Adhesive sheet

Abstract

To provide an adhesive sheet capable of achieving high levels of adhesion to high-polarity materials, adhesion to low-polarity materials, and holding power.SOLUTION: The adhesive sheet has an adhesive agent layer containing an acrylic polymer. The acrylic polymer is a polymer of a monomer component containing n-heptyl acrylate and a carboxy-group-containing monomer. The monomer component of the acrylic polymer contains more than 3 wt.% of the carboxy-group-containing monomer. Furthermore, the gel fraction of the adhesive agent layer is less than 70%. The weight-average molecular weight of the acrylic polymer is greater than 600,000.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an adhesive sheet. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) exhibit a soft solid (viscoelastic) state at temperatures around room temperature and have the property of adhering to a substrate under pressure. Taking advantage of this property, adhesives are widely used in various industrial fields, from 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 surface protection. Patent documents 1 and 2 are cited as technical documents relating to adhesive sheets. Patent documents 1 and 2 describe adhesives containing acrylic polymers polymerized using n-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 [Overview of the project] [Problems that the invention aims to solve]

[0004] Generally, adhesive sheets are required to have good adhesion to various materials. For example, adhesives used to fix components of electronic devices such as the aforementioned home appliances may require reliable fixing of components where one is made of a highly polar material such as stainless steel and the other is made of a low-polarity material such as polyolefin, or where the surface is composed of both highly polar and low-polarity materials. Usually, adhesion to dissimilar materials such as highly polar and low-polarity materials can be easily obtained by using a soft adhesive whose storage modulus is limited to below a predetermined value. However, such adhesives generally tend to have reduced holding power. There is a trade-off relationship between adhesion to dissimilar materials and holding power. In particular, in recent years, due to the demand for miniaturization, weight reduction, and precision of the aforementioned electronic devices, the bonding area of ​​adhesives tends to decrease. In such applications, it tends to be more difficult to achieve high levels of adhesion to highly polar materials, adhesion to low-polarity materials, and holding power.

[0005] As a result of diligent research, the inventors have discovered that an adhesive can be obtained that exhibits high adhesion to both highly polar and low-polarity materials, as well as sufficient holding power, by using an acrylic polymer containing n-heptyl acrylate as a monomer component, thus completing the present invention. In other words, the present invention aims to provide an adhesive sheet that can achieve a high level of adhesion to highly polar materials, adhesion to low-polarity materials, and holding power simultaneously. [Means for solving the problem]

[0006] This specification provides an adhesive sheet having an adhesive layer containing an acrylic polymer. The acrylic polymer is a polymer of monomer components containing n-heptyl acrylate and a carboxyl group-containing monomer. The monomer component of the acrylic polymer contains more than 3% by weight of the carboxyl group-containing monomer. Furthermore, the gel fraction of the adhesive layer is less than 70%. The weight-average molecular weight of the acrylic polymer is greater than 600,000. By using an adhesive containing an acrylic polymer with n-heptyl acrylate as a monomer component and a gel fraction of less than 70%, sufficient adhesive strength can be achieved not only for highly polar materials but also for low-polarity materials. Furthermore, by copolymerizing the acrylic polymer with a carboxyl group-containing monomer in a proportion of more than 3% by weight and designing the weight-average molecular weight (Mw) to be greater than 600,000, it is possible to improve the holding power while maintaining high adhesive strength to dissimilar materials. The use of the carboxyl group-containing monomer also improves adhesion to highly polar materials. In other words, the above configuration makes it possible to achieve a high level of adhesion to high-polarity materials, adhesion to low-polarity materials, and retention force simultaneously. Patent Document 1 evaluates the adhesion and retention force to polypropylene (40°C, bonding area 25mm x 25mm, load 1kg), and Patent Document 2 evaluates the retention force (80°C, bonding area 25mm x 25mm, load 1kg). However, the acrylic polymers used in both cases have low Mw or a low copolymerization ratio of carboxyl group-containing monomers. Therefore, the retention force evaluated in the examples described later (80°C, bonding area 10mm x 20mm, load 1.5kg) cannot be obtained, and the adhesion to high-polarity materials, adhesion to low-polarity materials, and retention force are not sufficiently satisfied.

[0007] In some preferred embodiments, the adhesive composition for forming the adhesive layer includes a crosslinking agent. The use of a crosslinking agent increases the cohesive force of the adhesive, thereby suitably achieving sufficient holding power.

[0008] In some preferred embodiments, the adhesive layer contains an adhesion - imparting resin. By using an adhesion - imparting resin, the gel fraction of the adhesive layer can be adjusted to an appropriate range, and the adhesive force to high - polarity materials and low - polarity materials can be improved.

[0009] In some preferred embodiments, the thickness of the adhesive layer is 0.1 - 500 μm. The technology disclosed herein can be implemented in a configuration having an adhesive layer with the above thickness.

[0010] In some preferred embodiments, the gel fraction of the adhesive layer is 20% or more and less than 70%. By setting the gel fraction of the adhesive layer within the above range, the adhesive force and the holding force can be preferably balanced.

[0011] The adhesive sheet according to some preferred embodiments has a 180 - degree peel strength (adhesive force to SUS) of 15 N / 25 mm or more with respect to a stainless - steel plate. The adhesive sheet having the above adhesive force to SUS can exhibit excellent adhesive force to high - polarity materials.

[0012] The adhesive sheet according to some preferred embodiments has a 180 - degree peel strength (adhesive force to PP) of 10 N / 25 mm or more with respect to polypropylene. The adhesive sheet having the above adhesive force to PP can have sufficient adhesion reliability with respect to low - polarity materials.

[0013] The adhesive sheet according to some preferred embodiments has a 180 - degree peel strength (adhesive force to PE) of 5 N / 25 mm or more with respect to polyethylene. The adhesive sheet having the above adhesive force to PE can have sufficient adhesion reliability with respect to low - polarity materials.

[0014] The adhesive sheet according to some preferred embodiments has a displacement distance of 10 mm or less in a holding - force test conducted under the conditions of 80°C, an adhesive area of 10 mm×20 mm, a load of 1.5 kg, and 1 hour. The adhesive sheet that is difficult to displace in the above holding - force test can have sufficient holding force (specifically, high - temperature holding force).

[0015] The adhesive sheets disclosed herein offer both adhesion to dissimilar materials and holding power, making them suitable for applications requiring adhesion to highly polar or low-polarity materials, or for applications requiring long-term adhesive reliability. For example, they are suitable for fixing components in electronic devices, including home appliances, office automation equipment, and portable electronic devices such as smartphones. Therefore, this specification provides an electronic device using any of the adhesive sheets disclosed herein, in other words, an electronic device containing such an adhesive sheet. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to another embodiment. [Figure 3] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to another embodiment. [Figure 4] This is a schematic front view showing an example of a portable electronic device comprising an adhesive sheet. [Modes for carrying out the invention]

[0017] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein but necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. Furthermore, in the following drawings, members and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Also, the embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the adhesive sheets of the present invention that are actually provided as products.

[0018] In this specification, "adhesive" refers to a material that, as described above, exhibits a soft solid (viscoelastic) state at temperatures around room temperature and has the property of easily adhering to a substrate under pressure. The adhesive referred to here is generally defined as having a complex tensile modulus E, as defined in "CA Dahlquist, “Adhesion: Fundamentals and Practice”, McLaren & Sons, (1966) p. 143". * (1Hz) < 10 7 dyne / cm 2 It may be a material having properties that satisfy the above conditions (typically, a material having the above properties at 25°C).

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

[0020] <Composition of the adhesive sheet> The adhesive sheet disclosed herein comprises an adhesive layer. The adhesive sheet may be in the form of a substrate-less double-sided adhesive sheet comprising, for example, a first adhesive surface formed by one surface of the adhesive layer and a second adhesive surface formed 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 sides of a support substrate. Hereinafter, the support substrate may simply be referred to as the "substrate." The concept of an adhesive sheet as used herein may include adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet processed into various shapes.

[0021] Figure 1 schematically shows the structure of an adhesive sheet according to one embodiment. This adhesive sheet 1 is configured as a substrate-less double-sided adhesive sheet consisting of an adhesive layer 21. The adhesive sheet 1 is used by attaching a first adhesive surface 21A, which is formed by one surface (first surface) of the adhesive layer 21, and a second adhesive surface 21B, which is formed by the other surface (second surface) of the adhesive layer 21, to different locations on an object to be adhered to. The locations to which the adhesive surfaces 21A and 21B are attached may be different locations on different members, or they may be different locations within a single member. Before use (i.e., before being attached to an object to be adhered to), as shown in Figure 1, the adhesive sheet 1 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 having a release surface on at least the side facing the adhesive layer 21. As the release liners 31 and 32, it is preferable to use, for example, a sheet-like base material (liner base material) on which a release layer is provided by a release agent on one side so that the one side becomes a release surface. Alternatively, the release liner 32 may be omitted, and a release liner 31 with release surfaces on both sides may be used, and this and the adhesive sheet 1 may be overlapped and wound in a spiral shape to form an adhesive sheet with a release liner in a form (roll form) where the second adhesive surface 21B abuts against and protects the back surface of the release liner 31.

[0022] Figure 2 schematically shows the structure of an adhesive sheet according to another embodiment. This adhesive sheet 2 is configured as a single-sided adhesive sheet with a substrate, comprising a sheet-like support 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 support substrate 10, that is, without any intention to separate the adhesive layer 21 from the support substrate 10. As shown in Figure 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 on the side facing the adhesive layer 21. Alternatively, the release liner 31 may be omitted, and a support substrate 10 with the second surface 10B as the release surface may be used, and the adhesive sheet 2 may be wound so that the adhesive surface 21A abuts against and is protected by the second surface (back surface) 10B of the support substrate 10 (roll form).

[0023] Furthermore, Figure 3 schematically shows the structure of an adhesive sheet according to another embodiment. This adhesive sheet 3 is configured as a double-sided adhesive sheet with a base material, comprising a sheet-like support base material (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, a first adhesive layer 21 fixedly provided on the first surface 10A side, and a second adhesive layer 22 fixedly provided on the second surface 10B side. Before use, the adhesive sheet 3 may be a component of an adhesive sheet with a release liner 300, in which the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 are protected by release liners 31 and 32, as shown in Figure 3. Alternatively, the release liner 32 may be omitted, and a release liner 31 with release surfaces on both sides may be used, and the adhesive sheet 3 and this liner may be overlapped and wound in a spiral shape to configure an adhesive sheet with a release liner in which the second adhesive surface 22A abuts against and is protected by the back surface of the release liner 31 (roll form).

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

[0025] <Adhesive layer> The adhesive layer constituting the adhesive sheet disclosed herein contains an acrylic polymer. The adhesive layer is typically an adhesive layer with an acrylic polymer as the base polymer. Such an adhesive layer is also called an acrylic adhesive layer. The base polymer refers to the main component of the rubbery polymer (a polymer that exhibits rubber elasticity in the temperature range around room temperature) contained in the adhesive layer. In this specification, unless otherwise specified, "main component" refers to a component contained in more than 50% by weight. Furthermore, the following description of components that may be contained in the adhesive and adhesive layer is also applicable to adhesive compositions used to form the adhesive (layer) unless otherwise specified.

[0026] Furthermore, in this specification, "acrylic polymer" means a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, monomers having at least one (meth)acryloyl group in one molecule will also be referred to as "acrylic monomers." Therefore, in this specification, acrylic polymers are defined as polymers that contain monomer units derived from acrylic monomers. In this specification, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic.

