Golf ball with high coefficient of restitution

[0002] The Present Application is a continuation-in-part of U.S. patent application Ser. No. 09/710,591 filed on Nov. 11, 2000, which is a divisional application of Ser. No. 09/361,912 is now U.S. Pat. No. 6,190,268, filed on Jul. 27, 1999.

[0003] 1. Field of the Invention

[0004] The present invention relates to a golf ball. More specifically, the present invention relates to a golf ball with a high coefficient of restitution and an initial velocity limited to less than 255 feet per second.

[0005] 2. Description of the Related Art

[0006] The Rules of Golf, as set forth by the United States Golf Association (“USGA”) and the Royal and Ancient Golf Club of Saint Andrews, have placed controls on the construction and performance of golf balls. The golf ball rules require that the golf ball have a diameter no less than 1.68 inches (42.67 mm), a weight no more than 1.620 ounces avoirdupois (45.93 g), spherical symmetry, an overall distance no greater than 296.8 yards (the limit is 280 yards, or 256 m, plus a six percent tolerance for the total distance of 296.8 yards), and an initial velocity no greater than 255.0 feet per second (the limit is 250 feet or 76.2 m, per second with a two percent maximum tolerance that allows for an initial velocity of 255 feet per second) measured on a USGA approved apparatus.

[0007] The initial velocity test is comprised of a large 275 pound wheel that rotates around a central axis at a rate of 143.8 feet per second (striker tangential velocity) and strikes a stationary golf ball resting on a tee. The wheel has a flat plate that protrudes during its final revolution prior to impact with the golf ball. The ball's velocity is then measured via light gates as it travels approximately six feet through an enclosed tunnel. Balls are kept in an incubator at a constant temperature of 23 degrees Celsius for at least three hours before they are tested for initial velocity performance. To test for initial velocity, balls are placed on a tee and hit with the metal striker described above. Twenty-four balls of a particular type make up one test. Each ball is hit with the spinning wheel a total of four times. The highest and lowest recorded velocities are eliminated and the remaining two velocities are averaged to determine the ball speed for that specific ball. The individual speeds of the 24 balls in the group are then averaged, and that is considered the mean initial velocity (IV) of the group for the test.

[0008] For USGA conformance purposes, a ball with a mean initial velocity of less than 255.0 feet per second is considered conforming to the USGA Rule of Golf and can be played in sanctioned events. For reference to USGA Wheel Test see USGA web-site at www.usga.com, or reference U.S. Pat. No. 5,682,230 for further information.

[0009] Generally speaking, the USGA IV test is designed to be a consistent measurement tool capable of regulating the speed (and ultimately distance) of golf balls. It is commonly known in the industry that golf ball manufacturers perform a simpler test on prototype golf balls and then attempt to correlate the results to the USGA Wheel Test. One type of correlation test is the Coefficient of Restitution (“COR”) test, which consists of firing a golf ball from a cannon into a fixed plate and taking the ratio of outgoing velocity to incoming velocity.

[0010] The Coefficient of Restitution is the ratio of the velocity of separation (V_out1-V_out2) to the velocity of approach (V_in1-V_in2), where COR=(V_out1-V_out2)/(V_in1-V_in2). The value of COR will depend on the shape and material properties of the colliding bodies. In elastic impact, the COR is unity and there is no energy loss. A COR of zero indicates perfectly inelastic or plastic impact, where there is no separation of the bodies after collision and the energy loss is a maximum. In oblique impact, the COR applies only to those components of velocity along the line of impact or normal to the plane of impact. The coefficient of restitution between two materials can be measured by making one body many times larger than the other so that m₂(mass of larger body) is infinitely large in comparison to m₁(mass of the smaller body). The velocity of m₂is unchanged for all practical purposes during impact and

[0011] COR=V_out/V_in

[0012] One particular type of COR test device that is commonly used in the golf ball industry is the ADC COR machine developed by Automated Design Corporation. Based on the definition of COR above, m₂is a large 400 lb plate fixed vertically that the ball (m₁) is fired into. The impact of golf ball to large fixed plate is an oblique impact. Software developed by Automated Design Corporation accurately calculates the normal velocities given the dimensions of the machine and outputs a value for Coefficient of Restitution as defined above.

