Removable pressure-sensitive adhesive composition, surface protective film, and pressure-sensitive adhesive layer-carrying optical member

Abstract

An object of the present invention is to provide a removable pressure-sensitive adhesive composition which is excellent in wettability and reduces the pressure-sensitive adhesive force at the time of low-speed and high-speed peeling.SOLUTION: A (meth) acryl-based polymer (A) containing 85 to 98.5% by mass of an alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms and 1.5 to 15% by mass of a polymerizable monomer (a2) having a functional group, wherein the alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms contains at least n-octyl acrylate, and the (meth) acryl-based polymer (A) has an acid number of 7. 5mgKOH / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a removable pressure-sensitive adhesive composition, a surface protective film, and an optical member with a pressure-sensitive adhesive layer. [Background technology]

[0002] In the manufacturing process of optical components (e.g., polarizing plates) that constitute liquid crystal displays, surface protection films are attached to the optical components to temporarily protect their surfaces. Because the user peels the surface protection film off the optical component after use, the surface protection film has a mildly adhesive adhesive layer. Recently, as the size of liquid crystal displays has increased, the size of surface protection films for optical components has also increased. Generally, the larger the surface protection film, the more difficult it becomes to quickly peel it off the optical component. Therefore, surface protection films are required to have reduced adhesive strength during high-speed peeling. Furthermore, the adhesive layer is required to have good wettability, which allows it to sufficiently wet the surface of the substrate (i.e., the cut edge does not peel up when cut).

[0003] Therefore, Patent Documents 1 and 2 propose a pressure-sensitive adhesive composition containing 2-ethylhexyl acrylate and a copolymerizable vinyl monomer containing a functional group. Patent Documents 3 and 4 propose a pressure-sensitive adhesive containing n-octyl acrylate and acrylic acid. Patent Documents 5 and 6 propose a surface protection film having a pressure-sensitive adhesive layer formed by crosslinking a pressure-sensitive adhesive composition containing 2-ethylhexyl acrylate and n-octyl acrylate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 63-225677 [Patent Document 2] Japanese Patent Application Publication No. 2023-133557 [Patent Document 3] Patent No. 6607330 [Patent Document 4] Patent No. 7338444 [Patent Document 5] Japanese Patent Publication No. 2023-160818 [Patent Document 6] Japanese Patent Application Publication No. 2020-183460 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Documents 1 and 2, the crosslink density of the pressure-sensitive adhesive layer needs to be increased to reduce adhesive strength during high-speed peeling, but this results in reduced wettability. In Patent Documents 3 and 4, the acid value of the acrylic copolymer is high, which increases the polarity of the pressure-sensitive adhesive layer and results in strong intermolecular forces with the adherend surface, making it impossible to reduce adhesive strength during low-speed and high-speed peeling. In Patent Documents 5 and 6, the content of n-octyl acrylate is low, making it impossible to reduce adhesive strength during low-speed peeling. In addition, wettability deteriorates.

[0006] Therefore, an object of the present invention is to provide a removable pressure-sensitive adhesive composition that has excellent wettability and reduces adhesive strength during low-speed and high-speed peeling. [Means for solving the problem]

[0007] In order to achieve the object of the present invention, the removable pressure-sensitive adhesive composition of the present invention has the following constitution: Namely, it contains a (meth)acrylic polymer (A) composed of 85 to 98.5 mass % of an alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms and 1.5 to 15 mass % of a polymerizable monomer (a2) having a functional group, wherein the alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms contains at least n-octyl acrylate, and the acid value of the (meth)acrylic polymer (A) is 7.5 mg KOH / g or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a removable pressure-sensitive adhesive composition that has excellent wettability and reduces adhesive strength during low-speed and high-speed peeling. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes the embodiments in detail. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features among the multiple features described in the embodiments may be combined in any desired manner.

[0010] In this specification, the expression "A to B" representing a range of numerical values ​​is synonymous with "A or more" and "B or less," and includes both A and B.

[0011] As used herein, the term "(meth)acrylic" refers to both "acrylic" and "methacrylic." Additionally, the term "(meth)acrylate" refers to both "acrylate" and "methacrylate."

[0012] The monomer component that is the constituent unit of the (meth)acrylic polymer (A) can be one or more types of monomers having a polymerizable unsaturated bond (hereinafter, sometimes referred to as "polymerizable monomers"). The (meth)acrylic polymer (A) is preferably a copolymer of two or more types of polymerizable monomers.

[0013] <Removable Adhesive Composition> The removable pressure-sensitive adhesive composition according to one embodiment comprises at least a (meth)acrylic polymer (A). In this specification, removable property refers to properties including ease of removal and reduced adhesive residue when a surface protection film having a pressure-sensitive adhesive layer made of the removable pressure-sensitive adhesive composition is attached to various adherends and then peeled off after a certain period of time has elapsed.

[0014] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) according to one embodiment comprises 85 to 98.5 mass% of an alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms and 1.5 to 15 mass% of a polymerizable monomer (a2) having a functional group. The alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms contains at least n-octyl acrylate. The alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms may further contain, in addition to n-octyl acrylate, a monomer other than n-octyl acrylate. In this case, it is sufficient that the content of n-octyl acrylate is greater than the content of the monomer other than n-octyl acrylate. In other words, the type and content of the monomer other than n-octyl acrylate are not particularly limited as long as the above relationship is satisfied. The (meth)acrylic polymer (A) has an acid value of 7.5 mg KOH / g or less. The acid value is a calculated value determined from the amount of the polymerizable monomer having a carboxy group used in producing the (meth)acrylic polymer (A).

[0015] The (meth)acrylic polymer (A) according to one embodiment contains, as structural units, an alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms and 1.5 to 14.5 mass% of a polymerizable monomer (a2) having a functional group. Here, the alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms contains 20 to 85 mass% of n-octyl acrylate. The (meth)acrylic polymer (A) has an acid value of 7.5 mg KOH / g or less. The acid value is a calculated value obtained from the amount of the polymerizable monomer having a carboxy group used in producing the (meth)acrylic polymer (A).

[0016] Here, the acid value is a parameter indicating the amount of acidic functional groups called carboxy groups. More specifically, the acid value refers to the number of milligrams of potassium hydroxide required to neutralize the free fatty acids contained in 1 g of sample (unit: mg KOH / g). The acid value can be adjusted based on the amount of polymerizable monomer having a carboxy group, as described below. From the viewpoint of reducing adhesive strength during low-speed and high-speed peeling, the upper limit of the acid value of the (meth)acrylic polymer (A) is 7.5 mg KOH / g or less, 7.4 mg KOH / g or less, 7.3 mg KOH / g or less, 7.2 mg KOH / g or less, 7.1 mg KOH / g or less, 7.0 mg KOH / g or less, 6.9 mg KOH / g or less, 6.8 mg KOH / g or less, 6.7 mg KOH / g or less, 6.6 mg KOH / g or less, 6.5 mg KOH / g or less, 6.4 mg KOH / g or less, and preferably 6.3 mg KOH / g or less. In this specification, the lower limit of the acid value of the (meth)acrylic polymer (A) is defined as including 0 mg KOH / g. The lower limit of the acid value is 0 mg KOH / g or more, 0.1 mg KOH / g or more, 0.2 mg KOH / g or more, 0.3 mg KOH / g or more, 0.4 mg KOH / g or more, 0.5 mg KOH / g or more, 0.6 mg KOH / g or more, 0.7 mg KOH / g or more, 0.8 mg KOH / g or more, 0.9 mg KOH / g or more, 1.0 mg KOH / g or more, 1.5 mg KOH / g or more, 2.0 mg KOH / g, 2.5 mg KOH / g or more, or 3.0 mg KOH / g or more. The acid value range may be any combination of the above lower and upper limits. Note that if the acid value of the (meth)acrylic polymer (A) exceeds 7.5 mg KOH / g, the adhesive strength during low-speed and high-speed peeling increases.

[0017] <Alkyl-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms> Examples of the alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms 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, 1-methylheptyl(meth)acrylate, n-nonyl(meth)acrylate, Examples of suitable (meth)acrylic acid alkyl esters include those having a linear or branched alkyl group, such as n-octyl (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 those having an alicyclic hydrocarbon group, such as cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate. These may be used alone or in combination of two or more. The alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms includes at least n-octyl acrylate. The alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms may further contain 2-ethylhexyl acrylate.

[0018] The content of n-octyl acrylate according to one embodiment is preferably 85 to 98.5% by mass relative to 100% by mass of all polymerizable monomers. The upper limit of the content of n-octyl acrylate is 98.5% by mass or less, 98% by mass or less, 97.5% by mass or less, 97% by mass or less, 96.5% by mass or less, 96% by mass or less, 95.5% by mass or less, 95% by mass or less, 94.5% by mass or less, or 94.2% by mass or less. The lower limit of the content of n-octyl acrylate is 85% by mass or more, 86% by mass or more, 87% by mass or more, 88% by mass or more, 89% by mass or more, or 90% by mass or more. When the content of n-octyl acrylate is within the above range, adhesive strength during low-speed and high-speed peeling can be reduced. On the other hand, if the content of n-octyl acrylate exceeds 98.5% by mass or is less than 85% by mass, the adhesive strength during low-speed and high-speed peeling increases.

[0019] In one embodiment, when the (meth)acrylic polymer (A) contains a monomer other than n-octyl acrylate as a constituent unit as component (a1), the content of n-octyl acrylate is preferably 20 to 85% by mass relative to 100% by mass of all polymerizable monomers. The upper limit of the content of n-octyl acrylate is 85% by mass or less, 84% by mass or less, 83% by mass or less, 82% by mass or less, 81% by mass or less, or 80% by mass or less. The lower limit of the content of n-octyl acrylate is 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, or 50% by mass or more. The range of the content of n-octyl acrylate may be any combination of the above lower and upper limits. When the content of n-octyl acrylate is within the above specified range, adhesive strength during low-speed and high-speed peeling can be reduced, and good wettability can be obtained. On the other hand, if the content of n-octyl acrylate is less than 20% by mass, the adhesive strength during slow peeling increases and the wettability decreases.

