JP2000244174A - Radio interference prevention body and how to use radio interference prevention body - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for effectively using a radio wave interference preventer when used in various electronic devices. SOLUTION: An electromagnetic interference preventing body formed from a composition having an electromagnetic interference preventing function is placed at a distance of 0.1 m from an electromagnetic wave generating source.
It is arranged at a distance of m to 20 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio interference preventing body made of a radio wave interference preventing composition which is used for measures against radiation noise of electronic equipment, is lightweight, flexible, durable, hardly burns and covers a wide band. Regarding how to use it.

[0002]

2. Description of the Related Art The use of electronic equipment is wide and diversified, and the frequency used ranges from a few kHz near DC to a GHz band called microwave. Furthermore, wireless devices such as mobile phones and wireless LAN systems that emit radio waves into the air have been remarkably increasing in recent years.

[0003] On the other hand, there is a strong demand for reducing unnecessary radiation from a device and enhancing its resistance to extraneous electromagnetic waves, as radiated electromagnetic waves may cause malfunctions of other electronic devices. Furthermore, it has been pointed out that the emitted electromagnetic waves may adversely affect the human body, and there is a strong social demand for reducing unnecessary electromagnetic waves.

[0004] Parts used for such purposes include:
Filters, shields, and radio wave absorbers can be mentioned as typical examples. A filter is a component that uses a coil and a capacitor to protect a device that passes a necessary signal component but does not allow a noise component to pass through but rebounds. The shield blocks the outside and the inside by surrounding the device to be protected with a conductive film.
The radio wave absorber has a feature that an incident electromagnetic wave is converted into heat and a reflected wave is not generated.

However, a component such as a filter reflects a noise component and restores the noise component, and the returned noise component may adversely affect other circuits and devices.
Furthermore, at a frequency of GHz, the signal component not only flows in the circuit but also radiates to the space as a radio wave, so that it is difficult to effectively take measures against components such as a filter.

[0006] As for the shield, it is almost impossible to completely cover the equipment as a practical problem due to the presence of a signal introduction part and a heat radiation hole. When the frequency is further increased, the radiation leaks from even a small gap, and when the shield is improperly designed, the shield plate plays a role of an antenna, and the radiation may increase.

On the other hand, a radio wave absorber can be an ideal countermeasure against radiation noise because it converts incident electromagnetic waves into heat and does not generate reflected waves. However, applicable frequencies are limited for each material, and a wide spectrum component is obtained. It is not suitable for unnecessary radiation having Radio wave absorbers that can handle a wide frequency range have been developed for use in an anechoic chamber, but have a thickness of several tens of cm or more and cannot be used for electronic devices.

Several examples of radio wave absorbers adapted to each frequency band are disclosed. For example, JP-A-58-7319
No. 8 discloses a matrix of a conductive composite polymer material obtained by mixing conductive carbon fiber, carbon black, graphite or metal powder with a polymer material such as plastic or rubber and kneading and dispersing the polymer. There is described a radio wave shielding casing formed by impregnating or casting a mat, cloth, net, or flake material of a material obtained by metalizing a carbon-based fibrous material, a metal-based fibrous material, or a non-metallic fibrous material. I have. However, in the present invention, 1 MHz to 100
The attenuation of the electric field intensity in the range of MHz is increased,
There is no effect on radio waves having a frequency exceeding 00 MHz. Further, since the radio wave shielding casing contains a metal-based material, the total weight increases and the range of use is limited.

Japanese Patent Application Laid-Open No. Sho 60-249392 discloses a ferrite fine powder mainly composed of manganese and zinc.
An electromagnetic shielding material comprising a composition in which conductive carbon fine powder is dispersed in an organic polymer material is described.
The content of the ferrite fine powder in this composition is 30 to
70 Vol.%, And the specific volume resistivity of the composition is 10 ² to 1
It is 0 Ω · cm and has radio wave absorption. However, this composition can only absorb radio waves having a frequency in the range of 500 MHz to 1000 MHz. In addition, the above composition also contains manganese, zinc, etc., and has a high specific gravity and poor flexibility, so that its use range is limited.

[0010] Further, Japanese Patent Application Laid-Open No. 5-21984 describes that
An electromagnetic shielding composite material is described in which a plurality of coiled carbon fiber pieces are dispersed and carried in a low electrical conductivity material such as cement, synthetic resin, rubber, paper, etc. without any direction. However, since the coil-shaped carbon fiber pieces are easily entangled with each other, it is difficult to uniformly disperse the carbon fiber pieces in the fabric, and there is a disadvantage that the electromagnetic wave shielding effect tends to vary. Therefore, it is difficult to uniformly produce a thickness equal to or less than a certain value.

In addition, in the related art, a sheet-shaped radio wave absorber called a matching type which is commercially available, or in a conventional disclosure example, a conductor plate is provided on the opposite side of the electromagnetic wave incident surface,
The thickness of the electromagnetic wave is usually designed to be one quarter of the wavelength of the electromagnetic wave in order to convert the energy of the electromagnetic wave into heat by utilizing the interference effect between the incident electromagnetic wave component and the component reflected by the conductor plate. Such a radio wave absorber exhibits excellent electromagnetic wave absorption for electromagnetic waves of a specific wavelength, but hardly absorbs electromagnetic waves when the wavelength is shifted. Furthermore, it only absorbs electromagnetic waves from one direction, has a wide spectrum, and is not effective for noise components having various incident directions. Further, if a matching type radio wave absorber is used without a conductor plate, the electromagnetic wave is hardly absorbed and transmitted.

A conventional sheet-shaped radio wave interference preventing material is used by directly attaching it to electronic equipment such as an electromagnetic wave generating source that generates noise. However, although sticking has a certain effect in reducing radiated noise, in such a usage mode, noise may increase depending on the frequency of the noise. In this regard, a method for effectively implementing the radio wave interference preventive body has not been sufficiently established.

[0013]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for effectively using a radio wave interference preventer when it is used in various electronic devices.

[0014]

The above object is achieved by disposing a radio interference preventer formed of a composition having a radio interference prevention function at a distance of 0.1 mm to 20 mm from an electromagnetic wave generation source. Will be resolved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When applying a radio wave interference preventive to an electromagnetic wave generating source, it is considered that the reason for improving noise reduction performance by devising the shape of the radio wave interference preventive is as follows. . If the radio wave absorber has perfect radio wave absorption performance, radiation noise and the like can be reduced by arranging the radio wave absorber close to the noise source. However, the radio wave absorber currently under development does not have 100% absorption capacity at all target frequencies. That is, some reflected waves and transmitted waves are also generated. Therefore, a reflected wave of a specific frequency is generated, and the radio wave intensity may increase in some cases due to interference with the direct wave. Considering a simple rectangle or other shape as the applicable shape of the radio interference prevention body, radio waves corresponding to the lengths of the long and short sides increase the radio noise at that frequency due to interference as described above. Will be done. It is also considered that the antenna acts as an antenna and radio wave noise increases. On the other hand, as the shape of the radio wave absorber, if a space is provided so as to form a concave curved surface instead of a simple square, or if a cone or polygonal pyramid is formed, as described above for radio waves of a specific frequency It is considered that the occurrence of serious adverse effects is suppressed.

FIG. 1 is a schematic perspective sectional view showing an example of the mode of use of the radio wave interference preventer according to the present invention, and FIG. 2 is a sectional view taken along line AA in FIG. FIG. 3 is a sectional view showing another embodiment of FIG. As shown in FIG. 1, an electromagnetic wave generation source such as an antenna or a noise source 3 is mounted on an upper surface of a substrate 1 on which printed wiring and / or electronic components are mounted. A tunnel-shaped radio wave interference preventive body 5 covering the antenna 3 is provided. The entrance and exit of the tunnel-like radio wave interference preventive body 5 may be open or sealed. The electromagnetic wave generation source 3 is not limited to the illustrated antenna. All electronic components and electronic devices that generate electromagnetic waves can be targeted by the radio interference prevention body of the present invention.

Referring to FIG. What is important in the present invention is that
The distance D between the electromagnetic wave generation source 3 mounted on the substrate 1 and the radio wave interference preventive body 5 is maintained in a range of 0.1 mm to 20 mm. Electromagnetic wave source 3 and radio wave interference preventer 5
Is less than 0.1 mm, the result is the same as in the case of using the conventional electromagnetic wave absorber in close contact, and a sufficient effect of preventing electromagnetic waves cannot be obtained. On the other hand, when the distance D between the electromagnetic wave generation source 3 and the radio wave interference preventer 5 is more than 20 mm, it is not only difficult to apply to a small device, but also impractical in terms of cost. The distance D between the electromagnetic wave source 3 and the radio wave interference preventer 5 can be appropriately determined in consideration of factors such as the type and shape of the electromagnetic wave source 3 mounted on the substrate 1 and the intensity and frequency of the generated electromagnetic wave. .

As shown in FIG. 2, the space 7 between the electromagnetic wave generation source 3 and the radio wave interference preventer 5 can be hollow. However, in the case where the radio wave interference preventing body 5 does not have autonomy, as shown in FIG. 3, a polymer material 9 such as silicon resin is placed in the space between the electromagnetic wave generating source 3 and the radio wave interference preventing body 5. It can also be filled. Accordingly, the present invention can be implemented even when the radio wave interference prevention member 5 is relatively thin and cannot stand on the surface of the substrate 1 independently. Space 7
The polymer material 9 to be filled does not need to have a radio wave interference preventing function. Of course, polymer materials other than silicone resin can also be used. Such materials will be apparent to those skilled in the art. If desired, a material having an anti-interference function can also be used as a filling material for the space 7.

FIG. 4 is a schematic perspective sectional view of another example of the mode of use of the radio wave interference preventer 5 according to the present invention. As shown in the figure, the radio wave interference preventer 5 can be formed in a pyramid shape of a quadrangular pyramid. However, the shape is not limited to the illustrated quadrangular pyramid, and a triangular pyramid or a conical shape is also possible.

FIG. 5 is a schematic perspective sectional view of another example of the mode of use of the radio wave interference preventer 5 according to the present invention. As shown in the figure, a dome-shaped or hemispherical space 7 exists inside a radio wave interference preventer 5 having a rectangular cubic shape as a whole, and the electromagnetic wave generation source 3 is accommodated inside this space 7. . In this case, as an alternative, the radio wave interference prevention body 5 is not a rectangular cubic shape as shown, but has a dome shape or a hemisphere as if the bowl is lying down, and a dome shape or a hemisphere inside. Can be provided.

The thickness of the radio wave interference preventer 5 used in the present invention is not particularly limited. Generally, 0.1mm-20m
It is preferably within the range of m. If the thickness of the radio wave interference preventing body 5 is less than 0.1 mm, a sufficient radio wave interference preventing effect cannot be obtained. On the other hand, the thickness of the radio wave interference prevention body 5 is 20 mm.
Above this, the effect of preventing radio wave interference is only saturated, which is uneconomical. Further, the flexibility is unfavorably deteriorated.

The radio wave interference preventive used in the present invention can be formed from a known composition having a function of preventing radio wave interference. However, at least one kind of carbon fiber or magnetic particles is insulated from the graphitized carbon black. Dispersed in a conductive substrate, wherein the graphitized carbon black is blended at a weight ratio of 0.3 to 5 with respect to the total amount of the carbon fibers or the magnetic particles. Preferably, it is formed from a novel composition having

The graphitized carbon black composite particles used in the present invention are composed of crystalline graphite and amorphous carbon black. The graphitized carbon black composite particles are obtained by treating carbon black at a high temperature and gradually crystallizing the carbon black from the particle surface. The graphitized carbon black composite particles themselves are disclosed in Japanese Unexamined Patent Publication No.
No. 274493, which is well known.

In the radio interference preventing composition of the present invention, the content of the graphitized carbon black is 0.3 to 0.3 by weight based on the total amount of the carbon fibers and the magnetic particles.
5, a more preferred range is 1-3. Since the graphitized carbon black exhibits electromagnetic wave absorption and the magnetic particles and carbon fibers exhibit shielding properties, a radio wave interference preventive body having an excellent balance over a wide band can be obtained.

In the radio interference preventing composition of the present invention, the carbon fiber has a fiber length of less than 5,000 with respect to the particle size of the graphitized carbon black, and more preferably 13
By setting the ratio to 00 to 4000, excellent absorption characteristics are exhibited in a high frequency band exceeding 1000 MHz.

In the radio interference preventing composition of the present invention, the fiber length of the carbon fibers is 5,000 or more, more preferably 10 to the particle diameter of the graphitized carbon black.
500 MHz
It exhibits excellent absorption characteristics in the low frequency band below.

The specific gravity of the radio interference preventing composition of the present invention is 2.
5 or less, and a preferred range is 1.5 or less. For this reason,
Relatively lightweight.

The anti-interference body obtained from the anti-interference composition of the present invention has a hardness of 5 according to JIS K6253.
0 (JISA) or less, and a preferred range is 40 or less.
Therefore, it is very flexible and easy to use.

The tensile strength of a radio interference preventing body obtained from the radio interference preventing composition of the present invention in a tensile test according to JIS K6251 (balance method) is 4 × 10 ⁶ (Pa) or more, and a preferable range is 6 × 10 ⁶ (Pa). ) That is all. For this reason, it is very robust.

The anti-interference body obtained from the anti-interference composition of the present invention was obtained by a burning test using UL94HB using a test piece having a thickness of 3.05 mm, a width of 10.0 mm, and a length of 200 mm, and a burner of 30 mm. It has excellent flame retardancy of 38.1 mm / min or less when burned off for a second.

The anti-interference body obtained from the anti-interference composition of the present invention has a power of 10% or more when converted into a thickness of 2 mm at at least one frequency within a wide frequency range of 30 MHz to 20 GHz. It is a lightweight and flexible material that also absorbs electromagnetic waves and has a shielding property of transmitting 10% or less.

The role of the graphitized carbon black composite particles in the radio wave interference preventing composition of the present invention is as follows.
Mainly has the effect of absorbing electromagnetic waves. It is well known that when only conductive fibers are contained, high conductivity is obtained and an excellent shield is obtained.In this case, the incident electromagnetic wave is blocked, but the incident electromagnetic wave is shielded. And has little effect of absorbing electromagnetic waves. Graphitized carbon black composite particles alone exhibit a certain amount of electromagnetic wave absorption, but have a large amount of transmission components and are inferior in shielding properties. By coexisting the graphitized carbon black composite particles and the conductive fibers, it is possible to obtain a radio wave interference preventive having high electromagnetic wave shielding properties and also having electromagnetic wave absorbing properties.

Since it is extremely difficult to predict the amount of generated noise and its frequency distribution in advance in noise suppression of electronic equipment, various noise suppression parts may be added after the assembly of the equipment as necessary. It is in a situation where it has to be set up. There is a demand for a component that can be completely within the range of the noise standard by a simple means even if it cannot completely absorb the noise component. In this sense,
It is considered that the radio wave interference preventer of the present invention exerts an excellent effect.

The insulating substrate used in the composition for preventing radio interference of the present invention has properties such as strength, heat resistance, moldability, flame retardancy, flexibility and the like according to the use of the radio interference prevention body. Organic polymer materials are mainly used. Such organic polymer materials, for example, chloroprene rubber, acrylonitrile butadiene rubber, styrene butadiene rubber, natural rubber, various elastomers such as polyisoprene rubber,
Polyolefin resin, vinylidene chloride resin, polyamide resin, polyether ketone resin, vinyl chloride resin, polyester resin, alkyd resin, phenol resin, epoxy resin, acrylic resin, urethane resin, silicone resin, cellulose resin, vinyl acetate resin, polycarbonate resin And the like, and these may be used as a mixture if necessary. In particular, it is desirable to use a silicone resin. If necessary, solvents, dispersants, stabilizers, lubricants, fillers, extenders, plasticizers, crosslinking agents, antioxidants, vulcanization accelerators, photopolymerization initiators and the like may be added.

As a characteristic value of the graphitized carbon black composite particles, an abundance ratio (graphitization ratio) of crystalline graphite calculated from a peak area of a (002) plane in an X-ray diffraction diagram is used. The percentage is in the range of 5-90%, more preferably 10-70%.

The particle size of the graphitized carbon black is preferably from 1 nm to 10 μm, more preferably 1 nm to 10 μm.
It is desirable to be within the range of 0 nm to 100 nm.

As the magnetic particles used in the radio interference preventing composition of the present invention, magnetic particles classified as soft ferrite having a small coercive force are preferable. Magnetic particles are similar in effect to graphitized carbon black in that they have the effect of absorbing electromagnetic waves, but differ in the frequency range in which the effect is exhibited. That is, in the graphitized carbon black, the effective frequency is a high frequency of 1 GHz or more, while the magnetic particles are effective in a low frequency range of several tens MHz to several hundred MHz. . Typical magnetic particles are soft magnetic particles such as Mn-Zn ferrite, but magnetite and gamma iron oxide can also be used. Further, hexagonal planar ferrite, permalloy, flexible amorphous alloy powder, and a material obtained by heat-treating these may be used. The particle size is preferably in the range from 0.1 μm to 5 μm.

When the ratio of the total amount of the graphitized carbon black to the carbon fibers or the magnetic particles is less than 0.3 and the balance is magnetic particles, the weight of the anti-interference material increases. It is difficult to make a lightweight radio interference prevention material.
In addition, bending becomes difficult and flexibility tends to be impaired.

The radio interference preventing composition of the present invention can be produced by a conventional method such as kneading. Generally, as a method of kneading graphitized carbon black, conductive fibers and / or magnetic particle particles with an insulating substrate such as rubber or synthetic resin and uniformly dispersing them, there are kneaders, ball mills, roll mills, jets, and the like. This is performed using a mill or the like.

An example of a dispersing machine used for producing the radio interference preventing composition of the present invention is a device of a type called a kneader, which is characterized by applying strong compression, shearing force and the like. . The filler components may be dispersed after being charged together, but since the optimal dispersion conditions are different for each type of filler, each is separately dispersed to prepare a master batch, and these are later blended and mixed according to a predetermined It is preferable to prepare a liquid crystal interference preventing composition having a composition.

As an example, a method for dispersing graphitized carbon black particles will be described. Graphitized carbon black is charged in advance and crushed for several minutes. Thereafter, the resin component of the insulating substrate is added only in a minimum weight part necessary for the graphitized carbon black to become a uniform paste, and the initial kneading is performed. According to this method, extremely high compression, shearing force and the like can be applied. Such kneading is carried out for 30 minutes to 2 hours.

If an excessive amount of the resin component is added in the initial kneading, the viscosity of the paste is reduced, and the necessary compression, shearing force, etc. cannot be applied. On the other hand, when the resin component is too small, uniform paste and shear force cannot be applied to the entire paste, so that a uniform paste cannot be obtained. After completion of the initial kneading, the kneader,
An additional resin component is added by any means such as a mixer to prepare a paste having a predetermined composition. Since high shearing force or the like is not required for the purpose of additional mixing of the resin component, a general-purpose mixer or the like can be used. Thus, a master batch is prepared.

The production of a masterbatch containing conductive fibers and magnetic particles can be carried out in the same manner as in the case of graphitized carbon black.

Next, the obtained master batches are mixed to have a predetermined composition, and a desired viscosity is adjusted by adding a solvent and the like. Further, additives such as a curing agent, a polymerization initiator, and a cross-linking agent are added as needed to finally complete the composition.

The method for producing the radio wave interference preventive of the present invention from the above-mentioned radio wave interference preventing composition is not particularly limited. All methods commonly used by those skilled in the art for forming planar shapes such as sheets, three-dimensional shapes such as hemispheres, and the like can be used. Such methods include, for example, extrusion, casting, vacuum forming, injection molding, and the like.

[0046]

The following examples illustrate the manufacture of the radio wave interference preventer of the present invention and the effect of reducing noise.

Example 1 The production of a radio wave interference preventer will be described in three stages: a master batch production process, and a subsequent composition adjustment and molding process.

First Step: Preparation of Masterbatch (1) Preparation of Graphitized Carbon Black Masterbatch Graphitized carbon black particles (graphitization ratio: 31% (Rigaku X-ray diffractometer RINT15)
00, the target is Cu, and the acceleration voltage is 50 k.
X, X-ray diffraction measurement was performed while changing 2θ from 10 ° to 100 ° at an electric current of 100 mA and the peak area corresponding to the (002) plane in the obtained diffraction diagram. Was calculated. ), A particle size of 30 nm), and 220 g thereof were charged into a kneader (PNV-5H type for tabletop kneader 51 manufactured by Irie Shokai).
Run for 0 minutes to disintegrate. 1351 g of a silicone resin (TSE3032 (complex relative permittivity: real part 2.9, imaginary part 0.0026) manufactured by Toshiba Silicone Co., Ltd., base material) is added, and kneading is performed for 2 hours while cooling the kneader with water. Next, use a silicone resin (TSE303 manufactured by Toshiba Silicone).
2, main ingredient) 2451 g was added dropwise over 1 hour to prepare a carbon black master batch. The carbon black content was 14.0 wt%.

(2) Preparation of Conductive Fiber Masterbatch A carbon fiber (length: 40 microns, Vesfight HTA-CMF type manufactured by Toho Rayon) 2,000 g was put into a kneader (PNV-5H type for tabletop kneader 51 manufactured by Irie Shokai). Run for 10 minutes to break up. To this was added 2000 g of silicone resin (TES3032, manufactured by Toshiba Silicone Co., Ltd.), and kneading was performed for 2 hours while cooling the kneader with water to produce a carbon fiber masterbatch. 50wt carbon fiber content
%. Carbon fibers having lengths of 1 mm and 3 mm were similarly kneaded to prepare a master batch having a carbon fiber content of 50 wt%.

(3) Preparation of Magnetic Particle (Ferrite) Masterbatch 2000 g of soft ferrite particles (MAT-305 manufactured by Toda Kogyo, coercive force: 5 Oersted) were put into a kneader (PNV-5H type for tabletop kneader 51 manufactured by Irie Shokai). 10
Run for 1 minute to disintegrate. To this was added 2000 g of a silicone resin (TSE3032 manufactured by Toshiba Silicone, the main ingredient), and kneading was performed for 2 hours while cooling the kneader with water to prepare a ferrite masterbatch. Ferrite content is 50wt
%Met.

Second step: Composition adjustment 8.57 g from the graphitized carbon black composite particle masterbatch, 0.60 g from the 3 mm carbon fiber masterbatch, and further 18.24 g of a silicone resin (base agent), and defoaming The mixture was placed in a container for a mixer and mixed in a defoaming mixer for 8 minutes. next,
2.59 g of a silicone resin (curing agent) was added and mixed for another 2 minutes.

Third step: molding The obtained mixture was heated at 120 ° C. for 1 minute using an injection molding machine using a mold for 1 mm thickness. After being removed from the test press, it was further kept in an oven at 120 ° C. for 1 hour to complete the curing. Thus, a predetermined thickness of 1 mm
Thus, a semi-arc-shaped and long (ie, tunnel-shaped) radio wave interference preventive body containing 4 wt% of carbon black and 1 wt% of carbon fiber and having a radius of 3 mm was produced.

Example 2 Using the radio wave interference preventing composition produced in Example 1, a quadrangular pyramid-shaped pyramid-shaped radio wave interference preventing body was produced by the same molding method as in Example 1. The thickness of the side wall of the radio wave interference preventing body was 1 mm. The internal space remained hollow. The height from the bottom to the top of the pyramid was 1 mm.

Example 3 Using the radio wave interference preventing composition produced in Example 1, another quadrangular pyramid-shaped pyramid-shaped radio wave interference preventing body was produced by the same molding method as in Example 1. The thickness of the side wall of the radio wave interference preventing body was 1 mm, and the height from the bottom to the top of the quadrangular pyramid was 5 mm.

Example 4 Using the radio wave interference preventing composition produced in Example 1, a radio wave interference preventing body having a spherical surface having a radius of curvature of 50 mm was produced by the same molding method as in Example 1. The thickness of the side wall of the radio wave interference preventing body having the spherical surface was 10 mm, and the internal space covered by the spherical surface remained hollow.

Example 5 A radio interference preventing body having the same shape as that of Example 4 was produced by the same molding method as in Example 1 using the radio wave interference preventing composition produced in Example 1. The thickness of the side wall of the radio wave interference preventing body having the spherical surface was 10 mm, and the inner space of the hemisphere was filled with silicone resin.

Example 6 Each material was mixed in the following composition ratio of composition 1, and the obtained mixture was heated at 120 ° C. for 5 minutes using a test press using a mold having a thickness of 1 mm. In order to further complete the curing, it was kept in an oven at 120 ° C. for 1 hour. The shape was the same as in Example 1. Thus, a 1 mm-thick tonell-shaped radio wave interference preventive body was manufactured. (Composition 1) Soft magnetic amorphous alloy powder 70 parts by weight Thermosetting silicone resin 30 parts by weight

Example 7 A radio interference preventing body was produced in the same manner as in Example 1 except that carbon black w 04 wt%, carbon fiber 3 wt%, and ferrite magnetic particles 3 wt% were contained in the production process.

COMPARATIVE EXAMPLE 1 Using the composition for preventing radio wave interference produced in Example 1, a flat sheet-type radio interference preventive body having a thickness of 1 mm was produced by the same molding method as in Example 1.

Comparative Example 2 Using the radio wave interference composition produced in Example 6, a 1 mm thick flat sheet type radio wave interference preventer was produced by the same molding method as in Example 6.

The noise reduction effect of each radio wave interference preventer obtained in Examples 1 to 7 and Comparative Examples 1 and 2 was measured. A circuit equipped with a crystal oscillator was used as a model device for examining the noise reduction effect. The noise reduction effect was evaluated using a near-field electromagnetic field evaluation device EPS-M1 (manufactured by Noise Research Laboratories) using a magnetic field probe. FIG. 6 shows the outline of this measuring method. FIG. 6 shows Comparative Example 1.
FIG. 1 is a schematic view of a state in which a radio interference preventive body is measured. In the figure, reference numeral 1 denotes a substrate, 3 denotes an antenna, 5 denotes a radio interference preventive body, 11 denotes an oscillator, 13 denotes a power supply, and 15 denotes a near electromagnetic field measurement. The probes are shown respectively. The distance between the radio wave interference preventer 5 and the near electromagnetic field measurement probe was 15 mm. Note that the electric field strength is obtained by setting the measured frequency of the oscillator 11 to 50 MHz.
z, 200 MHz, and 500 MHz were set and measured, and the measured value of the electric field strength by the radio wave interference preventive body of Comparative Example 1 was set as a reference (that is, zero point), and the increase / decrease of the electric field strength with respect to this reference value was determined. . The measurement results are summarized in Table 1 below.

