JPH0621683A - Electromagnetic shield and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture an electromagnetic wave shield of a highly processed layer having high corrosion resistance and stable electromagnetic wave shielding characteristics by providing thermoplastic synthetic resin layers at both sides of a conductive composition layer made of carbon fiber, metal fiber and thermoplastic synthetic resin. CONSTITUTION:When thermoplastic synthetic resin 3 is formed as a single sheet by a heating roll, a conductive composition layer 2 is interposed between the sheets 3 and contact pressed by the roll or a hot press or the resin 3 is sheeted by the roll, the layer 2 is interposed between both the surface layers, simultaneously sheeted to simultaneously obtain a laminated composite sheet 1. The sheet 1 can be used as an electromagnetic wave shield to be bonded to a wall surface or a floor surfaces as it is. Or, an electromagnetic wave shield having a box state or other various shape such as a housing for an electronic apparatus or a shielded case for an electronic apparatus can be simultaneously molded by heat molding means such as a hot press, a vacuum molding, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite sheet-like electromagnetic wave shield, and more particularly to a method for producing an electromagnetic wave shield such as a casing for electronic equipment or a shield case for electronic equipment using the composite sheet.

[0002]

2. Description of the Related Art Recently, with the spread of electronic devices such as computers and office automation equipment, electromagnetic waves generated from various devices are often the cause of malfunction of these electronic devices. Conventionally, such electronic device casings and electronic device shield cases have been press-molded from metal plates such as aluminum and steel, but are often formed from synthetic resin from the viewpoint of weight reduction and productivity improvement. It has become to. And to protect electronic devices from electromagnetic interference,
It is necessary to impart electromagnetic wave shielding properties to a synthetic resin housing.

Therefore, for electromagnetic wave shielding, for example, metal foil, carbon fiber paper or carbon fiber cloth, synthetic resin film in which powder or fiber of conductive material such as metal oxide or metal or conductive carbon is mixed in the molded housing. Methods such as pasting sheet material, applying conductive paint, and providing a metal layer by thermal spraying or plating have been proposed, but workability is poor and productivity is low, and metal is used. In this case, there is a problem that the electromagnetic wave shielding property is impaired due to corrosion. There is also a method of molding a housing using a conductive synthetic resin composition in which powder or fibers of a conductive material is mixed, but such a conductive synthetic resin composition is generally not freely colored and has poor processability. However, there is a disadvantage in that it is necessary to further coat the molded housing because the appearance of the molded product is unsatisfactory.

Then, on the back surface of the thermoplastic synthetic resin sheet,
For example, a metal layer such as aluminum or copper is laminated by a method such as adhesion, thermal spraying, or plating to obtain an electromagnetic wave shielding sheet material, which is hot-pressed to form a housing for electronic equipment or a shield case for electronic equipment. A method of forming is proposed. However, this method also has a drawback that the metal layer is easily corroded, and there is a problem that when the drawing process is performed, the metal foil is cracked and the electromagnetic wave shielding property is impaired, which is suitable only for a process such as a slight bending. .

Therefore, there has been proposed a method (Japanese Patent Application Laid-Open No. 2-125730) for obtaining a sheet which can be highly processed by laminating a synthetic resin and a metal foil which is provided with wrinkles and which can be stretched and deformed. Is not suitable for deep drawing.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention is to provide a sheet-like electromagnetic wave shield which is lightweight, has excellent corrosion resistance, and retains excellent electromagnetic wave shielding properties even when subjected to advanced processing. Further, it is an object of the present invention to provide a method for manufacturing an electromagnetic wave shield such as a housing for electronic equipment or a shield case for electronic equipment using the electromagnetic wave shield.

[0007]

The electromagnetic wave shield of the present invention that can achieve the above object has a conductive composition layer composed of carbon fiber, metal fiber and thermoplastic synthetic resin sandwiched between the two sides. A composite sheet having a laminated structure in which a thermoplastic synthetic resin layer is provided, and by further heat-molding such a composite sheet, an electromagnetic wave shield such as a casing for electronic equipment or a shield case for electronic devices can be obtained. It is manufactured.

