JPH05299871A - Resin composition for absorbing high-frequency electromagnetic wave - Google Patents

Abstract

PURPOSE:To enhance the absorption of high-frequency electromagnetic wave and the strength by including a fibrous alkaline earth metal titanate and a thermoplastic resin. CONSTITUTION:No particular restrictions is placed on the fibrous alkaline earth metal titanate, and publicly known ones can widely be used. Among them, preferably, a fibrous alkaline earth metal titanate is used which is expressed by a general formula MO.nTiO2 (where M is an alkaline earth metal, and n is a real number between 1 to 12) and obtained by depositing the carbonate of an alkaline earth metal on the surface of fibrous titania by solution reaction and heat-treating it at 500 to 1300 deg.C. The concrete examples of M include Be, Mg, Ca, Sr, Ba, Ra, etc. Since the resin composition contains a fibrous alkaline earth metal titanate, an excellent pulling strength can be given to a molded part obtained by molding the resin composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a resin composition for absorbing high frequency electromagnetic waves.

[0002]

2. Description of the Related Art Conventionally, electronic devices generate high-frequency pulse signals (electromagnetic waves), and particularly in electronic devices to which digital technology is applied, a harmonic component of about 500 MHz.
It is known that the above extremely high electromagnetic waves are generated. For example, in an electronic device equipped with a magnetron tube or the like for generating electromagnetic waves or an electronic device equipped with a high-frequency transmitter, the electromagnetic wave itself leaks to the outside of the device. In addition, in equipment for the purpose of generating electromagnetic waves such as communication equipment,
The electromagnetic wave may leak from a portion other than the portion to which the electromagnetic wave should be output (for example, an antenna). It is already known that such high-frequency electromagnetic waves adversely affect the inside and outside of the device.

Sheet metal is conventionally used for housings of electronic devices, and since the sheet metal has a property of blocking electromagnetic waves, no special measures are required. However, with the progress of mass production and price reduction of electronic devices, plastics having no electromagnetic wave shielding performance have been adopted as housings, and it has become necessary to prevent leakage again.

At present, various attempts have been made to prevent electromagnetic waves from leaking from electronic devices. The most powerful method among them is to absorb electromagnetic waves and convert them into heat. Specifically, it is a method in which a ferrite powder having a high magnetic permeability and a high soft magnetic property having an electromagnetic wave absorbing ability is sintered and processed into a plate shape, and applied as a radio wave absorber. However, ferrite powder has a relatively low electromagnetic absorption band,
It has a drawback that the absorption performance of high frequency electromagnetic waves of 1 GHz or more is insufficient. Further, the sintered body is not suitable for mass production because the workability and formability are extremely poor,
It is also not practical because it has brittle properties.

In order to solve such a problem, ferrite powder is mixed with resin and molded and used as a radio wave absorber. However, high frequency electromagnetic waves of 1 GHz or more related to the basic properties of ferrite are used. The drawback of inadequate absorption performance remains unresolved. Moreover, it is necessary to mix a large amount of ferrite powder in order to develop the electromagnetic wave absorption characteristics, but since the powder has a large specific surface area, the compatibility with the resin is low, and the amount of the resin capable of expressing the electromagnetic wave absorption characteristics is set to be low. It is almost impossible to mix. Further, even if it can be mixed with the resin by some method, there is a problem that the strength of the obtained molded product is extremely low.

In addition to ferrite, alkaline earth metal titanate powder is also used as a dielectric material to be mixed with resin, but its electromagnetic wave absorption characteristics are not satisfactory.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a resin composition which can well absorb high frequency electromagnetic waves, especially high frequency electromagnetic waves of 1 GHz or more and which has high strength.

The present inventor has conducted extensive studies to develop a resin composition which meets the above object, and as a result, when a fibrous alkaline earth metal titanate metal was mixed with a thermoplastic resin as a dielectric material, titanic acid was used. A radio wave absorption characteristic that cannot be seen when an alkaline earth metal powder is used is exhibited, and it is possible to obtain a molded product that can absorb high frequency (especially high frequency electromagnetic wave of 1 GHz or more) very well and has high strength. Found out. The present invention has been completed based on such findings.

That is, the present invention relates to a resin composition for absorbing high frequency electromagnetic waves, which comprises a fibrous alkaline earth metal titanate and a thermoplastic resin.

