JP7065230B2 - Adhesive composition and surface protective film - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive composition containing an antistatic agent and a surface protective film. More specifically, it has excellent adhesive performance for a surface protective film used for protecting the surface of a polarizing plate by being attached to a polarizing plate constituting a liquid crystal display, and excellent without deterioration over time. The present invention relates to a pressure-sensitive adhesive composition having antistatic performance and a surface protective film using the same.

Conventionally, in the manufacturing process of an optical member such as a polarizing plate which is a member constituting a liquid crystal display, a surface protective film for temporarily protecting the surface of the optical member is attached. Such a surface protective film is used only in the process of manufacturing the optical member, and is peeled off from the optical member and removed when the optical member is incorporated into the liquid crystal display. Since such a surface protective film for protecting the surface of the optical member is used only in the manufacturing process, it is also generally called a process film.

In the surface protective film used in the process of manufacturing the optical member as described above, an adhesive layer is formed on one side of an optically transparent polyethylene terephthalate (PET) resin film. A release-treated release film for protecting the pressure-sensitive adhesive layer is bonded onto the pressure-sensitive adhesive layer until it is bonded to the optical member.
In addition, optical members such as polarizing plates undergo product inspections with optical evaluations such as display ability, hue, contrast, and contamination of liquid crystal displays with a surface protective film attached. Therefore, as the required performance for the surface protective film, it is required that air bubbles, foreign substances, and low molecular weight components of the pressure-sensitive adhesive composition do not adhere to the pressure-sensitive adhesive layer, that is, it has stain resistance.
Further, when the surface protective film is peeled off from an optical member such as a polarizing plate, the peeling charge generated by the static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend affects the failure of the electric control circuit of the liquid crystal display. Is a concern. Therefore, the pressure-sensitive adhesive layer is required to have excellent antistatic performance.
Furthermore, in recent years, as a protective layer (sometimes called a protective film) for the polarizing element of the polarizing plate, in addition to the conventional triacetyl cellulose (TAC), an acrylic resin such as polymethylmethacrylate (PMMA) and polyethylene terephthalate. The use of materials such as polyester resins such as (PET), cyclic olefin polymers, and polycarbonates, which are prone to peel charge when the surface protective film of the polarizing plate is peeled off, is increasing. Therefore, it is required that the antistatic performance required for the pressure-sensitive adhesive layer for the surface protective film of the polarizing plate is superior to that of the conventional one.
Further, when the surface protective film is finally peeled off from an optical member such as a polarizing plate, it is required to be able to peel it off quickly. It is required that the adhesive strength does not change much depending on the peeling speed so that the peeling can be performed quickly even by so-called high-speed peeling.

As described above, in recent years, as the required performance for the pressure-sensitive adhesive layer constituting the surface protective film, (1) balancing the adhesive strength at a low peeling speed and a high peeling speed, and (2) stain resistance. It is required to have the property and (3) excellent antistatic performance from the viewpoint of ease of use when using the surface protective film.
However, although each of these (1) to (3), which is the required performance for the pressure-sensitive adhesive layer constituting the surface protective film, can be satisfied, the pressure-sensitive adhesive layer of the surface protective film is required. It was a very difficult task to satisfy all the required performances (1) to (3) at the same time.

In order to solve such problems, for example, (1) balancing the adhesive force at a low peeling speed and a high peeling speed, (2) having stain resistance, and (3) The following proposals are known for excellent antistatic performance.

(1) With respect to balancing the adhesive strength at a low peeling speed and a high peeling speed, a (meth) acrylic acid alkyl ester having an alkyl group having 7 or less carbon atoms and a carboxyl group-containing copolymerizable compound. In the acrylic pressure-sensitive adhesive layer, which is mainly composed of a copolymer of There was a problem that the adhesive strength increased with time. In order to avoid this, a copolymer of a (meth) acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms and a copolymer compound having an alcoholic hydroxyl group was used, and this was crosslinked with a crosslinking agent. Those provided with a pressure-sensitive adhesive layer are known (Patent Document 1).
Further, a copolymer of the same copolymer as above is mixed with a small amount of a copolymer of a (meth) acrylic acid alkyl ester and a carboxyl group-containing copolymer compound, and a pressure-sensitive adhesive layer obtained by cross-linking the copolymer with a cross-linking agent is provided. Etc. have been proposed. However, when they are used to protect the surface of plastic plates with low surface tension and a smooth surface, they cause peeling phenomena such as floating due to heating during processing and storage, and at high speeds, which is a manual work area. There was also a problem that the re-peelability at the time of peeling was inferior.

In order to solve these problems, a) 100 parts by weight of a (meth) acrylic acid alkyl ester containing a (meth) acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms as a main component, b) a carboxyl group is contained. The above b is added to a copolymer of a monomer mixture consisting of 1 to 15 parts by weight of a copolymerizable compound and c) 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms. A pressure-sensitive adhesive composition containing an equivalent or more of a cross-linking agent with respect to the carboxyl group of the component) has been proposed (Patent Document 2).
The pressure-sensitive adhesive composition described in Patent Document 2 does not cause a peeling phenomenon such as floating during processing or storage, and moreover, it has a small adhesive strength with time and is excellent in re-peelability. Even if it is stored for a long period of time, especially in a high temperature atmosphere, it can be peeled off again with a small force, and at that time, no adhesive residue is generated on the adherend, and even when high-speed peeling is performed, it can be peeled off again with a small force.

Regarding (2) stain resistance, a carboxyl group-containing monomer of 0 parts by mass or more and less than 0.5 parts by mass, a hydroxy group-containing (meth) acrylic monomer of 0.6 to 9 parts by mass, and 99. 100 parts by mass of the (meth) acrylic copolymer consisting of 4 to 90.5 parts by mass of the (meth) acrylic acid ester monomer and having a weight average molecular weight of 100,000 or more and less than 1 million; and 0.1 parts of the carbodiimide-based cross-linking agent. A pressure-sensitive adhesive composition containing up to 5 parts by mass is disclosed (Patent Document 3).
The pressure-sensitive adhesive composition described in Patent Document 3 is characterized in that a carbodiimide-based cross-linking agent is used as a cross-linking agent for a (meth) acrylic copolymer having a specific composition. This makes it possible to provide the pressure-sensitive adhesive layer with a crosslinked structure that can follow the shrinkage due to pressure and temperature during the autoclave treatment. Therefore, the pressure-sensitive adhesive layer formed by using the pressure-sensitive adhesive composition can suppress and prevent foaming even under high temperature and high pressure conditions (during autoclave treatment), has excellent adherend contamination resistance, and is also excellent. , It is said that it is also excellent in transparency.

