Low Compression, Resilient Golf Balls Including an Inorganic Sulfide Catalyst and Methods for Making the Same

The present invention relates to low compression, resilient golf balls and portions thereof formed from the conversion reaction of an amount of polybutadiene, a free radical source, and a cis-to-trans catalyst including at least one inorganic sulfide at a sufficient temperature to form a polybutadiene reaction product.

Conventional golf balls can be divided into several general classes: (a) solid golf balls having one or more layers, and (b) wound golf balls. Solid golf balls include one-piece balls, which are easy to construct and relatively inexpensive, but have poor playing characteristics and are thus generally limited for use as range balls. Two-piece balls are constructed with a generally solid core and a cover and are generally the most popular with recreational golfers because they are very durable and provide maximum distance. Balls having a two-piece construction are commonly formed of a polymeric core encased by a cover. Typically, the core is formed from polybutadiene that is chemically crosslinked with zinc diacrylate and/or other similar crosslinking agents. These balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Solid golf balls also include multi-layer golf balls that are comprised of a solid core of one or more layers and/or a cover of one or more layers. These balls are regarded as having an extended range of playing characteristics.

Wound golf balls are generally preferred by many players due to their high spin and soft "feel" characteristics. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material and a cover. Wound balls generally are more difficult and expensive to manufacture than solid two-piece balls.

A variety of golf balls designed to provide a wide range of playing characteristics, i.e., the compression, velocity, "feel," and spin, that can be optimized for various playing ability, are known in the prior art. One of the most common polymer components present in modern golf ball construction, in addition to ionomers, is polybutadiene and, more specifically, polybutadiene having a high cis- isomer concentration. The use of a polybutadiene having a high cis- concentration results in a very resilient and rigid golf ball, especially when coupled with a hard cover material. These highly resilient golf balls have a relatively hard "feel" when struck by a club. Soft "feel" golf balls constructed with a high cis-polybutadiene have low resilience. In an effort to provide improved golf balls, various other polybutadiene formulations have been prepared, as discussed below.

U.S. Pat. No. 3,239,228 discloses a solid golf ball having a core molded of polybutadiene rubber with a high sulfur content, and a cover. The polybutadiene content of the core is stereo-controlled to the configuration 25-100 percent cis- and 0-65 percent trans-1,4-polybutadiene, with any remainder having a vinyl configuration of polybutadiene. A preferred embodiment of the polybutadiene golf ball core contains 35 percent cis-, 52 percent trans-, and 13 percent vinyl-polybutadiene. The level of trans- and vinyl- content are disclosed to be unimportant to the overall playing characteristics of the polymer blend.

British Patent No. 1,168,609 discloses a molding composition from which improved golf ball cores can be molded and which contains cis-polybutadiene as a basic polymer component. The core polymer component typically includes at least 60 percent cis-polybutadiene, with the remainder being either the trans- or vinyl- forms of polybutadiene. In a preferred embodiment, the core polybutadiene component contains 90 percent cis- configuration, with the remaining 10 percent being either the trans- or vinyl-configurations of 1,4-polybutadiene.

U.S. Pat. Nos. 3,572,721 and 3,572,722 disclose a solid, one- or two-piece golf ball, with the two-piece ball having a core and a cover. The cover material can include any one of a number of materials, or blends thereof, known to those of ordinary skill in the art, including trans-polybutadiene which may be present in an amount from at least 90 percent, with the remainder being the cis- and/or vinyl configuration.

British Patent No. 1,209,032 discloses a two- or three-piece golf ball having a core and a cover. The core or cover material can be any material capable of being crosslinked. In particular, the material can be a polymer or a copolymer of butadiene or isoprene. Preferably, the polymer component is polybutadiene having a cis content of greater than 50 percent by weight.

U.S. Pat. No. 3,992,014 discloses a one-piece, solid golf ball. The golf ball material is typically polybutadiene, with a stereo-configuration selected to be at least 60 percent cis-polybutadiene, with the remaining 40 percent being the trans-polybutadiene and/or 1,2-polybutadiene (vinyl) isomers.

U.S. Pat. No. 4,692,497 discloses a golf ball and material thereof formed by curing a diene polymer including polybutadiene and a metal salt of an alpha, beta ethylenically unsaturated acid using at least two free radical initiators.

U.S. Pat. No. 4,931,376 discloses a process for producing butadiene polymers for use in various applications, including golf ball cover materials. One embodiment of the invention employs a blended polymeric resin material, including at least 30 percent by weight of a trans-polybutadiene polymer as a golf ball cover on a two-piece ball. In a preferred embodiment, the golf ball cover material contains a blend including 30 to 90 percent by weight of a trans-polybutadiene polymer.

U.S. Pat. No. 4,971,329 discloses a solid golf ball made from a polybutadiene admixture of cis-1,4 polybutadiene and 1,2 polybutadiene, a metal salt of an unsaturated carboxylic acid, an inorganic filler, and a free radical initiator. The admixture has about 99.5 percent to about 95 percent by weight of cis-1,4 polybutadiene and about 0.5 percent to about 5 percent by weight of 1,2 polybutadiene.

U.S. Pat. No. 5,252,652 discloses a one-piece or multi-layered golf ball core with improved flying performance from a rubber composition comprising a base rubber, preferably 1,4-polybutadiene with a cis- content of at least 40 mole percent, an unsaturated carboxylic acid metal salt, an organic peroxide, and an organic sulfur compound and/or a metal salt thereof. The organic sulfur compound and/or a metal salt is typically present in an amount from about 0.05 to 2 parts per hundred by weight and the organic peroxide is typically present in an amount from about 0.5 to 3 parts per hundred by weight of the total polymer component.

European Patent No. 0 577 058 discloses a golf ball containing a core and a cover that is formed as two separate layers. The inner layer of the cover is molded over the core and is formed from ionomer resin. The outer layer of the cover is molded over the inner layer and is formed from a blend of natural or synthetic balata and a crosslinkable elastomer, such as polybutadiene. In one embodiment of the outer layer of the cover, the elastomer is 1,4-polybutadiene having a cis- structure of at least 40 percent, with the remaining 60 percent being the trans- isomer. A preferred embodiment contains a cis- structure of at least 90 percent and more preferably, a cis- structure of at least 95 percent.

U.S. Pat. No. 5,421,580 discloses a wound golf ball having a liquid center contained in a center bag, a rubber thread layer formed on the liquid center, and a cover over the wound layer and liquid center. The cover material can include any one of a number of materials, or blends thereof, known to those of ordinary skill in the art, including trans-polybutadiene and/or 1,2-polybutadiene (vinyl), such that the cover has a JIS--C hardness of 70-85; preferred trans- percentages are not disclosed.

U.S. Pat. No. 5,697,856 discloses a solid golf ball having a core and a cover wherein the core is produced by vulcanizing a base rubber composition containing a butadiene rubber having a cis-polybutadiene structure content of not less than 90 percent before vulcanization. The amount of trans-polybutadiene structure present after vulcanization is 10 to 30 percent, as amounts over 30 percent are alleged to detrimentally result in cores that are too soft with deteriorated resilience performance, and to cause a decrease in golf ball performance. The core includes a vulcanizing agent, a filler, an organic peroxide, and an organosulfur compound.

