Golf Ball With Resin Inner Core

Abstract

A high performance golf ball includes a resin inner core, a rubber outer core, and a cover. The resin inner core is made of a blend of highly neutralized polymers and a low flexural modulus ionomer, and may include a blend of different highly neutralized polymers. The inner core has a specified range of coefficients of restitution when measured at different velocities. The cover is a single layer ionomer cover, and may be made from a blend of different grades of the ionomer. The ball as a whole has properties to maximize performance and aesthetic properties, such as backspin off the irons, feel, and sound.

Claims

What is claimed is: 1 . A golf ball, comprising: an inner core formed from a resin blend made of a highly neutralized acid polymer and a first ionomer, the highly neutralized acid polymer having a first flexural modulus of less than 8,000 psi, and the first ionomer having a second flexural modulus of less than 8,000 psi and the first ionomer including from about 1 to about 20 parts by weight of the inner core, based on 100 parts by weight of the inner core; an outer core surrounding the inner core; and a cover layer surrounding the outer core. 2 . The golf ball according to claim 1 , wherein the highly neutralized acid polymer has a first Vicat softening temperature and the first ionomer has a second Vicat softening temperature, the absolute value of difference between the first Vicat softening temperature and the second Vicat softening temperature is not greater than 10 degrees Celsius. 3 . The golf ball according to claim 2 , wherein the inner core has a first surface hardness, the outer core has a second surface hardness, and the cover layer has a third surface hardness, the absolute value of the difference between the first surface hardness and the second surface hardness being greater than about 1 and less than about 10. 4 . The golf ball according to claim 1 , wherein the inner core has a first surface hardness, the outer core has a second surface hardness, and the cover layer has a third surface hardness, the absolute value of the difference between the first surface hardness and the second surface hardness being greater than about 1 and less than about 10. 5 . The golf ball according to claim 4 , wherein the absolute value of the difference between the third surface hardness and the second surface hardness is greater than about 15 and less than about 25 Shore D. 6 . The golf ball according to claim 1 , wherein the inner core has a diameter of about 24 mm to about 30 mm. 7 . The golf ball according to claim 6 , wherein the outer core is made of rubber and has a thickness of about 4 mm to about 8 mm. 8 . The golf ball according to claim 6 , wherein the cover layer has a thickness of about 1.2 mm to about 2 mm. 9 . The golf ball according to claim 1 , wherein the inner core further comprises a second ionomer having a third flexural modulus. 10 . The golf ball according to claim 9 , wherein the sum of the first flexural modulus and the second flexural modulus is less than the third flexural modulus. 11 . The golf ball according to claim 9 , wherein the second ionomer is between 0 and 25 parts by weight of inner core, based on 100 parts by weight of the inner core. 12 . The golf ball according to claim 1 , wherein the inner core has a coefficient of restitution measured at 131 ft/s of less than 0.8. 13 . The golf ball according to claim 1 , wherein the inner core has a compression deformation value of between about 4 mm and about 5 mm, when measured with an initial load of 10 kg and a final load of 130 kg. 14 . The golf ball according to claim 1 , wherein the inner core has a specific gravity of less than 1. 15 . The golf ball according to claim 1 , wherein the difference between the specific gravity of outer core and the specific gravity of inner core is greater than about 0.2. 16 . The golf ball according to claim 1 , wherein the golf ball has a moment of inertia between about 83 g/cm̂2 and about 85 g/cm̂2. 17 . The golf ball according to claim 1 , wherein the coefficient of restitution (COR) value of the golf ball is greater than the COR value of inner core. 18 . A golf ball, comprising: an inner core formed from a resin blend made of a highly neutralized acid polymer and a first ionomer, the highly neutralized acid polymer has a first Vicat softening temperature and the first ionomer has a second Vicat softening temperature and the absolute value of difference between the first Vicat softening temperature and the second Vicat softening temperature is not greater than 10 degrees Celsius; an outer core surrounding the inner core; and a cover layer surrounding the outer core. 19 . The golf ball according to claim 18 , wherein the inner core further comprises a second ionomer having a third flexural modulus, the sum of the first flexural modulus and the second flexural modulus being less than the third flexural modulus. 20 . The golf ball according to claim 18 , wherein the second ionomer is between 0 and 25 parts by weight of inner core, based on 100 parts by weight of the inner core. 21 . The golf ball according to claim 18 , wherein the inner core has a diameter of about 24 mm to about 30 mm, the outer core has a thickness of about 4 mm to about 8 mm, and the cover layer has a thickness of about 1.2 mm to about 2 mm. 22 . The golf ball according to claim 18 , wherein the inner core has a coefficient of restitution (COR) measured at 131 ft/s of less than 0.8 and the inner core has a compression deformation value of between about 4 mm and about 5 mm, when measured with an initial load of 10 kg and a final load of 130 kg. 23 . The golf ball according to claim 18 , wherein the COR value of the golf ball is greater than the COR value of the inner core surrounded by the outer core.
