A golf ball 2 includes a core 4 , a mid layer 6 , a reinforcing layer 8 , and a cover 10 . A hardness Hm of the mid layer 6 is greater than a hardness Hc of the cover 10 . A difference (Hm−Hc) is greater than 28. A hardness Hs2 at a surface of a sphere consisting of the core 4 and the mid layer 6 is greater than a hardness Hs3 at a surface of the golf ball 2 . A difference (Hs2−Hs3) is less than 5. A thickness Tm of the mid layer 6 is larger than a thickness Tc of the cover 10 . A ratio (Tm/Tc) is greater than 3.0 and less than 5.0. A diameter of the core 4 is equal to or greater than 38.2 mm. The hardness Hc of the cover 10 is equal to or less than 37.
1. A golf ball comprising a core, a mid layer positioned outside the core, a reinforcing layer positioned outside the mid layer, and a cover positioned outside the reinforcing layer, wherein
the mid layer material Shore D hardness Hm is greater than the cover material Shore D hardness Hc by an amount greater than 28,
the surface of a sphere including the core and the mid layer has a Shore D hardness Hs2 that is greater than the golf ball surface Shore D hardness Hs3 by an amount less than 5,
the mid layer thickness Tm is larger than the cover thickness Tc, and a ratio (Tm/Tc) of both thicknesses is greater than 3.0 and less than 5.0,
a diameter of the core is equal to or greater than 38.2 mm,
the hardness He is equal to or less than 37,
the reinforcing layer is formed from an adhesive, and
a gel fraction of the adhesive is equal to or greater than 40% but equal to or less than 80%.
2. The golf ball according to claim 1 , wherein an amount of compressive deformation D 1 of the core which is measured under conditions of an initial load of 98 N and a final load of 1274 N is equal to or greater than 3.6 mm, and an amount of compressive deformation D 3 of the golf ball which is measured under the same conditions is equal to or greater than 2.9 mm.
3. The golf ball according to claim 1 , wherein the hardness Hs2 is equal to or greater than 50 but equal to or less than 70.
4. The golf ball according to claim 1 , wherein the hardness Hs3 is equal to or greater than 55 but equal to or less than 70.
5. The golf ball according to claim 1 , wherein
the cover is formed from a resin composition,
a principal component of a base material of the resin composition is a thermoplastic polyurethane, and
a polyol component of the thermoplastic polyurethane is polytetramethylene ether glycol having a number average molecular weight of 1500 or less.
6. The golf ball according to claim 1 , wherein
the core is composed of one or more layers,
any one of these layers 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) a carboxylic acid and/or a salt thereof, 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.
7. The golf ball according to claim 6 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 3 parts by weight or greater but 40 parts by weight or less of the carboxylic acid and/or the salt thereof (d).
8. The golf ball according to claim 6 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d) is equal to or greater than 4 but equal to or less than 30.
9. The golf ball according to claim 6 , wherein the carboxylic acid and/or the salt thereof (d) is a fatty acid and/or a salt thereof.
10. The golf ball according to claim 6 , wherein the carboxylic acid and/or the salt thereof (d) is a zinc salt of a carboxylic acid.
11. The golf ball according to claim 6 , wherein the carboxylic acid and/or the salt thereof (d) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate.