JPH02127035A - Manufacture of electromagnetic wave shield sheet - Google Patents

Abstract

PURPOSE:To form an electromagnetic wave shield sheet having excellent quality characteristics by forming a laminate sheet by integrating a porous metal fiber sheet and a transparent plastic sheet by sticking or extrusion. CONSTITUTION:A porous metal fiber sheet is formed by baking a sheet which is obtained by mixing natural organic fiber or synthetic fiber and metal fiber, making them into the sheet and then subjecting the sheet to thermocompression bonding. Next, this porous metal fiber sheet is integrated with a transparent plastic sheet by sticking or extrusion to form a laminate sheet, and thereby an electromagnetic wave shield sheet is manufactured. It is suitable to form the porous metal fiber sheet by applying wet-type manufacture to the natural organic fiber or the synthetic fiber and the metal fiber out of which the amount of the compounded metal fiber is set to be 30 to 60wt.% of the whole fiber sheet before baking, by applying heating and contact-bonding to the fiber sheet thus obtained and by baking the same thereafter.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention has excellent transparency and flexibility, and can be applied to window glass of shield rooms, etc., used as a shield curtain, or directly applied to objects to be shielded. The present invention relates to a method for manufacturing an electromagnetic shielding sheet that can be used as a substitute for a covering sheet or bag, and also for a wire mesh for shielding cables.

(Prior Art) In recent years, with the rapid development of electronic devices, their housings have become plastic, and electromagnetic interference generated during the operation of electronic devices has become a major social problem.

Various electromagnetic shielding sheets have been developed as part of the prevention measures. To date, there are four methods for producing electromagnetic shielding materials based on plastic that have been proposed or implemented: zinc spraying, conductive paint, metal vapor deposition, chemical plating, and other surface treatments; There is a method of making a composite material by mixing conductive materials such as fine fibers, particles, flakes, etc. Among these, the typical methods for producing sheets for windows in shielded rooms that require transparency and for bags that have shielding performance that allows the contents to be seen are (1) a method in which conductive metal is vapor-deposited in the form of a mesh; , (2) a method of printing a conductive paint in a mesh shape, and (3) imparting conductivity by surface treatment of plastics, for example, after plating Cu, Ni, etc. on a woven fabric such as a grid-like polyester net, A method is known in which this is sandwiched between transparent plastic sheets in a sandwich-like manner and laminated, and the technique of imparting conductivity to a highly transparent plastic sheet base material is attracting attention.

(Problems to be Solved by the Invention) In the conventional technique described above, the method (1) of vapor depositing a conductive metal in a mesh shape is not suitable for mass production because the vapor deposition equipment is expensive and requires multiple steps. Moreover, since the deposited film is as thin as a human being, its physical surface strength is low, and it is easily peeled off by scratching or pressure, and it also suffers from poor flexibility, such as cracking when bent, resulting in poor manufacturing yields. In addition, regarding the method (2) of printing conductive paint in a mesh shape, it is necessary to increase the amount of coating in order to obtain the target shielding properties when printing in a mesh shape on a large area sheet. However, there are technical problems such as uniform printing over the entire surface and a lack of sharpness in the printed area due to the large number of sheets printed.

All of the techniques for imparting conductivity to plastic molded bodies through surface treatment (3) involve secondary processing to form a conductive thin layer on the plastic surface; for example, grid-like polyester nets, etc. Cu, Nj on the woven fabric of
The method of layering the materials by sandwiching them between transparent plastic sheets in a sandwich-like manner is difficult to control the tension after secondary processing such as the lamination process using transparent plastic sheets. If it is applied too strongly, there is a technical problem in that the intersecting parts of the mesh fabric will be misaligned, and the unplated parts will be rough, reducing the shielding properties.

On the other hand, composite materials obtained by mixing plastic with a conductive material made of fine metal fibers have the conductive material dispersed in the plastic, so compared to a case where a conductive layer appears on the plastic surface. Therefore, there is little impact on electronic devices due to destruction of the conductive layer, deterioration in performance due to oxidation, or peeling of the conductive layer. However, in the case of composite materials, the conductive material is dispersed throughout the plastic, so in order to impart a high degree of conductivity, it is necessary to add a large amount of conductive material compared to the case of surface treatment. be.

Furthermore, when conductive fine fibers or fillers are added to plasticized plastic, the apparent viscosity of the plastic composition increases rapidly as the amount added increases. This not only makes it difficult to uniformly disperse the conductive material into the plastic during processes such as kneading, but also increases the shearing force acting on the conductive material when kneading is strengthened to achieve uniform dispersion. In many cases, the aspect ratio of metal fine fibers and the like is significantly lowered, and the expected effect of imparting conductivity cannot be obtained.

The present invention provides a composite plastic material that exhibits electrical conductivity without the risk of deterioration in performance due to destruction or oxidation of the conductive layer, or peeling, compared to the case where the conductive layer is exposed, due to the special nature of the means used. It is.

(Means for Solving the Problems) The purpose of the present invention is to solve the problems of the above-mentioned conventional techniques and provide a method for manufacturing an electromagnetic shielding sheet with good quality and performance, the outline of which is as follows. .

The method for manufacturing the electromagnetic shielding sheet of the present invention is to first mix natural organic fibers or synthetic fibers and metal fibers using a wet papermaking method, then heat and press the resulting fiber sheet, and then press the sheet with a reducing gas or inert gas. A porous sheet made of metal fibers is produced by firing in an atmosphere. Further, an electromagnetic shielding sheet is manufactured by combining the porous metal fiber sheet from which the natural organic fibers or synthetic fibers have been completely removed by baking with a transparent plastic film or by extrusion processing. The sintered metal fiber sheet produced by the present invention has a three-dimensional network structure with length, width, and thickness. A two-dimensional network structure is created by reducing the thickness to a thickness approximately equal to the size of each individual fiber (in units of several microns),
Since this is laminated and fixed with a transparent plastic film, transparency is maintained. For mixed papermaking of metal fibers and organic fibers, a papermaking method in a normal paper manufacturing process is used. In addition, the metal fiber sheet is sintered at a temperature below the melting point of the metal, and in the case of easily oxidized metal fibers such as stainless steel, a reducing gas atmosphere or an inert gas atmosphere such as hydrogen, nitrogen or CO is used to prevent oxidation. It is preferable to fire in a gas atmosphere.

(Function) The conductive metal fibers used in the present invention include nickel, precious metals, stainless steel, and silver, which are difficult to oxidize, as well as those treated with special oxidation prevention treatment to prevent deterioration of performance over time. Preferred are brass, copper, aluminum, etc., and these may be used alone or as a mixture of two or more. The diameter of the metal fiber is 2 to 20 μmφ, especially 4 to 20 μmφ.
Fibers with a diameter of 12 μm are preferable, and fibers with a fiber length of 2 to 20 mm, especially 3 to 10 mm, are preferable.As for the natural organic fibers used for mixed papermaking, cellulose fibers, leather fibers, and vegetable fibers are preferable.
As for synthetic fibers, polyamide fibers, polyalkylene fibers, polyester fibers, etc. are preferable.The diameter of the fibers is preferably 10 to 40 IImφ, and the fiber length is 0.5 to 2fi.In particular, the synthetic fibers include polyalkylene fibers,
Particularly preferred are polyethylene fibers and polypropylene fibers.

The blending ratio of metal fibers and natural organic fibers or synthetic fibers that act as organic binders has a large effect on electromagnetic shielding properties, but the degree of entanglement of the metal fibers after firing also affects transparency. The inventors of the present invention conducted extensive studies on the blending ratio, and found that by selecting the blend so that the metal fibers accounted for 30 to 60% by weight in the total fiber (metal fiber + organic fiber) sheet before firing, it was possible to achieve better results. It was discovered that the same characteristics can be obtained. 60% metal fiber by weight
If it exceeds 30% by weight, the transparency after firing will be poor, while if it is less than 30% by weight, not only will sufficient T-magnetic wave shielding properties not be obtained after firing, but the tensile strength required for the next step will also be weakened.

The transparent plastic sheet used in the present invention is not particularly limited as long as it is a thermoplastic resin that can be used for lamination molding by ordinary extrusion molding or heat bonding. Examples of such thermoplastic resins include polyolefin-based resins, Examples include polystyrene, polyvinyl chloride, polyacrylic ester, polymethacrylic ester, polybutadiene, polyamides, polyesters, modified products thereof, and mixtures of copolymers. These thermoplastic resins can be selected depending on the moldability and physical property requirements of the molded product.

When laminating a metal fiber sheet and a transparent plastic sheet, bonding or extrusion processing is used. For example, in the case of calender processing, the processing temperature in rolls is usually heated at a temperature of 160°C to 180°C. ,
Both are laminated. Thermoplastic synthetic resins are plasticized according to rolling conditions, so either hard or soft synthetic resins that retain this plasticity can be used in a laminating machine (not shown). A backup roll is installed in the lowermost hole, and the integrated resin sheet that has been rolled and heated and laminated between the lowermost roll and the backup roll is cooled.

In addition, although the present invention has been described as a method for manufacturing a laminate of a metal fiber sheet and a transparent plastic sheet, the laminated resin sheet after extrusion molding or bonding molding is made of resin by heating means such as press molding, vacuum forming, or pressure forming. It is also used to manufacture molded products, and is used not only as a sheet for shielded rooms to prevent electromagnetic interference, but also for making plastic housings for electronic devices.

The method for manufacturing the porous metal fiber sheet is as described below, and the case where stainless steel fibers are used as the metal fibers will be described. First, stainless steel fibers treated with a sizing agent and synthetic fibers with an organic binder are dispersed in cold water and slowly stirred with a low-speed stirrer such as an agitator to dissociate the fibers to create a slurry-like aqueous suspension of fibers. The obtained slurry-like aqueous suspension is pressed and dried on a drying drum using a wet paper machine.

