JP2903165B2 - Manufacturing method of incombustible radio wave absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a radio wave absorbing material useful for building structural members, wall members of a radio wave anechoic chamber, cabinet members of electronic equipment, etc. The present invention relates to a method for producing a non-combustible electromagnetic wave absorbing material having both electric wave absorbing performance and electric wave absorbing performance.

(Prior art) In recent years, the use of radio waves has been rapidly expanding, mainly in the field of mobile communications, in order to realize an advanced information society, and with the advance of microelectronics technology today, various electronic devices have been developed. Equipment is widespread.

Against this background, electromagnetic interference caused by unnecessary radio waves secondary to various wireless devices and electronic devices tends to increase year by year.
There is an urgent need to develop electromagnetic wave absorbers with good performance required for providing a good electromagnetic environment (EMC) as an anechoic chamber or electromagnetic shield material.

It is important that the materials used for radio wave absorbers be composed of substances with large electrical and magnetic losses that effectively attenuate electromagnetic energy. Conventionally, various ohmic loss materials, dielectric loss materials, Loss materials have been developed and provided.

Among these, the most typical radio wave absorbers are those in which a carbon-based material is held in an insulating resin material such as urethane foam or styrene foam, or those in which a carbon material is mixed with rubber or plastic.

However, the above-mentioned radio wave absorbing material has a disadvantage in that it is extremely flammable because the material for supporting and bonding the carbon-based substance is made of resin, rubber, or the like. In addition, the type using a foamed resin material has a problem that the building structural member cannot be formed by itself because the material is fragile.

[Problems to be Solved by the Invention] As a radio wave absorber having a non-combustible and strong structure which solves such a problem, the present invention relates to a structure made of a foamed inorganic material mixed with at least a radio wave absorbing material. It has already been proposed by those (Japanese Patent Application No. 63-177830).

The inventors have further developed the above-mentioned prior art and clarified the material composition for obtaining the best non-combustible electromagnetic wave absorber, leading to the development of the present invention.

Accordingly, an object of the present invention is to provide a method for producing a non-combustible radio wave absorbing material which does not contain a flammable substance such as resin and rubber and has a light and strong structure and excellent radio wave absorbing performance.

[Means for solving the problem]

The present invention achieves the above object by using silica sol, cement-based binder, silica compound, perlite, an inorganic foamed binder composed of an aluminum compound, carbon fiber as a chop cut to a length of 3 to 4 mm, and water. A method for producing a non-combustible electromagnetic wave absorber having a winter mixture as a main component, wherein when the reference amount is 1, 580 g of the inorganic foamed binder in powder form and the inorganic foamed binder are used. 580 cc of a liquid made with water and 160 to 350 g of carbon fiber are blended and uniformly kneaded with a kneader, and the kneaded material is foamed in a desired mold, and then dried to obtain a molded body. The gist is that.

The inorganic foamed binder applied to the present invention is a foamable and nonflammable binder containing components such as silica and alumina powders and sols. For example, silica sol 31% by weight, cement-based binder 9% by weight, silica A composition composed of 5% by weight of a compound, 7% by weight of pearlite and 48% by weight of an aluminum compound is effectively used.

Among them, the cement-based binder mainly indicates Portland cement, and in addition, fly ash cement, alumina cement, and the like.

Among them, the silica compound is silica, silica sand, kaolin, kuruku, sericite, and the like, and the aluminum compound means a mixed system of an alumina cement-based binder and a foamed material such as metallic aluminum.

In this composition, foaming starts at room temperature due to the action of the aluminum compound component, and swells to about 3 to 4 times the volume after about 1 hour.

The carbon fiber mixed with the inorganic foamed binder functions as a conductive material, and various types such as polyacrylonitrile, rayon, and pitch can be used.
However, the carbon fiber used is provided as a chop cut to a length of 3 to 4 mm. The reason for this is that if carbon fibers having too short a length are used, the foaming of the inorganic foamed binder will be incomplete, and the carbon fibers will be insufficiently fitted to each other, preventing good bonding strength from being obtained. Is too large, the result is that the dispersion and mixing properties are destroyed.

The non-combustible electromagnetic wave absorbing material of the present invention is prepared by uniformly kneading a liquid or powder inorganic foamed binder and carbon fiber with a kneading machine such as an omni mixer and foaming in a desired mold at room temperature. be able to. At this time, the blending amount of the inorganic foaming binder and the carbon fiber is appropriately set in consideration of the radio wave absorption characteristics and the tissue strength. 580g
When 580 cc of a liquid inorganic foamed binder and 160 to 350 g of carbon fiber cut to a length of 3 to 4 mm are blended, the best properties can be obtained.

The incombustible radio wave absorbing material of the present invention has a strong foamed skeleton structure as it is, but can be mixed with a building material component such as Portland cement at the same time to further enhance its suitability as a building structural member.

[Action]

According to the composition of the present invention, a silica sol, a cement-based binder, a silica compound, a perlite, and an inorganic foamed binder composed of an aluminum compound function to form a non-combustible, lightweight, but rigid foamed structure. The carbon fiber of a specific length acts as a molding holding material by mixing three-dimensionally by acting on the suitable radio wave absorption performance.

These functions act synergistically to form a non-combustible, lightweight, and strong molded structure that is suitable for the frequency of the radio wave to be absorbed. In addition, the composition is silica sol,
Since it is composed of a carbon fiber and a ceramic component composed of a cement-based binder, a silica compound, a pearlite, and an aluminum compound, it has good weather resistance and is a radio wave absorber suitable as a building structural member.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Example 1 A powdery inorganic foamed binder 58 composed of 31% by weight of silica sol, 9% by weight of cement-based binder, 5% by weight of silica compound, 7% by weight of pearlite, and 48% by weight of aluminum compound
0 g, a liquid inorganic foamed binder in which the above components are suspended in water
580cc, 320g carbon fiber 14.5μm in diameter and 3.5mm in length
Were combined and compounded using 1 as a reference amount, and this was uniformly kneaded with an omni mixer and allowed to stand at room temperature.

The specific contents of the cement-based binder, the silica compound, and the aluminum compound are as described in the section of the means for solving the invention.

The kneaded material started foaming after 15 minutes, and swelled to about 3 times the volume after 1 hour. Then, this was dried to obtain a molded body.

The obtained molded article had a lightweight, rigid, strong, non-combustible foam structure. FIG. 1 shows the frequency characteristics of the permittivity, FIG. 2 shows the result of calculation of the radio wave absorption rate from the dielectric constant of the test piece, and FIG. 3 shows the radio wave absorption material. The experimental results of radio wave absorption for spatial radio waves when is a pyramid-shaped radio wave absorber with a height of 12.5 cm are shown.

From the results shown in FIGS. 1 and 2, it was confirmed that the above-mentioned molded product exhibited proper radio wave absorption performance.

Comparative Example 1 As in Example 1, powdery inorganic foamed binder 350 g, liquid inorganic foamed binder 350 cc, diameter 14.5 μm, length 1
145 g of carbon fibers having a length of 1 mm were combined and compounded using 1 as a reference amount and kneaded under the same conditions as in Example 1. When this kneaded material was left at room temperature, foaming was incomplete and a normal foamed molded article was not formed.

The dielectric constant (ε
r) and the dielectric loss tangent (tan δ) were measured and are shown in Table 1.

Example 2 A molded body was prepared under the same conditions as in Example 1 except that the amount of the carbon fiber having the same properties as in Example 1 was 160 g. The obtained molded article had a lightweight, rigid and uniform foam structure. When the dielectric constant of this molded product was measured, as shown in Table 1, the molded product showed better radio wave absorption characteristics than that of Comparative Example 1.

Comparative Example 2 A molded article was produced under the same conditions as in Comparative Example 1 except that the blending amount of the carbon fibers in Comparative Example 1 was changed to 85 g. Although the obtained molded article had a foamed structure, its dielectric constant was inferior to that of Example 2 as shown in Table 1.

[Effects of the Invention] As described above, the radio wave absorber provided by the present invention has good nonflammability, light weight and rigidity in terms of material,
It also has excellent radio wave absorption performance. In addition, since an expensive ferrite component is not required, it can be manufactured at low cost.

Therefore, it is expected to be useful as a radio wave absorbing material such as various building structural members, radio wave non-reflective wall members, and cabinet members of electronic devices.

[Brief description of the drawings]

FIG. 1 shows a radio wave absorption characteristic of the non-combustible radio wave absorber according to the first embodiment. FIG. 1 is a dielectric constant frequency characteristic diagram, and FIG. 2 is a graph showing the frequency and reflection loss of the radio wave absorber based on the dielectric constant. FIG. 3 is a graph showing the relationship between the experimental results of the radio wave absorptivity for actual radio waves.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisashi Sato 2-9-1-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. (72) Mikio Takano 2-191-1, Tobita-Shi, Chofu-shi, Tokyo No. Kashima Construction Co., Ltd. Technical Research Institute (72) Inventor Tadahiro Shimazu 1-2-7 Moto-Akasaka, Minato-ku, Tokyo Kashima Construction Co., Ltd. (72) Inventor Shuichi Takasaka 2-191 Tobita Pay, Chofu-shi, Tokyo No. Kashima Construction Co., Ltd. Technical Research Institute (72) Inventor Kiichiro Muta 2-9-1-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. Technical Research Institute (56) References JP-A-1-298798 (JP, A (58) Fields surveyed (Int. Cl. ⁶ , DB name) H05K 9/00

Claims (1)

(57) [Claims] 1. A mixture mainly composed of an inorganic foamed binder comprising silica sol, a cement-based binder, a silica compound, a pearlite, and an aluminum compound, carbon fibers as chops cut to a length of 3 to 4 mm, and water. A method for producing a non-combustible electromagnetic wave absorbing material, wherein when the reference amount is 1, 580 g of the inorganic foamed binder in powder form
And 580 cc of the inorganic foamed binder made liquid with water.
And 160 to 350 g of carbon fiber are blended and uniformly kneaded with a kneading machine, the kneaded product is foamed in a desired mold, and then dried to obtain a molded product. Manufacturing method of radio wave absorber.