U.S. 8,557,388 B2
Hontek Corporation has been granted a patent for a polyurethane or polyurea rain erosion resistant coating composition for protecting a leading edge substrate on an airfoil against liquid and solid particle erosion comprised of an isocyanate-terminated prepolymer with an isocyanate content of 0.5-40 weight percent, based on the weight of the prepolymer; a curing agent selected from the group consisting of an aldimine, a ketimine, a polyaspartic ester, a polyamine, a polyol and mixtures thereof; and a flatting agent, having a particle size of one-20 micrometers present at a level of one-15  weight percent based on the total weight of the the polyurethane or polyurea coating composition, and selected from the group consisting of silica, polymeric beads, talc, alumina, calcium carbonate, urea-formaldehydes and mixtures thereof; the polyurethane or polyurea rain erosion resistant coating composition in dry cured form having a tensile strength greater than 1000 psi (70 kg/cm2), an elongation at break greater than 350 percent, a tensile set after break of less than 150 percent, and a Shore A hardness of 44A to 95A as measured at 68° F, a matte finish as measured according to ASTM D 523-89 (1999) with an 85 degree surface gloss less than 15, and having a rain erosion resistance of greater than or equal to 70 minutes.