[0062]

[Table 1]

As is clear from the results shown in Table 1,
The three-dimensionally shaped radio interference prevention body of the present invention has a very excellent noise reduction effect as compared with a conventional planar radio interference prevention body.

[0064]

As described above, according to the present invention,
Instead of the conventional planar use of the radio wave interference preventive body, the distance between the electromagnetic wave generation source and the radio wave interference preventive body is 0.1 mm to 20 mm.
So that a space having a separation distance within the range of
By using a three-dimensional shape such as a tunnel shape, a conical shape, a hemispherical shape, etc., it is possible to exhibit a very excellent noise reduction effect as compared with a conventional planar use.

[Brief description of the drawings]

FIG. 1 is a schematic perspective sectional view of an example of a usage mode of a radio wave interference preventer according to the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a sectional view showing another embodiment of FIG. 2;

FIG. 4 is a schematic perspective sectional view of another example of a usage mode of the radio wave interference preventer according to the present invention.

FIG. 5 is a schematic perspective sectional view of another example of a usage mode of the radio wave interference preventer according to the present invention.

FIG. 6 is a schematic diagram of a state in which noise of the radio wave interference prevention body of Comparative Example 1 is measured.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 3 Electromagnetic wave generation source 5 Radio interference prevention body 7 Space 9 Filler 11 Oscillator 13 Power supply 15 Proximity electromagnetic field measurement probe

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Futagawa 884-1, Kamikurata-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture 229 Totsuka High Rise 229 Inventor Yuji Sasaki 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Shinichi Kitahata 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Masato Nishida 1-88 Ushitora, Ibaraki-shi, Osaka F-term (reference) in Hitachi Maxell, Ltd. 5E321 AA21 BB32 BB33 GG05 GG09 GG11

Claims (8)

[Claims] 1. A radio wave interference preventer formed from a composition having a function of preventing radio wave interference and disposed at a distance of 0.1 mm to 20 mm from an electromagnetic wave generation source. 2. The composition having the function of preventing radio wave interference, wherein at least one of carbon fibers or magnetic particles and a graphitized carbon black are dispersed and mixed in an insulating substrate. The radio wave interference preventive body according to claim 1, wherein the composition is a composition in which the weight ratio is 0.3 to 5 with respect to the total amount of the carbon fibers and the magnetic particles. 3. The radio wave interference preventive body according to claim 1, wherein a space between the electromagnetic wave generation source and the radio wave interference preventive body is hollow. 4. The radio wave interference preventive body according to claim 1, wherein the space between the electromagnetic wave generation source and the radio wave interference preventive body is solid. 5. An electromagnetic interference preventive formed from a composition having an electromagnetic interference preventing function is placed at a distance of 0.1 m from an electromagnetic wave generation source.
A method for using a radio wave interference preventer, wherein the radio wave interference preventer is disposed at a position at a separation distance of m to 20 mm. 6. The composition having the function of preventing radio wave interference, wherein at least one of carbon fibers or magnetic particles and graphitized carbon black are dispersed and mixed in an insulating substrate, and the graphitized carbon black is
The method according to claim 5, wherein the composition is a composition blended at a weight ratio of 0.3 to 5 with respect to the total amount of the carbon fibers or the magnetic particles. 7. The method according to claim 5, wherein the space between the electromagnetic wave generating source and the radio wave interference preventive body is hollow. 8. The method according to claim 5, wherein the space between the electromagnetic wave generation source and the radio wave interference preventive body is solid.