The present invention relates to a cross-country ski comprising a slide surface composed of a first material, a top surface, a tail, a tip, a first edge side and a sec- ond edge side between the slide surface and the top surface, said edge sides being composed of a second material and wherein surface energy of the first material is smaller than the surface energy of the second material. The invention relates also to a manufacturing method of a cross-county ski.

Background Cross-country skiing is travelling on skis over snow. Cross-country skiers rely on their own exercise rather than on ski lifts or other forms of external assistance i.e. gravity in the alpine skiing, ski jumping or telemark skiing. This means that the skis for the cross-country skiing are quite different compared to the skis for the other skiing forms. Also the problems to be solved are different in the cross-country ski- ing.

Skis used in cross-country are lighter and narrower than those used in alpine skiing. Ski bottoms are designed to provide a slide surface for having good gliding properties. At least for classic style, the slide surface may have a traction zone under foot. The base of the slide surface may be for example a plastic material that is designed both to minimize friction and, in many cases, to accept waxes. Glide wax may be used on the tails and tips of classic skis and across the whole length of skate skis.

In figures 1 and 2 a simplified example of a known cross-country ski 100 is shown. The cross-country ski comprises a slide surface 102, a top surface 101 , a tail 104 and a tip 103. There is a first edge side 105 and a second edge side 202 between the slide surface and the top surface. On the slide surface there is a running groove 204 that runs along the ski in the longitudinal direction of the ski. Inside the ski there is a core 203. With the core properties the overall attributes of the ski can be defined. The vertical sides of the core define the first edge side and the second edge side. The vertical direction means here a direction when the ski is in a use position. Ski boots are attached to the ski by ski bindings that are fixed to the top surface of the ski approximately at the middle part 107 of the ski. The ski has a camber part 108. It is a section where the ski arches upwards, supported by a point at each end where the ski touches the snow or other surface where it is placed.

In this document all references to a ski mean a cross-country ski unless it is otherwise stated. The top surface, the first edge side and the second edge side are covered usually by some polyamide product or similar material. The slide surface is placed against snow when the ski is used. In the specification of the FIS (Federation International de Ski) for the cross-country skiing regulations for the skis are given. The entire width of the slide surface may be smooth or slightly grooved length-wise. With the exception of the running groove the level must be constant in the entire length and width. Climbing aids in the form of scale patterns or step patterns are permitted. The edge sides may not face up and outwards, making the slide surface narrower than the top surface i.e. the ski may not be wedge shaped.

Classic skis for classic style are designed for skiing in tracks prepared beforehand. For adult skiers (between 155 cm/50 kg and 185 cm/75 kg), recommended lengths are between 180 to 210 centimeters (approximately 1 15% of the skier's height). Traction comes from a kick zone underfoot that when bearing the skier's weight engages either a textured gripping surface or a kick wax. When the skier's weight is distributed on both skis, the ski's camber diminishes the pressure of the kick zone on the snow and promotes bearing on the remaining area of the ski, which has the best glide.

Skate skis are designed for skiing on groomed surfaces. Recommended lengths of skis are between 170 to 200 cm (up to 1 10% of the skier's height) for adult skiers. The entire slide surface of skate skis is optimized for maximum glide.

All cross-country skis have a need to retain kinetic energy and avoid friction loss. 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 has an influence on the sliding properties. Thus, different compositions are required for different snow conditions. Skis require waxing or lubricants to enhance their sliding properties. Especially in competitive skiing exceptional and sometimes very expensive waxes tailored to specific snow conditions are used.

Friction phenomena related to skis involves the formation of a liquid layer of water between the surfaces of snow and the ski. Frictional heat is generated at the inter- face between the slide surface and the snow crystals and that heat melts the local snow crystals into water. 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 the slide surface of the ski are partially separated by melt water layer leading to hydrodynamic lubrication. Melt water layers are found to be about 5 to 10 micrometers depending on the properties of the snow. The slide surface therefore should have good gliding and water repelling properties.

Due to climate change the ski tracks used for competitions and exercise are usual- ly composed of warm, wet and soft snow. This is also the situation when ski tracks are constructed with transported or artificial snow. The organizers of the skiing competitions want to make competitions easily accessible for general public by bringing the competitions near or in big cities where the weather conditions are warm and amount of snow is scarce. This creates complicated situations when the best gliding properties are tried to be archived for the ski. Because of the reasons described above the snow is frequently dirty and contains impurities. That causes more problems for keeping the gliding properties of the ski as good as possible.

