JPS6334639B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a sheet-like radio wave absorbing material. Radio wave absorbing materials have been used in recent years to prevent reflected electromagnetic interference from high-rise buildings lining urban spaces, and to prevent false radar images generated on ship radars during navigation due to high-rise buildings near the coast and bridges on the sea. It is a new component whose uses are expanding. Conventionally, barium ferrite (BaO・6Fe ₂ O ₃ )
Plastic or rubber mixed with an appropriate amount of ferrite powder such as by-product ferrite is used for the purpose of absorbing these radio waves. However, conventional radio wave absorbers using a single layer of these have a narrow frequency band width that exhibits radio wave absorption performance.
In actual use, the applications are limited and there are cases where it is extremely inconvenient, so the emergence of a radio wave absorber with a wide frequency band has been desired. In order to solve such conventional drawbacks, the inventor of the present application has filed Japanese Patent Application No. 109686/1986 and Japanese Patent Application No.
As shown in Figure 1 in No. 169492, metal plate 1
We proposed a radio wave absorber structure in which a radio wave absorber 2 and a metamorphic layer 3 are laminated on top. 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, 100 to 500 parts by weight of ferrite powder and 10 parts by weight of ferrite powder are added to 100 parts by weight of liquid polymer material.
Add 5 to 150 parts by weight of conductive fibers with a length of ~100 μm and a length of 500 μm to 5 mm, stir and mix at a circumferential speed of 1 m/sec or less, and pour the resulting mixed paste using a constant speed roll or roll coater at 50 rpm or less, or pour it. A method for producing a radio wave absorbing material is obtained, which is characterized by forming the material into a sheet and vulcanizing it. It becomes possible to easily construct a radio wave absorbing material by stacking the radio wave absorbing material sheet 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 liquid rubber, but also solid rubber dissolved or emulsified, and fine plastic powder emulsion or dispersion can be used. That is, liquid rubber such as nitrile rubber, natural rubber dissolved in a solvent, polyethylene fine powder dispersed in water, or a polymer made into an esulsion can all be used, depending on the purpose. Polymeric materials should be selected. As the ferrite used in the present invention, iron oxide powders such as barium ferrite, manganese, ferrite, and iron ferrite can be used. Needless to say, smaller particles are preferable during mixing. As the conductive fibers, carbon fibers or metals such as brass are suitable, and both preferably have a diameter of about 10 μm to 100 μm and a length of about 500 μm to 5 mm. When mixing and molding, it is practically necessary to stir without shearing force, and for this purpose, do not use a stirrer that has a mechanical effect, and rotate the stirrer slowly so that the fibers are Must be mixed without cutting damage. 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. This is the same when forming into a sheet, and when using rolls, methods such as constant-velocity rotating rolls, roll coaters, and flow casting must be used. Adding appropriate amounts of vulcanizing agents, accelerators, and anti-aging agents is the same as in ordinary mold vulcanization. The sheets formed in this way also have directionality depending on the method, so it is preferable to shift a plurality of sheets and overlap them. This will be described in detail below with reference to Examples. Example 1 Add various additives and ferrite powder in the proportions shown in Table 1 to liquid nitrile rubber (Nipol 1312 manufactured by Nippon Zeon), mix uniformly using a rubber glue stirrer, and then add brass in the amount shown in Table 1. The fibers were gradually added and mixed thoroughly without applying substantial shearing force. 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 a radio wave absorber. Example 2 25 parts by weight of toluene was added to 100 parts by weight of liquid nitrile rubber (Nipol 1312 manufactured by Nippon Zeon),
Various additives, ferrite powder and brass fibers in the proportions shown in Table 1 were added to this and molded in the same manner as in Example 1 to obtain a vulcanized rubber sheet for a radio wave absorber. Example 3 100 parts by weight of natural rubber were uniformly kneaded with various additives and ferrite powder in the proportions shown in Table 1 using two rolls. Example 1: To this, an equal volume of rubber volatile oil was added and dissolved into a paste.
Brass fibers were added and thoroughly mixed using a rubber glue stirrer in the same manner as above. After slightly evaporating the solvent and adjusting the viscosity to an appropriate level, it was rotated at a constant speed of 2.
It was passed through a main roll and heated and vulcanized in a vulcanizing pot to a predetermined thickness to obtain a sheet for a radio wave absorber. The formulation relationships of Examples 1 to 3 are summarized in Table 1.

