Golf ball layer having reduced surface hardness and method of making same
The invention is directed to a golf ball comprising a core and a cover, wherein the core has a geometric center having a hardness (H g ) and the core has an outer surface that is treated with a surface-softening material comprising at least one fatty acid and/or fatty acid salt plasticizer composition such that the outer surface has an extrapolated hardness (H E ) and an actual hardness (H OS ) wherein H E is derived from a five point extrapolation within three quarters of an outer core diameter and H OS is measured on the curved surface of the core, and the cover has a hardness (H C ), wherein H C >H E >H g >H OS .
1. A golf ball comprising a core and a cover, wherein the core has an inner core comprising a geometric center having—a hardness (H g ) and the core has an outer surface that is treated with a surface-softening material comprising at least one fatty acid and/or fatty acid salt plasticizer composition, wherein the inner core does not comprise the at least one fatty acid and/or fatty acid salt plasticizer composition, such that the outer surface has an extrapolated hardness (H E ) and an actual hardness (H OS ) wherein H E is derived from a five point extrapolation within three quarters of an outer core diameter and H OS is measured on the curved surface of the core, and the cover has a hardness (H C ), wherein H C >H E >H g >H OS .
2. The golf ball of claim 1 , wherein the core comprises a thermoset rubber composition.
3. The golf ball of claim 2 , wherein the thermoset rubber composition comprises a polybutadiene material having a surface hardness of at least about 50 Shore C.
4. The golf ball of claim 2 , wherein the thermoset rubber composition comprises a polybutadiene composition that is at least partially crosslinked.
5. The golf ball 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 golf ball of claim 1 , 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 golf ball 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.
8. The golf ball of claim 1 , wherein H OS is at least 5 Shore C less than H E .
9. The golf ball of claim 1 , wherein H OS is at least 10 Shore C less than H E .