Removable adhesive composition, surface protective film, and optical component with adhesive layer

Abstract

The present invention aims to provide a removable adhesive composition that exhibits excellent low-staining properties and a good balance of adhesive strength. [Solution] The (meth)acrylic polymer (A) comprises an alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms, and a monomer (a2) having a functional group, as constituent units, and a curing agent (B), wherein the alkyl group-containing unsaturated monomer (a1) contains at least 2-octyl (meth)acrylate, the (meth)acrylic polymer (A) contains 30% by mass or more of 2-octyl (meth)acrylate and 3.5 to 15% by mass of the monomer (a2) having a functional group, the monomer (a2) having a functional group does not contain a monomer having a carboxyl group, and the curing agent (B) is contained in an amount of 5.0 to 30.0% by mass of 100% by mass of the (meth)acrylic polymer (A).

Description

Technical Field

[0001] The present invention relates to an adhesive composition for re-peeling, a surface protection film, and an optical member with an adhesive layer.

Background Art

[0002] In the manufacturing process of an optical member (for example, a polarizing plate) constituting a liquid crystal display, a surface protection film is adhered to the surface of the optical member in order to temporarily protect the surface of the optical member. Since the surface protection film is peeled off from the optical member by the user after use, the surface protection film has a slightly sticky adhesive layer. Recently, with the increase in the size of liquid crystal displays, the size of the surface protection film for optical members has also increased. Generally, the larger the size of the surface protection film, the more difficult it is to quickly peel the surface protection film from the optical member. Therefore, there is a demand for reducing the adhesive force during high-speed peeling of the surface protection film.

[0003] However, since it is further required as the performance of the surface protection film that it cannot be peeled off from the adherend until it is used up, it is desirable that the adhesive force during low-speed peeling of the surface protection film is somewhat high. Further, when the surface protection film is peeled off, it is required as the performance of the surface protection film that there is no adherend contamination (that is, the adhesive does not contaminate the adherend). Hereinafter, this performance is referred to as low contamination property.

[0004] Conventionally, when the adhesive composition contains butyl acrylate having a high glass transition temperature Tg (-55°C), the film becomes hard, so the low contamination property is improved. However, since the adhesive force during high-speed peeling increases, the balance of the adhesive force deteriorates. Thus, it has been difficult to realize an adhesive composition excellent in both the low contamination property and the adhesive force balance.

[0005] Therefore, Patent Document 1 proposes an adhesive composition containing 2-ethylhexyl acrylate having a low glass transition temperature Tg (-70°C) and a copolymerizable monomer containing a carboxyl group. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-185008 [Overview of the project] [Problems that the invention aims to solve]

[0007] In Patent Document 1, while the adhesive strength is reduced during high-speed peeling, the adhesive strength is too low during low-speed peeling, resulting in a poor balance of adhesive strength. Therefore, a re-peelable adhesive composition that excels in both low contamination and adhesive strength balance has not yet been realized.

[0008] Therefore, the present invention aims to provide a removable adhesive composition that exhibits excellent low-staining properties and a good balance of adhesive strength. [Means for solving the problem]

[0009] To achieve the objectives of the present invention, the re-peelable adhesive composition of the present invention comprises the following: a (meth)acrylic polymer (A) comprising an alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms, and a monomer (a2) having a functional group as constituent units, and a curing agent (B), wherein the alkyl group-containing unsaturated monomer (a1) contains at least 2-octyl (meth)acrylate, the (meth)acrylic polymer (A) contains 30% by mass or more of the 2-octyl (meth)acrylate and 3.5 to 15% by mass of the monomer (a2) having a functional group, the monomer (a2) having a functional group does not contain a monomer (a2) having a carboxyl group, and the curing agent (B) is contained in an amount of 5.0 to 30.0% by mass relative to 100% by mass of the (meth)acrylic polymer (A). [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a removable adhesive composition that has excellent low-stain properties and a good balance of adhesive strength. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way.

[0012] In this specification, the notation "A~B" representing a numerical range is synonymous with "greater than or equal to A" and "less than or equal to B," and includes both A and B.

[0013] In this specification, "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, "(meth)acrylate" means both "acrylate" and "methacrylate."

[0014] In this specification, "mass%" has the same definition as "parts by mass," "parts by weight," and "parts." Therefore, "mass%" may be interpreted as any of "parts by mass," "parts by weight," or "parts."

[0015] <Removable adhesive composition> The repositionable adhesive composition is used as an adhesive layer for a surface protective film or an adhesive layer for an optical component after the solvent has been removed from the composition and it has been dried. The repositionable adhesive composition according to one embodiment comprises at least a (meth)acrylic polymer (A) and a curing agent (B). The repositionable adhesive composition may further contain at least one of a curing retarder (C) and an antistatic agent (D), depending on the performance requirements of the user.

[0016] Here, "repositionable" refers to the property of a surface protective film having an adhesive layer made of a repositionable adhesive composition, which, after being attached to various substrates and a certain period of time has elapsed, is easy to peel off and leaves little adhesive residue.

[0017] <(meth)acrylic polymer (A)> A (meth)acrylic polymer (A) according to one embodiment comprises an alkyl group-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms, and a monomer (a2) having a functional group, as constituent units. In addition to the above constituent units, the (meth)acrylic polymer (A) may also contain a vinyl monomer (a3) ​​and / or a polyalkylene glycol chain-containing mono(meth)acrylate (a4). The polyalkylene glycol chain-containing mono(meth)acrylate (a4) having at least one hydroxyl group is not considered to belong to the monomer (a2) having a functional group.

[0018] In one embodiment, the (meth)acrylic polymer (A) contains 30% by mass or more of 2-octyl (meth)acrylate and 3.5 to 15% by mass of a monomer (a2) having a functional group, in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). Here, the alkyl group-containing unsaturated monomer (a1) contains at least 2-octyl (meth)acrylate.

[0019] In other words, alkyl group-containing unsaturated monomer (a1) may further contain 2-octyl (meth)acrylate and monomers other than 2-octyl (meth)acrylate. The type and content of monomers other than 2-octyl (meth)acrylate are not particularly limited. Furthermore, monomers having a functional group (a2) do not contain monomers having a carboxyl group. Note that "monomers having a functional group (a2) do not contain monomers having a carboxyl group" means that monomers having a carboxyl group are not used intentionally, and the inclusion of monomers having a carboxyl group unintentionally is permissible.

[0020] (Meta)acrylic polymer (A) contains 2-octyl (meta)acrylate at 30% by mass or more, so that the Tg of (meta)acrylic polymer (A) can be increased and the film becomes hard. Thereby, a releasable adhesive composition excellent in low contamination property and adhesion balance can be realized. In addition, since 2-octyl acrylate can be obtained from biomass-derived materials, the dependence on monomers derived from fossil resources can be reduced. The releasable adhesive composition of the present invention contains 2-octyl acrylate, which is a biomass-derived material, and is excellent in being friendly to both humans and the environment.