The conductive composition layer constituting the intermediate layer of the electromagnetic wave shield in the form of a composite sheet of the present invention comprises carbon fiber, metal fiber and thermoplastic synthetic resin. Such thermoplastic synthetic resin is conductive. It is necessary to be a material having good compatibility with the thermoplastic synthetic resin layer provided on both sides of this intermediate layer as a binder of the organic fiber, for example, polyolefin resin, ethylene vinyl acetate copolymer resin, vinyl chloride resin,
An appropriate one can be selected and used from thermoplastic synthetic resins such as diene / styrene copolymer resin and ABS resin.

As the carbon fiber, for example, toluene,
Aromatic hydrocarbons such as benzene and naphthalene, propane,
Hydrocarbon compounds such as ethane and aliphatic hydrocarbons such as ethylene, preferably benzene or naphthalene are used as raw materials, and these raw materials are gasified to form a catalyst composed of ultrafine metal at 900-1500 ° C. with a carrier gas such as hydrogen, for example, Iron, nickel, iron-nickel alloy or the like having a particle size of 100 to 300 angstrom is contacted with or decomposed with a material such as ceramics or graphite coated on a substrate, or such a raw material is gasified together with a carrier gas such as hydrogen. A catalyst composed of ultrafine metal particles dispersed and suspended in a reaction zone of 900 to 1500 ° C., for example, iron, nickel and iron having a particle diameter of 100 to 300 angstroms.
Vapor grown carbon fiber obtained by a method of contacting with nickel alloy or decomposing it, for example, polyacrylonitrile fiber is heat-treated at high temperature to carbonize to obtain PAN-based carbon fiber, petroleum pitch, coal pitch, etc. Of the pitch-based carbon fibers obtained by heating in a neutral atmosphere to infusibilize them, heat-treating them at a high temperature to carbonize them, and these fibers for a further 150
0 to 3500 ° C, preferably 2500 ° C or higher,
It is possible to use graphite fibers obtained by heat-treating for 3 to 120 minutes, preferably 30 minutes or more, in an atmosphere of an inert gas such as argon. These carbon fibers may be used alone or in combination of two or more, and graphitized vapor grown carbon fiber is particularly preferable.

The metal fiber used in combination with the carbon fiber is used to suppress the destabilization of the conductivity of the carbon fiber in the thermoplastic synthetic resin matrix.
Fibers such as copper, aluminum, nickel, and stainless steel. The ratio of carbon fiber to metal fiber used is 1 by weight.
It is 0:90 to 95: 5. If the ratio of the metal fibers is 90 or more, heat molding becomes difficult, and if an attempt is made to forcibly perform advanced processing, defects will easily occur in the electromagnetic wave shielding layer of the molded product. On the other hand, if it is 5 or less, the electric conductivity of the electromagnetic wave shielding layer becomes unstable. Therefore, when the working degree is high, the electric conductivity becomes insufficient, and good electromagnetic wave shielding performance cannot be expected.

The conductive composition layer composed of these conductive fibers and thermoplastic synthetic resin contains 10 to 200 parts by weight of carbon fiber and metal fiber with respect to 100 parts by weight of thermoplastic synthetic resin. Accordingly, a plasticizer, an additive, and the like may be added, and the mixture may be kneaded under heating and formed into a sheet by using a roll or the like. Alternatively, a volatile solvent may be added and the mixture may be intimately kneaded to form a conductive paint, which may be coated on a flat releasable support surface and dried to form a conductive film. It is also possible to obtain a conductive sheet by dispersing fibers and water, adding an aqueous dispersion of a thermoplastic synthetic resin, and optionally adding pulp or the like to make a paper.

The surface layers of the thermoplastic synthetic resin provided on both sides with the conductive composition layer interposed therebetween are of the same kind as the thermoplastic synthetic resin used for the conductive composition layer. Alternatively, if they are compatible with each other, they can be appropriately selected and used from different types of thermoplastic synthetic resins. Needless to say, the thermoplastic synthetic resin for the surface layer is required to have good workability and moldability, and further, in order to improve physical properties and appearance, a filler, a reinforcing material, a processing aid, a colorant, or A compounding agent such as a flame retardant can be added depending on the purpose of use.

