AU693248B2 - Golf ball - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Sumitomo Rubber Industries, Ltd.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

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INVENTION TITLE: Golf ball The following statement is a full description of this invention, including the best method of performing it known to me/us:- FIELD OF THE INVENTION The present invention relates to a golf ball. More particularly, it relates to a golf ball which has a high impact resilience and excellent durability as well as satisfactory flying distance and hit feeling (feeling at the time of hitting).

r r BACKGROUND OF THE INVENTION Hitherto, ionomer resins have been widely used for a cover of golf balls, because of excellent impact resistance, cut resistance, impact resilience etc. There have bee commercially available ionomer resins obtained by neutralizing with sodium ion sodium-neutralized ionomer resin), ionomer resins obtained by neutralizing with zinc ion zincneutralized ionomer resin), ionomer resins obtained by neutralizing with lithium ion lithium-neutralized ionomer resin), etc. under the trade name of "Surlyn" from Du Pont Co. in U.S.A. and "Hi-milan" from Mitsui Du Pont Polychemical Co., Ltd. in Japan, etc.

Among the above ionomer resins, the sodium-neutralized ionomer resin is superior in impact resilience to the zinc-neutralized ionomer resin. It is also known that a mixture of the sodium-neutralized ionomer resin and the zinc neutralized resin at an appropriate mixing ratio improves impact resilience in comparison with the sole use of the sodiumneutralized ionomer resin. Also, a golf ball using such a mixture of the sodium-neutralized ionomer resin and zinc-neutralized ionomer resin for Li

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the cover is suggested U.S. Patent 3,819,768).

Also, in Japanese Laid-Open Publication No. 61-82768, it is suggested that a neutralization degree can be enhanced by adding metal ions such as lithium Ion, potassium ion, cesium ion, rubidium ion, etc. to the sodium-neutralized ionomer resin or a mixture of the sodium-neutralized ionomer resin and zinc-neutralized ionomer resin to neutralize, thereby imparting high impact resilience to the golf ball.

Japanese Laid-Open Publication Nos. 2-149277 and 2- 297383 disclose a golf ball which employs a cover mainly formed from a lithium-neutralized ionomer resin.

However, since the above suggestions improve impact resistance by enhancing cover stiffness, durability of the golf ball is adversely deteriorated. In addition, the resulting golf gall has hard ball compression and poor hit feeling. Accordingly, it has been desired to 15 develop a cover material which has appropriate stiffness and higher impact resilience than the conventionally used golf balls.

In the above mentioned modification of ionomer resin by introducing metal ion, a modification reaction generally generates foam .due to reactivity and by-product carbon dioxide gas, water vapor, etc.).

20 Therefore, reactants, amount of the reactants, etc, are limited and it is difficult to obtain a resin having a high neutralization degree. The golf ball using such cover materials still leaves room for improvement.

OBJECTS OF THE INVENTION Under these circumstances, the present inventors have intensively studied about various ionomer resins in order to obtain a cover material having higher impact resilience. As a result, it has been found that the ionomer resin obtained by neutralizing with a potassium ion shows an impact resilience similar to that of the sodium-neutralized ionomer resin or the lithium-neutralized ionomer resin, although it has low stiffness. It is also found that a mixture of the potassium-neutralized ionomer resin and an ionomer resin obtained by netralizing with divalent or trivalent metal ion has higher impact resilience with keeping stiffness equal to the conventional golf ball cover. The use of the above mentioned ionomer resin mixture as a cover of a golf ball can provide a golf ball which has a high impact resilience and excellent durability as well as satisfactory flying distance and hit feeling. Thus, the present invention has been accomplished.

BRIEF EXPLANATION OF DRAWING Fig. 1 is a schematic cross section illustrating one embodiment of the golf ball of the present invention.

SUMMARY OF THE INVENTION 2 That is, the present invention provides a golf ball having a core and a cover covering the core, wherein the cover comprises as a base resin, a mixture of the following resins and 10 to 90% by weight of an ionomer resin obtained by neutralizing 20 to 70 molar of carboxyl groups in an ethylene- a, unsaturated carboxylic acid copolymer containing 10 to 20% by weight of an a, -unsaturated carboxylic acid with a potassium ion (hereinafter referred to as potassium-neutralized ionomer resin), and having a melt index of 0.1 to 8 and a Shore D-scale hardness of 55 to 75; and 0 90 to 10% by weight of an ionomer resin obtained by neutralizing 30 to 70 molar of carboxyl groups in an ethylene- a, unsaturated carboxylic acid copolymer containing 10 to 30% by weight of an a, 3 -unsaturated carboxylic acid with a divalent or trivalent metal ion (hereinafter referred to as divalent or trivalent metal-neutralized ionomer resin), and having a melt index of 0.1 to 8 and a Shore D-scale hardness of to 1 9 *1 r DETAILED DESCRIPTION OF THE INVENTION The potassium-neutralized ionomer resin to be used in the present invention is prepared from an ethylene- a, S -unsaturated carboxylic acid copolymer having a carboxyl group content of 10 to 20% by weight. The carboxyl group content is obtained by the following equation: (Weight of carboxyl group) X 1 00 (Weight of ethylene-a,p -unsaturated carboxylic acid copolymer) 1 a.

0 a aa a a. a When the content of carboxylic acid is smaller than 10 by weight, stiffness is too low due to the lack of the carboxylic acid. On the other hand, when the content of the carboxylic acid is more than 20% by weight, it is difficult to obtain a resin having a high neutralization degree and, further, it is brittle because the stiffness of the cover is too high.

in addition, it is necessary that 20 to 70 motar of carboxyl groups of the above potassium-neutralized ionomer resin is neutralized with potassium ion. It is particularly preferred that 20 to 50 molar of carboxyl groups Is neutralized with potassium ion. When the neutralization degree due to the potassium ion is less than the above range, the stiffness of the cover is insufficient and the impact resilience of the golf ball is deteriorated. On the other hand, when the neutralization degree due to the potassium ion is more than the above range, the stiffness of the cover is too high and the hit feeling of the golf ball is inferior. In addition, fluidity of 15 cover when heated is deteriorated, which results in inferior moldability, and the impact resistance of the golf ball is deteriorated.

It is necessary that a melt index of the potassium-neutralized ionomer resin to be used in the present invention is 0.1 to 8, preferably to 5. The melt index is measured at a temperature of 190'C under a load of 2,160 g according to JIS-K6760. When the melt index of the potassiumneutralized ionomer resin is less than the above range, the fluidity of the cover is too low, which results in inferior moldability, and the impact resistance of the golf ball is deteriorated. On the other hand, when the melt index is more than the above range, the molecular weight is low or the neutralization degree is low, which results in deterioration of impact resilience and impact resistance.

Furthermore, it is necessary that a Shore D-scale hardness of the potassium-neutralized ionomer resin to be used in the present invention is 55 to 75, preferably 55 to 70. When the Shore D-scale hardness of the potassium-neutralized ionomer resin is less than the above range, the impact resilience is deteriorated. On the other hand, when the Shore D-scale hardness is more than the above range, the stiffness of the cover is too high, which results in deterioration of hit feeling.

The divalent or trivalent metal-neutralized ionomer resin used in the present invention is obtained from the ethylene- a, 3 -unsaturated carboxylic acid copolymer having a carboxyl group content of 10 to 30 by weight. When the content of carboxylic acid is less than 10% by weight, the stiffness of the cover is deteriorated because of the lack of the carboxylic acid. On the other hand, when the content of .arboxylic acid is 15 more than 30% by weight, it is difficult to obtain a resin having a high neutralization degree and it is brittle because the stiffness of the cover is too high.

