Multi-layer core golf ball having opposing hardness gradient with steep gradient outer core layer

Abstract

A golf ball comprising an inner core formed from a substantially homogenous composition such that the geometric center hardness is about 56 to 80 Shore C. An outer core layer has an outer surface having hardness of about 85 to 98 Shore C and an inner surface hardness of about 68 to 78 Shore C and being formed from a second homogenous rubber composition. A cover layer is formed over the outer core layer. The hardness of the second outer surface is greater than the hardness of the inner surface to define a positive hardness gradient of about 7 to 30 Shore C, and the hardness of the first outer surface is lower than the hardness of the geometric center to define a negative hardness gradient of about 1 to 15 Shore C.

What is claimed is: 
     
         1 . A golf ball comprising:
 an inner core layer having an outer diameter of about 0.50 to 1.55 inches, a first outer surface, and a geometric center, the inner core layer comprising a first substantially homogenous composition such that the geometric center has a hardness of about 51 to 76 Shore C;   an outer core layer disposed about the inner core layer, the outer core layer having an outer diameter of about 1.30 to 1.62 inches, a second outer surface having a hardness of about 85 to 98 Shore C, and comprising a second substantially homogenous rubber composition; and   a cover layer disposed about the outer core layer;   wherein the geometric center and the first and second outer surfaces each have 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 about 7 to 30 Shore C.   
     
     
         2 . The golf ball of  claim 1 , wherein the inner core has an outer diameter of about 0.75 inches to 1.50 inches. 
     
     
         3 . The golf ball of  claim 2 , wherein the inner core has an outer diameter of about 1.00 inch to 1.40 inches. 
     
     
         4 . The golf ball of  claim 1 , wherein the outer core layer has an outer diameter of about 1.40 inches to 1.60 inches. 
     
     
         5 . The golf ball of  claim 4 , wherein the outer core layer has an outer diameter of about 1.50 inches to 1.59 inches 
     
     
         6 . The golf ball of  claim 1 , wherein the hardness of the geometric center is about 68 Shore C to 76 Shore C. 
     
     
         7 . The golf ball of  claim 1 , wherein the cover layer comprises an inner cover layer and an outer cover layer. 
     
     
         8 . The golf ball of  claim 7 , wherein the inner cover layer comprises a high acid ionomer comprising a copolymer of ethylene and methacrylic or acrylic acid and having an acid content of at least 16 to about 25 weight percent. 
     
     
         9 . The golf ball of  claim 1 , wherein the cover layer comprises a thermoset or thermoplastic polyurethane material. 
     
     
         10 . The golf ball of  claim 1 , wherein the first composition comprises an antioxidant in an amount of about 0.1 pph to 1.0 pph.