WO2008018747A1

WO2008018747A1 - Compositions comprising electromagnetic shielding materials and the sheets using the same

Info

Publication number: WO2008018747A1
Application number: PCT/KR2007/003805
Authority: WO
Inventors: Byoung-Soo Lee; Min-Seok Song; Jang-Soon Kim; Geun-Hee Lee; Seung-Min Yoo
Original assignee: Lg Chem, Ltd.
Priority date: 2006-08-08
Filing date: 2007-08-08
Publication date: 2008-02-14

Abstract

The present invention relates to a composition comprising a binder and an electromagnetic shielding material, wherein said electromagnetic shielding material is antimony (Sb), a mixture of antimony and a metal or a mixture of antimony and ceramic, and a sheet using the same. The present composition or sheet has excellent electromagnetic shielding effect, not only in high frequency band, but also in low frequency band, as well as has superior heat radiating characteristic, so that it may effectively shield electromagnetic waves occurring from various electronic products and prevent malfunction and shortened service life of products by high heat, without installing separate heat radiating sheet. Therefore, slimmed electronic products such as PDP, enhanced productivity and reduced production costs can be contrived.

Description

COMPOSITIONS COMPRISING ELECTROMAGNETIC SHIELDING MATERIALS AND THE SHEETS USING THE

SAME

Technical Field

[1] The present invention relates to a composition having excellent electromagnetic shielding effect and heat radiating characteristic, and a sheet using the same. More specifically, the present invention relates to a composition having excellent electromagnetic shielding effect, not only in high frequency bands, but also in low frequency bands, as well as having superior heat radiating characteristic, using antimony (Sb) as an electromagnetic shielding material, and a sheet using said composition.

[2]

Background Art

[3] Recently, following development and a large supply of electronic communications equipment, pollution caused by electromagnetic waves or electromagnetic interference (EMI) and the like has been raised into social issues. As one effort to minimize such issues caused by electromagnetic waves, electromagnetic shielding materials have been suggested, which are generally dispersed in binders to be coated on electronic components or appliances or are prepared in a sheet to be adhered thereto.

[4] The electromagnetic shielding materials are defined as functional materials usually transforming incident electromagnetic energy to heat energy. The mechanism of electromagnetic shielding materials is due to loss characteristic of materials. They are roughly classified as conductive loss materials, dielectric loss materials, magnetic loss materials and composite materials comprising two or more of the foregoing, depending on the materials used. In addition, performance of electromagnetic shielding materials is evaluated in terms of matching frequency, matching thickness, return loss and band width, and the like.

[5] As the electromagnetic shielding materials, magnetic metal powders or nonmagnetic powders are generally used. Representative magnetic metal powders include ferrite, permalloy or sendust, and the like. Non-magnetic powders include metal powders such as copper (Cu), aluminum (Al), molybdenum (Mo) or tungsten (W) and the like, or ceramics such as AiN, BN, Si N , SiC, Al O or BeO and the like. To

3 4 2 3 realize high magnetic permeability, said magnetic shielding materials are usually more used as a flake shape, in a chip form, rather than a spherical shape. [6] Said magnetic metal powders are explained in more detail as follows. [7] Ferrite means a solid solution that alloying elements or impurities are dissolved in iron with a body-centered cubic structure which is stable at 900? or less, and use mainly magnetic loss by a resonance phenomenon represented in a band of several MHz or more. They have a thin thickness and relatively various matching frequencies and thus are most used in industries. Permalloy is inherently a trade name of an alloy having high magnetic permeability and means a binary alloy of 78.5% nickel and 21.5% iron. If permalloy is subjected to a suitable heat treatment, it becomes an excellent magnetic material representing high magnetic permeability. Sendust means an alloy with high magnetic permeability having a composition of 5% aluminum, 10% silicone and 85% iron. Since both magnetic anisotropy constant and magnetostriction constant are 0 from the ternary composition of Al-Si-Fe, it has high magnetic permeability.

[8] However, if electromagnetic waves radiated from various electronic appliances are shielded using the previously described materials, certain degree of shielding effect is shown at high frequency bands of 2 GHz or more, but since the above materials have low return loss, the shielding performance is very lowered at low frequency bands of 1 GHz or less and the thickness becomes thick. Therefore, there was a disadvantage of being practically restricted.

