JP7688522B2 - Double-sided adhesive sheet, double-sided adhesive sheet with release sheet, and decorative body with adhesive sheet - Google Patents

Description

This disclosure relates to a double-sided adhesive sheet, a double-sided adhesive sheet with a release sheet, and a decorative body with an adhesive sheet.

Conventionally, a method of applying decoration to motorcycles involves attaching a decorative film or sheet (hereinafter also referred to as "decorative film, etc.") to the surface of an exterior part of the motorcycle. Because motorcycles are exposed to the outside air, the adhesive sheet used to attach the decorative film, etc. is required to be difficult to peel off from the exterior part of the motorcycle even when placed in either a low-temperature or a high-temperature, high-humidity environment. Various reports have been made so far about adhesive sheets that exhibit good adhesion and adhesion to adherends in low-temperature or high-temperature, high-humidity environments.

For example, Patent Document 1 discloses a resin layer that exhibits good adhesion even at low temperatures, which is formed from a resin composition that contains a (meth)acrylic polymer having a glass transition temperature of -40°C or lower and a tackifier resin in an amount of 5 to 40 parts by weight relative to 100 parts by weight of the (meth)acrylic polymer, wherein the (meth)acrylic polymer is a resin composition that is a polymer of monomer components including 50 to 97% by weight of an alkyl (meth)acrylate (A1) having a homopolymer glass transition temperature of -50°C or lower and a branched alkyl group having 8 to 18 carbon atoms at an ester group terminal, and 3 to 50% by weight of a (meth)acrylate (A2) having a homopolymer glass transition temperature of -40°C or lower and an ether bond in the molecular skeleton.
Patent Document 2 discloses a pressure-sensitive adhesive layer that is resistant to lifting and peeling from an adherend after exposure to a high-temperature environment or a high-temperature, high-humidity environment, the pressure-sensitive adhesive comprising an acrylic polymer (A), a tackifier (B), and a crosslinking agent (C), the acrylic polymer (A) being a polymer having a weight-average molecular weight of 500,000 to 2,000,000 obtained by polymerizing a monomer containing 0.1% by weight to 20% by weight of a carboxyl group-containing monomer, the tackifier (B) having an acid value of 5 mgKOH/g to 200 mgKOH/g and a softening point of 75° C. to 160° C. and containing a rosin-based compound (excluding compounds having a hydroxyl group and a rosin skeleton) having at least one aromatic ring in the molecule, the content of the tackifier (B) being 10 parts by weight to 30 parts by weight relative to 100 parts by weight of the acrylic polymer (A), and the crosslinking agent (C) being formed from a removable pressure-sensitive adhesive containing a polyisocyanate compound.

JP 2019-119845 A Patent No. 6600954

In recent years, due to their high design potential, there has been an increase in methods for decorating motorcycles by attaching decorative bodies having three-dimensional (i.e., solid) shapes (hereinafter also referred to as "three-dimensional decorative bodies").
However, since the exterior parts of motorcycles have few flat parts and are mostly curved, when a three-dimensional decorative body is attached to an exterior part of a motorcycle via a double-sided adhesive sheet, a force that tries to return the three-dimensional decorative body to the shape before it was attached, i.e., a repulsive force, is applied to the double-sided adhesive sheet. Due to this repulsive force, the end of the double-sided adhesive sheet tends to peel off and float up in the three-dimensional decorative body attached to the exterior part of a motorcycle, and this tendency becomes more pronounced when placed in a high-temperature and high-humidity environment. For this reason, a double-sided adhesive sheet used to attach an attached body having a three-dimensional shape such as a three-dimensional decorative body to an adherend having a curved shape that is often exposed to the outside air, such as an exterior part of a motorcycle, is required to have excellent adhesion that can suppress the end from peeling off and floating up even when placed in a high-temperature and high-humidity environment after the attached body is attached to the adherend.

Furthermore, because motorcycles are used outdoors, the three-dimensional decorative body attached to the exterior part of the motorcycle may be subjected to an impact from an external force. In general, double-sided adhesive sheets tend to harden when placed in a low-temperature environment. For this reason, when the three-dimensional decorative body is subjected to an impact from an external force in a low-temperature environment, the double-sided adhesive sheet is likely to peel off from the exterior part of the motorcycle. For this reason, a double-sided adhesive sheet used to attach an adherend having a three-dimensional shape, such as a three-dimensional decorative body, to an adherend that may be subjected to an impact from an external force, such as an exterior part of a motorcycle, is required to have a property (hereinafter also referred to as "impact resistance") that makes it difficult to peel off from the adherend even when it is subjected to an impact in a low-temperature environment after the adherend is attached to the adherend.

Regarding the above-mentioned points, the resin layer described in Patent Document 1 and the pressure-sensitive adhesive layer described in Patent Document 2 are not intended for adhering to an object having a three-dimensional shape, nor are they intended for adhering to an object having a curved shape. In other words, Patent Documents 1 and 2 do not focus on the adhering of an object having a three-dimensional shape, and do not at all anticipate adhering an object having a three-dimensional shape to an object having a curved shape.
In addition, the resin layer described in Patent Document 1 has a low cohesive strength and is soft due to the design of the resin composition, and therefore exhibits good adhesion to the adherend in a low-temperature environment, but cohesive failure occurs in a high-temperature and high-humidity environment, and the adherend may peel off. On the other hand, the adhesive layer described in Patent Document 2 is said to be less likely to float or peel off from the adherend in a high-temperature and high-humidity environment, but since it is designed to contain a large amount of tackifier resin, it is thought that the adhesive layer hardens in a low-temperature environment, and there is a risk of the adherend peeling off when it is subjected to an impact.
It is difficult to design a double-sided adhesive sheet that is unlikely to peel off from an adherend in either a low-temperature environment or a high-temperature, high-humidity environment, and it has traditionally been difficult to realize a double-sided adhesive sheet that can prevent peeling from an adherend when attached to an adherend having a three-dimensional shape, or even when the adherend has a curved shape.

The problem that the present disclosure aims to solve is to provide a double-sided adhesive sheet, a double-sided adhesive sheet with a release sheet, and a decorative body with an adhesive sheet that can prevent the ends from peeling off and floating up from the adherend even when placed in a high-temperature, high-humidity environment after an object having a three-dimensional shape is attached to an adherend having a curved shape, and that is difficult to peel off from the adherend even when it is subjected to an impact in a low-temperature environment after an object having a three-dimensional shape is attached to the adherend.

Specific means for solving the problems include the following aspects.
<1> A double-sided pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer, a crosslinking agent, and a tackifier, and having a film thickness of 80 μm or more,
The (meth)acrylic copolymer contains 5% by mass to 10% by mass of structural units derived from a monomer having a carboxy group, based on the total structural units, and has a weight average molecular weight of 400,000 to 1,000,000;
The crosslinking agent includes an isocyanate-based crosslinking agent and at least one crosslinking agent selected from the group consisting of an epoxy-based crosslinking agent and a metal chelate-based crosslinking agent,
the ratio of the total mass content of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent to the mass content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition (i.e., the total mass content of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent/the mass content of the isocyanate-based crosslinking agent) is 0.01 to 0.1;
The double-sided pressure-sensitive adhesive sheet has a content of the tackifier in the pressure-sensitive adhesive composition of 1 to 5 parts by mass per 100 parts by mass of the (meth)acrylic copolymer.
<2> The double-sided pressure-sensitive adhesive sheet according to <1>, having a loss factor tan δ at −30° C. of 0.10 or more.
<3> The double-sided pressure-sensitive adhesive sheet according to <1> or <2>,
release sheets provided on both sides of the double-sided pressure-sensitive adhesive sheet;
A double-sided adhesive sheet with a release sheet.
<4> The double-sided pressure-sensitive adhesive sheet according to <1> or <2>,
A decorative body provided on one surface of the double-sided pressure-sensitive adhesive sheet and having a three-dimensional shape;
A decorative body with an adhesive sheet.

According to the present disclosure, there are provided a double-sided adhesive sheet, a double-sided adhesive sheet with a release sheet, and a decorative body with an adhesive sheet, which can prevent the ends from peeling off and floating up from the adherend even when the adherend is placed in a high-temperature, high-humidity environment after an object having a three-dimensional shape is attached to an adherend having a curved shape, and which is difficult to peel off from the adherend even when the object is subjected to an impact in a low-temperature environment after the object having a three-dimensional shape is attached to the adherend.

