DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The present invention is directed to improved solid, non-wound, golf balls comprising a polymeric core component with a pressurized center, or nucleus, and one or more outer core layers and a polymeric cover component with either a single or multi-layer cover. Preferably, the pressurized center core component has a relatively low density. The golf balls of the present invention can be of standard or enlarged size.

[0049] In this regard, in the present invention, the nucleus is pressurized in-situ during the molding process of the surrounding core stock. Preferably, a small “plug” or “pill” of polymeric material containing a blowing agent is inserted into the middle of two uncured preformed hollow core halves. Both halves are cured together under heat and pressure to decompose the blowing agent and cure the rubber matrix and core stock. Alternately, the two hollow halves may be cured separately and joined together with rubber adhesive with the plug or pill of polymeric material containing the blowing agent inside. The assembly is reheated in a metal mold under pressure to decompose the blowing agent and release the gas pressure.

[0050] As explained herein, the resulting center core component is pressurized and exhibits a foam-like structure comprising a plurality of cells. These terms are defined as follows. The term “pressurized” as used herein refers to the center core component being at a relatively high pressure, and one that is greater than atmospheric pressure. As described herein, the preferred embodiment of the center core component is in the form of a matrix of cross-linked polymer. The center core component includes a plurality of relatively small voids or interior hollow spaces defined throughout the matrix. These voids or spaces are referred to herein as “cells” and are described in greater detail herein. The resulting structure of the described matrix is also generally referred to herein as “foamed” or obtained by subjecting the center core component to a foaming process. The interior voids or cells, as described in greater detail herein, contain one or more gases. And, the term “pressurized” refers to the pressure of that gas within the cells as being greater than atmospheric pressure.

[0051] The golf balls of the present invention utilize a unique dual or multi-component core configuration. Preferably, the core comprises (i) an interior spherical center component formed from a blend including a first matrix material such as a thermoset material, a thermoplastic material, or combinations thereof; a blowing agent and a cross-linking agent and (ii) a core layer disposed about the spherical center component, the core layer formed from a second matrix material such as a thermoset material, a thermoplastic material, or combinations thereof. The cores may further comprise (iii) an optional outer core layer(s) disposed about the core layer. The outer core layer may be formed from a third matrix material such as a thermoset material, a thermoplastic material, or combinations thereof. The first, second or third matrix materials can be of the same or different materials.

[0052] The center core component has a specific gravity of from about 0.02 to about 4.0, and preferably about 0.10 to 2.0, most preferably, from about 0.30 to about 1.0. The weight of the remaining components are adjusted so that the ball will not exceed the U.S.G.A. golf ball weight requirement.

[0053] In this regard, the present invention is directed to golf balls comprising a dual core component having a pressurized foamed spherical center having a diameter of from about 0.15 to 1.0 inches, preferably about 0.25 to 0.75 inches. Most preferably, the pressurized formed spherical center has a diameter of about 0.340 to 0.344 inches. The pressurized foamed center is formed from in a first matrix material selected from thermosets, thermoplastics, and combinations thereof, a blowing or gas releasing agent and a cross-linking agent. Preferably, the first matrix material is a polyisoprene.

[0054] An outer core layer is then disposed about the spherical center. The outer core layer comprises a second matrix material selected from thermosets, thermoplastics, and combinations thereof. Preferably, this second matrix material is a polybutadiene. The outer diameter of the core is from about 1.25″ to 1.60″, and most preferably, 1.47″ to 1.56″. A cover comprising one or more layers is subsequently molded about the dual core component to form a solid, non-wound golf ball.

[0055] In a particularly preferred form of the present invention, the golf ball comprises a dual core assembly that includes a pressurized and relatively small but light-weight spherical center component, a thick core layer disposed about the spherical center component, and a cover assembly disposed about the dual core assembly. The light-weight center of the core preferably comprises a foamed polyisoprene rubber having an effective amount of cells dispersed throughout the center core component to produce the compression and feel desired.

[0056] The cover assembly may include a single cover or a multi-layered cover configuration. Preferably, the multi-layer golf ball covers of the present invention include a first or inner layer or ply of a high acid (greater than 16 weight percent acid) ionomer blend or a low acid (16 weight percent acid or less) ionomer blend and second or outer layer or ply comprised of a comparatively softer, low modulus ionomer, ionomer blend or other non-ionomeric thermoplastic or thermosetting elastomer such as polyurethane or polyester elastomer. Most preferably, the inner layer or ply includes a blend of low and/or high acid ionomers and has a Shore D hardness of 58 or greater and the outer cover layer is comprised of ionomer or polyurethane and has a Shore D hardness of at least I point softer than the inner layer.

[0057] Although the present invention is primarily directed to solid, non-wound, golf balls comprising a dual core component and a multi-layer cover as described herein, the present invention also includes golf balls having a dual core component and conventional covers comprising ionomer, balata, various thermoplastic polyurethanes, cast polyurethanes, or any other cover materials capable of being cross-linked via radiation after cover molding.

[0058] Accordingly, the present invention is directed to golf balls having a dual-core configuration and a single or multi-layer cover which produces, upon molding each layer around a pressurized inner center, a golf ball exhibiting enhanced feel (i.e., compression) without adversely affecting the ball's resiliency (i.e., distance) and/or durability (i.e., cut resistance, scuff resistance, etc.) characteristics.

[0059] The term resilience is generally defined as the ability of a strained body, by virtue of high yield strength and low elastic modulus, to recover its size and form following deformation. Simply stated, resilience is a measure of the energy retained to the energy lost when the ball is impacted with the club.

[0060] In the field of golf ball production, resilience is determined by the coefficient of restitution (C.O.R.), the constant “e” which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the coefficient of restitution (“e”) can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.

