Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

Abstract

To provide an adhesive composition which enables formation of an adhesive layer that is environment-friendly and is excellent in re-peelable property and re-sticking property, and an adhesive sheet having an adhesive layer formed from the adhesive composition.SOLUTION: There are provided an adhesive composition which contains (meth)acrylic resin particles (A) having a glass transition temperature of 0°C or lower and an average particle diameter of 1-80 μm, (meth)acrylic resin particles (B) having an average particle diameter of 50-900 nm, tackifier resin particles (C) having a biomass degree of 45% or more, a substance (D) having an average diameter smaller than the average particle diameter of the (meth)acrylic resin particles (B) and a probe tackiness value of a film surface when the film is formed of 0.40 N / cm2 or less, and water, wherein the content of the tackifier resin particles (C) is 50-150 pts.mass with respect to 100 pts.mass of the (meth)acrylic resin particles (A); and an adhesive sheet.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. [Background technology]

[0002] As interest in environmental issues such as global warming grows, there is a strong social demand, particularly for chemical manufacturers, to use materials derived from plants and other living organisms instead of conventional petroleum-derived materials.In the field of adhesives, too, the development of products using 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 use a high proportion of biomass raw materials, so-called high biomass content.

[0003] For example, Patent Document 1 discloses an adhesive tape that contains 50 to 150 parts by mass of a tackifier resin relative to 100 parts by mass of adhesive resin solid content, has an adhesive layer that exhibits a peak loss tangent (tanδ) at a frequency of 1 Hz at a temperature of -10°C to 50°C, and has a biomass degree of 45% or more. The adhesive tape disclosed in Patent Document 1 uses a large amount of tackifier resin, thereby increasing the biomass degree while ensuring the performance of the adhesive tape. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-041023 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, from the perspective 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, the adhesive resins used in water-based pressure-sensitive adhesives have lower compatibility with tackifier resins than the adhesive resins used in solvent-based pressure-sensitive adhesives, and therefore the tackifier resin is likely to be unevenly distributed in a pressure-sensitive adhesive layer formed from the water-based pressure-sensitive adhesive. For this reason, if a large amount of tackifier resin is used in a water-based pressure-sensitive adhesive to increase the biomass content, as in the solvent-based pressure-sensitive adhesive described in Patent Document 1, the uneven distribution of the tackifier resin will reduce the tackiness of the pressure-sensitive adhesive layer, resulting in extremely low initial adhesive strength when attached to an adherend, and possibly impairing the function of the pressure-sensitive adhesive.

[0006] Incidentally, aqueous adhesives are sometimes used for removable labels. The adhesives used for removable labels are required to be capable of forming an adhesive layer that can be easily removed from an adherend and that is unlikely to leave adhesive residue on the surface of the adherend, i.e., an adhesive layer with excellent removability. However, when a tackifier resin is used in an aqueous adhesive, the adhesive strength of the adhesive layer increases over time after application to an adherend, which may result in a loss of the removability required for a removable label. Furthermore, since removable labels may be reapplied after being removed, the adhesives used for removable labels are required to be capable of forming an adhesive layer that is difficult to remove from an adherend when reapplied, i.e., an adhesive layer with excellent reappliability. However, if a large amount of tackifier resin is used in an aqueous adhesive, as mentioned above, the uneven distribution of the tackifier resin reduces the tackiness of the adhesive layer, thereby reducing the adhesive strength and making reapplication difficult.

[0007] 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 has excellent removability and repositionability. Another 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 removability and repositionability. [Means for solving the problem]

[0008] Specific means for solving the problems include the following aspects. <1> (Meth)acrylic resin particles (A) having 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) having an average particle size of 50 nm to 900 nm, tackifying resin particles (C) having a biomass degree of 45% or higher, and a tackifying resin particle (D) having an average particle size smaller than the average particle size of the (meth)acrylic resin particles (B) and having a probe tack value of 0.40 N / cm on the film surface when the film is formed. 2 A pressure-sensitive adhesive composition comprising the following substance (D) and water, wherein the content of the tackifier resin particles (C) is 50 to 150 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A): <2> 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). <1> The pressure-sensitive adhesive composition according to claim 1. <3> The (meth)acrylic resin particles (B) have a glass transition temperature of 0°C or lower. <1> or <2> The pressure-sensitive adhesive composition according to claim 1. <4> The tackifier resin particles (C) are particles of at least one resin selected from the group consisting of rosin-based resins and terpene-based resins. <1> ~ <3> The pressure-sensitive adhesive composition according to any one of the above. <5> The average particle diameter of the tackifier resin particles (C) is 100 nm to 500 nm. <1> ~ <4> The pressure-sensitive adhesive composition according to any one of the above. <6> The average particle size of the substance (D) is smaller than the average particle size of the tackifier resin particles (C). <1> ~ <5> The pressure-sensitive adhesive composition according to any one of the above. <7> The substance (D) is at least one selected from the group consisting of silica, titanium oxide, cellulose fiber, chitin fiber, and chitosan fiber. <1> ~ <6> The pressure-sensitive adhesive composition according to any one of the above. <8> The content of the substance (D) is 3 to 30 parts by mass relative to 100 parts by mass of the (meth)acrylic resin particles (A). <1> ~ <7> The pressure-sensitive adhesive composition according to any one of the above. <9> <1> ~ <8> 1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above items. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition that is environmentally friendly and capable of forming a pressure-sensitive adhesive layer that has excellent removability and repositionability. According to another embodiment of the present disclosure, there is provided a pressure-sensitive adhesive sheet that is environmentally friendly and includes a pressure-sensitive adhesive layer that has excellent removability and repositionability. DETAILED DESCRIPTION OF THE INVENTION

[0010] The pressure-sensitive adhesive composition and pressure-sensitive 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 implemented with appropriate modifications within the scope of the object of the present disclosure.

[0011] 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 stages 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 stages. Furthermore, 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.

[0012] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0013] In the present disclosure, when the PSA composition contains a plurality of substances corresponding to each component, the amount of each component in the PSA composition means the total amount of the plurality of substances present in the PSA composition, unless otherwise specified.

[0014] In the present disclosure, "(meth)acrylic resin" means a resin in which the content of structural units derived from monomers having a (meth)acryloyl group is 50 mass% or more relative to all structural units (i.e., all structural units of the resin).

[0015] In the present 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."

[0016] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0017] In the present disclosure, the terms "adhesive" and "adhesive composition" have the same meaning.

[0018] [Adhesive composition] The pressure-sensitive adhesive composition according to the present disclosure comprises (meth)acrylic resin particles (A) having 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) having an average particle size of 50 nm to 900 nm, tackifying resin particles (C) having a biomass degree of 45% or higher, and a tackifying resin particle (D) having an average particle size smaller than the average particle size of the (meth)acrylic resin particles (B) and having a probe tack value of 0.40 N / cm on the surface of the film formed therefrom. 2 The composition contains the following substance (D) and water, and the content of the tackifier resin particles (C) is 50 to 150 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 removability and repositionability. The reason why the PSA 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 PSA composition according to the present disclosure, but is merely an example.