The fibrous alkaline earth metal titanate used in the present invention is not particularly limited, and conventionally known ones can be widely used. Among these, a general formula MO · nTiO ₂ (where M is an alkaline earth metal) obtained by depositing a carbonate of an alkaline earth metal on the surface of the fibrous titania compound by a solution reaction and performing heat treatment at 500 to 1300 ° C. It is preferable to use a fibrous alkaline earth metal titanate represented by a group metal, and n is a real number of 1 to 12. Here, specific examples of M include Be, Mg, Ca, Sr, and B.
Examples thereof include a and Ra. The alkaline earth metal titanate has already been disclosed in JP-A-3-16917.
The shape of the fibrous alkaline earth metal titanate is not particularly limited, but a fiber having a fiber length of about 3 to 1000 μm and a fiber diameter of about 0.1 to 10 μm is usually used. Among them, those having an aspect ratio (ratio of fiber length / fiber diameter) of 10 or more are preferable. Further, those having an average fiber length of about 10 to 20 μm and an average fiber diameter of about 0.2 to 1 μm are particularly preferable.

The thermoplastic resin used in the present invention is not particularly limited. For example, a thermoplastic urethane resin,
Chlorotrifluoroethylene resin, tetrafluoroethylene-hexafluoropropylene resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride resin, ethylene-tetrafluoroethylene copolymer, ethylene-chlorofluoroethylene copolymer, Vinyl chloride resin, vinylidene chloride resin, polyethylene, polypropylene, chlorinated polyolefin, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polystyrene, ABS resin, polyamide, methacrylic resin, polyacetal, polycarbonate, cellulose resin, Polyvinyl alcohol,
Polyurethane elastomer, polyimide, polyetherimide, polyamideimide, ionomer resin, polyphenylene oxide, methylpentene polymer, polyallyl sulfone, polyallyl ether, polyether ketone,
Examples thereof include polyphenylene sulfide, polysulfone, aromatic polyester, polyethylene terephthalate, polybutylene terephthalate, thermoplastic polyester elastomers, polymer alloys of various other polymeric substances, and blends.

In the present invention, it is preferable to further add ferrite, and by using the ferrite together with the fibrous alkali metal titanate, the radio wave absorption characteristics can be further improved. The ferrite to be used is not particularly limited, but soft magnetic ferrite is preferable, and the real part of the complex permeability at low frequency (1 MHz) is 500 or more, the decrease at high frequency is small, and the imaginary part is high at high frequency. Soft magnetic ferrite is particularly preferred. The composition and shape of the ferrite are not particularly limited.

The mixing ratio of the fibrous alkali metal titanate and the thermoplastic resin is not particularly limited, but when the ferrite is not further mixed, the amount of the fibrous alkali metal titanate is usually mixed. 30-9 in the composition
0% by weight (hereinafter simply referred to as "%"), preferably 4
It is preferable to set it to about 0 to 80%. When the content of the alkali metal titanate is much less than 30%, the radio wave absorption property tends to deteriorate, while when it is more than 90%,
All of them are not preferable because they tend to be difficult to form.

When ferrite is blended in the composition of the present invention, the blending amount of ferrite in the composition is preferably about 10 to 70%, more preferably about 30 to 50%. However, it is important that the sum of the weights of the fibrous alkali metal titanate and the ferrite is within the range of 40 to 90% with respect to the total weight of the composition.

Further, in the present invention, in addition to the above-mentioned thermoplastic resin, fibrous alkali metal titanate and ferrite, a powdery dielectric inorganic substance may be optionally used in combination, and the original purpose of the present invention. Other additives such as a surface treatment agent, a compatibilizer, a heat conduction improver, a lubricity improver, and a colorant can be appropriately added as long as the achievement is not adversely affected.

By injection molding the resin composition for absorbing high frequency electromagnetic waves of the present invention, high strength high frequency electromagnetic wave absorbers of various shapes can be easily manufactured.

The characteristics of the high-frequency electromagnetic wave absorber thus obtained are 500 MHz or more (the most effective range is 2-3 GH).
In z), the strength is high, the productivity is good, and the cost is low because it is reinforced with fibrous alkali metal titanate while having a radio wave absorption characteristic with an attenuation factor of −10 dB or more.

[0018]

EXAMPLES The present invention will be further clarified with reference to Examples and Comparative Examples below.

Examples 1 to 7 10 g of fibrous titania hydrate (TiO ₂ .1 / 2H ₂ O, average fiber length 15 μm, average fiber diameter 0.2 μm) was used.
% Of barium chloride aqueous solution 233 g homogeneously dispersed under stirring at room temperature with 20 g of 20% aqueous ammonium carbonate solution for 30 minutes, followed by stirring for another 30 minutes, followed by filtration and washing with water. Then, 32 g of a white fibrous substance was obtained by drying. From the observation of X-ray diffraction, infrared absorption spectrum (hereinafter referred to as “IR”) and scanning electron microscope (hereinafter referred to as “SEM”), this product retains the fiber shape of the raw material titania hydrate and has barium carbonate on its surface. Was uniformly deposited and had a composition of BaCO ₃ / TiO ₂ = 1/1 (molar ratio).

10 g of the product obtained by this method was transferred to an alumina crucible and heat-treated in a muffle furnace at 950 ° C. for 2 hours to obtain 8.1 g of a white fibrous substance.
By IR analysis of this product, absorption of barium carbonate completely disappeared, no diffraction peak other than BaO.TiO ₂ was observed in X-ray diffraction, and it was further confirmed by SEM observation that the raw material fiber shape was retained. Fibrous BaO.TiO ₂ could be synthesized with a yield of not less than%.

Next, the obtained fibrous BaO.TiO ₂ was kneaded with a thermoplastic resin, and in some cases, with soft magnetic ferrite [BSF-547, manufactured by Toda Kogyo Co., Ltd.] at a compounding ratio shown in Table 1, A resin composition of the present invention was obtained. Table 1
In, PPS is polyphenylene sulfide, PB
T is polybutylene terephthalate and PA-66 is polyamide-66.

[0022]

[Table 1]

Comparative Examples 1-3 25 g of barium carbonate (special grade reagent) was sufficiently ground in a mortar (average particle size 0.8 μm) and 10 g of the fibrous titania hydrate used in Examples 1 to 7 was dry-processed. The homogeneous mixture was added to an alumina crucible in the same manner as in Examples 1 to 10 to give 10 g.
The mixture was put in and baked at 950 ° C. for 2 hours to obtain 8.2 g of a white powder. In the IR analysis of this product, barium carbonate disappeared, but in X-ray diffraction, BaO.TiO ₂
In addition, it was an aggregate of various compositions such as TiO ₂ (rutile) and BaO · 3TiO ₂ . In addition, the shape of the raw material fiber was a partially broken, damaged, melted, granular, or powdery mixture. The powder thus obtained is converted to a “calcining method BaO.Ti
O ₂ ”.

Next, the obtained BaO.TiO ₂ obtained by the firing method was added to P
A resin composition was obtained by kneading with PS, and in some cases, with soft magnetic ferrite at a mixing ratio shown in Table 2.

[0025]

[Table 2]

Comparative Examples 4 to 6 In addition to the fibrous BaO.TiO ₂ obtained in Examples 1 to 7 and the baked BaO.TiO ₂ obtained in Comparative Examples 1 to 3,
Commercially available powdered barium titanate [KYORI ×
BT-S, manufactured by Kyoritsu Ceramic Materials Co., Ltd.] was fired at 1400 ° C. for 6 hours, and then pulverized into a powder. Thus the powder obtained is referred to as "powder BaO · TiO _2".

Then, the obtained powder BaO.TiO ₂ was added to PP.
The resin composition was obtained by kneading with S, and in some cases, with soft magnetic ferrite at a blending ratio shown in Table 3.

[0028]

[Table 3]

Characteristics of each resin composition obtained in Examples 1 to 7 and Comparative Examples 1 to 6 (radio wave absorption characteristics and tensile strength)
Was measured by the following method, and the results are shown in Table 4 below.

Radio wave absorption characteristics: The sample for measuring the radio wave absorption characteristics is a donut having an inner diameter of 17.0 mm, an outer diameter of 38.2 mm and a thickness of 3.0 mm, which is obtained by heating to the softening point of the resin and sufficiently kneading the mixture. It was formed into a shape. The electromagnetic wave absorption characteristics of the sample were measured by the S parameter measurement method.

Tensile strength: Tensile strength was measured according to JIS-K7113.

[0032]

[Table 4]

[0033]

According to the present invention, high frequency electromagnetic waves, especially 1
Provided is a resin composition which can well absorb high frequency electromagnetic waves of GHz or higher and has high strength. That is, since the resin composition of the present invention contains a fibrous alkaline earth metal titanate, a molded product obtained by molding the resin composition can have excellent tensile strength. Therefore, the resin composition of the present invention is extremely excellent in mass productivity because cracks and the like are unlikely to occur even when it is injection molded into molded articles of various shapes. Further, because the fibrous alkaline earth metal titanate used in the present invention has good absorption characteristics for high frequencies, particularly radio waves of 500 MHz or more, and because of the effect of reflection attenuation because the fibrous material is dispersed in the resin, Since the radio wave absorption characteristics of the obtained molded body are particularly effective in the microwave band, the molded body can be suitably used as an absorber of high frequency electromagnetic waves generated from electronic devices.

Claims (3)

[Claims] 1. A resin composition for absorbing high frequency electromagnetic waves, which contains a fibrous alkaline earth metal titanate and a thermoplastic resin. 2. A fibrous alkaline earth metal titanate is generally obtained by depositing a carbonate of an alkaline earth metal on the surface of a fibrous titania compound by a solution reaction and further heat-treating at 500 to 1300 ° C. Formula MO ・ nTiO ₂
(In the formula, M is an alkaline earth metal, and n is a real number of 1 to 12.) The resin composition according to claim 1. 3. The resin composition according to claim 2, wherein M is Ba.