EP2235130A2

EP2235130A2 - Adhesive tape and method for preparing the same

Info

Publication number: EP2235130A2
Application number: EP08867664A
Authority: EP
Inventors: Hun Jeong; Jeongwan Choi
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2007-12-21
Filing date: 2008-12-11
Publication date: 2010-10-06
Also published as: WO2009085631A3; RU2010125988A; CN101903484A; CA2709934A1; WO2009085631A2; KR20090067964A; JP2011508012A; TW200948927A; BRPI0821289A2

Abstract

Disclosed are adhesive tapes which include a flake conductive filler material. According to the disclosed invention, the adhesive tapes comprising a flake conductive filler that can be changed depending on the light-shielding pattern of the mask, can be have a relatively small thickness of around about 100 µm and different electrical conductivity.

Description

ADHESIVE TAPE AND METHOD FOR PREPARING THE SAME

Technical Field

The present invention relates to adhesive tapes for electromagnetic interference shielding useful in a variety of electronic application, and to methods of preparing the same.

Background

Electromagnetic radiation, which is generated in the circuits of various electronic devices, can, in some cases, disturb the functions of surrounding electronic devices or parts, reduce device performance, create environmental noise and interference, damage electronic images and reduce electronic device life spans. To date, a variety of materials have been developed to shield electromagnetic waves causing such problems. These materials include metal plates, metal plated fabrics, conductive paints, conductive tapes, conductive elastomers and the like.

In particular, conductive adhesive tapes are used mainly in miniaturized electronic devices. Such conductive tapes are prepared by adding fine conductive fillers, such as carbon black, graphite, silver, copper, nickel, aluminum or the like to an adhesive polymer resin to impart conductivity to the resin. In order for such conductive fillers to impart conductivity to the adhesive polymer resin, the conductive filler particles must form a continuous conductive path in the adhesive polymer resin. For this reason, a relative excess of conductive filler is generally added to the adhesive polymer resin. When an excess of conductive filler is added, however, the melt viscoelasticity of the adhesive resin is reduced, allowing the filler particles to agglomerate thereby increasing the viscosity of the polymer resin. This viscosity increase, in turn, results in an increase in specific gravity and a deterioration in the physical properties, including a reduction in impact and vibration absorbing properties. In addition, it is difficult to control the electrical conductivity of the conductive tapes using conventional methods of manufacture.

Summary

Accordingly, the present inventors have made efforts to prepare a conductive adhesive tape, which can shield electromagnetic waves without causing the above- mentioned problems.

In addition, the present inventors have made efforts to prepare an adhesive tape suitable for application in electronic devices, which gradually become miniaturized and slim.

As a result, the present inventors have found that, when flake conductive filler is used in adhesive polymer resin, it is possible to prepare an adhesive tape, which has a very small thickness while maintaining the adhesive properties and electrical conductivity of the resin.

Furthermore, the present inventors have found that, when a mask having a light- shielding pattern formed thereon is attached to both sides of an adhesive tape, and the adhesive tape is irradiated with light, the movement of conductive filler can be controlled using the light- shielding pattern of the mask, thus making it possible to prepare a conductive adhesive tape having the desired electrical conductivity.

The present invention is based on such findings.

In one aspect, the present invention provides an adhesive tape, comprising: an adhesive polymer resin; and flake conductive filler distributed in the adhesive polymer resin, wherein the flake conductive filler is electrically and continuously arranged in the adhesive polymer resin in the horizontal directions (x and y directions) and thickness direction (z direction) of the adhesive tape, and thus the adhesive tape shows various electrical conductivity. In another aspect, the present invention provides a method for preparing an adhesive tape, comprising the steps of: (i) mixing a monomer for forming adhesive polymer resin with flake conductive filler; (ii) forming the mixture into a sheet; (iii) placing a mask on the surface of the sheet; and (iv) irradiating one side or both sides of the sheet with light to photopolymerize the monomer so as to form adhesive polymer resin, wherein the mask has a light-shielding pattern formed thereon, and the light is radiated on all or part of the surface of the sheet depending on the light- shielding pattern.

Brief Description of the Drawings FIG. l(a) shows an adhesive tape, prepared in Example 1 of the present invention, in which flake conductive filler is generally arranged in a network configuration.

FIG. l(b) shows an adhesive tape, prepared in Example 2 of the present invention, in which flake conductive filler is arranged from one surface of polymer syrup to the inner middle portion in the horizontal direction and the thickness direction.

FIG. l(c) shows an adhesive tape, prepared in Example 3 of the present invention, in which flake conductive filler is arranged in the inner middle layer of polymer syrup in the horizontal direction.

FIGS. 2 and 3 schematically show that the arrangement of filler varies depending on the pattern of a mask, used in the light irradiation step of the inventive method for preparing the adhesive tape.

FIG. 4(a) is a scanning electron microscope ("SEM") photograph showing the surface of an adhesive tape prepared according to Example 1 of the present invention. FIGS. 4(b) and 4(c) are scanning electron microscope ("SEM") photographs showing the cross-sections of the adhesive tape prepared according to Example 1 of the present invention. FIGS. 5(a) and 5(b) are scanning electron microscope ("SEM") photographs showing both sides of an adhesive tape prepared according to Example 2 of the present invention, respectively.

FIG. 6 schematically shows a process of preparing an adhesive tape according to the present invention.

Detailed Description of Preferred Embodiments

Adhesive tapes according to the present invention generally have a structure in which flake conductive filler material is distributed in an adhesive polymer resin. The flake conductive filler material is arranged on the surface or inside (or both) of the adhesive tape in the horizontal direction and/or the thickness direction. Due to such ordered arrangement of the flake conductive filler material, the adhesive tapes of the invention exhibit improved electrical conductivity.

The flake conductive filler particles used in the present invention may be substantially flatly arranged in the adhesive polymer resin. Alternatively, the filler particles may move differently from each other, due to the difference in polymerization initiation between portions of the polymer resin which results from the presence of a light- shielding pattern in the photopolymerization step.

A sheet-like adhesive tape according to one aspect of the invention can be prepared, for example, by adding flake conductive filler to a syrup-like polymer material (hereinafter, referred to as "polymer syrup") that is not fully cured; forming the mixture into a sheet; placing a peelable release film on both sides of the sheet; and irradiating both sides of the sheet with light to photopolymerize the polymer syrup. By arranging the flake conductive filler material flatly (i.e., oriented in a plane) in the horizontal directions (x and y directions), an adhesive tape having a thickness of less than about 100 μm can be prepared. The step of forming the polymer syrup into a sheet may be carried out at the same time as the step of placing the release film on both sides of the sheet. Particularly, in the process of forming the polymer syrup into a sheet, the light- shielding patterned release film may be placed on both sides of the sheet. If such a light- shielding pattern is used, light irradiation is selectively conducted depending on the light- shielding pattern of the release film, and the photopolymerization of the syrup surface is selectively initiated. The flake conductive filler moves accordingly to the portion of the polymer syrup that is not yet polymerized, and this principle can be used to control the arrangement of the flake conductive filler material.

Specifically, if light is irradiated through a mask having a light-shielding pattern formed thereon, either the light cannot pass through the light-shielding pattern region, or the amount of light passed through that region will be significantly small. Thus, in the portion of the polymer syrup corresponding to the light-shielding pattern, photopolymerization will not be initiated, or, if it is initiated, the polymerization rate will be very slow. Conversely, in the portion of the polymer syrup above which the light- shielding pattern is not placed, photopolymerization will be actively initiated, and the polymerization will progress towards the lower portion of the polymer syrup via radicals resulting from initiation of the photopolymerization.

In this manner, the flake conductive filler material present in the portion of the polymer syrup in which polymerization is initiated will move to other portions in which polymerization has not yet occurred. If photopolymerization progresses from both sides of the polymer syrup, polymerization will be initiated from the surface of the polymer syrup, and conductive filler present on the surface of polymer syrup will migrate to the interior portions of the polymer syrup in which the polymerization has not yet occurred. On the other hand, in the portion of the polymer syrup positioned below the light- shielding pattern, photopolymerization does not occur, and conductive filler present in that portion does not migrate or move to other portions. Using the movement properties of the flake conductive filler, various adhesive tapes according to the invention can be made. One such embodiment is illustrated in FIG. 2. Polymer syrup 1 is placed between masks 3 having no light- shielding pattern and is irradiated with light 4. In this way, an adhesive tape is formed in which the flake conductive filler is arranged in the inner middle layer of the polymer syrup in the horizontal direction. Another embodiment is illustrated in FIG. 3, where polymer syrup 1 is disposed between masks 3 having a light- shielding pattern and is irradiated with light 4. In this way, an adhesive tape is formed in which flake conductive filler 2 is arranged in the interior portion of the syrup above which the light-shielding pattern is not placed. Conversely, in that portion of the syrup above which the light-shielding pattern is placed, the flake conductive filler 2 remains on the surface of the polymer syrup without any significant movement or is present throughout the entire thickness direction due to photopolymerization initiated only by weak light. With this combination, the flake conductive filler 2 form a network structure which electrically connects one side of the tape to the other side. In addition, where a light-shielding patterned mask is used only on one side of the polymer syrup, an adhesive tape can be made in which flake conductive filler is arranged from one side of the polymer syrup to the interior portion in both the horizontal direction and the thickness direction.

