Pressure-sensitive adhesive composition, pressure-sensitive adhesive layer and adhesive tape

Abstract

To provide a pressure-sensitive adhesive composition which when a pressure-sensitive adhesive layer is formed on base material, the formed pressure-sensitive adhesive layer has such tack force that the layer is not to easily peeled, and the layer can be easily peeled from the adherend without requiring excessive force, and is excellent in curved surface adhesion.SOLUTION: A pressure-sensitive adhesive composition is provided, including a (meth)acrylic copolymer and a hexamethylene diisocyanate-based crosslinking agent, wherein the (meth)acrylic copolymer includes a constitutional unit (a) derived from an acrylic acid alkyl ester monomer having a linear alkyl moiety having 10 to 13 carbon atoms, and a constitutional unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, a ratio of the constitutional unit (a) to the total constitutional unit is 65.0 to 98.5 mass%, a ratio of the constitutional unit (b) is 1.0 to 8.0 mass% to the total constitutional unit, and a content of the hexamethylene diisocyanate-based crosslinking agent is 1.1 to 2.8 pts.mass with respect to 100 pts.mass of the (meth)acrylic copolymer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an adhesive composition, an adhesive layer, and an adhesive tape.

Background Art

[0002] Conventionally, for electronic components and optical components, a protective tape is attached to the surface of the components so that the surface of the components is not damaged and defective during transportation. Since the protective tape is a tape that is supposed to be peeled off after finishing its protective role, the protective tape is required to have a performance (so-called easy peelability) that can be easily peeled off without requiring excessive force when peeling from the object to be protected.

[0003] For example, Patent Document 1 discloses an adhesive tape having an adhesive layer, wherein the adhesive layer has a shear storage modulus at 23°C and 1 Hz of 1×10 4 Pa or more and 5×10 4 Pa or less, a 180° adhesive force of 0.3 N / 25 mm or more and 0.7 N / 25 mm or less, and a thickness of 30 μm or more.

[0004] By the way, in recent years, devices using electronic components and / or optical components have requirements for multifunctionality, weight reduction, and thinning, and thinning of electronic components and optical components is also desired. However, when electronic components and optical components are thinned, the components are likely to be damaged when the protective tape is peeled off from the components. For this reason, the adhesive layer provided on the protective tape is required to have an even lower adhesive force than before. On the other hand, the adhesive layer provided on the protective tape also requires sufficient tack force so that the protective tape does not peel off during transportation of the components even if the adhesive force is low.

[0005] As an adhesive composition that satisfies such requirements, for example, Patent Document 2 discloses an adhesive composition based on a (meth)acrylic (co)polymer containing 70% by mass to 99.9% by mass of an alkyl (meth)acrylate having an alkyl group with 10 to 16 carbon atoms and 0.1% by mass to 15% by mass of a functional group-containing monomer as a monomer component, characterized in that the gel content after crosslinking with a crosslinking agent is 80% or more.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The protective tape may be used to protect a planar member using a hard base material such as polyethylene terephthalate, or to protect a curved member using a soft base material such as polyolefin or polyurethane. Comparing the adhesive layer formed on a hard base material with the adhesive layer formed on a soft base material, the adhesive layer formed on the soft base material has a higher adhesive strength. Therefore, in a protective tape using a soft base material, it tends to be difficult to achieve easy peelability. For this reason, the adhesive composition for forming an adhesive layer on a soft base material is required to form an adhesive layer that does not easily peel off from the adherend while protection is required, and can be easily peeled off without requiring excessive force when it becomes unnecessary to protect and is peeled off from the adherend. Also, as described above, the protective tape using a soft base material is used to protect a curved member, but the protective tape attached to the curved member tends to be peeled off due to distortion in the curved surface of the adhesive layer. For this reason, the adhesive composition for forming an adhesive layer on a soft base material is also required to have excellent adhesion to a curved surface.

[0008] Note that the pressure-sensitive adhesive compositions disclosed in Patent Document 1 and Patent Document 2 are not assumed to form a pressure-sensitive adhesive layer on a soft substrate.

[0009] The present disclosure has been made in view of the above circumstances. The problem to be solved by one embodiment of the present disclosure is that when a pressure-sensitive adhesive layer is formed on a soft substrate, the formed pressure-sensitive adhesive layer has a tack force that does not easily peel off from the adherend, can be easily peeled off without requiring excessive force when peeled off from the adherend, and provides a pressure-sensitive adhesive composition having excellent curved surface adhesiveness. Another problem to be solved by an embodiment of the present disclosure is to provide a pressure-sensitive adhesive layer that has a tack force that does not easily peel off from the adherend when formed on a soft substrate, can be easily peeled off without requiring excessive force when peeled off from the adherend, and has excellent curved surface adhesiveness, and a pressure-sensitive adhesive tape including the above pressure-sensitive adhesive layer.

Means for Solving the Problem

[0010] Specific means for solving the problem include the following aspects. <1> A pressure-sensitive adhesive composition containing a (meth)acrylic copolymer and a hexamethylene diisocyanate crosslinking agent, wherein the (meth)acrylic copolymer contains a structural unit (a) derived from an acrylic acid alkyl ester monomer having a linear alkyl moiety with 10 to 13 carbon atoms and a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, the proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all structural units, and the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all structural units, and the content of the hexamethylene diisocyanate crosslinking agent is 1.1 parts by mass to 2.8 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer. <2> The above (meth)acrylic copolymer further contains a structural unit (c) derived from a vinyl group-containing monomer having a carboxy group, and the proportion of the above structural unit (c) is 1.0% by mass or less based on all the structural units. The pressure-sensitive adhesive composition according to <1>. <3> The above (meth)acrylic copolymer has a proportion of the above structural unit (b) of 1.0% by mass to 4.0% by mass based on all the structural units. The pressure-sensitive adhesive composition according to <1> or <2>. <4> The pressure-sensitive adhesive composition according to any one of <1> to <3>, wherein the vinyl group-containing monomer having a hydroxyl group contains 4-hydroxybutyl acrylate. <5> The pressure-sensitive adhesive composition according to any one of <1> to <4>, wherein the weight average molecular weight of the above (meth)acrylic copolymer is 400,000 to 1,000,000. <6> A pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition according to any one of <1> to <5>, having a thickness of 3 μm to 15 μm. <7> A base material, The pressure-sensitive adhesive layer according to <6> provided on the above base material, And a pressure-sensitive adhesive tape comprising. <8> The pressure-sensitive adhesive tape according to <7>, wherein the tensile elastic modulus of the above base material is 50 MPa to 1000 MPa. <9> The pressure-sensitive adhesive tape according to <7> or <8>, wherein the material of the above base material is a polyolefin resin, a polyurethane resin, or a polyvinyl chloride resin. <10> The pressure-sensitive adhesive tape according to <9>, wherein the polyolefin resin is a polyethylene resin.

Advantages of the Invention

[0011] According to an embodiment of the present disclosure, when a pressure-sensitive adhesive layer is formed on a soft base material, the formed pressure-sensitive adhesive layer has a tack force that does not easily peel off from the adherend, can be easily peeled off without requiring excessive force when peeled off from the adherend, and a pressure-sensitive adhesive composition excellent in curvature adhesiveness is provided. According to other embodiments of the present disclosure, when formed on a soft substrate, there is provided an adhesive layer having a tack force that does not easily peel off from an adherend, can be easily peeled off without requiring excessive force when peeled off from the adherend, and has excellent adhesion to a curved surface, and an adhesive tape including the adhesive layer.

