Copolymer, Adhesive Composition, Adhesive Tape, and Method for Producing Copolymer

Abstract

Provided are a copolymer containing biomass carbon atoms, an adhesive composition and an adhesive tape using the copolymer, and a method for producing the copolymer, which can form an adhesive layer that has a low environmental impact during production, exhibits strong adhesive force in a wide temperature range from low temperature to high temperature, and has excellent holding power in a high temperature environment. A copolymer obtained by emulsion polymerization, having 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, a copolymer containing biomass carbon atoms, an adhesive composition and an adhesive tape using the copolymer, and a method for producing the copolymer.

Description

Technical Field

[0001] The present disclosure relates to a copolymer, an adhesive composition, an adhesive tape, and a method for producing a copolymer.

Background Art

[0002] Most of the raw materials for producing 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 a long time. Therefore, biodegradably treating or incinerating synthetic resins and releasing carbon dioxide into the atmosphere means releasing carbon that was fixed deep underground and did not exist in the atmosphere as carbon dioxide into the atmosphere, which can be a factor in global warming.

[0003] Plants are attracting attention as a carbon source because they absorb carbon dioxide circulating in the global environment, perform a photosynthesis reaction using carbon dioxide and water as raw materials, and assimilate or immobilize it as an organism. If materials obtained from plants are used as raw materials for synthetic resins, even if they are biodegradably treated or incinerated to generate carbon dioxide, since the carbon dioxide existing in the global environment circulates, there is no change in the total amount of carbon constituting the carbon dioxide.

[0004] By the way, an adhesive is a typical use of synthetic resins. An adhesive is processed, for example, into an adhesive tape having a layer containing an adhesive, that is, an adhesive layer formed thereon, and is attached to an article in order to repair various articles or fix articles to each other.

[0005] As an adhesive using a biomass-derived material, an adhesive containing natural rubber is known. However, an adhesive containing natural rubber has a problem that it cannot exhibit sufficient reliability in the usage environments of electronic components, vehicles, houses, and building materials because it is inferior in heat resistance and the like.

[0006] As an adhesive tape excellent in heat resistance and the like, an adhesive tape having a (meth)acrylic pressure-sensitive adhesive layer containing a (meth)acrylic copolymer is widely used. Even with such an adhesive tape, it was possible to select and use biomass-derived materials such as rosin and terpene as the tackifier. However, depending on the method of using only additives derived from biomass, it is difficult to increase the carbon content rate derived from biomass as a whole adhesive tape 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 a structural unit derived from a (meth)acrylic monomer containing carbon derived from a living organism.

[0008] Patent Document 2 describes an adhesive containing a reaction product of at least one polymerizable monomer at least partially derived from a non-petroleum source, a reaction initiator, and a stabilizer.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] Both the adhesive tape of Patent Document 1 and the fine particle adhesive of Patent Document 2 exhibit good adhesive strength under normal temperature environment, but there is room for improvement in the adhesive strength under high temperature environment and low temperature environment and the holding power under high temperature environment. Furthermore, since an organic solvent is used as the liquid medium, it may cause a burden on the environment.

[0011] The present disclosure aims to provide a copolymer containing biomass carbon atoms, an adhesive composition and an adhesive tape using the copolymer, and a method for producing the copolymer, which have a low environmental impact during production, exhibit strong adhesive force in a wide temperature range from low to high temperatures, and can form an adhesive layer with excellent holding power under high temperature environments.

Means for Solving the Problems

[0012] [1] A copolymer obtained by emulsion polymerization, a first structural unit derived from an alkyl (meth)acrylate, 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 having, a copolymer containing biomass carbon atoms. [2] The copolymer according to [1] above, wherein the biomass carbon content determined by method B in ASTM D6866-22 is 10% or more. [3] The copolymer according to [1] or [2] above, wherein at least one of the structural units included as the first structural unit has an alkyl group containing biomass carbon atoms. [4] When the carbon atoms constituting the alkyl group derived from the alkyl (meth)acrylate contained in the first structural unit are regarded as carbon atoms (C 1A ), the biomass carbon content determined by method B in ASTM D6866-22 in the total number of carbon atoms (C 1A ) contained in the copolymer is 20% or more. The copolymer according to [3] above. [5] The copolymer according to any one of [1] to [4] above, having a glass transition point Tg of -80 to 30°C. [6] The copolymer according to any one of [1] to [5] above, wherein the first structural unit contains 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 one of [1] to [6] above, further having a structural unit derived from a vinyl ester compound. [8] An adhesive composition comprising the copolymer according to any one of [1] to [7] above and an aqueous medium. [9] The adhesive composition according to [8] above, wherein the copolymer is dispersed as particles in the aqueous medium to form an emulsion.

[10] Comprising a substrate and an adhesive layer formed on the surface of the substrate. An adhesive tape, wherein the adhesive layer is formed using the 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 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. A method for producing a copolymer, wherein at least one of the monomers contains biomass carbon atoms.

[12] The method for producing a copolymer according to

[11] above, wherein the monomer contains an alkyl (meth) acrylate containing biomass carbon atoms.

