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
1999-12-23
2001-08-28
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...
C525S305000, C473S371000, C473S372000, C473S377000
Reexamination Certificate
active
06281294
ABSTRACT:
This application is based on patent application No. 10-370914 filed in Japan, the contents of which are hereby incorporated by references.
FIELD OF THE INVENTION
The present invention relates to a golf ball having an increased productivity by improving a mold releasing property of a rubber composition in a press molding without decreasing a flight performance, shot feeling and durability thereof.
BACKGROUND OF THE INVENTION
Generally, a core for a solid golf ball is made from a rubber composition. It is known that the conventional rubber composition includes a base rubber, a zinc salt of acrylic acid or methacrylic acid as a co-crosslinking agent of the base rubber, and organic peroxide as a crosslinking initiator.
The solid core made from such a rubber composition has an excellent resilience and flight performance. However, the rubber composition including zinc (meth)acrylate (i.e., zinc acrylate or zinc methacrylate) is not easily released from a metal mold. Accordingly, it is difficult to improve the productivity of the golf ball. The poor mold releasing property may be improved by mixing a fluorine-type or silicon-type releasing agent with the rubber composition. Alternatively, a surface treatment such as chrome plating and fluororesin coating is applied to the mold surface to improve the releasing operation between the mold surface and the rubber composition.
However, in the case that the rubber composition contains such a releasing agent, the vulcanization of the rubber composition may be softer as the content of the releasing agent increases. To compensate for the problem, it is necessary to add a curing agent to the rubber composition. As a result, the content of the base rubber to the rubber composition decreases, causing a poor durability of the obtained rubber.
On the other hand, in the case that the mold surface is treated to improve the releasing operation, the rubber composition does not have the above-mentioned problem about the former case, since the rubber composition itself is not affected by such a surface treatment. However, if a releasing agent which is liable to adhere is used for the surface treatment, a further washing step is needed to remove the adhered releasing agent from the inner surface of the mold before a following step. The additional washing step hinders the improvement of productivity of golf ball. On the other hand, if a releasing agent which is unlikely to adhere is used for the surface treatment, the washing step is not necessary. Such a releasing agent, however, is expensive, thereby raising the production costs of golf ball.
In addition, instead of using the releasing agent, magnesium (meth)acrylate having a better mold releasing property than zinc (meth)acrylate may be used as a co-crosslinking agent. However, the rubber composition containing magnesium (meth)acrylate provides less resilience and thereby worse flight performance to the obtained golf ball than that containing zinc (meth)acrylate.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a golf ball which can improve the mold releasing property in a press molding to ensure an increased productivity without decreasing a flight performance, shot feeling and durability thereof.
According to an aspect of the present invention, a golf ball has a part including a vulcanized rubber composition. The vulcanized rubber composition includes 100 parts by weight of a base rubber and 100 parts by weight or less of unsaturated carboxylic acid compounds. The unsaturated carboxylic acid compounds includes magnesium (meth)acrylate (Component (A)) and &agr;, &bgr;-unsaturated carboxylic alkyl ester (Component (B)). The content ratio of the Component (A) to the Component (B) (A/B) is 0.2 to 4.
According to another aspect of the present invention, a golf ball has a part including a vulcanized rubber composition. The vulcanized rubber composition includes 100 parts by weight of a base rubber, 10 to 60 parts by weight of magnesium (meth)acrylate (Component (A)) and 10 to 60 parts by weight of &agr;, &bgr;-unsaturated carboxylic alkyl ester (Component (B)). The total content of the Component (A) and Component (B) (Component (A)+Component (B)) is 100 parts by weight or less, and the content ratio of the Component (A) to the Component (B) (A/B) is 0.2 to 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A golf ball according to the present invention has a part, i.e., a layer, made by vulcanizing a rubber composition. The rubber composition has a base rubber and unsaturated carboxylic acid compounds including magnesium salt of acrylic or methacrylic acid (hereinafter, referred to as “(meth)acrylic acid”) and &agr;, &bgr;-unsaturated carboxylic alkyl ester.
As the base rubber, any diene rubber having a diene component in a molecule may be used. Specifically, butadiene rubber (BR), ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR), styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) can be used solely or in a combination of two or more kinds. Of these, rubbers having butadiene as a main component are preferably used. Specifically, 50 wt % or more of butadiene rubber is included in the base rubber in the rubber composition. As the butadiene rubber, cis-1,4-polybutadiene rubber having 90% or more of cis-bonds may be preferably used. This is because the cis-1,4-polybutadiene rubber can provide an excellent resilience to the golf ball. The unsaturated carboxylic acid compounds may include, if necessary, other unsaturated carboxylic acids compounds than magnesium (meth)acrylate and &agr;, &bgr;-unsaturated carboxylic alkyl ester.
In the present invention, magnesium (meth)acrylate (hereinafter, referred to as “Component A”) is added to the rubber composition as a co-crosslinking agent. The magnesium salt has the highest releasing property among any metal salt of &agr;, &bgr;-unsaturated carboxylic acid which is generally used as a co-crosslinking agent.
The preferable content of magnesium (meth)acrylate is 10 to 60 parts by weight, preferably 15 to 60 parts by weight, per 100 parts by weight of the base rubber. In the case that the content is less than 10 parts by weight, the obtained rubber has an unsatisfactory low hardness due to the low crosslinking density in the core. Thus, the resilience of the golf ball at a shot is likely to decrease, resulting in a decreased flying distance. On the other hand, in the case that the content of co-crosslinking agent is more than 60 parts by weight, the obtained core is likely to have an excessively high hardness due to the high crosslinking density in the core. Thus, the impact by a shot against the golfer may increase, resulting in a poor shot feeling.
As described above, the rubber composition according to the present invention includes &agr;, &bgr;-unsaturated carboxylic alkyl ester (hereinafter, referred to as “Component B”). The Component B is an ester obtained as a reaction product between (meth)acrylic acid and fatty alcohol. Preferable Component B has a melting point of 100° C. or less. This is because of the fact that, since the mixing of the rubber composition is generally performed with heat at 120° C. or more, Component B having such a low melting point can melt during the mixing to show an improved dispersibility. As examples of the fatty alcohol, there may be any of linear alkyl alcohols and non-linear alkyl alcohols having branches, and any of monohydric alcohols having a hydroxyl group per a molecule and polyhydric alcohols having two or more hydroxyl groups per a molecule, as far as the alcohols are capable of making an ester. Preferably used may be linear alkyl alcohols having 1 to 3 hydroxyl groups per a molecule. This is because the preferable alcohols provide a small stereostructure to the resulting &agr;, &bgr;-unsaturated carboxylic alkyl ester in order that the resulting ester facilitates crosslinking reaction with diene rubber or unsaturated carboxylic acid and also shows an excellent dispersibility to the rubber composition to thereby give a satisfactory resilienc
Buttner David J.
Sumitomo Rubber Industries Limited
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