Golf ball layer having reduced surface hardness and method of making same
A method of making a golf ball comprising the steps of providing an untreated golf ball core comprising a thermoset rubber composition, the untreated golf ball core comprising an untreated outer surface having a hardness; treating the untreated outer surface of the untreated golf ball core with a surface-softening material comprising at least one fatty acid or fatty acid salt composition to form a golf ball core comprising a treated outer surface having a hardness less than the hardness of the untreated outer surface; and forming at least one cover layer about the core to form the golf ball. Also, the untreated core may comprise a geometric center and an untreated outer surface, each having a hardness such that the hardness of the treated outer surface is less than both the hardness of the untreated geometric center and the hardness of the untreated outer surface.
1. A method of making a golf ball comprising the steps of:
providing an untreated golf ball core comprising a thermoset rubber composition, said untreated golf ball core comprising a geometric center and an untreated outer surface;
treating the untreated outer surface of the untreated golf ball core with a surface-softening material comprising at least one fatty acid or fatty acid salt plasticizer composition to form a golf ball core comprising a treated outer surface having a first hardness and a geometric center that does not comprise the at least one fatty acid or fatty acid salt plasticizer composition and has a second hardness that is greater than the first hardness; and
forming a cover layer about the core to form the golf ball.
2. The method of claim 1 , wherein the thermoset rubber composition comprises a polybutadiene composition having a surface hardness of at least about 50 Shore C.
3. The method of claim 1 , wherein the thermoset rubber composition comprises a polybutadiene composition that is at least partially crosslinked.
4. The method of claim 1 , wherein the step of treating the untreated golf ball core comprises coating, rolling, dipping, soaking, spraying, dusting or exposing.
5. The method of claim 1 , wherein the at least one fatty acid or fatty acid salt composition comprises oleic acid, palmitic acid, stearic acid, behenic acid, pelargonic acid, linoleic acid, linolenic acid, arachidonic acid, caproic acid, caprylic acid, capric acid, lauric acid, erucic acid, myristic acid, benzoic acid, phenylacetic acid, or naphthalenoic acid.
6. The method of claim 5 , wherein the fatty acid salt composition comprises a cation selected from the group comprising barium, lithium, sodium, zinc, bismuth, chromium, cobolt, copper, potassium, strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin and calcium.
7. The method of claim 1 , wherein the hardness of the treated outer surface is at least 5 Shore C less than the hardness of the untreated golf ball core surface.
8. The method of claim 1 , wherein the hardness of the treated outer surface is at least 10 Shore C less than the hardness of the untreated golf ball core surface.
9. The method of claim 1 , wherein the at least one fatty acid or fatty acid salt composition further comprises antioxidants, sulfur-bearing compounds, zinc methacrylate, zinc dimethacrylate, softening acrylate monomers or oligomers, soft powdered thermoplastic resins, phenol-comprising antioxidants, or hydroquinones.
10. The method of claim 9 , wherein the soft powdered thermoplastic resins comprise polyethylene vinyl acetate, polyethylene butyl acrylate, polyethylene methyl acrylate, or very-low-modulus ionomer.
11. The method of claim 1 , wherein the treating step is preceded by a step of forming an outer core layer about the core to form a dual core comprising an untreated outer surface having a hardness.
12. The method of claim 1 , further comprising the step of forming an intermediate layer about the core prior to forming the cover layer.
13. A method of making a golf ball comprising the steps of:
providing an untreated golf ball core comprising a thermoset rubber composition, said untreated golf ball core comprising a geometric center and an untreated outer surface;
treating the untreated outer surface of the untreated golf ball core with a surface-softening material comprising at least one fatty acid or fatty acid salt plasticizer composition to form a crosslinked golf ball core comprising a treated outer surface having a first hardness and a geometric center that does not comprise the at least one fatty acid or fatty acid salt plasticizer composition and has a second hardness, wherein the first hardness is less than the second hardness; and
forming a cover layer about the core to form the golf ball.
14. The method of claim 13 , wherein the thermoset rubber composition comprises a polybutadiene composition that is at least partially crosslinked.
15. The method of claim 13 , wherein the step of treating the untreated golf ball core comprises coating, rolling, dipping, soaking, spraying, dusting or exposing.
