Dual core golf ball having negative-hardness-gradient thermoplastic inner core and shallow positive-hardness-gradient thermoset outer core layer

Abstract

A golf ball comprising a thermoplastic inner core layer that has a geometric center hardness greater than its surface hardness to define a 'negative' hardness gradient. An outer core layer is disposed about the inner core and is formed from a substantially homogenous thermoset composition, typically rubber, and has an inner surface hardness less than its outer surface hardness to define a 'positive' hardness gradient. An inner cover layer is disposed about the outer core layer and an outer cover layer is disposed about the inner cover layer. The “negative” hardness gradient of the inner core is typically −1 to −5 Shore C and the “positive” hardness gradient of the core layer is less than 25 Shore C points. The difference between the inner core surface hardness and the outer core inner surface hardness, Δh, should be less than 25 Shore C points.