To obtain a stainproofing agent which, when added to a water-based coating composition, can give a composition having a long pot life and excellent stability by heating a hydrophilic organic solvent solution containing a hydroxy polymer, a specified amount of a specified atkoxysilane and water in an acidic atmosphere until a solution having an at most specified content of a specified primary alcohol is formed.
This agent comprises a solution obtained by heating a hydrophilic organic solvent solution containing a hydroxy polymer (e.g. methyl methacrylate/butyl methacrylate/2-hydroxyethyl methacrylate copolymer) or both this polymer and a polyalkylene glycol, an alkoxysilane having at least two 2-4 C alkoxyl groups and water in an acidic atmosphere. This solution should have a content of Si derived from the alkoxysilane of 50-600 pts.wt. (in terms of the SiO2), per 100 pts.wt. solid matter derived from the hydroxiy polymer or both this polymer and the alkylene glycol, and a content of a 1-4 C primary alcohol content of at most 5 wt.%.
INUKAI HIROSHI
MARUMOTO ETSUZO