[0020] When the (meth)acrylic polymer (A) contains n-octyl acrylate as a structural unit, the content of the monomer other than n-octyl acrylate according to one embodiment is preferably 0.5 to 78% by mass relative to 100% by mass of all polymerizable monomers. The upper limit of the content of the monomer other than n-octyl acrylate is 78% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 59% by mass or less, or 58.5% by mass or less. The lower limit of the content of monomers other than n-octyl acrylate is 0.5% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 38.5% by mass or more, 40% by mass or more, 45% by mass or more, 48.5% by mass or more, 50% by mass or more, 55% by mass or more, or 58.5% by mass or more. The range of the content of monomers other than n-octyl acrylate may be any combination of the above lower and upper limits.

[0021] <Polymerizable Monomer (a2) Having a Functional Group> The polymerizable monomer (a2) having a functional group includes at least one of a polymerizable monomer having a carboxy group, a polymerizable monomer having a hydroxy group, and a polymerizable monomer having an amide group. The polymerizable monomer (a2) having a functional group is a radically polymerizable monomer having a functional group that can react with the curing agent (B) described below. A crosslinking reaction between the functional group and the curing agent (B) forms a polymer network, which can improve the cohesive strength and removability of the removable pressure-sensitive adhesive composition. From the viewpoint of improving the removability of the removable pressure-sensitive adhesive composition, the polymerizable monomer (a2) having a functional group is preferably a polymerizable monomer having a hydroxy group.

[0022] The content of the polymerizable monomer (a2) having a functional group according to one embodiment is preferably 1.5 to 15% by mass or 1.5 to 14.5% by mass, based on 100% by mass of all polymerizable monomers. The upper limit of the content of the polymerizable monomer (a2) having a functional group is 15% by mass or less, 14.9% by mass or less, 14.8% by mass or less, 14.7% by mass or less, 14.6% by mass or less, or 14.5% by mass or less. The lower limit of the content of the polymerizable monomer (a2) having a functional group is 1.5% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, or 5.8% by mass or more. The content of the polymerizable monomer (a2) having a functional group may be within any combination of the above-mentioned lower and upper limits. When the content of the polymerizable monomer (a2) having a functional group is within the above-mentioned range, the adhesive strength during low-speed and high-speed peeling can be reduced. On the other hand, if the content of the polymerizable monomer (a2) having a functional group is less than 1.5% by mass or more than 15% by mass, the adhesive strength during low-speed and high-speed peeling increases.

[0023] Examples of polymerizable monomers having a carboxy group include (meth)acrylic acid esters having a carboxy group, such as 2-carboxyethyl (meth)acrylate; and unsaturated carboxylic acids, such as (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, and mesaconic acid. These may be used alone or in combination of two or more. The polymerizable monomer having a carboxy group preferably includes acrylic acid.

[0024] In one embodiment, the content of the polymerizable monomer having a carboxy group is 0.1 to 0.8% by mass, preferably 0.2 to 0.8% by mass, based on 100% by mass of all polymerizable monomers. The upper limit of the content of the polymerizable monomer having a carboxy group is 0.8% by mass or less, 0.75% by mass or less, 0.7% by mass or less, 0.65% by mass or less, or 0.6% by mass or less. The lower limit of the content of the polymerizable monomer having a carboxy group is 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more. The content of the polymerizable monomer having a carboxy group may be within any combination of the above-mentioned lower and upper limits. When the content of the polymerizable monomer having a carboxy group is within the above-mentioned range, the acid value of the (meth)acrylic polymer (A) can be adjusted to a predetermined acid value, thereby reducing adhesive strength during low-speed and high-speed peeling. If the content of the polymerizable monomer having a carboxy group exceeds 0.8% by mass, the adhesive strength increases during low-speed and high-speed peeling.

[0025] Examples of polymerizable monomers having a hydroxy group include (meth)acrylic acid esters (hydroxyalkyl (meth)acrylates) having a hydroxy group, 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. The polymerizable monomer having a hydroxy group preferably includes at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0026] In one embodiment, the content of the polymerizable monomer having a hydroxy group is preferably 1.5 to 15% by mass or 1.5 to 14.5% by mass, based on 100% by mass of all polymerizable monomers. The upper limit of the content of the polymerizable monomer having a hydroxy group is 15% by mass or less, 14.9% by mass or less, 14.8% by mass or less, 14.7% by mass or less, 14.6% by mass or less, or 14.5% by mass or less. The lower limit of the content of the polymerizable monomer having a hydroxy group is 1.5% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, or 5.8% by mass or more. The range of the content of the polymerizable monomer having a hydroxy group may be any combination of the above lower and upper limits. When the content of the polymerizable monomer having a hydroxy group is within the above specified range, adhesive strength during low-speed and high-speed peeling can be reduced. On the other hand, if the content of the polymerizable monomer having a hydroxy group is less than 1.5% by mass or more than 15% by mass, the adhesive strength during low-speed and high-speed peeling increases.

[0027] Examples of polymerizable monomers having an amide group include (meth)acrylamide, isopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and hydroxyethyl(meth)acrylamide. These may be used alone or in combination of two or more. The polymerizable monomer having an amide group preferably includes methacrylamide.

