Metallic pressure equalization fabric equipped with a high-temperature resistant elastomer material

Abstract

Pressure equalization fabric or press pad for use in hydraulic single- or multi-stage heating presses, consisting of a metal fabric, part of the metal threads of which are reinforced with a high-temperature-resistant plastic thread that contributes to dimensional stability, wherein the metal fabric comprises a high-temperature-resistant, vulcanizable elastomer material, such as HTV / HCR silicone rubber, characterized in that the elastomer material is rolled onto the metal fabric and anchored in the spaces in such a way that the raised tips of the metal fabric protrude from the press pad and the elastomer material is end-cured by the application of heat.

Description

[0001] The invention relates to a pressure-equalizing fabric, also known as a press pad, for use in hydraulic single- and multi-stage heating presses, wherein a metallic fabric is equipped with an elastomer material, and the warp and / or weft threads may include high-temperature-resistant plastic threads for stabilization. During the weaving process of the metallic threads, the intersection points of the warp and weft result in direct and very rapid heat conduction from the heating plate of the press system via the press plate to the surfaces of the wood-based materials to be coated. After the weaving process of the metal fabric, these surfaces are coated with a high-temperature-resistant elastomer material by rolling, which is responsible for pressure equalization.

[0002] When coating wood-based panels with thermoset resins, so-called pressure pads are required for pressure equalization. These pads compensate for thickness tolerances in the heating plates, press plates, and coating materials. Thermoset resins, which are very pressure-sensitive during surface formation, are used to coat wood-based panels, which can consist of particleboard, HDF, MDF, or plywood. Therefore, uniform pressure must be applied across the entire surface. The coating of these wood-based panels is primarily carried out in single-stage, short-cycle presses without recooling. Short pressing times and relatively low heat loss are essential. Therefore, heat transfer from the heating plates of the presses, via the press plates, to the resin surfaces must occur relatively quickly, as short pressing times are a significant economic factor.The thermoset resins used can consist of melamine, melamine and / or urea or phenolic resin. For decorative coatings, melamine or mixed resins are predominantly used. The high-quality pulp papers, which may be printed with a design, are then impregnated with aqueous resin solutions in impregnation plants and subsequently dried. During drying, the resins begin to pre-condense, and this condensation is stopped during the subsequent cooling process. Final condensation of the resins then occurs under pressure and temperature in the presses. Unlike thermoplastics, thermoset resins are plastics that cannot be returned to their original state after final condensation. Thermoset resins cross-link spatially and irreversibly, releasing water and formaldehyde in the process.Since water and formaldehyde are released in gaseous form during crosslinking under pressure and temperature, the gas must diffuse into the paper layer and wood surface through the surface seal provided by the inserted metal press plate. If the gas bubbles remain in the resin layer, they become embedded in the resin surface and later result in surface defects in the form of white spots due to differing light reflection. Therefore, it is necessary to achieve rapid and uniform heat transfer in the initial phase. The press pad plays an important role in heat transfer and cushioning, especially in the production of flooring panels made of MDF or HDF boards with very hard surfaces. The bulk density of the HDF boards ranges from 800 to 1000 kg / m³. 3and generally possess no spring properties. It is therefore particularly important to use a compression pad with excellent resilience and rapid heat dissipation. Compression pads currently considered state-of-the-art and available on the market typically contain elastomeric and metal threads in the warp and / or weft, or they are metal fabrics impregnated with LSR elastomers (liquid elastomers). The latter are extremely problematic in their manufacture and use.

[0003] Various press pads are known from patent literature; for example, patent EP0 735 949 B1 and EP 1136 248 A1 describe a press pad in which the warp and / or weft threads comprise a silicone elastomer or a copolymer consisting of silicone rubber and fluorosilicone rubber. The warp and / or weft threads made from the aforementioned elastomer threads have a metal thread as their core.

[0004] The prior art includes a press pad from DE 20 2012 005 265 U1, which is designed as a woven fabric. It contains high-temperature-resistant elastomeric threads with a core thread in the warp and / or weft direction, which form direct thermal contact with other intersecting thermally conductive threads in the warp and / or weft direction. It is reported that, prior to crosslinking the elastomeric threads, they are equipped with thermally conductive contact threads in such a way that a significantly free, thermally conductive contact surface is formed and the threads are sufficiently firmly anchored in the elastomeric material. Since the thermally conductive contact threads are 50% embedded in the elastomeric material, only a limited amount of heat can be transferred to the resin surfaces.

[0005] Another patent specification, EP 0 713 762 A2, describes a press pad for high- and low-pressure presses, which comprises various materials. These include, for example, yarn made of aromatic polyamide with metal threads, 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.