[0013] U.S. Pat. No. 5,209,485, filed in 1991, discloses a restricted flight golf ball that has a reduced COR. However, the '485 patent also discloses, for comparison purposes, that the TOP FLITE® XL golf balls, manufactured and sold by Spalding had a COR value of 0.813 when fired at a speed of 125 feet per second. The '485 patent also discloses that the Spalding SUPER RANGE golf ball had a COR value of 0.817 when fired at a speed of 125 feet per second. However, the SUPER RANGE golf ball was a non-conforming golf ball and thus had an IV value greater than 255 feet per second.

[0014] U.S. Pat. No. 5,803,831, filed in 1996 discloses in Table 14 a finished solid three-piece golf ball that has a COR of 0.784 at a speed of what is believed to be 125 feet per second.

[0015] However, the prior art golf balls fail to provide a golf ball that conforms to the USGA IV limit of 255 feet per second while having a high COR.

[0016] The present invention provides a solution to the problem of adhering to the USGA initial velocity limit of 255 feet per second for a golf ball while increasing the distance a golf ball travels when struck with a golf club. The solution is a golf ball that has a greater coefficient of restitution than other golf balls yet adheres to the USGA initial velocity limit.

[0017] One aspect of the present invention is a golf ball with a core, a cover disposed over the core, and wherein the golf ball has a coefficient of restitution at 143 feet per second greater than 0.8015, and a USGA initial velocity less than 255.0 feet per second.

[0018] Another aspect of the invention is a golf ball that includes a core composed of a polybutadiene blend, an intermediate layer disposed about the core, a cover disposed over the intermediate layer, and wherein the golfball has a coefficient of restitution at 143 feet per second greater than 0.7964, and an USGA initial velocity less than 255.0 feet per second. The intermediate layer is composed of a blend of ionomers, and the cover is composed of a thermosetting polyurethane material.

[0019] Yet another aspect of the present invention is a golf ball that includes a core, an intermediate layer disposed about the core, a cover disposed over the intermediate layer, and wherein the golf ball has a coefficient of restitution at 143 feet per second greater than 0.7964, and a USGA initial velocity less than 255.0 feet per second. The core is composed of a polybutadiene blend having a diameter between 1.45 inches and 1.55 inches, with a PGA compression between 70 points and 110 points. The intermediate layer is composed of a blend of ionomers, having a thickness between 0.040 inch and 0.080 inch, and a Shore D hardness ranging from 62 to 75 as measured according to ASTM-D2290. The cover is composed of a thermosetting polyurethane material and has a thickness between 0.015 inch and 0.040 inch.

[0020] Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

[0021] FIG. 1 is a cross-sectional view of a solid three-piece golf ball.

[0022] FIG. 2 is a cross-sectional view of a solid two-piece golf ball.

[0023] FIG. 3 is a cross-sectional view of a wound three-piece golf ball.

[0024] FIG. 4 is a cross-sectional view of a four-piece solid golf ball.

[0025] FIG. 5 is a graph of the outgoing speed (y-axis) versus the incoming speed (x-axis) to demonstrate the curve fitting operation for determining the COR of the golf ball of the present invention.

[0026] As shown in FIGS. 1-4, a golf ball of the present invention is generally designated 10. The golf ball 10 has a coefficient of restitution at 143 feet per second greater than 0.7964, and an USGA initial velocity less than 255.0 feet per second. The golf ball of FIG. 1 is a solid three-piece golf ball 10 having a core 12, a cover 14 and an intermediate layer 16. In FIG. 2, the golf ball 10 is a two-piece golf ball with a core 12 and a cover 14. The golf ball of FIG. 3 is a wound golf ball 10 with a liquid-filled core 12, a cover 14 and a wound layer 18. The golf ball of FIG. 4 is a four-piece solid golf ball 10 with a core 12, a cover 14, an intermediate layer 16 and a second intermediate layer 20. However, those skilled in the pertinent art will recognize that other golf balls may be utilized without departing from the scope and spirit of the present invention.