Adhesive tapes having different arrangements of flake conductive filler according to the invention can be used in various applications. For example, an adhesive tape in which flake conductive filler is arranged from one side of the adhesive tape to the opposite side to form a continuous network structure (as in the embodiment depicted in FIG. l(a)), can be used as a double-sided adhesive tape for ground connectivity in all directions (x, y and z directions). An adhesive tape in which the flake conductive filler is arranged continuously from one side of the adhesive tape to the interior portion in the thickness direction and the horizontal directions (as in the embodiment depicted in FIG. l(b)), can be used as a double-sided adhesive tape for ground connectivity in the horizontal directions (x and y directions) and insulation in the vertical, or thickness, direction (z direction). In addition, the adhesive tape, in which the flake conductive filler is arranged continuously in the interior portion of the adhesive tape in the horizontal directions (as in the embodiment depicted in FIG. l(c)), can be used as a double-sided adhesive tape for insulation.

In the inventive adhesive tapes described above, arrangement of the flake conductive filler can be controlled, unlike prior adhesive tapes in which conductive filler is irregularly dispersed. Thus, the inventive adhesive tapes can be prepared to be used in a variety of different applications requiring electrical conductivity. Particularly, according to the present invention, because a flake conductive filler material is used, it is possible to prepare an adhesive tape having a relatively small thickness (e.g., around about 100 μm). Accordingly, the adhesive tapes of the invention will typically have a surface resistance of about 0.1 Ω /m² or more and a vertical resistance of about 0.001 Ω or more. In the adhesive tapes of the invention, the flake conductive filler is introduced to impart electrical conductivity and provide an ability to make the adhesive tapes thinner. Any material may be selected for use as the flake conductive filler as long as it serves to impart electrical conductivity and is flake in shape.

Examples of useful flake conductive filler materials in the present invention include: flake metals, including: flake noble and non-noble metals; flake noble and non- noble metals plated with another noble or non-noble metal; noble metal- or non-noble metal-plated flake non-metals; flake conductive non-metals; and mixtures of two or more of these materials.

Specific examples of flake conductive filler materials include: noble metals such as gold, silver and platinum; non-noble metals such as nickel, copper, tin and aluminum; noble metal-plated noble and non-noble metals, such as silver-plated copper, nickel, aluminum, tin and gold; non-noble metal-plated noble and non-noble metals, such as nickel-plated copper and silver; noble or non-noble metal-plated non-metals, such as silver- or nickel-plated graphite, glass, ceramics, plastics, elastomers and mica; conductive non-metals such as carbon black and carbon fiber; and mixtures of two or more of any of these materials. The size of the flake conductive filler may vary depending on the type of material used. The size of the flake conductive filler is not specifically limited, but in one embodiment of the invention, if the flake conductive filler is square or rectangular in shape, it will generally have a thickness ranging from about 100 nm to about 25 μm and a side length of about 0.25-25 μm. The content of the flake conductive filler material in the adhesive tapes made according to the invention will generally range from about 20-60 wt% based on the total weight of the adhesive tape. In one illustrative embodiment of the invention, the content of the adhesive polymer resin in the adhesive tape is about 40-80 wt%, and the content of the flake conductive filler is about 20-60 wt%. In the present invention, an acrylic polymer resin can be used as the adhesive polymer resin. In one embodiment, an acrylic polymer resin, which can be prepared by polymerizing a photopolymerizable monomer, may be used.

Photopolymerizable monomers useful to make such acrylic polymer resins include alkyl acrylate ester monomers having a C_1-14 alkyl group. Non-limiting examples of such alkyl acrylate ester monomers include: butyl(meth)acrylate, hexyl(meth)acrylate, n- octyl(meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isononyl(meth)acrylate and the like. Other examples include isooctyl acrylate, isononylacrylate, 2-ethyl-hexyl acrylate, decyl acrylate, dodecyl acrylate, n-butyl acrylate, hexylacrylate and the like. Although alkyl acrylate ester monomers can be used alone to form an acrylic adhesive polymer resins, they can also be copolymerized with other polar copolymerizable monomers to form acrylic adhesive polymer resins. One useful such resin can be made from a copolymer of an alkyl acrylate ester monomer having a C_1-14 alkyl group with a polar copolymerizable monomer. In this case, although the weight ratio of the alkyl acrylate ester monomer to the polar copolymerizable monomer is not specifically limited, it is preferably 99-50:1-50 in view of the physical properties of the resulting adhesive polymer resin.

Non- limiting examples of the polar copolymerizable monomer include acrylic acid, itaconic acid, hydroxyalkyl acrylate, cyanoalkyl acrylate, acrylamide, substituted acrylamide, N-vinyl pyrrolidone, N-vinyl caprolactam, acrylonitrile, vinyl chloride, diallyl phthalate and the like. Such polar copolymerizable monomers can serve to impart adhesiveness and cohesiveness to the polymer resin and improve adhesion.

The content of the adhesive polymer resin in the adhesive tapes made according to the invention will generally be about 40-80 wt% based on the total weight of the adhesive tape.

Also, in order for the adhesive tapes to possess physical properties required in products in which they are applied, the adhesive tapes of the invention may further comprise one or more additional fillers. Any such additional fillers can be used, as long as they do not impair the properties and usefulness of the adhesive tape. Non- limiting examples of such additional fillers include thermally conductive fillers, flame retardant fillers, antistatic agents, foaming agents and the like. Such additional fillers will generally be used in an amount less than about 100 parts by weight, for example, about 10-100 parts by weight, based on 100 parts by weight of the adhesive polymer resin.

The adhesive tapes of the invention may further comprise additives, for example, polymerization initiators, crosslinkers, photoinitiators, pigments, antioxidants, UV stabilizers, dispersants, antifoaming agents, plasticizers and tackifying resins. Such additives may be added during the preparation process of the adhesive tape.

Hereinafter, a method for preparing the adhesive tape will be described in detail. Adhesive tapes of the invention can be prepared by mixing either a monomer for forming adhesive polymer resin or a prepolymer syrup of the monomer with flake conductive filler for imparting electrical conductivity, adding additional fillers or additives, if used, and polymerizing the mixture. Specifically, the adhesive tape of the present invention can be prepared by carrying out the steps of: mixing a monomer for forming adhesive polymer resin with flake conductive filler; forming the mixture into a sheet; placing a mask on the surface of the sheet; and irradiating both sides of the sheet with light to photopolymerize the monomer for forming adhesive polymer resin. A mask having a light-shielding pattern formed on it may be used, and all or part of the sheet surface may be irradiated with light depending on the light-shielding pattern of the mask. In this case, the flake conductive filler present in the portion of the sheet in which polymerization is initiated will move to other portions in which polymerization has not yet occurred.

In one embodiment of the invention, the monomer for forming the adhesive polymer resin is prepolymerized to prepare a polymer syrup, and the flake conductive filler and other necessary additives are added to the polymer syrup. This method can be used to uniformly disperse the flake conductive filler and facilitate the initiation of selective photopolymerization. More specifically, the step of mixing the monomer for forming the adhesive polymer resin with the flake conductive filler may comprise the steps of: partially polymerizing the monomer composition to prepare a polymer syrup and adding flake conductive filler to the polymer syrup. In one embodiment of the invention, the polymer syrup may have a viscosity of about 500 to about 20,000 cPs.

