AU705472B2 - Golf ball - Google Patents

Description

la FIELD OF THE INVENTION The present invention relates to a golf ball.

More particularly, it relates to a golf ball having good shot feel, good controllability at approach shot, excellent rebound characteristics and excellent flight performance.

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C C 2 BACKGROUND OF THE INVENTION Recently, ionomer resin is generally used as base resin for golf ball cover (Japanese Patent Kokoku Publication No. 27093/1974 etc.). Particularly, in case of two-piece solid golf ball using a solid core, ionomer resin is almostly used as base resin for the cover, because ionomer resin has excellent durability, excellent cut resistance, excellent rebound characteristics and easiness of processing.

However, since ionomer resin has high hardness and rigidity, the resulting golf ball employing ionomer resin cover is inferior in shot feel and controllability at approach shot (easiness of applying spin to golf ball) to golf balls employing balata (transpolyisoprene) which has been conventionally used as base resin for a cover of multi-layer structured golf balls having a thread rubber layer.

In order to improve shot feel and P:\OPER\AXD\204081.SPE 25/2/99 -2controllability of the gold ball, it is attempted to make the ionomer resin soft by various means.

For example, Japanese Patent Kokai publication Nos.

308577/1989 and 3931/1993 propose that rigid ionomer is mixed with a soft ionomer formed from a-olefin-unsaturated carboxylic acid (such as acrylic acid, methacrylic acid)-acrylic ester terpolymer, of which a portion of carboxylic acid groups is neutralized with sodium ion or zinc ion.

However, shot feel equal to or more than golf balls using balata cover have not been obtained by the blend method of softening ionomer resin. The blend method adversely affects on rebound characteristics and flight performance.

Advantageously, the present invention provides a golf ball having good shot feel and good controllability at approach 15 shot, as well as having excellent rebound characteristics and *se* excellent flight performance.

According to the present invention, the above described advantage may be accomplished by employing a cover which comprises 5 to 100% by weight of thermoplastic elastomer 20 composed of acrylic resin as a hard segment and olefin resin as a soft segment (referred to as "special acrylic thermoplastic elastomer: hereinafter), based on the total cover resin component, thus providing a golf ball having good shot feel and 0 0 good controllability at approach shot, as well as having excellent rebound characteristics and excellent flight performance.

SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided a two piece solid golf ball comprising a core and a cover formed on the core, wherein the cover comprises: to 100 by weight of a thermoplastic elastomer (a) 1\ composed of acrylic resin as a hard segment and olefin resin as P:\OPER\AXD\204081,.SPE 25/2/99 -3a soft segment, based on the total cover resin component, and the balance amount of an ionomer resin, a thermoplastic elastomer other than said thermoplastic elastomer or a polar group-modified thermoplastic elastomer, wherein said thermoplastic elastomer has a JIS-A hardness of to 99 and said cover has a Shore D hardness of 20 to According to another aspect of the invention, there is provided a multi-piece solid golf ball comprising a core and a multi-layered cover formed on the core, wherein at least one layer of the cover comprises: 5 to 100% by weight of a thermoplastic elastomer (a) composed of acrylic resin as a hard segment and olefin resin as a soft segment, based on the total cover resin component, and the balance amount of an ionomer resin, a 15 thermoplastic elastomer other than said thermoplastic elastomer or a polar group-modified thermoplastic elastomer, wherein said thermoplastic elastomer has a JIS-A hardness of 50 to 99 and said cover has a Shore D hardness of 20 to 20 DETAILED DESCRIPTION OF THE INVENTION The golf ball of the present invention is composed of a core and a cover formed on the core. The golf ball of the present invention may be either solid golf ball such as two- .2 piece solid golf ball or thread wound golf ball. The core for solid golf ball (solid core) may be the same one that has been conventionally used, and may be obtained by mixing a rubber composition using a mixer such as a mixing roll, and then vulcanizing (crosslinking) or press-molding the rubber composition in a given mold into a spherical form. The rubber 4 *15 a.

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composition comprises 10 to 60 parts by weight of a vulcanizer (crosslinking agent), for example a,Pmonoethylenically unsaturated carboxylic acid (such as acrylic acid, methacrylic acid, etc.) or a metal salt thereof, or a functional monomer such as trimethylolpropane trimethacrylate, or a combination thereof; 0.5 to 5 parts by weight of organic peroxides such as dicumyl peroxide, etc.; 10 to 30 parts by weight of filler such as zinc oxide, barium sulfate and the like, based on 100 parts by weight of a base rubber such as polybutadiene. The vulcanization may be conducted, for example, by heating at 140 to 170 0 C under pressure for 10 to 40 minutes.

