WO2000073384A2

WO2000073384A2 - Soft ionomer compositions and blends thereof for golf ball covers

Info

Publication number: WO2000073384A2
Application number: PCT/US2000/014328
Authority: WO
Inventors: John Francis Hagman; Frank Michael Simonutti; Robert Joseph Statz
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1999-06-01
Filing date: 2000-05-24
Publication date: 2000-12-07
Also published as: WO2000073384A3

Abstract

Novel, soft, low modulus enthylene copolymer ionomer compositions containing an acrylate softening monomer, neutralized with magnesium or lithium ions possess a higher level of resilience at a given level of PGA Compressibility than known ionomers. The advantage is maintained in certain blend compositions with hard ionomers of lithium and magnesium for blends having a neat-sphere PGA Compression below about 155, for blends with hard sodium ionomer for blends with a neat-sphere PGA Compression below about 155 provided there is at least 50 % soft ionomer, and for stiffer blend compositions having 51 - 80 % hard ionomer, where the hard ionomer is sodium, potassium or zinc. The soft ionomers and blends are useful for golf ball cover material.

Description

TITLE SOFT IONOMER COMPOSITIONS AND BLENDS THEREOF FOR GOLF

BALL COVERS CROSS REFERENCE TO RELATED APPLICATIONS This application is a Continuation-In-Part of copending application serial number 08/843,767, filed April 22, 1997, which is a Continuation-In-Part of copending application, serial number 08/497,664, filed 6/30/95 which is a Continuation-In-Part of application, serial number 08/345,349, filed 11/21/94, which is a Continuation-In-Part of application serial number 08/077,581, filed 6/18/93 and now abandoned, and also of copending Application, serial number 08/617,061, filed 3/18/96.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to novel, soft, flexible ethylene copolymer ionomer compositions which have very high resilience combined with good playability. The compositions are useful particularly as covers for golf balls as well as other uses where high resilience is desirable. The ionomers are copolymers of ethylene, a softening comonomer and methacrylic acid, neutralized with magnesium or lithium. As golf ball cover material they possess a combination of flexibility and high resilience. This is an ideal property combination for materials used alone or in blends with other ionomers. Description of Related Art

Ethylene copolymer ionomers based on copolymers of ethylene with methacrylic acid, and optionally a third monomer which could be any of a vast range of monomers, specifically including vinyl acetate, methyl methacrylate and ethyl acrylate, were first disclosed in U.S. Patent No. 3,264,272 (Rees). The list of metal ions disclosed as possible neutralizing ions included metals of groups I, II, III, IV-A and VIII of the Periodic Table, including Na, K, Li, Cs, Ag, Hg, Cu, Be, Mg, Ca, Sr, Ba, and many more. As used herein, reference to neutralizing ions or neutralizing metals refers to the metal counterions included in the metal salt ionic polymers (ionomers) of the present invention. Ionomers with a third monomer exemplified included ethylene/vinyl acetate/me hacrylic acid neutralized with sodium and magnesium, and ethylene/methyl methacrylate/methacryhc acid neutralized with sodium.

The use of 'soft' , flexible ionomers, softened by such a third monomer, only became of commercial interest around 1987. Alkyl acrylates are the preferred softening monomers, vinyl acetate producing a less stable polymer. The employment of n-butyl acrylate as a softening monomer in terpolymer ionomers is disclosed in U.S. Patent No. 4,690,981 (Statz). This patent lists the possible neutralizing ions as those of groups la, lb, Ila, lib, Ilia, rVa, Vlb and VIII of the periodic table, such as Na, K, Zn, Ca, Mg, Li, Al, Ni and Cr. U.S. Patent No. 5,415,939 (Cadorniga), filed 12/21/93, discloses soft lithium ionomers and blends of such ionomers with hard ionomers. The parent case of which this present application is a continuation-in-part, which was filed 6/18/93, (i.e., prior to Cadorniga), discloses lithium and magnesium soft ionomers and blends with hard ionomers. Many other patents have referred to bipolymer and terpolymer ionomers of various metals, also in a general way. No terpolymer ionomer using an alkyl acrylate with methacrylic acid and neutralized with either lithium or magnesium is known to have been specifically disclosed or exemplified. References to them are merely of the shotgun type, such as those described above.

Golf balls have certain measurable properties which strongly and directly affect play characteristics. Most important of these are resilience and compressibility. Resilience and compressibility can be measured for the material itself, by testing a sphere made from the material. These material properties can affect golf ball play characteristics when used to form the cover of a ball. High resilience increases the distance a golf ball can be driven upon impact with a gof club, and compressibility increases the playability in terms of 'spin' and 'feel'.

In the case of ionomers, resilience and compressibility tend to be inversely related. Thus a highly resilient material is generally a harder, less compressible material, and vice versa. It has been a continuing object in the art of preparing materials for golf ball manuacture, to search for a material which is either better than previously known materials with respect to the relationship between resilience and compressibility, or has lower cost, or has additional advantages along with a similar balance of the material properties. One characteristic, in relation to golf balls, not related directly to the playability but to the general utility of a ball, is the ball's durability in use. Poor durability is manifest in ball cracking, and cracking at low temperatures is a particular problem. The properties of the material itself will affect golf ball durability significantly when the material is used for one-piece balls or for golf ball covers. Balata was an early preferred golf ball cover material because it imparted good spin characteristics with some resilience, as well as good Compression molding characteristics. However Balata covers impart very poor cut resistance to a ball. Ionomers, which generally impart better durability, soon began to take over a significant portion of the market, most particularly for cover materials.

