A golf ball is provided which suppresses twisting due to external forces while maintaining sufficient deflection at the time of impact, reduces the spin rate without lowering ball rebound, and is thus able to effectively increase the distance traveled by the ball, particularly on shots with a driver. In the golf ball, which includes a core and a cover, the core has a core body made of a first polybutadiene rubber and having a surface with a plurality of groves or holes thereon, which grooves or holes are filled with a second polybutadiene rubber of a differing composition from the first polybutadiene rubber. The polybutadiene rubber-filled groove portions or hole portions have a higher surface hardness than the core body.

A golf ball including 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 thermoplastic material and has an inner surface hardness substantially 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.

An object of the present invention is to provide a golf ball traveling a great distance on driver shots and on iron shots. The present invention provides a golf ball comprising a spherical core including an inner layer and an outer layer, and a cover, wherein a difference (H.sub.X+1−H.sub.X−1) between a hardness (H.sub.X+1) at a point outwardly away in a radial direction from a boundary between the inner layer and the outer layer of the spherical core by 1 mm and a hardness (H.sub.X−1) at a point inwardly away in the radial direction from the boundary between the inner layer and the outer layer of the spherical core by 1 mm is 0 or more in Shore C hardness, a surface hardness (H.sub.X+Y) of the spherical core is more than 65 in Shore C hardness, an angle α of a hardness gradient of the inner layer is 0° or more, a difference (α−β) between the angle α and an angle β of a hardness gradient of the outer layer is 0° or more, a thickness of the cover is 3 mm or less, a difference (Hc−H.sub.x+y) between a hardness (Hc) of the cover and the surface hardness (H.sub.X+Y) of the spherical core is 2 or more in Shore C hardness, and the cover has a highest hardness among the constituent members of the golf ball.

Multi-piece golf balls containing a multi-layered core structure are provided. The core structure includes a small, heavy inner core (center) having a relatively high specific gravity, an intermediate core layer, and a surrounding outer core layer. The layers of the core structure may have different hardness gradients. In one preferred embodiment, each core layer has a positive hardness gradient. The center of the core comprises a metal material such as copper, steel, brass, tungsten, titanium, aluminum, and alloys thereof. The intermediate core layer is preferably formed from a first thermoset composition such as polybutadiene rubber, and the outer core layer is preferably formed from a second thermoset composition. The resulting ball has high resiliency and good spin control.

A golf ball includes a core, a mid layer, and a cover. The core includes an inner core, a mid core, and an outer core. The mid layer includes an inner mid layer and an outer mid layer. A hardness H(C) is equal to or greater than a hardness H(B). A hardness H(E) is equal to or greater than a hardness H(D). An angle α is calculated by (Formula 1). An angle β is calculated by (Formula 2). The angle α is 0° or greater. A difference (α−β) is 0° or greater. A hardness Hm2 of the outer mid layer is greater than a hardness Hm1 of the inner mid layer.
α=(180°/π)*atan [{H(D)−H(C)}/Y]  (Formula 1)
β=(180°/π)*atan [{H(F)−H(E)}/Z]  (Formula 2)

Multi-piece golf balls having a multi-layered solid core and multi-layered cover are provided.

Golf balls comprising a multi-layer core and a cover are disclosed. The multi-layer core comprises a zero or positive hardness gradient center that is hard relative to an intermediate core layer.

A golf ball comprising a core comprising an inner core center and an outer core layer disposed over the inner core center. The inner core center has a deflection of greater than 0.210 inch under a load of 100 kilograms, and the entire the core has a deflection ranging from 0.130 inch to 0.105 inch under a load of 100 kilograms. A mantle layer is disposed over the core and a cover is disposed over the mantle.

Golf ball incorporating core consisting of: a solid inner core layer consisting of a peroxide cured polybutadiene rubber composition and having a diameter of 1.25 inches or less and a center Shore C hardness (H.sub.center) of 50 or less; and an outer core layer consisting of a thermoplastic composition Tc as defined herein and having a thickness of 0.400 inches or greater and an outer surface Shore C hardness (H.sub.outer surface) of 70 or greater, wherein H.sub.outer surface>H.sub.center, and H.sub.outer surface−H.sub.center≧40. The peroxide cured polybutadiene rubber composition may comprise a reaction product of polybutadiene and a sufficient amount of peroxide to form the solid inner layer having the center Shore C hardness (H.sub.center) of 50 or less. In one embodiment, 100 phr polybutadiene and from about 0.05 phr to about 3.0 phr of peroxide are mixed with at least one of 5 phr or less of a metal oxide; 5 phr or less of a metal coagent; or 5 phr or less of a metal carbonate. Alternatively, the solid inner core layer has a diameter of 1.10 inches or less or less than 1.0 inches.

Multi-piece golf balls containing a multi-layered core structure having layers with different hardness gradients and specific gravities are provided. The core structure includes a small, heavy inner core (center) having a relatively high specific gravity with metal material preferably dispersed in a first thermoset composition. The intermediate core layer is preferably formed from a thermoplastic composition such as an ethylene acid copolymer ionomer resin; and the outer core layer is preferably formed from a second thermoset composition. The resulting ball has high resiliency and good spin control.