Abstract:
A method for increasing adhesion between golf ball layers comprising the steps of providing a golf ball layer having a first surface; preparing the first surface for treatment; exposing the first layer to a silane; providing a second golf ball layer; and adhering the second layer to the first via the silane. Additionally, a golf ball including an inner component, a molecular monolayer, and at least one cover layer, wherein the inner component and the at least one cover layer have differing surface energies and the cover layer is adhered to inner component with the molecular monolayer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a non-provisional application claiming priority to U.S. Provisional Application No. 60/291,275, filed May 16, 2001. 

   FIELD OF THE INVENTION 
   This invention relates generally to promoting adhesion between golf ball layers. In particular, this invention relates to the use of silane coupling agents to promote adhesion between layers of a golf ball cores, intermediate layers, and cover layers. 
   BACKGROUND 
   Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover. Solid balls have traditionally been considered longer and more durable than wound balls, but also lack the preferred “feel” provided by the wound construction. 
   By altering ball construction and composition, manufacturers can vary a wide range of playing characteristics, such as compression, velocity, “feel,” and spin, each of which can be optimized for various playing abilities. In particular, a variety of core and cover layer(s) constructions, such as multi-layer balls having dual cover layers and/or dual core layers, have been investigated. These golf ball layers are typically constructed with a number of polymeric compositions and blends, including polybutadiene rubber, polyurethanes, polyamides, and ethylene-based ionomers. 
   One problem sometimes encountered by manufacturers when attempting to construct multi-layered golf balls, however, is improper adhesion between layers. This problem arises when the compositions of adjacent layers are chemically incompatible, even if only by a small amount, or when processing conditions required for a particular layer are inconsistent with those required for an adjacent layer. Therefore, a need exists for development of a better adhesive promoter between layers. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a method for increasing adhesion between golf ball layers comprising the steps of providing a golf ball layer having a first surface; preparing the first surface for treatment; exposing the first layer to a silane; providing a second golf ball layer; and adhering the second layer to the first via the silane. 
   The step of preparing the first surface may include corona discharge, plasma treatment, washing, drying, rinsing, heating, chilling, a combination thereof, or, additionally, may include the steps of washing the first surface; exposing the first surface to plasma for a predetermined time; and rotating the first surface. Ideally, the exposure time is less than 10 seconds. To ensure proper exposure to silane, the first surface should be rotated by at least ¼ turn. The step of preparing the first surface may also include roughening or gleebar grinding the surface. 
   The silane may include a variety of silanes, such as silane esters; vinyl silanes; methacryloxy silanes; epoxy silanes; sulfur silanes; amino silanes; ureido silanes; or a mixture thereof. Preferably, the silanes include silane esters, octyltriethoxysilane, methyltriethoxylsilane, methyltrimethoxysilane, nonionic silane dispersing agents; vinyl silanes, vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris-(2-methoxyethoxy) silane, vinylmethyldimethoxysilane; methacryloxy silanes, γ-methacryloxypropyltrimethoxysilane; epoxy silanes, β-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane; sulfur silanes, γ-mercaptopropyltrimethoxysilane proprietary polysulfidesilane, bis-(3-[triethoxisily]-propyl)-tetrasulfane; amino silanes, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, aminoalkyl silicone solution, modified aminoorganosilanes, γ-aminopropyltrimethoxysilane, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, modified aminoorganosilanes, modified aminosilanes, triaminofinctional silanes, bis-(γ-trimethoxysilylpropyl)amine, n-phenyl-γ-aminopropyltrimethoxysilane, organomodified polydimethylsiloxane, polyazamide silane, n-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; ureido silanes, γ-ureidopropyltrialkoxysilane, γ-ureidopropyltrimethoxysilane; isocyanate silanes, γ-isocyanatopropyltriethoxysilane; or a mixture thereof. 
   A preferred class of silanes includes amino silanes, the most preferably one being bis-(γ-trimethoxysilylpropyl) amine. Ideally, the silane is in a solution and is present in an amount of less than about 10% by weight. The step of exposing the first surface to a silane typically includes the step of drying the silane-coated first surface. The second surface, such as an outer cover layer, is typically cast about the first surface and includes saturated or unsaturated thermoplastic polyurethanes, thermoset polyurethanes, polyureas, epoxies, acrylics, or a mixture thereof. 
   The first surface, on the other hand, includes thermoplastics, thermosets, ionic copolymers of ethylene and an unsaturated monocarboxylic acid, vinyl resins, polyolefins, polyurethanes, polyureas, polyamides, acrylic resins, polyphenylene oxide resins, thermoplastic polyesters, thermoplastic rubbers, or a mixture thereof. 
   The silane may be a silane coupling agent. Additionally, the step of preparing the first surface comprises generating surface hydroxyl groups prior to the exposing step. The first surface should also have a first surface energy and the second golf ball layer should have a second surface second surface having a second energy different from the first 
   The present invention is also directed to a golf ball comprising an inner component, a molecular monolayer, and at least one cover layer, wherein the inner component and the at least one cover layer have differing surface energies and the cover layer is adhered to inner component with the molecular monolayer. 
