HOLLOW CORE GOLF BALL HAVING A HARDNESS GRADIENT
A golf ball including a hollow core formed from a spherical inner core shell layer including a stiff thermoplastic composition. The shell layer has an outer surface, an inner surface, and an inner diameter to define a hollow center. Ann outer core layer is disposed about the shell layer and includes a thermoset material. An inner cover layer is disposed about the outer core layer and includes an ionomeric material having a first hardness. An outer cover layer is disposed about the inner cover layer and includes a polyurethane having a second hardness different from the first. The hollow center has a diameter of 0.15 to 1.1 inches, the thermoplastic inner core shell layer has a hardness of 85 Shore C or greater, and the stiff thermoplastic composition has a melt volume flow rate of about 5.0 cm 3 /10 min or less at 230° C./2.16 kg.
1 . A golf ball comprising a hollow core, the golf ball comprising:
a spherical inner core shell layer formed from a stiff thermoplastic composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center;
an outer core layer disposed about the shell layer, the outer core layer comprising a thermoset material;
an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a first hardness; and
an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a second hardness different from the first;
wherein the hollow center has a diameter of about 0.15 to 1.1 inches, the thermoplastic inner core shell layer has a hardness of about 85 Shore C or greater, and the stiff thermoplastic composition has a melt volume flow rate of about 5.0 cm 3 /10 min or less at 230° C./2.16 kg.
2 . The golf ball of claim 1 , wherein the stiff thermoplastic composition has a melt volume flow rate of about 3.0 cm 3 /10 min or less at 230° C./2.16 kg.
3 . The golf ball of claim 2 , wherein the stiff thermoplastic composition has a melt volume flow rate of about 1.0 cm 3 /10 min or less at 230° C./2.16 kg.
4 . The golf ball of claim 1 , wherein the stiff thermoplastic inner shell layer comprises two pre-molded half shells.
5 . The golf ball of claim 1 , wherein the stiff thermoplastic inner shell layer is blow molded, rotationally molded, or gas injection molded.
6 . The golf ball of claim 1 , wherein the stiff thermoplastic composition has a hardness of about 90 Shore C or greater.
7 . The golf ball of claim 1 , wherein the outer core layer comprises a polybutadiene rubber and has a hardness equal to or less than the shell layer hardness.
8 . The golf ball of claim 1 , wherein the outer core layer has a thickness of about 0.025 inches to about 0.115 inches.
9 . The golf ball of claim 1 , wherein the golf ball further comprises an intermediate layer disposed between the outer core layer and the inner cover layer, the intermediate layer comprising a thermoset or thermoplastic material.
10 . The golf ball of claim 1 , wherein the second hardness is greater than the first.
11 . The golf ball of claim 1 , wherein the first hardness is greater than the second.
12 . The golf ball of claim 1 , wherein the golf ball has a first volume and the hollow center has a second volume that is about 2% to 30% of the first volume.
13 . The golf ball of claim 1 , wherein the spherical inner core shell layer has a coefficient of restitution less than about 0.700 when measured at an incoming velocity of 125 ft/s.
14 . The golf ball of claim 1 , wherein the outer core layer has a coefficient of restitution, measured at an incoming velocity of 125 ft/s, higher than the coefficient of restitution, measured at an incoming velocity of 125 ft/s, of the inner core shell layer by 10-50%.
15 . A golf ball comprising a hollow core, the golf ball comprising:
a spherical inner core shell layer formed from a stiff thermoplastic composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center;
an outer core layer disposed about the shell layer, the outer core layer comprising a thermoplastic material;
an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a first hardness; and
an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a second hardness different from the first;
wherein the hollow center has a diameter of about 0.15 to 1.1 inches, the thermoplastic inner core shell layer has a hardness of about 85 Shore C or greater, and the stiff thermoplastic composition has a melt volume flow rate of about 5.0 or less cm 3 /10 min at 230° C./2.16 kg.
16 . The golf ball of claim 15 , wherein the outer core layer comprises a highly-neutralized ionomer and has a hardness equal to or less than the shell layer hardness.
17 . The golf ball of claim 15 , wherein the stiff thermoplastic composition has a melt volume flow rate of about 3.0 or less cm 3 /10 min at 230° C./2.16 kg.
18 . The golf ball of claim 17 , wherein the stiff thermoplastic composition has a melt volume flow rate of about 1.0 or less cm 3 /10 min at 230° C./2.16 kg.
19 . The golf ball of claim 15 , wherein the stiff thermoplastic inner shell layer comprises two pre-molded half shells.
20 . The golf ball of claim 15 , wherein the stiff thermoplastic inner shell layer is blow molded, rotationally molded, or gas injection molded.