[0019] 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 comprises (meth)acrylic resin particles (A) having a glass transition temperature of 0°C or lower 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 a pressure-sensitive adhesive layer formed from such a pressure-sensitive adhesive composition (the so-called interface with an adherend; the same applies hereinafter) is thought to have an uneven shape formed by the large-particle-size (meth)acrylic resin particles (A) and the small-particle-size (meth)acrylic resin particles (B). Therefore, when a pressure-sensitive adhesive layer formed from 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 protrusions formed by the large-particle-size (meth)acrylic resin particles (A) adhere to the adherend, and the pressure-sensitive adhesive layer is thought to exhibit excellent removability. The PSA composition according to the present disclosure contains a relatively high ratio of tackifier resin particles (C) relative to the (meth)acrylic resin particles (A). If a large amount of tackifier resin particles (C) that are not compatible with the (meth)acrylic resin particles (A) is contained, the tackifier resin particles (C) will be unevenly distributed on the surface of the PSA layer formed, which is thought to reduce the tackiness of the PSA layer and thus reduce adhesive strength. However, as described above, the surface of the PSA layer formed from the PSA composition according to the present disclosure has an uneven shape formed by the (meth)acrylic resin particles (A) and the (meth)acrylic resin particles (B). Furthermore, the content ratio of tackifier resin particles (C) relative to the (meth)acrylic resin particles (A) is not excessively high. Therefore, it is thought that uneven distribution of tackifier resin particles (C) occurs in the recesses of the PSA layer surface, which has an uneven shape, and is less likely to occur in the protrusions that bond to the adherend. Therefore, a decrease in adhesive strength due to uneven distribution of tackifier resin particles (C) is suppressed. Furthermore, since the glass transition temperature of the (meth)acrylic resin particles (A) is 0°C or lower, the pressure-sensitive adhesive layer formed has a small adhesive surface area with the adherend, but still has a moderate adhesive strength to the adherend, which is thought to result in the pressure-sensitive adhesive layer exhibiting excellent repositionability. The unevenness of the surface of the pressure-sensitive adhesive layer tends to collapse over time as it is attached to an adherend. When the unevenness of the surface of the pressure-sensitive adhesive layer collapses, the adhesion area of ​​the protruding portions formed by the (meth)acrylic resin particles (A) to the adherend increases, and an adhesion surface with the portions that previously formed the recesses is created. The portions that previously formed the recesses contain the (meth)acrylic resin particles (B) and tackifier resin particles (C), which is thought to result in high adhesive strength to the adherend. However, in addition to the (meth)acrylic resin particles (B) and tackifier resin particles (C), the portions that previously formed the recesses also contain a non- or low-adhesion substance (D) that has an average diameter smaller than the average particle diameter of the (meth)acrylic resin particles (B) and is more likely to appear on the surface of the pressure-sensitive adhesive layer than the (meth)acrylic resin particles (B). The presence of this substance (D) creates portions that exhibit non- or low-adhesion on the surface that contacts the adherend. This prevents excessive increases in the adhesive strength of the pressure-sensitive adhesive layer over time. This is also thought to be one of the reasons why a pressure-sensitive adhesive layer exhibiting excellent removability can be formed. 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 has excellent removability and repositionability.

[0020] Hereinafter, "(meth)acrylic resin particles (A) having a glass transition temperature of 0°C or lower and 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)", "tackifier resin particles (C) having a biomass degree of 45% or more" will also be referred to as "specific tackifier resin particles (C)", and "a film having a probe tack value of 0.40 N / cm on the film surface when formed" will also be referred to as "specific (meth)acrylic resin particles (A)". 2 The following substance (D) is also referred to as "specific substance (D)".

[0021] [Specific (meth)acrylic resin particles (A)] The pressure-sensitive adhesive composition according to the present disclosure contains (meth)acrylic resin particles (A) having a glass transition temperature of 0°C or lower and an average particle size of 1 μm to 80 μm [i.e., specific (meth)acrylic resin particles (A)]. The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of specific (meth)acrylic resin particles (A), or may contain two or more types.

[0022] -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 -10°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower, and particularly 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.

[0023] The glass transition temperature of the specific (meth)acrylic resin particles (A) is a value obtained by converting the absolute temperature (unit: K) calculated from the following formula 1 into Celsius temperature (unit: ° C.). 1 / Tg=m1 / Tg1+m2 / Tg2+ +m(k-1) / Tg(k-1)+mk / Tgk (Formula 1)

[0024] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk respectively represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic resin particles (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 particles (A), and the equation is m1 + m2 + . . . + m(k-1) + mk = 1. Note that absolute temperatures can be converted to Celsius degrees by subtracting 273 from the absolute temperature, and Celsius degrees can be converted to absolute temperatures by adding 273 to the Celsius degrees.

[0025] In the present disclosure, the "glass transition temperature when converted into a homopolymer" refers to a value disclosed in a publicly known document or a value measured using a differential scanning calorimeter (DSC). The specific value to be used is as follows:

[0026] The "glass transition temperature when made into a homopolymer" of the following monomers is determined by the value shown below. 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-hydroxybutyl 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.

[0027] Regarding the "glass transition temperature when made into a homopolymer" of a monomer other than the above-mentioned monomers, the value described in the Polymer Handbook (4th edition, Wiley-Interscience; the same applies hereinafter) is adopted. If there is no description in the Polymer Handbook, the value of the glass transition temperature of the homopolymer obtained by the following measurement method is adopted.

[0028] <<Measurement of the glass transition temperature of homopolymers>> Measurement is performed using a differential scanning calorimeter (DSC) in a nitrogen gas flow with 10 mg of a measurement sample (i.e., homopolymer) at a heating rate of 10°C / min, and the inflection point of the obtained DSC curve is taken as the glass transition temperature of the homopolymer. As a differential scanning calorimeter, for example, a differential scanning calorimeter (trade 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.

[0029] The glass transition temperature of the specific (meth)acrylic resin particles (A) can be appropriately adjusted, for example, by using two or more kinds of monomers that have different glass transition temperatures when made into homopolymers.

[0030] -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 spherical shape but also an approximately spherical shape.

[0031] -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. 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 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.

[0032] The average particle size of the specific (meth)acrylic resin particles (A) can be adjusted, for example, by changing the stirring speed during production of 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) decreases as the stirring speed increases, and increases as the stirring speed decreases.

[0033] 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 analyzer. In the present disclosure, "particle size distribution" is also referred to as "particle size distribution." The specific (meth)acrylic resin particles (A) are diluted with distilled water and thoroughly stirred. Then, the solution is placed in a 10 mm x 75 mm x 85 mm glass cell using a Pasteur pipette and placed in a laser diffraction particle size distribution analyzer. 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 at a measurement temperature of 25°C. The measurement results are processed by computer to determine 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 defined as the volume-average particle size. As the laser diffraction particle size distribution measuring device, for example, the "Laser Scattering Particle Size Distribution Analyzer LA-960" manufactured by Horiba, Ltd. can be suitably used. However, the laser diffraction particle size distribution measuring device is not limited to this.

[0034] The structural units that the specific (meth)acrylic resin particles (A) may contain will be described below.

[0035] <Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The specific (meth)acrylic resin particles (A) preferably contain structural units derived from a (meth)acrylic acid alkyl ester monomer. In the present disclosure, the term "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 term "(meth)acrylic acid alkyl ester monomer" in the present disclosure does not include monomers that fall under the category of monomers having a carboxy group, which will be described later.

[0036] The type of (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 of the (meth)acrylic acid alkyl ester monomer preferably has 1 to 18 carbon atoms, and more preferably 1 to 12 carbon atoms, for example.

[0037] 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 2-ethylhexyl acrylate, n-octyl acrylate, and methyl methacrylate.

[0038] When the specific (meth)acrylic resin particles (A) contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer, they may contain only one type of structural unit derived from a (meth)acrylic acid alkyl ester monomer, or may contain two or more types of structural units derived from a (meth)acrylic acid alkyl ester monomer.

