JP7684891B2 - Adhesive composition and adhesive tape - Google Patents

Description

The present disclosure relates to an adhesive composition and an adhesive tape.

As demand for large-capacity and high-speed data communication increases, there is a demand for materials with low dielectric constants. In the field of adhesives, adhesive compositions with low dielectric constants have been developed to prevent malfunctions caused by attaching parts or exterior parts that can generate high-frequency noise to electronic devices such as image display devices and input/output devices.

For example, Patent Document 1 discloses an optical pressure-sensitive adhesive composition comprising: (a1) 3% by mass to 39% by mass of a methacrylic acid alkyl ester monomer having an alkyl group with 10 to 18 carbon atoms; and (a2) 20% by mass to 97% by mass of a methacrylic acid alkyl ester monomer having an alkyl group with 1 to 9 carbon atoms, the total of the (a1) component and the (a2) component being 45% by mass to 100% by mass; a crosslinking agent; and a plasticizer, the content of the plasticizer being 5 parts by mass to 40 parts by mass relative to 100 parts by mass of the copolymer.
Furthermore, for example, Patent Document 2 discloses a pressure-sensitive adhesive composition for touch panels, which contains 60% by mass or more of structural units derived from an alkyl methacrylate having a branched alkyl group having 5 to 9 carbon atoms, and 0.1% by mass to 20% by mass of structural units derived from a monomer having a hydroxyl group, based on all structural units, and contains 100 parts by mass of a (meth)acrylic polymer having a glass transition temperature (Tg) of -15°C or higher, 0.1 to 3 parts by mass of a crosslinking agent, and 5 to 70 parts by mass of polybutene having a number average molecular weight (Mn) of 100 to 700.

JP 2015-105329 A JP 2018-172567 A

In recent years, frequencies in the quasi-millimeter wave band to millimeter wave band have been used for data communications. In this frequency band, transmission loss is greater than in the past, and therefore adhesive compositions are required to be able to form adhesive layers with lower relative dielectric constants and lower dielectric loss tangents. Furthermore, electronic devices and vehicles equipped with electronic devices tend to become hot due to their own heat generation and exposure to high-temperature environments. For this reason, adhesive compositions are required to be able to form adhesive layers with high adhesive strength, as well as adhesive layers with excellent holding strength even in high-temperature environments.

An object of one embodiment of the present disclosure is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having high adhesive strength, low relative dielectric constant and dielectric tangent, and excellent holding strength in a high-temperature environment.
The problem to be solved by another embodiment of the present disclosure is to provide an adhesive tape having an adhesive layer that has high adhesive strength, low relative dielectric constant and dielectric tangent, and excellent holding strength in high temperature environments.

Specific means for solving the problems include the following aspects.
<1> A methacrylic copolymer containing 80% by mass to 99% by mass of structural units derived from a methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms, and 1% by mass to 8% by mass of structural units derived from a monomer having a hydroxyl group, based on all structural units, and having a glass transition temperature of -28°C to -8°C;
a hydrocarbon-based resin that is liquid at 25° C. and has a number average molecular weight of more than 700 and not more than 2,000;
A cross-linking agent;
Including,
The pressure-sensitive adhesive composition has a content of the hydrocarbon resin of 15 to 45 parts by mass relative to 100 parts by mass of the methacrylic copolymer.
<2> The pressure-sensitive adhesive composition according to <1>, wherein the monomer having a hydroxyl group is 4-hydroxybutyl acrylate.
<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the content of structural units derived from the methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms in the methacrylic copolymer is 90% by mass to 99% by mass based on all structural units.
<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the content of the crosslinking agent is 0.1 parts by mass to 4.0 parts by mass per 100 parts by mass of the methacrylic copolymer.
<5> A pressure-sensitive adhesive tape comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <4>.

According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer having high adhesive strength, low relative dielectric constant and dielectric dissipation factor, and excellent holding strength in a high-temperature environment.
According to another embodiment of the present disclosure, there is provided an adhesive tape including an adhesive layer having high adhesive strength, low relative dielectric constant and dielectric tangent, and excellent holding strength in high temperature environments.

The adhesive composition and adhesive tape of the present disclosure are described in detail below. The following description of the requirements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and may be modified as appropriate within the scope of the purpose of the present disclosure.

In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits, respectively.
In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in the present disclosure. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

In the present disclosure, combinations of two or more preferred aspects are more preferred aspects.
In the present disclosure, when the adhesive composition contains multiple substances corresponding to each component, the amount of each component in the adhesive composition means the total amount of the multiple substances present in the adhesive composition, unless otherwise specified.

In the present disclosure, a "methacrylic copolymer" refers to a copolymer in which the content of structural units derived from monomers having a methacryloyl group is 50 mass% or more of all structural units (i.e., all structural units of the methacrylic copolymer).
In the present disclosure, the term "(meth)acrylic copolymer" refers to a copolymer in which the content of structural units derived from monomers having a (meth)acryloyl group is 50 mass% or more of all structural units (i.e., all structural units of the (meth)acrylic copolymer).

In this disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic", "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate", and "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl".

In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present disclosure comprises a methacrylic copolymer that contains 80% by mass to 99% by mass of structural units derived from methacrylic acid alkyl ester monomers having an alkyl group having 5 or more carbon atoms, relative to all structural units, and 1% by mass to 8% by mass of structural units derived from monomers having a hydroxyl group, relative to all structural units, and has a glass transition temperature of -28°C to -8°C; a hydrocarbon-based resin that is liquid at 25°C and has a number average molecular weight of more than 700 and not more than 2000; and a crosslinking agent, wherein the content of the hydrocarbon-based resin is 15 parts by mass to 45 parts by mass relative to 100 parts by mass of the methacrylic copolymer.
The pressure-sensitive adhesive composition of the present disclosure, having the above-described configuration, can form a pressure-sensitive adhesive layer having high adhesive strength, low relative dielectric constant and dielectric tangent, and excellent holding strength in high-temperature environments.

In this disclosure, "methacrylic acid alkyl ester monomers having an alkyl group with 5 or more carbon atoms" are also referred to as "specific methacrylic acid alkyl ester monomers." In addition, in this disclosure, "methacrylic copolymers containing 80% by mass to 99% by mass of structural units derived from methacrylic acid alkyl ester monomers having an alkyl group with 5 or more carbon atoms, and 1% by mass to 8% by mass of structural units derived from monomers having hydroxyl groups, and having a glass transition temperature of -28°C to -8°C" are also referred to as "specific methacrylic copolymers." In addition, in this disclosure, "hydrocarbon resins that are liquid at 25°C and have a number average molecular weight of more than 700 and not more than 2000" are also referred to as "specific hydrocarbon resins."

[Specific methacrylic copolymer]
The pressure-sensitive adhesive composition of the present disclosure contains a methacrylic copolymer (i.e., a specific methacrylic copolymer) that contains 80% by mass to 99% by mass of structural units derived from a methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms (i.e., a specific methacrylic acid alkyl ester monomer) relative to all structural units, and 1% by mass to 8% by mass of structural units derived from a monomer having a hydroxyl group, relative to all structural units, and has a glass transition temperature of -28°C to -8°C.
The pressure-sensitive adhesive composition of the present disclosure may contain only one type of specific methacrylic copolymer, or may contain two or more types.

<Structural Unit Derived from Specific Methacrylic Acid Alkyl Ester Monomer>
The specific methacrylic copolymer contains 80% by mass to 99% by mass of structural units derived from a methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms (i.e., a specific methacrylic acid alkyl ester monomer) based on all structural units.

In the present disclosure, "a structural unit derived from a methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms" means a structural unit formed by addition polymerization of a methacrylic acid alkyl ester monomer having an alkyl group having 5 or more carbon atoms.
The "specific methacrylic acid alkyl ester monomer" in the present disclosure does not include monomers that fall under the category of monomers having a hydroxyl group described below.

