Press pad and method for the production thereof

Abstract

In a press pad (2) for use in hydraulic single- or multi-stage heating presses, comprising a fabric (10) made of weft (14) and warp threads (13), each consisting of metal, and comprising an elastomeric material located in and preferably filling the spaces between the weft (14) and warp threads (13) of the fabric (10), the elastomeric material is applied to the fabric (10) in a partially crosslinked form and spatially bonded with it, and then end-crosslinked in a bonded state. To enable the efficient production of such a press pad (2), it is proposed that the partially crosslinked elastomeric material be applied to the fabric (10) as a sheet structure (11) and spatially bonded with it by the application of pressure and temperature, and then end-crosslinked in a bonded state.

Description

Introduction

[0001] The invention relates to a press pad for use in hydraulic single- or multi-stage heating presses, with a fabric consisting of weft and warp threads, each consisting of metal or having a metal component, and with an elastomeric material that is located in spaces between the weft and warp threads of the fabric and preferably fills these spaces, wherein the elastomeric material is applied to the fabric in a partially cross-linked form and is spatially combined with it and is end-cross-linked in a combined state.

[0002] Furthermore, the invention relates to a method for producing a press cushion for use in hydraulic single- or multi-stage heating presses, comprising a press cushion a fabric made of weft and warp threads, each consisting of metal or having a metal component, and an elastomeric material that is located in the spaces between the weft and warp threads of the fabric and preferably fills them, wherein the elastomer material is applied to the fabric in a partially cross-linked form and spatially combined with it and is end-cross-linked in a combined state.

[0003] These pressure pads, also known as pressure equalization fabrics or pressure equalization mats, are required in coating presses to adequately compensate for dimensional tolerances in heating plates, press plates, and coating materials. Thermosetting resins, which are very pressure-sensitive during surface formation, are used for coating wood-based panels such as particleboard, HDF, MDF, or plywood. Therefore, the coating press should maintain the most uniform pressure possible across the entire surface. The coating of wood-based panels is usually carried out in single- or multi-stage short-cycle presses without recooling. To maximize throughput and minimize energy consumption in such press systems, the shortest possible pressing times are targeted, thus minimizing heat loss to the environment.Therefore, the heat transfer from the heating plates of the press systems, which are usually supplied with thermal oil, via the press plates, which are usually provided with a surface relief for realistic wood imitation, to the resin surfaces should happen as quickly as possible, since short pressing times are an important economic factor.

[0004] The thermoset resins used can consist of melamine, urea, and / or phenolic resins. For decorative coatings, such as simulated wood surfaces or tile looks, melamine or mixed resins are predominantly used. For the coating process, high-quality pulp papers are printed with a decorative design and then impregnated with an aqueous resin solution and dried in impregnation units. During drying, the resins begin to condense, and this condensation is stopped during subsequent cooling. Final condensation of the resins then occurs under the influence of pressure and temperature in the presses.

[0005] Thermoset resins are plastics that cannot be returned to their original state after final condensation. They thus behave in the opposite way to so-called thermoplastics, which can be reversibly returned to a molten state even after curing through exposure to heat. Thermoset resins cross-link irreversibly in three dimensions, releasing water and formaldehyde in the process. Due to the gaseous release of water and formaldehyde under the prevailing pressure and temperature conditions, the resulting gas must diffuse into the paper layer and the wood surface because of the hermetic surface seal created by the metal press plates used.If gas bubbles remain trapped in the resin layer, meaning they do not diffuse into the paper or wood-based material, they become permanently embedded in the resin surface. After subsequent curing, the different light reflections result in surface defects in the form of so-called white spots. Therefore, it is essential to achieve rapid and uniform heat transfer in the initial phase of the pressing process. The pressure pad plays a crucial role in heat transfer and cushioning, i.e., pressure equalization, particularly in the production of so-called flooring panels ("floor laminate") made of MDF or HDF boards with very hard surfaces. The density of these boards ranges from 800 kg / m³ to 1000 kg / m³ for HDF boards, meaning they exhibit virtually no springiness.It is therefore particularly important to use a compression pad that has very good resilience combined with rapid heat transfer. State of the art

[0006] From EP 1 300 235 B1, a press pad is known which consists of an inner support fabric in the form of a wire mesh made of metal threads or a mixture of metal and plastic threads. This wire mesh is placed in a mold that is open at the top and into which liquid silicone rubber, specifically LSR (Liquid Silicone Rubber), is poured. The flowable silicone rubber is evenly distributed over the surface of the wire mesh, which covers the entire area of ​​the future press pad, by scraping or spreading it with a type of scraper or spatula. To increase the thermal conductivity of the press pad, the silicone rubber can be mixed with metal powder or other highly thermally conductive substances.After the silicone material is evenly distributed over the wire mesh, the silicone rubber material is cured by applying temperature in an oven or press, resulting in a terminally oriented silicone elastomer.