[0021] <An alkyl group-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms> Examples of alkyl-containing unsaturated monomers (a1) having alkyl groups with 1 to 18 carbon atoms (hereinafter also referred to as alkyl-containing unsaturated monomers (a1)) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate Examples include alkyl (meth)acrylates having linear or branched alkyl groups such as n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-undecyl(meth)acrylate, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, cetyl(meth)acrylate, and stearyl(meth)acrylate; and (meth)acrylates having alicyclic hydrocarbon groups such as cyclohexyl(meth)acrylate, 4-tert-butylcyclohexyl(meth)acrylate, isobornyl(meth)acrylate, and dicyclopentanyl(meth)acrylate. These may be used individually or in combination of two or more. The alkyl-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms contains at least 2-octyl (meth)acrylate. Preferably, the alkyl-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms contains at least 2-octyl acrylate. In addition, the alkyl-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms may further contain 2-ethylhexyl acrylate or butyl acrylate in addition to 2-octyl (meth)acrylate.

[0022] In one embodiment, the (meth)acrylic polymer (A) contains 2-octyl (meth)acrylate at 30% by mass or more based on 100% by mass of all the monomers constituting the (meth)acrylic polymer (A). When the content of 2-octyl (meth)acrylate is less than 30% by mass, the Tg of the (meth)acrylic polymer (A) decreases, resulting in a brittle film and a decrease in low contamination property.

[0023] In one embodiment, when the alkyl group-containing unsaturated monomer (a1) is 2-octyl (meth)acrylate, the (meth)acrylic polymer (A) contains 2-octyl (meth)acrylate at 85 to 96.5% by mass based on 100% by mass of all the monomers constituting the (meth)acrylic polymer (A).

[0024] In one embodiment, when the alkyl group-containing unsaturated monomer (a1) further contains 2-ethylhexyl acrylate in addition to 2-octyl (meth)acrylate, the (meth)acrylic polymer (A) contains 2-octyl (meth)acrylate at 30 to 90% by mass and 2-ethylhexyl acrylate at 5 to 65% by mass based on 100% by mass of all the monomers constituting the (meth)acrylic polymer (A).

[0025] In one embodiment, when the alkyl group-containing unsaturated monomer (a1) further contains butyl acrylate in addition to 2-octyl (meth)acrylate, the (meth)acrylic polymer (A) contains 2-octyl (meth)acrylate at 40 to 90% by mass, preferably 48 to 90% by mass, and butyl acrylate at 5 to 47% by mass based on 100% by mass of all the monomers constituting the (meth)acrylic polymer (A).

[0026] The upper limit for the content of 2-octyl (meth)acrylate is 96.5% by mass or less, 94% by mass or less, 92% by mass or less, 90% by mass or less, 89% by mass or less, 87% by mass or less, 84% by mass or less, or 82% by mass or less. On the other hand, the lower limit for the content of 2-octyl (meth)acrylate is 30% by mass or more, 48% by mass or more, 76.5% by mass or more, 79% by mass or more, or 81.5% by mass or more. The predetermined range for the content of 2-octyl (meth)acrylate may be any combination of the above lower and upper limits. When the content of 2-octyl (meth)acrylate is within the predetermined range, a re-peelable adhesive composition that is excellent in both low contamination and adhesive balance can be realized. On the other hand, when the content of 2-octyl (meth)acrylate is outside the predetermined range (for example, less than 30% by mass), the low contamination performance decreases or the adhesive balance deteriorates.

[0027] <Monomer having a functional group (a2)> The monomer (a2) having a functional group may be any monomer having a functional group other than a carboxyl group, and may include, for example, at least one of a monomer having a hydroxyl group and a monomer having an amide group. The monomer (a2) having a functional group according to one embodiment does not contain a monomer having a carboxyl group. If the monomer (a2) having a functional group contains a monomer having a carboxyl group, the low-contamination properties will decrease or the adhesion balance will deteriorate.

[0028] The monomer (a2) having a functional group is a radical polymerizable monomer having a functional group that can react with the curing agent (B) described later. A polymer network is formed by the crosslinking reaction between the functional group and the curing agent (B), which can improve the cohesive force and re-peelability of the re-peelable adhesive composition. From the viewpoint of improving the re-peelability of the re-peelable adhesive composition, the monomer (a2) having a functional group is preferably a monomer having a hydroxyl group.

[0029] A monomer (a2) having a functional group according to one embodiment is a monomer having a hydroxyl group.

[0030] A monomer (a2) having a functional group according to one embodiment includes a monomer having a hydroxyl group and a monomer having an amide group.

[0031] In one embodiment, when the monomer (a2) having a functional group is a monomer having a hydroxyl group, the (meth)acrylic polymer (A) contains 3.5 to 15% by mass of the monomer (a2) having a functional group in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). By having the content of the monomer (a2) having a functional group within the predetermined range defined in this invention, a re-peelable adhesive composition with excellent low-contamination properties and adhesive balance can be realized. If the content of the monomer (a2) having a functional group is less than 3.5% by mass, the adhesive strength during high-speed peeling becomes high, and the adhesive balance deteriorates. On the other hand, if the content of the monomer (a2) having a functional group exceeds 15% by mass, the adhesive strength during low-speed peeling becomes high, and the adhesive balance deteriorates.

[0032] In one embodiment, when the monomer (a2) having a functional group includes a monomer having a hydroxyl group and a monomer having an amide group, the (meth)acrylic polymer (A) contains 2.5 to 14.9% by mass of monomers having a hydroxyl group and 0.1 to 1% by mass of monomers having an amide group, out of 100% by mass of all monomers constituting the (meth)acrylic polymer (A).

[0033] Examples of monomers having a hydroxyl group include hydroxyalkyl (meth)acrylates (hydroxyalkyl (meth)acrylates) such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These may be used alone or in combination of two or more. Preferably, the monomer having a hydroxyl group includes at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0034] Examples of monomers having an amide group include (meth)acrylamide, isopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and hydroxyethyl(meth)acrylamide. These may be used individually or in combination of two or more. The monomer having an amide group is preferably methacrylamide.

[0035] <Vinyl monomer (a3)> A (meth)acrylic polymer (A) according to one embodiment further comprises a vinyl monomer (a3) ​​as a constituent unit, in addition to an alkyl group-containing unsaturated monomer (a1) and a monomer having a functional group (a2). Examples of vinyl monomers (a3) ​​include styrene, α-methylstyrene, vinyltoluene, vinylpyridine, vinylpyrrolidone, vinyl acetate, and acrylonitrile. These may be used individually or in combination of two or more. The vinyl monomer (a3) ​​is preferably vinyl acetate.

[0036] When the acrylic polymer (A) further contains vinyl acetate as the vinyl monomer (a3), the tackiness balance of the adhesive layer is further improved.

