TWI708823B - Adhesive composition for surface protective film, and surface protective film - Google Patents

Abstract

An objective of the present invention is to provide an adhesive composition for surface protective film capable of forming an adhesive layer that can reduce staining property and metal-corroding property on an adherend, have appropriate adhesion and suppressed increase in the adhesive strength after a high temperature production process, and a protective film having the adhesive layer.

The adhesive composition for surface protective film is characterized by comprising a (meth)acrylic resin (A) and a hexamethylene diisocyanate crosslinking agent (B), wherein the (meth)acrylic resin (A) is obtained by solution polymerization of polymerizable monomer components containing an alkyl (meth)acrylate ester of which alkyl group has 4 or more carbon atoms in an amount in a range of 30.0 to 99 mass%, and have the characteristics of the following (a1), (a2) and (a3).

The hexamethylene diisocyanate crosslinking agent (B) is contained in an amount to allow the adhesive layer which is formed by the adhesive composition for surface protective film to have a gel fraction in a range of 90.9 to 99.9 mass%. (a1) a weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC) is in the range of 1,200,000 to 2,000,000, (a2) a molecular weight distribution (Mw/Mn) is in the range of 4 to 9, (a3) a hydroxyl value is 2 mgKOH/g or less.

Description

Adhesive composition for surface protective film and surface protective film

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

In recent years, liquid crystal display devices such as smart phones 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 from its cross-section, and the optical functional film forming the multi-layered structure is becoming more and more functional. In order to stably produce and store display devices including such high-functional optical functional films, it is indispensable to attach a surface protection film to prevent 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 adhesive layer is partially connected to the adherend, thereby making the surface protective film adhere to the adherend. As far as the surface protective film is concerned, it is required to exhibit sufficient adhesive force when attached to an adherend, and the adhesion of residues caused by the aforementioned adhesive layer during peeling is small.

In addition, as an example of optical functional films used in display devices, indium tin oxide is popular for the development/production of touch panels (ITO) films are mostly manufactured through high-temperature manufacturing processes. Therefore, as for the surface protection film and the adhesive layer, it is required that the problem of peeling failure due to corrosion of metal oxides and the like and increase in adhesive force should not occur even after high-temperature processing.

Regarding the adhesive for surface protective films, for example, Patent Document 1 discloses an adhesive formed of an acrylic resin and a crosslinking agent. However, there is a problem that the gelation rate of the adhesive is as low as 0 to 30% by mass and is easily contaminated, and the adhesive force after heat resistance increases.

Patent Document 2 describes an adhesive prepared with an acrylic resin and a crosslinking agent. The acrylic resin is obtained by copolymerizing a monomer including a monomer containing a carboxyl group. However, the weight average molecular weight of the acrylic resin disclosed in the examples of Patent Document 2 is 600,000, and the molecular weight cannot be said to be sufficiently large, and the stain resistance is insufficient. In addition, the amount of carboxyl group-containing monomer used is 5 to 10% by mass in 100% by mass of polymerizable monomers forming acrylic resin, which is relatively large. Therefore, when it is attached to an adhesive containing metal oxides, it will Corrosion of adherends, and then there is a problem of increased adhesion after heat resistance.

Patent Document 3 describes an adhesive formed of an acrylic resin obtained by copolymerizing a specific alkyl (meth)acrylate and a monomer including a carboxyl group-containing monomer and an epoxy crosslinking agent. However, in addition to the corrosion of metal oxides and other adhesives due to the acid value of acrylic resins as high as 16 to 120 mgKOH/g, and the increase in adhesive strength after heat resistance, there are also adhesives due to the use of epoxy crosslinking agents. The flexibility of the layer is insufficient, and the wettability of the adherend is deteriorated.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2009-79074 A

[Patent Document 2] JP 2007-126606 A

[Patent Document 3] International Publication No. 2011/148721

The subject of the present invention is to provide an adhesive composition for surface protection film, which can form and reduce the adhesion of optical functional films such as hard coat films, anti-reflection films, and ITO films. It is an adhesive layer that has adequate adhesion to materials and metal corrosion, and the increase in adhesion after the high-temperature manufacturing process is suppressed, and provides a surface protective film with the aforementioned adhesive layer.

The adhesive composition for a surface protective film of the present invention contains a (meth)acrylic resin (A) and a hexamethylene diisocyanate crosslinking agent (B), wherein the (meth)acrylic resin (A) ) Is obtained by solution polymerization of polymerizable monomers, and has the following characteristics (a1), (a2) and (a3), wherein the polymerizable monomer system is within the range of 30.0 to 99.9% by mass The amount contains alkyl (meth)acrylate having an alkyl group with a carbon number of 4 or less, and the adhesive composition for the surface protective film is such that the adhesive layer formed by the adhesive composition for the surface protective film is Gelation rate becomes The amount within the range of 90.0 to 99.9% by mass contains the aforementioned hexamethylene diisocyanate-based crosslinking agent (B).

(a1) The weight average molecular weight (Mw) converted from polystyrene measured by gel permeation chromatography (GPC method) is in the range of 1.2 million to 2 million, and (a2) the molecular weight distribution (Mw/Mn) is 4 Within the range of 9, (a3) the acid value is 2 mgKOH/g or less.

The adhesive composition for a surface protective film of the present invention preferably contains the aforementioned hexamethylene diisocyanate in an amount in the range of 2 to 15 parts by mass relative to 100 parts by mass of the aforementioned (meth)acrylic resin (A) Department of crosslinking agent (B).

