WO2024161910A1 - Adhesive sheet - Google Patents

Abstract

Provided is an adhesive sheet that has an adhesive agent layer containing an acrylic polymer. Monomer components of the acrylic polymer include 2-octyl acrylate (m1), and at least 10 wt% of a co-polymerizable monomer (m3) that is different from the 2-octyl acrylate (m1) and a carboxy group-containing monomer (m2). The adhesive agent layer further contains a tackifier.

Description

Adhesive sheet

The present invention relates to a pressure-sensitive adhesive sheet.
This application claims priority based on Japanese Patent Application No. 2023-014855, filed on February 2, 2023, the entire contents of which are incorporated herein by reference.

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

Japanese Patent No. 5457186

2-octyl acrylate, which is synthesized using 2-octanol, can be obtained from biomass-derived materials, and so its use as an adhesive material that can reduce dependency on fossil resource-based materials is being considered. For example, in Patent Document 1, the adhesive properties (peel adhesion and shear strength) and thermal stability of an adhesive formed from an acrylic polymer synthesized from monomer components of 95% by weight 2-octyl acrylate and 5% by weight acrylic acid are evaluated.

However, adhesives composed of a polymer mainly composed of 2-octyl acrylate (2-octyl acrylate-based polymer) as proposed in Patent Document 1 tend to have a relatively high glass transition temperature and low flexibility. The inventors' investigations revealed that such adhesives have difficulty in obtaining high adhesive strength due to their low flexibility, and that they are particularly lacking in adhesive strength for rough surfaces. As a result of intensive investigations into improving rough surface adhesion while enjoying the effects of containing a 2-octyl acrylate-based polymer, the inventors succeeded in creating an adhesive with good rough surface adhesion and a composition containing an acrylic polymer copolymerized with 2-octyl acrylate, thereby completing the present invention. In other words, the present invention relates to an improvement of an adhesive containing an acrylic polymer synthesized using 2-octyl acrylate, and aims to provide an adhesive sheet that can effectively improve rough surface adhesion and has a composition containing an acrylic polymer copolymerized with 2-octyl acrylate.

According to this specification, a pressure-sensitive adhesive sheet is provided having an adhesive layer containing an acrylic polymer containing 2-octyl acrylate (m1) as a monomer component. The monomer component of the acrylic polymer contains 10% by weight or more of a copolymerizable monomer (m3) different from 2-octyl acrylate (m1) and the carboxyl group-containing monomer (m2). The adhesive layer further contains a tackifier. According to the above configuration, the rough surface adhesion of an adhesive containing an acrylic polymer synthesized using 2-octyl acrylate can be effectively improved. One of the reasons for this, which is not to be interpreted as being particularly limited, is that by copolymerizing a certain amount or more of the above-mentioned copolymerizable monomer (m3) with the acrylic polymer, the side chain crystallinity of the acrylic polymer is reduced, resulting in a lower glass transition temperature of the adhesive, and the adhesive strength improving effect of adding a tackifier is well expressed, and it is believed that these actions effectively improve the rough surface adhesion. In short, according to the above configuration, an adhesive with good rough surface adhesion is realized while obtaining the effect of using 2-octyl acrylate.

In some embodiments, the copolymerizable monomer (m3) has the formula:
_CH2 =C( ^R1 ) ^COOR2
(wherein R ¹ is a hydrogen atom or a methyl group, and R ² is a chain alkyl group having 1 to 20 carbon atoms (excluding 2-octyl group when R ¹ is a hydrogen atom).) By selecting and using an appropriate type of alkyl (meth)acrylate having the above chemical structure as the copolymerizable monomer (m3), it is possible to preferably improve rough surface adhesion while maintaining good adhesive properties.

In some preferred embodiments, the copolymerizable monomer (m3) includes at least one selected from n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). By using at least one selected from BA and 2EHA as the copolymerizable monomer (m3), the effect of improving adhesion to rough surfaces can be better achieved.

In some embodiments, the tackifier preferably includes at least one selected from a rosin-based tackifier resin, a terpene-based tackifier resin, and an acrylic oligomer. By using the above types of tackifier, the effects of the technology disclosed herein can be preferably achieved.

In some embodiments, the adhesive composition for forming the adhesive layer contains a crosslinking agent. By using a crosslinking agent, the cohesive strength of the adhesive can be appropriately increased.

In some embodiments, the weight average molecular weight (Mw) of the acrylic polymer is 400,000 or more. By using an acrylic polymer with a large Mw, it is easy to obtain an adhesive with good high-temperature properties. In addition, by using the high-molecular-weight acrylic polymer in combination with a tackifier, it is possible to preferably achieve both good high-temperature properties and rough-surface adhesion.

In some embodiments, the dispersity (Mw/Mn) of the acrylic polymer is 2 or more and less than 50. The dispersity (Mw/Mn) is determined from the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic polymer. An acrylic polymer having a dispersity (Mw/Mn) in the above range has a predetermined molecular weight distribution, and is likely to provide rough surface adhesion due to the wettability based on its low molecular weight, and is likely to provide good adhesive properties due to the cohesive force based on its high molecular weight.

In some preferred embodiments, the adhesive sheet has a 180-degree peel strength against a stainless steel plate (adhesive strength against SUS) of 10 N/20 mm or more. An adhesive sheet having the above-mentioned adhesive strength against SUS can exhibit excellent adhesive strength to the adherend.

The adhesive sheet disclosed herein has improved rough surface adhesion and can be preferably used to fasten various components as an adhesive means with good adhesion reliability even when attached to a rough surface. For example, it is suitable for fastening components in electronic devices including home appliances, office automation equipment, and mobile electronic devices such as smartphones. As described above, this specification provides an electronic device that uses any of the adhesive sheets disclosed herein, in other words, an electronic device that includes the adhesive sheet.

1 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 4 is a cross-sectional view illustrating a schematic configuration of a pressure-sensitive adhesive sheet according to another embodiment. 1 is a front view showing a schematic diagram of an example of a portable electronic device configured to include an adhesive sheet.

Below, preferred embodiments of the present invention are described. Note that matters necessary for the implementation of the present invention other than those specifically mentioned in this specification can be understood by a person skilled in the art based on the teachings on the implementation of the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In addition, in the following drawings, components and parts that perform the same function may be described using the same reference numerals, and duplicate descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the adhesive sheet of the present invention that is actually provided as a product.

As used herein, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state in a temperature range near room temperature and that has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here may generally be a material that has a complex tensile modulus E ^* (1Hz)< ¹⁰⁷ dyne/ ^cm2 (typically, a material that has the above property at 25°C), as defined in "C. A. Dahlquist, "Adhesion: Fundamentals and Practice", McLaren & Sons, (1966) P. 143".

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

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

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

The structure of an adhesive sheet according to another embodiment is shown in FIG. 2. The adhesive sheet 2 is configured as a substrate-attached single-sided adhesive sheet including a sheet-like 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 the intention of separating the adhesive layer 21 from the support substrate 10. As shown in FIG. 2, the adhesive sheet 2 before use may be a component of an adhesive sheet 200 with a release liner in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, at least the side facing the adhesive layer 21 being the release surface. Alternatively, the release liner 31 may be omitted, and a support substrate 10 with a second surface 10B being the release surface may be used, and the adhesive sheet 2 may be rolled up so that the adhesive surface 21A is protected by contacting the second surface (rear surface) 10B of the support substrate 10.

The structure of an adhesive sheet according to yet another embodiment is shown in FIG. 3. The adhesive sheet 3 is configured as a substrate-attached double-sided adhesive sheet including a sheet-like support substrate (e.g., a resin film) 10 having a first surface 10A and a second surface 10B, a first 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. As shown in FIG. 3, the adhesive sheet 3 before use may be a component of an adhesive sheet 300 with a release liner 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, 32. Alternatively, the release liner 32 may be omitted, and a release liner 31 with both sides being release surfaces may be used, which is superimposed on the adhesive sheet 3 and rolled up in a spiral shape to form an adhesive sheet with a release liner in which the second adhesive surface 22A is protected by contacting the back surface of the release liner 31 (roll form).

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

Furthermore, although not particularly limited, the technology disclosed herein can be preferably implemented in the form of a substrate-less double-sided adhesive sheet. Substrate-less double-sided adhesive sheets can be made thinner since they do not have a substrate, which can contribute to the miniaturization and space-saving of products to which the double-sided adhesive sheet is applied. Furthermore, substrate-less adhesive sheets can maximize the effect of the adhesive layer in improving adhesion to rough surfaces.

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

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

As the acrylic polymer, a polymer of a monomer component containing 2-octyl acrylate (m1) is used. Acrylic polymers polymerized using a monomer component containing 2-octyl acrylate (m1) tend to have excellent high-temperature properties (e.g. high-temperature adhesive strength) and are preferably used in applications where they may be exposed to high temperatures. In addition, although not limited thereto, 2-octyl acrylate (m1) can be obtained from biomass-derived materials, and therefore the use of 2-octyl acrylate (m1) can reduce dependency on fossil resource-based materials.

In some embodiments, 2-octyl acrylate (m1) is preferably included as the main monomer of the acrylic polymer (the component that is most abundant among the monomer components), and the proportion of 2-octyl acrylate (m1) in the monomer components of the acrylic polymer may be, for example, approximately 34% by weight or more, and is suitably 50% by weight or more (e.g., more than 50% by weight), preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 75% by weight or more (e.g., more than 75% by weight), particularly preferably 80% by weight or more, and may be 82% by weight or more, 84% by weight or more, or 85% by weight or more. By increasing the amount of 2-octyl acrylate (m1) used, the effect of its use (e.g., high temperature properties) can be effectively expressed. On the other hand, from the viewpoint of improving rough surface adhesion by copolymerizing the copolymerizable monomer (m3) described below, the proportion of 2-octyl acrylate (m1) in the monomer components is 90% by weight or less, and in some preferred embodiments, it is 87% by weight or less, may be 85% by weight or less, 80% by weight or less (e.g., less than 80% by weight), may be 75% by weight or less, may be 72% by weight or less, or may be 70% by weight or less.

The monomer component of the acrylic polymer preferably contains a carboxyl group-containing monomer (m2). The carboxyl group-containing monomer (m2) can improve the cohesive strength based on its polarity. When a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used, the carboxyl group of the carboxyl group-containing monomer (m2) can become a crosslinking point of the acrylic polymer. The use of the carboxyl group-containing monomer (m2) can provide better adhesion to adherends such as highly polar materials.