16. The method of claim 13 , wherein the at least one fatty acid or fatty acid salt composition comprises oleic acid, palmitic acid, stearic acid, behenic acid, pelargonic acid, linoleic acid, linolenic acid, arachidonic acid, caproic acid, caprylic acid, capric acid, lauric acid, erucic acid, myristic acid, benzoic acid, phenylacetic acid, or naphthalenoic acid.
17. The method of claim 13 , wherein the hardness of the treated outer surface is at least 5 Shore C less than the hardness of the untreated golf ball core surface.
18. The method of claim 13 , wherein the hardness of the treated outer surface is at least 10 Shore C less than the hardness of the untreated golf ball core surface.
19. The method of claim 13 , wherein the hardness of the treated outer surface is at least 5 Shore C less than the hardness of the untreated golf ball core geometric center.
20. The method of claim 13 , wherein the hardness of the treated outer surface is at least 10 Shore C less than the hardness of the untreated golf ball core geometric center.
21. The method of claim 13 , wherein the at least one fatty acid or fatty acid salt composition further comprises antioxidants, sulfur-bearing compounds, zinc methacrylate, zinc dimethacrylate, softening acrylate monomers or oligomers, soft powdered thermoplastic resins, phenol-comprising antioxidants, or hydroquinones.
22. The method of claim 21 , wherein the soft powdered thermoplastic resins comprise polyethylene vinyl acetate, polyethylene butyl acrylate, polyethylene methyl acrylate, or very-low-modulus ionomer.
23. The method of claim 13 , wherein the treating step is preceded by a step of forming an outer core layer about the core to form a dual core comprising an untreated outer surface having a hardness.
24. The method of claim 13 , further comprising the step of forming an intermediate layer about the core prior to forming the cover layer.
25. A method of making a golf ball comprising the steps of:
providing a preform comprising an uncured polybutadiene composition;
coating the preform with a surface-softening material comprising at least one of a fatty acid or a fatty acid salt plasticizer compound;
curing the coated preform at a predetermined temperature to form a crosslinked golf ball core having a coated outer surface having a first hardness and a geometric center that does not comprise the at least one fatty acid or fatty acid salt plasticizer compound and has a second hardness, wherein the first hardness is less than the second hardness; and
forming a cover layer about the core to form the golf ball.
26. The method of claim 25 , wherein the step of coating the preform comprises rolling, spraying, dipping, dusting, soaking or exposing.
27. The method of claim 25 , wherein the at least one fatty acid comprises oleic acid, palmitic acid, stearic acid, behenic acid, pelargonic acid, linoleic acid, linolenic acid, arachidonic acid, caproic acid, caprylic acid, capric acid, lauric acid, erucic acid, myristic acid, benzoic acid, phenylacetic acid, or naphthalenoic acid.
28. The method of claim 25 , wherein the step of treating the untreated golf ball core is preceded by a step of pre-treating the untreated golf ball core with a cure-altering material different from the fatty acid or fatty acid salt composition of the treating step.
29. The method of claim 28 , wherein the different cure-altering material comprises an antioxidant or a peroxide.
30. The method of claim 25 , wherein the step of providing the untreated golf ball core further comprises extruding the polybutadiene rubber composition to form an extrudate and cutting the extrudate to form a preform.
31. The method of claim 30 , wherein the step of forming the preform further comprises cold-forming the diene rubber preform into a spherical shape.
32. A method of making a golf ball comprising the steps of:
extruding a polybutadiene composition to form a cylindrical extrudate;
cutting the extrudate to form an uncured polybutadiene preform;
uniformly coating the preform with a surface-softening material comprising at least one fatty acid or fatty acid salt plasticizer composition;
curing the coated preform to form a crosslinked core having an outer surface having a first hardness and a geometric center that does not comprise the at least one fatty acid or fatty acid salt plasticizer composition and has a second hardness greater than the first hardness;
centerless-grinding the cured core to form a uniformly-spherical core having increased surface roughness;
forming an inner cover layer about the uniformly-spherical core; and
forming an outer cover layer about the inner cover layer to form the golf ball.
33. The method of claim 32 , further comprising the step of forming an outer core layer about the uniformly-spherical core to form a dual core.