In addition, the surface protection film of the present invention has a film-like support and an adhesive layer formed on at least one side of the film-like support, wherein the adhesive layer is composed of the following adhesive composition for surface protection film Formation: In the adhesive composition for surface protective films, the (meth)acrylic resin (A) is obtained by solution polymerization of polymerizable monomers, and has the above (a1), (a2) and (a3) The characteristics of the polymerizable monomer system in the range of 30.0 to 99.9% by mass, containing alkyl (meth)acrylate having an alkyl group with a carbon number of 4 or less; and the aforementioned adhesive composition for surface protective film The hexamethylene diisocyanate-based crosslinking agent (B) is contained in an amount such that the gelation rate of the adhesive layer formed of the adhesive composition for surface protection films is within the range of 90.0 to 99.9% by mass.

The 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 (meth)acrylate in a specific amount, and a specific The cross-linking agent can form an adhesive layer that exhibits sufficient adhesive force without contaminating the adherend and thereby not corroding the adherend.

According to the present invention, it is possible to provide an adhesive composition for a surface protective film, which can be formed when attached to an adherend to exert sufficient adhesive force, while reducing the pollution and metal corrosion to the adherend, and the high-temperature manufacturing process The subsequent increase in adhesive force is suppressed and the adhesion of residues caused by the adhesive layer is less for an adhesive layer. The present invention also provides a surface protective film with the aforementioned adhesive layer.

Hereinafter, the adhesive composition for surface protection films and the surface protection film of the present invention will be described. Hereinafter, the adhesive composition for surface protection films of the present invention is also referred to simply as "adhesive composition".

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

[Adhesive composition for surface protective film]

The adhesive composition for surface protective film of the present invention contains (meth)acrylic resin (A) and hexamethylene diisocyanate crosslinking agent (B) (below It is also called HDI-based crosslinking agent (B)), and the adhesive composition usually contains an organic solvent (C).

[(Meth) acrylic resin (A)]

The (meth)acrylic resin (A) is a polymer composed of a polymerizable monomer containing alkyl (meth)acrylic acid alkyl ester (i) with a carbon number of 4 or less, and is a polymer of the aforementioned polymerizable monomer The body is obtained by solution polymerization in an organic solvent. In this way, the (meth)acrylic resin (A) has a structural unit derived from the aforementioned (i).

The aforementioned polymerizable monomers, in addition to alkyl (meth)acrylates (i) with an alkyl group of 4 or less carbon atoms, may also contain at least one selected from (meth)acrylates (ii) and containing acid groups A group consisting of monomer (iii), monomer (iv) containing other polar groups, and other monomer (v). For example, a polymerizable monomer containing the aforementioned (i) and (iv), and optionally the aforementioned (ii), (iii), or (v) can be cited.

Hereinafter, the aforementioned alkyl (meth)acrylate (i) is referred to as "monomer (i)", (meth)acrylate (ii) is referred to as "monomer (ii)", and acid group-containing monomers (iii) is called "monomer (iii)", monomers (iv) containing other polar groups are called "monomers (iv)", and other monomers (v) are called "monomers (v)".

[Alkyl (meth)acrylate (i) with an alkyl group of 4 or less carbon atoms]

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

CH ₂ =CR ¹ -COOR ² . . . (i-1)

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 in R ² is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tertiary butyl and second butyl.

Monomer (i) includes, for example: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate Esters, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate and second butyl (meth)acrylate.

Monomer (i) can be used individually by 1 type or in 2 or more types.

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

If the usage amount of the monomer (i) is within the above range, the adhesive layer formed of the adhesive composition containing the (meth)acrylic resin (A) will be sufficient for adhesives such as optical functional films The adhesive force can prevent peeling or floating during transportation.

[(Meth)acrylate (ii)]

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

CH ₂ =CR ³ -COOR ⁴ . . . (ii-1)

R ³ is a hydrogen atom or a methyl group. R ⁴ is an organic group that excludes an alkyl group having 4 or less carbon atoms and does not have polar groups such as a hydroxyl group, an amino group, an amido group, a cyano group, and a carboxyl group.

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

-(R ⁵ O) _n R ⁶ . . . (g-1)

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 carbon number of the alkylene group is usually 1-10, preferably 1-5. The carbon number of the alkyl group is usually 1 to 10, preferably 1 to 4, and the carbon number of the aryl group is usually 6 to 10, preferably 6. n is preferably from 1 to 20, more preferably from 1 to 4, and still more preferably from 1 to 2.

The monomer (ii) includes, for example, (meth)acrylates containing alicyclic groups such as alkyl (meth)acrylates having an alkyl group with 5 or more carbon atoms, cycloalkyl (meth)acrylates, etc. Aryl (meth)acrylate, aralkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, alkoxypolyalkylene glycol mono(meth)acrylate and (methyl) ) Aryloxyalkyl acrylate.

Examples of alkyl (meth)acrylates having an alkyl group with a carbon number of 5 or more that can be used in the present invention include n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, and n-heptyl (meth)acrylate Ester, 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 (meth)acrylate )acrylic acid Isostearyl ester.

In addition, cycloalkyl (meth)acrylate and other alicyclic group-containing (meth)acrylates, aryl (meth)acrylates, and aralkyl (meth)acrylates include, for example: (meth) ) Cyclohexyl acrylate, isobornyl (meth)acrylate, phenyl (meth)acrylate and benzyl (meth)acrylate.

In addition, examples of the alkoxyalkyl (meth)acrylate include methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-methoxyethyl (meth)acrylate. Ethoxyethyl, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate and (meth)acrylate Base)-4-ethoxybutyl acrylate.

