Games using tangible projectile – Golf – Ball
Reexamination Certificate
2001-08-08
2004-03-30
Sewell, Paul T. (Department: 3711)
Games using tangible projectile
Golf
Ball
C473S357000
Reexamination Certificate
active
06712716
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to golf balls including a core having at least one wound layer and a cover disposed thereabout, and more particularly to wound golf balls having a wound thread layer between rubber-based layers.
BACKGROUND OF THE INVENTION
Conventional golf balls can be divided into two general types of groups: solid balls or wound balls. The difference in play characteristics resulting from these different types of construction can be quite significant. Balls having a solid construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a single solid core, which is enclosed by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents. The cover is generally a material such as SURLYN®, which is a trademark for an ionomer resin produced by DuPont. Because these materials are very rigid, solid balls can have a hard “feel” when struck with a club. Likewise, due to their construction, these balls have a relatively low spin rate which provides greater distance.
At the present time, the wound ball provides the advanced player better spin and feel characteristics. Wound balls typically have either a spherical solid rubber or liquid center core around which many yards of a tensioned elastic thread are wound. The wound core is then covered with a durable cover material, such as a SURLYN® or similar material, or a softer cover such as Balata or polyurethane. Wound balls are generally softer and provide more spin, which enables a skilled golfer to have more control over the ball's flight and position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enable the golfer to stop the ball very near its landing position.
Regardless of ball construction, players generally seek a golf ball that maximizes total game performance for their requirements. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with a wide variety of performance characteristics to meet the players individual requirements. Thus, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers of all skill levels.
To meet the needs of golfers with various levels of skill, golf ball manufacturers are also concerned with varying the level of the compression of the ball, which is a relative measurement of the golf ball stiffness under a fixed load. A ball with a higher compression feels harder than a ball of lower compression. Wound golf balls generally have a lower compression which is preferred by better players. Whether wound or solid, golf balls typically become more resilient (i.e., have higher initial velocities) as compression increases. Manufacturers of both wound and solid construction golf balls must balance the requirement of higher initial velocity resulting from a higher compression with the desire for a softer feel from lower compression.
To make wound golf balls, manufacturers use winding machines to stretch the threads to various degrees of elongation during the winding process without subjecting the threads to unnecessary incidents of breakage. Generally, as the elongation and winding tension increase, the compression and initial velocity of the ball increase. Thus, a more resilient wound ball is produced, which is desirable.
Referring to
FIG. 1
, a conventional golf ball thread
10
is shown. In general, a single-ply golf ball thread or two-ply thread
10
is formed and wound around a center. Single-ply threads are generally made using a liquid latex that is cast into a sheet and then slit into threads having a generally rectangular or square cross-section. Two-ply threads are generally made by mixing synthetic cis-polyisoprene rubbers, natural rubber and a curing system together, calendering this mixture into two sheets, calendering the sheets together, curing the sheets to vulcanize and bond the sheets together, and slitting the resultant sheet into threads having a generally rectangular or square cross-section. Another method of forming threads is through an extrusion process. Extruded thread, however, has not previously been used in golf ball applications. An example of an extruded thread that is not used in golf balls is disclosed in U.S. Pat. No. 5,679,196 to Wilhelm et al. This patent discloses a thread formed from a mixture having more than 50 percent natural rubber.
A number of different windings have been disclosed for use in golf balls. U.S. Pat. No. 4,473,229 to Kloppenburg et al. discloses a golf ball having a core formed of graphite fibers and windings made of graphite filaments and resins. Yarns are made with the graphite filaments and resins, and as many as four or more yarns are combined to form a final yarn used for winding. U.S. Pat. No. 5,713,801 to Aoyama discloses the use of a layer of high tensile elastic modulus fibers wound about the core. The fibers have a tensile elastic modulus of at least 10,000 kpsi. Also, U.S. Pat. No. 5,816,939 to Hamada et al. discloses a rubber thread for winding with a tensile strength retention of up to 70 percent, a hysteresis loss of at least 50 percent, and an elongation of 900 percent to 1400 percent.
Prior art wound golf balls and cores typically use polyisoprene rubber thread. The polyisoprene thread is wound onto the cores at elongations between 500 percent to 1000 percent. The amount of thread required for a golf ball core is dependent on the elastic modulus of the thread in the elongated state. Elongated polyisoprene thread has an elastic modulus between 10,000 psi and 20,000 psi. Further, the properties, in particular resilience, of the wound ball or core are dependent on how well the thread packs during winding. The dimensions of the thread control the packing density. Polyisoprene threads are typically 0.0625 inches wide by 0.02 inches thick, measured prior to winding. However, present art polyisoprene thread is commonly produced in thicknesses between 0.014 inches and 0.024 inches.
There are some drawbacks to the conventional single-ply threads used in golf balls. The single-ply occasionally contains weak points. As a result, manufacturers of wound balls do not wind using the maximum tension or stretch the thread to the maximum elongation, because to do so would cause an excessive amount of breakage during winding. When a thread breaks during manufacturing, an operator must restart the operation. This decreases production, and is thus undesirable. The use of two-ply threads in golf balls reduces but does not eliminate this problem.
The thread can also break during play due to impact of a club with the ball. These breaks can result in various consequences. Cover material is disposed around the thread portions adjacent the cover. When the thread portions adjacent the cover break, the cover material tends to hold these thread portions in the proper position. If enough thread portions break near the cover, however, a lump will be created on the outside surface of the ball, which makes the ball unplayable.
More severe problems can occur, however, when thread portions near the center break. In a wound ball with a solid rubber center, the resilient rubber of the center is relatively soft compared to the hardness of the highly stretched thread portions. After a thread portion adjacent the center breaks, the thread portion can contract and cause a loss of compression and resiliency. This results in an undesirable distance loss.
In a wound ball with a fluid-filled center, after a thread portion adjacent the center breaks, the resultant imbalance in stress adjacent the center causes the thread to cut through the envelope that contains the fluid. This destroys the structural integrity of the ball and makes it unplayable. If this type of failure happens during a shot, it can result in a short shot. It can also result in t
Acushnet Company
Hunter Alvin A.
Sewell Paul T.
Swidler Berlin Shereff & Friedman, LLP
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