SKI BOOT ELEMENT

Description

Technical field of the invention

[0001] The invention relates to a component of a sports shoe comprising at least one plastic wall, such as all or part of a shell, for example a lower shell, a collar, or a tongue, or a sole, particularly of alpine ski boots, cross-country ski boots, or ski touring boots, and to a sports shoe as such comprising such a component. It relates particularly to all or part of a ski boot. It also relates to a method for manufacturing such a sports shoe component. State of the art

[0002] A ski boot requires both significant rigidity and strength, as well as a high level of comfort. Indeed, such a boot undergoes considerable stress during use and must therefore be highly durable. High rigidity is also necessary for optimal boot performance, as the boot, acting as an intermediary between the skier and the ski, transmits the skier's forces to the ski to guide it.

[0003] Thus, in the case of an alpine ski boot, the ski boot is often characterized by its "flex" rating, which represents the boot's fore-aft flexing properties. This flex rating represents the effort required to achieve a certain forward flex of the cuff relative to the bottom of the ski boot shell, allowing the user's ankle to pivot. This back-to-fore flex, characterized by the flex rating, is an important indicator of a ski boot's performance, essential for skiers to reliably choose their ski boots. The higher the flex rating, the stiffer the ski boot will be in fore-aft flex, and therefore, the more responsive and precise it will be. Conversely, the lower the flex rating, the more comfortable the ski boot will be.Choosing the flex of a ski boot therefore represents a compromise between these conflicting characteristics, bearing in mind, however, that a high flex is necessarily required for the minimum performance of the ski boot, as mentioned above. The comfort of the ski boot is achieved through a softer inner liner, which reduces the discomfort caused by the rigid outer shell.

[0004] The components of a ski boot that give it its rigidity are generally manufactured by plastic injection molding. To increase the flexural stiffness and / or flexibility of a ski boot, manufacturers can, for example, thicken the walls of various components, such as the shell, cuff, sole, or heel counters (etc.). However, this approach contributes to increasing the amount of material used. Increasing the flexural stiffness and / or flexibility of a ski boot therefore results in a heavier, bulkier, and more expensive ski boot.

[0005] Furthermore, the design and manufacture of ski boots must meet various requirements or objectives, including: The components of ski boots often have a complex geometric shape to conform to the foot. Their injection-molded plastic construction requires high dimensional stability, both for user comfort and the boot's aesthetic appeal. Ski boots must be suitable for use in very low temperatures and therefore offer good thermal insulation. They must be able to absorb impact energy to protect the user's foot. Ski boots must be chemically compatible with the external environment; in particular, the materials used must be water-resistant. Finally, ski boots must be as lightweight as possible to reduce strain on the skier during use, whether skiing, walking, or hiking uphill.

[0006] More generally, mastering the flex properties in the front-to-back and / or lateral directions of any sports shoe, particularly a rather rigid shoe used for sliding sports, is important. Specifically, the flex index must be high to achieve good performance from these shoes in sports, especially sliding sports; that is to say, the shoe's structure must be such that it strongly resists the forward pivoting of the user's lower leg, primarily in the case of alpine ski boots.

[0007] US document 2013 / 298427 A1 relates to a sports shoe component, comprising all or part of a side / front / rear / lower wall where a thermoplastic material is used to trap glass microbeads to shape the support structure around a user's limb. Object of the invention

[0008] The object of the invention is to provide a sports shoe component, in particular forming all or part of the outer wall of a sports shoe, remedying all or part of the disadvantages of the prior art mentioned above, and thus improving known sports shoe components.

[0009] In particular, the object of the invention is to provide an article according to claim 1, with preferred embodiments in dependent claims 2 to 9, as well as a shoe comprising said article, according to claim 10, with preferred embodiments in claim 11, and a method according to claim 12, with preferred embodiments in dependent claims 13 and 14.

[0010] To this end, the invention is based on a sports shoe element, comprising all or part of a wall intended to form at least part of a lateral and / or front and / or rear and / or lower wall of a sports shoe, characterized in that all or part of its wall comprises a material comprising a polymer and a charge of hollow microbeads.

[0011] The said wall comprising a polymer and a charge of microbeads can be a rigid wall.

