JPS58200599A - Electromagnetically shielded molded article - 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 thermoplastic resin molded article containing a conductive filler.

With the rapid development of electronics technology represented by IC and LSI, computers, electronic games, video games, electronic cash registers, and
Switching power supplies, digital clocks, calculators.

Digital electronic devices such as word processors have become widely used.

At the same time, plastic housings have come to be widely used as housings for digital electronic devices because they can be mass-produced, have excellent moldability and workability, and have good electrical insulation properties.

On the other hand, digital electronic devices generate to, ooo pulses and more than seven pulses every second, and these electromagnetic waves are radiated into space. Electromagnetic wave energy radiated from such digital electronic devices can cause problems such as noise and image disturbance (so-called electromagnetic interference) in radios, televisions, and wireless communication devices.

This is because plastic transmits electromagnetic waves in the interference radio wave range, and plastics used in the housings of digital electronic devices must be shielded from interference radio waves.
・Shield... is required. The basic method of providing shielding properties to plastic is to make it conductive by metallizing it.There are two methods: (1) forming a conductive layer on the surface of the plastic, and (2) forming a conductive layer inside the plastic. A method of adding fillers has been considered.

Specific methods for (1) include zinc spraying, conductive paint coating, vacuum deposition, sputtering, and plating.
Specific methods for 2) include addition of conductive fillers such as carbon black, metallized glass, metal ribbons, metal flakes, metal powder, and carbon fibers.

However, the following problems have been pointed out regarding (1) and (2).

First, in (1), after the conductive layer is molded from plastic, it is subjected to several types of surface treatments, and then thermal sprayed and sprayed.

It is formed by vapor deposition, sputtering, plating, etc., so it takes 0 hours, ■ It takes a lot of labor, ■ Extra equipment is required, ■
Mass production is low and costs are high. Regarding durability,
When used for a long time, the adhesion between the plasti glue and the surface conductivity deteriorates, eventually causing cracks and peeling.

If cracks or peeling occur, electromagnetic waves may be emitted from the location, or peeled pieces may fall onto the printed circuit board or internal wiring, causing damage, electric shock, or fire, and reducing reliability. Poor.

Although (2) has no peeling problem, it is difficult to mix the conductive filler uniformly and to obtain a uniform molded product. This is because the flow characteristics of plastic and filler are different.
This is because, although it is necessary to increase the amount of conductive filler in order to improve the shielding characteristics, increasing the amount of filler deteriorates the flowability. Therefore, when adding a conductive filler, it is absolutely necessary to devise a method that does not reduce the shielding properties even if the amount added is reduced.

As a method of providing shielding to the plastic housings of digital electronic devices, we investigated various problems with the method of adding conductive fillers, which is a simple and highly reliable method, and as a result, we developed a method that uses metal flakes as the main component. They discovered that by blending conductive fibers or carbon black with a hollow seal-like particle structure in a certain proportion, the shielding properties would not deteriorate even if the amount added was reduced, and they applied for a patent earlier.

However, in order to put this method into practical use, a box-shaped product was first formed, but a problem arose in that the filler was exposed on the surface near some corners, reducing the surface quality.

The reason why the filler is exposed near a part of the corner is that the flow direction changes by 90'' at the corner during molding, so it is thought that a part of the filler caused a stagnation phenomenon and was exposed on the surface.

On the other hand, regarding the desired shielding performance, good shielding performance was obtained across all frequencies even in the box shape.

In order to prevent the filler from being exposed in some corners, we investigated the molding conditions, but it was not possible to completely prevent the filler from being exposed.

Therefore, surface coating has become essential for the practical application of thermoplastic resin molded products blended with a conductive filler mainly composed of metal flakes to provide shielding properties.

In this case, normal painting will hide the exposed filler and
In order to obtain a beautiful painted surface, it is necessary to repeat the process of painting and drying 5 to 6 times, which is expensive and cannot be used.

As a result of considering various paints and painting methods with the goal of easy painting and beautiful appearance, we found that by making the painted surface have an uneven pattern, it is easy to paint and there is no effect of the filler exposed on the surface of the molded object, resulting in a beautiful appearance. It has been found that molded products can be obtained.

The paint to be used is preferably an acrylic paint (one-liquid type) or an acrylic urethane type (two-liquid type) in terms of performance such as weather resistance, hardness, and adhesion.

Also, in order to create an uneven pattern on the painted surface, the air pressure for spray painting should be increased from 2 to 5 kg/nA compared to the usual 4.5 to 5 kg/nA.
3/- to increase the size of the paint particles ejected from the soufflé nozzle so that they are applied in a bead shape.

In this case, if the first coat is a regular coat and the second coat is a textured pattern, the density of the bumps can be reduced, but if only one coat is applied, the filler on the surface of the molded product is hidden. Therefore, it is necessary to increase the density of the uneven pattern.

Next, the present invention will be explained in detail using the drawings. FIG. 1 is a sectional view showing the structure of the electromagnetic shield molded product according to the present invention, and 1 in the figure indicates a thermoplastic resin. Regarding the use of thermoplastic resin l, there are no particular restrictions on the type of resin, but for example, polystyrene.

ABS, polyamide, polycarbonate, polypropylene, polyphenylene oxide, polyvinyl chloride, etc. are suitable for molding. 2 in the figure is a metal flake added to the thermoplastic resin l, and the material is aluminum.

