KR100888048B1 - Electromagnetic wave shielding and absorbing sheet and preparation method thereof - Google Patents

Abstract

The present invention discloses a composite sheet for shielding and absorbing electromagnetic waves and a method of manufacturing the same. The composite sheet of the present invention includes an electrically conductive layer that reflects incident electromagnetic waves, liquid silicone, silicon oil, and magnetic powder for absorbing electromagnetic waves, and includes an electromagnetic wave absorbing layer laminated on one or both surfaces of the conductive layer. According to the present invention, a thin composite sheet shielding electromagnetic waves radiated from one side of the composite sheet, effectively absorbing electromagnetic waves radiated from another side, and applicable to a narrow space such as a mobile communication terminal or a high frequency circuit can be applied. You can get it. In addition, since the electromagnetic wave absorbing layer of the present invention is flexible and easy to compress, it can be applied regardless of the shape of the bonding / bonding site of the electronic product, thereby obtaining a gel pad effect.

Description

Electromagnetic wave shielding and absorbing sheet and preparation method

1 is a structural diagram showing an electromagnetic shielding and absorption sheet according to an embodiment of the present invention.

2 is a structural diagram showing an electromagnetic shielding and absorption sheet according to another embodiment of the present invention.

3 is a conceptual diagram illustrating a concept in which electromagnetic waves are reflected and absorbed in the composite sheet for shielding and absorbing electromagnetic waves of the present invention.

4 is a schematic view showing a system for measuring the electromagnetic shielding effect of the composite sheet for electromagnetic shielding and absorption of the present invention.

5 is a reference diagram showing the electromagnetic shielding effect of the electromagnetic shielding and absorption composite sheet of the present invention.

6 is a flowchart illustrating a method of manufacturing a composite sheet for shielding and absorbing electromagnetic waves according to an embodiment of the present invention.

The present invention relates to a composite sheet for shielding and absorbing electromagnetic waves, and more particularly to a novel composite sheet for absorbing and shielding electromagnetic waves generated from circuit elements inside various electronic devices such as cellular phones, PCS, and RF communication equipment.

Electromagnetic waves affect various automation equipment and automatic control devices, causing malfunctions, and when infiltrated into the human body, cause various problems such as increasing the temperature of biological tissue cells by thermal action and weakening immune function. In addition, due to the development of the integration technology of electronic circuits, it has become technically possible to use unit circuits having various functions in a narrow space, but at the same time, electromagnetic disturbances generated from the respective circuits between adjacent circuits have been made. Interference (EMI) is an important issue, and there is an increasing demand for products that meet Electromagnetic Compatibility (EMC).

In order to satisfy electromagnetic compatibility, the electromagnetic noise generated from the electrical and electronic equipment should be reduced as much as possible, and the electromagnetic susceptibility of the equipment itself should be strengthened by reducing the electromagnetic sensitivity to the external electromagnetic environment. The most important characteristics required for electromagnetic compatibility products inserted into mobile communication terminals or electric and electronic devices are that the electromagnetic wave absorption rate and shielding rate should be large, and the electromagnetic compatibility products should be thinner according to the recent miniaturization of electronic devices. Moreover, recently developed mobile phones require very thin electromagnetic compatibility products because there is little gap between the internal printed circuit board (PCB) circuit module and the inner wall of the housing.

Conventional electromagnetic wave absorbers are functional materials that attenuate radio wave energy by using high frequency loss characteristics of constituent materials or reduce reflected waves below a reference value, and according to the materials used, conductive loss materials, dielectric loss materials, magnetic loss materials, or both It is classified as a material containing the above loss. The composite ferrite electromagnetic wave absorber, which is mainly used as an electromagnetic wave absorber, is a ferrite mixed with a nonmagnetic material such as silicone rubber and plastic as a support material. The composite ferrite electromagnetic wave absorber is manufactured in the form of a sheet of about 1 mm and used for anti-radar reflection in the GHz band.

In addition, the electromagnetic shielding material is usually manufactured in the form of a conductive mesh, fiber, rubber, etc. by adding metals (Fe, Cu, Ni, etc.) to the plastic, it can shield or reflect the electromagnetic wave to avoid direct influence from the electromagnetic wave. The electromagnetic wave environment continues to exist, and in the case of the electromagnetic shielding material in which copper and nickel are plated on polyester, there is a risk of electric shock due to conductivity.