Further, regarding (3) excellent antistatic performance, a method of kneading an antistatic agent into a base film is shown as a method for imparting antistatic properties to the surface protective film. Examples of the antistatic agent include (a) various cationic antistatic agents having a cationic group such as a quaternary ammonium salt, a pyridinium salt, and a primary to tertiary amino group, and (b) a sulfonic acid base and a sulfuric acid. Anionic antistatic agents having anionic groups such as ester bases, phosphate ester bases and phosphonic acid bases, (c) amphoteric antistatic agents such as amino acid-based and aminosulfate ester-based, (d) amino alcohol-based and glycerin-based , Nonionic antistatic agents such as polyethylene glycol type, (e) high molecular weight antistatic agents obtained by increasing the molecular weight of the antistatic agents as described above, and the like are disclosed (Patent Document 4).
Further, in recent years, it has been proposed to contain such an antistatic agent in the base film, or to directly contain the antistatic agent in the pressure-sensitive adhesive layer instead of applying it to the surface of the base film.

Further, the antistatic pressure-sensitive adhesive composition in which a salt having an anion having a fluoro group and a sulfonyl group is dispersed, and the salt having an anion having a fluoro group and a sulfonyl group is a polyether group. Disclosed is an antistatic pressure-sensitive adhesive composition characterized by being dispersed in a state of being dissolved in a polyether ester-based plasticizing agent containing the above (Patent Document 5).
In the pressure-sensitive adhesive composition described in Patent Document 5, a mono or dicarboxylic acid having a saturated or unsaturated acyclic hydrocarbon group as a plasticizer, and an alcohol having an acyclic hydrocarbon group having 1 to 20 carbon atoms are used. It is disclosed to use an ester formed from an ester, or a plasticizer consisting of an ester in which an unsaturated group in the unsaturated acyclic hydrocarbon group is epoxidized. The mono or dicarboxylic acid having such a saturated or unsaturated acyclic hydrocarbon group has a carbon number close to that of the acrylic monomer constituting the acrylic copolymer used for the pressure-sensitive adhesive layer. As a result, the compatibility with the antistatic pressure-sensitive adhesive composition is improved, and the bleed-out is suppressed because it is suitably retained in the plasticizer acrylic antistatic pressure-sensitive adhesive composition.

Japanese Unexamined Patent Publication No. 63-225677 Japanese Unexamined Patent Publication No. 11-256111 Japanese Unexamined Patent Publication No. 2011-12254 Japanese Unexamined Patent Publication No. 11-070629 Japanese Unexamined Patent Publication No. 2014-118469

As described above, in the prior art, the required performance for the adhesive layer constituting the surface protective film is to balance the adhesive force at a low peeling speed and a high peeling speed, and to have stain resistance. Although excellent antistatic performance has been required, it has not been possible to satisfy all the required performances for the pressure-sensitive adhesive layer of the surface protective film at the same time, although each of them can meet the individual required performances.

The present invention has been made in view of the above circumstances, and has an excellent balance of adhesive strength in a low-speed peeling speed and a high-speed peeling speed, and further has excellent adhesive performance and stain resistance. An object of the present invention is to provide a pressure-sensitive adhesive composition and a surface protective film having excellent antistatic performance without deterioration over time.

In the pressure-sensitive adhesive composition having antistatic performance and the surface protection film using the same, the relationship between the antistatic performance and the stain resistance to the adherend is a trade-off relationship, and the antistatic performance is maintained. However, it was extremely difficult to improve the stain resistance.
By the way, the inventors of the present invention describe the pressure-sensitive adhesive composition as a copolymer obtained by copolymerizing a copolymerizable monomer containing a carboxyl group, a polyether-containing silicone compound, and a number of fluorine atoms of F7 or more. It is a technical idea of the present invention to solve this problem by containing an antioxidant made of an ionic compound having a melting point of 25 ° C. or higher having an anion (for example, nonafluorobutane sulfonate anion). Was completed.

In order to solve the above problems, the present invention is a pressure-sensitive adhesive composition containing an antioxidant and a cross-linking agent, wherein the pressure-sensitive adhesive composition has (A) an alkyl group having C1 to C18 carbon atoms. The acid value of the copolymerized (meth) acrylic acid ester monomer, (B) a copolymerizable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group is 0.1. Of the 100 parts by weight of the (meth) acrylic acid ester monomer having the (A) alkyl group having C1 to C18 carbon atoms, the acrylic polymer contains an acrylic polymer of a copolymer of up to 1.0. The acrylic polymer contains 2-ethylhexyl acrylate in a proportion of 70 parts by weight or more, the glass transition temperature of the acrylic polymer is 0 ° C. or less, the cross-linking agent is (D) a trifunctional or higher isocyanate compound, and the above. The antistatic agent is an ionic compound having a cation and an anion having a melting point of 25 to 50 ° C., which has an anion having an number of fluorine atoms of F7 or more, and the pressure-sensitive adhesive composition further comprises (E) a crosslink delay. Provided is a pressure-sensitive adhesive composition comprising an agent and (F) a crosslinking catalyst other than a tin compound as a crosslinking catalyst.

The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition for a surface protective film bonded to a protective layer of a polarizing element of a polarizing plate, and the protective layer of the polarizing element of the polarizing plate is a TAC-based film. One of the surface treatments selected from the group consisting of PMMA-based films and PET-based films, and the surface treatment applied to the surface of the protective layer of the polarizing element of the polarizing plate is untreated, AG treated, LR treated, and the like. It is preferably one selected from the group consisting of AR treatment, AG-LR treatment, and AG-AR treatment.

The anions of the ionic compound are C ₆ F ₅ (CF ₂ ) _n COO ⁻ , C ₆ F ₅ (CF ₂ ) _n SO ₃ ⁻ , C ₆ F ₅ (CF ₂ ) _n O ⁻ , C ₆ F ₅ O. (CF ₂ ) _n SO _3- ^, (C ₆ F ₅ CO) ₂ N- ^, (C ₆ F ₅ CO) ₃ C- ^, (C ₆ F ₅ SO ₂ ) ₂ N- ^, (C ₆ F ₅ SO ₂ ) ) ₃ C- ^, (C ₆ F ₅ OSO ₂ ) ₂ N- ^, (C ₆ F ₅ OSO ₂ ) ₃ C- ^, (C ₆ F ₅ ) ₄ B- ^, CF ₃ (CF ₂ ⁾ ₃ SO _3- At least one selected from the above group is contained as an anion, and the ionic compound is contained as an essential component in a ratio of 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic polymer. It is preferably contained.

