Sulfuric Acid → Zirconium hydroxide (Zr(OH)4), (T-4)-

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TiO2 particles (average particle diameter: 0.26 μm) produced through sulfuric acid process was added to water, to prepare aqueous slurry (TiO2 concentration: 400 g/L). This slurry (0.5 L) was heated to 80° C. under stirring. While maintaining this temperature, a 150 g/L aqueous solution of sodium silicate, which corresponded to 5% by mass (in terms of SiO2) of TiO2, was added to the slurry. Then, 30% sulfuric acid was added thereto over 120 minutes such that the pH of the mixture should be 7. The resultant slurry was aged for 30 minutes. Next, under stirring, the temperature of the slurry was regulated so as to be 40° C. While the pH of the slurry was maintained to 7, a 100 g/L aqueous solution of zirconium oxychloride, which corresponded to 1% by mass (in terms of ZrO2) of TiO2, and 30% aqueous sodium hydroxide were added to the slurry as a single portion over 60 minutes. The resultant slurry was aged for 30 minutes. Then, under stirring, while the pH of the slurry was maintained to 7, a 250 g/L aqueous solution of sodium aluminate, which corresponded to 2% by mass (in terms of Al2O3) of TiO2, and 30% sulfuric acid were added as a single portion to the slurry over 60 minutes. The resultant slurry was aged for 60 minutes. Thus, on the surface of TiO2, coating layers of silicon hydroxide, zirconium hydroxide, and aluminum hydroxide were formed in the order as set forth.

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