WO2009002110A2

WO2009002110A2 - Pressure sensitive adhesive composition with improved peeling characteristics and protection films using the same

Info

Publication number: WO2009002110A2
Application number: PCT/KR2008/003693
Authority: WO
Inventors: Kwang Suck Suh; Jong Eun Kim; Tae Young Kim; Tae Hee Lee; Young Hee Lee
Original assignee: Kwang Suck Suh; Jong Eun Kim; Tae Young Kim; Tae Hee Lee; Young Hee Lee
Priority date: 2007-06-27
Filing date: 2008-06-26
Publication date: 2008-12-31
Also published as: TW200920806A; KR20100032885A; KR101198929B1; WO2009002110A3

Abstract

Disclosed herein is a pressure-sensitive adhesive composition for a protective film, which functions to prevent a phenomenon in which an adhesive is transferred to an adherend by local pressing or scratching, including: a (meth)acrylic copolymer, serving as an adhesive; and a monofunctional or difunctional isocyanate compound, serving as a cross-linking agent. The protective film manufactured using the pressure-sensitive adhesive composition of the present invention is advantageous in that an adhesive layer of the protective film does not remain on the surface of an adherend at the time of removing the protective film from the adherend even when the protective film has been locally pressed or scratched by an external force.

Description

PRESSURE SENSITIVE ADHESIVE COMPOSITION WITH

IMPROVED PEELING CHARACTERISTICS AND

PROTECTION FILMS USING THE SAME

Technical Field

[1] The present invention relates to a pressure-sensitive adhesive composition for pressure-sensitive adhesive tapes or protective films (hereinafter, referred to as "a protective film"), which has improved peeling performance, and, more particularly, to a pressure-sensitive adhesive for protective films, which can improve a phenomenon (hereinafter, referred to as "an adhesive transfer phenomenon from local pressing or scratching") in which a part of an adhesive layer of a protective film remains on the surface of an adherend or is transferred to the surface of the adherend when a strong force is locally applied to the surface of the protective film attached to the surface of an electronic part or an electronic product, for example, the protective film is scratched by the corners or edges of a workbench. Background Art

[2] Generally, various displays, including flat panel displays (FPDs), such as polarizing films, mobile phone screens, and the like, are processed on a workbench in a state in which a protective film is attached to them in order to protect their surfaces.

[3] A pressure-sensitive film or a protective film (hereinafter, referred to as "a protective film") is a film having an adhesive layer, which is formed by applying a mixture in which an acrylic or methacrylic copolymer adhesive having curable functional groups is mixed with an initiator or a curing agent at a predetermined mixing ratio on one side or both sides of a base film made of polyester, such as polyethyleneterephthalate (PET), polyethylene (PE), polypropylene (PP), ethylenevinyl acetate (EVA), or the like, and then heating the base film coated with the mixture or irradiating the base film coated with the mixture with ultraviolet rays. In this case, various functions can be imparted to the respective surfaces of the protective film. A typical example of the protective film includes an antistatic film imparted with an antistatic property.

[4] Regardless of the layer structure of the protective film, a layer facing an adherend is an adhesive layer. This adhesive layer is a very important factor for determining the peeling force between the adhesive layer and the adherend or determining the adhesive transfer phenomenon from local pressing or scratching.

[5] When a product to which a protective film is attached is treated and transported, the surface of the product often collides with the corners or edges of a workbench. Further, the surface of the product is locally pressed by things placed on the workbench or things attached to the surface of the protective film. This phenomenon serves to increase the force which locally attaches the protective film to the things placed on the workbench, thereby also locally increasing the force which attaches the adhesive layer of the protective film to the surface of a product. Therefore, the peeling strength of the protective film, which is the force required to remove the protective film, is locally changed.

[6] In the case where the adhesion of the protective film is uniformly high, there is no problem. However, in the case where the adhesion of the protective film is locally increased, since the adhesion of the protective film is locally changed when the protective film is removed from the product, the adhesive layer of the protective film is not uniformly removed from the surface thereof, so that part of the adhesive layer to which a strong force had been applied, remains on the surface of the product even after the protective film is removed.

