A golf ball 2 includes an inner core 4, an outer core 6, a mid layer 8, and a cover 10. A diameter D1, a volume V1, a hardness H1o at a central point, and a boundary inside hardness H1in of the inner core 4; a volume V2, a boundary outside hardness H2out, and a surface hardness H2s of the outer core 6; a thickness Tm and a hardness Hm of the mid layer 8; and a thickness Tc and a hardness Hc of the cover 10 meet the following mathematical formulas (1) to (4): 1.0<V2/V1<7.0 (1); 2<H2sH2out<2 (2); 600<(H1o+H1in)*(D1/2)/2<1000 (3); 620<Tc*Hc*Hm/Tm<900 (4). The cover 10 includes a polyrotaxane.

An object of the present invention is to provide a golf ball showing an increased spin rate on approach shots under a wet condition while maintaining a spin rate on approach shots under a dry condition. The present invention provides a golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein the paint film has a multi-layered construction composed of two or more layers, and a difference (M.sub.outM.sub.in) between a 10% elastic modulus (M.sub.out) of an outermost layer of the paint film and a 10% elastic modulus (M.sub.in) of an innermost layer of the paint film is 25 kgf/cm.sup.2 or more.

A golf ball 2 includes a core 4, a mid layer 6, and a cover 8. A difference DH in hardness between a surface and a central point of the core 4, a thickness Tm and a hardness Hm of the mid layer 6, a thickness Tc and a hardness Hc of the cover 8, and an amount of compressive deformation Sb of the golf ball 2 meet the following mathematical formulas (DH*Hm)/(Hc*Tc)>80 and ((Sb*Tc)/(Hc*Hm*Tm))*1000>0.75. A hardness Hc of the cover 8 is equal to or less than 40. A material of the cover 8 is a resin composition. The resin composition includes a polyurethane (A) and a polyrotaxane (B).

An object of the present invention is to provide a golf ball having an excellent spin performance on approach shots under a wet condition. The present invention provides a golf ball comprising a spherical core and a cover covering the spherical core, wherein the cover is formed from a cover composition containing (A) a polyurethane and (B) a polyrotaxane as a resin component, and wherein (B) the polyrotaxane has a cyclodextrin, a linear molecule piercing through the cyclic structure of the cyclodextrin, and blocking groups 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 OC.sub.3H.sub.6O group.

Multi-piece golf balls having a solid core of at least one layer and cover of at least one layer are provided. Thermoplastic ethylene acid copolymer ionomer compositions are used to form the core layers. Preferably, the ball contains a dual-core having an inner core and surrounding outer core layer. Low modulus and high modulus ionomer compositions may be used in the core structure. In one embodiment, a first ionomer composition is used to form the inner core and a second ionomer composition is used to form the outer core, and the flex modulus of the first composition is greater than the flex modulus of the second composition. The ionomer compositions have varying levels of hardness. The resulting ball has high resiliency and rebounding properties.

A golf ball having an inner core layer, an outer core layer enclosing the inner core layer, and a cover layer enclosing the outer core layer. The inner core layer includes a blend of a first highly neutralized acid polymer having a first Vicat softening temperature and a first specific gravity, a second highly neutralized acid polymer having a second Vicat softening temperature and a second specific gravity, and an ionomer-based masterbatch comprising an additive and an ionomer resin having a third Vicat softening temperature and a third specific gravity. The absolute values of the differences among the Vicat softening temperatures is no more than about 15 C. and the absolute value of the difference between the specific gravities is no more than about 0.015. The cover layer may include an inner cover layer enclosing the outer core layer and an outer layer enclosing the inner cover layer.

An object of the present invention is to provide a golf ball showing an increased spin rate on approach shots under a wet condition while maintaining a spin rate on approach shots under a dry condition. The present invention provides a golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein the paint film has a multi-layered construction composed of two or more layers, and a difference (M.sub.inM.sub.out) between a 10% elastic modulus (M.sub.in) of an innermost layer of the paint film and a 10% elastic modulus (M.sub.out) of an outermost layer of the paint film is 25 kgf/cm.sup.2 or more.

A multi-layer golf ball includes a core, and intermediate layer, and a cover. The core has an outer surface that includes a plurality of depressions extending from a spherical land portion. Each depression has a maximum depth relative to the spherical land portion of between 0.15 mm and 2.0 mm. The intermediate layer surrounds the core and has a radially inward surface that is flush with the outer surface of the core. The cover layer surrounds the intermediate layer and defines an outermost portion of ball.

An object of the present invention is to provide a golf ball traveling a great flight distance. The present invention provides a golf ball comprising a spherical core and a cover covering the spherical core, wherein the golf ball has a ratio (t2/t1) of a time (t2) to a time (t1) of 1.05 or more in a hitting test using a driver (at a head speed of 40 m/sec), wherein the time (t1) is a time taken from a moment that the driver begins to contact with the golf ball to a moment that the golf ball reaches a maximum deformation amount, and the time (t2) is a time taken from the moment that the golf ball reaches the maximum deformation amount to a moment that the golf ball leaves the driver.

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.