Multi-piece solid golf ball

Abstract

In a multi-piece solid golf ball having a core with a two-layer construction consisting of an inner layer and an outer layer and having also, over the core, a cover of two or more layers that includes an intermediate layer and an outermost layer, the core inner layer is formed primarily of a specific thermoplastic elastomer, the core outer layer is formed of a rubber material, and both the hardness relationship between the core inner layer and the core outer layer and the hardness relationship between the intermediate layer and the outermost layer are optimized. This golf ball allows even amateur golfers who do not have a high head speed to impart sufficient deformation to the ball and thus achieve an excellent flight performance and a comfortable feel at impact, and also has an excellent durability.

1 . A multi-piece solid golf ball comprising:
 a core having a two-layer construction consisting of an inner layer and an outer layer, and   a cover of two or more layers which is formed over the core and includes one or more intermediate layer and an outermost layer,   
       wherein the core inner layer is formed primarily of one or more type of thermoplastic elastomer selected from the group consisting of polyester, polyamide, polyurethane, olefin and styrene-type thermoplastic elastomers, and has a material hardness, expressed in terms of Shore D hardness, of from 10 to 55;
 the core outer layer is formed of a rubber composition consisting primarily of a rubber material, and has a surface hardness, expressed in terms of Shore D hardness, of from 50 to 66; and 
 the intermediate layer and the outermost layer have surface hardnesses (Shore D hardnesses) which satisfy the following condition:
   intermediate layer surface hardness<outermost layer surface hardness. 
 
 
     
     
         2 . The golf ball of  claim 1 , wherein the core inner layer is formed primarily of a polyether ester elastomer. 
     
     
         3 . The golf ball of  claim 1 , wherein the core inner layer has a diameter of from 10 to 30 mm and the overall core has a diameter of from 30 to 40 mm. 
     
     
         4 . The golf ball of  claim 1 , wherein the intermediate layer is formed of a resin composition comprising:
 100 parts by weight of a resin component composed of, in admixture,
 (a) a base resin of (a-1) an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer mixed with (a-2) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer in a weight ratio between 100:0 and 0:100, and 
 (b) a non-ionomeric thermoplastic elastomer 
   in a weight ratio between 100:0 and 50:50;
 (c) from 5 to 120 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of from 228 to 1500; and 
 (d) from 0.1 to 17 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in components (a) and (c). 
   
     
     
         5 . The golf ball of  claim 1 , wherein the outermost layer is formed of a material which is composed primarily of an ionomer and contains a granular inorganic filler. 
     
     
         6 . The golf ball of  claim 1 , wherein the core, intermediate layer and outermost layer have hardnesses (Shore D hardnesses) which satisfy the following conditions:
   intermediate layer surface hardness<outermost layer surface hardness, and     core inner layer center hardness<core inner layer surface hardness<core outer layer surface hardness.   
     
     
         7 . The golf ball of  claim 1 , wherein the core and the intermediate layer have thicknesses which satisfy the following condition:
   core inner layer radius>core outer layer thickness>intermediate layer thickness.   
     
     
         8 . The golf ball of  claim 1 , wherein the core having a two-layer construction consisting of an inner layer and an outer layer has formed over the periphery thereof a cover having a three-layer construction consisting of an envelope layer encasing the core, an intermediate layer encasing the envelope layer, and an outermost layer encasing the intermediate layer. 
     
     
         9 . The golf ball of  claim 8 , wherein the envelope layer is formed primarily of a polyether ester elastomer. 
     
     
         10 . The golf ball of  claim 8 , wherein the core, envelope layer, intermediate layer and outermost layer have hardnesses (Shore D hardnesses) which satisfy the following conditions:
   envelope layer surface hardness<intermediate layer surface hardness<outermost layer surface hardness, and     core inner layer center hardness<core inner layer surface hardness<core outer layer surface hardness.   
     
     
         11 . The golf ball of  claim 8 , wherein the core inner layer and the envelope layer have material hardnesses (Shore D hardnesses) which satisfy the following condition:
   −15≦(envelope layer material hardness−core inner layer material hardness)≦35.