[0061] Resilience (C.O.R.), along with additional factors such as club head speed, club head mass, angle of trajectory, ball size, density, composition and surface configuration (i.e., dimple pattern and area of coverage) as well as environmental conditions (i.e., temperature, moisture, atmospheric pressure, wind, etc.) generally determine the distance a golf ball will travel when hit. Along this line, the distance a golf ball will travel under controlled environmental conditions is a function of the speed and mass of the club and the size, density, composition and resilience (C.O.R.) of the ball and other factors. The velocity of the club, the mass of the club and the angle of the ball's departure are essentially provided by the golfer upon striking. Since club head, club head mass, the angle of trajectory and environmental conditions are not determinants controllable by golf ball producers and the ball size and weight are set by the U.S.G.A., these are not factors of principal concern among golf ball manufacturers. The factors or determinants of interest with respect to improved distance are generally the coefficient of restitution (C.O.R.), spin and the surface configuration (dimple pattern, ratio of land area to dimple area, etc.) of the ball.

[0062] The coefficient of restitution (C.O.R.) in solid core balls (i.e., molded cores and covers) is a function of the composition of the molded core and of the cover. The molded core and/or cover may be comprised of one or more layers such as in multi-layered balls.

[0063] In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings. As in the solid core balls, center and cover of a wound core ball may also consist of one or more layers.

[0064] The resilience or coefficient of restitution of a golf ball can be analyzed by determining the ratio of the outgoing velocity to the incoming velocity. In the examples of this writing, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125+/−1 feet per second (fps) against a generally vertical, hard, flat steel plate and measuring the ball's incoming and outgoing velocities electronically. Speeds were measured with a pair of Oehler Mark 55 ballistic screens (available from Oehler Research Austin Tex.), which provide a timing pulse when an object passes through them. The screens are separated by 36″ and are located 25.25″ and 61.25″ from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36″), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it.

[0065] As indicated above, the incoming speed should be 125+/−1 fps. Furthermore, the correlation between C.O.R. and forward or incoming speed has been studied and a correction has been made over the +/− fps range so that the C.O.R. is reported as if the ball had an incoming speed of exactly 125.0 fps.

[0066] The coefficient of restitution must be carefully controlled in all commercial golf balls if the ball is to be within the specifications regulated by the U.S.G.A. As discussed to some degree above, the U.S.G.A. standards indicate that a “regulation” ball cannot have an initial velocity exceeding 255 feet per second in an atmosphere of 75° F. when tested on a U.S.G.A. machine. Since the coefficient of restitution of a ball is related to the ball's initial velocity, it is highly desirable to produce a ball having sufficiently high coefficient of restitution (C.O.R.) to closely approach the U.S.G.A. limit on initial velocity, while having an ample amount of softness (i.e., hardness) to produce the desired degree of playability (i.e., spin, etc.).

[0067] Furthermore, as mentioned above, the maximum distance a golf ball can travel (carry and roll) when tested on a U.S.G.A. driving machine set at a club head speed of 160 feet/second is 296.8 yards. While golf ball manufacturers design golf balls which closely approach this driver distance specification, there is no upper limit for how far an individual player can drive a ball. Thus, while golf ball manufacturers produce balls having certain resilience characteristics in order to approach the maximum distance parameter set by the U.S.G.A. under controlled conditions, the overall distance produced by a ball in actual play will vary depending on the specific abilities of the individual golfer.

[0068] The surface configuration of a ball is also an important variable in affecting a ball's travel distance. The size and shape of the ball's dimples, as well as the overall dimple pattern and ratio of land area to dimpled area are important with respect to the ball's overall carrying distance. In this regard, the dimples provide the lift and decrease the drag for sustaining the ball's initial velocity in flight as long as possible. This is done by displacing the air (i.e., displacing the air resistance produced by the ball from the front of the ball to the rear) in a uniform manner. Moreover, the shape, size, depth and pattern of the dimple affect the ability to sustain a ball's initial velocity.

[0069] Additionally, compression is another property involved in the overall performance of a golf ball. The compression of a ball will influence the sound or “click” produced when the ball is properly hit. Similarly, compression can effect the “feel” of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.

[0070] Moreover, while compression by itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influence the resultant spin rate. Typically, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. This is because at impact a hard core serves to compress the cover of the ball against the face of the club to a much greater degree than a soft core thereby resulting in more “grab” of the ball on the clubface and subsequent higher spin rates. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.

[0071] The term “compression” utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, PGA compression indicates the amount of change in golf ball's shape upon striking.

[0072] The development of solid core technology in two-piece balls has allowed for much more precise control of compression in comparison to thread wound three-piece balls. This is because in the manufacture of solid core balls, the amount of deflection or deformation is precisely controlled by the chemical formula used in making the cores. This differs from wound three-piece balls wherein compression is controlled in part by the winding process of the elastic thread. Thus, two-piece and multi-layer solid core balls exhibit much more consistent compression readings than balls having wound cores such as the thread wound three-piece balls.

[0073] Additionally, cover hardness and thickness are important in producing the distance, playability and durability properties of a golf ball. As mentioned above, cover hardness directly affects the resilience and thus distance characteristics of a ball. All things being equal, harder covers produce higher resilience. This is because soft materials detract from resilience by absorbing some of the impact energy as the material is compressed on striking.

