Copolymer, adhesive composition, adhesive tape, and method for producing copolymer

Abstract

Provided are: a copolymer obtained by means of emulsion polymerization, the copolymer having a first structural unit that is derived from an alkyl (meth)acrylate and a second structural unit that is derived from an ethylenically unsaturated compound having at least one selected from the group consisting of carboxy groups and salts of carboxy groups, and the copolymer including biomass carbon atoms; an adhesive composition and adhesive tape in which the copolymer is used; and a method for producing the copolymer.

Description

Copolymer, pressure-sensitive adhesive composition, pressure-sensitive adhesive tape, and method for producing copolymer

[0001] The present disclosure relates to a copolymer, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive tape, and a method for producing the copolymer.

[0002] Most of the raw materials used to manufacture synthetic resins are produced using compounds derived from fossil fuels such as petroleum, coal, and natural gas as starting materials. Fossil fuels contain carbon that has been fixed underground for many years. Therefore, if synthetic resins are biodegraded or incinerated to release carbon dioxide into the atmosphere, carbon that was fixed deep underground and not present in the atmosphere will be released into the atmosphere as carbon dioxide, which could be a factor in global warming.

[0003] Plants are attracting attention as a carbon source because they are organisms that absorb carbon dioxide circulating in the global environment, undergo photosynthesis using carbon dioxide and water as raw materials, and assimilate or fix the carbon dioxide as an organic body. If materials obtained from plants are used as raw materials for synthetic resins, even if they are biodegraded or incinerated to generate carbon dioxide, the total amount of carbon that makes up the carbon dioxide does not change because the carbon dioxide present in the global environment is circulating.

[0004] A typical application of synthetic resins is as an adhesive. For example, adhesive tapes are made by forming an adhesive-containing layer, i.e., an adhesive layer, on a substrate, and the tapes are then applied to various articles to repair them or to secure them together.

[0005] As a pressure-sensitive adhesive using a biomass-derived material, a pressure-sensitive adhesive containing natural rubber is known, but the pressure-sensitive adhesive containing natural rubber has a problem in that it is poor in heat resistance and the like and therefore cannot demonstrate sufficient reliability in the usage environments of electronic components, vehicles, houses, and building materials.

[0006] As adhesive tapes with excellent heat resistance, etc., adhesive tapes having a (meth)acrylic adhesive layer containing a (meth)acrylic copolymer are widely used. Even in such adhesive tapes, it has been possible to selectively use biomass-derived materials as tackifiers, such as rosin and terpene. However, by using only biomass-derived additives, it is difficult to increase the content of biomass-derived carbon in the adhesive tape as a whole while exhibiting excellent performance such as adhesive strength and holding power.

[0007] Patent Document 1 describes an adhesive tape having an adhesive layer containing a (meth)acrylic copolymer containing structural units derived from a (meth)acrylic monomer containing carbon of biological origin.

[0008] US Patent No. 5,949,999 describes an adhesive comprising the reaction product of at least one polymerizable monomer, at least a portion of which is derived from a non-petroleum source, a reaction initiator, and a stabilizer.

[0009] JP 2019-218458 A JP 2014-077141 A

[0010] The adhesive tape of Patent Document 1 and the particulate adhesive of Patent Document 2 both exhibit good adhesive strength at room temperature, but there is room for improvement in adhesive strength at high and low temperatures, as well as in holding power at high temperatures. Furthermore, the use of organic solvents as the liquid medium can be a source of burden to the environment.

[0011] The present disclosure aims to provide a copolymer containing biomass carbon atoms, which has a low environmental impact during production, exhibits strong adhesive strength over a wide temperature range from low to high, and is capable of forming an adhesive layer that has excellent holding power in high-temperature environments; a pressure-sensitive adhesive composition and pressure-sensitive adhesive tape using the copolymer; and a method for producing the copolymer.

[0012] [1] A copolymer obtained by emulsion polymerization, comprising a first structural unit derived from an alkyl(meth)acrylate, and a second structural unit derived from an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group, and containing a biomass carbon atom. [2] The copolymer according to [1] above, having a biomass carbon content of 10% or more as determined by method B in ASTM D6866-22. [3] The copolymer according to [1] or [2] above, in which at least one structural unit among the structural units contained as the first structural unit has an alkyl group containing a biomass carbon atom. [4] The copolymer according to [1] above, in which the carbon atom constituting the alkyl group derived from an alkyl(meth)acrylate contained in the first structural unit is replaced by a carbon atom (C １Ａ ), the carbon atoms (C １ＡThe copolymer according to [3] above, wherein the biomass carbon content, determined by method B of ASTM D6866-22, of the total number of carbon atoms in the copolymer is 20% or more. [5] The copolymer according to any of [1] to [4] above, wherein the glass transition temperature Tg is -80 to 30°C. [6] The copolymer according to any of [1] to [5] above, wherein the first structural unit comprises at least one selected from the group consisting of a structural unit derived from n-butyl (meth)acrylate, a structural unit derived from isoamyl (meth)acrylate, a structural unit derived from n-octyl (meth)acrylate, a structural unit derived from 2-octyl (meth)acrylate, and a structural unit derived from lauryl (meth)acrylate. [7] The copolymer according to any of [1] to [6] above, further comprising a structural unit derived from a vinyl ester compound. [8] A pressure-sensitive adhesive composition comprising the copolymer according to any of [1] to [7] above and an aqueous medium. [9] The pressure-sensitive adhesive composition according to [8] above, wherein the copolymer is dispersed as particles in the aqueous medium to form an emulsion.

[10] A pressure-sensitive adhesive tape comprising a substrate and a pressure-sensitive adhesive layer formed on the surface of the substrate, wherein the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive composition according to [8] or [9] above.

[11] A method for producing the copolymer according to any one of [1] to [7] above, comprising a step of emulsion polymerizing monomers comprising an alkyl(meth)acrylate and an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group, wherein at least one of the monomers comprises a biomass carbon atom.

[12] A method for producing the copolymer according to

[11] above, wherein the monomer comprises an alkyl(meth)acrylate comprising a biomass carbon atom.

[13] A method for producing the copolymer according to

[12] above, wherein the alkyl(meth)acrylate comprising a biomass carbon atom comprises a biomass carbon atom in the alkyl group bonded to the (meth)acryloyloxy group.

[0013] According to the present disclosure, it is possible to provide a copolymer containing biomass carbon atoms, which has a low environmental impact during production, exhibits strong adhesive strength over a wide temperature range from low to high temperatures, and is capable of forming an adhesive layer that has excellent holding power in high-temperature environments, a pressure-sensitive adhesive composition and pressure-sensitive adhesive tape using the copolymer, and a method for producing the copolymer.

[0014] In the following explanation, unless otherwise specified, surface means "surface."

[0015] "(Meth)acrylic" is a general term for acrylic and methacrylic, and "(meth)acrylate" is a general term for acrylate and methacrylate.

[0016] The term "ethylenically unsaturated compound" refers to a compound having an ethylenically unsaturated bond. Unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability.

[0017] In a polymer of an ethylenically unsaturated compound, a structural unit derived from a certain ethylenically unsaturated compound has a corresponding relationship in that the chemical structure of the portion other than the ethylenically unsaturated bond of the ethylenically unsaturated compound is the same as the chemical structure of the portion of the polymer other than the portion corresponding to the ethylenically unsaturated bond of the structural unit. For example, a structural unit derived from acrylic acid has a structure of -CH ２ It has a structure represented by CH(COOH)-.