[7] This phenomenon usually occurs during a process of handling a polarizing film for liquid crystal displays (LCDs). Further, the polarizing film, the surface of which is composed of triacetyl cellulose or is functionally coated with triacetyl cellulose, may be locally scratched. In this process of handling a polarizing film for liquid crystal displays (LCDs), it is most important to completely remove the adhesive adhered to the surface of the polarizing film before conducting subsequent procedures. Therefore, this work incurs the result that working time is increased and the surface of the polarizing film is damaged. Recently, in a process of removing a protective film from LCDs, a sash frame is applied, and then the protective film is removed. In this case, the protective film is pressed by the edges of the sash made of Steel Use Stainless (SUS), so that adhesive residues are left between the protective film and the sash, with the result that it is difficult to suitably conduct subsequent procedures.

[8] In order to solve the above problems, efforts to prevent mistakes, such as scratching, pressing, and the like, must be made, and, most of all, it is required to develop a protective film having improved peeling performance, the adhesive layer of which is completely removed from the surface of a product at the time of removing the protective film from the product even when the protective film has been locally pressed or scratched by an external force. Disclosure of Invention Technical Problem

[9] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a pressure-sensitive adhesive composition for a protective film, by which, in a protective film to be used for protecting the surface of optical products, the protective film being used for flat panel displays (FPDs), an adhesive layer of the protective film does not remain on the surface of an adherend at the time of removing the protective film even when the protective film has been locally pressed or scratched by an external force during treatment or transportation, that is, an adhesive transfer phenomenon from local pressing or scratching is remarkably improved, thereby improving the peeling performance of the protective film.

[10] Another object of the present invention is to provide a protective film manufactured using the pressure-sensitive adhesive composition, in which an adhesive transfer phenomenon from local pressing or scratching is remarkably improved. Technical Solution

[11] In order to accomplish the above objects, the present invention provides a pressure- sensitive adhesive composition for a protective film, which prevents a phenomenon in which an adhesive is transferred to an adherend from local pressing or scratching, thus improving the peeling performance of the protective film, including a curing agent having a monofunctional group or a difunctional group.

[12] Further, the pressure-sensitive adhesive composition according to the present invention may include an acrylic copolymer or a methacrylic copolymer as an adhesive and an isocyanate compound as a curing agent.

[13]

[14] Further, a protective film having improved peeling performance can be manufactured using the pressure-sensitive adhesive composition according to the present invention.

[15] As described above, in the protective film, an adhesive layer is formed on the surface of a base film to have a predetermined thickness. In this case, the desired peeling force of an adhesive layer can be attained by suitably controlling the kind of an adhesive, the content ratio of the adhesive to a reaction initiator, and reaction conditions, such as temperature, pressure, reaction time, etc. Further, as described above, a functional protective film can also be manufactured by imparting additional functions, such as antistatic properties, etc., thereto.

[16]

[17] The present inventors discovered a very important fact concerning adhesive transfer phenomenon from local pressing or scratching while researching into methods of improving the adhesive transfer phenomenon from local pressing or scratching.

[18] As described above, the adhesive layer for a protective film, having desired adhesivity, is formed by mixing an acrylic copolymer or methacrylic copolymer having a hydroxyl group, an amino group or a carboxyl group, this copolymer being a major component of an adhesive, with a reaction initiator or curing agent, such as a metal chelate compound, an isocyanate compound, a melamine compound or an epoxy compound, in a predetermined mixing ratio, applying the resulting mixture onto the surface of a base film, and then drying the base film coated with the mixture by passing it through a drying furnace of a coating machine, which also induces a reaction. After the coating and drying, the coated and dried base film may be additionally cured at a temperature ranging from room temperature to 6O⁰C for 1 day ~ 1 week.

[19] The adhesivity of an adhesive is determined depending on the content ratio of an acrylic/methacrylic copolymer to a reaction initiator. When the initial amount of the acrylic/methacrylic copolymer is constant, the adhesivity of the adhesive is decreased as the amount of the reaction initiator is increased. When the initial amount of the acrylic/methacrylic copolymer is not constant, the amount of the reaction initiator may be suitably adjusted in order to obtain an adhesive having desired adhesivity.

