JP2020117723A - Surface protective film - Google Patents

Abstract

To provide a surface protective film which has a long pot life without using an organic tin compound and has a high crosslinking rate.SOLUTION: There is provided a surface protective film, in which an adhesive layer obtained by crosslinking an adhesive composition containing an acrylic polymer and a crosslinking agent is formed on one surface of a resin film, that contains 0.1-10 pts.wt. of (C) a bi- or higher functional isocyanate compound, 0.001-0.5 pts.wt. of (D) a crosslinking catalyst of a metal chelate compound and 0.1-300 pts.wt. of (E) a keto-enol tautomeric compound with respect to 100 pts.wt. of a copolymer obtained by copolymerization of (A) at least one or more (meth)acrylate monomer having a C4 to C18 alkyl group and (B) at least one or more copolymerizable monomers containing a hydroxyl group as a copolymerizable monomer group, and further contains a tocopherol compound that is oil soluble and a liquid at normal temperature as an antioxidant.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive composition and a surface protective film. More specifically, while the use of organotin compounds is restricted due to recent environmental problems, by using a cross-linking catalyst of a metal chelate compound other than the organotin compound, the pot life can be improved without using the organotin compound. The present invention relates to providing a pressure-sensitive adhesive composition having a long cross-linking speed and a surface protective film.

As a pressure-sensitive adhesive for optical use, since it has excellent transparency, a copolymer obtained by copolymerizing an alkyl (meth)acrylate as a main component with an acrylic monomer having a hydroxyl group, a carboxyl group, etc. as a functional group. An acrylic pressure-sensitive adhesive consisting of is preferably used. Further, it is required that various physical properties such as the adhesive strength of the adhesive are appropriately adjusted. In particular, the pressure-sensitive adhesive for surface protection film is suitable for laminating the surface protection film with an automatic laminating device so that it can be adapted to the manufacturing process of factory production, at a low peeling speed and a high peeling speed. Therefore, there is a demand for an adhesive having an excellent balance of adhesive strength. Furthermore, in addition to the balance of adhesive strength, an adhesive having excellent physical properties such as a long pot life is required.

For such various physical properties of the pressure-sensitive adhesive, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, etc., which react with functional groups such as hydroxyl groups and carboxyl groups contained in the acrylic pressure-sensitive adhesive made of a copolymer, are used. The cross-linking reaction is performed by adjusting the adhesive force and cohesive force.

Conventionally, isocyanate crosslinking agents have been widely used as crosslinking agents for acrylic pressure-sensitive adhesives. Further, in a crosslinking reaction using an isocyanate crosslinking agent, a metal chelate is often used as a catalyst for promoting the crosslinking reaction.
Generally, because of the excellent reaction rate of the crosslinking reaction, dibutyltin dilaurate, which is an organotin compound, has been used as a catalyst for the crosslinking reaction, but the dibutyltin compound exhibits harmful toxicity. It is avoided to use.
Therefore, there is a demand for a cross-linking catalyst which is used in combination with an isocyanate cross-linking agent and is an alternative to the dibutyl tin compound, which is inexpensive and has an excellent reaction rate of the cross-linking reaction, but it is difficult to find it. It was

Among them, Patent Document 1 discloses that, as a crosslinking catalyst used in combination with an isocyanate-based crosslinking agent, an iron chelate is preferable among metal chelates, and tris(acetylacetonato)iron is particularly preferable because it has excellent catalytic activity. There is.

By the way, in the acrylic pressure-sensitive adhesive composition containing a crosslinking catalyst, the crosslinking reaction gradually progresses even while being left at room temperature. Therefore, in industrial production of pressure-sensitive adhesives, after mixing the raw materials of the pressure-sensitive adhesive composition, until the time to start the cross-linking reaction, in order to leave the cross-linking reaction stopped, a cross-linking catalyst and a reaction retarder, in general, Are used together.
Regarding the combined use of the crosslinking catalyst and the reaction retarder, Patent Document 2 discloses a method for producing a polyurethane, which comprises a mixture of at least one metal acetylacetonate and acetylacetone, and the metal acetylacetonate and acetylacetone. It is disclosed to use a reactive urethane mixture containing a catalyst system having a weight ratio of 2:1.

JP, 2011-001440, A JP, 2008-285681, A

In the pressure-sensitive adhesive composition described in Patent Document 1, the addition amount of the metal compound (crosslinking catalyst) is shown with respect to the copolymer containing (meth)acrylate as a constituent monomer unit and containing a hydroxyl group and a carboxyl group. However, there is no description about the addition amount of the crosslinking retarder. Further, in Patent Document 1, as a method for suppressing the viscosity increase rate after the crosslinking agent is added to the pressure-sensitive adhesive composition, a method of using a reaction retarder, a method of adding a viscosity increase suppressing solvent, a functional group such as blocked isocyanate Although a method of using a cross-linking agent having a group blocked is mentioned, there is no specific explanation.

Further, in Patent Document 2, even if a metal acetylacetonate catalyst such as iron or copper having a very high activity at a low temperature is used, a metal having excellent stability and good catalytic activity, which does not cause premature curing. A method for producing polyurethane using a catalyst system containing acetylacetonate and acetylacetone is disclosed.
However, in the method described in Patent Document 2, the weight ratio of metal acetylacetonate and acetylacetone is 2:1, but even if this mixing ratio is applied to the production process of the acrylic pressure-sensitive adhesive, the crosslinking reaction is temporarily stopped. Couldn't stop.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a pressure-sensitive adhesive composition having a long pot life and a high crosslinking rate without using an organotin compound, and a surface protective film. To do.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention contains (B) hydroxyl group as a monomer group with at least 1 type of (A) alkyl group carbon number C4-C18 (meth)acrylic acid ester monomer. 0.1 to 10 parts by weight of (C) a bifunctional or more isocyanate compound, and (D) a metal chelate compound crosslinking catalyst 0.001 to 100 parts by weight of a copolymer with a copolymerizable monomer 0.5 parts by weight and 0.1 to 300 parts by weight of the (E) keto-enol tautomer compound, and the (E)/(D) parts by weight ratio is 70 to 1000. A characteristic adhesive composition is provided.