[9] Japanese Unexamined Patent Publication No. 2000-114440 discloses those that magnetic powders with a spherical shape and magnetic powders with a flat shape, and optionally non-magnetic powders are added to a soft substrate such as rubber or resin and the like, as a heat radiating sheet having heat radiating characteristic and electromagnetic shielding characteristic. However, in case of said sheet, a certain degree of effect is shown in high frequency bands of 2 GHz or more, but the effect is not shown in low frequency bands of 1 GHz or less.

[10] In addition, Japanese Unexamined Patent Publication No. 2002-299112 discloses a method for preparing a sheet by dispersing soft magnetic metal powders of a flake shape in a matrix material. However, said method uses a press molding. Particularly, if it uses a heat press molding, since the cross-linking hardening is proceeded to interfere orientation of powders, it cannot be expected enhanced effect of magnetic permeability. In addition, said sheet does not also show the shielding effect at low frequency bands of 1 GHz or less.

[11] There was a problem that such conventionally used electromagnetic shielding materials did not show sufficient electromagnetic shielding effect, or had hardly the shielding effect at low frequency bands, though it showed a certain shielding effect at high frequency bands. Additionally, after mainly preparing sheets from conventionally used electromagnetic shielding materials, they are attached to various electronic appliances by forming separate pressure sensitive adhesive layers on said sheets. But, in such cases, since a process of coating the pressure sensitive adhesive layer and the like are separately required, the production processes are complicated and the production costs are raised.

[12] In addition, in electronic products and the like, there are problems, besides electromagnetic interference (EMI), such as malfunction and shortened service life of appliances by heat occurred in procedures of shielding electromagnetic waves or components themselves. To solve these problems, heat radiating sheets are required, in addition to an electromagnetic shielding sheet. Therefore, there were also problems not only being caused of complicated processes for preparation and raised costs, but also not complying with a request for slimming electronic equipment, which has been recently increased.

[13] Some cases were conventionally present, such as using antimony in a form of oxide as a fire retardant adjuvant (KR Patent Publication No. 1987-1535 and US Patent No. 6,410,137) or using powders coating barium sulfate with antimony doped tin oxide for conductivity (Japanese Unexamined Patent Publication No. H07-70479). But, no example using antimony as an electromagnetic shielding material was present. It was disclosed even in the Japanese Patent Publication above that tin oxide showed conductivity, whereas it was not disclosed whether antimony had any function.

[14]

Disclosure of Invention

Technical Problem

[15] The present inventors had researched to solve the previously described problems in the prior art. As a result, when antimony (Sb) was used as an electromagnetic shielding material, they found for the material to show excellent shielding effect not only at high frequency bands but also at low frequency bands and to have excellent heat radiating characteristic, whereby they accomplished the present invention.

[16] That is, the present inventors initially found for antimony to have the electromagnetic shielding performance, whereby they accomplished the present invention. Therefore, one object of the present invention is to provide a composition comprising a binder and an electromagnetic shielding material, wherein said electromagnetic shielding material is antimony. The other object of the present invention is to provide a sheet formed from said composition.

[17]

Technical Solution

[18] The present invention provides, as a means for solving the above objects, a composition comprising a binder and an electromagnetic shielding material, wherein said electromagnetic shielding material is antimony. [19] In the present composition above, the electromagnetic shielding material may further comprise one or more selected from the group consisting of metal and ceramic.

[20] In addition, in the present composition above, the electromagnetic shielding material is preferably included in an amount of 5 to 100 vol% relative to the binder.

[21] The electromagnetic shielding material included in the present composition has preferably one or more shapes selected from the group consisting of a spherical shape, a flake shape, an oval shape and a cylinder shape. Also, the electromagnetic shielding material has preferably a size of 1 nm to 200 D.

[22] The present invention provides, as a means for solving the above objects, a sheet comprising an electromagnetic shielding layer containing the present composition and a plasma display panel comprising said sheet.

[23]

Brief Description of the Drawings

[24] Fig. 1 is a cross-section view representing a first embodiment of a sheet according to the present invention.

[25] Fig. 2 is a cross-section view representing a second embodiment of a sheet according to the present invention.

[26] Fig. 3 is a cross-section view representing a third embodiment of a sheet according to the present invention.

[27] Fig. 4 is a cross-section view representing a fourth embodiment of a sheet according to the present invention.

