Patent Publication Number: US-6213896-B1

Title: Multi-piece solid golf ball

Description:
This invention relates to a multi-piece solid golf ball comprising at least three layers, a solid core, an intermediate layer, and a cover. 
     BACKGROUND OF THE INVENTION 
     Many two-piece solid golf balls are known in the art. As compared with wound golf balls, solid golf balls have the advantage of an increased total flight distance on both driver and iron shots, because of a so-called straight line trajectory and a low spin receptivity due to their structure, which allows for a long run. On the other hand, the two-piece solid golf balls are more difficult to control than the wound golf balls in that they do not stop short on the green because of low spin receptivity on iron shots. 
     Like flight distance, a soft feel when hit is essential for golf balls. The absence of a soft feel represents a substantial loss of commodity value of the golf ball. As compared with two-piece solid golf balls, wound golf balls have the structural characteristics ensuring a soft and pleasant feel. 
     On two-piece solid golf balls consisting of a core and a cover, attempts have been made to soften the ball structure in order to accomplish a soft feel upon impact. A soft core is often used to obtain such soft-feel two-piece solid golf balls, but making the core softer lowers the resilience of the golf ball, compromises flight performance, and also markedly reduces durability. As a result, not only do these balls lack the excellent flight performance and durability characteristic of ordinary two-piece solid golf balls, but they are often in fact unfit for actual use. 
     Various three-piece solid golf balls having a three-layer construction in which an intermediate layer is situated between a solid core and a cover have been proposed to resolve these problems as disclosed, for example, in JP-A 7-24084, 6-23069, 4-244174, 9-10358, and 9-313643. 
     Golf balls having the cover and the intermediate layer made soft according to these proposals have a soft feel, but a shorter flight distance on full shots with a driver. To insure distance, the cover and the intermediate layer must be formed hard at the sacrifice of the feel upon approach shots and putting. Additionally, the spin performance on iron shots is also exacerbated. None of the prior art proposals succeeded in providing a solid golf ball capable of fully meeting the demand. A further improvement is thus desired. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the invention is to provide a multi-piece solid golf ball comprising at least three layers, a solid core, an intermediate layer, and a cover, which has a very soft pleasant feel upon approach shots and putting, ease of control upon iron shots, and improved flight performance upon full shots with a driver. 
     The invention provides a multi-piece solid golf ball comprising a solid core, an intermediate layer of at least one layer around the core, and a cover of at least one layer around the intermediate layer. (1) When the solid core has a deflection A (mm) under an applied load of 100 kg and a spherical body consisting of the core and the intermediate layer has a deflection B (mm) under an applied load of 100 kg, the value of B/A is from 1.0 to 1.5. (2) The solid core is preferably formed mainly of a rubber base and has a specific gravity of 1.1 to 1.5 and a deflection A of at least 2.5 mm under an applied load of 100 kg. (3) The intermediate layer preferably has a thickness of 0.2 to 5.0 mm and a specific gravity of at least 0.8. (4) The cover is preferably formed of a cover stock composed mainly of a thermoplastic resin and has a thickness of 1.0 to 5.0 mm and a specific gravity of at least 0.9. (5) The specific gravity of the intermediate layer is desirably lower than the specific gravity of the solid core. When all these features are fulfilled, the ball is given a very soft pleasant feel upon approach shots and putting and a high spin receptivity and hence, ease of control upon iron shots, without detracting from the flight distance characteristic of ordinary solid golf balls. Additionally, the ball is improved in durability against consecutive strikes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a multi-piece solid golf ball according to one embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a multi-piece solid golf ball G according to the invention is schematically illustrated as comprising a solid core  1 , an intermediate layer  2  of at least one layer surrounding the core  1 , and a cover  3  of at least one layer surrounding the intermediate layer  2 . 
