Patent ID: 7794641

Claim:
A method of manufacturing golf balls composed of a core and a cover of one or more cover layers that encloses the core, the method comprising: forming at least one cover layer of a thermoplastic polyurethane composition that includes at least 90 wt % of a thermoplastic polyurethane obtained by a polyurethane-forming reaction between a long-chain polyol, an organic diisocyanate compound and a chain extender, the thermoplastic polyurethane composition cover layer having an inherent viscosity in a dimethylformamide solvent of larger than 1.5 dl/g and an inherent viscosity in a 0.05 mol/L n-butylamine-containing dimethylformamide solution of larger than 0.5 dl/g, wherein the thermoplastic polyurethane composition cover layer is composed of two kinds of thermoplastic polyurethane or polyurethane composition A and B which satisfy the condition that the inherent viscosity of “B” in dimethylformamide is larger than the inherent viscosity of “A” in dimethylformamide and the condition that the inherent viscosity of “B” in 0.05 mol/L n-butylamine-containing dimethylformamide solution is larger than the inherent viscosity of “A” in 0.05 mol/L n-butylamine-containing dimethylformamide and which have been blended in proportions that satisfy the following conditions: A1<500 ppm B1<5,000 ppm 100/1≧ A 2/ B 2≧100/150 ( A 1× A 2+ B 1× B 2)/( A 2+ B 2)≦3,000 ppm (wherein A1 is the moisture content in thermoplastic polyurethane or polyurethane composition A, A2 is the weight of thermoplastic polyurethane or polyurethane composition A, B1 is the moisture content in thermoplastic polyurethane or polyurethane composition B, and B2 is the weight of thermoplastic polyurethane or polyurethane composition B).