The specific methacrylic acid alkyl ester monomer may be one in which the alkyl group is unsubstituted or substituted, but a methacrylic acid alkyl ester monomer in which the alkyl group is unsubstituted is preferable.
The alkyl group contained in the specific methacrylic acid alkyl ester monomer may be linear, branched, or cyclic, but is preferably linear or branched, and more preferably branched.

The number of carbon atoms in the alkyl group of the specific methacrylic acid alkyl ester monomer is 5 or more. Compared with methacrylic acid alkyl ester monomers having an alkyl group with 5 or more carbon atoms, methacrylic acid alkyl ester monomers have a larger molar volume and a smaller dipole moment, and therefore the dielectric constant of the pressure-sensitive adhesive layer formed tends to be lower. From this viewpoint, the number of carbon atoms in the alkyl group of the specific methacrylic acid alkyl ester monomer is 5 or more, and preferably 6 or more.
The number of carbon atoms in the alkyl group of the specific methacrylic acid alkyl ester monomer is not particularly limited as long as it is 5 or more. However, from the viewpoint of suitability for producing the specific methacrylic copolymer, for example, it is preferably 22 or less, and more preferably 20 or less.
The number of carbon atoms in the alkyl group of the specific methacrylic acid alkyl ester monomer is preferably 10 or less, for example, from the viewpoint of the adhesive strength of the pressure-sensitive adhesive layer to be formed and its holding power in a high-temperature environment.

Specific examples of alkyl groups having 5 or more carbon atoms include n-hexyl group (carbon number: 6), n-octyl group (carbon number: 8), 2-ethylhexyl group (carbon number: 8), isodecyl group (carbon number: 10), isobornyl group (carbon number: 10), lauryl group (carbon number: 12), myristyl group (carbon number: 14), cetyl group (carbon number: 16), stearyl group (carbon number: 18), and eicosyl group (carbon number: 20).

Specific examples of the specific methacrylic acid alkyl ester monomer include n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, isobornyl methacrylate, lauryl methacrylate, myristyl methacrylate, cetyl methacrylate, stearyl methacrylate, and eicosyl methacrylate.
The specific methacrylic acid alkyl ester monomer is preferably at least one selected from n-hexyl methacrylate (n-HMA) and 2-ethylhexyl methacrylate (2EHMA), and more preferably 2-ethylhexyl methacrylate (2EHMA).

The specific methacrylic copolymer may contain only one type of structural unit derived from the specific methacrylic acid alkyl ester monomer, or may contain two or more types.

The content of the structural units derived from the specific methacrylic acid alkyl ester monomer in the specific methacrylic copolymer is 80% by mass to 99% by mass based on the total structural units of the specific methacrylic copolymer.
When the content of the structural unit derived from the specific methacrylic acid alkyl ester monomer in the specific methacrylic copolymer is 80% by mass or more relative to the total structural units of the specific methacrylic copolymer, a pressure-sensitive adhesive layer having excellent holding power can be formed in a high temperature environment.The reason is considered to be that the pressure-sensitive adhesive layer formed is given sufficient cohesive force.In addition, when the content of the structural unit derived from the specific methacrylic acid alkyl ester monomer in the specific methacrylic copolymer is 80% by mass or more relative to the total structural units of the specific methacrylic copolymer, a pressure-sensitive adhesive layer having a low dielectric tangent can be formed.The reason is considered to be that the orientation polarization of the specific methacrylic copolymer is suppressed.
The content of the structural units derived from the specific methacrylic acid alkyl ester monomer in the specific methacrylic copolymer is preferably 85% by mass to 99% by mass, more preferably 90% by mass to 99% by mass, even more preferably 90% by mass to 98.5% by mass, and particularly preferably 90% by mass to 98% by mass, based on all structural units of the specific methacrylic copolymer.

<Structural Unit Derived from Monomer Having a Hydroxyl Group>
The specific methacrylic copolymer contains 1% by mass to 8% by mass of structural units derived from monomers having a hydroxyl group based on the total amount of structural units.
The hydroxyl group of the structural unit derived from a monomer having a hydroxyl group can contribute to crosslinking with a crosslinking agent described below.

In this disclosure, "structural unit derived from a monomer having a hydroxyl group" means a structural unit formed by addition polymerization of a monomer having a hydroxyl group.

The type of the monomer having a hydroxyl group is not particularly limited.
The monomer having a hydroxyl group may, for example, be a monomer having at least one hydroxyl group and an ethylenically unsaturated group in one molecule.
The type of the ethylenically unsaturated group is not particularly limited.
Specific examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group.
The ethylenically unsaturated group is preferably a (meth)acryloyl group.

Specific examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate.

The monomer having a hydroxyl group is preferably a hydroxyalkyl(meth)acrylate in that it has good copolymerizability with other monomers, and more preferably a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms in that it has good compatibility with other monomers and good reactivity with a crosslinking agent (particularly an isocyanate-based crosslinking agent).
In addition, the monomer having a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, from the viewpoint of providing a pressure-sensitive adhesive layer having better holding power in a high-temperature environment, more preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (2HEA), 2-hydroxyethyl methacrylate (2HEMA), and 4-hydroxybutyl acrylate (4HBA), and even more preferably 4-hydroxybutyl acrylate (4HBA).

The specific methacrylic copolymer may contain only one type of structural unit derived from a monomer having a hydroxyl group, or may contain two or more types.

The content of the structural units derived from the monomer having a hydroxyl group in the specific methacrylic copolymer is 1% by mass to 8% by mass based on the total structural units of the specific methacrylic copolymer.
When the content of the structural unit derived from the monomer having a hydroxyl group in the specific methacrylic copolymer is 1% by mass or more relative to the total structural units of the specific methacrylic copolymer, a pressure-sensitive adhesive layer having excellent holding power can be formed in a high-temperature environment.The reason is considered to be that the crosslinking reaction with the crosslinking agent proceeds appropriately, and the cohesive force of the pressure-sensitive adhesive layer formed is sufficiently high.From this viewpoint, the content of the structural unit derived from the monomer having a hydroxyl group in the specific methacrylic copolymer is 1% by mass or more relative to the total structural units of the specific methacrylic copolymer, preferably 1.5% by mass or more, and more preferably 2% by mass or more.
When the content of the structural unit derived from the monomer having a hydroxyl group in the specific methacrylic copolymer is 8% by mass or less relative to the total structural units of the specific methacrylic copolymer, the pressure-sensitive adhesive layer formed tends to have high adhesive strength. In addition, the pressure-sensitive adhesive layer formed tends to have excellent holding power in a high-temperature environment. The reason for this is considered to be that the compatibility between the specific methacrylic copolymer and the specific hydrocarbon resin is good, and the cohesive strength of the pressure-sensitive adhesive layer caused by poor compatibility is unlikely to decrease. From this perspective, the content of the structural unit derived from the monomer having a hydroxyl group in the specific methacrylic copolymer is 8% by mass or less relative to the total structural units of the specific methacrylic copolymer, preferably 5% by mass or less, and more preferably 3% by mass or less.

<Other structural units>
The specific methacrylic copolymer may contain structural units (so-called other structural units) other than the structural units described above, as necessary, to the extent that the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired.

Examples of monomers constituting the other structural units include (meth)acrylic acid alkyl ester monomers in which the alkyl moiety has a carbon number of 1 to 4. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, and t-butyl (meth)acrylate.
Furthermore, examples of monomers constituting the other structural units include acrylic acid alkyl ester monomers in which the alkyl moiety has 5 or more carbon atoms. Specific examples include n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, myristyl acrylate, cetyl acrylate, stearyl acrylate, and eicosyl acrylate.

Furthermore, examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; vinyl cyanides, such as acrylonitrile and methacrylonitrile; and vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Examples of monomers constituting other structural units include various derivatives of these monomers.