[0037] In one embodiment, the (meth)acrylic polymer (A) further contains vinyl monomer (a3) ​​as a constituent unit, wherein 100% by mass of the total monomers constituting the (meth)acrylic polymer (A) contains 70 to 89% by mass, preferably 79 to 89% by mass, of 2-octyl acrylate and preferably 5 to 15% by mass of vinyl monomer (a3).

[0038] In one embodiment, the vinyl monomer (a3) ​​is vinyl acetate.

[0039] <Polyalkylene glycol chain-containing mono(meth)acrylate (a4)> A (meth)acrylic polymer (A) according to one embodiment further comprises a polyalkylene glycol chain-containing mono(meth)acrylate (a4) as a constituent unit, in addition to an alkyl group-containing unsaturated monomer (a1) and a monomer having a functional group (a2). Here, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) having at least one hydroxyl group does not belong to the monomer having a functional group (a2).

[0040] A polyalkylene glycol chain-containing mono(meth)acrylate (a4) is any compound in which one of the multiple hydroxyl groups of the polyalkylene glycol is esterified as a (meth)acrylate. Since the acryloyl group of the polyalkylene glycol chain-containing mono(meth)acrylate (a4) is a polymerizable group, it can copolymerize with the polymerizable monomer of the (meth)acrylic polymer (A) described above. The other hydroxyl groups may remain as hydroxyl groups, or they may be alkyl ethers such as methyl ether or ethyl ether, or saturated carboxylic acid esters such as acetate esters. Note that a polyalkylene glycol chain-containing mono(meth)acrylate (a4) in which the other hydroxyl groups remain as hydroxyl groups, i.e., a polyalkylene glycol chain-containing mono(meth)acrylate (a4) having a hydroxyl group, does not belong to the monomer (a2) having a functional group.

[0041] In the polyalkylene glycol chain-containing mono(meth)acrylate (a4), the alkylene groups of the polyalkylene glycol include, but are not limited to, ethylene groups, propylene groups, and butylene groups. The polyalkylene glycol may be a polyalkylene glycol having two or more types of alkylene groups in one molecule, such as polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, and polypropylene glycol-polybutylene glycol. Preferably, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) is at least one compound in which the average number of repeating alkylene oxides constituting the polyalkylene oxide is 4 to 14.

[0042] The polyalkylene glycol chain-containing mono(meth)(meth)acrylate (a4) is preferably at least one selected from, for example, polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.

[0043] More specific examples of polyalkylene glycol chain-containing mono(meth)acrylates (a4) include polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polybutylene glycol mono(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, methoxypolybutylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, ethoxypolypropylene glycol (meth)acrylate, and ethoxypolybutylene glycol (meth)acrylate. These may be used individually or in combination of two or more. Preferably, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) is methoxypolyethylene glycol methacrylate.

[0044] When the acrylic polymer (A) further contains methoxypolyethylene glycol methacrylate as a polyalkylene glycol chain-containing mono(meth)acrylate (a4), the tackiness balance of the adhesive layer is further improved.

[0045] In one embodiment, the (meth)acrylic polymer (A) further contains polyalkylene glycol chain-containing mono(meth)acrylate (a4) as a constituent unit, and contains 70.0 to 89.5% by mass, preferably 76.5 to 89.5% by mass, of 100% by mass of the total monomers constituting the (meth)acrylic polymer (A), and preferably contains 5 to 15% by mass of polyalkylene glycol chain-containing mono(meth)acrylate (a4). Note that the polyalkylene glycol chain-containing mono(meth)acrylate (a4) having at least one hydroxyl group does not belong to the monomer (a2) having a functional group.

[0046] In one embodiment, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) is methoxypolyethylene glycol methacrylate.

[0047] <Supplement to the embodiment> In one embodiment, the (meth)acrylic polymer (A) further comprises, in addition to an alkyl group-containing unsaturated monomer (a1) and a monomer having a functional group (a2), butyl acrylate, a vinyl monomer (a3), and a polyalkylene glycol chain-containing mono(meth)acrylate (a4) as constituent units. In other words, when the (meth)acrylic polymer (A) is composed of the following compositions 1 to 4, an effect is obtained in which the tackiness balance of the adhesive layer is improved.

[0048] Composition 1 is a composition in which the (meth)acrylic polymer (A) comprises an alkyl group-containing unsaturated monomer (a1) other than butyl acrylate, a monomer having a functional group (a2), and butyl acrylate. In one embodiment, the (meth)acrylic polymer (A) contains 30.0 to 80.0% by mass, preferably 30.0 to 74.0% by mass, of 2-octyl (meth)acrylate and 5 to 15% by mass, preferably 5 to 10% by mass, of butyl acrylate. In this case, the mass percentage of the remaining monomers constituting the (meth)acrylic polymer (A) may include the mass percentage of the alkyl group-containing unsaturated monomer (a1) other than 2-octyl (meth)acrylate and butyl acrylate, the mass percentage of the monomer having a functional group (a2), the mass percentage of the vinyl monomer (a3), and the mass percentage of the polyalkylene glycol chain-containing mono(meth)acrylate (a4). Furthermore, the types and content of the remaining monomers constituting the (meth)acrylic polymer (A) are not particularly limited, as long as composition 1 is satisfied.

[0049] Composition 2 is a composition in which the (meth)acrylic polymer (A) comprises an alkyl group-containing unsaturated monomer (a1), a monomer having a functional group (a2), and a vinyl monomer (a3). In one embodiment, the (meth)acrylic polymer (A) contains 30.0 to 80.0% by mass, preferably 30.0 to 74.0% by mass, of 2-octyl (meth)acrylate, and 5 to 15% by mass, preferably 5 to 10% by mass, of vinyl monomer (a3). In this case, the mass percentage of the remaining monomers constituting the (meth)acrylic polymer (A) may include mass percentage of alkyl group-containing unsaturated monomers (a1) other than 2-octyl (meth)acrylate, mass percentage of monomer having a functional group (a2), and polyalkylene glycol chain-containing mono(meth)acrylate (a4). The types and content of the remaining monomers constituting the (meth)acrylic polymer (A) are not particularly limited as long as composition 2 is satisfied.

[0050] Composition 3 is a composition in which the (meth)acrylic polymer (A) comprises an alkyl group-containing unsaturated monomer (a1), a monomer having a functional group (a2), and a polyalkylene glycol chain-containing mono(meth)acrylate (a4). In one embodiment, the (meth)acrylic polymer (A) contains 30.0 to 80.0% by mass, preferably 30.0 to 74.0% by mass, of 2-octyl (meth)acrylate, and 5 to 15% by mass, preferably 5 to 10% by mass, of polyalkylene glycol chain-containing mono(meth)acrylate (a4). In this case, the mass percentage of the remaining monomers constituting the (meth)acrylic polymer (A) includes the mass percentage of alkyl group-containing unsaturated monomers (a1) other than 2-octyl (meth)acrylate, the mass percentage of the monomer having a functional group (a2), and a vinyl monomer (a3). Furthermore, the types and content of the remaining monomers constituting the (meth)acrylic polymer (A) are not particularly limited, as long as composition 3 is satisfied.