[20] Recently, it has been known that it is preferred that a trifunctional or more curing agent be used in order to prevent the stickiness and extraneous matter transfer resulting from unreacted reactants, because the stickiness of the adhesive does not disappear due to the high- velocity peeling characteristics and the uncuring of the adhesive. It is disclosed in Japanese Unexamined Patent Application Publication No. 2003-00187775 (Korean Unexamined Patent Application Publication No. 10-2006-0018883) that an adhesive, which has excellent high- velocity peeling characteristics, has a gel fraction of 90% or more, and does not transfer extraneous matter to a product, can be prepared using an acrylate copolymer having a hydroxyl group and a trifunctional isocyanate. That is, it is mentioned in this patent document that a multifunctional isocyanate can be used in order to prevent an adhesive from being rapidly cured and in order to prevent an adherend from being contaminated.

[21] However, according to the research of the present inventors, when the adhesivity of a protective film was controlled by mixing an adhesive copolymer with a curing agent, it was found that there are many problems with an adhesive transfer phenomenon from local pressing or scratching.

[22] For example, the present inventors mentioned that in the case where an acrylate copolymer is used as an adhesive and isocyanate is used as a curing agent, when Coronate L, which is a trifunctional cross-linking agent, is used, an adhesive, which has excellent high- velocity peeling characteristics and a gel fraction of 92%, can be prepared. In this case, the trifunctional cross-linking agent enables the adhesive to have a gel fraction of 92% through a sufficiently complete cross-linking reaction and enables the adhesive to exhibit a peeling force of 40 gf/inch at a rate of 2000 mm/min, as the adhesivity of the adhesive is sufficiently decreased compared to the initial adhesivity thereof. However, the adhesive becomes hard due to the rapid reaction of the trifunctional curing agent, but becomes poor in toughness. [23] The present inventors found that the phenomenon in which an adhesive is transferred to an adherend by local pressure or scratching or is detached from a base film depends on the toughness of the adhesive, rather than depending on the gel fraction.

[24] According to the research of the present inventors, as mentioned in conventional technologies, it was found that, compared to the adhesive prepared using a multifunctional curing agent, the adhesive prepared using a monofunctional or difunctional curing agent can prevent an adhesive transfer phenomenon caused by scratching.

[25] The reason for this is determined to be because the multifunctional curing agent causes a rapid curing reaction, and thus the hardness of an adhesive layer is increased, but the toughness of the adhesive layer is decreased. Now, when the monofunctional or difunctional curing agent is used as a curing agent, the rapid curing reaction is prevented, with the result that the toughness of the adhesive layer is increased, thereby preventing extraneous matter from being locally deposited on the adhesive layer.

[26] For example, in the case where monofunctional isocyanate is used instead of tri- functional isocyanate, when a force is increasingly applied to the surface of a protective film, it is found to prevent an adhesive from being detached from the protective film.

[27] In order to confirm this fact, in the preparation of an adhesive composition, in order that the number of functional groups of a difunctional isocyanate curing agent may be the same as the number of functional groups of a trifunctional isocyanate curing agent, the amount of a monofunctional isocyanate curing agent used is three times the amount of trifunctional isocyanate curing agent used, and other curing conditions are maintained constant. That is, as described above, when a multifunctional curing agent is used in the preparation of an adhesive composition, the gel fraction of the prepared adhesive is increased, and the contamination of an adherend is prevented, but the adhesive has a compact net structure, rather than a compact linear structure. It was observed from the use of the multifunctional curing agent that the phenomenon in which the adhesive is transferred to the adherend from local pressing or scratching is slightly prevented. In contrast, when a monofunctional or difunctional curing agent is used, a linear polymer adhesive is formed. Since this linear polymer adhesive has excellent impact resistance and cohesion, it was observed from the use of the mono- functional or difunctional curing agent that the phenomenon in which the adhesive is transferred to the adherend from local pressing or scratching is remarkably prevented.