     The solid core may be formed of a rubber composition primarily comprising a base rubber which is based on polybutadiene rubber, polyisoprene rubber, natural rubber or silicone rubber. Polybutadiene rubber is preferred especially for improved resilience. The preferred polybutadiene rubber is cis-1,4-polybutadiene containing at least 40% cis structure. In the base rubber, another rubber component such as natural rubber, polyisoprene rubber or styrene-butadiene rubber may be blended with the polybutadiene if desired. For high resilience, the other rubber component should preferably be less than about 10 parts by weight per 100 parts by weight of polybutadiene. 
     In the rubber composition, a crosslinking agent may be blended with the rubber component. Exemplary crosslinking agents are zinc and magnesium salts of unsaturated fatty acids such as zinc methacrylate and zinc diacrylate, and esters such as trimethylpropane methacrylate. Of these, zinc diacrylate is preferred because it can impart high resilience. The crosslinking agent is preferably used in an amount of about 15 to 40 parts by weight per 100 parts by weight of the base rubber. A vulcanizing agent such as dicumyl peroxide or a mixture of dicumyl peroxide and 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane may also be blended in the rubber composition, preferably in an amount of about 0.1 to 5 parts by weight per 100 parts by weight of the base rubber. In the rubber composition, an antioxidant and a specific gravity adjusting filler such as zinc oxide or barium sulfate may be blended. The amount of filler blended is 0 to about 130 parts by weight per 100 parts by weight of the base rubber. 
     The core-forming rubber composition is obtained by kneading the above-mentioned components in a conventional mixer such as a kneader, Banbury mixer or roll mill. The resulting compound is molded in a mold by injection or compression molding. 
     Preferably the solid core has a diameter of 25 to 40 mm, more preferably 27 to 39 mm, and most preferably 30 to 38 mm; a weight of 10 to 40 g, more preferably 15 to 35 g, and most preferably 20 to 32 g; and a specific gravity of 1.1 to 1.5, more preferably 1.12 to 1.45, and most preferably 1.15 to 1.40. 
     The core should preferably have a deflection A under an applied load of 100 kg of at least 2.5 mm, more preferably 2.8 to 6.0 mm, further preferably 3.0 to 5.5 mm, and most preferably 3.3 to 5.0 mm. With a core deflection A of less than 2.5 mm, the feel of the ball would become hard. With a core deflection of more than 6.0 mm, the resilience becomes too low. 
     The core is usually formed to a single layer structure from one material although it may also be formed to a multilayer structure of two or more layers of different materials. 
     According to the invention, the intermediate layer  2  of at least one layer, preferably one or two layers, is formed around the core  1 . 
     The material of which the intermediate layer is made is not critical, and thermoplastic resins and rubber materials may be used. For resilience and durability, thermoplastic resins are appropriate. Preferred thermoplastic resins are heated mixtures of (E 1 ) a thermoplastic polyester elastomer and (E 2 ) at least one thermoplastic elastomer selected from olefin elastomers, modified olefin elastomers, styrene block copolymers and hydrogenated styrene block copolymers. It is also preferred to use the thermoplastic elastomers (E 2 ) alone. 
     Of the thermoplastic polyester elastomers (E 1 ), polyether ester type multi-block copolymers are preferred which are synthesized from terephthalic acid, 1,4-butane diol, and polytetramethylene glycol (PTMG) or polypropylene glycol (PPG) so that polybutylene terephthalate (PBT) moieties and polytetramethylene glycol (PTGM) or polypropylene glycol (PPG) moieties may serve as hard and soft segments, respectively. For example, commercially available elastomers such as Hytrel 3078, Hytrel 4047 and Hytrel 4767 from Toray-Dupont K.K. may be used. 
