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Multi-piece solid golf ballRelated Patent Categories: Games Using Tangible Projectile, Golf, Ball, Particular Unitary Or Layered ConstructionMulti-piece solid golf ball description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060014595, Multi-piece solid golf ball. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERRENCE TO RELATED APPLICATION [0001] This application is a continuation of application Ser. No. 10/635,610 filed on Aug. 7, 2003, which is a continuation-in-part of copending application Ser. No. 10/156,950 filed on May 30, 2002, the entire contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a multi-piece solid golf ball which has been imparted with a good, soft feel upon impact and an excellent spin performance that makes it possible to achieve an increased distance. [0004] 2. Prior Art [0005] 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. [0006] 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. [0007] However, further improvements in the materials are required in the above art to achieve golf balls endowed with a good, soft feel upon impact and an excellent spin performance that helps increase the distance the ball travels when played. [0008] 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 with a good, soft feel upon impact and an excellent spin performance that helps increase the distance traveled by the ball cannot be obtained in this way. [0009] 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 have a good, soft feel upon impact and an excellent spin performance that helps increase the distance traveled by the ball. [0010] Golf balls having a cover composed of a relatively hard inner layer and a relatively soft outer layer have already been disclosed in JP-A 6-218078, JP-A 6-343718, JP-A 7-24085, JP-A 9-239068, JP-A 10-151226, JP-A 10-201880, JP-A 11-104273, JP-A 11-104271, and Japanese Patent Applications No. 2000-274807 and 2000-274843. However, further improvements in distance are desired for the golf balls described in all of these specifications. SUMMARY OF THE INVENTION [0011] It is therefore an object of the present invention to provide multi-piece solid golf balls which are endowed with a good, soft feel when hit with a golf club and an excellent spin performance that helps increase the distance traveled by the ball when played. [0012] The inventor has discovered that golf balls having a solid core, an inner cover layer over the cover, and an outer cover layer over the inner cover layer, wherein the solid core is made of a rubber composition formulated from a particular type of base rubber combined in specific proportions with certain other materials, and the inner and outer cover layer are specified in specific hardness range, respectively and the outer cover layer is softer than the inner cover layer, exhibit a good synergy from optimization of the solid core materials and an appropriate distribution of hardness between the inner and outer cover layers. Multi-piece solid golf balls thus constituted have a good, soft feel when hit with a golf club and an excellent spin performance that enables the ball to travel further when played. [0013] Accordingly, the invention provides a multi-piece solid golf ball having a solid core, an inner cover layer enclosing the core, and an outer cover layer enclosing the inner cover layer. The solid core is molded from 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 .eta. at 25.degree. C. as a 5 wt % solution in toluene of up to 600 mPas, and having the Mooney viscosity (ML.sub.1+4 (100.degree. C.)) of the polybutadiene of 50 to 80, being synthesized using a rare-earth catalyst, in combination with (b) 0 to 80 wt % of a diene rubber other than component (a), in combination with (b) 0 to 80 wt % of a diene rubber other than component (a). The rubber composition includes also (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. In the multi-piece solid golf ball of the invention, it is generally advantageous for the inner cover layer to have a Shore D hardness of 50 to 80 and the outer cover layer to have a Shore D hardness of 35 to 60, and the outer cover layer has a lower Shore D hardness than the inner cover layer. [0014] Preferably, the diene rubber (b) includes 30 to 100 wt % of a second polybutadiene which has a cis-1,4 content of at least 60% and a 1,2 vinyl content of at most 5%, has a Mooney viscosity (ML.sub.1+4 (100.degree. C.)) of not more than 55, and satisfies the relationship .eta..ltoreq.20A-550, wherein A is the Mooney viscosity (ML.sub.1+4 (100.degree. C.)) of the second polybutadiene and .eta. is the viscosity, in mPas, of the second polybutadiene at 25.degree. C. as a 5 wt % solution in toluene. The second polybutadiene in component (b) is typically synthesized using a Group VIII catalyst. DETAILED DESCRIPTION OF THE INVENTION [0015] The golf ball of the invention includes a solid core made of a rubber composition in which the base rubber is at least partly polybutadiene. It is critical that the base rubber contain as component (a) a specific amount of a polybutadiene in which the cis-1,4 and 1,2 vinyl contents, the viscosity .eta. at 25.degree. 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. [0016] 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 resilience declines. [0017] The polybutadiene (a) must also have a viscosity .eta. at 25.degree. C. as a 5 wt % solution in toluene of not more than 600 mPas. "Viscosity .eta. at 25.degree. C. as a 5 wt % solution in toluene" refers herein to the value in mPas 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.degree. C. using a standard solution for the viscometer (JIS Z8809). [0018] The polybutadiene (a) has a viscosity .eta. at 25.degree. C. as a 5 wt % solution in toluene of not more than 600 mPas, preferably not more than 550 mPas, more preferably not more than 500 mPas, even more preferably not more than 450 mPas, and most preferably not more than 400 mPas. Too high a viscosity .eta. lowers the workability of the rubber composition. It is recommended that the viscosity .eta. be at least 50 mPas, preferably at least 100 mPas, more preferably at least 150 mPas, and most preferably at least 200 mPas. Too low a viscosity .eta. may lower the resilience. [0019] In addition, it is preferred that the polybutadiene (a) satisfies the relationship: 10B+5.ltoreq.A.ltoreq.10B+60, wherein A is the Mooney viscosity (ML.sub.1+4 (100.degree. 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, the resilience declines. On the other hand, if A is too high, the workability of the rubber composition worsens. [0020] The polybutadiene (a) have a Mooney viscosity (ML.sub.1+4 (100.degree. C.)) of 50 to 80, which dramatically enhance the rebound. It is recommended that the polybutadiene (a) have a Mooney viscosity (ML.sub.1+4 (100.degree. C.)) of at least 52, preferably at least 54, but not more than 70, preferably not more than 65, more preferably not more than 60. Continue reading about Multi-piece solid golf ball... Full patent description for Multi-piece solid golf ball Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Multi-piece solid golf ball patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Multi-piece solid golf ball or other areas of interest. ### Previous Patent Application: Golf club head structure for improving casting fluidity in a slurry shell Next Patent Application: Golf ball teeing apparatus and tee Industry Class: Games using tangible projectile ### FreshPatents.com Support Thank you for viewing the Multi-piece solid golf ball patent info. 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