WO2006135182A1

WO2006135182A1 - Thin multi-layered electro-magnetic absorption film by controlling surface resistance

Info

Publication number: WO2006135182A1
Application number: PCT/KR2006/002245
Authority: WO
Inventors: Kyung Sub Lee; Jun Young Lee; Doo In Kang; Seon Tae Kim
Original assignee: Chang Sung Corporation
Priority date: 2005-06-15
Filing date: 2006-06-13
Publication date: 2006-12-21
Also published as: KR20060131055A; JP2008544518A; CN101213893A; CN101213893B; KR100701832B1; JP4975743B2

Abstract

The present invention relates to a thin multi-layered electro-magnetic wave absorption film. More specifically, the present invention relates to a thin multi-layered electro-magnetic wave absorption film wherein a conductive polymer layer with a consistent electric resistance and a magnetic metal composite layer comprise a layered structure, and the present invention shows a very high electro-magnetic damping effect of not less than 35% in a frequency of 10MHz~6GHz, or a damping effect of a specific numerical value or above can be obtained consistently in a wide band frequency of 10MHz~6GHz. According to the present invention, a damping effect of an electric-magnetic wave can be remarkably increased by a constitution wherein a conductive polymer layer with a consistent electric resistance of between 20Ω and 1000Ω and a magnetic metal composite layer to which a soft magnetic metal is dispersed and coupled by an organic binder comprise a layered structure of at least 2 layers.

Description

THIN MULTI-LAYERED ELECTRO-MAGNETIC ABSORPTION FILM BY CONTROLLING SURFACE

RESISTANCE

Technical Field

[1] The present invention relates to a thin multi-layered electro-magnetic wave absorption film. More specifically, the present invention relates to a thin multi-layered electro-magnetic wave absorption film wherein a conductive polymer layer with a consistent electric resistance and a magnetic metal composite layer comprise a layered structure, and the present invention shows a conduction electro-magnetic wave noise damping effect of not less than 35% in a frequency of 10MHz~6GHz, or a conduction electro-magnetic wave noise damping effect of greater than a specific numerical value can be obtained consistently in a wide band frequency of 10MHz~6GHz. Background Art

[2] Generally, electro-magnetic wave interference in a digital and high frequency electric circuit device is generated by the electro-magnetic coupling between the electronic parts and micro strip line when the electronic parts and micro strip line are installed onto the substrate.

[3] Conventionally, in order to inhibit the interference of such electro magnetic wave, the problem has been solved by using a relatively thick monolayer electromagnetic absorber of more than 0.2mm by connecting a low-pass filter or noise filter on its respective output of circuit substrate, or by inhibiting interference of electro-magnetic wave in the problematic circuit by keeping intervals between electronic parts and micro strip line.

[4] However, the above method of inhibiting the interference of an electro-magnetic wave requires a space and interval for arranging the absorber of having said filter or a thickness of not less than 0.2mm, and thus, it has a problem of enlarging the size and weight of electronic device.

[5] Without using the low-pass filter or noise filter which requires a relatively large space and interval, in order not only to make the most of the limited space between the parts and circuit substrate, but also to inhibit the radiation of electro-magnetic wave generated in a circuit substrate and parts and to inhibit the electromagnetic interference generated between other circuit parts adjacent thereto, a thin electro-magnetic wave absorption film which is composed of a monolayer having a thickness of not greater than 0.1mm has been used.

[6] The absorption mechanism of the electro-magnetic absorber is fundamentally attributed to the high-frequency loss property of materials. The materials used for the electro-magnetic absorber are, by and large, classified into materials having: conductive loss, dielectric loss, magnetic loss, or at least two of the losses. Out of these materials, materials using magnetic loss are produced in the form of a film having a thin thickness of not greater than 0.1mm by dispersing the magnetic metal powders into an organic binder. In a frequency band of not greater than IGHz, however, the power loss of electro-magnetic wave is not greater than 35% due to the thin thickness, and it shows its limitation of its property. The result of measuring the above is as shown in Fig. 1.

