USOO5824740A United States Patent (19) 11 Patent Number: 5,824,740 Yabuki et al. (45) Date of Patent: *Oct. 20, 1998

54 GOLF BALL 56) References Cited 75 Inventors: Yoshikazu Yabuki; Yoshinori Sano, U.S. PATENT DOCUMENTS both of Sirakawa; Hiroaki Tanaka, 4,985,545 1/1991 Sullivan ...... 273/235 R Kobe, all of Japan 4,994.508 2/1991 Shiraki ...... 525/74 5,066,726 11/1991 Modic ...... 525/263 73 Assignee: Sumitomo Rubber Industries, Ltd., 5,504,156 4/1996 Takezaki ...... 525/93 Hyogo-ken, Japan FOREIGN PATENT DOCUMENTS * Notice: This patent issued on a continued pros 0557069 8/1993 European Pat. Off.. ecution application filed under 37 CFR 0652254 5/1995 European Pat. Off.. 1.53(d), and is subject to the twenty year Primary Examiner David Buttner patent term provisions of 35 U.S.C. Attorney, Agent, or Firm-Birch, Stewart, Kolasch & Birch, 154(a)(2). LLP 21 Appl. No.: 580,249 57 ABSTRACT 22 Filed: Dec. 28, 1995 Disclosed is a golf ball having good shot feel and control lability as well as Satisfactory flight performance and cut 30 Foreign Application Priority Data resistance. The golf ball has a core and a cover for covering Dec. 29, 1994 JP Japan ...... 6-338789 the core, wherein said cover has a stiffness modulus of 100 Dec. 29, 1994 JP Japan ...... 6-338790 to 250 MPa and comprises a heated mixture of an ionomer resin and a glycidyl group-modified Styrene-based block (51) Int. Cl." ...... A63B 37/12 copolymer having a JIS-Ahardness of 30 to 90 as base resin, 52 U.S. Cl...... 525/71; 525/72; 525/74; and optionally a maleic anhydride-modified olefin copoly 525/93; 473/378; 473/372; 473/385 C. 58 Field of Search ...... 525/71, 72, 74, 525/93, 94; 473/378,372, 385 19 Claims, 2 Drawing Sheets U.S. Patent Oct. 20, 1998 Sheet 1 of 2 5,824,740

U.S. Patent Oct. 20, 1998 Sheet 2 of 2 5,824,740

5,824,740 1 2 GOLF BALL controllability, as well as Satisfactory flight performance and cut resistance can be obtained. Thus, the present invention FIELD OF THE INVENTION has been completed. The present invention relates to a golf ball. More A main object of the present invention is to provide a golf particularly, it relates to a golf ball having good shot feel and ball having good shot feel and controllability as well as controllability as well as Satisfactory flight performance and Satisfactory flight performance and cut resistance. cut resistance. This object as well as other objects and advantages of the present invention will become apparent to those skilled in BACKGROUND OF THE INVENTION the art from the following description with reference to the Recently, an ionomer resin has widely been used as a base accompanying drawings. resin for a cover of the golf ball (e.g. Japanese Patent BRIEF EXPLANATION OF THE DRAWINGS Publication No. 49-27093). Particularly, the ionomer resin is exclusively used as the base resin for a cover in a two-piece FIG. 1 is a Schematic croSS Section illustrating one embodiment of the golf ball of the present invention. Solid golf ball using a Solid core. This is because the ionomer 15 resin is Superior in durability, cut resistance and coefficient FIG. 2 is a Schematic croSS Section illustrating another of restitution (C.O.R.) and, it is easily processed. embodiment of the golf ball of the present invention. However, the ionomer resin is inferior in shot feel and SUMMARY OF THE INVENTION controllability (ease of putting spin on the ball) in compari The present invention provides a golf ball having a core Son with a balata (transpolyisoprene) resin used as the base and a cover for covering the core, wherein the cover has a resin for a cover of a thread wound golf ball since the stiffness modulus of 100 to 250 MPa and comprises a heated ionomer resin has considerably high hardneSS and rigidity. mixture of an ionomer resin and a glycidyl group-modified Therefore, an improvement of shot feel and controllability Styrene-based block copolymer having a JIS-A hardness of by Softening the ionomer resin with various means has been 30 to 90 as base resin. made. 25 The present invention also provide a golf ball having a For example, Japanese Laid-Open Patent Publication core and a cover for covering the core, wherein Said cover Nos. 1.(1989)-308577 and 5(1993)-3931 suggest that a high has a stiffness modulus of 100 to 250 MPa and comprises a rigid ionomer resin is Softened by blending or mixing a Soft heated mixture of an ionomer resin, a maleic anhydride ionomer resin to improve shot feel and controllability, modified olefin copolymer and a glycidyl group-modified wherein the Soft ionomer resin is obtained by neutralizing a Styrene-based block copolymer having a JIS-A hardness of terpolymer of an O-olefin, an unsaturated carboxylic acid 30 to 90 as base resin. (e.g. acrylic acid, methacrylic acid, etc.) and an acrylate with a Sodium or Zinc ion. DETAILED DESCRIPTION OF THE INVENTION However, even if the Soft ionomer resin as described 35 above is blended, shot feel similar to a balata covered golf In the present invention, when the ionomer resin and the ball has not been obtained. Further, blending of the soft glycidyl group-modified Styrene-based block copolymer are ionomer resin is accompanied by deterioration of the coef mixed together with heating, a glycidyl group contained in ficient of restitution and flight performance and, therefore, the glycidyl group-modified Styrene-based block copolymer Satisfactory results have not been obtained. 40 reacts with a free carboxyl group in the ionomer resin to In addition, Japanese Laid-Open Patent Publication No. form a Soft block or graft copolymer at the interface. 5(1993)-220240 suggests that shot feel and controllability Furthermore, the copolymers are finely dispersed in the are improved by blending an ionomer resin and a polymer matrix of the ionomer resin, uniformly, by a shear force at containing a glycidyl group. According to this method, an the time of kneading and the ionomer resin is Softened, improvement effect with respect to shot feel and controlla 45 thereby improving the coefficient of restitution. bility is admitted, but satisfactory results have not been Accordingly, when using the heated mixture of the iono obtained with respect to coefficient of restitution and flight mer resin and glycidyl group-modified Styrene-based block performance, because the polymer containing a glycidyl copolymer as base resin of the cover, shot feel and control group to be blended has not been clearly defined and is lability are improved and, at the same time, deterioration of difficult to select. 50 flight performance (coefficient of restitution) and cut resis AS described above, the golf ball using the ionomer resin tance is inhibited, thereby obtaining a golf ball having good as the base resin for a cover is inferior in shot feel and shot feel and controllability as well as satisfactory flight controllability. In addition, a Suggestion to improve shot feel performance and cut resistance. and controllability causes deterioration of the coefficient of In the present invention, the ionomer resin and the gly restitution and flight performance, and Satisfactory results 55 cidyl group-modified Styrene-based block copolymer having have not been obtained. a JIS-A hardness of 30 to 90 are represented as the compo nents (A) and (B), respectively, just for the sake of conve OBJECTS OF THE INVENTION nience. The ionomer resin as the component (A) is obtained, Under these circumstances, in order to attain excellent for example, by neutralizing at least a part of carboxyl shot feel and controllability, which are similar to those of the 60 groups in a copolymer of an O-olefin and an C, B-unsaturated balata covered golf ball, as well as excellent flight perfor carboxylic acid having 3 to 8 carbon atoms with metal ion, mance and cut resistance due to the ionomer resin, the or neutralizing at least a part of carboxyl groups in a present inventors have intensively Studied the base resin for terpolymer of an O-olefin, an C, B-unsaturated carboxylic a cover. As a result, it has been found that, when a heated acid having 3 to 8 carbon atoms and an O, B-unsaturated mixture of an ionomer resin and a Soft glycidyl group 65 carboxylate with metal ion. modified Styrene-based block copolymer is used as the base The C-olefin includes ethylene, propylene, 1-butene resin for a cover, a golf ball having good shot feel and 1-pentene, etc. Among them, ethylene is particularly pre 5,824,740 3 4 ferred. Examples of the C, B-unsaturated carboxylic acid resistance. On the other hand, when the hardness of the having 3 to 8 carbon atoms are acrylic acid, methacrylic glycidyl group-modified Styrene-based block copolymer of acid, fumaric acid, maleic acid, crotonic acid, etc. Among the component (B) is higher than 90, Softening can not be them, acrylic acid and methacrylic acid are particularly accomplished Sufficiently and properties of the ionomer preferred. Examples of the unsaturated carboxylic acid ester resin appear Strongly, which results in deterioration of shot are alkyl acrylate, alkyl methacrylate, alkyl fumarate and feel and controllability. The JIS-A hardness means a hard alkyl maleate wherein the alkyl group includes methyl, neSS measured using a JIS-A hardneSS tester. ethyl, propyl, n-butyl, isobutyl, etc. Among them, acrylate The Styrene content of the