[0028] According to one embodiment, the content of the polymerizable monomer having an amide group is 0.1 to 3% by mass, preferably 0.1 to 2% by mass, based on 100% by mass of all polymerizable monomers. The upper limit of the content of the polymerizable monomer having an amide group is 3% by mass or less, 2.5% by mass or less, 2% by mass or less, 1.5% by mass or less, or 1% by mass or less. The lower limit of the content of the polymerizable monomer having an amide group is 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more. The range of the content of the polymerizable monomer having an amide group may be any combination of the above lower and upper limits.

[0029] <Polyalkylene glycol chain-containing mono(meth)acrylate (a3)> The (meth)acrylic polymer (A) according to one embodiment further comprises a polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​as a structural unit, wherein the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​having at least one hydroxy group does not belong to the polymerizable monomer (a2) having a functional group.

[0030] The polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​may be a compound in which one of the multiple hydroxy groups of a polyalkylene glycol is esterified as a (meth)acrylate. The acryloyl group in the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​serves as a polymerizable group, and therefore can be copolymerized with the polymerizable monomer of the (meth)acrylic polymer (A) described above. The other hydroxy group may remain as a hydroxy group or may be converted into an alkyl ether such as methyl ether or ethyl ether, or a saturated carboxylic acid ester such as acetate ester. Note that a polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​in which the other hydroxy group remains as a hydroxy group, i.e., a polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​having a hydroxy group, does not belong to the polymerizable monomer (a2) having a functional group.

[0031] In the polyalkylene glycol chain-containing mono(meth)acrylate (a3), examples of the alkylene group contained in the polyalkylene glycol include, but are not limited to, an ethylene group, a propylene group, and a butylene group. 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, or polypropylene glycol-polybutylene glycol. The polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​is preferably at least one compound having an average repeating number of 4 to 14 alkylene oxides constituting the polyalkylene oxide.

[0032] The polyalkylene glycol chain-containing mono(meth)(meth)acrylate (a3) ​​is preferably at least one selected from, for example, polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.

[0033] More specific examples of the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​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 alone or in combination of two or more. The polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​preferably contains methoxypolyethylene glycol methacrylate.

[0034] The content of the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​according to one embodiment is 5 to 25% by mass, preferably 5 to 20% by mass, based on 100% by mass of all polymerizable monomers. The upper limit of the content of the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​is 25% by mass or less, 20% by mass or less, or 15% by mass or less. The lower limit of the content of the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​is 5% by mass or more, or 10% by mass or more. The range of the content of the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​may be any combination of the above lower and upper limits.

[0035] <Other monomers> The (meth)acrylic polymer (A) according to one embodiment may contain other monomers as structural units.

[0036] Examples of other monomers include (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, and 2-phenoxyethyl (meth)acrylate; (meth)acrylic acid aralkyl esters such as benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and naphthylmethyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate, tolyl (meth)acrylate, and naphthyl (meth)acrylate; and vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, vinylpyridine, vinylpyrrolidone, vinyl acetate, and acrylonitrile.

[0037] <Method for producing (meth)acrylic polymer (A)> The (meth)acrylic polymer (A) can be produced by known methods, but is preferably produced by solution polymerization. Specifically, a solvent, monomers, a polymerization initiator, and the like are generally heated to a reaction temperature of about 50 to 90°C in an inert gas atmosphere such as nitrogen gas, and the polymerization reaction is carried out for 4 to 12 hours. In solution polymerization, preferred solvents used during polymerization include 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 alone or in combination of two or more.

[0038] The polymerization initiator may be any one capable of initiating radical polymerization, and any known polymerization initiator may be used.

[0039] Examples of the polymerization initiator 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(isobutyrate) dimethyl, and 1,1'-azobis(cyclohexane-1-carbonitrile); water-soluble azo compounds such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] and its salts, 2,2'-azobis(2-methylpropionamidine) and its salts, and 4,4'-azobis(4-cyanovaleric acid) and its salts; and organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butylperoxy-2-ethylhexanoate, and t-butylperoxyisobutyrate. These may be used alone or in combination of two or more.

[0040] <Curing agent (B)> The removable pressure-sensitive adhesive composition according to one embodiment further comprises a curing agent (B). When the removable pressure-sensitive adhesive composition comprises the curing agent (B), the cohesive strength of the removable pressure-sensitive adhesive composition increases, improving the removability.

[0041] The content of the curing agent (B) according to one embodiment is 0.3 to 8 parts by mass, preferably 0.3 to 5 parts by mass, and more preferably 0.3 to 4 parts by mass, relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0042] Examples of the curing agent (B) include isocyanate-based curing agents, epoxy-based curing agents, metal chelate-based curing agents, and aziridine-based curing agents. These may be used alone or in combination of two or more. The (meth)acrylic polymer (A) is preferably crosslinked by at least one of the curing agents (B). The curing agent (B) according to one embodiment is preferably an isocyanate-based curing agent.

[0043] Examples of the isocyanate curing agent include adducts of isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate with polyol compounds such as trimethylolpropane, as well as biuret compounds and isocyanurate compounds thereof, and adducts of the above isocyanate compounds with any of polyols such as polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols; and compounds having two isocyanate groups in the molecule, such as allophanate compounds thereof.

