Patent ID: 8512165

Claim:
A multi-piece solid golf ball comprising a solid core encased by a cover of one or more layer, which solid core has an inner core layer and an outer core layer, wherein the inner core layer is formed primarily of a thermoplastic resin, has a diameter of from 3 to 20 mm, and has a cross-sectional hardness difference of within ±5 between any two points on a cross-section obtained by cutting the inner core layer in half; the outer core layer is formed of a rubber composition made primarily of polybutadiene rubber; the core of the inner core layer and the outer core layer combined has a diameter of from 35 to 42 mm; and, letting (b) represent the JIS-C cross-sectional hardness of the inner core layer 1 mm inside a boundary between the inner core layer and the outer core layer, (c) represent the JIS-C cross-sectional hardness of the outer core layer 1 mm outside the boundary, and (d) represent the JIS-C surface hardness of the outer core layer, the value (b) is in a range of from 60 to 90, the value (c)-(b) is in a range of from −22 to -3 and the value (d)-(b) is within ±10, and the surface hardness (d) is higher than the cross-sectional hardness (c), and wherein the outer core layer rubber composition includes an organic peroxide having a half-life at 155° C. of from 5 to 120 seconds in an amount of from 0.3 to 4 parts by weight per 100 parts by weight of the base rubber.