The top surface and the edge sides are usually covered with polyamides or similar material that is strong and protects the core of the ski and is easy to embed with colours and figures. The surface energy of the surface material of the top surface and edge sides is lower than the surface energy of the material of the slide surface of the ski. Therefore the slide surface glides better on the snow than the edge sides. However, when the ski sinks into the soft snow, not only the slide surface but also the edge sides of the ski became in contact with the snow causing some additional friction due between the ski and the snow. This effect is small but significant especially in competitions where only fractions of seconds could determine the winner.

Summary

A purpose of the invention is to provide a cross-county ski and a method for manu- facturing one in which the disadvantages of the prior art skis are diminished. Particularly, the purpose of the invention is to provide a cross-county ski with enhanced gliding properties. The purpose is achieved with a cross-country ski and a method defined in the independent claims. Some preferred embodiments of the invention are disclosed in the dependent claims.

The main idea of the invention is to a side coating made of a material of a slide surface or material having similar properties than the slide surface on at least a part of the edge side. A cross-country ski comprises a slide surface composed of a first material, a top surface, a tail, a tip and a first edge side and a second edge side. Said edge sides are between the slide surface and the top surface and they are composed of a second material. The surface energy of the first material is smaller than the surface energy of the second material . This means that the slide surface is composed of a material having a lower surface energy value than surface energy value of a material used to cover the edge sides of the ski. According to the invention the first edge side is at least partly covered with a side coating, which side coating is at least partly composed of a first material or material having substantially similar properties than the first material. In the invention, the slide surface and the side coating are formed in a way that a layer of water is generated not only between the slide surface and the snow but also between the side coating and the snow when the ski is moving on the snow in a way that the slide surface and the side coating are both at least partly in touch with snow. Preferably the width of the top surface is same or less than the width of the slide surface. This means that the edge sides are vertical or inclined inwards, i.e. the angle between the slide surface and the edge side is less than 90 degrees.

In a preferred embodiment of the invention the slide surface is arranged to extend at least partly on the first edge side and on the second edge side for forming side coatings on both edge sides.

In a second preferred embodiment of the invention the side coatings on the first edge side and on the second edge side are symmetrical.

In a third preferred embodiment of the invention the side coatings on the first edge side and on the second edge side are not symmetrical. In yet another preferred embodiment of the invention there is no seam between the slide surface and/or the side coating on the first edge side or on the second edge side. The slide surface in the corner of the slide surface and the first edge side and/or on the corner of the slide surface and the second edge side is therefore continuous. In yet another preferred embodiment of the invention the ski is part of a pair of skis and both skis in the pair are mirror images of each other.

In yet another preferred embodiment of the invention the ski further comprises a place for a ski binding on the top surface in the middle part of the ski, and the side coating reaches the border of the edge side and the top surface, i.e. the slide surface material covers the whole height of the edge side at least on the first edge side or on the second edge side, in a area that is at least 10 % of the total length of the ski in the vicinity of the place for a ski binding.

In yet another preferred embodiment of the invention the length and the position of the area where the side coating reaches the border of the edge side and the top surface is different on the first edge side and the second edge side.

In yet another preferred embodiment of the invention the slide surface and the side coating comprise different materials or shaping, for example grinding, which have or cause different physical properties. In yet another preferred embodiment of the invention the side coating extends from the tail to the tip.

The height of the ski is defined to mean the vertical distance from the lowest part of the slide surface to the end of the tip of the ski when the ski is on its use position. In yet another preferred embodiment of the invention the side coating extend- ing towards the tip covers at least 50 % of the height of the ski.

In yet another preferred embodiment of the invention the maximum thickness of the slide surface is bigger than the maximum thickness of the side coating.

In yet another preferred embodiment of the invention the thickness of the side coating is greater near the slide surface than near the top surface. In yet another preferred embodiment of the invention the side coating is at least partly transparent.

In yet another preferred embodiment of the invention the first material, i.e. the material of the slide surface and the side coating, is polyethylene or at least the main part of the material is polyethylene. In yet another preferred embodiment of the invention in the edge of the slide surface there is an elongated strip of composed material that is harder than the material of the slide surface.

