Titanium dioxide pigment particles

Titanium dioxide pigment particles are coated with at least 0,01% based on the dry weight of the pigment of a salt, soluble in water to the extent of at least 1% by weight, of a tertiary amine with an organic acid, the acid having a solubility between 1/20 % and 2% by weight in water at 20 DEG C. in order to improve the dispersibility in surface-coating compositions after compaction and storage. The pigment may be coated by leading the tertiary amine salt and the pigment into a fluid energy mill, or by dissolving the salt in water or an organic liquid, and adding the solution to a slurry of titanium dioxide pigment. It is preferred to add the amine salt to the slurry resulting from the hydroclassification step to which pigment is subjected to remove oversize (>4n ) particles. The slurry is dewatered and dried and passed through a fluid energy mill. The amine salts may be prepared by mixing a tertiary amine and an organic acid in stoichiometric proportions. Specified acids are 2,4-hexadienoic acid, octadecyl sulphonic acid, cinnamic acid, adipic acid, 2-ethyl hexanoic acid, benzoic acid and the diester of phosphoric acid with two mols of 2-ethyl-1-pentanol. Suitable amines specified are N-methyl morpholine, pyridine, tribenzylamine, triethylamine, 2-methyl pyridine, 4-picoline and triethanolamine. The grades of titanium dioxide which may be coated include those containing conditioning agents such as alkali and alkaline earth metal salts, brighteners and rutile converters, e.g. antimony and zinc salts extending agents such as calcium sulphate, barium sulphate and lithopone and agents for improving the colour and chalk resistance of the pigment, e.g. oxides and hydrous oxides of aluminium, zirconium, titanium and silicon.