Patent GB-566920-A (GB)
Title: Titanium oxide pigment production
IPC: C01G23/08
Filed: 1943-01-26
Abstract: 566,920. Disintegrating. DU PONT DE NEMOURS & CO., E. I. Jan. 26, 1943, No. 1319. Convention date, Jan. 9, 1942. [Class 59] [4lso in Group III] Raw pigment-titanium oxide is subjected to a disintegration treatment to reduce the particle size prior to calcining. Preferably, a raw anatase pigment obtained by hydrolysis of titanium sulphate solution, for example as described in U.S. Re-issue Specification 18,854 is subjected to mechanical milling, grinding, pulverizing or extrusion while in the wet or dry state, and then calcined at about 750‹-1000‹ C. in the presence of a small amount of a titaniumoxygen compound rutile conversion promoter as in Specification 565,349, [Group III], or of an alkali metal salt, e.g. sodium and/or potassium sulphate, or of both an alkali metal salt and compounds of polyvalent metals such as Al, Zn, Mg or Be, as described in Specification 580,734, [Group III], as open to inspection under Sect. 91. The initial raw pigment may, however, be any type of TiO2, either in the anatase or rutile form and obtained by neutralization or hydrolysis of other titanium salts such as the nitrate, chloride or oxalate, or an extended pigment comprising' such extenders as barium or calcium sulphate, calcium carbonate or magnesium silicate. Conventional types of grinding, milling and like apparatus may be used such as mills of the ball, pebble or other type, disintegrators, pulverizers, and extruding or ejecting apparatus exerting high fluid or mechanical pressure on the body of pigment being ejected. The time of treatment may vary from say 1-100 hrs. to give optimum particle size. The raw pigment may first be partially dried at 50-200‹ C., dry ground, preferably for 1-4 hrs., and then wet ground, say for 1-4 hrs., in the form of a slurry containing about 300 g./l. TiO2. Ejection or extrusion of aqueous suspensions through a small orifice under high fluid pressure say 1,000-20,000 once, preferably about 1,000- 15,000 lb/in. may be effected. Several ejections at a lower pressure can generally be used instead of one at a high pressure. The pigment slurry containing about 250 g./l. TiO2 may be placed in a pressure vessel with a restricted or' valve-controlled outlet and equipped with a valve control leading to a gas reservoir. Air, hydrogen, steam or other gas is forced into the reservoir which is then connected with the free space in the vessel. The outlet valve is slowly opened to force the slurry through the orifice. A piston, pressure roller or other mechanical means may alternatively be used for forcing the slurry through one or more restricted orifices. Where a rutile promoter is admixed with the raw pigment, it may be added prior to the disintegration treatment. The process may be a batch or continuous one, and ordinary or elevated temperatures and pressures may be maintained during the disintegration. The products have a particle size of the order of 200 millimicrons. Examples describe the wet grinding of an anatase raw pigment in a pebble mill for 16 hrs. followed by calcination and the disintegration of the same pigment mixed with a raw rutile by dry or wet grinding or dry followed by wet grinding in a pebble, ball or colloid mill, in some cases with the addition of sodium and potassium sulphates prior to the subsequent calcining step, or by ejection under a hydrogen pressure of 15,000 lbs/sq. in. or five successive ejections at 7,500 lbs/sq. in.