JP2783427B2 - Carbon fiber / thermoplastic compound - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carbon fiber / thermoplastic resin compound used for injection molding and the like, and particularly to a reinforcing property of added fiber,
The present invention relates to a compound that can sufficiently bring out other properties such as conductivity.

[Conventional technology]

Carbon fiber / thermoplastic resin composite (hereinafter referred to as CFRP) is prepared by kneading and extruding a resin filled with carbon fiber and resin in an appropriate amount in advance into pellets called a compound. It is common to shape it into a shape. In the compound production process, carbon fibers and a desired resin are kneaded and extruded by a uniaxial or biaxial kneader at a temperature higher than the softening temperature of the resin, and then cut to an appropriate length while cooling to obtain pellets.

[Problems to be solved by the invention]

It is known that carbon fibers are destroyed by the shearing force or the like in a kneader in the compound manufacturing process. Particularly, in the case of highly viscous ABS resin, etc., the shearing force applied to the fibers is large, and the degree of breakage is remarkable. The destruction of the carbon fibers in the compound used for CFRP molding means that the properties (reinforcement, conductivity, etc.) of the molded CFRP are degraded. There is a risk of becoming.

In the CFRP injection molding stage, the compound is kneaded by the screw of the molding machine, so fiber destruction in this process is unavoidable to some extent. However, eliminating or reducing the shearing force applied to the fiber in the compound production stage is a total This is effective in keeping the fiber breakage low. The phenomenon that fiber destruction increases with the number of passes through a kneader is known in the literature (Reference: Nagano Industrial Research Institute, Research Report, Vol. 6, p. 9).

Therefore, an object of the present invention is to obtain a compound which does not destroy the added carbon fiber as much as possible when producing a compound necessary for injection molding of CFRP.

[Means for solving the problem]

The gist of the present invention is that the carbon fiber alone is granulated or molded to an appropriate size in advance, and the granulated product or molded product is impregnated with a thermoplastic resin at a temperature equal to or higher than the melting point. It is crushed into a carbon fiber / thermoplastic resin compound. This is an effective means especially for a compound using vapor-grown carbon fiber, which is a microfiber with relatively little fiber breakage due to granulation and molding.

The thermosetting resin can easily impregnate the liquid material before hardening into the fiber assembly, but the thermoplastic resin has a high viscosity even if it is melted, and is difficult to impregnate.

For granulation of carbon fiber, particularly vapor-grown carbon fiber, a rolling granulator or an extrusion granulator is used. This is done by first spraying or dripping a liquid such as water or ethanol on the fiber,
The fiber and the liquid are mixed or agglomerates are formed, and in the case of a tumbling granulator, they are tumbled in a rolling granulator to grow and agglomerate the agglomerates.
In the case of an extrusion granulator, it is extruded and cut into pellets. In addition, it can be formed by various methods such as press molding. Since the granulated product or the molded product can be crushed to an appropriate size after impregnation with the resin, the size is not particularly limited. Addition of commonly used binders such as starch and molasses when mixing liquids facilitates the formation of granules, but may result in the incorporation of substances other than carbon fibers into the resulting compound. When this causes disturbance, it is necessary to remove or heat carbonize the binder after granulation.

In order to avoid this complication, it is well known that the thermoplastic resin for the target compound does not affect the properties. For example, when the target resin is polyolefin such as polypropylene or polyethylene, paraffins and the target resin are used. In the case of polyamide such as nylon, the post-treatment after granulation and molding can be simplified by selecting a binder such as epoxy.

The granulated or formed carbon fiber, especially the vapor-grown carbon fiber formed as described above, is dried (after baking if necessary), degassed under reduced pressure, and placed in a pressure-filled container such as an autoclave. Perform the desired thermoplastic resin impregnation. The impregnation is performed by melting the resin at a temperature in the range of its melting point and about 100 ° C. higher than the melting point and applying pressure. Appropriate pressure for pressurization is 1 to 10 kg / cm ² . At this stage, the amount of carbon fiber to be added to the compound can be arbitrarily changed by adjusting the density of the granulated product or molded product and the amount of resin impregnated, but usually contains 5 to 50% by weight of carbon fiber. Things are suitable.

After impregnation, remove from the container and cool to obtain a composite. The product using the granulated material can be used as it is as a compound, but the product using a molded product or the granulated product having irregular sizes is lightly pulverized to a suitable size. Considering that the compound has a particle diameter of at most 2-3 mm, this pulverization has little effect on the original fiber length, especially the fiber length of minute vapor-grown carbon fiber, and the carbon fiber in the compound The fiber length is almost the same as before production.

As the carbon fibers, general short fibers can be used, but those particularly suitable for the present invention are carbon fibers produced by a vapor phase method and having a diameter of 0.01 to 1 mm.
It is about μm in length and about 1 to 100 μm in length.