Styrene block copolymer and methacrylate are particularly preferred. Examples of the moiety in the component (B) is preferably 10 to 40% by metalion with which at least a part of carboxyl groups in the weight, particularly 15 to 35% by weight. When the styrene copolymer of the C-ethylene and C, B-unsaturated carboxy content is smaller than 10% by weight, the cover is too soft, lic acid or the terpolymer of the C-ethylene, Cl, B-unsaturated which results in deterioration of cut resistance. On the other carboxylic acid and C, B-unsaturated carboxylate include hand, when the Styrene content is larger than 40% by weight, Sodium ion, lithium ion, Zinc ion, magnesium ion, potassium Softening can not be accomplished Sufficiently and proper ion, etc. 15 ties of the ionomer resin appear Strongly, which results in Examples of the above ionomer resin are commercially deterioration of shot feel and controllability. available under Several trade names. Examples of those In addition, the glycidyl group content of the glycidyl commercially available from Mitsui Du Pont Polychemical group-modified Styrene-based block copolymer of the com Co., Ltd. include ionomer resins such as Hi-milan 1605, ponent (B) is preferably 0.05 to 10% by weight, particularly (Na), Hi-milan 1707 (Na), Hi-milan AM7318, (Na), 0.2 to 5% by weight. When the glycidyl group content is Hi-milan 1706 (Zn), Hi-milan AM7315 (Zn), Hi-milan smaller than 0.05% by weight, the amount of the reaction AM7317 (Zn), Hi-milan AM7311 (Mg), Hi-milan MK7320 between the glycidyl group and free carboxyl group in the (K), etc., terpolymer ionomer resins Such as Hi-milan 1856 ionomer resin is Small and the dispersion of the glycidyl (Na), Hi-milan 1855 (Zn), Hi-milan AM7316 (Zn), etc. group-modified Styrene-based block copolymer as the com Examples of those commercially available from Du Pont 25 U.S.A. Co. include ionomer resins such as Surlyn 8920 (Na), ponent (B) into the ionomer resin as the component (A) is Surlyn 8940 (Na), Surlyn AD8512 (Na), Surlyn 9910 (Zn), deteriorated, which results in deterioration of the durability. Surlyn AD8511 (Zn), Surlyn 7930 (Li), Surlyn 7940 (Li), On the other hand, when the glycidyl group content is larger etc.; terpolymer ionomer resins such as Surlyn AD8265 than 10% by weight, the amount of the reaction between the (Na), Surlyn AD8269 (Na), etc. Examples of those com glycidyl group and free carboxyl group in the ionomer resin mercially available from EXXon chemical Co. include iono becomes too large and the fluidity is inferior. Therefore, it is mer resins such as lotek 7010 (Zn), lotek 8000 (Na), etc. difficult to mold the golf ball. Note that Na, Zn, K, Li, Mg, etc., which are described in The glycidyl group-modified Styrene-based block copoly parentheses at the back of the trade name of the above mer of the component (B) is commercially available and, for ionomer resin show neutralization metalion species, respec 35 example, glycidyl methacrylate adducts of hydrogenated tively. In the present invention, as the ionomer resin of the styrene-butadiene-styrene block copolymers (SEBS) which component (A), a mixture of an ionomer resin neutralized are commercially available from Asahi Kasei Industries Co., with the above described monovalent metal ion and an Ltd. under the trade name of “Taftek Z513 and “Taftek ionomer resin neutralized with the divalent metalion may be Z514, and these are suitably used in the present invention. used. 40 In the present invention, the base resin for cover is In the present invention, the glycidyl group-modified composed of the heated mixture of the ionomer resin as the styrene-based block copolymer as the component (B) means component (A) and glycidyl group-modified Styrene-based a styrene-based block copolymer modified with a glycidyl block copolymer as the component (B) and it is necessary group. The Styrene-block copolymer moiety in the compo that the stiffness modulus of the cover composition, which nent (B) is a block copolymer having polystyrene (S) at both 45 contains the heated mixture, is within a range of 100 to 250 terminal ends. AS the intermediate phase, there are basic MPa. When the stiffness modulus of the cover composition three Sorts Such as polybutadiene (B), polyisoprene (I) and is lower than 100 MPa, the cover is too soft and spin amount hydrogenated type poly(ethylene-butyrene) (EB) and they is too large. Therefore, flight distance is decreased and cut are abbreviated to SBS, SIS and SEBS, respectively. The resistance is deteriorated. When the stiffness modulus of the component (B) is composed by adding a glycidyl group to 50 cover composition is higher than 250 MPa, it is impossible these copolymers. The compounds for introducing the gly to obtain a Suitable backSpin amount and, therefore, con cidyl group includes unsaturated glycidyl esters, unsaturated trollability is deteriorated and hit feeling also is inferior. The glycidyl ethers, epoxyalkenes, p-glycidylstyrenes, etc. cover composition is mainly composed of the heated mix Examples thereof are glycidyl methacrylate, glycidyl ture of the ionomer resin as the component (A) and the acrylate, glycidyl itaconate, allyl glycidyl ether, 55 glycidyl group-modified Styrene-based block copolymer 2-methylallyl glycidyl ether, p-glycidylstyrene, etc. The (B), and a small amount of titanium dioxide, barium Sulfate, styrene-based block copolymer moiety in the component (B) etc. is merely added. Therefore, the stiffness modulus is may be SBS, SIS, SEBS, etc., as described above. Among substantially the same as that of the heated mixture of the them, SEBS is particularly preferred in view of coefficient of ionomer resin of the component (A) and glycidyl group restitution, weather resistance and heat aging resistance. 60 modified Styrene-based block copolymer of the component In addition, in order to soften the ionomer resin of the (B). component (A), it is necessary that JIS-A hardness of the In the present invention, the mixing ratio of the ionomer glycidyl group-modified Styrene-based block copolymer of resin of the component (A) to the glycidyl group-modified the component (B) is 30 to 90, preferably 45 to 88. When the styrene-based block copolymer of the component (B) is hardness of the glycidyl group-modified Styrene-based block 65 preferably within a range of 95:5 to 50:50, particularly 90:10 copolymer as the component (B) is lower than 30, the cover to 55:45. When the proportion of the ionomer resin is larger is ecomes too Soft, which results in deterioration of cut than the above range, Softening can not be accomplished 5,824,740 S 6 Sufficiently and properties of the ionomer resin appear ening of the ionomer resin can not be accomplished Suffi Strongly, which results in deterioration of shot feel and ciently. On the other hand, when the proportion of the maleic controllability. On the other hand, when the proportion of the anhydride-modified olefin copolymer (C) is larger than ionomer resin is Smaller than the above range, the cover is 69.5% by weight, the flight performance and cut resistance too Soft and Spin amount is increased. Therefore, flight are deteriorated. Therefore, it is impossible to obtain a distance is decreased and cut resistance is deteriorated. Satisfactory golf ball. In the present invention, it is possible to obtain desired characteristics by mixing the ionomer resin of the compo When the amount of the glycidyl group-modified Styrene nent (A) and the glycidyl group-modified Styrene-based based block copolymer (B) is less than 0.5% by weight, the block copolymer of the component (B) together with heat amount of the reaction between the glycidyl group and a free ing. They are normally mixed with heating at 150 to 260 carboxyl group in the ionomer resin or maleic anhydride in C., using internal mixerS Such as a kneading type twin-Screw the maleic anhydride-modified olefin copolymer is Small. AS extruder, a Banbury, a kneader, etc. a result, the dispersion of the maleic anhydride-modified In another embodiment of the present invention, the olefin copolymer into the ionomer resin is deteriorated and maleic anhydride-modified olefin copolymer (component the flight performance and durability become inferior. On (C)) may be contained, in addition to the above components 15 the other hand, when the amount of the glycidyl group (A) and (B). The maleic anhydride-modified olefin copoly modified Styrene-based block copolymer (B) is larger than mer (C) may be one which contains polyolefin blocks as the 20% by weight, the reaction between the glycidyl group and copolymer component, which is compatible with the iono free carboxyl group in the ionomer resin or maleic anhydride mer resin. The olefin preferably has 2 to 8 carbon atoms and in the maleic anhydride-modified olefin copolymer proceeds examples thereof include ethylene, propylene, 1-butene, excessively. Therefore, it is difficult to mold the cover isobutylene, 1-pentene, 1-octene, etc. Among them, ethylene because of deterioration of the fluidity of the resin. and propylene are particularly preferred. In the present invention, it is possible to obtain desired In addition, monomer components other than olefin may characteristics by mixing the above two or three Sorts of be added to the maleic anhydride-modified olefin copolymer resins with