JP7684890B2 - Adhesive composition and adhesive sheet - Google Patents

Description

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

As interest in environmental issues such as global warming grows, there is strong social demand, particularly for chemical manufacturers, to use materials derived from plants and other living organisms instead of conventional petroleum-based materials. In the field of adhesives, too, the development of products that use reusable organic resources derived from living organisms (also known as "biomass") as raw materials is progressing, and there have been reports of adhesive tapes that contain a high proportion of biomass raw materials, or so-called high biomass content.

For example, Patent Document 1 discloses an adhesive tape that contains 50 to 150 parts by mass of tackifier resin per 100 parts by mass of adhesive resin solids, has an adhesive layer with a temperature at which the loss tangent (tan δ) at a frequency of 1 Hz peaks is between -10°C and 50°C, and has a biomass degree of 45% or more. The adhesive tape described in Patent Document 1 uses a large amount of tackifier resin to ensure the performance of the adhesive tape while increasing the biomass degree.

JP 2020-041023 A

In recent years, from the viewpoint of global environmental conservation, there has been a demand for the development of water-based pressure-sensitive adhesives that use water instead of solvent-based pressure-sensitive adhesives that use organic solvents.
However, when an aqueous dispersion containing tackifier resin particles is used in an aqueous adhesive, the water resistance of the formed adhesive layer may decrease. Aqueous adhesives are used for removable labels, but if the water resistance of the adhesive layer decreases, for example, when the label is attached to an adherend for a long time under a humid environment, the adhesive layer swells, and when the label is peeled off, a part of the adhesive layer remains on the adherend, which is called a "glue residue" phenomenon, and this causes stickiness. In particular, in a high humidity environment where condensation may occur, moisture generated by condensation penetrates the interface between the adhesive layer and the adherend, which makes the adhesive layer swell easily. For this reason, it is required that the aqueous adhesive be capable of forming an adhesive layer with excellent water resistance.
In addition, since aqueous pressure-sensitive adhesives are sometimes used in, for example, removable labels, the aqueous pressure-sensitive adhesive is required to be capable of forming an adhesive layer that can be easily peeled off from an adherend and that is unlikely to leave adhesive residue on the surface of the adherend, i.e., an adhesive layer that has excellent removability. In addition, in removable labels, a label that has been peeled off may be reattached, so the aqueous pressure-sensitive adhesive is required to be capable of forming an adhesive layer that is unlikely to peel off from an adherend when reattached, i.e., an adhesive layer that has excellent reattachability.

An object of one embodiment of the present disclosure is to provide a pressure-sensitive adhesive composition that is environmentally friendly and capable of forming a pressure-sensitive adhesive layer that is excellent in water resistance, removability and repositionability.
The problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive sheet that is environmentally friendly and includes a pressure-sensitive adhesive layer that has excellent water resistance, removability, and repositionability.

Specific means for solving the problems include the following aspects.
<1> A pressure-sensitive adhesive composition comprising: (meth)acrylic resin particles (A) which contain structural units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms, and which have a glass transition temperature of 0° C. or lower, and an average particle size of 1 μm to 80 μm; (meth)acrylic resin particles (B) which have an average particle size of 50 nm to 900 nm; tackifier resin particles (C) which have a biomass degree of 45% or more; and water, wherein the content of the tackifier resin particles (C) is 20 parts by mass to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A).
<2> The pressure-sensitive adhesive composition according to <1>, wherein a content of structural units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms in the (meth)acrylic resin particles (A) is 10.0% by mass to 99.8% by mass based on all structural units of the (meth)acrylic resin particles (A).
<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms has a biomass degree of 50% or more.
<4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the content of the (meth)acrylic resin particles (B) is 5 parts by mass to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A).
<5> The pressure-sensitive adhesive composition according to any one of <1> to <4>, wherein the (meth)acrylic resin particles (B) have a glass transition temperature of 0° C. or lower.
<6> A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <5>.

According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that is environmentally friendly and has excellent water resistance, removability and repositionability.
According to another embodiment of the present disclosure, there is provided a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer that is environmentally friendly and has excellent water resistance, removability and repositionability.

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

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

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

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.

In this disclosure, "adhesive" and "adhesive composition" are synonymous.

The pressure-sensitive adhesive composition according to the present disclosure comprises (meth)acrylic resin particles (A) which contain constituent units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms, and which have a glass transition temperature of 0° C. or lower and an average particle size of 1 μm to 80 μm, (meth)acrylic resin particles (B) which have an average particle size of 50 nm to 900 nm, tackifier resin particles (C) which have a biomass degree of 45% or more, and water, wherein the content of the tackifier resin particles (C) is 20 parts by mass to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A).
The pressure-sensitive adhesive composition according to the present disclosure is environmentally friendly and can form a pressure-sensitive adhesive layer that is excellent in water resistance, removability and repositionability.
The reason why the pressure-sensitive adhesive composition according to the present disclosure can exhibit such an effect is unclear, but the present inventors speculate as follows, however, the following speculation is not intended to limit the pressure-sensitive adhesive composition according to the present disclosure, but is merely an example.

The PSA composition according to the present disclosure is an aqueous PSA composition containing tackifier resin particles (C) having a biomass degree of 45% or more and water, and is therefore environmentally friendly.
The pressure-sensitive adhesive composition according to the present disclosure includes (meth)acrylic resin particles (A) having a glass transition temperature of 0° C. or less and an average particle size of 1 μm to 80 μm, and (meth)acrylic resin particles (B) having an average particle size of 50 nm to 900 nm. The surface of the pressure-sensitive adhesive layer formed by such a pressure-sensitive adhesive composition is considered to have an uneven shape formed by the (meth)acrylic resin particles (A) having a large particle size and the (meth)acrylic resin particles (B) having a small particle size. Therefore, when the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition according to the present disclosure is applied to an adherend, the adhesion between the pressure-sensitive adhesive layer and the adherend is so-called point adhesion, in which the convex parts formed by the (meth)acrylic resin particles (A) having a large particle size are adhered to the adherend, and the pressure-sensitive adhesive layer is considered to exhibit excellent removability. In addition, the adhesive composition according to the present disclosure contains tackifier resin particles (C) at a specific ratio or more relative to the (meth)acrylic resin particles (A), and the tackiness of the formed adhesive layer decreases over time, and the adhesive strength also decreases, which is thought to cause the adhesive layer to exhibit excellent removability. On the other hand, the content of the tackifier resin particles (C) contained in the adhesive composition according to the present disclosure is a specific ratio or less relative to the (meth)acrylic resin particles (A), so that the tackiness of the formed adhesive layer does not decrease excessively. In addition, since the glass transition temperature of the (meth)acrylic resin particles (A) is 0° C. or less, the formed adhesive layer has a small adhesive surface with the adherend, but ensures moderate adhesive strength with the adherend. Therefore, the formed adhesive layer is thought to be excellent in both removability and reattachability.
The (meth)acrylic resin particles (A) that adhere to the adherend when the adhesive layer and the adherend are laminated together contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer having a relatively large number of carbon atoms, and therefore are relatively highly hydrophobic, and moisture is prevented from entering between the adhesive layer and the adherend. Therefore, it is considered that the adhesive layer exhibits excellent water resistance. In addition, the (meth)acrylic resin particles (A) contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer having a relatively large number of carbon atoms, and therefore the polarity of the particle surface is reduced, and the adhesive layer is prevented from spreading wet on the adherend. Therefore, it is considered that the adhesive layer exhibits excellent removability.
From the above, it is presumed that the pressure-sensitive adhesive composition according to the present disclosure is environmentally friendly and capable of forming a pressure-sensitive adhesive layer that is excellent in water resistance, removability and repositionability.

The adhesive described in Patent Document 1 (JP Patent Publication No. 2020-041023) is a solvent-based adhesive, so it is believed that there will be no water resistance problems caused by tackifier resin particles.

Hereinafter, "(meth)acrylic resin particles (A) containing structural units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms, having a glass transition temperature of 0° C. or lower, and having an average particle size of 1 μm to 80 μm" contained in the pressure-sensitive adhesive composition according to the present disclosure will also be referred to as "specific (meth)acrylic resin particles (A)", "(meth)acrylic resin particles (B) having an average particle size of 50 nm to 900 nm" will also be referred to as "specific (meth)acrylic resin particles (B)", and "tackifier resin particles (C) having a biomass degree of 45% or more" will also be referred to as "specific tackifier resin particles (C)".
In addition, hereinafter, the "(meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms" is also referred to as the "specific (meth)acrylic acid alkyl ester monomer."

[Specific (meth)acrylic resin particles (A)]
The pressure-sensitive adhesive composition according to the present disclosure contains (meth)acrylic resin particles (A) [i.e., specific (meth)acrylic resin particles (A)] which contain structural units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms, have a glass transition temperature of 0° C. or lower, and have an average particle size of 1 μm to 80 μm.
The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of the specific (meth)acrylic resin particles (A), or may contain two or more types.

<Structural Unit Derived from Specific (Meth)acrylic Acid Alkyl Ester Monomer>
The specific (meth)acrylic resin particles (A) contain structural units derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms (that is, a specific (meth)acrylic acid alkyl ester monomer).

In this disclosure, "structural unit derived from (meth)acrylic acid alkyl ester monomer having an alkyl group with 10 to 22 carbon atoms [i.e., specific (meth)acrylic acid alkyl ester monomer]" means a structural unit formed by addition polymerization of (meth)acrylic acid alkyl ester monomer having an alkyl group with 10 to 22 carbon atoms [i.e., specific (meth)acrylic acid alkyl ester monomer]. In this disclosure, "specific (meth)acrylic acid alkyl ester monomer" does not include monomers corresponding to monomers having a carboxy group and monomers corresponding to polyfunctional (meth)acrylic acid ester monomers, which will be described later.

The specific (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer.
The specific (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
The alkyl group contained in the specific (meth)acrylic acid alkyl ester monomer may be any of linear, branched, and cyclic, but is preferably linear or branched.

The alkyl group of the specific (meth)acrylic acid alkyl ester monomer has 10 to 22 carbon atoms.
When the carbon number of the alkyl group of the specific (meth)acrylic acid alkyl ester monomer is 10 or more, the pressure-sensitive adhesive layer formed tends to have excellent removability. Also, when the carbon number of the alkyl group of the specific (meth)acrylic acid alkyl ester monomer is 10 or more, the pressure-sensitive adhesive layer formed tends to have excellent water resistance. From these viewpoints, the carbon number of the alkyl group of the specific (meth)acrylic acid alkyl ester monomer is 10 or more, and preferably 12 or more.
From the viewpoint of suitability for producing the specific (meth)acrylic resin particles (A), the number of carbon atoms in the alkyl group of the specific (meth)acrylic acid alkyl ester monomer is 22 or less. The number of carbon atoms in the alkyl group of the specific (meth)acrylic acid alkyl ester monomer may be 20 or less, or may be 18 or less.

Specific examples of the specific (meth)acrylic acid alkyl ester monomer include isobornyl (meth)acrylate in which the alkyl group has 10 carbon atoms, lauryl (meth)acrylate in which the alkyl group has 12 carbon atoms, myristyl (meth)acrylate in which the alkyl group has 14 carbon atoms, cetyl (meth)acrylate in which the alkyl group has 16 carbon atoms, stearyl (meth)acrylate in which the alkyl group has 18 carbon atoms, and eicosyl (meth)acrylate in which the alkyl group has 20 carbon atoms.
The specific (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of lauryl (meth)acrylate and stearyl (meth)acrylate, and more preferably at least one selected from lauryl methacrylate and stearyl methacrylate.

The biomass degree of the specific (meth)acrylic acid alkyl ester monomer is not particularly limited, but for example, from the viewpoint of forming an environmentally friendly pressure-sensitive adhesive layer, it is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 65% or more.
The upper limit of the biomass degree of the specific (meth)acrylic acid alkyl ester monomer may be, for example, 100%.

The biomass content of a specific (meth)acrylic acid alkyl ester monomer is a value measured by a method conforming to ASTM D6866-20, and means the mass ratio of carbon derived from biomass to the total carbon contained in the specific (meth)acrylic acid alkyl ester monomer.

Specific examples of specific (meth)acrylic acid alkyl ester monomers with a biomass degree of 50% or more include isobornyl acrylate (biomass degree: 65.4%), isobornyl methacrylate (biomass degree: 61.3%), lauryl acrylate (biomass degree: 76.0%), lauryl methacrylate (biomass degree: 71.4%), stearyl acrylate (biomass degree: 81.7%), stearyl methacrylate (biomass degree: 78.3%), myristyl acrylate (biomass degree: 78.3%), myristyl methacrylate (biomass degree: 74.1%), cetyl acrylate (biomass degree: 80.1%), and cetyl methacrylate (biomass degree: 76.4%).

The specific (meth)acrylic resin particles (A) may contain only one type of structural unit derived from the specific (meth)acrylic acid alkyl ester monomer, or may contain two or more types.

The content of the structural units derived from the specific (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A) is not particularly limited, but for example, it is preferably 10.0 mass% to 99.8 mass%, more preferably 15.0 mass% to 99.8 mass%, even more preferably 20.0 mass% to 99.8 mass%, and particularly preferably 25.0 mass% to 99.8 mass%, relative to all structural units of the specific (meth)acrylic resin particles (A).
When the content of the structural units derived from the specific (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A) is 10.0 mass% or more relative to the total structural units of the specific (meth)acrylic resin particles (A), the formed pressure-sensitive adhesive layer tends to have better water resistance.
When the content of the structural units derived from the specific (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A) is 99.8 mass% or less relative to the total structural units of the specific (meth)acrylic resin particles (A), the specific (meth)acrylic resin particles (A) tend to have better storage stability.

<Constituent units derived from other monomers>
The specific (meth)acrylic resin particles (A) may contain a constituent unit derived from a monomer (so-called other monomer) other than the specific (meth)acrylic acid alkyl ester monomer.

Examples of the structural units derived from other monomers include structural units derived from (meth)acrylic acid alkyl ester monomers other than the specific (meth)acrylic acid alkyl ester monomer (so-called other (meth)acrylic acid alkyl ester monomers).
In the present disclosure, the term "structural units derived from other (meth)acrylic acid alkyl ester monomers" refers to structural units formed by addition polymerization of other (meth)acrylic acid alkyl ester monomers. The term "(meth)acrylic acid alkyl ester monomer" in the present disclosure does not include monomers corresponding to monomers having a carboxy group and monomers corresponding to polyfunctional (meth)acrylic acid ester monomers, which will be described later.

The other (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer.
The other (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
The alkyl group contained in the other (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The number of carbon atoms in the alkyl group of the other (meth)acrylic acid alkyl ester monomer is preferably, for example, 1 to 9.

Specific examples of other (meth)acrylic acid alkyl ester monomers 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, and cyclohexyl (meth)acrylate.
As the other (meth)acrylic acid alkyl ester monomer, at least one selected from methyl methacrylate and 2-ethylhexyl acrylate is preferable.

When the specific (meth)acrylic resin particles (A) contain structural units derived from other (meth)acrylic acid alkyl ester monomers, they may contain only one type of structural unit derived from the other (meth)acrylic acid alkyl ester monomers, or may contain two or more types of structural units derived from the other (meth)acrylic acid alkyl ester monomers.

When the specific (meth)acrylic resin particles (A) contain structural units derived from other (meth)acrylic acid alkyl ester monomers, the content of the structural units derived from other (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic resin particles (A) is not particularly limited, and may be, for example, 10.0% by mass to 89.9% by mass, 10.0% by mass to 79.9% by mass, or 20.0% by mass to 74.8% by mass relative to the total structural units of the specific (meth)acrylic resin particles (A).

Examples of the structural units derived from other monomers include structural units derived from monomers having a carboxy group.
When the specific (meth)acrylic resin particles (A) contain a structural unit derived from a monomer having a carboxy group, the dispersion stability of the specific (meth)acrylic resin particles (A) tends to be improved.

In this disclosure, "structural unit derived from a monomer having a carboxy group" means 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 anhydride, 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.
As the monomer having a carboxy group, a (meth)acrylic monomer having a carboxy group is preferable, and acrylic acid is more preferable.

When the specific (meth)acrylic resin particles (A) contain a structural unit derived from a monomer having a carboxy group, the structural unit may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types of structural units derived from a monomer having a carboxy group.

When the specific (meth)acrylic resin particles (A) contain structural units derived from monomers having a carboxy group, the content of the structural units derived from monomers having a carboxy group in the specific (meth)acrylic resin particles (A) is not particularly limited, but is preferably 0.05% by mass to 5.0% by mass, more preferably 0.1% by mass to 3.0% by mass, and even more preferably 0.2% by mass to 1.0% by mass, relative to the total structural units of the specific (meth)acrylic resin particles (A).

Examples of the structural units derived from other monomers include structural units derived from polyfunctional (meth)acrylic acid ester monomers.
In the present disclosure, the term "polyfunctional (meth)acrylic acid ester monomer" refers to a (meth)acrylate compound having two or more (meth)acryloyl groups in one molecule, and the term "structural unit derived from a polyfunctional (meth)acrylic acid ester monomer" refers to a structural unit formed by addition polymerization of a polyfunctional (meth)acrylic acid ester monomer.

The type of the polyfunctional (meth)acrylic acid ester monomer is not particularly limited.
The polyfunctional (meth)acrylic acid ester monomer may be a difunctional (meth)acrylic acid ester monomer, a trifunctional (meth)acrylic acid ester monomer, or a tetrafunctional or higher functional (meth)acrylic acid ester monomer.
As the polyfunctional (meth)acrylic acid ester monomer, for example, from the viewpoint of the coatability of the pressure-sensitive adhesive composition, it is preferable that it is at least one type selected from the group consisting of a bifunctional (meth)acrylic acid ester monomer and a trifunctional (meth)acrylic acid ester monomer, and it is more preferable that it is at least one type selected from a bifunctional (meth)acrylic acid ester monomer.

Specific examples of polyfunctional (meth)acrylic acid ester monomers include bifunctional (meth)acrylate compounds such as 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol diacrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclodecane di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylethylpropanediol (meth)acrylate, 3-methyl-1,5-pentanediol diacrylate, dimethylol-tricyclodecane diacrylate, EO adduct diacrylate of bisphenol A, PO adduct diacrylate of bisphenol A, and neopentyl glycol/hydroxypivalic acid ester diacrylate. trifunctional (meth)acrylate compounds such as trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and glycerin propoxy triacrylate; tetrafunctional (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate; pentafunctional (meth)acrylate compounds such as sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate; and hexafunctional (meth)acrylate compounds such as dipentaerythritol hexa(meth)acrylate and sorbitol hexa(meth)acrylate.
As the polyfunctional (meth)acrylic acid ester monomer, ethylene glycol di(meth)acrylate is preferred, and ethylene glycol dimethacrylate is more preferred.

When the specific (meth)acrylic resin particles (A) contain a structural unit derived from a polyfunctional (meth)acrylic acid ester monomer, the structural unit may contain only one type or two or more types of the structural unit derived from the polyfunctional (meth)acrylic acid ester monomer.

When the specific (meth)acrylic resin particles (A) contain structural units derived from a polyfunctional (meth)acrylic acid ester monomer, the content of the structural units derived from the polyfunctional (meth)acrylic acid ester monomer in the specific (meth)acrylic resin particles (A) is not particularly limited, but is preferably 0.1% by mass to 5.0% by mass, more preferably 0.5% by mass to 4.0% by mass, and even more preferably 1.0% by mass to 3.0% by mass, relative to the total structural units of the specific (meth)acrylic resin particles (A).

In addition to the structural units already mentioned, examples of structural units derived from other monomers include structural units derived from monomers having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene and vinyltoluene; structural units derived from vinyl cyanide, such as acrylonitrile and methacrylonitrile; structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate and vinyl versatate; and the like.

--Glass transition temperature of specific (meth)acrylic resin particles (A)--
The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic resin particles (A) is 0°C or lower. When the glass transition temperature of the specific (meth)acrylic resin particles (A) is 0°C or lower, the pressure-sensitive adhesive layer formed tends to have excellent repositionability. From this viewpoint, the glass transition temperature of the specific (meth)acrylic resin particles (A) is 0°C or lower, preferably -20°C or lower, more preferably -30°C or lower, and even more preferably -40°C or lower.
The lower limit of the glass transition temperature of the specific (meth)acrylic resin particles (A) is not particularly limited, but is preferably, for example, −80° C. or higher.

The "glass transition temperature of the specific (meth)acrylic resin particles (A)" is a value calculated from the following formula 1, which is calculated by converting the absolute temperature (unit: K) into Celsius temperature (unit: °C).
However, in the case where the specific (meth)acrylic resin particles (A) contain a constituent unit derived from a monomer that does not show a clear glass transition temperature when made into a homopolymer, a value measured by a differential scanning calorimetry (DSC) according to a method described below shall be adopted as the "glass transition temperature of the specific (meth)acrylic resin particles (A)".
Specific examples of monomers that do not exhibit a clear glass transition temperature when made into a homopolymer include ethylene glycol dimethacrylate, triethylene glycol methacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

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 resin particle (A) is made into a homopolymer. m1, m2, ..., m(k-1), and mk respectively represent the molar fractions of each monomer constituting the specific (meth)acrylic resin particle (A), and m1+m2+...+m(k-1)+mk=1.
Note that absolute temperature can be converted to Celsius temperature by subtracting 273 from the absolute temperature, and Celsius temperature can be converted to absolute temperature by adding 273 to the Celsius temperature.

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

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

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

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

In the case where the specific (meth)acrylic resin particles (A) contain a constituent unit derived from a monomer that does not show a clear glass transition temperature when made into a homopolymer, the glass transition temperature of the specific (meth)acrylic resin particles (A) is a value measured by the following method using a differential scanning calorimeter (DSC).
The specific (meth)acrylic resin particles (A) are applied onto the release paper using a 4 mil (101.6 μm) applicator. The applied specific (meth)acrylic resin particles (A) are then dried (drying temperature: 105° C., drying time: 10 minutes) to obtain a dried product. The obtained dried product is used as a measurement sample. Next, 10 mg of the dried product, which is the measurement sample, is packed into an aluminum sample pan (trade name: Tzero Pan, manufactured by TA Instrument Co., Ltd.), and sealed with an aluminum lid (trade name: Tzero Hermetic Lid, manufactured by TA Instrument Co., Ltd.), and then the glass transition temperature is measured under the following conditions using a differential scanning calorimeter. In this measurement, the glass transition temperature is determined as the temperature at the intersection of a straight line extending the low-temperature side baseline to the high-temperature side in the obtained DSC curve and a tangent line drawn at a point where the gradient of the curve of the stepwise change part of the glass transition is maximum. The measurement is carried out twice for the same sample, and the value obtained in the second measurement is adopted as the glass transition temperature of the specific (meth)acrylic resin particles (A).
As the differential scanning calorimeter, for example, a differential scanning calorimeter (product name: Discovery DSC 2500) manufactured by TA Instruments Japan Co., Ltd. can be suitably used. However, the differential scanning calorimeter is not limited to this.

～Conditions～
Atmospheric conditions: under air Measurement temperature range: -90℃ to 100℃
Heating rate: 10°C/min. Standard material: empty sample pan

The glass transition temperature of the specific (meth)acrylic resin particles (A) can be adjusted as appropriate, for example, by using two or more monomers that have different glass transition temperatures when made into homopolymers.

-Shape of specific (meth)acrylic resin particles (A)-
The shape of the specific (meth)acrylic resin particles (A) is not particularly limited, but is preferably spherical. In the present disclosure, "spherical" includes not only a perfect sphere but also an approximately spherical shape.

--Average particle size of specific (meth)acrylic resin particles (A)--
The specific (meth)acrylic resin particles (A) have an average particle size of 1 μm to 80 μm.
When the average particle size of the specific (meth)acrylic resin particles (A) is 1 μm or more, the pressure-sensitive adhesive layer formed tends to have excellent removability and water resistance. From this viewpoint, the average particle size of the specific (meth)acrylic resin particles (A) is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.
The average particle size of the specific (meth)acrylic resin particles (A) is 80 μm or less from the viewpoint of the dispersion stability of the specific (meth)acrylic resin particles (A).
The average particle size of the specific (meth)acrylic resin particles (A) may be, for example, 70 μm or less, 60 μm or less, or 50 μm or less.

The average particle size of the specific (meth)acrylic resin particles (A) can be adjusted, for example, by changing the stirring speed when producing the specific (meth)acrylic resin particles (A), the amount of suspension stabilizer used, etc. The particle size of the specific (meth)acrylic resin particles (A) becomes smaller as the stirring speed increases, and becomes larger as the stirring speed decreases, for example.

The average particle size of the specific (meth)acrylic resin particles (A) means the volume average particle size.
The average particle diameter of the specific (meth)acrylic resin particles (A) is a value measured by the following method using a laser diffraction particle size distribution measurement device. In the present disclosure, the "particle size distribution" is also referred to as the "particle size distribution".
The specific (meth)acrylic resin particles (A) are diluted with distilled water, thoroughly stirred and mixed, and then collected in a 10 x 75 x 85 mm glass cell using a Pasteur pipette, which is then set in a laser diffraction particle size distribution measuring device. The concentration of the diluted solution of the specific (meth)acrylic resin particles (A) is adjusted so that the laser light transmittance is 85%, and the particle size distribution is measured under the condition of a measurement temperature of 25°C. The measurement results are processed by computer to obtain the volume average particle size of the specific (meth)acrylic resin particles (A). Specifically, the particle size at an integrated value of 50% (volume basis) in the obtained particle size distribution is taken as the volume average particle size.
As the laser diffraction type particle size distribution measuring device, for example, "Laser Scattering Particle Size Distribution Analyzer LA-960" manufactured by Horiba, Ltd. can be suitably used. However, the laser diffraction type particle size distribution measuring device is not limited to this.

<<Content of specific (meth)acrylic resin particles (A)>>
The content of the specific (meth)acrylic resin particles (A) in the pressure-sensitive adhesive composition according to the present disclosure is not particularly limited, but is, for example, preferably 40% by mass to 83.3% by mass, more preferably 50% by mass to 83.3% by mass, and even more preferably 60% by mass to 82% by mass, relative to the total solid content in the pressure-sensitive adhesive composition.

In this disclosure, "total solid content in the adhesive composition" means the mass of the residue remaining after removing the solvent from the adhesive composition. In this disclosure, "solvent" means water and organic solvent.

[Method for producing specific (meth)acrylic resin particles (A)]
The method for producing the specific (meth)acrylic resin particles (A) is not particularly limited as long as the above-mentioned specific (meth)acrylic resin particles (A) can be produced.
As a method for producing the specific (meth)acrylic resin particles (A), a suspension polymerization method is preferred from the viewpoint of ease of producing the specific (meth)acrylic resin particles (A).

As the suspension polymerization method for producing the specific (meth)acrylic resin particles (A), for example, the following method is suitable.
In a reactor equipped with a thermometer, a stirrer, a raw material introduction pipe, a reflux condenser, a nitrogen introduction pipe, etc., water, a surfactant, and a suspension stabilizer used as required are charged and thoroughly mixed and stirred to dissolve. A mixed liquid containing a monomer component and a polymerization initiator is added to this, and after stirring at a predetermined stirring speed for a certain period of time, water is added. After replacing the inside of the reactor with nitrogen, the temperature is raised to start the polymerization reaction, and the polymerization reaction is carried out for a predetermined period of time.

The surfactant is not particularly limited, but anionic surfactants and/or nonionic surfactants are preferred, and anionic surfactants are more preferred.

Examples of the anionic surfactant include polyoxyalkylene styrenated diphenyl ether sulfates, such as polyoxyethylene styrenated diphenyl ether ammonium sulfate, polyoxyalkylene alkyl phenyl ether sulfates, such as polyoxyethylene nonyl phenyl ether sodium sulfate, polyoxyalkylene alkyl ether sulfates, and alkyl phosphates.
Examples of the nonionic surfactant include polyoxyalkylene alkyl ethers such as polyoxyethylene oleyl ether and polyoxyethylene lauryl ether, and polyoxyalkylene styrenated phenyl ethers such as polyoxyethylene styrenated phenyl ether.

In the suspension polymerization method, only one type of surfactant may be used, or two or more types may be used.

The amount of surfactant used is not particularly limited, but is generally 0.01 to 5 parts by mass per 100 parts by mass of the total monomers.

A suspension stabilizer is used as necessary.
The suspension stabilizer is not particularly limited, and examples thereof include polyvinyl alcohol compounds such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and modified polyvinyl alcohol, as well as cellulose derivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose salts.

In the suspension polymerization method, when a suspension stabilizer is used, only one type of suspension stabilizer may be used, or two or more types may be used.

The amount of suspension stabilizer used is not particularly limited, but is generally 0 to 5 parts by mass per 100 parts by mass of the total monomers.

The polymerization initiator is not particularly limited as long as it can be used in ordinary suspension polymerization.
Examples of the polymerization initiator include organic peroxides and azo compounds.
Specific examples of organic peroxides include t-butyl hydroperoxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and t-butyl peroxypivalate.
Specific examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyrate)dimethyl.

In the suspension polymerization method, 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, but is preferably 0.1 to 3 parts by mass per 100 parts by mass of the total monomers.

The polymerization temperature is, for example, 50°C to 90°C, and preferably 60°C to 80°C.
The polymerization time is, for example, 1 to 5 hours, and preferably 2 to 4 hours.

The pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (A) is preferably adjusted to 7 to 9. When the pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (A) is 7 to 9, the dispersibility of the specific (meth)acrylic resin particles (A) tends to be good.
The method for adjusting the pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (A) is not particularly limited, and examples thereof include a method using a pH adjuster.
As the pH adjuster, for example, ammonia water can be suitably used.

The pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (A) is measured using a pH meter in accordance with JIS Z 8802:2011 at a liquid temperature of 30°C. For example, a pH meter (product name: F-51) manufactured by Horiba Ltd. can be used as the measuring device. However, the measuring device is not limited to this.

[Specific (meth)acrylic resin particles (B)]
The pressure-sensitive adhesive composition according to the present disclosure contains (meth)acrylic resin particles (B) having an average particle size of 50 nm to 900 nm [that is, specific (meth)acrylic resin particles (B)].
The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of the specific (meth)acrylic resin particles (B), or may contain two or more types.

--Average particle size of specific (meth)acrylic resin particles (B)--
The specific (meth)acrylic resin particles (B) have an average particle size of 50 nm to 900 nm.
When the average particle size of the specific (meth)acrylic resin particles (B) is 50 nm or more, the pressure-sensitive adhesive layer formed tends to have excellent removability. From this viewpoint, the average particle size of the specific (meth)acrylic resin particles (B) is 50 nm or more, preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more.
When the average particle size of the specific (meth)acrylic resin particles (B) is 900 nm or less, the pressure-sensitive adhesive layer formed tends to have excellent repositionability. From this viewpoint, the average particle size of the specific (meth)acrylic resin particles (B) is 900 nm or less, preferably 800 nm or less, more preferably 700 nm or less, and even more preferably 600 nm or less.

The average particle size of the specific (meth)acrylic resin particles (B) can be adjusted, for example, by adjusting the amount of surfactant used when producing the specific (meth)acrylic resin particles (B). The particle size of the specific (meth)acrylic resin particles (B) becomes smaller when a larger amount of surfactant is used, and becomes larger when a smaller amount of surfactant is used.

The average particle size of the specific (meth)acrylic resin particles (B) means the volume average particle size. The average particle size of the specific (meth)acrylic resin particles (B) is a value measured by a dynamic light scattering method described in "New Experimental Chemistry Lecture 4, Basic Technology 3, Light (II)" pp. 725-741 (published by Maruzen Co., Ltd. on July 20, 1976) edited by the Chemical Society of Japan using a particle size distribution measuring device. The specific method is shown below.
The specific (meth)acrylic resin particles (B) are diluted with distilled water, thoroughly stirred and mixed, and then 5 mL is collected using a Pasteur pipette in a 10 mm square glass cell, which is then set in a particle size distribution measuring device. The set value of the attenuation rate (Attenuator) is set to x8 (8 times), and the concentration of the diluted solution of the specific (meth)acrylic resin particles (B) is adjusted so that the Count Rate of the attenuation rate is 150 kCps to 200 kCps. The particle size distribution of the specific (meth)acrylic resin particles (B) is measured under conditions of a measurement temperature of 25°C and a light scattering angle of 90°. The measurement results are processed by computer to determine the average particle size of the specific (meth)acrylic resin particles (B). Specifically, the particle size at an integrated value of 50% (volume basis) in the obtained particle size distribution is taken as the volume average particle size.
As a particle size distribution measuring device, for example, "Zetasizer Nano ZS-90" manufactured by Malvern can be suitably used. However, the particle size distribution measuring device is not limited to this.

-Shape of specific (meth)acrylic resin particles (B)-
The shape of the specific (meth)acrylic resin particles (B) is not particularly limited.
The shape of the specific (meth)acrylic resin particles (B) may be spherical or irregular, with spherical being preferred.

--Glass transition temperature of specific (meth)acrylic resin particles (B)--
The glass transition temperature of the specific (meth)acrylic resin particles (B) is not particularly limited, but is, for example, preferably 5° C. or lower, more preferably 0° C. or lower, even more preferably −10° C. or lower, still more preferably −20° C. or lower, and particularly preferably −30° C. or lower.
When the glass transition temperature of the specific (meth)acrylic resin particles (B) is 5° C. or lower, the pressure-sensitive adhesive layer formed tends to exhibit excellent removability.
The lower limit of the glass transition temperature of the specific (meth)acrylic resin particles (B) is not particularly limited, but is preferably, for example, −70° C. or higher.

The glass transition temperature of the specific (meth)acrylic resin particles (B) is determined in the same manner as the glass transition temperature of the specific (meth)acrylic resin particles (A) described above.

The glass transition temperature of the specific (meth)acrylic resin particles (B) can be adjusted as appropriate, for example, by using two or more monomers that have different glass transition temperatures when made into homopolymers.

The structural units that the specific (meth)acrylic resin particles (B) may contain are described below.

<Structural Unit Derived from (Meth)acrylic Acid Alkyl Ester Monomer>
The specific (meth)acrylic resin particles (B) preferably contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer.
In the present disclosure, a "structural unit derived from a (meth)acrylic acid alkyl ester monomer" refers to a structural unit formed by addition polymerization of a (meth)acrylic acid alkyl ester monomer.

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.
The (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The alkyl group in the (meth)acrylic acid alkyl ester monomer 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.
The (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of methyl methacrylate, 2-ethylhexyl acrylate, and n-octyl acrylate.

When the specific (meth)acrylic resin particles (B) contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the structural unit may contain only one type or two or more types derived from the (meth)acrylic acid alkyl ester monomer.

When the specific (meth)acrylic resin particles (B) contain a constituent unit derived from a (meth)acrylic acid alkyl ester monomer, the content of the constituent units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (B) is not particularly limited, but is, for example, preferably 50% by mass to 99.95% by mass, more preferably 60% by mass to 99.9% by mass, and even more preferably 70% by mass to 99.8% by mass, relative to all constituent units of the specific (meth)acrylic resin particles (B).
Here, the content of the constituent units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (B) being 50 mass% or more relative to the total constituent units of the specific (meth)acrylic resin particles (B) 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 resin particles (B).

<Structural Unit Derived from Monomer Having a Carboxy Group>
The specific (meth)acrylic resin particles (B) may contain a structural unit derived from 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 the monomer having a carboxy group are the same as the specific examples of the monomer having a carboxy group in the specific (meth)acrylic resin particles (A).
As the monomer having a carboxy group, a (meth)acrylic monomer having a carboxy group is preferable, and acrylic acid is more preferable.

When the specific (meth)acrylic resin particles (B) contain a structural unit derived from a monomer having a carboxy group, the structural unit may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types of structural units derived from a monomer having a carboxy group.

When the specific (meth)acrylic resin particles (B) contain structural units derived from a monomer having a carboxy group, the content of the structural units derived from the monomer having a carboxy group in the specific (meth)acrylic resin particles (B) is not particularly limited, but is preferably 0.05% by mass to 5.0% by mass, more preferably 0.1% by mass to 3.0% by mass, and even more preferably 0.2% by mass to 1.0% by mass, relative to the total structural units of the specific (meth)acrylic resin particles (B).

<Constituent units derived from other monomers>
The specific (meth)acrylic resin particles (B) may contain a structural unit derived from a monomer other than the monomers already described (so-called other monomer).

Examples of structural units derived from other monomers that may be contained in the specific (meth)acrylic resin particles (B) include structural units derived from monomers having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene and vinyltoluene; structural units derived from vinyl cyanides, such as acrylonitrile and methacrylonitrile; structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate and vinyl versatate; and the like.

When the specific (meth)acrylic resin particles (B) contain structural units derived from other monomers, they may contain only one type of structural unit derived from the other monomers, or may contain two or more types of structural units derived from the other monomers.

When the specific (meth)acrylic resin particles (B) contain structural units derived from other monomers, the content of the structural units derived from other monomers in the specific (meth)acrylic resin particles (B) can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition according to the present disclosure.

<<Content of specific (meth)acrylic resin particles (B)>>
The content of the specific (meth)acrylic resin particles (B) in the pressure-sensitive adhesive composition according to the present disclosure is not particularly limited, but for example, it is preferably 2 parts by mass to 110 parts by mass, more preferably 5 parts by mass to 100 parts by mass, further preferably 10 parts by mass to 80 parts by mass, and particularly preferably 15 parts by mass to 60 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic resin particles (A).
When the content of the specific (meth)acrylic resin particles (B) in the pressure-sensitive adhesive composition according to the present disclosure is 2 parts by mass or more per 100 parts by mass of the specific (meth)acrylic resin particles (A), the pressure-sensitive adhesive layer formed tends to have better repositionability.
When the content of the specific (meth)acrylic resin particles (B) in the pressure-sensitive adhesive composition according to the present disclosure is 110 parts by mass or less per 100 parts by mass of the specific (meth)acrylic resin particles (A), the pressure-sensitive adhesive layer formed tends to have better removability.

[Method for producing specific (meth)acrylic resin particles (B)]
The method for producing the specific (meth)acrylic resin particles (B) is not particularly limited as long as the above-mentioned specific (meth)acrylic resin particles (B) can be produced.
As a method for producing the specific (meth)acrylic resin particles (B), for example, an emulsion polymerization method is preferred from the viewpoint of ease of producing the specific (meth)acrylic resin particles (B).

Examples of the emulsion polymerization method for producing the specific (meth)acrylic resin particles (B) include the following methods (1) to (3).
(1) A method in which the above-mentioned monomer components, surfactant, and water are charged into a reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux condenser, a nitrogen inlet pipe, and the like, and the temperature is raised while stirring under a nitrogen stream, and then a polymerization initiator, a reducing agent, and the like are appropriately added to allow the emulsion polymerization reaction to proceed (the so-called lump-sum charging method).
(2) A method in which at least a surfactant and water are charged into a reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux condenser, a nitrogen inlet pipe, etc., and the temperature is raised while stirring under a nitrogen stream, and then a monomer component is dropped, and a polymerization initiator, a reducing agent, etc. are appropriately added to proceed with an emulsion polymerization reaction (the so-called monomer dropping method).
(3) Water is charged into a reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux condenser, a nitrogen inlet pipe, etc., and the temperature is raised while stirring under a nitrogen gas flow. Meanwhile, in a separate vessel, a monomer component is emulsified in advance using at least a surfactant and water to prepare an emulsion containing the monomer component as a dispersoid. The emulsion containing the monomer component as a dispersoid is dropped into the reactor, and a polymerization initiator, a reducing agent, etc. are appropriately added to proceed with the emulsion polymerization reaction (the so-called emulsion monomer dropping method).
Among these, the emulsion polymerization method for producing the specific (meth)acrylic resin particles (B) is preferably the above-mentioned emulsion monomer dropping method (3) from the viewpoint of industrial productivity, for example.

The surfactant is not particularly limited, but is preferably, for example, an anionic surfactant and/or a nonionic surfactant.

Specific examples of anionic surfactants are the same as those described in the suspension polymerization method. Specific examples of nonionic surfactants are the same as those described in the suspension polymerization method.

In the emulsion polymerization method, only one type of surfactant may be used, or two or more types may be used.

The amount of surfactant used is not particularly limited, but is generally 0.2 to 3 parts by mass per 100 parts by mass of the total monomers.

The polymerization initiator is not particularly limited as long as it can be used in ordinary emulsion polymerization.
Examples of the polymerization initiator include persulfates, organic peroxides, and azo compounds.
Specific examples of persulfates include ammonium persulfate, sodium persulfate, and potassium persulfate.
Specific examples of the organic peroxide are the same as those described in the suspension polymerization method, and specific examples of the azo compound are the same as those described in the suspension polymerization method.

In the emulsion polymerization method, 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, but is preferably 0.5 to 10 parts by mass per 100 parts by mass of the total monomers.

In the emulsion polymerization method, a reducing agent may be used together with the polymerization initiator.
Specific examples of reducing agents include sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium pyrosulfite, sodium pyrophosphate, thioglycolic acid, sodium thiosulfate, L-ascorbic acid, tartaric acid, citric acid, and glucose.

In the emulsion polymerization method, only one type of reducing agent may be used, or two or more types may be used.

The amount of reducing agent used is not particularly limited, but is preferably 0.5 to 10 parts by mass per 100 parts by mass of the total monomers.

The polymerization temperature is, for example, 50°C to 90°C, and preferably 60°C to 80°C.
The polymerization time is, for example, 1 to 5 hours, and preferably 2 to 4 hours.

The pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (B) is preferably adjusted to 7 to 9. When the pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (B) is 7 to 9, the dispersibility of the specific (meth)acrylic resin particles (B) tends to be good.
The method for adjusting the pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (B) is not particularly limited, and examples thereof include a method using a pH adjuster.
As the pH adjuster, for example, ammonia water can be suitably used.

The pH of the aqueous dispersion containing the specific (meth)acrylic resin particles (B) is measured using a pH meter in accordance with JIS Z 8802:2011 at a liquid temperature of 30°C. For example, a pH meter (product name: F-51) manufactured by Horiba, Ltd. can be used as the measuring device. However, the measuring device is not limited to this.

[Specific tackifying resin particles (C)]
The pressure-sensitive adhesive composition according to the present disclosure contains 20 to 100 parts by mass of tackifier resin particles (C) having a biomass degree of 45% or more [i.e., specific tackifier resin particles (C)] per 100 parts by mass of the specific (meth)acrylic resin particles (A). Because the pressure-sensitive adhesive composition according to the present disclosure contains the specific tackifier resin particles (C), it is possible to realize the formation of an environmentally friendly pressure-sensitive adhesive layer.

In the present disclosure, the term "tackifier resin" refers to a resin other than a (meth)acrylic resin that has the property of being able to impart tackiness by blending and has a molecular weight of less than 10,000 (preferably in the range of 500 or more and less than 10,000). Also, "tackiness" refers to a sticky property.
Tackifying resins are also called tackifiers.

The molecular weight of the specific tackifier resin particles (C) is a value measured by gel permeation chromatography (GPC). Specifically, the weight average molecular weight of the specific tackifier resin particles (C) is determined as a standard polystyrene equivalent value by 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

However, when a commercially available product is used as the specific tackifying resin particles (C) and the molecular weight is listed in the catalog of the commercially available product, the molecular weight of the specific tackifying resin particles (C) shall be the value in the catalog of the commercially available product.

From the viewpoint of forming an environmentally friendly adhesive layer, the biomass degree of the specific tackifier resin particles (C) is 45% or more, preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more, and may be, for example, 100%.

The biomass degree of the specific tackifier resin particles (C) is a value measured by a method in accordance with ASTM D6866-20, and means the mass proportion of biomass-derived carbon in the total carbon contained in the specific tackifier resin particles (C).
However, when a commercially available product is used as the specific tackifier resin particles (C) and the biomass degree is listed in the catalog of the commercially available product, the catalog value of the commercially available product is used as the biomass degree of the specific tackifier resin particles (C).

At least a part of the raw materials of the specific tackifier resin particles (C) is preferably a plant-derived component.
Examples of the specific tackifying resin particles (C) include particles of a resin having a rosin skeleton (so-called rosin-based resin), particles of a resin having a terpene skeleton (so-called terpene-based resin), and particles of a resin having a styrene skeleton (so-called styrene-based resin).
The specific tackifier resin particles (C) are preferably particles of at least one resin selected from the group consisting of rosin-based resins and terpene-based resins.

Specific examples of rosin-based resins include rosin, esterified rosin (so-called rosin ester resin), hydrogenated rosin, and disproportionated rosin.
As the rosin-based resin, a rosin ester resin is preferable.

Specific examples of terpene resins include polyterpenes which are homopolymers of terpene, terpene phenol resins, aromatic modified terpene resins, and hydrogenated terpene resins.
As the terpene resin, an aromatic modified terpene resin is preferable.

The softening point of the specific tackifier resin particles (C) is not particularly limited, but is, for example, preferably 30°C to 160°C, more preferably 60°C to 160°C, even more preferably 80°C to 160°C, and particularly preferably 100°C to 160°C.
When the softening point of the specific tackifier resin particles (C) is 30° C. or higher, the removability of the formed pressure-sensitive adhesive layer tends to be improved regardless of the material of the adherend.
When the softening point of the specific tackifier resin particles (C) is 160° C. or lower, it is easy to obtain a commercially available product.

The softening point of the specific tackifier resin particles (C) is a value measured by a method in accordance with JIS K 7234:1986 (so-called ring and ball method).
However, when a commercially available product is used as the specific tackifying resin particles (C) and the softening point is described in the catalog of the commercially available product, the softening point of the specific tackifying resin particles (C) is the value in the catalog of the commercially available product.

The shape of the specific tackifier resin particles (C) is not particularly limited, but it is preferable that they are spherical.

The average particle size of the specific tackifier resin particles (C) is not particularly limited, but is, for example, preferably 100 nm to 600 nm, more preferably 100 nm to 500 nm, and even more preferably 200 nm to 500 nm.
When the specific tackifier resin particles (C) have an average particle size of 100 nm or more, they are readily available as commercial products.
When the average particle size of the specific tackifier resin particles (C) is 600 nm or less, the adhesive strength of the formed adhesive layer tends to be more appropriate.

The average particle size of the specific tackifier resin particles (C) means the volume average particle size.
The average particle size of the specific tackifier resin particles (C) is a value measured by the same method as that for measuring the average particle size of the specific (meth)acrylic resin particles (B).

As the specific tackifier resin particles (C), commercially available products can be used.
Commercially available examples of the specific tackifier resin particles (C) include "SUPER ESTER E-900-NT", "SUPER ESTER E-788", and "SUPER ESTER E-865-WR" manufactured by Arakawa Chemical Industries, Ltd., "HARIESTAR SK-130D" manufactured by Harima Chemical Industries, Ltd., and "NANOLET (registered trademark) T1050" manufactured by Yasuhara Chemical Co., Ltd.

The adhesive composition according to the present disclosure may contain only one type of specific tackifier resin particles (C), or may contain two or more types.

