TWI631199B - Adhesive composition - Google Patents

Abstract

The present invention provides an adhesive composition comprising: an acrylic copolymer, based on 100 parts by weight of all monomers, by including 1 to 10 parts by weight of a (meth) acrylic ester system having a carboxyl group A monomer and 0.1 to 2 parts by weight of a monomer having a linear or cyclic alkyl (meth) acrylate monomer containing 4 or more carbon atoms substituted with a hydroxyl group are prepared by copolymerization; a trifunctional group or Higher toluene diisocyanate cross-linking agents; and ionic antistatic agents with Na ⁺ or K ⁺ ions, making the adhesive composition change over time without fear of physical characteristics (high temperature or high temperature and high humidity environment) In the case of deterioration, the antistatic properties and durability are improved, and the curing period is shortened.

Description

Adhesive composition

The invention relates to an adhesive composition, which has good antistatic properties, liquid stability and short curing period.

Generally, a liquid crystal display (LCD) includes a polarizing plate and a liquid crystal cell having a liquid crystal. An adhesive layer suitable for combining the liquid crystal cell and the polarizing plate is used. As the adhesive, an acrylic adhesive including an acrylic polymer having good adhesiveness and transparency as a base material is widely used.

During the process of bonding the polarizing plate to the liquid crystal cell, the release film may peel off from the adhesive layer and cause static electricity. Static electricity will affect the alignment of the liquid crystal, cause liquid crystal defects, or induce electrostatic attraction, so that foreign matter flows into the liquid crystal cell and the adhesive and causes pollution.

To solve those problems, a monoionic antistatic agent is mixed with an adhesive composition. However, the bleeding phenomenon caused by the overflow of the ionic antistatic agent to the surface will cause curling, blistering, delamination, and the like. More specifically, those defects may be more severe under high temperature or high temperature and humidity.

At the same time, a conventionally disclosed adhesive composition includes an acrylic copolymer obtained by copolymerizing an oxyalkylene group-containing monomer [Korean Patent Publication Nos. 2012-0073093 and 2009-0055576]. However, it is possible that As time goes on, the viscosity of the acrylic copolymer also increases. Therefore, during mass production, the acrylic copolymer will be difficult to preserve.

In addition, for this adhesive composition, in addition to antistatic properties and durability, it also plays an important role in productivity during curing. More specifically, it can affect storage capacity, inventory management, and emergency shipment handling. , And the like.

Therefore, conventionally, various catalysts which can increase the crosslinking reaction speed to shorten the curing period are introduced [Korean Patent Publication Nos. 2012-0091549 and 2010-0039274]. However, it is important to control the amount of catalyst used in the cross-linking reaction. More specifically, if too much catalyst is added, there will be a risk of equipment clogging or the like.

The present invention solves the problems occurring in the conventional knowledge, and an object of the present invention is to provide an adhesive composition, which can improve antistatic properties and durability at the same time without fear of increasing viscosity over time, and Without using a crosslinking catalyst, the curing period is shortened.

According to an object of the present invention, there is provided an adhesive composition including: an acrylic copolymer, based on 100 parts by weight of all monomers, by including 1 to 10 parts by weight of a carboxyl group ( (Meth) acrylic acid ester-based monomer and 0.1 to 2 parts by weight of a monomer having a (meth) acrylic acid ester-based monomer having a linear or cyclic alkyl group having 4 or more carbon atoms substituted with a hydroxyl group are copolymerized to Preparation; trifunctional or higher toluene diisocyanate cross-linking agents; and ionic antistatic agents with Na ⁺ or K ⁺ ions.

The (meth) acrylate-based monomer having a linear or cyclic alkyl group having 4 or more carbon atoms substituted with a hydroxyl group may be at least one selected from the group consisting of 4-hydroxybutyl acrylate, 6-hydroxyhexyl (methyl Acrylate), octyl 8-hydroxy (meth) acrylate, and A group of people.

The monomer used to prepare the acrylic copolymer may further include a (meth) acrylate monomer having an aromatic ring.

The antistatic agent may be a fluorine-containing anion.

The fluorine-containing anion may be OTF ( ), TFSI ( ), Or FSI ( ).

Based on 100 parts by weight of all monomers, the acrylic copolymer may contain: (1) 88 to 98 parts by weight of a (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms 2) 1 to 10 parts by weight of a (meth) acrylate-based monomer having a carboxyl group; and 3) 0.1 to 2 parts by weight having a linear or cyclic alkyl group containing a hydroxyl group to replace 4 or more carbon atoms The monomer of (meth) acrylate type monomer is copolymerized and prepared.

Based on 100 parts by weight of the acrylic copolymer, the adhesive composition may include 0.1 to 1 part by weight of a trifunctional or higher toluene diisocyanate-based crosslinking agent; and 0.5 to 5 parts by weight of Na ⁺ Or K ⁺ ion ionic antistatic agent.

The curing period of the adhesive composition may be 48 hours or less at a time point based on 23 ° C. and 65% RH that does not change with time, and the adhesive composition is left to stand at room temperature for 24 hours with Later viscosity changes can be 50% or less.

The invention discloses an adhesive composition, which has good antistatic properties, liquid stability and short curing period.

Next, the details of the present invention will be described below.

The adhesive composition of the present invention includes: an acrylic copolymer, based on 100 parts by weight of all monomers, by including 1 to 10 parts by weight of a (meth) acrylate monomer having a carboxyl group And 0.1 to 2 parts by weight of a monomer having a (meth) acrylic acid ester-based monomer having a linear or cyclic alkyl group substituted with 4 or more carbon atoms by a hydroxyl group; trifunctional group or higher Toluene diisocyanate cross-linking agent; and ionic antistatic agent with Na ⁺ or K ⁺ ions.

The (meth) acrylic acid ester monomer having a carboxyl group can suppress the appearance of bleeding caused by the migration of the ionic antistatic agent to the surface, and improve the durability by enhancing the adhesion with glass. The (meth) acrylate monomer having a monohydroxy group can shorten the curing period of the adhesive composition by increasing the crosslinking reaction.

In addition, Na + or K + ions of the ionic antistatic agent will form a coordination bond with the hydroxyl group, thereby inhibiting the reaction between the hydroxyl group and the isocyanate, thereby improving the liquid stability of the adhesive composition.

In addition, the trifunctional or higher toluene diisocyanate-based cross-linking agent is an aromatic isocyanate, which has good reactivity with a (meth) acrylate monomer having a hydroxyl group, thereby shortening the adhesive combination. During the curing of the material.

In other words, the present invention is characterized by a (meth) acrylate monomer having a carboxyl group and a (meth) acrylate having a linear or cyclic alkyl group containing 4 or more carbon atoms substituted with a hydroxyl group. All monomers are included in the monomers used to prepare acrylic copolymers; trifunctional or higher toluene diisocyanate crosslinkers and ionic antistatic agents with Na ⁺ and K ⁺ ions are used; and The monomers used to prepare acrylic copolymers are also optimally mixed to improve antistatic properties, durability, curing period, and liquid stability.

Based on 100 parts by weight of all monomers, the acrylic copolymer of the present invention is preferably a (meth) acrylic acid ester containing: 88 to 98 parts by weight of an alkyl group having 1 to 12 carbon atoms. Monomer; 1 to 10 parts by weight of a (meth) acrylate-based monomer having a carboxyl group; and 0.1 to 2 parts by weight of a linear or cyclic alkyl group containing a hydroxyl group to replace 4 or more carbon atoms ( A monomer of a meth) acrylate-based monomer is prepared by copolymerization.

Examples of the (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, (meth) Butyl acrylate, n- (meth) acrylate, butyl 2- (meth) acrylate, t- (meth) acrylate, ethylhexyl 2- (meth) acrylate, (meth) Ethyl acrylate, propyl n- (meth) acrylate, isopropyl (meth) acrylate, amyl (meth) acrylate, octyl n- (meth) acrylate, isooctyl (meth) acrylate, (Meth) acrylic acid Esters, decyl (meth) acrylate, lauryl (meth) acrylate, and the like. Among these, n-butyl acrylate, 2-ethylhexyl acrylate, or a mixture thereof is preferred. They can be used alone or in combination of two or more.