[0006] Utility model DE 20 2007 0195 06 U1 describes a press pad for use in a laminate press. It comprises a fabric made of heat-resistant threads, wherein at least the warp (14) and / or the weft (10) comprises a core (11) consisting of several threads (15) in a sheath (13) made of an elastomeric material, and at least one or the other of the warp or weft comprises metal threads, characterized in that the threads (15) forming the core (11) are essentially parallel to each other and to the longitudinal axis of the core (11).

[0007] A press pad is reported to have a fabric containing threads made of at least a high-temperature resistant polymer material.

[0008] This is described in patent specification DE 103 37 403 A1. The special feature in this case is that the threads, which contain the polymer material, contain a gas content of at least 1%.

[0009] European patent EP 0 8427 64 A1 discloses a press pad made of a textile yarn which is intended to show an extended service life under high mechanical stress, wherein the textile yarn consists of a flame-retardant melamine resin fiber.

[0010] Patent DE 197 00 371 C1 describes a method for producing a press pad used in a hot press for manufacturing high-pressure laminates or for surface treatment of sheet-shaped pressed materials. The press pad is coated on one side with a temperature-resistant adhesive, for example, in the form of an adhesive film. This bonds the press pad to the respective heating plates. This type of fixation is intended to promote heat transfer from the heating plate to the pressed material.

[0011] Patent EP 1 300 235 B1 describes a press pad consisting of a combined wire mesh made of metal and plastic threads. A liquid silicone coating is then applied to this mesh. This coating can only be LSR silicone, as the patent further states that the silicone layer is subsequently scraped off. Scraping is only possible with LSR material and not with HTV / HCR material. The patent further states that the silicone rubber should be enriched with metal powder to increase its thermal conductivity. All additives impair the hardness of the material and negatively affect the resilience of the press pad.Furthermore, the production of such press pads is very complex in terms of process technology, and the properties of LSR silicone rubber and HTV rubber are very different, with HTV / HCR silicone rubber having significantly better properties.

[0012] All press pads listed in the patent specifications or available on the market exhibit technological weaknesses and do not meet the requirements currently placed on a press pad. These press pads show weaknesses in manufacturing technology, process engineering, and environmental requirements.

[0013] The invention is based on the objective of proposing a press pad for hydraulic single- and multi-stage heating presses, which meets the required requirements for the different coating processes of wood-based and plastic panels, such as thermal conductivity, pressure distribution, durability and resilience properties.

[0014] This problem is solved according to the invention by producing a fabric of metal threads in warp and weft and then applying an HTV / HCR silicone rubber elastomer to it, whereby the application can be done in different forms.

[0015] It has also been shown that HTV / HCR rubber exhibits significantly better properties than LSR rubber. LSR rubber requires platinum catalysis, while HTV rubber can be catalyzed with both systems: platinum catalysts and organic peroxides, which are considerably less expensive. Temperature resistance and service life are higher with HTV types due to the formation of relatively long polymer chains. Copolymers can also be formed with HTV types, for example, with fluorosilicone rubber or fluororubber, resulting in significantly improved durability. The manufacturing process in this form of the invention is technologically much simpler, less expensive, and meets the requirements for a compression pad. Compression pads manufactured with LSR rubber produce high waste rates and are more expensive to manufacture.Since the heating platen formats vary between different press systems, the resulting press pad formats also differ. This means that, to minimize changeover and cleaning times for liquid silicone coating, the width formats must be aligned with the largest pad formats. However, this results in extremely high cutting losses for smaller formats, leading to higher pad prices. Furthermore, this process is not environmentally friendly.

[0016] To avoid all the disadvantages of a liquid coating, the new development was designed so that an HTV / HCR silicone rubber or silicone copolymer coating is applied to a metallic fabric by rolling or pressing. This has the advantage that the cushion formats can be selected and produced according to the order specifications. This prevents high cutting losses and has been shown to improve heat transfer, resilience, and pressure distribution, resulting in a long service life.

[0017] The manufacturing process involves first producing a metal fabric, with the warp and weft threads made of metal threads. The metal wires can be made of copper, brass, steel, silver, aluminum, or alloys thereof. To reinforce the metal wires, the stranded wires should be reinforced with a plastic thread. Suitable high-temperature-resistant plastic threads include polyamides in the form of Nomex or Kevlar yarn, but other yarns, such as those made from melamine resin fibers, can also be used.

