for 5 hours to obtain an acrylic oligomer with a solid content concentration of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0170] (Preparation of adhesive sheet) The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form an adhesive layer having a thickness of 35 μm. The release surface of a 25 μm thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was bonded to this adhesive layer. In this way, a substrate-less double-sided adhesive sheet having a thickness of 35 μm and both sides protected by the above two polyester release liners was obtained.

[0171] <Examples 2 to 7, 10 to 16 and Comparative Examples 1 to 2> The adhesive compositions of each example were prepared in the same manner as in Example 1, except that the monomer composition of the acrylic polymer, Mw, type and amount of tackifier resin, amount of acrylic oligomer, type and amount of crosslinker, and thickness of the adhesive layer were changed as shown in Table 1, and the resulting adhesive compositions were used to produce substrate-less double-sided adhesive sheets of each example in the same manner as in Example 1. The Mw of the acrylic polymer was adjusted by adjusting the concentration of the monomer components during polymerization. In Table 1, 2EHA represents 2-ethylhexyl acrylate, BA represents n-butyl acrylate, and HEA represents hydroxyethyl acrylate. In Table 1, the terpene phenol resin B as a tackifier resin is a product name "YS Polystar S-145" manufactured by Yasuhara Chemical Co., Ltd. (a terpene phenol resin with a softening point of about 145°C and a hydroxyl value of 70 to 110 mgKOH / g), and the rosin ester is a product name "Haritac SE10" manufactured by Harima Chemical Co., Ltd. (hydrogenated rosin glycerin ester, softening point of 75 to 85°C, and a hydroxyl value of 25 to 40 mgKOH / g).

[0172] <Example 8> A pressure-sensitive adhesive composition prepared by the method described in Example 1 was prepared, and the pressure-sensitive adhesive composition was applied to one surface (first surface) of a 2 μm-thick PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) as a base layer, and dried at 100° C. for 2 minutes to form a first pressure-sensitive adhesive layer with a thickness of 17 μm. The release surface of a 25 μm-thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was attached to the first pressure-sensitive adhesive layer. In addition, a 38 μm-thick polyester release liner (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) was prepared, and the pressure-sensitive adhesive composition was applied to the release surface of the release liner, and dried at 100° C. for 2 minutes to form a second pressure-sensitive adhesive layer with a thickness of 17 μm. This second pressure-sensitive adhesive layer was transferred to the non-pressure-sensitive adhesive layer surface of the base layer on which the first pressure-sensitive adhesive layer was formed. In this manner, a substrate-attached double-sided pressure-sensitive adhesive sheet according to this example was produced.

[0173] <Example 9> A substrate-attached double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 8, except that the thicknesses of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer were each changed to 2 μm.

[0174] <Comparative Example 3> A double-sided pressure-sensitive adhesive sheet with a substrate according to this example was produced in the same manner as in Example 8, except that the composition of the pressure-sensitive adhesive layer was changed as shown in Table 1.

[0175] <Evaluation method> (Normal pressure bonding strength) A 50 μm thick PET film was attached to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) to form a backing, and the sheet was cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by rolling a 2 kg roller back and forth once. After leaving the sample in the same environment for 30 minutes, the peel strength (normal pressure-bonding adhesive strength) [N / 25 mm] was measured using a tensile tester in accordance with JIS Z 0237:2000 at a tensile speed of 300 mm / min and a peel angle of 180 degrees. In measuring the peel strength, the tensile tester used is Shimadzu Corporation's "Precision Universal Tester, Autograph AG-IS 50N" or an equivalent product. When performing the peel strength measurement on a single-sided adhesive sheet, it is not necessary to back the sheet with a PET film. When the substrate is thin (for example, when the substrate is 25 μm or less), the substrate may be backed with a PET film.

[0176] (Light pressure bonding strength) The peel strength (light pressure adhesion) [N / 25 mm] was measured in the same manner as in the measurement of normal pressure adhesion described above, except that the roller used for pressing the adherend onto the adherend was changed from 2 kg to 0.5 kg.

[0177] (Adhesive strength ratio of light pressure bonding / normal pressure bonding) The adhesive strength ratio (light / normal) of the light adhesive strength [N / 25mm] to the normal adhesive strength [N / 25mm] measured by the above method was calculated as a percentage [%]. If the adhesive strength ratio (light / normal) is higher than 85%, it is judged to have excellent light adhesive strength.

