WO1993016764A1

WO1993016764A1 - Process for thermoplastic golf balls

Info

Publication number: WO1993016764A1
Application number: PCT/US1993/001458
Authority: WO
Inventors: Jon Paul Braemer
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1992-02-28
Filing date: 1993-02-24
Publication date: 1993-09-02
Also published as: AU3724493A

Abstract

The invention provides a process for making cores for two-piece golf balls, centers for three-piece golf balls, and one-piece golf balls by injection molding blends of a copolyetherester or copolyetheramide, an epoxy-containing compound, and an acid-containing ethylene copolymer ionomer in a runnerless injection molding apparatus.

Description

TITLE

PROCESS FOR THERMOPLASTIC GOLF BALLS

CROSS REFERENCE TO RELATED APPLICATION

Th s application is a continuation-in-part of Serial No.

07/681,431, filed March 26, 1991, which is a continuation in part of Serial No. 07/634,793, filed December 27, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to a process for manufacturing thermoplastic golf ball cores, golf ball centers and one-piece golf balls and, more particularly, to the use of runnerless injection molding apparatus.

BACKGROUND OF THE INVENTION

There currently exist two general types of premium golf balls: a "three-piece" ball which comprises a spherical molded center having an elastomeric thread-like material wound around it (wound center) covered with either a thermoplastic or thermoset material; and a "two-piece" ball which comprises a spherical molded core covered with a thermoplastic material. The material used to mold the three-piece centers and the two-piece cores has traditionally been a thermoset rubber, for example, polybutadiene rubber. As with any thermoset material, however, there are major disadvantages, such as the inability to recycle scrap materials and the need for complex multistep manufacturing processes. Of course, three-piece balls and two-piece balls are by their very nature more complicated and costly to manufacture than the long sought after one-piece golf ball, which has yet to be successfully demonstrated except for limited flight golf balls.

Conventionally, thermoplastic covers are formed about the solid cores, in the case of two-piece golf balls, or about the wound center, in the case of the three-piece golf ball, in a one-step molding process by either compression molding or injection molding in which cover stock is molded about the core. The center in a three-piece golf ball is typically either a small balloon filled with liquid or a solid mass of material.

Solid cores and centers are typically manufactured by first producing a preform of a thermosetting material. A thermosetting material is a polymer that "sets" irreversibly upon heating to a cure temperature. The preform is generally made by blending a rubber, such as polybutadiene, with various additives such as fillers, curing agents, activators, accelerators, property changers and property maskers in a Banbury mixer. Preforms are placed into a plurality of mold cups housed in a mold plate of a

compression mold in which the core or center is formed and cured. The compression mold generally comprises two or more mold plates , each of which houses a plurality of mold cavities or cups. Typically the mold plates are positioned horizontally, that is one above the other.

While manufacture of cores and centers in injection molds is possible, it generally is not economical, since the material which cures in the sprues and runners cannot be recycled. Also, removing cured material from the sprues and runners presents an operational problem. Runnerless mold systems with thermodynamically isolated regions wherein a lesser heat is applied to the sprue and runner system to assure non-curing conditions for material that has not reached the mold cavities have been taught. Other systems having provisions for stripping the sprues and runners during ejection of the molded part are also known.

When applying covers with compression molding, the wrapped centers or solid cores are placed in half-shells of cover stock in a compression mold, the mold is closed, and the core and cover stock are subjected to heat and pressure. The heat and pressure cause the preformed cover half-shells to soften and flow about the core to pick up the dimple pattern of the mold cups. An equator line is formed where the two cover half-shells meet.

With injection molding, cores are placed in a mold in which the mold cups are typically equipped with retractable pins. The pins ensure correct positioning of the core in the cup. Once the core is correctly positioned in the closed mold, cover stock is injected into the mold cups and flows about the core. The cover stock picks up the dimple pattern of the mold cups. Once the mold cups are filled with cover stock, the pins are retracted while the cover stock is still at least semi-flowable, allowing the cover stock to close the pinholes. Retractable-pin molds are expensive, difficult to operate, often result in surface defects, and limit the number of compositions which can be used as cover stock. Also, the injection molding machines are typically cold-runner systems in which the runners are ejected with the molded golf ball. The thermoplastic runner material is separated from the golf ball and recycled. U.S. Patent No.4,959,000, which is incorporated herein by reference, however, discloses a retractable pin mold for golf balls in which a hot-runner system is indicated as being preferred. In an effort to overcome the deficiencies of the traditional thermoset three-piece centers and two-piece cores, and in the quest to produce a one-piece golf ball, attempts have been made to utilize certain thermoplastic materials in the molding of such centers, cores and one-piece balls, but with limited success. For example, U.K. Patent Application 2,164,342A describes moldable compositions comprising ionic copolymers (or potentially ionizable acid copolymers) blended with certain

thermoplastic materials such as a polyester block copolyamide, a polyether copolyamide, a copolyester and the like. Those compositions are said to be useful as three-piece centers, two-piece cores and one-piece solid golf balls, but they lack, e.g., durability. Therefore, there still exists the need for a material that is thermoplastic, yet resilient and durable enough, and imparting adequate compression, to be useful as a three-piece center, two-piece core and a one-piece golf ball.

Cross-referenced Patent Application Serial No. 07/681431, having the inventor of this invention as one of its joint inventors, discloses a material that is thermoplastic, yet resilient and durable enough while having adequate compression to be useful as a three-piece center, a two-piece core and a one-piece golf ball. The material comprises a thermoplastic polymer selected from copolyetheramides and copolyetheresters, an epoxycontaining compound and an acid-containing ethylene copolymer ionomer. This material, while categorized as a thermoplastic, does not melt in the manner of the thermoplastics conventionally used for covers. That is, it does not exhibit the typical thermoplastic rheology of readily flowing at low shear at temperatures above the thermoplastic's crystalline melting point or softening point but below the polymer's degradation temperature. The thermoplastics conventionally used for covers flow at temperatures above their crystalline melting point at virtually zero shear.

There remains a need for an improved process for producing one-piece golf balls, cores and centers employing an injection molding system. The system should not require provisions for stripping the sprues and runners during ejection of the molded part as doing so generates scrap. The system also should not require thermodynamically isolated regions wherein a lesser heat is applied to the sprue and runner system to assure non-curing conditions for material that has not reached the mold cavities.