   The molecular monolayer is preferably a silane including silane esters; vinyl silanes; methacryloxy silanes; epoxy silanes; sulfur silanes; amino silanes; ureido silanes; or a mixture thereof. The molecular monolayer, when a silane, includes silane esters, octyltriethoxysilane, methyltriethoxylsilane, methyltrimethoxysilane, nonionic silane dispersing agents; vinyl silanes, vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris-(2-methoxyethoxy) silane, vinylmethyldimethoxysilane; methacryloxy silanes, γ-methacryloxypropyltrimethoxysilane; epoxy silanes, β-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane; sulfur silanes, γ-mercaptopropyltrimethoxysilane proprietary polysulfidesilane, bis-(3-[triethoxisily]-propyl)-tetrasulfane; amino silanes, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, aminoalkyl silicone solution, modified aminoorganosilanes, γ-aminopropyltrimethoxysilane, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, modified aminoorganosilanes, modified aminosilanes, triaminofunctional silanes, bis-(γ-trimethoxysilylpropyl)amine, n-phenyl-γ-aminopropyltrimethoxysilane, organomodified polydimethylsiloxane, polyazamide silane, n-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; ureido silanes, γ-ureidopropyltrialkoxysilane, γ-ureidopropyltrimethoxysilane; isocyanate silanes, γ-isocyanatopropyltriethoxysilane; or a mixture thereof. Preferably, the silane comprises an amino silane, ideally bis-(γ-trimethoxysilylpropyl) amine. The silane is in a solution and is present in an amount of less than about 10% by weight. 
   The inner component is any golf ball component and typically includes a core, solid center, liquid center, intermediate layer, wound layer, an inner cover layer, or an outer core layer. Ideally, the inner component includes a solid center and an inner cover layer. 
   The cover layer includes a saturated or unsaturated thermoplastic polyurethanes, thermoset polyurethanes, polyureas, epoxies, acrylics, or a mixture thereof. In a preferred construction, at least one of the inner component and the cover layer has a thickness of less than about 0.05 inches, preferably, between about 0.02 inches and about 0.04 inches. In another embodiment, the inner component includes a solid center, an outer core layer, and an inner cover layer. The cover layer has a material hardness of less than about 45 Shore D. Additionally, the inner component may be a casing layer having a material hardness of less than about 70 Shore D. 

   DETAILED DESCRIPTION 
   The golf ball of the present invention includes a core and a cover surrounding the core. The core and/or the cover may have more than one layer and an intermediate layer may be disposed between the core and the cover of the golf ball. 
   The golf ball cores of the present invention may comprise any of a variety of constructions. For example, the core of the golf ball may comprise a conventional center surrounded by an intermediate or outer core layer disposed between the center and the inner cover layer. The core may be a single layer or may comprise a plurality of layers. The innermost portion of the core may be solid or it may be a liquid filled sphere. As with the core, the intermediate layer or outer core layer may also comprise a plurality of layers. The core may also comprise a solid or liquid filled center around which many yards of a tensioned elastomeric material are wound. 
   The materials for solid cores include compositions having a base rubber, a crosslinking agent, a filler, and a co-crosslinking or initiator agent. The base rubber typically includes natural or synthetic rubbers. A preferred base rubber is 1,4-polybutadiene having a cis-structure of at least 40%. Most preferably, the base rubber comprises high-Mooney-viscosity rubber. If desired, the polybutadiene can also be mixed with other elastomers known in the art such as natural rubber, polyisoprene rubber and/or styrene-butadiene rubber in order to modify the properties of the core. 
   The crosslinking agent includes a metal salt of an unsaturated fatty acid such as a zinc salt or a magnesium salt of an unsaturated fatty acid having 3 to 8 carbon atoms such as acrylic or methacrylic acid. Suitable cross linking agents include one or more metal salt diacrylates, dimethacrylates and monomethacrylates wherein the metal is magnesium, calcium, zinc, aluminum, sodium, lithium or nickel. Preferred acrylates include zinc acrylate, zinc diacrylate, zinc methacrylate, and zinc dimethacrylate, and mixtures thereof. The crosslinking agent is typically present in an amount greater than about 10 phr of the polymer component, preferably from about 10 to 40 phr of the polymer component, more preferably from about 10 to 30 phr of the polymer component. 
   The initiator agent can be any known polymerization initiator which decomposes during the cure cycle. Suitable initiators include peroxide compounds such as dicumyl peroxide, 1,1-di(t-butylperoxy) 3,3,5-trimethyl cyclohexane, a-a bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di(t-butylperoxy) hexane or di-t-butyl peroxide and mixtures thereof. 
   Fillers typically include materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, regrind (recycled core material typically ground to about 30 mesh particle), high-Mooney-viscosity rubber regrind, and the like. 
   Fillers added to one or more portions of the golf ball typically include processing aids or compounds to affect rheological and mixing properties, density-modifying fillers, tear strength, or reinforcement fillers, and the like. The fillers are generally inorganic, and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Fillers may include polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers are typically also added to one or more portions of the golf ball to modify the density thereof to conform to uniform golf ball standards. Fillers may also be used to modify the weight of the center or at least one additional layer for specialty balls, e.g., a lower weight ball is preferred for a player having a low swing speed. 
   The invention also includes a method to convert the cis-isomer of the polybutadiene resilient polymer component to the trans-isomer during a molding cycle and to form a golf ball. A variety of methods and materials have been disclosed in U.S. Pat. No. 6,162,135 and U.S. application Ser. No. 09/461,736, filed Dec. 16, 1999; Ser. No. 09/458,676, filed Dec. 10, 1999; and Ser. No. 09/461,421, filed Dec. 16, 1999, each of which are incorporated herein, in their entirety, by reference. 
   The materials used in forming either the golf ball center or any portion of the core, in accordance with the invention, may be combined to form a mixture by any type of mixing known to one of ordinary skill in the art. Suitable types of mixing include single pass and multi-pass mixing. Suitable mixing equipment is well known to those of ordinary skill in the art, and such equipment may include a Banbury mixer, a two-roll mill, or a twin screw extruder. 
   Conventional mixing speeds for combining polymers are typically used. The mixing temperature depends upon the type of polymer components, and more importantly, on the type of free-radical initiator. Suitable mixing speeds and temperatures are well-known to those of ordinary skill in the art, or may be readily determined without undue experimentation. 