[28] Fig. 5 is a cross-section view representing a fifth embodiment of a sheet according to the present invention.

[29] Fig. 6 is a pattern diagram of a coaxial cable measuring method.

[30] Figs. 7 and 8 are graphs representing measurements of electromagnetic shielding effect by a coaxial cable measuring method.

[31] Fig. 9 is a pattern diagram of an electromagnetic scanning method.

[32] Figs. 10 to 13 are graphs representing measurements of electromagnetic shielding effect by an electromagnetic scanning method.

[33]

Best Mode for Carrying Out the Invention

[34] The present invention relates to a composition comprising a binder and an electromagnetic shielding material, wherein said electromagnetic shielding material is antimony. As described above, in case of conventional electromagnetic shielding materials, there was a problem that they had insufficient electromagnetic shielding effect or they had a certain shielding effect at high frequency bands, but did not show satisfactory shielding effect at low frequency bands of 1 GHz or less. However, in case of the present composition, by using antimony as an electromagnetic shielding material, it represents excellent electromagnetic shielding effect not only at high frequency bands but also at low frequency bands.

[35] The present composition is explained in detail below.

[36] The present composition comprises a binder and an electromagnetic shielding material, and it is characterized in that said electromagnetic shielding material is antimony. Said electromagnetic shielding material herein may use antimony alone. In addition, it may further comprise other materials, besides said material. Said other materials are not specifically restricted, as long as they have electromagnetic shielding effect. But, it is preferred to use one or more selected from metal and ceramic.

[37] Said metal or ceramic may use any one, and is not specifically restricted, as long as it has electromagnetic shielding performance. But, for example, in case of the metal, it is preferred to use one species or two or more species, in a mixture thereof, selected from ferrite, permalloy, sendust, alnico (an alloy of aluminum, nickel and cobalt), silicon steel, stainless steel, copper (Cu), nickel (Ni), iron (Fe), molybdenum (Mo), tungsten (W), zinc (Zn), magnesium (Mg), manganese (Mn), aluminum (Al), titanium (Ti) and silver (Ag) or an alloy of two or more species of the foregoing. And, in case of ceramic, it is preferred to use aluminum nitride (AlN), boron nitride (BN), silicon nitride (Si N ), silicon carbide (SiC), aluminum oxide (Al O ) or beryllium oxide (BeO) alone or in a mixture of two or more species of the foregoing.

[38] In the present composition, by using antimony or a mixture thereof with other materials as an electromagnetic shielding material as above, it exhibits excellent shielding effect not only at high frequency bands but also at low frequency bands, and represents superior heat radiating characteristic, even without adding separate conductive materials, because antimony itself has excellent thermal conductivity.

[39] Said electromagnetic shielding material herein is preferably included so as to be in an amount of 5 to 100 vol% (volume of binder: volume of electromagnetic shielding material = 1: 0.05 to 1: 1), more preferably 20 to 70 vol%, relative to said binder.

[40] In the present invention, said electromagnetic shielding material may have various shapes such as a spherical shape, a flake shape, an oval shape, a cylinder shape or other polyhedron shapes. The shape herein is not specifically limited, but it is preferred that the electromagnetic shielding material has a flake shape to embody high magnetic permeability.

[41] Preferably, said electromagnetic shielding material has a size of 1 nm to 200 D. The size of electromagnetic shielding material herein means, for example, a particle diameter in case of the spherical shape, and its wide and long lengths and thickness in case of a flake shape. If said size is less than 1 nm, it is hard to homogeneously mix the material with the binder. It the size is in excess of 200 D, it is concerned that film coatability, or moldability, when the material is prepared into a sheet, is lowered and surface properties are hindered. When the present electromagnetic shielding material has a spherical shape, it has preferably a particle diameter of 1 nm to 200 D. When it has a flake shape in a chip form, it is preferred to use one with wide and long lengths of 1 nm to 200 D and a thickness of 0.5 times or less than said length.

[42] In the present invention, the binder functions to cohere between particles themselves of the electromagnetic shielding material and to impart a pressure sensitive adhesion strength to adherends, so that they may be bound after coating them with the binder. It is not specifically limited, as long as it represents such functions. But, it is preferred to use synthetic resins, natural resins or rubbers and the like.