Mode for Carrying Out the Invention

[0012] Hereinafter, the adhesive composition, adhesive layer, and adhesive tape of the present disclosure will be described in detail. The description of the requirements described below may be based on typical embodiments of the present disclosure, but the present disclosure is not limited to such embodiments, and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0013] In the present disclosure, the numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0014] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0015] In the present disclosure, the amount of each component in the adhesive composition means the total amount of the plurality of substances present in the adhesive composition, unless otherwise specified, when there are a plurality of substances corresponding to each component in the adhesive composition.

[0016] In the present disclosure, "solid content" means components other than the solvent contained in the composition, unless otherwise specified, and "solvent" means water and organic solvents. For example, when the solvent contained in the composition is only water, the solid content means the components other than water contained in the composition. When the solvent contained in the composition is only an organic solvent, the solid content means the components other than the organic solvent contained in the composition. When the solvent contained in the composition is water and an organic solvent, the solid content means the components other than water and the organic solvent contained in the composition.

[0017] In the present disclosure, the “(meth)acrylic copolymer” means a copolymer containing structural units derived from (meth)acrylic monomers and having a proportion of structural units derived from (meth)acrylic monomers of 50% by mass or more. In the present disclosure, the “(meth)acrylic monomer” means a monomer having a (meth)acryloyl group.

[0018] In the present disclosure, “(meth)acrylic” is a term encompassing both “acrylic” and “methacrylic”, “(meth)acrylate” is a term encompassing both “acrylate” and “methacrylate”, and “(meth)acryloyl” is a term encompassing both “acryloyl” and “methacryloyl”.

[0019] In the present disclosure, “n-” means normal, “i-” means iso, “s-” means secondary, and “t-” means tertiary.

[0020] In the present disclosure, “monomer” and “monomeric unit” are synonymous, and “polymer”, “polymerized product” and “copolymer” are synonymous.

[0021] In the present disclosure, “% by mass” and “% by weight” are synonymous, and “parts by mass” and “parts by weight” are synonymous.

[0022] In the present disclosure, the term “process” includes not only independent processes but also those that cannot be clearly distinguished from other processes, provided that the intended purpose of the process is achieved.

[0023] [Adhesive Composition] The pressure-sensitive adhesive composition of the present disclosure contains a (meth)acrylic copolymer and a hexamethylene diisocyanate crosslinking agent. The (meth)acrylic copolymer contains a structural unit (a) derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms and a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group. The proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all the structural units, the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all the structural units, and the content of the hexamethylene diisocyanate crosslinking agent is 1.1 parts by mass to 2.8 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer. By having the above configuration, when the pressure-sensitive adhesive layer is formed on a soft substrate, the formed pressure-sensitive adhesive layer has a tack force that does not easily peel off from the adherend, can be easily peeled off without requiring excessive force when peeled off from the adherend, and has an excellent effect of excellent curvature adhesiveness.

[0024] In the present disclosure, the “(meth)acrylic copolymer containing a structural unit (a) derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms and a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, wherein the proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all the structural units, and the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all the structural units” is also referred to as “specific (meth)acrylic copolymer”. In the present disclosure, the “alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms” is also referred to as “specific alkyl acrylate monomer”.

[0025] 〔Specific (meth)acrylic copolymer〕 The pressure-sensitive adhesive composition of the present disclosure contains a structural unit (a) derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms, and a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, and the proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all the structural units, and the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all the structural units, and contains a (meth)acrylic copolymer [i.e., a specific (meth)acrylic copolymer]. The pressure-sensitive adhesive composition of the present disclosure may contain only one kind of the specific (meth)acrylic copolymer, or may contain two or more kinds.

[0026] <Structural unit (a)> The specific (meth)acrylic copolymer contains a structural unit (a) derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms [i.e., a specific alkyl acrylate monomer], and the proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all the structural units. In the present disclosure, the "structural unit derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms" means a structural unit formed by the addition polymerization of an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms.

[0027] An alkyl acrylate monomer having a linear alkyl moiety with 10 or more carbon atoms is presumed to be likely to crystallize at room temperature (for example, 23°C) and under dynamic conditions. Therefore, when the (meth)acrylic copolymer contains a structural unit derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 or more carbon atoms, the polymer chains of the (meth)acrylic copolymer are crystallized at room temperature (for example, 23°C) and under dynamic conditions, and the adhesive strength of the pressure-sensitive adhesive layer is suppressed. Thus, the pressure-sensitive adhesive layer formed on a soft substrate tends to be easily peeled off without requiring excessive force when peeling from the adherend. On the one hand, it is presumed that an alkyl acrylate monomer having a linear alkyl moiety with 13 or fewer carbon atoms is less likely to crystallize at room temperature (e.g., 23°C) under static conditions. Therefore, when a (meth)acrylic copolymer contains a structural unit derived from an alkyl acrylate monomer having a linear alkyl moiety with 13 or fewer carbon atoms, under room temperature (e.g., 23°C) and static conditions, the adhesive layer does not become overly hard and the tack force does not become overly weak. Also, when attached to a curved surface, the adhesive layer is less likely to be distorted. Thus, the adhesive layer formed on a soft substrate has a tack force that does not easily peel off from the adherend and tends to have excellent adhesion to curved surfaces.

[0028] Specific examples of the alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms [i.e., the specific alkyl acrylate monomer] include decyl acrylate (number of carbon atoms in the linear alkyl moiety: 10), undecyl acrylate (number of carbon atoms in the linear alkyl moiety: 11), lauryl acrylate (number of carbon atoms in the linear alkyl moiety: 12), and tridecyl acrylate (number of carbon atoms in the linear alkyl moiety: 13). The specific alkyl acrylate monomer preferably contains at least one of lauryl acrylate and tridecyl acrylate, more preferably contains lauryl acrylate or tridecyl acrylate, still more preferably contains lauryl acrylate, and particularly preferably is lauryl acrylate.

[0029] The specific (meth)acrylic copolymer may contain only one type of structural unit (a) or may contain two or more types.

[0030] The proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer is 65.0% by mass to 98.5% by mass based on all the structural units of the specific (meth)acrylic copolymer. When the proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer is 65.0% by mass or more based on all the structural units of the specific (meth)acrylic copolymer, the polymer chain of the (meth)acrylic copolymer is appropriately crystallized by the specific alkyl acrylate monomer at room temperature (for example, 23°C) under dynamic conditions, and the adhesive strength of the adhesive layer is suppressed. Therefore, even when an adhesive layer is formed on a soft substrate, it tends to be easily peeled off without requiring excessive force when peeling the adhesive layer from the adherend. The proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer is preferably 70.0% by mass or more, more preferably 80.0% by mass or more, and still more preferably 90.0% by mass or more based on all the structural units of the specific (meth)acrylic copolymer. When the proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer is 98.5% by mass or less based on all the structural units of the specific (meth)acrylic copolymer, the adhesive layer can ensure a sufficient degree of crosslinking by the reaction of the vinyl group-containing monomer having a hydroxyl group described below and the hexamethylene diisocyanate-based crosslinking agent described below. Therefore, even when an adhesive layer is formed on a soft substrate, it tends to be peeled off without the adhesive layer being destroyed when peeling the adhesive layer from the adherend. The proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer is preferably 98.3% by mass or less, more preferably 98.0% by mass or less, and still more preferably 97.5% by mass or less based on all the structural units of the specific (meth)acrylic copolymer. In one aspect, the proportion of the structural unit (a) contained in the specific (meth)acrylic copolymer may be 70.0% by mass to 98.5% by mass, 80.0% by mass to 98.5% by mass, 90.0% by mass to 98.5% by mass, 90.0% by mass to 98.3% by mass, 90.0% by mass to 98.0% by mass, or 90.0% by mass to 97.5% by mass based on all the structural units of the specific (meth)acrylic copolymer.

