CN109844052B - Adhesive composition for protective film and protective film - Google Patents

Abstract

The pressure-sensitive adhesive composition for a protective film according to one embodiment of the present invention contains a (meth) acrylic polymer, a crosslinking agent, and an antistatic agent, wherein the acid value of the (meth) acrylic polymer is 9mgKOH/g to 65mgKOH/g, and the content of a structural unit derived from a monomer having a polyalkylene oxide chain is more than 1% by mass and less than 20% by mass relative to the mass of all the structural units.

Description

Adhesive composition for protective film and protective film

Technical Field

The present disclosure relates to an adhesive composition for a protective film and a protective film.

Background

Generally, optical components such as polarizing plates used in liquid crystal display devices are protected by protective films in many cases. The protective film prevents contamination and damage of the surface of the optical member which are likely to occur in the respective steps of punching, inspection, transportation, assembly of the liquid crystal display panel, and the like, and is peeled and removed at a stage where the surface of the optical member is not required to be protected.

If static electricity is generated when the protective film is peeled off from the optical member, a defect that dust or the like is attached to the optical member or a circuit of the liquid crystal display device is broken is likely to occur. Therefore, the protective film is required to have a property of preventing static electricity generated during peeling (hereinafter, also referred to as "antistatic property").

The pressure-sensitive adhesive layer of the protective film is required to have such a pressure-sensitive adhesive property that the pressure-sensitive adhesive layer does not deviate from the surface of the adherend or fall off from the surface of the adherend while the adherend is required to be protected, and to be easily peeled off from the adherend at a stage when the adherend is not required to be protected (hereinafter, also referred to as "peelability").

In recent years, for the purpose of improving work efficiency, peeling of a protective film from an adherend tends to be performed under high-speed peeling conditions (for example, 30 m/min), and there is a demand for easy peeling from the adherend even in high-speed peeling (hereinafter, also referred to as "high-speed peeling property").

As an antistatic adhesive composition having excellent antistatic properties, an adhesive composition comprising a (meth) acrylic polymer containing an alkyl (meth) acrylate as a main component and having an acid value of 29 or less and a fluorine-containing imide lithium salt is disclosed (for example, see japanese patent application laid-open No. 2005-306937).

Further, as an adhesive composition having excellent antistatic properties and reduced staining properties to a protected object, an adhesive composition containing an alkali metal salt and using 15 to 100 wt% of an alkylene oxide adduct of (meth) acrylic acid as a monomer component has been disclosed (for example, see japanese patent application laid-open No. 2005 314579).

Disclosure of Invention

The antistatic pressure-sensitive adhesive composition described in jp 2005-306937 a contains an acidic group in a (meth) acrylic polymer, and therefore wettability is likely to change depending on the material of an adherend due to the polar effect of the acidic group. Therefore, when the antistatic pressure-sensitive adhesive composition described in jp 2005-306937 a is used, it is difficult to make the peeling condition constant at the time of high-speed peeling regardless of the material of the adherend. Further, when the antistatic pressure-sensitive adhesive composition described in jp 2005-306937 a is used, the antistatic property may be deteriorated depending on the material of the adherend. In addition, an antistatic pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition described in japanese patent application laid-open No. 2005-314579 sometimes has difficulty in obtaining sufficient antistatic properties due to the material of the adherend and has no high-speed peelability.

Therefore, in order to provide a conventional pressure-sensitive adhesive composition for a protective film with a degree of adhesive force and antistatic property that allows easy peeling from an adherend at high speed peeling, it is necessary to change the composition of the pressure-sensitive adhesive depending on the material of the adherend. Since the material of the adherend is numerous, it is practically difficult to prepare a pressure-sensitive adhesive composition in accordance with the material of the adherend, and a pressure-sensitive adhesive composition that does not depend on the material of the adherend has been desired.

The present disclosure has been made in view of the above circumstances.

An object of one embodiment of the present invention is to provide an adhesive composition for a protective film and a protective film, which are excellent in high-speed peelability and antistatic property regardless of the material of an adherend.

Specific means for solving the above problems include the following embodiments.

< 1 > an adhesive composition for protective films, comprising a (meth) acrylic polymer, a crosslinking agent and an antistatic agent, wherein the acid value of the (meth) acrylic polymer is 9mgKOH/g to 65mgKOH/g, and the content of a structural unit derived from a monomer having a polyalkylene oxide chain is more than 1% by mass and less than 20% by mass relative to the mass of all the structural units.

< 2 > the adhesive composition for protective films according to < 1 >, wherein the (meth) acrylic polymer contains a structural unit represented by the following general formula (1).

In the general formula (1), R¹Represents a hydrogen atom or a methyl group. L represents a linking group having a valence of 2 consisting of at least 1 selected from the group consisting of an alkylene group, an arylene group, a carbonyl group and an oxygen atom.

< 3 > the adhesive composition for protective films according to < 1 > or < 2 >, wherein the (meth) acrylic polymer contains a structural unit derived from an alkyl (meth) acrylate, and the content of the structural unit derived from an alkyl (meth) acrylate is 65 to 99% by mass based on the mass of all the structural units.

< 4 > the adhesive composition for protective films according to any one of < 1 > to < 3 >, further comprising a (meth) acrylic oligomer having a weight average molecular weight of 3000 to 20000, wherein the content of the (meth) acrylic oligomer is 0.05 to 5.00 parts by mass based on 100 parts by mass of the (meth) acrylic polymer.

< 5 > the adhesive composition for protective films < 4 >, wherein the (meth) acrylic oligomer contains a structural unit derived from a monomer having a polyalkylene oxide chain, and the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 5 to 30% by mass based on the mass of all the structural units.

< 6 > the adhesive composition for protective films according to any one of < 1 > to < 5 >, wherein the crosslinking agent is a metal chelate compound.

< 7 > a protective film comprising an adhesive layer and a substrate, wherein the adhesive layer is a crosslinked product of the adhesive composition for protective films described in any one of < 1 > to < 6 >.

According to one embodiment of the present invention, it is possible to provide an adhesive composition for a protective film and a protective film which are excellent in high-speed peelability and antistatic property regardless of the material of an adherend.

Drawings

Fig. 1 is an explanatory view illustrating a method of evaluating adhesive force and antistatic property at the time of high-speed peeling.

Detailed Description

Hereinafter, an adhesive composition for a protective film and a protective film according to an embodiment of the present invention will be described in detail. In the present invention, "to" in the numerical range means a numerical value before and after including "to".

In the present specification, the amount of each component in the composition means the total amount of a plurality of substances present in the composition when the plurality of substances corresponding to each component are present in the composition unless otherwise specified.

In the present specification, a (meth) acrylic polymer or a (meth) acrylic oligomer means a polymer or oligomer in which at least a monomer as a main component among monomers constituting the polymer or oligomer is a monomer having a (meth) acryloyl group. The monomer as the main component is a monomer having the highest content (mass%) among monomers constituting the polymer or oligomer. The (meth) acrylic polymer may be, for example, a polymer in which the content of the structural unit derived from the (meth) acrylate monomer as the main component is 50% by mass or more of the total structural units.

In the present specification, "(meth) acrylic acid" is meant to include both "acrylic acid" and "methacrylic acid", "meth (acrylate) is meant to include both" acrylate "and" methacrylate ", and" (meth) acryl "is meant to include both" acryl "and" methacryl ".

Adhesive composition for protective film

An adhesive composition for a protective film according to an embodiment of the present invention (hereinafter, also referred to as "adhesive composition") includes a (meth) acrylic polymer having an acid value of 9mgKOH/g to 65mgKOH/g and a content of a structural unit derived from a monomer having a polyalkylene oxide chain exceeding 1% by mass and less than 20% by mass relative to the mass of all the structural units, a crosslinking agent, and an antistatic agent.

Since the pressure-sensitive adhesive composition has the above-mentioned structure, a protective film excellent in high-speed peelability and antistatic property is obtained regardless of the material of the adherend. The reason is not clear, but can be presumed as follows.

Generally, the peelability of the protective film at the time of high-speed peeling tends to largely depend on the material of the adherend. In particular, in a pressure-sensitive adhesive composition containing a structural unit derived from a monomer having an acid group, wettability to an adherend is changed due to a polar effect of the acid group, and the adhesive force exerted may be different depending on the material of the adherend. Therefore, peeling tends to be difficult at high-speed peeling. Further, an adhesive composition containing a polymer having an acid value of 1mgKOH/g or more tends to have a tendency that antistatic performance is easily lowered.

It is presumed that the pressure-sensitive adhesive composition according to one embodiment of the present invention contains the (meth) acrylic polymer in which the content of the structural unit derived from the monomer having a polyalkylene oxide chain is more than 1% by mass and less than 20% by mass based on the mass of the entire structural units, and therefore, the surface free energy of the pressure-sensitive adhesive layer which is likely to increase due to the polar effect of the acid group is suppressed. Structural units derived from a monomer having a polyalkylene oxide chain tend to be present in large amounts at the interface between an adherend and an adhesive composition. Therefore, even when the (meth) acrylic polymer having an acid value of 9mgKOH/g to 65mgKOH/g is contained in the pressure-sensitive adhesive composition according to one embodiment of the present invention, it is possible to suppress a change in wettability with respect to an adherend due to a polar effect of an acid group, and to exhibit a constant adhesive force regardless of the material or state of the adherend. In addition, the pressure-sensitive adhesive composition according to an embodiment of the present invention has an acid value of the (meth) acrylic polymer in the above range and contains a crosslinking agent, and therefore has an appropriate peelability, and also has a hardness of a degree that the adhesive force at the time of high-speed peeling becomes appropriately small, and therefore tends to be excellent in the high-speed peeling property.

Further, since the pressure-sensitive adhesive composition according to an embodiment of the present invention contains an antistatic agent, even if the acid value of the (meth) acrylic polymer is in the above range, the decrease in antistatic property can be suppressed. In particular, since a (meth) acrylic polymer containing a structural unit derived from a monomer having a polyalkylene oxide chain at a specific content is used in combination with an antistatic agent, the decrease in antistatic properties is further suppressed, and the antistatic properties tend to be excellent regardless of the material of the substrate.

As described above, it is assumed that the protective film formed from the pressure-sensitive adhesive composition according to one embodiment of the present invention is excellent in high-speed peelability and antistatic property regardless of the material of the adherend.

Hereinafter, each component of the pressure-sensitive adhesive composition according to an embodiment of the present invention will be described in detail.

(meth) acrylic polymer

The adhesive composition according to one embodiment of the present invention contains at least 1 of (meth) acrylic polymers (hereinafter, also referred to as "specific (meth) acrylic polymers") having an acid value of 9mgKOH/g to 65mgKOH/g and a content of structural units derived from a monomer having a polyalkylene oxide chain of more than 1% by mass and less than 20% by mass relative to the mass of all the structural units. The adhesive composition according to an embodiment of the present invention may further contain a (meth) acrylic polymer different from the specific (meth) acrylic polymer, as necessary.

The specific (meth) acrylic polymer contains a structural unit derived from a monomer having a polyalkylene oxide chain. Examples of the polyalkylene oxide chain include a polyethylene oxide chain and a polypropylene oxide chain. From the viewpoint of obtaining sufficient antistatic properties regardless of the material of the adherend, a polyethylene oxide chain is preferred as the polyalkylene oxide chain.

Examples of the monomer having a polyalkylene oxide chain include 2- (ethoxyethoxy) ethyl acrylate, polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, and methoxypolyethylene glycol (meth) acrylate.

Among them, from the viewpoint of exhibiting both antistatic properties and high-speed peelability regardless of the material of the adherend, the monomer having a polyalkylene oxide chain is preferably methoxypolyethylene glycol (meth) acrylate or methoxypolypropylene glycol (meth) acrylate, and more preferably methoxypolyethylene glycol (meth) acrylate.

The average molar number of addition of the alkylene oxide unit in the polyalkylene oxide chain is preferably 2 to 25 moles, and more preferably 4 to 15 moles, from the viewpoint that a sufficient antistatic effect can be obtained regardless of the material of the adherend.

The average addition mole number of the alkylene oxide unit in the polyalkylene oxide chain means an average value of the addition mole number of the alkylene oxide unit in the monomer contained.

The content of the structural unit derived from the monomer having a polyalkylene oxide chain contained in the specific (meth) acrylic polymer is more than 1% by mass and less than 20% by mass relative to the mass of all the structural units.

If the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 1% by mass or less, antistatic properties may not be sufficiently exhibited depending on the material of the adherend. If the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 20% by mass or more, the high-speed peelability may not be sufficiently exhibited depending on the material of the adherend. From the above viewpoint, the content of the structural unit derived from the monomer having a polyalkylene oxide chain is preferably 2 to 18% by mass, more preferably 3 to 15% by mass, and still more preferably 3 to 10% by mass.

The specific (meth) acrylic polymer contains a structural unit derived from a monomer having an acidic group.

As the monomer having an acidic group, for example, examples thereof include monomers having a carboxyl group such as (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethylhexahydrophthalic acid, 2- (meth) acryloyloxypropylhexahydrophthalic acid, 2- (meth) acryloyloxyethylphthalic acid, ω -carboxy-polycaprolactone mono (meth) acrylate, 2- (meth) acryloyloxyethylsuccinic acid, 2- (meth) acryloyloxyethylfumaric acid, 2- (meth) acryloyloxyethylhexahydrophthalic acid, and (meth) acrylate having a carboxyl group represented by 2- (meth) acryloyloxyethylphthalic acid, and monomers having a phosphoric acid group represented by 2- (meth) acryloyloxyethyl acid phosphate.

As the structural unit derived from the monomer having an acidic group, a structural unit derived from a monomer having a carboxyl group is preferable. The structural units derived from the monomer having a carboxyl group may be 1 kind alone or 2 or more kinds.

The structural unit derived from a (meth) acrylate having a carboxyl group is preferably a structural unit represented by the following general formula (1). When the structural unit represented by the general formula (1) is contained, the carboxyl group is bonded to the (meth) acrylic acid via L, and the adhesive force at the time of high-speed peeling can be suppressed to be lower. More specifically, from the viewpoint of steric hindrance, the reactivity of the monomer having a carboxyl group represented by the general formula (1) with a crosslinking agent described later is greatly improved as compared with a short-chain monomer having a carboxyl group such as (meth) acrylic acid.

In the structural unit represented by the above general formula (1), L represents a 2-valent linking group composed of at least 1 selected from the group consisting of an alkylene group, an arylene group, a carbonyl group and an oxygen atom, and R is¹Represents a hydrogen atom or a methyl group. Wherein, when L contains an oxygen atom, it forms a group in which the oxygen atom is bonded to at least 1 selected from the group consisting of an alkylene group, an arylene group and a carbonyl group, and is bonded to-COO-and-CO-.

The alkylene group in L may be linear, branched, or cyclic. When the alkylene group in L is linear or branched, the number of carbon atoms in the alkylene group is preferably 1 to 12, more preferably 2 to 10, and still more preferably 2 to 6.

Examples of the alkylene group having 1 to 12 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, an arylene group, a decylene group, a dodecylene group, and the like.

When the alkylene group in L is cyclic, L may be an alicyclic group (carbocyclic ring). The cyclic alkylene group may be a carbocyclic group having 3 to 5 carbon atoms, and a specific example thereof is preferably cyclohexylene or the like.

The arylene group in L preferably has 6 to 10 carbon atoms, and more preferably a phenylene group. The bonding position of the arylene group is not particularly limited. For example, when the arylene group is a phenylene group, the bonding position may be any of the 1-and 4-positions, the 1-and 2-positions, and the 1-and 3-positions, and preferably the 1-and 2-positions.

The alkylene group and the arylene group in L may have a substituent. Examples of the substituent include an alkyl group having 1 to 12 carbon atoms, a halogen atom, a hydroxyl group, an amino group, a nitro group, a phenyl group, and the like.

From the viewpoint of antistatic properties and high-speed peelability, the linking group having a valence of 2 represented by L in the general formula (1) is preferably a linking group having a valence of 2 represented by the following general formula (2a) or general formula (2 b).

In the general formulae (2a) and (2b), R²¹～R²⁴Each independently represents an alkylene group having 1 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms. N represents a number of 0 to 10, and m represents a number of 1 to 10.

R²¹～R²⁴The alkylene group in (b) may be linear, branched or cyclic, preferably linear or branched, more preferably linear.

R²¹～R²⁴The bonding position of the arylene group in (1) is not particularly limited. For example, when the arylene group is a phenylene group or when the cyclic alkylene group is, for example, a cyclohexylene group, the bonding position may be any of the 1-and 4-positions, the 1-and 2-positions, and the 1-and 3-positions, preferably the 1-and 2-positions.

R²¹And R²²The alkylene group in (1) is preferably a C2-10, more preferably a C2-6, independently. As R²¹And R²²Examples of the alkylene group in (1) include a methylene group, an ethylene group, a propylene group, a butylene group, and a cyclohexylene group. R²¹And R²²The alkylene groups in (A) may be the same or different.

R²¹And R²²The arylene group in (a) is preferably a phenylene group or a naphthylene group, respectively, and more preferably a phenylene group.

R in the general formula (2a) is R from the viewpoint of antistatic properties and high-speed peelability²¹And R²²Each independently preferably represents an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 2 to 6 carbon atoms, and still more preferably a linear or branched alkylene group having 2 to 6 carbon atoms.

In the general formula (2a), n represents a number of 0 to 10. When the specific (meth) acrylic polymer contains only 1 structural unit represented by the general formula (1), n is an integer, and when it contains 2 or more, n is a rational number as an average value. n is preferably 0 to 4, more preferably 0 to 2.

General formula (2)b) In, R²³The alkylene group in (1) is preferably an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 2 to 6 carbon atoms, and still more preferably an alkylene group having 2 to 4 carbon atoms. As R²³Examples of the alkylene group in (1) include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, and a dodecylene group.

In the general formula (2b), R²⁴The alkylene group in (3) is preferably a linear or branched alkylene group having 2 to 6 carbon atoms, a cyclic alkylene group having 4 to 8 carbon atoms (a 2-valent carbocyclic ring), or an arylene group having 6 to 10 carbon atoms, more preferably a linear or branched alkylene group having 2 to 4 carbon atoms, a cyclic alkylene group having 5 to 6 carbon atoms, or a phenylene group, and still more preferably a linear or branched alkylene group having 2 to 4 carbon atoms, a cyclohexylene group, or a phenylene group.

In the general formula (2b), m represents a number of 1 to 10. When the specific (meth) acrylic polymer contains only 1 structural unit represented by the general formula (1), m is an integer, and when it contains 2 or more, m is a rational number as an average value. m is preferably 1 to 4, more preferably 1 to 2.

The structural unit represented by the general formula (1) can be introduced into the specific (meth) acrylic polymer by, for example, copolymerizing a monomer represented by the following general formula (1a) with another monomer constituting the specific (meth) acrylic polymer.

In the general formula (1a), R¹And L is independently from R in the formula (1)¹And L have the same meaning.

The monomer represented by the general formula (1a) can be produced by a conventional method, and can be appropriately selected from commercially available monomers. Examples of the monomer represented by the general formula (2a) in which L is represented by the general formula (2a) in the monomer represented by the general formula (1a) include (meth) acrylic acid dimer (preferably, n in the general formula (2a) has an average value of about 0.4) and ω -carboxy-polycaprolactone mono (meth) acrylate (preferably, n in the general formula (2a) has an average value of about 1.0).

As these monomers, commercially available products such as "ARONIX M-5600" and "ARONIX M-5300" (trade name, manufactured by Toyo Synthesis Co., Ltd.) can be used.

Examples of the monomer represented by the general formula (1a) in which L is represented by the general formula (2b) include 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl fumaric acid, 2- (meth) acryloyloxyethyl hexahydrophthalic acid and 2- (meth) acryloyloxyethyl phthalic acid. As these monomers, for example, "LIGHT ESTER HO-MS", "LIGHT ACRYLATE HOA-MS (N)", "LIGHT ACRYLATE HOA-HH (N)", and "LIGHT ACRYLATE HOA-MPL (N)" (hereinafter, trade name, manufactured by Kyoeisha chemical Co., Ltd.) can be used as commercially available products.

The content of the structural unit represented by the general formula (1) is preferably 4 to 30% by mass, more preferably 5 to 20% by mass, and still more preferably 8 to 15% by mass, based on the mass of the entire structural units of the specific (meth) acrylic polymer.

When the content of the structural unit represented by the general formula (1) is 4% by mass or more, the adhesive force at the time of high-speed peeling tends to be suppressed to be lower. When the content of the structural unit represented by the general formula (1) is 30% by mass or less, the decrease in adhesive force due to the material of the adherend and the antistatic property tend to be suppressed.

The specific (meth) acrylic polymer preferably contains at least 1 structural unit derived from an alkyl (meth) acrylate in addition to a structural unit derived from a monomer having a polyalkylene oxide chain and a structural unit having an acidic group.

Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, and isobornyl (meth) acrylate. The alkyl group of the alkyl (meth) acrylate may be any of linear, branched, or cyclic.

The structural units derived from the alkyl (meth) acrylate may be 1 kind alone or contain 2 or more kinds.

From the viewpoint of easy adjustment of the adhesive force suitable for the protective film, the alkyl (meth) acrylate is preferably one having a glass transition temperature of-30 ℃ or lower when it is a homopolymer.

The glass transition temperature of the homopolymer is obtained as follows: the homopolymer was measured for 10mg of a sample in a nitrogen gas flow using a Differential Scanning Calorimetry (DSC) (EXSTAR 6000, manufactured by Seiko Instruments Inc.) and measured at a temperature increase rate of 10 ℃/min, and the inflection point of the obtained DSC curve was defined as the glass transition temperature of the homopolymer.

Examples of the alkyl (meth) acrylate having a glass transition temperature of-30 ℃ or lower when a homopolymer is prepared include n-butyl acrylate (-57 ℃), 2-ethylhexyl acrylate (-76 ℃), n-dodecyl methacrylate (-65 ℃), n-octyl acrylate (-65 ℃), isooctyl acrylate (-58 ℃), isononyl acrylate (-58 ℃), isomyristyl acrylate (-56 ℃) and 2-acryloyloxyethyl-succinic acid (-40 ℃).

Among them, from the viewpoint of easy adjustment of the adhesive force suitable for the protective film, at least one selected from the group consisting of n-butyl acrylate and 2-ethylhexyl acrylate is preferable as the alkyl (meth) acrylate having a glass transition temperature of-30 ℃ or lower when made into a homopolymer.

When the specific (meth) acrylic polymer contains a structural unit derived from an alkyl (meth) acrylate (preferably a structural unit derived from an alkyl (meth) acrylate having a glass transition temperature of-30 ℃ or lower when the polymer is a homopolymer), the total content of the structural units derived from an alkyl (meth) acrylate (the structural units derived from an alkyl (meth) acrylate having a glass transition temperature of-30 ℃ or lower when the polymer is a homopolymer) is preferably 65 to 99% by mass, more preferably 75 to 97% by mass, and still more preferably 80 to 95% by mass, based on the mass of all the structural units. When the total content of the structural units derived from the alkyl (meth) acrylate is 65% by mass or more, the affinity (wettability) tends to be more excellent. Further, if the total content of the structural units derived from the alkyl (meth) acrylate is 99% by mass or less, the adhesive force during high-speed peeling tends not to be excessively high, and the high-speed peeling property tends to be more excellent.

The specific (meth) acrylic polymer may contain other structural units in addition to the structural unit derived from the monomer having a polyalkylene oxide chain, the structural unit having an acidic group, and the structural unit derived from the alkyl (meth) acrylate. The monomer that can form another structural unit is not particularly limited as long as it can copolymerize with a monomer having a polyalkylene oxide chain, a monomer represented by a structural unit having an acidic group and a structural unit derived from an alkyl (meth) acrylate, and can be appropriately selected according to the purpose.

Examples of the monomer capable of forming another structural unit include (meth) acrylic monomers having a hydroxyl group represented by 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate, (meth) acrylic monomers having an aromatic ring represented by phenoxyethyl (meth) acrylate and benzyl (meth) acrylate, (meth) acrylic monomers having a nitrogen atom represented by aminoethyl (meth) acrylate and dimethylaminoethyl (meth) acrylate, aromatic monovinyl monomers represented by styrene and α -methylstyrene, vinyl cyanide monomers represented by acrylonitrile and methacrylonitrile, and vinyl carboxylate monomers represented by vinyl formate, vinyl acetate and vinyl propionate.

The acid value of the specific (meth) acrylic polymer is from 9mgKOH/g to 65 mgKOH/g. If the acid value of the specific (meth) acrylic polymer exceeds 65mgKOH/g, the pressure-sensitive adhesive layer formed when the pressure-sensitive adhesive composition is crosslinked to form the pressure-sensitive adhesive layer becomes too hard, the adhesive force of the pressure-sensitive adhesive layer becomes low, and the protective film may be detached from the surface of the adherend while the adherend needs to be protected. In addition, the antistatic property tends to be easily lowered. If the acid value of the specific (meth) acrylic polymer is less than 9mgKOH/g, the pressure-sensitive adhesive layer is too soft, the adhesive strength tends to be high, and peeling tends to be difficult in high-speed peeling. From the viewpoint of further improving the high-speed peelability, the acid value of the specific (meth) acrylic polymer is preferably 9mgKOH/g to 50mgKOH/g, more preferably 9mgKOH/g to 35mgKOH/g, and still more preferably 16mgKOH/g to 25 mgKOH/g.

The acid value of the specific (meth) acrylic polymer or the (meth) acrylic oligomer described later is determined by the following calculation formula.

Acid value (mgKOH/g) { (a/100) ÷ B } × 56.1 × 1000 × C

Content ratio (mass%) of monomer having acidic group in all monomers used in specific (meth) acrylic polymer or (meth) acrylic oligomer

Molecular weight of monomer having acidic group used for specific (meth) acrylic polymer or (meth) acrylic oligomer

Number of acid groups contained in monomer 1 having acid groups

56.1 is the molecular weight of KOH.

When a plurality of monomers having an acid group are present, the acid value can be determined by summing up the values determined by the above formulae for each monomer.

The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is not particularly limited. The weight average molecular weight (Mw) of the specific (meth) acrylic polymer is preferably 10 to 100 ten thousand, more preferably 10 to 60 ten thousand, and still more preferably 10 to 40 ten thousand. When the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 10 ten thousand or more, the specific (meth) acrylic polymer can be more effectively inhibited from remaining on an adherend at the time of high-speed peeling, and the tendency to further reduce contamination of the adherend is exhibited. Further, if the weight average molecular weight (Mw) of the specific (meth) acrylic polymer is 100 ten thousand or less, the intimacy (wettability) tends to be further excellent.

The weight average molecular weight (Mw) of the specific (meth) acrylic polymer or (meth) acrylic oligomer described later is a value measured in accordance with the following items (1) to (3).

(1) The solution of the specific (meth) acrylic polymer or (meth) acrylic oligomer was applied to release paper, and dried at 100 ℃ for 2 minutes to obtain a film-like specific (meth) acrylic polymer or (meth) acrylic oligomer.

(2) Using the film-like specific (meth) acrylic polymer or (meth) acrylic oligomer obtained in the above (1) and tetrahydrofuran, a sample solution having a solid content concentration of 0.2 mass% was obtained.

(3) The weight average molecular weight (Mw) of the specific (meth) acrylic polymer or (meth) acrylic oligomer was measured as a standard polystyrene conversion value using Gel Permeation Chromatography (GPC) under the following conditions.

