Patent ID: 9505022
Filing Date: 2016-11-29
CPC Classification: B05D,C01P,C09C,C09D

Claim Text:
1. A method for post treatment of titanium dioxide pigment particles comprising, in sequence: a) preparing an aqueous slurry of titanium dioxide pigment core particles with a pH value of from 4.0 to 6.0, b) adding to the aqueous slurry of titanium dioxide pigment core particles a sufficient quantity of water soluble compounds of zirconia and silica, in sequence, to precipitate a hydrous zirconia-silica composite layer on the core particles and form a first mixture, the adding comprising adding the water soluble compounds of zirconia and silica without the addition of any pH-adjusting compounds other than the water soluble compounds of zirconia and silica, c) digesting the first mixture for 10 to 30 minutes to complete the precipitation and form a suspension, d) adding a sufficient quantity of water soluble alkaline alumina compound to the suspension in a single step to form a second mixture, the adding a sufficient quantity comprising adding the water soluble alkaline alumina compound without the addition of any pH-adjusting compound other than the water soluble alkaline alumina compound, wherein steps b), c), and d) are carried out in order without adding any pH-adjusting compounds, during or between steps b), c), and d), other than the water soluble compounds of zirconia and silica added in step b) and the water soluble alkaline alumina compound added in step d), e) after the single step addition of step d), adjusting the pH of the second mixture, if needed, to achieve a pH of the second mixture of from 8.0 to 8.5, f) digesting the second mixture resulting from step e) for 10 to 30 minutes to complete precipitation of a hydrous alumina layer on the hydrous zirconia-silica composite layer and to form a second suspension comprising a multi-layered pigment, g) adjusting the pH of the second suspension, if needed, to achieve a pH value of from 6.0 to 8.0, h) filtering the second suspension resulting from step g), and i) drying the multi-layered pigment.