[0031] <Structural unit (b)> The specific (meth)acrylic copolymer contains a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, and the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all the structural units. In the present disclosure, the "structural unit derived from a vinyl group-containing monomer having a hydroxyl group" means a structural unit formed by the addition polymerization of a vinyl group-containing monomer having a hydroxyl group.

[0032] The vinyl group-containing monomer having a hydroxyl group is not particularly limited as long as it is a monomer having at least one hydroxyl group and one vinyl group in one molecule. The vinyl group-containing monomer having a hydroxyl group may be a (meth)acrylic monomer having a hydroxyl group, or may be a monomer other than the (meth)acrylic monomer having a hydroxyl group. The number of hydroxyl groups of the vinyl group-containing monomer having a hydroxyl group is not particularly limited, but for example, it is preferably 1 to 4, more preferably 1 to 2, and still more preferably 1. In the present disclosure, the vinyl group includes an acryloyl group, a methacryloyl group, an allyl group, and a vinyl ether group.

[0033] Specific examples of the vinyl group-containing monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono (meth)acrylate, polypropylene glycol mono (meth)acrylate, polyethylene glycol mono (meth)acrylate, poly(ethylene glycol-propylene glycol) mono (meth)acrylate, allyl alcohol, allyloxy-1,2-propanediol, allyl glycol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, and cyclohexanedimethanol monovinyl ether.

[0034] The vinyl group-containing monomer having a hydroxyl group preferably contains at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate, more preferably contains 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate, still more preferably contains 4-hydroxybutyl acrylate, and particularly preferably is 4-hydroxybutyl acrylate.

[0035] The specific (meth)acrylic copolymer may contain only one kind of the structural unit (b) or may contain two or more kinds.

[0036] The proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer is 1.0% by mass to 8.0% by mass based on all the structural units of the specific (meth)acrylic copolymer. When the proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer is 1.0% by mass or more based on all the structural units of the specific (meth)acrylic copolymer, the adhesive layer can secure a sufficient degree of crosslinking by the reaction of the vinyl group-containing monomer having a hydroxyl group and the hexamethylene diisocyanate-based crosslinking agent described below. Therefore, even when an adhesive layer is formed on a soft substrate, when the adhesive layer is peeled from the adherend, the adhesive layer tends to be peeled without being destroyed. The proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer is preferably 1.1% by mass or more, more preferably 1.2% by mass or more, based on all the structural units of the specific (meth)acrylic copolymer. When the proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer is 8.0% by mass or less based on all the structural units of the specific (meth)acrylic copolymer, the hydroxyl group present on the surface of the adhesive layer and the polar group present on the surface of the adherend do not overly affinity. Therefore, the wettability of the adhesive layer does not become overly high. Thus, even when an adhesive layer is formed on a soft substrate, when the adhesive layer is peeled from the adherend, it tends to be easily peeled without requiring excessive force. The proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, still more preferably 4.0% by mass or less, based on all the structural units of the specific (meth)acrylic copolymer. In one aspect, the proportion of the structural unit (b) contained in the specific (meth)acrylic copolymer may be 1.0% by mass to 6.0% by mass, may be 1.0% by mass to 5.0% by mass, may be 1.0% by mass to 4.0% by mass, may be 1.1% by mass to 4.0% by mass, or may be 1.2% by mass to 4.0% by mass, based on all the structural units of the specific (meth)acrylic copolymer.

[0037] <Structural unit (c)> The specific (meth)acrylic copolymer may further contain a structural unit (c) derived from a vinyl group-containing monomer having a carboxy group. In the present disclosure, the "structural unit derived from a vinyl group-containing monomer having a carboxy group" means a structural unit formed by the addition polymerization of a vinyl group-containing monomer having a carboxy group.

[0038] The vinyl group-containing monomer having a carboxy group is not particularly limited as long as it is a monomer having at least one carboxy group and one vinyl group in one molecule. The number of carboxy groups in the vinyl group-containing monomer having a carboxy group is not particularly limited, but for example, it is preferably 1 to 2, and more preferably 1.

[0039] Specific examples of the vinyl group-containing monomer having a carboxy group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [for example, ω-carboxy-polycaprolactone (n≈2) monoacrylate], and succinic acid derivatives (for example, 2-acryloyloxyethyl-succinic acid). The vinyl group-containing monomer having a carboxy group preferably contains acrylic acid, and more preferably is acrylic acid.

[0040] When the specific (meth)acrylic copolymer contains the structural unit (c), it may contain only one kind of the structural unit (c) or two or more kinds of the structural unit (c).

[0041] When the specific (meth)acrylic copolymer contains the structural unit (c), the proportion of the structural unit (c) contained in the specific (meth)acrylic copolymer is not particularly limited, but for example, it is preferably 1.0% by mass or less based on all the structural units of the specific (meth)acrylic copolymer. When the proportion of the structural unit (c) contained in the specific (meth)acrylic copolymer is 1.0% by mass or less based on all the structural units of the specific (meth)acrylic copolymer, the carboxyl groups present on the surface of the pressure-sensitive adhesive layer and the polar groups present on the surface of the adherend do not overly affinity with each other. Therefore, the wettability of the pressure-sensitive adhesive layer does not become overly high. Thus, even when the pressure-sensitive adhesive layer is formed on a soft base material, it tends to be easily peeled off without requiring excessive force when peeling the pressure-sensitive adhesive layer from the adherend. The proportion of the structural unit (c) contained in the specific (meth)acrylic copolymer is more preferably 0.8% by mass or less, and even more preferably 0.5% by mass or less, based on all the structural units of the specific (meth)acrylic copolymer. When the specific (meth)acrylic copolymer contains the structural unit (c), the lower limit of the proportion of the structural unit (c) contained in the specific (meth)acrylic copolymer may be, for example, 0.05% by mass or more, or may be 0.1% by mass or more. Also, the proportion of the structural unit (c) contained in the specific (meth)acrylic copolymer may be 0% by mass.

[0042] <Structural units derived from other monomers> The specific (meth)acrylic copolymer may contain, as necessary, structural units derived from a monomer (so-called other monomer) that does not fall under any of the specific alkyl acrylate monomers, vinyl group-containing monomers having a hydroxyl group, and vinyl group-containing monomers having a carboxyl group, as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired. In the present disclosure, "structural units derived from other monomers" means structural units formed by the addition polymerization of other monomers.

