JP2009292683A - Electromagnetic wave shielding ceramic and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding ceramic having excellent corrosion resistance and retains electromagnetic wave absorption characteristics and electromagnetic wave reflection characteristics and to provide a production method thereof. <P>SOLUTION: A metal oxide, carbon black, alumina, and a binder are mixed together in a specified ratio, for example, in such a ratio that titanium oxide or molybdenum oxide as the metal oxide is 20 wt.% based on the alumina. The resulting mixture is molded, and the molding is fired in a reducing atmosphere at 1,500°C or higher without performing debinding for vaporizing the binder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio wave shielding ceramic having an effect of shielding radio waves and a method for manufacturing the same.

  Traditionally, metals reflect radio waves and have been used as radio wave shielding materials. However, a fatal drawback of metals is corrosion. Corrosion proceeds especially when used in coastal areas and oceans. Further, a radio wave shielding material using porous ceramics has been proposed in JP-A-7-215776 (Patent Document 1).

JP-A-7-215776

  Alumina ceramics are a corrosion-resistant and inexpensive material that can be adapted to various usage environments, but the electrical characteristics of alumina ceramics are insulators, and the characteristics regarding radio waves are slight absorption. There was a problem that could not be obtained.

  The present invention solves the above-mentioned problems. The object of the present invention is to have a property that a material obtained by mixing and firing alumina ceramics and carbon reflects a radio wave like a metal and a radio wave like a ceramic mixed with carbon. Due to the knowledge that it has the properties of absorbing properties, alumina ceramics that have been mixed and baked with carbon have the effect of absorbing radio waves. It is an object of the present invention to provide a radio wave shielding ceramic that retains characteristics and radio wave reflection characteristics and a method of manufacturing the same.

  The first configuration of the radio wave shielding ceramic according to the present invention for achieving the above object is characterized in that a metal oxide, carbon black, alumina, and a binder are mixed, molded, and fired. Here, the binder is made of various organic substances.

  The second configuration of the radio wave shielding ceramic according to the present invention is characterized in that, in the first configuration of the radio wave shielding ceramic, the metal oxide is titanium oxide or molybdenum oxide.

  The third configuration of the radio wave shielding ceramic according to the present invention is characterized in that, in the first configuration of the radio wave shielding ceramic, the titanium oxide or the molybdenum oxide is mixed in an amount of 20% by weight with respect to the alumina. .

  A first configuration of the method for producing a radio wave shielding ceramic according to the present invention is characterized in that a metal oxide, carbon black, alumina, and a binder are mixed, molded, and fired.

  The second configuration of the radio wave shielding ceramic manufacturing method according to the present invention is characterized in that, in the first configuration of the manufacturing method, the firing is performed in a reducing atmosphere of 1500 ° C. or higher.

  Moreover, the 3rd structure of the manufacturing method of the electromagnetic wave shielding ceramic which concerns on this invention is the degreasing | defatting for vaporizing the said binder when baking by 1500 degreeC or more in a reducing atmosphere in the 2nd structure of the said manufacturing method. It is characterized by not performing.

  According to the above configuration, the radio wave shielding ceramic of the present invention has a radio wave shielding effect equivalent to that of a metal plate while being a ceramic, has resistance to corrosion such as seawater, and the metal oxide is 20% by weight of the whole. Since it has the same performance as that of metal, there is an effect of saving metal resources.

  The present inventors believe that alumina ceramics having radio wave shielding effects may be possible by combining a metal having radio wave shielding effects and carbon-alumina ceramics having a radio wave absorption effect that is inexpensive and excellent in corrosion resistance. The experiment was repeated.

  According to the above configuration, after mixing and forming a carbon-alumina mixed material having radio wave absorption characteristics and a metal oxide that is reduced to precipitate a metal, the ceramic is baked in a reducing atmosphere of 1500 ° C. or higher. It retains physical and chemical properties and can provide a radio wave shielding effect.

  Carbon acts as a metal oxide reducing agent and is released into the atmosphere as carbon monoxide and carbon dioxide in the course of firing at 1500 ° C. or higher. And it is estimated that the reaction shown by the following chemical formulas 1 and 2 passes. This reaction is considered to be performed in the voids of the crystal grains of alumina ceramics. In addition, n and m of the following chemical formulas show arbitrary integers.

[Chemical 1]
TiO ₂ + C = Ti + CO ₂

In addition to metallic titanium, Ti _n O _m produced by reduction of TiO ₂ coexists as a product.

[Chemical 2]
MoO ₂ + C = Mo + CO ₂

In addition to metallic molybdenum, Mo ₂ C (molybdenum carbide) produced by reduction coexists as a product.

  The mixing amount of carbon is determined from the chemical reaction formulas 1 and 2, and 1 mol of carbon is required for 1 mol of titanium oxide.

  Since carbon oxidizes (combusts) under high temperature conditions and is consumed as carbon dioxide gas, firing is performed in either a reducing atmosphere or an inert gas atmosphere to suppress carbon oxidation and reduce titanium oxide. Facilitate.

  Further, as a carbon source, it is generally used in the production of ceramics, and is a binder (for example, PVA (polyvinyl alcohol)) required for molding that vaporizes or decomposes at 500 ° C. or higher (hereinafter referred to as “degreasing process”). When reduction firing is performed without degreasing the acrylic resin or the like, carbon remains and becomes a carbon source.

