JP2001127482A - Molded object absorbing electric wave and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light and non-combustible molded object absorbing electric waves of superior durability, which has superior wave-absorbing characteristics over a wide frequency band, at a low cost. SOLUTION: A molded object absorbing electric wave is manufactured by a first process, where potassium silicate solution of 62-85 pts.wt. whose concentration is 25-30 wt.% and alumina cement of 10-30 pts.wt. are added and mixed with a mixture of 100 pts.wt., consisting of a large amount of inorganic hollow small spheres and ferrite powder, a second process, where the added mixture obtained in the first process is granulated into undersize of semi-dry condition, a third process, where the granulated material of the semi-dry condition is injected into a frame, and a fourth process, where carbonic acid gas is injected into the injected granulated material in the frame in the third process to cure the injected granulated material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a radio wave absorbing molded article which is nonflammable, compact, lightweight, inexpensive, and exhibits excellent radio wave absorbing characteristics in a wide frequency band.

[0002]

2. Description of the Related Art Radio wave absorbers include. A dielectric (eg, a resistor in which carbon is dispersed in a polyurethane foam); Magnetic material (mainly ferrite); There are three types of composites consisting of a combination of a dielectric and a magnetic material. . The dielectric type has a problem that the tip is deformed and burns easily when used for many years since the polyurethane foam is formed in a pyramid shape. In addition, a flame retardant is applied to increase heat resistance, but the change with time is large and requires replacement in several years. Furthermore, in order to have sufficient radio wave absorption characteristics, a thickness of 1 m or more is required, and there is a problem that a dedicated space is required. In addition, the resin-based resin has a problem regarding nonflammability.

[0003] Ferrite tiles commonly used in magnetic materials are excellent in low frequency radio wave absorption characteristics,
When the thickness is less than m, sufficient absorption characteristics can be obtained, but there is a problem that the band is narrow and the absorption characteristics deteriorate as the frequency increases. Therefore, in order to compensate for the disadvantages of both, even when a dielectric and a magnetic material are combined, the thickness becomes 90 cm or more, and the problem of miniaturization of the anechoic chamber cannot be solved. And, in the case of a commercially available foamed ferrite absorber, the manufacturing process is complicated and tends to be expensive,
Since it is heavy, there is a problem that the strength of the room must be reinforced in construction. The present invention solves the above-mentioned drawbacks of the conventional radio wave absorber, is nonflammable, has excellent radio wave absorption characteristics, is lightweight, compact, and has excellent durability at a low cost. It is intended to be provided by.

[0004]

In order to solve the above-mentioned problems, as a result of various investigations and studies, potassium silicate aqueous solution was mixed with inorganic hollow small spheres (for example, shirasu balloon) and mixed powder of ferrite and alumina cement. Addition and mixing to form a granulated body, and then filling the granulated body in a mold, injecting and curing carbon dioxide gas, to obtain a radio wave absorbing molded body that can solve the above problems, and Preferably, an inorganic surface treatment liquid such as colloidal silica, lithium silicate, or aluminum phosphate is applied to the cured molded body during the production process, and then a heat treatment is performed at 300 to 800 ° C. to produce a more preferable radio wave absorbent molded body. It was possible to do. That is, the present invention is a method for manufacturing a radio wave absorption molded article having the following configuration. (1) With respect to 100 parts by weight of a mixture comprising a large number of inorganic hollow small spheres and ferrite powder, 65 to 85 parts by weight of a carbonic acid reaction hardened product of potassium silicate and 10 to 30 parts by weight of a hydrated hardened product of alumina cement. A radio wave absorption molded article characterized in that a mixture is interposed as a matrix. (2) A molded product in which 65 to 85 parts by weight of a carbon dioxide reaction hardened product of potassium silicate is interposed as a matrix with respect to 100 parts by weight of a mixture composed of a large number of inorganic hollow small spheres and ferrite powder, and A radio wave absorption molded article having a surface coated with a heat reaction product with one or more kinds selected from colloidal silica, lithium silicate and aluminum phosphate. (3) 62-85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25-30% by weight and 10-30 parts by weight of alumina cement are mixed with 100 parts by weight of a mixture composed of a large number of inorganic hollow small spheres and ferrite powder. A first step, a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state, and placing the semi-dry granule in the second step in a mold. A third step of filling and a fourth step of injecting carbon dioxide into the filled granules in the mold of the third step to cure the filled granules, Production method.