[0018] In the following description, the compound from which a certain structural unit is derived refers to a compound that has the above-mentioned relationship with the structural unit, and does not necessarily correspond to the compound used in the actual manufacturing process. When the chemical structure of the monomer does not correspond to the chemical structure of the polymer, such as when a portion other than the chain corresponding to the ethylenically unsaturated bond is chemically reacted after polymerization, the chemical structure after polymerization is used as the basis. For example, when vinyl acetate is polymerized and then saponified, the chemical structure of the polymer is used as the basis, and the structural unit of the polymer is considered to be a structural unit derived from vinyl alcohol, not a structural unit derived from vinyl acetate.

[0019] Unless otherwise specified, a structural unit having an ionic functional group such as a carboxy group is considered to be a structural unit derived from the same ionic compound, regardless of whether a part of the functional group has been ion-exchanged or not. For example, —CH ２ C(CH ３ Unless otherwise specified, the structural unit represented by (COONa)- is also a structural unit derived from methacrylic acid.

[0020] The term "salt of a carboxy group" refers to a structure in which a carboxy group forms a salt, such as -COONa, -COOK, or -COONH. ４ etc.

[0021] A "dispersion" is a solid-liquid mixture in which a solid is dispersed as particles in a liquid without dissolving in the liquid. A "slurry" is a fluid in which solid particles such as clay or pigment are suspended in a liquid.

[0022] In the following description, "adhesive strength" refers to the force required to peel the adhesive surface from the adherend, and "holding strength" refers to the strength of an adhesive layer constituting the adhesive surface of an adhesive tape or the like to resist slippage due to a static load applied in a direction parallel to the adhesive surface.

[0023] "Biomass" means organic resources derived from living organisms, excluding fossil resources. "Biomass compounds" means compounds derived from biomass. "Biomass carbon atoms" means carbon atoms derived from biomass.

[0024] <1. Copolymer> The copolymer of this embodiment (hereinafter also referred to as "copolymer (A)") is obtained by emulsion polymerization. Copolymer (A) has a first structural unit derived from an alkyl (meth)acrylate and a second structural unit derived from an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group, and contains biomass carbon atoms. In addition to the first structural unit and the second structural unit, copolymer (A) may have other structures that do not fall into either the first structural unit or the second structural unit. Details of the other structures will be described later.

[0025] (1-1. Biomass Carbon Content of Copolymer (A)) The biomass carbon content [%] of copolymer (A) is a value determined by method B of ASTM D6866-22 (hereinafter sometimes abbreviated as "ASTM method"). In method B of ASTM D6866-22, the biomass carbon content of the analyzed object is a value obtained by correcting the percent of modern carbon (pMC) of the analyzed object determined by accelerator mass spectrometry (AMS) measurement by the atmospheric correction factor (REF value) described in 9.4 of the same standard.

[0026] Here, the biomass carbon content of copolymer (A) determined by method B in ASTM D6866-22 is referred to as "biomass carbon content B （Ａ） The molar fraction of the monomer i (i=1, 2, 3, ...) used to synthesize the copolymer (A) is defined as R ｉ [0<R ｉ <1], the number of carbon atoms contained in the molecule of monomer i is C ｉ , the number of carbon atoms derived from the biomass compound contained in the molecule of monomer i determined by the ASTM method is C Ｂｉ Then, these values ​​and the biomass carbon content B （Ａ） The following equation (1) holds between B （Ａ） = 100 × Σ(R ｉ ×C Ｂｉ ) / Σ(R ｉ ×C ｉ ) (1)

[0027] Biomass carbon content B （Ａ） can be determined by analyzing the copolymer (A) itself according to the ASTM method, or can be calculated according to the formula (1).

[0028] That is, the molar fraction R of each monomer used to synthesize the copolymer (A) ｉ and the number of carbon atoms contained in each monomer, C ｉand the number of carbon atoms in the portion derived from the biomass compound contained in each monomer molecule is C Ｂｉ The biomass carbon content calculated from the above and the biomass carbon content calculated by measuring the copolymer (A) according to the ASTM method are the same value B （Ａ） is.

[0029] Biomass carbon content B of copolymer (A) （Ａ） is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 40% or more. （Ａ） may be 100%, may be 100% or less, may be 80% or less, or may be 60% or less.

[0030] The biomass carbon content B of the copolymer (A) （Ａ） may be 10 to 100%, may be 20 to 80%, may be 30 to 60%, or may be 40 to 60%.

[0031] (1-2. Glass Transition Point of Copolymer (A)) The glass transition point Tg of copolymer (A) is calculated by Fox's formula based on the glass transition point when each structural unit contained in copolymer (A) is treated as a homopolymer. A specific method for calculating the glass transition point Tg of copolymer (A) is to calculate it by Fox's formula 1 / Tg = Σ(Xi / Tgi) from the glass transition point Tgi of the homopolymer of each structural unit Mi (i = 1, 2, 3, ...) and the mass fraction Xi of structural unit Mi in copolymer (A) (ΣXi (total structural units) = 1).

[0032] In the Fox equation, Tg and Tgi are both calculated as absolute temperature (K) values. Here, by converting 0°C = 273.15K, the glass transition temperature Tg of the copolymer (A) can be determined as a Celsius temperature.

[0033] The glass transition temperature Tg of each homopolymer is a value described in the literature "Polymer Handbook (3rd Edition, John Wiley & Sons, Inc., 1989)." The glass transition temperature Tg of a homopolymer not described in the literature is the peak top temperature of a differential scanning calorimetry (DSC) chart obtained as the temperature derivative of DSC measured using a DSC apparatus (EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere.

[0034] The glass transition point Tg of the copolymer (A) is preferably −80° C. or higher, more preferably −65° C. or higher, and even more preferably −55° C. or higher, because the cohesive strength of the pressure-sensitive adhesive formed using the copolymer (A) can be improved, and the pressure-sensitive adhesive layer can be endowed with better holding power at high temperatures.

[0035] The glass transition temperature Tg of the copolymer (A) is preferably 30°C or lower, more preferably 0°C or lower, even more preferably -20°C or lower, and even more preferably -35°C or lower. This is because the wettability of the pressure-sensitive adhesive composition formed using the copolymer (A) can be improved, thereby improving the adhesion of the pressure-sensitive adhesive layer to the substrate. Furthermore, this is because the flexibility of the pressure-sensitive adhesive layer formed using the copolymer (A) can be increased, thereby improving the tackiness of the pressure-sensitive adhesive layer when used dry.

[0036] The glass transition temperature Tg of the copolymer (A) may be -80 to 30°C, -65 to 0°C, -55 to -20°C, or -55 to -35°C.

[0037] (1-3. First structural unit) The first structural unit is a structural unit derived from an alkyl(meth)acrylate. Here, the alkyl group contained in the first structural unit has the same structure as the alkyl group bonded to the (meth)acryloyloxy group contained in the alkyl(meth)acrylate from which the first structural unit is derived. In other words, the alkyl group contained in the first structural unit refers to an alkyl group bonded to the oxygen atom of —COO— directly bonded to the main chain of the copolymer (A).

[0038] The structure of the first structural unit is preferably designed depending on the glass transition temperature Tg of the copolymer (A), but is not limited thereto. The alkyl group contained in the first structural unit may have a linear structure or a branched structure.

[0039] The number of carbon atoms in the alkyl group contained in the first structural unit may be 1 or more, 2 or more, 4 or more, or 6 or more. The number of carbon atoms in the alkyl group contained in the first structural unit may be 20 or less, 15 or less, or 10 or less. The number of carbon atoms in the alkyl group contained in the first structural unit may be 1 to 20, 2 to 15, 4 to 10, or 6 to 10.

[0040] Of the structural units contained as first structural units, the content of structural units having an alkyl group having 2 to 15 carbon atoms is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. Of the structural units contained as first structural units, the content of structural units having an alkyl group having 2 to 15 carbon atoms may be 100% by mass or less. Of the structural units contained as first structural units, the content of structural units having an alkyl group having 4 to 10 carbon atoms is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. Of the structural units contained as first structural units, the content of structural units having an alkyl group having 4 to 10 carbon atoms may be 100% by mass or less.

