WO2014028390A1

WO2014028390A1 - Golf ball with two soft layers and one hard layer

Info

Publication number: WO2014028390A1
Application number: PCT/US2013/054546
Authority: WO
Inventors: Arthur Molinari
Original assignee: Nike International Ltd.
Priority date: 2012-08-13
Filing date: 2013-08-12
Publication date: 2014-02-20
Also published as: KR20150030776A; US20140045622A1; CN104768618A; JP2015528333A; EP2882505A4; KR101650673B1; EP2882505A1

Abstract

A golf ball is provided that has a certain relationship among the hardness values of its various layers. The golf ball may have a four-piece construction, including an inner core, an outer core, a mantle layer, and the cover layer. Of the inner core, outer core, and mantle layer, two may be considered soft while one may be considered hard. The inner core may be made from a highly neutralized polymer.

Description

GOLF BALL WITH TWO SOFT LAYERS AND ONE HARD LAYER

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a non-provisional application claiming the benefit of priority to U.S. Provisional Application Serial No. 61/682,754, entitled "Golf Ball with Two Soft Layers and One Hard Layer", filed August 13, 2012, which is incorporated by reference in its entirety.

BACKGROUND

[0002] The present invention relates generally to golf balls having an inner core, an outer core, and a mantle layer where at least two of those three layers are hard and the third is soft. Such golf balls may achieve favorable play characteristics as well as produce a sound that is preferred by golfers.

[0003] 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, in terms of initial velocity, spin, and total distance.

[0004] In recent years, golf balls with high performance resins, in particular, highly neutralized polymer materials, have been introduced into the market. Highly neutralized acid polymers are known to be used as the material for a golf ball core. For example, U.S. Patent 6,653,382 to Statz et al., entitled "Highly Neutralized Ethylene Copolymers and Their Use in Golf Balls" and filed October 18, 2000, discloses a golf core having melt-processable, highly-neutralized ethylene acid copolymers. U.S. Patent 6,756,436 to Rajagopalan et al., entitled "Golf Balls Comprising Highly-Neutralized Acid Polymers" and filed April 9, 2002, discloses golf balls having highly neutralized acid polymer cores. The disclosure of this patent is hereby incorporated by reference. Other conventional highly neutralized acid polymers are generally disclosed in U.S. Patent No. 7,652,086 to Sullivan et al., entitled "Highly-neutralized Thermoplastic Copolymer Center for Improved Multi-layer Core Golf Ball" and filed February 3, 2006, the disclosure of which is hereby incorporated by reference.

[0005] Known golf balls with a core made of highly neutralized polymer materials may achieve desirable performance properties, but may have an unconventional sound when impacted by the face of the golf club. Golfers, especially skilled and professional golfers, are very particular about the sound produced by a golf ball when it is hit. Many golfers consider the sound of a correctly hit golf ball as a factor in ball purchase, as this sound may be

aesthetically pleasing or convey information as to the accuracy of the ball hit.

[0006] Therefore, there exists a need in the art for a golf ball with a highly neutralized polymer core that also produces a favorable sound when struck by a golf club.

SUMMARY

[0007] Generally, this disclosure relates to golf balls having an inner core made from a highly neutralized polymer, an outer core, and a mantle layer. The three layers have a relationship among their hardness values such that the golf ball produces both favorable play characteristics and a desirable sound when struck by a golf club. Namely, two of the three mentioned layers should be relatively soft, and one of the three should be relatively hard. A description of the sound of a golf club striking a golf ball is provided in U.S. Patent Application Number 13/048,665 filed on March 15, 201 1 , published as U.S. Patent Application US2012-0070009, the contents of which are hereby incorporated by reference.

[0008] In one aspect, this disclosure provides a golf ball comprising: an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer; an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber; a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer; wherein at least two of the inner core, the outer core, and the mantle layer are soft; and at least one of the inner core, the outer core, and the mantle layer are hard; and wherein a soft inner core has a cross-sectional hardness of from about 50 to about 72 JIS C, a hard inner core has a cross-sectional hardness of from about 73 to about 95 JIS C, a soft outer core has a cross-sectional hardness of from about 50 to about 83 JIS C, a hard outer core has a cross-sectional hardness of from about 84 to about 95 JIS C, a soft mantle layer has a cross-sectional hardness of from about 50 to about 86 JIS C, and a hard mantle layer has a cross-sectional hardness of from about 87 to about 95 JIS C. [0009] In another aspect, this disclosure provides a golf ball comprising: an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer; an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber; a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer; wherein the inner core has a cross- sectional hardness of from about 70 to about 72 JIS C, the outer core has a cross- sectional hardness of from about 80 to about 83 JIS C, and the mantle layer has a cross-sectional hardness of from about 87 to about 91 JIS C.

[0010] In a third aspect, this disclosure provides a golf ball comprising: an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer; an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber; a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer; wherein the inner core has a cross- sectional hardness of from about 70 to about 72 JIS C, the outer core has a cross- sectional hardness of from about 83 to about 85 JIS C, and the mantle layer has a cross-sectional hardness of from about 82 to about 86 JIS C.

[0011] In a fourth aspect, this disclosure provides a golf ball comprising: an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer; an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber; a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer; wherein the inner core has a cross- sectional hardness of from about 72.51 to about 76 JIS C, the outer core has a cross-sectional hardness of from about 80 to about 83 JIS C, and the mantle layer has a cross-sectional hardness of from about 82 to about 86 JIS C.