In a method according to the invention for producing a cross-country ski including a core, a slide surface and a side coating a sliding part is formed, said sliding part comprising a slide surface and at least one side coating. The sliding part is attached to the core by a heating process.

In a preferred embodiment of the method according to the invention the sectional profile of the sliding part is L- or U-shaped at least on the middle part of the ski. In a second preferred embodiment of the method according to the invention the core is formed at least partly at the same time as the sliding part is attached to the core.

In a third preferred embodiment of the method according to the invention the sectional profile of the sliding part varies in the longitudinal direction of the ski.

An advantage of the invention is that it provides better gliding properties for a cross-country ski in circumstances that are usually quite challenging to control, i.e. when the snow is wet. The invention diminishes the friction between the ski and the snow and thus makes the ski glide better on the snow. Also the dirt does not cling to the edge sides of the ski so easy. The invention also improves the gliding properties of the ski when the ski track or the surface of the snow is uneven.

A further advantage of the invention is that manufacturing a ski according to the invention does not require any major changes to the manufacturing equipment.

A further advantage of the invention is that it is applicable to all kind of skies used in different cross-country skiing styles enhancing skiing performances. A further advantage of the invention is that it enhances the gliding properties of the ski within the regulations of the FIS so it can be used in the official competitions.

A further advantage of the invention is that it can be easily tailored for different circumstances or snow properties or for different kind of skis.

Various embodiments will become apparent from the detailed description given hereafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

Brief description of the figures

In the following the invention will be described in detail. In the description, refer- ence is made to the enclosed drawings, in which:

Figure 1 shows a prior art cross-country ski;

Figure 2 shows a cross-section of the cross-country ski of figure 1 ;

Figure 3a shows an example of a cross-country ski according to the invention;

Figure 3b shows a second example of a cross-country ski according to an embod- iment of the invention;

Figure 3c shows a third example of a cross-country ski according to an another embodiment of the invention;

Figure 4 shows an example of a cross-section of a cross-country ski according to the invention; Figure 5 shows a second example of a cross-section of a cross-country ski according to an embodiment of the invention;

Figure 6 shows a third example of a profile of a cross-country ski according to an another embodiment of the invention; and

Figure 7 shows an example of a process for manufacturing a cross-country ski according to the invention.

Detailed description of the figures

The embodiments in the following description are given as examples only, and a person skilled in the art may realise the basic idea of the invention also in some other way than what is described in the description. Though the description may refer to a certain embodiment or embodiments in several places, this does not mean that the reference would be directed towards only one described embodiment or that the described characteristic would be usable only in one described embodiment. The individual characteristics of two or more embodiments may be combined and new embodiments of the invention may thus be provided. Figure 1 and 2 are discussed in the background section.

In Figure 3 cross-country ski 300 according to the invention is shown. The ski comprises a slide surface 302, a top surface 301 , a tail 304 and a tip 303. In the description by the height of the ski the vertical distance from the lowermost part of the slide surface and the highest point of the tip is meant. In the middle part of the ski on the top surface there is a place 307 for a ski binding. Between the top surface and the slide surface on the sides of the ski are a first edge side 306 and a second edge side (not shown in the figure). In this example the ski has a camber part 308 where the ski arches upwards. In the middle part of the ski 300 there is a side coating 305a on the first edge side 306. The side coating covers the edge side of the ski on the length of the camber part 308. On the tip side part of the camber part the side coating extends from the slide surface 302 edge to the border of the first edge side and the top surface 301 . On the tail side part of the camber part the height of the side coating is slightly lower than the height of the first edge side. The side coating 305a depicted in figure 3 could, of course, cover the whole height of the edge side and some other sizes and shapes of the side coatings are possible. Some examples of these are presented in figures 3b and 3c. The structure and cover area of the side coating on the edge sides may vary depending on the use of the ski (for example the ski- ing style or the size of the skier) and the circumstances (for example moisture, temperature, characteristics of the snow and the ski track and so on) where the ski is meant to be used. To work efficiently the side coating extends advantageously to at least 50% of the height of the edge side (first or second or both) in those places where the side coating covers the edge side. In the invention this area is at least the edge side on the length of the camber part or at least 10 % of the length of the ski in the middle part of the ski in the vicinity of the place for a ski binding.

