CROSS REFERENCES TO RELATED APPLICATIONS
The Present Application is a continuation application of U.S. patent application Ser. No. 11/276,223, which was filed on Feb. 17, 2006.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
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1. Field of the Invention
The present invention relates to a thermoplastic material, a process for producing the thermoplastic material and use of the thermoplastic material in a golf ball.
2. Description of the Related Art
Traditional golf ball covers have been comprised of balata or blends of balata with elastomeric or plastic materials. Balata-related covers, often referred to as soft balata covers, are relatively soft and flexible. Upon impact, soft balata covers compress against the surface of the club producing high spin. Consequently, these soft and flexible covers provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade, or a backspin which causes the ball to “bite” or stop abruptly on contact with the green. Moreover, soft balata covers produce a soft “feel” to the low handicap player. Such playability properties as, workability and feel are particularly important in short iron play with low swing speeds and are exploited significantly by relatively skilled players.
Despite all the benefits of balata, balata-related golf ball covers are easily cut and/or damaged if hit improperly. Golf balls produced with balata or balata-containing cover compositions therefore have a relatively short lifespan. As a result of this negative property, balata and its synthetic substitutes, trans-polybutadiene and trans-polyisoprene, have been essentially replaced as the cover materials of choice by new cover materials comprising ionomeric resins.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E.I. du Pont de Nemours and Company (DuPont), under the trade name “Surlyn7” (Surlyn7™), and, more recently, by the ExxonMobil Corporation (ExxonMobil) (see, for example, U.S. Pat. No. 4,911,451), under the trade name “Iotek” (Iotek™), have become the materials of choice for the construction of golf ball covers over traditional balata (trans-polyisoprene, natural or synthetic) rubbers.
Ionomeric resins are generally ionic copolymers of an olefin (such as ethylene) and a metal salt of an unsaturated carboxylic acid (such as acrylic acid, methacrylic acid or maleic acid). Metal cations such as sodium or zinc are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties such as durability for golf ball cover construction over balata. However, some of the advantages gained in increased durability have been offset to some degree by decreases produced in playability. This is because although ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction and, thus, lack the degree of softness required to impart the spin necessary to control the ball in flight. Since the ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionomeric resins lack the feel characteristic associated with the softer balata-related covers. As a result, while there are many commercial grades of ionomers available both from DuPont and ExxonMobil, with a wide range of properties that vary according to the type and amount of metal cations, molecular weight, composition of the base resin (such as relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, or the like, a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the “hard” ionomeric resins, but also the playability (for example, “spin”, “feel” and the like) characteristics previously associated with soft balata-related covers, properties that are still desired by the more skilled golfer.
Consequently, a number of golf balls have been produced to address these needs. The different types of materials utilized to formulate the cores, mantles and covers of these balls dramatically alter the balls' overall characteristics. In addition, multi-layered covers containing one or more ionomeric resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired.
Such formulations are described in U.S. Pat. No. 4,431,193 ('193), where a multi-layered golf ball is produced by initially molding a first cover layer on a spherical core and then adding a second layer. The first layer consists of a hard, high flexural modulus resinous material such as Surlyn7™ 8940, a sodium ion based low acid (less than or equal to 16 weight percent methacrylic acid) ionomeric resin having a flexural modulus of about 51,000 psi. An outer layer of a comparatively soft, low flexural modulus resinous material such Surlyn7™ 9020 is molded over the inner cover layer. Surlyn7™ 9020 is a zinc ion based low acid (10 weight percent methacrylic acid) ionomeric resin having a flexural modulus of about 14,000 psi.
The '193 patent also teaches that the hard, high flexural modulus resin, which comprises the first layer, provides for a gain in coefficient of restitution over the coefficient of restitution of the core. The increase in the coefficient of restitution provides a ball that attains or approaches the maximum initial velocity limit of 255 feet per second, as provided by the United States Golf Association (USGA) rules. The relatively soft, low flexural modulus outer layer provides for the advantageous feel and playing characteristics of a balata covered golf ball.