     With respect to (E 2 ), the olefin elastomers include copolymers of ethylene with alkenes of at least 3 carbon atoms, preferably copolymers of ethylene with alkenes of 3 to 10 carbon atoms, and copolymers of α-olefins with unsaturated carboxylic acid esters or carboxyl or carboxylic anhydride group-bearing polymerizable monomers. Exemplary olefin elastomers are ethylene-propylene copolymer rubber, ethylene-butene copolymer rubber, ethylene-hexene copolymer rubber, and ethylene-octene copolymer rubber. Also included are copolymers obtained by adding to the above components a third component, for example, by adding to ethylene-propylene copolymers a non-conjugated diene such as 5-ethylidene norbornene, 5-methylnorbornene, 5-vinylnorbornene, dicyclopentadiene or butene. Illustrative examples are ethylene-propylene-butene copolymers, ethylene-propylene-butene copolymer rubber, and ethylene-ethyl acrylate copolymer resins. These olefin elastomers are commercially available under the trade name of MITUIEPT and Toughmer from Mitsui Chemical Industry K.K., ENGAGE from Dow Chemical, and Dynaron from Nippon Synthetic Rubber K.K. 
     Modified products of the above-mentioned olefin elastomers are also useful. Such modified olefin elastomers include ethylene-ethyl acrylate copolymer resins graft modified with maleic anhydride. They are commercially available under the trade name of HPR from Mitsui-Dupont Polychemical K.K. 
     Component (E 2 ) also includes styrene block copolymers, preferably those copolymers having conjugated diene blocks composed of butadiene alone, isoprene alone or a mixture of isoprene and butadiene. Also useful are hydrogenated products of these styrene block copolymers, for example, hydrogenated styrene-butadiene-styrene block copolymers and hydrogenated styrene-isoprene-styrene block copolymers. Such hydrogenated styrene-conjugated diene block copolymers are commercially available under the trade name of Dynaron from Nippon Synthetic Rubber K.K., Septon and Hiblur from Kurare K.K., and Toughtec from Asahi Chemicals Industry K.K. 
     In the preferred embodiment wherein the intermediate layer is formed of a composition primarily comprising a heated mixture of (E 1 ) a thermoplastic polyester elastomer and (E 2 ) at least one thermoplastic elastomer selected from olefin elastomers, modified olefin elastomers, styrene block copolymers and hydrogenated styrene block copolymers, these components are preferably mixed so that the mixture may contain up to 95% by weight of component (E 1 ). That is, the mixture preferably has an (E 1 )/(E 2 ) ratio of from 95/5 to 0/100, more preferably from 90/10 to 5/95, most preferably from 80/20 to 10/90, expressed in % by weight. The mixture of (E 1 ) and (E 2 ) is commercially available under the trade name of Primalloy from Mitsubishi Chemical K.K. 
     The intermediate layer may also be formed of a composition primarily comprising the thermoplastic elastomer (E 2 ) selected from olefin elastomers, modified olefin elastomers, styrene block copolymers and hydrogenated styrene block copolymers, alone or mixtures thereof. 
     In addition to the above-mentioned resin components, the composition of which the intermediate layer is formed may further contain a weight adjusting agent, coloring agent, dispersant, and other additives, if necessary. 
     Any desired method may be used in forming the intermediate layer around the core. Conventional injection or compression molding may be employed. 
     The thus molded intermediate layer preferably has a Shore D hardness of 8 to 35, more preferably 9 to 30, further preferably 10 to 29, still further preferably 12 to 27, and most preferably 15 to 24. A layer with a Shore D hardness of less than 8 would be too soft, less resilient, less durable and unfit for actual use. An intermediate layer with a Shore D hardness of more than 35 would be too hard, leading to a hard feel on approach shots and putting and failing to achieve the objects of the invention. 
     The intermediate layer preferably has a thickness of 0.2 to 5.0 mm, more preferably 0.5 to 4.0 mm, most preferably 0.7 to 3.5 mm, and a specific gravity of at least 0.8, more preferably 0.85 to 1.4, further preferably 0.87 to 1.2, most preferably 0.89 to 1.15. Preferably, the specific gravity of the intermediate layer is lower than the specific gravity of the solid core. 
     According to the invention, a spherical body obtained by enclosing the core with the intermediate layer has a deflection B (mm) under an applied load of 100 kg of preferably 2.5 to 6.5 mm, more preferably 2.8 to 6.0 mm, further preferably 3.0 to 5.7 mm, most preferably 3.3 to 5.4 mm. The deflection B (mm) of the spherical body and the deflection A (mm) of the solid core, both under an applied load of 100 kg, should meet the relationship that the value of B/A is from 1.0 to 1.5. Preferably the value of B/A is from 1.01 to 1.4, more preferably from 1.02 to 1.3, most preferably from 1.03 to 1.2. B/A&lt;1.0 gives a hard feel and B/A&gt;1.5 detracts from resilience and durability, both failing to achieve the objects of the invention. 
     The cover  3  of at least one layer, preferably one or two layers, is formed around the intermediate layer  2 . 
     The cover may be formed mainly of a conventional thermoplastic resin, examples of which include ionomer resins, polyester elastomers, polyamide elastomers, styrene elastomers, polyurethane elastomers, olefin elastomers and mixtures thereof. Of these, the ionomer resins are preferred. Use may be made of commercially available ionomer resins such as “Himilan” from Mitsui-Dupont Polychemical K.K. and “Surlyn” from Dupont. To the cover composition, there may be added UV absorbers, antioxidants and dispersants such as metal soaps, if necessary. 
     Any desired method may be used in forming the cover around the intermediate layer. Conventional injection or compression molding may be employed. 
     The thus molded cover preferably has a Shore D hardness of 40 to 70, more preferably 45 to 65. The cover preferably has a thickness of 1.0 to 5.0 mm, more preferably 1.2 to 4.0 mm, further preferably 1.3 to 3.0 mm, most preferably 1.4 to 2.5 mm, and a specific gravity of at least 0.9, more preferably 0.92 to 1.4, further preferably 0.93 to 1.3, most preferably 0.96 to 1.2. 
     A spherical body obtained by enclosing the intermediate layer with the cover, that is, the ball preferably has a deflection under an applied load of 100 kg of 2.6 to 5.5 mm, more preferably 2.8 to 4.8 mm. 
     An appropriate amount of an inorganic filler may be added to the cover composition because the loading of the cover with the inorganic filler can effectively compensate for a loss of durability resulting from the intermediate layer made very soft. Preferably 5 to 40 parts, more preferably 15 to 38 parts, most preferably 18 to 36 parts by weight of the inorganic filler is added to 100 parts by weight of the resin component of which the cover is formed. Less than 5 parts of the filler would provide little reinforcement whereas more than 40 parts of the filler would adversely affect dispersion and resilience. 
     The inorganic filler blended herein generally has a mean particle size of 0.01 to 100 μm, preferably 0.1 to 10 μm, and more preferably 0.1 to 1.0 μm. Outside the range, larger or smaller filler particles would be difficult to disperse, failing to achieve the objects of the invention. Examples of the inorganic filler include barium sulfate, titanium dioxide, calcium carbonate, and tungsten, though not limited thereto. They may be used alone or in admixture of two or more. Barium sulfate and titanium dioxide are most preferable. 
     An appropriate amount of an inorganic filler may also be added to the intermediate layer. By adding the inorganic fillers to both the cover and the intermediate layer, a further improvement in durability is made. Preferably 5 to 40 parts, more preferably 15 to 38 parts by weight of the inorganic filler is added to 100 parts by weight of the resin component of which the intermediate layer is formed. The type, mean particle size and other parameters of the inorganic filler are the same as described for the cover. 
