| abstract |
A method for preparing an aqueous polyurethane dispersion, comprising (a) preparing a prepolymer with free NCO groups by reacting an aliphatic or cycloaliphatic polyisocyanate with a polyol, and an anionic compound; (b) dispersing said prepolymer in water; (c) reacting said water-dispersed prepolymer with a diamino hydrazide of the formula: <IMAGE> wherein R is an alkylene group of 2 to 15 carbon atoms or a cycloalkylene or arylene group of 6 to 15 carbon atoms as a chain lengthening agent; (d) reacting the prepolymer of step (c) in said dispersion with formaldehyde to effect crosslinking. |