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Nos. 61/682,724, 61/682,727, and 61/682,732, each entitled “Golf Ball with Resin Inner Core”, and all filed on Aug. 13, 2012, wherein each application is hereby incorporated by reference. BACKGROUND [0002] The game of golf is an increasingly popular sport at both amateur and professional levels. A wide range of technologies related to the manufacture and design of golf balls are known in the art. Such technologies have resulted in golf balls with a variety of play characteristics and durability. For example, some golf balls have a better flight performance than other golf balls. Some golf balls with a good flight performance do not have a good feel when hit with a golf club. Some golf balls with good performance and feel lack durability. Thus, it would be advantageous to make a conforming and durable golf ball with a good flight performance that also has a good feel. SUMMARY [0003] A high performance golf ball includes a resin inner core, a rubber outer core, and a cover. The resin inner core is made of a highly neutralized polymer and at least one ionomer. The cover is a dimpled ionomer cover, made of a blend of different grades of ionomer. This construction provides desirable compression, coefficient of restitution, and moment of inertia properties. The ball as a whole has properties to maximize performance and aesthetic properties, such as driver distance, iron control, feel, and sound. The ball is particularly well-suited to balancing driver initial velocity and compression so that driver trajectory and distance is maintained or improved while greater control and feel is enhanced. [0004] In one aspect of the invention, a golf ball comprises an inner core, an outer core surrounding the inner core, and a cover layer surrounding the outer core, wherein the inner core is formed from a resin blend made of a highly neutralized acid polymer and a first ionomer. The highly neutralized acid polymer has a first flexural modulus of less than 8,000 psi, and the first ionomer has a second flexural modulus of less than 8,000 psi. The first ionomer includes from about 1 to about 20 parts by weight of the inner core, based on 100 parts by weight of the inner core. [0005] In another aspect of the invention, a golf ball comprises an inner core, an outer core surrounding the inner core, and a cover layer surrounding the outer core, wherein the inner core is formed from a resin blend made of a highly neutralized acid polymer and a first ionomer. The highly neutralized acid polymer has a first Vicat softening temperature and the first ionomer has a second Vicat softening temperature and the absolute value of difference between the first Vicat softening temperature and the second Vicat softening temperature is not greater than 10 degrees Celsius. [0006] Other systems, methods, features and advantages of the invention will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the invention, and be protected by the following claims. BRIEF DESCRIPTION OF THE DRAWINGS [0007] The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. [0008] FIG. 1 is an exemplary embodiment of a golf ball with a resin inner core and a rubber outer core; [0009] FIG. 2 is a table showing the structure and static data of the exemplary embodiment and comparative example high performance golf balls; and [0010] FIG. 3 is performance data collected from a ball made according to the present design and comparative example high performance golf balls. DETAILED DESCRIPTION [0011] Generally, the present disclosure relates to a golf ball with a resin inner core and a rubber outer core. While many advantageous performance and feel properties may be found in a golf ball with a resin inner core and a rubber outer core, it is believed by the inventors that the design disclosed herein allows these advantageous performance and feel properties to be more fully realized. [0012] The golf ball may be made by any suitable process. The process of making the golf ball may be selected based on a variety of factors, but in most embodiments will generally include injection molding the resin inner core, compression molding the rubber outer core onto the resin inner core, and then injection molding the resin cover onto the rubber outer core. For example, the process of making the golf ball may be selected based on the type of materials used and/or the number of layers included. Exemplary processes are discussed below with respect to the individual layers of the exemplary embodiment. [0013] As used herein, the term “about” is intended to allow for engineering and manufacturing tolerances, which may vary depending upon the type of material and manufacturing process, but which are generally understood by those in the art. For example, “about” generally corresponds to +/−2 units, regardless of scale, when measuring hardness; +/−0.15 mm when measuring compression when the initial load is 10 kg and the final load is 130 kg; and +/−0.005 when measuring specific gravity. Also, as used herein, unless otherwise stated, compression, hardness, COR, durability, and flexural modulus are measured as follows: [0014] Compression deformation: The compression deformation herein indicates the deformation amount of the ball under a force; specifically, when the force is increased to become 130 kg from 10 kg, the deformation amount of the ball under the force of 130 kg subtracts the deformation amount of the ball under the force of 10 kg to become the compression deformation value of the ball. All of the tests herein are performed using a compression testing machine available from Automated Design Corp. in Illinois, USA or EKTRON TEK Co., LTD.; Model name: EKTRON-2000 GBMD-CS. Both compression tester machines can be set to apply a first load and obtain a first deformation amount, and then, after a selected period, apply a second, typically higher load and determine a second deformation amount. Thus, the first load herein is 10 kg, the second load herein is 130 kg, and the compression deformation is the difference between the second deformation and the first deformation. Herein, this distance is reported in millimeters. The compression can be reported as a distance, or as an equivalent to other deformation measurement techniques, such as Atti compression. [0015] Hardness: Hardness of golf ball layer is measured generally in accordance with ASTM D-2240, but measured on the land area of a curved surface of a molded ball. Other types of hardness, such as Shore C or JIS-C hardnesses may be provided as specified herein. For material hardness, such as those materials intended to be used in a golf ball, but not yet manufactured into a golf ball, the hardness is measured in accordance with ASTM D-2240 (on a plaque). [0016] Method of measuring COR: A golf ball for test is fired by an air cannon at an initial velocity of 131 ft/s, or another selected velocity, but if not otherwise specified, 131 ft/s is the initial velocity for COR tests and values discussed herein. The test golf ball is fired at a steel plate positioned about 1.2 meters away from the air cannon. A speed monitoring device is located over a distance of 0.6 to 0.9 meters from the cannon. After striking the steel plate, the golf ball rebounds through the speed-monitoring device. The return velocity divided by the initial velocity is the COR. A COR measuring system is available from ADC. [0017] Durability: Durability is generally measured by following the protocol for measuring COR, as described above, for 150 shots or until the golf ball fails. When the golf ball fails, the COR noticeably and suddenly drops. [0018] Flexural Modulus: The material is measured generally in accordance with ASTM D790, which measures the deflection in a beam of the material in a three point bending system. [0019] Any ball described herein is considered conforming if the ball adheres to the Rules of Golf established by the United States Golf Association (USGA). All other balls are considered non-conforming. [0020] As shown in FIG. 1 , golf ball 100 includes an inner core 110 , an outer core 120 , and a cover layer 140 . Inner core 110 is generally made from a resin, such as a thermoplastic polymer. Outer core 120 is generally made from rubber. Cover layer 140 is generally made from a resin material, such as a thermoplastic polymer. Outer cover layer 140 includes dimples. Cover layer 140 is coated by a single top coat or includes two layers of coating, where one layer is a primer layer adjacent outer cover layer 140 and the other layer is a top coat positioned on the primer layer. The inventors have found that an exemplary embodiment of this three-piece design, discussed herein in greater detail and referred to as either the first exemplary embodiment or Design 1, has performance properties that may prove particularly advantageous to amateur golfers whose focus is on improving flight distance. While the exemplary embodiment has good flight performance and initial velocity off the driver, the exemplary embodiment also has a soft feel, satisfactory spinnability and control on iron and wedge shots along with good durability. The inventors have found another exemplary embodiment of this three-piece design, discussed herein in greater detail and referred to as either the second exemplary embodiment of Design 2, has performance properties that may prove particularly advantageous to amateur golfers whose focus is on improving flight distance, but who prefer a slightly harder feel and increased spinnability over the first exemplary embodiment. [0021] Inner core 110 is made from a highly neutralized polymer composition, sometimes called a highly neutralized acid polymer or highly neutralized acid polymer composition, and at least one additional component, such as a filler. Highly neutralized polymer compositions may be considered to be at least 80 percent neutralized, though many highly neutralized polymer compositions are neutralized to greater than 90 percent, greater than 95 percent, or are even substantially completely neutralized. Inner core 110 generally includes a first highly neutralized polymer and a second highly neutralized polymer. Inner core 110 generally includes HPF resins such as HPF2000 and HPF AD1035, produced by and available from E. I. DuPont de Nemours and Company, though any highly neutralized polymer that has the properties specified herein, particularly hardness, would be appropriate. [0022] The flexural modulus of the highly neutralized polymer in some embodiments is less than about 8,000 psi. In some embodiments, the highly neutralized polymer is about 95 parts by weight of the total composition of the core. In some embodiments, the highly neutralized polymer is about 80 parts by weight of the total composition of the core. In some embodiments, such as the exemplary embodiments, the highly neutralized polymer is HPF AD1035, which has a flexural modulus between 6,300 and 7,300 psi. The highly neutralized polymer of inner core has a first Vicat softening temperature between 45 degrees C. and 65 degrees C. For example, HPF AD1035 has a Vicat softening temperature of about 54 degrees C. [0023] Inner core 110 also includes a second component, a first ionomer. In some embodiments, such as the first exemplary embodiment, the ionomer is used as a carrier for another component, such as color. In these embodiments, the amount of ionomer is between 1 and 20 parts by weight, based on 100 parts by weight of inner core 110 . In some embodiments, the amount of first ionomer is relatively low, such as between 1 and 10 parts by weight, based on 100 parts. In the exemplary embodiment, the first ionomer is about 5 parts by weight of inner core 110 , based on 100 parts by weight of inner core 110 . [0024] Inner core 110 may also include a third component, a second ionomer. In some embodiments, the second ionomer is used to increase the hardness of inner core 110 and flexural modulus of inner core 110 . In some embodiments, such as the second exemplary embodiment which has a harder cover layer than the first exemplary embodiment, as discussed below, the ionomer may be used to balance the ball so that the ball has good initial velocity off the driver while remaining a conforming ball with good feel. In these embodiments, the ionomer may be about 10 to about 30 parts by weight of inner core 110 , based on 100 parts by weight of inner core 110 . In other embodiments, the second ionomer may be between 0 and 25 parts by weight of inner core 110 , based on 100 parts by weight of inner core 110 . In the second exemplary embodiment, the ionomer is about 15 percent by weight of inner core 110 . Because the first exemplary embodiment contains only the first ionomer, the first exemplary embodiment could be considered to have 0 parts by weight of the second ionomer. [0025] It is intended in some embodiments that the first ionomer is a different ionomer or grade of ionomer than the second ionomer. For example, in some embodiments, the first ionomer may be Surlyn® 6320 and the second ionomer may be Surlyn® 8940. The first ionomer has a flexural modulus of less than about 8,000 psi. For example, the first ionomer may have a flexural modulus between 4,000 psi and 8,000 psi. In some embodiment, the first ionomer has a flexural modulus of about 4,300 psi. In some embodiments, the first ionomer has a flexural modulus of about 7,700 psi. The second ionomer has a flexural modulus of greater than about 10,000 psi. In some embodiments, the second ionomer has a flexural modulus of about 50,800 psi. In some embodiments, the sum of the flexural modulus of the highly neutralized polymer and the flexural modulus of the first ionomer is less than the flexural modulus of the second ionomer. [0026] In any of the embodiments, the first ionomer and/or the second ionomer may be Surlyn®, available from E.I. DuPont de Nemours and Company. In some embodiments, the first ionomer and the second ionomer is Surlyn® 9320, Surlyn® 9320W, or Surlyn® 6320, all available from E.I. DuPont de Nemours and Company. In some embodiments, the second ionomer is Surlyn® 8940. In other embodiments, the first ionomer and the second ionomer may be another type or brand name of ionomer. The ionomer, whether used for the first ionomer or the second ionomer, has a Vicat softening temperature such that the absolute value of the difference between the Vicat softening temperature of the ionomer and the highly neutralized polymer is not greater than about 10 degrees C. [0027] By adding the ionomer or ionomers to the resin inner core, the flexibility of ball design is increased. For example, a designer is more able to fine tune COR, flexural modulus, hardness, specific gravity, spin, speed, launch angle, and impact sound by including the low flexural modulus ionomer. Further the manufacturing facility can account more readily for inconsistencies in any single material when incorporating the low flexural modulus ionomer. In particular, adding the second ionomer when the cover hardness is greater than about 68 Shore D helps to balance the feel of the ball, since inner core is relatively soft, as is discussed further below. [0028] Inner core 110 may also include additives, fillers, and flow modifiers. Suitable additives and fillers may include, for example, blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, mica, talc, nanofillers, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, impact modifiers, acid copolymer wax, surfactants. Suitable fillers may also include inorganic fillers, such as zinc oxide, titanium dioxide, tin oxide, calcium oxide, magnesium oxide, barium sulfate, zinc sulfate, calcium carbonate, zinc carbonate, barium carbonate, mica, talc, clay, silica, lead silicate. Suitable fillers may also include high specific gravity metal powder fillers, such as tungsten powder and molybdenum powder. Suitable melt flow modifiers may include, for example, fatty acids and salts thereof, polyamides, polyesters, polyacrylates, polyurethanes, polyethers, polyureas, polyhydric alcohols, and combinations thereof. [0029] In some embodiments, inner core 110 may have a high resilience. Such a high resilience may cause golf ball 100 to have increased carry and distance. The coefficient of restitution (COR) value of golf ball 100 is greater than the COR value of inner core 110 or the COR value of the entire core (inner core 110 surrounded by outer core 120 ). In some embodiments, inner core 110 has a COR of less than 0.8, depending on the initial velocity of the test. In some embodiments, inner core 110 may have a COR value ranging from 0.7 to less than 0.8, depending on the initial velocity of the test. Each layer of the ball has a COR. Inner core 110 has a first COR (i.e., conducting a COR test of just inner core 110 ), outer core 120 has a second COR (i.e., conducting a COR test of the entire core, inner core 110 surrounded by outer core 120 ), and cover layer 140 has a third or ball COR (i.e., conducting a COR test of the entire ball). The COR of the layers should also satisfy the following conditions for optimum feel: the third COR is greater than the first COR and the second COR. The difference between the third COR and the first COR is greater than 0.01. The difference between the third COR and the second COR is greater than 0.02. [0030] In the first exemplary embodiment, inner core 110 has a first COR of about 0.7772 when measured with an initial velocity 131 ft/s, a second COR of about 0.7696 when measured with an initial velocity of 140 ft/s, and a third COR of about 0.7362 when measured with an initial velocity 160 ft/s. In the second exemplary embodiment, inner core 110 has a first COR of about 0.7854 when measured with an initial velocity 131 ft/s, a second COR of about 0.7763 when measured with an initial velocity of 140 ft/s, and a third COR of about 0.7462 when measured with an initial velocity 160 ft/s. These COR ranges are advantageous so that the overall COR value of golf ball 100 may be dampened by the outer layers to a desired level, such as less than 0.8. It is believed that such an inner core having a higher COR than 0.8 may have an undesirable feel. [0031] Inner core 110 has a diameter between about 24 mm and 30 mm, and in the exemplary embodiment has a diameter of about 28 mm+/−0.3 mm. It is believed by the inventors that if the inner core diameter is less than about 24 mm, then the initial velocity off of the driver may be too low. It is also believed that if the inner core diameter is greater than about 30 mm, then more filler may need to be added to any layer of the ball to maintain the proper weight distribution, which makes the fabrication process more complicated and, therefore, may compromise consistent quality of batches or of different batches during production. A diameter of about 28 mm, in combination with the other layers of the exemplary embodiment, appears to balance driver initial velocity and feel, as will be discussed later. [0032] The weight of inner core 110 in the first exemplary embodiment is about 11.23 g. The weight of inner core 110 in the second exemplary embodiment is about 11.22 g. Inner core 110 has a specific gravity of less than 1. In the first exemplary embodiment inner core 110 has a specific gravity of about 0.951. In the second exemplary embodiment, inner core 110 has a specific gravity of about 0.949. It is believed by the inventors that if the specific gravity of inner core 110 is higher than about 1, then the moment of inertia of the ball and the spin may be negatively impacted. [0033] In the exemplary embodiment, inner core 110 has a compression deformation value of between about 4 mm and about 5 mm, when measured with an initial load of 10 kg and a final load of 130 kg. It is believed by the inventors that a compression deformation value of less than 4 mm when coupled with the other layers of the exemplary embodiments results in a ball with undesirable high pitched sound properties, an overly hard feel, and reduction of distance off the driver. It is