Solid golf ball

Details Solid golf ball Solid golf ball

1998-05-22

2001-02-06

Buttner, David J. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S288000, C473S371000, C473S372000, C473S373000, C473S374000, C473S377000

Reexamination Certificate

active

06184301

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a solid golf ball having a good feel when hit and improved flight performance.
2. Prior Art
Solid golf balls are one-piece balls or multi-piece balls, the latter being composed either of a solid core enclosed within a cover (two-piece golf balls) or a solid core and a cover with one or more intermediate layers disposed therebetween (three or multi-piece golf balls). These solid golf balls are composed in part (the solid core, and sometimes the intermediate layer, in multi-piece golf balls) or in whole (one-piece golf balls) of an elastic portion obtained by molding and vulcanizing a rubber composition.
Conventional rubber compositions for this elastic portion are obtained by blending a base rubber composed primarily of polybutadiene rubber with a co-crosslinking agent, which is an unsaturated carboxylic acid or a metal salt thereof, in order to give the ball a certain degree of hardness and improve the impact resistance and resiliency. Through the action of a crosslinking initiator such as a peroxide, this co-crosslinking agent grafts or crosslinks to the backbone of the polybutadiene rubber, forming a three-dimensionally crosslinked polymer composed of polybutadiene and the co-crosslinking agent. This imparts a suitable degree of hardness, as well as durability and resiliency, to one-piece golf balls or to the core or intermediate layer of multi-piece golf balls, thus providing solid golf balls with a good flight performance and durability.
However, golfers have very strong desires concerning the flight performance of golf balls, today they expect even better flight performance as well as, to this end, further improvement in the resiliency of golf ball materials. In addition, the high regard for soft-type golf balls, which are solid two-piece or other multi-piece balls having softer cores to soften the feel of the ball when hit, and for spin-type balls in which soft cover stock is used to achieve improved spin performance, has also led to a heightened demand for better resiliency in golf ball materials.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide solid golf balls having a rubber portion with a high resiliency and exhibiting a soft feel when hit and an excellent flight performance.
The inventions have discovered that, by adding sulfur halide to a rubber composition of a base rubber such as polybutadiene rubber in which an unsaturated carboxylic acid or a metal salt thereof is blended as a co-crosslinking agent, or by pre-treating the base rubber with sulfur halide, the rubber elastomer obtained when the resulting composition is vulcanized has an improved resiliency. Moreover, by using this rubber composition to form a one-piece golf ball or the core and/or intermediate layer of a multi-piece golf ball, solid golf balls can be obtained having an improved initial velocity, an excellent flight performance, and a soft feel when hit.
Accordingly, the present invention provides a solid golf ball in the form of a one-piece golf ball or a multi-piece golf ball having a solid core enclosed directly in a cover or with an intermediate layer disposed therebetween. In one embodiment, the one-piece golf ball or the solid core and/or intermediate layer of the multi-piece golf ball is formed of a rubber composition comprising a base rubber, an unsaturated carboxylic acid or a metal salt thereof, and a sulfur halide. In another embodiment, the one-piece golf ball or the solid core and/or intermediate layer of the multi-piece golf ball is formed of a rubber composition comprising a base rubber treated with a sulfur halide, and an unsaturated carboxylic acid or a metal salt thereof.
DETAILED DESCRIPTION OF THE INVENTION
The solid golf balls of the invention encompass both one-piece golf balls and multi-piece golf balls having a solid core enclosed directly in a cover (two-piece) or having a solid core enclosed in a cover with an intermediate layer disposed therebetween (multi-piece). As mentioned above, the one-piece golf ball or the core and/or intermediate layer of a multi-piece solid golf ball is made of a rubber composition containing a base rubber, an unsaturated carboxylic acid or a metal salt thereof, and a sulfur halide, or of a rubber composition containing a base rubber treated with a sulfur halide, and an unsaturated carboxylic acid or a metal salt thereof.
The base rubber included in the rubber composition may be any rubber used in conventional solid cores. This is typically a natural rubber and/or synthetic rubber, with the use of 1,4-polybutadiene containing at least 40% of cis structure being especially preferable. Natural rubber, polyisoprene rubber and the like may also be blended as desired into this polybutadiene. When polybutadiene rubber is included as the primary component of the base rubber, the polybutadiene content is preferably set at not less than 80% by weight, and more preferably 90 to 100% by weight, of all the base rubber components. A content of less than 80% by weight may make it difficult to achieve the high resilience desired.
The unsaturated carboxylic acid or a metal salt thereof is blended as a co-crosslinking agent. Examples include unsaturated carboxylic acids having 3 to 8 carbons, such as acrylic acid, methacrylic acid, maleic acid and fumaric acid, and the zinc salts thereof. Of these, the use of acrylic acid, methacrylic acid, or their zinc salts is especially preferred. The content of the unsaturated carboxylic acid or its metal salt may be suitably adjusted, although it is generally preferable to use this within a range of 15 to 35 parts by weight, and especially 20 to 33 parts by weight, per 100 parts by weight of the base rubber.
A co-crosslinking initiator may be used in the rubber compositions of the invention. This co-crosslinking initiator is preferably an organic peroxide, suitable examples of which include dicumyl peroxide, t-butyl peroxybenzoate, di-t-butyl peroxide, and 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane. This organic peroxide is generally included in an amount of 0.5 to 2.5 parts by weight, and preferably 0.7 to 1.5 parts by weight, per 100 parts by weight of the base rubber.
In addition, other components such as inert fillers and antioxidants may also be blended in the rubber composition. Examples of these include substances familiar to the art, such as zinc oxide and barium sulfate.
It is essential to the practice of the invention that either sulfur halide be blended into a rubber composition comprising the above base rubber and the above unsaturated carboxylic acid or a metal salt thereof, or that use be made a base rubber treated with sulfur halide. The use of sulfur halide serves to impart the solid core with both a good degree of deformation and resiliency. In the finished golf ball, the sulfur halide helps to provide an improved flight distance while yet maintaining a good feel when the ball is hit.
Any sulfur halide may be used, examples of which include disulfur dichloride, sulfur dichloride, sulfur monochloride, thionyl chloride and sulfur bromide. These may be used singly or in combinations of two or more. The use of disulfur dichloride and thionyl chloride is especially preferred.
The sulfur halide may be used in any amount, although the sulfur halide content of the rubber composition is preferably 0.03 to 0.5 parts by weight, and especially 0.05 to 0.4 parts by weight, per 100 parts by weight of the base rubber. At a content of less than 0.03 parts by weight, the resilience-improving effect is too small, conversely a content of more than 0.5 parts by weight results in the rubber having a higher viscosity in the unvulcanized state, thereby compromising the workability of the rubber during extrusion.
Any suitable method may be employed to blend the sulfur halide into the rubber composition. For example, it may be kneaded together with the above components used in preparing the rubber composition. Another method that can be used is to first knead and disperse the sulfur halide in the base rubber

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