Abstract: A practice golf ball has a core and a cover. The core is made of a rubber composition which includes a base rubber, a co-crosslinking agent which is methacrylic acid, a crosslinking initiator and a metal oxide. The respective ingredients in the rubber composition are formulated in specific amounts, and the core has an optimized hardness profile. The cover is made of a resin component which is composed primarily of polyurethane. The cover has a thickness of 0.3 mm to 1.9 mm, and a material hardness, expressed as the Shore D hardness, of 30 to 57. The respective deflections of the core and the ball under a specific load, and the relationship therebetween, are optimized.

Abstract: A practice golf ball has a core made of a rubber composition which includes a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, and has a cover which encases the core and is made of a resin material. The co-crosslinking agent is methacrylic acid. The resin material has a breaking strength of 20 to 80 MPa and an elongation of 150 to 600%. The ball is endowed with the properties required of practice balls intended for long-term use, including better durability to cracking and durability of appearance than ordinary game balls, and also better durability to ball surface loss than the one-piece golf balls which are commonly used as practice balls.

Abstract: A practice golf ball has a core and a cover. The core is made of a rubber composition which includes a base rubber, a co-crosslinking agent which is methacrylic acid, a crosslinking initiator and a metal oxide. The respective ingredients in the rubber composition are formulated in specific amounts, and the core has an optimized hardness profile. The cover includes a resin component which is composed primarily of polyurethane. The cover has a thickness of 0.3 mm to 1.9 mm, and a material hardness, expressed as the Shore D hardness, of 30 to 48. The respective deflections of the core and the ball under a specific load, and the relationship therebetween, are optimized. The volume ratio VR of dimples on the surface of the ball is optimized.

Abstract: The invention provides a rubber composition for golf balls which includes a base rubber, (B) a metal salt of an unsaturated carboxylic acid and/or an unsaturated carboxylic acid and zinc oxide, (C) an organic peroxide, and (D) from 0.1 to 5 parts by weight of a metal salt of a thiol having the general formula (R—S)nM (wherein R is a monovalent hydrocarbon group having from 12 to 30 carbons, exclusive of aromatic groups; n is an integer such as 1, 2 or 3; and M is a metal) per 100 parts by weight of the base rubber. The golf ball-forming rubber composition of the invention is suitable for pressure molding and has an excellent productivity because it does not lower the rate of vulcanization. The golf ball of the invention, which is formed using the composition, is endowed with an excellent rebound.

Abstract: The invention provides a rubber composition for golf balls which includes (A) a base rubber containing a polybutadiene having a cis-1,4 bond content of at least 60 wt %, (B) an unsaturated carboxylic acid and/or a metal salt thereof, and (C) two or more organic peroxides which include (C-1) an organic peroxide having a solubility parameter (SP) of 9 or less and (C-2) an organic peroxide having a solubility parameter (SP) of 10 or more. The golf ball rubber composition of the invention enables a high-quality molded and crosslinked product having a suitable hardness and a high resilience to be obtained.

Abstract: The invention provides a rubber composition for golf balls which includes (A) a base rubber containing a polybutadiene having a cis-1,4 bond content of at least 60 wt %, (B) an unsaturated carboxylic acid and/or a metal salt thereof, and (C) two or more organic peroxides which include (C-1) an organic peroxide having a one-minute half-life temperature of 145 to 185° C. and (C-2) an organic peroxide having a one-minute half-life temperature of 110 to 135° C. The golf ball rubber composition of the invention enables a high-quality molded and crosslinked product having a suitable hardness and a high resilience to be obtained.

Abstract: The invention provides a rubber composition for golf balls which includes (A) a base rubber containing a polybutadiene having a cis-1,4 bond content of at least 60 wt %, (B) an unsaturated carboxylic acid and/or a metal salt thereof, and (C) two or more organic peroxides which include (C-1) an organic peroxide other than a diacyl peroxide and (C-2) an organic peroxide which is a diacyl peroxide. The golf ball rubber composition of the invention enables a high-quality molded and crosslinked product having a suitable hardness and a high resilience to be obtained.

Abstract: A golf ball includes, as a constituent element thereof, a molded and crosslinked product obtained from a rubber composition containing (A) a base rubber which includes a polybutadiene having a cis-1,4 bond content of at least 60 wt %, (B) an unsaturated carboxylic acid and/or a metal salt thereof, (C) an organosulfur compound, (D) one or more organic peroxide selected from the group consisting of peroxyketals and/or dialkyl peroxides, and (E) one or more organic peroxide selected from the group consisting of hydroperoxides. In the golf ball, the value obtained by subtracting a center hardness of the molded and crosslinked product from a surface hardness thereof, expressed as the JIS-C hardness, is at least 20. The golf ball has a reduced spin rate on shots with a driver and therefore is able to follow a reliable trajectory that does not tend to dip or to rise in a high arc, enabling an increased distance to be achieved.

Abstract: The invention provides a rubber composition for golf balls which includes a base rubber, (B) a metal salt of an unsaturated carboxylic acid and/or an unsaturated carboxylic acid and zinc oxide, (C) an organic peroxide, and (D) from 0.1 to 5 parts by weight of a metal salt of a thiol having the general formula (R—S)nM (wherein R is a monovalent hydrocarbon group having from 12 to 30 carbons, exclusive of aromatic groups; n is an integer such as 1, 2 or 3; and M is a metal) per 100 parts by weight of the base rubber. The golf ball-forming rubber composition of the invention is suitable for pressure molding and has an excellent productivity because it does not lower the rate of vulcanization. The golf ball of the invention, which is formed using the composition, is endowed with an excellent rebound.