KR102178126B1 - Pressure-sensitive adhesive composition for surface protection film and surface protection film - Google Patents

Abstract

A pressure-sensitive adhesive composition for a surface protective film and a surface having the pressure-sensitive adhesive layer capable of forming a pressure-sensitive adhesive layer that reduces contamination and metal corrosiveness to an adherend, has appropriate adhesion, and suppresses an increase in adhesion after a high-temperature manufacturing process Provide a protective film. The pressure-sensitive adhesive composition for a surface protective film is obtained by solution polymerization of a polymerizable monomer in which (meth)acrylic resin (A) contains an alkyl (meth)acrylate having 4 or less carbon atoms in the alkyl group in an amount within the range of 30.0 to 99% by mass. , In addition, it has the following characteristics (a1), (a2) and (a3), and the gel fraction of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a surface protective film using a hexamethylene diisocyanate crosslinking agent (B) is 90.0~ It is characterized by containing in an amount within the range of 99.9% by mass. (a1) The weight average molecular weight (Mw) in terms of polystyrene measured by the GPC method is 1.2 million to 2 million. (a2) The molecular weight distribution (Mw/Mn) is 4-9. (a3) The acid value is 2 mgKOH/g or less.

Description

A pressure-sensitive adhesive composition for a surface protective film, and a surface protective film TECHNICAL FIELD [PRESSURE-SENSITIVE ADHESIVE COMPOSITION FOR SURFACE PROTECTION FILM AND SURFACE PROTECTION FILM}

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

Recently, liquid crystal displays such as smartphones and tablet PCs, and display devices such as plasma displays have been widely used. Such a display device has a thin multi-layered structure having various functions when viewed in its cross-section, and optical functional films forming these multi-layered structures are increasingly becoming highly functional. In order to stably produce and store a display device comprising such a functional film for optics having such a high function, it is indispensable to affix a surface protective film for preventing damage to the surface of the display device.

The surface protective film usually has a film-like support and an adhesive layer formed on at least one surface thereof, and the surface protective film adheres to the adherend by contacting the adhesive layer portion with the adherend. The surface protective film is required to exhibit sufficient adhesive strength when affixed to an adherend, and less adherence of residues due to the adhesive layer when peeled off.

In addition, as an example of an optical functional film used in a display device, an indium tin oxide (ITO) film, which is actively developed and produced for a touch panel, is often manufactured through a high-temperature manufacturing process. Therefore, it is required that the surface protective film or the pressure-sensitive adhesive layer does not cause problems such as corrosion of metal oxides or peeling failure due to an increase in adhesive strength even after a high-temperature process.

As an adhesive for a surface protective film, for example, Patent Document 1 discloses an adhesive formed by an acrylic resin and a crosslinking agent. However, since the gel fraction of the pressure-sensitive adhesive is as low as 0 to 30% by mass, it is easily contaminated, and there is a problem that the adhesive strength after heat resistance is increased.

Patent Document 2 describes a pressure-sensitive adhesive in which an acrylic resin obtained by copolymerizing a monomer containing a carboxyl group-containing monomer and a crosslinking agent are blended. However, the weight average molecular weight of the acrylic resin disclosed in Examples of Patent Document 2 is 600,000, and it cannot be said that the molecular weight is sufficiently large, and stain resistance is not sufficient. In addition, since the amount of the carboxyl group-containing monomer used is relatively high, 5 to 10% by mass among 100% by mass of the polymerizable monomer forming the acrylic resin, when affixed to an adherend containing a metal oxide or the like, the adherend is corroded and further heat resistant. There is a problem that the adhesive strength afterwards increases.

Patent Document 3 describes an acrylic resin obtained by copolymerizing a monomer containing a specific (meth)acrylic acid alkyl ester and a carboxyl group-containing monomer, and an adhesive formed by an epoxy crosslinking agent. However, the flexibility of the pressure-sensitive adhesive layer is sufficient because an epoxy crosslinking agent is used in addition to the corrosion of the adherend containing metal oxides, etc., due to the high acid value of the acrylic resin as high as 16 to 120 mgKOH/g, and the increase in adhesion after heat resistance. Without doing so, there is a problem that the wettability to the adherend is poor.

Japanese Patent Application Publication No. 2009-79074 Japanese Unexamined Patent Publication No. 2007-126606 International Publication No. 2011/148721

The subject of the present invention is to reduce contamination and metal corrosiveness to adherends, including optical functional films such as hard coat films, antireflection films, and ITO films, to have adequate adhesion, and to increase adhesion after high-temperature manufacturing processes. It is to provide the pressure-sensitive adhesive composition for a surface protective film capable of forming the pressure-sensitive adhesive layer suppressing the pressure-sensitive adhesive layer and a surface protective film having the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive composition for a surface protective film of the present invention is a pressure-sensitive adhesive composition for a surface protective film containing a (meth)acrylic resin (A) and a hexamethylenediisocyanate-based crosslinking agent (B),

The (meth)acrylic resin (A) is obtained by solution polymerization of a polymerizable monomer containing a (meth)acrylic acid alkyl ester having 4 or less carbon atoms in the alkyl group in an amount within the range of 30.0 to 99.9% by mass, and the following (a1) , has the characteristics of (a2) and (a3),

It is characterized in that it contains the hexamethylene diisocyanate-based crosslinking agent (B) in an amount such that the gel fraction of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a surface protective film is in the range of 90.0 to 99.9% by mass.

(a1) the weight average molecular weight (Mw) in terms of polystyrene measured by the gel permeation chromatography method (GPC method) is in the range of 1.2 million to 2 million,

(a2) the molecular weight distribution (Mw/Mn) is in the range of 4 to 9,

(a3) The acid value is 2 mgKOH/g or less.

The pressure-sensitive adhesive composition for a surface protective film of the present invention contains the hexamethylenediisocyanate-based crosslinking agent (B) in an amount within the range of 2 to 15 parts by mass per 100 parts by mass of the (meth)acrylic resin (A). desirable.

