Negative hardness gradient inner core for dual core golf ball
View Patent ↗A golf ball includes an inner core having a first outer surface and a center formed from a homogenous composition such that the inner core has a hardness of 40 to 80 Shore C; an outer core layer disposed about the inner core having a second outer surface and an inner surface, formed from a homogenous composition such that the outer core layer has a hardness of 60 to 90 Shore C; and a cover layer including at least two layers. The center, first and second outer surfaces, and inner surface each have a hardness, the first outer surface hardness being lower than the center hardness to define a negative hardness gradient, and the second outer surface hardness being greater than the inner surface hardness by 10 to 20 Shore C to define a positive hardness gradient.
1. A golf ball comprising:
a dual core comprising:
an inner core having a first outer surface and a geometric center and being formed from a first substantially homogenous composition such that the inner core has a hardness of about 40 Shore C to about 80 Shore C;
an outer core layer disposed about the inner core having a second outer surface and an inner surface and being formed from a second substantially homogenous composition, different from the first, such that the outer core layer has a hardness of about 60 Shore C to about 90 Shore C; and
a cover layer comprising at least two layers disposed about the outer core layer;
wherein the geometric center, the first and second outer surfaces, and the inner surface each have a hardness, the hardness of the first outer surface being lower than the hardness of the geometric center to define a negative hardness gradient, and the hardness of the second outer surface being greater than the hardness of the inner surface by about 10 Shore C to about 20 Shore C to define a positive hardness gradient.
2. The golf ball of claim 1 , wherein the outer core layer has a positive gradient of about 12 Shore C to about 18 Shore C.
3. The golf ball of claim 1 , wherein the hardness of the second outer surface is 65 Shore C to 86 Shore C.
4. The golf ball of claim 1 , wherein the negative hardness gradient is at least about 10 Shore C.
5. The golf ball of claim 1 , wherein the negative hardness gradient is at least about 12 Shore C points lower than a hardest point in the core.
6. The golf ball of claim 1 , wherein the cover layer comprises a castable polyurea or a castable polyurethane.
7. The golf ball of claim 1 , wherein the inner core has an outer diameter of about 0.75 inches to about 1.4 inches and the outer core layer has an outer diameter of about 1.5 inches to about 1.59 inches.
8. The golf ball of claim 1 , wherein the cover layer comprises an inner cover layer and an outer cover layer.
9. The golf ball of claim 8 , wherein the inner cover layer comprises a high-acid ionomer and the outer cover layer comprises a castable polyurea or a castable polyurethane.
10. The golf ball of claim 9 , wherein the inner cover layer further comprises a metallocene-grafted polymer.
11. The golf ball of claim 1 , wherein the inner core comprises a diene rubber and, optionally, a soft and fast agent.
12. The golf ball of claim 1 , wherein the outer core layer comprises a diene rubber and, optionally, a soft and fast agent.