[0027] (Acrylic polymer) The acrylic polymer used in the technology disclosed herein is a polymer of a monomer component containing n-heptyl acrylate. Acrylic polymers polymerized using a monomer component containing n-heptyl acrylate exhibit superior flexibility and better adhesion to both highly polar and low-polarity materials compared to polymers of other alkyl acrylates such as n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). The reason for this is not to be interpreted in a particularly restrictive way, but it is thought that polymers containing n-heptyl acrylate as a monomer unit have a low glass transition temperature and relatively long linear side chains, resulting in relatively large spaces between the main chains within the adhesive.

[0028] The proportion of n-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, 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, and may also be 92% by weight or more, 94% by weight or more, or 96% by weight or more. By increasing the amount of n-heptyl acrylate used, its effects can be effectively expressed. On the other hand, from the viewpoint of copolymerizing carboxyl group-containing monomers and other monomers, the proportion of n-heptyl acrylate in the monomer component is less than 97% by weight, and in some embodiments, may be 95% by weight or less, 93% by weight or less, or 91% by weight or less.

[0029] Acrylic polymers may also be copolymerized with alkyl (meth)acrylates other than n-heptyl acrylate (hereinafter also referred to as "arbitrary alkyl (meth)acrylate"). For example, compounds represented by the following formula (1) can be suitably used as arbitrary alkyl (meth)acrylates. CH2=C(R 1 )COOR 2 (1) Here, in equation (1) above, R 1R is a hydrogen atom or a methyl group. 2 These are linear alkyl groups having 1 to 20 carbon atoms (excluding the n-heptyl group).

[0030] Examples of the above optional alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl methacrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate. Examples include acrylates, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc. These arbitrary alkyl (meth)acrylates can be used individually or in combination of two or more. Preferably used arbitrary alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0031] The proportion of optional alkyl (meth)acrylate in the monomer component is, for example, less than 47% by weight in some embodiments, may be 45% by weight or less, 30% by weight or less, 10% by weight or less, 5% by weight or less, or 1% by weight or less. The techniques disclosed herein can preferably be carried out in embodiments in which the monomer component is substantially free of optional alkyl (meth)acrylate.

[0032] In this specification, "substantially free of monomer A (e.g., the arbitrary alkyl (meth)acrylates mentioned above)" means that monomer A is not used intentionally, and it is permissible for monomer A to be unintentionally included in amounts of, for example, 0.01% by weight or less.

[0033] In some embodiments, the monomer component may include an alkyl (meth)acrylate having a biomass-derived alkyl group at its ester terminus (hereinafter also referred to as "biomass alkyl (meth)acrylate"). In recent years, environmental issues such as global warming have become a major concern, and there is a desire to reduce the amount of fossil fuel-based materials used, such as petroleum. Under these circumstances, there is also a need to reduce the amount of fossil fuel-based materials used in the field of adhesives. By using biomass alkyl (meth)acrylate, it is possible to suitably realize an acrylic adhesive that takes into consideration the reduction of reliance on fossil fuel-based materials.

[0034] Biomass alkyl (meth)acrylates are not particularly limited and include, for example, esters of biomass-derived alkanols and biomass-derived or non-biomass-derived (meth)acrylic acid. Examples of biomass-derived alkanols include biomass ethanol, alkanols derived from plant raw materials such as palm oil, palm kernel oil, coconut oil, and castor oil. When the number of carbon atoms in the biomass-derived alkanol is three or more, the alkanol may be linear or branched. In some embodiments, esters of biomass-derived alkanols and non-biomass-derived (meth)acrylic acid are used as biomass alkyl (meth)acrylates for the synthesis of acrylic polymers. In such biomass alkyl (meth)acrylates, the more carbon atoms the alkanol has, the higher the ratio of biomass-derived carbons to the total number of carbon atoms in the biomass alkyl (meth)acrylate, i.e., the biomass carbon ratio of the alkyl (meth)acrylate. Therefore, in the biomass alkyl (meth)acrylate described above, a high number of carbon atoms in the alkyl group derived from biomass is desirable in terms of reducing dependence on fossil fuel-based materials. On the other hand, if the number of carbon atoms in the alkyl group constituting the alkyl (meth)acrylate is too high, it tends to become difficult to obtain adhesive properties such as adhesion strength, and it may also be disadvantageous in terms of productivity, such as synthesis, handling, and cost. In embodiments where an ester of biomass-derived alkanol and non-biomass-derived (meth)acrylic acid is used as the biomass alkyl (meth)acrylate, it is desirable to use a material that balances adhesive properties with a reduction in dependence on fossil fuel-based materials (more specifically, the biomass carbon ratio of the alkyl (meth)acrylate described above).

[0035] In some preferred embodiments, biomass-derived n-heptyl acrylate (biomass n-heptyl acrylate) is used as the n-heptyl acrylate. By using biomass n-heptyl acrylate, the effects of the technologies disclosed herein can be achieved while reducing the dependence on fossil fuel-based materials. The biomass n-heptyl acrylate is an ester of a biomass-derived alkanol and a biomass-derived or non-biomass-derived acrylic acid. For example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid may be used. In such compounds, only the linear heptyl group is biomass-derived.

[0036] The proportion of biomass alkyl (meth)acrylate (preferably biomass n-heptyl acrylate) in the monomer component of the above 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, and may also be 92% by weight or more, 94% by weight or more, or 96% by weight or more. In addition, the proportion of biomass alkyl (meth)acrylate (preferably biomass n-heptyl acrylate) in the monomer component is less than 97% by weight, and in some embodiments, may be 95% by weight or less, 93% by weight or less, or 91% by weight or less. In some other embodiments, the proportion of biomass alkyl (meth)acrylate in the monomer component may be 90% by weight or less, 70% by weight or less, 50% by weight or less, 30% by weight or less, 10% by weight or less, or 1% by weight or less.

[0037] Furthermore, the monomer component of the acrylic polymer contains more than 3% by weight of carboxyl group-containing monomers. Carboxyl group-containing monomers can exhibit improved cohesiveness due to their polarity. In addition, when using crosslinking agents such as isocyanate-based or epoxy-based crosslinking agents, these carboxyl groups can act as crosslinking points for the acrylic polymer. By using more than 3% by weight of carboxyl group-containing monomers, it is possible to obtain sufficient holding power while maintaining high adhesive strength to dissimilar materials. Moreover, by using carboxyl group-containing monomers, even better adhesion to highly polar materials can be obtained.

[0038] Examples of carboxyl group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Among these, AA and MAA are preferred carboxyl group-containing monomers. AA is particularly preferred. Carboxyl group-containing monomers can be used individually or in combination of two or more.

[0039] The proportion of carboxyl group-containing monomers in the monomer component of the acrylic polymer is more than 3% by weight (specifically, 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 also be 6.0% by weight or more. In some embodiments, the proportion of carboxyl group-containing monomers in the monomer component may be 7.0% by weight or more, 8.0% by weight or more (e.g., more than 8.0% by weight), or 9.0% by weight or more. By increasing the amount of carboxyl group-containing monomers used, the cohesive force of the adhesive layer is improved based on the action of the carboxyl group-containing monomers, making it possible to design the Mw of the acrylic polymer to be moderately low and to increase the adhesive strength. Furthermore, the amount of carboxyl group-containing monomers is appropriately 20% by weight or less of the total monomer component, preferably 15% by weight or less, and more preferably 12% by weight or less. In some embodiments, the amount of the carboxyl group-containing monomer may be less than 10% by weight, less than 8% by weight, less than 6% by weight, or less than 5% by weight. By appropriately adjusting the amount of carboxyl group-containing monomer used within the above range, a good balance can be achieved between adhesive strength to highly polar materials and adhesive strength and retention strength to low-polarity materials.

[0040] Acrylic polymers may also be copolymerized with functional group-containing monomers other than carboxyl group-containing monomers (monomers containing arbitrary functional groups). Examples of monomers containing optional functional groups that can be introduced into acrylic polymers to serve as crosslinking sites or contribute to improved adhesive strength include monomers containing hydroxyl groups (OH groups) (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; polypropylene glycol mono(meth)acrylate, etc.), monomers containing acid anhydride groups, monomers containing amide groups ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), monomers containing amino groups (aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers containing epoxy groups, monomers containing cyano groups, monomers containing keto groups, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), monomers containing alkoxysilyl groups, and monomers containing imide groups. The above-mentioned monomers containing any functional group can be used individually or in combination of two or more.

[0041] When the monomer component constituting the acrylic polymer contains the above-mentioned arbitrary functional group-containing monomer, the content of the arbitrary functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exhibiting the effects of using the arbitrary functional group-containing monomer, the content of the arbitrary functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, is appropriate to be 0.5% by weight or more, and may be 1% by weight or more. Furthermore, from the viewpoint of easily balancing the adhesive performance in relation to n-heptyl acrylate and carboxyl group-containing monomer, the content of the arbitrary functional group-containing monomer in the monomer component is appropriate to be 40% by weight or less, is 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 the arbitrary functional group-containing monomer in the monomer component can be, for example, less than 3% by weight, may be less than 1% by weight, may be less than 0.5% by weight, may be less than 0.3% by weight, and may be less than 0.1% by weight. The technology disclosed herein can preferably be implemented in a manner in which the monomer component of the acrylic polymer substantially does not contain the arbitrary functional group-containing monomer.

[0042] Furthermore, when a hydroxyl group-containing monomer is used as the above-mentioned optional functional group-containing monomer, its content may be approximately 0.001% by weight or more, approximately 0.01% by weight or more, or approximately 0.02% by weight or more of the total monomer components. Also, the content of the hydroxyl group-containing monomer is appropriately approximately 10% by weight or less of the total monomer components, preferably approximately 5% by weight or less, and more preferably approximately 2% by weight or less. In some embodiments, the content of the hydroxyl group-containing monomer in the monomer components 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 components of the acrylic polymer may not substantially contain the hydroxyl group-containing monomer. According to the technology disclosed herein, the desired effect can be achieved without relying on the hydroxyl group-containing monomer.

[0043] The proportion of carboxyl group-containing monomers in the total functional group-containing monomers (including carboxyl group-containing monomers) used as copolymer components of acrylic polymers is preferably 30% by weight or more, more preferably 50% 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. For example, it may be 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 carboxyl group-containing monomers in the total functional group-containing monomers is 100% by weight, but for example, it may be 95% by weight or less.

[0044] The monomer components constituting the acrylic polymer may include other copolymer components other than the functional group-containing monomers mentioned above for purposes such as improving cohesiveness. Examples of other copolymer 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)acrylate (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylate (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 mentioned above can be used individually or in combination of two or more.

[0045] The amount of such other copolymer components is not particularly limited and can be appropriately selected according to the purpose and application, but from the viewpoint of appropriately exhibiting the effects of use, it is appropriate to set it to 0.05% by weight or more, and may be set to 0.5% by weight or more. Furthermore, from the viewpoint of easily balancing the adhesive performance, it is appropriate to set the content of other copolymer components in the monomer component to 20% by weight or less, and from the viewpoint of suitably exhibiting the adhesive properties based on the essential monomer component, it is preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably less than 5% by weight, and may be, for example, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be preferably implemented in a manner in which the monomer component does not substantially contain other copolymer components.

[0046] Acrylic polymers may also contain polyfunctional monomers as other monomer components, having at least two polymerizable functional groups (typically radical polymerizable functional groups) that have unsaturated double bonds, such as (meth)acryloyl groups or vinyl groups. By using polyfunctional monomers as monomer components, the cohesive force of the adhesive layer can be increased. Polyfunctional monomers can be used as crosslinking agents. Polyfunctional monomers are not particularly limited and include, for example, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, etc. Polyfunctional monomers can be used individually or in combination of two or more.