   The mixture can be subjected to, e.g., a compression or injection molding process, to obtain solid spheres for the center or hemispherical shells for forming an intermediate layer. The temperature and duration of the molding cycle are selected based upon reactivity of the mixture. The molding cycle may have a single step of molding the mixture at a single temperature for a fixed time duration. The molding cycle may also include a two-step process, in which the polymer mixture is held in the mold at an initial temperature for an initial duration of time, followed by holding at a second, typically higher temperature for a second duration of time. In a preferred embodiment of the current invention, a single-step cure cycle is employed. The materials used in forming either the golf ball center or any portion of the core, in accordance with the invention, may be combined to form a golf ball by an injection molding process, which is also well-known to one of ordinary skill in the art. Although the curing time depends on the various materials selected, those of ordinary skill in the art will be readily able to adjust the curing time upward or downward based on the particular materials used and the discussion herein. 
   The cover provides the interface between the ball and a club. Properties that are desirable for the cover include good moldability, high abrasion resistance, high tear strength, high resilience, and good mold release. The cover typically has a thickness to provide sufficient strength, good performance characteristics, and durability. The cover preferably has a thickness of less than about 0.1 inches, more preferably, less than about 0.05 inches, and most preferably, between about 0.02 inches and about 0.04 inches. The invention is particularly directed towards a multilayer golf ball which comprises a core, an inner cover layer, and an outer cover layer. In this embodiment, preferably, at least one of the inner and outer cover layer has a thickness of less than about 0.05 inches, more preferably between about 0.02 inches and about 0.04 inches. Most preferably, the thickness of either layer is about 0.03 inches. 
   When the golf ball of the present invention includes an inner cover layer, this layer can include any materials known to those of ordinary skill in the art, including thermoplastic and thermosetting material, but preferably the inner cover can include any suitable materials, such as ionic copolymers of ethylene and an unsaturated monocarboxylic acid which are available under the trademark SURLYN® of E.I. DuPont de Nemours &amp; Co., of Wilmington, Del., or IOTEK® or ESCOR® of Exxon. These are copolymers or terpolymers of ethylene and methacrylic acid or acrylic acid partially neutralized with salts of zinc, sodium, lithium, magnesium, potassium, calcium, manganese, nickel or the like, in which the salts are the reaction product of an olefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylic acid having 3 to 8 carbon atoms. The carboxylic acid groups of the copolymer may be totally or partially neutralized and might include methacrylic, crotonic, maleic, fumaric or itaconic acid. 
   This golf ball can likewise include one or more homopolymeric or copolymeric inner cover materials, such as: 
   (1) Vinyl resins, such as those formed by the polymerization of vinyl chloride, or by the copolymerization of vinyl chloride with vinyl acetate, acrylic esters or vinylidene chloride; 
   (2) Polyolefins, such as polyethylene, polypropylene, polybutylene and copolymers such as ethylene methylacrylate, ethylene ethylacrylate, ethylene vinyl acetate, ethylene methacrylic or ethylene acrylic acid or propylene acrylic acid and copolymers and homopolymers produced using a single-site catalyst or a metallocene catalyst; 
   (3) Polyurethanes, such as those prepared from polyols and diisocyanates or polyisocyanates and those disclosed in U.S. Pat. No. 5,334,673; 
   (4) Polyureas, such as those disclosed in U.S. Pat. No. 5,484,870; 
   (5) Polyamides, such as poly(hexamethylene adipamide) and others prepared from diamines and dibasic acids, as well as those from amino acids such as poly(caprolactam), and blends of polyamides with SURLYN®, polyethylene, ethylene copolymers, ethyl-propylene-non-conjugated diene terpolymer, and the like; 
   (6) Acrylic resins and blends of these resins with poly vinyl chloride, elastomers, and the like; 
   (7) Thermoplastics, such as urethanes; olefinic thermoplastic rubbers, such as blends of polyolefins with ethylene-propylene-non-conjugated diene terpolymer; block copolymers of styrene and butadiene, isoprene or ethylene-butylene rubber; or copoly(ether-amide), such as PEBAX®, sold by ELF Atochem of Philadelphia, Pa.; 
   (8) Polyphenylene oxide resins or blends of polyphenylene oxide with high impact polystyrene as sold under the trademark NORYL® by General Electric Company of Pittsfield, Mass.; 
   (9) Thermoplastic polyesters, such as polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate/glycol modified and elastomers sold under the trademarks HYTREL® by E.I. DuPont de Nemours &amp; Co. of Wilmington, Del., and LOMOD® by General Electric Company of Pittsfield, Mass.; 
   (10) Blends and alloys, including polycarbonate with acrylonitrile butadiene styrene, polybutylene terephthalate, polyethylene terephthalate, styrene maleic anhydride, polyethylene, elastomers, and the like, and polyvinyl chloride with acrylonitrile butadiene styrene or ethylene vinyl acetate or other elastomers; and 
   (11) Blends of thermoplastic rubbers with polyethylene, propylene, polyacetal, nylon, polyesters, cellulose esters, and the like. 
   Preferably, the inner cover includes polymers, such as ethylene, propylene, butene-1 or hexane-1 based homopolymers or copolymers including functional monomers, such as acrylic and methacrylic acid and fully or partially neutralized ionomer resins and their blends, methyl acrylate, methyl methacrylate homopolymers and copolymers, imidized, amino group containing polymers, polycarbonate, reinforced polyamides, polyphenylene oxide, high impact polystyrene, polyether ketone, polysulfone, poly(phenylene sulfide), acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethelyne vinyl alcohol), poly(tetrafluoroethylene) and their copolymers including functional comonomers, and blends thereof. Suitable cover compositions also include a polyether or polyester thermoplastic urethane, a thermoset polyurethane, a low modulus ionomer, such as acid-containing ethylene copolymer ionomers, including E/X/Y terpolymers where E is ethylene, X is an acrylate or methacrylate-based softening comonomer present in about 0 to 50 weight percent and Y is acrylic or methacrylic acid present in about 5 to 35 weight percent. More preferably, in a low spin rate embodiment designed for maximum distance, the acrylic or methacrylic acid is present in about 16 to 35 weight percent, making the ionomer a high modulus ionomer. In a higher spin embodiment, the inner cover layer includes an ionomer where an acid is present in about 10 to 15 weight percent and includes a softening comonomer. One skilled in the art would recognize that many of the above materials are suitable moisture barriers. 
