Patent GB-1044350-A (GB)
Title: Corrosion inhibiting pigments
Inventor: LEDERER GERALD
IPC: C09C1/36
Filed: 1964-04-11
Abstract: Pigmentary TiO2 particles have an anticorrosive coating of a chromate of lead, barium, or strontium, lead benzoate, or calcium plumbate. The TiO2 is preferably at least 90% rutile and the pigment may also be coated with one or more metal oxides, e.g. Al2\O3, TiO2, CeO2 or ZO2 or silicon oxide and/or a phosphate, the oxide being present in an amount of 0.1 to 6% by weight, and the phosphate in an amount of 0.1 to 3% by weight (as P2O5).  The pigment is coated by forming an aqueous suspension of the pigment particles, adding to the suspension a water-soluble compound of aluminium and a water-soluble chromate, adjusting the pH to at least 6 and adding a water-soluble compound of Pb, Ba or Sr, and then, if necessary, adjusting the pH to at least 7. The lead benzoate is produced by using water-soluble salts of lead and benzoic acid, and the calcium plumbate by utilizing water-soluble salts of Ca and Pb adjusting the pH to precipitate the mixed hydroxides, filtering off the treated particles and calcining, e.g. at 200 DEG  C., to complete the conversion of the coating to calcium plumbate.  The preferred Ca/Pb ratio in this coating is given as 1.5:1 to 2.5:1. The Specification gives preferred ranges for the amount of each coating on the TiO2 particles. The coated particles are used as pigments in anti-corrosion paints, the preferred film forming medium in such paints being alkyd resin, oil-modified or epoxy-modified alkyd resin, linseed oil, or epoxy-modified linseed oil, alkyd amino resin, a melamine acrylic resin, or a watersoluble acrylic or phenolic based resin, the pigment volume concentration in said paints being in the range 15 to 50%, preferably 25 to 35%.ALSO:Pigmentary TiO2 particles have a coating of a chromate of lead, barium, or strontium, lead benzoate, or calcium plumbate. The TiO2 is preferably at least 90% rutile and the pigment may also be coated with one or more metal oxides, e.g. Al2O3, TiO2, CeO2, or ZrO2 or silicon oxide and/or a phosphate, the oxide being present in an amount of 0.1 to 6% by weight, and the phosphate in an amount of 0.1 to 3% by weight (as P2O5).  The pigment is coated by forming an aqueous suspension of the pigment particles, adding to the suspension a water-soluble compound of aluminium and a water-soluble chromate, adjusting the pH to at least 6 and adding a water-soluble compound of Pb, Ba, or Sr, and then, if necessary, adjusting the pH to at least 7.  The lead benzoate is produced by using water-soluble salts of lead and benzoic acid, and the calcium plumbate by utilizing water-soluble salts of Ca and Pb, adjusting the pH to precipitate the mixed hydroxides, filtering off the treated particles and calcining, e.g at 200 DEG  C, to complete the conversion of the coating to calcium plumbate.  The preferred Ca/Pb ratio in this coating is given as 1.5:1 to 2.5:1. The Specification gives preferred ranges for the amount of each coating on the TiO2 particles.  The coated particles are used as pigments in anti-corrosion paints, the preferred film forming medium in such paints being alkyd resin, oil-modified or epoxy-modified alkyd resin, linseed oil, or epoxy-modified linseed oil, alkyd amino resin, a melamine acrylic resin, or a water-soluble acrylic or phenolic based resin, the pigment volume concentration in said paints being in the range 15 to 50%, preferably 25 to 35%.