[0043] Examples of the structural units derived from other monomers include structural units derived from alkyl acrylate monomers other than the specific alkyl acrylate monomers, and structural units derived from (meth)acrylate monomers. In the present disclosure, the “alkyl acrylate monomer other than the specific alkyl acrylate monomer and the (meth)acrylate monomer” may be collectively referred to as the “other (meth)acrylate monomer”.

[0044] In addition, examples of the structural unit derived from other monomers include, for example, a structural unit derived from a (meth)acrylate having an aromatic ring typified by benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; a structural unit derived from an alkoxyalkyl (meth)acrylate typified by methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; a structural unit derived from an aromatic monovinyl typified by styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; a structural unit derived from a vinyl cyanide typified by acrylonitrile and methacrylonitrile; a structural unit derived from a vinyl ester typified by vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; and the like.

[0045] When the specific (meth)acrylic copolymer contains a structural unit derived from other monomers, it may contain only one kind of the structural unit derived from other monomers, or may contain two or more kinds.

[0046] When the specific (meth)acrylic copolymer contains a structural unit derived from other monomers, the proportion of the structural unit derived from other monomers contained in the specific (meth)acrylic copolymer can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0047] <<Weight-average molecular weight of the specific (meth)acrylic copolymer>> The weight-average molecular weight of the specific (meth)acrylic copolymer (also referred to as “Mw”) is not particularly limited, but for example, it is preferably 400,000 or more, and more preferably 450,000 or more. When the weight average molecular weight of the specific (meth)acrylic copolymer is 400,000 or more, the adhesive layer can sufficiently secure the physical crosslinking degree due to the entanglement of polymer chains. Therefore, even when the adhesive layer is formed on a soft substrate, the adhesive layer tends to be peeled off without being broken when the adhesive layer is peeled from the adherend. From the viewpoint of ease of production, for example, the weight average molecular weight of the specific (meth)acrylic copolymer is preferably 1,000,000 or less. In certain embodiments, the weight average molecular weight of the specific (meth)acrylic copolymer may be 400,000 to 1,000,000, may be 450,000 to 1,000,000, or may be 450,000 to 900,000.

[0048] The weight average molecular weight of the specific (meth)acrylic copolymer is a value measured by the following method. Specifically, it is measured according to the following (1) to (3). (1) After applying a solution of the specific (meth)acrylic copolymer to release paper, it is dried at 100 °C for 1 minute to obtain a film-like specific (meth)acrylic copolymer. (2) Using the film-like specific (meth)acrylic copolymer obtained in (1) above and tetrahydrofuran, a sample solution with a solid content concentration of 0.2 mass% is obtained. Here, the "solid content concentration" means the mass ratio of the specific (meth)acrylic copolymer in the sample solution. (3) The weight average molecular weight of the specific (meth)acrylic copolymer is determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) under the following conditions.

[0049] ~Conditions~ Measuring device: High-speed GPC [Model number: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential refractive index meter (RI) [Incorporated in HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Two [manufactured by Tosoh Corporation] are used Column temperature: 40 °C Eluent: Tetrahydrofuran Injection volume of sample solution: 100 μL Flow rate: 0.8 mL / min

[0050] The weight average molecular weight of the specific (meth)acrylic copolymer can be adjusted to a desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomers.

[0051] <<Content ratio of the specific (meth)acrylic copolymer>> The content ratio of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited. For example, it is preferably 66.0% by mass to 98.9% by mass, more preferably 75.0% by mass to 98.8% by mass, and even more preferably 85.0% by mass to 98.5% by mass with respect to the total solid content in the pressure-sensitive adhesive composition.

[0052] In the present disclosure, the "total solid content in the pressure-sensitive adhesive composition" means the total mass of the pressure-sensitive adhesive composition when the pressure-sensitive adhesive composition does not contain a solvent, and means the mass of the residue obtained by removing the solvent from the pressure-sensitive adhesive composition when the pressure-sensitive adhesive composition contains a solvent.

[0053] 〔Method for producing the specific (meth)acrylic copolymer〕 The method for producing the specific (meth)acrylic copolymer is not particularly limited. The specific (meth)acrylic copolymer can be produced, for example, by a known polymerization method typified by a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method, by polymerizing the above-mentioned monomers. As the polymerization method, in preparing the pressure-sensitive adhesive composition of the present disclosure, the solution polymerization method is preferable in that the treatment process is relatively simple and can be carried out in a short time.

[0054] In the solution polymerization method, generally, a predetermined organic solvent, monomer, polymerization initiator, and, if necessary, a chain transfer agent used are charged into a polymerization tank, and, for example, a heat reaction is carried out with stirring for several hours at the reflux temperature of the organic solvent. In this case, at least a part of the organic solvent, monomer, polymerization initiator, and, if necessary, the chain transfer agent used may be sequentially added. Also, the reaction may be carried out in a nitrogen stream.

[0055] Examples of the organic solvent used during the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. More specifically, examples of the organic solvent used during the polymerization reaction include aromatic hydrocarbon compounds typified by benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds typified by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine oil; ester compounds typified by methyl acetate, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; ketone compounds typified by acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds typified by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol compounds typified by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

[0056] In the production of a specific (meth)acrylic copolymer, it is preferable to use an organic solvent that hardly causes chain transfer during the polymerization reaction, such as an aromatic hydrocarbon compound, an ester compound, or a ketone compound. In particular, from the viewpoints of the solubility of the specific (meth)acrylic copolymer and the ease of the polymerization reaction, it is preferable to use methyl acetate and / or ethyl acetate.

[0057] During the polymerization reaction, only one kind of organic solvent may be used, or two or more kinds may be used.

[0058] Examples of the polymerization initiator include organic peroxides and azo compounds used in a normal solution polymerization method. Specific examples of the organic peroxide include t-butyl peroxy-2-ethylhexanoate, t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxy pivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane. Specific examples of the azo compound include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyric acid)dimethyl.

[0059] During the polymerization reaction, only one kind of polymerization initiator may be used, or two or more kinds may be used.

[0060] The amount of the polymerization initiator used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the target specific (meth)acrylic copolymer.

[0061] In the production of the specific (meth)acrylic copolymer, a chain transfer agent may be used as necessary. Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, α-methylstyrene, anthracene, phenanthrene, fluorene, and aromatic compounds represented by 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives represented by benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives represented by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and halogenated hydrocarbon compounds represented by 3-chloro-1-propene, aldehyde compounds represented by chloral and furaldehyde, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds represented by thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds represented by pinene and terpinolene.

[0062] When a chain transfer agent is used in the production of the specific (meth)acrylic copolymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set according to, for example, the molecular weight of the target specific (meth)acrylic copolymer.

[0063] The polymerization temperature is not particularly limited and can be appropriately set according to, for example, the molecular weight of the target specific (meth)acrylic copolymer.

[0064] Hexamethylene diisocyanate - based cross - linker The pressure - sensitive adhesive composition of the present disclosure contains a hexamethylene diisocyanate - based cross - linker, and the content of the hexamethylene diisocyanate - based cross - linker is 1.1 parts by mass to 2.8 parts by mass with respect to 100 parts by mass of a specific (meth) acrylic copolymer. In the pressure - sensitive adhesive composition of the present disclosure, when a hexamethylene diisocyanate - based cross - linker is included, the elastic modulus of the cross - linked pressure - sensitive adhesive layer tends not to become excessively high as compared with the case where other isocyanate - based cross - linkers are included.

