JPH05193942A - Production of black titanium oxide powder - Google Patents

Abstract

PURPOSE:To partially reduce titanium dioxide powder and to obtain black titanium oxide powder excellent in miscibility and dispersibility by heating a mixture of the titanium dioxide powder with sodium borohydride to a prescribed temp. in an inert gaseous atmosphere. CONSTITUTION:Titanium dioxide powder such as anatase type titanium dioxide powder of <=0.2mum particle diameter is mixed with sodium borohydride and this mixture is heated to 300-950 deg.C in an inert atmosphere. By this heating, the sodium borohydride is decomposed, the titanium dioxide is partially reduced and black titanium oxide powder excellent in miscibility and dispersibility is obtd.

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 black titanium oxide powder, and more particularly to a method for producing black titanium oxide powder using sodium borohydride as a reducing agent.

[0002]

2. Description of the Related Art Conventionally, carbon black or ferric tetroxide has been mainly used as a black pigment.

However, since carbon black is hydrophobic, it is hard to get wet with water. In addition, the particle size is generally as small as 0.005 μm. Therefore, when used in combination with other commonly used pigments, for example, titanium dioxide powder (particle size: about 0.3 μm), there is a problem that the fluidity is sensitively changed depending on the compounding ratio, resulting in poor mixability. In addition, when producing carbon black industrially, it is a carcinogen 3,4-
Since benzpyrene may be mixed in, there is a problem in safety.

On the other hand, ferrosoferric oxide is easily magnetized and has a large specific gravity of 5.2. Therefore, when used as a pigment,
There are problems such as color separation and poor dispersibility.
There is also a problem that when heated to about 150 ° C in the atmosphere, it changes to γ-Fe ₂ O ₃ and discolors.

As described above, conventionally used black pigments have various problems, and there is a demand for black pigments having excellent mixing properties and dispersibility and excellent quality.
One of such black pigments is black low order titanium oxide powder.

As a method for obtaining a black low-order titanium oxide compound, for example, a mixture of titanium dioxide powder and metallic titanium powder disclosed in JP-B-52-12733 is used in a vacuum or reducing atmosphere at 550 to 1100. A method of heating at 1 ° C. for 1 to 5 hours can be mentioned.

However, in order to obtain a titanium oxide compound having a high degree of blackness by this conventional method, a step of heating a mixture of titanium dioxide powder and metallic titanium powder at a high temperature of 950 to 1,100 ° C. is required. When the titanium dioxide powder is heated at such a high temperature, the particles sinter with each other and become coarse. Therefore, it is difficult to obtain a black titanium oxide powder having a uniform particle size with good mixability and dispersibility by the conventional titanium dioxide reduction method.

Further, Japanese Patent Laid-Open Nos. 64-72921 and Sho
64-72922 discloses a method of heating and reducing titanium dioxide powder in a special atmosphere such as anhydrous hydrazine gas.

However, since these reducing gases are generally highly corrosive, there are various restrictions in terms of handling, reaction equipment, equipment and the like.

[0010]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and an object thereof is to heat and reduce titanium dioxide powder at a low reduction treatment temperature without using a reducing gas. Accordingly, it is an object of the present invention to provide a highly safe and low-cost method for producing a black titanium oxide powder capable of providing a black titanium oxide powder having excellent mixability and dispersibility.

[0011]

[Means for Solving the Problems] As a result of intensive research to solve the above-mentioned problems, the inventors of the present invention
It has been found that the above object can be achieved by heating at a temperature of 0 to 950 ° C, and the present invention has been achieved. That is, the present invention is characterized by heating a mixture of titanium dioxide powder and sodium borohydride at a temperature of 300 ~ 950 ° C. under an inert atmosphere, and is characterized by a method for producing a black titanium oxide powder. Is.

The titanium dioxide powder that can be used in the present invention may be any of the anatase, rutile and brookite types. The particle size of the powder is not particularly limited, but a powder having a particle size of 0.2 μm or less is preferable in order to obtain a black titanium oxide powder having good mixability and dispersibility.
Such titanium dioxide powder is commercially available, for example, Wako Pure Chemical Industries, Ltd., "Reagent first-grade titanium dioxide",
Examples include "JR" and "JA-1" manufactured by Teika Co., Ltd., and "A-HR" and "R-SM3" manufactured by Freund Sangyo Co., Ltd.

