Abstract: Half shell 10 has a bowl-like shape, and is composed of a thermoplastic resin composition. The half shell 10 has a top part 11 and a side part 12. The thickness Tt of the top part 11 is less than the thickness Ts of the side part 12. The difference (Ts−Tt) between both thicknesses is 0.02 mm or greater and 0.30 mm or less. Two half shells 10 and a core covered by the half shells 10 are placed into a mold comprising an upper portion and a lower portion both of which having a semi hemispherical cavity. Upon clamping, the thermoplastic resin composition is compressed while being heated, resulting in outflow of the excess thermoplastic resin composition from the cavity. A cover is formed having the nominal thickness of 0.3 mm or greater and 1.0 mm or less with remained thermoplastic resin composition.

Abstract: A golf ball and a method of manufacturing thereof are provided, the golf ball having a core containing a Mg vulcanized rubber powder crosslinked by a magnesium salt of an unsaturated carboxylic acid and another vulcanized rubber powder crosslinked by a co-crosslinking agent other than the magnesium salt of the unsaturated carboxylic acid. Preferably, the ratio &agr;/&bgr; between the content &agr; of the Mg vulcanized rubber powder and the content &bgr; of another vulcanized rubber powder is 1/4 to 4, and the total content &agr;+&bgr; of the vulcanized rubber powders based on 100 parts by mass of a base rubber of the core is 5 to 30 parts by mass.

Abstract: A golf ball (1) comprises a core (2) and a cover (3). In the forming of the cover (3), first of all, a half shell is formed by a thermoplastic resin composition. Next, two half shells and the core (2) covered with the half shells are put in a mold. Then, the mold is clamped. Thereafter, the thermoplastic resin composition is heated in a spherical cavity and is pressurized at a pressure of 5 kgf/cm2 to 50 kgf/cm2, and the excessive thermoplastic resin composition flows out of the spherical cavity. Subsequently, the thermoplastic resin composition is heated in the spherical cavity and is pressurized at a pressure of 70 kgf/cm2 or more so that the cover (3) is formed. The total volume of the two half shells is set to be 105% to 120% of the volume of the cover (3).

Abstract: A golf ball and a method of manufacturing thereof are provided, the golf ball having a core containing a Mg vulcanized rubber powder crosslinked by a magnesium salt of an unsaturated carboxylic acid and another vulcanized rubber powder crosslinked by a co-crosslinking agent other than the magnesium salt of the unsaturated carboxylic acid. Preferably, the ratio &agr;/&bgr; between the content &agr; of the Mg vulcanized rubber powder and the content &bgr; of another vulcanized rubber powder is ¼ to 4, and the total content &agr;+&bgr; of the vulcanized rubber powders based on 100 parts by mass of a base rubber of the core is 5 to 30 parts by mass.

Abstract: The present invention provides a golf ball having excellent durability, sufficient for use in driving ranges while maintaining sufficient flight distance and shot feel for use in playing a round of golf. The golf ball comprises a core and a cover covering the core, wherein the core is composed of a vulcanized molded article of a rubber composition comprising 100 parts by weight of a base rubber containing not less than 80% by weight of a butadiene rubber having not less than 80 molar % of cis-1,4 bond, 10 to 30 parts by weight of calcium carbonate, 18 to 35 parts by weight of zinc acrylate or methacrylate and 0.5 to 2.5 parts by weight of a peroxide, and the cover is made from a resin composition having a flexural modulus of 1,400 to 3,800 kgf/cm2, wherein the total volume of dimples of the cover is from 250 to 400 mm3.

Abstract: The present invention provides a method for preparing a rubber composition for golf balls having excellent workability. The present invention related to a method for preparing a rubber composition for golf balls comprising at least a base rubber, a metal salt of .alpha.,.beta.-unsaturated carboxylic acid, a filler and an organic peroxide, comprising the steps of,(a) mixing the base rubber and the metal salt of .alpha.,.beta.-unsaturated carboxylic acid to obtain a pre-mixture,(b) adding the filler and the peroxide to the pre-mixture, and mixing in a mixing machine at the number of revolutions of 10 to 50 rpm for 2 to 6 minutes, and(c) discharging the mixed rubber composition with controlling the temperature of the rubber composition to 100.degree. to 120.degree. C.

Abstract: Disclosed is a thread wound golf ball having uniform flying performances, which causes little scattering of weight and inclusion of air into the liquid center, wherein no separation of the paste is arisen. The thread wound golf ball comprises a liquid center, a thread rubber layer and a cover. The liquid center is composed of a paste and a center bag for coating the paste. A viscosity at 23.degree. C. (measured by a B type viscometer) of the paste is 15 to 70 poise.