In various attempts to produce a durable, high spin golf ball, the golfing industry has blended the hard ionomeric resins with a number of softer ionomeric resins. For example, U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid and an acrylate ester. However, it has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of a hard ionomeric resin alone. It would be useful to develop a golf ball having a combination of softness and durability that is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend.
Most professional golfers and good amateur golfers desire a golf ball that provides distance when hit off a driver, control and stopping ability on full iron shots as well as high spin on short “touch and feel” shots. Many conventional golf balls have undesirable high spin rates on full shots. The excessive spin on full shots is a sacrifice made in order to achieve more spin on the shorter touch shots. It would be beneficial to provide a golf ball that has high spin for touch shots, without generating excessive spin on full shots, while maintaining or improving some of the other properties of the golf ball.
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OF THE INVENTION
The present invention is directed to a novel thermoplastic material and to its use in a golf ball as a core, cover or intermediate layer. The thermoplastic material of the invention includes a blend of two or more copolymers and fatty acids or salts of fatty acids. The material of the invention is partially to highly neutralized (preferably 50 to 100%), and has a greater coefficient of restitution than other thermoplastic materials.
One embodiment of the present invention is a golf ball comprising a core and a cover layer disposed on and, preferably, covering the core, wherein at least one of the cover and the core is formed from the thermoplastic material of the invention. The material of the invention preferably comprises, as part of the blend, (1) a copolymer comprising an alpha olefin and an acid, such as ethylene/acrylic acid (an alpha, beta-unsaturated carboxylic acid) and (2) a copolymer or “plastomer” comprising a metallocene-catalyzed alpha olefin and a softening comonomer. Alternatively, the first copolymer may include an alpha olefin, an acid and a softening comonomer such as an alkyl acrylate (wherein the first copolymer is also referred to as a “terpolymer”). Exemplary softeners for the second copolymer include an alpha olefin such as butene-1, hexene-1, octene-1,4-methyl-1-pentene, etc. Preferably, the second copolymer, or “plastomer,” is a metallocene-catalyzed ethylene/alpha olefin copolymer. A thermoplastic material blend of the invention further comprises fatty acids or fatty acid salts. Exemplary fatty acids or fatty acid salts can include metal stearates or stearic acids. Other materials such as metallocene-catalyzed plastomers, urethanes or other materials known in the art may also be used for thermoplastic material blend modification as desired.
In a particularly preferred form of the invention the thermoplastic material of the invention comprises a blend of two or more copolymers, wherein the first copolymer is formed from an alpha olefin having 2 to 8 carbon atoms, and an acid which includes at least one member selected from the group consisting of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acids with a portion of the acid being neutralized with cations, and the second copolymer is formed from an alpha olefin having 2 to 8 carbon atoms, and a softening comonomer. The optional softening comonomer that may be added to the first copolymer is preferably an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms.
Another embodiment of the present invention is a golf ball having a core, boundary layer and cover. The core includes a polybutadiene mixture, has a diameter ranging from 1.35 inches to 1.64 inches and has a PGA compression ranging from 50 to 90. The boundary layer is formed over the core and is composed of a thermoplastic material of the invention. The boundary layer has a thickness ranging from 0.020 to 0.075 inches and a Shore D hardness ranging from 50 to 70 as measured according to standard test method D2240 of the American Society for Testing and Materials (ASTM-D2240). The cover is formed over the boundary layer. The cover is composed of a fast chemical reaction aliphatic polyurethane material formed from reactants that comprise a polyurethane prepolymer and a polyol. The polyurethane material has a Shore D hardness ranging from 30 to 60 as measured according to ASTM-D2240 and a thickness ranging from 0.015 to 0.044 inches. The polyurethane material of the cover also provides for an aerodynamic surface geometry.
Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 illustrates a perspective view of a golf ball of the present invention including a cut-away portion showing a core, a boundary layer and a cover.
FIG. 2 illustrates a perspective view of a golf ball of the present invention including a cut-away portion showing a core and a cover.
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OF THE INVENTION
The present invention relates to a novel thermoplastic material and to its use in golf equipment, particularly, a golf ball 10. As shown in FIG. 1, a three-piece solid golf ball comprises a core 12, a boundary 14 and a cover 16. As shown in FIG. 2, a two-piece golf ball comprises a core 12 and a cover 16. At least one of the components of the golf ball comprises a thermoplastic material of the invention.
More particularly, the invention provides a neutralized thermoplastic material comprising a blend of (1) a copolymer comprising an alpha olefin and an alpha, beta-unsaturated carboxylic acid (an acid copolymer referred to as EX), (2) a copolymer or plastomer comprising a metallocene-catalyzed alpha olefin and a softening comonomer, e.g., a metallocene-catalyzed ethylene/alpha olefin copolymer (a metallocene copolymer referred to as EM) and (3) a fatty acid or salt of a fatty acid. The first copolymer may also include a softening comonomer such as an alkyl acrylate, which copolymer (or terpolymer) is referred to as EXY. Other materials including, but not limited to, urethanes, and the like, may be used to modify the blend.
The acid copolymer of a thermoplastic material of the invention may contain anywhere from 1 to 30% by weight acid. A high acid copolymer containing greater than 16% by weight acid, preferably, from about 17 to about 25 weight % acid and, more preferably, about 20 weight % acid, or a low acid copolymer containing 16% by weight acid or less may be used as desired. The acid copolymer is neutralized with a metal cation of a salt (a metal cation salt) capable of ionizing or neutralizing the copolymer to the extent desired, generally from about 10 to 100%, preferably, from 30 to 100% and, more preferably, from 40 to 90%. The amount of metal cation salt needed varies with the extent of neutralization desired.
The acid copolymer is preferably made up of from about 10 to about 30% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha olefin. Optionally, a softening comonomer can be included in the copolymer. Generally, the alpha olefin has from 2 to 10 carbon atoms and is, preferably, ethylene. The unsaturated carboxylic acid is an acid having from about 3 to 8 carbon atoms. Examples of such acids include, but are not limited to, acrylic acid, methacrylic acid, ethacrylic acid, chloro acrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, with acrylic acid and methacrylic acid being preferred. The optional softening comonomer, such as an alkyl acrylate, has, e.g., from 1 to 8 carbon atoms in the alkyl group. The acid copolymer broadly contains from 1 to about 30% by weight unsaturated carboxylic acid, from about 70 to about 99% by weight ethylene and from 0 to about 40% by weight of a softening comonomer.
Examples of acid copolymers suitable for use in a thermoplastic material of the invention include, but are not limited to, an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic acid/alkyl acrylate terpolymer, or an ethylene/acrylic acid/alkyl acrylate terpolymer.
Acid copolymers are well known in the golf ball art. Examples of acid copolymers that fulfill the criteria set forth above include, but are not limited to, those sold under the trade names Escor™ (ethylene/acrylic acid copolymers) and Iotek™ (ethylene/acrylic acid/acrylate terpolymers) by ExxonMobil, namely, Escor™ 959, Escor™ 960, Escor™ AT325 and Iotek™ 7510. Other examples of acid copolymers include those sold under the trade name Primacor™ (ethylene/acrylic acid copolymers) by Dow Chemical Company, namely Primacor™ 5980I and Primacor™ 3340I. Other acid copolymers that may be used include ethylene/methacrylic acid copolymers such as sold under the trade names Surlyn™ and Nucrel™ by DuPont. Surlyn™ copolymers are neutralized with zinc, sodium or lithium ions. Nucrel™ copolymers are inherently flexible like ethylene vinyl acetate (EVA) copolymers and offer desirable performance characteristics similar to those of Surlyn™ Nucrel™ copolymers are produced by reacting ethylene and methacrylic acid in the presence of free radical initiators. A branched, random ethylene/methacrylic acid (EMAA) copolymer is produced thereby. Carboxyl groups are distributed along the polymer chain and interact with carboxyl groups on adjacent molecules to form a weakly cross-linked network through hydrogen bonding. Nucrel™ and Surlyn™ terpolymers are also available for use in a thermoplastic material of the invention.