Examples of the alkoxypolyalkylene glycol mono(meth)acrylate include: methoxydiethylene glycol mono(meth)acrylate, methoxydipropylene glycol mono(meth)acrylate, and ethoxy Triethylene glycol mono(meth)acrylate, ethoxydiethylene glycol mono(meth)acrylate, and methoxytriethylene glycol mono(meth)acrylate.

Examples of aryloxyalkyl (meth)acrylate include: phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and 2-toluene (meth)acrylate Oxyethyl, xyloxymethyl (meth)acrylate and naphthoxymethyl (meth)acrylate.

Monomer (ii) can be used individually by 1 type or in 2 or more types.

In 100% by mass of the polymerizable monomer forming the (meth)acrylic resin (A), the amount of monomer (ii) used is preferably 0 to 69.9% by mass, more preferably 0 to 66.9% by mass, and more Preferably, it is 0 to 49.5% by mass.

[Monomers containing acid groups (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.

The carboxyl group-containing monomers usable in the present invention include, for example, β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloxyethyl succinate And ω-carboxyl polycaprolactone mono(meth)acrylate and other carboxyl-containing (meth)acrylates; (meth)acrylic acid; crotonic acid; maleic acid; fumaric acid; itaconic acid; citrine Conic acid.

Examples of the monomer containing an acid anhydride group include maleic anhydride and itaconic anhydride. The phosphoric acid group-containing monomer may be exemplified by (meth)acrylate having a phosphoric acid group in the side chain, and the sulfuric acid group-containing monomer may be exemplified by the (meth)acrylate having a sulfuric acid group in the side chain.

Monomer (iii) can be used individually by 1 type or in 2 or more types.

In 100% by mass of polymerizable monomers forming the (meth)acrylic resin (A), the amount of monomer (iii) used is preferably 0 to 0.3% by mass, more preferably 0 to 0.2% by mass, particularly preferred It is 0% by mass. 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, if the usage amount of the monomer (iii) is within the above range, the acid value of the (meth)acrylic resin (A) can be reduced. If the acid value is low, for example, when a metal oxide such as an ITO film is used for the adherend, corrosion can be reduced, and the performance degradation of hard coats and anti-reflection layers including ITO films can be suppressed. In addition, it is possible to suppress the increase in adhesion after heat treatment.

When the usage amount of the monomer (iii) is 0% by mass, in order to introduce a hexamethylene diisocyanate-based crosslinking agent to the (meth)acrylic resin (A) As the crosslinking point of (B), it is preferable to use the monomer (iv) mentioned later which introduces the group reactive with the isocyanate group of a hexamethylene diisocyanate-type crosslinking agent (B). When using monomers (iii) and (iv), the cross-linking point of the monomer (iii) and the cross-linking point of the monomer (iv) should be used, so as not to damage the adhesive for surface protective film of the present invention It goes without saying that the characteristics of the composition are used to adjust the amount of use.

[Monomers containing other polar groups (iv)]

The monomer (iv) includes, for example, a hydroxyl group-containing monomer, an amine group-containing monomer, an amide group-containing monomer, a nitrogen-based heterocyclic ring-containing monomer, and a cyano group-containing monomer. However, monomers containing acid groups are excluded.

Examples of monomers containing hydroxyl groups include (meth)acrylates containing hydroxyl groups, and specific examples include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylic acid. Hydroxyalkyl (meth)acrylates such as -4-hydroxybutyl ester, 6-hydroxyhexyl (meth)acrylate and 8-hydroxyoctyl (meth)acrylate. The carbon number of the hydroxyalkyl group in the hydroxyalkyl (meth)acrylate is usually 1-12, preferably 1-8.

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

Examples of monomers containing amide groups include: (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(methyl) ) Acrylamide, N-hexyl (meth)acrylamide and N,N-dimethyl (meth)acrylamide.

Examples of the monomer containing a nitrogen-based heterocyclic ring include vinylpyrrolidone, acrylomorpholine, and vinylcaprolactam. Examples of the cyano group-containing monomer include cyano (meth)acrylate and (meth)acrylonitrile.

The monomer (iv) can also serve as a crosslinking point between the (meth)acrylic resin (A) and the HDI-based crosslinking agent (B), so a monomer containing a hydroxyl group is preferred. By using a hydroxyl-containing monomer as the monomer (iv), even if the acid value of the (meth)acrylic resin (A) is 0 mgKOH/g, the hydroxyl-containing monomer causes the hydroxyl group to become hexamethylene bis The cross-linking point of the isocyanate-based cross-linking agent (B) can reduce the fouling and metal corrosion of the optical functional film of the adherend, and make it exhibit appropriate adhesion.

In 100% by mass of polymerizable monomers forming the (meth)acrylic resin (A), the amount of monomer (iv) used is preferably 0.1 to 10% by mass, more preferably 1 to 8% by mass, and more It is preferably 2 to 8% by mass. If the usage amount of the monomer (iv) is above the aforementioned lower limit, the crosslinking point with the hexamethylene diisocyanate-based crosslinking agent (B) can be secured, and if the usage amount of the monomer (iv) is the aforementioned upper limit Below the limit value, the viscosity of the (meth)acrylic resin (A) can be suppressed from becoming too high, and good coating properties can be obtained.

