Golf ball

Abstract

A golf ball 2 includes a core 4 , a mid layer 6 , a reinforcing layer 8 , an inner cover 10 , and an outer cover 12 . The core 4 includes a center 18 and an envelope layer 20 . The envelope layer 20 is formed by a rubber composition being crosslinked. The rubber composition includes a base rubber, a co-crosslinking agent, a crosslinking initiator, and an acid and/or a salt. The co-crosslinking agent is (1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or (2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A hardness Hc1 of the inner cover is greater than a hardness Hc2 of the outer cover. A thickness T1 of the inner cover is equal to or greater than 0.1 mm but equal to or less than 0.8 mm.

What is claimed is: 
     
         1 . A golf ball comprising a core, amid layer positioned outside the core, an inner cover positioned outside the mid layer, and an outer cover positioned outside the inner cover, wherein
 the core comprises a center and an envelope layer positioned outside the center,   the envelope layer is formed by a rubber composition being crosslinked,   the rubber composition includes:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) an acid and/or a salt, 
   the co-crosslinking agent (b) is:
 (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, 
   a Shore D hardness Hc1 of the inner cover is greater than a Shore D hardness Hc2 of the outer cover, and   a thickness T1 of the inner cover is equal to or greater than 0.1 mm but equal to or less than 0.8 mm.   
     
     
         2 . The golf ball according to  claim 1 , wherein an amount of the acid and/or the salt (d) is equal to or greater than 0.5 parts by weight but equal to or less than 45 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         3 . The golf ball according to  claim 1 , wherein the acid and/or the salt (d) is a carboxylic acid and/or a salt thereof (d1). 
     
     
         4 . The golf ball according to  claim 3 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d1) is equal to or greater than 1 but equal to or less than 30. 
     
     
         5 . The golf ball according to  claim 3 , wherein the carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or a salt thereof. 
     
     
         6 . The golf ball according to  claim 1 , wherein
 a JIS-C hardness H(0) at a central point of the core is equal to or greater than 40 but equal to or less than 70, and   a JIS-C hardness H(100) at a surface of the core is equal to or greater than 78 but equal to or less than 96.   
     
     
         7 . The golf ball according to  claim 6 , wherein a difference (H(100)−H(0)) between the hardness H(100) and the hardness H(0) is equal to or greater than 15. 
     
     
         8 . The golf ball according to  claim 1 , wherein a Shore D hardness Hm of the mid layer is greater than the hardness Hc1. 
     
     
         9 . The golf ball according to  claim 8 , wherein a difference (Hm−Hc1) between the hardness Hm and the hardness Hc1 is equal to or greater than 15. 
     
     
         10 . The golf ball according to  claim 1 , wherein a Shore D hardness Hm of the mid layer is greater than the hardness Hc2. 
     
     
         11 . The golf ball according to  claim 10 , wherein a difference (Hm−Hc2) between the hardness Hm and the hardness Hc2 is equal to or greater than 20. 
     
     
         12 . The golf ball according to  claim 1 , wherein a difference (Hc1−Hc2) between the hardness Hc1 and the hardness Hc2 is equal to or greater than 5. 
     
     
         13 . The golf ball according to  claim 1 , wherein a thickness Tm of the mid layer is equal to or greater than 0.5 mm but equal to or less than 1.6 mm. 
     
     
         14 . The golf ball according to  claim 1 , wherein a thickness T2 of the outer cover is equal to or greater than 0.1 mm but equal to or less than 0.8 mm. 
     
     
         15 . The golf ball according to  claim 1 , wherein a difference (T1−T2) between the thickness T1 and a thickness T2 of the outer cover is equal to or greater than −0.4 mm but equal to or less than 0.4 mm. 
     
     
         16 . The golf ball according to  claim 1 , wherein a sum (T1+T2) of the thickness T1 and a thickness T2 of the outer cover is equal to or less than 1.0 mm. 
     
