JP2022141932A - Adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acrylic adhesive sheet with an improved adhesive force against a low-surface free energy face, while maintaining an excellent holding force.

SOLUTION: There is provided an adhesive sheet including an adhesive layer. The adhesive layer contains an acrylic polymer and a tackifier resin. In the acrylic polymer, an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at an ester terminal is polymerized at a rate of 15 wt.% or more. In the acrylic polymer, a carboxy group-containing monomer is not copolymerized or a copolymerization ratio of the carboxy group-containing monomer is less than 10 wt.%. In the adhesive layer, a content of the tackifier resin is 40 to 80 pts.wt., inclusive, based on 100 pts.wt. of the acrylic polymer. The adhesive layer contains, as the tackifier resin, a tackifier resin T_L with a softening point of 110°C or lower. The tackifier resin T_L accounts for 60 wt.% or more of the total amount of the tackifier resin contained in the adhesive layer.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to an adhesive sheet.

In general, pressure-sensitive adhesives (also referred to as pressure-sensitive adhesives; hereinafter the same) exhibit a soft solid (viscoelastic) state in a temperature range around room temperature, and have the property of adhering to adherends under pressure. Taking advantage of such properties, adhesives are widely used in various industrial fields such as home electric appliances, automobiles, and OA equipment, typically in the form of adhesive sheets containing an adhesive layer, for the purpose of joining parts and protecting surfaces. It's being used. Patent Documents 1 and 2 are cited as technical documents relating to pressure-sensitive adhesive sheets.

WO2019/167712 JP 2019-189790 A

Adhesive sheets are required to have various performances depending on the application. For example, an adhesive that is used by attaching it to a surface (low surface free energy surface, hereinafter also referred to as "LSE surface") made of a material with low surface free energy such as polyethylene (PE), polypropylene (PP), and fluororesin. The agent is required to exhibit stable adhesion performance to the LSE surface. For example, some members constituting electronic devices such as home appliances are made of PE, PP, fluororesin, etc., and the above adhesive is applied to such adherends (LSE adherends). The agent is required to have a certain level of adhesive strength. However, in general, the adhesive strength of pressure sensitive adhesives tends to decrease with respect to the LSE surface. Also, rubber-based pressure-sensitive adhesives are known to be relatively easy to adhere to the LSE surface, but they tend to deteriorate and it is difficult to maintain stable adhesion performance over a long period of time. Furthermore, in recent years, the adhesive area of the pressure-sensitive adhesive tends to decrease due to the demand for miniaturization, weight reduction, and precision of electronic devices and the like to which LSE adherends are used. Therefore, it is becoming more difficult to obtain sufficient adhesion reliability to the LSE surface of various products.

The present invention has been created in view of the above circumstances, and an object of the present invention is to provide an acrylic pressure-sensitive adhesive sheet having good holding power and improved adhesion to surfaces with low surface free energy.

According to this specification, a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer is provided. The adhesive layer contains an acrylic polymer and a tackifying resin. The acrylic polymer is polymerized with 15% by weight or more of an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end. Further, the acrylic polymer has no carboxy group-containing monomer copolymerized therein, or the copolymerization ratio of the carboxy group-containing monomer is less than 10% by weight. Furthermore, the content of the tackifier resin in the adhesive layer is 40 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive layer contains a tackifier resin T _L having a softening point of 110° C. or lower as the tackifier resin. The tackifying resin _TL accounts for 60% by weight or more of the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet configured as described above can exhibit improved adhesion to a low surface free energy surface (LSE surface) while having good holding power.

In some preferred embodiments, the pressure-sensitive adhesive layer contains a rosin-based tackifying resin as the tackifying resin. By using a rosin-based tackifying resin, the adhesive strength to the LSE surface is preferably improved.

In some preferred embodiments, the pressure-sensitive adhesive layer does not contain a terpene phenol resin, or contains less than 5 parts by weight of the terpene phenol resin with respect to 100 parts by weight of the acrylic polymer. By limiting the amount of the terpene phenol resin used, the effect of improving the adhesive force to the LSE surface is likely to be obtained.

In some preferred embodiments, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an epoxy-based cross-linking agent. By using an epoxy-based cross-linking agent as a cross-linking agent for the acrylic pressure-sensitive adhesive, a predetermined amount of the tackifying resin containing the low-softening-point tackifying resin _TL as a main component is included to obtain adhesive strength to the LSE surface, while maintaining good adhesion. It can preferably have holding power.

In some preferred embodiments, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent. By using both an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent as cross-linking agents, more excellent performance can be suitably realized.

The pressure-sensitive adhesive sheet according to some embodiments is configured as a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of the pressure-sensitive adhesive layer. Since the substrate-less double-sided PSA sheet does not have a substrate, it can be made thinner, and can contribute to miniaturization and space saving of products to which the double-sided PSA sheet is applied. In addition, according to the substrate-less pressure-sensitive adhesive sheet, the effect of the pressure-sensitive adhesive such as adhesive strength can be maximized. The substrate-less pressure-sensitive adhesive sheet is suitable for use in portable electronic devices, where there is a strong demand for miniaturization and weight reduction, and a thin pressure-sensitive adhesive sheet is desired.

A pressure-sensitive adhesive sheet according to some other embodiments is configured as a pressure-sensitive adhesive sheet with a substrate having a substrate and the pressure-sensitive adhesive layer provided on at least one surface of the substrate. For example, a substrate-attached pressure-sensitive adhesive sheet provided with a substrate such as a resin film substrate is excellent in handleability and workability, and thus can be processed into various shapes for use in various applications.

The pressure-sensitive adhesive sheet disclosed herein has good holding power and improved adhesion to the LSE surface. It can be preferably used. For example, it is suitable for fixing members in electronic devices including home electric appliances, OA devices, and portable electronic devices such as smartphones. Some of the members constituting the electronic device have an LSE surface made of materials such as PE, PP, and fluororesin. Adhesive fixation with excellent adhesive reliability can be realized. From the above, according to this specification, an electronic device using any one of the adhesive sheets disclosed herein, in other words, an electronic device including the adhesive sheet is provided.

1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to one embodiment; FIG. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment; FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment;

Preferred embodiments of the present invention are described below. Matters other than the matters specifically mentioned in the present specification, which are necessary for the implementation of the present invention, are based on the teaching of the implementation of the invention described in the present specification and the common general knowledge at the time of filing. can be understood by those skilled in the art. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. Further, in the following drawings, members and portions having the same function may be denoted by the same reference numerals, and redundant description may be omitted or simplified. In addition, the embodiments described in the drawings are schematic for the purpose of clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the pressure-sensitive 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 around room temperature and has the property of easily adhering to an adherend under pressure, as described above. . The adhesive used herein generally has a complex tensile modulus E ^* (1 Hz) as defined in "CA Dahlquist, "Adhesion: Fundamental and Practice", McLaren & Sons, (1966) P. 143" It may be a material having properties satisfying <10 ⁷ dyne/cm ² (typically, a material having the above properties at 25°C).

<Structure of Adhesive Sheet>
The adhesive sheet disclosed here includes an adhesive layer. The pressure-sensitive adhesive sheet is, for example, a substrate-less double-sided pressure-sensitive adhesive sheet comprising a first pressure-sensitive adhesive surface configured by one surface of the pressure-sensitive adhesive layer and a second pressure-sensitive adhesive surface configured by the other surface of the pressure-sensitive adhesive layer. can be of the form Alternatively, the pressure-sensitive adhesive sheet disclosed herein may be in the form of a substrate-attached pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is laminated on one or both sides of a supporting substrate. Hereinafter, the supporting substrate may be simply referred to as "substrate". Note that the concept of the adhesive sheet as used herein can include what is called an adhesive tape, an adhesive label, an adhesive film, and the like. The pressure-sensitive adhesive sheet disclosed herein may be roll-shaped or sheet-shaped. Alternatively, it may be a pressure-sensitive adhesive sheet processed into various shapes.

FIG. 1 schematically shows the structure of a pressure-sensitive adhesive sheet according to one embodiment. This pressure-sensitive adhesive sheet 1 is configured as a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer 21 . The adhesive sheet 1 has a first adhesive surface 21A configured by one surface (first surface) of the adhesive layer 21 and a second adhesive surface configured by the other surface (second surface) of the adhesive layer 21. 21B are attached to different parts of the adherend. The locations where the adhesive surfaces 21A and 21B are attached may be locations on different members or different locations within a single member. As shown in FIG. 1, the pressure-sensitive adhesive sheet 1 before use (that is, before being attached to an adherend) has a first pressure-sensitive adhesive surface 21A and a second pressure-sensitive adhesive surface 21B that are peeled off at least on the side facing the pressure-sensitive adhesive layer 21. It can be a constituent element of the PSA sheet 100 with a release liner in a form protected by the release liners 31 and 32 which are surfaces. As the release liners 31 and 32, for example, one having a sheet-like base material (liner base material) provided with a release layer by a release treatment agent on one side so that the one side becomes a release surface is preferably used. obtain. Alternatively, the release liner 32 is omitted, and a release liner 31 having release surfaces on both sides is used. A release liner-attached pressure-sensitive adhesive sheet in a form (roll form) protected by contacting the back surface of the adhesive sheet may be configured.

FIG. 2 schematically shows the structure of a pressure-sensitive adhesive sheet according to another embodiment. The pressure-sensitive adhesive sheet 2 includes a sheet-like support base material (for example, a resin film) 10 having a first surface 10A and a second surface 10B, and a base material provided with an adhesive layer 21 provided on the first surface 10A side. It is configured as a single-sided adhesive sheet with The pressure-sensitive adhesive layer 21 is fixedly provided on the first surface 10A side of the supporting substrate 10 , that is, without the intention of separating the pressure-sensitive adhesive layer 21 from the supporting substrate 10 . In the pressure-sensitive adhesive sheet 2 before use, as shown in FIG. 2, the surface (adhesive surface) 21A of the pressure-sensitive adhesive layer 21 is protected by a release liner 31 having a release surface on at least the side facing the pressure-sensitive adhesive layer 21. It can be a component of the pressure-sensitive adhesive sheet 200 with a release liner. Alternatively, by omitting the release liner 31 and using the supporting substrate 10 whose second surface 10B is the releasing surface, the adhesive sheet 2 is wound so that the adhesive surface 21A becomes the second surface (back surface) of the supporting substrate 10. ) 10B may be in a protected form (roll form).

FIG. 3 schematically shows the structure of a pressure-sensitive adhesive sheet according to still another embodiment. This adhesive sheet 3 consists of a sheet-like supporting substrate (for example, a resin film) 10 having a first surface 10A and a second surface 10B, and 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. The pressure-sensitive adhesive sheet 3 before use, as shown in FIG. , 32 can be a component of the pressure-sensitive adhesive sheet 300 with a release liner. Alternatively, the release liner 32 is omitted, and a release liner 31 having release surfaces on both sides is used. A release liner-attached pressure-sensitive adhesive sheet in a form (roll form) protected by contacting the back surface of the adhesive sheet may be configured.