In particular, when the usage amount of the hydroxyl-containing monomer is more than the aforementioned lower limit, even when the usage amount of the monomer (iii) is 0 to 0.3% by mass, 0 to 0.2% by mass, or 0% by mass, it is still effective. Cross-linked structure to obtain an adhesive layer with appropriate cohesion.

Monomer (iv) can be used individually by 1 type or in 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; and styrene monomers such as styrene and α-methylstyrene. Body; Diene monomers such as butadiene, isoprene and chloroprene.

The other monomers (v) may be used alone or in two or more types.

[Production conditions of (meth)acrylic resin (A)]

The (meth)acrylic resin (A) using the above-mentioned monomer is produced by a solution polymerization method. Since the solution polymerization method contains few impurities, the adhesive composition containing the (meth)acrylic resin (A) produced by the method is suitable for use in optical members such as display devices.

Specifically, for example, a polymerization solvent and a polymerizable monomer are added to the reaction vessel, and a polymerization initiator is added under an inert gas atmosphere such as nitrogen. The reaction initiation temperature is usually set at 40 to 100°C, preferably at 50°C. To 80°C, the reaction system is usually maintained at a temperature of 50 to 90°C, preferably 60 to 90°C, and allowed to react for 4 to 24 hours. By performing solution polymerization under the above conditions, the weight average molecular weight (Mw) of the (meth)acrylic resin (A) used in the present invention can be set in the range of (a1), and the molecular weight distribution can be set in (a2) Within the specified 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 the polymerization solvent. Examples of the polymerization initiator include azo-based initiators and peroxide-based polymerization initiators.

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-methylbutane) Nitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(aminomethanoylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2 ,4-Dimethylvaleronitrile, 2,2'-Azobis(2-carboxamidinopropane) dihydrochloride, 2,2'-Azobis(N,N'-dimethylene isobutyl Amidine), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis(isobutylamide) dihydrate , 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-cyanopropanol) and dimethyl-2,2'-azobis(2- Methyl propionate) and other azo compounds.

In addition, the peroxide-based polymerization initiator includes, for example, tertiary butyl hydroperoxide, cumyl hydroperoxide, dicumyl peroxide, benzyl peroxide, and lauryl peroxide. Compound, hexyl peroxide, di-iso-propyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, tertiary butyl peroxy pivalate, 2, 2-bis(4,4-di-tertiary butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-tertiary pentylperoxycyclohexyl)propane, 2,2- Bis(4,4-bis-third octylperoxycyclohexyl)propane, 2,2-bis(4,4-bis-α-cumylperoxycyclohexyl)propane, 2,2- Bis(4,4-di-tertiary butylperoxycyclohexyl)butane and 2,2-bis(4,4-di-tertiary octylperoxycyclohexyl)butane.

A polymerization initiator can be used individually by 1 type or in 2 or more types.

The above-mentioned polymerization initiator can be used in the entire amount at the beginning of the polymerization, or can be added in multiple times during the polymerization, and the method of addition is not special. limit.

The polymerization initiator is usually used in an amount in the range of 0.001 to 5 parts by mass, preferably 0.001 to 3 parts by mass, relative to 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 by (a1). Furthermore, in addition to the polymerization initiator, a polymerization initiator, a chain transfer agent, a polymerizable monomer, and a polymerization solvent may be added appropriately in the above-mentioned polymerization reaction.

烷、大茴香醚、苯基乙基醚及二苯基醚等醚類；氯仿、四氯化碳、1,2-二氯乙烷及氯苯等鹵化烴類；乙酸乙酯、乙酸丙酯、乙酸丁酯及丙酸甲酯等酯類；丙酮、甲基乙基酮、二乙基酮、甲基異丁基酮及環己酮等酮類；N,N-二甲基甲醯胺、N,N-二甲基乙醯胺及N-甲基吡咯啶酮等醯胺類；乙腈及苯甲腈等腈類；二甲基亞碸及環丁碸等亞碸類等。 The (meth)acrylic resin used in the present invention is produced by a solution polymerization method. Here, the polymerization solvent used in the solution polymerization method includes, for example, aromatic hydrocarbons such as benzene, toluene, and xylene; Aliphatic hydrocarbons such as pentane, n-hexane, n-heptane and n-octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane and cyclooctane; diethyl ether, diisopropyl Ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, di

Ethers such as alkane, anisole, phenyl ethyl ether and diphenyl ether; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane and chlorobenzene; ethyl acetate, propyl acetate , Butyl acetate and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; N,N-dimethylformamide , N,N-dimethylacetamide and N-methylpyrrolidone and other amides; acetonitrile and benzonitrile and other nitriles; dimethyl sulfinium and cyclobutyl sulfide, etc.

A polymerization solvent can be used individually by 1 type or in 2 or more types. In the present invention, it is preferable to use a solvent that dissolves the polymerizable monomer and also the produced (meth)acrylic resin (A), and it is particularly preferable to use a solvent containing ethyl acetate 的polymerization solvent.

[Physical properties and content of (meth)acrylic resin (A)]

(Meth)acrylic resin (A), the weight average molecular weight (Mw) measured by the gel permeation chromatography method (GPC method), expressed in terms of polystyrene conversion value, is 1.2 million to 2 million, compared to Preferably, it is in the range of 1.3 million to 1.8 million. When Mw is more than the aforementioned lower limit, the cohesive force of the (meth)acrylic resin (A) is increased, and the migration component from the (meth)acrylic resin (A) in the adhesive layer is greatly suppressed, thereby reducing The point of pollution is better. In addition, the durability of the adhesive layer also increases. When Mw is equal to or lower than the aforementioned upper limit, it is preferable in terms of the coatability of the adhesive composition.