The cation of the ionic compound is one selected from the group consisting of pyridinium, imidazolium, phosphonium, sulfonium, pyrrolidinium, guanidinium, ammonium, isouronium, thiouronium, piperidinium, pyrazolium, methylium, lithium and morpholinium, and the acrylic. It is preferable that the ionic compound is contained as an essential component in a ratio of 0.01 to 10 parts by weight with respect to 100 parts by weight of the system polymer.

The pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition has a surface resistance of 1.0 × 10 ⁺¹² Ω / □ or less, and is formed by using a composition for forming a low refractive index layer containing a fluorine compound. The peeling band voltage of the pressure-sensitive adhesive layer with respect to the low refractive index layer is in the range of −0.3 to +0.3 kV, and the speed of the pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition is low with respect to the polarizing plate. The adhesive strength at a peeling speed of 0.3 m / min is preferably 0.04 to 0.2 N / 25 mm, and the adhesive strength at a high peeling speed of 30 m / min is preferably 2.0 N / 25 mm or less.

The copolymerizable monomer containing the (B) hydroxyl group is 8-hydroxyoctyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, or 2-hydroxyethyl (meth) acrylate. , N-Hydroxy (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, and N-hydroxyethyl (meth) acrylamide, which are at least one selected from the compound group.
0.1 to 10 parts by weight of the copolymerizable monomer containing the (B) hydroxyl group with respect to 100 parts by weight of the (meth) acrylic acid ester monomer having C1 to C18 carbon atoms in the (A) alkyl group. It is contained in the ratio of
The copolymerizable monomer containing the (C) carboxyl group is (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2- (Meta) acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl maleic acid, At least one selected from the group of compounds consisting of carboxypolycaprolactone mono (meth) acrylate and 2- (meth) acryloyloxyethyl tetrahydrophthalic acid.
The copolymerizable monomer containing the (C) carboxyl group is 0.01 to 0 with respect to 100 parts by weight of the (meth) acrylic acid ester monomer having the carbon number of C1 to C18 of the (A) alkyl group. It is preferably contained in a proportion of 5.5 parts by weight.

The (E) cross-linking retarder is a compound of a ketoenol tectonic compound, and the (E) cross-linking retarder is contained in a ratio of 0.1 to 300 parts by weight with respect to 100 parts by weight of the acrylic polymer. The crosslinking catalyst (F) is at least one metal chelate compound selected from the group consisting of an aluminum chelate compound, a titanium chelate compound, and an iron chelate compound, and is 100 weight by weight of the acrylic polymer. The cross-linking catalyst (F) is contained in a proportion of 0.001 to 0.5 parts by weight, and the weight ratio of (E) / (F) is 80 to 1000. Is preferable.

The pressure-sensitive adhesive composition contains 0.01 to 0.5 parts by weight of a polyether-modified siloxane compound having an HLB value of 6 to 12 and a weight average molecular weight of 10,000 or less with respect to 100 parts by weight of the acrylic polymer. It is preferable to contain it in the ratio of.

The pressure-sensitive adhesive composition comprises a (meth) acrylic acid ester monomer having an alkyl group having C1 to 18 carbon atoms and a polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer with respect to 100 parts by weight of the acrylic polymer. It is preferable to contain a copolymer having a weight average molecular weight of more than 100,000 and 300,000 or less obtained by copolymerizing with 0.1 to 5.0 parts by weight.

The polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer has an average number of repetitions of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14, and the polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer has an average number of repetitions of 3 to 14. The diester content in the content is 0.2% or less, and the polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer includes polyalkylene glycol mono (meth) acrylate, methoxypolyalkylene glycol (meth) acrylate, and ethoxypolyalkylene. At least one selected from the group consisting of glycol (meth) acrylates is selected from 1 to 50 parts by weight of 100 parts by weight of the copolymer having a weight average molecular weight of more than 100,000 and 300,000 or less. It is preferably contained.

The present invention also provides a pressure-sensitive adhesive film, wherein a pressure-sensitive adhesive layer obtained by cross-linking the above-mentioned pressure-sensitive adhesive composition is laminated on one side of the resin film.

The present invention also provides a surface protective film using the above-mentioned adhesive film.

The present invention also provides a surface protective film for a polarizing plate using the above-mentioned adhesive film.

The present invention also provides an optical film with a pressure-sensitive adhesive, in which a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive composition is laminated on at least one surface of the optical film.

Further, the present invention provides the above-mentioned pressure-sensitive adhesive film which has been subjected to antistatic treatment and antifouling treatment on one side of the resin film opposite to the side on which the pressure-sensitive adhesive layer is formed.

The pressure-sensitive adhesive composition according to the present invention has excellent pressure-sensitive adhesive performance and excellent peeling antistatic performance without deterioration over time, as compared with the conventional pressure-sensitive adhesive composition for surface protective films.
In particular, the surface protective film according to the present invention is a composition for forming an antifouling layer containing a fluorine compound or a low refractive index layer containing a fluorine compound, in which the adherend is laminated on the surface of the optical film. In the low refractive index layer formed by using It has a remarkable effect on compatibility with stain resistance.
That is, the pressure-sensitive adhesive composition according to the present invention and the surface protective film using the same have excellent pressure-sensitive adhesive performance and excellent peeling antistatic performance without deterioration over time, and thus have an industrial utility value. It is extremely large.

Hereinafter, the present invention will be described based on a preferred embodiment.
The pressure-sensitive adhesive composition of the present embodiment is a pressure-sensitive adhesive composition containing an antioxidant and a cross-linking agent, and the pressure-sensitive adhesive composition is (A) having an alkyl group having C1 to C18 carbon atoms (A). The acid value of the copolymer of a (meth) acrylic acid ester monomer, (B) a crosslinkable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group is 0.1 to 1. The acrylic polymer contains the acrylic polymer of the copolymer of .0, and the acrylic polymer is 2-out of 100 parts by weight of the (meth) acrylic acid ester monomer having the (A) alkyl group having C1 to C18 carbon atoms. The acrylic polymer contains ethylhexyl acrylate in a proportion of 70 parts by weight or more, the glass transition temperature of the acrylic polymer is 0 ° C. or less, the cross-linking agent is (D) a trifunctional or higher isocyanate compound, and the antistatic agent is used. The agent is an ionic compound having a cation and an anion having a melting point of 25 to 50 ° C. and having an anion having an number of fluorine atoms of F7 or more. , (F) The cross-linking catalyst is characterized by containing a cross-linking catalyst other than the tin compound.

The acrylic polymer used in the pressure-sensitive adhesive composition of the present embodiment is the main polymer of the pressure-sensitive adhesive composition, and has a glass transition temperature of 0 ° C. or lower. Further, the acrylic polymer is preferably a copolymer containing (A) a (meth) acrylic acid ester monomer having an alkyl group having C1 to C18 as a main component.

(A) Examples of the (meth) acrylic acid ester monomer having an alkyl group having C1 to C18 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and isobutyl (meth). ) Acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) ) Acrylate, decyl (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, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate and the like. The alkyl group of the alkyl (meth) acrylate monomer may be linear, branched or cyclic.

The acrylic polymer used in the pressure-sensitive adhesive composition of the present embodiment contains 70 parts by weight of 2-ethylhexyl acrylate out of 100 parts by weight of the (meth) acrylic acid ester monomer having (A) an alkyl group having C1 to C18 carbon atoms. It is preferably contained in a portion or more.

The acrylic polymer used in the pressure-sensitive adhesive composition of the present embodiment contains (B) a copolymerizable monomer containing a hydroxyl group. (B) Examples of the copolymerizable monomer containing a hydroxyl group include 8-hydroxyoctyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate. , N-Hydroxy (meth) acrylamide, N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide and the like, preferably at least one selected from the compound group.
0.1 to 10 parts by weight of a copolymerizable monomer containing (B) a hydroxyl group with respect to 100 parts by weight of the (meth) acrylic acid ester monomer having C1 to C18 carbon atoms in the (A) alkyl group. It is preferably contained in a proportion of 1.6 to 8.5 parts by weight, more preferably in a proportion of 2.1 to 7.5 parts by weight, and particularly preferably to be contained in a proportion of 2.1 to 7.5 parts by weight.

The acrylic polymer used in the pressure-sensitive adhesive composition of the present embodiment contains (C) a copolymerizable monomer containing a carboxyl group. Examples of the copolymerizable monomer (C) containing a carboxyl group include (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, and the like. 2- (Meta) acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl maleic acid, It is preferably at least one selected from the compound group consisting of carboxypolycaprolactone mono (meth) acrylate, 2- (meth) acryloyloxyethyl tetrahydrophthalic acid and the like.
The copolymerizable monomer containing the (C) carboxyl group was 0.01 to 0. With respect to 100 parts by weight of the (meth) acrylic acid ester monomer having the number of carbon atoms of the (A) alkyl group of C1 to C18. It is preferably contained in a proportion of 5 parts by weight, more preferably in a proportion of 0.01 to 0.45 parts by weight, and more preferably in a proportion of 0.01 to 0.4 parts by weight. Especially preferable.

The method for producing the acrylic polymer contained in the pressure-sensitive adhesive composition according to the present embodiment is not particularly limited, and known polymerization methods such as a solution polymerization method and an emulsion polymerization method can be used as appropriate. The weight average molecular weight of the copolymer of the acrylic polymer is, for example, 500 to 3 million. The acid value of the acrylic polymer is preferably 0.1 to 1.0. Thereby, the stain resistance can be improved. Here, the "acid value" is one of the indexes representing the acid content, and is represented by the number of mg of potassium hydroxide required to neutralize 1 g of the polymer containing a carboxyl group.

The pressure-sensitive adhesive composition according to this embodiment contains (G) an antistatic agent. The (G) antistatic agent of the present embodiment is an ionic compound composed of a cation and an anion having an anion having a fluorine atom number of F7 or more. This ionic compound has a melting point of 25 to 50 ° C., and is preferably a solid at room temperature (for example, 25 ° C.). It is preferable that the ionic compound is contained as an essential component in a ratio of 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic polymer.
If it is necessary to improve the antistatic performance of the adhesive layer and reduce the lower limit of the surface resistivity to 1.0 × 10 ⁺¹⁰ Ω / □ or less, add 100 parts by weight of the acrylic polymer. On the other hand, it is more preferable to contain the ionic compound in a proportion of 0.01 to 15 parts by weight.

The anions of the ionic compound include C ₆ F ₅ (CF ₂ ) _n COO ⁻ , C ₆ F ₅ (CF ₂ ) _n SO ₃ ⁻ , C ₆ F ₅ (CF ₂ ) _n O ⁻ , and C ₆ F ₅ . O (CF ₂ ) _n SO _3- ^, (C ₆ F ₅ CO) ₂ N- ^, (C ₆ F ₅ CO) ₃ C- ^, (C ₆ F ₅ SO ₂ ) ₂ N- ^, (C ₆ F ₅ SO) ₂ ) ₃ C- ^, (C ₆ F ₅ OSO ₂ ) ₂ N- ^, (C ₆ F ₅ OSO ₂ ) ₃ C- ^, (C ₆ F ₅ ) ₄ B- ^, CF ₃ (CF ₂ ⁾ ₃ SO _3- At least one selected from the group consisting of. Here, n is an integer of 1 or more.
Examples of the cation of the ionic compound include at least one selected from the group consisting of pyridinium, imidazolium, phosphonium, sulfonium, pyrrolidinium, guanidinium, ammonium, isouronium, thiouronium, piperidinium, pyrazolium, methylium, lithium and morpholinium. Be done.

Specific examples of the (G) antistatic agent include, for example, methyltrioctylammonium tris (pentafluorobenzenesulfonyl) methide salt, 3-methyl-1-octylpyridinium nonaflatebutanesulfonate salt, 1-ethyl-3-methyl. Examples thereof include imidazolium tetrakispentafluorophenylborate salt, 1-butyl-1-methylpiperidinium bis (pentafluorobenzenesulfonyl) imide salt and the like.

