JP4870744B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball. Specifically, the present invention relates to a multi-piece golf ball having a center, an envelope layer, and a cover.

  A golfer's greatest demand for a golf ball is flight performance. Golfers attach great importance to flight performance with drivers, long irons and middle irons. The flight performance correlates with the resilience performance of the golf ball. When a golf ball excellent in resilience performance is hit, it flies at a high speed and a large flight distance is achieved. Flight performance is further correlated with spin speed. By flying at a low spin speed, a proper trajectory is obtained and a large flight distance is achieved. From the viewpoint of flight performance, a golf ball that has high resilience and is difficult to spin is desired. Golfers also place importance on the feel of a golf ball. Golfers prefer a soft feel at impact.

  There are golf balls having an outer-hard / inner-soft structure. The launch angle when this golf ball is hit with a golf club is large. The spin speed when this golf ball is hit with a golf club is small. Large flight distances can be achieved with large launch angles and small spin speeds.

  A golf ball having a soft center can have an outer-hard / inner-soft structure. Even when a high-rigidity cover is used, an outer-hard / inner-soft structure can be achieved. By using an ionomer resin having a high acid content or an ionomer resin having a high degree of neutralization for the cover, high rigidity of the cover can be achieved.

  JP-A-6-80718 discloses a resin composition used for a golf ball cover. This resin composition contains an ionomer resin having a high acid content.

  Japanese Patent Application Laid-Open No. 9-10357 discloses a golf ball including a core, an inner cover, and an outer cover. This outer cover is made of a resin composition. This resin composition contains an ionomer resin having a high acid content.

  Japanese Patent Application Laid-Open No. 9-56848 discloses a golf ball having a core, an intermediate layer, and a cover. This core has a two-layer structure. The main component of the intermediate layer is polyester, and the main component of the cover is an ionomer resin. The cover has a high hardness.

  Japanese Patent Application Laid-Open No. 10-127822 discloses a golf ball having a core, an intermediate layer, and a cover. This cover is made of a resin composition. The base material of this resin composition is an ionomer resin containing a diamine complex.

  JP-A-10-314341 discloses a resin composition used for a golf ball cover. This resin composition contains an ionomer resin and a rubber-like functional copolymer.

  JP-T-2001-514561 discloses a golf ball including a core, an intermediate layer, and a cover. This cover is made of a resin composition. This resin composition contains an ionomer resin and polyamide.

Japanese Unexamined Patent Application Publication No. 2007-622 discloses a resin composition used for a golf ball cover. This resin composition contains an ionomer resin, a thermoplastic resin, and a thermoplastic resin having an acid group.
JP-A-6-80718 Japanese Patent Laid-Open No. 9-10357 JP-A-9-56848 Japanese Patent Laid-Open No. 10-127822 JP-A-10-314341 Special table 2001-514561 gazette JP 2007-622 A

  In a golf ball in which an outer-hard / inner-soft structure is achieved by a soft center, the hardness distribution from the surface of the intermediate layer to the center point of the center has a large step at the boundary between the center and the intermediate layer. This step prevents spin suppression. A soft center inhibits resilience.

  In a golf ball in which an outer-hard / inner-soft structure is achieved by a highly rigid cover, this cover impairs the feel at impact. A cover having high rigidity achieved by an ionomer resin having a high acid content is inferior in durability. A cover having high rigidity achieved by an ionomer resin having a high degree of neutralization is inferior in moldability.

  Golfers' demand for golf balls is increasingly escalating. An object of the present invention is to provide a golf ball having excellent flight performance and durability.

  The golf ball according to the present invention includes a core and a cover positioned outside the core. The core has a center and an envelope layer located outside the center. The center has a diameter of 1 mm or more and 15 mm or less. In this center, the JIS-C hardness H1 at the center point is 20 or more and 50 or less. The difference (H4−H3) between the JIS-C hardness H4 on the surface of the core and the JIS-C hardness H3 in the innermost part of the envelope layer is 10 or more. The bending elastic modulus of the cover is 300 MPa or more and 1000 MPa or less. The tensile elastic modulus of the cover is 400 MPa or more and 1500 MPa or less. Preferably, the Shore D hardness of the cover is 65 or more and 75 or less.

The cover is made of a resin composition. Preferably, the resin composition is
(A) a highly elastic polyamide resin having a flexural modulus of 700 MPa to 5000 MPa,
(B) an ethylene- (meth) acrylic acid copolymer neutralized with metal ions and (C) a resin having a polar functional group. The mass ratio of the polyamide resin (A) and the copolymer (B) is 5/95 or more and 80/20 or less. The amount of the resin (C) with respect to 100 parts by mass of the total amount of the polyamide resin (A) and the copolymer (B) is 0.1 parts by mass or more and 20 parts by mass or less.

  Preferably, the polyamide resin (A) comprises polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide 612, and a polyether block amide copolymer. 1 or 2 or more selected from the group is included.

  Preferably, the copolymer (B) includes an ethylene- (meth) acrylic acid binary copolymer and / or an ethylene- (meth) acrylic acid- (meth) acrylic acid ester terpolymer.

  Preferably, the resin (C) includes one or more selected from the group consisting of an ethylene-glycidyl methacrylate copolymer, an ethylene-acrylic acid-glycidyl methacrylate copolymer, and a methyl methacrylate-glycidyl methacrylate copolymer. .

  The golf ball may further include an intermediate layer positioned between the core and the cover. Preferably, the cover hardness H6 is greater than the Shore D hardness H5 of the intermediate layer. Preferably, the intermediate layer is made of a thermoplastic resin composition.

  Preferably, the difference (H3−H2) between the hardness H3 and the JIS-C hardness H2 of the center surface is 35 or less. Preferably, the difference (H4−H1) between the hardness H4 and the hardness H1 is 40 or more.

  The center can be formed by crosslinking the rubber composition. Preferably, the main component of the base rubber of this rubber composition is polybutadiene. Preferably, the rubber composition contains sulfur as a crosslinking agent. The envelope layer can be formed by crosslinking the rubber composition. Preferably, the main component of the base rubber of the rubber composition of the envelope layer is polybutadiene.

  In the golf ball according to the present invention, an outer-hard / inner-soft structure is achieved by a center having a small center point hardness H1 and a highly rigid cover. In this golf ball, the center has a small diameter and the envelope layer has a large hardness difference (H4-H3). Therefore, the difference in hardness at the boundary between the center and the envelope layer is small. A conventional golf ball has an outer-hard / inner-soft structure with poor hardness distribution continuity, whereas a golf ball according to the present invention has an outer-hard / inner-soft structure with excellent hardness distribution. In this golf ball, spin is sufficiently suppressed. Since the diameter of the center is small, this center does not hinder the resilience performance of the golf ball. Since the cover is highly rigid, even if the center is soft, this golf ball has excellent resilience performance.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a partially cutaway sectional view showing a golf ball 2 according to an embodiment of the present invention. The golf ball 2 includes a spherical core 4, an intermediate layer 6 positioned outside the core 4, and a cover 8 positioned outside the intermediate layer 6. The core 4 includes a spherical center 10 and an envelope layer 12 positioned outside the center 10. A large number of dimples 14 are formed on the surface of the cover 8. A portion of the surface of the golf ball 2 other than the dimples 14 is a land 16. The golf ball 2 includes a paint layer and a mark layer on the outside of the cover 8, but these layers are not shown.