     
         17 . The golf ball according to  claim 1 , wherein the rubber composition further includes an organic sulfur compound (e). 
     
     
         18 . The golf ball according to  claim 17 , wherein the organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof. 
     
     
         19 . The golf ball according to  claim 17 , wherein the rubber composition includes 0.05 parts by weight or greater but 5.0 parts by weight or less of the organic sulfur compound (e) per 100 parts by weight of the base rubber (a). 
     
     
         20 . The golf ball according to  claim 1 , wherein
 the rubber composition includes the α,β-unsaturated carboxylic acid (b1), and   the rubber composition further includes a metal compound (f).   
     
     
         21 . The golf ball according to  claim 1 , wherein
 the mid layer is formed from a resin composition,   the inner cover is formed from a resin composition whose base resin is different from a base resin of the mid layer, and   the golf ball further comprises a reinforcing layer between the mid layer and the inner cover.   
     
     
         22 . The golf ball according to  claim 1 , wherein a diameter of the center is equal to or greater than 10 mm but equal to or less than 20 mm. 
     
     
         23 . The golf ball according to  claim 1 , wherein the acid and/or the salt (d) is a zinc salt of a carboxylic acid. 
     
     
         24 . The golf ball according to  claim 23 , wherein the zinc salt of the carboxylic acid is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. 
     
     
         25 . A golf ball comprising a core, amid layer positioned outside the core, an inner cover positioned outside the mid layer, and an outer cover positioned outside the inner cover, wherein
 the core comprises a center and an envelope layer positioned outside the center,   the envelope layer is formed by a rubber composition being crosslinked,   the rubber composition includes:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) an acid and/or a salt, 
   the co-crosslinking agent (b) is:
 (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, 
   a Shore D hardness Hm of the mid layer is greater than a Shore D hardness Hc1 of the inner cover, and   the Shore D hardness Hc1 of the inner cover is less than a Shore D hardness Hc2 of the outer cover.   
     
     
         26 . The golf ball according to  claim 25 , wherein an amount of the acid and/or the salt (d) is equal to or greater than 0.5 parts by weight but equal to or less than 45 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         27 . The golf ball according to  claim 25 , wherein the acid and/or the salt (d) is a carboxylic acid and/or a salt thereof (d1). 
     
     
         28 . The golf ball according to  claim 27 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d1) is equal to or greater than 1 but equal to or less than 30. 
     
     
         29 . The golf ball according to  claim 27 , wherein the carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or a salt thereof. 
     
     
         30 . The golf ball according to  claim 25 , wherein
 a JIS-C hardness H(0) at a central point of the core is equal to or greater than 40 but equal to or less than 70, and   a JIS-C hardness H(100) at a surface of the core is equal to or greater than 78 but equal to or less than 96.   
     
     
         31 . The golf ball according to  claim 30 , wherein a difference (H(100)−H(0)) between the hardness H(100) and the hardness H(0) is equal to or greater than 15. 
     
     
         32 . The golf ball according to  claim 25 , wherein a difference (Hm−Hc1) between the Shore D hardness Hm of the mid layer and the hardness Hc1 of the inner cover is equal to or greater than 20. 
     
     
         33 . The golf ball according to  claim 25 , wherein a difference (Hc2−Hc1) between the hardness Hc2 of the outer cover and the hardness Hc1 of the inner cover is equal to or greater than 5. 
     
     
         34 . The golf ball according to  claim 25 , wherein the hardness Hm is greater than the hardness Hc2. 
     
     
         35 . The golf ball according to  claim 34 , wherein a difference (Hm−Hc2) between the hardness Hm and the hardness Hc2 is equal to or greater than 15. 
     
     
         36 . The golf ball according to  claim 25 , wherein a thickness Tm of the mid layer is equal to or greater than 0.5 mm but equal to or less than 1.6 mm. 
     
     
         37 . The golf ball according to  claim 25 , wherein a thickness T1 of the inner cover is equal to or greater than 0.1 mm but equal to or less than 0.8 mm. 
     
