JPH0475167B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a powder for radio wave absorber material used for preventing radio wave leakage or radio wave reflection, and it is a method for producing a radio wave absorber material with excellent radio wave absorption properties in a simple manner. The object of the present invention is to provide a powder for a radio wave absorber material made of Mn--Zn ferrite particle powder that can be manufactured through a process. [Prior Art] As is well known, many devices (eg, microwave ovens, food and drink vending machines with a heating function, etc.) equipped with heating means using microwave irradiation have been used recently. However, if there is a slight gap between the movable opening/closing parts or joints of equipment that uses microwaves, the microwaves can leak outside through the gap.
Radio wave absorbing materials are used as a measure to prevent radio wave leakage, as they not only have a negative effect as a noise source on televisions, radios, etc., but also pose a major hindrance to the human body. Furthermore, with the development of microwave communications, materials for radio wave absorbers are being reconsidered as an anti-reflection measure to minimize the reflection of radio waves from buildings in densely populated urban areas with tall buildings. Conventionally, as radio wave absorbers used in the microwave region to prevent radio wave leakage or radio wave reflection, ferrite molded products, composite ferrites in which ferrite powder is dispersed in non-magnetic materials such as rubber and synthetic resins, and A pyramid type radio wave absorber in which carbon powder is held in styrofoam or the like is well known. In particular, radio wave absorbers made of Mn-Zn ferrite particles, various rubbers, and synthetic resins have been attracting attention. and is used here
Mn-Zn ferrite particle powder is a functional material:
Vol. 2, No. 1, pp. 38-46: Published by CMC (1982), molded and sintered Mn-Zn ferrite is widely used in the field of electronic equipment as a high magnetic permeability material. The powder is ground using a powerful grinder for a long period of time to produce fine particles with high powder density. In addition,
The radio wave absorption characteristic (attenuation amount) of the radio wave absorber using this fine particle powder is about 10 to 20 dB for microwaves in the range of 2 to 16 GHz. [Problems to be solved by the invention] Conventionally, Mn-Zn ferrite particles for radio wave absorber materials have been produced by mixing raw materials of Fe ₂ O ₃ , MnO and ZnO → mixing → pre-calcination → pulverization → molding → main firing. →It is obtained through a manufacturing process called pulverization,
More specifically, Mn− obtained by calcining
After molding the Zn ferrite particle powder, main firing is performed at high temperature to obtain a dense Mn-Zn ferrite molded sintered body, and then the sintered body is crushed to form a high-density powder that is effective as a powder for radio wave absorber materials. Mn-Zn ferrite particle powder (with high compressed density) is obtained. In this way, the complicated manufacturing process described above is necessary to produce Mn-Zn ferrite particles with high powder density that are effective as powders for _{radio wave} absorber materials. This is because iron oxide powder with a small diameter was used. Further, in order to increase the powder density of Mn-Zn ferrite particles, manufacturing methods using various additives are also known, and SiO ₂ is usually used as the additive. Although the addition of this additive has the effect of increasing the density of the Mn-Zn ferrite particle powder, it leads to an increase in impurities in the product.
As a result, the use of additives is inevitably limited, and there are limits to increasing the density of the powder. [Means for Solving the Problems] In view of the above-mentioned current situation, the inventor of the present invention has determined that the composition of the raw materials →
Studies have been carried out to obtain powder with high density without the need for complex manufacturing processes such as mixing → pre-calcination → pulverization → molding → main firing → pulverization, or without the need for additives. and,
By using iron oxide powder with a large compaction density and average particle size as the Fe ₂ O ₃ raw material, the present inventors were able to omit the complex steps of molding, firing, and pulverization in the manufacturing process. Powder density (compressed density) that is effective as a powder for radio wave absorber materials that has excellent radio wave absorption characteristics that are the same as or better than powders for radio wave absorber materials obtained by conventional manufacturing methods without using agents.
They discovered that it is possible to obtain Mn-Zn ferrite particles with a high content, and have completed the present invention. That is, in the present invention _{, Fe2O3} : 50 to 85 mol%,
A raw material mixture consisting of MnO: 2 to 35 mol% and ZnO: 10 to 25 mol% is granulated, then calcined at a temperature range of 1200 to 1350°C, cooled in air, and pulverized.
In obtaining a powder for radio wave absorber material consisting of Mn-Zn ferrite particles, the compressed density is 3.0 when compressed at a pressure of 1 ton/cm ² as Fe ₂ O ₃ raw material.
This is a method for producing a powder for a radio wave absorber material, characterized by using iron oxide powder having a particle size of ~4.5 g/cm ³ and an average particle size of 1.5 to 6.0 μm. [Function] First, the powder for radio wave absorber material obtained by the present invention is Mn-Zn ferrite particle powder with high powder density, regardless of the presence or absence of additives for increasing the density of the powder. It is effective as a material powder for radio wave absorbers that are kneaded with rubber or synthetic resin. Next, to explain the Fe ₂ O ₃ raw material that is the most characteristic of the present invention, in the method of the present invention
As the Fe ₂ O ₃ raw material, it is necessary to use iron oxide powder having a compressed density of 3.0 to 4.5 g/cm ³ when compressed at a pressure of 1 ton/cm ² and an average particle size of 1.5 to 6.0 μm. If the powder properties of iron oxide powder are outside the powder property range, it is difficult to obtain Mn-Zn ferrite particle powder with high powder density, and it is difficult to improve the radio wave absorption properties of radio wave absorbers using this powder as powder for radio wave absorber materials. Almost unrecognized.
In particular, when the compressed density is 3.0 g/cm ³ or less, Mn has a powder density that is effective as a powder for radio wave absorber materials.
-Unfavorable because a large amount of additives must be used to obtain Zn ferrite particle powder. In the method of the present invention, the compressed density is 3.3 to 4.5 g/
Iron oxide powder in the cm ³ range is preferred. As the iron oxide powder that satisfies the above-mentioned powder properties, there is a so-called "mill scale powder" obtained by collecting the iron oxide film generated during rolling of a steel plate and directly pulverizing it. The mill scale powder is preferably a pulverized mill scale that has a relatively small amount of impurities generated in the finishing process when rolling the steel plate, and a mill scale that is generated during the initial process when rolling the steel plate has a large amount of impurities. Undesirable. Next, a radio wave absorber material powder made of Mn--Zn ferrite particles, which is the object of the method of the present invention, will be explained. The main components are Fe ₂ O ₃ : 50-85 mol%, MnO: 2-
35 mol%, ZnO: 10 to 25 mol%, and outside the composition range
When Mn-Zn ferrite particle powder is used as a powder for radio wave absorber material, no improvement in the radio wave absorption properties of the radio wave absorber is observed, and especially when Fe ₂ O ₃ : 50 mol% or less, the magnetic properties (4πIs) deteriorate. It is not suitable for use as a powder for radio wave absorber materials because it has a significant decrease in practicality. The firing temperature in the method of the present invention is 1200 to 1350℃
must be within the range. Temperatures below 1,200°C are insufficient for complete ferrite formation, and temperatures above 1,350°C result in grain growth of the particles themselves during the firing process and strong sintering between particles, which inhibits subsequent pulverization. This is difficult and undesirable. The pulverization performed after firing may be done to obtain a powder of a desired size depending on the processing conditions such as the molding conditions of the kneaded body with rubber or synthetic resin, and the wavelength of the radio waves to be absorbed. There is no need for a powerful grinder; a regular grinder can be used. [Example] Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the compressed density in Examples and Comparative Examples is the density of the molded product when 25.0 g of the weighed sample to be measured is put into a cylindrical mold with a diameter of 25.4 mm and compression molded with a pressure of 1 ton/cm ² The average particle size was measured using the Fisher subsieve sizer method, and the magnetic field of the product was measured using a DC BH tracer (Yokogawa Electric Manufacturing Co., Ltd. Type 3257) with a magnetic field of 10 KOe. did. Example 1 Mill scale powder (FeO 69.44 ^wt %, total Fe ₂ O ₃
Conversion 106.82wt%, MnO 0.328wt%, SiO ₂ 0.062wt
%), 217.1 g of manganese dioxide, and 101.7 g of zinc oxide were mixed in a Raikai machine for 30 minutes, then granulated, and then the granulated material was fired in an electric furnace in the atmosphere at 1320°C for 2 hours. Ivy (Temperature rise is 180℃/
hr). After firing, it is taken out into the atmosphere, cooled to room temperature, and then crushed to a compressed density of 3.51 g/cm ³ and an average particle size.
_Fe2O3 : _55.39wt %, MnO: 29.43wt%, at 2.78μm
Mn--Zn ferrite particle powder having a composition of ZnO: 15.18 wt% was obtained. Next, the above Mn-Zn ferrite particle powder was
Weigh 20g, add and mix 1.5ml of 6.5% by weight PVA (polyvinyl alcohol) solution, and pressure mold to a height of 11.8mm in a 25.4mmφ cylindrical mold (molding density 3.30g/cm ³ ). This was then dried to form a cylindrical molded product. The saturation magnetic flux density (4πIs) of the obtained cylindrical molded product was measured and found to be 3650 Gauss. Furthermore, the obtained Mn-Zn ferrite particle powder
141g and ethylene-vinyl acetate copolymer resin (product name Evaflex #EV-410 Mitsui Polychemical Co., Ltd.)
After kneading 25 g of Zinc Stearate and 1 g of zinc stearate using a hot roll heated to 55°C, it was made into a sheet with a thickness of 1.0 mm. Prepare 11 such sheets, and then stack them on a plating board and roll-press them at 70°C and a pressure of 3.5 kg/cm ² to obtain a composite ferrite sheet (150 mm x 150 mm x 10 mm) that is a radio wave absorber. ) was created. Using the obtained composite ferrite sheet, 2
As a result of measuring radio wave absorption characteristics in the ~20GHz band,
Attenuation in the 2.45GHz frequency band is 21dB・cm ^-1
The maximum attenuation is in the 7GHz frequency band.
It was 67dB・cm ^-1 . Examples 2 to 9 Radio wave absorption characteristics were obtained in the same manner as in Example 1, except that the compressed density and average particle size of the iron oxide raw material, the composition ratio of the ferrite-forming metal oxide, the SiO ₂ content, and the firing temperature were varied. A powder for a radio wave absorber material was obtained, which was made of Mn-Zn ferrite particle powder having excellent properties and high powder density and effective as a powder for a radio wave absorber material. Table 1 shows the results of the saturation magnetic flux density measured in the same manner as in Example 1 and the radio wave absorption characteristics measured in the same manner as in Example 1 using the obtained powder for radio wave absorber material. In addition, the maximum attenuation in Examples 4 and 5 is 11 GHz.
It was in the frequency band of Comparative Examples 1 to 3 Mn-Zn ferrite was produced in the same manner as in Example 1, except that the compressed density and average particle size of the iron oxide raw material, the composition ratio of the ferrite-forming metal oxide, the SiO ₂ content, and the firing temperature were varied. A particulate powder was obtained. Table 1 shows the results of the saturation magnetic flux density measured in the same manner as in Example 1 and the radio wave absorption characteristics measured in the same manner as in Example 1 using the obtained Mn--Zn ferrite particle powder. In addition, the attenuation in the 11 GHz frequency band in Examples 1, 2, and 3 was 16 db·cm ^-1 and
They were 14db・cm ^-1 and 10db・cm ^-1 . Comparative Example 4 846.4 g of iron oxide powder (α-Fe ₂ O ₃ ) having a compressed density of 2.51 g/cm ³ and an average particle size of 0.6 μm, 298.2 g of manganese dioxide, and 103.3 g of zinc oxide were mixed for 30 minutes using a Raikai machine. After that, the granules were granulated, and then the granules were pre-calcined at 1180°C for 2 hours in an electric furnace in the atmosphere, followed by pulverization, press molding, and main firing at 1320°C for 3 hours in a nitrogen gas atmosphere. Then, after cooling to room temperature, it was pulverized to give a compressed density of 3.40 g/cm ³ and an average particle size of 3.5 μm, Fe ₂ O ₃ : 53.0 wt%, MnO: 34.3 wt%,
Mn--Zn ferrite particle powder having a composition of ZnO: 12.7 wt% was obtained. The saturation magnetic flux density of the obtained Mn--Zn ferrite particles was measured in the same manner as in Example 1, and the result was 3000 Gauss. In addition, as a result of measuring the radio wave absorption characteristics in the same manner as in Example 1, 2.45GHz,
The amount of attenuation in the 11GHz frequency band is
12db・cm ^-1 and 10db・cm ^-1 , and the maximum attenuation is
It was 20db・cm ^-1 in the 7GHz frequency band.