[0027] The surface geometry of the golf ball 10 is preferably a conventional dimple pattern such as disclosed in U.S. Pat. No. 6,224,499 for a Golf Ball With Multiple Sets Of Dimples, which pertinent parts are hereby incorporated by reference. Alternatively, the surface geometry of the golf ball 10 may have a non-dimple pattern such as disclosed in co-pending U.S. patent Application Ser. No. 09/442,860, filed on Nov. 18, 1999 for A Golf Ball Having Pyramidal Protrusions, which pertinent parts are hereby incorporated by reference.

[0028] The golf ball 10 is finished with either a very thin (microns in thickness) single top coating, or is painted with one more or more base coats of paint, typically white, before application of a clear coat. The material of the cover 14 may be doped for coloring, as is well known in the art.

[0029] The core 12 of the golf ball 10 is the “engine” for the golf ball 10 such that the inherent properties of the core 12 will strongly determine the initial velocity and distance of the golf ball 10. A higher initial velocity will usually result in a greater overall distance for a golf ball. However, the initial velocity and overall distance of a golf ball must not exceed the USGA and R&A limits in order to conform to the Rules of Golf. Therefore, the core 12 for a USGA approved golf ball is constructed to enable the golf ball 10 to meet, yet not exceed, these limits.

[0030] The COR is a measure of the resilience of a golf ball. A golf ball having a COR value closer to 1 will generally correspond to a golf ball having a higher initial velocity and a greater overall distance. In general, a higher compression core will result in a higher COR value.

[0031] The core 12 of the golf ball 10 is generally composed of a blend of a base rubber, a cross-linking agent, a free radical initiator, and one or more fillers or processing aids. A preferred base rubber is a polybutadiene having a cis-1,4 content above 90%, and more preferably 98% or above.

[0032] The use of cross-linking agents in a polybutadiene core is well known, and metal acrylate salts are examples of such cross-linking agents. Metal salt diacrylates, dimethacrylates, or mono(meth)acrylates are preferred for use in the core 12 of the golf ball 10 of the present invention, and zinc diacrylate is a particularly preferred cross-linking agent. A commercially available suitable zinc diacrylate is SR-416 available from Sartomer Co., Inc., Exton, Pa. Other metal salt di- or mono- (meth)acrylates suitable for use in the present invention include those in which the metal is calcium or magnesium. In the manufacturing process it may be beneficial to pre-mix some cross-linking agent(s), such as zinc diacrylate with the polybutadiene in a master batch prior to blending with other core components.

[0033] Free radical initiators are used to promote cross-linking of the base rubber and the cross-linking agent. Suitable free radical initiators for use in the core 12 of the golf ball 10 of the present invention include peroxides such as dicumyl peroxide, bis-(t-butyl peroxy) diisopropyl benzene, t-butyl perbenzoate, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-5-butylperoxy-hexane, 1,1-di (t-butylperoxy) 3,3,5-trimethyl cyclohexane, and the like, all of which are readily commercially available.

[0034] Zinc oxide is also preferably included in the core formulation. Zinc oxide may primarily be used as a weight adjusting filler, and is also believed to participate in the cross-linking of the other components of the core (e.g. as a coagent). Additional processing aids such as dispersants and activators may optionally be included. In particular, zinc stearate may be added as a processing aid (e.g. as an activator). Any of a number of specific gravity adjusting fillers may be included to obtain a preferred total weight of the core 12. Examples of such fillers include tungsten and barium sulfate. All such processing aids and fillers are readily commercially available. The present inventors have found a particularly useful tungsten filler is WP102 Tungsten (having a 3 micron particle size) available from Atlantic Equipment Engineers (a division of Micron Metals, Inc.), Bergenfield, N.J.

[0035] Table One below provides the ranges of materials included in the preferred core formulations of the present invention.

