Golf ball manufacturing method
The invention provides a method of manufacturing golf balls having a core and at least one cover layer which involves injecting a molten cover resin material around a core so as to form a cover layer. The cover resin material is a single resin composition made up of (A) a thermoplastic polyurethane, (B) a polyisocyanate compound and (C) a thermoplastic elastomer other than the thermoplastic polyurethane in a weight ratio (A):(B):(C)=100:{2-50}:{0-50}, and is injected with from 10 to 99% of the total number of isocyanate groups in component B remaining in an unreacted state within the cover resin material. The method of the invention provides a high manufacturability and a good amenability to mass production, and the manufactured golf balls thus obtained have a high rebound and excellent scuff resistance.
1. A method of manufacturing golf balls having a core and at least one cover layer, the method comprising the steps of
premixing a cover resin material comprising (A) a thermoplastic polyurethane, (B) a polyisocyanate compound and (C) a thermoplastic elastomer other than the thermoplastic polyurethane in a weight ratio (A):(B):(C)=100:{2-50}:{0-50} under an inert gas atmosphere in a mixing apparatus,
cooling the cover resin material in an environment isolated from moisture and pelletizing it so as to form single pellets in an incompletely reacted state,
charging the cover resin material in the form of the single resin pellets into a molding machine, and
injecting the cover resin material in a molten state around a core at 150 to 250° C. so as to form a cover layer,
wherein the cover resin material is injected with from 10 to 99% of the total number of isocyanate groups in component B remaining in an unreacted state within the cover resin material.
2. The golf ball manufacturing method of claim 1 wherein, when the cover resin material is injected with an injection molding machine, the unreacted state of the isocyanate groups in component B is maintained from a cover resin material feeder and throughout the interior of the injection molding machine by filling the molding machine with an inert gas or low dew-point air.
3. The golf ball manufacturing method of claim 1 wherein the components of the cover resin material are present in a weight ratio (A):(B):(C)=100:{2-30}:{8-50}.
4. The golf ball manufacturing method of claim 1 , wherein the cover resin material has a melt mass flow rate (MFR) at 210° C. of at least 5 g/10 min.
5. The golf ball manufacturing method of claim 1 , wherein the cover resin material includes a recycled resin material.
6. The golf ball manufacturing method of claim 1 , wherein the mixing apparatus is a twin-screw extruder.