[0044] Examples of epoxy curing agents include epoxy resins obtained by reacting bisphenol A with 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.

[0045] Examples of metal chelate 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 acetoacetate.

[0046] Examples of aziridine 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.

[0047] <Cure retarder (C)> The removable pressure-sensitive adhesive composition according to one embodiment further comprises a curing retarder (C).

[0048] The content of the curing retarder (C) according to one embodiment is 0.3 to 8 parts by mass, preferably 0.3 to 5 parts by mass, and more preferably 0.3 to 4 parts by mass, relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0049] The removable pressure-sensitive adhesive composition preferably further contains a keto-enol tautomer compound as a curing retarder (C). When a polyisocyanate compound such as a tri- or higher functional isocyanate compound is used as the curing agent (B), the keto-enol tautomer compound blocks the isocyanate groups of the curing agent (B). This can suppress excessive viscosity increase and gelation of the removable pressure-sensitive adhesive composition after blending with the curing agent (B), thereby extending the pot life of the removable pressure-sensitive adhesive composition.

[0050] Examples of keto-enol tautomer compounds include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. These may be used alone or in combination of two or more. The keto-enol tautomer compound is preferably acetylacetone.

[0051] <Antistatic agent (D)> The removable pressure-sensitive adhesive composition according to one embodiment further comprises an antistatic agent (D). The removable pressure-sensitive adhesive composition may contain the antistatic agent (D) to impart antistatic properties to the pressure-sensitive adhesive layer. This allows the surface protection film of the present invention to be suitably used as a surface protection film having antistatic properties.

[0052] The surface resistivity of the pressure-sensitive adhesive layer according to one embodiment is 1.0×10 +11 The surface resistivity is Ω / □ or less. Surface resistivity is an index showing the ease of electrical conduction per unit area of ​​a substance. A high surface resistivity indicates poor performance in dissipating static electricity generated by charging when the pressure-sensitive adhesive layer is peeled off from the adherend. On the other hand, a low surface resistivity indicates high performance in dissipating static electricity generated by charging when the pressure-sensitive adhesive layer is peeled off from the adherend. By minimizing the surface resistivity of the pressure-sensitive adhesive layer, the peeling charge generated when the pressure-sensitive adhesive layer is peeled off from the adherend is reduced, thereby preventing damage and malfunction of the adherend (e.g., optical component). Note that the antistatic property of the pressure-sensitive adhesive layer is not an essential property, and may be an optional property depending on the type of adherend.

[0053] The content of the antistatic agent (D) according to one embodiment is 0.05 to 10 parts by mass, preferably 0.05 to 7 parts by mass, and more preferably 1 to 4 parts by mass, relative to 100 parts by mass of the (meth)acrylic polymer (A).

[0054] The antistatic agent (D) may be, for example, a cation such as a pyridinium cation, an imidazolium cation, an ammonium cation, or an alkali metal cation, or a hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 -Examples of the antistatic agent (D) include ionic compounds having an anion such as lithium bis(trifluoromethanesulfonyl)imide (FSI), bis(trifluoromethanesulfonyl)imide (TFSI), tetrabutylammonium bis(trifluoromethanesulfonyl)imide, and trifluoromethanesulfonate (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.

[0055] <Other additives> The removable pressure-sensitive adhesive composition of the present invention may contain various resins and additives within the range that does not affect performance. Examples of additives include tackifiers, antioxidants, silane coupling agents, heat or light stabilizers, UV absorbers, leveling agents, antifoaming agents, antibacterial agents, moisturizing agents, pigments, dyes, and fragrances. These may be used alone or in combination of two or more.

[0056] <Surface protection film> The surface protection film has a pressure-sensitive adhesive layer, which is a cured product of the removable pressure-sensitive adhesive composition of the present invention, on a substrate. The surface protection film can be produced, for example, by applying the removable pressure-sensitive adhesive composition to a substrate and drying it. The pressure-sensitive adhesive layer may be provided on at least one surface of the substrate. A release sheet may also be provided on the adhesive surface of the pressure-sensitive adhesive layer. The removable pressure-sensitive adhesive composition used in the surface protection film is as described above, and therefore a detailed description thereof will be omitted.

[0057] The pressure-sensitive adhesive layer is a layer having slight adhesion for adhering the surface protection film to optical components such as polarizing plates and retardation plates. Furthermore, the pressure-sensitive adhesive layer may have antistatic properties when the adherend is sensitive to static electricity. The reason for making the pressure-sensitive adhesive layer slightly adhesive is to ensure that the surface protection film can be easily peeled off from the optical component after use without leaving any adhesive residue. When the surface protection film is to be adhered to an optical component, it is preferable that the pressure-sensitive adhesive layer has sufficient transparency.

[0058] <Optical member with pressure-sensitive adhesive layer> An optical member with a pressure-sensitive adhesive layer according to one embodiment can be obtained by laminating a pressure-sensitive adhesive layer obtained by curing the removable pressure-sensitive adhesive composition of the present invention on at least one surface of the optical member. Examples of optical members include polarizing films, retardation films, antireflection films, antiglare films, ultraviolet absorbing films, infrared absorbing films, optical compensation films, and brightness enhancing films. Examples of display devices equipped with optical members include liquid crystal displays, organic electroluminescence displays, and touch panels.