  The golf ball 2 has a diameter of 40 mm to 45 mm. The diameter is preferably 42.67 mm or more from the viewpoint that the American Golf Association (USGA) standard is satisfied. In light of suppression of air resistance, the diameter is preferably equal to or less than 44 mm, and more preferably equal to or less than 42.80 mm. The golf ball 2 has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is preferably 44 g or more, and more preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is preferably equal to or less than 45.93 g.

  The center 10 is obtained by crosslinking the rubber composition. Examples of preferable base rubber include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of resilience performance, polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the ratio of the amount of polybutadiene to the total amount of the base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. The ratio of cis-1,4 bonds in the polybutadiene is preferably 40% or more, particularly preferably 80% or more.

  For the center 10, sulfur crosslinking, peroxide crosslinking, electron beam crosslinking, or the like can be applied. Crosslinking with sulfur is preferred. The center 10 obtained by crosslinking with sulfur is soft. The center 10 achieves the outer-hard / inner-soft structure of the core 4. The core 4 suppresses spin. The core 4 also contributes to a shot feeling.

  In light of the resilience performance of the golf ball 2, the amount of sulfur is preferably equal to or greater than 2.0 parts by weight and particularly preferably equal to or greater than 3.0 parts by weight with respect to 100 parts by weight of the base rubber. In light of the softness of the center 10, the amount of sulfur is preferably 10.0 parts by mass or less, and particularly preferably 6.5 parts by mass or less.

  When crosslinking by sulfur is employed, the rubber composition of the center 10 preferably includes a vulcanization accelerator. With the vulcanization accelerator, a short cross-linking time of the center 10 is achieved. Guanidine vulcanization accelerator, thiazole vulcanization accelerator, sulfenamide vulcanization accelerator, aldehyde ammonia vulcanization accelerator, thiourea vulcanization accelerator, thiuram vulcanization accelerator, dithiocarbamate vulcanization accelerator Sulfur accelerators, xanthate vulcanization accelerators, and the like can be used. Guanidine vulcanization accelerators, thiazole vulcanization accelerators and sulfenamide vulcanization accelerators are preferred. Two or more vulcanization accelerators may be used in combination.

  Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide and di-o-tolylguanidine salt of dicatechol borate. As specific examples of 1,3-diphenylguanidine, trade names “Noxeller D” and “Noxeller DP” of Ouchi Shinsei Chemical Industry Co., Ltd. and trade names “Soxinol D”, “Soxinol DG” and “ Soxinol DO ". Specific examples of 1,3-di-o-tolylguanidine include trade name “Noxeller DT” of Ouchi Shinsei Chemical Industry Co., Ltd. and trade names “Soccinol DT” and “Soccinol DT-O” of Sumitomo Chemical Co., Ltd. . As a specific example of 1-o-tolyl biguanide, trade name “Noxeller BG” of Ouchi Shinsei Chemical Industry Co., Ltd. may be mentioned. As a specific example of the di-catechol borate di-o-tolylguanidine salt, trade name “Noxeller PR” of Ouchi Shinsei Chemical Industry Co., Ltd. may be mentioned.

  Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-mercaptobenzothiazole zinc salt, cyclohexylamine salt of 2-mercaptobenzothiazole, 2- (N, N- Examples include diethylthiocarbamoylthio) benzothiazole and 2- (4′-morpholinodithio) benzothiazole. Specific examples of 2-mercaptobenzothiazole include trade names “Noxeller M” and “Noxeller MP” of Ouchi Shinsei Chemical Industry Co., Ltd. Specific examples of di-2-benzothiazolyl disulfide include “Noxeller DM” and “Noxeller DM-P” trade names of Ouchi Shinsei Chemical Industry Co., Ltd. As a specific example of 2-mercaptobenzothiazole zinc salt, trade name “Noxeller MZ” of Ouchi Shinsei Chemical Co., Ltd. may be mentioned. As a specific example of the cyclohexylamine salt of 2-mercaptobenzothiazole, trade name “Noxeller M-60-OT” of Ouchi Shinsei Chemical Industry Co., Ltd. may be mentioned. As a specific example of 2- (N, N-diethylthiocarbamoylthio) benzothiazole, trade name “Noxeller 64” of Ouchi Shinsei Chemical Industry Co., Ltd. may be mentioned. Specific examples of 2- (4′-morpholinodithio) benzothiazole include trade names “Noxeller MDB” and “Noxeller MDB-P” of Ouchi Shinsei Chemical Industry Co., Ltd.

  Examples of the sulfenamide-based vulcanization accelerator include N-cyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolylsulfuride. Examples include phenamide and N, N′-dicyclohexyl-2-benzothiazolylsulfenamide. Specific examples of N-cyclohexyl-2-benzothiazolylsulfenamide include trade names “Noxeller CZ” and “Noxeller CZ-G” of Ouchi Shinsei Chemical Industry Co., Ltd. Specific examples of N-tert-butyl-2-benzothiazolylsulfenamide include trade names “Noxeller NS” and “Noxeller NS-P” of Ouchi Shinsei Chemical Industry Co., Ltd. As a specific example of N-oxydiethylene-2-benzothiazolylsulfenamide, trade name “Noxeller MSA-G” of Ouchi Shinsei Chemical Industry Co., Ltd. may be mentioned. Specific examples of N, N′-dicyclohexyl-2-benzothiazolylsulfenamide include trade names “Noxeller DZ” and “Noxeller DZ-G” of Ouchi Shinsei Chemical Industry Co., Ltd.

  The amount of the vulcanization accelerator is preferably 0.5 parts by mass or more, particularly preferably 2.0 parts by mass or more with respect to 100 parts by mass of the base rubber. The amount of the vulcanization accelerator is preferably 7.0 parts by mass or less, and particularly preferably 5.0 parts by mass or less.

  When crosslinking with sulfur is employed, a reinforcing agent is preferably blended in the center 10. A preferred reinforcing agent is silica (white carbon). With silica, a moderate rigidity of the center 10 can be achieved. Dry process silica and wet process silica can be used. From the viewpoint of the rigidity of the center 10, the amount of silica is preferably 5 parts by mass or more and particularly preferably 7 parts by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of the softness of the center 10, the amount of silica is preferably 25 parts by mass or less, and particularly preferably 15 parts by mass or less. A silane coupling agent may be blended together with silica.

  The center 10 may be crosslinked with a co-crosslinking agent and an organic peroxide. A soft center 10 can be obtained by using a small amount of a co-crosslinking agent compared to the center of a general golf ball. As will be described later, a special resin composition is used for the cover 8 of the golf ball 2. Even if the amount of the co-crosslinking agent is small, the co-crosslinking agent and the organic peroxide are used in combination, and a special resin composition is used for the cover 8, thereby obtaining a golf ball 2 having excellent durability. Can be.

  A preferred co-crosslinking agent is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. From the viewpoint of resilience performance, zinc acrylate and zinc methacrylate are particularly preferred.

  In light of the resilience performance of the golf ball 2, the amount of the co-crosslinking agent is preferably 1 part by mass or more and particularly preferably 2 parts by mass or more with respect to 100 parts by mass of the base rubber. In light of the softness of the center 10, the amount of the co-crosslinking agent is preferably 14 parts by mass or less, more preferably 12 parts by mass or less, and particularly preferably 10 parts by mass or less.

