US 20040072630 A1
A golf ball includes a wound center and a cover made from fast curing polyurethane. The fast curing polyurethane is a two-component polyurethane which includes an isocyanate and a mixture of isocyanate reactive compounds comprising polyether or polyester polyol, aliphatic or aromatic (di) amines, and chain extenders, catalysts, internal mold release agent as needed.
1. A golf ball comprising:
a layer of elastic windings surrounding the center,
a cover having a Shore D hardness of 50 to 65 and formed from a fast curing two component polyurethane system which includes:
1. An isocyanate, and
2. One or more isocyanate reactive components selected from the class consisting of:
a. polyether polyols,
b. polyester polyols,
c. aliphatic (di)amines, and
d. aromatic (di)amines.
2. The golf ball of
3. The golf ball of
4. The golf ball of
5. The golf ball of
6. A golf ball comprising:
a center having a diameter of 1 to 1.4 inch,
a layer of elastic windings surrounding the center and having an outer diameter of 1.52 to 1.60 inch, and
a cover having a Shore D hardness of 50 to 65 and formed from a fast curing two component polyurethane system comprising:
1. An aromatic isocyanate prepolymer,
2. an isocyanate reactive compound comprising a polyol, an aliphatic amine, an aromatic diamine, and a catalyst.
7. The golf ball of
8. The golf ball of
9. The golf ball of
10. The golf ball of
11. The golf ball of
 This application is a continuation-in-part of co-pending application Ser. No. 09/624,703, filed Jul. 24, 2000.
 This invention relates to golf balls, and, more particularly, to a golf ball which includes a cover made from fast curing polyurethane.
 Balata (trans-polyisoprene) was the primary material used for golf ball covers until the late 1960's. Balata covered golf balls were (and are) preferred because of the soft feel and the control which the better player can impart to the ball. However, balata covered golf balls are expensive, and difficult to produce. Balata balls also generally exhibit poor cut resistance, which is also not beneficial.
 In the late 1960's, ionomers were introduced by DuPont, under the trade name Surlyn. Ionomers are copolymers of an olefin (generally ethylene), and an alpha-beta ethylenically unsaturated carboxylic acid (generally methacrylic acid). Neutralization of a number of the acid groups is effected with metal ions, currently chosen from the group of sodium, lithium, zinc and magnesium. Ionomer covers are more durable than balata, and are currently the material of choice on most solid core, and many wound core, golf balls. However, ionomer materials are generally harder than balata, and do not provide the golfer with the feel and control of a balata covered golf ball.
 In the mid-1980's, soft ionomers (known as Very Low Modulus Ionomers or VLMI) were produced by DuPont. These ionomers are similar in chemical structure to standard ionomers, with the addition of an acrylate monomer to soften the material. These materials allowed for the development of softer ionomer covered golf balls, but did not produce properties similar to balata.
 Other soft thermoplastic materials (such as thermoplastic polyurethanes, thermoplastic polyester elastomers, polyether block amide copolymers, etc.) have been used as covers on golf balls, with limited success. Although these materials have been successfully used as mantle (inner cover) layers for golf balls, they generally produce insufficient resilience properties to be used as covers for premium golf balls. U.S. Pat. Nos. 5,688,191, 5,759,676, 5,810,678 and 5,813,923 all illustrate the use of a thermoplastic polyurethane material as a mantle material. Thermoplastic polyurethane materials have also been used in blends with other materials, such as ionomers. U.S. Pat. No. 4,674,751 describes blends of thermoplastic polyurethanes with ionomers.
 More recently, wound golf balls made using castable polyurethane have been developed. Balls made using castable polyurethane covers have many properties comparable to balata—similar feel (slightly harder) and comparable performance properties. Balls made using castable polyurethane materials are available from Titleist (Titleist Professional) and Maxfli (Maxfli Revolution).
 U.S. Pat. No. 3,979,126 describes a polyurethane cover comprising a prepolymer and curing agent having at least two amine groups. U.S. Pat. No. 3,989,568 describes a castable polyurethane material made with curing agents having different rates of reaction to allow for polyurethane to cure sufficiently to form half-shells, but not cure completely. U.S. Pat. No. 4,123,061 also describes a polyurethane compound that is cured sufficiently to form preform half-shells, but not cured to completion until molding of half shells around a wound core. U.S. Pat. No. 5,334,673 describes a castable polyurethane golf ball formed using a slow reacting polyamine curing agent. However, the polyurethane covered golf balls described in this patent are made using a casting process which is both difficult and time-consuming. U.S. Pat. Nos. 5,006,297, 5,733,428, 5,888,437 and 5,947,843 all describe various methods for molding slow curing polyurethane covered golf balls.
 The invention provides a golf ball with a cover made using a fast-curing thermoset polyurethane material produced from the reaction of two components: 1. an isocyanate, and 2. a mixture of isocyanate reactive compounds. The resulting golf ball yields comparable performance properties (feel, resilience, spin rate) to golf balls made using balata or castable polyurethane covers. The golf ball can be produced in a closed injection mold (Reaction Injection Molding) process, which is significantly less time-consuming, and more economical than standard castable polyurethane process of the prior art.
FIG. 1 is a sectional view of a three-piece wound golf ball with a cover which is formed in accordance with the invention.
 Referring to FIG. 1, a three-piece golf ball 10 includes a center 11, a layer of elastic windings 12, and a cover 13. The center can be solid or liquid filled and has a diameter within the range of 1 to 1.4 inches, more preferably 1.0 to 1.25 inches. The windings can be formed, for example, from isoprene or natural rubber thread. The outer diameter of the layer of windings is within the range of 1.52 to 1.60 inches, more preferably 1.56 to 1.58 inches. According to the rules of the United States Golf Association, the outer diameter of the cover must be at least 1.680 inches.
