JPH0552336B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a sheet-like radio wave absorbing material. [Prior art and its problems] Radio wave absorbing materials are used to prevent reflected radio waves and jamming radio waves from the skyscrapers that proliferate in urban spaces, or from high-rise structures near the coast, bridges on the sea, etc. that are generated on the radar of ships during navigation. It is a new component whose demand has been increasing in recent years for purposes such as preventing radar false images. Conventionally, an appropriate amount of ferrite powder such as barium ferrite (BaO・6Fe ₂ O ₂ ) or by-product ferrite,
Molded products mixed with polymeric materials such as plastic and rubber are used to absorb these radio waves. However, conventional radio wave absorbers that use a single layer of these have a narrow frequency band width that exhibits radio wave absorption performance, and in actual use, their applications are often limited and extremely inconvenient; There has been a strong desire for the emergence of a radio wave absorber that has excellent absorption capacity relative to the bandwidth. In response to this request, the inventors of the present application previously filed a patent application.
No. 56-109686 and Japanese Patent Application No. 56-169492, as shown in FIG.
proposed a radio wave absorber structure in which metamorphic layers 3 are stacked. [Object of the Invention] The present invention provides a method for manufacturing the radio wave absorber, particularly a method for manufacturing a radio wave absorber that eliminates the directionality of radio wave absorption. [Structure of the Invention] The present invention provides that, for 100 parts of powdered elastomer,
100 to 500 parts of ferrite powder is mixed with 2 to 150 parts of conductive fibers with a diameter of 10 to 100 microns and a length of 0.5 to 5 mm, and the resulting conductive fibers are uniformly oriented. This method of manufacturing a radio wave absorbing material sheet is characterized in that a mixture mixed so as not to have a radioactive substance is formed into a sheet of a predetermined thickness using a hot press molding machine, and is vulcanized if necessary. It becomes possible to easily construct a radio wave absorbing material by stacking the radio wave absorbing material sheet itself produced according to the present invention in many layers, or by combining it with a sheet formed by mixing only ferrite powder. . [Detailed description of the structure] The present invention is made of a mixture of powdered elastomer, ferrite powder, and conductive fibers, and the conductive fibers are uniformly distributed in the structure without directionality. Since it is important to mix the elastomer with the elastomer, it is necessary that the elastomer used be in powder form. Therefore, any powder of various elastomers can be used. For example, powdered styrene-butadiene rubber, powdered butadiene rubber, powdered isoprene rubber, powdered nitrile rubber, powdered chloroprene rubber,
Elastic polymer materials such as powdered ethylene propylene rubber, powdered ethylene propylene terpolymer rubber, powdered butyl rubber, powdered acrylic rubber, powdered chlorosulfonated polyethylene, and powdered natural rubber can be selected depending on the purpose and the characteristics of the elastomer. . Of course, various plastic powders such as powdered polyethylene and powdered polyamide can be used instead of powdered elastomer, but when used as a product, there are certain issues such as workability, adhesion to other base materials, flexibility, weather resistance, etc. In many cases, it is preferable to use an elastomer. As the ferrite used in the present invention, iron oxide powder such as barium ferrite, manganese ferrite, iron ferrite, etc. can be used. Needless to say, finer ferrite particles are preferable during mixing. Considering practical conditions such as workability and strength retention, the appropriate amount of addition is 100 to 500 parts per 100 parts of the elastomer. The conductive fiber is used to adjust the dielectric constant of the tissue, and suitably carbon fiber or metal fiber such as brass. In order to resonate with a wide range of electromagnetic waves, it is best to make them as thin as possible and randomly mix them with various lengths, but in reality, from the viewpoint of workability and stability of properties, it is best to make them as thin as possible and randomly mix them with a diameter of 10 to 100 mm.
Preferably, it has a length of about 0.5 to 5 mm. When mixing powdered elastomer, ferrite, and conductive fibers, it is necessary to stir and mix in a state where no shearing force is applied. The mixture must be mixed by gentle rotation without cutting or damaging the conductive fibers. Otherwise, the conductive fibers will be cut and shortened, making it impossible to obtain the effects of the present invention. This also applies when molding into a sheet, so
A press that avoids extruders, kneading rolls, calender rolls, and other objects that apply shearing force, and allows conductive fibers to be molded in any direction without being cut or damaged, and without being oriented in a fixed direction. It is preferable to mold the material into a sheet by applying heat and pressure. Of course, adding appropriate amounts of a vulcanizing agent, accelerator, and anti-aging agent is the same as in the case of ordinary mold vulcanization. A plurality of sheets molded in this manner can also be stacked at different angles if necessary. [Example] The present invention will be specifically explained below with reference to Examples. Example 1 Various additives and ferrite powder in the proportions shown in Table 1 were added to powdered chloroprene rubber (Skyprene B-30 medium particle size 500μ manufactured by Toyo Soda) and mixed by stirring at high speed using a Henschel type stirrer. After, Table 1
The amount of brass fiber shown was added and thoroughly mixed at low speed with no substantial shearing force applied. The obtained powder mixture was heated under pressure using a press molding machine to obtain a vulcanized rubber sheet for a radio wave absorber. Example 2 Chlorosulfonated polyethylene (Hypalon)
40 (manufactured by Dubon) was frozen and ground to a medium particle size of 500μ.
A powder of chlorosulfonated polyethylene was obtained.
Various additives, ferrite powder, and brass fiber were added in the proportions shown in Table 1, and the mixture was molded in the same manner as in Example 1 to obtain a vulcanized rubber sheet for a radio wave absorber. Example 3 Ethylene propylene terpolymer (Espren
505 (manufactured by Sumitomo Chemical) was freeze-pulverized to obtain a powdered ethylene propylene terpolymer with a median particle size of 500μ. Various additives, ferrite powder, and brass fiber were added to this in the proportions shown in Table 1, and Example 1
A vulcanized rubber sheet for a radio wave absorber was obtained in the same manner as above. Example 4 A vulcanized rubber sheet for a radio wave absorber having the composition shown in Table 1 was obtained in the same manner as in Example 1 using pulverized nitrile rubber (Nipol 1042, manufactured by Nippon Zeon, medium particle size 500μ).

