JPS58127744A - Thermoplastic resin composition - Google Patents

Abstract

PURPOSE:To provide a resin compsn. useful as a shielding material against jamming wave radiated by digital electronic devices, consisting of a thermoplastic resin, a metallic flake and carbon black having a hollow shell particle structure. CONSTITUTION:A thermoplastic resin compsn. consists of 25-35wt% metallic flake 2 such as aluminum flake having a thickness of 0.1mm. or below and an area (larger surface) of 4mm.<2> or below, 1-4wt% carbon black 3 having a hollow shell particle structure such as ketjen black EC (a product of AKZO N.V.) and the balance of a thermoplastic resin 1 such as PVC, PS or ABS. This compsn. is useful as a shielding material against jamming wave radiated by digital electronic devices. The metallic flake 2 and carbon black 3 constitute horizontal and vertical directions of an electrically conductive network, respectively. The network can be formed by using smaller amounts of components 2, 3 than when they are individually used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shielding material that shields interference waves emitted by digital electronic devices.

With the rapid advancement of electronics technology represented by ICs and LSIs, computers, electronic games, video games, electronic cash registers, switching power supplies, and digital watches that use ICs and LSIs.

Digital electronic devices such as calculators and word processors became widely used.

Digital electronic devices operate at 10,000 speeds per second.
It generates more than a pulse, and radio frequency energy is emitted along with the pulse.

Therefore, when using such digital electronic devices, the radiated radio frequency energy may cause problems such as noise and image disturbance (so-called electromagnetic interference) on radios, televisions, and wireless devices.

In the future, digital electronic technology will be used in all industrial fields, including various manufacturing equipment, office equipment, household equipment, transportation equipment, etc.
It is expected that electromagnetic interference will spread into the daily life field, and that electromagnetic interference problems will occur frequently.

In order to prevent electromagnetic interference in such situations,
Digital electronic devices must be shielded from interference radio waves...
... Shielding ...... has become required, and the Cl5PRO standard (international standard), FCC standard (American standard), and VDE standard (West German standard) have been established.

Polystyrene, AB for housing of digital electronic equipment
S, polyamide, polycarbonate, polypropylene,
Thermoplastic plastics such as polyphenylene oxide and polyvinyl chloride are often used, but since plastics transmit electromagnetic waves in the interference radio wave range, shielding technology is absolutely necessary. The basic idea of giving 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 manpower, ■ It requires extra equipment, ■
Mass production is low and costs are high.

Regarding durability, when used for a long time, the adhesion between the plastic and the surface conductive layer 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 short circuits, causing malfunctions, electric shocks, and fires, resulting in poor reliability. .

In case (2), there is no peeling problem, but it is difficult to mix the conductive filler uniformly and to obtain a uniform molded product. This is because the water flow characteristics of plastic and filler are different, so it is necessary to increase the amount of conductive filler to improve shielding characteristics, but increasing the amount of filler worsens water flow.

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.

We have developed a method for providing shielding properties to plastic housings for digital electronic devices that is easy to process and that
As a result of various studies on the problems of highly reliable conductive filler addition methods, we found that by blending metal flakes and carbon black with a hollow shell particle structure in a certain ratio, the shielding properties will not deteriorate even if the amount added is small. I discovered this surprising phenomenon.

The reason why good shielding properties can be obtained even with a small amount when metal flakes and carbon black having a hollow shell particle structure are used in a certain ratio is considered to be related to the shapes of the two. In other words, whether the shielding property is high or low is related to the density of the conductive network, and when metal flakes and carbon black with a hollow shell particle structure are used together, as shown in Figure 1, both the horizontal and vertical directions of the conductive network. It is envisioned that a network can be formed more efficiently with a smaller amount than in the case of a single method.

Next, the present invention will be explained in detail using the drawings. Fig. 1 is a sectional view showing the structure of the thermoplastic resin composition according to the present invention, and 1 in the figure indicates the thermoplastic resin. Regarding the use of the thermoplastic resin, there is no particular restriction on the type of resin, but for example, polystyrene.

ABS, polyamide, polycarbonate, polypropylene, polyphenylene oxide, polyvinyl chloride, etc. are suitable for molding. In the figure, 2.3 is carbon black (hereinafter referred to as A carbon black 3) having a metal flake and hollow shell particle structure added to the thermoplastic resin 1, but the material of the metal flake 2 is aluminum, copper, nickel, zinc.

It is preferably a copper-zinc alloy with a thickness Q of 1 mm or less and a large surface area of 4 rust or less.

Regarding carbon black 3 having a hollow shell-like particle structure (hereinafter referred to as A carbon black 3), for example,
Kettin Black EC manufactured by Akzo Corporation is used, and its particles are hollow and therefore have a large surface area.

The amount of metal flakes 2 added is 25 to 35% by weight.

