JPS608014A - plastic molding materials - 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 molding material used as a material for plastic molded articles containing a conductive filler.

Examples include computers using ICs and LSIs, electronic or video game devices, electronic cash registers, switching power supplies, digital clocks, and calculators.

Digital electronic devices such as word processors are rapidly becoming popular these days, but such electronic devices typically operate at speeds of 1 per second.
Pulse signals of 0.000 pulses or more are generated, and electromagnetic waves based on such pulse signals are emitted from digital electronic devices, which may cause electromagnetic interference to radios, televisions, wireless communication devices, etc. The problem of electromagnetic interference becomes particularly important when plastic housings are used, and in order to prevent electromagnetic interference, it is necessary to provide electromagnetic wave breakability to the housings of digital electronic devices, radios, televisions, wireless communication equipment, etc. It is hoped that

Conventionally, in order to impart electromagnetic wave shielding properties to plastic housings, it has been considered to mix plastic with a fibrous conductive filler and injection mold it.

However, in order to impart high electromagnetic wave shielding properties to a plastic housing, it is necessary to distribute the conductive filler in an arm-shaped manner in a plane perpendicular to the direction of propagation of electromagnetic waves.

Therefore, when selecting a conductive filler, it is desirable to use the aforementioned fibrous or flake-like material with a large surface area so that a conductive filler layer can be formed efficiently.

Even if a conductive filler with a large surface area and therefore a high addition efficiency is selected, the conductive filler undergoes a shape change during processing and becomes powder, reducing the surface area and reducing the addition efficiency. Processing stages in which the shape of the conductive filler may change include the pounding stage, in which the conductive filler is mixed with plastic to form a tape-shaped molding material, and the injection molding stage. However, the possibility of shape change during the compound processing stage is greater. This process involves uniformly mixing a non-flowing conductive filler into a plastic that has been heated to a highly viscous fluid state, and then pressing it under high pressure through a die attached to the tip of an extruder in order to make a pellet-shaped molding material. This is because it is released.

As this unavoidable change in the shape of the conductive filler during processing, there is a method of increasing the amount of conductive filler blended, but as the proportion of plastic decreases, the fluidity of the compound deteriorates, making it difficult to mold. A problem arises above.

Moreover, even if a molded product is somehow obtained by manipulating various conditions, it cannot maintain the physical properties of a plastic product and becomes extremely brittle. Therefore, increasing the amount of conductive filler blended is not a solution.

In order to solve the problem of the conventional gap, the inventors of the present invention conducted intensive studies on a method to minimize the change in the shape of the conductive filler during the compound processing stage. We have found that it is effective to do the above.

The invention will be explained in detail below.

The conductive filler used in the present invention is made of metals such as stainless steel, aluminum, brass, and magnesium, and carbon, and has a shape with a thickness of 0.
．． A flake-like material with a surface area of 4 dpI or less and/or a fibrous material with a diameter of 10 to 100 μm and a diameter of 1 to 4 μm is used. This is thought to be due to the fact that if a die with a pellet shape smaller than 3.5*M is used, strong pressure is applied at the hole in the die during extrusion, causing the shape to change. This means that if the diameter of the pellet is 8.5 f1 or more, it is possible to stably extrude a pellet containing conductive filler for a long time, but if the diameter of the pellet is smaller than 3.5 mm, it is possible to extrude the pellet with a conductive filler stably for a long time. This is also supported by the fact that the holes are easily clogged, making it impossible to extrude for a long time.

It is therefore very desirable to increase Vt's ff1i beyond 8.5wg in order to prevent changes in the shape of the conductive filler, but if it becomes too large, heat transfer at the material input section will occur when molding with an injection molding machine. decreases, and plasticization is delayed, resulting in changes in the shape of the conductive filler during the plasticization process. For these reasons, the upper limit of the diameter of the pellet is set to 7 Wys. The length of the pellet is not particularly limited from the viewpoint of electromagnetic wave shielding properties and formability, but from the viewpoint of handling, it is preferably 20 mm or less.

The thermoplastic plastic used in the present invention and 17 are polyvinyl chloride, polypropylene, polyethylene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, and acrylonitrile-butadiene-styrene copolymer.

Examples include polystyrene, polymethacrylate, polyamide, polyphenylene oxide, and polycarbonate.

Thermoplastics have strength, rigidity, and heat resistance.

Selected as appropriate depending on required characteristics such as chemical resistance.

Additives such as colorants, flame retardants, stabilizers, etc. are also used.

These thermoplastic plastics and the above-mentioned conductive filler are generally used in a volume ratio of 90:10 to 75:25. If the amount of the conductive filler is less than 10%, the demagnetization wave and water resistance will be poor, and if the amount is more than 25%, the physical properties as a plastic or wood product cannot be maintained.

