JPH0763971B2 - Conductive resin molding - Google Patents

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, and the composition has been used 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 are used to improve conductivity.

However, when a metal-based conductive fiber (hereinafter simply referred to as a metal fiber) is blended, there is a problem that the specific gravity becomes large and the original characteristics of the resin are greatly impaired.
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 fiber and its molded product have the problems that their applications are restricted, their characteristics are unstable, and their reliability is low.

On the other hand, a method of blending a low melting point metal with a thermoplastic resin is known. However, the low melting point metal has poor adhesion to the resin, and the low melting point metal does not adhere to the resin due to blanking when changing colors. There is a problem in that it is extremely dangerous in the molding process such as separation from the melting point metal and scattering of only the metal. Further, it is also known to use a metal fiber and a low melting point metal together, but the metal fiber causes an oxide film on its surface due to drying before molding,
There has been a problem that the wettability of the metal fiber is deteriorated and, as a result, the conductivity is greatly deteriorated.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and the conductive fiber has good wettability and is firmly bonded to a low melting point metal to deteriorate the conductivity at high temperature. It is an object of the present invention to provide a conductive resin molded product which is free from the problems, has excellent stability over time, is safe in molding, and has high reliability.

[0006]

Means for Solving the Problems As a result of intensive studies aimed at achieving the above object, the present inventor has found that a conductive filler, a low melting point metal and a flux are used in combination as a conductive filler. The inventors have completed the present invention by discovering that the conductivity is not deteriorated even by the change with time at high temperature and the moldability is excellent. That is, the present invention provides a pellet-shaped master in which (D) a thermoplastic resin layer is formed on the surface of a conductive filler composed of (A) conductive fibers, (B) low melting point metal, and (C) flux. A conductive resin molded article, which is obtained by injection-molding a conductive resin composition in which pellets and (E) thermoplastic resin pellets are mixed, at a temperature equal to or higher than the melting point of the thermoplastic resin.

As the conductive fiber (A) used in the present invention, metal fibers such as long fiber copper fiber, stainless fiber, brass fiber, aluminum fiber and nickel fiber, and metal layer such as copper, aluminum and nickel on the surface Examples of the organic fiber include an inorganic fiber and an inorganic fiber. The diameter of the electrically conductive fiber is preferably about 5 to 100 μm, and the electrically conductive filler is assembled with the low melting point metal (B) described later to form a conductive filler, and the surface is coated with a thermoplastic resin to form an integral body. ~
Cut into 8 mm to make master pellets. It is desirable that the conductive fiber is blended in an amount of 0.5 to 30% by weight based on the total composition. If the content is less than 0.5% by weight, the electroconductivity is low, and if it exceeds 30% by weight, the fluidity and other properties of the electroconductive resin composition are deteriorated, which is not preferable.

Examples of the (C) flux used in the present invention include commonly used organic acid-based stearic acid, lactic acid, oleic acid, glutamic acid, resin-based rosin, active rosin and the like. Halogen-based flux is not preferable because it easily corrodes the conductive fiber or the mold. The amount of flux mixed is 0.1 with respect to the low melting point metal described later.
It is desirable to mix it up to 5% by weight. If it is less than 0.1% by weight, it has no effect on improving the wettability, and if it exceeds 5% by weight,
It is not preferable because it may cause deterioration of physical properties of the molded product, corrosion of the mold, stains and the like. The flux is usually used by being contained in a low melting point metal to improve the wettability of the conductive fiber and strengthen the bond between the low melting point metal and the conductive fiber.

The low melting point metal (B) used in the present invention is selected according to the molding processing temperature of the thermoplastic resin used here, and preferably has a melting point slightly higher than that of the thermoplastic resin. The low melting point metal is Sn or Sn-P.
Examples thereof include b-based general solder, Sn-Pb-Ag-Zn-based high temperature solder, Sn-Pb-Bi-based low temperature solder, and the like. These may be fibrous, granular, rod-shaped, or linear and are not particularly limited to that shape. The compounding amount of the low melting point metal is sufficient to bond and coat the conductive fibers, and it is desirable to mix it in an amount of 5 to 30% by weight based on the conductive fibers. If it is less than 5% by weight, it is not preferable to bond and coat the conductive fibers, and the conductivity is low, which is not preferable. On the other hand, if it exceeds 30% by weight, the low melting point metal is liberated and the physical properties of the resin are deteriorated, which is not preferable. The low-melting-point metal may be converged into long-fiber-shaped conductive fibers, each conductive fiber may be coated with a molten low-melting-point metal, or the whole conductive fibers may be coated with the low-melting-point metal. It is important that the conductive fiber and the low melting point metal are integrated. These are used as the conductive filler.

Examples of the thermoplastic resin (D) used in the present invention include polypropylene resin, polyethylene resin, polystyrene resin, acrylonitrile-butadiene-styrene resin, modified polyphenylene oxide resin, polybutylene terephthalate resin, polycarbonate resin and the like. These thermoplastic resins coat the surface of a conductive filler in which conductive fibers and a low melting point metal are aggregated, and are cut into master pellets.

