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
2000-09-13
2002-12-10
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, C525S330600, C473S378000, C473S385000
Reexamination Certificate
active
06492464
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to golf balls having ionomeric covers, and more particularly to golf balls having covers formed from acrylate ester-containing ionic copolymers.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E. I. DuPont deNemours & Company under the trademark “Surlyn®” and by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademark “Escor®” and the tradename “lotek”, have become the materials of choice for the construction of golf ball covers over the traditional “balata” (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability necessary for repetitive play.
Ionomeric resins are ionic copolymers of an olefin such as ethylene and a metal salt of an 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 groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc., for golf ball cover construction over balata. However, the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because the durable ionomeric resins tend to be very 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.
As a result, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, 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 reinforcements, 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”) characteristics previously associated with the “soft” balata covers, properties which are still desired by the more skilled golfer.
In various attempts to produce a durable, high spin ionomeric golf ball, the golfing industry has blended the hard ionomeric resins with a number of softer ionomeric resins. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid, and an acrylate ester. It has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of hard ionomer alone. It would be useful to develop a golf ball having a combination of softness and durability which is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball with a soft cover which has good scuff resistance.
Yet another object of the invention is to provide a golf ball having a favorable combination of spin rate and durability.
A further object of the invention is to provide a golf ball having a soft cover made from a cover material which is blended with minimal mixing difficulties.
Another object of the invention is to provide a method of making a golf ball which has a soft cover with good scuff resistance and cut resistance.
Yet another object of the invention is to provide a method of making a durable golf ball with a relatively high spin rate.
Other objects will be in part obvious and in part pointed out more in detail hereafter.
The invention in a preferred form is a golf ball comprising a core and a scuff-resistant cover. The cover comprises an ionomeric resin having more than 90 weight % of one or more acrylate ester-containing ionic copolymers. The one or more acrylate ester-containing ionic copolymers are each formed from (a) an olefin having 2 to 8 carbon atoms, (b) an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms, and (c) an acid which includes at least one member selected from the group consisting of &agr;, &bgr;-ethylenically unsaturated mono- or dicarboxylic acids with a portion of the acid groups being neutralized with cations. The one or more acrylate ester-containing ionic copolymers have an overall Shore D hardness of 40-64. The resulting golf ball has a coefficient of restitution of at least 0.770.
The one or more acrylate ester-containing ionic copolymers preferably are terpolymers. In each copolymer, the olefin preferably is an alpha olefin, and the acid preferably is acrylic acid. The overall cover preferably has a Shore D hardness of no more than about 64, and more preferably about 40 to 64.
The one or more acrylate ester-containing ionic copolymers typically have a degree of neutralization of the acid-groups in the range of about 10-100%. In a preferred form of the invention, the covers have a scuff resistance rating of 3.0 or better when subjected to the Golf Ball Cover Scuff Test which is described below.
In a particularly preferred form of the invention, the cover comprises an ionomeric resin having at least 95 weight % of one or more acrylate ester-containing ionic copolymers. The cover preferably contains at least 90 weight % ionomeric resin. Each of the acrylate ester-containing copolymers preferably comprises ethylene, at least one acid selected from the group consisting of acrylic acid, maleic acid, fumaric acid, itaconic acid, methacrylic acid, and half-esters of maleic, fumaric and itaconic acids, and at least one comonomer selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl, and 2-methoxyethyl-1-acrylates.
Another preferred form of the invention is a method of making a golf ball. The method comprises the steps of obtaining a golf ball core and forming a scuff-resistant cover over the core. The cover comprises an ionomeric resin having more than 90 weight % of one or more acrylate ester-containing ionic copolymers formed from (a) an olefin having 2 to 8 carbon atoms, (b) an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms, and (c) an acid which is selected from the group consisting of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acids with a portion of the acid groups being neutralized with cations. The one or more acrylate ester-containing ionic copolymers preferably have a Shore D hardness of about 40-64.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others and the article possessing the features, properties, and the relation of elements exemplified in the following detailed disclosure.
DETAILED DESCRIPTION OF THE INVENTION
The present invention overcomes mixing difficulties associated with the preparation of soft-covered ionomeric golf balls by forming the cover of soft ionomeric golf balls from a cover composition in which the ionomer has more than 90 weight % of an acrylate ester-containing ionic copolymer or blend of acrylate ester-containing ionic copolymers. Furthermore, the invention provides golf ball covers having a favorable combination of durability and spin rate.
The one or more acrylate ester-containing ionic copolymers to be used in forming the cover of the inventive golf ball each contain an olefin, an acrylate ester, and an acid. In a blend of two or more acrylate ester-containing ionic copolymers, each copolymer may contain the same or a different olefin, acrylate ester and acid than are contained in the other copolymers. Preferably, the acrylate ester-containing ionic copolymer or copolymers are terpolym
Buttner David J.
Spalding Sports Worldwide Inc.
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