Further, it is preferable that the viscosity of the pressure-sensitive adhesive composition after storage for 8 hours after mixing the pressure-sensitive adhesive composition after being mixed at 23° C. is less than 1.25 times the viscosity immediately after mixing.

In addition, the copolymerizable monomer having a hydroxyl group (B) is 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth). ) At least one selected from the group of compounds consisting of acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide is preferable.

Further, among the (C) bifunctional or higher functional isocyanate compounds, the bifunctional isocyanate compound is preferably an acyclic aliphatic isocyanate compound produced by reacting a diisocyanate compound and a diol compound. .. The diisocyanate compound is an aliphatic diisocyanate, and is preferably one selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate and lysine diisocyanate. The diol compounds include 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl. 2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, polypropylene glycol It is preferably composed of one selected from the above.
Further, among the (C) bifunctional or higher-functional isocyanate compounds, as the trifunctional isocyanate compound, a hexamethylene diisocyanate compound isocyanurate body, an isophorone diisocyanate compound isocyanurate body, a hexamethylene diisocyanate compound adduct body, an isophorone diisocyanate compound is used. Adduct, burette of hexamethylene diisocyanate compound, burette of isophorone diisocyanate compound, isocyanurate of tolylene diisocyanate compound, isocyanurate of xylylene diisocyanate compound, isocyanurate of hydrogenated xylylene diisocyanate compound, tolylene diene At least one selected from the compound group consisting of an adduct of an isocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound is preferable.

Further, it is preferable that the pressure-sensitive adhesive composition does not contain an organotin compound as the crosslinking catalyst.

Further, the copolymer is preferably an acrylic polymer containing at least one or more of a carboxyl group-containing monomer and a hydroxyl group-free nitrogen-containing vinyl monomer as the other copolymerizable monomer group.

Further, the gel fraction of the pressure-sensitive adhesive composition after crosslinking is preferably 90 to 100%.

The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has an adhesive force of 0.05 to 0.2 N/25 mm at a low peeling speed of 0.3 m/min and a high peeling speed of 30 m/min. It is preferable that the adhesive strength at 2.0 N/25 mm or less.

The present invention also provides a pressure-sensitive adhesive film comprising a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition on one side or both sides of a resin film.

The present invention also provides a surface protection film, which is a surface protection film formed by forming a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition on one surface of a resin film.

Further, the surface protective film of the present invention can be used as a surface protective film for a polarizing plate.

Further, the surface protective film of the present invention is used as a surface protective film for any precision electric/electronic component selected from a group of precision electric/electronic components consisting of a flexible printed wiring board, a rigid printed wiring board, and a transparent conductive film. Can be used as

According to the present invention, it is possible to provide a pressure-sensitive adhesive composition having a long pot life and a high crosslinking rate, and a surface protective film without using an organotin compound.

The present invention will be described below based on preferred embodiments.
The pressure-sensitive adhesive composition of the present invention is a copolymer containing (A) at least one (meth)acrylic acid ester monomer having an alkyl group having a carbon number of C4 to C18 and a hydroxyl group (B) as a copolymerizable monomer group. 0.1 to 10 parts by weight of (C) a bifunctional or higher isocyanate compound, and (D) a metal chelate compound crosslinking catalyst 0.001 to 0.5 per 100 parts by weight of a copolymer with a possible monomer. Parts by weight and 0.1 to 300 parts by weight of the (E) keto-enol tautomer compound, and the ratio by weight of (E)/(D) is 70 to 1000. ..

The copolymer may be an acrylic polymer containing at least one or more of a carboxyl group-containing monomer and a hydroxyl group-free nitrogen-containing vinyl monomer as another copolymerizable monomer group.

Examples of the (A) (meth)acrylic acid ester monomer having an alkyl group of C4 to C18 include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, and heptyl (meth). ) Acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth) ) Acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, myristyl (meth)acrylate , Isomyristyl (meth)acrylate, cetyl (meth)acrylate, isocetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and the like.
It is preferable to contain 50 to 98 parts by weight of the (meth)acrylic acid ester monomer having (A) an alkyl group having a carbon number of C4 to C18 with respect to 100 parts by weight of the copolymer.

Examples of the (B) hydroxyl group-containing copolymerizable monomer include 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. Examples thereof include hydroxyalkyl (meth)acrylates and the like, hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and the like.
8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy (meth)acrylamide, N-hydroxymethyl (meth) ) It is preferable that at least one selected from the group of compounds consisting of acrylamide and N-hydroxyethyl(meth)acrylamide.
It is preferable that 0.1 to 10 parts by weight of the (B) hydroxyl group-containing copolymerizable monomer is contained in 100 parts by weight of the copolymer.

The copolymer may further include at least one or more of a carboxyl group-containing monomer, a hydroxyl group-free nitrogen-containing vinyl monomer, and a polyalkylene glycol mono(meth)acrylic acid ester monomer as another copolymerizable monomer group.

The carboxyl group-containing monomer is (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl. Hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, It is preferably at least one selected from the group of compounds consisting of 2-(meth)acryloyloxyethyl tetrahydrophthalic acid.
When the copolymer contains a carboxyl group-containing monomer as another copolymerizable monomer group, 0.1 to 1.0 part by weight of the carboxyl group-containing monomer is added to 100 parts by weight of the copolymer. It is preferable to contain in a ratio. The copolymer may not contain the carboxyl group-containing monomer.