In addition, the surface protective film of the present invention is a surface protective film having a film-like support and an adhesive layer formed on at least one surface of the film-like support,

The pressure-sensitive adhesive layer is obtained by solution polymerization of a polymerizable monomer containing a (meth)acrylic acid alkyl ester having 4 or less carbon atoms of the alkyl group in the (meth)acrylic resin (A) in an amount within the range of 30.0 to 99.9 mass%, and It has the characteristics of (a1), (a2) and (a3),

A pressure-sensitive adhesive composition for a surface protective film containing the hexamethylene diisocyanate-based crosslinking agent (B) in an amount such that the gel fraction of the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a surface protective film is in the range of 90.0 to 99.9% by mass. It is characterized by being made.

The pressure-sensitive adhesive composition for a surface protective film of the present invention contains a (meth)acrylic resin obtained by solution polymerization of a polymerizable monomer containing a specific amount of a specific (meth)acrylic acid ester and a specific crosslinking agent, so that sufficient adhesive strength can be expressed. In addition, it is possible to form an adhesive layer that does not contaminate the adherend and does not cause metal corrosion on the adherend.

Advantageous Effects of Invention According to the present invention, when affixed to an adherend, a sufficient adhesive force is exhibited, contamination and metal corrosion resistance to the adherend is reduced, and an increase in adhesive force after a high-temperature manufacturing process is suppressed, resulting from the pressure-sensitive adhesive layer. It is possible to provide a pressure-sensitive adhesive composition for a surface protective film capable of forming a pressure-sensitive adhesive layer with less adhesion of residues, and a surface protective film having the pressure-sensitive adhesive layer.

Hereinafter, the pressure-sensitive adhesive composition for a surface protective film and a surface protective film of the present invention will be described. Hereinafter, the pressure-sensitive adhesive composition for a surface protective film of the present invention is also simply referred to as "adhesive composition".

In the present invention, acryl and methacrylic are collectively referred to as "(meth)acrylic".

(Adhesive composition for surface protection film)

The pressure-sensitive adhesive composition for a surface protective film of the present invention contains a (meth)acrylic resin (A) and a hexamethylenediisocyanate-based crosslinking agent (B) (hereinafter also referred to as an HDI-based crosslinking agent (B)), and this pressure-sensitive adhesive The composition usually contains an organic solvent (C).

[( Meta )Acrylic resin (A)]

The (meth)acrylic resin (A) is a polymer of a polymerizable monomer containing an alkyl (meth)acrylate (i) having 4 or less carbon atoms in the alkyl group, and is obtained by solution polymerization of the polymerizable monomer in an organic solvent. In this way, the (meth)acrylic resin (A) has a structural unit derived from (i).

As the polymerizable monomer, in addition to the (meth)acrylic acid alkyl ester (i) having an alkyl group having 4 or less carbon atoms, (meth)acrylic acid ester (ii), an acid group-containing monomer (iii), another polar group-containing monomer (iv), and other monomers (v ) You may contain at least 1 type selected from. For example, a polymerizable monomer containing the above (i) and (iv) and, if necessary, the above (ii), (iii) or (v) can be mentioned.

Hereinafter, the (meth)acrylic acid alkyl ester (i) is referred to as "monomer (i)", the (meth)acrylic acid ester (ii) is referred to as "monomer (ii)", and the acid group-containing monomer (iii) is referred to as "monomer (iii)". The polar group-containing monomer (iv) is also referred to as "monomer (iv)", and other monomers (v) are also referred to as "monomer (v)".

<< of alkyl group Carbon number Less than 4 ( Meta ) Acrylic acid Alkyl ester (i)》

The monomer (i) is represented by the following formula (i-1), for example.

R ¹ is a hydrogen atom or a methyl group, and R ² is an alkyl group having 4 or less carbon atoms.

The alkyl group for R ² is any one of methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group and sec-butyl group.

As the monomer (i), for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (Meth)acrylate, tert-butyl (meth)acrylate, and sec-butyl (meth)acrylate are mentioned.

Monomer (i) may be used individually by 1 type, and may use 2 or more types.

The amount of monomer (i) used in 100% by mass of the polymerizable monomer forming the (meth)acrylic resin (A) is 30.0 to 99.9% by mass, preferably 33.0 to 99.9% by mass, and more preferably 50.0 to 99.5% by mass , More preferably 50.0 to 99.0 mass%, particularly preferably 50.0 to 98.0 mass%.

When the amount of the monomer (i) is within the above range, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition containing the (meth)acrylic resin (A) has sufficient adhesive strength to an adherend such as an optical functional film, and peels off during transport or It can suppress lift.

《( Meta )Acrylic acid ester (ii)》

The monomer (ii) is represented by the following formula (ii-1), for example.

R ³ is a hydrogen atom or a methyl group. R ⁴ is an organic group other than an alkyl group having 4 or less carbon atoms and not having a polar group such as a hydroxyl group, an amino group, an amide group, a cyano group, and a carboxyl group.

Examples of R ⁴ include alicyclic groups such as an alkyl group having 5 or more carbon atoms and a cycloalkyl group, an aryl group, an aralkyl group, and an organic group having an ether bond. The number of carbon atoms in the alkyl group is usually 5 to 24. The cycloalkyl group usually has 5 to 15 carbon atoms. The aryl group usually has 6 to 10 carbon atoms. The aralkyl group usually consists of an alkylene group having 1 to 6 carbon atoms and an aryl group having 6 to 10 carbon atoms. As an organic group having an ether bond, a group represented by the following formula (g-1) is mentioned, for example.

Here, R ⁵ is an alkylene group, R ⁶ is an alkyl group or an aryl group, and n is an integer of 1 or more. The number of carbon atoms of the alkylene group is usually 1 to 10, preferably 1 to 5. The number of carbon atoms of the alkyl group is usually 1 to 10, preferably 1 to 4, and the number of carbon atoms of the aryl group is usually 6 to 10, preferably 6. n is preferably 1 to 20, more preferably 1 to 4, and still more preferably 1 to 2.