Carboxy group-containing monomers (m2) include, for example, ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid. The carboxy group-containing monomer (m2) may be a monomer having a metal salt of a carboxy group (e.g., an alkali metal salt). The carboxy group-containing monomer (m2) may be used alone or in combination of two or more. Among them, AA and MAA are preferred as the carboxy group-containing monomer (m2). AA is particularly preferred. When one or more types of carboxy group-containing monomers (m2) are used, the proportion of AA in the carboxy group-containing monomer (m2) is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. In a particularly preferred embodiment, the carboxy group-containing monomer (m2) is substantially composed of AA alone.

The proportion of the carboxyl group-containing monomer (m2) in the monomer components of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 0.5% by weight or more, and in some preferred embodiments, 1.0% by weight or more, 2.0% by weight or more, 2.5% by weight or more, 3.0% by weight or more, 3.5% by weight or more, 4.0% by weight or more, 4.5% by weight or more, or 5.0% by weight or more. By increasing the amount of the carboxyl group-containing monomer (m2) used, the cohesive force of the adhesive layer is improved based on the action of the carboxyl group-containing monomer (m2), so that good adhesive properties are easily obtained. In addition, the amount of the carboxyl group-containing monomer (m2) is, for example, appropriately 20% by weight or less of the total monomer components, preferably 15% by weight or less, and more preferably 12% by weight or less. In some preferred embodiments, the amount of the carboxyl group-containing monomer (m2) may be 10% by weight or less, 8.0% by weight or less, 6.0% by weight or less, or 5.0% by weight or less. By reducing the amount of the carboxyl group-containing monomer (m2) used within a certain range, good rough surface adhesion tends to be obtained.

In an embodiment using an acrylic polymer copolymerized with a carboxyl group-containing monomer (m2), the proportion of the carboxyl group-containing monomer (m2) in the total functional group-containing monomers (total functional group-containing monomers including the carboxyl group-containing monomer (m2)) used as a copolymerization component of the acrylic polymer is, from the viewpoint of effectively exerting the effect of copolymerizing the carboxyl group-containing monomer (m2), appropriately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more, and may be, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (for example, 99.9% by weight or more). The upper limit of the proportion of the carboxyl group-containing monomer (m2) in the total functional group-containing monomers is 100% by weight, and may be, for example, 95% by weight or less.

The monomer component of the acrylic polymer contains 10% by weight or more of a copolymerizable monomer (m3) different from 2-octyl acrylate (m1) and the carboxyl group-containing monomer (m2). This effectively improves the rough surface adhesion of an adhesive containing an acrylic polymer synthesized using 2-octyl acrylate (m1). It is believed that this is because copolymerizing a certain amount or more of the copolymerizable monomer (m3) with the acrylic polymer reduces the side chain crystallinity of the acrylic polymer, resulting in a lower glass transition temperature (Tg) of the adhesive. Note that the technology disclosed herein is not limited to the above considerations.

It is important that the proportion of the copolymerizable monomer (m3) in the monomer components of the acrylic polymer is 10% by weight or more. As confirmed by the results of the examples described later, compared to the example in which the copolymerization proportion of the copolymerizable monomer (m3) is 8% by weight, it is considered that by increasing the copolymerization proportion of the copolymerizable monomer (m3) more than that, the effect of lowering the Tg of the adhesive is more easily manifested, and the rough surface adhesion is effectively improved. From such a viewpoint, in some preferred embodiments, the proportion of the copolymerizable monomer (m3) in the above-mentioned monomer components may be 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 22% by weight or more, or 24% by weight or more. By increasing the copolymerization proportion of the copolymerizable monomer (m3), the effect of copolymerization of the copolymerizable monomer (m3) can be preferably obtained. In addition, the upper limit of the proportion of the copolymerizable monomer (m3) in the monomer components is approximately 50% by weight or less (e.g., less than 50% by weight), and may be 40% by weight or less, 30% by weight or less, or 25% by weight or less in some embodiments. In some preferred embodiments, the proportion of the copolymerizable monomer (m3) in the monomer components is less than 25% by weight, and may be 23% by weight or less, 20% by weight or less, 15% by weight or less, or 12% by weight or less. By using an appropriate amount of the copolymerizable monomer (m3) in the above range, it is possible to obtain the effect of using 2-octyl acrylate (m1) while preferably obtaining good rough surface adhesion.

As the copolymerizable monomer (m3), one or more monomers that are different from 2-octyl acrylate (m1) and the carboxyl group-containing monomer (m2) and are copolymerizable with 2-octyl acrylate (m1) can be used without any particular limitation. Suitable examples of the copolymerizable monomer (m3) include alkyl (meth)acrylates other than 2-octyl acrylate (m1). As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used.
CH ₂ =C(R ¹ )COOR ² (1)
Here, R ¹ in the above formula (1) is a hydrogen atom or a methyl group. R ² is a chain alkyl group having 1 to 20 carbon atoms (excluding 2-octyl group when R ¹ is a hydrogen atom). By selecting and using an appropriate type of alkyl (meth)acrylate having the above chemical structure, a pressure-sensitive adhesive having good adhesive properties and good adhesion to rough surfaces can be preferably obtained.

Examples of alkyl (meth)acrylates that can be used as the copolymerizable monomer (m3) 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 (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-octyl (meth)acrylate. Examples of the alkyl (meth)acrylates include isooctyl (meth)acrylate, 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, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more.

As the alkyl (meth)acrylate, either one in which the alkyl group is linear or branched can be used, but from the viewpoint of flexibility, an alkyl (meth)acrylate having a linear alkyl group is preferred. From the same viewpoint, an alkyl acrylate is preferably used as the copolymerizable monomer (m3).

In an embodiment in which an alkyl (meth)acrylate is used as the copolymerizable monomer (m3), the proportion of the alkyl (meth)acrylate in the monomer components of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 1% by weight or more, 5% by weight or more, 8% by weight or more (e.g., more than 8% by weight), or 9% by weight or more. In some preferred embodiments, the proportion of the alkyl (meth)acrylate in the monomer components is 10% by weight or more, more preferably 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 22% by weight or more, or 24% by weight or more. By copolymerizing the alkyl (meth)acrylate in a predetermined amount or more, the effect as the copolymerizable monomer (m3) is preferably obtained, and the effect of using the alkyl (meth)acrylate is also preferably obtained. In addition, the upper limit of the proportion of the alkyl (meth)acrylate in the monomer component is, in some embodiments, approximately 50% by weight or less (e.g., less than 50% by weight), and may be 40% by weight or less, 30% by weight or less, or 25% by weight or less. In some preferred embodiments, the proportion of the alkyl (meth)acrylate in the monomer component is less than 25% by weight, and may be 23% by weight or less, 20% by weight or less, 15% by weight or less, or 12% by weight or less. By using an appropriate amount of alkyl (meth)acrylate within the above range as the copolymerizable monomer (m3), it is possible to obtain the effect of using 2-octyl acrylate (m1) while preferably obtaining good rough surface adhesion.

In an embodiment in which an alkyl (meth)acrylate is used as the copolymerizable monomer (m3), the proportion of the alkyl (meth)acrylate in the copolymerizable monomer (m3) is not particularly limited, and in some embodiments, for example, is 10% by weight or more, may be 30% by weight or more, preferably 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, and even more preferably 90% by weight or more (e.g., 95 to 100% by weight). In an embodiment in which an alkyl (meth)acrylate having a linear alkyl group is used as the copolymerizable monomer (m3), the proportion of the alkyl (meth)acrylate having a linear alkyl group in the copolymerizable monomer (m3) is not particularly limited, and in some embodiments, for example, is 10% by weight or more, may be 30% by weight or more, preferably 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, and even more preferably 90% by weight or more (e.g., 95 to 100% by weight). In addition, in embodiments in which an alkyl acrylate is used as the copolymerizable monomer (m3), the proportion of the alkyl acrylate in the copolymerizable monomer (m3) is not particularly limited, and in some embodiments, for example, is 10% by weight or more, may be 30% by weight or more, is preferably 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, and even more preferably 90% by weight or more (e.g., 95 to 100% by weight).

In some preferred embodiments, an alkyl(meth)acrylate in which R ² in the above formula (1) is a chain alkyl group having 1 to 6 carbon atoms (hereinafter, such a range of carbon atoms may be expressed as "C _1-6 ", and an alkyl(meth)acrylate having an alkyl group in the above range of carbon atoms may be referred to as "C _1-6 alkyl(meth)acrylate" or the like) is used as the copolymerizable monomer (m3). By using a C _1-6 alkyl(meth)acrylate as the copolymerizable monomer (m3), the free volume between polymer molecules increases due to the difference in the side chain structure with 2-octyl acrylate, and flexibility is improved, which makes it easier to obtain good rough surface adhesion. Note that the technology disclosed herein is not limited to the above considerations. As the C _1-6 alkyl(meth)acrylate, from the viewpoint of improving flexibility, a C _2-6 alkyl(meth)acrylate is preferable, a C _2-4 alkyl(meth)acrylate is more preferable, or a C _4-6 alkyl(meth)acrylate may also be preferably used. In addition, the C _1-6 alkyl group may be either linear or branched, but from the viewpoint of flexibility, an alkyl (meth)acrylate having a C _1-6 linear alkyl group is preferred. From the same viewpoint, the use of a C _{1-6 alkyl acrylate is preferred. The C 1-6 alkyl} (meth)acrylate may be used alone or in combination of two or more.

In an embodiment in which a C _1-6 alkyl (meth)acrylate is used as the copolymerizable monomer (m3), the proportion of the C _1-6 alkyl (meth)acrylate (preferably a C _2-6 alkyl (meth)acrylate, more preferably a C _2-4 alkyl (meth)acrylate or a C _4-6 alkyl (meth)acrylate, or for example, a C _1-6 linear alkyl (meth)acrylate; the same applies hereinafter unless otherwise specified) in the monomer components of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 1% by weight or more, 5% by weight or more, 8% by weight or more (e.g., more than 8% by weight), or 9% by weight or more, and in some preferred embodiments, 10% by weight or more, more preferably 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 22% by weight or more, or 24% by weight or more. The upper limit of the proportion of the C _1-6 alkyl (meth)acrylate in the monomer component is about 50% by weight or less (e.g., less than 50% by weight), may be 40% by weight or less, 30% by weight or less, or 25% by weight or less, and in some preferred embodiments, it is less than 25% by weight, may be 23% by weight or less, may be 20% by weight or less, may be 15% by weight or less, or may be 12% by weight or less. The proportion of the C _1-6 alkyl (meth)acrylate in the alkyl (meth)acrylate as the copolymerizable monomer (m3) is not particularly limited, and in some embodiments, it is, for example, 10% by weight or more, or may be 30% by weight or more, preferably 50% by weight or more (e.g., more than 50% by weight), more preferably 70% by weight or more, and even more preferably 90% by weight or more (e.g., 95 to 100% by weight).

In some preferred embodiments, n-butyl acrylate (BA) or 2-ethylhexyl acrylate (2EHA) is used as the copolymerizable monomer (m3). BA and 2EHA may be used alone or in combination. By using BA or 2EHA as the copolymerizable monomer (m3), the resulting adhesive has better flexibility and can better exhibit the effect of improving adhesion to rough surfaces. Of these, the use of BA is particularly preferred.

In embodiments in which BA and/or 2EHA are used as the copolymerizable monomer (m3), the proportion of BA and/or 2EHA in the monomer components of the acrylic polymer is not particularly limited and may be 0.1% by weight or more, 1% by weight or more, 5% by weight or more, 8% by weight or more (e.g., more than 8% by weight), 9% by weight or more, and in some preferred embodiments, 10% by weight or more, more preferably 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 22% by weight or more, or 24% by weight or more. In addition, the upper limit of the proportion of BA and/or 2EHA in the above monomer components is approximately 50% by weight or less (e.g., less than 50% by weight) in some embodiments, may be 40% by weight or less, 30% by weight or less, or 25% by weight or less, and in some preferred embodiments, it is less than 25% by weight, may be 23% by weight or less, 20% by weight or less, 15% by weight or less, or 12% by weight or less.

In addition, the monomer component of the acrylic polymer may contain a functional group-containing monomer (any functional group-containing monomer) other than the carboxy group-containing monomer (m2) as a copolymerizable monomer (m3). Examples of optional functional group-containing monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or contribute to improving adhesive strength include hydroxyl group (OH group)-containing monomers (hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; polypropylene glycol mono(meth)acrylate, etc.), acid anhydride group-containing monomers, amide group-containing monomers ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), amino group-containing monomers (aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, and imide group-containing monomers. The above optional functional group-containing monomers can be used alone or in combination of two or more.

When the monomer component constituting the acrylic polymer contains the above-mentioned optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effect of using the optional functional group-containing monomer, the content of the optional functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, and is suitably 0.5% by weight or more, and may be 1% by weight or more. Also, from the viewpoint of easily balancing the adhesive performance in relation to the monomer component containing, for example, 2-octyl acrylate, the content of the optional functional group-containing monomer in the monomer component is suitably 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less). In some embodiments, the content of the optional functional group-containing monomer in the monomer component is, 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, or may be less than 0.1% by weight. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components of the acrylic polymer are substantially free of any functional group-containing monomer.

In this specification, when the monomer components are substantially free of monomer A (e.g., the optional functional group-containing monomer described above), this means that the monomer A is not used at least intentionally, and it is acceptable for the monomer A to be unintentionally included in an amount of, for example, about 0.01% by weight or less.

Also, a hydroxyl-containing monomer may be used as the optional functional group-containing monomer. In this case, the content of the hydroxyl-containing monomer is suitably about 10% by weight or less (e.g., 0.001 to 10% by weight) of the total monomer components, preferably about 5% by weight or less, and more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl-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 be substantially free of a hydroxyl-containing monomer. According to the technology disclosed herein, rough surface adhesion can be improved by limiting the amount of hydroxyl-containing monomer used or by not using it at all.

The monomer components constituting the acrylic polymer may contain other copolymerization components other than the functional group-containing monomers described above as copolymerizable monomers (m3) for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components can be used alone or in combination of two or more.

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

The acrylic polymer may contain a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, as another monomer component included in the copolymerizable monomer (m3). By using a polyfunctional monomer as a monomer component, the cohesive strength of the adhesive layer can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and examples thereof include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, etc. The polyfunctional monomer can be used alone or in combination of two or more types.

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

In some preferred embodiments, a monomer having a homopolymer glass transition temperature (Tg) of less than 0°C (low Tg monomer) may be used as the copolymerizable monomer (m3). For example, by copolymerizing a predetermined amount or more of the low Tg monomer, the effect of lowering the Tg of the adhesive by copolymerization of the copolymerizable monomer (m3) can be suitably exhibited. The homopolymer Tg of the low Tg monomer may be -10°C or less, or -20°C or less. In some preferred embodiments, the homopolymer Tg of the low Tg monomer is approximately -30°C or less, -35°C or less, -40°C or less, -45°C or less, -50°C or less, -55°C or less, -60°C or less, or -65°C or less. Although not particularly limited, in some embodiments, a monomer having a homopolymer Tg lower than the homopolymer Tg of 2-octyl acrylate (m1) may be preferably used as the low Tg monomer. The lower limit of the homopolymer Tg of the low Tg monomer is, for example, -80°C or higher, suitably -75°C or higher, may be -70°C or higher, may be -65°C or higher, or may be -60°C or higher. The low Tg monomer is not particularly limited, but is preferably an alkyl (meth)acrylate. Suitable examples of the low Tg monomer include, for example, BA and 2EHA. Other examples of the low Tg monomer include alkyl acrylates such as hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, isooctyl acrylate, and isononyl acrylate. The low Tg monomers can be used alone or in combination of two or more.

For the homopolymer Tg of a monomer, the value given in a publicly available source should be used. For example, the values given in "Polymer Handbook" (3rd ed., John Wiley & Sons, Inc., 1989) should be used. If multiple values are given in this document, the highest value should be used.

For monomers whose homopolymer Tg is not listed in the Polymer Handbook, the value obtained by the following measurement method shall be used (see JP 2007-51271 A). Specifically, 100 parts by weight of monomer, 0.2 parts by weight of 2,2'-azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as a polymerization solvent are charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture is stirred for 1 hour while circulating nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. The mixture is then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by weight. The homopolymer solution is then cast onto a release liner and dried to prepare a test sample (sheet-shaped homopolymer) with a thickness of approximately 2 mm. The test sample was punched out into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and the viscoelasticity was measured in shear mode using a viscoelasticity tester (manufactured by TA Instruments Japan, model name "ARES") while applying a shear strain of 1 Hz frequency in the temperature range of -70°C to 150°C at a heating rate of 5°C/min. The temperature corresponding to the peak temperature of tan δ was taken as the Tg of the homopolymer.

In an embodiment in which the low Tg monomer is used as the copolymerizable monomer (m3), the proportion of the low Tg monomer in the monomer components of the acrylic polymer is not particularly limited, and may be 0.1% by weight or more, 1% by weight or more, 5% by weight or more, 8% by weight or more (e.g., more than 8% by weight), or 9% by weight or more. In some preferred embodiments, the proportion of the low Tg monomer in the monomer components is 10% by weight or more, more preferably 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 22% by weight or more, or 24% by weight or more. By copolymerizing the low Tg monomer in a predetermined amount or more, in addition to the effect as the copolymerizable monomer (m3), an effect based on the Tg of the low Tg monomer is preferably obtained. In addition, the upper limit of the proportion of the low Tg monomer in the monomer components is, in some embodiments, approximately 50% by weight or less (e.g., less than 50% by weight), and may be 40% by weight or less, 30% by weight or less, or 25% by weight or less. In some embodiments, the proportion of the low Tg monomer in the monomer components may be less than 25% by weight, 23% by weight or less, 20% by weight or less, 15% by weight or less, or 12% by weight or less.

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

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

In some preferred embodiments, biomass-derived 2-octyl acrylate (biomass 2-octyl acrylate) is used as the 2-octyl acrylate. By using biomass 2-octyl acrylate, it is possible to realize the effects of the technology disclosed herein while reducing the dependency on fossil resource-based materials. The biomass 2-octyl acrylate is an ester of a biomass-derived alkanol (specifically, 2-octanol) and a biomass-derived or non-biomass-derived acrylic acid, and for example, an ester of a biomass-derived alkanol and a non-biomass-derived acrylic acid can be used. In such a compound, only the 2-octyl group is biomass-derived.

The proportion of biomass alkyl (meth)acrylate (e.g., biomass 2-octyl acrylate) in the monomer components of the acrylic polymer is, for example, in some embodiments, 50% by weight or more (e.g., more than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 82% by weight or more, and may be 90% by weight or more. In some embodiments, the proportion of biomass alkyl (meth)acrylate in the monomer components may be 92% by weight or more, 94% by weight or more, or 96% by weight or more. In some embodiments, the proportion of biomass alkyl (meth)acrylate (e.g., biomass 2-octyl acrylate) in the monomer components is, for example, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

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

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

The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one of the following solvents or a mixture of two or more solvents can be used: aromatic compounds such as toluene (typically aromatic hydrocarbons); acetate 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 (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

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

The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and from the viewpoint of obtaining good adhesive properties, an acrylic polymer having a Mw of about 100,000 or more is usually used. In some embodiments, the Mw of the acrylic polymer is preferably 400,000 or more, more preferably 600,000 or more, even more preferably 700,000 or more, and may be 800,000 or more. The higher the Mw of the acrylic polymer, the easier it is to obtain an adhesive with good high-temperature properties, and by using such a high-molecular-weight acrylic polymer in combination with a tackifier, it is possible to preferably achieve both good high-temperature properties and rough surface adhesion. On the other hand, from the viewpoint of adhesive strength, rough surface adhesion, ease of synthesis, etc., the Mw of the acrylic polymer is usually about 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 may be 1 million or less (for example, less than 1 million).

Although not particularly limited, the acrylic polymer is usually one having a dispersity (Mw/Mn) of less than 50, which is expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). The dispersity (Mw/Mn) may be approximately 40 or less, approximately 30 or less, or approximately 20 or less. In some embodiments, the dispersity (Mw/Mn) of the acrylic polymer is preferably 15 or less, and may be 12 or less, 10 or less, 8 or less, or 6 or less. The dispersity (Mw/Mn) of the acrylic polymer is theoretically 1 or more, and from the viewpoint of ease of preparation, etc., it may be, for example, 2 or more, 3 or more, or 4 or more (typically 5 or more). An acrylic polymer having a dispersity (Mw/Mn) in the above range has a predetermined molecular weight distribution, and is likely to have rough surface adhesion due to its wettability based on its low molecular weight, and is likely to have good adhesive properties due to its cohesive force based on its high molecular weight.

