Golf ball having a hollow center
Golf balls including a spherical inner core shell layer formed from a thermoset or thermoplastic composition are provided. The shell layer has an outer surface, an inner surface, and an inner diameter to define a hollow center. A thermoset or thermoplastic outer core layer is formed about the shell layer and optional intermediate layer(s) disposed between the shell layer and the outer core layer. A cover is formed about the outer core layer.
1. A golf ball comprising a core and a cover, the core comprising:
a spherical shell layer enclosing a spherical hollow interior portion, the shell layer being formed from a thermoset rubber composition and having an outer surface and an inner surface; and
an outer core layer formed from a thermoplastic composition;
wherein the hollow interior portion enclosed by the shell layer has a diameter of from 0.5 inches to 1.1 inches, the shell layer has a thickness of from 0.125 inches to 0.4 inches, and the difference in Shore C surface hardness between the outer surface of the shell layer and the inner surface of the shell layer is from 3 Shore C to 25 Shore C;
wherein the volume of the hollow interior portion enclosed by the shell layer is from 5% to 30% of the total golf ball volume; and
wherein the thermoplastic composition of the outer core layer is a highly neutralized polymer composition having a solid sphere Atti compression of 50 or less and comprising:
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;
a non-acid polymer selected from the group consisting of ethylene-alkyl acrylate rubber and ethylene-alkyl methacrylate rubber, present in an amount of from 15 wt % to 50 wt %, based on the combined weight of the acid copolymer and the non-acid polymer;
an organic acid or salt thereof; and
a cation source present in an amount sufficient to neutralize greater than 80% of all acid groups present in the composition.
2. The golf ball of claim 1 , wherein the acid copolymer of ethylene and an α,β-unsaturated carboxylic acid does not include a softening monomer, and the organic acid salt is magnesium oleate present in an amount of 20 parts or greater per 100 parts of acid copolymer and non-acid copolymer combined.
3. The golf ball of claim 1 , wherein the cation source is present in an amount sufficient to neutralize 110% or greater of all acid groups present in the composition.