Acid copolymers of a thermoplastic material of the invention are neutralized to a desired percentage through the use of metal cation salts. The salts utilized are those that provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the acid copolymer. These salts include, for example, acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, aluminum, zirconium or manganese.
Some examples of salts comprising lithium cations are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Salts comprising calcium cations include calcium hydroxide, calcium acetate and calcium oxide. Suitable salts comprising zinc cations are zinc acetate dihydrate, zinc acetate or a blend of zinc oxide and acetic acid. Examples of salts comprising sodium cations include sodium hydroxide and sodium acetate. Similarly, salts comprising potassium cations include potassium hydroxide and potassium acetate. Suitable salts comprising nickel cations are nickel acetate, nickel oxide and nickel hydroxide. Salts comprising magnesium cations include magnesium oxide, magnesium hydroxide and magnesium acetate. Salts comprising manganese cations include manganese acetate and manganese oxide.
Additionally a wide variety of pre-neutralized acid polymers are commercially available for a thermoplastic material of the invention. These pre-neutralized acid polymers include both hard and soft pre-neutralized ionomeric resins as well as both low and high acid pre-neutralized ionomeric resins.
Hard (high modulus) pre-neutralized ionomeric resins include those having a hardness greater than 50 on the Shore D scale as measured in accordance with ASTM D-2240 and a flexural modulus from about 15,000 to about 70,000 psi as measured in accordance with ASTM standard test method D-790 (ASTM D-790).
Soft (low modulus) pre-neutralized ionomeric resins are generally acrylic acid or methacrylic acid based. One example of a soft pre-neutralized ionomer resin comprises a zinc based ionomer made from an acrylic acid polymer and unsaturated monomers of the acrylate ester class. The soft ionomeric resins generally have a hardness from about 20 to about 50 or, preferably, from about 30 to about 40 as measured on the Shore D scale and a flexural modulus from about 2,000 to about 15,000 psi or, preferably, from about 3,000 to 10,000 psi as measured in accordance with ASTM D-790. Examples of hard and soft ionomeric resins include those sold under the Iotek™ and Surlyn™ trade names.
The golf ball 10 has at least one layer composed of the thermoplastic material of the invention comprising about 10 to about 95% by weight of at least one neutralized acid copolymer and, preferably, from about 15 to about 90% acid copolymer.
Generally, ethylene/alkyl acrylate copolymers include ethylene and acrylic or methacrylic esters of linear, branched or cyclic alkanols. Preferably, the copolymers contain from about 1 to about 35 weight % alkyl acrylate and from about 99 to about 65 weight % ethylene.
Examples of ethylene/alkyl acrylate copolymers that may be used include, among others, ethylene/ethyl acrylate (EEA), ethylene/methyl acrylate (EMA) and ethylene/butyl acrylate (EBA). EEA copolymers are made by the polymerization of ethylene units with randomly distributed ethylene acrylate (EA) monomer groups. The copolymers contain up to about 30% by weight of EA. The copolymers are tough and flexible having a relatively high molecular weight. The copolymers have good flexural fatigue and low temperature properties (down to −65° C.). In addition, EEA resists environmental stress cracking as well as ultraviolet (UV) radiation. Examples of EEA copolymers include those sold under the trade name Bakelite™ by the Union Carbide Corporation. EEA is similar to ethylene vinyl acetate (EVA) in its density-property relationships and high-temperature resistance. In addition, like EVA, EEA is not resistant to aliphatic and aromatic hydrocarbons.
EMA copolymers contain up to about 30% by weight of methyl acrylate and yield blown films having rubberlike limpness and high impact strength. These copolymers may be useful in coating and laminating applications as a result of their good adhesion to commonly used substrates. EMA also has good heat-seal characteristics.