[0007] One disadvantage of this well-known compression pad is its complex manufacturing process. A separate mold must be produced for each length and width dimension of the pad. Furthermore, the processing technology for liquid silicone rubber materials is complex, and a large amount of waste material is generated.

[0008] While the aforementioned press pad forms a kind of rigid mat due to its continuous and closed coating or filling with the elastomeric material, numerous press pads are also known from the prior art that are designed as woven fabrics in their finished state. For example, DE 20 2012 005 265 U1 describes a press pad fabric made of high-temperature-resistant elastomeric threads with a core thread, wherein the elastomeric threads can run in the warp and / or weft direction. Furthermore, the known fabric contains heat-conducting threads that can run in the warp and / or weft direction, cross the elastomeric threads, and enable heat-conducting contact at the surfaces of the press pad, thus ensuring good heat transfer from one surface of the press pad to another.Before the elastomer threads are cross-linked, the thermally conductive contact threads are to be prepared in such a way that individual, essentially free, thermally conductive contact surfaces are formed, whereby the threads are firmly anchored in the elastomer material by the cross-linking process. Since the thermally conductive contact threads are embedded approximately 50% in the elastomer material, only a limited amount of heat can be transferred from the press pad. EP 0 713 762 A2 discloses a press pad for high- and low-pressure presses that comprises various materials. These include, for example, yarn made of aromatic polyamide with metal threads, pure metal threads, heat-resistant filament made of rubber or a rubber compound, heat-resistant silicone or silicone compounds, and mixtures thereof with or without metal threads.

[0009] German patent application DE 20 2007 019 506 U1 describes a press pad intended for use in a laminate press. This press pad comprises a fabric made of heat-resistant threads, wherein at least the warp and / or weft includes a core consisting of several threads. The core is surrounded by a sheath of elastomeric material. In addition to the aforementioned heat-resistant threads, metal threads are present in the other thread system. A distinctive feature of this press pad is the design of the aforementioned thread core, whose individual threads run essentially parallel to each other and parallel to the longitudinal axis of the core.

[0010] DE 103 37 403 A1 describes a press pad whose special feature is that the threads containing the polymer material contain a gas content of at least one percent, which is intended to improve the spring and recovery properties of the press pad. EP 0 842 764 A1 discloses a press pad made of a textile yarn that is intended to exhibit an extended service life under high mechanical stress. A characteristic feature of this previously known press pad is the use of flame-retardant fibers made of a melamine resin.

[0011] From EP 0 735 949 B1 and EP 1 136 248 A1, press pads are known in which the warp threads and / or the weft threads comprise a silicone elastomer or a blend or copolymer consisting of silicone rubber and fluorosilicone rubber. The threads comprising the aforementioned elastomer material have a metal core thread that increases tensile strength and thus enables weaving. Finally, DE 197 00 371 C1 describes a method for producing a press pad intended for use in a hot press for manufacturing high-pressure laminates or for surface treatment of sheet-shaped pressed material. The press pad is to be coated on one side with a temperature-resistant adhesive, which may, for example, be in film form. This adhesive bonds the press pad to the respective heating plates. This type of fixation is intended to improve heat transfer from the heating plate to the pressed material.

[0012] None of the aforementioned compression pads meet the requirements for high thermal conductivity, thus enabling short compression cycles, while simultaneously requiring high temperature resistance of the elastomer material and therefore a long service life for the compression pad, as well as good pressure distribution and resilience properties. With regard to the aforementioned EP 1 300 235 B1, both the manufacturing process and the heat resistance of the elastomer material must be considered disadvantageous. Task

[0013] Based on the prior art of the aforementioned type, the invention is based on the objective of further developing a press cushion in such a way that the thermal conductivity is high, the spring and recovery properties are very good, and at the same time resistance to abrasion even at very high pressing temperatures as well as dimensional stability is very good. Solution

[0014] Starting from a pressure pad of the type described above, the aforementioned task is solved by applying the elastomer material, which is present in partially cross-linked form, as a sheet structure onto the fabric and spatially uniting it with the fabric through the action of pressure and temperature, and finally cross-linking it in a united state.