The (E) thermoplastic resin pellets (hereinafter referred to as "natural pellets") used in the present invention may be the same as or the same as the (D) thermoplastic resin. Further, the third synthetic resin formed on the interface by mixing with the thermoplastic resin of the master pellet may have a reinforcing effect, that is, a blended polymer. For example,
When a modified PPO resin, a polycarbonate resin or the like is used as the thermoplastic resin of the master pellet, good results can be obtained by using a styrene-based thermoplastic resin as the natural pellet. By doing so, the third synthetic resin formed on the interface has a reinforcing effect. By using such a combination, it becomes possible to obtain a molded product having more excellent characteristics.

The conductive resin molded article of the present invention is usually manufactured as follows. A long-fiber-shaped conductive fiber and a low-melting-point metal containing flux are aggregated to form a conductive filler,
Extruded through a die of an extruder with a thermoplastic resin,
A thermoplastic resin layer is coated on the surface of the conductive filler, and then cut into an appropriate size to be pelletized to obtain a master pellet. The master pellet usually has a circular cross section, but may have a flat shape or another shape, and is not particularly limited in shape. 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 in a batch system. This master pellet is blended with a natural pellet made of only a thermoplastic resin to produce a conductive resin composition. For the natural pellets to be blended, the thermoplastic resin and its amount are appropriately selected according to the properties required for the conductive resin composition and its molded product. The conductive resin composition thus produced is injection-molded at a temperature equal to or higher than the melting point of the thermoplastic resin, and an electronic device, a measuring device, which requires an electromagnetic wave shield,
It can be used as a molded article of a housing or parts of communication equipment and the like.

[0013]

According to the present invention, it has been found that an excellent effect can be obtained by using the conductive fiber, the low melting point metal and the flux in combination as the conductive filler.

That is, the conductive fibers in the conductive resin composition are formed at the time of manufacturing or drying by the reducing action of the flux when dispersed and kneaded with the thermoplastic resin in the heating cylinder of the injection molding machine. The oxide film is removed and cleaned, and good wettability is imparted. Then, in the high temperature portion in the cylinder, the molten low melting point metal firmly covers the surface of the conductive fiber. When this is poured into a mold, and cooled and solidified, the low melting point metal is fused at the joining point of the conductive fibers to form a mesh state, which is cooled and solidified. Since the conductive fibers are fusion-bonded to each other by the low-melting metal without separating the bonding points, the conductivity is not deteriorated even in a high temperature environment. This means that when the resin component of the molded product is dissolved with a solvent, the mesh state between the conductive fibers and the conductive fibers can be clearly confirmed. As in the prior art, if the oxide film of the conductive fiber is insufficiently removed, or if the wettability is poor, the corrosion of the conductive fiber or the low melting point metal is liberated and the physical properties of the resin are deteriorated, which is not preferable. is there.

[0015]

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

Example 300 300 copper fibers having a diameter of 50 μm were converged, and a low melting point metal (Sn 60%, Pb 40) containing a rosin (5% by weight) having a diameter of 300 μm.
%) To form a conductive filler,
No. 0 (manufactured by Mitsubishi Monsanto Kasei Co., Ltd., ABS resin, trade name) was used to melt-coat the surface of the conductive filler with the Toflex 410 through a die of an extruder. This was cooled and cut into a length of 6 mm in the fiber direction with a pelletizer to obtain master pellets. Tough Rex 4 on this master pellet
Ten natural pellets were blended to produce a conductive resin composition. The filling rate of the copper fibers in this case was 20% by weight. Injection molding was performed using this conductive resin composition to obtain a molded product. The obtained molded product was tested for volume resistivity and electromagnetic wave shielding effect. The results are shown in Table 1. The extremely remarkable effects of the present invention were confirmed.

Comparative Example A master pellet, a conductive resin composition and a molded article were prepared in the same manner as in the Example except that the flux was removed, and the molded article 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 resin composition used in the conductive resin molded article of the present invention contains conductive fibers and a low melting point metal in combination and a flux. As a result, the bonding between the conductive fibers was strengthened, and the filling amount of the conductive fibers could be reduced, and the molding processability was improved without separation or scattering of the thermoplastic resin and the low melting point metal during the molding process. And the molded article of the present invention using this resin composition, the conductivity is not deteriorated due to environmental changes at high temperatures, and the electromagnetic wave shielding effect is excellent in stability over time, and the thermoplastic resin retains its original physical properties. It has become possible. If this molded product is used in electronic equipment, communication equipment, measuring equipment, etc., extremely high reliability can be imparted.

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Claims (1)

[Claims] 1. A pellet-shaped master pellet in which (D) a thermoplastic resin layer is integrally formed by coating on the surface of a conductive filler composed of (A) conductive fiber, (B) low melting point metal and (C) flux. And (E) a thermoplastic resin pellet are mixed, and the conductive resin composition is injection-molded at a temperature equal to or higher than the melting point of the thermoplastic resin.