An object of the present invention is to provide a golf ball having excellent durability and good shot feeling. The present invention provides a golf ball comprising a core, wherein a difference (crosslinking density at surface of core-crosslinking density at center of core) between a crosslinking density at a surface of the core and a crosslinking density at a center of the core is more than 1.0×10.sup.2 mol/m.sup.3 and less than 9.0×10.sup.2 mol/m.sup.3, and a hardness difference (Hs−Ho) between Hs and Ho is 13.0 or more and 30.0 or less, and the core satisfies H50-Ho>Hs-H50, wherein Hs (Shore C hardness) is a hardness at the surface of the core, Ho (Shore C hardness) is a hardness at the center of the core, and H50 (Shore C hardness) is a hardness at a midpoint between the center of the core and the surface of the core.

Golf balls having covers made of thermoplastic polyurethane compositions are provided. Multi-piece golf balls can be made. In one embodiment, the outer cover layer is formed from a composition comprising a thermoplastic polyurethane and polydimethylsiloxane compound. Functionalized polydimethylsiloxane compounds also can be used to treat thermoplastic polyurethane golf ball covers. The cover composition and surface coatings can further include catalysts, ultraviolet (UV)-light stabilizers, and other additives. The coating methods have many benefits and the finished balls with thermoplastic polyurethane covers have good physical properties.

An object of the present invention is to provide a golf ball having excellent abrasion resistance and spin performance on driver shots. The present invention provides a golf ball having a spherical core and a cover covering the spherical core, wherein the cover contains a polyurethane, wherein the polyurethane comprises, as a constituent component, (A) a polyisocyanate component and (B) a polyol component containing (b1) a polyrotaxane, and wherein (b1) the polyrotaxane has a cyclodextrin, a linear molecule piercing through the cyclic structure of the cyclodextrin, and a blocking group located at both terminals of the linear molecule to prevent disassociation of the cyclodextrin, and at least a part of hydroxyl groups of the cyclodextrin is modified with a caprolactone chain via —O—C.sub.3H.sub.6—O— group.

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

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. The center of the core comprises a metal material such as copper, steel, brass, tungsten, titanium, aluminum, and alloys thereof dispersed in a thermoset polymeric matrix. The intermediate core layer is preferably formed from a first thermoplastic composition such as an ethylene acid copolymer ionomer resin; and the outer core layer is preferably formed from a second thermoplastic composition. The resulting ball has high resiliency and good spin control.

A golf ball is provided that achieves a satisfactory distance on full shots with an iron, is superior in the short game, and has a good feel at impact and a good durability. The golf ball has a core formed of a rubber composition as one or more layer, an envelope layer formed of a resin material as one or more layer, an intermediate layer formed of a resin material as one layer, and a cover formed of a resin material as one layer having a thickness of not more than 1.0 mm. The layers of the ball have Shore C hardnesses at the respective surfaces thereof which together satisfy certain specific conditions, the core and the ball have respective deflections which satisfy certain conditions and the core has a specific internal hardness profile.

Golf balls having a multi-layered core made of a foamed composition are provided. The core assembly preferably includes a foam inner core (center) and surrounding outer core layer. Preferably, a polyurethane foam composition is used to form the foam center. The core layers have different hardness gradients and specific gravity values. The foamed inner core assembly includes a geometric center, outer surface (skin), and thermal barrier layer that helps protect the foamed center region from the negative effects of high temperatures used during the ball-manufacturing process. Non-foamed thermoset materials such as polybutadiene rubber may be used to form the thermal barrier layer. The foam cores have good resiliency, thermal stability, and durability over a wide temperature range. The ball further includes a cover that may be multi-layered.

A golf ball 2 includes a spherical core 4, an inner mid layer 6, an outer mid layer 8, a reinforcing layer 10, and a cover 12. When distances (%) from a central point of the core 4 to nine points and JIS-C hardnesses at the nine points, which nine points are obtained by dividing a region from the central point of the core 4 to a surface of the core 4 at intervals of 12.5% of a radius of the core 4, are plotted in a graph, R.sup.2 of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95. Hm1 is greater than Hm2. Hc is less than Hm1. T2 is equal to or greater than 0.5 mm but equal to or less than 1.6 mm.

Golf ball multi-layered core sub-assemblies and the resulting golf balls are provided. The core structure includes a foam inner core (center); and intermediate and outer core layers. Foamed polyurethane is preferably used to make the inner core. The intermediate and outer core layers are preferably made from non-foamed thermoplastic compositions such as ethylene acid copolymer ionomer. In an alternative version, the intermediate core layer may be made of a thermoset rubber such as polybutadiene. The core layers have different hardness and specific gravity levels. The core structure and resulting ball have relatively good resiliency.

A golf ball includes a core having an outer surface and a geometric center. The core is formed from a substantially homogenous rubber composition. An ionomeric inner cover layer is formed about the core and has a material hardness of about 60 Shore D or greater. The golf ball includes an outer cover layer formed from a polyurea or a polyurethane and having a material hardness of about 60 Shore D or less. The outer surface of the core has a trans content of about 12% or less and a hardness of about 71 to 88 Shore C. The geometric center of the core has a trans content of about 10% or less and a hardness of about 60 to 80 Shore C. The core has an outer surface hardness greater than a geometric center hardness by about 5 to 19 Shore C to define a positive hardness gradient.