(Condition)

GPC: HLC-8220 GPC (manufactured by Tosoh corporation)

Column: 4 TSK-GEL GMHXL were used

Mobile phase solvent: tetrahydrofuran (THF)

Flow rate: 0.6 mL/min

Column temperature: 40 deg.C

The content of the specific (meth) acrylic polymer in the adhesive composition may be appropriately selected according to the purpose. The content of the specific (meth) acrylic polymer is preferably 80 to 99% by mass, more preferably 85 to 99% by mass, and still more preferably 90 to 98% by mass, based on the total mass of the solid content of the pressure-sensitive adhesive composition. The total mass of the solid content means the total mass of the residue obtained by removing volatile components such as a solvent from the binder composition.

The method for producing the specific (meth) acrylic polymer is not particularly limited. For example, the polymer can be produced by polymerizing monomers by a known polymerization method such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Among these polymerization methods, solution polymerization is preferable in that the treatment method is relatively simple and can be carried out in a short time.

Generally, solution polymerization is carried out by charging a polymerization vessel with a predetermined organic solvent, a monomer, a polymerization initiator, a catalyst and, if necessary, a chain transfer agent, and heating the mixture for a reaction for several hours under stirring in a nitrogen gas flow or under reflux of the organic solvent. The polymerization initiator is not particularly limited, and for example, an azo compound can be used.

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth) acrylic polymer can be adjusted to desired molecular weights by adjusting the reaction temperature, the reaction time, the amount of the organic solvent, and the type or amount of the catalyst.

[ (meth) acrylic acid-based oligomer ]

The adhesive composition according to one embodiment of the present invention preferably contains a (meth) acrylic oligomer having a weight average molecular weight of 3000 to 20000.

By further including a (meth) acrylic oligomer in the adhesive composition, the content of the antistatic agent can be suppressed. When the adhesive composition contains the polyether-modified silicone described later, the content of the polyether-modified silicone tends to be suppressed by further containing the (meth) acrylic oligomer. Thus, when the protective film is peeled off from the adherend, a part of the pressure-sensitive adhesive layer is less likely to remain on the adherend, and the occurrence of contamination of the adherend tends to be suppressed. Further, the reduction in compatibility of the specific (meth) acrylic polymer tends to be suppressed, and the occurrence of white turbidity tends to be suppressed.

From the viewpoint of suppressing the occurrence of contamination to an adherend, the (meth) acrylic oligomer preferably contains a structural unit derived from a monomer having a carboxyl group. The kind of the monomer having a carboxyl group is not particularly limited.

Examples of the structural unit derived from a monomer having a carboxyl group include the structural units derived from a monomer having a carboxyl group in the specific (meth) acrylic polymer described above. As the structural unit derived from a monomer having a carboxyl group, a structural unit derived from (meth) acrylic acid is preferable.

From the viewpoint of further reducing contamination to an adherend, the content of the structural unit derived from the monomer having a carboxyl group in the (meth) acrylic oligomer is preferably 0.1 to 10% by mass, more preferably 0.5 to 7.0% by mass, and still more preferably 1.0 to 5.0% by mass, based on the mass of the entire structural units.

The (meth) acrylic oligomer preferably contains a structural unit derived from an alkyl (meth) acrylate. The (meth) acrylic oligomer contains a structural unit derived from an alkyl (meth) acrylate, and thus the adhesive force can be easily adjusted.

Examples of the alkyl (meth) acrylate include the alkyl (meth) acrylates in the specific (meth) acrylic polymers described above.

The alkyl (meth) acrylate contained in the (meth) acrylic oligomer is preferably an alkyl (meth) acrylate having 4 to 12 carbon atoms, more preferably an alkyl (meth) acrylate having 4 to 12 carbon atoms and a branched chain, and still more preferably 2-ethylhexyl methacrylate, in view of exhibiting high durability even when the pressure-sensitive adhesive layer is exposed to a high-temperature and high-humidity environment.

The content of the structural unit derived from an alkyl (meth) acrylate ester contained in the (meth) acrylic oligomer is preferably 65 to 99% by mass, more preferably 75 to 95% by mass, and still more preferably 80 to 90% by mass, based on the mass of the entire structural unit, from the viewpoint of durability.

The (meth) acrylic oligomer preferably contains a structural unit derived from a monomer having a polyalkylene oxide chain. Examples of the monomer having a polyalkylene oxide chain include the monomers having a polyalkylene oxide chain in the specific (meth) acrylic polymers described above.

When the (meth) acrylic oligomer contains a structural unit derived from a monomer having a polyalkylene oxide chain, the average number of moles of alkylene oxide units added in the polyalkylene oxide chain is preferably 2 to 25 moles, and more preferably 9 to 23 moles, from the viewpoint that a sufficient antistatic effect can be obtained regardless of the material of an adherend. The average molar number of addition is the same as the average molar number of addition of the polyalkylene oxide chain in the specific (meth) acrylic polymer described above.

The content of the structural unit derived from the monomer having a polyalkylene oxide chain in the (meth) acrylic oligomer is preferably 5 to 30% by mass, more preferably 5 to 20% by mass, and particularly preferably 5 to 15% by mass, based on the mass of the entire structural units.

If the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 5% by mass or more, the antistatic property tends to be more excellent. Further, if the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 30% by mass or less, the content of the monomer remaining without being polymerized after the polymerization reaction is suppressed, and the contamination of the adherend can be further reduced.

The (meth) acrylic oligomer may contain other structural units in addition to the structural unit derived from the monomer having a carboxyl group, the structural unit derived from the alkyl (meth) acrylate, and the structural unit derived from the monomer having a polyalkylene oxide chain within the range in which the effects obtained by the embodiment of the present invention are exhibited.

In this case, the total content of the structural unit derived from the monomer having a carboxyl group, the structural unit derived from the alkyl (meth) acrylate, and the structural unit derived from the monomer having a polyalkylene oxide chain, which is contained in the total structural units of the (meth) acrylic oligomer, is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, based on the mass of the total structural units.

Examples of the monomer capable of forming another structural unit include a (meth) acrylic monomer having a hydroxyl group represented by 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate, a (meth) acrylic monomer having an aromatic ring represented by phenoxyethyl (meth) acrylate and benzyl (meth) acrylate, a (meth) acrylic monomer having a nitrogen atom represented by aminoethyl (meth) acrylate and dimethylaminoethyl (meth) acrylate, an aromatic monovinyl monomer represented by styrene and α -methylstyrene, a vinyl cyanide monomer represented by acrylonitrile and methacrylonitrile, and a vinyl carboxylate monomer represented by vinyl formate, vinyl acetate and vinyl propionate.

When the pressure-sensitive adhesive composition of one embodiment of the present invention contains a (meth) acrylic oligomer, the number of the (meth) acrylic oligomer may be 1 alone, or may be 2 or more different in monomer composition, weight average molecular weight, and the like.

The content of the (meth) acrylic oligomer is preferably 0.05 to 5.00 parts by mass with respect to 100 parts by mass of the specific (meth) acrylic polymer. When the content of the (meth) acrylic oligomer is 0.05 parts by mass or more, the adhesive force at the time of high-speed peeling does not become too high, and the high-speed peeling property tends to be excellent. When the content of the (meth) acrylic oligomer is 5.00 parts by mass or less, the protective film can be prevented from falling off from the surface of the adherend while the adherend needs to be protected, and the high-speed peelability tends to be more excellent. From the above viewpoint, the content of the (meth) acrylic oligomer is more preferably 0.10 to 3.00 parts by mass, and still more preferably 0.10 to 2.50 parts by mass.

The acid value of the (meth) acrylic oligomer is preferably from 10 to 200mgKOH/g, more preferably from 15 to 100mgKOH/g, and still more preferably from 15 to 50 mgKOH/g.

When the acid value of the (meth) acrylic oligomer is not less than 10mgKOH/g, the specific (meth) acrylic polymer can be sufficiently crosslinked with a crosslinking agent described later, and the high-speed peelability tends to be further improved. When the acid value of the (meth) acrylic oligomer is 200mgKOH/g or less, the antistatic property tends to be maintained more favorably.

The method of calculating the acid value of the (meth) acrylic oligomer is as described above.

The (meth) acrylic oligomer preferably has a weight average molecular weight of 3000 to 20000. If the weight average molecular weight of the (meth) acrylic oligomer is 3000 or more, the (meth) acrylic oligomer tends to be prevented from remaining on an adherend. Further, if the weight average molecular weight of the (meth) acrylic oligomer is 20000 or less, the haze of the pressure-sensitive adhesive layer tends to be reduced. From the above viewpoint, the weight average molecular weight of the (meth) acrylic oligomer is preferably 4000 to 15000, and more preferably 5000 to 10000.

The weight average molecular weight (Mw) of the (meth) acrylic oligomer is measured in the same manner as the method for measuring the weight average molecular weight (Mw) of the specific (meth) acrylic polymer described above.

< crosslinking agent >

The adhesive composition of an embodiment of the present invention comprises at least 1 crosslinker. The inclusion of the crosslinking agent enables the formation of a crosslinked structure by reacting with an acidic group represented by a carboxyl group in the specific (meth) acrylic polymer. The crosslinking agent is not particularly limited as long as it can react with an acid group in the specific (meth) acrylic polymer contained in the adhesive composition according to one embodiment of the present invention to form a crosslinked structure, and examples thereof include epoxy compounds, isocyanate compounds, aziridine compounds, and metal chelates. From the viewpoint that the crosslinking reaction is faster and the curing completion time can be shortened as compared with the case of using an isocyanate compound, an epoxy compound, or the like, a metal chelate compound is preferable as the crosslinking agent.