In addition, the molecular weight distribution (Mw/Mn) of the (meth)acrylic resin (A) is in the range of 4-9. When Mw/Mn is within the aforementioned range, the content of low-molecular-weight compounds will decrease, so the cohesive force of (meth)acrylic resin (A) will increase, and the adhesive layer is derived from (meth)acrylic resin ( A) The migration component will be greatly suppressed, which is better in terms of reducing pollution.

The glass transition temperature (Tg) of the (meth)acrylic resin (A) can be measured by, for example, a differential scanning calorimeter, and the type of monomer unit constituting the (meth)acrylic resin (A) In terms of its content ratio, it can be calculated by the formula of Fox. For example, it is usually such that the glass transition temperature (Tg) of the (meth)acrylic resin (A) obtained by the formula of Fox is -70 to 10°C, preferably -60 to 0°C. In this way, (meth)acrylic resin (A) can be synthesized. Fox’s formula is one of the homopolymers composed of each monomer For the glass transition temperature, for example, the value described in the Polymer Handbook Fourth edition (Wiley-Interscience 2003) can be used.

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

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

In this way, the (meth)acrylic resin (A) dissolved in the polymerization solvent can be used by adding a poor solvent to separate it from the polymerization solvent, or it can be used in the subsequent step in the state of being dissolved in the polymerization solvent .

[HDI series crosslinking agent (B)]

The adhesive composition of the present invention contains an HDI-based crosslinking agent (B). The (meth)acrylic resin (A) is cross-linked with HDI-based cross-linking agent (B) to form The crosslinked body (web polymer) can provide an adhesive layer with excellent heat resistance. By using the HDI-based crosslinking agent (B), the increase in adhesive strength after heat resistance can be suppressed, and the wettability becomes better due to the softening of the adhesive layer, making it difficult for optical functional films to be adhered to. Defects during the bonding step.

Examples of HDI-based crosslinking agents include hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene, which are HDI-based crosslinking agents with two isocyanate groups in one molecule Diisocyanate. It is a biuret or trimer isocyanate of hexamethylene diisocyanate and a reaction product of trimethylol propane and hexamethylene diisocyanate, which is an HDI crosslinking agent with 3 isocyanate groups in one molecule ( For example, the tri-molecular adduct of hexamethylene diisocyanate), specifically including: Asahi Kasei Chemicals (stock) TPA-100 (compound name; hexamethylene diisocyanate trimeric isocyanate body), Nippon Polyurethane (stock) Coronate HX (3-molecular adduct of hexamethylene diisocyanate), etc. In view of high reactivity with the (meth)acrylic resin (A), an HDI-based crosslinking agent having three isocyanate groups in one molecule is more preferable.

The HDI-based crosslinking agent (B) can be used alone or in two or more types.

In the 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 relative to 100 parts by mass of the (meth)acrylic resin (A). , Preferably 2 to 15 parts by mass, more preferably 2 to 10 parts by mass. By blending the crosslinking agent (B) so that the gelation rate of the adhesive composition becomes 90.0 to 99.9% by mass within the above range, the adhesive layer formed of the adhesive composition is derived from (methyl)acrylic acid The migration component of the acrylic resin (A) is greatly suppressed, and pollution is reduced. In addition, the adhesive layer can obtain sufficient heat resistance due to the cohesive force of the adhesive layer, and is excellent in flexibility and adhesiveness.

The HDI-based crosslinking agent (B) has a structure in which an isocyanate group is bonded at the end of the alkylene group. From the viewpoint of the high mobility of the alkylene group, when the isocyanate group at the end is bonded, it is at the other end The isocyanate group can move relatively freely, so the reactivity becomes higher. In addition, the (meth)acrylic resin (A) having a cross-linked structure formed by the reaction of isocyanate groups at both ends does not have a rigid structure, so the adhesive layer has flexibility.

[Organic Solvent (C)]

In order to adjust the coating property of the adhesive composition of this invention, it is preferable to contain an organic solvent (C). As the organic solvent, it is preferable to directly use the polymerization solvent described in the paragraph [Production conditions of (meth)acrylic resin (A)] as the organic solvent. For example, a monomer solution containing a (meth)acrylic resin (A) and a polymerization solvent can be mixed with an HDI-based crosslinking agent (B) to prepare an adhesive composition. In the 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, the "solid content" refers to all the components contained in the adhesive composition after removing the above-mentioned organic solvent (C), and the "solid content concentration" refers to the aforementioned relative to 100% by mass of the adhesive composition The ratio of solid fractions.

[additive]

In addition to the above-mentioned components, the adhesive composition of the present invention may also contain antistatic agents, antioxidants, light stabilizers, anti-metal corrosion agents, tackifiers, plasticizers, and cross-linking agents within a range that does not impair the effects of the present invention. Co-accelerators, surfactants, (meth)acrylic resins other than the aforementioned (A), and other components such as heavy-duty agents.

[Preparation of adhesive composition for surface protective film]

The adhesive composition for surface protection films of the present invention can be prepared by mixing (meth)acrylic resin (A), HDI-based crosslinking agent (B), and other components as necessary by a conventionally known method. For example, it can be mentioned that the HDI-based crosslinking agent (B) is formulated in a monomer solution containing the (meth)acrylic resin (A) obtained when the (meth)acrylic resin (A) is synthesized by the solution polymerization method And other ingredients as needed.

