Games using tangible projectile – Golf – Ball
Reexamination Certificate
2000-04-05
2002-09-24
Wong, Steven (Department: 3711)
Games using tangible projectile
Golf
Ball
C473S351000
Reexamination Certificate
active
06454667
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to golf balls, particularly those for practice which are superior in durability and highly resistant to burr and cutting due to the grooves on the club face of an iron.
2. Description of the Background Art
Conventional golf balls used in the practice field (practice balls) have mainly been one-piece balls because durability is considered highly important. However, the one-piece balls are significantly inferior to the balls used for a round of golf (round balls as distinguished from practice balls) in the flight performance and shot feel.
Golfers would prefer to use the round balls having excellent shot feel and flight performance. Although the round balls, specifically thread-wound balls formed by winding a rubber thread around a center and molding the exterior of the rubber thread layer with a cover have remarkably superior shot feel, they are extremely inferior in durability and are expensive, and accordingly are inappropriate as practice balls.
Two-piece balls for a round of golf which are formed by a core with a relatively rigid ionomer cover are superior to the thread-wound balls in the durability. However, if the two-piece ball is struck particularly by an iron club to attain loft, the surface of the cover wears due to the grooves of the club face and accordingly dimples become shallower, resulting in a shorter carry. Paint having white pigment blended therein is usually applied onto the surface of the cover of the golf ball. The white paint could undesirably attach to and thus foul the club face when the club hits the ball.
According to a proposal in Japanese Patent Laying-Open No. 8-322961, the average thickness of a coating layer or the pencil hardness of a coating film is set in a specific range so as to optimize initial conditions of shot (shot angle, spin rate) and to enhance protection of a mark and the like provided on the surface of a golf ball. However, this prior art does not discuss the effect of the resistance to burr and wearing.
Round balls are superior in the flight characteristics and shot feel while they are inferior in: 1) the resistance to wear (durability); and 2) the resistance to burrs of the cover surface, as may be caused by dirt on the club face. Therefore, the round balls are not proper for use as practice balls.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a golf ball which is highly resistant to wear as well as burr and cutting due to grooves of the club face of an iron while maintaining characteristics of the flight performance and shot feel as a round ball.
In order to achieve the above object, a golf ball according to the present invention has a cover with which a core is molded, the cover is prepared to have Shore D hardness of 50 to 65 and flexural modulus of 98 MPa to 196 MPa, and paint applied onto the surface of the cover has 100% modulus of 0.49 to 4.9 MPa so as to improve the resistance to burr and wear.
Conventional golf balls are designed such that there is a great difference between cover material and paint in their values of hardness and flexural modulus. In this case, deformation of a struck golf ball causes strain on the boundary between the cover and paint, leading to fatigue and damage to the paint. The present invention accordingly allows the cover to have a lower hardness than that of a conventional cover so as to enhance the shot feel, and uses a relatively flexible material as the paint applied onto the cover according to the characteristics of the cover. Consequently, the cover and paint take the same deformation behavior when the golf ball is hit, so that coating fatigue can be reduced remarkably.
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 when taken in conjunction with the accompanying drawings.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a cover is prepared to have Shore D hardness in a range of 50 to 65 which is lower than that of a cover of a normal ball for golf range. If the Shore D hardness is smaller than 50, the resilience of ball decreases and thus the carry becomes shorter. On the other hand, if the Shore D hardness exceeds 60, the resistance to wear and burr of the ball deteriorates.
It is noted that the Shore D hardness is measured according to ASTM D-2240 by using a thermal press molded sheet with a thickness of about 2 mm which is formed of each cover composition and preserved at 23° C. for two weeks.
Further, the cover is prepared to have flexural modulus in a range of 98 to 196 MPa. If the flexural modulus is smaller than 98 MPa, the impact resistance as well as the hardness decrease, resulting in a shorter carry. If the flexural modulus is greater than 196 MPa, the duralibility as well as the resistance to burr deteriorate.
It is noted that the flexural modulus is measured according to JISK 7106 using a thermal press molded sheet with a thickness of about 2 mm which is formed of each cover composition and preserved at 23° C. for two weeks.
Ionomer resin is used as a base material of the cover, and the cover is prepared by blending one or at least two types of the ionomer resin such that the Shore D hardness is in a range of 50 to 65 and the flexural modulus is in a range of 98 to 196 MPa. In addition to the ionomer resin, titanium oxide (TiO
2
), photo-stabilizer, colorant, antioxidant and the like are blended as required the ionomer resin may partially be substituted with other polymers such as polyethylene and polyamide without deteriorating the characteristics (e.g. high resistance to cutting) of the ionomer resin.
As the ionomer resin, Hi-milan #1065, Hi-milan #1705, Hi-milan #1706 and the like manufactured by Mitsui-DuPont Polychemical Co., Ltd. may be used. However, if any of them is solely employed, the ranges of the Shore D hardness of 50 to 65 and of the flexural modulus of 98 to 196 Mpa are difficult to achieve in most cases. Therefore, preferably an monomer resin having a small flexural modulus such as Hi-milan #1855 (flexural modulus: 87 MPa) manufactured by Mitsui-DuPont Polychemical Co., Ltd. is additionally employed so as to adjust the flexural modulus within the above range.
In the present invention, commercially available materials having the trade names of ESCOR and IOTEK produced by Exxon Chemical Japan Ltd., for example, may be used as the ionomer resin. Regarding the blend of the ionomer resin, ionomer resin materials neutralized by sodium ion and zinc ion respectively may be blended. More preferably, ionomer resin materials all neutralized by zinc ion may be blended.
The present invention is applicable to a single layer cover as well as a multi-layer cover. In the case of the multi-layer cover, the Shore D hardness and the flexural modulus of the outermost layer of the cover contacting the paint should be in the ranges of the Shore D hardness and flexural modulus respectively mentioned above.
Paint applied onto the cover in the present invention is prepared to have 10% modulus in a range of 0.49 to 4.9 MPa, preferably in a range of 1.47 to 3.9 MPa in particular.
The paint may consist of either a single layer or a multi-layer. If the paint has a multi-layer, the outermost layer should have 10% modulus in a range of 0.49 to 4.9 MPa. Excessively thick paint is not preferable, and accordingly the thickness of the paint is set in a range of 10 to 40 &mgr;m so as to allow the paint to follow the deformed cover when it is struck. In particular, if the paint is formed of a plurality of layers, the thickness of at least the outermost layer is set in a range of 5 to 20 &mgr;m.
Although there is no restriction as to the types of paint materials used in the present invention, thermoplastic resin-based paint or thermoset resin-based paint is appropriate for the paint material. Employable materials are urethane resin-based paint, epoxy resin-based paint, acrylic resin-based paint, vinylacetate resin
Birch & Stewart Kolasch & Birch, LLP
Hunter Alvin A.
Sumitomo Rubber Industries Ltd.
Wong Steven
LandOfFree
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