British Patent No. 2,321,021 discloses a solid golf ball having a core and a cover formed on the core and having a two-layered cover construction having an inner cover layer and an outer cover layer. The outer cover layer is comprised of a rubber composite that contains 0.05 to 5 parts by weight of an organic sulfide compound. The core rubber composition comprises a base rubber, preferably 1,4-polybutadiene having a cis-content of at least 40 percent by weight, a crosslinking agent, a co-crosslinking agent, an organic sulfide, and a filler. The crosslinking agent is typically an organic peroxide present in an amount from 0.3 to 5.0 parts by weight and the co-crosslinking agent is typically a metal salt of an unsaturated fatty acid present in an amount from 10 to 40 parts by weight. The organic sulfide compound is typically present from 0.05 to 5 parts by weight.

U.S. Pat. No. 5,816,944 discloses a solid golf ball having a core and a cover wherein the core has a JIS--C hardness of 50 to 80 and the cover has a Shore-D hardness of 50 to 60. The core material includes vulcanized rubber, such as cis-polybutadiene, with a crosslinker, an organic peroxide, an organosulfur compound and/or a metal-containing organosulfur compound, and a filler.

Additionally, conventional polymers that have a high percentage of the trans-polybutadiene conformation, such as DIENE 35NF, from Firestone Corp., that has 40 percent cis- isomer and 50 percent trans-polybutadiene isomer, and mixtures of high-cis-and high-trans- polybutadiene isomers, such as CARIFLEX BR1220, from Shell Corporation, and FUREN 88, from Asahi Chemical Co., respectively, typically do not yield high resilience values and therefore are not desirable.

It is thus desired to prepare golf balls having lower compression, i.e., a softer ball, while having the same or higher resilience than conventional balls. It is alternatively desired to obtain the same or lower compression while achieving greater resilience.

All of the embodiments according to the invention below may be used in any golf ball. Particularly, each embodiment may be used in one of the three following embodiments. In the first such embodiment, the golf ball is a one-piece golf ball. In the second such embodiment, the golf ball includes a core and a cover disposed concentrically about the core and the reaction product is disposed in at least a portion of the core. In the third such embodiment, the golf ball includes a core having a center and at least one intermediate layer; and a cover disposed concentrically about the core, wherein the reaction product is disposed in a portion of the core.

The invention relates to a golf ball formed from the conversion reaction of an amount of polybutadiene, a free radical source, and a cis-to-trans catalyst including at least one inorganic sulfide at a sufficient temperature to form a polybutadiene reaction product which includes an amount of trans-polybutadiene greater than the amount of trans-polybutadiene present before the conversion reaction, and a cis-to-trans catalyst including at least one inorganic sulfide. In one embodiment, the reaction product has a first dynamic stiffness measured at -50.degree. C. that is less than about 130 percent of a second dynamic stiffness measured at 0.degree. C.

In one embodiment, the inorganic sulfide includes a metal sulfide. In a preferred embodiment, the metal sulfide includes at least one of a titanium sulfide, manganese sulfide, iron sulfide, calcium sulfide, cobalt sulfide, molybdenum sulfide, tungsten sulfide, copper sulfide, selenium sulfide, yttrium sulfide, zinc sulfide, tin sulfide, potassium sulfide, or bismuth sulfide. The cis-to-trans catalyst is typically present in an amount from about 0.1 to 25 parts per hundred of polybutadiene. In a preferred embodiment, the cis-to-trans catalyst is present in an amount from about 0.1 to 12 parts per hundred of polybutadiene. In a more preferred embodiment, the cis-to-trans catalyst is present in an amount from about 0.1 to 8 parts per hundred of polybutadiene. In another embodiment, the cis-to-trans catalyst further comprises at least one of an organosulfur compound, an aromatic organometallic compound, a metal-organosulfur compound, elemental sulfur, a polymeric sulfur, or an aromatic organic compound.

In one embodiment, the polybutadiene reaction product includes less than about 7 percent vinyl isomer content based on the total polybutadiene. In a preferred embodiment, the polybutadiene reaction product includes less than about 4 percent vinyl isomer. In a more preferred embodiment, the polybutadiene reaction product includes less than about 2 percent vinyl isomer.

In another embodiment, the reaction product further includes a vulcanization accelerator. At least one vulcanization accelerator is typically present when the inorganic sulfide is elemental or polymeric sulfur. In a preferred embodiment, the vulcanization accelerator includes at least one of sulfenamide, thiazole, dithiocarbamate, thiuram, xanthate, thiadiazine, thiourea, guanadine, or aldehyde-amine. The accelerator is typically present in an amount from about 0.05 to 2 phr. In a preferred embodiment, the accelerator is present in an amount from about 0.1 to 1 phr.

In one embodiment, the portion of the core is the center. In another embodiment, the center includes a fluid. In yet another embodiment, the intermediate layer may include a wound layer of tensioned elastomeric material. In a preferred embodiment, the tensioned elastomeric material includes a reaction product that includes polybutadiene or polyisoprene and a cis-to-trans catalyst that includes at least one inorganic sulfide. In another embodiment, the golf ball further includes a density-modifying filler.

The invention also relates to a method for forming a golf ball which includes combining (a) at least one of a cis-to-trans catalyst including at least one inorganic sulfide, (b) a free radical source, (c) a first resilient polymer component having a cis-polybutadiene component present in an amount greater than about 70 percent, and optionally, (d) a crosslinking agent, converting a portion of the first resilient polymer component to a second resilient polymer component, wherein at least a portion of the cis-polybutadiene component is converted to a trans-polybutadiene component and wherein the polybutadiene in the second resilient polymer component is at least about 10 percent trans-polybutadiene and less than about 7 percent vinyl-polybutadiene, and forming the second resilient polymer component into at least a portion of the golf ball.

In one embodiment, the portion of the second resilient polymer component is formed into a solid sphere. In another embodiment, which may be alternative or in addition to the forming of the sphere, the portion may be formed into at least one layer disposed about the solid sphere. In the alternative embodiment, the sphere is formed but the portion is disposed in at least one layer disposed about the sphere. In the additive embodiment, an additional portion of the second resilient polymer component is formed into a cover disposed concentrically about a sphere.

In one embodiment, the polybutadiene component includes cis-polybutadiene present in an amount of at least 80 percent of the total first resilient polymer component. In another embodiment, a density-modifying filler is also included in the combining step. In yet another embodiment, the steps of combining the first resilient polymer component and the cis-to-trans catalyst and forming the portion, includes forming a sphere having a midpoint having a first amount of trans-polybutadiene and a surface having a second amount of trans-polybutadiene, wherein the first amount is at least about 6 percent less than the second amount.

In another embodiment, the second amount of trans-polybutadiene component is selected to include a vinyl polybutadiene component present in an amount of less than about 4 percent of the total resilient polymer component.

