AU724301B2 - Thread rubber for golf balls - Google Patents

Description

AUSTRALIA

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

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

INVENTION TITLE: Thread rubber for golf balls The following statement is a full description of this invention, including the best method of performing it known to me/us:-

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FIELD OF THE INVENTION The present invention relates to thread rubber and a thread wound golf ball using the thread rubber. Particularly it relates to thread rubber for golf balls, which has high impact resilience and high strength, and to a thread wound golf ball using the thread rubber.

BACKGROUND OF THE INVENTION A thread wound golf ball is generally produced by winding thread rubber around a center in a high drawn condition to form a thread wound core and then covering a cover thereon. The thread rubber S requires high strength sufficient for tightly winding on the center and high impact rubber resilience at high drawn condition sufficient for enhancing •flight distance.

In order to satisfy the above mentioned requirement to thread 00050.

S 15 rubber, the thread rubber is conventionally formed from a mixture of natural rubber or high-cis polyisoprene rubber and low-cis polyisoprene rubber, o••because the natural rubber or high-cis polyisoprene rubber imparts high strength and the low-cis polyisoprene rubber imparts high impact resilience.

20 Japanese Kokoku Publication 54 (1979)-4733 proposes that 00g0 •a disulfide compound is mixed with natural rubber, because the disulfide compound improves the impact resilience of the natural rubber while maintaining the strength of the natural rubber.

The above publication considerably improves strength and impact resilience, but further improvement of them has been desired.

SUMMARY OF THE INVENTION The present invention has made to satisfy the above desire and provides thread rubber suitable for use in golf balls, obtained by vulcanizing a rubber composition which comprises a rubber component selected from the group consisting of natural rubber, a synthetic high-cis-polyisoprene rubber and a mixture thereof, 0 at least one compound selected from the group consisting of a diphenyl disulfide compound represented by o.

r r o wherein X, the same or different, represents an attractive substituent and n shows number of X and is an integer of 1 to and a dinaphthyl disulfide compound represented by

(I)

electron substituent

(II)

Xm

-S

wherein X, the same or different, represents an electron attractive substituent and m shows number of X substituent and is an integer of 0 to 7, a vulcanizing agent, and antioxidant; the compound being present in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the rubber component The compound is a kind of disulfides, but has not been used for thread rubber for golf balls. The addition of the specific disulfide of the component gives the thread high impact resilience and sufficient strength.

The present invention also provides a thread wound golf ball of which a thread rubber layer is formed from the above thread rubber.

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0* 054 S S DETAILED DESCRIPTION OF THE INVENTION The rubber component used in the present invention is selected from the group consisting of natural rubber, a synthetic high-cis polyisoprene rubber and a mixture thereof. The rubbers may be served in solid or latex. The latex contains rubber particles with micron order particle size colloidally dispersed in water and is preferred for the present invention, because no kneading process which is generally associated with but of molecular chains and reduces strength thereby is necessary.

The natural rubber can be anyone which has been used for this field and includes RSS#1, RSS#2, RSS#3, pale crepe, blown crepe and the like. The synthetic high-cis polyisoprene rubber is a rubber which is artificially synthesized and has a micro-structure similar to natural rubber having cis-1,4 structure of more than 98 thus usable as same as natural 5050 0 6.

S eSS S 6* 0 *r 0 0* 0 rubber. The synthetic high-cis polyisoprene rubber is commercially available from several rubber companies, examples of which are JSR IR 2200 available from Japan Synthetic Rubber Co., Ltd.; IR-10 available from Kuraray Co., Ltd.; Nipole IR 2200 available from Nippon Zeon Co., Ltd.; and the like. The latex type natural rubber includes high-ammonia preserved natural rubber latex having a solid content of about 60 by weight; highlypurified deproteinized natural rubber latex having a solid content of about by weight in which non-rubber content is less than 0.1 by weight by deproteinization; and the like. The natural rubber can preferably be deproteinized natural rubber for enhancing impact resilience, because deproteinization removes fatty acid which accelerates the orientation and crystallization of the rubber.

The rubber component may contain another rubber in addition to the above mentioned natural rubber and synthetic polyisoprene 15 rubber, but the other rubber is preferably limited to not more than 50 by weight, more preferably not more than 30 by weight based on the total rubber weight. Otherwise, strength would be degraded. Examples of the other rubbers are low-cis polyisoprene rubber, polybutadiene rubber, ethylene-propylene rubber (EPDM) and the like. The low-cis polyisoprene rubber is polyisoprene rubber having a cis-1,4 content of less than 92 of which solid type is available from Shell Chemical Co., as Kaliflex IR 305, 307, 309 etc. and the latex is available from Sumitomo Seika Chemicals Co., Ltd. as Maxprene IR; and the like.

According to the present invention, at least one compound (I) or (II) of the component is formulated into the rubber composition for the thread rubber of the present invention in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the rubber component It has not been clear what mechanism the compound and (II) fulfills in the chemical reaction or vulcanization, but the present inventors consider as follow. The diphenyl (or dinaphthyl) disulfide having electron attractive substituents of the component is easily changed to free radical by cleavage between two sulfur atoms. Accordingly, when the diphenyl (or dinaphthyl) disulfide having electron attractive substituents is added to the high-cis polyisoprene rubber or natural rubber and vulcanized, the free radicals thiyl radial) produced from the sulfide are functioned on the double bonds to produce many trans-isomers which enhance the impact resilience of the resulting thread rubber.

By the term "electron attractive substituent" used herein is meant a substituent which has a substituent coefficient (o-value) according to Hammet rule of more than zero, for example, chloro, bromo, iodo, fluoro, carboxyl, carboxyl ester, cyano, amido, nitro, acetyl, formyl and the like. In the present invention, the electron attractive substituent may be one kind or Stwo or more kinds from the above listed groups. Preferred are chloro, bromo, carboxyl ester, cyano and acetyl.

Typical examples of the compound represented by the formula are bis(4-chlorophenyl) disulfide, bis(2-chlorophenyl) disulfide, bis(3-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2bromophenyl) disulfide, bis(3-bromophenyl) disulfide, bis(4-fluorophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, bis(3,5-dichlorophenyl) disulfide, bis(2,4-dichlorophenyl) disulfide, bis(2,6dichiorophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl) disulfide, bis(2,4,6trichlorophenyl) disulfide, bis(2,3,4,5,6-pentachlorophenyl) disulfide, bis(4cyanophenyl) disulfide, bis(2-cyanophenyl) disulfide, bis(4-nitrophenyl) disulfide, bis(2-nitrophenyl) disulfide, 2,2'-dithiodibenzoic ethyl, 2,2'dithiodibenzoic methyl, 2,2'-dithiodibenzoic acid, 4,4'-dithiodibenzoic ethyl, bis(4-acetylphenyl) disulfidle, bis(2-acetylphenyl) disulfide, bis(4formylphenyl) disulfide, bis(4-carbamoyl phenyl) disulfide and the like.

Preferred are bis(4-chlorophenyl) disulfidle, bis(2-chlorophenyl) disulfide, bis(4-bromophenyl) disulfidle, bis(2-bromophenyl) disulfide, dichlorophenyl) disulfide, bi s(3,5-di chilorophenyl) disulfidle, bis(2,4dichiorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, O N dibromophenyl) disulfide, bis(3,5-dibromophenyl) disulfide, 4.bromophenyl) disulfide, bis(4-cyanophenyl) disulfide and bis(2- 15 cyanophenyl) disulfide.

Typical examples of the dinaphthyl sulfides represented by the formula (11) are 1,1'-dinaphthyl disulfide, 2,2'-dinaphthyl disulfide, 1,2'dinaphthyl disulfide 2,2'-bis(1 -chlorodinaphthyl) disulfide, 2,2'-bis(1 bromonaphthyl) disulfide, 1,1 '-bis(2-chloronaphthyl) disulfide, 2,2'-bis(1 cyanonaphthyl) disulfidle, 2,2'-bis(1-acetylnaphthyl) disulfide and the like.