*4 .9 9 *9 9 9 oo 9 9 *9 9 fc b 9 9 9 e *999 49 9 99 .9 9 o o o r o In addition, it is necessary that 30 to 70 molar of carboxyl groups of the divalent or trivalent metal-neutralized ionomer resin are 20 neutralized with a divalent or trivalent metal ion. It is particularly preferred that 35 to 60 molar of carboxyl groups is neutralized with a divalent or trivalent metal ion. The ion source of the above divalent or trivalent metal ion includes carbonates, acetates, hydroxides, oxides, etc. of magnesium, calcium, zinc, aluminum, barium, copper, etc. As the ion species, zinc ion magnesium ion etc. are preferred. In addition, when the

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oo *o o e neutralization degree due to the divalent or trivalent metal ion is less than the above range, the stiffness of the cover is too low and the impact resilience of the golf ball is deteriorated. On the other hand, when the neutralization degree due to the divalent or trivalent metal ion is more than the above range, the stiffness of the cover is too high and the hit feeling is inferior. In addition, the fluidity of the cover when heated is considerably deteriorated, which results in inferior moldability, and the impact resistance of the ball is also deteriorated.

It is necessary that a melt index of the divalent or trivalent 10 metal-neutralized ionomer resin to be used in the present invention is 0.1 to 8, preferably 0,3 to 5. When the melt index of the divalent or trivalent metal-neutralized ionomer resin is less than the above range, the fluidity is too low, which results in inferior moldability, and the impact resistance is also deteriorated. On the other hand, when the melt index is more than the above range, the molecular weight is low or the neutralization degree is low, which results in deterioration of impact resilience and impact resistance.

Furthermore, it is necessary that a Shore D-scale hardness of the divalent or trivalent metal-neutralized ionomer resin to be used in the present invention is 60 to 85, preferably 60 to 75. When the Shore D-scale hardness of the divalent or trivalent metal-neutralized ionomer resin is less than the above range, the impact resilience is deteriorated. On the other hand, when the Shore D-scale hardness is more than the above range, the stiffness of the cover is too high, which results in deterioration of hit feeling.

The mixture of the potassium-neutralized ionomer resin and Lu

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~O TAIY9QP~I-lrW~"I~-n ~run~ divalent or trivalent metal-neutralized ionomer resin to be used as the base resin for the cover in the golf ball of the present invention shows a high impact resilience in comparison with the commercially available potassium-neutralized ionomer resin and the lithium-neutralized ionomer resin as well as mixture of them and the divalent or trivalent metalneutralized ionomer resin, even if the comparison is made at the same stiffness. In addition, it is also superior in durability. The reason is as follows. The potassium-neutralized ionomer resin has the same impact resilience as that of the commercially available sodium-neutralized ionomer resin or lithium-neutralized ionomer resin in spite of its low stiffness in comparison with them and, therefore, high impact resilience can be obtained when using the potassium-neutralized ionomer resin as the base in comparison with the case that the commercially available sodiumneutralized ionomer resin or lithium-neutralized ionomer resin as the base, 15 even if the comparison is made at the same stiffness.

Regarding the mixing ratio of the above potassiumneutralized ionomer resin to the divalent or trivalent metal-neutralized ionomer resin, it is preferred that an amount of the potassium-neutralized ionomer resin is 10 to 90% by weight, preferably 30 to 70% by weight, based on the weight of the mixture and that of the divalent or trivalent metal-neutralized, ionomer resin is 90 to 10% by weight, preferably 70 to by weight, based on the weight of the mixture. When the amount of the potassium-neutralized ionomer resin is less than the above range, physical properties of the resulting mixture is similar to those of the divalent or trivalent metal-neutralized ionomer resin alone, and the technical effects ii 0 0 0 0 0000 *0 0 0 0 0 o 00 0 o o* 0 00 00e 0o 0 0 0 o o

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due to the potassium-neutralized ionomer resin does not develop sufficiently. When the amount of the potassium-neutralized ionomer resin is more than the above range, the impact resilience is poor.