In order to obtain the electromagnetic wave shield of the present invention in the form of a composite sheet from the conductive composition and the thermoplastic synthetic resin as described above, the thermoplastic synthetic resin is made into a single sheet by a heating roll or the like, and then the conductive sheet is prepared. When the composition layer is sandwiched in the middle and pressure-bonded and laminated by a heating roll or heat press, or when the thermoplastic synthetic resin is formed into a sheet by a heating roll or the like, the conductive composition layer is sandwiched in the middle and both surface layers are simultaneously formed into a sheet. To obtain a composite sheet that is laminated all at once, apply a coating composition of a conductive composition on a thermoplastic synthetic resin sheet obtained by a heating roll, etc. to form a conductive composition layer by drying, and further apply the thermoplastic composition. A method of pressure-bonding and laminating a synthetic resin sheet with a heating roll or a heat press can be used, but the method is not limited to this, and an appropriate method can be used, and the method is not particularly limited.

The composite sheet obtained as described above can be used as it is as an electromagnetic wave shield attached to a wall surface, a floor surface or the like, but it can be formed into a box shape or the like by a heat forming processing means such as hot pressing or vacuum forming. It is possible to mold electromagnetic wave shields having various shapes, such as a housing for electronic devices and a shield case for electronic devices, all at once. As the molding means at this time, in consideration of the processability of the thermoplastic synthetic resin used and the processability of the conductive composition layer, heat molding suitable for forming an electromagnetic wave shield having a target shape. It is desirable to select an appropriate method.

[0015]

The electromagnetic wave shield of the present invention can be formed into a box-shaped electromagnetic wave shield having a high degree of workability by heat molding, but it is not only easy to process, but also a conductive composition layer during processing. Stable electromagnetic wave shielding performance is maintained without the occurrence of damage.

[0016]

Example (First Reference Example) Low-density polyethylene (Mirason 3530, trade name of Mitsui Petrochemical) was masticated at 140 ° C. using a two-roll mill, drawn out into a sheet, and heated to a thickness of 0. A thermoplastic synthetic resin sheet of 0.5 mm was prepared.

(Second Reference Example) Benzene as a carbon source and ferrocene as a catalyst were sent into a cracking furnace at 1100 ° C. together with hydrogen as a carrier gas, and the generated length was 50 μm or less and the diameter was 0.01 to 0. 0.5 μm vapor-grown carbon fiber was further added at 3000 ° C. in an argon gas atmosphere.
Then, it was heat-treated for 30 minutes to manufacture carbon fiber as a conductive material.

(First Example) For 100 parts by weight of low-density polyethylene (Mirason 3530, trade name of Mitsui Petrochemical), 40 parts by weight of carbon fiber of the second reference example and copper fiber 20 having a diameter of 10 μm and a length of 300 μm were used. Parts by weight, kneaded for 30 minutes at 150 to 160 ° C. using a two-roll mill, and then drawn out into a sheet, using a hot press to give a thickness of 0.2 mm.
A conductive sheet was prepared. Next, this conductive sheet is sandwiched between two thermoplastic synthetic resin sheets of the first reference example,
By hot pressing again, a composite sheet A having a thickness of 1.0 mm and 150 mm square was prepared.

(Second Example) 50 parts by weight of carbon fiber of the second reference example and the same as those used in the first example per 100 parts by weight of ethylene vinyl acetate copolymer resin (EV250, trade name of DuPont Mitsui Chemicals). 20 parts by weight of copper fibers were mixed, kneaded with a two-roll mill at 150 to 160 ° C. for 30 minutes, drawn out into a sheet, pelletized with a pelletizer, and dissolved in toluene. Zahn viscometer No. A conductive paint having a viscosity of 3 and 30 seconds was prepared. Then, the above-mentioned conductive paint is applied to one surface of the thermoplastic synthetic resin sheet of the first reference example to form a conductive coating film having a thickness of 40 μm, and the thermoplastic resin of the first reference example is also formed on the conductive coating film. Put a synthetic resin sheet on it and heat press it to a thickness of 1.0mm for 150
A mm-square composite sheet B was prepared.

