Golf ball cores having foam center and thermoplastic outer layers

1. A core assembly for a golf ball, comprising:

i) an inner core layer comprising a foamed composition, the inner core layer having a diameter in the range of about 0.100 to about 1.100 inches, a specific gravity (SG inner ), and an outer surface hardness (H inner core surface ) and a center hardness (H inner core center ), the H inner core surface being greater than the H inner core center to provide a positive hardness gradient;

ii) an intermediate core layer comprising a thermoplastic or thermoset material, the intermediate layer being disposed about the inner core and having a thickness in the range of about 0.050 to about 0.400 inches, a specific gravity (SG intermediate ), and an outer surface hardness (H outer surface of IC ) and an inner surface hardness (H inner surface of IC ), the H outer surface of IC being the same or less than the H inner surface of IC to provide a zero or negative hardness gradient; and

iii) an outer core layer comprising a thermoplastic material, the outer core layer being disposed about the intermediate core layer and having a thickness in the range of about 0.100 to about 0.750 inches, a specific gravity (SG outer ), and an outer surface hardness (H outer surface of OC ) and an inner surface hardness (H inner surface of OC ), the H outer surface of OC being greater than the H inner surface of OC to provide a positive hardness gradient,

wherein the SG outer , is greater than the SG inner , and the SG intermediate is greater than the SG inner .

2. The core assembly of claim 1 , wherein the inner core comprises a foamed polyurethane composition.

3. The core assembly of claim 2 , wherein the foamed polyurethane composition is prepared by adding water to a mixture of polyisocyanate, polyol, and curing agent compounds, surfactant and catalyst, the water being added in a sufficient amount to cause the mixture to foam.

4. The core assembly of claim 1 , wherein the intermediate and outer core layer comprises at least one thermoplastic material selected from the group consisting of partially-neutralized ionomers; highly-neutralized ionomers; polyesters; polyamides; polyamide-ethers, polyamide-esters; polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl alcohols; polyester-ethers; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures thereof.

5. The core assembly of claim 4 , wherein the thermoplastic material is a highly-neutralized ionomer composition comprising an E/X/Y-type copolymer, wherein E is ethylene, X is a C 3 -C 8 α,β-ethylenically unsaturated carboxylic acid present in an amount of 10 to 20 wt. %, based on total weight of the copolymer, and Y is an acrylate selected from alkyl acrylates and aryl acrylates present in an amount of 0 to 50 wt. %, based on total weight of the copolymer, wherein greater than 70% of the acid groups present in the composition are neutralized with a metal ion.

6. The core assembly of claim 1 , wherein the intermediate core layer comprises at least one thermoset rubber material selected from the group consisting of polybutadiene, ethylene-propylene rubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene rubber, polyalkenamers, butyl rubber, halobutyl rubber, polystyrene elastomers, copolymers of isobutylene and p-alkylstyrene, halogenated copolymers of isobutylene and p-alkylstyrene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and mixtures thereof.

7. The core assembly of claim 1 , wherein the inner core has a diameter in the range of about 0.100 to about 0.500 inches and specific gravity in the range of about 0.25 to about 0.95 g/cc.

8. The core assembly of claim 1 , wherein the inner core has a diameter in the range of about 0.40 to about 0.80 inches and specific gravity in the range of about 0.30 to about 0.80 g/cc.

9. The core assembly of claim 1 , wherein the H inner core center is in the range of about 10 Shore C or less to about 50 Shore C and the H inner core surface is in the range of about 13 Shore C to about 60 Shore C.

10. The core assembly of claim 1 , wherein the inner surface hardness (H inner surface of IC ) is in the range of about 35 Shore C to about 96 Shore C, and the outer surface hardness (H outer surface of IC ) is in the range of about 32 Shore C to and about 93 Shore C.

11. The core assembly of claim 1 , wherein the outer core layer has a thickness in the range of about 0.150 to about 0.650 inches and specific gravity in the range of about 0.90 to about 2.90 g/cc.

12. The core assembly of claim 1 , wherein the H inner surface of OC is in the range of about 40 Shore C to about 87 Shore C and the H outer surface of OC is in the range of about 43 Shore C to about 90 Shore C.

13. The core assembly of claim 1 , wherein the center hardness of the inner core (H inner core center ) is in the range of about 10 Shore C to about 60 Shore C and the outer surface hardness of the outer core layer (H outer surface of OC ) is in the range of about 40 Shore C to about 90 Shore C to provide a positive hardness gradient across the core assembly.

14. The core assembly of claim 13 , wherein the center hardness of the inner core (H inner core center ) is in the range of about 13 Shore C to about 55 Shore C and the outer surface hardness of the outer core layer (H outer surface of OC ) is in the range of about 43 Shore C to about 87 Shore C to provide a positive hardness gradient across the core assembly.