JPH046120B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic shielding material suitable for shielding plastic housings of electronic devices and shielding noise prevention between electronic devices.
Conventionally, conductors have generally been used as electromagnetic shielding materials, and metal plates (iron, permalloy, copper, aluminum, etc.) have excellent shielding effects, but have the drawbacks of being expensive and heavy. There is.
Other methods include applying a metal thin film to plastic by plating, vapor deposition, etc., or applying conductive powder (carbon powder, metal powder, etc.) or conductive fiber (carbon long fiber or short fiber, metal long fiber or metal fiber) to plastic. There are some methods that use conductive plastics mixed and kneaded with short fibers, but these have the drawbacks of poor electromagnetic shielding properties and higher costs. In addition, the use of conductors in the first place simply utilizes electric field reflection in most cases, which has disadvantages such as magnetic field problems (weak magnetic field shielding effect) and side effects due to the generation of reflected waves.

In view of the above points, the present invention combines a composite ferrite cloth made of composite ferrite fibers with the function of absorbing radio waves and a reticular conductor, thereby providing an excellent electromagnetic shielding effect and high flexibility. The aim is to provide an electromagnetic shielding material that is lightweight and strong and can accommodate a variety of shapes.

The electromagnetic shielding material of the present invention has an average particle size of 0.3 to
A mixture of 20 μm ferrite powder mixed with a polymer material at a volume mixing ratio of 0.2 to 0.8 is made to a thickness of 50 μm.
The thickness of the coating is applied to a polymeric material film of less than m.
It has a structure in which a cloth made of composite ferrite fibers obtained by cutting a composite ferrite sheet formed with a composite ferrite layer of 100 μm or less into slits into widths of 100 μm or less and a net-like conductor are laminated.

Examples of the electromagnetic shielding material according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. In this figure, when the direction of incidence of radio waves is indicated by arrow A,
A composite ferrite cloth 2 is provided on the front surface of the reticular conductor 1. Here, the net conductor 1 is formed of a metal net made of iron, permalloy, copper, aluminum, etc., or is made of conductive fiber made by diffusing copper ions into acrylic fibers and chemically bonding copper between molecules. (for example,
The product name is ``Thunderon SSN'' (Japan Silk Hair Dyeing Co., Ltd.). In addition, composite ferrite cloth 2
As shown in Figure 2, a liquid composite ferrite material prepared by mixing ferrite powder with an average particle size of 0.3 to 20 μm with a polymeric material such as an adhesive at a volume mixing ratio of 0.2 to 0.8 is mixed with a material such as polyester or the like having a thickness of 50 μm or less. The composite ferrite sheet 5, which is coated onto a polymer material film 3 to a thickness of 100 μm or less to form a composite ferrite layer 4 and dried, is cut into slits with a width of 100 μm or less as shown in FIG.
The composite ferrite layer 4 forms a composite ferrite fiber 6 in the form of a ribbon, and the composite ferrite fiber 6 is woven into a cloth. Here, the reason why the average particle size of the ferrite powder is set to 0.3 to 20 μm is because fine particles with a diameter smaller than 0.3 μm increase in particles smaller than the crystal grain size, deteriorating magnetic properties, and coarse particles larger than 20 μm. This is because processability deteriorates and becomes an obstacle to obtaining sufficiently thin and flexible composite ferrite fibers. In addition, the volume mixing ratio of the ferrite powder to the polymeric material was set in the range of 0.2 to 0.8 because if the ratio is smaller than 0.2, the magnetic properties of the resulting composite ferrite layer 4 will be insufficient.
This is because if the ratio is larger than 0.8, there is a problem that the flexibility of the composite ferrite layer 4 is impaired.
Furthermore, the reason why the thickness of the polymer material film is 50 μm or less and the thickness of the composite ferrite layer 4 is 100 μm or less is to obtain sufficient flexibility, and the composite ferrite sheet 5 is cut into slits with a width of 100 μm or less. The reason for this is to obtain composite ferrite fibers with sufficient flexibility. In addition, the composite ferrite fiber 6 may be wound and blended with a thread having a core of nylon fiber, acrylic fiber, or polyester fiber, and then woven into a cloth. Alternatively, the reticular conductor 1 and the composite ferrite cloth 2 may be bonded together using an adhesive.

