The invention relates to a reaction injection molding process and compositions for forming golf equipment or components thereof, particularly for forming layers of golf balls in one embodiment.  The reaction injection molding process of the invention involves providing at least two reactable components that have a fast reaction time and injecting them with sufficient speed after they are mixed so that they are polymerized, solidified, or gelled in a mold cavity. 
It is well known to even the average golfer that the equipment used in playing the game is subject to a great deal of friction, impact, and other stresses during a typical round of golf.  Both the performance and the useful life of such equipment would benefit from the use of materials having increased durability.  For instance, many types of golf clubs, such as putters, drivers, and wedges, contain polymer inserts in the face of the club.  Since the club face directly strikes a golf ball thousands of times over the life of the club, improved durability is of great importance.  Additionally, club components, such as shafts, grips, and hosels, undergo significant stress during a golf swing and contact with a golf ball and, therefore, could stand to benefit from more durable materials. 
Of course, golf balls are repeatedly struck against very hard objects as well, including golf clubs, and it is very desirable to maintain their performance properties over as long a period of time as possible.  Golfers of all skill levels seek out a variety of properties in their golf balls for a variety of golfing situations, although resilience, durability, and longevity are always important.  The type of materials used in forming the different golf ball layers can greatly affect these properties, as well as the xe2x80x9cclick,xe2x80x9d xe2x80x9cfeel,xe2x80x9d spin, initial velocity, xe2x80x9cplayability,xe2x80x9d and other properties. 
Golf equipment is typically formulated from a variety of different materials.  Most conventional materials, however, do not entirely address the problems associated with stress, durability, and repeated impact.  Therefore, it is clear that improved materials, having material properties that address these preferred physical requirements, are necessary. 
In addition, the manner in which golf equipment, or components thereof, is fabricated can affect certain properties of the materials, for example, such as durability.  The types of chemistries present in the golf equipment materials can also sometimes indicate or dictate the preferred method of fabrication used to form them. 
Particularly with respect to polyurethane-containing materials, commercially available golf equipment or components, especially for golf balls, can be currently made by casting or injection molding processes.  The nature of current casting processes is such that materials that require a relatively long time (in comparison to other fabrication methods) to sufficiently solidify, i.e., react thoroughly.  As a result, materials or compounds with particular chemistries that react or solidify relatively quickly are generally restricted from use in commercial casting processes, particularly in the golf art. 
By using an alternative fabrication technique, reaction injection molding, as opposed to traditional injection molding, thermosetting materials and/or materials with relatively quick reaction or solidification times can be processed into certain articles.  Reaction injection molding processes, due to the nature of the chemistries of the materials used, tend to result in decreased fabrication times, and can facilitate a decrease in the cost of fabricating such articles.  The technique of reaction injection molding (RIM) using a variety of materials has been demonstrated in various publications. 
For example, U.S. Pat.  No.  4,762,322 discloses golf clubs with heads that can be made from a hollow metal shell or a low density, high strength material, such as a reaction injection molded polyurethane, formed around weighted inserts. 
With respect to manufacture of golf balls, RIM has been disclosed, for example, in International Publication No.  WO 00/57962, which claims golf balls, and processes for making such balls, comprising a reaction injection molded material, such as polyurethanes/polyureas. 
In addition, U.S. Pat.  No.  6,083,119 discloses a multi-layer golf ball with an inner and outer cover layer, at least one of which can contain a reaction injection molded polyurethane material. 
U.S. Pat.  Nos.  4,695,055 and 4,878,674 also disclose illuminated, translucent golf balls having a permanent diametric hole into which a chemiluminescent light stick is added, so that the golf balls may be visible in the dark.  These golf balls can be fabricated by a method such as reaction injection molding. 
Additionally, conventional non-reactive injection molding can be used to form relatively thin layers of material in golf equipment, or components thereof, generally in golf balls.  Examples of thin components or layers made by conventional non-reactive injection molding have also been demonstrated in various publications. 
