Golf ball cores based on polyalkenamer rubber having positive hardness gradients

Abstract

Golf balls having a core comprising a polyalkenamer rubber composition are provided. The rubber composition may further include other rubbers such as, for example, polybutadiene, polyisoprene, ethylene propylene rubber, ethylene propylene diene rubber, and styrene-butadiene rubber. The rubber composition helps improve resiliency of the core and provides the ball with a comfortable and soft feel. In one version, a solid, single core having an outer surface and geometric center is provided, wherein the outer surface has a hardness greater than the hardness of the geometric center to define a positive hardness gradient of at least 10 Shore C. In a second version, a dual-core having an inner core and surrounding outer core layer is provided. The inner core has a positive hardness gradient, while the outer core has a zero; negative; or positive hardness gradient.

We claim: 
     
         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 greater than the hardness of the geometric center to define a positive hardness gradient of at least 10 Shore C units;   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 zero or negative hardness gradient; and   a cover layer surrounding the outer core layer.   
     
     
         2 . The golf ball of  claim 1 , wherein the cycloalkene rubber has a trans-content of 75% or greater and a melting point of 50° C. or greater. 
     
     
         3 . The golf ball of  claim 1 , wherein the rubber composition comprises the cycloalkene rubber in an amount in the range of about 60 to about 100 weight percent based on weight of polymer. 
     
     
         4 . The golf ball of  claim 1 , wherein the rubber composition comprises peroxide in an amount of 2.5 phr or greater based on weight of the cycloalkene rubber. 
     
     
         5 . The golf ball of  claim 1 , wherein the overall diameter of the dual-core is from 1.51 to 1.59 inches. 
     
     
         6 . The golf ball of  claim 1 , wherein the hardness of the second outer surface is 65 to 76 Shore C units and the hardness of the inner surface is 67 to 82 Shore C units. 
     
     
         7 . The golf ball of  claim 1 , wherein the outer core layer has a zero hardness gradient. 
     
     
         8 . The golf ball of  claim 1 , wherein the outer core layer has a negative hardness gradient in the range of − 1  to −20 Shore C units. 
     
     
         9 . The golf ball of  claim 8 , wherein the negative hardness gradient is in the range of −6 to −15 Shore C units. 
     
     
         10 . The golf ball of  claim 8 , wherein the negative hardness gradient is in the range of −8 to −12 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 . The golf ball of  claim 11 , wherein the outer cover layer has a material hardness less than the inner cover layer. 
     
     
         13 . 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 greater than the hardness of the geometric center to define a positive hardness gradient of at least 10 Shore C units;   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 outer core layer and inner surface each has a hardness, the hardness of the second outer surface being in the range of 51 to 86 Shore C units and the hardness of the inner surface being in the range of 50 to 85 Shore C units, the hardness of the second outer surface being greater than the hardness of the inner surface to define a second positive hardness gradient; and   a cover layer surrounding the outer core layer.   
     
     
         14 . The golf ball of  claim 13 , wherein the cycloalkene rubber has a trans-content of 75% or greater and a melting point of 50° C. or greater. 
     
     
         15 . The golf ball of  claim 13 , wherein the rubber composition comprises the cycloalkene rubber in an amount in the range of about 60 to about 100 weight percent based on weight of polymer. 
     
     
         16 . The golf ball of  claim 13 , wherein the rubber composition comprises peroxide in an amount of 2.5 phr or greater based on weight of the cycloalkene rubber. 
     
     
         17 . The golf ball of  claim 13 , wherein the cover layer comprises an inner cover layer and an outer cover layer.