Golf ball core with soft outer transition volume and negative hardness gradient
A golf ball includes a unitary core having an outer surface, a geometric center, and a soft transition region adjacent to the outer surface, and is formed from a substantially homogenous composition. The ball further includes an outer cover layer. The soft transition region has a thickness of up to 4 mm, has about 8 to 20 percent trans-polybutadiene isomer, and has a negative hardness gradient of up to 15 Shore C. The core has an overall negative hardness gradient of up to 20 Shore C and has a gradient quotient, GQ, defined by the equation: G + T 10 × COR ≤ 7 where G is the overall negative hardness gradient in Shore C, T is the percent of trans-polybutadiene isomer at the core outer surface, and COR is the coefficient of restitution measured at an incoming velocity of 125 ft/s.
1. A golf ball comprising:
a core comprising an inner core layer and an outer core layer, the inner core layer having a first outer surface and a geometric center, and the outer core layer having an inner surface, a second outer surface, and a soft transition region adjacent to the second outer surface; and
a cover layer;
wherein the soft transition region has a thickness of about 0.001 to 0.1 inches, comprises about 8 to 20 percent trans-polybutadiene isomer, and has a negative hardness gradient of up to 15 Shore C, and wherein the second outer surface has a hardness less than a geometric center hardness to define a negative hardness gradient across the core of up to 20 Shore C;
and wherein the core has a gradient quotient, GQ, defined by the equation:
G
+
T
10
×
COR
≤
7
where G is the overall negative hardness gradient, T is the percent of trans-polybutadiene isomer at the second outer surface, and COR is the coefficient of restitution measured at an incoming velocity of 125 ft/s.
2. The golf ball of claim 1 , wherein the transition region comprises about 9 to about 15 percent trans-polybutadiene isomer.
3. The golf ball of claim 1 , wherein the geometric center comprises about 5 to 15 percent trans-polybutadiene isomer.
4. The golf ball of claim 1 , wherein the second outer surface comprises about 10 to 30 percent trans-polybutadiene isomer.
5. The golf ball of claim 1 , wherein the core has a COR of about 0.800 or greater.
6. The golf ball of claim 5 , wherein the COR is about 0.810 or greater.
7. The golf ball of claim 1 , wherein the gradient quotient, GQ, is about 6 or less.
8. The golf ball of claim 7 , wherein the gradient quotient, GQ, is about 5 or less.
9. The golf ball of claim 1 , wherein the golf ball comprises an inner cover layer disposed between the cover layer and the core, the inner cover layer comprising an ionomer.
10. The golf ball of claim 1 , wherein the second outer surface hardness is less than a hardness at the inner surface to define a negative hardness gradient across the outer core layer.
11. The golf ball of claim 10 , wherein the negative hardness gradient is about 1 to about 5 Shore C.
12. The golf ball of claim 10 , wherein the negative hardness gradient is about 6 to about 20 Shore C.