[13] The method for producing a copolymer according to

[12] above, wherein the alkyl (meth) acrylate containing biomass carbon atoms contains biomass carbon atoms in the alkyl group bonded to the (meth) acryloyloxy group. [Advantages of the Invention]

[0013] According to the present disclosure, it is possible to provide a copolymer containing biomass carbon atoms, an adhesive composition and an adhesive tape using the copolymer, and a method for producing the copolymer, which can form an adhesive layer with a small environmental load during production, exhibit strong adhesion in a wide temperature range from low temperature to high temperature, and have excellent holding power under high temperature environments.

Mode for Carrying Out the Invention

[0014] In the following description, unless otherwise specified, the 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] “Ethylenically unsaturated compound” means a compound having an ethylenically unsaturated bond. “Ethylenically unsaturated bond” refers to an ethylenically unsaturated bond having radical polymerizability, unless otherwise specified.

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

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

[0019] For a structural unit having an ionic functional group such as a carboxy group, unless otherwise specified, the structural unit is regarded as being derived from the same ionic compound whether a part of the functional group is ion-exchanged or not. For example, -CH 2 C(CH 3 )(COONa)- is also regarded as a structural unit derived from methacrylic acid unless otherwise specified.

[0020] "Salt of carboxy group" means a structure in which the carboxy group forms a salt, and examples include -COONa, -COOK, -COONH 4 and the like.

[0021] "Dispersion" means a solid-liquid mixture in which a solid that is not dissolved in a liquid exists as particles dispersed in the liquid. "Slurry" means a fluid in which solid particles such as clay and pigment are suspended in a liquid.

[0022] In the following description, "adhesive force" means the force required to peel the adhesive surface from the adherend. Also, in the following description, "holding force" means the force with which the adhesive layer constituting the adhesive surface resists displacement against a static load in a direction parallel to the adhesive surface of an adhesive tape or the like.

[0023] "Biomass" means an organic resource derived from living organisms, excluding fossil resources. "Biomass compound" means a compound derived from biomass. "Biomass carbon atom" means a carbon atom derived from biomass.

[0024] <1. Copolymer> The copolymer of this embodiment (hereinafter also referred to as "copolymer (A)") is obtained by emulsion polymerization. The 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, the copolymer (A) may have other structures that do not correspond to 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 the copolymer (A) is a value determined by method B in ASTM D6866-22 (hereinafter may be abbreviated as "ASTM method"). In method B in ASTM D6866-22, the biomass carbon content of the analyte is a value obtained by correcting the modern carbon ratio (pMC, percent of Modern Carbon) of the analyte determined by accelerator mass spectrometry (AMS) measurement with the atmospheric correction factor (REF value) described in section 9.4 of the same standard.

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

[0027] The biomass carbon content B (A) can be determined by using the copolymer (A) itself as the analysis target of the above ASTM method, or can be calculated by the above formula (1).

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

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

[0030] The above biomass carbon content B (A) of the copolymer (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. Copolymer (A) glass transition point) The glass transition point Tg of copolymer (A) is calculated by Fox's equation based on the glass transition points of the respective structural units contained in copolymer (A) as homopolymers. The specific calculation method of the glass transition point Tg of copolymer (A) is from the glass transition point Tgi of the homopolymer of each structural unit Mi (i = 1, 2, 3...), and the mass fraction Xi of the structural unit Mi in copolymer (A) (ΣXi (total structural units) = 1), calculated by Fox's equation 1 / Tg = Σ(Xi / Tgi).

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

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

[0034] The glass transition point Tg of copolymer (A) is preferably -80 °C or higher, more preferably -65 °C or higher, and even more preferably -55 °C or higher. This is because the cohesive force of the pressure-sensitive adhesive formed using copolymer (A) can be improved, and a more excellent holding force at high temperatures can be imparted to the pressure-sensitive adhesive layer.

[0035] The glass transition temperature Tg of the copolymer (A) is preferably 30°C or lower, more preferably 0°C or lower, still 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, and the adhesion of the pressure-sensitive adhesive layer to the substrate can be improved. Further, this is because the flexibility of the pressure-sensitive adhesive layer formed using the copolymer (A) can be enhanced, and the tackiness of the pressure-sensitive adhesive layer during dry use can be improved.

[0036] The glass transition temperature Tg of the copolymer (A) may be -80 to 30°C, may be -65 to 0°C, may be -55 to -20°C, or may be -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. That is, the alkyl group contained in the first structural unit refers to the 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 according to 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-chain structure.

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

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

[0041] Among the structural units included as the first structural unit, it is preferable that at least one kind of structural unit has an alkyl group containing biomass carbon atoms.

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

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

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

[0045] The above 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 above biomass carbon content B (1A) may be 20 - 100%, may be 30 - 90%, may be 40 - 65%, may be 50 - 65%, or may be 65 - 90%.

[0047] The number of carbon atoms of the alkyl group containing biomass carbon atoms may be 1 or more, may be 2 or more, may be 4 or more, or may be 6 or more. Also, the number of carbon atoms of the alkyl group containing biomass carbon atoms may be 20 or less, may be 15 or less, or may be 10 or less. The number of carbon atoms in the alkyl group containing biomass carbon atoms may be 1 to 20, may be 2 to 15, may be 4 to 10, or may be 6 to 10. The alkyl group containing biomass carbon atoms preferably contains only biomass carbon atoms.

[0048] Examples of the compound 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, and the like. The compound from which the first structural unit is derived may be one kind or two or more kinds.