The double-sided adhesive sheet, double-sided adhesive sheet with release sheet, and decorative body with adhesive sheet of the present disclosure are described in detail below. The explanation of the requirements described below may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and can be implemented with appropriate modifications 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 this disclosure, a combination of two or more preferred aspects is a more preferred aspect.

In this 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 this disclosure, "(meth)acrylic copolymer" means a copolymer in which the content of constituent units derived from monomers having a (meth)acryloyl group is 50% by mass or more relative to the total constituent units (i.e., all constituent units of the 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.

[Double-sided adhesive sheet]
The double-sided pressure-sensitive adhesive sheet of the present disclosure is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer, a crosslinking agent, and a tackifier, and has a film thickness of 80 μm or more, the (meth)acrylic copolymer contains 5% by mass to 10% by mass of structural units derived from a monomer having a carboxy group, based on all structural units, and has a weight average molecular weight of 400,000 to 1,000,000, and the crosslinking agent is selected from the group consisting of an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and a metal chelate-based crosslinking agent. and at least one crosslinking agent selected from the group consisting of acrylic and non-acrylic copolymers, wherein the ratio of the total mass content of the epoxy crosslinking agent and the metal chelate crosslinking agent to the mass content of the isocyanate crosslinking agent in the pressure-sensitive adhesive composition [i.e., the total mass content of the epoxy crosslinking agent and the metal chelate crosslinking agent/the mass content of the isocyanate crosslinking agent] is 0.01 to 0.1, and the content of the tackifier in the pressure-sensitive adhesive composition is 1 to 5 parts by mass relative to 100 parts by mass of the (meth)acrylic copolymer.
The double-sided adhesive sheet of the present disclosure can prevent the ends from peeling off and floating away from the adherend, even when the adherend is placed in a high-temperature, high-humidity environment after an object having a three-dimensional shape is attached to an adherend having a curved shape, and is also unlikely to peel off from the adherend even when the adherend is subjected to an impact in a low-temperature environment after the object having a three-dimensional shape is attached to the adherend.

The present disclosure is characterized in that a double-sided adhesive sheet exhibits a good balance between high cohesive strength and excellent adhesion to the adherend by selecting a (meth)acrylic copolymer, a crosslinking agent, and a tackifier as components of an adhesive composition for forming the double-sided adhesive sheet, adjusting the weight average molecular weight of the (meth)acrylic copolymer and the content of a constituent unit derived from a monomer having a carboxy group, selecting a combination of an isocyanate-based crosslinking agent having a relatively slow crosslinking reaction and an epoxy-based crosslinking agent and/or a metal chelate-based crosslinking agent having a relatively fast crosslinking reaction for the crosslinking agent, and adjusting the content ratio of these crosslinking agents, adjusting the content of the tackifier, and adjusting the film thickness of the double-sided adhesive sheet. The double-sided adhesive sheet of the present disclosure exhibits the effects of the present disclosure by having a good balance between high cohesive strength and excellent adhesion to the adherend.

The double-sided pressure-sensitive adhesive sheet of the present disclosure will be described in detail below.
Hereinafter, the "(meth)acrylic copolymer containing 5% by mass to 10% by mass of structural units derived from monomers having a carboxy group, relative to all structural units, and having a weight average molecular weight of 400,000 to 1,000,000" contained in the pressure-sensitive adhesive composition of the present disclosure is also referred to as a "specific (meth)acrylic copolymer."

[Adhesive composition]
The pressure-sensitive adhesive composition according to the present disclosure contains a specific (meth)acrylic copolymer, a crosslinking agent, and a tackifier, which will be described below.

<Specific (meth)acrylic copolymer>
The pressure-sensitive adhesive composition according to the present disclosure contains a (meth)acrylic copolymer (i.e., a specific (meth)acrylic copolymer) that contains 5% by mass to 10% by mass of structural units derived from a monomer having a carboxy group, based on the total structural units, and has a weight average molecular weight of 400,000 to 1,000,000.
The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of specific (meth)acrylic copolymer, or may contain two or more types.

<<Structural units derived from monomers having a carboxy group>>
The specific (meth)acrylic copolymer contains 5% by mass to 10% by mass of structural units derived from a monomer having a carboxy group, based on the total amount of structural units.
In the present disclosure, a "structural unit derived from a monomer having a carboxy group" refers to a structural unit formed by addition polymerization of a monomer having a carboxy group.

The type of the monomer having a carboxy group is not particularly limited.
An example of a monomer having a carboxy group is a monomer having at least one carboxy 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 carboxy group include (meth)acrylic acid, crotonic acid , maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinic acid esters (e.g., 2-acryloyloxyethyl-succinic acid), vinyl formate, vinyl acetate, vinyl propionate, and vinyl neodecanoate.
Among these, acrylic acid (AA) is preferred as the monomer having a carboxy group.

The specific (meth)acrylic copolymer may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types.

The specific (meth)acrylic copolymer contains 5% by mass to 10% by mass of structural units derived from monomers having a carboxy group, based on the total structural units of the specific (meth)acrylic copolymer. In other words, the content of structural units derived from monomers having a carboxy group in the specific (meth)acrylic copolymer is 5% by mass to 10% by mass, based on the total structural units of the specific (meth)acrylic copolymer.
When the content of constituent units derived from monomers having a carboxy group in the specific (meth)acrylic copolymer is 5% by mass to 10% by mass with respect to all constituent units of the specific (meth)acrylic copolymer, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend even when placed in a high-temperature and high-humidity environment after a three-dimensional object is attached to a curved adherend. Also, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend over time after a three-dimensional object is attached to a curved adherend.
The reason is that when the content of the constituent units derived from the monomer having a carboxyl group in the specific (meth)acrylic copolymer is 5% by mass or more relative to the total constituent units of the specific (meth)acrylic copolymer, the crosslinking points are appropriately increased, and the cohesive force of the double-sided pressure-sensitive adhesive sheet is appropriately increased, and the repulsive force of the three-dimensionally shaped object to be attached (the force that the object to be attached tries to return to the shape before being attached; the same applies below) can be suppressed.In addition, when the content of the constituent units derived from the monomer having a carboxyl group in the specific (meth)acrylic copolymer is 10% by mass or less relative to the total constituent units of the specific (meth)acrylic copolymer, the double-sided pressure-sensitive adhesive sheet does not become excessively hard, and the wettability of the double-sided pressure-sensitive adhesive sheet to the object to be attached is good.
The content of the structural units derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer is, for example, preferably 5.5% by mass to 10% by mass, more preferably 6% by mass to 10% by mass, even more preferably 6.5% by mass to 10% by mass, and particularly preferably 7% by mass to 10% by mass, relative to all structural units of the specific (meth)acrylic copolymer.

<<Structural units derived from (meth)acrylic acid alkyl ester monomers>>
The specific (meth)acrylic copolymer preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer.
The structural units derived from the (meth)acrylic acid alkyl ester monomer can contribute to adjusting the adhesive strength of the double-sided PSA sheet.

In this disclosure, "structural units derived from (meth)acrylic acid alkyl ester monomers" refers to structural units formed by addition polymerization of (meth)acrylic acid alkyl ester monomers. In addition, "(meth)acrylic acid alkyl ester monomers" in this disclosure does not include monomers that correspond to monomers having a carboxy group.

The type of the (meth)acrylic acid alkyl ester monomer is not particularly limited.
The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer, but is preferably an acrylic acid alkyl ester monomer.
The (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
The alkyl group of the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The alkyl group preferably has 1 to 18 carbon atoms, and more preferably has 1 to 12 carbon atoms.

Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.
Among these, the (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of methyl acrylate (MA), n-butyl acrylate (n-BA), lauryl acrylate (LA), and 2-ethylhexyl acrylate (2EHA).

When the specific (meth)acrylic copolymer contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, it may contain only one type of structural unit derived from the (meth)acrylic acid alkyl ester monomer, or it may contain two or more types of structural units derived from the (meth)acrylic acid alkyl ester monomer.