  An embodiment of a radio wave shielding ceramic according to the present invention and a method for manufacturing the same will be described specifically with reference to the drawings. FIG. 1 is a manufacturing process diagram showing a method of manufacturing a radio wave shielding ceramic according to the present invention, FIG. 2 is a general manufacturing process diagram, and FIG. 3 is a relationship between a mixing ratio of titanium oxide and a radio wave shielding effect when degreasing is not performed. FIG. 4 is a diagram for explaining the difference in radio wave shielding effect depending on the presence or absence of degreasing when the mixing ratio of titanium oxide to alumina is 15 wt% and 20 wt%, and FIG. 5 is the mixing ratio of molybdenum oxide to alumina being 5 wt%. It is a figure explaining the electromagnetic wave shielding effect in% -20 weight%.

  In FIG. 1, in the manufacturing process of the radio wave shielding ceramic of the present invention, titanium oxide as a metal oxide and carbon black as a carbon source are mixed at a predetermined mixing ratio, and the mixed powder is 2 μm to 3 μm. The slurry was prepared by adjusting the addition rate to the adjusted alumina and mixing it, and further adding a binder necessary for forming the ceramic. This slurry was allowed to stand for 24 hours in order to familiarize each raw material, and then a granule serving as a raw material for the radio wave shielding ceramic was produced using a spray dryer.

  Using granules adjusted to 5%, 10%, 15% and 20% by weight, respectively, with respect to alumina, the addition rate of titanium oxide was molded using a 50t press at 120mm length, 120mm width and 5mm thickness. . This molded product was subjected to gas exchange and fired using a reducing atmosphere firing furnace in which argon gas was passed. The firing was performed at 100 (° C./hour), held at 1500 ° C. for 2 hours, and then naturally cooled to room temperature. After firing, radio wave shielding was measured using a plate-like sample cut and polished to a 100 mm square and a thickness of 2 mm.

  The sample production method shown in FIG. 2 is basically a conventional method, and degreasing was performed to vaporize the binder added during granulation at 1000 ° C. or lower before the main baking at 1500 ° C. Is.

  The system used for the measurement was a free space method using a beam converging horn antenna, and the radio wave shielding effect was measured at 34 GHz to 50 GHz. The manufactured radio wave shielding ceramic was compared with an aluminum plate which is a metal plate having the same area.

  FIG. 3 shows the relationship between the mixing ratio of titanium oxide when not degreased and the radio wave shielding effect at 34 GHz to 50 GHz. As the mixing ratio of titanium oxide increases, the radio wave shielding effect increases. When the mixing ratio of titanium oxide to alumina is 20% by weight, a radio wave shielding effect comparable to an aluminum plate, which is a metal plate, can be confirmed.

  FIG. 4 shows the difference depending on the presence or absence of the degreasing step when the mixing ratio of titanium oxide is 15 wt% and 20 wt% with respect to alumina. When compared near 42 GHz, a sample in which 20% by weight of titanium oxide is mixed with alumina shows about −70 dB without degreasing. However, when degreasing, the radio wave shielding effect is reduced to about −12 dB, and titanium oxide Is about -25 dB without degreasing, but when degreasing, the radio wave shielding effect is reduced to about -7 dB. Therefore, the presence or absence of degreasing shows a significant difference in the radio wave shielding effect.

  When degreasing is not performed, the organic matter added during granulation is heated in a reducing atmosphere to generate carbon. Whether the generated carbon directly absorbs radio waves or is consumed in the reduction reaction in the main firing and the products of the reduction reaction increase and contributes to the radio wave shielding effect is unclear.

  According to the above configuration, it is possible to provide a radio wave shielding ceramic having characteristics that combine a property of reflecting a radio wave like a metal and a property of absorbing a radio wave like a ceramic mixed with carbon.

  In FIG. 5, a material in which molybdenum oxide is mixed 5 wt%, 10 wt%, 15 wt%, and 20 wt% with respect to alumina and a chemical equivalent amount of carbon is mixed is the same as the material in which titanium oxide is mixed. The result which measured the radio wave shielding effect between 34 GHz and 50 GHz was shown. In FIG. 5, the electromagnetic wave shielding effect is not seen when the mixing ratio of molybdenum oxide is 5 wt% to 15 wt% with respect to alumina, but when the mixing ratio of molybdenum oxide is 20 wt% with respect to alumina, Almost the same radio wave shielding effect can be confirmed.

  As an application example of the present invention, the present invention can be applied to a radio wave shielding ceramic having an effect of shielding radio waves and a manufacturing method thereof.

It is a manufacturing process figure which shows the manufacturing method of the radio wave shielding ceramic which concerns on this invention. It is a general manufacturing process diagram. It is a figure which shows the relationship between the mixing rate of the titanium oxide when not degreasing, and a radio wave shielding effect. It is a figure explaining the difference of the radio wave shielding effect by the presence or absence of degreasing in the mixing rate with respect to the alumina of titanium oxide at 15 weight% and 20 weight%. It is a figure explaining the electromagnetic wave shielding effect in the mixing rate with respect to the alumina of molybdenum oxide with respect to 5 to 20 weight%.

Claims (6)

A radio wave shielding ceramic characterized in that a metal oxide, carbon black, alumina, and a binder are mixed, molded, and fired. The radio wave shielding ceramic according to claim 1, wherein the metal oxide is titanium oxide or molybdenum oxide. 2. The radio wave shielding ceramic according to claim 1, wherein the titanium oxide or the molybdenum oxide is mixed in an amount of 20% by weight with respect to the alumina. A method for producing radio wave shielding ceramics, comprising mixing, molding, and firing a metal oxide, carbon black, alumina, and a binder. The said baking is performed in 1500 degreeC or more of reducing atmosphere, The manufacturing method of the radio wave shielding ceramics of Claim 4 characterized by the above-mentioned. The method for producing a radio wave shielding ceramic according to claim 5, wherein degreasing for vaporizing the binder is not performed when firing in a reducing atmosphere at 1500 ° C or higher.