In yet another embodiment, the inorganic sulfide is selected to include at least one metal sulfide. In a preferred embodiment, the at least one metal sulfide is selected to include at least one of a titanium sulfide, manganese sulfide, iron sulfide, calcium sulfide, cobalt sulfide, molybdenum sulfide, tungsten sulfide, copper sulfide, selenium sulfide, yttrium sulfide, zinc sulfide, tin sulfide, potassium sulfide, or bismuth sulfide. The cis-to-trans catalyst is typically present in an amount from about 0.1 to 25 parts per hundred of the total resilient polymer component. In a preferred embodiment, the cis-to-trans catalyst is present in an amount from about 0.1 to 12 parts per hundred of the total resilient polymer component. In a more preferred embodiment, the cis-to-trans catalyst is present in an amount from about 0.1 to 8 parts per hundred of the total resilient polymer component.

In yet another embodiment, the cis-to-trans catalyst is selected to further include at least one of an organosulfur compound, an aromatic organometallic compound, a metal-organosulfur compound, elemental sulfur, a polymeric sulfur, or an aromatic organic compound.

In another embodiment, the method further includes providing an accelerator in an amount sufficient to facilitate cis-to-trans conversion. In a preferred embodiment, the accelerator is selected to include at least one of sulfenamide, thiazole, dithiocarbamate, thiuram, xanthate, thiadiazine, thiourea, guanadine, or aldehyde-amine. The accelerator is typically provided in an amount from about 0.05 to 2 phr of the total resilient polymer component. In a preferred embodiment, the accelerator is provided in an amount from about 0.1 to 1 phr of the total resilient polymer component.

In one embodiment, a portion of the sphere comprises a fluid. In another embodiment, a tensioned elastomeric material is wound about the sphere. In a preferred embodiment, the tensioned elastomeric material includes a reaction product including polybutadiene or polyisoprene and a cis-to-trans catalyst that includes at least one inorganic sulfide.

In yet another embodiment, the forming includes single- or multi-step compression molding of the first resilient polymer component to convert the first resilient polymer component to the second resilient polymer, and forming the second resilient polymer component into a solid sphere. In a preferred embodiment, the converting and forming are substantially simultaneous.

The invention also relates to a golf ball prepared by a process that includes combining (a) at least one of a cis-to-trans catalyst including at least one inorganic sulfide; (b) a free radical source; and (c) a first resilient polymer component including a cis-polybutadiene component present in an amount greater than about 70 percent of the resilient polymer component, converting a portion of the first resilient polymer component to a second resilient polymer component, wherein at least a portion of the cis-isomer content is converted to a trans-isomer content and wherein the polybutadiene in the second resilient polymer component is at least about 10 percent trans-polybutadiene and less than about 7 percent vinyl-polybutadiene, and forming the second resilient polymer component into at least a portion of the golf ball.

Further features and advantages of the invention can be ascertained from the following detailed description that is provided in connection with the drawing(s) described below:

FIG. 1 is a cross-sectional view of a two-piece golf ball having a cover and a core according to the invention.

FIG. 2 is a cross-section of a golf ball having an intermediate layer between a cover and a core according to the invention.

FIG. 3 is a cross-section of a golf ball having more than one intermediate layer between a cover and a core according to the invention.

The term "about," as used herein in connection with one or more numbers or numerical ranges, should be understood to refer to all such numbers, including all numbers in a range.

As used herein, the term "active ingredients" is defined as the specific components of a mixture or blend that are essential to the chemical reaction.

As used herein, the term "Atti compression" is defined as the deflection of an object or material relative to the deflection of a calibrated spring, as measured with an Atti Compression Gauge, that is commercially available from Atti Engineering Corp. of Union City, N.J. Atti compression is typically used to measure the compression of a golf ball. However, when referring to the compression of a core, it is preferred to use a compressive load measurement.

As used herein, the term "coefficient of restitution", for one body impacting another, is defined as the ratio of the difference in velocity after impact to the difference before impact. The initial difference in velocity is understood to be 125 ft/s.

As used herein, the term "compressive load" is defined as the normalized load in pounds for a 10.8-percent diametrical deflection for a spherical object having a diameter of 1.58 inches.

As used herein, the term "dynamic stiffness" is defined as load divided by the deflection for a 1.4-mm spherical radius penetration probe oscillating at 1 Hz with an amplitude of 100 .mu.m. The probe dynamically penetrates the surface of a sample material. Material samples of spherical cores were prepared by sectioning out a 6-mm-thick layer along the equator of core to produce a disk 6 mm thick with one surface containing the center of the core. By positioning the probe at any selected radial position on the disk, a dynamic stiffness measurement may be obtained. Accurate dynamic measurements may be made by keeping the material sample at a substantially uniform temperature. The dynamic stiffness was acquired using a Dynamic Mechanical Analyzer, Model DMA 2980 available from TA Instruments Corporation of New Castle, Del. The instrument setting for the DMA 2980 were 1-Hz frequency, 100-.mu.m amplitude, 0.3-N static load, and auto strain of 105 percent. The 1.4-mm spherical radius probe is available from TA Instruments as a penetration kit accessory to the DMA 2980. The DMA 2980 is equipped with a temperature-controlled chamber that enables testing at a wide variety of ambient temperatures.

As used herein, the term "fluid" includes a liquid, a paste, a gel, a gas, or any combination thereof.

As used herein, the term "loss tangent," or tan .delta., is defined as unrecoverable energy divided by recoverable energy, where the energy of deflection is measured at the operating criteria specified herein for dynamic stiffness. The loss tangent was acquired using the same Dynamic Mechanical Analyzer and setting as above.

As used herein, the term "molecular weight" is defined as the absolute weight average molecular weight.

As used herein, the term "multilayer" means at least two layers and includes liquid center balls, wound balls, hollow-center balls, and balls with at least two intermediate layers and/or an inner or outer cover.

As used herein, the term "midpoint," when referring to a center or core, means a point equidistant from every point on the surface of a sphere.

As used herein, the term "parts per hundred", also known as "phr", is defined as the number of parts by weight of a particular component present in a mixture, relative to 100 parts by weight of the total polymer component. Mathematically, this can be expressed as the weight of an ingredient divided by the total weight of the polymer, multiplied by a factor of 100.

The present invention relates to one-piece golf balls and two piece golf balls having a core and a cover, or multilayer golf balls having a solid, hollow, or fluid-filled center, at least one intermediate layer disposed concentrically adjacent to the center, and a cover. At least one of the center, cover, or intermediate layer is formed from the conversion reaction of an amount of polybutadiene, a free radical source, and a cis-to-trans catalyst including at least one inorganic sulfide at a sufficient temperature to form a polybutadiene reaction product that includes an amount of trans-polybutadiene greater than the amount of trans-polybutadiene present before the conversion reaction, and a cis-to-trans catalyst including at least one inorganic sulfide. The reactants, reaction product, or both, may optionally include other components, such as a free radical source, a crosslinking agent, a filler, or any combination thereof. Preferably, the reaction product has a first dynamic stiffness measured at -50.degree. C. that is less than about 130 percent of a second dynamic stiffness measured at 0.degree. C. More preferably, the first dynamic stiffnesses is less than about 125 percent of the second dynamic stiffness.

