CA2356180A1 - Low spin golf ball - Google Patents

Abstract

A golf ball comprising a core having a Riehle compression of at least .075 a nd a cover having a Shore D hardness of at least 65, wherein the cover is comprised of at least one high acid ionomer resin comprising a copolymer of greater than 16 % by weight of an alpha, beta-unsaturated carboxylic acid, a nd an alpha olefin of which about 10 to about 90 % of the carboxyl groups of th e copolymer are neutralized with a metal cation.

Description

LOW SPIN GOLF BALL
This is a continuation-in-part of co-pending U.S.
Application No. 09/102,342 filed on June 22, 1998, which is a continuation of U.S. Application No. 08/716,016, filed September 19, 1996 (U.S. Patent No. 5,820,489); which, in turn, is a divisional of U.S.
Application No. 08/255,442, filed June 8, 1994; which is a continuation of U.S. Application No. 08/054,406 filed April 28, 1993 (U.S. Patent No.
5,368,304).
,o Field of the Invention The present invention relates to golf balls and, more particularly, to improved golf balls (two-piece, wound three-piece, etc.) balls having low spin rates. The improvement in the golf balls results from a combination of a softened core and a hard cover made from ,5 blends of one or more specific hard, high stiffness ionomers. The combination of a soft core and a hard cover leads to an improved golf ball having a lower than anticipated spin rate while maintaining the resilience and durability characteristics necessary for repetitive play.
In an additional embodiment of the invention, the spin rate zo is further reduced by decreasing the weight of the softened core andlor by increasing the thickness of the cover.
Backgiround of the Invention Spin rate is an important golf ball characteristic for both 25 the skilled and unskilled golfer. High spin rates allow for the more skilled golfer, such as PGA 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 _Z_ 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.
However, a high spin golf ball is not desirous by all golfers, particularly high handicap players who cannot intentionally control the spin of the ball. In this regard, less skilled golfers, have, among others, two substantial obstacles to improving their game: slicing and hooking.
,0 When a club head meets a ball, an unintentional side spin is often imparted which sends the ball off its intended course. The side spin reduces one's control over the ball as well as the distance the ball will travel. As a result, unwanted strokes are added to the game.
Consequently, while the more skilled golfer desires a high spin golf ball, a more efficient ball for the less skilled player is a golf ball that exhibits low spin properties. The low spin ball reduces slicing and hooking and enhances roll distance for the amateur golfer.
The present inventors have addressed the need for developing a golf ball having a reduced spin rate after club impact, 2o while at the same time maintaining durability, playability and resiliency characteristics needed for repeated use. The reduced spin rate golf ball of the present invention meets the rules and regulations established by the United States Golf Association (U.S.G.A.).
Along these lines, the U.S.G.A. has set forth five (5) 25 specific regulations that a golf ball must conform to. The U.S.G.A. rules require that a ball be no smaller than 1.680 inches in diameter.
However, notwithstanding this restriction, there is no specific limitation as to the maximum permissible diameter of a golf ball. As a result, a golf ball can be as large as desired so long as it is larger than 1.680 inches in diameter and so long as the other four (4) specific regulations are met.
The U.S.G.A. rules also require that balls weigh no more than 1.620 ounces, and that their initial velocity may not exceed 250 feet per second with a maximum tolerance of 2%, or up to 255 ft./sec.
Further, the U.S.G.A. rules state that a ball may not travel a distance greater than 280 yards with a test tolerance of 6% when hit by the U.S.G.A. outdoor driving machine under specific conditions.
It has been determined by the present inventors that the ,° combination of a relatively soft core (i.e. Riehle compression of about .075 to .115) and a hard cover (i.e. Shore D hardness of 65 or more) sign~cantly reduces the overall spin rate of the resulting golf ball. The inventors have also learned that an increase in cover thickness, and/or increasing the overall diameter of the resulting molded golf ball, further ,5 reduces spin rate.
Top-grade golf balls sold in the United States may be generally classified as one of two types: two-piece or three-piece balls.
The two-piece ball, exemplified by the balls sold by Spalding & Evenflo Companies, Inc. (the assignee of the present invention through its za wholly owned subsidiary, Lisco, Inc.) under the trademark TOP-FLITS, consists of a solid polymeric core and a separately formed outer cover.
The so-called three-piece baits, exemplified by the balls sold under the trademark TITLEIST by the Acushnet Company, consist of a liquid (e.g., TITLEIST TOUR 384) or solid (e.g., TITLEIST DT) center, elastomeric thread windings about the center, and a cover.
Spalding's two-piece golf balls are produced by molding a natural (balata) or synthetic (i.e. thermoplastic resin such as an ionomer resin) polymeric cover composition around a preformed polybutadiene (rubber) core. During the molding process, the desired dimple pattern is molded into the cover material. In order to reduce the number of coating steps involved in the finishing of the golf balls, a color pigment or dye and, in many instances, an optical brightener, are added directly to the generally "off white" colored polymeric cover composition prior to molding. By incorporating the pigment and/or optical brightener in the cover composition molded onto the golf ball core, this process eliminates the need for a supplemented pigmented painting step in order to produce a white or colored (notably orange, pink and yellow) golf ball.
,o With respect to multi-layered golf balls, Spalding is the leading manufacturer of two-piece golf balls in the world. Spalding manufactures over sixty (60) different types of two-piece balls which vary distinctly in such properties as playability (i.e. spin rate, compression, feel, etc.), travel distance (initial velocity, C.O.R., etc.), ,5 durability (impact, cut and weather resistance) and appearance (i.e.
whiteness, reflectance, yellowness, etc.) depending upon the ball's core, cover and coating materials, as well as the ball's surface configuration {i.e. dimple pattern). Consequently, Spalding's two-piece golf balls offer both the amateur and professional golfer a variety of performance Zo characteristics to suit an individual's game.
In regard to the specific components of a golf ball, although the nature of the cover can, in certain instances, make a significant contribution to the overall feel, spin (control), coefficient of restitution (C.O.R.) and initial velocity of a ball (see, for example, U.S.
25 Patent 3,819,768 to Molitor), the initial velocity of two-piece and three-piece balls is determined mainly by the coefficient of restitution of the core. The coefficient of restitution of the core of wound (i.e. three-piece) balls can be controlled within limits by regulating the winding tension and the thread and center composition. With respect to two-piece balls, the coefficient of restitution of the core is a function of the properties of the elastomer composition from which it is made.
The cover component of a golf ball is particularly influential in effecting the compression (feel), spin rates (control), distance (C.O.R.), and durability (i.e. impact resistance, etc.) of the resulting ball.
Various cover compositions have been developed by Spalding and others in order to optimize the desired properties of the resulting golf balls.
Over the last twenty (20) years, improvements in cover ,o and core material formulations and changes in dimple patterns have more or less continually improved golf ball distance. Top-grade golf balls, however, must meet several other important design criteria. To successfully compete in today's golf ball market, a golf ball should be resistant to cutting and must be finished well; it should hold a line in ,5 putting and should have good click and feel. In addition, the ball should exhibit spin and control properties dictated by the skill and experience of the end user. The present invention is directed to improved top-grade golf balls (two-piece and three-piece) having reduced spin rates.
The improved golf balls offer the less skilled golfer better control over 20 his or her shots and allow for greater distance.
In an alternative embodiment, the spin rate of the ball is further reduced by increasing the thickness of the cover and/or decreasing the weight and softness of the core. By increasing the cover thickness and/or the overall diameter of the resulting molded golf z5 ball, enhanced reduction in spin rate is observed.
With respect to the increased size of the ball, over the years golf ball manufacturers have generally produced golf balls at or around the minimum size and maximum weight specifications set forth by the U.S.G.A. There have, however, been exceptions, particularly in -b-connection with the manufacture of golf balls for teaching aids. For example, oversized, overweight (and thus unauthorized) golf balls have been on sale for use as golf teaching aids (see U.S. Patent 3,201,384 to Barber).
Oversized golf balls are also disclosed in New Zealand Patent 192,618 dated January 1, 1980, issued to a predecessor of the present assignee. This patent teaches an oversize golf ball having a diameter between 1.700 and 1.730 inches and an oversized core of resilient material (i.e. about 1.585 to 1.595 inches in diameter) so as to ,0 increase the coefFcient of restitution. Additionally, the patent discloses that the ball should include a cover having a thickness less than the cover thickness of conventional balls (i.e. a cover thickness of about 0.050 inches as opposed to 0.090 inches for conventional two-piece balls).
,5 In addition, it is also noted that golf balls made by Spalding in 1915 were of a diameter ranging from 1.630 inches to 1.710 inches. As the diameter of the ball increased, the weight of the ball also increased. These balls were comprised of covers made up of balata/gutta percha and cores made from solid rubber or liquid sacs and Zo wound with elastic thread.
Golf balls known as the LYNX JUMBO were also commercially available by Lynx in October, 1979. These balls had a diameter of 1.76 to 1.80 inches. It met with little or no commercial success. The LYNX JUMBO balls consisted of a core comprised of wound core and a cover comprised of natural or synthetic balata.
However, notwithstanding the enhanced diameters of these golf balls, none of these balls produced the enhanced spin reduction characteristics and overall playability, distance and durability properties of the present invention and/or fall within the regulations set forth by the U.S.G.A. An object of the present invention is to produce a U.S.G.A. regulation golf ball having improved low spin properties while maintaining the resilience and durability characteristics necessary for repetitive play.
5 These and other objects and features of the invention will be apparent from the following summary and description of the invention and from the claims.
,o Summaryr of the Invention The present invention is directed to improved golf balls having a low rate of spin upon club impact. The golf balls comprise a soft core and a hard cover. The hard cover can be sized to be larger than conventional diameters. The low spin rate enables the ball to ,5 travel a greater distance. In addition, the low spin rate provides the less skilled golfer with more control. This is because the low spin rate decreases undesirable side spin which leads to slicing and hooking.
The combination of a hard cover and a soft core provides for a ball having a lower than anticipated spin rate while maintaining high zo resilience and good durability.
The golf ball comprises a core and a cover. The core (which may be molded or wound) has a Riehle compression of at least 0.075, preferably 0.075 to about .115, and a PGA compression of about 45 to 85. The cover has a Shore, D hardness of at least 65.
25 , In an alternative embodiment, the resulting ball is larger than the standard 1.680 inch golf ball. Its diameter is in the range of about 1.680 to 1.800 inches, more likely in the range of about 1.700 to 1.800 inches, preferably in the range of 1.710 - 1.730 inches, and most preferably in the range of about 1.717 - 1.720 inches.