According to the first embodiment, in addition to the electrostatic shielding effect provided by the mesh conductor 1, the magnetic shielding effect provided by the composite ferrite cloth 2 is added, and electromagnetic shielding can be performed satisfactorily. Furthermore, since the composite ferrite cloth 2 has a radio wave absorbing effect, the radio waves incident on the composite ferrite cloth 2 are attenuated by the magnetic loss of the composite ferrite cloth 2, and the radio waves are incident on the net-like conductor 1, causing the net-like conductor to The magnetic field generated when a current flows through the body 1 can be absorbed by the magnetic loss of the composite ferrite cloth 2 laminated on the net-like conductor 1, and the side effects of reflected wave generation can be eliminated. As a result, the amount of attenuation can be improved by several dB or more compared to the case of a simple mesh conductor alone, and this improvement effect becomes more noticeable as the frequency becomes higher. Also,
The combination of the net-like conductor 1 and the composite ferrite cloth 2 is highly flexible and can accommodate a variety of shapes.
Lightweight and strong electromagnetic shielding material can be easily created.

FIG. 4 shows a second embodiment of the invention. In this figure, when the direction of incidence of radio waves is indicated by arrow A,
A composite ferrite cloth 2 is provided on the back side of the mesh conductor 1. The effects in this case are also almost the same as in the first embodiment.

FIG. 5 shows a third embodiment of the invention. In this figure, when the direction of incidence of radio waves is indicated by arrow A,
A composite ferrite cloth 2 is provided on the back surface of the net-like conductor 1, and an aluminum plate 10 is further provided on this back surface. The attenuation characteristic of the radio wave in this case is the curve X in Figure 6.
The result is a conductive fiber (product name: Thunderon SSN) in which copper is chemically bonded between molecules by diffusing copper ions into the acrylic fiber shown by curve Z.
10dB compared to the case of only Nippon Kasuke Dyeing Co., Ltd.)
It can be seen that the amount of attenuation increases. Note that if a sufficiently thin foil-like aluminum plate 10 is used, the net conductor 1 and the composite ferrite cloth 2
It can be adapted to various shapes without sacrificing its flexibility.

FIG. 7 shows a fourth embodiment of the invention. In this figure, when the direction of incidence of radio waves is indicated by arrow A,
A mesh conductor 1 is provided on the back surface of the composite ferrite cloth 2, and an aluminum plate 10 is further provided on this back surface. The attenuation characteristic of the radio wave in this case is the curve Y in Figure 6.
It can be seen that the amount of attenuation is considerably larger than in the case of only conductive fibers shown by curve Z. In addition, in the case of this fourth embodiment as well, if a sufficiently thin foil-like material is used as the aluminum plate 10,
The mesh conductor 1 and the composite ferrite cloth 2 can be made to correspond to various shapes without impairing their flexibility.

As explained above, the electromagnetic shielding material of the present invention has a good electromagnetic shielding effect because it combines a cloth made of composite ferrite fibers and a net-like conductor, and it generates reflected waves due to the radio wave absorption effect of the composite ferrite fibers. can be prevented. Furthermore, since it has flexibility, it can be adapted to various shapes, and has the advantage of being lightweight.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the electromagnetic shielding material according to the present invention, FIGS. 2 and 3 are perspective views showing the process of making a composite ferrite cloth, and FIG. 4 is a second embodiment of the present invention. 5 is a sectional view showing the third embodiment of the present invention, FIG. 6 is a graph showing the radio wave attenuation characteristics of the embodiment, and FIG. 7 is a sectional view showing the fourth embodiment of the present invention. It is a diagram. 1... Reticular conductor, 2... Composite ferrite cloth,
3... Polymer material film, 4... Composite ferrite layer, 10... Aluminum plate.

Claims (1)

[Claims] 1. A mixture of ferrite powder with an average particle diameter of 0.3 to 20 μm mixed with a polymer material at a volume mixing ratio of 0.2 to 0.8 is applied to a polymer material film with a thickness of 50 μm or less to form a composite ferrite layer with a thickness of 100 μm or less. The width of the composite ferrite sheet is
An electromagnetic shielding material characterized by laminating a cloth made of composite ferrite fiber cut into slits of 100 μm or less and a mesh conductor.