[28] According to a pressure-sensitive adhesive composition of the present invention,

(meth)acrylic monomers having an alkyl group of 1 to 14 carbon atoms are used as major components of the pressure-sensitive adhesive composition. Examples of the alkyl group of 1 to 14 carbon atoms may include methyl, ethyl, n-butyl, s-butyl, t- butyl, iso-butyl, hexyl, 2-ethylhexyl, n-octyl, iso-octyl, n-nonyl, iso-nonyl, n-decyl, iso-decyl, n-dodecyl, n-tridecyl, n-tetradecyl, and the like. The (meth) acrylic monomers having an alkyl group of 1 to 14 carbon atoms may be each independently used or may be used by mixing two or more monomers.

[29] Further, (meth)acrylic monomers having a hydroxy group, which are copolymerized with the (meth)acrylic monomers having an alkyl group of 1 to 14 carbon atoms, are also used as major components of the pressure-sensitive adhesive composition. The hydroxy group is a functional group acting as an origin of cross-linking, and a (meth)acrylic monomer having the hydroxy group serves to impart cohesion to the pressure-sensitive adhesive by reacting with an isocyanate-based cross-linking agent. Examples of the (meth)acrylic monomers having the hydroxy group may include 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 8-hydroxyoctyl(meth)acrylate, and the like. The (meth)acrylic monomers having the hydroxy group may be independently used or may be used by mixing two or more monomers.

[30] A pressure-sensitive adhesive composition of the present invention includes a

(meth)acrylic copolymer, serving as an adhesive; and a monofunctional or difunctional isocyanate compound, serving as a cross-linking agent. In the pressure-sensitive adhesive composition, the (meth)acrylic copolymer may be prepared by copolymerizing 80 ~ 99 wt% of (meth)acrylic monomer having an alkyl group of 1 to 14 carbon atoms with 1 - 20 wt% of (meth) acrylic monomer having a hydroxy group. When the amount of the (meth)acrylic copolymer is below 80 wt%, there is a problem in that the adhesion of the pressure-sensitive adhesive is decreased, and thus the pressure-sensitive adhesive can be easily peeled off, and when the amount thereof is above 99 wt%, there is a problem in that the content ratio of the monomers acting as a cross-linking origin is decreased, and thus the cohesion of the pressure-sensitive adhesive is decreased. Further, when the amount of the (meth)acrylic monomer having a hydroxy group is below 1 wt%, there is a problem in that the pressure-sensitive adhesive is not sufficiently cross-linked, so that the cohesion of the pressure-sensitive adhesive is decreased, thereby the pressure-sensitive adhesive may remain on an adherend, and when the amount thereof is above 20 wt%, there is a problem in that the cohesion of the pressure-sensitive adhesive is excessively decreased, so that the pressure-sensitive adhesive becomes hard, thereby deteriorating workability.

[31] In addition to the above monomers, in order to control the adhesion, peeling performance, cohesion, heat resistance and other physical properties of the pressure- sensitive adhesive, other polymerizable monomers may be used. Examples of such polymerizable monomers may include carboxyl group-containing monomers, amide group-containing monomers, epoxy group-containing monomers, aromatic vinyl monomers, alkylene oxide-containing monomers, and the like. Here, the amounts of the polymerizable monomers are not limited as long as the effects of the present invention do not become deteriorated.

[32]

[33] It is preferred that the (meth)acrylic copolymer, prepared by copolymerizing the

(meth)acrylic monomer having an alkyl group of 1 to 14 carbon atoms with the (meth)acrylic monomer having a hydroxy group, have a weight-average molecular weight of 300,000 ~ 3,000, 000. When the weight- average molecular weight of the (meth)acrylic copolymer is below 300,000, there is a problem in that the cohesion of the pressure-sensitive adhesive is overly decreased, and thus pressure-sensitive adhesive remains on an adherend even when a weak force is applied thereto. In contrast, when the weight- average molecular weight thereof is above 3,000, 000, there is a problem in that the fluidity of the pressure-sensitive adhesive is decreased, thus deteriorating workability.

[34]

[35] In the pressure-sensitive adhesive composition of the present invention, a cross- linking reaction is performed using a monofunctional or difunctional isocyanate-based cross-linking agent. The monofunctional or difunctional isocyanate-based cross-linking agent is referred to as a compound having two or less isocyanate groups in a single molecule, and its structure is not particularly limited. Examples of the monofunctional or difunctional isocyanate-based cross-linking agent may include tolylene di- isocyanate, xylene diisocyanate, chlorophenylene diisocyanate, hexamethylene di- isocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hydrated diphenylmethane diisocyanate, and commonly-known isocyanate compounds.

