A rubber composition for a golf ball core includes (a) a conjugated diene polymer, (b) a copolymer of a conjugated diene compound and a non-conjugated olefin, and (c) an organic peroxide. Golf balls having at least one core layer formed of such a rubber composition and a cover of one or more layers encasing the core exhibit improved durability to cracking on repeated impact while maintaining the basic properties required of golf balls, such as flight and spin controllability on approach shots.

The present invention provides methods for producing golf balls having polyurethane covers and the resultant balls. Multi-piece golf balls having an inner core and outer cover with one or more intermediate layers disposed between the core and cover can be formed. The methods involve producing hydroxyl-terminated adducts and isocyanate-terminated prepolymers. Thermoset and thermoplastic polyurethane compositions can be prepared. The resulting polyurethane compositions and golf ball covers have high thermal stability and good wear-resistance and durability.

Provided are a golf ball and a resin composition for a cover or topcoat thereof which can suppress the yellowing of the golf ball caused by ultraviolet rays even if a naturally derived substance is used as an ultraviolet absorber, and they are environmentally and human friendly. A resin composition for a cover or topcoat of a golf ball of the present invention contains: a resin for a cover or topcoat; and a plant-derived extract which absorbs ultraviolet rays. The resin composition has a color difference ΔE of 10.0 or less in a Lab color system between before and after a color tone change test, the color tone change test being carried out by irradiating a film formed from the resin composition with a xenon lamp. In the golf ball of the present invention, the cover or the topcoat is formed by using the resin composition.

Provided are a golf ball which has a surface that sparkles when exposed to ultraviolet rays even if a naturally derived substance is used as a fluorescent material, and it is environmentally and human friendly, and a resin composition for a cover or a topcoat therefor. A resin composition for a cover or a topcoat of a golf ball of the present invention includes: a resin for a cover or a topcoat; and a plant-derived or alga-derived extract which emits light using an absorbed light as an energy source, as a fluorescent material. In the golf ball of the present invention, the cover or the topcoat is formed by using such a resin composition.

A golf ball comprising layers that have from 0.05% to 70% by weight of a radio-opaque filler, and wherein the concentration of the radio-opaque filler is measurably different in each layer is disclosed herein. The radio-opaque filler is preferably a compound based on barium, bismuth, tungsten, iodine, or reduced iron.

Golf balls having a single or dual-layered solid core are provided. In one embodiment, the golf ball has dimensions and properties that do not conform to the rules of the United States Golf Association (USGA). For example, the ball weight; ball size; ball spherical symmetry; ball initial velocity; and/or ball overall distance may fall outside of the USGA standards. The dual-layered core can have an inner core comprising a thermoplastic composition and surrounding outer core comprising a thermoset composition. In another embodiment, the dual-layered core has an inner core comprising a thermoplastic composition and outer core comprising a thermoset composition. The thermoplastic composition preferably comprises an ethylene acid copolymer ionomer and plasticizer. The thermoset composition preferably comprises polybutadiene rubber. The ball further includes a cover of at least one layer.

In a golf ball having a core and a cover of one or more layer, at least one layer of the cover is formed of a resin composition which includes in a specific weight ratio: (I) a thermoplastic polyurethane resin that uses polytetramethylene glycol having a number-average molecular weight of from 1,900 to 2,100 as the polyol component, (II) a thermoplastic polyurethane resin that uses polytetramethylene glycol having a number-average molecular weight of from 900 to 1,100 as the polyol component, and (III) an aromatic vinyl elastomer. The cover layer formed of this resin composition has a Martens hardness and an elastic work recovery which together satisfy a specific formula. The golf ball has an excellent controllability on approach shots without losing distance on driver shots. In addition, the scuff resistance and moldability are good.

An object of the present invention is to provide a novel golf ball having excellent spin performance on approach shots. The present invention provides a golf ball comprising a golf ball body and a paint film composed of at least one layer and formed on a surface of the golf ball body, wherein a base resin constituting an outermost layer of the paint film is a polyurethane obtained by a reaction between (A) a polyol composition and (B) a polyisocyanate composition, and a loss modulus (E″) at the temperature of −50° C. obtained by measuring a dynamic viscoelasticity of the polyurethane is 1.00×10.sup.8 Pa or more.

Multi-layered golf balls having an inner core with a relatively large diameter are provided. In one embodiment, the golf ball comprises an inner core, outer core, and cover. The inner core comprises a thermoset or thermoplastic composition. For example, a blend of polybutadiene rubbers can be used to form the inner core. The outer core layer is relatively thin and comprises a thermoset or thermoplastic composition. The dimensions and compressions of the core layers have specific relationships referred to as the Core Profile. The golf ball further comprises a cover having at least one layer. Ethylene acid copolymer ionomers and polyurethanes, particularly thermoplastic polyurethane, can be used to form the cover.

A golf ball 2 includes a core 4, an inner cover 6 positioned outside the core 4, and an outer cover 8 positioned outside the inner cover 6. The core 4 has a capsule 14, a plurality of separators 16, an electronic unit 18, and a plurality of fillings 20. The capsule 14 has a melting point of not lower than 100° C. A ratio P1 of a volume Vr of the capsule 14 to a volume Vc of the core 4 is not less than 25% and not greater than 75%. The electronic unit 18 is housed in the capsule 14. The electronic unit 18 detects behavior of the golf ball 2.