Silane modified colloidal silica in water-borne pud coatings for galvanized steel

 
The use of silane modified colloidal silica in PUD resin-based metal coating formulations in combination with resin and optional epoxy silane has been investigated. The samples were evaluated regarding their mechanical, physical properties and corrosion resistances on galvanized steel. Addition of modified colloidal silica enhanced the corrosion resistance significantly. The corrosion resistance of coatings was evaluated with either 5 or 15-microns dry film thicknesses applied. The results of a salt spray test were best in formulations with 10 % and 20 % Levasil® CC301 product on formulation. The cross-linking density of the coatings increased upon silica and silane addition. Synergy between silane, colloidal silica and resin in corrosion resistance could be noted but did not correlate to any further increase in cross-linking density. A good compatibility was observed. The hardness of the samples was in agreement with their very good flexibility and impact resistance. Drying time was similar for dust free and tack free times. However, differences occurred in the hard-dry times. Addition of silane prolonged the drying while the combination of silane and silica partly off-set this.