The invention also includes a method to convert the cis- isomer of polybutadiene to the trans- isomer during a molding cycle and to form a golf ball. Various combinations of polymers, cis-to-trans catalysts, fillers, crosslinkers, and a source of free radicals, may be used. To obtain a higher resilience and lower modulus (compression), a high-molecular weight polybutadiene with a cis- isomer content preferably greater than about 70 percent is converted to increase the percentage of trans- isomer content during the molding cycle. More preferably, the cis-polybutadiene isomer is present in an amount of greater than about 80 percent of the total polybutadiene content. Most preferably, the cis-polybutadiene isomer is initially present in an amount of greater than about 90 percent of the total polybutadiene content. Without wishing to be bound by any particular theory, it is believed that a low amount of 1,2-polybutadiene isomer ("vinyl-polybutadiene") is desired in the initial polybutadiene, and the reaction product. Typically, the vinyl polybutadiene isomer content is less than about 7 percent. Preferably, the vinyl polybutadiene isomer content is less than about 4 percent. More preferably, the vinyl polybutadiene isomer content is less than about 2 percent. Without wishing to be bound by any particular theory, it is also believed that the resulting mobility of the combined cis- and trans-polybutadiene backbone is responsible for the lower modulus and higher resilience of the reaction product and golf balls including the same.

To produce a polymer reaction product that exhibits the higher resilience and lower modulus (low compression) properties that are desirable and beneficial to golf ball playing characteristics, high-molecular-weight cis-1,4-polybutadiene, preferably may be converted to the trans- isomer during the molding cycle. The polybutadiene material typically has a molecular weight of greater than about 200,000. Preferably, the polybutadiene molecular weight is greater than about 250,000, more preferably between about 300,000 and 500,000. Without wishing to be bound by any particular theory, it is believed that the cis-to-trans catalyst compound(s), in conjunction with the free radical source, acts to convert a percentage of the polybutadiene polymer component from the cis-to the trans- conformation. The cis-to-trans conversion requires the presence of a cis-to-trans catalyst, such as an organosulfur or metal-containing organosulfur compound, a substituted or unsubstituted aromatic organic compound that does not contain sulfur or metal, an inorganic sulfide compound, an aromatic organometallic compound, or mixtures thereof. As used herein, "cis-to-trans catalyst" means any compound or a combination thereof, that will convert at least a portion of cis-polybutadiene isomer to trans-polybutadiene isomer at a given temperature. The cis-to-trans catalyst component may include one or more of the other cis-to-trans catalysts described above, but must include at least one inorganic sulfide compound.

Suitable organosulfur compounds include, but are not limited to, 4,4'-diphenyl disulfide, 4,4'-ditolyl disulfide, or 2,2'-benzamido diphenyl disulfide, or a mixture thereof. When used, the organosulfur cis-to-trans catalyst is present in an amount sufficient to produce the reaction product so as to contain at least about 12 percent trans-polybutadiene isomer, but preferably is present in an amount of greater than about 32 percent trans-polybutadiene isomer based on the total resilient polymer component. Suitable metal-containing organosulfur compounds include, but are not limited to, cadmium, copper, lead, and tellurium analogs of diethyldithiocarbamate, diamyldithiocarbamate, and dimethyldithiocarbamate, or mixtures thereof. Suitable substituted or unsubstituted aromatic organic compounds that do not include sulfur or a metal include, but are not limited to, 4,4'-diphenyl acetylene, azobenzene, or a mixture thereof. The aromatic organic group preferably ranges in size from C.sub.6 to C.sub.20, and more preferably from C.sub.6 to C.sub.10.

Suitable inorganic sulfide compounds include, but are not limited to a titanium sulfide, manganese sulfide, and sulfide analogs of iron, calcium, cobalt, molybdenum, tungsten, copper, selenium, yttrium, zinc, tin, potassium, and bismuth. For example, a suitable molybdenum sulfide is molybdenum disulfide. The cis-to-trans catalyst may also be a blend of the at least one inorganic sulfide compound and at least one of (a) an organosulfur compound substituted or unsubstituted aromatic organic compound that does not include a metal or sulfur; (b) a metal-containing organosulfur compound; (e) elemental sulfur; (f) polymeric sulfur; or (g) an aromatic organometallic compound.

When elemental sulfur is included in the cis-to-trans catalyst, an accelerator may be used to improve the performance of the cis-to-trans catalyst and increase the trans-conversion. Suitable accelerators include, but are not limited to, sulfenamide, such as N-oxydiethylene 2-benzothiazole-sulfenamide, thiazole, such as benzothiazyl disulfide, dithiocarbamate, such as bismuth dimethyldithiocarbamate, thiuram, such as tetrabenzyl thiuram disulfide, xanthate, such as zinc isopropyl xanthate, thiadiazine, thiourea, such as trimethylthiourea, guanadine, such as N,N'-di-ortho-tolylguanadine, or aldehyde-amine, such as a butyraldehyde-aniline condensation product, or mixtures thereof.

The cis-to-trans catalyst is preferably present in an amount from about 0.1 to 25 parts per hundred of the total resilient polymer component. More preferably, the cis-to-trans catalyst is present in an amount from about 0.1 to 12 parts per hundred of the total resilient polymer component. Most preferably, the cis-to-trans catalyst is present in an amount from about 0.1 to 8 parts per hundred of the total resilient polymer component. The cis-to-trans catalyst is typically present in an amount sufficient to produce the reaction product so as to increase the trans- polybutadiene isomer content to contain from about 5 percent to 70 percent trans-polybutadiene based on the total resilient polymer component.

A free-radical initiator is required in the reactants to form the reaction product of the invention. The free-radical source is typically a peroxide, and preferably an organic peroxide. Suitable free-radical sources include di-t-amyl peroxide, di(2-t-butyl-peroxyisopropyl)benzene peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide, di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, n-butyl-4,4-bis(t-butylperoxy)valerate, lauryl peroxide, benzoyl peroxide, t-butyl hydroperoxide, and the like, and any mixture thereof. The peroxide is typically present in an amount greater than about 0.1 parts per hundred of the total resilient polymer component, preferably about 0.1 to 15 parts per hundred of the resilient polymer component, and more preferably about 0.2 to 5 parts per hundred of the total resilient polymer component. The free radical initiator may also be one or more sources such as an electron beam, UV or gamma radiation, x-rays, or any other high energy radiation source capable of generating free radicals.

Crosslinkers are typically included to increase the hardness of the reaction product. Suitable crosslinking agents include one or more metallic salts of unsaturated fatty acids or monocarboxylic acids, such as zinc, calcium, or magnesium acrylate salts, and the like, and mixtures thereof. Preferred acrylates include zinc acrylate, zinc diacrylate, zinc methacrylate, and zinc dimethacrylate, and mixtures thereof. The crosslinking agent must be present in an amount sufficient to crosslink a portion of the chains of polymers in the resilient polymer component. For example, the desired compression may be obtained by adjusting the amount of crosslinking. This may be achieved, for example, by altering the type and amount of crosslinking agent, a method well-known to those of ordinary skill in the art. The crosslinking agent is typically present in an amount greater than about 0.1 percent of the resilient polymer component, preferably from about 10 to 40 percent of the resilient polymer component, more preferably from about 10 to 30 percent of the resilient polymer component. When an organosulfur is included in the cis-to-trans catalyst, zinc diacrylate may be selected as the crosslinking agent and is typically present in an amount of less than about 20 phr.

Fillers are typically added to one or more portions of the golf ball typically include processing aids or compounds to affect rheological and mixing properties, the specific gravity (i.e., density-modifying fillers), the modulus, the tear strength, reinforcement, and the like. The fillers are generally inorganic, and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Foamed polymer blends may be formed by blending ceramic or glass microspheres with polymer material. Polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers are typically also added to one or more portions of the golf ball to modify the density thereof to conform to uniform golf ball standards. Fillers may also be used to modify the weight of the center or at least one additional layer for specialty balls, e.g. a lower weight ball is preferred for a player having a low swing speed.

The resilient polymer component may also include one or more additional polymers, such as a thermoplastic copolyesterester block copolymer, dynamically vulcanized thermoplastic elastomer, hydrogenated or non-hydrogenated styrene-butadiene elastomer with functional groups such as maleic anhydride or sulfonic acid attached, thermoplastic polyurethane or polymers made using a metallocene catalyst, or blends thereof. Suitable thermoplastic copolyetheresters include HYTREL.RTM. 3078 and HYTREL.RTM. 4069, which are commercially available from E.I. DuPont de Nemours & Co. of Wilmington, Del. Suitable dynamically vulcanized thermoplastic elastomers include SANTOPRENE.RTM., commercially available from Advanced Elastomer Systems of Akron, Ohio. Examples of suitable functionalized styrene-butadiene elastomers, include KRATON FG-1901x and FG-1921x, which are available from the Shell Corporation of Houston, Tex. Examples of suitable thermoplastic polyurethanes include ESTANE.RTM. 58133 and ESTANE.RTM. 58144, which are commercially available from the B.F. Goodrich Company of Cleveland, Ohio. Further, the materials for the mantle layer described above may be in the form of a foamed polymeric material. For example, suitable metallocene polymers include foams of thermoplastic elastomers based on metallocene single-site catalyst-based foams. Suitable thermoplastic polyetheramides include PEBAX.RTM. 2533, PEBAX.RTM. 1205 and PEBAX.RTM. 4033 which are available from Elf-Atochem of Philadelphia, Pa. Suitable thermoplastic ionomer resins include any number of olefinic based ionomers including SURLYN.RTM. and IOTEK.RTM., which are commercially available from E.I. DuPont de Nemours & Co. of Wilmington, Del., and Exxon Corporation of Irving, Tex., respectively. When the resilient polymer component includes any additional polymers in addition to polybutadiene, polybutadiene will be present in at least 50 phr of the resilient polymer component, preferably in an amount greater than about 90 phr.

The resilient polymer component, additional polymers, free-radical initiator, filler(s), and any other materials used in forming either the golf ball center or any portion of the core, in accordance with invention, may be combined to form a mixture by any type of mixing known to one of ordinary skill in the art. Suitable types of mixing include single pass and multi-pass mixing, and the like. The crosslinking agent, and any other optional additives used to modify the characteristics of the golf ball center or additional layer(s), may similarly be combined by any type of mixing. A single-pass mixing process where ingredients are added sequentially is preferred, as this type of mixing tends to increase efficiency and reduce costs for the process. The preferred mixing cycle is single step wherein the polymer, cis-trans catalyst, filler, zinc diacrylate, and peroxide are added sequentially. Suitable mixing equipment is well known to those of ordinary skill in the art, and such equipment may include a Banbury mixer, a two-roll mill, or a twin screw extruder. Conventional mixing speeds for combining polymers are typically used, although the speed must be high enough to impart substantially uniform dispersion of the constituents. On the other hand, the speed should not be too high, as high mixing speeds tend to break down the polymers being mixed and particularly may undesirably decrease the molecular weight of the resilient polymer component. The speed should thus be low enough to avoid high shear, which may result in loss of desirably high molecular weight portions of the polymer component. Also, too high a mixing speed may undesirably result in creation of enough heat to initiate the crosslinking before the preforms are shaped and assembled around a core. The mixing temperature depends upon the type of polymer components, and more importantly, on the type of free-radical initiator. For example, when using di(2-t-butyl-peroxyisopropyl)benzene as the free-radical initiator, a mixing temperature of about 80.degree. C. to 125.degree. C., preferably about 88.degree. C. to 110.degree. C., and more preferably about 90.degree. C. to 100.degree. C., is suitable to safely mix the ingredients. Additionally, it is important to maintain a mixing temperature below the peroxide decomposition temperature. For example, if dicumyl peroxide is selected as the peroxide, the temperature should not exceed 200.degree. F. Suitable mixing speeds and temperatures are well-known to those of ordinary skill in the art, or may be readily determined without undue experimentation.

The mixture is typically subjected to a compression or injection molding process to obtain solid spheres for the center or hemispherical shells for forming an intermediate layer. The polymer mixture is subjected to a molding cycle in which heat and pressure are applied while the mixture is confined within a mold. The cavity shape depends on the portion of the golf ball being formed. The compression and heat liberates free radicals by decomposing one or more peroxides, which may initiate the cis-to-trans conversion and crosslinking simultaneously. The temperature and duration of the molding cycle are selected based upon the type of peroxide and cis-trans catalyst selected. The molding cycle may have a single step of molding the mixture at a single temperature for a fixed time duration. An example of a single step molding cycle, for a mixture that contains dicumyl peroxide, would hold the polymer mixture at 340.degree. F. for a duration of 15 minutes. The molding cycle may also include a two-step process, in which the polymer mixture is held in the mold at an initial temperature for an initial duration of time, followed by holding at a second, typically higher temperature for a second duration of time. An example of a two-step molding cycle would be holding the mold at 290.degree. F. for 40 minutes, then ramping the mold to 340.degree. F. where it is held for a duration of 20 minutes. In a preferred embodiment of the current invention, a single-step cure cycle is employed. Single-step processes are effective and efficient, reducing the time and cost of a two-step process. The resilient polymer component, polybutadiene, cis-to-trans conversion catalyst, additional polymers, free-radical initiator, filler, and any other materials used in forming either the golf ball center or any portion of the core, in accordance with the invention, may be combined to form a golf ball by an injection molding process, which is also well-known to one of ordinary skill in the art.

The cover provides the interface between the ball and a club. Properties that are desirable for the cover are good moldability, high abrasion resistance, high tear strength, high resilience, and good mold release, among others. The cover typically has a thickness to provide sufficient strength, good performance characteristics and durability. The cover of the golf balls typically has a thickness of at least about 0.03 inches, preferably 0.03 to 0.125 inches, and more preferably from about 0.05 to 0.1 inches. The golf balls also typically have at least about 60 percent dimple coverage, preferably at least about 70 percent dimple coverage, of the surface area of the cover.