In another embodiment of the invention the side coating extends from the tail of the ski to the tip of the ski (figure 3b). In yet another embodiment the side coating extends in the tip of the ski to at least 50 % of the height of the ski (figure 3c). The highest part of the side edges in the tip of the ski does not fall into contact with snow so often as the other parts of the side edges, so the side coating is not so essential on the highest part of the side edge, i.e. near the tip of the ski. The surfaces of the first side edge that are not covered by the side coating may be covered with for example some kind of polyamide or similar material that is used for covering the top surface. Of course, the side edge under the side coating could be covered by the polyamides or similar material. The material of the side coating 305a is the same as the material that is used on the slide surface 302 or some other material that has substantially similar properties, especially gliding properties. At least part of the material of the side coating has a lower surface energy value than the surface energy value of polyamide. A very common material for the slide surface is a subset of the polyethylene called UHMWPE (Ultra-high-molecular-weight polyethylene). Some variants of UHMWPE have a surface tension value of 0.032 N/m. This value can be still lowered by waxing the slide surface. This value is significantly lower than the surface energy level of polyamide. Polyamide is a material that is commonly used as a cover material on the edge sides and top surfaces of skis. It must be noted that the material of the slide surface does not need to be same or having similar properties all the places of the slide surface. Naturally, other materials than polyethylene can be used for the side coating. The material of the side coating 305a has the same surface energy value than the slide surface. Therefore the side coating functions in a similar way than the slide surface, i.e., the melting snow easily forms a thin layer of water between the side coating and the snow surface when the edge side is at least partly against the snow. This reduces the friction force between the snow and the side edge of the ski making skiing faster. It must be noted that even small improvements in the speed of the skier may be significant in very tight races. The improvement is most evident when the circumstances are the most challenging i.e. when the snow is soft and the ski track breaks down under the ski. The invention makes possible to wax the side edges (i.e. the side coatings) of the ski because the material of side coating is similar or has similar properties as the material of the slide surface. This may further improve to properties of the ski in all circum- stances and especially when the weather and the conditions are difficult for skiing.

The surface energy of the side coatings 305 is lower than the surface energy of polyamide coated side edges. Therefore the total friction of the ski according to the invention is less than prior art skis. This is particularly beneficial when the snow is soft and the ski will sink in the snow even partly. The side coatings 305 may be treated similarly as the slide surface. Of course, the side coating 305 and the slide surface 302 may also treated differently. There may be different polishing or grooving or similar treatment on the side coating and the slide surface. Of course the treatment could be focused only on a slide surface. Using that kind of selective treatments the ski could be matched for some particu- lar situation (for example a combination of a skiing style, weather and snow conditions), that would have been difficult without the invention. In a preferred embodiment of the invention an elongated strip or ribbon may be attached to the edge of the slide surface 302. The strip may be some hard material to provide protection to at least to the edge of the slide surface. Also, the strip may provide some additional grip for example in situations where the skier is making a tight turn. The strip may extend to the side coating 305. The strip needs not to cover all of the length of the side coating.

In a preferred embodiment of the invention there is no seam between the side coating 305a and the slide surface 302. Thus, the material is continuous on the corner of the side coating and the slide surface. This is for eliminating sources of additional friction. Even the most carefully constructed seam could increase friction for example due to the capillary phenomenon. Also the durability increases when there is less places that could break. Further, having the slide surface and the side coating as one monolithic piece could be used as enhancing the flexibility or other properties. In figure 3b the features of the ski 300 are similar as in the figure 3a but the side coating 305b now covers the whole first edge side 306. This increases the gliding properties of the ski 300 on the all occasions where the ski and especially the edge sides are in contact with snow.

In figure 3c the features of the ski 300 are similar as in the figure 3a but the side coating 305c now covers the whole first edge side 306 up to the height that is 50% of the height of the ski. Usually the uppermost edge side parts of the tip 303 are not in contact with snow, so it is not necessary to have the side coating there. However, for example for some skating skis it may be beneficial to have the side coating described in figure 3b. In figure 4 an example of a cross-section of a cross-country ski according to the invention is described. The ski comprises a slide surface 402, a top surface 401 , a core 403, a first edge side 406 and a second edge side 407. On the first edge side there is a first side coating 404 and on the second edge side there is a second side coating 405. The surfaces of the side coatings are vertical so the sides of the skis are also vertical when the ski lies on a horizontal level. The side edges may be covered for example by the same material as the top surface and the side coatings are attached on top of that material. The side edge covering material may be any suitable material. Also the sides of the core of the ski may form the side edges. In a preferred embodiment of the invention the maximum thickness of the slide surface is greater than the maximum thickness of the side coating. In skiing great- er forces are directed to the slide surface compared to the side coatings. Therefore there is not so much wearing on side coatings, and the thickness of the side coating may be smaller than the thickness of the slide surface. The side coating may be at least partly transparent making colourings or patters on the edge sides visible.

