Golf Ball Cover Compositions

The present invention relates to improved golf ball cover compositions produced by blending new metal cation neutralized high acid ionomer resins with ionomer resins containing a comonomer of the acrylate ester class. The improved golf ball cover compositions are useful for producing golf balls, particularly multi-piece balls, exhibiting enhanced overall travel distance and/or playability properties while maintaining or improving durability characteristics necessary for repetitive play.

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 Nemours & Company under the trademark "Surlyn.RTM." and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks "Escor.RTM." and the tradename "Iotek", have become the materials of choice for the construction of golf ball covers over the traditional "balata" (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability properties required for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin having from about 2 to about 8 carbon atoms, such as ethylene, and a metal salt of an alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid such as acrylic acid, methacrylic acid or maleic acid. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, lithium, 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.

Generally, the ionic copolymers comprise one or more alpha-olefins and from about 9 to about 15 weight percent of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired. Usually, at least 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, zinc, lithium, and the like) and exist in the ionic state. In some instances, an additional softening comonomer can also be included to form a terpolymer.

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, .alpha.-chloroacrylic, crotonic, maleic, fumaric, itaconic acids, and the like. The ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e. Escor.RTM.) and/or methacrylic (i.e. Surlyn.RTM.) acid. In addition, two or more types of ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

Along this line, the properties of the cover compositions and/or the ionomeric resins utilized in the golf ball industry vary according to the type and amount of the metal cation, the molecular weight, the composition of the base resin (i.e. the nature and the relative content of the olefin, the unsaturated carboxylic acid groups, etc.), the amount of acid, the degree of neutralization and whether additional ingredients such as reinforcement agents or additives are utilized. Consequently, the properties of the ionomer resins can be controlled and varied in order to produce golf balls having different playing characteristics, such as differences in hardness, playability (i.e. spin, feel, click, etc.), durability (i.e. impact and/or cut resistance), and resilience (i.e. coefficient of restitution).

However, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups), the degree of neutralization and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the playability characteristics previously associated with the balata cover, but also the improved impact resistance and carrying distance properties produced by the ionomeric resins.

An object of the present invention is to provide golf ball cover compositions which, when utilized in golf ball construction, produce balls exhibiting improved overall travel distance and/or playability characteristics while maintaining satisfactory durability properties.

Along this line, two of the principal properties involved in the performance of golf balls are resilience and hardness. Resilience (i.e. coefficient of restitution), along with ball size, weight and additional factors such as club head speed, angle of trajectory, and ball aerodynamics (i.e., dimple pattern), generally determine the distance a ball will travel when hit. Since club head speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors of concern among manufacturers are the coefficient of restitution and the surface dimple pattern of the ball.

A golf ball's coefficient of restitution (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.

The coefficient of restitution of a one-piece golf ball is a function of the ball's composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 255 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.

The hardness of the ball is the second principal property involved in the performance of a golf ball. The hardness of the ball can affect the playability of the ball on striking and the sound or "click" produced. Hardness is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the hall's diameter (i.e. the lower the compression value, the harder the material). As indicated in U.S. Pat. No. 4,674,751, "softer" covers permit the accomplished golfer to impart proper spin. This is because the softer covers deform on impact significantly more than balls having "harder" ionomeric resin covers. As a result, this allows the better player to impart fade, draw, or backspin to the ball thereby enhancing playability. Such properties can be determined by various "spin rate tests", such as the "nine-iron" spin rate test set forth below.

In various attempts to produce a high coefficient of restitution golf ball exhibiting the enhanced travel distance desired, the golfing industry has blended various ionomeric resins. However, many of these blends do not exhibit the durability and playability characteristics necessary for repetitive play and/or the enhanced travel distance desired.

The present invention is directed, in part, to the preparation of new cation neutralized ionomer resins containing relative 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 acid) and partially neutralized with sodium, manganese, lithium, potassium, zinc, magnesium, calcium and nickel ions. The new cation neutralized high acid ionomers produce, when blended and melt processed according to the parameters set forth below, cover compositions exhibiting enhanced coefficient of restitution values when compared to low acid ionomers, or blends of low acid ionomer resins containing 16 weight percent acid or less. The new high acid ionomer cover compositions produce golf balls which exhibit properties of enhanced carrying distance (i.e. possess higher coefficient of restitution values) over known ionomer blends such as those set forth in U.S. Pat. Nos. 4,884,814, 4,911,451 and 5,120,791.

Along this line, until relatively recently, all of the ionomer resins commercially available contained at most 15 to 16 weight percent carboxylic acid. These are now defined by the present inventor as being "low acid" ionomer resins. In 1989, the Research and Development Division of DuPont formulated one or more ionomer resins containing greater than 15 weight percent acid and indicated that these new ionomers may have some use in previously known ionomer resin applications. Specifically, DuPont suggested in a brief Research Disclosure (E. I. DuPont de Nemours & Co., Research Disclosure No. 297,003) that ionomers produced from polymers of ethylene acrylic acid or methacrylic acid containing greater than 15 weight percent acid can be melt processed to produce articles (i.e. golf balls, foot wear, ski boots, cosmetic bottle cap closures and so on) with good properties (i.e. improved stiffness, hardness and clarity) when compared with ionomers with lower acid levels.

However, not only has little information been provided concerning the acid levels and types of effective ionomers, particularly with respect to the art of golf ball manufacturing, it has been found that many cover compositions produced from polymers of ethylene/acrylic acid or ethylene/methacrylic acid containing greater than 15 weight percent acid were unsatisfactory in that these compositions exhibit processing problems or were generally short on distance and/or durability and thus, were not particularly commercially viable. Similar poor results were produced with covers composed of blends of high and low acid ethylene/acrylic acid or ethylene/methacrylic acid polymers and/or covers produced from single high acid ionomers containing greater than 15 weight percent acid.

However, notwithstanding the above difficulties, it has been discovered that improved golf ball covers can be produced from specific blends of high acid ionomers (i.e. ionomer resins containing 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 acid) which do not exhibit the processing, distance and/or durability limitations demonstrated by the prior art.

In this regard, it has been found that blends of specific high acid ionomer resins, particularly blends of sodium and zinc high acid ionomers, as well as blends of sodium and magnesium high acid ionomers, extend, when utilized in golf ball cover construction, the range of hardness beyond that previously obtainable while maintaining the beneficial properties (i.e. durability, click, feel, etc.) of the softer low acid ionomers disclosed in U.S. Pat. Nos. 4,884,814 and 4,911,451. These blends produce harder, stiffer golf balls having higher C.O.R. values, and thus longer distance. This discovery is the subject matter of U.S. application Ser. No. 776,803, filed on Oct. 15, 1991, and currently co-pending herewith.

In addition, a number of new high acid ionomers, particularly new metal cation neutralized acrylic acid based high acid ionomer resins have been developed by the present inventor, which exhibit, when utilized for golf ball cover construction, cover compositions having further improved hardness and resilience (C.O.R.) properties. The new metal cation neutralized acrylic acid based high acid ionomer resins, as well as specific blends of these resins, are particularly valuable in the field of golf ball production.

Furthermore, as a result of the development of a number of new acrylic acid based 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 many of these new cation neutralized high acid ionomer blends produce cover compositions exhibiting enhanced resilience (i.e. longer distance) due to synergies which occur during processing. Consequently, the new metal cation neutralized acrylic acid based high acid ionomer resins may be blended to produce substantially harder golf balls having higher C.O.R. values than those produced by the low acid ionomer covers presently commercially available.

Moreover, it has been further discovered that the new cation neutralized high acid ionomers produce, when blended with low acid ionomer resins containing an unsaturated comonomer of the acrylate ester class having from 1 to 21 carbon atoms, and melt processed according to the parameters set forth below, cover compositions exhibiting enhanced playability and durability characteristics. Consequently, the addition of the ionomer resin containing the acrylate comonomer to the new cation neutralized high acid ionomers are useful in preparing softer ionomer blends that have utility in softer cover golf balls such as the Top-Flite.RTM. Tour and Tour Edition.RTM. golf balls produced by Spalding & Evenflo Companies, Inc., the assignee of the present invention.

These and other objects and features of the invention will be apparent from the following description and from the claims.

In one aspect, the present invention is directed to improved cover compositions for golf ball construction and to the resulting golf balls produced thereby. The novel golf ball cover compositions of the invention comprise blends of recently developed metal cation neutralized high acid ionomer resins and ionomer resins containing a comonomer of the acrylate ester class. When the cover compositions are used to manufacture golf balls, the golf balls produced thereby exhibit properties of improved overall distance (resilience), playability (i.e. softness and spin) and/or durability when compared to golf balls produced by blends of high acid ionomer resins and/or blends of low acid ionomer resins. The cover compositions of the present invention are also useful in preparing softer covers that have utility in soft covered balls such as Top-Flite.RTM. and Tour Edition.RTM. balls trademarked and sold by Spalding & Evenflo Companies, Inc., without the necessity of using only those ionomer resins commercially available from DuPont or Exxon.

In another aspect, the instant invention relates to a golf ball comprising a core and a cover. The cover is comprised of a blend of a copolymer consisting of a recently developed metal cation neutralized high acid ionomer and a ionomer resin containing a softening comonomer of the acrylate ester class. The metal cation neutralized high acid ionomer resin is a copolymer of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid (preferably from about 17% to about 25% by weight acid, and more preferably from about 18.5% to about 21.5% by weight acid) and an alpha-olefin, of which 10% to 90% of the carboxyl groups of the copolymer are neutralized with a metal cation. The ionomer resin containing a softening comonomer of the acrylate ester class is a metal salt of an acid terpolymer of an olefin having from about 2 to 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid, and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms. In addition, the cover may contain one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners.

In still a further aspect, the invention is directed to a golf ball comprising a core and a cover, wherein the cover is comprised of a metal cation neutralized high acid ionomer resin which is a copolymer of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid, (preferably from about 17% to about 25% by weight acid, and more preferably from about 18.5% to about 21.5% by weight acid) and an olefin, of which 10% to 90% of the carboxyl groups of the copolymer are neutralized with one or more metal cations selected from the group consisting of sodium, zinc, magnesium, manganese, lithium, potassium, calcium and nickel; and, ii) an ionomer resin containing a softening acrylate comonomer which is a terpolymer of an olefin having from about 2 to 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms of which 10% to 90% of the carboxyl groups of the terpolymer are neutralized with one or more metal cations selected from the group consisting of sodium, zinc, magnesium, manganese, lithium, potassium, calcium and nickel. Moreover, the cover may contain of one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners.

In a further additional aspect, the invention concerns the preparation of a golf ball cover composition having the improved combination of playability, durability and/or travel distance properties by the first pre-blending of a high acid copolymer with an acid terpolymer containing a softening comonomer of the acrylate ester class followed by neutralization of the blended mixture with one or more metal cations. By the in-situ pre-blending of a high acid copolymer with an acid terpolymer containing a softening acrylate termonomer, followed by neutralization of the copolymer/terpolymer mixture with one or more metal cations, improvements in the overall combination of characteristics such as C.O.R., spin and scuff/abrasion resistance can be produced.

Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and 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.

The present invention relates to the development of a number of new metal cation neutralized high acid ionomers, and to the use of these new metal cation neutralized high acid ionomers in combination with ionomer resins containing additional softening comonomers of the acrylate ester class for the purpose of producing golf ball covers exhibiting enhanced overall distance, playability and/or durability characteristics.

In this regard, several new metal cation neutralized high acid ionomer resins have been produced by the present inventor 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. More particularly, 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 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. 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, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.

Consequently, examples of a number of copolymers suitable for use in the invention include, but are not limited to, high acid embodiments of an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic acid, and less than 84% by weight alpha-olefin. 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, Mich., under the "Primacor" designation. These high acid base copolymers exhibit the typical properties set forth below in Table 1.

Due to the high molecular weight of the Primacor 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more 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, 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 dihydrate 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 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 cation neutralized high acid ionomer resins of the invention are produced by reacting the high acid base copolymer with various amounts of the metal cation salts above the crystalline melting point of the copolymer, such as at a temperature from about 200.degree. F. to about 500.degree. F., preferably from about 250.degree. F. to about 350.degree. F. under high shear conditions at a pressure of from about 100 psi to 10,000 psi. Other well known blending techniques may also be used. The amount of metal cation salt utilized to produce the new metal cation neutralized high acid based ionomer resins is the quantity which provides a sufficient amount of the metal cations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of neutralization is generally from about 10% to about 90%.

As indicated more specifically in Example 1 below, a number of new types of metal cation neutralized high acid ionomers can be obtained from the process of this invention. These include new high acid ionomer resins neutralized to various extents with manganese, lithium, potassium, calcium and nickel cations. 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 cation 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.

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.

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 ionomer blends are now available for golf ball production. By using the high acid ionomer resins of the present invention, harder, stiffer golf balls having higher C.O.R.s, and thus longer distance, can be obtained.

Examples of high acid methacrylic acid based ionomers include Surlyn.RTM. AD-8422 (sodium cation), Surlyn.RTM. 8162 (zinc cation), Surlyn.RTM. SEP-503-1 (an experimental zinc cation), and Surlyn.RTM. SEP-503-2 (an experimental magnesium cation). According to DuPont, all of these ionomers contain from about 18.5% to about 21.5% by weight methacrylic acid.

More particularly, Surlyn.RTM. AD-8422, is currently (as of January, 1992) commercially available from DuPont in a number of different grades (i.e. AD-8422-2, AD-8422-3, AD-8422-5, etc.) based upon differences in melt index. According to DuPont, Surlyn.RTM. AD-8422 offers the following general properties when compared to Surlyn.RTM. 8920 the stiffest, hardest of all of the low acid grades (referred to as "hard" ionomers in U.S. Pat. No. 4,884,814):

In comparing Surlyn.RTM. 8920 to Surlyn.RTM. 8422-2 and Surlyn.RTM. 8422-3, it is noted that the high acid Surlyn.RTM. 8422-2 and 8422-3 ionomers have a higher tensile yield, lower elongation, slightly higher Shore D hardness and much higher flexural modulus. Surlyn.RTM. 8920 contains 15 weight percent methacrylic acid and is 59% neutralized with sodium.

In addition, Surlyn.RTM. SEP-503-1 (an experimental zinc cation neutralized high acid methacrylic acid based ionomer resin) and Surlyn.RTM. SEP-503-2 (an experimental magnesium cation neutralized high acid methacrylic acid based ionomer resin) are high acid zinc and magnesium versions of the Surlyn.RTM. AD 8422 high acid ionomers. When compared to the Surlyn.RTM. AD 8422 high acid ionomers, the Surlyn.RTM. SEP-503-1 and SEP-503-2 ionomers can be defined as follows:

Furthermore, Surlyn.RTM. 8162 is a zinc cation neutralized methacrylic acid based high acid ionomer resin containing approximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acid copolymer that has been 30-70% neutralized. Surlyn.RTM. 8162 is currently (as of January, 1992) commercially available from DuPont.

For comparison purposes, examples of commercially available low acid methacrylic acid based ionomer resins are set forth below. These are many of the "hard" ionomers utilized in the cover composition disclosed in U.S. Pat. No. 4,884,814. Along this line, the low acid ionomer resin cover compositions disclosed in the '814 patent are generally considered to be among the best prior art methacrylic acid based cover compositions currently available from Spalding & Evenflo Companies, Inc., the assignee of the present application and U.S. application Ser. No. 776,803.

Examples of existing high acid acrylic acid based ionomer resins include the Escor.RTM. or the Iotek acrylic acid based high acid ionomers recently experimentally produced by Exxon. In this regard, Escor.RTM., or Iotek, 959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor.RTM., or Iotek, 960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Ioteks 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 ions respectfully. The physical properties of these high acid acrylic acid based ionomers are as follows:

For comparison purposes, examples of commercially available low acid acrylic acid based ionomer resins, such as these utilized in U.S. Pat. No. 4,911,451 are set forth below.

According to the present invention, it has been found that when the above indicated new metal cation neutralized acrylic acid based high acid ionomers, are processed according to the parameters set forth below to produce the covers of multi-layered golf balls, the resulting golf balls will travel further than previously known low acid ionomer resin covers and/or covers produced from high acid ionomers and/or high acid/low acid ionomer blends due to the balls' enhanced coefficient of restitution values. This is particularly important in that an improvement of 0.001 in C.O.R. generally relates to an improvement of about 0.2 to 0.5 yards in travel distance.

When blends of two of the above indicated metal cation neutralized acrylic acid high acid ionomers are used (i.e. "dibends"), the ratio of one type of metal cation neutralized acrylic acid high acid ionomer to another is generally from about 75% to about 25% and from about 25% to about 75%. In addition, "triblends" can also be formulated utilizing the new metal cation neutralized acrylic acid based high acid ionomers of the present invention. The general ratio for such "triblends" is 33.33% /33.33% /33.33% by weight.

However, notwithstanding the above indicated improvements in hardness and travel distance properties produced by the new metal cation neutralized high acid ionomers, it has also been further found that improvements in playability (i.e. enhanced Riehle compression, higher spin rates, lower Shore hardness, etc.) and durability (i.e. scuff resistance, etc.) characteristics can be obtained by blending the new high acid ionomers with ionomer resins containing a softening comonomer of the acrylate ester class. The addition of the ionomer resins containing the softening comonomer of the acrylate ester class to the high acid ionomer resins produces a significant increase in playability characteristics (i.e. spin rates, etc.) with only moderate decreases in C.O.R. and hardness values depending upon the amount of terpolymer incorporated.

Moreover, it was also observed that the addition of the ionomer resins containing the softening comonomer of the acrylate ester class generates enhanced cut resistance values, particularly in comparison with Spalding's current Tour Edition.RTM. balls. This is of some importance since the Spalding Tour Edition.RTM. balls are considered to be generally among the best prior art balls exhibiting enhanced playability properties while maintaining reasonable travel distance characteristics.

Consequently, the blends of the new metal cation neutralized high acid ionomer and the ionomer resins (i.e. metal cation neutralized terpolymers) containing a softening comonomer of the acrylate ester class are useful in preparing softer ionomer resins that have utility in producing soft covered golf balls such as Spalding, Top-Flite.RTM. Tour and Tour Edition.RTM. balls. While these balls could only previously be manufactured utilizing hard/soft blends of commercially available low acid ionomers (i.e. U.S. Pat. Nos. 4,884,414 and 5,120,791), the present invention allows for the production of golf ball covers exhibiting even further enhanced properties (i.e. superior cut resistance, durability, etc.) through the use of non-commercially available ionomer resins, i.e. through the use of the recently formulated high acid ionomer resins.

In addition, it has also been found that the new cover composition can be produced "in-situ" by first pre-blending a high acid copolymer, such as a poly(ethylene-acrylic acid) or poly(ethylene-methacrylic acid), with an acid terpolymer containing a softening comonomer (or termonomer) of the acrylate ester class, such as poly(ethylene-acrylic acid-methylacrylate), poly(ethylene-methacrylic acid-butyl acrylate) etc., followed by neutralization of the blended mixture with one or more metal cations. By the in-situ pre-blending of the acid copolymer and the acid terpolymer and then the subsequent neutralization of the copolymer/terpolymer blend with a wide variety of metal cations, or mixtures thereof, further improvements in C.O.R., spin and scuff/abrasion resistance can be produced.

The ionomer resin containing the softening comonomer of the acrylate ester class is a metal salt of an acid terpolymer comprising an alpha-olefin having from about 2 to about 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid, and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms. The alpha-olefin is preferably ethylene. Suitable acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic and methacrylic acid being the preferred acids. The softening comonomer is preferably an alkyl acrylate with methyl acrylate and butyl acrylate being the most preferred. Examples of acid terpolymers suitable for use in the invention include poly(ethylene-methacrylic acid-butyl acrylate), poly(ethylene-acrylic acid-methyl acrylate), etc.

The acid terpolymer contains from about 40 to about 85% by weight alpha-olefin, from about 2 to about 20% by weight of unsaturated carboxylic acid, and from about 10 to about 40% by weight of the softening acrylate comonomer. Preferably, the terpolymer contains from about 65 to about 85% by weight ethylene, from about 5 to about 20% by weight unsaturated carboxylic acid, and from about 10 to about 30% by weight of the softening acrylate comonomer. More preferably, the acid terpolymer contains from about 69 to about 84 by weight ethylene, from about 6 to about 10% by weight acrylic acid or methacrylic acid and from about 10 to about 21% by weight methyl acrylate or butyl acrylate.

Representations of acid terpolymers which fulfill the criteria set forth above include a series ethylene/methacrylic acid/butyl acrylate terpolymers (i.e. poly›ethylene-methacrylic acid-butyl acrylate!) produced and sold by DuPont under the trade designation "Nucrel.RTM. 035" and "Nucrel.RTM. 010". The typical properties of these terpolymers are set forth below:

These terpolymers consist essentially of about 80% by weight ethylene, about 10% by weight acrylic acid and about 10% by weight iso-butyl acrylate.

Examples of suitable ethylene/acrylic acid/methyl acrylate terpolymers (i.e. poly(ethylene acrylic acid-methyl acrylate)) include those acid terpolymers produced and sold by Exxon under the designation "Escor ATX".

The typical properties of these terpolymers are set forth below:

The "Escor ATX" acid terpolymers consist essentially of about 72% to about 77% by weight ethylene, about 2% to about 7% by weight acrylic acid and about 21% by weight methyl acrylate.

By reacting the acid terpolymer with a metal cation salt capable of ionizing or neutralizing the carboxylic acid groups of the acid terpolymer to the extent desired (i.e. from about 10% to about 100%), the ionomer resin containing the softening comonomer of the acrylate ester class is produced. The processes and metal cation salts utilized in the invention to neutralized the terpolymer are essentially the same as those utilized to neutralize the high acid copolymer set forth above. The metal cation neutralized terpolymer containing the acrylate softening comonomer have a hardness from about 20 to about 45 as measured on the Shore D scale and a flexural modulus from about 1,500 to about 15,000 psi as measured in accordance with ASTM method D-790.

When the metal cation neutralized terpolymers containing the acrylate softening comonomer are blended with the new metal cation neutralized high acid ionomers described above, in the combinations more clearly define below and demonstrated in the Examples, and the blends are used to produce a golf ball cover, a more desirable golf ball in the terms of overall distance, playability and/or durability characteristics can be obtained. Moreover, in addition to the dry blending of the different ionomer resins, the new cover compositions can also be produced "in-situ" by first pre-blending the high acid copolymer with the acid terpolymer containing the softening acrylate ester comonomer prior to neutralization with one or more metal cations.

The enhanced golf balls of the present invention containing the improved new metal cation neutralized terpolymers containing a comonomer of the acrylate ester class can be generally produced from a central core and an outer cover wherein the outer cover is made from a composition comprised of a blend of about 90 to about 10% of a metal cation neutralized high acid ionomer, and of about 10 to about 90% of a metal cation neutralized terpolymer containing a comonomer of the acrylate ester class.

More preferably, it has been found that golf balls exhibiting properties of enhanced overall distance (i.e. higher C.O.R. values), playability (i.e. higher spin rates, etc.) and/or durability characteristics, can be produced from a core and a cover, wherein the cover is made from a composition comprised of about 80 to about 20% of a high acid ionomer resin and from about 20 to 80% of an ionomer resin containing a comonomer of the acrylate ester class, depending upon the C.O.R. value and/or the degree of softness desired. The optimal ranges of the high acid ionomer resin to the ionomer resins containing the softening comonomer of the acrylate ester class are from about 60 to about 40% high acid ionomer resin and from about 40 to about 60% of the ionomer resins containing the softening comonomer of the acrylate ester class.

Additional compatible additive materials may also be added to the compositions of the present invention, such as dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, N.J.), 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. Pat. No. 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 and/or 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 these are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added 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 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 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. Pat. No. 4,679,795, may also be included in the cover 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, Ardaley, N.Y. Uvitex OB is thought to be 2,5-Bis(5-tert-butyl-2-benzoxazoly)thiopene. 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-(2h-naphthol(1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-20G2 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 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 0.020% 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 copolymer blends.

The cover compositions of the present invention may be produced according to conventional melt blending procedures. In this regard, the above indicated high acid ionomeric resins and ionomer resins containing a comonomer of the acrylate ester class are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. If the "in-situ" process is utilized, the cations are first blended and are then added to the acid copolymer/acid terpolymer mixture in the Banbury mixer. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state 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 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 compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. The standards for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result of their lower cost and superior performance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an .alpha., .beta., ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than those that are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.

The term "solid cores" as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multilayer and/or non-wound cores (such as those described in U.S. Pat. No. 4,848,770).

Wound cores are generally produced by winding a very large elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380.degree. F. to about 450.degree. F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200.degree.-300.degree. F. for 2-10 minutes, followed by cooling at 50.degree.-70.degree. 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.degree. F. to about 100.degree. F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Pat. No. 4,911,451.

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.

By blending the ingredients set forth in the Tables below, a series of new metal cation neutralized high acid ionomer resins and golf ball cover formulations containing these resins were produced. In addition, the new high acid ionomer resins were blended (i.e. "in-situ" produced) with ionomer resins containing a comonomer of the acrylate ester class. The new cover formulations were evaluated for the purpose of determining changes in playability, travel distance and durability characteristics.

Finished golf balls were prepared using the cover compositions of the present invention, controls and comparative cover compositions by positioning a solid preformed cross-linked polybutadiene core in an injection molding cavity in such a manner to permit the uniform injection of the selected cover composition over each core. Along this line, the cover formulations were injection molded at about 400.degree. F. around identical solid type cores having a finished diameter of 1.545 inches to produce golf balls approximately 1.680 inches in diameter having a normal cover thickness of 0.0675 inches. All materials were molded under essentially identical conditions.

Upon completion of the fabrication process, the properties of coefficient of restitution (C.O.R.) of the molded and finished balls, Shore D hardness, cold crack resistance, spin rates, cut resistance, etc. for the cover compositions were determined.

In conducting the comparative testing, Escor.RTM. 4000/7030 and Escor.RTM. 900/8000 ionomers were utilized. In this regard, blends of Escor.RTM. 4000/7030 and Escor.RTM. 900/8000 (i.e. the subject of U.S. Pat. No. 4,911,451) are considered by the inventors to be generally among the best cover compositions for producing enhanced distance properties concerning ethylene-acrylic acid ionomer (low acid) blends. In addition, blends of Escor.RTM. 4000/7030, Escor.RTM. 900/8000 and Escor 7520 (i.e. the subject of U.S. Pat. No. 5,120,791), which are representative of the chemical composition of Spalding's Tour Edition.RTM. 90 and Top Flits.RTM. Tour 100 balls and which are considered to be among the best cover compositions for producing enhanced playability properties while maintaining reasonable travel distance characteristics, were utilized to evaluate the new blends of the metal cation neutralized high acid ionomers with the ionomer resins containing a comonomer of the acrylate ester class.

The data for each example represents the average data 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.) was measured by firing the resulting golf ball in an air cannon at a velocity of 125 feet per second against a steel plate which is positioned 12 feet from the muzzle of the cannon. The rebound velocity was then measured. The rebound velocity was divided by the forward velocity to give the coefficient of restitution.

Unless indicated differently, Shore hardness was measured in accordance with ASTM Test D-2240.

Cold cracking resistance was measured by firing balls from an air cannon, 5 blows at 165 feet/sec, after the balls had been conditioned for 24 hours at -10.degree. F. After allowing the balls to equilibrate to room temperature the balls are inspected for cover cracking.

The spin rate of the golf ball was measured by striking the resulting golf balls with a pitching wedge or 9-iron wherein the club-head speed is about 80 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.

Cut resistance was measured in accordance with the following procedure: A golf ball is fired at 135 feet per second against the leading edge of a pitching wedge, wherein the leading edge radius is 1/32 inch, the loft angle is 51 degrees, the sole radius is 2.5 inches, and the bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scale of 1-5. 1 represents a cut that extends completely through the cover to the core, 2 represents a cut that does not extend completely through the cover but that does break the surface; a 3 does not break the surface of the cover but does leave a permanent dent; a 4 leaves only a slight indentation which is permanent but not as severe as 3; and 5 represents virtually no visible indentation or damage of any sort.

A number of new cation neutralized acrylic acid based high acid ionomer resins were prepared utilizing as the copolymer of an olefin and an alpha, beta-unsaturated carboxylic acid, a 20 weight percent acrylic acid/ethylene copolymer produced by The Dow Chemical Company, Midland, Mich. under the designation "Primacor 5981." According to The Dow Chemical Company, Primacor 5981 has a melt index (at 190.degree. C., 2150 g) of 300 g/10 min. The carboxylic acid groups present in the 20 weight percent acrylic acid/ethylene copolymer were neutralized to various weight percentages by a number of different metal cation salts resulting in the production of several new thermoplastic elastomers exhibiting enhanced properties for golf ball cover production. Due to differences in the nature of the cation salts, the amount of cation salts utilized, etc., the new high acid ionomer resins produced differed substantially in the extent of neutralization and in melt indices, as well as in resilience (i.e. C.O.R.) and hardness values.

For the purpose of determining the weight percent of neutralization of the carboxylic acid groups in the acrylic acid/ethylene copolymer after reacting with various cation salts, it was assumed that 1 mole of sodium (Na.sup.+), potassium (K.sup.+), and lithium (Li.sup.+) neutralized one mole of acrylic acid, and that one mole of zinc (Zn.sup.2+), magnesium (Mg.sup.2+), manganese (Mn.sup.2+), calcium (Ca.sup.2+) and nickel (Ni.sup.2+) neutralized two moles of acrylic acid. The calculations of neutralization were based upon an acrylic acid molecular weight of 79 g/m, giving 0.2778 moles per 100 grams of copolymer.

As indicated below in Table 7, the various cation salts were added in variable amounts to the 20 weight percent acrylic acid/ethylene copolymer in order to determine the optimal level of neutralization for each of the cations. In Table 7, NaOH refers to sodium hydroxide (formula weight of 40). MnAc refers to manganese acetate tetrahydrate having a formula weight of 245. LiOH is lithium hydroxide, fwt=24. KOH is potassium hydroxide, fwt=56. ZnAc is zinc acetate dihydrate, fwt=219.5. MgAc is magnesium acetate tetrahydrate, fwt=214.4. CaAc is calcium acetate, fwt=158. MgO is magnesium oxide, fwt=40.3. NiAc is nickel acetate, fwt=176.8. All of these cation salts are solids at room temperature.

