JPH0348136B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND ART AND PROBLEMS The present invention relates to a titanium dioxide pigment with excellent weather resistance, gloss and dispersibility, and a method for producing the same. Titanium dioxide pigments are widely used as white pigments with excellent coloring and hiding power. Recently, there has been a lot of demand for it as a white pigment for high-grade baking paints used in products such as automobiles, home appliances, and colored galvanized iron. A high degree of weather resistance, gloss and dispersibility are required for such applications. Many proposals have been made to date for the development of titanium dioxide pigments that meet these requirements, and although some are on the market, none of them completely satisfies these requirements. Known proposals concern the coating of the surface of titanium dioxide crystal particles, one of which is a coating of dense silica as an inner layer and a hydrous oxide of aluminum as an outer layer. Other methods do not apply dense silica, but instead use other hydrous oxides (e.g., zinc, magnesium, zirconium,
This method involves applying a coating of cerium, aluminum, etc.). However, the former has improved weather resistance but poor gloss and dispersibility, while the latter has insufficient weather resistance, and neither of them can satisfy all of weather resistance, gloss, and dispersibility at the same time. The object of the present invention is to provide a titanium dioxide pigment that satisfies all of these properties at the same time, and a method for producing the same. Solution Method The present invention provides a method of adding 0.1 to 2% tin hydrated oxide as SnO ₂ and 0.1 to 2% zirconium hydrated oxide zirconium oxide as ZrO ₂ based on the weight of the core titanium dioxide crystal on the surface of the core titanium dioxide crystal. is coated in the innermost layer, then a hydrous oxide of titanium is coated in the middle layer with 0.1-2% of _TiO2 based on the weight of the core titanium dioxide, and finally _Al2O based on the weight of the core titanium dioxide. ₃ provides a titanium dioxide pigment whose outermost layer is coated with 0.1 to 5% of a hydrous oxide of aluminum. Further, according to the present invention, there is provided a method for producing the titanium dioxide pigment, which method comprises adding 0.1 to 2% of SnO ₂ based on the weight of the core titanium dioxide to an aqueous suspension of core titanium dioxide crystals. The coating consisting of hydrated oxides of tin and zirconium is completely removed by adding a water-soluble tin compound and 0.1-2% of a water-soluble zirconium compound as ZrO ₂ under acidic conditions and then neutralizing the suspension. Formed in the inner layer,
Then add to the suspension the weight of the core titanium dioxide.
By simultaneously adding 0.1 to 2% of a water-soluble titanium compound as TiO ₂ and an alkali while maintaining the pH of 5 to 8, a coating consisting of a hydrous titanium oxide is formed in the middle, and the core is added to the suspension. By simultaneously adding 0.1 to 5% of a water-soluble aluminum compound as Al ₂ O ₃ to the weight of titanium dioxide and a neutralizing agent while maintaining the pH of 5 to 8, a coating consisting of a hydrous oxide of aluminum is formed as the outermost layer. The formed and coated suspended particles are characterized by filtration, washing and drying. Detailed Discussion The titanium dioxide crystal used as the core in the present invention may be either anatase type or rutile type, and it does not matter whether the manufacturing method is a so-called sulfuric acid method or a chlorine method. Titanium dioxide crystals are suspended in water to form a slurry. At this time, dispersion aids such as sodium hydroxide, sodium hexametaphosphate, and monoisopropanolamine may be added. The slurry is preferably passed through a dispersing machine such as a sand mill to crush and disperse titanium dioxide crystals. Next, an acid such as sulfuric acid, hydrochloric acid, or nitric acid is added to the slurry to make it acidic. At that time, the pH is 3 or less,
In particular, it is preferable to set it to around 2.0. Next, a water-soluble tin compound and a water-soluble zirconium compound are added to this suspension. The amount added is based on the weight of the core titanium dioxide.
0.1-2% as _SnO2 and _ZrO2 . If the amount added is insufficient, a sufficient effect cannot be obtained, whereas if the amount added is too large, it is not only economically disadvantageous but also may cause adverse effects. Examples of water-soluble tin compounds include tin chloride, tin sulfate, tin acetate, sodium stannate, potassium stannate, etc. Examples of water-soluble zirconium compounds include zirconium chloride, zirconium sulfate, zirconium nitrate, zirconium acetate, Examples include zirconium oxychloride. Next, add alkali to the suspension to neutralize the pH to approximately 7.0. As the alkali, for example, sodium hydroxide, potassium hydroxide, ammonia, etc. can be used. Upon neutralization, fine particles of hydrous oxides of tin and zirconium are precipitated and deposited on the surface of the core titanium dioxide crystal to form the innermost coating layer. After forming a coating layer of hydrous oxides of tin and zirconium, a water-soluble titanium compound and an alkali are simultaneously added while maintaining the liquid property at pH 5 to 8. Examples of water-soluble titanium compounds include titanyl sulfate and titanium tetrachloride, the amount of which is added based on the weight of the core titanium dioxide for the same reasons as for water-soluble tin and zirconium compounds.