There are a large number of patents relating to use of ionomers as golf ball cover materials, almost all of which are concerned with ionomer blends. These are based on the disclosure that, for certain desirable characteristics, blends show synergistic behavior over single ionomers. Two distinct types of ionomer blends have been disclosed. The first type is a blend of ionomers that have been neutralized with different metals (that is, the blend includes salts of various metals), and the second is a blend of hard bipolymer ionomers with soft terpolymer ionomers. The second type of blend may also include the first type of blend; that is to say the soft ionomer may use a different metal ion from the hard ionomer. Interspersed with these combinations is the use of a particular acid as the acid comonomer, generally methacrylic acid or acrylic acid. In some cases, either of these acids has been disclosed as being preferred over the other for some particular utility. In addition, the amount of acid comonomer may have preferred limits, with increasing emphasis on high levels of acid to achieve high resilience. Examples of these patents or publications include the following.

U.S. Patent No. 3,819,768 (Molitor) disclosed blends of sodium and zinc hard bipolymer ionomers as cover material. Zinc was shown to improve durability in terms of 'cold-crack' resistance. Sodium is generally particularly poor with regard to cold-crack durability.

U.S. Patents 4,884,814 (Sullivan) and 5,120,791 (Sullivan), the former terminally disclaimed with respect to the latter, both disclose blends of hard bipolymer and soft terpolymer ionomers, the second patent limiting the soft terpolymer ionomer to acrylic acid based ionomer. The hard ionomers are disclosed as sodium or zinc ionomers, with lithium and magnesium also disclosed in the second patent. The soft ionomers in both are limited to sodium and zinc ionomers. The preferred compositions are sodium zinc blends.

Patent publication WO 95/00212, published Jan. 5, 1995 is the published application of a parent case of the present application. It discloses other blends of hard and soft ionomers. It discloses that the ions used to neutralize soft ionomers may be sodium, zinc, magnesium and lithium. No magnesium or lithium soft ionomers are exemplified.

US. Patent No. 5,298,571 (Statz et al.) discloses blends of hard ionomers of zinc, lithium, sodium and magnesium. Blends of zinc and lithium hard ionomers of high acid copolymers are disclosed as having optimum resilience. The presence of magnesium was shown to be a disadvantage for obtaining the highest resiliency in any blend with any or all of zinc, lithium and sodium ionomers. The polymers disclosed are very hard however, and do not generally fall within the range of flexibility or compressibility of interest for the polymers of the present invention. Ionomers are disclosed for use as one polymer component of a filled three polymer blend useful for centers, cores and one-piece golf balls in U.S. Patent No. 5,155,157 (Statz et al.). Both terpolymer and bipolymer ionomers, with various metal ions, are disclosed for use as part of the polymer blend, but bipolymers are preferred in each type of use. Sodium and lithium hard bipolymers are the only polymers exemplified. The ionomers form only one polymer component of a three polymer blend which also included a non- ionomer thermoplastic and an ethylene glycidyl monomer copolymer which acts as a compatibilizing agent for the other two polymers. The golf ball industry is highly competitive, and even a small improvement in a golf ball can have a significant impact. As the art above shows, there are a vast number variables involved in formulating ionomer cover materials. Discerning which particular manipulation of variables can produce even a small, but real advantage is a daunting task. In general, lithium ionomers are harder than sodium or magnesium ionomers and zinc produces the softest ionomers. Lithium and magnesium hard ionomers are known, and lithium is a preferred hard ionomer for certain uses. Generally, a virtually unlimited number of ionomer compositions is possible, with any metal, either methacrylic or acrylic or other suitable carboxylic acid, at any level and, for terpolymer ionomers, almost every possible softening monomer. Also possible is an equally unlimited number of blend possibilities. The number of possible compositions, based on combinations of the above variables is enormous. The number which possess particularly desirable qualities is however far more limited. Soft ionomers using an alkyl acrylate softening monomer, methacrylic acid or acrylic acid as the acid, and lithium and magnesium as the neutralizing ion do not appear to have ever been made prior to the present invention. Thus, while broadly disclosed among a vast range of possible ionomers, there has been no recognition that such ionomers were worth making or that they might possess unique properties compared with other ionomers. There remains a continuing need for soft ionomers, particularly for use as covers for golf balls, which provides the playability imparted by a softer material, yet which imparts an improved level of resilience compared with known soft ionomers. There is also a need for such an ionomer which can impart some of its resilience/playability advantage when blended with hard ionomers when used as a component in golf balls.

SUMMARY OF THE INVENTION The invention resides in the discovery that lithium and magnesium ions used as the ion in soft ionomers produce ionomers which can show a major increase in the level of compressibility for a given level of resilience or, conversely, a higher level of resilience for the same compressibility. This discovery is magnified even more strongly with acrylic acid ionomers than with methacrylic acid ionomers. Specifically, the present invention is a golf ball comprising a core and a cover, the cover consisting essentially of: a polymeric component which is a soft, flexible ionomer having a neat-sphere

PGA Compression of below about 155, prepared from a first acid copolymer of; a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid or acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the acid copolymer with a metal-containing neutralizing compound, wherein the metal is selected from the group consisting of lithium, magnesiums, or both, with the proviso that the golf ball cover composition excludes soft acid copolymers having ethylene, an alkyl acrylate, and a partially neutralized carboxylic acid comonomer that includes the combination of lithium, zinc and potassium ions. h a further embodiment, the present invention is golf ball, comprising a core and a cover, the cover consisting essentially of a polymer blend of,

(i) at least 10 weight percent of a first polymeric component which is a soft, flexible ionomer having a neat-sphere PGA Compression of below about 155, prepared from a first acid copolymer of: a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid and acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the first acid copolymer to obtain lithium salts, or magnesium salts, or both, and (ii) a second polymeric component which is a hard, stiff ionomer having a flexural modulus of from 40,000 to 110,000 psi, prepared from a second acid copolymer of: a) ethylene, and b) 5-25 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, the ionomer made by neutralizing 20 to 80 percent of the acid groups of the second acid copolymer with magnesium or lithium ions or both, with the proviso that the neat-sphere PGA Compression of the blend composition does not exceed about 155 and with the further proviso that when the carboxylic acid of the first polymeric component is methacrylic acid, the metal of the ionomer cannot be lithium or lithium on the soft ionomer and magnesium on the hard ionomer.

