Games using tangible projectile – Golf – Ball
Reexamination Certificate
2002-05-30
2004-09-07
Gorden, Raeann (Department: 3711)
Games using tangible projectile
Golf
Ball
Reexamination Certificate
active
06786836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a golf ball having a soft feel when hit with a golf club and good rebound characteristics.
2. Prior Art
Various improvements are being made in formulating the polybutadiene used as the base rubber in golf balls so as to confer the balls with outstanding rebound characteristics.
For example, JP-A 62-89750 describes rubber compositions for use as the base rubber in solid golf balls, which compositions are arrived at by blending a polybutadiene having a Mooney viscosity of 70 to 100 and synthesized using a nickel or cobalt catalyst with another polybutadiene having a Mooney viscosity of 30 to 90 and synthesized using a lanthanide catalyst or polybutadiene having a Mooney viscosity of 20 to 50 and synthesized using a nickel or cobalt catalyst.
However, further improvements are required in the above art to achieve golf balls endowed with a sufficiently soft feel and excellent rebound.
JP-A 2-268778 describes golf balls molded using a blend composed of a polybutadiene having a Mooney viscosity of less than 50 and synthesized using a Group VIII catalyst in combination with a polybutadiene having a Mooney viscosity of less than 50 and synthesized with a lanthanide catalyst. However, golf balls having both a soft feel and excellent rebound cannot be obtained in this way.
The existing art also teaches multi-piece solid golf balls in which an intermediate layer is molded of a low-Mooney viscosity polybutadiene (JP-A 11-70187), solid golf balls molded from rubber compositions comprising a polybutadiene having a Mooney viscosity of 50 to 69 and synthesized using a nickel or cobalt catalyst in combination with a polybutadiene having a Mooney viscosity of 20 to 90 and synthesized using a lanthanide catalyst (JP-A 11-319148), solid golf balls molded from compositions based on a rubber having a 1,2 vinyl content of at most 2.0% and a weight-average molecular weight to number-average molecular weight ratio Mw/Mn of not more than 3.5 (JP-A 11-164912), golf balls molded from rubber compositions containing a high Mooney viscosity polybutadiene (JP-A 63-275356), and golf balls molded from rubber compositions comprising polybutadiene having a high number-average molecular weight in admixture with polybutadiene having a low number-average molecular weight (JP-A 3-151985). However, none of these prior-art golf balls truly achieve both a soft feel upon impact and excellent rebound characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide golf balls which are endowed with both a soft feel when hit with a golf club and excellent rebound characteristics.
The inventor has discovered that golf balls containing as an essential component a hot-molded product which is made of a rubber composition formulated from a particular type of base rubber combined in specific proportions with certain other materials and which is endowed with specific hardness properties exhibit a good synergy of effects owing to optimization of the composition and hardness. Golf balls containing such a hot-molded product have a soft feel upon impact and outstanding rebound characteristics.
Accordingly, the invention provides a golf ball containing a hot-molded product of a rubber composition comprising
100 parts by weight of a base rubber composed of (a) 20 to 100 wt % of a polybutadiene having a cis-1,4 content of at least 60% and a 1,2 vinyl content of at most 2%, having a viscosity &eegr; at 25° C. as a 5 wt % solution in toluene of up to 600 mPa·s, and satisfying the relationship: 10B+5≦A≦10B+60, wherein A is the Mooney viscosity (ML
1+4
(100° C.)) of the polybutadiene and B is the ratio Mw/Mn between the weight-average molecular weight Mw and the number-average molecular weight Mn of the polybutadiene, in combination with (b) 0 to 80 wt % of a diene rubber other than component (a),
(c) 10 to 60 parts by weight of an unsaturated carboxylic acid and/or a metal salt thereof,
(d) 0.1 to 5 parts by weight of an organosulfur compound,
(e) 5 to 80 parts by weight of an inorganic filler, and
(f) 0.1 to 5 parts by weight of an organic peroxide.
The hot-molded product has a difference in JIS-C hardness between the center and surface thereof of more than 15 and up to 40 JIS-C hardness units.
Preferably, the polybutadiene (a) is synthesized using a rare-earth catalyst and satisfies the relationship: &eegr;≧20A−600 (&eegr; and A being as defined above).
The base rubber typically contains as component (b) a polybutadiene synthesized with a Group VIII catalyst and having a Mooney viscosity of not more than 55.
DETAILED DESCRIPTION OF THE INVENTION
The golf ball of the invention includes as a constituent component a hot-molded product of a rubber composition in which the base rubber is polybutadiene. It is critical that the base rubber contain as component (a) a specific amount of polybutadiene in which the cis-1,4 and 1,2 vinyl contents, the viscosity &eegr; at 25° C. as a 5 wt % solution in toluene, and the relationship between the Mooney viscosity and the polydispersity index Mw/Mn have each been optimized. Optimization of the relationship between the Mooney viscosity and the above viscosity &eegr; is also desirable.
That is, the polybutadiene (a) has a cis-1,4 content of at least 60%, preferably at least 80%, more preferably at least 90%, and most preferably at least 95%; and has a 1,2 vinyl content of at most 2%, preferably at most 1.7%, more preferably at most 1.5%, and most preferably at most 1.3%. Outside of the above ranges, the rebound characteristics of the golf ball decline.
The polybutadiene (a) must also have a viscosity &eegr; at 25° C. as a 5 wt % solution in toluene of not more than 600 mPa·s. “Viscosity &eegr; at 25° C. as a 5 wt % solution in toluene” refers herein to the value in mPa·s units obtained by dissolving 2.28 g of the polybutadiene to be measured in 50 ml of toluene and carrying out measurement with a specified viscometer at 25° C. using a standard solution for the viscometer (JIS Z8809).
The polybutadiene (a) has a viscosity &eegr; at 25° C. as a 5 wt % solution in toluene of not more than 600 mPa·s, preferably not more than 550 mPa·s, more preferably not more than 500 mPa·s, even more preferably not more than 450 mPa·s, and most preferably not more than 400 mPa·s. Too high a viscosity &eegr; lowers the workability of the rubber composition. It is recommended that the viscosity &eegr; be at least 50 mPa·s, preferably at least 100 mPa·s, more preferably at least 150 mPa·s, and most preferably at least 200 mPa·s. Too low a viscosity &eegr; may lower rebound characteristics.
In addition, the polybutadiene (a) must satisfy the relationship:
10
B
+5
≦A
≦10
B
+60,
wherein A is the Mooney viscosity (ML
1+4
(100° C.)) of the polybutadiene and B is the ratio Mw/Mn between the weight-average molecular weight Mw and the number-average molecular weight Mn of the polybutadiene. A is preferably at least 10B+7, more preferably at least 10B+8 and most preferably at least 10B+9, but preferably not more than 10B+55, more preferably not more than 10B+50, and most preferably not more than 10B+45. If A is too low, rebound characteristics decline. On the other hand, if A is too high, the workability of the rubber composition worsens.
It is also desirable for the polybutadiene (a) to satisfy the relationship:
20
A
−600≦&eegr;≦20
A
−100,
wherein &eegr; and A are as defined above. The viscosity &eegr; is preferably at least 20A−580, more preferably at least 20A−560, and most preferably at least 20A−540, but preferably not more than 20A−150, more preferably not more than 20A−200, and most preferably not more than 20A−250. The use of a polybutadiene having such an optimized relationship of &eegr; and A, that suggests the high linearity of polybutadiene molecules, is effective for conferring better resilience.
It is recommended as well that the polybutadiene (a) have a Mooney vis
Higuchi Hiroshi
Nanba Atsushi
Bridgestone Sports Co. Ltd.
Gorden Raeann
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