DUAL-CORE COMPRISING ZERO GRADIENT CENTER AND POSITIVE GRADIENT OUTER CORE LAYER
A golf ball including an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition, and an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface. An inner cover layer is formed over the core and includes an ionomeric material. An outer cover layer is formed over the inner cover layer and includes a castable polyurea or a castable polyurethane. The first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 18 Shore C greater than the geometric center hardness to define a positive gradient outer core layer and a shallow positive hardness gradient core.
1 . A golf ball comprising
an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;
an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface;
an inner cover layer disposed about the core, the inner cover comprising an ionomeric material and having a material hardness of about 55 Shore D or greater; and
an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a material hardness of 20 Shore D to 70 Shore D;
wherein the first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 43 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.
2 . The golf ball of claim 1 , wherein the inner core has an outer diameter of about 0.5 to about 1.40 inches.
3 . The golf ball of claim 2 , wherein the inner core has an outer diameter of about 0.8 to about 1.30 inches.
4 . The golf ball of claim 1 , wherein the geometric center hardness is about 55 Shore C to about 82 Shore C.
5 . The golf ball of claim 4 , wherein the geometric center hardness is about 60 Shore C to about 80 Shore C.
6 . The golf ball of claim 1 , wherein the second outer surface hardness is about 84 Shore C to about 98 Shore C.
7 . The golf ball of claim 6 , wherein the second outer surface hardness is about 84 Shore C to about 95 Shore C.
8 . The golf ball of claim 1 , wherein the second outer surface has a hardness of about 2 to 43 Shore C points greater than the geometric center hardness.
9 . The golf ball of claim 1 , wherein the second outer surface has a hardness of about 3 to 37 Shore C points greater than the geometric center hardness.
10 . The golf ball of claim 1 , wherein the first substantially homogenous rubber composition comprises an antioxidant-to-initiator ratio of about 0.4 or greater.
11 . The golf ball of claim 1 , wherein the ionomeric material comprises a Na-, Li-, or Zn-ionomer having an acid content of about 11 wt % to about 20 wt %.
12 . The golf ball of claim 1 , wherein the ionomeric material comprises an ionomer having an acid content of about 16 wt % or greater and a maleic-anhydride grafted metallocene-catalyzed polyolefin.
13 . A golf ball comprising
an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;
an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface;
an inner cover layer disposed about the core, the inner cover comprising an ionomeric material and having a material hardness of about 55 Shore D or greater; and
an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a material hardness of 20 Shore D to 70 Shore D;
wherein the first outer surface has a hardness of about 16 to 34 Shore C points less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of about 3 to 37 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.
14 . The golf ball of claim 13 , wherein the first outer surface has a hardness of about 20 to 27 Shore C points less than a hardness at the geometric center.
15 . A golf ball consisting of
an inner core having a geometric center and a first outer surface, the inner core being formed from a first substantially homogenous rubber composition;
an outer core layer formed from a second substantially homogenous rubber composition, the outer core layer having a second outer surface; and
an outer cover layer disposed about the core, the outer cover having a material hardness of 50 Shore D to 70 Shore D;
wherein the first outer surface has a hardness of up to about 20 Shore C less than a hardness at the geometric center to define a negative hardness gradient inner core and the second outer surface has a hardness of up to 43 Shore C points greater than the geometric center hardness to define a positive hardness gradient core.