JPH0123882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a conductive material made of a thermoplastic synthetic resin and a conductive fiber, and more specifically, the present invention relates to a method for producing a conductive material made of a thermoplastic synthetic resin and a conductive fiber. The present invention relates to a method for producing a conductive material in which 5 to 200 parts by weight of discontinuous conductive fibers are substantially uniformly dispersed.

Organic polymeric materials, such as thermoplastic synthetic resins, generally belong to advanced electrical insulators with a volume resistivity of about 10 ¹⁰ to ^{10 18} Ω・cm, and are used in fields such as wire sheaths and electrical components that take advantage of this property. It is widely used in However, recently, with the diversification of market demands, so-called conductive polymer materials (this name means that they have considerable electrical conductivity and are not necessarily similar to metals) have lowered the resistivity of thermoplastic synthetic resins. Applications have been developed and already have a significant market.
Currently, the most common method for imparting conductivity to thermoplastic synthetic resins is to knead carbon black into the resin, and the volume resistivity of the resulting material is
Even materials incorporating Ketchen Black, which currently has the highest conductivity, have a conductivity of about 10 ¹ Ω・cm.
Furthermore, the commercial value of resin materials containing such non-reinforcing fillers is significantly reduced due to deterioration in mechanical strength. On the other hand, recently, products made by kneading carbon fiber into thermoplastic synthetic resin (mainly polypropylene) have begun to be commercially available, but this material also has a volume resistivity of 10 ⁶ Ω.・It is more than cm, and its conductivity is not satisfactory.

The present invention provides an industrially advantageous method for producing a conductive material based on a thermoplastic synthetic resin having excellent mechanical strength and sufficient conductivity, which eliminates the above-mentioned problems. That is, an object of the present invention is to provide a manufacturing method in which conductive fibers are mixed with thermoplastic synthetic resin powder while being opened, and the mixture is molded.

Thermoplastic synthetic resins used in the present invention include low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, and polybutene.
1. Polyolefin resins such as polymethylpentene-1, polyvinyl chloride resins, polystyrene resins, acrylic resins such as polymethyl methacrylate, polyamide resins such as 6-nylon and 6,6-nylon, polyethylene terephthalate, Examples include polyester resins such as polybutylene terephthalate, polycarbonate resins, polyacetal resins, and fluorine resins.
Furthermore, the present resin also includes copolymers of the above resins, modified products with rubber and fillers, and the like.

In the present invention, these thermoplastic synthetic resins are most preferably used in the form of powder, and the particle size thereof is preferably 500 microns or less, particularly 300 microns or less. If there is a large amount of powder with a particle size of 500 microns or more, it will be difficult to mix it uniformly with the conductive fibers.
These thermoplastic synthetic resin powders are used by mechanically pulverizing general pellet-like, bead-like products or molded product waste, but it is most economically viable to use powder obtained during synthetic resin manufacturing. It's advantageous.

The conductive fibers used in the present invention are not particularly limited, but currently available ones include carbon fibers (including graphite fibers), glass fibers coated with metals such as aluminum, and metal fibers (for example, aluminum fibers). ), etc. These are generally commercially available as products made by bundling dozens to hundreds of single fibers such as roving, tow, or chopped strands cut to a certain length, and in the present invention, these are used as materials. Available for use. However, there are two conditions for the conductive fibers used in the present invention.

The first condition is that the above-mentioned material is not used in a bundled state, but is dispersed in an opened state in a thermoplastic synthetic resin. However, opening here refers to a state in which the fibers are loosened from the bundle by external force.

The second condition is that the length of the conductive fibers be 0.5 mm or more. As mentioned above, products in which conductive fibers are spread and dispersed in thermoplastic synthetic resin are already on the market, and these products are made by kneading and dispersing carbon fibers into resin.
In this product, during the process of kneading the fibers into the resin, most of the fibers are cut into lengths of 0.5 mm or less, and the original strength and conductivity of carbon fibers are no longer exhibited.
In the present invention, since opened fibers with an average length of 0.5 mm or more are dispersed in a thermoplastic synthetic resin, a product with very good mechanical strength and electrical conductivity can be obtained. In particular, in the present invention, it is preferable to use chopped strands with a length of 0.5 mm or more as the conductive fiber material.

In carrying out the present invention, it is most preferable to use chopped strands as the conductive fibers and to use the thermoplastic synthetic resin in the form of powder. There are various methods for uniformly opening and dispersing conductive fibers into thermoplastic synthetic resin powder, but one preferred example is mixing the two in a mixer with rotary blades at the bottom, heating and press-molding the mixture. It is. To explain in more detail, chopped strands such as carbon fiber and thermoplastic synthetic resin powder are put into a Henschel type mixer, which is a typical example of a mixer with rotary blades at the bottom, and the blades are rotated at a rotation speed of about 200 to 2000 rpm. The carbon fibers are rotated to gradually open the carbon fibers, and at the same time, the resin powder is encapsulated in the opened fibers to form a uniform mixture. At this time, first charge the entire amount of thermoplastic synthetic resin into the container,
Similar results can be obtained by adding chopped strands gradually.