[0047] The amount of polyfunctional monomer used is not particularly limited and can be appropriately set so as to achieve the purpose of using the polyfunctional monomer. The amount of polyfunctional monomer used can be approximately 3% by weight or less of the monomer component, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less). The lower limit of the amount used when using polyfunctional monomer is not particularly limited as long as it is greater than 0% by weight. Usually, by using an amount of polyfunctional monomer of approximately 0.001% by weight or more of the monomer component (for example, approximately 0.01% by weight or more), the effect of using the polyfunctional monomer can be appropriately achieved.

[0048] The biomass-carbon ratio of the monomer components constituting the above-mentioned acrylic polymer (the biomass-carbon ratio of the acrylic polymer) may be, for example, 1% or more, 10% or more is appropriate, preferably 30% or more, more preferably 50% or more (for example, more than 50%), and may also be 70% or more, 80% or more, or even 90% to 100%. By designing in this way, an acrylic adhesive that takes into consideration the reduction of reliance on fossil fuel-based materials can be obtained.

[0049] The method for obtaining acrylic polymers is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. As for the monomer supply method when performing solution polymerization, a batch supply 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 employed. 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, around 20°C to 170°C (typically around 40°C to 140°C).

[0050] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0051] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and so on. Another example of polymerization initiators is a redox initiator, which is a combination of a peroxide and a reducing agent. Such polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used can be the usual amount, for example, it can be selected from a range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of the total monomer components.

[0052] As the acrylic polymer, an acrylic polymer with a weight-average molecular weight (Mw) greater than 600,000 is used. This yields an adhesive that exhibits good cohesive force, providing high adhesion to dissimilar materials while maintaining sufficient holding power. The Mw of the acrylic polymer is preferably 650,000 or more. In some embodiments, the Mw of the acrylic polymer is suitable, for example, 700,000 or more, preferably 750,000 or more, more preferably 800,000 or more, even more preferably 850,000 or more, and particularly preferably 900,000 or more (e.g., over 900,000). By setting a high Mw of the acrylic polymer to increase the cohesive force of the adhesive, for example, the monomer composition can be adapted to prioritize adhesion to dissimilar materials. Furthermore, from the viewpoint of adhesion to dissimilar materials, ease of synthesis, etc., the Mw of the acrylic polymer is usually suitable to be approximately 3 million or less, preferably 2 million or less, more preferably 1.5 million or less, even more preferably 1.2 million or less, and particularly preferably 1 million or less. In some embodiments, from the viewpoint of improving adhesion to dissimilar materials, the Mw of the acrylic polymer may be 900,000 or less, 850,000 or less, 800,000 or less, 750,000 or less, or 700,000 or less.

[0053] The Mw of acrylic polymers can be measured by gel permeation chromatography (GPC) and determined as a value equivalent to standard polystyrene. Specifically, it can be measured using the "HLC-8220GPC" (manufactured by Tosoh Corporation) GPC measuring device under the following conditions. The same applies to the examples described later. [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 columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: Product name "TSKgel SuperH-RC" 1 piece (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0054] (Adhesive-forming resin) In some preferred embodiments, the adhesive layer includes a tackifying resin. Using a tackifying resin can improve adhesion to both highly polar and low-polarity materials. Furthermore, by using an appropriate amount of tackifying resin, the gel fraction of the adhesive layer can be adjusted to a suitable range. The tackifying resin is not particularly limited, and various tackifying resins can be used, such as rosin-based tackifying resins, terpene-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, phenol-based tackifying resins, and ketone-based tackifying resins. Such tackifying resins can be used individually or in combination of two or more.

[0055] Specific examples of rosin-based tackifying resins include unmodified rosins (raw rosin) such as gum rosin, wood rosin, and tall oil rosin; modified rosins obtained by hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins; the same applies hereinafter); and various other rosin derivatives. Examples of the above rosin derivatives include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., rosin esters) and modified rosin with alcohols (i.e., modified rosin esters); unsaturated fatty acid modified rosins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acids; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid modified rosins, or unsaturated fatty acid modified rosin esters; metal salts of rosins (especially rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; and rosinphenol resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and then thermal polymerization. Among these, rosin esters are preferred.

[0056] While 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, glycerol esters, and pentaerythritol esters.

[0057] Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers; and modified terpene resins obtained by modifying these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modification, etc.). An example of the above-mentioned modified terpene resin is terpenephenol resin.

[0058] Terpene phenol resins refer to polymers containing terpene and phenol residues, and the concept encompasses both copolymers of terpenes and phenol compounds (terpene-phenol copolymer resins) and homopolymers or copolymers of terpenes modified with phenol (phenol-modified terpene resins). Specific examples of terpenes that constitute such terpene phenol resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-isomers, l-isomers, and d / l-isomers (dipentene)). Hydrogenated terpene phenol resins refer to hydrogenated terpene phenol resins that have a structure obtained by hydrogenating such terpene phenol resins. They are sometimes also called hydrogenated terpene phenol resins.

[0059] Examples of hydrocarbon-based tackifying resins include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymer (C5 / C9) petroleum resins, hydrogenated versions thereof (for example, alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified versions thereof (for example, maleic anhydride modified versions), coumarone resins, coumarone indene resins, and other various hydrocarbon-based resins.

[0060] In some embodiments, it is preferable to use at least one selected from rosin-based tackifying resins and terpene-based tackifying resins as the tackifying resin. Embodiments using at least one selected from rosin-based tackifying resins and terpene-based tackifying resins include embodiments in which the tackifying resin consists only of rosin-based tackifying resins, embodiments in which the tackifying resin consists only of terpene-based tackifying resins (e.g., terpene phenol resins), and embodiments in which the tackifying resin consists of both rosin-based and terpene-based tackifying resins. By incorporating rosin-based and / or terpene-based tackifying resins into the acrylic adhesive, excellent adhesive properties such as adhesive strength can be easily obtained. In some preferred embodiments, the total proportion of rosin-based and terpene-based tackifying resins in the total tackifying resin contained in the adhesive layer can be, for example, more than approximately 50% by weight (more than 50% by weight and 100% by weight or less), more than approximately 70% by weight, more than approximately 80% by weight, more than approximately 90% by weight, more than 95% by weight, or more than 99% by weight.

[0061] In some embodiments, it is more preferable to use a rosin-based tackifying resin as the tackifying resin. By incorporating a rosin-based tackifying resin into the adhesive, the adhesion to high-polarity and low-polarity materials can be preferably improved. Among these, rosin esters are preferred. The proportion of rosin-based tackifying resin in the total tackifying resin contained in the adhesive layer can be, for example, more than approximately 50% by weight, may be approximately 70% by weight or more, or may be approximately 80% by weight or more. The techniques disclosed herein can preferably be implemented in an embodiment in which substantially all of the tackifying resin (for example, approximately 97% by weight or more, or 99% by weight or more, and may be 100% by weight) is a rosin-based tackifying resin.

[0062] When a rosin-based tackifying resin is used as the tackifying resin, the content ratio of tackifying resins other than the rosin-based tackifying resin (non-rosin-based tackifying resin) in the adhesive layer is appropriately set to, for example, 40 parts by weight or less per 100 parts by weight of acrylic polymer. This allows the effect of incorporating rosin ester to be suitably exhibited. The amount of non-rosin-based tackifying resin used is preferably about 20 parts by weight or less (for example, less than 20 parts by weight) per 100 parts by weight of acrylic polymer, but may also be about 10 parts by weight or less, about 5 parts by weight or less, or about 1 part by weight or less.

[0063] In some preferred embodiments, the content of terpene phenol resin as a tackifying resin in the adhesive layer is, for example, 40 parts by weight or less per 100 parts by weight of acrylic polymer, and may be 35 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less. By adopting such an amount of terpene phenol resin, an effect of improving adhesion to low-polarity materials is easily obtained. Here, the statement that the content of terpene phenol resin is X parts by weight or less per 100 parts by weight of acrylic polymer is used to encompass both the case that the adhesive layer does not contain terpene phenol resin and the case that the terpene phenol resin is contained in a ratio of X parts by weight or less per 100 parts by weight of acrylic polymer. In some embodiments, the content of terpene phenol resin in the adhesive layer may be 3 parts by weight or less per 100 parts by weight of acrylic polymer, and may be in the range of 1 part by weight or less (e.g., 0 to 0.1 parts by weight). In some other embodiments, the content of terpene phenol resin in the adhesive layer may be, for example, 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, 7 parts by weight or more, or 9 parts by weight or more, per 100 parts by weight of acrylic polymer. By using an appropriate amount of terpene phenol resin within the above range, the effects of the technology disclosed herein can be preferably realized. In some other preferred embodiments using terpene phenol resin, the content of terpene phenol resin in the adhesive layer may be 10 parts by weight or more, 12 parts by weight or more, or 14 parts by weight or more, per 100 parts by weight of acrylic polymer. By using an appropriate amount of terpene phenol resin, it is possible to improve adhesion to high-polarity materials while maintaining adhesion to low-polarity materials. The amount of terpene phenol resin used within the above range is applicable to embodiments in which only terpene phenol resin is used as the tackifying resin, and embodiments in which terpene phenol resin and non-terpene phenol resin (preferably rosin-based tackifying resin) are used in combination.In some embodiments, the amount of terpene phenol resin used within the above range can be preferably adopted, for example, in an embodiment where it is used in combination with a non-terpene phenol resin (preferably a rosin-based tackifying resin).

[0064] In some embodiments, as the tackifying resin, a tackifying resin T with a softening point of less than 150 °C L is used. By using the tackifying resin T L a higher adhesive force can be obtained for both high-polarity materials and low-polarity materials. The softening point of the above-mentioned tackifying resin T L may be less than 140 °C, and may also be less than 130 °C, from the perspective of improving the adhesive force for high-polarity materials and low-polarity materials. In some preferred embodiments, the softening point of the above-mentioned tackifying resin T L is less than 120 °C, suitably less than 110 °C, preferably approximately 105 °C or less, more preferably approximately 100 °C or less, still more preferably approximately 95 °C or less (for example, less than 95 °C), particularly preferably approximately 90 °C or less (for example, approximately 85 °C or less). The lower limit of the softening point of the tackifying resin T L is not particularly limited. In some embodiments, the softening point of the tackifying resin T L may be, for example, approximately 50 °C or higher, approximately 60 °C or higher, approximately 65 °C or higher, approximately 70 °C or higher, from the perspective of exerting appropriate cohesive force. In some other embodiments, the softening point of the tackifying resin T L may be, for example, approximately 80 °C or higher, approximately 90 °C or higher, approximately 100 °C or higher, approximately 110 °C or higher.

[0065] As the tackifying resin T L one kind appropriately selected from those of the tackifying resins exemplified above with a softening point of less than 150 °C can be used alone or in combination of two or more kinds. In some embodiments, the tackifying resin T L preferably contains at least one kind selected from rosin-based tackifying resins and terpene-based tackifying resins, and more preferably contains a rosin-based tackifying resin. The tackifying resin T LThis may contain one type of rosin-based tackifying resin alone, or it may contain a combination of two or more types of rosin-based tackifying resins.

[0066] While not particularly limited, tackifying resin T L Examples of rosin-based tackifying resins that can be preferably used include rosin esters such as unmodified rosin esters and modified rosin esters. 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 methyl esters and glycerin esters, can be used as tackifying resin T L It can be used as such.

[0067] An adhesive layer according to some preferred embodiments includes an adhesive resin T L It contains hydrogenated rosin ester. Also, tackifying resin T L This may include non-hydrogenated rosin esters. Here, non-hydrogenated rosin esters are a comprehensive concept that refers to all rosin esters other than hydrogenated rosin esters among the rosin esters mentioned above. Examples of non-hydrogenated rosin esters include unmodified rosin esters, disproportionated rosin esters, and polymerized rosin esters. Tackifying resin T L The rosin esters may include a combination of hydrogenated rosin esters and non-hydrogenated rosin esters, or may contain only one or more hydrogenated rosin esters, or may contain only one or more non-hydrogenated rosin esters. The adhesive layer according to some preferred embodiments includes the tackifying resin T L The rosin esters contained in this product include only one or more hydrogenated rosin esters.

[0068] Tackifying resin T L The rosin-based tackifying resin may also contain other tackifying resins. As the other tackifying resins, one or more resins can be appropriately selected from the tackifying resins exemplified above that have a softening point of less than 150°C, and used alone or in combination of two or more.

[0069] In some embodiments, the tackifying resin T L The proportion of rosin-based tackifying resin in the total can be, for example, more than approximately 50% by weight, more than approximately 65% ​​by weight, or more than approximately 75% by weight. The technology disclosed herein relates to tackifying resin T L This can preferably be carried out in a manner in which substantially all of it (for example, approximately 97% or more by weight, or 99% or more by weight, and may be 100% by weight) is a rosin-based tackifying resin.

[0070] Also, adhesive resin T L For example, it may or may not include a tackifying resin having a softening point of less than 50°C, more preferably around 40°C or less (typically rosin-based, terpene-based, hydrocarbon-based, etc., such as hydrogenated rosin methyl ester). Such a low-softening-point tackifying resin may be a liquid tackifying resin that is liquid at 30°C. The liquid tackifying resin can be used alone or in combination of two or more types. The content of the liquid tackifying resin is determined from the viewpoint of cohesive force, etc., of the tackifying resin T L It can be approximately 30% or less of the total weight, and it is appropriate to be approximately 10% or less of the total weight (for example, 0-10%), and it may also be approximately 2% or less of the total weight (0.5-2%), or even less than 1% of the total weight.

[0071] Tackifying resin T L Content (of two or more tackifying resins T L The total amount of (if any) is included is not particularly limited, but it is appropriate to use approximately 100 parts by weight or less (for example, less than 100 parts by weight) per 100 parts by weight of acrylic polymer. L By limiting the amount used to a predetermined amount or less, it is possible to improve adhesion to high-polarity and low-polarity materials while maintaining sufficient holding power. In some preferred embodiments, the tackifying resin T LFrom the viewpoint of holding power, etc., the amount used should be 90 parts by weight or less per 100 parts by weight of the acrylic polymer, preferably 80 parts by weight or less, but may also be 60 parts by weight or less, 55 parts by weight or less, 50 parts by weight or less, or 45 parts by weight or less. In some other embodiments, the tackifying resin T L The amount used may be 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less (for example, less than 20 parts by weight) per 100 parts by weight of the acrylic polymer. In addition, in some embodiments, from the viewpoint of improving adhesive strength, the tackifying resin T L The amount used is, for example, more than 10 parts by weight, may be 12 parts by weight or more, 14 parts by weight or more, more than 15 parts by weight, and 20 parts by weight or more, preferably 30 parts by weight or more, more preferably 35 parts by weight or more, even more preferably 38 parts by weight or more, may be 45 parts by weight or more, may be 50 parts by weight or more (for example more than 50 parts by weight), may be 55 parts by weight or more, may be 60 parts by weight or more, may be 65 parts by weight or more, may be 70 parts by weight or more, and may be 75 parts by weight or more. The acrylic polymer containing n-heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifying resins, so it is possible to include more tackifying resin and improve adhesion to dissimilar materials while maintaining holding power.

[0072] In some embodiments, the adhesive layer is made of tackifying resin T L And, a tackifying resin T with a softening point of 150°C or higher (for example, 150°C to 200°C) H It may also include a combination of the following: Tackifying resin T H For example, one of the tackifying resins exemplified above with a softening point of 150°C or higher can be used alone or in combination of two or more.

[0073] In this specification, the softening point of the tackifying resin is defined as the value measured based on the softening point test method (ring-ball method) specified in JIS K5902 and JIS K2207. Specifically, the sample is melted as quickly as possible at the lowest possible temperature and carefully filled into a ring placed on a flat metal plate, taking care not to create bubbles. After cooling, the portion raised from the plane including the upper end of the ring is cut off with a slightly heated knife. Next, a support (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 in 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 the glycerin so that they do not come into contact with each other, and the temperature of the glycerin is maintained at 20°C ± 5°C for 15 minutes. Next, the steel ball is placed in the center of the surface of the sample in the ring and placed in a fixed position on the support. Next, maintain a distance of 50 mm from the top of the ring to the glycerin surface, place a thermometer, and position the center of the thermometer's mercury bulb at the same height as the center of the ring, then heat the container. The flame of the Bunsen burner used for heating should be positioned midway between the center and edge of the container's bottom to ensure even heating. After heating begins and the bath temperature reaches 40°C, the rate of increase must be 5.0 ± 0.5°C per minute. Read the temperature when the sample gradually softens, flows out of the ring, and finally contacts the bottom plate; this is defined as the softening point. Two or more softening points should be measured simultaneously, and the average value should be used.

[0074] In some embodiments, the tackifying resin T L It is preferable that the tackifying resin T accounts for more than 50% by weight of the total amount of tackifying resin contained in the adhesive layer. L The effect of the contained substance is easily expressed. The tackifying resin T is a percentage of the total amount of tackifying resin contained in the adhesive layer. L The proportion of the tackifying resin T LFrom the viewpoint of more effectively exhibiting the effects of use, the amount 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 also be 95% by weight or more, or 98% by weight or more. In some preferred embodiments, the tackifying resin contained in the adhesive layer is substantially tackifying resin T L It consists only of the following. In this embodiment, the tackifying resin T is the total amount of tackifying resin contained in the adhesive layer. L The proportion is in the range of 99-100% by weight.

[0075] While not particularly limited, in some embodiments, the tackifying resin may include a tackifying resin having a hydroxyl value of less than 70 mgKOH / g. Among these, a tackifying resin having a hydroxyl value of less than 60 mgKOH / g (more preferably less than 50 mgKOH / g, and even more preferably less than 45 mgKOH / g) is preferred. Hereinafter, a tackifying resin having a hydroxyl value of less than 70 mgKOH / g may be referred to as a "low hydroxyl value resin." Using a tackifying resin containing such a low hydroxyl value resin, an adhesive layer having high adhesion to both high-polarity and low-polarity materials can be preferably realized. The lower limit of the hydroxyl value of the low hydroxyl value resin is 0 mgKOH / g or more, and may be approximately 10 mgKOH / g or more, or approximately 15 mgKOH / g or more. The low hydroxyl value resin can be used alone or in combination of two or more types. As the low hydroxyl value resin, one type can be appropriately selected from the tackifying resins exemplified above that have a hydroxyl value of less than 70 mgKOH / g, and this can be used alone or in combination of two or more types. In some embodiments, the low hydroxyl value resin preferably comprises at least one type selected from rosin-based tackifying resins and terpene-based tackifying resins, and more preferably comprises a rosin-based tackifying resin. The low hydroxyl value resin may contain one type of rosin-based tackifying resin alone, or it may contain two or more types of rosin-based tackifying resins in combination. Furthermore, the low hydroxyl value resin may contain the tackifying resin T mentioned above. L It may also be the case that the tackifying resin T H It may also be the case that the tackifying resin T L It is preferable that the resin is a low hydroxyl value resin.

[0076] In some embodiments, it is preferable that the low hydroxyl value resin accounts for more than 50% by weight of the total amount of tackifying resin contained in the adhesive layer. This preferably improves adhesion to low-polarity materials. In some preferred embodiments, the proportion of the low hydroxyl value resin to the total amount of tackifying resin contained in the 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 also be 95% by weight or more, or 98% by weight or more, from the viewpoint of more effectively exhibiting the effects of using the low hydroxyl value resin. In some preferred embodiments, the tackifying resin contained in the adhesive layer consists substantially only of the low hydroxyl value resin. In such embodiments, the proportion of the low hydroxyl value resin to the total amount of tackifying resin contained in the adhesive layer is in the range of 99 to 100% by weight.

[0077] While not particularly limited, the adhesive layer disclosed herein preferably contains less than 5 parts by weight of a tackifying resin with a hydroxyl value of 70 mgKOH / g or more (hereinafter also referred to as "high hydroxyl value resin") per 100 parts by weight of the acrylic polymer. By limiting the amount of high hydroxyl value resin used in this way, an improvement in adhesion strength to low polarity materials is easily obtained. Here, the statement that the content of high hydroxyl value resin is less than 5 parts by weight per 100 parts by weight of the acrylic polymer is used to encompass both the case where the adhesive layer does not contain high hydroxyl value resin and the case where the high hydroxyl value resin is contained in a ratio of less than 5 parts by weight per 100 parts by weight of the acrylic polymer. The content of high hydroxyl value resin in the adhesive layer is preferably less than 3 parts by weight per 100 parts by weight of the acrylic polymer, and more preferably in the range of 1 part by weight or less (for example, 0 to 0.1 parts by weight).

[0078] Here, the hydroxyl value can be the value measured by the potentiometric titration method 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 approximately 12.5 g (approximately 11.8 mL) of acetic anhydride, add pyridine to make a total volume of 50 mL, and stir thoroughly before use. Alternatively, take approximately 25 g (approximately 23.5 mL) of acetic anhydride, add pyridine to make a total volume of 100 mL, and stir thoroughly before use. (2) A 0.5 mol / L potassium hydroxide ethanol solution is used as the measurement reagent. (3) Prepare toluene, pyridine, ethanol, and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of the sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) After heating the flask in a 100°C bath for 70 minutes, allow it to cool, add 35 mL of toluene as a solvent from the top of the condenser and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. To complete the decomposition, heat it again in the bath for 10 minutes and allow it to cool. (3) Wash the condenser 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 a 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the resulting titration curve is taken as the endpoint. (6) For a blank test, perform steps (1) to (5) above without adding a sample. 3.Calculation The hydroxyl value is calculated using the following formula. Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D Here, B: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample. f: Factor of 0.5 mol / L potassium hydroxide ethanol solution. S: Weight of the sample (g), D: Acid value, 28.05: Half the molecular weight of potassium hydroxide, 56.11. That is the case.

[0079] When the adhesive layer disclosed herein contains a tackifying resin, a plant-derived tackifying resin (plant-based tackifying resin) may be preferred as the tackifying resin from the viewpoint of improving the biomass carbon ratio of the adhesive layer. Examples of plant-based tackifying resins include the rosin-based tackifying resin and terpene-based tackifying resin mentioned above. One type of plant-based tackifying resin may be used alone or in combination of two or more types. When the adhesive layer disclosed herein contains a tackifying resin, the proportion of the plant-based tackifying resin to the total amount of tackifying resin 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 plant-based tackifying resin to the total amount of tackifying resin is 90% by weight or more (e.g., 95% by weight or more, typically 99-100% by weight). The technology disclosed herein can preferably be implemented in a manner that substantially does not contain tackifying resins other than plant-based tackifying resins.

[0080] The content of the tackifying resin (the total amount if two or more types of tackifying resins are included) is not particularly limited, but it is appropriate to set it to about 100 parts by weight or less (for example, less than 100 parts by weight) per 100 parts by weight of acrylic polymer. By limiting the amount of tackifying resin used to a predetermined amount or less, it is possible to improve the adhesion to high-polarity and low-polarity materials while maintaining sufficient holding power. In some preferred embodiments, from the viewpoint of holding power, the amount of tackifying resin used is appropriate to be 90 parts by weight or less per 100 parts by weight of acrylic polymer, preferably 80 parts by weight or less, but may also be 60 parts by weight or less, 55 parts by weight or less, 50 parts by weight or less, or 45 parts by weight or less. In some other embodiments, the amount of tackifying resin used may be 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less (for example, less than 20 parts by weight) per 100 parts by weight of acrylic polymer. Furthermore, in some embodiments, from the viewpoint of improving adhesive strength, the amount of tackifying resin used is, for example, more than 10 parts by weight, may be 12 parts by weight or more, may be 14 parts by weight or more, may be more than 15 parts by weight, and 20 parts by weight or more is appropriate, preferably 30 parts by weight or more, more preferably 35 parts by weight or more, even more preferably 38 parts by weight or more, may be 45 parts by weight or more, may be 50 parts by weight or more (for example, more than 50 parts by weight), may be 55 parts by weight or more, may be 60 parts by weight or more, may be 65 parts by weight or more, may be 70 parts by weight or more, and may be 75 parts by weight or more. The acrylic polymer containing n-heptyl acrylate as a monomer unit used in the technology disclosed herein has good compatibility with tackifying resin, so by including more tackifying resin, it is possible to improve the adhesive strength to dissimilar materials while maintaining holding power.

[0081] In the technologies disclosed herein, the total content of the acrylic polymer and tackifying resin in the adhesive layer is appropriately set to achieve the effects of the technologies disclosed herein and is not limited to a specific range. From the viewpoint of favorably achieving the effects of the technologies disclosed herein, the total amount of the acrylic polymer and tackifying resin contained in the adhesive layer according to some preferred embodiments is preferably more than 50% by weight, preferably about 70% by weight or more, more preferably about 90% by weight or more, and even more preferably 95% by weight or more (for example, 95% by weight or more and 100% by weight or less than 100% by weight), and may be 97% by weight or more.

[0082] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may optionally contain a crosslinking agent. The type of crosslinking agent is not particularly limited, and examples 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, silane coupling agents, and the like. The crosslinking agent can 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 acquire cohesive force, and a desirable balance of adhesion and retention force to dissimilar materials can be achieved. The adhesive layer in the technology disclosed herein may contain the crosslinking agent in the form after the crosslinking reaction, in the form before the crosslinking reaction, in a partially crosslinked form, or in intermediate or combined forms therein. Typically, the crosslinking agent is contained in the adhesive layer exclusively in the form after the crosslinking reaction.

[0083] As isocyanate-based crosslinking agents, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. Isocyanate-based crosslinking agents can be used individually or in combination of two or more.

[0084] Examples of polyfunctional isocyanates 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; and 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, and the like.

[0085] 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.

[0086] 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'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Examples include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropanediisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0087] Examples of preferred polyfunctional isocyanates include those having an average of three or more isocyanate groups per molecule. Such trifunctional or trifunctional isocyanates may be macromers (typically dimers or trimers) of bifunctional or trifunctional or trifunctional isocyanates, derivatives (e.g., addition reaction products of a polyhydric alcohol and two or more polyfunctional isocyanates), polymers, etc. Examples of polyfunctional isocyanates include dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts of isocyanurate structures), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other such polyfunctional isocyanates. Examples of commercially available polyfunctional isocyanates include "Duranate TPA-100" from Asahi Kasei Chemicals, and "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096" from Tosoh Corporation.

[0088] The amount of isocyanate-based crosslinking agent used is not particularly limited. For example, it can be approximately 0.1 parts by weight or more per 100 parts by weight of acrylic polymer. From the viewpoint of achieving both cohesive force and adhesion, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of acrylic polymer can be, for example, 0.5 parts by weight or more, 1.0 part by weight or more is appropriate, and preferably 1.5 parts by weight or more. Furthermore, the amount of isocyanate-based crosslinking agent used is appropriately 10 parts by weight or less per 100 parts by weight of acrylic polymer, preferably less than 5 parts by weight, more preferably less than 4.0 parts by weight, and even more preferably less than 3.0 parts by weight (for example, 2.5 parts by weight or less).

[0089] As the epoxy crosslinking agent, any compound having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups in one molecule are preferred. Epoxy crosslinking agents can be used individually or in combination of two or more.

[0090] While not particularly limited, specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available epoxy crosslinking agents include "TETRAD-C" and "TETRAD-X" from Mitsubishi Gas Chemical Company, "Epiclon CR-5L" from DIC Corporation, "Denacol EX-512" from Nagase ChemteX Corporation, and "TEPIC-G" from Nissan Chemical Industries, Ltd.

[0091] The amount of epoxy crosslinking agent used is not particularly limited. For example, the amount of epoxy crosslinking agent used can be greater than 0 parts by weight and approximately 1 part by weight or less (typically about 0.001 to 1 part by weight) per 100 parts by weight of acrylic polymer. From the viewpoint of suitably exhibiting the effect of improving cohesive force, it is appropriate to use an amount of epoxy crosslinking agent of approximately 0.005 parts by weight or more per 100 parts by weight of acrylic polymer, preferably approximately 0.01 parts by weight or more, and more preferably approximately 0.02 parts by weight or more. Furthermore, from the viewpoint of improving adhesion to the adherend, it is appropriate to use an amount of epoxy crosslinking agent of approximately 0.5 parts by weight or less per 100 parts by weight of acrylic polymer, preferably approximately 0.2 parts by weight or less, more preferably approximately 0.1 parts by weight or less (for example, less than 0.1 parts by weight), and it may also be 0.07 parts by weight or less, or 0.04 parts by weight or less.

[0092] In some preferred embodiments, an epoxy crosslinking agent is used in combination with at least one crosslinking agent having a different type of crosslinkable functional group than the epoxy crosslinking agent. According to the techniques disclosed herein, by using a crosslinking agent other than an epoxy crosslinking agent (i.e., a crosslinking agent having a different type of crosslinkable reactive group than the epoxy crosslinking agent; hereinafter also referred to as a "non-epoxy crosslinking agent") in combination with an epoxy crosslinking agent, it is possible to suitably achieve both adhesion to dissimilar materials and high retention strength.

[0093] The types of non-epoxy crosslinking agents that can be used in combination with epoxy crosslinking agents are not particularly limited, and can be appropriately selected from the crosslinking agents described above. Non-epoxy crosslinking agents can be used individually or in combination of two or more.

[0094] In some preferred embodiments, isocyanate-based crosslinking agents can be used as non-epoxy crosslinking agents. For example, by using epoxy-based crosslinking agents and isocyanate-based crosslinking agents in combination, better adhesive properties can be achieved. The relationship between the content of epoxy-based crosslinking agents and the content of non-epoxy crosslinking agents (preferably isocyanate-based crosslinking agents) is not particularly limited. The content of epoxy-based crosslinking agents can be, for example, approximately 1 / 10 or less of the content of non-epoxy crosslinking agents (preferably isocyanate-based crosslinking agents). From the viewpoint of more favorably balancing adhesion to the adherend and cohesive force, the content of epoxy-based crosslinking agents is appropriate to be approximately 1 / 30 or less of the content of non-epoxy crosslinking agents, preferably approximately 1 / 50 or less, more preferably approximately 1 / 75 or less, and may be approximately 1 / 90 or less. Furthermore, from the viewpoint of suitably exhibiting the effects of using a combination of epoxy crosslinking agents and non-epoxy crosslinking agents (preferably isocyanate crosslinking agents), it is generally appropriate for the content of the epoxy crosslinking agent to be approximately 1 / 1000 or more of the content of the non-epoxy crosslinking agent, for example, approximately 1 / 500 or more, preferably approximately 1 / 300 or more, more preferably 1 / 150 or more, and even more preferably 1 / 120 or more.

[0095] The total amount of crosslinking agent used is not particularly limited and can be selected from a range of approximately 0.005 parts by weight or more (e.g., 0.01 parts by weight or more, typically 0.1 parts by weight or more) or approximately 10 parts by weight or less (e.g., approximately 8 parts by weight or less, preferably approximately 5 parts by weight or less) per 100 parts by weight of acrylic polymer.

[0096] (Other additives) In addition to the components described above, the adhesive composition may optionally contain various additives common in the field of adhesives, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, anti-aging agents, UV absorbers, antioxidants, and light stabilizers. Such additives can be used by conventional methods if they are conventionally known, and do not particularly characterize the present invention, so a detailed explanation is omitted.

[0097] The adhesive layer (layer consisting of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-type adhesive composition, a hot-melt adhesive composition, or an active energy ray-curable adhesive composition. An aqueous adhesive composition refers to an adhesive composition in which an adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) mainly composed of water, and typically includes what is called a water-dispersible adhesive composition (a composition in which at least a part of the adhesive is dispersed in water). A solvent-type adhesive composition refers to an adhesive composition in which an adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-type adhesive composition, one or more of the organic solvents exemplified above as those that can be used in solution polymerization (such as toluene and ethyl acetate) can be used without particular limitation. The technology disclosed herein can preferably be implemented in a form comprising an adhesive layer formed from a solvent-type adhesive composition, from the viewpoint of adhesive properties, etc.

[0098] The adhesive layer disclosed herein can be formed by conventionally known methods. For example, a method can be employed in which an adhesive layer is formed by applying an adhesive composition to a peelable surface (release surface) or a non-peelable surface and drying it. In the case of an adhesive sheet having a substrate, for example, a method can be employed in which an adhesive layer is formed by directly applying (typically coating) the adhesive composition to the substrate and drying it (direct method). Alternatively, a method can be employed in which an adhesive layer is formed on a peelable surface (release surface) by applying an adhesive composition to the surface and drying it, and then the adhesive layer is transferred to the substrate (transfer method). From the viewpoint of productivity, the transfer method is preferred. As the release surface, the surface of a release liner or the back surface of a released substrate can be used. Although the adhesive layer disclosed herein is typically formed continuously, it is not limited to this form, and may be formed in a regular or random pattern such as dots or stripes.

[0099] The adhesive composition can be applied using conventionally known coaters, such as gravure roll coaters, die coaters, or bar coaters. Alternatively, the adhesive composition may be applied by impregnation or curtain coating methods. From the viewpoint of promoting the crosslinking reaction and improving manufacturing efficiency, it is preferable to dry the adhesive composition under heating. The drying temperature can be, for example, around 40 to 150°C, and is usually preferably around 60 to 130°C. After drying the adhesive composition, aging may be performed for the purpose of adjusting the migration of components within the adhesive layer, promoting the crosslinking reaction, and alleviating any strain that may exist within the adhesive layer.