In yet a further embodiment, the present invention is a golf ball comprising a core and a cover, the cover consisting essentially of a polymer blend of: (i) at least 50 weight percent of a first polymeric component which is a soft, flexible ionomer having a neat-sphere PGA Compression of below about 155, prepared from a first acid copolymer of: a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid and acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the first acid copolymer to obtain an ionomer having lithium, or magnesium, or both, and

(ii) a second polymeric component which is a hard, stiff ionomer having a flexural modulus of from 40,000 to 110,000 psi, prepared from a second acid copolymer of a) ethylene, and b) 5-25 weight percent of carboxylic acid which is methacrylic acid or acrylic acid or mix of methacrylic and acrylic acid, the ionomer made by neutralizing 20 to 80 percent of the acid groups of the second acid copolymer with a sodium-containing compound to obtain an ionomer having sodium ions, with the proviso that the neat-sphere PGA Compression of the blend composition does not exceed about 155.

In yet a further embodiment the present invention is a A golf ball comprising a core and a cover, where the cover comprises a blend of, (i) 20 - 49 weight percent of a first polymeric component which is an ionomer formed from a first acid copolymer consisting of a) ethylene, b) 15 - 25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6 - 12 weight percent of acrylic or methacrylic acid or both, the ionomer formed by neutralizing from between 10 and 90 % of the acid to obtain ionomer having only magnesium ions, and having a flexural modulus of 3000 to 10,000 psi, a Shore 'D' hardness of 45-55, and a melt index of 0.5 to 5.0 g/10 min., and

(ii) 51 - 80 weight percent of a second polymeric component which is an ionomer prepared from a second acid copolymer consisting of, a) ethylene, b) 19-25 weight percent of acrylic acid or methacrylic acid or both, the ionomer formed by neutralizing from between 10 to 90 % of the acid to obtain ionomer having sodium, zinc or potassium salts, the ionomer having a flexural modulus of 70,000 - 110,000 psi, a Shore 'D' hardness of 65 or greater, and a melt index of 0.5 to 5.0 g/10 min.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plot of PGA Compression versus COR measured on neat-spheres, showing compositions within the invention compared with other compositions. Figure 2 is a similar plot for the same properties, but measured on golf balls having the compositions as cover material.

DETAILED DESCRIPTION OF THE INVENTION This application is a continuation-in-part of three applications. Application 08/617,061, filed March 18, 1996, is one of those applications. Part of 08/617,061 is hereby incorporated by reference, as part of the present disclosure. Specifically, Figures 1,2,3 and 4 and the description of those figures or drawings on page 4 of that application, as well as the Description of Specific Embodiments starting on page 4, and all subsequent pages through page 10. The claims are specifically excluded from incorporation, since two sets of claims would then be part of the application. Pages 1 through page 4, line 3, while part of the priority document, are also excluded from incorporation, since information in those pages is subsumed and/or modified to form part of the present continuation-in-part disclosure. In this disclosure, the term copolymer is used to refer to polymers containing two or more monomers. The term bipolymer or terpolymer refers to monomers containing only two or three monomers respectively. The phrase 'copolymer of (various monomers) means a copolymer whose units are derived from the various monomers. The ionomers of this invention are prepared from 'direct' acid copolymers, that is to say copolymers polymerized by reacting all monomers simultaneously, as distinct from a graft copolymer, where a monomer or other unit is grafted onto an existing polymer, often by a subsequent polymerization reaction. Methods of preparing ionomers are well known, and are described in U.S. Patent No. 3,264,272, (Rees) which is hereby incorporated by reference. Methods of preparing the acid copolymers on which the ionomers are based is described in U.S. Patent No. 4,351,931, which is also incoφorated by reference hereby.

The materials of this invention, while useful for other purposes are particularly useful as materials for use as golf ball covers. This disclosure emphasizes the particular properties of interest in that end use, the excellent properties so revealed showing the uniqueness of these ionomers. In view of the large difference in the particular properties measured from other ionomers, it is believed that other characteristics or properties which related to other particular end uses will also be unique, and thus the compositions will, in many cases, be advantageous for other end uses.

There are different types of golf balls, suited to different levels of playing skill and playing conditions. One goal has been to emphasize resilience, since higher resilience corresponds to greater driving length. Higher resilience is associated with harder balls. Softer balls generally have higher playability or spin. A holy grail has always been to have the best of both worlds, high resilience and high spin. Thus if a softer ball could be made with higher resilience than hitherto, it would be highly desirable. The present invention is directed to softer materials, specifically magnesium and lithium soft ionomers, as well as blends of these with certain hard ionomers. Both these soft ionomers and blends with hard ionomers can be used for golf ball covers with varying hardness levels.

A common measure of resilience in the golf ball industry is the Coefficient of Restitution (COR) of the ball. The COR of a 'neat-sphere' of a material however can be a useful guide to the utility of that material for golf ball use, particularly for one-piece balls, but also to covers and even, to some extent, to the material's utility as a component of cores, and centers of balls. However, the COR on a ball clearly depends on the nature of the core, and thus careful choice of the core is necessary. Because determination of COR has been carried out under a bewildering variety of conditions, comparison with much of the patent or other published data, is difficult. For any particular method however, comparisons of various materials can be meaningfully made using measurements on 'neat- spheres' of the resin. The phrase neat-sphere in this disclosure means spheres molded from the resin alone, without filler or additive.

