Dual cores for golf balls

The present invention is directed to a golf ball comprising a dual core component. The dual core comprises an interior center component formed from a thermoset material, a thermoplastic material, or combinations thereof. The dual core also comprises a core layer disposed about the center component, formed from a thermoset material, a thermoplastic material, or combinations thereof. The present invention golf ball may further comprise an outer core layer that surrounds the dual core. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known golf balls. In one preferred embodiment, the present invention golf ball includes a dual core having a center component of a thermoset material and a core layer of a thermoplastic material and a cover layer disposed about the core. The cover layer includes an inner cover layer with a Shore D hardness of 65 or greater and an outer cover layer having a Shore D hardness of 65 or less. In another preferred embodiment, the golf ball includes the previously noted dual core and a cover layer that includes an inner cover layer having a Shore D hardness of 65 or less and an outer cover layer of 65 or greater. In yet another preferred embodiment, the golf ball, as noted, includes the previously described dual core and a cover layer that includes a single outer cover layer having a Shore D hardness of from about 40 to 80. The center component of the preferred dual core has an outer diameter of from about 0.500 inches to about 1.250 inches. And, the preferred dual core has an outer diameter of from about 1.250 to about 1.600 inches.

FIELD OF THE INVENTION
 The present invention relates to golf balls and, more particularly, to
 improved golf balls comprising a unique dual core configuration. The
 improved golf balls provide for enhanced distance and durability
 properties.
 BACKGROUND OF THE INVENTION
 A number of two-piece (a solid resilient center or core with a molded
 cover) and three-piece (a liquid or solid center, elastomeric winding
 about the center, and a molded cover) golf balls have been produced. The
 different types of materials utilized to formulate the cores, covers, etc.
 of these balls dramatically alters the balls' overall characteristics. In
 addition, multi-layered covers containing one or more ionomer resins have
 also been formulated in an attempt to produce a golf ball having the
 overall distance, playability and durability characteristics desired.
 Despite the great number of materials and combinations of materials
 utilized in prior art golf balls, there still remains a need for an
 improved golf ball exhibiting superior properties.
 These and other objects and features of the invention will be apparent from
 the following summary and description of the invention, the drawings and
 from the claims.
 SUMMARY OF THE INVENTION
 In one aspect, the present invention provides a golf ball comprising a dual
 core comprising a center component and a core layer disposed about the
 center component. The center component comprises a thermoplastic material
 and the core layer comprises a thermoset material.
 In yet another aspect, the present invention provides a multi-layer golf
 ball comprising a dual core component that includes a center component and
 a core layer disposed about the center component. The center component
 comprises a thermoset material and the core layer comprises a
 thermoplastic material.
 In yet another embodiment, the present invention provides a multi-layer
 golf ball comprising a dual core, having a center component and a core
 layer, both of which comprise a thermoplastic material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention is directed to a golf ball comprising a dual-core
 component. The present invention golf balls preferably utilize a
 multi-layer cover. However, the golf balls may instead utilize
 conventional cover materials such as balata or blends of balata with
 elastomeric or plastic materials. The multi-layer golf ball covers include
 a first or inner layer or ply of a high acid (greater than 16 weight
 percent acid) ionomer blend or, more preferably, 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. The multi-layer golf balls of the
 present invention can be of standard or enlarged size. Preferably, the
 inner layer or ply includes a blend of low acid ionomers and has a Shore D
 hardness of 70 or greater and the outer cover layer comprised of
 polyurethane and has a Shore D hardness of about 45 (i.e., Shore C
 hardness of about 65).
 The present invention golf balls utilize a unique dual-core configuration.
 Preferably, the cores comprise (i) an interior spherical center component
 formed from a thermoset material, a thermoplastic material, or
 combinations thereof; and (ii) a core layer disposed about the spherical
 center component, the core layer formed from a thermoset material, a
 thermoplastic material, or combinations thereof. The cores may further
 comprise (iii) an optional outer core layer disposed about the core layer.
 The outer core layer may be formed from a thermoset material, a
 thermoplastic material, or combinations thereof.
 Although the present invention is primarily directed to golf balls
 comprising a dual core component and preferably in conjunction with a
 multi-layer cover as described herein, the present invention also includes
 golf balls having a dual core component and conventional covers comprising
 balata, various thermoplastic materials, cast polyurethanes, or any other
 known cover material.
 It has been found that multi-layer golf balls having inner and outer cover
 layers exhibit higher C.O.R. values and have greater travel distance in
 comparison with balls made from a single cover layer. In addition, it has
 been found that use of an inner cover layer constructed of a blend of low
 acid (i.e., 16 weight percent acid or less) ionomer resins produces softer
 compression and higher spin rates than inner cover layers constructed of
 high acid ionomer resins. This is compounded by the fact that the softer
 polyurethane outer layer adds to the desirable "feel" and high spin rate
 while maintaining respectable resilience. The soft 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 polyurethane cover provides the ball with a
 balata-like feel and playability characteristics with improved distance
 and durability.
 Consequently, the overall combination of the unique dual core
 configuration, described in greater detail herein, and the multi-layer
 cover construction of inner and outer cover layers made, for example, from
 blends of low acid ionomer resins and polyurethane results in a standard
 size or oversized golf ball having enhanced resilience (improved travel
 distance) and durability (i.e. cut resistance, etc.) characteristics while
 maintaining and in many instances, improving the ball's playability
 properties.
 The combination of a low acid ionomer blend inner cover layer with a soft,
 relatively low modulus ionomer, polyurethane based elastomer outer cover
 layer provides for good overall coefficient of restitution (i.e., enhanced
 resilience) while at the same time demonstrating improved compression and
 spin. The outer cover layer generally contributes to a more desirable feel
 and spin, particularly at lower swing speeds with highly lofted clubs such
 as half wedge shots.
 Accordingly, the present invention is directed to a golf ball comprising a
 dual-core configuration and an improved multi-layer cover which produces,
 upon molding each layer around a core to formulate a multi-layer cover, a
 golf ball exhibiting enhanced distance (i.e., resilience) without
 adversely affecting, and in many instances, improving the ball's
 playability (hardness/softness) and/or durability (i.e., cut resistance,
 fatigue resistance, etc.) characteristics.
 FIGS. 1 and 2 illustrate a preferred embodiment golf ball 5 in accordance
 with the present invention. It will be understood that 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. The golf ball 5 comprises a multi-layered
 cover 12 disposed about a core 10. The core 10 of the golf ball can be
 formed of a solid, a liquid, or any other substances that may be utilized
 to form the novel dual core described herein. The core 10 is preferably a
 dual core as described herein. The multi-layered cover 12 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.
 In a first preferred 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. In a
 second 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
 (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.
 Two principal properties involved in golf ball performance are resilience
 and hardness. 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.
 Resilience (C.O.R.), along with additional factors such as club head speed,
 angle of trajectory and ball configuration (i.e., dimple pattern)
 generally determine the distance a ball will travel when hit. Since club
 head speed and the angle of trajectory are factors not easily controllable
 by a manufacturer, factors of concern among manufacturers are the
 coefficient of restitution (C.O.R.) and the surface configuration of the
 ball.
 The coefficient of restitution (C.O.R.) in solid core balls is a function
 of the composition of the molded core and of the cover. In balls
 containing a dual core (i.e., balls comprising an interior spherical
 center component, a core layer disposed about the spherical center
 component, and a cover), the coefficient of restitution is a function of
 not only the composition of the cover, but also the composition and
 physical characteristics of the interior spherical center component and
 the core layer. Both the dual core and the cover contribute to the
 coefficient of restitution in the golf balls of the present invention.