The core for thread wound golf ball (thread wound core) comprises a center and a thread rubber layer formed by winding thread rubber in a stretched state around the center, wherein the center may be either liquid center or solid center formed from rubber composition. The thread rubber can be the same one that has been conventionally used. For example, the thread rubber can be obtained by vulcanizing a rubber composition prepared by formulating sulfur, a vulcanization aid, a vulcanization accelerator, an antioxidant and the like to a natural rubber or a blend rubber of the natural rubber and a synthetic polyisoprene. The examples of solid core and thread

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a. a a a P:\OPER\AXD\2040811.SPE 25/2/99 wound core are only for purpose of illustration, and are not to be construed to limit thereto.

In the golf ball of the present invention, the core is covered with a cover. The cover may have single layer structure or multi-layer structure which has two or more layers. When the cover has multi-layer structure which has two or more layers, at least one layer of the cover comprises 5 to 100% by weight of special acrylic thermoplastic elastomer, based on the total cover resin component in each layer. The special acrylic 10 thermoplastic elastomer has a JIS-A hardness of 50 to 99, and the cover comprising the special acrylic thermoplastic elastomer has a Shore D hardness of 20 to 60 and preferably a flexural modulus of 50 to 300 Mpa. When the JIS-A hardness of the special acrylic thermoplastic elastomer is smaller than 50, it 15 is difficult to adjust the Shore D hardness of the cover to to 60, and rebound characteristics and cut resistance are degraded. On the other hand, when the JIS-A hardness is larger than 99, it is difficult to adjust the Shore D hardness of the cover to 20 to 60, and rebound characteristics are degraded.

S. 20 When Shore D hardness is smaller than 20 and flexural modulus is smaller than 50 Mpa, in the cover comprising the special acrylic S. thermoplastic elastomer, the cover is too soft. Therefore, the rebound characteristics, flight 6 ***15 performance and cut resistance of the resulting golf ball are degraded. On the other hand, when the Shore D hardness is larger than 60 and the flexural modulus is larger than 300 MPa, the cover is too hard, and thus the shot feel and controllability at approach shot of the resulting golf ball are degraded.

The special acrylic thermoplastic elastomer used in the golf ball of the present invention is a polymer alloy which is composed of acrylic resin as hard segment and olefin resin as soft segment. Examples of the special acrylic thermoplastic elastomer include SB- 2031S, SB-21531S, which are commercially available from Kuraray Co., Ltd., and the like. An amount of the special acrylic thermoplastic elastomer is 5 to 100, preferably 20 to 100, more preferably 40 to 100 by weight, based on the total cover resin component. When the amount of the special acrylic thermoplastic elastomer is smaller than 5 by weight, the technical effects of the shot feel and controllability, rebound characteristics and flight performance of the resulting golf ball are not sufficiently exhibited. Although the special acrylic thermoplastic elastomer used in the golf ball of the present invention has the same level of hardness and flexural modulus as conventional ionomer resin having low rigidity, such as Surlyn 8320 (Na) and Surlyn 9320 which are commercially available from *r S S 7 15 Du Pont Co., rebound characteristics are very high. The use of the special acrylic thermoplastic elastomer in covers of golf balls can provide golf balls having good shot feel, good controllability, excellent rebound characteristics and excellent flight performance.

Incidentally, Na and Zn, which are described in parentheses after the trade name of the above ionomer resin, indicate metal ion species for neutralization.

The cover of the golf ball of the present invention, can contain resin components other than the above special acrylic thermoplastic elastomer. The resin components include ionomer resin which has been conventionally used as a cover resin for golf balls, the other thermoplastic elastomer, polar group-modified thermoplastic elastomer and the like. The ionomer resin can be either a copolymer of ethylene and (meth)acrylic acid, or a terpolymer of ethylene, (meth)acrylic acid and an ester of a,j-unsaturated carboxylic acid, of which a portion of carboxylic acid groups is neutralized with metal ion. Five to eighty of carboxylic acid groups in the ionomer resin may be neutralized with metal ion.

