A golf ball (2) includes a core (4), an inner cover (6), a main cover (8), and an outer cover (10). X=HcRc0.05, S=HsRc0.05, M=HmTm, I=HiTi, O=HoTo, and Q=(I+O)/2 that are calculated from a radius Rc of the core (4), a Shore C hardness Hc at a central point of the core (4), a Shore C hardness Hs at a surface of the core (4), a thickness Tm of the main cover (8), a Shore C hardness Hm of the main cover (8), a thickness Ti of the inner cover (6), a Shore C hardness Hi of the inner cover (6), a thickness To of the outer cover (10) and a Shore C hardness Ho of the outer cover (10), satisfy 15MS100, 0.25<Q/M<0.5, 10IO30, and Q/X0.8.

Golf ball having at least three layers comprising ionomeric and/or HNP compositions, wherein for each two adjacent layers, a relationship is established between a ratio of the volumes of the two adjacent layers and a ratio of the percent neutralizations of those two layers such that the volumes and % neutralizations of all layers are interrelated and interdependent to produce unique and desirable playing characteristics. In one embodiment, a golf ball of the invention has T layers, wherein T3 and each of T layers has a different volume V and comprises an ionomeric and/or HNP composition having a different % neutralization N; and wherein each of n inner layers of the T layers (n<T) has an adjacent surrounding layer n+1 such that a volume V.sub.n and a % neutralization N.sub.n of each inner layer and a volume V.sub.(n+1) and % neutralization N.sub.(n+1) of each adjacent surrounding layer n+1 satisfy the relationship (V.sub.(n+1)V.sub.n)/V.sub.(n+1)(N.sub.nN.sub.(n+1))/N.sub.(n+1).

An object of the present invention is to provide a golf ball having excellent flying performance on driver shots. The present invention provides a golf ball having a spherical core and at least one cover layer covering the spherical core, wherein the spherical core is formed from a rubber composition containing: (a) a base rubber, (b) an ,-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, (d) an unsaturated fatty acid and/or a metal salt thereof (excluding an ,-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof), and (e) a saturated fatty acid and/or a metal salt thereof, provided that the rubber composition further contains (f) a metal compound in the case of containing only (b) the ,-unsaturated carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent.

In a multi-piece solid golf ball having a core, a cover and an intermediate layer therebetween, the core, an intermediate layer-encased sphere and the ball have surface hardnesses which satisfy a specific relationship, and the intermediate layer and the cover have thicknesses which satisfy a specific relationship. Also, the core has a hardness profile in which the hardnesses at the core surface, core center, a position 5 mm from the core center, and a position midway between the surface and center of the core satisfy specific relationships. This golf ball, when used by mid- and high-level amateurs, enables the golfer to maintain an adequate distance on shots with a driver and achieve a good distance on iron shots, has a good spin performance on approach shots and has a good feel on impact. In addition, the ball has an excellent scuff resistance when struck with a grooved wedge.

In a multi-piece solid golf ball made up of, successively, a core, an intermediate layer and a cover having numerous dimples on the surface thereof, the intermediate layer is formed of a resin material and the cover is formed of a urethane resin material, each having a specific respective Shore D hardness. The ball has a specific (intermediate layer thickness)/(core diameter) value and a specific (cover thickness)/(core diameter) value, and the core has a specific deflection. The sphere consisting of the core encased by the intermediate layer has an initial velocity A and the core has an initial velocity B which together satisfy the condition AB0 m/s. This golf ball provides an increased distance and has both a soft feel when played and a high durability to repeated impact.

In a multi-piece solid golf ball having a core, a cover and an intermediate layer therebetween, the core, an intermediate layer-encased sphere and the ball have surface hardnesses which satisfy a specific relationship, and the intermediate layer and the cover have thicknesses which satisfy a specific relationship. Also, the core has a hardness profile in which the hardnesses at the core surface, core center, a position 5 mm from the core center, and a position midway between the surface and center of the core satisfy specific relationships. This golf ball, when used by mid- and high-level amateurs, enables the golfer to maintain an adequate distance on shots with a driver and achieve a good distance on iron shots, has a good spin performance on approach shots and has a good feel on impact. In addition, the ball has an excellent scuff resistance when struck with a grooved wedge.

Multi-layered golf balls containing a three-layered core assembly are provided. Preferably, at least one of the core layers is formed from a thermoplastic composition that comprises: a) thermoplastic non-acid polymer, and b) plasticizer. In one preferred embodiment, the inner core is made of a first thermoset composition, for example, polybutadiene rubber; and the intermediate core layer is made of a thermoplastic composition; and the outer core is made of a second thermoset composition. A fatty acid ester such as ethyl oleate is preferably used as the plasticizer. Suitable non-acid polymers include, for example, polyesters, polyamides, polyolefins, and polyurethanes. The core assembly has a relatively high resiliency at given compressions.

In a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover with a plurality of dimples thereon, the core is a two-layer core consisting of an inner core layer and an outer core layer each formed primarily of a base rubber, the envelope layer, the intermediate layer and the cover layer are each composed of at least one layer and formed primarily of a synthetic resin material, and the initial velocities and surface hardnesses of the core, the envelope layer-encased sphere and the intermediate layer-encased sphere are designed within specific ranges. This golf ball satisfies at a very high level the flight and control performances expected for use by professional golfers and skilled amateurs, has the ability to move forward on a straight path particularly on full shots, and also has an excellent scuff resistance.

In a multi-piece solid golf ball which includes a core of at least one layer, a cover of at least one layer, and at least one intermediate layer interposed between the core and the cover, the cover is composed primarily of polyurethane and the following parameters are controlled within specific ranges: core deflection, melt flow rate of intermediate layer material, thickness of intermediate layer, thickness and Shore D hardness of cover, combined thickness of intermediate layer and cover, and the value of (Shore D hardness of cover material)(Shore D hardness of intermediate layer material). This golf ball has a good, soft feel at impact and lowers the rate of spin on full shots, achieving a good distance.

In order to satisfy at a high level the golf ball flight and control performances relied on by professional golfers and skilled amateurs, this invention provides a multi-piece solid golf ball G having a core 1, a cover 3 and an intermediate layer 2 therebetween wherein, letting Hc be the JIS-C hardness at a center of the core, H12 be the JIS-C hardness at a position 12 mm from the core center and Ho be the JIS-C hardness at a surface of the core, the core has a hardness profile which satisfies the condition (HoH12)(H12Hc)10; letting (HoH12)(H12Hc) above be A, the spin index of the ball, defined as the dynamic coefficient of friction of the ball multiplied by A, is at least 3.0; and the hardness profile index, defined as the deflection (mm) of the core when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) multiplied by A, is at least 40.