VARIABLE TRACTION WHEEL FOR IN-LINE ROLLER SKATE

Abstract: Disclosed is an in-line skate wheel (1) that includes: (a) a braking portion (4) including a high friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.45 to about 1.5; and (b) a skating portion (5) including a low friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.1 to about 0.45. The skating portion includes a higher proportion of low friction surface material than the braking portion. The wheel delivers variable traction in response to the angle of wheel contact with the ground, without sacrificing a smooth ride or wheel durability. Utilizing the variable traction of the wheel a skater can stop safely and reliably, using known iceskating maneuvers, wherein the wheel is turned away from the skater's direction of travel.

Description: VARIABLE TRACTION WHEEL FOR IN-LINE ROLLER SKATE FIELD OF THE INVENTION The invention relates to in-line roller skates. Background of the Invention Despite the growing popularity of in-line skating, and advances in in-line skate technology, rapid, controlled stopping has continued to present a problem for skaters of all skill levels. Various stopping devices have been employed on in-line skates, e.g., a braking system located on the toe of the skate (Landers, U.S. Pat. No. 5,207,438), a replaceable brake pad located at the rear of the skate (Roberts, U.S. Pat. No. 5,197,572), and a spring-loaded friction device that engages a skate wheel (Allison, U.S. Pat. No. 5,135,244). O'Donnell et al. (U.S. Pat. No. 5,401,037) discloses a composite wheel for an in-line skate. The O'Donnell wheel includes a center section made of a hard material having a low coefficient of friction, e.g., high density polyethylene. The center section of the wheel is flanked by side sections made of a relatively soft material having a high coefficient of friction, e.g., cast polyurethane. To stop or reduce speed, a skater using the O'Donnell wheel turns the skates away from the direction of travel, and leans away from the direction of travel, as if on ice skates. This causes a portion of the soft material to engage the ground and generate friction. Summary of the Invention Generally, the invention features an in-line skate wheel that delivers variable traction in response to wheel angle, without sacrificing a smooth ride or wheel durability. Utilizing the variable traction of the wheel, an in-line roller skater can stop safely and reliably. The skater does so in a maneuver similar to an ice-skating maneuver known as the hockey stop. Utilizing the variable traction of the wheel, the snow plow maneuver, which involves turning the toes of both feet inward, to slow forward or backward speed, can also be executed safely and effectively. The wheel includes: (a) a braking portion including a high friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.45 to about 1.5; and (b) a skating portion including a low friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.1 to about 0.45. The skating portion includes a higher proportion of low friction surface material than the braking portion. Typically, the low friction surface material is arranged around the entire circumference of the wheel. As a skater initiates a hockey stop, the skating surface of the wheel is in contact with the ground, and the low friction surface material enables the skate to skid or slide momentarily. This momentary sliding prevents the skater from pitching forward uncontrollably. The skater then quickly and smoothly engages the braking surface against the ground. This quickly stops the skater, without loss of balance. The low friction material and high friction material are similar in hardness. The nearly uniform hardness of the wheel's surface avoids clattering or vibration caused by alternating contact of a hard material and a soft material with the ground. The nearly uniform hardness also inhibits initiation and propagation of tearing. Preferably, the high friction surface material includes a castable thermoset polymer resin containing an isocyanate-reactive functional group, and the low friction surface material includes a thermoplastic polymer resin containing an isocyanate-reactive functional group. The castable thermoset polymer resin can be cast around the thermoplastic polymer resin. The castable thermoset polymer resin can be, for example, castable thermoset polyurethane, and the thermoplastic polymer resin can be an injection-molded thermoplastic polyurethane. Preferably, the castable thermoset polyurethane and the injection-molded thermoplastic polyurethane are durably joined, for example, by covalent bonds. The covalent bonds include, for example, urea linkages or urethane linkages. The low friction surface material can be in the form of floating insets. The floating insets can be, for example, rods, tubes, or fiber bundles. Alternatively, the low friction surface material can be an inner ring with spokes radiating from the inner ring to the surface of the skating portion of the wheel. The invention also features a method of making a wheel for an in-line roller skate. The method includes the steps of: (a) providing in a casting mold a low friction surface material consisting of a thermoplastic polymer resin that has a hardness from about 75 Shore A to about 95 Shore A, has a coefficient of friction from about 0.1 to about 0.45, and contains an isocyanate- reactive functional group; and (b) placing into the mold a mixture of a bifunctional isocyanate and a polyol under conditions suitable for polymerization into a thermoset polyurethane having a hardness from about 75 to about 95 Shore A and a coefficient of friction from