[7] Fig. 1 is a graph showing the power loss of a conduction electro-magnetic wave of an electro-magnetic wave absorption film produced by coating a magnetic metal composite layer as a monolayer while using Sendust (Fe-Si-Al alloy) powder, and the thickness of the film is (1) 0.025mm, (2) 0.05mm, (3) 0.075mm and (4) 0.1mm. It can be understood that as the thickness of the film is getting thicker, the power loss is becoming higher.

[8] In the curves of (1), (2), (3) and (4) of Fig. 1, as the frequency is getting higher, the wave is becoming shorter, and thus the power loss of the electro-magnetic wave is becoming higher. However, in the frequency band of not greater than IGHz, there is a problem in that it would be very difficult to obtain an electro-magnetic wave absorption rate of not less than 35% or above with an electro-magnetic wave absorption film whose thickness of not greater than 0.1mm.

Disclosure of Invention

Technical Problem

[9] The invention was created in order to solve the conventional problem as above. In order to maximize the conduction noise suppression effect of the thin electro-magnetic wave absorption film having the thickness of not greater than 0. lmm, its purpose is to provide an improved thin electro-magnetic wave absorption film having the electromagnetic wave absorption rate of not less than 35% in a frequency of 10MHz~6GHz by laminating a conducting polymer film onto a magnetic metal composite layer so as to show a consistent electric resistance.

[10] Another purpose of the present invention is to provide a thin multi-layered electromagnetic wave absorption film having a flexibility of the thickness of not greater than 0. lmm that maximizes the damping effect for the leak tightness of electro-magnetic wave or noise damping of electro-magnetic wave in the electronic device by laminating the conducting polymer layer and the magnetic metal composite layer.

[11] Another purpose of the present invention is to provide a coated thin multi-layered electro-magnetic wave absorption film by polymerizing PEDOT, a conductive polymer, directly on the magnetic metal composite.

[12] Another purpose of the present invention is to provide a thin multi-layered electromagnetic wave absorption film having a thickness of not greater than 0. lmm that can obtain not less than 50% of a superior damping effect in a quasi-microwave band (0.3~3GHz). Technical Solution

[13] In order to attain the purpose of the invention as discussed above, the present invention provides a thin multi-layered electro-magnetic wave absorption film comprising a magnetic metal composite layer where a conductive polymer layer with a consistent electric resistance of between 20Ω and 1000Ω and a soft magnetic metal are dispersed and coupled by an organic binder, said magnetic metal composite layer comprising a layered structure of at least 2 layers and having a thickness of not greater than 0.1mm.

[14] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein said magnetic metal composite layer is located in the middle of said layered structure and said conductive polymer layers are laminated on the upper and lower surfaces of said magnetic metal composite layer, or a conductive polymer layer is located in the middle and a magnetic metal composite layer is laminated on the upper and lower surfaces of the conductive polymer layer.

[15] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein an interlayer bond in said layered structure is established by means of direct coating, an adhesive element, or compression.

[16] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein said conductive polymer layer is made of one of PEDOT, polyaniline, polypyrrole, and polythiophene.

[17] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein an electro-magnetic wave absorption rate is maximized in a frequency band width of not greater than 500MHz by controlling the surface resistance of said PEDOT layer of said conductive polymer layers to 100Ω ~ 500Ω.

[18] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein said conductive polymer layer is formed by the monomer solution of said PEDOT being coated directly on said magnetic metal composite layer and then dried and polymerized.

[19] In addition, the present invention further provides a thin multi-layered electromagnetic wave absorption film, wherein said conductive polymer layer is formed by said PEDOT being coated on a PET film or PP film. [20] Hereinafter, the constitution of the present invention will be explained in detail.

Advantageous Effects

[21] According to the present invention as above, with a thin multi-layered electromagnetic wave absorption film comprising a magnetic metal composite layer and a conductive polymer and having a thickness of not greater than 0. lmm, the materials for a conductive polymer and magnetic metal powder produce a superior effect over the materials for a known electro-magnetic wave absorption film.