Examples of the ionomer resin, which is commercially available from Mitsui Du Pont Polychemical Co., Ltd. include Hi-milan 1605 Hi-milan 1707 (Na), Hi-milan AM7318 Hi-milan 1706 Hi-milan AM7315 Hi-milan AM7317 Hi-milan AM7311 (Mg) and Hi- 8 15 milan MK7320 and Hi-milan 1856 Hi-milan 1855 (Zn) and Hi-milan AM7316 (Zn) as the terpolymer ionomer resin. Examples of the ionomer resin, which is commercially available from Du Pont include Surlyn 8920 Surlyn 8940 Surlyn AD8512 (Na), Surlyn 9910 Surlyn AD8511 Surlyn 7930 (Li) and Surlyn 7940 and Surlyn AD8265 (Na) and Surlyn AD8269 (Na) as the terpolymer ionomer resin. Examples of the ionomer resin, which is commercially available from Exxon Chemical Co., include lotec 7010 (Zn) and Iotec 8000 These ionomer resins are used alone or in combination thereof. Incidentally, Na, Zn, Li, K and Mg, which are described in parentheses after the trade name of the above ionomer resin indicate metal ion species for neutralization.

Examples of the thermoplastic elastomer other than the special acrylic thermoplastic elastomer include polyolefin elastomer, polyester elastomer, polyamide elastomer, styrene elastomer (such as elastomer having styrene-butadiene-styrene structure, elastomer having styrene-isoprene-polystyrene structure), and the like.

The thermoplastic elastomer may be used in combination with ionomer resin.

In order to improve the compatibility between thermoplastic elastomer and ionomer resin, polar groupmodified (such as maleic anhydride-modified, epoxy group- 09 9 *C 15

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modified, sulfonic acid-modified) thermoplastic elastomer may be used in combination with ionomer resin. A mixture of the ionomer resin, thermoplastic elastomer and polar group-modified thermoplastic elastomer may be used.

Examples of the maleic anhydride-modified thermoplastic elastomers are maleic anhydride adducts of hydrogenated styrene-butadiene-styrene block copolymers, which are commercially available from Asahi Chemical Industries Co., Ltd. under the trade name of "Taftek M" series; ethylene-ethyl acrylate-maleic anhydride terpolymers, which are commercially available from Sumitomo Chemical Industries Co., Ltd. under the trade name of "Bondine"; and products obtained by graftmodifying ethylene-ethyl acrylate copolymers with maleic anhydride, which are commercially available from Mitsui Du Pont Polychemical Co., Ltd. under the trade name of "AR" series.

Examples of the epoxy group-modified thermoplastic elastomers include styrene-butadienestyrene structured block copolymer having polybutadiene block with epoxy groups, which are commercially available from Daicel Chemical Industries Co., Ltd.; ethyleneglycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-methyl acrylate terpolymer, ethyleneglycidyl methacrylate-vinyl acetate terpolymer, which are commercially available from Sumitomo Chemical Industries Ge

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Ga S C C Ge C G C 10 15 20 Co., Ltd. under the trade name of "Bondfast"; glycidyl methacrylate adducts of hydrogenated styrene-butadienestyrene (SBS) block copolymers, which are commercially available from Asahi Chemical Industries Co., Ltd. under the trade name of "Taftek Z514", "Taftek Z513"; adducts of ethylene-acrylic ester-glycidyl methacrylate terpolymer, which is commercially available from Du Pont U.S.A. under the trade name of "Elvaloy-AS".

The cover used in the present invention may optionally contain various additives such as pigments, dispersants, antioxidants, UV absorbers, photostabilizers, etc., in addition to the resin component.

When the cover composition is prepared, the cover formulation materials are mixed using an internal mixer, such as a kneading type twin-screw extruder, a Banbury mixer, a kneader, at 150 to 260 0 C for 0.5 to minutes.

A method of covering the core with the cover is not specifically limited, but may be a conventional method. For example, there can be used a method comprising molding the cover composition into a semispherical half-shell in advance, covering a core with the two half-shells, followed by pressure molding at 130 to 170 0 C for 1 to 15 minutes, or a method comprising injection molding the cover composition directly on the 11 9 15 15 core to cover it. When molding the cover, dimples may be optionally formed on the surface of the golf ball.

Furthermore, paint finishing or stamping may be optionally conducted after molding the cover. The thickness of the cover is not specifically limited, but is typically within the range of 1 to 4 mm.

EXAMPLES

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

Production of cores The rubber compositions having formulations shown in Table 1 were vulcanized by heating at 140°C for 30 minutes, and then 170°C for 10 minutes to obtain solid cores having an average diameter of 38.9 mm. The resulting cores have a JIS-C hardness of 78 3, which were measured at an optional portion in the core.