     The multi-piece solid golf ball constructed as described above according to the invention has a very soft pleasant feel upon approach shots and putting, a high spin receptivity and hence, ease of control upon iron shots, improved flight performance upon full shots with a driver, and an improved durability against consecutive strikes. 
     The golf ball of the invention is provided on its surface with a multiplicity of dimples. Typically the ball surface is subject to various finish treatments including stamping and paint coating. The golf ball must have a diameter of not less than 42.67 mm and a weight of not greater than 45.93 grams in accordance with the Rules of Golf. Preferably the ball has a weight of 44.5 to 45.8 grams, more preferably 44.9 to 45.7 grams, and most preferably 45.2 to 45.6 grams. 
     EXAMPLE 
     Examples of the invention are given below by way of illustration and not by way of limitation. The amounts of ingredients in Tables 1 to 3 are parts by weight. 
     Examples 1-6 &amp; Comparative Examples 1-5 
     Core-forming rubber compositions of the formulation shown in Table 1 were mixed in a kneader and molded and vulcanized in a core mold at a temperature of 155° C. for about 15 minutes, forming a solid core. 
     Around the core, the intermediate layer and cover were formed by injection molding the intermediate layer compositions of the formulation shown in Table 2 and the cover compositions of the formulation shown in Table 3, respectively. There were obtained three-piece solid golf balls in Examples 1-6 and Comparative Examples 1, 2, 4 and 5. 
     The three-piece ball of Comparative Example 3 was prepared by preforming a pair of half shells from the intermediate layer composition of the formulation shown in Table 2, encasing the core within the half shells, vulcanizing the assembly in a mold at 155° C. for 15 minutes to form a dual solid core, and injection molding the cover composition around the dual solid core. 
     The golf balls were examined for several properties by the following tests. The results are shown in Tables 4 and 5. 
     Solid core deflection A 
     The deflection A (mm) of the solid core under an applied load of 100 kg was measured. 
     Spherical body deflection B 
     After the core was enclosed within the intermediate layer to form a spherical body, the deflection B (mm) of this spherical body under an applied load of 100 kg was measured. 
     Flight performance 
     A swing robot (by Miyamae K. K.) was equipped with a driver (W#1, PRO 230 Titan, loft angle 10°, by Bridgestone Sports Co., Ltd.). The ball was struck with the driver at a head speed of 45 m/sec (HS 45), and the carry, total distance, and spin rate were measured. The club was changed to No. 9 iron (I#9, Model 55-HM, loft angle 44°, by Bridgestone Sports Co., Ltd.). The ball was struck with the iron at a head speed of 33 m/sec (HS 33), and the spin rate was measured. 
     Feel 
     Five professional golfers actually hit the ball with the driver (W#1), No. 9 iron (I#9), and putter (PT) and evaluated according to the following criterion. 
     VS: very soft 
     Av: ordinary 
     Hard: hard 
     Durability 
     Using a swing robot (by Miyamae K. K.), the ball was repeatedly struck with a driver (PRO 230 Titan, loft angle 10°, Bridgestone Sports Co., Ltd.) at a head speed of 45 m/sec. The surface state of the ball was evaluated relative to the number of strikes and rated according to the following criterion. 
     OK: no problem 
     W: relatively premature breakage 
     VW: premature breakage 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Example 
                 Comparative Example 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 1 
                 2 
                 3 
                 4 
                 5 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Polybutadiene* 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Zinc diacrylate 
                 29.5 
                 22 
                 26 
                 29 
                 30 
                 20 
                 33 
                 33 
                 38 
                 34 
                 34 
               