[0012] The said wall may include a proportion of microbeads between 5% and 25% inclusive, or even between 10% and 15% inclusive, of the weight of said whole or part of the wall of the sports shoe element.

[0013] Microbeads can have an average diameter between 15 and 25 µm and / or a density between 0.30 and 0.60 g / cm3. Microbeads can have a compressive strength greater than or equal to 1000 bars, or even 1100 bars.

[0014] Microbeads can be glass microbeads, polymer microbeads, plastic microbeads, or ceramic microbeads.

[0015] The said wall comprising a polymer and a microbead charge may have a flexural modulus greater than or equal to 100 MPa, and / or exhibit a stiffness greater than or equal to the stiffness of an element of the same shape made solely of a polyurethane with a hardness of 45 Shore D.

[0016] The polymer can be a thermoplastic polymer, in particular a thermoplastic polyurethane.

[0017] The polymer may have a hardness greater than or equal to that of a polyurethane of the same shape and of equal hardness 45 Shore D and / or the polymer may have a hardness between 50 and 60 Shore D inclusive, and / or the polymer may have a flexural modulus between 100 and 200 MPa inclusive.

[0018] The sports shoe element may be intended to contribute to the flexural stiffness of a sports shoe, in particular the element may form all or part of an outer shell, or lower shell, or collar, or tongue of the sports shoe.

[0019] The sports shoe element may form all or part of a shoe sole and / or may form at least one sports shoe tread.

[0020] The invention also relates to a ski boot, characterized in that it comprises at least one element of a sports shoe as described above.

[0021] The ski boot may include a hinged cuff on a lower shell, and the cuff and / or lower shell may be boot components as described previously.

[0022] The invention also relates to a method for manufacturing a sports shoe component as described above, characterized in that it includes an injection step into an injection mold of a material comprising a polymer and a charge of hollow microbeads.

[0023] The manufacturing process for a sports shoe component may include a granulation step comprising the manufacture of the first material by incorporating microbeads into a polymer, including a step of coating microbeads with a layer of polymer material.

[0024] The manufacturing process for a sports shoe component may include a second step of injecting a second material, different from the first material, into the same injection mold according to a co-injection or overinjection principle. Brief description of the drawings

[0025] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which: There figure 1 is a schematic view of a ski boot according to one embodiment of the invention. figure 2 is a microscopic view of a material implemented according to an embodiment of the invention. figure 3 is a graph showing the evolution of the physical properties of the material constituting a ski boot shell as a function of its composition. figure 4 is a first flowchart of a manufacturing process for a sports shoe component according to an embodiment of the invention. Description of preferred modes of the invention

[0026] In the following description, we assume that the shoe rests on a horizontal surface. Furthermore, we will refer to the outer face of a shoe element as its surface facing outwards from the shoe, and the inner face as a surface facing inwards from the foot.

[0027] There figure 1Figure 1 illustrates a ski boot according to an embodiment of the invention. According to this embodiment, the ski boot is adapted for alpine skiing; alternatively, the invention is implemented for a cross-country ski boot, a ski touring boot, or even a snowboard boot. The ski boot according to the embodiment comprises a rigid outer shell formed from several elements obtained by plastic injection molding. The shell comprises, in particular, two main elements: a cuff 2 and a lower shell 3, the cuff being articulated to the lower shell 3 around a connecting axis forming a pivot axis 4, positioned substantially at the ankle joint.

[0028] The lower shell 3 extends from a walking sole 5 to the hinge axis 4, has an overall shape designed to surround a skier's foot, and includes an opening at the top at the skier's ankle. The sole 5 is extended at both its front and rear ends by sidewalls 7, sized to accommodate the jaws of a ski boot binding. The walking surface of the sole 5, which contacts the ground while walking, can be directly integrated into the lower shell 3, or added, for example, using separate heel pieces, at the front and / or rear. The height of the sidewalls 7 and the overall shape of the sole are standardized to ensure compatibility with the jaws of standard bindings. Therefore, the sole 5 and the sidewalls 7 cannot be modified to adjust the stiffness of the ski boot.The sole 5 and the sidewalls 7 are considered non-deformable compared to the other parts of the ski boot. In alpine skiing, when the boot is engaged in the bindings, the sole extends along a plane substantially parallel to the plane of the ski.