heating. They are normally mixed with heating for the purpose of Softening. Examples of the monomer 25 at 150 to 260 C. for 0.5 to 15 minutes, using internal component include acrylates Such as methyl acrylate, ethyl mixerS Such as a kneading type twin-Screw extruder, a acrylate, butyl acrylate, etc., methacrylates Such as methyl Banbury mixer, a kneader, etc. methacrylate, ethyl methacrylate, butyl methacrylate, etc.; Further, a very Small amount of water contained in the Vinyl aceate, etc. Among them, acrylates and methacrylates resin is Sufficient for water content required to the reaction are preferred taking compatibility with ionomer resin into between the maleic anhydride and glycidyl group. In consideration. addition, about 0.1 to 0.2% by weight of water content may The maleic anhydride-modified olefin copolymer includes be optionally added to mix the resins with heating. various grades of maleic anhydride adducts of hydrogenated In the present invention, when the base resin for the cover Styrene-butadiene-Styrene block copolymers commercially 35 is composed of the heated mixture of the ionomer resin (A), available from Asahi Kasei Industries Co., Ltd. under the maleic anhydride-modified olefin copolymer (C) and gly trade name of “TUFTEC M Series'. In addition various cidyl group-modified Styrene-based block copolymer (B) as grades of ethylene-ethyl acrylate-maleic anhydride terpoly base resin. A Stiffness modulus of the cover composition mers are commercially available from Sumitomo Chemical must be within a range of 100 to 250 MPa. When the Industries Co., Ltd. under the trade name of "Bondine' and 40 stiffness modulus of the cover composition is lower than 100 graft-modified products of ethylene-ethyl acrylate copoly MPa, the cover is too Soft and Spin amount is too large. mers due to maleic anhydride are commercially available Therefore, flight distance is decreased and cut resistance is from Mitsui Du Pont Polychemical Co., Ltd. under the trade deteriorated. When the stiffness modulus of the cover com name of “AR series'. position is higher than 250 MPa, it is impossible to obtain a In addition, the maleic anhydride-modified olefin copoly 45 Suitable backSpin amount and, therefore, controllability is mer is formulated for the purpose of Softening of the deteriorated and shot feel also is inferior. The cover com ionomer resin, and the Stiffness modulus is lower than that position is mainly composed of the heated mixture of the of the ethylene-methacrylic acid copolymer or ethylene ionomer resin, maleic anhydride-modified olefin copolymer acrylic acid copolymer high-rigid ionomer resin of which and glycidyl group-modified Styrene-based block stiffness modulus of these copolymers is normally 250 to 50 copolymer, and a Small amount of titanium dioxide, barium 350 MPa. It is therefore preferred that the stiffness modulus Sulfate, etc. is merely added. Therefore, the Stiffness modu is about 1 to 100 MPa. lus is Substantially the same as that of the heated mixture of When using the three components (A), (B) and (C), the the ionomer resin, maleic anhydride-modified olefin copoly composition ratio of three Sorts of resins is preferably as mer and glycidyl group-modified Styrene-based block follows. That is, the proportion of the ionomer resin (A), 55 copolymer. maleic anhydride-modified olefin copolymer (C) and gly Various additives Such as pigments, dispersants, cidyl group-modified Styrene-based block copolymer (B) is antioxidants, UV absorbers, photoStabilizers, etc. can be 30 to 70% by weight, 10 to 69.5% by weight and 0.5 to 20% optionally formulated in the cover to be used in the present by weight, respectively. invention, in addition to the mixture of the above three sorts That is, when the proportion of the ionomer resin (A) is 60 of resins as the components (A), (B) and (C). In addition, smaller than 30% by weight, the flight performance and cut another resin can also be added unless characteristics of the resistance are deteriorated. On the other hand, when the heated mixture of the above resins are not deteriorated. proportion of the ionomer resin is larger than 70% by When the other resin is added to form a base resin of the weight, Softening can not be accomplished Sufficiently, cover as described above, an amount of the heated mixture which results in deterioration of shot feel and controllability. 65 of the above resins is preferably not less than 70% by When the proportion of the maleic anhydride-modified weight, particularly not less than 80% by weight. In the olefin copolymer (C) is smaller than 10% by weight, soft present invention, “the heated mixture of the ionomer resin 5,824,740 7 8 (A), maleic anhydride-modified olefin copolymer (C) and golf ball shown in FIG. 1 is a thread wound golf ball. In FIG. glycidyl group-modified Styrene-based block copolymer (B) 1, 1 is a core comprising a center 1a and a thread rubber 1b, is used as base resin of the cover” means the case that the 2 is a cover and 2a is a dimple. base resin of the cover is composed of the heated mixture of The center 1a and thread rubber 1b are not specifically the ionomer resin, maleic anhydride-modified olefin copoly 5 limited, and those which are similar to a conventional one mer and glycidyl group-modified Styrene-based block can be used. AS the center 1a, a liquid or rubber center may copolymer or the case that the other resin is added to the be used. The thread rubber 1b is wound around the center 1a above mixture to form the base resin of the cover. In the in a stretched State, thereby forming a core 1 referred to as present invention, the heated mixture of the ionomer resin, a thread core. The cover 2 is that for covering the core 1. The maleic anhydride-modified olefin copolymer and glycidyl cover 2 is formed from the above cover composition of the group-modified Styrene-based block copolymer may be pre present invention. viously mixed, followed by mixing with the other resin. In FIG. 2 is a Schematic croSS Section illustrating another addition, the mixture may be mixed with the other additives embodiment of the golf ball of the present invention. The when the cover composition is prepared. golf ball shown in FIG. 2 is a two-piece golf ball comprising Further, a golf ball can be obtained by covering the cover 15 a core 1 and a cover 2 for covering the core. The core 1 is on the core. AS the core, any of a core for Solid golf ball referred to as a Solid core but is not Specifically limited, for (solid core) and a core for thread wound golf ball (thread example, a Vulcanized product of a rubber composition wound core) can be used. comprising polybutadiene as a main material as described The Solid core may be not only a core of a two-piece golf above. The cover 2 for covering the core is formed from the ball, but also a core with two or more layers of a multi-layer above cover composition of the present invention. In golf ball. For example, the core for a two-piece golf ball is addition, 2a is a dimple provided on the cover 2. In the golf obtained by Subjecting a rubber composition to a preSS ball shown in FIG. 2, the core 1 is composed of a Vulcanized Vulcanization to compress with heating (e.g. at a temperature molded product of a Single-layer rubber, but it may also be of 140° to 170° C. for 10 to 40 minutes) into a spherical a two-layer Solid core obtained by further forming an outer Vulcanized article can be used, the rubber composition being 25 core of a Vulcanized molded product of a rubber composi prepared by formulating 10 to 60 parts by weight of at least tion comprising polybutadiene as a main material around an one Vulcanizing agent (crosslinking agent) of C., inner core of a Vulcanized molded product of a rubber f-ethylenically unsaturated carboxylic acids (e.g. acrylic composition comprising polybutadiene as a main material. acid, methacrylic acid, etc.) or metal Salts thereof and A Suitable number/embodiment of dimples 2a are option functional monomers (e.g. trimethylol propane ally provided on the cover 2 of the golf ball so that desired trimethacrylate, etc.), 10 to 30 parts by weight of a filler (e.g. characteristics may be obtained. In addition, painting or Zinc oxide, barium Sulfate, etc.), 0.5 to 5 parts by weight of marking is optionally provided on the Surface of the golf a peroxide (e.g. dicumyl peroxide, etc.) and 0.1 to 1 parts by ball. weight of an antioxidant, based on 100 parts by weight of 35 AS described above, according to the present invention, polybutadiene. there is provided a golf ball which is superior in shot feel, The thread wound core may be composed of a center and controllability, flight performance, durability and cut resis a thread rubber wound on the center. AS the center, any of a tance. liquid center and a rubber center can be used. AS the rubber EXAMPLES center, there can be used those obtained by Vulcanizing the 40 Same rubber composition as that of the Solid core. The following Examples and Comparative Examples fur The thread rubber may be those which have hitherto been ther illustrate the present invention in detail but are not to be used. For example, there can be used those obtained by construed to limit the Scope thereof. Vulcanizing a rubber composition wherein an antioxidant, a Vulcanizing accelerator and Sulfur are formulated in a natu Examples 1 to 9 and Comparative Examples 1 to 6 ral rubber or a natural rubber and Synthetic polyisoprene. 45 (thread wound golf ball) The core is not limited to the Solid core or thread wound Thread wound golf balls of Examples 1 to 9 and Com COC. parative Examples 1 to 6 were produced through the fol A method of covering the cover on the core is not lowing processes (1) to (3). specifically limited, but may be a normal method. For 50 (1) Production of core example, there can be used a method comprising molding a A thread wound core having an outer diameter of 39.5 mm cover composition, which contains the heated mixture of the was produced by winding a thread rubber comprising a ionomer resin (A), maleic anhydride-modified olefin copoly natural rubber/low-cis isoprene rubber Shell IR-309 (trade mer (C) and glycidyl group-modified Styrene-based block name) (=50:50) as the base rubber on a liquid center having copolymer (B), into a semi-spherical half-shell in advance, 55 an Outer diameter of 28.1 mm, Said liquid center comprising covering a core with two half-shells and then Subjecting to a paste obtained by dispersing barium Sulfate in water and a a pressure molding at 130 to 170° C. for 5 to 15 minutes, center bag of a Vulcanized natural rubber having a thickness or a method comprising Subjecting the cover composition to of 1.7 mm, which covers the paste. an injection molding directly to cover the core. The thick (2) Production of cover composition neSS of the cover is normally about 1 to 4 mm. In case of 60 The formulation components shown in Tables 1 to 3 were cover molding, a dimple may be formed on the Surface of the mixed using a kneading type twin-Screw extruder to obtain ball, if necessary. Further, if necessary, a paint or marking a pelletized cover composition. Further, the composition of may be provided after cover molding. the compositions for cover of Preparation Examples 1 to 5 The structure of the golf ball of the present invention will to be used for the golf balls of Examples 1 to 5 and the be explained with reference to the accompanying drawing. 65 stiffness modulus are shown in Table 1. The composition of FIG. 1 is a Schematic croSS Section illustrating one the compositions for cover of Preparation Examples 6 to 9 embodiment of the golf ball of the present invention. The to be used for the golf balls of Examples 6 to 9 and the 5,824,740 9 10 stiffness modulus are shown in Table 2. The composition of Evaluation criteria: the compositions for cover of Comparative Preparation O: No cut mark is formed. Examples 1 to 6 to be used for the golf balls of Comparative A: Slight cut mark is formed. Examples 1 to 6 and the Stiffness modulus are shown in X: Large cut mark is formed. Table 3. In addition, the amount of each component to be XX: Large cut mark which can not stand use is formed. formulated in the tables is represented by parts by weight, Further, in order to examine the durability of the above and it is also the same in the following tables. In the tables, golf ball, a golf ball was hit at a head Speed of 45 m/second the ionomer resin as the component (A) and the glycidyl using a Swing robot mounted with a No. 1 wood club group-modified Styrene-based block copolymer as the com manufactured by True Temper Co., and the number of times ponent (B) are represented by the trade name, and the details until breakage was arisen was measured. The resulting value will be explained at the back of Table 3 in order. Regarding was indicated as a durability indeX in case of the number of Comparative Preparation Example 6 to be used as the cover Comparative Example 6 being 100. composition of the golf ball of Comparative Example 6, the Further, shot feel and the control properties of the result formulation component is not shown in Table 3 and is shown ing golf ball were evaluated by 10 top professional golfers at the back of Table 3 as * 17 because of its balata cover. 15 according to a practical hitting test. The evaluation criteria The extrusion conditions are as follows: a Screw diameter: are as follows. The results shown in the Tables below are 45 mm; a Screw revolution per minute: 200 rpm; a Screw based on the fact that not less than 8 out of 10 professional L/D: 35. The formulation components were heated at 220 golferS evaluated with the same criterion about each test to 260 C. at the die position of the extruder. The stiffness item. modulus is measured according to ASTM D-747 after a Evaluation criteria: sheet having a thickness of about 2 mm obtained by heat O: Good, shot feel and control properties are similar to press molding was preserved at 23° C. for two weeks. those of the golf ball with the balata cover. The compositions for cover of Comparative Preparation A: Control properties are similar to those of the golf ball with Examples 1 to 6 to be used for the cover of the golf balls of the balata cover, but shot feel is quite different from that Comparative Examples 1 to 6 will be explained. The com 25 of the golf ball with the balata cover, that is, it is too position of Comparative Preparation Example 1 is a cover heavy, which results in too strong impact, or it is too Soft, composition wherein only a high-rigid ionomer resin is used which results in heavy feeling. as the base resin, and the cover composition of Comparative X: Both shot feel and control properties are inferior. Preparation Example 1 corresponds to a conventional Stan In Table 4, the ball weight, ball compression, ball initial dard composition for ionomer cover. In addition, the cover Velocity, flight distance, Spin, cut resistance, durability, shot composition of Comparative Preparation Example 6 is a feel and controllability of the golf balls of Examples 1 to 5 standard composition for balata cover. The golf ball of as well as kind of the cover composition used in the Comparative Example 1 wherein the cover composition of production of the golf ball are shown. Those of the gold balls Comparative Preparation Example 1 is used and golf ball of of Examples 6 to 9, those of the golf balls of Comparative Comparative Example 6 wherein the cover composition of 35 Examples 1 to 3 and those of the golf balls of Comparative Comparative Preparation Example 6 is used are golf balls Examples 4 to 6 are shown in Tables 5, 6 and 7, respectively. for a criterion of comparison. In addition, the cover com position of Comparative Examples 2 to 5 are compositions TABLE 1. for cover wherein a high-rigid ionomer is used in combina tion with a terpolymer Soft ionomer resin as the base resin. 40 Preparation Example No. (3) Production of golf ball 1. 2 3 4 5 A thread wound golf ball was obtained by molding a semispherical half-shell from the cover composition of the Hi-milan 1605 *1 25 22.5 O O O H-man 1707 *2 O O 2O O O above item (2), covering the core of the item (1) with two 45 Hi-milan AM7318 *3 O O O 2O O half-shells and then Subjecting to a press molding in a die for Hi-milan 1856 *4 O O O 40 O the golf ball. The thread wound golf ball was coated with a Hi-milan 1706 *5 25 22.5 2O O 25 Hi-milan AM7317 *6 O O O 2O O paint to give a coated golf ball of 42.7 mm in outer diameter. H-man 1855 *7 35 40 40 O 35 The ball weight, ball compression, ball initial velocity, Hi-milan MK7320 *8 O O O O 25 flight distance (carry) and spin of the golf ball thus obtained 50 TUFTEC Z513 * 14 15 O O 2O O TUFTEC Z514 * 15 O 15 2O O 15 were measured. The ball compression was measured by Titanium dioxide 2.O 2.O 2.0 2.O 2.0 PGA method, and the ball initial velocity was measured by Barium sulfate 2.O 2.O 2.0 2.O 2.0 R & A initial Velocity measuring method. The flight distance Stiffness modulus (MPa) 175 150 125 185 155 was measured by hitting with a No. 1 wood club at a head Speed of 45 m/second, using a Swing robot manufactured by 55 True Temper Co. Spin was measured by hitting with a No. 9 iron club at a head Speed of 34 m/second, using a Swing TABLE 2 robot manufactured by True Temper Co., and then taking a Preparation Example No. photograph of a mark provided on the hit golf ball using a high-Speed camera. 60 6 7 8 9 Furthermore, in order to examine cut resistance of the golf Hi-milan 1706 *5 O 3O O O balls of the Examples 1 to 9 and Comparative Examples 1 Hi-milan AM7317 *6 O O 3O O to 6, the top part of the golf ball was hit at a head Speed of H-man 1855 *7 O 2O 25 40 Surlyn AD8512 *9 25 O O 2O 30 m/second using a Swing robot mounted with a pitching Surlyn AD8269 *10 1O O O O wedge manufactured by True Temper Co. to examine 65 Surlyn AD8511 *11 25 O O 2O whether a cut mark is arisen or not. The evaluation criteria Surlyn 7940 * 12 O 3O O O are as follows. 5,824,740 11 12 Kasei Industries Co. Ltd., styrene content: about 30% by weight, hydroge TABLE 2-continued nated butadiene content: about 70% by weight, glycidyl methacrylate content: about 1% by weight, JIS-A hardness: 84 Preparation Example No. * 15: TUFTEC Z514 (trade name), hydrogenated glycidyl methacrylate adduct of hydrogenated styrene-butadiene-styrene block copolymer, manu 6 7 8 9 factured by Asahi Kasei Industries Co. Ltd., styrene content: about 20% by weight, hydrogenated butadiene content: about 80% by weight, glycidyl Iotek 8000 *13 O O 3O O TUFTEC Z514 * 15 40 2O 15 O methacrylate content: about 1% by weight, JIS-A hardness: 65 TUFTEC trial product * 16 O O O 2O * 16: TUFTEC trial product, glycidyl methacrylate adduct of hydrogenated Titanium dioxide 2.O 2.0 2.O 2.0 styrene-butadiene-styrene block copolymer, manufactured by Asahi Kasei Barium sulfate 2.O 2.0 2.O 2.0 Industries Co. Ltd., styrene content: about 20% by weight, hydrogenated Stiffness modulus (MPa) 160 2OO 215 145 butadiene content: about 80% by weight, glycidyl methacrylate content: about 0.5% by weight, JIS-A hardness: 65 * 17: Balata cover Normal composition for balata cover