Preferably, the process should minimize or eliminate temperature imbalances in the mold, provide a product having more consistent volume and weight as well as surface characteristics, and produce a golf ball that does not require roughening prior to painting or imprinting. Preferably, the process should be such that flash at the golf ball equator (location of mold separation) is essentially eliminated, thereby eliminating the need to buff the golf ball around its equator and permitting variations in dimple design (placing dimples on the equator).

SUMMARY OF THE INVENTION

The subject invention is a process comprising injection molding thermoplastic compositions useful in the manufacture of cores, centers or one-piece golf balls in a runnerless, hot runner or insulated runner injection molding apparatus, which will be referred to generically as a runnerless system.

More specifically, the subject invention provides for injection molding a composition for the manufacture of a one-piece golf ball comprising 40-65 polymer weight percent of a thermoplastic polymer selected from copolyetheresters and copolyetheramides; 1-10 polymer weight percent of an epoxy-containing compound; 5-20 total weight percent of a filler having a density greater than or equal to about 4 gm/cc, and the remainder, to total 100 polymer weight percent, of an acid-containing ethylene copolymer ionomer.

In another embodiment, the subject invention provides for injection molding a core for a two-piece golf ball, the core composition comprising 50-65 weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters; 1-10 weight percent of an epoxy-containing compound; and the remainder, to total 100 percent, of an acid-containing ethylene copolymer ionomer; preferably provided that the thermoplastic polymer is present in greater than 50 volume percent of the composition.

In another embodiment, the subject invention provides for injection molding a core for a two-piece golf ball in which the core composition comprises between 30 and 50 polymer weight percent of a thermoplastic polymer selected from copolyetheramides and

copolyetheresters; 1-10 polymer weight percent of an epoxy-containing compound; 15-25 total weight percent of a filler having a density greater than about 5 gm/cc; and the remainder, to total 100 polymer weight percent, of an acid-containing ethylene copolymer ionomer.

In yet another embodiment, the subject invention provides for injection molding the center for a three-piece golf ball in which the center composition comprises 65-90 weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters; 1-10 weight percent of an epoxy-containing compound; and the remainder, to total 100 weight percent of an acid-containing ethylene copolymer ionomer. DETAILED DESCRIPTION OF THE INVENTION

Process

Specific thermoplastic compositions, more fully described below as useful in the manufacture of cores, centers or one-piece golf balls, are injection molded in a runnerless, hot runner or insulated runner injection molding apparatus, which will be referred to generically as a runnerless system. By "runnerless", it is meant that the conduits that carry the hot thermoplastic directly to the mold cavity through one or more ports (referred to as gates) are heated or insulated sufficiently to maintain the thermoplastic composition in a fluid or soft state, while the material in the cooler mold cavity solidifies. When the molded golf balls are ejected upon opening the mold, they are not attached to solidified runner material. By contrast, in a conventional cold-runner system, the molded golf ball and solidified material that filled the cold runner are ejected together when the mold is opened. The balls must be cut from the runner material.

U.S. Patent No.5,069,615, incorporated herein by reference, teaches a preferred stack molding apparatus for use in the process of this invention. In the background of that patent, numerous other runnerless systems are described. They include the hot-runner and insulated-runner systems. They also describe the use of hot channels, heated distribution plates, heating probes and the like for keeping the thermoplastic that is not in the mold cavities hot. The present invention is not limited to any particular one of the many runnerless systems known in the injection molding art.

For illustration, the runnerless injection mold apparatus used in the process of this invention can be described as including a sprue and runner system that can be maintained at an elevated temperature for delivering softened thermoplastic composition to mold spaces or cavities for forming spherical cores, centers or one-piece golf balls. The sprue and runner system are part of a fixed distribution plate that can be heated and maintained at an elevated temperature. At the terminal end of each runner is a valved gate through which softened thermoplastic composition can be injected under pressure into a mold cavity. The mold cavities are formed by moving a moveably mounted plate containing one half of the spherical mold against a second fixed plate containing the second half of the spherical mold. The fixed plate is secured to the distribution plate.

Sufficient force (in the order of 3 tons per square inch of projected area) or a latching means is used to secure the first moveably mounted plate to the second fixed plate so as to hold the mold in the closed position while thermoplastic is injected into it and while the thermoplastic hardens. In a stack mold, two movable plates containing half mold cavities are positioned on opposite sides of central fixed distribution and mold containing plates.

For each composition described below, the thermoplastic composition is injected into one or more closed mold cavities maintained at a cool enough temperature (preferably 34° F to 122° F ( 1° C to 50º C), more preferably 34° F to 50° F (1° C to 10° C)) to cause the molded spherical object to solidify sufficiently to not become distorted upon ejection and to be readily ejected after a relatively short period of time. Times up to 300 to 500 seconds or even higher may be needed if the higher temperatures are used or if the spherical object is to be completely solidified. Much shorter times (preferably 30 to 120 seconds, more preferably about 30 to 50 seconds) are possible particularly with lower mold temperatures. With short cycle times, the inside of the sphere may still be hot and therefore soft even though the outside of the sphere is cool and solid enough to prevent distortion upon ejection. In such a case, post cooling can be used to solidify the inside.

The mold cavities are in a runnerless injection molding apparatus, preferably a stack, runnerless injection molding apparatus, preferably positioned so as the mold is opened horizontally. The mold cavities are spherical, appropriately sized for the finished core, center or one-piece golf ball, as the case maybe, and have desired surface characteristics (smooth for cores and centers and dimpled for one-piece balls).

While injection molding machines used to put covers on golf balls typically are limited to eight mold cavities, significantly more cavities should be possible with the present invention. This is particularly due to better heat balance achievable with a runnerless system and since retractable pins are not employed as in the case of cover injection. Up to 64 mold cavities in a single face mold and 128 in a stacked mold are possible. Using a stack mold with a 30 second cycle time would result in a producing one-piece golf balls, cores or centers, as the case may be, at a rate of up to 256 per minute.

The thermoplastic composition is introduced into the mold cavities through ports, generally called gates. The gates are preferably positioned at locations other than at the equator parting line of the mold, more preferably at the pole of the golf ball mold cavity, and are valved so as to control flow of thermoplastic composition into the spherical mold cavity. Preferably, for the one-piece golf ball, the valved gates are sized and configured so that the point of thermoplastic entry into the mold is disguised as a spherical dimple on the finished golf ball and so that gate vestiges that would have to be machined from the finished golf ball are not apparent. Figure 5 in U.S. Patent No. 4,959,000 shows a valved gate designed to form a dimple in the golf ball.

