JPH05318467A - Preparation of raw material pellet for molding of box for electromagnetic shielding - Google Patents

Abstract

PURPOSE:To make it possible to prepare easily a pellet for injection molding contg. a metal fiber obtd. by means of a coil cutting method by a method wherein a bundle of the metal fibers prepd. by means of the coil cutting method have a mixed soln. of a polystyrene and a styrenic thermoplastic elastomer deposited on them and after the solvent is removed, the bundles are collected and are cut into a specified length. CONSTITUTION:A thin metal sheet 1 such as brass is wound on a mandrel 2 and a metal fiber 3 with a rectangular crosssection is prepd. by means of a cutting bite 4 etc. As this fiber 3 is short in length but is lightly entangled each other, it is possible that the fibers are collected together into a long bundle 5. This bundle 5 is impregnated with a 30% toluene soln. of a 50/50 mixture of a polystyrene and a styrenic thermoplastic elastomer and is squeezed through a die and is immediately dried by heating and is pelletized by means of a pelletizer. It is possible thereby to obtain a pellet with an extremely high metal content without bringing the fibers into separated pieces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a raw material pellet for forming an electromagnetic shield casing, which is suitable for injection molding of an electromagnetic shield casing.

[0002]

2. Description of the Related Art The development and popularization of electronic devices in recent years has been remarkable, and tends to become more sophisticated and sophisticated. Along with that, electromagnetic waves generated from the elements used in these electronic devices affect peripheral devices and cause electromagnetic interference such as malfunction, which has recently become a problem. It became so.

In particular, plastic molded products have come to be used for housings of various electronic devices in place of conventional metal,
It is, so to speak, defenseless against the above electromagnetic waves.
For this reason, metallic ribbons, flakes or powder,
A method of mixing a conductor such as metallized glass, carbon black, and carbon fiber with a plastic material has been noticed and implemented. Among them, recently, a method in which a bundle of metal fibers is extrusion-coated with a thermoplastic resin, which is cut into pellets and which is then used as an injection material to perform injection molding of a housing, has been considered promising. The ultrafine stainless steel and the copper wire having a circular cross section, which are drawn as the above-mentioned metal fiber, are widely used.

On the other hand, as a result of diligent examination of metal fibers obtained by the coil cutting method developed by Yanagisawa and Suzuki of Nippon Institute of Technology (for example, described in the proceedings of Spring Meeting of Precision Engineering Society of 1989) It was confirmed to have excellent performance as a shield material. As shown in FIG. 1, this coil cutting method is, for example, a metal thin plate 1 made of brass or the like is wound around a mandrel 2 in a multiple manner and rotated, and the metal thin plate 1 wound in multiple turns is used as a cutting tool such as a cutting tool 4. It is a method of manufacturing a metal fiber bundle 5 made of metal fibers 3 having a rectangular cross section by cutting from one end surface using.

[0005]

By the way, the metal fiber bundle 5 obtained by this coil cutting method is a set of metal fibers 3 having a length that maximizes the winding length of the thin metal plate 1.
The continuity in the length direction is extremely poor as compared with the bundle of metal fibers obtained by the conventional drawing process. Therefore, the metal fiber bundle 5 is frayed or cut with a slight tension.

Therefore, it is extremely difficult to coat the metal fiber bundle 5 obtained by the coil cutting method with the thermoplastic resin. Specifically, since the metal fiber bundles 5 are easily cut, continuous production cannot be performed. Large voids are formed between the metal fibers 3 and between the metal fibers 3 and the coating resin layer, and if the metal fibers 3 are cut into pellets, the metal fibers 3 fall out. That is, if a high resin pressure is applied to prevent the formation of the voids and extrusion coating is performed, tension is applied to the metal fiber bundle 5 and the metal fiber bundle 5 is immediately cut. On the contrary, when it is attempted to prevent this cutting, the above-mentioned void is formed. Therefore, the present invention has been devised to effectively solve the above problems, and an object thereof is to easily produce resin pellets for injection molding containing metal fibers obtained by a coil cutting method. A new method for producing resin pellets for injection molding is provided.

[0007]

Means for Solving the Problems To achieve the above object, the present invention is to attach a mixed solution of polystyrene and a styrene-based thermoplastic elastomer to a metal fiber bundle produced by a coil cutting method, and then add the mixed solution. By removing the solvent in the bundle, the metal fiber bundle is bundled and cut into a predetermined length to form the bundle.

