Multilayer golf ball

[0002] This application is a continuation-in-part of U.S. patent application Ser. Nos. 08/996,718, 08/706,008, 08/603,057, 08/606,373, and 08/746,362 filed Dec. 23, 1997, Aug. 30, 1996, Feb. 16, 1996, Feb. 23, 1996, and Nov. 8, 1996, now U.S. Pat. Nos. 6,124,309; 5,813,923; 5,759,676; 5,721,304; 5,810,678 respectively, which are continuation-in-part applications of patent application Ser. No. 08/482,522 filed Jun. 7, 1995, now U.S. Pat. No. 5,688,191.

[0003] This invention relates generally to golf balls, and more specifically, to a multilayer golf ball. In particular, this invention relates to a golf ball having a core, a cover and one or more mantle layers disposed between the core and cover. This invention is also directed to a composition used for the manufacture of golf ball cores, mantle layers and covers for multilayer golf balls. The multilayer golf balls of the present invention have been found to provide improved playing characteristics.

[0004] Conventional golf balls can be divided into two general types or groups: two-piece balls or wound balls (also known as three-piece balls). The difference in play characteristics resulting from these different types of constructions can be quite significant.

[0005] Balls having a two-piece construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Two-piece balls are made with a single solid core, usually made of a crosslinked rubber, which is encased by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-proof blended cover. The cover is generally a material such as SURLYN®, which is a trademark for an ionomer resin produced by DuPont. The combination of the core and cover materials provide a “hard” ball that is virtually indestructible by golfers. Further, such a combination imparts a high initial velocity to the ball which results in improved distance. Because these materials are very rigid, two-piece balls have a hard “feel” when struck with a club. Likewise, due to their hardness, these balls have a relatively low spin rate which provides greater distance.

[0006] A number of polymers, such as polybutadiene, natural rubber, styrene butadiene, and isoprene, are commonly used in fabricating golf ball cores. Today, golf ball cores are predominantly made of polybutadiene. Moreover, in order to obtain the desired physical properties for golf balls, manufacturers have added cross-linking agents, such as metallic salts of an unsaturated carboxylic acid. The amount of cross-linking agent added is typically about 20 to 50 parts per hundred parts of polybutadiene. Most commonly, zinc diacrylate or zinc dimethacrylate are used for this purpose. Of these two cross-linkers, zinc diacrylate has been found to produce golf balls with greater initial velocity than zinc dimethacrylate.

[0007] Typically, about 5 to 50 pph (parts per hundred) of zinc oxide (ZnO) is also added to the composition. This material serves as both a filler and an activation agent for the zinc diacrylate/peroxide cure system. The zinc diacrylate/peroxide cure system, which is well known to those of ordinary skill in this art, cross-links the polybutadiene during the core molding process. The high specific gravity of zinc oxide (5.57) can serve the dual purposes of adjusting the weight of the golf ball, in addition to acting as an activation agent.

[0008] At the present time, the wound ball remains the preferred ball of the more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or liquid center core around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material such as a SURLYN® or similar material or a softer cover such as Balata or polyurethane. Wound balls are generally softer and provide more spin, which enables a skilled golfer to have more control over the ball's flight and final position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.

[0009] Several patents have been issued which are directed towards modifying the properties of a conventional two-piece ball by altering the typical single layer core and single cover layer construction to provide a multi-layer core. The inventions disclosed in the prior art patents are directed towards improving a variety of golf ball characteristics.

[0010] Several patents are directed towards improving the carry distance of the ball. For example, U.S. Pat. No. 4,863,167 relates to a three-piece solid golf ball having improved rebound characteristics in order to increase its flight distance. This golf ball has a center portion and the outer layer formed from a rubber composition, preferably having a base rubber of polybutadiene, wherein the outer layer further contains a gravity filler such as tungsten or tungsten carbide so as to impart a higher specific gravity to the outer layer than that of the inner layer. The difference in specific gravity of the layers should be 0.15-0.8 for small balls and 0.15-0.45 for large balls. Preferably, the outer layer is harder than the center portion.