[0029] Collar 2 covers the lower part of a skier's shin and calf. It extends substantially from the ankle to the lower leg of a skier.

[0030] The lower shell 3 and the cuff 2 are very rigid and include at least one opening dividing the boot into two flaps positioned on either side. The spacing of these flaps allows sufficient opening of the outer shell, enabling a skier to put on and take off the ski boot. To this end, the ski boot also includes tightening buckles 8, arranged on the outer shell. These buckles allow the lower shell to be tightened against the foot and the cuff against the shin and lower leg by bringing the aforementioned flaps together. This keeps the rigid outer shell closed around the skier's foot and lower leg once the ski boot is on.

[0031] Finally, according to another embodiment, the rigid outer shell could include a tongue extending across the front of the boot from the top of the lower shell to the top of the cuff. The use of such a tongue, in addition to the lower shell and cuff, allows, for example, for the design of a more open lower shell and / or cuff, thus facilitating the insertion of the foot into the boot.

[0032] The rigid outer shell forms a boot that completely surrounds the skier's foot and lower leg. Because this outer shell is very rigid, a comfort liner (size 6) is inserted inside it to ensure good skier comfort. This comfort liner is removable, and the outer shell and comfort liner together form two separate, complementary boots.

[0033] As mentioned above, the cuff 2 is mounted to rotate freely relative to the lower shell 3 around the pivot axis 4. The rotational connection nevertheless requires a certain force to be actuated because the lower part of the cuff rests on the lower shell. The forward rotational movement of the cuff therefore requires deformation of the lower shell and / or the cuff, which opposes this rotational movement due to its rigidity. The resistance to rotational movement can increase with the amplitude of the rotation. In other words, the force required to tilt the cuff forward relative to the lower shell increases as the cuff is tilted. Thus, this flexural property of the ski boot can be characterized by a flexural force required to tilt the cuff relative to the lower shell in a given orientation 9, schematically illustrated in the diagram. figure 1The "flex" index of a ski boot indicates its forward flexing property and indirectly reflects its ability to transmit a skier's impulses to the ski. The higher the flex, the more responsive and precise the ski boot will be. The lower shell, the cuff (and possibly the tongue, if present) are elements of the ski boot that particularly contribute to defining its flex, and more specifically, the properties of their walls contribute to defining its flex. Generally, the lower shell extends up into the cuff, which slows the cuff's rotation around its pivot point and limits the cuff's forward flex. This is due to the rigidity of the front and rear walls of the upper part of the lower shell, which work in conjunction with the cuff's internal walls.This flex, or stiffness property in bending, is generally measured by a flex index, as explained previously. Note that the outer shell's sole (section 5) contributes little or not at all to the definition of flex, but it does contribute to the definition of the stiffness of the lower part of the shell, which is important for regulatory reasons.

[0034] A ski boot component is defined as all or part of the shell, lower shell, cuff, tongue, or even the sole, comprising at least a portion of the outer wall of the boot's rigid shell, thus contributing to the boot's flex. Therefore, a ski boot component forms at least part of a lateral and / or front and / or rear wall of the ski boot, and to a lesser extent, a lower wall. The wall thickness can range from 1 mm to 15 mm inclusive. This component, which helps define the boot's flex (bending stiffness), can be deformed or stressed by the bending force exerted by a skier's leg on the ski boot.

[0035] According to the embodiment of the invention, the ski boot component is the lower shell and / or the cuff, manufactured using an injection molding process. In particular, the ski boot component comprises a material 10 including a polymer 11 and a filler mixed with the polymer. In the embodiment envisaged, the wall of both the lower shell and cuff components is formed entirely from this material 10.

[0036] The polymer can be polyurethane, in particular polyurethane with a density between 1 and 1.5 g / cm3, in particular between 1.1 and 1.2 g / cm3. Alternatively, the polymer could also be any other thermoplastic material such as polypropylene, polyamide, polycarbonate, polyetherimide, polyphenylsulfone, or a styrenic polymer such as ABS.

