Games using tangible projectile – Golf – Ball
Reexamination Certificate
2003-05-29
2004-07-13
Gorden, Raeann (Department: 3711)
Games using tangible projectile
Golf
Ball
Reexamination Certificate
active
06761648
ABSTRACT:
TECHNICAL FIELD
This invention relates to a golf ball comprising a core and a cover of one or more layers enclosing the core.
BACKGROUND ART
Ionomer resins are frequently used as the base resin for forming the cover of modern golf balls because the ionomer resins have improved durability, cut resistance and resilience or rebound and are easy to work.
However, golf balls using ionomer resins as the cover base resin still leave room for further improvement in rebound performance and flight distance. In particular, many users complain to the manufacturer of their request to drive the ball farther even a little. There is a need to have a golf ball having higher rebound performance and better flight performance.
To meet such a demand, acrylic acid base ionomer resins having higher rebound performance have been used as the cover base resin. See JP-B 4-49426, Japanese Patent Nos. 3,047,919, 3,119,858, 2,979,272, 3,257,739 and JP-A 9-225068. These patents use as the cover base resin a blend of an acrylic acid ionomer resin neutralized with a monovalent ion such as sodium ion and an acrylic acid ionomer resin neutralized with a divalent ion such as zinc ion, or a blend of a binary acrylic acid ionomer resin and a ternary acrylic acid ionomer resin.
The use of a ternary acrylic acid ionomer resin is effective for softening at the substantial sacrifice of resilience. Also, a blend of a monovalent ion-neutralized acrylic acid ionomer resin and a divalent ion-neutralized acrylic acid ionomer resin is insufficient in resilience. There exists a need for further improvement.
Related improvements taught by the prior art (see U.S. Pat. No. 5,312,857, U.S. Pat. No. 5,306,760, and International Application WO 98/46671) include cover materials in which a large amount of metallic soap is added to the ionomer resin to improve the cost and rebound characteristics of the ionomer cover material.
These cover materials, however, fall far short of practical levels. During injection molding, the metallic soap in the cover material decomposes and vaporizes to generate a large amount of fatty acid gas, often causing molding defects. In addition, gas constituents settle on the surface of the molded part to greatly lower the paintability thereof. Moreover, although such cover material in which a large amount of metallic soap has been added to the ionomer resin does exhibit a rebound which is about the same as or better than that of metallic soap-free ionomer cover material 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 of cover material may in fact be severely compromised.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a golf ball using a cover material based on a binary acrylic acid ionomer resin and having improved thermal stability, fluidity and moldability, which ball has improved rebound, feel and durability.
It has been found that a mixture comprising (a) an ionomer resin in the form of a divalent metal-neutralized ethylene-acrylic acid copolymer, (b) an optional copolymer which is an olefin-unsaturated carboxylic acid copolymer or olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer, (c) a specific thermoplastic elastomer, (d) a fatty acid or derivative thereof having a molecular weight of 280 to 1,500, and (e) a basic metal compound, in a specific proportion is useful as a cover material because this mixture is thermally stable, flowable and easy to mold, and that a golf ball obtained by molding the mixture has improved rebound, feel and durability.
The present invention relates to a golf ball comprising a core and a cover of one or more layers enclosing the core. According to the invention, at least one layer of the cover is formed primarily of a mixture comprising a blend of (a) an ionomer resin in the form of a divalent metal-neutralized ethylene-acrylic acid copolymer and (b) an olefin-unsaturated carboxylic acid copolymer or an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer, (c) a thermoplastic elastomer, (d) a fatty acid or derivative thereof having a molecular weight of 280 to 1,500, and (e) a basic metal compound. The thermoplastic elastomer (c) is selected from the group consisting of an olefin base thermoplastic elastomer, styrene base thermoplastic elastomer, polyester base thermoplastic elastomer, polyurethane base thermoplastic elastomer, and polyamide base thermoplastic elastomer. The ionomer resin (a) and the copolymer (b) are blended in a weight ratio (a)/(b) of from 100/0 to 80/20. The blend and the thermoplastic elastomer (c) are mixed in a weight ratio [(a)+(b)]/(c) of from 100/0 to 50/50. Components (a) to (c) are mixed with components (d) and (e) in a weight ratio [(a)+(b)+(c)]/(d) of from 100/5 to 100/25 and in a weight ratio [(a)+(b)+(c)]/(e) of from 100/0.1 to 100/10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Component (a) is an ionomer resin in the form of a divalent metal-neutralized ethylene-acrylic acid copolymer. This ionomer resin is obtained by partially neutralizing acid groups on an ethylene-acrylic acid copolymer with divalent metal ions. The divalent metal ions used herein are, for example, Zn
++
, Mg
++
and Ca
++
, but not limited thereto, with Zn
++
being preferred.
Well-known methods may be employed in partially neutralizing acid groups on the ethylene-acrylic acid copolymer with divalent metal ions. One typical method is to mix the ethylene-acrylic acid copolymer with suitable compounds of the metal ions such as formates, acetates, nitrates, carbonates, hydrogen carbonates, chlorides, hydroxides and alkoxides.
The degree of neutralization of acid groups on the ethylene-acrylic acid copolymer with divalent metal ions is preferably 10 to 90%, more preferably 20 to 70%, though not critical. With too high or too low a degree of neutralization, the efficiency of mixing may be compromised.
The ethylene-acrylic acid copolymer can be obtained through random copolymerization of ethylene monomer and acrylic acid monomer by well-known methods. It is recommended that the content of acrylic acid (simply referred to as acid content) in the copolymer be at least 4%, preferably at least 6%, more preferably at least 8%, even more preferably at least 10% by weight, and up to 30%, preferably up to 25%, more preferably up to 20%, even more preferably up to 15% by weight. Too low an acid content may lead to a decline of resilience whereas too high an acid content may detract from workability.
The ionomer resin (a) in the form of a divalent metal-neutralized ethylene-acrylic acid copolymer usually has a Shore D hardness of at least 50, preferably at least 55, more preferably at least 60, and up to 80, preferably up to 75, more preferably up to 70. Too high a hardness may adversely affect the feel of the ball when hit whereas too low a hardness may lead to a decline of resilience.
The ionomer resin (a) in the form of a divalent metal-neutralized ethylene-acrylic acid copolymer is commercially available, for example, under the trade name of Iotek 7010, 7610, 7020, 7030, 7410, 7310 and 4200 from ExxonMobil Chemical, but not limited thereto.
Component (b) is an olefin-unsaturated carboxylic acid copolymer or an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer, which can be obtained through random copolymerization of an olefin, an unsaturated carboxylic acid and optionally, an unsaturated carboxylate by well-known methods.
The olefin in the copolymer preferably has at least 2 carbons and up to 8 carbons, more preferably up to 6 carbons. Examples include ethylene, propylene, butene, pentene, hexene, heptene and octene, with ethylene being especially preferred. The olefins may be used alone or in admixture of any.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Acrylic acid and methacrylic acid are preferred for compati
Ichikawa Yasushi
Takesue Rinya
Bridgestone Sports Co. Ltd.
Gorden Raeann
LandOfFree
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