The object of the present invention is to provide a golf ball that satisfies both of the flight distance at the shot with a driver, a long iron, and a middle iron and the controllability at the approach shot with a short iron and is also excellent in the abrasion resistance of the cover. The present invention provides a golf ball comprising a core consisting of a center and at least one intermediate layer covering the center, and a cover covering the core, wherein the cover is formed from a cover composition containing, as a resin component, a thermoplastic polyurethane (A) and a polyisocyanate mixture (B) in which a urethane prepolymer (b-1) having at least two isocyanate groups or a polyisocyanate (b-2) having at least three isocyanate groups is dispersed in a thermoplastic resin (b-3) which does not substantially react with an isocyanate group; and wherein the cover composition has a slab hardness of 60 or less in Shore D hardness, and the core has a hardness difference (Hs−Ho) between a surface hardness Hs and a center hardness Ho of from 15 to 50 in Shore D hardness.
1. A golf ball comprising
a core consisting of a center and at least one intermediate layer covering the center, and a cover covering the core,
wherein the cover is formed from a cover composition containing, as a resin component, a thermoplastic polyurethane (A) and
a polyisocyanate mixture (B) in which a urethane prepolymer (b-1) having at least two isocyanate groups or a polyisocyanate (b-2) having at least three isocyanate groups is dispersed in a thermoplastic resin (b-3) which does not substantially react with an isocyanate group; and
wherein a number average molecular weight of a polyol component constituting the urethane prepolymer (b-1) is 650 or more,
the polyisocyanate (b-2) is an isocyanurate of a diisocyanate,
the intermediate layer has a slab hardness of 61 or more in Shore D hardness,
the cover composition has a slab hardness of less than 30 in Shore D hardness,
the cover has a thickness of from 0.1 mm to 0.8 mm, and
the core has a hardness difference (Hs−Ho) between a surface hardness Hs and a center hardness Ho of from 15 to 50 in Shore D hardness,
wherein the polyisocyanate mixture (B) has an NCO content (NCO %) of 0.1 mass % to 10.0 mass % in the case that the polyisocyanate mixture (B) contains the urethane prepolymer (b-1), and
wherein the polyisocyanate mixture (B) has an NCO content (NCO %) of 5.0 mass % to 30.0 mass % in the case that the polyisocyanate mixture (B) contains the polyisocyanate (b-2).
2. The golf ball according to claim 1 , wherein the urethane prepolymer (b-1) has an NCO content (NCO %) of 0.5 mass % or more and less than 10.0 mass %.
3. The golf ball according to claim 1 , wherein the polyisocyanate (b-2) has an NCO content (NCO %) of 10.0 mass % to 30.0 mass %.
4. The golf ball according to claim 1 , wherein the urethane prepolymer (b-1) is a bifunctional isocyanate group-terminated urethane prepolymer represented by the following formula (1):
polyisocyanate-(polyol-polyisocyanate)n (1),
wherein the connecting number n is an integer of not less than 1 and not higher than 10.
5. The golf ball according to claim 1 , wherein the cover composition contains the polyisocyanate mixture (B) in an amount of 1 to 50 parts by mass based on 100 parts by mass of the thermoplastic polyurethane (A).
6. The golf ball according to claim 1 , wherein the mixing ratio (100% by mass in total) of the urethane prepolymer (b-1) or the polyisocyanate (b-2) to the thermoplastic resin (b-3) in the polyisocyanate mixture (B) is: (urethane prepolymer (b-1) or polyisocyanate (b-2))/thermoplastic resin (b-3)=(5% to 50% by mass)/(50% to 95% by mass).
7. The golf ball according to claim 1 , wherein the thermoplastic resin (b-3) is at least one selected from the group consisting of a polyester elastomer, an acrylic elastomer, a styrene elastomer, an olefin elastomer, and a vinyl chloride elastomer.
8. A golf ball comprising
a core consisting of a center and at least one intermediate layer covering the center, and
a cover covering the core,
wherein the cover is formed from a cover composition containing, as a resin component, a thermoplastic polyurethane (A) and
a polyisocyanate mixture (B) in which a urethane prepolymer (b-1) having at least two isocyanate groups or a polyisocyanate (b-2) having at least three isocyanate groups is dispersed in a thermoplastic resin (b-3) which does not substantially react with an isocyanate group; and
wherein a number average molecular weight of a polyol component constituting the urethane prepolymer (b-1) is 650 or more,
the polyisocyanate (b-2) is an isocyanurate of a diisocyanate,
the cover composition has a slab hardness of 38 or less in Shore D hardness,
the cover has a thickness of from 0.1 mm to 0.5 mm, and
the core has a hardness difference (Hs−Ho) between a surface hardness Hs and a center hardness Ho of from 15 to 50 in Shore D hardness,
wherein the urethane prepolymer (b-1) has an NCO content (NCO %) of 0.5 mass % or more and less than 10.0 mass %,
wherein the polyisocyanate (b-2) has an NCO content (NCO %) of 10.0 mass % to 30.0 mass %, and
wherein the golf ball has a surface hardness ranging from 57 to 68 in Shore D hardness.
9. The golf ball according to claim 8 , wherein the polyisocyanate mixture (B) has an NCO content (NCO %) of 0.1 mass % to 30.0 mass %.
10. The golf ball according to claim 8 , wherein the urethane prepolymer (b-1) is a bifunctional isocyanate group-terminated urethane prepolymer represented by the following formula (1):
polyisocyanate-(polyol-polyisocyanate)n (1),
wherein the connecting number n is an integer of not less than 1 and not higher than 10.
11. The golf ball according to claim 8 , wherein the cover composition contains the polyisocyanate mixture (B) in an amount of 1 to 50 parts by mass based on 100 parts by mass of the thermoplastic polyurethane (A).
12. The golf ball according to claim 8 , wherein the mixing ratio (100% by mass in total) of the urethane prepolymer (b-1) or the polyisocyanate (b-2) to the thermoplastic resin (b-3) in the polyisocyanate mixture (B) is: (urethane prepolymer (b-1) or polyisocyanate (b-2))/thermoplastic resin (b-3)=(5% to 50% by mass)/(50% to 95% by mass).
13. The golf ball according to claim 8 , wherein the thermoplastic resin (b-3) is at least one selected from the group consisting of a polyester elastomer, an acrylic elastomer, a styrene elastomer, an olefin elastomer, and a vinyl chloride elastomer.