JP2002252492A - Method for producing fine powder for shielding electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a general purpose fine powder for shielding an electromagnetic wave which can solve both problems of recycling of waste and shielding of the electromagnetic wave. SOLUTION: A material mixture produced by kneading any one of tar, pitch and asphalt, or a mixture of any one of them and an aluminum compound or a titanium compound is fired in a reducing atmosphere having a highest temperature in the range of 850-950 deg.C and then powdered to produce fine powder for shielding the electromagnetic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shielding plate, various casings, paints, clothes such as waistcoats, and other various articles which require electromagnetic shielding performance.
The present invention relates to a method for producing an electromagnetic shielding fine powder capable of exhibiting a shielding function by being held by impregnation or other means.

[0002]

2. Description of the Related Art With the advance of industrialization and the development of a consumer society, so-called industrial wastes such as asphalts, tars and pitches are increasing. In addition, the amount of waste paper (waste paper) and wood waste made of cellulosic materials is increasing steadily. Reuse is as important an issue as other industrial waste.

On the other hand, effects of electromagnetic waves on the human body have been reported,
In recent years, technology for shielding electromagnetic waves has been actively developed. Since many effects on the human body when using devices that emit high-frequency electromagnetic waves such as mobile phones have been reported, countermeasures have been mainly studied for the effects in high-frequency bands emitted by mobile phones and the like. Shield technology is also mainly in that band. For example, JP-A-11-409
No. 82 describes a material in which carbon powder is laminated and integrated on a conductive metal sheet such as an aluminum foil via an insulating sheet material. In Japanese Patent Application Laid-Open No. 9-86910, when carbonizing an organic substance to produce a carbide,
There has been proposed a method for producing a carbide, characterized in that the temperature is raised to a temperature in the range of ~ 700 ° C and firing is performed, and then the organic material is heated to a temperature exceeding 700 ° C and fired again.
Japanese Patent Application Laid-Open No. 2000-7426 discloses that, based on clay, 15 to 20% by weight of a self-curing phenol resin, 10 to 15% by weight of activated carbon,
There has been proposed a method for producing carbon ceramics, which comprises adding 5 to 7% by weight of titanium oxide and 1 to 3% by weight of a rare earth metal, and baking with LPG at 1040 ° C. in a nitrogen stream.

[0004]

As described above, although many proposals have been made, they have electromagnetic wave shielding performance and are industrial waste, especially tar or pitch-like materials, and furthermore, cellulosic materials such as waste paper. There seems to be no idea of mixing and recycling resources for effective use. Therefore, the present inventor has solved both the problems of the recycling of waste and the shielding of electromagnetic waves, and studied a manufacturing method for providing fine powder for electromagnetic shielding with high versatility. In addition, the improvement of electromagnetic wave absorption was also studied.

[0005]

As a result of studying the above-mentioned problems, a raw material mixture obtained by kneading a tar or pitch-like bituminous substance and an aluminum compound or a titanium compound is mixed in a reducing atmosphere at a maximum temperature of 850 to 950 ° C. A method for producing a fine powder for shielding electromagnetic waves, characterized in that it is powdered after firing within the range.

[0006] As the tar, pitch or asphalt used herein, asphalts such as petroleum asphalt such as straight asphalt, blown asphalt, semi-blown asphalt, cutback asphalt and propane deasphalted asphalt, and rock asphalt, lake asphalt and sand Natural asphalt such as asphalt, asphaltite, gilsonite, grahamite, trinidate asphalt, heavy oil (residue oil such as diesel heavy oil, bunker heavy oil), tars such as gas furnace coal tar, coke oven coal tar, blast furnace coal tar, and produsaga Coal tar such as squall tar, oil gas tar, generator gas tar, water gas tar, fatty acid tar, wood tar, bone ash tar Pitch, petroleum pitch, oil gas tar pitch, water gas tar pitch, wood tar pitch, gas furnace tar pitch, coal tar pitch (plast furnace coal tar pitch, coke oven coal tar pitch, etc.) ), Producer gas tar pitch, fatty acid tar pitch, desulfurized pitch and the like.

As a specific method for producing a fine powder for shielding electromagnetic waves, tar, pitch, or asphalt or a mixture of any of them is used in an amount of 50 to 70% by weight, and a cellulosic material is used in an amount of 20 to 40% by weight. 10 aluminum oxide
~ 20% by weight and a raw material mixture containing 5-10% by weight of titanium oxide, and the maximum temperature is 850-950 in a reducing atmosphere.
By firing within the range of ℃, the carbon ratio after firing is reduced
This is a method for producing a fine powder for shielding electromagnetic waves, wherein the powder is made into powder after adjusting to 60 to 85% by weight.

The blending of tar, pitch, or asphalt, or a mixture of any of these, serves to maintain the shape of the raw material mixture during molding and before firing, and serves as a carbon source. Below 50% by weight, the hardness increases and becomes harder,
If it is 70% by weight or more, it becomes brittle and easily collapses. Preferably
50 to 70% by weight.

The cellulosic material referred to herein includes waste paper (papermaking waste and wastepaper) derived from paper, wood, bamboo, etc., wood waste, thinned wood, sawmill, and other processing waste used in plants. It is processed into a body or fiber and used. Particularly, use of waste paper is preferable. When these are cut into fine pieces, they are easily mixed into tar or pitch-like bituminous products. Both are carbon sources. If it is less than 20% by weight, it is insufficient as a carbon source.
On the other hand, if it is 40% by weight or more, kneading and molding becomes difficult. Preferably it is 20 to 40% by weight.

[0010] Aluminum imparts conductivity to the electromagnetic wave shielding fine powder to enhance the electromagnetic wave shielding performance. Although many metals provide conductivity, silver is expensive and copper is toxic. Iron is easily rusted. The use of aluminum is preferred because there is no such difficulty. Aluminum is difficult to turn into a fine powder after firing of the product of the present invention if it is in a metallic form. Therefore, aluminum compounds such as oxides and hydroxides are preferable. 10-20% by weight of aluminum oxide
Is preferred. If the content is less than 10% by weight, the conductivity is reduced and it is difficult to obtain the electromagnetic wave shielding performance. If the content is 20% by weight or more, excessive addition is required. The use of aluminum oxide is preferred over the use of metallic aluminum.

[0011] Titanium is also preferably a compound rather than a metallic one. In the case of titanium oxide, the content is preferably 5 to 10% by weight.
This is also added for imparting conductivity. If it is less than 5% by weight, the conductivity is insufficient, and if it is more than 10% by weight, the hardness increases and pulverization becomes difficult.

The raw material mixture is fired in a reducing atmosphere. The reducing atmosphere is to remove oxygen. At this time, a halogen gas is also preferable, but an inert gas is preferably used.
As the inert gas, a rare gas such as nitrogen, helium, neon, argon, krypton, or xenon can be used. However, it is preferable to use an inert gas in a carbon monoxide atmosphere because of its low cost.

[0013] The firing temperature is also important.
Perform low-temperature baking at ℃. The low-temperature firing time is preferably 1 to 2 hours. By this low-temperature firing, the moisture is evaporated and dried,
Prevent cracking of the fired body. The maximum firing temperature is 800
It is preferably in the range of 1,0001000 ° C., preferably 850 ° -950 ° C. When the maximum temperature exists in this range, the carbonization of the pitch-like bituminous matter is likely to become fine powder later.
Further, it becomes conductive carbon and has high electromagnetic wave shielding performance. If the firing temperature is 850 ° C. or lower, a material having good conductivity cannot be obtained, and if the firing temperature is 950 ° C. or higher, the powder becomes hard and hardly becomes fine powder. As a means for forming fine powder, an existing ball mill method, grinder method, mixer method, or the like can be employed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. Examples of blending of petroleum pitch, coal pitch, shredded waste paper, aluminum oxide, titanium oxide, and other iron oxides were prepared as shown in Examples 1 to 6 in Table 1.

[0015]

[Table 1]

Each of the compositions No. 1 to No. 6 shown in Table 1 was supplied from a room temperature to 25% while supplying nitrogen gas into the furnace.
The temperature was raised to 0 ° C. over 1 hour and calcined at 250 ° C. for 2 hours at low temperature. Next, the temperature was raised over 2 hours until the maximum firing temperature shown in the right column in Table 1 was reached, and then the high temperature was maintained at that maximum temperature for 4 hours to perform high-temperature firing. Thereafter, it was cooled to room temperature, and the fired product after cooling was turned into fine powder of 300 to 370 mesh by a ball mill method.

Table 2 shows the results of elemental analysis of the fired products No. 1 to No. 6. The carbon ratio is 70-80%. None of them had cracks.