Mw, Mn and Mw/Mn can be adjusted by polymerization conditions (time, temperature, etc.), use of a chain transfer agent, etc. The Mw and Mn of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated as standard polystyrene equivalent values. Specifically, they can be measured under the following conditions using a GPC measuring device with the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation). The same applies to the examples described below.
[GPC measurement conditions]
Sample concentration: 0.2% by weight (tetrahydrofuran solution)
Sample injection volume: 10 μL
Eluent: tetrahydrofuran (THF)
Flow rate (flow rate): 0.6 mL/min Column temperature (measurement temperature): 40° C.
column:
Sample column: 1 "TSKguard column Super HZ-H" + 2 "TSKgel Super HZM-H" (manufactured by Tosoh Corporation)
Reference column: one "TSKgel Super H-RC" (manufactured by Tosoh Corporation)
Detector: differential refractometer (RI)
Standard sample: polystyrene

(Tackifier)
The adhesive layer disclosed herein includes a tackifier. The use of a tackifier can improve adhesive strength, and in particular can improve the rough surface adhesion of an adhesive containing an acrylic polymer containing 2-octyl acrylate (m1) as a monomer component. As the tackifier, any component that can improve adhesive strength by being added to the adhesive can be used without particular limitation, and typically, tackifier resins such as rosin-based tackifier resins and terpene-based tackifier resins described below, and acrylic oligomers can be used. The tackifier can be used alone or in combination of two or more types. Although not particularly limited, in some embodiments, the effect of using a tackifier can be effectively exerted in a composition containing an acrylic polymer with a high molecular weight (e.g., Mw 400,000 or more).

The content of the tackifier in the adhesive layer is usually about 1 part by weight or more per 100 parts by weight of the acrylic polymer, from the viewpoint of obtaining the effect of adding the tackifier, and is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (e.g., 15 parts by weight or more). The more the amount of the tackifier used, the easier it is to obtain the effect of improving the rough surface adhesion. In some preferred embodiments, the content of the tackifier may be 20 parts by weight or more, or may be 25 parts by weight or more per 100 parts by weight of the acrylic polymer. The upper limit of the content of the tackifier in the adhesive layer is not particularly limited, but from the viewpoint of compatibility with the acrylic polymer, it is appropriate to set it to about 100 parts by weight or less (e.g., less than 100 parts by weight) per 100 parts by weight of the acrylic polymer, and may be about 80 parts by weight or less. In some embodiments, the content of the tackifier in the adhesive layer is, for example, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, from the viewpoint of flexibility, adhesive properties (cohesive strength, etc.), etc., the content of the tackifier is 40 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer.

(Tackifier resin)
In some preferred embodiments, the adhesive layer contains a tackifier resin. By using a tackifier resin, the rough surface adhesion can be preferably improved. The tackifier resin is not particularly limited, and various tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins can be used. Such tackifier resins can be used alone or in combination of two or more.

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

Specific examples of rosin esters include, but are not limited to, esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, etc.

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

Terpene phenolic resin refers to a polymer containing terpene residues and phenol residues, and is a concept that includes both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and phenol-modified homopolymers or copolymers of terpenes (phenol-modified terpene resins). Specific examples of terpenes that make up such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d/l-forms (dipentene)). Hydrogenated terpene phenolic resins are those that have a structure obtained by hydrogenating such terpene phenolic resins. They are also sometimes called hydrogenated terpene phenolic resins.

Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic/aromatic copolymer (C5/C9) petroleum resins, hydrogenated versions of these (e.g., alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), various modified versions of these (e.g., maleic anhydride modified versions), coumarone resins, and coumarone-indene resins.

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. By incorporating a rosin-based tackifying resin and/or a terpene-based tackifying resin into the acrylic adhesive, the rough surface adhesion can be favorably improved. In some preferred embodiments, the total proportion of the rosin-based tackifying resin and the terpene-based tackifying resin 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 not more than 100% by weight), and may be approximately 70% by weight or more, approximately 80% by weight or more, approximately 90% by weight or more, 95% by weight or more, or 99% by weight or more.

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

The content of the terpene phenol resin in the adhesive layer is not particularly limited as long as the desired properties are satisfied. In some embodiments, the content of the terpene phenol resin is usually about 1 part by weight or more, and it is appropriate to set it to about 5 parts by weight or more, preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (e.g., 15 parts by weight or more) per 100 parts by weight of the acrylic polymer, from the viewpoint of improving adhesive strength and rough surface adhesion. In some preferred embodiments, the content of the terpene phenol resin may be 20 parts by weight or more, or may be 25 parts by weight or more, per 100 parts by weight of the acrylic polymer. In some embodiments, the content of the terpene phenol resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, or may be 50 parts by weight or less, per 100 parts by weight of the acrylic polymer. In some preferred embodiments, from the viewpoint of cohesive strength, etc., the content of the terpene phenol resin is 40 parts by weight or less, may be 30 parts by weight or less, may be 25 parts by weight or less, may be 20 parts by weight or less, or may be 18 parts by weight or less.

The softening point of the tackifier resin is not particularly limited. For example, a tackifier resin having a softening point of approximately 50°C or higher can be used, and from the viewpoint of improving cohesive strength, a tackifier resin having a softening point (softening temperature) of approximately 80°C or higher can be preferably used. For example, a terpene-based tackifier resin (such as a terpene phenol resin) having such a softening point can be preferably used. In some preferred embodiments, from the viewpoint of high-temperature adhesive strength, the softening point of the tackifier resin may be approximately 100°C or higher, approximately 105°C or higher, or approximately 110°C or higher. The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of adhesion to the adherend, a tackifier resin having a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower) can be preferably used. In some preferred embodiments, the softening point of the tackifier resin may be about 160°C or less (e.g., less than 160°C), about 150°C or less (e.g., less than 150°C), less than 145°C, less than 140°C, less than 130°C, or less than 120°C.

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

In some embodiments, a tackifier resin T _L having a softening point of less than 150° C. is used as the tackifier resin. By using the tackifier resin T _L , it is easy to obtain high adhesion to various adherends and improve rough surface adhesion. The softening point of the tackifier resin T _L may be 145° C. or less. In some preferred embodiments, the softening point of the tackifier resin T _L is less than 140° C., may be less than 130° C., or may be less than 120° C. The lower limit of the softening point of the tackifier resin T _L is not particularly limited. In some embodiments, the softening point of the tackifier resin T _L may be, for example, about 50° C. or more, 60° C. or more, 70° C. or more, 80° C. or more, or 90° C. or more from the viewpoint of exerting a moderate cohesive force, and in some preferred embodiments, it may be 100° C. or more, 105° C. or more, or 110° C. or more from the viewpoint of high temperature adhesive strength, etc.

As the tackifier resin T _L , one type selected from the above-exemplified tackifier resins having a softening point of less than 150° C. may be used alone or in combination of two or more types. In some embodiments, the tackifier resin T _L preferably contains a terpene phenol resin. The tackifier resin T _L may contain one type of terpene phenol resin alone or may contain two or more types of terpene phenol resins in combination.

In some embodiments, the proportion of the terpene phenol resin in the entire tackifier resin T _L can be, for example, more than about 50% by weight, may be about 65% by weight or more, may be about 75% by weight or more, may be 85% by weight or more, or may be 95% by weight or more. The technology disclosed herein can be preferably implemented in an embodiment in which substantially all of the tackifier resin T _L (for example, about 97% by weight or more, or 99% by weight or more, or may be 100% by weight) is a terpene phenol resin.

The tackifier resin T _L may or may not contain a tackifier resin having a softening point of less than 50° C., more preferably about 40° C. or less (typically a tackifier resin such as a rosin-based, terpene-based, or hydrocarbon-based resin, for example, hydrogenated rosin methyl ester). Such a low-softening-point tackifier resin may be a liquid tackifier resin that is liquid at 30° C. The liquid tackifier resin may be used alone or in combination of two or more. From the viewpoint of cohesive strength, etc., the content of the liquid tackifier resin may be about 30% by weight or less of the entire tackifier resin T _L , and is suitably about 10% by weight or less (for example, 0 to 10% by weight), and may be about 2% by weight or less (0.5 to 2% by weight), or may be less than 1% by weight.

The content of the tackifier resin T _L is not particularly limited, but in some embodiments, it is, for example, 1 part by weight or more, 5 parts by weight or more is appropriate, preferably 8 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 12 parts by weight or more, and may be 15 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. The more the amount of the tackifier resin T _L used, the more the adhesive strength, especially the rough surface adhesion, tends to improve. From this viewpoint, in some preferred embodiments, the content of the tackifier resin T _L may be 20 parts by weight or more, or may be 25 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. In addition, in some embodiments, the content of the tackifier resin T _L is appropriately about 100 parts by weight or less (for example, less than 100 parts by weight) relative to 100 parts by weight of the acrylic polymer, and may be about 80 parts by weight or less. In some preferred embodiments, from the viewpoint of adhesive properties and the like, the content of the tackifier resin T _L is suitably about 70 parts by weight or less relative to 100 parts by weight of the acrylic polymer, and may be 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 18 parts by weight or less.

In some embodiments, the pressure-sensitive adhesive layer may contain a combination of a tackifier resin T _L and a tackifier resin T _H having a softening point of 150° C. or higher (e.g., 150° C. to 200° C.). As the tackifier resin T _H , one type or two or more types selected from the tackifier resins exemplified above having a softening point of 150° C. or higher may be used alone or in combination.

In some embodiments, the tackifier resin T _L preferably accounts for more than 50% by weight of the total amount of tackifier resin contained in the pressure-sensitive adhesive layer. This makes it easier for the effect of containing the tackifier resin T _L to be effectively expressed. From the viewpoint of more effectively exerting the effect of using the tackifier resin T _{L, the ratio of the tackifier resin T L to} the total amount of tackifier resin contained in the pressure-sensitive adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and may be 95% by weight or more, or may be 98% by weight or more. In some preferred embodiments, the tackifier resin contained in the pressure-sensitive adhesive layer is substantially composed of only the tackifier resin T _L. In such an embodiment, the ratio of the tackifier resin T _L to the total amount of tackifier resin contained in the pressure-sensitive adhesive layer is in the range of 99 to 100% by weight.

The hydroxyl value of the tackifier resin is not particularly limited. In some embodiments, the hydroxyl value of the tackifier resin is usually about 300 mgKOH/g or less, and about 200 mgKOH/g or less is appropriate, from the viewpoint of compatibility with the acrylic polymer, and in some preferred embodiments, it may be about 150 mgKOH/g or less, or may be 120 mgKOH/g or less. In some embodiments, the hydroxyl value of the tackifier resin is 0 mgKOH/g or more, may be about 10 mgKOH/g or more, or may be about 20 mgKOH/g or more.