also believed that a compression deformation value of greater than 5 mm results in a ball with too soft a feel, an undesirable amount of spin off of the mid-irons, and undesirable low pitched sound properties. In the first exemplary embodiment, the compression of inner core 110 is about 4.69 mm when measured with an initial load of 10 kg and a final load of 130 kg. In the second exemplary embodiment, the compression of inner core 110 is about 4.32 mm when measured with an initial load of 10 kg and a final load of 130 kg. [0034] Inner core 110 may have a surface Shore D hardness from 40 to 50. In the first exemplary embodiment, inner core 110 has a surface Shore D hardness of about 44. In the second exemplary embodiment, inner core 110 has a surface Shore D hardness of about 47. [0035] Inner core 110 may be made by any suitable process, but in the examples herein, inner core 110 is made by an injection molding process. During injection molding process, the temperature of the injection machine may be set within a range of about 190° C. to about 220° C. Generally, before the injection molding process, the highly neutralized polymer composition may be kept sealed in a moisture-resistant dryer capable of producing dry air. Drying conditions for the highly neutralized polymer composition may include 2 to 24 hours at a temperature below 50° C. [0036] Outer core 120 generally surrounds and encloses inner core 110 . Outer core 120 may be considered to be positioned radially outward of inner core 110 . Outer core 120 in the exemplary embodiment comprises a thermoset rubber material. Outer core 120 in some embodiments has a thickness of between 4 mm and 8 mm. In both of the exemplary embodiments, the thickness of outer core 120 is about 5.5 mm. In the exemplary embodiment, where inner core 110 is made of a highly neutralized polymer composition having a diameter of about 28 mm, if the thickness of outer core 120 is less than about 4 mm, it is believed by the inventors that more filler may need to be added to any layer of the ball to maintain the proper weight distribution, which makes the fabrication process more complicated and, therefore, may compromise consistent quality of batches or of different batches during production. It is believed by the inventors that the beneficial performance and aesthetic characteristics are maximized when the thickness of outer core 120 ranges from about 5.0 mm to about 6.0 mm. In some embodiments, the diameter of the entire core (inner core 110 and outer core 120 together) ranges from about 34 mm to about 40 mm. In the first exemplary embodiment, the diameter of the entire core is about 39.31 mm. In the second exemplary embodiment, the diameter of the entire core is about 39.28 mm. [0037] Outer core 120 is generally formed by crosslinking a polybutadiene rubber composition as described in U.S. patent application Ser. No. 12/827,360, entitled Golf Balls Including Crosslinked Thermoplastic Polyurethane, filed on Jun. 30, 2010, and applied for by Chien-Hsin Chou et al., the disclosure of which is hereby incorporated by reference in its entirety. Various additives may be added to the base rubber to form a compound. The additives may include a cross-linking agent and a filler. In some embodiments, the cross-linking agent may be zinc diacrylate, magnesium acrylate, zinc methacrylate, or magnesium methacrylate. In some embodiments, zinc diacrylate may provide advantageous resilience properties. The filler may be used to alter the specific gravity of the material. The filler may include zinc oxide, barium sulfate, calcium carbonate, or magnesium carbonate. In some embodiments, zinc oxide may be selected for its advantageous properties. Metal powder, such as tungsten, may alternatively be used as a filler to achieve a desired specific gravity. [0038] In some embodiments, a polybutadiene synthesized with a rare earth element catalyst may be used to form outer core 120 . Such a polybutadiene may provide excellent resilience performance of golf ball 100 . Examples of rare earth element catalysts include lanthanum series rare earth element compound, organoaluminum compound, and almoxane and halogen containing compounds. Polybutadiene obtained by using lanthanum rare earth-based catalysts usually employs a combination of a lanthanum rare earth (atomic number of 57 to 71) compound, such as a neodymium compound. [0039] In some embodiments, a polybutadiene rubber composition having at least from about 0.5 parts by weight to about 5 parts by weight of a halogenated organosulfur compound may be used to form outer core 120 . In some embodiments, the polybutadiene rubber composition may include at least from about 1 part by weight to about 4 parts by weight of a halogenated organosulfur compound. The halogenated organosulfur compound may be selected from the group consisting of pentachlorothiophenol; 2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol; 2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol; 3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol; 2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol; pentafluorothiophenol; 2-fluorothiophenol; 3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol; 2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol 2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol; 2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol; 4-chlorotetrafluorothiophenol; pentaiodothiophenol; 2-iodothiophenol; 3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol; 2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol; 2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol; 2,3,5,6-tetraiodothiophenol; pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol 4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol; 3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol; 3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol; 2,3,5,6-tetrabromothiophenol; and their zinc salts, the metal salts thereof and mixtures thereof. [0040] In the exemplary embodiment, outer core 120 is made from a composition of neodymium-catalyzed polybutadiene rubber (NdPBR) compounded with activated pentachlorothiophenol (PCTP). [0041] In some embodiments, the specific gravity of outer core 120 may be from about 1 to about 1.45. In some embodiments, the specific gravity of outer core 120 may be from about 1.05 to about 1.35. In the first exemplary embodiment, the specific gravity of outer core 120 is about 1.277. In the second exemplary embodiment, the specific gravity of outer core 120 is about 1.274. In the exemplary embodiments, the difference between the specific gravity of outer core 120 and the specific gravity of inner core 110 is