               
                 Dicumyl peroxide 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 Antioxidant 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 Barium sulfate 
                 23.3 
                 13 
                 19.1 
                 25.6 
                 69.5 
                 16.4 
                 17 
                 19 
                 20.4 
                 12.6 
                 20.3 
               
               
                 Zinc oxide 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
                 5 
               
               
                 Zinc salt of 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 pentachlorothiophenol 
               
               
                   
               
               
                 *BR01 by Nippon Synthetic Rubber K.K.  
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 a 
                 b 
                 c 
                 d 
                 e 
                 f 
                 g 
                 h 
                 i 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Hytrel 3078 
                 80 
                 40 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Hytrel 4047 
                 — 
                 — 
                 — 
                 — 
                 — 
                 100 
                 — 
                 — 
                 — 
               
               
                 PEBAX 3533 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 100 
                 — 
                 — 
               
               
                 Primalloy A1500 
                 — 
                 — 
                 100 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 HPR AR 201 
                 — 
                 60 
                 — 
                 — 
                 100 
                 — 
                 — 
                 — 
                 — 
               
               
                 Toughtec M1943 
                 20 
                 — 
                 — 
                 100 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Himilan 1706 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 60 
               
               
                 Surlyn 8120 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 40 
               
               
                 Barium sulfate 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 5.6 
               
               
                 Polybutadiene 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 100 
                 — 
               
               
                 Zinc diacrylate 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 34 
                 — 
               
               
                 Dicumyl peroxide 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 1 
                 — 
               
               
                 Antioxidant 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 — 
               
               
                 Barium sulfate 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 6.4 
                 — 
               
               
                 Zinc oxide 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 5 
                 — 
               
               
                 Zinc salt of 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 1 
                 — 
               
               
                 pentachlorothiophenol 
               
               
                   
               
               
                 Note:  
               
               
                 Hytrel is the trade name of polyester elastomers by Toray-Dupont K.K.  
               
               
                 PEBAX is the trade name of polyamide elastomers by Atochem.  
               
               
                 Primalloy is the trade name of polyester elastomer base polymer alloys by Mitsubishi Chemical Industry K.K.  
               
               
                 HPR AR 201 is the trade name of maleic anhydride-graft-modified ethylene-ethyl acrylate copolymer resins by Mitsui-Dupont K.K.  
               
               
                 Toughtec is the trade name of styrene elastomers by Asahi Chemicals K.K.  
               
               
                 Himilan is the trade name of ionomer resins by Mitsui-Dupont Polychemical K.K.  
               
               
                 Surlyn is the trade name of ionomer resins by Dupont.  
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Himilan 1601 
                 25 
                 33 
                 40 
                 25 
                 50 
                 — 
                 — 
                 — 
                 — 
               
               
                 Himilan 1557 
                 50 
                 33 
                 40 
                 25 
                 50 
                 — 
                 — 
                 — 
                 — 
               
               
                 Himilan 1605 
                 25 
                 — 
                 — 
                 — 
                 — 
                 50 
                 — 
                 — 
                 — 
               
               
                 Himilan 1706 
                 — 
                 — 
                 — 
                 — 
                 — 
                 50 
                 — 
                 45 
                 70 
               
               
                 Surlyn 8120 
                 — 
                 34 
                 20 
                 50 
                 — 
                 — 
                 100 
                 55 
                 30 
               
               
                 Titainium dioxide 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
                 5.6 
               
               
                 Barium sulfate 
                 — 
                 28 
                 — 
                 — 
                 28 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
               
                 Note:  
               
               
                 Himilan is the trade name of ionomer resins by Mitsui-Dupont Polychemical K.K.  
               
               
                 Surlyn is the trade name of ionomer resins by Dupont.  
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Example 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Core 
                 Weight (g) 
                 27.7 
                 26.0 
                 33.6 
                 27.9 
                 21.6 
                 26.3 
               
               
                   
                 Outer diameter 
                 35.2 
                 35.2 
                 37.9 
                 35.2 
                 30.6 
                 35.2 
               
               
                   
                 (mm) 
               
               
                   
                 Deflection A (mm) 
                 3.5 
                 4.8 
                 4.0 
                 3.6 
                 3.4 
                 5.2 
               
               
                   
                 Specific gravity 
                 1.211 
                 1.136 
                 1.180 
                 1.222 
                 1.441 
                 1.150 
               
               
                 Intermediate 
                 Type 
                 a 
                 b 
                 c 
                 b 
                 d 
                 e 
               
