Negative hardness gradient cores made of polyalkenamer rubber for golf balls
View Patent ↗Golf balls having cores with negative hardness gradients are provided. The cores are made of polyalkenamer rubber compositions that may further include other rubbers such as, for example, polybutadiene, polyisoprene, ethylene propylene rubber, ethylene propylene diene rubber, and styrene-butadiene rubber. In one version, a solid, single core having an outer surface and center is provided, wherein the outer surface has a hardness substantially the same or lower than the hardness of the center to define a zero or negative hardness gradient. Dual-cores having inner and outer cores can be made, wherein the inner core has a negative hardness gradient and the outer core has a positive or negative hardness gradient. The rubber composition helps improve resiliency of the core and provides the ball with a comfortable and soft feel.
1. A golf ball, comprising:
a dual-core comprising an inner core and outer core layer, wherein the outer core layer surrounds the inner core, the inner core having a first outer surface and a geometric center, the inner core being formed from a first rubber composition, the first rubber composition comprising a cycloalkene rubber having a trans-content of 55% or greater and a melting point of 30° C. or greater in an amount of at least 50 weight percent, wherein the first outer surface and geometric center each has a hardness, the hardness of the first outer surface being the same or less than the hardness of the geometric center to define a zero or negative hardness gradient;
the outer core layer having a second outer surface and an inner surface, the outer core layer being formed from a second rubber composition, wherein the second outer surface and inner surface each has a hardness, the hardness of the second outer surface being greater than the hardness of the geometric center to define a positive hardness gradient of at least 10 Shore C units; and
a cover layer surrounding the outer core layer.
2. The golf ball of claim 1 , wherein the inner core layer has a zero hardness gradient.
3. The golf ball of claim 1 , wherein the inner core layer has a negative hardness gradient in the range of −1 to −20 Shore C units.
4. The golf ball of claim 1 , wherein the negative hardness gradient is in the range of −6 to −15 Shore C units.
5. The golf ball of claim 1 , wherein the hardness of the geometric center is in the range of 50 to 84 Shore C units and the hardness of the first outer surface is in the range of 49 to 83 Shore C units.
6. The golf ball of claim 1 , wherein the overall diameter of the dual-core is from 1.51 to 1.64 inches.
7. The golf ball of claim 1 , wherein the hardness of the inner surface of the outer core layer is in the range of 50 to 84 Shore C units.
8. The golf ball of claim 1 , wherein the hardness of the inner surface of the outer core layer is in the range of 55 to 82 Shore C units.
9. The golf ball of claim 1 , wherein the hardness of the second outer surface is at least 60 Shore C units.
10. The golf ball of claim 1 , wherein the hardness of the second outer surface is in the range of 65 to 95 Shore C units.
11. The golf ball of claim 1 , wherein the cover layer comprises an inner cover layer and an outer cover layer.
12. A golf ball, comprising:
a dual-core comprising an inner core and outer core layer, wherein the outer core layer surrounds the inner core, the inner core having a first outer surface and a geometric center, the inner core being formed from a first rubber composition, the first rubber composition comprising a cycloalkene rubber having a trans-content of 55% or greater and a melting point of 30° C. or greater in an amount of at least 50 weight percent, wherein the first outer surface and geometric center each has a hardness, the hardness of the first outer surface being the same or less than the hardness of the geometric center to define a first zero or negative hardness gradient;
the outer core layer having a second outer surface and an inner surface, the outer core layer being formed from a second rubber composition, wherein the second outer surface and inner surface each has a hardness, the hardness of the second outer surface being in the range of 50 to 85 Shore C units and the hardness of the inner surface being in the range of 51 to 86 Shore C units, the hardness of the second outer surface being the same or less than the hardness of the inner surface to define a second zero or negative hardness gradient; and
a cover layer surrounding the outer core layer.
13. The golf ball of claim 12 , wherein at least one of the inner core layer and outer core layer has a negative hardness gradient in the range of −1 to −20 Shore C units.
14. The golf ball of claim 12 , wherein the hardness of the second outer surface is 62 to 72 Shore C units and the hardness of the inner surface of the outer core layer is 67 to 76 Shore C units.
15. The golf ball of claim 12 , wherein the cover layer comprises an inner cover layer and an outer cover layer.