One aspect of the invention relates to a method for forming golf equipment, or a portion thereof, preferably for forming one or more layers of a golf ball, including: providing a first reactable component including an isocyanate-reactive component, preferably including a polyisocyanate or including a prepolymer or quasi-prepolymer containing the reaction product of a polyol, polyamine, or epoxy-containing compound with at least one polyisocyanate, and a second reactable component including at least one of a polyol, polyamine, or epoxy-containing compound; combining the reactable components together to form a reactive mixture; and injecting the reactive mixture into a cavity or mold having a desired shape within a time sufficient to avoid substantial gelation or solidification.  Advantageously, the polymerization, solidification, or gelation times of the reactive mixture of the present invention should typically be within about 60 seconds, preferably within about 45 seconds, more preferably from about 0.25 seconds to 30 seconds, most preferably from about 0.5 seconds to 15 seconds, after combining, either at ambient or elevated temperatures.  In various other embodiments, the polymerization, solidification, or gelation times of the reactive mixture of the present invention are from about 1 second to 10 seconds or from about 1 second to 5 seconds after combining. 
In a preferred embodiment, each of the at least two reactable components have a viscosity not more than about 20,000 cPs, preferably not more than about 15,000 cPs, more preferably from about 25 cPs to 10,000 cPs, most preferably from about 25 cPs to 5,000 cPs, all at ambient or elevated temperatures.  In another preferred embodiment, all the reactable components, or mixtures thereof each contained separately, that form the reactive mixture have viscosities similar to those of the first and second reactable components at ambient or elevated temperatures.  In yet another preferred embodiment, each reactable component has a viscosity not more than about 5,000 cPs, preferably not more than about 1,000 cPs, at a temperature of about 150xc2x0 F. In one embodiment, the mixture is injected into the mold or cavity at an injection pressure of not more than about 2,500 psi.  In another embodiment, the viscosity index of any two of the reactable components is from about 1000 to 1, preferably from about 800 to 20, at ambient temperature or at a temperature at which the reactable components are combined. 
In one preferred embodiment, the isocyanate-containing compound or the polyisocyanate includes a diisocyanate having the generic structure:
Oxe2x95x90Cxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90Cxe2x95x90O
where R is a cyclic, aromatic, or linear branched or unbranched hydrocarbon chain each having a moiety containing from about 1 to 20 carbon atoms.  When multiple aromatic or cyclic groups are present, linear and/or branched hydrocarbons containing from about 1 to 10 carbon atoms can be present as spacers between the aromatic or cyclic groups.  In some cases, the cyclic or aromatic group(s) may be substituted at the 2-, 3-, and/or 4-positions, or at the ortho-, meta-, and/or para-positions, respectively, with: halogens; primary, secondary, or tertiary hydrocarbon groups; or a mixture thereof.  In another preferred embodiment, the isocyanate-containing compound or the polyisocyanate includes higher functional adducts of diisocyanates, e.g., such as the isocyanurate of TDI, the isocyanurate of a hexamethylene diisocyanate, the uretdione of TDI, the uretdione of HDI, or a mixture thereof.  In yet another preferred embodiment, the isocyanate-containing compound or the polyisocyanate includes a triisocyanate or higher functional polyisocyanate that is not an adduct of a diisocyanate, or a mixture thereof.  In a more preferred embodiment, the polyisocyanate contains PPDI, MPDI, MDI, or TDI, more preferably MDI.  In one preferred embodiment, the second reactable component can include more than one polyol, polyamine, or epoxy-containing compound, at least one compound which preferably has a molecular weight less than about 400 g/mol, and at least a second compound of which is preferably a polyether polyol, a hydroxy-terminated polybutadiene, a polyester polyol, a polycarbonate polyol, or a mixture thereof, more preferably a partially or fully hydrogenated hydroxy-terminated polybutadiene.  In this preferred embodiment, the second reactable component preferably has a number average molecular weight of not less than about 200 g/mol, more preferably from about 200 g/mol to 4,000 g/mol.  In one embodiment, the second polyol, polyamine, or epoxy-containing compound may advantageously be present in an amount from about 40% to 95% based on the total weight of the first and second reactable components.  In another embodiment, the total amount of the first reactable component plus the first polyol, polyamine, or epoxy-containing compound may advantageously be from about 5% to 60% based on the total weight of the first and second reactable components.  In one preferred embodiment, the first reactable component includes greater than about 14% by weight of unreacted isocyanate groups.  In another preferred embodiment, the first reactable component includes less than about 14% by weight of unreacted isocyanate groups.  In yet another preferred embodiment, the first reactable component includes a low free isocyanate monomer composition. 