[0049] The first structural unit preferably contains 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 contains 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 contains 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 the compound from which the second structural unit is derived include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, itaconic acid, maleic acid, and the like. 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 biomass carbon atoms.

[0051] The second structural unit preferably contains 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 contains a structural unit derived from (meth)acrylic acid. Among the structural units contained 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 still more preferably 90% by mass or more. Among the structural units contained as the second structural unit, the content of the structural unit derived from (meth)acrylic acid may be 100% by mass or less than 100% by mass.

[0052] (1-5. Other structures) Other structures that the copolymer (A) may have include other structural units that do not correspond to 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, and the like; and the like.

[0053] [Other structural units] The compounds serving as the source of other structural units are not particularly limited. For example, vinyl ester compounds such as vinyl acetate, vinyl formate, vinyl propionate, vinyl versatate; conjugated diolefin compounds such as butadiene, isoprene, chloroprene; vinyl compounds containing an amine imide group such as 1,1,1-trimethylamine methacrylimide; (meth)acrylamide compounds such as (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide; alkoxysilyl group-containing vinyl compounds such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane; epoxy group-containing vinyl compounds such as glycidyl (meth)acrylate, glycidyl vinyl ether, 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, t-butyl vinyl ketone; light stabilizers having radical polymerizability such as 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate; polymerizable surfactants; and the like. The compounds serving as the source of other structural units may be one kind or two or more kinds.

[0054] When the copolymer (A) has the above 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% by mass or more, more preferably 2.5% by mass or more, and even more preferably 4.0% by mass or more. This is because the adhesive strength of the adhesive containing the copolymer (A) at room temperature is improved.

[0056] 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 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8.0% by mass or less. This is because the adhesive strength of the pressure-sensitive adhesive containing the copolymer (A) at room temperature is improved.

[0057] 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) may be 1.0 to 15% by mass, may be 2.5 to 10% by mass, or may be 4.0 to 8.0% by mass.

[0058] The polymerizable surfactant serving as the source of the other structural unit is a compound having an ethylenically unsaturated bond and also functioning as a surfactant. The polymerizable surfactant may be nonionic, anionic, or cationic, but is preferably anionic. Examples of the anionic polymerizable surfactant include ether sulfate type, ammonium salt of ether sulfate type, phosphate ester type, etc. Among these, the ammonium salt of ether sulfate type is preferable.

[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. This is 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. This is 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% by mass, may be 0.30 to 3.0% by mass, or may be 0.60 to 1.5% by 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 part by mass or less with respect to 100 parts by mass of the total amount of the structural units contained in the copolymer (A). When the content of the terminal structure in the copolymer (A) is 0.50 part by mass or less with respect to 100 parts by mass of the total amount of the structural units contained in the copolymer (A), the presence of the terminal structure may be ignored in calculating the content of each structural unit and the content of 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 the copolymer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. This is because it can suppress an increase in the glass transition point of the copolymer (A) and improve the tackiness, wettability, and further the adhesive strength of the adhesive layer.

[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 still more preferably 93% by mass or less. This is because it can appropriately maintain the polarity of the copolymer (A) and the cohesive force of the adhesive layer, and an adhesive layer having high adhesiveness can be obtained not only at normal temperature but also at high and low temperatures.

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

[0067] The content rate 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. This is because the cohesive force of the pressure-sensitive adhesive layer containing the copolymer (A) can be improved and the holding power at high temperatures can be enhanced.

[0068] The content rate 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. This is because an increase in the glass transition point of the copolymer (A) can be suppressed, and the tackiness, wettability, and even the adhesive strength of the pressure-sensitive adhesive layer can be improved.

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

[0070] The total content rate 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 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 the adhesive strength of the pressure-sensitive adhesive layer can be improved. The total content rate of the first structural unit and the second structural unit in the copolymer (A) may be 100% by mass or may be 100% by mass or less.

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

[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 force of the pressure-sensitive adhesive and impart better holding power at high temperatures to the pressure-sensitive adhesive layer. In addition, since emulsion polymerization can be carried out in an aqueous medium as described later, the environmental load during production is small.

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

[0074] Biomass carbon content B (M)The total raw material monomers of the copolymer (A) can be determined as the analysis target of method B in ASTM D6866-22, or can also be calculated by the above formula (3).

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

[0077] The raw material monomers of the copolymer (A) preferably contain an alkyl (meth) acrylate containing a biomass carbon atom. It is more preferable that the alkyl group bonded to the (meth) acryloyloxy group in the alkyl (meth) acrylate contains a biomass carbon atom.

