JPH10150291A - Compound electric wave absrober and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the alteration of mixing amount and ratio of high-frequency electric wave absorbing carbonyl iron and low-frequency electic wave absorbing soft ferrite by a method wherein the magnetic particles for high-frequency electric wave absorption and low-frequency electric wave absorption are dispersed respectively in aggregation state. SOLUTION: In order to manufacture the electric wave absorber, after mixing the high-frequency electric wave absorbing magnetic particles and the low-frequency electric wave absorbing magnetic particles individually with high molecular resin to be formed into pellets, respective pellets are dryblended to be thermally formed. Besides, respective magnetic particles are dispersed in aggregation state i.e., in roughly dispersed state to be evenly dispersed in the high molecular resin in such a state. Through these procedures, the dryblending step of different kinds of magnetic particles can be eliminated. Furthermore, if the pellets made of soft ferrite particles evenly dispersed in the high molecular resin and the other pellets made of carbonyl iron particles evenly dispersed also in the high molecular resin are prepared, both magnetic particles in arbitrary mixing ratio can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite electromagnetic wave absorber obtained by mixing a magnetic powder capable of absorbing high-frequency electric waves and a magnetic powder capable of absorbing low-frequency electric waves with a polymer resin and heating the mixture. The present invention relates to a composite electromagnetic wave absorber in which an intermediate frequency band of radio waves that can be absorbed by both magnetic powders can be absorbed by dry blending pellets of each magnetic powder before heat molding, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, wireless communication has rapidly progressed in homes and businesses, and indoor wireless local area networks (indoor wireless LAN), digital mobile phones, and simple mobile phones (personal computers) have been increasingly used. -Sonal handy-phone system (PHS) has become very popular. However, in the case of wireless communication, if a device that emits electromagnetic waves is present near a communication device, noise is generated and it becomes difficult to hear. For this reason, in home electric appliances and the like, an outer plate and an electromagnetic wave generating component are covered with a radio wave absorber or an electromagnetic wave shield material so that the generated electromagnetic wave does not leak outside.

[0003] Among them, as the radio wave absorber, a magnetic powder uniformly dispersed in a polymer resin and extruded has been used. Conventionally, the frequency of a radio wave which generates noise at a radio communication frequency is used. Has a low-frequency band of several hundred MHz and a high-frequency band of several tens of GHz. Therefore, a composite type compounded with a magnetic powder capable of absorbing radio waves in each band was used. Many of these composite types used carbonyl iron as a magnetic powder for absorbing high frequency radio waves and soft ferrite for absorbing low frequency radio waves.

In this composite type electromagnetic wave absorber, both magnetic powders are mixed by dry blending, then melt-blended with a polymer resin, the melt-blended material is formed into pellets, and then extruded into a desired shape. It was manufactured by a molding method, but it was said that both magnetic powders needed to be uniformly dispersed in the resin. However, when dry blending of different kinds of powders, secondary agglomeration occurs, so a complicated method is required for uniform mixing, and since magnetic powders are difficult to disperse in a polymer resin, it is difficult to uniformly disperse them. Needed to repeat the melt blending 2-3 times.

[0005] In recent years, with the lower frequency of communication equipment,
Radio waves having a frequency of 1 to 4 GHz also generate noise in communication equipment, and it has been necessary to change the mixing ratio of the two magnetic powders accordingly. You have to start with
There was a disadvantage that the production became complicated.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a radio wave absorber in which the mixing amount and ratio of carbonyl iron for absorbing high frequency radio waves and soft ferrite for absorbing low frequency radio waves can be easily changed, and a preferred method of manufacturing the same. Is provided.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a radio wave absorber formed by mixing magnetic powder for high frequency radio wave absorption and low frequency radio wave absorption with a polymer resin and molding the same. The magnetic powder for absorption was dispersed in a state of aggregation. When manufacturing the composite type electromagnetic wave absorber by forming a mixture of magnetic powder and a polymer resin to manufacture the electromagnetic wave absorber, magnetic powders for high-frequency wave absorption and low-frequency wave absorption are individually separated. After being mixed with a polymer resin and molded into pellets, each pellet was dry-blended and heat-molded.

[0008]

In the conventional composite-type electromagnetic wave absorber, the soft ferrite powder and the carbonyl iron powder were both uniformly dispersed in the polymer resin as shown in FIG. Are dispersed in an aggregate state, that is, a coarse dispersion state, as shown in FIG. 1, and when uniformly dispersed in a polymer resin in that state, the same electromagnetic wave absorption performance as that of a conventional composite type electromagnetic wave absorber is exhibited. Was found.

When the electromagnetic wave absorber has such a structure, dry blending of different magnetic powders becomes unnecessary, and the mixing ratio of both magnetic powders is such that soft ferrite powder is uniformly dispersed in a polymer resin. Prepared pellets and pellets prepared by uniformly dispersing carbonyl iron powder in a polymer resin, it is possible to easily mix the two magnetic powders simply by mixing and heating them. Can be manufactured. For example, if it is desired to absorb radio waves having a frequency of 1 to 4 GHz, the mixing amount of the carbonyl iron powder-mixed pellets should be the same as that of the 10 GHz-compatible radio wave absorber, and the mixing amount of the soft ferrite powder-mixed pellets should be increased. I just need. In addition, the obtained radio wave absorber simply dry blends the pellets and fuses them by heat molding, so the magnetic powder in the pellets does not move, and the magnetic powders are kept in an aggregated state and melted again. The step of dispersing becomes unnecessary.

The composite type electromagnetic wave absorber according to the present invention has a soft ferrite having a different band of an electromagnetic wave, for example, Mn-
There is no problem even if a Zn-based, Ni-Zn-based, Mg-Zn-Ni-based, or the like, or a material having a different particle size or purity is used. There is no problem even if carbonyl iron having various particle diameters and purity is used.

It is preferable that the mixing ratio of the soft ferrite powder and the carbonyl iron powder in the pellets is 70 to 90 wt% for each magnetic powder. The mixing ratio of the magnetic powder is 9
When the content is more than 0 wt%, the radio wave absorption performance is high, but the strength of the radio wave absorber is inferior because the amount of the binder polymer resin is small. When the content is less than 70 wt%, high radio wave absorption performance cannot be obtained. In addition, if the amount of magnetic powder of both pellets is the same, a radio wave absorber having the same amount of magnetic powder as that of the pellets can be manufactured regardless of the mixing ratio of both pellets, which is advantageous.

[0012] The polymer resin used for pelletization is not particularly limited, and a conventionally used thermoplastic resin or thermosetting resin may be used. As the former, polyethylene, polypropylene, polystyrene, polyvinyl chloride,
ABS resin, poly (meth) acrylate, acrylonitrile-styrene copolymer, ethylene-vinyl acetate copolymer, polyamide, polyethylene terephthalate,
Isoprene rubber, butadiene rubber, chloroprene rubber,
Examples thereof include ethylene-propylene rubber, nitrile rubber, and polyurethane, and the latter include unsaturated or saturated polyester resins, epoxy resins, phenol resins, melamine resins, and urethane resins. Mixing of each magnetic powder with the polymer resin may be performed by a known method such as melt blending using the same resin, and pelletization may be performed by extruding the melt blended material.

For processing into a radio wave absorber, a soft ferrite powder-mixed pellet and a carbonyl iron powder-mixed pellet are put into a mold such that both magnetic powders have a predetermined ratio, and the mold is heated under pressure. The pellets may be fused together.

[0014]

EXAMPLE Melt-blended Mn-Zn-based soft ferrite powder and carbonyl iron powder were separately melt-blended with an ethylene-vinyl acetate copolymer, and then extruded to have a magnetic powder content of 8%.
0 wt% and 90 wt% pellets were produced. afterwards,
Both pellets having the same magnetic powder content were mixed at various ratios, and heated and molded at 130 ° C. for 10 minutes to obtain a plate-shaped radio wave absorber. The soft ferrite powder is 80
In the case of wt% mixture, -26 dB, 90 w at 0.8 GHz
In the case of the t% mixture, the radio wave absorption characteristic of -30 dB at 0.6 GHz is shown, and the carbonyl iron powder is -30 dB at the frequency of 6 GHz when mixed with 80 wt%, and the radio wave absorption characteristic of -32 dB at the frequency of 5 GHz with the mixture of 90 wt%. Is shown.

Next, the amount of return loss of the obtained radio wave absorber was measured with a network analyzer manufactured by Hewlett-Packard Company, and the radio wave absorption performance was evaluated. This evaluation was performed based on the frequency at which the return loss shows the maximum and the return loss at that time. Table 1 shows the results.

[0016]

[Table 1] (Note) In the pellet mixing ratio, A is a soft ferrite powder mixed pellet, and B is a carbonyl iron powder mixed pellet.

[0017]

As described above, the radio wave absorber of the present invention
Although the electromagnetic wave absorption performance is the same as that of the conventional one, the one having a different mixing ratio of the magnetic powder can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a dispersion state of magnetic powder in a polymer resin in a radio wave absorber of the present invention.

FIG. 2 is a schematic diagram showing a dispersion state of magnetic powder in a polymer resin in a conventional radio wave absorber.

Claims (4)

[Claims] 1. A radio wave absorber formed by mixing magnetic powders for high frequency radio wave absorption and low frequency radio wave absorption with a polymer resin, wherein the magnetic powders for high frequency radio wave absorption and low frequency radio wave absorption are respectively A composite electromagnetic wave absorber characterized by being dispersed in an aggregate state. 2. The composite radio wave absorber according to claim 1, wherein the magnetic powder for high frequency radio wave absorption is carbonyl iron and the magnetic powder for low frequency radio wave absorption is soft ferrite. 3. When manufacturing a radio wave absorber by molding a mixture of a magnetic powder and a polymer resin, magnetic powders for high frequency radio wave absorption and low frequency radio wave absorption are individually mixed with the polymer resin. And then forming the pellets, dry blending the pellets, and heat-molding the pellets. 4. The method according to claim 3, wherein carbonyl iron is used as the magnetic powder for absorbing high frequency radio waves, and soft ferrite is used as the magnetic powder for absorbing low frequency radio waves. .