_g_ In a further embodiment, the cover thickness of the ball can vary. The cover thickness ranges from more than the standard 0.0675 inches up to about 0.130, preferably from about O.Ofi75 to about 0.1275 inches, more preferably in the range of about 0.0825 to 0.0925, and most preferably in the range of about 0.0860 to 0.0890 inches. The core is preferably of a standard size, roughly about 1.540 to 1.545 inches. In one embodiment, the core used in the present invention is a specially produced softened polybutadiene elastomeric solid core having a conventional diameter of about 1.540 to 1.545 ,o inches. The core is produced from a composition comprising a base elastomer selected from pofybutadiene and mixtures of polybutadiene with other elastomers, at least one metallic salt of an unsaturated carboxylic acid (a co-crosslinking agent), and free radical initiator (a co-crosslinking agent). In addition, a suitable and compatible modifying ,5 ingredient including, but not limited to metal activators, fatty acids, fillers, polypropylene powder and other additives may be included.
Of particular concern, only a limited amount of the metallic salt of an unsaturated carboxylic acid is included in the core compositions in order to produce the degree of core softness and 20 weight desired. In this regard, it is understood that when a larger overall ball is desired, the composition of the core is adjusted so that the molded finished ball falls within the weight parameters set forth by the U.S.G.A. Since the finished golf balls must still meet the U.S.G.A.
weight limitation of 1.620 ounces, the core component of the targer and 25 thicker covered balls are designed to be not only softer, but also lighter in weight.
in such circumstances, the specific gravity of the core is less than that of a standard core since the larger ball must weigh the same as a standard ball. The core generally weighs about 36 to 37 grams for an standard sized finished ball and about 33 to 34 grams for an oversized finished ball.
The core composition produces a softer molded core which still maintains the resilience (C.4.R.), compression (hardness) and durability characteristics required. In addition, in a further embodiment, a wound core can also be utilized. The overall core has a PGA compression of about 45 to 85, preferably in the range of about 70 - 80. Its Riehle compression is about 0.075 or more, preferably in the range of .075 to .115, and the resilience of the core is about .760 ,o to .780.
The cover is preferably comprised of a hard, high-stiffness ionomer resin, most preferably a metal cation neutralized high acid ionomer resin containing more than 16% carboxylic acid by weight, or blend thereof. The cover has a Shore D hardness of about 65 or ,5 greater.
With respect to the ionomeric cover composition of the invention, ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E.I. DuPont de zo Nemours & Company under the trademark "Surlyn~" and more recently, by the Exxon Corporation (see U.S. Patent No. 4,911,451) under the trademark "Escort" and the tradename "lotek", have become the materials of choice for the construction of golf ball covers over the traditional "balata" (trans-polyisoprene, natural or synthetic) rubbers.
lonomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacryfic acid or malefic acid. In some instances, an additional softening comonomer such as an acrylate can also be included to form a terpolymer. The pendent ionic groups in the WO 00/38790 PCTlUS99/17861 ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, magnesium, lithium, potassium, calcium, etc. are used to neutralize some portion of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e., improved durability, etc. for golf ball construction over balata.
The ionomeric resins utilized to produce cover compositions can be formulated according to known procedures such as those set forth in U. S. Patent No. 3,421,766 or British Patent No.
,0 963,380, with neutralization effected according to procedures disclosed in Canadian Patent Nos. 674,595 and 713,631, wherein the ionomer is produced by copolymerizing the olefin and carboxylic acid to produce a copolymer having the acid units randomly distributed along the polymer chain. Broadly, the ionic copolymer generally comprises one or more a-olefins and from about 9 to about 20 weight percent of a, ~3-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired.
At least about 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, zo potassium, zinc, calcium, magnesium, and the like) and exist in the ionic state. Suitable olefins for use in preparing the ionomeric resins include ethylene, propylene, butene-1, hexene-1 and the like.
Unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, a-chloroacrylic, crotonic, malefic, fumaric, itaconic acids, and the like. The 25 ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e., Escor~) and/or methacrylic (i.e., Surlyn~) acid. In addition, two or more types of ionomeric resins may be blended in to the cover compositions in order to produce the desired properties of the resulting golf balls.

The cover compositions which may be used in making the golf balls of the present invention are set forth in detail but not limited to those in copending U.S. Serial No. 07/776,803 filed October 15, 1991, and Serial No. 07/901,660 filed June 19, 1992, both incorporated herein by reference. In short, the cover material is comprised of hard, high stiffness ionomer resins, preferably containing relatively high amounts of acid (i.e., greater than 16 weight percent acid, preferably from about 17 to about 25 weight percent acid, and more preferably from about 18.5 to about 21.5 weight percent) and at least partially ,0 neutralized with metal ions (such as sodium, zinc, potassium, calcium, magnesium and the like). The high acid resins are blended and melt processed to produce compositions exhibiting enhanced hardness and coefficient of restitution values when compared to low acid ionomers, or blends of low acid ionomer resins containing 16 weight percent acid or ,5 less.
The preferred cover compositions are made from specific blends of two or more high acid ionomers with other cover additives which do not exhibit the processing, playability, distance and/or durability limitations demonstrated by the prior art. However, as more 2o particularly indicated below, the cover composition can also be comprised of one or more low acid ionomers so long as the molded covers exhibit a hardness of 65 or more on the Shore D scale.
Through the use of the softer cores and the hard cover, overall finished balls of the invention exhibit significantly lower spin 2s rates than conventional balls of equal size and weight. Further, reduction in spin are also produced by increasing the thickness of the cover and/or by decreasing the weight of the softened core.
As is apparent from the above discussions, two principal properties involved in golf ball performance are resilience and PGA

