CROSS REFERENCES TO RELATED APPLICATIONS
The present invention is a continuation of U.S. patent application Ser. No. 11/277,389 filed Mar. 24, 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 golf ball. More specifically, the present invention relates to a method for treating a thermoplastic polyurethane golf ball cover.
2. Description of the Related Art
Traditional golf ball covers have been comprised of balata or blends of balata with elastomeric or plastic materials. The traditional balata covers are relatively soft and flexible. Upon impact, the soft balata covers compress against the surface of the club producing high spin. Consequently, the soft and flexible balata 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, the soft balata covers produce a soft “feel” to the low handicap player. Such playability properties (workability, feel, etc.) 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 covered golf balls are easily cut and/or damaged if mis-hit. Golf balls produced with balata or balata-containing cover compositions therefore have a relatively short life span.
As a result of this negative property, balata and its synthetic substitutes, trans-polybutadiene and transpolyisoprene, have been essentially replaced as the cover materials of choice by other cover materials such as ionomeric resins and polyurethanes.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E.I. DuPont de Nemours & Company under the trademark Surlyn® and by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks Escor® and Iotek®, have become widely utilized for the construction of golf ball covers over the traditional “balata” (transpolyisoprene, natural or synthetic) rubbers. As stated, the softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play.
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 ions, such as sodium or zinc, are used to neutralize some portion of the acidic groups 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 the decreases produced in playability. This is because although the 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 different commercial grades of ionomers available both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (for example, relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc., 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”, etc.) characteristics previously associated with the “soft” balata covers, properties which are still desired by the more skilled golfer.
Furthermore, a number of different golf ball constructions, such as one-piece, two-piece (a solid resilient center or core with a molded cover), three-piece (a liquid or solid center, elastomeric winding about the center, and a molded cover), and multi-piece golf balls, have been developed to produce golf balls exhibiting enhanced playability and durability. The different types of materials utilized to formulate the cores, mantles, windings, covers, etc. of these balls dramatically alters the balls' overall characteristics. In addition, multi-layered covers containing one or more ionomer resins or other materials have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired.
For example, in various attempts to produce a durable, high spin golf ball, the golfing industry has blended the hard ionomer resins with a number of softer ionomeric resins and applied these blends to two-piece and three-piece golf balls. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. 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 hard ionomer alone. Consequently, it would be useful to develop a golf ball having a combination of softness and durability which is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend.
Additionally, thermoset and thermoplastic polyurethanes have recently become popular materials of choice for golf ball cover construction. However, these polyurethanes are difficult and time consuming to process. Moreover, the molding of relatively thin wall cover layer(s), i.e., cover layers 0.075 inches or less in cross-sectional thickness, is difficult to accomplish. This limits the desired performance achieved by thin wall cover molding, such as improved distance. Furthermore, golf balls produced utilizing these materials tend to be soft and readily susceptible to scuffing.
As a result, it would be further desirable to produce a thermoplastic polyurethane covered golf ball having a thin wall cover construction which exhibits enhanced durability, namely improved cut and scuff (groove shear) resistance, while maintaining and/or improving such characteristics as playability and distance.
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OF THE INVENTION
The present invention provides a method of improving the durability, namely scuff resistance, of a golf ball with a thermoplastic cover. The invention is able to increase the durability of a golf ball with a thermoplastic polyurethane cover through the addition of reactive moieties to the cover prior to subsequent treatment with gamma irradiation.
One aspect of the present invention is a method of forming a golf ball with a thermoplastic polyurethane cover. The method includes placing a golf ball precursor product in a solution to create a solution covered golf ball precursor product. The solution includes a hydroxyl or isocyanate terminated polybutadiene in an amount of 10% to 30% by weight of the solution and a solvent. Next, the solution covered golf ball precursor product is removed from the solution. Next, the solution covered golf ball precursor product may or may not be heated to remove the solvent. Next, the solution covered golf ball precursor product is placed in an isocyanate solution to create a isocyanate solution covered golf ball precursor product. Next, the isocyanate solution covered golf ball precursor product is heated to create a final golf ball precursor product. The final golf ball precursor product may then be send for gamma or electron beam irradiation.