greater than about 0.2. [0042] The weight of the entire core, outer core 120 and inner core 110 together, ranges from about 35 g to about 38 g. In the first exemplary embodiment, the weight of the entire core is about 36.97 g. In the second exemplary embodiment, the weight of the entire core is about 37.12 g. [0043] Outer core 120 has a surface hardness, as measured on the curved surface of outer core 120 , which is higher than the surface hardness of inner core 110 . It is believed by the inventors that driver distance for lower club head speeds and feel are improved when outer core 120 has a higher hardness than inner core 110 when inner core 110 has a hardness that is less than 50 Shore D. Additionally, for golfers with lower club head speeds, such as less than about 90 mph, a harder outer core can make driver and iron shots have improved feel when inner core 110 has a hardness that is less than 50 Shore D. In some embodiments, outer core 120 may have a surface Shore D hardness of from about 45 to about 60. In the first exemplary embodiment, outer core 120 has a Shore D hardness of about 52 Shore D. In the second exemplary embodiment, outer core 120 has a Shore D hardness of about 49 Shore D. [0044] In some embodiments, the entire core, i.e., outer core 120 enclosing inner core 110 , has a compression between 3 mm and 4 mm, when measured with an initial load of 10 kg and a final load of 130 kg. It is believed by the inventors that a compression deformation value of less than 3 mm results in a ball that may lack durability, particularly with respect to delamination between inner core 110 and outer core 120 when inner core 110 is much softer than outer core 120 , have an undesirably hard feel, and have undesirable high pitched sound properties. It is also believed that a compression deformation value of greater than 4 mm may produce an undesirable amount of spin off of the mid-irons, short distance off the driver, and undesirable low pitched sound properties. In the first exemplary embodiment, the entire core has a compression of about 3.85 when measured with an initial load of 10 kg and a final load of 130 kg. In the second exemplary embodiment, the entire core has a compression of about 3.75 when measured with an initial load of 10 kg and a final load of 130 kg. [0045] The entire core also has a coefficient of restitution, measured by firing the completed core (inner core 110 and outer core 120 ) from the testing cannon. In some embodiments, the COR of the entire core ranges from about 0.72 to less than about 0.78 based on different testing conditions. For example, the COR of the entire core of the first exemplary embodiment is about 0.772 when measured with an initial velocity of 131 ft/s, about 0.7558 when measured with an initial velocity of 140 ft/s, and about 0.7256 when measured with an initial velocity of 160 ft/s. The COR of the entire core of the second exemplary embodiment is about 0.7672 when measured with an initial velocity of 131 ft/s, about 0.7504 when measured with an initial velocity of 140 ft/s, and about 0.7234 when measured with an initial velocity of 160 ft/s. [0046] Outer core 120 may be made by any suitable process. For example, in some embodiments, outer core 120 may be made by a compression molding process. The process of making the outer core may be selected based on a variety of factors. For example, the process of making the outer core may be selected based on the type of material used to make the outer core and/or the process used to make the other layers. [0047] In some embodiments, outer core 120 may be made through a compression molding process including a vulcanization temperature ranging from 130° C. to 190° C. and a vulcanization time ranging from 5 to 20 minutes. In some embodiments, the vulcanization step may be divided into two stages: (1) the outer core material may be placed in an outer core-forming mold and subjected to an initial vulcanization so as to produce a pair of semi-vulcanized hemispherical cups and (2) a prefabricated inner core may be placed in one of the hemispherical cups and may be covered by the other hemispherical cup and vulcanization may be completed. In some embodiments, the surface of inner core 110 placed in the hemispherical cups may be roughened before the placement to increase adhesion between inner core 110 and outer core 120 . In some embodiments, inner core surface may be pre-coated with an adhesive before placing inner core 110 in the hemispherical cups to enhance the durability of the golf ball and to enable a high rebound. [0048] Cover layer 140 substantially surrounds and encompasses outer core 120 . Cover layer 140 may be considered to be positioned radially outward of outer core 120 . [0049] In some embodiments, cover layer 140 may be made from a thermoplastic material including at least one of an ionomer resin, a highly neutralized polymer composition, a polyamide resin, a polyester resin, and a polyurethane resin. In some embodiments, cover layer 140 is made from Surlyn®, and, in particular, a blend of different grades of Surlyn®. In some embodiments, two grades of ionomer are blended to make the material of cover layer 140 . In the first exemplary embodiment, two grades of Surlyn® are blended to make the material of cover layer 140 . At least a first grade of ionomer is a high flexural modulus ionomer (a flexural modulus greater than about 20,000 psi). In some embodiments, three grades of ionomer are blended to make the material of cover layer 140 . In the second exemplary embodiment, cover layer 140 is made from a blend of three grades of Surlyn®. In the second exemplary embodiment, the first grade of Surlyn® and the second grade are each about 40% of the blend, while the third grade of Surlyn® is about 10% of the blend for cover layer 140 . Similar to the first exemplary embodiment, at least a first grade of ionomer is a high flexural modulus ionomer. In some embodiments, the percentage in the cover material blend of the first grade of ionomer may range from about 30 to about 50, with 30%, 40%, and 50% being particularly advantageous percentages. In some embodiments, the percentage in the cover material blend of the second grade of Surlyn® may range from about 25 to about 50, with 25%, 30%, 35%, and 50% being particularly advantageous percentages. In some embodiments, the percentage in the cover material blend of the third grade of Surlyn®, a low flexural modulus ionomer (having a flexural modulus of less than about 8,000 psi) may range from zero (0) to about 35, with no third grade, 25%, 30%, and 35% being particularly advantageous percentages. [0050] In some embodiments, cover layer 140 of golf ball 