DUAL CORE GOLF BALL HAVING POSITIVE-HARDNESS-GRADIENT THERMOPLASTIC INNER CORE AND POSITIVE-HARDNESS-GRADIENT THERMOSET OUTER CORE LAYER
A golf ball includes a thermoplastic inner core and a thermoset outer core layer. The inner core has a surface hardness of about 40 to 80 Shore C and a center hardness of about 30 to 75 Shore C, the center hardness being less than the surface hardness to define a first positive hardness gradient. The cover includes an inner cover layer and an outer cover layer. The thermoplastic inner core comprises a highly-neutralized ionomer including an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to 100% of the acid groups present. The outer core layer includes a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a positive hardness gradient of less than about 25 Shore C
1 . A golf ball comprising:
a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a surface hardness of about 60 to 90 Shore C and a center hardness of about 65 to 95 Shore C and is less than the surface hardness to define a first positive hardness gradient; and
a cover comprising an inner cover layer and an outer cover layer;
wherein the thermoplastic inner core comprises an ionomer composition and a plasticizer; and the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a second positive hardness gradient of about 25 Shore C or less.
2 . The golf ball of claim 1 , wherein the ionomer composition comprises an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate.
3 . The golf ball of claim 2 , wherein the ionomer composition comprises a cation source present in an amount sufficient to neutralize up to about 90% of all acid groups present in the material.
4 . The golf ball of claim 2 , wherein the acid copolymer comprises a softening comonomer.
5 . The golf ball of claim 4 , wherein the softening comonomer comprises ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, grafted- or non-grafted metallocene-catalyzed polymers, single-site polymers, high-crystalline acid polymers, or cationic ionomers.
6 . The golf ball of claim 1 , wherein the thermoplastic inner core comprises an ethylene/acid copolymer or ionomer.
7 . The golf ball of claim 1 , wherein the second positive hardness gradient is 1 to 15 Shore C.
8 . A golf ball comprising:
a core comprising a thermoplastic inner core and a thermoset outer core layer, the inner core having a surface hardness of about 40 to 80 Shore C and a center hardness of about 30 to 80 Shore C and is less than the surface hardness to define a first positive hardness gradient; and
a cover comprising an inner cover layer and an outer cover layer;
wherein the thermoplastic inner core comprises an ionomer composition and a plasticizer; and the outer core layer comprises a polybutadiene rubber and has a surface hardness greater than an interior hardness to define a second positive hardness gradient of about 25 Shore C or less.
9 . The golf ball of claim 8 , wherein the ionomer composition comprises an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer comprising alkyl acrylate or methacrylate.
10 . The golf ball of claim 9 , wherein the ionomer composition comprises a cation source present in an amount sufficient to neutralize up to about 90% of all acid groups present in the material.
11 . The golf ball of claim 9 , wherein the acid copolymer comprises a softening comonomer.
12 . The golf ball of claim 11 , wherein the softening comonomer comprises ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, grafted- or non-grafted metallocene-catalyzed polymers, single-site polymers, high-crystalline acid polymers, or cationic ionomers.
13 . The golf ball of claim 8 , wherein the thermoplastic inner core comprises an ethylene/acid copolymer or ionomer.
14 . The golf ball of claim 8 , wherein the second positive hardness gradient is 1 to 15 Shore C.