The above compound is added to the rubber composition for the thread rubber in an amount of 0.5 to 10 parts by weight, preferably 1 to 7 parts by weight, based on 100 parts by weight of the rubber component Amounts of less than 0.5 parts by weight do not improve sufficiently and do not enhance impact resilience and those of more than 10 parts by see*& a 6*

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The rubber composition for the thread rubber of the present invention contains the vulcanizing agent and the antioxidant in addition to the above two components and The vulcanizing agent employed in the present invention can be anyone which has been used for the vulcanization of thread rubber for golf balls, but includes sulfur; an organic sulfur compound excepting the above mentioned compound such as morpholine disulfide and a sodium salt dihydrate of hexamethylene-1,6-bisthiosulfate; an organic peroxide, such as dicumyl peroxide; and the like. Sulfur is most preferred.

The vulcanizing agent may be contained in the rubber composition in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the rubber component 15 The antioxidant employed in the present invention can be anyone which has been used for the thread rubber for golf balls. Typical examples thereof are 4-methyl-2,6-di-t-butylphenol, 2,2'-methylenebis-(4ethyl-6-t-butylphenol), tetrakis-[methylene-3-(3',5'-di-t-butyl-4'hydroxyphenyl)propionate]methane, 4,4'-thiobis-(6-t-butyl-3-methylphenol) 20 and the like. The antioxidant may be contained in the rubber composition in an amount of 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber component The rubber composition for the thread rubber of golf balls may contain vulcanization accelerator, filler, oil and the like if necessary, in addition to the above components to The vulcanization accelerator used in the present invention can be anyone which has been used for the vulcanization of the thread rubber for golf balls. Typical examples thereof are butyl aldehyde-aniline condensate (available from Ohuchi Shinko Chemical K.K. as Noccelar 8), diphenylguanidine (DPG), benzothiazole dibenzothiadyl disulfide n-cyclohexyl-2-benzothiazole sulfenamide n-t-butyl-2benzothiazole sulfenamide (NS) and the like. The accelerator may be contained in the rubber composition in an amount of 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber component Typical examples of the fillers are kaoline, clay, calcium carbonate and the like. The oil can include naphtenic oil, diocryl adipate, dioctyl azelate, isooctyl tallate and the like. The amount of the filler may be S within the range of 0 to 5 parts by weight, based on 100 parts by weight of the rubber component The amount of the oil may be within the range of *i ;4 15 0 to 10 parts by weight, based on 100 parts by weight of the rubber component fee** The thread rubber may be prepared by mixing the above mentioned components in a mixer a kneader or a Banbury mixer) and then extruding it in the form of sheet having a thickness of about 0.5 mm, followed by vulcanizing at a temperature of 100 to 200 °C for 15 to 240 minutes. The resulting vulcanized sheet is cut into threads having a width of 1 to 2 mm.

0:06 A thread wound golf ball can be produced using the above obtained thread rubber. The thread rubber is wound on a center to form a thread wound core. The length of the thread rubber wound on the center is not limited, but can be within the range of 4 to 8 m. The center can be one which has used for thread wound golf balls, such as a solid center formed from a vulcanized rubber and a liquid center composed of a rubber bag and liquid encapsulated in the rubber bag. The rubber for the solid center is known to the art, and may contains butadiene rubber, curing agent, filler and the like. The liquid used for the liquid center may be water, or a paste containing filler in water. The thread wound core is then covered with a cover material selected from the group consisting of ionomer resin and tranpolyisoprene (balata). When forming a cover, many depressions called "dimples" are generally formed on the cover for controlling air resistance when flying. The golf ball having a dimpled cover is then coated with paint Oto finish for serving commercial sell.

EXAMPLES

The present invention will be illustrated by Examples which, however, are not to be construed as limiting the present invention to their details.

,Examples 1 to 11 and Comparative Examples 1 to S. •(Preparation of latex compositions)

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Sixteen kinds of latex compositions were prepared from the ingredients shown in Tables 1 to 3 by mixing. In Tables 1 to 3, the numbers show parts by weight and in case of latex, it shows an amount of rubber content. The other components are shown in an amount of effective component. Details of the formulated chemicals are shown after Table 3.