[22] Depending on laminating methods, the thin multi-layered electro-magnetic wave absorption film of the present invention produces an effect of very efficiently blocking the electro-magnetic wave so as not to affect electric semiconductors, appliances of the electric communication field, parts and cases of cellular phones and appliances for mobile communication, electric-digital imaging equipment, etc. Brief Description of the Drawings

[23] Fig. 1 is a graph showing electro-magnetic wave absorption rate according to the thickness of the electro-magnetic wave absorption film having a thickness of not greater than 0.1mm which is composed of a magnetic metal composite layer.

[24] Fig. 2 is a cross-sectional view of a thin multi-layered electro-magnetic wave absorption film of the present invention.

[25] (a) from the top, magnetic metal composite layer— conductive polymer layer-

-adhesive element— release film

[26] (b) from the top, conductive polymer layer— magnetic metal composite layer-

-adhesive element— release film

[27] (c) from the top, magnetic metal composite layer— conductive polymer layer-

-magnetic metal composite layer— adhesive element— release film

[28] (d) film from the top, conductive polymer layer— magnetic metal composite layer-

-conductive polymer layer— adhesive element-release

[29] Fig. 3 is an equipment drawing for measuring the electro-magnetic wave absorption rate of the thin multi-layered electro-magnetic wave absorption film of the present invention.

[30] Fig. 4 is a graphic drawing illustrating the electro-magnetic wave absorption rate as an embodiment of the thin multi-layered electro-magnetic wave absorption film of the present invention.

[31] -Explanation on reference numerals for major parts on drawings-

[32] 21: magnetic metal composite layer 22: conductive polymer

[33] 23: adhesive element 24: release film

Best Mode for Carrying Out the Invention

[34] The conductive polymer layer of the present invention comprises a consistent electric resistance of between 20Ω and 1000Ω, whereas the surface resistance of a magnetic metal composite layer is between 10 -10 Ω, close to insulation.

[35] Generally, an electro-magnetic absorber using resistance loss uses an electric resistance. It is commonly produced in the form of a urethane containing carbons. If the electric resistance is 20Ω or below, the conductivity is relatively high and its loss is reduced due to low impedance when the electro-magnetic wave is absorbed. The absorbed electro-magnetic wave disappears after being converted into heat by the loss of the resistance inside. The principle is similar to the principle of wire or electric mattresses producing heat. In the process of the electro-magnetic wave being absorbed into the electro-magnetic absorber and then disappearing, the impedance of electromagnetic absorber has a significant influence. The impendence of air is 377Ω, and if the impedance of the electro-magnetic absorber is 377Ω to be the same as the impedance of air, its electro-magnetic wave would penetrate the electromagnetic absorber 100%. However, if the impedance of the electro-magnetic absorber is below 20Ω, and thus greatly lower than the impendence of air of 377Ω, the electro-magnetic wave would not be able to penetrate the electro-magnetic absorber, but mostly would be reflected. Thus it cannot be used for the electro-magnetic wave because the electromagnetic wave is reflected before being absorbed.

[36] Meanwhile, the electro-magnetic absorber having the surface resistance of greater than 1000Ω is excellent at penetrability of the electro-magnetic wave; however, there is a problem of a small resistance loss. It is because that the electro-magnetic absorber using the resistance loss causes the absorption of the electro-magnetic wave by polarization of the internal charge but the amount of the charge to be polarized is very small. Accordingly, for the superior penetrability of electro-magnetic wave a big loss by polarization of the charge, material having surface resistance between 20Ω-1000Ω would be preferred.

[37] The reason that the material has an effect of absorbing the electric wave even though the surface resistance of the magnetic metal composite is between 10 -10 Ω is because the electric wave absorption loss of the magnetic metal composite uses a magnetic loss, not a resistance loss.

[38] The conductive polymer layer is laminated onto one side or both sides of a magnetic metal composite with any one selected from PEDOT (polyethylenedioxythioprene), poly aniline, polypyrrole and polythiophene. The method of laminating the above is established by means of direct coating, an adhesive element, or compression.

[39] Especially, in order to maximize an electro-magnetic wave absorption rate in a frequency band width of not greater than 500MHz, the surface resistance of the PEDOT layer of said conductive polymer layer is controlled to 100Ω-500Ω. Referring to the graph of Fig. 4, in the case where the surface resistance is 300Ω which is similar to that of the impedance in the atmosphere, it shows the absorption rate is maximized in a frequency band width of not greater than 500MHz. In 300MHz, an electromagnetic wave absorption rate is about 43%. However, in case of having a surface resistance of 200Ω, in a frequency band width of 300MHz, an electro-magnetic wave absorption rate is approximately 18%, whereas in case of having the surface resistance of not greater than 100Ω, an electro-magnetic wave absorption does not occur.

[40] Meanwhile, in case of the electro-magnetic absorber having the surface resistance of greater than 500Ω, it would be very difficult to obtain an electro-magnetic wave absorption rate of 30% or above in a frequency band width of 300MHz.

[41] Polymer layer according to the present invention is as follows. The monomer solution is prepared by dissolving 3,4-ethylenedioxythiophene as an electrically conductive polymer monomer, polyvinyl pyrrolidone as a matrix polymer, and n- methylpyrrolidone and dimethylformamide as basic additives in an organic solvent such as 1-butanol or 1-propanol. An oxidizer solution is prepared by dissolving ferric p-toluene sulfonate used as an oxidizer in a solvent of the same kind. After preparing the homogenous solution by mixing the prepared monomer solution with the oxidizer solution, thus obtained solution is coated on the PET film or PP film by a method of spin coating, bar coating or tape coating on a magnetic metal composite. If the coated substrate is heated for a certain period of time in an oven, that means a predetermined temperature, the monomer is polymerized and then an electrically conductive PEDOT thin film is formed, which is cleansed with methanol, acetone, and the like to obtain a final PEDOT thin film. The surface non-resistance of the prepared PEDOT thin film can easily change the surface resistance of the coated PEDOT thin film if the content of polyvinylpyrrolidone, the content of basic additive, the concentration of an oxidizer, and polymerization temperature and time are changed. Another embodiment of coating a conductive polymer layer of the present invention is as follows. After preparing a soluble polypyrrole according to the reported method (Korean Patent No. 0162864-0000), preparing a polypyrrole solution by dissolving it in chloroform and coating this solution on the substrate. Dry it for a certain period of time then cleanse it with methanol, acetone, etc., and then dry it; then the final electrically conductive polypyrrole thin film can be obtained.

[42] Another embodiment of coating a conductive polymer layer of the present invention is as follows.

[43] After preparing a soluble polypyrrole according to the reported method (Korean

Patent No. 0205912-0000), prepare polypyrrole solution by dissolving it in a chloroform and coat this solution on the substrate. Dry it for a certain period of time and cleans it with methanol, acetone, etc.; then the final electrically conductive polypyrrole thin film can be obtained.

[44] Meanwhile, the magnetic metal powder for the conductive polymer layer of the present invention consists of any one of Sendust (Fe-Si-Al), permalloy (Fe-Ni), pure iron powder (fe), carbonyl iron, molybdenum permalloy (Fe-No-Mo), ferrite, stainless steel (Fe-Cr, Fe-Cr-Ni) or silicon steel (Fe-Si) powder.

[45] In addition, the organic binder used for the magnetic metal composite layer is composed of any one of PVC (polyvinyl-butyral), urethane rubber, epoxy, silicone rubber, polyethylene, chlorinated polyethylene, EPDM, neoprene, polypropylene or polystyrene, or natural rubber. The organic binders mentioned above is characterized in that they are excellent in holding powders together, and can be dissolved by an organic solvent, thus allowing the powders held together by the binders to be well dispersed.

[46] The thin multi-layered electro-magnetic wave absorption film which consists of a magnetic metal composite layer and a conductive polymer layer can be formed by coupling by means of the adhesive element such as an electrically insulated adhesive, adhesion paste or double tape. This adhesive element can be easily attached to electronic devices.

[47] The thin multi-layered electro-magnetic wave absorption film of the present invention constituted as above will be explained in detail through embodiment referring to the drawings as follows.

[48] Fig. 2 is drawings showing the embodiments of the present invention.