Copper, nickel, zinc, copper-zinc alloy, thickness 0.1
It is desirable that the area of the large surface is 1a+ or less and 4- or less.

3 in the figure is carbon black having a conductive fiber or hollow seal particle structure, which is also added to the thermoplastic resin 1. In the case of conductive fibers, the material is the same as flakes and carbon, with a diameter of 109 m and 100 μm and a length of l~
4fi microfibers are preferred.

An example of carbon black having a hollow shell particle structure is Ketjenblack EC manufactured by Axo.

The amount of metal flakes added is 25 to 35% by weight.

Contains 1 to 4% by weight of conductive fibers or carbon fiber having a hollow seal-like grain tongue structure, and 74 to 6% of thermoplastic resin.
It is 1% by weight. The amount of these conductive fillers added is smaller than that of conventional fillers, and as shown in FIG. 1, it is imagined that a conductive network can be efficiently formed with a small amount.

In the figure, numeral 4 indicates a coating film with an uneven pattern, which hides the conductive filler exposed on the surface of the molded product and makes the molded product aesthetically pleasing.

The molded product thus obtained has excellent electromagnetic shielding properties,
It is also aesthetically pleasing and satisfies all conditions for use as a housing for digital electronic devices.

Hereinafter, the present invention will be described in detail based on Examples.

Example 1 JSRABS 35 (ABS resin manufactured by Japan Synthetic Rubber Co., Ltd.)
68 parts by weight, 28 parts by weight of Transrret K-102 (aluminum flakes made by Transmet), aluminum fiber (diameter 20μ).

4 parts by weight (length 3fi) was applied to a single-screw extruder, cross-wire extruded, and then capped to pelletize.

Next, use this pellet to make 200x150x50 m+
1. A box with a wall thickness of 3 cm was manufactured by injection molding.

Aluminum flakes were exposed at some of the corners of the resulting box, and the appearance was poor.

Hiauto 1000 enamel (acrylic urethane paint) manufactured by Tanabe Chemical Co., Ltd. was prepared according to a standard recipe. Using a spray gun with nozzle diameter III+1, spray air pressure 5 to 6.
To? /- to coat the outer surface of the upper molded product uniformly at 55±5℃.
and dried for 10 minutes. Next, add 2 to 3 more air pressure on top of this.
Lowered the temperature to 9/- and painted using the same paint at 55±5℃.
It was dried for 20 minutes.

The obtained coated product had an uneven appearance, and the flakes on the surface of the molded product were completely hidden, giving it a beautiful appearance.

Furthermore, the electromagnetic wave shielding effect of this molded product was excellent and equivalent to that of a molded product that was not coated.

Example 2 65 parts by weight of Noryl 731J (polyfunylene oxide resin manufactured by Engineering Plastics Co., Ltd.).

32 parts by weight of aluminum flakes, Ketjen Black EC3
Parts by weight were mixed in an extruder and extruded into pellets.

Using this pellet, 200X$5 was prepared in the same manner as in Example 1.
A box with a wall thickness of 0x50 mm and 3 mm was manufactured by injection molding, but aluminum flakes were exposed at some corners of the box, and the appearance was poor.

Tanabe Chemical Co., Ltd. 0R-900 enamel (acrylic paint)
was prepared according to standard recipes. Using a spray gun with a nozzle diameter of 1.2 mm, paint the outer surface of the upper molded product at a spraying air pressure of 2 to 3 kp/- without leaving any unpainted areas at 50±5℃.
and dried for 20 minutes.

The obtained coated product had an uneven appearance, and the flakes on the surface of the molded product were completely hidden, giving it a beautiful appearance.

Further, the electromagnetic wave shielding effect of this molded product was also good.

Comparative Example 1 Molding, painting, and drying were carried out in the same manner as in Example 1, except that the air pressure for the second coating was changed to 5 to 6 and 9/i (same as the first coating). The resulting coated product had an unsightly appearance because it could not completely hide the flakes on the surface of the molded product.

In order to completely hide the flakes on the molded surface using this method, it was necessary to repeat the coating three more times.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an electromagnetic shield molded product according to the present invention. The plate is easily rounded at 5° when shaped into a hemline ■...Thermoplastic resin 2...Metal flakes 3...Carbon bra having a conductive fiber or hollow seal-like particle structure 4...・Patent applicant for a coating film with an uneven pattern (Aron Kasei Co., Ltd.) ^ No.L District Co procedural amendment (spontaneous) September 27, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi, -11, Indication of the case 1988 Patent application No. 084518 No. 8, Relationship with the person making the amendment Patent applicant address 1-14-1 Nishi-Shinbashi, Minato-ku, Tokyo Name (0
50) Aron Kasei Co., Ltd. Representative Katsuta Eguchi 4, Agent 5, Date of amendment order 6, Number of inventions increased by amendment 7, Subject of amendment Claims column 8 of the specification, Contents of the amendment As shown in the attached sheet, the scope of claims in Attachment 8, Description of the contents of the amendment, is amended as follows. 2. Claims Conductive filler 26-39% by weight, thermoplastic resin 74-39% by weight
An electromagnetic shielding molded product with an uneven pattern coating formed on the surface of the molded product made of 61% by weight.

Claims (1)

[Claims] Conductive wire filler 26~39% by weight, thermoplastic resin 74~
An electromagnetic shield molded product having a painted surface with an uneven pattern on the surface of the molded product made of 61% by weight.