               
                 layer 
                 Shore D hardness 
                 29 
                 20 
                 17 
                 20 
                 25 
                 13 
               
               
                   
                 Weight* (g) 
                 35.2 
                 33.3 
                 37.8 
                 35.2 
                 35.2 
                 33.3 
               
               
                   
                 Outer diameter* 
                 38.6 
                 38.6 
                 39.7 
                 38.6 
                 38.6 
                 38.6 
               
               
                   
                 (mm) 
               
               
                   
                 Deflection B (mm) 
                 3.6 
                 4.9 
                 4.1 
                 3.8 
                 3.8 
                 5.3 
               
               
                   
                 Specific gravity 
                 1.04 
                 1.00 
                 0.98 
                 1.00 
                 0.90 
                 0.96 
               
               
                   
                 Gage (mm) 
                 1.70 
                 1.70 
                 0.90 
                 1.70 
                 4.00 
                 1.70 
               
               
                 Cover 
                 Type 
                 A 
                 B 
                 C 
                 D 
                 D 
                 E 
               
               
                   
                 Specific gravity 
                 0.98 
                 1.17 
                 0.98 
                 0.98 
                 0.98 
                 1.17 
               
               
                   
                 Gage (mm) 
                 2.05 
                 2.05 
                 1.50 
                 2.05 
                 2.05 
                 2.05 
               
               
                   
                 Shore D hardness 
                 60 
                 56 
                 56 
                 52 
                 52 
                 62 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Deflection ratio B/A 
                 1.01 
                 1.02 
                 1.03 
                 1.06 
                 1.12 
                 1.02 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Ball 
                 Weight (g) 
                 45.3 
                 45.3 
                 45.3 
                 45.3 
                 45.3 
                 45.3 
               
               
                   
                 Diameter (mm) 
                 42.7 
                 42.7 
                 42.7 
                 42.7 
                 42.7 
                 42.7 
               
               
                 Flight 
                 Carry (m) 
                 208.8 
                 208.6 
                 208.5 
                 209.2 
                 209.2 
                 208.3 
               
               
                 performance 
                 Total (m) 
                 223.5 
                 222.8 
                 222.5 
                 222.6 
                 222.6 
                 223.0 
               
               
                 W#1/HS45 
                 Spin (rpm) 
                 2683 
                 2669 
                 2811 
                 2915 
                 2922 
                 2503 
               
               
                 I#9 
                 Spin (rpm) 
                 9290 
                 9201 
                 9352 
                 9481 
                 9496 
                 9022 
               
               
                 Feel 
                 W#1 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
               
               
                   
                 I#9 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
               
               
                   
                 PT 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
                 VS 
               
               
                 Durability 
                   
                 OK 
                 OK 
                 OK 
                 OK 
                 OK 
                 OK 
               
               
                   
               
               
                 *core + intermediate layer  
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Comparative Example 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Core 
                 Weight (g) 
                 27.1 
                 30.2 
                 16.7 
                 29.6 
                 30.7 
               
               
                   
                 Outer diameter 
                 35.2 
                 36.4 
                 29.7 
                 36.5 
                 36.5 
               
               
                   
                 (mm) 
               
               
                   
                 Deflection A (mm) 
                 3.5 
                 3.3 
                 2.3 
                 2.9 
                 2.9 
               
               
                   
                 Specific gravity 
                 1.185 
                 1.196 
                 1.214 
                 1.164 
                 1.205 
               
               
                 Intermediate 
                 Type 
                 f 
                 g 
                 h 
                 f 
                 i 
               
               
                 layer 
                 Shore D hardness 
                 40 
                 42 
                 55 
                 40 
                 56 
               
               
                   
                 Weight* (g) 
                 35.2 
                 38.6 
                 35.5 
                 37.8 
                 37.8 
               
               
                   
                 Outer diameter* 
                 38.6 
                 40.0 
                 38.7 
                 39.7 
                 39.7 
               
