Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-10
2003-11-11
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S261000, C525S274000, C523S202000, C473S371000, C473S372000, C473S373000
Reexamination Certificate
active
06646053
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 homogeneity, and a manufacturing method thereof.
2. Description of the Background Art
Conventionally, a core of a golf ball or a one-piece golf ball has been manufactured by heating a rubber composition having a co-curing 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-curing agent to cause graft polymerization of the co-curing agent to the main chain of the rubber molecule or the crosslinking between the main chains. The state of dispersion of the co-curing 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 multilayer-structured golf ball with its solid core formed of a vulcanizate of the rubber composition, or of a one-piece golf ball formed of the vulcanizate of the rubber composition.
Thus, in order to improve dispersibility of the co-curing 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-curing 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-curing 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-curing agent within the rubber composition is improved and thus hardness of the rubber composition is increased. However, due to the co-curing agent being so finely dispersed, the density of crosslinking between the rubber molecule main chains, which is most likely to contribute to rebound performance, is decreased, whereas the graft polymerization of the co-curing agent with the rubber molecule main chain, which is unlikely to contribute to the rebound performance, is increased, resulting in unsatisfactory rebound performance.
Proposed to improve such rebound performance is a technique to use an organic sulfur compound together with a 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-curing agent in a rubber composition for use in manufacturing a solid core of a golf ball or a one-piece golf ball, by micro-encapsulating the co-curing agent. Another object of the present invention is to provide a golf ball improved in rebound performance, by micro-encapsulating an organic sulfur compound together with the co-curing agent to properly restrict the speed of graft polymerization of the co-curing 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 vulcanized molded product of a rubber composition containing a co-curing agent micro-encapsulated within a thermoplastic resin. Here, the thermoplastic resin preferably has a softening point in a range of 80-250° C. Further, the co-curing agent is preferably an &agr;,&bgr;-unsaturated carboxylic acid and/or a metallic salt thereof.
The vulcanized molded product is either a one-piece golf ball or a solid core of a golf ball having a multi-layered structure.
According to another aspect of the present invention, the golf ball includes a vulcanized molded product of a rubber composition containing a co-curing agent and an organic sulfur compound micro-encapsulated within a thermoplastic resin. Here, the organic sulfur compound is preferably one of polysulfides, thiophenols and bivalent metallic salts of the thiophenols.
According to yet another aspect of the present invention, the manufacturing method of a golf ball including a vulcanized molded product of a rubber composition containing a co-curing agent micro-encapsulated within a thermoplastic resin includes:
(1) a step of blending the co-curing agent micro-encapsulated within the thermoplastic resin into the rubber composition, and
(2) a step of heating the rubber composition to a temperature higher than the 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
In the case of a golf ball having a multi-layered structure such as a two-piece golf ball or a thread-wound golf ball, the golf ball according to the present invention is formed by covering a solid core with a thermoplastic resin, such as ionomer resin or trans 1,4-polyisoprene (TPI), as a cover material. A rubber composition of the solid core contains a microcapsule having a co-curing agent covered with a thermoplastic resin.
The co-curing 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 rebound performance. 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-curing agent, two or more types selected from the foregoing can be used together.
In the present invention, it is preferable to encapsulate an organic sulfur compound together with the co-curing agent 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, including dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, and dithiobenzoyl polysulfide. As such sulfides, those including various types of substituent groups, such as methyl group, ethyl group, amino group
Kishimoto Hiroyuki
Yokota Masatoshi
Buttner David J.
Sumitomo Rubber Industries Ltd.
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