In the double-sided pressure-sensitive adhesive sheet with a substrate, at least one pressure-sensitive adhesive layer (for example, the first pressure-sensitive adhesive layer) of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be the pressure-sensitive adhesive layer described below. The other pressure-sensitive adhesive layer (for example, the second pressure-sensitive adhesive layer) may be the pressure-sensitive adhesive layer disclosed herein, and the pressure-sensitive adhesive layer disclosed herein (specifically, the one pressure-sensitive adhesive layer The adhesive layer may have a composition different from that of the adhesive layer (eg, the first adhesive layer). Such other pressure-sensitive adhesive layer may be formed from, for example, a known or commonly used pressure-sensitive adhesive.

<Adhesive layer>
The pressure-sensitive adhesive layer that constitutes the pressure-sensitive adhesive sheet disclosed herein contains an acrylic polymer. The pressure-sensitive adhesive layer is typically a pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer (the main component of the polymer component, that is, the component occupying 50% by weight or more). Such an adhesive layer is also called an acrylic adhesive layer. The base polymer is the main component of the rubber-like polymer (polymer exhibiting rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive layer. In this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight unless otherwise specified. In addition, the following descriptions of components that can be included in the adhesive and adhesive layer are also applicable to the adhesive composition used to form the adhesive (layer) unless otherwise specified.

In the present specification, the term "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. . Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as "acrylic monomer". Accordingly, an acrylic polymer in this specification is defined as a polymer containing monomeric units derived from an acrylic monomer. In this specification, "(meth)acryloyl" is meant to comprehensively refer to acryloyl and methacryloyl. Similarly, "(meth)acrylate" is a generic term for acrylate and methacrylate, and "(meth)acrylic" is generic for acrylic and methacrylic.

(acrylic polymer)
The acrylic polymer used in the technology disclosed herein is preferably a polymer of monomer raw materials containing an alkyl (meth)acrylate as a main monomer and further containing a sub-monomer copolymerizable with the main monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used.
_CH2 =C( ^R1 ) ^COOR2 (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. Hereinafter, such a carbon atom number range may be expressed as "C _1-20 ". From the viewpoint of the storage elastic modulus of the pressure-sensitive adhesive, it is possible to use an alkyl (meth)acrylate in which R ² is a chain alkyl group of C _1-14 (eg, C _2-10 or C _4-8 ) as the main monomer. Appropriate. From the viewpoint of adhesive properties, the main monomer is an alkyl acrylate in which R ¹ is a hydrogen atom and R ² is a C _4-8 chain alkyl group (hereinafter also simply referred to as C _4-8 alkyl acrylate). is preferred.

Examples of alkyl (meth)acrylates in which R ² is a C _1-20 chain alkyl group 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 , octyl (meth)acrylate, 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, eicosyl (meth)acrylate and the like. . These alkyl (meth)acrylates may be used singly or in combination of two or more. Preferred alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

The acrylic polymer used in the technology disclosed herein is polymerized with 15% by weight or more of an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end. This makes it possible to improve the adhesive force to the LSE surface. Although not particularly limited, the polymerization ratio of the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end is 15% by weight or more, so that the pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer It is believed that the compatibility with the imparting resin is improved and the wettability to the LSE surface is improved.

Alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end, which is used as a monomer unit of the acrylic polymer, is typically an alkyl (meth)acrylates (ie C _6-20 alkyl (meth)acrylates). The number of carbon atoms in the alkyl group of the C _1-20 alkyl (meth)acrylate is preferably 7 or more, more preferably 8 or more, from the viewpoint of adhesion to the LSE surface. The upper limit of the number of carbon atoms in the alkyl group of the C _6-20 alkyl (meth)acrylate may be, for example, 14 or less, or 12 or less, from the viewpoint of compatibility with the tackifying resin and viscoelastic properties. It may be 10 or less, or 9 or less. In some aspects, the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end, which is used as a monomer unit of the acrylic polymer in a proportion of 15% by weight or more, is preferably C _6-14 alkyl ( meth)acrylates, more preferably C _7-14 alkyl (meth)acrylates, even more preferably C _7-10 alkyl (meth)acrylates.

The polymerization ratio of the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end in the acrylic polymer may be 20% by weight or more, preferably 30% by weight, from the viewpoint of adhesion to the LSE surface. % by weight or more, more preferably 40% by weight or more, more preferably 50% by weight or more, may be 60% by weight or more, may be 70% by weight or more, may be 80% by weight or more, or may be 90% by weight or more (eg, 92% by weight or more). The upper limit of the polymerization ratio of the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end is, for example, 99.9% by weight or less. Yes, preferably 97% by weight or less, for example, 75% by weight or less, or less than 50% by weight.

Alkyl (meth)acrylate accounts for preferably 70% by weight or more, more preferably 85% by weight or more, and still more preferably 90% by weight or more in the total monomer components used for synthesizing the acrylic polymer. Although the upper limit of the ratio of alkyl (meth)acrylate is not particularly limited, it is usually suitable to be 99.5% by weight or less (for example, 99% by weight or less), and the action of a submonomer such as a carboxy group-containing monomer is suitable. From the viewpoint of expressing a high content, it is preferably about 98% by weight or less (for example, 97% by weight or less).

A secondary monomer may be copolymerized with the acrylic polymer in the technology disclosed herein. A carboxyl group-containing monomer, a hydroxyl group (OH group)-containing monomer, an acid anhydride group-containing monomer, and an amide group-containing sub-monomer that introduces a functional group that can serve as a cross-linking base point into the acrylic polymer or that can contribute to the improvement of adhesive strength. 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, Examples include cyano group-containing monomers, keto group-containing monomers, nitrogen atom-containing ring-containing monomers (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, imide group-containing monomers, and the like. be done. The said submonomer can be used individually by 1 type or in combination of 2 or more types.

When the monomer component constituting the acrylic polymer contains the functional group-containing monomer described above, the content of the functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exhibiting the effect of using the functional group-containing monomer, the content of the functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, and should be 0.5% by weight or more. is suitable, and it may be 1% by weight or more. In addition, from the viewpoint of easily balancing the adhesion performance in relation to the main monomer, the content of the functional group-containing monomer in the monomer component is appropriately 40% by weight or less, and is 20% by weight or less. is preferable, and it may be 10% by weight or less (for example, 5% by weight or less).

The acrylic polymer used in the technique disclosed herein has substantially no carboxy group-containing monomer copolymerized therein, or the copolymerization ratio of the carboxy group-containing monomer is less than 10% by weight. As a result, a decrease in wettability to the LSE surface is suppressed, and the adhesiveness to the LSE surface is preferably exhibited. In this specification, the carboxy group-containing monomer is not substantially copolymerized means that the carboxy group-containing monomer is not intentionally polymerized, or that the carboxy group-containing monomer is not substantially copolymerized. Alternatively, the copolymerization ratio of the carboxy group-containing monomer is less than 0.1% by weight (for example, less than 0.03% by weight, further less than 0.01% by weight).

In some preferred embodiments, a carboxy group-containing monomer is used as the secondary monomer. Carboxy group-containing monomers can improve cohesiveness based on their polarity. When using a cross-linking agent such as an isocyanate-based or epoxy-based cross-linking agent, the carboxy group becomes a cross-linking point of the acrylic polymer. By using the carboxy group-containing monomer while limiting the copolymerization ratio to less than 10% by weight, it is possible to achieve both adhesion to the LSE surface and good holding power.

Carboxy group-containing monomers that can be used in the technology disclosed herein include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, Acids, crotonic acid, isocrotonic acid and the like are exemplified. Among them, preferred carboxyl group-containing monomers include AA and MAA. AA is particularly preferred. A carboxy group-containing monomer can be used individually by 1 type or in combination of 2 or more types.

When a carboxyl group-containing monomer is used as a copolymerization component of the acrylic polymer, the content thereof is usually about 0.1% by weight or more, preferably about 0.5% by weight, based on the total monomer components. % or more, more preferably about 1.0 wt% or more, still more preferably about 2.0 wt% or more (e.g., more than 2.0 wt%), particularly preferably 3.0 wt% or more (e.g., 3.0 wt% greater than) and may be 4.0% by weight or more (eg, 4.5% by weight or more). As the content of the carboxy group-containing monomer increases, the cohesive strength of the pressure-sensitive adhesive layer generally tends to improve. Also, the amount of the carboxy group-containing monomer is suitably 8% by weight or less, preferably about 7% by weight or less, more preferably about 6% by weight or less, for example about 3% by weight, of the total monomer components. It may be below. By setting the amount of the carboxy group-containing monomer to be used within the above range, a pressure-sensitive adhesive layer exhibiting good adhesion to the LSE adherend can be suitably realized.

When a carboxy group-containing monomer is used as a copolymerization component (specifically, a functional group-containing monomer) of the acrylic polymer, 10% by weight or more of the functional group-containing monomer used may be the carboxy group-containing monomer. As a result, the cohesive force of the carboxyl group and the action as a cross-linking point are preferably exhibited. From the viewpoint of better exhibiting the effect of copolymerizing the carboxy group-containing monomer, the ratio of the carboxy group-containing monomer to the total functional group-containing monomer is appropriately 30% by weight or more, preferably 50% by weight or more, and more. It is preferably 70% by weight or more, more preferably 90% by weight or more, for example, may be 97% by weight or more, may be 98% by weight or more, or may be 99% by weight or more (for example, 99.9% by weight or more). . The upper limit of the ratio of the carboxy group-containing monomer to the total functional group-containing monomer is 100% by weight, and may be, for example, 95% by weight or less.

Another example of the acrylic polymer used in the technique disclosed herein is an acrylic polymer obtained by copolymerizing a hydroxyl group-containing monomer as the secondary monomer. A hydroxyl group-containing monomer may be copolymerized with a carboxy group-containing monomer. Examples of hydroxyl-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, ) hydroxyalkyl (meth)acrylate such as acrylate; polypropylene glycol mono(meth)acrylate; N-hydroxyethyl (meth)acrylamide and the like. A hydroxyl-containing monomer can be used individually by 1 type or in combination of 2 or more types.

When a hydroxyl group-containing monomer is used as the submonomer, its content is usually about 0.001% by weight or more, preferably about 0.01% by weight or more (typically 0.02% by weight or more). Also, the content of the hydroxyl group-containing monomer is suitably about 10% by weight or less, preferably about 5% by weight or less, more preferably about 2% by weight or less, in the total monomer components. Moreover, the technique disclosed here can be implemented using the adhesive containing the acrylic polymer in which the hydroxyl-containing monomer is not copolymerized.

