Process for making a water dispersible titanium dioxide pigment useful in paper laminates
View Patent ↗The present invention relates to a process for making a titanium dioxide pigment consisting of titanium dioxide and single layer of inorganic surface treatment consisting of aluminum phosphate wherein the pigment is characterized by and isoelectric point which is greater than pH 6 and a negative zeta potential of at a pH of 7.5 or more.
1. A process for making a water dispersible titanium dioxide slurry comprising:
(a) mixing dry titanium dioxide pigment with water to form a first mixture having a pigment concentration of from about 14 to 40 weight percent based on the weight of the first mixture then adjusting the pH of this first mixture to about 7 with aqueous sodium hydroxide;
(b) heating the first mixture of step a) to a temperature of about 40 C to form a heated first mixture;
(c) adding to the heated first mixture about 0.15 to 0.65 moles of a phosphoric acid per kilogram of dry titanium dioxide pigment and a sodium aluminate aqueous solution to form a second mixture comprising aluminum phosphate, wherein the phosphoric acid and the sodium aluminate aqueous solutions are added to the heated first mixture at a rate such that the pH of the second mixture is maintained at about 5 to 8;
(d) curing the second mixture for about 10 to 30 minutes to form a cured mixture;
(e) filtering the cured mixture and recovering, washing, drying, and fluid energy milling a treated titanium dioxide pigment consisting of a coating consisting of aluminum phosphate;
(f) blending the treated titanium dioxide pigment consisting of a coating consisting of aluminum phosphate with water to form a third mixture;
(g) adjusting the pH of the third mixture to form a slurry wherein the slurry comprises 70 to 80 percent by weight of the treated titanium dioxide pigment consisting of a coating consisting of aluminum phosphate based on the weight of the slurry.
2. The process of claim 1 wherein in step (c) the addition of the sodium aluminate aqueous solution is such that the ratio of the moles of a phosphorous to the moles of an aluminum in the second mixture is from about 0.25 to 0.6.
3. The process of claim 1 wherein in step (c) the addition of the sodium aluminate aqueous solution is such that the ratio of the moles of phosphorous to the moles of aluminum in the second mixture is about 0.5.
4. The process of claim 1 wherein the amount of the phosphoric acid added in step (c) is from about 0.23 to 0.52 moles per kilogram of the dry titanium dioxide pigment.
5. The process of claim 1 wherein the dry titanium dioxide pigment is rutile.
6. A slurry produced from the process of claim 1 .