The thermoplastic composition is preferably pre-dried to remove moisture and to thereby avoid formation of bubbles in parts. Predrying can be achieved by holding the thermoplastic composition at a low temperature for an extended period or at a higher temperature for a shorter period. The thermoplastic composition is heated to a temperature above the crystalline melting point of the thermoplastic component of the composition but below the degradation point of the composition (preferably 350° F to 425° F (176.7° C to 218.3° C)) and fed under sufficient pressure through one or more sprues and runners which are maintained at a temperature about that of the heated composition to one or more valved gates and into one or more closed, cold mold cavities. The pressure required will vary depending on factors such as the thermoplastic composition, the temperature of the thermoplastic composition, the sprue and runner design, the gate size, the number and size of the cavities, and the venting of the injection molding apparatus. Optimum pressures can easily be determined by routine experimentation based on the disclosure herein.

When sufficient thermoplastic composition has been added to the mold cavity, the valved gate closes and the material in the cavity is allowed to cool sufficiently that it can be removed without the golf ball becoming distorted. As noted above, post cooling may be required. It can be accomplished by dropping the partially cooled object into a quench bath or by contacting with a spray of cold water.

Component Description

Because the species and relative ratios of the components in the thermoplastic composition used in the process of this invention vary somewhat depending on whether centers for three-piece balls, cores for two-piece balls or one-piece balls are to be made, it is useful to first consider the components themselves.

The thermoplastic polymer component is selected from copolyetheresters and copolyetheramides, both classes of polymers being well known in the art.

The copolyetheresters are discussed in detail in, e.g., U.S. Patents 3,651,014; 3,766,146; and 3,763,109. They are comprised of a multiplicity of recurring long chain units and short chain units joined head-to-tail through ester linkages, the long chain units being represented by the formula and the short chain units being represented by the formulawhere G is a divalent radical remaining after the removal of terminal hydroxyl groups from a poly(alkylene oxide) glycol having a molecular weight of about 400-6000 and a carbon to oxygen ratio of about 2.0-4.3; R is a divalent radical remaining after removal of hydroxyl groups from a dicarboxylic acid having a molecular weight less than about 300; and D is a divalent radical remaining after removal of hydroxyl groups from a diol having a molecular weight less than about 250; provided said short chain ester units amount to about 15-95 percent by weight of said

copolyetherester. The preferred copolyetherester polymers are those where the polyether segment is obtained by polymerization of tetrahydrofuran and the polyester segment is obtained by polymerization of tetramethylene glycol and phthalic acid. Of course, the more polyether units incorporated into the copolyetherester, the softer the polymer. For purposes of the subject invention, the molar ether:ester ratio can vary from 90:10 to 10:90, preferably 80:20 to 60:40; and the shore D hardness is less than 70, preferably about 40.

The copolyetheramides are also well known in the art as described in, e.g., U.S.4,331,786. They are comprised of a linear and regular chain of rigid polyamide segments and flexible polyether segments, as represented by the general formulawherein PA is a linear saturated aliphatic polyamide sequence formed from a lactam or aminoacid having a hydrocarbon chain containing 4 to 14 carbon atoms or from an aliphaticC₆-C₉ diamine, in the presence of a chain-limiting aliphatic carboxylic diacid having 4-20 carbon atoms; said polyamide having an average molecular weight between 300 and 15,000; and PE is a polyoxyalkylene sequence formed from linear or branched aliphatic polyoxyalkylene glycols, mixtures thereof or copolyethers derived therefrom said polyoxyalkylene glycols having a molecular weight of less than or equal to 6000 and n indicates a sufficient number of repeating units so that said polyetheramide copolymer has an intrinsic viscosity of from about 0.8 to about 2.05. The preparation of these polyetheramides comprises the step of reacting a dicarboxyhc polyamide, the COOH groups of which are located at the chain ends, with a polyoxyalkylene glycol hydroxylated at the chain ends, in the presence of a catalyst such as a tetraalkylorthotitanate having the general formula Ti(OR)₄, wherein R is a linear branched aliphatic hydrocarbon radical having 1 to 24 carbon atoms. Again, the more polyether units incorporated into the copolyetheramide, the softer the polymer. The ether:ester ratios are as described above for the ether:ester ratios, as is the shore D hardness.

The epoxy-containing compound component of the subject invention can be any compound that has an epoxy functionality readily available for reaction with the carboxylic acid groups in the ethylene copolymer ionomers detailed below. Such compounds include, for example, epoxidized oils such as epoxidized soy bean oil, epoxidized elastomers such as epoxidized natural rubber or epoxidized polybutadiene rubber, or an epoxy-containing copolymer E/X/Y wherein E is ethylene, X is a softening comonomer, for example, an acrylate, methacrylate, vinyl ether or vinyl ester comonomer present in 0-50 (preferably 0-35, most preferably 0-30) weight percent of the polymer, and Z is an epoxy-containing vinyl unsaturated monomer present in 1-25 (preferably 1-20, most preferably 1-15) weight percent of the polymer; such copolymers include without limitation, ethylene copolymers copolymerized with one or more reactive monomers selected from unsaturated epoxides of 4-11 carbon atoms, such as glycidyl acrylate, glycidyl methacrylate, and vinyl glycidyl ether, and optionally additionally containing alkyl acrylate, alkyl methacrylate, carbon monoxide, sulfur dioxide and/or alkyl vinyl ether, where the alkyl radical is from 1-12 carbon atoms. Preferred glycidyl containing copolymers for use in the compositions of the present invention include ethylene/glycidyl acrylate, ethylene/n-butyl acrylate/glycidyl acrylate, ethylene/methyl acrylate/glycidyl acrylate, ethylene/glycidyl methacrylate, ethylene/n-butyl acrylate/glycidyl methacrylate and ethylene/methyl acrylate/glycidyl methacrylate copolymers. The most preferred glycidyl-containing copolymers are ethylene/n-butyl acrylate/ glycidyl methacrylate and ethylene/glycidyl methacrylate copolymers.

These glycidyl-containing ethylene copolymers are made by processes well known in the art, e.g., by direct copolymerization of ethylene, glycidyl methacrylate or glycidyl acrylate, and the above-defined acrylate or methacrylate in the presence of a free-radical polymerization initiator at elevated temperatures, preferably 100° -270° C. and most preferably 130° -230° C, and at elevated pressures, preferably at least 70 MPa, and most preferably 140-350 MPa.