[0041] Of the structural units contained as the first structural unit, at least one structural unit preferably has an alkyl group containing a biomass carbon atom.

[0042] Here, the carbon atoms constituting the alkyl group derived from alkyl(meth)acrylate contained in the first structural unit are referred to as carbon atoms (C １Ａ ), the carbon atoms (C １Ａ The biomass carbon content determined by method B in ASTM D6866-22 in the total number of （１Ａ） The molar fraction of the monomer Ai (i=1, 2, 3, . . . ) corresponding to the first structural unit used to synthesize the copolymer (A) is defined as R Ａｉ [0<R Ａｉ <1], the number of carbon atoms contained in the alkyl group of the monomer Ai is C Ａｉ The number of carbon atoms derived from the biomass compound contained in the alkyl group of the monomer Ai determined by the ASTM method is C ＢＡｉ Then, these values ​​and the biomass carbon content B （１Ａ） The following formula (2) holds between B and [%]. （１Ａ） = 100 × Σ(R Ａｉ ×C ＢＡｉ ) / Σ(R Ａｉ ×C Ａｉ ) (2)

[0043] Biomass carbon content B （１Ａ） can be determined by analyzing the alkyl alcohol obtained by saponifying the copolymer (A) according to the above ASTM method. Also, by analyzing the alkyl alcohol obtained by saponifying the monomer according to the above ASTM method, the number of carbon atoms C of the portion derived from the biomass compound contained in the alkyl group of the monomer Ai can be determined. ＢＡｉ " can also be calculated by the above formula (2).

[0044] The biomass carbon content B （１Ａ）is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, and particularly preferably 65% ​​or more.

[0045] The biomass carbon content B （１Ａ） may be 100%, may be 100% or less, may be 90% or less, or may be 65% or less.

[0046] The biomass carbon content B （１Ａ） may be 20 to 100%, may be 30 to 90%, may be 40 to 65%, may be 50 to 65%, or may be 65 to 90%.

[0047] The number of carbon atoms in the alkyl group containing a biomass carbon atom may be 1 or more, 2 or more, 4 or more, or 6 or more. Furthermore, the number of carbon atoms in the alkyl group containing a biomass carbon atom may be 20 or less, 15 or less, or 10 or less. The number of carbon atoms in the alkyl group containing a biomass carbon atom may be 1 to 20, 2 to 15, 4 to 10, or 6 to 10. It is preferable that the alkyl group containing a biomass carbon atom contains only biomass carbon atoms.

[0048] Examples of compounds from which the first structural unit is derived include methyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, etc. The compound from which the first structural unit is derived may be one type, or two or more types.

[0049] The first structural unit preferably comprises at least one selected from the group consisting of a structural unit derived from methyl (meth)acrylate, a structural unit derived from n-butyl (meth)acrylate, a structural unit derived from isoamyl (meth)acrylate, a structural unit derived from 2-ethylhexyl (meth)acrylate, a structural unit derived from n-octyl (meth)acrylate, a structural unit derived from 2-octyl (meth)acrylate, and a structural unit derived from lauryl (meth)acrylate; more preferably comprises at least one selected from the group consisting of a structural unit derived from n-butyl (meth)acrylate, a structural unit derived from isoamyl (meth)acrylate, a structural unit derived from n-octyl (meth)acrylate, a structural unit derived from 2-octyl (meth)acrylate, and a structural unit derived from lauryl (meth)acrylate; and even more preferably comprises at least one selected from the group consisting of a structural unit derived from n-butyl (meth)acrylate and a structural unit derived from 2-octyl (meth)acrylate.

[0050] (1-4. Second structural unit) The second structural unit is a structural unit derived from an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group. The number of carboxy groups or salts of carboxy groups contained in the second structural unit is not particularly limited, and may be one or two. Examples of compounds from which the second structural unit is derived include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, itaconic acid, and maleic acid. The compound from which the second structural unit is derived may be one type, or two or more types. The second structural unit may or may not contain a biomass carbon atom.

[0051] The second structural unit preferably includes a structural unit derived from a compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group and an acryloyl group, and more preferably includes a structural unit derived from (meth)acrylic acid. Of the structural units included as the second structural unit, the content of the structural unit derived from (meth)acrylic acid is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. Of the structural units included as the second structural unit, the content of the structural unit derived from (meth)acrylic acid may be 100% by mass or less.

[0052] (1-5. Other Structures) Examples of other structures that the copolymer (A) may have include other structural units that do not fall under either the first structural unit or the second structural unit (hereinafter, also simply referred to as "other structural units"); terminal structures derived from a polymerization initiator, a chain transfer agent, etc.; and the like.

[0053] [Other Structural Units] Compounds from which other structural units are derived are not particularly limited, and examples thereof include vinyl ester compounds such as vinyl acetate, vinyl formate, vinyl propionate, and vinyl versatate; conjugated diolefin compounds such as butadiene, isoprene, and chloroprene; amine imide group-containing vinyl compounds such as 1,1,1-trimethylamine methacrylimide; (meth)acrylamide compounds such as (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, and N,N-dimethylaminopropyl(meth)acrylamide; 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and vinyltriethoxysilane; Examples of the compound from which the other structural units are derived include alkoxysilyl group-containing vinyl compounds such as glycidyl (meth)acrylate, glycidyl vinyl ether, and glycidyl (meth)allyl ether; ethylenically unsaturated compounds having a carbonyl group such as diacetone acrylamide, methyl vinyl ketone, phenyl vinyl ketone, ethyl vinyl ketone, n-propyl vinyl ketone, isopropyl vinyl ketone, n-butyl vinyl ketone, and t-butyl vinyl ketone; radically polymerizable light stabilizers such as 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate; and polymerizable surfactants. The compound from which the other structural units are derived may be one type or two or more types.

[0054] When the copolymer (A) has the above-mentioned other structural units, it preferably has a structural unit derived from a vinyl ester compound, and more preferably has a structural unit derived from ethyl acetate.

[0055] When the copolymer (A) has a structural unit derived from a vinyl ester compound, the content of the structural unit derived from the vinyl ester compound in the copolymer (A) is preferably 1.0 mass% or more, more preferably 2.5 mass% or more, and even more preferably 4.0 mass% or more, since this improves the adhesive strength of the pressure-sensitive adhesive containing the copolymer (A) at room temperature.

[0056] When the copolymer (A) has structural units derived from a vinyl ester compound, the content of the structural units derived from the vinyl ester compound in the copolymer (A) is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8.0% by mass or less, since this improves the adhesive strength of the pressure-sensitive adhesive containing the copolymer (A) at room temperature.

[0057] When the copolymer (A) has a structural unit derived from a vinyl ester compound, the content of the structural unit derived from a vinyl ester compound in the copolymer (A) may be 1.0 to 15 mass%, 2.5 to 10 mass%, or 4.0 to 8.0 mass%.

[0058] The polymerizable surfactant from which the other structural units are derived is a compound having an ethylenically unsaturated bond and also functions as a surfactant. The polymerizable surfactant may be nonionic, anionic, or cationic, but is preferably anionic. Examples of anionic polymerizable surfactants include ether sulfate type, ether sulfate type ammonium salt, and phosphate ester type, and among these, ether sulfate type ammonium salt is preferred.

[0059] When the copolymer (A) has a structural unit derived from a polymerizable surfactant, the content of the structural unit derived from the polymerizable surfactant in the copolymer (A) is preferably 0.10% by mass or more, more preferably 0.30% by mass or more, and even more preferably 0.60% by mass or more, in order to further improve the dispersion stability of the copolymer (A).