In a specific embodiment of the preparation method, a monomer for forming an adhesive polymer resin, for example, a monomer for forming acrylic polymer resin, is first partially polymerized using a polymerization initiator under an oxygen- free condition to prepare a syrup having a viscosity of from about 500 to about 20,000 cPs. The flake conductive filler, crosslinker, photoinitiator and any other necessary additives are added to the syrup, and the mixture is formed into a sheet. Light-transmitting release films may be used such that the polymer syrup sheet is disposed between two release film layers. By disposing the polymer syrup between the release films, a substantially oxygen-free condition can be maintained. If a light-shielding pattern is formed on one or both of the release films, the release films can serve as a mask on which a light-shielding pattern is formed. Thereafter, the polymer syrup may be polymerized and crosslinked under a substantially oxygen-free condition by directing irradiating light (preferably UV light) through the release films or other masks having a light-shield pattern. In this step, the light may be irradiated on all or part of the surface of the polymer syrup depending on the light-shielding pattern, so that photopolymerization is selectively initiated. The flake conductive filler present in the portion of the syrup in which the polymerization is initiated moves to other portions in which the polymerization has not yet occurred. As a result, the flake conductive filler is arranged three-dimensionally, and an adhesive tape having a desired electrical conductivity can be prepared. During irradiation of the surface of the sheet with light, a decrease in the content of oxygen in the sheet can lead to an increase in the adhesion of the adhesive polymer resin, because unnecessary oxidation reactions in the adhesive tape are avoided. The blockage of oxygen can be achieved by disposing the polymer syrup between the release films as described above and forming the polymer syrup into a sheet. It is also generally preferable to initiate the photopolymerization through light irradiation in a substantially oxygen- free chamber, for example, a chamber having an oxygen concentration of less than about 1000 ppm. Doing so can more effectively block oxygen and prevent oxidation reactions. In some cases, the concentration of oxygen is more preferably less than about 500 ppm. In the photopolymerization step, in order for a only a selective portion of the surface of the sheet to be irradiated with light, a mask having a light-shielding pattern may be used, and in order for all the surface of the sheet to be irradiated with light, a mask having no light-shielding pattern (that is, a transparent mask) may be used. The mask having a light-shielding pattern generally comprises a region through which light can pass, and a region through which light cannot pass or light passes in only a very small amount. Thus, the portion of the sheet above which the light-shielding pattern is placed will not be irradiated with light or will be irradiated with weak light, and the flake conductive filler present in that portion will remain on the surface of the sheet without any substantial movement. Conversely, the portion of the sheet above which the light-shielding pattern is not placed will be irradiated with light to initiate photopolymerization, and the flake conductive filler present in that portion will move to other portions in which photopolymerization has not yet occurred. As a result, the flake conductive filler can form a network structure in the sheet. In addition, in order for the flake conductive filler to be arranged in the interior portion of the sheet, a mask having no light-shielding pattern may be used such that light can be irradiated on substantially all of the surface of the sheet. Non- limiting examples of the mask include light-transmitting release films on which a desired light-shielding pattern (such as a network structure or a lattice structure) is formed and light-transmitting release films having no light-shielding pattern. A transparent plastic film having a low surface area or on which a release layer is coated may be used as a light-transmitting release film. Examples of suitable light-transmitting release films include polyethylene films, polypropylene films, polyethylene terephthalate ("PET") films and the like.

Any material capable of shielding about 10-100% of light reaching the light- shielding pattern may be used to form the light-shielding pattern. Preferably, a material capable of shielding more than about 50% of light reaching the light-shielding pattern is used. In some embodiments of the invention, the light- shielding pattern can be designed such that it shields more than about 70% of incident light. If necessary, the light- shielding pattern can also be designed such that it completely (100%) shields incident light.

There is no limitation on the method for forming the light-shielding pattern on the surface of the light-transmitting release film. Any method may be used that deposits on the surface of the light-transmitting release film a material for forming the light-shielding pattern that reduces or shields the passage of light. Printing methods, for example, can be applied for this purpose. Such printing methods are known in the art and include, for example, screen printing methods, printing methods that use heat transfer paper, gravure printing methods, etc. A black ink having good light-absorbing properties may be used to from the light- shielding pattern. The shape of the light- shielding pattern formed on the release film is not specifically limited and can be selected to coincide with the particular network structure desired for the conductive filler material.

In embodiments of the invention, the thickness of the release film may be about 5 μm to about 2 mm, but there is no particular limitation on the thickness of the release film. It is generally more difficult to form a light-shielding pattern and apply a polymer syrup on the release films having thicknesses of less than about 5 μm. It can also be difficult to carry out the photopolymerization of the polymer syrup if the release film is very thick {e.g., more than about 2 mm).

