Golf Ball

Abstract

One-piece, nonhomogeneous, molded golf ball is obtained by forming a center of an uncured elastomeric material, surrounding the center with a compatible but different uncured elastomeric material, and curing both elastomeric materials, such that when said materials are cured they become integral with each other to form an one-piece molded golf ball which is harder at its center than at its outer surface.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a novel solid golf ball and more particularly, to an one-piece, nonhomogeneous, molded golf ball formed by curing two elastomeric materials such that the cured elastomeric materials become integral and the resulting golf ball is harder at its center than its outside surface.

The United States Golf Association (USGA) has established certain requirements and characteristics for golf balls used in tournament play. For example, golf balls must have a diameter greater than 1.680 inches; must weigh less than 1.620 ounces; and cannot have an initial velocity of more than 255 feet per second, as measured on a standard USGA golf ball testing machine. In addition to these required characteristics, golf balls must be round and retain their roundness even after use; must be well balanced for travel in the air and on the ground; and must be able to withstand the rigors of play without adverse physical effect.

For many years the wound golf ball was the standard used by all golfers. The wound golf ball, developed by Haskell prior to 1900, involves the laborious winding of elastic thread tightly around a suitable core (either solid or liquid) and then enclosing the winding within a protective cover, such as a cover of a gutta-percha compound. The characteristics of the wound golf ball can be controlled by suitable selection of the core, the winding tension and the cover. Wound golf balls, however, have two major drawbacks. They are expensive to fabricate, typically involving an eight step process which includes: core-forming, core-filling, thread-making, thread-winding, coverstock mixing, cap-making, cover-pressing, and vulcanizing. The other major drawback of wound golf balls is their tendency to be rendered unsatisfactory for further use due to cutting and damage of the outer cover -- particularly when hit with the edge of a golf club.

In order to eliminate many of the disadvantages of the wound golf ball, a unitary golf ball composed of a homogeneous solid was developed. The homogeneous molded golf balls simplified the procedure for making golf balls -- requiring only mixing, extruding, slug forming and heat molding. Although less expensive to manufacture, homogeneous golf balls have had the serious disadvantage of being substantially inflexible resulting in the golf ball fracturing when contact by a golf club is made with the golf ball. It has been estimated that a golf club head may be moving at a speed approximately 166 feet per second when striking a golf ball and that the club exerts an impact as much as 1000 pounds when the golf ball is struck.

In order to improve the playing characteristics of unitary golf balls and eliminate the "shock" or "jolt" transmitted to the player when contact by a golf club is made with a solid golf ball, an attempt was made to provide a molded and cured golf ball center with a separate cover. It was hoped that this would result in a golf ball having a desirable combination of characteristics which would be acceptable for tournament use. Nevertheless, in spite of constant and continual efforts to produce a completely satisfactory molded golf ball, none have been successfully produced. The separately molded cover tends to fracture or separate from the golf ball center in actual use.

SUMMARY OF THE INVENTION

It is an object of this invention to produce a novel one piece, non-homogeneous, molded golf ball possessing improved properties and characteristics which is cheaper to manufacture than a conventional wound golf ball.

Another object of this invention is to provide an one-piece, non-homogeneous, molded golf ball having characteristics satisfactory to players while meeting the requirements necessary for tournament use.

Still another object of this invention is to produce a nonhomogeneous, molded solid golf ball having a center which is harder than its cover, as determined by durometer measurements.

In accordance with the invention, I have discovered that an one-piece, nonhomogeneous molded golf ball can be produced by (a) forming a center of uncured elastomeric material (center material), (b) providing a cover for the center material of a compatible uncured elastomeric material (cover material), (c) enclosing the two elastomeric materials (center and cover materials) in a mold, and (d) curing both elastomeric materials in a single operation whereby the elastomeric materials become integral with each other to form an one-piece, molded golf ball which has a center which is harder than the cover, as determined by durometer measurements.

While the compositions of each of the two elastomeric materials can be different, normally the compositions are composed of varying amounts of the same elastomer, copolymerizable monomer, polymerization initiator and filler. Heat, with pressure, is used to cure the elastomeric compositions into the form of a golf ball.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The elastomers which may be used for the center and cover of the golf ball can be the same (provided the other ingredients are different) or different (provided the elastomers are compatible). Suitable elastomers include any elastomer which is capable of being cross-linked and preferably such elastomers constitute a homopolymer, copolymer or terpolymer of butadiene, isoprene or chloroprene. Most preferably, the elastomer is a cisbutadiene rubber containing at least 40 percent cis. Examples of other elastomers which can be used, provided they have sufficient molecular weight for the intended purpose, include chlorinated polyethylene; olefins, such as ethylene and propylene, in the form of homopolymers, copolymers and terpolymers; silicone rubbers; propylene oxide polymers; butyl rubber, polysulfides; urethane elastomers; styrene copolymerized with either acrylic or methacrylic esters of alcohols containing at least 4 carbon atoms; and the like.

The monomers which can be used in connection with the aforementioned elastomers are those capable of cross-linking the aforementioned elastomers and undergoing further polymerization. Examples of such monomers include: vinyl, allyl, methallyl, furfuryl, crotyl and cinnamyl esters of the following acids: oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, maleic, itaconic, citraconic, mesaconic, furmaric, aconitic, phthalic, isophthalic, terephthalic, naphthalic, dicarboxylic, mellitic, pyromellitic, trimesic, acrylic, methacrylic, cinnamic and crotonic. Also suitable are polyamine amides and imides of the following acids: maleic, itaconic, acrylic, methacrylic, crotonic, citaconic, aconitic and cinnamic; polyol esters and anhydrides of acrylic, methacrylic, crotonic and cinnamic acids. Other suitable materials include di- and triallyl cyanurate; di- and triallylmelamine, divinyl benzene; diallyl benzene; diallyl amine; allyl ether; allyl gycolates; di-, tri and tetravinyl and allyl silanes. Still further suitable materials are low molecular weight reactive monomers of butadiene, isoprene, chloroprene and epoxidized derivatives of these materials. The diacrylates and dimethacrylates, as for example butylene glycol dimethacrylate, are preferable though divinyl compounds, such as divinyl benzene, are also highly suitable.

The amount of the monomer must be at least 20 percent by weight of the elastomer in order to obtain the necessary degree of cross-linking to form the required three dimensional molecular network and to give the ball its characteristics. Amounts of the cross-linking monomer used in the elastomeric composition in the center of the golf ball, as high as 90 percent by weight of the elastomer, may be used, but amounts between about 30 and 60 percent by weight of the elastomer are preferred. The amount of monomer used in the elastomeric composition at the outer surface of the golf ball may be as high as 80 percent by weight of the elastomer, but amounts between about 35 and 70 percent by weight of the elastomer are preferred.

Any known or conventional filler may be used to reinforce the elastomeric compositions. The filler should be in finely divided form, as for example in a form between about +20 and -325 and preferably +60 and -325 mesh U. S. Standard screen size. Most preferably the filler material is in the form of a silica or silicate as fillers. In addition to silica and silicate fillers, such as finely divided porous SiO.sub.2, alkali metal silicates, such as calcium silicate; and the like, and other fillers in addition or in place of the silica, or silicates, such as carbon black, cork, titania, cotton flock, cellulose flock, leather fiber, plastic fiber, plastic flour, leather flour; fibrous fillers, such as asbestos, glass, and synthetic fibers, metal oxides, carbonates, and talc can be used.

The amount of the filler material is dictated by its type and the type of the other constituents and may vary between about 20 and 90 percent by weight of the elastomer, and preferably 30 and 70 percent of the elastomer. A lesser amount of filler can be used for the elastomeric composition of the outer portion of the golf ball.

The polymerization initiator may be any known or conventional initiator capable of causing the monomer to polymerize and cross-link. Generally, these initiators are of the free radical type, such as a peroxide, persulfate, azo compounds hydrozines, amine oxides, and the like. Peroxides, such as dicumyl peroxide and other commercially available peroxides conventionally used as polymerization catalysts may be most conveniently used.

The polymerization initiator need only be present in the catalytic amount required for this function and may be in general used in the amounts that the particular agent is generally used as a polymerization catalyst. In connection with peroxides, the same, for example, may be used in amounts of about 0.2 - 10 percent by weight of the elastomer.

When using the preferred components, the best results are obtained with compositions having 100 parts by weight of the cis-butadiene rubber and approximately 20 - 80 parts by weight of methacrylate ester and 30 - 60 parts by weight of filler.