[0074] However, soft covered balls are generally preferred by the more skilled golfer because he or she can impart high spin rates that give him or her better control or workability of the ball. Spin rate is an important golf ball characteristic for both the skilled and unskilled golfer. As mentioned, high spin rates allow for the more skilled golfer, such as PGA and LPGA professionals and low handicap players, to maximize control of the golf ball. This is particularly beneficial to the more skilled golfer when hitting an approach shot to a green. The ability to intentionally produce “back spin”, thereby stopping the ball quickly on the green, and/or “side spin” to draw or fade the ball, substantially improves the golfer's control over the ball. Thus, the more skilled golfer generally prefers a golf ball exhibiting high spin rate properties.

[0075] The term or designation “2×2” or “2×2 construction” as used herein refers to a golf ball construction utilizing two central core components, e.g. a central core component and a core layer disposed about the core component, and two cover components, e.g. a first inner cover layer and a second outer cover layer. The present invention however is not limited to 2×2 configurations and includes 2×1 (two core components and a single cover component), 3×2 (three core components and two cover components), 2×3 configurations (two core components and three cover components), 3×3 configurations (three core components and three cover components), and additional configurations such as 4×2, 4×3, 4×4, 2×4, 3×4, . . . etc.

[0076] The term “moment of inertia,” sometimes designated “MOI” herein, for the golf balls of the present invention is defined as the sum of the products formed by multiplying the mass of each element by the square of its distance from a specified line or point. This is also known as rotational inertia. Since the present invention golf balls comprise a number of components, the MOI of the resulting golf ball is equal to the sum of the moments of inertia of each of its various components, taken about the same axis or point. All of the moments of inertia of golf balls referred to herein are with respect to, or are taken with regard to, the geometric center of the golf ball.

[0077] FIGS. 1 and 2 illustrate preferred embodiments of the golf balls in accordance with the present invention. It will be understood that all of the figures referenced herein are schematic in nature and none of the referenced figures are to scale. And so, the thicknesses and proportions of the various layers and the diameter of the various core components are not necessarily as depicted.

[0078] The golf ball 8 comprises a single layer 11 ( FIG. 1 ) or a multi-layered cover 12 ( FIG. 2 ) disposed about a core 10 . The core 10 of the golf ball is formed of a pressurized foamed spherical or center core layer center 20 , preferably having a low density, and an outer core layer 22 . The low density spherical center 20 is designed to produce a greater resilience and feel characteristics.

[0079] The multi-layered cover 12 ( FIG. 2 ) comprises two layers: a first or inner layer or ply 14 and a second or outer layer or ply 16 . The inner layer 14 can be ionomer, ionomer blends, non-ionomer, non-ionomer blends, or blends of ionomer and non-ionomer. The outer layer 16 is softer than the inner layer and can be ionomer, ionomer blends, non-ionomer, non-ionomer blends or blends of ionomer and non-ionomer.

[0080] In a first multi-layered cover embodiment, the inner layer 14 is comprised of a high acid (i.e. greater than 16 weight percent acid) ionomer resin or high acid ionomer blend. Preferably, the inner layer is comprised of a blend of two or more high acid (i.e., at least 16 weight percent acid) ionomer resins neutralized to various extents by different metal cations. The inner cover layer may or may not include a metal stearate (e.g., zinc stearate) or other metal fatty acid salt. The purpose of the metal stearate or other metal fatty acid salt is to lower the cost of production without affecting the overall performance of the finished golf ball.

[0081] In a second multi-layered cover embodiment, the inner layer 14 is comprised of a low acid (i.e., 16 weight percent acid or less) ionomer blend. Preferably, the inner layer is comprised of a blend of two or more low acid (i.e., 16 weight percent acid or less) ionomer resins neutralized to various extents by different metal cations. The inner cover layer may or may not include a metal stearate (i.e., zinc stearate) or other metal fatty acid salt.

[0082] It has been found that a hard inner layer in the multi-cover embodiment provides for a substantial increase in resilience (i.e., enhanced distance) over known multi-layer covered balls. The softer outer layer along with the particular multi-component core of the present invention provides the desirable “feel” and high spin rate characteristic while maintaining the golf ball's resiliency. The softer outer layer allows the cover to deform more during impact and increases the area of contact between the club face and the cover, thereby imparting more spin on the ball. As a result, the soft cover provides the ball with a balata-like feel and playability characteristics with improved distance and durability.

[0083] Consequently, the overall combination of the pressurized foamed inner center, one or more outer core layers and the inner and outer cover layers results in a golf ball having enhanced resilience (and improved soft feel due to the foamed rubber nucleus).

[0084] FIGS. 3 and 4 relate to further preferred embodiments of the present invention, where in a layer 23 is included around the pressurized nucleus 20 to reduce or eliminate pressure loss, over time, of the gas contained in the nucleus.

[0085] The specific components and characteristics of the solid, non-wound golf balls of the present invention are more particularly set forth below.

[0086] Core Assembly

[0087] As noted, the present invention golf balls utilize a unique dual core configuration. Preferably, the cores comprise (i) an inner, pressurized, spherical center or center core layer component formed from a first matrix material comprised of thermoset material, thermoplastic material, or combinations thereof, blowing agent(s) and a cross-linking agent(s), and (ii) an outer core layer disposed about the spherical center component, the core layer being formed from a second matrix material comprised of thermoset material, thermoplastic material, or combinations thereof.

[0088] More preferably, the pressurized core component of the present invention consists of a foamed, spherical center and comprises a mixed or blended matrix of polyisoprene, cross-linking agent(s) and blowing agent(s). As indicated below, other polymeric materials can also be utilized. The ingredients of the center core component are mixed together and formed into a spherical shape and then encapsulated within at least one outer core layer. The resulting assembly is then molded under heat and pressure. Heating causes cross-linking of the polyisoprene to occur and also results in activation of the blowing agent (i.e. conversion into a gaseous state). This process and the resulting foamed matrix are described in greater detail below.

