GOLF BALL AND METHOD OF MANUFACTURING A GOLF BALL CROSS-REFERENCE TO RELATED APPLICATIONS

[01] This application claims the benefit of U.S. Provisional Application Nos. 61/366183, filed July 21, 2010 and 61/370096, filed August 2, 2010, which are incorporated by reference in their entireties as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

[02] This invention relates to golf balls and methods of manufacturing golf balls. The physical properties, composition, and design of a golf ball determine its performance characteristics during play, including distance, loft, flight symmetry, spin, and durability. Golf balls can be constructed so that certain performance characteristics are emphasized and/or deemphasized to execute various types of shots in view of the different golf clubs used to make such shots.

[03] For example, golf balls can be constructed to emphasize or deemphasize the spin characteristic of the ball according to the distance of the desired shot and the club used to make such shot. For long distance shots, where drivers, woods, and long irons are used, high spin is generally not desirable. High spin can increase lift which can result in a loss of distance. In contrast, for mid to short distance shots, high spin (approximately 5,000 to 12,000 rpm) can be desirable. High spin can improve control during flight and stopping power ("grab") when the ball hits the green. The characteristic of a ball to have low spin for long distance shots and high spin for mid to short distance shots can be referred to as spin separation. Multilayer golf balls with soft covers (low flex modulus and low hardness) and hard intermediate layers provide good spin separation.

[04] However, soft covers are susceptible to "scuffing" or shear yielding of the polymer that compromises the integrity and performance of the ball. The irons and wedges used to perform mid to short distance shots have a clubface with a large angle of loft when measured in reference to the ground with 0 degrees being with the face of the club perpendicular to the ground and 90 degrees being with the face of the club parallel to the ground. The large angled clubfaces impart relatively high shear force on the cover of the ball when the clubface strikes the ball. These shear forces are high enough to cause the polymer material of the cover to shear yield or "scuff." A high degree of scuffing renders the ball unfit for play. It can also cause the spin rate to decrease during the shot when the scuffing occurs, thus giving inconsistent spin characteristics to the golf ball. Accordingly, it is desirable to construct a golf ball cover that is soft for use in multilayer golf balls with good spin separation but less susceptible to shear yielding or scuffing.

[05] One attempted solution is described in U.S. Patent Numbers 6,458,307 and 6,729,975.

These patents disclose hardening the surface of a golf ball cover made of thermoplastic resin by allowing a polyisocyanate compound to permeate into the surface of the cover and cause a reaction between the polyisocyanate compound and active hydrogen groups contained in the thermoplastic resin to form a number of urethane linkages and urea linkages to crosslink the thermoplastic resin. Nonetheless, scuffing continues to be problem.

SUMMARY OF THE INVENTION

[06] In one embodiment, a multi-layer golf ball includes a core, at least one intermediate layer, and a cover. The cover can be made of a thermoplastic resin and includes an outer portion and an inner portion. The outer portion of the cover includes an interpenetrating polymer network of the thermoplastic resin and at least one of a carbodiimide, an isocyanate dimer, an isocyanate trimer, a polyisocyanurate, an uretonimine, and an oxazolidone. The inner portion is substantially devoid of the interpenetrating polymer network. The outer portion of the cover has a microindentation hardness that is greater than the microindentation hardness of the inner portion of the cover.

[07] In one embodiment, a multi-layer golf ball includes a cover, at least one intermediate layer, and a cover. The cover can be made of a thermoplastic resin and include an outer portion and an inner portion. The outer portion can include the thermoplastic resin and a reaction product of an isocyanate compound and a co-reactant compound having a non- active hydrogen group, the isocyanate compound having reacted with the non-active hydrogen group of the co-reactant compound in the presence of a catalyst to form the reaction product.

[08] In one embodiment, a method of manufacturing a golf ball includes molding a cover made of thermoplastic resin over at least one intermediate layer of a golf ball; permeating an isocyanate solution comprising an isocyanate compound, a co-reactant compound, and a catalyst into an outer portion of the cover. The catalyst catalyzes a reaction between the isocyanate compound and the co-reactant compound to form a reaction product. The co- reactant compound can be a second isocyanate compound, the catalyst can be a quaternary ammonium salt, and the reaction product can be isocyanurate. The reaction product modifies at least one physical property of the outer portion such that the physical property of the outer portion is different than the physical property of the inner portion. The modified physical property can be microindentation hardness, where the microindentation hardness of the outer portion is greater than the microindentation hardness of an inner portion of the cover.