[0078] Here, let the carbon contained in the alkyl group of the alkyl (meth) acrylate contained in the raw material monomers of the copolymer (A) be C (1M) When, the C (1M) contained in the total number of the raw material monomers of the copolymer (A), the biomass carbon content determined by method B in ASTM D6866-22 is defined as the "biomass carbon content B (1M) ". Let the mole fraction of the alkyl (meth) acrylate Ai (i = 1, 2, 3, ···) contained in the raw material monomers of the copolymer (A) be R Ai [0 < R Ai < 1], and the number of carbon atoms contained in the alkyl group of the alkyl (meth) acrylate Ai be C Ai, let the number of carbon atoms derived from the biomass compound contained in the alkyl group of monomer Ai be C BAi Then, the following formula (4) holds between these values and the above biomass carbon content B (1M) [%]. B (1M) = 100×Σ(R Ai ×C BAi ) / Σ(R Ai ×C Ai ) (4)

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

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

[0081] The 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] The 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] Examples of the ethylenically unsaturated compound having at least one selected from the group consisting of an alkyl (meth) acrylate and a carboxy group and a salt of a carboxy group contained in the raw material monomer of the copolymer (A) are the same as those of the ethylenically unsaturated compound having at least one selected from the group consisting of an alkyl (meth) acrylate derived from the first structural unit of the copolymer (A) in the present embodiment and a carboxy group and a salt of a carboxy group derived from the second structural unit, and the preferred embodiments are also the same.

[0084] (2-2: Step of emulsion polymerization) The production method of the present embodiment has 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 the alkyl (meth) acrylate in the total amount (100% by mass) of the raw material monomers of the copolymer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. This is because it can suppress the increase in the glass transition point of the obtained copolymer (A) and improve the tackiness, wettability, and further adhesion strength of the pressure-sensitive adhesive layer. The content of the alkyl (meth) acrylate in the total amount (100% by mass) of the raw material monomers of the copolymer (A) is preferably 98% by mass or less, more preferably 95% by mass or less, and still more preferably 93% by mass or less. This is because it can appropriately maintain the polarity of the obtained copolymer (A) and the cohesive force of the pressure-sensitive adhesive layer, and a pressure-sensitive adhesive layer having high adhesiveness not only at room temperature but also at high and low temperatures can be obtained. The content of the alkyl (meth) acrylate in the total amount (100% by mass) of the raw material monomers of the copolymer (A) may be 60 to 98% by mass, may be 70 to 95% by mass, or may be 80 to 93% by mass.

[0086] The content rate 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 the raw material monomers of the copolymer (A) is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and still more preferably 3.0% by mass or more. This is because it can improve the cohesive force of the pressure-sensitive adhesive layer containing the obtained copolymer (A) and enhance the holding power at high temperatures. The content rate 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 the raw material monomers of the copolymer (A) is preferably 12% by mass or less, more preferably 9.0% by mass or less, and still more preferably 6.0% by mass or less. This is because it can suppress the increase in the glass transition point of the copolymer (A) and improve the tackiness, wettability, and further the adhesive strength of the pressure-sensitive adhesive layer. The content rate 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 the raw material monomers of the copolymer (A) may be 1.0 to 12% by mass, may be 2.0 to 9.0% by mass, or may be 3.0 to 6.0% by mass.

[0087] The total content rate of the alkyl (meth) acrylate and 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 the raw material monomers of the copolymer (A) is preferably 65% by mass or more, more preferably 75% by mass or more, and still more preferably 85% by mass or more. It can suppress the increase in the glass transition point of the obtained copolymer (A) and improve the tackiness, wettability, and further the adhesive strength of the pressure-sensitive adhesive layer. The total content rate of the alkyl (meth) acrylate and 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 the raw material monomers of the copolymer (A) may be 90% by mass or more, may be 100% by mass, or may be 100% by mass or less.

[0088] In emulsion polymerization, a polymerization initiator for promoting 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 monomer, etc. may be used. The raw material monomers of the copolymer (A) may be charged in the entire amount into the reactor in advance, or may be polymerized while being continuously or intermittently supplied from the viewpoint of obtaining uniform particles. The raw material monomers to be continuously or intermittently supplied may be a part or all of the raw material monomers of 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 the present embodiment, the emulsion polymerization of the monomer is preferably carried out in an aqueous medium. Thereby, a copolymer-containing liquid (copolymer dispersion) in which the copolymer (A) is dispersed as emulsion particles in the aqueous medium, that is, an emulsion is obtained. The aqueous medium is water, a hydrophilic organic solvent, or a mixture thereof. Examples of the hydrophilic organic solvent include methanol, ethanol, isopropyl alcohol, N-methylpyrrolidone, etc. From the viewpoint of polymerization stability, the aqueous medium is preferably water. Note that as long as the polymerization stability is not impaired, a mixed solvent of water and a hydrophilic solvent may be used as the aqueous medium.

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

[0091] Optionally, 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 metal salts of formaldehyde sulfoxylate; reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite; and the like. Only one type of reducing agent may be used, or two or more types may be used.

[0092] Examples of the chain transfer agent 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, benzyl alcohol, and the like. Only one type of chain transfer agent may be used, or two or more types may be used. The amount of the chain transfer agent used is preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less, still more preferably 0.50 parts by mass or less, and even more preferably 0.30 parts by mass or less with respect to 100 parts by mass of the total amount of the raw material monomers of the copolymer (A). This is because the cohesive force of the adhesive is improved, and the holding force at high temperature of the adhesive layer can be improved. The amount of the chain transfer agent used may be 0.01 parts by mass or more, or 0.05 parts by mass or more with respect to 100 parts by mass of the total amount of the monomers. This is because the adhesive force of the adhesive layer can be improved.