【table】

[Table] Comparative Example 1 General-purpose chloroprene rubber (Skyprene B-30 manufactured by Toyo Soda) without using powdered chloroprene rubber
Brass fiber was kneaded using a conventional two-roller according to the formulation of Example 1. This was heated under pressure using a press molding machine to obtain a vulcanized rubber sheet for a radio wave absorber. Figure 2 shows a frequency characteristic diagram when the return loss is measured by rotating the polarization plane of the incident radio wave by 90 degrees.
In the figure, A and B are planes of polarization that differ by 90 degrees from each other. The limit frequencies at which the return loss for the polarization plane A is 20 dB or less are indicated by f ₁ and f ₁ ', and those for the polarization plane B are indicated by f ₂ and f ₂ '. Generally, the amount of attenuation of radio waves incident on a radio wave absorber with the plane of polarization rotated by 90 degrees will be different values at the same frequency. Therefore, the deflection planes indicated by A and B in Fig. 2 are
Radio wave absorption performance as shown by 90° different characteristics
It can be said that the radio wave absorber is excellent as the frequency band defined by f ₁ and f ₁ ' matches the band defined by f ₂ and f ₂ '. Table 2 shows the radio wave absorption performance (the above f ₁ , f ₁ ′, f ₂ , f ₂ ′) measurement results are shown.

[Table] As is clear from Table 2 above, when the sheet made from general-purpose chloroprene rubber of the comparative example was used as a sheet for a radio wave absorber, f ₁ and
While the value of f ₁ ' is completely different from the values of f ₂ and f ₂ ' in FIG. 2, in other embodiments the values of f ₁ and f ₂ and
This shows that f ₁ ′ and f ₂ ′ are almost equal. This shows that the medium in the example does not have any unique properties in the in-plane direction of the sheet, that is, it is an isotropic medium, and the present invention is effective as a method for manufacturing a sheet for radio wave absorbers. It shows that.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a radio wave absorber according to the present invention, and FIG. 2 is a diagram showing frequency characteristics when the return loss is measured by rotating the deflection plane of the incident radio wave by 90 degrees. 1 is a metal plate, 2 is a radio wave absorbing material targeted by the present invention, and 3 is a metamorphic layer.

Claims (1)

[Claims] 1. A method for producing a radio wave absorbing material by mixing an elastomer, ferrite powder, and conductive fiber, comprising:
A powdered elastomer is used as the elastomer, and 100 to 100 parts of ferrite powder is used for 100 parts of the elastomer.
500 copies, diameter 10-100 microns, length 0.5-5
2 to 150 parts of millimeter conductive fibers are added and mixed with stirring, and the resulting mixture is press-molded into a sheet of a predetermined thickness so that the conductive fibers are uniformly mixed without directionality. A method for manufacturing a radio wave absorbing material. 2. The method according to claim 1, wherein the elastomer is powdered chloroprene rubber. 3. The method of claim 1, wherein the elastomer is powdered cross-sulfonated polyethylene. 4. The method of claim 1, wherein the elastomer is a powdered ethylene propylene terpolymer. 5. The method according to claim 1, wherein the elastomer is powdered nitrile rubber. 6. The method according to claim 1, wherein the conductive fiber is a brass fiber.