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.

Golf ball incorporating thermoplastic blend of (i) ionomer(s); (ii) different thermoplastic polymer(s) selected from thermoplastic polyurethane(s), thermoplastic urea(s), thermoplastic urea-urethane hybrid(s), or combinations thereof; and (iii) polymethyl (meth)acrylate-based copolymer(s) and/or core-shell polymer(s) having a core and/or a shell containing polymethyl (meth)acrylate-based copolymer(s). Ionomer(s) are present in thermoplastic blend in amount of about 45 wt % or greater. Different thermoplastic polymer present in blend in amount of: from about 8 wt % to about 50 wt %; or greater than 20 wt %, or from about 25 wt % to about 45 wt %; or from about 35 wt % to about 50 wt %. In a particular embodiment, amount of ionomer(s) is greater than thermoplastic polyurethane amount. Component (iii) may be present in an amount of about 2 wt % to about 35 wt %, and in a specific embodiments, polymethyl (meth)acrylate-based copolymer(s) and/or core-shell polymer(s) included in blend in amount of from about 15 wt % to about 35 wt %.

Golf ball incorporating thermoplastic blend of (i) ionomer(s); (ii) different thermoplastic polymer(s) selected from thermoplastic polyurethane(s), thermoplastic urea(s), thermoplastic urea-urethane hybrid(s), or combinations thereof; and (iii) polymethyl (meth)acrylate-based copolymer(s) and/or core-shell polymer(s) having a core and/or a shell containing polymethyl (meth)acrylate-based copolymer(s). Ionomer(s) are present in thermoplastic blend in amount of about 45 wt % or greater. Different thermoplastic polymer present in blend in amount of: from about 8 wt % to about 50 wt %; or greater than 20 wt %, or from about 25 wt % to about 45 wt %; or from about 35 wt % to about 50 wt %. In a particular embodiment, amount of ionomer(s) is greater than thermoplastic polyurethane amount. Component (iii) may be present in an amount of about 2 wt % to about 35 wt %, and in a specific embodiments, polymethyl (meth)acrylate-based copolymer(s) and/or core-shell polymer(s) included in blend in amount of from about 15 wt % to about 35 wt %.

Golf ball incorporating thermoplastic blend of (i) ionomer(s); (ii) different thermoplastic polymer(s) selected from thermoplastic polyurethane(s), thermoplastic urea(s), and/or thermoplastic urea-urethane hybrid(s); and (iii) polyester elastomer(s) and/or polyamide elastomer(s) (PEPA). Ionomer is present in amount of about 45 wt % or greater and PEPA present in amount of from about 2 wt % to about 35 wt %. Thermoplastic polymer(s) may be present in amount of from about 8 wt % to about 50 wt %; or from about 25 wt % to about 45 wt %; or from about 35 wt % to about 50 wt %. Ionomer amount may be greater than amount of thermoplastic polymer. Thermoplastic polymer may be a polyurethane present in amount of greater than 20 wt % and to about 40 wt %; while the PEPA is present in amount of from about 5 wt % to about 30 wt %. PEPA is sometimes present in an amount of from about 15 wt % to about 35 wt %.

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.

Multi-layered golf balls containing a dual-core structure are provided. The core structure includes an inner core (center) comprising a foam composition, preferably foamed polyurethane. The outer core layer is preferably formed from a non-foamed thermoset composition such as polybutadiene rubber. The core layers have different hardness and specific gravity levels. The specific gravity (density) of the foam inner core is preferably less than the density of the outer core layer. The core assembly preferably has a positive hardness gradient extending across the entire assembly. The core structure and resulting ball have relatively good resiliency.

An object of the present invention is to provide a golf ball having an excellent initial velocity when being hit at a head speed of 50 m/sec and an improved initial velocity when being hit at a head speed of 40 m/sec. The present invention provides a golf ball comprising a spherical core and a cover covering the spherical core, wherein the golf ball has a rebound equivalence energy ratio (R.sub.40) ranging from 65.50% to 99.0% at a deformation amount of 7%, and a rebound equivalence energy ratio (R.sub.50) ranging from 20.0% to 70.0% at a deformation amount of 19%, in a compression test (measurement temperature: 70 C., compression speed: 30 mm/min) applying a load to the golf ball along a radial direction 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.

The present invention provides a golf ball comprising a spherical core composed of a spherical inner core layer and an outer core layer, an intermediate layer and a cover, wherein the inner core layer has a hardness difference (Hs1Ho) between a surface hardness (Hs1) and a center hardness (Ho) of 5 or less in JIS-C hardness, the outer core is such that R.sup.2 of a linearly approximated curve obtained from a least square method is 0.95 or higher, when JIS-C hardness, measured at nine points obtained by dividing a thickness of the outer core in a radius direction of the spherical core into equal parts having 12.5% intervals therebetween, is plotted against distance (%) from a border point between the outer core layer and the inner core layer, and the intermediate layer has a slab hardness which is greater than a slab hardness of the cover.

Casing compositions including carboxylic acid groups, cover compositions including an adhesion promoter with functional groups that crosslink with carboxylic acid groups, and golf balls made from such compositions that have crosslinks between functional groups of the cover compositions and the carboxylic acid groups. The type and concentration of the components in the casing and cover compositions, including the adhesion promoter, affect the adhesion between golf balls having components made from such compositions and, thus, can be used to produce a golf ball having increased durability. Additionally, methods of crosslinking casing and cover layers made from such casing and cover compositions to increase interlayer adhesion are disclosed.