It should be 0.1-2% as _TiO2 . If alkali is not added at the same time as the water-soluble titanium compound, the liquid will become acidic and the previously formed innermost layer of hydrous oxides of tin and zirconium will dissolve, and when neutralized with alkali, these substances will be dissolved. Simultaneous precipitation occurs. Therefore, in the present invention, when adding the water-soluble titanium compound, it is important to add an alkali at the same time to maintain the liquid pH within the range of 5 to 8. The pH at the end of the addition should be approximately 7.0. The outermost coating layer made of a hydrous oxide of aluminum is prepared by adding a water-soluble aluminum compound of 0.1 to 5% as Al ₂ O ₃ and a neutralizing agent to the suspension at a pH of 5 to 8 based on the weight of the core titanium dioxide. It can be formed by adding it at the same time while maintaining it. The reason why the neutralizing agent is added simultaneously with the water-soluble aluminum compound is to prevent redissolution and reprecipitation of the hydrated oxide in the intermediate layer and the innermost layer, as described above. When the water-soluble aluminum compound is an aluminum salt such as aluminum sulfate or aluminum chloride, the above-mentioned alkali is used as a neutralizing agent, and when the water-soluble aluminum compound is an aluminate such as sodium aluminate, the above-mentioned acid is used as a neutralizing agent. Of course it is the right thing to do. The titanium dioxide particles thus coated in an aqueous suspension are heated in the suspension to, for example, 60°C, and the pH
It is preferable to adjust the temperature to about 7.0 and then stir for, for example, about 30 minutes to age. Further, it is preferable that each step up to ripening is carried out under constant stirring. After aging, the suspension is filtered and washed with water in a conventional manner, and dried at, for example, 120° C. for 15 hours to obtain the desired titanium dioxide pigment. After drying, if necessary, it is preferable to pulverize using a pulverizer such as a steam energy mill. Further, the titanium dioxide pigment of the present invention may be coated with an organic substance such as polyhydric alcohol, alkanolamine, silicone, etc., if necessary. The titanium dioxide pigment of the present invention is superior to conventional coated titanium dioxide pigments in terms of weather resistance, gloss, and dispersibility. Therefore, it is useful as a white pigment for high-grade baking paints applied to automobiles, home appliances, colored galvanized iron, etc., but it can of course also be used in fields other than paints, such as inks, plastics, and paper. The present invention will be explained in more detail by giving Examples and Comparative Examples below. Example 1 Hydrous titanium oxide obtained by hydrolyzing a titanium sulfate solution was added to an aqueous slurry (TiO ₂ concentration 300 g/) containing rutile titanium dioxide produced by calcination, pulverization, and classification treatment in the following order. processed. The pH of the slurry was adjusted to 2.0 by adding sulfuric acid. Stannous chloride solution based on titanium dioxide weight
0.5% _SnO2 was added and stirred for 10 minutes. A zirconium sulfate solution was added at 0.5% as ZrO ₂ based on the weight of titanium dioxide and stirred for 10 minutes. A sodium hydroxide solution was added to adjust the pH to 7.0, and hydrous oxides of tin and zirconium were precipitated on the surface of titanium dioxide. Titanyl sulfate solution based on titanium dioxide weight
PH sodium hydroxide solution with 1.5% as _TiO2
After simultaneous addition for 10 minutes at = 5 to 8, 10 at PH = 7.0
The mixture was stirred for a minute to precipitate the hydrous oxide of titanium. Sodium aluminate solution is 3.0% _TiO2 based on the weight of titanium dioxide and sulfuric acid has a pH of 5 to 8.