[0089] The gas phase in the foamed core component is distributed in voids, pores, or pockets referred to herein as cells. If these cells are interconnected in such a manner that gas can pass from one to another, the material is termed open-celled. If the cells are discrete and the gas phase of each is independent of that of the other cells, the material is termed closed-celled.

[0090] For example, hydrazide blowing agents such as Celogen® TSH release nitrogen gas (N ₂ ) to produce closed cells. In turn, sodium bicarbonate and ammonium carbonate release CO ₂ gas to produce open cells. Nitrogen gas is preferred in the present invention as it has much lower permeability than carbon dioxide.

[0091] The nomenclature of cellular polymers is not standardized. to Classifications have been made according to the properties of the base polymer, the methods of manufacture, the cellular structure, or some combination of these.

[0092] The foamed core component can be prepared by a variety of methods. The most preferred process comprises expanding a fluid polymer phase to a low density cellular state and then preserving this state. This is the foaming or expanding process.

[0093] The expansion process generally includes three steps: creating small discontinuities or cells in a fluid or plastic phase; causing these cells to grow to a desired volume; and stabilizing this cellular structure by physical or chemical means such as peroxides or cross-linking agents.

[0094] The initiation or nucleation of cells is the formation of cells of such size that they are capable of growth under the given conditions of foam expansion. Generally, the growth of a hole or cell in a fluid medium at equilibrium is controlled by the pressure difference between the inside and the outside of the cell, the surface tension of the fluid phase, and the radius of the cell. The pressure outside the cell is the pressure imposed on the fluid surface by its surroundings. The pressure inside the cell is the pressure generated by the blowing agent dispersed or dissolved in the polymer matrix. If blowing pressures are low, the radii of initiating cells must be large. The hole that acts as an initiating site can be filled with either a gas or a solid that breaks the fluid surface and thus enables blowing agent to surround it.

[0095] During the time of cell growth in a foam, a number of properties of the system change greatly. Cell growth can, therefore, be treated only qualitatively. The following considerations are of primary importance: (1) the fluid viscosity is changing considerably, influencing both the cell growth rate and the flow of polymer to intersections from cell walls leading to collapse; (2) the pressure of the blowing agent decreases, falling off less rapidly than an inverse volume relationship because new blowing agent diffuses into the cells as the pressure falls off; (3) the rate of growth of the cell depends on the viscoelastic nature of the polymer phase, the blowing agent pressure, the external pressure on the foam, and the permeation rate of blowing agent through the polymer phase; and (4) the pressure in a cell of small radius is greater than that in a cell of larger radius.

[0096] The increase in surface area corresponding to the formation of many cells in the plastic phase is accompanied by an increase in the free energy of the system; hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, e.g. the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, e.g. the cooling of an expanded thermoplastic polymer to a temperature below its melting point to prevent polymer flow.

[0097] Concerning chemical stabilization, the chemistry of the system determines both the rate at which the polymer phase is formed and the rate at which it changes from a viscous fluid to a dimensionally stable cross-linked polymer phase. It also governs the rate at which the blowing agent is activated, whether it is due to temperature rise or to insolubilization in the liquid phase.

[0098] The blowing agent should have a lower decomposition temperature than the decomposition temperature of the peroxide or cross-linking agent so that cells are formed first, then cross-linked to stabilize the structure.

[0099] The type and amount of blowing agent governs the amount of gas generated, the rate of generation, the pressure that can be developed to expand the polymer phase, and the amount of gas lost from the system relative to the amount retained in the cells.

[0100] Additives to the foaming system (cell growth-control agents) can greatly influence nucleation of foam cells, either through their effect on the surface tension of the system, or by acting as nucleating sites from which cells can grow. They can influence the mechanical stability of the final solid foam structure considerably by changing the physical properties of the plastic phase and by creating discontinuities in the plastic phase that allow blowing agent to diffuse from the cells to the surroundings. Environmental factors such as temperature and pressure also influence the behavior of thermoset foaming systems.

[0101] As to physical stabilization, the factors are essentially the same as for chemically stabilized systems but for somewhat different reasons. Chemical composition of the polymer phase determines the temperature at which foam must be produced, the type of blowing agent required, and the cooling rate of the foam necessary for dimensional stabilization. Blowing agent composition and concentration controls the rate at which gas is released, the amount of gas released, the pressure generated by the gas, escape or retention of gas from the foam cells for a given polymer, and heat absorption or release owing to blowing agent activation.

[0102] Additives have the same effect on thermoplastic foaming processes as on thermoset foaming processes. Environmental conditions are important in this case because of the necessity of removing heat from the foamed structure in order to stabilize it. The dimensions and size of the foamed structure are important for the same reason.

[0103] The following is an exemplary description for forming a preferred embodiment pressurized core component in accordance with the present invention. A decomposable blowing agent, along with vulcanizing systems and other additives, is compounded with the uncured elastomer at a temperature below the decomposition temperature of the blowing agent. When the uncured elastomer is heated in a forming mold, it undergoes a viscosity change. The blowing agent and vulcanizing systems are chosen to yield preferably closed-celled cellular rubber from the release of nitrogen gas from blowing agents such as 2,2′-azobisisobutyronitrile, azodicarbonamide, 4,4′-oxy-bis (benzenesulfonyl hydrazide), and dinitrosopentamethylenetetramine. Sodium bicarbonate produces an open cell structure with CO ₂ gas.

[0104] A preferred blowing or foaming agent for use in forming the center cores described herein is Celogen® TSH. This is available from Crompton Uniroyal Chemical of Naugatuck CT. Celogen® TSH is p-toluene sulfonyl hydrazide. Various data associated with this agent is set forth below: 1

[0105] The timing for blowing-agent decomposition should occur first before the cross-linking initiates.

[0106] The spherical center component may further comprise a blend of one or more heavy weight metals and/or filler materials preferably in particulate or powder form, dispersed throughout the thermoset or thermoplastic material to increase the specific gravity if desired.

[0107] As shown in FIGS. 1 and 2 , the outer core layer is disposed immediately adjacent to, and in intimate contact with the center component. In an alternative embodiment, see FIGS. 3 and 4 , a barrier layer is used to reduce the permeability of the gas through the outer layers. The matrix material of the spherical center and the core layers may be of similar or different composition.

[0108] The core layers of the golf balls of the present invention generally are more resilient than that of the cover layers, exhibiting a PGA compression of about 85 or less, preferably about 30 to 85, and more preferably about 40-60.

[0109] The core compositions and resulting molded core layers of the present invention are manufactured using relatively conventional techniques. In this regard, the core compositions of the invention preferably are based on a variety of materials, particularly the conventional rubber based materials such as cis-1,4 polybutadiene and mixtures of polybutadiene with other elastomers blended together with cross-linking agents, a free radical initiator, optional specific gravity controlling fillers and the like.

[0110] Natural rubber, isoprene rubber, EPR, EPDM, styrene-butadiene rubber, or similar thermoset materials may be appropriately incorporated into the base rubber composition of the butadiene rubber to form the rubber component. It is preferred to use isoprene rubber as the base material for the central core component. Butyl and halobutyl rubber may also be used to reduce the gas permeability if no barrier layer is used. If maximum shelf life is desired to preserve the internal gas pressure, the golf balls may be packaged in pressurized cans, similar to tennis balls and hand balls. It is preferred to use butadiene rubber as a base material of the composition for the outer core layer as it produces maximum C.O.R. Different compositions can readily be used in the different layers, including thermoplastic materials such as a thermoplastic elastomer or a thermoplastic rubber, or a thermoset rubber or thermoset elastomer material.

[0111] Some examples of materials suitable for use as an outer core layer include the above materials as well as polyether or polyester thermoplastic urethanes, thermoset polyurethanes or metallocene polymers or blends thereof. 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 and are readily suitable for forming the outer core layer.

[0112] Examples of a thermoset material include a rubber based, castable urethane or a silicone rubber. The silicone elastomer may be any thermoset or thermoplastic polymer comprising, at least partially, a silicone backbone. Preferably, the polymer is thermoset and is produced by intermolecular condensation of silanols. A typical example is a polydimethylsiloxane cross-linked by free radical initiators, or by the cross-linking of vinyl or allyl groups attached to the silicone through reaction with silylhydride groups, or via reactive end groups. The silicone may include a reinforcing or non-reinforcing filler. Additionally, the present invention also contemplates the use of a polymeric foam material, such as the metallocene based foamed resin for the outer core layers.

[0113] More particularly, a wide array of thermoset materials can be utilized in the core components of the present invention. Examples of suitable thermoset materials include polybutadiene, polyisoprene, styrene/butadiene, ethylene propylene diene terpolymers, natural rubber polyolefins, polyurethanes, silicones, polyureas, or virtually any irreversibly cross-linkable resin system. It is also contemplated that epoxy, phenolic, and an array of unsaturated polyester resins could be utilized.

[0114] The thermoplastic material utilized in the present invention golf balls and, particularly their dual cores, may be nearly any thermoplastic material. Examples of typical thermoplastic materials for incorporation in the golf balls of the present invention include, but are not limited to, ionomers, polyurethane thermoplastic elastomers, and combinations thereof. It is also contemplated that a wide array of other thermoplastic materials could be utilized, such as polysulfones, polyamide-imides, polyarylates, polyaryletherketones, polyaryl sulfones/polyether sulfones, polyether-imides, polyimides, liquid crystal polymers, polyphenylene sulfides; and specialty high-performance resins, which would include fluoropolymers, polybenzimidazole, and ultra-high molecular weight polyethylenes.

[0115] Additional examples of suitable thermoplastics include metallocenes, polyvinyl chlorides, polyvinyl acetates, acrylonitrile-butadiene-styrenes, acrylics, styrene-acrylonitriles, styrene-maleic anhydrides, polyamides (nylons), polycarbonates, polybutylene terephthalates, polyethylene terephthalates, polyphenylene ethers/polyphenylene oxides, reinforced polypropylenes, and high-impact polystyrenes.

[0116] Preferably, the thermoplastic materials have relatively high melting points, such as a melting point of at least about 300° F. Several examples of these preferred thermoplastic materials and which are commercially available include, but are not limited to, Capron™ (a blend of nylon and ionomer), Lexan™ polycarbonate, Pebax®, polyether amide, and Hytrel™ polyester amide. The polymers or resin system may be cross-linked by a variety of means such as by peroxide agents, sulphur agents, radiation or other cross-linking techniques, if applicable. However, the use of peroxide cross-linking agents is generally preferred in the present invention.

[0117] Any or all of the previously described components in the cores of the golf ball of the present invention may be formed in such a manner, or have suitable fillers added, so that their resulting density is decreased or increased. For example, heavy weight metals and/or filler materials can be optionally incorporated into the inner spherical center. This is discussed in more detail herein.

[0118] Additionally, the inner core component may be formed or otherwise produced to be light in weight. For instance, the components could be foamed, either separately or in-situ. Related to this, a foamed light weight filler agent or density reducing filler may also be added to the outer core layers.

[0119] The preferred core composition for the center core component comprises polyisoprene, a peroxide cross-linking agent, and an effective amount of a blowing agent. A most preferred type of polyisoprene is Natsyn™ 2200, available from The Goodyear Tire & Rubber Co., Akron, Ohio.