Next, in order to mold this mixture, it is heated and pressed at a temperature higher than the melting point or the softening point of the thermoplastic synthetic resin and molded into a shape such as a sheet. In the batch type, it is possible to use a general-purpose hot press machine, but in the case of the continuous type, which has good productivity, the mixture is first formed into a continuous mat shape using a fleece former like a batting machine. After that, it is heated and pressurized using a continuous press machine such as a double belt press. This double belt press is a well-known product from Sandvik Conveyor Systems. In addition, after forming into a sheet, preheating to above the melting (softening) point of the thermoplastic synthetic resin and press forming (stamping) using a matte metal die etc. can be used to post-process products into complex shapes. It is possible.

The molded product obtained by the heating and pressing method of the present invention has a higher concentration of conductive fibers than molded products obtained by extrusion or injection methods after kneading conventional conductive fibers and synthetic fibers. It has almost no breakage and has excellent mechanical strength and electrical conductivity. As described above, since the conductive material according to the present invention has excellent properties, it can be used in antistatic containers (e.g., IC magazines), antistatic workbenches, antistatic tools, surface heating elements, electrode radio wave shields, etc. It can be used for a wide range of purposes, including boards or cases, electroplating materials, and calculator keyboards.

The present invention will be specifically described below with reference to Examples.

Example 1 100 parts by weight of powder (particle size of 300 microns or less) of polypropylene (trade name "Mitsui Noblen JHH (G)" manufactured by Mitsui Toatsu Chemical Co., Ltd.) was added to the thermoplastic synthetic resin, and the average length of carbon fiber was added to the conductive fiber. Using 67 parts by weight of a 6 mm chopped strand (product name "Kureka C-106T" manufactured by Kureha Chemical Industry Co., Ltd.), mix it with a mixer with rotary blades at the bottom (product name "Super Mixer 20L").
(manufactured by Kawada Seisakusho) and stirred for 5 minutes at a rotational speed of 500 rpm to obtain a mixture in which polypropylene powder was almost uniformly dispersed and adhered to the opened chopped strands.

Next, this mixture was piled up in a 3.5 mm thick metal frame into a pine-like shape of approximately the same thickness, and the top and bottom of the pine was covered with two pressing iron plates. This was charged into a 100 ton hydraulic press and preheated to 220℃ for 5 minutes, then pressurized to a pressure of 100Kg/cm ² G for 5 minutes at the same temperature, then transferred to another hydraulic press and heated to 100Kg/cm 2 G. Cooled at 35° C. for 5 minutes under a pressure of cm ² G. The obtained molded product is a polypropylene sheet with a length of 6 mm in which opened carbon fibers are almost uniformly dispersed, and its volume resistivity is
It was 0.11Ω・cm.

Example 2 Chopped strands of conductive fibers and carbon fibers with an average length of 0.7 mm (product name: ``Kureka M-107T'')
Example 1, except for using the following: (manufactured by Kureha Chemical Industry Co., Ltd.)
The sheet was created in exactly the same way. The obtained sheet was a polypropylene sheet in which opened carbon fibers having a length of 0.7 mm were almost uniformly dispersed, and its volume resistivity was 4 Ω·cm.

Comparative Example Using the same amount of the same material as Example 1 as a raw material,
The mixture was kneaded using a pressure kneader at 190°C for 5 minutes. The obtained kneaded product was press-molded into a sheet in the same manner as in Example 1. The obtained sheet was a polypropylene sheet in which opened carbon fibers were uniformly dispersed, but the carbon fibers were cut to an average length of 0.5 mm or less, and the volume resistivity was 65Ω.
It was cm.

Reference example A commercially available conductive material (product name: Tonen
A flat plate was obtained by injection molding CFRPP J-15 (manufactured by Tonen Petrochemical Co., Ltd.), and the volume resistivity of this flat plate was 10 ⁶
It was over Ω・cm.

Claims (1)

[Claims] 1. 100 parts by weight of thermoplastic synthetic resin powder and 5 to 200 parts by weight of discontinuous conductive fibers having an average length of 0.5 mm or more are uniformly spread and mixed, and the melting point of the thermoplastic synthetic resin is A method for producing a conductive material characterized by heating and pressure forming at a temperature above or above the softening point. 2. The method for producing a conductive material according to claim 1, wherein the conductive fiber is carbon fiber. 3. The thermoplastic synthetic resin powder and the discontinuous conductive fibers are spread and mixed using a mixer having rotary blades at the bottom of a container while opening the fibers at a rotation speed of 200 to 2000 rpm. A method for producing a conductive material according to claim 1 or 2, which is carried out by: