Method for forming polyurethane covers for golf balls using foam compositions

1. A golf ball, comprising:

i) a core having at least one layer;

ii) an inner cover layer comprising a non-foamed thermoplastic composition, the inner cover layer being disposed about the core and having a Shore D midpoint hardness in the range of about 55 to about 75; and

iii) an outer cover layer comprising a foamed polyurethane composition disposed about the inner cover layer and having a Shore D outer surface hardness in the range of about 15 to about 60, wherein the outer surface hardness of the outer cover is less than the midpoint hardness of the inner cover layer;

wherein the foamed polyurethane composition further comprises clay particulate, and wherein the clay particulate has a chemically-modified surface, the surface being chemically-modified with a compound selected from the group consisting of ammonium compounds, protonated amines, organic phosphonium ions, and/or aminocarboxylic acids.

2. The golf ball of claim 1 , wherein the non-foamed thermoplastic composition comprises:

a) an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and

b) a cation source present in an amount sufficient to neutralize from about 1 to about 100% of all acid groups present in the composition.

3. The golf ball of claim 1 , wherein the core is single-layered and comprises a polybutadiene rubber composition.

4. The golf ball of claim 1 , wherein the outer cover layer has a thickness in the range of about 0.010 to about 0.050 inches.

5. The golf ball of claim 1 , wherein the outer cover layer has a hardness in the range of about 20 to about 50 Shore D.

6. The golf ball of claim 1 , wherein the outer cover layer has a specific gravity in the range of about 0.90 to about 1.20.

7. The golf ball of claim 6 , wherein the outer cover layer has a specific gravity in the range of about 0.95 to about 1.15.

8. A golf ball formed by a method, the method comprising the steps of:

i) providing a spherical core having at least one layer;

ii) providing an upper and lower mold cavity, each mold cavity having an arcuate inner surface defining an inverted dimple pattern;

iii) introducing a polyurethane composition comprising a foaming agent into at least one mold cavity and loading the core into a mold cavity, wherein the foamed polyurethane composition further comprises clay particulate, and wherein the clay particulate has a chemically-modified surface, the surface being chemically-modified with a compound selected from the group consisting of ammonium compounds, protonated amines, organic phosphonium ions, and/or aminocarboxylic acids;

iv) joining the mold cavities together under compressive force and heating the polyurethane composition so that the foaming agent is activated and foaming of the composition is initiated and a spherical foamed polyurethane cover layer is formed over the core; and

v) detaching the mold cavities and removing the golf ball, the foamed polyurethane cover layer having a specific gravity of from about 0.90 to about 1.20.

9. The golf ball of claim 8 , wherein the foaming agent is water.

10. The golf ball of claim 8 , wherein the foamed polyurethane composition is prepared by adding water to a mixture of polyisocyanate, polyol, and curing agent compounds, the water being added in a sufficient amount to cause the mixture to foam.

11. The golf ball of claim 8 , wherein the polyurethane composition further comprises a catalyst.

12. The golf ball of claim 8 , wherein the outer cover has a Shore D outer surface hardness in the range of about 15 to about 60.

13. The golf ball of claim 8 , wherein the outer cover layer has a Shear Durability Rating of 4.00 or greater.