EP2527014B1 - Ski sole - Google Patents

Description

The invention relates to a plastic ski coating with a filler mixture for improving the sliding properties.

For plastic ski layer materials are preferably used with hydrophobic character, in particular polyethylene.

The gliding on snow and ice on skis, which include snowboards, is complex and not known in every detail. After all, it has been shown that due to the friction between the tread material on the one hand and the snow crystals on the other hand locally melt by the resulting frictional heat snow crystals and that the resulting water leads to hydrodynamic lubrication conditions. As a result, the low kinetic friction coefficients measured during skiing of about 0.02 to 0.05 can be explained. The kinetic friction coefficients measured with solid friction are about 10 times higher.

It is also known that at higher speeds the locally formed melt water can spread over the entire tread, which leads to an undesirable and the sliding speed negatively influencing "suction effect". By admixtures of materials, such as carbon in the modifications of carbon black and / or graphite, which have higher thermal conductivities than the unmodified polyethylene, this negative effect can be prevented or reduced (cf., for example CH-A-657 993 or CH-A-660018 ).

The document EP-A-0821 030 describes low friction polyethylene materials with admixtures of fluoro graphite of the formula CF _n where n can vary from 0.5 to 1.3. Measurements on press sintered polyethylene samples with 10 to 30% CF _n against steel gave kinetic coefficients of friction of 0.27 to 0.13 according to ASTM 03702, compared to 0.35 for polyethylene versus steel. In EP-A-0821 030 It also proposes the use of such materials for skis. However, since hydrodynamic lubrication is present when gliding skis on snow, as explained above, it can not be readily assumed that skis made of such materials will slip when gliding on snow would have reduced friction. Measurements with real skis taking the example of EP-A-821,030 As described above, polyethylene fluoride graphite polyethylene skim materials have shown that fluoro graphite, as an additive in polyethylene, does not significantly reduce friction or increase slip rate. EP-0 960 905 shows that blends of fluorite graphite with carbon black as an additive to polyethylene significantly reduce the friction of skis on snow in some cases or increase the sliding speed.

The publication " Tribology Study of Reduced Graphene Oxide Sheets on Silicon Substrate Synthesized via Covalent Assembly "by Junfei Ou et al. (Langmuir 26 (20), 15830-15836, 2010) Among other things, it deals with friction properties of layers of reduced graphene oxide.

Soot consists of the smallest, mostly spherical particles, which are also called primary particles. These usually have a size of 10-300 nm, therefore one speaks of so-called nanoparticles. They are thus more than a thousand times smaller than the diameter of a hair. These primary particles have grown together into chain-like, partially lumpy aggregates. Many of these aggregates pool together to form the agglomerates. By varying the production conditions, both the size of the primary particles and their aggregation can be adjusted specifically.

In these dimensions, it is no longer just the chemical composition alone, but also the size and shape of the particles that determine the properties. In addition, there are influences from those structures that lie between the pure carbon and the large molecules of hydrocarbons (residues). Optical, electrical and magnetic properties, but also hardness, toughness or melting point of nanomaterials differ significantly from those of macroscopic solids, which can be attributed to special properties of the carbon black. The specific surface area of soot particles is about 10-1000 m ² / g.

The addition of carbon nanotubes in UHMWPE as usual for skis has two drawbacks according to the literature. On the one hand, the coefficient of friction depends on the speed and, unfortunately, rises sharply with the speed, in particular in the range of 50 km / h which is of interest for skiing and upwards. On the other hand, the friction coefficient depends on the orientation of the CNT, in the direction of the nanotubes less than transverse to it. Unfortunately, the orientation of the nanotubes in the usual sintering process is not controllable.

It is therefore an object of the present invention to provide a covering for a ski (or a snowboard) with improved sliding friction, which takes into account the problem discussed above. This object is achieved by a covering for a ski (or a snowboard) according to the independent claims.

Accordingly, the ski coating, preferably a plastic ski coating, contains a filler compound for improving the sliding properties, the filler mixture containing graphene and carbon black.

Graphene (Graphene, sometimes also written in German graphs to distinguish it from mathematical graphs) is the term for a modification of carbon with a two-dimensional structure in which each carbon atom is surrounded by three others, forming a honeycomb-shaped pattern formed.

The outline sketch in FIG. 1 shows how now the two-dimensional crystal form of the graphene can wrap around the PE grains, while the carbon black primary particles fill the space between the PE particles. Here, instead of the polyethylene (PE) find another suitable plastic use.

The FIGS. 2A to 2D show microscope images in 50-fold magnification of thin sections of different Skibeläge: The FIGS. 2A and 2B show a conventional coating with standard black, the Figure 2C a ski coating according to the invention with graphene and carbon black and the FIG. 2D a conventional coating without soot.

It can be clearly seen in the figures that the two mixtures with carbon black have similar optical appearances. In the case of these additives, the localized blackening of the thin sections initially occurs. This is due to agglomeration of the components. In the coating according to the invention ( Figure 2C ) this is not so pronounced - the dispersion has a more optically homogeneous appearance.

This better dispersion and the attachment of the graphene to the PE grain now has surprising effects with regard to the hardness and thus the abrasion behavior of the coating and also with regard to the thermal conductivity of the material and the lubricity. A generally disadvantageous directionality of the coefficient of friction could not be observed.

Surprisingly, it was also found that significantly thinner pads (0.7-0.9 mm) than the prior art of 1-1.6 mm withstand the sustained loads. A comparable improvement of this behavior with other aggregates including carbon nanotubes has not been observed so far.

It was also surprisingly found that the additions made it easier to sand. This had the effect that sufficient surface quality in production and service was already present after a noticeably smaller number of sanding processes for fine sanding (reduction: approx. 25-30%). A sufficient surface for further operations such as waxing or a ready to drive state is characterized by a soapy grip with a uniform roughness profile. Less grinding operations lead to a cost advantage due to reduced work steps.

The plastic may preferably be pressed-sintered plastic powder or plastic granules, preferably of polyethylene, in particular low-pressure polyethylene having a molecular weight of 4 to 12 × 10 ⁶ g / mol. It may preferably contain 5 to 30, more preferably 10 to 20 parts by weight of carbon black and 0.1 to 10 parts by weight of graphene per 100 parts by weight of plastic.

The thickness of the plastic ski coating according to the invention is preferably less than 1 mm, preferably 0.7 to 0.9 mm.

In a preferred embodiment, the surface of the graphene is silanized. Functionalized graphenes, especially those modified with silane, showed better properties in terms of wear and friction.

An inventive ski coating can be produced, for example, by the following process steps: In a first phase, an intimate mixture of 100 parts by weight of an ultrahigh molecular weight low density polyethylene (UHMWPE) and 5 parts by weight of graphene is prepared. In a second phase, the thus prepared mixture of UHMWPE and graphene is intimately mixed with 15 parts by weight of carbon black in a mixer for 15 minutes and then in a cylindrical die under known heat and steam Pressure ratios (as given in the booklet of Hoechst to their low-density polyethylene "Hostalen GUR" [Brochure HKR112-7089C12299 / 14] given) to a homogeneous cylindrical sintered compacted.

After cooling, of the cylindrical sintered body is an endless belt in the desired thickness of the ski coating of e.g. 1.4 mm peeled off. The ski base is then roughened in a known manner on one side with a sanding belt and pretreated by an oxidizing flame for bonding to the ski body.

Of course, the ski coating can be produced not only in the press sintering process with subsequent peeling, but also, for example, in the extrusion process, as long as there is an admixture of an additive consisting of a mixture of carbon black and graphene.

Furthermore, it has been found that a similar arrangement of the substances as well as similar properties can also be achieved with graphene oxides as a precursor in the production of graphenes. Accordingly, according to the invention, the graphene in the ski coating can be replaced either completely or partially by graphene oxide.

Examples:

A test track was traversed with structurally identical skis, which differed by the covering used, with a mean speed of 100 km / h and recorded the time required for this by means of electronic time measurement. On fresh snow with a temperature of -3 ° C, with air temperatures of -2.5 to - 3.5 ° C and humidities of 70 to 85%, the following times were measured: Composition tread Measured time in s Measured time in% 85% PE, 15% soot 22.84 100 85% PE, 14% carbon black, 1% graphene 22,03 96.45 85% PE, 13% carbon black, 2% graphene 21.79 95.4 85% PE, 13% carbon black, 2% graphene oxide 22,01 96.41

As can be seen from the above table, with a layer of graphene or graphene oxide, a significantly improved lubricity can be achieved, which is reflected in the times reduced compared to a standard covering.

Claims (5)

1. A plastic ski sole having a filling material mixture for improving the sliding properties, wherein the filling material mixture contains graphene or graphene oxide and soot and wherein the percentage of graphene or graphene oxide lies between 0.1 and 10 weight percent.
2. The plastic ski sole according to claim 1 wherein the plastic is a press-sintered plastic powder or plastic granulate.
3. The plastic ski sole according to any one of the preceding claims having a thickness of less than 1 mm.
4. The plastic ski sole according to any one of the preceding claims wherein the surface of the graphene or graphene oxide is silanized.
5. The plastic ski sole according to any one of the preceding claims wherein the filling material mixture contains graphene and graphene oxide.

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