BRIEF DESCRIPTION OF THE DRAWINGS

[09] Figure 1 depicts a sectional view of a multilayer golf ball;

[010] Figure 2 depicts a portion of a cross-sectional view of a multilayer golf ball; and

[011] Figure 3 depicts a portion of a cross-sectional view of an embodiment of a multilayer golf ball of the current invention.

DETAILED DESCRIPTION

[012] An embodiment of the current invention can be useful, for example, to improve the performance of multilayer golf balls. As used herein, the term multi-layer golf ball means a golf ball constructed of at least two layers and can include, for example, two- piece, three-piece, and four-piece golf balls. Referring to Figures 1 through 3, an example of a three-piece multi-layer golf ball can include a core 2, an intermediate layer 3, and a cover 4. The cover 4 can include dimples 5 molded thereon. Multilayer golf balls and corresponding individual layers of the ball may be made by any suitable materials and methods known to those of ordinary skill in the art, including those described in, for example, U.S. Patent Number 7,491 ,878.

[013] In one embodiment of the current invention, a golf ball with cover formed of thermoplastic resin, such as thermoplastic polyurethane, is permeated with an isocyanate solution. The solution can include an isocyanate compound, a co-reactant compound, and a catalyst. The co-reactant can include at least one non-active hydrogen group. A non-active hydrogen group is a hydrogen group on a compound that is typically not labile or exchangeable during a reaction. The co-reactant compound can be, for example, at least one of a second isocyanate compound, a carbodiimide, and an epoxide.

[014] Isocyanates are the derivatives of isocyanic acid (H-N=C=0). The functionality of the isocyanate (-N=C=0) group is highly reactive toward proton-bearing nucleophiles (such as primary hydroxyl and primary amine compounds), and the reaction of the isocyanate usually proceeds with addition to the carbon-nitrogen bond. The reactions of isocyanates fall into two main categories:

1. Active hydrogen reaction; and

2. Non-active hydrogen reaction.

[015] An active hydrogen is one such as those attached to hydroxyl (-OH) groups, amine groups (-NH2) and water (HOH) molecules. Polyurethane chemistry is based on the reactions of isocyanates with active hydrogen-containing compounds. Isocyanates are compounds having one or more of the highly reactive isocyanate group (-N= C= O). This group will readily react with hydrogen atoms that are attached to atoms more electronegative than carbon. The reactivity of the isocyanate group can be explained by considering the resonance possibilities presented in the figure below. [016] Electron density is expected to be greatest on the oxygen atom and least on the carbon atom. This results in the oxygen atom having the largest net negative charge, the carbon a net positive charge, and the nitrogen, an intermediate net negative charge.

[017] Non-proton bearing nucleophiles (non-active hydrogens), such as other isocyanates, will react with the aid of a catalyst. For example, in the presence of a trimerization catalyst, the nitrogen atom of one isocyanate will react with the carbon atom of a second isocyanate and the nitrogen atom of a third isocyanate will then react with carbon atom of the first isocyanate. This forms the isocyanurate ring. There is no nucleophilic addition of hydrogen to the nitrogen atom of the isocyanate group. The isocyanurate molecule that is formed is very thermally stable.

[018] In one embodiment, the isocyanate solution can be caused to permeate through the surface of the cover 4 and into the thermoplastic resin of the cover 4 to a depth that is less than the entire thickness of the cover 4. The portion between the surface of the cover 4 and the depth to which the solution is allowed to permeate can be referred to as the outer portion 7 of the cover 4. In one embodiment, the outer portion 7 has a thickness of about 0.1 mm to 1.0 mm. In another embodiment, the solution is allowed to permeate to a depth of about 15 to 20 mils. The permeation can cause the isocyanate compound, co- reactant, and catalyst to diffuse through the network of thermoplastic resin within the outer portion 7 of the cover 4. The portion of the cover in which the solution does not permeate can be referred to as the inner portion 8 of the cover 4. An example of the outer portion 7 and inner portion 8 of the cover 4 as those terms are used herein is depicted in Figure 3.

[019] The catalyst can catalyze a reaction between the isocyanate compound and the co- reactant compound to form a reaction product. In one embodiment, the catalyst can be at least one of a phosphine oxide, a pyridine, an alkali soap, a quaternary ammonium salt, a strong base, an organoantimony iodide, a zinc acetyl-acetonate, and a benzoyl chloride. The catalyst can catalyze the reaction between the isocyanate compound and the non- active hydrogen group of the co-reactant compound to form the reaction product. The reaction product can be, for example, at least one of a carbodiimide, an isocyanate dimer, an isocyanate trimer, a polyisocyanurate, an uretonimine, and an oxazolidone. Example typical reactions between the isocyanate compound and co-reactant compound in the presence of the catalyst to form the reaction product are included in Table 1.

TABLE 1

[020] Figure 3 depicts an example of the reaction product 6 in the outer portion 7 of the cover 4. In the example depicted in figure 3, a higher concentration of reaction product is shown near the surface of the cover 4 so as to form a gradient of reaction product in the outer portion 7. In one embodiment, the reaction product penetrates into the cover to a depth of about 15 to 20 mils, thereby forming an outer portion 7 of the cover having thickness of about 15 to 20 mils. The inner portion 7 of the cover can be substantially devoid of the reaction product. For purposes this application, substantially devoid means a di minimums amount or an amount insubstantial to impact the physical properties of the material or performance characteristics of the ball.

[021] The reaction between the isocyanate compound and the co-reactant can occur within the network of thermoplastic resin in the outer portion 7 and form an interpenetrating polymer network of the reaction product and the thermoplastic resin in the outer portion 7 of the cover 4. An interpenetrating polymer network (IPN) as used herein means a polymer material comprising two or more networks which are at least partially interlaced on a polymer scale but not covalently bonded to each other and cannot be separated unless chemical bonds are broken. In addition, the inner portion 8 of the cover 4 can be substantially devoid of the IPN of thermoplastic resin and reaction product. [022] The reaction product and/or IPN of thermoplastic resin and reaction product can result in the modification of at least one physical property of the outer portion of the cover. For example, the reaction product and/or IPN can increase the hardness of the outer portion 7 of the cover 4 so that the hardness of the outer portion 7 is greater than the hardness of the inner portion 8. Hardness can be determined by, for example, microindentation hardness testing in accordance with the Vickers hardness test (HV) or Knoop hardness test (HK). Increased hardness of the outer portion 7 can, for example, improve the shear resistance and spin separation properties of the golf ball.

[023] Example isocyanate compounds suitable for purposes of the invention include: toluene 2,4-diisocyanate (TDI) / 2,4-diisocyanato-l-mehybenzene; toluene 2,6-diisocyanate (TDI) / 2,6-diisocyanato-l-mehybenzene; 65:35 mixture of toluene 2,4 and 2,6- diisocyanate (TDI-65/35); 80:20 mixture of toluene 2,4 and 2,6-diisocyanate (TDI- 80/20); 4,4'-diphenyl methane diisocyanate (MDI) / l,l '-methylenebis(4-isocyanato- benzene); 2,4'-diphenyl methane diisocyanate (MDI)/ l-isocyanato-2-(4- isocyanatophenyl) methylbenzene; 2,2'-diphenyl methane diisocyanate (MDI)/ 1, 1 '- methylenebis(2-isocyanato-benzene); hexamethylene diisocyanate (HDI) /1,6- diisocyanatohexane; isophorone diisocyanate (IPDI) / 5-isocyabato-l-(isocyanatomethy)- 1,3,3-trimethylcyclohexane; m-tetramethylxylene diisocyanate (m-TMXDI) / l ,3-bis(l- isocyanato-l -methylethy) benzene; dicyclohexylmethane 4,4 '-diisocyanate (HMDI)/ 1, 1 '-methylebis(4-isocyanato-cyclohexane); triphenylmethane-4,4',4"-(triisocyanate / Ι, Γ,Γ'-methylidynetris (4-isocyanatobenzene); naphthalene 1,5-diisocyanate (NDI) / 1,5- diisocyanatonaphthalene; p-phenylene diisocynate (PPDI) / 1,4-diidocyanatobenzene. An example of a useful diisocyanate is MONDUR MR LIGHT produced by Bayer Corporation.