(Third Example) Softwood kraft pulp was beaten with a beater to obtain Canadian standard freeness (JIS P081).
A fibrillated pulp having 2) of 430 was obtained. Next, for 100 parts by weight of this pulp, carbon fiber 1 of the second reference example
An aqueous dispersion of 20 parts by weight and 20 parts by weight of the same copper fiber as used in the first embodiment was added and mixed by stirring to obtain JIS P820.
Paper was made according to the method for preparing handmade paper of 9, and was dehydrated under pressure and dried with hot air to obtain a conductive sheet having a thickness of 0.2 mm. Then, this conductive sheet was sandwiched between two thermoplastic synthetic resin sheets in the same manner as in Example 1 and hot pressed to form a composite sheet C having a thickness of 1.0 mm and a size of 150 mm square.

(First Comparative Example) An aluminum foil having a thickness of 15 μm was sandwiched between two thermoplastic synthetic resin sheets of the first reference example in the same manner as in the first example, and hot pressed to a thickness of 1.0.
A composite sheet D having a size of 150 mm square was prepared.

(Second Comparative Example) To 100 parts by weight of the same fibrillated pulp used in the third example, an aqueous dispersion of 100 parts by weight of the same copper fibers used in the first example was added and mixed by stirring. Thereafter, a conductive sheet is obtained in the same manner as in the third embodiment, and further, in the same manner as in the third embodiment, a sheet having a thickness of 1.0 mm and a thickness of 150 mm is used.
A mm-square composite sheet E was prepared.

(Test Example) Using the composite sheet prepared in each of the examples and comparative examples, 5 cm in length and 5 c in width by hot pressing.
An evaluation housing having a size of m, a depth of 3 cm and a thickness of 1.0 mm was formed. This housing was attached to the antenna so that the pole antenna for transmission having a length of 10 mm provided in the shield box was located at the center, and the antenna was grounded. Radio waves transmitted at 500 MHz from the transmitting pole antenna were received by a pole antenna of the same shape located at a position 50 mm away, the electric field strengths were compared with and without the case, and the shield effect was calculated.
The results are shown in Table 1.

[0024]

[Table 1] Table 1 ─────────────────────── Sample Shielding effect (dB) ────────────── ───────── A 30 B 25 C 40 D ^* 15 E ^* 12 ──────────────────────── *: Comparative example

[0025]

INDUSTRIAL APPLICABILITY The electromagnetic wave shield of the present invention has good conductivity of a conductive composition layer composed of carbon fiber, metal fiber and thermoplastic synthetic resin, and processability capable of withstanding a high degree of bending and stretching. In addition, because the surface layer is formed of a thermoplastic synthetic resin that has not only good processability but also necessary physical properties such as electrical insulation, it is lightweight, has good corrosion resistance, and has stable electromagnetic wave shielding properties. It is possible to easily manufacture the box-shaped electromagnetic wave shield having a high degree of processing by a heat molding method.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a configuration of an electromagnetic wave shield of the present invention.

FIG. 2 is a perspective view showing an example of an electromagnetic wave shield of the present invention.

[Explanation of symbols]

 1, 1'Electromagnetic wave shield 2 Conductive composition layer 3 Thermoplastic synthetic resin layer

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Claims (3)

[Claims] 1. A composite sheet having a laminated structure in which a thermoplastic synthetic resin layer is provided on both sides of a conductive composition layer composed of carbon fiber, metal fiber and thermoplastic synthetic resin sandwiched in between. Electromagnetic wave shield. 2. A composite sheet having a laminated structure in which a thermoplastic synthetic resin layer is provided on both sides of a conductive composition layer composed of carbon fibers, metal fibers and a thermoplastic synthetic resin sandwiched in between, and heat-molded. A method of manufacturing a characteristic electromagnetic wave shield. 3. The electromagnetic wave shield according to claim 1, which is a housing for electronic equipment or a shield case for electronic equipment.