Multi-piece solid golf ball

Abstract

In a golf ball having a core, a cover and an intermediate layer therebetween, the ball and a sphere consisting of the core encased by the intermediate layer have surface hardnesses which satisfy a specific relationship, the intermediate layer and the cover have thicknesses which satisfy a specific relationship, and the core has a hardness profile in which the hardnesses at the core center, at positions 5 mm, 10 mm and 15 mm from the core center and at the core surface satisfy specific relationships. This ball, when played by mid- and high-level amateur golfers, achieves a good distance on driver shots, has a soft feel at impact and maintains the spin performance at a high level on approach shots.

1 . A multi-piece solid golf comprising a core, a cover and an intermediate layer therebetween, wherein a sphere comprising the core and the intermediate layer which peripherally encases the core (intermediate layer-encased sphere) and the ball have respective surface hardnesses, expressed in terms of Shore D hardness, which satisfy the relationship:
 surface hardness of ball≦surface hardness of intermediate layer-encased sphere;   
       the intermediate layer and the cover have respective thicknesses which satisfy the relationship:
 cover thickness≦intermediate layer thickness; and 
 
       the core has a hardness profile which, expressed in terms of JIS-C hardness, satisfies conditions (1) to (6) below, wherein Cc is the JIS-C hardness at a center of the core, C5 is the JIS-C hardness at a position 5 mm from the core center, C10 is the JIS-C hardness at a position 10 mm from the core center, C15 is the JIS-C hardness at a position 15 mm from the core center, and Cs is the JIS-C hardness at a surface of the core:
   20≦Cs−Cc,  (1)
 
   0< C 10−Cc≦10,  (2)
 
     C 10−Cc<Cs− C 10,  (3)
 
   15<Cs− C 10,  (4)
 
   Cs≧80,  (5)
 
   and 
   Cc≧52.  (6)
 
 
     
     
         2 . The golf ball of  claim 1  which further satisfies condition (3′) below:
   (Cs− C 10)/( C 10−Cc)≧3.  (3′)
 
 
     
     
         3 . The golf ball of  claim 1  which further satisfies condition (1′) below:
   26≦Cs−Cc.  (1′)
 
 
     
     
         4 . The golf ball of  claim 1  which further satisfies condition (7) below:
   ( C 10− C 5)≦( C 5− C 0)≦(Cs− C 15)≦( C 15− C 10).  (7)
 
 
     
     
         5 . The golf ball of  claim 1 , wherein the core is formed of a material molded under heat from a rubber composition comprising:
 (A) a base rubber,   (B) an organic peroxide, and   (C) water or a metal monocarboxylate or both.   
     
     
         6 . The golf ball of  claim 1  wherein, letting tan δ 1  be the loss tangent at a dynamic strain of 1% and tan δ 10  the loss tangent at a dynamic strain of 10% when the loss tangents of the core center and the core surface are measured at a temperature of −12° C. and a frequency of 15 Hz, and defining the tan δ slope as (tan δ 10 −tan δ 1 )/(10%−1%), the difference between the tan δ slope at the core surface and the tan δ slope at the core center is larger than 0.002. 
     
     
         7 . The golf ball of  claim 1  which satisfies the condition V 0 −V 60 <0.7, where V 0  is the initial velocity of the core in the golf ball after the intermediate layer and cover, collectively referred to as “the core-covering layers,” have been molded, as measured after peeling away the core-covering layers, and V 60  the core initial velocity measured 60 days after measuring V 0 . 
     
     
         8 . The golf ball of  claim 1 , wherein the intermediate layer is formed of a resin composition comprising: 
       a combined amount of 100 parts by weight of the following two base resins (I) and (II):
 (I) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terpolymer, or a metal neutralization product thereof, having a weight-average molecular weight (Mw) of at least 140,000, an acid content of 10 to 15 wt % and an ester content of at least 15 wt %, and 
 (II) an olefin-acrylic acid random copolymer, or a metal neutralization product thereof, having a weight-average molecular weight (Mw) of at least 140,000 and an acid content of 10 to 15 wt % 
 blended in a weight ratio (I):(II) of from 90:10 to 10:90; 
 (III) from 1.0 to 2.5 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in the resin composition; and 
 (IV) from 1 to 100 parts by weight of an anionic surfactant having a molecular weight of from 140 to 1500, 
 
       and wherein the component (I) and (II) resins each have a melt flow rate of 0.5 to 20 g/10 min, component (I) and component (II) have a melt flow rate difference therebetween of not more than 15 g/10 min, the composition comprising components (I) to (IV) has a melt flow rate of at least 1.0 g/10 min, and a molded material obtained by molding the composition under applied heat has a Shore D hardness of 35 to 60. 
     
     
         9 . The golf ball of  claim 1  wherein, when the core surface is photographed with a camera and image data collected by the camera is image processed in such manner as to identify and digitize scratches appearing on the core surface, the number of digitized scratches is 100 or more.