The pressure-sensitive adhesive composition according to the present embodiment further contains (D) a trifunctional or higher functional isocyanate compound as a cross-linking agent. Examples of the trifunctional or higher functional isocyanate compound include bullet-modified and isocyanurate-modified, trimethylolpropane of diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate. Examples thereof include an adduct with a trivalent or higher polyol such as glycerin. (D) Examples of the ratio of the trifunctional or higher functional isocyanate compound include 0.01 to 5 parts by weight with respect to 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive composition according to the present embodiment may contain (E) a cross-linking retarder. (E) Examples of the cross-linking retarder include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetic acid, lauryl acetoacetic acid and stearyl acetoacetic acid, acetylacetone, 2,4-hexanedione and benzoylacetone. Etc., β-diketone and the like. These are compounds of the ketoenol homomorphic compound, and in a pressure-sensitive adhesive composition using a polyisocyanate compound as a cross-linking agent, by blocking the isocyanate group contained in the cross-linking agent, an excess of the pressure-sensitive adhesive composition after the compounding of the cross-linking agent is performed. It is possible to suppress an increase in viscosity and gelation, and extend the pot life of the pressure-sensitive adhesive composition. The (E) cross-linking retarder is preferably a compound of a keto-enol tautomer, and more preferably at least one selected from the compound group consisting of acetylacetone and ethyl acetoacetate. It is preferable that the (E) cross-linking retarder is contained in a ratio of 0.1 to 300 parts by weight with respect to 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive composition according to the present embodiment may contain a cross-linking catalyst other than the tin compound as the (F) cross-linking catalyst. (F) The cross-linking catalyst 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 of the cross-linking catalyst other than the tin compound include amine compounds such as tertiary amines, metal chelate compounds, organolead compounds, and organometallic compounds such as organozinc compounds.

(F) The metal chelate compound of the cross-linking catalyst 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 ligands X attached to the metal atom M. Specific examples of the metal chelate compound include tris (2,4-pentandionato) iron (III), iron trisacetylacetonate, titaniumtrisacetylacetonate, rutheniumtrisacetylacetonate, zinc bisacetylacetonate, and aluminum tris. Acetylacetonate, Zirconite Telux Acetylacetonate, Tris (2,4-hexanedionato) Iron (III), Bis (2,4-hexanezonato) Zinc, Tris (2,4-hexanezonato) Titanium, Tris Examples thereof include (2,4-hexanezonato) aluminum and tetrakis (2,4-hexanezonato) zinc.

The (F) cross-linking catalyst is preferably at least one metal chelate compound selected from the group consisting of an aluminum chelate compound, a titanium chelate compound, and an iron chelate compound. It is preferable that the (F) crosslinking catalyst is contained in a proportion of 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the acrylic polymer.

Since the (E) cross-linking retarder has an effect of suppressing cross-linking as opposed to the (F) cross-linking catalyst, it is possible to appropriately set the ratio of the (E) cross-linking retarder and the (F) cross-linking catalyst. preferable. In order to prolong the pot life of the pressure-sensitive adhesive composition and improve the storage stability, the weight ratio of (E) / (F) is preferably 80 to 1000. Here, the weight part ratio of (E) / (F) is the value of the quotient obtained by dividing the weight part of (E) by the weight part of (F).

The pressure-sensitive adhesive composition according to the present embodiment may contain (H) a polyether-modified siloxane compound as an optional component. (H) The polyether-modified siloxane compound is a siloxane compound having a polyether group, and is a siloxane unit having a polyether group [-SiR ¹ (R)] in addition to the usual siloxane unit [-SiR ¹ ₂ -O-]. It has ² O (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 a polyoxyalkylene group such as a polyoxyethylene group [(C ₂ H ₄ O) _n ] and a polyoxypropylene group [(C ₃ H ₆ O) _n ]. In the siloxane unit having a polyether group, the terminal of the polyether group may be an OH group ( ^R4 = H in the above general formula).
The (H) polyether-modified siloxane compound is preferably a polyether-modified siloxane compound having an HLB value of 6 to 12. Further, the (H) polyether-modified siloxane compound is preferably contained in an amount of 0.01 to 0.5 parts by weight, preferably 0.02 to 0.35 parts by weight, based on 100 parts by weight of the acrylic polymer. Is more preferable, and 0.02 to 0.25 parts by weight is particularly preferable. The HLB value is, for example, a hydrophilic lipophilic balance (hydrophilic lipophilic ratio) defined in JIS K3211 (surfactant term) and the like.
The polyether-modified siloxane compound can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group on a polyorganosiloxane backbone having a silicon hydride group by a hydrosilylation reaction. Specifically, dimethylsiloxane / methyl (polyoxyethylene) siloxane copolymer, dimethylsiloxane / methyl (polyoxyethylene) siloxane / methyl (polyoxypropylene) siloxane copolymer, dimethylsiloxane / methyl (polyoxypropylene) Examples thereof include siloxane polymers.
By blending the (H) polyether-modified siloxane compound into the pressure-sensitive adhesive composition, the adhesive strength and rework performance of the pressure-sensitive adhesive layer can be improved. The weight average molecular weight of the (H) polyether-modified siloxane compound is preferably 10,000 or less. From the viewpoint of compatibility with acrylic polymers, the lower the HLB value and the lower the molecular weight, the better the compatibility, but the low molecular weight polyether-modified siloxane compound has a relatively high HLB value and is a polymer. Excellent antistatic properties can be obtained even if the compatibility with is slightly low.

The pressure-sensitive adhesive composition according to the present embodiment has, as optional components, a (meth) acrylic acid ester monomer having an alkyl group having C1 to 18 carbon atoms and an (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer. A copolymer having a weight average molecular weight of more than 100,000 and a weight average molecular weight of 300,000 or less (hereinafter referred to as “polymer B”) may be contained as an antistatic auxiliary agent. The copolymer B is preferably contained in a proportion of 0.1 to 5.0 parts by weight, preferably 0.1 to 3.5 parts by weight, based on 100 parts by weight of the acrylic polymer. It is more preferable that the content is 0.1 to 2.5 parts by weight, and it is particularly preferable that the content is contained in a proportion of 0.1 to 2.5 parts by weight.

(I) The polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer may be a compound in which one hydroxyl group is esterified as a (meth) acrylic acid ester among a plurality of hydroxyl groups of the polyalkylene glycol. .. Since the (meth) acrylic acid ester group becomes a polymerizable group, it can be copolymerized with the acrylic polymer. It may be a polyalkylene glycol mono (meth) acrylate in which the other hydroxyl group remains OH, or an alkoxypolyalkylene glycol mono (meth) acrylate in which the other hydroxyl group is converted into an alkyl ether.

The polyalkylene glycol constituting the polyalkylene glycol chain may be a glycol compound having one or more alkylene groups, for example, polyethylene glycol, polypropylene glycol, polybutylene glycol, polyethylene glycol-polypropylene glycol, polyethylene. Glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, polyethylene glycol-polyethylene glycol-polybutylene glycol and the like can be mentioned.