[0036] In the present invention, the core components are mixed and compression molded in a conventional manner known to those skilled in the art. In a preferred form, the finished core 12 has a diameter of about 1.35 to about 1.64 inches for a golf ball 10 having an outer diameter of 1.68 inches. The core weight is preferably maintained in the range of about 32 to about 40 g. The core PGA compression is preferably maintained in the range of about 70 to 110, most preferably about 90 to 105, and the most preferred is a PGA compression of 100.

[0037] As used herein, the term “PGA compression” is defined as follows:

[0038] PGA compression value=180−Riehle compression value

[0039] The Riehle compression value is the amount of deformation of a golf ball in inches under a static load of 200 pounds, multiplied by 1000. Accordingly, for a deformation of 0.095 inches under a load of 200 pounds, the Riehle compression value is 95 and the PGA compression value is 85.

[0040] In a preferred embodiment, the cover 14 is composed of a thermosetting polyurethane material. Preferably the thermosetting polyurethane material is formed from a blend of polyurethane prepolymers and curing agents such as disclosed in U.S. Pat. No. 6,190,268 which is hereby incorporated by reference in its entirety. However, in an alternative embodiment such as a two-piece golf ball 10, the cover 14 is composed of a blend of ionomers, as discussed below in reference to the intermediate layer 16.

[0041] If the golf ball 10 has an intermediate layer 16, then it is preferably composed of a thermoplastic material or a blend of thermoplastic materials (e.g. metal containing, non-metal containing or both). Most preferably the intermediate layer 16 is composed of at least one thermoplastic material that contains organic chain molecules and metal ions. The metal ion is sodium, zinc, magnesium, lithium, potassium, cesium, or any polar metal ion that serves as a reversible cross-linking site and results in high levels of resilience and impact resistance. Suitable commercially available thermoplastic materials are ionomers based on ethylene copolymers and containing carboxylic acid groups with metal ions such as described above. The acid levels in such suitable ionomers may be neutralized to control resiliency, impact resistance and other like properties. In addition, other fillers with ionomer carriers may be used to modify the specific gravity of the thermoplastic material blend to adjust the moment of inertia and other like properties. Exemplary commercially available thermoplastic materials suitable for use in an intermediate layer 16 of a golf ball 10 of the present invention include, for example, the following materials and/or blends of the following materials: HYTREL® and/or HYLENE® products from DuPont, Wilmington, Del. PEBAX® products from Elf Atochem, Philadelphia, Pa., SURLYN® products from DuPont, and/or ESCOR® or IOTEK® products from Exxon Chemical, Houston, Tex.

[0042] The Shore D hardness of the intermediate layer 16 is preferably 62 to 75. It is preferred that the intermediate layer 16 have a hardness of between about 65-70 Shore D. In a preferred embodiment, the intermediate layer 16 has a Shore D hardness of about 68. It is also preferred that the intermediate layer 16 is composed of a blend of SURLYN® ionomer resins.

[0043] SURLYN® 8150, 9150, and 6320 are, respectively, an ionomer resin composed of a sodium neutralized ethylene/methacrylic acid, an ionomer resin composed of a zinc neutralized ethylene/methacrylic acid, and an ionomer resin composed of a terpolymer of ethylene, methacrylic acid and n-butyl acrylate partially neutralized with magnesium, all of which are available from DuPont, Polymer Products, Wilmington, Del.

[0044] The intermediate layer 16 may include a predetermined amount of a baryte mixture. The baryte mixture is included as 8 or 9 parts per hundred parts of the ionomer resins. One preferred baryte mixture is composed of 80% barytes and 20% of an ionomer, and is available from Americhem, Inc., Cuyahoga Falls, Ohio, under the trade designation 38534X1.