[0012] In a fifth aspect, this disclosure provides a golf ball comprising: an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer; an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber; a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer; wherein the golf ball has a peak frequency sound of less than about 3.75 kHz, a COR value of at least 0.772, and a driver initial velocity at a club head speed of 89 mph of at least 131.5 mph.

[0013] 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

[0014] The disclosure 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.

[0015] FIG. 1 shows a representative golf ball in accordance with this disclosure, the golf ball being of a four-piece construction, having an inner core, an outer core, a mantle layer, and a cover layer;

[0016] FIG. 2 is a chart showing various values of the peak frequency sound and COR for several example golf balls in accordance with this disclosure as contrasted with several comparative example golf balls that are not within the scope of this disclosure;

DETAILED DESCRIPTION

[0017] This disclosure provides golf balls with at least three layers: an inner core, an outer core, and a mantle layer. The three layers may have a relationship among their hardness values so as to simultaneously achieve good play characteristics and produce a desirable sound when struck by a golf ball.

[0018] As used herein, unless otherwise stated, certain material properties and golf ball properties are defined as follows.

[0019] The term "hardness" as used herein is measured generally in accordance with ASTM D-2240 and JIS K 6253. The hardness of a material is taken as the slab hardness, while the hardness of a golf ball component is measured on the curved surface of the molded golf ball component. The "cross- sectional" hardness of a golf ball component is the hardness measured in accordance with the above testing procedures, as measured on a cross-section of a golf ball that has been cut in half. When a hardness measurement is made on a dimpled cover layer, hardness is measured on a land area of the dimpled cover layer. Hardness units are generally given in Shore D, Shore C, and JIS C, as indicated.

[0020] The "coefficient of restitution" or "COR" is measured generally according to the following procedure: a test object is fired by an air cannon at an initial velocity of 40 m/sec, and a speed monitoring device is located over a distance of 0.6 to 0.9 meters from the cannon. After striking a steel plate positioned about 1.2 meters away from the air cannon, the test object rebounds through the speed-monitoring device. The return velocity divided by the initial velocity is the COR.

[0021] The "flexural modulus" is measured generally in accordance with ASTM D-790.

[0022] The "Vicat softening temperature" is measured generally in accordance with ASTM D-1525. [0023] 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 (ADC). The ADC compression tester 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. While the ADC compression testing machine identified above can be programmed to perform these compression tests, these types of compression tests may also be performed on other testing machines.

[0024] The "peak frequency sound" is determined according to the following procedure. A golf ball is dropped from a height of 70 inches, onto a polished concrete slab having a thickness of no less than 4 inches. The sound made when the golf ball impacts the concrete is recorded with an array

microphone. The sound is subject to a spectral analysis in order to determine the frequency with the highest decibel level. Peak frequency is generally major component of the overall sound of the golf ball, and is considered to characterize the sound of the ball as perceived by a golfer. The details of a spectral analysis are known to a person having ordinary skill in the art of audio engineering. As used herein, the term "frequency" refers to the peak frequency sound.

[0025] Other properties and tests may be conducted as disclosed herein, and as may be known to a person having ordinary skill in the art of golf ball manufacturing. [0026] Except as otherwise discussed herein below, any golf ball discussed herein may generally be any type of golf ball known in the art. Namely, unless the present disclosure indicates to the contrary, a golf ball may generally be of any construction conventionally used for golf balls, such as a conforming or non-conforming construction. Conforming golf balls are golf balls that meet the Rules of Golf as approved by the United States Golf Association (USGA). Golf balls discussed herein may also be made of any of the various materials known to be used in golf ball manufacturing, except as otherwise noted.

[0027] Furthermore, it is understood that any feature disclosed herein (including but not limited to elements of the various embodiments shown in the FIGS, and various chemical formulas or mixtures) may be combined with any other features disclosed here, as may be desired, in any combination, subcombination, or arrangement.

[0028] Finally, as used herein, the terms "about" and "substantially" are intended to account for engineering and manufacturing tolerances.

[0029] FIG. 1 shows an embodiment of a golf ball in accordance with this disclosure. Golf ball 100 is a four-piece golf ball. Namely, golf ball 100 includes inner core 102, outer core 104, mantle layer 106, and cover layer 108.

[0030] Golf ball 100 includes radius 200 that extends from center 101 to outer surface 103. Each component may also have the dimensions as shown in FIG. 1 , however FIG. 1 is not necessarily shown to scale. Namely, inner core 102 may have radius 202, outer core 104 may have thickness 204, mantle layer 106 may have thickness 206, cover layer 108 may have thickness 208. The compositions of these layers, and the thicknesses and other properties, are discussed below.

[0031] Additional embodiments, not shown, of golf ball in accordance with this disclosure may have one or more additional layers or pieces beyond those shown in Fig. 1. For example, additional core layers and/or additional cover layers may be present to form five, six, seven, or even higher piece balls.

Generally, unless otherwise stated herein, the various layers of golf balls according to the various embodiments may be made from any known golf ball material.

[0032] First, inner core 102 may be comprised of a highly neutralized polymer. Highly neutralized polymer compositions, sometimes called highly neutralized acid polymers or highly neutralized acid polymer compositions, are a type of ionomer.