When the specific (meth)acrylic copolymer contains a constituent unit derived from a (meth)acrylic acid alkyl ester monomer, the content of the constituent unit derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer is not particularly limited, but for example, is preferably 50% by mass to 95% by mass, more preferably 60% by mass to 95% by mass, even more preferably 70% by mass to 95% by mass, and particularly preferably 80% by mass to 95% by mass, relative to all constituent units of the specific (meth)acrylic copolymer.
Here, the content of the constituent units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer being 50 mass% or more relative to the total constituent units of the specific (meth)acrylic copolymer means that the constituent units derived from the (meth)acrylic acid alkyl ester monomer are contained as a main component of the constituent units constituting the specific (meth)acrylic copolymer.

<<Other building blocks>>
The specific (meth)acrylic copolymer may contain, as necessary, structural units other than the structural units already described, i.e., the structural unit derived from a monomer having a carboxy group, which is an essential structural unit, and the structural unit derived from an alkyl (meth)acrylate monomer, which is an optional structural unit (so-called other structural units), within the scope of the invention that does not impair the effects of the double-sided pressure-sensitive adhesive sheet of the present disclosure.

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; vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; and derivatives thereof.

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

When the specific (meth)acrylic copolymer contains other structural units, the content of the other structural units in the specific (meth)acrylic copolymer is not particularly limited and can be set appropriately according to the purpose within a range that does not impair the effect of the double-sided pressure-sensitive adhesive sheet of the present disclosure.

- Weight average molecular weight of specific (meth)acrylic copolymer -
The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic copolymer is 400,000 to 1,000,000.
When the weight-average molecular weight of the specific (meth)acrylic copolymer is 400,000 or more, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend even when the double-sided pressure-sensitive adhesive sheet is placed in a high-temperature and high-humidity environment after a three-dimensional object is attached to a curved adherend. Also, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend over time after a three-dimensional object is attached to a curved adherend.
The reason for this is believed to be that the cohesive strength of the double-sided pressure-sensitive adhesive sheet is increased appropriately, making it possible to suppress the repulsive force of an object to be attached, which has a three-dimensional shape.
From this viewpoint, the weight average molecular weight of the specific (meth)acrylic copolymer is 400,000 or more, preferably 450,000 or more, and more preferably 500,000 or more.
When the weight average molecular weight of the specific (meth)acrylic copolymer is 1,000,000 or less, the double-sided pressure-sensitive adhesive sheet tends to be less likely to peel off from the adherend even when the sheet is subjected to an impact in a low-temperature environment after the sheet is attached to an object having a three-dimensional shape.
The reason for this is believed to be that the double-sided pressure-sensitive adhesive sheet does not become excessively hard, and the double-sided pressure-sensitive adhesive sheet has good wettability with respect to the adherend.
From this viewpoint, the weight average molecular weight of the specific (meth)acrylic copolymer is 1,000,000 or less, preferably 900,000 or less, and more preferably 800,000 or less.

The weight average molecular weight of the specific (meth)acrylic copolymer is a value determined by the following method, specifically, according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic copolymer.
(2) Using the film-like specific (meth)acrylic 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 (meth)acrylic copolymer in the sample solution.
(3) The weight average molecular weight of the specific (meth)acrylic 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 (meth)acrylic 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.

- Glass transition temperature of specific (meth)acrylic copolymer -
The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic copolymer is not particularly limited, but is, for example, preferably -30°C or lower, more preferably -35°C or lower, even more preferably -37°C or lower, and particularly preferably -40°C or lower.
When the glass transition temperature of the specific (meth)acrylic copolymer is −30° C. or lower, the double-sided pressure-sensitive adhesive sheet tends to be less likely to peel off from the adherend when the sheet is subjected to an impact in a low-temperature environment after being attached to an object having a three-dimensional shape.
The lower limit of the glass transition temperature of the specific (meth)acrylic copolymer is not particularly limited, but is preferably, for example, −70° C. or higher.

The glass transition temperature of the specific (meth)acrylic copolymer is a value calculated from the following formula 1, which is calculated by converting the absolute temperature (unit: K) 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 glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic copolymer is made into a homopolymer, and m1, m2, ..., m(k-1), and mk respectively represent the molar fractions of each monomer constituting the specific (meth)acrylic 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 the present disclosure, the "glass transition temperature expressed as absolute temperature when made into a homopolymer" refers to the glass transition temperature expressed as absolute temperature of a homopolymer produced by polymerizing the monomer alone.
The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) [model: EXSTAR6000, manufactured by Seiko Instruments Inc.] under conditions of a nitrogen gas flow, a measurement sample of 10 mg, and a heating rate of 10° C./min, and the inflection point of the obtained DSC curve was taken as the glass transition temperature of the homopolymer.

The glass transition temperatures of representative monomers, expressed in Celsius degrees when made into homopolymers, are: 2-ethylhexyl acrylate -76°C, 2-ethylhexyl methacrylate -10°C, n-butyl acrylate -57°C, n-butyl methacrylate 21°C, t-butyl acrylate 41°C, t-butyl methacrylate 107°C, i-butyl methacrylate 48°C, methyl acrylate 5°C, methyl methacrylate 103°C, isobornyl methacrylate 155°C, isobornyl acrylate 96°C, ethyl acrylate -27°C, and methacrylic acid 18°C. 5°C, 4-hydroxybutyl acrylate -39°C, 2-hydroxyethyl acrylate -15°C, 2-hydroxyethyl methacrylate 55°C, 2-hydroxypropyl acrylate -7°C, acrylic acid 106°C, n-octyl acrylate -65°C, i-octyl acrylate -75°C, i-decyl acrylate -62°C, lauryl acrylate 15°C, dimethylaminoethyl methacrylate 18°C, ω-carboxy-polycaprolactone (n≒2) monoacrylate -30°C, and 2-acryloyloxyethyl-succinic acid -40°C.

The glass transition temperature of the specific (meth)acrylic 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.

- Content of specific (meth)acrylic copolymer -
The content of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition according to the present disclosure is not particularly limited, but is, for example, preferably 75.0 mass % to 98.7 mass %, more preferably 80.0 mass % to 98.5 mass %, and even more preferably 85.0 mass % to 98.0 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 (meth)acrylic copolymer-
The method for producing the specific (meth)acrylic copolymer is not particularly limited.
The specific (meth)acrylic 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 ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl ethyl acetate, and the like. Examples of the alcohol compounds include ketones, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds, such as 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, such as 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 (meth)acrylic 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 (meth)acrylic 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 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-butylperoxycyclohexyl)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.
In producing the specific (meth)acrylic copolymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and it is particularly preferable to use an azo compound.

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 (meth)acrylic copolymer.

In producing the specific (meth)acrylic 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 (meth)acrylic 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 (meth)acrylic copolymer.

The polymerization temperature is not particularly limited and can be set appropriately depending on, for example, the molecular weight of the desired specific (meth)acrylic copolymer.

<Crosslinking Agent>
The pressure-sensitive adhesive composition according to the present disclosure contains a crosslinking agent.
The crosslinking agent includes an isocyanate-based crosslinking agent and at least one crosslinking agent selected from the group consisting of an epoxy-based crosslinking agent and a metal chelate-based crosslinking agent.
When the pressure-sensitive adhesive composition of the present disclosure contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent and/or a metal chelate-based crosslinking agent as a crosslinking agent, the double-sided pressure-sensitive adhesive sheet can suppress the ends from peeling off and floating up from the adherend even when placed in a high-temperature, high-humidity environment after a three-dimensional object is attached to an adherend having a curved shape, and also tends to be less likely to peel off from the adherend even when the sheet is subjected to an impact in a low-temperature environment after a three-dimensional object is attached to the adherend. Furthermore, the double-sided pressure-sensitive adhesive sheet also tends to suppress the ends from peeling off and floating up from the adherend over time after a three-dimensional object is attached to an adherend having a curved shape.
In general, the crosslinking reaction by an isocyanate-based crosslinking agent is relatively slow, while the crosslinking reaction by an epoxy-based crosslinking agent and a metal chelate-based crosslinking agent is relatively fast. The pressure-sensitive adhesive composition of the present disclosure contains an isocyanate-based crosslinking agent with a relatively slow crosslinking reaction and an epoxy-based crosslinking agent and/or a metal chelate-based crosslinking agent with a relatively fast crosslinking reaction, and thus can form a double-sided pressure-sensitive adhesive sheet having flexibility while enabling the formation of a dense crosslinked structure equivalent to that in the case of containing a single crosslinking agent. Therefore, it is considered that the double-sided pressure-sensitive adhesive sheet of the present disclosure can exert a sufficient effect not only on an adherend having a flat shape, but also on an adherend having a curved shape.