As the monomer (ii), for example, (meth)acrylic acid alkyl ester having an alkyl group having 5 or more carbon atoms, alicyclic group-containing (meth)acrylic acid ester, such as (meth)acrylic acid cycloalkyl ester, (meth)acrylic acid aryl ester, (meth)acrylic acid Aralkyl ester, alkoxyalkyl (meth)acrylate, alkoxypolyalkylene glycol mono(meth)acrylate, and (meth)acrylic acid aryloxyalkylester.

Examples of the (meth)acrylic acid alkyl ester having an alkyl group having 5 or more carbon atoms that can be used in the present invention include n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2 -Ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth) ) Acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and isostearyl (meth) acrylate.

In addition, as (meth)acrylic acid esters containing alicyclic groups such as (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid aryl esters and (meth)acrylic acid aralkyl esters, for example, cyclohexyl (meth)acrylate, isobornyl (meth) ) Acrylate, phenyl (meth) acrylate, and benzyl (meth) acrylate.

Moreover, as alkoxyalkyl (meth)acrylate, for example, methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate ) Acrylate, 3-ethoxypropyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, and 4-ethoxy butyl (meth) acrylate.

As alkoxypolyalkylene glycol mono(meth)acrylate, for example, methoxydiethylene glycol mono(meth)acrylate, methoxydipropylene glycol mono(meth)acrylate, ethoxytriethylene glycol Colmono(meth)acrylate, ethoxydiethylene glycol mono(meth)acrylate, and methoxytriethylene glycol mono(meth)acrylate are mentioned.

As aryloxyalkyl (meth)acrylate, for example, phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-tolyloxyethyl (meth)acrylate, xylyloxymethyl (meth) Acrylate and naphthyloxymethyl (meth)acrylate.

The monomers (ii) may be used alone or in combination of two or more.

The amount of the monomer (ii) used in 100% by mass of the polymerizable monomer forming the (meth)acrylic resin (A) is preferably 0 to 69.9% by mass, more preferably 0 to 66.9% by mass, further preferably 0 It is -49.5 mass%.

<< acid group-containing monomer (iii) >>

Examples of the acid group contained in the monomer (iii) include a carboxyl group, an acid anhydride group, a phosphoric acid group, and a sulfuric acid group.

Examples of the carboxyl group-containing monomers that can be used in the present invention include β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloyloxyethyl succinic acid, and ω-carboxypolycapro. Carboxyl group-containing (meth)acrylates such as lactone mono(meth)acrylate; (Meth)acrylic acid; Crotonic acid; Maleic acid; Fumaric acid; Itaconic acid; Citraconic acid is mentioned.

As an acid anhydride group-containing monomer, maleic anhydride and itaconic anhydride are mentioned, for example. Examples of the phosphoric acid group-containing monomer include (meth)acrylic acid ester having a phosphoric acid group in the side chain, and examples of the sulfuric acid group-containing monomer include (meth)acrylic acid ester having a sulfuric acid group in the side chain.

Monomer (iii) may be used individually by 1 type, and may use 2 or more types.

The amount of the monomer (iii) used in 100% by mass of the polymerizable monomer forming the (meth)acrylic resin (A) is preferably 0 to 0.3% by mass, more preferably 0 to 0.2% by mass, particularly preferably 0% by mass %to be. In the present invention, the acid value of the (meth)acrylic resin (A) can be controlled by adjusting the amount of the acid group-containing monomer (iii) used. That is, when the amount of the monomer (iii) used is within the above range, the acid value of the (meth)acrylic resin (A) can be lowered. When the acid value is low, for example, when a metal oxide such as an ITO film is used for an adherend, corrosion can be reduced, and deterioration in performance of a hard coat layer or an antireflection layer including an ITO film can be suppressed. Further, it is possible to suppress an increase in adhesive force after heat treatment.

When the amount of monomer (iii) is 0% by mass, in order to introduce a crosslinking point with the hexamethylenediisocyanate crosslinking agent (B) in the (meth)acrylic resin (A), hexamethylenediisocyanate It is preferable to use the monomer (iv) required after the group having reactivity with the isocyanate group of the crosslinking agent (B) is introduced. When using the monomers (iii) and (iv), the crosslinking point supplied by the monomer (iii) and the crosslinking point supplied by the monomer (iv) do not impair the properties of the pressure-sensitive adhesive composition for a surface protective film of the present invention. Of course, adjust the usage.

<< another polar group-containing monomer (iv) >>

Examples of the monomer (iv) include a hydroxyl group-containing monomer, an amino group-containing monomer, an amide group-containing monomer, a nitrogen-based heterocycle-containing monomer, and a cyano group-containing monomer. However, acid group-containing monomers are excluded.

Examples of the hydroxyl-containing monomer include hydroxyl-containing (meth)acrylate, specifically 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl ( And hydroxyalkyl (meth)acrylates such as meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate. The number of carbon atoms of the hydroxyalkyl group in the hydroxyalkyl (meth)acrylate is usually 1 to 12, preferably 1 to 8.

Examples of the amino group-containing monomer include amino group-containing (meth)acrylates such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate.

Examples of the amide group-containing monomer include (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-hexyl (meth)acrylamide, and N,N-dimethyl(meth)acrylamide is mentioned.

Examples of the nitrogen-based heterocycle-containing monomer include vinylpyrrolidone, acryloylmorpholine, and vinylcaprolactam. As a cyano group-containing monomer, cyano(meth)acrylate and (meth)acrylonitrile are mentioned, for example.

The monomer (iv) is preferably a hydroxyl group-containing monomer because it can be a crosslinking point of the (meth)acrylic resin (A) and the HDI-based crosslinking agent (B). By using a hydroxyl group-containing monomer as the monomer (iv), even if the acid value of the (meth)acrylic resin (A) is 0 mgKOH/g, the hydroxyl group attributable to the hydroxyl group-containing monomer is the hexamethylenediisocyanate crosslinking agent (B). From the point of becoming a crosslinking point, contamination and metal corrosiveness to the optical functional film as an adherend are reduced, and an appropriate adhesive force can be expressed.