The monomer components constituting the acrylic polymer may contain copolymer components other than the sub-monomers described above for the purpose of improving the cohesive force and the like. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; ) acrylate; aryl (meth)acrylate (e.g. phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g. phenoxyethyl (meth)acrylate), arylalkyl (meth)acrylate (e.g. benzyl (meth)acrylate), etc. Aromatic ring-containing (meth)acrylates; olefinic monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate group-containing monomers; vinyl ether-based monomers such as methyl vinyl ether and ethyl vinyl ether; The above-mentioned other copolymerization components can be used singly or in combination of two or more.

The amount of such other copolymerization components may be appropriately selected according to the purpose and application and is not particularly limited, but from the viewpoint of appropriately exhibiting the effects of use, it is suitable to be 0.05% by weight or more. , 0.5% by weight or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymer components in the monomer component is suitably 20% by weight or less, from the viewpoint of suitably exhibiting the adhesive properties based on the main monomer. Therefore, it is preferably 10% by weight or less, more preferably 8% by weight or less, still more preferably less than 5% by weight, and may be less than 3% by weight or less than 1% by weight. The technology disclosed herein can also be preferably practiced in a mode in which the monomer component does not substantially contain other copolymerization components. Here, the monomer component does not substantially contain other copolymerization components means that other copolymerization components are not used at least intentionally, and other copolymerization components are, for example, 0.01 wt% or less. To some extent, unintentional inclusion is acceptable.

Acrylic polymers are polyfunctional having at least two polymerizable functional groups (typically radically polymerizable functional groups) having unsaturated double bonds such as (meth)acryloyl groups and vinyl groups as other monomer components. It may contain a monomer. By using a polyfunctional monomer as the monomer component, the cohesive force of the pressure-sensitive adhesive layer can be increased. Polyfunctional monomers can be used as cross-linking agents. Polyfunctional monomers are not particularly limited, and examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and neopentyl glycol di(meth)acrylate. etc. A polyfunctional monomer can be used individually by 1 type or in combination of 2 or more types.

The amount of the polyfunctional monomer used is not particularly limited, and can be appropriately set so as to achieve the intended use of the polyfunctional monomer. The amount of the polyfunctional monomer used can be approximately 3% by weight or less, preferably approximately 2% by weight or less, and more preferably approximately 1% by weight or less (for example, approximately 0.5% by weight or less) based on the above monomer components. The lower limit of the amount used when using a polyfunctional monomer is not particularly limited as long as it is greater than 0% by weight. Usually, by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component, the effect of using the polyfunctional monomer can be appropriately exhibited.

The copolymer composition of the acrylic polymer is suitably designed so that the Tg of the polymer is approximately −15° C. or lower (typically approximately −70° C. or higher and −15° C. or lower). Here, the Tg of the acrylic polymer refers to the Tg determined by the Fox formula based on the composition of the monomer components used in synthesizing the polymer. The Fox equation 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 is the glass transition temperature of the copolymer (unit: K), Wi is the weight fraction of the monomer i in the copolymer (copolymerization ratio based on weight), and Tgi is the content of the monomer i. It represents the glass transition temperature (unit: K) of a homopolymer.

As the glass transition temperature of the homopolymer used for calculating the Tg, the value described in the known materials shall be used. For example, for the monomers listed below, the following values are used as the glass transition temperatures of the homopolymers of the monomers.
2-ethylhexyl acrylate -70°C
n-butyl acrylate -55°C
2-hydroxyethyl acrylate -15°C
4-hydroxybutyl acrylate -40°C
Vinyl acetate 32°C
Acrylic acid 106°C
Methacrylic acid 228°C

For the glass transition temperatures of homopolymers of monomers other than those exemplified above, the values described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values are listed in this document, the highest value is adopted. If it is not described in the above Polymer Handbook, the value obtained by the measurement method described in JP-A-2007-51271 shall be used.

Although not particularly limited, from the viewpoint of adhesion to the adherend, the Tg of the acrylic polymer is advantageously about −25° C. or less, preferably about −35° C. or less, more preferably about −35° C. or less. The temperature is -45°C or lower, more preferably about -55°C or lower, particularly preferably -60°C or lower, and may be -62°C or lower (for example, -64°C or lower). A low Tg of the acrylic polymer is also advantageous in terms of impact resistance. Further, from the viewpoint of the cohesive strength of the pressure-sensitive adhesive layer, the Tg of the acrylic polymer is advantageously about -70°C or higher, preferably about -68°C or higher, and about -65°C or higher. good too. The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the types and usage ratios of the monomers used in synthesizing the polymer).

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization. can be adopted as appropriate. For example, a solution polymerization method can be preferably employed. As a method for supplying the monomers when carrying out solution polymerization, a batch charging method for supplying all monomer raw materials at once, a continuous supply (dropping) method, a divided supply (dropping) method, or the like can be appropriately employed. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20° C. to 170° C. (typically about 40° C. to 140° C.). can be done.

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo 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; group carbonyl compounds; and the like. Still another example of the polymerization initiator is a redox initiator obtained by combining a peroxide and a reducing agent. Such polymerization initiators can be used singly or in combination of two or more. The amount of the polymerization initiator to be used may be a normal amount, for example, about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of all the monomer components. degree).

(tackifying resin)
The adhesive layer disclosed herein comprises a tackifying resin. The tackifier resin is not particularly limited, and examples thereof include rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, Various tackifying resins such as phenol-based tackifying resins and ketone-based tackifying resins can be used. Such tackifying resins can be used singly or in combination of two or more.

Specific examples of rosin-based tackifying resins include unmodified rosins (fresh rosins) such as gum rosin, wood rosin and tall oil rosin; hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosin, etc. (same below); other various rosin derivatives; Examples of the rosin derivative include rosins obtained by esterifying unmodified rosin with alcohols (that is, esterified rosin), and esterifying modified rosin with alcohols (that is, esterified rosin). Esters; Undenatured rosin and rosins modified with unsaturated fatty acids obtained by modifying rosin with unsaturated fatty acids; Rosin esters modified with unsaturated fatty acids obtained by modifying rosin esters with unsaturated fatty acids; Unmodified rosin, modified rosin, unsaturated Rosin alcohols obtained by reducing the carboxy group in fatty acid-modified rosins or unsaturated fatty acid-modified rosin esters; metal salts of rosins (especially rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosins rosin phenol resin obtained by adding phenol to (unmodified rosin, modified rosin, various rosin derivatives, etc.) with an acid catalyst and thermally polymerizing; and the like. Among them, rosin ester is 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 ester, triethylene glycol ester, and glycerin ester. , pentaerythritol ester and the like.

Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymer, β-pinene polymer, dipentene polymer; modification of these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modified terpene resin; An example of the modified terpene resin is a terpene phenol resin.

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

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

In some aspects, it is preferred to use a rosin-based tackifying resin as the tackifying resin. By including the rosin-based tackifying resin in the pressure-sensitive adhesive, the adhesive force to the LSE surface can be preferably improved. Among them, rosin ester is preferred. The proportion of the rosin-based tackifying resin in the total tackifying resin contained in the pressure-sensitive adhesive layer may be, for example, more than about 50% by weight, may be about 70% by weight or more, or may be about 80% by weight or more. . In the technology disclosed herein, substantially all of the tackifying resin (for example, approximately 97% by weight or more, or 99% by weight or more, or even 100% by weight) is preferably a rosin-based tackifying resin. can be implemented.

When a rosin-based tackifying resin is used as the tackifying resin, the content of the tackifying resin (non-rosin-based tackifying resin) other than the rosin-based tackifying resin in the pressure-sensitive adhesive layer is, for example, 100 parts by weight of the acrylic polymer. 40 parts by weight or less. As a result, the effect of including the rosin ester is favorably exhibited. The amount of the non-rosin-based tackifying resin used is preferably about 20 parts by weight or less (for example, less than 20 parts by weight), more preferably about 10 parts by weight or less, still more preferably about 5 parts by weight, relative to 100 parts by weight of the acrylic polymer. It is not more than a part by weight, and may be about 1 part by weight or less. The amount of the non-rosin tackifying resin used may be, for example, approximately 1 part by weight or more, approximately 5 parts by weight or more, or 15 parts by weight or more with respect to 100 parts by weight of the acrylic polymer.

In some preferred embodiments, the pressure-sensitive adhesive layer contains less than 5 parts by weight of the terpene phenolic resin as the tackifying resin with respect to 100 parts by weight of the acrylic polymer. By limiting the amount of the terpene phenol resin to be used in this way, the effect of improving the adhesive force to the LSE surface is likely to be obtained. Here, the fact that the content of the terpene phenol resin is less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer means that the pressure-sensitive adhesive layer does not contain the terpene phenol resin, and that the terpene phenol resin is added to the acrylic polymer. It is used in the sense of including both of containing at a ratio of less than 5 parts by weight with respect to 100 parts by weight. The content of the terpene phenol resin in the adhesive layer is preferably less than 3 parts by weight with respect to 100 parts by weight of the acrylic polymer, and is in the range of 1 part by weight or less (for example, 0 to 0.1 parts by weight). is more preferable.

The tackifying resin includes a tackifying resin T _L having a softening point of 110° C. or less. By using the tackifying resin _TL , high adhesion to the LSE surface can be obtained. From the viewpoint of adhesion to the LSE surface, the softening point of the tackifying resin T _L is suitably less than 110°C, preferably about 105°C or less, more preferably about 100°C or less, and even more preferably about 100°C or less. 95° C. or less (eg, less than 95° C.), particularly preferably about 90° C. or less (eg, about 85° C. or less). The lower limit of the softening point of the tackifying resin _TL is not particularly limited. In some aspects, the softening point of the tackifying resin T _L may be, for example, approximately 50° C. or higher, approximately 60° C. or higher, or approximately 65° C. or higher, from the viewpoint of exhibiting an appropriate cohesive force. It may be about 70° C. or higher.

As the tackifying resin _TL , one selected from those having a softening point of 110° C. or lower among the tackifying resins exemplified above can be used singly or in combination of two or more. In some embodiments, the tackifying resin T _L preferably comprises a rosin-based tackifying resin. The tackifying resin _TL may contain one type of rosin-based tackifying resin alone, or may contain two or more types of rosin-based tackifying resin in combination.

Examples of rosin-based tackifying resins that can be preferably employed as the tackifying resin _TL include, but are not particularly limited to, rosin esters such as unmodified rosin esters and modified rosin esters. Preferred examples of modified rosin esters include hydrogenated rosin esters. For example, esters of unmodified rosin or modified rosin (eg, hydrogenated rosin), eg, rosin esters such as methyl esters, glycerin esters, etc., can be used as tackifying resins T _L .