In figure 5 a cross-section of a cross-country ski according to another embodiment of the invention is described. The ski comprises a slide surface 502, a top surface 501 , a first edge side 506 and a second edge side 507. On the first edge side there is a first side coating 504 and on the second edge side there is a second side coating 505. The thicknesses of the side coatings are greater near the slide surface than near the top surface. The width of the slide surface 502 is therefore greater than the width of the top surface 501 . In this embodiment the side coatings extend to cover the whole side edges in vertical direction.

In figure 6 a cross-section of a cross-country ski according to another embodiment of the invention is described. The ski comprises a slide surface 602, a top surface 601 , a first edge side 606 and a second edge side 607. On the first edge side there is a side coating 604. On the second edge side there is no side coating but the second edge side has a cross section, which is a mirror image of the cross- section of the combination of the first edge side 606 and side coating 604 on the first side of the ski. Thus, the profile of the ski is symmetrical in a way that the ski fulfils FIS-regulations. The side coating 604 extends to the height that is approximately 50 % of the height of the first edge side. This kind of side coating asymmetry (i.e. the other side coating extends to a different height on the side edge) may be beneficial for example in a skating ski. It must be noted that on different places of the ski the cross-section of the side coatings may be different. For example on some places the side coating may reach the edge of the top surface and on some another places it may reach only the height of 50 % of the total height of the side edge. Also on some other places there may be no side coating at all. Especially for a skating ski it may beneficial if the ski has side coatings on the both edge sides for example in a ski track route where there is a lot of downhill parts. On that kind of case there may be a situation where both edge sides of the ski glide at least partly against the snow when skiing down.

In a preferred embodiment of the invention a ski is a part of pair of skis and the skis in the pair are mirror images of each other. This may be beneficial for skis designed especially for skating style. Preferably a skating ski has more side coating than a ski that is designed for classical style of skiing. In figure 7 a process for producing a cross-country ski according to the invention is described. For producing a ski there is a core 701 and a sliding part 702. The sliding part comprises parts that form a slide surface and side coatings. The sliding part will be attached to the core using a heating process under pressure. The at- taching method is practically similar as attaching a conventional slide surface to the core. The running part comprises a first rim 703 and a second rim 704 and between them a bottom part 705. The cross-section of the sliding part is U-shaped. The cross-section of the sliding part may be different when manufacturing different embodiments of the ski. Also, the cross-section of the sliding part may be different in different parts of the ski. For example, in some part of the ski the cross section of the sliding part may comprise only a bottom part. The material of the sliding part is advantageously the same as the material of the slide surface i.e. the first rim, the second rim and the bottom part are all made of the same material.

In an embodiment of the invention the material of the rims is different than the ma- terial of the bottom part but the used materials have at least some substantially similar properties. Preferably these substantially similar properties include at least gliding properties, i.e. friction coefficient and/or surface tension energy values. In another embodiment of the invention the materials or at least some properties of the materials of the rims and the bottom are substantially similar at the cross sec- tion but they change along the sliding part.

The cross-section of the sliding part in figure 7 is U-shaped but it can be different, such as L-shaped.

It is possible to manufacture a core of a ski in a process where suitable core material is heated under pressure. Therefore an embodiment of the invention suggests that the core can be produced at least partly simultaneously with the attaching of the sliding part 702 in a way that during manufacturing of the core the sliding part adheres to the core.

In the manufacturing process of the ski a core 701 or parts of a core and the sliding part 702 are combined and then further processed with an appropriate pro- cess. This further processing may contain heating and pressing but the exact details will vary depending on the materials to be used. The result of the manufacturing process is a ski comprising a slide surface and at least a side coating on a first edge side of the ski. Above, some preferred embodiments of the invention is explained. The invention is not limited to the solutions described above, but the inventive idea can be applied in numerous ways within the scope of the claims.