JPH04294122A - Preparation of electromagnetic shielding plastic molded item - Google Patents

Abstract

PURPOSE:To provide a method for preparing a plastic molded item with highly reliable and good electromagnetic shielding characteristics and electrically insulating surface by a low manufacturing cost and being suitable for small scale production. CONSTITUTION:A laminated mixed sheet prepd. by laminating a sheet-like material made of a thermoplastic resin on at least one face of two facing faces of a metal net-like material is used as an electromagnetic shielding material and this is compression-molded to mold a molded item with a required shape.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electromagnetic shielding plastic molded article.

0002

[Background Art] With the spread of electronic and electrical equipment in recent years,
BACKGROUND OF THE INVENTION There are many cases in which electronic and electrical devices generate noise or malfunction due to the operation of their own electronic or electrical circuits being affected by electromagnetic waves generated by other electronic and electrical devices. One of the measures to prevent disturbances caused by electromagnetic waves from other electronic and electrical devices is to provide electromagnetic shielding properties to the casings of electronic and electrical devices to shield them from electromagnetic waves arriving from other electronic and electrical devices. It is to be. The following methods are currently being proposed or implemented as methods for imparting electromagnetic shielding properties to the casings of plastic molded products, which are most commonly used as casings for electronic and electrical equipment. (1) A method of producing an electromagnetic wave shielding plastic casing by depositing a metal layer on the surface of the plastic casing by means such as thermal spraying, plating, or painting. (2) A method of producing a desired electromagnetic shielding plastic casing by injection molding a thermoplastic resin composition containing a conductive filler.

0003

[Problem to be solved by the invention] However, the above (
Method 1) has problems such as poor adhesion between the plastic casing and the metal layer, resulting in unreliable electromagnetic shielding and high manufacturing costs. Furthermore, since the surface of the casing manufactured by method (1) is conductive, if an electrically insulating surface is required, it is necessary to additionally electrically insulate the casing surface. The method (2) above is
This method is suitable for producing large quantities of plastic casings of one type of shape, but when producing small quantities of plastic casings of many different shapes, the cost of molds or low production costs may be a problem. Production costs increase due to efficiency, etc. Further, as in method (1), since the surface of the casing is conductive, if an electrically insulating surface is required, it is necessary to additionally electrically insulate the surface of the casing. In view of these problems, an object of the present invention is to provide a method for manufacturing a plastic molded product having good electromagnetic shielding properties with high reliability and an electrically insulating surface at a low production cost, The purpose is to provide a method that is also suitable for small-scale production.

0004

SUMMARY OF THE INVENTION The above objects are achieved by a method of the present invention having the following features. The feature of the present invention is that when an electromagnetic wave shielding plastic composite sheet is molded into a molded product of a desired shape by air pressure molding, at least one of the two opposing surfaces of a metal mesh material is used as the electromagnetic wave shielding plastic composite sheet. This method uses a laminated composite sheet whose surface is laminated with thermoplastic resin sheet materials.

The metal mesh material used in the present invention is not particularly limited as long as it is a flexible metal mesh member. The shape may be, for example, a so-called wire mesh, i.e., a large number of metal wires or metal strips continuously knitted in the vertical and horizontal directions to form a net or mesh shape, an expanded metal or a lath mesh, i.e., a metal thin plate woven in one direction. Examples include a mesh made by inserting a large number of slits in a staggered pattern and pulling from a direction intersecting the one direction, and a porous metal plate in which a large number of through holes are made in a thin metal plate. Depending on the shape of the molded product,
For example, in forming processes with a large drawing ratio, a metal mesh whose mesh structure is easily deformed, such as a loosely woven metal mesh or a loosely stretched lath mesh (expanded metal), is used as the metal mesh material. The material of the metal mesh material is not particularly limited as long as it is a conductive and flexible metal, and inexpensive metals with high conductivity such as stainless steel, copper, and aluminum are preferably used.

[0006] The above-mentioned metal net material has sufficient flexibility and continuous surface conductivity due to its net structure and metal material, so a laminated composite sheet with a thermoplastic resin sheet material is formed by air pressure. In this case, the metal mesh material can freely follow deformation such as elongation or compression of the laminated composite sheet during molding while maintaining surface conductivity. Therefore, firstly, it is necessary to obtain a molded product that has good electromagnetic shielding properties without the risk of deterioration of electromagnetic shielding performance due to discontinuity of electrical conduction due to breakage of the conductor due to deformation caused by molding. can. Second, since the laminate of the metal mesh material and the thermoplastic resin sheet material can be molded into a desired shape while maintaining the integrity, the metal mesh material and the thermoplastic resin sheet material are in close contact with each other. It is possible to obtain a plastic molded product with high mechanical strength and electromagnetic shielding properties.

[0007] As the thermoplastic resin sheet material used in the present invention, commercially available thermoplastic resin sheets can generally be used. Examples include polyethylene, polypropylene, acrylic modified polyvinyl chloride, polyamide, polyester, polycarbonate, ABS (acrylonitrile butadiene styrene), polyphenyl ether, and polyetherimide resin sheets. A sheet made of a single resin or a resin mixture of a plurality of types of these resins can also be used. Furthermore, the thermoplastic resin sheet can be blended with fillers, reinforcing materials, and other low-melting point metals such as solder within a range that does not impair electromagnetic shielding properties.

In the present invention, the laminated composite sheet of a metal mesh material and a thermoplastic resin sheet material is a soft thermoplastic resin sheet in an uncured state immediately after sheet forming in the sheet manufacturing process by resin extrusion method. It is formed by a method of bonding a thermoplastic resin sheet and a metal mesh material together, a method of adhering a thermoplastic resin sheet that has been cured after sheet molding of a thermoplastic resin sheet and a metal mesh material to each other with an adhesive, or the like. In addition, a method can also be applied in which a metal mesh material and a thermoplastic resin sheet are superimposed, heated, and then directly transferred to a pressure molding process, and the two are bonded and integrated during molding.

In the present invention, the structure of the laminated composite sheet of the metal net material and the thermoplastic resin sheet can be freely designed depending on the use of the final plastic molded product. For example, when imparting electrical conductivity to the inner surface of a plastic casing and electrical insulation to the outer surface, a metal mesh material and one layer of thermoplastic resin sheet are laminated, and the metal mesh material is laminated with one layer of thermoplastic resin sheet. Shape so that the material is inside the casing. If it is necessary to form electrically insulating layers on both the inner and outer surfaces of a plastic housing, a metal mesh material is used as the intermediate layer, and thermoplastic resin sheets are laminated and molded on both sides in a sandwich structure. In addition, the thickness of the metal mesh layer and thermoplastic resin sheet layer of the laminated composite sheet depends on the intended use of the electromagnetic shielding plastic molded product, that is, the required electromagnetic shielding properties of the final plastic molded product, The thickness of each layer is determined by considering electrical insulation, mechanical strength, etc.

[0010] In the present invention, a laminated composite sheet is air-formed by a commonly used method using an ordinary air-forming machine. That is, the heated and softened laminated composite sheet is brought into contact with a mold, and while the cavity side of the mold is vacuumed as necessary, pressure is applied to the side of the laminated composite sheet that is not in contact with the mold. Air is sent to press the laminated composite sheet toward the mold. The pressed laminated composite sheet is pressed onto the surface of the mold cavity and molded into the shape of the mold cavity. In the pressure forming of the present invention,
The pressurizing pressure is preferably 3 kg/cm2 or more. This is because if the pressure is less than 3 kg/cm2, the pressing force tends to be insufficient in order to obtain the adhesion between the thermoplastic resin sheet and the metal mesh material and the moldability of the metal mesh material.

[0011]

EXAMPLES The present invention will be explained in more detail based on examples below. Example 1 Metal mesh material made of copper wire with a wire diameter of 75 microns 2
A laminated composite sheet was formed by using a 0.00 mesh copper mesh and pressing 3 mm thick ABS resin sheets on both sides of the mesh under a hot press. This electromagnetic shielding plastic laminated composite sheet was fixed to a square metal frame with a clamp, heated in a heating furnace to soften it, and then vertically molded using an aluminum female mold at a pressure of 3.5 kg/cm2. Box-shaped, 500mm wide, 200mm wide, 100mm high, and 500mm long and 20mm wide.
Two identically shaped box-like casings were fabricated with a 0 mm opening and an outwardly extending flange-like collar of 10 mm width. This was designated as Example Product 1 obtained by the manufacturing method according to the present invention.

The electromagnetic shielding properties of the box-shaped cabinet of Example 1 were evaluated as follows. That is, the upper surface of the brim of the opening of each of the two obtained box-shaped casings was cut until the internal copper mesh was exposed, and the brim was overlapped on the surface where the copper mesh was exposed, and the airtight box was made. Formed. After installing a small antenna inside the sealed box, I fixed it in four places on the brim with screws. An electromagnetic wave receiving circuit was constructed by connecting an antenna installed inside the sealed box to an external receiver using a lead wire passed through a through hole provided in one wall of the sealed box. This electromagnetic wave receiving circuit transmits electromagnetic waves at different frequencies from a transmitter outside the sealed box, and receives the electromagnetic waves that have passed through the electromagnetic wave shield made of the copper mesh of the housing and reached the internal antenna, and then measures the strength of the electromagnetic waves. The attenuation ratio of the strength of the electromagnetic waves on the transmitting side and the receiving side was calculated, and the results are shown in Table 1 in dB.

[0013]

Example 2 A lath net made by the Exband method, in which a large number of slits in one direction were made in a staggered manner in a 37 micron thick copper foil, was used as the metal net material, and 7 mm thick acrylic was placed on both sides of the lath net. A modified PVC resin sheet was pressed under a hot press to form an electromagnetic shielding plastic laminated composite sheet. This laminated composite sheet was fixed to a rectangular metal frame with a clamp, heated in a heating furnace to soften it, and then pressure-formed in the same manner as in Example 1 at a pressure of 3.2 kg/cm2 to obtain Example product 1. Two identical box-shaped casings were produced, and these were designated as Example product 2 obtained by the manufacturing method according to the present invention. The electromagnetic shielding effect of the obtained Example Product 2 was evaluated in the same manner as Example Product 1, and the results are also shown in Table 1. As is clear from Table 1, the electromagnetic wave shielding plastic casings of Example Products 1 and 2 obtained by the method according to the present invention exhibited a high electromagnetic wave shielding effect over a wide frequency range of electromagnetic waves, and had excellent electromagnetic wave shielding effects. Has an electrically insulating surface.

[0015]

[Effects of the Invention] As explained above, the method for producing an electromagnetic shielding plastic molded article of the present invention uses a metal mesh material as an electromagnetic shielding material, a laminated composite sheet of the same and a thermoplastic resin sheet, By pressure forming this, it is possible to produce an electromagnetic shielding plastic molded product that has excellent electromagnetic shielding properties and has electrical insulation properties on the molded product surface without the need for additional processes. . Since the present invention is molded using a pressure molding method, the present invention has the advantage of being able to manufacture electromagnetic shielding plastic molded products through simple processes and at low production costs, and can also be manufactured in a wide variety of different shapes. It is also suitable for small quantity production or for molding large molded products. Furthermore, the method of the present invention has the advantage that a laminated composite structure including an electromagnetic shielding layer and an electrically insulating layer can be freely set as required.

Claims (1)

[Claims] Claim 1: When molding an electromagnetic wave shielding plastic composite sheet into a molded product of a desired shape by air pressure molding, the electromagnetic wave shielding plastic composite sheet is formed on at least one of two opposing surfaces of a metal mesh material. A method for manufacturing an electromagnetic wave shielding plastic molded product, characterized by using a laminated composite sheet in which sheet materials made of thermoplastic resin are laminated.