The amount of the monomer (iv) used in 100% by mass of the polymerizable monomer forming the (meth)acrylic resin (A) is preferably 0.1 to 10% by mass, more preferably 1 to 8% by mass, further preferably 2 to It is 8% by mass. If the amount of the monomer (iv) is equal to or greater than the lower limit, a crosslinking point with the hexamethylene diisocyanate crosslinking agent (B) can be secured, and if the amount of the monomer (iv) is less than the upper limit, (meth)acrylic resin (A The viscosity of) can be suppressed from becoming too high, and good coatability can be obtained.

In particular, when the amount of the hydroxyl group-containing monomer is more than the above lower limit, the crosslinked structure is effectively formed even when the amount of monomer (iii) is 0 to 0.3% by mass, 0 to 0.2% by mass or 0% by mass, and an adhesive having an appropriate cohesive strength A layer is obtained.

Monomer (iv) may be used individually by 1 type, and may use 2 or more types.

<< other monomers (v) >>

Examples of other monomers (v) include vinyl esters such as vinyl acetate and vinyl propionate; Halogenated olefins such as vinyl chloride and vinylidene chloride; Styrene-based monomers such as styrene and α-methylstyrene; And diene-based monomers such as butadiene, isoprene, and chloroprene.

Other monomers (v) may be used alone or in combination of two or more.

《( Meta )Acrylic resin (A) production conditions>>

The (meth)acrylic resin (A) using the above monomers is prepared by a solution polymerization method. Since the solution polymerization method does not contain impurities, the pressure-sensitive adhesive composition containing the (meth)acrylic resin (A) produced by this method is suitable for use as an optical member such as a display device.

Specifically, for example, a polymerization solvent and a polymerizable monomer are put in a reaction vessel, and a polymerization initiator is added under an inert gas atmosphere such as nitrogen gas, and the reaction start temperature is usually 40 to 100°C, preferably 50 to 80°C. It is set, and the reaction system is maintained at a temperature of usually 50 to 90°C, preferably 60 to 90°C, and reacted for 4 to 24 hours. By performing solution polymerization under the conditions as described above, the weight average molecular weight (Mw) of the (meth)acrylic resin (A) used in the present invention can be within the range of (a1), and the molecular weight distribution is changed from (a2). It can be done within the prescribed range.

In the production of the acrylic resin (A), it is preferable to use a polymerization initiator, and the polymerization initiator used here is preferably a compound that can be dissolved or dispersed in a polymerization solvent. As a polymerization initiator, an azo initiator and a peroxide polymerization initiator are mentioned, for example.

Examples of azo-based initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'- Azobis (2-cyclopropylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-methylbutyronitrile), 1 ,1'-azobis(cyclohexane-1-carbonitrile), 2-(carbamoylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile , 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis [2 -Methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis(isobutylamide)dihydrate, 4,4'-azobis(4-cyanopentanoic acid), 2, And azo compounds such as 2'-azobis(2-cyanopropanol) and dimethyl-2,2'-azobis(2-methylpropionate).

In addition, as a peroxide polymerization initiator, for example, t-butyl hydroperoxide, cumene hydroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, di- 2-ethylhexylperoxydicarbonate, t-butylperoxybivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4- Di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α- Cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane and 2,2-bis(4,4-di-t-octylperoxycyclo Hexyl) butane is mentioned.

Polymerization initiators may be used alone or in combination of two or more.

The entire amount of the polymerization initiator as described above may be used at the time of polymerization initiation, or may be added dividedly in multiple times during polymerization, and the method of addition is not particularly limited.

The polymerization initiator is usually used in an amount within the range of 0.001 to 5 parts by mass, and preferably 0.001 to 3 parts by mass per 100 parts by mass of the polymerizable monomer forming the (meth)acrylic resin (A). By using the polymerization initiator in such an amount, the weight average molecular weight (Mw) of the (meth)acrylic resin (A) used in the present invention can be adjusted within the range specified in (a1). In addition to the polymerization initiator, a polymerization initiator, a chain transfer agent, a polymerizable monomer, and a polymerization solvent may be appropriately added during the polymerization reaction.

The (meth)acrylic resin used in the present invention is produced by a solution polymerization method, and examples of the polymerization solvent used in the solution polymerization method include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; Alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; Ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, and diphenyl ether; Halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane and chlorobenzene; Esters such as ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; Ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; Amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; Nitriles such as acetonitrile and benzonitrile; And sulfoxides such as dimethyl sulfoxide and sulfolane.

Polymerization solvents may be used alone or in combination of two or more. In the present invention, it is preferable to use a solvent that dissolves the polymerizable monomer and also dissolves the produced (meth)acrylic resin (A), and particularly, a polymerization solvent containing ethyl acetate is preferably used.

《( Meta ) Physical properties and content of acrylic resin (A) >>

(Meth) acrylic resin (A) has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC method) in terms of polystyrene of 1.2 million to 2 million, preferably in the range of 1.3 million to 1.8 million Within. When Mw is more than the above lower limit, the cohesive strength of the (meth)acrylic resin (A) is improved, the transition component derived from the (meth)acrylic resin (A) in the pressure-sensitive adhesive layer is greatly suppressed, and contamination is reduced. . Also, the durability of the pressure-sensitive adhesive layer is improved. When Mw is less than or equal to the above upper limit, it is preferable from the viewpoint of coatability of the pressure-sensitive adhesive composition.

Moreover, the molecular weight distribution (Mw/Mn) of the (meth)acrylic resin (A) is in the range of 4-9. If Mw/Mn is within the above range, the content of the low molecular weight substance is reduced, so the cohesive strength of the (meth)acrylic resin (A) is improved, and the transition component derived from the (meth)acrylic resin (A) in the pressure-sensitive adhesive layer is significantly suppressed. It is preferable from the viewpoint of reducing contamination.