The content of the (meth) acrylate monomer of the alkyl group having 1 to 12 carbon atoms may be 88 to 98 parts by weight based on 100 parts by weight of all monomers. If the (meth) acrylate monomer is less than 88 parts by weight, insufficient adhesion will be caused, but if it exceeds 98 parts by weight, cohesion will be reduced.

As the (meth) acrylate monomer having a carboxyl group, acrylic acid or methacrylic acid can be used.

The content of the (meth) acrylate monomer having a carboxyl group is preferably 1 to 10 parts by weight based on 100 parts by weight of all monomers. If its content is less than 1 part by weight, the effect of suppressing the appearance of ionic antistatic agents will be small, resulting in poor durability, or its role as a catalyst for cross-linking reactions will be weakened, and the curing period cannot be shortened. If the content exceeds 10 parts by weight, the liquid stability of the adhesive composition is deteriorated due to excessive crosslinking reaction.

The (meth) acrylate-based monomer having a linear or cyclic alkyl group having 4 or more carbon atoms substituted with a hydroxyl group may be at least one selected from the group consisting of 4-hydroxybutyl (meth) acrylate, 6- Hydroxyhexyl (meth) acrylate, octyl 8-hydroxy (meth) acrylate, and A group of people. Considering the curing period, 4-hydroxybutyl acrylate or .

The content of the (meth) acrylic acid ester-based monomer having a linear or cyclic alkyl group containing 4 or more carbon atoms substituted with a hydroxyl group on the basis of 100 parts by weight of all monomers is preferably 0.1 to 2 parts by weight. If it is less than 0.1 part by weight, the curing period may be shortened only slightly. If the content exceeds 2 parts by weight, the liquid stability of the adhesive composition is deteriorated due to excessive crosslinking reaction.

In addition, in order to prevent light leakage, the monomer used to prepare the acrylic copolymer of the present invention may further include a (meth) acrylate monomer having an aromatic ring group.

Examples of the (meth) acrylate monomer having an aromatic ring group may be at least one selected from the group consisting of 2-ethylphenoxy (meth) acrylate, 2-ethylthiophenyl (meth) acrylate, Phenyl (meth) acrylate, benzyl (meth) acrylate, ethyl 2-phenyl (meth) acrylate, propyl 3-phenyl (meth) acrylate, 4-phenyl (meth) Butyl acrylate, ethyl 2-2-methylphenyl (meth) acrylate, ethyl 2-2-3methylphenyl (meth) acrylate, ethyl 2-2-4methylphenyl (meth) acrylate Ester, 2- (4-propylphenyl) (meth) acrylate, 2- (4- (1-methylethyl) phenyl) (meth) acrylate, 2- (4-formyl (Oxyphenyl) ethyl (meth) acrylate, ethyl 2- (4-cyclohexylphenyl) (meth) acrylate, ethyl 2- (2-chlorobenzene) (ethyl) acrylate, 2- ( 3-chlorobenzene) ethyl (meth) acrylate, ethyl 2- (4-chlorobenzene) (meth) acrylate, ethyl 2- (4-bromobenzene) (meth) acrylate, 2- (3- A group consisting of ethyl phenylbenzene) (meth) acrylate and ethyl 2- (4-benzylphenyl) (meth) acrylate. In consideration of copolymerization reactivity, 2-ethylphenoxy (meth) acrylate or benzyl (meth) acrylate is preferred.

(Meth) acrylic acid ester monomer having an alkyl group having 1 to 12 carbon atoms, (meth) acrylic acid ester monomer having a carboxyl group, and having 4 hydroxyl groups When the (meth) acrylate monomer of a linear or cyclic alkyl group having a plurality of carbon atoms is 100 parts by weight, the content of the (meth) acrylate monomer having an aromatic ring group is preferably 6 To 12 parts by weight. If it is added in an amount of less than 6 parts by weight or more than 12 parts by weight, light leakage will occur.

The method for preparing the copolymer is not particularly limited. Copolymers can be prepared by conventional methods such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization. Among these, solution polymerization is preferred. In addition, solvents, polymerization initiators, chain transfer agents for controlling molecular weight, and the like commonly used in conventional polymerization can also be used.

The weight average molecular weight (in terms of polystyrene, Mw) of the copolymer, as measured by colloidal permeation chromatography, is 50,000 to 2,000,000, and preferably 400,000 to 2,000,000. If the weight average molecular weight of the copolymer is less than 50,000, the cohesive force with the copolymer will be insufficient, resulting in a problem of adhesion durability. If the weight average molecular weight of the copolymer exceeds 200,000, a large amount of a diluent solvent will be required during coating to ensure processability.

This cross-linking agent can improve adhesion and durability, maintain reliability at high temperatures, and retain the shape of the adhesive. More specifically, considering the (meth) acrylic acid ester monomer having a carboxyl group and the (meth) acrylic acid ester group having a linear or cyclic alkyl group having 4 or more carbon atoms substituted with a hydroxyl group For monomer reactivity, durability, and prevention of light leakage, a trifunctional or higher toluene diisocyanate-based crosslinking agent is preferably used.

Examples of trifunctional or higher toluene diisocyanate-based cross-linking agents are trimethylolpropane adduct of toluene diisocyanate (Urethane, Japan, CORONATE-L) and toluene diisocyanate terpolymer (Aekyung Chemical Corporation) Division, AKNATE TR-50).

The content of the trifunctional or higher toluene diisocyanate-based crosslinking agent may be 0.1 to 1 part by weight based on 100 parts by weight of all the monomers. If the content is less than 0.1 parts by weight, the degree of cross-linking will be insufficient, resulting in a decrease in cohesive force, which will result in poor durability, such as peeling and poor cuttability. If it exceeds 1.0 part by weight, it will be difficult to ensure the stability of the liquid.

In order to improve the liquid stability, the present invention may include an ionic antistatic agent having Na ⁺ and K ⁺ ions, which can reduce the reaction rate of hydroxyl and isocyanate groups in the acrylic copolymer.

As the anion of the ionic antistatic agent, a fluorine-containing anion or an iodine ion can be used. The fluorine-containing anion may be trifluoromethanesulfonic acid ( ), Bis (trifluorosulfonyl) imine ( ), And bis (fluorosulfonyl) imine ( ).

The content of the ionic antistatic agent is 0.5 to 5 parts by weight based on 100 parts by weight of the acrylic copolymer. If the content of the ionic antistatic agent is less than 0.5 parts by weight, the antistatic properties will be insufficient, and if the content of the ionic antistatic agent exceeds 5 parts by weight, its durability cannot be maintained.

In addition, the adhesive composition of the present invention may further include a silane coupling agent.

The type of the silane coupling agent is not particularly limited. Examples of the silane coupling agent are vinylchlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-cyclo Oxypropoxy Propyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyl Triethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methyl Acryloyloxymethyldimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, 3-acryloyloxypropyltrimethoxysilane, N-2- (aminoethyl ) -3-aminopropylmethyldimethoxysilane, N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropyl Triethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethyl-butylene Propylamine, N-phenyl-3-aminopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane Silane, bis (triethoxysilylpropyl) tetrasulfide, 3-isocyanatepropyltriethoxysilane, and others . They can be used alone or in combination of two or more.

The adhesive composition may further include, in addition to the above composition, adducts such as a tackifier resin, an antioxidant, a leveling agent, a surface lubricant, a dye, a pigment, an antifoaming agent, a filler, and a light stabilizer to control adhesion. Force, cohesion, viscosity, elastic modulus, glass transition temperature, and the like.

The content of the additives can be appropriately controlled within a range that does not deteriorate the effects of the present invention.

The adhesive composition of the present invention can be used as an adhesive for combining a polarizing plate and a liquid crystal cell, or an adhesive for a surface protection film. In addition, the adhesive composition of the present invention can be used for a protective film, a reflective sheet, an adhesive sheet for molding, and Photographic adhesives, adhesives for marking land, adhesives for optical products, adhesives for electronic products, and adhesive products for general advertising products.

The preferred embodiments are provided to help understand the present invention, and the examples described below are only for presenting the present invention and not for limiting the present invention. Any person with ordinary knowledge in the technical field can make some modifications and retouching without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Preparation example: acrylic copolymer

Preparation Examples 1 to 11 and Comparative Preparation Examples 1 to 5

The monomer mixture prepared according to the composition shown in Table 1 was placed in a 1 liter reactor with a cooling device to promote the reflux of nitrogen and control the temperature, and then 100 parts by weight of ethyl acetate was added as a solvent. among them. After that, it was purged with nitrogen for 1 hour to remove oxygen, and the temperature was maintained at 78 ° C. Stir the mixture evenly. Then, 0.03 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator, and the reaction was further performed for 8 hours to prepare an acrylic copolymer having a weight average molecular weight of about 780,000.

Examples 1 to 18 and Comparative Examples 1 to 12

Each adhesive composition having a solid content of 15% was prepared by mixing an acrylic copolymer, an ionic antistatic agent, and a cross-linking agent as shown in Table 2, and then diluting the mixture with ethyl acetate.

Each of the adhesive compositions prepared as described above was coated on a release film coated with a silicon release agent to have a thickness of 25 μm, followed by drying at 100 ° C. for 1 minute. Thereby, an adhesive layer is formed. Another release film was laminated thereon, thereby producing an adhesive sheet.

The release film of the manufactured adhesive sheet was peeled off, and then the formed adhesive layer was laminated to a 185 μm-thick iodine-based polarizing plate through an adhesive treatment to manufacture an adhesive-attached polarizing plate. The manufactured polarizing plate was stored under the conditions of 23 ° C and 60% RH.

Test case

The physical properties of the adhesive composition, the adhesive sheet, and the adhesive-attached polarizing plate obtained by this example and the comparative example were measured by the following methods, and the measurement results are recorded in Table 3.

1. Storage stability (viscosity change,%)

A viscometer (Brookfield LVDV-II + B (rotor code 3, 30 rpm)) was used to measure the initial viscosity of the adhesive composition and the viscosity of the adhesive composition after being left at room temperature for 24 hours, and calculate the viscosity Change (Δη).

<Evaluation criteria>

￮: △ η <50%

△: 50% △ η <100%

×: 100% △ η

2. During curing

When the manufactured adhesive sheet was cured at 23 ° C and 65% RH for 1 to 10 days, the gel fraction was measured daily as described below. The number of days of curing is extended until the gelation rate no longer increases, that is, the curing period is judged accordingly.

The adhesive layer of about 0.25g of adhesive sheet was fixed on a 250-mesh wire mesh (100mm X 100mm), and the wire mesh was wrapped so that the gel would not escape from it. The weight was accurately measured using a precision balance, and the wire mesh was immersed in an ethyl acetate solution for 3 days. The soaked wire mesh was taken out, rinsed with a small amount of ethyl acetate solution, dried at 120 ° C. for 24 hours, and then weighed. The measured weight is used to calculate the gel fraction by Equation 1. Determine the curing period based on the time point at which the calculated gel fraction falls within the range of 70% to 80% and no change with time is observed: [Equation 1] Gel fraction (%) = (CA) / (BA) x 100

Wherein in Equation 1, A is the weight of the wire mesh (g); B is the weight of the adhesive layer fixed to the wire mesh (BA: weight of the adhesive layer, g); and C is the metal wire mesh after soaking and drying. Weight (CA: weight of gel resin, g)].

3.Durability (heat resistance, damp heat resistance)

The manufactured polarizer with an adhesive was cut into a size of 90 mm × 170 mm to prepare a sample, and the release film was peeled off therefrom, and then the polarizer was attached to both sides of the glass substrate (110 mm × 190 mm × 0.7 mm). The light absorption axes of the polarizing plates are made orthogonal to each other. Here, a pressure of 5 kg / cm ² is applied, and it is performed in a clean room to avoid the generation of bubbles or foreign materials. In order to measure the heat resistance, the sample was left at a temperature of 80 ° C for 1000 hours, and then, it was observed whether blistering or peeling occurred. In order to measure the humidity and heat resistance, the samples were placed under the conditions of 60 ° C and 90% RH for 1000 hours, and then observed whether blistering or peeling occurred. Here, the sample is placed at room temperature for 24 hours before the sample is evaluated.

<Evaluation criteria>

◎: No bubbles or peeling:

￮: Number of bubbles or peeling <5

△: 5 Number of bubbles or peeling <10

×: 10 Number of bubbles or peeling

4. Antistatic characteristics (surface resistivity, Ω / □)

After the release film was peeled from the adhesive sheet, the surface resistance values of the three points were measured 10 times respectively, and the measured values were averaged.

Here, a surface resistance analyzer (MCP-HT450 / MITSUBISHI CHEMICAL), a probe (URS, UR100), and a probe test piece (for URS, for UR 100) were used to measure the surface resistance.

It can be seen from Table 3 that the curing period of the adhesive compositions according to Examples 1 to 18 of the present invention is shortened to 12 to 36 hours, and compared with the adhesive compositions of Comparative Examples 1 to 12, it also improves antistatic properties and durability. Properties, and not afraid of physical characteristics change with time (high temperature or changes in high temperature and high humidity environment) will deteriorate.

As described above, the adhesive composition of the present invention can simultaneously improve antistatic properties and durability without fear of physical properties changing with time (changes in high temperature or high temperature and high humidity environment).

Furthermore, the curing time of the adhesive composition according to the present invention is significantly shortened to 48 hours or less, and preferably 36 hours or less, as compared with the conventional one. Therefore, excessive use of additives commonly used to shorten the curing period can be suppressed, thereby improving conventional problems such as blockage of equipment and the like.

Claims (7)

An adhesive composition includes: an acrylic copolymer, based on 100 parts by weight of all monomers, by including 1 to 10 parts by weight of a (meth) acrylate monomer having a carboxyl group and 0.1 to 2 parts by weight of a monomer having a (meth) acrylic acid ester-based monomer containing a linear or cyclic alkyl group substituted with 4 or more carbon atoms by a hydroxyl group; copolymerized by tri-functional group or higher Toluene diisocyanate-based cross-linking agent; and an ionic antistatic agent having Na ⁺ or K ⁺ ions, wherein the curing period of the adhesive composition is at a time point based on 23 ° C. and 65% RH that does not change with time. Is 48 hours or less, and the viscosity change of the adhesive composition before and after being left at room temperature for 24 hours is 50% or less. The adhesive composition according to item 1 of the scope of patent application, wherein the (meth) acrylate monomer having a linear or cyclic alkyl group containing 4 or more carbon atoms substituted with a hydroxyl group is at least one option Free 4-hydroxybutyl acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxy (meth) acrylate octyl, and A group of people. The adhesive composition according to item 1 of the scope of patent application, wherein the monomer used to prepare the acrylic copolymer further comprises a (meth) acrylate monomer having an aromatic ring. The adhesive composition according to item 1 of the patent application scope, wherein the antistatic agent is a fluorine-containing anion. The adhesive composition according to item 4 of the scope of patent application, wherein the fluorine-containing anion is trifluoromethanesulfonic acid ( ), Bis (trifluorosulfonium) imine ( ), Or bis (fluorosulfonyl) imine ( ). The adhesive composition according to item 1 of the patent application range, wherein the acrylic copolymer is based on 100 parts by weight of all monomers, and will include: 1) 88 to 98 parts by weight having 1-12 (Meth) acrylic acid ester monomer of alkyl group having 1 carbon atom; 2) 1 to 10 parts by weight of (meth) acrylic acid ester monomer having a carboxyl group; and 3) 0.1 to 2 parts by weight A monomer of a linear or cyclic alkyl (meth) acrylate monomer substituted with 4 or more carbon atoms is prepared by copolymerization. The adhesive composition according to item 1 of the scope of patent application, based on 100 parts by weight of the acrylic copolymer, including 0.1 to 1 part by weight of a trifunctional or higher toluene diisocyanate-based crosslinking agent. And 0.5 to 5 parts by weight of an ionic antistatic agent having Na ⁺ or K ⁺ ions.