In some preferred embodiments of the pressure-sensitive adhesive layer, the tackifying resin _TL comprises a hydrogenated rosin ester. The tackifying resin T _L may also include non-hydrogenated rosin esters. Here, the non-hydrogenated rosin ester is a concept that comprehensively refers to those other than the hydrogenated rosin ester among the rosin esters described above. Examples of non-hydrogenated rosin esters include unmodified rosin esters, disproportionated rosin esters and polymerized rosin esters. The tackifying resin T _L may contain, as rosin esters, a combination of a hydrogenated rosin ester and a non-hydrogenated rosin ester, or may contain only one or two or more hydrogenated rosin esters. It may contain only seeds or two or more non-hydrogenated rosin esters. The pressure-sensitive adhesive layer according to some preferred embodiments contains only one or more hydrogenated rosin esters as the rosin esters contained in the tackifying resin _TL .

The tackifier resin _TL may contain other tackifier resins in addition to the rosin-based tackifier resin. As the other tackifying resin, one selected from those having a softening point of 110° C. or lower among the tackifying resins exemplified above can be used alone or in combination of two or more.

In some embodiments, the proportion of the rosin-based tackifying resin in the total tackifying resin T _L can be, for example, approximately greater than 50% by weight, may be approximately 65% by weight or greater, or approximately 75% by weight or greater. good too. The technology disclosed herein is an aspect in which substantially all of the tackifying resin T _L (for example, about 97% by weight or more, or 99% by weight or more, or even 100% by weight) is a rosin-based tackifying resin. can be preferably implemented in

Further, as the tackifying resin T _L , for example, a tackifying resin having a softening point of less than 50° C., more preferably about 40° C. or less (typically a tackifying resin such as a rosin-based, terpene-based, or hydrocarbon-based tackifying resin, such as Hydrogenated rosin methyl ester, etc.) may or may not be included. Such a low softening point tackifying resin may be a liquid tackifying resin that exhibits a liquid state at 30°C. Liquid tackifying resins can be used singly or in combination of two or more. The content of the liquid tackifying resin can be about 30% by weight or less of the entire tackifying resin T _L from the viewpoint of cohesive strength, etc., and should be about 10% by weight or less (for example, 0 to 10% by weight). is suitable, and may be about 2% by weight or less (0.5 to 2% by weight), or less than 1% by weight.

The content of the tackifier resin T _L (the total amount when two or more tackifier resins T _L are included) is 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. By setting the amount of the tackifying resin _TL within the above range, the adhesive strength to the LSE surface is improved, and it is easy to maintain good holding power. The amount of the tackifying resin T _L used is preferably about 70 parts by weight or less, more preferably about 60 parts by weight or less, and even more preferably about 55 parts by weight, relative to 100 parts by weight of the acrylic polymer, from the viewpoint of holding power and the like. parts or less, and may be about 45 parts by weight or less. The amount of the tackifier resin T _L used is, for example, about 24 parts by weight or more, preferably about 30 parts by weight or more (for example, more than 30 parts by weight), more preferably about 100 parts by weight of the acrylic polymer. It is 35 parts by weight or more, more preferably about 38 parts by weight or more, and may be about 45 parts by weight or more (for example, 60 parts by weight or more).

In some preferred embodiments, the adhesive layer comprises a combination of a tackifying resin T _L and a tackifying resin T _H having a softening point above 110° C. (typically above 110° C. and 200° C. or less). By using the tackifying resin T _L and the tackifying resin T _H together, it is easy to achieve higher adhesion to the LSE surface. As the _tackifying resin TH, among the tackifying resins exemplified above, those having a softening point of over 110° C. can be used singly or in combination of two or more. The _tackifying resin TH preferably contains one or more selected from rosin-based tackifying resins. More preferably, both the tackifying resin T _L and the tackifying resin T _H contain a rosin-based tackifying resin.

The softening point of the _tackifier resin TH is preferably about 115° C. or higher, more preferably about 120° C. or higher, may be about 130° C. or higher, or may be about 140° C. or higher, from the viewpoint of improving the cohesive strength. . The upper limit of the softening point of the tackifying resin T _H is not particularly limited, and from the viewpoint of adhesion to the adherend, the softening point is about 200 ° C. or lower (more preferably about 160 ° C. or lower, further preferably 145 ° C. or lower, for example about 130° C. or less) can be preferably used.

The softening point of the tackifying resin as used herein 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 the lowest possible temperature and carefully filled into a ring placed on a flat metal plate to avoid the formation of bubbles. After it cools down, cut off the raised part from the plane including the top of the ring with a slightly heated knife. Next, a supporter (ring base) is placed in a glass container (heating bath) having 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, the steel ball (diameter 9.5 mm, weight 3.5 g) and the ring filled with the sample are immersed in the glycerin without touching each other, and the temperature of the glycerin is kept at 20° C.±5° C. for 15 minutes. . A steel ball is then centered on the surface of the sample in the ring and placed in position on the support. Next, the distance from the upper end of the ring to the glycerin surface is kept at 50 mm, a thermometer is placed, the center of the mercury ball of the thermometer is set at the same height as the center of the ring, and the container is heated. The Bunsen burner flame used for heating is directed halfway between the center and the rim of the bottom of the vessel to ensure even heating. The rate at which the bath temperature rises after reaching 40° C. from the start of heating must be 5.0±0.5° C. per minute. The temperature at which the sample gradually softens and flows down the ring and finally touches the bottom plate is read and taken as the softening point. Two or more softening points are measured at the same time, and the average value is adopted.

The tackifier resin T _L accounts for 60% by weight or more of the total amount of tackifier resins contained in the adhesive layer. This makes it possible to improve the adhesive strength to the LSE surface while having good holding power. In some preferred embodiments, the tackifying resin comprises a tackifying resin T _L and a tackifying resin T _H. In this embodiment, the proportion of the _tackifying resin TL in the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer is preferably 70% by weight or more from the viewpoint of more effectively exhibiting the effect of using the tackifying resin _TL . and may be 75% by weight or more, or may be 78% by weight or more. Further, the proportion of the tackifying resin T _L in the total amount of the tackifying resin is preferably 95% by weight or less, more preferably 90% by weight, from the viewpoint of better expressing the effect of using the tackifying resin T _H. Below, it is more preferably 85% by weight or less, and may be 80% by weight or less. In some other embodiments, the tackifying resin contained in the adhesive layer consists essentially of the tackifying resin _TL . In this embodiment, the ratio of the tackifier resin T _L to the total amount of tackifier resin contained in the adhesive layer is in the range of 99 to 100% by weight.

Although not particularly limited, in some embodiments, the tackifying resin may comprise a tackifying resin having a hydroxyl value of less than 70 mg KOH/g. Among them, a tackifying resin having a hydroxyl value of less than 60 mgKOH/g (more preferably less than 50 mgKOH/g, still more preferably less than 45 mgKOH/g) is preferred. Hereinafter, a tackifying resin having a hydroxyl value of less than 70 mgKOH/g may be referred to as a "low hydroxyl value resin". A tackifying resin containing such a low hydroxyl value resin can preferably realize a pressure-sensitive adhesive layer having excellent adhesion to an LSE adherend. 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. Low hydroxyl value resin can be used individually by 1 type or in combination of 2 or more types. As the low hydroxyl value resin, one selected from among the tackifier resins exemplified above having a hydroxyl value of less than 70 mgKOH/g can be used alone or in combination of two or more. In some embodiments, the low hydroxyl value resin preferably comprises a rosin-based tackifying resin. The low hydroxyl value resin may contain one type of rosin-based tackifying resin alone, or may contain two or more types of rosin-based tackifying resin in combination. Further, the low hydroxyl value resin may be the tackifying resin T _L described above, or may be the tackifying resin T _H , and both the tackifying resin T _L and the tackifying resin T _H are low hydroxyl value resins. may be

It is preferable that the low hydroxyl value resin accounts for 60% by weight or more of the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer. This makes it possible to improve the adhesive force to the LSE surface. In some preferred embodiments, the ratio of the low hydroxyl value resin to the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer is preferably 70% by weight from the viewpoint of more effectively exerting the effect of using the low hydroxyl value resin. or more, and may be 75% by weight or more, or may be 78% by weight or more. In some other embodiments, the tackifying resin contained in the adhesive layer consists essentially of low hydroxyl value resin. In this embodiment, the ratio of the low hydroxyl value resin to the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer is in the range of 99-100% by weight.

In addition, the pressure-sensitive adhesive layer disclosed herein contains, as a tackifying resin, a tackifying resin having a hydroxyl value of 70 mgKOH/g or more (hereinafter also referred to as a "high hydroxyl value resin"). It is preferably less than 5 parts by weight per part. By limiting the amount of the high hydroxyl value resin to be used in this manner, the effect of improving the adhesive force to the LSE surface is likely to be obtained. Here, the fact that the content of the high hydroxyl value resin is less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer means that the adhesive layer does not contain the high hydroxyl value resin, and that the high hydroxyl value resin is not included. It is used in the sense of including both of containing at a ratio of less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. The content of the high hydroxyl value resin in the adhesive layer is preferably less than 3 parts by weight with respect to 100 parts by weight of the acrylic polymer, and is in the range of 1 part by weight or less (for example, 0 to 0.1 parts by weight). It is more preferable to have

Here, as the value of the hydroxyl value, a value measured by a potentiometric titration method specified in JIS K0070:1992 can be adopted. A specific measuring method is as follows.
[Method for measuring hydroxyl value]
1. Reagent (1) As the acetylation reagent, approximately 12.5 g (approximately 11.8 mL) of acetic anhydride is taken, pyridine is added to bring the total amount to 50 mL, and the mixture is thoroughly stirred and used. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to bring the total amount to 100 mL, and use the mixture after thorough stirring.
(2) A 0.5 mol/L potassium hydroxide ethanol solution is used as a measurement reagent.
(3) In addition, prepare toluene, pyridine, ethanol and distilled water.
2. Operation (1) About 2 g of a sample is accurately weighed and collected in a flat-bottomed flask, 5 mL of an acetylation reagent and 10 mL of pyridine are added, and an air cooling tube is attached.
(2) After heating the flask in a bath at 100°C for 70 minutes, allowing it to cool, adding 35 mL of toluene as a solvent from the top of the cooling tube and stirring, then adding 1 mL of distilled water and stirring to obtain acetic anhydride. decompose. Heat again in the bath for 10 minutes for complete decomposition and allow to cool.
(3) Wash the cooling tube with 5 mL of ethanol and remove. Then, 50 mL of pyridine is added as a solvent and stirred.
(4) Add 25 mL of 0.5 mol/L potassium hydroxide ethanol solution using a whole pipette.
(5) Perform potentiometric titration with 0.5 mol/L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is taken as the end point.
(6) In the blank test, the above (1) to (5) are performed without any sample.
3. Calculation Calculate the hydroxyl value by the following formula.
Hydroxyl value (mgKOH/g) = [(BC) x f x 28.05]/S + D
here,
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 for the sample,
f: factor of 0.5 mol/L potassium hydroxide ethanol solution,
S: weight of sample (g),
D: acid value,
28.05: ½ of the molecular weight of potassium hydroxide, 56.11;
is.

The content of the tackifier resin (the total amount when two or more tackifier resins are included) is in the range of 40 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer. By setting the amount of the tackifier resin to be used within the above range, the adhesive strength to the LSE surface can be improved. Also, by setting the amount of the tackifying resin used to 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer, it is easy to maintain good holding power. In some embodiments, the amount of tackifying resin used can be, for example, greater than 40 parts by weight, may be approximately 42 parts by weight or more, or approximately 45 parts by weight or more, relative to 100 parts by weight of the acrylic polymer. It may be about 48 parts by weight or more, or about 50 parts by weight or more (for example, 60 parts by weight or more). The amount of the tackifying resin used is preferably about 70 parts by weight or less, more preferably about 65 parts by weight or less, and even more preferably about 60 parts by weight with respect to 100 parts by weight of the acrylic polymer, from the viewpoint of holding power and the like. parts or less, and may be about 55 parts by weight or less.

In the technology disclosed herein, the total content of the acrylic polymer and the tackifying resin in the pressure-sensitive adhesive layer is appropriately set so that the effect of the technology disclosed herein is exhibited, and is limited to a specific range. not something. The total amount (total amount) of the acrylic polymer and the tackifying resin contained in the pressure-sensitive adhesive layer according to some preferred embodiments is more than 50% by weight from the viewpoint of preferably exhibiting the effects of the technology disclosed herein. is suitable, preferably about 70% by weight or more, more preferably about 90% by weight or more, still 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 97% by weight % or more.

(crosslinking agent)
In the technique disclosed here, the adhesive composition used for forming the adhesive layer may contain a cross-linking agent as needed. The type of cross-linking agent is not particularly limited. Alkoxide cross-linking agents, metal chelate cross-linking agents, metal salt cross-linking agents, carbodiimide cross-linking agents, hydrazine cross-linking agents, amine cross-linking agents, silane coupling agents and the like can be mentioned. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types. Among them, isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, and melamine-based cross-linking agents are preferable, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are more preferable, and epoxy-based cross-linking agents are particularly preferable. . By appropriately selecting and using a cross-linking agent, the cohesive force of the pressure-sensitive adhesive layer can be obtained, and the adhesive force and the like to the LSE surface can be improved. The pressure-sensitive adhesive layer in the technology disclosed herein contains the cross-linking agent in the form after the cross-linking reaction, the form before the cross-linking reaction, the form after the cross-linking reaction, the intermediate or composite form thereof, and the like. can contain The cross-linking agent is typically contained in the pressure-sensitive adhesive layer exclusively in the form after the cross-linking reaction.

As the epoxy-based cross-linking agent, a compound having two or more epoxy groups in one molecule can be used without particular limitation. An epoxy-based cross-linking agent having 3 to 5 epoxy groups in one molecule is preferred. Epoxy-based cross-linking agents may be used singly or in combination of two or more.

Specific examples of epoxy-based cross-linking agents include, but are not limited to, N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl ) cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether and the like. Commercially available epoxy-based cross-linking agents include Mitsubishi Gas Chemical Company's trade name "TETRAD-C" and trade name "TETRAD-X", DIC's trade name "Epiclon CR-5L", and Nagase ChemteX Corporation. and "TEPIC-G" manufactured by Nissan Chemical Industries, Ltd. under the trade name of "Denacol EX-512".

The amount of the epoxy-based cross-linking agent used is not particularly limited. The amount of the epoxy-based cross-linking agent used is, 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) with respect to 100 parts by weight of the acrylic polymer. can. From the viewpoint of suitably exhibiting the effect of improving the cohesive strength, the amount of the epoxy-based cross-linking agent to be used is appropriately about 0.005 parts by weight or more, and about 0.01 part by weight, relative to 100 parts by weight of the acrylic polymer. A weight part or more is preferable, and about 0.02 weight part or more is more preferable. In addition, from the viewpoint of improving the adhesion to the adherend, the amount of the epoxy-based cross-linking agent to be used is appropriately about 0.5 parts by weight or less, and about 0.2 parts by weight, per 100 parts by weight of the acrylic polymer. It is preferably not more than 0.1 part by weight, more preferably not more than about 0.1 part by weight, may be not more than 0.07 part by weight, or may be not more than 0.04 part by weight. Impact resistance tends to be improved by reducing the amount of the epoxy-based cross-linking agent used.

In some preferred embodiments, an epoxy-based cross-linking agent and at least one cross-linking agent having a different type of cross-linkable functional group from the epoxy-based cross-linking agent are used in combination as the cross-linking agent. According to the technique disclosed herein, a cross-linking agent other than an epoxy-based cross-linking agent (that is, a cross-linking agent having a different type of cross-linkable reactive group from the epoxy-based cross-linking agent; hereinafter also referred to as a "non-epoxy cross-linking agent"). By using it in combination with an epoxy-based cross-linking agent, it is possible to favorably achieve both adhesion to the LSE surface and high holding power.

The type of non-epoxy cross-linking agent that can be used in combination with the epoxy cross-linking agent is not particularly limited, and can be appropriately selected from the cross-linking agents described above. Non-epoxy crosslinking agents may be used singly or in combination of two or more.

In some preferred embodiments, an isocyanate cross-linking agent can be employed as the non-epoxy cross-linking agent. For example, by using an epoxy-based cross-linking agent and an isocyanate-based cross-linking agent in combination, more excellent adhesive properties can be achieved. As the isocyanate-based cross-linking agent, a polyfunctional isocyanate (meaning 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 cross-linking agents may be used singly or in combination of two or more.

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

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; 1,2-cyclopentyl diisocyanate, 1,3 - cyclopentyl diisocyanate such as cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and the like.

Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate. , 4,4′-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4′-diisocyanate, 2,2′-diphenylpropane-4,4′-diisocyanate, 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, xylylene-1,3-diisocyanate, and the like.

Examples of preferred polyfunctional isocyanates include polyfunctional isocyanates having an average of 3 or more isocyanate groups per molecule. Such tri- or more functional isocyanates are polymers (typically dimers or trimers) of di- or tri- or more functional isocyanates, derivatives (for example, polyhydric alcohols and two or more molecules of polyfunctional isocyanates). addition reaction products), polymers, and the like. For example, dimers and trimers of diphenylmethane diisocyanate, isocyanurate of hexamethylene diisocyanate (trimer adduct of isocyanurate structure), reaction products of trimethylolpropane and tolylene diisocyanate, trimethylolpropane and hexa Polyfunctional isocyanates such as reaction products with methylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and the like can be mentioned. Commercially available polyfunctional isocyanates include "Duranate TPA-100" (trade name) manufactured by Asahi Kasei Chemicals, "Coronate L" (trade name), "Coronate HL", "Coronate HK" (trade name) and "Coronate HK" (trade names) manufactured by Tosoh Corporation. HX", "Coronate 2096", and the like.

The amount of the isocyanate-based cross-linking agent used is not particularly limited. For example, it can be about 0.1 part by weight or more with respect to 100 parts by weight of the acrylic polymer. From the viewpoint of cohesion and adhesion, impact resistance, etc., the amount of the isocyanate cross-linking agent used relative to 100 parts by weight of the acrylic polymer can be, for example, 0.5 parts by weight or more, and 1.0 parts by weight. 1 part or more is suitable, preferably 1.5 parts by weight or more. The amount of the isocyanate-based cross-linking agent used is suitably 10 parts by weight or less per 100 parts by weight of the acrylic, preferably less than 5 parts by weight, more preferably less than 4.0 parts by weight, and further It is preferably less than 3.0 parts by weight (for example, 2.5 parts by weight or less).

The technology disclosed herein is preferably implemented in a mode in which an epoxy-based cross-linking agent and an isocyanate-based cross-linking agent are used in combination. In this embodiment, the relationship between the content of the epoxy-based cross-linking agent and the content of the isocyanate-based cross-linking agent is not particularly limited. The content of the epoxy-based cross-linking agent can be, for example, about 1/10 or less of the content of the isocyanate-based cross-linking agent. From the viewpoint of achieving both adhesion and cohesive strength to adherends and substrates, it is appropriate that the content of the epoxy-based cross-linking agent is about 1/30 or less of the content of the isocyanate-based cross-linking agent. It is preferable to make it about 1/50 or less (for example, 1/60 or less). In addition, from the viewpoint of suitably exhibiting the effect of using the epoxy-based cross-linking agent and the isocyanate-based cross-linking agent in combination, the content of the epoxy-based cross-linking agent is usually about 1/1000 of the content of the isocyanate-based cross-linking agent. above, for example, about 1/500 or more, preferably about 1/300 or more, more preferably 1/120 or more, still more preferably 1/100 or more, particularly preferably 1/80 or more (for example, 1/80 or more) /70).

The total amount of the cross-linking agent used is not particularly limited, and for example, about 0.005 parts by weight or more (for example, 0.01 parts by weight or more, typically 0.1 parts by weight or more) with respect to 100 parts by weight of the acrylic polymer. about 10 parts by weight or less (for example, about 8 parts by weight or less, preferably about 5 parts by weight or less).

(Other additives)
In addition to the components described above, the pressure-sensitive adhesive composition may optionally contain a leveling agent, a cross-linking aid, a plasticizer, a softening agent, a filler, a coloring agent (pigment, dye, etc.), an antistatic agent, and an anti-aging agent. , ultraviolet absorbers, antioxidants, light stabilizers, and other additives commonly used in the field of adhesives. In addition, the pressure-sensitive adhesive composition may optionally contain a polymer (rubber-based polymer, etc.) other than the acrylic polymer within a range that does not impair the effects of the invention. As for such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed description thereof will be omitted.

The pressure-sensitive adhesive layer (layer comprising pressure-sensitive adhesive) disclosed herein is formed from a water-based pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition. It can be a pressure-sensitive adhesive layer. The water-based pressure-sensitive adhesive composition refers to a pressure-sensitive adhesive composition in the form of containing a pressure-sensitive adhesive (adhesive layer-forming component) in a water-based solvent (aqueous solvent), typically water-dispersed. Also included are so-called type adhesive compositions (compositions in which at least part of the adhesive is dispersed in water) and the like. Moreover, the solvent-type adhesive composition refers to an adhesive composition in the form of containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based pressure-sensitive adhesive composition, one or two or more of the organic solvents (toluene, ethyl acetate, etc.) exemplified as the organic solvent (toluene, ethyl acetate, etc.) that can be used in the above solution polymerization can be used without particular limitation. From the viewpoint of adhesive properties, the technology disclosed herein can be preferably practiced in a mode comprising a pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition.