After adding for 10 minutes, stir at PH = 7.0 for 10 minutes,
A hydrous oxide of aluminum was precipitated. Aged with stirring for 30 minutes. The slurry was filtered, washed, dried at 120° C. for 15 hours, and ground in a fluid steam energy mill to obtain the titanium dioxide pigment of the present invention coated with hydrous oxides of tin, zirconium, titanium, and aluminum. (Pigment A) Example 2 A titanium dioxide pigment of the present invention was obtained by carrying out a coating treatment in the same manner as in Example 1, except that titanium dioxide obtained by oxidizing titanium tetrachloride in the gas phase was used. (Pigment B) Comparative Example C: Processed in the same manner as in Example 1 except that sodium hydroxide was not added in combination when coating the surface with a hydrous oxide of titanium. D: Processed in the same manner as in Example 1 except that sulfuric acid was not added in combination when coating the surface with a hydrous oxide of aluminum. E: Processed in the same manner as in Example 1 except that the hydrous oxide of titanium was not coated. F: Processed in the same manner as in Example 1 except that the coating treatment was not performed with a hydrous tin oxide. G: Processed in the same manner as in Example 1 except that zirconium hydrous oxide was not coated. H: Processed in the same manner as in Example 1 except that aluminum hydrate oxide was not coated. I: Processing was carried out in the same manner as in Example 1, except that instead of coating the hydrous oxide of titanium, a sodium silicate solution was used to coat the hydrous oxide of silicon at 1.0% as SiO ₂ . J: Chlorine method, commercially available highly weather resistant brands (high density SiO ₂ and Al ₂ O ₃ coated products) Titanium dioxide pigments A to J of Examples and Comparative Examples
The dispersibility, initial gloss and weather resistance were measured. The results are shown in the table below.

[Table] Test method 1 Preparation of test plate Titanium dioxide pigment was mixed with commercially available coconut oil-modified alkyd resin, Becosol J-524 (Dainippon Ink Chemical Co., Ltd.)/butylated melamine resin, Super Betsukamine J-820 (Dainippon Ink Chemical Co., Ltd.). Zinc phosphate Approximately 40 μm thick (dry coating) on treated steel plate (manufactured by Nippon Test Panel Co., Ltd., Bt144)
A white test board was prepared by applying the coating and baking it at 140°C for 30 minutes. 2 Evaluation of dispersibility During dispersion using a paint conditioner, the dispersibility was checked every 5 minutes using a blind gauge (manufactured by Taisuke Kizai Co., Ltd.). 3 Initial gloss measurement of white test plate Gloss meter (manufactured by Suga Test Instruments Co., Ltd., UGV-
4D), 20°-20° and 60°-60° gloss were measured. 4 Weather resistance measurement The gloss retention rate was measured using a carbon arc type tanshear-in weather meter device (manufactured by Suga Test Instruments Co., Ltd., WE
-SUN-DC type) Exposure of white test panel (12 minutes of precipitation during 60 minutes of irradiation, black panel temperature 63 ± 3
℃), and the 60°-60° gloss was measured and evaluated every 40 hours. The onset of chalking was measured in accordance with the coating film evaluation standards of the Japan Paint Inspection Association.

Claims (1)

[Claims] 1. On the surface of the core titanium dioxide crystal, 0.1 to 2% of SnO ₂ is added to the weight of the core titanium dioxide.
0.1-2% as hydrous oxide of tin and _ZrO2
The innermost layer is coated with a hydrous oxide of zirconium,
Next, the intermediate layer is coated with 0.1 to 2% hydrous oxide of titanium as TiO ₂ based on the weight of the core titanium dioxide, and finally, based on the weight of the core titanium dioxide,
A titanium dioxide pigment whose outermost layer is coated with a hydrous oxide of aluminum containing 0.1 to 5% as Al ₂ O ₃ . 2 To the aqueous suspension of the core titanium dioxide crystals,
0.1~ as _SnO2 to the weight of core titanium dioxide
0.1 to 2% water-soluble tin compounds and _ZrO2
A coating of hydrated oxides of tin and zirconium is formed in the innermost layer by adding 2% of a water-soluble zirconium compound under acidic conditions and then neutralizing the suspension; By simultaneously adding 0.1 to 2% of a water-soluble titanium compound and an alkali as TiO ₂ based on the weight of the core titanium dioxide to the liquid while maintaining the pH of 5 to 8, a coating made of a hydrous oxide of titanium is formed in the middle. form and further add Al ₂ O ₃ to the suspension based on the weight of the core titanium dioxide.
By simultaneously adding 0.1 to 5% of a water-soluble aluminum compound and a neutralizing agent while maintaining the pH of 5 to 8, a coating made of a hydrous oxide of aluminum is formed as the outermost layer, and the coated suspended particles are filtered. A method for producing a titanium dioxide pigment, characterized by washing with water and drying.