[0059] Examples of liquid media used when applying the removable pressure-sensitive adhesive composition include organic solvents such as 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 alone or in combination of two or more. Viscosity can be adjusted by adding any liquid medium to the removable pressure-sensitive adhesive composition. The viscosity of the removable pressure-sensitive adhesive composition can also be reduced by heating.

[0060] Examples of substrates include cellophane, plastic sheets, rubber, foams, fabrics, rubber fabrics, resin-impregnated fabrics, glass plates, and wood. The substrate may be in the form of a plate or a film. Furthermore, the substrate may be made of a single material, or may be made of a multi-layer substrate formed by laminating substrates made of multiple materials. Furthermore, the surface of the substrate may be subjected to a release treatment. When the surface protective film is attached to an optical component, it is preferable that the substrate has sufficient transparency.

[0061] Examples of plastic sheets include polyvinyl alcohol film, triacetyl cellulose film, polypropylene, polyethylene, polycycloolefin, ethylene-vinyl acetate copolymer and other polyolefin resin films, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and other polyester resin films, polyvinyl chloride and other vinyl resin films, 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, epoxy resin films, etc. These may be used alone or in combination of two or more.

[0062] A resin film such as a polyester film can be used as the release sheet (separator) that protects the adhesive surface of the pressure-sensitive adhesive layer. The surface of the release sheet that faces the adhesive surface of the pressure-sensitive adhesive layer is subjected to a release treatment using a silicone-based or fluorine-based release agent.

[0063] Examples of methods for applying the removable pressure-sensitive adhesive composition include a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. Examples of drying methods include hot air drying, infrared radiation, and reduced pressure methods. Drying conditions can be appropriately changed depending on the cured form of the removable pressure-sensitive adhesive composition, film thickness, and type of solvent, but may be, for example, hot air drying at 60 to 130°C.

[0064] The thickness of the pressure-sensitive adhesive layer according to one embodiment is 1 to 200 μm, preferably 3 to 100 μm.

[0065] <Production of removable pressure-sensitive adhesive composition> Table 1 shows the raw material composition and physical properties of the (meth)acrylic polymer (A) in Production Examples 1 to 6. Table 2 shows the raw material composition and physical properties of the (meth)acrylic polymer (A) in Production Examples 7 to 13. Table 3 shows the raw material composition and physical properties of the (meth)acrylic polymer (A) in Production Examples 14 to 17. Table 4 shows the raw material composition and test results of the removable pressure-sensitive adhesive compositions in Examples 1 to 7. Table 5 shows the raw material composition and test results of the removable pressure-sensitive adhesive compositions in Examples 8 to 15. Table 6 shows the raw material composition and test results of the removable pressure-sensitive adhesive compositions in Comparative Examples 1 to 4.

[0066] [Table 1] (Explanation of Abbreviations) Component (a1): represents an alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms. Component (a2): represents a polymerizable monomer (a2) having a functional group. Component (a3): Polyalkylene glycol chain-containing mono(meth)acrylate (a3). NOAA: n-octyl acrylate 2EHA: 2-Ethylhexyl acrylate MPEGMA: Methoxypolyethyleneglycol methacrylate 4HBA: 4-hydroxybutyl acrylate HEA: 2-hydroxyethyl acrylate AAc: Acrylic acid mAM: methacrylamide

[0067] [Table 2] (Explanation of Abbreviations) See Table 1 for explanation of abbreviations

[0068] [Table 3] (Explanation of Abbreviations) See Table 1 for explanation of abbreviations

[0069] [Table 4] (Explanation of Abbreviations) Hardener (B): Isocyanate-based hardener (manufactured by Saiden Chemical Co., Ltd.) Li-TFSI: Lithium bis(trifluoromethanesulfonyl)imide FC-4400: Tetrabutylammonium bis(trifluoromethanesulfonyl)imide (3M) Adhesion strength at low peel speed (gf / 25mm) 0.3m / min: See Test 1 below Adhesion strength at high speed (gf / 25mm) 30m / min: See Test 1 below Wettability (seconds): See Test 2 below Surface resistivity (Ω / □): See Test 3 below

[0070] [Table 5] (Explanation of Abbreviations) See Table 4 for explanation of abbreviations

[0071] [Table 6] (Explanation of Abbreviations) See Table 4 for explanation of abbreviations

[0072] <Production Example 1: Production method for (meth)acrylic polymer (A)> The production method for the (meth)acrylic polymer (A) of Production Example 1 will be described with reference to Table 1. A reactor equipped with a stirrer, thermometer, sequential dropping device, and reflux condenser was charged with 45 parts of ethyl acetate, 5 parts of acetone, and 0.05 parts of a polymerization initiator (azobisisobutyronitrile). Meanwhile, a monomer / solvent mixture consisting of 98.5 parts of n-octyl acrylate, 1.5 parts of 4-hydroxybutyl acrylate, and 30 parts of ethyl acetate was prepared in a separate vessel. The reactor was heated to 73°C while stirring, and the monomer / solvent mixture weighed in the separate vessel was added dropwise over 75 minutes, allowing the polymerization reaction to proceed at 80°C for 7 hours. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain a (meth)acrylic polymer (A) solution with a solids content of 44.0% by mass.