The adhesive layer disclosed here can be formed by a conventionally known method. For example, a method of forming a pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive composition to a releasable surface (release surface) or a non-releasable surface and drying can be employed. In a pressure-sensitive adhesive sheet having a substrate, for example, a method (direct method) of forming a pressure-sensitive adhesive layer by directly applying (typically applying) a pressure-sensitive adhesive composition to the substrate and drying it is adopted. be able to. Alternatively, a method of applying a pressure-sensitive adhesive composition to a surface having releasability (release surface) and drying to form a pressure-sensitive adhesive layer on the surface and transferring the pressure-sensitive adhesive layer to a substrate (transfer method). may be adopted. 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 base material subjected to a release treatment, or the like can be used. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form. It may be a formed pressure-sensitive adhesive layer.

Application of the adhesive composition can be performed using a conventionally known coater such as a gravure roll coater, a die coater, and a bar coater. Alternatively, the adhesive composition may be applied by impregnation, curtain coating, or the like.
From the viewpoint of promoting the cross-linking reaction, improving production efficiency, etc., it is preferable to dry the pressure-sensitive adhesive composition under heating. The drying temperature can be, for example, about 40 to 150°C, preferably about 60 to 130°C. After drying the pressure-sensitive adhesive composition, it may be further aged for the purpose of adjusting migration of components in the pressure-sensitive adhesive layer, progressing the crosslinking reaction, relaxing strain that may exist in the pressure-sensitive adhesive layer, and the like.

The thickness of the adhesive layer is not particularly limited. From the viewpoint of avoiding excessive thickness of the adhesive sheet, the thickness of the adhesive layer is usually about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, and even more preferably about 50 μm or less. is. The thickness of the pressure-sensitive adhesive layer may be approximately 35 μm or less, for example approximately 30 μm or less. A pressure-sensitive adhesive layer with a limited thickness can well meet demands for thinning and weight reduction. In general, when the thickness of the pressure-sensitive adhesive layer becomes small, the adhesion to the adherend tends to decrease. , an improvement in adhesion to the LSE surface can be realized. The lower limit of the thickness of the pressure-sensitive adhesive layer is not particularly limited, and from the viewpoint of adhesion to the adherend, it is advantageous to set it to about 3 μm or more, preferably about 10 μm or more, more preferably about 12 μm or more (for example, 12 μm), more preferably about 15 μm or more, for example about 18 μm or more. The pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers having the thicknesses described above on both sides of a substrate. Further, in a double-sided pressure-sensitive adhesive sheet with a substrate having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on each side of the substrate, the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer have the same thickness. There may be one, or they may have mutually different thicknesses.

<Base material>
In the embodiment in which the pressure-sensitive adhesive sheet disclosed herein is in the form of a single-sided pressure-sensitive adhesive type or double-sided pressure-sensitive adhesive type pressure-sensitive adhesive sheet with a substrate, the substrate that supports (backs) the pressure-sensitive adhesive layer may be a resin film, paper, cloth, or rubber. Sheets, foam sheets, metal foils, composites thereof, and the like can be used. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene/propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; resin film; polyamide resin film; fluorine resin film; cellophane and the like. Examples of paper include Japanese paper, kraft paper, glassine paper, woodfree paper, synthetic paper, top coat paper, and the like. Examples of fabrics include woven fabrics and non-woven fabrics obtained by spinning various fibrous materials alone or by blending them. Examples of the fibrous substance 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, foamed polychloroprene rubber sheets, and the like. Examples of metal foil include aluminum foil and copper foil. The substrate supporting the adhesive layer is also referred to as a substrate layer in the adhesive sheet.

As the base material constituting the pressure-sensitive adhesive sheet with a base material, a base film containing a resin film can be preferably used. The base film is typically an independently shape-maintainable (independent) member. The substrate in the technology disclosed herein can be substantially composed of such a base film. Alternatively, the substrate may contain 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 containing a resin material as a main component (for example, a component contained in the resin film in an amount exceeding 50% by weight). Examples of resin films include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene/propylene copolymer; polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and the like. vinyl chloride resin film; vinyl acetate resin film; polyimide resin film; polyamide resin film; fluorine resin film; The resin film may be a rubber-based film such as a natural rubber film or a butyl rubber film. Among them, from the viewpoint of handleability and workability, a polyester film is preferred, and a PET film is particularly preferred.

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

If necessary, the base material (for example, resin film) may contain fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet Various additives such as absorbents, antistatic agents, lubricants and plasticizers may be added. The blending ratio of various additives is about less than 30% by weight (for example, less than 20% by weight, typically less than 10% by weight).

The base material (for example, resin film) may have a single-layer structure, or may have a multi-layer structure of two layers, three layers, or more. From the viewpoint of shape stability, the substrate preferably has a single-layer structure. In the case of a multilayer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (for example, polyester resin). A method for manufacturing the substrate (typically a resin film) is not particularly limited, and a conventionally known method may be appropriately adopted. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be employed as appropriate.

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

Moreover, when the technology disclosed herein is implemented in the form of a single-sided pressure-sensitive adhesive sheet with a substrate, the back surface of the substrate may be subjected to release treatment as necessary. For the release treatment, for example, a general silicone-based, long-chain alkyl-based, fluorine-based, etc. release agent is typically applied to a thin film of about 0.01 μm to 1 μm (eg, 0.01 μm to 0.1 μm). It can be a treatment to give. By performing such a peeling treatment, it is possible to obtain effects such as facilitating the unwinding of the adhesive sheet wound into a roll.

In the pressure-sensitive adhesive sheet containing a substrate, the thickness of the substrate is not particularly limited. From the viewpoint of avoiding excessive thickness of the pressure-sensitive adhesive sheet, 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. The thickness of the base material may be approximately 70 μm or less, approximately 50 μm or less, or approximately 30 μm or less (for example, approximately 25 μm or less) depending on the intended use and usage mode of the pressure-sensitive adhesive sheet. In some embodiments, the thickness of the base film layer may be about 20 μm or less, about 15 μm or less, about 10 μm or less (eg, about 5 μm or less). By reducing the thickness of the substrate, the thickness of the adhesive layer can be increased even if the total thickness of the adhesive sheet is the same. This can be advantageous from the viewpoint of improving adhesion to adherends and substrates. The lower limit of the base material is not particularly limited. From the standpoint of handleability and workability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (eg, 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 approximately 15 μm or greater, and can be approximately 25 μm or greater.

<Release liner>
In the technology disclosed herein, a release liner can be used in the formation of the adhesive layer, production of the adhesive sheet, storage of the adhesive sheet before use, distribution, shape processing, and the like. 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, a release liner made of a fluoropolymer (such as polytetrafluoroethylene), or the like is used. be able to. The release treatment layer may be formed by surface-treating the liner base material with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide release agent.

<Total thickness of adhesive sheet>
The total thickness of the adhesive sheet disclosed herein (including an 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 can be, for example, approximately 300 μm or less, and from the viewpoint of thinning, approximately 200 μm or less is suitable, and approximately 150 μm or less (for example, approximately 100 μm or less) may be used. In some preferred embodiments, the thickness of the adhesive sheet can be approximately 50 μm or less, such as approximately 35 μm or less, or even less than 30 μm. The lower limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited. It may be 100 μm or more. A pressure-sensitive adhesive sheet having a thickness of a predetermined value or more tends to have good adhesion to adherends and impact resistance, and also tends to be excellent in handleability. In addition, in the substrate-less adhesive sheet, the thickness of the adhesive layer is the total thickness of the adhesive sheet.

<Characteristics of adhesive sheet>
The pressure-sensitive adhesive sheet disclosed herein preferably has a 180-degree peel strength to polypropylene (adhesive strength to PP) of approximately 12 N/20 mm or more. A pressure-sensitive adhesive sheet exhibiting such adhesive strength to PP can adhere well to an LSE adherend and exhibit high adhesion reliability to the adherend. The adhesive strength to PP is more preferably about 12.5 N/20 mm or more, more preferably about 13.5 N/20 mm or more, and particularly preferably about 14.5/20 mm or more (e.g. about 15.0 N/20 mm or more). . The upper limit of the adhesive strength to PP is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually about 30 N/20 mm or less, and may be 25 N/20 mm or less. The adhesive strength to PP is measured using PP as an adherend under the conditions of a tensile speed of 300 mm/min and a peeling angle of 180 degrees in a measurement environment of 23° C. and 50% RH. More specifically, it is measured by the method described in Examples below.

The pressure-sensitive adhesive sheet disclosed herein preferably has a 180-degree peel strength to polyethylene (adhesive strength to PE) of approximately 6 N/20 mm or more. A pressure-sensitive adhesive sheet exhibiting such PE-adhesive strength adheres well to an LSE adherend, and can exhibit high adhesion reliability to the adherend. The adhesion to PE is more preferably about 7.0 N/20 mm or more, more preferably about 8.0 N/20 mm or more, particularly preferably about 9.0/20 mm or more (e.g. about 10.0 N/20 mm or more, and further 12 N/20 mm or more). The upper limit of the adhesive strength to PE is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually about 30 N/20 mm or less, and may be 20 N/20 mm or less. The adhesion to PE is measured using PE as an adherend under the conditions of a tensile speed of 300 mm/min and a peeling angle of 180 degrees in a measurement environment of 23° C. and 50% RH. More specifically, it is measured by the method described in Examples below.

The pressure-sensitive adhesive sheet disclosed herein can exhibit a predetermined value or more of pressure-sensitive adhesive strength to PP and PE, as described above. The pressure-sensitive adhesive sheet exhibiting the adhesive strength to PP and the adhesive strength to PE can stably have sufficient adhesion reliability to the adherend surface (LSE surface) composed of various LSE materials. It is useful in a wide range of applications.

Although not particularly limited, the adhesive sheet disclosed herein preferably has a 180-degree peel strength to a stainless steel plate (adhesive strength to SUS) of about 12 N/20 mm or more. A pressure-sensitive adhesive sheet exhibiting such adhesive strength to SUS can exhibit high adhesion reliability to various adherends (for example, adherends such as metal members) other than LSE adherends. The adhesion to SUS is more preferably about 13.0 N/20 mm or more, still more preferably about 14.0 N/20 mm or more, and particularly preferably about 15.0/20 mm or more. The upper limit of the adhesive strength to SUS is not particularly limited, but from the viewpoint of compatibility with other adhesive properties such as holding power, it is usually about 50 N/20 mm or less, and may be 30 N/20 mm or less. The adhesion to SUS is measured using a SUS plate as an adherend under the conditions of a tensile speed of 300 mm/min and a peeling angle of 180 degrees in a measurement environment of 23° C. and 50% RH. More specifically, it is measured by the method described in Examples below.

