Cores made from thermoset and plasticized thermoplastic materials for golf balls
Multi-layered golf balls containing a two or three-layered core assembly are provided. In one embodiment, the core assembly includes an inner core (center) comprising a thermoset composition, an intermediate core layer; and surrounding outer core layer. 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. A second thermoset composition such as polybutadiene rubber may be used to form the outer core layer. The core layers have different hardness levels. In another embodiment, a two-layered core structure is provided. For example, the inner core and/or outer core layer may be made of the plasticized thermoplastic composition. The core structure and resulting ball have relatively good resiliency at given compressions.
1. A core assembly for a golf ball, comprising:
i) an inner core layer comprising a first thermoplastic material, the inner core having 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 outer core layer comprising a second thermoplastic material, the outer core layer being disposed about the inner core layer and having an outer surface hardness (H outer surface of OC ) and a midpoint hardness (H midpoint of OC ), the H outer surface of OC being greater than the H midpoint of OC to provide a positive hardness gradient, the second thermoplastic material comprising:
a) an add 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 material; and
iii) an intermediate core layer comprising a thermoset rubber material, the intermediate layer being disposed between the inner core and outer core and having an outer surface hardness (H outer surface of Inter Core ) and a midpoint hardness (H midpoint of Inter Core ), the H outer surface of the Inter Core being greater than the H midpoint of the Inter Core to provide a positive hardness gradient;
wherein the center hardness of the inner core (H inner core surface ) is in the range of about 10 Shore C to about 70 Shore C and the outer surface hardness of the outer core layer (H outer surface of OC ) is in the range of about 20 Shore C to about 95 Shore C to provide a positive hardness gradient across the core assembly.
2. The core assembly of claim 1 , wherein the first thermoplastic material 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; b) plasticizer; and c) cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the material.
3. The core assembly, of claim 1 , wherein the first thermoplastic material is selected from the group consisting of 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.