[0065] Examples of the hexamethylene diisocyanate - based cross - linker include hexamethylene diisocyanate (HDI), multimers of hexamethylene diisocyanate, adducts of hexamethylene diisocyanate with polyol - based compounds, and biuret compounds of hexamethylene diisocyanate. Examples of the polyol - based compound include trimethylolpropane (TMP). The hexamethylene diisocyanate - based cross - linker preferably contains at least one of a biuret compound of HDI (so - called dimer) and an isocyanurate compound of HDI (so - called trimer), more preferably contains a biuret compound of HDI or an isocyanurate compound of HDI, and even more preferably is a biuret compound of HDI or an isocyanurate compound of HDI.

[0066] As the hexamethylene diisocyanate - based cross - linker, commercially available products can be used. Examples of commercially available hexamethylene diisocyanate-based crosslinking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HK", "Coronate (registered trademark) HL", "Coronate (registered trademark) 2770", "Coronate (registered trademark) 2785", and "Coronate (registered trademark) 2793" manufactured by Tosoh Corporation; "Desmodur (registered trademark) N75 MPA / X", "Desmodur (registered trademark) N100", "Desmodur (registered trademark) N3200", and "Desmodur (registered trademark) N3400" manufactured by Sumitomo Chemical Covestro Urethane Co., Ltd.; "Duranate (registered trademark) 24A-100", "Duranate (registered trademark) TMA-100", and "Duranate (registered trademark) E405-70B" manufactured by Asahi Kasei Corporation; and "Takenate (registered trademark) D-160N" and "Takenate (registered trademark) D-172N" manufactured by Mitsui Chemicals, Inc.

[0067] The pressure-sensitive adhesive composition of the present disclosure may contain only one type of hexamethylene diisocyanate-based crosslinking agent, or may contain two or more types.

[0068] The content of the hexamethylene diisocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 1.1 parts by mass to 2.8 parts by mass with respect to 100 parts by mass of the specific (meth)acrylic copolymer. When the content of the hexamethylene diisocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 1.1 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer, the adhesive layer can ensure a sufficient degree of crosslinking by the reaction of the hexamethylene diisocyanate-based crosslinking agent and the vinyl group-containing monomer having the above-mentioned hydroxyl group. Therefore, even when the adhesive layer is formed on a soft substrate, the adhesive layer can be peeled off without being damaged when the adhesive layer is peeled off from the adherend. The content of the hexamethylene diisocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is preferably 1.2 parts by mass or more, and more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer. When the content of the hexamethylene diisocyanate - based cross - linking agent in the pressure - sensitive adhesive composition of the present disclosure is 2.8 parts by mass or less with respect to 100 parts by mass of the specific (meth) acrylic copolymer, the cross - linking of the pressure - sensitive adhesive layer does not become excessively high. Therefore, the wettability of the pressure - sensitive adhesive layer can be appropriately ensured. Thus, even when a pressure - sensitive adhesive layer is formed on a soft substrate, the formed pressure - sensitive adhesive layer tends to have a tack force that does not easily peel off from the adherend and also tends to have excellent adhesion to a curved surface. The content of the hexamethylene diisocyanate - based cross - linking agent in the pressure - sensitive adhesive composition of the present disclosure is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, with respect to 100 parts by mass of the specific (meth) acrylic copolymer. In one aspect, the content of the hexamethylene diisocyanate - based cross - linking agent in the pressure - sensitive adhesive composition of the present disclosure may be 1.2 to 2.5 parts by mass, may be 1.2 to 2.0 parts by mass, or may be 1.5 to 2.0 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic copolymer.

[0069] 〔Organic solvent〕 The pressure - sensitive adhesive composition of the present disclosure may contain an organic solvent. When the pressure - sensitive adhesive composition of the present disclosure contains an organic solvent, the coatability can be improved. Examples of the organic solvent include the same ones as those used in the polymerization reaction of the aforementioned specific (meth) acrylic copolymer.

[0070] When the pressure - sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one kind of organic solvent or may contain two or more kinds of organic solvents.

[0071] When the pressure - sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set according to the purpose.

[0072] 〔Other components〕 The pressure - sensitive adhesive composition of the present disclosure may contain components other than the aforementioned components (so - called other components) as necessary, as long as the effects are not impaired. Examples of other components include various additives such as polymers other than the specific (meth)acrylic copolymer, crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0073] When the pressure-sensitive adhesive composition of the present disclosure contains other components, the content of the other components can be appropriately set as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired.

[0074] [[Use of the pressure-sensitive adhesive composition]] The use of the pressure-sensitive adhesive composition of the present disclosure is not particularly limited. When the pressure-sensitive adhesive composition of the present disclosure forms a pressure-sensitive adhesive layer on a soft substrate, the formed pressure-sensitive adhesive layer has a tack force that does not easily peel off from the adherend, can be easily peeled off without requiring excessive force when peeling from the adherend, and has excellent adhesion to a curved surface. Therefore, for example, it is suitable as a pressure-sensitive adhesive composition (i.e., a pressure-sensitive adhesive composition for a protective tape) used for protecting components such as electronic components and optical components.

[0075] [[Pressure-sensitive adhesive layer]] The pressure-sensitive adhesive layer of the present disclosure is a layer formed by the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer of the present disclosure contains a cured product of the pressure-sensitive adhesive composition of the present disclosure. The cured product includes, for example, a crosslinked product of a specific (meth)acrylic copolymer crosslinked and cured with a hexamethylene diisocyanate-based crosslinking agent. Since the pressure-sensitive adhesive layer of the present disclosure is a layer formed by the pressure-sensitive adhesive composition of the present disclosure, when formed on a soft substrate, it has a tack force that does not easily peel off from the adherend, can be easily peeled off without requiring excessive force when peeling from the adherend, and has excellent adhesion to a curved surface.

[0076] The thickness of the pressure-sensitive adhesive layer of the present disclosure is not particularly limited, but for example, it is preferably 3 μm to 15 μm, more preferably 5 μm to 15 μm, and even more preferably 5 μm to 10 μm. When the thickness of the pressure-sensitive adhesive layer of the present disclosure is 3 μm or more, the tack force is improved, and it tends to be difficult to easily peel off from the adherend. When the thickness of the pressure-sensitive adhesive layer of the present disclosure is 15 μm or less, the adhesive force does not become excessively high, and when peeling from the adherend, it tends to be easily peeled without requiring excessive force.

[0077] In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" means the average thickness of the pressure-sensitive adhesive layer. The average thickness of the pressure-sensitive adhesive layer is a value obtained by the following method. The thicknesses of 10 randomly selected locations in the thickness direction of the pressure-sensitive adhesive layer are measured using a film thickness gauge. The arithmetic mean value of the measured values is obtained, and the obtained value is taken as the average thickness of the pressure-sensitive adhesive layer.

[0078] [Adhesive tape] The adhesive tape of the present disclosure includes a base material and the pressure-sensitive adhesive layer of the present disclosure provided on the base material. Since the adhesive tape of the present disclosure includes the pressure-sensitive adhesive layer of the present disclosure, it does not easily peel off from the adherend, can be easily peeled without requiring excessive force when peeling from the adherend, and has excellent adhesion to a curved surface.

