Coatings for golf balls having a thermoplastic polyurethane cover
Methods for coatings for golf balls, particularly golf balls having thermoplastic polyurethane covers, and the resulting finished balls are provided. The coating is preferably a topcoat comprising a polyurethane composition containing optical brighteners. The topcoat composition preferably comprises a low concentration of optical brighteners. For example, the concentration of optical brightener can be in the range of 0.01 to about 0.20 weight %. The optical brighteners provide the desired brightness to the golf ball without sacrificing color stability. Multi-piece golf balls having inner cores, outer cores, inner covers, and intermediate layers can be made. The finished ball with the topcoat has many advantageous physical and playing performance properties.
1. A coated golf ball formed by a method, the method comprising the steps of:
providing a golf ball comprising at least one core layer and an outer cover layer, wherein the outer cover layer is formed from a thermoplastic polyurethane composition;
applying a mixture comprising multi-functional isocyanate and solvent to the outer cover layer;
applying a first polyurethane coating comprising unreacted isocyanate groups and having an isocyanate index of at least about 115 to the outer cover layer;
treating the golf ball with heat; and
applying a second polyurethane coating to the outer cover of the golf ball, the second polyurethane coating comprising an optical brightener in a concentration of about 0.01 to about 1.0 wt %, to form a coated golf ball.
2. The coated golf ball of claim 1 , wherein the wet weight of the second polyurethane coating is from about 0.20 g to about 0.42 g.
3. The coated golf ball of claim 1 , wherein the optical brightener is present in a concentration of about 0.1 wt % to about 1.0 wt %.
4. The coated golf ball of claim 1 , wherein the optical brightener is present in a concentration of about 0.1 wt % to about 0.5 wt %.
5. The coated golf ball of claim 1 , wherein the optical brightener is selected from the group consisting of di-, tetra-, and hexa-sulfonated triazine-stilbenes; coumarins; imidazolines; diazoles; triazoles; benzooxazolines; and biphenyl-stilbenes; and mixtures thereof.