[43] Preferred examples of said binder include a synthetic resin such as an acrylic resin, a silicone resin, a urethane resin, a melamine resin or an epoxy resin; rubber such as natural rubber, butadiene rubber, isoprene rubber, ethylene propylene rubber, nitrile rubber, acrylonitrile butadiene rubber, isobuthylene isoprene rubber or silicone rubber. Each of the foregoing may use alone or in a mixture of two or more thereof. In addition, although it is not specifically restricted, it is preferred that said binder has self-adhesion so as to be able to prepare a sheet which may be easily adhered to adherends without any separate process of coating a pressure sensitive adhesive layer.

[44] More preferred example of said binder herein is an acrylic resin. Such an acrylic resin has excellent self-adhesion, and has good adhesion strength with adherends. Therefore, there is an effect that it has enhanced thermal conductivity. It is preferred that as said acrylic resin, a copolymerized resin is used, in which a (meth)acrylic acid ester monomer having an alkyl group of 1 to 12 carbon atoms is copolymerized with a polar monomer being capable of copolymerizing with said monomer.

[45] Examples of said (meth)acrylic acid ester monomer include, but not limited to, one or more selected from the group consisting of butyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and isononyl (meth)acrylate. In addition, said polar monomer functions to enhance bonding strength by imparting high cohesion strength. If the monomer exhibits such function, it is not specifically restricted, but includes carboxyl group containing monomer such as (me th) acrylic acid, maleic acid or fumaric acid or nitrogen containing monomer such as acrylamide, N-vinylpyrrolidone or N- vinylcaprolactam. Each of the foregoing may use alone or in a mixture of two or more species thereof.

[46] The ratio of said (meth)acrylic acid ester monomer and said polar monomer may be suitably selected in a range which may accomplish the desired effect, and is not specifically restricted. But, it is preferred that the polar monomer is used in an amount of 1 to 20 parts by weight, relative to 100 parts by weight of (meth)acrylic acid ester monomer.

[47] In the present composition, the used binder includes a thermal curing binder and a light curing binder. In addition, the present composition may further comprise a thermal initiator or a photo-initiator, depending on the kind of said binder. The degree of polymerization of binder may be appropriately controlled by regulating an amount of said thermal initiator or photo-initiator used. By further including all said thermal initiator and photo-initiator in the present composition, it may be formulated, so that dual curing is allowed. In this case, it is preferred that light curing is initially practiced, followed by thermal curing in turn. But, it is not limited to this order.

[48] Said initiator may be appropriately selected and used by those skilled in this field, depending on the binder, and is not specifically restricted. But, for example, in case of using an acrylic resin as the binder, an amine, a peroxide such as benzoyl peroxide or azobisisobutyronitrile and the like are preferably used as a thermal initiator, and - hydroxy acetophenone, 1 -hydroxy cyclohexylphenyl ketone, 2,2-dimethoxy-2-phenyl-acetophenone, xanthone, benzaldehide, anthraquinone, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxy benzophenone, 4,4'-diaminobenzophenone, benzoin propyl ether, benzoin ethyl ether, l-(4-isopropyl-phenol)-2-hydroxy-2-methyl propan-1-one or thioxanthone, and the like, is preferably used as a photo-initiator. In addition, the amount of said initiator used is not specifically limited, but preferably 0.01 to 10 parts by weight relative to 100 parts by weight of said binder.

[49] In the present composition, a cross-linking agent may be further included. By regulating the added amount of said cross-linking agent, the adhesion property of the present composition may be controlled. The amount of the cross-linking agent used may be appropriately selected by those skilled in this field and is not specifically limited. But, 0.01 to 10 parts by weight of the cross-linking agent is preferably included, relative to 100 parts by weight of said binder. In addition, the kind of the used cross-linking agent also is not specifically limited and those usually used may be used. But, in case of using acrylic resins as said binder, one or more cross-linkable monomers selected from multifunctional acrylates, 1,2-ethylene glycol diacrylates, 1,6-hexanediol diacrylates and 1,12-dodecanediolacrylates are preferably used.