     
         38 . The golf ball according to  claim 25 , wherein a thickness T2 of the outer cover is equal to or greater than 0.1 mm but equal to or less than 0.8 mm. 
     
     
         39 . The golf ball according to  claim 25 , wherein a difference (T1−T2) between a thickness T1 of the inner cover and a thickness T2 of the outer cover is equal to or greater than −0.4 mm but equal to or less than 0.4 mm. 
     
     
         40 . The golf ball according to  claim 25 , wherein a sum (T1+T2) of a thickness T1 of the inner cover and a thickness T2 of the outer cover is equal to or less than 1.0 mm. 
     
     
         41 . The golf ball according to  claim 25 , wherein the rubber composition further includes an organic sulfur compound (e). 
     
     
         42 . The golf ball according to  claim 41 , wherein the organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof. 
     
     
         43 . The golf ball according to  claim 41 , wherein the rubber composition includes 0.05 parts by weight or greater but 5.0 parts by weight or less of the organic sulfur compound (e) per 100 parts by weight of the base rubber (a). 
     
     
         44 . The golf ball according to  claim 25 , wherein
 the rubber composition includes the α,β-unsaturated carboxylic acid (b1), and   the rubber composition further includes a metal compound (f).   
     
     
         45 . The golf ball according to  claim 25 , wherein
 the mid layer is formed from a resin composition,   the inner cover is formed from a resin composition whose base resin is different from a base resin of the mid layer, and   the golf ball further comprises a reinforcing layer between the mid layer and the inner cover.   
     
     
         46 . The golf ball according to  claim 25 , wherein a diameter of the center is equal to or greater than 10 mm but equal to or less than 20 mm. 
     
     
         47 . The golf ball according to  claim 25 , wherein the rubber composition includes 15 parts by weight or greater but 50 parts by weight or less of the co-crosslinking agent (b) per 100 parts by weight of the base rubber (a). 
     
     
         48 . The golf ball according to  claim 25 , wherein the rubber composition includes 0.2 parts by weight or greater but 5.0 parts by weight or less of the crosslinking initiator (c) per 100 parts by weight of the base rubber (a). 
     
     
         49 . The golf ball according to  claim 25 , wherein the acid and/or the salt (d) is a zinc salt of a carboxylic acid. 
     
     
         50 . The golf ball according to  claim 49 , wherein the zinc salt of the carboxylic acid is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. 
     
     
         51 . A golf ball comprising a spherical core, an inner mid layer positioned outside the core, an outer mid layer positioned outside the inner mid layer, and a cover positioned outside the outer mid layer, wherein
 the core comprises a center and an envelope layer positioned outside the center,   when distances (%) from a boundary between the center and the envelope layer to nine points and JIS-C hardnesses at the nine points, which nine points are obtained by dividing a distance from the boundary between the center and the envelope layer to a surface of the core at intervals of 12.5% of the distance, are plotted in a graph, R 2  of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95,   a Shore D hardness Hm1 of the inner mid layer is less than a Shore D hardness Hm2 of the outer mid layer, and   the hardness Hm2 is greater than a Shore D hardness Hc of the cover.   
     
     
         52 . The golf ball according to  claim 51 , wherein
 a JIS-C hardness Ho at a central point of the core is equal to or greater than 40 but equal to or less than 70, and   a JIS-C hardness Hs at the surface of the core is equal to or greater than 80 but equal to or less than 96.   
     
     
         53 . The golf ball according to  claim 51 , wherein
 a JIS-C hardness Hs at the surface of the core is greater than a JIS-C hardness Ho at a central point of the core, and   a difference (Hs−Ho) between the hardness Hs and the hardness Ho is equal to or greater than 20.   
     
     
         54 . The golf ball according to  claim 51 , wherein
 a difference (Hm2−Hm1) between the hardness Hm2 and the hardness Hm1 is equal to or greater than 8, and   a difference (Hm2−Hc) between the hardness Hm2 and the hardness Hc is equal to or greater than 30.   
     