[0060] When the copolymer (A) has a structural unit derived from a polymerizable surfactant, the content of the structural unit derived from the polymerizable surfactant in the copolymer (A) is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.5% by mass or less, in order to more effectively obtain the intended function of the copolymer (A).

[0061] When the copolymer (A) has a structural unit derived from a polymerizable surfactant, the content of the structural unit derived from the polymerizable surfactant in the copolymer (A) may be 0.10 to 5.0 mass%, 0.30 to 3.0 mass%, or 0.60 to 1.5 mass%.

[0062] The copolymer (A) may further have a structural unit other than the structural units exemplified above.

[0063] [Terminal Structure] The copolymer (A) may have a terminal structure derived from a polymerization initiator, a chain transfer agent, or the like. The content of the terminal structure in the copolymer (A) is preferably 0.50 parts by mass or less relative to 100 parts by mass of the total amount of structural units contained in the copolymer (A). When the content of the terminal structure in the copolymer (A) is 0.50 parts by mass or less relative to 100 parts by mass of the total amount of structural units contained in the copolymer (A), the presence of the terminal structure may be ignored when calculating the content of each structural unit and the various biomass carbon contents. Details of the polymerization initiator and chain transfer agent from which the terminal structure is derived will be described later.

[0064] (1-6. Content of each structural unit in copolymer (A)) The content of the first structural unit in copolymer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. This is because an increase in the glass transition point of copolymer (A) can be suppressed, and the tackiness, wettability, and adhesion strength of the adhesive layer can be improved.

[0065] The content of the first structural unit in the copolymer (A) is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 93% by mass or less, because the polarity of the copolymer (A) and the cohesive strength of the adhesive layer are kept at an appropriate level, and an adhesive layer having high adhesiveness not only at room temperature but also at high and low temperatures can be obtained.

[0066] The content of the first structural unit in the copolymer (A) may be 60 to 98% by mass, 70 to 95% by mass, or 80 to 93% by mass.

[0067] The content of the second structural unit in the copolymer (A) is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more, because this can improve the cohesive strength of the adhesive layer containing the copolymer (A) and increase the holding power at high temperatures.

[0068] The content of the second structural unit in the copolymer (A) is preferably 12% by mass or less, more preferably 9.0% by mass or less, and even more preferably 6.0% by mass or less, because this can suppress an increase in the glass transition temperature of the copolymer (A) and improve the tackiness, wettability, and adhesion strength of the adhesive layer.

[0069] The content of the second structural unit in the copolymer (A) may be 1.0 to 12% by mass, 2.0 to 9.0% by mass, or 3.0 to 6.0% by mass.

[0070] The total content of the first structural unit and the second structural unit in the copolymer (A) is preferably 65% ​​by mass or more, more preferably 75% by mass or more, even more preferably 85% by mass or more, and may even be 90% by mass or more. This is because an increase in the glass transition temperature of the copolymer (A) can be suppressed, and the tackiness, wettability, and even adhesion strength of the adhesive layer can be improved. The total content of the first structural unit and the second structural unit in the copolymer (A) may be 100% by mass or less.

[0071] <2. Method for Producing Copolymer> The method for producing copolymer (A) according to this embodiment includes a step of emulsion polymerizing monomers (hereinafter also referred to as "raw material monomers for copolymer (A)") containing an alkyl(meth)acrylate and an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group, and at least one of the monomers contains a biomass carbon atom.

[0072] By producing the copolymer (A) by emulsion polymerization, a high molecular weight copolymer (A) can be obtained. The high molecular weight copolymer (A) can improve the cohesive strength of the pressure-sensitive adhesive and impart superior holding power at high temperatures to the pressure-sensitive adhesive layer. Furthermore, since emulsion polymerization can be carried out in an aqueous medium as described below, the environmental impact of production is low.

[0073] (2-1: Monomer) At least one of the raw material monomers of the copolymer (A) contains a biomass carbon atom. Here, the biomass carbon content of all the raw material monomers of the copolymer (A) according to method B in ASTM D6866-22 is referred to as the "biomass carbon content B" （Ｍ） The molar fraction of the raw material monomer i (i=1, 2, 3, ...) of the copolymer (A) is defined as R ｉ [0<R ｉ <1], the number of carbon atoms contained in the molecule of monomer i is C ｉ , the number of carbon atoms derived from the biomass compound contained in the molecule of monomer i determined by the ASTM method is C Ｂｉ Then, these values ​​and the biomass carbon content B of the entire raw material monomers of copolymer (A) （Ｍ） The following equation (3) holds between B （Ｍ） = 100 × Σ(R ｉ ×C Ｂｉ ) / Σ(R ｉ ×C ｉ ) (3)

[0074] Biomass carbon content B （Ｍ） can be determined by analyzing all the raw material monomers of the copolymer (A) according to method B of ASTM D6866-22, or can be calculated by the above formula (3).

[0075] The biomass carbon content B （Ｍ） is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 40% or more. （Ｍ）may be 100%, may be 100% or less, may be 80% or less, or may be 60% or less.

[0076] The biomass carbon content B （Ｍ） may be 10 to 100%, may be 20 to 80%, may be 30 to 60%, or may be 40 to 60%.

[0077] The raw material monomers for copolymer (A) preferably contain an alkyl(meth)acrylate containing a biomass carbon atom. More preferably, the alkyl(meth)acrylate containing a biomass carbon atom contains a biomass carbon atom in the alkyl group bonded to the (meth)acryloyloxy group.

[0078] Here, the carbon atoms contained in the alkyl group of the alkyl (meth)acrylate contained in the raw material monomer of the copolymer (A) are represented by C （１Ｍ） In this case, C contained in the raw material monomer of copolymer (A) （１Ｍ） The biomass carbon content determined by method B in ASTM D6866-22 is referred to as "biomass carbon content B." （１Ｍ） The molar fraction of alkyl (meth)acrylate Ai (i = 1, 2, 3, ...) contained in the raw material monomer of copolymer (A) is defined as R Ａｉ [0<R Ａｉ <1], the number of carbon atoms contained in the alkyl group of the alkyl (meth)acrylate Ai is C Ａｉ , the number of carbon atoms derived from the biomass compound contained in the alkyl group of the monomer Ai is C ＢＡｉ Then, these values ​​and the biomass carbon content B （１Ｍ） The following formula (4) holds between B and [%]. （１Ｍ） = 100 × Σ(R Ａｉ ×C ＢＡｉ ) / Σ(R Ａｉ ×C Ａｉ ) (4)

[0079] Biomass carbon content B （１Ｍ）can be determined by analyzing the alkyl alcohol obtained by saponifying all of the raw material monomers of the copolymer (A) according to method B of ASTM D6866-22. Also, by analyzing the alkyl alcohol obtained by saponifying the raw material monomers according to method B of ASTM D6866-22, the number of carbon atoms C contained in the alkyl group of the alkyl (meth)acrylate Ai can be determined. Ａｉ " can also be calculated using the above formula (4).

[0080] Biomass carbon content B （１Ｍ） is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, and particularly preferably 65% ​​or more.

[0081] Biomass carbon content B （１Ｍ） may be 100%, may be 100% or less, may be 90% or less, or may be 65% or less.

[0082] Biomass carbon content B （１Ｍ） may be 20 to 100%, may be 30 to 90%, may be 40 to 65%, may be 50 to 65%, or may be 65 to 90%.

[0083] The ethylenically unsaturated compound having at least one selected from the group consisting of alkyl(meth)acrylates, carboxy groups, and salts of carboxy groups, which are contained in the raw material monomers of copolymer (A), can be explained in the same way as the ethylenically unsaturated compound having at least one selected from the group consisting of alkyl(meth)acrylates from which the first structural unit of copolymer (A) of the present embodiment is derived and carboxy groups and salts of carboxy groups from which the second structural unit is derived, and preferred embodiments are also the same.