The glass transition temperature (Tg) of the (meth)acrylic resin (A) can be measured with, for example, a differential scanning calorimeter, and the type and content of the monomer units constituting this (meth)acrylic resin (A) It can be calculated from Fox's equation. For example, (meth)acrylic resin (A) so that the glass transition temperature (Tg) of the (meth)acrylic resin (A) determined by Fox's formula is usually -70 to 10°C, preferably -60 to 0°C. Can be synthesized. The glass transition temperature of the homopolymer composed of each monomer in Fox's formula can be, for example, a value described in Polymer Handbook Fourth edition (Wiley-Interscience 2003).

In the present invention, the acid value of the acrylic resin (A) obtained as described above is required to be 2 mgKOH/g or less, preferably 0 to 1 mgKOH/g, and more preferably 0 mgKOH/g. In addition, the acid value here refers to the number of mg of potassium hydroxide required to neutralize 1 g of (meth)acrylic resin (A). When the content of the (meth)acrylic resin (A) is in the above range, for example, when a metal oxide such as an ITO film is used as an adherend, corrosion of the adherend can be reduced. Further, it is possible to suppress an increase in adhesive force after heat treatment. In order for the acrylic resin (A) to have the above acid value, for example, as a component constituting the acrylic resin (A), the amount of the monomer (iii) used in the amount within the range described in ``The acid group-containing monomer (iii)'' is included. have.

The (meth)acrylic resin (A) obtained as described above is usually obtained in a state dissolved in a polymerization solvent, and the concentration of the (meth)acrylic resin (A) in the polymerization solvent at this time is usually 10 to 80 mass %, more preferably 15 to 70% by mass, particularly preferably 15 to 50% by mass.

The (meth)acrylic resin (A) dissolved in the polymerization solvent as described above may be used by separating and separating from the polymerization solvent by adding a poor solvent, but may be used in the next step in a state dissolved in the polymerization solvent.

[ HDI series Crosslinking agent (B)]

The pressure-sensitive adhesive composition of the present invention contains an HDI-based crosslinking agent (B). By crosslinking the (meth)acrylic resin (A) with the HDI crosslinking agent (B), a crosslinked product (network polymer) can be formed, and an adhesive layer having excellent heat resistance can be obtained. By using the HDI-based crosslinking agent (B), an increase in adhesive strength after heat resistance can be suppressed, and since the pressure-sensitive adhesive layer becomes soft, the wettability is improved, and defects are less likely to occur in the bonding step to an adherend such as an optical functional film.

As an HDI-based crosslinking agent, for example, hexamethylene diisocyanate and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate as an HDI-based crosslinking agent having two isocyanate groups per molecule. Can be mentioned. As an HDI-based crosslinking agent having three isocyanate groups in one molecule, the biuret or isocyanurate compound of hexamethylenediisocyanate, and the reaction product of trimethylolpropane and hexamethylenediisocyanate (For example, a three-molecular adduct of hexamethylene diisocyanate), specifically, Asahi Kasei Chemicals Co., Ltd. TPA-100 (compound name; hexamethylene diisocyanate isocyanate) Anurate), Nippon Polyurethane Co., Ltd. product coronate HX (a three-molecular adduct of hexamethylene diisocyanate), etc. are mentioned. The HDI-based crosslinking agent having three isocyanate groups per molecule is more preferable from the viewpoint of high reactivity with the (meth)acrylic resin (A).

HDI type crosslinking agent (B) may be used individually by 1 type, and may use 2 or more types.

In the pressure-sensitive adhesive composition of the present invention, the content of the HDI crosslinking agent (B) is appropriately selected according to the (meth)acrylic resin (A), and is 2 to 15 parts by mass based on 100 parts by mass of the (meth)acrylic resin (A). It is preferably, and more preferably 2 to 10 parts by mass. By blending the crosslinking agent (B) so that the gel fraction of the pressure-sensitive adhesive composition is 90.0 to 99.9% by mass within the above range, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition significantly suppresses the transition component derived from the (meth)acrylic resin (A), Pollution is reduced. In addition, the pressure-sensitive adhesive layer can obtain sufficient heat resistance by the cohesive force of the pressure-sensitive adhesive layer, and is excellent in flexibility and adhesiveness.

HDI-based crosslinking agent (B) has a structure in which an isocyanate group is bonded to the end of an alkylene group, and the mobility of the alkylene group is high, so that the isocyanate group at the end is bonded to the isocyanate group at the other end. Since the nate group can act relatively freely, the reactivity increases. In addition, since the (meth)acrylic resin (A) having a crosslinked structure formed by reacting the isocyanate groups at both ends does not adopt a rigid structure, the pressure-sensitive adhesive layer has flexibility.

[Organic solvent (C)]

It is preferable that the pressure-sensitive adhesive composition of the present invention contains an organic solvent (C) in order to prepare its coatability. As an organic solvent, it is preferable to use the polymerization solvent described in the column of "Production conditions of (meth)acrylic resin (A)" as it is as an organic solvent. For example, a pressure-sensitive adhesive composition can be prepared by mixing a monomer solution containing a (meth)acrylic resin (A) and a polymerization solvent and an HDI-based crosslinking agent (B). In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent is usually 20 to 90% by mass, preferably 30 to 80% by mass.

In addition, in the present invention, "solid content" refers to all components excluding the organic solvent (C) among the components contained in the pressure-sensitive adhesive composition, and "solid content concentration" refers to the ratio of the solid content to 100% by mass of the pressure-sensitive adhesive composition.

[additive]

The pressure-sensitive adhesive composition of the present invention is an antistatic agent, an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, a crosslinking accelerator, a surfactant, other than the above (A) within the range that does not impair the effects of the present invention. Other components, such as a meth)acrylic resin and a rework agent, may be contained.