[0093] Examples of the emulsifier include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium polyoxyethylene alkyl ether sulfate; nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene nonylphenyl ether; cationic surfactants such as cetyltrimethylammonium bromide and laurylpyridinium chloride; amphoteric surfactants such as lauryl betaine; and the above-mentioned polymerizable surfactants; and the like. Only one type of these surfactants may be used, or two or more types may be used. The amount of the emulsifier used is not particularly limited, but is preferably 0.1 to 6.0 parts by mass, more preferably 1.0 to 4.0 parts by mass, based on 100 parts by mass of the total amount of the monomers. In calculating the content ratio of each structural unit of the copolymer (A) and the content ratio of various biomass carbons, the polymerizable surfactant is classified as a monomer of the copolymer (A), and its presence is taken into consideration. On the other hand, an emulsifier other than the polymerizable surfactant is not classified as a monomer of the copolymer (A), and its presence is ignored.

[0094] <3. Adhesive Composition> The adhesive composition according to this embodiment contains the copolymer (A) of this embodiment and an aqueous medium (hereinafter also referred to as "aqueous medium (B)"). The adhesive composition according to this embodiment may contain other additives and the like. Examples of the form of the adhesive composition of this embodiment include, but are not limited to, a solution, a dispersion (for example, an emulsion), a slurry, and the like.

[0095] In the adhesive composition, the copolymer (A) is preferably dispersed as particles in the 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 the hydrophilic organic solvent include methanol, ethanol, isopropyl alcohol, N-methylpyrrolidone, and the like. Among these, the aqueous medium (B) is preferably water. The aqueous medium (B) may have the same composition as the aqueous medium used for the polymerization of the copolymer (A), or may have a different composition. The aqueous medium (B) may use only one type, or may use two or more types.

[0097] (3-2. Other Additives) As other additives, for example, pH adjusters, tackifiers, plasticizers, antioxidants, fillers, pigments, colorants, wetting agents, defoamers, thickeners, crosslinking agents, etc. can be appropriately used. 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-based petroleum resins, C9 fraction-based petroleum resins, C5 fraction / C9 fraction-based petroleum resins, dicyclopentadiene-based 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. Nonvolatile content concentration, etc. of the adhesive composition) The nonvolatile 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 more adhesive layers can be formed with a smaller application amount of the adhesive composition. Also, the drying time of the applied adhesive composition is shortened, and productivity is further improved. Note that the "nonvolatile content" of the adhesive composition is the component remaining after weighing 1 g of the adhesive composition in an aluminum dish with a diameter of 5 cm and drying it at 105°C for 1 hour while circulating air in a dryer at 1 atmospheric pressure (1013 hPa). The "nonvolatile content concentration" of the adhesive composition is the mass ratio (% by mass) of the nonvolatile content after drying under the above conditions to the mass (1 g) of the adhesive composition before drying.

[0100] The nonvolatile content concentration of the 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. This is because gelation of the copolymer (A) in the adhesive composition can be more effectively suppressed.

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

[0102] The content rate of the copolymer (A) in the non-volatile content of the pressure-sensitive adhesive composition is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. This is because the adhesive force and holding force of the pressure-sensitive adhesive layer containing the copolymer (A), particularly the holding force at high temperatures, are improved.

[0103] The content rate of the copolymer (A) in the non-volatile content of the pressure-sensitive adhesive composition is preferably 95% by mass or less, and more preferably 92% by mass or less. This is because the adhesive force and holding force of the pressure-sensitive adhesive layer containing the copolymer (A), particularly the adhesive force at normal temperature and high temperatures, are improved.

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

[0105] (3-4. Method for producing the pressure-sensitive adhesive composition) The method for producing the pressure-sensitive adhesive composition of the present embodiment is not particularly limited. For example, a method of adding and mixing the above-mentioned other additives used as necessary to an emulsion containing emulsion particles containing the copolymer (A) and water can be mentioned. The timing of adding the other additives is not particularly limited.

[0106] (3-5. Application products of the pressure-sensitive adhesive composition) The pressure-sensitive adhesive composition of the present embodiment is not particularly limited, but can be used, for example, for pressure-sensitive adhesive tapes, pressure-sensitive adhesive sheets, pressure-sensitive adhesive labels, stickers, liquid pressure-sensitive adhesives, etc.

[0107] <4. Pressure-sensitive adhesive layer and pressure-sensitive adhesive tape> The pressure-sensitive adhesive layer of the present embodiment is a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present embodiment. The pressure-sensitive adhesive layer of the present embodiment is formed on a substrate, for example, by applying the pressure-sensitive adhesive composition of the present embodiment to the substrate, drying, and, if necessary, subjecting it to a crosslinking reaction. The drying conditions after applying the pressure-sensitive adhesive composition of the present embodiment to the substrate are not particularly limited. For example, drying conditions of 80 to 110 °C for 1 to 5 minutes are preferable. Further, after drying, if necessary, it may be left standing at 20 to 50 °C for one day or more. The non-volatile content concentration of the pressure-sensitive adhesive layer is preferably 95% by mass or more, more preferably 97% by mass or more, still more preferably 99% by mass or more, and may be 100% by mass, or may be 100% by mass or less. The thickness of the pressure-sensitive adhesive layer is not particularly limited, and may be 5 to 200 μm, may be 10 to 100 μm, or may be 20 to 50 μm.

[0108] The pressure-sensitive adhesive tape of the present embodiment includes a substrate and a pressure-sensitive adhesive layer formed on the surface of the substrate, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive composition of the present embodiment. The pressure-sensitive adhesive layer may be formed on only one surface of the substrate, or may be formed on both surfaces. The substrate is not particularly limited, and examples thereof include resin films such as polyethylene terephthalate (PET) films; woven fabrics; non-woven fabrics; metal foils; and the like. In addition to the substrate and the pressure-sensitive adhesive layer, the pressure-sensitive adhesive tape may also include other layers (for example, an intermediate layer, a primer layer, etc.) as long as the effects of the invention are not impaired. Further, the pressure-sensitive 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 the present embodiment is described in the same manner as the manufacturing method of the pressure-sensitive adhesive layer of the present embodiment described above.

[0109] <5. Applications of the 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 various applications and fields such as packaging, joining, fixing, protecting, decorating, and transporting various articles. Further, the material of the object (adherend) to 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 plastics, metals, glass, wood, ceramics, paper, cloth, etc., and can be widely applied.

Examples

[0110] Hereinafter, examples and comparative examples of the present embodiment will be described. However, the present 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. While stirring the ion-exchanged water in the polymerization apparatus, it was maintained at 80°C, and 2.0 parts by mass of a 5.0 mass% aqueous potassium persulfate solution as a polymerization initiator was added to obtain a mixed solution containing the polymerization initiator.

[0112] A monomer emulsion (1) containing 20 parts by mass of ion-exchanged water, "Adekaria Soap 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, sodium polyoxyethylene alkyl ether sulfate) in the amounts shown in the first stage of Table 1 as emulsifiers, and the monomers and chain transfer agents of the types and amounts shown in the first stage of Table 1 was dropped into the mixed solution containing the polymerization initiator in the above polymerization apparatus over 4 hours. Simultaneously with the start of dropping of the monomer emulsion (1), 20 parts by mass of a 2.5 mass% aqueous potassium persulfate solution was dropped over 4 hours. During the dropping of the monomer emulsion (1), the mixed solution in the polymerization apparatus was stirred at 120 revolutions per minute, and the liquid temperature was maintained at 80°C. After the dropping was completed, the reaction was carried out at 80°C for 1 hour while continuing stirring. This step is referred to as the first-stage polymerization.

[0113] Subsequently, the monomer emulsion (2) containing the types and amounts of monomers and chain transfer agents shown in the second stage in Table 1 was dropped over 2 hours. Simultaneously with the start of dropping of the monomer emulsion (2), 20 parts by mass of a 2.5 mass% aqueous potassium persulfate solution was dropped over 2 hours. During the dropping of the monomer emulsion (2), the mixed solution in the polymerization apparatus was stirred at 120 revolutions per minute, and the liquid temperature was maintained at 80°C. After the dropping was completed, the reaction was carried out at 80°C for 1 hour while continuing the stirring. This step is taken as the second-stage polymerization.

[0114] Subsequently, the mixed solution in the polymerization apparatus was cooled to 25°C. Aqueous ammonia was added as a neutralizing agent to adjust the pH to 6.0, and an emulsion containing emulsion particles containing the copolymer (A) and water was obtained.

[0115] To 100 parts by mass of the obtained emulsion, 7.5 parts by mass of "Hari Ester SK-70D" (trade name, manufactured by Harima Kasei 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 an adhesive composition.

[0116] (Examples 2 to 5 and Examples 7 to 9) Copolymers and 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 blending of the monomers and the chain transfer agent was the blending described in Table 1.

[0117] (Example 6) Regarding the first-stage polymerization, it was carried out in the same manner as in Example 1 except that the blending of the monomers and the chain transfer agent was the blending described in Table 1, and the second-stage polymerization was not carried out. The subsequent steps were the same as in Example 1 to obtain the copolymer and the adhesive composition of Example 6.

[0118] (Comparative Examples 1 to 2) Copolymers and adhesive compositions of Comparative Examples 1 to 2 were obtained in the same manner as in Example 1 except that the blending of the monomers and the chain transfer agent was the blending described in Table 1.

[0119] (Comparative Example 3) In Comparative Example 3, the copolymer was prepared in toluene by a solution polymerization process. Specifically, a mixed solution containing 120 parts by mass of toluene, the monomers and chain transfer agents of the types and amounts shown in the first stage of Table 1 was heated to 70°C under a nitrogen atmosphere in a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser. While stirring the mixed solution in the polymerization apparatus, it was maintained at 70°C, and 1.0 part by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. After reacting the mixed solution at 70°C for 5 hours while stirring, the mixed solution in the polymerization apparatus was cooled to 25°C to obtain a copolymer. During and after the above reaction, the monomers and the resulting polymer were in a state of being uniformly dissolved in the solvent. Subsequent steps were carried out in the same manner as in Example 1 to obtain the pressure-sensitive adhesive composition of Comparative Example 3.

[0120] (Comparative Example 4) The copolymer and pressure-sensitive adhesive composition of Comparative Example 4 were obtained in the same manner as in Comparative Example 3, except that the blending of the monomers and chain transfer agent was the blending described in Table 1.