【table】

〔effect〕

According to the method for producing powder for radio wave absorber material according to the present invention, as shown in the previous example, iron oxide powder having a large compacted density and a large average particle size is used as the Fe ₂ O ₃ raw material. It is possible to obtain Mn-Zn ferrite particle powder with high powder density through a simplified manufacturing process and without using additives to increase powder density, and it is compatible with rubber or synthetic resin. Mn-
It is possible to supply powder for radio wave absorber material made of Zn ferrite particle powder. In addition, by changing the composition ratio of the powder for radio wave absorber material made of Mn-Zn ferrite particles obtained by the method of the present invention, it is possible to improve the range from low frequency range to high frequency in the frequency band of 2 to 20 GHz. Excellent radio wave absorption properties can be obtained over the entire region, making it suitable as a powder for radio wave absorber materials used in a wide range of frequency bands. Furthermore, when manufacturing powder for radio wave absorber materials, mill scale powder having a large compressed density and a large average particle size can be used as the iron oxide raw material. This is effective in the use of resources and the elimination of sources of pollution in these days when resource shortages have become a problem.

Claims (1)

[Claims] 1 Fe ₂ O ₃ : 50 to 85 mol%, MnO: 2 to 35 mol%
and ZnO: A raw material mixture consisting of 10 to 25 mol% is granulated, then fired at a temperature range of 1200 to 1350°C, allowed to cool in air, and pulverized to produce a radio wave absorber made of Mn-Zn ferrite particle powder. In order to obtain powder for materials, iron oxide powder having a compressed density of 3.0 to 4.5 g/cm ³ and an average particle size of 1.5 to 6.0 μm when compressed at a pressure of 1 ton/cm ₂ is used as Fe ₂ O 3 raw material ^. A method for producing a powder for radio wave absorber material, characterized by using.