The adhesive composition for a surface protective film of the present invention is manufactured through the following steps: for example, a step of polymerizing a polymerizable monomer to produce a (meth)acrylic resin (A), wherein the polymerizable monomer system In the range of 30.0 to 99.9% by mass, an alkyl (meth)acrylate having an alkyl group with a carbon number of 4 or less is contained; in the aforementioned (meth)acrylic resin (A), so as to be protected by the surface The step of preparing the hexamethylene diisocyanate-based crosslinking agent (B) when the gelation rate of the adhesive layer formed by the adhesive composition for films is within the range of 90.0 to 99.9% by mass.

[Adhesive layer]

The adhesive layer is formed of the above-mentioned adhesive composition. For example by To advance the crosslinking reaction in the above-mentioned adhesive composition, specifically, the (meth)acrylic resin (A) is crosslinked with an HDI-based crosslinking agent (B) to obtain the above-mentioned adhesive layer.

The formation conditions of the adhesive layer are as follows, for example. The adhesive composition of the present invention is coated on a film-like support, although it may vary depending on the type of solvent, it is usually carried out at 50 to 150°C, preferably 60 to 100°C, usually for 1 to 10 minutes , Preferably it is dried for 2 to 7 minutes to remove the solvent to form a coating film. The average film thickness of the dried coating film is usually 5 to 75 μm, preferably 10 to 50 μm.

The adhesive layer is preferably formed under the following conditions. After coating the adhesive composition of the present invention on a film-like support, and attaching a release film to the coating film formed under the above conditions, it is usually 3 days or more, preferably 7 to 10 days, usually 5 The aging is carried out at 60°C, preferably 15 to 40°C, usually 30 to 70%RH, preferably 40 to 70%RH. When cross-linked under the above-mentioned aging conditions, a cross-linked body (network polymer) can be efficiently formed.

The application method of the adhesive composition can be a well-known method such as a spin coating method, a knife coating method, a roll coating method, a bar coating method, a knife coating method, a die coating method, and a gravure coating method. In this way, the adhesive composition is coated to a predetermined thickness, the solvent is removed, and the coating layer is aged, thereby forming the adhesive layer.

The film-like support and release film will be described in the section of [Surface Protection Film] below.

Adhesive formed by the adhesive composition of the present invention The gelation rate of the layer is 90.0 to 99.9% by mass, more preferably 95.0 to 99.9% by mass. If the gelation rate of the adhesive layer is within the above range, the migration component from the (meth)acrylic resin (A) contained in the adhesive layer is greatly suppressed, which is preferable in terms of reducing pollution . In addition, the gelation rate of the adhesive layer can be adjusted to a preferable range depending on the blending amount of the HDI-based crosslinking agent (B) and the reaction conditions.

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

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

[Surface protective film]

The surface protective film of the present invention has an adhesive layer formed of the adhesive composition for a surface protective film. The surface protection film may further have a release film. Examples include: forming the adhesive layer on one side of the film-like support, and attaching the release film to the other side of the adhesive layer that does not have the film-like support Surface protection film.

Examples of the film-like support include polyester films such as polyethylene terephthalate (PET); polyethylene, polypropylene, and ethylene-vinyl acetate Film-like supports such as polyolefin films such as ester copolymers. Among them, from the viewpoints of transparency and thermal dimensional stability, a PET film is preferred.

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

The formation conditions and gelation rate of the adhesive layer are the same as the conditions described in the paragraph [Adhesive layer].

The film thickness of the 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 be mainly attached to the surface of optical display devices such as liquid crystal displays, plasma displays, surface conduction electron emission displays (SED), etc., to protect the surface of the above-mentioned display devices. In addition, it can be attached not only to the display device, but also to the surface of the elements constituting the display device, such as the polarizing plate, the phase difference plate, the liquid crystal cell, the transparent electrode plate and the like constituting the display device, to protect the optical elements s surface.

The surface protection film of the present invention can inhibit the corrosion of metal oxides and inhibit the increase in adhesion after heat treatment, so it is particularly suitable for being attached to the surface of ITO film that requires a high-temperature manufacturing process.

(Example)

Hereinafter, the present invention will be explained more specifically based on examples, but the present invention is not limited to these examples. In the description of the following examples and the like, unless otherwise stated, "parts" means "parts by mass".

[GPC]

The (meth)acrylic resin (A) is based on the gel permeation chromatography method (GPC method), and the weight average molecular weight (Mw) and number average molecular weight (Mn) are determined under the following conditions.

‧Measuring device: HLC-8320GPC (TOSOH (stock) system)

‧GPC string composition: the following 4-pipe strings (all made by TOSOH (stock))

(1) TSKgel HxL-H (protection column)

(2) TSKgel GMHxL

(3) TSKgel GMHxL

(4) TSKgel G2500HxL

‧Flow rate: 1.0mL/min

‧Column temperature: 40℃

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

‧Mobile phase solvent: Tetrahydrofuran

‧Standard polystyrene conversion

[Acid value]

It was calculated by calculating the mg number of potassium hydroxide required to neutralize 1 g of acrylic resin.

[Synthesis Example A1]

Add 95.0 parts of n-butyl acrylate, 5.0 parts of 4-hydroxybutyl acrylate and 100 parts of ethyl acetate solvent to a reaction device equipped with a stirrer, a reflux cooler, a thermometer and a nitrogen introduction tube. 80°C. Next, 0.1 part of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was carried out at 80°C for 6 hours in a nitrogen atmosphere. After the reaction, it was diluted with ethyl acetate to prepare a polymer solution having a solid content of 20% by mass. The Mw of the obtained (meth)acrylic resin A1 was 1.6 million, and the Mw/Mn was 6.0. The acid value obtained by calculation is zero.

