JPH04284204A - Manufacture of starting material pellet for molding electromagnetic shielding casing - Google Patents

Abstract

PURPOSE:To produce easily pellets for molding an electromagnetic shielding casing, which contain metallic fibers obtained by a coil cutting method. CONSTITUTION:In a method of producing starting material pellets 9 suitable for the injection molding of an electromagnetic shielding casing, the method is characterized in that, after a bundle 5 of metallic fibers 3 produced by a coil cutting method is coated with a thermoplastic resin 11 whose elastic modulus in flexure is not more than 1.8GPa, and whose hardness is not less than 80 in A hardness according to JIS, the coated bundle is cut in a predetermined length.

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 raw material pellets for molding electromagnetic shield housings, which are suitable for injection molding of electromagnetic shield housings.

0002

BACKGROUND OF THE INVENTION The development and spread of electronic equipment in recent years has been remarkable, and they are becoming increasingly sophisticated and precise. Along with this, electromagnetic waves generated from the elements used in these electronic devices are affecting peripheral devices, causing electromagnetic interference such as malfunctions, and these devices are suddenly becoming seen as a problem. It became so.

In particular, plastic molded products have come to be used instead of conventional metal for the housings of various electronic devices.
It is, so to speak, defenseless against the electromagnetic waves mentioned above. Therefore, in order to make the plastic housing conductive, metal ribbons, flakes, powder, etc.
A method of mixing a conductor such as metallized glass, carbon black, or carbon fiber into a plastic material has attracted attention and has been put into practice. Among these, recently, a method of injection molding a housing using a bundle of metal fibers extruded and coated with a thermoplastic resin and then cut into pellets as an injection material has been considered promising. As the above-mentioned metal fibers, drawn ultrafine stainless steel and circular cross-section copper wire are widely used.

On the other hand, as a result of intensive study on metal fibers obtained by the coil cutting method developed by Yanagisawa, Suzuki et al. of the Nippon Institute of Technology (for example, described in the Proceedings of the 1989 Society for Precision Engineering Spring Conference), it was found that electromagnetic shielding It was confirmed that it has excellent performance as a material. As shown in FIG. 2, the coil cutting method involves winding a metal thin plate 1 multiple times around a mandrel 2 and rotating it, and cutting this multiple-wound metal thin plate 1 from one end surface using a cutting tool 4. This is a method for manufacturing metal fibers 3 having a rectangular cross section.

[0005]

[Problems to be Solved by the Invention] However, the bundle 5 of metal fibers 3 obtained by the coil cutting method is a collection of metal fibers 3 with a length that maximizes the winding length of the thin metal plate 1. Compared to a bundle of metal fibers obtained by drawing, the continuity in the length direction is extremely poor. Therefore, even a slight tension causes the bundle 5 to fray or break, and it is extremely difficult to coat the bundle 5 of metal fibers 3 obtained by the coil cutting method with a thermoplastic resin. Specifically, large gaps are formed between the metal fibers 3 and between the metal fibers 3 and the coating resin layer, and when these are cut into pellets, the metal fibers 3 fall out. If an attempt is made to apply extrusion coating by applying high resin pressure to prevent this, there is a drawback that tension is applied to the metal fibers 3 and the metal fibers 3 are easily cut.

Furthermore, since the resin coated on the metal fibers 3 has a non-solid pipe shape, the coated resin cracks when it is cut into pellets, causing the resin and fibers to scatter.

An object of the present invention is to solve the above-mentioned problems and to provide an electromagnetic seal that can easily produce resin pellets for injection molding containing metal fibers obtained by a coil cutting method.
An object of the present invention is to provide a method for producing raw material pellets for molding a molded housing.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the method for producing raw material pellets according to the present invention is such that a bundle of metal fibers produced by a coil cutting method has a flexural modulus of elasticity of 1.8G.
After coating with a thermoplastic resin having a hardness of JIS A hardness of 80 or less, the resin is cut into a predetermined length.

[0009]

[Operation] If the flexural modulus of the thermoplastic resin is greater than 1.8 GPa, when cutting the resin-coated metal fiber bundle into pellets, the resin will crack and the metal fibers will scatter. This resin cracking is a unique phenomenon that occurs when a metal fiber bundle manufactured by the coil cutting method is coated with resin, and is more likely to occur than when using metal fibers manufactured by a conventional method that does not involve the coil cutting method. This is thought to be due to the increased porosity. Further, if the hardness of the resin is less than 80 in terms of JIS A hardness, sufficient mechanical strength to restrain the metal fibers will not be obtained in the pellet state obtained by cutting. The method of the invention eliminates these problems.

[0010] The cutting length when cutting the resin-coated metal fiber into pellets is selected from within the range of 4 to 10 mm. The reason for this is that if the thickness is less than 4 mm, the metal fibers in the resin pellet will be finely chopped, and a sufficient electromagnetic shielding effect cannot be expected. This is because problems such as the resin pellets being difficult to penetrate into the resin pellets and uneven mixing when mixed with general resin pellets that do not contain metal fibers arise. Further, the content of metal fibers in the resin pellets is selected within the range of 40 to 85% by weight. this is,
If the content is less than 40% by weight, sufficient electromagnetic shielding is required.
This is because no rudo effect can be expected, and if the amount exceeds 85% by weight, the fiber dispersibility in the injection molded article will be greatly reduced. Thermoplastic resin has its flexural modulus (JIS K-72
Polystyrene, ABS, polyethylene, polyamide, polypropylene, PPO, etc. may be used as long as the
Furthermore, a flexible component such as a rubber-like polymer may be mixed with these resins so that the flexural modulus is 1.8 GPa or less.