TABLE 3 TABLE 4 15 Comparative Preparation Example No Example No. 1. 2 3 4 5 6 1. 2 3 4 5 Hi-milan 1605 *1 50 3O O O 15 Balata Hi-milan AM7318 *3 O O 25 O O COWe Hi-milan 1706 *5 50 3O O 60 15 * 17 Cover composition 1. 2 3 4 5 Hi-milan AM7317 *6 O O 25 O O H-man 1855 *7 O O O 40 70 (Preparation Example No.) Surlyn AD8269 *10 O 40 50 O O Ball weight (g) 45.4 45.4 45.3 45.3 45.3 Titanium dioxide 2.O 2.O 2.0 2.O 2.O Ball compression (PGA) 87 85 84 87 86 Barium sulfate 2.O 2.O 2.0 2.O 2.O 25 Stiffness modulus (MPa) 340 16O 2OO 18O 150 Ball initial velocity 252.9 252.7 252.5 253.0 252.7 (feet/second) * 1: Hi-milan 1605 (trade name), ethylene-methacrylic acid copolymer iono Flight distance (yard) 229 228 227 229 228 mer resin obtained by neutralizing with a sodium ion, manufactured by Mitsui Du Pont Polychemical Co., MI (melt index): 2.8, stiffness modulus: 310 MPa, Spin (rpm) 85OO 86OO 865O 840O 86OO Shore D-scale hardness: 62, Cut resistance O O O O O * 2: Hi-milan 1707 (trade name), ethylene-methacrylic acid copolymer iono mer resin obtained by neutralizing with a sodium ion, manufactured by Mitsui Durability (index) 250 275 3OO 250 275 Du Pont Polychemical Co., MI: 0.9, stiffness modulus: 320 MPa, Shore Shot feel and controllability O O O O O D-scale hardness: 63 * 3: Hi-milan AM7318 (trade name), ethylene-methacrylic acid copolymer ionomer resin obtained by neutralizing with a sodium ion, manufactured by 35 Mitsui Du Pont Polychemical Co., MI: 2.1, stiffness modulus: 345 MPa, Shore D-scale hardness: 65 *4: Hi-milan 1856 (trade name), ethylene-butyl acrylate-methacrylic acid TABLE 5 terpolymer ionomer resin obtained by neutralizing with a sodium ion, manufactured by Mitsui Du Pont Polychemical Co., MI: 1.0, stiffness Example No. modulus: 85 MPa, Shore D-scale hardness: 53 40 *5: Hi-milan 1706 (trade name), ethylene-methacrylic acid copolymer iono 6 7 8 9 mer resin obtained by neutralizing with a zinc ion, manufactured by Mitsui Cover composition 6 7 8 9 Du Pont Polychemical Co., MI: 0.8, stiffness modulus: 260 MPa, Shore (Preparation Example No.) D-scale hardness: 61 Ball weight (g) 45.4 45.4 45.3 45.3 * 6: Hi-milan AM7317 (trade name), ethylene-methacrylic acid copolymer Ball compression (PGA) 86 88 89 85 ionomer resin obtained by neutralizing with a zinc ion, manufactured by 45 Ball initial velocity (feet/second) 252.8 253.O 253.2 252.6 Mitsui Du Pont Polychemical Co., MI: 1.2, stiffness modulus: 310 MPa, Flight distance (yard) 228 229 230 228 Shore D-scale hardness: 64 Spin (rpm) 85SO 835O 83OO 865O *7: Hi-milan 1855 (trade name), ethylene-butyl acrylate-methacrylic acid Cut resistance O O O O terpolymer ionomer resin obtained by neutralizing with a zinc ion, manufac Durability (index) 263 195 238 3OO tured by Mitsui Du Pont Polychemical Co., MI: 1.0, stiffness modulus: 90 Shot feel and controllability O O O O MPa, Shore D-scale hardness: 55 *8: Hi-milan MK7320 (trade name), ethylene-methacrylic acid copolymer 50 ionomer resin obtained by neutralizing with a potassium ion, manufactured by Mitsui Du Pont Polychemical Co., MI: 2.8, stiffness modulus: 290 MPa, Shore D-scale hardness: 61 TABLE 6 *9: Surlyn AD8612 (trade name), ethylene-methacrylic acid copolymer ionomer resin obtained by neutralizing with a sodium ion, manufactured by Comparative Du Pont Co., MI: 4.4, stiffness modulus. 280 MPa, Shore D-scale hardness: 55 Example No. 62 * 10: Surlyn AD8269 (trade name), ethylene-butyl acrylate-methacrylic acid 1. 2 3 terpolymer resin obtained by neutralizing with a zinc ion, manufactured by Du Pont Co., MI: 1.0, stiffness modulus: 26 MPa, Shore D-scale hardness: 36 Cover composition 1. 2 3 * 11: Surlyn AD8511 (trade name), ethylene-methacrylic acid copolymer (Comparative Preparation Example No.) Ball weight (g) 45.3 45.3 45.4 ionomer resin obtained by neutralizing with a zinc ion, manufactured by Du 60 Pont Co., MI: 3.4, stiffness modulus: 220 MPa, Shore D-scale hardness: 60 Ball compression (PGA) 92 87 88 * 12: Surlyn 7940 (trade name), ethylene-methacrylic acid copolymer ionomer Ball initial velocity (feet/second) 253.O 251.O 251.2 resin obtained by neutralizing with a lithium ion, manufactured by Du Pont Flight distance (yard) 230 222 223 Co., MI: 2.8, stiffness modulus: 350 MPa, Shore D-scale hardness: 63 Spin (rpm) 7OOO 8100 7800 * 13: lotek 8000 (trade name), ethylene-acrylic acid copolymer ionomer resin Cut resistance O O O Durability (index) 15O 243 225 obtained by neutralizing with a sodium ion, manufactured by Exxon Chemical 65 Co., MI: 0.8, stiffness modulus: 370 MPa, Shore D-scale hardness: 64 Shot feel and controllability X O A * 14: TUFTEC Z513 (trade name), glycidyl methacrylate adduct of hydroge nated styrene-butadiene-styrene block copolymer, manufactured by Asahi 5,824,740 13 14 (2) Preparation of cover composition TABLE 7 The pelletized compositions for the cover prepared in Comparative Preparation Examples 1 to 9 and Comparative Preparation Example No. Examples 1 to 5 were used. 5 4 5 6 (3) Production of golf ball The cover composition obtained in the above item (2) was Cover composition 4 5 6 (Comparative Preparation Example No.) covered on the solid core obtained in the above item (1) by Ball weight (g) 45.3 45.4 45.3 an injection molding to give a coated golf ball of 42.7 mm Ball compression (PGA) 88 86 87 in diameter. Ball initial velocity (feet/second) 251.1 2SO.8 251.0 The ball weight, ball compression, ball initial velocity, Flight distance (yard) 222 221 223 Spin (rpm) 7900 8150 8500 flight distance, Spin, cut resistance and durability of the golf Cut resistance O A XX ball thus obtained were measured and, further, shot feel and Durability (index) 213 220 100 controllability were examined. Shot feel and controllability A A O 15 In Table 8, the ball weight, ball compression, ball initial Velocity, flight distance, Spin, cut resistance, durability, shot AS is apparent from a comparison between the character feel and controllability of the golf balls of Examples 10 to istics of the golf balls of Examples 1 to 9 shown in Tables 14 as well as kind of the cover composition used in the 4 to 5 and those of the golf balls of Comparative Examples production of the golf ball are shown. Those of the golf balls 1 to 6 shown in Tables 6 to 7, all golf balls of Examples 1 of Examples 15 to 18 anindeX in case of the impact resis to 9 had excellent shot feel, controllability and spin perfor tance number of Comparative Example 7 being 100. mance, which are similar to those of the golf balls with the balata cover of Comparative Example 6 for a criterion of TABLE 8 comparison. And besides, they attained the flight distance of 227 to 230 yards, which is almost the same as that of the golf 25 Preparation Example No. ball of Comparative Example 1 wherein only a high-rigid 1O 11 12 13 14 ionomer resin is used as the base resin. Cut resistance was Cover composition 1. 2 3 4 5 also the same as that of the golf ball of Comparative (Preparation Example Example 1 and it reached a Satisfactory level. In addition, the No.) golf balls of Examples 1 to 9 were considerably Superior in Ball weight (g) 45.4 45.4 45.3 45.3 45.4 durability in comparison with the golf balls of Comparative Ball compression (PGA) 91 90 89 91 90 Examples 1 and 6. Ball initial velocity (feet/second) 253.1 253.0 252.9 253.2 253.0 Flight distance (yard) 233 232 232 234 232 To the contrary, the golf ball of Comparative Example 1 Spin (rpm) 845O 85OO 8600 83SO 85OO as the thread wound golf ball with a Standard ionomer cover Cut resistance O O O O O wherein only a high-rigid ionomer resin is used as the cover 35 Durability (index) 167 175 183 163. 175 resin of the cover showed a hard shot feel and was inferior Shot feel and controllability O O O O O in controllability. Regarding the golf balls of Comparative Examples 2 to 5 wherein the mixture of the high-rigid ionomer resin and terpolymer Soft ionomer resin is used as TABLE 9 the base resin of the cover, the Spin performance and 40 controllability were similar to those of the golf ball with the Example No. balata cover but shot feel was not Satisfactory. And besides, the flight distance was 221 to 223 yards and was consider 15 16 17 18 ably inferior in comparison with that of the golf balls of Cover composition 6 7 8 9 Examples 1 to 9. Regarding the normal thread wound golf 45 (Preparation Example No.) Ball weight (g) 45.4 45.3 45.3 45.4 ball with balata cover of Comparative Example 6, shot feel, Ball compression (PGA) 90 92 92 89 controllability and Spin performance are excellent, but the Ball initial velocity (feet/second) 253.O 253.3 253.3 253.0 flight distance was 223 yards and was considerably inferior Flight distance (yard) 233 234 234 232 in comparison with the golf balls of Examples 1 to 9. Cut Spin (rpm) 845O 835O 83OO 85.50 50 Cut resistance O O O O resistance is particularly inferior and the durability became Durability (index) 172 162 160 183 half to one-third of those of the golf balls of Examples 1 to Shot feel and controllability O O O O 9 and was considearably inferior. Examples 10 to 18 and Comparative Examples 7 to 12 (two-piece solid golf ball) 55 TABLE 10 (1) Production of core Comparative Example No. Arubber composition prepared by formulating 36 parts by 7 8 9 1O 11 weight of Zinc acrylate, 20 parts by weight of Zinc oxide, 1.2 Cover composition 1. 