Golf balls having dual cores made of polybutadiene rubber/ionomer blends

1. A multi-piece golf ball, comprising:

a dual-core comprising an inner core and outer core layer, the inner core having an outer surface and geometric center and the outer core layer having an outer surface and inner surface; the outer core being formed from a first rubber composition comprising polybutadiene rubber and ionomer resin, wherein the center of the inner core and surface of the outer core layer each has a hardness, and the center hardness of the inner core is in the range of about 52 to about 98 Shore C units and the surface hardness of the outer core is in the range of about 50 to 96 Shore C units, and wherein the center hardness of the inner core is greater than the surface hardness of the outer core layer; and

a cover disposed about the outer core layer.

2. The golf ball of claim 1 , wherein the specific gravity of the inner core is less than or equal to the specific gravity of the outer core layer.

3. The golf ball of claim 1 , wherein the inner core has a specific gravity in the range of about 0.50 to about 1.20 g/cc.

4. The golf ball of claim 1 , wherein the inner core has a specific gravity in the range of about 0.80 to about 1.18.

5. The golf ball of claim 1 , wherein the inner core has a specific gravity in the range of about 0.90 to about 1.13 g/cc, and the outer core has a specific gravity in the range of about 1.00 to about 1.18 g/cc.

6. The golf ball of claim 1 , wherein the center hardness of the inner core and surface hardness of the outer core are each greater than 80 Shore C units.

7. The golf ball of claim 6 , wherein the center hardness of the inner core is in the range of about 82 to about 96 Shore C units and the surface hardness of the outer core is in the range of about 81 to about 95 Shore C units.

8. The golf ball of claim 1 , wherein the ionomer resin contains greater than 5 weight percent acid groups.

9. The golf ball of claim 1 , wherein the ionomer resin contains greater than 11 weight percent acid groups.

10. The golf ball of claim 8 or 9 , wherein the acid groups of the ionomer resin are neutralized greater than 70%.

11. The golf ball of claim 8 or 9 , wherein the acid groups of the ionomer resin are neutralized greater than 90%.

12. The golf ball of claim 1 , wherein the ionomer resin is E/X/Y copolymer, wherein E is ethylene; X is a C 3 to C 8 α,β-ethylenically unsaturated mono- or dicarboxylic acid; and Y is a softening monomer.

13. The golf hall of claim 12 , wherein the copolymer is selected from the group consisting of ethylene/(meth)acrylic acid/n-butyl acrylate; ethylene/(meth)acrylic acid/ethyl acrylate; ethylene/(meth)acrylic acid/methyl acrylate; ethylene/(meth)acrylic acid/n-butyl acrylate; and ethylene/(meth)acrylic acid/isobutyl acrylate copolymers.

14. The golf ball of claim 1 , wherein the ionomer composition further comprises a fatty acid or salt thereof.

15. The golf ball of claim 1 , wherein the first rubber composition further comprises a polymer selected from the group consisting of polyesters; polyamides; polyamide-ethers, polyamide-esters; polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes and polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl alcohols; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures thereof.

16. The golf ball of claim 1 , wherein the inner core layer is formed from a second rubber composition comprising polybutadiene rubber.

17. The golf ball of claim 1 , wherein the cover is formed from a composition comprising a polymer selected from the group consisting of polyesters; polyamides; polyamide-ethers, polyamide-esters; polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes and polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl alcohols; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures thereof.

18. The golf ball of claim 1 , wherein the cover comprises an inner cover layer and outer cover layer.