[Action]

When a CFRP molded body was produced using the carbon fiber / thermoplastic resin compound produced by the above method and using an appropriate mold, the compound obtained through a conventional single-screw or twin-screw kneader was used. CFRP has excellent mechanical properties (strength, impact resistance, etc.), electrical properties (electrical conductivity, electromagnetic wave shielding properties, etc.) and thermal properties (thermal conductivity, etc.) as compared to the case. This is due to the fact that the degree of breakage of the carbon fibers in the molded body is small and the fibers are made longer than before, so that hardening such as improvement of the reinforcing property and improvement of the electric and heat transfer properties has appeared.

(Example 1) 100 g of ethanol was added to 350 g of fine vapor-grown carbon fiber (calcined product and 2 types of graphitized product) having an average fiber length of 10 μm and a fiber diameter of 0.3 μm.
Was kneaded and press-molded to a size of 150 mm in diameter and 100 mm in thickness. The bulk density of the dried compact was about 0.4 g / cm ³ .

The above molded product and polypropylene (ACE Polypro MA41
About 1,000 g of the pellet from 0) is placed in an autoclave, and the inside of the container is degassed under reduced pressure using an oil rotary pump. Then, the container is heated to 220 ° C, which is higher than the melting point of polypropylene, with a nitrogen pressurization of 5 kg / c.
Pressure impregnation was performed at m ² .

Since the formed fiber of the vapor-grown carbon fiber has minute fibers, the inside of the formed body has a small pore size and is excellent in liquid retention. Therefore, the polypropylene can be impregnated efficiently. The bulk density of the compact after impregnation is 0.65 g / cm
^{It was 3} , and the content of vapor grown carbon fiber was about 30% by weight, as determined from the weight ratio of the resin and the fiber actually impregnated.

The vapor-grown carbon fiber / polypropylene composite produced as described above was lightly pulverized with a mixer to obtain pellets having an average particle diameter of 2 mm. The pellets were molded into test pieces for tensile test, specific resistance measurement, and the like by an injection molding machine (Nissei Plastics Industry Co., Ltd. NC-8000), and various physical properties were evaluated.

(Comparative Example 1) The same composition as in Example 1, that is, 700 g of vapor-grown carbon fiber (calcined product and two types of graphitized product) and 1600 g of polypropylene were mixed with a twin-screw kneader (Model RT35-2S, Tsukada Juki Co., Ltd.). The compound was kneaded and extruded at 230 ° C. to prepare a compound having a carbon fiber addition rate of 30%. This compound was injection-molded in the same manner as in Example 1, and the physical properties of the test pieces were compared with those in Example 1.

 Table 1 shows the physical property values of Example 1 and Comparative Example 1.

(Example 2) Vapor-grown carbon fiber (calcined product, 2 types of graphitized products) 1 kg of water 500
g was added and the mixture was kneaded with a Henschel mixer, and then granulated into a pellet having a diameter of 3 mm and a length of 4 mm with an extrusion granulator (F-20, Fuji Paudal Co., Ltd.). The bulk density of the dried granules was 0.35 g / cm ³ .

800 g of the above granulated material was placed in an autoclave in the same manner as in Example 1, and nylon 6,6 pellets (Technyl A21
6) 2.5 kg was heated at 265 ° C. to perform pressure impregnation. The granules after impregnation became a compound having a carbon fiber content of about 25%.

A test piece was injection-molded using the compound prepared as described above, and physical properties were measured.

(Comparative Example 2) Set using 1 kg of vapor grown carbon fiber and 3 kg of nylon 6,6 260
Compound production was performed using a twin-screw kneader at ~ 270 ° C. A test piece was prepared by injection molding of the obtained compound, and physical properties were measured.

 Table 2 shows the physical property values of Example 2 and Comparative Example 2.

(Example 3) Only carbon fibers were extracted from the vapor-grown carbon fiber (fired product) / polypropylene-based compound and the injection molded product produced in Example 1 (and Comparative Example 1), and the fiber length was measured.

For the extraction of carbon fiber, a method of dissolving polypropylene with decalin heated to 140 ° C was used. The extracted carbon fiber was placed on a slide glass, and the fiber was dispersed with a small amount of oil for microscope use, and then covered with a cover glass to obtain a fiber length measurement sample.

The fiber length was measured by inputting an image from an optical microscope using NIRECO Corporation LUZEX-5000. Table 3 shows the obtained average fiber length and standard deviation. Example 1 and Comparative Example 1
When the former is compared, the former has less degree of fiber destruction,
As a result, it was confirmed that the physical properties were improved.

[Effect of the Invention] The carbon fiber / thermoplastic resin compound produced according to the present invention exhibits its characteristics sufficiently because the carbon fiber as an additive is hardly destroyed, and exhibits sufficient properties, such as reinforcement, electric conductivity, and heat transfer. It can be expected as a compound suitable for producing CFRP excellent in injection molding by injection molding.

Claims (3)

(57) [Claims] 1. A carbon fiber / thermoplastic resin compound obtained by impregnating a thermoplastic resin into a carbon fiber granulated or molded article. 2. The carbon fiber according to claim 1, wherein the carbon fiber is a vapor grown carbon fiber.
A carbon fiber / thermoplastic resin compound as described. 3. The carbon fiber / thermoplastic resin compound according to claim 1, wherein the content of the carbon fiber is 5 to 50% by weight.