_12_ compression. The resilience or coefficient of restitution (COR) of a golf ball is 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 COR ("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.
COR, along with additional factors such as club head speed, club head mass, ball weight, ball size and density, spin rate, angle of trajectory and surface configuration (i.e., dimple pattern and ,0 area of dimple coverage) as well as environmental conditions (e.g.
temperature, moisture, atmospheric pressure, wind, etc.) generally determine the distance a 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 size, density and ,5 resilience (COR) of the ball and other factors. The initial 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 2o weight are set by the U.S.G.A., these are not factors of concern among golf ball manufacturers. The factors or determinants of interest with respect to improved distance are generally the coefficient of restitution (COR) and the surface configuration (dimple pattern, ratio of land area to dimple area, etc.) of the ball.
25 , The COR of solid core balls is a function of the composition of the core and of the cover. The core andlor cover may be comprised of one or more layers such as in multi-layer balls. 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, the center and cover of a wound core ball may also consist of one or more layers. The COR of the golf balls of the present invention is a function of the composition and physical properties of the core and cover layer materials such as flex modulus, hardness and particularly, their resilience, i.e. ability to quickly recover from a high impact deformation.
The coefficient of restitution is the ratio of the outgoing ,o velocity to the incoming velocity. In the examples of this application, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125 t 5 feet per second (fps) and corrected to 125 fps against a generally vertical, hard, flat steel plate and measuring the ball's incoming and outgoing velocity electronically.
,5 Speeds were measured with a pair of Oehler Mark 55 ballistic screens available from Oehler Research, Inc., P.O. Box 9135, Austin, Texas 78766, which provide a timing pulse when an object passes through them. The screens were separated by 36" and are located 25.25" and 61.25" from the rebound wall. The ball speed was measured by timing 2o 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 25 that frred it. The rebound wall is solid steel 2.0 inches thick.
As indicated above, the incoming speed should be 125 t fps but corrected to 125 fps. The correlation between COR and forward or incoming speed has been studied and a correction has been made over the t 5 fps range so that the COR is reported as if the ball had an incoming speed of exactly 125.0 fps.
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 United States Golf Association (U.S.G.A.). As mentioned 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 ,o 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.).
PGA compression is another important property involved in the performance of a golf ball. The compression of the ball can ,5 affect the playability of the ball on striking and the sound or "click"
produced. Similarly, compression can affect the "feel" of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.
Moreover, while compression itself has little bearing on the distance performance of a ball, compression can affect the playability 2~ of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influences 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 softer core. This is because at impact a hard core serves to 25 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 _15_ compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.
The term "compression" utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a 5 compressive load. For example, PGA compression indicates the amount of change in golf ball's shape upon striking.
In the past, PGA compression related to a scale of 0 to 200 given to a golf ball. The lower the PGA compression value, the softer the feel of the ball upon striking. In practice, tournament quality ,o balls have compression ratings around 70 -110, preferably around 80 to 100.
In determining PGA compression using the 0 - 200 scale, a standard force is applied to the external surface of the ball. A ball which exhibits no deflection (0.0 inches in deflection) is rated 200 and ,5 a ball which deflects 2/10th of an inch (0.2 inches) is rated 0. Every change of .001 of an inch in deflection represents a 1 point drop in compression. Consequently, a ball which deflects 0.1 inches (100 x .001 inches) has a PGA compression value of 100 (i.e., 200 - 100) and a ball which deflects 0.110 inches (110 x .001 inches) has a PGA
2~ compression of 90 {i.e., 200 -110).
In order to assist in the determination of compression, several devices have been employed by the industry. For example, PGA compression in determined by an apparatus fashioned in the form of a small press with an upper and lower anvil. The upper anvil is at 25 rest against a 200-pound die spring, and the lower anvil is movable through 0.300 inches by means of a crank mechanism. In its open position the gap between the anvils is 1.780 inches allowing a clearance of 0.100 inches for insertion of the ball. As the lower anvil is raised by the crank, it compresses the ball against the upper anvil, such compression occurring during the last 0.200 inches of stroke of the lower anvil, the ball then loading the upper anvil which in turn loads the spring. The equilibrium point of the upper anvil is measured by a dial micrometer if the anvil is deflected by the ball more than 0.100 inches (less deflection is simply regarded as zero compression) and the reading on the micrometer dial is referred to as the compression of the ball. In practice, tournament quality balls have compression ratings around 80 to 100 which means that the upper anvil was deflected a total of 0.120 to 0.100 inches.
,o An example to determine PGA compression can be shown by utilizing a golf ball compression tester produced by Atti Engineering Corporation of Newark, N.J. The value obtained by this tester relates to an arbitrary value expressed by a number which may range from 0 to 100, although a value of 200 can be measured as indicated by two ,5 revolutions of the dial indicator on the apparatus. The value obtained defines the deflection that a golf ball undergoes when subjected to compressive loading. The Atti test apparatus consists of a lower movable platform and an upper movable spring-loaded anvil. The dial indicator is mounted such that it measures the upward movement of the 20 springloaded anvil. The golf ball to be tested is placed in the lower platform, which is then raised a fixed distance. The upper portion of the golf ball comes in contact with and exerts a pressure on the springloaded anvil. Depending upon the distance of the golf ball to be compressed, the upper anvil is forced upward against the spring.
z5 ~ Alternative devices have also been employed to determine compression. For example, Applicant also utilizes a modified Riehle Compression Machine originally produced by Riehle Bros. Testing Machine Company, Phil., PA to evaluate compression of the various components (i.e., cores, mantle cover balls, finished balls, etc.) of the golf balls. The Riehle compression device determines deformation in thousandths of an inch under a fixed initialized load of 200 pounds.
Using such a device, a Riehle compression of 61 corresponds to a deflection under load of 0.061 inches.
Additionally, an approximate relationship between Riehle compression and PGA compression exists for balls of the same size.
It has been determined by Applicant that Riehle compression corresponds to PGA compression by the general formula PGA
compression = 160 - Riehle compression. Consequently, 80 Riehle ,o compression corresponds to 80 PGA compression, 70 Riehle corresponds to 90 PGA compression, and 60 PGA compression corresponds to 100 PGA compression. For reporting purposes, Applicant's compression values are usually measured as Riehle compression and converted to PGA compression.
,5 Furthermore, additional compression devices may also be utilized to monitor golf ball compression so long as the correlation to PGA compression is known. These devices have been designed, such as a Whitney Tester, to correlate or correspond to PGA compression through a set relationship or formula.
2o As used herein, "Shore D hardness" of a cover is measured generally in accordance with ASTM D-2240, except the measurements are made on the curved surface of a molded cover, rather than on a plaque. Furthermore, the Shore D hardness of the cover is measured while the cover remains over the core. When a 5 hardness measurement is made on a dimpled cover, Shore D hardness is measured at a land area of the dimpled cover.
In describing the components of the subject golf ball herein, the term "spherical" is used in conjunction with the shell (center).
It is understood by those skilled in the art that when referring to golf _18_ balls and their components, the term "spherical" includes surfaces and shapes which may have minor insubstantial deviations from the perfect ideal geometric spherical shape. In addition the inclusion of dimples on the exterior surface of the shell, to effect its aerodynamic properties, does not detract from its "spherical" shape for the purposes therein or in the art. Further the internal surface of the shell as well as the core may likewise incorporate intentionally designed patterns and still be considered "spherical" within the scope of this invention.
The rotational moment of inertia of a golf ball is the ,o resistance to change in spin of the ball and is conventionally measured using an "Inertia Dynamics Moment of Inertia Measuring Instrument".
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter.
It should, however, be understood that the detailed description and ,5 specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
2o Brief Description of the Drawings The following is a brief description of the drawings which are present for the purpose of illustrating the invention and not for purposes of limiting the same.
Fig. 1 illustrates a partially broken-away view of the z5 improved golf ball of the present invention wherein D is the diameter of the ball; C is the diameter of the core and T is the thickness of the cover.

Detailed Description of the Invention The present invention relates to the development of a golf ball having a low spin rate as a result of combining a relatively soft core and a hard cover. Such a lower spin rate after club impact contributes to straighter shots when the ball is mis-hit, greater efficiency in flight, and a lesser degree of energy loss on impact with the ground, adding increased roll or distance.
Further, by increasing the diameter of the overall ball of the present invention beyond the U.S.G.A. minimum of 1.680 inches in ,o an additional embodiment, the spin rate is still further decreased by up to around 500 r.p.m. or more upon being hit with a No. 9 iron traveling at a speed of 105 feet per second (fps). In this embodiment of the invention, the ball, even though of larger diameter, uses substantially the same size core as a standard golf ball, the difference in size is ,5 provided by the additional thickness in the cover of the ball. This larger, low spin ball produces even greater control and flight efficiency than the standard size ball embodiment of the present invention.
Notwithstanding the overall size differences of the various embodiments of the present invention, the core of the present invention 2o is relatively soft and of similar size. It has a Riehle compression of about 0.075 or more, preferably about 0.075 to about 0.115, and a relatively low PGA compression of about 40 to 85, preferably about 70-80.
The specially produced core compositions and resulting 25 molded cores of the present invention are manufactured using relatively conventional techniques. In this regard, the core compositions of the invention may 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 composition, cis-polybutadiene is preferably employed, or a blend of cis-polybutadiene with other elastomers 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. Along this line, it has been found that the high cis-polybutadiene manufactured and sold by Shell Chemical Co., Houston, ,o Texas, under the tradename Cariflex BR-1220, and the polyisoprene available from Muehlstein, H & Co., Greenwich, Connecticut under the designation "SKI 35" are particularly well suited.
The unsaturated carboxylic acid component of the core composition (a co-crosslinking agent) is the reaction product of the ,5 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.
Zo 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 15 to about 25, and preferably from about 17 25 to 'about 21 parts by weight of the carboxylic acid salt, such as zinc diacrylate, is included in the core composition. The unsaturated carboxylic acids and metal salts thereof are generally soluble in the elastomeric base, or are readily dispersible.
The free radical initiator included in the core composition is any _2~_ known polymerization initiator (a co-crosslinking 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 crosslinking 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 ,0 readily commercially available are conveniently used in the present invention, generally in amounts of from about 0.1 to about 10.0 and preferably in amounts of from about 0.3 to about 3.0 parts by weight per each 100 parts of elastomer.
Exemplary of suitable peroxides for the purposes of the ,5 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 2o and the particular initiators employed.
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, Illinois. In this regard Luperco 230 XL and Trigonox 17/40 are 25 comprised of n-butyl 4,4-bis (butylperoxy) valerate; and, Luperco 231 XL and Trigonox 29/40 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 29/40 is about 129 °C.