[0121] (Comparative Example 5) In Comparative Example 5, the 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, 80 parts by mass of ion-exchanged water, the amounts of "Adekaria Soap 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, sodium polyoxyethylene alkyl ether sulfate) shown in the first stage of Table 1 as emulsifiers, and a total of 100 parts by mass of the monomers and chain transfer agent of the formulation described in Table 1 were mixed at 350 revolutions per minute for 30 minutes to obtain a monomer droplet diameter of about 50 μm. The temperature was raised to 70°C under a nitrogen atmosphere, and while stirring the mixed solution in the polymerization apparatus, it was maintained at 70°C, and 0.2 part by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. Thereafter, agglomerates were generated during the reaction, and the pressure-sensitive adhesive composition of Comparative Example 5 could not be obtained.

[0122] <2. Biomass Carbon Content> (Biomass Carbon Content of the Copolymer) The biomass carbon content of the copolymer (A) obtained in Examples 1 to 9 in Table 1 was determined by the formula on the right side of the above formula (1). Also, the biomass carbon content of the copolymers obtained in Comparative Examples 1 to 5 was determined by the formula obtained by replacing "monomer i used for synthesizing the copolymer (A)" with "monomer i used for synthesizing the copolymers of Comparative Examples 1 to 5" in the above formula (1).

[0123] (Biomass Carbon Content of the Alkyl Group in the First Structural Unit) The biomass carbon content of the alkyl group in the first structural unit in Table 1 was determined by the formula on the right side of the above formula (2). Also, the biomass carbon content of the alkyl group in the first structural unit of the copolymers obtained in Comparative Examples 1 to 5 was determined by the formula obtained by replacing "monomer Ai corresponding to the first structural unit used for synthesizing the copolymer (A)" with "monomer Ai corresponding to the first structural unit used for synthesizing the copolymers of Comparative Examples 1 to 5" in the above formula (2).

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

[0125] <3. Measurement of non-volatile content concentration of the adhesive composition> 1 g of the adhesive composition was weighed in an aluminum dish with a diameter of 5 cm, and after drying at 105 °C for 1 hour while circulating air in a dryer at 1 atmospheric pressure (1013 hPa), the mass of the non-volatile content remaining was measured. The mass ratio of the non-volatile content after drying under the above conditions to the mass of the adhesive composition before drying (1 g) was determined as the non-volatile content concentration (%) of the adhesive composition.

[0126] <4. Preparation of the adhesive tape> The adhesive compositions obtained in Examples 1 to 9 and Comparative Examples 1 to 4 were applied to a PET film (A4 size, thickness 50 μm). 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. After laminating the release surface (silicone-coated surface) of the release paper on the adhesive layer on the PET film, it was cured at 23 °C for 1 day to obtain an adhesive tape comprising a base material and an adhesive layer formed on the base material, with the release paper laminated on the adhesive layer.

[0127] <5. Evaluation of the adhesive tape> For the adhesive tapes prepared in each example and comparative example, the following evaluations 1 to 4 were carried out. In the following description, the operations in each example and comparative example are common unless otherwise specified.

[0128] 〔5-1. Evaluation 1: Measurement of adhesive force at room temperature (room temperature adhesive force)〕 The release paper of the adhesive tape cut into a tape width of 25 mm and a length of 100 mm was peeled off halfway in the longitudinal direction and cut out, and then laminated on a SUS#304 plate to prepare an evaluation sample. The lamination was performed by reciprocating a 2 kg roller once in an atmosphere at 23°C. The atmospheric temperature during lamination when preparing the evaluation sample is hereinafter referred to as the lamination temperature. (Lamination temperature in Evaluation 1: 23°C) In the evaluation sample, the portion where the adhesive tape and the SUS#304 plate were laminated was made into a rectangle of 25 mm × 50 mm. The ends of the laminated portion of the adhesive tape were not overlapped with the ends of the SUS#304 plate. That is, in this state, half of one end side in the longitudinal direction of the adhesive tape was laminated with the SUS#304 plate, and the other half of the other end side was laminated with the release paper.

[0129] After preparing the evaluation sample, it was left standing in an atmosphere at a temperature of 23°C for 30 minutes. The atmospheric temperature during standing after preparing the evaluation sample is hereinafter referred to as the standing temperature. (Standing temperature in Evaluation 1: 23°C) Thereafter, the following measurements were carried out 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 is a so-called 180° peel test. The 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 fold line. One end of the side of the adhesive tape to which the SUS#304 plate was not attached (the folded side) was gripped by the upper chuck of a testing machine (Tensilon RTG-1210 (manufactured by A&D Company)). One end of the SUS#304 plate facing the upper chuck across the fold line was gripped by the lower chuck.

[0131] In that state, the adhesive tape was peeled off from the SUS#304 plate at a speed of 300 mm / min, and a graph of peel length (mm) - peel force (N) was obtained. The average value (N) of the peel force at a peel length of 25 to 50 mm in the obtained graph (the 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 numerical value was taken as the normal temperature adhesive force (N / 25 mm).

[0132] [5-2. Evaluation 2: Measurement of Adhesive Force in High-Temperature Environment (High-Temperature Adhesive Force)] The adhesive force (N / 25 mm) in a high-temperature environment was measured in the same procedure as the above "Evaluation 1", except that the static temperature was 70°C and the measurement temperature was 70°C.