     
         55 . The golf ball according to  claim 51 , wherein
 a sum (Tm1+Tm2) of a thickness Tm1 of the inner mid layer and a thickness Tm2 of the outer mid layer is equal to or greater than 1.0 mm but equal to or less than 3.0 mm, and   a thickness Tc of the cover is equal to or less than 0.8 mm.   
     
     
         56 . The golf ball according to  claim 51 , wherein a diameter of the center is equal to or greater than 10 mm but equal to or less than 25 mm. 
     
     
         57 . The golf ball according to  claim 51 , wherein
 the envelope layer is obtained by a rubber composition being crosslinked,   the rubber composition includes:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) an acid and/or a salt, and 
   the co-crosslinking agent (b) is:
 (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. 
   
     
     
         58 . The golf ball according to  claim 57 , wherein the acid and/or the salt (d) is a carboxylic acid and/or a salt thereof (d1). 
     
     
         59 . The golf ball according to  claim 58 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d1) is equal to or greater than 1 but equal to or less than 30. 
     
     
         60 . The golf ball according to  claim 58 , wherein the carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or a salt thereof. 
     
     
         61 . The golf ball according to  claim 58 , wherein the carboxylic acid and/or the salt thereof (d1) is a zinc salt of a carboxylic acid. 
     
     
         62 . The golf ball according to  claim 58 , wherein the carboxylic acid and/or the salt thereof (d1) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. 
     
     
         63 . The golf ball according to  claim 57 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 1.0 parts by weight or greater but less than 40 parts by weight of the acid and/or the salt (d). 
     
     
         64 . The golf ball according to  claim 57 , wherein
 the rubber composition includes the α,β-unsaturated carboxylic acid (b1), and   the rubber composition further includes a metal compound (f).   
     
     
         65 . The golf ball according to  claim 57 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 15 parts by weight or greater but 50 parts by weight or less of the co-crosslinking agent (b). 
     
     
         66 . The golf ball according to  claim 57 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 0.2 parts by weight or greater but 5 parts by weight or less of the crosslinking initiator (c). 
     
     
         67 . The golf ball according to  claim 57 , wherein the rubber composition includes the metal salt (b2) of the α,β-unsaturated carboxylic acid. 
     
     
         68 . The golf ball according to  claim 51 , wherein
 the outer mid layer is formed from a resin composition,   the cover is formed from another resin composition,   a principal component of a base resin of the resin composition of the outer mid layer is different from a principal component of a base resin of the resin composition of the cover, and   the golf ball further comprises a reinforcing layer between the outer mid layer and the cover.   
     
     
         69 . The golf ball according to  claim 57 , wherein the rubber composition further includes an organic sulfur compound (e). 
     
     
         70 . The golf ball according to  claim 69 , wherein the organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof. 
     
     
         71 . The golf ball according to  claim 69 , wherein the organic sulfur compound (e) is 2-thionaphthol. 
     
     
         72 . The golf ball according to  claim 69 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 0.05 parts by weight or greater but 5.0 parts by weight or less of the organic sulfur compound (e). 
     
     
         73 . A golf ball comprising a spherical core, an inner mid layer positioned outside the core, an outer mid layer positioned outside the inner mid layer, and a cover positioned outside the outer mid layer, wherein
 the core comprises a center and an envelope layer positioned outside the center,   when distances (%) from a boundary between the center and the envelope layer to nine points and JIS-C hardnesses at the nine points, which nine points are obtained by dividing a distance from the boundary between the center and the envelope layer to a surface of the core at intervals of 12.5% of the distance, are plotted in a graph, R 2  of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95,   a Shore D hardness Hm1 of the inner mid layer is greater than a Shore D hardness Hm2 of the outer mid layer,   the hardness Hm1 is greater than a Shore D hardness Hc of the cover, and   a thickness Tm2 of the outer mid layer is equal to or greater than 0.5 mm but equal to or less than 1.5 mm.   
     
     
         74 . The golf ball according to  claim 73 , wherein
 a JIS-C hardness Ho at a central point of the core is equal to or greater than 40 but equal to or less than 70, and   a JIS-C hardness Hs at the surface of the core is equal to or greater than 80 but equal to or less than 96.   
     
     
         75 . The golf ball according to  claim 73 , wherein
 a JIS-C hardness Hs at the surface of the core is greater than a JIS-C hardness Ho at a central point of the core, and   a difference (Hs−Ho) between the hardness Hs and the hardness Ho is equal to or greater than 20.   
     
     
         76 . The golf ball according to  claim 73 , wherein
 a difference (Hm1−Hm2) between the hardness Hm1 and the hardness Hm2 is equal to or greater than 8, and   a difference (Hm1−Hc) between the hardness Hm1 and the hardness Hc is equal to or greater than 30.   
     
     
         77 . The golf ball according to  claim 73 , wherein a sum (Tm1+Tm2) of a thickness Tm1 of the inner mid layer and the thickness Tm2 is equal to or greater than 1.0 mm but equal to or less than 3.0 mm, and
 a thickness Tc of the cover is equal to or less than 0.8 mm.   
     
     
         78 . The golf ball according to  claim 73 , wherein a diameter of the center is equal to or greater than 10 mm but equal to or less than 25 mm. 
     
     
         79 . The golf ball according to  claim 73 , wherein
 the envelope layer is obtained by a rubber composition being crosslinked,   the rubber composition includes:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) an acid and/or a salt, and 
   the co-crosslinking agent (b) is:
 (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. 
   
     
     
         80 . The golf ball according to  claim 79 , wherein the acid and/or the salt (d) is a carboxylic acid and/or a salt thereof (d1). 
     
     
         81 . The golf ball according to  claim 80 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d1) is equal to or greater than 1 but equal to or less than 30. 
     
     
         82 . The golf ball according to  claim 80 , wherein the carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or a salt thereof. 
     
     
         83 . The golf ball according to  claim 80 , wherein the carboxylic acid and/or the salt thereof (d1) is a zinc salt of a carboxylic acid. 
     
     
         84 . The golf ball according to  claim 80 , wherein the carboxylic acid and/or the salt thereof (d1) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. 
     
     
         85 . The golf ball according to  claim 79 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 1.0 parts by weight or greater but 40 parts by weight or less of the acid and/or the salt (d). 
     
     
         86 . The golf ball according to  claim 79 , wherein
 the rubber composition includes the α,β-unsaturated carboxylic acid (b1), and   the rubber composition further includes a metal compound (f).   
     
     
         87 . The golf ball according to  claim 79 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 15 parts by weight or greater but 50 parts by weight or less of the co-crosslinking agent (b). 
     
     
         88 . The golf ball according to  claim 79 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 0.2 parts by weight or greater but 5 parts by weight or less of the crosslinking initiator (c). 
     
     
         89 . The golf ball according to  claim 79 , wherein the rubber composition includes the metal salt (b2) of the α,β-unsaturated carboxylic acid. 
     
     
         90 . The golf ball according to  claim 73 , wherein
 the outer mid layer is formed from a resin composition,   the cover is formed from another resin composition,   a principal component of a base resin of the resin composition of the outer mid layer is different from a principal component of a base resin of the resin composition of the cover, and   the golf ball further comprises a reinforcing layer between the outer mid layer and the cover.   
     
     
         91 . The golf ball according to  claim 79 , wherein the rubber composition further includes an organic sulfur compound (e). 
     
     
         92 . The golf ball according to  claim 91 , wherein the organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof. 
     
     
         93 . The golf ball according to  claim 91 , wherein the organic sulfur compound (e) is 2-thionaphthol. 
     
     
         94 . The golf ball according to  claim 91 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 0.05 parts by weight or greater but 5.0 parts by weight or less of the organic sulfur compound (e).