[50] In the present composition, a foaming agent also may be further included. By including said foaming agent, when the present composition is prepared to a sheet, it may be formed into a foam structure to impart lightweight property to the sheet. When it is adhered to adherends, they are allowed to have more enhanced safe adhesion. Said foaming agent may be used without special limitation, if it is usually used in this field. But, it is preferred to use an organic foaming agent or an inorganic foaming agent. As said organic foaming agent, sulfonylhydrazide such as p,p'-oxybis(benzenesulfonylhydazide), benzenesulfonylhydrazide or toluenesulfonyl- hydrazide; an azo compound such as azodicarbonamide (ADCA) or azobisisoph- thalonitrile; a nitroso compound such as N,N'-dinitrosopentamethylenetetramine or N,N'-dimethyl-N,N'-dinitrosoterephthalamide is preferred, and as said inorganic foaming agent, sodium bicarbonate or ammonium bicarbonate is preferred.

[51] In the present composition, it is preferred that a heat radiating material is further included. Said heat radiating material is included and dispersed in the composition to more enhance the heat radiating characteristic. Said heat radiating material may be used without special limitation, if it has thermal conductivity. But, a metal such as aluminum, nickel or an alloy thereof; a ceramic such as boron carbide; a polymer molding material; carbon black; carbon fiber; or acetylene black, and the like, is preferred. Each of the foregoing may be used alone or in a mixture of two or more thereof. Said polymer molding material is one coating a surface of the polymer with a heat conductive metal or ceramic and the like. In view of lightening, said polymer molding material is preferably one molded from a polymer with low density, and more preferably fine hollow spheres. Preferably, said heat radiating material has a particle size of 1 nm to 200 D. It is preferred that it is contained in an amount of 0.05 to 10 parts by weight relative to 100 parts by weight of said binder. But, it is not limited thereto.

[52] In addition to the above materials, additives such as pigments, antioxidants, stabilizers, dispersants, antifoamers, thickeners, plasticizers, tackifier resins, coupling agents, for example, silane coupling agents or brighteners may be appropriately added to the present composition, within a range without affecting the effect of invention.

[53] The present composition includes a liquid phase, a paste phase or a dough phase with high viscosity, and may be coated on a surface of various electronic products to form a film, or may be prepared into certain shape molding materials and used as electromagnetic shielding and heat radiating components. The present composition may be also contained in a certain amount as a raw material of electronic products themselves, or may be also used by molding it in a form of sheet and then attaching it to surfaces of electronic products. When the present composition is prepared into a sheet, it is preferred to suitably regulate its viscosity in view of moldability. The range of said viscosity may be appropriately selected and regulated by those skilled in this field. But, it is preferred to be in a range of 1,000 to 10,000 cps.

[54] The present invention also relates to a sheet comprising an electromagnetic shielding layer containing said composition. The present sheet may be included in electronic products and the like to carry out functions as an electromagnetic shielding sheet and a heat radiating sheet at the same time.

[55] The present sheet is explained below, with reference to drawings. [56] The present sheet comprises an electromagnetic shielding layer 10 containing the previously described composition, and may consist of a single layer of said shielding layer 10 or consist of a form such that a substrate sheet 20 is attached to one or both surfaces of said shielding layer 10. Also, it may further comprise a releasing sheet to be detached and removed on attaching the shielding sheet to an electronic product, although this is not depicted in drawings.

[57] Furthermore, the present sheet may be prepared into a sheet with a foam structure, since a foaming agent is included in the composition, as previously described, whereby lightweight properties are imparted to the sheet, and when it is attached to adherends such as electronic products, more enhanced safe adhesion is represented.

[58] When the present sheet consists of a single layer of electromagnetic shielding layer

10, said shielding layer 10 has preferably a self-adhesion, so that said sheet may be easily attached to an electronic product. In addition, said sheet may have a structure that embossings 15 are formed on one or both sides thereof, whereby air can come out of intaglio parts of the embossings 15 on attaching it to an electronic product to enhance the initial adhesion. Also, the contact area of side in contact with the electronic product or the outside is so large that electromagnetic shielding efficiency and heat radiating characteristic may be improved. Appearances of said embossings 15 are not specifically limited and an optional appearance may be formed. For example, it includes moire patterns or cross stripes and the like as those formed by the embossings 15.

[59] The present sheet may also have a structure that a substrate sheet 20 is bound to one or both sides of the electromagnetic shielding layer 10, wherein said substrate sheet 20 may consist of a substrate 22 alone or a substrate 22 and a pressure sensitive adhesive 24 coated on one side thereof.