The sodium borohydride usable in the present invention is not particularly limited as long as it is a powdery sodium borohydride having a purity of 98% or more. The sodium borohydride powder is preferably a fine powder having a particle size of about 250 μm or less. This is because the smaller the particle size of the powder, the higher the mixing uniformity and the reactivity. Such sodium borohydride are commercially available, for example, Inc. Morton International, Inc. of "NaBH _4", and by Kawaken Fine Chemicals Co., Ltd. of "NaBH _4".

In the present invention, first, a mixture of sodium borohydride powder and titanium dioxide powder is prepared. The mixing ratio of the sodium borohydride powder and the titanium dioxide powder is preferably in the range of 1: 8 to 1: 2 in terms of molar ratio. When the mixing ratio is 1: 8 or less, the reducing ability is lowered, so that sufficient blackness cannot be obtained. When the mixing ratio is 1: 2 or more, the blackness increases, but the manufacturing cost increases.

Sodium borohydride powder and titanium dioxide powder in such amounts are mixed by methods well known to those skilled in the art. For example, by mixing with a rocking mixer, a mixture of sodium borohydride powder and titanium dioxide powder that can be used in the present invention can be obtained.

The resulting mixture is placed in a heating container. Since the heating step of the present invention does not require a special atmosphere and the heating temperature is low, the heating container used is not particularly limited, and a normal stainless steel or ceramics container is used. In a preferred embodiment of the invention, for example,
SUS-309S (manufactured by Nippon Stainless Steel Co., Ltd.) is used.

Next, the air inside the container is replaced with the inert gas by purging the inside of the heating container with the inert gas. Examples of the inert gas that can be used in the present invention include:
Examples thereof include nitrogen, argon and helium.

The mixture, which is sealed in a heating vessel, is then heated to a temperature in the range 300 to 950 ° C, preferably in the range 400 to 850 ° C.

When the heating temperature is lower than 300 ° C., the titanium oxide color obtained is grayish, which is not preferable as a black pigment. This is because the decomposition temperature of sodium borohydride is about
Since it is 300 ° C, it is considered that the reduction of the titanium dioxide powder does not proceed sufficiently below 300 ° C. On the other hand, when heated to a temperature higher than 950 ° C., particle growth occurs due to sintering of the titanium powder as a raw material. Therefore, a black titanium oxide powder having good dispersibility and uniform particle size cannot be obtained. In addition, there is a problem in that the manufacturing cost increases when heated to such a high temperature.

In the above heating step, the partial reduction reaction of titanium dioxide occurs due to the decomposition of sodium borohydride. The heat treatment time is preferably about 1 to 4 hours. Therefore, in the present invention, the reduction reaction proceeds in a relatively short time.

The powdery product obtained is treated in an inert atmosphere
It is cooled to 50 ° C or lower, preferably to room temperature, then washed with water in an amount of about twice the sample weight, filtered, and statically dried at 120 ° C. Then, a dry method, a wet method, or a combination thereof is pulverized to obtain a black low-order titanium oxide powder.

According to the method of the present invention, it is possible to produce a black titanium oxide powder at a low temperature and with a simple apparatus as compared with the conventional method. Further, since the titanium oxide particles are prevented from being sintered together during the heating step, fine powdery black titanium oxide having a uniform particle size with good mixability and dispersibility can be obtained.

[0023]

The present invention will be described in more detail with reference to the following examples.

The color tone was measured by the powder cell method using a fully automatic color difference meter Color Ace TC-8600A manufactured by Tokyo Denshoku Co., Ltd., and the L value of the Hunter color system was measured.

The generated particle size was measured using a scanning electron microscope JSM-5200 manufactured by JEOL Ltd.

[0026]

Example 1 Sodium borohydride powder and average particle size of 0.
18 μm titanium dioxide powder was uniformly mixed in a molar ratio of 1: 8, and this mixture was heated at 450 ° C. for 3 hours in an inert atmosphere in a nitrogen gas stream. The obtained powdery product was cooled to 50 ° C. in the same atmosphere, washed with water, dried and pulverized. L of the obtained black titanium oxide powder
The values are shown in Table 1 and the average particle size is shown in Table 2.

[0027]

Example 2 Sodium borohydride and average particle size 0.18μ
The titanium dioxide powder of m was uniformly mixed at a molar ratio of 1: 4, and this mixture was heated at 450 ° C. for 3 hours in an inert atmosphere in a nitrogen gas stream. The obtained powdery product is cooled to 50 ° C. in the same atmosphere, washed with water, dried,
It was crushed. The L value and the average particle diameter of the obtained black titanium oxide powder are shown in Table 1 and Table 2, respectively.

[0028]

Example 3 Sodium borohydride and average particle size 0.18μ
The titanium dioxide powder of m was uniformly mixed at a molar ratio of 1: 4, and the mixture was heated at 450 ° C. for 1 hour in an inert atmosphere in a nitrogen gas stream. The obtained powdery product is cooled to 50 ° C. in the same atmosphere, washed with water, dried,
It was crushed. The L value and the average particle diameter of the obtained black titanium oxide powder are shown in Table 1 and Table 2, respectively.

[0029]

Example 4 Sodium borohydride and average particle size 0.18μ
The titanium dioxide powder of m was uniformly mixed at a molar ratio of 1: 4, and the mixture was heated at 600 ° C. for 3 hours in an inert atmosphere in a nitrogen gas stream. The obtained powdery product is cooled to 50 ° C. in the same atmosphere, washed with water, dried,
It was crushed. The L value and the average particle diameter of the obtained black titanium oxide powder are shown in Table 1 and Table 2, respectively.

[0030]

Comparative Example 1 Titanium metal powder and titanium dioxide powder having an average particle size of 0.18 μm were uniformly mixed at a molar ratio of 1: 4, and the mixture was heated at 450 ° C. in an inert atmosphere in a nitrogen gas stream. Heated for 3 hours. The obtained powdery product was cooled to 50 ° C. in the same atmosphere and pulverized. The L value and the average particle diameter of the obtained black titanium oxide powder are shown in Table 1 and Table 2, respectively.

[0031]

Comparative Example 2 Sodium borohydride and average particle size 0.18μ
The titanium dioxide powder of m was uniformly mixed at a molar ratio of 1: 4, and the mixture was heated at 1000 ° C. for 1 hour in an inert atmosphere in a nitrogen gas stream. The obtained powdery product is cooled to 50 ° C. in the same atmosphere, washed with water, dried,
It was crushed. The L value and the average particle diameter of the obtained black titanium oxide powder are shown in Table 1 and Table 2, respectively.

[Table 1] Color tone (L value of Hunter color system) Sample color tone (L value) Example 1 16 Example 2 13 Example 3 15 Example 4 13 Comparative Example 1 67 Comparative Example 2 12

In Table 1, the L value is a numerical value representing the lightness,
The smaller the number, the darker it is. Example 2 and Comparative Example 1
In spite of the same heating condition, the difference in L value is 5
4 also occurred. This is because in Example 2, the reduction proceeded even at low temperature due to the action of sodium borohydride.

On the other hand, as in Example 2, the higher the mixing ratio of sodium borohydride and the longer the treatment time, the more the reduction reaction proceeded and the L value decreased. Further, when the treatment was carried out at a high temperature as in Comparative Example 2, the L value became small.

Table 2 Mean particle diameter sample average particle diameter ([mu] m) Example 1 0.18 Example 2 0.18 Example 3 0.18 Example 4 0.19 Comparative Example 1 0.32 Comparative Example 2 0.63

From the results shown in Table 1, it can be seen that the average particle size of the black titanium oxide powders obtained in Examples 1 to 4 is substantially the same as the average particle size of the titanium dioxide powder used as the raw material. Therefore, it was shown that the heating step of the present invention did not cause the coarsening of the particles due to the sintering of the particles.

On the other hand, the average particle size of the black titanium oxide powder obtained in Comparative Example 1 was 0.32 μm, which was increasing. It is considered that this is due to the large particle size of the metal titanium powder added as the reducing agent. Further, in Comparative Example 2 which was heat-treated at 1000 ° C., the average particle size was increased to 0.63 μm, and apparently coarsening occurred due to sintering of the particles.

[0036]

EFFECTS OF THE INVENTION According to the present invention, by heating and reducing titanium dioxide powder at a low reduction treatment temperature without using a reducing gas, a black titanium oxide powder having excellent mixability and dispersibility is safely and at low cost. It can be manufactured.

[Brief description of drawings]

Fig. 1 Titanium dioxide powder used as a raw material
It is a scanning electron microscope photograph taken at a magnification of 2 times.

FIG. 2 shows the black titanium oxide powder obtained in Example 1.
It is a scanning electron micrograph taken at a magnification of 20000 times.

FIG. 3 shows the black titanium oxide powder obtained in Comparative Example 2.
It is a scanning electron micrograph taken at a magnification of 20000 times.

Claims (1)

[Claims] 1. A method for producing a black titanium oxide powder, which comprises heating a mixture of titanium dioxide powder and sodium borohydride at a temperature of 300 to 950 ° C. under an inert gas atmosphere.