The pressure-sensitive adhesive sheet disclosed herein may have a displacement distance of 1.0 mm or less from the adherend 1 hour after the start of the holding force test in the holding force test conducted by the method described in Examples below. . Such a pressure-sensitive adhesive sheet has high cohesion and good holding power. The displacement distance in the holding force test is preferably 0.5 mm or less, more preferably 0.3 mm or less, still more preferably 0.2 mm or less, and particularly preferably 0.1 mm or less (0 to 0.1 mm). .

<Application>
The pressure-sensitive adhesive sheet disclosed herein has good holding power and exhibits improved adhesiveness to the LSE surface, and is therefore suitable for adhesively fixing a member having an LSE surface. For example, it is suitable for applications in which the components to be bonded have an LSE surface and long-term bonding reliability is required. Materials constituting such an LSE surface include polyolefin resins such as polyethylene (PE) and polypropylene (PP), which are generally known as materials with low surface free energy, fluorine-based polymers (such as polytetrafluoroethylene), Examples include polystyrene, polyoxymethylene, polyvinyl acetate and the like. Among others, the pressure-sensitive adhesive sheet disclosed herein is preferably used for adhesively fixing an adherend having a surface composed of a material containing polyolefins such as PE, PP, and fluoropolymers. When the pressure-sensitive adhesive sheet disclosed herein is used in the form of a double-sided pressure-sensitive adhesive sheet, the surface of at least one (for example, both) of the adherends to which the respective adhesive surfaces of the pressure-sensitive adhesive sheet are attached is made of the above material. preferably configured. The adhesive sheet disclosed herein can have sufficient adhesive strength not only for LSE materials but also for various materials. It can also be preferably used for attaching a member (LSE adherend) having.

The adhesive sheet disclosed herein is suitable for fixing members in electronic devices such as home electric appliances, OA devices, and portable electronic devices. Materials with low surface free energy such as PE, PP, and fluororesin can be used for the members constituting the electronic device. It is significant to realize excellent adhesive fixation in Examples of the electronic devices include various home electric appliances, personal computers (desktop type, notebook type, tablet type, etc.) and the like. Non-limiting examples of the above portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wrist wear type worn on the wrist like a wristwatch, Eyewear type including glasses type (monocular type and binocular type, including head-mounted type), clothes type attached to shirts, socks, hats, etc. in the form of accessories, earphones ear-wear type, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, electronic books, vehicle-mounted information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, the term “portable” means not only being able to be simply carried, but also having a level of portability that allows an individual (a typical adult) to carry it relatively easily. shall mean.

Matters disclosed by this specification include the following.
[1] An electronic device,
A pressure-sensitive adhesive sheet is bonded to a member constituting the electronic device,
The adhesive sheet has an adhesive layer,
The pressure-sensitive adhesive layer contains an acrylic polymer and a tackifying resin,
The acrylic polymer is polymerized at a rate of 15% by weight or more of an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end,
In the acrylic polymer, the carboxy group-containing monomer is not copolymerized, or the copolymerization ratio of the carboxy group-containing monomer is less than 10% by weight,
The content of the tackifier resin in the adhesive layer is 40 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer,
The pressure-sensitive adhesive layer contains, as the tackifying resin, a tackifying resin _TL having a softening point of 110° C. or less,
The electronic device, wherein the tackifying resin _TL accounts for 60% by weight or more of the total amount of the tackifying resin contained in the adhesive layer.
[2] The electronic device according to [1] above, wherein the surface of the member is made of polyolefin resin or fluororesin.
[3] The electronic device according to [1] or [2] above, wherein the electronic device is a home appliance.
[4] The electronic device according to [1] or [2] above, wherein the electronic device is a portable electronic device.
[5] The electronic device according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer contains a rosin-based tackifying resin as the tackifying resin.
[6] The above [1] to [5], wherein the pressure-sensitive adhesive layer does not contain a terpene phenol resin, or contains the terpene phenol resin in a proportion of less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. The electronic device according to any one of
[7] The electronic device according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an epoxy-based cross-linking agent.
[8] The electronic device according to any one of [1] to [7] above, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate cross-linking agent and an epoxy cross-linking agent.
[9] The electronic device according to any one of [1] to [8] above, wherein the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of the pressure-sensitive adhesive layer.
[10] The electronic device according to any one of [1] to [8] above, wherein the adhesive sheet has a substrate and the adhesive layer provided on at least one surface of the substrate.

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
The pressure-sensitive adhesive layer contains an acrylic polymer and a tackifying resin,
The acrylic polymer is polymerized at a rate of 15% by weight or more of an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end,
In the acrylic polymer, the carboxy group-containing monomer is not copolymerized, or the copolymerization ratio of the carboxy group-containing monomer is less than 10% by weight,
The content of the tackifier resin in the adhesive layer is 40 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer,
The pressure-sensitive adhesive layer contains, as the tackifying resin, a tackifying resin _TL having a softening point of 110° C. or less,
The pressure-sensitive adhesive sheet, wherein the tackifying resin _TL accounts for 60% by weight or more of the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer.
[12] The pressure-sensitive adhesive sheet according to [11] above, wherein the pressure-sensitive adhesive layer contains a rosin-based tackifying resin as the tackifying resin.
[13] The above [11] or [12], wherein the pressure-sensitive adhesive layer does not contain a terpene phenol resin, or contains the terpene phenol resin in a proportion of less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. The adhesive sheet described in .
[14] The pressure-sensitive adhesive sheet according to any one of [11] to [13] above, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an epoxy-based cross-linking agent.
[15] The pressure-sensitive adhesive sheet according to any one of [11] to [14] above, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate cross-linking agent and an epoxy cross-linking agent.
[16] The pressure-sensitive adhesive sheet according to any one of [11] to [15] above, which is a substrate-less double-sided pressure-sensitive adhesive sheet comprising only the pressure-sensitive adhesive layer.
[17] The pressure-sensitive adhesive sheet according to any one of [11] to [15] above, comprising a substrate and the pressure-sensitive adhesive layer provided on at least one surface of the substrate.
[18] The pressure-sensitive adhesive sheet according to any one of [11] to [17] above, which is used for fixing members in an electronic device.
[19] An electronic device comprising the adhesive sheet according to any one of [11] to [17] above.

Several examples relating to the present invention are described below, but the present invention is not intended to be limited to those shown in such examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Evaluation method>
[Adhesive strength against SUS]
Under the measurement environment of 23° C. and 50% RH, a PET film having a thickness of 50 μm is adhered to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) for backing, and the sheet is cut into a size of 20 mm in width and 100 mm in length. Prepare a measurement sample. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample is pressed against the surface of a stainless steel plate (SUS304BA plate) washed with ethyl acetate by reciprocating a 2 kg roller 2.5 times. After leaving it in the same environment for 30 minutes, using a universal tensile compression tester, according to JIS Z 0237: 2000, the peel strength (vs. SUS Adhesive force) [N/20 mm] is measured.

[Adhesive strength against PP]
Under the measurement environment of 23° C. and 50% RH, a PET film having a thickness of 50 μm is adhered to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) for backing, and the sheet is cut into a size of 20 mm in width and 100 mm in length. Prepare a measurement sample. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample is pressed against the surface of a polypropylene plate (PP plate) washed with ethanol by reciprocating a 2 kg roller 2.5 times. After leaving it in the same environment for 30 minutes, using a universal tension and compression tester, according to JIS Z 0237: 2000, the peel strength (vs. PP Adhesive force) [N/20 mm] is measured. As the PP plate, for example, the product name “Kobe Poly Sheet PP-N-AN” (thickness: 2 mm) manufactured by Showa Denko Materials Co., Ltd. is used.

[Adhesive strength against PE]
Under the measurement environment of 23° C. and 50% RH, a PET film having a thickness of 50 μm is adhered to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) for backing, and the sheet is cut into a size of 20 mm in width and 100 mm in length. Prepare a measurement sample. In an environment of 23° C. and 50% RH, the other adhesive surface of the measurement sample is pressed against the surface of a polyethylene plate (PE plate) washed with ethanol by reciprocating a 2 kg roller 2.5 times. After leaving it in the same environment for 30 minutes, using a universal tensile compression tester, according to JIS Z 0237: 2000, the peel strength (vs. PE Adhesive force) [N/20 mm] is measured. As the PE plate, for example, the product name “Kobe Poly Sheet EL-N-AN” (thickness: 2 mm) manufactured by Showa Denko Materials Co., Ltd. is used.

In the measurement of each peel strength described above, as a universal tension/compression tester, “Tensile/compression tester, TG-1kN” manufactured by Minebea Co., Ltd. or its equivalent is used. When performing the peel strength measurement on a single-sided pressure-sensitive adhesive sheet, the backing of the PET film is unnecessary. If the substrate thickness is thin (for example, if the substrate thickness is 25 μm or less), it may be lined with a PET film.

If the adhesive strength to PP is 12 N/20 mm or more and the adhesive strength to PE is 6 N/20 mm or more, it is judged to have high adhesive strength to the LSE surface.

[Holding power]
Under an environment of 23° C. and 50% RH, a PET film having a thickness of 50 μm is adhered to one adhesive surface of the adhesive sheet (double-sided adhesive sheet) for lining, and a measurement sample is prepared by cutting it into a length of 10 mm in width. . The other adhesive surface of the measurement sample is press-bonded to a bakelite plate (phenolic resin plate) as an adherend by reciprocating a 2-kg roller once over an application area of 10 mm in width and 20 mm in length. After leaving the sample attached to the adherend in this way for 30 minutes in the same environment, the adherend was suspended so that the length direction of the sample was in the vertical direction, and 500 g of water was applied to the free end of the sample. A load is applied, and in accordance with JIS Z0237, the sample is left in an environment of 60° C. for 1 hour while the load is applied. After 1 hour has passed, the displacement distance [mm] from the initial attachment position of the upper end of each sample is measured (displacement distance after 1 hour). Measurements are made using 3 samples for each PSA sheet (ie N=3) and their arithmetic mean is determined. If the deviation distance is 1.0 mm or less, it is determined that the holding force is good.

<Example 1>
(Synthesis of acrylic polymer)
A reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser and dropping funnel was charged with 95 parts of 2-ethylhexyl acrylate (2EHA) and 5 parts of acrylic acid (AA) as monomer components, and Ethyl acetate was charged, and the mixture was stirred for 2 hours while nitrogen gas was introduced. After removing oxygen in the polymerization system in this way, 0.3 part of benzoyl peroxide (BPO) is added as a polymerization initiator, and the solution is polymerized at 60° C. to 70° C. for 8 hours to obtain a solution of the acrylic polymer A1. Obtained.

