DICARBOXYLIC ANHYDRIDE DISPERSION SOL OF SILANE-TREATED MODIFIED METAL OXIDE, METHOD FOR PRODUCING THE SAME, EPOXY CURING AGENT CONTAINING THE SAME, AND EPOXY RESIN CURED PRODUCT

PROBLEM TO BE SOLVED: To provide an epoxy curing agent which is suitable for use in a resin composition for sealing an optical semiconductor and has a high refractive index and excellent transparency.SOLUTION: There is provided a sol in which silane-treated modified metal oxide colloidal particles are dispersed in a dicarboxylic anhydride which is liquid at 30°C. The silane-treated modified metal oxide colloidal particles are formed as follows: the outer surfaces of metal oxide colloidal particles (A) having a primary particle diameter of 5-60 nm as cores are coated with silicon dioxide-stannic oxide composite oxide colloidal particles (B) having a mass ratio of silicon dioxide/stannic oxide of 0.1-5.0, having an amine compound bonded thereto in a molar ratio of M/(SnO+SiO) of 0.001-0.08, and having a primary particle diameter of 1-4 nm to obtain modified metal oxide colloidal particles (C), wherein a mass ratio (B)/(A) of the composite oxide colloidal particles (B) to the metal oxide colloidal particles (A) is 0.05-0.50, and to the particle surfaces of the colloidal particles (C) 1-4 silyl groups per 1 nmof the surface area are bonded.