[49] Fig. 2 (a) is a cross-sectional view of a thin multi-layered electro-magnetic wave absorption film with a thickness of not greater than 0.1mm, wherein a magnetic metal composite layer (21) is formed by dispersing-coupling soft magnetic metal powder which is flaked by an organic binder; a conductive polymer layer (22) is formed by coating a conductive polymer on its one side; and then onto the other side of the conductive polymer layer (22), an adhesive element, such as an adhesive, adhesion paste or double tape, is coupled to attach a release film (24).

[50] In the conductive polymer layer (22), the electro-magnetic wave is firstly damped by the resistance loss, and in the magnetic metal composite layer (21), the electromagnetic wave is secondly damped by the magnetic loss. Compared to the magnetic metal composite film which is composed of one layer, its characteristics are excellent.

[51] In the above multi-layered film, the coupling between layers is made by uniform coating through the methods of Dr. Blade, bar coating, spin coating, etc. in the state of a liquid phase dispersed by the organic binder. Or, it can be formed by electrically coupling or compressing them by adhesion paste, adhesive or double tape.

[52] Meanwhile, as illustrated in Fig. 2(b), a conductive polymer layer (22) is located on the upper part, a magnetic metal composite layer (21) is laminated on the lower part, and an adhesive element (23) and a release film (24) are formed.

[53] In addition, as for an embodiment of the present invention, as a multi-layered electro-magnetic wave absorption film having three layers, as illustrated in Fig. 2 (c), the present invention can choose a structure of coupling a conductive polymer layer (21) onto the upper and lower surfaces of the magnetic metal composite layer (22). In addition, as shown in Fig. 2(d), a structure of coupling a magnetic metal composite layer (22) onto the upper and lower surfaces of the conductive polymer layer (21) can be chosen.

[54] In order to examine the effect of the thin multi-layered electro-magnetic abortion film according to the present invention, the electro-magnetic wave absorption rate is measured by the following method.

[55] In order to measure the electro-magnetic wave absorption rate of the electromagnetic wave absorption film of the present invention, as shown in Fig. 3, a copper (83) having a width of about 2mm and a length of 80mm is placed on the upper part of a microstrip circuit substrate (81), and its ends is connected to the SMA-type terminal (85) of 3.5mm.

[56] The lower part of the microstrip circuit substrate is composed of a copper layer

(84), and an absorption film (82) having a predetermined size is located on the upper part of the copper wire, and then the power loss of conduction electro-magnetic wave noise is measured.

[57] The size of the electro-magnetic wave absorption film used for the above invention has a shape of square whose side is 50mm. It can be understood that the damping effect of the electro-magnetic wave absorption film using the device for measuring said electro-magnetic wave absorption rate is analyzed, such that the film is connected to the equipment for analyzing vector network and a signal transmitting from one terminal to another is damped.

[58] The result on the absorption rate measured by said method is shown in Fig. 4.

[59] The graph illustrated in Fig. 4 shows the electro-magnetic wave absorption rate of a thin multi-layered film that comprises a two-layer structure, as illustrated in Fig. 2(a), by coating a conductive polymer (PEDOT) on the magnetic metal composite layer which is dispersed and coupled by an organic binder, an adhesive element being coupled onto the lower part of the conductive polymer layer.

[60] The thickness of the magnetic metal composite layer is fixed at 0.03mm, on which the conductive polymer is coated with a thickness of 0.005~0.020mm by controlling the surface resistance uniformly to 20Ω (71), 50Ω (72), 80Ω (73), 100Ω (74), 230Ω (75) and 300Ω (76), the total thickness of the thin multi-layered film being constituted to be 0.05mm.

[61] Comparison of said data in the graph of said Fig. 4 with the data of the electro- magnetic wave absorption rate shows that the electro-magnetic wave absorption rate according to the thickness of conductive metal composite monolayer film is not greater than 30% in a frequency of not greater than 1 GHz, whereas the present invention obtains an electro-magnetic wave absorption rate of 85% or above (74) in a frequency of IGHz.