100 may have a Shore D hardness, as measured on the curved surface, ranging from about 60 to about 73. In some embodiments, the Shore D hardness of cover layer 140 is greater than about 65 and less than about 70. A cover hardness of less than about 70 Shore D maintains soft feel while chipping and putting. This hardness range yields beneficial feel, spinnability off of irons and wedges, and durability. In the first exemplary embodiment, cover layer 140 has a Shore D hardness of about 68. In the second exemplary embodiment, cover layer 140 has a Shore D hardness of about 69. [0051] The relationship of the hardnesses of the layers of golf ball 100 to each other can also impact feel, durability, spin, and both driver and iron distance. Inner core 110 has a first surface hardness, outer core 120 has a second surface hardness, and cover layer 140 has a third surface hardness. In the first exemplary embodiment, the first surface hardness is about 44 Shore D, the second surface hardness is about 52 Shore D, and the third surface hardness is about 68 Shore D. In the second exemplary embodiment, the first surface hardness is about 47 Shore D, the second surface hardness is about 49 Shore D, and the third surface hardness is about 69 Shore D. In all embodiments, the third surface hardness is greater than the first surface hardness. In all embodiments, the first surface hardness is less than the second surface hardness. The absolute value of the difference between the first surface hardness and the second surface hardness is greater than about 1 and less than about 10. In the first exemplary embodiment, the absolute value of the difference between the first surface hardness and the second surface hardness is about 8 Shore D. In the second exemplary embodiment, the absolute value of the difference between the first surface hardness and the second surface hardness is about 2 Shore D. The absolute value of the difference between the third surface hardness and the second surface hardness is greater than about 15 and less than about 25 Shore D. In the first exemplary embodiment, the difference between the third surface hardness and the second surface hardness is about 16 Shore D. In the second exemplary embodiment, the absolute value of the difference between the third surface hardness and the second surface hardness is about 20 Shore D. [0052] In some embodiments, cover layer 140 of golf ball 100 may have a thickness ranging from 1.2 mm to 2 mm for optimized durability and feel. In the first exemplary embodiment and second exemplary embodiment, cover layer 140 has a thickness of about 1.7 mm. In any embodiment, cover layer 140 may have a thickness selected to ensure that golf ball 100 is conforming. In the exemplary embodiments, golf ball 100 has an outer diameter of about 42.8 mm. [0053] In some embodiments, golf ball 100 may have a moment of inertia between about 80 g/cm̂2 and about 90 g/cm̂2. In some embodiments, golf ball 100 may have a moment of inertia between about 83 g/cm̂2 and about 85 g/cm̂2. Such a moment of inertia may produce a desirable distance and trajectory, particularly when golf ball 100 is struck with a driver or driven against the wind. [0054] In some embodiments, golf ball 100 may include a ball compression deformation of about 2.8 mm to about 4 mm when measured with an initial load of 10 kg and a final load of 130 kg. As is well known in the art, compression of a golf ball can influence driver distance and feel. In the first exemplary embodiment, the ball compression deformation is about 3.3 mm when measured with an initial load of 10 kg and a final load of 130 kg. In the second exemplary embodiment, the ball compression deformation is about 3.19 mm when measured with an initial load of 10 kg and a final load of 130 kg. [0055] In the first exemplary embodiment, golf ball 100 has a weight of 45.38 g. In the second exemplary embodiment, golf ball 100 has a weight of 45.37 g. [0056] Golf ball 100 as a whole also has a ball COR. The first exemplary embodiment has a COR of 0.7952 at an initial velocity of 131 ft/s, 0.782 at an initial velocity of 140 ft/s, and 0.751 at an initial velocity of 160 ft/s. The second exemplary embodiment has a COR of 0.7957 at an initial velocity of 131 ft/s, 0.7833 at an initial velocity of 140 ft/s, and 0.753 at an initial velocity of 160 ft/s. Golf ball 100 may be considered to have a first COR, the COR of inner core 110 measured with an initial velocity of 131 ft/s; a second COR, the COR of the entire core measured with an initial velocity of 131 ft/s; and a third COR or ball COR, the COR of the ball when measured with an initial velocity of 131 ft/s. The third COR is greater than the second COR and the first COR. The difference between the first COR and the second COR is greater than about 0.01. This design provides a beneficial driver ball speed while remaining a conforming ball. It is possible for the designer to optimize sound and feel off the driver while maintaining high initial velocity off the driver. [0057] In some embodiments, golf ball 100 may have 300 to 400 dimples on the outer surface of cover layer 140 . In some embodiments, golf ball 100 may have 310 to 360 dimples on the outer surface of cover layer 140 . It is believed by the inventors that having a dimple count in this range provides an improved trajectory over higher or lower dimple counts. In the exemplary embodiment, golf ball 100 has 314 dimples. [0058] In particularly successful embodiments of the high performance golf ball according to the present design, the first referred to above as the first exemplary embodiment and below as Design 1, the second referred to above as the second exemplary embodiment and below as Design 2, in terms of durability, driver distance, driver initial velocity, iron and wedge spin, and aesthetically pleasing feel and sound. The details of Table 1 were included in the Design 1. The inner core and outer core in Design 1 are adhered together with an adhesive. [0000] TABLE 1 Details of Design 1 Inner Core HPF AD1035 Surlyn ®, grade 1 Outer Core NdPBR Outer Cover Surlyn ®, blend of two grades Coating Paint [0000] TABLE 2 Details of Design 2 Inner Core HPF AD1035 Surlyn ®, grade 1 Surlyn ®, grade 2 Outer Core NdPBR Outer Cover Surlyn ®, blend of three grades Coating Paint [0059] Comparisons were made against other balls of similar construction but with minor construction variations and one commercially available high performance golf ball. All of the comparison balls have a resin inner core, a rubber outer core, and a Surlyn® cover. All of the comparison balls have an inner core diameter of 28 mm. [0000] TABLE 3 Details of Comp1 Inner Core HPF2000 