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, and diisocyanates and polypropylene powder resin. For example, Papi 94, a polymeric diisocyanate, commonly available from Dow Chemical Co., Midland, Ml., 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 acts as a moisture scavenger. In addition, it has been found that the addition of a polypropylene powder resin ,o results in a core which is too hard (i.e. exhibits low compression) and thus allows for a reduction in the amount of crosslinking agent utilized to soften the core to a normal or below normal compression.
Furthermore, because polypropylene powder resin can be added to core composition without an increase in weight of the molded ,5 core upon curing, the addition of the polypropylene powder allows for the addition of higher specific gravity fillers, such as mineral fillers.
Since the crosslinking agents utilized in the polybutadiene core compositions are expensive andlor the higher specific gravity fillers are relatively inexpensive, the addition of the polypropylene powder resin 2o substantially lowers the cost of the golf ball cores while maintaining, or lowering, weight and compression.
The polypropylene (C3H5) powder suitable for use in the present invention has a specific gravity of about 0.90 glcm3, a melt flow rate of about 4 to about 12 and a particle size distribution of greater 25 than 99% through a 20 mesh screen. Examples of such polypropylene powder resins include those sold by the Amoco Chemical Co., Chicago, I(iinois, under the designations "6400 P", "7000 P" and "7200 P".
Generally, from 0 to about 25 parts by weight polypropylene powder per each 100 parts of elastomer are included in the present invention.

Various activators may also be included in the compositions of the present invention. For example, zinc 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.
Moreover, filler-reinforcement agents may be added to the composition of the present invention. Since the specific gravity of polypropylene powder is very low, and when compounded, the polypropylene powder produces a lighter molded core, when ,o polypropylene is incorporated in the core compositions, relatively large amounts of higher gravity fillers may be added so long as the specific core weight limitations are met. Additional benefits may be obtained by the incorporation of relatively large amounts of higher specific gravity, inexpensive mineral fillers such as calcium carbonate. Such fillers as ,5 are incorporated into the core compositions should be in finely divided form, as for example, in a size generally less than about 30 mesh and preferably less than about 100 mesh U.S. standard size. The amount of additional filler included in the core composition is primarily dictated by weight restrictions and preferably is included in amounts of from Zo about 10 to about 100 parts by weight per 100 parts rubber.
The preferred fillers are relatively inexpensive and heavy and serve to lower the cost of the ball and to increase the weight of the ball to closely approach the U.S.G.A. weight limit of 1.620 ounces.
However, if thicker cover compositions are to be applied to the core to 25 produce larger than normal (i.e. greater than 1.680 inches in diameter) balls, use of such fillers and modifying agents will be limited in order to meet the U.S.G.A. maximum weight limitations of 1.620 ounces.
Exemplary fillers include mineral fillers such as limestone, silica, mica, barytes, calcium carbonate, or clays. Limestone is ground calciumlmagnesium carbonate and is used because it is an inexpensive, heavy filler.
As indicated, ground flash filler may be incorporated and is preferably 20 mesh ground up center stock from the excess flash from compression molding. it lowers the cost and may increase the hardness of the ball.
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 ,0 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 ,5 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).
It is preferred that the core compositions include stearic acid as the fatty acid adjunct in an amount of from about 2 to about 5 2o parts by weight per 100 parts of rubber.
Diisocyanates may also be optionally included in the core compositions 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 is 4,4'-diphenylmethane dii~socyanate and other polyfunctional isocyanates know to the art.
Furthermore, the dialkyl tin difatty acids set forth in U.S.
Patent No. 4,844,471, the dispersing agents disclosed in U.S. Patent No. 4,838,556, and the dithiocarbamates set forth in U.S. Patent No.
4,852,884 may also be incorporated into the polybutadiene WO 00/38790 PC'T/US99/17861 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.
The core compositions 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, 15 to 25 parts by weight of at least one metallic salt of an unsaturated carboxylic acid, and 0.1 to 10 parts by weight of a free radical initiator.
,o As indicated above, additional suitable and compatible modifying agents such as particulate polypropylene resin, fatty acids, and secondary additives such as Pecan shell flour, ground flash (i.e.
grindings from previously manufactured cores of substantially identical construction), barium sulfate, zinc oxide, etc. may be added to the core ,5 compositions to adjust the weight of the ball as necessary in order to have the finished molded ball (core, cover and coatings) to closely approach the U.S.G.A. weight limit of 1.620 ounces.
In producing golf ball cores utilizing the present compositions, the ingredients may be intimately mixed using, for Zo example, 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 as follows.
The elastomer, polypropylene powder resin (if desired), 25 fillers, zinc salt, metal oxide, fatty acid, and 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 initiator and diisocyanate are then added and the PG"T/US99/17861 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.
The sheet is rolled into a "pig" and then placed in a Barwell preformer and slugs are produced. The slugs are then subjected to compression molding at about 320°F for about 14 minutes.
After molding, the molded cores are cooled, the cooling effected at room temperature for about 4 hours or in cold water for about one hour.
The molded cores are subjected to a centerless grinding operation ,o whereby a thin layer of the molded core is removed to produce a round core having a diameter of 1.540 to 1.545 inches. Alternatively, the cores are used in the as-molded state with no grinding needed to achieve roundness.
The mixing is desirably conducted in such a manner that ,5 the composition does not reach incipient polymerization temperatures during the blending of the various components.
Usually the curable component of the composition will be cured by heating the composition at elevated temperatures on the order of from about 275°F to about 350°F, preferably and usually from about 20 290°F to about 325°F, with molding of the composition effected simultaneously with the curing thereof. The composition can be formed into a core structure by any one of a variety of molding techniques, e.g.
injection, compression, or transfer molding. When the composition is cured by heating, the time required for heating will normally be short, z5 generally from about 10 to about 20 minutes, depending upon the particular curing agent used. Those of ordinary skill in the art relating to free radical curing agents for polymers are conversant with adjustments of cure times and temperatures required to effect optimum results with any specific free radical agent.