[0100] (thickness) The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer with an appropriate thickness in the range of 0.1 to 500 μm can be adopted depending on the application and intended use. In some embodiments, from the viewpoint of avoiding the adhesive sheet becoming excessively thick, the thickness of the adhesive layer is usually appropriate to be approximately 100 μm or less, preferably approximately 70 μm or less, more preferably approximately 60 μm or less, and even more preferably approximately 50 μm or less. The thickness of the adhesive layer can be approximately 35 μm or less, and may be approximately 30 μm or less, for example. An adhesive layer with a limited thickness can be well met in response to the demands for thinning and weight reduction. Generally, when the thickness of the adhesive layer decreases, the adhesion to the adherend tends to decrease, but according to the technology disclosed herein, a configuration having an adhesive layer with a limited thickness can achieve sufficient adhesion to both high-polarity and low-polarity materials. From the viewpoint of adhesion to the adherend, the lower limit of the thickness of the adhesive layer is suitable in some embodiments to be approximately 0.5 μm or more, may be approximately 1 μm or more, is advantageous to be approximately 3 μm or more, preferably approximately 10 μm or more, more preferably approximately 12 μm or more (e.g., greater than 12 μm), even more preferably approximately 15 μm or more, and may be approximately 18 μm or more. In some preferred embodiments, the thickness of the adhesive layer is greater than 20 μm, may be 24 μm or more, and may be 27 μm or more. The greater the thickness of the adhesive layer, the easier it tends to be to achieve the target adhesive strength. The adhesive sheet disclosed herein may be an adhesive sheet having an adhesive layer of the above thickness on both sides of the substrate. Furthermore, in a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer on each side of the substrate, the first adhesive layer and the second adhesive layer may be of the same thickness or may be of different thicknesses.

[0101] (Gel fraction) The gel fraction of the adhesive layer disclosed herein is less than 70% (by weight). By using an adhesive with a gel fraction of less than 70%, sufficient adhesive strength can be achieved not only for highly polar materials but also for low-polarity materials. In some embodiments, the gel fraction of the adhesive layer is preferably less than 65%, may be less than 60%, may be less than 55%, may be less than 50%, may be less than 45%, may be less than 40%, and may be less than 35%. Furthermore, from the viewpoint of obtaining sufficient holding power, in some preferred embodiments, the gel fraction of the adhesive layer is 20% or more, more preferably 25% or more, even more preferably 30% or more, may be 35% or more, may be 40% or more, may be 45% or more, may be 50% or more, may be 55% or more, and may be 60% or more. By adjusting the gel fraction of the adhesive layer within the above range depending on the monomer composition, Mw of the acrylic polymer and the adhesive composition, a suitable balance between adhesive strength and holding power can be achieved. The gel fraction described above is measured specifically by the method described in the examples below.

[0102] (Biomass carbon ratio) In some embodiments, the adhesive layer contains biomass-derived material, and its biomass-carbon ratio may be above a predetermined value. The biomass-carbon ratio of the adhesive layer is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass-carbon ratio of the adhesive means that less fossil resource-based material, such as petroleum, is used. From this viewpoint, a higher biomass-carbon ratio of the adhesive is preferable. For example, the biomass-carbon ratio of the adhesive layer may be 55% or more, may be 60% or more, may be 70% or more, may be 75% or more, may be 80% or more, and may be over 80%. The upper limit of the biomass-carbon ratio is 100% by definition, may be 99% or less, and from the viewpoint of material availability, may be 95% or less, or 90% or less. From the viewpoint of easily exhibiting good adhesive performance, in some embodiments, the biomass-carbon ratio of the adhesive layer may be, for example, 90% or less, may be 85% or less, or 80% or less.

[0103] <Base material> In embodiments where the adhesive sheet disclosed herein is in the form of a single-sided adhesive type or a double-sided adhesive type adhesive sheet with a substrate, the substrate supporting (backing) the adhesive layer can be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, composites thereof, etc. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluororesin film; cellophane, etc. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, topcoat paper, etc. Examples of cloth include woven fabrics and nonwoven fabrics made by combining or blending various fibrous materials. Examples of the above fibrous materials include cotton, rayon, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, etc. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foamed 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 that supports the adhesive layer is also called the substrate layer in adhesive sheets.

[0104] The base material may be made from biomass-derived materials or from non-biomass-derived materials. From the viewpoint of producing adhesive sheets that take into consideration the reduction of reliance on fossil fuel-based materials, biomass-derived base material materials (typically resin films) are preferably used.

[0105] Furthermore, the base material may be formed using recyclable materials or recycled materials (also called recycled materials). Resin film is preferably used as such recycled material. Since resin film (for example, polyester film such as PET film) is recyclable, regardless of whether plant-derived materials are used, reuse of used resin film enables sustainable reproduction and reduces environmental impact. Such recyclable resin film or recycled resin film is also called recycled film. The above-mentioned recycled material (e.g., recycled film) may be formed from biomass-derived materials or from non-biomass-derived materials.

[0106] As the substrate constituting the adhesive sheet with a substrate, a resin film is preferably used as the base film. The base film is typically an independently shape-retaining (independent) component. The substrate in the art disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include a colored layer, a reflective layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the base film.

[0107] The above-mentioned resin film is a film whose main component is a resin material (for example, a component that is present in the resin film in an amount exceeding 50% by weight). Examples of resin films include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; cellophane; and the like. The resin film may also be a rubber film such as natural rubber film or butyl rubber film. Among these, polyester films are preferred from the viewpoint of handling and processability, and PET films are particularly preferred among them.

[0108] In this specification, "resin film" typically refers to a non-porous sheet and is a concept distinct from so-called nonwoven or woven fabrics (in other words, a concept excluding nonwoven or woven fabrics). The above resin film may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, such a resin film may be non-foamed. Here, a non-foamed resin film refers to a resin film that has not undergone any intentional treatment to become a foam. Specifically, a non-foamed resin film may be a resin film with a foaming ratio of less than 1.1 times (for example, less than 1.05 times, typically less than 1.01 times).

[0109] The above-mentioned substrate (e.g., resin film) may contain various additives as needed, such as fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), anti-aging agents, antioxidants, UV absorbers, antistatic agents, lubricants, and plasticizers. The proportion of each additive is less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0110] The above-mentioned substrate (e.g., resin film) may have a single-layer structure, or it may have a multilayer structure of two, three, or more layers. From the viewpoint of shape stability, a single-layer structure is preferred for the substrate. In the case of a multilayer structure, it is preferable that at least one layer (preferably all layers) is a layer having a continuous structure of the above-mentioned resin (e.g., polyester resin). The method for manufacturing the substrate (typically resin film) is not particularly limited and may be any conventionally known method as appropriate. For example, conventionally known general film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be appropriately employed.

[0111] The surface of the substrate may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer. Such surface treatments may be intended to improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the substrate.

[0112] Furthermore, when the technology disclosed herein is implemented in the form of a single-sided adhesive sheet with a substrate, the back surface of the substrate may be subjected to a release treatment as needed. The release treatment may involve applying a release agent such as a general silicone-based, long-chain alkyl-based, or fluorine-based release agent in a thin film typically of about 0.01 μm to 1 μm (e.g., 0.01 μm to 0.1 μm). By performing such a release treatment, effects such as facilitating the unwinding of a roll of adhesive sheets can be obtained.

[0113] In an adhesive sheet comprising a substrate, the thickness of the substrate is not particularly limited. From the viewpoint of avoiding the adhesive sheet becoming excessively thick, the thickness of the substrate can be, for example, approximately 200 μm or less, preferably approximately 150 μm or less, and more preferably approximately 100 μm or less. Depending on the purpose and manner of use of the adhesive sheet, the thickness of the substrate may be approximately 70 μm or less, approximately 50 μm or less, or approximately 30 μm or less (for example, approximately 25 μm or less). In some embodiments, the thickness of the substrate film layer may be approximately 20 μm or less, approximately 15 μm or less, or approximately 10 μm or less (for example, approximately 5 μm or less). By reducing the thickness of the substrate, the thickness of the adhesive layer can be increased even if the total thickness of the adhesive sheet is the same. This can be advantageous from the viewpoint of improving adhesion to the adherend or substrate. The lower limit of the substrate is not particularly limited. From the viewpoint of handling and processability of the adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (for example, 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 even be about 25 μm or more.

[0114] <Removable Liner> In the technologies disclosed herein, release liners can be used in the formation of adhesive layers, the manufacture of adhesive sheets, storage of adhesive sheets before use, distribution, and shaping. The release liners are not particularly limited, and for example, release liners having a release treatment layer on the surface of a liner substrate such as a resin film or paper, or release liners made of fluoropolymers (such as polytetrafluoroethylene) can be used. The release treatment layer may 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 for the liner substrate, similar to the substrate for the adhesive sheet described above, materials made from biomass or recycled materials (such as recycled film) can preferably be used.

[0115] <Total thickness of adhesive sheet> The total thickness of the adhesive sheet disclosed herein (including an adhesive layer and possibly a base layer, but not a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, approximately 1 mm or less, may be approximately 500 μm or less, can be approximately 300 μm or less, and from the viewpoint of thinning, approximately 200 μm or less is appropriate, and may be approximately 150 μm or less (for example, approximately 100 μm or less). In some preferred embodiments, the thickness of the adhesive sheet can be approximately 50 μm or less, for example, approximately 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), may be approximately 3 μm or more, preferably approximately 10 μm or more, more preferably approximately 15 μm or more, may be approximately 50 μm or more, and may be approximately 100 μm or more. Adhesive sheets having a thickness of a predetermined value or more tend to have good adhesion to the adherend and also have excellent handling properties. In the case of adhesive sheets without a base material, the thickness of the adhesive layer becomes the total thickness of the adhesive sheet.

[0116] <Characteristics of adhesive sheets> In some embodiments, the adhesive sheet preferably has a 180-degree peel strength (adhesion to SUS) of approximately 15 N / 25 mm or more (e.g., 17 N / 25 mm or more) against a stainless steel plate. An adhesive sheet exhibiting such adhesion to SUS can exhibit excellent adhesion to highly polar materials. The above adhesion to SUS is more preferably approximately 20 N / 25 mm or more, even more preferably approximately 25 N / 25 mm or more, particularly preferably 30 N / 25 mm or more, and may be 32 N / 25 mm or more. There is no particular upper limit to the above adhesion to SUS, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually, for example, approximately 50 N / 25 mm or less. The above adhesion to SUS is measured using a SUS plate as the adherend, under measurement conditions of 23°C, 50% RH, tensile speed of 300 mm / min, and peel angle of 180 degrees. More specifically, it is measured by the method described in the examples below.

[0117] The adhesive sheet disclosed herein preferably has a 180-degree peel strength (PP adhesion strength) of approximately 10 N / 25 mm or more against polypropylene. An adhesive sheet exhibiting such PP adhesion strength adheres well to low-polarity materials and can exhibit high adhesive reliability to the above-mentioned adherend. The PP adhesion strength is more preferably approximately 12 N / 25 mm or more, even more preferably approximately 14 N / 25 mm or more, particularly preferably approximately 16 N / 25 mm or more, and may be approximately 18 N / 25 mm or more (for example, approximately 20 N / 25 mm or more). There is no particular upper limit to the PP adhesion strength, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually, for example, approximately 40 N / 25 mm or less, and may be 30 N / 25 mm or less. The PP adhesion strength is measured using PP as the adherend, under measurement conditions of 23°C, 50% RH, tensile speed of 300 mm / min, and peel angle of 180 degrees. More specifically, it is measured by the method described in the examples below.

[0118] The adhesive sheet disclosed herein preferably has a 180-degree peel strength (PE adhesion strength) of approximately 5 N / 25 mm or more against polyethylene. An adhesive sheet exhibiting such PE adhesion strength can demonstrate sufficient adhesive reliability to low-polarity materials. The above PE adhesion strength is more preferably approximately 7 N / 25 mm or more, even more preferably approximately 10 N / 25 mm or more, particularly preferably approximately 12 N / 25 mm or more, and may be 14 N / 25 mm or more (for example, approximately 15 N / 25 mm or more). There is no particular upper limit to the above PE adhesion strength, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually, for example, approximately 30 N / 25 mm or less, and may be 25 N / 25 mm or less. The above PE adhesion strength is measured using PE as the adherend, under measurement conditions of 23°C, 50% RH, tensile speed of 300 mm / min, and peel angle of 180 degrees. More specifically, it is measured by the method described in the examples below.

[0119] The adhesive sheets disclosed herein may exhibit adhesive strength to PP and PE at or above a predetermined value, as described above. Since adhesive sheets exhibiting the above-mentioned adhesive strength to PP and PE can provide stable and sufficient adhesive reliability to dissimilar materials, including various low-polarity materials, they have a wide range of applications and are therefore useful.

[0120] The adhesive sheet disclosed herein may exhibit a displacement distance of 10 mm or less from the adherend after 1 hour from the start of a retention strength test conducted at 80°C, with an adhesive area of ​​10 mm × 20 mm, a load of 1.5 kg, and for 1 hour. Such an adhesive sheet has high cohesive force and sufficient retention strength. The displacement distance in the above retention strength test is preferably 5 mm or less, more preferably 3 mm or less, and even more preferably 1 mm or less (0 to 0.1 mm). More specifically, the above retention strength test is carried out by the method described in the examples below.

[0121] In some embodiments, the adhesive sheet contains biomass-derived material, and its biomass-carbon ratio may be above a predetermined value. The biomass-carbon ratio of the adhesive sheet is, for example, 1% or more, may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass-carbon ratio of the adhesive sheet means that less fossil resource-based material, such as petroleum, is used. From this viewpoint, a higher biomass-carbon ratio of the adhesive sheet is preferable. For example, the biomass-carbon ratio of the adhesive sheet may be 55% or more, may be 60% or more, may be 70% or more, may be 75% or more, may be 80% or more, and may be over 80%. The upper limit of the biomass-carbon ratio is 100% by definition, may be 99% or less, may be 95% or less, or 90% or less from the viewpoint of material availability. From the viewpoint of easily exhibiting good adhesive performance, in some embodiments, the biomass-carbon ratio of the adhesive sheet may be, for example, 90% or less, may be 85% or less, or 80% or less.

[0122] <Application> The adhesive sheets disclosed herein are not particularly limited in their applications and can be used in a variety of applications. The adhesive sheets disclosed herein exhibit high adhesive strength to both high-polarity and low-polarity materials and have sufficient holding power, making them suitable for bonding and fixing components made of high-polarity materials, including metal components, and components made of low-polarity materials. For example, they are suitable for applications where the components to be bonded have high-polarity or low-polarity surfaces and long-term adhesive reliability is required. Examples of materials constituting such high-polarity surfaces include metal materials such as stainless steel, glass materials, and polyester resin components such as PET. Examples of materials constituting low-polarity surfaces include polyolefin resins such as polyethylene (PE) and polypropylene (PP), which are generally known to have low surface free energy, as well as fluoropolymers (such as polytetrafluoroethylene), polystyrene, polyoxymethylene, and polyvinyl acetate. Among these, the adhesive sheets disclosed herein are particularly preferred for bonding and fixing adherends having surfaces composed of polyolefins such as PE and PP, and materials containing fluoropolymers.

[0123] Suitable applications for the adhesive sheet disclosed herein include fixing components in electronic devices such as home appliances, office automation equipment, and portable electronic devices. Since the components constituting the above-mentioned electronic devices may include highly polar materials such as metals and low-polarity materials such as PE, PP, and fluororesins, it is beneficial to apply the adhesive sheet disclosed herein to achieve adhesive fixing with excellent adhesive reliability to various dissimilar materials, including both highly polar and low-polarity materials. Examples of the above-mentioned electronic devices include various home appliances and personal computers (desktop, notebook, tablet, etc.). Non-limiting examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information systems, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" means not merely being able to carry, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0124] Figure 4 is a schematic example of a portable electronic device (smartphone) using the adhesive sheet disclosed herein. As shown in Figure 4, a battery (heat-generating element) 540 is built into the 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 is a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the components constituting the portable electronic device 500. The portable electronic device 500 is equipped 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 (component joining means) of the portable electronic device described above.

[0125] Furthermore, since the adhesive sheets disclosed herein may, in some embodiments, have an adhesive layer containing an acrylic polymer with a high biomass-carbon ratio, they can be used as a substitute for conventional acrylic adhesives (i.e., acrylic adhesives with a low biomass-carbon ratio) in various applications where such adhesives are used, thereby contributing to reducing reliance on fossil fuel-based materials. The adhesive sheets disclosed herein can be preferably used as adhesive sheets with reduced reliance on fossil fuel-based materials.

[0126] The matters disclosed in this specification include the following: [1] Electronic equipment, An adhesive sheet is attached to the components that make up the electronic device. The aforementioned adhesive sheet has an adhesive layer containing an acrylic polymer, The aforementioned acrylic polymer is a polymer of monomer components including n-heptyl acrylate and a carboxyl group-containing monomer. The monomer component of the acrylic polymer contains more than 3% by weight of the carboxyl group-containing monomer. The gel fraction of the adhesive layer is less than 70%. The aforementioned acrylic polymer has a weight-average molecular weight greater than 600,000, and is used in electronic devices. [2] The electronic device according to [1] above, wherein the surface of the member is made of a material selected from metal, polyolefin resin, and fluororesin. [3] The electronic device described in [1] or [2] above, wherein the electronic device is a home appliance. [4] The electronic device described in [1] or [2] above, wherein the electronic device is a portable electronic device. [5] The electronic device according to any one of [1] to [4] above, wherein the adhesive composition for forming the adhesive layer comprises a crosslinking agent. [6] The electronic device according to any one of [1] to [5] above, wherein the adhesive layer includes a tackifying resin. [7] The electronic device according to any one of [1] to [6] above, wherein the thickness of the adhesive layer is 0.1 to 500 μm. [8] The electronic device according to any one of [1] to [7] above, wherein the gel fraction of the adhesive layer is 20% or more and less than 70%. [9] The electronic device according to any one of [1] to [8] above, wherein the adhesive sheet is a substrate-less double-sided adhesive sheet consisting only of the adhesive layer.

[10] The electronic device according to any one of [1] to [8] above, wherein the adhesive sheet comprises a base material and the adhesive layer provided on at least one surface of the base material.

[0127]

[11] Having an adhesive layer containing an acrylic polymer, The aforementioned acrylic polymer is a polymer of monomer components including n-heptyl acrylate and a carboxyl group-containing monomer. The monomer component of the acrylic polymer contains more than 3% by weight of the carboxyl group-containing monomer. The gel fraction of the adhesive layer is less than 70%. An adhesive sheet in which the weight-average molecular weight of the aforementioned acrylic polymer is greater than 600,000.

[12] The adhesive sheet according to

[11] above, wherein the adhesive composition for forming the adhesive layer comprises a crosslinking agent.

[13] The adhesive sheet according to

[11] or

[12] above, wherein the adhesive layer includes a tackifying resin.

[14] The adhesive sheet according to any one of

[11] to

[13] above, wherein the thickness of the adhesive layer is 0.1 to 500 μm.

[15] The adhesive sheet according to any one of

[11] to

[14] above, wherein the gel fraction of the adhesive layer is 20% or more and less than 70%.

[16] An adhesive sheet according to any of

[11] to

[15] above, wherein the 180-degree peel strength to stainless steel plate is 15 N / 25 mm or more.

[17] An adhesive sheet according to any of

[11] to

[16] above, wherein the 180-degree peel strength against polypropylene is 10 N / 25 mm or more.

[18] An adhesive sheet according to any of

[11] to

[17] above, wherein the 180-degree peel strength against polyethylene is 5 N / 25 mm or more.

[19] An adhesive sheet as described in any of

[11] to

[18] above, wherein the shear distance in a holding strength test conducted at 80℃, with an adhesive area of ​​10mm x 20mm, a load of 1.5kg, and for 1 hour is 10mm or less.

[20] The adhesive sheet according to any one of

[11] to

[19] above, which is a substrate-less double-sided adhesive sheet consisting only of the adhesive layer.

[21] An adhesive sheet according to any one of

[11] to

[19] above, comprising a base material and the adhesive layer provided on at least one surface of the base material.

[22] An adhesive sheet as described in any of

[11] to

[21] above, used for fixing components in electronic equipment.

[23] Electronic device containing an adhesive sheet as described in any of

[11] to

[21] above. [Examples]

[0128] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments. In the following description, "parts" and "%" refer to weight unless otherwise specified.

[0129] <Evaluation Method> [Gel fraction] Approximately 0.1 g of adhesive sample (weight Wg1) is wrapped in a drawstring-like shape with a porous polytetrafluoroethylene membrane (weight Wg2) having an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). As the porous polytetrafluoroethylene (PTFE) membrane, the product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product available from Nitto Denko Corporation is used. The package is immersed in 50 mL of ethyl acetate and kept at room temperature (approximately 23°C) for 7 days to elute only the sol component in the adhesive layer outside the film. Then, the package is removed, the ethyl acetate adhering to the outer surface is wiped off, and the package is dried at 130°C for 2 hours. The weight of the package (Wg4) is then measured. The gel fraction of the adhesive layer can be determined by substituting each value into the following formula. Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] × 100

[0130] [Adhesion to SUS (stainless steel)] Under a measurement environment of 23°C and 50%RH, a 50μm thick PET film is attached to one adhesive surface of an adhesive sheet (double-sided adhesive sheet) as a backing, and the sheet is cut to a size of 25mm wide and 100mm long to prepare a measurement sample. Under a measurement environment of 23°C and 50%RH, the other adhesive surface of the measurement sample is pressed onto the surface of a stainless steel plate (SUS304BA plate) that has been cleaned with ethyl acetate by applying pressure with a 2kg roller for one back-and-forth motion. After leaving this in the same environment for 72 hours, the peel strength (adhesion to SUS) [N / 25mm] is measured using a universal tensile and compression testing machine in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300mm / min and a peel angle of 180 degrees.

[0131] [Adhesion to PP] Under a measurement environment of 23°C and 50% RH, a 50 μm thick PET film is attached to one adhesive surface of an adhesive sheet (double-sided adhesive sheet) as a backing, and the sheet is cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. Under a measurement environment of 23°C and 50% RH, the other adhesive surface of the measurement sample is pressed onto the surface of a polypropylene board (PP board) that has been cleaned with ethanol by applying pressure with a 2 kg roller for one back-and-forth motion. After leaving this in the same environment for 72 hours, the peel strength (adhesion to PP) [N / 25 mm] is measured using a universal tensile and compression tester in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees. As the PP board, for example, the product name "Kobe Poly Sheet PP-N-AN" (thickness 2 mm) manufactured by Showa Denko Materials Co., Ltd. is used.

[0132] [Adhesion to PE] Under a measurement environment of 23°C and 50% RH, a 50 μm thick PET film is attached to one adhesive surface of an adhesive sheet (double-sided adhesive sheet) as a backing, and the sheet is cut to a size of 25 mm wide and 100 mm long to prepare a measurement sample. Under a measurement environment of 23°C and 50% RH, the other adhesive surface of the measurement sample is pressed onto the surface of a polyethylene board (PE board) that has been cleaned with ethanol by applying pressure with a 2 kg roller for one back-and-forth motion. After leaving this in the same environment for 72 hours, the peel strength (adhesion to PE) [N / 25 mm] is measured using a universal tensile and compression tester in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees. As the PE board, for example, the product name "Kobe Poly Sheet EL-N-AN" (thickness 2 mm) manufactured by Showa Denko Materials Co., Ltd. is used.