Surlyn ®, grade 1 Surlyn ®, grade 2 Outer Core PBR Outer Cover Surlyn ® Coating Paint [0000] TABLE 4 Details of Comp2 Inner Core HPF2000 HPF AD1035 Surlyn ®, grade 1 Surlyn ®, grade 2 Outer Core NdPBR Outer Cover Surlyn ®, blend of three grades Coating Paint [0000] TABLE 5 Details of Comp3 Inner Core HPF2000 HPF AD1035 Surlyn ®, grade 1 Outer Core NdPBR Outer Cover Surlyn ®, blend of three grades, Shore D 68.9 Coating Paint [0000] TABLE 6 Details of Comp4 Inner Core HPF AD1035 Surlyn ®, grade 1 Surlyn ®, grade 2 Outer Core NdPBR Outer Cover Surlyn ®, blend of two grades, Shore D 71 Coating Paint [0060] FIG. 2 shows the differences in structure and static performance data between Design 1, Design 2, and some of the comparison balls. The static performance data includes layer and ball compression, and layer and ball COR at various speeds. FIG. 3 shows performance data gathered for Design 1, Design 2 and the comparison balls. For the data shown in FIG. 3 , the following test set up and conditions were used: Driver: A VR Pro driver available from Nike Golf of Beaverton, Oreg. with a 9.5 degree loft angle was swung by a robot with a club head speed of about 96 mph, plus or minus 1 mph (to account for swing variations and tolerances.) Ball impact was high top-to-bottom and centered heel-to-toe on the face. Trackman radar system was used for measurements. 6-Iron: A VR Pro 6-iron available from Nike Golf of Beaverton, Oreg. with a 28.0 degree loft angle was swung by a robot with a club head speed of about 79 mph, plus or minus 1 mph (to account for swing variations and tolerances.) Ball impact was 1-2 grooves from the bottom and centered heel-to-toe on the face. Trackman radar system was used for measurements. Wedge: A VR Pro wedge available from Nike Golf of Beaverton, Oreg. with a 52.0 degree loft angle was swung by a robot indoors. Ball impact was 1-2 grooves from the bottom and centered heel-to-toe on the face. GC2 photo-based system was used for measurements. [0063] As can be seen from the data in FIGS. 2 and 3 , Design 1 and Design 2 each offer benefits over similar three-piece resin core balls, though the benefits of Design 1 are realized by golfers who prefer a softer feel and may have trouble controlling spin in the irons and wedge and Design 2 by golfers who prefer a harder feel and who need less assistance in driver trajectory or spinnability and control. In particular, Design 1 provides higher backspin off the driver and lower backspin for the mid-irons and wedge to maximize optimal trajectories and short game control for golfers who may have trouble controlling spin in the mid-irons and wedge. Design 2 provides lower driver backspin and increased mid-iron and wedge backspin for golfers who have greater ability to control their swing. [0064] Both Design 1 and Design 2 offer benefits for certain types of golfers over the comparison balls. For example, comparing Design 1 and Comp1, as discussed above, Comp1 has a harder core and a harder cover than Design 1. As shown in FIG. 3 , the performance difference from at least these differences is a significant decrease in driver backspin and a reduction in 6-iron backspin. Wedge spin, however, is greater for Design 1 than Comp1. The significant reduction in driver backspin could be beneficial in limiting a tendency for a ball trajectory to blow up during a drive. Therefore, Design 1 is a better choice of ball than Comp1 for golfers who are not seeking increased control off the irons but who generally have trouble with driver ball trajectory. [0065] Comparing Design 2 with Comp1, Comp1 has a harder inner core and a harder cover than Design 2. Design 2 offers greatly reduced spin off the driver, providing better control for golfers whose trajectories tend to blow up. Design 2 offers greater spin on wedge shots, giving the golfer playing with Design 2 greater control on the wedge shots. [0066] Comparing Design 1 with Comp2, Design 1 has a softer inner core and a harder cover than Comp2. Design 1 offers greater driver initial velocity, increased driver launch angle, and reduced driver spin. Thus, Design 1 is a better choice of ball for golfers whose driver trajectories and distance are problematic. Design 1 offers reduced wedge spin compared to Comp2. Therefore, Design 1 is a better choice of ball than Comp2 for golfers whose control on the wedge shots needs assistance. [0067] Comparing Design 2 with Comp2, Design 2 also has a softer inner core and a harder cover than Comp2. Design 2 offers greater driver initial velocity, increased driver launch angle even over Design 1, and reduced driver spin even as compared with Design 1. Thus, Design 2 is a better choice of ball than Comp2 for golfers whose driver trajectories and distance are problematic. [0068] Comparing Design 1 and Design 2 with Comp3, Design 1 and Design 2 each uses only a single type of highly neutralized polymer in the inner core, while Comp3 uses a blend of two highly neutralized polymers in the inner core. While the performance of the balls is somewhat similar, the durability of Design 1 and Design 2 is better than the durability of Comp3. Comp3 was unable to complete a standard complement of 150 shots during the durability tests, while both Design 1 and Design 2 easily exceeded 150 shots in durability. Therefore, Design 1 and Design 2 are viable commercial balls while Comp3 may not be. [0069] Comparing Design 1 with Comp4, Design 1 uses only a single grade of Surlyn® in the inner core while Comp4 uses two grades and, therefore, a much higher percentage of the inner core of Comp4 is ionomer as opposed to highly neutralized polymer than Design 1. Again, the durability of Comp3 was problematic, as Comp3 was unable to complete a standard complement of 150 shots during the durability tests, while Design 1 was easily capable of passing the 150 shot durability level. Therefore, Design 1 is a viable commercial ball while Comp4 may not be. [0070] Comparing Design 2 with Comp4, Comp4 has a harder cover but overall softer compression than Design 2. Design 2 has a compression of 3.19 mm when tested with an initial load of 10 kg and a final load of 130 kg. Comp4 has a compression of 3.6 when tested under the same conditions. The softer compression of Comp4 potentially yields the decrease in durability compared to Design 2, as Comp4 was unable to complete 150 shots during the durability test while Design 2 is able to complete the full complement of 150 shots. Therefore, Design 2 is a viable commercial ball while Comp4 may not be. [0071] While various embodiments of the invention have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.

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