As the styrene thermoplastic elastomer,
Styrene / butadiene / block copolymer, styrene /
Isopropylene / styrene block copolymers, styrene / ethylene / butylene styrene block copolymers, or acid modified products of these, such as Ravalon of Mitsubishi Yuka Co., TPE-SB of Sumitomo Chemical Co., Ltd., and Nippon Synthetic Rubber Co., Ltd. JSR-SIS, Califlex of Shell Chemical Co.,
Examples include Kraton and Tuftex of Asahi Kasei.

[0009]

In the present invention, as described above, the use of a mixture of polystyrene or polypropylene and a styrene thermoplastic elastomer as the sizing material improves the adhesiveness with the metal fibers and prevents the fibers from becoming disjointed. That is, if polystyrene or polypropylene alone is inferior in adhesiveness to the metal fibers, the metal fiber bundles are scattered and cannot be bundled when the solvent is removed. The reason for using polystyrene or polypropylene is that the resin for the housing is generally polystyrene,
Since it is an ABS resin, a PPO resin, or a polypropylene resin, it is necessary to be compatible with these.

Since the mixed solution sufficiently penetrates and adheres between the metal fiber bundles, the metal fibers and the resin have good adhesion after the solvent is removed, and the metal fibers do not come apart during cutting. Preferably, the fibers are mechanically pressed together when the solvent is removed. In this cutting step, the pellet is cut into a length of 3 to 10 mm. The metal fiber-containing resin pellets obtained in this manner are suitable materials for the electromagnetic shield casing by injection molding.

[0011]

EXAMPLES Examples of the present invention will be described below.

[Example 1] The metal fibers contained in the pellets can be manufactured by the apparatus shown in FIG. In this example, a brass thin plate 1 having a thickness of 50 μm was wound around a mandrel 2 and cut to manufacture a brass fiber 3 having a rectangular cross section of 50 μm × 20 μm. The maximum length of each fiber is 2.
The length was 5 m, but since the fibers 3 were loosely entwined with each other, it was possible to obtain a long bundle 5 in which 500 fibers were baked.

Polystyrene (HI-E manufactured by Denki Kagaku Co., Ltd .: specific gravity 1.05, melt flow index 4.0 g / 10 min) and styrene thermoplastic elastomer (Tuftec M-1913, Asahi Kasei Co., Ltd.) are added to the bundle 5 of the fibers 3. : 5
After blending with 0, a viscous liquid made up of a 30 wt% solution of toluene was added, passed through a die and squeezed, and immediately heated and dried to remove toluene. Then, when the fiber bundle was cut into a length of 7 mm by a pelletizer, the fibers could be easily cut without breaking. The weight content ratio of the obtained fiber and resin was 93: 7, and it was found that pellets having an extremely high metal content could be obtained.

Example 2 As Example 2, polypropylene was used in place of the polystyrene used in Example 1 (Showaroma MA210 (Showa Denko KK) (melt flow rate 3).
g / 10 min, density 0.9 g / cm ³ )) and using the other conditions exactly as in Example 1 above, it is easy to obtain resin-focused brass fiber pellets having a length of 7 mm as in the above Example. I was able to. Further, the metal content in the pellet was 12 wt%.

[Comparative Example 1] An experiment was conducted in exactly the same manner as in Example 1 except that the solution of polystyrene alone was used. However, it was not possible to focus the fibers. Moreover, when the cutting was forcibly performed, the fibers were completely separated.

Comparative Example 2 In Example 2, an experiment was conducted using polypropylene alone. However, the solubility was poor and a solution could not be prepared successfully. In addition, I tried to focus, but could not focus at all.

[0017]

In summary, according to the method of the present invention, resin pellets for injection molding containing brass fibers produced by the coil cutting method can be easily produced. Moreover, it has been confirmed that the metal fiber manufactured by the coil cutting method as described above has excellent performance as an electromagnetic shield material, and it is industrially possible that the resin pellet containing this metal fiber can be easily manufactured. It has an excellent effect that the value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for producing metal fibers by a coil cutting method.

[Explanation of symbols]

 1 Metal thin plate 2 Mandrel 3 Fiber 4 Cutting tool 5 Fiber bundle

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location B29K 105: 06 (72) Inventor Hideki Asano 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Hitachi Electric Cable Co., Ltd. Power Systems Laboratory (72) Inventor Toshio Ozone 3-11-7 Kanda, Uchida, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. A metal fiber bundle produced by a coil cutting method is adhered with a mixed solution of polystyrene and a styrene thermoplastic elastomer, and then the solvent in the mixed solution is removed to bundle the metal fiber bundle, A method of manufacturing a raw material pellet for forming an electromagnetic shield casing, which is formed by cutting it into a predetermined length.