Method for surface treating reinforcing material with aqueous carbodiimide containing composition

A method of surface treating a reinforcing material, comprising contacting a reinforcing material with an aqueous surface-treating agent comprising a carbodiimide compound, wherein the carbodiimide compound is water-soluble or self-emulsifiable and is represented by the following formula

• Z--OOC--NH--(R.sub.3 --NCN).sub.n --R.sub.3 --NH--COO--Z
• wherein R.sub.3 is a residue of a diisocyanate compound selected from the group consisting of
• m- or p-tetramethylxylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and
• isophorone diisocyanate;
• Z is a residue of a poly(alkylene oxide) which has at least one reactive hydroxyl group and is blocked with an alkoxyl group at one terminal and which is represented by the following formula
• R.sub.8 --(O--CHR.sub.9 --CH.sub.2).sub.m --OH
• wherein R.sub.8 is a lower alkyl group having 1-4 carbon atoms, R.sub.9 is a hydrogen atom or a methyl group, and m is an integer of 4 to 30;
• and n is an integer of 2 to 30,
• and wherein the reinforcing material is selected from the group consisting of glass fiber, carbon fiber and aramid fiber.