[0033] An ionomer is generally understood as any polymer material that includes ionized functional groups therein, lonomeric resins are often ionic copolymers of an olefin and a salt of an unsaturated carboxylic acid. The olefin may have from about 2 to about 8 carbon atoms, and may be an alpha-olefin. The acid may be an unsaturated monocarboxylic acid having from about 3 to about 8 carbon atoms, and may be an alpha, beta-unsaturated carboxylic acid. Commonly, ionomers are copolymers of ethylene and either acrylic acid or methacrylic acid. In some circumstances, an additional co-monomer (such as an acrylate ester, i.e., iso- or n-butylacrylate, etc.) can also be included to produce a terpolymer. A wide range of ionomers are known to the person of ordinary skill in the art of golf ball manufacturing.

[0034] When a large portion of the acid groups in the ionomer is neutralized by a cation, the ionomer material may be considered to be a highly neutralized acid polymer. Generally, such a polymer is considered highly neutralized when at least 70% of the acid groups are neutralized by a cation. In various embodiments, the highly neutralized acid polymer may be neutralized to at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or substantially 100%.

[0035] The acid content of an ionomer, including highly neutralized polymers, is defined as the percentage of unsaturated carboxylic acid by weight relative to the total weight of the polymer. Generally, the acid content may range from 1 % to 50%. In general, the acid content is considered "normal" when the acid content does not exceed 15%. In particular embodiments where the ionomer has a "high" acid content, the acid content is above 15% but still below 50%. In some embodiments, the acid content is considered high when between 20% and 50% or between 20% and 40%. Generally, higher acid levels may enable higher densities, but higher acid levels may also result in a loss of melt-processibility and related properties such as elongation and toughness. The acid content of an ionomer may affect the hardness. Namely, high acid levels may reduce any crystallinity otherwise present in the polymer.

[0036] In some embodiments, inner core 102 may comprise only one type or formulation of highly neutralized polymer. In other embodiments, blends of different types or formulations of highly neutralized polymers in various

percentages are used. The innermost core layer may be made using any technique known in the art, including but not limited to injection molding.

[0037] In some embodiments, inner core 102 may generally include one or two highly neutralized polymer compositions with additives, fillers, and melt flow modifiers. In some embodiments, inner core 102 generally includes HPF resins such as HPF2000 and HPF AD1035, produced by E. I. DuPont de Nemours and Company. In some embodiments, inner core 102 includes 100% by weight of HPF AD1035. In some embodiments, inner core 102 includes 80% by weight of HPF AD1035 and 20% by weight of additives, fillers, and melt flow modifiers. In some embodiments, inner core 102 includes 70% by weight of HPF AD1035 and 30% by weight of HPF2000. In some embodiments, inner core 102 includes 60% by weight of HPF AD1035, 20% by weight of HPF2000, and 20% by weight of additives, fillers, and melt flow modifiers. In some embodiments, the relative percentages of HPF AD1035, HPF2000, and additives, fillers, and melt flow modifiers may change, with HPF2000 ranging from 0% to 100% by weight of the composition, HPF AD1035 ranging from 0% to 100% by weight of the composition, and/or additives, fillers, and melt flow modifiers ranging from 0% to about 25% by weight of the composition.

[0038] In a particular embodiment, inner core 102 may comprise a blend of highly neutralized polymers, at least one ionomer and optionally weight fillers for adjusting the mass and specific gravity of the ball to desired levels. An inner core may comprise from about 40% to about 85% by weight of a first highly neutralized polymer (such as HPF AD1035), from about 0% to about 45% by weight of a second highly neutralized polymer (such as HPF 2000), about 2% to about 8% by weight of an ionomer (such as Surlyn®), and about 0% to about 15% by weight BaS0₄ additives.

[0039] Inner core 102 may have certain average cross-sectional hardness values. An average cross-sectional hardness value is defined as the average value taken from at least five sample measurements, or from exactly five sample measurements in particular. Generally, inner core 102 may be either "soft" or "hard" on its cross-section. A soft inner core may have an average hardness value of from about 50 to less than about 72.5 JIS C on its cross section, or from 50 to about 72 JIS C. Soft inner core 102 may alternatively have an average cross-sectional hardness value of from about 70 to less than about 72.5 JIS C on its cross section, or from 70 to about 72 JIS C. A hard inner core 102 may have an average cross-sectional hardness of from about 72.5 to about 95 JIS C, or from about 73 to about 95 JIS C. Hard inner core 102 may alternatively have an average cross-sectional hardness value of from about 72.5 to about 76 JIS C, or from about 73 to about 76 JIS C. In golf balls in accordance with this disclosure, whether inner core 102 is within the "soft" range or the "hard" range depends on the hardness of outer core 104 and the hardness of mantle layer 106.

[0040] Generally, each of inner core 102, outer core 104, and mantle layer 106 may have a "hard" hardness value range and a "soft" hardness value range for their respective cross-sections. The values for "hard" and soft" are different for each layer, and are discussed variously below. Only one of the three layers may be within its "hard" range in any particular embodiment, while the other two are accordingly in their "soft" range. For example, if inner core 102 is "soft" then either: outer core 104 is soft and mantle layer is hard, or outer core 104 is hard and mantle layer 106 is soft. Conversely, if inner core 102 is hard then both outer core 104 and mantle layer 106 are soft. [0041] In some embodiments, the hardness is the same throughout the entire cross-section of inner core 102, as the inner core 102 may be substantially homogeneous.