It is necessary that a melt index of a mixture of the potassiumneutralized ionomer resin and the divalent or trivalent metal-neutralized ionomer resin in the present invention is 0.5 to 5, preferably 1 to 3.5. When the melt index of the above ionomer resin mixture is less than the above range, the fluidity of the resin when heated is inferior. On the other hand, when the melt index is more than the above range, the molecular weight is 10 low or the neutralization degree is low, which results in deterioration of impact resilience and impact resistance of the golf ball.

Furthermore, it is necessary that a Shore D-scale hardness of the mixture of the potassium-neutralized ionomer resin and the divalent or trivalent metal-neutralized ionomer resin in the present invention is 60 to 15 80, preferably 60 to 70. When the Shore D-scale hardness of the above ionomer resin mixture is less than the above range, the stiffnessis low and the impact resilience is deteriorated. On the other hand, when the Shore D-scale hardness is more than the above range, the stiffness of the cover is too high, which results in high impact resilience, but the durability is likely to be deteriorated, which results in inferior hit feeling.

The potassium-neutralized ionomer resin and the divalent or trivalent metal-neutralized ionomer resin are normally mixed using an extruder, buotare not limited thereto. The extruder may be a single-screw extruder, but it is preferred to melt and mix using a twin-screw extruder.

In the preparation of the composition for cover, various -T CC-- P l additives such as pigments titanium dioxide, etc.), antioxidants, ultraviolet absorbers, polymer stabilizers, etc. may be optionally added to the base resin of a mixture of the above potassium-neutralized ionomer resin and divalent or trivalent metal-neutralized ionomer resin. In addition, other resins may be added to the above base resin unless performance of t' a base resin are damaged. It is necessary that the amount of the base resin is at least 80%0 by weight. The base resin of a mixture of the above potassium-neutralized ionomer resin and the divalent or trivalent metalneutralized ionomer resin may be in a mixed state in the cover, and it may also be mixed in advance. In addition, it may also be mixed with pigments in the preparation of a cover composition.

The cover using a base resin comprising a mixture of the above potassium-eutralized ionomer resin and the divalent or trivalent metal-neutralized ionomer resin can be applied to either a core for solid golf ball (solid core) or a core for thread wound golf ball (thread wound core).

The solid core may be a core for a multi-layer structures of two or more layers, in addition to a core for a single-layer structure. For example, as the core for a two-piece golf ball, those obtained by subjecting a rubber composition to a press vulcanization to compress with heating at a temperature of 140 to 170'C for 10 to 40 minutes) into a spherical vulcanized article can be used. The rubber composition may be prepared by formulating 10 to 60 parts by weight of at least one vulcanizing agent (crosslinking agent) of a, /-ethylenically unsaturated carboxylic acids acrylic acid, methacrylic acid, etc.) or metal salts thereof and ~e 9 9 *9 9 9 9 S* 99, 9 eD 9 ego o°° oo 11 functional monomers trimethylolpropane trimethacrylate, etc.), 10 to parts by weight of a filler zinc oxide, barium sulfate, etc.), 0.5 to parts by weight of a peroxide dicumyl peroxide, etc,) and 0.1 to 1 parts by weight of an antioxidant, to 100 parts by weight of polybutadiene.

The thread wound core is composed of a center and a thread rubber wound on the center. As the center, either a liquid center or a rubber center can be used. The rubber center can be obtained by vulcanizing a same rubber composition as that of the solid core.

The thread rubber may be those which have hitherto been used. For example, there can be used those obtained by vulcanizing a rubber composition wherein an antioxidant, a vulcanizing accelerator and sulfur are formulated in a natural rubber or a mixture of a natural rubber and synthetic polyisoprene. The core is not limited to the solid core and thread wound core.

15 A method of covering the cover on the core is not specifically limited, but including a method comprising molding a cover composition prepared by formulating a suitable amount of a requisite additive in the specific base material for the cover into a semi-spherical half-shell in advance, covering a core with two half-shells and then subjecting to a pressure molding at 130 to 170'C for 1 to 15 minutes, or a method comprising subjecting the composition for the cover to an injection molding directly to cover the core. The thickness of the cover is generally about 1 to 4 mm. In case of cover molding, a dimple may be optionally formed on the surface of the ball. Further, a paint or marking may be optionally provided.

