The object of the present invention is to provide a golf ball having superior abrasion resistance, durability and spin performance. The present invention provides a golf ball of the present invention has a core and a cover, wherein the cover is formed from a cover composition that contains, as a resin component, a thermoplastic polyurethane (A) and a urethane prepolymer (B) having two or more isocyanate groups.
1. A golf ball comprising a core and a cover,
wherein the cover is formed from a cover composition that contains, as a resin component, only a reaction mixture (A+B) obtained by melt-mixing a thermoplastic polyurethane (A) and a urethane prepolymer (B) having two or more isocyanate groups; and
wherein the urethane prepolymer (B) has a NCO content from 2.0 mass % to 7.0 mass %.
2. The golf ball according to claim 1 , wherein the reaction mixture (A+B) is obtained by mixing the urethane prepolymer (B) in an amount of from 1 part to 50 parts by mass with respect to 100 parts by mass of the thermoplastic polyurethane (A).
3. The golf ball according to claim 1 , wherein the temperature difference (T A+B −T A ) between the flow beginning temperature (T A + B ) of the reaction mixture (A+B) and the flow beginning temperature (T A ) of the thermoplastic polyurethane (A) is in a range from −5° C. to 40° C.
4. The golf ball according to claim 1 , wherein the ratio (ηA+B/ηA) of the melt viscosity (ηA+B) of the reaction mixture (A+B) to the melt viscosity (ηA) of the thermoplastic polyurethane (A) is in a range from 0.7 to 12.0.
5. The golf ball according to claim 1 , wherein a polyol component constituting the urethane prepolymer (B) has a number average molecular weight of 650 or more.
6. The golf ball according to claim 1 , wherein a polyol component constituting the urethane prepolymer (B) has a number average molecular weight from 650 to 3000.
7. The golf ball according to claim 1 , wherein the cover composition has a slab hardness of from 20 to 60 in Shore D hardness.
8. The golf ball according to claim 1 , wherein the thermoplastic polyurethane (A) has a flow beginning temperature (T A ) from 100° C. to 210° C.
9. The golf ball according to claim 1 , wherein the thermoplastic polyurethane (A) has a melt viscosity (ηA) at 210° C. from 1,000 P to 45,000 P.
10. A golf ball comprising a core and a cover,
wherein the cover is formed from a cover composition that contains, as a resin component, only a reaction mixture (A+B) obtained by melt-mixing a thermoplastic polyurethane (A) and a urethane prepolymer (B) having two or more isocyanate groups in an amount of 1 part to 50 parts with respect to 100 parts of the thermoplastic polyurethane (A) by mass,
the thermoplastic polyurethane (A) has a flow beginning temperature (T A ) from 100° C. to 210° C., and a melt viscosity (ηA) at 210° C. from 1,000 P to 45,000 P, and
the urethane prepolymer (B) has a NCO content from 2.0 mass % to 7.0 mass %.
11. The golf ball according to claim 10 , wherein a polyol component constituting the urethane prepolymer (B) has a number average molecular weight from 650 to 3000.
12. A process for manufacturing a golf ball having a core and a cover covering the core, comprising
mixing a thermoplastic polyurethane (A) and a urethane prepolymer (B) having two or more isocyanate groups to form a reaction mixture (A+B), wherein the urethane prepolymer (B) has a NCO content from 2.0 mass % to 7.0 mass %,
preparing a cover composition comprising, as a resin component, only the reaction mixture (A+B), and
molding the cover composition into the cover.
13. The process for manufacturing the golf ball according to claim 12 , wherein the mixing is conducted by feeding the thermoplastic polyurethane (A) into a extruder, and subsequently side-feeding the urethane prepolymer (B) into the feed of the thermoplastic polyurethane (A).
14. The process for manufacturing the golf ball according to claim 12 , further comprising post curing the molded cover.
15. The process for manufacturing the golf ball according to claim 14 , wherein the post curing is conducted at a temperature of 40° C. or more for 4 hours to 96 hours.