A good correlation of 'playability' or 'spin' of a ball may be made using a test referred to as 'PGA Compression', which is a standard industry test. It may be carried out on neat-spheres and, like COR, such a determination will be the best characterization of the nature of the material itself. Perhaps confusingly, high values of the numbers referred to as PGA Compression correspond to high hardness and stiffness, or lower compressibility. Use of the word 'Compression' in relation to the PGA test and the general term 'compressibility' should not be confused, since they are inversely related. The soft ionomers and many of the ionomer blends of this invention will have a PGA Compression value below about 155, based on neat- resin sphere determinations. For softer golf ball materials, values above 155 are generally too high for the material to provide balls with good spin. Preferably, the materials have a PGA Compression value below about 140. Resins of this invention, with PGA Compression in the 80 to 120 range show the biggest advantage compared with prior art materials. Materials with higher PGA

Compression values are in general stiffer, higher modulus materials. However it has been found that, of the two soft ionomers which are the basis of this invention, one of these, the soft magnesium ionomer, is particularly useful even in higher modulus blends. While there is no precise correlation between flexural modulus and PGA Compression, resins with flexural modulus of 35,000 psi will have a PGA Compression in the 130 to 160 range. The increased resilience at a given PGA Compression value seen in the materials of this invention may diminish at PGA values above about 130. For stiffer blends, such as those having a modulus generally above about 35,000 psi, and a PGA compression above about 150 and even considerably higher, magnesium soft ionomers blended with sodium, zinc and potassium hard ionomers having a flexural modulus of 70,000 to 110,000 psi, and a Shore 'D' Hardness of 65 or greater, form useful harder cover materials. In such blends, the amount of hard ionomer is from about 51 to 80 weight percent.

As noted, one other quality is always desirable, and often essential, and that is durability of the material in golf ball structures. Typically this is measured on a finished golf ball, having a cover made of the material, using a repeated impact test, including tests at low temperature. Determination of durability on a neat-sphere is generally not so definitive because of the inherent toughness of many neat resins. The durability measured on spheres consisting of neat resin and filler would, of course, be relevant for one-piece balls. Without at least some durability in a finished ball, high COR and low PGA Compression may be almost without value. It has now been found, surprisingly, that lithium, the ion which makes the hardest and stiffest of all ionomers, all else being equal, is ideally suited to make an excellent soft ionomer. Magnesium, which also makes one of the harder ionomers, is also ideally suited to make an excellent soft ionomer. Soft ionomers of terpolymer acid copolymers neutralized with these ions have now been found to result in a much improved balance between low PGA Compression and high COR resilience compared with prior art materials. Soft lithium are generally preferred over soft magnesium ionomers in single ionomer compositions for covers. These soft ionomers can particularly also form part of a soft ionomer/hard ionomer blend. If the resulting PGA Compression of the ionomer blend remains below about 155, this will typically, correspond to a flexural modulus below about 35,000, though it may exceed this slightly. However, certain blends having a higher flexural modulus than this, specifically when the hard ionomer is sodium, potassium or zinc and the soft ionomer is magnesium have also been found to be particularly useful.

The acid copolymer precursors of the soft ionomers of this invention are copolymers of ethylene, from 3 to 40 weight percent of alkyl acrylate, whose alkyl group has from 1 to 8 carbons, and from 5 to 15 weight percent of methacrylic or acrylic acid. The preferred alkyl acrylate is n-butyl acrylate. It is to be understood that there can be more than one alkyl acrylate and both acrylic and methacrylic acid present, provided the percent limits for alkyl acrylate and acid are met. For this reason, the generic term copolymer is used rather than terpolymer, in referring to the claimed compositions, because terpolymer implies just three monomers. It is also to be understood the acid copolymer may be a blend of different soft acid copolymers having differing levels and/or species of either the softening comonomer, the acid or both. The term 'soft acid copolymer', 'soft flexible ionomer' and the like, encompasses this possibility. Many preparations of copolymers are sufficiently non-uniform in comonomer content from molecule to molecule that such 'copolymers' are, in effect, blends anyway.

Below 3% softening comonomer insufficient softening (modulus reduction) occurs, and above 40% the polymer and resultant ionomer is too soft. From 10 to 30 percent weight is preferred and 15 to 25 weight percent is most preferred. Acrylic acid in the soft acid copolymer leads to somewhat more resilient soft ionomers, and is generally preferred.

For soft ionomers and hard ionomers which form blends of the present invention of the percent neutralization of the acid groups present for magnesium or lithium ions, or both, is from 10 to 90, preferably from 20 to

80%. More preferably the level is from 25 to 65% and most preferably from 30 to 60%. For soft ionomers, the modulus will typically be about 5000 to 35,000 psi. The modulus will be higher for lithium than magnesium, and will increase with the level of acid. The modulus will be lower the higher the amount of alkyl acrylate. The modulus of the soft lithium and magnesium ionomers prepared here, ranged from about 5000 to 27000 psi, but it is readily possible to prepare magnesium and lithium terpolymer ionomers with a modulus up to 35,000 psi, and even higher. Certain terpolymer ionomer compositions can be made, such as ones with very high acid, particularly acrylic acid, using lithium ions and with low amounts of alkyl acrylate which will give higher than 35,000 psi flexural modulus. However, provided the PGA Compression of neat- spheres of the soft ionomers is below about 155, it will be suitable. It is readily within the skill of the artisan to determine which combinations of monomers, neutralization level and acid type will produce ionomer within the required neat- sphere PGA Compression limits.

In the prior art, it has been common often to refer to 'soft' ionomers as possessing a flexural modulus below about 10,000 psi and to 'hard' ionomers as those with modulus above about 30,000 psi. In this disclosure, the terpolymer ionomers with a softening alkyl acrylate termonomer are still referred to as 'soft' even when the flexural modulus is much higher. As noted above, the soft ionomers of this invention can have a flexural modulus of up to 35,000, and even in some cases above this.

Typically, to achieve modulus values in the region of 35,000 psi, so that the neat-sphere PGA Compression of the ionomer is as high as 155, using prior art soft ionomers such as zinc or sodium soft ionomers it would generally be necessary to blend with a hard ionomer. However, it can be seen from the modulus values in Table 1 , that when lithium and magnesium are the neutralizing ions, the flexural modulus values can be considerably higher than those of old art zinc and sodium soft ionomers. For this reason, soft ionomers of the present invention are useful alone, that is, without blending with a hard ionomer. The resilience advantage at a given PGA Compression value in the soft ionomers however, could mean that higher stiffness soft ionomers alone would give as good properties as blends of comparable stiffness.

