JPH0419644B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention enables conductive fillers to be uniformly dispersed without lowering the strength of the molding material compared to the strength of thermoplastic resins, and molded products can be heated at high temperatures. The present invention relates to a conductive molding material that does not lose its shielding effect even when left in the environment.

[Technical background of the invention and its problems] In recent years, electronic circuits have been protected from external interference radio waves,
In addition, in order to prevent unnecessary radio waves generated from oscillation circuits and the like from leaking to the outside, it is required that the housings of electronic devices be made of electromagnetic shielding material. Examples of such electromagnetic shielding materials include metals and conductive resins, but while the former metals have excellent electromagnetic shielding effects,
Due to drawbacks such as being heavy, expensive, and poor processability, the latter type of conductive resin is becoming mainstream. There are two methods of imparting conductivity to resin: forming a conductive layer on the surface by applying conductive paint, spraying or plating metal after molding the resin, and applying carbon or metal inside the resin. There is an internal addition method in which a conductive filler such as powder or fiber is added and molded. The method of forming a conductive layer on the surface of a resin molded product requires many steps and is not suitable for mass production, and also has the disadvantage that the conductive layer peels off after long-term use, so there are high expectations for the internal addition method. There is.

However, the internal addition method also has the following problems. In other words, it is desirable to reduce the amount of conductive filler as much as possible in order to reduce the cost of the molded product without reducing its strength, but if the amount of conductive filler is reduced, the conductivity will decrease. If the molded product is left at a high temperature of 60 to 80℃, the bond between the conductive fillers separates due to the difference in linear expansion coefficient between the resin and the conductive filler and molding distortion, causing the conductivity to deteriorate. At the same time, so-called conductivity deterioration occurs, in which the shielding effect decreases, resulting in a drawback that significantly impairs reliability.

[Object of the Invention] The object of the present invention was to eliminate the above-mentioned drawbacks, and it is possible to uniformly disperse the filler without reducing the strength of the thermoplastic resin, and to maintain conductivity even in high-temperature environments. The purpose of this invention is to provide a conductive molding material with excellent shielding effect without deterioration in properties.

[Summary of the Invention] As a result of extensive research to achieve the above-mentioned object, the present invention has discovered that the object can be achieved by adding a conductive deterioration-preventing filler.

That is, the present invention mainly consists of a thermoplastic resin, a conductive filler, and a conductive anti-deterioration filler, and the thermoplastic resin contains 5 to 40% by weight of the conductive filler and the conductive anti-deterioration filler.
0.3 to 10% by weight of each of the above-mentioned conductive fillers in the form of long fibers, a thermoplastic resin layer is formed on the surface of a bundle of the conductive fillers, which is then cut into pellets to form a master pellet; A mixed master pellet is mixed therein, which is obtained by forming a thermoplastic resin layer on the surface of a bundle of conductive filler and the conductive deterioration prevention filler in the form of long fibers, and cutting the bundle into pellets. It is an electrically conductive molding material.

Thermoplastic resins used in the present invention include polystyrene resin, ABS resin, polypropylene resin,
Examples include modified PPO resin and PPE resin. These resins may be used in the form of pellets, such as natural pellets as they are, coated with a conductive filler, or coated with a conductive deterioration-preventing filler. When covering the filler, the resin of the natural pellets and the resin that covers the conductive filler or the resin that covers the conductive deterioration prevention filler may be the same or different resins may be used. .

Examples of the conductive filler used in the present invention include long fiber copper fibers and aluminum fibers, and the thinner these fibers are, the better. The thinner the fibers, the higher the number of fibers per unit weight in the resin, and the better the conductivity and the better the shielding effect. This fiber is used in bundles of about 100 to 50,000 fibers. The long fiber conductive filler can of course be used as is, but it is also possible to form a thermoplastic resin layer on the bundled surface and cut it into pellets to use as a master pellet, or to remove the long fiber conductive filler and the conductivity deterioration. A thermoplastic resin is formed on the surface of a bundle of preventive fillers and is then cut into pellets to be used as a mixed master pellet.

Examples of the conductive deterioration-preventing filler used in the present invention include glass fiber, carbon fiber, stainless steel fiber, or glass fiber or carbon fiber having a metal layer such as tin, nickel, or aluminum. These can of course be used as they are, but they can also be used as reinforced pellets having a thermoplastic resin layer on the surface.

Next, the blending amounts of the conductive filler and the conductive deterioration preventing filler will be explained.

The conductive filler is 5 to 40 for thermoplastic resin.
It is necessary to mix the amount by weight. If it is less than 5% by weight, sufficient conductivity cannot be obtained, and if it exceeds 40% by weight, the resin strength will decrease and moldability will deteriorate, which is not preferable. The conductive deterioration-preventing filler needs to be blended in an amount of 0.3 to 10% by weight based on the thermoplastic resin. This is because if it is less than 0.3% by weight or more than 10% by weight, the conductivity of the molded product at high temperature (70° C.) will decrease, which is undesirable.

The conductive molding material of the present invention is composed of a thermoplastic resin, a conductive filler, and a conductive deterioration-preventing filler,
Deterioration of conductivity could be prevented by blending the filler to prevent conductivity deterioration. The reason is,
This is because the linear expansion coefficient of the thermoplastic resin becomes smaller by adding the conductive anti-deterioration filler.
Further, by providing a metal layer on the surface of the conductive deterioration-preventing filler and bringing its conductivity close to that of the conductive filler, high conductivity can be obtained as a whole. Furthermore, by pelletizing these materials, the filler is uniformly dispersed in the resin and an excellent shielding effect can be obtained.

The conductive molding material of the present invention may be a molding material by mixing a thermoplastic resin, a conductive filler, and a conductive deterioration prevention filler, but it may be made by mixing the above-mentioned master pellets and reinforcing pellets, or a mixed master pellet. By blending appropriate amounts of pellets and natural pellets, it is extremely easy to blend and the process can be greatly shortened, which is very advantageous.

Next, it will be explained using drawings.

FIG. 1 shows a master pellet A obtained by integrally covering and integrally forming a thermoplastic resin layer 1 on the surface of a bundle of long fibrous conductive fillers 2, pressing it, and cutting it into pellets. The shape of the master pellet is
The cross section can be transformed into a circular, elliptical, flattened shape, etc. as necessary, and there are no particular limitations. A thermoplastic resin layer 1 is placed on the surface where the conductive deterioration prevention filler 3 is bundled.
Fig. 2 shows a reinforced pellet B obtained by integrally forming a coating, pressing it, and cutting it into pellets. Figure 3 shows a master pellet A on the surface of a bundle of long fiber conductive filler 2 and conductive anti-deterioration filler 3.
and a mixed master pellet C formed by coating the thermoplastic resin layer 1 in the same manner as the reinforced pellet B.
showed that. A conductive molding material can be easily obtained by combining and mixing these pellets A, B, and C with natural pellets made only of thermoplastic resin.

[Effects of the Invention] As explained above, the conductive molding material of the present invention is capable of uniformly dispersing the filler without reducing the strength of the thermoplastic resin by blending the conductive deterioration-preventing filler. Moreover, it is a molding material with excellent shielding effect without reducing conductivity even in high-temperature environments, and in addition, it can be made into a molding material through an extremely easy process.

[Embodiments of the Invention] Next, embodiments of the present invention will be described. The present invention is not limited to the following examples.

Example: 300 long copper fibers with a diameter of 50 μm are bundled, the surface of which is coated with a thin layer of polystyrene resin, and the diameter is approximately 2 mm.Then, the fibers are pressed into a flat shape, cut into a length of 5 mm, and made into master pellets. I got the trick. Next, a long carbon fiber with a diameter of 8 μm was
10,000 pellets were bundled, thinly coated with polystyrene resin, pressed into a flat shape, and cut into 5 mm lengths to obtain reinforced pellets. A conductive molding material was prepared by mechanically mixing 80 parts by weight of the master pellets thus obtained, 3 parts by weight of reinforced pellets, and 100 parts by weight of natural pellets made of polystyrene resin. When a molded product was obtained using this molding material and the electromagnetic shielding effect was measured, it was 40 dB at 500 MHz. The conductive filler is uniformly dispersed in the molded product, and when the electromagnetic shielding effect was measured after 1000 hours at 70°C, it was 40 dB with no deterioration.

Comparative example: 300 long copper fibers with a diameter of about 50 μm are bundled,
The surface of the pellet was coated with a thin layer of polystyrene resin to give a diameter of approximately 2 mm, and the pellet was cut into a length of 5 mm to obtain a master pellet. A conductive molding material was produced by mechanically mixing 100 parts by weight of natural pellets made of polystyrene resin with 80 parts by weight of master pellets. A molded article was obtained using this molding material. The electromagnetic shielding effect of this molded product is
Initially, it was 40dB at 500MHz, but after heating at 70℃ for 1000 hours, the electromagnetic shielding effect deteriorated to 15dB.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the master pellet used in the present invention, Fig. 2 is a cross-sectional view of the reinforced pellet used in the present invention, and Fig. 3 is a partially enlarged cutaway cross-sectional view of the mixed master pellet used in the present invention. . 1... Thermoplastic resin layer, 2... Long fibrous conductive filler, 3... Conductive deterioration prevention filler.

Claims (1)

[Scope of Claims] 1 The main components are a thermoplastic resin, a conductive filler, and a conductive deterioration prevention filler, and the conductive filler is 5 to 40% by weight and the conductive deterioration prevention filler is based on the thermoplastic resin. 0.3 to 10% by weight of each of the above-mentioned conductive fillers in the form of long fibers, a thermoplastic resin layer is formed on the surface of a bundle of the conductive fillers, which is then cut into pellets to form a master pellet; A mixed master pellet is mixed therein, which is obtained by forming a thermoplastic resin layer on the surface of a bundle of conductive filler and the conductive deterioration prevention filler in the form of long fibers, and cutting the bundle into pellets. conductive molding material. 2. The conductive molding material according to claim 1, wherein the conductive deterioration-preventing filler is glass fiber, carbon fiber, stainless fiber, or glass fiber or carbon fiber having a metal layer such as tin, nickel, or aluminum. . 3. Claim 1 or 3, in which master pellets are mixed with reinforcing pellets formed by forming a thermoplastic resin layer on the surface of a bundle of conductive anti-deterioration fillers and cutting the pellets into pellets. The conductive molding material according to item 2. 4. The conductive molding material according to claim 3, wherein master pellets, reinforcing pellets, and natural pellets of thermoplastic resin are mixed. 5. The conductive molding material according to claim 1 or 2, wherein the mixed master pellets and natural thermoplastic resin pellets are mixed.