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.

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.

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.

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.

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.

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.

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.

SUMMARY OF THE INVENTION

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.
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Alternatively, the extent of the phase transition, and therefore the extent of the customization, may take the weather conditions into account. For example, a golfer planning to play on an extremely warm day may wish to effect less of a disruption of the secondary crystal structure by heating the ball to a lower temperature, knowing that the golf ball will also be softened somewhat by equilibrating to the ambient temperature. Complementarily, a golfer planning to play on a particularly cold day may wish to effect more of a disruption of the secondary crystal structure by preheating the ball to a higher temperature, knowing that the golf ball will also be hardened somewhat by equilibrating to the ambient temperature.

Parenthetically, it is noted that the properties of traditional golf ball materials, such as polybutadiene rubbers, may be customizable via simple thermal effects. Even so, their performance is generally not affected to the same extent as that of a phase transition material. Stated alternatively, the range of compression, e.g., that may be attained by changing the temperature of the polybutadiene is much narrower than the range of compression that may be attained by partially or completely disrupting the secondary crystal structure of an acid copolymer or ionomer.
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In one embodiment, the present invention provides a golf ball comprising a phase transition material and a susceptor. The suitable and preferred phase transition materials for use in this embodiment are as set forth above. The term "susceptor", as used herein, refers to any material that is capable of transforming energy, which may be in the form of radiation or a field, into thermal energy. As used herein, the term "susceptor" does not include organic acids or materials that are known to have been used in golf balls as fillers and in amounts that are typical of fillers. The energy sought to be converted to heat is typically radiofrequency (RF) or high frequency (HF) energy. Typical RF power supplies for susceptor heating provide power in a range of from about 1 to about 20 kW.

Preferred susceptors include, without limitation, microwave susceptors and induction susceptors. Suitable microwave susceptors include metals, inorganic compounds such as silicon carbide, and the like. Suitable induction susceptors also include metals such as molybdenum, stainless steel, niobium, aluminum, silicon carbide, graphite and other conductive materials, in addition to ceramic flakes, including flakes of ferromagnetic ceramics, for example. For convenience, susceptors may be added to the phase transition materials via conventional methods, such as pre-extrusion melt mixing. To promote uniformity of distribution of the susceptor throughout the golf ball, or throughout the desired portion of the golf ball, it is preferable that the susceptors be in the form of small particles, such as powders or flakes, for example.

In some embodiments of the phase transition golf ball, the phase transition material may comprise the microwave susceptor or induction susceptor. Alternatively, the phase transition material may comprise at least a portion of the microwave susceptor or the induction susceptor, or the phase transition material and the microwave susceptor or induction susceptor may be located in different parts of the golf ball. For example, the phase transition material may be located in the core, and the microwave susceptor or induction susceptor may be located in an intermediate layer or mantle. When the susceptor(s) ands the phase transition material are not located in the same portion of the golf ball, the susceptor(s) increase the efficiency of the heating of the portion of the golf ball in which they reside. The temperature of the portion in which the phase transition material resides is raised by conduction of the heat to the phase transition material from the susceptor-enhanced portion of the golf ball.

Advantageously, including a susceptor in a phase transition golf ball may increase the speed or efficiency with which the temperature of the phase transition golf ball is raised to the desired level. For example, many polymers have relatively low heat transfer coefficients. Therefore, a relatively long period of time may be required to achieve a uniform depth profile of temperature throughout a polymer sample that is about the size of a golf ball. It may therefore be advantageous to include a susceptor in the core of a phase transition golf ball. The exterior of this phase transition golf ball may be heated via conduction or convention, and the core may be heated via electromagnetic energy, to achieve, in a relatively shorter time, a uniform depth profile of temperature throughout the phase transition golf ball. In this connection, it is apparent that susceptor heating may be used independently of or in conjunction with other forms of heating, such as conductive or convective heating. It is further apparent that over heating the phase transition golf ball, by any method, could lead to undesirable degradation of performance properties and deformation, for example through partial or complete melting of the golf ball.

Further provided are methods of using phase transition golf balls. In one embodiment, an off-the-shelf golf ball can be customized to various pre-determined compressions by applying heat. For example, the golf ball can be heated to a specific temperature in a microwave for a certain number of seconds to achieve a certain compression level. By changing the heating time to adjust the final temperature, one can customize the compression level. The compression level may be measured with an Atti compression gauge, for example. The compression level can be related to golfer handicap level, swing speed, outside temperatures, etc. Therefore, a golfer will have the ability to customize off-the-shelf golf balls to match his or her individual skill level or temperature conditions of play by heating the golf ball and playing the golf ball within the extended time after thermally treating the balls. In addition, the golf ball may be reheated many times and still continue to allow customization of the compression level.

Further, in this preferred embodiment, the performance properties of the ball may be adjusted to a desired compression range based on individual preferences. Alternatively, the performance properties of the ball may be adjusted to correlate with one or more of the parameters that are used to specify the design of a custom-fitted set of golf clubs, including, without limitation, gender, age, height, arm length, hand size, wrist-to-floor distance, club length, handicap, swing speed, swing tempo, swing trajectory, loft, lie, grip, swing weight, driver distance (carry and roll), ball flight pattern, and choice of club at 150 yard marker. Other parameters to which the customizable golf ball performance properties may be correlated include weather conditions, for example.
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As a footnote, in the past golf balls were imprinted with the value of their compression. Moreover, golf balls with one of only two compression ratings, 90 or 100, were available. By custom, "average" golfers were encouraged to play with the golf balls that had the lower compression rating, and "proficient" golfers used the balls with the higher rating. (According to a competing theory, however, less skilled golfers were encouraged to use golf balls of higher stiffness, to minimize hook or slice shots, and more skilled golfers were encouraged to use softer golf balls, for better control. Whence, no doubt, the predominating effect of idiosyncratic preferences.)

In certain embodiments, however, the present invention overcomes the disadvantages resulting from these limited choices and from the stereotypical, if inconsistent, implications of those choices. Using the golf balls and methods described herein, two golfers may select identical golf balls, with identical manufacturer's markings, and each may alter the performance properties of his or her ball to suit him or herself. In addition, the altered performance properties are not apparent from the appearance of the ball. Thus, the performance properties may also be concealed from other players.
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After this conditioning, the Atti compression of each sphere was measured with an Atti Compression Gauge, which measures resistance to deformation. Each measurement was replicated twice, so that every data point in the Figures represents the average of nine measurements.

Each conditioned sphere was heated in an oven for at least 24 h at either 120.degree. F. (48.9.degree. C.), 135.degree. F. (57.2.degree. C.) or 149.degree. F. (65.0.degree. C.), with the exception of Examples 5 through 8, for which the spheres were heated to 120.degree. F. (48.9.degree. C.) only. This length of time is believed to be sufficient to guarantee that the entire ball has reached the target temperature. The Atti compression and coefficient of resilience of each heated sphere was then re-measured, by the methods identified above, immediately upon removal from the oven and at intervals of about 1, 2, 4, 24, 72, and 168 hours after removal from the oven. The results of these measurements are tabulated in Table 2. The data obtained for Examples 1 through 5 and the Comparative Example are displayed in FIGS. 1 through 6, in which the horizontal dashed lines represent the value of the Atti compression prior to the oven treatment.
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Referring now to FIG. 1, the data depicted therein demonstrate that the compression of the phase change material of Example 1 is affected strongly by the heat treatment. This graph of compression vs. time shows a rapid stiffness increase in the first few hours immediately after removal from the oven. This is the thermal effect caused by cooling the ball to room temperature. After the ball has reached room temperature, the stiffness stabilizes at a level that is significantly lower than the baseline level. This stable lower level of compression is due to the phase transition induced by the heat treatment. FIG. 1 shows that the effects of the phase transition persist for a significant period of time, here specifically at least one week.

Moreover, the compression of the sphere that was heated at 149.degree. F. (65.0.degree. C.) was lower than that of the sphere that was heated at 120.degree. F. (48.9.degree. C.) at every measurement interval for which both spheres were measured. Also, the average of the compression measurements of the sphere that was heated at 149.degree. F. (65.0.degree. C.) was lower than the average of the compression measurements of the sphere that was heated at 120.degree. F. (48.9.degree. C.).

Thus, in customizing the properties of a golf ball that contains a significant amount of the phase change material of Example 1, the extent of the change in compression is a function of the temperature at which the ball is heated. Conversely, being aware of the relationship between the compression and the temperature at which the ball is heated, a golfer may select a treatment temperature for the ball that is appropriate to achieve the compression that is desired.

Likewise, the data depicted in the graphs of FIGS. 2 and 3 also demonstrate that the compression of the phase change material of Example 2 is decreased markedly by the heat treatment, and that the properties return more rapidly towards their baseline in the first 1 to 2 hours after heating, due to thermal effects, than they do afterwards, when the effects on the performance properties are determined in large part by the phase transition. The presence of the BaSO.sub.4 filler in the phase transition material of Example 3 appears to affect the absolute values of the compressions more strongly than it affects the shape of the compression vs. time curves.