When the specific methacrylic copolymer contains other structural units, it may contain only one type of other structural unit, or it may contain two or more types.

When the specific methacrylic copolymer contains other constituent units, the content of the other constituent units in the specific methacrylic copolymer is not particularly limited and can be set appropriately according to the purpose within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

<<Glass transition temperature of specific methacrylic copolymers>>
The glass transition temperature (also referred to as "Tg") of the specific methacrylic copolymer is -28°C to -8°C.
When the glass transition temperature of the specific methacrylic copolymer is −8° C. or lower, the pressure-sensitive adhesive layer formed tends to have high adhesive strength. This is thought to be because the pressure-sensitive adhesive layer formed has high wettability to the adherend. From this viewpoint, the glass transition temperature of the specific methacrylic copolymer is preferably −8° C. or lower, more preferably −10° C. or lower.
When the glass transition temperature of the specific methacrylic copolymer is −28° C. or higher, a pressure-sensitive adhesive layer having excellent holding power in a high-temperature environment can be formed. The reason for this is believed to be that the cohesive power of the pressure-sensitive adhesive layer formed is increased.
From this viewpoint, the glass transition temperature of the specific methacrylic copolymer is −28° C. or higher, preferably −25° C. or higher, more preferably −20° C. or higher, and even more preferably −15° C. or higher.

The glass transition temperature of the specific methacrylic copolymer is a value obtained by converting the absolute temperature (unit: K) calculated from the following formula 1 into Celsius temperature (unit: ° C.).
1/Tg=m1/Tg1+m2/Tg2+...+m(k-1)/Tg(k-1)+mk/Tgk (Formula 1)

In formula 1, Tg1, Tg2, ..., Tg(k-1), and Tgk respectively represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific methacrylic copolymer is made into a homopolymer, and m1, m2, ..., m(k-1), and mk respectively represent the mass fractions of each monomer constituting the specific methacrylic copolymer, where m1 + m2 + ... + m(k-1) + mk = 1.
Note that absolute temperature can be converted to Celsius temperature by subtracting 273 from the absolute temperature, and Celsius temperature can be converted to absolute temperature by adding 273 to the Celsius temperature.

In this disclosure, the "glass transition temperature when made into a homopolymer" refers to a value that is disclosed in a publicly known document or a value that is measured using a differential scanning calorimeter (DSC). The specific values to be used are as follows:

For the "glass transition temperature when made into a homopolymer" of the monomers shown below, the respective values shown are adopted.
2-Ethylhexyl acrylate: -70°C, 2-Ethylhexyl methacrylate: -10°C, n-butyl acrylate: -54°C, n-butyl methacrylate: 20°C, t-butyl acrylate: 43°C, t-butyl methacrylate: 118°C, i-butyl methacrylate: 53°C, methyl acrylate: 10°C, methyl methacrylate: 105°C, ethyl acrylate: -22°C, ethyl methacrylate: 65°C, methacrylic acid: 228°C, 4-hydroxybutyric acid: acrylate: -80°C, 2-hydroxyethyl acrylate: -15°C, 2-hydroxyethyl methacrylate: 85°C, acrylic acid: 106°C, n-octyl acrylate: -65°C, stearyl acrylate: 30°C, stearyl methacrylate: 38°C, lauryl acrylate: -3°C, lauryl methacrylate: -65°C, dimethylaminoethyl methacrylate: 18°C, ω-carboxy-polycaprolactone (n≒2) monoacrylate: -30°C.

For the "glass transition temperature when made into a homopolymer" of monomers other than the above-mentioned monomers, the value given in the Polymer Handbook (4th edition, Wiley-Interscience; the same applies below) shall be used. If there is no description in the Polymer Handbook, the glass transition temperature of the homopolymer obtained by the following measurement method shall be used.

<<Measurement of glass transition temperature of homopolymer>>
Using a differential scanning calorimeter (DSC), measurements are performed under conditions of a nitrogen gas flow, 10 mg of a measurement sample (i.e., homopolymer), and a heating rate of 10°C/min. The inflection point of the obtained DSC curve is regarded as the glass transition temperature of the homopolymer.
As the differential scanning calorimeter, for example, a differential scanning calorimeter (product name: Discovery DSC 2500) manufactured by TA Instruments Japan Co., Ltd. can be suitably used. However, the differential scanning calorimeter is not limited to this.

The glass transition temperature of the specific methacrylic copolymer can be adjusted as appropriate, for example, by using two or more monomers that have different glass transition temperatures when made into a homopolymer.

<<Weight average molecular weight of specific methacrylic copolymer>>
The weight average molecular weight (hereinafter also referred to as "Mw") of the specific methacrylic copolymer is not particularly limited, but is preferably, for example, 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and even more preferably 300,000 to 1,000,000.
When the weight average molecular weight of the specific methacrylic copolymer is 100,000 or more, the cohesive strength of the pressure-sensitive adhesive layer formed tends to be increased.
When the weight average molecular weight of the specific methacrylic copolymer is 2,000,000 or less, the viscosity of the pressure-sensitive adhesive composition does not increase excessively, and the pressure-sensitive adhesive composition tends to have better coatability.

The weight average molecular weight of the specific methacrylic copolymer is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).
(1) A solution of the specific methacrylic copolymer is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the specific methacrylic copolymer.
(2) Using the film-like specific methacrylic copolymer obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. Note that the "solid content concentration" here means the mass ratio of the specific methacrylic copolymer in the sample solution.
(3) The weight average molecular weight of the specific methacrylic copolymer is determined, in terms of standard polystyrene, by gel permeation chromatography (GPC) under the following conditions.

～Conditions～
Measuring device: High-speed GPC [Model: HLC-8220 GPC, manufactured by Tosoh Corporation]
Detector: differential refractometer (RI) [installed in HLC-8220, manufactured by Tosoh Corporation]
Column: 4 TSKgel GMH _XL (manufactured by Tosoh Corporation) Column temperature: 40°C
Eluent: tetrahydrofuran Injection amount of sample solution: 100 μL
Flow rate: 0.8mL/min

The weight average molecular weight of the specific methacrylic copolymer can be adjusted to the desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomers.

<<Content of specific methacrylic copolymer>>
The content of the specific methacrylic copolymer in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but for example, it is preferably 67.1% by mass to 86.9% by mass, more preferably 71.0% by mass to 82.8% by mass, and even more preferably 73.6% by mass to 79.8% by mass, relative to the total solid content in the pressure-sensitive adhesive composition.

In the present disclosure, the "total solid content in the PSA composition" means the total mass of the PSA composition when the PSA composition does not contain a solvent, and means the mass of the residue remaining after removing the solvent from the PSA composition when the PSA composition contains a solvent.
In this disclosure, "solvent" means water and organic solvents.

[Method for producing specific methacrylic copolymer]
The method for producing the specific methacrylic copolymer is not particularly limited.
The specific methacrylic copolymer can be produced by polymerizing the above-mentioned monomers by a known polymerization method typified by, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or a bulk polymerization method.
As the polymerization method, a solution polymerization method is preferred in that the processing steps for preparing the pressure-sensitive adhesive composition after production are relatively simple and can be carried out in a short time.

In the solution polymerization method, a predetermined organic solvent, monomer, polymerization initiator, and optionally used chain transfer agent are generally charged into a polymerization tank, and the mixture is heated and reacted for several hours with stirring, for example, at the reflux temperature of the organic solvent. In this case, at least a portion of the organic solvent, monomer, polymerization initiator, and optionally used chain transfer agent may be added successively. The reaction may also be carried out in a nitrogen gas flow.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds.
More specifically, examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine oil; ester compounds such as methyl acetate, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl Examples of the alcohol compounds include ketone compounds represented by ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds represented by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol compounds represented by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

When producing the specific methacrylic copolymer, it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction of aromatic hydrocarbon compounds, ester compounds, ketone compounds, etc., and in particular, it is preferable to use ethyl acetate from the viewpoints of the solubility of the specific methacrylic copolymer and the ease of the polymerization reaction.

During the polymerization reaction, only one type of organic solvent may be used, or two or more types may be used.

Examples of the polymerization initiator include organic peroxides and azo compounds that are used in ordinary solution polymerization methods.
Specific examples of organic peroxides include t-butyl peroxy-2-ethylhexanoate, t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butyl peroxysilane), peroxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.
Specific examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyrate)dimethyl.

During the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

The amount of polymerization initiator used is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the desired specific methacrylic copolymer.

In producing the specific methacrylic copolymer, a chain transfer agent may be used, if necessary.
Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds such as α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives such as benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, ... Examples of the halogenated hydrocarbon compounds include carbon chloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene, aldehyde compounds such as chloral and furaldehyde, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds such as thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds such as pinene and terpinolene.

When a chain transfer agent is used in the production of the specific methacrylic copolymer, the amount of the chain transfer agent used is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the desired specific methacrylic copolymer.

The polymerization temperature is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the specific methacrylic copolymer of interest.

[Specific Hydrocarbon Resin]
The pressure-sensitive adhesive composition of the present disclosure contains 15 to 45 parts by mass of a hydrocarbon resin (i.e., a specific hydrocarbon resin) that is liquid at 25°C and has a number average molecular weight (Mn) of more than 700 and not more than 2000, relative to 100 parts by mass of the specific methacrylic copolymer.
In the pressure-sensitive adhesive composition of the present disclosure, the specific hydrocarbon resin can contribute to reducing the relative dielectric constant and dielectric loss tangent of the pressure-sensitive adhesive layer formed, and also to improving the adhesive strength and holding power of the pressure-sensitive adhesive layer formed.

The specific hydrocarbon resin is a hydrocarbon resin that is liquid at 25°C.
The term "hydrocarbon resin that is liquid at 25°C" refers to a hydrocarbon resin having a pour point, as defined in JIS K 2269:1987, of 25°C or lower.
When mixed with a specific methacrylic copolymer, the specific hydrocarbon resin can penetrate into the molecules of the specific methacrylic copolymer, thereby exerting the effect of imparting flexibility to the specific methacrylic copolymer. By imparting flexibility to the specific methacrylic copolymer, it is believed that the pressure-sensitive adhesive layer formed becomes appropriately soft, improving the adhesive strength and holding power. A hydrocarbon resin that is liquid at 25°C is more likely to penetrate into the molecules of the specific methacrylic copolymer than a hydrocarbon resin that is solid at 25°C, and is therefore believed to be effective in imparting flexibility to the specific methacrylic copolymer.

The hydrocarbon resin that is liquid at 25°C is not particularly limited, but is preferably at least one selected from the group consisting of polybutene and polybutadiene, and more preferably polybutene.

In the present disclosure, "polybutene" refers to a polymer in which the content of butene-derived structural units is 50% by mass or more relative to all structural units. In the present disclosure, the content of butene-derived structural units relative to all structural units is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, and may be, for example, 100% by mass.
Specific examples of butenes include 1-butene, cis-2-butene, trans-2-butene, and 2-methylpropene.
The polybutene in the present disclosure may be a hydrogenated product.

In the present disclosure, "polybutadiene" refers to a polymer in which the content of butadiene-derived structural units is 50% by mass or more relative to all structural units. In the present disclosure, the content of butadiene-derived structural units relative to all structural units is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, and may be, for example, 100% by mass.
A specific example of butadiene is 1,3-butadiene.

The specific hydrocarbon resin has a number average molecular weight (Mn) of more than 700 and 2,000 or less.
When the number average molecular weight (Mn) of the specific hydrocarbon resin exceeds 700, the pressure-sensitive adhesive layer formed tends to have high adhesive strength. The reason for this is thought to be that the cohesive strength of the pressure-sensitive adhesive layer formed increases. From this viewpoint, the number average molecular weight (Mn) of the specific hydrocarbon resin exceeds 700, and is preferably 750 or more, more preferably 800 or more, even more preferably 850 or more, and particularly preferably 1100 or more.
When the number average molecular weight (Mn) of the specific hydrocarbon resin is 2000 or less, the pressure-sensitive adhesive layer formed tends to have high adhesive strength. This is believed to be because the pressure-sensitive adhesive layer formed has high wettability to the adherend.
Furthermore, when the number average molecular weight (Mn) of the specific hydrocarbon resin is 2000 or less, the pressure-sensitive adhesive layer formed tends to have excellent holding power in a high temperature environment. This is thought to be because the compatibility between the specific methacrylic copolymer and the specific hydrocarbon resin is good, and a decrease in the cohesive strength of the pressure-sensitive adhesive layer caused by poor compatibility is unlikely to occur.
Furthermore, when the number average molecular weight (Mn) of the specific hydrocarbon resin is 2000 or less, it tends to be easier to obtain a commercially available product.
From the above viewpoints, the number average molecular weight (Mn) of the specific hydrocarbon resin is 2000 or less, preferably 1800 or less, more preferably 1600 or less, and even more preferably 1400 or less.

The number average molecular weight (Mn) of a specific hydrocarbon resin is a value measured by the vapor pressure molecular weight measurement method (VPO method).

As the specific hydrocarbon resin, a commercially available product can be used.
Examples of commercially available specific hydrocarbon resins include NOF Polybutene 3N (trade name, component: polybutene, number average molecular weight (Mw): 720, manufactured by NOF Corp.), NOF Polybutene 10N (trade name, component: polybutene, number average molecular weight (Mn): 1000, manufactured by NOF Corp.), NOF Polybutene 30N (trade name, component: polybutene, number average molecular weight (Mn): 1350, manufactured by NOF Corp.), and Nisseki Polybutene HV-35 (trade name, component: polybutene, number average molecular weight (Mn): 750, manufactured by ENEOS ( Examples of suitable polybutenes include Nippon Oil Polybutene HV-50 (trade name, component: polybutene, number average molecular weight (Mn): 800, manufactured by ENEOS Corporation), Nippon Oil Polybutene HV-100 (trade name, component: polybutene, number average molecular weight (Mn): 980, manufactured by ENEOS Corporation), Nippon Oil Polybutene HV-300 (trade name, component: polybutene, number average molecular weight (Mn): 1400, manufactured by ENEOS Corporation), and Ricon 156 (trade name, component: polybutadiene, number average molecular weight (Mn): 1400, manufactured by CRAY VALLEY Corporation).

The adhesive composition of the present disclosure may contain only one type of specific hydrocarbon resin, or may contain two or more types.

The content of the specific hydrocarbon resin in the pressure-sensitive adhesive composition of the present disclosure is 15 to 45 parts by mass based on 100 parts by mass of the specific methacrylic copolymer.
When the content of the specific hydrocarbon resin in the pressure-sensitive adhesive composition of the present disclosure is 15 parts by mass or more relative to 100 parts by mass of the specific methacrylic copolymer, the pressure-sensitive adhesive layer formed tends to have high adhesive strength. The reason for this is believed to be that the pressure-sensitive adhesive layer formed is moderately plasticized. From this viewpoint, the content of the specific hydrocarbon resin in the pressure-sensitive adhesive composition of the present disclosure is 15 parts by mass or more, preferably 20 parts by mass or more relative to 100 parts by mass of the specific methacrylic copolymer.
When the content of the specific hydrocarbon resin in the pressure-sensitive adhesive composition of the present disclosure is 45 parts by mass or less relative to 100 parts by mass of the specific methacrylic copolymer, the pressure-sensitive adhesive layer formed tends to have excellent holding power in a high-temperature environment. The reason for this is thought to be that the cohesive force of the pressure-sensitive adhesive layer formed is increased. From this perspective, the content of the specific hydrocarbon resin in the pressure-sensitive adhesive composition of the present disclosure is 45 parts by mass or less relative to 100 parts by mass of the specific methacrylic copolymer, preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less.

[Crosslinking Agent]
The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent.
When the pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent, a crosslinked structure is formed, imparting cohesive strength to the pressure-sensitive adhesive layer.
The type of crosslinking agent is not particularly limited.
Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and a metal chelate-based crosslinking agent.

In this disclosure, an "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate compounds). An "epoxy-based crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy compounds). A "metal chelate-based crosslinking agent" refers to a metal chelate compound that functions as a crosslinking agent.

The crosslinking agent is preferably an isocyanate-based crosslinking agent.
The type of the isocyanate-based crosslinking agent is not particularly limited.
Examples of the isocyanate crosslinking agent include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and aromatic polyisocyanate compounds.

The "aliphatic polyisocyanate compound" includes, for example, an aliphatic polyisocyanate compound, a polymer of an aliphatic polyisocyanate compound, an adduct of an aliphatic polyisocyanate compound and a polyol compound (e.g., trimethylolpropane (TMP); the same applies below), and a biuret of an aliphatic polyisocyanate compound.
Specific examples of the aliphatic polyisocyanate compound include hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

The "alicyclic polyisocyanate compound" includes, for example, an alicyclic polyisocyanate compound, a polymer of an alicyclic polyisocyanate compound, an adduct of an alicyclic polyisocyanate compound and a polyol compound, and a biuret of an alicyclic polyisocyanate compound.
Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

The "aromatic polyisocyanate compound" includes, for example, an aromatic polyisocyanate compound, a polymer of an aromatic polyisocyanate compound, an adduct of an aromatic polyisocyanate compound and a polyol compound, and a biuret of an aromatic polyisocyanate compound.
Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

The isocyanate-based crosslinking agent is preferably an aromatic polyisocyanate-based compound, and more preferably a tolylene diisocyanate-based compound.
The "tolylene diisocyanate-based compound" includes, for example, TDI, a polymer of TDI, an adduct of TDI and a polyol-based compound, and a biuret of TDI.
As the tolylene diisocyanate compound, an adduct of TDI and TMP is preferable.

As the isocyanate-based crosslinking agent, a commercially available product can be used.
Examples of commercially available isocyanate crosslinking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", "Coronate (registered trademark) L-45E", "Coronate (registered trademark) 2031", "Coronate (registered trademark) 2037", "Coronate (registered trademark) 2234", "Coronate (registered trademark) 2785", "Aquanate (registered trademark) 200", and "Aquanate (registered trademark) 210" (all manufactured by Tosoh Corporation), "Sumidur (registered trademark) N3300", "Desmodur (registered trademark) N3400", and "Sumidur (registered trademark) N75" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate (registered trademark) D201", "Duranate (registered trademark) E405-70B", "Duranate (registered trademark) E405-80T, "Duranate (registered trademark) AE700-100, "Duranate (registered trademark) 24A-100, and "Duranate (registered trademark) TSE-100" (all manufactured by Asahi Kasei Corporation), as well as "Takenate (registered trademark) D-110N", "Takenate (registered trademark) D-120N", "Takenate (registered trademark) D-140N", "Takenate (registered trademark) M-631N", "MT-Olestar (registered trademark) NP1200", and "STABIO (registered trademark) XD-340N" (all manufactured by Mitsui Chemicals, Inc.).

The adhesive composition of the present disclosure may contain only one type of crosslinking agent, or may contain two or more types.

The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but for example, it is preferably 0.1 parts by mass to 4.0 parts by mass, more preferably 0.3 parts by mass to 3.0 parts by mass, and even more preferably 0.5 parts by mass to 2.0 parts by mass, relative to 100 parts by mass of the specific methacrylic copolymer.
When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.1 parts by mass or more relative to 100 parts by mass of the specific methacrylic copolymer, the pressure-sensitive adhesive layer formed tends to have better holding power in a high-temperature environment. This is thought to be because the crosslinking reaction between the hydroxyl groups of the specific methacrylic copolymer and the crosslinking agent proceeds appropriately, and the cohesive strength of the pressure-sensitive adhesive layer formed is sufficiently increased.
When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 4.0 parts by mass or less relative to 100 parts by mass of the specific methacrylic copolymer, the pressure-sensitive adhesive layer formed tends to have a higher adhesive strength. This is thought to be because the hydroxyl groups of the specific methacrylic copolymer are not excessively crosslinked with the crosslinking agent, and the pressure-sensitive adhesive layer formed exhibits a more appropriate hardness.

[Organic Solvent]
The pressure-sensitive adhesive composition of the present disclosure may contain an organic solvent.
When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the coatability can be improved.
As the organic solvent, for example, the same organic solvents as those used in the polymerization reaction of the above-mentioned specific methacrylic copolymer can be used.

When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvent.

When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be set appropriately depending on the purpose.

[Other ingredients]
The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components described above (so-called other components) as necessary, provided that the effects of the composition are not impaired.
Examples of other components include various additives such as polymers other than the specific methacrylic copolymer, crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

When the pressure-sensitive adhesive composition of the present disclosure contains other components, the content of the other components can be set appropriately within a range that does not impair the effect of the pressure-sensitive adhesive composition of the present disclosure.

<Uses of the Pressure-Sensitive Adhesive Composition>
The application of the pressure-sensitive adhesive composition of the present disclosure is not particularly limited.
The pressure-sensitive adhesive composition of the present disclosure is capable of forming a pressure-sensitive adhesive layer that has high adhesive strength, low relative dielectric constant and dielectric tangent, and excellent holding strength in high-temperature environments. Therefore, the pressure-sensitive adhesive composition is suitable for use in attaching and fixing parts or exterior parts that may generate noise (e.g., high-frequency noise) that may cause malfunctions to objects that tend to become hot due to being placed in a high-temperature environment, generating heat, or the like, such as vehicles equipped with data communication equipment or data communication terminals.

[Adhesive tape]
The pressure-sensitive adhesive tape of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore has high adhesive strength, low dielectric constant and dielectric loss tangent, and excellent holding strength in high-temperature environments.
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive tape of the present disclosure contains a cured product of the pressure-sensitive adhesive composition of the present disclosure. The cured product includes, for example, a crosslinked product of a specific methacrylic copolymer obtained by crosslinking and curing with a crosslinking agent.

The thickness of the pressure-sensitive adhesive layer is not particularly limited.
The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, more preferably 10 μm to 45 μm, and even more preferably 15 μm to 40 μm.

In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" means the average thickness of the pressure-sensitive adhesive layer.
The average thickness of the pressure-sensitive adhesive layer is a value determined by the following method.
The thickness of the pressure-sensitive adhesive layer is measured at 10 randomly selected locations in the thickness direction using a thickness meter. The arithmetic mean of the measured values is calculated and the obtained value is regarded as the average thickness of the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive tape of the present disclosure may be a substrate-free type pressure-sensitive adhesive tape that does not have a substrate, or a substrate-containing type pressure-sensitive adhesive tape that has a pressure-sensitive adhesive layer on one or both sides of a substrate.
When the adhesive tape of the present disclosure is a substrate-free adhesive tape that does not have a substrate, or when it is a substrate-containing adhesive tape that has an adhesive layer on one side of a substrate, the exposed surface of the adhesive layer in the adhesive tape of the present disclosure may be protected by a release sheet.
In general, the release sheet protects the surface of the adhesive layer until the adhesive tape is put to practical use, and is peeled off at the time of use.

The release sheet is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer.
Examples of the release sheet include a resin film, paper, synthetic paper, and a composite sheet obtained by laminating two or more of these, the surface of which is treated with a release agent on one or both sides (so-called easy-release treatment). In the present disclosure, a release sheet in an embodiment in which a resin film is surface-treated with a release agent on one or both sides (so-called easy-release treatment) is also referred to as a "release film".
Examples of the release agent include silicone-based release agents (eg, silicone), wax-based release agents (eg, paraffin wax), and fluorine-based release agents (eg, fluorine-based resins).
An example of the resin film is a polyester film, typically a polyethylene terephthalate (PET) film.
Examples of the paper include fine paper and coated paper.
The thickness of the release sheet is not particularly limited, but is generally from 20 μm to 180 μm.