Another aspect of the invention relates to a method for forming golf equipment, or a portion thereof, including: providing at least two sets of precursor components that can be reacted to form at least two different polymers of an interpenetrating polymer network, at least one polymer being crosslinked; combining the sets of precursor components together to form a reactive mixture; and injecting the reactive mixture into a cavity or mold having a desired shape within a time sufficient to avoid substantial polymerization, gelation, or solidification.  In one preferred embodiment, the at least two sets of precursor components include a first reactable component, which contains an isocyanate-containing compound, and a second reactable component, which contains an isocyanate-reactive compound. 
Another aspect of the invention relates to a method for forming golf equipment, or a portion thereof, including: providing at least two reactable components that, when combined, can form a foamed polymeric material; combining the reactable components together to form a reactive mixture; and injecting the reactive mixture into a cavity or mold having a desired shape within a time sufficient to avoid substantial polymerization, gelation, or solidification, and such that the reactive mixture forms a foamed material, preferably an open-cell, a closed-cell, or a microcellular foam, also preferably with a specific gravity of not more than about 1, more preferably not more than about 0.8, most preferably not more than 0.5. 
In one embodiment where the golf equipment that is formed includes one or more layers of a golf ball, the golf ball can have a solid or fluid-filled center, optionally at least one intermediate layer disposed about the center, and at least one cover layer disposed about the center and the optional intermediate layer, if present.  In one embodiment, the cover layer of the golf ball has a first material hardness and the layer disposed immediately inside the cover layer has a second material hardness, and the first material hardness is greater than the second material hardness.  In that embodiment, the first material hardness can be at least about 55 Shore D, or the second material hardness can be up to about 55 Shore D. In another embodiment, the second material hardness is greater than the first material hardness.  In that embodiment, the first material hardness can be up to about 55 Shore D, or the second material hardness can be at least about 55 Shore D. In yet another embodiment, the cover material hardness is greater than about 15 Shore A. In a preferred embodiment, the core of the golf ball has an outer diameter from about 1.55 inches to 1.67 inches.  In another embodiment, the injecting results in the formation of golf equipment, or a portion thereof, which has a thickness less than about 0.065 inches, alternately less than 0.01 inches.  In another preferred embodiment, the equipment has a coefficient of restitution of greater than about 0.7, preferably greater than about 0.75, and more preferably greater than about 0.78, at an initial velocity of 125 ft/s. In another preferred embodiment, the golf ball, or a portion thereof, has an Atti compression of at least about 40, preferably from about 50 to 120, more preferably from about 60 to 100. 
In one embodiment, the injecting or the method results in the formation of golf equipment, or a layer or portion thereof, which layer or portion has a moisture vapor transmission rate (xe2x80x9cMVTRxe2x80x9d) of less than about 1000 (gxc2x7mil)/(100 in2xc2x7day), preferably less than about 750 (gxc2x7mil)/(100 in2xc2x7day), more preferably less than about 500 (gxc2x7mil)/(100 in2xc2x7day). 
In an embodiment where the golf equipment includes a golf ball or a portion thereof, the method according to the invention further includes optionally adding from about 0.1% to 50% by weight of a filler material.  Adding this filler material may alter the specific gravity or other mechanical, physical, optical, or processing properties of the golf ball or the portion thereof. 
In another embodiment, the method further includes adding to one or more of the reactable components a catalyst to facilitate or speed up the reaction between the at least two reactable components when they are combined.  Preferably, the catalyst is present in an amount from about 0.001% to 3% by weight and includes a metal catalyst, preferably a tin catalyst, an amine catalyst, an organic acid, a delayed catalyst, or a combination thereof. 
Another aspect of the invention relates to golf equipment, preferably golf balls, or a portion thereof, prepared by any of the processes detailed herein.  For example, the invention includes golf equipment, or a portion thereof, including: a first reactable component comprising an isocyanate-containing compound; and a second reactable component comprising at least one of a polyol, polyamine, or epoxy-containing compound, wherein the golf equipment, or portion thereof, is formed by reaction injection molding of the first and second reactable components, which react with each other after contact sufficiently to be substantially gelled or solidified within about 60 seconds, and wherein the isocyanate-containing compound contains: a diisocyanate having the generic structure, Oxe2x95x90Cxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90Cxe2x95x90O, where R is a moiety containing from about 1 to 20 carbon atoms, optionally including one or more substituted or unsubstituted phenyl or cyclic groups; a dimeric or multimeric adduct of a diisocyanate; a triisocyanate or higher functional polyisocyanate that is not an adduct of a diisocyanate; or a mixture thereof.