The acid-containing ethylene copolymer ionomer component of the subject invention includes E/X/Y copolymers where E is ethylene, X is a softening comonomer such as acrylate or methacrylate present in 0-50 (preferably 0-25, most preferably 0-2) weight percent of the polymer, and Y is acrylic or methacrylic acid present in 5-35 (preferably 10-35, most preferably 15-35) weight percent of the polymer, wherein the acid moiety is neutralized 1-90% (preferably at least 40%, most preferably at least about 60%) to form an ionomer by a cation such as lithium*, sodium*, potassium, magnesium*, calcium, barium, lead, tin, zinc* or aluminum (* = preferred), or a combination of such cations. Specific acid-containing ethylene copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/ methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl methacrylate.

Preferred acid-containing ethylene copolymers include ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/methacrylic acid/n-butyl acrylate, ethylene/ acrylic acid/n-butyl acrylate,

ethylene/methacrylic acid/methyl acrylate and ethylene/acrylic acid/ methyl acrylate copolymers. The most preferred acid-containing ethylene copolymers are ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylic acid/methyl acrylate copolymers. The manner in which the ionomers are made is well known in the art as described in, e.g., U.S.3,262,272 (Rees).

The optional filler component of the subject invention is chosen to impart additional density to blends of the previously described components, the selection being dependent upon the type of golf ball desired (i.e., one-piece, two-piece or three-piece), as will be more fully detailed below. Generally, the filler will be inorganic having a density greater than about 4 gm/cc, preferably greater than 5 gm/cc, and will be present in amounts between 5 and 65 weight percent based on the total weight of the polymer components. Examples of useful fillers include zinc oxide, barium sulfate, lead silicate and tungsten carbide, as well as the other well known corresponding salts and oxides thereof. It is preferred that the filler materials be non-reactive with the polymer components described above. Additional optional additives useful in the practice of the subject invention include acid copolymer waxes (e.g., Allied wax AC143 believed to be an ethylene/16-18% acrylic acid copolymer with a number average molecular weight of 2,040) which assist in preventing reaction between the filler materials (e.g., ZnO) and the acid moiety in the ethylene copolymer; TiO₂ which is used as a whitening agent; optical brighteners; surfactants; processing aids; etc.

The specific combinations of components used in the practice of the subject invention will in large part be dependent upon the type of golf ball desired (i.e., one-piece, two-piece or three-piece), as detailed below. In general, the molding techniques used in the manufacture of one-piece, two-piece, and three-piece balls are well known. It is preferable to use runnerless molding techniques, most preferably valve gated, where the polymer is injection molded into the cavity. This technology greatly improves efficiency and cost as runners are eliminated, as is all of the effort and cost relative to rework. In the case of one-piece balls, the valve gate(s) can be disguised as a dimple in the ball eliminating the need for secondary finishing of the gate vestige. Also most preferably, the use of the traditional stack molding techniques can significantly reduce costs and improve efficiency.

THREE-PIECE GOLF BALL PREFERRED EMBODIMENTS

As used herein, the term "three-piece ball" refers to a golf ball comprising a center made from the compositions of copending application Serial No. 07/634,793, a traditional elastomeric winding wound around the center, and a cover made from any traditional golf ball cover material such as SurlynR ionomer resin, balata rubber and the like. These three-piece golf balls are manufactured by well known techniques as described in, e.g., U.S.4,846,910.

For purposes of this invention, the center is made by injection molding of the compositions using valve gated, runnerless molding techniques, where the polymer preferably is injection molded into the cavity at the pole or poles instead of the equator as is commonly done. For use in making centers for three-piece balls, the preferred composition comprises 65-90 weight percent of the thermoplastic component, 1-10 weight percent of the epoxy-containing compound and the remainder, to total 100 weight %, of the acid-containing ethylene copolymer ionomer. The most preferred compositions also contain about 40-60 weight percent of the previously described filler material, based on total weight of the three polymer components plus filler. The most preferred thermoplastic component is a copolyetherester; the most preferred epoxy-containing compound is a glycidyl-containing ethylene copolymer; and the most preferred acid-containing ethylene copolymer ionomer is an

ethylene/methacrylic acid or ethylene/acrylic acid copolymer. The three-piece ball that performs most satisfactorily, as seen in the Examples below, contains a center molded from a composition that comprises from about 35 weight percent (total composition) of the polyetherester, described in Table 1 below as "H1", 1-5 weight percent of an

ethylene/n-butylacrylate (28%)/glycidyl methacrylate (8%) copolymer, about 10 weight percent of an ethylene/methacrylic acid (20%) copolymer highly neutralized with Na cations to form the ionomer, about 50 weight percent ZnO, and about 5 weight percent Allied wax AC143. Note that these weight percentages are given as a percent based on total composition to more clearly show the relative proportion of components in an actual three-piece center formulation.

TWO-PIECE GOLF BALL PREFERRED EMBODIMENTS

As used herein, the term "two-piece ball" refers to a golf ball comprising a core made from the compositions of copending application Serial No. 07/634,793, and a cover made from any traditional golf bah cover material as discussed above. These two-piece balls are manufactured by first molding the core from the compositions of the subject invention, positioning these preformed cores in an injection molding cavity using retractable pins, then injection molding the cover material around the core. As mentioned above for purposes of this invention, cores for two-piece golf balls are produced using valve gated, runnerless molding techniques, where the polymer is injection molded into the cavity at the pole or poles instead of the equator as is commonly done.

For use as the core material for two-piece balls, one preferred composition comprises 50 to 65 polymer weight percent of the thermoplastic component, 1-10 polymer weight percent of the

epoxy-containing compound, and the remainder to total 100 weight percent, of the acid-containing ethylene copolymer ionomer; preferably provided that the thermoplastic component is present in greater than 50 volume percent of the composition. It is also preferred that such compositions contain 15-25 total weight percent of the previously described filler material. In another preferred composition, the thermoplastic component is present between 30 and 50 polymer weight percent, the epoxy-containing component present between 1 and 10 polymer weight percent, and the ionomer the remainder to total 100 weight percent, but in such a

composition the filler material is necessarily present in 15-25 weight percent based on total composition, and must have a density of greater than about 5 gm/cc (e.g., zinc oxide, lead silicate or tungsten carbide). In both

embodiments, the most preferred thermoplastic component is a

copolyetherester; the most preferred epoxy-containing compound is a glycidyl-containing ethylene copolymer; and the most preferred

acid-containing ethylene copolymer ionomer is an ethylene/(meth)acrylic acid copolymer. The two-piece ball that performs most satisfactorily, as seen in the Examples below, contains a core molded from a composition that comprises 50-60 polymer weight percent of the polyetherester described in Table 1, 1-5 polymer weight percent of an ethylene/n-butyl acrylate (28%)/glycidyl methacrylate (5%) copolymer, 40-45 polymer weight percent of an ethylene/(meth)acrylic acid (20%) copolymer highly neutralized with Na cations to form the ionomer, about 20 total weight percent ZnO, and about 5 weight percent Allied wax.

