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
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OF THE INVENTION
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.