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

Abstract

To provide a copolymer, enabling formation of an adhesive layer with superior heat resistance and exhibiting strong adhesive force; an adhesive composition and an adhesive tape in which the copolymer is used; and a method for producing the copolymer.SOLUTION: A copolymer obtained by emulsion polymerization, the copolymer 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 carboxy groups and salts of carboxy groups, wherein the first structural unit includes a structural unit derived from an octyl (meth)acrylate.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[0002] A typical application of pressure-sensitive adhesives is pressure-sensitive adhesive tape. Pressure-sensitive adhesive tape typically has a layer containing a pressure-sensitive adhesive, i.e., an adhesive layer, formed on a substrate. Pressure-sensitive adhesive tapes are attached to various articles, for example, to repair the articles or to secure the articles together. Double-sided pressure-sensitive adhesive tapes, in which adhesive layers are formed on both sides of the substrate, are used in a wide range of applications, including transportation equipment such as automobiles, home appliances such as refrigerators, mobile devices such as laptops, and architectural applications such as wallpaper. These industrial applications require stricter performance requirements, such as adhesion to very difficult-to-adhere adherends, adhesive reliability under harsh environmental conditions, and adhesion over a small area.

[0003] A typical method for manufacturing adhesive tapes is to apply a coating liquid in which an adhesive is dissolved or dispersed in a liquid medium onto a substrate and then dry the coating liquid to form an adhesive layer on the surface of the substrate. For example, natural rubber-based adhesives, synthetic rubber-based adhesives, and acrylic-based adhesives are widely used, and acrylic-based adhesives are particularly notable for their ability to impart various functionalities. In recent years, the use of water as a liquid medium has been widely considered, taking into account environmental impact and other factors.

[0004] Patent Document 1 describes a pressure-sensitive adhesive composition containing 2-octyl (meth)acrylate, a (meth)acrylic acid copolymer, and optionally a crosslinking agent.

[0005] Patent Document 2 describes a resin composition containing a homopolymer or copolymer of 1-methyl alkyl acrylate.

[0006] Patent Document 3 describes an adhesive comprising a reaction product of 2-octyl (meth)acrylate, at least partly derived from castor oil, a reaction initiator, and a stabilizer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2011-516690 [Patent Document 2] Japanese Patent Application Publication No. 10-231325 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-077141 Summary of the Invention [Problem to be solved by the invention]

[0008] The adhesive composition described in Patent Document 1 solidifies during polymerization, and an emulsion cannot be obtained. Both the acrylic copolymer described in Patent Document 2 and the adhesive described in Patent Document 3 have room for improvement in adhesive strength under high temperature environments, and furthermore, there is room for improvement in holding power under high temperature environments.

[0009] An object of the present disclosure is to provide a copolymer capable of forming an adhesive layer that has excellent heat resistance and exhibits strong adhesive strength, a pressure-sensitive adhesive composition and pressure-sensitive adhesive tape that use the copolymer, and a method for producing the copolymer. [Means for solving the problem]

[0010] [1] A copolymer obtained by emulsion polymerization, which 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, wherein the first structural unit includes a structural unit derived from octyl(meth)acrylate. [2] The copolymer according to [1], wherein the content of structural units derived from octyl (meth)acrylate among the structural units contained as the first structural units is 20 to 100 mass %. [3] The copolymer according to [2], wherein the content of structural units derived from 2-octyl(meth)acrylate among the structural units contained as the first structural units is 20 to 100 mass %. [4] The copolymer according to any one of [1] to [3], wherein the content of the second structural unit is 1.0 to 10% by mass. [5] The copolymer according to any one of [1] to [4], wherein the first structural unit further includes 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, and a structural unit derived from 2-ethylhexyl (meth)acrylate. [6] The copolymer according to any one of [1] to [5], further comprising a structural unit derived from a vinyl ester compound. [7] A pressure-sensitive adhesive composition comprising the copolymer according to any one of [1] to [6] and an aqueous medium. [8] The pressure-sensitive adhesive composition according to [7], wherein the copolymer is dispersed as particles in the aqueous medium to form an emulsion. [9] The pressure-sensitive adhesive composition according to [8], wherein the particles dispersed in the aqueous medium have an average particle size of 10 to 50,000 nm.