ONE-PIECE GOLF BALL PREFERRED EMBODIMENTS

As used herein, the term "one-piece ball" refers to a golf ball molded in toto from the compositions of the subject invention, i.e., not having elastomeric windings nor a cover. As mentioned above for purposes of this invention, one-piece golf balls are produced using valve gated, runnerless molding techniques, where the polymer is injection molded into the cavity at the pole or poles instead of the equator as is commonly done. The valve gate is disguised as a dimple in the ball. The one-piece molded ball will have a traditional dimple pattern or may even have a unique pattern with dimples on the equator and may be coated with a urethane lacquer or be painted for appearance purposes.

For use in one-piece balls, the preferred composition comprises 40 to 65 polymer weight percent of the thermoplastic component, 1-10 polymer weight percent of the epoxy-containing compound, 5-20 weight percent, based on the total weight percent, of the previously described filler material and the remainder, to total 100 polymer weight percent, of the acid-containing ethylene copolymer ionomer. Again, the most preferred thermoplastic component is a copolyetherester; the most preferred epoxy-containing compound is a glycidyl-containing ethylene copolymer; and the most preferred acid-containing ethylene copolymer ionomer is an ethylene/methacrylic acid copolymer. The one-piece ball that performs the most satisfactorily, as seen in the Examples below, is molded from a composition of the subject invention comprising about 55 polymer weight percent of the polyetherester described in Table 1, 1-5 polymer weight percent of ethylene/n-butyl acrylate (28%)/glycidyl methacrylate (8%) copolymer, 40-45 polymer weight percent of an ethylene/methacrylic acid (20%) copolymer highly neutralized with Na cations to form the ionomer, about 10 total weight percent ZnO, about 5 total weight percent AC143 Allied wax, and about 5 total weight percent TiO₂.

Those skilled in the art will appreciate that certain variations of the compositions of the subject invention will also be useful in the manufacture of one-piece and two-piece restricted flight golf balls, also commonly known as range balls; the distance that such range balls can travel being dependent upon the resihency of the materials used and the compression imparted. Further, compositions having flex modulus of about 14,000-30,000 (ASTM D790, procedure B), preferably without filler, may also be employed as golf ball cover materials.

TESTING CRITERIA

In the Examples set out below, a number of testing criteria are utilized in the evaluation of golf ball performance: percent rebound, total distance travelled, initial velocity, coefficient of restitution (COR) and compression. Percent rebound is determined by dropping the ball (or three-piece center/two-piece core) from a height of 100 inches and measuring the rebound from a hard, rigid surface such as a thick steel plate or a stone block; an acceptable result is about 65-80%. Total distance is determined by striking a ball with a 10.5 degree loft driver at a clubhead speed of 95 mph; an acceptable result is about 220-250 yds. Initial velocity is the measured speed of the ball off a clubhead as described for total distance (acceptable result approaching but less than 215 ft/sec as used in Table 2A) or the measured speed of the ball when hit at 230 feet per second by an implement having a face angle of 13° with respect to the vertical (acceptable result approaching but less than 255 ft/sec as used in Table 1C). COR is measured by firing a golf ball (or two piece core) from an air cannon at a velocity determined by the air pressure. The initial velocity generally employed is between 125 to 255 feet/second. The ball strikes a steel plate positioned three feet away from the point where initial velocity is determined, and rebounds through a speed-monitoring device. The return velocity divided by the initial velocity is the COR; acceptable results are .550-.750 at 180 ft/sec or .500-.650 at 230 ft/sec. Compression is defined as the resistance to deformation of a golf ball, measured using an ATM machine; an acceptable result is about 70-120.

EXAMPLES 1, 2, 3: COMPARATIVE EXAMPLES C1, AND C2; AND CONTROL EXAMPLE.

These examples and comparative examples illustrate the preparation and properties of centers for three-piece golf balls and of finished balls from such centers. Blends for the thermoplastic centers of such balls were prepared by extrusion in a twin screw extruder. The compositions are given in Table 1, and extrusion conditions shown in Table 1A. These blends were then molded into spheres of 1.08 in. diameter using an 8 oz. Van Dora Injection molding machine, with molding conditions shown in Table 1B. Density and percent rebound were measured on these centers. The centers were also made into three piece balls using conditions similar to those described in U.S. Pat. No.4,846,910 to Acushnet Corp., by winding with natural rubber threads, and compression molding a cover on top of the windings using a SurlynR ionomer blend. As a control, the properties of an Acushnet 'Titleist DT' ball are shown. This ball is made of a crosslinked (non thermoplastic) polybutadiene center, natural rubber windings and the same ionomer cover used for the thermoplastic center balls. All property measurements are shown in Table 1C.

TABLE I

CENTER COMPOSITIONS

HytrelR EBAGMA

Ex# Ref# (H1) (G1) Ionomer Filler Additive

1 62-4 36(78) 3(4) I1,8(18) F1,51 A1

2 62-1 36(75) 2(4) I1,10(21) F1.48 A1

3 41-5 41(73) 1(2) I2,14(25) F1,40 A1

4 10-3 44(73) 1(2) I2,15(25) F2,40 -

5 10-2 51(73) 1(2) I2,18(25) F2,30 -

(Values are weight percentages. Percentages given in parentheses are on a polymer only basis.)

H1 is a HytrelR resin with composition:

18.2/0.3/72.3/9.1:terphthaloyl/TMTM/PTMEG2000/1,4 butane diol, plus an antioxidant. PTMEG is polytetramethylene glycol. TMTM is trimethyltrimellitoyl.

(G1) Ethylene/28% butyl acrylate/8.4% glycidyl methacrylate with a melt index of 10.6.