[60] The method for binding the electromagnetic shielding layer 10 and the substrate sheet 20 may use a method usually applied to this field, and is not specifically limited. But, they may also be bound by a method such as thermal adhesion or ultrasonic adhesion and the like, by coating and hardening the composition on the substrate sheet 20, or by such adhesion, if said electromagnetic shielding layer 10 has self-adhesion.

[61] Said substrate 22 is not specifically limited, but it is preferred to use a material such as plastic, paper, non-woven fabric, glass or metal. More preferably, a polyethyleneterephthalate (PET) film is used. In addition, as long as said pressure sensitive adhesive 24 may accomplish purposes of the present invention, it may be used without special limitation. But, it is preferred to use one or more selected from the group consisting of acrylic resins, urethane resins and epoxy resins. More preferably, in view of compatibility with a binder, acrylic resins are used. In addition, as said acrylic resins, a copolymer of (meth)acrylic acid ester monomer having an alkyl group of 1 to 12 carbon atoms, and a copolymerizable polar monomer with said monomer may be used.

[62] The thickness of the present sheet may be appropriately selected in a range that the desired effect can be exhibited and is not specifically limited. But, it is preferred to have a thickness of 1 D to 100 mm. If the thickness of said sheet is thinner than 1 D, the capacity, which can shield electromagnetic waves, is too little to have sufficient shielding effect. If the thickness is thicker than 100 mm, it is concerned that the sheet is hardly applied to electronic products or industrial machinery in practice, due to increase in price and weight of the sheet

[63] The present sheet may be prepared by a usual method in the field to which this invention belongs. Such a method is not specifically limited. For example, the process for preparing the present sheet is as follows.

[64] Using (meth)acrylic acid ester monomer having an alkyl group of 1 to 12 carbon atoms, and a copolymerizable polar monomer with the monomer, syrup with a certain viscosity, for example, 1,000 to 10,000 cps is prepared. Then, a thermal initiator or a photo-initiator, and if desired, an additive such as a cross-linking agent or a foaming agent are suitably added to said syrup, and stirred and mixed to prepare a mixture. Subsequently, an electromagnetic shielding material, that is, antimony (Sb) powders or mixed powders of antimony (Sb) are added thereto and the mixture is sufficiently mixed and dispersed. The obtained dispersion is applied to a substrate, and the polymerization and cross-linking reaction are performed by thermal irradiation or UV irradiating. Thus, a sheet may be prepared, which has a layer structure that the electromagnetic shielding layer is formed on the substrate.

[65] Since the present sheet as above has excellent electromagnetic shielding effect at high frequency bands and low frequency bands, it may be variously used in various electronic products or industry machinery being able to cause problems such as an electromagnetic pollution.

[66] Also, in addition to the electromagnetic shielding effect, the present sheet exhibits excellent heat radiating effect in electronic products. That is, since the present composition has excellent heat radiating characteristic even without adding separate heat radiating materials, and thus heat occurred in electromagnetic shielding procedures or components themselves, may promptly transmit to heat radiating elements, without installing separate heat radiating sheets, it can comply with the request of slimming electronic products and the like.

[67] Since the present sheet has electromagnetic shielding performance and heat radiating performance at the same time, and also has excellent moldability, it may be usefully applied to all the electronic products having a problem such as elec- tromagnetic pollution or exothermic heat. As its representative example, a plasma display panel (PDP) may be included. PDP is a device displaying image, using a plasma generated by gas discharge and requires thorough preparation against electromagnetic pollution, because it is used in home appliances and the like. In addition, since it is prepared in a form of thin-shaped PDP, it has a weakness for heat by high voltage and the like occurred due to electromagnetic interference or a plasma light source.

[68] However, when a heat radiating sheet for PDP is constructed using the composition or sheet according to the present invention, it has not only excellent shielding effect of electromagnetic waves occurred from the PDP, but also need not install a separate heat radiating sheet together with the electromagnetic shielding sheet. Therefore, the PDP may be slimmer prepared.

[69]

Mode for the Invention

[70] Hereinafter, the present invention is explained in more detail, through examples according to the present invention and comparative examples not according to the present invention. But, the scope of the present invention is not restricted to the examples set forth below.