about 0.45 to about 1.5. The thermoplastic resin can be, for example, thermoplastic polyurethane. The bifunctional isocyanate can be, for example, MDI. The polyol can be, for example, polytetrahydrofuran polyol. The invention also features an in-line roller skate. The skate includes: (a) a boot; (b) a wheel- mounting frame; and (c) a wheel including: (1) a braking portion including a high friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.45 to about 1.5; and (2) a skating portion including a low friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.1 to about 0.45 Shore A; wherein the skating portion includes a higher proportion of low friction surface material than the braking portions. As used herein, "braking portion" means the portion of the wheel that can contact the ground during a hockey stop. As used herein, "coefficient of friction" means a coefficient measured using a normal force (90° angle) of 0.5 pound, against 20-pound bond paper, using an Instron device adjusted to a head speed of 20 inches per minute. As used herein, "durably joined" materials means materials joined with a bond strength greater than about 50 pounds per linear inch (pli) . The pli value is determined according to ASTM D429 method B, modified so that stripping force is applied at an angle of 180° instead of 90°, and Instron head speed is 2 inches per minute. Typically, durably joined materials are joined with a bond strength of greater than about 75 pli. As used herein, "floating inset" means an inset that is not connected to other insets, either directly, or via an inner ring or hub. As used herein, "high friction surface material" means a material that has a coefficient of friction from about 0.45 to about 1.5, and is exposed on the surface of a wheel. As used herein, "isocyanate-reactive" functional group means a functional group that reacts with an isocyanate. Exemplary isocyanate-reactive functional groups are amino groups, amide groups, and hydroxyl groups. Exemplary isocyanates are MDI and TDI. As used herein, "low friction surface material" means a material that has a coefficient of friction from about 0.1 to about 0.45, and is exposed on the surface of a wheel. As used herein, "MDI" means a mixture of 4,4'- and 2,4'-diisocyanato diphenylmethane. As used herein, "skating portion" of a wheel means the portion of the wheel that contacts the ground when the wheel is rolling substantially straight forward or substantially straight backward, during normal skating. As used herein, "TDI" means a mixture of 2,4- and 2 , 6-toluene diisocyanate. As used herein, "thermoplastic polymer resin" means a polymer resin that can be melted or softened in the polymerized form. As used herein, "thermoset polymer resin" means a polymer resin that decomposes before melting, upon application of heat. All patents mentioned herein are incorporated by reference in their entirety. Various features and advantages of the invention will be apparent from the following detailed description and from the claims. Brief Description of the Drawing Fig. 1 is a perspective view of an in-line roller skate with variable traction wheels in accordance with the invention. Fig. 2A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 2A depicts low friction surface material in a 14-spoke angled arrangement. Fig. 2B is an axial plan view of the wheel depicted in Fig. 2A. Fig. 3A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 3A depicts low friction surface material in an open tube honeycomb arrangement. Fig. 3B is an axial plan view of the wheel depicted in Fig. 3A. Fig. 4A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 4A depicts low friction surface material in a hollow tube spoke arrangement. Fig. 4B is an axial plan view of the wheel depicted in Fig. 4A. Fig. 5A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 5A depicts low friction surface material in an impact absorbing arrangement. Fig. 5B is an axial plan view of the wheel depicted in Fig. 5A. Fig. 6A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 6A depicts low friction surface material in a triangle spoke angled arrangement. Fig. 6B is an axial plan view of the wheel depicted in Fig. 6A. Fig. 7A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 7A depicts low friction surface material in a radial orientation fiber arrangement. Fig. 7B is an axial plan view of the wheel depicted in Fig. 7A. Fig. 8A is a radial cross-section of an in-line skate wheel of the present invention. Fig. 8A depicts low friction surface material in a 14-spoke straight arrangement. Fig. 8B is an axial plan view of the wheel depicted in Fig. 8A. Fig. 9 is a graph of coefficient of friction as a function of distance from the center of the wheel, for a hypothetical wheel with a friction gradient. Distance from the center of the wheel is indicated in arbitrary units. Detailed Description An in-line roller skate in accordance with this invention is shown in Fig. 1. The skate 7 includes a boot 8, a wheel-mounting frame 9, and wheels 1. Referring to Fig. 2, a wheel 1 of the invention includes a high-friction surface material 4 and a low friction surface material 5. The wheel 1 includes a conventional hub 3 with a center hole 6. The low friction surface material 5 is arranged around the entire circumference of the wheel 1. The amount of contact between the high friction material 4 and the ground increases, and thus friction increases, as the wheel 1 is tilted significantly away from a vertical orientation. A material suitable for use as the high friction surface material 4 is a castable thermoset polymer resin such as a castable thermoset polyurethane. Such material is