Moreover, although the thickness of the adhesive tapes prepared according to the invention is not specifically limited, the adhesive tapes preferably have a thickness of from about 10-200 μm. In some embodiments of the invention, the thickness of the adhesive tape is preferably from about 20-150 μm, and more preferably from about 30-100 μm, in view of photopolymerization, the thickness and movement of the flake conductive filler, etc. The intensity of light used to carry out the photopolymerization of the polymer syrup may be any intensity of light conventionally applied for photopolymerization. In one embodiment of the invention, the intensity of light corresponding to that of UV light is preferred.

One or more crosslinkers or crosslinking agents may be used for crosslinking the adhesive polymer resin. Depending on the amount of crosslinker used, the properties (particularly the adhesive properties) of the adhesive polymer resin can be controlled.

The crosslinker will generally be used in an amount of about 0.05-2 parts by weight based on 100 parts by weight of the adhesive polymer resin. Specific examples useful crosslinkers and crosslinking agents include, but are not limited to, multifunctional actylates such as 1 ,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 1,2-ethylene glycol diacrylate, 1,12-dodecanediol acrylate, and the like.

In addition, one or more photoinitiators may be used in the preparation process of the adhesive tapes of the invention. Depending on the amount of photoinitiator used, the degree of polymerization of the polymer resin can be controlled. The photoinitiator may be used in an amount of about 0.01-2 parts by weight based on 100 parts by weight of the adhesive polymer resin. Specific examples of useful photoinitiators include, but are not limited to, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6- trimethylbenzoyl)phenylphosphine oxide, α,α-methoxy-α-hydroxyacetophenone, 2- benzoyl-2(dimethylamino)- 1 - [4-(4-morphonyl)phenyl] - 1 -butanone, 2,2-dimethoxy-2- phenylacetophenone, etc. The adhesive tapes made according to the invention can be applied in various electronic devices requiring electrical conductivity, since the arrangement of the flake conductive filler can be changed depending on the light- shielding pattern of the mask so as to change electrical conductivity.

Examples

The present invention will hereinafter be described in further detail with reference to examples and comparative examples. It will be understood that these examples are offered for illustrative purposes only, and the scope of the present invention is not to be construed as limited thereto.

The term "parts" in the following examples means "parts by weight" relative to 100 parts by weight of adhesive polymer resin, which is formed by polymerization of a monomer. Example 1

90 parts of 2-ethylhexyl acrylate as an acrylic monomer and 10 parts of acrylic acid as a polar copolymerizable monomer were placed in a 1 -liter glass reactor, and 0.1 parts of photoinitiator Irgacure 651 (α,α-methoxy-α-hydroxyacetophenone) and 0.1 parts of crosslinker 1,6-hexanediol diacrylate ("HDDA") were added thereto. The monomers were partially polymerized by photoinitiation, thus preparing syrup having a viscosity of 3000 cPs. To the syrup, 40 parts of flake silver as flake conductive filler was added, and the mixture was stirred, thus preparing a uniform polymer syrup.

Meanwhile, a lattice structure having a width of 350 μm and an interval of 1 mm was patterned on a release film made of a 75 μm thicker transplant polyethyleneterephthalate film ("PET") using black ink, thus preparing a mask having a light-shielding pattern.

As shown in FIG. 6, the polymer syrup was extruded from the glass reactor, while the patterned release film was placed on both sides of the polymer syrup using a roll coating machine, such that the thickness of the polymer syrup reached about 50 μm. By placing the release film on both sides of the polymer syrup, the polymer syrup could be prevented from coming into contact with air, particularly oxygen.

The polymer syrup was cured by irradiating both sides with UV light via the release film at a energy dose of 4.5 mW/cm³ for 520 seconds using a metal halide UV lamp, thereby preparing an adhesive tape. Example 2

An adhesive tape was prepared in the same manner as in Example 1, except that a patterned release film was placed on the top side of the polymer syrup, and a transparent release film rather than the patterned release film was placed on the bottom side.

Example 3

An adhesive tape was prepared in the same manner as in Example 1 , except that a transparent release film rather than the patterned release film was placed on both sides of the polymer syrup.

Test Example 1: Resistance Measurement

The surface resistance and vertical resistance of each of the adhesive tapes prepared in Examples 1 to 3 was measured by the surface probe method adapted from MiI- G-83528B using a Kietheley 580 micro-ohmmeter. The average value of measurement results are shown in Table 1 below.

Table 1

As can be seen in Table 1 above, the adhesive tapes prepared in Examples 1 to 3 had various electrical conductivities depending on the light-shielding patterns of the masks. Test Example 2: Adhesion Test

In accordance with ASTM D 1000, each of the adhesive tapes prepared in Examples 1 to 3 was laminated with aluminum sheets, and then the adhesion of each adhesive tape to the top side and the bottom side in a 180° direction was measured using a Universal Test Machine ("UTM"). The measurement results are shown in Table 2 below.

Table 2

Claims

1. An adhesive tape, comprising: an adhesive polymer resin; and a flake conductive filler distributed in the adhesive polymer resin, wherein the flake conductive filler is electrically and continuously arranged in the adhesive polymer resin in the horizontal directions (x and y directions) and the thickness direction (z direction).

2. The adhesive tape of Claim 1, which has a thickness of 10-200 /M.

3. The adhesive tape of Claim 1, which has a surface resistance of 0.1 Ω/m² or more.

4. The adhesive tape of Claim 1, which has a vertical resistance of 0.001 Ω or more.

5. The adhesive tape of Claim 1, wherein the flake conductive filler has a thickness ranging from 100 nm to 25 /M.

6. The adhesive tape of Claim 1, wherein the flake conductive filler is contained in an amount of 20-60 wt% based on the total weight of the adhesive tape.

7. The adhesive tape of Claim 1, wherein the flake conductive filler is selected from the group consisting of: flake metals, including noble metals and non-noble metals; noble metal-plated, flake noble metals or non-noble metals; non-metal-plated, flake noble metals or non-noble metals; noble metal- or non-noble metal-plated, flake non-metals; flake conductive non-metals; and mixtures thereof.

8. The adhesive tape of Claim 7, wherein the noble metals include gold, silver and platinum; the non-noble metals include nickel, copper, tin and aluminum; the noble metal-plated flake noble metals or non-metals include silver-plated copper, nickel, aluminum, tin and gold; the non-noble metal-plated, flake noble metals or non-noble metals include nickel-plated copper and silver; the noble metal or non-noble metal-plated, flake non-metals include silver- or nickel-plated graphite, glass, ceramics, plastics, elastomers and mica; and the flake conductive non-metals include carbon black and carbon fiber.

9. The adhesive tape of Claim 1, wherein the adhesive polymer resin is contained in an amount of 40-80 wt% based on the total weight of the adhesive tape.

10. The adhesive tape of Claim 1, wherein the adhesive polymer resin includes acrylic polymer resin.

11. The adhesive tape of Claim 10, wherein the acrylic polymer resin is a copolymer of an alkyl acrylate ester monomer, having a C_1-14 alkyl group, with a polar copolymerizable monomer.

12. The adhesive tape of Claim 11, wherein the ratio of the alkyl acrylate ester monomer to the polar copolymerizable monomer is 99-50:1-50.

13. A method for preparing an adhesive tape, comprising the steps of:

(i) mixing a monomer for forming adhesive polymer resin with flake conductive filler;

(ii) forming the mixture into a sheet;

(iii) placing a mask on one side or both sides of the sheet; and

(iv) irradiating both sides of the sheet with light to photopolymerize the monomer so as to form adhesive polymer resin, wherein the mask has a light-shielding pattern formed thereon, and the light is irradiated on all or part of the surface of the sheet depending on the light- shielding pattern.

14. The method of Claim 13, wherein, in the photopolymerization step, the flake conductive filler is arranged in the horizontal directions (x and y directions) and the thickness direction (z direction) depending on the configuration of the light- shielding pattern.

15. The method of Claim 13, wherein the mask consist of a light-transmitting release film having a light-shielding pattern formed thereon.

16. The method of Claim 13, wherein the light-shielding pattern formed on the mask is a network structure or a lattice structure.

17. The method of Claim 15, wherein the light-transmitting release film is a polyethylene film, a polypropylene film or a polyethylene terephthalate (PET) film.

18. The method of Claim 13, wherein the step of mixing the monomer for adhesive polymer resin with the flake conductive filler comprises the sub-steps of: partially polymerizing the monomer for adhesive polymer resin to form polymer syrup; and adding the flake conductive filler to the polymer syrup and stirring the mixture.

19. The method of Claim 18, wherein the polymer syrup has a viscosity of 500- 20,000 cPs.

20. The method of Claim 13, wherein the concentration of oxygen in the light irradiation is less than 1000 ppm.