[0015] The invention thus deliberately departs from the application of a flowable elastomer material (or a rubber material that, after its final cross-linking, forms the resilient elastomer material) and instead utilizes, although also only partially cross-linked, an elastomer material (or rubber material) that is not flowable but dimensionally stable and exists as a sheet structure. A sheet structure within the meaning of the present application is understood to be a material that is flexible but retains its basic shape, for example, in the form of a plastically deformable sheet or a plastically deformable web or film. The thickness of the sheet structure made of an elastomer material used according to the invention is approximately between 0.1 mm and 1.5 mm, depending on the thickness of the finished compression pad. (Mr. Espe, are these values ​​accurate?).The sheet material can be designed as a closed web or "sheet", but can also have holes or perforations which - if desired - can also lead to an inhomogeneous thickness distribution over the surface of the sheet material (e.g. with evenly distributed perforations) and possibly also over the surface of the press pad.

[0016] The use of a sheet-like structure, i.e., a dimensionally stable material, offers advantages in both processing and material properties of the resulting compression pad compared to the use of a liquid rubber material known from EP 1 300 325 B1: From a production engineering perspective, processing dimensionally stable forms of the partially cross-linked elastomer material is significantly "cleaner" than working with liquid, or flowable, rubber material: while the sheet-like structure according to the invention can be divided in a defined and geometrically precise manner, in particular into sections of any size, the previously known process of applying the liquid requires a mold specifically adapted to the later dimensions of the compression pad in order to avoid undefined flow of the material.Furthermore, working with liquid rubber material requires elaborate cleaning processes after the work is completed, both for the mold and the tool.

[0017] Furthermore, the liquid rubber material (LSR silicone) required for the production of compression pads according to EP 1 300 235 B1 exhibits significantly inferior material properties when subsequently used as a compression pad compared to an HTV / HCR silicone, which is preferably used in the compression pad and / or process according to the invention. The advantages of HTV silicone rubber and the resulting HTV silicone elastomer are its high heat resistance, which extends up to 300°C, and in some cases even higher, without any degradation process occurring. HTV silicone is also considerably more durable than LSR rubber and more resistant to wear and environmental influences. Despite its very good mechanical strength, HTV / HCR silicone elastomer remains flexible and retains its properties over long periods.Furthermore, HTV elastomer material is characterized by its high resistance to a wide variety of chemicals, especially oils and solvents.

[0018] Despite its dimensional stability, the sheet-like structure made of the partially cross-linked elastomer material used according to the invention possesses such residual flowability, or at least plastic deformability, that the elastomer material can be pressed into the spaces between the fabric and fill these spaces—at least to a large extent. Surprisingly, such a "fusion process" between the supporting fabric and the surrounding, or filling, elastomer material can—as has been discovered in corresponding experiments—even occur unilaterally, meaning that a sheet-like structure is pressed into the spaces between the fabric only from one side. In this way, after the final cross-linking of the elastomer material, a classic composite material is produced, in which the fabric forms the reinforcing phase ("supporting fabric") and the elastomer material the so-called matrix.

[0019] As an alternative to the one-sided application or insertion of the elastomer material into the fabric described above, it is also possible and particularly advantageous if a fabric consisting of partially cross-linked elastomer material is applied to both sides of the fabric, preferably with the elastomer material oriented symmetrically to a central plane of the fabric. In this case, the distance traveled by the pressurized portion of the elastomer material to achieve near-complete filling of the fabric's interstices is only half that of a one-sided application or insertion.

[0020] If, at least on one side of the pressure pad, partial areas of the fabric, preferably bends of the weft and / or warp threads of the fabric, protrude above a surface of the elastomer material, the thermal conductivity of the pressure pad thus obtained is particularly high, which is especially true if the weft and / or warp threads of the fabric are made of metal.

[0021] It is particularly advantageous if the elastomer material is a silicone elastomer, a fluoroelastomer, a fluorosilicone elastomer, or a co- or blend elastomer made from one of the aforementioned elastomer materials.

[0022] In addition, a further embodiment of the invention consists in the elastomer material being made from a silicone rubber of the type HTV / HCR or a fluororubber or a fluorosilicone rubber, each with a low viscosity setting.

[0023] According to a further development of the press pad according to the invention, it is provided that warp threads, preferably all warp threads, of the fabric and / or weft threads, preferably all weft threads, of the fabric consist of a plurality of individual wires, which are preferably interlaced with each other and / or have at least one plastic thread, preferably made of an aromatic polyamide or of a melamine resin, which is preferably interlaced with the wires of the respective warp and / or weft threads of the fabric or forms their core thread.

[0024] To increase thermal conductivity, thermally conductive particles, especially metal particles or quartz particles or those made of barium titanate, beryllium oxide or aluminum oxide, can be embedded in the surface structure of the elastomer material.

[0025] Starting from a method of the type described above, the underlying problem is solved by applying the elastomer material, which is present in partially cross-linked form, as a sheet structure to the fabric and spatially bonding it to the fabric by applying pressure and temperature, and then fully cross-linking it in a bonded state. The advantages already described above in connection with the press pad according to the invention are similarly realized in the implementation of the method according to the invention.

[0026] The production of the press pad according to the invention can be carried out in a particularly rational and efficient manner if the sheet structure is made of the partially cross-linked elastomer material and / or the fabric is available as a web material and that Elastomeric sheet material and fabric sheet material or elastomeric sheet material and the fabric or the sheet structure made of elastomeric material and fabric sheet material

[0027] The fabric is spatially joined in a joining zone and end-crosslinked in a crosslinking zone, preferably with elastomeric material, in particular elastomeric web material, being introduced to the fabric from two sides and into the spaces between it in a single joining zone. The use of web material enables the inventive process to be carried out as a continuous process and offers the advantage of high productivity combined with low losses or waste. For example, a web of the inventive press pad can be continuously produced from one web of the fabric and one or two webs of the sheet material by joining and end-crosslinking. This can later be cut into individual press pads with the required length and width dimensions by simply laying them down or additionally reducing their width.For better storage and transport, the press cushion web can also be wound into a roll or reel beforehand. Similarly, the fabric can be unwound from a roll or reel and fed into the bonding and end-curing process. The same applies to the sheet structure of the elastomer material. This sheet structure can also be produced as a web by appropriate extrusion immediately before the bonding and end-curing process and processed directly into the desired press cushion web without intermediate storage or changes in size or format.

[0028] While it is generally possible for the joining zone and the end-crosslinking zone to be spatially separated, it is preferable for them to coincide or at least overlap spatially over a predominant area. This improves the compactness of a system for carrying out the manufacturing process according to the invention. The result of the joining process of the woven and sheet structure, i.e., partially crosslinked elastomer material, is improved by increasing the temperature and the associated reduction in viscosity, which immediately initiates the end-crosslinking process. In the process according to the invention, both processes—the joining and the end-crosslinking—are sometimes difficult to distinguish spatially and temporally, or even merge into one another.In the case of a separation of joining and end cross-linking, the latter can, for example, take place in a separate oven or heat treatment zone. This applies both to a continuous, through-process and to an intermittent process in which successively pre-fabricated pieces of fabric of a certain size are joined with similarly pre-fabricated pieces of the sheet structure (of mostly the same size) and then "vulcanized", i.e. end-cross-linked, in an end-cross-linking zone designed as an oven or heat treatment chamber.It has proven particularly advantageous if the joining zone is located in a pressure roller device, especially a calender, which has at least two pressure rollers whose axes of rotation are aligned parallel to each other and which define a gap between them running parallel to the axes of rotation, the width of which is less than the sum of the thickness of the fabric and the thickness of the sheet made of the elastomer material or the thicknesses of two sheet materials brought into contact with the fabric on opposite sides. The pressure roller device described above is known in particular as a so-called calender, which, however, does not function as a type of extruder, but rather as a type of "laminating device". The joining zone is formed here by the aforementioned gap.The end-curing zone can also be located in the gap, in which case the pressure rollers forming the gap are typically heated (or a heating device heats the gap area from the outside) and introduce the temperature required for end curing into the partially cured elastomer material. Examples of implementation