[0051] Composition 4 is a composition in which the (meth)acrylic polymer (A) comprises an alkyl group-containing unsaturated monomer (a1), a monomer having a functional group (a2), a vinyl monomer (a3), and a polyalkylene glycol chain-containing mono(meth)acrylate (a4). In one embodiment, the (meth)acrylic polymer (A) contains 30.0 to 80.0% by mass, preferably 30.0 to 74.0% by mass, of 2-octyl (meth)acrylate, 5 to 15% by mass, preferably 5 to 10% by mass, of vinyl monomer (a3), and 5 to 15% by mass, preferably 5 to 10% by mass, of polyalkylene glycol chain-containing mono(meth)acrylate (a4). In this case, the mass % of the remaining monomers constituting the (meth)acrylic polymer (A) includes mass % of alkyl group-containing unsaturated monomers (a1) other than 2-octyl (meth)acrylate and mass % of monomers having a functional group (a2). More specifically, alkyl group-containing unsaturated monomers (a1) further include 2-ethylhexyl acrylate and butyl acrylate. The (meth)acrylic polymer (A) contains 5 to 50% by mass, preferably 5 to 44% by mass, of 2-ethylhexyl acrylate and 2 to 8% by mass, preferably 3 to 7% by mass, of butyl acrylate in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). In one embodiment, the (meth)acrylic polymer (A) contains 4 to 10% by mass, preferably 5 to 9% by mass, of monomers having a hydroxyl group as monomers having a functional group (a2). The monomers having a functional group (a2) preferably include 4-hydroxybutyl acrylate. Here, the type and content of the monomer (a2) having a functional group are not particularly limited. However, a mono(meth)acrylate (a4) containing a polyalkylene glycol chain having at least one hydroxyl group does not belong to the monomer (a2) having a functional group.

[0052] <Other monomers> The (meth)acrylic polymer (A) according to one embodiment may further contain other monomers as constituent units.

[0053] Other monomers include, for example, alkoxyalkyl esters of (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, and 2-phenoxyethyl (meth)acrylate; aralkyl esters of (meth)acrylates such as benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and naphthylmethyl (meth)acrylate; and aryl esters of (meth)acrylates such as phenyl (meth)acrylate, tolyl (meth)acrylate, and naphthyl (meth)acrylate. These may be used individually or in combination of two or more.

[0054] <Hardening agent (B)> A removable adhesive composition according to one embodiment contains a curing agent (B). The inclusion of the curing agent (B) in the removable adhesive composition increases the cohesive force of the removable adhesive composition, thereby improving its removable properties.

[0055] In one embodiment, the re-peelable adhesive composition contains 5.0 to 30.0% by mass of a curing agent (B) relative to 100% by mass of a (meth)acrylic polymer (A). When the content of the curing agent (B) is within the above predetermined range, a re-peelable adhesive composition with excellent low-staining properties and a good balance of adhesive strength can be realized. On the other hand, if the content of the curing agent (B) is less than 5.0% by mass, the low-staining properties decrease. Furthermore, if the content of the curing agent (B) exceeds 30.0% by mass, the adhesive strength during slow peeling decreases, resulting in a deterioration of the adhesive strength balance.

[0056] In one embodiment, the curing agent (B) is an isocyanate-based curing agent.

[0057] Examples of curing agents (B) include isocyanate-based curing agents, epoxy-based curing agents, metal chelate-based curing agents, and aziridine-based curing agents. These may be used individually or in combination of two or more. The (meth)acrylic polymer (A) is preferably crosslinked with at least one of the above curing agents. Curing agent (B) is preferably an isocyanate-based curing agent.

[0058] Examples of isocyanate-based curing agents include adducts of isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate, and polyol compounds such as trimethylolpropane, as well as their burettes and isocyanurates, and adducts of the above isocyanate compounds with any polyol such as polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol, which have three or more isocyanate groups in their molecules; or compounds such as allophanates thereof that have two isocyanate groups in their molecules.

[0059] Examples of epoxy curing agents include epoxy resins obtained from the reaction of bisphenol A and epichlorohydrin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, N,N-diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane.

[0060] Examples of metal chelating curing agents include coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or ethyl acetoethyl acetate.

[0061] Examples of aziridine-based curing agents include N,N'-(4,4'-methylenediphenyl)bis(aziridine-1-carboxamide), 1,1'-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, 1,1'-hexamethylenebis(iminocarbonyl)bisaziridine, trimethylolpropane-tris(2-aziridinylpropionate), and 2,4,6-tris(1-aziridinyl)-1,3,5-triazine.

[0062] <Curing retarder (C)> A removable adhesive composition according to one embodiment further comprises a curing retarder (C).

[0063] In one embodiment, the re-peelable adhesive composition contains 4.1 to 14.1% by mass, preferably 6.1 to 12.1% by mass, and more preferably 8.1 to 10.1% by mass, of a curing retarder (C) based on 100% by mass of a (meth)acrylic polymer (A).

[0064] The repositionable adhesive composition preferably further contains a ketoenol tautomer compound as a curing retarder (C). The ketoenol tautomer compound blocks the isocyanate groups of the curing agent (B) when a polyisocyanate compound such as a trifunctional or higher isocyanate compound is used as the curing agent (B). This suppresses excessive viscosity increase and gelation of the repositionable adhesive composition after the addition of the curing agent (B), thereby extending the pot life of the repositionable adhesive composition.

[0065] Examples of ketoenol tautomer compounds include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, as well as β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. These may be used individually or in combination of two or more. The ketoenol tautomer compound is preferably acetylacetone.

[0066] <Antistatic agent (D)> A removable adhesive composition according to one embodiment further comprises an antistatic agent (D). The removable adhesive composition may contain an antistatic agent (D) in order to impart antistatic properties to the adhesive layer. This allows the surface protective film of the present invention to be suitably used as a surface protective film having antistatic properties.

[0067] The surface resistivity of the adhesive layer according to one embodiment is 1.0 × 10 +12 It is less than or equal to Ω / □. Surface resistivity is an indicator of how easily electricity flows per unit area of ​​a material. A high surface resistivity indicates poor performance in dissipating static electricity generated by charging when the adhesive layer is peeled from the adherend. On the other hand, a low surface resistivity indicates high performance in dissipating static electricity generated by charging when the adhesive layer is peeled from the adherend. By making the surface resistivity of the adhesive layer as low as possible, the peeling charge generated when the adhesive layer is peeled from the adherend is reduced, thus preventing damage and failure of the adherend (e.g., optical components). Note that the antistatic properties of the adhesive layer are not a required property and may be any property depending on the type of adherend.

[0068] In one embodiment, the re-peelable adhesive composition contains 1.0 to 6.0% by mass, preferably 1.5 to 5.5% by mass, and more preferably 2.0 to 5.0% by mass, of an antistatic agent (D) based on 100% by mass of a (meth)acrylic polymer (A).