[0073] <Production Examples 2 to 13: Methods for producing (meth)acrylic polymer (A)> Detailed explanations are omitted here because the (meth)acrylic polymers (A) of Production Examples 2 to 13 were produced based on the raw material compositions in Tables 1 and 2 and the same production method as Production Example 1. The acid value (mg KOH / g) of the (meth)acrylic polymer (A) of Production Example 11 was 6.22 (calculated value).

[0074] <Production Examples 14 to 17: Methods for producing (meth)acrylic polymer (A)> Detailed explanations are omitted here because the (meth)acrylic polymers (A) of Production Examples 14 to 17 were produced based on the raw material compositions in Table 3 and the same production method as Production Example 1. The acid value (mg KOH / g) of the (meth)acrylic polymer (A) of Production Example 17 was 7.78 (calculated value).

[0075] <Example 1: Method for producing removable adhesive composition> A method for producing the removable pressure-sensitive adhesive composition of Example 1 will be described with reference to Table 4. 3.4 parts by solids of an isocyanate-based curing agent (manufactured by Saiden Chemical Industry Co., Ltd.) as the curing agent (B) and 4.0 parts of acetylacetone as the curing retarder (C) were added to 100 parts by solids of the (meth)acrylic polymer (A) solution of Production Example 1, and the mixture was thoroughly mixed to obtain a removable pressure-sensitive adhesive composition.

[0076] <Example 1: Method for manufacturing a surface protection film> The removable adhesive composition of Example 1 was directly coated onto a 38 μm-thick polyethylene terephthalate (PET) film substrate. The solvent was then removed by drying at 110°C, forming an adhesive layer with a thickness of 15 μm. A silicone resin-coated polyester film (release sheet) was then applied to the surface on which the adhesive layer was formed, to prepare a surface protection film. The surface protection film thus prepared was then aged at 40°C for 3 days to obtain samples for each test.

[0077] <Examples 2 to 15: Methods for producing removable pressure-sensitive adhesive compositions> The removable pressure-sensitive adhesive compositions of Examples 2 to 15 were produced based on the raw material compositions in Tables 4 and 5 and the same production method as in Example 1, so detailed explanations are omitted. In Example 9, 1 part of lithium bis(trifluoromethanesulfonyl)imide was added as the antistatic agent (D). In Example 10, 4 parts of tetrabutylammonium bis(trifluoromethanesulfonyl)imide was added as the antistatic agent (D).

[0078] <Examples 2 to 15: Method for manufacturing a surface protection film> The surface protection films of Examples 2 to 15 were produced based on the same production method as in Example 1, and therefore detailed description thereof will be omitted.

[0079] <Comparative Examples 1 to 4: Methods for producing removable pressure-sensitive adhesive compositions> Removable pressure-sensitive adhesive compositions of Comparative Examples 1 to 4 were produced based on the raw material compositions in Table 6 and the same production method as in Example 1, and detailed explanations thereof will be omitted.

[0080] <Comparative Examples 1 to 4: Methods of Manufacturing Surface Protection Films> The surface protection films of Comparative Examples 1 to 4 were produced based on the same production method as in Example 1, and therefore detailed explanations will be omitted.

[0081] <Test Method> The surface protection films of Examples 1 to 15 and Comparative Examples 1 to 4 were used to carry out the following tests 1 to 3.

[0082] (Test 1: Adhesion measurement) Test pieces were prepared by cutting the sample (surface protection film) to a width of 25 mm and a length of 70 mm. The release sheet was peeled off from the test piece, and the piece was attached to the surface of the PET substrate. A 2 kg roll was then rolled back and forth to press the piece together. The piece was then left for 24 hours in an atmosphere of 23°C and 50% humidity. After leaving the piece, the adhesive strength was measured using a tensile tester in accordance with JIS Z-0237:2000 at a tensile speed of 0.3 m / min or 30 m / min and a peel angle of 180°. [Evaluation criteria] - Adhesion strength at low peeling speed (gf / 25mm), pulling speed 0.3m / min ○: 2.0~9.9gf / 25mm ×:10.0gf / 25mm or more High-speed peeling adhesive strength (gf / 25mm), pulling speed 30m / min ○: Less than 100gf / 25mm ×:100gf / 25mm or more

[0083] (Test 2: Checking wettability) The sample (surface protection film) was cut into a 100mm x 100mm piece to prepare a test piece. The release sheet was peeled off the test piece and placed on the PET substrate. The center of the test piece was lightly pressed with a finger. The time from pressing the center of the test piece until the entire surface of the test piece was wetted and spread onto the PET was measured. [Evaluation criteria] ○: Less than 12.0 seconds ×: 12.0 seconds or more

[0084] (Test 3: Measurement of surface resistivity) The release sheet was peeled off from the test piece (surface protection film) to expose the pressure-sensitive adhesive layer, and the surface resistivity of the pressure-sensitive adhesive layer was measured using a resistivity meter.

[0085] <Test Results> With reference to Tables 4 to 6 above, the test results of Examples 1 to 15 and Comparative Examples 1 to 4 will be explained.