The specific cation salts were added in differing amounts with the 20 weight percent acrylic acid/ethylene copolymer (i.e. the Primacot 5981) to an internal mixer (Banbury type) for the neutralization reaction. The only exception was calcium acetate, which, due to problems encountered in solid form, was added as a 30 wt-% solution in water.

In the neutralization reaction, the cation salts solubilized in the Primacor 5981 acrylic acid/ethylene copolymer above the melting point of the copolymer and a vigorous reaction took place with a great deal of foaming occurring as the cation reacted with the carboxylic acid groups of the acrylic acid/ethylene copolymer and the volatile by-products of water (in the case of oxides or hydroxides) or acetic acid (when acetates are used) were evaporated. The reaction was continued until foaming ceased (i e. about 30-45 minutes at 250.degree.-350.degree. F.) and the batch was removed from the Banbury mixer. Mixing continued of the batch obtained from the mixer on a hot two-roll mill (175.degree.-250.degree. F.) to complete the neutralization reaction. The extent of the reaction was monitored by measuring melt flow index according to ASTM D-1238-E. As indicated below, the neutralized products exhibited drastically different properties depending upon the nature and amount of the cation salts utilized.

As indicated in Table 7, a number of the new cation neutralized acrylic acid based high acid ionomer resins exhibited C.O.R. and Shore D hardness values greater than that exhibited by a 50/50 blend of the Iotek low acid acrylic acid based hard ionomer resins, such as the Iotek 8000/7030 blend utilized in the cover compositions disclosed in U.S. Pat. No. 4,911,451. Moreover, included in new acrylic acid based high acid ionomer resins were numerous cation neutralized high acid ionomer resins previously not available, such as those acrylic acid based high acid ionomer resins neutralized to various degrees by the manganese, lithium, potassium, magnesium, calcium and nickel salts. Furthermore, the new cation neutralized acrylic acid based high acid ionomers produced C.O.R. and hardness values greater than those shown by the methacrylic acid based high acid ionomer resins recently produced by DuPont (i.e. Surlyn.RTM. 8422 (Na) and Surlyn.RTM. 8162 (Zn)) and the acrylic acid based high acid resins experimentally produced by Exxon (i.e. Iotek EX-959 and Ex-960 (Zn)), collectively referred to as "the controls."

In addition, the results produced by Formulation Nos. 1 through 3 directed to the sodium ion neutralized ethylene-acrylic acid copolymers and Formulation Nos. 15 through 17 directed to the zinc ion neutralized ethylene-acrylic acid copolymers in comparison to the new Iotek high acid ethylene acrylic acid ionomers were also of interest. As indicated above, Escor.RTM. or Iotek Ex-959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor.RTM. or Iotek Ex-960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Ioteks 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 ions, respectfully.

Formulation No. 2 (i.e. 5.66 wt-% sodium salt, 54 wt-% neutralization, 2.4 melt index, 0.808 C.O.R. and 73 Shore D hardness) is somewhat similar to Iotek 959 and Formulation No. 16 (i.e. 13.9 wt-% zinc salt, 53 wt-% neutralization, 0.9 melt index, 0.797 C.O.R. and 69 Shore D hardness) is somewhat similar to Iotek 960.

However, not only did the new cation neutralized acrylic acid based high acid ionomers of the present invention exhibit similar or better resilience (C.O.R.) at comparable or better hardness values than those exhibited by the sodium or zinc high acid Iotek ionomers, as a result of the neutralization of the acrylic acid/ethylene copolymer with several different cation salts, to a number of different neutralization percentages, a wide variety of new cation neutralized acrylic acid based high acid ionomers were produced having improved resilience and hardness values. These new cation neutralized high acid ionomer resins are particularly valuable in the field of golf ball production.

More particularly, the development of a number of separate different cation neutralized high acid ionomers besides the sodium or zinc high acid ionomers available from DuPont or Exxon, such as the new manganese, lithium, potassium, magnesium, calcium and nickel acrylic acid based high acid ionomer resins, allows for the production of a wide variety of cation neutralized high acid ionomer blends. Furthermore, since the new sodium or zinc neutralized high acid ionomers produced improved properties over those produced by the existing available sodium or zinc high acid ionomers, a number of new cover compositions can be produced having enhanced characteristics.

Along this line, several of the cation neutralized acrylic acid based high acid ionomer resins produced above which exhibited enhanced C.O.R. and Shore D hardness values were blended together and evaluated for the purpose of determining whether any synergistic effects were produced particularly with respect to enhanced C.O.R. values.

Specifically, from each group of the different cation neutralized high acid ionomer resins set forth in Table 7, the best overall ionomer (based upon C.O.R., melt index and Shore D hardness) was utilized to produce a number of blends ("diblends" and "triblends") and processed to produce the cover component of multi-layered golf balls. The "diblends" consisted of 50/50 mixtures and the "triblends" consisted of a 33.33/33.33/33.33 mixtures.

With respect to the blends set forth in Tables 8 and 9, Na refers to Formulation No. 3, C.O.R. (molded/finished) of 0.812/817; Mn refers to Formulation No. 6, C.O.R. (molded/finished) of 0.814/0.814; Li refers to Formulation No. 10, C.O.R. (molded/finished) of 0.818/0.819; K refers to Formulation No. 13, C.O.R. (molded/finished) of 0.805/0.809; Zn refers to Formulation No. 16, C.O.R. (molded/finished) of 0.797/0.796; Mg refers to Formulation No. 18, C.O.R. (molded/finished) of 0.814/0.820; Ca refers to Formulation No. 21, C.O.R. (molded/finished) of 0.813/0.812; Ni refers to Formulation No. 28, C.O.R. (molded/finished) of 0.799/0.817; and 50/50 Iotek 8000/7030 refers to control of 50/50 blend of Iotek 8000/7030, C.O.R. (molded/finished) of 0.810/0.812.

The C.O.R. values of the "diblends" and "triblends" were then evaluated after molding with a center stock having the following composition:

In addition, the molded balls were coated and finished according to the procedure mentioned above. The C.O.R. values of the finished balls were determined in order to evaluate whether any improvement in resilience was produced. Generally, it is typical to observe a 0.002 to 0.003 point pick up in C.O.R. values of the finished balls in comparison to the molded balls. The results are set forth in Tables 8A, 8B and 9 below.

In Table 8B above, the C.O.R. synergy values are based upon the data from Table 7 of the various metal cation neutralized high acid acrylic acid based ionomer resins and the following calculations:

(COR)calc=coefficient calculated as weighted average of as-molded COR's for polymers of salts 1 and 2

(COR) exp=experimental as-molded COR for blend

FINAL (COR)calc=coefficient calculated as weighted average of finished COR's for polymers of salts 1 and 2

FINAL (COR) exp=experimental finished COR for blend

FINAL (COR) diff=difference between FINAL (COR) exp and FINAL (COR) (calc)

As noted in Table 8B, positive synergy in resilience is observed for nearly all of the finished (final) blends, with substantial synergy being produced in Formulation Nos. 34, 38, 39, 43, 46, 48, 49, 50.

Moreover, the diblends were also evaluated against a control Formulation No. 59 (see Table 8A), a 50/50 blend of Iotek 959/960, the best available high acid blends, with respect to improved C.O.R. values (i.e. 811/0.818). Similar or enhanced C.O.R. values (molded/finished) were observed in Formulation Nos. 31 (Na/Mn), 32 (Na/Li), 34 (Na/Zn), 35 (Na/Mg), 36 (Na/Ca), 38 (Mn/K), 43 (Li/Zn), 44 (Li/Mg), 45 (Li/Ca), and 47 (K/Mg).

Furthermore, when reviewed for cold cracking, with the exception of Formulation No. 35, all of the diblends tested exhibited resistance to breaking. With respect to Formulation No. 35, some breakage did occur with 2 out of the 12 balls tested exhibiting breakage.

When the small test sample of the triblends were evaluated (see Table 9 below) in comparison to a 50/50 blend of the low acid acrylic acid based hard ionomers (i.e. Iotek 8000/7030 U.S. Pat. No. 4,911,451), all of the cation neutralized high acid acrylic acid based triblends produced enhanced C.O.R. values upon molding and finishing. In addition, when subjected to cold cracking, no breakages were observed.

Consequently, not only are a number of new cation neutralized acrylic acid based high acid ionomers now available for golf ball cover construction, these new cation neutralized acrylic acid based high acid ionomers may be blended together in various combinations to produce cover compositions exhibiting enhanced resilience (i.e. distance) due to the synergies noted above.

In order to determine whether the diblends or triblends of the new cation neutralized acrylic acid based high acid ionomer resins produced different results when dry blended (i.e. prepared as simple dry blends of pre-made single cation neutralized acrylic acid based high acid ionomers, such as those set forth in Example 1 above) or when produced as "in-situ" cation blends (i.e. the cations were first blended and then added to the acrylic acid/ethylene copolymers in the Banbury mixer), a number of comparison reactions were generated. Specifically, in-situ Formulation Nos. 68-72 in Table 10 below correspond to dry-blended Formulation Nos. 31, 32, 43, 44 and 46, respectively, and in-situ Formulation Nos. 73 and 74 in Table 10 below correspond to dry-blended Formulation Nos. 62 and 63, respectively.

The results indicated that little difference in C.O.R. was produced (relative to a control of 50/50 mixture of the high acid Iotek 959/960) whether a dry blending process or an in-situ blending process was used. Moreover, the data further clearly indicated that the cation neutralized acrylic acid based high acid ionomer blends of the present invention generally exhibit higher C.O.R. values and significantly lower spin rates than the best acrylic acid based high acid ionomers (i.e. the Ioteks 959(Na)/960(Zn) blend), see Formulation Nos. 68, 70, 71, 73 and 74 in comparison to Formulation No. 75 (control). The lower C.O.R. value and the substantially similar spin rate produced by the Zn/K blend in Formulation 72 was attributed to the slightly lower hardness of this blend versus the others. As indicated in Table 7, the K and Zn acrylic acid based high acid ionomers are a little softer than the Na, Mn, Li and Mg acrylic acid based high acid ionomers. Similarly, the higher spin rate of the Na/Li blend in Formulation 69 was due to its relative softness versus the other blends. In addition, other more subtle factors may also be at play, such as differences in coefficient of friction, deformation under load, etc., which have not quantified.

In addition, when compared with a number of commercially available balls produced by Spalding & Evenflo Companies, Inc., the assignee of the present invention, with low acid ionomer resin covers (i.e. the Tour Edition.RTM. 100, Tour Edition.RTM. 90 and Top-Flite.RTM. XL II balls), the spin rates of the cation neutralized acrylic acid high acid ionomer blends of the present invention (i.e. Formulations 68-75) exhibited much lower spin rates. Consequently, the cation neutralized acrylic acid based high acid ionomer blends of the present invention produced, when utilized to formulate the cover of a multi-layered golf ball, a much harder surface then those produced by the low acid ionomer covers presently available. This may be desirable to a golfer who imparts unmanageable spin (slice/hook) to the ball and therefore may benefit from a "low spin" ball.

In addition to the 50/50 blends of various combinations of the new cation neutralized acrylic acid based high acid ionomers set forth in Example 1, di-blends varying from 25/75 to 75/25 ratios were produced utilizing the more preferred diblends in the "in-situ" process described in Example 2. In this regard, the more preferred diblend formulations set forth in Example 1 (i.e. Formulation No. 31 (Na/Mn), Formulation No. 32 (Na/Li), Formulation 43 (Li/Zn), Formulation No. 44 (Li/Mg), and Formulation No. 46 (Zn/K)) were produced in-situ in 50/50, 25/75 and 75/25 combinations according to the following formulations:

The di-blends produced the following C.O.R. values:

The results indicated that in general the new cation neutralized acrylic acid based high acid ionomer diblends produced enhanced C.O.R. values over the known acrylic acid based low acid ionomer blends. See Formulation Nos. 76-81, 84-88 and 90. While Formulation 82 produced a lower C.O.R. value than expected, the data suggested that in some cases, a 50/50 blend is not optimal (particularly in the Zn/K and the Li/Zn blends), while in others (i.e. Li/Mg, Na/Li) the blend ratio is not significantly different.

Since the data set forth in Examples 1-3 indicated the resilience (C.O.R.) and/or hardness properties of the cover compositions can be substantially enhanced through the use of the new cation neutralized acrylic acid based high acid ionomers and/or diblends or triblends of such ionomers, the molecular weight property of the acrylic acid/ethylene copolymers utilized to produce the ionomers was evaluated. Specifically, the molecular weight of the acid copolymers was assessed for the purpose of determining whether further enhanced properties can be produced by varying the molecular weight of the acid copolymer.

In this regard, since the data indicated that there was little difference between using the dry blending process or the in-situ blending method for processing the cations, the in-situ method of producing the cation neutralized high acid ionomer blends was used in this analysis.

Along this line, the diblend and triblends set forth in Formulation Nos. 68, 73 and 74 are essentially the same as those set forth below in Formulation Nos. 91, 94 and 97, respectively. However, since a different batch of cores was utilized than those used in Example 2, the C.O.R.'s are slightly lower. While the cores utilized in the present Example were of the same composition, the lower C.O.R. was due to the age of the cores, i.e. molded cores will lose C.O.R. upon aging mainly due to moisture pickup. Formulation Nos. 92-93, 95-96 and 98-99, are similar to those set forth in Formulation Nos. 91, 94 and 97, respectively, with the exception that the molecular weight of the acrylic acid/ethylene copolymer utilized was varied. Specifically, Primacor 5983 and Primacor 5990 both contain the same acid content as Primacor 5981 (i.e. 20 weight percent acrylic acid) but have lower viscosities (lower molecular weights) and lower densities. Primacor 5981 has a melt index of 300 g/10 minute (ASTM Method D-1238 at 190.degree. C.) and a Brookfield viscosity of 51,000 cps at 350.degree. F. Primacor 5983 has a melt index of 500 and a Brookfield viscosity of 26,000 cps at 350.degree. F.; and Primacor 5990 has a melt index of 1300 and viscosity of 13,000 cps at 350.degree. F.

The resilience (C.O.R.) of the molded balls produced utilizing the different molecular weight acrylic acid/ethylene copolymers are set forth below in Table 13.

The data indicated that a higher molecular weight acid copolymer is preferred for obtaining high resilience (i.e. C.O.R.) and required toughness.

The new metal cation neutralized high acid ionomer resins were blended with ionomer resins containing a comonomer of the acrylate ester class in order to evaluate the improved playability and scuff resistance of the new formulated cover compositions. The compositions were produced "in-situ" as indicated above with the exception that the acid copolymers, such as a 20 weight percent acrylic acid/ethylene copolymer (i.e. "Primacor 5981", "Primacor 5983", etc.), were first mixed with the acid terpolymers containing a comonomer (or termonomer) of the acrylate ester class, such as poly(ethylene-methacrylic acid-butyl acrylate) (i.e. "Nucrel.RTM. 035 or 010") or poly(ethylene-acrylic acid-methyl acrylate), (i.e. "Escor.RTM. ATX 310, 320, 325 or 350"), and then the appropriate cation (i.e. cation salt) or cation blend (i.e. blend of cation salts) was added to neutralize the carboxylic acid groups of the copolymer/terpolymer mixture. The selection of the type and ratio of acid copolymer to acid terpolymer was based upon the desired final hardness of the cover material. The weight, Riehle compression, C.O.R., hardness, spin rate and cut resistance of the new cover compositions in comparison with the known formulations were observed.

The results set forth in Table 14 indicate that when relatively small amounts (i.e. approximately 40% by weight) of the ionomer resin containing a comonomer of the acrylate ester class were added to the new metal cation neutralized high acid ionomer resins, modest decreases in hardness and C.O.R. values were observed. See, for example, the intermediate hardness covers of Formulation NOs. 103 and 104 in comparison to that of the hard covers produced by the new metal cation neutralized high acid ionomer resins set forth in Formulation No. 102 and by the Top Flite.RTM. XL II (U.S. Pat. No. 4,911,451) representative formulation set forth in Formulation No. 105. This is further demonstrated in comparison with the soft cover produced in Formulation No. 106 which is representative of the cover formulation of Spalding's Tour Edition.RTM. 90 and Top Flite.RTM. Tour 100 balls (i.e. U.S. Pat. No. 5,120,791). Formulation Nos. 107-110 represented non-neutralized acid copolymer/terpolymer blends, and thus, the C.O.R. values were substantially lower.

The data set forth in Table 15 demonstrates the effect of adding higher levels of the acid terpolymers (i.e. 50% by weight) to the acid copolymers (i.e. Formulation Nos. 113-116 and 117-118). A moderate decrease in hardness and C.O.R. values and a significant increase in spin rates (playability) and cut resistance properties were observed. In this regard, the cut resistance properties of Formulation Nos. 113-116 and 117-118 were improved at similar or slightly lower spin rates when compared to the representative Tour Edition.RTM. and Top Flite.RTM. Tour cover formulations of Formulation No. 120. Furthermore, in comparison with the high acid ionomers of Formulation Nos. 111 and 119, Formulation Nos. 113-116 and 117-118 demonstrated substantial improvements in spin rates with moderate decreases in C.O.R. values.

The data set forth in Table 16 shows that cover compositions produced from the copolymer/terpolymer blends comprised of relatively high amounts of an ionomer resin containing a comonomer of the acrylate ester class (see, for example, Formulation No. 126 compared with Formulation No. 128) were softer than those previously prepared. Consequently, by adjusting the amount of ionomer resins containing a comonomer of the acrylate ester class, the present invention offers the latitude to tailor properties such as C.O.R., spin and scuff/abrasion resistance.

Furthermore, as demonstrated by the above Formulations, the addition of the ionomer resins containing a comonomer of the acrylate ester class to the high acid ionomer resins, enables the production of a golf ball cover composition having an improved combination of playability, durability and distance properties. Specifically, golf balls having the unique combination Shore C hardness of about 80 to about 95, spin rates of about 8,000 to about 10,600, Riehle compressions of about 55 to about 65, C.O.R. values of about 0.770 to about 0.810, and cut resistance of about 3 to about 5 can be produced by the present invention.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will 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.