JPH06128494A - Production of electrically conductive resin composition - Google Patents

Abstract

PURPOSE:To obtain a resin composition, excellent in stability with time and electric conductivity and having high reliability by coating an electrically conductive filler composed of electrically conductive fiber having a low-melting metallic layer on the surface with a thermoplastic resin containing a low-melting metal for forming intersection points, mixed and dispersed therein. CONSTITUTION:The electrically conductive resin composition is produced by bundling 300 electrically conductive fibers formed by electroplating, etc., the surface with a low-melting metallic layer such as an Sn-Pb alloy having 1mum thickness thereon (e.g. copper fiber), providing an electrically conductive filler and then coating the resultant filler with (B) a thermoplastic resin (e.g. a polyphenylene oxide resin). In the process, the thermoplastic resin of the component (B) containing (C) a low-melting metal (e.g. a powdery Sn-Pb alloy) for forming intersection points, mixed and dispersed therein is passed through a die of an extruder to melt coat the surface of the electrically conductive filler of the component (A), then cooled and cut to 6mm length in the fiber direction with a pelletizer. This resin composition is excellent in electric conductivity and stability with time and has high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a highly reliable conductive resin composition, which gives a molded article conductivity which is excellent in stability over time especially at high temperatures.

[0002]

2. Description of the Related Art A conductive resin composition is basically obtained by blending a conductive resin with a thermoplastic resin, and is molded to be used as a conductive resin molded product. Among these conductive resin compositions, a thermoplastic resin, a mixture of metal-based conductive fibers, a low melting point metal, and a phosphorus-based antioxidant, first, in the plasticizing cylinder of the injection molding machine , The oxide film of the conductive fibers formed during the manufacturing process or drying is removed by the reducing action of the phosphorus-based antioxidant to enhance solder wettability, and the conductive fibers are coated with the low melting point metal melted in the cylinder, Next, when it is poured into the mold and cooled, the low melting point metal fuses in a mesh state at the joining point of the conductive fibers and cools and solidifies as it is, so the finished molded product is placed in a high temperature environment Even if there is swelling, the joint point between the conductive fibers does not separate and the conductivity does not deteriorate. Therefore, it is widely used as an electromagnetic wave shield case for office automation equipment and the like.

Conventionally, the production of an electrically conductive resin composition containing such a low melting point metal is performed by combining a long fiber-like conductive fiber and a long fiber-like low melting point metal together and passing them through a die of an extruder to obtain the surface thereof. A thermoplastic resin layer containing a phosphorus-based antioxidant is continuously coated to form a master pellet in the form of pellets by cutting into an appropriate size, and the master pellet is provided with a conductive resin composition or a molded article thereof. It is manufactured by the method of adding natural pellets according to the properties required for.

However, when a resin, such as a modified polyphenylene ether resin or a polycarbonate resin, which has a high softening point or melting point and whose oxidative degradation is significantly promoted by the filling of metal fibers, is used as a conductive resin, the temperature of the die is reduced. Since it must be adjusted to the softening point or melting point of the thermoplastic resin, its temperature is higher than the melting point of the low melting point metal, and long fibrous low melting point metal is cut at the die part, so the low melting point metal must be added. I can't. Also,
When a heavy metal deactivator is used to prevent the catalytic action of the metal fiber, a metal complex compound is formed on the metal fiber surface,
Since the solder wettability of the metal fiber is significantly reduced, there is a drawback that the conductive fiber is not covered with the low melting point metal in the cylinder and is not fused at the joining point. As a countermeasure for this, a method of coating the conductive fiber with a low-melting point metal in advance is used, but as a method of coating the conductive fiber with a low-melting point metal, workability is excellent and dispersion of the conductive fiber at the time of molding is performed. In the best and best electroplating method, it is not possible to plate a sufficient amount for intersection fusion with only the low melting point metal to be coated, and it is necessary to newly add a low melting point metal for forming the intersection. The method of addition was a problem.

[0005]

The present invention has been made in order to solve and solve the above-mentioned drawbacks and problems. It has a high softening point or melting point, and oxidative degradation decomposition is significantly promoted by the filling of metal fibers. Even when using a thermoplastic resin
An attempt is to provide a method for producing a highly reliable conductive resin composition in which conductive fibers are firmly bonded to each other by a low-melting metal, the conductivity of a molded product does not deteriorate even at high temperatures, and stability over time is excellent. To do.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies aimed at achieving the above object, the present inventors have found that a low melting point metal is required in a thermoplastic resin coating a conductive filler. It was found that the above object can be achieved by mixing and dispersing a heavy metal deactivator, and the present invention has been completed.

That is, the present invention provides (A) a conductive filler comprising a conductive fiber having a low melting point metal layer on the surface thereof, (B)
In producing a conductive resin composition coated with a thermoplastic resin, 0.5 to 15% by weight of (C) a low melting point metal for forming an intersection is mixed and dispersed in the conductive fiber (B) with a thermoplastic resin. A method for producing a conductive resin composition, which comprises coating.

The present invention will be described in detail below.

The conductive filler (A) used in the present invention comprises a conductive fiber having a low melting point metal layer on its surface. As the conductive fibers, copper fibers, stainless fibers, brass fibers, aluminum fibers, long fiber metal fibers such as nickel fibers, copper, aluminum, organic fibers having a metal layer such as nickel on the surface, carbon fibers and the like. Used. The low melting point metal layer on the surface is electroplated, chemical plated,
Examples include those coated by a method such as melt dipping. The low melting point metal used here is a general solder alloy containing Sn or Sn-Pb as a main component, a high-temperature solder alloy containing Sn-Pb-Ag as a main component, and a low-temperature metal containing Sn-Pb-Bi as a main component. Examples include solder alloys.

Examples of the thermoplastic resin (B) used in the present invention include modified polyphenylene ether resin, polybutylene terephthalate resin, polycarbonate resin, polyamide resin, polyphenylene sulfide resin, and the like.
These can be used alone or in combination. These are thermoplastic resins having a softening point or melting point higher than that of the low-melting point metal and easily oxidatively deteriorated and decomposed by filling the metal fiber.

As the low melting point metal (C) for forming an intersection used in the present invention, a general solder alloy containing Sn or Sn-Pb as a main component, a high temperature solder alloy containing Sn-Pb-Ag as a main component, and further Sn. A low-temperature solder alloy containing -Pb-Bi as a main component may be used, and it may have the same component as the low melting point metal coating the conductive fibers, or may have a different component.

The low melting point metal for forming the intersection is kneaded into the thermoplastic resin for coating the conductive filler even if it is kneaded in advance in the thermoplastic resin for coating the conductive filler. However, in any case, it is desirable to adjust the resin temperature so that the melt viscosity of the thermoplastic resin when kneading is about 10 ³ to 10 ⁴ poise. If the melt viscosity is less than 10 ³ poise, it will be difficult to make pellets unless the rotation speed of the extruder is increased, and if it exceeds 10 ⁴ poise, the low melting point metal will agglomerate due to the viscosity difference between the low melting point metal and the molten resin. It is not preferable because it is difficult to obtain a uniform dispersion. The mixing ratio of the low melting point metal for forming the intersection is based on the conductive fiber.
It is desirable to contain 0.5 to 15% by weight. If the content is less than 0.5% by weight, it will be insufficient to bond and coat the conductive fibers, and if it exceeds 15% by weight, the low melting point metal will be liberated and the physical properties of the resin will be deteriorated, such being undesirable.

[0013]

According to the method for producing a conductive resin composition of the present invention, by using a conductive filler previously coated with a low melting point metal layer, continuous thermoplastic resin coating is performed with a die having a high temperature. be able to. In addition, by kneading a predetermined amount of the low melting point metal for forming the intersection in the thermoplastic resin that coats the conductive filler, a sufficient amount of the low melting point metal for binding and coating the conductive fibers is obtained, and the heavy metal The conductive fibers could be firmly fused and bonded without lowering the solder wettability due to the addition of the deactivator.

[0014]

EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

EXAMPLE 300 copper fibers having a diameter of 50 μm coated with 1 μm of Sn—Pb alloy on the surface by electroplating were bundled to form a conductive filler, and a modified PPO resin, Zylon 220Z (trade name, manufactured by Asahi Kasei Co., Ltd.). Powder Sn-Pb alloy is added to and the Zylon 22 is applied to the surface of the conductive filler through the die of the extruder.
0Z (all out) was melt coated. This was cooled and cut into a length of 6 mm in the fiber direction with a pelletizer to obtain master pellets. The master pellets had a copper fiber loading of 50% by weight and a Sn-Pb alloy loading of 5% by weight. The master pellets were blended with Zylon 220Z (previously described) natural pellets to produce a conductive resin composition.
The composition had a copper fiber loading of 25% by weight and a Sn-Pb alloy loading of 2.5% by weight.

Comparative Example A master pellet and a conductive resin composition were produced in the same manner as in Example except that the powder Sn—Pb alloy was not added.

A molded product was made using the conductive resin compositions produced in the examples and comparative examples, and the molded product was cut to examine the bonding state of the conductive fibers inside the molded product. The cut surface was taken as an electron micrograph, so Reference Photo 1 (Example)
Also, a reference photograph 2 (comparative example) is attached. In the embodiment of the present invention, the surface of the conductive fiber (the halftone portion of the photograph) is thinly coated with the low melting point metal layer (the light shaded portion of the photograph), and the surface of the conductive fiber (the halftone portion of the photograph) is Is firmly fused and bonded by the low melting point metal for forming intersections (bright part in the photo), but in the comparative example, the low melting point metal layer (bright part in the photo) on the surface of the conductive fiber (halftone part in the photo) is used. Although the toned part is formed, the low melting point metal for forming the intersection (bright part) does not exist between the conductive fibers (the intermediate part in the photograph), and the conductive fibers are bonded to each other. I know there isn't. The dark tone portion in the photograph is a thermoplastic resin.

The molded products of Examples and Comparative Examples are as follows.
The initial value of the volume resistivity and the volume resistivity after the lapse of 3000 hours at 80 ° C. were measured and are shown in Table 1.

[0019]

[Table 1]

[0020]

As is clear from the above description, Table 1 and the drawings, according to the method for producing a conductive resin composition of the present invention, the softening point or melting point is higher than that of the low melting point metal, Even when a thermoplastic resin that is oxidatively degraded by filling is used, it is possible to obtain a highly reliable conductive resin composition having excellent conductivity and stability over time and a molded product thereof.

Claims (1)

[Claims] 1. When producing a conductive resin composition in which (A) a conductive filler comprising a conductive fiber having a low melting point metal layer on the surface is coated with (B) a thermoplastic resin, the conductive fiber is used. And 0.5 to 15% by weight of (C) a low melting point metal for forming an intersection, which is mixed and dispersed, and coated with a thermoplastic resin (B) to produce a conductive resin composition.