Multi-piece solid golf ball

Abstract

The present invention provides a multi-piece solid golf ball having 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. The core is composed overall of an inner layer and an outer layer which are each formed primarily of a rubber material, with the outer core layer being harder than the inner core layer. The envelope layer, intermediate layer and cover have respective thicknesses which satisfy the condition: cover thickness<intermediate layer thickness<envelope layer thickness, and have respective material hardnesses (Shore D hardness) which satisfy the condition: envelope layer material hardness<intermediate layer material hardness>cover material hardness. The golf ball has a lower spin rate on full shots with a driver, further increasing the distance traveled by the ball. Moreover, it has a good controllability, maintaining in particular a straight trajectory on full shots, and also has an excellent scuff resistance.

Description

BACKGROUND OF THE INVENTION[0001]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 satisfactory flight performance and controllability when used by professionals and other skilled golfers, is able in particular to maintain a straight trajectory on full shots, and has an excellent scuff resistance.[0002]A variety of golf balls have hitherto been developed for professionals and other skilled golfers. Of these, multi-piece solid golf balls in which the hardness relationships among layers encasing the core, such as an intermediate layer and a cover layer, have been optimized 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 pro...

AI Technical Summary

Benefits of technology

[0107]In the practice of invention, the cover material is not subject to any particular limitation, although it is preferable for the cover to be formed primarily of a thermoplastic resin or a thermoplastic elastomer. The use of a polyurethane as the primary material is especially preferred because it enables the intended effects of the invention, i.e., both a good controllability and a good scuff resistance, to be achieved.

[0108]The polyurethane used as the cover material, while not subject to any particular limitation, is preferably a thermoplastic polyurethane, particularly from the standpoint of amenability to mass production.

[0109]It is preferable to use a specific thermoplastic polyurethane composition composed primarily of (A) a thermoplastic polyurethane and (B) a polyisocyanate compound. This resin blend is described below.

[0110]To fully exhibit the advantageous effects of the invention, a necessary and sufficient amount of unreacted isocyanate groups should be present in the cover resin material. Specifically, it is recommended that the total weight of above components A and B combined be at least 60%, and preferably at least 70%, of the overall weight of the cover. Components A and B are described in detail below.

[0111]The thermoplastic polyurethane serving as component A has a structure which includes soft segments made of a polymeric polyol that is a long-chain polyol (polymeric glycol), and hard segments made of a chain extender and a polyisocyanate compound. Here, the long-chain polyol used as a starting material is not subject to any particular limitation, and may be any that is used in the prior art relating to thermoplastic polyurethanes. Exemplary long-chain polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. These long-chain polyols may be used singly or as combinations of two or more thereof. Of the long-chain polyols mentioned here, polyether polyols are preferred because they enable the synthesis of thermoplastic polyurethanes having a high rebound resilience and excellent low-temperature properties.

[0112]Illustrative examples of the above polyether polyol include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol) and poly(methyltetramethylene glycol) obtained by the ring-opening polymerization of cyclic ethers. The polyether polyol may be used singly or as a combination of two or more thereof. Of the above, poly(tetramethylene glycol) and / or poly(methyltetramethylene glycol) are preferred.

Problems solved by technology

Such a combination of effects was entirely unanticipated.

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