[0084] (2-2: Emulsion Polymerization Step) The production method of the present embodiment includes a step of emulsion polymerizing a monomer containing an alkyl(meth)acrylate and an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group.

[0085] The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers for copolymer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. This is because it suppresses an increase in the glass transition temperature of the resulting copolymer (A) and improves the tackiness, wettability, and adhesion of the adhesive layer. The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers for copolymer (A) is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 93% by mass or less. This is because it moderately maintains the polarity of the resulting copolymer (A) and the cohesive strength of the adhesive layer, resulting in an adhesive layer with high adhesion not only at room temperature but also at high and low temperatures. The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers for copolymer (A) may be 60 to 98% by mass, 70 to 95% by mass, or 80 to 93% by mass.

[0086] The content of ethylenically unsaturated compounds having at least one selected from the group consisting of carboxy groups and carboxy salts in the total amount (100% by mass) of raw material monomers for copolymer (A) is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more. This is because the cohesive strength of the resulting adhesive layer containing copolymer (A) can be improved and the holding power at high temperatures can be increased. The content of ethylenically unsaturated compounds having at least one selected from the group consisting of carboxy groups and carboxy salts in the total amount (100% by mass) of raw material monomers for copolymer (A) is preferably 12% by mass or less, more preferably 9.0% by mass or less, and even more preferably 6.0% by mass or less. This is because an increase in the glass transition temperature of copolymer (A) can be suppressed, and the tackiness, wettability, and adhesion strength of the adhesive layer can be improved. The content of the ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group in the total amount (100% by mass) of raw material monomers of the copolymer (A) may be 1.0 to 12% by mass, 2.0 to 9.0% by mass, or 3.0 to 6.0% by mass.

[0087] The total content of alkyl (meth)acrylate and ethylenically unsaturated compound having at least one selected from the group consisting of carboxyl groups and carboxyl salts in the total amount (100% by mass) of raw material monomers for copolymer (A) is preferably 65% ​​by mass or more, more preferably 75% by mass or more, and even more preferably 85% by mass or more. This can suppress an increase in the glass transition temperature of the resulting copolymer (A) and improve the tackiness, wettability, and adhesion of the adhesive layer. The total content of alkyl (meth)acrylate and ethylenically unsaturated compound having at least one selected from the group consisting of carboxyl groups and carboxyl salts in the total amount (100% by mass) of raw material monomers for copolymer (A) may be 90% by mass or more, 100% by mass, or 100% by mass or less.

[0088] In emulsion polymerization, a polymerization initiator for accelerating the polymerization reaction, a chain transfer agent for controlling the molecular weight and molecular weight distribution of the copolymer (A) within an appropriate range, an emulsifier for emulsifying the monomers, etc. may be used. The raw material monomers for the copolymer (A) may be charged in their entirety into a reactor in advance, or may be polymerized while being continuously or intermittently supplied from the viewpoint of obtaining uniform particles. The raw material monomers supplied continuously or intermittently may be a part or all of the raw material monomers for the copolymer (A). The polymerization temperature is not particularly limited, but is preferably 5 to 100°C, more preferably 50 to 90°C.

[0089] In the production method of this embodiment, the emulsion polymerization of the monomers is preferably carried out in an aqueous medium. This results in a copolymer-containing liquid (copolymer dispersion) in which the copolymer (A) is dispersed as emulsified particles in the aqueous medium, i.e., an emulsion. The aqueous medium is water, a hydrophilic organic solvent, or a mixture thereof. Examples of hydrophilic organic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium is preferably water. Note that a mixed solvent of water and a hydrophilic solvent may be used as the aqueous medium as long as it does not impair polymerization stability.

[0090] Examples of the polymerization initiator include persulfate initiators such as potassium persulfate and ammonium persulfate; water-soluble azo initiators such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride; organic peroxides such as t-butyl hydroperoxide and cumene hydroperoxide; and hydrogen peroxide. One type of polymerization initiator may be used alone, or two or more types may be used. The amount of the polymerization initiator used is not particularly limited, but is preferably 0.1 to 2.0 parts by mass per 100 parts by mass of the total amount of the raw material monomers of the copolymer (A).

[0091] If necessary, a reducing agent can be used together with the polymerization initiator. Examples of such reducing agents include reducing organic compounds such as ascorbic acid, tartaric acid, citric acid, glucose, and formaldehyde sulfoxylate metal salts; and reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite. Only one type of reducing agent may be used, or two or more types may be used.

[0092] Examples of chain transfer agents include n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol. Only one type of chain transfer agent may be used, or two or more types may be used. The amount of chain transfer agent used is preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 0.50 parts by mass or less, and even more preferably 0.30 parts by mass or less, relative to 100 parts by mass of the total amount of raw material monomers for copolymer (A). This is because the cohesive strength of the pressure-sensitive adhesive is improved, thereby improving the holding power of the pressure-sensitive adhesive layer at high temperatures. The amount of chain transfer agent used may be 0.01 parts by mass or more, or even 0.05 parts by mass or more, relative to 100 parts by mass of the total amount of monomers. This is because the adhesive strength of the pressure-sensitive adhesive layer can be improved.

[0093] Examples of emulsifiers include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium polyoxyethylene alkyl ether sulfate; nonionic surfactants such as polyoxyethylene alkyl ethers and polyoxyethylene nonylphenyl ether; cationic surfactants such as ceciltrimethylammonium bromide and lauryl pyridinium chloride; amphoteric surfactants such as lauryl betaine; and the polymerizable surfactants described above. These surfactants may be used alone or in combination of two or more. The amount of emulsifier used is not particularly limited, but is preferably 0.1 to 6.0 parts by mass, and more preferably 1.0 to 4.0 parts by mass, per 100 parts by mass of the total amount of monomers. When calculating the content of each structural unit of copolymer (A) and the various biomass carbon contents, polymerizable surfactants are classified as monomers of copolymer (A) and their presence is taken into consideration. On the other hand, emulsifiers other than polymerizable surfactants are not classified as monomers of copolymer (A), and their presence is ignored.

[0094] <3. Pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition according to the present embodiment contains the copolymer (A) according to the present embodiment and an aqueous medium (hereinafter also referred to as "aqueous medium (B)"). The pressure-sensitive adhesive composition according to the present embodiment may contain other additives, etc. Examples of the form of the pressure-sensitive adhesive composition according to the present embodiment include, but are not limited to, a solution, a dispersion (e.g., an emulsion), a slurry, etc.

[0095] In the pressure-sensitive adhesive composition, the copolymer (A) is preferably dispersed as particles in an aqueous medium to form an emulsion.

[0096] (3-1. Aqueous Medium (B)) The aqueous medium (B) is water, a hydrophilic organic solvent, or a mixture thereof. Examples of hydrophilic organic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. Among these, the aqueous medium (B) is preferably water. The aqueous medium (B) may have the same composition as the aqueous medium used in the polymerization of the copolymer (A), or may have a different composition. Only one type of aqueous medium (B) may be used, or two or more types may be used.

[0097] (3-2. Other Additives) As other additives, for example, pH adjusters, tackifiers, plasticizers, antioxidants, fillers, pigments, colorants, wetting agents, antifoaming agents, thickeners, crosslinking agents, etc. may be used as appropriate. Only one type of other additive may be used, or two or more types may be used.

[0098] Examples of tackifiers include rosin resins, rosin ester resins, hydrogenated rosin resins, polymerized rosin resins, α-pinene resins, β-pinene resins, terpene phenol resins, C5 fraction petroleum resins, C9 fraction petroleum resins, C5 fraction / C9 fraction petroleum resins, dicyclopentadiene petroleum resins, alkylphenol resins, xylene resins, coumarone resins, coumarone-indene resins, etc. Only one type of tackifier may be used, or two or more types may be used.

[0099] (3-3. Non-volatile content concentration of adhesive composition, etc.) The non-volatile content concentration of the adhesive composition is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more. This is because a larger adhesive layer can be formed with a smaller amount of adhesive composition applied. This is also because the drying time of the applied adhesive composition is shortened, further improving productivity. The "non-volatile content" of the adhesive composition refers to the components remaining after 1 g of the adhesive composition is weighed out on an aluminum dish with a diameter of 5 cm and dried at 105°C for 1 hour with air circulating in a dryer at 1 atmosphere (1013 hPa). The "non-volatile content concentration" of the adhesive composition refers to the mass ratio (% by mass) of the non-volatile content after drying under the above conditions relative to the mass (1 g) of the adhesive composition before drying.

[0100] The nonvolatile content of the pressure-sensitive adhesive composition is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less, because this can more effectively suppress gelation of the copolymer (A) in the pressure-sensitive adhesive composition.

[0101] The nonvolatile content of the pressure-sensitive adhesive composition may be 20 to 90% by mass, 40 to 80% by mass, or 60 to 75% by mass.

[0102] The content of copolymer (A) in the nonvolatile matter of the pressure-sensitive adhesive composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, because this improves the adhesive strength and holding power, particularly the holding power at high temperatures, of the pressure-sensitive adhesive layer containing copolymer (A).

[0103] The content of copolymer (A) in the nonvolatile matter of the pressure-sensitive adhesive composition is preferably 95% by mass or less, and more preferably 92% by mass or less, because the adhesive strength and holding power of the pressure-sensitive adhesive layer containing copolymer (A), particularly the adhesive strength at room temperature and high temperature, are improved.

[0104] The content of the copolymer (A) in the nonvolatile matter of the pressure-sensitive adhesive composition may be 50 to 95 mass %, 60 to 92 mass %, or 70 to 92 mass %.

[0105] (3-4. Method for producing pressure-sensitive adhesive composition) The method for producing the pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and examples thereof include a method in which the other additives described above, which are used as needed, are added to an emulsion containing emulsified particles containing copolymer (A) and water, and then mixed. The timing of adding the other additives is not particularly limited.

[0106] (3-5. Products to which the Pressure-Sensitive Adhesive Composition is Applied) The pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and can be used for, for example, pressure-sensitive adhesive tapes, pressure-sensitive adhesive sheets, pressure-sensitive adhesive labels, stickers, liquid pressure-sensitive adhesives, and the like.

[0107] <4. Adhesive Layer and Adhesive Tape> The adhesive layer of this embodiment is an adhesive layer formed using the adhesive composition of this embodiment. The adhesive layer of this embodiment is formed on a substrate, for example, by applying the adhesive composition of this embodiment to the substrate, drying, and, if necessary, allowing a crosslinking reaction. The drying conditions after applying the adhesive composition of this embodiment to the substrate are not particularly limited, but, for example, drying at 80 to 110°C for 1 to 5 minutes is preferred. After drying, the adhesive composition may be allowed to stand at 20 to 50°C for one day or more, if necessary. The nonvolatile content of the adhesive layer is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more. It may be 100% by mass or less. The thickness of the adhesive layer is not particularly limited, but may be 5 to 200 μm, 10 to 100 μm, or 20 to 50 μm.

[0108] The pressure-sensitive adhesive tape of this embodiment comprises a substrate and an adhesive layer formed on the surface of the substrate, the adhesive layer being formed using the pressure-sensitive adhesive composition of this embodiment. The adhesive layer may be formed on only one side of the substrate, or on both sides. Examples of the substrate include, but are not limited to, resin films such as polyethylene terephthalate (PET) films; woven fabrics; nonwoven fabrics; and metal foils. In addition to the substrate and adhesive layer, the pressure-sensitive adhesive tape may also comprise other layers (e.g., intermediate layers, primer layers, etc.) as long as the effects of the invention are not impaired. Furthermore, the adhesive layer of the pressure-sensitive adhesive tape may be protected by a known release liner such as release paper or release PET. The pressure-sensitive adhesive tape of this embodiment can be described in the same manner as the method for producing the adhesive layer of this embodiment described above.

[0109] <5. Uses of Pressure-Sensitive Adhesive Composition, Pressure-Sensitive Adhesive Layer, and Pressure-Sensitive Adhesive Tape> The pressure-sensitive adhesive composition, pressure-sensitive adhesive layer, and pressure-sensitive adhesive tape of the present embodiment can be used in a variety of applications and fields, such as packaging, joining, fixing, protecting, decorating, and transporting various articles. Furthermore, the material of the object (adherend) on which the pressure-sensitive adhesive composition, pressure-sensitive adhesive layer, and pressure-sensitive adhesive tape of the present embodiment are provided is not particularly limited, and examples thereof include plastic, metal, glass, wood, ceramics, paper, and cloth, and the pressure-sensitive adhesive composition, pressure-sensitive adhesive layer, and pressure-sensitive adhesive tape of the present embodiment can be used in a wide range of applications.

[0110] Examples and comparative examples of this embodiment will be described below, but this embodiment is not limited to these examples.

[0111] 1. Preparation of Copolymer and Pressure-Sensitive Adhesive Composition Example 1 In a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, 23 parts by mass of ion-exchanged water was heated to 80° C. under a nitrogen atmosphere. The ion-exchanged water in the polymerization apparatus was kept at 80° C. while being stirred, and 2.0 parts by mass of a 5.0 mass % aqueous potassium persulfate solution was added as a polymerization initiator to obtain a mixed solution containing the polymerization initiator.

[0112] A monomer emulsion (1) containing 20 parts by mass of ion-exchanged water, "ADEKA REASOAP SR-10" (trade name, manufactured by ADEKA Corporation, ether sulfate-type ammonium salt, polymerizable surfactant) and "LATEMUL E-118B" (trade name, manufactured by Kao Corporation, polyoxyethylene alkyl ether sodium sulfate) as emulsifiers in the amounts shown in the first stage in Table 1, and the types and amounts of monomers and chain transfer agents shown in the first stage in Table 1, was added dropwise to the mixture containing the polymerization initiator in the polymerization reactor over 4 hours. Simultaneously with the start of dropwise addition of the monomer emulsion (1), 20 parts by mass of a 2.5% by mass aqueous potassium persulfate solution was added dropwise over 4 hours. During the dropwise addition of the monomer emulsion (1), the mixture in the polymerization reactor was stirred at 120 revolutions per minute, and the liquid temperature was maintained at 80°C. After completion of the dropwise addition, the mixture was allowed to react at 80°C for 1 hour while continuing to stir. This process is referred to as the first-stage polymerization.

[0113] Thereafter, monomer emulsion (2) containing the types and amounts of monomers and chain transfer agent shown in the second stage in Table 1 was added dropwise over 2 hours. Simultaneously with the start of the dropwise addition of monomer emulsion (2), 20 parts by mass of a 2.5% by mass aqueous potassium persulfate solution was added dropwise over 2 hours. During the dropwise addition of monomer emulsion (2), the mixed liquid in the polymerization apparatus was stirred at 120 revolutions per minute, and the liquid temperature was maintained at 80°C. After the dropwise addition was completed, the mixture was allowed to react at 80°C for 1 hour while continuing to stir. This process is referred to as the second-stage polymerization.

[0114] Thereafter, the mixed liquid in the polymerization apparatus was cooled to 25° C. Ammonia water was added as a neutralizing agent to adjust the pH to 6.0, thereby obtaining an emulsion containing water and emulsified particles containing copolymer (A).

[0115] To 100 parts by mass of the obtained emulsion, 7.5 parts by mass of "Hariestar SK-70D" (trade name, manufactured by Harima Chemicals Group Co., Ltd., rosin ester resin) as a tackifier and 2.0 parts by mass of "Adekanol UH-420" (trade name, manufactured by ADEKA Corporation, nonionic thickener) as a thickener were added to obtain a pressure-sensitive adhesive composition.

[0116] (Examples 2 to 5 and Examples 7 to 9) Copolymers and pressure-sensitive adhesive compositions of Examples 2 to 5 and Examples 7 to 9 were obtained in the same manner as in Example 1, except that the monomers and chain transfer agents were blended as shown in Table 1.

[0117] (Example 6) The first-stage polymerization was carried out in the same manner as in Example 1, except that the monomers and chain transfer agent were blended as shown in Table 1, and the second-stage polymerization was not carried out. The subsequent steps were carried out in the same manner as in Example 1, and a copolymer and a pressure-sensitive adhesive composition of Example 6 were obtained.

[0118] Comparative Examples 1 and 2 Copolymers and pressure-sensitive adhesive compositions of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the monomers and chain transfer agents were blended as shown in Table 1.

[0119] Comparative Example 3 In Comparative Example 3, a copolymer was prepared in toluene by a solution polymerization process. Specifically, a mixed solution containing 120 parts by mass of toluene and the types and amounts of monomers and chain transfer agents shown in the first step in Table 1 was heated to 70°C under a nitrogen atmosphere in a polymerization apparatus equipped with a stirrer, thermometer, and reflux condenser. The mixed solution in the polymerization apparatus was maintained at 70°C while stirring, and 1.0 part by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. The mixed solution was reacted at 70°C for 5 hours while stirring, and then the mixed solution in the polymerization apparatus was cooled to 25°C to obtain a copolymer. Note that during and after the reaction, the monomers and the product polymer were in a state of uniform solution in the solvent. Subsequent steps were the same as in Example 1 to obtain a pressure-sensitive adhesive composition of Comparative Example 3.

[0120] Comparative Example 4 A copolymer and a pressure-sensitive adhesive composition of Comparative Example 4 were obtained in the same manner as in Comparative Example 3, except that the monomers and chain transfer agent were blended as shown in Table 1.

[0121] Comparative Example 5 In Comparative Example 5, a copolymer was prepared in water by a suspension polymerization process. Specifically, in a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, a mixed solution containing 80 parts by mass of ion-exchanged water, "ADEKA REASOAP SR-10" (trade name, manufactured by ADEKA Corporation, ether sulfate-type ammonium salt, polymerizable surfactant) and "LATEMUL E-118B" (trade name, manufactured by Kao Corporation, polyoxyethylene alkyl ether sodium sulfate) as emulsifiers in the amounts shown in the first step in Table 1, and a total of 100 parts by mass of the monomers and chain transfer agent in the formulations shown in Table 1 was mixed at 350 revolutions per minute for 30 minutes, resulting in a monomer droplet size of approximately 50 μm. The temperature was raised to 70°C under a nitrogen atmosphere, and the mixed solution in the polymerization apparatus was maintained at 70°C while being stirred, and 0.2 parts by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. Thereafter, aggregates were generated during the reaction, and the PSA composition of Comparative Example 5 was not obtained.

[0122] 2. Biomass Carbon Content (Biomass Carbon Content of Copolymer) The biomass carbon contents of copolymers (A) obtained in Examples 1 to 9 in Table 1 were calculated using the right-hand side of the above formula (1). The biomass carbon contents of copolymers obtained in Comparative Examples 1 to 5 were calculated using the formula in which "monomer i used to synthesize copolymer (A)" in the above formula (1) was replaced with "monomer i used to synthesize the copolymers of Comparative Examples 1 to 5."

[0123] (Biomass carbon content of alkyl group in first structural unit) The biomass carbon content of the alkyl group in the first structural unit in Table 1 was calculated using the formula on the right side of the above formula (2). The biomass carbon content of the alkyl group in the first structural unit of the copolymers obtained in Comparative Examples 1 to 5 was calculated using the formula in which "monomer Ai corresponding to the first structural unit used to synthesize copolymer (A)" in the above formula (2) was replaced with "monomer Ai corresponding to the first structural unit used to synthesize the copolymers of Comparative Examples 1 to 5."

[0124] (Biomass Carbon Content of Monomer) The biomass carbon contents of the monomers from which the first structural unit and the second structural unit shown in Table 1 are derived, as determined by method B in ASTM D6866-22, are as follows. n-Butyl acrylate: biomass carbon content 57.1% (n-butyl group derived from biomass) 2-Octyl acrylate: biomass carbon content 72.7% (2-octyl group derived from biomass) Isoamyl acrylate: biomass carbon content 62.5% (isoamyl group derived from biomass) n-Octyl acrylate: biomass carbon content 72.7% (n-octyl group derived from biomass) Lauryl acrylate: biomass carbon content 80.0% (lauryl group derived from biomass) 2-Ethylhexyl acrylate: biomass carbon content 0% Methyl methacrylate: biomass carbon content 0% Methacrylic acid: biomass carbon content 0%

[0125] 3. Measurement of Nonvolatile Content of Pressure-Sensitive Adhesive Composition 1 g of the pressure-sensitive adhesive composition was weighed onto an aluminum dish having a diameter of 5 cm, and the composition was dried at 105°C for 1 hour while circulating air in a dryer at 1 atmosphere (1013 hPa), and the mass of the remaining nonvolatile content was measured. The mass ratio of the nonvolatile content after drying under the above conditions to the mass (1 g) of the pressure-sensitive adhesive composition before drying was calculated as the nonvolatile content concentration (%) of the pressure-sensitive adhesive composition.

[0126] 4. Preparation of Adhesive Tapes The adhesive compositions obtained in Examples 1 to 9 and Comparative Examples 1 to 4 were applied to a PET film (A4 size, 50 μm thick). A doctor blade with a coating width of 15 cm was used as the applicator. The applied adhesive composition was dried at 100°C for 2 minutes to remove the aqueous medium from the adhesive composition, and an adhesive layer with a thickness of 30 μm was formed on the PET film. The release surface (silicone-coated surface) of a release paper was laminated onto the adhesive layer on the PET film, and then the resulting product was aged at 23°C for 1 day to obtain an adhesive tape comprising a substrate and an adhesive layer formed on the substrate, with the release paper laminated to the adhesive layer.

[0127] 5. Evaluation of Pressure-Sensitive Adhesive Tapes The pressure-sensitive adhesive tapes produced in each of the Examples and Comparative Examples were subjected to the following evaluations 1 to 4. In the following description, the procedures in each of the Examples and Comparative Examples are common unless otherwise specified.

[0128] [5-1. Evaluation 1: Measurement of Adhesive Strength at Room Temperature (Room-Temperature Adhesive Strength)] A piece of adhesive tape cut to a width of 25 mm and a length of 100 mm was stripped of its release paper in half longitudinal direction and adhered to a SUS#304 plate to prepare an evaluation sample. The adhesion was performed by rolling a 2 kg roller back and forth once in an atmosphere of 23°C. The ambient temperature during adhesion in preparing the evaluation sample is hereinafter referred to as the adhesion temperature. (Adhesion temperature in Evaluation 1: 23°C) In the evaluation sample, the adhesive tape and SUS#304 plate were adhered to a rectangle measuring 25 mm x 50 mm. Neither edge of the adhesive tape adhered to the edge of the SUS#304 plate. That is, in this state, one half of one longitudinal end of the adhesive tape was adhered to the SUS#304 plate, and the release paper was adhered to the other half.