Once the ingredients for each of the elastomeric materials have been selected, the ingredients for each elastomeric material are separately and intimately mixed together using conventional means, such as a Banbury mixer, until reasonably uniform compositions are obtained. The temperature of mixing is not critical, provided it is maintained below the curing temperature of the elastomeric materials. Normally, the uncured compatible elastomeric material, which is to provide the outer surface of the golf ball, is placed around the inner uncured elastomeric material and the elastomeric materials are then placed in the mold.

Molding is effectd in mating precision hemisphere molds or dies whose molding surfaces are covered with multiple regular projections to give the molded golf balls conventional dimpled or waffled surface appearance for desired aerodynamic characteristics. By preportioning the material placed in the mold, the mold is fully filled when the mating halves of the mold are closed. The mold halves are then held together with a pressure above 100 pounds per square inch and preferably in the range of 300 to 1,000 psi. The molding temperature may vary, depending on the various compositions used, but is normally between about 200.degree. and about 400.degree. F. The molding temperature is selected to be sufficient to cure both the uncured elastomeric material in the center of the golf ball and the uncured compatible elastomeric material which surrounds the center. The nature of the elastomeric materials in the mold and the molding temperatures are so selected that both uncured elastomeric materials cure almost simultaneously, thereby forming an one-piece, molded, solid golf ball having a center which is harder than its outside surface as determined using a durometer. Optimum results are obtained in the neighborhood of 320.degree. F., with a molding time of between ten and twenty minutes. While there is no real upper limitation on the length of the curing time, the molding should be effected until both elastomeric compositions are substantially completely cured. In general, curing times may range between about 2 and 60 minutes and preferably between about 4 and 30 minutes. Higher temperatures, i.e., temperatures above about 400.degree. F. may be used, but are generally unnecessary and undesirable.

After the molding operation is complete, the golf ball is removed from the mold. Any mold mark, where the molds mate, may be removed by suitable means such as buffing and the golf ball is then painted and marked. Painting may be effected in the conventional manner using paint such as enamel, polyurethane, epoxy, acrylic or vinyl paints.

The finished golf ball is characterized by a diameter between 1.680 and 1.685 inches in diameter; a weight controlled between 1.600 and 1.620 ounces; a roundness within at least 0.01 inch; and a density within the range of 1.11 and 1.13. The hardness of the golf ball at its center is between about 65 and about 95 and above about 30 and below about 65 at the surface of the golf ball, as measured by the Shore durometer on the "D" scale which runs from 0 for full extension to 100 for zero extension of the calibrated spring measuring instrument. Suitable Shore durometers are illustrated in the 1968 Vanderbilt Handbook at pages 307 and 308. The compression, as measured on a standard golf ball compression test machine, is between 40 and 150 points and the golf balls bounce between about 60 and 75 percent of the height from which they are dropped in accordance with the Standard Bounce Test.

The invention will be further illustrated by the following specific examples, it being understood that there is no intention to be necessarily limited by any details thereof since variations can be made within the scope of the invention.

EXAMPLE 1

A suitable composition for the uncured elastomeric material used in the center of the golf ball constitutes 100 parts by weight of cisbutadiene, 62.5 parts by weight of butylene glycol dimethacrylate, 62.5 parts by weight of fine silica filler and 3.13 parts by weight of dicumyl peroxide. The ingredients are mixed thoroughly at room temperature until the resulting material is completely homogeneous. The material (composition 1) is then formed into spherical shape of suitable size.

The compatible uncured elastomeric material is also formed from a composition containing 100 parts by weight of cisbutadiene polymer, 40 parts by weight of divinyl benzene, 65 parts by weight of fine silica filler and 3.13 parts by weight of dicumyl peroxide. These ingredients are mixed at room temperature until completely homogeneous. The resulting material (composition 2) is then placed around the spherical shaped uncured elastomeric material of composition 1 as a substantially uniform layer and both compositions are placed into a precision hemisphere mold.

Molding is effected at pressure of 150 psi and a mold temperature of 300.degree. F. for a molding time of ten minutes. This curing operation simultaneously cures both uncured elastomeric compositions to obtain an one-piece, nonhomogeneous, molded golf ball having a hardness at the center of about 70 and a hardness on the outer surface of about 45, as determined by Shore Hardness Test on the "D" scale.