[0079] The base material is not particularly limited as long as an adhesive layer can be formed on its surface. The base material is preferably in the form of a film. The base material is preferably soft. For example, the tensile elastic modulus of the base material is preferably 1000 MPa or less, more preferably 800 MPa or less, and still more preferably 500 MPa or less. The lower limit of the tensile elastic modulus of the base material is preferably 50 MPa or more, more preferably 100 MPa or more, and still more preferably 200 MPa or more from the viewpoint of workability when pasting on the adherend. In one aspect, the tensile elastic modulus of the base material may be 50 MPa to 1000 MPa, may be 50 MPa to 800 MPa, may be 50 MPa to 500 MPa, may be 100 MPa to 800 MPa, may be 100 MPa to 500 MPa, or may be 200 MPa to 500 MPa.

[0080] The tensile elastic modulus of the base material in the present disclosure is the tensile elastic modulus at 25°C and is a value measured in accordance with JIS K 7127:1999.

[0081] The material of the base material is not particularly limited, but for example, it is preferably a resin, more preferably a soft resin, still more preferably a polyolefin resin, a polyurethane resin, or a polyvinyl chloride resin, and particularly preferably a polyolefin resin. Examples of the polyolefin resin include a polyethylene resin and a polypropylene resin. The polyolefin resin is preferably a polyethylene resin.

[0082] On the surface of the base material on the side where the adhesive layer is provided, surface treatment such as corona discharge treatment or plasma discharge treatment (so-called easy adhesion treatment) may be performed from the viewpoint of improving the adhesion between the base material and the adhesive layer.

[0083] The base material may contain various additives such as a plasticizer, a colorant (for example, a dye and a pigment), a heat stabilizer, a light stabilizer, an antistatic agent, a flame retardant, an antioxidant, and a filler. The base material may be patterned partially or entirely.

[0084] The thickness of the base material is not particularly limited, but for example, it is preferably 100 μm or less, more preferably 5 μm to 100 μm, and still more preferably 10 μm to 80 μm.

[0085] The "thickness of the base material" in the present disclosure means the average thickness of the base material. The average thickness of the base material is a value obtained by the following method. The thicknesses of 10 randomly selected locations in the thickness direction of the base material are measured using a film thickness gauge. The arithmetic mean value of the measurement values is obtained, and the obtained value is taken as the average thickness of the base material.

[0086] The adhesive tape of the present disclosure includes the adhesive layer of the present disclosure. Since the adhesive layer of the present disclosure is as described above, the description thereof is omitted here.

[0087] When the adhesive tape of the present disclosure is an adhesive tape having an adhesive layer on one side of a base material, the exposed surface of the adhesive layer may be protected by a release sheet. Generally, the release sheet protects the surface of the adhesive layer until the adhesive tape is put into practical use and is peeled off during use.

[0088] The release sheet is not particularly limited as long as it can be easily peeled off from the adhesive layer. Examples of the release sheet include a resin film, paper, synthetic paper, and a composite sheet obtained by laminating two or more of these, which are surface-treated (so-called easy-peeling treatment) with a release treatment agent on one or both sides. In the present disclosure, a release sheet in which one or both sides of a resin film are surface-treated (so-called easy-peeling treatment) with a release treatment agent is also referred to as a "release film". Examples of the release treatment agent include a silicone-based release treatment agent (e.g., silicone), a wax-based release treatment agent (e.g., paraffin wax), and a fluorine-based release treatment agent (e.g., fluorine-based resin). Examples of the resin film include a polyester film typified by a polyethylene terephthalate (PET) film. Examples of the paper include high-quality paper and coated paper. The thickness of the release sheet is not particularly limited and is generally 20 μm to 180 μm.

[0089] [Method for producing an adhesive tape] The method for producing the adhesive tape of the present disclosure is not particularly limited. The adhesive tape of the present disclosure can be produced by a known method. Examples of the method for producing the adhesive tape of the present disclosure include the following methods.

[0090] By applying the pressure-sensitive adhesive composition of the present disclosure to one surface of the base material (preferably, the surface subjected to easy adhesion treatment), a coating film is formed on the base material. Next, by drying the formed coating film, a pressure-sensitive adhesive film is formed on the base material. Next, after overlapping and bonding the exposed surface of the formed pressure-sensitive adhesive film to the easily peelable treatment surface of the release sheet, and then performing curing, the pressure-sensitive adhesive tape of the present disclosure having a laminated structure of base material / pressure-sensitive adhesive layer / release sheet can be produced.

[0091] As another method, for example, the following method can also be mentioned. By applying the pressure-sensitive adhesive composition of the present disclosure to the easily peelable treatment surface of the release sheet, a coating film is formed on the release sheet. Next, by drying the formed coating film, a pressure-sensitive adhesive film is formed on the release sheet. Next, after overlapping and bonding the exposed surface of the formed pressure-sensitive adhesive film to one surface of the base material (preferably, the surface subjected to easy adhesion treatment), and then performing curing, the pressure-sensitive adhesive tape of the present disclosure having a laminated structure of base material / pressure-sensitive adhesive layer / release sheet can be produced.

[0092] The method of applying the pressure-sensitive adhesive composition is not particularly limited. Examples of the method of applying the pressure-sensitive adhesive composition include known methods using a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a knife coater, a spray coater, a bar coater, an applicator, etc. The coating amount of the pressure-sensitive adhesive composition is not particularly limited and is appropriately set according to, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

[0093] The method of drying the coating film is not particularly limited. Examples of the method of drying the coating film include methods such as natural drying, heat drying, hot air drying, and vacuum drying. The drying temperature and drying time of the coating film are not particularly limited and are appropriately set according to the thickness of the coating film, the amount of the organic solvent in the coating film, etc. As an example of the drying conditions, there is a condition of drying at 60°C to 120°C for 30 seconds to 180 seconds using a hot air circulation dryer.

[0094] As a health preservation method, for example, there is a method of standing still for 2 to 7 days in an environment with an ambient temperature of 20°C to 35°C and a relative humidity of 45% to 55%.

Example

[0095] Hereinafter, the adhesive composition, adhesive layer, and adhesive tape of the present disclosure will be described in more detail with reference to examples. The present disclosure is not limited to the following examples as long as the gist thereof is not exceeded.

[0096] [Manufacture of (meth)acrylic copolymer] [Production Example A-2] Into a reactor equipped with a stirrer, reflux condenser, sequential dropping device, and thermometer, 270.0 parts by mass of ethyl acetate [organic solvent] and 0.025 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were charged. Next, in another container, 485.0 parts by mass of lauryl acrylate [LA; specific acrylic acid alkyl ester monomer], 12.5 parts by mass of 4-hydroxybutyl acrylate [4HBA; vinyl group-containing monomer having a hydroxyl group], and 2.5 parts by mass of acrylic acid [AA; vinyl group-containing monomer having a carboxyl group] were put and mixed to prepare 500.0 parts by mass of a monomer mixture. Next, 125.0 parts by mass (corresponding to 25% by mass of the monomer mixture) of the prepared monomer mixture was charged into the above reactor, and then the reactor was heated and refluxed at the reflux temperature for 20 minutes. Next, under the reflux temperature condition, the remaining 375.0 parts by mass (corresponding to 75% by mass of the monomer mixture) of the monomer mixture, 50.0 parts by mass of ethyl acetate, and 0.18 parts by mass of AIBN were sequentially dropped into the reactor over 90 minutes. After the dropping was completed, it was held for 240 minutes to carry out a polymerization reaction. Next, the solution obtained by carrying out the polymerization reaction was diluted with butyl acetate so that the solid content concentration became 44% by mass to obtain a solution of (meth)acrylic copolymer A-2.

