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Multi-piece solid golf ball

Multi-piece solid golf ball description/claims

The present invention relates to a multi-piece solid golf ball composed of a core, an envelope layer, an intermediate layer and a cover that have been formed as successive layers. More specifically, the invention relates to a multi-piece solid golf ball which has a flight performance and controllability that satisfy the needs of professionals and other skilled golfers, and which also has a good feel on impact and an excellent scuff resistance.

A variety of golf balls have hitherto been developed for professionals and other skilled golfers. Of these, multi-piece solid golf balls having an optimized hardness relationship between an intermediate layer encasing the core and the cover layer are in wide use because they achieve both a superior distance in the high head speed range and good controllability on shots taken with an iron and on approach shots. Another important concern is the proper selection of thicknesses and hardnesses for the respective layers of the golf ball so as to optimize not only flight performance, but also both the feel of the ball when played as well as its spin rate after being struck with the club, particularly given the large influence these latter factors have on ball control. A further key concern in ball development, arising from the desire that golf balls also have durability under repeated impact and scuff resistance against burr formation on the surface of the ball when repeatedly played with different types of clubs, is how best to protect the ball from external factors.

The three-piece solid golf balls having an outer layer cover formed primarily of a thermoplastic polyurethane which are disclosed in, for example, JP-A 2003-190330, JP-A 2004-049913, JP-A 2004-97802 and JP-A 2005-319287 were intended to meet such needs. However, because these prior-art golf balls fail to achieve a sufficiently lower spin rate when hit with a driver, professionals and other skilled golfers have desired a ball which delivers an even longer distance.

Meanwhile, efforts to improve the flight and other performance characteristics of golf balls have led to the development of balls having a four-layer construction—i.e., a core enclosed by three intermediate or cover layers—that allows the ball construction to be varied among the several layers at the interior. Such golf balls have been disclosed in, for example, JP-A 2004-180822, JP-A 10-127818, JP-A 10-127819, JP-A 10-295852, U.S. Pat. No. 5,816,937, U.S. Pat. No. 6,152,834, U.S. Pat. No. 6,123,630, U.S. Pat. No. 6,468,169, U.S. Pat. No. 6,045,460, U.S. Pat. No. 6,248,027, U.S. Pat. No. 6,117,026 and U.S. Pat. No. 6,277,036.

Yet, as golf balls for the skilled golfer, such balls provide a poor balance of distance and controllability or they fall short in terms of achieving a lower spin rate on shots with a driver, thus limiting the extent to which the total distance can be increased.

It is therefore an object of the present invention to provide a multi-piece solid golf ball which has a flight performance and controllability that are fully acceptable to professionals and other skilled golfers, while also having an excellent durability to cracking on repeated impact and an excellent scuff resistance.

In the present invention, the golf ball design consists basically of an outermost layer made of polyurethane and a multilayer structure of three or more outer layers (envelope layer/intermediate layer/cover) encasing the core. By making the cover, or outermost layer, of polyurethane, which is relatively soft, a spin performance on approach shots that is acceptable to professionals and other skilled golfers and a high scuff resistance are obtained. By forming the envelope layer of a material which is harder than the core surface and the intermediate layer, the spin rate of the ball on shots with a driver (W#1) can be lowered. In addition, by imparting to the respective layers in the core/envelope layer/intermediate layer/cover construction the following hardness relationship: cover material hardness<intermediate layer material hardness<envelope layer material hardness>core surface hardness, and by optimizing the core diameter and the relationship between the intermediate layer and the cover layer thicknesses, it was possible through the synergistic effects of these hardness relationships and layer thickness relationships to resolve the above-described problems encountered in the prior art. That is, the golf ball of the invention, when used by professionals and other skilled golfers, provides a fully acceptable flight performance and controllability, in addition to which it exhibits an excellent durability to cracking on repeated impact and excellent scuff resistance, effects which were entirely unanticipated. Having thus found that the technical challenges recited above can be overcome by the foregoing arrangement, the inventors ultimately arrived at the present invention.

Accordingly, the invention provides the following multi-piece solid golf balls. [1] A multi-piece solid golf ball comprising a core, an envelope layer encasing the core, an intermediate layer encasing the envelope layer, and a cover which encases the intermediate layer and has formed on a surface thereof a plurality of dimples, wherein the core is formed primarily of a rubber material and has a diameter of at least 31 mm, the envelope layer and the intermediate layer are each formed primarily of the same or different resin materials, and the cover is formed primarily of polyurethane; the intermediate layer and the cover have thicknesses which satisfy the relationship: cover thickness<intermediate layer thickness; and the core has a surface hardness (Durometer D hardness) and the envelope layer, intermediate layer and cover have material hardnesses (Durometer D hardness) which together satisfy the relationship: cover material hardness<intermediate layer material hardness<envelope layer material hardness>core surface hardness. [2] The multi-piece solid golf ball of [1], wherein the thicknesses of the envelope layer, the intermediate layer and the cover satisfy the relationship: cover thickness<intermediate layer thickness<envelope layer thickness. [3] The multi-piece solid golf ball of [1], wherein the resin material which forms the envelope layer comprises an ionomer resin having an acid content of at least 16 wt %. [4] The multi-piece solid golf ball of [1], wherein the resin material which forms the cover is composed primarily of (A) a thermoplastic polyurethane material, and (B) an isocyanate mixture obtained by dispersing (b-1) a compound having two or more isocyanate groups as functional groups per molecule in (b-2) a thermoplastic resin which is substantially non-reactive with isocyanate. [5] The multi-piece solid golf ball of [1], wherein the envelope layer, intermediate layer and cover have material hardnesses (Durometer D hardnesses) such that: 60≦envelope layer material hardness≦70, 55≦intermediate layer material hardness≦70, and 30≦cover material hardness≦55. [6] The multi-piece solid golf ball of [1], wherein the ball and the core have deflections (mm), when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), which satisfy the following respective conditions: 2.0 mm≦ball deflection≦3.0 mm, and 3.5 mm≦core deflection≦6.0 mm.

• Provisional Patent
• Utility Patent

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