Methods for cross-linking thermoplastic polyurethane golf ball covers and resultant golf balls
A coated golf ball includes a single or dual core and a cover layer formed from a thermoplastic polyurethane (TPU). The TPU cover preferably has a first polyurethane coating layer and a second polyurethane coating layer disposed about the first polyurethane coating layer. In a preferred embodiment, he first polyurethane coating layer includes unreacted isocyanate groups and has an isocyanate index of at least about 120. Preferably, the first polyurethane coating layer has an isocyanate index of at least about 150, more preferably, at least about 200, and most preferably at least about 250.
1. A coated golf ball comprising:
a core;
a cover layer comprising a thermoplastic polyurethane; and
a first polyurethane coating layer; and
a second polyurethane coating layer disposed about the first polyurethane coating layer, wherein the first polyurethane coating layer comprises unreacted isocyanate groups and has an isocyanate index of at least about 120 and wherein the second polyurethane coating layer has an isocyanate index of less than about 96.
2. The golf ball of claim 1 , wherein the first polyurethane coating layer has an isocyanate index of at least about 150.
3. The golf ball of claim 1 , wherein the first polyurethane coating layer has an isocyanate index of at least about 200.
4. The golf ball of claim 1 , wherein the first polyurethane coating layer has an isocyanate index of at least about 250.
5. The golf ball of claim 1 , wherein the first polyurethane coating layer comprises an aliphatic isocyanate and an aromatic isocyanate.
6. The golf ball of claim 5 , wherein the isocyanate comprises toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, 4,4′-methylene diphenyl diisocyanate, 2,4′-methylene diphenyl diisocyanate, polymeric methylene diphenyl diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, naphthalene 1,5-diisocynate, naphthalene 2,4-diisocyanate, 3,3′-bitolulene-4,4′-diisocyanate, p-xylene diisocyanate, and isophorone diisocyanate, 1,6-hexamethylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, hydrogenated xylenediisocyanate, m-tetramethylxylyene diisocyanate, trans-cyclohexane diisocyanate, and norbornene diisocynate, or homopolymers and copolymers and blends thereof.
7. The golf ball of claim 6 , wherein the isocyanate comprises 4,4′-methylene diphenyl diisocyanate.
8. The golf ball of claim 5 , wherein the aromatic isocyanate and the aliphatic isocyanate are present in a ratio of about 2:1.
9. The golf ball of claim 1 , wherein the core comprises an inner core layer and outer core layer.
10. The golf ball of claim 1 , wherein the golf ball comprises an inner cover layer disposed between the core and the cover.
11. The golf ball of claim 1 , wherein the first and second polyurethane coating layers are applied by spray-coating.
12. A coated golf ball comprising:
a core;
a cover layer comprising a thermoplastic polyurethane;
a first polyurethane coating layer comprising aromatic isocyanate; and
a second polyurethane coating layer disposed about the first polyurethane coating layer, the second polyurethane coating having an isocyanate index of less than about 96;
wherein the first polyurethane coating layer comprises unreacted isocyanate groups and has an isocyanate index of at least about 120.
13. The golf ball of claim 12 , wherein the first polyurethane coating layer is substantially free of aliphatic isocyanate.
14. The golf ball of claim 12 , wherein the isocyanate comprises 4,4′-methylene diphenyl diisocyanate, 2,4′-methylene diphenyl diisocyanate, toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, p-phenylene diisocyanate, or homopolymers and copolymers and blends thereof.
15. A method for forming a coated golf ball, comprising the steps of:
providing a golf ball comprising a core and a cover layer, the cover layer comprising a thermoplastic polyurethane composition;
applying a first polyurethane coating to the cover layer, the coating comprising unreacted isocyanate groups and having an isocyanate index of at least about 120;
treating the first polyurethane coating with sufficient heat to partially cure the first coating layer; and
applying a second polyurethane coating over the first polyurethane coating to form a coated golf ball and wherein the second polyurethane coating layer has an isocyanate index of less than about 96.
16. The method of claim 15 , wherein the steps of applying the first or second polyurethane coatings include spray-coating.
17. The method of claim 15 , wherein the step of applying the second polyurethane coating over the first polyurethane coating includes treating with sufficient heat to fully cure the first and second coating layers.
18. The golf ball of claim 15 , wherein the first polyurethane coating layer is substantially free of aliphatic isocyanate.
19. The method of claim 15 , wherein the at least one of the first and second polyurethane coatings further comprises an ultraviolet (UV) light stabilizer.
20. The method of claim 15 , wherein at least one of the first and second polyurethane coatings further comprises a catalyst.
21. The method of claim 15 , wherein at least one of the first and second polyurethane coatings further comprises an optical brightener.