[10] An adhesive tape comprising a substrate and an adhesive layer formed on the surface of the substrate, the adhesive layer being formed using the adhesive composition according to [7] or [8].

[11] A method for producing the copolymer according to any one of [1] to [6], 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, wherein the alkyl(meth)acrylate contains octyl(meth)acrylate.

[12] The method for producing a copolymer according to

[11] , wherein the alkyl(meth)acrylate includes 2-octyl(meth)acrylate.

[13] The method for producing a copolymer according to

[11] or

[12] , wherein the content of octyl (meth)acrylate in the monomer is 20 to 90 mass %. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a copolymer capable of forming an adhesive layer that has excellent heat resistance and exhibits strong adhesive strength, a pressure-sensitive adhesive composition and pressure-sensitive adhesive tape that use the copolymer, and a method for producing the copolymer. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following explanation, unless otherwise specified, surface means "surface."

[0013] "(Meth)acrylic" is a general term for acrylic and methacrylic, and "(meth)acrylate" is a general term for acrylate and methacrylate.

[0014] 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.

[0015] In a polymer of an ethylenically unsaturated compound, a structural unit derived from a certain ethylenically unsaturated compound has a corresponding chemical structure in which the chemical structure of the portion of the ethylenically unsaturated compound other than the ethylenically unsaturated bond 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 represented by -CHCH(COOH)- in the polymer.

[0016] 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.

[0017] Unless otherwise specified, structural units having an ionic functional group such as a carboxyl group are considered to be structural units derived from the same ionic compound, regardless of whether part of the functional group has been ion-exchanged or not. For example, a structural unit represented by -CHC(CH)(COONa)- is also considered to be a structural unit derived from methacrylic acid, unless otherwise specified.

[0018] The term "salt of a carboxy group" refers to a structure in which a carboxy group forms a salt, and examples thereof include -COONa, -COOK, and -COONH4.

[0019] A "dispersion" is a solid-liquid mixture in which a solid is present that is not dissolved in the liquid but is dispersed as particles in the liquid. "Slurry" means a fluid in which solid particles such as clay, pigments, etc. are suspended in a liquid.

[0020] 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.

[0021] <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. 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.

[0022] (1-1. First structural unit) The first structural unit includes a structural unit derived from octyl(meth)acrylate. The first structural unit preferably includes at least one selected from the group consisting of a structural unit derived from n-octyl(meth)acrylate and a structural unit derived from 2-octyl(meth)acrylate, more preferably includes at least one selected from the group consisting of a structural unit derived from 2-octylacrylate and a structural unit derived from 2-octyl methacrylate, and even more preferably includes a structural unit derived from 2-octyl acrylate.

[0023] Of the structural units contained as the first structural units, the content of structural units derived from octyl (meth)acrylate is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the pressure-sensitive adhesive composition containing the copolymer (A) in a high-temperature environment.

[0024] Of the structural units contained as the first structural unit, the content of structural units derived from octyl (meth)acrylate may be 100% by mass, or may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0025] Of the structural units contained as the first structural units, the content of structural units derived from octyl (meth)acrylate may be 20 to 100% by mass, 20 to 90% by mass, 40 to 80% by mass, or 45 to 70% by mass.

[0026] Among the structural units contained as the first structural units, the content of structural units derived from 2-octyl(meth)acrylate is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the pressure-sensitive adhesive composition containing the copolymer (A) in a high-temperature environment.

[0027] Of the structural units contained as the first structural unit, the content of structural units derived from 2-octyl(meth)acrylate may be 100% by mass, or may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0028] Of the structural units contained as the first structural units, the content of structural units derived from 2-octyl(meth)acrylate may be 20 to 100% by mass, 20 to 90% by mass, 40 to 80% by mass, or 45 to 70% by mass.

[0029] The first structural unit may further include a structural unit derived from an alkyl (meth)acrylate other than octyl (meth)acrylate. Examples of compounds other than octyl (meth)acrylate from which the first structural unit is derived include methyl (meth)acrylate, n-butyl (meth)acrylate, 1-methylpropyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobutyl (meth)acrylate, isoamyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate. The compounds other than octyl (meth)acrylate from which the first structural unit is derived may be one type or two or more types.

