Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-05-26
2001-01-16
Gerrity, Stephen F. (Department: 3729)
Games using tangible projectile
Golf
Ball
C473S371000, C473S372000, C473S373000, C473S374000
Reexamination Certificate
active
06174246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-piece solid golf ball and, specifically, to a multi-piece solid golf ball which is excellent impact resilience, flying performance, shot feeling and durability.
2. Description of the Related Art
A multi-piece solid golf ball is a golf ball comprising two or more core layers or two or more cover layers and is now being developed to improve a shot feeling which is the demerit of a two-piece solid golf ball while retaining or improving impact resilience and flying performance which are the merits of the two-piece solid golf ball.
For example, Japanese Patent Application Laid-open No. Sho 60-241464 proposes a multi-piece solid golf ball comprising an inner layer core and an outer layer core which differ from each other in specific gravity. However, compared with the two-piece solid golf ball, this multi-piece solid golf ball has a good driving feeling but is inferior in impact resilience. Meanwhile, Japanese Patent Application Laid-open No. Hei 2-228978 proposes a multi-piece solid golf ball comprising two core layers which differ from each other in hardness. However, since there is a large difference in hardness between the inner layer core and the outer layer core, breakage readily occurs from the interface between these layers and this multi-piece solid golf ball lacks durability.
Although many multi-piece solid golf balls other than the above ones are proposed, none of them satisfies all requirements for shot feeling, impact resilience, flying performance and durability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a multi-piece solid golf ball which is excellent impact resilience, flying performance, shot feeling and durability.
That is, the present invention provides a multi-piece solid golf ball which comprises a core consisting of an inner layer core and an outer layer core and a cover layer for covering the core, wherein the diameter of the inner layer core is 20 to 35 mm, the thickness of the outer layer core is 2 to 11 mm, the Shore D hardness (A) of the surface of the inner layer core and the Shore D hardness (B) of the surface of the outer layer core satisfy relational expressions, 15≦(A)≦50, 35≦(B)≦70 and (A)≦(B), and the cover layer is made from a resin composition comprising 50 to 90 parts by weight of an ionomer resin and 50 to 10 parts by weight of diene-based rubber.
Preferably, the specific gravity (C) of the inner layer core and the specific gravity (D) of the outer layer core satisfy relational expressions, 1.0≦(C)≦1.5, 1.0≦(D)≦1.5 and |(C)−(D)|≦0.1.
Preferably, the above diene-based rubber is dispersed in the ionomer resin and thermally crosslinked.
The surface of the cover layer preferably has a Shore D hardness of 40 to 70, more preferably 40 to 65.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is a multi-piece solid golf ball which comprises a core consisting of an inner layer core and an outer layer core and a cover layer for covering the core, wherein the diameter of the inner layer core is 20 to 35 mm, the thickness of the outer layer core is 2 to 11 mm, the Shore D hardness (A) of the surface of the inner layer core and the Shore D hardness (B) of the surface of the outer layer core satisfy relational expressions, 15≦(A)≦50, 35≦(B)≦70 and (A)≦(B), and the cover layer is made from a resin composition comprising 50 to 90 parts by weight of an ionomer resin and 50 to 10 parts by weight of diene-based rubber.
The cover layer of the multi-piece solid golf ball of the present invention is made from a resin composition comprising 50 to 90 parts by weight of an ionomer resin and 50 to 10 parts by weight of diene-based rubber. Since the cover layer contains diene-based rubber, durability is greatly improved and impact resilience, flying performance and shot feeling are also improved compared with a case where the cover layer is made from a resin composition containing an ionomer resin alone.
The ionomer resin contains an ethylene-unsaturated carboxylic acid copolymer as a base resin and is obtained from an ethylene-unsaturated carboxylic acid copolymer and a metal compound capable of supplying cations, for example.
The ethylene-unsaturated carboxylic acid copolymer is, for example, a copolymer of ethylene and an unsaturated carboxylic acid having 3 to 6 carbon atoms, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid or vinyl benzoate.
The metal compound capable of supplying cations is, for example, a formate, acetate, nitrate, carbonate, bicarbonate, oxide, hydroxide, alkoxide or the like of an alkali metal, alkali earth metal or transition metal. Illustrative examples of the metal include sodium, zinc, lithium, magnesium, manganese, calcium, cobalt, potassium and the like.
The ionomer resin preferably has a Shore D hardness of 55 to 80. Since the surface of the cover layer preferably has a Shore D hardness of 40 to 70 as will be described hereinafter, when the Shore D hardness of the ionomer resin is higher than 80, the control of the hardness of the cover layer becomes difficult. When the Shore D hardness of the ionomer resin is higher than 55, the impact resilience of the cover layer become satisfactory.
Illustrative examples of the ionomer resin include metal salts of a copolymer of ethylene and methacrylic acid. The commercial products of the ionomer resin include Himilan 1605, Himilan 1706, Himilan 1707, Himilan AM7315, Himilan AM7317 and Himilan AM7318 of Mitsui Du Pont•Polychemical Co., Ltd. and Sarlin 7930 and Sarlin 7940 of Du Pont Co., Ltd. and the like.
Illustrative examples of the diene-based rubber used for the cover layer include natural rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, ethylene-propylene-diene terpolymer rubber, acrylonitrile-butadiene copolymer rubber and the like. Butadiene rubber is preferred, and butadiene rubber having 40% or more of a cis-1,4 bond is particularly preferred. The commercial products of the diene-based rubber include BR-01, BR-11, BR-18 of Japan Synthetic Rubber Co., Ltd., Nipol 1220 of Nippon Zeon Co., Ltd., UBEPOL BR-210, 150L and 360L of Ube Corporation, and the like.
The particle diameter of the diene-based rubber is preferably 0.1 to 5 &mgr;m. This is because the impact resilience, durability and appearance of the cover layer become satisfactory.
The weight ratio of the ionomer resin to the diene-based rubber in the resin composition is 50/50 to 10/90. When the proportion of the ionomer resin is higher than the above range, the shot feeling becomes too hard. When the proportion of the diene-based rubber is higher than the above range, impact resilience and flying performance deteriorate.
Preferably, the diene-based rubber is dispersed in the ionomer resin and thermally crosslinked. The impact resilience, durability and appearance of the cover layer become satisfactory by thermal crosslinking. The expression “appearance becomes satisfactory” means that the cover layer has a good appearance without a nap. When not thermal crosslinking but a crosslinking agent is used, the following problem arises. For example, when crosslinking is carried out with an organic peroxide, the ionomer resin is crosslinked as well, thereby reducing the flowability of the cover layer and making molding difficult. When crosslinking is carried out with sulfur, the resin composition is colored yellow.
The Shore D hardness of the surface of the cover layer is preferably 40 to 70, more preferably 40 to 65, particularly preferably 55 to 65. Within the above range, durability becomes satisfactory. When the Shore D hardness is higher than 70, the shot feeling becomes hard and when the Shore D hardness is lower than 40, flying performance may deteriorate.
The resin composition preferably has a tan &sgr; at 0° C. of 0.01 to 0.07. This is because impact resilience become satisfactory.
The reason why tan &sgr; at 0° C. is set to 0.01 to 0.07 is the use of the ionomer resin hav
Hase Toshiya
Ono Shinya
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Gerrity Stephen F.
Kim Paul D.
The Yokohama Rubber Co.,Ltd.
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