The content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 20 parts by mass to 100 parts by mass per 100 parts by mass of the specific (meth)acrylic resin particles (A).
When the content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 20 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic resin particles (A), the pressure-sensitive adhesive layer formed tends to have excellent removability. From this viewpoint, the content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 20 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic resin particles (A), preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more.
When the content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 100 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic resin particles (A), the pressure-sensitive adhesive layer formed tends to have excellent water resistance. From this viewpoint, the content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 100 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic resin particles (A), preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less.

〔water〕
The pressure-sensitive adhesive composition according to the present disclosure contains water.
The water is not particularly limited, but from the viewpoint of having fewer impurities, for example, distilled water, ion-exchanged water, pure water, and the like are preferable.

The water content in the adhesive composition according to the present disclosure is not particularly limited, but is preferably 50% by mass to 90% by mass, and more preferably 60% by mass to 80% by mass, relative to the total mass of the adhesive composition.

[Aqueous media other than water]
The pressure-sensitive adhesive composition according to the present disclosure may contain an aqueous medium other than water.
Examples of aqueous media other than water include water-miscible organic solvents.
Examples of water-miscible organic solvents include monohydric alcohol compounds such as methanol, ethanol, propanol, and isopropanol; polyhydric alcohol compounds such as glycerin, ethylene glycol, diethylene glycol, and propylene glycol; and glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

When the pressure-sensitive adhesive composition according to the present disclosure contains an aqueous medium other than water, it may contain only one type of aqueous medium other than water, or may contain two or more types of aqueous medium other than water.

The content of the aqueous medium other than water in the pressure-sensitive adhesive composition according to the present disclosure can be set appropriately within a range that does not impair the effects of the pressure-sensitive adhesive composition according to the present disclosure.

[Water-immiscible organic solvent]
From the viewpoint of environmental consideration, for example, the pressure-sensitive adhesive composition according to the present disclosure preferably does not contain a water-immiscible organic solvent or the content of the water-immiscible organic solvent is in the range of more than 0 mass% to 5 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition; more preferably does not contain a water-immiscible organic solvent or the content of the water-immiscible organic solvent is in the range of more than 0 mass% to 3 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition; even more preferably does not contain a water-immiscible organic solvent or the content of the water-immiscible organic solvent is in the range of more than 0 mass% to 1 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition; and particularly preferably does not contain a water-immiscible organic solvent or the content of the water-immiscible organic solvent is in the range of more than 0 mass% to 0.5 mass% or less, relative to the total mass of the pressure-sensitive adhesive composition.

Examples of water-immiscible organic solvents include aromatic hydrocarbon compounds such as benzene, toluene, and xylene; ether compounds such as diethyl ether and diisopropyl ether; aliphatic hydrocarbon compounds such as hexane and heptane; halogenated hydrocarbon compounds such as dichloroethane and chloroform; ester compounds such as ethyl acetate and butyl acetate; alcohol compounds such as octanol; and ketone compounds such as methyl isobutyl ketone.

[Other ingredients]
The pressure-sensitive adhesive composition according to the present disclosure may contain components other than the components described above (so-called other components) as necessary, within the scope that does not impair the effects of the pressure-sensitive adhesive composition.
Examples of other components include (meth)acrylic resin particles other than the specific (meth)acrylic resin particles (A) and the specific (meth)acrylic resin particles (B), tackifier resin particles other than the specific tackifier resin particles (C), and various additives such as antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[Adhesive sheet]
The pressure-sensitive adhesive sheet according to the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to the present disclosure, and is therefore environmentally friendly and has excellent water resistance, removability, and repositionability.

The thickness of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet according to the present disclosure is not particularly limited.
The thickness of the pressure-sensitive adhesive layer is generally from 1 μm to 300 μm, preferably from 5 μm to 200 μm, and more preferably from 10 μm to 100 μm.

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

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

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

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

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

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

The thickness of the substrate is not particularly limited, but is generally 5 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 10 μm to 100 μm.

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

[Method of producing adhesive sheet]
The method for producing the pressure-sensitive adhesive sheet according to the present disclosure is not particularly limited.
The pressure-sensitive adhesive sheet according to the present disclosure can be produced by a known method.
Examples of methods for producing the pressure-sensitive adhesive sheet according to the present disclosure include the following methods.

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

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

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

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

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

The adhesive composition and adhesive sheet according to 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 resin particles (A)]
[Manufacture example A-4]
A reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a nitrogen inlet pipe, and a reflux condenser was charged with 130 parts by mass of ion-exchanged water, 60 parts by mass of a 5% by mass aqueous solution of partially saponified polyvinyl alcohol "Gohsenol (registered trademark) KH-17" (trade name; manufactured by Mitsubishi Chemical Corporation) (active ingredient amount: 3 parts by mass), and 0.32 parts by mass of an aqueous solution (active ingredient concentration: 30% by mass) of an anionic surfactant "Newcol (registered trademark) 707SF" (trade name; polyoxyethylene (number of repeating units of ethylene oxide chain: 7) distyrenated phenyl ether sulfate ester sodium salt and ammonium salt; manufactured by Nippon Nyukazai Co., Ltd.), and the mixture was thoroughly stirred to obtain an aqueous solution. Next, in a separate vessel, 69.3 parts by mass of 2-ethylhexyl acrylate [2EHA; other (meth)acrylic acid alkyl ester monomer], 30 parts by mass of lauryl methacrylate [LMA; specific (meth)acrylic acid alkyl ester monomer, number of carbon atoms in alkyl group: 12], 0.7 parts by mass of acrylic acid [AA; monomer having a carboxy group], and 0.34 parts by mass of "Perbutyl PV" [product name; t-butyl peroxypivalate (PBPV; polymerization initiator), manufactured by NOF Corporation] (active ingredient concentration: 70% by mass) (active ingredient amount: 0.24 parts by mass) were placed and mixed with stirring to obtain a monomer mixture. The obtained monomer mixture was added to the aqueous solution in the reactor previously prepared, and stirred for 1 hour at a stirring speed of about 200 rpm (revolutions per minute), and then 200 parts by mass of ion-exchanged water was added to the reactor. Next, the inside of the reactor was replaced with nitrogen, and heating was started. The polymerization reaction started at 58° C. to 62° C., and the internal temperature rose rapidly to 75° C. due to heat generation. The mixture was cooled, and the reaction was carried out for 4 hours while the internal temperature was maintained at 75° C. The resulting liquid was cooled to 30° C., and then 25% by mass of aqueous ammonia was added to adjust the pH to 8 to 9, to obtain an aqueous dispersion of (meth)acrylic resin particles A-4.
The resulting aqueous dispersion of (meth)acrylic resin particles A-4 had a solids concentration of 20.6% by mass and a pH of 8.3.

The "solid content concentration" here means the mass ratio of (meth)acrylic resin particles A-4 in the aqueous dispersion of (meth)acrylic resin particles A-4. The same applies to each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-3 and A-5 to A-15 produced below.

[Production Examples A-1 to A-3 and A-5]
In Production Examples A-1 to A-3 and A-5, the same operation as in Production Example A-4 was performed except that the stirring speed, the amount of suspension stabilizer used, etc. were appropriately changed, to obtain aqueous dispersions of (meth)acrylic resin particles A-1 to A-3 and A-5.

[Production Examples A-6, A-7, A-9, A-10, and A-13 to A-15]
In Production Examples A-6, A-7, A-9, A-10, and A-13 to A-15, the same operation as in Production Example A-4 was performed except that the monomer composition of the (meth)acrylic resin particles (A) was changed to the monomer composition shown in Table 1, thereby obtaining aqueous dispersions of (meth)acrylic resin particles A-6, A-7, A-9, A-10, and A-13 to A-15.

[Production Examples A-8, A-11 and A-12]
In Production Examples A-8, A-11, and A-12, the monomer composition of the (meth)acrylic resin particles (A) was changed to the monomer composition shown in Table 1, and the stirring speed, the amount of the suspension stabilizer used, and the like were appropriately changed, except that the same operation as in Production Example A-4 was performed to obtain aqueous dispersions of (meth)acrylic resin particles A-8, A-11, and A-12.

The solids concentration of each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-3 and A-5 to A-15 obtained above is shown below.

-Solid content concentration-
A-1: 20.6% by mass, A-2: 20.6% by mass, A-3: 20.6% by mass, A-5: 20.6% by mass, A-6: 35.0% by mass, A-7: 30.5% by mass, A-8: 20.0% by mass, A- 9: 20.6% by mass, A-10: 20.6% by mass, A-11: 20.6% by mass, A-12: 20.6% by mass, A-13: 20.6% by mass, A-14: 37.0% by mass, A-15: 35.0% by mass.

The pH of each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-3 and A-5 to A-15 obtained above is shown below. The pH of each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-15 was measured at a liquid temperature of 30°C using a pH meter (product name: F-51) manufactured by Horiba Ltd., in accordance with a method conforming to JIS Z 8802:2011.

-pH-
A-1:8.3, A-2:8.3, A-3:8.3, A-5:8.3, A-6:8.3, A-7:8.3, A-8:8.5, A-9:8.3, A-10:8.3, A-11:8.5, A-12:8.5, A-13:8.3, A-14:8.3, A-15:8.4

The monomer composition (unit: mass%) of (meth)acrylic resin particles A-1 to A-15, the glass transition temperature (Tg, unit: °C) of (meth)acrylic resin particles A-1 to A-15, and the average particle size (volume average particle size, unit: μm) of (meth)acrylic resin particles A-1 to A-15 are shown in Table 1.

The glass transition temperatures of (meth)acrylic resin particles A-1 to A-15 were determined using the same method as that for determining the glass transition temperature of specific (meth)acrylic resin particles (A) described above.

The average particle size of the (meth)acrylic resin particles A-1 to A-15 was measured by the same method as the above-mentioned method for measuring the average particle size of the specific (meth)acrylic resin particles (A).
The measurement device used was a Laser Scattering Particle Size Distribution Analyzer LA-960 (product name), a laser diffraction type particle size distribution measurement device manufactured by Horiba, Ltd.

Of the (meth)acrylic resin particles A-1 to A-15 obtained above, (meth)acrylic resin particles A-2 to A-9, A-11 to A-13, and A-15 correspond to the specific (meth)acrylic resin particles (A) in this disclosure.

Details of each monomer listed in Table 1 are as follows.
<Specific (meth)acrylic acid alkyl ester monomer>
"LMA": Lauryl methacrylate (number of carbon atoms in alkyl group: 12, biomass ratio: 71.4%, Tg when homopolymerized: -65°C)
"STMA": stearyl methacrylate (number of carbon atoms in alkyl group: 18, biomass degree: 78.3%, Tg when homopolymerized: 38°C)

<Other monomers>
<<Other (meth)acrylic acid alkyl ester monomers>>
"2EHA": 2-ethylhexyl acrylate
(Tg when homopolymerized: -70°C)
"OA": n-octyl acrylate (Tg when homopolymerized: -65°C)
"MMA": methyl methacrylate (Tg when homopolymerized: 105°C)
<<Monomers with carboxy groups>>
"AA": acrylic acid (Tg when homopolymerized: 106°C)
<<Polyfunctional (meth)acrylic acid ester monomer>>
"EDMA": ethylene glycol dimethacrylate

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

[Production of (meth)acrylic resin particles (B)]
[Manufacture example B-4]
In a reactor equipped with a thermometer, a stirrer, a raw material introduction tube, a nitrogen introduction tube, and a reflux condenser, 28.8 parts by mass of ion-exchanged water was charged, and the internal temperature was raised to 75° C. Meanwhile, in another vessel, 23.3 parts by mass of ion-exchanged water, 1.0 part by mass of a nonionic surfactant "EMULGEN (registered trademark) 430" [trade name; polyoxyethylene oleyl ether (active ingredient concentration: 100% by mass), manufactured by Kao Corporation], and 1.05 parts by mass (active ingredient amount: 1.0 part by mass) of an anionic surfactant "Hitenol (registered trademark) NF-17" [trade name; polyoxyethylene distyrenated phenyl ether sulfate ester ammonium salt (active ingredient concentration: 95% by mass), manufactured by Kao Corporation] were charged, and an aqueous solution was obtained by stirring. To the obtained aqueous solution, 84.5 parts by mass of 2-ethylhexyl acrylate [2EHA; (meth)acrylic acid alkyl ester monomer], 15.0 parts by mass of methyl methacrylate [MMA; (meth)acrylic acid alkyl ester monomer], and 0.5 parts by mass of acrylic acid [AA; monomer having a carboxy group] were added and stirred to obtain a monomer premix. Next, the contents of the reactor were heated while stirring under a nitrogen stream, and when the water temperature in the reactor reached 75°C, 0.058 parts by mass of ammonium persulfate (APS; polymerization initiator) and sodium metabisulfite (SMBS; reducing agent) were added, and then the monomer premix, 8.3 parts by mass of a 4.2% by mass APS aqueous solution, and 8.3 parts by mass of a 4.2% by mass SMBS aqueous solution were successively added to initiate polymerization, and the polymerization reaction was carried out for about 2.5 hours. After the polymerization reaction was completed, stirring was continued for about 1 hour while maintaining the temperature, and then the mixture was cooled and 25% by mass of aqueous ammonia was added to adjust the pH to 8 to 9, thereby obtaining an aqueous dispersion of (meth)acrylic resin particles B-4.
The resulting aqueous dispersion of (meth)acrylic resin particles B-4 had a solids concentration of 58.0% by mass and a pH of 8.3.

The "solid content concentration" here means the mass ratio of (meth)acrylic resin particles B-4 in the aqueous dispersion of (meth)acrylic resin particles B-4. The same applies to each of the aqueous dispersions of (meth)acrylic resin particles B-1 to B-3 and B-5 to B-9 produced below.

[Production Examples B-1 to B-3, B-5 and B-6]
In Production Examples B-1 to B-3, B-5, and B-6, the same operation as in Production Example B-4 was carried out except that the amount of the surfactant used was appropriately changed, to obtain aqueous dispersions of (meth)acrylic resin particles B-1 to B-3, B-5, and B-6.

[Production examples B-7 to B-9]
In Production Examples B-7 to B-9, the same operation as in Production Example B-4 was performed except that the monomer composition of the (meth)acrylic resin particles (B) was changed to the monomer composition shown in Table 2, to obtain aqueous dispersions of (meth)acrylic resin particles B-7 to B-9.

The solids concentration of each of the aqueous dispersions of (meth)acrylic resin particles B-1 to B-3 and B-5 to B-9 obtained above is shown below.

-Solid content concentration-
B-1: 40.0 mass%, B-2: 40.0 mass%, B-3: 50.0 mass%, B-5: 50.0 mass%, B-6: 45.0 mass%, B-7: 50.0 mass%, B-8: 50.0 mass%, B-9: 50.0 mass%

The pH of each of the aqueous dispersions of (meth)acrylic resin particles B-1 to B-3 and B-5 to B-9 obtained above is shown below. The pH of each of the aqueous dispersions of (meth)acrylic resin particles B-1 to B-9 was measured at a liquid temperature of 30°C using a pH meter (product name: F-51) manufactured by Horiba Ltd., in accordance with a method conforming to JIS Z 8802:2011.

-pH-
B-1: 8.3, B-2: 8.3, B-3: 8.3, B-5: 8.3, B-6: 8.3, B-7: 8.5, B-8: 8.5, B-9: 8.4

The monomer composition (unit: mass%) of (meth)acrylic resin particles B-1 to B-9, the glass transition temperature (Tg, unit: °C) of (meth)acrylic resin particles B-1 to B-9, and the average particle size (volume average particle size, unit: nm) of (meth)acrylic resin particles B-1 to B-9 are shown in Table 2.

The glass transition temperatures of (meth)acrylic resin particles B-1 to B-9 were determined in the same manner as the glass transition temperature of specific (meth)acrylic resin particles (A) described above.

The average particle size of the (meth)acrylic resin particles B-1 to B-9 was measured by the same method as the above-mentioned method for measuring the average particle size of the specific (meth)acrylic resin particles (B).
The measurement device used was Zetasizer Nano ZS-90 (product name), a particle size distribution measurement device manufactured by Malvern.

Of the (meth)acrylic resin particles B-1 to B-9 obtained above, (meth)acrylic resin particles B-2 to B-5 and B-7 to B-9 correspond to the specific (meth)acrylic resin particles (B) in this disclosure.

Details of each monomer listed in Table 2 are as follows.
"2EHA": 2-ethylhexyl acrylate
(Tg when homopolymerized: -70°C)
"OA": n-octyl acrylate (Tg when homopolymerized: -65°C)
"MMA": methyl methacrylate (Tg when homopolymerized: 105°C)
"AA": acrylic acid (Tg when homopolymerized: 106°C)

In Table 2, a "-" in the monomer composition column means that the monomer in that column is not used.

[Preparation of Pressure-Sensitive Adhesive Composition]
Example 1
100 parts by mass (solid content equivalent) of the aqueous dispersion of the (meth)acrylic resin particles A-2 obtained above, 20 parts by mass (solid content equivalent) of the aqueous dispersion of the (meth)acrylic resin particles B-4, and 50 parts by mass (solid content equivalent) of Super Ester E-900-NT (trade name, biomass degree: 80%, volume average particle size: 0.3 μm, manufactured by Arakawa Chemical Industries, Ltd.) as tackifier resin particles (C) were thoroughly mixed to prepare a pressure-sensitive adhesive composition of Example 1.

[Examples 2 to 13]
In Examples 2 to 13, the adhesive compositions of Examples 2 to 13 were prepared in the same manner as in Example 1, except that the formulations of the adhesive compositions were as shown in Table 3.

[Examples 14 to 27]
In Examples 14 to 27, the adhesive compositions of Examples 14 to 27 were prepared in the same manner as in Example 1, except that the formulations of the adhesive compositions were as shown in Table 4.

Comparative Examples 1 to 7
In Comparative Examples 1 to 7, the adhesive compositions of Comparative Examples 1 to 7 were prepared in the same manner as in Example 1, except that the compositions of the adhesive compositions were as shown in Table 5.

[Preparation of Pressure-Sensitive Adhesive Sheet for Evaluation]
The adhesive composition prepared above was applied to a substrate of fine paper (trade name: OK Prince fine, basis weight: 81.4 g/m ² , manufactured by Oji Paper Co., Ltd.) using a wire bar so that the coating amount after drying was 15 g/m ² to form a coating film. The formed coating film was then dried using a hot air circulation dryer under conditions of a drying temperature of 105° C. and a drying time of 40 seconds to form an adhesive layer on the surface of the fine paper. Next, a release sheet (trade name: SL-80KCM, manufactured by Sumika Kakoshi Co., Ltd.) was placed on the exposed surface of the adhesive layer formed on the surface of the fine paper so that the easy-release treated surface of the release sheet was in contact with the surface, and the two were bonded together to prepare an adhesive sheet for evaluation. The prepared adhesive sheet for evaluation has a laminated structure of substrate (fine paper)/adhesive layer (thickness: 20 μm)/release sheet.

[Measurement and Evaluation]
1. Adhesive strength (1) Initial adhesive strength The adhesive sheet for evaluation prepared above was cut into a size of 25 mm x 100 mm, and an adhesive sheet piece for evaluation was prepared. The release sheet was peeled off from the prepared adhesive sheet for evaluation (structure: substrate/adhesive layer/release sheet), and the surface of the adhesive layer exposed by peeling was placed on the surface of SUS304 (stainless steel plate; hereinafter, simply referred to as "SUS") polished with #360 waterproof abrasive paper specified in JIS R 6253:2006 according to the method conforming to JIS Z 0237:2009, and pressed to prepare a test piece. The prepared test piece was left to stand for 30 minutes in an environment of an atmospheric temperature of 23 ° C and 50% RH. After leaving the test piece stationary, the adhesive strength (unit: N/25 mm) when the evaluation adhesive sheet piece (structure: substrate/adhesive layer) was peeled off from the SUS at 180° in the long side (100 mm) direction was measured using a single column type material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd. as the measuring device under conditions of an atmospheric temperature of 23° C., 50% RH, and a peeling speed of 300 mm/min. Evaluation was then performed according to the following evaluation criteria. The measured values and evaluation results are shown in Tables 3 to 5.
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: The adhesive strength was 0.5 N/25 mm or more.
B: The adhesive strength was greater than 0.1 N/25 mm and less than 0.5 N/25 mm.
C: The adhesive strength was 0.1 N/25 mm or less.

(2) Adhesive strength after time The adhesive sheet for evaluation prepared above was cut into a size of 25 mm x 100 mm to prepare an adhesive sheet piece for evaluation. The release sheet was peeled off from the prepared adhesive sheet piece for evaluation (structure: substrate/adhesive layer/release sheet), and the surface of the adhesive layer exposed by peeling was placed on the surface of SUS304 (stainless steel plate; hereinafter, simply referred to as "SUS") polished with #360 waterproof abrasive paper specified in JIS R 6253:2006 according to the method conforming to JIS Z 0237:2009, and pressed to prepare a test piece. The prepared test piece was left in a thermostatic and hygroscopic chamber with a set temperature of 40°C for 7 days, and then removed from the thermostatic and hygroscopic chamber and left in an environment of an atmospheric temperature of 23°C and 50% RH for 30 minutes. After leaving the test piece stationary, the adhesive strength (unit: N/25 mm) when the evaluation adhesive sheet piece (structure: substrate/adhesive layer) was peeled off from the SUS at 180° in the long side (100 mm) direction was measured using a single column type material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd. as the measuring device under conditions of an atmospheric temperature of 23° C., 50% RH, and a peeling speed of 300 mm/min. Evaluation was then performed according to the following evaluation criteria. The measured values and evaluation results are shown in Tables 3 to 5.
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: The adhesive strength was less than 2.5 N/25 mm.
B: The adhesive strength was 2.5 N/25 mm or more and less than 4.0 N/25 mm.
C: The adhesive strength was 4.0 N/25 mm or more.

2. Removability When measuring adhesive strength in "(2) Adhesive strength after aging" of "1. Adhesive strength" above, the peeling state of the evaluation adhesive sheet piece (composition: substrate/adhesive layer) from the SUS was visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 to 5.
In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable. Note that "glue" in the evaluation criteria is synonymous with pressure-sensitive adhesive.

-Evaluation criteria-
A: Neither glue residue nor stringy glue was observed on the SUS during peeling, nor was the substrate broken.
B: Although slight residue of glue and stringiness of glue were observed on the SUS when peeled off, no breakage of the substrate was observed.
C: Breaking of the substrate was confirmed, and adhesive remained on the SUS surface when peeled off.

3. Repositionability In the above "1. Adhesive strength""(1) Initial adhesive strength", the evaluation adhesive sheet piece (structure: substrate/adhesive layer) peeled off from SUS when measuring adhesive strength was cut into a size of 16 mm x 20 mm (long side) to prepare a test piece. This test piece was attached to the side of a cylindrical paper with a diameter of 50 mm [product name: K Liner, manufactured by Oji Materia Co., Ltd.] so that the long side (20 mm) was curved. After attachment, the test piece was left to stand for 24 hours, and the degree of lifting and peeling of the test piece was visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 to 5.
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 lifting or peeling of the test piece was observed.
B: The percentage of the area of the portion of the test piece where neither lifting nor peeling was confirmed was 80% or more and less than 100% of the total application area.
C: The percentage of the area of the portion of the test piece where neither lifting nor peeling was confirmed was 0% or more and less than 80% of the total application area.

4. Water resistance The adhesive sheet for evaluation prepared above was cut into a size of 25 mm x 100 mm to prepare an adhesive sheet piece for evaluation. The release sheet was peeled off from the prepared adhesive sheet piece for evaluation (structure: substrate/adhesive layer/release sheet), and the surface of the adhesive layer exposed by peeling was placed on the surface of SUS304 (stainless steel plate; hereinafter, simply referred to as "SUS") polished with #360 waterproof abrasive paper specified in JIS R 6253:2006 according to the method conforming to JIS Z 0237:2009, and pressed to prepare a test piece. The prepared test piece was left in a thermostatic chamber with a set temperature of 60°C and a set humidity of 95%RH for 7 days, and then removed from the thermostatic chamber and left in an environment of an atmospheric temperature of 23°C and 50%RH for 30 minutes. After the test piece was left stationary, a test was performed in which the adhesive sheet piece for evaluation (structure: substrate/adhesive layer) was peeled from the SUS at 180° in the long side (100 mm) direction under conditions of an atmospheric temperature of 23° C., 50% RH, and a peeling speed of 300 mm/min, using a single column type material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd. as a measuring device. During the peeling test, the peeling state of the adhesive sheet piece for evaluation (structure: substrate/adhesive layer) from the SUS was visually observed, and evaluation was performed according to the following evaluation criteria. The evaluation results are shown in Tables 3 to 5.
In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable. Note that "glue" in the evaluation criteria is synonymous with pressure-sensitive adhesive.

-Evaluation criteria-
A: Neither glue residue nor stringiness of glue was observed on the SUS when peeled off.
B: Some glue residue and stringiness of glue on the SUS was observed upon peeling, but only slightly.
C: The adhesive remained on the SUS surface when peeled off.

Details of the specific tackifier resin particles (C) shown in Tables 3 to 5 are as follows.
"Super Ester E-900-NT" (product name, rosin-based resin, biomass ratio: 80%, softening point: 160°C, average particle size: 300 nm, solid content: 50% by mass, manufactured by Arakawa Chemical Industries, Ltd.)
"Super Ester E-788" (product name, rosin-based resin, biomass ratio: 80%, softening point: 160°C, average particle size: 300 nm, solid content: 50% by mass, manufactured by Arakawa Chemical Industries, Ltd.)
"Hariestar SK-130D" (product name, rosin-based resin, biomass content: 90%, softening point: 130°C, average particle size: 450 nm, solid content: 54% by mass, manufactured by Harima Chemicals Co., Ltd.)
"Super Ester E-865-WR" (product name, rosin-based resin, biomass content: 48%, softening point: 160°C, average particle size: 300 nm, solid content: 50% by mass, manufactured by Arakawa Chemical Industries, Ltd.)
"Nanolet T1050" (product name, terpene resin, biomass ratio: 70%, softening point: 105°C, average particle size: 350 nm, solid content: 50% by mass, manufactured by Yasuhara Chemical Co., Ltd.)

The "average particle size" described in the details of the specific tackifier resin particles (C) above is the volume average particle size measured by the same method as the method for measuring the average particle size of the specific (meth)acrylic resin particles (B) described above. The measurement device used was a Zetasizer Nano ZS-90 (product name), a particle size distribution measurement device manufactured by Malvern.

As shown in Tables 3 and 4, it was confirmed that the adhesive layer formed by the adhesive composition of the Example exhibited good adhesive strength at the initial stage of bonding so as not to peel off from the adherend, and that the adhesive strength was unlikely to increase excessively over time. It was also confirmed that the adhesive layer formed by the adhesive composition of the Example had excellent water resistance, removability, and repositionability. The adhesive composition of the Example contains tackifier resin particles with a biomass ratio of at least 45%, and can form an environmentally friendly adhesive layer.

On the other hand, as shown in Table 5, it was confirmed that the adhesive layer formed with the adhesive composition of the comparative example was inferior to the adhesive layer formed with the adhesive composition of the example in at least one of water resistance, removability, and repositionability.

Claims (6)

(Meth)acrylic resin particles (A) containing a structural unit derived from a (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms, having a glass transition temperature of 0° C. or lower, and having an average particle size of 1 μm to 80 μm;
(Meth)acrylic resin particles (B) having an average particle size of 50 nm to 900 nm;
tackifier resin particles (C) having a biomass ratio of 45% or more;
Water,
Including,
The pressure-sensitive adhesive composition has a content of the tackifier resin particles (C) of 20 to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A). The pressure-sensitive adhesive composition according to claim 1, wherein the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer having an alkyl group having 10 to 22 carbon atoms in the (meth)acrylic resin particles (A) is 10.0% by mass to 99.8% by mass relative to the total structural units of the (meth)acrylic resin particles (A). The adhesive composition according to claim 1 or 2, wherein the biomass degree of the (meth)acrylic acid alkyl ester monomer having an alkyl group with 10 to 22 carbon atoms is 50% or more. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the content of the (meth)acrylic resin particles (B) is 5 parts by mass to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A). The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the glass transition temperature of the (meth)acrylic resin particles (B) is 0°C or lower. An adhesive sheet having an adhesive layer formed from the adhesive composition according to any one of claims 1 to 5.