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15 Table 1 Core composition Amount (parts by weight) Polybutadiene *1 100 Zinc acrylate 36 Zinc oxide Dicumyl peroxide Antioxidant *2 Polybutadiene (trade name "BR-11") from JSR Co., Ltd.

2: Antioxidant (trade name "Yoshinox 425") from Yoshitomi Pharmaceutical Inds., Ltd.

Preparation of cover composition The cover compositions having formulations shown in Table 2 were mixed using a kneading type twinscrew extruder to obtain a pelletized cover compositions.

The extrusion condition were; a screw diameter of 45 mm, a screw speed of 200 rpm, and a screw L/D of The formulation materials were heated at 200 to 260 0 C at the die position of the extruder. The flexural modulus and Shore D hardness of the resulting cover composition were measured, and the results are shown in Table 2. The test methods will be written after the explanation of *r S

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13 Examples 1 to 4 and Comparative Examples 1 to 3.

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Table 2 Example No. Comparative Kind Example No.

1 2 3 4 1 2 3 Hi-milan 1605 *3 25 0 40 15 50 25 0 Hi-milan 1706 *4 25 40 40 0 50 25 Surlyn 8320 *5 50 SB-2031S 6 50 60 20 85 Titanium dioxide 2 2 2 2 2 2 2 Flexural modulus 190 130 280 80 340 190 125 (MPa) Shore D hardness 53 50 58 46 62 52 49 3: Hi-milan 1605 (trade name), ethylene-methacrylic acid copolymer ionomer resin obtained by neutralizing with sodium ion, manufactured by Mitsui Du Pont Polychemical Co., Ltd., flexural modulus about 310 MPa, Shore D hardness 62 Hi-milan 1706 (trade name), ethylene-methacrylic acid copolymer ionomer resin obtained by neutralizing with zinc ion, manufactured by Mitsui Du Pont

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Polychemical Co., Ltd., flexural modulus about 260 MPa, Shore D hardness 61 Surlyn 8320 (trade name), ethylene-methacrylic acidacrylic acid terpolymer ionomer resin obtained by neutralizing with sodium ion, manufactured by DuPont Co., flexural modulus about 29 MPa, Shore D hardness 37 SB-2031S (trade name), special acrylic thermoplastic elastomer, manufactured by Kuraray Co., Ltd., JIS-A hardness Examples 1 to 4 and Comparative Examples 1 to 3 A cover layer was formed by directly injection molding the cover composition on the solid core obtained above. Then, a paint was applied on the surface to produce a golf ball having a diameter of 42.7 cm and a weight of 45.3 g. With respect to the resulting golf balls, ball compression (compression), coefficient of restitution, spin amount at the time of hitting by an iron club, run (rolling distance) when hitting by a sand wedge, shot feel and controllability at approach shot were determined and evaluated. The results are shown in Table 3 and Table 4. The test methods are as follows.

Test method Flexural modulus The flexural modulus was determined according C CC

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15 to ASTM D-747, using a sample of a heat and press molded sheet having a thickness of about 2 mm from each cover composition, which had been stored at 231C for 2 weeks.

Shore D hardness The Shore D hardness was determined according to ASTM D-2240, using a sample of a stack of the three or more sheets which were obtained by heat and press molding a cover composition into a sheet having a thickness of about 2 mm and storing for 2 weeks at 23 0

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Ball compression The ball compression of golf balls was determined by PGA method.

:i Coefficient of restitution ~*SA cylinder having a weight of 198.4 g was fired at a speed of 45 cm/sec to strike against a golf ball, and the velocity of the golf ball and the cylinder before and after the strike was measured. The coefficient of restitution of the golf ball was calculated from the velocity and the weight of both the cylinder and the golf 20 ball.

•cog Spin amount and flight distance After No. 5 iron club and No.9 iron club were respectively mounted to a swing robot manufactured by True Temper Co. and a golf ball was hit at head speeds of 38 and 34 m/seconds respectively, the spin amount was measured by taking photographs of marks 16 provided on the golf ball using a high-speed camera.

After a No. 1 wood club (a driver) was mounted to a swing robot manufactured by True Temper Co. and a golf ball was hit at a head speed of 45 m/second, flight distance (carry) to the dropping point of the hit golf ball was measured.