[024] Example catalysts suitable for the purposes of the invention follow. An example phosphine oxide is isopropyl methylphosphonofluoridate. An example pyridine is pyridine-N-oxide. An example alkali soap includes lithium salicylate. Example quaternary ammonium salts include those available from Air Products and Chemicals, Inc. under the trade names DABCO TMR, DABCO TMR-2, DABCO TMR-3, DABCO TMR-4, and DABCO TMR-5. The quaternary ammonium salts may also be used with organotin compounds as a co-catalyst. An example strong base is ammonia hydroxide. As an example, an embodiment of a golf ball of the current invention can be made according to the following process. A golf ball with a thermoplastic polyurethane cover is permeated with a solution of isocyanate. The solution of isocyanate can be a solvent, at least one isocyanate compound and a catalyst. The solvent can be, for example, acetone or methyl ethyl ketone (MEK). The isocyanate compound can be about 0.1 to 40% of the solution, with 4 to 5% preferred. Unless otherwise defined herein, the term about means ±10% of the referenced amount. The permeating can be performed by, for example, contacting the golf ball with the isocyanate solution for a contacting time from about 1 to about 10 minutes, with 4 to 5 minutes preferred. The contacting can be performed by, for example, soaking or immersing the golf ball in the solution. The contacting of the ball with the solvent can cause the solvent to swell the thermoplastic polyurethane and permit the isocyanate compound to permeate the cover. The greater the contacting time, the deeper the isocyanate can permeate into the cover. The catalyst can catalyze the reaction between the isocyanate compound and a second isocyanate compound in the solution (in this example, isocyanate is the co-reactant). The reaction can occur via the non-active hydrogens of the isocyanate to form isocyanurate, which is a trimer of isocyanate. To form isocyanurate, the catalyst can be, for example, an alkali soap or quaternary ammonium salt, to speed the reaction from. The solution can optionally be heated to between about 76 °F and about 120 °F during contact with the ball to speed the reaction. The ball is removed from contact with the isocyanate solution and heated to a temperature of about 76 °F to about 180 °F, with about 76 °F to about 120 °F preferred, for a time from about 10 minutes to about 5 hours. The heating can take place in an oven. After heating, the ball can be cleaned with an alcohol, such as isopropanol or methanol, and allowed to dry. The ball can then be coated with a waterborne primer and allowed to dry. Such waterborne primer can include, for example, a polyurethane dispersion, such as Witcobond 234 from Chemtura. The ball can then be given a final coat of a polyurethane and allowed to dry. Such polyurethane can include, for example, a two-part polyurethane such as a saturated polyester mixed with a HDI pre-polymer. [026] In one embodiment, a golf ball with a thermoplastic polyurethane cover was soaked in an isocyanate solution of acetone, an isocyanate compound in about 15% of the solution, and 0.05% of lithium salicylate. The ball was soaked in the solution for about 2 minutes. The golf ball was removed from the solution and heated to 180 °F for about 4 hours. The ball was then cleaned with isopropanol and allowed to dry. The ball was then coated with a waterborne primer and allowed to dry. A final coating of a two part polyurethane was applied to the ball and allowed to dry.

[027] In one embodiment, a golf ball with a thermoplastic polyurethane cover was soaked in an isocyanate solution of acetone, an isocyanate compound in about 15% of the solution, and 0.1% of Dabco TMR (a quaternary ammonium salt catalyst). The ball was soaked in the solution for about 2 minutes. The golf ball was removed from the solution and heated to 180 °F for about 4 hours. The ball was then cleaned with isopropanol and allowed to dry. The ball was then coated with a waterborne primer and allowed to dry. A final coating of a two part polyurethane was applied to the ball and allowed to dry.

[028] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[029] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.