[0011] U.S. Pat. No. 4,431,193 relates to a solid core golf ball with a multilayer cover construction. The first layer includes a hard, high flexural modulus resinous material and the second layer includes a soft low flexural modulus resinous material. The construction and material allows the ball to obtain the maximum initial velocity permitted by the United States Golf Association Rules while having a good playing characteristics or “feel.” Preferably, the first layer is made of SURLYN® resin type 1605 and the second layer is made of SURLYN® resin type 1855.

[0012] U.S. Pat. No. 5,184,828 relates to a solid three-piece golf ball having improved rebound characteristics and carry distance while maintaining an adequate spin rate. These characteristics are obtained by controlling the size of the inner core and outer layer as well as the specific gravity and hardness. The core and mantle layers are made from a rubber compound such as polybutadiene, and have a Shore D hardness of 30-62 and 30-56 respectively. The key to obtaining the desired rebound characteristics is that the maximum hardness (42-62) must be located at the interface between the core and the mantle and the hardness must then decrease both inwardly and outwardly.

[0013] U.S. Pat. No. 4,714,253 is also directed towards a three-piece golf ball having an excellent rebound coefficient. This golf ball has a core with a Shore C hardness of 57-80 in its center, but not more than 83 at a distance between 5-10mm from its center and an outer layer with a Shore C hardness of 70-83.

[0014] Additionally, there are a number of patents also directed towards improving the spin, click and feel of solid balls while maintaining the distance provided by the solid construction. A variety of approaches to manipulating the core construction are described in the art. For example, U.S. Pat. No. 5,072,944 discloses a three-piece solid golf ball having a center and outer layer which are prepared from a rubber composition, preferably having a base rubber of polybutadiene. It is desirable that the center core is softer than the outer layer, each having a hardness (Shore C) of 25-50 and 70-90 respectively.

[0015] U.S. Pat. No. 4,625,964 relates to a solid golf ball having a polybutadiene rubber core of a diameter not more than 32mm, and a polybutadiene rubber intermediate layer having a specific gravity of higher than that of the core material, and a cover.

[0016] U.S. Pat. No. 4,650,193 is directed towards a solid golf ball having a core comprising of a central portion and an integral outer layer. Preferably the core is a curable elastomer such as polybutadiene which is treated with a cure altering agent to soften an outer layer of the core, thereby producing a central layer with a hardness (Shore C) of greater than 75 and an outer layer with a hardness (Shore A) of less than 80.

[0017] U.S. Pat. No. 4,848,770 discloses a non-wound three-piece golf ball which includes a core of a highly filled synthetic rubber or polymeric material, an intermediate mantle of an unfilled synthetic rubber and a cover. The core and intermediate mantle have a hardness of between 50-95.

[0018] U.S. Pat. No. 5,002,281 is directed towards a three-piece solid golf ball which has an inner core having a hardness of 25-70 (Shore C), an outer shell having a hardness of 80-95 (Shore C) and a cover. Further, the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.

[0019] U.S. Pat. No. 5,253,871 concerns a golf ball having a three-piece structure comprising an elastomer core, an intermediate layer of a thermoplastic material containing at least 10% of ether block copolymer, preferably blended with an ionomer and a thermoplastic cover.

[0020] Further, there are also several patents which are directed to golf balls having multiple cover layers. For example U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, high flexural modulus ionomer resin, and wherein either or both layers may comprise a foamed ionomer resin.

[0021] U.S. Pat. No. 5,314,187 also relates to golf balls having a multiple layer cover, wherein the outer layer is molded over the inner layer and comprises a blend of balata and an elastomer and the inner layer is an ionomer resin.

[0022] U.S. Pat. No. 4,919,434 is directed towards a golf ball having a cover which comprises an inner layer and an outer layer each of which comprise a thermoplastic resin, preferably the layers comprise of materials that are capable of fusion bonding with each other.

[0023] U.S. Pat. No. 5,556,098 is directed to a three-piece solid golf ball comprising a center core, an intermediate layer, and a cover. The center core is formed of a polybutadiene base rubber and a specific gravity of less than 1.4, and a hardness up to 80 on JIS C scale. The intermediate layer is formed of a thermoplastic polyester elastomer and has a specific gravity of less than 1.2, and a hardness of less than 80 on JIS C scale. The cover has a hardness of at least 85 on JIS C scale.

[0024] U.S. Pat. No. 5,439,227 is directed to a multi-piece solid golf ball having a solid core including an inner layer circumscribed by an outer layer. The core inner layer is formed from a rubber composition. The core outer layer is formed by a polyether ester type thermoplastic elastomer having a Shore D hardness of 30-50. The core is surrounded by a cover of an ethylene-(meth)acrylate copolymer ionomer having a flexural modulus of 200-450 MPa and a Shore D hardness of 55-68.

[0025] U.S. Pat. No. 5,415,937 is directed to a golf ball cover comprised on 80 to 50% by weight of a high stiffness ionomer and 20 to 50% by weight of a low stiffness ionomer.

[0026] However, none of these patents disclose a multi-layer ball having the materials and material property requirements as disclosed herein to provide the improved golf balls of the present invention.

[0027] The present invention is directed towards a multi-layer golf ball which provides improved playing characteristics by using specific core, mantle and cover formulations. More particularly, the present invention is directed to balls having good distance, spin, durability and ease of manufacturing. The present invention is directed to improved golf balls that have durability, lower driver spin rates and substantial distance more like conventional two-piece balls, but have a soft feel and higher 5 iron spin by using a thermoplastic mantle layer, a harder core and a soft cover.

[0028] The present invention is further directed towards a multi-layer golf ball which comprises a core with one or more layers; at least one cover layer; and one or more mantle layers disposed between the core and cover layer. The core is preferably comprised of a polybutadiene rubber having an activation agent of calcium oxide and/or zinc oxide. The mantle layer has a Shore D hardness greater than 60 and preferably comprises thermoplastic copolyetherester block copolymer, thermoplastic copolyesterester block copolymer, thermoplastic polyurethane, thermoset polyurethane, dynamically vulcanized thermoplastic elastomer, styrene-butadiene, styrene-isoprene and styrene-isoprene elastomers with a functional group such as maleic anhydride or sulfonic acid, polymer made using a metallocene catalyst, or blends thereof and/or thermoset materials. The cover preferably comprises a thermoplastic or thermosetting material.

[0029] The present invention is still further directed to a multi-layer golf ball which comprises a core, at least one cover layer and at least one mantle layer disposed between the core and cover layer wherein properties such as the thickness, specific gravity, hardness, flexural modulus, tensile modulus, compression or Bashore resilience of the various layers is such as to provide a ball with improved playing characteristics.

[0030] The present invention is also directed to an improved high-spin, multilayer golf ball having a harder golf ball core. The composition of the golf ball core comprises a base mixture of polybutadiene, a metal salt diacrylate or dimethacrylate, preferably, zinc diacrylate in an amount of about 20 to 50 parts per hundred parts of polybutadiene, and a free radical initiator, to which some calcium oxide (CaO) may be added instead of zinc oxide as an activation agent in an amount sufficient to produce a golf ball core with the advantageous properties discussed below.

[0031] Still further, in the preferred high spin golf ball, fillers may be added to the core to give the core a high specific gravity. By keeping weight in the core, the spin rate of the ball is increased.

[0032] The invention thus provides a novel golf ball composition that offers enhanced performance properties.

[0033] FIG. 1 is a cross-sectional view of a golf ball according to the present invention.

[0034] FIG. 2 is a perspective view of a golf ball according to the present invention.

[0035] The following terms that are used in this application are defined in terms of the enumerated ASTM tests:

[0036] 1Tests were carried out in lab conditions where temperature was controlled to 20-23° C. Humidity was not controlled.

