Patent ID: 8372999

Claim:
A protective coating for metal surfaces, the protective coating comprising: a. one part by weight of the organosilane-modified silica nanoparticles made by: i. hydrolyzing an alkali silicate under acid conditions to obtain a silicic acid dispersion, ii. adding an organosilane having hydroxyl and/or hydrolyzable groups to the dispersion under acid conditions to form a silicic acid-organosilane dispersion, wherein silica seed particles of an average size of 2 to 200 nm are added to the silicic acid-organosilane dispersion, and iii. raising the pH of the dispersion to at least eight to cause condensation of the organosilane and silicic acid to form nanoparticles comprising an aggregate of silica and said organosilane; and b. from 0.3 to 3 parts by weight of the reaction product of (1) a compound comprising a polyamine in which a plurality of amine groups are bonded to at least one radical selected from the group consisting of hydrocarbon and hydrocarbon ether groups that separate nitrogen atoms of said amine groups by at least four intermediate atoms in a chain, and (2) a silane which carries a plurality of silicon-bonded hydrolyzable groups and a silicon-bonded organic group that is covalently reactive to and which bonds with said amine group, said silane also comprising hydrolyzable groups, to provide a reaction product molecule which comprises an average of 2.5 to 3.5 silane groups per molecule.