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

A golf ball comprising:

• an inner core layer consisting of a thermoplastic material and having a geometric center hardness greater than a surface hardness to define a negative hardness gradient between −1 Shore C and −5 Shore C;
• an outer core layer disposed about the inner core, the outer core being formed from a substantially homogenous thermoset composition comprising a diene rubber and having an inner surface hardness less than an outer surface hardness to define a substantially positive hardness gradient of less than 25 Shore C;
• a cover layer disposed outer core layer, the cover layer comprising an inner cover layer comprising an ionomer and an outer cover layer comprising a castable polyurethane or polyurea material,
• wherein a difference between the inner core surface hardness and the outer core inner surface hardness, Δh, is less than 20 Shore C.

A golf ball comprising:

• an inner core layer consisting of a thermoplastic material and having a geometric center hardness greater than a surface hardness to define a negative hardness gradient between −1 Shore C and −5 Shore C, the center hardness being about 90 Shore C to about 100 Shore C and the surface hardness being about 85 Shore C to about 95 Shore C;
• an outer core layer disposed about the inner core, the outer core being foamed from a substantially homogenous thermoset composition comprising a diene rubber and having an inner surface hardness less than an outer surface hardness to define a positive hardness gradient of less than 25 Shore C, the inner surface being about 65 Shore C to about 75 Shore C and the surface being about 80 Shore C to about 90 Shore C;
• a cover layer disposed outer core layer, the cover layer comprising an inner cover layer comprising an ionomer and an outer cover layer comprising a castable polyurethane or polyurea material,
• wherein a difference between the inner core surface hardness and the outer core inner surface hardness, Δh, is less than 20 Shore C.