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Then, the construction of the golf ball of the present invention will be explained with reference to the accompanying drawing. Fig.1 is a schematic cross section illustrating one embodiment of the golf ball of the present invention. The golf ball shown in Fig.1 is a two-piece solid golf ball comprising a core 1 of a vulcanized molded article of a rubber composition and a cover 2 for covering the core. The core 1 is that referred to as a solid core but is not limited their to., For example, the vulcanized molded article of the above rubber composition comprising polybutadiene as the main material is used. The cover 2 for covering the 10 core is made of a composition for cover using the above mixture of the potassium-neutralized ionomer resin and the divalent or trivalent metalneutralized ionomer resin as the base resin.

Also, 2a is a dimple provided on the cover 2. In the golf ball shown in Fig. 1, the core 1 is composed of a vulcanized molded article of a single-layer structure rubber composition, but a thread wound core formed by winding a thread rubber at a stretched state on a liquid or rubber center, or a two-layer structure solid core wherein an outer core of a vulcanized article of a rubber composition comprising polybutadiene as the main material is further formed around an inner core of a vulcanized article of a rubber composition comprising polybutadiene as the main material may be used in place of this.

The suitable number/embodiment of dimples 2a may be optionally provided on the cover 2 of the golf ball so as to obtain the desired characteristics. Further, painting, marking, etc. may be optionally provided on the surface of the golf ball.

a. 13 As described above, according to the present invention, there can be provided a golf ball which has a high impact resilience and an excellent durability as well as satisfactory flying distance and hit feeling (feeling at the time of hitting),

EXAMPLES

The following Examples and Comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof.

Examples 1 to 5 and Comparative Examples 1 to Two-piece solid golf balls of Examples 1 to 5 and Comparative Examples 1 to 10 were made by the following processes (1) to Preparation of core A rubber composition obtained by formulating 36 parts by 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 of an antioxidant (Yoshinox 425 (trade name), manufactured by Yoshitomi Seiyaku Co., Ltd.) in 100 parts by weight of polybutadiene (BR-11 (trade name), manufactured by Nihon Synthetic Rubber Co., Ltd.) was subjected to vulcanization molding at 160 OC for 25 minutes to obtain a solid core. An average diameter of the resulting core was 38.2 mm.

Preparation of composition for cover lonomer resins having the formulation shown in Tables 1 to 3 were kneaded using a kneading type twin-screw extruder. To 100 parts by o S p p p pp p p p weight of the resulting ionomer resin mixture, 2 parts by weight of titanium dioxide and 2 parts by weight of barium sulfate were added and the mixture was further kneaded to give a pelletized cover composition. The formulation of the ionomer resin mixture as the base resin for the cover of golf balls of Examples 1 to 5 is shown in Table 1, respectively. The formulation of the ionomer resin mixture as the base resin for the cover of golf balls of Comparative Examples 1 to 5 is shown in Table 2, respectively. The formulation of the ionomer resin mixture as the base resin for the cover of golf balls of Comparative Examples 6 to 10 is shown 10 in Table 3, respectively.

In the respective tables, the ionomer resin is indicated by the trade name, but the details are explained after the respective tables.

Incidentally, "MI" in the explanation of the ionomer resin is an abbreviation for "melt index". The amounts in tables are parts by weight. The extrusion conditions are as follows: a screw diameter: 45 mm; a screw revolution per minute: 200 rpm; a screw L/D: 35. The formulation components were heated at 200 to 250'C at the die position of the extruder.

The measurement results oa the stiffness, Shore D-scale hardness and melt index of the resulting composition for cover are shown in the respective tables, Incidentally, regarding the cover composition, 2 parts by weight of titanium dioxide and 2 parts by weight of barium sulfate were merely formulated to 100 parts by weight of the base resin and, therefore, it is considered that the stiffness, Shore D-scale hardness and melt index thereof are substantially the same as those of the base resin.

