Golf balls having multi-layered core with thermoplastic outer layer
Multi-piece golf balls containing a multi-layered core structure are provided. The core structure includes a small, heavy inner core (center) having a relatively high specific gravity, an intermediate core layer, and a surrounding outer core layer. The layers of the core structure may have different hardness gradients. In one preferred embodiment, each core layer has a positive hardness gradient. The center of the core comprises a metal material such as copper, steel, brass, tungsten, titanium, aluminum, and alloys thereof. The intermediate core layer is preferably formed from a thermoset composition such as polybutadiene rubber, and the outer core layer is preferably formed from a thermoplastic composition such as an ethylene acid copolymer. The resulting ball has high resiliency and good spin control.
1. A golf ball, comprising:
a multi-layered core including i) an inner core comprising a metal material, the the inner core having a diameter in the range of about 0.100 to about 1.100 inches, a specific gravity (SG inner ), and an outer surface hardness (H center surface ) and a center hardness (H center material ), the H center surface being the same or less than the H center material to provide a zero or negative hardness gradient;
ii) an intermediate core layer comprising a thermoset material, the intermediate layer being disposed about the inner core and having a thickness in the range of about 0.050 to about 0.400 inches, and an outer surface hardness (H outer surface of IC ) and an inner surface hardness (H inner surface of IC ), the H outer surface of IC being the same or less than the H inner surface of IC to provide a zero or negative hardness gradient; and
iii) an outer core layer comprising a thermoplastic material, the outer core layer being disposed about the inner core and having a thickness in the range of about 0.200 to about 0.750 inches, a specific gravity (SG outer ), and an outer surface hardness ((H outer surface of OC ) of 42 to 92 Shore C and an inner surface hardness (H inner surface of OC ) of 40 to 89 Shore C, the H outer surface of OC being greater than the H inner surface of OC to provide a positive hardness gradient, wherein the SG inner is greater than the SG outer , and the volume of the outer core layer is greater than the volume of each of the inner core and intermediate core layers; and
a cover having at least one layer disposed about the multi-layered core.
2. The golf ball of claim 1 , wherein the metal material of the inner core is a metal selected from the group consisting of copper, steel, brass, tungsten, titanium, aluminum, magnesium, molybdenum, cobalt, nickel, iron, tin, zinc, barium, bismuth, bronze, silver, gold, and platinum, and alloys and combinations thereof.
3. The golf ball of claim 1 , wherein the inner core has a diameter in the range of about 0.100 to about 0.500 inches and specific gravity in the range of about 1.60 to about 6.25 g/cc.
4. The golf ball of claim 1 , wherein the outer core layer has a thickness in the range of about 0.250 to about 0.750 inches and specific gravity in the range of about 0.60 to about 2.90 g/cc.