Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-24
2001-12-11
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S394000, C524S398000, C524S399000, C473S351000, C473S365000, C473S376000, C473S377000, C473S378000, C473S379000, C473S380000, C473S381000, C473S382000, C473S383000, C473S384000
Reexamination Certificate
active
06329458
ABSTRACT:
This invention relates to golf ball cover compositions and golf balls. More particularly, it relates to ionomer resin base cover compositions and golf balls having a cover made thereof.
BACKGROUND OF THE INVENTION
Ionomer resins have been widely used as the golf ball cover material. Since ionomer resins can impart improved play characteristics such as durability and resilience, they are advantageously used as the base resin of golf ball cover materials.
The ionomer resins are ionic copolymers of an olefin such as ethylene and an unsaturated carboxylic acid such as methacrylic acid or maleic acid wherein some acidic groups are neutralized with a metal ion such as sodium, lithium, zinc or magnesium ion.
The use of the ionomer resins as the golf ball cover material, however, has drawbacks including a hard hitting feel and the lack of flexibility necessary to impart a sufficient spin to control the ball in flight. Since the ionomer resins are relatively hard, the ball cannot be fully impressed against the club head surface upon impact so that the ball may receive a reduced spin rate. If a harder ionomer resin is used as the cover material, the feel of the ball accordingly becomes very hard.
It is thus desirable to have a golf ball having good spin properties and a pleasant feel in which experienced low-handicap golfers and professional golfers are interested. Great efforts have been made to this end.
Specifically, in order to overcome the drawback of ionomer resin that the feel of the ball when hit is hard and to further improve the resilience characteristic of ionomer resin, a number of golf ball cover compositions have been proposed. For example, JP-A 5-3931 discloses a cover composition in which a soft ionomer resin obtained by neutralizing an olefin-acrylic acid-(meth)acrylate ternary copolymer is blended with a high hardness ionomer resin for the purpose of improving the feel of the ball when hit. Using as the cover material a mixture of a hard ionomer resin and a soft ternary ionomer resin containing a (meth)acrylate as one monomer, the ball is increased in distance at no sacrifice of durability.
The cover material comprising in simple admixture the hard ionomer resin and the soft ternary ionomer resin maintains approximately equivalent resilience as compared with a single ionomer resin of the same hardness, but fails to achieve a significant improvement in resilience.
U.S. Pat. Nos. 5,312,857 and 5,306,760 disclose cover compositions in which high levels of metal soaps are added to ionomer resins for the purpose of improving the cost and resilience of ionomer cover material. Allegedly, these compositions are cost effective and increased in resilience (or coefficient of restitution) as compared with prior art ionomer cover materials.
The cover compositions of these patents, however, have very low paint coatability. When the cover of a two-piece ball or the outer cover layer of a multi-piece ball is made of such a cover composition and coated with paint, the cover is often repellent to the paint coating. Even when the paint coating uniformly adheres to the cover, the coating can be readily peeled off by impact. As compared with ionomer resin covers of the same hardness, an improvement in resilience is made by the addition of metal soaps to the same extent or a slightly greater extent, but not to a greater extent. A particular type of metal soap added can significantly detract from moldability and resilience. From these points of view, the cover compositions of the above patents are unacceptable for practical use.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball cover composition which has improved moldability, resilience and coating receptivity while providing the ball with a pleasant feel when hit. Another object of the invention is to provide a golf ball using the cover composition.
In one aspect, the invention provides a golf ball cover composition primarily comprising a mixture of a base resin and a metal soap defined herein as (d). The base resin is comprised of an ionomer resin component containing (a) a ternary ionomer resin in the form of a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer having an acid content of up to 12% by weight and (b) a binary ionomer resin in the form of a metal ion neutralized product of an olefin-unsaturated carboxylic acid copolymer having an acid content of up to 15% by weight in a weight ratio of from 40:60 to 100:0. The ionomer resin component is blended with (c) a non-neutralized random copolymer formed from olefin and unsaturated carboxylic acid monomers in a weight ratio of from 75:25 to 100:0, yielding the base resin. The base resin is mixed with (d) a metal soap obtained by neutralizing an organic acid having up to 29 carbon atoms with a monovalent to trivalent metal ion. The weight ratio of the base resin to the metal soap is from 95:5 to 80:20. The composition has a melt index (MI) of at least 1 dg/sec.
Preferably, the mixture has a Shore D hardness which is higher than the Shore D hardness of the base resin by 1 to 5 units.
In one preferred embodiment, the metal soap (d) has been formed by double decomposition. The metal soap is selected from among magnesium stearate, calcium stearate, zinc stearate or a mixture thereof, and more preferably is a mixture of magnesium stearate and calcium stearate in a weight ratio of from 25:75 to 75:25.
The golf ball cover composition may further contain (e) 0.5 to 5 parts by weight of an epoxy group-modified polyolefin or acid-modified polyolefin wax per 100 parts by weight of the mixture.
Also contemplated herein is a golf ball comprising a core and a cover formed around the core. In one embodiment, the cover is formed of the cover composition of the invention. In another embodiment, the cover has a multilayer structure of at least two layers, and at least one layer of the cover other than the outermost layer is formed of the cover composition of the invention.
The cover composition of the invention is based on the mixture of the ionomer resin-containing base resin and the metal soap. As compared with the prior art ionomer resin/metal soap blend cover compositions, the cover composition of the invention is drastically improved in moldability, resilience and paint coating receptivity by optimizing its hardness and melt index. The golf ball having a cover made of the composition has improved resilience and a good feel when hit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The cover composition of the invention contains the above-mentioned components (a) to (d), of which components (a) and (d) are essential and components (b) and (c) are optional.
Component (a) is essential to constitute the ionomer resin component in the inventive cover composition. It is a ternary ionomer resin comprising a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer. It is obtainable by polymerizing olefin, unsaturated carboxylic acid and unsaturated carboxylic ester monomers to form a random copolymer and neutralizing the copolymer with a metal ion.
The olefins used herein include those of 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms, for example, ethylene, propylene, butene, hexene, heptene, and octene, with ethylene being preferred.
The unsaturated carboxylic acids used herein include, for example, acrylic acid, methacrylic acid, maleic acid and fumaric acid, with acrylic acid and methacrylic acid being preferred.
The unsaturated carboxylic esters used herein are lower alkyl esters of the above-described unsaturated carboxylic acids and include, for example, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, propyl methacrylate, and propyl acrylate.
Component (a) is a random copolymer of the olefin, unsaturated carboxylic acid and unsaturated carboxylic ester wherein some carboxyl groups in the unsaturated carboxylic acid are neutralized with metal ions. The degree of neutralization is generally 20 to 80 mol %, preferably 25 to 75 mol %. With too low a de
Ichikawa Yasushi
Kashiwagi Shunichi
Takesue Rinya
Bridgestone Sports Co. Ltd.
Sughrue & Mion, PLLC
Szekely Peter
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