  Preferred organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butyl). Peroxy) hexane and di-t-butyl peroxide. From the viewpoint of versatility, dicumyl peroxide is preferable.

  In light of the resilience performance of the golf ball 2, the amount of the organic peroxide is preferably equal to or greater than 0.1 parts by weight, more preferably equal to or greater than 0.3 parts by weight, based on 100 parts by weight of the base rubber. Part or more is particularly preferable. From the viewpoint of soft feel at impact, the amount of the organic peroxide is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, and 1.5 parts by mass or less with respect to 100 parts by mass of the base rubber. Is particularly preferred.

  The rubber composition of the center 10 may contain an organic sulfur compound together with the co-crosslinking agent and the organic peroxide. Preferred organic sulfur compounds include diphenyl disulfide, bis (4-chlorophenyl) disulfide, bis (3-chlorophenyl) disulfide, bis (4-bromophenyl) disulfide, bis (3-bromophenyl) disulfide, and bis (4-fluorophenyl). ) Monosubstituted compounds such as disulfide, bis (4-iodophenyl) disulfide and bis (4-cyanophenyl) disulfide; bis (2,5-dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide, bis (2 , 6-dichlorophenyl) disulfide, bis (2,5-dibromophenyl) disulfide, bis (3,5-dibromophenyl) disulfide, bis (2-chloro-5-bromophenyl) disulfide and bis (2-cyano-5- The Di-substituted compounds such as mophenyl) disulfide; tri-substituted compounds such as bis (2,4,6-trichlorophenyl) disulfide and bis (2-cyano-4-chloro-6-bromophenyl) disulfide; Tetra substituents such as 3,5,6-tetrachlorophenyl) disulfide; and bis (2,3,4,5,6-pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) ) Examples of penta-substituted compounds such as disulfides. Organic sulfur compounds contribute to resilience performance. Particularly preferred organic sulfur compounds are diphenyl disulfide and bis (pentabromophenyl) disulfide.

  In light of the resilience performance of the golf ball 2, the amount of the organic sulfur compound is preferably equal to or greater than 0.1 parts by weight and particularly preferably equal to or greater than 0.2 parts by weight with respect to 100 parts by weight of the base rubber. From the viewpoint of soft feel at impact, the amount of the organic sulfur compound is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and 0.8 part by mass or less with respect to 100 parts by mass of the base rubber. Particularly preferred.

  The center 10 may be blended with a filler for the purpose of adjusting specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The amount of the filler is appropriately determined so that the intended specific gravity of the center 10 is achieved. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjusting role but also as a crosslinking aid.

  In the center 10, various additives such as an anti-aging agent, a coloring agent, a plasticizer, and a dispersing agent are blended in an appropriate amount as necessary. The center 10 may be blended with a crosslinked rubber powder or a synthetic resin powder.

  From the viewpoint of durability, the center 10 has a center hardness H1 of preferably 20 or greater, more preferably 25 or greater, and particularly preferably 30 or greater. From the viewpoint of spin suppression, the center hardness H1 is preferably 50 or less, more preferably 45 or less, and particularly preferably 40 or less. The center hardness H1 is measured by pressing a JIS-C type hardness meter against the center point of the cut surface of the hemisphere obtained by cutting the center 10. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  The hardness of the center 10 gradually increases from the center point toward the surface. The surface hardness H2 of the center 10 is greater than the center hardness H1. Due to the large surface hardness H2, continuity of hardness between the center 10 and the envelope layer 12 can be achieved. From this viewpoint, the surface hardness H2 of the center 10 is preferably 25 or more, and particularly preferably 30 or more. In light of feel at impact, the surface hardness H2 is preferably equal to or less than 60, more preferably equal to or less than 50, and particularly preferably equal to or less than 40. The surface hardness is measured by pressing a JIS-C type hardness meter against the surface of the center 10. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  In light of feel at impact, the difference (H2−H1) between the surface hardness H2 and the center hardness H1 is preferably 1 or greater, and particularly preferably 2 or greater. In light of resilience performance, the difference (H2−H1) is preferably 15 or less, more preferably 10 or less, and particularly preferably 5 or less.

  In light of feel at impact, the center 10 has an amount of compressive deformation D1 of preferably 0.5 mm or greater, more preferably 1.0 mm or greater, and particularly preferably 1.1 mm or greater. In light of resilience performance, the amount of compressive deformation D1 is preferably equal to or less than 2.5 mm, more preferably equal to or less than 2.3 mm, and particularly preferably equal to or less than 2.0 mm.

  In the measurement of the amount of compressive deformation, a sphere is placed on a metal rigid plate. A metal cylinder gradually descends toward the sphere. The sphere sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load is applied to the sphere to the state where the final load is applied is the amount of compressive deformation. In the measurement of the amount of compressive deformation of the center 10, the initial load is 0.3N and the final load is 29.4N. In the measurement of the amount of compressive deformation D2 of the core 4, the amount of compressive deformation D3 of the sphere composed of the core 4 and the intermediate layer 6, and the amount of compressive deformation D4 of the golf ball 2, the initial load is 98N and the final load is 1274N.

  The diameter of the center 10 is smaller than that of a general golf ball center 10. With a small center 10 a sufficiently thick envelope layer 12 can be formed. The envelope layer 12 can achieve an outer-hard / inner-soft structure with excellent hardness distribution continuity. The small center 10 suppresses spin. Even if the small center 10 is soft, it does not hinder the resilience performance of the golf ball 2. From the viewpoint of the continuity of the hardness distribution and the resilience performance, the diameter of the center 10 is preferably 15 mm or less, more preferably 14 mm or less, and particularly preferably 10 mm or less. From the viewpoint that the center 10 can contribute to spin suppression, the diameter is preferably 2 mm or more, more preferably 4 mm or more, and particularly preferably 5 mm or more.

  The mass of the center 10 is preferably 0.05 g or more and 3 g or less. The crosslinking temperature of the center 10 is usually 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the center 10 is usually 3 minutes or longer and 30 minutes or shorter. The center 10 may be formed from two or more layers. The center 10 may include a rib on the surface thereof.

  The envelope layer 12 is obtained by crosslinking the rubber composition. Examples of preferable base rubber include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of resilience performance, polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the ratio of the amount of polybutadiene to the total amount of the base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. The proportion of cis-1,4 bonds in the polyurethane is preferably 40% or more, particularly preferably 80% or more.

  For crosslinking of the envelope layer 12, a co-crosslinking agent is preferably used. A preferred co-crosslinking agent from the viewpoint of resilience performance is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. From the viewpoint of resilience performance, zinc acrylate and zinc methacrylate are particularly preferred.

  From the viewpoint of the resilience performance of the golf ball 2, the amount of the co-crosslinking agent is preferably 10 parts by mass or more and particularly preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber. In light of soft feel at impact, the amount of the co-crosslinking agent is preferably 50 parts by mass or less, particularly preferably 45 parts by mass or less, relative to 100 parts by mass of the base rubber.

  Preferably, the rubber composition of the envelope layer 12 includes an organic peroxide together with a co-crosslinking agent. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide. From the viewpoint of versatility, dicumyl peroxide is preferable.

  In light of the resilience performance of the golf ball 2, the amount of the organic peroxide is preferably equal to or greater than 0.1 parts by weight, more preferably equal to or greater than 0.3 parts by weight, based on 100 parts by weight of the base rubber. Part or more is particularly preferable. From the viewpoint of soft feel at impact, the amount of the organic peroxide is preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, and 2.5 parts by mass or less with respect to 100 parts by mass of the base rubber. Is particularly preferred.