(Preparation of adhesive composition)
100 parts of acrylic polymer A1, tackifier resin B1 (product name "Haritac SE10", manufactured by Harima Chemicals, hydrogenated rosin glycerin ester, softening point 75 to 85 ° C., hydroxyl value 25 to 40 mgKOH / g) 40 parts, 2 parts of an isocyanate cross-linking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane/tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), an epoxy cross-linking agent (trade name "TETRAD-C , Mitsubishi Gas Chemical Co., Ltd., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) was stirred and mixed to prepare a pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The resulting pressure-sensitive adhesive composition was applied to the release surface of a 38 μm thick polyester release film (trade name “Diafoil MRF”, manufactured by Mitsubishi Polyester Co., Ltd.) and dried at 120° C. for 2 minutes to form a film having a thickness of 20 μm. to form an adhesive layer. After bonding the release surface of a 25 μm thick polyester release film (trade name “Diafoil MRF”, 25 μm thick, manufactured by Mitsubishi Polyester) to this adhesive layer, aging was performed at 50° C. for 24 hours. rice field. Thus, a substrate-less double-sided PSA sheet having a thickness of 20 μm and having both sides protected by the two polyester release films was obtained.

<Examples 2-3>
The amount of the epoxy-based cross-linking agent used was changed to 0.03 part (Example 2) or 0.05 part (Example 3) with respect to 100 parts of the acrylic polymer. A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 1, and a substrate-less double-sided pressure-sensitive adhesive sheet according to each example was produced using the pressure-sensitive adhesive composition.

<Example 4>
As a tackifying resin, 30 parts of tackifying resin B1 for 100 parts of acrylic polymer, tackifying resin B2 (Polymerized rosin ester manufactured by Arakawa Chemical Industries, Ltd., trade name "Pencel D-125", softening point 120 to 130 °C) was used. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using the pressure-sensitive adhesive composition.

<Example 5>
The amount of tackifying resin B1 used was changed to 50 parts per 100 parts of the acrylic polymer. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using the pressure-sensitive adhesive composition.

<Example 6>
As tackifying resins, 40 parts of tackifying resin B1 and 10 parts of tackifying resin B2 were used with respect to 100 parts of acrylic polymer. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 4, and a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using the pressure-sensitive adhesive composition.

<Example 7>
The amount of tackifying resin B1 used was changed to 75 parts per 100 parts of the acrylic polymer. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using the pressure-sensitive adhesive composition.

<Example 8>
A solution of acrylic polymer A2 was obtained in the same manner as in Example 1, except that the monomer composition was changed to 25 parts of 2EHA, 70 parts of n-butyl acrylate (BA) and 5 parts of AA. Also, 100 parts of acrylic polymer A2, 40 parts of tackifying resin B1, 10 parts of tackifying resin B2, 2 parts of isocyanate cross-linking agent (trade name "Coronate L", manufactured by Tosoh Corporation), epoxy cross-linking agent (trade name “TETRAD-C”, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was stirred and mixed to prepare a pressure-sensitive adhesive composition according to this example. A substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced in the same manner as in Example 1, except that the obtained pressure-sensitive adhesive composition was used.

<Example 9>
A solution of acrylic polymer A3 was obtained in the same manner as in Example 1 except that the monomer composition was changed to 42 parts of 2EHA, 43 parts of BA and 5 parts of AA. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 8 except that the obtained acrylic polymer A3 was used, and the substrate-less double-sided pressure-sensitive adhesive sheet according to this example was prepared using the pressure-sensitive adhesive composition was made.

<Example 10>
As the tackifying resin, 40 parts of tackifying resin B3 (product name “Superester A-100”, rosin ester manufactured by Arakawa Chemical Industries, softening point 95 to 105° C.) was used with respect to 100 parts of acrylic polymer. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 2, and a substrate-less double-sided pressure-sensitive adhesive sheet according to this example was produced using the pressure-sensitive adhesive composition.

<Comparative Examples 1 to 3>
The amount of tackifying resin B1 used was changed as shown in Table 2. A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 2, and a substrate-less double-sided pressure-sensitive adhesive sheet according to each example was produced using the pressure-sensitive adhesive composition.

<Comparative Examples 4 to 8>
A pressure-sensitive adhesive composition according to each example was prepared in the same manner as in Example 2, except that the type and amount of tackifier resin used were changed as shown in Table 2, and the pressure-sensitive adhesive composition was used in each example. A substrate-less double-sided pressure-sensitive adhesive sheet was produced. In Table 2, the tackifying resin B4 is the product name "Super Ester A-125" (rosin ester manufactured by Arakawa Chemical Industries, softening point 120 to 130°C).

<Comparative Example 9>
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel was charged with 90 parts of 2EHA and 10 parts of AA as monomer components and ethyl acetate as a polymerization solvent, while introducing nitrogen gas. Stirred for 2 hours. After removing oxygen in the polymerization system in this manner, 0.6 part of benzoyl peroxide (BPO) is added as a polymerization initiator, and the solution is polymerized at 50° C. for 6 hours and then at 70° C. for 3 hours to obtain an acrylic polymer. A solution of A4 was obtained. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 6, except that the obtained acrylic polymer A4 was used. was made.

<Comparative Example 10>
A reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser and a dropping funnel was charged with 95 parts of BA and 5 parts of AA as monomer components and ethyl acetate as a polymerization solvent, while introducing nitrogen gas. Stirred for 2 hours. After removing oxygen in the polymerization system in this way, 0.2 parts of 2,2′-azobisisobutyronitrile (AIBN) is added as a polymerization initiator, and the solution is polymerized at 60° C. for 8 hours to obtain acrylic resin. A solution of system polymer A5 was obtained. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 6, except that the obtained acrylic polymer A5 was used. was made.

<Comparative Example 11>
A solution of acrylic polymer A6 was obtained in the same manner as in Comparative Example 10, except that the monomer composition was changed as shown in Table 2. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 6, except that the obtained acrylic polymer A6 was used. was made.

The adhesive sheet of each example was evaluated for adhesive strength to SUS [N/20 mm], adhesive strength to PP [N/20 mm], adhesive strength to PE [N/20 mm], and holding power [mm]. The obtained results are shown in Tables 1 and 2 together with an outline of the adhesive sheet.

As shown in Table 1, the adhesives according to Examples 1 to 10 have an adhesive strength to PP of 12 N/20 mm or more, an adhesive strength to PE of 6 N/20 mm or more, and a displacement distance of 1 in the holding power test. 0 mm or less, exhibited high adhesion to the LSE surface, and had good holding power. On the other hand, in Comparative Examples 1 and 2 in which the amount of tackifying resin used is less than 40 parts by weight with respect to 100 parts of the acrylic polymer, Examples 1 to 2 in which the amount of tackifying resin used is 40 parts, 50 parts, and 75 parts 3 (especially Example 2) and Examples 5 and 7, the adhesive strength to PP was lower, and the adhesive strength to PE also tended to be lower. Comparative Examples 3 and 4, in which the amount of the tackifying resin used was 100 parts, exhibited a marked decrease in adhesive strength to PP and poor holding power. These results show that it is important to use 40 to 80 parts of tackifying resin per 100 parts of acrylic polymer to obtain high adhesion to various LSE surfaces.

Further, Comparative Examples 5 to 7, in which the usage ratio of the tackifying resin T _L having a softening point of 110° C. or lower is less than 60%, are similar to Examples 4 and 6, in which the usage ratio of the tackifying resin T _L is 60% or higher. As a result, the adhesion to PP was low. By using a sufficient amount of the low softening point tackifying resin _TL , it is believed that high adhesion to various LSE surfaces (especially PP) can be obtained. Even in Comparative Example 8 in which the type of tackifying resin was changed, in comparison with Example 10, it can be seen that when the amount of tackifying resin _TL having a softening point of 110° C. or lower is small, it is difficult to obtain adhesive strength to PP. .

Moreover, in Comparative Example 9 using an acrylic polymer copolymerized with 10% by weight of acrylic acid, both the adhesive strength to PP and the adhesive strength to PE were low. It is believed that this is because the presence of a considerable amount of carboxyl groups such as acrylic acid lowered the wettability with respect to the LSE surface, and the adhesiveness of the tackifier resin was not exhibited.

In addition, in Comparative Examples 10 and 11 using acrylic polymers in which the proportion of alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end was less than 15%, compared with Examples 8 and 9, , the adhesive strength tended to decrease with respect to all adherends. From the results of Examples 8 and 9 and Comparative Examples 10 and 11, by setting the polymerization ratio of the alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end to 15% or more, It is believed that the compatibility was improved and the effect of containing the tackifying resin was effectively exhibited, resulting in an improvement in adhesive strength. In addition, since Examples 8 and 9 have a greater effect of improving the adhesion to the LSE surface than Comparative Examples 10 and 11, polymerization of alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end It is believed that the use of an acrylic polymer with a ratio of 15% or more also improved the wettability to the LSE surface.

From the above, the alkyl (meth) acrylate having an alkyl group having 6 or more carbon atoms at the ester end is polymerized at a rate of 15% by weight or more, and the carboxy group-containing monomer is not copolymerized, or the carboxy A tackifying resin having a softening point of 110° C. or less, using an acrylic polymer in which the copolymerization ratio of the group-containing monomer is less than 10% by weight, using a tackifying resin at a rate of 40 to 80 parts per 100 parts of the acrylic polymer. A pressure-sensitive adhesive sheet containing a pressure-sensitive adhesive containing _TL and having a content of 60% by weight or more of the total amount of the tackifying resin has good holding power and improved adhesion to surfaces with low surface free energy. Recognize.

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

Reference Signs List 1, 2, 3 Adhesive sheet 10 Supporting substrate 10A First surface 10B Second surface (back surface)
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 PSA sheet with release liner

Claims (9)

A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer,
The pressure-sensitive adhesive layer contains an acrylic polymer and a tackifying resin,
The acrylic polymer is polymerized at a rate of 15% by weight or more of an alkyl (meth)acrylate having an alkyl group having 6 or more carbon atoms at the ester end,
In the acrylic polymer, the carboxy group-containing monomer is not copolymerized, or the copolymerization ratio of the carboxy group-containing monomer is less than 10% by weight,
The content of the tackifier resin in the adhesive layer is 40 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of the acrylic polymer,
The pressure-sensitive adhesive layer contains, as the tackifying resin, a tackifying resin _TL having a softening point of 110° C. or less,
The pressure-sensitive adhesive sheet, wherein the tackifying resin _TL accounts for 60% by weight or more of the total amount of the tackifying resin contained in the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer contains a rosin-based tackifying resin as the tackifying resin. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer does not contain a terpene phenol resin, or contains the terpene phenol resin in a proportion of less than 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an epoxy-based cross-linking agent. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate-based cross-linking agent and an epoxy-based cross-linking agent. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, which is a substrate-less double-sided pressure-sensitive adhesive sheet comprising only the pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, comprising a base material and the pressure-sensitive adhesive layer provided on at least one surface of the base material. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is used for fixing members in electronic equipment. An electronic device comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 7.

Images