(I1)Ethylene/20% methacrylic acid, 57% Na neutral., MI= 1

(I2)Ethylene/15% methacrylic acid, 52% Li neutral., MI =1.8

(F1)Fisher Zinc Oxide

(F2)Wittaker Clark Barium Sulfate, Blanc Fix N

(A1)AC143 Ethylene/15.66% acrylic acid with Mn=2040, Mw=5670

TABLE 1A

EXTRUSION CONDITIONS FOR BALL COMPOSITIONS

Screw

Speed Zone l Zone 2 Zone 3 Rate Vacuum

RPM Temp° C Temp° C Temp° C Die 1bs/hr Inches

150 161 194 202 207 16.4 26

TABLE 1B

MOLDING CONDITIONS FOR THREE PIECE CENTERS*

Temperatures ° C

Rear 174

Center 177

Front 177

Nozzle 171

Mold Fixed 10

Movable 10

Pressures Kg/sq.cm.

Injection 1st stage 140

Injection Second Stage 84

Injection Hold 14

Cycle Times Sec:

Injection 10

Hold 300

Booster 7

Screw Retraction 1.75

Pad (cm) 0.05

Screw Speed (RPM) 55

Back Pressure (kg/sq.cm) 8.4

Mold Size 1.092 Inches Diameter (0.429 cm)

Part Size 1.08 Inches Diameter (0.425 cm)

*Prototype mold, limited cooling, two cavity

TABLE 1C

PROPERTIES OF THREE P ECE CENTERS OR BALLS

Center Ball

Density % Compr. Wt. Velocity

Ex# MKD (g/cc) Rebound ATTI (g) (ft/sec) %Rej⁽²⁾.

1 11.1 1.71 67 85.9 45.2 250.9 0

2 17.6 1.56 69.6 85.9 43.8 251.8 7.1

3 20.0 1.45 67.4 97.2 42.2 252.0 17

C1 17.0 1.48 69.4 94.7 42.6 251.4 68

C2 22.0 131 70.5 98.0 41.0 253.0 62

Control 70.0 77.3 45.2 252.8 22.7 ⁽¹⁾Measured using ASTM D1238, with 10 Kg.weight at 220° C.

(²⁾Percent Reject based on out-of-roundness as measured by a fluoroscope on finished ball. Out of roundness is caused by the combined effect of pressure due to winding and the heat associated with the compression molding of the cover. Out of round balls behave unsatisfactorily, and would have properties outside USGA standards. The first three examples show that balls may be made satisfactorily with respect to number of rejects, and these are actually less than in the case of the thermoset center bah control. Compression is somewhat higher than for the control, but within the acceptable range of about 70 to 120. Initial velocity is below the acceptable maximum of 255. The % rebound is comparable to the control center, and an indication of generally acceptable performance. It will be noted however, that the best balls are produced when the EBAGMA level is highest. In the two

comparative examples, while measured properties were acceptable, the level of rejects was totally unacceptable. Comparative example C1 has a low level of polyetherester and filler. Comparative example C2 has a very low level of filler.

EXAMPLES 4, 5, AND 6: COMPARATIVE EXAMPLE C3 AND

CONTROL EXAMPLE

These examples describe the preparation of blends for the core for two piece golf balls, golf balls made therefrom, and the properties of the cores and finished balls. The composition of these blends is shown in

Table 2. The blends were made using extrusion conditions the same as those for three piece center compositions shown in Table 1A. The blends were molded into cores using conditions shown in Table 2B. The core is 1.5 inches in diameter. Balls were prepared by positioning preformed thermoplastic cores in an injection molding cavity. The cores were centrally positioned in the cavity by the use of retractable pins. A cover of mixed

SurlynR ionomer resin was then injection molded around the core.

Properties of the resultant cores or balls are shown in Table 2A,

TABLE 2

CORE COMPOSITIONS

HytrelR

Ex# Ref# (H1) EBAGMA Ionomer Filler Additive

4 72-1 41(53) G2,3(4) I1,33(43) F3,19 A1,4

5 8143-3 42(52) G2,3(4) I2,35(44) F4,20 -

6 115-3 42(55) G1,1(2) I1,33(43) F3,19 A1,4

C3 104-2 21(27) G3,7(9) I3,49(64) F2,22 -

C4 016R 43(56) 0 I1,34(44) F3,19 A1,4

Values are weight percentages. Percentages given in parenthesis are on a polymer only basis.

H 1, Gl, I1, 12, A1, F2 as in Table 1.

G2 Ethylene/28% n-butyl acrylate/5.3% glycidyl methacrylate with a melt index of 12.0

G3 Ethylene/34.5% n-butyl acrylate/5.3% glycidyl methacrylate with a

melt index of 6.0.

I3 Ethylene/15% methacrylic acid, 57% Na neutralized,MI= 1.2

F3 Zinc Oxide, grade XX503R, Zinc Corp. of America.

F4 Barium Sulfate, 'Barmite' 4.3 microns, Cyprus Corp.

TABLE 2A

PROPERTIES OF TWO PIECE CORES OR BALLS

Core Ball

Ex# Compr. Durabil. COR Compr. Reb. Velocity COR Carry

ATTI Hits/Break ATTI % & at/psi Roll

(yds)

4 17/50,20/40 .638 121 77 209.8 .614 236

5 118 74 208.0 .582 229

6 111 74 208.4 .586 235

C3 122 133 67.8 - - -

C4 4/50,7/40 .635

Cntrl. 111 81 213.5 .641 249 The Control ball is a Ram LP ball which has a thermoset butadiene core and a mixed ionomer cover. Coefficient of restitution for cores was measured at 180 ft/sec. Coefficient of restitution for balls was measured using an air canon with a pressure of 45 psi. which gives a velocity of about 230 ft./sec. Values for balls can be compared from one to another, but not with the COR values for cores or the one piece balls shown below, which are measured using different conditions. The test is used for general guidance to ball performance.

Examples 4 and 5 indicate that zinc oxide and a high acid ionomer give slightly superior resilience than barium sulfate and ionomer containing lower acid levels. Properties of all the thermoplastic cores are acceptable, though not quite equal to that of the control thermoset core ball. Comparative Example C3 has a low HytrelR and a high ionomer level; as a result, the compression is very high. High compression values indicate a high force to compress, and a ball with a 'hard' feel. Example C4 used a blend with no epoxy-containing polymer. The blend was compared with example 4 for coefficient of restitution and durability. Durability was determined by firing from an air canon at the indicated pressure against a steel rebound plate, and counting the number of hits before the ball breaks. While it had a comparable coefficient of restitution, it's durability was extremely poor, indicating a strong need to compatibilize the blend with the epoxy containing polymer.