[0039] When the specific (meth)acrylic resin particles (A) contain structural units derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A) is not particularly limited, but is, for example, preferably 50% by mass to 99.95% by mass, more preferably 70% by mass to 99.9% by mass, and even more preferably 90% by mass to 99.7% by mass, relative to the total structural units of the specific (meth)acrylic resin particles (A). Here, the content of structural units derived from (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic resin particles (A) being 50 mass% or more relative to the total structural units of the specific (meth)acrylic resin particles (A) means that structural units derived from (meth)acrylic acid alkyl ester monomers are contained as the main component of the structural units constituting the specific (meth)acrylic resin particles (A).

[0040] <Structural Units Derived from Monomers Having a Carboxy Group> The specific (meth)acrylic resin particles (A) may contain a structural unit derived from a monomer 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.

[0041] In the present disclosure, the term "structural unit derived from a monomer having a carboxy group" refers to a structural unit formed by addition polymerization of a monomer having a carboxy group.

[0042] The type of the monomer having a carboxy group is not particularly limited. Examples of the monomer having a carboxy group include 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.

[0043] Specific examples of the monomer 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 preferred, and acrylic acid is more preferred.

[0044] When the specific (meth)acrylic resin particles (A) contain a structural unit derived from a monomer having a carboxy group, they 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.

[0045] When the specific (meth)acrylic resin particles (A) 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 (A) is not particularly limited, but is, for example, 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 0.3% by mass to 1.0% by mass, relative to the total structural units of the specific (meth)acrylic resin particles (A).

[0046] <Other structural units> Other structural units that the specific (meth)acrylic resin particles (A) may contain 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; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0047] When the specific (meth)acrylic resin particles (A) contain other structural units, they may contain only one type of other structural unit, or may contain two or more types of other structural units.

[0048] When the specific (meth)acrylic resin particles (A) contain other structural units, the content of the other structural units in the specific (meth)acrylic resin particles (A) can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition according to the present disclosure.

[0049] <<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 30% by mass to 66.6% by mass, more preferably 35% by mass to 66.6% by mass, and even more preferably 40% by mass to 66.6% by mass, relative to the total solid content in the pressure-sensitive adhesive composition.

[0050] In the present disclosure, the "total solid content in the PSA composition" refers to the mass of the residue remaining after removing the solvent from the PSA composition. In the present disclosure, the "solvent" refers to water and organic solvents.

[0051] [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 it is possible to produce the above-described specific (meth)acrylic resin particles (A). As a method for producing the specific (meth)acrylic resin particles (A), suspension polymerization is preferred from the viewpoint of ease of producing the specific (meth)acrylic resin particles (A).

[0052] As the suspension polymerization method for producing the specific (meth)acrylic resin particles (A), for example, the following method is suitable. Water, surfactants, and optional suspension stabilizers are charged into a reactor equipped with a thermometer, a stirrer, raw material inlet pipes, a reflux condenser, a nitrogen inlet pipe, etc., and thoroughly mixed and stirred to dissolve. A mixed solution containing monomer components and a polymerization initiator is added to the reactor, and after stirring at a predetermined stirring speed for a certain period of time, water is added. After replacing the atmosphere in the reactor with nitrogen, the temperature is raised to initiate the polymerization reaction, which is then carried out for a predetermined period of time.

[0053] The surfactant is not particularly limited, but is preferably an anionic surfactant and / or a nonionic surfactant, and more preferably an anionic surfactant.

[0054] Examples of anionic surfactants include polyoxyalkylene styrenated diphenyl ether sulfates, such as polyoxyethylene styrenated diphenyl ether ammonium sulfate; polyoxyalkylene alkyl phenyl ether sulfates, such as polyoxyethylene nonylphenyl ether sodium sulfate; polyoxyalkylene alkyl ether sulfates; and alkyl phosphate esters. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers such as polyoxyethylene oleyl ether and polyoxyethylene lauryl ether, and polyoxyalkylene styrenated phenyl ethers such as polyoxyethylene styrenated phenyl ether.

[0055] In the suspension polymerization method, only one type of surfactant may be used, or two or more types may be used.

[0056] 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 of the monomers.

[0057] A suspension stabilizer is used as needed. 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.

[0058] 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 of suspension stabilizers may be used.

[0059] 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 amount of the monomers.

[0060] 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.

[0061] In the suspension polymerization method, only one type of polymerization initiator may be used, or two or more types may be used.

[0062] The amount of the polymerization initiator used is not particularly limited, but is preferably 0.1 to 3 parts by mass, for example, per 100 parts by mass of the total of the monomers.

[0063] The polymerization temperature is, for example, 50 to 90°C, and preferably 60 to 80°C. The polymerization time is, for example, 1 hour to 5 hours, and preferably 2 hours to 4 hours.

[0064] 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, aqueous ammonia can be suitably used.

[0065] 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. The measuring device may be, for example, a pH meter (product name: F-51) manufactured by Horiba, Ltd. However, the measuring device is not limited to this.

[0066] [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 [ie, specific (meth)acrylic resin particles (B)]. The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of specific (meth)acrylic resin particles (B), or may contain two or more types.

[0067] -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 diameter 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 diameter 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.

[0068] The average particle size of the specific (meth)acrylic resin particles (B) can be adjusted, for example, by adjusting the amount of surfactant used in producing the specific (meth)acrylic resin particles (B). The particle size of the specific (meth)acrylic resin particles (B) decreases when the amount of surfactant used increases, and increases when the amount of surfactant used decreases.

[0069] 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 using a particle size distribution measuring device by the dynamic light scattering method described in "New Experimental Chemistry Lectures 4, Basic Technology 3, Light (II)" edited by the Chemical Society of Japan, pp. 725-741 (published by Maruzen Co., Ltd. on July 20, 1976). The specific method is described below. The specific (meth)acrylic resin particles (B) are diluted with distilled water and thoroughly mixed. 5 mL of the solution is then collected using a Pasteur pipette in a 10 mm square glass cell and placed in a particle size distribution analyzer. The attenuation factor (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 factor is 150 kCps to 200 kCps. The particle size distribution of the specific (meth)acrylic resin particles (B) is measured at 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 50% of the cumulative value (volume basis) in the obtained particle size distribution is defined 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, but the particle size distribution measuring device is not limited to this.

[0070] -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.

[0071] -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 preferably, for example, 5°C or lower, more preferably 0°C or lower, even more preferably -10°C or lower, even 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.

[0072] The glass transition temperature of the specific (meth)acrylic resin particles (B) is determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic resin particles (A) described above.

[0073] The glass transition temperature of the specific (meth)acrylic resin particles (B) can be appropriately adjusted, for example, by using two or more types of monomers that have different glass transition temperatures when made into homopolymers.

[0074] The structural units that the specific (meth)acrylic resin particles (B) may contain will be described below.

[0075] <Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The specific (meth)acrylic resin particles (B) preferably contain structural units derived from a (meth)acrylic acid alkyl ester monomer. In the present disclosure, the term "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.

[0076] The type of (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 of the (meth)acrylic acid alkyl ester monomer preferably has 1 to 18 carbon atoms, and more preferably 1 to 12 carbon atoms, for example.

[0077] Specific examples of the (meth)acrylic acid alkyl ester monomer are the same as the specific examples of the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A). 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.

[0078] When the specific (meth)acrylic resin particles (B) contain a structural unit derived from a (meth)acrylic acid alkyl ester monomer, they may contain only one type of structural unit derived from a (meth)acrylic acid alkyl ester monomer, or may contain two or more types of structural units derived from a (meth)acrylic acid alkyl ester monomer.

[0079] When the specific (meth)acrylic resin particles (B) contain structural units derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural 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 the total structural units of the specific (meth)acrylic resin particles (B). Here, the content of structural units derived from (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic resin particles (B) being 50 mass% or more relative to the total structural units of the specific (meth)acrylic resin particles (B) means that structural units derived from (meth)acrylic acid alkyl ester monomers are contained as the main component of the structural units constituting the specific (meth)acrylic resin particles (B).

