Golf balls having foam, hollow, or metal center and plasticized thermoplastic core layer
Multi-layered golf balls containing a dual-core structure are provided. The core structure includes an inner core (center) made from a foam or metal-containing composition, or it has a hollow shell construction, and the outer core layer is made of a thermoplastic composition. Preferably, the thermoplastic composition comprises: a) ethylene acid copolymer, b) plasticizer, and c) cation source. A fatty acid ester such as ethyl oleate is preferably used as the plasticizer. The core assembly preferably has a positive hardness gradient extending across the entire assembly. The core structure and resulting ball have relatively good resiliency at given compressions.
1. A golf ball, comprising a core assembly and cover having at least one layer, the core assembly comprising:
i) a spherical inner core shell layer formed from a thermoset or thermoplastic composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center, the shell layer having a diameter in the range of about 0.100 to about 1.100 inches; and
ii) an outer core layer formed from a plasticized thermoplastic composition comprising;
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;
b) a plasticizer; and
c) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition; and
d) a non-acid polymer, wherein the non-acid polymer is an alkyl acrylate rubber selected from ethylene-alkyl acrylates and ethylene-alkyl methacrylates and is present in an amount of greater than 50 wt. %, based on the combined weight of the acid copolymer and the non-acid polymer;
the outer core layer being disposed about the inner core layer, wherein the difference in Shore C hardness between the outer surface of the shell layer and inner surface of the shell layer is in the range of about 3 to about 25 Shore C.
2. The golf ball of claim 1 , wherein the shell layer is formed from a thermoset rubber composition.
3. The golf ball of claim 1 , wherein the shell layer is formed from a plasticized thermoplastic composition comprising;
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;
b) a plasticizer; and
c) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition.
4. The golf ball of claim 3 , wherein the thermoplastic material comprises an ethylene acid copolymer containing acid groups such that 20% or less of the acid groups are neutralized.
5. The golf ball of claim 3 , wherein the thermoplastic material comprises an ethylene acid copolymer containing acid groups such that 90% or greater of the acid groups are neutralized.
6. The golf ball of claim 3 , wherein the thermoplastic composition comprises about 10 to about 30% by weight plasticizer.
7. The golf ball of claim 3 , wherein the plasticizer is a fatty acid ester.
8. The golf ball of claim 7 , wherein the plasticizer is an alkyl oleate selected from the group consisting of methyl oleate, ethyl oleate, propyl oleate, butyl oleate, and octyl oleate, and mixtures thereof.