 In this regard, the coefficient of restitution of a golf ball is generally
 measured by propelling a ball at a given speed against a hard surface and
 measuring the ball's incoming and outgoing velocity electronically. As
 mentioned above, the coefficient of restitution is the ratio of the
 outgoing velocity to the incoming velocity. The coefficient of restitution
 must be carefully controlled in all commercial golf balls in order for the
 ball to be within the specifications regulated by the United States Golf
 Association (U.S.G.A.). Along this line, the U.S.G.A. standards indicate
 that a "regulation" ball cannot have an initial velocity (i.e., the speed
 of the club) exceeding 255 feet per second. 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 to closely approach the U.S.G.A. limit on initial velocity,
 while having an ample degree of softness (i.e., hardness) to produce
 enhanced playability (i.e., spin, etc.).
 The hardness of the ball is the second principal property involved in the
 performance of a golf ball. The hardness of the ball can affect the
 playability of the ball on striking and the sound or "click" produced.
 Hardness is determined by the deformation (i.e., compression) of the ball
 under various load conditions applied across the ball's diameter (i.e.,
 the lower the compression value, the harder the material). As indicated in
 U.S. Pat. No. 4,674,751, softer covers permit the accomplished golfer to
 impart increased spin. This is because the softer covers deform on impact
 significantly more than balls having "harder" ionomeric resin covers. As a
 result, the better player is allowed to impart fade, draw or backspin to
 the ball thereby enhancing playability. Such properties may be determined
 by various spin rate tests.
 It has been found that a hard inner cover layer provides for a substantial
 increase in resilience (i.e., enhanced distance) over known multi-layer
 covered balls. The softer outer cover layer provides for desirable "feel"
 and high spin rate while maintaining respectable resiliency. The soft
 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. Consequently, the overall combination of the inner and
 outer cover layers and the unique dual core configuration results in a
 golf ball having enhanced resilience (improved travel distance) and
 durability (i.e., cut resistance, etc.) characteristics while maintaining
 and in many instances, improving the playability properties of the ball.
 The combination of a dual core component and a hard inner cover layer with
 a soft, relatively low modulus ionomer, ionomer blend or other
 non-ionomeric thermoplastic elastomer outer cover layer provides for
 excellent overall coefficient of restitution (i.e., excellent resilience)
 because of the improved resiliency produced by the inner cover layer.
 Moreover, the configuration of, and the ability to select the materials
 used in, the dual core component enables the formulator to readily tailor
 the end properties and characteristics of the resulting golf ball. While
 some improvement in resiliency is also produced by the outer cover layer,
 the outer cover layer generally provides for a more desirable feel and
 high spin, particularly at lower swing speeds with highly lofted clubs
 such as half wedge shots.
 Inner Cover Layer
 The inner cover layer is harder than the outer cover layer and generally
 has a thickness in the range of 0.01 to 0.10 inches, preferably 0.03 to
 0.07 inches for a 1.68 inch ball and 0.05 to 0.10 inches for a 1.72 inch
 (or more) ball. The core and inner cover layer together form an inner ball
 having a coefficient of restitution of 0.780 or more and more preferably
 0.790 or more, and a diameter in the range of 1.48-1.66 inches for a 1.68
 inch ball and 1.50-1.70 inches for a 1.72 inch (or more) ball. The inner
 cover layer has a Shore D hardness of 60 or more. It is particularly
 advantageous if the golf balls of the invention have an inner layer with a
 Shore D hardness of 65 or more. The above-described characteristics of the
 inner cover layer provide an inner ball having a PGA compression of 100 or
 less. It is found that when the inner ball has a PGA compression of 90 or
 less, excellent playability results.
 The inner layer compositions include the high acid ionomers such as those
 developed by E. I. DuPont de Nemours & Company under the trademark
 "Surlyn.RTM." and by Exxon Corporation under the trademark "Escor.RTM." or
 trade name "Iotek", or blends thereof. Examples of compositions which may
 be used as the inner layer herein are set forth in detail in a
 continuation of U.S. application Ser. No. 08/174,765, which is a
 continuation of U.S. application Ser. No. 07/776,803 filed Oct. 15, 1991,
 and Ser. No. 08/493,089, which is a continuation of Ser. No. 07/981,751,
 which in turn is a continuation of Ser. No. 07/901,660 filed Jun. 19,
 1992, all of which are incorporated herein by reference. Of course, the
 inner layer high acid ionomer compositions are not limited in any way to
 those compositions set forth in said applications.
 The high acid ionomers which may be suitable for use in formulating the
 inner layer compositions are ionic copolymers which are the metal, i.e.,
 sodium, zinc, magnesium, etc., salts of the reaction product of an olefin
 having from about 2 to 8 carbon atoms and an unsaturated monocarboxylic
 acid having from about 3 to 8 carbon atoms. Preferably, the ionomeric
 resins are copolymers of ethylene and either acrylic or methacrylic acid.
 In some circumstances, an additional comonomer such as an acrylate ester
 (i.e., iso- or n-butylacrylate, etc.) can also be included to produce a
 softer terpolymer. The carboxylic acid groups of the copolymer are
 partially neutralized (i.e., approximately 10-100%, preferably 30-70%) by
 the metal ions. Each of the high acid ionomer resins which may be included
 in the inner layer cover compositions of the invention contains greater
 than about 16% by weight of a carboxylic acid, preferably from about 17%
 to about 25% by weight of a carboxylic acid, more preferably from about
 18.5% to about 21.5% by weight of a carboxylic acid.
 Although the inner layer cover composition of several embodiments of the
 present invention preferably includes a commercially available high acid
 ionomeric resin, the scope of the patent embraces all known high acid
 ionomeric resins falling within the parameters set forth above. Only a
 relatively limited number of these high acid ionomeric resins have
 recently become commercially available.
 The high acid ionomeric resins available from Exxon under the designation
 "Escor.RTM." and or "Iotek", are somewhat similar to the high acid
 ionomeric resins available under the "Surlyn.RTM." trademark. However,
 since the Escor.RTM./Iotek ionomeric resins are sodium or zinc salts of
 poly(ethylene-acrylic acid) and the "Surlyn.RTM." resins are zinc, sodium,
 magnesium, etc. salts of poly(ethylene-methacrylic acid), distinct
 differences in properties exist.
 Examples of the high acid methacrylic acid based ionomers found suitable
 for use in accordance with this invention include Surlyn.RTM.8220 and 8240
 (both formerly known as forms of Surlyn AD-8422), Surlyn.RTM.9220 (zinc
 cation), Surlyn.RTM.SEP-503-1 (zinc cation), and Surlyn.RTM.SEP-503-2
 (magnesium cation). According to DuPont, all of these ionomers contain
 from about 18.5 to about 21.5% by weight methacrylic acid.
 More particularly, Surlyn.RTM. AD-8422 is currently commercially available
 from DuPont in a number of different grades (i.e., AD-8422-2, AD-8422-3,
 AD-8422-5, etc.) based upon differences in melt index. According to
 DuPont, Surlyn.RTM. 8422, which is believed recently to have been
 redesignated as 8220 and 8240, offers the following general properties
 when compared to Surlyn.RTM. 8920, the stiffest, hardest of all on the low
 acid grades (referred to as "hard" ionomers in U.S. Pat. No. 4,884,814):

Size Specifications: Preferred Most Preferred
 Inner Core - Max. 1.250" 1.00"
 - Min. 0.500" 0.70"
 OuterCore - Max. 1.600" 1.570"
 - Min. 1.500" 1.550"
 Cover Thickness (Total)
 - Max. 0.090" 0.065"
 - Min. 0.040" 0.055"
 In a particularly preferred embodiment of the invention, the golf ball has
 a dimple pattern which provides coverage of 65% or more. The golf ball
 typically is coated with a durable, abrasion-resistant, relatively
 non-yellowing finish coat.