exemplified by Vibrathane™ B625 (Uniroyal Chemical, Middletown, CT) . A material suitable for use as the low friction surface material 5 is a thermoplastic polymer resin such as thermoplastic, injected-molded polyurethane. Such material is exemplified by Estane™ formulations (B.F. Goodrich, Cleveland, OH) . Another preferred injection moldable polyurethane is commercially available as Estaloc™ (B.F. Goodrich) . Figs. 3A-8B illustrate alternative embodiments. There is wide latitude in the size, shape, and arrangement of pieces of low friction surface material 5 incorporated into the wheel. The low friction material 5 can be arranged so that the highest ratio of low friction surface area-to- high friction surface area occurs in the center of the wheel 1, and decreases with distance from the center. This results in a friction gradient, which enhances smoothness and control in stopping. Fig. 9 is a graph illustrating the relationship between coefficient of friction and distance from the center of a hypothetical wheel 1 of the present invention. Alternatively, the low friction material 5 can be arranged so that the highest ratio of low friction surface area-to-high friction surface area occurs on either side of the center of the wheel 1. A friction gradient can be produced in various ways. For example, pieces of low friction material 5 can be tapered (as viewed end-on) and oriented so the taper narrows with distance from the center of the wheel 1 (Figs. 6B and 8B) . Alternatively, tapered or non-tapered pieces of low friction material 5 can be arranged to constitute a greater proportion of the wheel's surface near the center of the wheel 1 (Figs. 3B, 4B, 5B, and 7B) . The invention encompasses low friction surface material 5 in the form of an inner ring with integral spokes radiating out to the wheel's surface, and a continuous ring at the wheel's surface. In preferred embodiments of the invention, however, the low friction surface material 5 is in the form of floating insets, i.e., pieces unattached to an inner ring or to each other. In general, the ride is smoother, quieter, and more comfortable when the low friction surface material 5 is incorporated as floating insets. Preferably, floating insets 5 extend into the wheel 1 at least half the distance from the wheel's surface to the wheel hub 3. When the floating insets 5 are arranged as spokes, the spokes can be angled (Figs. 2A and 6A) . In general, angling the spokes enhances the smoothness, and hence the comfort, of the ride. The wheel can be made by the following general procedure. A mixture of a diisocyanate and a polyol is placed in a conventional wheel casting mold that contains a prefabricated low friction surface material containing an isocyanate-reactive functional group. The diisocyanate reacts with the polyol to produce a high friction material castable thermoset polyurethane in intimate contact with the low friction surface material. Without intending to be limited by theory, it is believed that in addition to reacting with the polyol to produce the high friction polyurethane, the diisocyanate also reacts with the isocyanate-reactive functional groups on the low friction thermoplastic resin and on the high friction thermoset polyurethane. This covalently cross-links the low friction thermoplastic resin and high friction thermoset polyurethane through urea linkages or urethane linkages. Thus, the high friction surface material and the low friction surface material are covalently joined without the use of an adhesive layer between them. The durable joining maintains the integrity of the wheel under the extreme stress associated with turning or skidding under the full weight of the skater. It also inhibits initiation and propagation of tearing. Example 1: Thermoset Polyurethane Casting Butanediol (630 g) and trimethyol propane (50 g) were mixed in a 1000 ml container. The mixture (Curative A) was mechanically stirred (400 rpm) at 150° F for one hour and then cooled to room temperature. Vibrathane™ B625 (Uniroyal Chemical, Middletown, CT) was heated to 160° F and poured into a 1000 ml resin reactor. Curative A (68 g) was warmed to 100° F and added to the resin reactor. This mixture was stirred for 60 seconds, poured into a conventional mold heated to 220° F. After 20 minutes of curing, the cast was removed from the mold and subjected to a 12-hour postcuring treatment in an oven at 180° F. A conventional amine catalyst and conventional pigment were included in the curing process. Example 2 : Peel Testing A slab, measuring 4.75" x 4.75" x 0.125", of Estane™ 58134 (thermoplastic polyurethane; B.F. Goodrich, Cleveland OH) was placed in a mold heated to 180° F. Castable thermoset polyurethane precursors (e.g., Vibrathane™ 625 prepolymer) and curatives (e.g., Curative A, above) were poured on top of the slab in the mold. After a 20-minute curing time, the slab was removed from the mold and placed in an oven heated to 128° F, for a 12-hour postcuring treatment. Each cured slab was cut into a test strip measuring of 4.75" x 1" x 1.25". An Instron™ device was used to perform peel strength measurements according to ASTM D429 method B, except that the stripping force was applied at an angle of 180° instead of 90°. The Instron head speed was 2 inches per minute. Thermoset polyurethane having a final hardness of 83 Shore A was cast onto several Estane™ thermoplastic polyurethane formulations. The resulting interface between the two materials was then subjected to a peel test, to determine bond strength. Exemplary peel test results are presented in Table 1. TABLE 1 Other embodiments of the invention are within the following claims.