[0178] The outline of each example and the evaluation results are shown in Table 1.

[0179] [Table 1]

[0180] As shown in Table 1, the adhesives according to Examples 1 to 16 contained an acrylic polymer and an acrylic oligomer, and contained an alkyl (meth)acrylate (specifically, n-HpA or 2EHA) having 7 or more carbon atoms in the alkyl group as a monomer component of the acrylic polymer, and further contained 3% or more of a carboxyl group-containing monomer (specifically, AA) or a hydroxyl group-containing monomer (specifically, HEA), and had a storage modulus at -20°C of less than 220 MPa. The adhesive sheets according to Examples 1 to 16 above had an adhesive strength ratio (light compression / normal compression) higher than 85%. On the other hand, in Comparative Example 1, like Examples 1 to 12, the acrylic polymer contained 3% or more of n-HpA and AA as monomer components, but the adhesive's storage modulus at -20°C was 220 MPa, and the adhesive strength ratio (light compression / normal compression) was inferior to those of the Examples. Moreover, from the results of Comparative Examples 2 and 3, it was found that the adhesive strength ratio (light compression bond / normal compression bond) tended to decrease as the -20°C storage modulus became larger than 220MPa. In particular, in Comparative Example 2, in which an alkyl (meth)acrylate having 7 or more carbon atoms in the alkyl group was not used as the monomer component of the acrylic polymer and BA was used instead, the Mw of the acrylic polymer was relatively low and the amount of crosslinking agent used was also relatively small, but the -20°C storage modulus was a high value of 527MPa, and the adhesive strength ratio (light compression bond / normal compression bond) decreased the most. The above results show that excellent light pressure adhesion can be achieved by using an adhesive that contains an acrylic polymer and an acrylic oligomer, where the acrylic polymer is a polymerization product of monomer components including an alkyl (meth)acrylate having a chain-like alkyl group with 7 or more carbon atoms and a monomer having a reactive functional group, where the proportion of monomers having reactive functional groups is 3% or more, and where the storage modulus at -20°C is less than 220 MPa.

[0181] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. [Explanation of symbols]

[0182] 1,2,3 Adhesive sheet 10 Supporting base material 10A 1st side 10B 2nd side (back) 21 Adhesive layer (first adhesive layer) 21A Adhesive surface (1st adhesive surface) 21B 2nd adhesive side 22 Adhesive layer (second adhesive layer) 22A Adhesive surface (second adhesive surface) 31,32 Release liner 100,200,300 Adhesive sheet with release liner

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains an acrylic polymer and an acrylic oligomer having a glass transition temperature of 0°C or higher, The acrylic polymer is an alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms; a monomer having a reactive functional group; A polymer of a monomer component comprising: the monomer component contains 3% by weight or more of the monomer having the reactive functional group, The pressure-sensitive adhesive layer has a storage modulus at −20° C. of 150 MPa or less.

2. The adhesive layer further comprises a tackifying resin, a ratio (CT / C0) of the content of the tackifier resin CT [wt%] to the content C0 [wt%] of the acrylic oligomer is 0.1 or more and 10 or less; The pressure-sensitive adhesive sheet according to claim 1 , wherein the total amount of the acrylic oligomer and the tackifier resin is 1 part by weight or more and less than 120 parts by weight per 100 parts by weight of the acrylic polymer.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms is an alkyl acrylate having a chain alkyl group having 7 or 8 carbon atoms.

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes heptyl acrylate.

5. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the alkyl (meth)acrylate having a chain alkyl group having 7 or more carbon atoms includes 2-ethylhexyl acrylate.

6. The pressure-sensitive adhesive sheet according to claim 1 , wherein the monomer having a reactive functional group is at least one selected from the group consisting of a carboxyl group-containing monomer and a hydroxyl group-containing monomer.

7. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the weight-average molecular weight of the acrylic polymer is in the range of 300,000 to 1,500,000.

8. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the acrylic oligomer has a glass transition temperature of 20°C or higher and 200°C or lower.

9. The pressure-sensitive adhesive sheet according to claim 1 , wherein the content of the acrylic oligomer in the pressure-sensitive adhesive layer is less than 30 parts by weight based on 100 parts by weight of the acrylic polymer.

10. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used to fix components in an electronic device.

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