[0030] It is preferable that the first structural unit further includes at least one of a structural unit derived from methyl (meth)acrylate, a structural unit derived from n-butyl (meth)acrylate, and a structural unit derived from 2-ethylhexyl (meth)acrylate, and it is more preferable that the first structural unit further includes a structural unit derived from methyl (meth)acrylate and at least one of a structural unit derived from n-butyl (meth)acrylate and a structural unit derived from 2-ethylhexyl (meth)acrylate.

[0031] 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 method for determining the glass transition temperature Tg of the copolymer (A) and the preferred range thereof will be described later. The alkyl group contained in the first structural unit may have a linear structure or a branched structure. Here, the alkyl group contained in the first structural unit has the same structure as the alkyl group bonded to the (meth)acryloyloxy group in the alkyl (meth)acrylate constituting the first structural unit.

[0032] 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 alkyl group contained in the first structural unit may have 1 to 20 carbon atoms, 2 to 15 carbon atoms, 4 to 10 carbon atoms, or 6 to 10 carbon atoms.

[0033] (1-2. Second structural unit) The second structural unit is a structural unit derived from an ethylenically unsaturated compound having at least one carboxy group or carboxy salt selected from the group consisting of a carboxy group and a salt of a carboxy group. The number of carboxy groups or carboxy salts contained in the second structural unit is not particularly limited and may be one or two or more. Examples of compounds from which the second structural unit is derived include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, itaconic acid, maleic acid, etc. The number of compounds from which the second structural unit is derived may be one or more.

[0034] 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. Of the structural units contained as the second structural units, the content of structural units derived from (meth)acrylic acid is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

[0035] (1-3. 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 simply referred to as "other structural units"); terminal structures derived from a polymerization initiator, a chain transfer agent, etc.; and the like.

[0036] [Other structural units] The compounds from which other structural units are derived are not particularly limited, but 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 suitable compounds include alkoxysilyl group-containing vinyl compounds such as silane, vinyltrimethoxysilane, and vinyltris(β-methoxyethoxy)silane; epoxy 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 compounds from which the other structural units are derived may be one type or two or more types.

[0037] 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.

[0038] 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 1.0 mass% or more, more preferably 2.5 mass% or more, and even more preferably 4.0 mass% or more, because this improves the adhesive strength of the pressure-sensitive adhesive containing the copolymer (A) at room temperature.

[0039] 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, because this improves the adhesive strength of the pressure-sensitive adhesive containing the copolymer (A) at room temperature.

[0040] When the copolymer (A) has structural units derived from a vinyl ester compound, the content of the structural units 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%.

[0041] The polymerizable surfactant from which the other structural units are derived 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 more 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.

[0042] When the copolymer (A) has structural units derived from a polymerizable surfactant, the content of the structural units 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).

[0043] When the copolymer (A) has structural units derived from a polymerizable surfactant, the content of the structural units 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).

[0044] 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%.

[0045] The copolymer (A) may further have structural units other than the structural units exemplified above.

[0046] [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 per 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 parts by mass or less per 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 when calculating the content of each structural unit. The polymerization initiator and chain transfer agent from which the terminal structure is derived will be described in detail below.

[0047] (1-4. 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 even more preferably 80% by mass or more, because this can suppress an increase in the glass transition temperature of the copolymer (A) and improve the tackiness, wettability, and adhesive strength of the adhesive layer.

[0048] The content of the first structural unit in the copolymer (A) is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less, because this allows the polarity of the copolymer (A) and the cohesive strength of the adhesive layer to be 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.

[0049] The content of the first structural unit in the copolymer (A) may be 60 to 99 mass %, 70 to 98 mass %, or 80 to 97 mass %.

[0050] 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 improves the cohesive strength of the adhesive layer containing the copolymer (A) and increases the holding power at high temperatures.

[0051] The content of the second structural unit in the copolymer (A) is preferably 10% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% 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 adhesive strength of the adhesive layer.

[0052] The content of the second structural unit in the copolymer (A) may be 1.0 to 10% by mass, 2.0 to 7.0% by mass, or 3.0 to 5.0% by mass.

[0053] 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 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 adhesive 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 95% by mass or more, 100% by mass, or 100% by mass or less.