[62] Especially, in the case where the electro-magnetic wave absorption film is composed of a magnetic metal composite layer and a conductive polymer layer according to the present invention, the present invention exhibits an excellent electromagnetic wave absorption rate that cannot be achieved by a magnetic metal composite mono-layer even in a frequency of not greater than 500MHz.

[63] Accordingly, the film of the present invention where a magnetic metal composite layer and conductive polymer layer of the present invention are laminated, can prevent a short circuit and maximize the electro-magnetic wave absorption rate, while maintaining the thickness to 0.1mm or below.

[64] The present invention is explained mainly based on the preferred embodiments of the present invention as above. However, the present invention can be appropriately changed or modified to the extent that does not go beyond the scope of the present invention by a person having ordinary skill in the art. As long as this sort of change or modification does not deviate from the gist of the present invention, it is obvious that it is within the scope of the right of the present invention.

[65] The technical scope of the present invention is not limited to the detailed description of the specification. Industrial Applicability

[66] In order to maximize the electro-magnetic wave absorption property of the thin electro-magnetic wave absorption film having the thickness of not greater than 0. lmm, the present invention can provide an improved thin electro-magnetic wave absorption film having the electro-magnetic wave absorption rate of not less than 35% in a frequency of 10MHz~6GHz by laminating a conducting polymer film onto a magnetic metal composite layer so as to show a consistent electric resistance.

[67] In addition, the present invention can provide a thin multi-layered electro-magnetic wave absorption film having a flexibility of a thickness of not greater than 0.1mm, which maximizes the damping effect by the leak tightness of electro-magnetic wave or by the noise damping of an electro-magnetic wave in the electronic device by laminating a conducting polymer layer and a magnetic metal composite layer.

[68] In addition, the present invention can provide a coated thin multi-layered electromagnetic wave absorption film by polymerizing PEDOT, a conductive polymer, directly onto a magnetic metal composite. [69] In addition, the present invention can provide a thin multi-layered electro-magnetic wave absorption film having a thickness of not greater than 0.1mm that can obtain a superior damping effect of not less than 50% in a quasi-microwave band: 0.3~3GHz.

Claims

[1] Thin multi-layered electro-magnetic wave absorption film comprising a layered structure of at least 2 layersmagnetic metal composite layer includingwhere a conductive polymer layer with a consistent electric resistance of between 20Ω and 1000Ω and a magnetic metal composite layer where soft magnetic metals are dispersed and bonded coupled by an organic binder, said magnetic metal composite layer comprising a layered structure of at least 2 layers and having a thickness of not greater than 0.1mm.

[2] Thin multi-layered electro-magnetic wave absorption film according to Claim 1, wherein said layered structure is characterized in that said magnetic metal composite layer is located in the middle of said layered structure and said conductive polymer layers is are laminated on the upper and lower surfaces of said magnetic metal composite layer, or in that a conductive polymer layer is located in the middle and a magnetic metal composite layer is laminated on its upper and lower surfaces of the conductive polymer layer.

[3] Thin multi-layered electro-magnetic wave absorption film according to Claim 1 or 2, wherein interlayer bond in said layered structure is coupled established by means of direct coating, using of an adhesive element, or compressionng.

[4] Thin multi-layered electro-magnetic wave absorption film according to Claim 1 or 2, wherein said conductive polymer layer is made of one of PEDOT, polyaniline, polypyrrole, and polythiophene.

[5] Thin multi-layered electro-magnetic wave absorption film according to Claim 4, wherein said conductive polymer layer is characterized in that an electro-magnet ic wave absorption rate is maiximized in a frequency band width of not greater than 500MHz by controlling the surface resistance of said PEDOT layer of said conductive polymer layers to 100Ω ~ 500Ω.

[6] Thin multi-layered electro-magnetic wave absorption film according to Claim 4 or 5, wherein said conductive polymer layer is characterized in that the formed by monomer solution of said PEDOT being is formed by being dried and polymerized by being coated directly on said magnetic metal composite layer and then dried and polymerized.

[7] Thin multi-layered electro-magnetic wave absorption film according to Claim 4 or 5, wherein said conductive polymer layer ischaracterized in that it is manufactured formed by said PEDOT being coated on a PET film or PP film.