Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Ptfe
Reexamination Certificate
2001-10-15
2002-10-15
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Ptfe
C508S451000, C106S270000, C106S271000, C106S272000, C280S601000, C280S610000
Reexamination Certificate
active
06465398
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to lubricant compositions made from a combination of paraffin waxes and fluoropoylmer micro powders, for use in snow slider equipment and other products and articles where reduced friction is desirable. When mixtures of this type are applied to snow slider surfaces the result is improved sliding and faster descent times under a variety of snow conditions.
TECHNICAL BACKGROUND
Skiing, sledding, snowmobiling and snow-boarding are popular sports in snow conditions. There is a need retain to kinetic energy and avoid friction loss in products such as skis and other snow sliding types of equipment to improve travel speed on a snowy or icy surfaces. While certain lubricant compositions have been made commercially available, these products may perform differently in colder snow condition temperatures than in warmer snow condition temperatures. This performance difference may affect snow sliding performance. Thus, different compositions may be required for different snow conditions.
Snow sliding equipment products that are used in snow conditions need to be able to avoid damage to the desirable sliding characteristics when in use. Skis require waxing or lubricating with waxes or lubricants to facilitate their sliding abilities. Ski and snowboard racing are determined by 100
ths
of a second in descent times requiring exceptional and sometimes very expensive waxes tailored to specific snow conditions. Although there is much speculation, the process which forms the basis for sliding friction on snow and ice with snow sliders is not known in exact detail and is assumed to quite complex. This situation has given rise to a wide range of possibilities for improving snow slider lubricity, as well as a wide range of claims.
Friction phenomena related to snow slider equipment involves the formation of a liquid layer of water between the surfaces of melting snow and the slider equipment. Frictional heat that is generated at the interface between the snow slider surface and the snow crystals melts the local snow crystals. At higher temperatures, near or above the freezing point where melt water is present, and at higher speeds where there is sufficient heat generated to create melt water, snow and slider surfaces are partially separated by melt water leading to hydrodynamic lubrication. Melt water layers are found to be about 5 to 10 &mgr;m. The frictional heat that is associated with the motion of the snow sliding equipment causes more of the crystals to melt, creating more melt water. When additional melt water between the snow sliding equipment and the snow increases, it reduces the travel speed of the snow sliding equipment. This is an undesirable feature in snow sliding equipment. Friction heat increases with travel velocity, with waxes with high coefficients of friction, or from poor thermal conductivity of the ski base material. As a result, the locally formed melted water may extend over the entire running surface, which is thought to lead to an undesirable capillary or suction effect.
In colder snow conditions, the ice crystals do not melt as quickly as they would in warmer snow temperatures. The ice crystals tend to rub against the waxed surfaces that are commonly applied to snow sliding equipment, affecting the integrity of the snow slider surface and velocity capability of the equipment.
Polyethylene has been found to be a useful material for some snow sliding equipment. For example, polyethylene has been useful for ski sole materials due to its high resistance to oxidation and favorable mechanical properties, including elasticity modulus, high tensile strength, and high breaking load, which are all factors that increase with increasing molecular weight. However, polyethylene exhibits a surface energy of about 31 to about 33 nJm-2 (mJ-2 is equivalent to dynes/cm), and thus the use of wax coating on the snow slider equipment sole is recommended. Wax is used in order to eliminate the corrugations and irregularities on the sole surface, lower the surface tension of the ski sole surface, and provide a lubricant between the sole surface and the snow surface.
In general, ski waxes are composed predominately of linear paraffins which, because of their chemical structure, are partially soluble in the polyethylene ski bases. The impregnation capacity of the ski soles by the paraffin wax depends essentially on absorption exhibited due to the physical nature including porosity of the material. The coefficient of dynamic friction of polyethylene on snow is in the range of &mgr;
k
=0.05-0.07. The coefficient of dynamic friction, &mgr;
k
, of polyethylene on snow can be reduced slightly at velocities of 0 to 1 m/s when lubricated with paraffin waxes. With an increase in sliding speed, snow melting processes intensify and this increases the contact area and friction forces increase. See Aparin, V. I., Bezrukov, A. P., Dukhovskoi, E. A., On the Ski-Snow Sliding Mechanism,
Trenie l lznos
, Vol. 11, No.4. pp. 639-642, 1990.
The lubricating properties of hydrocarbon ski waxes vary with snow temperature and moisture content. For maximum performance, waxes of increasing hardness are used as snow temperatures decrease. This is done to eliminate the shear to the coating on the snow sliding equipment described above.
Coatings of fluorinated materials are reported to exhibit surface tensions of about 16 to about 18 mJm-2 (dynes/cm), as opposed to about 28 to about 30 mJm-2 (dynes/cm) for normal paraffin wax. Discussions of the mechanisms for reductions of snow ski friction using these compounds surround the contact angle and the reduced wetting and therefore surface contact area for a fully wetted ski. In high humidity conditions fluorinated paraffins are added to or replace hydrocarbon waxes in wax formulations to reduce liquid water friction as taught in U.S. Pat. Nos. 4,724,093 and 5,202,041 (fluorinated ski waxes), U.S. Pat. Nos. 5,571,779, 6,028,136, and U.S. Pat. No. 6,063,739 (fluorinated waxes with graphite), U.S. Pat. No. 5,423,994, and U.S. Pat. No. 4,529,826. Perfluorinated waxes of these types, with melting points around 100° C., are available from various suppliers including Miteni of Italy and Hoechst Aktiengessellschaft of Germany.
Solid fluoropolymers having a melting point around 280° C., such as polytetraethylene (hereinafter referred to as “PTFE”), are not by themselves suitable for waxing skis. The melting points of PFTE materials are above those of polyethylene ski bases and most materials of ski construction. Therefore, the application of a solid fluoropolymer wax to the polyethylene snow sliding equipment is difficult to achieve.
Fluoropoylmers are not miscible in hydrocarbon waxes. However, fluoropolymer micro powders comprising agglomerates of average size of 200 &mgr;m, the agglomerates comprising loosely compacted particles of 0.1 &mgr;m average particle size can be suspended in solidified hydrocarbon or other waxes. This composition is applied by rubbing dry polyethylene snow sliding equipment surfaces, such as ski soles, against the composition to apply a thin, relatively uniform layer. Afterwards, and before use of the equipment, the surface may be polished to achieve smoothness. The composition is not expected to have a surface tension lower than the fluorinated materials used in known ski wax compositions. However the addition of particles with greater surface energies than the paraffin lowers the average surface tension of the compound.
Snow slider wax compositions that contain fluorinated materials are commercially available. Some contain blends of perfluoroalkylpolyether liquids that are not recommended for use in cold/dry snow conditions. Under such conditions the material becomes more viscous and the wax composition itself becomes sticky.
There is a need for a snow slider wax composition that is cost effective, performs well under a range of skiing snow conditions, can be easily manufactured, and has flexibility of application. The present invention provides for a wax composition comprising fluorinated micropowder that
E. I. du Pont de Nemours and Company
McAvoy Ellen M.
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