JP4190715B2 - Method for producing cobalt black pigment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cobalt-based black pigment, and relates to a method for producing a fine-particle cobalt-based black pigment excellent in heat resistance, insulation, and color developability.
[0002]
More specifically, the present invention relates to a method for producing a cobalt-based black pigment useful as a colorant for black matrix pigments such as cathode ray tubes, liquid crystal displays and plasma displays, paints, inks and ceramics.
[0003]
[Prior art]
Conventionally, as a metal oxide black pigment, a chromium-containing composite oxide such as a Cu-Cr type or Cu-Cr-Mn type is used, but it contains chromium which is a harmful metal and has a particle size. There are disadvantages such as that a small fine particle pigment cannot be obtained.
[0004]
Moreover, although carbon black is used as a black pigment, since it has electroconductivity, there exists a fault that it cannot be used for the use which needs insulation.
[0005]
[Problems to be solved by the invention]
In the present invention, there is a demand for a fine black pigment having a small particle size, having an insulating property, not containing chromium, as a metal oxide black pigment.
[0006]
[Means for Solving the Problems]
The present invention uses cobalt raw material as a consumption anode electrode to produce substantially brown cobalt oxide fine particles having a CoO and Co ₃ O ₄ crystal structure produced by a direct current arc plasma method, and then using the cobalt oxide fine particles. The method for producing a cobalt-based black pigment is characterized in that fine particles having a Co ₃ O ₄ crystal structure are obtained by firing in an oxygen-containing atmosphere.
[0007]
The black fine particles having the above Co ₃ O ₄ crystal structure have an average particle size of 80 to 300 nm, preferably 100 to 250 nm.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As a result of intensive studies on a method for producing a cobalt-based black pigment, the present inventors have obtained a substantially brown cobalt oxide having a crystal structure of CoO and Co ₃ O ₄ having an average particle diameter of 20 to 90 nm produced by a direct current arc plasma method. It was found that fine particles having an average particle size of 80 to 300 nm, which is excellent as a black pigment, can be obtained by producing a fine particle and then heat-treating in an oxygen-containing atmosphere.
[0009]
The direct current arc plasma method used in the present invention uses a direct current arc plasma apparatus, uses various cobalt raw materials such as cobalt metal and cobalt oxide as a consumption anode electrode, generates a plasma flame such as argon gas from the cathode electrode, and consumes the anode. Cobalt oxide spherical fine particles can be produced by heating and evaporating the cobalt raw material and oxidizing and cooling the cobalt in the plasma state. The oxide microparticles produced by this plasma method are substantially brown oxide microparticles when co-existing with the crystal structure of CoO and Co ₃ O ₄ when measured with an X-ray diffractometer.
[0010]
By firing the substantially brown oxide fine particles in an oxygen-containing atmosphere, for example, in the air atmosphere, at 650 to 850 ° C., preferably at 700 to 800 ° C. for about 30 minutes to 2 hours in an electric furnace or the like, The crystal structure is oxidized, and almost entirely converted into a crystal structure of Co ₃ O ₄ to obtain a fine particle-like black pigment. If the firing temperature is less than 650 ° C., oxidation is not promoted, and if it exceeds 850 ° C., fine particles are melted by firing to increase the particle size.
[0011]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
[0012]
Example 1
In a direct current arc plasma apparatus, metallic cobalt is used as a consumption anode electrode, a plasma flame of argon gas is generated from the cathode electrode, the cobalt is heated and evaporated, the cobalt in the plasma state is oxidized and cooled, and the average particle size is 50 nm. Thus, substantially brown cobalt oxide fine particles having a crystal structure of CoO and Co ₃ O ₄ were obtained. Next, the substantially brown cobalt oxide fine particles were put in a ceramic container and fired at 750 ° C. for 1 hour in an air atmosphere using an electric furnace. The obtained black fine particles had a Co ₃ O ₄ crystal structure and an average particle diameter of 150 nm (converted value by the BET method) as measured by an X-ray diffractometer (manufactured by Rigaku Corporation).
[0013]
Example 2
The substantially brown cobalt oxide fine particles of Example 1 were used and baked at 800 ° C. for 1 hour in an air atmosphere using an electric furnace. The obtained black fine particles had a Co ₃ O ₄ crystal structure and an average particle size of 170 nm (converted value by the BET method) as measured by an X-ray diffractometer.
[0014]
【The invention's effect】
The black pigment having a Co ₃ O ₄ crystal structure produced according to the present invention is a substantially spherical fine particle having an average particle diameter of 80 to 300 nm, and has an effect of being excellent in heat resistance, coloring power, and color developability.

Claims (3)

Cobalt raw material was used as a consumption anode electrode, and after producing substantially brown cobalt oxide fine particles having a crystal structure of CoO and Co ₃ O ₄ produced by a direct current arc plasma method, an oxygen-containing atmosphere was produced using the cobalt oxide fine particles. A method for producing a cobalt-based black pigment, characterized in that black fine particles having a crystal structure of Co ₃ O ₄ are obtained by firing in a medium.   The method for producing a cobalt-based black pigment according to claim 1, wherein the firing temperature is 650 to 850 ° C. 2. The method for producing a cobalt-based black pigment according to claim 1, wherein an average particle diameter of the black fine particles having a crystal structure of Co ₃ O ₄ is 80 to 300 nm.