The pressure-sensitive adhesive composition of the present disclosure may contain, as necessary, a crosslinking agent other than an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and a metal chelate-based crosslinking agent (so-called other crosslinking agent), as long as the effect of the double-sided pressure-sensitive adhesive sheet of the present disclosure is not impaired.
The crosslinking agent may be a combination of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, a combination of an isocyanate-based crosslinking agent and a metal chelate-based crosslinking agent, or a combination of 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 pressure-sensitive adhesive composition according to the present disclosure contains an isocyanate-based crosslinking agent.
The type of the isocyanate-based crosslinking agent is not particularly limited.
Examples of the isocyanate crosslinking agent include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI); aliphatic polyisocyanate compounds or alicyclic polyisocyanate compounds such as hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), isophorone diisocyanate, and hydrogenated aromatic polyisocyanate compounds.
Further, examples of the isocyanate-based crosslinking agent include dimers, trimers, and pentamers of the above polyisocyanate compounds, adducts of the above polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret products of the above polyisocyanate compounds.

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) E-405-80T", "Duranate (registered trademark) AE700-100, "Duranate (registered trademark) 24A-100," and "Duranate (registered trademark) TSE-100" (all manufactured by Asahi Kasei Corporation); and "Takenate (registered trademark) D-110N,""Takenate (registered trademark) D-120N,""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 isocyanate-based crosslinking agent, or may contain two or more types.

The content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition according to the present disclosure is not particularly limited, but for example, is preferably 0.1 parts by mass to 5 parts by mass, more preferably 0.2 parts by mass to 4 parts by mass, and even more preferably 0.3 parts by mass to 3 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition according to the present disclosure is within the above range relative to 100 parts by mass of the specific (meth)acrylic copolymer, it tends to be possible to form a double-sided pressure-sensitive adhesive sheet that has a better balance between high cohesive strength and excellent adhesion to the adherend.

The pressure-sensitive adhesive composition according to the present disclosure contains at least one crosslinking agent selected from the group consisting of epoxy-based crosslinking agents and metal chelate-based crosslinking agents.
Of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent, the pressure-sensitive adhesive composition according to the present disclosure may contain only an epoxy-based crosslinking agent, may contain only a metal chelate-based crosslinking agent, or may contain both an epoxy-based crosslinking agent and a metal chelate-based crosslinking agent.

The type of the epoxy crosslinking agent is not particularly limited.
Specific examples of epoxy crosslinking agents include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol di ... Examples of such glycidyl ethers include glycerol polyglycidyl ether, resorcinol diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris(glycidyl)isocyanurate, tris(glycidoxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine).

As the epoxy crosslinking agent, a commercially available product can be used.
Examples of commercially available epoxy crosslinking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" (both manufactured by Mitsubishi Gas Chemical Company, Inc.), and "Denacol (registered trademark) EX-201" and "Denacol (registered trademark) EX-931" (both manufactured by Nagase ChemteX Corporation).

When the adhesive composition of the present disclosure contains an epoxy-based crosslinking agent, it may contain only one type of epoxy-based crosslinking agent, or may contain two or more types of epoxy-based crosslinking agents.

When the pressure-sensitive adhesive composition according to the present disclosure contains an epoxy-based crosslinking agent, the content of the epoxy-based crosslinking agent in the pressure-sensitive adhesive composition is not particularly limited, but is, for example, preferably 0.001 parts by mass to 0.1 parts by mass, more preferably 0.003 parts by mass to 0.05 parts by mass, and even more preferably 0.005 parts by mass to 0.03 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the epoxy crosslinking agent in the pressure-sensitive adhesive composition according to the present disclosure is within the above range relative to 100 parts by mass of the specific (meth)acrylic copolymer, there is a tendency that a double-sided pressure-sensitive adhesive sheet having more appropriate flexibility can be formed.

The type of the metal chelate crosslinking agent is not particularly limited.
Examples of metal chelate crosslinking agents include aluminum chelate compounds, titanium chelate compounds, zirconium chelate compounds, and cobalt chelate compounds.
As the metal chelate crosslinking agent, an aluminum chelate compound is preferred.
Specific examples of aluminum chelate compounds include aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(ethylacetoacetate), and aluminum tris(acetylacetonate).

As the metal chelate crosslinking agent, commercially available products can be used.
Examples of commercially available metal chelate crosslinking agents include Aluminum Chelate A (trade name, aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.), Aluminum Chelate D (trade name, aluminum monoacetylacetonate bis(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.), and ALCH-TR (trade name, aluminum tris(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.).

When the pressure-sensitive adhesive composition of the present disclosure contains a metal chelate crosslinking agent, it may contain only one type of metal chelate crosslinking agent, or may contain two or more types of metal chelate crosslinking agents.

When the pressure-sensitive adhesive composition according to the present disclosure contains a metal chelate-based crosslinking agent, the content of the metal chelate-based crosslinking agent in the pressure-sensitive adhesive composition is not particularly limited, but is, for example, preferably 0.01 parts by mass to 0.3 parts by mass, more preferably 0.02 parts by mass to 0.2 parts by mass, and even more preferably 0.03 parts by mass to 0.1 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the metal chelate crosslinking agent in the pressure-sensitive adhesive composition according to the present disclosure is within the above range relative to 100 parts by mass of the specific (meth)acrylic copolymer, there is a tendency that a double-sided pressure-sensitive adhesive sheet with more appropriate flexibility can be formed.

In the pressure-sensitive adhesive composition of the present disclosure, the ratio of the total mass content of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent to the mass content of the isocyanate-based crosslinking agent (i.e., the total mass content of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent/the mass content of the isocyanate-based crosslinking agent) is 0.01 to 0.1.
When the ratio of the total mass content of the epoxy crosslinking agent and the metal chelate crosslinking agent to the mass content of the isocyanate crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.01 to 0.1, the double-sided pressure-sensitive adhesive sheet can suppress the end portions from peeling off and floating up from the adherend even when placed in a high-temperature and high-humidity environment after a three-dimensional object is attached to an adherend having a curved shape, and also shows a tendency to be less likely to peel off from the adherend even when subjected to an impact in a low-temperature environment after a three-dimensional object is attached to the adherend. Furthermore, the double-sided pressure-sensitive adhesive sheet shows a tendency to suppress the end portions from peeling off and floating up from the adherend over time after a three-dimensional object is attached to an adherend having a curved shape.
According to the pressure-sensitive adhesive composition of the present disclosure, the specific (meth)acrylic copolymer described above is crosslinked with an epoxy-based crosslinking agent and/or a metal chelate-based crosslinking agent, which has a relatively fast crosslinking reaction, and then crosslinked with an isocyanate-based crosslinking agent, which has a relatively slow crosslinking reaction, thereby making it possible to realize a double-sided pressure-sensitive adhesive sheet that has a good balance between the wettability required for adhesion to the adherend and the cohesive force required to suppress the repulsive force of the adherend having a three-dimensional shape.

When the crosslinking agent is a combination of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, the ratio of the mass content of the epoxy-based crosslinking agent to the mass content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure (i.e., mass content of the epoxy-based crosslinking agent/mass content of the isocyanate-based crosslinking agent) is, for example, preferably 0.01 to 0.07, more preferably 0.01 to 0.05, and even more preferably 0.01 to 0.02.
When the crosslinking agent is a combination of an isocyanate-based crosslinking agent and a metal chelate-based crosslinking agent, the ratio of the mass content of the metal chelate-based crosslinking agent to the mass content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure (i.e., mass content of metal chelate-based crosslinking agent/mass content of isocyanate-based crosslinking agent) is, for example, preferably 0.05 to 0.1, and more preferably 0.07 to 0.1.