(4) Numerous inorganic hollow small spheres 30 to 50
First, 65-85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25-30% by weight and 10-30 parts by weight of alumina cement are mixed with 100 parts by weight of a mixture consisting of 50% by weight and 50-70% by weight of ferrite powder. The step and the first
A second step of granulating the dispensed mixture obtained in the step into small particles in a semi-dried state, a third step of filling the granulated substance in the semi-dried state obtained in the second step in a mold, A fourth step of injecting carbon dioxide into the filled granules in the mold in the third step to cure the filled granules. (5) for a number of inorganic hollow microspheres 30 to 50 wt% and ferrite powder 50-70 by weight percent consisting of 100 parts by weight of a mixture, the concentration of 25-30% by weight of potassium silicate aqueous 65-85 parts by weight A first step of dispensing and mixing 10 to 30 parts by weight of alumina cement, and a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state,
A third step of filling the semi-dried granules obtained in the second step into a mold; and a filling granulation by injecting carbon dioxide into the filled granules in the mold of the third step. A fourth step of curing the article, and applying one or more surface treatment liquids selected from colloidal silica, an aqueous solution of lithium silicate or an aqueous solution of aluminum phosphate to the cured article obtained in the fourth step. And a fifth step of performing a heat treatment at 300 to 800 ° C. (6) 65-85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25-30% by weight is added to 100 parts by weight of a mixture of 30-50% by weight of a large number of inorganic hollow small spheres and 50-70% by weight of ferrite powder. A first step of mixing, a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state, and a mold forming the semi-dry granule in the second step. A third step of filling the inside, a fourth step of injecting carbon dioxide gas into the filled granules in the mold of the third step to cure the filled granules, and the curing obtained in the fourth step A step of applying one or more surface treatment liquids selected from colloidal silica, an aqueous solution of lithium silicate or an aqueous solution of aluminum phosphate to the molded article, and heat-treating at 300 to 800 ° C. Of manufacturing a radio wave absorption molded article.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for producing a radio-wave absorption molded article in which a mixed powder of an inorganic hollow sphere and a ferrite is powder-filled with a granulated substance mixed with alumina cement and potassium silicate and molded. Is described. When only sodium silicate is used as a binder, a light-weight and non-flammable radio wave absorbing molded article can be obtained, but has the disadvantage that the molded article has low strength, easily absorbs moisture in the air, and easily causes a flare-up phenomenon. Was. Thus, as a result of a test using various binders, it was found that the strength, water absorption and phenomena were improved by using potassium silicate. further,
When a small amount of alumina cement was added to the mixture of the inorganic hollow spheres and the ferrite, the strength of the molded body was dramatically improved, so that the amount of potassium silicate added could be reduced. This makes it possible to produce a compact, lightweight, and highly durable radio-wave-absorbing molded article having high strength, light weight, hardly absorbing moisture in the air, and having no fear of the occurrence of a fragrance phenomenon. It is also preferable to add tourmaline powder to the mixture of the inorganic hollow sphere and ferrite in order to improve the radio wave absorption characteristics.

Next, a semi-dry granule obtained by mixing inorganic hollow spheres and ferrite as main raw materials and using potassium silicate as a binder is filled in an arbitrary frame, and carbon dioxide gas is injected. A method for producing a radio wave absorbing molded body, characterized in that a surface treatment liquid is applied to the molded body cured by heat treatment and heat treatment is performed at 300 to 800 ° C. In the case of a molded body that is only hardened with carbon dioxide gas using only potassium silicate as a binder, unreacted potassium silicate may remain in the molded body, and although it is lightweight, the strength of alumina cement is low. There was a drawback that it was weaker than when used and was easily broken when absorbing water. Therefore, after curing with carbon dioxide gas, colloidal silica is applied and 300
By performing the heat treatment as described above, it was possible to produce a light-weight radio wave absorbing molded article having excellent characteristics that the molded article surface was densified, the strength was improved, and the sheet was not broken even when containing water.
Similar strength improvement was observed when lithium silicate or aluminum phosphate was used instead of colloidal silica.