 The cover 13 is formed from a fast curing two-component polyurethane system comprising:
 1. an isocyanate;
 2. a mixture of isocyanate reactive compounds comprising one or more of:
 a. a polyether or polyester polyol;
 b. aliphatic or aromatic amines or diamines;
 c. chain extenders or crossliners;
 d. catalysts;
 e. internal mold release agents;
 f. colorants fillers, and other standard cover ingredients.
 The polyurethane cover has a Shore D hardness of 50 to 65.
 Isocyanates suitable for use in this compound include (but are not limited to) diphenylmethane-4,4′-diisocyanate (MDI) or an aliphatic isocyanate such as isophorone diisocyanate.
 Polyether polyols suitable for use in the isocyanate reactive compound include (but are not limited to) propylene glycol, glycerine and trimethylolpropane.
 Polyester polyols suitable for use in the isocyanate reactive compound include (but are not limited to) ethylene glycol, diethylene glycol, and butanediol.
 Chain extenders, catalysts, internal mold releases, colorants, etc. are used as needed.
 A preferred construction for the golf ball is:
 1. a solid or liquid-filled center having diameter of 1.0-1.25 inches;
 2. a center wound with isoprene or natural rubber thread to an outside diameter of about 1.56 to 1.58 inches;
 3. a cover formed from a fast-curing polyurethane comprising two components;
 a. an aromatic isocyanate prepolymer (Diphenylmethane Diisocyanate prepolymer) and
 b. an isocyanate reactive compound, consisting of a polyol (propylene glycol), an aliphatic amine, an aromatic diamine (diethyltoluene diamine), and a catalyst (an organotin compound).
 Polyurethane materials suitable for use as the cover are commercially available from Bayer Corporation, under the trade name Bayer.
 Table 1 lists the properties of polyurethane materials from Bayflex Corporation which are suitable for use in the invention.
 Golf balls were prepared in accordance with Table 2. The physical properties of the golf balls are also listed in Table 2.
 The ball of Example 1 was made using a liquid filled center (produced by Abbott Laboratories, and wound with Fulflex thread to a diameter of 1.57 inches. The cover was reaction injection molded from Bayflex 110-25 polyurethane.
 The ball of Example 2 was made using a solid center, and wound to a diameter of about 1.57 inches. The cover was reaction injection molded from Bayflex 110-50.
 The ball of Example 3 was made using a solid center, and wound to a diameter of about 1.58 inches. The cover was reaction injection molded from Bayflex 110-35.
 The covers of all of the golf balls of the Examples were injection molded over the core using a Hennecke 55 Reaction Injection Molding press and a single cavity mold. The Bayflex cover material was mixed at a ratio consistent with the ratios described in Table 1, with the following injection conditions:
 1. Throughput of about 35 g/s.
 2. Injection time set at 0.8 seconds.
 3. Mold temperature of 150° F.
 4. Isocyanate prepolymer pressure of about 2500 psi.
 5. Polyether Polyol system pressure of about 2000 psi.
 The Bayflex grades used for these covers cure to sufficient hardness to allow demolding in about 10 seconds. The balls were actually removed form the mold (in fully cured state) after about 30 seconds.
 The ball of Example 1 was molded using Bayflex 110-25 fast curing polyurethane system, tested for physical properties, and compared to Titleist Professional (a competitive golf ball made using a slow curing, castable polyurethane cover). Results indicate that the balls of Example 1 yield comparable ball compression, slightly softer cover, and slightly lower resilience properties.
 The ball of Example 2 was molded using Bayflex 110-50 fast curing polyurethane system, tested for physical properties, and also compared to the Titleist Professional ball. The Bayflex 110-50 cover resulted in a slightly higher Shore D hardness than the Titleist Professional, and comparable compression and slightly lower resilience properties. The resilience properties of Example balls 1 and 2, although slightly lower than the Titleist Professional, are still sufficient for a premium level golf ball.
 The ball of Example 3 was molded using Bayflex 110-35 fast curing polyurethane system, tested for physical properties, and compared to Maxfli Revolution (also a competitive golf ball made using a slow curing, castable polyurethane cover). The ball of Example 3 yielded slightly lower cover hardness (Shore D) and higher ball PGA compression than the Maxfli Revolution. The ball of Example 3 also yielded comparable resilience properties (Coefficient of Restitution, Initial Velocity) to the Maxfli Revolution.
 Overall, the balls of Examples, 1, 2 and 3 illustrate that a ball with the properties (cover hardness, PGA compression and resilience properties) required for a premium golf ball can be made using a fast curing polyurethane cover material. The making of a polyurethane cover ball using the cover described herein also allows for a much faster, easier, and less expensive method of processing than is necessary if using a slow curing, castable polyurethane cover.
 Curing agents which are suitable for the fast curing polyurethane system are unhindered aromatic or aliphatic (di)amines. More specifically, the system includes an aromatic isocyanate and unhindered aromatic (di)amines. Diethyltoluene diamine should be considered an unhindered diamine.
 The polyurethane cover is preferably reaction injected molded around the wound center by placing the wound center in a two-part mold, closing the mold, mixing the two components of the polyurethane, and injecting the mixed components into the closed mold. The details of the reaction injection molding apparatus and method are described in co-pending United States patent application entitled “Reaction Injection Molded Golf Ball”, Serial No. 09/176,445, filed Oct. 21, 1998, which is incorporated herein by reference.
 While in the foregoing specification a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it will be understood that many of the details hereingiven may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.