Conventionally, 0.2 mm or more thick sheet-shaped absorbents prepared by mixing ferrite or soft magnetic metal powder into rubber or plastic and rolling or extrusion are mainly used. In addition, there was also a composite sheet, which was rolled or press-laminated by inserting a conductor layer in the form of a mesh between the two absorbent sheets thus manufactured. In this case, since the thickness is relatively thick, internal space such as a mobile communication terminal or a high frequency circuit may be There is a problem that is not applicable to the narrow field.

In consideration of the problems of the prior art, the present invention is a composite sheet for shielding and absorbing electromagnetic waves that can be applied in a narrow space, such as a mobile communication terminal or a high frequency circuit, a conductive layer reflecting electromagnetic waves, liquid silicon, silicon It is an object of the present invention to provide a composite sheet including an electromagnetic wave absorbing layer including oil and electromagnetic wave absorbing magnetic powder and laminated on one or both surfaces of the conductive layer.

According to an aspect of the present invention, there is provided a composite sheet for shielding and absorbing electromagnetic waves, the conductive layer having electrical conductivity and reflecting incident electromagnetic waves; And liquid silicon, silicon oil, and magnetic powder for absorbing electromagnetic waves, and an electromagnetic wave absorbing layer laminated on one or both surfaces of the conductive layer.

According to another aspect of the present invention, there is provided a method of manufacturing an electromagnetic shielding and absorption sheet according to the present invention comprising the steps of: a) forming a slurry comprising magnetic powder for absorbing electromagnetic waves, liquid silicon and silicone oil; b) removing the bubbles of the formed slurry; c) applying the slurry from which the bubbles are removed to one or both surfaces of the conductive fabric.

Hereinafter, with reference to the drawings and the embodiments will be described in detail for the electromagnetic shielding and absorption sheet and its manufacturing method of the present invention.

1 shows an electromagnetic shielding and absorption sheet 1 according to an embodiment of the present invention.

As shown in FIG. 1, the composite sheet 1 for shielding and absorbing electromagnetic waves of the present embodiment includes a conductive layer 10 and an electromagnetic wave absorbing layer 20.

The conductive layer 10 has electrical conductivity and reflects electromagnetic waves incident from one side or both sides of the composite sheet. Specific examples of the conductive layer 10 in the present embodiment include a conductive fiber fabric, a conductive mesh or a metal foil.

The conductive fibers are coated with a conductive material by a method such as plating, impregnation, spray, or the like, for example, a nickel fiber fabric. Examples of the conductive material for imparting conductivity to the conductive fiber fabric include metal powders such as silver, copper, nickel, gold, aluminum, silver coated copper, silver coated nickel, and gold coated copper.

The electromagnetic wave absorbing layer 20 includes liquid silicon, silicone oil, and magnetic powder for absorbing electromagnetic waves. The electromagnetic wave absorbing layer is laminated on one or both surfaces of the conductive layer 10. The electromagnetic wave absorbing layer 20 not only absorbs electromagnetic waves and noise generated from electronic devices, but also compresses and uses a silicone oil and liquid silicone, and functions substantially as a gel pad. In addition, the electromagnetic wave absorbing layer of the present embodiment is excellent in adhesiveness and can be directly applied to a product without providing a separate adhesive layer, which is suitable for a communication terminal having a narrow internal space.

The liquid silicone which is one component constituting the electromagnetic wave absorbing layer 20 is preferably an additive two-component liquid silicone rubber. Liquid silicone basically has the inherent elasticity of rubber and no deformation of shape in a wide temperature range, and has good electrical properties and weather resistance. In particular, the two-part liquid silicone rubber of the addition type is cured through crosslinking of polysiloxane having a vinyl group at the end and polysiloxane having a Si—H bond. In this embodiment, the liquid silicone is preferably a type crosslinked and cured in accordance with the addition reaction of the siloxane containing Si—H in an unsaturated group in the presence of a platinum catalyst. Examples of platinum catalysts include fine platinum powders, thermoplastic blacks or thermoplastic resins containing platinum components.