Examples of the metal chelate compound include a metal chelate compound in which a polyvalent metal atom is coordinately bonded to an organic compound. Examples of the polyvalent metal atom include Al, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn and Ti. Among them, Al, Zr, and Ti are preferable, and Al is more preferable, from the viewpoint of low cost and easiness of obtaining.

Examples of the atom in the organic compound to which the polyvalent metal atom is coordinately bonded include an oxygen atom and the like. Examples of the organic compound include alkyl esters, alcohol compounds, carboxylic acid compounds, ether compounds, and ketone compounds.

As the metal chelate compound, aluminum triacetylacetonate or the like which is easy to handle stably can be particularly preferably used. Further, the metal chelate may be 1 kind alone or 2 or more kinds in combination.

The equivalent of the crosslinking agent is preferably 0.3 to 2.0 equivalents, more preferably 0.4 to 1.5 equivalents, and still more preferably 0.6 to 1.2 equivalents, based on 1 equivalent of the acid group of the specific (meth) acrylic polymer.

If the content of the crosslinking agent is 0.3 equivalents or more, the adhesive force at the time of high-speed peeling tends to be suppressed low, and if the content of the crosslinking agent is 2.0 equivalents or less, the adhesive force to such an extent that the protective film does not unintentionally peel from the adherend tends to be imparted to the adhesive layer.

The equivalent weight of the crosslinking agent is a value calculated by the following formula.

Equivalent weight ═ a × B/C)/(D₁×E₁/F₁+D₂×E₂/F₂+····+D_n×E_n×F_n)

A ═ valence of metal of crosslinking agent

Mass fraction of the crosslinking agent (amount as solid component)

Molecular weight of C ═ crosslinking agent

D₁、D₂、···D_nThe content ratio (% by mass) of each monomer having an acidic group in all the monomers used for the specific (meth) acrylic polymer

E₁、E₂、···E_nThe number of acid groups contained in 1 molecule of each monomer having an acid group

F₁、F₂、···F_nMolecular weight of each monomer having an acidic group used for specific (meth) acrylic polymer

N represents the number of types of monomers used, and when 1 (meth) acrylic monomer is used, for example, only D is used in the calculation₁Without using D₂···D_n。

< antistatic agent >

The adhesive composition of one embodiment of the present invention contains at least 1 antistatic agent.

Examples of the antistatic agent include ionic compounds such as alkali metal salts and organic salts. As the antistatic agent, alkali metal salts and organic salts are preferable in terms of high ion dissociation and easy realization of excellent antistatic properties even when used in a small amount.

The alkali metal salt is only required to be a lithium ion (Li)⁺) Sodium ion (Na)⁺) Potassium ion (K)⁺) Rubidium (Rb)⁺) The metal salt, etc. which is a cation, is not particularly limited.

As the combination of alkali metal salts, for example, those selected from Li are preferably used⁺、Na⁺And K⁺With a cation selected from Cl^－、Br^－、I^－、BF₄ ^－、PF₆ ^－、SCN^－、ClO₄ ^－、CF₃SO₃ ^－、(FSO₂)₂N^－、(CF₃SO₂)₂N^－、(C₂F₅SO₂)₂N^－And (CF)₃SO₂)₃C^－A metal salt composed of an anion of at least 1 kind of (1).

Among them, the alkali metal salt is preferably selected from LiBr, LiI and LiBF in view of antistatic property₄、LiPF₆、LiSCN、LiClO₄、LiCF₃SO₃、Li(FSO₂)₂N、Li(CF₃SO₂)₂N、Li(C₂F₅SO₂)₂N and Li (CF)₃SO₂)₃Lithium salt of at least 1 of C, more preferably selected from LiClO₄、LiCF₃SO₃，Li(CF₃SO₂)₂N、Li(C₂F₅SO₂)₂N and Li (CF)₃SO₂)₃Lithium salt of at least 1 of C. These alkali metal salts may be used alone in 1 kind or in combination of 2 or more kinds.

The organic salt preferably contains an organic cation and a counterion thereof.

The melting point of the organic salt is preferably 30 ℃ or higher. When the melting point of the organic salt is 30 ℃ or higher, migration to an adherend is small, and contamination tends to be suppressed, which is preferable.

Examples of the organic cation include imidazole

Cation, pyridine

Cationic, alkyl pyrrolidines

Cation, ammonium cation having an organic group as a substituent, sulfonium cation having an organic group as a substituent, and

a cation. Among them, the organic cation is preferably selected from pyridines from the viewpoint of antistatic property

Cation and imidazole

At least 1 of the cations.

The anion which is a counter ion of the organic cation is not particularly limited, and may be an inorganic anion or an organic anion. Among them, the anion portion which is a counter ion of the organic cation is preferably a fluorine-containing anion containing a fluorine atom, a hexafluorophosphate anion (PF) because the antistatic property is particularly excellent₆ ^－) More preferably.

As the organic salt, pyridine is preferably mentioned

Salts, imidazoles

Salts, alkylammonium salts, alkylpyrazolesPyrrolidine derivatives

Salt, alkyl

Salts and the like. Among them, the organic salt is preferably selected from pyridine

Salts and imidazoles

At least 1 of the salts, more preferably pyridine

Cationic or imidazole

Salts of cations with fluorine-containing anions.

The content of the antistatic agent is preferably 0.05 to 1.50 parts by mass, more preferably 0.10 to 1.00 parts by mass, per 100 parts by mass of the specific (meth) acrylic polymer. When the content of the antistatic agent is 0.05 parts by mass or more per 100 parts by mass of the specific (meth) acrylic polymer, the antistatic property tends to be more excellent. When the content of the antistatic agent is 1.50 parts by mass or less, the efficiency of the antistatic effect tends to be higher with respect to the content of the antistatic agent.

[ polyether-modified Silicone ]

The adhesive composition of an embodiment of the present invention preferably contains at least 1 polyether modified silicone. Further, since the polyether-modified silicone has a reactive group, the adhesive film can be more easily peeled from the adherend and an adhesive film with less contamination to the adherend tends to be obtained.

When the polyether-modified silicone is used together with the specific (meth) acrylic polymer having the structural unit represented by the general formula (1), the antistatic agent, and the crosslinking agent, the antistatic property can be more effectively exhibited.

When the polyether-modified silicone has a polyether group and a hydroxyl group at the end of the polyether group, it shows more excellent antistatic properties and tends to effectively suppress contamination of an adherend. In particular, the polyether-modified silicone has a polyalkylene oxide chain having a hydroxyl group at the end in the molecule, and thus tends to effectively exhibit antistatic properties. Since the polyether-modified silicone is localized near the surface of the adhesive layer from the adhesive composition, there is a tendency that a polyalkylene oxide chain interacting with an alkali metal salt is localized near the surface of the adhesive layer. It is presumed that as a result, the surface resistance value of the surface of the pressure-sensitive adhesive layer is lowered. By modifying the silicone with the polyether in combination, there is a tendency that the amount of the antistatic agent in the adhesive composition can be suppressed.

From the viewpoint of further reducing antistatic properties and staining on an adherend, the polyether-modified silicone is preferably a polysiloxane compound containing a structural unit derived from a dialkylsiloxane and a structural unit derived from an alkyl (hydroxypolyalkyleneoxyalkyl) siloxane.

The number of carbon atoms in the alkyl group in the dialkylsiloxane is preferably 1 to 4, more preferably 1.

The number of carbon atoms in the polyalkylene oxide chain in the alkyl (hydroxypolyalkyleneoxyalkyl) siloxane is preferably 2 to 4, more preferably 2 to 3. The number of carbon atoms in the polyalkylene oxide chain in the alkyl (hydroxypolyalkyleneoxyalkyl) siloxane is preferably 1 to 100, more preferably 10 to 100. The number of carbon atoms of the alkyl group in the alkyl (hydroxypolyalkyleneoxyalkyl) siloxane is preferably 1 to 4.

When the polyether-modified silicone contains a structural unit derived from a dialkylsiloxane and a structural unit derived from an alkyl (hydroxypolyalkyleneoxyalkyl) siloxane, the content of the structural unit derived from a dialkylsiloxane is preferably 100 or less, and more preferably 1 to 80. The number of structural units derived from an alkyl (hydroxypolyalkyleneoxyalkyl) siloxane is preferably 2 to 100, more preferably 2 to 80.

The polyether-modified silicone is preferably a polysiloxane compound represented by the following general formula (3) from the viewpoints of adhesiveness, antistatic properties and further reduction of contamination to an adherend.

In the general formula (3), p represents the number of repeating dimethylsiloxane structural units and is a number of 0 to 100. q represents a number of 2 to 100 and is the number of repetitions of a methyl propylidene siloxane structural unit having a polyethylene oxide chain. In addition, a is the number of repetition of the ethylene oxide structural unit and represents a number of 1 to 100. Here, when the compound represented by the general formula (3) is a collection of a plurality of compounds, p, q, and a are the average values of the collection of compounds, and are rational numbers.