   In one embodiment, the outer cover preferably includes a polyurethane composition comprising the reaction product of at least one polyisocyanate, polyol, and at least one curing Ears agent. Any polyisocyanate available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyisocyanates include, but are not limited to, 4,4′-diphenylmethane diisocyanate (“MDI”); polymeric MDI; carbodiimide-modified liquid MDI; 4,4′-dicyclohexylmethane diisocyanate (“H 12 MDI”); p-phenylene diisocyanate (“PPDI”); m-phenylene diisocyanate (“MPDI”); toluene diisocyanate (“TDI”); 3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”); isophoronediisocyanate (“IPDI”); hexamethylene diisocyanate (“HDI”); naphthalene diisocyanate (“NDI”); xylene diisocyanate (“XDI”); p-tetramethylxylene diisocyanate (“p-TMXDI”); m-tetramethylxylene diisocyanate (“m-TMXDI”); ethylene diisocyanate; propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate;1,6-hexamethylene-diisocyanate (“HDI”); dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methyl cyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate (“TMDI”); tetracene diisocyanate; napthalene diisocyanate; anthracene diisocyanate; trimer of IPDI; isocyanurate of toluene diisocyanate; uretdione of hexamethylene diisocyanate; and mixtures thereof. Polyisocyanates are known to those of ordinary skill in the art as having more than one isocyanate group, e.g., di-isocyanate, tri-isocyanate, and tetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and more preferably, the polyisocyanate includes MDI. It should be understood that, as used herein, the term “MDI” includes 4,4′-diphenylmethane diisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, and mixtures thereof and, additionally, that the diisocyanate employed may be “low free monomer,” understood by one of ordinary skill in the art to have lower levels of “free” monomer isocyanate groups, typically less than about 0.1% free monomer groups. Examples of “low free monomer” diisocyanates include, but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, and Low Free Monomer PPDI. 
   The at least one polyisocyanate should have less than about 14% unreacted NCO groups. Preferably, the at least one polyisocyanate has no greater than about 7.5% NCO, and more preferably, less than about 7.0%. 
   Any polyol available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyols include, but are not limited to, polyether polyols, hydroxy-terminated polybutadiene (including partially/fully hydrogenated derivatives), polyester polyols, polycaprolactone polyols, and polycarbonate polyols. In one preferred embodiment, the polyol includes polyether polyol. Examples include, but are not limited to, polytetramethylene ether glycol (“PTMEG”), polyethylene propylene glycol, polyoxypropylene glycol, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds and substituted or unsubstituted aromatic and cyclic groups. Preferably, the polyol of the present invention includes PTMEG. 
   In another embodiment, polyester polyols are included in the polyurethane material of the invention. Suitable polyester polyols include, but are not limited to, polyethylene adipate glycol; polybutylene adipate glycol; polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol; poly(hexamethylene adipate) glycol; and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups. 
   In another embodiment, polycaprolactone polyols are included in the materials of the invention. Suitable polycaprolactone polyols include, but are not limited to, 1,6-hexanediol-initiated polycaprolactone, diethylene glycol initiated polycaprolactone, trimethylol propane initiated polycaprolactone, neopentyl glycol initiated polycaprolactone, 1,4-butanediol-initiated polycaprolactone, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups. 
   In yet another embodiment, the polycarbonate polyols are included in the polyurethane material of the invention. Suitable polycarbonates include, but are not limited to, polyphthalate carbonate and poly(hexamethylene carbonate) glycol. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups. In one embodiment, the molecular weight of the polyol is from about 200 to about 4000. 
   Polyamine curatives are also suitable for use in the polyurethane composition of the invention and have been found to improve cut, shear, and impact resistance of the resultant balls. Preferred polyamine curatives include, but are not limited to, 3,5-dimethylthio-2,4-toluenediamine and isomers thereof, 3,5-diethyltoluene-2,4-diamine and isomers thereof, such as 3,5-diethyltoluene-2,6-diamine; 4,4′-bis-(sec-butylamino)-diphenylmethane; 1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) (“MCDEA”); polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline (“MDA”); m-phenylenediamine (“MPDA”); 4,4′-methylene-bis-(2-chloroaniline) (“MOCA”); 4,4′-methylene-bis-(2,6-diethylaniline) (“MDEA”); 4,4′-methylene-bis-(2,3-dichloroaniline) (“MDCA”); 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane; 2,2′,3,3′-tetrachloro diarnino diphenylmethane; trimethylene glycol di-p-aminobenzoate; and mixtures thereof. Preferably, the curing agent of the present invention includes 3,5-dimethylthio-2,4-toluenediamine and isomers thereof, such as ETHACURE® 300, commercially available from Albermarle Corporation of Baton Rouge, La. Suitable polyamine curatives, which include both primary and secondary amines, preferably have molecular weights ranging from about 64 to about 2000. 