[36] As mentioned above, it is not preferred that tri or more functional isocyanate-based curing agents be used. These curing agents may be each independently used or may be used by mixing two or more kinds of curing agents. The amount of the isocyanate- based curing agent may be 0.1 ~ 20 parts by weight based on 100 parts by weight of the (meth)acrylic copolymer. When the amount of the isocyanate-based curing agent is below 0.1 parts by weight, a curing reaction has a low completion rate, so that the adhesion of the pressure-sensitive adhesive is decreased, and an adherend may be contaminated. In contrast, when the amount thereof is above 20 parts by weight, the curing reaction is quickly performed, so that the compactness and cohesion of the pressure- sensitive adhesive may be deteriorated. Therefore, it is preferred that the amount of the isocyanate-based curing agent be 0.1 ~ 20 parts by weight based on the total amount of the (me th) acrylic copolymer.

[37] The pressure-sensitive adhesive composition prepared as above is dried, and is then additionally cured at from room temperature to 6O⁰C for 1 day ~ 1 week to exhibit a gel fraction of 85 ~ 99%. When the gel fraction is below 85%, the cohesion and toughness of the pressure-sensitive adhesive is decreased. In contrast, when the gel fraction is above 99%, even though a pressure-sensitive adhesive having a high cohesion can be prepared using a monofunctional or difunctional curing agent, the cohesion of the pressure-sensitive adhesive is excessively increased, so that the hardness thereof is also excessively increased, with the result that the pressure- sensitive adhesive may be cracked when a force is locally applied thereto.

[38] The pressure-sensitive adhesive composition of the present invention can be applied to a base film of optical or general protective films. The base film may be made of polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), heat-treated polyethyleneterephthalate (PET), polyethylene (PE), polypropylene (PP), ethylene vinyl acetate copolymer (EVA), polyimide, or the like. In addition to these polymers, other polymers may be applied to make the base film of protective films or pressure- sensitive adhesive films as long as they can be used to make them.

[39] Further, the pressure-sensitive adhesive composition of the present invention may be used for functional protective films in which layers other than an adhesive layer are imparted with functionality. For example, the pressure-sensitive adhesive composition may be used for an antistatic protective film, which has been imparted with an antistatic property, before the pressure-sensitive adhesive composition is applied on its surface on which an adhesive layer to be formed, or may be used for protective films, which have been imparted with other properties, such as water repellency, contamination resistance, and the like, on the opposite surface to the surface on which an adhesive layer is to be formed. Since the present invention is a technology for controlling the physical properties of an adhesive layer, it may be used regardless of the functionality imparted to layers other than the adhesive layer. For example, in order to impart an antistatic property to a protective film using the pressure-sensitive adhesive composition, an antistatic agent containing a conductive polymer as an active component may be included in an intermediate layer located between the base film and the adhesive layer, and poly(3,4-ethylenedioxythiophene) may be used as the conductive polymer.

[40] Further, the adhesive layer formed from the pressure-sensitive adhesive composition of the present invention can be imparted with various functions. In this case, ionic liquids including lithium ionic liquid, and/or alkaline metal salts including a quaternary ammonium metal salt may be mixed with the pressure-sensitive adhesive composition as an antistatic agent. However, the antistatic agent must be used in a suitable amount because the curing ability and cohesion of the pressure-sensitive adhesive are subject to being decreased, so that the pressure-sensitive adhesive is pressed or scratched by a local impact and is thus detached from an adherend. Further, it is preferred that the antistatic agent be used after its characteristics are evaluated.

Advantageous Effects

[41] The protective film manufactured using the pressure-sensitive adhesive composition of the present invention is advantageous in that an adhesive layer of the protective film does not remain on the surface of an adherend at the time of removing the protective film from the adherend even when the protective film is locally pressed or scratched by an external force, and in that an adhesive transfer phenomenon from local pressing or scratching is remarkably improved at the time of removing the protective film, thus greatly decreasing the process loss. Further, the pressure-sensitive adhesive composition of the present invention can be applied to protective films having various functions, such as antistatic properties, and the like. Mode for the Invention

[42] As described above, in order to observe the adhesive remaining on the surface of an adherend after a protective film is locally pressed or scratched by an external force and is then peeled off from the adherend, the present invention provides a novel peeling performance test method. In conventional peeling performance test methods, a protective film having a predetermined width and length is attached to the surface of an adherend using a rubber roller, and then this protective film is detached from the adherend, and simultaneously the force necessary for peeling the protective film from the surface of the adherend is measured. Experimentally, a protective film having a width of 25 mm or 1 inch is chiefly used, and as a result, the unit of adhesion is represented by g /25mm or g /inch.

[43] In this test method, the adhesion of the protective film is measured throughout the entire width of 25 mm. In order to completely attach a test piece of the protective film to an adherend, a constant force is applied to the entire test piece using a rubber roller. In this case, since the force applied to the test piece using the rubber roller is uniform throughout the entire test piece, a local application of force to the test piece cannot be accurately simulated.

[44] In the present invention, a tool for locally applying a force to the test piece was fabricated. The tool is a metal pin having a shape similar to that of the tip of a ball point pen which is a kind of pencil and has a curvature radius of 300 μm. Further, an apparatus for applying a constant force to the test piece using the tool was fabricated. When this apparatus is used, the time taken to apply the force to the test piece and the intensity of the force can be controlled.

[45] A method of simulating situations in which a force is locally applied to the test piece using this apparatus is performed as follows. First, a test piece (a protective film) is unif oraily attached to the surface of an adherend by applying a uniform force to the entire test piece using a rubber roller. Subsequently, the adherend to which the test piece is attached is placed in the above apparatus, and then desired load is applied to the adherend for a predetermined time (in the present invention, 10 seconds), thereby locally applying a force to the surface of the adherend. This procedure simulates a circumstance in which a force is locally applied to a product to which the protective film has been attached. Subsequently, the test piece is taken out of the apparatus and is then peeled from the adherend. Finally, whether or not the adhesive materials of the protective film remain on the surface of the adherend is determined.

[46] In the test method, a metal pin with a sharp point, such as the tip of the ball point pen, is used in order to simulate a circumstance in which the test piece is sharply pressed. However, various types of pressed marks, such as longitudinal pressed marks, circular pressed marks, and the like, can be simulated by changing the shape of the tool or varying the curvature radius of the portion of the tool contacting the test piece. The time taken to press the test piece and the force used to test the test piece may alter depending on various factors, such as experimental conditions, kinds of materials used, and the like. Further, if desired, in addition to the metal pin, a tool made of polymer or ceramic may be used.

[47] This test method is simple, but is very advantageous in that whether or not the adhesive materials of the protective film remain on the surface of the adherend, in other words, whether or not the adhesive materials of the protective film are transferred to the adherend can be evaluated straight away without any delay.

[48] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the following Examples. Here, the following examples are set forth to illustrate, but are not to be construed as the limit of the present invention.

[49]

[50] Test method

[51] <Measurement of gel fraction>

[52] The measurement of gel fraction was conducted as follows.

[53] 1) An adhesive and a curing agent were mixed with each other in a predetermined amount, stirred, and then cured in an oven at 8O⁰C.

[54] 2) The weight of the cured mixture was measured and recorded.

[55] 3) The cured mixture was mixed in xylene at 12O⁰C, and then stirred for 24 hours.

[56] 4) The stirred mixture was filtered using a 400 mesh filter to prepare a sample. At this time, xylene at 12O⁰C was continuously supplied.

[57] 5) The sample was dried in a vacuum oven at 12O⁰C for 48 hours.

[58] 6) The gel fraction of the sample was calculated by the following Equation represented by dried sample weight / prepared sample weight X 100 = gel fraction (%). [59]

[60] <Measurement of adhesion>

[61] I) A protective film having predetermined width and length was attached to the surface of an adherend using a rubber roller.

[62] 2) While the protective film was detached from the adherend at a rate of 300 mm/ min, a force necessary to peel the protective film from the surface of a product was measured and recorded. In this case, experimentally, a protective film having a width of 25 mm or 1 inch is chiefly used, and as a result, the unit of adhesion is represented by g /25mm or g /inch.

[63] 3) The average value of the measured force was calculated and recorded.

[64]

[65] <Measurement of pressing phenomenon>

[66] I) A protective film was attached to the surface of an adherend using a rubber roller.

[67] 2) The protective film attached to the surface of the adherend was pressed using a metal pin having a curvature radius of 300 μm. The metal pin applies a constant force to the protective film.

[68] 3) Extraneous matter formed on the pressed protective film was observed using an optical microscope, and the size of the extraneous matter was measured.

[69] 4) The above procedures were repeatedly conducted ten times, and the average thereof was obtained.

[70]

[71 ] <Measurement of surface resistance>

[72] The surface resistance of a protective film was measured through an ESD STM 11.11 method using PRS-801, manufactured by Prostat Corp. in U.S.

[73]

[74] <Measurement of electrostatic voltage>

[75] A protective film, manufactured in the present invention, was attached to a polarizer film and was then peeled therefrom, and then electrostactic voltage occurring on the surface of the protective film was measured through an ESD STM 11.2 method using FMS-003, manufactured by Shimco Corp. in Japan.

[76]

[77] <Measurement of voltage attenuation time>

[78] A voltage of 1000 V was applied to a protective film using a CPM 288, manufactured by Monroe Electronics Corp., and then the time taken to be attenuated to a voltage of 100 V was measured through an FTMS 101C method.

[79]

[80] <Coating method>

[81] The above adhesive and curing agent were mixed with each other in a predetermined mixing ratio to form a mixture, stirred, and then applied on a base film. Subsequently, the base film coated with the mixture was dried at 8O⁰C for 2 minutes to a coating thickness of 10 ~ 20 μm, and then the dried base film coated with the above mixture was aged at a temperature of 25⁰C and a relative humidity of 50% for 7 days.

[82]

[83] <Comparative Example 1>

[84] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.54 g of trifunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, the mixture was then stirred, and applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 1.

[85] <Comparative Example 2>

[86] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.54 g of an epoxy curing agent, as a curing agent, were mixed with each other to form a mixture, stirred, and then applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 1.

[87]

[88] <Example 1>

[89] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.16 g of monofunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to have a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 1.

[90] <Example 2>

[91] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.32 g of monofunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 1.

[92] <Example 3>

[93] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.8 g of monofunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, the mixture was stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to have a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 1. [94] <Example 4>

[95] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.54 g of difunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method.

The physical properties of the polyester film coated with the mixture are shown in

Table 1.

[96] <Example 5>

[97] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 1.08 g of difunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method.

Table 1.

[98] <Example 6>

[99] 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 2.7 g of difunctional isocyanate, as a curing agent, were mixed with each other to form a mixture, stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method.

Table 1.

[100] <Example 7> [101] Example 7 was conducted using the same method as in Example 3, except that the mixture has a coating thickness of 20 μm. The physical properties of the polyester film coated with the mixture are shown in Table 1. [102] [103] Table 1

[Table 1] [Table ]

[104] Physical properties of protective films manufactured in Comparative Examples 1 and 2 and Examples 1 to 7

[105] [106] Hereinafter, Examples for imparting an antistatic performance to the pressure- sensitive adhesive composition of the present invention will be described based on Example 1.

[107] <Example 8> [108] An antistatic agent was prepared by mixing 4 g of LiN(CF SO ) with 6 g of polyethyleneglycol dilaurate at a temperature of 7O⁰C for 6 hours. 0.1 g of the prepared antistatic agent was mixed with 20 g of SK1499M, manufactured by Soken Corp., as an acrylate adhesive, and 0.16 g of monofunctional isocyanate, as a curing agent, to form a mixture, the mixture was stirred, and then the stirred mixture was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the mixture are shown in Table 2.

