Multi-layered golf balls having a thin outer cover
Multi-layered golf balls having an inner core, at least one intermediate layer, and outer cover are provided. The outer cover is made from am ultra-low melt index (ULMI) thermoplastic material using an in-molding coating process that involves applying a thin layer of the material to the interior surface of the cover mold members. Preferably, the ultra-low melt index material is a highly neutralized ionomer ethylene-based copolymer. The cover layers made from these highly neutralized polymers (HNPs) are thin and uniform and provide the golf ball with good playing performance properties. Yet, the cover layers also are tough and provide the golf ball with good impact durability.
1. A method for molding a multi-layered golf ball, comprising the steps of:
coating a powder composition comprising a blend of first and second ultra-low melt index ionomer copolymers of α-olefin, C 3 to C 8 α, β-ethylenically unsaturated mono-or dicarboxylic acid, and optional softening monomer, each ionomer copolymer having acid groups, wherein 70% to 100% of the acid groups are neutralized in the first ionomer copolymer and 20% to 70% of the acid groups are neutralized in the second ionomer copolymer, to interior surfaces of upper and lower mold members, the upper and lower mold members defining a mold cavity, wherein the surfaces of the upper and lower mold cavities have dimple patterns;
placing a golf ball subassembly comprising a core of at least one layer into the mold cavity, wherein the interior surfaces of the mold members and surface of the ball subassembly have been pre-treated with an amino-silane agent;
applying heat and pressure to the mold members so the powder composition fuses and encapsulates the subassembly and forms an outer cover having a dimpled pattern, the cover comprising the blend of ultra-low melt index ionomer copolymers; and
removing the molded, multi-layered golf ball from the mold cavity.
2. The method of claim 1 , wherein the ionomer copolymer is a E/X/Y copolymer, wherein E is ethylene; X is a C 3 to C 8 α, β-ethylenically unsaturated mono- or dicarboxylic acid; and Y is a softening monomer.
3. The method of claim 2 , wherein the copolymer is selected from the group consisting of ethylene/(meth)acrylic acid/n-butyl acrylate; ethylene/(meth)acrylic acid/ethyl acrylate; and ethylene/(meth)acrylic acid/methyl acrylate copolymers.
4. The method of claim 1 , wherein the acid moieties of the ionomer copolymer are neutralized greater than 90%.
5. The method of claim 1 , wherein the golf ball subassembly comprises a single layer core.
6. The method of claim 5 , wherein the core is prepared from polybutadiene rubber.
7. The method of claim 1 , wherein the golf ball subassembly comprises a dual-layer core.
8. The method of claim 1 , wherein the cover comprising the ultra-low melt index thermoplastic polymer is the outer cover of the golf ball.
9. The method of claim 1 , wherein the cover comprising the ultra-low melt index thermoplastic polymer is the inner cover of the golf ball.
10. The method of claim 1 , wherein the golf ball further comprises an intermediate layer formed of a material selected from the group consisting of ethylene-based ionomer copolymers; polyesters; polyamides; polyamide-ethers, polyamide-esters; polyurethanes, polyureas, polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes and polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl alcohols; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures thereof.
11. The method of claim 8 , wherein the outer cover has a thickness of less than about 0.030 inches.
12. The method of claim 8 , wherein the outer cover has a thickness of less than about 0.020 inches.
13. The method of claim 8 , wherein the outer cover has a thickness of less than about 0.010 inches.
14. The method of claim 8 , wherein the outer cover has a Shore D material hardness in the range of about 55 to about 70.
15. The method of claim 1 , further comprising the step of pre-heating the golf ball subassembly.
16. The method of claim 1 , further comprising the step of treating the golf ball subassembly with corona treatment, plasma treatment or coupling agent.
17. The method of claim 1 , further comprising the step of treating the golf ball subassembly by vibrating.