[0080] <Structural Units Derived from Monomers 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. Examples of the monomer having a carboxy group include 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.

[0081] 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 preferred, and acrylic acid is more preferred.

[0082] When the specific (meth)acrylic resin particles (B) contain a structural unit derived from a monomer having a carboxy group, they 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.

[0083] 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, for example, 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).

[0084] <Other structural units> Other structural units that the specific (meth)acrylic resin particles (B) may contain 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; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0085] When the specific (meth)acrylic resin particles (B) contain other structural units, they may contain only one type of other structural unit, or may contain two or more types of other structural units.

[0086] When the specific (meth)acrylic resin particles (B) contain other structural units, the content of the other structural units 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.

[0087] <<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 is, for example, preferably 2 to 110 parts by mass, more preferably 5 to 100 parts by mass, even more preferably 10 to 80 parts by mass, and particularly preferably 15 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 re-applicability. 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.

[0088] [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 it is possible to produce the above-described specific (meth)acrylic resin particles (B). As a method for producing the specific (meth)acrylic resin particles (B), for example, an emulsion polymerization method is preferred from the viewpoint that the specific (meth)acrylic resin particles (B) can be easily produced.

[0089] Examples of emulsion polymerization methods 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, etc., and the temperature is raised while stirring under a nitrogen stream, and then a polymerization initiator, a reducing agent, etc. are added as appropriate to allow the emulsion polymerization reaction to proceed (the so-called bulk 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 the monomer components are added dropwise, and a polymerization initiator, a reducing agent, etc. are added as appropriate, to allow the emulsion polymerization reaction to proceed (the so-called monomer dropping method). (3) A reactor equipped with a thermometer, a stirrer, a raw material inlet pipe, a reflux condenser, a nitrogen inlet pipe, etc. is charged with water, 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 added dropwise to the reactor, and a polymerization initiator, a reducing agent, etc. are added as appropriate to allow the emulsion polymerization reaction to proceed (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 (3) emulsion monomer dropping method, from the viewpoint of industrial productivity, for example.

[0090] The surfactant is not particularly limited, but is preferably, for example, an anionic surfactant and / or a nonionic surfactant.

[0091] Specific examples of the anionic surfactant are the same as those described in the suspension polymerization method, and specific examples of the nonionic surfactant are the same as those described in the suspension polymerization method.

[0092] In the emulsion polymerization method, only one type of surfactant may be used, or two or more types may be used.

[0093] 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 amount of monomers.

[0094] 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.

[0095] In the emulsion polymerization method, one type of polymerization initiator may be used alone, or two or more types may be used.

[0096] The amount of the polymerization initiator used is not particularly limited, but is preferably 0.5 to 10 parts by mass, for example, relative to 100 parts by mass of the total of the monomers.

[0097] 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.

[0098] In the emulsion polymerization method, only one type of reducing agent may be used, or two or more types may be used.

[0099] The amount of the 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 of the monomers, for example.

[0100] The polymerization temperature is, for example, 50 to 90°C, and preferably 60 to 80°C. The polymerization time is, for example, 1 hour to 5 hours, and preferably 2 hours to 4 hours.

[0101] 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, aqueous ammonia can be suitably used.

[0102] 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. The measuring device may be, for example, a pH meter (product name: F-51) manufactured by Horiba, Ltd. However, the measuring device is not limited to this.

[0103] [Specific tackifying resin particles (C)] The pressure-sensitive adhesive composition according to the present disclosure contains 50 to 150 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 form an environmentally friendly pressure-sensitive adhesive layer.

[0104] In the present disclosure, the term "tackifying resin" refers to a resin other than a (meth)acrylic resin that has the property of being able to impart tackiness when blended and has a molecular weight of less than 10,000 (preferably in the range of 500 or more but less than 10,000). Also, "tackiness" refers to a sticky property. Tackifying resins are also called tackifiers.

[0105] The molecular weight of the specific tackifying resin particles (C) is a value measured by gel permeation chromatography (GPC). Specifically, the weight average molecular weight of the specific tackifying resin particles (C) is determined as a standard polystyrene equivalent value by GPC under the following conditions.

[0106] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8220 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8220, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Four Tosoh Corporation products are used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0107] 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) is the value in the catalog of the commercially available product.

[0108] From the viewpoint of forming an environmentally friendly pressure-sensitive adhesive layer, the biomass degree of the specific tackifying 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%.

[0109] The biomass content of the specific tackifying 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 tackifying resin particles (C). However, when a commercially available product is used as the specific tackifying resin particles (C) and the biomass degree is listed in the catalog of the commercially available product, the value in the catalog of the commercially available product shall be used as the biomass degree of the specific tackifying resin particles (C).

[0110] At least a part of the raw materials of the specific tackifying resin particles (C) is preferably plant-derived components. 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 tackifying resin particles (C) are preferably particles of at least one resin selected from the group consisting of rosin-based resins and terpene-based resins.

[0111] 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 preferred.

[0112] Specific examples of terpene resins include polyterpenes, which are homopolymers of terpene, terpene phenol resins, aromatic modified terpene resins, and hydrogenated terpene resins. The terpene resin is preferably an aromatic modified terpene resin.

[0113] The softening point of the specific tackifying resin particles (C) is not particularly limited, but is preferably, for example, 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 tackifying resin particles (C) is 30° C. or higher, the removability of the pressure-sensitive adhesive layer formed tends to be improved regardless of the material of the adherend. When the softening point of the specific tackifying resin particles (C) is 160° C. or lower, commercial products are readily available.

[0114] The softening point of the specific tackifying 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.

[0115] The shape of the specific tackifying resin particles (C) is not particularly limited, but is preferably spherical.

[0116] The average particle size of the specific tackifying resin particles (C) is not particularly limited, but is preferably from 100 nm to 600 nm, more preferably from 100 nm to 500 nm, and even more preferably from 200 nm to 500 nm. When the average particle size of the specific tackifying resin particles (C) is 100 nm or more, it is easy to obtain a commercially available product. When the average particle size of the specific tackifying resin particles (C) is 600 nm or less, the adhesive strength of the pressure-sensitive adhesive layer formed tends to be more appropriate.

[0117] The average particle size of the specific tackifying resin particles (C) means the volume average particle size. The average particle size of the specific tackifying 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).

[0118] As the specific tackifying resin particles (C), commercially available products can be used. Examples of commercially available specific tackifying resin particles (C) include "Superester E-900-NT," "Superester E-788," and "Superester E-865-WR" manufactured by Arakawa Chemical Industries, Ltd., "Hariestar SK-130D" manufactured by Harima Chemicals Co., Ltd., and "Nanolet (registered trademark) T1050" manufactured by Yasuhara Chemical Co., Ltd.

[0119] The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of specific tackifying resin particles (C), or may contain two or more types.

[0120] The content of the specific tackifying resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 50 to 150 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 50 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 50 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic resin particles (A), preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 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 150 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 excellent repositionability. From this viewpoint, the content of the specific tackifier resin particles (C) in the pressure-sensitive adhesive composition according to the present disclosure is 150 parts by mass or less per 100 parts by mass of the specific (meth)acrylic resin particles (A), preferably 140 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less.

[0121] [Specified substance (D)] The pressure-sensitive adhesive composition according to the present disclosure has a probe tack value of 0.40 N / cm on the film surface when the film is formed. 2 The specific substance (D) has an average particle size smaller than the average particle size of the specific (meth)acrylic resin particles (B).