   At least one of a diol, triol, tetraol, or hydroxy-terminated curatives may be added to the aforementioned polyurethane composition. Suitable diol, triol, and tetraol groups include ethylene glycol; diethylene glycol; polyethylene glycol; propylene glycol; polypropylene glycol; lower molecular weight polytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl) ether; hydroquinone-di-(β-hydroxyethyl) ether; and mixtures thereof. Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol, and mixtures thereof. Preferably, the hydroxy-terminated curatives have molecular weights ranging from about 48 to 2000. It should be understood that molecular weight, as used herein, is the absolute weight average molecular weight and would be understood as such by one of ordinary skill in the art. 
   Both the hydroxy-terminated and amine curatives can include one or more saturated, unsaturated, aromatic, and cyclic groups. Additionally, the hydroxy-terminated and amine curatives can include one or more halogen groups. The polyurethane composition can be formed with a blend or mixture of curing agents. If desired, however, the polyurethane composition may be formed with a single curing agent. 
   In a preferred embodiment of the present invention, saturated polyurethanes used to form cover layers, preferably the outer cover layer, and may be selected from among both castable thermoset and thermoplastic polyurethanes. 
   In this embodiment, the saturated polyurethanes of the present invention are substantially free of aromatic groups or moieties. Saturated polyurethanes suitable for use in the invention are a product of a reaction between at least one polyurethane prepolymer and at least one saturated curing agent. The polyurethane prepolymer is a product formed by a reaction between at least one saturated polyol and at least one saturated diisocyanate. As is well known in the art, a catalyst may be employed to promote the reaction between the curing agent and the isocyanate and polyol. 
   Saturated diisocyanates which can be used include, without limitation, ethylene diisocyanate; propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate (“HDI”); 2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate; dodecane-1,12-diisocyanate; dicyclohexylmethane diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; isophorone diisocyanate (“IPDI”); methyl cyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of 2,2,4-trimethyl-1,6-hexane diisocyanate (“TMDI”). The most preferred saturated diisocyanates are 4,4′-dicyclohexylmethane diisocyanate (“HMDI”) and isophorone diisocyanate (“IPDI”). 
   Saturated polyols which are appropriate for use in this invention include without limitation polyether polyols such as polytetramethylene ether glycol and poly(oxypropylene) glycol. 
   Suitable saturated polyester polyols include polyethylene adipate glycol, polyethylene propylene adipate glycol, polybutylene adipate glycol, polycarbonate polyol and ethylene oxide-capped polyoxypropylene diols. Saturated polycaprolactone polyols which are useful in the invention include diethylene glycol initiated polycaprolactone, 1,4-butanediol initiated polycaprolactone, 1,6-hexanediol initiated polycaprolactone; trimethylol propane initiated polycaprolactone, neopentyl glycol initiated polycaprolactone, and polytetramethylene ether glycol-initiated polycaprolactone. The most preferred saturated polyols are polytetramethylene ether glycol and PTMEG-initiated polycaprolactone. 
   Suitable saturated curatives include 1,4-butanediol, ethylene glycol, diethylene glycol, polytetramethylene ether glycol, propylene glycol; trimethanolpropane; tetra-(2-hydroxypropyl)-ethylenediamine; isomers and mixtures of isomers of cyclohexyldimethylol, isomers and mixtures of isomers of cyclohexane bis(methylamine); triisopropanolamine, ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, 4,4′-dicyclohexylmethane diamine, 2,2,4-trimethyl-1,6-hexanediamine; 2,4,4-trimethyl-1,6-hexanediamine; diethyleneglycol di-(aminopropyl)ether; 4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 1,2-bis-(sec-butylamino)cyclohexane; 1,4-bis-(sec-butylamino)cyclohexane; isophorone diamine, hexamethylene diamine, propylene diamine, 1-methyl-2,4-cyclohexyl diamine, 1-methyl-2,6-cyclohexyl diamine, 1,3-diaminopropane, dimethylamino propylamine, diethylamino propylamine, imido-bis-propylamine, isomers and mixtures of isomers of diaminocyclohexane, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, and diisopropanolamine. The most preferred saturated curatives are 1,4-butanediol, 1,4-cyclohexyldimethylol and 4,4′-bis-(sec-butylamino)-dicyclohexylmethane. 
   Suitable catalysts include, but are not limited to bismuth catalyst, oleic acid, triethylenediamine (DABCO®-33LV), di-butyltin dilaurate (DABCO®-T12) and acetic acid. The most preferred catalyst is di-butyltin dilaurate (DABCO®-T12). DABCO® materials are manufactured by Air Products and Chemicals, Inc. 
   It is well known in the art that if the saturated polyurethane materials are to be blended with other thermoplastics, care must be taken in the formulation process so as to produce an end product which is thermoplastic in nature. Thermoplastic materials may be blended with other thermoplastic materials, but thermosetting materials are difficult if not impossible to blend homogeneously after the thermosetting materials are formed. Preferably, the saturated polyurethane comprises from about 1 to about 100%, more preferably from about 10 to about 75% of the cover composition and/or the intermediate layer composition. About 90 to about 10%, more preferably from about 90 to about 25% of the cover and/or the intermediate layer composition is comprised of one or more other polymers and/or other materials as described below. Such polymers include, but are not limited to polyurethane/polyurea ionomers, polyurethanes or polyureas, epoxy resins, polyethylenes, polyamides and polyesters, polycarbonates and polyacrylin. Unless otherwise stated herein, all percentages are given in percent by weight of the total composition of the golf ball layer in question. 
   Polyurethane prepolymers are produced by combining at least one polyol, such as a polyether, polycaprolactone, polycarbonate or a polyester, and at least one isocyanate. Thermosetting polyurethanes are obtained by curing at least one polyurethane prepolymer with a curing agent selected from a polyamine, triol or tetraol. Thermoplastic polyurethanes are generally obtained by curing at least one polyurethane prepolymer with a diol curing agent. The choice of the curatives is critical because some urethane elastomers that are cured with a diol and/or blends of diols do not produce urethane elastomers with the impact resistance required in a golf ball cover. Blending the polyamine curatives with diol cured urethane elastomeric formulations leads to the production of thermoset urethanes with improved impact and cut resistance. 
   Thermoplastic polyurethanes may be blended with suitable materials to produce a thermoplastic end product. Examples of such additional materials may include ionomers such as the SURLYN®, ESCOR® and IOTEK® copolymers described above. 
   Other suitable materials which may be combined with the saturated polyurethanes in forming the cover and/or intermediate layer(s)of the golf balls of the invention include ionic or non-ionic polyurethanes and polyureas, epoxy resins, polyethylenes, polyamides and polyesters. For example, the cover and/or intermediate layer may be formed from a blend of at least one saturated polyurethane and thermoplastic or thermoset ionic and non-ionic urethanes and polyurethanes, cationic urethane ionomers and urethane epoxies, ionic and non-ionic polyureas and blends thereof. Examples of suitable urethane ionomers are disclosed in U.S. Pat. No. 5,692,974 entitled “Golf Ball Covers”, the disclosure of which is hereby incorporated by reference in its entirety. Other examples of suitable polyurethanes are described in U.S. Pat. No. 5,334,673. Examples of appropriate polyureas are discussed in U.S. Pat. No. 5,484,870 and examples of suitable polyurethanes cured with epoxy group containing curing agents are disclosed in U.S. Pat. No. 5,908,358, the disclosures of which are hereby incorporated herein by reference in their entirety. 
   A variety of conventional components can be added to the cover compositions of the present invention. These include, but are not limited to, white pigment such as TiO 2 , ZnO, optical brighteners, surfactants, processing aids, foaming agents, density-controlling fillers, UV stabilizers and light stabilizers. Saturated polyurethanes are resistant to discoloration. However, they are not immune to deterioration in their mechanical properties upon weathering. Addition of UV absorbers and light stabilizers therefore helps to maintain the tensile strength and elongation of the saturated polyurethane elastomers. Suitable UV absorbers and light stabilizers include TINUVIN® 328, TINUVIN® 213, TINUVIN® 765, TINUVIN® 770, TINUVIN® 292, and TINUVIN® 622. The preferred UV absorber is TINUVIN® 328, and the preferred light stabilizer is TINUVIN 765. TINUVIN® products are available from Ciba-Geigy. Dyes, as well as optical brighteners and fluorescent pigments may also be included in the golf ball covers produced with polymers formed according to the present invention. Such additional ingredients may be added in any amounts that will achieve their desired purpose. 
   Any method known to one of ordinary skill in the art may be used to polyurethanes of the present invention. One commonly employed method, known in the art as a one-shot method, involves concurrent mixing of the polyisocyanate, polyol, and curing agent. This method results in a mixture that is inhomogenous (more random) and affords the manufacturer less control over the molecular structure of the resultant composition. A preferred method of mixing is known as a prepolymer method. In this method, the polyisocyanate and the polyol are mixed separately prior to addition of the curing agent. This method affords a more homogeneous mixture resulting in a more consistent polymer composition. Other methods suitable for forming the layers of the present invention include reaction injection molding (“RIM”), liquid injection molding (“LIM”), and pre-reacting the components to form an injection moldable thermoplastic polyurethane and then injection molding, all of which are known to one of ordinary skill in the art. 
   Additional components which can be added to the polyurethane composition include UV stabilizers and other dyes, as well as optical brighteners and fluorescent pigments and dyes. Such additional ingredients may be added in any amounts that will achieve their desired purpose. 
   It has been found by the present invention that the use of a castable, reactive material, which is applied in a fluid form, makes it possible to obtain very thin outer cover layers on golf balls. Specifically, it has been found that castable, reactive liquids, which react to form a urethane elastomer material, provide desirable very thin outer cover layers. 
   The castable, reactive liquid employed to form the urethane elastomer material can be applied over the core using a variety of application techniques such as spraying, dipping, spin coating, or flow coating methods which are well known in the art. An example of a suitable coating technique is that which is disclosed in U.S. Pat. No. 5,733,428, filed May 2, 1995 entitled “Method And Apparatus For Forming Polyurethane Cover On A Golf Ball,” the disclosure of which is hereby incorporated by reference in its entirety in the present application. 
   The outer cover is preferably formed around the inner cover by mixing and introducing the material in the mold halves. It is important that the viscosity be measured over time, so that the subsequent steps of filling each mold half, introducing the core into one half and closing the mold can be properly timed for accomplishing centering of the core cover halves fusion and achieving overall uniformity. Suitable viscosity range of the curing urethane mix for introducing cores into the mold halves is determined to be approximately between about 2,000 cP and about 30,000 cP, with the preferred range of about 8,000 cP to about 15,000 cP. 
   To start the cover formation, mixing of the prepolymer and curative is accomplished in motorized mixer including mixing head by feeding through lines metered amounts of curative and prepolymer. Top preheated mold halves are filled and placed in fixture units using centering pins moving into holes in each mold. At a later time, a bottom mold half or a series of bottom mold halves have similar mixture amounts introduced into the cavity. After the reacting materials have resided in top mold halves for about 40 to about 80 seconds, a core is lowered at a controlled speed into the gelling reacting mixture. 
   A ball cup holds the ball core through reduced pressure (or partial vacuum). Upon location of the coated core in the halves of the mold after gelling for about 40 to about 80 seconds, the vacuum is released allowing core to be released. The mold halves, with core and solidified cover half thereon, are removed from the centering fixture unit, inverted and mated with other mold halves which, at an appropriate time earlier, have had a selected quantity of reacting polyurethane prepolymer and curing agent introduced therein to commence gelling. 