[0069] Examples of antistatic agents (D) include cations such as pyridinium cation, imidazolium cation, ammonium cation, alkali metal cation, and hexafluoride phosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 -Examples include ionic compounds having anions such as bis(fluorosulfonyl)imide salt (FSI), bis(trifluoromethanesulfonyl)imide salt (TFSI), tetrabutylammonium bis(trifluoromethanesulfonyl)imide salt, and trifluoromethanesulfonate salt (TF). These may be used alone or in combination of two or more. The antistatic agent (D) preferably contains lithium bis(trifluoromethanesulfonyl)imide (TFSI) or tetrabutylammonium bis(trifluoromethanesulfonyl)imide.

[0070] <Other additives> The repositionable adhesive composition of the present invention may contain various resins and additives, provided that they do not affect the required performance specified in the present invention. Examples of additives include tackifiers, antioxidants, silane coupling agents, heat or light stabilizers, UV absorbers, leveling agents, defoamers, antibacterial agents, humectants, pigments, dyes, and fragrances. These may be used individually or in combination of two or more.

[0071] <Physical properties> In one embodiment, the adhesive strength of the adhesive layer made of a re-peelable adhesive composition during low-speed peeling (when peeled at a tensile speed of 0.3 m / min) is 10.0 to 19.9 gf / 25 mm. The adhesive strength during low-speed peeling is measured using PET as the adherend. More specifically, the adhesive strength of the adhesive layer during low-speed peeling is 10.0 to 19.0 gf / 25 mm.

[0072] In one embodiment, the adhesive strength of the adhesive layer made of a re-peelable adhesive composition during high-speed peeling (when peeled at a tensile speed of 30 m / min) is less than 150 gf / 25 mm. The adhesive strength during high-speed peeling is measured using PET as the adherend. More specifically, the adhesive strength of the adhesive layer during high-speed peeling is 8 to 137 gf / 25 mm.

[0073] In one embodiment, the adhesive strength balance of the adhesive layer made of a re-peelable adhesive composition is less than 10.0 and is calculated by the following formula: Adhesive strength balance = Adhesive strength at a tensile speed of 30 m / min / Adhesive strength at a tensile speed of 0.3 m / min ... (formula). Here, adhesive strength balance refers to a parameter that quantitatively represents the relationship between two types of adhesive strength necessary for the user to comfortably use the surface protective film. The two types of adhesive strength include the adhesive strength at low speed peeling and the adhesive strength at high speed peeling. The adhesive strength at low speed peeling refers to the adhesive strength required to prevent the surface protective film from peeling off the substrate until it is no longer needed. On the other hand, the adhesive strength at high speed peeling refers to the adhesive strength required to quickly and without leaving any residue on the substrate (e.g., a large optical component). Thus, adhesive strength balance is a parameter that takes into account the adhesive strength of the surface protective film from before use to after use. The inventors of the present invention have found an adhesive strength balance value (less than 10.0) that provides high user satisfaction through trial and error. By having an adhesive layer with the adhesive strength balance defined in this invention, a surface protection film with high user satisfaction can be realized. A surface protection film with high user satisfaction is one that is difficult to peel off before use and can be cleanly peeled off after use (after it has been used up).

[0074] In one embodiment, the adhesive layer, which is made of a removable adhesive composition, has low contamination properties. Here, low contamination properties mean that when a surface protective film is attached to an object, and an object (for example, a pencil) is traced over the surface protective film through the adhesive layer, the adhesive does not detach and contaminate the object even when the film is peeled off.

[0075] In one embodiment, the surface resistivity of the adhesive layer made of a re-peelable adhesive composition is 1.0 × 10⁻⁶ +12 It is less than or equal to Ω / □.

[0076] <Meth)acrylic polymer (A) manufacturing method> (Meth)acrylic polymer (A) can be produced by known methods, but it is preferable to produce it by solution polymerization. Specifically, it is common to heat a solvent, monomer, polymerization initiator, etc., in an inert gas atmosphere such as nitrogen gas to a reaction temperature of about 50 to 90°C and carry out the polymerization reaction for 4 to 12 hours. As solvents used in solution polymerization, it is preferable to use ester solvents such as methyl acetate, ethyl acetate, and butyl acetate, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and hydrocarbon solvents such as toluene, xylene, hexane, and heptane. These may be used individually or in combination of two or more.

[0077] Any polymerization initiator that has the ability to initiate radical polymerization is acceptable, and conventionally known polymerization initiators can be used.

[0078] Examples of polymerization initiators include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; oil-soluble azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyric acid)dimethyl, and 1,1'-azobis(cyclohexane-1-carbonitride); and 2,2'-azobis[2-methyl-N Examples include water-soluble azo compounds such as [2-hydroxyethyl]propionamide, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] and its salts, 2,2'-azobis(2-methylpropionamidine) and its salts, 4,4'-azobis(4-cyanovaleric acid) and its salts; and organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyisobutyrate. These may be used individually or in combination of two or more.

[0079] <Surface protective film> The surface protection film has an adhesive layer on a substrate which is a cured product of the re-peelable adhesive composition of the present invention. The surface protection film can be manufactured, for example, by coating the substrate with the re-peelable adhesive composition and drying it. The adhesive layer only needs to be provided on at least one surface of the substrate. A release sheet may also be provided on the adhesive surface of the adhesive layer. The re-peelable adhesive composition used in the surface protection film is as described above, so a detailed explanation is omitted.

[0080] The adhesive layer is a slightly tacky layer for attaching the surface protection film to optical components such as polarizing plates and phase difference plates. The adhesive layer may also have antistatic properties if the adherend is sensitive to static electricity. The reason for making the adhesive layer slightly tacky is to make it easy to peel off the surface protection film from the optical component after use, without leaving any adhesive residue. When the surface protection film is attached to the optical component, it is preferable that the adhesive layer has sufficient transparency. The size (area) of the optical component to which the surface protection film is attached is not particularly limited; it may be small or large. Furthermore, the shape of the optical component is not limited to a flat surface; it may also have a curved surface or one or more irregularities.

[0081] <Optical component with adhesive layer> An optical member with an adhesive layer according to one embodiment is obtained by laminating an adhesive layer, which is formed by curing the re-peelable adhesive composition of the present invention, onto at least one surface of the optical member. Examples of optical members include polarizing films, phase difference films, anti-reflective films, anti-glare films, ultraviolet absorbing films, infrared absorbing films, optical compensation films, and brightness-enhancing films. Examples of display devices incorporating optical members include liquid crystal displays, organic EL displays, and touch panels.

[0082] Examples of liquid media used when applying the repositionable adhesive composition include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as methyl acetate, ethyl acetate, and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane; and other hydrocarbon solvents. These may be used individually or in combination of two or more. The viscosity can be adjusted by adding any liquid media to the repositionable adhesive composition. The viscosity can also be reduced by heating the repositionable adhesive composition.

[0083] Examples of substrates include cellophane, plastic sheets, rubber, foam, fabric, rubber cloth, resin-impregnated cloth, glass plates, and wood. The substrate may be in the form of a plate or a film. Furthermore, the substrate may be composed of a single material or a multilayer substrate formed by laminating multiple substrates of different materials. In addition, a substrate with a peeled surface may be used. When the surface protective film is attached to an optical component, it is preferable that the substrate has sufficient transparency.

[0084] Examples of plastic sheets include polyvinyl alcohol film, triacetylcellulose film, polyolefin resin films such as polypropylene, polyethylene, polycycloolefin, and ethylene-vinyl acetate copolymer; polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; vinyl resin films such as polyvinyl chloride; polycarbonate resin films; polynorbornene resin films; polyarylate resin films; acrylic resin films; polyphenylene sulfide resin films; polystyrene resin films; polyamide resin films; polyimide resin films; and epoxy resin films. These may be used individually or in combination of two or more types.

[0085] As a release sheet (separator) to protect the adhesive surface of the adhesive layer, a resin film such as a polyester film can be used. The surface of the release sheet that comes into contact with the adhesive surface of the adhesive layer may be treated with a release agent such as a silicone-based or fluorine-based release agent.

[0086] Methods for applying the repositionable adhesive composition include, for example, a Meyer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. Methods for drying include, for example, hot air drying, infrared drying, and reduced pressure drying. Drying conditions can be appropriately changed depending on the curing form, film thickness, and type of solvent of the repositionable adhesive composition, but for example, hot air drying at 60 to 130°C may be used.

[0087] In one embodiment, the thickness of the adhesive layer is 1 to 200 μm, preferably 3 to 100 μm.

[0088] <(Meth)acrylic polymer (A) and repositionable adhesive composition manufacturing> The definitions of the abbreviations in Tables 1 to 8 are as follows: Definition of an abbreviation 2OA 2-Octylacrylate 2EHA 2-Ethylhexylacrylate BA Butyl Acrylate VAc vinyl acetate MPEGMA Methoxypolyethylene Glycol Methacrylate 4HBA 4-hydroxybutyl acrylate HEA 2-Hydroxyethyl Acrylate AAc Acrylic acid mAM methacrylamide Hardener: Isocyanate-based hardener manufactured by Saiden Chemical Co., Ltd. Li-TFSI Lithium bis(trifluoromethanesulfonyl)imide FC-4400 (manufactured by 3M): Tetrabutylammonium bis(trifluoromethanesulfonyl)imide (A) Component (meth)acrylic polymer (A) (a1) Component: Alkyl-containing unsaturated monomer having an alkyl group with 1 to 18 carbon atoms (a1) (a2) Component: Monomer having a functional group (a2) (a3) Ingredient: Vinyl monomer (a3) (a4) Ingredients: Polyalkylene glycol chain-containing mono(meth)acrylate (a4) Adhesion strength (gf / 25mm): 0.3m / min. Adhesion strength during low-speed peeling; see Test 1 below. Adhesion strength (gf / 25mm): 30m / min. Adhesion strength during high-speed peeling; see Test 1 below. Adhesion balance: See Test 2 below. Low contamination properties: See Test 3 below. Surface resistivity (Ω / □): See Test 4 below.

[0089] Table 1 shows the raw material formulations for (meth)acrylic polymer (A) in Production Examples 1-7. Table 2 shows the raw material formulations for (meth)acrylic polymer (A) in Production Examples 8-14. Table 3 shows the raw material formulations for (meth)acrylic polymer (A) in Production Examples 15-21. Table 4 shows the raw material formulations for (meth)acrylic polymer (A) in Production Examples 22-28. The unit of the numerical values ​​for the raw material formulations of component (A) in Tables 1-4 is "parts".

[0090] Table 5 shows the raw material formulations and test results of the repositionable adhesive compositions of Examples 1 to 8. Table 6 shows the raw material formulations and test results of the repositionable adhesive compositions of Examples 9 to 16. Table 7 shows the raw material formulations and test results of the repositionable adhesive compositions of Examples 17 to 24. Table 8 shows the raw material formulations and test results of the repositionable adhesive compositions of Comparative Examples 1 to 9. The unit of the numerical values ​​for the raw material formulations of the repositionable adhesive compositions in Tables 5 to 8 is "parts".

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] [Table 5]

[0096] [Table 6]

[0097] [Table 7]

[0098] [Table 8]

[0099] <Manufacturing Example 1: Method for Manufacturing (Meth)acrylic Polymer (A)> The method for producing the (meth)acrylic polymer (A) in Production Example 1 will be described with reference to Table 1. In a reaction apparatus equipped with a stirrer, thermometer, sequential dropper, and reflux condenser, 37 parts of ethyl acetate, 10 parts of acetone, and 0.1 parts of polymerization initiator (azobisisobutyronitrile) were charged. Meanwhile, in a separate container, a monomer-solvent mixture consisting of 95 parts of 2-octyl acrylate, 5 parts of 4-hydroxybutyl acrylate, and 10 parts of ethyl acetate was prepared. While stirring the reaction apparatus, the temperature was raised to 68°C, and the monomer-solvent mixture measured in the separate container was added dropwise over 90 minutes, and the polymerization reaction was carried out at 80°C for 7 hours. After the reaction was complete, it was cooled, diluted with ethyl acetate, and a (meth)acrylic polymer solution with a solid content of 44.0% by mass was obtained.

[0100] <Manufacturing Examples 2-28: Method for Manufacturing (Meth)acrylic Polymer (A)> Since the (meth)acrylic polymer (A) in Production Examples 2-28 was produced based on the raw material formulations in Tables 1 and 2 and the same manufacturing method as in Production Example 1, a detailed explanation is omitted.

[0101] <Example 1: Method for producing a removable adhesive composition> The method for producing the repositionable adhesive composition of Example 1 will be described with reference to Table 5. To 100 parts of the solid content of the (meth)acrylic polymer solution of Production Example 1, 6.1 parts of isocyanate-based curing agent (manufactured by Saiden Chemical Co., Ltd.) as curing agent (B) and 9.1 parts of acetylacetone as curing retarder (C) were added and thoroughly mixed to obtain the repositionable adhesive composition.

[0102] <Example 1: Method for manufacturing a surface protective film> The repositionable adhesive composition of Example 1 was directly coated onto a 38 μm thick polyethylene terephthalate (PET) film, which served as the substrate. The solvent was then removed by drying at 90°C, forming a 15 μm thick adhesive layer. A silicone resin-coated polyester film (release sheet) was then applied to the surface of this adhesive layer to create a surface protection film. Furthermore, the prepared surface protection film was cured at 23°C for 3 days to obtain samples for each test.