[0045] A preferred embodiment of the golf ball 10 of the present invention is a solid three-piece golf ball. The core 12 is composed of a polybutadiene blend as described above. The core 12 has a diameter between 1.45 inches and 1.55 inches, and most preferably 1.49 inches. The core 12 has a PGA compression ranging from 70-110 points, and most preferably 100 points. The intermediate layer 16 is preferably composed of substantially equal parts of the ionomer resins, SURLYN 8150 and SURLYN 9150, with a range of 40 to 60 parts of SURLYN 8150 to a range of 60 to 40 of SURLYN 9150. The ionomer blend of materials is preferably injection molded over the core to a thickness of between 0.040 inch to 0.080 inch, and most preferably 0.075 inch. The Shore D hardness of the materials of the intermediate layer 16 is preferably between 62 to 75 Shore D as measured according to ASTM D-2290. The cover 14 is preferably composed of thermosetting polyurethane material, preferably formed from a tri-blend of polyurethane prepolymers and curing agents. The cover 14 is preferably cast over the intermediate layer 16 and core 12, in a casting process such as described in co-pending U.S. patent application Ser. No. 09/496,126 for a System And Method For Forming A Thermoset Golf Ball Cover, filed on Feb. 01, 2000 and hereby incorporated by reference. The cover preferably has a thickness of between 0.015 inch to 0.030 inch, and most preferably 0.020 inch. The Shore D hardness of the golf ball 10, as measured on the golf ball is between 55 Shore D points to 70 Shore D points, and most preferably 65 Shore D points. The hardness of the golf ball 10 is measured using an Instron Shore D Hardness measurement device wherein the golf ball 10 is placed within a holder and the pin is lowered to the surface to measure the hardness. The average of five measurements is used in calculating the ball hardness. The ball hardness is preferably measured on a land area of the cover 14. The surface geometry of the golf ball 10 of this example is preferably 382 dimples arranged as described in U.S. Pat. No. 6,224,499. The overall diameter of the golf ball is approximately 1.68 inches, and the weight is approximately 45.5 grams. The preferred golf ball 10 had a COR of approximately 0.8152 at 143 feet per second, and an initial velocity between 250 feet per second to 255 feet per second under USGA initial velocity conditions.

[0046] Several golf balls 10 of the present invention were tested for COR against golf balls currently on the market. The balls were kept in an incubator at a constant temperature of 23 degrees Celsius for at least three hours before they were tested for COR performance. To test the COR of a particular ball type, six balls were loaded into a COR machine and fired one at a time through a cannon via compressed air. The test begins by firing the first balls at approximately 80 feet per second, and ends with the last ball firing approximately 180 feet per second. Each of the six balls are fired six times for a combined 48 shots over the range of speeds between 80-180 feet per second.

[0047] To determine the COR of a golf ball at any specific incoming velocity, a third-order polynomial curve is fit through the 48 data points and constrained at the origin. This polynomial fit is extremely accurate (with an R{circumflex over ( )}2 fit value greater than 0.999) and allows the COR to be determined at an exact speed of 143 fps without actually having to achieve that specific cannon velocity. The COR is then obtained by plugging in 143 into the third-order polynomial equation and taking the ratio of outgoing velocity to incoming velocity to calculate the coefficient of restitution. For reference to ADC COR machine see Automated Design Corporation web-site at www.automateddesign.com.

[0048] Table Two illustrates the results of COR testing of commercially available golf balls. The Callaway Golf RULE 35® golf balls (FIRMFEEL and SOFTFEEL), the Titleist PRO V1 392, Nike TOUR ACCURACY, Spalding STRATA TOUR PROFESSIONAL, and the Bridgestone BIIM, are all solid three-piece golf balls. The Maxfli REVOLUTION and the Titleist PROFESSIONAL are both wound golf balls. The other golf balls are two-piece golf balls. All of the non-two-piece golf balls had a COR below 0.797 at a speed of 143 fps, and all of the golf balls of Table Two had a COR below 0.801 at speed of 143 fps.

[0049] Table Three illustrates the COR calculation of golf balls 10 of the present invention. The four columns are the COR at speeds of 80 feet per second, 125 feet per second, 143 feet per second and 180 feet per second. The COR at 143 feet per second for each of the golf balls 10 of the present invention is at least 0.8115, and most have a COR over 0.815. FIG. 5 illustrates the curve fitting operation that generated the numbers for Table Three.

[0050] From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.