[0011]

[Example] Next, an example of the present invention will be described.

[Example 1] Metal fibers to be contained in pellets can be manufactured by a coil cutting method using the apparatus shown in FIG. Copper or brass fibers are suitable as the metal fibers in terms of both electromagnetic shielding properties and workability. In this example, a brass thin plate 1 having a thickness of 50 μm was wound around a mandrel 2 and cut to produce a brass fiber 3 having a rectangular cross section of 50 μm×20 μm. The maximum length of each individual fiber was 2.5 m, but since the fibers 3 were loosely intertwined with each other, a long brass fiber bundle 5 made up of approximately 500 fibers could be obtained.

The bundle 5 of fibers 3 was melt coated with a thermoplastic resin 11 using an extrusion coater 6 as shown in FIG. Resin 11 is polystyrene (manufactured by Showa Denko, "S-Bright GP8": melt flow rate 3.0 g/10
min) 70 parts of styrene ethylene butylene styrene block copolymer (manufactured by Asahi Kasei Co., Ltd., "Tuftex H105")
1": Melt flow rate 1.0 g/10min)
30 parts were uniformly mixed in a 30 m/m twin-screw extruder at 260°C. The flexural modulus of this mixed resin is 1
．． 4 GPa, and the hardness was 98 or higher on the JISA hardness scale. Resin-coated brass fiber 10 is finally formed by coating treatment.
The outer diameter of the fiber was 3.5 mm, and the content of the brass fiber was 70% by weight.When this was cut into lengths of 6 mm using the pelletizer 8, there were almost no fibers coming out or cracking of the resin 11, and the brass fiber 3 was cut into pieces with a length of 6 mm. It was possible to obtain resin pellets 9 containing the following. Even when the obtained metal fiber-containing resin pellets 9 were mechanically mixed with general resin pellets not containing metal fibers, the brass fibers 3 were retained in the metal fiber-containing resin pellets 9. Therefore, this resin pellet 9 can be used as a master pellet containing metal fibers.

[Example 2] The ratio of polystyrene to styrene ethylene butylene styrene block copolymer is 50
Resin pellets 9 containing brass fibers 3 were produced in the same manner as in Example 1 using a mixed resin of: 50%. The resin mixture had a flexural modulus of 1.5 GPa and a hardness of 98 or more, and as in Example 1, good resin pellets 9 could be obtained.

[0015] As described above, by using a thermoplastic resin 11 that has a bending modulus of elasticity of 1.8 GPa or less and a hardness of JIS A hardness of 80 or more as the thermoplastic resin 11 that coats the brass fiber bundle 5, it can be manufactured by the coil cutting method. The resin pellets 9 for injection molding containing the brass fibers 3 can be easily produced. As mentioned above, it has been confirmed that metal fibers manufactured by the coil cutting method have excellent performance as electromagnetic shielding materials, and the industrial value of being able to easily manufacture resin pellets 9 containing these metal fibers. is extremely large.

[0016] A comparative example will be disclosed to help understand how effective the above pellet manufacturing method is.

[Comparative Example 1] An attempt was made to produce brass fiber-containing pellets in the same manner as in Example 1 except that polystyrene was used alone as the thermoplastic resin 11. The flexural modulus of resin 11 was 2.9 GPa, and the hardness was 98 or higher. However, when the pellets were cut, the resin 11 cracked and the brass fibers 3 were scattered. This is because the bending elastic modulus of the resin 11 was too large.

[Comparative Example 2] The mixing ratio of polystyrene and styrene ethylene butylene styrene block copolymer was 9
An attempt was made to produce pellets in the same manner as in Example 1 above, except that the ratio was 0:10. The bending modulus of resin 11 is 2.0
GPa and hardness were 98 or higher. In this case as well, resin 11
Resin 1 was used when cutting the pellets because the bending modulus of
1 broke and the brass fibers 3 were scattered.

[Comparative Example 3] Ethylene α-olefin copolymer (manufactured by Mitsui Petrochemical Co., Ltd., “Tafuma P”) was used as the thermoplastic resin 11.
0280": Melt float 5.4 g/10min
) Pellet production was attempted in the same manner as in Example 1 above, except that the pellets were used. The bending modulus of resin 11 is 1.0GP
Below a, the hardness was 60. Although resin cracking did not occur when cutting the pellets, the holding force of the brass fibers 3 was weak due to the insufficient hardness of the resin 11, and it was not possible to cut the resin 11 and the fibers 3 together. That is, when an attempt was made to cut the resin-coated brass fibers 10 into lengths of 6 mm using the pelletizer 8, the fibers 11 were not cut and began to elongate.

[0020]

[Effects of the Invention] In summary, according to the present invention, an excellent effect can be exhibited in that injection molding resin pellets containing coil-cut metal fibers suitable for electromagnetic shielding can be easily produced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an apparatus configuration for carrying out a pellet manufacturing method according to the present invention.

FIG. 2 is a diagram showing an example of an apparatus configuration for manufacturing metal fibers by a coil cutting method.

[Explanation of symbols]

3 Metal fiber (brass fiber) 5 bundles 9 Pellets 11 Thermoplastic resin

Claims (1)

[Claims] Claim 1: In a method for producing raw material pellets suitable for injection molding of an electromagnetic shielding case, a bundle of metal fibers produced by a coil cutting method has a bending elastic modulus of 1.8 GPa.
Hereinafter, a method for producing raw material pellets for forming an electromagnetic shield casing is provided, which comprises coating a thermoplastic resin with a JIS A hardness of 80 or higher and then cutting the coated resin into predetermined lengths.