The cover can include any suitable cover or intermediate layer materials, known to those of ordinary skill in the art, including thermoplastic and thermosetting materials, but preferably the cover or intermediate layer can include any suitable materials, such as ionic copolymers of ethylene and an unsaturated monocarboxylic acid which are available under the trademark SURLYN of E.I. DuPont de Nemours & Co., of Wilmington, Del., or IOTEK or ESCOR of Exxon. These are copolymers or terpolymers of ethylene and methacrylic acid or acrylic acid partially neutralized with salts of zinc, sodium, lithium, magnesium, potassium, calcium, manganese, nickel or the like, in which the salts are the reaction product of an olefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having 3 to 8 carbon atoms. The carboxylic acid groups of the copolymer may be totally or partially neutralized and might include methacrylic, crotonic, maleic, fumaric or itaconic acid.

This golf ball can likewise include one or more homopolymeric or copolymeric cover materials, such as:

(1) Vinyl resins, such as those formed by the polymerization of vinyl chloride, or by the copolymerization of vinyl chloride with vinyl acetate, acrylic esters or vinylidene chloride;

(2) Polyolefins, such as polyethylene, polypropylene, polybutylene and copolymers such as ethylene methylacrylate, ethylene ethylacrylate, ethylene vinyl acetate, ethylene methacrylic or ethylene acrylic acid or propylene acrylic acid and copolymers and homopolymers produced using a single-site catalyst;

(3) Polyurethanes, such as those prepared from polyols and diisocyanates or polyisocyanates and those disclosed in U.S. Pat. No. 5,334,673;

(4) Polyureas, such as those disclosed in U.S. Pat. No. 5,484,870;

(5) Polyamides, such as poly(hexamethylene adipamide) and others prepared from diamines and dibasic acids, as well as those from amino acids such as poly(caprolactam), and blends of polyamides with SURLYN, polyethylene, ethylene copolymers, ethyl-propylene-non-conjugated diene terpolymer, and the like;

(6) Acrylic resins and blends of these resins with poly vinyl chloride, elastomers, and the like;

(7) Thermoplastics, such as urethanes; olefinic thermoplastic rubbers, such as blends of polyolefins with ethylene-propylene-non-conjugated diene terpolymer; block copolymers of styrene and butadiene, isoprene or ethylene-butylene rubber; or copoly(ether-amide), such as PEBAX, sold by ELF Atochem of Philadelphia, Pa.;

(8) Polyphenylene oxide resins or blends of polyphenylene oxide with high impact polystyrene as sold under the trademark NORYL by General Electric Company of Pittsfield, Mass.;

(9) Thermoplastic polyesters, such as polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate/glycol modified and elastomers sold under the trademarks HYTREL by E.I. DuPont de Nemours & Co. of Wilmington, Del., and LOMOD by General Electric Company of Pittsfield, Mass.;

(10) Blends and alloys, including polycarbonate with acrylonitrile butadiene styrene, polybutylene terephthalate, polyethylene terephthalate, styrene maleic anhydride, polyethylene, elastomers, and the like, and polyvinyl chloride with acrylonitrile butadiene styrene or ethylene vinyl acetate or other elastomers; and

(11) Blends of thermoplastic rubbers with polyethylene, propylene, polyacetal, nylon, polyesters, cellulose esters, and the like.

Preferably, the cover includes polymers, such as ethylene, propylene, butene-1 or hexane-1 based homopolymers or copolymers including functional monomers, such as acrylic and methacrylic acid and fully or partially neutralized ionomer resins and their blends, methyl acrylate, methyl methacrylate homopolymers and copolymers, imidized, amino group containing polymers, polycarbonate, reinforced polyamides, polyphenylene oxide, high impact polystyrene, polyether ketone, polysulfone, poly(phenylene sulfide), acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethelyne vinyl alcohol), poly(tetrafluoroethylene) and their copolymers including functional comonomers, and blends thereof. Suitable cover compositions also include a polyether or polyester thermoplastic urethane, a thermoset polyurethane, a low modulus ionomer, such as acid-containing ethylene copolymer ionomers, including E/X/Y terpolymers where E is ethylene, X is an acrylate or methacrylate-based softening comonomer present in about 0 to 50 weight percent and Y is acrylic or methacrylic acid present in about 5 to 35 weight percent. More preferably, in a low spin rate embodiment designed for maximum distance, the acrylic or methacrylic acid is present in about 15 to 35 weight percent, making the ionomer a high modulus ionomer. In a high spin embodiment, the cover includes an ionomer where an acid is present in about 10 to 15 weight percent and includes a softening comonomer.

The cover may also be formed from the present invention, as discussed herein.

Depending on the desired properties, balls prepared according to the invention can exhibit substantially the same or higher resilience, or coefficient of restitution (CoR), with a decrease in compression or modulus, compared to balls of conventional construction. Additionally, balls prepared according to the invention can also exhibit substantially higher resilience, or coefficient of restitution (CoR), without an increase in compression, compared to balls of conventional construction. Another measure of this resilience is the "loss tangent," or tan .delta., which is obtained when measuring the dynamic stiffness of an object. Loss tangent and terminology relating to such dynamic properties is typically described according to ASTM D4092-90. Thus, a lower loss tangent indicates a higher resiliency, thereby indicating a higher rebound capacity. Low loss tangent indicates that most of the energy imparted to a golf ball from the club is converted to dynamic energy, i.e., launch velocity and resulting longer distance. The rigidity or compressive stiffness of a golf ball may be measured, for example, by the dynamic stiffness. A higher dynamic stiffness indicates a higher compressive stiffness. To produce golf balls having a desirable compressive stiffness, the dynamic stiffness of the crosslinked reaction product material should be less than about 50,000 N/m at -50.degree. C. Preferably, the dynamic stiffness should be between about 10,000 and 40,000 N/m at -50.degree. C., more preferably, the dynamic stiffness should be between about 20,000 and 30,000 N/m at -50.degree. C.

The dynamic stiffness is similar in some ways to dynamic modulus. Dynamic stiffness is dependent on probe geometry as described herein, whereas dynamic modulus is a unique material property, independent of geometry. The dynamic stiffness measurement has the unique attribute of enabling quantitative measurement of dynamic modulus and exact measurement of loss tangent at discrete points within a sample article. In the case of this invention, the article is a golf ball core. The polybutadiene reaction product preferably has a loss tangent below about 0.1 at -50.degree. C., and more preferably below about 0.07 at -50.degree. C.

