Titanium dioxide pigment composition and a method for making the same

Claim 1

A silicate encapsulated TiO2 pigment according to claim 1 wherein the amount of sponge alumina on said silicate encapsulated TiO2 is about 1.5 percent calculated on a TiO2 weight basis.

Claim 4

A method for producing a silicate encapsulated TiO2 pigment characterized by a dense impervious skin of hydrateD aluminum silicate and having exceptionally good color and durability when incorporated in acrylic coating compositions which comprises forming an aqueous slurry of pigmentary TiO2, adjusting the pH of the slurry to fall within the range of from 8.5 to 10.5 and coprecipitating SiO2 and Al2O3 onto the pigmentary TiO2 in two successive stages to form successive coatings of hydrated aluminum silicate on said pigmentary TiO2 the first stage coprecipitation of SiO2 and Al2O3 being effected by heating the slurry to a temperature of at least 70* C. to boiling, simultaneously adding solutions of soluble salts of silicon and aluminum to said slurry at a rate not to exceed 10 percent total silicate coating per hour on a TiO2 weight basis and maintaining the pH of said slurry in the range 8.5 to 10.5 and the temperature of said slurry at least 70* C. to boiling during the addition of said solutions, thereafter adjusting the pH of the slurry in the range of from 7.0 to 10.5 and maintaining the slurry at a temperature of at least 70* C. to boiling for at least 45 to 90 minutes to age the hydrated aluminum silicate coating on said pigmentary TiO2, the second stage coprecipitation of SiO2 and Al2O3 being effected by readjusting the pH of the said slurry in the range of from 8.5 to 10.5 and again simultaneously adding solutions of soluble salts of silicon and aluminum to said slurry in the same manner as that described for the first stage coprecipitation, thereafter readjusting the pH of the slurry at a temperature of at least 70* C. to boiling for at least 45 to 90 minutes to age the second coating of hydrated aluminum silicate, the amount of soluble salts of silicon and aluminum added to said slurry being such that the total amount of hydrated aluminum silicate deposited on said pigmentary TiO2 is from 5 percent to 20 percent based on weight of said TiO2 whereby said pigmentary TiO2 is completely encapsulated by said hydrated aluminum silicate, said soluble salts being added in proportions to provide a ratio of SiO2:Al2O3 in the range from 2:1 to 8:1, and thereafter finishing the silicate encapsulated TiO2 by drying at from 120* C. to 350* C. followed by milling.

Claim 12

A method for producing a silicate encapsulated TiO2 pigment characterized by a dense impervious skin of hydrated aluminum silicate and having exceptionally good color and durability when incorporated in acrylic coating compositions which comprises forming an aqueous slurry of pigmentary TiO2, adjusting the pH of the slurry to fall within the range of from 8.5 to 10.5 and coprecipitating SiO2 and Al2O3 onto the pigmentary TiO2 to form a coating of hydrated aluminum silicate on said pigmentary TiO2 the coprecipitation of SiO2 and Al2O3 being effected by heating the slurry to a temperature of at least 70* C. to boiling, simultaneously adding solutions of soluble salts of silicon and aluminum to said slurry at a rate not to exceed 10 percent total silicate coating per hour on a TiO2 weight basis and maintaining the pH of said slurry in the range 8.5 to 10.5 and the temperature of said slurry at least 70* C. to boiling during the addition of said solutions, thereafter adjusting the pH of the slurry in the range from 7.0 to 10.5 and maintaining the slurry at a temperature of at least 70* C. to boiling for at least 45 to 90 minutes to age the hydrated aluminum silicate coating on said pigmentary TiO2, the amount of soluble salts of silicon and aluminum added to said slurry being such that the total amount of hydrated aluminum silicate deposited on said pigmentary TiO2 is from 5 percent to 20 percent based on weight of said TiO2 whereby said pigmentary TiO2 is completely encapsulated by said hydrated aluminum silicate, said soluble salts being added in proportions to provide a ratio of SiO2:Al2O3 in the range from 2:1 to 8:1, and thereafter finishing the silicate encapsulated TiO2 by coating with from 1.0 to 2.0 percent hydrous aluminum oxide followed by drying and milling.