The number a of repetition of the ethylene oxide structural unit is a number of 1 to 100, preferably a number of 10 to 100. When a is 1 or more, sufficient conductivity is obtained and antistatic property tends to be further improved. When a is 100 or less, the compatibility with other components constituting the pressure-sensitive adhesive composition is improved, and the transparency of the pressure-sensitive adhesive layer tends to be further improved.

The number of repeating dimethylsiloxane structural units p is 0 to 100, preferably 1 to 80. The number q of repetitions of the methyl propylidene siloxane structural unit is a number of 2 to 100, preferably a number of 2 to 80. When q is 2 or more, sufficient conductivity is obtained and antistatic property tends to be further improved. When q is 100 or less, the compatibility with other components constituting the pressure-sensitive adhesive composition is improved, and the transparency of the pressure-sensitive adhesive layer tends to be improved.

The weight average molecular weight of the polyether-modified silicone is not particularly limited, and may be, for example, 5000 to 20000, and preferably 6000 to 15000.

Further, the HLB value of the polyether-modified silicone is not particularly limited. The HLB value is preferably 5 to 16, more preferably 7 to 15, from the viewpoint of compatibility with the resin, surface unevenness, and adhesiveness.

The HLB value is a scale representing the balance of hydrophilicity and hydrophobicity of the polyether-modified silicone. In the present specification, the HLB value is defined by the griffin method calculated from the following formula, but when the polyether-modified silicone is a commercially available product, the catalog data thereof is preferably used.

HLB { (sum of formula weights of hydrophilic group moieties)/(molecular weight of polyether-modified silicone) } × 20

The polyether modified organosilicon has a dimethyl siloxane structural unit and a methyl propylene siloxane structural unit with a polyethylene oxide chain in a molecule. These structural units may constitute a block copolymer or a random copolymer.

Specific examples of the polyether-modified silicone represented by the general formula (3) include "SF-8428", "FZ-2162" and "SH-3773M" (manufactured by Toray Dow Corning Co., Ltd.).

The polyether-modified silicone may be selected from the above-mentioned commercially available products. In addition, the polyether-modified silicone can be obtained by grafting an organic compound having an unsaturated bond and a polyethylene oxide chain onto a dimethylpolysiloxane backbone having silane by a hydrosilylation reaction.

The content of the polyether-modified silicone is preferably 0.05 to 1.00 parts by mass, more preferably 0.05 to 0.70 parts by mass, and still more preferably 0.05 to 0.30 parts by mass, based on 100 parts by mass of the specific (meth) acrylic polymer.

If the content of the polyether-modified silicone is 0.05 parts by mass or more, the antistatic property tends to be more excellent. Further, if the content of the polyether-modified silicone is 1.00 parts by mass or less, the occurrence of contamination (fog) to an adherend is suppressed, and the decrease in compatibility with the specific (meth) acrylic polymer and the occurrence of white turbidity tend to be suppressed.

The adhesive composition may include a polysiloxane compound represented by general formula (3) and a polyethyleneoxy-containing dimethylpolysiloxane compound having a structure different from that of general formula (3).

Examples of the polyethylene oxide chain-containing dimethylpolysiloxane compound having a structure different from that of general formula (3) include a compound in which the terminal of the polyethylene oxide chain is an alkoxy group or an acyloxy group, and a compound in which the main chain or the terminal does not have a side chain and has a polyethylene oxide chain.

Specific examples of the polyethylene oxide chain-containing dimethylpolysiloxane compound having a structure different from that of general formula (3) include "BY-16-201", "FZ-77", "FZ-2104", "FZ-2110", "FZ-2203", "FZ-2207", "FZ-2208", "L-7001", "L-7002", "SF-8427", "SH-3749" and "SH-8400" (manufactured BY Toray Dow Corning Co., Ltd.).

When the pressure-sensitive adhesive composition contains a polyethylene oxide chain-containing dimethylpolysiloxane compound having a structure different from that of general formula (3), the content thereof is preferably 0.05% by mass or less, more preferably 0.03% by mass or less, based on the total mass of the polysiloxane compound.

[ other ingredients ]

The pressure-sensitive adhesive composition may contain, in addition to the specific (meth) acrylic polymer, the crosslinking agent, the antistatic agent, and the optional (meth) acrylic oligomer and polyether-modified silicone, a weather-resistant stabilizer, a tackifier, a plasticizer, a softener, a release aid, a dye, a pigment, an inorganic filler, a surfactant, and the like as needed.

Protective film

The protective film according to an embodiment of the present invention includes an adhesive layer of a crosslinked product of the adhesive composition according to an embodiment of the present invention and a base material. The protective film according to an embodiment of the present invention has a tendency to have excellent high-speed peelability and antistatic property regardless of the material of the adherend by the pressure-sensitive adhesive layer having the pressure-sensitive adhesive composition according to an embodiment of the present invention.

The substrate used in the protective film according to an embodiment of the present invention is not particularly limited as long as the adhesive layer can be formed on the substrate.

From the viewpoint of inspection and management of optical parts by fluoroscopy, examples of the base material include films using resins such as polyester resins, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, and acrylic resins. Among them, from the viewpoint of surface protection performance, a film of a polyester resin is preferably used as the base material, and if practical, a film of a polyethylene terephthalate (PET) resin is more preferably used.

The thickness of the substrate may be generally 500 μm or less, preferably 5 to 300 μm, and more preferably 10 to 200 μm.

An antistatic layer may be provided on one or both sides of the substrate. The surface of the substrate on the side where the pressure-sensitive adhesive layer is provided may be subjected to corona discharge treatment or the like for the purpose of improving adhesion to the pressure-sensitive adhesive layer.

An adhesive layer of the adhesive composition according to one embodiment of the present invention is provided on a substrate.

As a method for forming the pressure-sensitive adhesive layer, for example, a method of diluting the pressure-sensitive adhesive composition with an appropriate solvent as it is or if necessary, coating the composition on a substrate, and then drying the coated substrate to remove the solvent can be employed.

In addition, the following method may be employed: first, a pressure-sensitive adhesive composition is applied to a release sheet comprising an appropriate film such as a paper or polyester film subjected to a release treatment with a silicone resin or the like, and the pressure-sensitive adhesive layer is formed by heating and drying, and then the pressure-sensitive adhesive layer side of the release sheet is pressed against a substrate to transfer the pressure-sensitive adhesive layer to the substrate.

The pressure-sensitive adhesive layer in one embodiment of the present invention is a pressure-sensitive adhesive layer obtained by crosslinking a specific (meth) acrylic polymer with a crosslinking agent. This can suppress the adhesive strength of the pressure-sensitive adhesive layer at the time of high-speed peeling to a low level.

The conditions for crosslinking the specific (meth) acrylic polymer with the crosslinking agent are not particularly limited. For example, the crosslinking reaction of the adhesive composition is terminated by aging at 23 ℃ and 50% RH for several tens of minutes to several days.

The thickness of the pressure-sensitive adhesive layer formed on the substrate can be appropriately set in accordance with the required adhesive force of the protective film, the surface roughness of the optical member, and the like. The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100. mu.m, preferably 5 μm to 50 μm, and more preferably about 10 μm to 30 μm.

Since the pressure-sensitive adhesive layer tends to be difficult to peel from an adherend at a high speed of peeling a large area if the pressure-sensitive adhesive layer has a high adhesive force, the adhesive force (peel force) at a peeling speed of 30 m/min (high speed peeling) is preferably less than 2.00N/25mm, and more preferably 1.00N/25mm or less.

In terms of preventing the protective film from coming off from the surface of the adherend during the period when the adherend needs to be protected, the adhesive force (peel strength) at a peel speed of 30 m/min (high-speed peeling) is preferably more than 0.15N/25mm, and more preferably 0.20N/25mm or more.

The use of the protective film according to an embodiment of the present invention is not particularly limited, and for example, the protective film according to an embodiment of the present invention may be laminated on the surface of the optical member to protect the surface of the optical member from being contaminated or damaged. The protective film according to an embodiment of the present invention may be attached to a metal plate such as iron or stainless steel (SUS) to protect the surface of the metal plate from contamination or damage.

When the protective film is used for an optical member, the optical member is subjected to various steps such as punching, inspection, conveyance, and assembly of a liquid crystal display panel in a state where the protective film is laminated on the optical member, and is subjected to heat and pressure treatment such as autoclave treatment and high-temperature aging treatment as necessary, and is peeled and removed from the optical member at a stage where surface protection is not necessary.

Examples of the optical member include members constituting an apparatus (optical apparatus) such as an image display apparatus and an input apparatus, and members used in these apparatuses. Specific examples of the optical member include a polarizing plate, a wavelength plate, a retardation plate, an optical compensation film, a brightness enhancement film, a light guide plate, a reflection film, an antireflection film, a transparent conductive film (ITO film), and the like.

[ examples ]

Hereinafter, an embodiment of the present invention will be specifically described with reference to examples. The present invention is not limited to these examples.