   Similarly, U.S. Pat. No. 5,006,297 to Brown et al. and U.S. Pat. No. 5,334,673 to Wu both also disclose suitable molding techniques which may be utilized to apply the castable reactive liquids employed in the present invention. Further, U.S. Pat. Nos. 6,180,040 and 6,180,722 disclose methods of preparing dual core golf balls. The disclosures of these patents are hereby incorporated by reference in their entirety. However, the method of the invention is not limited to the use of these techniques. 
   Depending on the desired properties, balls prepared according to the invention can exhibit substantially the same or higher resilience, or coefficient of restitution (“COR”), with a decrease in compression or modulus, compared to balls of conventional construction. Additionally, balls prepared according to the invention can also exhibit substantially higher resilience, or COR, without an increase in compression, compared to balls of conventional construction. Another measure of this resilience is the “loss tangent,” or tan δ, which is obtained when measuring the dynamic stiffness of an object. Loss tangent and terminology relating to such dynamic properties is typically described according to ASTM D4092-90. Thus, a lower loss tangent indicates a higher resiliency, thereby indicating a higher rebound capacity. Low loss tangent indicates that most of the energy imparted to a golf ball from the club is converted to dynamic energy, i.e., launch velocity and resulting longer distance. The rigidity or compressive stiffness of a golf ball may be measured, for example, by the dynamic stiffness. A higher dynamic stiffness indicates a higher compressive stiffness. To produce golf balls having a desirable compressive stiffness, the dynamic stiffness of the crosslinked reaction product material should be less than about 50,000 N/m at −50° C. Preferably, the dynamic stiffness should be between about 10,000 and 40,000 N/m at −50° C., more preferably, the dynamic stiffness should be between about 20,000 and 30,000 N/m at −50° C. 
   The molding process and composition of golf ball portions typically results in a gradient of material properties. Methods employed in the prior art generally exploit hardness to quantify these gradients. Hardness is a qualitative measure of static modulus and does not represent the modulus of the material at the deformation rates associated with golf ball use, i.e., impact by a club. As is well known to one skilled in the art of polymer science, the time-temperature superposition principle may be used to emulate alternative deformation rates. For golf ball portions including polybutadiene, a 1-Hz oscillation at temperatures between 0° C. and −50° C. are believed to be qualitatively equivalent to golf ball impact rates. Therefore, measurement of loss tangent and dynamic stiffness at 0° C. to −50° C. may be used to accurately anticipate golf ball performance, preferably at temperatures between about −20° C. and −50° C. 
   The resultant golf balls typically have a coefficient of restitution of greater than about 0.7, preferably greater than about 0.75, and more preferably greater than about 0.78. The golf balls also typically have an Atti compression of at least about 40, preferably from about 50 to 120, and more preferably from about 60 to 100. The golf ball cured polybutadiene material typically has a hardness of at least about 15 Shore A, preferably between about 30 Shore A and 80 Shore D, more preferably between about 50 Shore A and 60 Shore D. 
   The core composition should comprise at least one rubber material having a resilience index of at least about 40. Preferably the resilience index is at least about 50. Polymers that produce resilient golf balls and, therefore, are suitable for the present invention, include but are not limited to CB23, CB22, commercially available from of Bayer Corp. of Orange, Tex., BR60, commercially available from Enichem of Italy, and 1207G, commercially available from Goodyear Corp. of Akron, Ohio. 
   Additionally, the unvulcanized rubber, such as polybutadiene, in golf balls prepared according to the invention typically has a Mooney viscosity of between about 40 and about 80, more preferably, between about 45 and about 65, and most preferably, between about 45 and about 55. Mooney viscosity is typically measured according to ASTM-D1646. 
   When golf balls are prepared according to the invention, they typically will have dimple coverage greater than about 60 percent, preferably greater than about 65 percent, and more preferably greater than about 75 percent. The flexural modulus of the cover on the golf balls, as measured by ASTM method D6272-98, Procedure B, is typically greater than about 500 psi, and is preferably from about 500 psi to 150,000 psi. As discussed herein, the outer cover layer is preferably formed from a relatively soft polyurethane material. In particular, the material of the outer cover layer should have a material hardness, as measured by ASTM-D2240, less than about 45 Shore D, preferably less than about 40 Shore D, more preferably between about 25 and about 40 Shore D, and most preferably between about 30 and about 40 Shore D. The casing preferably has a material hardness of less than about 70 Shore D, more preferably between about 30 and about 70 Shore D, and most preferably, between about 50 and about 65 Shore D. 
   In a preferred embodiment, the casing material hardness is between about 40 and about 70 Shore D and the outer cover layer material hardness is less than about 40 Shore D. In a more preferred embodiment, a ratio of the casing material hardness to the outer cover layer material hardness is greater than 1.5. 
   It should be understood, especially to one of ordinary skill in the art, that there is a fundamental difference between “material hardness” and “hardness, as measured directly on a golf ball.” Material hardness is defined by the procedure set forth in ASTM-D2240 and generally involves measuring the hardness of a flat “slab” or “button” formed of the material of which the hardness is to be measured. Hardness, when measured directly on a golf ball (or other spherical surface) is a completely different measurement and, therefore, results in a different hardness value. This difference results from a number of factors including, but not limited to, ball construction (i.e., core type, number of core and/or cover layers, etc.), ball (or sphere) diameter, and the material composition of adjacent layers. It should also be understood that the two measurement techniques are not linearly related and, therefore, one hardness value cannot easily be correlated to the other. 
   The core of the present invention has an Atti compression of between about 50 and about 90, more preferably, between about 60 and about 85, and most preferably, between about 65 and about 85. The overall outer diameter (“OD”) of the core is less than about 1.590 inches, preferably, no greater than 1.580 inches, more preferably between about 1.540 inches and about 1.580 inches, and most preferably between about 1.525 inches to about 1.570 inches. The OD of the casing of the golf balls of the present invention is preferably between 1.580 inches and about 1.640 inches, more preferably between about 1.590 inches to about 1.630 inches, and most preferably between about 1.600 inches to about 1.630 inches. 
   The present multilayer golf ball can have an overall diameter of any size. Although the United States Golf Association (“USGA”) specifications limit the minimum size of a competition golf ball to 1.680 inches. There is no specification as to the maximum diameter. Golf balls of any size, however, can be used for recreational play. The preferred diameter of the present golf balls is from about 1.680 inches to about 1.800 inches. The more preferred diameter is from about 1.680 inches to about 1.760 inches. The most preferred diameter is about 1.680 inches to about 1.740 inches. 
   The golf balls of the present invention should have a moment of inertia (“MOI”) of less than about 85 and, preferably, less than about 83. The MOI is typically measured on model number MOI-005-104 Moment of Inertia Instrument manufactured by Inertia Dynamics of Collinsville, Conn. The instrument is plugged into a PC for communication via a COMM port and is driven by MOI Instrument Software version #1.2. 
   In a preferred embodiment of the present invention, it has been found that improved adhesion between golf ball layers, such as between inner and outer cover layers, can be achieved when low surface energy materials, such as ionomers and/or polyurethanes, are treated with silane coupling agents. 
   Silane coupling agents have two different types of reactive groups: 
                        
 
X represents an organofunctional group that reacts with organic materials, such as synthetic resins, and is typically a vinyl, epoxy, amino, methacryl, acryl, isocyanato, or mercapto group; and OR represents the silicon functional group that reacts with inorganic materials and is typically a methoxy, ethoxy, or acetoxy groups.
 
   In the presence of water, coupling agents produce highly reactive silanols which, in turn, condense to form oligomeric structures. In this manner, silanes can form durable chemical “bridges” between materials, facilitating bonding between a low energy surface and a polymer matrix. The silane coupling agent forms a covalent bond with both the polymer matrix and the lower energy surface, thereby making a durable, UV and moisture stable, crosslinked network between the two materials. 
   Corona/plasma treatment of the low energy surface creates reaction sites (reactive —OH groups) to which the silicon-functional group can bond. Corona discharge/plasma treatment of golf ball cores and layers is disclosed in U.S. application Ser. No. 09/389,058, filed Sep. 2, 1999, which is incorporated herein, in its entirety, by express reference thereto. The silane coupling agent is preferably present in a aqueous bath and the corona-treated substrate, preferably a golf ball core or center (with optional layers), is immersed in the bath. In this manner, the silane is hydrolized. One of ordinary skill in the art would be aware that a silane may also be hydrolized with ambient moisture. The silane then undergoes a condensation reaction with reactive sites on the substrate surface allowing the coupling agent to be covalently bound to the surface, and the surface is removed from the bath. Excess water on the core surface is allowed to evaporate and the substrate is introduced to a reactive layer component, preferably a polyurethane outer cover layer. The organofunctional group reacts with the layer precurser to complete the “bridge,” improving adhesion between the two layers. 
   Suitable silanes include, but are not limited to, silane esters, such as octyltriethoxysilane, methyltriethoxylsilane, methyltrimethoxysilane, and proprietary nonionic silane dispersing agent; vinyl silanes, such as proprietary, vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris-(2-methoxyethoxy) silane, vinylmethyldimethoxysilane; methacryloxy silanes, such as γ-methacryloxypropyltrimethoxysilane; epoxy silanes, such as β-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane; sulfur silanes, such as gamma-mercaptopropyltrimethoxysilane proprietary polysulfidesilane, bis-(3-[triethoxisily]-propyl)-tetrasulfane; amino silanes, such as γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, aminoalkyl silicone solution, modified aminoorganosilane, gamma-aminopropyltrimethoxysilane, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, modified aminoorganosilane (40% in methanol), modified aminosilane (50% in methanol), triaminofunctional silane, bis-γ-trimethoxysilylpropyl)amine, n-phenyl-γ-aminopropyltrimethoxysilane, organomodified polydimethylsiloxane, polyazamide silane (50% in methanol), n-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; ureido silanes, such as gamma-ureidopropyltrialkoxysilane (50% in methanol), γ-ureidopropyltrimethoxysilane; isocyanate silanes, such as γ-isocyanatopropyltriethoxysilane; and mixtures thereof. Preferably, the silane is an amino silane and more preferably, the amino silane is bis-(γ-trimethoxysilylpropyl) amine. 
   The silane treatment may be performed alone or in combination with corona discharge and/or plasma treatment. Further, the method of improving adhesion may be combined with a plurality of washing and/or drying steps. Preferably, the surface on which improved adhesion is desired are washed. The washing step is optionally followed by a rinsing step but preferably, no rinse step is performed after the first wash. The surface to be treated is then exposed to plasma or corona discharge for a predetermined time, preferably greater than about 1 sec, more preferably less than about 10 sec. The surface to be treated can be rotated by a predetermined amount to ensure that the maximum surface area is properly exposed to the plasma treatment. Preferably the surface to be treated is rotated by at least about ¼ turn. The surface may optionally undergo surface roughening or gleebar grinding in preparation for receiving the silane. 
   The surface to be treated is exposed to the silane of choice, preferably an amino silane and more preferably, bis-(γ-trimethoxysilylpropyl)amine, commercially available under the tradename Silquest A-1170 from OSi Specialties of Endicott, N.Y. The silane may be neat or in solution. Preferably, the silane is present in an amount less than about 10%, more preferably less than about 2%. The treated surface is then dried and prepared for final construction into a golf ball. This step may include chilling or preheating a center or a core (and any optional layers thereon), followed by casting of at least one outer layer.