[0133] For the measurement of each of the above peel strengths, a universal tensile and compression testing machine, such as the "Tensile and Compression Testing Machine, TG-1kN" manufactured by Minebea Co., Ltd. or an equivalent product, is used. When performing the above peel strength measurement on a single-sided adhesive sheet, PET film backing is not required. However, if the substrate thickness is thin (for example, if the substrate thickness is 25 μm or less), PET film backing may be used.

[0134] [Holding force] Under conditions of 23°C and 50% RH, a 50 μm thick PET film is attached to one side of an adhesive sheet (double-sided adhesive sheet) as a backing, and the sheet is cut to a width of 10 mm and a length of 10 mm to prepare a measurement sample. The other side of the measurement sample is then attached to a bakelite plate (phenol resin plate) as the substrate, with an adhesive area of ​​10 mm in width and 20 mm in length (adhesion area of ​​200 mm²). 2 The sample is pressed down by passing a 2kg roller back and forth once. The sample attached to the substrate in this manner is left in the same environment for 30 minutes. Then, the substrate is suspended so that the length of the sample is vertical, and a load of 1.5kg is applied to the free end of the sample. The sample is left in an 80°C environment for 1 hour with the load applied, in accordance with JIS Z0237. After 1 hour, the displacement distance [mm] of the upper end of the sample from the initial attachment position is measured (displacement distance after 1 hour). The measurement is performed using 3 samples for each adhesive sheet (i.e., N=3), and the arithmetic mean is calculated. If the above displacement distance is 10mm or less, it is judged as passing; if the above displacement distance is more than 10mm or the sample falls off within 1 hour, it is judged as failing.

[0135] <Example 1> (Synthesis of acrylic polymers) In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 90 parts of n-heptyl acrylate (n-HpA) and 10 parts of acrylic acid (AA) as monomer components, along with ethyl acetate as the polymerization solvent, were charged and stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this manner, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was carried out at 60°C to 70°C for 8 hours to obtain a solution of acrylic polymer (A1). The weight-average molecular weight (Mw) of acrylic polymer (A1) was 670,000. The above-mentioned n-HpA is a compound synthesized using biomass-derived heptyl alcohol, and has a biomass-derived heptyl group at its ester terminus.

[0136] (Preparation of adhesive composition) The adhesive composition according to this example was prepared by stirring and mixing 100 parts of the above acrylic polymer (A1), 40 parts of a rosin-based tackifying resin (product name "Haritack SE10", manufactured by Harima Chemicals, hydrogenated rosin glycerin ester, softening point 75-85°C, hydroxyl value 25-40 mg KOH / g), and 2 parts of an isocyanate-based crosslinking agent (product name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation).

[0137] (Making adhesive sheets) The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release film (product name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100°C for 2 minutes to form a 30 μm thick adhesive layer. The release surface of a 25 μm thick polyester release film (product name "Diafoil MRF", 25 μm thick, manufactured by Mitsubishi Chemical Corporation) was then bonded to this adhesive layer. In this way, a 30 μm thick substrate-less double-sided adhesive sheet was obtained, with both sides protected by the two polyester release films.

[0138] <Example 2> In preparing the adhesive composition in Example 1, 0.02 parts of an epoxy crosslinking agent (trade name "TETRAD-C", manufactured by Mitsubishi Gas Chemical Company, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was further added to 100 parts of an acrylic polymer (A1), and the mixture was stirred to prepare the adhesive composition according to this example. A substrate-less double-sided adhesive sheet according to this example was prepared in the same manner as in Example 1, except that the obtained adhesive composition was used.

[0139] <Examples 3-5> A solution of acrylic polymer (A2) was obtained in the same manner as the synthesis of acrylic polymer (A1), except that the monomer composition was changed to 94 parts n-HpA and 6 parts AA, and the concentration of monomer components during polymerization was adjusted. Using the above acrylic polymer (A2), adhesive compositions for each example were prepared in the same manner as in Example 2, except that the composition was changed to those shown in Table 1, and substrate-less double-sided adhesive sheets for each example were made using these adhesive compositions.

[0140] <Example 6> A solution of acrylic polymer (A3) was obtained in the same manner as the synthesis of acrylic polymer (A1), except that the monomer composition was changed to 96 parts n-HpA and 4 parts AA. The adhesive compositions according to this example were prepared in the same manner as in Example 2, except that the above acrylic polymer (A3) was used, and a substrate-less double-sided adhesive sheet according to this example was made using the adhesive composition.

[0141] <Examples 7-9> Except for changing the type of tackifying resin as shown in Table 1, adhesive compositions for each example were prepared in the same manner as in Example 6, and substrate-less double-sided adhesive sheets for each example were made using these adhesive compositions. Specifically, in Example 7, instead of 40 parts of the rosin-based tackifying resin in Example 6, 25 parts of the rosin-based tackifying resin and 15 parts of a terpene-based tackifying resin (product name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., terpene phenol resin, softening point approximately 115°C, hydroxyl value 30-60 mg KOH / g) were used as the tackifying resin; in Example 8, instead of 40 parts of the rosin-based tackifying resin in Example 6, 15 parts of the terpene-based tackifying resin were used as the tackifying resin; and in Example 9, the amount of the rosin-based tackifying resin used was changed from 40 parts in Example 6 to 15 parts.

[0142] <Comparative Example 1> Except for adjusting the concentration of monomer components during polymerization, a solution of acrylic polymer (A4) with a lower molecular weight than acrylic polymer (A3) was obtained in the same manner as the synthesis of acrylic polymer (A3). The adhesive composition according to this example was prepared in the same manner as in Example 6, except for using the above acrylic polymer (A4), and a substrate-less double-sided adhesive sheet according to this example was made using this adhesive composition.

[0143] <Comparative Examples 2-3> A solution of acrylic polymer (A5) was obtained in the same manner as the synthesis of acrylic polymer (A1), except that the monomer composition was changed to 97 parts n-HpA and 3 parts AA. Using the above acrylic polymer (A5), adhesive compositions for each example were prepared in the same manner as in Example 2, except that the composition was changed to that shown in Table 1, and substrate-less double-sided adhesive sheets for each example were prepared using these adhesive compositions.

[0144] <Comparative Examples 4-5> Solutions of acrylic polymers (A6) and (A7) were obtained in essentially the same manner as the synthesis of acrylic polymer (A1), except that the monomer composition was changed to 95 parts n-butyl acrylate (BA) or 95 parts 2-ethylhexyl acrylate (2EHA) and 5 parts AA. Adhesive compositions for each example were prepared in the same manner as in Example 2, except that the above acrylic polymer (A6) or (A7) was used, and substrate-less double-sided adhesive sheets for each example were prepared using these adhesive compositions.

[0145] Table 1 shows an overview of the adhesive sheets for each example and the evaluation results.

[0146] [Table 1]

[0147] As shown in Table 1, the adhesives in Examples 1 to 9 contained n-heptyl acrylate as a monomer component, an acrylic polymer with a Mw of over 600,000 containing more than 3% by weight of carboxyl group-containing monomers, and a gel fraction of less than 70%. The adhesives in these examples had an adhesive strength of 15 N / 25 mm or more to SUS, 10 N / 25 mm or more to PP, and 5 N / 25 mm or more to PE, and the results of the retention strength test were also satisfactory (specifically, a shear distance of 1 mm or less). More specifically, Examples 1 and 2, which used the largest amount of carboxyl group-containing monomer, had high adhesive strength to low-polarity materials (PP and PE), and particularly excellent adhesive strength to SUS. Furthermore, the results from Examples 3 to 5 show that the adhesive strength to SUS, PP, and PE can be improved by increasing the amount of tackifying resin. From the results of these examples, it can also be seen that as the amount of tackifying resin increases, the gel fraction of the adhesive layer tends to decrease and the adhesive strength increases. On the other hand, Comparative Example 1, which used an acrylic polymer with an Mw of 600,000, failed the retention strength test. Similarly, Comparative Example 2, which used an acrylic polymer with a copolymerization ratio of 3% carboxyl group-containing monomer (specifically AA), also failed the retention strength test. Comparative Example 3, which increased the amount of crosslinking agent compared to Comparative Example 2, improved the retention strength, but the adhesion strength to SUS, PP, and PE all decreased significantly. Furthermore, the results from Comparative Examples 2 and 3 indicate that if the gel fraction becomes too high, it becomes difficult to satisfy the adhesion strength characteristics. In addition, Comparative Examples 4 and 5, which used alkyl acrylates other than n-heptyl acrylate (BA or 2EHA), could not obtain the same level of adhesion strength as Examples 1 to 9.

[0148] From the above results, it can be seen that by using an adhesive containing an acrylic polymer with n-heptyl acrylate as a monomer component and a gel fraction of less than 70%, sufficient adhesive strength can be obtained not only for highly polar materials but also for low-polarity materials. Furthermore, it can be seen that by copolymerizing the above acrylic polymer with a carboxyl group-containing monomer at a ratio of more than 3% by weight and designing it so that Mw is greater than 600,000, it is possible to improve the holding power while maintaining high adhesive strength to dissimilar materials. It can also be seen that the adhesion to highly polar materials can be improved by using the above carboxyl group-containing monomer. In other words, it can be seen that by using an adhesive in which an acrylic polymer containing n-heptyl acrylate and a monomer component polymer containing more than 3% by weight of a carboxyl group-containing monomer has a gel fraction of less than 70% in the adhesive layer and an acrylic polymer with an Mw greater than 600,000, it is possible to achieve a high level of adhesion to highly polar materials, adhesion to low-polarity materials, and holding power simultaneously.

[0149] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of Symbols]

[0150] 1, 2, 3 Adhesive sheets 10 Supporting base material 10A front page 10B Second side (back) 21 Adhesive layer (first adhesive layer) 21A Adhesive surface (first adhesive surface) 21B Second adhesive surface 22 Adhesive layer (second adhesive layer) 22A Adhesive surface (second adhesive surface) 31,32 Release Liner 100, 200, 300 Adhesive sheets with release liner

Claims

1. It has a pressure-sensitive adhesive layer containing an acrylic polymer, the acrylic polymer is a polymer of monomer components containing 70% by weight or more of n-heptyl acrylate and more than 3% by weight of a carboxyl group-containing monomer; the PSA layer contains a tackifier resin T L having a softening point of less than 150°C; the tackifier resin T L accounts for more than 50 wt % of the total amount of tackifier resins contained in the PSA layer; the pressure-sensitive adhesive layer has a gel fraction of less than 70%; The pressure-sensitive adhesive sheet, wherein the weight average molecular weight of the acrylic polymer is greater than 600,000.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains a crosslinking agent.

3. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer has a thickness of 0.1 to 500 μm.

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer has a gel fraction of 20% or more and less than 70%.

5. 3. The pressure-sensitive adhesive sheet according to claim 1, which has a 180-degree peel strength from a stainless steel plate of 15 N / 25 mm or more.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a 180-degree peel strength from polypropylene of 10 N / 25 mm or more.

7. 3. The pressure-sensitive adhesive sheet according to claim 1, which has a 180-degree peel strength to polyethylene of 5 N / 25 mm or more.

8. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the slippage distance in a holding power test carried out under the conditions of 80°C, an adhesion area of 10 mm x 20 mm, a load of 1.5 kg, and one hour is 10 mm or less.

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

Images