[0122] When a film is formed, the probe tack value of the film surface of specific substance (D) is 0.40 N / cm 2 These are so-called non-tacky or low-tacky substances. When a film of the specific substance (D) is formed, the probe tack value of the film surface is, for example, 0.20 N / cm 2 It may be less than 0.10 N / cm 2 It may be less than 0.05N / cm 2 It may be less than 0 N / cm 2 may be.

[0123] The probe tack value of the film surface when a film of the specific substance (D) is formed is a value measured by the following method. An aqueous dispersion of specific substance (D) (solid content: 2% by mass) is applied to paper using an applicator so that the film thickness after drying is 20 μm, and then dried using a hot air circulation dryer at a drying temperature of 105°C for 40 seconds to form a film on the paper surface. The probe tack value of the surface of the formed film is measured using a tack tester under the following measurement conditions. Examples of paper include fine paper. <70> can be preferably used. However, the paper is not limited to this. Furthermore, as a tack tester, for example, a tack tester manufactured by Rhesca Corporation (trade name: TAC1000) can be preferably used. However, the tack tester is not limited to this.

[0124] -Measurement conditions- Pressing speed: 5mm / sec Pressing load: 2N Hold time: 1 second Pulling speed: 10 mm / sec

[0125] The shape of the specific substance (D) is not particularly limited, and examples thereof include spherical, rod-like, plate-like, irregular, and fibrous shapes.

[0126] The average particle size of the specific substance (D) is smaller than the average particle size of the specific (meth)acrylic resin particles (B). When the average particle size of the specific substance (D) is smaller than the average particle size of the specific (meth)acrylic resin particles (B), the pressure-sensitive adhesive layer formed tends to have excellent removability.

[0127] The average particle size of the specific substance (D) is preferably smaller than that of the specific tackifying resin particles (C). When the average particle size of the specific substance (D) is smaller than that of the specific tackifying resin particles (C), the resulting pressure-sensitive adhesive layer tends to have better repositionability.

[0128] The average diameter of the specific substance (D) is not particularly limited as long as it is smaller than the average particle diameter of the specific (meth)acrylic resin particles (B), but for example, it is preferably 5 nm to 500 nm, more preferably 5 nm to 200 nm, even more preferably 5 nm to 100 nm, and particularly preferably 5 nm to 50 nm.

[0129] The average diameter of the specific substance (D), for example, when the specific substance (D) is spherical, means the volume-average particle diameter measured using a particle size distribution analyzer by the dynamic light scattering method described in "New Experimental Chemistry Lectures 4, Basic Technology 3, Light (II)" edited by the Chemical Society of Japan, pp. 725-741 (published by Maruzen Co., Ltd. on July 20, 1976). A specific method is shown below. The specific substance (D) is diluted with distilled water and thoroughly stirred and mixed. 5 mL is then collected using a Pasteur pipette into a 10 mm square glass cell, which is then placed in a particle size distribution analyzer. The attenuation factor (Attenuator) is set to x8 (8 times), and the concentration of the diluted solution of the specific substance (D) is adjusted so that the count rate of the attenuation factor is 150 kCps to 200 kCps. The particle size distribution of the specific substance (D) is then measured at a measurement temperature of 25°C and a light scattering angle of 90°. The measurement results are processed by computer to determine the average diameter of the specific substance (D). Specifically, the particle diameter at 50% of the cumulative value (volume basis) in the obtained particle size distribution (the so-called volume-average particle diameter) is taken as the average diameter. As a particle size distribution measuring device, for example, "Zetasizer Nano ZS-90" manufactured by Malvern can be suitably used, but the particle size distribution measuring device is not limited to this.

[0130] Furthermore, the average diameter of the specific substance (D) means, for example, the average fiber diameter measured by the following method when the specific substance (D) is in the form of fibers. The specific substance (D) is observed using a scanning electron microscope (SEM) at a magnification of 3000x to 30000x, and the diameters of 100 randomly selected points are measured from the observed image containing multiple specific substances (D), and the arithmetic mean value of the obtained values ​​is taken as the average fiber diameter. As a scanning electron microscope (SEM), for example, "Regulus8100" manufactured by Hitachi, Ltd. can be suitably used. However, the scanning electron microscope (SEM) is not limited to this.

[0131] The ratio (d / b) of the average diameter d of the specific substance (D) to the average particle diameter b of the specific (meth)acrylic resin particles (B) is not particularly limited as long as it is less than 1, but is preferably, for example, 0.01 to 0.9, more preferably 0.01 to 0.7, and even more preferably 0.01 to 0.5.

[0132] The specific substance (D) is preferably a water-insoluble or poorly water-soluble substance. In this disclosure, the term "water-insoluble substance" refers to a substance whose solubility in water at 25°C is 0 g / 100 mL. In addition, in this disclosure, the term "poorly water-soluble substance" refers to a substance whose solubility in water at 25°C is greater than 0 g / 100 mL and 0.1 g / 100 mL or less.

[0133] When a film is formed, the probe tack value of the film surface of specific substance (D) is 0.40 N / cm 2 There are no particular limitations on the substance as long as it satisfies the following conditions: Specific examples of the specific substance (D) include silica, titanium oxide, cellulose fiber, chitin fiber, chitosan fiber, carbon fiber, lime, and wood flour. The specific substance (D) is preferably at least one selected from the group consisting of silica, titanium oxide, cellulose fiber, chitin fiber, and chitosan fiber.

[0134] As the specific substance (D), a commercially available product can be used. Commercially available examples of aqueous dispersions of silica particles, which are specific substance (D), include "Snowtex (registered trademark) 50-T," "MP-1040," and "MP-4540M" manufactured by Nissan Chemical Industries, Ltd. Commercially available examples of aqueous dispersions of titanium oxide, which are specific substance (D), include "DIS-AB-10W" manufactured by Sakai Chemical Industry Co., Ltd. Commercially available examples of aqueous dispersions of cellulose fiber, which are specific substance (D), include "ELLEX-S" manufactured by Daio Paper Corporation Commercially available examples of aqueous dispersions of chitin fiber, which are specific substance (D), include "Sfo-200" manufactured by Sugino Machine Co., Ltd. Commercially available examples of aqueous dispersions of chitosan fiber, which are specific substance (D), include "Efo-080" manufactured by Sugino Machine Co., Ltd.

[0135] The pressure-sensitive adhesive composition according to the present disclosure may contain only one type of specific substance (D) having an average particle size smaller than the average particle size of the specific (meth)acrylic resin particles (B), or may contain two or more types of specific substance (D).

[0136] In the pressure-sensitive adhesive composition according to the present disclosure, the content of the specific substance (D) having an average diameter smaller than the average particle diameter of the specific (meth)acrylic resin particles (B) is not particularly limited, but is, for example, preferably 1 to 35 parts by mass, more preferably 3 to 30 parts by mass, even more preferably 5 to 25 parts by mass, and particularly preferably 7 to 20 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic resin particles (A). In the pressure-sensitive adhesive composition according to the present disclosure, when the content of the specific substance (D) having an average diameter smaller than the average particle diameter of the specific (meth)acrylic resin particles (B) is 1 part 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 removability. In the pressure-sensitive adhesive composition according to the present disclosure, when the content of the specific substance (D) having an average diameter smaller than the average particle diameter of the specific (meth)acrylic resin particles (B) is 35 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 repositionability.

[0137] 〔water〕 The pressure-sensitive adhesive composition according to the present disclosure contains water. The water is not particularly limited, but distilled water, ion-exchanged water, pure water, etc. are preferred from the viewpoint of having fewer impurities.

[0138] The water content in the pressure-sensitive adhesive composition according to the present disclosure is not particularly limited, but is preferably 40% by mass to 80% by mass, and more preferably 50% by mass to 70% by mass, relative to the total mass of the pressure-sensitive adhesive composition.

