Multi-piece golf balls having a multi-layered solid core and multi-layered cover are provided.

A golf ball comprising an inner core layer including a thermoplastic material and having a geometric center hardness less than the surface hardness to define a positive hardness gradient. An outer core layer is formed over the inner core. The outer core includes a thermoset rubber composition and has an inner surface hardness less than an outer surface hardness to define a positive hardness gradient. A cover layer is formed over the outer core layer. The cover layer includes an inner cover layer and an outer cover layer. The thermoplastic material of the core includes an acid copolymer of ethylene and an ,-unsaturated carboxylic acid, optionally a softening monomer comprising alkyl acrylate or methacrylate; a plasticizer; an organic acid or salt thereof; and a cation source present in an amount sufficient to neutralize from about 70 to about 100% of all acid groups present in the material.

Golf balls comprising a multi-layer core and a cover are disclosed. The multi-layer core comprises a layer formed from a highly neutralized polymer composition and a layer formed from a thermoset rubber.

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 ,-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.

A golf ball has an inner core layer including a thermoplastic highly-neutralized ionomer and having a geometric center hardness less than a surface hardness to define a first positive hardness gradient. An outer core layer is formed about the inner core and includes a homogenous thermoset composition. The outer core has an interior hardness less than an outer surface hardness to define a second positive hardness gradient. An inner and outer cover layers are disposed about outer core layer. The first and second hardness gradients each have a slope and the slope of the second hardness gradient is less than the slope of the first hardness gradient such that a ratio of the first and second slopes is 0.8 to 0.85.

A golf ball comprising at least one layer comprised of a neutralized acid polymer composition consisting of a mixture of: (a) at least one low molecular weight acid-containing wax; (b) at least one non-acid-polymer; and (c) at least one organic acid or salt thereof. Each low molecular weight acid-containing wax may have a molecular weight of from about 500 to about 7000, and in some embodiments, the molecular weight may be considered low up to 30,000. Interactions between components (a), (b) and (c) as disclosed herein advantageously produce a layer of ionomeric material having desirable physical properties, such as heat stability, and processability (excellent melt flow) without the need for blending high and low molecular weight acid-containing polymer(s)

In a golf ball having a core of at least one layer and a cover of at least one layer, at least one core or cover layer contains a butyl rubber ionomer. A method of manufacturing golf balls having a core of at least one layer and a cover of at least one layer includes the steps of preparing a treatment solution of butyl rubber ionomer dissolved in a solvent, applying the treatment solution to at least one layer of the golf ball, and covering the treated layer with, as an outer layer adjoining thereto, a rubber layer, a resin layer or a paint layer. With this golf ball and golf ball manufacturing method, adhesion between the layers can be improved, enabling the durability of the ball to cracking on impact to be increased.

The present invention provides resin compositions for golf balls which have excellent flexibility, fluidity, and resilience, and golf balls formed from the resin compositions. The present invention relates to a resin composition for golf balls including a polymer that contains a diene polymer moiety and a carboxylic acid-based moiety wherein carboxyl groups derived from the carboxylic acid-based moiety are neutralized.

A golf ball comprising a core and a cover, the core consisting of: a solid inner core layer formed from a first unfoamed thermoplastic composition TP.sub.1 and having a diameter of 1.10 inch or less and a center Shore C hardness (H.sub.center) of 50 or less, one or more optional intermediate core layers, and an outer core layer formed from a second thermoplastic composition TP.sub.2 and having a thickness of 0.200 inches or greater and an outer surface Shore C hardness (H.sub.outer surface) of 70 or greater, wherein H.sub.outer surface>H.sub.center, and H.sub.outer surfaceH.sub.center40.

Multi-layered golf balls containing a dual-core structure are provided. The core structure includes an inner core (center) made from a foam or metal-containing composition, or it has a hollow shell construction, and the outer core layer is made of a thermoplastic composition. Preferably, the thermoplastic composition comprises: a) ethylene acid copolymer, b) plasticizer, and c) cation source. A fatty acid ester such as ethyl oleate is preferably used as the plasticizer. The core assembly preferably has a positive hardness gradient extending across the entire assembly. The core structure and resulting ball have relatively good resiliency at given compressions.