JPS58184797A - Method of producing radio wave absorber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a sheet-like radio wave absorbing material.

Radio wave absorbing materials are used to prevent reflected electromagnetic interference from high-rise buildings in urban spaces, or to prevent false radar images generated on the radar of ships navigating by high-rise structures near the coast or bridges on the sea. It is a valuable component whose uses have been expanding in recent years. Conventionally, barium ferrite (B
Plastics or rubber mixed with an excess amount of femite powder such as a0.6Fe, O, ) or -ferrite are used for the purpose of absorbing these radio waves. However, conventional radio wave absorbers that use a single layer of these materials have a narrow frequency band that exhibits radio wave absorption performance, and in actual use, their applications are limited and may be extremely inconvenient.
It was hoped that a radio wave absorber with a wider frequency band would emerge.

In order to solve such conventional drawbacks, the inventor of the present application has filed the following patent application No. 56-109686 and I# No. 56-16.
In No. 9492, as shown in FIG. 1, a radio wave absorber structure was proposed in which a radio wave absorber 2 and a metamorphic layer 3 were laminated on a metal plate 1. The present invention relates to a method for manufacturing the radio wave absorbing material, and in particular, it is an object of the present invention to provide a method for manufacturing a radio wave absorbing material that eliminates the directionality of radio wave absorption.

According to the present invention, for 100 g of liquid polymer material, 100 to 500 parts of ferrite powder and a diameter of 10 to 1100 I
t, 5 to 150 conductive fibers with a length of 500 μm to 5 m
% and stirred and mixed at a circumferential speed of 1 w 1/9 Ilc or less, and the resulting mixed paste was formed into a sheet by a constant velocity roll or roll coater at 5 Orpm or less, or by pouring, and vulcanized. A method for manufacturing the material is obtained.

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 mixed only with ferrite powder.

In the present invention, it is important to uniformly mix the conductive fibers, so it is necessary to use a liquid polymer material. Therefore, not only rubber, which is essentially an enemy, but also solid rubber dissolved or emulsified, and fine plastic powder emulsified or dispersed can be used. In other words, liquid rubber such as tolyl rubber, natural rubber dissolved in a solvent, fine polyethylene powder dispersed in water, or polymer emulsion can all be used, so the high-quality rubber may be used depending on the purpose. Molecular materials should be selected.

The ferrites used in the present invention are barium ferrite, manganese, and ferri. Iron oxide powders such as iron ferrite and iron ferrite can be used. Needless to say, smaller particles are preferable during mixing. Suitable conductive fibers are carbon fibers or metals such as brass, both of which have a diameter of 10μ to 100μ and a length of 500μm5.
It is preferable to have a diameter of about m. When mixing and molding, it is necessary to stir without shearing force for practical purposes.
In order to do this, it is necessary not to use a stirrer that has a mechanical effect, but to rotate the stirrer slowly so that the fibers are not cut or damaged.

Otherwise, the fibers will be cut and the result will be the same as mixing metal powder, and the effect of the present invention will not be achieved. The same is true when forming a sheet into a sheet; in order to use a roll, a method such as a constant speed rotating roll or roll coater 1 flow must be used. Adding the appropriate amount of vulcanizing agent, accelerator, and anti-aging agent is no different from the case of ordinary mold vulcanization.

The sheets formed in this way also have directional properties depending on the method, so it is best to shift a plurality of sheets and wire them together.

Examples will be described in detail below.

Example 1 Each additive and ferrite powder in the proportions shown in 1st SE were added to Q body 2 l-'J rubber (Nipol 1312 manufactured by Nippon Zeon) and mixed uniformly using a rubber glue stirrer. The indicated amount of brass fibers was gradually added and mixed thoroughly so that substantially no shearing force was applied. The resulting paste-like mixture was passed through three uniformly rotating rolls whose surfaces had been subjected to mold release treatment to form a sheet of a predetermined thickness. This was heated under pressure using a piston-type mold to obtain a vulcanized rubber sheet for use as a radio wave absorber.

Example 2 25 parts of toluene was added to 100% liquid nitrile rubber (N1po11312 manufactured by Nippon Zeon), and the various additives shown in Table 1, ferrite powder, and brass fiber were added, and the same procedure as in Example 1 was made. A vulcanized rubber sheet for use as a radio wave absorber was obtained.