After molding, the core is removed from the mold and the surface thereof, preferably 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, and the like. Preferably, surface treatment is effected by grinding with an abrasive wheel.
In addition to using solid molded cores, wound cores may also be incorporated in the golf balls of the present invention. Such wound cores would include a generally spherical center and a rubber ,0 thread layer, or windings, enclosing the outer surface of the center.
In this regard, the generally spherical center of the wound cores may be a solid center or a liquid center. The solid center can consist of one or more layers. For example, the solid center can comprise a molded polybutadiene rubber sphere which, although ,5 smaller in size, is of similar construction to the molded cores in the two-piece molded golf balls described above.
Suitable solid centers used in the invention are not particularly limited to, but include those made of vulcanized rubber.
Such solid centers may be prepared by adding to butadiene rubber, zo additives such as vulcanizing agents, accelerators, activating agents, fillers, modifiers and aids and then subjecting the mixture to vulcanization and molding.
The solid center (whether of single unitary construction or of multi-layers) generally is from 1 to 1.5 inches in diameter, preferably Z5 1.0625 to 1.42 inches, with a weight of 15 grams to 36 grams, preferably 16.5 to 30 grams.
Alternatively, a liquid center can be incorporated into the wound core of the present invention. The liquid center consists of a hollow spherical bag or sack of conventional vulcanized rubber filled _28_ with a liquid, paste or gel. Examples of such a liquid include water, glycerin, sugar-water solutions, corn-syrup, saline solutions, oils, etc.
and/or combinations thereof. Examples of pastes can be produced by adding clay, sodium sulfate, barytes, barium sulfate to a minor amount of ethylene glycol in water. Examples of suitable gels include hydrogels, cellulose gels, water gels, etc. The specific gravity of the liquid is, in general, .6 to 3 and the specific gravity of the paste is from .6 to 3 and the gels from .6 to 3. The bag or sack is, in general, from .05" to .150" in thickness, preferably 0.08 to .105 inches in thickness.
,o The liquid center generally is from 1 to 1.25 inches in diameter, preferably 1.0625 to 1.14 inches, with a weight of 5.5 to 25.5 grams, preferably 15 to 21 grams.
The wound core is formed by winding conventional thread rubber around the outer periphery of the solid or liquid center. The ,s thread rubber may include, for example, those prepared by subjecting natural rubber, or a blend of natural rubber and polyisoprene rubber to vulcanization and molding. The winding process is under high tension to produce a threaded layer over the solid or liquid center.
Conventional techniques may be employed in winding the thread 2o rubber and known compositions may be used. Although the thread rubber is not limited with respect to specifrc gravity, dimension and gage, it usually has a specific gravity of .9 to 1.1, a width of .047 to .094 and a gage of .012 to .026 inches.
The rubber thread layer has a radial thickness of .010 to 25 .315 inches and comprises a wound core having an outer diameter of 1.52 to 1.63 inches. The overall weight of the wound core is 33 to 44 grams, preferably 35 to 39 grams.
The core is converted into a golf ball by providing at least one layer of covering material thereon, ranging in thickness from about 0.070 to about 0.130 inches and preferably from about 0.0675 to about 0.1275 inches.
The cover has a Shore D hardness of 65 or greater. Its composition includes a hard, high stiffness preferably high acid ionomer s such as that sold by E.I. DuPont de Nemours & Company under the trademark "Surlyn~" and by Exxon Corporation under the trademark "Escor~" or tradename "lotek", or blends thereof. In addition to the Surlyn~ and Escor~ or lotek ionomers, the cover may comprise any ionomer which either alone or in combination with other ionomers ,o produces a molded cover having a Shore D hardness of at least 65.
These include lithium ionomers or blends of ionomers with harder non-ionic polymers such as nylon, polyphenylene oxide and other compatible thermoplastics. As briefly mentioned above, examples of cover compositions which may be used are set forth in detail in ,5 copending t7.S. Serial No. 071776,803 filed October 15, 1991, and Serial No. 07/901,660 filed June 19, 1992, both incorporated herein by reference. Of course, the cover compositions are not limited in any way to those compositions set forth in said copending applications.
The high acid ionomers suitable for use in the present 20 invention 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.
25 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 10-75%, preferably 30-70%) by the metal ions. Each of the high acid ionomer resins included in the 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 cover composition preferably includes a high acid ionomeric resin and 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 are currently available. In this regard, the high acid ionomeric resins ,0 available from E.I. DuPont de Nemours Company under the trademark "Surlyn~", and the high acid ionomer resins available from Exxon Corporation under the trademark "Escor~" or tradename "lotek" are examples of available high acid ionomeric resins which may be utilized in the present invention.
,5 The high acid ionomeric resins available from Exxon under the designation "Escor~" and or "lotek", are somewhat similar to the high acid ionomeric resins available under the "Surlyn~" trademark.
However, since the Escor~/lotek ionomeric resins are sodium or zinc salts of polyethylene acrylic acid} and the "Surlyn~" resins are zinc, zo sodium, magnesium, etc. salts of polyethylene 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~ AD-8422 (sodium cation), Surlyn~ 8162 (zinc cation), 25 Surlyn~ SEP-503-1 (zinc cation), and Surlyn~ SEP-503-2 (magnesium ration). According to DuPont, all of these ionomers contain from about 18.5 to about 21.5% by weight methacrylic acid.
More particularly, Surlyn~ 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~ AD-8422 offers the following general properties when compared to Surlyn~ 8920 the stiffest, hardest of all on the tow acid grades (referred to as "hard"
ionomers in U.S. Patent No. 4,884,814):
LOW ACID HIGH ACID

(15 wt% Acid)(>20 wt% Acid) SURLYN~ SURLYN~ SURLYN~

,0 8920 8422-2 8422-3 IONOMER

Cation Na Na Na Melt Index 1.2 2.8 1.0 Sodium, Wt% 2.3 1.9 2.4 ~s Base Resin MI 60 60 60 MP'. C 88 86 85 FP, C 47 48.5 45 COMPRESSION MOLDINGz Tensile Break, psi 4350 4190 5330 z5 Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod, K psi 53.2 76.4 88.3 Shore D

3o hardness 66 67 68 'DSC second heat, 10°Clmin heating rate.
2Samples compression molded at 150°C annealed 24 hours at 60°C.
8422-2, -3 were homogenized at 190°C before molding.
In comparing Surlyn~ 8920 to Surlyn~ 8422-2 and Surlyr~ 8422-3, it is noted that the high acid Surlyn~ 8422-2 and 8422-3 ionomers have a higher tensile yield, lower elongation, slightly higher Shore D hardness and much higher flexural modulus. Surlyn~ 8920 contains 15 weight percent methacrylic acid and is 59% neutralized with sodium.
In addition, Surlyn~ SEP-503-1 (zinc ration) and Surlyn~
SEP-503-2 (magnesium ration) are high acid zinc and magnesium versions of the Surlyn~ AD 8422 high acid ionomers. When compared to the Surlyn~ AD 8422 high acid ionomers, the Surlyn SEP-503-1 and SEP-503-2 ionomers can be defined as follows:
Surlyn~ lonomer Ion Melt Index Neutralization AD 8422-3 Na 1.0 45 ,o SEP 503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43 Furthermore, Surlyn~ 8162 is a zinc ration ionomer resin ,5 containing approximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acid copolymer that has been 30-70% neutralized. Surlyn~
8162 is currently commercially available from DuPont.
Examples of the high acid acrylic acid based ionomers suitable for use in the present invention include the Escor~ or lotek 2o high acid ethylene acrylic acid ionomers produced by Exxon. In this regard, Escort or lotek 959 is a sodium ion neutralized ethylene-acrylic acid copolymer. According to Exxon, loteks 959 and 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc 25 ions, respectively. The physical properties of these high acid acrylic acid based ionomers are as follows:
PR~PERTY ESCOR~ (IOTEK)ESCOR~ (IOTEK) Melt index, gN0 2.0 1.8 min so Cation Sodium Zinc Melting Polnt, 172 174 F

Vicat Softening 130 131 Point, F

Tensile ~ Break, 4600 3500 psi Elongation ~ Break,325 430 %

as Hardness, Shore55 57 D

Flexural Modulus, 66,000 27,000 psi Furthermore, as a result of the development by the inventors of a number of new high acid ionomers neutralized to various extents by several different types of metal cations, such as by manganese, lithium, potassium, calcium and nickel cations, several new high acid ionomers and/or high acid ionomer blends besides sodium, zinc and magnesium high acid ionomers or ionomer blends are now available for golf ball cover production. It has been found that these new cation neutralized high acid ionomer blends produce cover compositions exhibiting enhanced hardness and resilience due to ,o synergies which occur during processing. Consequently, the metal cation neutralized high acid ionomer resins recently produced can be blended to produce substantially harder covered golf balls having higher C.O.R.'s than those produced by the low acid ionomer covers presently commercially available.
,5 More particularly, several new metal cation neutralized high acid ionomer resins have been produced by the inventors by neutralizing, to various extents, high acid copolymers of an alpha-olefin and an alpha, beta-unsaturated carboxylic acid with a wide variety of different metal cation salts. This discovery is the subject matter of U.S.
20 Application Serial No. 901,680, incorporated herein by reference. It has been found that numerous new metal cation neutralized high acid ionomer resins can be obtained by reacting a high acid copolymer (i.e.
a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably 25 about 20 weight percent acid), with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. from about 10% to 90%).
The base copolymer is made up of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, a softening comonomer can be included in the copolymer. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons.' Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, malefic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.
The softening comonomer that can be optionally included in the invention may be selected from the group consisting of vinyl ,o esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms, vinyl ethers wherein the alkyl groups contains 1 to 10 carbon atoms, and alkyl acrylates or methacrylates wherein the alkyl group contains 1 to 10 carbon atoms. Suitable softening comonomers include vinyl acetate, methyl acrylate, methyl methacrylate, ethyl ,5 acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, or the like.
Consequently, examples of a number of copolymers suitable for use to produce the high acid ionomers included in the present invention include, but are not limited to, high acid embodiments Zo of an ethylenelacrylic acid copolymer, an ethylenelmethacrylic acid copolymer, an ethylenelitaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylenelmethacrylic acidlvinyl acetate copolymer, an ethylenelacrylic acid/vinyl alcohol copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic 25 acid, from about 30 to about 83% by weight ethylene and from 0 to about 40% by weight of a softening comonomer. Preferably, the copolymer contains about 20% by weight unsaturated carboxylic acid and about 80% by weight ethylene. Most preferably, the copolymer contains about 20% acrylic acid with the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic copolymers which are commercially available from The Dow Chemical Company, Midland, Michigan, under the "Primacor"
designation. These high acid base copolymers exhibit the typical properties set forth below in Table 1.