[Synthesis Example A2]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain A polymer solution with a solid content concentration of 20% by mass of (meth)acrylic resin A2. The results are shown in Table 1-1.

[Synthesis Example A3]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain A polymer solution with a solid content concentration of 20% by mass of (meth)acrylic resin A3. The results are shown in Table 1-1.

[Synthesis Example A4]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A4 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-1.

[Synthesis Example A5]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A5 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-1.

[Synthesis Example A6]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A6 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-1.

[Synthesis Example A7]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A7 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-1.

[Synthesis Example A8]

Except for preparing the polymerizable monomer as described in Table 1-1 and changing the compounding amount of the ethyl acetate solvent to 115 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A8 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-1.

[Synthesis Example A9]

Except that the polymerizable monomer was formulated as described in Table 1-2 and the blending amount of the ethyl acetate solvent was changed to 130 parts by mass, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain (Meth) acrylic resin A9 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-2.

[Synthesis Example A10]

Except that the polymerizable monomer was formulated as described in Table 1-2 and the blending amount of the ethyl acetate solvent was changed to 160 parts by mass, the polymerization reaction and the preparation of the polymer solution were performed in the same manner as in Synthesis Example A1. (Meth) acrylic resin A10 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-2.

[Synthesis Example A11]

Add 95.0 parts of n-butyl acrylate and 4-hydroxybutyl acrylate to a reaction device equipped with a stirrer, a reflux cooler, a thermometer and a nitrogen introduction tube 5.0 parts and 130 parts of ethyl acetate solvent, and then heated up to 80°C while introducing nitrogen. Next, 0.1 part of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was started under a nitrogen atmosphere. After 3 hours from the start of the reaction, 0.1 parts by mass of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was further performed at 80°C for 3 hours. After completion of the reaction, it was diluted with ethyl acetate to prepare a polymer solution containing (meth)acrylic resin A11 with a solid content concentration of 20% by mass. The results are shown in Table 1-2.

[Synthesis Example A12]

Except for preparing the polymerizable monomer as described in Table 1-2, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain a solid content concentration of 20% by mass containing (meth)acrylic resin A12的polymer solution. The results are shown in Table 1-2.

[Synthesis Example A13]

Except for preparing the polymerizable monomer as described in Table 1-2, the polymerization reaction and the preparation of the polymer solution were carried out in the same manner as in Synthesis Example A1 to obtain a solid content concentration of 20% by mass containing (meth)acrylic resin A13的polymer solution. The results are shown in Table 1-2.

[Synthesis Example A14]

Except that the polymerizable monomer was formulated as described in Table 1-2 and the blending amount of the ethyl acetate solvent was changed to 160 parts by mass, the polymerization reaction and the preparation of the polymer solution were performed in the same manner as in Synthesis Example A1. (Meth) acrylic resin A14 is a polymer solution with a solid content concentration of 20% by mass. The results are shown in Table 1-2.

[Synthesis Example A15]

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

[Example 1] (1) Preparation of adhesive composition

Mix the (meth)acrylic polymer solution (solid content concentration 20% by mass) obtained in Synthesis Example A1 and (B1) as HDI-based crosslinking agent (B): "TPA-100" manufactured by Asahi Kasei Chemicals Co., Ltd. , Get the adhesive composition. In addition, with respect to 100 parts of resin A1 contained in the (meth)acrylic polymer solution obtained in Synthesis Example A1, the ratio of each component was (B1) 5 parts (all solid content values).

(2) Formation of surface protective film

After defoaming, on the peeled polyethylene terephthalate film (PET film), apply the adhesive composition obtained in (1) above using a doctor blade at a liquid temperature of 25°C, and apply it at a temperature of 90°C. Dried at °C for 3 minutes to form a coating film with a dry film thickness of 20 μm. On the surface of the above-mentioned PET film of the coating film opposite to the sticking surface, the peeled PET film was further laminated, and it was allowed to stand for 7 days under a 23°C/50%RH environment to mature to obtain a sandwich of 2 sheets The surface protection film of the adhesive layer of 20μm thickness of PET film.

[Examples 2 to 10, Comparative Examples 1 to 11]

In Example 1, the adhesive composition and the surface protective film were obtained in the same manner as in Example 1, except that the formulation composition was changed according to Tables 2-1 and 2-2.

In addition, the materials in Tables 2-1 and 2-2 are as follows.

HDI series crosslinking agent (B) and other crosslinking agents

B1: Trimeric isocyanate body of hexamethylene diisocyanate (manufactured by Asahi Kasei Chemicals Co., Ltd., TPA-100)

B2: 3-molecular adduct of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industrial Co., Ltd., Coronaate HX)

B3: Trimethylolpropane adduct of phenylmethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., Corona L, solid content 75% by mass)

B4: m-xylene diisocyanate adduct type (manufactured by Mitsui Chemicals Co., Ltd., D-120N)

B5: Epoxy hardener (manufactured by Mitsubishi Gas Chemical Co., Ltd., TETRAD-C)

[Assessment] [Gel rate]

Take about 0.1 g of the adhesive layer from the surface protection film obtained in the Examples/Comparative Examples to a sample bottle, add 30 mL of ethyl acetate, and shake for 4 hours, and then use a 200-mesh stainless steel metal mesh for the contents of the sample bottle After filtration, the residue on the metal mesh was dried at 100°C for 2 hours to measure the dry weight. According to the following formula, the gelation rate of the adhesive layer is obtained.