<Tackifier>
The pressure-sensitive adhesive composition according to the present disclosure contains a tackifier. The content of the tackifier in the pressure-sensitive adhesive composition according to the present disclosure is 1 part by mass to 5 parts by mass per 100 parts by mass of the specific (meth)acrylic copolymer.

In the present disclosure, the term "tackifier" refers to a compound that has the property of being able to impart tackiness when incorporated and has a molecular weight of less than 10,000 (preferably in the range of 500 or more and less than 10,000).
Tackifiers are also called tackifiers.

The type of tackifier is not particularly limited.
Examples of tackifiers include compounds having a rosin skeleton (e.g., rosin resins), compounds having a terpene skeleton (e.g., terpene resins), and compounds having a styrene skeleton (e.g., styrene resins).

Specific examples of compounds having a rosin skeleton include rosin compounds represented by abietic acid, neoabietic acid, and palustric acid, diol compounds having a rosin skeleton obtained by reacting hydrogenated rosin with diglycidyl ether, and hydrogenated rosin diol compounds.
Specific examples of compounds having a terpene skeleton include copolymers of monocyclic monoterpene compounds such as α-pinene, β-pinene, and dipentene (limonene) with phenol compounds such as phenol, cresol, and bisphenol A.
Specific examples of the compound having a styrene skeleton include polystyrene and a copolymer of styrene and α-methylstyrene.

As the tackifier, commercially available products can be used.
Examples of commercially available tackifiers include "YS Polystar U115", "YS Polystar U130", "YS Polystar T80", "YS Polystar T100", "YS Polystar T115", "YS Polystar T130", "YS Polystar TH30", "YS Polystar TH130", "YS Polystar T145", "YS Polystar T160", "YS Polystar S145", "YS Polystar G125", "YS Polystar G150", "YS Polystar N125", "YS Polystar K125", "YS Polystar K140", and "YS Resin CP" manufactured by Yasuhara Chemical Co., Ltd., "FTR (registered trademark) 6100" manufactured by Mitsui Chemicals, Inc., and "Pine Crystal (registered trademark) KE-359" and "Pine Crystal (registered trademark) D-6011,""Pensel (registered trademark) D-125,""Tamanol (registered trademark) 803L," and "Tamanol (registered trademark) 901" (all of which are trade names) are examples.

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

The content of the tackifier in the pressure-sensitive adhesive composition according to the present disclosure is 1 part by mass to 5 parts by mass per 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the tackifier in the pressure-sensitive adhesive composition of the present disclosure is 1 part by mass or more per 100 parts by mass of the specific (meth)acrylic copolymer, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend even when placed in a high-temperature and high-humidity environment after a three-dimensional object is attached to a curved adherend. Also, the double-sided pressure-sensitive adhesive sheet shows a tendency to be able to suppress the end portions from peeling off and floating up from the adherend over time after a three-dimensional object is attached to a curved adherend.
Because the molecular weight of the tackifier is lower than that of the specific (meth)acrylic copolymer, the tackifier tends to collect at the interface between the double-sided pressure-sensitive adhesive sheet and the adherend due to compatibility, which is thought to result in a decrease in the apparent molecular weight at the interface of the double-sided pressure-sensitive adhesive sheet and an increase in adhesion to the adherend.
From such a viewpoint, the content of the tackifier in the pressure-sensitive adhesive composition according to the present disclosure is 1 part by mass or more, preferably 1.5 parts by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the tackifier in the pressure-sensitive adhesive composition according to the present disclosure is 5 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic copolymer, the double-sided pressure-sensitive adhesive sheet tends to be less likely to peel off from the adherend even when the sheet is subjected to an impact in a low-temperature environment after being attached to an object having a three-dimensional shape.
The reason for this is believed to be that the double-sided pressure-sensitive adhesive sheet does not become excessively hard, and the double-sided pressure-sensitive adhesive sheet has good wettability with respect to the adherend.
From such a viewpoint, the content of the tackifier in the pressure-sensitive adhesive composition according to the present disclosure is 5 parts by mass or less, preferably 4.5 parts by mass or less, and more preferably 4 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic copolymer.

<Organic Solvent>
The pressure-sensitive adhesive composition according to the present disclosure may contain an organic solvent.
When the pressure-sensitive adhesive composition according to the present disclosure contains an organic solvent, the coatability can be further improved.
As the organic solvent, for example, the same organic solvents as those used in the polymerization reaction of the above-mentioned specific (meth)acrylic copolymer can be used.

When the 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 within a range that does not impair the effects of the double-sided pressure-sensitive adhesive sheet of the present disclosure.

<Other ingredients>
The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components already described (so-called other components) as necessary, provided the effects of the double-sided pressure-sensitive adhesive sheet of the present disclosure are not impaired.
Examples of other components include various additives such as polymers other than the specific (meth)acrylic copolymer, 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 is not particularly limited and can be set appropriately within a range that does not impair the effect of the double-sided pressure-sensitive adhesive sheet of the present disclosure.

<Physical properties of double-sided adhesive sheet>
(Film Thickness)
The double-sided pressure-sensitive adhesive sheet of the present disclosure has a film thickness of 80 μm or more, preferably 85 μm or more, and more preferably 90 μm or more.
When the double-sided pressure-sensitive adhesive sheet of the present disclosure has a film thickness of 80 μm or more, even if the double-sided pressure-sensitive adhesive sheet is placed in a high-temperature and high-humidity environment after a three-dimensional object is attached to a curved adherend, the double-sided pressure-sensitive adhesive sheet tends to be less likely to peel off from the adherend even if the double-sided pressure-sensitive adhesive sheet is subjected to an impact in a low-temperature environment after the three-dimensional object is attached to the adherend. Moreover, the double-sided pressure-sensitive adhesive sheet tends to be able to suppress the double-sided pressure-sensitive adhesive sheet over time from peeling off and floating up from the adherend after the three-dimensional object is attached to the curved adherend.
The reason for this is believed to be that the volume in the thickness direction is sufficiently secured, thereby increasing the cohesive force appropriately.
There is no particular upper limit to the film thickness of the double-sided pressure-sensitive adhesive sheet of the present disclosure, but from the standpoint of manufacturability, for example, it is preferably 150 μm or less.

In the present disclosure, the "film thickness of the double-sided pressure-sensitive adhesive sheet" refers to the average film thickness of the double-sided pressure-sensitive adhesive sheet.
The average film thickness of the double-sided pressure-sensitive adhesive sheet is a value measured by the following method.
The arithmetic mean value of the average film thickness of the double-sided pressure-sensitive adhesive sheet measured at 10 randomly selected points in the thickness direction of the double-sided pressure-sensitive adhesive sheet is determined, and the obtained value is regarded as the average film thickness of the double-sided pressure-sensitive adhesive sheet. The film thickness of the double-sided pressure-sensitive adhesive sheet is measured using a film thickness meter.

(Loss factor at -30°C)
The double-sided pressure-sensitive adhesive sheet of the present disclosure preferably has a loss factor tan δ at −30° C. of 0.10 or more, more preferably 0.11 or more, and even more preferably 0.12 or more.
The higher the loss factor tan δ of a double-sided PSA sheet, the more of the energy generated by an external force that is diffused to the outside rather than stored inside the double-sided PSA sheet. In other words, the higher the loss factor tan δ of a double-sided PSA sheet, the better the impact diffusion property of the double-sided PSA sheet.
When the double-sided pressure-sensitive adhesive sheet of the present disclosure has a loss factor tan δ of 0.10 or more at -30°C, it tends to be less likely to peel off from the adherend when an impact is received in a low-temperature environment after an object having a three-dimensional shape is attached to the adherend.
There is no particular upper limit to the loss factor tan δ at −30° C. of the double-sided pressure-sensitive adhesive sheet of the present disclosure, but it is preferably, for example, 0.40 or less.

The loss factor tan δ at −30° C. is a value measured using a dynamic viscoelasticity measuring device under the following conditions.
As a dynamic viscoelasticity measuring device, for example, Rheogel-E4000 (product name) manufactured by UBM Co., Ltd. can be suitably used. However, the dynamic viscoelasticity measuring device is not limited to this.

～Conditions～
Measurement temperature range: -70℃ to 0℃
Temperature increase condition: 2°C/min Step temperature: 1°C
Measurement frequency: 10Hz

<Applications of double-sided adhesive sheets>
The uses of the double-sided pressure-sensitive adhesive sheet of the present disclosure are not particularly limited.
The double-sided adhesive sheet of the present disclosure can prevent the ends from peeling off and floating away from the adherend even when the adherend is placed in a high temperature and high humidity environment after an object having a three-dimensional shape is attached to an adherend having a curved shape, and is also unlikely to peel off from the adherend even when the adherend is subjected to an impact in a low temperature environment after the object having a three-dimensional shape is attached to the adherend. Therefore, a preferred application of the double-sided adhesive sheet is, for example, fixing an object having a three-dimensional shape to an adherend in an environment exposed to the outside air (e.g., outdoors).
An example of an object to be attached having a three-dimensional shape is a decorated object having a three-dimensional shape (i.e., a three-dimensional decorated object).
Examples of three-dimensional decorations include emblems, stickers, labels, etc. having three-dimensional shapes.

[Double-sided adhesive sheet with release sheet]
The double-sided adhesive sheet with a release sheet of the present disclosure includes the double-sided adhesive sheet of the present disclosure described above and release sheets provided on both sides of the double-sided adhesive sheet. That is, in the double-sided adhesive sheet with a release sheet of the present disclosure, the release sheet, the double-sided adhesive sheet of the present disclosure, and the release sheet are laminated in this order.

The double-sided pressure-sensitive adhesive sheet with a release sheet of the present disclosure comprises the double-sided pressure-sensitive adhesive sheet of the present disclosure.
The double-sided pressure-sensitive adhesive sheet of the present disclosure has been described above, and therefore description thereof will be omitted here.

The release-sheet-attached double-sided pressure-sensitive adhesive sheet of the present disclosure includes a release sheet.
In the double-sided pressure-sensitive adhesive sheet with a release sheet of the present disclosure, the release sheets are provided on both sides of the double-sided pressure-sensitive adhesive sheet and serve to protect the surface of the double-sided pressure-sensitive adhesive sheet.
The release sheet is peeled off when the double-sided pressure-sensitive adhesive sheet is used, and is not particularly limited as long as it can be easily peeled off from the double-sided pressure-sensitive adhesive sheet.
Examples of the release sheet include resin films, paper, synthetic paper, and composite sheets obtained by laminating two or more of these, each of which has been surface-treated with a release agent on one or both sides (so-called easy-release treatment).
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).
Examples of the resin film include polyester films, such as polyethylene terephthalate (PET) films, and polyolefin films, such as polyethylene (PE) films and polypropylene (PP) films.
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.

There are no particular limitations on the method for producing the double-sided pressure-sensitive adhesive sheet with a release sheet of the present disclosure.
The double-sided pressure-sensitive adhesive sheet with a release sheet of the present disclosure can be produced by a known method.
The double-sided pressure-sensitive adhesive sheet with a release sheet of the present disclosure can be produced, for example, by the following method.
The adhesive composition of the present disclosure is applied to the easy-release treated surface of the release sheet A to form a coating film X on the release sheet A. Next, the formed coating film X is dried to form an adhesive film X on the release sheet A. Next, the adhesive composition of the present disclosure is applied to the easy-release treated surface of the release sheet B to form a coating film Y on the release sheet B. The formed coating film Y is dried to form an adhesive film Y on the release sheet B. Next, the exposed surface of the adhesive film X formed on the release sheet A and the exposed surface of the adhesive film Y formed on the release sheet B are stacked and then pressed together to produce a laminate. Next, the produced laminate is cured. In this manner, a double-sided adhesive sheet with a release sheet of the present disclosure is obtained.

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 set appropriately depending on, for example, the thickness of the double-sided pressure-sensitive adhesive sheet 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.

Curing is carried out, for example, for 2 to 7 days in an environment with an ambient temperature of 20°C to 50°C and a relative humidity of 45% to 55% (i.e., 45% RH to 55% RH).

[Decorative body with adhesive sheet]
The decorative body with a pressure-sensitive adhesive sheet of the present disclosure includes the above-mentioned double-sided pressure-sensitive adhesive sheet of the present disclosure and a decorative body having a three-dimensional shape (i.e., a three-dimensional decorative body) provided on one side of the double-sided pressure-sensitive adhesive sheet. That is, in the decorative body with a pressure-sensitive adhesive sheet of the present disclosure, the double-sided pressure-sensitive adhesive sheet of the present disclosure and the three-dimensional decorative body are laminated.

The decorative article with a pressure-sensitive adhesive sheet of the present disclosure comprises the double-sided pressure-sensitive adhesive sheet of the present disclosure.
The double-sided pressure-sensitive adhesive sheet of the present disclosure has been described above, and therefore description thereof will be omitted here.

The decorative body with a pressure-sensitive adhesive sheet of the present disclosure includes a three-dimensional decorative body.
In the decorative body with a pressure-sensitive adhesive sheet of the present disclosure, the three-dimensional decorative body is provided on one side of the double-sided pressure-sensitive adhesive sheet.
Examples of three-dimensional decorations include emblems, stickers, labels, etc. having three-dimensional shapes.
Examples of materials for the three-dimensional decorative body include 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, acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins.

The adherend of the decorative body with a pressure-sensitive adhesive sheet of the present disclosure is not particularly limited.
Examples of the adherend include exterior parts of vehicles (for example, automobiles and motorcycles), various signs, various labels, and the like.
Examples of the material of the adherend include resin, metal, and glass.
The adherend may have a curved surface.
In general, when an adherend has a curved shape, when an object having a three-dimensional shape is attached to the adherend via a double-sided adhesive sheet, a force that causes the object to return to the shape before attachment, i.e., a repulsive force, is applied to the double-sided adhesive sheet, and the end of the double-sided adhesive sheet tends to peel off and float up from the adherend. Since the decorative body with adhesive sheet of the present disclosure includes the double-sided adhesive sheet of the present disclosure, the end of the adhesive sheet attached to the adherend having a curved shape is prevented from peeling off and floating up from the adherend over time. For this reason, the decorative body with adhesive sheet of the present disclosure can be preferably applied to an adherend having a curved shape.

The method for producing the decorative article with a pressure-sensitive adhesive sheet of the present disclosure is not particularly limited.
The decorative article with a pressure-sensitive adhesive sheet of the present disclosure can be produced by a known method.
The decorative body with a pressure-sensitive adhesive sheet of the present disclosure can be produced, for example, by bonding a three-dimensional decorative body to one side of the double-sided pressure-sensitive adhesive sheet of the present disclosure by pressure bonding.

The double-sided pressure-sensitive adhesive sheet and the like 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 exceed the gist of the disclosure.

[Production of (meth)acrylic copolymer]
[Manufacture example A-1]
Into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 90.0 parts by mass of n-butyl acrylate [n-BA; an acrylic acid alkyl ester monomer], 10.0 parts by mass of acrylic acid [AA; a monomer having a carboxy group], and 94.3 parts by mass of ethyl acetate [organic solvent] were placed and mixed to obtain a mixture, and then the atmosphere inside the reactor was replaced with nitrogen.
Next, the mixture in the reactor was heated to 82°C while being stirred, and then 0.09 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] and 3.2 parts by mass of ethyl acetate were successively added to the mixture in the reactor, and after completion of the addition, the mixture was maintained for 1.5 hours to complete the polymerization reaction. Next, the solution obtained by the completion of the polymerization reaction was diluted with ethyl acetate and then cooled to obtain a solution of (meth)acrylic copolymer A-1 (solid content concentration: 33.5% by mass).

The "solid content concentration" here means the mass ratio of (meth)acrylic copolymer A-1 in the solution of (meth)acrylic copolymer A-1. The same applies to each of the solutions of (meth)acrylic copolymers A-2 to A-11 produced below.

[Production examples A-2 to A-11]
In Production Examples A-2 to A-11, solutions of (meth)acrylic copolymers A-2 to A-11 were obtained in the same manner as in Production Example A-1, except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 1 and that the polymerization temperature, polymerization time, amount of organic solvent used, amount of polymerization initiator used, etc. were appropriately adjusted. The solids concentrations of the solutions of the obtained (meth)acrylic copolymers A-2 to A-11 are shown below.