The polyalkylene glycol mono(meth)acrylic acid ester monomer may be a compound in which one of the plural hydroxyl groups of the polyalkylene glycol is esterified as a (meth)acrylic acid ester. Since the (meth)acrylic acid ester group becomes a polymerizable group, it can be copolymerized with the copolymer of the main component. The other hydroxyl group may be OH as it is, or may be an alkyl ether such as methyl ether or ethyl ether, or a saturated carboxylic acid ester such as acetic acid ester.
Examples of the alkylene group contained in the polyalkylene glycol include, but are not limited to, an ethylene group, a propylene group, a butylene group, and the like. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polybutylene glycol. Examples of the polyalkylene glycol copolymer include polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, polyethylene glycol-polypropylene glycol-polybutylene glycol, and the like. It may be a block copolymer or a random copolymer.
The polyalkylene glycol mono(meth)acrylic acid ester monomer preferably has an average number of repeating alkylene oxides constituting the polyalkylene glycol chain of 3 to 14. The "average number of repeating alkylene oxides" is the average number of repeating alkylene oxide units in the "polyalkylene glycol chain" portion contained in the molecular structure of the polyalkylene glycol mono(meth)acrylic acid ester monomer.

The polyalkylene glycol mono(meth)acrylic acid ester monomer is at least one selected from polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol(meth)acrylate, and ethoxypolyalkylene glycol(meth)acrylate. The above is preferable.
More specifically, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-mono(meth)acrylate, polyethylene glycol-poly. Butylene glycol-mono(meth)acrylate, polypropylene glycol-polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol-mono(meth)acrylate; methoxy polyethylene glycol-(meth)acrylate, methoxy polypropylene glycol -(Meth)acrylate, methoxypolybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, methoxy-polypropylene glycol-polybutylene Glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate; ethoxypolyethylene glycol-(meth)acrylate, ethoxypolypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth). Acrylate, ethoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polypropylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polypropylene glycol -Polybutylene glycol-(meth)acrylate etc. are mentioned.
The polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably contained in a proportion of 0 to 50 parts by weight with respect to 100 parts by weight of the copolymer. The copolymer may not contain the polyalkylene glycol mono(meth)acrylic acid ester monomer.

Examples of the nitrogen-containing vinyl monomer having no hydroxyl group include vinyl monomers having an amide bond, vinyl monomers having an amino group, and vinyl monomers having a nitrogen-containing heterocyclic structure. More specifically, N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinyl. Cyclic nitrogen vinyl compounds having an N-vinyl-substituted heterocyclic structure, such as pyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, N-vinyllaurylolactam; N-( (Meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth) ) Acyclic nitrogen vinyl compounds having an N-(meth)acryloyl-substituted heterocyclic structure such as acryloylazepan and N-(meth)acryloylazocan; nitrogen atoms such as N-cyclohexylmaleimide and N-phenylmaleimide; Cyclic nitrogen vinyl compounds having a heterocyclic structure having an ethylenically unsaturated bond in the ring; (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, Nt-butyl(meth) Unsubstituted or monoalkyl-substituted (meth)acrylamide such as acrylamide; N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth ) Acrylamide, N,N-dibutyl(meth)acrylamide, N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, N-methyl-N-isopropyl(meth)acrylamide, etc. Dialkyl-substituted (meth)acrylamide; N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminoisopropyl (Meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminomethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N-ethyl-N-methylaminoethyl (meth ) Acrylate, N-methyl-N-propylaminoethyl (meth)acrylate, N-methyl-N-isopropylaminoethyl (meth) A) acrylate, dialkylamino(meth)acrylates such as N,N-dibutylaminoethyl(meth)acrylate, t-butylaminoethyl(meth)acrylate; N,N-dimethylaminopropyl(meth)acrylamide, N,N- Diethylaminopropyl (meth)acrylamide, N,N-dipropylaminopropyl (meth)acrylamide, N,N-diisopropylaminopropyl (meth)acrylamide, N-ethyl-N-methylaminopropyl (meth)acrylamide, N-methyl- N,N-dialkyl-substituted aminopropyl(meth)acrylamides such as N-propylaminopropyl(meth)acrylamide, N-methyl-N-isopropylaminopropyl(meth)acrylamide; N-vinylformamide, N-vinylacetamide, N- N-vinylcarboxylic acid amides such as vinyl-N-methylacetamide; N-methoxymethyl (meth)acrylamide, N-ethoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, diacetone acrylamide, N,N -(Meth)acrylamides such as methylenebis(meth)acrylamide; unsaturated carboxylic acid nitriles such as (meth)acrylonitrile; and the like.

It is preferable to contain the nitrogen-containing vinyl monomer having no hydroxyl group in a proportion of 0 to 20 parts by weight with respect to 100 parts by weight of the copolymer. The copolymer does not have to include the nitrogen-containing vinyl monomer having no hydroxyl group.

The (C) bifunctional or higher functional isocyanate compound may be at least one or two or more selected from polyisocyanate compounds having at least two or more isocyanate (NCO) groups in one molecule. The polyisocyanate compound is classified into an aliphatic isocyanate, an aromatic isocyanate, an acyclic isocyanate, an alicyclic isocyanate, and the like, but any of them may be used. Specific examples of the polyisocyanate compound include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and trimethylhexamethylene diisocyanate (TMDI), diphenylmethane diisocyanate (MDI) and xylylene diisocyanate (XDI). , Hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylene diisocyanate (TOID), tolylene diisocyanate (TDI), and other aromatic isocyanate compounds.
Examples of the trifunctional or higher isocyanate compound include a bifunctional isocyanate compound (compound having two NCO groups in one molecule), a buret modified product, an isocyanurate modified product, trimethylolpropane (TMP), glycerin, or the like having a valence of 3 or more. And the polyol (compound having at least 3 or more OH groups in one molecule) of 1).
As the (C) bifunctional or higher functional isocyanate compound, it is also possible to use only the (C-1) trifunctional isocyanate compound or the (C-2) bifunctional isocyanate compound. It is also possible to use the (C-1) trifunctional isocyanate compound and the (C-2) bifunctional isocyanate compound in combination.