When the pressure-sensitive adhesive tape of the present disclosure includes a substrate, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed on the substrate.
Examples of the substrate include films containing resins such as polyolefin resins (e.g., polyethylene (PE) and polypropylene (PP)), polyester resins (e.g., polyethylene terephthalate (PET)), acetate resins (e.g., triacetyl cellulose resin), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyurethane resins, acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins, paper (e.g., fine paper and coated paper), synthetic paper, and composite sheets obtained by laminating two or more of these resins.

The surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called adhesion-enhancing treatment) in order to improve adhesion between the substrate and the adhesive layer.

The substrate may contain various additives, such as plasticizers, colorants (eg, dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, and the like.
The substrate may be partially or entirely patterned.

The thickness of the substrate is not particularly limited, but is generally 10 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 10 μm to 100 μm.

"Substrate thickness" in this disclosure means the average thickness of the substrate.
The average thickness of the substrate is a value determined by the same method as for the average thickness of the pressure-sensitive adhesive layer.

The applications of the pressure-sensitive adhesive tape of the present disclosure are not particularly limited.
The pressure-sensitive adhesive tape of the present disclosure has high adhesive strength, low relative dielectric constant and dielectric tangent, and is provided with an adhesive layer that exhibits excellent holding power in high-temperature environments. Therefore, the pressure-sensitive adhesive tape is suitable for use in attaching and fixing components or exterior parts that may generate noise (e.g., high-frequency noise) that may cause malfunctions to objects that tend to become hot due to being placed in a high-temperature environment, generating heat, or the like, such as vehicles equipped with data communication equipment or data communication terminals.

[Method of producing adhesive tape]
The method for producing the pressure-sensitive adhesive tape of the present disclosure is not particularly limited.
The pressure-sensitive adhesive tape of the present disclosure can be produced by known methods.
The pressure-sensitive adhesive tape of the present disclosure can be produced, for example, by the following method.

When the adhesive tape of the present disclosure is a substrate-free type adhesive tape, first, the adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. Next, the formed coating film is dried to form an adhesive layer on the release sheet. Next, the exposed surface of the formed adhesive layer is laminated and attached to the easy-release treated surface of a separately prepared release sheet, and then cured as necessary to produce a substrate-free type adhesive tape having a laminated structure of release sheet/adhesive layer/release sheet.

When the adhesive tape of the present disclosure is a substrate-type adhesive tape, first, the adhesive composition of the present disclosure is applied to the easy-adhesion treated surface of the substrate to form a coating film on the substrate. The formed coating film is then dried to form an adhesive film on the substrate. Next, the exposed surface of the formed adhesive film is laminated and attached to the easy-release treated surface of a release sheet, and then cured as necessary to produce a substrate-type adhesive tape having a laminated structure of substrate/adhesive layer/release sheet.

When the pressure-sensitive adhesive tape of the present disclosure is a substrate-containing pressure-sensitive adhesive tape, another method may be mentioned, for example, the following method.
The adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet.Then, the formed coating film is dried to form an adhesive film on the release sheet.Then, the exposed surface of the formed adhesive film is laminated on the easy-adhesion treated surface of the substrate, and then cured as necessary to produce a substrate-type adhesive tape having a laminated structure of substrate/adhesive layer/release sheet.

The method for applying the pressure-sensitive adhesive composition is not particularly limited.
Examples of methods for applying the pressure-sensitive adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, applicator, and the like.
The amount of the pressure-sensitive adhesive composition to be applied is not particularly limited, and is appropriately set depending on, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

The method for drying the coating film is not particularly limited.
Examples of methods for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying.
The drying temperature and drying time of the coating film are not particularly limited, and are appropriately set depending on the thickness of the coating film, the amount of the organic solvent in the coating film, and the like.
An example of the drying conditions is drying using a hot air dryer at 70° C. to 120° C. for 30 to 180 seconds.

When curing is performed, the curing conditions include, for example, an ambient temperature of 20°C to 35°C and a relative humidity of 45% to 55% (i.e., 45% RH to 55% RH) for 2 to 7 days.

The adhesive composition and adhesive tape of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as they do not depart from the gist of the disclosure.

[Production of methacrylic copolymer]
[Manufacture example A-1]
A reactor equipped with a stirrer, a reflux condenser, a successive dropping device, and a thermometer was charged with 120 parts by mass of ethyl acetate [organic solvent for polymerization] and 0.13 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator]. In another vessel, 450 parts by mass of a monomer mixture consisting of 441 parts by mass of 2-ethylhexyl methacrylate (2EHMA) [carbon number of alkyl group: 8, specific methacrylic acid alkyl ester monomer] and 9 parts by mass of 2-hydroxyethyl acrylate (2HEA) [monomer having a hydroxyl group] was prepared. 247.5 parts by mass (corresponding to 55% by mass of the monomer mixture) of the prepared monomer mixture was charged into the reactor, and then heated and refluxed at the reflux temperature for 20 minutes.
Next, under reflux temperature conditions, the remaining 202.5 parts by mass of the monomer mixture (corresponding to 45% by mass of the monomer mixture), 45 parts by mass of ethyl acetate [polymerization organic solvent], and 0.18 parts by mass of t-butylperoxy-2-ethylhexanoate [product name: Perbutyl O, polymerization initiator, manufactured by NOF Corp.] were successively dropped into the reactor over 120 minutes, and the mixture was held for 240 minutes after the end of the dropping to carry out a polymerization reaction. The solution after the polymerization reaction was diluted with toluene [organic solvent] so that the solid content concentration was 43% by mass, to obtain a solution of methacrylic copolymer A-1.

The term "solid content concentration" used herein means the mass ratio of methacrylic copolymer A-1 in the solution of methacrylic copolymer A-1.
The same applies to each of the solutions of the following methacrylic copolymers A-2 to A-12.

[Production examples A-2 to A-12]
In Production Examples A-2 to A-12, the monomer composition of the methacrylic copolymer was changed to the monomer composition shown in Table 1, and the weight average molecular weight of the methacrylic copolymer was adjusted to the weight average molecular weight shown in Table 1 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used. Except for this, the same operation as in Production Example A-1 was performed to obtain solutions of methacrylic copolymers A-2 to A-12 each having a solid content concentration of 43 mass%.

The monomer compositions (unit: mass%) of methacrylic copolymers A-1 to A-12, the weight average molecular weights (Mw) of methacrylic copolymers A-1 to A-12, and the glass transition temperatures (unit: °C) of methacrylic copolymers A-1 to A-12 are shown in Table 1.

The weight average molecular weight (Mw) of each of the methacrylic copolymers A-1 to A-12 was measured by the same method as that for measuring the weight average molecular weight (Mw) of the specific methacrylic copolymer described above.
The glass transition temperatures (Tg) of the methacrylic copolymers A-1 to A-12 were determined in the same manner as in the determination of the glass transition temperature (Tg) of the specific methacrylic copolymer described above.

Of the methacrylic copolymers A-1 to A-12 obtained above, methacrylic copolymers A-1 to A-7 correspond to the specific methacrylic copolymers in this disclosure.

Details of each monomer listed in Table 1 are as follows.
<Specific methacrylic acid alkyl ester monomer>
"2EHMA": 2-ethylhexyl methacrylate [number of carbon atoms in the alkyl group: 8]
"n-HMA": n-hexyl methacrylate (number of carbon atoms in the alkyl group: 6)
"LMA": lauryl methacrylate [number of carbon atoms in alkyl group: 12]
<Other (meth)acrylic acid alkyl ester monomers>
"2EHA": 2-ethylhexyl acrylate [number of carbon atoms in the alkyl group: 8]
<Monomer having a hydroxyl group>
"2HEA": 2-hydroxyethyl acrylate, "2HEMA": 2-hydroxyethyl methacrylate, "4HBA": 4-hydroxybutyl acrylate

In Table 1, a "-" in the monomer composition column means that the monomer in that column is not used.