[Preparation of adhesive composition for surface protection film]

The pressure-sensitive adhesive composition for a surface protective film of the present invention can be prepared by mixing a (meth)acrylic resin (A), an HDI-based crosslinking agent (B), and other components as necessary by a conventionally known method. For example, mixing an HDI-based crosslinking agent (B) and other components as necessary in a monomer solution containing (meth)acrylic resin (A) obtained when synthesizing (meth)acrylic resin (A) by a solution polymerization method. Can be lifted.

The pressure-sensitive adhesive composition for a surface protective film of the present invention is solution-polymerized by solution polymerization of a polymerizable monomer containing, for example, a (meth)acrylate alkyl ester having 4 or less carbon atoms in an alkyl group in an amount within the range of 30.0 to 99.9 mass%, The gel fraction of the pressure-sensitive adhesive layer formed of the step of producing the resin (A) and the pressure-sensitive adhesive composition for a surface protective film with a hexamethylenediisocyanate-based crosslinking agent (B) in the (meth)acrylic resin (A) is 90.0~ It is manufactured through a process of blending in an amount within the range of 99.9% by mass.

〔 Adhesive layer 〕

The pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition described above. For example, by advancing the crosslinking reaction in the pressure-sensitive adhesive composition described above, specifically, by crosslinking the (meth)acrylic resin (A) with an HDI-based crosslinking agent (B), the pressure-sensitive adhesive layer is obtained.

The conditions for forming the pressure-sensitive adhesive layer are, for example, as follows. The pressure-sensitive adhesive composition of the present invention is applied on a film-like support and varies depending on the type of solvent, but is usually 50 to 150°C, preferably 60 to 100°C, usually 1 to 10 minutes, preferably 2 to 7 After drying for a minute, the solvent is removed and a coating film is formed. The average thickness of the dry coating film is usually 5 to 75 µm, preferably 10 to 50 µm.

It is preferable to form the pressure-sensitive adhesive layer under the following conditions. After applying the pressure-sensitive adhesive composition of the present invention on a film-like support and affixing a release film on the coating film formed under the above conditions, it is usually 3 days or more, preferably 7 to 10 days, usually 5 to 60°C, preferably It is cured in an environment of 15 to 40°C, usually 30 to 70%RH, and preferably 40 to 70%RH. When crosslinking is performed under the above aging conditions, it is possible to efficiently form a crosslinked product (network polymer).

As a method for applying the pressure-sensitive adhesive composition, a known method, for example, a spin coating method, a knife coating method, a roll coating method, a bar coating method, a blade coating method, a die coating method, a gravure coating method, or the like can be employed. In this way, the pressure-sensitive adhesive layer is formed by applying the pressure-sensitive adhesive composition to a predetermined thickness and aging the coating layer while removing the solvent.

The film-like support and the release film are described later in the column of [surface protection film].

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has a gel fraction of 90.0 to 99.9 mass%, more preferably 95.0 to 99.9 mass%. When the gel fraction of the pressure-sensitive adhesive layer is within the above range, the transition component derived from the (meth)acrylic resin (A) contained in the pressure-sensitive adhesive layer is significantly suppressed, and contamination is preferably reduced. In addition, the gel fraction of the pressure-sensitive adhesive layer can be adjusted to a preferable range depending on the amount of the HDI-based crosslinking agent (B) and the reaction conditions.

Further, since the pressure-sensitive adhesive layer of the present invention has sufficient adhesive force, the low-speed peeling force is sufficiently large, and can be easily peeled during high-speed peeling. The low-speed peeling force of the pressure-sensitive adhesive layer of the present invention is usually 0.05 N/25 mm or more, preferably 0.05 to 0.5 N/25 mm. The high-speed peeling force in the initial state is usually 1.5 N/25 mm or less, preferably 0.5 to 1.5 N/25 mm. Further, the high-speed peeling force after the high-temperature process is usually 2.5 N/25 mm or less, and preferably 0.5 to 2.5 N/25 mm.

In addition, the low-speed peeling force and the high-speed peeling force were measured according to the method described in Examples.

[Surface protection film]

The surface protection film of this invention has the adhesive layer formed from the adhesive composition for surface protection films mentioned above. The surface protection film may also have a release film, for example, the pressure-sensitive adhesive layer is formed on one side of the film-like support, and the release film is adhered to the other side of the pressure-sensitive adhesive layer which does not have the film-like support. A surface protection film is mentioned.

Examples of the film-like support include polyester films such as polyethylene terephthalate (PET); Film-like supports, such as polyolefin films, such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, are mentioned. Among them, it is preferable that it is a PET film from the viewpoint of transparency and thermal dimensional stability.

Examples of the release film include polyester films such as PET; And plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

The conditions for forming the pressure-sensitive adhesive layer and the gel fraction are the same as those described in the column of [Adhesive Layer].

The film thickness of the pressure-sensitive adhesive layer is usually 5 to 75 μm, preferably 10 to 50 μm from the viewpoint of maintaining adhesive performance. The film thickness of the film-like support and the release film is not particularly limited, but is usually 10 to 100 μm, preferably 25 to 100 μm.

The surface protection film of the present invention can protect the surface of the display device as described above by mainly sticking to the surface of an optical display device such as a liquid crystal display, a plasma display, and a surface conduction electron emission element display (SED). In addition to such a display device, the surface of these optical components can be protected by attaching to the surface of components constituting a display device such as a polarizing plate, a retardation plate, a liquid crystal cell, and a transparent electrode plate constituting such a display device.

Since the surface protective film of the present invention can suppress corrosion of metal oxides and suppress an increase in adhesive force after heat treatment, it is particularly suitable for bonding the surface of an ITO film requiring a high-temperature manufacturing process.

(Example)

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the description of the following Examples and the like, "part" represents "part by mass" unless otherwise specified.

〔 GPC 〕

About the (meth)acrylic resin (A), the weight average molecular weight (Mw) and the number average molecular weight (Mn) were calculated|required under the following conditions by the gel permeation chromatography method (GPC method).

