In a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer and a cover, the intermediate layer is formed into two layers—an inner layer and an outer layer. The surface hardness of the envelope layer-encased sphere, the surface hardness of the inner intermediate layer-encased sphere, the surface hardness of the outer intermediate layer-encased sphere and the surface hardness of the ball together satisfy a specific relationship. This ball has an excellent flight when struck by golfers whose head speeds are not that fast and has a soft yet good feel at impact, thus making it highly suitable for amateur golfers.

In a multi-piece solid golf ball having a core formed of a rubber composition, an intermediate layer formed of a polyurethane material and a cover, the ball satisfies the following condition: surface hardness of ballsurface hardness of intermediate layer-encased sphere. When the ball is struck with a driver at a head speed of 40 m/s, the sum of the time t1 required from contact initiation between the driver and ball for deformation of the ball to reach a maximum value and the time t2 required from the state of maximum ball deformation for the ball and driver clubface to separate is at least 705 microseconds. This ball has an excellent flight performance when hit by low or moderate head-speed golfers, is receptive to spin on approach shots and has a good, soft feel at impact.

Methods for coatings for golf balls, particularly golf balls having thermoplastic polyurethane covers, and the resulting finished balls are provided. The coating is preferably a topcoat comprising a polyurethane composition containing optical brighteners. The topcoat composition may comprise a low concentration of optical brighteners. For example, the concentration of optical brightener can be in the range of 0.01 to about 0.20 weight %. Multi-piece golf balls having inner cores, outer cores, inner covers, and intermediate layers can be made. The finished ball with the topcoat has many advantageous physical and playing performance properties.

A golf ball has a core, an inner cover, an outer cover, and dimples. The golf ball satisfies the following mathematical formulas.

Sa=4500+10(A0.5B2Cs)4000

0.04Sa+16020D0.04Sa+160+20 A: a compression (Atti) of the golfball B: a hardness difference (Shore C) between a surface and a center of the core

Cs: (HiTi+2HoTo)/(Ti+2To) D: a total volume (mm.sup.3) of the dimples Hi: a hardness (Shore D) of the inner cover Ho: a hardness (Shore D) of the outer cover Ti: a thickness (mm) of the inner cover To: a thickness (mm) of the outer cover

A golf ball has a core, an inner cover, an outer cover, and dimples, and satisfies the following mathematical formulas.

Vw=54+0.01(2.5AB+5Cv)58.0

0.08X.sup.24.25X+34520D0.08X.sup.24.25X+345+20

A: a compression of the golf ball

B: a hardness difference between a surface and a center of the core

Cv:(HiTi+HoTo)/(Ti+To)

Cs:(HiTi+2HoTo)/(Ti+2To)

D: a total volume of the dimples

X:Sw/Vw

Hi: a hardness of the inner cover

Ho: a hardness of the outer cover

Ti: a thickness of the inner cover

To: a thickness of the outer cover

Sw: 3000+10(AB1.5Cs)

Disclosed herein are golf balls having a thermoplastic outer cover layer formed from a thermoplastic polyurethane composition. The golf balls are produced without the use of a secondary treatment step that would result in the crosslinking of the polyurethane cover composition.

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

A resin composition for golf balls is made of (A) polyurethane or polyurea and (B) a styrene resin material, component (B) being included in an amount of 0.5 to 50 parts by weight per 100 parts by weight of component (A). In a golf ball having a core and a cover of one or more layer encasing the core, at least one cover layer is formed of this resin composition. The resin composition is especially useful as a golf ball cover material because the ball does not fly too far and is easier to control on approach shots, yet does not sacrifice distance on shots with a driver.

A golf ball of the present invention includes a core and a cover located outside the core and having a plurality of dimples on a surface thereof. A bottom of each of the dimples has a curved shape protruding toward an outside of the golf ball, and the protruding portion has a spherical crown shape having a radius of curvature R of 20 to 50 mm. A depth d of a center protruding portion of the bottom of the dimple is a perpendicular distance between a line S connecting both ends of an outer periphery of the dimple and a highest point of the protruding portion. A volume occupation ratio VR of the dimple is less than 0.75. A relationship between Shore D hardness H of a material of the cover and the depth d (unit: mm) satisfies the following Formula 1:

(H78)/(300)>d(Formula 1).

An object of the present invention is to provide a golf ball resin composition by which durability can be improved without substantially reducing hardness and resilience, and a golf ball using the same. The present invention provides a golf ball resin composition containing (A) at least one member selected from the group consisting of an ionomer resin, a polyamide and a styrene-based elastomer, and (B) an acid modified polyolefin having a weight average molecular weight in a range from 5,000 to 80,000.