[0037] The charge comprises 12 hollow glass microspheres. The 12 glass microspheres advantageously have an average diameter between 15 and25µm, specifically an average diameter of approximately 20 µm. The diameter of all glass microbeads is not necessarily identical. Some glass microbeads may be larger or smaller, or even not perfectly spherical. "Average diameter" refers to the average diameter of all the microbeads in the load. In the case of a non-perfectly spherical microbead, its diameter can be defined as the average of all the microbead's diameters or the diameter of the sphere in which it is contained. Glass microbeads are hollow, air-filled spheres. The glass can be borosilicate, particularly sodium borosilicate. Borosilicate, and especially sodium borosilicate, is water-resistant. Therefore, contact between ski boots and snow is unlikely to damage the glass microbeads.In all cases, the density of the filler is less than the density of the polymer, while the stiffness of the filler is greater than that of the polymer.

[0038] The wall thickness of a glass microbead can be generally uniform and range from 0.5 to 1.5 µm. The total volume of a glass microbead is therefore mostly air. The density of glass microbeads (12) ranges from 0.30 to 0.60 g / cm³, and can be as high as 0.46 g / cm³. For comparison, the density of borosilicate glass is approximately 2.3 g / cm³. Thanks to their spherical shape, glass microbeads (12) have high compressive strength, with a compressive strength greater than or equal to 1000 bars, and even greater than or equal to 1100 bars.

[0039] The glass microbeads 12 are mixed with the polymer 11: this combination forms a material 10, which can be used in an injection molding process to form all or part of the wall of the ski boot element. figure 2 Figure 10 represents a micrographic cross-sectional view of this material. The glass microspheres 12 are clearly visible in the middle of the polyurethane. The glass microspheres are spaced apart and completely coated with polyurethane.

[0040] By adding this filler, formed by hollow glass microspheres 12, the rigidity of the ski boot element is greater than that of an element with the same shape made solely of polymer 11. It is also observed that the use of this filled polymer increases the flex of a ski boot compared to the same boot with similar / identical geometry and wall thicknesses, which would be made with a material without glass microspheres. This increase in ski boot flex opens up possibilities for several modifications to ski boots. If the manufacturer wishes to prioritize comfort, they can consider reducing the wall thickness of the element while maintaining the same flex, and also reducing the overall weight of the boot.Alternatively, the manufacturer could consider using a less rigid, and for example less expensive, polymer, and compensate for the loss of rigidity by incorporating glass microbeads to maintain a flex value identical to state-of-the-art ski boots. Finally, the material chosen for the boot component naturally allows for easy flex increases, and therefore a greater forward and backward flex in a ski boot.

[0041] In addition, it is worth noting that due to the rigidity of such a material, it can advantageously be placed in the wall of the ski boot in areas subject to high stress, such as the lower part of the bottom of the shell, particularly at the level of the sole and / or the front and / or rear sidewalls.

[0042] Furthermore, thanks to the presence of air inside the glass microbeads, their density is significantly lower than that of polyurethane (polyurethane's density being between 1.1 g / cm³ and 1.2 g / cm³). Therefore, the higher the proportion of glass microbeads, the lighter the resulting material. The chosen solution thus offers the second advantage of reducing the weight of a component of a ski boot, and consequently, the weight of the entire ski boot. In addition, the air contained within the glass microbeads acts as thermal insulation. The chosen solution therefore has the further advantage of increasing the thermal insulation of the ski boot's outer shell.

[0043] There figure 3Figure 21 illustrates, with its first dotted curve, the evolution of the mass of a ski boot outer shell entirely molded from polyurethane containing a variable proportion of glass microbeads. For example, incorporating 10.5% glass microbeads by weight into the polyurethane results in a mass reduction of approximately 12% compared to the original mass of a shell without microbeads. Incorporating 15% glass microbeads by weight into the polyurethane results in a mass reduction of approximately 100g for a shell weighing 641.3g without glass microbeads.

[0044] In addition, the figure 3Figure 22 illustrates, with a second solid-line curve, the evolution of the alpine ski boot's flex as a function of the percentage of glass microbeads present in the polyurethane. It can be seen that the bending force required to tilt the cuff 2 relative to the lower shell 3 increases almost linearly with the proportion of glass microbeads. Advantageously, the proportion of glass microbeads 12 is between 5% and 25% inclusive, or even between 10% and 15% inclusive, of the element's weight.

[0045] Advantageously, the material 10 will be chosen to maintain the usual rigidity of the outer shell of a ski boot. According to the invention, the resulting plastic material is considered rigid when its flexural modulus is greater than or equal to 100 MPa. This results in a material with a rigidity greater than or equal to that of a polyurethane shell with a hardness of 45 Shore D. Thus, the material 10 advantageously has a hardness between 45 and 65 Shore D, preferably between 50 and 60 Shore D. This means that the polymer material 11 used also advantageously has a hardness greater than or equal to that of a polyurethane shell with a hardness of 45 Shore D. It can therefore have a hardness between 50 and 60 Shore D. Furthermore, the flexural modulus of the polymer material 11 used is advantageously between 100 and 200 MPa inclusive. The polymer material 11 used is therefore rigid.The sports shoe element of the invention is thus an element comprising at least a rigid wall part, that is to say, it comprises a rigidity significantly greater than, for example, rubber.

[0046] On the other hand, in the event of an impact against the ski boot element, for example following a fall, the glass microbeads contained within the element can shatter. Thus, at least some of the impact energy can be absorbed by the element. The user's foot and / or leg can therefore be protected from injury.

[0047] The invention also relates to a method for manufacturing such a ski boot component, as schematically illustrated by the figure 4In a first step E1, glass microbeads as defined previously are supplied. The glass microbeads can then optionally undergo a surface treatment to increase their resistance and / or to improve their compatibility with the polymer used.

[0048] In a second step, called the granulation step E2, the material 10 is manufactured by incorporating glass microbeads 12 into a polymer 11, preferably a thermoplastic material. The resulting material 10, according to the embodiment, is in the form of granules comprising the glass microbeads coated with polyurethane mixed with polyurethane. The granules can be cylindrical, rice-grain shaped, or spherical, and can be on the order of millimeters in size. The granulation step E2 can be carried out using a twin-screw extruder.

[0049] In the E3 injection step, the material 10 is injected into an injection mold. For this purpose, the granules are heated to a temperature that melts the polyurethane. The glass beads withstand the temperature required for injection and retain their initial shape, generally spherical. The glass microbeads then act like a conveyor belt, facilitating the flow of material within the mold. The material can thus penetrate quickly and efficiently into the various recesses of the mold. The rapid injection also ensures good temperature uniformity of the material within the mold. This results in a high-quality injected part, free from filling defects, shrinkage (or sink marks), or warping. Elements with complex geometries can therefore be easily molded. A lower injection temperature and / or injection pressure can also be considered.

[0050] Despite their high compressive strength, glass microspheres can break during the granulation stage E2 or the first injection stage E3. To mitigate the risk of breakage, a higher proportion of glass microspheres can be used in the material's composition. For example, during the granulation stage, approximately 25% glass microspheres can be used relative to the total weight of the manufactured material.

[0051] According to one embodiment, the manufacturing process includes at least a second injection step E4 of a material different from the material 10 used in step E3. The second material may be a polymer containing fillers, for example, hollow glass microspheres of a different size or density than the glass microspheres used previously. The second material could also be a polymer filled with glass or carbon fibers, or an unfilled polymer. The second injection step E4 may be carried out in the same injection mold according to a co-injection principle, comprising the successive and close injection of two materials through the same injection nozzle, or possibly in another mold according to an overinjection principle. Alternatively, this second material could be injected before the injection of the material of the invention according to step E3 of the process of the invention.Thus, the physical properties of the material including the glass microbeads can be combined with the physical properties of a second material.

[0052] It is clear from the foregoing that the invention enables the manufacture of a ski boot component comprising at least one wall section made of a polymer material filled with hollow glass microspheres. Alternatively, the microspheres can be obtained from various natural or synthetic materials. For example, in addition to glass microspheres, one could consider polymer microspheres (particularly plastic microspheres) such as polyethylene or polystyrene, or even ceramic microspheres. Advantageously, this wall section comprises this material throughout its entire thickness. Alternatively, this material extends over only a portion of the thickness, which is presented in a multilayer structure. Furthermore, the material could include another filler in addition to the glass microspheres, for example, glass fibers, particularly very short glass fibers.