  Preferably, the rubber composition of the envelope layer 12 includes an organic sulfur compound. The organic sulfur compounds described above with respect to the center 10 can be used for the envelope layer 12. In light of the resilience performance of the golf ball 2, the amount of the organic sulfur compound is preferably equal to or greater than 0.1 parts by weight and particularly preferably equal to or greater than 0.2 parts by weight with respect to 100 parts by weight of the base rubber. From the viewpoint of soft feel at impact, the amount of the organic sulfur compound is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and 0.8 part by mass or less with respect to 100 parts by mass of the base rubber. Particularly preferred.

  A filler may be added to the envelope layer 12 for the purpose of adjusting specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The amount of the filler is appropriately determined so that the intended specific gravity of the envelope layer 12 is achieved. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjusting role but also as a crosslinking aid.

  In the envelope layer 12, various additives such as sulfur, an anti-aging agent, a colorant, a plasticizer, and a dispersant are blended in appropriate amounts as necessary. The envelope layer 12 may be blended with a crosslinked rubber powder or a synthetic resin powder.

  The envelope layer 12 gradually increases in hardness from the innermost side to the surface (the surface of the core 4). The innermost hardness H3 is small, and the surface hardness H4 is large. With a small hardness H3, a continuity of hardness between the center 10 and the envelope layer 12 can be achieved. Due to the large hardness H4, the outer-hard / inner-soft structure of the core 4 is achieved. The envelope layer 12 sufficiently suppresses spin.

  In light of resilience performance, the innermost hardness H3 is preferably equal to or greater than 45, more preferably equal to or greater than 55, and particularly preferably equal to or greater than 63. From the viewpoint of the continuity of the hardness distribution, the innermost hardness H3 is preferably 75 or less, more preferably 70 or less, and particularly preferably 67 or less. The hardness H3 is measured in a hemisphere obtained by cutting the core 4. The hardness H3 is measured by pressing a JIS-C type hardness meter against the cut surface of the hemisphere. The hardness meter includes a first circle that is a boundary between the center 10 and the envelope layer 12 and a second circle that is concentric with the first circle and has a radius that is 1 mm larger than the radius of the first circle. It is pressed against the enclosed area. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  In light of achieving an outer-hard / inner-soft structure, the surface hardness H4 of the core 4 is preferably 65 or higher, more preferably 75 or higher, and particularly preferably 79 or higher. In light of feel at impact, the hardness H4 is preferably equal to or less than 90, and particularly preferably equal to or less than 85. The hardness H4 is measured by pressing a JIS-C type hardness meter against the surface of the core 4 (that is, the surface of the envelope layer 12). For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  From the viewpoint of spin suppression, the difference (H4−H3) between the surface hardness H4 of the core 4 and the innermost hardness H3 of the envelope layer 12 is preferably 10 or more, more preferably 13 or more, and particularly preferably 14 or more. From the viewpoint of ease of production, the difference (H4−H3) is preferably 25 or less, more preferably 20 or less, and particularly preferably 16 or less.

  From the viewpoint that a large difference (H4−H3) can be achieved, the thickness of the envelope layer 12 is preferably 10 mm or more, more preferably 11 mm or more, and particularly preferably 12 mm or more. The thickness is preferably 20 mm or less.

  The mass of the envelope layer 12 is preferably 30 g or greater and 44 g or less. The crosslinking temperature of the envelope layer 12 is usually 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the envelope layer 12 is usually 10 minutes or more and 60 minutes or less. The envelope layer 12 may include ribs on the surface thereof.

  From the viewpoint of the continuity of the hardness distribution, the difference (H3−H2) between the innermost hardness H3 of the envelope layer 12 and the surface hardness H2 of the center 10 is preferably 35 or less, and particularly preferably 34 or less. The difference (H3−H2) may be zero.

  From the viewpoint of spin suppression, the difference (H4−H1) between the surface hardness H4 of the core 4 and the center hardness H1 of the center 10 is preferably 40 or more, more preferably 43 or more, and particularly preferably 46 or more. From the viewpoint of ease of production, the difference (H4-H1) is preferably 65 or less, more preferably 60 or less, and particularly preferably 55 or less.

  In light of feel at impact, the core 4 has an amount of compressive deformation D2 of preferably 2.3 mm or greater, more preferably 2.4 mm or greater, and particularly preferably 2.5 mm or greater. In light of resilience performance, the amount of compressive deformation D2 is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.9 mm, and particularly preferably equal to or less than 3.8 mm.

  In light of resilience performance, the core 4 has a diameter of preferably 28.0 mm or greater, more preferably 30.0 mm or greater, and particularly preferably 32.0 mm or greater. In light of durability of the golf ball 2, the core 4 has a diameter of preferably 40.2 mm or less, more preferably 39.9 mm or less, and particularly preferably 39.6 mm or less.

  As described above, the golf ball 2 includes the mid layer 6 and the cover 8. The mid layer 6 is soft and the cover 8 is hard. By this cover 8, the outer-hard / inner-soft structure of the golf ball 2 is achieved. In the golf ball 2, spin is suppressed. The cover 8 further achieves excellent resilience performance of the golf ball 2. Since the mid layer 6 is soft, it can absorb the impact at the time of impact. Although the cover 8 is hard, the mid layer 6 achieves a soft shot feeling of the golf ball 2.

  A resin composition is suitably used for the mid layer 6. Examples of the base polymer of the resin composition include ionomer resins, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers.

  A particularly preferred base polymer is an ionomer resin. The ionomer resin is highly elastic. The golf ball 2 in which an ionomer resin is used for the mid layer 6 is excellent in resilience performance. An ionomer resin and another resin may be used in combination. When used together, from the viewpoint of resilience performance, the ratio of the amount of ionomer resin to the total amount of the base polymer is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 45% by mass or more.

  A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferable binary copolymer contains 80% by mass or more and 90% by mass or less α-olefin and 10% by mass or more and 20% by mass or less α, β-unsaturated carboxylic acid. This binary copolymer is excellent in resilience performance. Other preferable ionomer resins include ternary α-olefin, α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. A copolymer is mentioned. Preferred terpolymers are 70% to 85% by weight α-olefin, 5% to 30% by weight α, β-unsaturated carboxylic acid, and 1% to 25% by weight. α, β-unsaturated carboxylic acid ester. This ternary copolymer is excellent in resilience performance. In this binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid or methacrylic acid.

  In this binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  Specific examples of the ionomer resin include Mitsui Dupont Polychemical's trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN 1856” and “HIMILAN 1855”. "High Milan AM7311", "High Milan AM7315", "High Milan AM7317", "High Milan AM7318", "High Milan AM7329", "High Milan MK7320" and "High Milan MK7329"; DuPont's trade names "Surlin 6120" , “Surlin 7930”, “Surlin 7940”, “Surlin 8140”, “Surlin 8150”, “Surlin 8940”, “Surlin 8945”, “Surlin 9120”, “Surlin 915” ", Surlyn 9910," Surlyn 9945, Surlyn AD8546, "HPF 1000" and "HPF 2000"; IOTEK8000 "and" IOTEK8030 ".

  Two or more ionomer resins may be used in combination with the mid layer 6. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion may be used in combination.