A carbon black ranges from 3.1 to 4% by weight. This is because Metal Flake 2 is more effective for shielding performance, but if it is less than 25% (capacity is omitted, the same applies hereafter), the desired shielding performance cannot be obtained, and if it is more than 35%. Although the shielding property is sufficient, the fluidity becomes poor and it is difficult to obtain a uniform molded product. Regarding A carbon black 3, its addition effect is recognized from 1%, but the addition effect almost reaches its upper limit at 4%.

When using metal flakes 2 alone, a minimum of 40% is required, and even in that case, in order to obtain a molded product in which metal flakes 2 are evenly distributed, the molding conditions such as the size and number of gates and the shape of the molded product must be adjusted. Needs consideration.

On the other hand, the present invention has the remarkable effect that not only can sufficient shielding performance be obtained with a smaller amount added than before, but also that the manufacturing conditions can be the same as when no conductive filler is added.

Metal flakes mentioned above2. The process of manufacturing a plastic housing that uses carbon black 3 to shield interference radio waves emitted from digital electronic devices is as follows:
1) Blend specified metal flakes and A carbon black 3 into plastic; 2) Knead with an extruder and process into extrusion pellets.

3) Make the desired product using an injection molding machine. The steps other than A carbon black 3 are the same as the conventional process.

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

Example I JSRABS 85 (ABS resin manufactured by Japan Synthetic Rubber Co., Ltd.)
68 parts by weight, 30 parts by weight of Transmet K-102 (aluminum flakes manufactured by Transmet), and 2 parts by weight of Ketchin Black EC (manufactured by Akzo) were put into a single-screw extruder, cross-wire extruded, and cut into pellets.

Next, use this pellet, 140 x 100 x
3M panels were manufactured by injection molding.

The surface of the obtained panel was smooth, and when the state of dispersion of flakes was examined using an X-ray transmission method, the dispersion was also good.

Next, the shielding characteristics were measured according to the methods of W, D, Na5on, etc. A box measuring 180 x 140 x 200 mm is made from a copper plate, and a transmitting antenna and a receiving antenna are installed at intervals of 120 mm. Connect the standard signal generator MG645B manufactured by Yasuri Electric Co., Ltd. to the transmitting antenna, and connect the spectrum analyzer MS62A manufactured by Yasuri Electric Co., Ltd. to the receiving antenna.
Connect. 0.5~1000L Continuously supply the old frequency signal to the transmitting antenna,
This intensity is measured with a spectrum analyzer.

A similar measurement was carried out by setting a panel to which the flakes prepared above and Kettin Black EC were added between the transmitting antenna and the receiving antenna. Shielding performance is expressed as the value obtained by subtracting the signal strength with a panel from the signal strength without a panel, and it ranges from 0.52 to 100. 40 which is almost constant in the frequency range of 'OMf[
dB (99.0% of the signal intensity is absorbed and reflected by the panel, and the signal intensity passing through the panel is 1%), indicating sufficient shielding performance.

Example 2 JSRABS 85 74 parts by weight, aluminum flakes
A product containing 25 parts by weight and 1 part by weight of Kettin Black EC was molded in the same manner as in Example 1, and the shielding effect was measured. The shielding effect was almost constant at 359-dB (98.22% of the signal intensity was absorbed and reflected by the panel, and 1.78% passed through the panel), which was at the lower limit of the shielding performance.

Example 3 JSRABS 35 61 parts by weight, aluminum flakes 3
Panels containing 5 parts by weight and 4 parts by weight of Ketjenblack EC were similarly molded and the shielding properties were measured. The shielding effect is approximately 50 dB (99.67% of the signal intensity is absorbed by the panel, reflected by the panel, and 0.33% of the signal intensity passes through the panel)
%), indicating a sufficient number of shields, but the smoothness slightly decreased, perhaps because the surface quality deteriorated in water flow.

Comparative Example I JSRABS 35 60 parts by weight, aluminum flakes 3
5 parts by weight, 5 parts of Ketjenblack EC, :.

Panels were formed in the same manner and the shielding properties were measured. The shielding effect was about 50 dB, and no difference was observed in d compared to the case of Example 3.

IO- Example 4 68 parts by weight of Noryl 781 J (polyphenylene oxide resin manufactured by Engineering Plastics), 30 parts by weight of aluminum flakes, and 2 parts by weight of Ketjen Black EC were mixed in an extruder and cross-extruded, and then pelletized.

Using this pellet, a panel was molded in the same manner as in Example 1, and the shielding properties were measured. Shielding effect is approximately 45dB
(99.44% of the signal intensity was absorbed and reflected by the panel, and 0.56% passed through the panel), indicating sufficient shielding properties, and there were no problems with surface properties.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a thermoplastic resin composition according to the present invention. l・・・・・・Thermoplastic resin 2・・・・・・
...Metal flake 8...A carbon black (carbon black having a hollow shell-like particle structure) Patent applicant Aron Kasei Co., Ltd. 11- Flute 11 Sword 300-

Claims (1)

[Claims] l A thermoplastic resin composition useful for shielding interference radio waves, comprising 25 to 35% by weight of metal flakes, 1 to 4% by weight of carbon black having a hollow shell particle structure, and the balance being a thermoplastic resin.