TABLE 2B

MOLDING CONDITIONS FOR TWO PIECE CORES

AND ONE PIECE BALLS*

Temperatures ° C

Rear 183

Center 173

Front 173

Nozzle 177

Mold Front/Back 10

Melt 195

Pressures Kg/Square Cm

Injection 1st Stage 130

Injection 2nd Stage 110

Injection Hold 13

Cycle Times (sec)

Pack 10

Hold 480

Booster 10

Cure Time 15

Screw Retraction 5.35

Pad (cm) 0.6

Screw Speed RPM 55

Back Pressure (Kg/square cm) 0.0

Mold Diameter (cm) 3.88

*Prototype mold, limited cooling, four cavity

EXAMPLES 7, 8, 9 AND 10 AND CONTROL EXAMPLE

These examples illustrate the use of the thermoplastic blends of the invention for use in one piece balls. The blends were made using extrusion conditions as in Table 1A. Balls were molded using conditions as in Table 2B, except that the ball diameter was 1.65 inches. Compositions are given in Table 3, and properties are shown in Table 3B. TABLE 3

ONE PIECE BALL COMPOSITIONS

Ex# Ref# Hytrel® EBAGMA Ionomer Filler Additive

7 136-1 H1,42(51) G1,3(4) I3,37(45) F2,17 T,1

8 150-1 H2,44(52) G1,3(4) I3,37(44) F2,15 T,1

9 8143-3 H1,42(52) G1,3(4) I2,35(44) F4,20 -

10 H003A H1,46(56) G2,3(4) I1,34(41) F3,9.5 T,4

A1,4 Values are weight percentages. Percentages in parenthesis are on a polymer only basis.

H1,G1,G2,I1,I2,I3,F2,F3,F4,A1 as in previous tables.

H2 is a HytrelR resin with composition :

27.4/7.9/44.8/19.5%:ter/isophthaloyl/PTMEG2000/1,4butane diol, plus an antioxidant.

T is Ti02, grade R960 mfg. by the DuPont Company.

TABLE 3B

PROPERTIES OF ONE PIECE BALLS

Melt

Flow % Durability

Ex# (g/cc) Density Rebound Compr. COR (Hits)

7 3.0 1.16 64 83 .586 >200

8 5.3 1.17 - - .558 -

9 13.6 1.20 67 104 .602 >200

10 - 1.12 - 88 .653 -

Cntrl. 1.14 _ - 100 137 100

The control was a Wilson ULTRA two piece ball, with a thermoset butadiene core and a SurlynR blend cover.

Coefficient of Restitution was measured using an air cannon with initial bah velocity of 180 ft./sec. The results suggest that "soft" polyetherester appears to give superior results to a harder grade (example

8), and a harder ionomer (more methacrylic acid as in example 10) is also preferred.

EXAMPLE 11

This example illustrates the process of this invention for molding cores, centers and one-piece golf balls. ASTM D-638 Type 1 Tensile bars 8.5" long x 0.5" wide x 0.125" thick), instead of cores, centers and one-piece golf balls, were successfully made, but, based on this teaching, one skilled in the art can modify the mold cavities to produce the gram tensile bars on each cycle. The overall cycle averaged about 40 seconds.

The injection molding apparatus is described by Husky Injection Molding Systems as a Type XL150RS machine having a compression ratio of 2.5: 1, an L/D ratio of 20:1, a screw diameter of 35 millimeters (mm) and a nozzle diameter of 37 mm. The mold is described as a single face, four cavity mold having a 101.6 mm diameter locating ring, a "V" series nozzle housing, a 534426 nozzle tip with insulation, a 1.8 mm valve gate, and a 8.0 mm diameter manifold melt channel. The mold cavity and gate pad were kept at about 90° F (32.2° C).

The thermoplastic composition used in the test was 42 wt.% H1 HytrelR resin, 35 wt.% 12 ionomer, 3 wt.% G2 EBAGMA, and 20 wt.% F2 barium sulfate, as described in previous examples. It was pre-dried for 16 hours at 130° F (54.4° C).

Screw speed was 62 RPM. Injection time was 11.3 seconds.

The thermoplastic was injected at an injection pressure of 1100 pounds per square inch gauge (psig) and held at a pressure of 1600 psig. The back pressure was 120 psig. Temperature settings were as follows:

Machine Heat Settings Mold Heat Settings

Location No. Setting ° C Location No. Setting ° C

Extruder #1 ╌ Sprue Bar 380

Extruder #2 148 Manifold 380

Extruder #3 176 Tip #1 450

Extruder #4 180 Tip #2 450

Extruder #5 193 Tip #3 450

Barrel Head 196 Tip #4 450

Nozzle 196

Filling the mold cavities was reported as being easy, but the part could not be automatically ejected due to its flexibihty. No ejection difficulty, however, is anticipated for cores, centers and one-piece golf balls as they are not flexible. In one series of tests, the tip settings were raised to above 500° F. At that temperature, slight degradation in the bubble was observed.

While Examples 1 to 10 did not employ the runnerless mold apparatus of the present invention, they do provide useful data for demonstrating useful temperatures, cycle times, etc. that can be

extrapolated to the present invention.

Claims

CLAIMS What is claimed is:

1. A process for manufacturing a center for a three-piece golf ball comprising the following steps:

a) heating a thermoplastic composition comprising:

i) 65-90 weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters;

ii) 1-10 weight percent of an epoxy-containing compound; and

iii) the remainder, to total 100 weight percent of an acid-containing ethylene copolymer ionomer,

to a temperature greater than the crystalline melting point of the

thermoplastic polymer but below the degradation point of the thermoplastic composition;

b) feeding sufficient heated thermoplastic composition at sufficient pressure through a sprue and runner system in an injection molding apparatus, the sprue and runner system being maintained at a temperature about that of the heated thermoplastic composition, and then through one or more valved gates into one or more closed spherical mold cavities, the mold cavities designed to produce a center having the desired weight, size and surface characteristics, the mold cavities being at a temperature lower than the temperature at which the thermoplastic composition solidifies,

c) holding the thermoplastic composition under pressure in the one or more mold cavities for sufficient time so that the thermoplastic composition retains the shape of the mold cavity when the mold cavity is opener, and

d) then ejecting the center.

2. The process of claim 1 wherein the thermoplastic composition further containing about 40-60 weight percent, based on the total weight of the composition of a filler having a density greater than or equal to about 4 gm/cc.