[0139] [Aqueous media other than water] The PSA 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.

[0140] When the PSA 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.

[0141] 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.

[0142] [Water-immiscible organic solvent] From the viewpoint of environmental consideration, for example, the PSA 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 PSA 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 PSA 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 PSA 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 PSA composition.

[0143] 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.

[0144] [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 needed, within the range that does not impair the effects of the 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), tackifying resin particles other than the specific tackifying resin particles (C), and various additives such as antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0145] [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 removability and repositionability.

[0146] The thickness of the pressure-sensitive adhesive layer included 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 1 μm to 300 μm, preferably 5 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0147] In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" refers to 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 adhesive layer is measured at 10 randomly selected locations in the thickness direction using a film thickness meter. The arithmetic mean of the measured values ​​is calculated and this value is taken as the average thickness of the substrate.

[0148] The pressure-sensitive adhesive sheet according to the present disclosure may be a substrate-less type pressure-sensitive adhesive sheet that does not have a substrate, or may be a substrate-containing type 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 it 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. Generally, 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.

[0149] The release sheet is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer. Examples of release sheets include resin films, paper, synthetic paper, and composite sheets made 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 treatment agent (so-called easy-release treatment) is also referred to as a "release film." Examples of release agents include silicone-based release agents (e.g., silicone), wax-based release agents (e.g., paraffin wax), and fluorine-based release agents (e.g., fluorine-based resins). Examples of resin films include polyester films such as polyethylene terephthalate (PET) films. Examples of paper include fine paper and coated paper. The thickness of the release sheet is not particularly limited, and is generally 20 μm to 180 μm.

[0150] 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 formed by laminating two or more of these.

[0151] 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 easy-adhesion treatment) in order to improve the adhesion between the substrate and the adhesive layer.

[0152] 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.

[0153] 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.

[0154] In this disclosure, "thickness of the substrate" 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.

[0155] [How to make adhesive sheets] 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.

[0156] When the PSA sheet according to the present disclosure is a substrate-free PSA sheet, first, the PSA composition according to the present disclosure is applied to the easily releasable surface of a release sheet to form a coating film on the release sheet. The formed coating film is then dried to form a PSA layer on the release sheet. Next, the exposed surface of the formed PSA layer is laminated onto the easily releasable surface of a separately prepared release sheet, thereby producing a substrate-free PSA sheet having a laminate structure of release sheet / adhesive layer / release sheet.

[0157] When the PSA sheet according to the present disclosure is a substrate-type PSA sheet, first, the PSA 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 a PSA layer on the substrate. Next, the exposed surface of the formed PSA layer is laminated onto the easily peelable surface of a release sheet, thereby producing a substrate-type PSA sheet having a laminate structure of release sheet / adhesive layer / substrate.

[0158] When the pressure-sensitive adhesive sheet according to the present disclosure is a substrate-containing pressure-sensitive adhesive sheet, another method may be, for example, the following method. The pressure-sensitive 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 formed coating film is then dried to form a pressure-sensitive adhesive layer on the release sheet. The exposed surface of the formed pressure-sensitive adhesive layer is then laminated to the easy-adhesion treated surface of a substrate to produce a substrate-type pressure-sensitive adhesive sheet having a laminated structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0159] 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, etc. The amount of the pressure-sensitive adhesive composition to be applied is not particularly limited, and is set appropriately depending on, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

[0160] 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 set appropriately 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. [Example]

[0161] The pressure-sensitive adhesive composition and pressure-sensitive 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 depart from the gist of the disclosure.

[0162] [Production of (meth)acrylic resin particles (A)] [Manufacturing 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 50 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) (amount of active ingredient: 3 parts by mass), and 0.32 parts by mass of an aqueous solution (active ingredient concentration: 30% by mass) of 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, 99.3 parts by mass of 2-ethylhexyl acrylate (2EHA), 0.7 parts by mass of acrylic acid (AA), and 0.34 parts by mass of "Perbutyl PV" (trade name: t-butyl peroxypivalate (PBPV; polymerization initiator), NOF Corporation) (active ingredient concentration: 70% by mass) were added to a separate container and mixed with stirring to obtain a monomer mixture. The resulting monomer mixture was added to the aqueous solution in the reactor prepared earlier and stirred at a stirring speed of approximately 200 rpm (revolutions per minute) for 1 hour, after which 76 parts by mass of ion-exchanged water was added to the reactor. Next, the reactor was purged with nitrogen and the temperature was raised. The polymerization reaction began at 52-55°C, and the internal temperature rose rapidly to 80°C due to heat generation. The mixture was then 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 35.0% by mass and a pH of 8.3.

[0163] The "solid content concentration" herein means the mass proportion of the (meth)acrylic resin particles A-4 in the aqueous dispersion of the (meth)acrylic resin particles A-4. The same applies to each of the aqueous dispersions of the (meth)acrylic resin particles A-1 to A-3 and A-5 to A-9 produced below.

[0164] [Production Examples A-1 to A-3 and A-5] In Production Examples A-1 to A-3 and A-5, the same operations as in Production Example A-4 were carried out 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.

[0165] [Manufacturing examples A-6 to A-9] In Production Examples A-6 to A-9, the same operations as in Production Example A-4 were carried out, except that the monomer composition of the (meth)acrylic resin particles (A) was changed to the monomer composition shown in Table 1, to obtain aqueous dispersions of (meth)acrylic resin particles A-6 to A-9.

[0166] The solids concentration of each of the aqueous dispersions of the (meth)acrylic resin particles A-1 to A-3 and A-5 to A-9 obtained above is shown below.

[0167] -Solid content concentration- A-1: 20.6% by mass, A-2: 20.6% by mass, A-3: 35.0% by mass, A-5: 35.0% by mass, A-6: 35.0% by mass, A-7: 35.0% by mass, A-8: 35.0% by mass, A-9: 35.0% by mass.

[0168] The pH of each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-3 and A-5 to A-9 obtained above is shown below. The pH of each of the aqueous dispersions of (meth)acrylic resin particles A-1 to A-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 JIS Z 8802:2011.

[0169] -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-8:8.3, A-9:8.4

[0170] Table 1 shows the monomer composition (unit: mass %) of the (meth)acrylic resin particles A-1 to A-9, the glass transition temperature (Tg, unit: °C) of the (meth)acrylic resin particles A-1 to A-9, and the average particle size (volume average particle size, unit: μm) of the (meth)acrylic resin particles A-1 to A-9.

[0171] The glass transition temperatures of the (meth)acrylic resin particles A-1 to A-9 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic resin particles (A) described above.

[0172] The average particle diameters of the (meth)acrylic resin particles A-1 to A-9 were measured by the same method as the method for measuring the average particle diameter of the specific (meth)acrylic resin particles (A) described above. The measurement device used was a Laser Scattering Particle Size Distribution Analyzer LA-960 (product name), a laser diffraction particle size distribution measurement device manufactured by Horiba, Ltd.

[0173] Of the (meth)acrylic resin particles A-1 to A-9 obtained above, the (meth)acrylic resin particles A-2 to A-6, A-8, and A-9 correspond to the specific (meth)acrylic resin particles (A) of the present disclosure.

[0174] [Table 1]

[0175] Details of each monomer listed in Table 1 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)

[0176] In Table 1, "-" in the column of monomer composition means that the monomer in that column was not used.