While blending is not required to achieve superior results, blending wth a hard ionomer can offer cost advantages and various other advantages. In conventional practice, blends of hard and soft ionomers, concomitant with a given level of overall stiffness, have been preferred in the past. Blending with hard ionomers could, however, dilute the resilience advantage at a given PGA Compression value that these unique soft ionomers offer While blends of the soft ionomers of the present invention with hard ionomers are contemplated, they are not preferred embodiments of the present invention.

For cover material, the modulus should be preferably above 10,000 psi. and more preferably above 15,000, irrespective of whether using a single soft ionomer or a soft/hard ionomer blend. When a soft ionomer has a modulus much below 10,000 psi, for cover materials it is preferable to blend with a hard ionomer so the final modulus falls within the range 10,000 to 35,000 psi when using lithium and magnesium hard ionomers, or from 10,000 to above 35,000 psi if using sodium, zinc and potassium hard ionomers. If a soft ionomer is blended with hard ionomer, there should be at least 10 percent soft ionomer, preferably above 20 percent, or the advantages of the particular soft ionomers of this invention may not be realized, or may be considerably diluted. Hard ionomers which can be blended with the soft ionomers of the present invention are lithium, magnesium, sodium, zinc or potassium ionomers. Lithium, magnesium, and sodium ionomers are preferred. They are derived from acid copolymers of ethylene and, in the case of lithium and magnesium hard ionomers, from 5 to 25 weight percent acid where the acid is methacrylic or acrylic acid, or both, preferably from 10 to 22 weight percent. In the case of sodium, potassium or zinc hard ionomers, the acid level is preferably 19 to 25 weight percent. It is to be understood that the hard ionomer may be a blend of more than one hard ionomer each having different levels of and/or different acids in them, just as for the soft ionomer. The term 'hard acid copolymer', and 'hard stiff ionomer' and the like, encompasses this possibility. In the case of a hard ionomer/soft ionomer blend, it is preferable for the hard ionomer to have a higher level of acid than the soft ionomer. Higher acid increases the hardness, so that to produce a blend having a specific final blend modulus, the higher the acid level in the hard ionomer, the less of it will be required in the blend. The modulus may range from 40,000 to 110,000 psi. In the case of sodium, zinc and potassium hard ionomers, the modulus ranges from 70 to 110,000 psi. In general, if the composition is a blend containing hard ionomer, the higher the modulus of the hard ionomer, the greater the amount of soft ionomer possible in the blend for a given final blend modulus, whether the high modulus is due to acid level, acid type, neutralizing ion or degree of neutralization. Since it is the softer terpolymer ionomers which are here clearly shown to have such an attractive balance of PGA Compression and COR, it may be that the more magnesium or lithium soft ionomer, the higher the resilience, at a given PGA Compression level. Melt index of either the soft or hard ionomers can be from about 0.1 to 30 g/10 min., preferably 0.1 to 10 more preferably from 0.1 to 6 and most preferably from 0.5 to 5.0 g/10 min. The mell index of the acid copolymers from which the ionomers are derived may be from about 20 to 350 g./lO min. When the compositions of the invention are blends, the preferred blends for softer cover materials are lithium soft/magnesium hard. Magnesium/ magnesium and lithium/lithium blends are also attractive. Magnesium soft/lithium hard blends are generally less prefeπed, and one such blend showed a diminished resilience advantage compared with the reverse blend. The preferred soft resins, and those used in the examples, have less acid than the hard resins. Therefore, for a given percent of acid groups neutralized they will have less equivalents of metal present. Thus the number of equivalents of lithium in magnesium soft/lithium hard blends will be higher, when there is more acid in the hard ionomer, than in lithium soft/magnesium hard blends. For blends containing both lithium and magnesium ions therefore, a higher level of magnesium equivalents is preferable.

While not preferred, as noted, the hard ionomer can also be a sodium, potassium or zinc ionomer. In the case of zinc and potassium hard ionomers, the amount of hard ionomer is, by contrast to lithium and magnesium hard ionomers, between 51 and 80 weight percent.

It has commonly been assumed that ions in an ionomer blend are almost completely labile, and move freely from polymer chain to polymer chain. This may be true for a blend of two ionomers based on the same acid copolymer. However, without commitment in any particular way, it may not be completely true in blends where the underlying acid copolymers of the two ionomers are very different, such as with soft and hard ionomers. The ions originally associated with the soft ionomer, may, to some extent, tend to remain more associated with the soft ionomer in a blend, and this may produce blends with different properties than blends having the reverse ions in the soft and hard components. In practice, it has been found that there is a difference in properties in soft/hard blends, when the ions for the soft and hard ionomer are reversed.

The ionomers may also contain conventional additives such as pigments, antioxidants, UN. absorbers, brighteners and the like. Testing Methods and Criteria.

Flexural modulus is measured using ASTM D790-B, and is measured using a standard 'flex bar' and not on a sphere of material as for most other tests.

Coefficient of Restitution, COR, was measured both on neat- spheres and on finished balls having a cover of the material under test. It is measured by firing, either a covered ball having an the ionomer composition as cover or a neat-sphere of the ionomer composition, from an air cannon at an initial speed of 180 ft./sec. as measured by a speed monitoring device over a distance of 3 to 6 feet from the cannon. The ball strikes a steel plate positioned 9 feet away from the cannon, and rebounds through the speed-monitoring device. The return velocity divided by the initial velocity is the COR.

COR of neat-spheres may fall anywhere between 0.50 and 0.70. The range on useful covered balls of this invention however, is between about 0.67 and 0.74. PGA Compression is defined as the resistance to deformation of a golf ball, measured using a standard industry ATTI machine. It was measured on a neat-sphere of resin and on balls having a cover of resin. For adequate spin of a ball, when the ionomer is used as a cover material, the PGA Compression, measured on a neat-sphere should be less than about 155, preferably less than 140 and most preferably less than 130.

The PGA Compression of a ball using the resin as a cover is, of course, dependent on the core of the ball. Generally, the PGA Compression of finished balls is much lower than the 155, and is typically in the 80 to 100 range. Thus on finished balls with the material as cover, the values of COR and PGA Compression fall in a different range than for values for neat-spheres of the material. The desirable PGA Compression of a ball itself is typically in the 80 to 100 range. The PGA Compression COR correlation for balls is much more attractive than for neat-spheres, as indicated by a vast shift of the line to the right for finished balls. This range can be achieved however, using conventional cores, and cover material having neat-sphere PGA Compression values about in the 110 to 155 range.

Clearly, a one-piece ball, which is a sphere molded from resin and filler and minor quantities of typical additives, will not generally have as good a PGA Compression/COR relation as a ball made from a core and cover. While such one-piece balls would not have the same PGA Compression/COR relation as neat-spheres, because of the effect of filler, they would have a correlation more akin to that of neat-spheres than to balls with a core. While useful as 'range' balls, such one-piece balls will not have the superior properties of two and three-piece balls. Nevertheless, materials of this invention would still make superior balls having properties in the 'range' ball category. All the materials of the invention will be suitable for one piece balls. However, in view of the fact that filler will raise PGA Compression, it is clear that more flexible materials than for covers can be used.

Melt Index (MΙ).was measured using ASTM D-1238, condition E, at 190 deg. C, using a 2160 gram weight. Values of MI are in grams/10 minutes.

Durability was measured using a repeat impact test on finished balls, with the material of the invention as the cover, on a Wilson Ultra^® conventional solid core. Such cores are believed to be made of 1,4-cis polybutadiene, crosslinked with peroxides and co-crosslinking agents such as zinc (me h)acrylate. Durability is measured using the same machine as for COR, but using an initial velocity of 175 ft./sec. Durability values are the number of hits to break. Durability at low temperatures is especially desirable, and for this reason, durability tests at -20 ° F were carried out. While good durability only at room temperature is adequate for golf balls used in some locales, low temperature durability values, preferably above at least 10, as tested under these conditions, is preferred for cold weather use. Durability at room temperature is almost invariably better than durability at -20°F, so that low temperature durability is a guide to the worst performance to be expected. Good durability of a material, based on tests when the material is used as a cover, may indicate good durability for use as a material in a one-piece ball.

EXAMPLES. Table 1 lists various ionomers used in the examples. The list includes soft ionomers which are part of the invention as well as soft ionomers which are not. It also includes hard ionomers which can be part of a blend of this invention as well as hard ionomers which are not. Flexural modulus is shown, if measured. Note that S8 has a modulus of almost 27,000 psi. This is stiff enough even to make a relatively stiff cover material by itself, i.e., without blending with a hard ionomer.

Table 2 lists values of COR and PGA Compression on neat- spheres for the compositions indicated. Comparative examples are numbered with a suffix C. The same values are plotted in Figure 1. Durability of balls which employed the compositions as a cover on a conventional solid core are also shown, if measured.

Figure 1 shows comparative examples, outside the invention, indicated by a circle, and examples by a cross. A line is shown, correlating PGA Compression and COR values for prior art materials outside this invention, based on previous data (indicated by triangles), determined prior to this investigation, together with data on prior art materials measured during the present investigation (indicated by a circle). The line is a 'visually best-fit' line, and is based on materials which differed in their ion or ions, their MI, the acid used (whether acrylic of methacrylic), the amount of acid and, in the case of soft ionomer, the amount of acrylate softening monomer. The line is a good fit for data up to a PGA Compression of about 140. Above this, there appears to be a poorer correlation with more scatter in the data. Of course, the new soft lithium and magnesium ionomers and blends, whether part of this invention or not, are not part of the data on which the line is based, since they are new ionomers. The fact that such a line can be drawn suggests that, for most ionomers and blends, PGA Compression and COR are uniquely related, largely irrespective of comonomer or ion composition, and depend essentially only on the particular level of stiffness of interest. This is except, of course, for the compositions of the present invention.

Surprisingly, when one examines the data for soft ionomers of magnesium and lithium, and blends of these ionomers with hard ionomers, there is a dramatic shift to the right or to lower PGA values depending on the axis chosen for comparison. Thus, for these soft ionomers, and blends containing these soft ionomers, there is apparently a resilience advantage at a given PGA Compression level and vice versa. This will translate to, at the worst equivalent or slightly better, but generally significantly better compositions for one-piece balls, and for centers and cores and covers for two- or three-piece balls respectively, than previously known compositions. Of course the degree of advantage will depend on which of these golf ball applications is considered. Zinc has long been known to provide good durability at low temperatures, and compositions of comparative examples which contain zinc are clearly good in low temperature durability as seen from Table 2. Both zinc and sodium soft ionomers alone, generally will have a flexural modulus of 5,000 psi or less however. In general, this will be too flexible to be useful alone for use as materials of this invention. Zinc hard ionomer blended with lithium soft ionomer does seem to provide good compositions when the PGA Compression is above about 140. However, as noted above, the singularity of the correlation becomes less definite at high PGA values.

Sodium hard ionomer is known to provide poor low temperature durability (example 2C and blend 3C). However it can form the hard ionomer portion of blends (example 7), provided there is not more than 50 percent of it. Lithium soft ionomer is not particularly durable at low temperatures (example 2) though not nearly as poor as sodium (2C). However its effect on increasing COR at a given PGA level in lithium soft ionomer or in blends of this invention can provide good compositions in this respect. Magnesium ionomer as the hard segment provides excellent durability. Magnesium soft/magnesium hard blends can thus provide excellent overall compositions (see Example 8).

For use of the material for golf ball covers, using conventional cores, the advantage can show up in the PGA Compression and COR of the resulting ball itself. However, because the overall PGA Compression and COR is also dependent on the core, not just the cover, the PGA/COR improvement may be somewhat diminished in some cases. Different cores provide somewhat different PGA Compression/COR correlations, so that manipulation of core alone can lead to improved balls. Comparison of cover materials must be made on balls which use the same core. As noted above, the relationship between PGA Compression and COR for golf balls provides a line or lines which is shifted far from that observed for neat-spheres.

Table 3 shows PGA Compression and COR values measured on golf balls having a Wilson Ultra^® core, and a cover of the materials having the composition as indicated by the corresponding example number in Table 2. In Figure 2, the encircled crosses represent finished ball PGA Compression and COR values with prior art covers, and the crosses alone represent values using cover materials of the invention. The line drawn is a 'visually-best' line, but there are insufficient data at low PGA values to establish the line with great certainty. It can be seen that, while covers made with soft ionomers alone, which give PGA values in the 78-81 range, appear to show only a small improvement, if any, when blends are tested, giving PGA in the 83-94 range, the improvement, for the most part is dramatic. It is not clear why examples 7 (PGA 94) shows such a low COR value, and why example 8 (also PGA 94) shows only a small improvement. Nevertheless, it is clear that a dramatic improvement is possible.

TABLE 1 COMPOSITION OF IONOMERS

# Composition Monomer MI Ion Neutr Flex Ratios Modulus

SI E/nBA/MAA 68/23/9 0.6 Zn -50 -2700

S2 E/nBA/MAA 68/23/9 Na -50 4100

S3 E/nBA/MAA 68/23/9 Mg -50 7100

S4 E/nBA/MAA 68/23/9 Li -50 5000

S5 E/nBA/AA 70/22/8 1.9 Mg -45 7800

S6 E/nBA/AA 70/22/8 0.4 Li -75 9500

S7 E/nBA AA 69.4/18/11.6* 1.6 Mg -45 16700

S8 E/nBA/AA 69.4/18/11.6* 0.5 Li -75 26500

HI E/MAA 80/20 -1 Na -79000

H2 E/MAA 85/15 -1 Na -57 50000

H3 E/MAA 85/15 ~1 Zn -57 48000

H4 E/MAA 85/15 -1 Mg -50

H5 E/MAA 85/15 -4 Li -50

H6 E/MAA 81/19 -4 Li -50

H7 E/MAA 85/15 ~4 Mg -50

H8 E/MAA 85/15 ~1 Li -50

H9 E/MAA 80/20 -1 Mg -50

H10 E/AA 80/20 ~1 Mg -50

E = Ethylene, MAA = Methacrylic acid, AA = Acrylic acid, nBA = n-Butyl Acrylate.

Flexural Modulus values in psi. Neutralization values are based on the amount of neutralizing ion in the feed when making the ionomer, assuming complete ionomerization. * These comonomer contents are based on best data available. Some unconfirmed data have suggested these comonomer contents may be slightly in error. TABLE 2 »

PGA COMPRESSION AND COR OF IONOMER COMPOSITIONS

Ex.# Composition Blend COR PGA Durability

Ratio Compression Hits/Crack -20°F

1C SI - 0.511 58

2C S2 - 0.553 67 1

1 S3 - 0.593 86 28

2 S4 - 0.584 83 8

3 S5 - 0.618 95 25

4 S6 - 0.656 116

5 S7 - 0.621 126

6 S8 - 0.672 144

3C Sl/Hl 50/50 0.637 140 7

4C S1/H2 50/50 0.645 143 48

5C S2/H3 50/50 0.619 132 50

6C S3/H3 50/50 0.602 127 50

7C S4/H3 50/50 0.621 133 38

8C S5/H3 50/50 0.619 131 50

9C S6/H3 50/50 0.645 139 47

IOC S7/H3 75/25 0.618 135 50

11C S8/H3 75/25 0.674 148 26

12C S3/H3 75/25 0.590 109

7 S3/H2 50/50 0.645 130 22

8 S3/H4 50/50 0.641 136 50

9 S3/H5 50/50 0.647 142 8

10 S3/H6 50/50 0.654 146 14

11 S3/H7 75/25 0.620 117 15

13C S1/H2 50/50 0.650 143 50

12 S4/H4 50/50 0.644 141 45

13 S5/H8 50/50 0.638 142 5

14 S5/H4 50/50 0.634 138 50

15 S6/H9 50/50 0.668 147 44

16 S6/H10 50/50 0.633 132 7

17 S6/H9 75/25 0.655 126 50 TABLE 3

PGA COMPRESSION AND COR OF GOLF BALLS

(Cover composition as in Table 2, Ultra^® Core)

Ex.# COR PGA Compression

1 0.678 79

2 0.673 81

3 0.672 78

7 0.687 94

8 0.681 94

13C 0.693 90

12 0.708 83

13 0.709 87

14 0.711 88

15 0.714 89

16 0.708 86

17 0.708 85

Claims

CLAIMS:

1. A golf ball comprising a core and a cover, the cover consisting essentially of: a polymeric component which is a soft, flexible ionomer having a neat-sphere PGA Compression of below about 155, prepared from a first acid copolymer of; a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid or acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the acid copolymer with a metal-containing neutralizing compound, wherein the metal is selected from the group consisting of lithium, magnesiums, or both, with the proviso that the golf ball cover composition excludes soft acid copolymers having ethylene, an alkyl acrylate, and a partially neutralized carboxylic acid comonomer that includes the combination of lithium, zinc and potassium ions.