EMA copolymers are manufactured by reacting, at high temperatures and pressures, methyl acrylate monomers with ethylene and free radical initiators. Polymerization occurs such that the methyl acrylate forms random pendant groups on the polyethylene backbone. The acrylic functionality decreases polymer crystallinity and increases polarity, enhancing polymer properties. These properties depend on molecular weight (determined, for example, by melt index) and percent crystallinity. Percent crystallinity is determined by the extent of methyl acrylate comonomer incorporation. As the methyl acrylate content increases, the film becomes softer, tougher and easier to heat seal.
EMA films have low moduli (generally less than 10,000 psi), low melting points and good impact strengths. In addition, EMA copolymers are highly polar and, as a result, are compatible with olefinic and other polymers. They adhere well to many substrates including low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and EVA.
Examples of EMA copolymers for use in the golf ball components of the present invention include those sold under the trade names Optema™ or Escor™ by ExxonMobil. Optema™ and Escor™ are thermally stable polymers that will accept up to 65% or more fillers and pigments without losing their properties. These copolymers are more thermally stable than EVA and can be extruded or molded over a range of temperatures from 275 to 625° F. (compared to the limit of 450° F. for EVA copolymers). EMA copolymers are generally not corrosive as compared to EVA and EAA copolymers.
EBA copolymers can also be included in a thermoplastic material of the invention. These are generally similar to EMA copolymers with improved low temperature impact strength and high clarity. For example, the EBA copolymer sold under the trade name EBAC™ by the Chevron Corporation is stable at high temperatures and may be processed as high as 600° F.
Metal cation salts may also be utilized to neutralize ethylene/alkyl acrylate copolymers as a source of the corresponding carboxylic acid. The salts to be used are those salts that provide the metal cations capable of hydrolyzing and neutralizing, to various extents, the carboxylic acid ester groups of the copolymers. This converts the alkyl ester into a metal salt of the acid. These metal cation salts include, but are not limited to, oxide, carbonate or hydroxide salts of alkali metals such as lithium, sodium, potassium or mixtures thereof. Some examples hydroxide salts of alkali metals include, but are not limited to, lithium hydroxide monohydrate, lithium hydroxide, lithium carbonate, lithium oxide, sodium hydroxide, sodium oxide, sodium carbonate, potassium hydroxide, potassium oxide and potassium carbonate.
The amount of metal cation salt, preferably, an alkali metal cation salt reacted with an ethylene/alkyl acrylate copolymer varies depending upon such factors as the reactivity of the salt and copolymer used, reaction conditions (such as temperature, pressure, moisture content and the like) and the desired level of conversion. Preferably, the reaction occurs through saponification, wherein the carboxylic acid ester groups of the ethylene/alkyl acrylate copolymer are converted by alkaline hydrolysis to form the salt of the acid and alcohol. Examples of such reactions are set forth in U.S. Pat. Nos. 3,970,626, 4,638,034 and 5,218,057, which are incorporated herein by reference.
The products of the conversion reaction are an alkanol (the alkyl group of which comes from the alkyl acrylate comonomer) and a terpolymer of ethylene, alkyl acrylate, and an alkali metal salt of the (meth) acrylic acid. The degree of conversion or saponification is variable depending on the amount of alkali metal cation salt used and the saponification conditions. Generally, from about 10 to about 60% of the ester groups are converted during the saponification reaction. The alkanol and other by products can be removed by normal separation processes leaving the remaining metal cation neutralized (or hydrolyzed) ester-based ionomer resin reaction product.
Alternatively, the ethylene alkyl acrylate copolymer included in the invention can be commercially obtained in a pre-neutralized or saponified condition. For example, a number of metal cation neutralized ester-based ionomer resins produced under the saponification process of U.S. Pat. No. 5,218,057 are available from the Chevron Corporation.
Additional examples of the preferred copolymers that fulfill the criteria set forth above are a series of acrylate copolymers that are commercially available from ExxonMobil, such as Optema™ ethylene methyl acrylates and Enable™ ethylene butyl acrylates; Elvaloy™ ethylene butyl acrylates available from DuPont, and Lotryl™ ethylene butyl acrylic esters available from Atofina Chemical.
