Methods for cross-linking thermoplastic polyurethane covers for golf balls
Golf balls having covers made of thermoplastic polyurethane compositions are provided. Multi-piece golf balls can be made. The outer cover layer is formed from a composition comprising a thermoplastic polyurethane, a multi-functional hydroxyl compound, and a multi-functional compound selected from multi-functional amines and imines, and multi-functional isocyanates, and mixtures of two or more thereof. The cover composition can further include catalysts, ultraviolet (UV)-light stabilizers, and other additives.
1. A method for forming a cover for a golf ball, comprising the steps of:
providing a golf ball sub-assembly, the sub-assembly comprising a core and an intermediate layer; forming an outer cover layer over the sub-assembly, wherein the outer cover layer is formed from a composition comprising a thermoplastic polyurethane; a multi-functional hydroxyl compound; and a multi-functional compound selected from the group consisting of multi-functional amines, multi-functional imines, multi-functional isocyanates, and combinations of two or more thereof.
2. The method of claim 1 , wherein the multi-functional hydroxyl compound is selected from the group consisting of polyether polyols, hydroxy-terminated polybutadiene, polyester polyols, polycaprolactone polyols, polycarbonate polyols, polyvinyl alcohol, hydroxyl-functional acrylics, polyethylene glycol, polypropylene glycol, starch-based polymers, cellulosic polymers, polylactic acid, and mixtures thereof.
3. The method of claim 1 , wherein the multi-functional compound includes an isocyanate selected from the group consisting of 4,4′-methylene diphenyl diisocyanate; 2,4′-methylene diphenyl diisocyanate; toluene 2,4-diisocyanate; toluene 2,6-diisocyanate; 4,4′-dicyclohexylmethane diisocyanate; p-phenylene diisocyanate; and isophorone diisocyanate; and homopolymers and copolymers and blends thereof.
4. The method of claim 1 , wherein the multi-functional compound includes polyaziridine.
5. The method of claim 1 , wherein the multi-functional compound includes an amine selected from the group consisting of diethylene toluene diamine, mono or di-isopropanolamine, methy diethanol amine, methylene-bis-chloro diethylaniline, and mixtures thereof.
6. The method of claim 1 , wherein the core comprises an inner core layer formed from a first rubber composition and an outer core layer formed from a second rubber composition.
7. The method of claim 6 , wherein the intermediate layer is formed from an ionomer composition selected from the group consisting of salts of O/X- and O/X/Y-type acid copolymers and mixtures thereof, wherein O is an α-olefin, X is a C 3 -C 8 α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer.
8. The method of claim 1 , wherein the golf ball consists of the core, the intermediate layer, and the outer cover layer, and wherein the core consists of a single layer formed from a rubber composition.
9. The method of claim 8 , wherein the intermediate layer is formed from an ionomer composition selected from the group consisting of salts of O/X- and O/X/Y-type acid copolymers and mixtures thereof, wherein O is an α-olefin, X is a C 3 -C 8 α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer.