JPS621572B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing fine tin oxide powder.

Tin oxide powder is used as a catalyst, gas sensor, and conductive powder. As a catalyst, it is used as a catalyst for the allylic oxidation of olefins, for example, for the synthesis of acrolein from propene, butadiene from n-butene, and isoprene from isopentene.

Gas sensors utilize the fact that electrical resistance changes when a flammable gas such as city gas, propane gas, hydrogen gas, etc. is adsorbed.
As a conductive powder material, it is known that SnO ₂ doped with Sb has a low resistance, but there is a problem with the toxicity of Sb, so a material that does not contain Sb is desired. Products that do not contain doping agents have a higher resistance, but can be used as an antistatic agent, and the color is close to white, so they can be used as an antistatic agent for paper, resin, and fibers. Also, the wavelength of visible light (0.4~0.8μ
m) Since transparency is achieved by forming the particles below, it can also be mixed into paints and used as antistatic paints. A film coated with this paint not only becomes a transparent antistatic film, but also a film for photosensitive machines to control charging voltage. In either case, it is desirable that the powder be fine. That is, since the surface of the powder is used in catalysts and sensors, the finer the powder, the higher the activity, and the finer the powder, the better the transparency. Furthermore, it is desired that the powder has high dispersibility.

The following methods are known as methods for producing tin oxide powder.

(1) Oxidize metal tin by heating it in air at high temperatures.

(2) The white precipitate obtained by treating tin with concentrated nitric acid is calcined at high temperature.

(3) Neutralize an aqueous solution of a tetravalent tin salt with an alkali to obtain a white precipitate, which is then calcined at a high temperature.

In methods (1) and (2), the specific surface area is at most 10 m ² /g.
Only the following powders can be obtained, and even with method (3), sintering tends to occur during firing, and although a specific surface area of up to 50 m ² /g is possible, the dispersibility is poor and it is not desirable for the purpose of achieving transparency.

The present inventors have discovered that extremely fine tin oxide powder can be obtained when method (3) is carried out under specific conditions.

In the method of the present invention, a tin chloride () aqueous solution is added to an alkaline aqueous solution kept at 65° C. or higher, and the pH is finally adjusted to 5 or less. When tin chloride is added to alkaline water, the initial pH is naturally close to 14;
Even if an aqueous tin chloride solution is added until the value reaches 10, no precipitate is formed. Precipitate rapidly forms when the pH is below 10. In other words, tin chloride, which was dissolved at a pH of 10 or higher, precipitates out as tin hydroxide at once as the pH decreases, becoming a fine product. Furthermore, it was found that dispersibility was improved by adding tin chloride and ultimately maintaining the pH between 5 and 1. That is, in the subsequent firing process of the powder, sintering is reduced and the powder particles can be kept fine. If the reaction is terminated outside this range, the powder will easily sinter during firing. As a result of the above, it has been found that fine particles of 50 m ² /g or more and good dispersibility can be obtained. On the other hand, with the method of neutralizing an aqueous tin chloride solution with an alkali, a precipitate begins to form as soon as the alkali is added, and as the reaction progresses, particles grow and a fine powder is obtained. do not have.

Examples of alkaline aqueous solutions include sodium hydroxide,
A solution of ammonia, potassium hydroxide, and sodium carbonate in water can be used. As the tin chloride solution, a solution in which tetravalent tin chloride is dissolved in water, in an aqueous hydrochloric acid solution, or in alcohol can be used.

The concentration of the tin chloride solution injected into the alkaline aqueous solution is not particularly limited, but the preferred concentration is 10 to 60.
%. There is also no particular limitation on the injection rate. It was found that the critical temperature for precipitation was approximately 65°C.
If it is lower than this, particles tend to sinter during firing. Tin dioxide powder can be obtained by washing and drying the generated precipitate and further calcination, but if the calcination temperature is below 350°C, the crystals will not develop well and it will be amorphous, and if the temperature is above 700°C, it will become amorphous. A conclusion occurs. For this reason, the firing temperature was set at 350°C to 700°C, but in relation to the resistance and particle size of the powder, it is preferable to
The temperature is between 400℃ and 600℃. The fineness and dispersibility of the powder are measured by the specific surface area or the percentage of particles of 0.3 μm or less after dispersing the powder in an aqueous solution with a pH of 10.

Example 1 335g of sodium hydroxide was added to 10ml of water and heated to 70°C. Add to this a 60% aqueous solution of stannic chloride.
Add 610 ml of a 1:1 mixed solution of hydrochloric acid and water to 500 g and drop it using a metering pump to carry out the reaction.
The pH was set to 2. The resulting precipitate was collected, washed with water, dried, and calcined at 500°C. After pulverizing the obtained powder with an atomizer, use SA-1000 manufactured by Shibata Chemical Equipment Co., Ltd.
When the specific surface area was measured using a mold surface area meter, it was 75.9 m ² /
It was hot at g. Additionally, 7 g of sodium hydroxide/40 ml of solution was added to 5 g of this powder to make the pH = 10, and the diameter was 10 mm.
After performing a dispersion treatment in a 100 ml ball mill containing 50 alumina balls, particles of 0.3 μm or more were separated by sedimentation using a centrifugal sedimentation method, and the amount of particles of 0.3 μm or less was measured. As a result, the proportion of particles smaller than 0.3 μm was 61.3
It was %. The specific resistance of the powder was measured under a pressure of 100 kg/cm ² and found to be 8×10 ⁵ Ω·cm.

Comparative Example 1 335g of sodium hydroxide was added to 10ml of water and heated to 80°C. Add to this a 60% aqueous solution of stannic chloride 500
600 ml of a 1:1 mixed solution of hydrochloric acid and water was added to the sodium hydroxide solution to carry out a reaction, and the final pH was set to 6. The precipitate was collected, washed, dried, and calcined at 500°C, and the same measurements as in Example 1 were carried out. As a result, the specific surface area was 44m ² /g and 0.3μ
The content of the following particles was 30%.

Example 2 The dried precipitate obtained by the reaction in Example 1 was
It was fired at 350℃. The specific surface area of the fired powder is 78m ² /
g, 0.3 μm or less was 62%, and the specific resistance was 10 ⁸ Ω·cm or more.

Example 3 The dried precipitate obtained by the reaction in Example 1 was
It was fired at 700℃. Specific surface area is 52m ² /g, 0.3μm
The content of the following particles is 41%, and the specific resistance is 6×10 ⁵
It was Ω・cm.

Example 4 17 g of the calcined powder obtained in Example 1 was added to a varnish prepared by dissolving 8 g of polyester resin in 75 g of a 4:1 mixture of toluene: methyl ethyl ketone, and a varnish with a diameter of 10 mm was added.
An antistatic paint was produced by dispersing the mixture in a 250ml ball mill containing 125 alumina balls for 17 hours. This was applied onto a polyester film to a thickness of 1 μm using a wire bar. This coating film had a haze value of 17% and a surface resistance of 1.5×10 ⁹ Ω.

Example 5 The powder produced in Example 3 was made into a paint using the same method as in Example 4. This was applied to polyester film using a wire bar. The thickness was 1.1 μm. The haze value was 35% and the surface resistance was 7.2×10 ⁹ Ω.

Comparative Example 2 The heating temperature of the alkaline aqueous solution was 60℃.
A powder was produced under the same conditions as in Example 1. The specific surface area of the obtained powder was 77 m ² /g, and the content of particles of 0.3 μm or less was 40%.

Comparative Example 3 Under the same conditions as in Example 1, an aqueous alkaline solution was added to the tin chloride solution, and the same procedure was repeated to obtain tin oxide powder. The specific surface area of the obtained powder is 40m ² /g
The content of particles of 0.3μ or less was 30%.

Claims (1)

[Claims] 1. While keeping an alkaline aqueous solution with a pH of 10 or higher at 65°C or higher, a tin chloride solution is added thereto, and finally
The product is obtained by adjusting the pH to 5-1, and this is
A method for producing fine tin oxide powder by firing at 350℃ to 700℃. 2. A method for producing fine tin oxide powder according to claim 1, wherein the tin chloride solution has a concentration of 10 to 60
How to be %.