-Solid content concentration of each solution of (meth)acrylic copolymers A-2 to A-11-
A-2: 34.0% by mass, A-3: 34.0% by mass, A-4: 32.5% by mass, A-5: 34.5% by mass, A-6: 33.2% by mass, A-7: 35.2% by mass, A-8: 31.5% by mass, A-9: 37.6% by mass, A-10: 19.8% by mass, A-11: 38.7% by mass.

Table 1 shows the monomer compositions (unit: mass%) of the (meth)acrylic copolymers A-1 to A-11, the glass transition temperatures (Tg, unit: ° C.) of the (meth)acrylic copolymers A-1 to A-11, and the weight average molecular weights [Mw, unit: 10,000 (in the table, represented as "×10 ⁴ ")] of the (meth)acrylic copolymers A-1 to A-11.

The glass transition temperatures of the (meth)acrylic copolymers A-1 to A-11 were calculated in the same manner as the above-mentioned method for calculating the glass transition temperature of a specific (meth)acrylic copolymer.
The weight average molecular weights of the (meth)acrylic copolymers A-1 to A-11 were measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic copolymer described above.

Of the (meth)acrylic copolymers A-1 to A-11 obtained above, (meth)acrylic copolymers A-1 to A-6 correspond to the specific (meth)acrylic copolymers in this disclosure.

Details of each monomer listed in Table 1 are as follows.
<(Meth)acrylic acid alkyl ester monomer>
"n-BA": n-butyl acrylate "2EHA": 2-ethylhexyl acrylate "MA": methyl acrylate "LA": lauryl acrylate <monomer having a carboxy group>
"AA": acrylic acid

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

[Preparation of double-sided adhesive sheet with release sheet]
Example 1
1. Preparation of adhesive composition 100 parts by mass (solid content equivalent) of the solution of the (meth)acrylic copolymer A-1 obtained above, 1 part by mass (solid content equivalent) of an isocyanate-based crosslinking agent, CORONATE (registered trademark) L-45E [trade name, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), manufactured by Tosoh Corporation], 0.01 parts by mass (solid content equivalent) of an epoxy-based crosslinking agent, TETRAD (registered trademark)-X [trade name, manufactured by Mitsubishi Gas Chemical Co., Ltd.], and 4 parts by mass (solid content equivalent) of a tackifier, PENSEL (registered trademark) D-125 [trade name, compound having a rosin skeleton, manufactured by Arakawa Chemical Industries, Ltd.] were thoroughly mixed to prepare an adhesive composition.

2. Preparation of double-sided pressure-sensitive adhesive sheet with release sheet The pressure-sensitive adhesive composition prepared above was applied to a release sheet X [product name: SLK-110W, composition:
The adhesive composition was applied to the surface of a release sheet Y (trade name: PET25LT, thickness: 25 μm, manufactured by Lintec Corporation) so that the thickness after drying was 45 μm, forming a coating film. The coating film thus formed was then dried using a hot air circulation dryer under drying conditions of a drying temperature of 100° C. and a drying time of 1 minute, forming an adhesive film on the surface of the release sheet X. The adhesive composition thus prepared was then applied to the surface of a release sheet Y (trade name: PET25LT, thickness: 25 μm, manufactured by Lintec Corporation) so that the thickness after drying was 45 μm, forming a coating film. The coating film thus formed was then dried using a hot air circulation dryer under drying conditions of a drying temperature of 100° C. and a drying time of 1 minute, forming an adhesive film on the surface of the release sheet X. Next, the exposed surface of the adhesive film formed on the surface of release sheet X and the exposed surface of the adhesive film formed on the surface of release sheet Y were overlapped, and then pressed together using a rubber roller in an environment with an atmospheric temperature of 23° C. and 50% RH to produce a laminate. Next, the produced laminate was left to stand in an environment with an atmospheric temperature of 23° C. and 50% RH for 7 days to cure the adhesive film, thereby producing a double-sided adhesive sheet with release sheets provided on both sides (so-called double-sided adhesive sheet with release sheet). The produced double-sided adhesive sheet with release sheet has a laminate structure of release sheet X/double-sided adhesive sheet (film thickness: 90 μm)/release sheet Y.

[Examples 2 to 16]
In Examples 2 to 16, the double-sided PSA sheets with release sheets were prepared in the same manner as in Example 1, except that the formulations of the PSA composition and the film thicknesses of the double-sided PSA sheets were as shown in Table 2.

[Comparative Examples 1 to 15]
In Comparative Examples 1 to 15, the same operations as in Example 1 were carried out except that the formulations of the pressure-sensitive adhesive compositions and the film thicknesses of the double-sided pressure-sensitive adhesive sheets were as shown in Table 3, to prepare double-sided pressure-sensitive adhesive sheets with release sheets for Comparative Examples 1 to 15.

Details of each component described in Table 2 and/or Table 3 are as follows.
[Crosslinking Agent]
<Isocyanate-based crosslinking agent>
"Coronate L-45E" (product name, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content concentration: 45% by mass, manufactured by Tosoh Corporation)
"Duranate D201" (product name, hexamethylene diisocyanate (HMDI), solid content: 100% by mass, manufactured by Asahi Kasei Corporation)
<Epoxy-based crosslinking agent>
"TETRAD-X" (product name, solid content: 75% by mass, manufactured by Mitsubishi Gas Chemical Co., Ltd.)
<Metal chelate crosslinking agent>
"Aluminum Chelate A" (product name, chemical name: aluminum tris(acetylacetonate), solid content: 100% by mass, manufactured by Kawaken Fine Chemical Co., Ltd.)
The above-mentioned "Coronate,""Duranate," and "TETRAD" are all registered trademarks.

[Tackifier]
"PENSEL D-125" (product name, compound having a rosin skeleton, manufactured by Arakawa Chemical Industries, Ltd.)
"YS Polystar TH130" (product name, compound having a terpene skeleton, manufactured by Yasuhara Chemical Co., Ltd.)
"FTR 6100" (product name, compound having a styrene skeleton, manufactured by Mitsui Chemicals, Inc.)
The above "Pensel" and "YS Polystar" are registered trademarks.

In Table 3, "-" means that there is no corresponding item in that column.
In Tables 2 and 3, for the sake of convenience, the "isocyanate-based crosslinking agent" and the "epoxy-based crosslinking agent or metal chelate-based crosslinking agent" are classified into "(X)" and "(Y)", respectively, and the "ratio of the total content mass of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent to the content mass of the isocyanate-based crosslinking agent" is expressed as "(Y)/(X)."

[Preparation of decorative body with adhesive sheet]
A urethane resin composition was prepared by adding 22 parts by mass of a curing agent (trade name: Perurethane (registered trademark) MU-662A, manufactured by Pernox Co., Ltd.) to 100 parts by mass of a urethane resin (trade name: Perurethane (registered trademark) MU-210B, manufactured by Pernox Co., Ltd.) and mixing them. Next, the prepared urethane resin composition was used to form a film by pouring it into a polyethylene (PE) mold (depth: 2 mm), and a urethane sheet (so-called three-dimensional decorative body) with a thickness of 2 mm was prepared. Next, in an environment of an atmospheric temperature of 23°C and 50% RH, the release sheet Y of the double-sided adhesive sheet with release sheet prepared above was peeled off, and the surface of the double-sided adhesive sheet exposed by the peeling was overlapped with the surface of the urethane sheet prepared above, and then pressed with a rubber roller to prepare a decorative body with an adhesive sheet. The prepared decorative body with an adhesive sheet has a configuration of a urethane sheet (so-called three-dimensional decorative body)/double-sided adhesive sheet/release sheet X.

[Measurement and Evaluation]
1. Loss factor tan δ at -30°C
The double-sided pressure-sensitive adhesive sheet with release sheet prepared above was cut to a size of 7.5 mm × 15.0 mm (long side). Next, release sheet X and release sheet Y of the cut double-sided pressure-sensitive adhesive sheet with release sheet were peeled off, and the obtained double-sided pressure-sensitive adhesive sheet was used as a test piece.
The loss factor tan δ of the test piece was measured under the following conditions using a dynamic viscoelasticity measuring device (product name: Rheogel-E4000, manufactured by UBM Co., Ltd.) The measured values of the loss factor tan δ at −30° C. are shown in Table 4.
The loss factor tan δ at −30° C. is preferably 0.10 or more, and more preferably 0.12 or more.