               
                   
                 (mm) 
               
               
                   
                 Deflection B (mm) 
                 3.3 
                 3.1 
                 2.2 
                 2.8 
                 2.6 
               
               
                   
                 Specific gravity 
                 1.12 
                 1.01 
                 1.13 
                 1.12 
                 0.98 
               
               
                   
                 Gage (mm) 
                 1.70 
                 1.80 
                 4.50 
                 1.60 
                 1.60 
               
               
                 Cover 
                 Type 
                 F 
                 G 
                 F 
                 H 
                 I 
               
               
                   
                 Specific gravity 
                 0.98 
                 0.98 
                 0.98 
                 0.98 
                 0.98 
               
               
                   
                 Gage (mm) 
                 2.05 
                 1.35 
                 2.00 
                 1.50 
                 1.50 
               
               
                   
                 Shore D hardness 
                 63 
                 45 
                 63 
                 53 
                 58 
               
            
           
           
               
               
               
               
               
               
            
               
                 Deflection ratio B/A 
                 0.94 
                 0.94 
                 0.96 
                 0.97 
                 0.90 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Ball 
                 Weight (g) 
                 45.3 
                 45.3 
                 45.3 
                 45.3 
                 45.3 
               
               
                   
                 Diameter (mm) 
                 42.7 
                 42.7 
                 42.7 
                 42.7 
                 42.7 
               
               
                 Flight 
                 Carry (m) 
                 207.9 
                 205.3 
                 204.9 
                 205.8 
                 207.9 
               
               
                 performance 
                 Total (m) 
                 221.0 
                 217.5 
                 217.3 
                 218.1 
                 219.2 
               
               
                 W#1/HS45 
                 Spin (rpm) 
                 2548 
                 3001 
                 2657 
                 2898 
                 2689 
               
               
                 I#9 
                 Spin (rpm) 
                 8335 
                 9343 
                 8453 
                 8935 
                 8566 
               
               
                 Feel 
                 W#1 
                 VS 
                 Av 
                 Hard 
                 Hard 
                 Hard 
               
               
                   
                 I#9 
                 Av 
                 Av 
                 Hard 
                 VS 
                 VS 
               
               
                   
                 PT 
                 Hard 
                 Av 
                 Hard 
                 VS 
                 Av 
               
               
                 Durability 
                   
                 OK 
                 OK 
                 OK 
                 OK 
                 OK 
               
               
                   
               
               
                 *core + intermediate layer  
               
            
           
         
       
     
     As seen from Tables 4 and 5, the balls of Comparative Examples 1 to 5 have a deflection ratio (B/A) of less than 1.0, failing to accomplish the effect and performance of the invention. More particularly, Comparative Example 1, which is a three-piece ball of the same type as JP-A 7-24084, travels a relatively long distance on driver shots, but shows a low spin rate when hit with No. 9 iron and a hard unpleasant feel when hit with the putter. Comparative Example 2, which is a three-piece ball of the same type as JP-A 4-244174, travels a relatively short distance on full shots with the driver. Comparative Example 3, which is a three-piece ball of the same type as JP-A 6-23069, travels a relatively short distance on full shots with the driver and shows a hard unpleasant feel when hit with any of the driver, No. 9 iron and putter. Comparative Example 4, which is a three-piece ball of the same type as JP-A 9-10358, travels a relatively short distance on full shots with the driver and shows a hard unpleasant feel when hit. Comparative Example 5, which is a three-piece ball of the same type as JP-A 9-313643, travels a relatively long distance on full shots with the driver, but shows a low spin rate when hit with No. 9 iron and a hard unpleasant feel when hit with the driver. 
     In contrast, the three-piece balls of Examples 1 to 6 shows a very soft pleasant feel when hit with any of the driver, No. 9 iron and putter, a high spin receptivity when hit with No. 9 iron and a drastically increased flight distance upon full shots with the driver. 
     Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.