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
1999-11-22
2001-10-16
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...
C525S263000, C525S314000, C525S332500, C525S387000, C525S420000, C475S301000, C475S152000
Reexamination Certificate
active
06303704
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to game balls, and more particularly to a game ball, such as a golf ball, having a cover formed predominantly from a non-ionomer polymeric material.
Before the development of ionomers, balata was the preferred material for golf ball covers. Polyethylene also was proposed for use as a golf ball cover material but was generally deemed highly inferior to balata in imparting playability and durability characteristics to the ball due to its brittleness and high hardness, and thus never became a commercially successful golf ball cover material.
Balata golf ball covers have now been replaced to a great extent by ionomeric cover materials. Ionomers are copolymers of an olefin and an &agr;, &bgr;-ethylenically unsaturated carboxylic acid with a portion of the carboxylic acid groups neutralized by a metal ion. The metal ions serve as crosslinking agents, as they are ionically bonded to carboxylic acid groups in adjacent copolymer chains. Instead of having thermally irreversible covalent bonding, ionomers have thermolabile crosslinking bonds in which metal ions become part of the chemical structure of the ionomer upon crosslinking, and these crosslinks are reversible. For purposes of this application, this type of crosslinking is referred to as ionic crosslinking. One of the advantages of ionic crosslinking in golf ball materials is the ability of ionic bonds to re-form after breaking as a result of processing at elevated temperatures.
There are numerous advantages to the use of ionomers in making golf ball covers. On the other hand, one drawback of conventional golf balls with soft ionomeric covers are that the covers are prone to scuffing and cutting, particularly when hit with irons which have sharp grooves. It would be useful to develop a golf ball with a soft cover which is highly resistant to cutting and scuffing by sharp-grooved clubs.
SUMMARY OF THE INVENTION
An object of the invention is to provide a non-ionomeric game ball cover having improved scuff resistance and/or cut resistance.
Another object of the invention is to provide a method for imparting improved scuff resistance and/or cut resistance to a game ball cover.
Yet another object of the invention is to provide a golf ball with a soft cover which is well-suited for use with golf club irons having sharp grooves.
Yet another object of the invention is to provide a method of forming a golf ball with a soft cover which has excellent scuff resistance and/or cut resistance.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
The invention in a preferred form is a game ball having a cover comprised predominantly of a non-ionomer resin. The resin advantageously has a sufficient degree of covalent crosslinking to impart to the cover improved resistance to at least one of scuffing and cutting. In a particularly preferred form of the invention, the game ball is a golf ball and, preferably, has a dimpled surface. The covalent crosslinking preferably comprises peroxide or irradiation-induced covalent crosslinking.
In a preferred form of the invention, the degree of covalent crosslinking is appropriate to impart to the cover a Shore D hardness which is no more than about 10% greater, and more preferably no more than about 5% greater, than the Shore D hardness of a cover having an identical composition but which does not include a substantial degree of peroxide or radiation-induced covalent crosslinking.
Another preferred form of the invention is a method of treating a game ball. The method comprises the steps of obtaining a game ball having a cover comprised predominantly of a non-ionomer polymeric resin, and irradiating the resin in the cover under conditions appropriate to covalently crosslink the cover material in order to increase the resistance of the cover to at least one of scuffing and cutting without substantially impairing other playability or physical characteristics of the ball. In a particularly preferred form of the invention, the game ball is a golf ball. Preferably, the game ball has a dimpled surface.
Alternatively, the cover material can be formulated with an effective amount of peroxide to achieve the desired crosslinking and improved scuff and cut resistance. The peroxide-containing non-ionomeric polymers are formulated, milled, sheeted and chopped in a typical fashion and used to mold covers on standard golf ball cores. During the molding operation, the cover material is subjected to heat and pressure to effect the curing of the polymeric material.
According to the preferred method of the invention, the game ball cover is subjected to gamma radiation treatment at a dosage of at least 2 megarads. The game ball cover preferably is irradiated prior to application of a top coat over the cover. The method of the invention preferably further includes the step of applying a top coat over the cover before or after irradiation.
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 game balls of the present invention are surprisingly superior in their scuff (abrasion) resistance and cut resistance to conventional game balls which have not been crosslinked, and which contain similar quantities of non-ionomeric compositions, such as polyurethanes, with similar properties of compression, coefficient of restitution (COR) and hardness.
In accordance with one aspect of the invention, the cover compositions and resulting molded covers of the present invention are manufactured using relatively conventional techniques. In this regard, the compositions of the invention preferably are based on a variety of materials blended together with peroxide crosslinking agents and minor amounts of secondary constituents such as co-crosslinking agents, fillers and the like. Peroxides which are readily available are conveniently used in the present invention, generally in amounts of from about 0. 1 to about 10.0 and preferably in amounts of from about 0.3 to about 3.0 parts by weight of 40% active peroxide per each 100 parts of base polymer material.
Exemplary of suitable peroxides for the purposes of the present invention are dialkyl peroxides such as dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well as mixtures thereof. It will be understood that the total amount of crosslinking agent used will vary depending on the specific end product desired and the particular initiators employed. Commercially available peroxides include n-butyl 4,4-bis (butylperoxy) valerate having a one hour half life at about 112° C., and 1,1-bis(t-butylperoxy-3,3,5-trimethyl cyclohexane having a one hour half life at about 129° C.
In producing golf ball covers utilizing the present compositions, the ingredients may be intimately mixed using, for example, two roll mills or a Banbury® mixer until the composition is uniform, usually over a period of from about 5 to about 20 minutes. The sequence of addition of the components is not critical. A preferred blending sequence is as follows.
The primary polymeric material, crosslinking agent, fillers and the like are blended for about 7 minutes in an internal mixer such as a Banbury® mixer. As a result of shear during mixing, the temperature may rise to about 200° F. The mixing is desirably conducted in such a manner that the composition does not reach incipient polymerization temperatures during the blending of the various components. The batch is discharged onto a two roll mill, mixed for about one minute and sheeted out, following which it is chopped into granular form and molded as half shells. The molding process is carried out preferably at pressures up to 5 tons and temperatures of 200° to 250° C. for a heating time of 5
Buttner David J.
Spalding Sports Worldwide Inc.
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