[0042] Generally, the hardness of inner core 102 may be adjusted by changing the relative amounts of a first highly neutralized polymer and a second highly neutralized polymer. For example, a first highly neutralized polymer may have a first hardness, and a second highly neutralized polymer may have a second hardness. Then, the two highly neutralized polymers may be mixed together to form a mixture having a hardness that is between the first hardness and the second hardness, depending on the relative proportions thereof.

[0043] More particularly, in embodiments where inner core 102 is comprised of a mixture of two or more types of highly neutralized polymers, the relative amounts of each type of highly neutralized polymer may affect the cross- sectional hardness. Namely, as the percentage of HPF AD1035 relative to HPF2000 increases, the hardness generally decreases. The relationship of cross- sectional hardness to percentage HPF AD1035 is generally linear. In some embodiments, if H is the cross-sectional hardness and P is the percentage of HPF AD1035 in the inner core composition, the relationship between H and P, when HPF AD1035 is blended with HPF2000, is given by the following equation, Eq. 1 , within standard engineering/manufacturing tolerances: H = 78-0.12P. This equation is valid when no masterbatch is used.

[0044] Suitable additives and fillers for use with a highly neutralized polymer composition in inner core 102 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.

[0045] In some of the embodiments, inner core 102 may have a diameter of between 20 mm and 35 mm, or between 24mm and 30mm. Fig. 1 shows radius 202, which is half of this diameter value. In particular embodiments, a diameter of inner core 102 may be about 24 mm. In other embodiments, a diameter of inner core 102 may be about 28 mm. In further embodiments, a diameter of inner core 102 may be between about 28 mm and about 30 mm.

Such embodiments may achieve advantageous durability while having no detrimental impact on driver distance.

[0046] Next, Fig. 1 shows outer core 104. Outer core 104 is located radially outward of inner core 102, and outer core 104 substantially surrounds inner core 102.

[0047] Outer core 104 in some embodiments may have a thickness 204 of at least 4.8 mm. In embodiments where inner core 102 is made of a highly neutralized polymer composition having a diameter ranging from 20 mm to 28 mm, if the thickness of outer core 104 is less than about 4.8 mm, the golf ball may not have sufficient durability. Internal durability may be preferable when the thickness of outer core 104 ranges from 5.0 mm to 8 mm.

[0048] In some embodiments, the diameter of the core (inner core 102 and outer core 104 together) may range from about 34 mm to about 40 mm. In embodiments where inner core 102 is made of a highly neutralized polymer composition having a diameter ranging from greater than 28 mm to less than 35 mm, outer core 104 thickness 204 may be selected to maintain an overall core diameter of 34 mm to 40 mm. In any of the embodiments described herein, outer core 104 thickness 204 may be selected to have a conforming golf ball, where the total diameter of the confirming golf ball is not less than 1.68 inches. [0049] Outer core 104 may be made using any material, but in some embodiments may be made of a thermoset polybutadiene rubber. In some embodiments, outer core 104 may be generally formed by crosslinking a polybutadiene rubber composition as described in U.S. Patent No. 8,193,296, the disclosure of which is hereby incorporated by reference in its entirety.

[0050] 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. In some embodiments, the specific gravity of the outer core may be from about 1.05 to about 1.45. In some embodiments, the specific gravity of the outer core may be from about 1.05 to about 1.35.

[0051] In some embodiments, a polybutadiene synthesized with a rare earth element catalyst may be used to form outer core 104. Such a polybutadiene may provide excellent resilience performance of the golf ball. 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.

[0052] 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 the outer core. 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.

[0053] Outer core 104 may be made by any suitable process. For example, in some embodiments, outer core 104 may be made by a compression molding process. The process of making outer core 104 may be selected based on a variety of factors. For example, the process of making outer core 104 may be selected based on the type of material used to make outer core 104 and/or the process used to make the other layers.

[0054] In some embodiments, outer core 104 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 102 placed in the hemispherical cups may be roughened before the placement to increase adhesion between the inner core and the outer core. In some embodiments, inner core surface may be pre-coated with an adhesive before placing the inner core in the hemispherical cups to enhance the durability of the golf ball and to enable a high rebound.

[0055] Outer core 104 may have certain average cross-sectional hardness values. An average cross-sectional hardness value is defined as the average value taken from at least five sample measurements, or from exactly five sample measurements in particular. Generally, outer core 104 may be either "soft" or "hard" on its cross-section. A soft outer core 104 may have an average cross- sectional hardness value of from about 50 to about 83 JIS C, or from about 80 to about 83 JIS C. A hard outer core 104 may have an average cross-sectional hardness of from more than about 83 to about 95 JIS C, or from about 84 to about 85 JIS C, or from more than about 83 to 85 JIS C, or from about 84 to 85 JIS C. These ranges for "hard" and "soft" differ from the hard and soft ranges for inner core 102 (discussed above) and mantle layer 106 (discussed below). As mentioned above, in golf balls in accordance with this disclosure, whether outer core 104 is within its "soft" range or its "hard" range depends on the hardness of inner core 102 and the hardness of mantle layer 106. That is, two of the three are within their "soft" ranges and one is within its "hard" range. For example, if outer core 104 is "soft" then either: inner core 102 is soft and mantle layer is hard, or inner core 102 is hard and mantle layer 106 is soft. Conversely, if outer core 104 is hard then both inner core 102 and mantle layer 106 are soft.