(I) The polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer preferably has an average number of repetitions of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14. The "average number of repetitions of alkylene oxide" is the average number of repetitions of the alkylene oxide unit in the portion of (I) the "polyalkylene glycol chain" contained in the molecular structure of the polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer. It is a number. Further, the diester content in the (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer is preferably 0.2% or less. The "diester content in the monomer" is (I) the content (% by weight) of the polyalkylene glycol di (meth) acrylic acid ester contained in the (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer.

(I) The polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer is included in the group consisting of polyalkylene glycol mono (meth) acrylate, methoxypolyalkylene glycol (meth) acrylate, and ethoxypolyalkylene glycol (meth) acrylate. It is preferable that at least one selected from the above. The proportion of the (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer in the copolymer B is preferably 1 to 50 parts by weight, preferably 2 to 50 parts by weight, out of 100 parts by weight of the copolymer B. The proportion of 35 parts by weight is more preferable, and the proportion of 2 to 25 parts by weight is particularly preferable.

Examples of the monomer other than the (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomer copolymerized with the copolymer B include a (meth) acrylic acid ester monomer having an alkyl group having C1 to 18 carbon atoms. In addition, at least one kind of copolymerizable monomer containing a hydroxyl group and the like can be mentioned. Specific examples of these monomers include the (meth) acrylic monomers exemplified in the above (A) and (B), respectively. The monomer copolymerized with the copolymer B may be different from the monomer copolymerized with the acrylic polymer. The copolymer B does not have to be copolymerized with a copolymerizable monomer containing a carboxyl group.

The pressure-sensitive adhesive composition of the present embodiment is not limited to the above-mentioned additives, and is known as a surfactant, a curing accelerator, a plasticizer, a filler, a curing retarder, a processing aid, an antioxidant, an antioxidant and the like. Additives may be appropriately blended. These can be used alone or in combination of two or more.

The pressure-sensitive adhesive composition of the present embodiment is suitable as a pressure-sensitive adhesive composition for a surface protective film to be bonded to a protective layer of a polarizing element of a polarizing plate. Here, the protective layer of the polarizing element of the polarizing plate may be one selected from the group consisting of a TAC-based film, a PMMA-based film, and a PET-based film. Here, TAC is an abbreviation for triacetyl cellulose, PMMA is an abbreviation for polymethyl methacrylate, and PET is an abbreviation for polyethylene terephthalate.
Further, the surface treatment applied to the surface of the protective layer of the polarizing element of the polarizing plate was selected from the group consisting of untreated, AG treated, LR treated, AR treated, AG-LR treated, and AG-AR treated. It may be a seed. Here, AG is anti-glare, LR is low reflection, and AR is anti-reflection.

In the pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition of the present embodiment, the surface resistivity of the pressure-sensitive adhesive layer is preferably 1.0 × 10 ⁺¹² Ω / □ or less, and 5.0 × 10 ^{+ 11} Ω / □. It is more preferably 1.0 × 10 ^{+ 11} Ω / □ or less, and particularly preferably 1.0 × 10 + 11 Ω / □ or less. If the surface resistivity is large, the performance of releasing static electricity generated when the adhesive layer is peeled from the adherend is inferior. Therefore, by sufficiently reducing the surface resistivity, the peeling band voltage generated by the static electricity generated when the pressure-sensitive adhesive layer is peeled from the adherend is reduced, and the influence on the adherend is suppressed. Can be done.

The pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition of the present embodiment has a peeling band voltage of the pressure-sensitive adhesive layer with respect to the low-refractive index layer formed by using the composition for forming a low-refractive index layer containing a fluorine compound. Is preferably in the range of −0.3 to +0.3 kV. Examples of the fluorine compound used in the composition for forming a low refractive index layer include fluorine-containing polymers which are one or more polymers such as fluorinated olefins, fluorinated vinyl ethers, and fluorinated alkyl (meth) acrylates. Examples thereof include condensates such as polymers and fluorinated alkyl group-containing silane compounds. In the fluorine-containing copolymer, in addition to the fluorinated monomer, a non-fluorinated monomer such as olefins, vinyl ethers, and (meth) acrylate may be copolymerized. The low refractive index layer may be combined with a high refractive index layer or the like to form an antireflection layer.

The pressure-sensitive adhesive force of the pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition of the present embodiment with respect to a polarizing plate at a low peeling speed of 0.3 m / min is 0.04 to 0.2 N / 25 mm, and is high-speed. The adhesive strength at a peeling speed of 30 m / min is preferably 2.0 N / 25 mm or less, and more preferably 0.2 to 1.6 N / 25 mm at a high-speed peeling speed of 30 m / min. As a result, it is possible to obtain a performance in which the adhesive force does not change much depending on the peeling speed, and it is possible to quickly peel even by high-speed peeling. Further, since it is reattached, even when the surface protective film is once peeled off, it does not require an excessive force and can be easily peeled off from the adherend.

The gel fraction of the pressure-sensitive adhesive layer formed by cross-linking the pressure-sensitive adhesive composition of the present embodiment is preferably 95 to 100%, more preferably 97 to 100%. Due to such a high gel fraction, the adhesive strength does not become excessive at a low peeling speed, the elution of unpolymerized monomers or oligomers from the copolymer is reduced, and the reworkability and high temperature / high humidity are achieved. Durability is improved and contamination of the adherend can be suppressed.

The pressure-sensitive adhesive film of the present embodiment is formed by forming a pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition of the present embodiment on one side or both sides of the resin film. Further, the surface protective film of the present embodiment is a surface protective film formed by forming a pressure-sensitive adhesive layer formed by cross-linking the pressure-sensitive adhesive composition of the present embodiment on one side of a resin film. The pressure-sensitive adhesive composition of the present embodiment has excellent antistatic performance, has an excellent balance of adhesive strength at a low peeling speed and a high peeling speed, and has stain resistance. Therefore, it can be suitably used as a surface protective film for a polarizing plate.

As the base film of the pressure-sensitive adhesive layer and the release film (separator) that protects the pressure-sensitive adhesive surface, a resin film such as a polyester film can be used.
Antistatic treatment and antifouling treatment may be performed on one side of the resin film, which is opposite to the side on which the pressure-sensitive adhesive layer is formed. Examples of the antistatic treatment include application and kneading of an antistatic agent. Examples of the antifouling treatment include treatment with a silicone-based or fluorine-based mold release agent, a coating agent, silica fine particles, and the like. The release film may be subjected to a release treatment with a silicone-based, fluorine-based, long-chain alkyl-based release agent or the like on the surface of the pressure-sensitive adhesive layer on the side to be combined with the adhesive surface.

Further, an optical film with a pressure-sensitive adhesive layer can be obtained by laminating a pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition of the present embodiment on at least one surface of the optical film. Examples of the optical film include a polarizing film, a retardation film, an antireflection film, an antiglare film, an ultraviolet absorbing film, an infrared absorbing film, an optical compensation film, and a brightness improving film. Examples of the device to which the optical member is applied include a liquid crystal panel, an organic EL panel, a touch panel, and the like.
In the case of an optical surface protective film such as a surface protective film for a polarizing plate and an adhesive film, it is preferable that the base film and the adhesive layer have sufficient transparency.

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

<Manufacturing of acrylic polymer>
[Example 1]
Nitrogen gas was introduced into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen introduction pipe, and the air in the reaction apparatus was replaced with nitrogen gas. Then, a solvent (ethyl acetate) was added to the reaction apparatus together with 90 parts by weight of 2-ethylhexyl acrylate, 10 parts by weight of methyl acrylate, 5.5 parts by weight of 8-hydroxyoctyl acrylate, and 0.2 parts by weight of acrylic acid. 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 polymer used in Example 1.
[Examples 2 to 6 and Comparative Examples 1 to 3]
Examples 2 to 6 and Comparative Example 1 are the same as the acrylic polymer solution used in Example 1 above, except that the composition of the monomers is as described in (A) to (C) of Table 1. An acrylic polymer solution used in No. 3 was obtained.

<Manufacturing of adhesive composition and surface protective film>
[Example 1]
With respect to the acrylic polymer solution of Example 1 produced as described above, 2.0 parts by weight of a cross-linking agent (Coronate HX), 9 parts by weight of a cross-linking retarder (acetylacetone), and a cross-linking catalyst (titaniumtris acetylacetonate) 0. 1 part by weight, antistatic agent (methyltrioctylammonium tris (pentafluorobenzenesulfonyl) methide salt) 0.9 part by weight, polyether-modified siloxane compound (HLB = 7) 0.05 part by weight, copolymer B-1 (Molecular weight 150,000) 0.2 parts by weight was added, and the mixture was stirred and mixed to obtain the pressure-sensitive adhesive composition of Example 1. After applying this pressure-sensitive adhesive composition on a release film (a PET film coated with a silicone resin), the solvent was removed by drying at 90 ° C. to obtain a pressure-sensitive adhesive layer having a thickness of 20 μm. Then, the pressure-sensitive adhesive layer with a release film was transferred to the surface of the base film (a PET film whose one surface was antistatic and antifouling treated) opposite to the antistatic and antifouling surface. A surface protective film of Example 1 having a laminated structure of "base film / adhesive layer / release film" was obtained.
[Examples 2 to 6 and Comparative Examples 1 to 3]
Examples 2 to 6 are the same as the surface protective film of Example 1 above, except that the compositions of the additives are as described in (D) to (H) of Table 1 and the copolymer B, respectively. And the surface protective films of Comparative Examples 1 to 3 were obtained.

In Table 1, the parts by weight of each component were determined by taking the total of (meth) acrylic acid ester monomers having (A) alkyl groups having C1 to C18 as 100 parts by weight.
In Table 1, in each column of (D), (E), (F), (G), (H), and (copolymer B), 100 parts by weight of the acrylic polymer is contained and each component is contained. The ratio (part by weight) is shown by the numerical value in parentheses ().
The compound names of the abbreviations of each component used in Table 1 are shown in Tables 2 and 3. Table 2 also includes compound names of abbreviations for monomers other than (I) polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomers among the component monomers of the copolymer B shown in Table 3. Coronate (registered trademark) HX, HL and L are trade names of Tosoh Corporation, and Takenate (registered trademark) D-140N is a trade name of Mitsui Chemicals, Inc.

(G) Among the antistatic agents, G-1 to G-4 are all solid ionic compounds having an anion having an number of fluorine atoms of F7 or more and a melting point of 25 ° C. or more. G-5 is a solid ionic compound having an anion having an F5 number of fluorine atoms and a melting point of 25 ° C. or higher.
(H) Among the polyether-modified siloxane compounds, H-1 to H-6 all have a weight average molecular weight of 10,000 or less.
(I) Among the polyalkylene glycol chain-containing mono (meth) acrylic acid ester monomers, I-1 to I-3 have a diester content of 0.2% or less in the monomer, and I-4 is in the monomer. The diester content is 0.8%. Further, n in the column of group (I) in Table 3 is a numerical value indicating the average number of repetitions of alkylene oxide.

<Test method and evaluation>
The surface protective films of Examples 1 to 6 and Comparative Examples 1 to 3 were aged for 7 days in an atmosphere of 23 ° C. and 50% RH, respectively, and then evaluated by the following test method.

<Adhesive strength test method>
The release film was peeled off, and the surface protective film with the adhesive layer exposed was attached to the surface of the polarizing plate via the adhesive layer, left for 1 day, and then autoclaved at 50 ° C, 5 atm, and 20 minutes. The sample which was treated and left at room temperature for another 12 hours was used as a sample for measuring the adhesive strength. The peeling strength measured by peeling the obtained measurement sample in the 180 ° direction using a tensile tester at a low speed (0.3 m / min) or a high speed (30 m / min) was defined as the adhesive strength.
Here, the protective layer for the polarizing element of the polarizing plate is one selected from the group consisting of triacetyl cellulose (TAC), polymethyl methacrylate (PMMA), and polyethylene terephthalate (PET).
Further, in the LR polarizing plate and the AG-LR polarizing plate, the surface of the protective layer of the polarizing element of the polarizing plate is subjected to a low reflection surface treatment with a composition containing a fluorine compound.

<Test method of surface resistivity>
After aging the surface protective film and before bonding to the polarizing plate, the release film is peeled off to expose the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is exposed using the resistivity meter Hiresta UP-HT450 (manufactured by Mitsubishi Chemical Analytec). The surface resistivity of was measured.

<Test method for peeling band voltage>
The surface protective film from which the release film is peeled off to expose the pressure-sensitive adhesive layer has a low refractive index layer formed by using a composition for forming a low refractive index layer containing a fluorine compound on the adherend surface. It was affixed to a polarizing plate. High-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Co., Ltd.) can measure the voltage (band voltage) generated by charging the adherend when the surface protection film is peeled off by 180 ° at a tensile speed of 30 m / min. ), And the maximum value of the measured value was taken as the peeling band voltage.

