JPH06339921A - Conductive resin molded product - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the conductivity of a molded product even at high temp. by subjecting a conductive resin compsn. wherein a master pellet obtained by integrally applying and forming a thermoplastic resin layer to the surface of a conductive filler consisting of a copper fiber and a low m.p. metal is compounded with a thermoplastic resin pellet to injection molding at a temp. equal to or higher than the m.p. of the low m.p. metal. CONSTITUTION:A conductive resin compsn. wherein a master pellet obtained by integrally applying and forming a thermoplastic resin layer (C) (e.g; polypropylene resin) to the surface of a conductive filler consisting of a copper fiber (A) and a low m.p. metal (B) (e.g; tin) is compounded with a thermoplastic resin pellet (D) is subjected to injection molding at a temp. equal to or higher than the m.p. of the low m.p. metal. The obtained conductive resin molded product generates no separation and scattering of the low m.p. metal at the time of molding processing and does not lower in its conductivity even when a high temp. environmental change is applied and is excellent in the stability of electromagnetic wave shielding effect with the elapse of time. When the molded product is used in electronic machinery or communication machinery, extremely high reliability can be imparted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable conductive resin molded article having excellent conductivity, especially stability over time.

[0002]

2. Description of the Related Art Conventionally, a conductive resin is blended with a thermoplastic resin to form a conductive resin composition, which has been used as a material for a conductive resin molded article. Carbon-based conductive fibers have been mainly blended with these, but their use is mainly for the prevention of static electricity, and they have low conductivity and are not very effective for the electromagnetic wave shield which has become a problem in recent years. Therefore, for electromagnetic wave shielding, metal-based conductive fibers (hereinafter simply referred to as metal fibers) are used to improve conductivity.

However, when the metal fibers are blended, the specific gravity becomes large, and the original characteristics of the resin are greatly impaired, and it is required to minimize the blending amount. However, if the blending amount of these metal fibers is reduced, the conductivity is lowered, and further the use environment is greatly restricted. That is, due to the difference in thermal expansion between the resin used and the metal fiber, there arises a problem that the conductivity deteriorates at high temperatures. Therefore, at present, it has been put to practical use by increasing the blending amount of metal fibers to prevent the deterioration / deterioration of conductivity and limiting the use environment. As described above, the conventional conductive resin composition of metal fibers and molded products have the problems that their applications are restricted, their characteristics are unstable, and their reliability is low.

It is known that conductivity can be obtained by mixing a low melting point metal and a thermoplastic resin.
The low melting point metal has poor adhesion with the resin and separates from the resin to deteriorate the physical properties of the resin. Moreover, when the color of the material of the molding machine is changed, the resin and the low melting point metal are separated by blanking, etc. However, there is a problem in that it is extremely dangerous in the molding process, such as scatter.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and the conductivity of a molded product does not deteriorate even at high temperatures, and in particular, its stability with time is excellent, and during molding processing. Also in the above, there is a need to provide a highly reliable conductive resin molded product which is free from separation and scattering of a resin having a low melting point and has good moldability.

[0006]

Means for Solving the Problems As a result of intensive studies aimed at achieving the above-mentioned object, the present inventor has found that copper fibers as a conductive filler and a low melting point metal having a melting point higher than that of a thermoplastic resin are usually used. It was found that the combined use of and makes it possible to obtain a conductive resin molded product in which the conductivity of the molded product does not deteriorate even at high temperatures and the thermoplastic resin and the low melting point metal do not separate or scatter during molding. The present invention has been completed.

That is, according to the present invention, (C) is formed on the surface of a conductive filler composed of (A) copper fiber and (B) low melting point metal.
A conductive resin composition prepared by blending a pellet-shaped master pellet in which a thermoplastic resin layer is integrally formed by coating and (D) a thermoplastic resin pellet is injection-molded at a temperature equal to or higher than the melting point of a low-melting metal. Is a conductive resin molded product.

Examples of the copper fiber (A) used in the present invention include long fiber copper fibers, organic fibers having a copper layer, and carbon fibers. It is desirable that the diameter of the copper fiber is about 5 to 100 μm. The copper fiber is aggregated with a low melting point metal (B) to be described later to form a conductive filler, and then (C) a thermoplastic resin layer to form a coating. And cut it to a length of 5 to 8 mm to make a master pellet. The content of the copper fibers is preferably 0.5 to 30% by weight based on the whole conductive composition. If it is less than 0.5% by weight, the conductivity is low, and if it exceeds 30% by weight, the fluidity and physical properties of the composition are deteriorated, which is not preferable.

As the low melting point metal (B) used in the present invention, a general solder alloy containing Sn or Sn-Pb as a main component,
Examples thereof include a high temperature solder alloy containing Sn-Pb-Ag as a main component, and a low temperature solder alloy containing Sn-Pb-Bi as a main component. The low melting point metal may be fibrous, linear or rod-shaped, and is not particularly limited to the shape. The above-mentioned copper fiber is assembled with this low melting point metal,
The copper fiber and the fibrous low melting point metal may be simply aggregated, or the layer of the low melting point metal may be formed on the surface of the copper fiber.
The granular low melting point metal may be sized on the copper fiber, and the method of assembling the metal is not limited. Thus, a conductive filler made of copper fibers and a low melting point metal is prepared.
The melting point of these low melting point metals should be selected according to the molding processing temperature of the thermoplastic resin to be mixed, that is, it is desirable to have a melting point higher than the melting point of the thermoplastic resin, and such low melting point metals should be selected and used. Is. The content of the low melting point metal is preferably 5 to 30% by weight based on the copper fiber. If the content is less than 5% by weight, binding and coating of copper fibers will be insufficient, and if it exceeds 30% by weight, excessive low melting point metal will be liberated and the physical properties of the composition will be deteriorated, such being undesirable.

In the present invention, the (C) thermoplastic resin layer is formed by polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile butadiene styrene resin, modified polyphenylene oxide resin,
Examples thereof include polybutylene terephthalate resin, polycarbonate resin, polyamide resin, and polyetherimide resin. This thermoplastic resin coats the copper fibers and the low melting point metal.

The thermoplastic resin pellets (D) used in the present invention (hereinafter referred to as natural pellets) are the same as the above-mentioned (C).
It may be the same as or the same as the thermoplastic resin layer. Further, the third synthetic resin formed at the interface by being mixed with the thermoplastic resin layer (C) may have a reinforcing effect, that is, a blended polymer, for example,
(C) When using a modified PPO resin, a polycarbonate resin, or the like as the thermoplastic resin layer, good results can be obtained by using a styrene-based thermoplastic resin as the natural pellets. By doing so, the third synthetic resin formed on the interface has a reinforcing effect. By using these combinations, a molded article having excellent properties can be obtained.

The conductive resin molded article of the present invention can be usually manufactured as follows. Long fiber copper fiber,
A low melting point metal is aggregated to form a conductive filler, a thermoplastic resin layer is formed on the surface of the conductive filler through a die of an extruder, and then cut into an appropriate size to form a pellet, which is a master pellet. And The master pellet usually has a circular cross section, but the shape is not limited to a flat shape and may be any shape other than the circular shape. Further, although it is economically advantageous to carry out the manufacturing process of the master pellet continuously, the master pellet may not necessarily be manufactured continuously but may be manufactured by a batch method. This master pellet is blended with a natural pellet made of only a thermoplastic resin to prepare a conductive resin composition. For the natural pellets to be blended, the thermoplastic resin and the amount thereof are appropriately selected according to the properties required for the conductive resin composition and its molded product.

The conductive resin composition thus produced can be injection-molded at a temperature not lower than the melting point of the low melting point metal to obtain the conductive resin molded article of the present invention. The conductive resin molded product of the present invention is suitable for use in housings and parts of electronic devices, measuring devices, communication devices and the like that require electromagnetic wave shielding.

[0014]

According to the present invention, by using the copper fiber and the low melting point metal together as the conductive filler, the low melting point metal is fused at the joining point between the copper fibers to form a strong mesh-like bond. ,
As a result, the conductivity is not deteriorated. Therefore, it becomes possible to reduce the amount of copper fiber compounded, and the original characteristics of the resin are not impaired. Further, since a low melting point metal that melts depending on the molding processing temperature of the thermoplastic resin is selected and firmly fused with the copper fiber, there is no separation or scattering of the low melting point metal.

[0015]

EXAMPLES The present invention will now be described with reference to examples.

Example 300 300 copper fibers each having a diameter of 50 μm were converged, and the copper fibers were
300 μm fibrous low melting point metal (Sn 60%, Pb 40%)
Tufflex 4 by collecting and bundling them as a conductive filler
10 (Made by Mitsubishi Monsanto Kasei Co., ABS resin, trade name)
Was passed through a die of an extruder to melt-coat the surface of the conductive filler with ABS resin. This was cooled and cut into a length of 6 mm in the fiber direction with a pelletizer to obtain master pellets. Tough Rex 410 is added to this master pellet.
A conductive resin composition was produced by blending the natural pellets (described above). The filling rate of copper fiber in this case is 30% by weight
Met. Injection molding was performed using this conductive resin composition to obtain a molded product. The molded products were tested for volume resistivity and shielding effect. The results are shown in Table 1.
The extremely remarkable effect of the present invention was confirmed.

Comparative Example A master pellet, a conductive resin composition and a molded product were prepared in the same manner as in the Example except that the low melting point metal was not used, and the molded product was tested in the same manner as in the Example. The results are shown in Table 1.

[0018]

[Table 1]

[0019]

As is clear from the above description and Table 1, the conductive resin molded article of the present invention uses copper fibers and a low melting point metal together as the conductive filler to bond the copper fibers together. Becomes stronger, the amount of copper fiber compounded can be reduced,
In addition, there was no separation and scattering of the low melting point metal during the molding process, improving the moldability. Further, the molded article of the present invention, the conductivity does not decrease even when subjected to environmental changes at high temperatures,
The electromagnetic wave shielding effect is excellent in stability over time.
If this molded product is used in electronic devices, communication devices, etc., extremely high reliability can be imparted.

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Claims (1)

[Claims] 1. A pellet-shaped master pellet in which (C) a thermoplastic resin layer is coated and integrated on the surface of a conductive filler composed of (A) copper fibers and (B) a low melting point metal,
(D) A conductive resin molded article obtained by injection-molding a conductive resin composition containing a thermoplastic resin pellet at a temperature equal to or higher than the melting point of a low melting point metal.