[109] <Example 9> [HO] Example 9 was conducted using the same method as in Example 8, except that 0.5 g of the prepared antistatic agent was added. The physical properties of the polyester film coated with the mixture are shown in Table 2. [111] <Example 10> [112] Before the coating composition of Example 1 was applied on the polyester film, an antistatic composition including a conductive polymer as a main component (refer to Korean Patent Registration No. 422321) was prepared by mixing 1 g of poly(3,4-ethylenedioxythiophene) dispersed solution, 0.3 g of a water-soluble acrylic urethane binder, 0.03 g of an urethane curing agent, 0.3 g of ethylacetate, 0.3 g of NMP, 5.5 g of isopropyl alcohol, 3 g of water and 0.005 g of a wetting agent. Subsequently, the prepared antistatic composition was applied on a film, and was then dried using hot air of 8O⁰C to form an antistatic layer having a thickness of 0.2 μm on the surface of the film. Then, the film having the antistatic layer coated thereon was applied on a polyester film having a thickness of 38 μm to a coating thickness of 10 μm using the above coating method. The physical properties of the polyester film coated with the antistatic layer are shown in Table 2.

[113] <Example 11> [114] Example 11 was conducted using the same method as in Example 10, except that the coating composition of Example 9 was applied on the polyester film instead of the coating composition of Example 1. The physical properties of the polyester film coated with the mixture are shown in Table 2.

[115] [116] Table 2 [Table 2] [Table ]

[117] Physical properties of protective films manufactured in Example 1 and Examples 8 to 11 Industrial Applicability The pressure-sensitive adhesive composition of the present invention is used to manufacture protective films for various displays, such as polarizing films, mobile phone screens, etc., or surface protection products.

Claims

[1] A pressure-sensitive adhesive composition for a protective film, which functions to prevent a phenomenon in which an adhesive is transferred to an adherend by local pressing or scratching, comprising: a (meth)acrylic copolymer, serving as an adhesive; and a monofunctional or difunctional isocyanate compound, serving as a cross-linking agent.

[2] The pressure-sensitive adhesive composition according to claim 1, wherein the

(meth)acrylic copolymer is prepared by copolymerizing 80 ~ 99 wt% of (meth) acrylic monomer having an alkyl group of 1 to 14 carbon atoms with 1 ~ 20 wt% of (meth)acrylic monomer having a hydroxy group.

[3] The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the (meth)acrylic copolymer has a weight- average molecular weight of 300,000 ~ 3,000, 000.

[4] The pressure-sensitive adhesive composition according to any one of claims 1 to

3, wherein the monofunctional or difunctional isocyanate compound is one or more selected from among difunctional isocyanate compounds, such as tolylene diisocyanate, xylene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrated diphenylmethane diisocyanate; and monofunctional isocyanate compounds.

[5] The pressure-sensitive adhesive composition according to any one of claims 1 to

4, wherein an amount of the monofunctional or difunctional isocyanate compound is 0.1 ~ 20 parts by weight based on 100 parts by weight of the (meth) acrylic copolymer.

[6] A protective film manufactured using the pressure-sensitive adhesive composition of any one of claims 1 to 5.

[7] The protective film according to claim 6, wherein the protective film comprises a base film, which is coated with the pressure-sensitive composition, and which is any one film or is formed by layering two or more films selected among a p olyester-based film including polyethylene terephthalate, a polystyrene-based film including polystyrene, a polyolefin-based film including cyclic polyolefin, a polycarbonate-based film including polycarbonate, a polyimide-based film including polyimide, a polysulfone-based film including polyether sulfone, a cellulose-based film including triacetyl cellulose, and a polyacrylic-based film including polymethylmethacrylate.

[8] The protective film according to claim 6 or 7, wherein the protective film further comprises an adhesive layer including an antistatic agent to impart antistatic qualities to the protective film. [9] The protective film according to any one of claims 6 to 8, wherein the protective film further comprises an intermediate layer, which is located between the base film and the adhesive layer, including an antistatic agent containing a conductive polymer as an active component to impart imparting antistatic performance to the protective film. [10] The protective film according to claim 8, wherein the antistatic agent contains an ionic liquid or an alkaline metal salt as an active component. [11] The protective film according to claim 9, wherein the conductive polymer contains poly(3,4-ethylenedioxythiophene) as an active component.