[0056] Generally, the hardness of a rubber compound may be changed by varying the amount of cross-linking agent, such as zinc diacrylate (ZDA) or a peroxide. Varying the cross-linking agent to achieve a particular desired hardness level for the rubber is within the skill of one having ordinary skill in the art of golf ball manufacturing. [0057] Third, FIG. 1 shows mantle layer 106. Mantle layer 106 is located radially outward of outer core 104 and generally surrounds and encloses outer core 104.

[0058] In some embodiments, mantle layer 106 is made of an ionomer material, lonomers are discussed broadly above. In some embodiments, mantle layer 106 is comprised of Surlyn®. In some embodiments, the Surlyn® used in mantle layer 106 is normal acid, having an acid content that does not exceed about 15% by weight. In some embodiments, the Surlyn® used in mantle layer 106 is high acid, having an acid content of between 15% and 50% by weight. In some embodiments, the high acid Surlyn® of mantle layer 106 has an acid content of about 20% by weight.

[0059] Mantle layer 106 may have any desired thickness 206. In some embodiments, mantle layer thickness 206 may be selected so that the golf ball is a conforming golf ball. In some embodiments, mantle layer thickness 206 is between 0.5 and 1.3 mm. In some embodiments, mantle layer thickness 206 is between about 0.95 mm and about 1.2 mm. In some embodiments, mantle layer thickness 206 is between about 0.5 mm and 0.95 mm. In some embodiments, mantle layer thickness 206 is about 0.6 mm. In some embodiments, mantle layer thickness 206 is about 0.95 mm. In some embodiments, mantle layer thickness 206 is about 1.2 mm.

[0060] The combination of acid level and thickness for mantle layer 106 may impact performance. In some embodiments, the material making up mantle layer 106 is normal acid ionomer and has a thickness 206 of about 0.95 mm. In some embodiments, the mantle layer material is high acid ionomer and has a thickness 206 of about 0.95 mm. In some embodiments, the mantle layer material is high acid ionomer and has a thickness 206 of about 1.2 mm. In some

embodiments, the mantle layer material is normal acid ionomer and has a thickness 206 of about 1.2 mm. In some embodiments, the mantle layer material is normal acid ionomer and has a thickness 206 of about 0.6 mm. In some embodiments, the mantle layer material is high acid ionomer and has a thickness 206 of about 0.6 mm.

[0061] Mantle layer 106 may also have certain cross-sectional hardness values. An average cross-sectional hardness value is defined as the average value taken from at least five sample measurements, or from exactly five sample measurements in particular. Generally, mantle layer 106 may be either "soft" or "hard" on its cross-section. A soft mantle layer 106 may have an average cross- sectional hardness value of from about 50 to about 86.5 JIS C, or from about 50 to about 86 JIS C, or from about 82 to about 86.5 JIS C, or from about 82 to about 86 JIS C. A hard mantle layer 106 may have an average cross-sectional hardness of from about more than 86.5 to about 95 JIS C, or from about 87 to about 95 JIS C, or from about more than 86.5 to about 91 JIS C, or from about 87 to about 91 JIS C. These ranges for "hard" and "soft" may differ from the hard and soft ranges for the average cross-sectional hardnesses of inner core 102 and outer core 104 (both discussed above). As mentioned above, in golf balls in accordance with this disclosure, whether mantle layer 106 is within its "soft" range or its "hard" range depends on the hardness of inner core 102 and the hardness of outer core 104. That is, two of the three are within their "soft" ranges and one is within its "hard" range. For example, if mantle layer 106 is "soft" then either: inner core 102 is soft and outer core 104 is hard, or inner core 102 is hard and outer core 104 is soft. Conversely, if mantle layer 106 is hard then both inner core 102 and outer core 104 are soft.

[0062] Generally, the hardness of mantle layer 106 may be adjusted by varying the proportions of the stock materials used to form it. That is, in some embodiments, mantle layer 106 may be formed of a mixture of two or more stock Surlyn® materials. In such embodiments, the hardness of mantle layer 106 may be adjusted by changing the relative amounts of a first Surlyn® ionomer and a second Surlyn® ionomer, and additional Surlyn® ionomer(s) if applicable. For example, a first Surlyn® ionomer may have a first hardness, and a second

Surlyn® ionomer may have a second hardness. Then, the two Surlyn® ionomers may be mixed together to form a mixture having a hardness that is between the first hardness and the second hardness, depending on the relative proportions thereof. Generally, the amount of additives does not substantially affect the hardness of a mixture of two or more Surlyn® ionomers. In some embodiments, mantle layer 106 may be a mixture of one or more of DuPont's Surlyn® ionomers S9150, S8150, and S9320.

[0063] Finally, FIG. 1 shows cover layer 108. Cover layer 108 is located radially outward of mantle layer 106, and substantially surrounds mantle layer 106.