Example 3 100 parts of natural rubber were uniformly kneaded with various additives and ferrite powder in the proportions shown in Table 1 using two rolls. To this, an equal volume of rubber paste was added and dissolved into a paste, which was thoroughly mixed in the same manner as in Example 1 using a rubber paste stirrer while adding brass fibers. After drying and adjusting the viscosity to an appropriate level by evaporating the solvent, it is passed through two rolls rotating at a constant speed and heated and vulcanized in a vulcanizing pot of a predetermined thickness.

Comparative Example The formulation of Example 3 was kneaded with brass 7-ivar without making it into a liquid using a conventional two-roll roll, and the mixture was vulcanized in the same manner as in Example 3 to obtain a sheet for a radio wave absorber.

Example 4 Commercially available natural rubber latex with vulcanizing agent and activator.

Accelerators and anti-aging agents were added and mixed in the proportions shown in Table 2, ferrite powder was added and mixed, and then brass fibers were gradually added and mixed with gentle stirring. The resulting paste-like mixture is applied to a releasable base fabric at a constant thickness using a roll coater, heated and dried to form a sheet of a specified thickness, and this is heated and vulcanized in a vulcanization pot. A vulcanized rubber sheet for use as a radio wave absorber was obtained.

Example 5 Polyethylene fine powder (#! Tetsu Kagaku Frozen value 20
: MI20 average particle diameter □゛'i5μ) was used to prepare a Sibus version according to the formulation shown in Table 3. Next, after adding and mixing ferrite powder, copper 7 IPA was gradually added and mixed with gentle stirring.The resulting paste-like mixture was passed through two uniformly rotating rolls whose surfaces had been subjected to mold release treatment to form a sheet of a predetermined thickness. It was heated and dried. This was heated and pressed in a piston mold to obtain a sheet for a radio wave absorber.

Example 6 100 parts of ferrite powder was added and mixed to 100 parts of a commercially available ethylene vinyl acetate copolymer emulsion, and then 2 parts of brass fibers were gradually added and mixed with gentle stirring. The resulting paste-like mixture is poured into a frame plate of a predetermined thickness and heated and dried to produce a radio wave absorber sheet of a predetermined thickness. Table 4 shows the results of measuring the radio wave absorption performance of these radio wave absorber sheets in combination with a metamorphic layer.

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, as shown in the characteristics of the deflection planes A and B in Fig. 2, which differ by 90', it is excellent that the frequency band defined by fl and fl1 matches the band defined by f and fl, as shown in the characteristics of the polarization planes A and B in Fig. 2. It can be said that it is a radio wave absorber. Therefore, as the radio wave absorption characteristics in Table 4, the fee Re hg
f'* is being measured.

As is clear from Table 4 above, in the comparative example in which natural rubber was used as a radio wave absorber sheet, the values of f8 and fl in FIG. 2 were the same as f in FIG.

In contrast to the values of and fl, which are completely different from each other, other embodiments show that f, and f, and fl and ft are equal to t1. This means that in the example, the medium does not have any unique properties regarding the in-plane direction of sorting;
That is, it shows that the medium is isotropic, and the present invention is effective as a method for manufacturing a sheet for a radio wave absorber.

[Brief explanation of the drawing]

FIG. 1 shows the structure of a radio wave absorber related to the present invention,
1 is a metal plate, 2 is a radio wave absorbing material to be subject to non-invention, and 3 is a metamorphic layer. FIG. 2 shows the frequency characteristics when the return loss is measured by rotating the deflection plane of the incident radio wave by 90 degrees, and the deflection planes of A and B differ by 90 degrees. Agent, +1・,! (within) Prefecture sound ゛゛之-1″

Claims (6)

[Claims] (1) To 100 parts of liquid polymer material, add 100 to 500 parts of ferrite powder, 5 to 150 seconds of conductive fibers with a diameter of 10 to 110Ox and a length of 500μ to 5SW to increase the circumferential speed of 1 shoulder/- A method for producing a radio wave absorbing material, which comprises stirring and mixing the following, forming the resulting mixed paste into a sheet by using a constant velocity roll or roll coater at 50 rpm or less, or by pouring, and vulcanizing it. (2) The method for producing a radio wave absorbing material according to claim 1, wherein the liquid polymer material is liquid rubber. (3) The method for producing a radio wave absorbing material according to claim 1, wherein the liquid polymer material is a solid rubber dissolved in an organic solvent or softened by resin. (4) The method for producing a radio wave absorbing material according to claim 1, wherein the liquid polymer material is rubber latex. (5) The method for producing a '-radio wave absorbing material according to claim 1, wherein the molecular material is a plastic disperser because it is liquid. (6) The method for producing a radio wave absorbing material according to claim 1, wherein the liquid polymer material is a plasnac emulsion.