Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-10-09
2004-06-15
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S423000, C525S193000, C525S201000, C525S237000, C525S274000, C473S371000, C473S372000
Reexamination Certificate
active
06750281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to golf balls and methods of manufacturing thereof. In particular, the present invention relates to a golf ball having its core with the mold release property (easiness of removal of the core from a mold) improved without deteriorating the performance of the golf ball, and relates to a method of manufacturing such a golf ball.
2. Description of the Background Art
Golf balls are generally classified into thread-wound golf balls and solid golf balls. Any of the golf balls includes a core formed of at least one layer. The core is produced by vulcanization-molding a rubber composition in a mold. As the core has an unsatisfactory mold release property, the mold release property is ensured conventionally by those methods as described below.
According to one method, a silicon-based or fluorine-based mold release agent for example is applied to the surface of a mold, or the mold release agent is applied to a parting film which is provided on the surface of the mold in which a rubber composition is vulcanization-molded. With regard to this method, some cores exhibit the mold release property deteriorated in a short time. In addition, the mold release agent could be left on the surface of the core to hinder the core from adhering to a cover for example formed on the core, resulting in deterioration in the durability of the resultant golf ball. Further, if an additional process is incorporated into the production line in order to remove the mold release agent which is left attached to the surface of the core, a significant capital investment in equipment as well as enormous energy are necessary.
According to another method, the surface of a mold is subjected to surface treatment with a chromium coating. This method is excellent in that no mold release component is attached to the surface of the core while having a problem of the costly surface treatment and a problem that the mold release effect lasts for only a short period of time.
According to still another method, a mold is cooled after the vulcanization-molding to reduce the core in volume thereby facilitating removal of the core from the mold. A problem of this method is that considerable energy is required for cooling the mold after the vulcanization-molding process.
According to a further method, some of the materials constituting the core are changed. For example, Japanese Patent Laying-Open No. 8-100081 discloses a method of facilitating removal from the mold by adding a quinone-based compound for example to an ethylenic unsaturated nitrile-conjugated diene-based copolymer rubber composition. Japanese Patent Laying-Open No. 9-137000 discloses a method according to which a sulfur or phosphorous element-containing ion surface-active agent is added, and U.S. Pat. No. 5,244,955 discloses a method according to which a metal salt of higher fatty acid with at least 6 carbon atoms is added.
These methods could deteriorate the performance, resiliency for example, of golf balls. Moreover, the cost of golf ball products could increase if a costly material like the internal mold release agent as disclosed in Japanese Patent Laying-Open No. 9-137000 or U.S. Pat. No. 5,244,955 is employed.
SUMMARY OF THE INVENTION
One object of the present invention is, in view of the above-discussed circumstances, to provide a golf ball having a core with an improved mold release property without deterioration in such performance of the golf ball as resiliency, and to provide a method of manufacturing the golf ball.
The present invention is, with the purpose of achieving the above-described object, a golf ball having a core containing a vulcanized rubber powder crosslinked by a magnesium salt of unsaturated carboxylic acid (hereinafter “Mg vulcanized rubber powder”) and a vulcanized rubber powder crosslinked by a co-crosslinking agent other than the magnesium salt of the unsaturated carboxylic acid (hereinafter “another vulcanized rubber powder”).
Preferably, the ratio &agr;/&bgr; between the content &agr; of the Mg vulcanized rubber powder and the content &bgr; of another vulcanized rubber powder is 1/4 to 4, and the total content &agr;+&bgr; of the vulcanized rubber powders based on 100 parts by mass of a base rubber of the core is 5 to 30 parts by mass.
Preferably, the Mg vulcanized rubber powder contains, based on 100 parts by mass of the base rubber, 5 to 40 parts by mass of magnesium methacrylate, 1 to 50 parts by mass of at least one of tungsten, tungsten oxide and barium sulfate, and 0.1 to 5 parts by mass of organic peroxide.
The golf ball as discussed above is manufactured by blending the Mg vulcanized rubber powder with another vulcanized rubber powder to produce a core of the golf ball.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is hereinafter described in detail. According to the present invention, a golf ball is produced by forming a core in which a Mg vulcanized rubber powder and another vulcanized rubber powder are blended and surrounding the core with a cover for example.
[Mg Vulcanized Rubber Powder]
According to the present invention, a Mg vulcanized rubber powder is composed of a base rubber, a crosslinking agent, a co-crosslinking agent and a filler for example.
The base rubber is a natural rubber, a synthetic rubber or a mixture thereof. Examples of the synthetic rubber are polybutadiene rubber, polyisoprene rubber, styrene polybutadiene rubber, and ethylene-propylene-diene rubber, for example. A particularly preferable one of the synthetic rubbers is a high cis polybutadiene rubber having at least 40%, preferably at least 80% of cis-1,4 content, since the high cis polybutadiene rubber is superior in the resiliency.
The crosslinking agent used here is an organic peroxide for example, and examples of the organic peroxide are dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and t-butyl peroxide, for example. An appropriate one of them is dicumyl peroxide. Preferably, per 100 parts by mass of the base rubber, 0.1 to 5 parts by mass of the organic peroxide is blended with the base rubber. If the content of the blended organic peroxide is less than 0.1 parts by mass, a resultant golf ball is too soft which deteriorates the resiliency and thus decreases the carry of the golf ball, while the content of the blended organic peroxide exceeding 5 parts by mass makes the golf ball hard which impairs the shot feel.
The co-crosslinking agent used here is a magnesium salt of unsaturated carboxylic acid. Examples of the magnesium salt of the unsaturated carboxylic acid are magnesium acrylate and magnesium methacrylate, for example, and the magnesium salt of methacrylic acid is suitably used. Per 100 parts by mass of the base rubber, 5-40 parts by mass, preferably 10-40 parts by mass of the magnesium salt of the unsaturated carboxylic acid is blended with the base rubber. If the content of the co-crosslinking agent is less than 5 parts by mass, the crosslinking density decreases to impair the resiliency of the resultant golf ball. If more than 40 parts by mass of the co-crosslinking agent is blended, the increased crosslinking density makes the Mg vulcanized rubber powder hard, and consequently, the shot feel of the resultant golf ball tends to deteriorate. Here, an unsaturated carboxylic acid and a magnesium oxide may separately be blended to produce a rubber composition so that the resultant rubber composition contains the magnesium salt of the unsaturated carboxyic acid therein. An acrylic acid or methacrylic acid is suitably used as the unsaturated carboxyic acid.
The filler according to the present invention may be any which is normally used for the core. At least one of tungsten, tungsten oxide and barium sulfate is suitably used as the filler. Preferably, per 100 parts by mass of the base rubber, 1-50 parts by mass of the filler is blended with the base rubber. The content of the filler exceeding 50 parts by mass increases the mass of the core and accordingly makes t
Hirau Tsutomu
Tanaka Hiroaki
Buttner David J.
Sumitomo Rubber Industries Ltd.
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