Golf ball

Details Golf ball Golf ball

2000-11-28

2002-08-27

Graham, Mark S. (Department: 3711)

Games using tangible projectile

Golf

Ball

C473S374000

Reexamination Certificate

active

06440012

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to golf balls and specifically to the construction of solid, non-wound, golf balls for regulation play. More particularly, the invention is directed to improved golf balls comprising multiple core assemblies which have a comparatively small, high density, polymeric center, or nucleus, component. The small, heavy center component in combination with the particular remaining core and cover components produces a golf ball having a smaller moment of inertia about its central axis. This results in a golf ball which exhibits enhanced spin while maintaining or improving additional golf ball characteristics such as durability, resiliency and compression.
Furthermore, the small, heavy weight, polymeric center component of the invention is preferably produced without the use of one or more peroxide crosslinking, or co-crosslinking agents comprising a metal salt of an unsaturated fatty or carboxylic acid. These crosslinking agents or coagents are the reaction product of an unsaturated carboxylic acid or acids and an oxide or carbonate of a metal such as zinc. Examples of such crosslinking agents, which again are preferably not incorporated into the present inventions, or if so, only to a minimal amount, include zinc diacrylate and zinc dimethacrylate. Accordingly, the polymeric centers of the golf balls of the present invention are generally free from peroxide crosslinking agents and exhibit high densities.
Additionally, in a more preferred aspect, the small, heavy center component of the invention is produced through the use of a blend of polybutadiene and polyisoprene rubbers. Powdered metal materials and other materials, including curing agents, may be incorporated therein to produce a high density, spherical center component that is commercially processible.
Moreover, in a particularly preferred aspect, the balls of the invention further utilize a multi-layer cover assembly. The improved multi-layer cover golf balls provide enhanced distance and durability properties over single layer cover golf balls while at the same time offering enhanced “feel” and spin characteristics generally associated with soft balata and balata-like covers of the prior art.
BACKGROUND OF THE INVENTION
Golf balls traditionally have been categorized in three different groups, namely, as one piece balls, multi-piece solid (two or more pieces) balls, and wound (three piece) balls. The one piece ball typically is formed from a solid mass of moldable material which has been cured to develop the necessary degree of hardness. It possesses no significant difference in composition between the interior and exterior of the ball. These balls do not have an enclosing cover. One piece balls are described, for example, in U.S. Pat. Nos. 3,313,545; 3,373,123; and, 3,384,612.
The wound ball is frequently referred to as a three piece ball since it is made with a vulcanized rubber thread wound under tension around a solid or semisolid center to form a wound core and thereafter enclosed in a single or multilayer covering of tough protective material. For many years the wound ball satisfied the standards of the U.S.G.A. and was desired by many skilled, low handicap golfers.
The three piece wound ball typically has a balata cover which is relatively soft and flexible. Upon impact, it compresses against the surface of the club producing high spin. Consequently, the soft and flexible balata covers along with the wound cores provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade or a backspin which causes the ball to “bite” or stop abruptly on contact with the green. Moreover, the balata cover produces a soft “feel” to the low handicap player. Such playability properties of workability, feel, etc. are particularly important in short iron play with low swing speeds and are exploited significantly by high skilled players.
However, a three piece wound ball also has several disadvantages. For example, a wound ball is relatively difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, “click”, “feel”, and the like.
Additionally, a soft wound (three piece) ball is not well suited for use by the less skilled and/or high handicap golfer who cannot intentionally control the spin of the ball. For example, the unintentional application of side spin by a less skilled golfer produces hooking or slicing. The side spin reduces the golfer's control over the ball as well as reducing travel distance.
Similarly, despite all the benefits of balata, balata covered balls are easily cut and/or damaged if mishit. Consequently, golf balls produced with balata or balata containing cover compositions, can exhibit a relatively short life spans. As a result of this negative property, balata and its synthetic substitute, trans-polyisoprene, and resin blends, have been essentially replaced as the cover materials of choice by golf ball manufacturers by materials comprising ionomeric resins and other elastomers such as polyurethanes.
Conventional multi-piece solid golf balls, on the other hand, include a solid resilient core having single or multiple cover layers employing different types of material molded on the core. The one piece golf ball and the solid core for a multi-piece solid (nonwound) ball frequently are formed from a combination of materials such as polybutadiene and other rubbers cross linked with zinc diacrylate or zinc dimethacrylate, and containing fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. For multi-piece nonwound golf balls, the cover typically contains a substantial quantity of ionomeric resins that impart toughness and cut resistance to the covers.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of a unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer, resulting in a thermoplastic elastomer exhibiting enhanced properties, such as durability, for golf ball cover construction. However, some of the advantages gained in increased durability have been offset to some degree by decreases in playability. This is because, although the ionomeric resins are very durable, they also tend to be quite hard when utilized for golf ball cover construction and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since most ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionic resins lack the “feel” characteristic associated with the softer balata related covers.
As a result, while there are currently more than fifty (50) commercial grades of ionomers available, both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal ions, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients, such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the “hard” ionomeric resins, but also the playability (i.e. “spin”, “feel”, etc.) characteristics previously associated with the “soft” balata covers, properties which are still desired by the more skilled golfer.
Moreover, a number of multi-piece solid balls have also been produced to address the various needs of the golfing populations. The different types of material used to formulate the core(s), cover(s), etc. of these balls dramatically alter the balls' overall characte

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