After the golf ball is removed from the mold and the thin fin or flash from the mold is buffed off, the golf ball is painted and marked.

EXAMPLE II

Composition 3

A suitable composition for the uncured elastomeric material used as the center of the golf ball constitutes 100 parts by weight of cisbutadiene, 62.5 parts by weight of divinyl benzene, 37.5 parts by weight of fine silica, 6.2 parts by weight of cork, having a particle size below 60 mesh and 3.13 parts by weight of dicumyl peroxide. These ingredients are mixed until the resulting composition (composition 3) is homogeneous.

Composition 4

The compatible uncured elastomeric material comprises 100 parts by weight of cispolybutadiene, 50 parts by weight of diallyl benzene, 43 parts by weight of calcium silicate, and 2.95 parts by weight of dicumyl peroxide. These ingredients are thoroughly mixed until the resulting mixture (composition 4) is homogeneous.

Composition 4 is coated inside the surface of a mating precision hemisphere mold while composition 3 is placed in the center of the hemisphere mold. The mold is then closed and curing is effected at a pressure of 130 psi at a mold temperature of 300.degree. F. which is maintained for 12 minutes. The resulting golf ball is removed from the mold and after buffing off the thin fin, the golf ball is painted.

As an alternative to painting the golf balls, pigments (e.g., white, yellow, etc.) may be incorporated into the compatible uncured elastomeric material (composition 4) prior to molding. Thus, the resulting golf ball can be made perfectly white and thus does not have to be painted. This whiteness is permanent and the appearance is entirely adequate for use on practice ranges and other non-tournament play. Titanium dioxide is the preferred white pigment although other white pigments, such as barium sulphate, zinc sulfide, barium carbonate, etc., may be used. The amount of the white pigment should be different to give the molded ball its desired white appearance and in general amounts varying between 2 and 30 percent by weight of the total golf ball can be used.

Obviously, other ingredients which are compatible with the elastomeric materials employed to make the golf balls can be included to the extent that the overall characteristics of the golf ball are not adversely affected. Such other ingredients can include, for example, limited amounts of a plasticizer.

The thickness of the outer surface, having a hardness which is less than the center of the golf ball, normally will be greater than about one-sixteenth inch and less than about three-eighths inch.

The elastomeric materials can be placed in the curing mold either separately or together, provided both are cured together.

From the foregoing, it will be seen that this invention is well adapted to obtain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent therein. The golf balls produced in accordance with the present invention are manufactured more easily and more cheaply than conventional wound golf balls. Moreover, golf balls manufactured in accordance with the present invention may be marked by simply stamping with a flat die. The golf balls are abrasive resistant and have an almost infinite shelf life. Due to their one-piece construction, they will not waterlog and they have a superior texture and appearance. If the paint on the golf ball becomes worn or damaged, the golf ball may simply be reclaimed by removing the old paint and repainting the golf ball.

Like the best conventionally wound golf balls, the golf balls made in accordance with the present invention have all of the desirable play characteristics, including a good "click" and excellent feel when the golf balls are hit with a golf club. In contrast to the homogeneous, unitary golf ball, the shock obtained when the nonhomogeneous golf ball is struck is virtually eliminated. Unlike covered wound golf balls, the golf balls of the present invention are so highly resistant to cutting that they may, for all practical purposes, be considered cut proof and indestructible in play. Like the homogeneous unitary golf ball, the golf balls in the present invention have a perfect center of gravity, excellent aerodynamic properties and superior roll characteristics. Thus, the golf balls of the present invention combine the advantageous characteristics of both the conventionally wound balls and the homogeneous unitary golf balls without the objectionable drawbacks of either type of golf ball.

Obviously, many other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof.

Claims

What is claimed is:

1. A golf ball consisting of a solid center of an elastomeric material, an elastomeric cover material compatible with said elastomeric center material and encapsulating said center, said elastomeric cover and center materials being in direct contacting relationship and integrally bonded together, the structural characteristics of the bond between said cover and center materials corresponding to those achieved by simultaneously curing said cover and center materials while held under pressure in direct contacting engagement with each other, the hardness of said center being between about 65 and about 95, the hardness of the cover material being above about 30 and below about 65, as measured by the Shore Hardness Test on the "D" scale, and the thickness of said softer elastomeric cover material being between about one-sixteenth and about three-eighths inch.