That is, a semi-dry granule obtained by mixing a mixed powder of inorganic hollow small spheres and ferrite with an aqueous solution of potassium silicate as a binder is converted into a pyramid shape, a plate shape, a triangular prism shape or the like. Filled in a mold frame and cured by exposing it to a carbon dioxide atmosphere, and can be integrally molded.
Adding alumina cement to the raw material mixture; Alternatively, by using a simple manufacturing process of applying a surface strengthening aqueous solution to a molded body and heat-treating the same, a lightweight and small radio wave absorbing molded body can be provided at low cost.
Further, the radio wave absorbing molded article has a feature that simple repair on site is possible for damage during transportation and damage in an anechoic chamber.

[0009]

EXAMPLES Example 1: Composition ratio (weight ratio) shown in Table 1 below
First, ferrite (1.0 to 15 μm in diameter) and shirasu balloon (30 to 200 μm in diameter) are uniformly mixed, and then an aqueous solution of potassium silicate (aqueous solution containing 29% of potassium silicate) and alumina cement are added thereto, followed by stirring. To make a mixture. Next, as shown in the manufacturing process explanatory diagram of FIG. 1, a pyramid-shaped outer frame 1 having a base of 10 cm square and a height of 10 cm.
And a pyramid-shaped inner frame 2 with a base of 6 cm square and a height of 6 cm
In the meantime, the granules 3 are filled from a hopper 4, and a press lid 6 provided with a carbon dioxide ejection pipe 5 is pressed against the granules 3,
Carbon dioxide gas was injected into the granules 3, and the carbon dioxide jet pipe 5 and the press lid 6 were removed and cured to obtain a (radio wave absorbing) molded body 7. Note that the carbon dioxide gas was injected into the granules 3 by discharging the pressurized carbon dioxide gas sent from a carbon dioxide gas cylinder (not shown) from the jet pipe 5. A series of molding-related operations, such as powder filling of the granules, hardening by carbon dioxide injection, and removal from the mold, were completed within 5 minutes.

[0010]

[Table 1]

The radio wave absorption rate (dB) at each frequency of the obtained radio wave absorption molded article was measured, and the result is shown in FIG. As shown in the figure, the radio wave absorption molded article obtained in this example has a wide frequency band (for example, 1 to 17 GHz).
It was found to have an excellent radio wave absorption rate (average 25.09 dB).

Example 2: Ferrite and shirasu balloon are uniformly mixed at a composition ratio (weight ratio) shown in Table 2 below, then an aqueous solution of potassium silicate is added and stirred to produce a semi-dry mixture. . Then, the outer frame 1 of the same formwork as in Example 1
The granulated body 3 is filled between the inner frame 2 and pressed by applying a press lid 6 having a carbon dioxide discharge pipe 5 vertically provided thereto, and carbon dioxide gas is injected. 6 was removed and cured to obtain a molded body 7. Thereafter, an aqueous solution of colloidal silica was applied to the surface of the obtained molded body,
Heat treatment was performed at 0 ° C. for 15 minutes to obtain a radio wave absorption molded article.
Regarding the characteristics of the obtained radio wave absorption molded article, the same performance as that of the radio wave absorption molded article of Example 1 was obtained.

[0013]

[Table 2]

[0014]

EFFECTS OF THE INVENTION Since the radio wave absorption molded article provided by the present invention has excellent radio wave absorption characteristics in a wide frequency band, it can be added to the conventional radio wave absorption molded article up to the 1 GHz band, It can be used as an anechoic chamber up to the high frequency band. In addition, since it is lightweight and compact, a wider effective space can be secured in a small anechoic chamber, etc.The absorber itself is low cost and lightweight, so the purchase cost and initial investment such as reinforcement work are also reduced. You. Further, since it is composed only of inorganic substances, it is nonflammable, has excellent durability such as withstanding high temperatures and strong electromagnetic fields, and can be used stably for a long period of time. In particular, effective use of Shirasu, which is abundant in Kagoshima Prefecture, will lead to regional revitalization. Furthermore, with the increase in performance and speed of electronic devices and the spread of microwave devices such as mobile phones, the demand for microwave bands will continue to increase,
The demand for microwave anechoic chambers for microwaves is also expanding, and the supply of radio wave absorbing molded articles corresponding to the demands is desired, and the radio wave absorbing molded articles according to the present invention greatly contributes.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a manufacturing process of a radio wave absorption molded article.

FIG. 2 is a graph showing the radio wave absorption characteristics of the radio wave absorption molded article obtained in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold form (outer frame) 2 Press mold form (inner frame) 3 Granule in semi-dry state 4 Hopper 5 Carbon dioxide emission pipe 6 Press lid 7 (Electromagnetic absorption) molded object

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G019 LA02 LA03 LB02 LD02 5E321 AA42 BB31 BB60 GG11 5J020 BD02 EA02 EA04 EA08 EA10

Claims (6)

[Claims] 1. A mixture comprising a large number of inorganic hollow small spheres and ferrite powder, 100 parts by weight, 65 to 85 parts by weight of a carbon dioxide reaction hardened product of potassium silicate and 10 to 30 weights of a hydrated hardened alumina cement. A radio wave absorption molded article characterized in that a mixture of parts is interposed as a matrix. 2. A molded product in which 65 to 85 parts by weight of a carbon dioxide reaction-hardened product of potassium silicate is interposed as a matrix with respect to 100 parts by weight of a mixture comprising a large number of inorganic hollow small spheres and ferrite powder, And a radio wave absorption molded article whose surface is coated with a heating reaction product with one or more kinds selected from colloidal silica, lithium silicate and aluminum phosphate. 3. A concentration of 25 to 3 with respect to 100 parts by weight of a mixture comprising a large number of inorganic hollow small spheres and ferrite powder.
A first step of distributing and mixing 62 to 85 parts by weight of an aqueous solution of 0% by weight of potassium silicate and 10 to 30 parts by weight of alumina cement, and a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state. A second step, a third step of filling the granules in a semi-dry state obtained in the second step into a mold, and a third step of
A step of injecting carbon dioxide gas into the filled granules in the mold of the step to harden the filled granules. 4. A large number of inorganic hollow small spheres in an amount of 30 to 50% by weight.
1 comprising a ferrite powder and 50 to 70% by weight
65 to 85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25 to 30% by weight and alumina cement 10 to 100 parts by weight.
A first step of dispensing and mixing 30 parts by weight, a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state, and a step of granulating the semi-dry state obtained in the second step. A third step of filling the granules in the mold; and a fourth step of injecting carbon dioxide gas into the filled granules in the mold in the third step to harden the filled granules. A method for producing a radio wave absorption molded article. 5. A large number of inorganic hollow small spheres in an amount of 30 to 50% by weight.
1 comprising a ferrite powder and 50 to 70% by weight
65 to 85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25 to 30% by weight and alumina cement 10 to 100 parts by weight.
A first step of dispensing and mixing 30 parts by weight, a second step of granulating the dispensed mixture obtained in the first step into small particles in a semi-dry state, and a step of granulating the semi-dry state obtained in the second step. A third step of filling the granules in the mold, a fourth step of injecting carbon dioxide gas into the filled granules in the mold in the third step to harden the filled granules, and the fourth step To the cured product obtained in
A fifth step of applying one or more surface treatment liquids selected from colloidal silica, lithium silicate aqueous solution or aluminum phosphate aqueous solution, and heat-treating at 300 to 800 ° C. Manufacturing method. 6. A large number of inorganic hollow small spheres in an amount of 30 to 50% by weight.
1 comprising a ferrite powder and 50 to 70% by weight
A first step in which 65 to 85 parts by weight of an aqueous solution of potassium silicate having a concentration of 25 to 30% by weight is added to and mixed with 00 parts by weight, and the added mixture obtained in the first step is granulated into small particles in a semi-dry state. A second step of filling the semi-dried granules obtained in the second step into a mold;
A fourth step of injecting carbon dioxide gas into the filled granules in the mold of the step to cure the filled granules, and forming the cured product obtained in the fourth step into colloidal silica, an aqueous solution of lithium silicate or A fifth step of applying one or more surface treatment liquids selected from an aqueous solution of aluminum phosphate and heat-treating at 300 to 800 ° C.