[0029] The invention is described in more detail below with reference to a device for carrying out the inventive method and for producing the inventive compression cushion. It shows: Fig. 1: a schematic view of a device with a pressure roller assembly and Fig. 2: a cross-section through a pressure pad produced with a device according to Fig. 1

[0030] One in Figure 1The illustrated device 1 for producing a press pad 2 comprises a pressure roller assembly 3, a first unwinding unit 4, a second unwinding unit 5, and a third unwinding unit 6. It also includes a winding unit 7. The latter serves to wind up the press pad 2, which is produced in the form of web material and exits the pressure roller assembly 3. To produce a single press pad with individual dimensions, the web material must be cut to length and possibly further trimmed to reduce the width.

[0031] The pressure roller assembly 3 comprises an upper pressure roller 8 and a lower pressure roller 9, which are aligned parallel to each other and define a gap S between them. A web of fabric 10 wound on the unwinding unit 5 and a web each of a sheet 11 made of a partially cross-linked elastomer material, wound on the two unwinding units 6 and 7, can be guided through this gap. The two webs of the sheet 11 are guided to the fabric 10 on opposite sides. Various guide rollers F are provided for the precise guidance of both webs of the sheet 11 and the fabric 10, between which the respective web can be guided.

[0032] Due to the tapered gap S, the two webs of the sheet structure 11 are pressed into the spaces in the fabric 10 from both sides, resulting in the clear width of the gap S between the two pressure rollers 8 and 9 (measured without the fabric 10 and the two sheet structures 11 passing through it) being less than the sum of the thicknesses of the fabric 10 and the two sheet structures 11, preferably equal to or less than the thickness of the fabric 10. In In the latter case, the material of the two plastically deformable surface structures 11 is completely pressed into the fabric 10. The spaces between the fabric layers are essentially completely filled, and the warp and weft threads of the fabric 10 are tightly enclosed by the elastomeric material.

[0033] If the thickness of the fabric 10 is less than the width of the gap S, the fabric 10 is elastically compressed when passing through the gap, which is why the fabric 10 expands again after passing through the gap, whereby metallic threads (here: the warp threads, alternatively or additionally also the weft threads) of the fabric 10 emerge from the elastomer material and thus, due to the protrusion over one or both surfaces of the finished press pad 2, offer a particularly high thermal conductivity when the press pad is later used in the press operation.

[0034] End-curing of the elastomer material takes place either in the area of ​​the gap S between the two pressure rollers 8 and 9 (for which one or both of them are heated) or in a downstream heating device 12. The latter is particularly preferable if a protrusion of metal threads of the fabric 10 over one or both surfaces O of the press pad 2, as described above, is to be achieved. The temperature at which end-curing takes place should be between 140 °C and 180 °C.

[0035] The in Figure 2The fabric 10, shown schematically in cross-section, consists of warp threads 13, essentially made of copper, in the form of six intertwined individual threads of copper wire with a diameter of 0.20 mm and a stabilizing plastic thread made of meta-aramid with a diameter of 0.25 mm, and of weft threads 14, essentially made of brass, in the form of seven intertwined individual threads of brass wire with a diameter of 0.20 mm. The fabric 10 is woven in a plain weave, with a weft count of 400 / m. The thickness of the "uncoated" ("unfilled") fabric 10 is approximately 2.2 mm to 2.5 mm.

[0036] Each sheet of the elastomeric (pre-crosslinked rubber) sheet structure 11 consists of HTV / HCR silicone with a low viscosity setting, has a basis weight of approximately 700 g / m² to 1,400 g / m² and a thickness of approximately 0.5 mm to 1.0 mm.

[0037] The press pad 2 obtained after the bonding process in the gap S under the influence of heat retains the original thickness of the fabric 10 (approx. 2.20 mm to 2.50 mm) because the elastomer material E of the sheet structures 11 is completely absorbed into the spaces of the fabric 10, and the threads of the fabric 10 even have a slight protrusion on both sides beyond the press pad surfaces to increase heat transfer via metallic contact with the heating plate / pressing sheet. The basis weight of the finished press pad 2 is approximately 3,900 g / m² to 4,000 g / m². Reference symbol list

[0038] 1 Device 2 Press pad 3 Pressure roller device 4 Unwind device 5 Unwind device 6 Unwind device 7 Rewind device 8 Upper pressure roller 9 Lower pressure roller 10 Fabric 11 Sheet structure 12 Heating device 13 Warp thread 14 Weft thread F Guide roller E Elastomer material S Gap O Surface Ü Protrusion

Claims

1. Press pad (2), for use in hydraulic single- or multi-stage heating presses, - comprising a fabric (10) of weft (14) and warp threads (13), each consisting of metal, and - comprising an elastomeric material which is located in the spaces between the weft (14) and warp threads (13) of the fabric (10) and preferably fills these spaces, wherein the elastomeric material is applied to the fabric (10) in a partially cross-linked form and is spatially united with it and end-cross-linked in a united state, characterized by the fact that The elastomer material, which is present in a partially cross-linked form, is applied as a planar structure (11) to the fabric (10) and spatially united with it by the action of pressure and temperature and is end-cross-linked in a united state.

2. Press pad according to claim 1, characterized by the fact thata surface structure (11) consisting of partially cross-linked elastomer material is applied from both sides of the fabric (10) and preferably the elastomer material is oriented symmetrically to a central plane of the fabric (10).

3. Press pad according to claim 1 or 2, characterized by the fact that at least on one side of the press pad (2) partial areas of the fabric (10), preferably bends of the weft (14) and / or warp threads (13) of the fabric (10), protrude over a surface (O) of the elastomer material.

4. Press pad according to one of claims 1 to 3, characterized by the fact that the elastomer material is a silicone elastomer or a fluoroelastomer or a fluorosilicone elastomer or a co- or blend elastomer made from one of the aforementioned elastomer materials.

5. Press pad according to one of claims 1 to 4, characterized by the fact thatthe elastomer material is made from a silicone rubber of the type HTV / HCR or a fluororubber or a fluorosilicone rubber, each with a low viscosity setting.

6. Press pad according to one of claims 1 to 5, characterized by the fact that Warp threads (13), preferably all warp threads (13), of the fabric (10) and / or weft threads (14), preferably all weft threads (14), of the fabric (10) consist of a plurality of individual wires, which are preferably interlaced with each other and / or have at least one plastic thread, preferably of an aromatic polyamide or of a melamine resin, which is preferably interlaced with the wires of the respective warp (13) and / or weft threads (14) of the fabric (10) or forms their core thread.

7. Press pad according to one of claims 1 to 6, characterized by the fact thatthermally conductive particles, in particular metal particles or quartz particles or those made of barium titanate, beryllium oxide or aluminium oxide, are embedded in the surface structure (11) of the elastomer material.

8. Method for producing a press pad (2) for use in hydraulic single- or multi-stage heating presses, the press pad (2) comprising: - a fabric (10) made of weft (14) and warp threads (13), each consisting of metal, and - an elastomeric material which is located in the spaces between the weft (14) and warp threads (13) of the fabric and preferably fills these spaces, wherein the elastomeric material is applied to the fabric (10) in a partially crosslinked form and spatially combined with it and end-crosslinked in a combined state, characterized by the fact thatThe elastomer material, which is present in a partially cross-linked form, is applied as a planar structure (11) to the fabric (10) and spatially combined with it by the action of pressure and temperature and is end-cross-linked in a combined state.

9. Method according to claim 8, characterized by the fact that the sheet structure (11) is made of the partially cross-linked elastomer material and / or the fabric (10) is present as a sheet material and that - elastomer sheet material and fabric sheet material or - elastomer sheet material and the fabric or - the sheet structure (11) made of elastomer material and fabric sheet material are spatially combined in a union zone and are end-cross-linked in a cross-linking zone, wherein preferably in a single union zone elastomer material, in particular elastomer sheet material, is introduced from two sides to the fabric (10) and into its spaces.

10. Method according to claim 8 or 9, characterized by the fact thatthe union zone and the terminal networking zone are spatially separated or spatially converge, or at least overlap spatially to a predominant extent.

11. Method according to any one of claims 8 to 10, characterized by the fact that the union zone is located in a pressure roller device (3), in particular a calender, which has at least two pressure rollers (8, 9) whose axes of rotation are aligned parallel to each other and which define between them a gap (S) running parallel to the axes of rotation, the width of which is less than a sum of the thickness of the fabric (10) and the thickness of the at least one planar structure (11) made of the elastomer material or the thicknesses of two planar structures (11) brought up to the fabric (10) on opposite sides.

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