[0018] The advantages of HTV silicone rubber include heat resistance; it withstands extremely high temperatures, often up to 300°C or even more, without degrading. The vulcanization process increases the material's durability and makes it more resistant to wear and environmental influences. Despite its strength, HTV silicone rubber remains flexible, retains its shape and performance over time, and is resistant to many chemicals, oils, and solvents. To increase thermal conductivity, metal powders or other heat-transferring chemical compounds, such as barium titanate, beryllium oxide, silicon dioxide, or aluminum oxide, can be added to the elastomers.

[0019] The invention provides that a fabric made of metal threads is first produced, reinforced with Nomex threads. In a test sample, the warp threads were selected as six-ply copper wires, 0.20 mm thick, stranded with a Nomex yarn; the weft threads consisted of seven stranded brass wires, 0.20 mm thick. The metal fabric was first produced in a cloth weave, with a weft count of 400 / m. After the wire fabric was produced, a pre-cured, low-viscosity HTV / HCR silicone rubber, in film form of approximately 1400 g / m², was applied to a pressure roller device. 2and rolled on at a medium temperature setting. The silicone rubber completely pressed into the spaces between the metal mesh and encased the individual threads, making the surfaces of the metal wires slightly visible. Subsequent heat treatment was carried out to achieve final curing of the silicone rubber. This resulted in a compression pad with high temperature resistance, rapid heat transfer, high resilience, and uniform pressure distribution. The basis weight was subsequently 3900 to 4000 g / m². 2The production process using a heated or unheated pressure roller assembly is proposed, but other roller assemblies are also conceivable. If the pressure rollers are not heatable, subsequent heat treatment using a heat channel or heating chamber for final cross-linking is recommended. Depending on the hardener setting, the temperature can be selected between 140 and 180 °C. If faster heat transfer is desired, the wire mesh can be selected with correspondingly thicker metallic weft and / or warp threads, for example, with thicker copper threads. According to the invention, the cushions can be customized to customer specifications. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 0 735 949 B1

[0003] EP 1136 248 A1

[0003] DE 20 2012 005 265 U1

[0004] EP 0 713 762 A2

[0005] DE 20 2007 0195 06 U1

[0006] DE 103 37 403 A1

[0008] EP 0 8427 64 A1

[0009] DE 197 00 371 C1

[0010] EP 1 300 235 B1

[0011]

Claims

[1] Pressure equalization fabric or press pad for use in hydraulic single- or multi-stage heating presses, consisting of a metal fabric, some of the metal threads of which are reinforced with a high-temperature resistant plastic thread which contributes to dimensional stability, wherein the metal fabric comprises a high-temperature resistant, vulcanizable elastomer material, such as HTV / HCR silicone rubber, characterized by , that the elastomer material is rolled onto the metal mesh and anchored in the spaces in such a way that the raised tips of the metal mesh protrude from the press pad and the elastomer material is end-cured by the application of heat. [2] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer material consists of a vulcanizable silicone rubber of the HTV / HCR type with a low viscosity setting. [3] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer material consists of a vulcanizable fluorosilicone rubber with a low viscosity setting. [4] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer material consists of a vulcanizable copolymer of silicone rubber and fluorosilicone rubber. [5] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer material consists of a vulcanizable fluororubber with a low viscosity setting. [6] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer consists of a permanently elastic plastic with a continuous temperature resistance of at least 150 °C. [7] Pressure equalization fabric or compression pad according to claims 1 to 6, characterized by that the wire mesh consists of brass wires in the warp direction and copper wires with Nomex reinforcement in the weft direction. [8] Pressure equalization fabric or compression pad according to claims 1 to 6, characterized by that the wire mesh consists of steel wires and copper wires with a plastic fiber reinforcement. [9] Pressure equalization fabric or compression pad according to claims 1 to 6, characterized by that the wire mesh consists of combinations of copper, steel, brass or other metal wires with fast thermal conductivity and with plastic fiber reinforcement. [10] Pressure equalization fabric or compression pad according to claims 1 to 6, characterized by , that the wire mesh consists of metal wires with a thermal conductivity λ (J / mK) of 22 to 410 and with synthetic fiber reinforcement. [11] Pressure equalization fabric or compression pad according to claims 1 to 10, characterized by , that the elastomer material is calendered with the wire mesh on a heated or unheated printing roller device. [12] Pressure equalization fabric or compression pad according to claims 1 to 11, characterized by , that the elastomer material is end-crosslinked by the application of heat. [13] Pressure equalization fabric or compression pad according to claims 1 to 12, characterized by , that metal powder is added to the elastomer material to increase thermal conductivity. [14] Pressure equalization fabric or compression pad according to claims 1 to 12, characterized by , that chemical compounds which are thermally conductive are added to the elastomer material.