Here, the hydroxyl value can be a value measured by potentiometric titration as specified in JIS K0070: 1992. A specific measurement method is as follows.
[Method for measuring hydroxyl value]
1. Reagent (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make the total volume 50 mL, and stir thoroughly. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make the total volume 100 mL, and stir thoroughly.
(2) A 0.5 mol/L ethanol solution of potassium hydroxide is used as the measurement reagent.
(3) In addition, toluene, pyridine, ethanol and distilled water are prepared.
2. Procedure (1) Accurately weigh out about 2 g of sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser.
(2) The flask is heated in a 100°C bath for 70 minutes, then allowed to cool, and 35 mL of toluene is added from the top of the cooling tube as a solvent and stirred, followed by addition of 1 mL of distilled water and stirring to decompose the acetic anhydride. To complete the decomposition, the flask is heated again in the bath for 10 minutes and allowed to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove it. Next, 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) Potentiometric titration is performed using a 0.5 mol/L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is taken as the end point.
(6) A blank test is carried out by carrying out steps (1) to (5) above without adding any sample.
3. Calculation Calculate the hydroxyl value using the following formula.
Hydroxyl value (mgKOH/g) = [(B-C) x f x 28.05] / S + D
Where:
B: Amount (mL) of 0.5 mol/L potassium hydroxide ethanol solution used in the blank test,
C: Amount (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 sample (g),
D: acid value,
28.05: 1/2 of the molecular weight of potassium hydroxide, 56.11,
It is.

In some embodiments, the tackifier resin may include a tackifier resin having a hydroxyl value of less than 100 mgKOH/g. Hereinafter, a tackifier resin having a hydroxyl value of less than 100 mgKOH/g may be referred to as a "low hydroxyl value resin". The hydroxyl value of the low hydroxyl value resin may be less than 80 mgKOH/g, 70 mgKOH/g or less, or less than 65 mgKOH/g. A tackifier resin containing such a low hydroxyl value resin is likely to provide good rough surface adhesion. The lower limit of the hydroxyl value of the low hydroxyl value resin is 0 mgKOH/g or more, may be approximately 10 mgKOH/g or more, or may be approximately 15 mgKOH/g or more. The higher the hydroxyl value, the easier it is to obtain good cohesive strength. As the low hydroxyl value resin, one type selected from the tackifier resins exemplified above having a hydroxyl value of less than 100 mgKOH/g may be used alone or in combination of two or more types. In some embodiments, the low hydroxyl value resin preferably includes at least one selected from a rosin-based tackifier resin and a terpene-based tackifier resin. For example, a terpene phenol resin having a hydroxyl value of less than 100 mg KOH/g may be preferably used as the low hydroxyl value resin. Terpene phenol resins are advantageous because the hydroxyl value can be controlled as desired by the copolymerization ratio of phenol.

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

The softening point of the low hydroxyl value resin is not particularly limited. The softening point of the low hydroxyl value resin may be, for example, approximately 50°C or higher, and from the viewpoint of improving cohesive strength, a low hydroxyl value resin having a softening point (softening temperature) of approximately 80°C or higher may be preferably used. For example, a rosin-based tackifier resin or a terpene phenol resin having such a softening point may be preferably used. In some preferred embodiments, from the viewpoint of high-temperature adhesive strength, the softening point of the low hydroxyl value resin may be approximately 100°C or higher, 105°C or higher, or approximately 110°C or higher. In some embodiments, from the viewpoint of adhesive strength and rough surface adhesion, a low hydroxyl value resin having a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower) may be preferably used. In some preferred embodiments, the softening point of the low hydroxyl value resin may be about 160°C or less, about 150°C or less (e.g., less than 150°C), less than 145°C, less than 140°C, less than 130°C, or less than 120°C.

The content of the low hydroxyl value resin in the adhesive layer is not particularly limited, and in some embodiments, it is usually about 1 part by weight or more, and it is appropriate to make it about 5 parts by weight or more, preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (e.g., 15 parts by weight or more) per 100 parts by weight of the acrylic polymer. The more the low hydroxyl value resin is used, the more the adhesive strength and rough surface adhesion tend to improve. From this viewpoint, in some preferred embodiments, the content of the low hydroxyl value resin may be 20 parts by weight or more, or may be 25 parts by weight or more, per 100 parts by weight of the acrylic polymer. In addition, in some embodiments, the content of the low hydroxyl value resin in the adhesive layer is, for example, 70 parts by weight or less, may be 60 parts by weight or less, or may be 50 parts by weight or less, per 100 parts by weight of the acrylic polymer. In some preferred embodiments, from the viewpoint of cohesive strength, etc., the content of the low hydroxyl value resin is 40 parts by weight or less, may be 30 parts by weight or less, may be 25 parts by weight or less, may be 20 parts by weight or less, or may be 18 parts by weight or less.

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

The content of the tackifier resin in the adhesive layer is not particularly limited. In an embodiment in which a tackifier resin is used as a tackifier, the content of the tackifier resin is usually about 1 part by weight or more, and it is appropriate to set it to about 5 parts by weight or more, and preferably about 8 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably about 12 parts by weight or more (e.g., 15 parts by weight or more) per 100 parts by weight of the acrylic polymer. The more the tackifier resin is used, the more the adhesive strength and rough surface adhesion tend to improve. From this viewpoint, in some preferred embodiments, the content of the tackifier resin may be 20 parts by weight or more, or may be 25 parts by weight or more, per 100 parts by weight of the acrylic polymer. In addition, the content of the tackifier resin in the adhesive layer is, for example, about 100 parts by weight or less (e.g., less than 100 parts by weight) per 100 parts by weight of the acrylic polymer, and it may be about 80 parts by weight or less. In some embodiments, the content of the tackifier resin in the adhesive layer is, for example, 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. In some preferred embodiments, from the viewpoint of flexibility, cohesive strength, etc., the content of the tackifier resin is 40 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 18 parts by weight or less, relative to 100 parts by weight of the acrylic polymer.

(Acrylic Oligomer)
In some embodiments, the pressure-sensitive adhesive layer contains an acrylic oligomer. By including the acrylic oligomer, the adhesive strength of the pressure-sensitive adhesive can be improved. According to the technology disclosed herein, the pressure-sensitive adhesive layer can exhibit excellent rough surface adhesion in a composition containing an acrylic oligomer. Although not particularly limited, in some embodiments, the effect of using the acrylic oligomer can be effectively exhibited in a composition containing an acrylic polymer with a high molecular weight (e.g., Mw 400,000 or more).

The acrylic oligomer has a Tg of about 0°C or more and about 300°C or less, preferably about 20°C or more and about 300°C or less, and more preferably about 40°C or more and about 300°C or less. By having a Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the adhesive, the Tg of the acrylic oligomer is about 30°C or more, more preferably about 50°C or more (e.g. about 60°C or more), and from the viewpoint of adhesiveness, it is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (e.g. about 80°C or less).

In this specification, the Tg of the acrylic oligomer refers to the Tg calculated by the Fox formula based on the composition of the above monomer components. The Fox formula is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below.
1/Tg=Σ(Wi/Tgi)
In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction (copolymerization ratio on a weight basis) of monomer i in the copolymer, and Tgi represents the glass transition temperature (unit: K) of a homopolymer of monomer i. The Tg of the homopolymer used in the calculation of Tg is as described for the homopolymer Tg of the acrylic polymer monomer.

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

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

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

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

In addition to the above (meth)acrylate monomers, functional group-containing monomers can be used as constituent monomer components of the acrylic oligomer. Suitable examples of the functional group-containing monomers include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; and hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used alone or in combination of two or more. Among them, carboxy group-containing monomers are preferred, with AA being particularly preferred.

When all monomer components constituting the acrylic oligomer include functional group-containing monomers, the proportion of functional group-containing monomers (e.g., carboxyl group-containing monomers such as AA) in the total monomer components is suitably about 1% by weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and suitably about 15% by weight or less, preferably 10% by weight or less, more preferably 7% by weight or less.

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

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

When the adhesive layer disclosed herein contains an acrylic oligomer, its content is not particularly limited, and is suitably, for example, 0.1 parts by weight or more (e.g., 1 part by weight or more) per 100 parts by weight of the acrylic polymer. From the viewpoint of better exerting the effect of the acrylic oligomer, in some embodiments, the content of the acrylic oligomer is approximately 3 parts by weight or more, may be approximately 5 parts by weight or more, may be approximately 10 parts by weight or more, or may be approximately 12 parts by weight or more. Also, from the viewpoint of compatibility with the acrylic polymer, etc., the content of the acrylic oligomer is suitably less than 50 parts by weight (e.g., less than 40 parts by weight) per 100 parts by weight of the acrylic polymer, preferably less than 30 parts by weight, more preferably approximately 25 parts by weight or less, and even more preferably approximately 20 parts by weight or less. In some embodiments, the content of the acrylic oligomer may be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less (e.g., less than 1 part by weight) relative to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive layer may be substantially free of acrylic oligomer.

In some embodiments, the pressure-sensitive adhesive layer may contain one or more of the above-mentioned tackifier resins and one or more of the acrylic oligomers. The ratio ( _CT /CO) of the content _CT [ _wt %] of the tackifier resin to the content CO [wt%] of the acrylic oligomer in the pressure-sensitive adhesive layer is not particularly limited. In some embodiments, the above ( _CT / _CO ) is suitably set to, for example, 0.1 or more on a weight basis, preferably 0.5 or more, and may be 1 or more (e.g., more than 1), 2 or more, 3 or more, or 4 or more. _The larger the ratio ( _CT / _CO ), the easier it is to obtain the effect of using the tackifier resin. In addition, in some embodiments, the above ( _CT / _CO ) is suitably set to, for example, 10 or less on a weight basis, preferably 8 or less, 6 or less, or 5 or less. This allows the effect of using the acrylic oligomer to be preferably exhibited.

In the technology disclosed herein, the combined amount (total amount) of the acrylic polymer and tackifier in the adhesive layer is appropriately set so as to achieve the effects of the technology disclosed herein, and is not limited to a specific range. In some preferred embodiments, the combined amount (total amount) of the acrylic polymer and tackifier contained in the adhesive layer is appropriate for more than 50% by weight of the adhesive layer, from the viewpoint of preferably achieving the effects of the technology disclosed herein, and is preferably approximately 70% by weight or more, more preferably approximately 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, or less than 100% by weight), and may be 98% by weight or more.

(Crosslinking Agent)
In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. The crosslinking agents may be used alone or in combination of two or more. Among them, 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 may have an appropriate cohesive force. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form after partial crosslinking reaction, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

As an isocyanate-based crosslinking agent, a polyfunctional isocyanate (a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agents can be used alone or in combination of two or more types.

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

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.

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

Preferred polyfunctional isocyanates include polyfunctional isocyanates having an average of three or more isocyanate groups per molecule. Such trifunctional or higher isocyanates may be multimers (typically dimers or trimers) of bifunctional or trifunctional or higher isocyanates, derivatives (e.g., addition reaction products of polyhydric alcohols and two or more molecules of polyfunctional isocyanates), polymers, etc. Examples of polyfunctional isocyanates include dimers and trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimer 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 polyfunctional isocyanates.

