JPS5895899A - Plastic housing with electromagnetic shielding characteristic - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic housing having an electromagnetic wave shielding effect, which can be used as a housing material for accommodating industrial, office, household, and other electronic devices. The purpose of this invention is to provide a plastic casing that has the following characteristics.

Compared to conventional metal products such as sheet metal and guicast, plastic molded casings are lighter, more corrosion resistant, and have better appearance and
Due to its good feel, ability to absorb noise emitted by equipment, low production costs, and freedom of molding, it is possible to freely design the assembly of equipment parts to be installed inside and the assembly of the casing with each other. The demand for it is increasing because it has many features such as improved productivity by being

However, since the plastic molded casing is transparent to electromagnetic waves, the electromagnetic waves generated by the internal electronic equipment are transmitted through it, and the interference caused by the electromagnetic waves is caused to the outside.

Also, internal equipment may be adversely affected by electromagnetic waves from outside.

Furthermore, since plastic is electrically insulating, static electricity accumulates, which can interfere with the normal operation of equipment.

Currently, methods for shielding electromagnetic waves that are generally practiced include metallizing the inner surface of the housing using aluminum, mainly by vacuum evaporation, sputtering, ion blasting, etc. Electrolytic plating with silver, copper, nickel, etc. Metallizing by metal spraying mainly consisting of zinc, or silver,
The inner surface of the casing is coated with a conductive paint containing a large amount of conductive powder such as copper, nickel, graphite, carbon bran, etc. However, in all of these methods, the conductive surface layer is These methods require shielding treatment to be a separate process from the molding process, and not only require expensive equipment and special techniques, but also as the shape becomes more complex. Productivity decreases and costs rise significantly.

Furthermore, there are many other problems, such as the danger of short-circuiting of internal electronic equipment due to peeling or falling off of the conductive layer, deterioration of shielding effectiveness over time, and undesirable sanitary conditions in labor safety rooms during factory work.

On the other hand, SMC using a thermosetting compound filled with a large amount of conductive fibers, flakes, particles, etc.
, Compression molded products using BMC, etc., and conductive molded products using thermoplastic molding materials have also been developed, and since the molded products themselves are electrically conductive, these molded products cannot be made secondary to electrical conductivity. Since no processing is required, productivity is improved, but on the other hand, the shape of the casing made by compression molding is limited due to the molding technology, and it is extremely inefficient compared to injection molding of thermoplastic compound, and special limited to specific uses.

In addition, normal thermoplastic injection molded products have excellent productivity and can be mass-produced at low cost, but large molded products such as housings are prone to warping and distortion, especially in shapes with ribs and bosses. Poor appearance due to sink marks is unavoidable. For this reason, the large casing is made of structural foam (S,
F) is adopted.

This molding method fills the cavity by foaming the material and at the same time forms an integral skin layer on the cavity surface, so the pressure inside the mold is low and it is possible to prevent sink marks and distortion of the molded product. The surface of the product becomes rough and somewhat porous with a foam pattern, and if the entire product contains a large amount of conductive material, the appearance will be significantly impaired.
Finish painting is required. Furthermore, in any of the above-mentioned molding methods, a compound containing a large amount of conductive material is used for the entire casing, resulting in high costs and a decrease in mechanical strength.

The following is a technical overview of the conventional method. By solving the above-mentioned drawbacks of the conventional method, this invention provides a plastic casing that has excellent electromagnetic shielding properties and is highly productive. It is completed.

The configuration of this invention will be explained in detail below.

As shown in the drawings, the plastic casing having electromagnetic shielding properties according to the present invention has a non-foamed (solid) skin layer l that does not contain any conductive material, and contains a large amount of conductive material with a thickness of 1.05 to 1.5. It has a structure in which the entire surface of a core layer 2 which has been foamed to double its original size is covered, and both the solid skin layer 1 and the foamed core layer 2 are made of thermoplastic plastic.

The manufacture of the housing having this electromagnetic shielding property is carried out by, for example, Battenfeld Maschienenfab.
Using a multicomponent injection molding machine manufactured by Riken'GmbH (West Germany), conductive effects were applied to colored or unpigmented thermoplastic materials as solid skin materials and thermoplastic materials with or without blowing agents as core materials. This is made possible by using a material kneaded with a filler having a high viscosity, covering the surface with a solid skin layer, and molding it into a cross-sectional sandwich shape with a conductive core inside.

In this case, the injection of the two components may be carried out sequentially for the skin and the core, or it is optional to inject the skin slightly first and then inject the two components simultaneously. Regarding MODER, we have already given an example.
N PLASTIC■NTERNATIONAL6 [7
] 42-44 (1976).

Same < 10 (3) 18-21 (1980),
JOURNAL OF CELLULAR PLASTIC
5, March/Apri194-97 (1979
), PLASTIC5MACHINERY & EQU
IPMENT'9 (2) 9-17 (1980),
It is described in publications such as et al.

Here, the material for forming the solid skin layer may be any thermoplastic resin that has adhesive properties and similar curing shrinkage behavior to the material for the low foam core layer and is suitable for injection molding, including polycarbonate and modified PPO. Various materials are used in practical use, from engineering plastics such as , polyamide, etc. to general-purpose polyolefins, polystyrene, etc.
It can be selected depending on the application, taking into consideration the beauty of appearance, mechanical strength, chemical resistance, electrical properties, etc.

As the material for forming the low-foam core layer, a resin is used that has good adhesion to the skin layer material and mixes well with the conductive material to be mixed to improve conductivity.

As the conductive material mixed and filled in the low foam core layer, metal fibers such as aluminum, copper, nickel, etc., metal flakes, metal particles, metal coated glass fibers, graphite, carbon blank, etc. can be used. .

These are filled in the compound at 20-60%, taking into account the type of conductive material, the expansion ratio and the attenuation rate of the electromagnetic field strength.

As mentioned above, it is molded by two-component injection molding method,
The plastic casing, which has electromagnetic shielding properties and has the structure described above, has a smooth surface with no pinholes or bubbles, and is free from sink marks, warping, distortion, etc., just like ordinary one-component injection molded products. Furthermore, since the solid skin layer does not contain a conductive material, there is no coloring or discoloration caused by the conductive material.

Therefore, the shielding effect can be exerted without affecting the appearance at all, and there is no need for secondary treatment such as finish painting, which would lead to an increase in cost.

In addition, since the conductive layer is limited to the inner core layer and is not exposed to the surface, the electromagnetic shielding effect does not deteriorate over time due to oxidation of the conductive layer, and it does not peel off like a secondary conductive layer. Therefore, there is no risk of short-circuiting of internal equipment circuits. .

Furthermore, the amount of expensive conductive material used is limited to only the core layer, which greatly reduces the amount of use.

Furthermore, since it has an effective conductive layer inside, it is easy to ground it using a terminal.

That is, a feature of the present invention is that the plastic casing having the numerous features described above can be manufactured in one step with extremely high productivity using the two-component injection molding method.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional perspective view of a plastic casing having electromagnetic shielding properties according to the present invention. In the figure, 1: Solid skin layer, 2: Foamed core layer filled with conductive material. Drawing surface 1

Claims (1)

[Claims] In a plastic molded casing having a structure in which the entire surface is covered with a foamed core layer with a non-foamed skin layer, the core layer is made of a material containing a conductive filler in the form of fibers, flakes, or granules. , a plastic molded casing whose entire core layer is a conductive layer, giving it an electromagnetic shielding effect.