JPH03268398A - Pellet for electromagnetic shield molding and manufacture of enclosure of electromagnetic shield type - Google Patents

Abstract

PURPOSE:To maintain a molding working property and a shielding effect at a high degree by a method wherein the whole or one part of a group of metal fibers whose outside diameter corresponds to 20 to 200mum and which are intertwined mutually in the length direction is covered with a plastic and it is cut to a length of 5 to 20mm. CONSTITUTION:Metal fibers whose outside diameter corresponds to 20 to 200mum are intertwined mutually in the length direction; the whole or one part of a group of the metal fibers is covered with a plastic; and it is cut to a length of 5 to 20mm to be pelletized. As a manufacturing means of the metal fibers to be intertwined, nothing is specified. As a preferable method to be recommended, the following method is suitable: a metal thin sheet is wound on a mandrel; the mandrel is turned; a cutting tool is installed at its edge and is fed; and the metal fibers whose cross section is a rectangular shape and which are intertwined loosely are manufactured. Thereby, a molding working property and a shielding effect can be maintained at a high degree.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an electromagnetic shielding pellet in which metal fibers are arranged so as to exhibit an excellent electromagnetic shielding effect, and a relatively inexpensive shielding method using the same. The present invention relates to respective manufacturing methods for manufacturing highly effective electromagnetic shielding type casings.

[Prior Art] The development and spread of electronic devices 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 affect peripheral devices.
Recently, there have been cases of electromagnetic interference caused by malfunctions, and this has suddenly become a problem.

In particular, recently, devices have become more compact and mass-produced, and the housings of various electronic devices are now being replaced with plastic molded products instead of the conventional metal, making them virtually defenseless against the electromagnetic waves mentioned above. is in a state. That is, compared to metal, plastic is almost transparent to electromagnetic waves, and not only does it emit a large amount of electromagnetic radiation, but also foreign electromagnetic waves can easily penetrate into plastic.

Therefore, in order to electromagnetically shield plastic molded products,
It is common practice to provide a conductive layer on the surface of a molded product. Such methods include conductive paint application, metal spraying, foil adhesion, vapor deposition, sputtering, and plating.
Both are troublesome and unsuitable for mass production.

For this reason, methods of mixing conductors such as metal ribbons, flakes, powders, metallized glass, carbon black, and carbon fibers into plastics have attracted attention and are being implemented in order to make the plastic materials themselves conductive. It started to be done.

[Problems to be Solved by the Invention] None of the above conductor mixing methods exhibit the same characteristics, and in order to obtain a high shielding effect, the aspect ratio of the mixed conductor (parts that are aligned in the length direction) must be adjusted. It is necessary that the mixed conductors have a large cross-section ratio), that the mutual contact of the mixed conductors is maintained well, and that the fluidity of the plastic to be molded is not impaired.

Recently, 20μ
Shielding composite materials that are a mixture of unrestrained steel fibers with a diameter of m or less have come to be used relatively often.

However, the ultra-fine stainless steel fibers produced with a diameter of 20 μm or less are quite expensive, and there is a problem in that the molded product itself becomes expensive.

In addition, when attempting to increase the shielding effect by increasing the aspect ratio of such ultra-fine stainless fibers, there is a problem in that fiber balls, that is, a type of fluff, deteriorate moldability and shielding performance. there were.

The purpose of the present invention is to solve the problems of the prior art as described above, to maintain a high aspect ratio, to maintain good contact between metal fibers, and to eliminate the formation of fiber balls. The object of the present invention is to provide pellets for forming electromagnetic shields that can maintain high properties and shielding effects, and methods for producing electromagnetic shielding type casings using the pellets.

[Means for Solving the Problems] The present invention firstly provides an outer diameter equivalent to 20 to 200 μm.
metal fibers are intertwined with each other in the length direction, the entangled metal fibers are entirely or partially covered with plastic, and are cut into lengths of 5 to 20 m and pelletized. Second, the pellets are put into an injection molding machine and heated and extruded to increase the aspect ratio of the metal fibers and maintain good contact between the metal fibers. It is used to mold.

It includes those with an outer diameter equivalent to that of a circular cross section, but it may also have a non-circular cross section, and if it is possible to produce entangled metal fibers with an equivalent outer diameter of 20 to 200 μm when the cross section is made into a circular cross section,
The manufacturing method is not particularly specified; therefore, it does not matter whether the obtained result has a circular cross section or a non-circular cross section.

However, the recommended and preferred method is to wind a thin metal plate around a mandrel and rotate it, set a cutting tool on the end face of the metal plate, and then feed it to produce loosely intertwined metal fibers with a rectangular cross section. It is. The above-mentioned equivalent outer diameter can be adjusted depending on the thickness of the thin metal plate used and the feed rate of the cutting tool. Hereinafter, this will be referred to as the coil cutting method.

Through experiments, we found that the outer diameter range of metal fibers needs to be at least 20 μm to limit the formation of fiber balls, and that it is sufficient to set it to 200 μm or less in order to obtain a high shielding effect with the addition of a small amount of metal fibers. Ta. As the material constituting the metal fiber, copper or a copper alloy is preferable from the viewpoint of electrical conductivity.