Another aspect of the present invention is a method of forming a golf ball. The method begins with molding a thermoplastic polyurethane material comprising a hydroxyl or isocyanate functional polybutadiene over a golf ball insert, forming a golf ball precursor product. The functionalized polybutadience may be present in the cover material in an amount from 1% to 25% by weight. Furthermore, the polybutadiene material may be pre-compounded into the thermoplastic polyurethane or may be added directly into the barrel of the molding apparatus or may be incorporated by any method known to those skilled in the art. The insert may comprise any construction know to those skilled in the art, including, but not limited to solid cores, liquid cores, metal cores, or multi-layer constructions. The golf ball precursor product preferably includes a core, a boundary layer and a cover comprising a thermoplastic polyurethane material. Next, golf ball precursor product may be placed in an isocyanate solution to create an isocyanate solution covered golf ball precursor product. The isocyanate solution includes acetone and MDI. Next, the isocyanate solution covered golf ball precursor product is heated to create a treated golf ball precursor product, wherein the isocyanate solution covered golf ball precursor product is heated from two to four hours at a temperature ranging from 125° F. to 250° F. The golf ball precursor product or the treated precursor product is then irradiated with gamma or electron beam radiation, forming a final golf ball precursor product.
Still another aspect of the present invention is a golf ball having a cover composed of a thermoplastic polyurethane and a functionalized polybutadiene material in an amount ranging from 1 to 3 weight percent of the cover. The cover can be used on a two-piece, three-piece or multiple-piece golf ball. The thickness of the cover is preferably from 0.020 inch to 0.060 inch, and more preferably from 0.030 inch to 0.045 inch. The cover exhibits good scuff resistance.
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 is a flow chart of a preferred method of the present invention.
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OF THE INVENTION
As shown in FIG. 1, a method of the present invention is generally designated 200. At block 202, a golf ball precursor product (referred to as “GBPP” in FIG. 1) is formed having a cover comprising a thermoplastic polyurethane material. Alternatively, the cover comprises a thermoplastic polyurethane material and a functionalized polybutadiene material. Alternatively, the cover is composed of a blend of a thermoplastic polyurethane material and a polyurea, ionomeric or non-ionomeric material and a functionalized polybutadiene. In preferred embodiment, the golf ball precursor product is a three-piece solid golf ball. Alternatively, the golf ball precursor product is a two-piece golf ball with a thermoplastic polyurethane cover. Those skilled in the pertinent art will recognize other golf ball constructions that incorporate a thermoplastic polyurethane cover.
If the cover is composed of a thermoplastic polyurethane without a functionalized polybutadiene material, then at block 204, the golf ball precursor product is placed in a solution. The solution includes a hydroxyl or isocyanate terminated polybutadiene in an amount of 10% to 30% by weight of the solution and a solvent, and more preferably 20% by weight of the solution. A preferred material is a KRASOL LBH liquid low molecular weight polybutadiene with terminal secondary hydroxyl groups, which is available from Kaucuk of the Czech Republic. Another preferred material is KRASOL NN22. The solution also preferably includes a solvent. A preferred solvent is acetone. Other solvents include methyl ethyl ketone and toluene. The golf ball precursor product is preferably placed in the solution for approximately one to two minutes.
At block 206, a solution covered golf ball precursor product is removed from the solution. At block 208, the solution covered golf ball precursor product is heated to remove the solvent. Preferably, the solution covered golf ball precursor product is heated at a temperature ranging from 125° F. to 250° F. for approximately two to four hours. Alternatively, the solution covered golf ball precursor product is allowed to air dry at room temperature (approximately 72° F.) for two to six hours.