Method Of Post-Mold Crosslinking Thermoplastic Polyurethane Golf Ball Cover Compositions

Abstract

A golf ball includes a cover material containing a thermoplastic polyurethane composition which may be crosslinked post-mold by applying a radiation source such as ultraviolet light. The thermoplastic polyurethane composition may be crosslinked under controlled conditions selected to yield golf balls exhibiting desired physical properties and performance characteristics, such as hardness, spin, feel, and distance. In some examples, the golf ball contains one or more additional components, such as a UV curable topcoat, that may be simultaneously treated by the radiation source, thus improving processing efficiency.

1 . A method of preparing a multi-piece golf ball comprising:
 providing a core layer;   providing a cover layer, wherein the cover layer comprises at least one crosslinkable thermoplastic polyurethane;   molding the cover layer and core layer to form a golf ball preform in a mold;   removing the golf ball preform from the mold; and   irradiating the golf ball preform with an energy source under conditions sufficient to crosslink the crosslinkable thermoplastic polyurethane.   
     
     
         2 . The method of  claim 1  further comprising applying at least one intermediate layer between the core layer and the cover layer. 
     
     
         3 . The method of  claim 2  wherein the at least one intermediate layer comprises one or more dynamically vulcanized thermoplastic elastomers, functionalized styrene-butadiene elastomers, thermoplastic rubbers, thermoset elastomers, thermoplastic urethanes, metallocene polymers, thermoset urethanes, ionomer resins, or blends thereof. 
     
     
         4 . The method of  claim 1  wherein the cover layer further comprises a material selected from the group consisting of ionomer, thermoplastic, elastomer, urethane, balata, polybutadiene, and combinations thereof. 
     
     
         5 . The method of  claim 1  wherein the core layer is formed from a base composition comprising polybutadiene and about 20 to 50 parts of a metal salt diacrylate, dimethacrylate, or monomethacrylate. 
     
     
         6 . The method of  claim 5  wherein the base composition further comprises natural rubber, styrene butadiene, isoprene, or combinations thereof. 
     
     
         7 . The method of  claim 1  wherein the energy source comprises ultraviolet radiation. 
     
     
         8 . The method of  claim 7  wherein the cover layer further comprises a UV initiator selected from the group consisting of 1-hydroxycyclohexylphenylketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO). 
     
     
         9 . A method of preparing a multi-piece golf ball comprising:
 preparing a golf ball preform by molding a cover layer and a core layer to form the golf ball preform in a mold, wherein the cover layer comprises at least one crosslinkable thermoplastic polyurethane;   removing the golf ball preform from the mold;   storing the golf ball preform for at least one day;   determining demand for golf ball properties, performance characteristics, or both; and   irradiating the golf ball preform with an energy source under conditions sufficient to crosslink the crosslinkable thermoplastic polyurethane according to the determined golf ball properties, performance characteristics, or both.   
     
     
         10 . The method of  claim 9  wherein the energy source comprises ultraviolet radiation. 
     
     
         11 . The method of  claim 10  wherein the cover layer further comprises a UV initiator selected from the group consisting of 1-hydroxycyclohexylphenylketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO). 
     
     
         12 . The method of  claim 9  further comprising distributing the golf ball preform to at least one of a regional supplier, a wholesaler, a retailer, and an end user, prior to the step of irradiating. 
     
     
         13 . The method of  claim 9  further comprising applying indicia to the irradiated golf ball according to the golf ball properties, performance characteristics, or both. 
     
     
         14 . A method of preparing a multi-piece golf ball comprising:
 providing a core layer;   providing a cover layer, wherein the cover layer comprises at least one crosslinkable thermoplastic polyurethane;   molding the cover layer and core layer to form a golf ball preform in a mold;   removing the golf ball preform from the mold;   applying an ultraviolet curable topcoat composition to the golf ball preform; and   irradiating the golf ball preform with ultraviolet radiation under conditions sufficient to crosslink the crosslinkable thermoplastic polyurethane and cure the topcoat composition.   
     
     
         15 . The method of  claim 14  further comprising applying at least one intermediate layer between the core layer and the cover layer. 
     
     
         16 . The method of  claim 14  wherein the at least one intermediate layer comprises one or more dynamically vulcanized thermoplastic elastomers, functionalized styrene-butadiene elastomers, thermoplastic rubbers, thermoset elastomers, thermoplastic urethanes, metallocene polymers, thermoset urethanes, ionomer resins, or blends thereof. 
     
     
         17 . The method of  claim 14  wherein the cover layer further comprises a material selected from the group consisting of ionomer, thermoplastic, elastomer, urethane, balata, polybutadiene, and combinations thereof. 
     
     
         18 . The method of  claim 14  wherein the core layer is formed from a base composition comprising polybutadiene and about 20 to 50 parts of a metal salt diacrylate, dimethacrylate, or monomethacrylate. 
     
     
         19 . The method of  claim 18  wherein the base composition further comprises natural rubber, styrene butadiene, isoprene, or combinations thereof. 
     
     
         20 . The method of  claim 14  wherein the cover layer further comprises a UV initiator selected from the group consisting of 1-hydroxycyclohexylphenylketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (HHPMP), and bis(2,4,6-trimethylbenzoyl)-phenyl-phosphoneoxide (BTPPO).