A phase transition golf ball comprises a phase transition material. The phase transition material may optionally include a microwave susceptor or an induction susceptor. The phase transition material preferably comprises an ethylene acid copolymer, or an ionomer of an ethylene acid copolymer. The performance of the phase transition golf ball, for example its hardness or compression, is adjusted by inducing a complete or partial phase transition in the phase transition material. The extent of the adjustment in performance is correlated with the extent of the phase transition. Preferably, the phase transition is reversible and repeatable and takes place at temperatures that might be achieved through the use of common household appliances. Also preferably, the phase transition material returns to its original state over an extended period, for example hours or days.

[0013]Accordingly, the present invention provides a phase transition golf ball that comprises a phase transition material. The phase transition material may optionally include a microwave susceptor or an induction susceptor. The phase transition material preferably comprises an ethylene acid copolymer, an ionomer of an ethylene acid copolymer, or a blend of an organic acid or a salt of an organic acid with an ethylene acid copolymer or an ionomer of an ethylene acid copolymer. One or more performance properties of the phase transition golf ball, for example its hardness or stiffness, is adjusted by inducing a complete or partial phase transition in the phase transition material. The extent of the adjustment in performance is correlated with the extent of the phase transition. Preferably, the phase transition is reversible and repeatable and takes place at temperatures that might be achieved using common household appliances. Also preferably, the phase transition material returns to its original state over an extended period, for example hours or days. Thus, no additional equipment, such as a golf ball heating device, is necessary in order to maintain the performance adjustment throughout one or more rounds of golf.

[0004]Both professional golf players and amateurs of the game desire to improve the level of their play by using equipment that provides optimal performance. Golf ball performance, therefore, is an active field of research and development, and advances in golf ball technology are anticipated with interest by golf players of every stripe.

[0005]Golf ball performance is determined largely by the physical properties of the ball, or, more precisely, by the properties of the materials from which the ball is made. Recently, for example, manufacturers have been able to supply the market with polymer compositions that offer both superior softness and a high coefficient of resilience (COR). See, e.g., U.S. Pat. No. 6,562,906, issued to John Chu Chen. This particular combination of properties is highly desirable, because softness is correlated with better control of the ball, and high resilience is correlated with longer shot distance.

[0006]There are some generally accepted guidelines about what balance of properties is best for players at different levels of skill or with different styles of play. See, for example, "Golf Balls: Slicing through the Hype" Consumer Reports, Vol. 71(5), p. 30 (May, 2006.) Beyond these broad guidelines, however, and often superseding them, are the player's personal preferences, which may in cases be idiosyncratic.

[0007]Therefore, it is desirable to provide a golf ball whose physical properties, and, consequently, whose performance can be tailored to the skills or preferences of an individual player. Preferably, the means of tailoring the properties is convenient, straightforward, and accessible to the typical golfer.

[0008]Heating or cooling a golf ball is one approach to tailoring golf ball performance that meets these criteria. The relationship between the temperature of a traditional golf ball and its performance has long been recognized. In fact, most golfers are aware that heating or cooling traditional golf balls to temperatures no more extreme than those that might be achieved by a change in the weather can have a significant effect on the golf balls' performance properties.

[0009]Briefly, when a golf ball is fabricated with traditional polymeric materials, a decrease in temperature leads to increased stiffness. This is a simple thermal effect, which is not necessarily caused by a glass transition or any other phase change. Perhaps the best known example of this phenomenon is the temperature-induced hardening of the O-ring seals used on the space shuttle Challenger, which the late Professor Richard Feynman illustrated so dramatically by immersing a sample of the polymeric O-ring material in a glass of ice water.

[0010]Significantly, the changes in physical properties that are caused by simple thermal effects at cooler temperatures result in deleterious effects on the performance of the traditional golf ball. It is well known, for example, that increased stiffness causes the golfer to have a less favorable feeling of the golf ball's responsiveness and its connection with the club. Increased stiffness also results in less control of the spin of the traditional golf ball, when it rebounds from the face of the golf club.

[0011]Moreover, when a golf ball is fabricated with traditional materials, the property changes are essentially simultaneous with the material's temperature change. That is, the performance change due to heating or cooling is realized approximately contemporaneously with the change in the golf ball's temperature. For this reason, during cold weather it is considered necessary by some to carry the traditional golf ball in a heating device throughout the round of golf, in order to maintain a relatively more favorable performance. See, for example, U.S. Pat. No. 5,998,771, issued to Mariano et al.; U.S. Pat. No. 6,130,411, issued to Rockenfeller et al.; and U.S. Pat. No. 6,229,132, issued to Knetter.

[0012]Therefore, it would be advantageous to develop a golf ball whose properties can be adjusted to individual preferences by easy and convenient means, for example by heating. It would also be advantageous for the property change to persist over a period of time that is greater than or equal to the average duration of a golf game, and to be robust in the face of ambient temperature changes that adversely affect the traditional golf ball's performance, so that golfers need not be burdened, on or off the course, with the added expense and superfluous clutter of golf ball heating devices.

More specifically, the temperature of the phase transition material or the phase transition golf ball may be raised in a warm water bath, a boiling water bath, a steam bath, a conventional oven, in another environment with a temperature higher than ambient, such as a glove compartment or the trunk of a car, in a microwave oven, by removal from a cold environment such as the interior of a refrigerator, or by magnetic or electromagnetic induction, for example.

The disruption of the secondary crystal structure in an acid copolymer or ionomer is typically essentially simultaneous with the change in the polymer's temperature. The re-organization of the secondary crystal structure in these materials, however, generally occurs over a relatively long period of time when the phase transition golf ball is stored at room temperature, in some cases at least as long as four hours, eight hours, twelve hours; one, two, or three days; or one, two, three or four weeks. Consequently, when the performance of the golf ball is altered via disruption of the secondary crystal structure, the performance change persists for at least the approximate duration of a typical round of golf.