CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2018-245206 filed in Japan on Dec. 27, 2018, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a multi-piece solid golf ball with a construction of three or more layers that has a core, a cover and at least one intermediate layer interposed therebetween.

BACKGROUND ART

Generally, the cover serving as the outermost layer of a golf ball is made primarily of a synthetic resin material such as an ionomer or a polyurethane resin. Among the golf balls that have been described to date in the art are several in which the scuff resistance or durability of the ball is improved by using a rubber cover. Prior art relating to rubber covers is described in, for example, JP-A 2001-70478 and JP-A 2006-212116.

However, such golf balls have a higher spin rate on shots with a driver and are often unable to achieve the desired distance. Moreover, in such golf balls, a rubber material is used in the cover, and so the production efficiency is inferior to that for golf balls having resin covers. Also, in the hardness design of the golf ball cover, when endeavoring to lower the spin rate on shots with a driver, there is a risk of an accompanying decrease in the spin rate in the short game, but the desire is that the spin rate on approach shots be kept high.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golf ball which, even with the use of a rubber cover, compares favorably with balls having conventional resin covers in that it can achieve a lower spin rate on shots with a driver (W #1) and thus has an excellent flight performance and also in that it can improve controllability in the short game.

As a result of extensive investigations, I have discovered that, in a golf ball having at least one intermediate layer interposed between a core and a cover, by using as the cover material a rubber composition which includes (a) a diene rubber, (b) methacrylic acid, (c) a metal oxide and (d) an organic peroxide, designing the cover so as to have a Poisson's ratio of at least 0.49, a Shore D hardness of not more than 45 and a thickness of not more than 0.6 mm, and designing the intermediate layer so that at least one layer thereof has a Shore D hardness of at least 60 and a thickness of not more than 2.0 mm, a lower spin rate can be achieved on shots with a driver (W #1), resulting in an excellent flight performance, in addition to which the controllability in the short game can be improved.

Accordingly, the invention provides a golf ball having a core, a cover, and at least one intermediate layer interposed therebetween, wherein the cover is formed of a rubber composition which includes: (a) a diene rubber, (b) methacrylic acid, (c) a metal oxide and (d) an organic peroxide. The cover has a Poisson's ratio of at least 0.49, a Shore D hardness of not more than 45 and a thickness of not more than 0.6 mm. At least one intermediate layer has a Shore D hardness of at least 60 and a thickness of not more than 2.0 mm.

In a preferred embodiment of the golf ball of the invention, the diene rubber of component (a) includes a styrene-butadiene rubber (SBR) and/or an isoprene rubber (IR), these ingredients accounting for between 30 and 70 wt % of the total amount of diene rubber serving as component (a).

In another preferred embodiment of the inventive golf ball, in a dynamic viscoelasticity test on vulcanized rubber obtained from the rubber composition containing components (a) to (d), the loss tangent (tan δ) at an initial strain of 0.1 N, an amplitude of 1%, a frequency of 15 Hz and a temperature of −10° C. is at least 0.20.

In yet another preferred embodiment, at least one intermediate layer is formed of a resin material having a melting point of at least 100° C. In this embodiment, the resin material may include, based on the total amount thereof, at least 50 wt % of a synthetic rubber.

Advantageous Effects of the Invention

The golf ball of the present invention, even with the use of a rubber cover, compares favorably with balls having conventional resin covers, both in that it can achieve a lower spin rate on shots with a driver (W #1) and thus has an excellent flight performance and also in that it can improve controllability in the short game.