Further, as the (C-1) trifunctional isocyanate compound used in the present invention, an isocyanurate body of a hexamethylene diisocyanate compound, an isocyanurate body of an isophorone diisocyanate compound, an adduct body of a hexamethylene diisocyanate compound, an adduct body of an isophorone diisocyanate compound, At least one or more selected from the (C-1-1) first aliphatic isocyanate compound group consisting of a burette of a hexamethylene diisocyanate compound and a burette of an isophorone diisocyanate compound, and a tolylene diisocyanate compound Isocyanurate body, isocyanurate body of xylylene diisocyanate compound, isocyanurate body of hydrogenated xylylene diisocyanate compound, adduct body of tolylene diisocyanate compound, adduct body of xylylene diisocyanate compound, adduct body of hydrogenated xylylene diisocyanate compound It is preferable that at least one selected from the group consisting of (C-1-2) second aromatic isocyanate compound consisting of It is preferable to use the (C-1-1) first aliphatic isocyanate compound group and the (C-1-2) second aromatic isocyanate compound group in combination. In the present invention, as the (C-1) trifunctional isocyanate compound, at least one or more selected from the (C-1-1) first aliphatic isocyanate compound group and (C-1-2) ) By using in combination with at least one or more selected from the second aromatic isocyanate compound group, it is possible to further improve the balance of the adhesive strength in the low-speed peeling region and the high-speed peeling region.
Further, the (C-1) trifunctional isocyanate compound is at least one selected from the above (C-1-1) first aliphatic isocyanate compound group, and the above (C-1-2). ) At least one selected from the second aromatic isocyanate compound group, and 0.5 to 5.0 parts by weight in total with respect to 100 parts by weight of the copolymer. Preferably. In addition, at least one or more selected from the group of (C-1-1) first aliphatic isocyanate compound, and (C-1-2) of the second aromatic isocyanate compound group. The mixing ratio with at least one or more selected from (C-1-1):(C-1-2) is in the range of 10%:90% to 90%:10% by weight. Is preferred.

Further, the (C-2) bifunctional isocyanate compound used in the present invention is preferably an acyclic aliphatic isocyanate compound which is produced by reacting a diisocyanate compound and a diol compound.
For example, a diisocyanate compound is represented by the general formula "O=C=N-X-N=C=O" (where X is a divalent group) and a general formula "HO-Y-OH" (where Y is a divalent group). When the diol compound is represented by ), examples of the compound produced by reacting the diisocyanate compound with the diol compound include compounds represented by the following general formula Z.

[General formula Z]
O=C=N-X-(NH-CO-O-Y-O-CO-NH-X) _n- N=C=O

Here, n is an integer of 0 or more. When n is 0, the general formula Z represents "O=C=N-X-N=C=O". As the bifunctional acyclic aliphatic isocyanate compound, a compound in which n is 0 in the general formula Z (a diisocyanate compound not reacted with the diol compound) may be contained, but a compound in which n is an integer of 1 or more is an essential component. It is preferable to include as. The bifunctional acyclic aliphatic isocyanate compound may be a mixture of a plurality of compounds having different n in the general formula Z.

The diisocyanate compound represented by the general formula "O=C=N-X-N=C=O" is an aliphatic diisocyanate. X is preferably an acyclic, aliphatic divalent group. The aliphatic diisocyanate is preferably composed of one or more selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate and lysine diisocyanate.

The diol compound represented by the general formula "HO-Y-OH" is an aliphatic diol. Y is preferably an acyclic and aliphatic divalent group. Examples of the diol compound include 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2. -Butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, polypropylene glycol It is preferable to be composed of one kind or two or more kinds selected.

The weight ratio (C-1/C-2) of the (C-1) trifunctional isocyanate compound to the (C-2) bifunctional isocyanate compound is preferably 1 to 90. The amount of the (C) bifunctional or higher isocyanate compound is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the copolymer.

The cross-linking catalyst for the metal chelate compound (D) may be any substance that functions as a catalyst for the reaction (cross-linking reaction) between the copolymer and the cross-linking agent when the polyisocyanate compound is used as the cross-linking agent. Examples thereof include amine compounds such as tertiary amines, metal chelate compounds, organotin compounds, organolead compounds and organometallic compounds such as organozinc compounds. In the present invention, a metal chelate compound is used as the crosslinking catalyst.

The metal chelate compound is a compound in which one or more polydentate ligands L are bonded to the central metal atom M. The metal chelate compound may or may not have one or more monodentate ligand X bonded to the metal atom M. For example, when a general formula of a metal chelate compound having one metal atom M is represented by M(L) _m (X) _n , m≧1 and n≧0. When m is 2 or more, m Ls may be the same ligand or different ligands. When n is 2 or more, n Xs may be the same ligand or different ligands.

Examples of the metal atom M include Fe, Ni, Mn, Cr, V, Ti, Ru, Zn, Al, Zr and Sn.
Examples of the polydentate ligand L include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate and stearyl acetoacetate, acetylacetone (also known as 2,4-pentanedione), Examples include β-diketones such as 2,4-hexanedione and benzoylacetone. These are keto-enol tautomeric compounds, and in the polydentate ligand L, an enol deprotonated enolate (eg acetylacetonate) may be used.
Examples of the monodentate ligand X include halogen atoms such as chlorine atom and bromine atom, pentanoyl group, hexanoyl group, 2-ethylhexanoyl group, octanoyl group, nonanoyl group, decanoyl group, dodecanoyl group and octadecanoyl group. Examples thereof include alkoxy groups such as a group, a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group and a butoxy group.

Specific examples of the metal chelate compound include tris(2,4-pentanedionato)iron(III), iron trisacetylacetonate, titanium trisacetylacetonate, ruthenium trisacetylacetonate, zinc bisacetylacetonate, and aluminum tris. Acetylacetonate, zirconium tetrakisacetylacetonate, tris(2,4-hexanedionate)iron(III), bis(2,4-hexanedionato)zinc, tris(2,4-hexanedionato)titanium, tris Examples include (2,4-hexanedionate)aluminum and tetrakis(2,4-hexanedionate)zirconium.

Examples of the organotin compound include dialkyltin oxide, fatty acid salt of dialkyltin, and fatty acid salt of stannous tin. Conventionally, many dibutyltin compounds have been used, but in recent years, the toxicity problem of organotin compounds has been pointed out, and tributyltin (TBT) contained in dibutyltin compounds has been feared as an endocrine disrupting substance. From the viewpoint of safety, long-chain alkyltin compounds such as dioctyltin compounds are preferable. Specific examples of the organic tin compound include dioctyl tin oxide and dioctyl tin dilaurate. Temporarily, Sn compounds can also be used, but in view of the trend of requiring the use of substances with higher safety in the future, such as Al, Ti, Fe, etc., which have higher safety than Sn, can be used. It is preferable to use a metal chelate compound.
The metal chelate compound in the pressure-sensitive adhesive composition according to the present invention preferably contains at least one selected from the group consisting of an aluminum chelate compound, a titanium chelate compound, and an iron chelate compound.
The crosslinking catalyst of the metal chelate compound (D) is preferably contained in an amount of 0.001 to 0.5 part by weight, based on 100 parts by weight of the copolymer.

Examples of the (E) keto-enol tautomer compound include β-keto esters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate and stearyl acetoacetate, acetylacetone, and 2,4-hexanedione. , Β-diketones such as benzoylacetone. These are, in a pressure-sensitive adhesive composition using a polyisocyanate compound as a cross-linking agent, by blocking the isocyanate group of the cross-linking agent, to suppress excessive viscosity increase and gelation of the pressure-sensitive adhesive composition after the incorporation of the cross-linking agent. The pot life of the pressure-sensitive adhesive composition can be extended.
The (E) ketoenol tautomer compound is preferably contained in an amount of 0.1 to 300 parts by weight based on 100 parts by weight of the copolymer.

The (E) keto-enol tautomer compound has an effect of suppressing cross-linking, contrary to the cross-linking catalyst of the (D) metal chelate compound. It is preferable to appropriately set the ratio of the mutant compound. In order to extend the pot life of the pressure-sensitive adhesive composition and improve the storage stability, the weight ratio (E)/(D) of (E) keto-enol tautomer compound/(D) cross-linking catalyst of metal chelate compound is used. Is preferably higher. The value of (E)/(D) is preferably in the range of 70 to 1000, more preferably 70 to 800, and most preferably 80 to 600.

More specifically, the pressure-sensitive adhesive composition having a long pot life according to the present invention is stored at 23° C. after mixing the pressure-sensitive adhesive composition, and the viscosity of the pressure-sensitive adhesive composition after 8 hours has passed immediately after mixing. It is preferably less than 1.25 times the viscosity of. This makes it possible to obtain a pressure-sensitive adhesive composition in which the increase in viscosity after blending is suppressed.

The pressure-sensitive adhesive composition of the present invention can contain additives such as antistatic agents, polyether siloxane compounds, and other conventional antioxidants as additives.

Examples of the antistatic agent include an antistatic agent contained in the pressure-sensitive adhesive composition and an antistatic agent copolymerized in the copolymer. The antistatic agent is preferably contained in an amount of 0.05 to 5.0 parts by weight based on 100 parts by weight of the copolymer.
The antistatic agent is preferably an ionic compound having a melting point of 25 to 50° C. and/or an acryloyl group-containing ionic compound. Since these antistatic agents have a low melting point and have a long-chain alkyl group, they are presumed to have a high affinity with the acrylic copolymer.

The ionic compound having a melting point of 25 to 50° C. is an ionic compound having a cation and an anion, and the cation is a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, a pyrrolidinium cation. , Nitronium-containing onium cations such as ammonium cations, phosphonium cations, sulfonium cations, and the like, whose anions are hexafluorophosphate (PF ₆ ⁻ ), thiocyanate (SCN ⁻ ), and alkylbenzene sulfonate (RC _{6 ).} H ₄ SO ₃ ⁻ ), perchlorate (ClO ₄ ⁻ ), tetrafluoroborate (BF ₄ ⁻ ), bis(fluorosulfonyl)imide salt (FSI), bis(trifluoromethanesulfonyl)imide salt (TFSI). ), a compound that is an inorganic or organic anion such as trifluoromethanesulfonate (TF). It is preferably solid at room temperature (for example, 25° C.), and one having a melting point of 25 to 50° C. can be obtained by selecting the chain length of the alkyl group, the position of the substituent, the number of the substituents and the like. The cation is preferably a quaternary nitrogen-containing onium cation, and a quaternary pyridinium cation such as 1-alkylpyridinium (the carbon atoms at the 2 to 6 positions may have a substituent or may be unsubstituted), or 1, Examples thereof include quaternary imidazolium cations such as 3-dialkylimidazolium (the carbon atoms at the 2,4,5 position may have a substituent or unsubstituted), quaternary ammonium cations such as tetraalkylammonium, and the like. ..
The ionic compound having a melting point of 25 to 50° C. is preferably contained in 0.05 to 5 parts by weight with respect to 100 parts by weight of the copolymer.

The acryloyl group-containing ionic compound is an ionic compound having a cation and an anion, wherein the cation is (meth)acryloyloxyalkyltrialkylammonium [R ₃ N ⁺ —C _n H _2n —OCOCQ═CH ₂ , a Q = H or _CH 3, R = alkyl], etc. (meth) acryloyl group-containing cationic, anion, hexafluorophosphate (PF ₆ ^-), thiocyanate (SCN ^-), an organic sulfonic acid A compound that is an inorganic or organic anion such as a salt (RSO ₃ ⁻ ), a perchlorate (ClO ₄ ⁻ ), a tetrafluoroborate (BF ₄ ⁻ ), or an F-containing imide salt (R ^F ₂ N ⁻ ). Can be mentioned. F-containing imide salt (R F ² _N ^-) as the R ^F of, trifluoromethanesulfonyl group, and perfluoro alkane sulfonyl group or fluorosulfonyl group, such as pentafluoroethane sulfonyl group. The F-containing imide salt, bis (fluorosulfonyl) imide salt _{[(FSO 2)} 2 N ^-], bis (trifluoromethanesulfonyl) imide salt _{[(CF 3 SO 2) 2 N} - ], bis (pentafluoroethane sulfonyl ) Bissulfonylimide salts such as imide salt [(C ₂ F ₅ SO ₂ ) ₂ N ⁻ ].
The acryloyl group-containing ionic compound is preferably copolymerized in the copolymer in an amount of 0.1 to 5.0% by weight.

Specific examples of the antistatic agent are not particularly limited, but specific examples of the ionic compound having a melting point of 25 to 50° C. include 1-octylpyridinium hexafluorophosphate and 1-nonylpyridinium 6 Fluorophosphate, 2-methyl-1-dodecylpyridinium hexafluorophosphate, 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 1-dodecylpyridinium dodecylbenzenesulfonate, 4 -Methyl-1-octylpyridinium hexafluorophosphate, quaternary ammonium salt of trifluoromethanesulfonic acid and the like can be mentioned. In addition, specific examples of the acryloyl group-containing ionic compound include dimethylaminomethyl(meth)acrylate hexafluorophosphoric acid methyl salt [(CH ₃ ) ₃ N ⁺ CH ₂ OCOCQ=CH ₂ ·PF ₆ ⁻ , provided that Q = H or CH _3], dimethylaminoethyl (meth) acrylate bis (trifluoromethanesulfonyl) imidomethyl salt ^{_{[(CH 3) 3 N + (}} CH 2) 2 OCOCQ = CH 2 · (CF 3 SO 2) 2 N -, However, Q = H or CH _3], dimethylaminomethyl methacrylate bis (fluorosulfonyl) imidomethyl salt ^{_{[(CH 3) 3 N + CH}} 2 OCOCQ = CH 2 · (FSO 2) 2 N -, however, Q = H or CH ₃ ] and the like.

The polyether-modified siloxane compound is a siloxane compound having a polyether group, in addition to the normal siloxane units [-SiR ¹ ₂ -O-], siloxane units having polyether groups [-SiR ^{1 (R} 2 O having _{^{(R 3 O) n R 4}} ) -O- ]. Here, R ¹ is one or more kinds of alkyl groups or aryl groups, R ² and R ³ are one or more kinds of alkylene groups, and R ⁴ is one or more kinds of alkyl groups or acyl groups. Etc. (terminal group). Examples of the polyether group include polyoxyalkylene groups such as polyoxyethylene group [(C ₂ H ₄ O) _n ] and polyoxypropylene group [(C ₃ H ₆ O) _n ].
The polyether-modified siloxane compound is preferably a polyether-modified siloxane compound having an HLB value of 7 to 15. Further, it is preferable that the polyether-modified siloxane compound is contained in an amount of 0.01 to 1.0 part by weight based on 100 parts by weight of the copolymer. More preferably, it is 0.1 to 0.5 parts by weight.
HLB is a hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) defined in JIS K3211, (surfactant term), for example.
The polyether-modified siloxane compound can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group onto a polyorganosiloxane main chain having a silicon hydride group by a hydrosilylation reaction. Specifically, dimethyl siloxane-methyl (polyoxyethylene) siloxane copolymer, dimethyl siloxane-methyl (polyoxyethylene) siloxane-methyl (polyoxypropylene) siloxane copolymer, dimethyl siloxane-methyl (polyoxypropylene) Examples thereof include siloxane polymers.
By blending the polyether-modified siloxane compound in the pressure-sensitive adhesive composition, the pressure-sensitive adhesive strength and rework performance of the pressure-sensitive adhesive can be improved. When the pressure-sensitive adhesive composition does not contain the polyether-modified siloxane compound, the cost becomes lower.

Examples of the antioxidant include hindered phenol-based antioxidants, polyphenol compounds, tocopherol-based compounds, and the like. Of these, tocopherol compounds are preferable. The tocopherol compound is generally vitamin E, which is also a naturally occurring chemical substance. For this reason, there is little adverse effect on the human body, high safety in handling, and environmentally friendly. Further, since it is oil-soluble and liquid at room temperature, it has excellent compatibility with the pressure-sensitive adhesive composition and excellent precipitation resistance. By adding the tocopherol compound as the antioxidant, the storage stability of the pressure-sensitive adhesive is improved, so that the pot life of the pressure-sensitive adhesive composition containing the curing agent is improved.
As the tocopherol compound used in the present invention, since it is used by being blended with the adhesive composition (not metabolized as in the human body), the ferrule hydroxyl group of tocopherol is not changed to an ester or the like, and the ferrule property is obtained. A compound having a hydroxyl group is preferable. Examples include tocopherol and tocotrienol. It is known that tocopherol and tocotrienol are distinguished from each other as a natural type compound (d-form), a non-natural type compound (1-form), and a racemic form (dl-form) which is an equivalent mixture thereof. ing. Natural compounds (d-form) and racemic forms (dl-form) are preferable because some of them are used as food additives.
Specific tocopherol compounds include d-α-tocopherol, dl-α-tocopherol, d-β-tocopherol, dl-β-tocopherol, d-γ-tocopherol, dl-γ-tocopherol, d-δ-tocopherol. , Dl-δ-tocopherol, d-α-tocotrienol, dl-α-tocotrienol, d-β-tocotrienol, dl-β-tocotrienol, d-γ-tocotrienol, dl-γ-tocotrienol, d-δ-tocotrienol, dl At least one selected from the group of compounds consisting of -δ-tocotrienol can be mentioned. You may use together 2 or more types of tocopherol type compounds. As a food additive, what is called "mixed tocopherol" is a mixture containing d-α-tocopherol, d-β-tocopherol, d-γ-tocopherol and d-δ-tocopherol as main components, and "tocotrienol". What is called is a mixture based on d-α-tocotrienol, d-β-tocotrienol, d-γ-tocotrienol and d-δ-tocotrienol.
When the pressure-sensitive adhesive composition of the present invention contains a tocopherol compound, it is preferable to contain 0.01 to 5 parts by weight of the tocopherol compound with respect to 100 parts by weight of the copolymer.