[0120] The core compositions for the one or more core layers of the invention may also be based on polybutadiene, and mixtures of polybutadiene with other elastomers. It is preferred that the base elastomer have a relatively high molecular weight. The broad range for the molecular weight of suitable base elastomers is from about 50,000 to about 500,000. A more preferred range for the molecular weight of the base elastomer is from about 100,000 to about 500,000. As a base elastomer for the core layer (or outer core) composition, cis-polybutadiene is preferably employed, or a blend of cis-polybutadiene with other elastomers such as polyisoprene may also be utilized. Most preferably, cis-polybutadiene having a weight-average molecular weight of from about 100,000 to about 500,000 is employed.

[0121] Along this line, it has been found that the high cis-polybutadiene manufactured and sold by Dow France 13131 Berre I'Etang Cedex, France, tradename Cariflex BR-1220, either alone or in combination with a polyisoprene, such as Natsyn™ 2200, is particularly well suited.

[0122] Metal carboxylate cross-linking agents may be used for the various core layers The unsaturated carboxylic acid component of the core composition (a co-cross-linking agent) is the reaction product of the selected carboxylic acid or acids and an oxide or carbonate of a metal such as zinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium, lead, tin, and the like. Preferably, the oxides of polyvalent metals such as zinc, magnesium and cadmium are used, and most preferably, the oxide is zinc oxide.

[0123] Exemplary of the unsaturated carboxylic acids which find utility in the present core compositions are acrylic acid, methacrylic acid, itaconic acid, crotonic acid, sorbic acid, and the like, and mixtures thereof. Preferably, the acid component is either acrylic or methacrylic acid. Usually, from about 12 to about 40, and preferably from about 15 to about 35 parts by weight of the carboxylic acid salt, such as zinc diacrylate, is included in the outer core layers. The unsaturated carboxylic acids and metal salts thereof are generally soluble in the elastomeric base, or are readily dispersed.

[0124] The free radical initiator included in the core compositions is any known polymerization initiator (a co-cross-linking agent) which decomposes during the cure cycle. The term “free radical initiator” as used herein refers to a chemical which, when added to a mixture of the elastomeric blend and a metal salt of an unsaturated, carboxylic acid, promotes cross-linking of the elastomers by the metal salt of the unsaturated carboxylic acid. The amount of the selected initiator present is dictated only by the requirements of catalytic activity as a polymerization initiator. Suitable initiators include peroxides, persulfates, azo compounds and hydrazides. Peroxides which are readily commercially available are conveniently used in the present invention, generally in amounts of from about 0.5 to about 4.0 and preferably in amounts of from about 1.0 to about 3.0 parts by weight per each 100 parts of elastomer and based on 40% active peroxide with 60% inert filler.

[0125] Exemplary of suitable peroxides for the purposes of the present invention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxide and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well as mixtures thereof. It will be understood that the total amount of initiators used will vary depending on the specific end product desired and the particular initiators employed.

[0126] Examples of such commercially available peroxides are Luperco™ 230 or 231 XL sold by Atochem, Lucidol Division, Buffalo, N.Y., and Trigonox™ 17/40 or 29/40 sold by Akzo Chemie America, Chicago, Ill. In this regard Luperco™ 230 XL and Trigonox™ 17/40 are comprised of n-butyl 4,4-bis (butylperoxy) valerate; and, Luperco™ 231 XL and Trigonox™ 14/40 are comprised of 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane. The one hour half life of Luperco™ 231 XL is about 112° C., and the one hour half life of Trigonox™ 17/40 is about 129° C. Trigonox™ 42-40 B is preferred and is chemically tert-butyl peroxy -3,5,5, trimethyl hexanoate.

[0127] The core compositions of the present invention may additionally contain any other suitable and compatible modifying ingredients including, but not limited to, metal oxides, fatty acids, diisocyanates and polypropylene powder resin. For example, Papi™ 94, a polymeric diisocyanate, commonly available from Dow Chemical Co., Midland, Mich., is an optional component in the rubber compositions. It can range from about 0 to 5 parts by weight per 100 parts by weight rubber (phr) component, and it acts as a moisture scavenger. In addition, it has been found that the addition of a polypropylene powder resin results in a core which is harder (i.e. exhibits low compression) and thus allows for a reduction in the amount of cross-linking agent utilized to soften the core to a normal or below normal compression.

[0128] Various activators may also be included in the compositions of the present invention. For example, zinc oxide, calcium oxide and/or magnesium oxide are activators for the polybutadiene. The activator can range from about 2 to about 30 parts by weight per 100 parts by weight of the rubbers (phr) component.

[0129] Fatty acids or metallic salts of fatty acids may also be included in the compositions, functioning to improve moldability and processing. Generally, free fatty acids having from about 10 to about 40 carbon atoms, and preferably having from about 15 to about 20 carbon atoms, are used. Exemplary of suitable fatty acids are stearic acid and linoleic acids, as well as mixtures thereof. Exemplary of suitable metallic salts of fatty acids include zinc stearate. When included in the core compositions, the fatty acid component is present in amounts of from about 1 to about 25, preferably in amounts from about 2 to about 15 parts by weight based on 100 parts rubber (elastomer).

[0130] It is preferred that the core compositions include zinc stearate as the metallic salt of a fatty acid in an amount of from about 2 to about 20 parts by weight per 100 parts of rubber.

[0131] Diisocyanates may also be optionally included in the core compositions. The diisocyanates act here as moisture scavengers. When utilized, the diioscyanates are included in amounts of from about 0.2 to about 5.0 parts by weight based on 100 parts rubber. Exemplary of suitable diisocyanates are 4,4′-diphenylmethane diisocyanate and other polyfunctional isocyanates known to the art.