2. The golf ball of Claim 1 wherein the carboxylic acid is acrylic acid.

3. The golf ball of Claim 1 wherein the metal is magnesium.

4. A golf ball, comprising a core and a cover, the cover consisting essentially of a polymer blend of,

5. The golf ball of Claim 4 wherein the carboxylic acid of the first polymeric component is acrylic acid, the metal of the first polymeric component is lithium, and the metal of the second polymeric component is magnesium.

6. A golf ball comprising a core and a cover, the cover consisting essentially of a polymer blend of:

(i) at least 50 weight percent of a first polymeric component which is a soft, flexible ionomer having a neat-sphere PGA Compression of below about 155, prepared from a first acid copolymer of: a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid and acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the first acid copolymer to obtain an ionomer having lithium, or magnesium, or both, and

7. A golf ball comprising a core and a cover, where the cover comprises a blend of, (i) 20 - 49 weight percent of a first polymeric component which is an ionomer formed from a first acid copolymer consisting of a) ethylene, b) 15 - 25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6 - 12 weight percent of acrylic or methacrylic acid or both, the ionomer formed by neutralizing from between 10 and 90 % of the acid to obtain ionomer having only magnesium ions, and having a flexural modulus of 3000 to 10,000 psi, a Shore 'D' hardness of 45-55, and a melt index of 0.5 to 5.0 g/10 min., and (ii) 51 - 80 weight percent of a second polymeric component which is an ionomer prepared from a second acid copolymer consisting of, a) ethylene, b) 19-25 weight percent of acrylic acid or methacrylic acid or both, the ionomer formed by neutralizing from between 10 to 90 % of the acid to obtain ionomer having sodium, zinc or potassium salts, the ionomer having a flexural modulus of 70,000 - 110,000 psi, a Shore 'D' hardness of 65 or greater, and a melt index of 0.5 to 5.0 g/10 min.

8. The golf ball of Claim 7 wherein the hard ionomer has a Shore "D" hardness of greater than about 70, and the soft ionomer has a Shore "D" hardness of greater than 50.

9. The golf ball cover according to claim 4 or 5 wherein the percentage of terpolymer is at least 50 wt.% relative to the second polymeric component.

10. A method of making a flexible and resilient golf ball comprising

(i) forming a terpolymer consisting essentially of a) ethylene, b) 15-25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6-12 weight percent of carboxylic acid which is methacrylic acid or acrylic acid, or a mix of methacrylic acid or acrylic acid, the ionomer being made by neutralizing 20 to 80 percent of the acid groups of the acid copolymer to form a metal salt of the acid coplymer having a metal selected from the group consisting of lithium, magnesium, or a mix of both and

(ii) making a golf ball cover having said terpolymer wherein the golf ball having said cover has a PGA Compression of below about 155 and wherein the terpolymer provides a significant increase in the level of compressibility for a given level of resilience or a higher level of resilience for the same compressibility.

11. The method according to claim 10 wherein the carboxylic acid is acrylic acid.

12. The method according to claim 10 wherein the neutralizing ion is magnesium.

13. The method according to claim 10 wherein the golf ball cover further comprises a hard polymeric component having a flexural modulus of from 40,000-110,000 psi, prepared from an acid copolymer having a) ethylene, and b) 5-25 weight percent of carboxylic acid which is methacrylic acid or acrylic acid or both, the ionomer being made by neutralizing 20-80 percent of the acid groups with magnesium or lithium or both to form a cover blend.

14. The method according to claim 13 wherein the carboxylic acid of the soft ionomer is acrylic acid and the neutralizing ion of the soft ionomer is lithium, and the neutralizing ion of the hard polymeric component is magnesium.

15. A method of making a flexible and resilient golf ball comprising, (i) forming a polymer blend consisting essentially of:

(a) at least 50 wt.% of a first polymeric component which is a soft flexible ionomer having a neat-sphere PGA Compression of below about 155, prepared from a first acid copolymer of ethylene, 15-25 wt.% of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and 6-12 wt.% of carboxylic acid which is methacrylic acid or acrylic acid or both, the ionomer being made by neutralizing 20 to 80% of the acid groups of the first acid copolymer with lithium or magnesium or both, and

(b) a second polymeric component which is a hard, stiff ionomer having a flexural modulus of from 40,000 to 110,000 psi prepared from a second acid copolymer of ethylene and 5-25 wt.% of carboxylic acid which is methacrylic acid or acrylic acid or both, the ionomer being made by neutralizing 20 to 80 % of the acid groups of the second acid copolymer with sodium ions, with the proviso that the neat-sphere PGA Compression of the blend composition does not exceed about 155; and

(ii) making a golf ball cover comprising the blend composition wherein the golf ball has a significant increase in the level of compressibility for a given level of resilience or a higher level of resilience for the same compressibility.

16. A method of making a flexible and resilient golf ball comprising,

(I) forming a polymer blend consisting essentially of: (i) 20 - 49 weight percent of a first polymeric component which is an ionomer formed from a first acid copolymer consisting of a) ethylene, b) 15 - 25 weight percent of an alkyl acrylate or mix of alkyl acrylates, the alkyl groups having from 1 to 8 carbon atoms, and c) 6 - 12 weight percent of acrylic or methacrylic acid or both, the ionomer neutralized to between 10 and 90 % with magnesium ions, and having a flexural modulus of 3000 to 10,000 psi, a Shore 'D' hardness of 45-55, and a melt index of 0.5 to 5.0 g/10 min., and

(ii) 51 - 80 weight percent of a second polymeric component which is an ionomer prepared from a second acid copolymer consisting of, a) ethylene, b) 19-25 weight percent of acrylic acid or methacrylic acid or both, the ionomer formed by neutralizing to between 10 to 90 % with sodium, zinc or potassium ions, the ionomer having a flexural modulus of 70,000 - 110,000 psi, a Shore 'D' hardness of 65 or greater, and a melt index of 0.5 to 5.0 g/10 min; and

17. The method according to claim 10, 15 or 16 wherein the

PGA Compression of the golf ball is below 95 and the resilience is above 0.670.