[Table] Comparative Example The formulation of Example 3 was kneaded with brass fiber without making it into a liquid using a conventional two-roller, and the mixture was vulcanized in the same manner as in Example 3 to obtain a sheet for a radio wave absorber. Example 4 Adding a vulcanizing agent, an activator, and a commercially available natural rubber latex
After adding and mixing ferrite powder to a mixture of accelerator and anti-aging agent in the proportions shown in Table 2,
Brass fiber was gradually added and mixed while stirring gently. The obtained paste-like mixture is coated on a releasable base fabric at a constant thickness using a roll coater, and heated and dried to form a sheet of a predetermined thickness.
This was heated and vulcanized in a vulcanization pot to obtain a vulcanized rubber sheet for a radio wave absorber. Example 5 Polyethylene fine powder (Frozen manufactured by Steel Chemical Co., Ltd.)
A dispersion was prepared using UF20:MI20 (average particle size 15μ) according to the formulation shown in Table 3. Then, after adding and mixing the ferrite powder, the brass fiber 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 a mold release treatment to form a sheet of a predetermined thickness, and then heated and dried. This was heated and pressed in a piston mold to obtain a sheet for a radio wave absorber.

【table】

【table】

[Table] Example 6 Commercially available ethylene vinyl acetate copolymer emulsion 100
Add and mix 100 parts by weight of ferrite powder to parts by weight,
Next, 28 parts by weight of brass fibers were gradually added and mixed with gentle stirring. The obtained paste-like mixture was poured into a frame plate of a predetermined thickness and dried by heating to obtain a sheet for a radio wave absorber 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, the deflection planes indicated by A and B in Fig. 2 are
As shown in the 90° different characteristics, the radio wave absorption performance
It can be said that the more the frequency band defined by ₁ and ' ₁ matches the band defined by ₂ and ' ₂ , the better the radio wave absorber is. Therefore, the above-mentioned ₁ , ' ₁ , ₂ , and ' ₂ were measured as the radio wave absorption characteristics in Table 4.

[Table] As is clear from Table 4 above, in the comparative example in which natural rubber was used as a radio wave absorber sheet,
Whereas the values of ₁ and ' ₁ in FIG. 2 are completely different from the values of ₂ and ' ₂ in FIG. 2, other embodiments show that ₁ and ₂ and ' ₁ and ' ₂ are approximately equal. It shows. 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 shows the structure of a radio wave absorber according to the present invention, where 1 is a metal plate, 2 is a radio wave absorber to which the present invention is applied, and 3 is a metamorphic layer. Figure 2 shows the return loss calculated using the deflection plane of the incident radio wave.
Shows the frequency characteristics when measured by rotating 90 degrees,
The deflection planes of A and B differ by 90°.

Claims (1)

[Claims] 1. 100 to 500 parts by weight of ferrite powder, a diameter of 10 to 100 μm, per 100 parts by weight of liquid polymer material;
5 to 150 parts by weight of conductive fibers with a length of 500 μm to 5 mm are added and mixed by stirring at a circumferential speed of 1 m/sec or less,
1. A method for producing a radio wave absorbing material, which comprises forming the obtained mixed paste into a sheet 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 obtained by dissolving or softening solid rubber in an organic solvent. 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 liquid polymer material is a plastic dispersion. 6. The method for producing a radio wave absorbing material according to claim 1, wherein the liquid polymer material is a plastic emulsion.