Games using tangible projectile – Golf – Ball
Reexamination Certificate
2001-11-05
2003-11-18
Graham, Mark S. (Department: 3711)
Games using tangible projectile
Golf
Ball
C473S351000
Reexamination Certificate
active
06648779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a golf ball, in particular a solid golf ball excellent in resilience and durability, and a manufacturing method thereof.
2. Description of the Background Art
Conventionally, the core of a golf ball has been manufactured by heating a rubber composition having a co-crosslinking agent such as metallic salt of unsaturated carboxylic acid and a crosslinking initiator such as organic peroxide blended into a rubber component chiefly including polybutadiene, to crosslink rubber molecule main chains. As the metallic salt of unsaturated carboxylic acid, zinc acrylic acid has generally been used. When the rubber composition is heated, the crosslinking initiator such as dicumyl peroxide dissociates to generate a free radical, which is considered to attack the rubber molecule main chain or the co-crosslinking agent to cause graft polymerization of the co-crosslinking agent to the main chain of the rubber molecule or the crosslinking between the main chains. The state of dispersion of the co-crosslinking agent such as metallic salt of unsaturated carboxylic acid within the rubber composition, and the speed of its crosslinking reaction to the main chain of the rubber molecule will considerably affect basic physical properties of the rubber composition after crosslinking, and will further affect properties of a golf ball with its solid core formed thereof.
Thus, in order to improve dispersibility of the co-crosslinking agent within the rubber composition, a technique to coat a particle surface of the zinc acrylic acid with higher fatty acid or metallic salt of higher fatty acid has conventionally been proposed (U.S. Pat. No. 4,561,657 and Japanese Patent Laying-Open No. 60-92781).
Further, a technique to use, as the co-crosslinking agent, metallic salt of unsaturated carboxylic acid having an average particle size of not greater than 5 &mgr;m, or unsaturated carboxylate having particle size distribution of 0.1-5 &mgr;m and an average particle size of 1-4.5 &mgr;m has also been proposed to improve the dispersibility of the co-crosslinking agent within the rubber composition (Japanese Patent Laying-Open Nos. 8-196661, 9-235413, 11-57068, and U.S. Pat. No. 6,136,906).
These techniques are advantageous in that the dispersibility of the co-crosslinking agent within the rubber composition is improved and thus hardness of the rubber composition is increased. However, due to the co-crosslinking agent so finely dispersed, the density of crosslinking between the rubber molecule main chains, which is most likely to contribute to resilience, is decreased, whereas the graft polymerization of the co-crosslinking agent with the rubber molecule main chain, which is unlikely to contribute to the resilience, is increased, resulting in unsatisfactory resilience.
Proposed to improve such resilience is a technique to use an organic sulfur compound together with metallic salt of &agr;,&bgr;-unsaturated carboxylic acid (Japanese Patent Laying-Open Nos. 2-297384, 9-122273, 10-244019, 2000-102627, and U.S. Pat. No. 5,252,652). With this technique, however, the added organic sulfur compound captures the free radical of the crosslinking initiator, thereby limiting the activity of the crosslinking initiator. Thus, compared to the case where no organic sulfur compound is being added, the time of reaction is lengthened and a blended amount of crosslinking initiator should be increased. The basic characteristics of the rubber composition may also be impaired.
SUMMARY OF THE INVENTION
An object of the present invention is to improve dispersibility of a co-crosslinking agent in a rubber composition for use in manufacturing a solid core of a golf ball, by micro-encapsulating the co-crosslinking agent. Another object of the present invention is to provide a golf ball improved in resilience and durability, by micro-encapsulating an organic sulfur compound together with a portion of the co-crosslinking agent to properly restrict the speed of graft polymerization of the co-crosslinking agent with a rubber molecule main chain and to give priority to crosslinking reaction between the rubber molecule main chains.
According to an aspect of the present invention, the golf ball includes a solid core, and a cover surrounding the solid core, wherein the solid core includes a rubber composition having a co-crosslinking agent blended therein, with a portion of the co-crosslinking agent being micro-encapsulated within a thermoplastic resin.
Here, preferably 70-99 wt. % of the entire co-crosslinking agent is micro-encapsulated. As the co-crosslinking agent, an &agr;,&bgr;-unsaturated carboxylic acid and/or a metallic salt thereof is suitably employed. The thermoplastic resin preferably has a softening point in a range of 80-250° C.
According to another aspect of the present invention, the golf ball includes a solid core and a cover surrounding the solid core, wherein the solid core is formed of a rubber composition that contains a portion of a co-crosslinking agent and an organic sulfur compound micro-encapsulated within a thermoplastic resin, and a remaining portion of the co-crosslinking agent not encapsulated. Here, the organic sulfur compound is preferably one of polysulfides, thiophenols and bivalent metallic salts of the thiophenols.
According to a further aspect of the present invention, the manufacturing method of a golf ball having a solid core and a cover surrounding the solid core includes:
(1) a step of blending a portion of a co-crosslinking agent in a non-encapsulated state and a remaining portion of the co-crosslinking agent and possibly an organic sulfur compound micro-encapsulated within a thermoplastic resin into a rubber composition, and
(2) a step of heating the rubber composition to a temperature higher than a softening point of the thermoplastic resin for crosslinking.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The golf ball according to the present invention is formed with a solid core surrounded by a cover material. The cover material includes a thermoplastic resin such as ionomer resin or trans 1,4-polyisoprene (TPI). The rubber composition of the solid core contains a co-crosslinking agent, a portion of which is micro-encapsulated within a thermoplastic resin.
The co-crosslinking agent for use in the present invention may be &agr;,&bgr;-unsaturated carboxylic acid having a carbon number of 3-8 and/or metallic salt thereof. Examples of the &agr;,&bgr;-unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid and others. Among them, the acrylic acid is particularly suitable for the purpose of improving the resilience. Examples of the metallic salt include zinc salt, sodium salt, magnesium salt, calcium salt, aluminum salt and others. Among them, zinc salt is particularly preferable. Although zinc acrylic acid is suitably used as the co-crosslinking agent, two or more types selected from the foregoing can be used together.
In the present invention, it is preferable to encapsulate a portion of the co-crosslinking agent and an organic sulfur compound, where appropriate, within the thermoplastic resin. Herein, the organic sulfur compound is a concept including a metal-containing organic sulfur compound. As the organic sulfur compound, thiophenols such as pentachloro thiophenol, 4-t-butyl thiophenol and 2-benzamide thiophenol, thio carboxylic acids such as thio benzoic acid, and sulfides such as monosulfide, disulfide and polysulfide may be used. As the metal-containing organic sulfur compound, zinc salt, magnesium salt and sodium salt of thiophenols or thio carboxylic acids may be used. The monosulfide is, e.g., diphenyl monosulfide, and the disulfide is, e.g., diphenyl disulfide. The polysulfide is, e.g., diphenyl polysulfide, such as dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, or dithiobenzo
Birch, Stewart, Kolasch & Birch, LPP
Gordon Raeann
Sumitomo Rubber Industries Ltd.
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