[0064] Cover layer 108 may be made of any material known in the golf ball art, including but not limited to ionomers such as Surlyn®, urethanes, thermoplastic polyurethanes, balata, and combinations of these materials. In some embodiments, outer cover layer 108 is made from a crosslinked

thermoplastic polyurethane material that is a blend of PTMEG, BG, TMPME, DCP, and MDI in varying percentages by weight. "PTMEG" is polytetramethylene ether glycol, having a number average molecular weight of 2,000, and is commercially available from Invista, under the trade name of Terathane® 2000. "BG" is 1 ,4- butanediol, commercially available from BASF and other suppliers. "TMPME" is trimethylolpropane monoallylether, commercially available from Perstorp Specialty Chemicals AB. "DCP" is dicumyl peroxide, commercially available from LaPorte Chemicals Ltd. "MDI" is diphenylmethane diisocyanate, commercially available from Huntsman, under the trade name of Suprasec® 1 100. Specifically, these materials may be prepared by mixing the components in a high agitated stir for one minute, starting at a temperature of about 70°C, followed by a 10-hour post curing process at a temperature of about 100°C. The post cured polyurethane elastomers may be ground into small chips.

[0065] Other suitable outer cover layer compositions are disclosed in the following patent documents, each of which is incorporated herein in its entirety: [0066] US Patent Publication Number US-2012-0004050, currently US Patent Application Serial Number 12/829,131 to Yasushi Ichikawa et al., filed on July 1 , 2010 under the title "Golf Ball Incorporating Thermoplastic Polyurethane";

[0067] US Patent Publication Number , currently US Patent

Application Serial Number 13/341 ,544 to Thomas J. Kennedy III, filed on

December 30, 201 1 under the title "lonomer/Polyamide Alloy for Golf Balls"; and

[0068] US Patent Publication Number , currently US Patent

Application Serial Number 13/342,551 to Yasushi Ichikawa et al., filed on January 3, 2012 under the title "Over-Indexed Thermoplastic Polyurethane Elastomer, Method of Making, and Articles Comprising The Elastomer".

[0069] Cover layer 108 may be manufactured using any known technique, including but not limited to injection molding, RIM, and compression molding.

[0070] Thickness 208 of cover layer 108 may be any desired thickness. In some embodiments, the thickness 208 may be selected to allow golf ball 100 to be a conforming golf ball. In some embodiments, the thickness 208 may be selected to enhance the feel of golf ball 100. In some embodiments, thickness 208 may be between about 0.5 mm to about 1.5 mm. In some embodiments, thickness 208 may be about 1.1 mm.

[0071] Golf balls according to this disclosure are provided with dimples on the outer cover layer to enhance the aerodynamic performance of the golf ball. Any number of dimples having any shape and depth and in any pattern known in the art may be provided on cover layer 108. In some embodiments, between 200 and 500 dimples may be provided. In some embodiments, between 300 and 400 dimples may be provided. In some embodiments, between 320 and 350 dimples may be provided.

[0072] In some embodiments, one or more coating layers may be applied to cover layer 108. The coating layer(s) may be provided for any reason, such as for scuff resistance, altering a hardness of the cover layer 108, altering the aerodynamics of golf ball 100, enhancing the visibility of golf ball 100, and for aesthetic purposes. The coating may be any type of coating known in the art, including but not limited to paints, inks, clear coats, urethane coatings, sparkle coatings, and the like. The coating may be applied using any method known in the art, including but not limited to spraying, stamping, pad printing, brush applications, combinations of these techniques, and the like.

[0073] Once assembled, golf balls according to the present disclosure will exhibit various characteristics based upon the construction. Some of these characteristics include a ball COR, a ball weight, and a ball compression. In some embodiments, the COR of ball 100 is greater than about 0.772. In some

embodiments, golf ball 100 weights from about 35 g to about 55 g, in particular about 45 g to about 46 g. In some embodiments, golf ball 100 may have

compression deformation value of from about 2.4 to 3.3 mm, or from about 2.7 to about 3.0 mm.

[0074] In particular, finished golf balls according to the present

disclosure may achieve favorable peak frequency sounds. The peak frequency sound may have a particularly low value, such that the sound the golf ball makes when struck with a golf club is low pitch and "solid" sounding. Namely, the peak frequency sound may be less than about 3.75 kHz. This low frequency sound may be preferred by golfers because it may better convey the quality of the shot made.

[0075] This disclosure may be particularly understood in view of the following examples, which are not intended to limit the scope of this disclosure.

[0076] Examples

[0077] Examples E1 through E7 and comparative examples C1 through C8 were prepared as discussed below and as shown in Table 1. The results of testing examples E1 through E7 and comparative examples C1 - C8 are also shown in Table 1.

[0078] Generally, all samples were allowed to age at least 8 weeks after manufacturing before testing. All samples were incubated at approximately 23C with 0% humidity for 24 hours prior to conducting the test. [0079] Each inner core was made from a composition including one or more highly neutralized polymers. The inner cores were a mixture of HPF AD1035 and HPF2000, with minor amounts of additional Surlyn® ionomer added, as well as BaS0₄ additives for weight. The varying values of the hardness were achieved by varying the relative amounts of AD1035 and HPF2000. Where noted in Table 1 , the diameter of inner core in a particular comparative example is 24 mm, all others are 28 mm in diameter.

[0080] Each outer core was made from neodymium-catalysed butadiene rubber ("Nd-BR"). BaS0₄ was added to the outer core to add weight in sufficient amount to meet the mass limitations of the ball. The varying hardnesses of the outer core were achieved by varying the amounts of ZDA or peroxide in the rubber composition.