[0133] [5-3. Evaluation 3: Measurement of Adhesive Force in Low-Temperature Environment (Low-Temperature Adhesive Force)] The adhesive force (N / 25 mm) in a low-temperature environment was measured in the same procedure as the above "Evaluation 1", except that the pasting temperature was -20°C, the static temperature was -20°C, and the measurement temperature was -20°C.

[0134] [5-4. Evaluation 4: Measurement of High-Temperature Retaining Force] The release paper of the adhesive tape cut into a tape width of 25 mm and a length of 100 mm was peeled off by 25 mm from one end in the longitudinal direction, and a SUS plate (SUS#304) was bonded so as to cover all the parts where the release paper was peeled off, and an evaluation sample was prepared. That is, in the evaluation sample, the range where the adhesive tape and the SUS plate are bonded is a 25 mm × 25 mm square. The bonding was performed by reciprocating a 2 kg roller once in an atmosphere of 23°C. At this time, a part of the SUS plate where only the adhesive tape was not bonded on the extension of one end of the adhesive tape bonded to the SUS plate was provided as a SUS plate side chuck portion.

[0135] The evaluation sample was left standing in a constant temperature bath at 80°C for 30 minutes. Then, in the constant temperature bath at 80°C, the SUS plate side chuck portion of the evaluation sample was gripped with a chuck, a 1 kg weight was suspended from one end in the longitudinal direction of the adhesive tape where the SUS plate was not bonded, and the time (h) taken until the weight dropped was measured. The test was carried out until 24 hours later, and those in which the weight had not dropped at the time of 24 hours elapsed were described as "24<" in Table 1.

[0136] [6. Evaluation Results] The evaluation results of Evaluations 1 to 4 are as shown in Table 1.

[0137] [Table 1]

[0138] As shown in Table 1, in the pressure-sensitive adhesive tapes according to Examples 1 to 9 using the copolymer (A) containing biomass carbon atoms of the present embodiment, strong adhesive force is exhibited not only at normal temperature but also at high temperature and low temperature, and it can be seen that a pressure-sensitive adhesive layer having a high holding force at high temperature is formed.

[0139] On the other hand, in the pressure-sensitive adhesive tapes according to Comparative Example 1 and Comparative Example 2 produced from the pressure-sensitive adhesive composition using a copolymer not containing biomass carbon atoms, at least one of the respective adhesive forces and high-temperature holding forces is not sufficient. In Comparative Example 2, although the blending amounts of vinyl acetate and methyl methacrylate in the copolymer are increased, the adhesive force has not been improved.

[0140] From these facts, it can be seen that the object of the present embodiment cannot be achieved in a copolymer not containing biomass carbon atoms.

[0141] Further, in the pressure-sensitive adhesive tapes according to Comparative Example 3 and Comparative Example 4 produced using the pressure-sensitive adhesive composition using the copolymer produced by solution polymerization, at least one of the high-temperature adhesive force, low-temperature adhesive force, and high-temperature holding force is not sufficient.

[0142] From these facts, it can be seen that the object of the present 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 thereof that can form a pressure-sensitive adhesive layer that does not increase or increases only slightly the carbon dioxide present in the earth's environment even when incinerated to generate carbon dioxide. Further, according to the present embodiment, it is possible to provide a copolymer and a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that exhibits strong adhesive force not only at normal temperature but also at high temperature and low temperature, and further has a high holding force at high temperature. Furthermore, according to the present embodiment, it is possible to provide an adhesive layer that exhibits strong adhesive force not only at normal temperature but also at high temperature and low temperature, and further has a high holding force at high temperature, and an adhesive tape including the adhesive layer.

Claims

1. A copolymer obtained by emulsion polymerization, A first structural unit derived from an alkyl (meth)acrylate; 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; A structural unit derived from a vinyl ester compound; having The glass transition temperature Tg is −55 to 0° C. the first structural unit includes a structural unit derived from 2-octyl(meth)acrylate, The content of the first structural unit in the copolymer is 80 to 98 mass%. Copolymers 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 that includes 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 a carbon atom (C １Ａ ), the carbon atom (C １Ａ 4. The copolymer according to claim 3, wherein the biomass carbon content, determined by method B in ASTM D6866-22, in the total number of carbon atoms, is 20% or more.

5. The copolymer according to claim 1, having a glass transition temperature Tg of -55 to -20°C.

6. A pressure-sensitive adhesive composition comprising the copolymer according to any one of claims 1 to 5 and an aqueous medium.

7. The pressure-sensitive adhesive composition according to claim 6 , wherein the copolymer is dispersed as particles in the aqueous medium to form an emulsion.

8. The adhesive layer includes a substrate and an adhesive layer formed on the surface of the substrate. An adhesive tape, wherein the adhesive layer is formed using the adhesive composition according to claim 6.

9. A method for producing the copolymer according to any one of claims 1 to 5, comprising the steps of: The method includes a step of emulsion polymerizing a monomer including an alkyl (meth)acrylate and 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, The method for producing a copolymer, wherein at least one of the monomers contains a biomass carbon atom.

10. The method of claim 9, wherein the monomer comprises an alkyl (meth)acrylate that includes biomass carbon atoms.

11. The method for producing a copolymer according to claim 10 , wherein the alkyl (meth)acrylate containing a biomass carbon atom contains a biomass carbon atom in an alkyl group bonded to a (meth)acryloyloxy group.

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