In particular, the polymer which is the main component constituting the liquid silicone in the present embodiment is, for example, polydimethylsiloxane or divinylpolydimethylpolysiloxane (Di-Vinyl-poly-di-methyl-poly-siloxane). The liquid silicone may include a Si-H-based compound as a crosslinking agent, and may include aerosol silica, quartz powder, precipitated silica, diatomaceous earth, etc. as a filler, and may further include a curing rate regulator and an adhesion promoter as an additive. .

The liquid silicone employed in the present embodiment does not need water for the curing reaction, and the surface and the inside thereof are uniformly cured, so that the deep portion curability is good. In addition, since the curing rate has a large temperature dependency, the curing time becomes shorter as the temperature is increased, and since there are no by-products during curing, the numerical stability is good and the bowing ratio is small. Polydimethylsiloxane which forms the main chain of liquid silicone is excellent in electrical insulation. Conventional liquid silicones have been mainly used as screen printing inks, bases of various heat-dissipating materials, dental impression materials, roll materials such as copier facsimile machines, and the like.

Compared to the condensed liquid silicone rubber, the additional liquid silicone rubber does not require moisture to cure, and has a merit in that the surface and the inside are uniformly progressed in the curing reaction, so that the deep curing property is good.

Another component of the electromagnetic wave absorbing layer 20 is magnetic powder for absorbing electromagnetic waves. For example, one or more magnetic powders selected from the group consisting of ferrite, carbonyl iron, iron-silicon alloys, iron-silicon-aluminum alloys, iron-cobalt alloys and iron-nickel alloys can be used. The electromagnetic wave absorptivity of the electromagnetic wave absorbing layer 20 becomes maximum when the thickness is 1/4 of the wavelength?, And the matching thickness is inversely proportional to the square root of the permeability and permittivity of the constituent material. Therefore, in order to design the thin electromagnetic wave absorbing layer 20, a plate-shaped soft magnetic powder having a high permeability and permittivity at a use frequency is preferable. The magnetic powder for electromagnetic wave absorption is made of a mixed slurry based on silicone oil and liquid silicon, and then mixed by casting molding, Dr. blade, comma coating, spray spraying, or the like. The slurry can be applied over the conductive layer.

The silicone oil used in the present embodiment is a polymer in which silicon, to which organic groups are bonded, is connected by siloxane bonds (Si-O-Si), and has a chain-like molecular structure, which controls the viscosity of the electromagnetic wave absorbing layer and serves as a binder. do. The backbone of the silicone oil molecule is a siloxane bond. When molecules having this structure aggregate to form a substance, individual molecules are independent, and thus the molecular chains can move freely from each other. It is easy to control the viscosity because of the nature of the liquid, the surface tension is small and has anti-foaming. Silicone oil is distinguished according to the type of organic group bonded to the silicon atom and the magnitude of the siloxane polymerization degree. In addition, silicone oil can be divided into linear silicone oil and modified silicone oil according to the type of organic group. Among the linear silicone oils, dimethyl silicone oil has excellent heat resistance, physical and chemical stability, has an unusual interfacial property, and has excellent electrical characteristics, and thus has many unique characteristics unlike other mineral oils, animal and vegetable oils and various synthetic oils. have.

In addition, since silicone oil has a low viscosity change due to temperature, it is effective in preventing desorption of the absorbing layer due to temperature change when applied to an electric circuit, and is excellent in electrical insulation, and is suitable for an insulating portion of an electric circuit. When dimethyl silicone oil is used in this embodiment, since the oil remains on the surface of the molded product due to the release agent remaining on the surface, causing surface defects, it is cumbersome to work after wiping or scraping the surface of the product. The oil is colorless and odorless and exhibits low toxicity, low surface tension and complete volatilization at room temperature. Therefore, in this invention, volatile oil is preferable among silicone oil.

In the modified silicone oil, a part of the organic group bonded to the silicon atom is substituted with an organic group other than a methyl group. Examples of such organic groups include a chloropropyl group, a phenylethyl group, a long chain alkyl group, a trichloropropyl group, an epoxy group, and a cyano group. Etc. Since the modified silicone oil has excellent affinity with other materials, in this embodiment, the adhesion between the conductive fiber material and the absorbent layer can be improved.

The electromagnetic wave absorbing layer 20 of the present embodiment may further include a thermally conductive filler. For example, metal oxides such as nonmagnetic copper, alumina, magnesia, titania, or metal nitrides such as aluminum nitride and boron nitride or silicon carbide may be used as the thermally conductive filler. In particular, when the thermally conductive filler is applied to the conductive layer 10 to form a thermal conductive layer prior to laminating the electromagnetic wave absorbing layer 20 on the conductive layer 10, the heat generated from the conductive layer 10 can be efficiently radiated. Can be.

The content of the silicone oil with respect to 100 parts by weight of the liquid silicone is 10 to 30 parts by weight, the content of the magnetic powder is 250 to 400 parts by weight, and the content of the platinum catalyst is preferably 0.1 to 5 parts by weight. If the magnetic powder is less than the above range, the electromagnetic wave absorptivity is not sufficiently expressed. If the magnetic powder is above the above range, the viscosity becomes high, the dispersion is difficult, and the moldability and the flexibility decrease. In addition, when the content of the silicone oil is less than the above range there is a problem that the viscosity control is difficult.

2 is a structural diagram showing a composite sheet for shielding and absorbing electromagnetic waves according to another embodiment of the present invention.

The composite sheet for shielding and absorbing electromagnetic waves of FIG. 2 has a form in which conductive fibers 10 'and an electromagnetic wave absorbing layer 20' are stacked. When the composite sheet according to the present embodiment is manufactured according to the manufacturing method described below, the electromagnetic wave absorbing layer 20 'has a state of a fluidized slurry at the moment of being applied to the conductive fiber.

In the uncured mixed slurry, a part of the mixed slurry penetrates into the pores of the conductive fiber. In this case, the viscosity, curing time, drying time, etc. of the mixed slurry is prevented so that all or a substantial portion of the conductive fiber is not buried by the mixed slurry. You need to adjust Those skilled in the art will be able to easily modify the above conditions according to the application of the composite sheet.

3 is a conceptual view illustrating a concept in which electromagnetic waves are reflected and absorbed in the composite sheet for shielding and absorbing electromagnetic waves of the present invention.

로서,

은 대기중의 유전 상수이고,

은 대기중의 투자율을 나타낸다. Z_a는

이며,

는 흡수층에서의 유전 상수이고,

은 흡수층에서의 투자율을 나타낸다. 이상적인 경우 Z_L은 도전층 내부에서의 임피던스는 0이 된다. 본 발명의 경우 도전층과 전자파 흡수층이라는 2중 구조를 통해 일측으로부터 유입되는 전자파는 흡수되고, 또한 다른 일측으로부터 유입되는 전자파는 반사되는 효과를 얻을 수 있다.In FIG. 3, Z _o denotes an impedance outside the electromagnetic wave absorbing layer, Z _a denotes an impedance inside the absorbing layer, and Z _L denotes an impedance inside the conductive layer. Where Z _o is

as,

Is the dielectric constant in the atmosphere,

Represents the permeability of the atmosphere. Z _a is

Is,

Is the dielectric constant in the absorber layer,

Represents the permeability in the absorber layer. Ideally, Z _L has zero impedance inside the conductive layer. In the present invention, the electromagnetic wave flowing from one side is absorbed through the double structure of the conductive layer and the electromagnetic wave absorbing layer, and the electromagnetic wave flowing from the other side can be reflected.

It is a schematic diagram which shows the system for measuring the electromagnetic wave shielding effect which the composite sheet of this invention has. As the conductive layer of the composite sheet specimen, nickel fabric fibers having a thickness of 0.5 mm were used. As an absorbing layer, 100 parts by weight of LSR-based liquid silicone, 20 parts by weight of volatile silicone oil, 350 parts by weight of Fe-Ni soft magnetic metal powder, and platinum 3 parts by weight of catalyst was used and the thickness of the electromagnetic wave absorbing layer was 0.8 mm. Electromagnetic waves of a predetermined band injected through a network analyzer are incident on the specimen of the present invention through a coaxial line, and some of the incident electromagnetic waves are reflected again. After inserting the specimen for measuring the electromagnetic shielding rate to the measurement jig, the reference was set, and the shielding rate of the specimen was measured according to the S11 measurement method (KSC0305) for measuring the return loss after inserting the sample of the present invention.

5 is a reference diagram showing the electromagnetic shielding effect of the electromagnetic shielding and absorption composite sheet of the present invention.