Production example A-1

Production of (meth) acrylic acid-based Polymer (A-1)

In a reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube and a reflux condenser, 70.0 parts by mass of ethyl acetate was charged, and in another vessel, 60.0 parts by mass of n-Butyl Acrylate (BA), 24.9 parts by mass of 2-ethylhexyl acrylate (2EHA), 10.0 parts by mass of aronex M-5300 (monomer represented by general formula (1a), manufactured by east asian co. ltd.) and 5.1 parts by mass of methoxypolyethylene glycol acrylate (average number of moles of alkylene oxide units added 9) (MePEGA) were charged as monomers and mixed to prepare a monomer mixture. 20.0 mass% of the monomer mixture was charged into a reaction vessel, the air in the reaction vessel was replaced with nitrogen, 0.01 part by mass of azobisisobutyronitrile (hereinafter, also referred to as "AIBN") was added as a polymerization initiator, and the temperature of the mixture in the reaction vessel was raised to 85 ℃ under stirring in a nitrogen atmosphere to start an initial reaction. After the initial reaction was substantially completed, the mixture of the remaining 80.0 mass% of the monomer mixture and 15.0 parts by mass of ethyl acetate and 0.10 part by mass of AIBN were gradually added thereto, respectively, and the reaction was carried out for about 2 hours, followed by another 2 hours. Thereafter, a solution in which 0.10 parts by mass of AIBN was dissolved in 25.0 parts by mass of ethyl acetate was added dropwise to the above mixture over 1 hour, and reacted for 1.5 hours. After the reaction, a solution of the (meth) acrylic polymer (A-1) was obtained.

The solid content of the solution of the (meth) acrylic polymer (A-1) was 48.0% by mass. The acid value and the weight average molecular weight (Mw) of the obtained (meth) acrylic polymer (a-1) are shown in table 1.

The "solid content" refers to a residue obtained by removing a solvent from a solution of a (meth) acrylic polymer. The acid value and the weight average molecular weight (Mw) were determined by the methods described above.

The acid value was calculated as follows.

Acid value (mgKOH/g) { (a/100) ÷ B } × 56.1 × 1000 × C

Content (mass%) of a monomer having an acidic group in all monomers used in a (meth) acrylic polymer or a (meth) acrylic oligomer: 10.0

Molecular weight of ARONIX M-5300 of a monomer having an acidic group as a structural unit of the (meth) acrylic polymer (a-1): 300.4

C ═ the number of acidic groups contained in the molecule of monomer 1 having an acidic group: 1

Acid value { (10.0/100) ÷ 300.4} × 56.1 × 1000 × 1 { (18.7)

Production examples A-2 to A-21

Production of (meth) acrylic polymers (A-2) to (A-21)

Solutions of (meth) acrylic polymers (A-2) to (A-21) were prepared in the same manner as in production example A-1, except that the monomer components shown in Table 1 were changed and the amount of the polymerization initiator was appropriately adjusted in production example A-1. The acid value and the weight average molecular weight (Mw) of the obtained (meth) acrylic polymer are shown in table 1.

The acid value and the weight average molecular weight (Mw) were determined by the methods described above.

Production example B

Production of (meth) acrylic oligomer (B)

100.0 parts by mass of methyl ethyl ketone and 10.0 parts by mass of methoxypolyethylene glycol methacrylate (average molar number of alkylene oxide units added: 23) (MePEGMA) were charged into a reaction vessel equipped with a stirring blade, a thermometer, a nitrogen inlet, a cooler, and a dropping funnel, and heated to reflux temperature under stirring in a nitrogen atmosphere. A mixed solution of 85.0 parts by mass of 2-ethylhexyl methacrylate (2EHMA), 5.0 parts by mass of Acrylic Acid (AA), 100.0 parts by mass of methyl ethyl ketone, and 5.0 parts by mass of azobisisobutyronitrile, which had been mixed in advance, was added to the dropping funnel, and the mixture was gradually added to the reaction vessel at the reflux temperature over 120 minutes. Thereafter, the reaction was carried out for 240 minutes while maintaining the reflux temperature, and the reaction was terminated.

The solid content of the obtained solution of the (meth) acrylic oligomer (B) was 33.0 mass%. The acid value and the weight average molecular weight (Mw) of the (meth) acrylic oligomer (B) are shown in table 1.

The acid value and the weight average molecular weight (Mw) were determined by the methods described above.

[ Table 1]

Abbreviations in table 1 are as follows. In table 1, "-" indicates that the component is not contained.

BA: acrylic acid n-butyl ester

2 EHA: 2-ethylhexyl acrylate

2 HEA: 2-Hydroxyethyl acrylate

2 EHMA: 2-ethylhexyl methacrylate

2 MTA: 2-Methoxyethyl acrylate

M-5300: omega-carboxy-polycaprolactone (n 1. about.2) monoacrylate (monomer represented by the general formula (1 a)) (trade name: ARONIX M-5300, manufactured by Toyo Synthesis Co., Ltd.)

AA: acrylic acid

HOA-MS: 2-Acryloxyethyl-succinic acid (monomer represented by the general formula (1 a)) (trade name: LIGHT ACRYLATE HOA-MS (N), manufactured by Kyoeisha chemical Co., Ltd.)

MePEGA: methoxypolyethylene glycol acrylate (average molar number of alkylene oxide units added: 4 or 9, respectively)

MePEGMA: methoxypolyethylene glycol methacrylate (average number of moles of alkylene oxide units added: 23)

MePPGA: methoxypolypropylene glycol acrylate (average molar number of alkylene oxide units added: 2)

< example 1 >

Into a four-necked flask equipped with a stirring blade, a thermometer, a cooler and a dropping funnel were charged 208.3 parts by mass (100 parts by mass in terms of solid content) of the solution (48.0 parts by mass in terms of solid content) of the (meth) acrylic polymer (A-1) prepared in production example A-1, 1.2 parts by mass (0.40 parts by mass in terms of solid content) of the solution (33.0 parts by mass in terms of solid content) of the (meth) acrylic oligomer (B) prepared in production example B, and 0.150 parts by mass of Li (CF) as an antistatic agent₃SO₂)₂N (LiTFSI manufactured by Setan chemical Co., Ltd.) was added to the flask, and the mixture was stirred while keeping the liquid temperature in the flask at about 25 ℃ for 4 hours. Adding into it0.100 parts by mass of SH-3773M (solid content 100.0 mass%, product of Toray Dow Corning Co., Ltd.) as a polyether-modified silicone and 25.7 parts by mass (solid content 9.72 mass%) of an Aluminum Chelate diluent (solid content 9.72 mass%) obtained by diluting Aluminum triacetylacetone (trade name: Aluminum Chemate A, product of Kawaken Fine Chemical Co., Ltd.) with acetylacetone and toluene as a crosslinking agent were added thereto and sufficiently stirred to obtain an adhesive composition solution.

Using this adhesive composition solution, a test protective film was produced by the following test protective film production method, and various physical property tests were performed. The obtained results are shown in table 2.

The equivalent of aluminum triacetylacetonate (aluminum chelate) contained in the above-mentioned aluminum chelate dilution is the amount based on the acid group contained in the (meth) acrylic polymer.

The equivalent of the aluminum chelate compound is calculated by the method already described, specifically, as follows.

Equivalent weight ═ a × B/C)/(D₁×E₁/F₁+D₂×E₂/F₂+····+D_n×E_n×F_n)

A ═ valence of the metal of the aluminum chelate: 3.0

B ═ parts by mass of aluminum chelate (amount based on solid content): 2.5 parts by mass

C ═ molecular weight of aluminum chelate: 324.3

D₁Content (mass%) of each monomer having an acidic group in all monomers used for the (meth) acrylic polymer: 10.0% by mass

E₁The number of acid groups contained in 1 molecule of each monomer having an acid group: 1

F₁Molecular weight of aronexi M-5300: 300.4

n is the kind of (meth) acrylic monomer used: 1

Equivalent weight ═ a × B/C)/(D₁×E₁/F₁)＝(3×2.5/324.3)/(10.0×1/300.4)＝0.69

[ evaluation ]

(1) Production of protective film for test

As a substrate, a polyethylene terephthalate (PET) Film (trade name: Teijin Tetoron Film Type G2, thickness 38 μm, manufactured by Teijin DuPont Film Co., Ltd.) was coated in an amount of 20G/m after drying²The adhesive composition solution was applied and dried at 100 ℃ for 60 seconds by a hot air circulation dryer. Subsequently, the PET Film coated with the adhesive composition solution and a release Film (trade name: Film binder 100E-0010 NO23, thickness 100 μm, manufactured by Tenssen industries, Ltd.) surface-treated with a silicone-based release agent were superposed so that the coated surface of the adhesive composition solution and the surface-treated surface of the release Film were in contact with each other to prepare a laminate. The laminate was bonded by pressure bonding with a pair of pressure rollers, and then aged at 23 ℃ and 50% RH for 1 hour to prepare a protective film for testing.

< production of test samples 1 to 4 >

< test sample 1 >

The release film of the protective film for test produced in (1) above was peeled off, and a cellulose Triacetate (TAC) film (trade name: Lonza TAC100, manufactured by PANAC corporation) as an adherend was stacked, and pressure-bonded by a pressure roller, and cut into a size of 25mm × 150mm to produce a test sample 1 (for TAC).

< test sample 2 >

The release film of the protective film for test prepared in (1) was peeled off, and was laminated on a PET film (trade name: COSMOSHINE A-4300, manufactured by Toyo Seiki Co., Ltd.) as an adherend, and the laminate was pressure-bonded by a pressure roller, and cut into a size of 25mm × 150mm to prepare a test sample 2 (for PET).