3. The process of claim 1 where i) of the thermoplastic composition is a copolyetherester, h) of the thermoplastic composition is a glycidyl-containing copolymer, and iii) of the thermoplastic composition is an ethylene/(meth)acrylic acid copolymer.

4. The process of claim 2 where i) of the thermoplastic composition is a copolyetherester, ii) of the thermoplastic composition is a glycidyl-containing copolymer, and iii) of the thermoplastic composition is an ethylene/(meth)acrylic acid copolymer.

5. The process of claim 1 wherein the thermoplastic composition comprises about 35 weight percent (total composition) of a polyetherester having a shore D hardness of 40, 1-5 weight percent of an ethylene/n-butylacrylate (28%)/glycidyl methacrylate (5%) copolymer, about 10 weight percent of an ethylene/methacrylic acid (20%) copolymer highly neutralized with Na cation, and about 50 weight percent ZnO.

6. The process of claim 1 wherein the thermoplastic composition is heated to 350° F to 425 ° F.

7. The process of claim 1 wherein the thermoplastic composition is pre-dried before step a).

8. The process of claim 1 wherein the injection molding apparatus is a stack molding apparatus.

9. A process for manufacturing a core for a two-piece golf ball comprising the following steps:

a) heating a thermoplastic composition comprising:

i) 50-65 weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters;

ii) 1-10 weight percent of an epoxy-containing compound; and

iii) the remainder, to total 100 weight percent of an add-containing ethylene copolymer ionomer,

provided that i) is greater than 50 volume % of the volume of the composition,

to a temperature greater than the crystalline melting point of the

b) feeding sufficient heated thermoplastic composition at sufficient pressure through a sprue and runner system in an injection molding apparatus, the sprue and runner system being maintained at a temperature about that of the heated thermoplastic composition, and then through one or more valved gates into one or more closed spherical mold cavities, the mold cavities designed to produce a core having the desired weight, size and surface characteristics, the mold cavities being at a temperature lower than the temperature at which the thermoplastic composition solidifies,

c) holding the thermoplastic composition under pressure in the one or more mold cavities for sufficient time so that the thermoplastic composition retains the shape of the mold cavity when the mold cavity is opened, and

d) then ejecting the core.

10. The process of claim 9 wherein the thermoplastic composition further containing about 15-25 weight percent, based on the total weight of the composition of a filler having a density greater than or equal to about 4 gm/cc.

11. The process of claim 9 of the thermoplastic composition is a copolyetherester, ii) of the thermoplastic composition is a

glycidyl-containing copolymer, and iii) of the thermoplastic composition is an ethylene/(meth)acryhc acid copolymer.

12. The process of claim 10 where i) of the thermoplastic composition is a copolyetherester, ii) of the thermoplastic composition is a glycidyl-containing copolymer, and iii) of the thermoplastic composition is an ethylene/(meth)acryhc acid copolymer.

13. The process of claim 10 wherein the thermoplastic composition comprises 50-65 polymer weight percent of a polyetherester having a shore D hardness of about 40, 1-5 polymer weight percent of an ethylene/n-butyl acrylate (28%)/glycidyl methacrylate (5%) copolymer; 40-45 polymer weight percent of an ethylene/(meth)acryhc acid (20%) copolymer highly neutralized with Na cations, and about 20 total weight percent ZnO.

14. The process of claim 9 wherein the thermoplastic composition is heated to 350° F to 425° F.

15. The process of claim 9 wherein the thermoplastic composition is pre-dried before step a).

16. The process of claim 9 wherein the injection molding apparatus is a stack molding apparatus.

17. A process for manufacturing a core for a two-piece golf ball comprising the following steps:

a) heating a thermoplastic composition comprising:

i) 30-50 polymer weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters;

ii) 1-10 polymer weight percent of an epoxy-containing compound;

iii) 15-25 total weight percent of a filler having a density greater than about 5 gm/cc; and iv) the remainder, to 100 total polymer weight percent of an acid-containing ethylene copolymer ionomer,

to a temperature greater than the crystalline melting point of the

d) then ejecting the core.

18. The process of claim 17 wherein i) of the thermoplastic composition is a copolyetherester, wherein ii) of the thermoplastic composition is a glycidyl-containing copolymer,and wherein iv) of the thermoplastic composition is an efhylene/(meth)acrylic acid copolymer.

19. The process of claim 17 wherein the thermoplastic composition is heated to 350° F to 425º F.

20. The process of claim 17 wherein the thermoplastic composition is pre-dried before step a).

21. The process of claim 17 wherein the injection molding apparatus is a stack molding apparatus.

22. A process for manufacturing a one-piece golf ball comprising the following steps:

a) heating a thermoplastic composition comprising:

i) 40-65 polymer weight percent of a thermoplastic polymer selected from copolyetheramides and copolyetheresters;

ii) 1-10 polymer weight percent of an epoxy-containing compound;

iii) 5-20 total weight percent of a filler having a density greater than 4 gm/cc; and iv) the remainder, to total 100 polymer weight percent, of an acid-containing ethylene copolymer ionomer,

to a temperature greater than the crystalline melting point of the

b) feeding sufficient heated thermoplastic composition at sufficient pressure through a sprue and runner system in an injection molding apparatus, the sprue and runner system being maintained at a temperature about that of the heated thermoplastic composition, and then through one or more valved gates into one or more closed spherical mold cavities, the mold cavities designed to produce a one-piece golf ball having the desired weight, size and surface characteristics, the mold cavities being at a temperature lower than the temperature at which the thermoplastic composition solidifies,

d) then ejecting the golf ball; and

e) finishing the golf bah.

23. The process of claim 22 wherein i) of the thermoplastic composition is a copolyetherester, wherein ii) of the thermoplastic composition is a glycidyl-containing copolymer, wherein hi) is an

ethylene/(meth)acryllc acid copolymer.

24. The process of claim 22 wherein the thermoplastic composition comprises about 55 polymer weight percent of a polyester having a shore D hardness of about 40, 1-5 polymer weight percent of ethylene/n-butyl acrylate (28%/glycidyl methacrylate (5%) copolymer, 40-45 polymer weight percent of an ethylene/methacrylic acid (20%) copolymer highly neutralized with Na cations, and about 10 total weight percent ZnO.

25. The process of claim 22 wherein the thermoplastic composition is heated to 350° F to 425° F.

26. The process of claim 22 wherein the thermoplastic composition is pre-dried before step a).

27. The process of claim 22 wherein the injection molding apparatus is a stack molding apparatus.