The resultant golf balls typically have a coefficient of restitution of greater than about 0.7, preferably greater than about 0.75, and more preferably greater than about 0.78. The golf balls also typically have an Atti compression (which has been referred to as PGA compression in the past) of at least about 40, preferably from about 50 to 120, and more preferably from about 60 to 100. Compression values are dependent on the diameter of the article being measured. Typically, the Atti compression of cores is measured on a core having a diameter of 1.58 inches. If the compression were to be measured for centers, cores, or golf balls having a diameter other than 1.58 inches, one of ordinary skill in the art would readily be able to determine the Atti compression value at 10.8 percent deflection by normalization to 1.58 inches. The golf ball polybutadiene material of the present invention typically have a flexural modulus of from about 500 psi to 300,000 psi, preferably from about 2000 to 200,000 psi. The golf ball polybutadiene material typically has a hardness of at least about 15 Shore A, preferably between about 30 Shore A and 80 Shore D, more preferably between about 50 Shore A and 60 Shore D. The specific gravity is typically greater than about 0.7, preferably greater than about 1, for the golf ball polybutadiene material. The dynamic shear storage modulus, or storage modulus, of the golf ball polybutadiene material at about 23.degree. C. is typically at least about 10,000 dyn/cm.sup.2, preferably from about 10.sup.4 -10.sup.10 dyn/cm.sup.2, more preferably from about 10.sup.6 to 10.sup.10 dyn/cm.sup.2.

The molding process and composition of golf ball portions typically results in a gradient of material properties. Methods employed in the prior art generally exploit hardness to quantify these gradients. Hardness is a qualitative measure of static modulus and does not represent the modulus of the material at the deformation rates associated with golf ball use, i.e., impact by a club. As is well known to one skilled in the art of polymer science, the time-temperature superposition principle may be used to emulate alternative deformation rates. For golf ball portions including polybutadiene, a 1-Hz oscillation at temperatures between 0.degree. C. and -50.degree. C. are believed to be qualitatively equivalent to golf ball impact rates. Therefore, measurement of loss tangent and dynamic stiffness at 0.degree. C. to -50.degree. C. may be used to accurately anticipate golf ball performance, preferably at temperatures between about -20.degree. C. and -50.degree. C.

Additionally, the golf balls prepared according to the present invention typically have a Mooney viscosity greater than about 20, preferably greater than about 30, and more preferably greater than about 40. Mooney viscosity is typically measured according to ASTM D-1646.

Referring to FIG. 1, a golf ball 10 of the present invention can include a core 12 and a cover 16 surrounding the core 12. Referring to FIG. 2, a golf ball 20 of the present invention can include a core 22, a cover 26, and at least one intermediate layer 24 disposed between the cover and the core. Each of the cover and core may include more than one layer; i.e., the golf ball can be a conventional three-piece wound ball, a two-piece ball, a ball having a multi-layer core and an intermediate layer or layers, etc. Thus, referring to FIG. 3, a golf ball 30 of the present invention can include a core 32, a cover 38, and intermediate layers 34 and 36 disposed between the cover and the core. Although FIG. 3 shows only two intermediate layers, it will be appreciated that any number or type of intermediate layers may be used, as desired.

A variety of metal sulfide cis-to-trans catalysts that successfully converted a portion of the cis-polybutadiene isomer to the trans- isomer are presented in Table 1. CARIFLEX BR-1220 polybutadiene (100 phr) was reacted with zinc oxide (5 phr), dicumyl peroxide (3 phr, the free radical initiator), and zinc diacrylate (25 phr), to form the reaction product as described in the present invention.

Trans- isomer conversion percentages range from below 6 percent to above 16 percent for the various catalysts that are present in amounts ranging from below 2 phr to above 5 phr. The table clearly demonstrates the effectiveness of numerous different cis-to-trans catalysts, at varying concentrations, for generating soft, resilient golf balls or components thereof, according to the invention.

A Core Prepared From According to the Invention Employing an Organosulfur Cis-to-trans Catalyst

A core according to the present invention was created employing an organosulfur compound as the cis-to-trans conversion catalyst. The resultant core properties clearly demonstrate the advantages of a golf ball core made according to the current invention as compared to example cores constructed with conventional technology. The components and physical characteristics are presented in Table 2.

The compressive load of a core prepared according to the invention is approximately half of the compressive load of cores constructed in accordance with U.S. Pat. Nos. 5,697,856, 5,252,652, and 4,692,497, while at the same time retaining roughly the same, and in some cases higher, CoR (resilience). The core made according to the current invention has a lower compressive load (soft), yet resilient (fast). The compressive load is greater than that of a core constructed in accordance with U.S. Pat. No. 3,239,228, but has a significantly higher CoR. The core of U.S. Pat. No. 3,239,228 is very soft and very slow (very low CoR).

The percent change in dynamic stiffness from 0.degree. C. to -50.degree. C. was also measured at both the edge and center of the cores. The dynamic stiffness at both the edge and the center of the core of the current invention varied only slightly, less than 20 percent, over the temperature range investigated. The core made according to U.S. Pat. No. 3,239,228 varied over 230 percent, whereas the cores made according to other conventional technology, had a dynamic stiffness that varied by greater than 130 percent, and typically by as much as 150 percent, over the same temperature range.

The percent of trans- conversion was also measured at both the center and edge of the core prepared according to the current invention, and for cores prepared as disclosed in the same four patents mentioned above, allowing a trans- gradient to be calculated. The core according to the current invention had a trans- gradient of about 32 percent from edge to center. For the core prepared according to the current invention, the pre- and post-cure trans- percentages was also measured to determine the effectiveness of that process. The percentage of polybutadiene converted to the trans- isomer ranged from almost 40 percent at the center to greater than 55 percent at the edge. Two of the cores prepared according to conventional technology, U.S. Pat. Nos. 3,239,228 and 4,692,497, had a zero trans- gradient. A third core, prepared according to U.S. Pat. No. 5,697,856, had only a slight trans- gradient, less than 18 percent from edge to center. A fourth core, prepared according to U.S. Pat. No. 5,252,652, had a very large gradient, almost 65 percent from edge to center.

A Core Prepared From According to the Invention Employing an Inorganic Sulfide Cis-to-trans Catalyst

A core according to the present invention was created employing an inorganic sulfide compound as the cis-to-trans conversion catalyst. The resultant core properties clearly demonstrate the advantages of a golf ball core made according to the current invention as compared to example cores constructed with conventional technology. The components and physical characteristics are presented in Table 2.

The compressive load is approximately half of the compressive load of three cores constructed in accordance with U.S. Pat. Nos. 5,697,856, 5,252,652, and 4,692,497, while at the same time retaining roughly the same, and in some cases, a higher CoR (resilience). The core made according to the current invention is soft, yet resilient (fast). The compressive load is greater than a core constructed in accordance with U.S. Pat. No. 3,239,228, but has a significantly higher CoR. The core of U.S. Pat. No. 3,239,228 is very soft and very slow (low CoR).

The percent change in dynamic stiffness from 0.degree. C. to -50.degree. C. was also measured at both the edge and center of the cores. The dynamic stiffness at both the edge and the center of the core of the current invention varied only slightly, less than 125 percent, over the temperature range investigated. The core made according to U.S. Pat. No. 3,239,228 varied over 230 percent, whereas the cores made according to other conventional technology, had a dynamic stiffness that varied by greater than 130 percent, and typically by as much as 150 percent, over the same temperature range.