[0081] Each example mantle layer was made from DuPont's

commercially available Surlyn®. The Surlyn® used was a mixture of DuPont's S9150, S8150, and S9320. The varying values of the hardness of the mantle layers was achieved by varying the relative proportions of S9150, S8150, and S9320. Descriptions of various mantle layer formulations are provided in U.S. Patent Application Number 12/627,992 filed on November 30, 2009, and published as U.S. Patent Application Number US-201 1 -0130220-A1 , the contents of which is hereby incorporated by reference.

[0082] Each comparative example mantle layer that is made from a polyurethane.

[0083] Each cover layer was made from a polyurethane, such as those described in U.S. Patent Application Number 13/342,551 mentioned previously.

[0084] The following results were achieved: PLUMSEA DOCKET NO. 72-1837

Table 1

[0085] The following items are listed in Table 1 :

[0086] Configuration: refers to the relationship of the hardness values of the inner core, outer core, and mantle layer. Specifically, for example, "SSH" means the inner core is soft, the outer core is soft, and the mantle layer is hard. Table 2 shows definitions of soft and hard for each layer, each value is given in JIS C.

Table 2 - Ranges of Average Hardness Values

[0087] The measurements are based on JIS C taken from a sample that was cut in half and sanded (then incubated for 24 hours). Generally, the highly neutralized polymer inner core material and the Surlyn® mantle layer material are uniform in hardness, while the rubber outer core material may have a distribution of hardness values at various points on its cross-section. Each measurement was taken in the approximate center of the cross-section of the specified layer. The JIS C hardness gauge needle was held perpendicular to the half cut sample and then pressed firmly against the sample to get a clear reading. The numbers specified in Table 1 are the average of 10 measurements. The ball is cut roughly in half so that one hemisphere is slightly larger than the other. The cut side of the larger hemisphere is sanded flat to define a planar measuring surface. The resulting measuring surface corresponds to a center plane of the ball. Name: S = Surlyn® mantle layer, U = urethane mantle layer.

[0088] Mantle Layer: the Shore D hardness of a slab of the mantle material as measured by ASTM D-2240. [0089] Cover Layer, the Shore D hardness of a slab of the cover layer material as measured by ASTM D-2240.

[0090] Weight the finished ball weight in grams

[0091] Compression: the compression deformation of the finished golf ball compression.

[0092] COR: the coefficient of restitution of the finished golf ball.

[0093] Cover Layer Shore D: this is the measured shore D hardness of the cover on the ball, as an average of five measurements taken on the fret area (between dimples). The ASTM standard D-2240 is used, but instead of a flat plaque, the finished golf ball is positioned under the needle such that it contacts the area between dimples in a perpendicular orientation to the center of the golf ball.

[0094] Cover Layer JIS C : See Cover Layer Shore D method above, except a JIS C gauge (as detailed in JIS K 6253) is used instead of the ASTM standard D-2240 for Shore D.

[0095] Mantle Layer JIS C : The measurements are based on JIS C (JIS K 6253) taken from a sample that was cut in half and sanded (then incubated for 24 hours). Each measurement was taken in the approximate center of the cross section of the mantle layer. The JIS C hardness gauge needle was held

perpendicular to the half cut sample and then pressed firmly against the sample to get a clear reading. The numbers specified in Table 1 are the average of 10 measurements. Specifically, the ball is cut roughly in half so that one hemisphere is slightly larger than the other. The cut side of the larger hemisphere is sanded flat to define a planar measuring surface. The resulting measuring surface corresponds to a center plane of the ball.

[0096] Outer Core JIS C : The measurements are based on JIS C (JIS K 6253) taken from a sample that was cut in half and sanded (then incubated for 24 hours). All measurements were taken in the approximate center of the cross section of the specified layer (half way between the inner core and mantle layer). The JIS C hardness gauge needle was held perpendicular to the half cut sample and then pressed firmly against the sample to get a clear reading. The numbers specified in Table 1 are the average of 10 measurements. Specifically, the ball is cut roughly in half so that one hemisphere is slightly larger than the other. The cut side of the larger hemisphere is sanded flat to define a planar measuring surface. The resulting measuring surface corresponds to a center plane of the ball.

[0097] Inner Core JIS C : The measurements are based on JIS C (JIS K 6253) taken from a sample that was cut in half and sanded (then incubated for 24 hours). All measurements were taken in the approximate center of the inner core. The JIS C hardness gauge needle was held perpendicular to the half cut sample and then pressed firmly against the sample to get a clear reading. The numbers specified in Table 1 are the average of 10 measurements. Specifically, the ball is cut roughly in half so that one hemisphere is slightly larger than the other. The cut side of the larger hemisphere is sanded flat to define a planar measuring surface. The resulting measuring surface corresponds to a center plane of the ball.

[0098] Frequency: see peak frequency as defined previously.

[0099] Driver Test : 12 samples of each finished golf ball were hit outdoors with a Golf Labs robot. The tee was approximately 2 inches forward of the center of robot and the ball impacted the driver face centered left to right and approximately half an inch above the center point of the face. The head speed was approximately 89mph. The driver used was a VR Pro 9.5 degree loft with an extra stiff shaft. The trackman net system (radar based launch monitor) was used to gather the data.

[00100] FIG. 2 shows a chart of various values of the peak frequency sound and COR for the examples and comparatives examples from Table 1.

[00101] 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.

Claims

WHAT IS CLAIMED IS:

1. A golf ball comprising:

an inner core, the inner core encompassing a center of the golf ball and being comprised of a highly neutralized polymer;

an outer core, the outer core being positioned radially outward of the inner core and substantially surrounding the inner core, the outer core being comprised of a rubber;

a mantle layer, the mantle layer being positioned radially outward of the outer core and substantially surrounding the outer core, the mantle layer being comprised of an ionomer; and

a cover layer, the cover layer being positioned radially outward of the mantle layer and substantially surrounding the mantle layer;

wherein at least two of the inner core, the outer core, and the mantle layer are soft; and at least one of the inner core, the outer core, and the mantle layer are hard; and

wherein a soft inner core has an average cross-sectional hardness of from about 50 to less than about 72.5 JIS C, a hard inner core has an average cross- sectional hardness of from about 72.5 to about 95 JIS C, a soft outer core has an average cross-sectional hardness of from about 50 to about 83 JIS C, a hard outer core has an average cross-sectional hardness of from more than about 83 to about 95 JIS C, a soft mantle layer has an average cross-sectional hardness of from about 50 to about 86.5 JIS C, and a hard mantle layer has an average cross- sectional hardness of from more than about 86.5 to about 95 JIS C.

2. The golf ball according to claim 1 , wherein

the inner core has an average cross-sectional hardness of from about 70 to less than about 72.5 JIS C;

the outer core has an average cross-sectional hardness of from about 80 to about 83 JIS C; and

the mantle layer has an average cross-sectional hardness of from more than about 86.5 to about 91 JIS C.

3. The golf ball according to claim 1 , wherein

the inner core has an average cross-sectional hardness of from about 70 to about 72.5 JIS C;

the outer core has an average cross-sectional hardness of from more than about 83 to about 85 JIS C; and

the mantle layer has an average cross-sectional hardness of from about 82 to about 86.5 JIS C.

4. The golf ball according to claim 1 , wherein

the inner core has an average cross-sectional hardness of from about 72.5 to about 76 JIS C;

5. The golf ball according to claim 1 , wherein the golf ball has a peak frequency sound of less than about 3.75 kHz.

6. The golf ball according to claim 1 , wherein the golf ball has a COR value of at least 0.772.

7. The golf ball according to claim 1 , wherein a soft inner core has an average cross-sectional hardness of from about 70 to less than about 72.5 JIS C, a hard inner core has an average cross-sectional hardness of from about 72.5 to about 76 JIS C, a soft outer core has an average cross-sectional hardness of from about 80 to about 83 JIS C, a hard outer core has an average cross-sectional hardness of from more than about 83 to about 85 JIS C, a soft mantle layer has an average cross-sectional hardness of from about 82 to about 86.5 JIS C, and a hard mantle layer has an average cross-sectional hardness of from more than about 86.5 to about 91 JIS C.

8. The golf ball according to claim 1 , wherein the inner core comprises a mixture of at least two different types of highly neutralized polymers.

9. The golf ball according to claim 1 , wherein the inner core has a diameter of greater than 28 mm.

10. The golf ball according to claim 1 , wherein the inner core has a diameter of about 28 mm, and the inner core has a cross-sectional hardness of from about 73 to about 76 JIS C.

1 1. A golf ball comprising:

wherein the inner core has an average cross-sectional hardness of from about 70 to less than about 72.5 JIS C, the outer core has an average cross- sectional hardness of from about 80 to about 83 JIS C, and the mantle layer has an average cross-sectional hardness of from more than about 86.5 to about 91 JIS C.

12. A golf ball comprising:

wherein the inner core has an average cross-sectional hardness of from about 70 to about 72.5 JIS C, the outer core has an average cross-sectional hardness of from more than about 83 to about 85 JIS C, and the mantle layer has an average cross-sectional hardness of from about 82 to about 86.5 JIS C.

13. A golf ball comprising:

wherein the inner core has an average cross-sectional hardness of from about 72.5 to about 76 JIS C, the outer core has an average cross-sectional hardness of from about 80 to about 83 JIS C, and the mantle layer has an average cross-sectional hardness of from about 82 to about 86.5 JIS C.

14. A golf ball comprising:

wherein the golf ball has a peak frequency sound of less than about 3.75 kHz, a COR value of at least 0.772.

15. The golf ball of claim 14, wherein the inner core has a diameter of about 28 mm.

16. The golf ball of claim 15, wherein the inner core has a hardness of from 73 to 76 JIS C.

17. The golf ball of claim 14, wherein the inner core comprises a blend of at least two highly neutralized polymers, an ionomer, and a weight increasing filler.

18. The golf ball of claim 14, wherein the outer core comprises thermoset polybutadiene rubber.

19. The golf ball of claim 14, wherein the mantle layer comprises a Surlyn ionomer.

20. The golf ball of claim 14, wherein

at least two of the inner core, the outer core, and the mantle layer are soft; and

at least one of the inner core, the outer core, and the mantle layer are hard; wherein a soft inner core has an average cross-sectional hardness of from about 70 to less than about 72.5 JIS C, a hard inner core has an average cross- sectional hardness of from about 72.5 to about 76 JIS C, a soft outer core has an average cross-sectional hardness of from about 80 to about 83 JIS C, a hard outer core has an average cross-sectional hardness of from more than about 83 to about 85 JIS C, a soft mantle layer has an average cross-sectional hardness of from about 82 to about 86.5 JIS C, and a hard mantle layer has an average cross- sectional hardness of from more than about 86.5 to about 91 JIS C.