Claims: We claim: 1. A wheel for an in-line roller skate, comprising: (a) a braking portion comprising a high friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.45 to about 1.5; and (b) a skating portion, joined to said braking portion, comprising a low friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.1 to about 0.45 Shore A; wherein said skating portion comprises a higher proportion of low friction surface material than does said braking portion. 2. The wheel of claim 1, wherein said low friction surface material is arranged around the entire circumference of said wheel. 3. The wheel of claim 1, wherein said high friction surface material comprises a castable thermoset polymer resin containing an isocyanate-reactive functional group, and said low friction surface material comprises a thermoplastic polymer resin containing an isocyanate-reactive functional group. 4. The wheel of claim 3, wherein said castable thermoset resin is cast around said thermoplastic polymer resin. 5. The wheel of claim 3, wherein said castable, thermoset polymer resin is castable thermoset polyurethane, and said thermoplastic polymer resin is injection-molded thermoplastic polyurethane. 6. The wheel of claim 5, wherein said castable thermoset polyurethane and said injection-molded thermoplastic polyurethane are durably joined. 7. The wheel of claim 6, wherein said castable thermoset polyurethane and said injection-molded thermoplastic polyurethane are durably joined by covalent bonds. 8. The wheel of claim 7, wherein said covalent bonds comprise urea linkages. 9. The wheel of claim 7, wherein said covalent bonds comprise urethane linkages. 10. The wheel of claim 1, wherein said low friction surface material is in the form of floating insets. 11. The wheel of claim 10, wherein said floating insets are rods, tubes, or fiber bundles. 12. The wheel of claim 1, wherein said low friction surface material is an inner ring with spokes radiating from said inner ring to the surface of said skating portion of said wheel. 13. A method of making a wheel for an in-line roller skate, said method comprising the steps of: (a) providing in a casting mold a low friction surface material comprising a thermoplastic polymer resin containing an isocyanate-reactive functional group, said low friction surface material having a hardness from about 75 Shore A to about 95 Shore A and a coefficient of friction from about 0.1 to about 0.45; (b) placing into said mold a mixture of a bifunctional isocyanate and a polyol under conditions suitable for polymerization into a thermoset polyurethane containing an isocyanate-reactive functional group, said thermoset polyurethane having a hardness from about 75 to about 95 Shore A and a coefficient of friction from about 0.45 to about 1.5. 14. The method of claim 13 , wherein said thermoplastic resin is injection-molded thermoplastic polyurethane, said bifunctional isocyanate is MDI, and said polyol is polytetrahydrofuran polyol. 15. An in-line roller skate comprising: (a) a boot; (b) a wheel-mounting frame; and (c) a wheel comprising: (1) a braking portion comprising a high friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.45 to about 1.5; and (2) a skating portion comprising a low friction surface material having a hardness from about 75 to about 95 Shore A, and a coefficient of friction from about 0.1 to about 0.45; wherein said skating portion comprises a higher proportion of low friction surface material than does said braking portion.

Inventors: CHIANG ALBERT C, RODERICK JOHN A, SIPES CHARLES, WILLIS DAVID R, CHIANG, ALBERT, C., RODERICK, JOHN, A., SIPES, CHARLES, WILLIS, DAVID, R.
Applicants: CHIANG ALBERT C, MEARTHANE PROD CORP, RODERICK JOHN A, SIPES CHARLES, WILLIS DAVID R, CHIANG, ALBERT, C., MEARTHANE PRODUCTS CORPORATION, RODERICK, JOHN, A., SIPES, CHARLES, WILLIS, DAVID, R.
Application year: 1997
Main classification: A63C17
IPC codes: A63C17