[0086] As shown by the results of Tests 1 and 2, Examples 1 to 15 demonstrated excellent adhesive strength and wettability during both low-speed and high-speed peeling. Examples 9 and 10 demonstrated that the pressure-sensitive adhesive layers had excellent antistatic properties. On the other hand, as shown by the results of Tests 1 and 2, Comparative Examples 1 to 4 did not demonstrate excellent adhesive strength and wettability during low-speed and high-speed peeling.

[0087] According to the test results, in Comparative Example 1, the content of n-octyl acrylate was less than the lower limit specified in the present invention, resulting in high adhesive strength during slow peeling. Furthermore, wettability was also reduced. In Comparative Example 2, the content of the polymerizable monomer (a2) having a functional group exceeded the upper limit specified in the present invention, resulting in high polarity of the adhesive layer and strong intermolecular forces with the adherend surface, resulting in high adhesive strength during both slow and fast peeling. In Comparative Example 3, the content of the polymerizable monomer (a2) having a functional group was less than the lower limit specified in the present invention, resulting in low crosslink density and a soft coating, resulting in high adhesive strength during both slow and fast peeling. In Comparative Example 4, the acid value of the (meth)acrylic polymer (A) exceeded the upper limit specified in the present invention, resulting in high polarity of the adhesive layer and strong intermolecular forces with the adherend surface, resulting in high adhesive strength during both slow and fast peeling.

[0088] As described above, the removable pressure-sensitive adhesive composition of the present invention has excellent wettability and exhibits the remarkable effect of being able to reduce adhesive strength during low-speed and high-speed peeling.

[0089] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. The (meth)acrylic polymer (A) comprises 85 to 98.5 mass % of an alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms and 1.5 to 15 mass % of a polymerizable monomer (a2) having a functional group, the alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms includes at least n-octyl acrylate, The (meth)acrylic polymer (A) has an acid value of 7.5 mg KOH / g or less. Removable pressure-sensitive adhesive composition.

2. The present invention comprises a (meth)acrylic polymer (A) containing, as structural units, an alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms and 1.5 to 14.5 mass % of a polymerizable monomer (a2) having a functional group, the alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms contains 20 to 85 mass % of n-octyl acrylate, The (meth)acrylic polymer (A) has an acid value of 7.5 mg KOH / g or less. Removable pressure-sensitive adhesive composition.

3. The alkyl group-containing unsaturated monomer (a1) having an alkyl group having 1 to 18 carbon atoms further contains 0.5 to 78 mass% of 2-ethylhexyl acrylate. The removable pressure-sensitive adhesive composition according to claim 2 .

4. the (meth)acrylic polymer (A) further contains 5 to 25% by mass of a polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​as a structural unit, wherein the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​having at least one hydroxy group does not belong to the polymerizable monomer (a2) having a functional group; The removable pressure-sensitive adhesive composition according to claim 2 .

5. the alkyl group-containing unsaturated monomer (a1) having an alkyl group of 1 to 18 carbon atoms further contains 0.5 to 78 mass% of 2-ethylhexyl acrylate; the (meth)acrylic polymer (A) further contains 5 to 25% by mass of a polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​as a structural unit, wherein the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​having at least one hydroxy group does not belong to the polymerizable monomer (a2) having a functional group; The removable pressure-sensitive adhesive composition according to claim 2 .

6. The polymerizable monomer (a2) having a functional group includes a polymerizable monomer having a hydroxy group. The removable pressure-sensitive adhesive composition according to claim 1 or 2.

7. The polymerizable monomer (a2) having a functional group further includes a polymerizable monomer having a carboxy group or a polymerizable monomer having an amide group. The removable pressure-sensitive adhesive composition according to claim 1 or 2.

8. the polymerizable monomer (a2) having a functional group contains 0.1 to 0.8% by mass of a polymerizable monomer having a carboxy group or 0.1 to 3% by mass of a polymerizable monomer having an amide group; The removable pressure-sensitive adhesive composition according to claim 1 or 2.

9. the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​contains methoxypolyethylene glycol methacrylate, wherein the polyalkylene glycol chain-containing mono(meth)acrylate (a3) ​​having at least one hydroxy group does not belong to the polymerizable monomer (a2) having a functional group; The removable pressure-sensitive adhesive composition according to claim 4.

10. Further comprising a curing agent (B), The curing agent (B) includes an isocyanate-based curing agent. The removable pressure-sensitive adhesive composition according to claim 1 or 2.

11. Further comprising a cure retarder (C), The cure retarder (C) includes a keto-enol tautomer compound. The removable pressure-sensitive adhesive composition according to claim 10.

12. Further comprising an antistatic agent (D), The removable pressure-sensitive adhesive composition according to claim 1 or 2.

13. A substrate; a pressure-sensitive adhesive layer comprising the removable pressure-sensitive adhesive composition according to claim 1 or 2 provided on at least one surface of the substrate, Surface protection film.

14. The surface resistivity of the pressure-sensitive adhesive layer is 1.0×10 １１ Ω / □ or less, The surface protection film according to claim 13.

15. an optical member; a pressure-sensitive adhesive layer comprising the removable pressure-sensitive adhesive composition according to claim 1 or 2, provided on at least one surface of the optical member; Optical component with adhesive layer.

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