<Stain resistance test method>
The polarizing plate subjected to the low reflection (LR) surface treatment was bonded onto one side of the glass plate via an adhesive layer (double-sided adhesive tape) using a bonding machine. Then, a surface protective film was bonded to the surface of the polarizing plate using a bonding machine. After storage in an environment of 23 ° C. and 50% RH for a period of 3 days and 30 days, the surface protective film was peeled off and the state of contamination on the surface of the polarizing plate was visually observed. The criteria for determining stain resistance were evaluated as "◯" when the surface of the polarizing plate was not contaminated, "Δ" when the surface was slightly contaminated, and "x" when the surface was contaminated.

Table 4 shows the evaluation results of the surface protective film in Examples 1 to 6 and Comparative Examples 1 to 3. The "surface resistivity" is expressed by a method in which "m × 10 ^{+ n} " is set to "mE + n" (where m is an arbitrary real number and n is a positive integer). The column of "Protective layer of the polarizing element of the polarizing plate" indicates the material and surface treatment of the protective layer of the polarizing element of the polarizing plate used in the adhesive strength test. Plain of "surface treatment" means untreated.

The surface protective films of Examples 1 to 6 have an adhesive force of 0.04 to 0.2 N / 25 mm at a low peeling speed of 0.3 m / min with respect to the polarizing plate as an adherend, and have a high peeling speed. The adhesive strength at 30 m / min was 2.0 N / 25 mm or less, and the adhesive performance was excellent.
Further, in the surface protective films of Examples 1 to 6, the surface resistance of the pressure-sensitive adhesive layer is 1.0 × 10 ⁺¹² Ω / □ or less, and a composition for forming a low refractive index layer containing a fluorine compound is used. The peeling band voltage of the pressure-sensitive adhesive layer with respect to the low refractive index layer formed therein was in the range of −0.3 to +0.3 kV, and the antistatic performance was excellent.
Further, the surface protective films of Examples 1 to 6 were not contaminated with the polarizing plate as an adherend even after being stored for a period of 3 days and 30 days, and were excellent in stain resistance.
That is, the evaluation results shown in Table 4 for the surface protective films of Examples 1 to 6 demonstrate that the problem of the present invention could be solved.

In the surface protective film of Comparative Example 1, among 100 parts by weight of the (meth) acrylic acid ester monomer having (A) alkyl groups having C1 to C18 carbon atoms in the acrylic polymer contained in the pressure-sensitive adhesive composition. The proportion of 2EHA is as small as 50 parts by weight, and the (C) carboxyl group-containing copolymerizable monomer is not copolymerized. Further, in the pressure-sensitive adhesive composition related to the surface protective film of Comparative Example 1, the antistatic agent contains an anion having F5 having less than F7 fluorine atoms. Therefore, the surface protective film of Comparative Example 1 had a large adhesive force of the pressure-sensitive adhesive layer, a high peeling band voltage, and poor stain resistance.

Further, in the surface protective film of Comparative Example 2, the acid value of the acrylic polymer contained in the pressure-sensitive adhesive composition exceeded 1.0, and the stain resistance was poor.
Further, in the surface protective film of Comparative Example 3, the antistatic agent contained in the pressure-sensitive adhesive composition contained an anion having F5 having a fluorine atom number of less than F7, and the stain resistance was poor.
As described above, the surface protective films of Comparative Examples 1 to 3 could not solve the problem of the present invention.

Claims (8)

A pressure-sensitive adhesive composition containing an antistatic agent and a cross-linking agent.
The pressure-sensitive adhesive composition
(A) A (meth) acrylic acid ester monomer having an alkyl group having C1 to C18 carbon atoms and
(B) A copolymerizable monomer containing a hydroxyl group and
(C) A copolymerizable monomer containing a carboxyl group and
Contains an acrylic polymer, which is a copolymer having an acid value of 0.1 to 1.0.
The acrylic polymer contains 70 parts by weight or more of 2-ethylhexyl acrylate in 100 parts by weight of the (meth) acrylic acid ester monomer having (A) alkyl groups having C1 to C18 carbon atoms. ,
The glass transition temperature of the acrylic polymer is 0 ° C. or lower, and the temperature is 0 ° C. or lower.
The cross-linking agent is (D) a trifunctional or higher functional isocyanate compound.
The pressure-sensitive agent composition is characterized in that the antistatic agent is an ionic compound having an anion having a fluorine atom number of F7 or more and having a melting point of 25 to 50 ° C. consisting of a cation and an anion. The pressure-sensitive adhesive composition according to claim 1, wherein the surface resistivity of the pressure-sensitive adhesive layer formed by cross-linking the pressure-sensitive adhesive composition is 1.0 × 10 ⁺¹² Ω / □ or less. The pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition is characterized by having an adhesive force of 0.04 to 0.2 N / 25 mm with respect to a polarizing plate at a low peeling speed of 0.3 m / min. The pressure-sensitive adhesive composition according to claim 1. The anions of the ionic compound are C ₆ F ₅ (CF ₂ ) _n COO ⁻ , C ₆ F ₅ (CF ₂ ) _n SO ₃ ⁻ , C ₆ F ₅ (CF ₂ ) _n O ⁻ , C ₆ F ₅ O. (CF ₂ ) _n SO _3- ^, (C ₆ F ₅ CO) ₂ N- ^, (C ₆ F ₅ CO) ₃ C- ^, (C ₆ F ₅ SO ₂ ) ₂ N- ^, (C ₆ F ₅ SO ₂ ) ) ₃ C- ^, (C ₆ F ₅ OSO ₂ ) ₂ N- ^, (C ₆ F ₅ OSO ₂ ) ₃ C- ^, (C ₆ F ₅ ) ₄ B- ^, CF ₃ (CF ₂ ⁾ ₃ SO _3- Containing at least one selected from the group as an anion,
The invention according to any one of claims 1 to 3, wherein the ionic compound is contained in a ratio of 0.01 to 10 parts by weight with respect to 100 parts by weight of the acrylic polymer. Adhesive composition. A pressure-sensitive adhesive film, wherein a pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition according to any one of claims 1 to 4 is laminated on one side of the resin film. A surface protective film using the adhesive film according to claim 5. A surface protective film for a polarizing plate using the adhesive film according to claim 5. An optical film with a pressure-sensitive adhesive, in which a pressure-sensitive adhesive layer composed of the pressure-sensitive adhesive composition according to any one of claims 1 to 4 is laminated on at least one surface of the optical film.