[0132] Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat. No. 4,844,471, the dispersing agents disclosed in U.S. Pat. No. 4,838,556, and the dithiocarbamates set forth in U.S. Pat. No. 4,852,884 may also be incorporated into the polybutadiene compositions of the present invention. The specific types and amounts of such additives are set forth in the above identified patents, which are incorporated herein by reference.

[0133] The preferred center core component of the present invention generally comprises about 100 parts by weight of a polyisoprene, and effective amounts of a cross-linker and a blowing agent. These effective amounts are described in greater detail herein. Optionally, a heavyweight filler may also be included.

[0134] The preferred outer core components of the invention are generally comprised of 100 parts by weight of a base elastomer (or rubber) selected from polybutadiene and mixtures of polybutadiene with other elastomers, such as polyisoprene, 12 to 40 parts by weight of at least one metallic salt of an unsaturated carboxylic acid, and 0.5 to 4.0 parts by weight of a free radical initiator (40% active peroxide).

[0135] In addition, various polyisoprenes may also be included in the core components of the present invention. In particular, it is preferred that one or more polyisoprenes are utilized to form the pressurized center core component of the preferred embodiment golf ball. Examples of such polyisoprenes are as follows: 2

[0136] Additional details relating to polyisoprenes and their processing and incorporation in golf balls are set forth in U.S. Pat. Nos. 4,144,223; 4,714,253; 5,019,319; 5,725,443; 5,989,136; 6,120,390; 6,217,462; and 6,319,152; all of which are hereby incorporated by reference.

[0137] The inner spherical center preferably can be compression or transfer molded from an uncured or lightly cured elastomer composition. To achieve higher coefficients of restitution and/or to increase hardness in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. Non-limiting examples of other materials which may be used in the core composition include compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a curing or cross-linking reaction takes place.

[0138] Also optionally included in the matrix materials of the inner spherical centers and/or core layers are one or more heavyweight fillers or powder materials. Such core combinations may exhibit lower or higher moment of inertia than conventional two-piece golf balls.

[0139] The powdered metal in the core components may be in a wide array of types, geometries, forms, and sizes. The powdered metal may be of any shape so long as the metal may be blended with the other components which form the core.

[0140] Particularly, the metal may be in the form of metal particles, metal flakes, and mixtures thereof. However, again, the forms of powdered metal are not limited to such forms. The metal may be in a form having a variety of sizes so long as the objectives of the present invention are maintained. Preferably, the powdered metal is incorporated into the matrix material of the core in finely defined form, as for example, in a size generally less than about 20 mesh, preferably less than about 200 mesh and most preferably less than about 325 mesh, U.S. standard size. The amount of powdered metal included in the core is dictated by weight restrictions, the type of powdered metal, and the overall characteristics of the finished ball.

[0141] The core components may include more than one type of powdered metal. Particularly, the core components may include blends of the powdered metals disclosed below. The blends of powdered metals may be in any proportion with respect to each other in order for the spherical center and golf ball to exhibit the characteristics noted herein.

[0142] Examples of several suitable powdered metals which can be included in the present invention are as follows: 3

[0143] The amount and type of powdered metal utilized is dependent upon the overall characteristics of the golf ball desired. Generally, lesser amounts of high specific gravity powdered metals are necessary to produce a decrease in the moment of inertia in comparison to low specific gravity materials. Furthermore, handling and processing conditions can also affect the type of heavy weight powdered metals incorporated into the core.

[0144] The core having a two-layer structure composed of the inner core and the outer core is referred to as the solid core in the present invention. The above expression is in contrast to a thread-wound core (core formed by winding a rubber thread around the center portion which is solid or filled with a liquid material).

[0145] The double cores of the inventive golf balls typically have a coefficient of restitution of about 0.770 or more, more preferably 0.780 or more and a PGA compression of about 85 or less, preferably 70 or less, and more preferably 60 or less. The double cores have a weight of 25 to 40 grams and preferably 30 to 40 grams and a Shore C hardness of less than 80, with the preferred Shore C hardness being about 50 to 75.

[0146] As mentioned above, the present invention includes golf ball embodiments that utilize two or more core components. For example, in accordance with the present invention, a core assembly is provided that comprises a central core component and one or more core layers disposed about the central core component. Details for the second and third or more core layers are also included herein in the description of the core layer utilized in a dual core configuration.

[0147] In producing golf ball cores utilizing the present compositions, the ingredients may be intimately mixed using, for instance, two roll mills or a Banbury™ mixer until the composition is uniform, usually over a period of from about 5 to about 20 minutes. The sequence of addition of components is not critical. A preferred blending sequence is described below.

[0148] The matrix material or elastomer (such as polyisoprene for the center core component and polybutadiene for the one or more core layers), the blowing agent (if desired), the cross-linking agent (if desired), the powdered metal zinc salt (if desired), the low or high specific gravity additive such as powdered metal (if desired), metal oxide (if desired), fatty acid (if desired), the metallic dithiocarbamate (if desired), surfactant (if desired), and tin difatty acid (if desired), are blended for about 7 minutes in an internal mixer such as a Banbury™ mixer. As a result of shear during mixing, the temperature rises to about 200° F. The mixing is desirably conducted in such a manner that the composition does not reach incipient polymerization temperatures or the decomposition temperature of the blowing agent during the blending of the various components. The initiator and diisocyanate are then added and the mixing continued until the temperature reaches about 220° F. whereupon the batch is discharged onto a two roll mill, mixed for about one minute and sheeted out.

[0149] The sheet is rolled into a “pig” and then placed in a Barwell™ preformer and slugs of the desired weight are produced. The slugs are pre-formed using a three-plate multicavity mold assembly, wherein the slugs are placed in the bottom hemispherical cavities of the desired diameter. A middle forming plate, having hemispherical “buttons” on the top and bottom of this plate is placed on top of the slugs in the bottom cavities. A second set of slugs is placed on the top “buttons” of the forming plate. The mold is closed under heat and pressure to form the hollow half cores. The temperature is sufficient to allow the stock to flow and fill the cavities but not hot enough to fully cross-link the rubber cores. Cold water is applied to the mold to chill the rubber half cores to make them rigid. The mold is opened and the middle plate is removed, leaving hollow hemispherical uncured outer core stock in the top and bottom cavities.

[0150] An elastomeric “pill” containing blowing agent of the appropriate size and weight is placed in the center of the bottom hollow core stock. The mold is closed under heat and pressure that is sufficient to decompose the blowing agent and cross-link the cellular nucleus and the outer core stock together. Cold water is applied to the mold and the dual cores are removed. The above “pill” may also be encased with a barrier resin or film to resist the permeation of the nascent gas pressure from the nucleus.

[0151] Alternatively, the hemispherical hollow cores may be formed and cross-liked separately and joined together with uncured rubber adhesive with the pill inside. The assembly is reheated under pressure to activate the blowing agent and cross-link the core and adhesive. This method will insure a hollow concentric spherical inner core that will not collapse under the pressure of molding.

[0152] The center is converted into a dual core by providing at least one layer of core material thereon, as described above. For example, a layer of core material ranging in thickness from about 0.69 to about 0.38 inches and preferably from about 0.65 to about 0.60 inches produces an effective core layer. The outer core layers may be of similar or different matrix material as the spherical center. Preferably the outer core layer comprises polybutadiene. In some instances the polybutadiene is weight adjusted to compensate for the light-weight spherical center.

[0153] After molding, the core comprising a centrally located center surrounded by at least one outer core layer is removed from the mold and the surface thereof preferably is treated to facilitate adhesion thereof to the covering materials. Surface treatment can be effected by any of the several techniques known in the art, such as corona discharge, ozone treatment, sand blasting, brush tumbling, chemicals and the like. Preferably, surface treatment is effected by grinding with an abrasive wheel.

[0154] As previously noted, the center core component is preferably of a foamed structure. And, as previously noted, one or more blowing agents are incorporated into the composition of the center core component. Preferably, the blowing agent is activated prior to cross-linking of the composition and while the composition is flowable. Upon activation of the blowing agent, an amount of gas is generated, such as nitrogen. The resulting increase in volume from conversion of the agent, previously in a solid or liquid state, to a gaseous state causes a plurality of gas-filled cells or interior voids within the polymeric matrix to form. After formation of the cells, the polymer matrix is cross-linked. In the event that activation of the blowing agent occurs by heating and cross-linking by heating, it may be preferred to select a blowing agent having an activation temperature that is lower than the temperature at which cross-linking occurs. This practice will promote the formation of cells that are closed. In the event that it is desired to form an open-celled configuration, it would generally be preferred to solidify and cross-link the polymer matrix of the center core component first and then activate the blowing agent. However, the formation of cells that are either open or closed depends upon other factors, as previously described.

[0155] An important feature of the present invention is that the center core component is pressurized. As previously noted, this means that the entrapped gas within cells in the center component is at a pressure greater than atmospheric pressure. The activation of the blowing agent preferably occurs when the center core component is encapsulated within one or more core layers. This minimizes the amount of gas from activation of the blowing agent that escapes from the core. By retaining the gas within the center core component, the pressurized aspect of the center core is promoted.

[0156] An indication as to the degree or extent of pressurization of the center core component is the increase in volume exhibited by the center core component when surrounding core layers are removed. Generally, center core components as described herein, increase in size from about 10% to about 100% or more of their original diameter. It will be appreciated that such increase in volume is merely an indication of the relatively high internal pressure of the center core when constrained by a core layer. However, it is contemplated that the pressure of gas within a center core component, encapsulated within one or more core layers as described herein, is generally greater than atmospheric pressure and may be as high as 100 psi or more.

[0157] In yet another aspect of the present invention, it is preferred that the cross-linking operation, i.e. heating operation, performed upon the center core component is performed after at least one core layer has been formed about the center core component. It has been found that cross-linking occurs along the interface between the center core component and the core layer immediately adjacent to the center core component. The resulting cross-linking further promotes retention of the gas generated within the center core component upon activation of the blowing agent. Further sealing of the center core component, i.e. retention of gas within the center core component, is provided by the one or more core layers disposed about the center core component.

[0158] It has also been found that, in some instances, the molded cores and finished balls lose internal pressure over time as the gas dissipates through the core and cover into the atmosphere. This can be reduced or eliminated by the following methods:

[0159] The finished golf balls may be packaged in metal or plastic containers that are pressurized with the same pressure and gas that is contained in the nucleus of the golf balls. This would be similar to the packaging of tennis balls and hand balls.

[0160] Additionally, a barrier layer or film of polymer such as that shown in FIGS. 3 and 4 can be employed to reduce or eliminate the diffusion of the internal gas and pressure. This layer, or multiple layers thereof, may also be formed under the outside dimpled cover or in between any of the core and/or cover layers.

[0161] The preferred gas is nitrogen as it permeates less than carbon dioxide or oxygen. See for example the tables below showing the permeability of different gases in various polymers set forth in the Polymer Handbook, 3rd Edition, incorporated herein by reference. 4

[0162] 5

[0163] 6

[0164] 7