JP2002114521A - Method for manufacturing cobalt-based black pigment - Google Patents

Abstract

(57) [Problem] To provide a fine black pigment having a small particle size and containing no chromium as a metal oxide-based black pigment. SOLUTION: CoO and Co produced by a DC arc plasma method using a cobalt raw material as a consumed anode electrode.
After producing approximately brown cobalt oxide fine particles having a crystal structure of 3 O 4, firing is performed in an oxygen-containing atmosphere using the cobalt oxide fine particles to obtain black fine particles having a crystal structure of Co 3 O 4. The present invention relates to a method for producing a characteristic black-based black pigment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cobalt-based black pigment, and more particularly to a method for producing a particulate cobalt-based black pigment having excellent heat resistance, insulation properties and coloring properties.

More specifically, the present invention relates to a method for producing a cobalt-based black pigment useful as a pigment for a black matrix such as a cathode ray tube, a liquid crystal display, and a plasma display, and as a coloring agent for paints, inks, ceramics and the like.

[0003]

2. Description of the Related Art Conventionally, chromium-containing composite oxides such as Cu-Cr-based and Cu-Cr-Mn-based have been used as metal oxide-based black pigments. There is a drawback that a fine particle pigment having a small particle size cannot be obtained.

[0004] In addition, carbon black is used as a black pigment, but has a drawback that it cannot be used for applications requiring insulation because of its conductivity.

[0005]

SUMMARY OF THE INVENTION In the present invention, there is a demand for a metal oxide-based black pigment which is insulative, contains no chromium, and has a small particle size.

[0006]

SUMMARY OF THE INVENTION The present invention uses a cobalt source as a consumed anode electrode to produce approximately brown cobalt oxide fine particles having a crystal structure of CoO and Co3 O4 produced by a DC arc plasma method. This is a method for producing a cobalt-based black pigment, characterized in that fine particles having a crystal structure of Co3O4 are obtained by firing cobalt oxide fine particles in an oxygen-containing atmosphere.

The black fine particles having a Co3O4 crystal structure have an average particle size of 80 to 300 nm, preferably 100 to 250 nm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on a method for producing a cobalt-based black pigment, and as a result, have found that a CoO and Co3O4 crystal structure having an average particle diameter of 20 to 90 nm produced by a DC arc plasma method. After producing brown cobalt oxide fine particles, they are heat-treated in an oxygen-containing atmosphere to obtain an average particle size of 80 to 3 which is excellent as a black pigment.
It has been found that fine particles of 00 nm can be obtained.

In the DC arc plasma method used in the present invention, a DC arc plasma apparatus is used, various cobalt materials such as cobalt metal and cobalt oxide are used as consumed anode electrodes, and a plasma flame such as argon gas is generated from a cathode electrode. Heating the cobalt material of the consuming anode,
By evaporating, oxidizing and cooling the cobalt in the plasma state, spherical fine particles of cobalt oxide can be produced. The oxide fine particles produced by this plasma method showed CoO and Co3 when measured with an X-ray diffractometer.
O4 crystal structure coexists and is a substantially brown oxide fine particle.

The above substantially brown oxide fine particles are placed in an oxygen-containing atmosphere, for example, in an air atmosphere, in an electric furnace or the like.
By baking at 850 ° C., preferably 700 to 800 ° C. for about 30 minutes to 2 hours, the crystal structure of CoO is oxidized and almost entirely converted to the crystal structure of Co 3 O 4, and a fine black pigment is obtained. This firing temperature is 6
If the temperature is lower than 50 ° C., oxidation is not promoted.
Exceeding the particle size is not preferred because the particles are melted by firing and the particle size increases.

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples.

EXAMPLE 1 In a DC arc plasma apparatus, metallic cobalt is used as a consumed anode electrode, a plasma flame of argon gas is generated from a cathode electrode, the cobalt is heated and evaporated, and the cobalt in a plasma state is oxidized and cooled. Substantially brown cobalt oxide fine particles having a crystal structure of CoO and Co3O4 having an average particle diameter of 50 nm were obtained. Next, the substantially brown cobalt oxide fine particles were placed 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 crystal structure of Co3O4 and had an average particle size of 150 nm (converted by the BET method) as measured by an X-ray diffractometer (manufactured by Rigaku Corporation).

Example 2 The substantially brown cobalt oxide fine particles of Example 1 were fired at 800 ° C. for 1 hour in an air atmosphere using an electric furnace. The obtained black fine particles had a crystal structure of Co 3 O 4 and an average particle size of 17 as measured by an X-ray diffractometer.
It was 0 nm (converted value by the BET method).

[0014]

According to the present invention, Co3 O4 produced according to the present invention is provided.
Black pigment having an average particle size of 80 to 300 n
These particles are substantially spherical fine particles having an excellent heat resistance, coloring power, and coloring property.

Claims (3)

[Claims] 1. CoO and Co produced by a direct current arc plasma method using a cobalt raw material as a consumed anode electrode.
After producing approximately brown cobalt oxide fine particles having a crystal structure of 3 O 4, firing is performed in an oxygen-containing atmosphere using the cobalt oxide fine particles to obtain black fine particles having a crystal structure of Co 3 O 4. A method for producing a cobalt-based black pigment, which is a feature. 2. The method for producing a cobalt-based black pigment according to claim 1, wherein the firing temperature is 650 to 850 ° C. 3. The method for producing a cobalt-based black pigment according to claim 1, wherein the black fine particles having a Co3O4 crystal structure have an average particle size of 80 to 300 nm.