The measuring methods of the stiffness and Shore D-scale hardness are ic as follows.

Stiffness: It is measured according to ASTM D-747 after a sheet having a thickness of about 2 mm obtained by heat-press molding was preserved at 23 °C for two weeks.

Shore D-scale hardness: It is measured according to ASTM D-2240 after a sheet having a thickness of about 2 mm obtained by heatpress molding was preserved at 23'C for two weeks.

Production of golf ball A two-piece golf ball having an outer diameter of 42.7 mm "i 10 was produced by directly covering the solid core of the above with the composition for cover of the above item according to injection molding 4 and then painting the surface.

The ball weight, compression, resilience coefficient and flying distance of the golf ball thus obtained were measured, respectively. The 15 ball compression was measured by PGA method, and the resilience coefficient was calculated from the ball velocity when striking a cylindrical substance (198.4 g) to the golf ball at a velocity of 45 m/second. The flying distance was measured by hitting with a No.1 wood club at a head speed of 45 m/second, using a swing robot manufactured by True Temper Co.

Furthermore, in order to examine the durability of the above golf ball, a golf ball was hit with a No. 1 wood club at a head speed of m/second using a swing robot manufactured by True Temper Co., and the number of times until breakage arose was measured. The resulting value was indicated as a durability index in case of the number of Example 1 being 100.

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a a a a 4 a~ 4* a Further, the hit feeling of the resulting golf ball was evaluated by 10 top professional golfers according to a practical hitting test with a No.

1 wood club. The evaluation criteria are as follows. The results shown in the Tables below are based on the fact that not less than 8 out of professional golfers evaluated with the same criterion about each test item.

Evaluation criterteria 0: Hit feeling is light and good.

A: Hit feeling is slightly hard.

X: Hit feeling is hard and inferior.

10 The measurement results of the ball physical properties (i.e.

weight, compression, resilience coefficient, flying distance and durability) and evaluation results of the hit feeling of the golf balls of Examples 1 to are shown in Table 1, together with the formulation composition of the base resin for the cover, Furthermore, the measurement results of the ball 15 physical properties and evaluation results of the hit feeling of the gold balls of Comparative Examples to 5 are shown in Table 2, together with the formulation composition of the base resin for the cover. Incidentally, it is impossible to show the measurement results of the ball physical properties and evaluation results of the hit feeling of the gold balls of Comparative Examples 6 to 10 in the same table, together with the formulation composition of the base resin for the cover, due to lack of space.

Therefore, the formulation composition of the base resin for the cover is shown in Table 3, and the measurement results of the ball physical properties and evaluation results of the hit feeling are shown in Table 4.

L Table 1 Example No, 1 2 3 4 Hi-milan MK7320 *1 70 50 30 50 Hi-milanl706 *2 30 50 70 0 0 Hi-milan AM7315 *3 0 0 0 50 0 Hi-milanAM7317 '4 0 0 0 0 Cover composition Stiffness (MPa) 310' 305 300 340 335 Shore D-scale hardness 62 62 62 63 63 Melt index 2,5 2,0 1.6 2,0 Ball physical properties Weight 45.4 45.4 45.4 45.4 45.4 Compression (PGA) 93 92 92 96 Resilience coefficient 0.7815 0.7825 0.7824 0.7865 0.7862 Flying distance (yard) 236 234 234 240 238 Durability 100 105 120 97 98 Hit feeling O 0 0 0 0 o a ft °o e o Hi-milan MK7320 Trade name, ethylene-methacrylic acid ionomer resin obtained by neutralizing with a potassium ion, manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: 15% by weight, neutralization degree with potassium ion: 29 molar MI (melt index): 2.8, stiffness: 300 MPa, Shore D-scale hardness: 62 Hi-milan 1706 Trade name, ethylene-methacrylic acid ionomer resin obtained by neutralizing with a zinc ion, manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: 15% by weight, neutralization VT 00 I n l ICWB* Ps~arnrr~ou~--- l 18 degree with zinc ion: 58 molar Ml: 0.8, stiffness: 265 MPa, Shore Dscale hardness: 61 Hi-milan AM7315 Trade name, ethylene-methacrylic acid ionomer resin obtained by neutralizing with a zinc ion, manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: 20% by weight, neutralization degree with zinc ion: about 40 molar MI: 1.2, stiffness: 330 MPa, Shore D-scale hardness: 63 Hi-milan AM7317 10 Trade name, ethylene-methacrylic ionomer resin obtained by neutralizing with a zinc ion, manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: about 18% by weight, neutralization degree with zinc ion: about 40 molar MI: 1.1, stiffness: 310 MPa, Shore D-scale hardness: 62 I- I *4 .4 4 4 4 4 4 Table 2 Comparative Example No.