Further, as other components, copolymerizable (meth)acrylic monomers containing alkylene oxide, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing catalysts, plasticizers, fillers, curing retarders, processing Known additives such as auxiliaries, antiaging agents and antioxidants can be appropriately added. These may be used alone or in combination of two or more.

The copolymer of the main agent used in the pressure-sensitive adhesive composition of the present invention comprises (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18 as a copolymerizable monomer group ( It can be synthesized by copolymerizing B) a copolymerizable monomer containing a hydroxyl group. The polymerization method of the copolymer is not particularly limited, and an appropriate polymerization method such as solution polymerization or emulsion polymerization can be used.
In addition, the copolymer may include at least one or more of a carboxyl group-containing monomer and a hydroxyl group-free nitrogen-containing vinyl monomer as another copolymerizable monomer group.
In the pressure-sensitive adhesive composition of the present invention, (C) a bifunctional or higher isocyanate compound, (D) a cross-linking catalyst of a metal chelate compound, (E) a keto-enol tautomer compound, and further any optional compound are added to the above copolymer. It can be prepared by blending additives.

The copolymer is preferably an acrylic polymer, and preferably contains 50 to 100% by weight of an acrylic monomer such as (meth)acrylic acid ester monomer, (meth)acrylic acid, or (meth)acrylamide.
The acid value of the copolymer is preferably 8.0 or less, more preferably 0.01 to 8.0. As a result, the stain resistance can be improved and the adhesive residue generation preventing performance can be improved.
Here, the "acid value" is one of the indexes showing the content of the acid, and is represented by the mg number of potassium hydroxide required to neutralize 1 g of the polymer containing a carboxyl group.

The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has an adhesive force of 0.05 to 0.2 N/25 mm at a low peeling speed of 0.3 m/min, and a high peeling speed of 30 m/min. The adhesive strength is preferably 2.0 N/25 mm or less. As a result, it is possible to obtain a performance in which the adhesive strength is less changed by the peeling speed, and the peeling can be performed quickly even by the high speed peeling. Further, since the film is reattached, even when the surface protection film is once peeled off, it does not require an excessive force and can be easily peeled off from the adherend.

The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition of the present invention (pressure-sensitive adhesive after crosslinking) preferably has a gel fraction of 90 to 100%. Due to such a high gel fraction, the adhesive force does not become excessive at a low peeling speed, the elution of unpolymerized monomer or oligomer from the copolymer is reduced, and reworkability and high temperature and high humidity are reduced. The durability is improved, and contamination of the adherend can be suppressed.

The pressure-sensitive adhesive film of the present invention has a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one side or both sides of a resin film. The surface protective film of the present invention is a surface protective film obtained by forming a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one surface of a resin film. In the pressure-sensitive adhesive composition of the present invention, the components (A) to (E) described above are blended in a well-balanced manner, so that the pot life is long and the cross-linking speed is fast without using an organotin compound. Become. Therefore, the surface protective film of the present invention is used as a surface protective film for a polarizing plate, or selected from a group of precision electric/electronic components including a flexible printed wiring board, a rigid printed wiring board, and a transparent conductive film. It can be preferably used as a surface protection film for precision electric/electronic parts.

In the pressure-sensitive adhesive film and the surface protective film according to the present invention, a polyester film or the like can be used as the base material of the resin film or the release film (separator) that protects the pressure-sensitive adhesive layer.
In addition, the resin film, on the side opposite to the side on which the adhesive layer of the resin film is formed, is a silicone-based or fluorine-based release agent or coating agent, antifouling treatment with silica fine particles, and application of an antistatic agent. An antistatic treatment such as kneading or kneading can be performed.
Further, the release film is subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface of the release layer which is to be joined with the adhesive surface.

Hereinafter, the present invention will be specifically described with reference to examples.

<Production of acrylic copolymer>
[Example 1]
Nitrogen gas was introduced into a reactor equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Then, 100 parts by weight of 2-ethylhexyl acrylate and 3.5 parts by weight of 8-hydroxyoctyl acrylate were added to the reactor. Then, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours and reacted at 65° C. for 6 hours to obtain an acrylic copolymer solution having a weight average molecular weight of 500,000 and used in Example 1. Got 1. A part of the acrylic copolymer was collected and used as a sample for measuring an acid value described later.
[Examples 2 to 6 and Comparative Examples 1 to 3]
Example 1 was carried out in the same manner as the acrylic copolymer solution 1 used in Example 1 except that the compositions of the monomers were as shown in Table 1 (A), (B) and (I). Acrylic copolymer solutions used in Examples 2 to 6 and Comparative Examples 1 to 3 were obtained.

<Production of adhesive composition and surface protection film>
[Example 1]
To the acrylic copolymer solution 1 of Example 1 produced as described above, 6.0 parts by weight of acetylacetone was added and stirred, and then 1.5 parts by weight of Coronate HX (isocyanurate body of hexamethylene diisocyanate compound), 0.05 parts by weight of tris(2,4-pentanedionato)iron(III) was added and mixed by stirring to obtain an adhesive composition of Example 1. This adhesive composition is applied on a release film made of a polyethylene resin-coated polyethylene terephthalate (PET) film and dried at 90° C. to remove the solvent, and the adhesive layer has a thickness of 25 μm. Got the sheet.
After that, an adhesive sheet was transferred to the surface opposite to the surface of the polyethylene terephthalate (PET) film that had been subjected to antistatic and antifouling treatment on one side, to the surface opposite to the surface on which the antistatic and antifouling treatment had been performed. A surface protective film of Example 1 having a laminated structure of "PET film/adhesive layer/release film (PET film coated with silicone resin)" was obtained.
[Examples 2 to 6 and Comparative Examples 1 to 3]
Examples 2 to 6 and Comparative Example 1 were performed in the same manner as the surface protective film of Example 1 except that the compositions of the additives were as described in Table 1 (C) to (E). The surface protection film of -3 was obtained.

Table 1 shows the numerical values of parts by weight obtained by setting the total of the group (A) as 100 parts by weight in parentheses. Table 2 shows the value of the ratio (E)/(D). The compound names of the abbreviations of the components used in Table 1 are shown in Table 3. Coronate (registered trademark) HX, HL, and L are trade names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N are trade names of Mitsui Chemicals, Inc., and Duranate (registered trademark). D101 is a product name of Asahi Kasei Chemicals Corporation.

<Test method and evaluation>
The surface protection films in Examples 1 to 6 and Comparative Examples 1 to 3 were aged in an atmosphere of 23° C. and 50% RH for 7 days, and then the release film (a PET film coated with a silicone resin) was peeled off to give an adhesive property. The agent layer was exposed. Further, the surface protective film showing this pressure-sensitive adhesive layer was bonded to the surface of the polarizing plate bonded to the liquid crystal cell via the pressure-sensitive adhesive layer, and left for 1 day, then, at 50° C., 5 atmospheric pressure, 20 minutes. An autoclave-treated sample, which was left at room temperature for 12 hours, was used as a sample for measuring the adhesive strength.

<Adhesive strength>
The measurement sample (having a surface protective film with a width of 25 mm attached to the surface of a polarizing plate) obtained above was used in a 180° direction using a tensile tester to give a low peeling speed (0.3 m/min) and a high speed. Was peeled at a peeling speed (30 m/min), and the peel strength measured was taken as the adhesive strength.

<Pot life>
Immediately after adding the additives (C) to (E), the viscosity η ₀ (initial viscosity) of the pressure-sensitive adhesive composition was measured, and after the pressure-sensitive adhesive composition was left in a sealed state at 23° C. for 8 hours. The viscosity η ₁ (viscosity after 8 hours) of the pressure-sensitive adhesive composition was measured. As an index of pot life, the value of η ₁ when η ₀ was set to 1.0, that is, the ratio of η ₁ /η ₀ was obtained. The evaluation target standard is “◯” when the viscosity after 8 hours is less than 1.25 times the initial viscosity, “Δ” when it is 1.25 times or more and less than 1.50 times, 1.50 times or more, or The case of gelling after standing for 8 hours was evaluated as "x".

Table 4 shows the evaluation results.

The surface protective films of Examples 1 to 6 have an adhesive force of 0.05 to 0.2 N/25 mm at a low peeling speed of 0.3 m/min, and an adhesive force of 2 at a high peeling speed of 30 m/min. It was 0.0 N/25 mm or less, and the pot life was sufficiently long.
That is, at a low peeling speed and a high peeling speed, the balance of the adhesive strength is excellent, the pot life is long, and the characteristics as a surface protective film are excellent.
Further, according to the surface protective films of Examples 1 to 6, since the pressure-sensitive adhesive composition does not contain an organotin compound, the safety is high.

The surface protective film of Comparative Example 1 does not contain (C) a bifunctional or higher isocyanate compound serving as a cross-linking agent, probably because of a low peeling speed of 0.3 m/min and a high peeling speed of 30 m/min. Was too large.
The surface protection film of Comparative Example 2 had a short pot life because the ratio of the (E) ketoenol tautomer compound to the crosslinking catalyst of the (D) metal chelate compound was small.
The surface protective film of Comparative Example 3 had a small proportion of the (E) keto-enol tautomer compound to the crosslinking catalyst of the (D) metal chelate compound, so that the pot life was too short and the crosslinking proceeded before coating. I couldn't work.
As described above, in the surface protection films of Comparative Examples 1 to 3, at low peeling speeds and high peeling speeds, the balance of adhesive strength is excellent, and further, the pot life is long, and all the required performances are satisfied at the same time. I couldn't.

Claims (3)

A pressure-sensitive adhesive layer formed by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer and a cross-linking agent, which is a surface protective film formed on one side of a resin film,
The acrylic polymer is copolymerizable with (A) an alkyl group having at least one (meth)acrylic acid ester monomer having a C4 to C18 carbon number, and (B) a hydroxyl group as a copolymerizable monomer group. A copolymer obtained by copolymerizing at least one or more of various monomers,
Isooctyl (meth)acrylate and 2-ethylhexyl (meth)acrylate among 100 parts by weight in total of at least one kind of (meth)acrylic acid ester monomer having (A) alkyl group of C4 to C18. 50 parts by weight, or one kind selected from the group consisting of isooctyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is contained at a ratio of more than 50 parts by weight,
The adhesive composition contains 0.1 to 10 parts by weight of (C) a difunctional or more isocyanate compound as the crosslinking agent, and (D) a crosslinking catalyst for a metal chelate compound, relative to 100 parts by weight of the copolymer. 0.001 to 0.5 parts by weight and 0.1 to 300 parts by weight of the (E) keto-enol tautomer compound,
The pressure-sensitive adhesive composition further comprises, as an antioxidant, a tocopherol compound that is oil-soluble and is liquid at room temperature,
The tocopherol compound is d-α-tocopherol, dl-α-tocopherol, d-β-tocopherol, dl-β-tocopherol, d-γ-tocopherol, dl-γ-tocopherol, d-δ-tocopherol, dl- δ-tocopherol, d-α-tocotrienol, dl-α-tocotrienol, d-β-tocotrienol, dl-β-tocotrienol, d-γ-tocotrienol, dl-γ-tocotrienol, d-δ-tocotrienol, dl-δ- A surface protective film comprising at least one selected from the group of compounds consisting of tocotrienols. The copolymer is an acrylic polymer containing at least one or more of a carboxyl group-containing monomer and a hydroxyl group-free nitrogen-containing vinyl monomer as another copolymerizable monomer group. The surface protection film described. Use as a surface protection film for any precision electric/electronic component selected from a precision electric/electronic component group consisting of a polarizing plate, a flexible printed wiring board, a rigid printed wiring board, and a transparent conductive film. Or the surface protective film according to 2.