‧Gelization rate (%)=(dry weight/weight of adhesive layer taken)×100(%)

[ITO corrosive]

The surface protective film obtained in the example/comparative example was cut into 10mm×60mm, and the peeling film on one side was peeled off, and then attached to the cut 10mm×100mm ITO vapor-deposited PET film, and high pressure was performed at 50°C, 5atm for 20 minutes Cauldron Rationale. Next, after standing at room temperature for 1 hour, standing at 60°C and 90%RH for 500 hours, and then standing at 23°C and 65%RH for 1 hour, the resistance value of the ITO deposited film was measured to determine The resistance value change rate of the resistance value of the surface protection film that has not been subjected to the above-mentioned treatment is measured in advance, and evaluated with the following standards. In addition, the resistance value was measured using a testing machine (Sanwa Electric Meter Co., Ltd., digital multimeter PC510).

(Benchmark)

‧AA: The change rate of resistance value is less than 10%.

‧CC: The change rate of resistance value is more than 10%.

[Pollution]

The peeled PET film was peeled from the surface protection film obtained in the embodiment/comparative example, cut into 2.5cm×15cm, and attached to a stainless steel plate. After standing at 80°C for 24 hours, peel off the protective film from the stainless steel plate, visually confirm whether the surface of the stainless steel plate with the protective film is contaminated, and evaluate it according to the following criteria.

(Benchmark)

‧AA: No pollution is observed at all

‧BB: Clouds caused by the adhesive layer are slightly observed

‧CC: The pollution caused by the adhesive layer is clearly observed

[Low speed peel force]

The surface protection films obtained in the examples/comparative examples were cut into 25 mm×150 mm, and the PET films subjected to the peeling treatment were peeled off separately and attached to the stainless steel plate. Put it in an environment of 25°C and 50% humidity for 24 hours. After that, One end was stretched in the direction of 180° at a peeling speed of 300 mm/min, and the force at which peeling was started was the low-speed peeling force.

[High Speed Peeling Force]

The surface protection films obtained in the examples/comparative examples were cut into 25 mm×150 mm, and the PET films subjected to the peeling treatment were peeled off separately and attached to the stainless steel plate. Put it in an environment of 25°C and 50% humidity for 24 hours. After that, one end was stretched in the direction of 180° at a peeling and pulling speed of 30000 mm/min, and the initial high-speed peeling force was used as the initial peeling force.

The surface protection films obtained in the examples/comparative examples were cut into 25 mm×150 mm, and the PET films subjected to the peeling treatment were peeled off separately and attached to the stainless steel plate. Place it at 150°C for 1 hour. Thereafter, one end was stretched in the direction of 180° at a peeling and pulling speed of 30000 mm/min, and the force at which the peeling was started was the high-speed peeling force after heat resistance.

[Wettability]

The surface protection film obtained in the example/comparative example was cut into 40mm×150mm to make a test piece. Hold the two ends of the test piece on the stainless steel plate and approach it so that only the center of the test piece touches the stainless steel plate, then let go of the two ends of the test piece, and measure until the whole test piece is wetted and spread (adhered) to the stainless steel plate. The time is evaluated according to the following benchmarks.

(Benchmark)

‧AA: Less than 20 seconds

‧BB: More than 20 seconds, less than 60 seconds

‧CC: More than 60 seconds

Claims (3)

An adhesive composition for a surface protective film, which contains a (meth)acrylic resin (A) and a hexamethylene diisocyanate crosslinking agent (B), wherein the (meth)acrylic resin (A) ) Is obtained by solution polymerization of polymerizable monomers, and has the following characteristics (a1), (a2) and (a3), wherein the polymerizable monomer system is in an amount within the range of 95.0 to 99.9% by mass It contains alkyl (meth)acrylates having an alkyl group with a carbon number of 4 or less, and contains (meth)acrylates represented by CH ₂ =CR ³ -COOR ⁴ in an amount within the range of 0 to 30.0% by mass ( ii), and, in an amount within the range of 0.1 to 10.0% by mass, containing monomers selected from hydroxyl group-containing monomers, amine group-containing monomers, amide group-containing monomers, nitrogen-based heterocyclic ring-containing monomers, and One or more monomers (iv) of cyano monomers, wherein R ³ is a hydrogen atom or a methyl group, and R ⁴ is an organic group that excludes an alkyl group with less than 4 carbon atoms and does not have a polar group; and the aforementioned surface protective film The adhesive composition system contains the aforementioned hexamethylene diisocyanate-based cross-linking in an amount such that the gelation rate of the adhesive layer formed from the aforementioned adhesive composition for surface protection films is within the range of 90.0 to 99.9% by mass Agent (B); (a1) The weight average molecular weight (Mw) converted from polystyrene measured by gel permeation chromatography (GPC method) is in the range of 1.2 million to 2 million, (a2) molecular weight distribution (Mw /Mn) is in the range of 4 to 9, and (a3) the acid value is 2 mgKOH/g or less. Adhesive set for surface protective film as described in item 1 of the scope of patent application A product containing the hexamethylene diisocyanate-based crosslinking agent (B) in an amount in the range of 2 to 15 parts by mass relative to 100 parts by mass of the (meth)acrylic resin (A). A surface protective film having a film-like support and an adhesive layer formed on at least one surface of the aforementioned film-like support, wherein the aforementioned adhesive layer is the surface described in item 1 or item 2 of the scope of patent application The protective film is composed of an adhesive composition.