In this case, the wet paper machine may be used for fourdrinier or circular paper, but special care must be taken as setting conditions such as press pressure and dryer temperature are important points in obtaining a uniform fiber sheet. The obtained fiber sheet is subjected to heat-pressing treatment using a press device such as a calendar.

This improves the state of contact between the stainless steel fibers, resulting in a low and stable volume resistivity and improved electromagnetic shielding effect. This fiber sheet is fired at high temperature in a reducing atmosphere injected with hydrogen to completely remove the organic binder and sinter the stainless steel fibers to obtain a porous metal fiber sheet. In the present invention, a sheet for electromagnetic shielding is produced by laminating the porous metal fiber sheet with a transparent plastic sheet from both sides by a dry lamination method or a thermal lamination method. It is also possible to manufacture an electromagnetic shielding sheet by extruding a highly transparent resin and embedding a sintered stainless steel fiber sheet in the resin using an extrusion lamination method.

(Examples) Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

(Example 1) 30 parts by weight of stainless steel fiber with a fiber diameter of 8 μmφ and a fiber length of 61 mm (manufactured by Tokyo Seizo Co., Ltd., trade name: Susmic) and a fiber length of 1
．． 70 parts by weight of 6N SWP fiber (polyethylene fiber type, manufactured by Mikata Petrochemical Industry ■, trade name E-790) was dispersed in water at room temperature, and stirred with an agitator for 10 minutes. This slurry-like aqueous suspension was made into paper using a Fourdrinier paper machine with a target weight of 45 g/rd, and a wet fiber sheet obtained by dehydration pressing was pressed and heated at 100'C to obtain a dry sheet. This fiber sheet is further calendered to 15kg/c.
fl, and was heat-pressed at 125° C. to obtain an electrically sensitive sheet. This sheet was fired in a high-temperature (1120° C.) reducing atmosphere using hydrogen, resulting in a porous and transparent metal fiber sheet in which the stainless steel fibers were sintered together. Using a thermal lamination device, this metal fiber sheet is laminated in a sandwich-like manner with an ethylene-ethyl acrylate copolymer resin (manufactured by Mikata DuPont Polychemicals, product name: AS252) film that has good adhesion to plate glass. A transparent electromagnetic shielding sheet was obtained. When the electromagnetic shielding properties of this sheet were measured using the Atopan Test Co., Ltd. method, an attenuation of 35 dBm in electric field and 34 dBm in magnetic field was obtained at 500 MHz, confirming a sufficient shielding effect. Furthermore, a light transmittance of 62% was obtained, and the sheet could be used as an electromagnetic wave shielding sheet for windows.

(Example 2) Using the manufacturing conditions of Example 1 with a blend of 40 parts by weight of stainless steel fiber and 60 parts by weight of pineapple, the weight per square meter before firing was 45 g/
A rd conductive sheet was obtained. This fiber sheet was fired under the same conditions as in Example 1 to produce a porous metal fiber sheet. Using the extrusion lamination method, extrude the fired metal fiber sheet to extrude modified polyethylene (manufactured by Sumitomo Chemical, trade name: Bond First 7B-A) to a film thickness of 60 AIm, and use the fired sheet as a core to sandwich the resin. A translucent electromagnetic shielding sheet with good adhesion to the temporary glass was obtained. When we measured the electromagnetic shielding properties of this sheet, it was 500M)Iz
Attenuation of the electric field of 37 dBm and magnetic field of 39 dBm was obtained, confirming a sufficient shielding effect. Furthermore, a light transmittance of 55% was obtained, which was not a problem in practical use.

(Effects of the Invention) Since the present invention has the above-mentioned configuration, the conductivity of the stainless steel fibers themselves can be effectively absorbed into the sheet-like composite laminate, and since the stainless steel fibers are protected by the plastic coating layer, physical It is possible to obtain stable electromagnetic shielding properties without being subject to mechanical damage or abrasion, and because the stainless steel fibers are ultra-fine fibers with a thickness of 8 μmφ, they have excellent transparency, so they exhibit a high degree of conductivity. This technology can be applied to a wider range of applications, including technology for imparting electrical conductivity to plastic materials.

Agent Patent Attorney Mamoru Takeuchi

Claims (1)

[Claims] 1) A porous metal fiber sheet is created by mixing and forming natural organic fibers or synthetic fibers and metal fibers, and then baking the sheet obtained by thermocompression bonding. A method for producing an electromagnetic shielding sheet, which comprises forming a laminated sheet by laminating or extruding a textured metal fiber sheet and a transparent plastic sheet. 2) Natural organic fibers or synthetic fibers and metal fibers were obtained by wet papermaking by blending the metal fibers to 30 to 60% by weight of the total fiber (metal fiber + organic fiber) sheet before firing. 2. The method for producing an electromagnetic shielding sheet according to claim 1, wherein the fiber sheet is heat-pressed and then fired to produce a porous metal fiber sheet.