The technology disclosed herein can be preferably implemented in an embodiment using at least an isocyanate-based crosslinking agent as a crosslinking agent. The amount of the isocyanate-based crosslinking agent used is not particularly limited. The amount of the isocyanate-based crosslinking agent used can be, for example, approximately 0.1 parts by weight or more per 100 parts by weight of the acrylic polymer. From the viewpoint of achieving both cohesive strength and adhesion, it is usually preferable that the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is approximately 0.3 parts by weight or more (for example, 0.5 parts by weight or more). In some preferred embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer is approximately 0.8 parts by weight or more, more preferably approximately 1.0 parts by weight or more, even more preferably approximately 1.2 parts by weight or more, and may be approximately 1.5 parts by weight or more. In addition, the amount of the isocyanate-based crosslinking agent used is suitably 10 parts by weight or less per 100 parts by weight of the acrylic polymer, preferably less than 5 parts by weight, more preferably less than 4.0 parts by weight, even more preferably less than 3.0 parts by weight, and particularly preferably 2.5 parts by weight or less, and may be 2.0 parts by weight or less (for example, 1.7 parts by weight or less). By limiting the amount of the isocyanate-based crosslinking agent used within a predetermined range, it is possible to obtain good rough surface adhesion while maintaining cohesive strength based on the use of the isocyanate-based crosslinking agent.

As the epoxy-based crosslinking agent, any compound having two or more epoxy groups in one molecule can be used without any particular restrictions. Epoxy-based crosslinking agents having 3 to 5 epoxy groups in one molecule are preferred. Epoxy-based crosslinking agents can be used alone or in combination of two or more types.

Specific examples of epoxy crosslinking agents include, but are not limited to, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc.

The amount of epoxy crosslinking agent used is not particularly limited. The amount of epoxy crosslinking agent used can be, for example, more than 0 parts by weight and about 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 favorably exerting the effect of improving the cohesive force, it is usually appropriate that the amount of epoxy crosslinking agent used is about 0.002 parts by weight or more per 100 parts by weight of acrylic polymer, preferably about 0.005 parts by weight or more, and may be, for example, about 0.01 parts by weight or more. Also, from the viewpoint of improving adhesion to the adherend, it is appropriate that the amount of epoxy crosslinking agent used is about 0.5 parts by weight or less per 100 parts by weight of acrylic polymer, preferably about 0.2 parts by weight or less, more preferably about 0.1 parts by weight or less (for example, less than 0.1 parts by weight), and may be 0.07 parts by weight or less, or may be 0.04 parts by weight or less. In addition, from the viewpoint of avoiding a decrease in rough surface adhesion due to excessive crosslinking, in some embodiments, the amount of epoxy-based crosslinking agent used is appropriately about 0.03 parts by weight or less per 100 parts by weight of the acrylic polymer, and preferably about 0.02 parts by weight or less. By limiting the amount of epoxy-based crosslinking agent used within a specified range, it is easy to maintain sufficient adhesive strength and rough surface adhesion while having good cohesive strength.

In some preferred embodiments, an isocyanate-based crosslinking agent is used in combination with at least one crosslinking agent having a different type of crosslinkable functional group from that of the isocyanate-based crosslinking agent. The type of non-isocyanate-based crosslinking agent that can be used in combination with the isocyanate-based crosslinking agent is not particularly limited, and can be appropriately selected from the crosslinking agents described above. The non-isocyanate-based crosslinking agent can be used alone or in combination with two or more types. In some preferred embodiments, an epoxy-based crosslinking agent can be used as the non-isocyanate-based crosslinking agent. For example, by using an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent in combination, better adhesive properties can be achieved.

The relationship between the content of the isocyanate-based crosslinking agent and the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is not particularly limited. In some embodiments, the content of the isocyanate-based crosslinking agent is, for example, more than 1 time the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent), and is suitably approximately 10 times or more, preferably approximately 50 times or more, more preferably approximately 80 times or more, even more preferably approximately 100 times or more (e.g., more than 100 times), and particularly preferably approximately 120 times or more (e.g., approximately 150 times or more). In addition, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent), the content of the isocyanate-based crosslinking agent relative to the content of the non-isocyanate-based crosslinking agent (preferably an epoxy-based crosslinking agent) is usually, for example, approximately 1000 times or less, and it is appropriate to set it to approximately 500 times or less, and preferably approximately 300 times or less, and it may be approximately 200 times or less.

The content of the crosslinking agent (total amount of crosslinking agent) in the adhesive composition disclosed herein is not particularly limited. From the viewpoint of cohesion, the content of the crosslinking agent is usually about 0.001 parts by weight or more, and it is appropriate to set it to about 0.002 parts by weight or more relative to 100 parts by weight of the acrylic polymer, and it is preferably about 0.005 parts by weight or more, more preferably about 0.01 parts by weight or more, even more preferably about 0.02 parts by weight or more, and particularly preferably about 0.03 parts by weight or more. In some embodiments, the content of the crosslinking agent relative to 100 parts by weight of the acrylic polymer is about 0.1 parts by weight or more, more preferably about 0.5 parts by weight or more, even more preferably about 1.0 parts by weight or more, and it may be about 1.2 parts by weight or more, or it may be about 1.5 parts by weight or more. The content of the crosslinking agent in the adhesive composition is usually about 20 parts by weight or less, preferably about 15 parts by weight or less, and preferably about 10 parts by weight or less (e.g., about 5 parts by weight or less) relative to 100 parts by weight of the acrylic polymer. In some embodiments, the content of the crosslinking agent relative to 100 parts by weight of the acrylic polymer is 4.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 2.5 parts by weight or less, and may be 2.0 parts by weight or less (e.g., less than 2.0 parts by weight), or may be 1.8 parts by weight or less. In a configuration in which the amount of the crosslinking agent used is limited within the above range, good adhesion and rough surface adhesion tend to be easily obtained.

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

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

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

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

(Thickness)
The thickness of the adhesive layer is not particularly limited, and a configuration having an adhesive layer having an appropriate thickness, for example, in the range of 0.1 to 500 μm, can be adopted depending on the application and purpose of use. In some embodiments, from the viewpoint of avoiding an excessively thick adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, and even more preferably about 50 μm or less. In some preferred embodiments, the thickness of the adhesive layer can be about 35 μm or less, for example, about 30 μm or less, about 25 μm or less, or about 22 μm or less. An adhesive layer with a limited thickness can be well suited to the demand for a thinner and lighter adhesive. In addition, in terms of adhesion to the adherend, the lower limit of the thickness of the adhesive layer is, in some embodiments, appropriate to be about 0.5 μm or more, may be about 1 μm or more, and is advantageously about 3 μm or more, preferably about 10 μm or more, more preferably about 12 μm or more (e.g., more than 12 μm), even more preferably about 15 μm or more, and may be, for example, about 18 μm or more. The greater the thickness of the adhesive layer, the greater the tendency for the adhesive strength and rough surface adhesion to be improved. The adhesive sheet disclosed herein may be an adhesive sheet having an adhesive layer of the above thickness on both sides of the substrate. In addition, in a substrate-attached double-sided adhesive sheet 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 the same thickness, or may be different thicknesses.

(Glass transition temperature of adhesive)
Although not particularly limited, in some embodiments, the glass transition temperature (Tg) of the adhesive (layer) is 10°C or less (e.g., less than 10°C), may be 8.0°C or less, or may be 6.0°C or less. Here, the glass transition temperature of the adhesive (layer) refers to the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement. An adhesive containing a tackifier and having a low Tg is highly flexible and tends to exhibit excellent rough surface adhesion. In some preferred embodiments, the Tg of the adhesive (layer) is lower than 5.0°C, may be 4.0°C or less, 3.0°C or less, 2.0°C or less, 1.0°C or less, 0°C or less (e.g., less than 0.0°C), -1.0°C or less, -3.0°C or less, or -5.0°C or less. In addition, in some embodiments, the Tg of the pressure-sensitive adhesive (layer) is, from the viewpoint of cohesive strength and the like, suitably, for example, -30°C or higher, and preferably -15°C or higher, and may be -12°C or higher, -10°C or higher, -7.0°C or higher (e.g., greater than -7.0°C), -5.0°C or higher, -3.0°C or higher, -1.0°C or higher, 0°C or higher (e.g., greater than 0.0°C), 1.0°C or higher, or 3.0°C or higher (e.g., 4.0°C or higher).

In the technology disclosed herein, the Tg of the adhesive (layer) can be determined by dynamic viscoelasticity measurement. Specifically, a plurality of adhesive layers (adhesive sheets in the case of substrate-less adhesive sheets) to be measured are stacked to prepare an adhesive layer having a thickness of about 2 mm. The adhesive layer is punched into a disk shape having a diameter of 7.9 mm, and a sample is sandwiched and fixed between parallel plates. Dynamic viscoelasticity measurement is performed under the following conditions using a viscoelasticity tester (e.g., ARES or its equivalent, manufactured by TA Instruments), and Tg is determined from the peak temperature of the loss tangent tan δ (G″/G′), which is the ratio of the loss modulus G″ to the storage modulus G′.
・Measurement mode: Shear mode ・Temperature range: -70℃ to 150℃
Heating rate: 5°C/min
・Measurement frequency: 1Hz
The above method is also used in the Examples described later. The pressure-sensitive adhesive layer to be measured may be one formed by applying the corresponding pressure-sensitive adhesive composition in a layer form and drying or curing it.

(Biomass carbon ratio)
In some embodiments, the pressure-sensitive adhesive layer contains a biomass-derived material, and the biomass carbon ratio (also referred to as bio-based ratio) may be a predetermined value or more. The biomass carbon ratio of the pressure-sensitive adhesive layer is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the pressure-sensitive adhesive means that the amount of fossil resource-based materials, such as petroleum, used is small. In this respect, the higher the biomass carbon ratio of the pressure-sensitive adhesive, the more preferable it is. For example, the biomass carbon ratio of the pressure-sensitive adhesive layer may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and may be 95% or less or 90% or less from the viewpoint of material availability. From the viewpoint of making it easier to exhibit good adhesive performance, in some embodiments, the biomass carbon ratio of the adhesive layer may be, for example, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less.

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

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

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

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

The resin film is a film whose main component is a resin material (for example, a component contained in the resin film at more than 50% by weight). Examples of resin films include polyolefin-based resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; polyester-based resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride-based resin films; vinyl acetate-based resin films; polyimide-based resin films; polyamide-based resin films; fluororesin films; cellophane; and the like. The resin film may be a rubber-based film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoint of handling and processability, and PET films are particularly preferred.