[0037] 2Tests were carried out using a 0.2 in/min cross-head speed and a 2 inch span length in the three point bending mode. Test samples were annealed at 140° F. for 24 hours and the tests were performed no earlier than 24 hours after annealing.

[0038] 3Tests were carried out on type IV specimens using a 2 in/min cross-head speed without an extensiometer. Test samples were annealed at 140° F. for 24 hours and the tests were performed no earlier than 24 hours after annealing.

[0039] 4Four (4) ⅛ inch samples were plied together to achieve the 12 inch test thickness.

[0040] For purposes of the present invention, the term “reaction conditions” can refer to any reaction condition that can affect the ability of the inventive core compositions to form free radicals. Reaction conditions include, for example, temperature, time and pressure.

[0041] As used herein, the terms “points” or “compression points” refer to the compression scale or the compression scale based on the ATTI Engineering Compression Tester. This scale, which is well known to those working in this field, is used in determining the relative compression of a core or ball. Some artisans use the Reihle compression scale instead of the standard compression scale. Based on disclosure in U.S. Pat. No. 5,368,304, column 20, lines 55-53 it appears that Reihle compression values can be converted to compression values through the use of the following equation:

[0042] compression value=160−Reihle compression value.

[0043] Referring to FIGS. 1 and 2, this invention is particularly directed towards a multi-layer golf ball 1 which comprises a core 2, at least one cover layer 3 and at least one mantle layer 4 disposed therebetween.

[0044] A representative base composition for forming the golf ball core 2, prepared in accordance with the present invention, comprises polybutadiene and, in parts by weight based on 100 parts polybutadiene, 20-50 parts of a metal salt diacrylate, dimethacrylate, or monomethacrylate, preferably zinc diacrylate. The polybutadiene preferably has a cis 1,4 content of above about 90% and more preferably above about 96%. Commercial sources of polybutadiene include Shell 1220 manufactured by Shell Chemical, Neocis BR40 manufactured by Enichem Elastomers, and Ubepol BR150 manufactured by Ube Industries, Ltd. If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as natural rubber, styrene butadiene, and/or isoprene in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are usually based on 100 parts by weight of the total elastomer mixture.

[0045] Metal salt diacrylates, dimethacrylates, and monomethacrylates suitable for use in this invention include those wherein the metal is magnesium, calcium, zinc, aluminum, sodium, lithium or nickel. Zinc diacrylate is preferred, because it provides golf balls with a high initial velocity in the USGA test. The zinc diacrylate can be of various grades of purity. Suitable, commercially available zinc diacrylates include those from Rockland React-Rite and Sartomer. The preferred concentrations of zinc diacrylate that can be used are 20-50 pph and preferably 25-35 pph based upon 100 pph of polybutadiene or alternately, polybutadiene with a mixture of other elastomers that equal 100 pph.

[0046] Free radical initiators are used to promote cross-linking of the metal salt diacrylate, dimethacrylate, or monomethacrylate and the polybutadiene. Suitable free radical initiators for use in the invention include, but are not limited to peroxide compounds, such as dicumyl peroxide, 1,1-di (t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di (t-butylperoxy) hexane, or di-t-butyl peroxide, and mixtures thereof. Other useful initiators would be readily apparent to one of ordinary skill in the art without any need for experimentation. The initiator(s) at 100% activity are preferably added in an amount ranging between about 0.05 and 2.5 pph based upon 100 parts of butadiene, or butadiene mixed with one or more other elastomers. More preferably, the amount of initiator added ranges between about 0.15 and 2 pph and most preferably between about 0.25 and 1.5 pph.

[0047] A typical prior art golf ball core incorporates 5 to 50 pph of zinc oxide in a zinc diacrylate-peroxide cure system that cross-links polybutadiene during the core molding process. In the present invention, some of the zinc oxide (ZnO) can be eliminated in favor of calcium oxide (CaO) in the golf ball core composition. The cores and balls produced from such an admixture typically exhibit enhanced performance properties. The initial velocity of the standard ball is maintained, but the compression of the ball is reduced by at least about 2 compression points on the standard compression scale. On the other hand, the combination of the use of some calcium oxide and a higher percentage of zinc diacrylate can be used to maintain the same compression, but the initial velocity is significantly increased. Where the amount of zinc oxide incorporated in prior art cores is typically about 5 to 50 pph, the amount of calcium oxide added to the core-forming composition of the invention as an activator is typically in the range of about 0.1 to 15, preferably 1 to 10, most preferably 1.25 to 5, parts calcium oxide per hundred parts (pph) of polybutadiene.

[0048] The compositions of the present invention may also include fillers, added to the elastomeric composition to adjust the density and/or specific gravity of the core. As used herein, the term “fillers” includes any compound or composition that can be used to vary the density and other properties of the subject golf ball core. Fillers useful in the golf ball core according to the present invention include, for example, zinc oxide, barium sulfate, and regrind (which is recycled core molding matrix ground to about 30 mesh particle size). The amount and type of filler utilized is governed by the amount and weight of other ingredients in the composition, since a maximum golf ball weight of 1.620 ounces (45.92 gm) has been established by the USGA. Appropriate fillers generally used range in specific gravity from about 2.0 to 5.6. In the preferred golf ball, the amount of filler is higher than that of a typical golf ball such that the specific gravity of the core is increased.

[0049] In the golf ball core 2, as shown in FIG. 1, the preferred range of specific gravities is from about 1.2 to about 1.7, more preferably in the range of about 1.3 to about 1.5, depending upon the size of the core, cover, mantle layer and finished ball, as well as the specific gravity of the cover and mantle layer.

[0050] Other ingredients such as processing aids, processing oils, plasticizers, dyes and pigments, as well as other additives well known to the skilled artisan may also be used in the present invention in amounts sufficient to achieve the purpose for which they are typically used.

[0051] The core compositions of the invention are produced by forming a mixture comprising at least polybutadiene, zinc diacrylate, and calcium or zinc oxide.

[0052] When a set of predetermined conditions is met, i.e., time and temperature of mixing, the free radical initiator is added in an amount dependent upon the amounts and relative ratios of the starting components, as would be well understood by one of ordinary skill in the art. In particular, as the components are mixed, the resultant shear causes the temperature of the mixture to rise. Peroxide(s) free radical initiator(s) are blended into the mixture for crosslinking purposes in the molding process.

[0053] After completion of the mixing, the golf ball core composition is milled and hand prepped or extruded into pieces (“preps”) suitable for molding. The milled preps are then compression molded into cores at an elevated temperature. Typically, 160° C. (320° F.) for 15 minutes is suitable for this purpose. These cores can then be used to make finished golf balls by surrounding the cores with mantle and cover materials.

[0054] The core has a Shore D hardness of about 30 to about 65. The core has a compression of about 50 to about 100. Preferably, the core has a compression of about 80 to about 90. Most preferably, the core compression is about 85.

[0055] Turning now to the mantle layer 4, it preferably comprises thermoplastic copolyesterester block copolymer, dynamically vulcanized thermoplastic elastomer, 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.

[0056] In a preferred embodiment of the present invention, the mantle layer 4 is a thermoplastic copolyetherester block copolymer. Suitable thermoplastic copolyetheresters include Hytrel® 6356 and Hytrel® 7246 which are commercially available from DuPont. Hytrel® 6356 being the most preferred.

[0057] Prior art mantle layers generally have a specific gravity of about 1 or less. As stated above, the objective of most prior art multi-layer balls is to increase spin. The mantle layer according to the present invention preferably has a specific gravity greater than about 1.2. In one embodiment, the specific gravity of the mantle layer is increased to about 1.25 by adding about 20% of a filler such as barium sulfate, zinc oxide, titanium dioxide and combinations thereof. The most preferred high spin golf ball is comprised of a mantle layer made of Hytrel® 6356 and 20% zinc oxide. By increasing the specific gravity of the mantle layer and increasing the specific gravity of the core, the moment of inertia is decreased, which will contribute to a higher initial spin rate.

