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Mixed-resin mantle metal-core golf balls and methods of manufacturing same

Mixed-resin mantle metal-core golf balls and methods of manufacturing same description/claims

The present invention relates generally to metal core golf balls, and more particularly, to multi-sphere golf balls having a hollow metal core.

Currently, there are a myriad of commercially available golf balls. However, in order to meet the United States Golf Association (“U.S.G.A.”) specifications, the golf ball must be, among other things, spherical in shape, have equal aerodynamic properties, and equal moments of inertia about any axis through its center. In addition, the golf ball must have a minimum diameter of 1.68 inches (4.267 centimeters), a maximum weight of 1.620 ounces (45.926 grams), and a maximum initial ball velocity of 255 feet per second as measured on a standard U.S.G.A. ball-testing machine. There is also a maximum carry distance of 325 yards, again using the U.S.G.A. standard test machine.

The basic concept of the modern golf ball is the invention of Coburn Haskell and Bertram Work in 1898 at the B.F. Goodrich Co. of Akron, Ohio. The concept, as disclosed in U.S. Pat. No. 622,834, includes compressing a rubber inner core by wrapping it with an elastic thread or tape. The compression of the core results in a much higher coefficient of restitution (COR) when the ball is struck with the club head. A design-around of the U.S. Pat. No. 622,834 resulted in the replacement of the solid rubber core with a rubber pressure vessel containing compressed air. U.S. Pat. Nos. 707,263 and 785,184 to A. T. Saunders disclose a pneumatic golf ball whereby the pressure vessel was wrapped in latex-impregnated cotton or silk thread. The Saunders patents were acquired by the Goodyear Tire & Rubber Company and produced in the period prior to World War I. In its commercial embodiment, the pressure vessel was provided with about 800 psi of compressed air. Although the product produced excellent results in play, it was discontinued due to an unfortunate tendency towards catastrophic structural failures in mid-flight.

Further development of hollow-cored golf balls was delayed until the introduction of synthetic polymers, which removed the need for wrapped-pressurized cores. Examples of such hollow-cored polymer golf balls are provided in U.S. Pat. No. 5,980,395. These hollow-cored balls were designed to include a polybutadiene (specific gravity 0.92), to which a tungsten or similarly dense filler was added to increase the specific gravity. It should be appreciated that golf balls having specific gravities of about 2 g/cm3 are typically reported as being practical.

As golf ball technology advanced, golf balls with a metal hollow core were introduced. A metal hollow-cored golf ball having a polybutadiene mantle is described in U.S. Pat. Nos. 6,004,225, 6,976,925 and 705,957 to Owens et al. These Owens et al. patents disclose specifically, the use of titanium cores, and disclose generically, the use of carbon steel, nickel, molybdenum, tungsten and aluminum, and alloys thereof.

In general, a hollow core golf ball permits placement of more of the mass of the ball in its periphery, thus resulting in a substantially higher moment of inertia (MOI). The advantages of increased MOI are well known in the art and are provided in the Owens patents.

For most conventional golf balls, the core and mantle includes the incorporation of polybutadiene. However, the Owens patents disclose alternatives to the polybutadiene mantle of the metal-cored golf ball. These alternatives include synthetic rubbers, such as polyisoprene and styrene-butadiene. Other alternatives to polybutadiene have been disclosed in U.S. Pat. Nos. 6,100,321, 6,777,472 and 6,815,480, and in U.S. Publication No. 2005/0148525 to J. C. Chen and R. J. Statz et al., all of which are assigned to E.I. du Pont de Nemours and Company (“DuPont”). These highly complex thermoplastic resins include mixtures of: salts of ethylene/methylacrylic acid/butylacrylic acid “random” terpolymers (Surlyn®), magnesium stearate, and terpolymers of butylene/polyalkylene ether/phthalic acid diester (Hytrel®) mixed with ZnO. Mixtures of Surlyn®, Hytrel®/ZnO and magnesium stearate are marketed by DuPont for use in the manufacture of golf balls as High Performance plastics under the trade name “HPF.” For lack of an art-recognized generic name for such resins, these resins are hereinafter referred to as SHS resins.

Those skilled in the art can appreciate that golf ball polymers can be effectively characterized by two parameters: (1) the coefficient of restitution (“COR”), which is measured by firing a ball at a steel plate at 125 ft/sec and measuring the rebound velocity, and (2) the Atti compressibility or PGA compressibility (“Comp”), which is measured by the force needed to compress the ball. In general, a harder ball has a relatively larger Comp than the softer ball. The numerical relationship between the composition of HPF and its COR and Comp are described in U.S. Publication No. 2005/0148725 to Statz et al. Presently, there is commercially available a DuPont product marketed under the name HPF 2000® as a replacement for polybutadiene. The manufacturer reports a COR of 0.828 and Comp of 91 for HPF 2000® neat spheres (˜1.52″ O.D.).

The design of golf balls and materials for their construction generally requires a balance of the material resilience (i.e., the spring-like ability per unit volume to absorb stress energy without structural failure), elasticity (i.e., the ability to reflect (absorb and release) energy without hysteresis loss), and compressibility (i.e., the ability to undergo reversible deformation in response to pressure). It should be noted that material resilience and elasticity can allow for efficient transfer of energy from club head to ball. In general, when the ball is resilient and elastic, the initial velocity of the ball can typically be about 50% greater than the velocity of the club head. As such, the ball speed to head speed ratio (B/H ratio) can be 1.5. Highly compressible (easily deformable) balls, on the other hand, can be more satisfactory in the short game and more readily controlled. Golf balls that are not as compressible and feel like stones or steel ball bearing golfers are often shun.

Accordingly, it would be desirable to provide a golf ball that can consistently display an optimum balance of material resiliency, elasticity and compressibility.

The present invention provides, in one embodiment, a golf ball having a metal core made from a work-hardened metal alloy, for instance, American Iron and Steel Institute (AISD type 301 stainless steel. In an embodiment, the metal core may be a hollow core made from two substantially similar hemispheres welded to one another. The golf ball also includes a mantle layer enveloping the metal core. In an embodiment, the mantle layer includes a mixture of a long-ball resin, for instance HPF 2000, and a soft-ball resin, for instance AF 1035, so as to provide material resiliency, elasticity and compressibility. The golf ball further includes a cover positioned about the mantle layer, so as to protect the mantle. In an embodiment, the cover may include an aerodynamic pattern imprinted thereon.

The present invention also provides, in another embodiment, a method for manufacturing a golf ball. The method includes initially providing a metal core made from a work-hardened metal alloy. In an embodiment, the core may be made from two substantially similar hemispheres stamped from the work-hardened metal alloy. Next, the metal core may be enveloped with a mantle layer made from a mixture of a long-ball resin and a soft-ball resin. Thereafter, a cover may be placed about the mantle layer, so as to protect the mantle layer.

FIG. 1 illustrates a cross-sectional view of a golf ball of the present invention.

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• Utility Patent

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