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

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

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

The surface of the substrate may be subjected to a conventional surface treatment such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, etc. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the adhesive layer, in other words, the anchoring ability of the adhesive layer to the substrate.

In addition, when the technology disclosed herein is implemented in the form of a single-sided adhesive sheet with a substrate, a release treatment may be applied to the back surface of the substrate as necessary. The release treatment may be, for example, a treatment in which a general silicone-based, long-chain alkyl-based, fluorine-based or other release agent is applied in the form of a thin film, typically of about 0.01 μm to 1 μm (e.g., 0.01 μm to 0.1 μm). By applying such a release treatment, it is possible to obtain effects such as making it easier to unwind a roll of the adhesive sheet.

In an embodiment of the adhesive sheet including a substrate, the thickness of the substrate is not particularly limited. In order to avoid the adhesive sheet from 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 mode 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 (e.g., approximately 25 μm or less). In some embodiments, the thickness of the substrate may be approximately 20 μm or less, approximately 15 μm or less, or approximately 10 μm or less (e.g., approximately 5 μm or less). By reducing the thickness of the substrate, the thickness of the adhesive layer can be made larger even if the total thickness of the adhesive sheet is the same. This can be advantageous in terms of improving adhesion to the adherend and the substrate. The lower limit of the substrate is not particularly limited. From the viewpoint of the handleability and processability of the adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (e.g., 1 μm or more), preferably about 2 μm or more, for example, about 6 μm or more. In some embodiments, the thickness of the substrate can be about 15 μm or more, and may be about 25 μm or more.

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

<Total thickness of adhesive sheet>
The total thickness of the adhesive sheet disclosed herein (including the adhesive layer and may further include a base layer, but not including a release liner) is not particularly limited. The total thickness of the adhesive sheet is, for example, about 1 mm or less, may be about 500 μm or less, or may be about 300 μm or less, and from the viewpoint of thinning, it is appropriate to be about 200 μm or less, and may be about 150 μm or less (for example, about 100 μm or less). In some embodiments, the thickness of the adhesive sheet can be about 50 μm or less, for example, it may be about 35 μm or less, may be about 30 μm or less, may be about 25 μm or less, or may be about 22 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), and it is appropriate to be about 3 μm or more, preferably about 10 μm or more, more preferably about 15 μm or more, and may be about 18 μm or more. A pressure-sensitive adhesive sheet having a thickness equal to or greater than a certain value is likely to be able to adhere to an adherend and also tends to be easy to handle. In a substrate-less pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is the total thickness of the pressure-sensitive adhesive sheet.

<Characteristics of adhesive sheet>
Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet preferably has a 180-degree peel strength (adhesive strength against SUS) against a stainless steel plate of about 10 N/20 mm or more. A pressure-sensitive adhesive sheet exhibiting such adhesive strength against SUS can exhibit excellent adhesion. In some preferred embodiments, the adhesive strength against SUS may be about 12 N/20 mm or more, about 14 N/20 mm or more, or about 16 N/20 mm or more (e.g., 18 N/20 mm or more). The upper limit of the adhesive strength against SUS is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as cohesive strength, it may usually be, for example, about 50 N/20 mm or less. The adhesive strength against SUS is measured using a SUS plate as an adherend under the conditions of a measurement environment of 23° C. and 50% RH, a pulling speed of 300 mm/min, and a peel angle of 180 degrees. More specifically, it is measured by the method described in the Examples below.

The adhesive sheet disclosed herein preferably has a rough surface adhesion of about 1.0 N/20 mm or more, as measured by the method described in the Examples below. An adhesive sheet exhibiting such rough surface adhesion can exhibit good adhesion to the rough surfaces of various adherends, and can be used as an adhesive means with good adhesion reliability. In some embodiments, the rough surface adhesion is more preferably about 2.0 N/20 mm or more, even more preferably about 3.0 N/20 mm or more, and particularly preferably about 4.0 N/20 mm or more or about 5.0 N/20 mm or more (e.g., 5.5 N/20 mm or more). There is no particular upper limit to the rough surface adhesion, and from the viewpoint of compatibility with other adhesive properties such as cohesive strength, it may usually be, for example, about 10 N/20 mm or less.

In addition, although not particularly limited, in some embodiments, the adhesive sheet preferably has a 180-degree peel strength (high-temperature adhesive strength) at 65°C against a stainless steel plate of greater than about 4.5 N/20 mm. An adhesive sheet exhibiting such high-temperature adhesive strength tends to have excellent high-temperature characteristics, and can exhibit high adhesion reliability even when used in a high-temperature environment. In some preferred embodiments, the high-temperature adhesive strength may be about 5.0 N/20 mm or more, about 5.5 N/20 mm or more, or about 6.0 N/20 mm or more. The upper limit of the high-temperature adhesive strength is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as cohesive strength, it may usually be, for example, about 15 N/20 mm or less, or about 10 N/20 mm or less. The high-temperature adhesive strength is measured using a SUS plate as the adherend, in a measurement environment of 65°C, at a pulling speed of 300 mm/min and a peel angle of 180 degrees. The specific measurement conditions are the same as those for the adhesive strength to SUS described above, except that the temperature of the measurement environment is 65°C.

In some embodiments, the adhesive sheet contains a biomass-derived material, and the biomass carbon ratio (also referred to as biobased ratio) may be a predetermined value or more. The biomass carbon ratio of the adhesive sheet is, for example, 1% or more, and may be 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the adhesive sheet means that the amount of fossil resource-based materials, such as petroleum, used is small. From this perspective, the higher the biomass carbon ratio of the adhesive sheet, the more preferable it is. For example, the biomass carbon ratio of the adhesive sheet may be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or more than 80%. The upper limit of the biomass carbon ratio is 100% by definition, and may be 99% or less, and from the viewpoint of ease of material availability, it may be 95% or less, or 90% or less. From the viewpoint of making it easier to exhibit good adhesive performance, in some embodiments, the biomass carbon ratio of the adhesive sheet may be, for example, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less.

<Applications>
The use of the adhesive sheet disclosed herein is not particularly limited. Since the adhesive sheet disclosed herein has improved rough surface adhesion, it is preferably used in various applications in the form of being attached to an adherend having a rough surface, such as a foam material, a mesh material, graphite, or a metal or resin that has been roughened. The adhesive sheet disclosed herein can be preferably used for fixing various members as an adhesive means with good adhesion reliability even when used by attaching it to a rough surface. For example, it can be preferably used for fixing members in electronic devices such as various portable electronic devices. For example, the adhesive sheet is usually used for fixing members in a portable electronic device due to size, weight, and other restrictions, and therefore the adhesive area is small. The adhesive sheet used for this application needs to have an adhesive force that can achieve good fixation even in a small area, and the required performance is at a higher level due to the demands for high functionality, weight reduction, and miniaturization. In particular, in the case of mobile electronic devices equipped with touch panel displays, such as smartphones, the products themselves are becoming smaller and thinner, while the screens are becoming larger from the viewpoint of visibility and operability of the displays. Due to this unique situation, the adhesives used are required to have adhesion and fixing performance under more severe conditions. The adhesive sheet disclosed herein can be used for the above-mentioned mobile electronic device applications to achieve excellent adhesion reliability. In addition, since the members constituting electronic devices such as mobile electronic devices include materials having rough surfaces (e.g., foam materials, mesh materials, graphite, metals and resins subjected to roughening treatment, etc.), adhesive sheets having good rough surface adhesion are suitable for such applications. Furthermore, electronic devices such as mobile electronic devices may be used in high-temperature environments, and the internal space may become heated due to heat generation by electronic components. The adhesive disclosed herein also has excellent high-temperature properties due to the inclusion of an acrylic polymer in which 2-octyl acrylate is copolymerized, and in this respect, it is also preferably applied to electronic devices such as mobile electronic devices.

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

In some embodiments, the adhesive sheet is preferably used in electronic devices that include various light sources such as LEDs (light emitting diodes) and light emitting elements such as self-emitting organic electroluminescence (EL). For example, the adhesive sheet can be preferably used in electronic devices (typically portable electronic devices) that include an organic electroluminescence display device or a liquid crystal display device.

FIG. 4 is a schematic example of a portable electronic device (smartphone) using the adhesive sheet disclosed herein. As shown in FIG. 4, a battery (heat generating element) 540 is built into 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 has the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members that make up 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 (member joining means) of the portable electronic device described above.

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

The matters disclosed by this specification include the following:
[1] A portable electronic device,
an adhesive sheet is bonded to a member constituting the portable electronic device,
The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer,
the pressure-sensitive adhesive layer contains an acrylic polymer containing 2-octyl acrylate (m1) as a monomer component,
the monomer component of the acrylic polymer contains 10% by weight or more of a copolymerizable monomer (m3) different from 2-octyl acrylate (m1) and a carboxy group-containing monomer (m2);
The portable electronic device, wherein the adhesive layer further comprises a tackifier.
[2] The copolymerizable monomer (m3) is represented by the formula:
_CH2 =C( ^R1 ) ^COOR2
(wherein R ¹ is a hydrogen atom or a methyl group, and R ² is a chain alkyl group having 1 to 20 carbon atoms (however, when R ¹ is a hydrogen atom, a 2-octyl group is excluded).)
The portable electronic device according to the above item [1], comprising an alkyl (meth)acrylate represented by the following formula:
[3] The portable electronic device according to [1] or [2] above, wherein the copolymerizable monomer (m3) includes at least one selected from n-butyl acrylate and 2-ethylhexyl acrylate.
[4] The portable electronic device according to any one of [1] to [3] above, wherein the tackifier includes at least one selected from a rosin-based tackifier resin, a terpene-based tackifier resin, and an acrylic oligomer.
[5] The portable electronic device according to any one of the above [1] to [4], wherein the adhesive composition for forming the adhesive layer contains a crosslinking agent.
[6] The portable electronic device according to any one of [1] to [5] above, wherein the weight average molecular weight of the acrylic polymer is 400,000 or more.
[7] The mobile electronic device according to any one of [1] to [6] above, wherein the polydispersity (Mw/Mn) of the acrylic polymer is 2 or more and less than 50, and the polydispersity is determined from the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic polymer.
[8] The portable electronic device according to any one of the above [1] to [7], wherein the pressure-sensitive adhesive layer has a glass transition temperature of 10° C. or lower, and the glass transition temperature of the pressure-sensitive adhesive layer is a glass transition temperature determined from a peak temperature of tan δ in a dynamic viscoelasticity measurement.
[9] The portable electronic device according to any one of the above [1] to [8], wherein the pressure-sensitive adhesive sheet has a 180 degree peel strength against a stainless steel plate of 10 N/20 mm or more.

