JPH043601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a conductive molding material that does not damage the screw, cylinder, mold, etc. of a molding machine during molding and has a large electromagnetic shielding effect.

[Technical background of the invention and its problems] In recent years, electronic circuits have been protected from external interference radio waves,
Furthermore, in order to prevent unnecessary radio waves generated from transmitting circuits and the like from leaking to the outside, it is required that the housings of electronic devices be made of electromagnetic shielding material. Examples of such electromagnetic shielding materials include metals and conductive synthetic resins. Although the former metals have excellent electromagnetic shielding effects, they have drawbacks such as being heavy, expensive, and have poor processability. The use of synthetic resins is becoming mainstream.

There are two methods for imparting conductivity to synthetic resins: After molding the synthetic resin, a conductive paint is applied, or metal is sprayed or plated to form a conductive layer on the surface. There is an internal addition method in which a conductive filler such as carbon or metal powder is added.

The former method of forming a conductive layer on the surface of a synthetic resin requires more steps and is not suitable for mass production, and also has the disadvantage that the conductive layer peels off after long-term use, so there are high expectations for the latter method of internal addition. It is being

However, the latter internal addition method also had the following problems.

In other words, it is easy to add conductivity to synthetic resin by mixing metal fibers into it, but it has the disadvantage that the cost of the metal fibers accounts for more than 80% of the cost of the conductive synthetic resin, making it less expensive. The use of metal has become essential. Therefore, inexpensive iron and iron-based alloys were considered, but when these were molded with conductive molding materials mixed with synthetic resin, the screws and cylinders of the injection molding machine were seriously damaged, and the shape of the mold was worn out. It has disadvantages that cannot withstand practical use, such as changes to

[Object of the invention] The present invention was made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a conductive molding material that does not damage the screw, cylinder, mold, etc. of a molding machine during molding and has a high electromagnetic shielding effect. It is an object.

[Summary of the Invention] As a result of extensive research to achieve the above-mentioned object, the present invention has discovered that the above-mentioned object can be achieved by using copper-coated metal fibers.

That is, the present invention is a conductive molding material for injection molding, characterized in that the conductive filler is a metal fiber of iron or iron-based alloy having a copper layer on the surface.

Examples of the synthetic resin used in the present invention include polystyrene resin, acrylonitrile-butadiene-styrene resin, polypropylene resin, polyphenylene oxide resin, and modified polyphenylene oxide resin.

Examples of iron or iron-based alloy metal fibers having a copper layer on the surface used in the present invention include iron fibers, Fe-Ni
Alloy fibers, Ni-Cr-Fe alloy fibers, etc. may be used as long as their surfaces are coated with a copper layer.

The method of coating the surface of these metal fibers with copper may be a method of stretching a copper tube over a roughly drawn metal rod, a method of electroplating copper, etc., and the method is not limited. When a synthetic resin is filled with metal fibers made of iron or iron-based alloys having a copper layer on the surface, preferably the fibers have a diameter of 50 to 200 μm and a length of 3 to 6 mm, which can provide a sufficient electromagnetic shielding effect.

[Embodiments of the invention] The present invention will be explained below with reference to Examples.

Example As shown in Fig. 1, copper 2 was electroplated on the surface of a long iron-Ni alloy fiber 1 with a diameter of 50 μm to a thickness of 50 μm.
Coated to 5 μm. This was cut into lengths of 5 mm, and 20 parts by weight of the cut pieces were thoroughly mixed with 80 parts by weight of ABS resin to obtain a conductive molding material. This molding material was molded using a conventional injection molding machine to obtain a molded product.

The electromagnetic shielding effect of molded products is 500MHz.
It was 40dB. After molding a large quantity, the cylinder, screw, and mold of the injection molding machine were inspected for damage, but no damage was found.

[Effects of the Invention] As explained above, the conductive molding material of the present invention does not damage injection molding machines or molds due to the use of iron or iron-based alloy fibers having a copper layer on the surface. We were able to obtain an inexpensive molding material with excellent electromagnetic shielding effect. Further, when using the conductive molding material of the present invention, there is an advantage that conventional equipment can be used as is.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conductive filler having a copper layer on its surface used in the present invention. 1...Metal fiber, 2...Copper layer.

Claims (1)

[Claims] 1. A conductive molding material for injection molding, characterized in that the conductive filler is a metal fiber of iron or iron-based alloy having a copper layer on the surface.