Patent GB-999803-A (GB)
Title: Production of a modified titanium dioxide pigment
IPC: C09C1/36
Filed: 1962-06-18
Abstract: Modified titanium dioxide pigment is made by making an aqueous slurry containing (i) titanium dioxide pigment from vapour phase oxidation of titanium tetrachloride, e.g. up to 70% by weight, (ii) a titanium compound which on hydrolysis gives titanic acid and/or condensed titanic acid, (iii) an aluminium compound which on hydrolysis gives Al(OH)3 and/or condensed Al(OH)3, (iv) mole concentration of chloride ions greater than total mole concentration of other acid anions, e.g. 65% or even 75%, (v) pH less than 5, e.g. less than 3.5; the pH of the slurry is then raised, e.g. to pH 8.5, to give flocs of titanium dioxide pigment and modified pigment particles are recovered.  The slurry may also contain a silicon compound which on hydrolysis gives silicic acid and/or condensed silicic acid.  The floc may be filtered, washed, dried and milled. The titanium compound may be TiCl4, TiOSO4, a titanium ester, e.g. (C2H5O)4 Ti, (ClC2H4O)4Ti, (C8H17O)4Ti, (C5H5O)4Ti, tetra-acyloxy titanium, e.g. (CH3CO)4Ti, (C3H7CO)4Ti.  The aluminium compound used may be AlCl3, Al2(SO4)3, alkyl and aryl aluminium, e.g. (C2H5)3Al, (C6H13)3Al, alkoxy and aryloxy aluminium, e.g. (C2H5O)3Al, (C4H9O)3 Al, (C6H5O)3Al, acycloxy aluminium, e.g. (CH3CO)3Al, and cyclic aluminoxy trimers, e.g. trimethoxy trialuminoxy. The pH of the slurry may be raised by using any alkaline material which should preferably form a halogen salt that may be washed from the precipitate, e.g. ammonia, alkali and alkaline earth metal hydroxides, or carbonates, e.g. KOH, NaOH, LiOH, Ca(OH)2, Mg(OH)2, CaCO3, K2CO3, Na2CO3 and KHCO3 and NaHCO3, primary, secondary and tertiary amines, e.g. ethylene diamine, ethylamine, diethanolamine, diethylene triamine, pyridine, triethylamine and quaternary ammonium hydroxides, e.g. benzyl trimethyl ammonium hydroxide, polymeric materials such as water-soluble polyvinyl-pyridinium hydroxide or carbonate. The preferred silicon compound is sodium silicate but it may also be SiCl4, SiH4, (CH3CO2)4Si (CH3CO)4Si, (NH2)2Si, (NH2)4Si, (C2H5O)4Si. Any strong acid may be used to acidify the slurry, e.g. HCl, whilst AlCl3 and/or TiCl4 may also be used.  These three compounds are preferable since they also increase the chloride ion concentration. The floc may be washed with water, ketones, e.g. acetone and methyl ethyl ketone, alcohols, e.g. ethanol, propanol, 2-ethyl hexanol, ethers, e.g. diethyl ether, dioxan, tetrahydrofuran, to remove impurities such as salts. The pigment may then be gently heated to drive off any residual solvent.  The pigment may be dry ground in a ball mill, jet mill or fluid energy mill.  The titanium, aluminium and silicon compounds or mixtures thereof may be added to the aqueous slurry as an aqueous solution. TiO2 pigment may be of size 0.05 to 0.50 and may be slurried in dionized or distilled water. For continuous pigment production, the concentration of TiO2 may be maintained at 150-350 g./litre. The aluminium compound may be added in amount to produce 0.05 to 15% of Al2O3 in the pigment, titanium compound in amount 0.1 to 4% as HCl-soluble TiO2 silicon compound in amount 0.01 to 1.0% as SiO2.ALSO:Modified titanium dioxide pigment is made by making an aqueous slurry containing (i) titanium dioxide pigment from vapour phase oxidation of titanium tetrachloride, e.g. up to 70% by weight, (ii) a titanium compound which on hydrolysis gives titanic acid and/or condensed titanic acid, (iii) an aluminium compound which on hydrolysis gives Al(OH)3 and/or condensed Al(OH)3, (iv) mole concentration of chloride ions greater than total mole concentration of other acid anions, e.g. 65% or even 75%, (v) pH less than 5, e.g. less than 3.5; the pH of the slurry is then raised, e.g. to pH 8.5, to give flocs of titanium dioxide pigment and modified pigment particles are recovered.  The slurry may also contain a silicon compound which on hydrolysis gives silicic acid and/or condensed silicic acid.  The floc may be filtered, washed, dried and milled. The titanium compound may be TiCl4, TiOSO4, a titanium ester, e.g. (C2H5O)4Ti, (ClC2H4O)4Ti, (C8H17O)4Ti, (C6H5O)4Ti, tetra-acyloxy titanium, e.g. (CH3CO)4Ti, (C3H7CO)4Ti.  The aluminium compound used may be AlCl3, Al2(SO4)3, alkyl and aryl aluminium, e.g. (C2H5)3Al, (C6H13)3Al, alkoxy and aryloxy aluminium, e.g. (C2H5O)3Al, (C4H9O)3Al, (C6H5O)3Al, acycloxy aluminium, e.g. (CH3CO)3Al, and cyclic aluminoxy trimers, e.g. trimethoxy trialuminoxy.  The pH of the slurry may be raised by using any alkaline material which should preferably form a halogen salt that may be washed from the precipitate, e.g. ammonia, alkali and alkaline earth metal hydroxides, or carbonates, e.g. KOH, NaOH, LiOH, Ca(OH)2, Mg(OH)2, CaCO3, K2CO3 Na2CO3, KHCO3 and NaHCO3, primary, secondary and tertiary amines, e.g. ethylene diamine, ethylamine, diethanolamine, diethylene triamine, pyridine, triethylamine and quaternary ammonium hydroxides, e.g. benzyl trimethyl ammonium hydroxide, polymeric materials such as water-soluble polyvinylpyridinium hydroxide or carbonate.  The preferred silicon compound is sodium silicate but it may also be SiCl4, SiH4, (CH3CO2)4Si, (CH3CO)4Si, (NH2)2Si, (NH2)4Si, (C2H5O)4Si.  Any strong acid may be used to acidify the slurry, e.g. HCl, whilst AlCl3 and/or TiCl4 may also be used.  These three compounds are preferable since they also increase the chloride ion concentration.  The floc may be washed with water, ketones, e.g. acetone and methyl ethyl ketone, alcohols, e.g. ethanol, propanol, 2-ethyl hexanol, ethers, e.g. diethyl ether, dioxan, tetrahydrofuran, to remove impurities such as salts.  The pigment may then be gently heated to drive off any residual solvent. The pigment may be dry ground in a ball mill, jet mill or fluid energy mill.  The titanium, aluminium and silicon compounds or mixtures thereof may be added to the aqueous slurry as an aqueous solutions.  TiO2 pigment may be of size 0.05 to 0.50 and may be slurried in dionized or distilled water. For continuous pigment production, the concentration of TiO2 may be maintained at 150-350 g./litre.  The aluminium compound may be added in amount to produce 0.05 to 15% of Al2O3 in the pigment, titanium compound in amount 0.1 to 4% as HCl-soluble TiO2 silicon compound in amount 0.01 to 1.0% as SiO2.