[11] A pressure-sensitive adhesive layer including an acrylic polymer including 2-octyl acrylate (m1) as a monomer component,
the monomer component of the acrylic polymer contains 10% by weight or more of a copolymerizable monomer (m3) different from 2-octyl acrylate (m1) and a carboxy group-containing monomer (m2);
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer further comprises a tackifier.
[12] The copolymerizable monomer (m3) is represented by the formula:
_CH2 =C( ^R1 ) ^COOR2
(wherein R ¹ is a hydrogen atom or a methyl group, and R ² is a chain alkyl group having 1 to 20 carbon atoms (however, when R ¹ is a hydrogen atom, a 2-octyl group is excluded).)
The pressure-sensitive adhesive sheet according to the above-mentioned [11], which contains an alkyl (meth)acrylate represented by the following formula:
[13] The pressure-sensitive adhesive sheet according to the above [11] or [12], wherein the copolymerizable monomer (m3) includes at least one selected from n-butyl acrylate and 2-ethylhexyl acrylate.
[14] The pressure-sensitive adhesive sheet according to any one of the above [11] to [13], wherein the tackifier comprises at least one selected from a rosin-based tackifier resin, a terpene-based tackifier resin, and an acrylic oligomer.
[15] The pressure-sensitive adhesive sheet according to any one of the above [11] to [14], wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains a crosslinking agent.
[16] The pressure-sensitive adhesive sheet according to any one of [11] to [15] above, wherein the weight average molecular weight of the acrylic polymer is 400,000 or more.
[17] The pressure-sensitive adhesive sheet according to any one of the above [11] to [16], wherein the dispersity (Mw/Mn) of the acrylic polymer is 2 or more and less than 50, wherein the dispersity is determined from the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic polymer.
[18] The pressure-sensitive adhesive layer has a glass transition temperature of 10° C. or lower, wherein the glass transition temperature of the pressure-sensitive adhesive layer refers to a glass transition temperature determined from a peak temperature of tan δ in dynamic viscoelasticity measurement. The pressure-sensitive adhesive sheet according to any one of [11] to [17] above.
[19] The pressure-sensitive adhesive sheet according to any one of the above [11] to [18], which has a 180 degree peel strength against a stainless steel plate of 10 N/20 mm or more.
[20] The pressure-sensitive adhesive sheet according to any one of [11] to [19] above, which is used for fixing components in an electronic device.
[21] An electronic device comprising the pressure-sensitive adhesive sheet according to any one of [11] to [20] above.

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

Example 1
(Synthesis of Acrylic Polymer)
In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel, 85 parts of 2-octyl acrylate (2OcA), 10 parts of n-butyl acrylate (BA) and 5 parts of acrylic acid (AA) as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and the solution was polymerized at 60°C to 70°C for 8 hours to obtain a solution of an acrylic polymer. The weight average molecular weight (Mw) of this acrylic polymer was 880,000, and the dispersity (Mw/Mn) was 5.5. The above 2OcA is a compound having an alkyl group derived from biomass at the ester end, synthesized using 2-octanol derived from biomass.

(Preparation of Pressure-Sensitive Adhesive Composition)
To the acrylic polymer solution obtained above, 15 parts of a terpene phenol resin (product name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., softening point approximately 115°C, hydroxyl value 30 to 60 mgKOH/g) as a tackifier resin, 2 parts (solid content basis) of an isocyanate crosslinking agent (product name "Takenate D-101E", manufactured by Mitsui Chemicals, Inc.), and 0.01 part of an epoxy crosslinking agent (product name "TETRAD-C", manufactured by Mitsubishi Gas Chemical Co., Ltd.) were added per 100 parts of the acrylic polymer contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The obtained adhesive composition was applied to the release surface of a 38 μm thick polyester release film (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation) and dried at 100° C. for 2 minutes to form an adhesive layer having a thickness of 20 μm. The release surface of a 25 μm thick polyester release film (trade name "Diafoil MRF", thickness 25 μm, manufactured by Mitsubishi Chemical Corporation) was bonded to this adhesive layer. In this way, a substrateless double-sided adhesive sheet having a thickness of 20 μm and both sides protected by the two polyester release films was obtained. The glass transition temperature (Tg) of the adhesive layer was −5.9° C., and the biobased content (measured according to ASTM D6866) was 60%.

<Examples 2 to 9 and Comparative Examples 1 to 4>
A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 1, except that the monomer composition of the acrylic polymer, the type and amount of the tackifier, and the type and amount of the crosslinking agent were changed as shown in Table 1, and the resulting pressure-sensitive adhesive composition was used to produce a substrate-less double-sided adhesive sheet (thickness 20 μm) according to each example in the same manner as in Example 1. In Table 1, 2EHA stands for 2-ethylhexyl acrylate.

The acrylic oligomer used was prepared by the following method. Specifically, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and toluene as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, and the mixture was stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, after which the temperature was raised to 85°C and reacted for 5 hours to obtain an acrylic oligomer with a solids concentration of 50%. The Mw of the obtained acrylic oligomer was 3600.

<Evaluation method>
[Adhesion to SUS]
A 50 μm thick PET film was attached to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) to back it, and the sheet was cut to a size of 20 mm wide and 100 mm long to prepare a measurement sample. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample was pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by rolling a 2 kg roller back and forth once. After leaving the sample in the same environment for 30 minutes, a universal tensile compression tester was used to measure the peel strength (adhesive strength against SUS) [N/20 mm] in accordance with JIS Z 0237:2000 at a tensile speed of 300 mm/min and a peel angle of 180 degrees.

[Adhesion to rough surfaces]
A 50 μm thick PET film was attached to one of the adhesive surfaces of the adhesive sheet (double-sided adhesive sheet) to back it, and the sheet was cut to a size of 20 mm wide and 100 mm long to prepare a measurement sample. In addition, sandpaper (Riken Corundum Co., Ltd., grain size 320) was fixed to a stainless steel plate (SUS304BA plate) as an adherend. In an environment of 23 ° C. and 50% RH, the other adhesive surface of the measurement sample was pressed against the sandpaper surface (rough surface) of the adherend by rolling a 2 kg roller back and forth once. After leaving it in the same environment for 72 hours, a universal tensile compression tester was used to measure the peel strength (rough surface adhesive strength) [N / 20 mm] in accordance with JIS Z 0237: 2000 under the conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees.

In addition, when measuring the adhesive strengths above, a universal tensile/compression tester such as Minebea's "Tension/Compression Tester, TG-1kN" or an equivalent product is used. When measuring single-sided adhesive sheets, a PET film backing is not required. When the substrate thickness is thin (for example, when the substrate thickness is 25 μm or less), a PET film backing may be used.

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

As shown in Table 1, the adhesives according to Examples 1 to 9 contain an acrylic polymer containing 2OcA as a monomer component and 10% or more of BA or 2EHA as a copolymerizable monomer, and a tackifier, and the adhesive sheets using the adhesives had good rough surface adhesion. On the other hand, in Comparative Examples 1 and 2, in which the amount of the copolymerizable monomer used was less than 10%, the adhesives had high adhesion to SUS, but good rough surface adhesion was not obtained. In particular, a comparison between Example 4 and Comparative Example 2 confirmed that the rough surface adhesion changed significantly between the copolymerizable monomer amount of 10% (Example 4) and the copolymerizable monomer amount of 8% (Comparative Example 2). This change is considered to be largely due to the change in the side chain crystallinity of the acrylic polymer based on the difference in the copolymerization amount of the copolymerizable monomer, rather than the influence of the homopolymer Tg of the copolymerizable monomer. In Comparative Examples 3 and 4, in which a tackifier was not used, the degree of crosslinking was reduced to design the adhesive to be flexible, but rough surface adhesion was not obtained. From this result, it is found that the use of a tackifier is necessary to obtain good rough surface adhesion. Also, from the comparison of Examples 1 and 3, Examples 4 and 7, and Comparative Examples 3 and 4, it was found that the adhesive Tg was lowered and the rough surface adhesion was improved when BA with a higher homopolymer Tg than 2EHA was copolymerized. The reason for this is considered to be that the copolymerization of BA with a side chain structure that is more different from 2OcA than 2EHA caused a greater decrease in the side chain crystallinity derived from 2OcA and an increase in the free volume between polymer molecules.
From the above results, it can be seen that an adhesive sheet containing 2OcA as a monomer component, further containing 10% or more of a copolymerizable monomer different from 2OcA and a carboxy group-containing monomer, and in which the adhesive layer further contains a tackifier, can effectively improve the rough surface adhesion of an adhesive containing an acrylic polymer copolymerized with 2OcA.

　Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

1, 2, 3 Adhesive sheet 10 Support base material 10A First side 10B Second side (back side)
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 sheet with release liner

Claims (9)

1. a pressure-sensitive adhesive layer including an acrylic polymer including 2-octyl acrylate (m1) as a monomer component;
   the monomer component of the acrylic polymer contains 10% by weight or more of a copolymerizable monomer (m3) different from 2-octyl acrylate (m1) and a carboxy group-containing monomer (m2);
   The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer further comprises a tackifier.
2. The copolymerizable monomer (m3) has the formula:
   _CH2 =C( ^R1 ) ^COOR2
   (wherein R ¹ is a hydrogen atom or a methyl group, and R ² is a chain alkyl group having 1 to 20 carbon atoms (however, when R ¹ is a hydrogen atom, a 2-octyl group is excluded).)
   The pressure-sensitive adhesive sheet according to claim 1 , comprising an alkyl (meth)acrylate represented by the formula:
3. The adhesive sheet according to claim 1, wherein the copolymerizable monomer (m3) includes at least one selected from n-butyl acrylate and 2-ethylhexyl acrylate.
4. The adhesive sheet according to any one of claims 1 to 3, wherein the tackifier comprises at least one selected from a rosin-based tackifier resin, a terpene-based tackifier resin, and an acrylic oligomer.
5. The adhesive sheet according to any one of claims 1 to 3, wherein the adhesive composition for forming the adhesive layer contains a crosslinking agent.
6. The adhesive sheet according to any one of claims 1 to 3, wherein the weight average molecular weight of the acrylic polymer is 400,000 or more.
7. The adhesive sheet according to any one of claims 1 to 3, wherein the dispersity (Mw/Mn) of the acrylic polymer is 2 or more and less than 50, where the dispersity is determined from the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acrylic polymer.
8. The adhesive sheet according to any one of claims 1 to 3, which has a 180-degree peel strength against a stainless steel plate of 10 N/20 mm or more.
9. The adhesive sheet according to any one of claims 1 to 3, which is used to fasten components in electronic devices.

Images