[0177] [Production of (meth)acrylic resin particles (B)] [Manufacturing example B-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 28.8 parts by mass of ion-exchanged water, and the internal temperature was raised to 75 ° C. Meanwhile, in a separate vessel, 23.3 parts by mass of ion-exchanged water, 1.0 part by mass of the 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 the 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 stirred to obtain an aqueous solution. A monomer mixture consisting of 84.5 parts by weight of 2-ethylhexyl acrylate (2EHA), 15.0 parts by weight of methyl methacrylate (MMA), and 0.5 parts by weight of acrylic acid (AA) was added to the resulting aqueous solution and stirred to obtain a monomer premix. The contents of the reactor were then heated with stirring under a nitrogen stream. When the water temperature in the reactor reached 75°C, 0.058 parts by weight each of ammonium persulfate (APS; polymerization initiator) and sodium metabisulfite (SMBS; reducing agent) were added. Polymerization was then initiated by sequentially adding the monomer premix, 8.3 parts by weight of a 4.2% by weight APS aqueous solution, and 8.3 parts by weight of a 4.2% by weight SMBS aqueous solution. The polymerization reaction was carried out for approximately 2.5 hours. After completion of the polymerization reaction, stirring was continued for approximately 1 hour while maintaining the temperature, followed by cooling. 25% by weight aqueous ammonia was added to adjust the pH to 8-9 to obtain 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.

[0178] The "solid content concentration" herein means the mass proportion of the (meth)acrylic resin particles B-4 in the aqueous dispersion of the (meth)acrylic resin particles B-4. The same applies to each of the aqueous dispersions of the (meth)acrylic resin particles B-1 to B-3 and B-5 to B-9 produced below.

[0179] [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 operations as in Production Example B-4 were carried out except that the amount of surfactant used, etc. was appropriately changed, to obtain aqueous dispersions of (meth)acrylic resin particles B-1 to B-3, B-5 ​​and B-6.

[0180] [Manufacturing examples B-7 to B-9] In Production Examples B-7 to B-9, the same operations as in Production Example B-4 were carried out, 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.

[0181] The solids concentration of each of the aqueous dispersions of the (meth)acrylic resin particles B-1 to B-3 and B-5 to B-9 obtained above is shown below.

[0182] -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%

[0183] 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 JIS Z 8802:2011.

[0184] -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

[0185] Table 2 shows the monomer composition (unit: mass%) of the (meth)acrylic resin particles B-1 to B-9, the glass transition temperature (Tg, unit: °C) of the (meth)acrylic resin particles B-1 to B-9, and the average particle size (volume average particle size, unit: nm) of the (meth)acrylic resin particles B-1 to B-9.

[0186] The glass transition temperatures of the (meth)acrylic resin particles B-1 to B-9 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic resin particles (A) described above.

[0187] The average particle diameters of the (meth)acrylic resin particles B-1 to B-9 were measured by the same method as the method for measuring the average particle diameter of the specific (meth)acrylic resin particles (B) described above. The measurement device used was Zetasizer Nano ZS-90 (trade name), a particle size distribution measurement device manufactured by Malvern.

[0188] 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) of the present disclosure.

[0189] [Table 2]

[0190] 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)

[0191] In Table 2, "-" in the column of monomer composition means that the monomer in that column was not used.

[0192] [Preparation of Pressure-Sensitive Adhesive Composition] Example 1 The adhesive composition of Example 1 was prepared by thoroughly mixing 100 parts by mass (solids content equivalent) of the aqueous dispersion of (meth)acrylic resin particles A-2 obtained above, 20 parts by mass (solids content equivalent) of the aqueous dispersion of (meth)acrylic resin particles B-4, 100 parts by mass (solids content equivalent) of Superester E-900-NT (trade name, biomass content: 80%, volume average particle diameter: 0.3 μm, manufactured by Arakawa Chemical Industries, Ltd.) as tackifier resin particles (C), and 10 parts by mass (solids content equivalent) of silica A (average diameter (average particle diameter): 27 nm) as substance (D).

[0193] Examples 2 to 14 In Examples 2 to 14, the adhesive compositions of Examples 2 to 14 were prepared in the same manner as in Example 1, except that the formulations of the adhesive compositions were as shown in Table 3.

[0194] Examples 15 to 28 In Examples 15 to 28, the adhesive compositions of Examples 15 to 28 were prepared in the same manner as in Example 1, except that the formulations of the adhesive compositions were as shown in Table 4.

[0195] Comparative Examples 1 to 8 In Comparative Examples 1 to 8, the adhesive compositions were prepared in the same manner as in Example 1, except that the formulations of the adhesive compositions were as shown in Table 5.

[0196] [Preparation of adhesive sheets for evaluation] The pressure-sensitive adhesive composition prepared above was applied to a substrate of fine paper (product name: OK Prince fine paper, basis weight: 81.4 g / m 2 , manufactured by Oji Paper Co., Ltd.), and the amount of coating after drying was 15 g / m2 The adhesive was applied using a wire bar so that the adhesive layer was uniformly coated, forming a coating film. The resulting coating film was then dried using a hot air circulation dryer at a drying temperature of 105°C for 40 seconds, forming a pressure-sensitive adhesive layer on the surface of the fine paper. A release sheet (product name: SL-80KCM, manufactured by Sumika Kakoshi Co., Ltd.) was then placed on the exposed surface of the pressure-sensitive adhesive layer formed on the surface of the fine paper, with the easy-release treated surface of the release sheet in contact with the surface, and the two sheets were bonded together to produce a pressure-sensitive adhesive sheet for evaluation. The pressure-sensitive adhesive sheet produced for evaluation had a laminated structure of substrate (high-quality paper) / pressure-sensitive adhesive layer (thickness: 20 μm) / release sheet.

[0197] [Measurement and Evaluation] 1. Adhesive strength (1) Initial adhesive strength The pressure-sensitive adhesive sheet for evaluation prepared above was cut into pieces measuring 25 mm x 100 mm to prepare pressure-sensitive adhesive sheet pieces for evaluation. The release sheet was peeled off from the prepared pressure-sensitive adhesive sheet piece for evaluation (composition: substrate / pressure-sensitive adhesive layer / release sheet), and the surface of the pressure-sensitive adhesive layer exposed by the peeling was placed on the surface of a SUS304 (stainless steel plate; hereinafter simply referred to as "SUS") surface that had been polished using #360 waterproof abrasive paper specified in JIS R 6253:2006 according to a method conforming to JIS Z 0237:2009, and pressed against the surface to prepare a test piece. The prepared test piece was left to stand in an environment with an ambient temperature of 23°C and 50% RH for 30 minutes. After leaving the test piece stationary, the adhesive sheet piece for evaluation (composition: substrate / adhesive layer) was peeled off from the SUS at an angle of 180° in the long side (100 mm) direction to measure the adhesive strength (unit: N / 25 mm) using a single column material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd., at an ambient temperature of 23°C, 50% RH, and a peel speed of 300 mm / min. Evaluation was then carried out 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 levels that are practically acceptable, with "A" being the most preferable.

[0198] -Evaluation criteria- A: The adhesive strength was 0.5N / 25mm 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.

[0199] (2) Adhesion strength after aging The pressure-sensitive adhesive sheet for evaluation prepared above was cut into pieces measuring 25 mm × 100 mm to prepare pressure-sensitive adhesive sheet pieces for evaluation. The release sheet was peeled off from the prepared pressure-sensitive adhesive sheet piece for evaluation (composition: substrate / pressure-sensitive adhesive layer / release sheet), and the surface of the pressure-sensitive adhesive layer exposed by the peeling was placed on the surface of a SUS304 (stainless steel plate; hereinafter simply referred to as "SUS") surface that had been polished using #360 waterproof abrasive paper specified in JIS R 6253:2006 according to a method conforming to JIS Z 0237:2009, and pressed against the surface to prepare a test piece. The prepared test piece was left standing in a thermo-hygrostat chamber set at 40°C for 7 days, then removed from the chamber and left standing in an environment of an ambient temperature of 23°C and 50% RH for 30 minutes. After leaving the test piece stationary, the adhesive sheet piece for evaluation (composition: substrate / adhesive layer) was peeled off from the SUS at an angle of 180° in the long side (100 mm) direction to measure the adhesive strength (unit: N / 25 mm) using a single column material testing machine (model number: STA-1225) manufactured by A&D Co., Ltd., at an ambient temperature of 23°C, 50% RH, and a peel speed of 300 mm / min. Evaluation was then carried out 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 levels that are practically acceptable, with "A" being the most preferable.