[0053] The invention has been presented in particular for an alpine boot, for forming a component of a ski boot, and specifically for forming a wall of the lower shell and / or cuff to achieve optimal flex or rear / forefoot stiffness. This invention can also be considered for: To create a more rigid, localized area of ​​a shoe component, such as the sidewalls of a ski boot sole or the rear or lateral reinforcements of the shoe wall, particularly of a shell or cuff; to create a lighter sole for a ski boot shell while maintaining sufficient rigidity, possibly including front and / or rear sidewalls; to create a plastic component of a cross-country ski boot, such as a rear heel counter extending to the back and / or sides of the boot and / or a cuff hinged to this counter. In this case, the lateral flexural stiffness of the boot is optimized.

[0054] Moreover, the invention is naturally suited to all sliding sports shoes, including a part made of rigid plastic material, whose flexing property requires optimization, and whose lightness is advantageous.

Claims

1. Sports shoe element comprising all or part of a wall intended to form at least a portion of a lateral and / or front and / or rear and / or bottom wall of a sports shoe, wherein all or part of said wall comprises a material (10) including a polymer (11) and a filler of hollow microspheres (12), the polymer (11) being a thermoplastic polyurethane, the microspheres (12) being glass microspheres, the microspheres being spaced apart from one another and completely encapsulated in polyurethane.

2. Sports shoe element according to the preceding claim, characterized in that said wall comprising a polymer (11) and a filler of microspheres (12) is a rigid wall.

3. Sports shoe element according to any one of the preceding claims, characterized in that said wall comprises a proportion of microspheres (12) ranging from 5% to 25% inclusive, or even from 10% to 15% inclusive, of the weight of said entire wall or wall portion of the sports shoe element.

4. Sports shoe element according to any one of the preceding claims, characterized in that the microspheres (12) have an average diameter between 15 and 25 µm and / or a density between 0.30 and 0.60 g / cm3.

5. Sports shoe element according to any one of the preceding claims, characterized in that the microspheres (12) have a compressive strength greater than or equal to 1000 bar, or even 1100 bar.

6. Sports shoe element according to any one of the preceding claims, characterized in that said wall comprising a polymer (11) and a filler of microspheres (12) has a flexural modulus greater than or equal to 100 MPa, and / or exhibits a stiffness greater than or equal to that of an element of the same shape made solely of a polyurethane having a hardness of 45 Shore D.

7. Sports shoe element according to any one of the preceding claims, characterized in that the polymer (11) has a hardness greater than or equal to that of a polyurethane of the same shape and having a hardness of 45 Shore D, and / or in that the polymer (11) has a hardness between 50 and 60 Shore D inclusive, and / or in that the polymer (11) has a flexural modulus between 100 and 200 MPa inclusive.

8. Sports shoe element according to any one of the preceding claims, characterized in that it is intended to contribute to a bending stiffness of a sports shoe, in particular in that the element forms all or part of an outer shell, or a lower shell (3), or a cuff (2), or a tongue of the sports shoe.

9. Sports shoe element according to any one of the preceding claims, characterized in that it forms all or part of a shoe sole and / or forms at least one sidewall of a sports shoe.

10. Ski boot (1), characterized in that it comprises at least one sports shoe element according to any one of the preceding claims.

11. Ski boot (1) according to the preceding claim, characterized in that it comprises a cuff (2) articulated on a lower shell (3), and in that the cuff and / or the lower shell are sports shoe elements according to any one of claims 1 to 9.

12. Method for manufacturing a sports shoe element according to any one of claims 1 to 9, characterized in that it comprises an injection step (E3) in an injection mold of a material (10) comprising a polymer (11) and a filler of hollow microspheres (12).

13. Method for manufacturing a sports shoe element according to the preceding claim, characterized in that it comprises a granulation step (E2) including the production of the first material (10) by incorporating microspheres (12) into a polymer (11), comprising a step of coating the microspheres (12) with a layer of the polymer material (11).

14. Method for manufacturing a sports shoe element according to any one of claims 12 or 13, characterized in that it comprises a second injection step (E4) of a second material different from the first material into the same injection mold according to a co-injection or over-molding principle.