In order to mold the plastic molding material of the present invention into a pellet shape, use the above-mentioned thermoplastic.

Add various additives and conductive fillers to an extruder.

Conventionally, when extruding thermoplastics, it is common to input all molding materials such as thermoplastic filler, colorant, PR fuel, and stabilizer into one hopper of the extrusion machine. I fell. However, the material of conductive fillers is carbon or fibers, and the shape changes when the screw is stirred in the extruder.If the shape change is significant, the conductivity of the powder The situation will be similar to that when mixed materials are mixed, resulting in poor addition efficiency.

For this purpose, it is desirable to install two hoppers in the extrusion molding machine in parallel in the axial direction, and to introduce the conductive material from the hopper on the die side, thereby reducing the influence of the screw spacing.

If the molding method using an extrusion molding machine described in H is applied, the diameter of the plastic molded ion material can be set in the range of hn<g, 5 to 7 as described above, and the shape change of the conductive filler will be minimized, resulting in extremely good electromagnetic wave shielding. A molded article with properties is obtained.

-H Molding method will be explained in more detail based on the example shown in FIG.
) Adjust the temperature of the heaters (4) provided around each part of the cylinder (1) so that the material temperature measured at 197 to 203°C.

A die (2) was added while kneading under the above conditions, and the diameter and electromagnetic wave shielding properties of the resulting pellets were examined. The length of the beret is 5 mm, and the obtained beret is used to make it 130X13QX.
It was molded into a 4-furnace plate in 9.1 m and the electromagnetic wave fringing property was measured by the transmission line method. Table 1 shows the relationship between the diameter of the pellet and the electromagnetic wave shielding properties.

Table 1 The electromagnetic wave shielding property (dB) is expressed by the following formula.

Ei: Incident electric field strength (V/m2) Et: Electric field strength after transmission (V/m2) The larger the dB value, the better the blocking property [g#].

From this t* result, it is clear that a suitable diameter of the pellet is 3.5 to 7y.

Examples for specifically explaining the present invention will be described below.

Example 1 Using the extrusion molding machine shown in FIG. 1, a thermoplastic plastic mixed with a conductive filler was extruded at L7, and the relationship between the diameter of the pellet and the electromagnetic wave shielding property was investigated. In FIG. 1, a die (2) with a predetermined opening shape is attached to the tip of a cylinder (1), and a screw (3) is inserted inside the cylinder (]). Cylinder (1)
A heater (4) is provided around the molding material, and an insertion hole (5) for inserting a thermocouple and a gas vent hole (6) for removing gas generated from the molding material (F) are provided. Historically, two hoppers (7) and (8) are arranged in parallel in the cylinder (1) in the extrusion direction, that is, in the axial direction.

65 parts by weight of ABS 0-85 (acrylonitrile-butadiene-styrene copolymer manufactured by Nihon Gosei Rubber Co., Ltd.) was fed at a constant rate from the hopper (7) in the previous stage.

Next, from the latter hopper (8) to the transmitter
2HE () Aluminum flakes manufactured by Lancemet)
35 parts by weight of ABS 0-85 Transmit KIQ2i (Ei7) extrusion molded product with a mixing ratio of 63 to 63 parts by weight
67: Supply so that it becomes 87-33. In this case, the transmitter was supplied with 1102 HE preheated to 70°C.

This is to prevent ABS 0-35, which has been softened in the cylinder, from being cooled by the addition of Transmeth) K-102HE, resulting in a decrease in fluidity and a deterioration in kneading efficiency.

Example 2 In the same manner as Fabric Example 1, 55 parts by weight of Zylon 201V (modified polyphenylene ether resin manufactured by Asahi Kasei Corporation) was taken from the hopper (7) in the front stage, and brass/fiber (diameter 50μ, The relationship between the diameter of the beret and the electromagnetic wave shielding properties was investigated by supplying the 45-layered part (length 2 mm') so that the mixture was almost constant. During extrusion processing,
The brass fiber is heated to 80°C and the screw rotation speed]
00RPM.

1. Set the material temperature to 240-250°C. Ta. The relationship between the diameter of the obtained pellet and the electromagnetic wave shielding properties is shown in Table 2.

Table 2

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an extrusion molding machine for carrying out an embodiment of the present invention. In the figure, (1)...Cylinder, (2)...Die, (3)...Screw, (4)...Heater, (
5)... Thermocouple insertion hole, (6)... Gas vent hole, (7)... Pre-stage hopper, (8)...
・Late stage hopper, (9)... Thermoplastic plastic and various additives, 00... Conductive filler patent applicant Aron Kasei Co., Ltd.

Claims (1)

[Claims] It is made of conductive filler and thermoplastic and has a diameter of 3.
Plastirif molding material characterized by being in the shape of a 5-7 MM pellet