As shown, it can be seen that the electromagnetic shielding effect of the composite sheet of the present invention shows a shielding ratio of 60 Hz or more in the frequency band from 30 MHz to 1000 MHz.

6 is a flowchart illustrating a method of manufacturing the composite sheet 1 for shielding and absorbing electromagnetic waves according to an embodiment of the present invention.

Step 110 is a step of preparing a mixed slurry containing the magnetic powder for absorbing electromagnetic waves, liquid silicone and silicone oil. The mixed slurry is a flowable mixture in which absorbing electromagnetic wave absorbing powders, particularly fine metal composites, are dispersed in liquid silicone and silicone oil. The mixed slurry of this step may further include a platinum compound as a catalyst. In this step, a planetary mixer is preferable as a dispersing equipment for preparing the mixed slurry.

Step 120 is a degassing step of removing bubbles from the mixed slurry prepared in step 110 using a degassing machine. If molding is performed without removing the bubbles contained in the mixed slurry prepared in step 110, there is a problem of detachment or dimensional instability of the product.

Step 130 is a step of applying the degassed mixed slurry to one side or both sides of the conductive layer using a molding equipment such as casting in 120 steps. After the curing of the mixed slurry may further comprise a drying or curing process of curing the mixed slurry. In addition, the adhesive layer and the release film may be further formed on one side or both sides of the conductive layer or the electromagnetic wave absorbing layer.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will understand that the present invention can be embodied in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown not in the above description but in the claims, and all differences within the scope should be construed as being included in the present invention.

As described above, the present invention introduces a novel structure in which an electromagnetic wave absorbing layer containing liquid silicon and silicone oil is laminated as a binder of electromagnetic powder for absorbing electromagnetic waves on a conductive layer for shielding electromagnetic waves. It is a thin composite sheet that shields the electromagnetic waves emitted from one side of, effectively absorbs the electromagnetic waves emitted from the other side, and can be applied where the internal space is narrow, such as a mobile communication terminal or a high frequency circuit.

In addition, the electromagnetic wave absorbing layer of the composite sheet of the present invention has a substantially the same function as the gel pad because it is flexible and easy to compress and can be applied regardless of the shape of the bonding / bonding site of the electronic product, replacing the existing gasket It works. In addition, since the electromagnetic wave absorbing layer of the present invention has adhesiveness by itself, there is an advantage that it can be applied to an electric circuit without a separate adhesive member.

Claims (12)

A conductive layer having electrical conductivity and reflecting electromagnetic waves; And 100 parts by weight of a two-part addition liquid silicone rubber, 10 to 30 parts by weight of volatile silicone oil and 250 to 400 parts by weight of magnetic powder for absorbing electromagnetic waves, and an electromagnetic wave absorbing layer laminated on one or both surfaces of the conductive layer, The two-part addition liquid silicone rubber is cured through crosslinking of polysiloxane containing a vinyl group and polysiloxane having a Si-H bond, The conductive layer is a conductive fiber fabric, the electromagnetic wave shielding and absorption composite sheet, characterized in that a part of the electromagnetic wave absorbing layer penetrated into the conductive layer through the pores of the fiber fabric. The method of claim 1, The composite sheet for electromagnetic shielding and absorption, characterized in that it further comprises a platinum catalyst as a catalyst for the crosslinking of the polysiloxane containing the vinyl group and the polysiloxane having a Si-H bond. The method of claim 1, The magnetic powder for absorbing electromagnetic waves has a plate shape, and includes at least one selected from the group consisting of ferrite, carbonyl iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-cobalt alloy, and iron-nickel alloy. Electromagnetic shielding and absorption composite sheet, characterized in that. a) forming a mixed slurry comprising 100 parts by weight of the two-part addition liquid silicone rubber, 10 to 30 parts by weight of volatile silicone oil and 250 to 400 parts by weight of magnetic powder for absorbing electromagnetic waves; b) removing the bubbles of the formed mixed slurry; And c) applying the mixed slurry from which the bubbles are removed to one or both surfaces of the conductive fabric, In step c), the conductive fabric is a conductive fiber fabric, and the application of the mixed slurry in which the bubbles are removed is applied so that a portion of the mixed slurry penetrates into the conductive layer through the pores of the fabric fabric. Method for producing a composite sheet for absorption. delete delete delete delete delete delete delete delete

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