～Conditions～
Measurement temperature range: -70℃ to 0℃
Temperature increase condition: 2°C/min Step temperature: 1°C
Measurement frequency: 10Hz

2. Impact resistance in a low-temperature environment The decorative body with adhesive sheet prepared above was cut to prepare three pieces of the decorative body with adhesive sheet, each piece having a size of 10 mm x 25 mm (long side). Using the prepared decorative body pieces with adhesive sheet, three samples for evaluating impact resistance were prepared as follows.
In an environment with an atmospheric temperature of 23° C. and 50% RH, the release sheet X of the decorative body piece with the adhesive sheet was peeled off, and the surface of the double-sided adhesive sheet exposed by the peeling was attached to a melamine-coated board (product name: melamine white-coated board, manufactured by Paltec Co., Ltd.), and then the board was left to stand for 48 hours in an environment with an atmospheric temperature of 23° C. and 50% RH to prepare a sample for evaluating impact resistance. The prepared sample for evaluating impact resistance has a configuration of melamine-coated board/decorative body piece with adhesive sheet (layer configuration: double-sided adhesive sheet/decorative body).
The three samples for impact resistance evaluation prepared were subjected to an impact resistance evaluation test in a low-temperature chamber (product name: constant temperature and humidity chamber, built-in chamber E series, manufactured by Espec Corp.) with the ambient temperature set to -30°C. Specifically, in the low-temperature chamber, the samples for impact resistance evaluation were subjected to an impact test under the following conditions using a DuPont impact tester (product name: DuPont impact tester, manufactured by TP Giken Co., Ltd.) in accordance with JIS K 5600-5-3:1999.
After the impact test, the decorative piece with the adhesive sheet was visually inspected for peeling from the melamine-coated plate, and was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 4.
In the following evaluation criteria, "A" and "B" are at levels that are not problematic in practical use, with "A" being the most preferable.

～Conditions～
Center of impact: 12.7cm
Load: 3N
Height: 20cm

-Evaluation criteria-
A: The number of impact resistance evaluation samples in which peeling was confirmed was 0.
B: Peeling was confirmed in one of the impact resistance evaluation samples.
C: The number of impact resistance evaluation samples in which peeling was confirmed was 2 or 3.

3. Adhesion (1) Time The decorative body with adhesive sheet prepared above was cut into a size of 20 mm x 65 mm (long side) to obtain a decorative body piece with adhesive sheet. Next, in an environment of an atmospheric temperature of 23 ° C. and 50% RH, the release sheet X of the decorative body piece with adhesive sheet was peeled off, and the surface of the double-sided adhesive sheet exposed by peeling was attached to an acrylic dome [product name: acrylic dome (transparent), diameter: 350 mm, free blow molding, no flange, Sugawara Kogei Co., Ltd.] to prepare a sample for adhesion evaluation. The prepared sample for adhesion evaluation has a structure of acrylic dome / decorative body piece with adhesive sheet (layer structure: double-sided adhesive sheet / decorative body).
The prepared adhesion evaluation sample was left to stand for 240 hours in an environment with an atmospheric temperature of 23°C and 50% RH. After standing, the adhesion evaluation sample was visually observed to confirm the presence and extent of the phenomenon in which the edge of the decorative piece with the adhesive sheet peeled off and rose up from the acrylic dome (also called "edge lift"). Evaluation was then performed according to the following evaluation criteria. The evaluation results are shown in Table 4.
In the following evaluation criteria, "A" and "B" are at levels that are not problematic in practical use, with "A" being the most preferable.

-Evaluation criteria-
A: No edge lift was observed.
B: A slight amount of edge lift was observed, but was at a level that did not cause any practical problems.
C: Edge lift was observed, and was at a level that was problematic for practical use.

In addition, a 100 μm thick PET film was inserted between the acrylic dome and the double-sided PSA sheet of the adhesion evaluation sample after standing, and the distance (unit: mm) that the PET film had inserted was measured. The measured values are shown in Table 4.
The smaller the measured value, the better the double-sided PSA sheet's adhesion to the adherend over time.

(2) High temperature and high humidity The decorative body with adhesive sheet prepared above was cut into a size of 20 mm x 65 mm (long side) to obtain a decorative body piece with adhesive sheet. Next, in an environment of an atmospheric temperature of 23 ° C. and 50% RH, the release sheet X of the decorative body piece with adhesive sheet was peeled off, and the surface of the double-sided adhesive sheet exposed by the peeling was attached to an acrylic dome [product name: acrylic dome (transparent), diameter: 350 mm, free blow molding, no flange, Sugawara Kogei Co., Ltd.] to prepare a sample for adhesion evaluation. The prepared sample for adhesion evaluation has a configuration of acrylic dome / decorative body piece with adhesive sheet (layer structure: double-sided adhesive sheet / decorative body).
The prepared adhesion evaluation sample was left to stand for 48 hours in an environment with an atmospheric temperature of 23°C and 50% RH, and then left to stand for 120 hours in an environment with an atmospheric temperature of 50°C and 95% RH. The adhesion evaluation sample after standing was visually observed to confirm the presence and extent of the phenomenon in which the edge of the decorative piece with the adhesive sheet peeled off and rose up from the acrylic dome (also called "edge lift"). Evaluation was then performed according to the same evaluation criteria as those in "(1) Over time". The evaluation results are shown in Table 4.
In the above evaluation criteria, "A" and "B" are at levels that are acceptable for practical use, with "A" being the most preferable.

In addition, a 100 μm thick PET film was inserted between the acrylic dome and the double-sided PSA sheet of the adhesion evaluation sample after standing, and the distance (unit: mm) that the PET film had inserted was measured. The measured values are shown in Table 4.
The smaller the measured value, the better the double-sided PSA sheet's adhesion to the adherend even when placed in a high-temperature, high-humidity environment.

As shown in Table 4, it was confirmed that the double-sided pressure-sensitive adhesive sheets of Examples 1 to 16 can prevent the ends from peeling off and floating up from the adherend even when placed in a high-temperature, high-humidity environment after a three-dimensional object is attached to a curved adherend, and are also unlikely to peel off from the adherend even when subjected to an impact in a low-temperature environment after a three-dimensional object is attached to the adherend. It was also confirmed that the double-sided pressure-sensitive adhesive sheets of Examples 1 to 16 can prevent the ends from peeling off and floating up from the adherend over time after a three-dimensional object is attached to a curved adherend.

Claims (4)

A double-sided pressure-sensitive adhesive sheet formed solely from a pressure-sensitive adhesive composition comprising a (meth)acrylic copolymer, a crosslinking agent, and a tackifier,
The thickness of the double-sided pressure-sensitive adhesive sheet is 80 μm or more,
The (meth)acrylic copolymer contains 5% by mass to 10% by mass of structural units derived from a monomer having a carboxy group, based on the total structural units, and has a weight average molecular weight of 400,000 to 1,000,000;
the crosslinking agent includes an isocyanate-based crosslinking agent and at least one crosslinking agent selected from the group consisting of an epoxy-based crosslinking agent and a metal chelate-based crosslinking agent;
a ratio of a total mass content of the epoxy-based crosslinking agent and the metal chelate-based crosslinking agent to a mass content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition is 0.01 to 0.1;
The double-sided pressure-sensitive adhesive sheet has a tackifier content of 1 to 5 parts by mass relative to 100 parts by mass of the (meth)acrylic copolymer. The double-sided pressure-sensitive adhesive sheet according to claim 1, which has a loss factor tan δ of 0.10 or more at -30°C. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2,
release sheets provided on both sides of the double-sided pressure-sensitive adhesive sheet;
A double-sided adhesive sheet with a release sheet. The double-sided pressure-sensitive adhesive sheet according to claim 1 or 2,
A decorative body provided on one surface of the double-sided pressure-sensitive adhesive sheet and having a three-dimensional shape;
A decorative body with an adhesive sheet.