[Preparation of Pressure-Sensitive Adhesive Composition]
Example 1
232.6 parts by mass (100 parts by mass as solid content) of the solution of methacrylic copolymer A-1, 25 parts by mass (25 parts by mass as solid content) of a hydrocarbon-based resin [product name: NOF Polybutene 3N, specific hydrocarbon-based resin (properties at 25°C: liquid, number average molecular weight: 720), manufactured by NOF Corporation], and 1.8 parts by mass (0.8 parts by mass as solid content) of a crosslinking agent [product name: Coronate (registered trademark) L-45E, isocyanate-based crosslinking agent, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content concentration: 45% by mass, manufactured by Tosoh Corporation] were thoroughly mixed to obtain a pressure-sensitive adhesive composition of Example 1.

[Examples 2 to 13]
The same procedure as in Example 1 was carried out except that the composition of the adhesive composition in Example 1 was changed to the composition shown in Table 2, to obtain each of the adhesive compositions of Examples 2 to 13.

Comparative Examples 1 to 9
The same procedure as in Example 1 was carried out except that the composition of the adhesive composition in Example 1 was changed to the composition shown in Table 3, to obtain each of the adhesive compositions of Comparative Examples 1 to 9.

[Preparation of Pressure-Sensitive Adhesive Tape A for Evaluation]
The adhesive composition prepared above was applied to the easily peelable surface of a release film (trade name: Film Byna (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.) that had been treated for easy peeling with a silicone-based release treatment agent, so that the thickness after drying was 25 μm, forming a coating film. Next, the formed coating film was dried using a hot air circulation dryer under drying conditions of a drying temperature of 100° C. and a drying time of 2 minutes, forming an adhesive film on the release film. Next, the exposed surface of the adhesive film was laminated on one side of a polyethylene terephthalate (PET) film (trade name: Toyobo Ester (registered trademark) film E5001, thickness: 25 μm, manufactured by Toyobo Co., Ltd.) (hereinafter simply referred to as "PET") as a substrate, and then left to stand for 7 days in an environment with an atmospheric temperature of 23° C. and 50% RH to cure, and an evaluation adhesive tape A was prepared. The prepared pressure-sensitive adhesive tape A for evaluation has a laminated structure of release film/pressure-sensitive adhesive layer/substrate (PET).

[Preparation of Evaluation Adhesive Tape B]
The adhesive composition prepared above was applied to the easily peelable surface of a release film [trade name: Film Byna (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.] that had been treated for easy peeling with a silicone-based release treatment agent, so that the thickness after drying was 50 μm, forming a coating film. Next, the formed coating film was dried using a hot air circulation dryer under drying conditions of a drying temperature of 100 ° C. and a drying time of 2 minutes, forming an adhesive film on the release film. Next, the exposed surface of the adhesive film was laminated on the easily peelable surface of a release film [trade name: Film Byna (registered trademark) 25E-0010 BD, thickness: 25 μm, manufactured by Fujimori Kogyo Co., Ltd.] that had been treated for easy peeling with a separately prepared silicone-based release treatment agent, and then left to stand for 7 days in an environment of an atmospheric temperature of 23 ° C. and 50% RH to perform aging, and an evaluation adhesive tape B was produced. The prepared pressure-sensitive adhesive tape B for evaluation has a laminated structure of release film/pressure-sensitive adhesive layer/release film.

[Measurement and Evaluation]
1. Adhesive strength The adhesive tape A for evaluation prepared above was cut into a size of 25 mm × 150 mm to prepare an adhesive tape piece for evaluation. In addition, a stainless steel plate [SUS304 2B] with one side polished with sandpaper (roughness: #280) was prepared as an adherend.
The release film was peeled off from the evaluation adhesive tape piece (composition: release film/adhesive layer/PET), and the surface of the adhesive layer exposed by the peeling was laminated on the polished surface of a stainless steel plate, and then a 2 kg roller was rolled back and forth once to press the surface, thereby preparing a test piece. The prepared test piece has a laminated structure of adherend (stainless steel plate)/evaluation adhesive tape piece [adhesive layer/base material (PET)]. The prepared test piece was then left to stand for 24 hours in an environment with an atmospheric temperature of 23°C and 50% RH. After this standing, the test piece was peeled off at 180° in the long side (150 mm) direction from the adherend (stainless steel plate) to measure the adhesive strength (unit: N/25 mm) using a single column material testing machine (model: STA-1225) manufactured by A&D Co., Ltd. under conditions of an atmospheric temperature of 23° C., 50% RH, and a peeling speed of 300 mm/min. The adhesive strength of the adhesive layer in a high temperature environment was then evaluated according to the following evaluation criteria.
The results are shown in Tables 2 and 3.
In the following evaluation criteria, "A", "B", and "C" are at levels that are acceptable for practical use, with "A" being the most preferable.

-Evaluation criteria-
A: The adhesive strength was 15.0 N/25 mm or more.
B: The adhesive strength was 12.0 N/25 mm or more and less than 15.0 N/25 mm.
C: The adhesive strength was 10.0 N/25 mm or more and less than 12.0 N/25 mm.
D: The adhesive strength was less than 10.0 N/25 mm.

2. Holding Power The holding power of the pressure-sensitive adhesive layer to an adherend was measured by a method in accordance with JIS Z 0237: 2009. Specifically, the measurement was performed as follows.
The adhesive tape A for evaluation prepared above was cut into a size of 25 mm × 90 mm to prepare an adhesive tape piece for evaluation. In addition, a stainless steel plate [SUS304 2B] with one side polished with sandpaper (roughness: #280) was prepared as an adherend.
A part of the release film of the evaluation adhesive tape piece (composition: release film/adhesive layer/PET) was peeled off, and the surface of the adhesive layer exposed by the peeling was laminated on the polished surface of the stainless steel plate with an adhesion area of 25 mm x 25 mm, and then pressed with a 2 kg roller to prepare a test piece X1 in which a part of the adhesive layer of the evaluation adhesive tape piece was attached to the stainless steel plate. Next, the prepared test piece X1 was left to stand in an environment with an atmospheric temperature of 23 ° C and 50% RH for 30 minutes to obtain a test piece X2. After applying a static load of 1 kg in the long side (90 mm) direction to the evaluation adhesive tape piece attached to the stainless steel plate of this test piece X2 for 24 hours in an environment with an atmospheric temperature of 80 ° C, the distance of displacement of the evaluation adhesive tape piece from the stainless steel plate (i.e., the movement distance of the evaluation adhesive tape piece) was measured. Then, the holding power of the adhesive layer in a high temperature environment was evaluated according to the following evaluation criteria.
The results are shown in Tables 2 and 3.
In the following evaluation criteria, "A", "B", and "C" are at levels that are acceptable for practical use, with "A" being the most preferable.

-Evaluation criteria-
A: The distance traveled by the evaluation adhesive tape piece was 0.1 mm or less.
B: The distance traveled by the evaluation pressure-sensitive adhesive tape piece was more than 0.1 mm and 0.3 mm or less.
C: The distance traveled by the evaluation pressure-sensitive adhesive tape piece was more than 0.3 mm and was 1.0 mm or less.
D: The moving distance of the evaluation pressure-sensitive adhesive tape piece exceeded 1.0 mm, or the evaluation pressure-sensitive adhesive tape piece fell off the stainless steel plate.

3. Dielectric Constant Samples for measuring the dielectric constant were prepared according to the following steps (1) to (7).
(1) The pressure-sensitive adhesive tape B for evaluation produced above was cut into pieces measuring 75 mm x 75 mm to prepare four pieces of pressure-sensitive adhesive tape for evaluation.
(2) One of the release films of the evaluation adhesive tape piece was peeled off, and the surface of the adhesive layer exposed by the peeling was laminated on one surface of an electrolytic copper foil [product name: NC-WC (double-sided glossy) foil, foil thickness: 10 μm, manufactured by Furukawa Electric Co., Ltd.].
(3) One release film of another piece of pressure-sensitive adhesive tape for evaluation that had been prepared was peeled off.
(4) The remaining release film was peeled off from the piece of adhesive tape for evaluation that had been bonded to the electrolytic copper foil in (2) above, and the surface of the adhesive layer exposed by the peeling was bonded to the surface of the adhesive layer exposed of the piece of adhesive tape for evaluation from which the release film had been peeled off in (3) above.
(5) The above steps (3) and (4) were repeated until the thickness of the adhesive layer reached 200 μm.
(6) When the thickness of the adhesive layer reached 200 μm, the release film of the last laminated piece of adhesive tape for evaluation was peeled off, and the exposed surface of the adhesive layer was laminated onto one surface of a separately prepared electrolytic copper foil [product name: NC-WC (double-sided glossy) foil, foil thickness: 10 μm, manufactured by Furukawa Electric Co., Ltd.]. The obtained laminate had a laminate structure of electrolytic copper foil (thickness: 10 μm)/adhesive layer (thickness: 200 μm)/electrolytic copper foil (thickness: 10 μm).
(7) The laminate obtained by the above steps (1) to (6) was cut into a size of 50 mm x 50 mm to prepare a sample for measuring the relative dielectric constant.

The measurement of the relative dielectric constant was performed using a Material Analyzer 4291B manufactured by Agilent Technologies as a measuring device under the following measuring conditions.
The measurement results are shown in Tables 2 and 3.
If the measured dielectric constant was 3.0 or less, it was determined that the pressure-sensitive adhesive layer had a low dielectric constant.

- Measurement conditions -
Measurement fixture: Agilent Technologies Dielectric Test Fixture 16453A
Measurement frequency: 1 MHz

4. Dielectric Loss Tangent The dielectric loss tangent was measured in the same manner as in "3. Relative Dielectric Constant."
The results are shown in Tables 2 and 3.
In the following evaluation criteria, "A", "B", and "C" are at levels that are acceptable for practical use, with "A" being the most preferable.

-Evaluation criteria-
A: The dielectric tangent was 0.015 or less.
B: The dielectric loss tangent was more than 0.015 and 0.025 or less.
C: The dielectric loss tangent was more than 0.025 and 0.040 or less.
D: The dielectric tangent exceeded 0.040.

Details of the components listed in Table 2 and/or Table 3 are as follows.
<Hydrocarbon Resin>
-Specific hydrocarbon resin-
"3N" (product name: NOF Polybutene 3N, component: polybutene, properties at 25°C: liquid, number average molecular weight (Mw): 720, manufactured by NOF Corporation)
"10N" (product name: NOF Polybutene 10N, component: polybutene, properties at 25°C: liquid, number average molecular weight (Mn): 1000, manufactured by NOF Corporation)
"30N" (product name: NOF Polybutene 30N, component: polybutene, properties at 25°C: liquid, number average molecular weight (Mn): 1350, manufactured by NOF Corporation)

- Hydrocarbon resins other than specific hydrocarbon resins -
"015N" (product name: NOF Polybutene 015N, component: polybutene, properties at 25°C: liquid, number average molecular weight (Mn): 580, manufactured by NOF Corporation)
"200N" (product name: NOF Polybutene 200N, component: polybutene, properties at 25°C: liquid, number average molecular weight (Mn): 2650, manufactured by NOF Corporation)

<Crosslinking Agent>
"L-45E" (product name: Coronate (registered trademark) L-45, isocyanate-based crosslinking agent, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content concentration: 45% by mass, manufactured by Tosoh Corporation)

In Tables 2 and 3, the values shown in the "blended amount" column are all values calculated as solid content.
In Tables 2 and 3, "-" means that the component in that column was not blended.

As shown in Table 2, it was confirmed that the adhesive layers formed from the adhesive compositions of Examples 1 to 13 had high adhesive strength, low relative dielectric constants and dielectric tangents, and excellent retention strength in high-temperature environments.

On the other hand, as shown in Table 3, it was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 1, in which the content of the specific hydrocarbon resin was less than 15 parts by mass per 100 parts by mass of the specific methacrylic copolymer, had lower adhesive strength than the adhesive layers formed from the adhesive compositions of the Examples.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 2, in which the content of the specific hydrocarbon resin exceeded 45 parts by mass per 100 parts by mass of the specific methacrylic copolymer, had lower holding power in a high temperature environment than the adhesive layers formed from the adhesive compositions of the Examples.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 3, in which the content of structural units derived from monomers having a hydroxyl group in the methacrylic copolymer is less than 1 mass% relative to all structural units and the content of structural units derived from specific methacrylic acid alkyl ester monomers in the methacrylic copolymer exceeds 99 mass% relative to all structural units, had lower holding power in high temperature environments compared to the adhesive layers formed from the adhesive compositions of the Examples.
It was confirmed that the adhesive layer formed by the adhesive composition of Comparative Example 4, in which the content of constituent units derived from monomers having a hydroxyl group in the methacrylic copolymer exceeds 10 mass% relative to all constituent units, had lower adhesive strength than the adhesive layers formed by the adhesive compositions of Examples. It was also confirmed that the adhesive layer formed by the adhesive composition of Comparative Example 4 had lower holding strength in a high temperature environment than the adhesive layers formed by the adhesive compositions of Examples.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 5, in which the number average molecular weight of the hydrocarbon resin was 700 or less, had lower adhesive strength than the adhesive layers formed from the adhesive compositions of the Examples.
It was confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 6, in which the number average molecular weight of the hydrocarbon resin exceeds 2000, had lower adhesive strength than the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the Examples. It was also confirmed that the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of Comparative Example 6 had lower holding strength in a high temperature environment than the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the Examples.
It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 7, in which the content of structural units derived from a specific methacrylic acid alkyl ester monomer is less than 80 mass% relative to all structural units and the glass transition temperature is less than -28°C, has a lower holding power in a high temperature environment than the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the Example. It was also confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 7 has a higher dielectric tangent than the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the Example.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 8, which had a glass transition temperature of less than -28°C, had lower holding power in a high temperature environment than the adhesive layers formed from the adhesive compositions of the Examples.
It was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 9, which had a glass transition temperature exceeding −8° C., had lower adhesive strength than the adhesive layers formed from the adhesive compositions of the Examples.

Claims (5)

a methacrylic copolymer containing 80% by mass to 99% by mass of structural units derived from methacrylic acid alkyl ester monomers having an alkyl group having 5 or more carbon atoms, and 1% by mass to 8% by mass of structural units derived from monomers having a hydroxyl group, based on all structural units, and having a glass transition temperature of -28°C to -8°C;
a hydrocarbon-based resin that is liquid at 25° C. and has a number average molecular weight of more than 700 and not more than 2,000;
A cross-linking agent;
Including,
The pressure-sensitive adhesive composition has a content of the hydrocarbon resin of 15 to 45 parts by mass relative to 100 parts by mass of the methacrylic copolymer. The adhesive composition according to claim 1, wherein the monomer having a hydroxyl group is 4-hydroxybutyl acrylate. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the structural units derived from the methacrylic acid alkyl ester monomer having an alkyl group with 5 or more carbon atoms in the methacrylic copolymer is 90% by mass to 99% by mass with respect to all structural units. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the content of the crosslinking agent is 0.1 to 4.0 parts by mass per 100 parts by mass of the methacrylic copolymer. An adhesive tape having an adhesive layer formed from the adhesive composition according to any one of claims 1 to 4.