1 2 3 4 Hi-milan MK7320 100 50 0 0 0 I -1 Hi-milan#1706 0 0 30 50 Hi-milan#1605 *5 0 50 70 50 Cover composition Stiffness (MPa) 300 300 345 340 335 Shore D-scale hardness 62 62 63 63 63 Melt index 2.8 2.8 2.0 1.8 Ball physical properties Weight 45.4 45.4 45.4 45.4 45.4 Compression (PGA) 91 91 96 95 94 Resilience coefficient 0.7712 0.7718 0.7825 0.7816 0.7807 Flying distance (yard) 226 228 233 233 232 Durability 97 97 84 85 Hit feeling 0 0 A A Hi-milan 1605 Trade name, ethylene-methacrylic acid ionomer resin obtained by neutralizing with a sodium ion manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: 15% by weight, neutralization degree with sodium ion: 29 molar MI (melt index): 2.8, stiffness: 310 MPa, Shore D-scale hardness: 62

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Table 3 Comparative lExample No..

6 7 8 9 Ji0 Hi-milan #41706 50 50 0 0 0 HI-milan AM7315 0 0 50 0 Hi-milan AM7317 0 0 0 500 Hi-milan#1 605 0 T 0 To50 0 Hl-milan#1707 '6 50 0 0O 0 0 Surlyn 7930 -7 0 50 0 0 Cover composition Stiffness (MPa) 345 355 385 380 390 Shore D-scale hardness 63 64 66 65 66 Melt index 0.8 1.3 2.9 2.8 2.6 Hk-milan 1707 Trade name, ethyl ene-methacrylic acid ionomer resin obtainied by neutralizing with a sodium ion manufactured by Mitsui Du Pont Polychemical Co., methacrylic acid content: 15% by weight, neutralization degree with sodium ion: 59 molar Ml: 0.9, stiffness: 315 MPa, Shore Dscale hardness: 62 Surlyn 7930 Trade name, ethylene-methacrylic acid ionomer resin 1 0 obtained by neutralizing with a lithium ion manufactured by Du Pont Co., methacrylic acid content: 15% by weight, neutralization degree with lithium ion: 50 molar Ml1: 1 stiffness: 335 MPa, Shore D-scale hardness: 63 Table 4 Comparative Example No.

6 7 8 9 Ball physical properties Weight 45,4 45.4 45.4 45.4 45,4 Compression (PGA) 96 98 101 100 103 Resilience coefficient 0.7826 0,7829 0.7858 0.7855 0.7860 Flying distance (yard) 234 234 238 236 238 Durability 82 80 78 78 Hit feeling A X X X As is apparent from the results shown in Table 1, the golf balls of Examples 1 to 5 using a mixture of an potassium-neutralized ionomer resin "Hi-milan MK7320 (trade name)" with an zinc-neutralized ionomer resin "Hi-milan 1706 (trade name)", "Hi-milan AM7315 (trade name)" or "Hi-milan AM7317 (trade name)" as the base resin for the cover had a high impact resilience and an excellent durability as well as satisfactory flying distance and hit feeling.