[0018]

[Table 2]

All of the Examples No. 1 to No. 6 could be easily made into fine powder. The resulting fine powder has a specific gravity of 1.
2 to 1.3, the specific surface area 80~95m ² / g, total pore volume 0.01~0.02ml
/ g. Table 3 shows the measurement results of the electromagnetic wave shielding ability and the surface resistance of the fired products No. 1 to No. 6. Table 3 also shows the measured values shown for the conventionally known electromagnetic wave shielding materials. No.1
No. 6 is a method of measuring the electromagnetic wave shielding ability of the fired product,
According to the C (Kansai Electronics Industry Promotion Center) method. The measuring instrument is a spectrum analyzer TR4172: manufactured by Advantest (measuring conditions: 15 ° C.). The measurement of surface resistance value is performed by SANWA SD-420
According to C.

[0020]

[Table 3]

From the results shown in Table 3, the fired products of Nos. 1 to 6 of the present invention have better electromagnetic wave shielding ability than the conventional example at 100 MHz, 1 GHz and 5 GHz. Further, the measurement result of the surface resistance value shows good conductivity, which results in an electromagnetic wave shielding effect.

FIG. 1 shows the frequency of electromagnetic wave shielding of the fired product of Example No. 3. FIG. 2 shows Example Nos. 2 and 3
Shows the electromagnetic wave shielding ability when the composition is fired at a maximum temperature in the range of 800 to 950 ° C. When the maximum temperature was set to 950 ° C or higher, it was not tested because it becomes hard and hard to turn into powder.

From FIG. 1, it is clear that the fired product of the present invention exhibits an electromagnetic wave shielding ability by frequency of approximately 50 dB or more in the entire range of 10 MHz to 1 GHz. Further, it is clear from FIG. 2 that when the maximum temperature is baked in the range of 800 to 950 ° C., the electromagnetic wave shielding ability is excellent.

FIG. 3 shows the electromagnetic wave shielding ability when the composition is close to that of Example No. 1 and the maximum temperature is baked at 800 ° C. while changing the addition of aluminum oxide to 5 to 10% by weight. It can be seen that when the addition amount of aluminum oxide decreases, the surface resistance increases and the electromagnetic wave shielding ability decreases.

[0025]

According to the present invention, it is possible to solve both the problems of recycling of waste and shielding of electromagnetic waves. The obtained fine particles for shielding electromagnetic waves have high electromagnetic wave absorbing ability, and are characterized by a versatility in shielding plates, various casings, paints, clothes such as vests, and other various articles requiring electromagnetic wave shielding performance. It is resistant to aging, is stable, resistant to many chemicals, and can be used for a long time without changing its performance.

[Brief description of the drawings]

FIG. 1 is a graph showing the measured shielding ability of a fired product obtained according to the present invention with respect to a change in frequency of an electromagnetic wave.

FIG. 2 is a graph showing the measured shielding ability of a fired product when fired at a maximum temperature in the range of 800 to 950 ° C.

FIG. 3 is a graph showing a relationship between a surface resistance value and an electromagnetic wave shielding ability.

Claims (4)

[Claims] Claims 1. A raw material mixture obtained by kneading an aluminum compound or a titanium compound with any of tar, pitch, or asphalt or a mixture of any of these,
A method for producing a fine powder for electromagnetic wave shielding, comprising firing in a reducing atmosphere at a maximum temperature in the range of 850 to 950 ° C. and then pulverizing the powder. 2. Tar, pitch or asphalt or a mixture of any of them, 50 to 70% by weight, cellulosic material 20 to 40% by weight, aluminum oxide 10 to 20% by weight, oxidation A raw material mixture containing 5 to 10% by weight of titanium is kneaded, and the maximum temperature is reduced in a reducing atmosphere.
A method for producing a fine powder for electromagnetic wave shielding, characterized in that a carbon ratio after firing is reduced to 60 to 85% by weight by firing at a temperature in the range of 850 to 950 ° C, and then powdered. 3. The method for producing a fine powder for electromagnetic wave shielding according to claim 1, wherein the firing of the raw material mixture in a reducing atmosphere is performed in a carbon monoxide atmosphere. 4. The fine powder for shielding electromagnetic waves according to claim 1, wherein the low-temperature firing at 100 to 300 ° C. is performed before the high-temperature firing at a maximum temperature in the range of 850 to 950 ° C. How to make the body.