Measurement device: HLC-8320GPC (manufactured by Tosoh Corporation)

GPC column configuration: The following four columns (all manufactured by Tosoh Corporation)

(1) TSKgel HxL-H (guard column)

(2) TSKgel GMHxL

(3) TSKgel GMHxL

(4) TSKgel G2500HxL

Flow rate: 1.0 mL/min

·Column temperature: 40℃

Sample concentration: 1.5% (w/v) (diluted with tetrahydrofuran)

·Mobile phase solvent: Tetrahydrofuran

·Standard polystyrene conversion

〔 Acid 〕

The number of mg of potassium hydroxide required for neutralizing 1 g of acrylic resin was calculated by calculation.

[ Synthesis example A1]

95.0 parts of n-butyl acrylate, 5.0 parts of 4-hydroxybutyl acrylate, and 100 parts of ethyl acetate solvent were added to a reaction device equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube, and the temperature was raised to 80° C. while introducing nitrogen gas. did. Subsequently, 0.1 part of 2,2'-azobisisobutyronitrile was added, and polymerization reaction was performed at 80 degreeC under nitrogen gas atmosphere for 6 hours. After completion of the reaction, it was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 20% by mass. Mw of the obtained (meth)acrylic resin A1 was 1.6 million, and Mw/Mn was 6.0. The acid value obtained by calculation was 0.

[ Synthesis example A2]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A2 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A3]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A3 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A4]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A4 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A5]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A5 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A6]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A6 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A7]

A polymerization reaction and a polymer solution were prepared in the same manner as in Synthesis Example A1, except that the polymerizable monomer was blended as described in Table 1-1 and the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A7. A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A8]

Polymerizable monomers were blended as shown in Table 1-1, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A8 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-1.

[ Synthesis example A9]

Polymerizable monomers were blended as shown in Table 1-2, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 130 parts by mass, and (meth)acrylic resin A9 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-2.

[ Synthesis example A10]

Polymerizable monomers were blended as shown in Table 1-2, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 160 parts by mass, and the (meth)acrylic resin A10 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-2.

[ Synthesis example A11]

95.0 parts of n-butyl acrylate, 5.0 parts of 4-hydroxybutyl acrylate, and 130 parts of ethyl acetate solvent were put in a reaction device equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube, and the temperature was raised to 80° C. while introducing nitrogen gas. did. Next, 0.1 part of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was started under nitrogen gas atmosphere. 3 hours after the initiation of the reaction, 0.1 parts by mass of 2,2'-azobisisobutyronitrile was added, and a polymerization reaction was further carried out at 80°C for 3 hours. After completion of the reaction, it was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 20% by mass containing (meth)acrylic resin A11. The results are shown in Table 1-2.

[ Synthesis example A12]

In the same manner as in Synthesis Example A1, except that the polymerizable monomer was blended as shown in Table 1-2, the polymerization reaction and preparation of the polymer solution were carried out to obtain a polymer solution having a solid content concentration of 20% by mass containing (meth)acrylic resin A12. Got it. The results are shown in Table 1-2.

[ Synthesis example A13]

In the same manner as in Synthesis Example A1, except that the polymerizable monomer was blended as shown in Table 1-2, the polymerization reaction and the preparation of the polymer solution were carried out to obtain a polymer solution having a solid content concentration of 20% by mass containing (meth)acrylic resin A13. Got it. The results are shown in Table 1-2.

[ Synthesis example A14]

Polymerizable monomers were blended as shown in Table 1-2, and the polymerization reaction and polymer solution were prepared in the same manner as in Synthesis Example A1, except that the blending amount of the ethyl acetate solvent was changed to 160 parts by mass, and (meth)acrylic resin A14 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-2.

[ Synthesis example A15]

The polymerization reaction and preparation of a polymer solution were carried out in the same manner as in Synthesis Example A1, except that the polymerizable monomer was blended as shown in Table 1-2, and the blending amount of the ethyl acetate solvent was changed to 115 parts by mass, and (meth)acrylic resin A15 A polymer solution containing 20% by mass of solid content concentration was obtained. The results are shown in Table 1-2.

[Table 1-1]

[Table 1-2]

[ Example One]

(1) Preparation of pressure-sensitive adhesive composition

The (meth)acrylic polymer solution (solid content concentration: 20% by mass) obtained in Synthesis Example A1 was mixed with (B1) as an HDI-based crosslinking agent (B): "TPA-100" manufactured by Asahi Kasei Chemicals Co., Ltd. to prepare a pressure-sensitive adhesive composition. Got it. In addition, the ratio of each component is an amount of (B1) 5 parts per 100 parts of resin A1; contained in the (meth)acrylic polymer solution obtained in Synthesis Example A1 (all solid content values).

(2) Preparation of surface protection film

After removing the foam, the pressure-sensitive adhesive composition obtained in (1) was applied on the polyethylene terephthalate film (PET film) subjected to peeling treatment at a liquid temperature of 25° C. using a doctor blade, and dried at 90° C. for 3 minutes, and a dry film thickness of 20 μm. A coating film was formed. A peel-treated PET film is further affixed to the side opposite to the affixed surface of the PET film of the coating film, and allowed to stand for 7 days in an environment of 23°C/50%RH, aged, and a 20 μm-thick adhesive layer sandwiched between two PET films To obtain a surface protection film having.

[ Example 2-10, Comparative example 1~11]

In Example 1, a pressure-sensitive adhesive composition and a surface protective film were obtained in the same manner as in Example 1 except that the blending composition was changed as described in Tables 2-1 and 2-2.

In addition, each material in Tables 2-1 and 2-2 is as shown below.

HDI series Crosslinking agent (B) and others Crosslinking agent

B1: Isocyanurate of hexamethylene diisocyanate

(Asahi Kasei Chemicals Co., Ltd., TPA-100)

B2: 3-molecular adduct of hexamethylene diisocyanate

(Coronate HX, manufactured by Nippon Polyurethane Co., Ltd.)

