JPS6048881B2 - Radio wave absorbing material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a matching type radio wave absorbing material for microwave bands having a room temperature curing type unvulcanized rubber sheet of a specific composition as a radio wave absorbing layer, and more particularly, the present invention relates to a matching type radio wave absorbing material for microwave bands having a room temperature curing type unvulcanized rubber sheet of a specific composition as a radio wave absorbing layer. Absorption performance does not vary even after being pasted on a reflector and construction is easy.
The present invention relates to a room-temperature curing, unvulcanized rubber sheet-based matched radio wave absorbing material for microwave bands, which has excellent weather resistance and flexibility, and can be used even on iron members coated with heavy anti-corrosion coating.

Conventional radio wave absorbing materials are mainly made of vulcanized rubber.

This vulcanized rubber radio wave absorbing material is made by molding vulcanized rubber containing carbon, ferrite powder, etc. into a sheet, and by pre-coating adhesive on the back side of the rubber sheet with a brush or the like (Figure 1). , or one in which a metal foil is attached to the rubber sheet via an adhesive layer (Fig. 2), etc. are known. However, in such vulcanized rubber-based radio wave absorbing materials, in order to obtain good adhesion between the vulcanized rubber sheet and the metal foil or adherend, the surface of the rubber sheet is para-processed and physical It is necessary to form a catch or to activate the surface of the rubber sheet with a solvent swab, and as a result of these treatments, variations in the thickness of the rubber sheet are unavoidable.

Further, the adhesive was applied by brushing or the like, and no consideration was given to variations in the thickness of the adhesive layer. Therefore, due to these variations, the conventional matching type radio wave absorbing material has the disadvantage that the absorption performance varies. An object of the present invention is to provide a radio wave absorbing material that does not vary in absorption performance even after being applied to a radio wave reflector such as a steel member, and has flexibility with excellent workability and weather resistance.

The present invention is achieved by using a room temperature curing unvulcanized rubber sheet with excellent flexibility and weather resistance as a radio wave absorbing material. That is, the present invention provides a microphone i-mouth band matching type radio wave absorbing material having a radio wave absorbing layer, in which the radio wave absorbing layer is made of a room temperature curing unvulcanized rubber sheet containing a rubber component, ferrite powder, and carbon black. This is a characteristic radio wave absorbing material.

In the present invention, the room temperature curing unvulcanized rubber sheet refers to a rubber component,
It contains ferrite powder and carbon black, and the preferred blending ratio is 20-4% rubber content, 50-7% ferrite powder, and 2-2% carbon black, based on the unvulcanized rubber sheet. %.

If the volume of ferrite powder is less than 5%, the radio wave absorption performance will be poor, and if it exceeds 7%, it will be difficult to form a flexible sheet. By adding carbon black, the weight of the radio wave absorbing material can be reduced, and the green strength during processing can also be improved. If the amount of carbon black is less than 2% by weight, the green strength will be weak, and if it exceeds 2% by weight, the radio wave absorption performance will decrease. The most preferable range of carbon black that balances green strength and radio wave absorption performance is 6 to W weight %. The rubber content of the room-temperature-curing unvulcanized rubber sheet used in the present invention may be any room-temperature-curing rubber;
For example, chloroprene rubber, butyl rubber, natural rubber, polyisoprene rubber, etc. are used, and chloroprene rubber is most preferred from the viewpoint of weather resistance.

This unvulcanized rubber sheet is attached to an adherend such as a steel member via adhesive and used as a radio wave absorbing material, but the thickness of the adhesive layer must be uniform in order to stabilize the radio wave absorption performance. is necessary. This adhesive layer of uniform thickness can be obtained by applying the adhesive to the adherend by spraying, or by releasing a flexible pressure-sensitive adhesive such as acrylic or elastomer adhesive on the underside of the unvulcanized rubber sheet. Obtained by providing a sheet or film. In the present invention, an unvulcanized rubber sheet and an adherend. It is also possible to provide a metal foil between the layers to form a radio wave reflective layer.

The metal foil may be any conductive material such as aluminum, tin, copper, or iron, and its thickness is 8 microns or more, preferably 8 to 30 microns, from the viewpoint of reflective performance and economical efficiency. When the surface of the adherend is coated with heavy anti-corrosion coating 2, the surface of the adherend lacks smoothness and is not suitable as a radio wave reflective layer, so metal foil is preferably used as the radio wave reflective layer.
The unvulcanized rubber sheet and the metal foil are attached with an adhesive such as acrylic ester or liquid chloroprene, but it is necessary that the thickness of the adhesive layer be uniform from the viewpoint of electric wave absorption performance. Further, the metal foil and the adherend are attached by applying an adhesive to the adherend by spraying or the like, or by providing a release sheet of pressure-sensitive adhesive on the lower surface of the metal foil. The present invention will be specifically described below based on Examples and Comparative Examples.

Comparative Example 1 Figure 1 shows a cross-sectional view of a conventional radio wave absorber. 1 is a vulcanized rubber sheet prepared by vulcanizing a rubber composition having the composition shown in Table 1 at 160°C for 30 minutes, and the bottom surface was polished using a sander. After buffing, I am swabbing with toluene.

Esteflu acrylate (trade name: Olivine, manufactured by Toyo Ink Mfg. Co., Ltd.) is applied as an adhesive to the lower surface of this vulcanized rubber sheet 1 with a brush to form an adhesive layer 2, and the adhesive layer 2 is 250±80p.
It was attached to a steel member with a heavy anti-corrosion coating. The absorption effect of the radio wave absorbing material thus obtained and the peel strength of the rubber sheet were measured and the results are shown in Table 2. The absorption effect was determined by measuring the radio wave absorption rate using a generally known oblique incidence measurement method. Five samples measuring 40 eTffm (vertical) x 400 wrm (horizontal) and having the thickness shown in Table 2 were prepared, and the absorbance at a wavelength of 9.4 kHz was measured. Further, the peel strength was measured using 180°C beer (25 wrm width) in accordance with JIS K6854. Comparative Example 2 As shown in FIG. 2, an adhesive layer 2 made of acrylic ester (Olivine) was provided on the lower surface of the buffed and swabbed vulcanized rubber sheet 1 used in Comparative Example 1, and An aluminum foil 3 having a thickness of 127 TiXL was attached to the lower part of the aluminum foil 3 to obtain a radio wave absorbing material.

Comparative Example 1 An adhesive layer was provided on a steel member having a heavy anti-corrosion coating film of 250±80μ, and a radio wave absorbing material was pasted on this.
The absorption effect and peel strength of the rubber sheet were measured in the same manner as above.

The results are shown in Table 2. Example 1 Rubber components and compounding agents having the formulation shown in Table 1 were mixed in a Pan Bali mixer at a low rotor rotation speed of 45 rpm and under water-cooled conditions.

In order to suppress heat generation due to mixing to 100°C or less, ferrite and carbon black were added in two or three parts. The rubber composition thus obtained was subjected to low-temperature rolling using a calendar roll under water-cooled conditions so that the surface temperature was 60°C or less, and the rubber composition was rolled at a low temperature with a calendar roll as shown in FIG. Sa1.93wf
An unvulcanized rubber sheet 4 having n±0.01- was prepared to obtain a radio wave absorbing material. Acrylic acid ester (Olivine) was sprayed onto the iron member to a uniform thickness, and the radio wave absorbing material was attached thereon. The absorption effect and peel strength of the rubber sheet were measured in the same manner as in Comparative Example 1, and the results are shown in Table 2.
Example 2 As shown in FIG. 4, an adhesive layer 5 was provided by applying acrylic acid ester (Olivine) to a uniform thickness on the upper surface of a 12p thick aluminum foil using a knife coating method, and the adhesive layer 5 was applied on top of this. The unvulcanized rubber sheet 4 used in 1 was attached by roll pressure bonding to obtain a radio wave absorbing material.

Comparative Example 1 An adhesive layer was provided on a steel member having a heavy anti-corrosion coating with a thickness of 250 mm and 80 mm, and a radio wave absorbing material was pasted thereon.
The absorption effect and peel strength of the rubber sheet were measured in the same manner as above, and the results are shown in Table 2. Example 3 As shown in FIG. 5, an adhesive layer 6 on which acrylic acid ester (Olivine) was pre-coated on release paper using a knife coating method was applied to the lower surface of the metal foil of the radio wave absorbing material of Example 2 by roll pressure bonding. Then, the radio wave absorbing material was obtained.

This radio wave absorbing material was pasted on an iron member 8 having a heavy anti-corrosion coating film 7 with a thickness of 250 mm and 80 mm, and the absorption effect and peel strength of the rubber sheet were measured in the same manner as in Comparative Example 1.
Shown in the table. As shown in Table 2 and Figures 1 to 5, in Examples 1 to 3, absorbent materials having a uniform thickness are obtained, so that not only the absorption effect is stable but also the peel strength is excellent.

As explained above, the radio wave absorbing material of the present invention does not require pre-treatment with buffing or solvent swab on the surface of the rubber sheet before adhesion, and the absorption performance is stable because the thickness does not vary due to these pre-treatments. , there is no effect on absorption performance due to variations in the thickness of the undercoat and adhesive. Furthermore, since it uses a pressure-sensitive adhesive, it has the advantage of being easy to apply. Furthermore, since this radio wave absorbing material is flexible, it can be applied not only to flat surfaces but also to curved surfaces and bent portions.

[Brief explanation of the drawing]

Figure 1 shows a conventional radio wave absorber with adhesive pre-coated on the back side of a rubber sheet, Figure 2 shows a conventional radio wave absorber with a comb sheet lined with metal foil, and Figure 3 shows room-temperature curing unvulcanized rubber. Radio wave absorbing material as an embodiment of the present invention consisting of a sheet, No. 4
The figure shows another embodiment of the present invention in which the unvulcanized rubber sheet is lined with metal foil, and FIG. This is a radio wave absorbing material as yet another embodiment of the present invention, which is lined with foil and further provided with a pressure-sensitive adhesive on the outer surface of the metal foil.

Claims (1)

[Scope of Claims] 1. A microwave band matching type radio wave absorbing material having a radio wave absorption layer, wherein the radio wave absorption layer is made of a room temperature curing unvulcanized rubber sheet containing a rubber component, ferrite powder, and carbon black. Characteristic radio wave absorbing material. 2 Rubber content 2 for the room temperature curing unvulcanized rubber sheet
The radio wave absorbing material according to claim 1, which contains 0 to 40% by weight of ferrite powder, 50 to 70% by weight of ferrite powder, and 2 to 20% by weight of carbon black. 3. The radio wave absorbing material according to claim 1 or 2, wherein a metal foil is attached to the rubber sheet via an adhesive layer having a uniform thickness. 4. Claim 3, wherein a pressure-sensitive adhesive layer is provided on the surface of the metal foil opposite to the surface facing the rubber sheet.
Radio wave absorbing material described in section.