< test sample 3 >

The release Film of the protective Film for test produced in (1) above was peeled off, and a PET (hereinafter, also referred to as "HCPET") Film (trade name: KB Film G01S, manufactured by Kimoto corporation) having a hard-coated surface as an adherend was laminated so that the hard-coated surface was in contact with the pressure-sensitive adhesive layer, and the Film was bonded by pressure bonding using a pressure roller, and cut into a size of 25mm × 150mm to produce a test sample 3 (for HCPET).

< test sample 4 >

The release film of the protective film for test produced in (1) above was peeled off, and a stainless steel plate (BASUS) (trade name: SUS304(BA), manufactured by waltek corporation) which was cold-rolled and then bright-annealed (non-oxidation-tempered) as an adherend was overlaid, and the laminate was pressure-bonded by a pressure roller, and cut into a size of 25mm × 150mm to produce a test sample 4 (corresponding to BASUS).

(2) High speed peelability

The test samples 1 to 4 prepared above were left at 23 ℃ and 50% RH for 24 hours. Thereafter, using the apparatus shown in fig. 1, the adhesive force at 180 ° peel was measured under high speed conditions at a peel speed of 30 m/min. Specifically, as shown in fig. 1, a test sample was placed on a glass plate so that the glass plate was in contact with the surface of an adherend, one end of the test sample was held, and the test sample was pulled in a 180 ° direction along the surface of the glass plate, whereby the base material (PET film) was peeled off from the adhesive layer.

The high-speed peelability was evaluated according to the following evaluation criteria, and the results are shown in table 2.

[ evaluation standards ]

AA: the adhesive strength to all adherends is 0.20N/25mm to 1.00N/25mm, the peelability is very excellent, and the adhesive strength is excellent.

A: the adhesive strength to all adherends is more than 0.15N/25mm and less than 2.00N/25mm, and the adhesive strength to at least 1 adherend is more than 0.15N/25mm and less than 0.20N/25mm, or more than 1.00N/25mm and less than 2.00N/25mm, and the peelability is excellent and the adhesive strength is also excellent.

B: the adhesive strength to at least 1 adherend was 2.00N/25mm or more, and the releasability was slightly poor, which was not acceptable.

C: the adhesive strength to at least 2 adherends was 2.00N/25mm or more, and the releasability was poor and was not within the allowable range.

D: the adhesive force to at least 1 adherend is 0.15N/25mm or less, and the adhesive force is extremely poor in a range not allowed as a protective film, and the adhesive force is unexpectedly peeled off from the surface of the adherend.

(3) Antistatic properties

After the test samples 1 to 4 prepared in the above were respectively left to stand at 23 ℃ and 50% RH for 24 hours, the samples were peeled at a peeling speed of 30 m/min (high speed) in the 180 ° direction as shown in fig. 1 in the same manner as in the above (2).

The potential of the surface of the adherend generated upon peeling was measured by a potential measuring instrument (trade name: KSD-0303, manufactured by spring Motor Co., Ltd.) fixedly disposed at a predetermined position (position 10mm from the surface of the adherend). The absolute value of the measured value was used as a stripping charging voltage, and antistatic properties were evaluated according to the following evaluation criteria, and the results are shown in table 2.

[ evaluation standards ]

AA, the absolute value of the peeling electrification voltage of all the adherends is 0.5kv or less, and the antistatic property is very excellent.

A: the absolute value of the peeling electrification voltage of all adherends exceeds 0.5kv and is 1.0kv or less, and the antistatic property is excellent.

B: the absolute value of the peeling electrification voltage of at least 1 adherend is more than 1.0kv and 1.5kv or less, and the antistatic property is slightly inferior, which is an unallowable range.

C: the absolute value of the peeling electrification voltage of at least 1 adherend exceeded 1.5kv, and the antistatic property was poor, which was not acceptable.

< example 2 to example 23 and comparative examples 1 to 8 >

Adhesive compositions shown in table 2 were prepared in the same manner as in example 1, except that the composition in example 1 was changed to the composition shown in table 2. The obtained adhesive composition was used to prepare a protective film for testing, and test samples 1 to 4 were prepared using the protective film for testing. The results obtained by performing the evaluations using these samples 1 to 4 are shown in table 2.

Abbreviations in table 2 are as follows. In Table 2, "-" indicates that the component is not contained.

LiTFSI: lithium bis (trifluoromethanesulfonylimide), Li (CF)₃SO₂)₂N (manufactured by Sentian chemical industry Co., Ltd.)

LiTFS: lithium trifluoromethanesulfonate, LiCF₃SO₃(manufactured by Sentian chemical industry Co., Ltd.)

Ionic solid a: n-hexyl pyridine

·PF₆ ^－(having hexylpyridine as the organic cation)

Ionic organic salt, melting Point 45 ℃ C.)

SH-3773M: a dimethylsiloxane compound having a polyalkylene oxide chain introduced into a side chain thereof (Toray Dow Corning Co., Ltd., a polyalkylene oxide chain having a hydroxyl group at the end and an HLB value of 8)

Aluminum chelate complexes: aluminum triacetylacetone (trade name: Aluminum Chemate A, manufactured by Kawaken Fine Chemical Co., Ltd.) was diluted with toluene and acetylacetone to give a solution having a solid content of 9.7 mass%

The protective films of the crosslinked materials of the pressure-sensitive adhesive compositions of examples 1 to 23, which contained the (meth) acrylic polymer, the crosslinking agent and the antistatic agent having an acid value in the range of 9mgKOH/g to 65mgKOH/g and a content of the structural unit derived from the monomer having a polyalkylene oxide chain in the range of more than 1% by mass and less than 20% by mass relative to the mass of the entire structural units, were excellent in both high-speed releasability and antistatic property when used for any adherend.

In particular, the protective films having the crosslinked products of the adhesive compositions of examples 6, 8, 11 and 17 were more excellent in high-speed releasability and antistatic property.

On the other hand, comparative examples 1, 2, 7 and 8, which include (meth) acrylic polymers containing no structural unit derived from a monomer having a polyalkylene oxide chain, and comparative example 3, which includes a (meth) acrylic polymer having a content of a structural unit derived from a monomer having a polyalkylene oxide chain of 1.0 mass% based on the mass of all the structural units, all had a high value of peel charge voltage relative to PET, and were inferior in antistatic property. Comparative example 4, which contained a (meth) acrylic polymer having a content of a structural unit derived from a monomer having a polyalkylene oxide chain of 20 mass% based on the mass of the entire structural units, was inferior in high-speed peelability to PET.

In addition, comparative examples 5 and 6, which included (meth) acrylic polymers having acid values outside the range of 9mgKOH/g to 65mgKOH/g, were inferior in high-speed peelability, respectively. Comparative example 6, which had an acid value of 65mgKOH/g or more, was inferior in not only high-speed releasability but also antistatic property.

As described above, the protective film having the crosslinked product of the pressure-sensitive adhesive composition according to one embodiment of the present invention has a sufficient adhesive force to prevent the protective film from coming off from the surface of the adherend when the adherend needs to be protected, regardless of the material of the adherend, and also has a low adhesive force when the protective film is peeled off at a high speed, and is excellent in antistatic properties. Therefore, the protective film having the crosslinked product of the pressure-sensitive adhesive composition according to one embodiment of the present invention is excellent in high-speed peelability and antistatic property regardless of the material of the adherend.

Claims (7)

1. An adhesive composition for protective films comprising a (meth) acrylic polymer, a crosslinking agent and an antistatic agent,

the (meth) acrylic polymer has an acid value of 18.7 to 20.9mgKOH/g, a weight-average molecular weight of 10 to 100 ten thousand, a content of a structural unit derived from a monomer having a polyalkylene oxide chain of more than 1% by mass and less than 10% by mass relative to the mass of all the structural units, and an average number of moles of alkylene oxide units added in the polyalkylene oxide chain of 4 to 9 mol.

2. The adhesive composition for protective films according to claim 1, wherein the (meth) acrylic polymer comprises a structural unit represented by the following general formula (1),

in the general formula (1), R¹And L represents a 2-valent linking group composed of at least 1 selected from the group consisting of an alkylene group, an arylene group, a carbonyl group, and an oxygen atom.

3. The pressure-sensitive adhesive composition for protective films according to claim 1 or 2, wherein the (meth) acrylic polymer contains a structural unit derived from an alkyl (meth) acrylate, and the content of the structural unit derived from an alkyl (meth) acrylate is 65 to 99% by mass based on the mass of all the structural units.

4. The adhesive composition for protective films according to claim 1 or 2, further comprising a (meth) acrylic oligomer having a weight average molecular weight of 3000 to 20000, wherein the content of the (meth) acrylic oligomer is 0.05 to 5.00 parts by mass per 100 parts by mass of the (meth) acrylic polymer.

5. The adhesive composition for protective films according to claim 4, wherein the (meth) acrylic oligomer contains a structural unit derived from a monomer having a polyalkylene oxide chain, and the content of the structural unit derived from the monomer having a polyalkylene oxide chain is 5 to 30% by mass based on the mass of all the structural units.

6. The adhesive composition for protective films according to claim 1 or 2, wherein the crosslinking agent is a metal chelate.

7. A protective film comprising a substrate and an adhesive layer, wherein the adhesive layer is a crosslinked product of the adhesive composition for protective films according to any one of claims 1 to 6.

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