B3: Trimethylolpropane adduct body of tolylene diisocyanate

(Nippon Polyurethane Co., Ltd. product, Coronate L, solid content concentration 75% by mass)

B4: Metaxylene diisocyanate type adduct type

(Mitsui Chemicals Co., Ltd., D-120N)

B5: Epoxy curing agent

(Mitsubishi Gas Chemical Co., Ltd. product, tetrad C)

[evaluation]

〔Gel fraction〕

About 0.1 g of the pressure-sensitive adhesive layer from the surface protective film obtained in Examples and Comparative Examples was collected in a sampling bottle, 30 mL of ethyl acetate was added, and after shaking for 4 hours, the contents of the sample bottle were filtered through a 200 mesh stainless steel wire mesh, The residue on the wire mesh was dried at 100° C. for 2 hours to measure the dry weight. The gel fraction of the pressure-sensitive adhesive layer was determined by the following equation.

Gel fraction (%) = (dry weight / adhesive layer collection weight) × 100 (%)

〔ITO corrosiveness〕

The surface protection film obtained in Examples and Comparative Examples was cut to 10 mm×60 mm to an ITO-deposited PET film cut to 10 mm×100 mm, the release film on one side was peeled off and affixed, followed by autoclaving at 50°C and 5 atm for 20 minutes. Subsequently, after standing at room temperature for 1 hour, placing for 500 hours in an environment of 60°C and 90%RH, standing for 1 hour at 23°C and 65%RH, measuring the resistance value of the ITO vapor-deposited film, and the treatment previously measured The rate of change of the resistance value with respect to the resistance value of the surface protective film which was not performed was calculated, and evaluated according to the following criteria. In addition, a tester (manufactured by Sanwa Denki Keiki Co., Ltd., digital multimeter PC510) was used to measure the resistance value.

(standard)

AA: The rate of change of the resistance value was less than 10%.

CC: The rate of change of the resistance value was 10% or more.

〔 Contamination 〕

The PET film subjected to peeling treatment was peeled off from the surface protective film obtained in Examples and Comparative Examples, cut into 2.5 cm x 15 cm, and affixed on a stainless steel plate. After allowing to stand at 80°C for 24 hours, the protective film was peeled off from the stainless steel plate, and the presence or absence of contamination on the surface of the stainless steel plate to which the protective film was adhered was visually checked, and evaluated according to the following criteria.

(standard)

AA: No contamination was observed at all

BB: A little cloudiness due to the adhesive layer is observed

·CC: Contamination by a certain adhesive layer is observed

〔sleaze Peeling force 〕

The surface protection films obtained in Examples and Comparative Examples were cut into 25 mm x 150 mm, and the PET films each peeled off were attached to a stainless steel plate. It left to stand for 24 hours in an environment of 25 degreeC and 50% of humidity. Thereafter, one end was stretched in the 180° direction at a peeling rate of 300 mm/min, and the force to start peeling was taken as the low-speed peeling force.

〔high speed Peeling force 〕

The surface protection films obtained in Examples and Comparative Examples were cut into 25 mm x 150 mm, and the PET films each peeled off were attached to a stainless steel plate. It left to stand for 24 hours in an environment of 25 degreeC and 50% of humidity. Thereafter, one end was pulled in the 180° direction at a peeling rate of 30000 mm/min, and the force to start peeling was taken as the initial high-speed peeling force.

The surface protection films obtained in Examples and Comparative Examples were cut into 25 mm x 150 mm, and the PET films each subjected to the peeling treatment were peeled off and affixed to a stainless steel plate. It was left to stand for 1 hour in 150 degreeC environment. Thereafter, one end was stretched in the 180° direction at a peel rate of 30000 mm/min, and the force to start peeling was taken as the high-speed peeling force after heat resistance.

[Wetability]

A test piece was prepared by cutting the surface protective film obtained in Examples and Comparative Examples into 40 mm x 150 mm. Hold both ends of the test piece on the stainless plate, bring the center of the test piece close to contact with the stainless plate, then lift the both ends of the test piece, and measure the time until the entire test piece is wet and unfolded on the stainless plate. It evaluated by the criteria.

(standard)

AA: less than 20 seconds

BB: 20 seconds or more, less than 60 seconds

CC: more than 60 seconds

[Table 2-1]

[Table 2-2]

Claims (3)

As a pressure-sensitive adhesive composition for a surface protective film containing a (meth)acrylic resin (A) and a hexamethylene diisocyanate-based crosslinking agent (B),
The (meth)acrylic resin (A) contains a (meth)acrylic acid alkyl ester having 4 or less carbon atoms in the alkyl group in an amount within the range of 30.0 to 99.1% by mass, and a hydroxyl group-containing monomer, an amino group-containing monomer, an amide group-containing monomer, It is obtained by solution polymerization of a polymerizable monomer containing at least one monomer selected from the group consisting of a nitrogen-based heterocycle-containing monomer and a cyano group-containing monomer in an amount of 1 to 8% by mass, and the following (a1), ( has the characteristics of a2) and (a3),
Containing the hexamethylene diisocyanate-based crosslinking agent (B) in an amount within the range of 2 to 15 parts by mass per 100 parts by mass of the (meth)acrylic resin (A), and formed as the pressure-sensitive adhesive composition for the surface protective film A pressure-sensitive adhesive composition for a surface protective film, characterized in that the gel fraction of the pressure-sensitive adhesive layer is contained in an amount within the range of 90.0 to 99.9 mass%;
(a1) the weight average molecular weight (Mw) in terms of polystyrene measured by the gel permeation chromatography method (GPC method) is in the range of 1.2 million to 2 million,
(a2) the molecular weight distribution (Mw/Mn) is in the range of 4 to 9,
(a3) The acid value is 2 mgKOH/g or less. A surface protective film having a film-like support and an adhesive layer formed on at least one surface of the film-like support,
A surface protective film, wherein the pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive composition for a surface protective film according to claim 1. delete