The amount of the specific disulfide of the component in each Example is adjusted to be the same moles using a basis as 2.0 parts by weight of diphenyl disulfide of Comparative Examples 4 and 5, excepting Example 7 which used a larger amount.

Table 1 Example number 1 2 3f 4f 5 6 Rubber component (a) IOTEX C-60 -1 100 Deproteinized natural rubber latex 1 00 100 100 1 00 100 Maxprene I R latex *3 Specific disulfide (b)I Bis(4-chlorophenyl) disulfide 2.6 disulfide 3.3 3.3 Bis(4-bromophenyl) disulfide 3.4 2,2'-dithiobenzoic ethyl 3.3 Bis(2-acetylphenyl) disulfide 28 Vulcanization accelerator (emulsion; 1.0 1.0 1.0 1.0 1.0 effective component 20 Sulfur (dispersion; effective 3.0 3.0 3.0 3.0 component 50 1 Antioxidant (dispersion: effective 1 .0 1 .0 1 .0 1 .0 1 .0 1 .0 component 40 Each disulfide was formulated in the form of a dispersion having an effective component content of 33.3 by weight.

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g Table 2 Example number 7 8 9 10 11 Rubber component (a) IOTEX C-60 1 Deproteinized natural rubber latex (60 100 100 100 100 100 2 Maxprene IR latex *3 Specific disulfide (b) disulfide 5.0 Bis(2-cyanophenyl) disulfide 2,2'-Dinaphthyl disulfide 2.9 2,2'-Bis(1-chlorodinaphthyl) disulfide 3.6 disulfide 3.3 Vulcanization accelerator (emulsion; 1.0 1.0 1.0 1.0 effective component 20 *4 Sulfur (dispersion; effective component 3.0 3.0 3.0 3.0 50 Antioxidant (dispersion: effective 1.0 1.0 1.0 1.0 component 40 Each disulfide was formulated in the form of a dispersion having an effective component content of 33.3 by weight.

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Table 3 Comparative Example number 1 2 3 4 Rubber component (a) IOTEX C-60 1 40 100 100 Deproteinized natural rubber latex (60 100 100 Maxprene IR latex *3 Specific disulfide (b) Diphenyl disulfide 2.0 Vulcanization accelerator (emulsion; 1.0 1.0 1.0 1.0 effective component 20 "4 Sulfur (dispersion; effective component 3.0 3.0 3.0 3.0 Antioxidant (dispersion: effective 1.0 1.0 1.0 1.0 component 40 *5

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5** 4 Each disulfide was formulated in the form of a dispersion having an effective component content of 33.3 by weight.

*1 IOTEX C-60: High ammonia preserved natural rubber 5 latex available from Malaysia 101.

*2 Deproteinized ammonia preserved natural rubber latex having a non-rubber content of less than 0.05 by weight.

*3 Maxprene IR: Low cis-polyisoprene rubber latex available from Sumitomo Seika Chemicals Co., Ltd.

10 *4 Butyl aldehyde-aniline condensate available from Ohuchi Shinko Kagaku K.K. as Noccelar 8.

2,2'-Methylenebis-(4-ethyl-6-t-butylphenol) available from Yoshitomi Pharmaceutical Industries, Ltd.

(Preparation of thread rubber) Each latex composition according to the ingredients shown in Examples 1-11 and Comparative Examples 1-5 was solidified on an endless belt on which a solidifying solution of an aqueous calcium chloride was coated, to form a sheet. The sheet was dried and then rolled up on a drum which was vulcanized at 135 0C for 2 hours in a vulcanizer to form a vulcanized rubber sheet having width 350 mm X thickness 0.5 mm X length m. It was then cut into width 1.6 mm to form thread rubber. The resulting thread rubber was subjected to an evaluation of hysteresis loss and elongation at 100 Kg/cm 2 tensile force as the determination of impact resilience, and their results are shown in Tables 4 to 6.

(Preparation of thread wound golf balls) N WThe thread rubber obtained above was wound on a liquid *:so e, center having a diameter of 28.3 mm in a drawn condition to form a thread wound core having a diameter of about 39.5 mm. It was then covered with S15 balata cover to form a thread wound golf ball having a diameter of about •oooe 42.7 mm, a ball weight of 45.3 to 45.5 g and a PGA compression of about 90. The resulting thread wound golf ball was subjected to an evaluation of impact resilience. The impact resilience was determined by coefficient of o• restitution. The strength of the thread rubber was also evaluated by number of thread breakage when winding of a liquid center. The results :Eare shown in Tables 4 to 6.

(Method of test) Hysteresis loss and elongation at 100 Kg/cm 2 tensile force Fig. 1 explains how to determine the hysteresis loss and the elongation at 100 Kg/ 2 tensile force.

Fig. 1 shows a hysteresis curve of stress-strain when a sample of the thread rubber is stretched at a tensile rate of 500 mm/min until 100 Kg/2 constant stress by a tensile strength tester (Curve a in Fig. 1) and then restored to its original state (Curve b in Fig. Hysteresis loss is a value of energy loss (W 1 divided with supply energy (W 1

W

2 and is indicated in the unit of percentage.

Hysteresis loss W 1 /(W1 W 2 X 100 Elongation is a strain amount at 100 Kg/cm 2 tensile force, that is the point and is determined from the following equation in the unit of percentage.

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15 *44*4* 4 44 4944 4.

Elongation (stretched length/original length 1) Average number of thread breakage Ten dozens of thread wound cores were produced by winding the thread rubber on a liquid center and number of breakage of the thread rubber was given. It was then divided with number of cores to obtain an average number of thread breakage on one core.

Coefficient of restitution A golf ball was hit at a head speed of 45 m/sec and a coefficient of restitution was directly measured by an initial velocity tester available from R A.

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9 *got Table 4 Example number 1 2 3 4 5 6 Hysteresis loss 38 30 37 35 34 36 Elongation 1100 1200 1100 1150 1150 1100 Number of thread 0.01 0.03 0.01 0.02 0.02 0.01 breakage Coefficient of 0.7650 0.7750 0.7650 0.7700 0.7700 0.7650 restitution Table Example number 7 8 9 10 11 Hysteresis loss 34 32 37 36 Elongation 1250 1200 1100 1150 1200 Number of thread 0.07 0.05 0.03 0.04 0.04 breakage Coefficient of 0.7780 0.7700 0.7650 0.7670 0.7750 restitution Table 6 Comparative Example number 1 2 3 4 Hysteresis loss 40 60 53 45 44 Elongation 1100 800 850 1000 1030 Number of thread breakage 1.5 0.01 0.02 0.1 0.08 Coefficient of restitution 0.7650 0.7150 0.7250 0.7500 0.7550 As is apparent from the above results, the thread rubbers of Examples 1-11 are good in impact resilience and strength in comparison with the thread rubbers of Comparative Examples, and satisfy the required performance of golf balls. The thread rubber of Comparative Example 1 which mainly contained low cis-polyisoprene rubber shows good impact resilience but shows many thread breakage, thus poor strength.

Comparative Examples 2 and 3 show thread rubber which mainly contained natural rubber but did not contain the component of the present invention. The thread rubbers of Comparative Examples 2 and 3 show poor impact resilience. Comparative Examples 4 and 5 are thread rubber which improved those obtained in Comparative Examples 2 and 3 by adding diphenyl disulfide, which reduce number of thread breakage, but do not show sufficient impact resilience.

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.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms o..:part of the common general knowledge in Australia.

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Claims (14)

1. Thread rubber suitable for use in golf balls, obtained by vulcanizing a rubber composition which comprises a rubber component selected from the group consisting of natural rubber, a synthetic high-cis-polyisoprene rubber and a mixture thereof, at least one compound selected from the group consisting of a diphenyl disulfide compound represented by Xn SSXn "wherein X, the same or different, represents an electron attractive substituent and n shows number of X substituent and is an integer of 1 to and a dinaphthyl disulfide compound represented by Xm (Xm wherein X, the same or different, represents an electron attractive substituent and m shows number of X substituent and is an integer of 0 to 7, a vulcanizing agent, and antioxidant; 17 6eq. 6 15 S r *6 6 69* *00* 6 *6 *066 the compound being present in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the rubber component

2. The thread rubber according to claim 1, wherein the rubber component is latex.

3. The thread rubber according to claim 1, wherein the natural rubber is deproteinized natural rubber.

4. The thread rubber according to claim 1, wherein the rubber component contains another rubber in an amount of not more than by weight based on a total rubber component

5. The thread rubber according to claim 4, wherein the other rubber includes low-cis polyisoprene rubber, polybutadiene rubber or ethylene-propylene rubber (EPDM).

6. The thread rubber according to claim 1, wherein the electron attractive substituent X is selected from the group consisting of chloro, bromo, iodo, fluoro, carboxyl, caroxyl ester, cyano, amido, nitro, acetyl and formyl.

7. The thread rubber according to claim 1, wherein the compound is selected from the group consisting of bis(4-chlorophenyl) disulfide, bis(2-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2- bromophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, dichlorophenyl) disulfide, bis(2,4-dichlorophenyl) disulfide, bis(2,6- dichlorophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl) disulfide, bis(4- cyanophenyl) disulfide and bis(2-cyanophenyl) disulfide.

8. The thread rubber according to claim 1, wherein the compound (II) is selected from the group consisting of 1,1'-dinaphthyl disulfide, 2,2'-dinaphthyl disulfide, 1,2'-dinaphthyl disulfide 2,2'-bis(1- chlorodinaphthyl) disulfide, 2,2'-bis(1-bromonaphthyl) disulfide, 1,1'-bis(2- chloronaphthyl) disulfide, 2,2'-bis(1-cyanonaphthyl) disulfide and 2,2'- bis(1-acetylnaphthyl) disulfide.

9. The thread rubber according to claim 1, wherein the vulcanizing agent includes sulfur; an organic sulfur compound excepting the compound or an organic peroxide. The thread rubber according to claim 1, wherein the vulcanizing agent is contained in the rubber composition in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the rubber 0 e* component

11. The thread rubber according to claim 1, wherein the antioxidant is selected from the group consisting of 4-methyl-2,6-di-t- butylphenol, 2,2'-methylenebis-(4-ethyl-6-t-butylphenol), tetrakis- [methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane and 4,4'-thiobis-(6-t-butyl-3-methylphenol).

12. The thread rubber according to claim 1, wherein the antioxidant is contained in the rubber composition in an amount of 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber component :09 Ole 06 **so

13. The thread rubber according to claim 1, wherein the rubber composition further comprises a vulcanization accelerator selected from the group consisting of butyl aldehyde-aniline condensate, diphenylguanidine, benzothiazole, dibenzothiadyl disulfide, n-cyclohexyl- 2-benzothiazole sulfenamide and n-t-butyl-2-benzothiazole sulfenamide.

14. The thread rubber according to claim 3, wherein the vulcanization accelerator is contained in the rubber composition in an amount of 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber component A thread wound golf ball comprising a center, a thread rubber layer formed on the center and a cover covering on the thread layer, wherein said thread layer is formed from thread rubber obtained by vulcanizing a rubber composition which comprises a rubber component selected from the group consisting of natural rubber, a synthetic high-cis-polyisoprene rubber and a mixture thereof, at least one compound selected from the group consisting of a diphenyl disulfide compound represented by Xn ^s -Xn (I) s (I) 15 wherein X, the same or different, represents an electron attractive substituent and n shows number of X substituents and is an integer of 1 to and a dinaphthyl disulfide compound represented by XM Xm 1wrein t Q wherein X, the same or different, represents an electron attractive substituent and m shows number of X substituent and is an integer of 0 to 7, a vulcanizing agent, and antioxidant; the compound being present in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the rubber component a« 00 .r p os P-\OPER\MKR\I6547-97 doc-4)3/07A0 -22-

16. A thread rubber suitable for use in golf balls according to claim 1, or a golf ball incorporating same, substantially as hereinbefore described with reference to the Examples. DATED this 3 0 t h day of June 2000. SUMITOMO RUBBER INDUSTRIES, LTD. and SUMITOMO SEIKO CHEMICALS CO., LTD. by their Patent Attorneys i. DAVIES COLLISON CAVE C oo f oo* o ft oooo** oft