[0058] Suitable dynamically vulcanized thermoplastic elastomers include Santoprene®, Sarlink®, Vyram®, Dytron® and Vistaflex®. Santoprene® is the trademark for a dynamically vulcanized PP/EPDM. Santoprene® 203-40 is an example of a preferred Santoprene® and is commercially available from Advanced Elastomer Systems. An example of suitable finctionalized styrene-butadiene elastomers, i.e., styrene-butadiene elastomers with functional groups such as maleic anhydride or sulfonic acid, is Kraton G7680 which is available from the Shell Corporation. Examples of suitable thermoplastic polynrethanes include Estane® 58861 and Estane® 58091, which are commercially available from the B. F. Goodrich Company. Suitable metallocene polymers, i.e., polymers made with a metallocene catalyst, whose melting points are higher than the cover materials can also be employed in the mantle layer of the present invention. 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. Such metallocene-based foam resins are commercially available from Sentinel Products of Hyannis, Mass.

[0059] In another preferred embodiment of the present invention, the mantle layer is a blend of a first and a second thermoplastic, wherein the first thermoplastic is a thermoplastic copolyetherester, copolyesterester block copolymer, a dynamically vulcanized thermoplastic elastomer, a functionalized styrene-butadiene elastomer, a thermoplastic polyurethane or a metallocene polymer and the second thermoplastic is a material such as a thermoplastic polyurethane, a thermoplastic polyetherester or polyetheramide, a thermoplastic ionomer resin, a thermoplastic polyester, another dynamically vulcanized elastomer, another functionalized styrene-butadiene elastomer, another metallocene polymer or blends thereof.

[0060] Illustrated in Table I are a number of batch formulations for several mantle layer compositions of the present invention, as well as properties such a hardness (Shore D), Bashore resilience, flexural modulus, % strain at break and tensile modulus for each composition.

[0061] The following examples of batch compositions are given to illustrate the novel multi-layer golf balls of the present invention. However, it is to be understood that the examples are only for illustrative purposes and in no manner is the present invention limited to the specific disclosures therein.

[0062] The golf balls of the present invention have a mantle layer with a Shore D hardness of greater than about 60. Preferably, the Shore D hardness of the mantle layer is about 60 to about 70.

[0063] The cover layers of the present invention comprises at least one layer of a thermoplastic or thermosetting material. Any number of a wide variety of cover materials may be used in the present invention. Among the preferred conventional cover materials are ionomer resins. More particularly, ionomers, such as copolymer ionomers comprised of an olefin such as ethylene and an alpha, beta-unsaturated carboxylic acid such as methacrylic acid wherein 10% to 90% of the carboxylic acid groups are neutralized by a metal cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc or aluminum. Preferably, the cover is an E/X/Y terpolymer or blend of a copolymer and terpolymer where E is an olefin such as ethylene, X is a softening comonomer such as acrylate or methacrylate and Y is an alpha, beta-unsaturated carboxylic acid such as acrylic or methacrylic acid, wherein the carboxylic acid groups are neutralized by a metal cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc or aluminum. Specific acid-containing ethylene copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl methacrylate.

[0064] The manner in which these ionomers are made is well known in the art as described in e.g. U.S. Pat. No. 3,264,272. Such ionomer resins are commercially available from DuPont Co. under the tradename SURLYN®. Preferably, the flexural modulus of the cover is less than 60 ksi. Most preferably, the high spin embodiment has a hardness of between about 55 and about 63 Shore D. The preferred cover of the present invention is comprised of about 30 to 45% of SURLYN® 8320, which is a terpolymer having a softening agent, and 70 to 55% of SURLYN® 7940 which is a lithium copolymer SURLYN® having about 15% methacrylic acid.

[0065] The present invention also contemplates the use of a variety of non-conventional cover materials, i. e., not SURLYN®, balata or polyurethane. In particular, the covers of the present invention may comprise thermoplastic or engineering plastics such as ethylene or propylene based homopolymers and copolymers including functional monomers such as acrylic and methacrylic acid and fully or partially neutralized ionomers 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), reinforced engineering plastics, acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene-vinyl alcohol), poly(tetrafluoroethylene) and their copolymers including functional comonomers and blends thereof. These polymers or copolymers can be further reinforced by blending with a wide range of fillers and glass fibers or spheres or wood pulp.

[0066] The properties such as compression, specific gravity, hardness, Bashore resilience, modulus, core diameter and mantle layer thickness of the golf balls of the present invention have been found to effect play characteristics such as spin, initial velocity and feel of the present golf balls.

[0067] In particular, the thickness of the mantle layer of the present invention is about 0.02 inches to about 0.1 inches. Preferably, the thickness of the mantle layer is about 0.03 inches to about 0.08 inches. Most preferably, the thickness of the mantle layer is about 0.06 to 0.065 inches. The cover thickness of the invention is about 0.04 inches to about 0.15 inches. Most preferably, the thickness of the cover is about 0.05 inches. Similarly, the diameter of the core of the present invention is about 1.2 inches to about 1.55 inches. Preferably the diameter of the core is about 1.30 inches to about 1.48 inches. Most preferably, the diameter of the core is about 1.45 inches. The overall diameter of the core and mantle layer is about 84% to about 97% of the overall diameter of the finished ball, and is preferably about 1.58 inches.

[0068] The golf balls of the present invention can be made by any conventional process employed in the golf ball art. For example, the solid cores can be either injection or compression molded. Similarly, the undersized wound cores of the present invention are produced through conventional means. The mantle layer is subsequently injection or compression molded about the core. It is important that the mantle material be able to sustain the temperatures applied during the application of the cover layer. The cover layer or layers are then injection or compression molded or cast about the mantle layer.

[0069] In the manufacturing of the ball, the core is preferably compression molded as stated above. The mantle layer is molded over the core using a retractable-pin mold. The cover is molded over the mantle layer.

[0070] These and other aspects of the present invention may be more fully understood with reference to the following non-limiting examples, which are merely illustrative of the preferred embodiments of the present invention golf ball, as discussed above and are not to be construed as limiting the invention, the scope of which is defined by the appended claims.

[0071] A first golf ball according to the present invantion has a diameter of about 1.45. The core has a high specific gravity. Preferably, the core has a specific gravity of greater than 1.21 and most preferably about 1.23. The mantle layer covering the core has a thickness of about 0.05 to 0.2 inches, preferably about 0.13 inches. The mantle layer preferably has a specific gravity of 0.91 and is made of Kraton G7890. The cover of the ball has a thickness of about 0.5 to 0.15 and most preferably about 0.1 inches. The cover preferably has a specific gravity of about 0.96 and is made of SURLYN®. This first golf ball preferably weights 1.618 ounces.

[0072] A second golf ball made according to the present invention has a core with a low specific gravity and a mantle layer with a high specific gravity. Preferably, the mantle layer has a specific gravity of greater than 1.21, most preferably the mantle layer has a specific gravity of 1.25. In the preferred embodiment, the mantle layer is made of Hytrel 6356. The mantle layer has a thickness of about 0.05 to about 0.2, and most preferably about 0.13 inches.

[0073] The core of the second golf ball preferably has a specific gravity of less than 1.21 and most preferably a specific gravity of 1.13. The diameter of the core is preferably 1.4 to 1.5 inches and most preferably about 1.45 inches. The cover layer surrounding both the core and mantle layer has a thickness of about 0.05 to about 0.15 inches and most preferably about 0.1 inches. Further, the specific gravity of the cover is most preferably about 0.96 and is made of SURLYN®. The second example most preferably weighs 1.618 ounces.