Additionally, it was discovered through experiments that an extremely high shielding effect can be obtained by loosely intertwining metal fibers with each other. As will be detailed later, this allows the present invention to maintain good molding fluidity and high shielding performance,
and can realize economic efficiency.

Additionally, the pellets are coated with plastic to make them suitable for injection molding machines. The length of the pellet must be 5 or more in order to maintain shielding performance. In addition, from the M limit of the ability to penetrate into the screw of the molding machine, the pellet length is 20
It is necessary to keep it below rm.

On the other hand, as the plastic for the coating, general-purpose molding plastics such as ABS resin, polypropylene (PP), polyphenylene sulfide (PPS), polystyrene (PS), or polyphenylene oxide (PPO) may be used as appropriate.

[Example] The present invention will be described below with reference to Examples.

Example 1 A thin brass plate having a thickness of 25 μm was cut to a width of about 50 μm using the coil cutting method described above, and the cut piece was wound up so that the fibers were intertwined with each other. As a result, the length of each fiber was 50 to 80 aa, and the average length was about 5
As a result, 1000 m of continuous brass fiber bundles were obtained. 400 of these fibers
The bundle was coated with polystyrene to a thickness of 0.3 m+ at a temperature of 190° C. using an extruder, and then cut into the shape of an electric wire using a pelletizer to obtain pellets containing brass fibers of a predetermined length.

A predetermined amount of these pellets and polystyrene pellets were mixed and molded into 80 at 230° C. using an injection molding machine and a mold having a plate-shaped cavity. Injection molding was successful. As a result, 150% containing 4.0% by volume of brass fibers
A sheet of x150x2+m was obtained.

Next, the shielding effect of electric field waves and magnetic field waves was measured using a commonly used shield box and spectrum analyzer (both manufactured by Atopan Test Co., Ltd.).

Table 1 shows the results.

The values at 200MH7 for samples with different pellet lengths are higher as the pellet length increases, but all pellet lengths of 5 to 20 m show sufficient shielding effects.

Comparative Example 1 Example 1 except that the pellet length was 3 stops and 25n+n
A sheet containing brass fibers was prepared in the same manner as above. As a result of measuring the shielding effect, as shown in Table 1, a sufficient effect could not be obtained with 3 stops. The 2'zn+ pellets did not sink into the screw and a sheet could not be produced.

Example 2 Pellets with a length of 7 mm were obtained in the same manner as in Example 1 except that the outer diameter of the brass fibers was changed to 20 μm and 150 μm. next,
A molded sheet containing 4% by volume of yellow IPJ fibers and O was produced under exactly the same conditions as in Example 1, and the shielding effect was measured.

The results are shown in Table 2.

Both outer diameters of 20 μm and 150 μm show a good shielding effect.

Comparative Example 2 Example 2 except that the fiber outer diameter was 10 μm and 250 μm.
A molded sheet was prepared in the same manner as above, and the shielding effect was measured.

The results are also shown in Table 2.

In the case of 10 μm, aggregation of fibers (the above-mentioned fiber balls) occurred, and uniform dispersion could not be obtained, so that a sufficient shielding effect could not be obtained. In the case of 250 μm, no fiber balls are formed, but the shielding effect is greatly reduced at the same mixing amount (4.0% by volume).

Table 2 Comparative Example 3 A molded sheet was produced in the same manner as in Example 1 using (conventionally known) brass fibers with an outer diameter of 50 μm without fiber entanglement.

The measurement results of the shielding effect are shown in Table 3 in comparison with the corresponding example of Example 1.

This comparison clearly shows that the beret/t with entangled fibers provides a great shielding effect.

Comparative Example 4 Stainless steel fiber pellets with a pellet length of 7 mm and an outer diameter of 10 mm were prepared and injection molding was attempted with a composition of 2 and 4% by volume of stainless steel, but a uniform molded sheet with high viscosity was obtained. I couldn't.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention,
It is possible to provide pellets for electromagnetic shielding molding that can maintain a high aspect ratio and maintain a good contact state between metals, and that does not form fiber balls and can therefore maintain high moldability and shielding effect. Using the same, it is possible to manufacture a housing with extremely good electromagnetic shielding effect, and the present invention has extremely great industrial value in these days when electromagnetic interference is becoming a major social problem.

Claims (3)

[Claims] (1) Metal fibers with an outer diameter of 20 to 200 μm are intertwined with each other in the length direction, and all or part of the intertwined metal fibers are covered with plastic, and the length is 5 to 20 mm. Cut pellets for electromagnetic shield molding. (2) The pellet for forming an electromagnetic shield according to claim 1, wherein the metal fibers are made of copper or a copper alloy. (3) The pellets according to claim 1 or 2 are put into an injection molding machine and heated and extruded, thereby increasing the aspect ratio of the metal fibers and maintaining good contact between the metal fibers, thereby forming injection molding. A method for manufacturing an electromagnetic shield type casing.