  A preferred resin that can be used in combination with an ionomer resin is a styrene block-containing thermoplastic elastomer. This elastomer can contribute to the feel at impact of the golf ball 2. This elastomer does not hinder the resilience performance of the golf ball 2. This elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of the diene block compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

  The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  In light of the resilience performance of the golf ball 2, the content of the styrene component in the thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. In light of the feel at impact of the golf ball 2, the content is preferably equal to or less than 50% by mass, more preferably equal to or less than 47% by mass, and particularly preferably equal to or less than 45% by mass.

  In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or two or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and hydrogenated products thereof, and an olefin. included. The olefin component in the alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this alloy, the resilience performance of the golf ball 2 is improved. Preferably, an olefin having 2 to 10 carbon atoms is used. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of polymer alloys include Mitsubishi Chemical's trade names “Lavalon T3221C”, “Lavalon T3339C”, “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “ And “Lavalon SJ9400N” and “Lavalon SR04”. Other specific examples of the styrene block-containing thermoplastic elastomer include Daicel Chemical Industries' trade name “Epofriend A1010” and Kuraray's trade name “Septon HG-252”.

  When the ionomer resin and the styrene block-containing thermoplastic elastomer are used in combination in the mid layer 6, the mass ratio between them is preferably 30/70 or more and 95/5 or less. The mid layer 6 having this ratio of 30/70 or more contributes to the resilience performance of the golf ball 2. In this respect, the ratio is more preferably equal to or greater than 40/60 and particularly preferably equal to or greater than 50/50. The mid layer 6 having this ratio of 95/5 or less contributes to the feel at impact of the golf ball 2. In this respect, the ratio is more preferably equal to or less than 80/20 and particularly preferably equal to or less than 70/30.

  The intermediate layer 6 includes a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightening agent, and the like as necessary. An appropriate amount is blended. For the formation of the intermediate layer 6, known methods such as injection molding and compression molding can be employed.

  In light of resilience performance, the mid layer 6 has a hardness H5 of preferably 20 or greater, more preferably 30 or greater, and particularly preferably 35 or greater. In light of feel at impact, the hardness H5 is preferably equal to or less than 55, and particularly preferably equal to or less than 50.

  The hardness H5 is measured by a Shore D type spring hardness meter attached to an automatic rubber hardness measuring device (trade name “P1” of Kobunshi Keiki Co., Ltd.) in accordance with the provisions of “ASTM-D 2240-68”. Is done. For the measurement, a slab having a thickness of about 2 mm formed by hot pressing is used. A slab stored for 2 weeks at a temperature of 23 ° C. is used for the measurement. At the time of measurement, three slabs are overlaid. A slab made of the same resin composition as that of the mid layer 6 is used for the measurement.

  In light of the feel at impact of the golf ball 2, the mid layer 6 has a thickness of preferably 0.3 mm or greater, more preferably 0.5 mm or greater, and particularly preferably 0.7 mm or greater. In light of the resilience performance of the golf ball 2, the thickness is preferably equal to or less than 2.5 mm, more preferably equal to or less than 2.0 mm, and particularly preferably equal to or less than 1.5 mm.

  From the viewpoint of feel at impact, the amount of compressive deformation D3 of the sphere composed of the core 4 and the intermediate layer 6 is preferably 2.3 mm or more, more preferably 2.8 mm or more, and particularly preferably 3.2 mm or more. In light of resilience performance, the amount of compressive deformation D3 is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.6 mm, and particularly preferably equal to or less than 3.4 mm.

The cover 8 is made of a resin composition. This resin composition is
(A) a highly elastic polyamide resin having a flexural modulus of 700 MPa to 5000 MPa,
(B) an ethylene- (meth) acrylic acid copolymer neutralized with metal ions and (C) a resin having a polar functional group.

  The cover 8 including this polyamide resin (A) is highly rigid. By this cover 8, the outer-hard / inner-soft structure of the golf ball 2 is achieved. When the golf ball 2 having an outer-hard / inner-soft structure is hit with a driver, a large launch angle is obtained. When the golf ball 2 is hit with a driver, the golf ball 2 flies with a small spin speed. A large launch distance and a small spin speed provide a large flight distance. This polyamide resin (A) also contributes to the durability of the golf ball 2 at low temperatures.

  This polyamide resin (A) is a polyamide-containing resin or elastomer. Polyamide is a polymer having a plurality of amide bonds (—NH—CO—) in the main chain. Examples of the polyamide include aliphatic polyamides, aromatic polyamides, and amide copolymers. Examples of the aliphatic polyamide include polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, and polyamide 612. Examples of the aromatic polyamide include poly-p-phenylene terephthalamide and poly-m-phenylene isophthalamide. Examples of the amide copolymer include a polyether block amide copolymer, a polyester amide copolymer, a polyether ester amide copolymer, and a polyamideimide copolymer. The polyamide resin (A) may contain two or more polyamides. Aliphatic polyamides and polyether block amide copolymers are preferred. Polyamide 6, polyamide 11 and polyamide 12 are particularly preferred.

  The flexural modulus of this polyamide resin (A) is 700 MPa or more and 5000 MPa or less. High rigidity of the cover 8 is achieved by the polyamide resin (A) having a flexural modulus of 700 MPa or more. This cover 8 can suppress spin on driver shots. In this respect, the flexural modulus is preferably 750 MPa or more, and particularly preferably 800 MPa or more. The polyamide resin (A) having a flexural modulus of 5000 MPa or less does not impair the feel at impact and durability of the golf ball 2. In this respect, the flexural modulus is preferably 4500 MPa or less, and particularly preferably 4000 MPa or less.

  In the measurement of the flexural modulus, a test piece having a length of 80.0 ± 2 mm, a width of 10.0 ± 0.2 mm, and a thickness of 4.0 ± 0.2 mm is used. This test piece is obtained from a dry pellet of the polyamide resin (A) by an injection molding method. The molded test piece is held in a moisture-proof container for 24 hours or more. The temperature in the moisture-proof container is 23 ° C. ± 2 ° C. The flexural modulus is measured within 15 minutes after removal from the moisture-proof container in accordance with ISO 178 regulations. The measurement is performed in an environment where the temperature is 23 ° C. and the humidity is 50% RH.

  The brittle temperature of this polyamide resin (A) is preferably −20 ° C. or lower. The polyamide resin (A) having an embrittlement temperature of −20 ° C. or lower contributes to the durability of the golf ball 2 at a low temperature. In this respect, the embrittlement temperature is more preferably −30 ° C. or less, and particularly preferably −50 ° C. or less. The embrittlement temperature is measured according to the provisions of “JIS K 7216”.

  Specific examples of the highly elastic polyamide resin (A) include Mitsubishi Engineering's trade names “Novamid ST220”, “Novamid 1010C2” and “Novamid ST145”; Arkema's trade name “Pebax 7233SA”; Ube Industries, Ltd. trade name “UBE Nylon 1018I” and “UBE Nylon 1030J”; DuPont's trade names “Zeitel FN716” and “Zeitel ST811HS”; Toray Industries' trade names “Amilan U441”, “Amilan U328” and “Amilan U141” and Asahi Kasei The brand name “Leona 1300S” can be mentioned.

  The content of the polyamide resin (A) in the resin composition of the cover 8 is preferably 5% by mass or more and 80% by mass or less. An outer-hard / inner-soft structure can be achieved by the cover 8 having a content of 5% by mass or more. In this respect, the content is more preferably equal to or greater than 13% by mass, and particularly preferably equal to or greater than 15% by mass. The cover 8 having the content of 80% by mass or less does not hinder the durability and feel at impact of the golf ball 2. In this respect, the content is more preferably equal to or less than 75% by weight, and particularly preferably equal to or less than 70% by weight.

  The ethylene- (meth) acrylic acid copolymer (B) neutralized with metal ions contributes to the resilience performance of the golf ball 2. Furthermore, this copolymer (B) also contributes to the fluidity of the resin composition of the cover 8. This cover 8 can be easily molded.

  This copolymer (B) is obtained by a copolymerization reaction of a monomer composition containing ethylene and (meth) acrylic acid. In this specification, the term “(meth) acrylic acid” means acrylic acid and / or methacrylic acid. The copolymer (B) may be obtained by a multi-component copolymerization reaction of ethylene, (meth) acrylic acid and other monomers. Other monomers include vinyl esters such as vinyl acetate and vinyl propionate; methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, (meth ) Unsaturated carboxylic esters such as n-butyl acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dimethyl maleate and diethyl maleate; carbon monoxide and sulfur dioxide are exemplified . Typical copolymers are ethylene- (meth) acrylic acid binary copolymers and ethylene- (meth) acrylic acid- (meth) acrylic acid ester terpolymers. Two or more copolymers may be used in combination.

  The amount of the (meth) acrylic acid component in the copolymer (B) is preferably 2% by mass or more, particularly preferably 3% by mass or more. This amount is preferably 30% by mass or less, and particularly preferably 25% by mass or less.

  In this copolymer (B), some of the carboxyl groups are neutralized with metal ions. Neutralization includes monovalent metal ions such as sodium ion, potassium ion and lithium ion; divalent metal ions such as magnesium ion, calcium ion, zinc ion, barium ion and cadmium ion, and aluminum ion. Trivalent metal ions can be used. From the viewpoint of resilience performance and durability of the golf ball 2, sodium ion, zinc ion and magnesium ion are preferable.

  The degree of neutralization of the carboxyl group in this copolymer (B) is preferably at least 20 mol%, particularly preferably at least 30 mol%. The degree of neutralization is preferably 90 mol% or less, and particularly preferably 85 mol% or less. The degree of neutralization is the ratio of the number of moles of neutralized carboxyl groups to the total number of moles of carboxyl groups.

  The flexural modulus of this copolymer (B) is preferably 250 MPa or more and 1000 MPa or less. High rigidity of the cover 8 is achieved by the copolymer (B) having a flexural modulus of 250 MPa or more. This cover 8 can suppress spin on driver shots. In this respect, the flexural modulus is preferably 260 MPa or more, and particularly preferably 270 MPa or more. The copolymer (B) having a flexural modulus of 1000 MPa or less does not impair the feel at impact and durability of the golf ball 2. In this respect, the flexural modulus is preferably 800 MPa or less, and particularly preferably 600 MPa or less.

  As specific examples of this copolymer (B), trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN 1856” of Mitsui Dupont Polychemical Co., Ltd. "High Milan 1855", "High Milan AM 7311", "High Milan AM 7315", "High Milan AM 7317", "High Milan AM 7318", "High Milan MK 7320" and "High Milan MK 7329"; DuPont's trade names "Surlin 6120" and "Surlin 6320" , "Surlin 6910", "Surlin 7930", "Surlin 7940", "Surlin 8140", "Surlin 8150", "Surlin 8940", "Surlin 8945", "Surlin 9120", “Surlin 9910”, “Surlin 9945”, “Surlin AD8546”, “HPF1000” and “HPF2000”; And “IOTEK8030”. Two or more kinds of resins may be used in combination.

  As for the content rate of the copolymer (B) in the resin composition of the cover 8, 15 mass% or more and 90 mass% or less are preferable. The cover 8 having the content of 15% by mass or more can contribute to the resilience performance and durability of the golf ball 2. In this respect, the content is more preferably equal to or greater than 20% by weight, and particularly preferably equal to or greater than 25% by weight. An outer-hard / inner-soft structure can be achieved by the cover 8 having a content of 90% by mass or less. In this respect, the content is more preferably equal to or less than 80% by weight, and particularly preferably equal to or less than 70% by weight.

  The mass ratio of the polyamide resin (A) and the copolymer (B) in the resin composition of the cover 8 is preferably 5/95 or more and 80/20 or less. An outer-hard / inner-soft structure can be achieved by the resin composition having a mass ratio of 5/95 or more. In this respect, the mass ratio is more preferably 10/90 or more and particularly preferably 20/80 or more. The cover 8 having a mass ratio of 80/20 or less can contribute to the resilience performance of the golf ball 2. In this respect, the mass ratio is more preferably equal to or less than 75/25, and particularly preferably equal to or less than 70/30.

  The resin (C) having a polar functional group can be obtained by a copolymerization reaction between a monomer having a polar functional group and a monomer having no polar functional group. The polar functional group is excellent in affinity with the copolymer (B). On the other hand, portions other than the polar functional group of the resin (C) are excellent in affinity with the polyamide resin (A). When the resin composition contains the resin (C), the polyamide resin (A) and the copolymer (B) are dispersed. The strength of the cover 8 including this resin (C) is high. This resin (C) contributes to the durability of the golf ball 2.

  Examples of polar functional groups include epoxy groups, hydroxyl groups, amino groups, nitro groups, carboxyl groups, formyl groups, nitrile groups, and sulfonic acid groups. In particular, an epoxy group and a carboxyl group are preferable. Examples of the monomer having a polar functional group include epoxy group-containing monomers such as glycidyl (meth) acrylate, 2-vinyloxirane and (allyloxy) oxirane; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl ( Hydroxyl-containing monomers such as (meth) acrylate, vinyl alcohol, allyl alcohol and 2-hydroxyethyl vinyl ether; sulfonic acid group-containing monomers such as vinyl sulfonic acid; and (meth) acrylic acid, itaconic acid and maleic anhydride Examples thereof include carboxyl group-containing monomers such as acids. Two or more monomers may be used in combination.

  Epoxy group-containing monomers are preferred. In the composition using the resin (C) composed of this monomer, the epoxy group of the resin (C) reacts with the carboxyl group of the copolymer (B). Glycidyl (meth) acrylate is particularly preferred.

  Examples of the monomer having no polar functional group include olefins such as ethylene, propylene, 1-butene, isobutene and 1-pentene; and methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate. And alkyl (meth) acrylates such as n-butyl (meth) acrylate and isobutyl (meth) acrylate. Two or more monomers may be used in combination. Ethylene and methyl (meth) acrylate are preferred.

  As for the content rate of the monomer component which has a polar functional group in the said resin (C), 0.1 mass% or more is preferable. In the resin composition having this content of 0.1% by mass or more, the polyamide resin (A) and the copolymer (B) are sufficiently dispersed. In this respect, the content is more preferably equal to or greater than 0.5% by weight, and particularly preferably equal to or greater than 1% by weight. The content is preferably 30% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

  Examples of the resin (C) having a polar functional group include (meth) acrylic acid ester-glycidyl (meth) acrylate copolymer, epoxy group-containing (meth) acrylic polymer, ethylene-glycidyl (meth) acrylate copolymer, ethylene -(Meth) acrylic acid copolymer, ethylene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, ethylene- (meth) acrylic acid ester-glycidyl (meth) acrylate copolymer, maleic acid modified styrene -Ethylene-butylene-styrene block polymer (SEBS), maleic acid modified styrene-ethylene-butylene-olefin crystal block polymer (SEBC), maleic acid modified polyethylene (PE), maleic acid modified polypropylene (PP), maleic acid modified ethylene- Vinyl acetate copolymer EVA), maleic acid-modified ethylene - propylene - diene copolymer (EPDM) and an epoxy group-containing styrene polymer is exemplified. Two or more kinds of resins may be used in combination. An ethylene-glycidyl methacrylate copolymer, an ethylene-acrylic acid-glycidyl methacrylate copolymer and a methyl methacrylate-glycidyl methacrylate copolymer are particularly preferred.

  Specific examples of the resin (C) include a trade name “LOTADER AX8840” from Arkema; a trade name “ARUFON UG-4030” from Toagosei; a trade name “Bond Fast E” from Sumitomo Chemical. Asahi Kasei's trade names “Tuftec M1913” and “Toughtech M1943”; DuPont's trade name “FUSABOND NM052D”; JSR's trade name “Dynalon 4630P”; and Mitsui DuPont's trade name “NUCREL” ) AN4214C "," Nucleer AN4225C "," Nucleer AN42115C "," Nucleer N0903HC "," Nucleer N0908C "," Nucleer AN42012C "," Nucleer N410 "," Nucerer N1035 "," Nucleer N “050H”, “Nucleer N1108C”, “Nucleer N1110H”, “Nucleer N1207C”, “Nucleer N1214”, “Nucleer AN4221C”, “Nucleer N1525”, “Nucerer N1560”, “Nucleer N0200H”, “Nucleer AN4228C”, “Nucleer” N4213C "and" Nucleel N035C "are exemplified.

  The amount of the resin (C) having a polar functional group is 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass in total of the polyamide resin (A) and the copolymer (B). In the resin composition having this amount of 0.1 parts by mass or more, the polyamide resin (A) and the copolymer (B) are dispersed. In this respect, the amount is more preferably equal to or greater than 2 parts by weight. The resin composition whose amount is 20 parts by mass or less is excellent in moldability. In this respect, the amount is more preferably equal to or less than 15 parts by weight, and particularly preferably equal to or less than 10 parts by weight.

  The resin composition of the cover 8 may contain a small amount of a resin other than the polyamide resin (A), the copolymer (B), and the resin (C) having a polar functional group. This resin composition may contain an appropriate amount of a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersing agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent brightening agent. Good. The resin composition may include a powder made of a high specific gravity metal. Specific examples of the high specific gravity metal include tungsten and molybdenum.

  This resin composition is obtained by mixing the polyamide resin (A), the copolymer (B), the resin (C) and the additive with an extruder. The cover 8 is molded from this resin composition by a known method such as an injection molding method or a compression molding method. The resin composition may be obtained by dry blending the pellet containing the copolymer (B) and the additive and the pellet containing the polyamide resin (A) and the resin (C).

  The cover 8 has a hardness H6 of preferably 65 or greater and 75 or less. An outer-hard / inner-soft structure is achieved by the cover 8 having a hardness H6 of 65 or more. In this respect, the hardness H6 is more preferably equal to or greater than 66, and particularly preferably equal to or greater than 67. The cover 8 having a hardness H6 of 75 or less does not hinder the shot feel and durability of the golf ball 2. In this respect, the hardness H6 is more preferably equal to or less than 73, and particularly preferably equal to or less than 71.

  The hardness H6 is measured by a Shore D type hardness meter attached to an automatic rubber hardness measuring device (trade name “P1” of Kobunshi Keiki Co., Ltd.) in accordance with the provisions of “ASTM-D 2240-68”. For the measurement, a slab having a thickness of about 2 mm formed by hot pressing is used. A slab stored for 2 weeks at a temperature of 23 ° C. is used for the measurement. At the time of measurement, three slabs are overlaid. A slab made of the same resin composition as that of the cover 8 is used for the measurement.

  The bending elastic modulus of the cover 8 is preferably 300 MPa or more and 1000 MPa or less. An outer-hard / inner-soft structure is achieved by the cover 8 having a flexural modulus of 300 MPa or more. In this respect, the flexural modulus is more preferably 320 MPa or more, and particularly preferably 350 MPa or more. The cover 8 having a flexural modulus of 1000 MPa or less is excellent in moldability. Further, the cover 8 having a flexural modulus of 1000 MPa or less does not hinder the shot feel and durability of the golf ball 2. In this respect, the flexural modulus is more preferably 900 MPa or less, and particularly preferably 800 MPa or less. The bending elastic modulus of the cover 8 is measured by the same method as that for measuring the bending elastic modulus of the polyamide resin (A) described above. For the measurement, a test piece made of the same resin composition as that of the cover 8 is used.

  The tensile elastic modulus of the cover 8 is preferably 400 MPa or more and 1500 MPa or less. An outer-hard / inner-soft structure is achieved by the cover 8 having a tensile modulus of 400 MPa or more. In this respect, the tensile elastic modulus is more preferably 410 MPa or more, and particularly preferably 420 MPa or more. The cover 8 having a tensile elastic modulus of 1500 MPa or less does not impair the feel at impact and durability of the golf ball 2. In this respect, the tensile elastic modulus is more preferably 1400 MPa or less, and particularly preferably 1300 MPa or less.

  The tensile elastic modulus is measured in accordance with ISO 178. Prior to measurement, a sheet made of the same resin composition as the resin composition of the cover 8 is molded by an injection molding method. The thickness of this sheet is 2 mm. A dumbbell-shaped test piece is punched from a sheet stored at a temperature of 23 ° C. for 2 weeks. This test piece is used for measurement.

  The thickness of the cover 8 is preferably 0.3 mm or greater and 3.0 mm or less. The cover 8 having a thickness of 0.3 mm or more suppresses spin on driver shots. In this respect, the thickness is more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.7 mm. The cover 8 having a thickness of 3.0 mm or less does not impair the feel at impact. In this respect, the thickness is more preferably equal to or less than 2.0 mm, and particularly preferably equal to or less than 1.3 mm.

  For forming the cover 8, a known method such as an injection molding method or a compression molding method may be employed. When the cover 8 is molded, dimples 14 are formed by a large number of pimples formed on the cavity surface of the mold.

  The shore D hardness H6 of the cover 8 is larger than the shore D hardness H5 of the mid layer 6. In the golf ball 2, the spin is suppressed by the outer-hard / inner-soft structure, and an excellent shot feeling is obtained by the mid layer 6. From these viewpoints, the difference (H6-H5) between the hardness H6 and the hardness H5 is preferably 10 or more, more preferably 15 or more, and particularly preferably 20 or more. The difference (H6-H5) is preferably 40 or less.

  In light of feel at impact, the golf ball 2 has an amount of compressive deformation D4 of preferably 2.0 mm or greater, more preferably 2.1 mm or greater, and particularly preferably 2.2 mm or greater. In light of resilience performance, the amount of compressive deformation D4 is preferably equal to or less than 3.7 mm, more preferably equal to or less than 3.6 mm, and particularly preferably equal to or less than 3.5 mm.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by weight of high-cis polybutadiene (trade name “BR-730” from JSR), 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 10 parts by weight of silica (trade name “Nipsil AQ” from Tosoh Silica), 2.20 parts by weight of a sulfenamide-based vulcanization accelerator (previously “Noxeller CZ”), 2.26 parts by weight of a guanidine-based vulcanization accelerator (previously “Soxinol DG”) and 3.4 parts by weight Sulfur was kneaded to obtain a rubber composition (a), which was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity, and 5 ° C. at a temperature of 150 ° C. A center with a diameter of 10 mm was obtained by heating for a minute.

  100 parts by weight of high cis polybutadiene (previously referred to as “BR-730”), 29 parts by weight of zinc acrylate, 5 parts by weight of zinc oxide, appropriate amount of barium sulfate, 0.5 parts by weight of bis (pentabromophenyl) disulfide And 0.7 parts by mass of dicumyl peroxide (Nippon Yushi Co., Ltd.) were kneaded to obtain a rubber composition (f). A half shell was molded from this rubber composition (f). The center was covered with two half shells. The center and the half shell are both put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at a temperature of 170 ° C. for 20 minutes to obtain an envelope layer having a thickness of 14.4 mm. It was. The amount of barium sulfate was adjusted so that the specific gravity of the envelope layer coincided with the specific gravity of the center and the ball mass was 45.6 g.

  35 parts by weight of sodium-neutralized ionomer resin (previously “Surline 8945”), 34 parts by weight of zinc-neutralized ionomer resin (previously “Himilan AM7329”), 31 parts by weight of styrene block-containing thermoplastic elastomer (previously “previously“ Lavalon T3221C ") and 3 parts by mass of titanium dioxide were kneaded with a twin-screw kneading extruder to obtain a resin composition (B). The core was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity. The resin composition (B) was injected around the core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.0 mm.

  30 parts by mass of highly elastic polyamide (previously “Novamid ST220”), 30 parts by mass of sodium neutralized ionomer resin (ethylene- (meth) acrylic acid copolymer, “Surlin 8945” above), 40 parts by mass of zinc A neutralized ionomer resin (ethylene- (meth) acrylic acid copolymer, the above-mentioned “Himilan AM7329”), 5 parts by mass of a resin having a polar functional group (the above-mentioned “Rotada AX8840”) and 3 parts by mass of titanium dioxide. The resin composition (1) was obtained by kneading with a biaxial kneading extruder. A sphere including an intermediate layer was put into a final mold which was composed of an upper mold and a lower mold each having a hemispherical cavity, and had many pimples on the cavity surface. The resin composition (1) was injected around this sphere by an injection molding method to mold a cover. The thickness of this cover was 1.0 mm. A large number of dimples having a reversed pimple shape were formed on the cover. A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of 42.8 mm and a mass of 45.6 g.

[Examples 2 to 11 and Comparative Examples 1 to 10]
Golf balls of Examples 2 to 11 and Comparative Examples 1 to 10 are obtained in the same manner as in Example 1 except that the specifications of the center, envelope layer, intermediate layer and cover are as shown in Tables 4 to 8 below. It was. Details of the rubber composition of the center and envelope layer are shown in Table 1 below. Details of the resin composition of the intermediate layer are shown in Table 2 below. Details of the resin composition of the cover are shown in Table 3 below. The golf ball according to Comparative Example 1 does not have an envelope layer.

[Shot with driver (W # 1)]
A driver equipped with a titanium head (trade name “XXIO”, manufactured by SRI Sports, shaft hardness: R, loft angle: 11.0 °) was mounted on a golf laboratory swing machine. A golf ball was hit under the condition where the head speed was 40 m / sec, and the distance from the launch point to the rest point was measured. Furthermore, the ball speed and backspin speed immediately after hitting were also measured. The average values of the data obtained by 12 measurements are shown in Tables 4 to 8 below.

[durability]
A driver with a titanium head was attached to a swing machine from Golf Laboratory. A golf ball was hit under the condition that the head speed was 45 m / sec. The golf ball was hit repeatedly until it was damaged, and the number of times was counted. The average value of the data obtained by measuring 6 times is shown as an index in Tables 4 to 8 below. In addition, when the core or the intermediate layer was damaged without breaking the cover, this was recognized by the hitting sound or the shape of the golf ball.

  As shown in Tables 4 to 8, the golf ball of each example is excellent in flight performance and durability. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention can be used for playing on a golf course or practice in a driving range.

FIG. 1 is a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention.

Explanation of symbols

2 ... Golf ball 4 ... Core 6 ... Intermediate layer 8 ... Cover 10 ... Center 12 ... Enveloping layer 14 ... Dimple

Claims (11)

A core and a cover located outside the core;
The core has a center and an envelope layer located outside the center;
The center has a diameter of 1 mm to 15 mm,
In the center, JIS-C hardness H1 of the center point is 20 or more and 50 or less,
The difference (H4-H3) between the JIS-C hardness H4 of the surface of the core and the JIS-C hardness H3 of the innermost part of the envelope layer is 10 or more,
The bending elastic modulus of the cover is 300 MPa or more and 1000 MPa or less,
The tensile modulus of elasticity of the cover is Ri der more than 1500MPa below 400MPa,
The cover is made of a resin composition, and the resin composition is
(A) a highly elastic polyamide resin having a flexural modulus of 700 MPa to 5000 MPa,
(B) Ethylene- (meth) acrylic acid copolymer neutralized with metal ions
as well as
(C) Resin having a polar functional group
Including
The mass ratio of the polyamide resin (A) and the copolymer (B) is 5/95 or more and 80/20 or less,
The total amount 100 parts by mass of the polyamide resin (A) and the copolymer (B), and amount of, der Ru golf ball 20 parts by mass or less than 0.1 part by weight of the resin (C).   The golf ball according to claim 1, wherein the cover has a Shore D hardness H6 of 65 or more and 75 or less. The polyamide resin (A) is selected from the group consisting of polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide 612 and polyether block amide copolymer. The golf ball according to claim 1 , comprising 1 or 2 or more. The copolymer (B) is an ethylene - (meth) acrylic acid binary copolymer and / or ethylene - (meth) acrylic acid - (meth) claims 1-3 comprising acrylic acid ester terpolymer The golf ball according to any one of the above. The resin (C) is an ethylene - glycidyl methacrylate copolymer, ethylene - acrylic acid - glycidyl methacrylate copolymer and methyl methacrylate - claim 1 comprising one or more selected from the group consisting of glycidyl methacrylate copolymer 5. The golf ball according to any one of 4 to 4 . An intermediate layer located between the core and the cover;
6. The golf ball according to claim 1, wherein the hardness H6 is greater than the Shore D hardness H5 of the intermediate layer. The golf ball according to claim 1, wherein the intermediate layer is made of a thermoplastic resin composition. The golf ball according to claim 1 , wherein a difference (H3−H2) between the hardness H3 and a JIS-C hardness H2 of the center surface is 35 or less. The golf ball according to claim 1 , wherein a difference (H4−H1) between the hardness H4 and the hardness H1 is 40 or more. The center is formed by crosslinking the rubber composition,
The main component of the base rubber of this rubber composition is polybutadiene,
The golf ball according to claim 1 , wherein the rubber composition contains sulfur as a crosslinking agent. The envelope layer is formed by crosslinking the rubber composition,
The golf ball according to claim 1 , wherein the main component of the base rubber of the rubber composition is polybutadiene.

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