[71] Example 1

[72] 96 Parts by weight of 2-ethylhexyl acrylate as a (meth)acrylic acid monomer and 4 parts by weight of acrylic acid as a polar monomer were subjected to thermal polymerization in 1 liter glass reactor to obtain syrup with a viscosity of 3,500 cps. 0.7 Parts by weight of benzoylperoxide (BPO) as a thermal initiator and 0.7 parts by weight of 1,6-hexanediol diacrylate (HDDA) as a cross-linking agent were added to 100 parts by weight of said syrup and after mixing them, the mixture was sufficiently stirred to polymerize an acrylic resin as a binder. Antimony powders of spherical shape with an average particle diameter of 20 D as an electromagnetic shielding material were mixed with such polymerized acrylic resin so as to be present in 30 vol% of the acrylic resin, and the mixture was sufficiently stirred until it was homogenized. Then, after defoaming said mixture under reduced pressure using a vacuum pump, it was coated on a PET film in a thickness of 1 mm using Micro Bar, and left in an oven at 120? for 7 minutes to obtain an electromagnetic shielding sheet having self- adhesion.

[73]

[74] Example 2

[75] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing antimony powders of spherical shape with an average particle diameter of 20 D as an electromagnetic shielding material in 60 vol%.

[76]

[77] Example 3

[78] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing antimony of flake shape with wide and long lengths of 20 D and a thickness of 10 D as an electromagnetic shielding material in 60 vol%.

[79]

[80] Example 4

[81] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing antimony of flake shape with wide and long lengths of 80 D and a thickness of 10 D as an electromagnetic shielding material in 60 vol%.

[82]

[83] Comparative Example 1

[84] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing ferrite of flake shape with wide and long lengths of 20 D and a thickness of 10 D as an electromagnetic shielding material in 60 vol%.

[85]

[86] Comparative Example 2

[87] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing sendust of flake shape with wide and long lengths of 20 D and a thickness of 10 D as an electromagnetic shielding material in 60 vol%.

[88]

[89] Comparative Example 3

[90] The electromagnetic shielding sheet was prepared by the same method as Example

1 above except for mixing permalloy of flake shape with wide and long lengths of 20 D and a thickness of 10 D as an electromagnetic shielding material in 60 vol%.

[91]

[92] Physical properties of Examples 1 to 4 and Comparative Examples 1 to 3 as above were measured by the following methods.

[93]

[94] 1. Adhesion Strength Test

[95] For each pressure sensitive adhesive sheet prepared in Examples and Comparative

Examples above, adhesion strength in a direction of 180 degree against an aluminum plate was measured, based on JIS Z 1541. Here, a standing time was for 30 minutes and a temperature was at room temperature. The measuring results were arranged in Table 1 below.

[96]

[97] 2. Thermal Conductivity Test [98] Each pressure sensitive adhesive sheet prepared in Examples and Comparative

Examples above was cut in a size of about 60 mm 120 mm to prepare specimens. Thermal conductivity of said specimens was measured using Quick Thermal Conductivity Meter QTM-500 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the results were arranged in Table 1 below.

[99]

[100] 3. Measurement of Electromagnetic Reduction Rate

[101] The electromagnetic reduction rate was measured according to the following two methods.

[102] [103] (1) Coaxial Cable Measuring Method [104] The pattern diagram of a coaxial cable measuring method is as depicted in Fig. 6. That is, a specimen was inserted into a jig around a conductor in the jig linked with S port, and its back side was shorted. Then, the degree of return loss in the specimen was measured by counting input signals reflected after sending signals via S port. The measurements of electromagnetic reduction effect by the coaxial cable measuring method were graphed and represented in Figs. 7 and 8. Fig. 7 is the measuring results of specimens according to Examples 1 to 4 of the present invention, and Fig. 8 is the measuring results of specimens according to Comparative Example 1 to 3.

[105] [106] (2) Electromagnetic Scanning Method [107] The pattern diagram of an electromagnetic scanning method is as depicted in Fig. 9. That is, radiation waves were generated from Micro strip, and then electromagnetic waves were measured from an antenna. The measuring results of electromagnetic reduction effect by the electromagnetic scanning method were graphed and represented in Figs. 10 to 13. Fig. 10 is a measuring result of specimen according to Example 3 of the present invention. In addition, Fig. 11 is a measuring result of specimen according to Comparative Example 1, Fig. 12 a result of Comparative Example 2 and Fig. 13 a result of Comparative Example 3. [108] Table 1

[109]

[110] Through the results represented in Table 1 above, it could be noted that the adhesion strength is much affected by the added amounts of electromagnetic shielding materials rather than their kinds. This means that as the amount of an electromagnetic shielding material becomes large, the amount of shielding material positioned in the surface of sheet is also increased, whereby the adhesion strength is reduced, due to reduction of the surface area contacted with a substrate. It could be noted that the thermal conductivity is proportional to the amount of electromagnetic shielding material. It could be noted that the thermal conducting effect of a case with small size is superior to that of a case with large size and that a case of antimony (Sb) is superior to a case of ferrite, sendust or permalloy which has been used as a conventional electromagnetic shielding material.