[0097] The "solid content concentration" referred to here means the mass ratio of (meth)acrylic copolymer A-2 in the solution of (meth)acrylic copolymer A-2. The same applies to the solutions of (meth)acrylic copolymers A-1 and A-3 to A-18 produced below.

[0098] 〔Production Examples A-1, A-4, A-7, A-8 and A-12〕 In Production Examples A-1, A-4, A-7, A-8 and A-12, the same operations as in Production Example A-2 were carried out except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 1, and solutions of (meth)acrylic copolymers A-1, A-4, A-7, A-8 and A-12 with a solid content concentration of 44% by mass were obtained.

[0099] 〔Production Examples A-3, A-5, A-6, A-9 and A-13 to A-18〕 In Production Examples A-3, A-5, A-6, A-9 and A-13 to A-18, the monomer composition of the (meth)acrylic copolymer was changed, and at least one of the amount of the organic solvent used and the amount of the polymerization initiator used was adjusted. The same operations as in Production Example A-2 were carried out except that (meth)acrylic copolymers having the monomer composition and weight average molecular weight shown in Table 1 were produced, and solutions of (meth)acrylic copolymers A-3, A-5, A-6, A-9 and A-13 to A-18 with a solid content concentration of 44% by mass were obtained.

[0100] 〔Production Examples A-10 and A-11〕 In Production Examples A-10 and A-11, at least one of the amount of the organic solvent used and the amount of the polymerization initiator used was adjusted. The same operations as in Production Example A-2 were carried out except that (meth)acrylic copolymers having the weight average molecular weight shown in Table 1 were produced, and solutions of (meth)acrylic copolymers A-10 and A-11 with a solid content concentration of 44% by mass were obtained.

[0101] The monomer compositions [unit: mass%] and weight average molecular weights (denoted as "Mw") of the (meth)acrylic copolymers A-1 to A-18 are shown in Table 1.

[0102] The weight average molecular weights of the (meth)acrylic copolymers A-1 to A-18 were measured by the same method as the method for measuring the weight average molecular weight of the aforementioned specific (meth)acrylic copolymer.

[0103] Among the (meth)acrylic copolymers A-1 to A-18, the (meth)acrylic copolymers A-1 to A-11 and A-18 correspond to the specific (meth)acrylic copolymers in the present disclosure.

[0104]

Table 1

[0105] Details of each monomer described in Table 1 are as shown below. <Specific acrylic acid alkyl ester monomer> “LA”: Lauryl acrylate (number of carbon atoms in the straight-chain alkyl moiety: 12) “TrDA”: Tridecyl acrylate (number of carbon atoms in the straight-chain alkyl moiety: 13) <Other (meth)acrylic acid alkyl ester monomers> “NOA”: n-Octyl acrylate (number of carbon atoms in the straight-chain alkyl moiety: 8) “LMA”: Lauryl methacrylate “IDA”: Isodecyl acrylate “TeDA”: Tetradecyl acrylate (number of carbon atoms in the straight-chain alkyl moiety: 14) <Vinyl group-containing monomer having a hydroxyl group> “4HBA”: 4-Hydroxybutyl acrylate “2HEA”: 2-Hydroxyethyl acrylate <Vinyl group-containing monomer having a carboxy group> “AA”: Acrylic acid

[0106] In Table 1, “-” described in the column of monomer composition means that the monomer corresponding to that column is not used.

[0107] [Preparation of adhesive composition] 〔Example 1〕 227.3 parts by mass of a solution of (meth)acrylic copolymer A-1 (100 parts by mass as solid content) and 1.5 parts by mass of a crosslinking agent [trade name: Coronate (registered trademark) HX, isocyanurate of hexamethylene diisocyanate (HDI), hexamethylene diisocyanate-based crosslinking agent, solid content concentration: 100% by mass, manufactured by Tosoh Corporation] (1.5 parts by mass as solid content) were thoroughly mixed to obtain the pressure-sensitive adhesive composition of Example 1.

[0108] [Examples 2 to 15] In Examples 2 to 15, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 2, and the pressure-sensitive adhesive compositions of Examples 2 to 15 were obtained.

[0109] [Comparative Examples 1 to 10] In Comparative Examples 1 to 10, the same operations as in Example 1 were carried out except that the composition of the pressure-sensitive adhesive composition was changed to the composition shown in Table 2, and the pressure-sensitive adhesive compositions of Comparative Examples 1 to 10 were obtained.

[0110] [Preparation of Adhesive Tape for Evaluation] The pressure-sensitive adhesive composition prepared above was applied to the easily peelable treatment surface of a release film [trade name: Film Bina (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.] surface-treated with a silicone-based release treatment agent (so-called easy peel treatment) to form a coating film. The coating amount of the pressure-sensitive adhesive composition was set to an amount such that the thickness of the adhesive film described later would be 10 μm. The formed coating film was dried using a hot air circulation dryer under the conditions of a drying temperature of 100°C and a drying time of 120 seconds to form an adhesive film on the release film. The exposed surface of the adhesive film was overlapped and bonded to one surface of a polyethylene (PE) film [trade name: M-6, tensile modulus: 300 MPa, thickness: 50 μm, manufactured by Tamapoly Co., Ltd.] as a base material (hereinafter simply referred to as "PE"). The laminate obtained by the bonding was allowed to stand in an environment of an ambient temperature of 23°C and 50% RH for 7 days (so-called curing period) to cure the adhesive film. An adhesive tape for evaluation having a structure of release film / pressure-sensitive adhesive layer / base material (PE) was produced as described above.

[0111] [Measurement and Evaluation] 1. Peelability (1) Preparation of Test Specimen The adhesive tape for evaluation prepared above was cut into pieces with a size of 25 mm × 150 mm (long side) to prepare an adhesive tape piece X for evaluation. Also, a stainless steel plate [SUS304 BA] (hereinafter simply referred to as "SUS") was prepared as the adherend. The release film was peeled off from the adhesive tape piece X for evaluation (composition: release film / adhesive layer / base material) to obtain an adhesive tape piece X1 for evaluation (composition: adhesive layer / base material). After the exposed adhesive layer surface of the adhesive tape piece X1 for evaluation was overlapped with one surface of SUS, a 2 kg roller was reciprocated once for crimping to prepare a test specimen (composition: SUS / adhesive layer / base material).

[0112] (2) Measurement of Adhesive Force - Initial Adhesive Force - The test specimen prepared above was allowed to stand for 24 hours in an environment with an ambient temperature of 23°C. For the test specimen after this standing, the adhesive force (unit: N / 25 mm) when the adhesive tape piece X1 for evaluation was peeled off from SUS at 180° in the long side (150 mm) direction was measured using a single-column type material testing machine (model number: STA-1225) manufactured by A&D Company, Ltd. as the measuring device under the conditions of an ambient temperature of 23°C and a peeling speed of 300 mm / min.

[0113] - Adhesive Force after Aging - The test specimen prepared above was allowed to stand for 168 hours in an environment with an ambient temperature of 23°C. For the test specimen after this standing, the adhesive force (unit: N / 25 mm) when the adhesive tape piece X1 for evaluation was peeled off from SUS at 180° in the long side (150 mm) direction was measured using a single-column type material testing machine (model number: STA-1225) manufactured by A&D Company, Ltd. as the measuring device under the conditions of an ambient temperature of 23°C and a peeling speed of 300 mm / min.

[0114] Based on the measured values of the adhesive force, the peelability of the adhesive layer was evaluated according to the following evaluation criteria. The measured values of the adhesive force and the evaluation results of the peelability are shown in Table 2. In the following evaluation criteria, "A", "B", and "C" are at a level with no practical problems, and "A" is the most preferable.

[0115] -Evaluation Criteria- A: The adhesive force was less than 0.08 N / 25 mm. B: The adhesive force was in the range of 0.08 N / 25 mm or more and less than 0.09 N / 25 mm. C: The adhesive force was in the range of 0.09 N / 25 mm or more and less than 0.10 N / 25 mm. D: The adhesive force was 0.10 N / 25 mm or more, or the destruction of the adhesive layer was confirmed.

[0116] 2. Tack Force The evaluation adhesive tape prepared above was cut into a size of 25 mm × 200 mm to prepare an evaluation adhesive tape piece. The release film was peeled off from the prepared evaluation adhesive tape piece to expose one surface of the adhesive layer. A rolling ball tack test in accordance with ASTM D 3121 was conducted on the exposed adhesive layer. Specifically, in an environment with an ambient temperature of 23°C, a test ball was rolled from an inclined plate, and a test was conducted to measure the distance that the test ball advanced on the surface of the horizontally placed adhesive layer. A No. 10 steel ball was used as the test ball. Based on the measured value of the distance that the test ball advanced, the tack force of the adhesive layer was evaluated according to the following evaluation criteria. The measured value of the distance that the test ball advanced and the evaluation results are shown in Table 2. In the following evaluation criteria, "A", "B", and "C" are at a level with no practical problems, and "A" is the most preferable.

[0117] -Evaluation Criteria- A: The distance that the test ball advanced was less than 130 mm. B: The distance that the test ball advanced was in the range of 130 mm or more and less than 140 mm. C: The distance that the test ball advanced was in the range of 140 mm or more and less than 150 mm. D: The distance that the test ball advanced was 150 mm or more.

[0118] 3. Curved surface adhesiveness The prepared adhesive tape for evaluation was cut into pieces of 25 mm × 50 mm to prepare adhesive tape pieces for evaluation. The release film was peeled off from the prepared adhesive tape pieces for evaluation to expose one surface of the adhesive layer. The exposed surface of the adhesive layer was attached to the surface of a SUS cylinder with a diameter of 10 mm so that the width direction of the adhesive layer and the circumferential direction of the cylinder were aligned, and a test piece (structure: SUS cylinder / adhesive layer / base material) was prepared. The prepared test piece was left standing in an environment with an ambient temperature of 23°C for 168 hours. The test piece after this standing was visually observed. Based on the presence or absence of peeling of the adhesive layer from the SUS cylinder, the curved surface adhesiveness of the adhesive layer was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2. In the following evaluation criteria, "A" indicates a level with no practical problems.

[0119] - Evaluation criteria - A: No peeling of the adhesive layer was confirmed. D: Peeling of the adhesive layer was confirmed.

[0120]

Table 2

[0121] The details of the components described in Table 2 are as shown below. <Crosslinking agent> "HX" [Product name: Coronate (registered trademark) HX, isocyanurate form of hexamethylene diisocyanate (HDI), hexamethylene diisocyanate-based crosslinking agent, solid content concentration: 100% by mass, manufactured by Tosoh Corporation] "N75" [Product name: Desmodur (registered trademark) N75 MPA / X, biuret form of hexamethylene diisocyanate (HDI), hexamethylene diisocyanate-based crosslinking agent, solid content concentration: 75% by mass, manufactured by Sumika Covestro Urethane Co., Ltd.] "D-101E" [Trade name: Takenate (registered trademark) D-101E, trimethylolpropane (TMP) adduct of tolylene diisocyanate (TDI), tolylene diisocyanate-based crosslinking agent, solid content concentration: 45% by mass, manufactured by Mitsui Chemicals, Inc.] <Crosslinking catalyst> "Dibutyltin dilaurate" [Solid content concentration: 100% by mass, manufactured by Tokyo Chemical Industry Co., Ltd.]

[0122] In Table 2, the numerical values described in the column of "blending amount" are all values in terms of solid content. In Table 2, the "-" described in the column of the composition of the pressure-sensitive adhesive composition means that the component corresponding to that column is not blended.

[0123] As shown in Table 2, when the pressure-sensitive adhesive compositions of Examples 1 to 15 were used to form a pressure-sensitive adhesive layer on a soft substrate, it was confirmed that the formed pressure-sensitive adhesive layer was excellent in both the balance of adhesive force and tack force and the curvature adhesiveness. On the other hand, it was confirmed that the pressure-sensitive adhesive layers formed by the pressure-sensitive adhesive compositions of Comparative Examples 1 to 10 were inferior in at least one of the balance of adhesive force and tack force and the curvature adhesiveness as compared with the pressure-sensitive adhesive layers formed by the pressure-sensitive adhesive compositions of the examples.

Claims

1. A pressure-sensitive adhesive composition comprising a (meth)acrylic copolymer and a hexamethylene diisocyanate crosslinking agent, wherein the (meth)acrylic copolymer contains a structural unit (a) derived from an alkyl acrylate monomer having a linear alkyl moiety with 10 to 13 carbon atoms and a structural unit (b) derived from a vinyl group-containing monomer having a hydroxyl group, the proportion of the structural unit (a) is 65.0% by mass to 98.5% by mass based on all the structural units, and the proportion of the structural unit (b) is 1.0% by mass to 8.0% by mass based on all the structural units, and the content of the hexamethylene diisocyanate crosslinking agent is 1.1 parts by mass to 2.8 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic copolymer further contains a structural unit (c) derived from a vinyl group-containing monomer having a carboxy group, and the proportion of the structural unit (c) is 1.0% by mass or less based on all the structural units.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the proportion of the structural unit (b) in the (meth)acrylic copolymer is 1.0% by mass to 4.0% by mass based on all the structural units.

4. The pressure-sensitive adhesive composition according to claim 1, wherein the vinyl group-containing monomer having a hydroxyl group contains 4-hydroxybutyl acrylate.

5. The pressure-sensitive adhesive composition according to claim 1, wherein the weight-average molecular weight of the (meth)acrylic copolymer is 400,000 to 1,000,000.

6. A pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition according to any one of claims 1 to 5, having a thickness of 3 μm to 15 μm.

7. A base material, and the pressure-sensitive adhesive layer according to claim 6 provided on the base material, comprising a pressure-sensitive adhesive tape.

8. The pressure-sensitive adhesive tape according to claim 7, wherein the tensile elastic modulus of the base material is 50 MPa to 1000 MPa.

9. The pressure-sensitive adhesive tape according to claim 7, wherein the material of the base material is a polyolefin resin, a polyurethane resin, or a polyvinyl chloride resin.

10. The pressure-sensitive adhesive tape according to claim 9, wherein the polyolefin resin is a polyethylene resin.

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