2 3 4 5 parts by weight of dicumyl peroxide and 0.5 parts by weight 60 (Comparative Preparation Example of an antioxidant Yoshinox 425 (trade name), manufactured No.) by Yoshitomi Seiyaku Co., Ltd. in 100 parts by weight of Ball weight (g) 45.4 45.3 45.3 45.4 45.3 Ball compression (PGA) 96 92 93 93 92 a polybutadiene rubber BR-11 (trade name), manufactured Ball initial velocity (feet/second) 253.3 251.3 251.5 251.5 251.3 by Japan Synthetic Rubber Co., Ltd was subjected to a Flight distance (yard) 233 225 226 226 225 Vulcanization molding at 160° C. for 25 minutes to give a 65 Spin (rpm) 68OO 77OO 7500 745O 7900 Solid core. The average diameter of the Solid core thus Cut resistance O O O O O obtained was 38.2 mm. 5,824,740 15 16 the golf ball of Examples 33 and the stiffness modulus are TABLE 10-continued shown in Table 12. In addition, the amount of each compo nent to be formulated in the tables is represented by parts by Comparative Example No. weight, and it is also the same in the following tables. In the tables, the ionomer resin, maleic anhydride-modified olefin 7 8 9 1O 11 copolymer and glycidyl group-modified Styrene-based block Durability (index) 1OO 145 150 142 1.47 copolymer are represented by the trade name, and the details Shot feel and controllability X A A A A will be explained at the back of Table 14 in the order of the ionomer resin, maleic anhydride-modified olefin copolymer and glycidyl group-modified Styrene-based block copoly AS is apparent from a comparison between the character mer. Regarding Comparative Preparation Example 14 to be istics of the golf balls of Examples 10 to 18 shown in Tables used as the cover composition of the golf ball of Compara 8 to 9 and those of the golf balls of Comparative Examples tive Example 19, the formulation component is not shown in 7 to 11 shown in Table 10, the two-piece solid golf balls of Table 14 and is shown at the back of Table 14 as * 14 because Examples 10 to 18 of the present invention had excellent of its balata cover. shot feel, controllability and Spin performance, Similar to the 15 The extrusion conditions are as follows: a Screw diameter: thread wound golf balls of Example 1 to 9. And besides, they 45 mm; a Screw revolution per minute: 200 rpm; a Screw attained the flight distance of 232 to 234 yards, which is L/D: 35. The formulation components were heated at 220 almost the same as that of the golf ball of Comparative to 260 C. at the die position of the extruder. The stiffness Example 7 wherein only a high-rigid ionomer resin is used modulus is measured according to ASTM D-747 after a as the base resin. Cut resistance reached a Satisfactory level. sheet having a thickness of about 2 mm obtained by heat In addition, the golf balls of Examples 10 to 18 were press molding was preserved at 23° C. for two weeks. considerably Superior in durability to the golf ball of Com Among the compositions for cover of Comparative Prepa parative Example 7. ration Examples to be used for the cover of the golf balls of To the contrary, the golf ball of Comparative Example 7 Comparative Examples, typical one for a criterion of com as a normal two-piece Solid golf ball using only a high-rigid 25 parison will be explained. The composition of Comparative ionomer resin as the cover resin of the cover showed Preparation Example 12 is a cover composition wherein excellent flight performance and cut resistance, but was only a high-rigid ionomer resin is used as the base resin, and inferior in shot feel and controllability. The golf balls of the cover composition of Comparative Preparation Example Comparative Examples 8 to 11 using the high-rigid ionomer 12 corresponds to a conventional Standard composition for resin in combination with the terpolymer Soft ionomer resin ionomer cover. In addition, the cover composition of Com as the base resin were inferior in shot feel and controllability parative Preparation Example 14 is a Standard composition to the golf balls of Examples 10 to 18, and was also inferior for balata cover. The golf ball of Comparative Example 12 in flight distance to the golf balls of Examples 10 to 18. wherein the cover composition of Comparative Preparation Example 12 is used and golf ball of Comparative Example Examples 19 to 28 and Comparative Examples 12 35 14 wherein the cover composition of Comparative Prepara to 19 (thread wound golf ball) tion Example 19 is used are golf balls for a criterion of Thread wound golf balls of Examples 19 to 28 and comparison, Comparative Examples 12 to 19 were produced through the (3) Production of golf ball following processes (1) to (3). A thread wound golf ball was obtained by molding a (1) Production of core 40 Semi-spherical half-shell from the cover composition of the A thread wound core having an outer diameter of 39.5 mm above item (2) and then covering the core of the item (1) was produced by winding a thread rubber comprising a with two half-shells. The thread wound golf ball was coated natural rubber/low-cis isoprene rubber Shell IR-309 (trade with a paint to give a coated golf ball of 42.7 mm in outer name) (=50:50) as the base rubber on a liquid center having diameter. an Outer diameter of 28.1 mm, Said liquid center comprising 45 The ball weight, ball compression, ball initial velocity, a paste obtained by dispersing barium Sulfate in water and a flight distance (carry) and spin of the golf ball thus obtained center bag of a Vulcanized natural rubber having a thickneSS were measured, and the durability and cut resistance were of 1.7 mm, which covers the paste. examined. (2) Production of cover composition The ball compression was measured by PGA method, and The formulation components shown in Tables 11 to 14 50 the ball initial velocity was measured by R & A initial were mixed using a kneading type twin-Screw extruder to Velocity measuring method. The flight distance was mea obtain a pelletized cover composition. Further, the compo sured by hitting with a No. 1 wood club at a head speed of Sition of the compositions for cover of Preparation Examples 45 m/second, using a Swing robot manufactured by True 10 to 14 to be used for the golf balls of Examples 19 to 23 Temper Co. Spin was measured by hitting with a No. 9 iron and the stiffness modulus are shown in Table 11. The 55 club at a head Speed of 34 m/second, using a Swing robot composition of the compositions for cover of Preparation mounted with a No. 9 iron club manufactured by True Examples 15 to 19 to be used for the golf balls of Examples Temper Co., and then taking a photograph of a mark 24 to 28 and the stiffness modulus are shown in Table 12. provided on the hit golf ball using a high-speed camera. The composition of the compositions for cover of Compara In addition, the durability was evaluated as follows. That tive Preparation Examples 7 to 10 to be used for the golf 60 is, a golf ball was hit at a head Speed of 45 m/second using balls of Comparative Examples 12 to 15 and the stiffness a Swing robot mounted with a No. 1 wood club manufac modulus are shown in Table 13. The composition of the tured by True Temper Co., and the number of times until compositions for cover of Comparative Preparation breakage was arisen was measured. The resulting value was Examples 11 to 14 to be used for the golf balls of Com indicated as an indeX in case of the value of the golf ball of parative Examples 16 to 19 and the stiffness modulus are 65 Comparative Example 19 being 100. shown in Table 14. Further, the composition of the compo Furthermore, cut resistance was evaluated as follows. sitions for cover of Preparation Example 20 to be used for That is, the top part of the golf ball was hit at a head Speed 5,824,740 17 18 of 30 m/second using a Swing robot mounted with a pitching wedge manufactured by True Temper Co. to examine TABLE 13 whether a cut mark is arisen or not. The evaluation criteria Comparative Preparation are as follows. Example No. Evaluation criteria O: No cut mark is formed. 7 8 9 1O A: Slight cut mark is formed. Hi-milan 1605*1 50 45 25 2O Hi-milan 17062 50 45 25 2O X: Large cut mark is formed. H-man 1855*3 O 1O 40 40 XX: Large cut mark which can not stand use is formed. Bondine AX8390*9 O O 1O O Further, shot feel and controllability of the resulting golf TUFTEC M1943*10 O O O 2O ball were evaluated by 10 top professional golfers according Titanium dioxide 2 2 2 2 to a practical hitting test. The evaluation criteria are as Stiffness modulus (MPa) 34O 27O 17O 150 follows. The results shown in the Tables below are based on the fact that not less than 8 out of 10 professional golfers 15 evaluated with the same criterion about each test item. TABLE 1.4 Shot feel Comparative Preparation O: Good, impact force is Small, Soft feeling Example No. X: Inferior 11 12 13 14 Controlability Hi-milan 1605*1 25 25 30 Balata O: Good, spin is easily put when using an iron club, Soft Hi-milan 17062 25 25 3O COWe feeling H-man 1855*3 35 O O *14 X: Inferior Surlyn AD8269*8 O O 40 Bondine AX8390*9 O 50 O In Table 15, the ball weight, ball compression, ball initial 25 AR-2O111 15 O O Velocity, flight distance, Spin, durability, cut resistance, shot Titanium dioxide 2 2 2 feel and controllability of the golf balls of Examples 19 to Stiffness modulus (MPa) 170 90 160 240 23 as well as kind of the cover composition used in the production of the golf ball are shown. Those of the gold balls * 1: Hi-milan 1605 (trade name), ethylene-methacrylic acid copolymer iono of Examples 24 to 28, those of the golf balls of Comparative mer resin obtained by neutralizing with a sodium ion, manufactured by Mitsui Du Pont Polychemical Co., MI (melt index): 2.8, stiffness modulus: 310 MPa, Examples 12 to 15 and those of the golf balls of Compara shore D-scale hardness: 62. tive Examples 16 to 19 are shown in Tables 16, 17 and 18, *2: Hi-milan 1706 (trade name), ethylene-methacrylic acid copolymer iono respectively. The kind of the cover composition is shown by mer resin obtained by neutralizing with a zinc ion, manufactured by Mitsui Preparation Example No. or Comparative Preparation Du Pont Polychemical Co., MI: 0.8, stiffness modulus: about 260 MPa, Shore-D scale hardness: 61. Example No. 35 *3: Hi-milan 1855 (trade name), ethylene-butyl acrylate-methacrylic acid terpolymer ionomer resin obtained by neutralizing with a zinc ion, manufac TABLE 11 tured by Mitsui Du Pont Polychemical Co., MI: 1.0, stiffness modulus: about 90 MPa, Shore-D scale hardness: 55. *4: Hi-milan MK7320 (trade name), ethylene-methacrylic acid copolymer Preparation Example No. ionomer resin obtained by neutralizing with a potassium ion, manufactured by 40 Mitsui Du Pont Polychemical Co., MI: 2.8, stiffness modulus: about 290 MPa, 1O 11 12 13 14 Shore-D scale hardness: 61. Hi-milan 1605*1 2O 2O 2O 15 25 *5: Surlyn AD8511 (trade name), ethylene-methacrylic acid copolymer Hi-milan 17062 2O 2O 2O 15 25 ionomer resin obtained by neutralizing with a zinc ion, manufactured by Du H-man 1855*3 3O 3O 3O 40 2O Pont Co., MI:3.4, stiffness modulus: about 220 MPa, Shore-D scale hardness: Bondine AX8390*9 2O 15 O O O 60. TUFTEC M1943*10 O O 25 2O 1O 45 *6: Surlyn AD8512 (trade name), ethylene-methacrylic acid copolymer TUFTEC Z513*12 1O O 5 O O ionomer resin obtained by neutralizing with a sodium ion, manufactured by TUFTEC Z514*13 O 15 O 1O 2O Du Pont Co., MI: 4.4, stiffness modulus: about 280 MPa, Shore-D scale hardness: 62. Titanium dioxide 2 2 2 2 2 *7: Hi-milan AM7316 (trade name), ethylene-butyl acrylate-methacrylic acid Stiffness modulus (MPa) 150 135 145 120 160 terpolymer ionomer resin obtained by neutralizing with a zinc ion, manufac tured by Mitsui Du Pont Polychemical Co., MI: 3.0, stiffness modulus: about 50 24 MPa, Shore-D scale hardness: 34. *8: Surlyn AD8269 (trade name), ethylene-butyl acrylate-methacrylic acid TABLE 12 terpolymer resin obtained by neutralizing with a zinc ion, manufactured by DuPont Co., MI: 1.0, stiffness modulus: 26 MPa, Shore-D scale hardness: 36. Preparation Example No. *9: Bondine AX8390 (trade name), ethylene-ethyl acrylatemaleic anhydride terpolymer, manufactured by Sumitomo Chemical Industries Co., MI: 7.0, 15 16 17 18 19 2O 55 stiffness modulus:<10 MPa, content of ethyl acrylate--maleic anhydride:32% (maleic anhydride content: 1 to 4%). Hi-milan 1605*1 2O O O 25 O O * 10: TUFTEC M1943 (trade name), maleic anhydride adduct of styrene Hi-milan 17062 2O 2O O 25 O O butadiene-styrene block copolymer, manufactured by Asahi Kasei Industries H-man 1855*3 3O 3O 2O O O 40 Co. Ltd., JIS-A hardness: 67, styrene content: about 20% by weight. Hi-milan MK7320*4 O 2O O O O O *11: AR-201 (trade name), graft modified product of ethylene-ethyl acrylate Surlyn AD8511*5 O O 25 O 3O 2O 60 copolymer due to maleic anhydride, manufactured by Mitsui Du Pont Surlyn AD8512*6 O O 25 O 3O 2O Polychemical Co., JIS-A hardness: 51. Hi-milan AM73167 O O O O 1O O * 12: TUFTEC Z513 (trade name), glycidyl methacrylate adduct of hydroge TUFTEC M1943*10 O 2O O 40 O O nated styrene-butadiene-styrene block copolymer, manufactured by Asahi AR-2O111 2O O 2O O 2O 1O Kasei Industries Co. Ltd., JIS-A hardness: 84, styrene content: about 30% by TUFTEC Z514*13 1O 5 1O 1O 1O 1O weight, hydrogenated butadiene content: about 70% by weight, glycidyl Titanium dioxide 2 2 2 2 2 2 methacrylate content: about 1% by weight. Stiffness modulus (MPa) 130 155 145 12O 140 140 65 * 13: TUFTEC Z514 (trade name), glycidyl methacrylate adduct of hydroge nated styrene-butadiene-styrene block copolymer, manufactured by Asahi Kasei Co. Ltd., JIS-A hardness: 65, styrene content: about 20% by weight, 5,824,740 19 20 hydrogenated butadiene content: about 80% by weight, glycidyl methacrylate content: about 1% by weight. TABLE 18-continued * 14: Balata cover. Normal balata cover composition Comparative Examples No. TABLE 1.5 16 17 18 19

Examples Cut resistance A XX A XX Shot feel O X O O 19 2O 21 22 23 Controllability O O O O

Cover composition 1O 11 12 13 14 (Preparation Example No.) AS is apparent from a comparison between the character Ball weight (g) 45.4 45.3 45.4 45.4 45.3 istics of the golf balls of Examples 19 to 28 shown in Tables Ball compression 86 85 86 85 86 15 to 16 and those of the golf balls of Comparative Ball initial velocity (feet/second) 252.9 252.8 252.9 252.7 252.9 Examples 12 to 19 shown in Tables 17 to 18, the golf balls Flight distance (yard) 229 228 230 228 229 15 of the Examples 19 to 28 attained the flight distance of 228 Spin (rpm) 845O 85SO 85OO 86SO 8400 to 230 yards, which is almost the same as that of the golf ball Durability (index) 275 300 28O 315 265 of Comparative Example 12 wherein only a high-rigid Cut resistance O O O O O ionomer resin is used as the base resin for the cover and the Shot feel O O O O O flyight performance was excellent. In addition, the golf balls Controllability O O O O O of Examples 19 to 28 showed a large Spin amount and were Superior in Shot feel, controllability, durability and cut resistance. TABLE 16 The durability will be explained in detail. The golf balls of Examples 19 to 28 showed an index, which indicates the Example No. 25 durability, of 275 to 315 and have an excellent durability corresponding to a durability which is 2.75 to 3.15 times as 24 25 26 27 28 strong as that of the golf ball covered with the balata cover Cover composition 15 16 17 18 19 of Comparative Examples 19. As a matter of course, they are (Preparation Example No.) by far Superior in durability to the golf ball of Comparative Ball weight (g) 45.3 45.3 45.4 45.4 45.3 Ball compression 85 86 86 85 86 Example 19 and are superior in durability to the golf balls Ball initial velocity (feet/second) 252.8 253.O 252.9 252.8 253.0 covered with the soft cover of Comparative Examples 14 to Flight distance (yard) 228 229 229 228 229 18. Spin (rpm) 86OO 845O 85SO 86SO 85SO Durability (index) 300 275 285 310 285 In addition, cut resistance will also be explained in detail. Cut resistance O O O O O No cut mark was formed on the golf balls of Examples 19 Shot feel O O O O O 35 to 28 and Comparative Examples 12 to 13, but a small cut Controllability O O O O O mark was formed on the golfballs of Comparative Examples 14 to 16 and 18. In addition, a large cut mark which can not Stand use is formed on the golf ball of Comparative Example TABLE 1.7 17. As a matter of course, a large cut mark which can not 40 stand use is formed on the golf ball covered with the balata Comparative Example No. cover of Comparative Example 19. On the other hand, the golf balls of Comparative 12 13 14 15 Examples 12 to 13 wherein only a high-rigid ionomer resin Cover composition 7 8 9 1O is used as the base resin were inferior in shot feel and (Comparative Preparation Example No.) 45 controllability were inferior. The golf balls of Comparative Ball weight (g) 45.3 45.4 45.4 45.4 Examples 14 to 18 were 5 to 9 yards inferior in flight Ball compression 86 85 83 84 Ball initial velocity (feet/second) 252.7 252.3 250.9 251.0 distance to the golf balls of the Comparative Examples 19 to Flight distance (yard) 229 229 222 223 28. That is, the golf balls of Comparative Examples 14 to 17 Spin (rpm) 7OOO 73OO 7900 8150 wherein the glycidyl group-modified Styrene-based copoly Durability (index) 120 16O 21O 225 50 Cut resistance O O A A mer e.g. TUFTEC Z513, TUFTEC Z514 (both are trade Shot feel X X O O name) is not formulated and only ionomer resin and maleic Controllability X X O O anhydride-modified olefin copolymer are used and golf ball of Comparative Example 18 which was softened by using the Soft ionomer resin were Superior in shot feel and con 55 trollability, but were insufficient in flight performance. TABLE 1.8 In addition, the results of the practical test due to profes Comparative Examples No. Sional golfers will be explained in detail as follows. The golf balls of Examples 19 to 28 have shot feel and 16 17 18 19 controllability, which are similar to those of the golf ball Cover composition 11 12 13 14 60 covered with the balata cover of Comparative Example 19, (Comparative Preparation Example No.) and the flight distance reached to the Satisfactory level. Ball weight (g) 45.3 45.3 45.4 45.4 However, the golf balls of Comparative Examples 12 to 13 Ball compression 84 83 84 85 Ball initial velocity (feet/second) 251.2 2SOS 251.3 251.2 wherein only an ionomer resin is used as the base resin for Flight distance (yard) 223 217 223 223 the cover showed a hard shot feel, and Spin is not easily put Spin (rpm) 795O 9300 8050 8500 65 and controllability was inferior. The golf balls of Compara Durability (index) 21O 110 220 100 tive Examples 14 to 18 were Superior in shot feel and controllability, but were inferior in flight distance. 