The acrylate ester is preferably an unsaturated monomer having from 1 to 21 carbon atoms, which serves as a softening comonomer. The acrylate ester preferably is methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl or 2-methoxyethyl 1-acrylate and most preferably is methyl acrylate or n-butyl acrylate. Another suitable type of softening comonomer is an alkyl vinyl ether selected from the group consisting of n-butyl, n-hexyl, 2-ethylhexyl and 2-methoxyethyl vinyl ethers.
The acrylate ester-containing ionic copolymer or copolymers used in golf ball components can be obtained by neutralizing commercially available acrylate ester-containing acid copolymers such as poly (ethylene/methyl acrylate/acrylic acid) terpolymers sold by ExxonMobil under the trade name Escor™ ATX or poly (ethylene/butyl acrylate/methacrylic acid) terpolymers sold by DuPont under the trade name Nucrel™. The acid groups of these materials and blends thereof are neutralized with one or more of various metal cation salts that include zinc, sodium, magnesium, lithium, potassium, calcium, manganese, nickel and the like. The extent of neutralization can range from 10 to about 100%, preferably from about 30 to about 100% or, more preferably, from about 40 to about 90%. Generally, a higher degree of neutralization results in a harder and tougher thermoplastic material.
The metallocene-catalyzed copolymers or plastomers of a thermoplastic material of the invention include ethylene alpha olefin copolymers wherein the alpha olefin preferably has from 4 to 8 carbon atoms. Such plastomers are polyolefin copolymers developed using metallocene single-site catalyst technology. Polyethylene plastomers produced by metallocene single-site catalysis generally have better impact resistance than those made via Ziegler-Natta catalysis. Plastomers exhibit both thermoplastic and elastomeric characteristics. In addition to being comprised of a polyolefin such as ethylene, plastomers contain up to about 35 weight % softening comonomer. Plastomers of a thermoplastic material of the invention include, but are not limited to, ethylene/butene copolymers, ethylene/octene copolymers, ethylene/hexene copolymers, ethylene/hexene/butene terpolymers and mixtures thereof.
The plastomers included in a thermoplastic material of the invention may be formed by single-site metallocene catalysis such as disclosed in EP 0029358, U.S. Pat. Nos. 4,752,597, 4,808,561, and 4,937,299, the teachings of which are incorporated herein by reference. Blends of plastomers can also be used for the thermoplastic material. As is known in the art, plastomers can be produced by solution, slurry and gas phase processes, although preferred plastomers for a thermoplastic material of the invention are produced by metallocene catalysis. For example, a high pressure process can be used to polymerize ethylene in combination with other olefin monomers such as butene-1, hexene-1, octene-1 and 4-methyl-1-pentene in the presence of a catalyst system comprising a cyclopentadienyl-transition metal compound and an alumoxane.
Examples of plastomers that may be used in a thermoplastic material of the invention are those sold by ExxonMobil under the trade name Exact™, preferably, Exact™ 3024, Exact™ 3025, Exact™ 4049 and Exact™ 3027 (ethylene/butene copolymers). Other useful plastomers include, but are not limited to, ethylene/hexene copolymers such as Exact™ 3031.
Exact™ plastomers typically have a dispersion index (Mw/Mn, where Mw is weight average molecular weight and Mn is number average molecular weight) of about 1.5 to 4.0, a density of about 0.86 to about 0.93 g/cc, a melting point of about 140-220° F. and a melt index (MI) above about 0.5 g/10 mins Plastomers that may be employed in a thermoplastic material of the invention include copolymers of ethylene and at least one C3 to C20 alpha olefin, preferably a C4 to C8 alpha olefin present in an amount of about 5 to about 32 weight %. Such plastomers are believed to have a composition distribution breadth index of about 45% or more.