To the contrary, the golf balls of Comparative Examples 1 to 2 10 are superior in durability but is inferior in resilience coefficient and flying distance, as shown in Table 2. Regarding the golf balls of Comparative Examples 3 to 10, the resilience coefficient is high but the durability and hit feeling are inferior, as shown in Tables 2 and 4. Particularly, the golf balls of Comparative Examples 8 to 10 are inferior in hit feeling, and they are not satisfactory.

That, is, the golf ball of Comparative Example 1, using the potassium-neutralized ionomer resin is used alone as the base resin for ,jZ the cover and golf ball of Comparative Example 2 using a mixture of the potassium-neutralized ionomer resin and that obtained by neutralizing with a sodium ion as the base resin for the cover are superior in durability, but the resilience coefficient is lowered and the flight resistance is inferior, as shown in Table 2. In addition, regarding the golf balls of Comparative- Examples 3 to 6 and 8 using a mixture of the zinc-neutralized lonomer resin and that obtained by neutralizing with a sodium ion as the base resin for the cover and golf balls of Comparative Examples 7 and 10 using a mixture of the lithium-neutralized ionomer resin and that obtained by neutralizing with a sodium ion as the base resin for the cover have a high resilience, but are inferior in durability and hit feeling, as shown in tables 2 and 4. Particularly, regarding the golf balls of Comparative Examples 8 to the hit feeling is hard and inferior, as shown in table and they are not satisfactory.

Throughout this specification and the claims which follow, unless 15 the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (3)

1. A golf ball having a core and a cover covering the core, wherein said cover comprises as a base resin, a mixture of the following resins and 10 to 90% by weight of an ionomer resin obtained by neutralizing 20 to 70 molar of carboxyl groups in an ethylene- 3 unsaturated carboxylic acid copolymer containing 10 to 20% by weight of an a, 3 -unsaturated carboxylic acid with a potassium ion, and having a melt index of 0.1 to 8 and a Shore D-scale hardness of 55 to 75; and 90 to 10% by weight of an ionomer resin obtained by neutralizing 30 to 70 molar of carboxyl groups in an ethylene- a, unsaturated carboxylic acid copolymer containing 10 to 30% by weight of an a, 63-unsaturated carboxylic acid with a divalent or trivalent metal ion, and having a melt index of 0.1 to 8 and a Shore D-scale hardness of 60 to

2. The golf ball according to claim 1, wherein said cover has a melt index of 0.5 to 5 and a Shore D-scale hardness of 60 to a 24

3, A golf ball, substantially as hereinbefore described with reference to the drawings and/or Examples. DATED this FOURTH day of OCTOBER 1995 Sumitomo Rubber Industries, Ltd. by DAVIES COLLISON CAVE Patent Attorneys for the applicant(s) 0 0. C t S S @0 10 C 0 *0 0 C C0 C o 0 000 0 CO SCD 00 15 S 00 CO S 5000 00 C 00 O 00 0 ABSTRACT OF THE DISCLOSURE The present invention provides to a golf ball which has a high impact resilience and an excellent durability as well as satisfactory flying distance and hit feeling (feeling at the time of hitting). As a base resin of a cover of the golf ball having a core and a cover, a mixture of the following resins and is used: 10 to 90% by weight of an ionomer resin obtained by neutralizing 20 to 70 molar of carboxyl groups in an ethylene- a, 8 unsaturated carboxylic acid copolymer containing 10 to 20% by weight of an a, 3 -unsaturated carboxylic acid with a potassium ion, wherein a melt index is 0.1 to 8 and a Shore D-scale hardness is 55 to 75; and 90 to 10% by weight of an ionomer resin obtained by neutralizing 30 to 70 molar of carboxyl groups in an ethylene- a, 13- unsaturated carboxylic acid copolymer containing 10 to 30% by weight of an a, ,8-unsaturated carboxylic acid with a divalent or trivalent metal ion, wherein a melt index is 0,1 to 8 and a Shore D-scale hardness is 60 to