JPS599506B2 - Method for producing conductive zinc oxide - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing conductive zinc oxide.

Conductive zinc oxide is not only conductive but also odorless, heat resistant,
Because of its advantages such as light resistance, it is used as a conductive agent in facsimile recording paper and other information recording paper for electrostatic recording, current recording, discharge recording, etc., as well as in antistatic compositions for synthetic resin films and synthetic transverse fibers. ing. Among various methods for producing conductive zinc oxide, a method is already known in which zinc oxide powder and aluminum oxide powder are dry mixed and heated to produce conductive zinc oxide (Japanese Patent Publication No. 55-1
No. 9897).

According to this method, highly conductive zinc oxide can be obtained at a low cost, but there is still room for improvement in its whiteness.Furthermore, since dry mixed raw material powders are used, the raw material powders interact with each other during the heating and firing stage. Conductive zinc oxide is usually obtained as fine particles without adhesion and agglomeration and does not require pulverization, but depending on the application, it is preferable that the average particle size is smaller and the particle size distribution is narrower. In order to solve these problems, the inventors of the present invention conducted intensive research and found that by adding sulfur or metal sulfide to zinc oxide powder and aluminum oxide powder and heating and baking them, the conductivity and whiteness of the powders could be improved. The inventors have discovered that it is possible to improve the particle size distribution and further narrow the particle size distribution, leading to the present invention.

The method for producing conductive zinc oxide according to the present invention includes zinc oxide powder, 0.05 to 5 mol of aluminum oxide powder per 100 mol of zinc oxide, and 0.01% by weight or more of sulfur or metal based on the zinc oxide. It is characterized in that it is dry mixed with sulfide powder and heated to a temperature of 700 to 1100°C in the presence of solid carbon.

The aluminum oxide used in the present invention is preferably a powder mainly composed of aluminum aluminum oxide and having an average particle size of about 20 mμ or less. Using aluminum oxide with an average particle size significantly larger than about 20 mμ does not result in highly conductive zinc oxide. Incidentally, zinc oxide is not particularly limited, and the average particle size may be the same as that of ordinary commercially available products, that is, about 0.1 to several microns, but preferably about 0.1 to 2 microns. The mixing ratio of aluminum oxide to zinc oxide is 0.05 to 5 mol, preferably 0.5 to 1.5 mol, per 100 mol of zinc oxide.

When the mixing ratio of aluminum oxide is outside the above range, it is difficult to obtain highly conductive zinc oxide. In the present invention, in addition to aluminum oxide, 0.01% by weight or more, preferably 0.1% by weight or more of sulfur powder and/or metal sulfide powder is blended with respect to zinc oxide.

Sulfur includes powdered sulfur, elevated sulfur, and colloidal sulfur. The metal sulfide is preferably colorless or light-colored, such as nickel sulfide, tin sulfide, zinc sulfide, etc. The amounts of sulfur and metal sulfides are not limited by theory, but excessive amounts of sulfur and sulfur in metal sulfides become sulfur dioxide, etc., and volatilize from the reaction system when the raw powder mixture is heated and fired. There are no particular limitations on this. However, 10% by weight or less is usually sufficient. For dry mixing zinc oxide, aluminum oxide, and sulfur and/or metal sulfides, a rotating container type mixer such as a V-type mixer, or a fixed container type such as a ribbon type, screw type, or rotary blade type is used. A mixer or the like is used as appropriate.

The mixing method is not particularly limited as long as the raw material powders can be mixed uniformly. As the solid carbon used in the present invention, for example, powdered, granular or lumpy charcoal is suitable.

Such solid carbon is heated in a container while being separated from or mixed with the raw material mixed powder. When solid carbon is mixed with the raw material mixed powder and heated, it is sufficient that the carbon has a particle size that can be easily separated from the fired product using a screen or the like after the raw material mixed powder is heated and fired. However, in the case of fine powder solid carbon, it is quickly oxidized to carbon monoxide and carbon dioxide under the heat treatment conditions of the present invention and volatilized from the raw material powder mixture, so by selecting the amount to be used,
It is also possible to eliminate the need to separate the solid carbon used after heating and firing. In the present invention, it is convenient to use a closed container equipped with an inlet pipe and an exhaust pipe for introducing a non-oxidizing gas such as nitrogen as the container for heating and firing the raw material mixed powder.

That is, as one specific method, charcoal is laid in a layer at the bottom of a container, and a raw material mixed powder consisting of zinc oxide, aluminum oxide, and sulfur and/or metal sulfide is placed on the charcoal layer in an air atmosphere. The crucible is placed, the non-oxidizing gas inlet pipe is closed, the exhaust pipe is opened, and the container is heated to a predetermined temperature for a predetermined time in an electric furnace. The heating temperature of the raw material mixed powder was 700 to 110°C, and the heating time was 15°C.
It takes about 3 minutes to 3 hours.

When the heating temperature is outside the above range, it is generally difficult to obtain highly conductive zinc oxide. At temperatures higher than 1100° C., the formation of metallic zinc becomes noticeable, and there is also the disadvantage that the yield of the desired conductive zinc oxide decreases.

