JPH05267882A - Material for molding electromagnetic shield - Google Patents

Abstract

PURPOSE:To obtain a material for molding an electromagnetic shield having a good shielding effect, in both near and far distances, by containing metallic fibers such as copper, copper alloy, iron, iron alloy having a rectangular section and metallic fibers having a thinner wire diameter in a molding material. CONSTITUTION:A bundle of metallic fibers are mixed in a molding material, and a shielding effect to an electromagnetic wave noise of a plastic body is secured. In this case, a material in which one or more kinds of copper, copper alloy such as brass, iron, iron alloy fiber having a rectangular section and a reduced diameter of 30 to 100mum and one or more kinds of copper, copper alloy, iron, iron alloy fiber such as stainless having a circular section and a diameter of 20mum or less are mixed in the molding material is used as a material for molding an electromagnetic shield. Accordingly, the good shielding effect in a far distance is obtained in the metallic fiber having the rectangular section and also the good shielding effect in a near distance is obtained in the metallic fiber having the circular section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic shield molding material capable of molding a plastic casing having an excellent electromagnetic shield.

[0002]

2. Description of the Related Art In recent years, many techniques have been disclosed for imparting electroconductivity to a plastic housing in order to improve its defense against electromagnetic noise. For example, a method of mixing conductors such as metal flakes, powder, metallized glass, carbon black, and carbon fiber into a plastic material, and recently, metal fiber bundles coated with resin and cut into pellets are used as master pellets together with base resin pellets. The method of injection molding the housing has become mainstream. For example, molding resin pellets mixed with stainless fiber master pellets, molding resin pellets mixed with copper fiber master pellets, or metal fiber master pellets containing a low melting point alloy are mainly used, and these are electromagnetic shields. It is commercially available as a resin.

It is said that these electromagnetic shield resins can obtain a very large shield effect of 20 to 80 dB in an electric field shield measurement and a magnetic field shield measurement called the Advantest method.

[0004]

However, various evaluations of these commercially available shield materials have revealed that the shielding effect in the near field is certainly excellent, but the shielding effect in the far field is inferior. For example, both are 20 dB or less. It turns out that it will be.

Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art and provide an electromagnetic shield molding material having excellent shielding performance in both near field and far field.

[0006]

In order to achieve the above object, the present invention provides a molding material which comprises a copper alloy having a rectangular cross-section and a reduced diameter of 30 to 100 μm, a copper alloy such as brass, iron, and an iron alloy fiber. Any one or a plurality of types and an iron alloy fiber such as copper, a copper alloy, iron, and stainless steel having a diameter of 20 μm or less is included.

Brass fibers having a rectangular cross section, copper, copper alloys,
Fibers such as iron and iron alloys can be obtained by, for example, the coil cutting method of Yanagisawa et al. That is, a bundle of copper fibers having a rectangular cross section can be obtained by winding a thin metal sheet of brass or the like on the mandrel in multiple layers and sequentially cutting from the ends of the wound coil body with a cutting tool.

As the metal fiber such as stainless steel, an ultrafine fiber having a circular cross section obtained by a drawing method which is widely commercially available is used. The circular cross section is provided to prevent fiber cutting during processing. In addition, copper with a circular cross section, copper alloy,
The iron and iron alloy fibers can be obtained by drawing or drawing by passing through a repeating die.

In the case of a rectangular cross section, the contact area between fibers becomes large, which is advantageous for imparting conductivity. However, the thin cross section of 20 μm or less is inferior in strength and it is necessary to make a circular cross section.

The flat cross-section brass fiber, copper, copper alloy, iron, iron alloy fiber has a diameter of 30 to 30 in terms of circle (circular diameter equivalent to cross-sectional area).
It must be 100 μm. If the thickness is 30 μm or less, the shielding effect of frequency 100 MHz or less is insufficient,
With the above, it becomes difficult to obtain a sufficient shield effect regardless of the frequency. That is, a large amount of brass fibers must be mixed. As a result, the mechanical properties of the resin are impaired.
It is preferably 40 to 60 μm.

Stainless steel fiber, copper of round cross section, copper alloy,
Iron or iron alloy fiber has a diameter of 20 μm or less, preferably 16 μm.
~ 8 μm. If it is 6 μm or less, it is practically difficult to manufacture, so that 8 to 20 μm is preferable. If the diameter is 20 μm or more, the shielding effect at 200 MHz or more is insufficient.

[0012]

In the above, the rectangular cross-section brass fiber, copper, copper alloy, iron, iron alloy fiber has a good far-field shielding effect, that is, it exhibits a high shielding effect in the low frequency region, particularly 100 MHz or less, but in the high frequency region. It was found that stainless fiber, copper with a circular cross section, copper alloy, iron, and iron alloy fiber were inferior in shielding effect in the low frequency region but were very excellent in the high frequency region. Therefore, by appropriately using both in accordance with the purpose, the far-field shielding effect can be remarkably enhanced in a wide frequency range. Also, brass fiber, copper, copper alloy, iron, iron alloy fiber is 10 to 25 wt% with respect to resin, stainless fiber, copper with a circular cross section,
Copper alloy, iron, and iron alloy fibers are used in the range of 1 to 10 wt% as a guide.

[0013]

EXAMPLES Examples of the present invention will be described in detail below.

First, Table 1 shows Examples 1 to 4 and Comparative Examples 5 to 8.

[0015]

[Table 1]

Example 1 Rectangular brass fibers obtained by the coil cutting method (converted diameter 50 μm)
Polystyrene resin in a bundle (Sbright 55 manufactured by Showa Denko KK
After 5) was extrusion coated, it was cut into pellets with a length of 7 mm.
On the other hand, pellets of stainless fiber bundles (focused with a slight amount of polyvinyl alcohol resin) having a diameter of 8 μm and a length of 7 mm were prepared.

These pellets were mixed with polystyrene resin pellets to contain 12 wt% brass fiber and 5 wt% stainless fiber. 150t with well mixed pellets
It was injected into a mold at 240 ° C. by an injection molding machine to prepare a plate-like sample having a thickness of 2 mm and a size of 150 × 50 mm. The fibers on the surface of the sample were uniformly dispersed.

This sample was tested by Advantest, TR173.
02 Shield material evaluator and Hewlett-Packard network analyzer 10-1000MHz
The shield effect of was measured. The evaluator has two TEMs.
It consists of a cell and is set so that the impedance inside the cell is 377Ω.
Unlike the near-field measurement of the R17301 evaluator, the far-field shield effect can be evaluated. The measurement result is shown in FIG.

From FIG. 1, 20 dB at 10 to 1000 MHz
It was found that the above good shielding effect is given. The injection moldability was also good.

Examples 2 to 4 In the same manner as in Example 1, fibers having the diameters shown in Table 1 had a length of 7
The mixture was mixed as a pellet of mm to prepare an injection-molded sheet.
Far field shield effect in the same way 10,50,10
Evaluations were made at frequencies of 0, 300, and 1000 MHz, which are also shown in Table 1.

All the samples give a high shielding effect of 20 dB or more. The injection moldability was also good.

Comparative Example 5 A molded sheet was prepared in the same manner as in Example 1, except that the brass fiber alone was used to greatly increase the amount of admixture to 20 wt%. The shield effect is relatively good in the low frequency region, but 300,100MHz
It turns out that it is greatly inferior in the high frequency range.

Comparative Example 6 This is a case where 12 wt% of stainless fiber was mixed alone.
The resin viscosity at the time of molding is high, and it is expected that molding will be difficult if the mixing amount is further increased.

The shielding effect is remarkably inferior in the low frequency region of 100 MHz.

Comparative Example 7 This is a case where the diameter of the fiber is out of the range of the present invention. It can be seen that the shielding effect is greatly inferior even with the same amount and composition as in Example 1.

Comparative Example 8 This is a case where copper fibers having a circular cross section (diameter of 50 μm) were used together with stainless fibers. It can be seen that the shield effect is still far inferior to that of the present invention.

Table 2 shows Examples 9 to 14 and Comparative Examples 15 to 20.

[0028]

[Table 2]

Example 9 A rectangular copper fiber (converted diameter 45 μm) bundle obtained by a coil cutting method was added to a polystyrene resin (Sbright 55 manufactured by Showa Denko KK).
After 5) was extrusion coated, it was cut into pellets with a length of 7 mm.
On the other hand, a stainless fiber bundle having a diameter of 16 μm and a length of 7 mm produced by a drawing method was similarly produced to obtain pellets. Combine this with polystyrene resin pellets and use flat rectangular copper fiber for 15w
t%, stainless fiber is mixed to be 4 wt%,
A 150 t injection molding machine was used to perform injection molding into a mold at a temperature of 240 ° C. to prepare a plate-like sample having a thickness of 2 mm and a size of 150 × 50 mm.

This sample was used for 10 to 1000 by using a far field shield material evaluator TR17302 and a Hewlett Packard network analyzer.
It was evaluated in MHz. The measurement results are shown in FIG.

From FIG. 2, 20 dB at 10 to 1000 MHz
It was found that the above good shielding effect is given. The injection moldability was also good.

Example 10 A plate-shaped sample was manufactured in the same manner as in Example 9 except that the rectangular metal fiber was changed to rectangular stainless fiber (SUS-304), and the shield effect was measured. Far field shield effect is 10,50,
The evaluation was performed at each frequency of 100, 300 and 1000 MHz. From Table 2, a sufficient shielding effect was shown and the injection moldability was also good.

Examples 11 to 14 As shown in Table 2, a rectangular copper fiber having a converted diameter of 80 μm and 16 μm
m round stainless fiber (Example 11), converted diameter 35
Flat copper fibers of 16 μm and round stainless steel fibers of 16 μm (Example 12), flat copper fibers of reduced diameter 80 μm and 16 μm
The round-shaped copper fiber (Example 13), the rectangular stainless fiber having a reduced diameter of 60 μm and the round-shaped copper fiber (Example 14) were mixed in a predetermined amount, and a plate sample was injection-molded. All showed good far-field shielding effects.

Comparative Example 15 When a rectangular copper fiber having a converted diameter of 120 μms is used, the shielding effect is low in the entire frequency range as shown in Table 2.

Comparative Example 16 When the round stainless fiber has a thickness of 25 μm, the shielding effect in the high frequency range is largely insufficient.

Comparative Example 17 When the rectangular copper fiber is used alone, a sufficient shielding effect cannot be obtained at 300 and 1000 MHz.

Comparative Example 18 When round stainless steel fibers were used alone, the mixing amount was 14 wt.
% Is close to the limit in terms of injection moldability. Even in this case, the low frequency shield effect is insufficient.

Comparative Example 19 The case where the converted diameter of the rectangular stainless fiber was 25 μm, and the diameter of the round stainless fiber was 16 μm. The shielding effect in the entire frequency range is insufficient for the amount of admixture.
Observation revealed that the rectangular stainless fibers had been cut, and sufficient contact between the fibers could not be obtained.

Comparative Example 20 A sample using 50 μm round copper fibers and rectangular copper fibers. Almost no shielding effect in high frequencies.

[0040]

In summary, according to the present invention, it is possible to obtain a plastic molded case having excellent electromagnetic shielding characteristics in the far field, and the industrial value of the present invention is extremely high in the situation where electromagnetic noise troubles continue in recent years. It is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an electromagnetic shield characteristic in a frequency range in Example 1 of the present invention.

FIG. 2 is a diagram showing an electromagnetic shield characteristic in a frequency range in Example 9 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Asano Inventor Hideki Asano 5-1-1 Hidakacho, Hitachi City, Ibaraki Hitachi Power Systems Co., Ltd. Power Systems Laboratory (72) Inventor Toshio Ozone 3-chome Uchikanda, Chiyoda-ku, Tokyo 11th-7th Nitto Alloy Co., Ltd.

Claims (1)

[Claims] 1. A molding material comprising copper having a rectangular cross section and a reduced diameter of 30 to 100 μm, a copper alloy such as brass, iron, etc.
An electromagnetic shield molding material comprising any one or more kinds of iron alloy fibers and any one or more kinds of iron alloy fibers such as copper, copper alloy, iron and stainless having a diameter of 20 μm or less.