Plastomers such as those sold by Dow Chemical Co. under the trade name Engage™ also may be employed in a thermoplastic material of the invention. These plastomers maybe produced as disclosed in U.S. Pat. No. 5,272,236, the teachings of which are incorporated herein by reference. Such plastomers are substantially linear polymers having a density of about 0.85 g/cc to about 0.93 g/cc as measured in accordance with ASTM standard test method D-792 (ASTM D-792), a melt index (MI) of less than 30 g/10 minutes and a dispersion index Mw/Mn that is preferably less than 5. The plastomers include homopolymers of C2 to C20 olefins such as ethylene, propylene, 4-methyl-1-pentene and the like. Alternatively, the plastomers can be interpolymers of ethylene with at least one C3 to C20 alpha-olefin and/or C2 to C20 acetylenically unsaturated monomer and/or C4 to C18 diolefins. These plastomers can have a polymer backbone that is either unsubstituted or substituted with up to 3 long chain branches/1000 carbon atoms. As used herein, long chain branching means a chain length of at least about 6 carbon atoms, above which the length of the chain cannot be distinguished using 13C nuclear magnetic resonance (NMR) spectroscopy. Preferred Engage™ plastomers are characterized by a saturated ethylene/octene backbone and a narrow dispersion index Mw/Mn of about 2. Various commercially available plastomers may be useful in the invention, including those manufactured by Mitsui.
Plastomers of a thermoplastic material of the invention are compatible with many conventional plasticizers and fillers. Such fillers include, but are not limited to, clay, talc, asbestos, graphite, glass, mica, calcium metasilicate, barium sulfate, zinc sulfide, aluminum hydroxide, silicates, diatomaceous earth, carbonates (such as calcium carbonate, magnesium carbonate and the like), metals (such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, copper, brass, boron, bronze, cobalt, beryllium and alloys thereof), metal oxides (such as zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide and the like), particulate synthetic plastic (such as high molecular weight polyethylene, polystyrene, polyethylene ionomeric resins and the like), particulate carbonaceous materials (such as carbon black, natural bitumen and the like), as well as cotton flock, cellulose flock and/or leather fiber. Dark colored fillers generally are not preferred for use in an outer layer of a golf ball if a white ball is desired. In such an instance, a two-layer cover can be used in which a non-white filler is present only in the inner layer of the cover. The amount of filler employed is primarily a function of weight restrictions on a golf ball. For example, weight may be removed from a golf ball core and placed in an inner and/or outer layer of the golf ball cover. Such added weight will change the moment of inertia of the golf ball, thereby potentially altering its performance.
The dispersion index, of plastomers made in accordance with U.S. Pat. No. 5,272,236 is, preferably, about 2.0. Non-limiting examples of these plastomers include Engage™ CL 8001, CL 8002, CL 8003, EG 8100, 8150, 8200 and Engage™ EP 8500.
The fatty acids and salts of fatty acids generally comprise fatty acids neutralized with metal cations. The fatty acids can be saturated or unsaturated fatty acids and are generally composed of a chain of alkyl groups containing from about 2 to about 80 carbon atoms, preferably from about 4 to about 30, usually an even number, and terminate with a carboxyl (—COOH) group. The general formula for fatty acids (except for acetic acid) is CH3(CH2)xCOOH, wherein the carbon atom count includes the carboxyl group and X is from about 4 to about 30 carbon atoms. Examples of fatty acids suitable for use include, but are not limited to, stearic acid, oleic acid, palmitic acid, pelargonic acid, lauric acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, myristic acid, margaric acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, carboceric acid, montanic acid and melissic acid. Such fatty acids are preferably neutralized with metal cations such as zinc, calcium, magnesium, barium, sodium, lithium, aluminum or combinations thereof, although other metal cations may also be used. The metal cations are generally from metal cation salts that neutralize, to various extents, the carboxylic acid groups of the fatty acids. Examples of metal cation salts include sulfate, carbonate, acetate and hydroxylate salts of metals such as zinc, calcium, magnesium and barium. Examples of the fatty acid salts that may be utilized in a thermoplastic material of the invention include, but are not limited to, metal stearates, laureates, oleates, palmitates, pelargonates and the like such as zinc stearate, calcium stearate, magnesium stearate, barium stearate and so forth. Metal stearates are known in the art and are commercially available from various manufacturers.