[0103] <Examples 2-24: Method for producing a removable adhesive composition> Since the re-peelable adhesive compositions of Examples 2 to 24 were manufactured based on the raw material formulations in Tables 5, 6, and 7 and the same manufacturing method as in Example 1, a detailed explanation is omitted. In Examples 15, 16, 17, and 19, 2.2 parts of lithium bis(trifluoromethanesulfonyl)imide were added as the antistatic agent (D). In Examples 18, 23, and 24, 4.5 parts of tetrabutylammonium bis(trifluoromethanesulfonyl)imide were added as the antistatic agent (D).

[0104] <Examples 2-24: Method for manufacturing surface protective film> Since the surface protective films of Examples 2 to 24 were manufactured based on the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0105] <Comparative Examples 1-9: Methods for Producing Removable Adhesive Compositions> Since the re-peelable adhesive compositions of Comparative Examples 1 to 9 were manufactured based on the raw material formulations shown in Table 8 and the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0106] <Comparative Examples 1-9: Methods for Manufacturing Surface Protective Films> Since the surface protective films of Comparative Examples 1 to 9 were manufactured based on the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0107] <Testing Method> The following tests 1 to 4 were performed using the surface protective films of Examples 1 to 24 and Comparative Examples 1 to 9.

[0108] (Test 1: Measurement of adhesive strength) Test specimens were prepared by cutting the sample (surface protective film) into pieces 25 mm wide and 70 mm long. The release sheet was peeled off the test specimen and attached to the surface of the PET substrate, and then pressed down with a 2 kg roll for one pass. After that, it was left in an atmosphere of 23°C and 50% humidity for 24 hours. After standing, the adhesive strength was measured using a tensile testing machine under the conditions of a tensile speed of 0.3 m / min or 30 m / min and a peel angle of 180°. [Evaluation Criteria] • Adhesion force (gf / 25mm) at low-speed peeling, tensile speed 0.3m / min 〇···10.0~19.9gf / 25mm × Less than 10.0 gf / 25 mm, or 20.0 gf / 25 mm or more. • Adhesion force (gf / 25mm) during high-speed peeling, tensile speed 30m / min 〇···Less than 150gf / 25mm ×...150gf / 25mm or more

[0109] (Test 2: Calculation of adhesive balance) The adhesive strength balance was calculated based on the measurement results of the adhesive strength during low-speed and high-speed peeling, as measured in Test 1, and the following formula. Adhesion balance = Adhesion at a tensile speed of 30 m / min / Adhesion at a tensile speed of 0.3 m / min [Evaluation Criteria] ○···Less than 10.0 ×···10.0 or higher, or less than 10.0 (however, if the result of either the adhesive strength during low-speed peeling or the adhesive strength during high-speed peeling in Test 1 is "×")

[0110] (Test 3: Confirmation of low contamination) The sample (surface protective film) was cut into 15mm x 40mm lengths to prepare test pieces. The release sheet was peeled off the adhesive sheet of the test piece and attached to the surface of a polarizing plate. The plate was then pressed down with a 2kg roll for one pass. After that, it was left in an atmosphere of 23°C and 50% humidity for 24 hours. After standing, the surface protective film was traced with a 3H pencil using an automatic pencil scratch test machine (manufactured by Imoto Seisakusho) at a scratching speed of 30mm / min and a load of 0.7kg. [Evaluation Criteria] ○...The polarizing plate is free from contamination. ×...A clear mark remains on the polarizing plate.

[0111] (Test 4: Measurement of surface resistivity) The release sheet was peeled off the test specimen (surface protective film) to expose the adhesive layer, and the surface resistivity of the adhesive layer was measured using a resistivity meter.

[0112] <Test Results> Referring to Tables 5-8 above, the test results for Examples 1-24 and Comparative Examples 1-9 will be explained.

[0113] Examples 1-24 demonstrated excellent adhesion balance and low staining properties, as shown by the results of Tests 1-4. On the other hand, Comparative Examples 1-9 did not demonstrate excellent adhesion balance or low staining properties. The reasons why Comparative Examples 1-9 did not meet the required performance are explained below.

[0114] Comparative Example 1, containing 2-ethylhexyl acrylate with a low Tg, showed a slight improvement in adhesive balance, but its adhesive strength during slow peeling remained low. Furthermore, the film became brittle, reducing its stain resistance. It should be noted that Comparative Example 1 differs from Patent Document 1, described at the beginning of this specification, in that it contains a monomer with a hydroxyl group (4HBA) as the monomer with a functional group (a2).

[0115] Comparative Example 2, containing butyl acrylate with a high Tg, resulted in a harder film and improved stain resistance. However, the increased adhesive strength during high-speed peeling led to a deterioration in the adhesive strength balance. Comparative Example 2 corresponds to the prior art described at the beginning of this specification.

[0116] Comparative Example 3 contained a monomer (a2) having a functional group in an amount less than the lower limit specified in the present invention, resulting in a low crosslinking density and a softer film. Consequently, the adhesive strength during high-speed peeling increased, and the adhesive strength balance deteriorated.

[0117] Comparative Example 4 contains a monomer (a2) having a functional group in an amount exceeding the upper limit specified in the present invention. As a result, the polarity of the adhesive layer increases, and the intermolecular forces with the adherend surface become stronger. Consequently, the adhesive force during low-speed peeling increases, and the adhesive force balance deteriorates.

[0118] Comparative Example 5 contained 2-octyl acrylate in an amount below the lower limit specified in the present invention, resulting in a decrease in the Tg of the (meth)acrylic polymer (A). Consequently, the film became brittle and its stain resistance decreased.

[0119] Comparative Example 6, containing a monomer with a carboxyl group (acrylic acid), had increased polarity in the adhesive layer, resulting in stronger intermolecular forces with the adherend surface. This increased adhesive strength during both low-speed and high-speed peeling, leading to a deterioration in the adhesive strength balance. Furthermore, the film became brittle, reducing its stain resistance.

[0120] Comparative Example 7 contains a monomer having a hydroxyl group in an amount less than the lower limit specified in the present invention, and also contains a monomer having a carboxyl group (acrylic acid). As a result, the polarity of the adhesive layer increased, and the intermolecular forces with the adherend surface became stronger. Consequently, the adhesive force increased during low-speed and high-speed peeling, and the adhesive force balance deteriorated.

[0121] Comparative Example 8 contained a curing agent (B) in an amount less than the lower limit specified in the present invention, resulting in lower cohesive force and higher adhesion during slow peeling. Consequently, the adhesion balance deteriorated. In addition, the film became brittle and its stain resistance decreased.

[0122] Comparative Example 9 contained a curing agent (B) in an amount exceeding the upper limit specified in the present invention, resulting in increased cohesive force and decreased adhesive strength during low-speed peeling. Consequently, the adhesive strength balance deteriorated.

[0123] As described above, the re-peelable adhesive composition of the present invention has remarkable effects such as low contamination and excellent balance of adhesive strength.

[0124] Furthermore, since the present invention can provide an environmentally friendly repositionable adhesive composition using biomass-derived raw materials with low reliance on fossil resources, it can contribute to Goal 12 of the United Nations-led Sustainable Development Goals (SDGs), "Responsible Consumption and Production."

[0125] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. an alkyl group-containing unsaturated monomer (a1) having an alkyl group with 1 to 18 carbon atoms, A monomer having a functional group (a2), and a (meth)acrylic polymer (A) containing as a constituent unit, The hardening agent (B) is included, The alkyl group-containing unsaturated monomer (a1) contains at least 2-octyl (meth)acrylate, The (meth)acrylic polymer (A) contains 30% by mass or more of the 2-octyl (meth)acrylate and 3.5 to 15% by mass of the monomer (a2) having the functional group, in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). The monomer (a2) having the functional group does not include a monomer having a carboxyl group. The curing agent (B) is contained in an amount of 5.0 to 30.0% by mass relative to 100% by mass of the (meth)acrylic polymer (A). Removable adhesive composition.

2. The alkyl group-containing unsaturated monomer (a1) is 2-octyl (meth)acrylate, The (meth)acrylic polymer (A) contains 85 to 96.5% by mass of the 2-octyl (meth)acrylate in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). The re-peelable adhesive composition according to claim 1.

3. The alkyl group-containing unsaturated monomer (a1) further comprises 2-ethylhexyl acrylate. The re-peelable adhesive composition according to claim 1.

4. The alkyl group-containing unsaturated monomer (a1) further comprises 2-ethylhexyl acrylate, The (meth)acrylic polymer (A) contains 30 to 90% by mass of 2-octyl (meth)acrylate and 5 to 65% by mass of 2-ethylhexyl acrylate in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A). The re-peelable adhesive composition according to claim 1.

5. The alkyl group-containing unsaturated monomer (a1) further comprises butyl acrylate. The re-peelable adhesive composition according to claim 1.

6. The alkyl group-containing unsaturated monomer (a1) further comprises butyl acrylate, The (meth)acrylic polymer (A) contains 40 to 90% by mass of the 2-octyl (meth)acrylate and 5 to 47% by mass of the butyl acrylate in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A), or The above 2-octyl (meth)acrylate is contained in an amount of 30.0 to 80.0% by mass, and the above butyl acrylate is contained in an amount of 5 to 15% by mass. The re-peelable adhesive composition according to claim 1.

7. The monomer (a2) having the functional group is a monomer having a hydroxyl group. The re-peelable adhesive composition according to claim 1.

8. The monomer (a2) having the functional group includes a monomer having a hydroxyl group and a monomer having an amide group. The re-peelable adhesive composition according to claim 1.

9. The monomer (a2) having the functional group includes a monomer having a hydroxyl group and a monomer having an amide group. The (meth)acrylic polymer (A) contains, in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A), 2.5 to 14.9% by mass of monomers having a hydroxyl group and 0.1 to 1% by mass of monomers having an amide group. The re-peelable adhesive composition according to claim 1.

10. The (meth)acrylic polymer (A) further comprises a vinyl monomer (a3) ​​as a constituent unit. The re-peelable adhesive composition according to claim 1.

11. The (meth)acrylic polymer (A) further comprises vinyl monomer (a3) ​​as a constituent unit, The (meth)acrylic polymer (A) contains 70 to 89% by mass of the 2-octyl (meth)acrylate and 5 to 15% by mass of the vinyl monomer (a3) ​​in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A), or The above 2-octyl (meth)acrylate is contained in an amount of 30.0 to 80.0% by mass, and the vinyl monomer (a3) ​​is contained in an amount of 5 to 15% by mass. The re-peelable adhesive composition according to claim 1.

12. The vinyl monomer (a3) ​​is vinyl acetate. The re-peelable adhesive composition according to claim 11.

13. The (meth)acrylic polymer (A) further comprises a polyalkylene glycol chain-containing mono(meth)acrylate (a4) as a constituent unit, Here, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) having at least one hydroxyl group does not belong to the monomer (a2) having the functional group. The re-peelable adhesive composition according to claim 1.

14. The (meth)acrylic polymer (A) further comprises a polyalkylene glycol chain-containing mono(meth)acrylate (a4) as a constituent unit, The (meth)acrylic polymer (A) contains 70.0 to 89.5% by mass of the 2-octyl (meth)acrylate and 5 to 15% by mass of polyalkylene glycol chain-containing mono(meth)acrylate (a4) in 100% by mass of the total monomers constituting the (meth)acrylic polymer (A), or The above 2-octyl (meth)acrylate is contained in an amount of 30.0 to 80.0% by mass, and the polyalkylene glycol chain-containing mono(meth)acrylate (a4) is contained in an amount of 5 to 15% by mass. Here, the polyalkylene glycol chain-containing mono(meth)acrylate (a4) having at least one hydroxyl group does not belong to the monomer (a2) having the functional group. The re-peelable adhesive composition according to claim 1.

15. The polyalkylene glycol chain-containing mono(meth)acrylate (a4) is methoxypolyethylene glycol methacrylate. The re-peelable adhesive composition according to claim 14.

16. The curing agent (B) is an isocyanate-based curing agent. The re-peelable adhesive composition according to claim 1.

17. Further comprising a curing retarder (C), The re-peelable adhesive composition according to claim 16.

18. Further containing an antistatic agent (D), The re-peelable adhesive composition according to claim 1.

19. The adhesive strength balance of the adhesive layer made of the aforementioned re-peelable adhesive composition is less than 10.

0. The aforementioned adhesive strength balance is calculated using the following formula: Adhesion balance = Adhesion at a tensile speed of 30 m / min / Adhesion at a tensile speed of 0.3 m / min Here, the adhesive strength at a tensile speed of 30 m / min and the adhesive strength at a tensile speed of 0.3 m / min are measured using PET as the adherend. The adhesive force at the aforementioned tensile speed of 30 m / min is less than 150 gf / 25 mm. The adhesive strength at a tensile speed of 0.3 m / min is 10.0 to 19.9 gf / 25 mm. The re-peelable adhesive composition according to claim 1.

20. Substrate and The substrate comprises an adhesive layer provided on at least one surface of the substrate, the adhesive layer being made of the re-peelable adhesive composition according to any one of claims 1 to 19. Surface protective film.

21. The adhesive strength balance of the adhesive layer is less than 10.

0. The aforementioned adhesive strength balance is calculated using the following formula: Adhesion balance = Adhesion at a tensile speed of 30 m / min / Adhesion at a tensile speed of 0.3 m / min Here, the adhesive strength at a tensile speed of 30 m / min and the adhesive strength at a tensile speed of 0.3 m / min are measured using PET as the adherend. The adhesive force at the aforementioned tensile speed of 30 m / min is less than 150 gf / 25 mm. The adhesive strength at a tensile speed of 0.3 m / min is 10.0 to 19.9 gf / 25 mm. The surface protective film according to claim 20.

22. Optical components and The optical member comprises an adhesive layer provided on at least one surface of the optical member, the adhesive layer being made of the re-peelable adhesive composition according to any one of claims 1 to 19, Optical component with adhesive layer.

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