In the present invention, even if heating and smoking of the raw material powder mixture is started in an air atmosphere, solid carbon reacts with the air in the atmosphere and naturally forms a reducing atmosphere over time. There is no need to forcefully flow carbon monoxide or a mixed gas of these and nitrogen into the container. In the present invention, reducing gas is generated during heating and firing, so as mentioned above, this reducing gas is naturally discharged from the exhaust pipe along with the air to create a reducing atmosphere in the container at an approximately constant pressure. It is desirable to keep it. When cooling the raw material mixed powder after heating and firing for a predetermined period of time, it is desirable to isolate the inside of the container from the atmosphere or to circulate nitrogen gas in the container to place it in a non-oxidizing atmosphere. This is because if the fired product comes into contact with an oxidizing gas such as air during the cooling process, the conductivity of the resulting fired product may decrease. In the present invention, up to 200°C or lower, preferably at room temperature,
It is desirable to cool the heated and fired product under a non-oxidizing atmosphere in this manner. However, the cooling method may be natural cooling or forced cooling. In the present invention, if necessary, the raw material mixed powder may contain one or more acid compounds of metals such as gallium, indium, tin, nickel, and molybdenum. Amounts of up to 10% by weight based on zinc oxide are preferred.

As described above, the present invention is a method for obtaining conductive zinc oxide by heating and firing zinc oxide powder and aluminum oxide powder in a reducing atmosphere, in which sulfur and metal sulfide are further mixed with raw materials, This process not only makes zinc oxide even more conductive, but also provides superior whiteness compared to conventional methods, as well as a smaller average particle size and a finer particle size distribution. It is possible to obtain conductive zinc oxide whose volume resistivity is narrowed to a small diameter range of 10 -1 to 101 Ω. Of course, according to the method of the present invention, solid carbon is heated in an air atmosphere to generate a reducing gas, so there is no need to circulate hydrogen or carbon monoxide gas in the container, and the raw materials are also dry mixed. Therefore, conductive zinc oxide having a small particle size can be obtained immediately after heating and firing without causing the raw material particles to sinter and aggregate with each other during the heating and firing stage. Examples of the present invention are listed below,
The present invention is not limited to these examples.

Example 1 100 parts by weight of zinc oxide powder with an average particle size of 0.6 μm, aluminum oxide “Aluminum Oxide C” with an average particle size of 20 μm (manufactured by Degutsa AG in West Germany, sold by Nippon Aerosil Co., Ltd.) 0
．． 65 parts by weight (0.5 mol per 100 mol of zinc oxide) and a predetermined amount of powdered sulfur were dry mixed for 5 minutes in a small test mixer "Micro Speed Mixer" (manufactured by Takara Koki) to obtain a raw material mixed powder. Prepared.

8 parts by weight of coarsely crushed charcoal was spread in a layer on the bottom of a stainless steel heat-resistant copper container, and a crucible containing 30 parts by weight of the above raw material mixed powder was placed on the charcoal layer, and then heated to the temperature shown in Table 1 for 30 minutes.
Heated in an electric furnace for an hour.

During this time, the reducing gases generated were naturally vented from the container. Next, while slowly circulating nitrogen gas inside the container,
The heated and fired product was cooled to room temperature. Table 1 shows the volume resistivity (Ω·α) and average particle diameter (g) of the obtained zinc oxide powder. In addition, in the table, the amount of sulfur added is 100% of zinc oxide.
It shows the number of parts by weight of sulfur. Next, the above 9
5 For C-fired products, use the particle size distribution analyzer ``SEDIME''.
When the particle size distribution was measured by a sedimentation method using water as a medium using "NTOGRAPHSA-2 Model" (manufactured by Shimadzu Corporation), 96% of the particles were 4μ or less, and almost the entire amount was 5μ or less.

Further, when the solder whiteness was measured according to JISP8l23, it was 84.6. 98 in the same way as above
The whiteness of zinc oxide obtained by firing at 00C for 3 hours was 82.
It was 0. Comparing these with the average particle diameter, particle size distribution, and whiteness of zinc oxide obtained in the following comparative example, it is clear that the zinc oxide produced by the method of the present invention is superior. Comparative Example A mixed powder consisting of 100 parts by weight of zinc oxide and 0.65 parts by weight of aluminum oxide was calcined at 101°C for 2.5 hours in the same manner as in Example 1 except that sulfur powder was not used.

This zinc oxide has a volume resistivity of 60Ω・σ and an average particle size of 1.
It was 43μ. The particle size distribution measured in the same manner as in Example 1 shows that 72% of particles are 4μ or less, 87% are 5μ or less, and 130 particles are larger than 5μ! ) also existed. The whiteness of the solder was 78.8, and it was slightly grayish. Example 2 The same treatment as in Example 1 was performed except that nickel sulfide was used instead of powdered sulfur in Example 1, and the results shown in Table 2 were obtained.

The solder whiteness of the product baked at 950° C. in which 0.6 parts by weight of nickel sulfide was added was 80.3.

Example 3 The same procedure as in Example 1 was carried out except that tin sulfide was used instead of powdered sulfur in Example 1, and the results shown in Table 3 were obtained.

Claims (1)

[Claims] 1 Zinc oxide powder, 0.05 to 5 mol of aluminum oxide powder per 100 mol of zinc oxide, and 0.01% by weight or more of sulfur or metal sulfide powder relative to zinc oxide. A method for producing conductive zinc oxide, comprising dry mixing and heating to a temperature of 700 to 1100°C in the presence of solid carbon. 2. The method for producing conductive zinc oxide according to claim 1, wherein the aluminum oxide powder is a powder mainly composed of particles with an average particle size of 20 mμ or less. 3. The method for producing conductive zinc oxide according to claim 1, wherein the metal sulfide is nickel sulfide. 4. The method for producing conductive zinc oxide according to claim 1, wherein the metal sulfide is tin sulfide. 5. The method for producing conductive zinc oxide according to claim 1, wherein the metal sulfide is zinc sulfide.