[0200] -Evaluation criteria- A: The adhesive strength was less than 2.5N / 25mm. 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.

[0201] 2.Removability In measuring the 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.

[0202] -Evaluation criteria- A: No adhesive residue or stringiness of adhesive on the SUS during peeling, nor any tearing of the substrate was observed. B: Although slight adhesive residue and stringiness of adhesive were observed on the SUS during peeling, no breakage of the substrate was observed. C: Breaking of the substrate was confirmed, and adhesive remained on the SUS surface when peeled off.

[0203] 3. Reapplicability In "(1) Initial adhesive strength" of "1. Adhesive strength" above, a piece of the adhesive sheet for evaluation (composition: substrate / adhesive layer) peeled from the 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 piece of 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 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 levels that are practically acceptable, with "A" being the most preferable.

[0204] -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 applied 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 applied area.

[0205] [Table 3]

[0206] [Table 4]

[0207] [Table 5]

[0208] In Tables 3 to 5, the "ratio of the average diameter d of the specific substance (D) to the average particle diameter b of the (meth)acrylic resin particles (B)" is expressed as "average diameter d / average particle diameter b." The values ​​of the "ratio of the average diameter d of the specific substance (D) to the average particle diameter b of the (meth)acrylic resin particles (B)" listed in Tables 3 to 5 are values ​​obtained by rounding off to three significant digits.

[0209] Details of the specific tackifying resin particles (C) shown in Tables 3 to 5 are as follows. "Super Ester E-900-NT" (product name, rosin-based resin, biomass content: 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 content: 80%, softening point: 160°C, average particle size: 300 nm, solid content: 50% by mass, manufactured by Arakawa Chemical Industries, Ltd.) "Harie Star 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 content: 70%, softening point: 105°C, average particle size: 350 nm, solid content: 50% by mass, manufactured by Yasuhara Chemical Co., Ltd.)

[0210] The "average particle size" described in the details of the specific tackifying resin particles (C) is a volume-average particle size measured by the same method as that 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 (trade name), a particle size distribution analyzer manufactured by Malvern.

[0211] Details of the specific substances (D) listed in Tables 3 to 5 are as follows. "Silica A" [shape: spherical, average particle diameter: 27 nm, probe tack value of the film surface when the film is formed: 0.07 N / cm 2 , water-insoluble substances] "Silica B" [Shape: spherical, average particle size: 125 nm, probe tack value of the film surface when the film is formed: 0.07 N / cm 2 , water-insoluble substances] "Silica C" [Shape: spherical, average particle diameter: 445 nm, probe tack value of the film surface when the film is formed: 0.07 N / cm 2 , water-insoluble substances] "Titanium oxide" [shape: spherical, average particle diameter: 15 nm, probe tack value of the film surface when the film is formed: 0.07 N / cm 2 , water-insoluble substances] "Cellulose fiber" [shape: fibrous, average diameter (average fiber diameter): 25 nm, probe tack value of the film surface when film is formed: 0.07 N / cm 2 , water-insoluble substances] "Chitin fiber" [shape: fibrous, average diameter (average fiber diameter): 30 nm, probe tack value of the film surface when film is formed: 0.06 N / cm 2 , water-insoluble substances] "Chitosan fiber" [shape: fibrous, average diameter (average fiber diameter): 30 nm, probe tack value of film surface when film is formed: 0.06 N / cm 2 , water-insoluble substances]

[0212] The "average diameter (average particle diameter)" described in the details of the specific substance (D) above is the volume-average particle diameter measured by the same method as the method for measuring the average diameter of the specific substance (D) described above (when the specific substance (D) is spherical). The measurement device used was a Zetasizer Nano ZS-90 (trade name), a particle size distribution analyzer manufactured by Malvern. The "average diameter (average fiber diameter)" described in the details of the specific substance (D) is the average fiber diameter measured by the same method as the above-mentioned method for measuring the average diameter of the specific substance (D) (when the specific substance (D) is fibrous). The measuring device used was a Regulus 8100 (trade name) scanning electron microscope (SEM) manufactured by Hitachi, Ltd.

[0213] The "probe tack value of the film surface when a film is formed" described in the details of the above specific substance (D) was measured using a method similar to the method for measuring the probe tack value of the film surface when a film of the specific substance (D) is formed.

[0214] As shown in Tables 3 and 4, the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of the Examples exhibited sufficient adhesive strength to prevent peeling from the adherend in the early stages of application, and the adhesive strength did not increase excessively over time, demonstrating excellent removability and re-application properties. The pressure-sensitive adhesive compositions of the Examples contained tackifying resin particles with a biomass content of at least 45% and were capable of forming environmentally friendly pressure-sensitive adhesive layers.

[0215] On the other hand, as shown in Table 5, it was confirmed that the adhesive layer formed using the adhesive composition of the comparative example was inferior to the adhesive layer formed using the adhesive composition of the example in either removability or repositionability.

Claims

1. (Meth)acrylic resin particles (A) having 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) having an average particle diameter of 50 nm to 900 nm; tackifying resin particles (C) having a biomass content of 45% or more; The average particle size is smaller than that of the (meth)acrylic resin particles (B), and when a film is formed, the probe tack value of the film surface is 0.40 N / cm ２ a substance (D) which is: Water and Including, the content of the (meth)acrylic resin particles (B) is 2 parts by mass to 110 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A), the content of the tackifier resin particles (C) is 50 parts by mass to 150 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A), the content of the substance (D) is 1 part by mass to 35 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A), A pressure-sensitive adhesive composition, wherein the probe tack value is a value measured by the following measurement method. [Method for measuring probe tack value] An aqueous dispersion of substance (D) (solid content: 2% by mass) is applied to paper using an applicator so that the film thickness after drying is 20 μm, and then dried using a hot air circulation dryer at a drying temperature of 105° C. for 40 seconds to form a film on the paper surface. The probe tack value of the surface of the formed film is measured using a tack tester (trade name: TAC1000) manufactured by Rhesca Co., Ltd. under the following measurement conditions. - Measurement conditions - Pressing speed: 5 mm / sec Pressing load: 2N Hold time: 1 second Pulling speed: 10 mm / sec

2. 2. The pressure-sensitive adhesive composition according to claim 1, 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).

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the (meth)acrylic resin particles (B) have a glass transition temperature of 0°C or lower.

4. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the tackifier resin particles (C) are particles of at least one resin selected from the group consisting of rosin-based resins and terpene-based resins.

5. 5. The pressure-sensitive adhesive composition according to claim 1, wherein the tackifier resin particles (C) have an average particle size of 100 nm to 500 nm.

6. 6. The pressure-sensitive adhesive composition according to claim 1, wherein the average particle size of the substance (D) is smaller than the average particle size of the tackifier resin particles (C).

7. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, wherein the substance (D) is at least one selected from the group consisting of silica, titanium oxide, cellulose fiber, chitin fiber, and chitosan fiber.

8. The pressure-sensitive adhesive composition according to any one of claims 1 to 7, wherein the content of the substance (D) is 3 parts by mass to 30 parts by mass per 100 parts by mass of the (meth)acrylic resin particles (A).

9. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 8.

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