Surface-treated titanium dioxide pigments

Abstract

Coated titanium dioxide particles are provided and made from a method wherein a zirconium oxide coating and an aluminum oxide coating are formed on the surface of titanium dioxide particles. The zirconium oxide-forming and aluminum oxide-forming coating materials can be used to control the pH of the surface treatment process without the need for adding pH controlling agents.

What is claimed is: 
     
         1 . A coated titanium dioxide pigment prepared by a method comprising:
 (a) forming an aqueous suspension of titanium dioxide particles;   (b) adding a zirconium oxide-forming solution to the suspension in an amount sufficient to decrease the pH of the suspension to about 4.0 or lower;   (c) forming a zirconium oxide coating on the titanium dioxide particles to form a suspension of coated particles;   (d) adding an aluminum oxide-forming solution to the suspension of coated particles in an amount sufficient to increase the pH of the suspension to about 9.0 or higher; and   (e) forming an aluminum oxide coating on the coated particles to form a coated titanium dioxide pigment.   
     
     
         2 . The coated titanium dioxide pigment of  claim 1 , wherein the method further comprises, after step (e):
 (f) filtering the aqueous suspension to recover the product; and   (g) washing and drying the recovered product, such that the coated titanium dioxide pigment is dry.   
     
     
         3 . The coated titanium dioxide pigment of  claim 2 , wherein the final pH of the washed product is about 6.0. 
     
     
         4 . The coated titanium dioxide pigment of  claim 1 , wherein pigment comprises a titanium dioxide particle at its core and the titanium dioxide particle has an average particle diameter in a range of from about 0.01 micron to about 1.0 micron. 
     
     
         5 . The coated titanium dioxide pigment of  claim 4 , wherein the titanium dioxide particle has an average particle diameter of less than or equal to about 0.2 micron. 
     
     
         6 . The coated titanium dioxide pigment of  claim 1 , wherein the method comprises forming the zirconium oxide coating on the titanium dioxide particles in step (c) over a time period of at least about 10 minutes. 
     
     
         7 . The coated titanium dioxide pigment of  claim 1 , wherein the method comprises forming the aluminum oxide coating on the coated titanium dioxide particles in step (e) over a time period of at least about 10 minutes. 
     
     
         8 . The coated titanium dioxide pigment of  claim 1 , having a chemical composition of from 95.70% by weight to 96.40% by weight TiO 2  and from 3.60% by weight to 3.80% by weight Al 2 O 3 . 
     
     
         9 . The coated titanium dioxide pigment of  claim 1 , having a chemical composition of from 95.70% by weight to 95.82% by weight TiO 2 , from 3.70% by weight to 3.80% by weight Al 2 O 3 , and from 0.48% by weight to 0.50% by weight ZrO 2 . 
     
     
         10 . The coated titanium dioxide pigment of  claim 1 , having a Baidins et al. durability rating of from 7.90 to 10.0. 
     
     
         11 . A coated titanium dioxide pigment prepared by a method consisting essentially of:
 (a) forming an aqueous suspension of titanium dioxide particles;   (b) adding a zirconium oxide-forming solution to the suspension in an amount sufficient to decrease the pH of the suspension to about 4.0 or lower;   (c) forming a zirconium oxide coating on the titanium dioxide particles to form a suspension of coated particles;   (d) adding an aluminum oxide-forming solution to the suspension of coated particles in an amount sufficient to increase the pH of the suspension to about 9.0 or higher; and   (e) forming an aluminum oxide coating on the coated particles to form a coated titanium dioxide pigment.   
     
     
         12 . The coated titanium dioxide pigment of  claim 11 , wherein the method consists of steps (a) through (e). 
     
     
         13 . The coated titanium dioxide pigment of  claim 11 , having a chemical composition of from 95.70% by weight to 96.40% by weight TiO 2  and from 3.60% by weight to 3.80% by weight Al 2 O 3 . 
     
     
         14 . The coated titanium dioxide pigment of  claim 11 , having a chemical composition of from 95.70% by weight to 95.82% by weight TiO 2 , from 3.70% by weight to 3.80% by weight Al 2 O 3 , and from 0.48% by weight to 0.50% by weight ZrO 2 . 
     
     
         15 . The coated titanium dioxide pigment of  claim 11 , having a Baidins et al. durability rating of from 7.90 to 10.0. 
     
     
         16 . A coated titanium dioxide pigment prepared by a method comprising:
 (a) forming an aqueous suspension of titanium dioxide particles;   (b) adding an aluminum oxide-forming solution to the suspension of coated particles in an amount sufficient to increase the pH of the suspension to about 9.0 or higher;   (c) forming an aluminum oxide coating on the titanium dioxide particles; and   (d) filtering and drying the resulting coated titanium dioxide particles, to form a pigment.   
     
     
         17 . The coated titanium dioxide pigment of  claim 16 , having a chemical composition of 96.40% by weight TiO 2  and 3.60% by weight Al 2 O 3 .