5,824,740 21 22 Examples 29 to 33 and Comparative Examples 20 to 23 TABLE 20-continued (1) Production of core Arubber composition prepared by formulating 36 parts by Comparative Example No. weight of Zinc acrylate, 20 parts by weight of Zinc oxide, 1.2 parts by weight of dicumyl peroxide and 0.5 parts by weight 2O 21 22 23 Spin (rpm) 6900 78OO 8OSO 8OOO of an antioxidant Yoshinox 425 (trade name), manufactured Durability (index) 125 22O 230 225 by Yoshitomi Seiyaku Co., Ltd. in 100 parts by weight of Cut resistance O A A A a polybutadiene rubber BR-11 (trade name), manufactured Shot feel X O O O by Japan Synthetic Rubber Co., Ltd was subjected to a Controllability X O O O Vulcanization molding at 160° C. for 25 minutes to give a Solid core. The average diameter of the Solid core thus AS is apparent from a comparison between the character obtained was 38.2 mm. istics of the golf balls of Examples 29 to 33 shown in Table (2) Preparation of cover composition 19 and those of the golf balls of Comparative Examples 20 Among the cover compositions prepared in the above 15 to 23 shown in Table 20, the two-piece solid golf balls of Preparation Examples and Comparative Preparation Examples 29 to 33 of the present invention had excellent Examples, cover compositions of Preparation Examples 11, Spin performance, shot feel, controllability, flight 13, 15, 17 and 20 were used for Preparation Examples, and performance, durability and cut resistance, Similar to the those of Comparative Preparation Examples 7, 9, 10 and 13 golf balls of Examples 19 to 28. were used for Comparative Preparation Examples. That is, the golf balls of Examples 29 to 33 attained the (3) Production of golf ball flight distance of 229 to 230 yards, which is almost the same The cover composition obtained in the above item (2) was as that of the golf ball of Comparative Example 20 wherein covered on the solid core obtained in the above item (1) by only a high-rigid ionomer resin is used as the base resin. In an injection molding to give a coated golf ball of 42.7 mm addition, the golf balls of Examples 29 to 33 showed a large in diameter. 25 Spin amount and were Superior in Shot feel and The ball weight, ball compression, ball initial velocity, controllability, durability and cut resistance. flight distance, durability, cut resistance, shot feel and con To the contrary, the golf ball of Comparative Example 20 trollability of the golf ball thus obtained were examined. wherein only a high-rigid ionomer resin is used as the cover In Table 19, the ball weight, ball compression, ball initial resin of the cover was Superior in flight performance, but Velocity, flight distance, Spin, durability, cut resistance, shot were inferior in shot feel and controllability. The golf balls feel and controllability of the golf balls of Examples 29 to of Comparative Examples 21 to 23 were Superior in shot feel 33 as well as kind of the cover composition used in the and controllability, but they were 6 to 8 yards inferior in production of the golf ball are shown. Those of the golf balls flight distance to the golf balls of Examples 29 to 33. of Comparative Examples 20 to 23 are shown in Table 20. What is claimed is: The kind of the cover composition is shown by Preparation 35 1. A golf ball having a core and a cover for covering the Example No. or Comparative Preparation Example No. core, wherein said cover has a stiffness modulus of 100 to Further, the measuring method of various physical proper 250 MPa and comprises a heated mixture of an ionomer ties and evaluation method of shot feel and controllability resin and a glycidyl group-modified Styrene-based block are the same as those of Example 19. copolymer having a JIS-Ahardness of 30 to 90 as base resin. 40 2. The golf ball according to claim 1, wherein a mixing TABLE 1.9 weight ratio of ionomer resin to glycidyl group-modified Styrene-based block copolymer having a JIS-A hardness of Example No. 30 to 90 is 95:5 to 50:50. 29 3O 31 32 33 3. The golf ball of according to claim 1, wherein a 45 Styrene-based block copolymer moiety in the glycidyl Cover composition 11 13 15 17 2O group-modified Styrene-based block copolymer having a (Preparation Example No.) Ball weight (g) 45.4 45.3 45.4 45.3 45.4 JIS-A hardness of 30 to 90 is a block copolymer of poly Ball compression 92 91 91 92 92 styrene and poly(ethylene-butylene). Ball initial velocity (feet/second) 252.9 252.8 252.8 253.O 253.0 4. The golf ball according to claim 1, wherein a styrene Flight distance (yard) 230 229 229 23O 230 50 content of the Styrene-based block copolymer moiety in the Spin (rpm) 85OO 8600 85SO 85OO 85OO Durability (index) 31O 33O 315 275 3OO glycidyl group-modified Styrene-based block copolymer Cut resistance O O O O O having a JIS-Ahardness of 30 to 90 is 10 to 40% by weight. Shot feel O O O O O 5. The golf ball according to claim 1, wherein a glycidyl Controllability O O O O O group content of the glycidyl group-modified Styrene-based 55 block copolymer having a JIS-Ahardness of 30 to 90 is 0.05 to 10% by weight. TABLE 2.0 6. The golfball according to claim 1, wherein the ionomer resin is obtained by neutralizing with a metal ion at least a Comparative Example No. part of carboxyl groups in a copolymer of an O-olefin and an 60 Cl, B-unsaturated carboxylic acid having 3 to 8 carbon atoms, 2O 21 22 23 or neutralizing with a metal ion at least a part of carboxyl Cover composition 1O 12 13 16 groups in a terpolymer of an O-olefin, an C, B-unsaturated (Comparative Preparation Example No.) Ball weight (g) 45.3 45.4 45.3 45.3 carboxylic acid having 3 to 8 carbon atoms and an O, Ball compression 102 90 90 93 B-unsaturated carboxylate. Ball initial velocity (feet/second) 253.O 251.5 251.O 250.8 65 7. The golf ball according to claim 1, wherein the glycidyl Flight distance (yard) 230 223 223 222 group-modified Styrene-based block copolymer has a JIS-A hardness of 45 to 88. 5,824,740 23 24 8. The golf ball according to claim 4, wherein styrene from the group consisting of ethylene-acrylic acid content of the Styrene-based block copolymer moiety of the copolymer, ethylene-methacrylic acid copolymer and ter glycidyl group-modified Styrene based block copolymer is polymer of ethylene-methacrylic acid-acrylate. 15 to 35% by weight. 15. The golf ball according to claim 12, wherein the 9. The golf ball according to claim 1, wherein a glycidyl group content of the glycidyl group-modified Styrene-based maleic anhydride-modified olefin copolymer is a maleic block copolymer having a JIS-A hardness of 30 to 90 is 0.2 anhydride adduct of a hydrogenated block copolymer of to 5% by weight. Styrene-butadiene-Styrene block copolymer. 10. The golf ball according to claim 1, wherein a mixing 16. The golf ball according to claim 12, wherein the weight ratio of ionomer resin to glycidyl group-modified maleic anhydride-modified olefin copolymer is that obtained Styrene-based block copolymer having a JIS-A hardness of by Subjecting an ethylene-ethyl acrylate-maleic anhydride 30 to 90 is 90:10 to 55:45. terpolymer or an ethylene-ethyl acrylate copolymer to graft 11. The golf ball according to claim 1, wherein the modification using maleic anhydride. glycidyl group-modified block copolymer is a glycidyl 17. The golf ball according to claim 12, wherein a base methacrylate adduct of hydrogenated Styrene-butadiene 15 polymer of the glycidyl group-modified Styrene-based block Styrene block copolymer. copolymer is a hydrogenated Styrene-butadiene-styrene 12. A golf ball having a core and a cover for covering the block copolymer. core, wherein said cover has a stiffness modulus of 100 to 18. The golf ball according to claim 12, wherein the 250 MPa and comprises a heated mixture of an ionomer glycidyl group-modified Styrene-based block copolymer is a resin, a maleic anhydride-modified olefin copolymer and a glycidyl methacrylate adduct of a hydrogenated Styrene glycidyl group-modified Styrene-based block copolymer butadiene-styrene block copolymer. having a JIS-A hardness of 30 to 90 as base resin. 19. The golf ball according to claim 12, wherein the 13. The golf ball according to claim 12, wherein the Styrene content of the Styrene-based block copolymer moi heated mixture is obtained by mixing 30 to 70% by weight ety in the glycidyl group-modified Styrene-based block of the ionomer resin, 10 to 69.5% by weight of the maleic 25 anhydride-modified olefin copolymer and 0.5 to 20% by copolymer is 10 to 40% by weight and the glycidyl group weight of the glycidyl group-modified Styrene-based block content of the glycidyl group-modified Styrene-based block copolymer with heating. copolymer is 0.05 to 10% by weight. 14. The golf ball according to claim 12, wherein a base polymer of the ionomer resin is at least one Sort Selected