[0129] After preparing the evaluation sample, it was left to stand for 30 minutes in an atmosphere at a temperature of 23°C. The ambient temperature during standing after preparing the evaluation sample is hereinafter referred to as the standing temperature. (Standing temperature in Evaluation 1: 23°C) Then, the following measurements were performed in an atmosphere at a temperature of 23°C. The measurement temperature of the evaluation sample is hereinafter referred to as the measurement temperature. (Measurement temperature in Evaluation 1: 23°C)

[0130] The test was a so-called 180° peel test. The pressure-sensitive adhesive tape of the evaluation sample was folded back 180° with the boundary between the portion attached to the SUS#304 plate and the portion not attached as the folding line. One end of the pressure-sensitive adhesive tape on the side not attached to the SUS#304 plate (the folded back side) was gripped with the upper chuck of a testing machine (Tensilon RTG-1210 (manufactured by A&D Co., Ltd.)). One end of the SUS#304 plate facing the upper chuck across the folding line was gripped with the lower chuck.

[0131] In this state, the adhesive tape was peeled off from the SUS#304 plate at a rate of 300 mm / min to obtain a graph of peel length (mm) vs. peel force (N). In the obtained graph, the average value (N) of the peel force at a peel length of 25 to 50 mm (value obtained by dividing the area of ​​the graph at a peel length of 25 to 50 mm by the peel length) was calculated, and this value was defined as the room temperature adhesive strength (N / 25 mm).

[0132] [5-2. Evaluation 2: Measurement of adhesive strength in a high-temperature environment (high-temperature adhesive strength)] The adhesive strength (N / 25 mm) in a high-temperature environment was measured in the same manner as in "Evaluation 1" above, except that the standing temperature was 70°C and the measurement temperature was 70°C.

[0133] [5-3. Evaluation 3: Measurement of adhesive strength in a low-temperature environment (low-temperature adhesive strength)] The adhesive strength (N / 25 mm) in a low-temperature environment was measured in the same manner as in "Evaluation 1" above, except that the application temperature was -20°C, the standing temperature was -20°C, and the measurement temperature was -20°C.

[0134] [5-4. Evaluation 4: Measurement of High-Temperature Holding Power] The release paper of an adhesive tape cut to a tape width of 25 mm and a length of 100 mm was peeled off 25 mm from one end in the longitudinal direction, and an SUS plate (SUS #304) was attached so as to cover the entire area from which the release paper had been peeled off, to prepare an evaluation sample. That is, in the evaluation sample, the area where the adhesive tape and the SUS plate were attached was a 25 mm x 25 mm square. The attachment was performed by moving a 2 kg roller back and forth once in an atmosphere of 23°C. In addition, at this time, a portion of the adhesive tape on the extension of the end attached to the SUS plate, which was the SUS plate only and where the adhesive tape was not attached, was provided as a SUS plate-side chuck portion.

[0135] The evaluation sample was left to stand in a thermostatic chamber at 80°C for 30 minutes. Thereafter, in the thermostatic chamber at 80°C, the chuck portion of the evaluation sample on the SUS plate side was gripped with a chuck, and a 1 kg weight was hung from one end of the adhesive tape in the longitudinal direction on the side where the SUS plate was not attached, and the time (h) required for the weight to fall was measured. The test was carried out for up to 24 hours, and samples in which the weight had not fallen after 24 hours were recorded as "24<" in Table 1.

[0136] <6. Evaluation Results> The evaluation results of evaluations 1 to 4 are shown in Table 1.

[0137]

[0138] As shown in Table 1, the adhesive tapes of Examples 1 to 9, which use the copolymer (A) containing biomass carbon atoms of this embodiment, exhibit strong adhesive strength not only at room temperature but also at high and low temperatures, and it can be seen that an adhesive layer is formed that also has high holding power at high temperatures.

[0139] On the other hand, in the pressure-sensitive adhesive tapes according to Comparative Examples 1 and 2, which were made from a pressure-sensitive adhesive composition using a copolymer that did not contain biomass carbon atoms, at least one of the adhesive strength and high-temperature holding power was insufficient. In Comparative Example 2, the blending amounts of vinyl acetate and methyl methacrylate in the copolymer were increased, but this did not result in an improvement in adhesive strength.

[0140] From these facts, it can be seen that the object of this embodiment cannot be achieved with a copolymer that does not contain biomass carbon atoms.

[0141] Furthermore, the adhesive tapes of Comparative Examples 3 and 4, which were produced using adhesive compositions using copolymers produced by solution polymerization, were insufficient in at least one of high-temperature adhesive strength, low-temperature adhesive strength, and high-temperature holding power.

[0142] From these facts, it is clear that the object of this embodiment cannot be achieved in a configuration in which the copolymer is produced by a method other than emulsion polymerization.

[0143] As described above, according to the present embodiment, it is possible to provide a copolymer, a pressure-sensitive adhesive composition, and related technologies that can form an adhesive layer that does not increase or only increases the amount of carbon dioxide present in the global environment even when incinerated to generate carbon dioxide. Furthermore, according to the present embodiment, it is possible to provide a copolymer and a pressure-sensitive adhesive composition that can form an adhesive layer that exhibits strong adhesive strength not only at room temperature but also at high and low temperatures, and that also has high holding power at high temperatures. Furthermore, according to the present embodiment, it is possible to provide an adhesive layer that exhibits strong adhesive strength not only at room temperature but also at high and low temperatures, and that also has high holding power at high temperatures, and a pressure-sensitive adhesive tape that includes the adhesive layer.

Claims

1. A copolymer obtained by emulsion polymerization, comprising first structural units derived from an alkyl (meth)acrylate and second structural units derived from an ethylenically unsaturated compound having at least one member selected from the group consisting of a carboxy group and a salt of a carboxy group, and containing biomass carbon atoms.

2. The copolymer according to claim 1, having a biomass carbon content of 10% or more as determined by method B of ASTM D6866-22.

3. The copolymer according to claim 1, wherein at least one of the structural units contained as the first structural unit has an alkyl group containing a biomass carbon atom.

4. The carbon atom constituting the alkyl group derived from the alkyl (meth)acrylate contained in the first structural unit is replaced with a carbon atom (C １Ａ ), the carbon atoms (C １Ａ 4. The copolymer according to claim 3, wherein the biomass carbon content, as determined by method B in ASTM D6866-22, of the total number of carbon atoms in the copolymer is 20% or more.

5. The copolymer according to claim 1, having a glass transition temperature Tg of -80 to 30°C.

6. The copolymer according to claim 1, wherein the first structural unit comprises at least one selected from the group consisting of a structural unit derived from n-butyl (meth)acrylate, a structural unit derived from isoamyl (meth)acrylate, a structural unit derived from n-octyl (meth)acrylate, a structural unit derived from 2-octyl (meth)acrylate, and a structural unit derived from lauryl (meth)acrylate.

7. The copolymer according to claim 1, further comprising structural units derived from a vinyl ester compound.

8. A pressure-sensitive adhesive composition comprising the copolymer according to any one of claims 1 to 7 and an aqueous medium.

9. The pressure-sensitive adhesive composition according to claim 8, wherein the copolymer is dispersed as particles in the aqueous medium to form an emulsion.

10. An adhesive tape comprising a substrate and an adhesive layer formed on the surface of the substrate, wherein the adhesive layer is formed using the adhesive composition according to claim 8.

11. A method for producing the copolymer according to any one of claims 1 to 7, comprising a step of emulsion polymerizing monomers containing an alkyl (meth)acrylate and an ethylenically unsaturated compound having at least one selected from the group consisting of a carboxy group and a salt of a carboxy group, wherein at least one of the monomers contains a biomass carbon atom.

12. The method for producing the copolymer of claim 11, wherein the monomer comprises an alkyl (meth)acrylate containing biomass carbon atoms.

13. The method for producing a copolymer according to claim 12, wherein the alkyl (meth)acrylate containing a biomass carbon atom contains a biomass carbon atom in the alkyl group bonded to the (meth)acryloyloxy group.

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