Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-22
2003-09-02
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S196000, C525S201000, C525S330200, C473S373000, C473S378000, C473S385000
Reexamination Certificate
active
06613843
ABSTRACT:
This invention relates to golf ball materials which are effectively moldable and capable of providing golf balls with outstanding rebound and feel when hit. It also relates to golf balls made with such golf ball materials.
BACKGROUND OF THE INVENTION
Over the past few years, wide use has been made of ionomer resins in golf ball cover materials, also referred to hereinafter as “cover stock.” Ionomer resins are ionic copolymers composed of an olefin such as ethylene in combination with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid, wherein the acidic groups are partially neutralized with metal ions such as sodium, lithium, zinc or magnesium ions. They have excellent characteristics such as durability, rebound and scuff resistance, making them highly suitable as the base resin in golf ball cover stock.
Ionomer resins account for most of the cover stock resin in current use and enable the production of golf balls having the above properties. However, golfers are always on the lookout for golf balls having a high rebound and excellent flight characteristics.
Research works have been made on the use of ionomer resins in the cover stock for improving the rebound energy of golf balls. Many research works utilize the synergistic effect of blending two or more ionomer resins to provide better characteristics than a single ionomer resin. Prior art proposals include blending of ionomers neutralized with different metal species and blending of a hard binary ionomer with a soft ternary ionomer.
For example, U.S. Pat. No. 5,120,791 discloses a cover formed of a mixture of a sodium or zinc-neutralized binary ionomer and a sodium or zinc-neutralized ternary ionomer. This cover material, however, is less resilient than a cover material based on a magnesium-neutralized ternary ionomer which was recently marketed. Therefore, this material now finds only use as a low resilience cover material.
U.S. Pat. No. 5,688,869 discloses a cover composition comprising a binary ionomer having an acid content of at least 16% and neutralized with various metal ions and a ternary ionomer containing an acrylate as a comonomer and neutralized with various metal ions. The use of this cover composition provides a golf ball with somewhat improved flight performance over prior art cover compositions.
However, since the cover composition of the above formulation uses a high acid content ionomer having a very high rigidity, the resulting ball exhibits a hard feel when hit and discourages low-handicap golfers who make much of feel and controllability. While a number of cover compositions based on combinations of ionomer resins with various neutralizing metal ions are exemplified, any of these combinations merely achieves a resilience approximate to that of prior art cover compositions. An optimum combination of metal species has not been discovered.
In JP-A 10-15115, a cover material comprising a ternary magnesium ionomer is disclosed as exhibiting both a good feel and resilience. Although this cover material is more resilient than a prior art cover material comprising a blend of sodium and zinc ionomers, it has low productivity in that the magnesium ionomer is so hygroscopic that the percentage of molding defectives is very high due to moisture absorption as compared with prior art sodium and zinc ionomers.
As noted above, a number of methods have been proposed which utilize the synergistic improvements in physical properties by the blend of ionomers with different metal species or the blend of binary and ternary ionomers. However, a method of utilizing an ionomer resin neutralized with a single metal species or utilizing only a ternary ionomer has not been under consideration although such a method is essentially advantageous from step and cost aspects and easy to produce due to good compatibility. Regrettably, the use of a commercially available ionomer resin alone results in a substantial decline of resilience.
WO 98/46671 discloses a resin composition in which a large amount of metallic soap is added to an ionomer resin to improve the rebound characteristics of the ionomer cover stock. Specifically, a large amount of calcium stearate is added to an ionomer resin to formulate a cover composition which exhibits better rebound than earlier ionomer cover golf balls.
However, because a large amount of metallic soap is added to the ionomer resin in this prior-art cover stock, the fatty acids that form due to decomposition of the metallic soap vaporize during injection molding, generating a large amount of gas. The formation of a large amount of gas during injection molding causes molding defects. In addition, gas constituents settle on the surface of the molded article and greatly lower the paintability of the molded article. Moreover, although such cover stock in which a large amount of metallic soap is added to the ionomer resin does exhibit a rebound which is about the same as or better than that of ionomer having the same degree of hardness, the improvement in rebound is not all that large. Indeed, depending on the type of metallic soap used, the moldability and rebound may in fact be severely compromised and fall far short of practical levels.
SUMMARY OF THE INVENTION
Therefore, one object of the invention is to provide a golf ball material which is effectively moldable and capable of providing a golf ball of outstanding rebound and feel. Another object of the invention is to provide a golf ball made using the golf ball material.
In search of a golf ball material which is highly productive and resilient and capable of forming a golf ball with improved rebound and a soft feel, the inventors have found that a golf ball material comprising a soft calcium-neutralized ionomer is significantly improved in physical properties as compared with ionomers neutralized with other metal ions and that a blend thereof with a hard calcium-neutralized ionomer, that is, the use of soft and hard ionomers neutralized with the same metal species provides markedly high resilience or rebound characteristics as compared with the known ionomer blends. The present invention is predicated on this finding.
According to the invention, there is provided a golf ball material comprising (a) a ternary calcium ionomer in the form of a calcium ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer having an acid content of 2 to 12% by weight, and (b) a binary calcium ionomer in the form of a calcium ion-neutralized product of an olefin-unsaturated carboxylic acid random copolymer having an acid content of 8 to 15% by weight, in a weight ratio from 100:0 to 40:60, component (a) or the mixture of components (a) and (b) having a Shore D hardness of 30 to 60.
Preferably, component (a) or the mixture of components (a) and (b) has a melt index of 0.5 to 15 dg/min. Preferably, the ternary calcium ionomer (a) has a degree of neutralization of 10 to 90 mol % and the binary calcium ionomer (b) has a degree of neutralization of 10 to 90 mol %.
In a second aspect, the invention provides a golf ball comprising a core and a cover, the cover being made of the golf ball material defined above. The invention also provides a multi-piece golf ball comprising a core and a cover of at least two layers, at least one layer of the cover being made of the golf ball material defined above.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The golf ball of the invention uses as a golf ball material (a) a ternary calcium ionomer in the form of a calcium ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer having an acid content of 2 to 12% by weight, or a mixture consisting of component (a) and (b) a binary calcium ionomer in the form of a calcium ion-neutralized product of an olefin-unsaturated carboxylic acid random copolymer having an acid content of 8 to 15% by weight.
The olefin used as a monomer in the ternary calcium ionomer (a) and the binary calcium ionomer (b) is preferably an unsaturated hydrocarbon of 2 to 8 carbon atoms, for example, e
Ichikawa Yasushi
Takesue Rinya
Bridgestone Sports Co. Ltd.
Buttner David J.
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