[0054] The content of structural units derived from octyl (meth)acrylate in the copolymer (A) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the pressure-sensitive adhesive composition containing the copolymer (A) in a high-temperature environment.

[0055] The content of structural units derived from octyl (meth)acrylate in the copolymer (A) may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0056] The content of structural units derived from octyl (meth)acrylate in the copolymer (A) may be 20 to 90 mass %, 30 to 80 mass %, or 40 to 70 mass %.

[0057] The content of structural units derived from 2-octyl(meth)acrylate in the copolymer (A) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the pressure-sensitive adhesive composition containing the copolymer (A) in a high-temperature environment.

[0058] The content of structural units derived from 2-octyl(meth)acrylate in the copolymer (A) may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0059] The content of structural units derived from 2-octyl(meth)acrylate in the copolymer (A) may be 20 to 90 mass %, 30 to 80 mass %, or 40 to 70 mass %.

[0060] (1-5. Glass transition temperature of copolymer (A)) The glass transition temperature Tg of copolymer (A) is calculated by Fox's formula based on the glass transition temperature when each structural unit contained in copolymer (A) is treated as a homopolymer. The glass transition temperature Tg of copolymer (A) is calculated by Fox's formula 1 / Tg = Σ(Xi / Tgi) using the glass transition temperature 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).

[0061] 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.

[0062] The glass transition temperature Tg of each homopolymer is the 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.

[0063] The glass transition temperature 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 this improves the cohesive strength of the pressure-sensitive adhesive formed using the copolymer (A), and can impart superior holding power at high temperatures to the pressure-sensitive adhesive layer.

[0064] 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 -30°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.

[0065] The glass transition temperature Tg of the copolymer (A) may be from -80 to 30°C, from -65 to 0°C, from -55 to -20°C, or from -55 to -30°C.

[0066] <2. Method for producing copolymer> The method for producing copolymer (A) according to this embodiment includes a step of emulsion polymerizing a monomer (hereinafter also referred to as "raw material monomer 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, wherein the alkyl(meth)acrylate contains octyl(meth)acrylate.

[0067] By producing the copolymer (A) by emulsion polymerization, a high molecular weight copolymer (A) can be obtained. The high molecular weight copolymer (A) improves the cohesive strength of the adhesive and can impart superior holding power at high temperatures to the adhesive layer. Furthermore, as will be described later, emulsion polymerization can be carried out in an aqueous medium, so the environmental impact of production is low.

[0068] (2-1: Monomer) 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 contained in the raw material monomers of copolymer (A) can be explained in the same manner as the alkyl(meth)acrylate from which the first structural unit of copolymer (A) of the present embodiment is derived 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 from which the second structural unit is derived, and the preferred embodiments are also the same.

[0069] (2-2: Emulsion polymerization process) The production method of this 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.

[0070] The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of 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, because this can suppress an increase in the glass transition temperature of the resulting copolymer (A) and improve the tackiness, wettability, and adhesive strength of the adhesive layer.

[0071] The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of copolymer (A) is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less, because this allows the polarity of the resulting copolymer (A) and the cohesive strength of the adhesive layer to be kept appropriate, and an adhesive layer having high adhesiveness not only at room temperature but also at high and low temperatures can be obtained.

[0072] The content of alkyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of the copolymer (A) may be 60 to 99% by mass, 70 to 98% by mass, or 80 to 97% by mass.

[0073] 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 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 resulting adhesive layer containing copolymer (A) and increase the holding power at high temperatures.

[0074] 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) is preferably 10% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less, because this can suppress an increase in the glass transition temperature of the resulting copolymer (A) and can improve the tackiness, wettability, and adhesion strength of the adhesive layer.

[0075] 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 10% by mass, 2.0 to 7.0% by mass, or 3.0 to 5.0% by mass.

[0076] The total content of alkyl (meth)acrylate and 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 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, which can suppress an increase in the glass transition temperature of the resulting copolymer (A) and further improve the tackiness, wettability, and adhesion of the adhesive layer. The total content 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 raw material monomers of the copolymer (A) may be 90% by mass or more, 100% by mass, or 100% by mass or less.

[0077] The content of octyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of copolymer (A) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the resulting adhesive composition containing copolymer (A) in a high-temperature environment.

[0078] The content of octyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of copolymer (A) may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0079] The content of octyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of the copolymer (A) may be 20 to 90% by mass, 30 to 80% by mass, or 40 to 70% by mass.

[0080] The content of 2-octyl(meth)acrylate in the total amount (100% by mass) of raw material monomers of copolymer (A) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, because this improves the adhesive strength of the adhesive layer obtained from the resulting adhesive composition containing copolymer (A) in a high-temperature environment.

[0081] The content of 2-octyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of copolymer (A) may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0082] The content of 2-octyl (meth)acrylate in the total amount (100% by mass) of raw material monomers of the copolymer (A) may be 20 to 90% by mass, 30 to 80% by mass, or 40 to 70% by mass.

[0083] In the 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 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 copolymer (A). The polymerization temperature is not particularly limited, but is preferably 5 to 100°C, and more preferably 50 to 90°C.

[0084] In the production method of this embodiment, the emulsion polymerization of the monomers is preferably carried out in an aqueous medium, thereby obtaining 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 the hydrophilic organic solvent include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium is preferably water. As long as the polymerization stability is not impaired, a mixed solvent of water and a hydrophilic solvent may also be used as the aqueous medium.

[0085] 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 or more types of polymerization initiators 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 raw material monomers for the copolymer (A).

[0086] 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. One type of reducing agent may be used alone, or two or more types may be used.

[0087] 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, etc. Only one type of chain transfer agent may be used, or two or more types may be used.

[0088] 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, per 100 parts by mass of the total amount of raw material monomers of copolymer (A), because this improves the cohesive strength of the pressure-sensitive adhesive and can improve the holding power of the pressure-sensitive adhesive layer at high temperatures. The amount of the chain transfer agent used may be 0.01 parts by mass or more, or may be 0.05 parts by mass or more, relative to 100 parts by mass of the total amount of the monomers, because this can improve the adhesive strength of the adhesive layer.

[0089] Examples of emulsifiers include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyoxyethylene alkyl ether sodium sulfate; nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene nonylphenyl ether; cationic surfactants such as ceciltrimethylammonium bromide and laurylpyridinium chloride; amphoteric surfactants such as laurylbetaine; and the above-mentioned polymerizable surfactants. 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. In calculating the content of each structural unit of copolymer (A), polymerizable surfactants are classified as monomers of copolymer (A) and their presence is taken into consideration, whereas emulsifiers other than polymerizable surfactants are not classified as monomers of copolymer (A) and their presence is ignored.

[0090] <3. Pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition according to this embodiment contains the copolymer (A) according to this embodiment and an aqueous medium (hereinafter also referred to as "aqueous medium (B)"). The pressure-sensitive adhesive composition according to this embodiment may contain other additives. The pressure-sensitive adhesive composition of the present embodiment may be in the form of a solution, a dispersion (for example, an emulsion), a slurry, or the like, but is not limited to these.

[0091] In the pressure-sensitive adhesive composition, the copolymer (A) is preferably dispersed as particles in an aqueous medium to form an emulsion.

[0092] (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 or a different composition from the aqueous medium used in the polymerization of the copolymer (A). Only one type of aqueous medium (B) may be used, or two or more types may be used.

[0093] (3-2. Other additives) Other additives that can be used as appropriate include, for example, pH adjusters, tackifiers, plasticizers, antioxidants, fillers, pigments, colorants, wetting agents, antifoaming agents, thickeners, crosslinking agents, etc. Only one type of other additive may be used, or two or more types may be used.

[0094] 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.

[0095] (3-3. Non-volatile content of adhesive composition) The nonvolatile content of the pressure-sensitive 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 amount of pressure-sensitive adhesive layer can be formed with a smaller amount of pressure-sensitive adhesive composition applied. Also, the drying time of the applied pressure-sensitive adhesive composition is shortened, thereby further improving productivity. The "non-volatile content" of the adhesive composition refers to the components remaining after weighing 1 g of the adhesive composition onto an aluminum dish with a diameter of 5 cm and drying it for 1 hour at 105°C 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.

[0096] 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.

[0097] 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.

[0098] 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).

[0099] The content of copolymer (A) in the nonvolatile matter of the pressure-sensitive adhesive composition is preferably 99.5% by mass or less, and more preferably 99% by mass or less, because this improves the adhesive strength and holding power of the adhesive layer containing copolymer (A), particularly the adhesive strength at room temperature and at high temperature.

[0100] The content of the copolymer (A) in the nonvolatile matter of the pressure-sensitive adhesive composition may be 50 to 99.5 mass %, 60 to 99 mass %, or 70 to 99 mass %.

[0101] 3-4. Size of particles in pressure-sensitive adhesive composition The particles in the pressure-sensitive adhesive composition are particles dispersed in the aqueous medium (B). The average particle size of the particles in the pressure-sensitive adhesive composition is a value measured using a NANOTRAC WAVE II (manufactured by MicrotracBEL). The average particle size of the aqueous resin composition dispersed in the aqueous medium is preferably 10 nm or more, more preferably 50 nm or more, even more preferably 100 nm or more, and even more preferably 200 nm or more. This is because the particles can be more stably dispersed in the aqueous medium (B).

[0102] The average particle size of the particles in the pressure-sensitive adhesive composition is preferably 50,000 nm or less, more preferably 10,000 nm or less, even more preferably 1,000 nm or less, even more preferably 500 nm or less, and particularly preferably 350 nm or less, because this can increase the density of the pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition and improve the heat resistance of the pressure-sensitive adhesive layer when used dry.

[0103] The average particle size of the particles in the pressure-sensitive adhesive composition may be 10 to 50,000 nm, 50 to 10,000 nm, 100 to 1,000 nm, 100 to 500 nm, or 200 to 350 nm.

[0104] (3-5. Method for producing 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.

[0105] <3-6. Products to which the adhesive composition is applied> The pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and can be used, for example, as pressure-sensitive adhesive tapes, pressure-sensitive adhesive sheets, pressure-sensitive adhesive labels, stickers, liquid pressure-sensitive adhesives, and the like.

[0106] <4. Adhesive layer and adhesive tape> The pressure-sensitive adhesive layer of this embodiment is an adhesive layer formed using the pressure-sensitive adhesive composition of this 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 it, and, if necessary, causing a crosslinking reaction. The drying conditions after applying the pressure-sensitive adhesive composition of the present embodiment to a substrate are not particularly limited, but for example, drying conditions of 1 to 5 minutes at 80 to 110° C. After drying, the 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, even more preferably 99% by mass or more, and may be 100% by mass. 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.

[0107] The pressure-sensitive adhesive tape of the present embodiment comprises a substrate and an adhesive layer formed on the surface of the substrate, and the adhesive layer is formed using the pressure-sensitive adhesive composition of the present embodiment. The adhesive layer may be formed on only one surface of the substrate, or on both surfaces. The substrate is not particularly limited, but examples thereof include resin films such as polyethylene terephthalate (PET) films; woven fabrics; nonwoven fabrics; and metal foils. The pressure-sensitive adhesive tape may have other layers (e.g., an intermediate layer, an undercoat layer, etc.) in addition to the substrate and the pressure-sensitive adhesive layer, as long as the effects of the invention are not impaired. Furthermore, the pressure-sensitive adhesive tape may have the pressure-sensitive adhesive layer protected by a known release liner such as release paper or release PET. The adhesive tape of this embodiment can be explained in the same manner as the method for producing the adhesive layer of this embodiment described above.

[0108] <5. Uses 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 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. [Example]

[0109] Examples and comparative examples of this embodiment will be described below, but this embodiment is not limited to these examples.

[0110] <1. Preparation of copolymer and pressure-sensitive adhesive composition> Example 1 Copolymer (A) was synthesized by emulsion polymerization in water, specifically as follows.

[0111] 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% by mass aqueous solution of potassium persulfate was added as a polymerization initiator to obtain a mixed solution containing the polymerization initiator.

[0112] A monomer emulsion containing 20 parts by mass of ion-exchanged water, emulsifiers "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) in the amounts shown in Table 1, and the types and amounts of monomers and chain transfer agents shown in Table 1 was added dropwise to the mixture containing the polymerization initiator in the polymerization reactor over a period of 4 hours. Simultaneously with the start of the dropwise addition of the monomer emulsion, 20 parts by mass of a 2.5% by mass aqueous potassium persulfate solution was added dropwise over a period of 4 hours. During the dropwise addition of the monomer emulsion, the mixture in the polymerization reactor 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 with continued stirring.

[0113] 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 7.0, thereby obtaining an emulsion containing emulsified particles containing copolymer (A) and water.

[0114] To 100 parts by mass of the resulting emulsion, 2.0 parts by mass of "ADEKA NOL UH-420" (trade name, manufactured by ADEKA Corporation, nonionic thickener) was added as a thickener to obtain a pressure-sensitive adhesive composition.

[0115] Examples 2 to 4 Copolymers and pressure-sensitive adhesive compositions of Examples 2 to 4 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.

[0116] (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.

[0117] (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 listed 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 cooled to 25°C to obtain a copolymer. Note that during and after the reaction, the monomers and the resulting copolymer were uniformly dissolved in the solvent. The subsequent steps were the same as in Example 1, and a pressure-sensitive adhesive composition of Comparative Example 3 was obtained.

[0118] Comparative Example 4 In Comparative Example 4, a copolymer was prepared in water by a suspension polymerization process. Specifically, in a polymerization apparatus equipped with a stirrer, thermometer, and reflux condenser, a mixed solution containing 80 parts by mass of ion-exchanged water, emulsifiers "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) in the amounts shown in Table 1, and a total of 100 parts by mass of monomers and chain transfer agents in the formulations shown in Table 1 was mixed at 350 revolutions per minute for 30 minutes to obtain a monomer droplet diameter 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 stirring, and 0.2 parts by mass of 2,2'-azobisisobutyronitrile was added as a polymerization initiator. The mixed solution in the polymerization apparatus was reacted at 70°C for 5 hours while being stirred, and then the mixed solution in the polymerization apparatus was cooled to 25°C to obtain a copolymer and a pressure-sensitive adhesive composition of Comparative Example 4.

[0119] (Comparative Example 5) When the same procedure as in Comparative Example 4 was carried out except that the monomer and chain transfer agent were blended as shown in Table 1, aggregates were generated during the reaction, and no adhesive composition was obtained.

[0120] <2. Measurement of nonvolatile content of adhesive composition> 1 g of the adhesive composition was weighed onto an aluminum dish with a diameter of 5 cm, and 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 adhesive composition before drying was calculated as the nonvolatile content concentration (mass%) of the adhesive composition.

[0121] <3. Preparation of adhesive tape> The pressure-sensitive adhesive compositions obtained in Examples 1 to 4 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 pressure-sensitive adhesive composition was dried at 100°C for 2 minutes to remove the aqueous medium from the pressure-sensitive adhesive composition, forming a 30 μm thick adhesive layer 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 product was cured 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.

[0122] <4. Evaluation of adhesive tape> The pressure-sensitive adhesive tapes produced in each of the Examples and Comparative Examples were subjected to the following evaluations 1 to 3. In the following description, the procedures in each example and comparative example are common unless otherwise specified.

[0123] [4-1. Evaluation 1: Measurement of adhesive strength at room temperature (room temperature adhesive strength)] The release paper of the adhesive tape was cut into a tape width of 25 mm and a length of 100 mm, and half of the tape was peeled off in the longitudinal direction. The tape was then stuck to a SUS#304 plate to prepare a sample for evaluation. The lamination was performed by moving a 2 kg roller back and forth once in an atmosphere of 23° C. The ambient 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 SUS#304 plate were bonded together was a rectangle measuring 25 mm x 50 mm. None of the edges of the adhesive tape bonded portion overlapped the edges of the SUS#304 plate. That is, in this state, half of one end of the adhesive tape in the longitudinal direction was bonded to the SUS#304 plate, and half of the other end was bonded to the release paper.

[0124] After the evaluation sample was prepared, it was left to stand for 30 minutes in an atmosphere at a temperature of 23° C. The ambient temperature during standing after the preparation of 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.)

[0125] The test was a so-called 180° peel test. The adhesive tape of the evaluation sample was folded back 180°, with the boundary between the part attached to the SUS#304 plate and the part not attached as the folding line. The end of the adhesive tape not attached to the SUS#304 plate (the folded end) was gripped with the upper chuck of a testing machine (Tensilon RTG-1210 (manufactured by A&D Co., Ltd.)). The end of the SUS#304 plate facing the upper chuck across the folding line was gripped with the lower chuck.

[0126] In this state, the adhesive tape was peeled off from the SUS#304 plate at a rate of 300 mm / min, and a graph of peel length (mm) vs. peel force (N) was obtained. The average peel force (N) for peel lengths of 25 to 50 mm was calculated from the graph (the area of ​​the graph for peel lengths of 25 to 50 mm divided by the peel length), and this value was defined as the room temperature adhesive strength (N / 25 mm).

[0127] [4-2. 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.

[0128] [4-3. Evaluation 3: Measurement of high temperature retention] An evaluation sample was prepared by peeling 25 mm of the release paper from one longitudinal end of an adhesive tape cut to a tape width of 25 mm and a length of 100 mm, and then bonding a SUS plate (SUS#304) to cover the entire area where the release paper had been peeled off. That is, in the evaluation sample, the area where the adhesive tape and SUS plate were bonded together was a 25 mm x 25 mm square. Bonding was performed by rolling a 2 kg roller back and forth once in an atmosphere of 23°C. In addition, at this time, the portion of the SUS plate where the adhesive tape was not bonded, which was an extension of the end of the adhesive tape bonded to the SUS plate, was provided as a chuck portion on the SUS plate side.

[0129] The evaluation sample was left to stand in a thermostatic chamber at 80°C for 30 minutes. Then, 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) until the weight fell was measured. The test was continued for up to 24 hours, and samples in which the weight had not fallen after 24 hours were recorded as "24<" in Table 1.

[0130] <5. Evaluation Results> The results of evaluations 1 to 3 are shown in Table 1. The average particle size of the particles in the pressure-sensitive adhesive composition in Table 1 is a value measured using NANOTRAC WAVE II (manufactured by MicrotracBEL).

[0131] [Table 1]

[0132] As shown in Table 1, the adhesive tapes of Examples 1 to 4, which use copolymer (A) containing a structural unit derived from octyl (meth)acrylate of this embodiment, exhibit strong adhesive strength not only at room temperature but also at high temperatures, and form adhesive layers that also have high holding power at high temperatures.

[0133] On the other hand, in the adhesive tapes of Comparative Example 1 and Comparative Example 2, which were made from adhesive compositions using copolymers that did not contain structural units derived from octyl (meth)acrylate, at least one of the adhesive strength and high-temperature holding power was insufficient.

[0134] From these facts, it is clear that the object of this embodiment cannot be achieved with a copolymer that does not contain a structural unit derived from octyl (meth)acrylate.

[0135] Furthermore, the adhesive tape according to Comparative Example 3, which was produced using an adhesive composition using a copolymer produced by solution polymerization, did not have sufficient high-temperature adhesive strength. Moreover, the adhesive tape according to Comparative Example 4, which was produced using an adhesive composition using a copolymer produced by suspension polymerization, did not have sufficient adhesive strength and high-temperature holding power.

[0136] 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.

[0137] As described above, 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 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 temperatures, and that also has high holding power at high temperatures, and an adhesive tape including such an 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; and A copolymer, wherein the first structural unit includes a structural unit derived from octyl (meth)acrylate.

2. The copolymer according to claim 1, wherein the content of structural units derived from octyl (meth)acrylate among the structural units contained as the first structural units is 20 to 100 mass %.

3. The copolymer according to claim 2, wherein the content of structural units derived from 2-octyl(meth)acrylate among the structural units contained as the first structural units is 20 to 100 mass %.

4. The copolymer according to claim 1, wherein the content of the second structural unit is 1.0 to 10% by mass.

5. 2. The copolymer according to claim 1, wherein the first structural unit further includes 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, and a structural unit derived from 2-ethylhexyl (meth)acrylate.

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

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

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

9. The pressure-sensitive adhesive composition according to claim 8, wherein the particles dispersed in the aqueous medium have an average particle size of 10 to 50,000 nm.

10. 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 7.

11. A method for producing the copolymer according to any one of claims 1 to 6, 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 the alkyl(meth)acrylate includes octyl(meth)acrylate.

12. The method for producing a copolymer according to claim 11, wherein the alkyl(meth)acrylate includes 2-octyl(meth)acrylate.

13. The method for producing a copolymer according to claim 11, wherein the content of octyl (meth)acrylate in the monomer is 20 to 90 mass%.

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