[I l l] In addition, through the results of Figs. 7, 8, 10 to 13, it could be noted that the examples of the present invention using antimony powder have excellent electromagnetic shielding effect (attenuation) in low frequency bands over those using conventional electromagnetic shielding materials or antimony oxide. It could be identified that the electromagnetic reduction effect of flake shape is more or less excellent than that of spherical shape and that even in case of the same shape, the smaller the size is, the more it is advantageous.

[112] It could be noted from the above results that the present case using antimony exhibits excellent electromagnetic reduction effect not only in high frequency bands but also in low frequency bands over those using conventional electromagnetic shielding materials such as ferrite, sendust or permalloy or antimony oxide, and has also enhanced adhesion strength and thermal conductivity.

[113]

Industrial Applicability

[114] The present composition or sheet may effectively shield not only at high frequency bands but also at low frequency bands, and may have excellent heat radiating characteristic to promptly transmit heat to heat radiation elements. Accordingly, the present invention may inhibit system malfunction and shortened service life of devices by electromagnetic waves and heat, and may achieve the above objects, without installing any heat radiating sheet apart from the electromagnetic shielding sheet. Therefore, slimmed electronic products such as PDP, enhanced productivity and reduced production costs can be contrived.

[115]

Claims

[I] A composition comprising a binder and an electromagnetic shielding material, wherein said electromagnetic material is antimony.

[2] The composition of claim 1, wherein said electromagnetic shielding material further comprises one or more selected from the group consisting of metal and ceramic. [3] The composition of claim 2, wherein the metal is one species or two or more species, in a mixture thereof, selected from ferrite, permalloy, sendust, alnico, silicon steel, stainless steel, copper, nickel, iron, molybdenum, tungsten, zinc, magnesium, manganese, aluminum, titanium and silver, or an alloy of two or more species of the foregoing. [4] The composition of claim 2, wherein the ceramic is one or more selected from the group consisting of aluminum nitride, boron nitride, silicon nitride, silicon carbide, aluminum oxide and beryllium oxide. [5] The composition of claim 1, wherein the electromagnetic shielding material is included in an amount of 5 to 100 vol% relative to the binder. [6] The composition of claim 1, wherein the electromagnetic shielding material has one or more shapes selected from the group consisting of a spherical shape, a flake shape, an oval shape and a cylinder shape. [7] The composition of claim 6, wherein the electromagnetic shielding material has a flake shape, and said flake shape has wide and long lengths of 1 nm to 200 D. [8] The composition of claim 1, wherein the binder is an acrylic resin, a silicone resin, a urethane resin, a melamine resin or an epoxy resin, having pressure sensitive adhesion.

[9] The composition of claim 1, further comprising a thermal initiator or a photo- initiator. [10] The composition of claim 1, further comprising a cross-liking agent of 0.01 to 10 parts by weight relative to 100 parts by weight of the binder.

[I I] The composition of claim 1, further comprising a foaming agent.

[12] A sheet comprising an electromagnetic shielding layer containing a composition according to any one of claims 1 to 11.

[13] The sheet of claim 12, wherein the electromagnetic shielding layer has self- adhesion.

[14] The sheet of claim 12, wherein the electromagnetic shielding layer has an embossing structure formed on one or both surfaces thereof.

[15] The sheet of claim 12, wherein the electromagnetic shielding layer has a substrate sheet attached to one or both surfaces thereof. [16] The sheet of claim 15, wherein the substrate sheet consists of a substrate alone or a substrate and a pressure sensitive adhesive formed on one surface of the substrate.

[17] The sheet of claim 12, wherein the sheet has a thickness of 1 D to 100 mm.

[18] A plasma display panel comprising the sheet according to claim 12.