The percent of trans- conversion was also measured at both the center and edge of the core prepared according to the current invention, and for cores prepared according to the same four patents mentioned above, allowing a trans- gradient to be calculated. The core according to the current invention had a trans- gradient of about 45 percent from edge to center. Two of the cores prepared in accordance with U.S. Pat. Nos. 3,239,228 and 4,692,497 had a zero trans- gradient. A third core, prepared in accordance with U.S. Pat. No. 5,697,856, had only a slight trans- gradient, less than 18 percent from edge to center. A fourth core, prepared in accordance with U.S. Pat. No. 5,252,652, had a very large gradient, almost 65 percent, from edge to center.

A Core Prepared From According to the Invention Employing a Blend of Organosulfur and Inorganic Sulfide Cis-to-trans Catalyst

A core according to the present invention was created employing a blend of organosulfur and inorganic sulfide compounds as the cis-to-trans conversion catalyst. The resultant core properties clearly demonstrate the advantages of a golf ball core made according to the current invention as compared to example cores constructed with conventional technology. The components and physical characteristics are presented in Table 2.

The compressive load is approximately half of the compressive load of three cores constructed in accordance with U.S. Pat. Nos. 5,697,856, 5,252,652, and 4,692,497, while at the same time retaining roughly the same, and in some cases a higher CoR (resilience). The core made according to the current invention is soft, yet resilient (fast). The compressive load of the invention is greater than a fourth core constructed in accordance with U.S. Pat. No. 3,239,228, but has a significantly higher CoR. The core constructed in accordance with U.S. Pat. No. 3,239,228 is very soft and very slow (low CoR).

The percent change in dynamic stiffness from 0.degree. C. to -50.degree. C. was also measured at both the edge and center of the cores. The dynamic stiffness at both the edge and the center of the core of the current invention varied only slightly, less than 121 percent, over the temperature range investigated. The core made in accordance with U.S. Pat. No. 3,239,228 varied over 230 percent, whereas the cores made according to other conventional technology had a dynamic stiffness that varied by greater than 130 percent, and typically by as much as 150 percent, over the same temperature range.

The percent of trans- conversion was also measured at both the center and edge of the core prepared according to the current invention, and for cores prepared to the same four patents mentioned above, allowing a trans- gradient to be calculated. The core according to the current invention had a trans- gradient that about 44 percent from edge to center. For the core prepared according to the current invention, the pre- and post-cure trans- percentages was also measured to determine the effectiveness of that process. The percentage of polybutadiene converted to the trans- isomer ranged from almost 26 percent at the center to greater than 45 percent at the edge. Two of the cores prepared in accordance with U.S. Pat. Nos. 3,239,228 and 4,692,497 had a zero trans- gradient. A third core prepared in accordance with U.S. Pat. No. 5,697,856 had only a slight trans-gradient, less than 18 percent from edge to center. A fourth core, prepared in accordance with U.S. Pat. No. 5,252,652 had a very large gradient, almost 65 percent from edge to center.

Comparison of a Conventional Dual Core Ball to Dual Core Ball Prepared According to the Invention

A dual core golf ball according to the present invention was created having a solid center, an intermediate layer surrounding the solid center, and a cover disposed concentrically around the intermediate layer. The components and physical characteristics are presented in Table 3.

A solid center was constructed for the ball of the present invention and for a ball of conventional technology. The centers were both created from CARIFLEX BR1220 polybutadiene as the starting material, the only difference being replacing the VAROX 802-40KE-HP peroxide (conventional technology) with a DTDS cis-to-trans catalyst of the current invention and dicumyl peroxide. This substitution allows a portion of the polybutadiene material to be converted to the trans- configuration during the molding process. The resulting solid centers had outside diameters of approximately 1.15 inches. The polybutadiene reaction product prepared thereby had a trans- isomer content of 40 percent compared to the 1.5 percent trans- isomer of the conventional ball. Identical intermediate layers, having outside diameters of approximately 1.58 inches, were constructed around each solid center to form a core.

The compression and CoR values were measured for the two cores. The compression of the core prepared according to the current invention was measured to be 77 and the compression of the core of the conventional ball was measured to be 78. The CoR value of the conventional center was measured to be 0.774, whereas the CoR value of the core of the present invention was measured to be 0.789. Therefore, the present invention resulted in a center and a core having a higher resilience at similar compression compared to a center constructed with conventional technology.

An identical cover was added to both centers and the compression and CoR were measured again. The compression for both balls was measured to be 89, yet the CoR values were 0.791 and 0.802 for the conventional ball and the ball of the present invention, respectively. The present invention resulted in a ball having the same compression with a higher resilience (CoR) compared to a ball constructed with conventional technology.

Comparison of a Conventional Double Cover Ball to Double Cover Ball Prepared According to the Invention

A double cover golf ball according to the present invention was created having a solid center, an inner cover surrounding the solid center, and a cover disposed concentrically around the inner cover. The components and physical characteristics are presented in Table 3.

A solid center was constructed for the ball of the present invention and for a ball of conventional technology. The centers were both created from a CARIFLEX BR 220 polybutadiene starting material, the only difference being the replacing of a pair of peroxides, VAROX 231 XL and DBDB-60 (conventional technology), with a DTDS cis-to-trans catalyst of the current invention and dicumyl peroxide to facilitate cis-to-trans conversion. The resulting solid centers had outside diameters of approximately 1.39 inches. The polybutadiene reaction product of the current invention had a trans- isomer content of 55 percent compared to the 1.5 percent trans- isomer of the conventional center. Identical inner covers, having outside diameters of approximately 1.51 inches, were constructed around the solid center.

An identical cover was added to both centers and the compression and CoR values were measured. The compression for the conventional ball was measured to be 89 compared to the measured value of 70 for the ball of the current invention. The CoR values were 0.793 for both balls. The present invention resulted in a ball having the same resilience (CoR) and a significantly lower compression compared to a ball constructed with conventional technology.

Comparison of a Conventional Solid Core Ball to Solid Core Ball Prepared According to the Invention

A solid core was constructed for the ball of the present invention and for a ball of conventional technology. The components and physical characteristics are presented in Table 3.

The cores were both created from CARIFLEX BR1220 polybutadiene starting material. One core included VAROX 231 XL and DBDB-60 (conventional technology) and the other core included a DTDS cis-to-trans catalyst of the current invention and dicumyl peroxide. The resulting solid cores had outside diameters of approximately 1.58 inches. The polybutadiene reaction product of the current invention had a trans- isomer content of 45 percent compared to the 1.5 percent trans- isomer of the conventional core.

An identical cover was added to both cores compress and the compression and CoR values were measured. The compression for the conventional ball was measured to be 91 compared to the measured value of 48 for the ball of the current invention. The CoR values were 0.791 for both balls. The present invention resulted in a ball having the same resilience (CoR) and a significantly lower compression compared to a ball constructed with conventional technology.

The invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustrations of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.