Running distance when hitting by a sand wedge A golf ball was hit to a green by a sand wedge from the position 60 yards apart from the edge of putting green, a running distance was measured. The running distance is a distance between a dropping point firstly :i landed on the earth and a stop point finally reached.

Shot feel at approach shot

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15 The shot feel of the resulting golf ball was evaluated by 10 top professional golfers according to practical hitting test to a green by a pitting wedge.

The evaluation criteria are as follows. The results shown in Tables below are based on the fact that not less than 8 out of 10 professional golfers evaluated with the same criterion about each test item.

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~Evaluation criteria o Soft and good A Slightly hard x Hard and poor xx Very hard and very poor 17 Controllability at approach shot The controllability at approach shot of the resulting golf ball was evaluated by 10 top professional golfers according to practical hitting test to a green by a pitching wedge. The evaluation criteria are as follows. The results shown in Tables below are based on the fact that not less than 8 out of 10 professional golfers evaluated with the same criterion about each test item.

Evaluation criteria o It feels that a golf ball is placed on a face of a golf club, and spin is readily applied to the golf ball to easily stop on a green. Controllability is a good.

A Spin is applied a little, but is *.a."insufficient.

It does not feel that a golf ball is placed on a face of a golf club and it is slided the face, and it is difficult to apply spin on the golf ball 20 to stop on the green. Controllability is poor.

xx It is very difficult to apply spin on a golf ball and to stop on a green. Controllability is very poor.

very poor.

18 0 t 15 ,0 Table 3 Example No. 1 2 3 4 Ball compression 86 84 90 82 Coefficient of 0.779 0.774 0.785 0.770 restitution Spin amount (rpm) 4900 5100 4900 5500 I#9 7600 8100 7600 8600 Flight distance 236 234 239 230 (yard) Running distance when hitting by a 70 40 80 sand wedge (cm) Shot feel at o o o o approach shot Controllability at o o o o approach shot 0* 0 00 0 0 0 19 S. S.

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Ball compression 102 86 84 Coefficient of 0.780 0.762 0.758 restitution Spin amount (rpm) 3600 4700 4900 1#9 6000 7500 7900 Flight distance 237 225 222 (yard) Running distance when hitting by a 270 90 sand wedge (cm) Shot feel at xx x A approach shot Controllability at xx A A approach shot

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C C S 20 15 4 As is apparent from the results in Table 3 and Table 4, the golf balls of Examples 1 to 4 comprising a special thermoplastic elastomer have rebound characteristics and flight distance approximately equal to the golf ball of Comparative Example 1 comprising no special thermoplastic elastomer, but have much better shot feel and controllability than the golf ball of Comparative Example i. The golf balls of Examples 1 to 4 have larger coefficient of restitution, longer flight distance, better shot feel and better controllability than the golf balls of Comparative Example 2 and 3 using low rigidity ionomer resin "Surlyn 8320" instead of the special thermoplastic elastomer, which imparts flexural modulus and hardness of the cover approximately equal to the golf balls of Examples 1 to 4 to the resulting golf ball.

Throughout this specification and the claims which follow, unless 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.

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A p* A pA P:\OPER\AXD\204081 .SPE 25/2/99 -21- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A two piece solid golf ball comprising a core and a cover formed on the core, wherein the cover comprises: to 100 by weight of a thermoplastic elastomer (a) composed of acrylic resin as a hard segment and olefin resin as a soft segment, based on the total cover resin component, and the balance amount of an ionomer resin, a thermoplastic elastomer other than said thermoplastic elastomer or a polar group-modified thermoplastic elastomer, 10 wherein said thermoplastic elastomer has a JIS-A hardness of 50 to 99 and said cover has a Shore D hardness of 20 to S. 2. A multi-piece solid golf ball comprising a core and a multi-layered cover formed on the core, wherein at least one layer of the cover comprises: 15 5 to 100% by weight of a thermoplastic elastomer (a) composed of acrylic resin as a hard segment and olefin resin as a soft segment, based on the total cover resin component, and the balance amount of an ionomer resin, a thermoplastic elastomer other than said thermoplastic elastomer 20 or a polar group-modified thermoplastic elastomer, wherein said thermoplastic elastomer has a JIS-A hardness of 50 to 99 and said cover has a Shore D hardness of 20 to 3. A golf ball according to claim 1 or 2 substantially as hereinbefore described with reference to any one of the Examples.

DATED this 25TH day of FEBRUARY,1999 Sumitomo Rubber Industries, Ltd.

by DAVIES COLLISON CAVE Patent Attorneys for the Applicants