Typical Properties of Primacor Ethylene-Acrylic Acid Copolymers ,o GRADE PERCENTDENSITY,MELT TENSILEFLEXURALM CAT SHORE
ACID glcc INDEX, Y0. MODULUSSOFT D
/10min ST ( si) PT HARDNESS
< si) (C) 5980 20.0 0.958 300.0 - 4800 43 50 5990 20.0 0.955 1300.0 650 2600 40 42 ,s 5990 20.0 0.955 1300.0 650 3200 40 42 5981 20.0 0.960 300.0 900 3200 46 48 5981 20.0 0.960 300.0 900 3200 46 48 5983 20.0 0.958 500.0 850 3100 44 45 5991 20.0 0.953 2600.0 635 2600 38 40 zo 'The Melt Index values are obtained according to ASTM D-1238, at 190°C.
Due to the high molecular weight of the Primacor 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more 25 preferred grade utilized in the invention.
The metal cation salts utilized in the invention are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the high acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, 0 sodium, potassium, nickel, magnesium, and manganese.
Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate.
Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dehydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium s acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.
The new metal ration neutralized high acid ionomer resins ,o are produced by reacting the high acid base copolymer with various amounts of the metal ration salts above the crystalline melting point of the copolymer, such as at a temperature from about 200° F to about 500° F, preferably from about 250° F to about 350° F
under high shear conditions at a pressure of from about 10 psi to 10,000 psi. Other well ,s known blending techniques may also be used. The amount of metal ration salt utilized to produce the new metal ration neutralized high acid based ionomer resins is the quantity which provides a sufficient amount of the metal rations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of 20 neutralization is generally from about 10% to about 90%.
As indicated below in Table 2, more specifically in Example 1 in U.S. Application Serial No. 901,680, a number of new types of metal ration neutralized high acid ionomers can be obtained from the above indicated process. These include new high acid 25 ionomer resins neutralized to various extents with manganese, lithium, potassium, calcium and nickel rations.. In addition, when a high acid ethylene/acrylic acid copolymer is utilized as the base copolymer component of the invention and this component is subsequently neutralized to various extents with the metal ration salts producing acrylic acid based high acid ionomer resins neutralized with cations such as sodium, potassium, lithium, zinc, magnesium, manganese, calcium and nickel, several new cation neutralized acrylic acid based high acid ionomer resins are produced.

Melt Shore Formulation Cation Neutralization Index C.O.R. D
No. Salt Hardness 1(NaOH) 6.98 67.5 0.9 .804 71 2(NaOH) 5.66 54.0 2.4 .808 73 ,0 3(NaOH) 3.84 35.9 12.2 .812 69 4(NaOH) 2.91 27.0 17.5 .812 (brittle) 5(MnAc) 19.6 71.7 7.5 .809 73 6(MnAc) 23.1 88.3 3.5 .814 77 7(MnAc) 15.3 53.0 7.5 .810 72 ~s 8(MnAc) 26.5 106 0.7 .813 (brittle) 9(LiOH) 4.54 71.3 0.6 .810 74 10(LiOH) 3.38 52.5 4.2 .818 72 11(LiOH) 2.34 35.9 18.6 .815 72 12(KOH) 5.30 36.0 19.3 Broke 70 zo 13(KOH) 8.26 57.9 7.18 .804 70 14(KOH) 10.7 77.0 4.3 .801 67 15(ZnAc) 17.9 71.5 0.2 .806 71 16(ZnAc) 13.9 53.0 0.9 .797 69 17(ZnAc) 9.91 36.1 3.4 .793 67 zs 18~(MgAc) 17.4 70.7 2.8 .814 74 19(MgAc) 20.6 87.1 1.5 .815 76 20(MgAc) 13.8 53.8 4.1 .814 74 Controls: 50150 Blend of loteks 800017030 C.O.R.=.810165 Shore D Hardness DuPont High Acid Surlyn~ 8422 (Na) C.O.R.=.811170 Shore D Hardness DuPont High Acid Surlyn~ 8162 (Zn) C.O.R.=.807165 Shore D Hardness Exxon High Acid lotek EX-960 (Zn) C.O.R.=.796165 Shore D Hardness '° TABLE 2 (continue ~ % ~ oho Melt Formulation Index C.O.R.
No. Cation Salt Neutra~

23(Mg0) 2.91 53.5 2.5 .813 24(Mg0) 3.85 71.5 2.8 .808 25(Mg0) 4.76 89.3 1.1 .809 26(Mg0) 1.96 35.7 7.5 .815 zo Control for Formulations 23-26 is 50150 lotek 800017030, C.O.R.=.814, Formulation 26 C.O.R.
was normalized to that control accordingly TABLE 2 (continued) - ~ ono ~ ono Melt Formulation No. CatiJ Neutralization index C.O.R. Shore D
Hardnes s 27(NiAc) 13.04 61.1 0.2 .802 71 28(NiAc) 10.71 48.9 / 0.5 .799 72 so 29(NiAc) 8.26 36.7 1.8 .796 69 30(NiAc) 5.66 24.4 7.5 .786 Control for Formulation Nos. 27-30 is 50150 lotek 8000!7030, C.O.R.=.807 When compared to low acid versions of similar cation neutralized ionomer resins, the new metal cation neutralized high acid ionomer resins exhibit enhanced hardness, modulus and resilience characteristics. These are properties that are particularly desirable in a number of thermoplastic fields, including the field golf ball manufacturing.
When utilized in golf ball cover construction, it has been found that the new acrylic acid based high acid ionomers extend the range of hardness beyond that previously obtainable while maintaining the beneficial properties (i.e. durability, click, feel, etc.) of the softer low acid ionomer covered balls, such as balls produced utilizing the low acid ionomers disclosed in U.S. Patent Nos. 4,884,814 and 4,911,451, and the recently produced high acid blends disclosed in U.S. Application ,o Serial No. 776,803.
Moreover, as a result of the development of a number of new acrylic acid based high acid ionomer resins neutralized to various extents by several different types of metal cations, such as manganese, lithium, potassium, calcium and nickel cations, several new ionomers or ,5 ionomer blends are now available for golf ball production. By using these high acid ionomer resins harder, stiffer golf balls having higher C.O.R.s, and thus longer distance, can be obtained.
As will be further noted in the Examples below, other ionomer resins may be used in the cover compositions, such as low Zo acid ionomer resins, so long as the molded cover produces a Shore D
hardness of 65 or more. Properties of some of these low acid ionomer resins are provided in the following table:
Ti~ical Properties of Low Acid Escort (Iotek~
Ionomers zs Resin ASTM
Properties Method Units 4000 4010 8000 Cation type zinc zinc sodium sodium ao Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 Density D-1505 kg/m3 963 963 954 Melting Point D-3417 C 90 90 90 87.5 Crystallization Point D-3417 C 62 64 56 Vicat Softening 1o Point D-1525 C 62 63 61 Weight Acrylic Acid 16 -- 11 - -of Acid Groups 30 -- 40 Cation Neutralized zo Plaque ASTM

Properties Method Units 4000 4010 8000803'J

s (3 mm thick, compression molded) Tensile at ,o Break D-638 MPa 24 26 36 3Z.5 Yield point D-638 MPa none none 21 21 Elongation at ,s break D-638 % 395 420 350 41D

1% Secant modulus D-638 MPa 160 160 300 3yJ

Zo Shore Hardness D D-2240 -- 55 55 61 58 Resin ASTM

2s Properties Method Units 8030 7010 7020 Cation type sodium z~
zinc zinc Melt Index D-1238 g/10 min. 2.8 0.8 1.5 2.5 Density D-1505 kg/m3 960 960 960 Melting Point D-3417 oC 87.5 90 90 ao Crystallization Point D-3417 aC 55 -- --Vicat Softening 45 Point D-1525 aC 67 60 63 62.5 %Weight Acrylic Acid -- -- --of Acid Groups Cation Neutralized -- -- --Plaque ASTM
Method Units 8030 7010 i es Propert (3 mm thick, compression ,o molded) Tensile at Break D-638 MPa 2 ~5 Yield Point ~ D-638 MPa 23 none none Elongation at' Break D-638 % 395 500 zo 1% Secant modulus D-638 MPa 390 --Shore Hardness ~o In addition to the above noted ionomers, compatible additive materials may also be added to produce the cover 35 compositions of the present invention. These additive materials include dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, NJ), and pigments, i.e. white pigments such as titanium dioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, as well as fluorescent pigments. As indicated in U.S. Patent 40 4,884,814, the amount of pigment and/or dye used in conjunction with the polymeric cover composition depends on the particular base ionomer mixture utilized and the particular pigment andlor dye utilized.

The concentration of the pigment in the polymeric cover composition can be from about 1 % to about 10% as based on the weight of the base ionomer mixture. A more preferred range is from about 1 % to about 5%
as based on the weight of the base ionomer mixture. The most preferred range is from about 1 % to about 3% as based on the weight of the base ionomer mixture. The most preferred pigment for use in accordance with this invention is titanium dioxide.
Moreover, since there are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added ,0 to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.
In addition, it is within the purview of this invention to add ,5 to the cover compositions of this invention compatible materials which do not affect the basic novel characteristics of the composition of this invention. Among such materials are antioxidants (i.e. Santonox R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening 2° agents, such as plasticizers, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.
Furthermore, optical brighteners, such as those disclosed in U.S. Patent No. 4,679,795, may also be included in the cover 25 composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Uvitex OB as sold by the Ciba-Geigy Chemical Company, Ardsley, N.Y. Uvitex OB is thought to be 2,5-Bis(5-tert-butyl-2-benzoxazoly)thiophene. Examples of other optical brighteners suitable for use in accordance with this invention are as follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure EGM is thought to be 7-(2n-naphthol(1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-2062 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative, Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn., is thought to be 4,4-Bis(-benzoxaczoly) stilbene. The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical brighteners for use in accordance with this invention.
° Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.
The percentage of optical brighteners which can be used ,5 in accordance with this invention is from about 0.01 % to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about .020% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.
Generally, the additives are admixed with a ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the 25 copolymer blends.
The above cover compositions, when processed according to the parameters set forth below and combined with soft cores at thicknesses defined herein to produce covers having a Shore D
hardness of 65, provide golf balls with reduced spin ratio. It is noted, however, that the high acid ionomer resins provide for more significant reduction in spin rate than that observed for the low acid ionomer resins.
The cover compositions and balls of the present invention 5 may be produced according to conventional melt blending procedures.
In this regard, the ionomeric resins are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state ,o until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color 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 ,5 inorganic filler, etc., may be added and uniformly mixed before initiation of the molding process.
Moreover, golf balls of the present invention can be produced by molding processes currently well known in the golf ball art.
Specifically, the golf balls can be produced by injection molding or 2a compression molding the novel cover compositions about the soft cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. In an additional embodiment of the invention, larger molds are utilized to produce the thicker covered oversized golf balls. As indicated, the golf balls of the present invention 25 can be produced by forming covers consisting of the compositions of the invention around the softer cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380°F to about 450°F into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200-300°F for 2-10 minutes, followed by cooling at 50-70°F
for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50°F to about 100°F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Patent No. 4,911,451.
,o The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.
Examale 1 Using the ingredients tabled below, golf ball cores having a finished diameter of about 1.540 to about 1.545 inches were produced by compression molding and subsequent removal of a surface layer by grinding. Each core was formulated using 100 parts elastomer (rubber).
In the formulations, the amounts of remaining ingredients are expressed in parts by weight, and the weight, degrees of coefficient of restitution and compression (both Riehle and PGA) achieved are set forth below.
The data for these examples are the averages for twelve cores which 25 were produced for each example. The properties of the molded cores produced from each formulation were measured according to the parameters set forth above.
The following core formulations were prepared according WO 00/38?90 PCT/US99/17861 to the methods set forth above:
CORE
COMPOSITIONS

In4redients A B C D

s BR-1220' 100 100 100 100 Zinc Diacrylate 18 20 37 26 Ground Flash 17 20 20 17 Zinc Oxide 6 6 6 6 Limestone 7 25 15 --,o Zinc Stearate 15 20 20 15 6400 Polypropylene210 -- -- 10 Trigonox 17/403 1.5 1.5 1.5 1.5 Papi 944 0.5 0.5 0.5 0.5 ,s Molded Core A B C D
Properties Core Diameter 1.541 1.542 1.543 1.542 (in.) Weight (grams) 33.7 36.5 36.8 33.8 Compression (Riehle/PGA) 87/73 83/77 64196 74/86 C.O.R.(e) .773 .782 .802 .787 zo 1BR-1220 is a polybutadiene manufactured and sold by Shell Chemical Co., Houston, Texas.
26400 P. is a powdered polypropylene available from Amco Chemical Co., Chicago, Illinois.
2s 3Trig 17/40 is a peroxide manufactured and sold by Akzo Chemie, Chicago, Illinois (one hour half life is at 129°C>.
'Papi 94 is a polymeric diisocynanate available from Dow Chemical Co., Midland, Michigan.
so As noted by the above indicated data, core formulations A and B produce softer cores. Formulation A is appropriate for a molded ball having an overall diameter of about 1.720 inches (i.e., 35 1.717"). It has less filler, hence a lower specific gravity, than formulation B which is appropriate for a smaller ball, one having a diameter of about 1.680 inches. Formulations C and D are for conventional harder cores. Formulation C is slightly heavier and used for a ball having a diameter of about 1.680 inches. Formulation D is 4o used for producing a ball having a diameter of about 1.720 inches (1.717").

Cover compositions were produced by blending the following constituents:
COVER COMPOSITIONS

Ingredients Cover 1 Cover 2 Cover lotek 8000 45.2 -- 3 lotek 7030 45.2 -- 22.6 lotek 959 -- 45.2 . 22.6 lotek 960 -- 45.2 --,a lotek 7520' -- -- --White MB2 9.6 9.6 45.2 9.6 is ~Iotek 7520 is a relatively soft, low acid, ionomer resin produced by Exxon.
ZMB = 74.9 wt-% lotek 7030, 23.8 wt-% Ti02, 0.01 wt-% Unitex OB, 0.002 wt-X
ultra marine blue and 300 ppm Santonox R.
Of the three cover formulations provided above, formulation 2 is the hardest. It is comprised of two hard, high acid ionomer resins. lotek 959 has an acid content of about 19% to 21 and lotek 960 also has an acid content of about 19 to 21 %.
25 Formulation 3 provides the softest of the three cover formulations and is substantially similar to the formulation used in the TOP-FLITE TOUR EDITION 90 golf ball. Formulation 3 is comprised of lotek 8000 and fotek 7030, both hard, low acid ionomers, and lotek 7520, a soft, iow-acid ionomer, in the amounts set forth above.
3o Formulation 1 provides intermediate hardness, and is essentially the same formulation used in the TOP FLITE XL II ball (see U.S. Patent No. 4,911,481 ).

The cover formulations set forth in Example 2 were injection molded at about 400°F around cores of formulations A-D in Example 1 in a manner to permit uniform injection of the selected cover composition over each core. Each of the cores had an identical finished diameter of about 1.541-1.543 inches to produce golf balls of approximately 1.720 (1.717) inches (cores A and D) or about 1.680 inches (cores B and C) in diameter. The cover thickness varied between about 0.069 and about 0.088 inches. All materials were ,0 molded under essentially identical conditions. The properties of Riehle compression, PGA compression, coefficient of restitution (C.O.R.), barrel durability (100 blows), cover hardness and spin rate were determined. The results are set forth in Table 3 below.
The data for each example represents the average data ,5 for one dozen balls produced according to the desired manner. The properties were measured according to the following parameters:
Coefficient of restitution (C.O.R.) and Shore D
hardness was measured as indicated above.
The barrel test or barrel durability test involves Zo firing golf balls at 135 ft.lsec. (at 72°F), into a 5-sided container, the walls of which are steel plates that have grooves milled into them to simulate a golf club face. The balls are subjected to 100 to 300 blows and are inspected at regular intervals for breakage (i.e. any signs of cover ZS cracking or delamination). NB = no breakage.
The spin rate of the golf ball was measured by striking the resulting golf balls with a 9-iron wherein the club-head speed is about 105 feet per second and the ball is launched at an angle of 26 to 34 degrees with an initial velocity of about 110-115 feet per second. The spin rate was measured by observing the rotation of the ball in flight using stop action Strobe photography.

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Molded ball spin test results show that notwithstanding differences in ball size, the combination of a soft core (cores A and B) with a hard cover (cover formulations 1 and 2) minimizes spin rate.
Even in the instance where harder cores are used (cores C and D) the golf ball with the hardest cover formulation tested (formulation 2) provides for golf balls having the lowest spin rate.
Further reduction in spin rate is observed through the use of a soft core (core A and B) with the hardest cover (cover formulation 2), with the largest reduction in spin rate observed through the use of ,o the softest core (core A) with the hardest cover (cover formulation 2).
It should be further noted that increased diameter provides for lower spin rates. In comparing balls A,1-3 with corresponding balls B,1-3, the balls having the larger diameter (A,1-3) are lower in spin than balls B,1-3, respectively. The C.O.R. and compression are controlled ,5 mainly by the core formulation, with a hard fast core giving a harder, faster ball. As ball diameter increases upon increasing the cover thickness (core diameter remains the same), the thicker cover (0.0888 versus 0.0690 inches) provides for significant C.O.R. pick-up from center to ball. Further, the increased cover thickness plays a role in 2o added spin reduction observed for the larger balls.
With attention still focused on the tabulated results, the combination of a soft core with a hard cover gives the lowest spin. In comparing ball A,2 to ball D,2 (both at 1.72 inches in diameter) it is seen that the softer core A contributes to lower spin rates. Combination 2s A,2 (softer core, hardest cover) provides the lowest spin rate for the entire test. These same trends hold for the smaller balls, i.e. ball B,2 is lower in spin that ball C,2. While ball B,2 is the lowest spin among the 1.68 inch balls, its spin rate is not as low as ball A,2 which has a larger diameter. This is believed to be attributed to the differences in cover thickness.

A series of wound three-piece golf balls (with both solid and liquid centers) were produced having low spin characteristics.
Specifically, these balls were produced having the following properties:
A) Solid Center Wound Three-Piece Golf Balls (4SS9~
i) Solid Centers A 1.4 inches in diameter solid center was produced utilizing the following ingredients:

Cariflex BR-1220 70 Taktene 220 30 Zinc Oxide 40.5 Regrind 16 Zinc Stearate 16 Zinc Diacrylate 22 20 195.4 Upon molding, the solid center exhibited the characteristics noted below:
Center Size = 1.4 inches in diameter Center Weight = 29.40 grams Center Rebound (100 inch drop) = 81 inches Center Hardness = Approx. 47 D (peak) Center Compression = 73 PGA (87 Riehle) Center C.O.R. @ 125 Ft.lsec. _ .768 ii) Thread The solid centers were covered by windings comprising of .024" thick X 1116" wide, PIN 1511, elastomeric thread available from Fulflex Inc., Middletown, Rhode Island. The wound core exhibited the following characteristics:
Wound Core Size = 1.56 inches in diameter Wound Core Weight = 35.51 grams Wound Core Compression = 82 PGA (78 Riehle) Wound Core C.O.R. @ 125 Ft.lsec. _ .813 iii) Cover The wound cores were covered with a cover composition having the following formulation:
To Grade White Masterbatch MATERIALS PARTS

lotek 7030 100 Unitane 0-110 31.3 Eastobrite OB-1 0.34 Ultra Marine Biue 0.605 Santonox R 0.05 Final Cover Formulation MATERIALS PARTS
lotek 1002 38 lotek 1003 52.6 TG Masterbatch (above formulation) These balls had the following properties:
Ball Size, pole = 1.682"
Ball Size, equator = 1.683"
Ball Compression = 88 PGA
Ball Weight = 45.01 grams Ball C.O.R. @ 125 Ft./secl = .802 Ball Rebound (100" drop) = 79.4"
~5 Ball Moment of Inertia = .42675 02.-in. 2 Cover Hardness = approximately 70 Shore D (peak) Cover Thickness = .06" (based on a 1.56" diameter wound core) Dimple Pattern - modified tetrakaidecahedron 20 (D335C - Hogan Pattern) Number of Dimples = 428 B) Li uid Center Wound Three-Piece Golf Balls (8L957) i) Liauid Centers Liquid centers (1 ~/en diameter) from Abbott Labs, Chicago, Illinois, PlN 65 W 155L were utilized having the characteristics listed below:
Center Size = 1'/s" diameter Center Weight = 18.39 grams Liquid Center Volume = 6.57 cm3 Center Bag Thickness = .105 in.
Liquid Composition = water/glycerin based Abbott ,o proprietary formulation Liquid Spec. Gravity = .98 Bag Composition = sulphur cured rubber compound (Abbott proprietary formulation Bag Space Gravity = 2.1 ii) Thread The liquid centers were covered by windings comprising .024" thick X 1116" wide, PN 15111, elastomeric thread 2o available from Fulflex Inc., Middletown, Rhode Island. The wound liquid centers had the following general properties:
Wound Core Size = 1.56" diameter Wound Core Weight = 34.46 grams Wound Core Compression = 76 PGA (84 Riehle) Wound Core C.O.R. @ 125 Ft.lsec. _ .813 iii) Cover The wound cores were covered with the same cover composition utilized with the solid center wound balls noted above. The covered balls had the following characteristic:
Ball Size, pole = 1.682"
Ball Size, equator = 1.685"
,o Ball Compression = 80 PGA
Ball Weight = 44.53 grams Ball C.O.R. @ 125 Ft./sec. _ .785 BaN Rebound (100" drop) = 76"
Ball Moment of Inertia = .39688 oz.-in.2 ,5 Cover Hardness = approx. 70 Shore D (peak) Cover Thickness = .06" (based on a 1.56" diameter wound core) Dimple Pattern - modified tetrakaidecahedron (D335C - Hogan Pattern) Number of Dimples = 428 C) Split Tests The solid center (Top-Flite~ Dot 4SS97) and liquid center (Top-Flite~ Dot 8L957) wound three-piece golf balls were spin tested against Spalding's Top-Flite~ XL and Titleist~'s Tour Balata 100 golf balls. The results are given below:

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The solid center wound three-piece golf bails (ie. Top-Flite~ Dot 4SS97) produced substantially less spin than the Top Flite~
XL golf ball, a solid centered two-piece golf ball. Similarly, the liquid center wound three-piece golf balls (ie. Top Flite~ DST 8L 957) produced less spin than the liquid centered Titleist Tour Balata 100 golf ball. The data demonstrated that the low spin properties are obtained using hard high acid ionomer resin covers over the soft wound cores.
The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will ,o occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

Having thus described the invention, it is claimed:
1. A golf ball comprising:
a wound core having a Riehle compression of at least 75 (0.075 inches); and a cover having a Shore D hardness of at least 65, wherein the cover is comprised of at least three ionomer resins which include at least one high acid ionomer resin comprising a copolymer of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid, and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal ration, and the cover has a thickness from 0.050 to 0.160 inches.
2. A golf ball, as set forth in claim 1, wherein the cover is comprised of at least one high acid ionomer resin comprising a copolymer of about 17% to about 25% by weight of an alpha, beta-unsaturated carboxylic acid, and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal ration.
3. A golf ball, as set forth in claim 1, wherein the cover is comprised of at least one high acid ionomer resin comprising from about 18.5% to about 21.5% by weight of an alpha, beta-unsaturated carboxylic acid, and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal ration.
4. A golf ball, as set forth in claim 1, wherein the wound core is comprised of a solid center.
5. A golf ball, as set forth in claim 1, wherein the wound core is comprised of a liquid center.
7. A three-piece golf ball comprising a wound core and a cover, wherein said wound core has a Riehle compression of about 0.75 to about .115 inches, and wherein said cover has a Shore D
hardness of at least 65, a thickness of about 0.050 to 0.160 inches and is comprised of at least three ionomer resins which include one or more ionomeric resins comprising at least 16% by weight carboxylic acid and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal cation.

8. A golf ball as set forth in claim 7, wherein the wound core has a Riehle compression of .078 or more and the cover has a Shore D hardness of 70 or more.
9. A golf ball as set forth in claim 7, wherein the wound core has a Riehle compression of .084 or more and the cover has a Shore D hardness of 70 or more.
10. A golf ball as set forth in claim 7, wherein the finished golf ball has a Riehle compression of .078 or less.
11. A golf ball as set forth in claim 7, wherein said wound core comprises a solid center.
12. A golf ball as set forth in claim 7, wherein said wound core comprises a liquid center.
13. A three-piece wound golf ball, comprising:
a wound core having a Riehle compression of at least about .075 and a diameter of about 1.56 inches; and a cover comprised of at least one ionomer resin including a copolymer of about 17% to about 25% by weight of an alpha, beta-unsaturated carboxylic acid, and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal cation, said cover having a thickness of about 0.050 to 0.160 inches and a Shore D hardness of at least about 65.