Highly neutralized blends of copolymers used to form the golf ball components of the present invention can be produced by reacting the two copolymers with various amounts of the metal cation salts at a temperature above the crystalline melting point of the copolymers, for example, from about 200 to about 500° F. and, preferably, from about 250 to about 425° F. under high shear conditions at a pressures of from about 100 to 10,000 psi. Other well known blending techniques in the art may also be used. The amount of metal cation salt used to produce the highly neutralized blend of copolymers is the quantity that provides a sufficient amount of the metal cations to neutralize a desired percentage of the carboxylic acid groups of the acid copolymer. The copolymers can be blended before or after neutralization, or they can be mixed and neutralized at the same time (that is, the copolymers, metal cation salts and fatty acids or salts of fatty acids are mixed together). The fatty acids or salts of fatty acids are added in the desired amounts, generally from about 5 to about 100 parts by weight, preferably from about 10 to about 60 parts by weight, more preferably from about 20 to about 50 parts by weight and even more preferably from about 30 to about 40 parts by weight.
The various compositions of the present invention may be produced according to conventional melt blending procedures. In a preferred embodiment, the copolymers are blended in a Banbury™ type mixer, two-roll mill or extruder prior to neutralization. After blending, neutralization then occurs as the polymers are in a melt or molten state within the Banbury™ type mixer, two-roll mill or extruder. The blended composition is then formed into slabs, pellets or the like and maintained in such a state until molding is desired. Alternatively, a simple dry blend of the pelletized or granulated copolymers, which have previously been neutralized to a desired extent (and colored masterbatch, if desired) may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives such as inorganic fillers may be added and uniformly mixed in before initiation of the molding process.
The compatibility of a metallocene-catalyzed copolymer with an acid copolymer results in a thermoplastic material blend having superior properties over standard ionomeric resin blends as shown by the results provided in the Examples detailed below.
Additional materials may also be added to a thermoplastic material of the invention when utilized for golf equipment so long as such materials do not substantially reduce the playability properties of the equipment. Exemplary materials include dyes such as Ultramarine Blue™ sold by Whitaker, Clark & Daniels, Incorporated (see U.S. Pat. No. 4,679,795), pigments such as titanium dioxide, zinc oxide, barium sulfate and zinc sulfate, UV absorbers, antioxidants, antistatic agents, and stabilizers. Moreover, the ball cover compositions utilizing the thermoplastic material of the invention may also contain softening agents such as those disclosed in U.S. Pat. Nos. 5,312,857 and 5,306,760. Exemplary softeners include plasticizers, processing acids, and the like, and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties of the golf ball produced are not impaired.
Various fillers may be added to golf ball compositions to reduce manufacturing costs, to increase or decrease weight, to reinforce the thermoplastic material, adjust ball layer density or flex modulus, aid in ball mold release and/or adjust the melt flow index of the thermoplastic material and the like. Examples of heavy weight fillers include titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, steel, lead, copper, brass, boron, boron carbide whiskers, bronze, cobalt, beryllium, zinc, tin, metal oxides (such as zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide) and metal stearates (such as zinc stearate, calcium stearate, barium stearate, lithium stearate and magnesium stearate). Other preferred fillers include limestone (ground calcium or magnesium carbonate) and ground flash filler.
Fillers that may be used in the layers of a golf ball (other than the outer cover layer) are typically in a finely divided form such as, for example, in a particle size generally less than about 20 U.S. standard mesh and, preferably, less than about 100 U.S. standard mesh (except for fibers and flock, which are generally elongated). Flock and fiber sizes should be small enough to facilitate processing. Filler particle size will depend upon the desired effect, cost, ease of addition and dusting considerations. A filler for a golf ball layer preferably is selected from the group consisting of precipitated hydrated silica, clay, talc, asbestos, glass fibers, aramid fibers, mica, calcium metasilicate, barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide, diatomaceous earth, polyvinyl chloride, carbonates, metals, metal alloys, tungsten carbide, metal oxides, metal stearates, particulate carbonaceous materials, micro-balloons and combinations thereof. Non-limiting examples of suitable fillers, their densities or specific gravities (spec. gray.) and preferred uses are listed in Table 1: