Patent ID: 7476695

Claim:
A method for preparing a stable sol of modified stannic oxide-zirconium oxide complex colloidal particles having a particle diameter of 4.5-60 nm, wherein the particles are formed by coating surfaces of spherical stannic oxide-zirconium oxide complex colloidal particles having a bonded structure of stannic oxide colloidal particles obtained by a reaction of metal tin, an organic acid and hydrogen peroxide with zirconium oxide colloidal particles at a ZrO 2 /SnO 2 ratio of 0.02-1.0 based on weights of these oxides and having a particle diameter of 4-50 nm as nuclei, with tungsten oxide-stannic oxide-silicon dioxide complex colloidal particles having a WO 3 /SnO 2 weight ratio of 0.1-100, a SiO 2 /SnO 2 weight ratio of 0.1-100 and a particle diameter of 2-7 nm, and wherein the sol contains total metal oxides in an amount of 2-60% by weight, comprising the steps of: (a) forming spherical stannic oxide colloidal particles having a particle diameter of 4-50 nm by reacting hydrogen peroxide solution with metal tin in an organic acid aqueous solution in such a manner that a molar ratio of H 2 O 2 /Sn is maintained within a range of 2-4 and a concentration of tin oxides is 40% by weight or less; (b) mixing a stannic oxide aqueous sol which contains the spherical stannic oxide colloidal particles having a particle diameter of 4-50 nm obtained in step (a) at a concentration of 0.5-50% by weight calculated as SnO 2 , with an oxyzirconium salt aqueous solution having a concentration of 0.5-50% by weight calculated as ZrO 2 , at a weight ratio of ZrO 2 /SnO 2 of 0.02-1.0; (c) forming a stannic oxide-zirconium oxide complex aqueous sol having a particle diameter of 4-50 nm by heating the mixed solution obtained in step (b) at 60-200° C. for 0.1-50 hours; (d) forming a tungsten oxide-stannic oxide-silicon dioxide complex sol by preparing an aqueous solution containing tungstate, stannate and silicate in a WO 3 /SnO 2 weight ratio of 0.1-100 and a SiO 2 /SnO 2 weight ratio of 0.1-100 and removing cations present in the aqueous solution; (e) mixing 100 parts by weight, calculated as the total of ZrO 2 and SnO 2 contained, of the stannic oxide-zirconium oxide complex aqueous sol obtained in step (c) with 2-100 parts by weight, calculated as total of WO 3 , SnO 2 and SiO 2 contained, of the tungsten oxide-stannic oxide-silicon dioxide complex sol obtained in step (d) having a particle diameter of 2-7 nm, a WO 3 /SnO 2 weight ratio of 0.1-100 and a SiO 2 /SnO 2 weight ratio of 0.1-100 at 0-100° C.; and (f) removing anions present in the modified stannic oxide-zirconium oxide complex aqueous sol obtained in step (e) by bringing the sol into contact with an anion exchanger.