JPH01188000A - Plastic box body for electromagnetic shielding and molding method thereof - 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 [Field of Industrial Application] The present invention relates to a plastic casing for electromagnetic shielding and a method for molding the same.

[Conventional technology]

In recent years, with the rapid spread of electronic devices, high-frequency electromagnetic noise emitted from these devices has become a problem. By the way, as a method to prevent such electromagnetic noise, it is recommended to surround the electronic device with a casing made of a conductive material, such as a casing made of metal, or by metal spraying, metal plating, or conductive material on the inner surface of a plastic casing. It is best to cover it with paint, or there is also a method of mixing conductive filler such as metal fiber into plastic and molding the casing.

[Problem to be solved by the invention]

However, although metal casings have excellent electromagnetic shielding effects, they are inferior in workability and have problems in terms of weight. In addition, methods for applying conductive processing such as metal spraying, metal plating, and conductive paint to the inner surface of the plastic casing, which require post-processes such as welding and exterior painting, are not recommended due to the work environment and time required. There are problems such as the risk of peeling off and the need for complicated processing such as masking. Therefore, a method was invented to mold the casing by mixing conductive filler into plastic, but since the conductive filler was limited to dark colors, the casing could not be colored freely, so the outside surface was painted after molding. There is a need. In addition, if the temperature of the molding mold is not appropriate, the conductive filler may rise to the surface of the molded product, resulting in poor appearance, and if the conductive filler is a substance that easily oxidizes, it may have electromagnetic shielding properties. It is also possible that the deterioration of There is also a method of molding a two-layer ordinary plastic casing on the outer surface of a plastic casing molded with conductive filler mixed in, but in this case two sets of molding molds are required and the molding process is performed twice. There were problems such as high costs.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned problems.
The invention relates to a method for molding a plastic casing for electromagnetic shielding by injecting molten plastic mixed with a magnetic conductive filler into a molding tool, in which a magnetic field generating device is installed inside the inner molding tool that forms the inner surface of the plastic casing. The plastic casing is characterized in that the plastic casing is molded while a magnetic field is generated around the inner molding tool.

The present invention will be explained below based on FIGS. 1 to 3.

1 and 2 are a perspective view and a cross-sectional view, respectively, of a plastic casing for electromagnetic shielding according to the present invention, showing that the conductive filler 8 is unevenly distributed on the inner surface 9 of the plastic casing 10. Next, the molding method of the present invention will be explained. FIG. 3 is a schematic diagram of an injection molding apparatus for molding the plastic casing for electromagnetic shielding of the present invention, in which plastic containing a conductive filler 8 is supplied from a homper 6 and melted by a screw 5 in a cylinder 7. After stirring, from the spool 2 to the cavity 3 in the outer molding tool la.
While injecting the conductive filler 8, the magnetic field generator 4 embedded in the inner molding tool lb is driven to generate a magnetic field around the inner molding tool 1b, causing the conductive filler 8 to be unevenly distributed on the inner molding tool lb side, and then solidified. let

The matrix resin of the conductive filler-containing plastic used in the present invention is not limited as long as it is a thermoplastic resin, and examples thereof include ABS, polystyrene, polycarbonate, modified PP◯, and PBTSPP. The conductive filler is preferably a magnetic metal such as Fe, Ni, Go, or an alloy thereof in the form of fibers, powder, or flakes.As a magnetic field generator, any suitable magnetic field generator that has been used in the world can be used. An electromagnet or a permanent magnet that can be used may be used.

[Effect]

The conductive filler 8 contained in the plastic melted and injected into the outer molding tool 1a and the inner molding tool 1b is attracted by the magnetic field generated from the magnetic field generator 4 embedded in the inner molding tool 1b, thereby molding the inner surface. It is unevenly distributed with an appropriate distribution on the side of the ingredients. Therefore, the present invention can be similarly applied to extrusion molding, press molding, pressure molding, etc. in addition to injection molding, in which the conductive filler does not stand out on the outer surface of the obtained molded product.

〔Example〕

Next, a plastic casing for electromagnetic shielding (external dimensions: 30 CI
.

The electromagnetic shielding characteristics of a specimen 16 with a thickness of 3 mm were measured using an experimental apparatus as shown in FIG. As shown in the figure, the center conductor of a 5D-2W coaxial cable serving as the element portion 10CI was vertically erected in the specimen 16 and used as the radiation antenna 11.

This radiation antenna is installed under the specimen 16 on an aluminum plate (40C).
A ground brain 12 (IX40C 1 m, thickness 2 m) was provided and attached to the center thereof. A dipole antenna is used as the receiving antenna 13, and the frequency (80 to 600 MHz >
The antenna element is replaced accordingly. In addition, in order to widen the dynamic range for measurement, 20 dB
A gain preamplifier 14 was installed in front of the electric field strength measuring device 15. Attenuation with the measuring device 5 was performed using an attenuator built into the field strength measuring device. The contact situation between the specimen 16 and the ground brain 12 has a large effect on the shielding effect, so it is not provided.

A shield mesh was applied to the side of the shaped object 16, and a wooden weight was placed from above. Note that the signal to the radiation antenna 11 is sent from the signal generator 17 using an experimental device such as No. 6 or above, and the power of the radiation antenna is 16 dBm and the frequency is 1001'1) fz.
, 250 MHz, the shielding effect is defined as the difference in the received electric field value measured by the electric field strength measuring device when the specimen cannot be covered over the radiation antenna and when it can be covered, and the results are shown in Table 1. In addition, as a comparative example, the measurement σ of a sample in which the conductive filler is not unevenly distributed on the inner surface of the plastic casing is also listed in Table 1 in the same manner as in the examples.

The results showed that the shielding effect was higher when the conductive filler was unevenly distributed on the inner surface of the plastic casing.

〔Effect of the invention〕

As explained above, the plastic casing for electromagnetic shielding of the present invention has sufficient shielding effect characteristics, and the molding method thereof includes embedding a magnetic field generating device inside the inner molding tool forming the inner surface of the casing. Since the plastic casing is molded while generating a magnetic field around the inner surface molding tool, it is possible to easily construct a structure in which the conductive filler is unevenly distributed.

[Brief explanation of the drawing]

1 and 2 are respectively a perspective view and a sectional view of a plastic casing for electromagnetic shielding according to an embodiment of the present invention, and FIG. 3 is a molding apparatus for a plastic casing for electromagnetic shielding used in an embodiment of the present invention. Figure 4 shows a device for measuring the shielding effect of a plastic casing for electromagnetic shielding.
~Screw, 6~Hopper, 7~Cylinder,
8 - conductive filler, 9 - inner surface, 10 - plastic casing for electromagnetic shield.

Claims (2)

[Claims] (1) A plastic casing for electromagnetic shielding, characterized in that a magnetic conductive filler is unevenly distributed on the inner surface of the plastic casing. (2) In a method of molding a plastic casing for electromagnetic shielding by injecting molten plastic mixed with a magnetic conductive filler into a molding tool, a magnetic field generator is installed inside the inner molding tool that forms the inner surface of the plastic casing. 1. A method for molding a plastic casing for electromagnetic shielding, characterized in that the plastic casing is molded while embedding the inner molding tool and generating a magnetic field around the inner molding tool.