 The various cover composition layers of the present invention may be
 produced according to conventional melt blending procedures. Generally,
 the copolymer resins are blended in a Banbury type mixer, two-roll mill,
 or extruder prior to neutralization. After blending, neutralization then
 occurs in the melt or molten states in the Banbury mixer. Mixing problems
 are minimal because preferably more than 75 wt %, and more preferably at
 least 80 wt % of the ionic copolymers in the mixture contain acrylate
 esters and, in this respect, most of the polymer chains in the mixture are
 similar to each other. The blended composition is then formed into slabs,
 pellets, etc., and maintained in such a state until molding is desired.
 Alternatively, a simple dry blend of the pelletized or granulated resins
 which have previously been neutralized to a desired extent and colored
 masterbatch may be prepared and fed directly into the injection molding
 machine where homogenization occurs in the mixing section of the barrel
 prior to injection into the mold. If necessary, further additives such as
 an inorganic filler, etc., may be added and uniformly mixed before
 initiation of the molding process. A similar process is utilized to
 formulate the high acid ionomer resin compositions used to produce the
 inner cover layer. In one embodiment of the invention, a masterbatch of
 non-acrylate ester-containing ionomer with pigments and other additives
 incorporated therein is mixed with the acrylate ester-containing
 copolymers in a ratio of about 1-7 weight % masterbatch and 93-99 weight %
 acrylate ester-containing copolymer.
 The golf balls of the present invention can be produced by molding
 processes which include but are not limited to those which are currently
 well known in the golf ball art. For example, the golf balls can be
 produced by injection molding or compression molding the novel cover
 compositions around a wound or solid molded core to produce an inner ball
 which typically has a diameter of about 1.50 to 1.67 inches. The core,
 preferably of a dual core configuration, may be formed as previously
 described. The outer layer is subsequently molded over the inner layer to
 produce a golf ball having a diameter of 1.620 inches or more, preferably
 about 1.680 inches or more. Although either solid cores or wound cores can
 be used in the present invention, as a result of their lower cost and
 superior performance solid molded cores are preferred over wound cores.
 The standards for both the minimum diameter and maximum weight of the
 balls are established by the United States Golf Association (U.S.G.A.).
 In compression molding, the inner cover composition is formed via injection
 at about 380.degree. F. to about 450.degree. F. into smooth surfaced
 hemispherical shells which are then positioned around the core in a mold
 having the desired inner cover thickness and subjected to compression
 molding at 200.degree. to 300.degree. F. for about 2 to 10 minutes,
 followed by cooling at 50.degree. to 70.degree. F. for about 2 to 7
 minutes to fuse the shells together to form a unitary intermediate ball.
 In addition, the intermediate balls may be produced by injection molding
 wherein the inner cover layer is injected directly around the core placed
 at the center of an intermediate ball mold for a period of time in a mold
 temperature of from 50.degree. to about 100.degree. F. Subsequently, the
 outer cover layer is molded around the core and the inner layer by similar
 compression or injection molding techniques to form a dimpled golf ball of
 a diameter of 1.680 inches or more.
 After molding, the golf balls produced may undergo various further
 processing steps such as buffing, painting and marking as disclosed in
 U.S. Pat. No. 4,911,451.
 The resulting golf ball produced from the hard inner layer and the
 relatively softer, low flexural modulus outer layer provide for an
 improved multi-layer golf ball having a unique dual core configuration
 which provides for desirable coefficient of restitution and durability
 properties while at the same time offering the feel and spin
 characteristics associated with soft balata and balata-like covers of the
 prior art.
 The invention has been described with reference to the preferred
 embodiments. Obviously, modifications and alterations will occur to others
 upon a reading and understanding the preceding detailed description. It is
 intended that the invention be construed as including all such
 modifications and alterations in so far as they come within the scope of
 the appended claims or the equivalents thereof.