Pressure-equalizing fabric with fast and variable thermal conductivities for hydraulic single- and multi-stage heating presses

Abstract

Pressure equalization fabric or press pad for use in hydraulic single- or multi-stage heating presses, consisting of a fabric, characterized in that the fabric consists of a high-temperature resistant elastomer thread with a metal or a high-temperature resistant plastic core as weft or warp thread and of metal strands as weft or warp thread, wherein the elastomer thread Fig. 3 is braided with metal wires Fig. 1 and Fig. 2.

Description

[0001] The invention relates to a pressure-equalizing fabric, also known as a press pad, for use in hydraulic single- or multi-stage heating presses. This fabric is constructed with elastomeric threads, in which the weft and / or warp threads additionally feature heat-conducting threads on their surface. These heat-conducting threads can be varied as needed. The intersections with the other heat-conducting threads in the warp or weft direction, created during the weaving process, result in a direct and faster heat transfer from the heating plate, via the press plate, to the wood-based material being coated. By appropriately designing the heat-conducting threads, different temperature zones within the heating plate of the press system can also be compensated for.

[0002] Press pads are used in hydraulic single- or multi-stage heating presses and serve to equalize pressure during the coating of various wood panels with decorative papers impregnated with thermoset resins. Most of these presses are single-stage hydraulic systems and are referred to as short-cycle presses. These systems are operated with heated thermal oil; depending on the type of coating and the wood material, the specific pressing pressures range from 20 to 100 kg / cm². 2 or 200 to 1000 N / cm 2Wood-based panels such as plywood, particleboard, MDF, or HDF are coated with decorative synthetic resin films in these plants. When coated with synthetic resin films made from crosslinkable thermoset resins, such as melamine, urea, or mixed resins of both, these resins are highly sensitive to pressure and temperature variations during polycondensation in the presses. If the pressure and temperature distribution is not uniform, various defects can occur on the surfaces, such as resin foaming (also known as white spots) or opaque surfaces. Therefore, it is particularly important that the press pads ensure uniform pressure equalization and temperature transfer.

[0003] Melamine, urea, and phenolic resins belong to the thermosetting plastics, which become liquid under pressure and temperature. In the process, they release water and formaldehyde and, after a specific hardener concentration is applied, form a solid, irreversible surface in the press. The byproducts, such as water and formaldehyde, become vaporous during the pressing process and can only diffuse into the paper web and wood surfaces because the metal press plate seals the surface. Since the thermosetting resin is liquid in the initial phase and gradually transitions to a gel and then a solid state depending on the hardener concentration and pressing temperature, the vapor diffusion process must occur within the specified pressing time; otherwise, the aforementioned surface defects will result. This requires a pressing pressure that exceeds the vapor pressure of water, as otherwise the resulting water vapor cannot be forced into the receptive layers.

[0004] Especially in the production of flooring panels made from MDF or HDF boards with very hard surfaces, uniform and rapid temperature transfer and pressure distribution are of particular importance. The average density of these panels is between 800 and 1000 kg / m³. 3and generally have no inherent spring effect. Many press systems exhibit high pressure and temperature differentials, making it particularly important that a press cushion is designed to compensate for these differences. The press cushions are equipped with elastomer threads using state-of-the-art technology. These threads provide high resilience and high temperature resistance. The elastomer threads contain metal threads or high-temperature-resistant filaments at their core, which contribute to their stabilization. The elastomers can be made of cross-linked silicone rubber, fluororubber, fluorosilicone rubber, silicone and fluorosilicone rubber blends, and various other temperature-resistant, elastic materials. These elastomer threads can be configured as warp or weft threads.

[0005] Various press pads are known from patent literature; for example, patents EP 0 735 949 B1 and EP 1 136 248 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.

[0006] Patent EP 1 300 235 B1 describes a compression pad consisting of a combined wire mesh made of metal and plastic threads. A liquid silicone coating is then applied to this mesh and subsequently scraped off over the entire surface, exposing the metal threads on top for heat transfer. The patent also describes how the silicone rubber can be enriched with metal powder to increase its thermal conductivity. However, additives to the elastomer material impair the material's hardness, negatively affecting the compression pad's resilience.

[0007] The prior art also includes a 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 heat-conducting threads in the warp and / or weft direction. It should be noted that before the elastomeric threads are cross-linked, they are equipped with thermally conductive contact threads in such a way that a substantial free, heat-conducting contact area is formed and the threads are sufficiently firmly anchored in the elastomeric material. Since the heat-conducting contact threads are embedded in the elastomeric threads to a depth of 50%, only a limited amount of heat can be transferred to the resin surfaces.

[0008] Patent 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.

[0009] 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).

[0010] 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.

[0011] Another patent specification, DE 103 37 403 A1, describes a press pad comprising a fabric containing threads that consist at least partially of a high-temperature-resistant polymer material. The special feature in this case is that the threads containing the polymer material also contain a gas content of at least 1%.

[0012] Patent DE197 00 371C1 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 material. The press pad is coated on one side with a temperature-resistant adhesive, for example, in the form of an adhesive film. This adheres 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.

[0013] All press pads listed in the patent documents or other press pads available on the market were able to meet the requirements for a universal pad, which take into account the different temperature influences of a press system and the variable thermal conductivities required for resin condensation depending on the setting.

[0014] The invention is based on the objective of proposing a press pad for hydraulic single- and multi-stage heating presses that can variably meet the required thermal conductivities for the various coating processes of wood-based and plastic panels and adapt to the different conditions of the heating plates in these press systems.

[0015] This problem is solved according to the invention by producing a fabric from elastic weft or warp threads, wherein the weft or warp threads are braided with metal wires. The number of wires, the choice of metal types, the thicknesses, and the braiding density can be varied according to the required thermal conductivities. Depending on the arrangement of the elastic threads, the warp or weft threads consist of appropriately selected, stranded metal wires. The elastic threads can be made of silicone rubber, fluorosilicone rubber, mixtures of silicone rubber and fluorosilicone rubber, fluororubber, or, at low temperatures up to a maximum of 120°C, of ​​styrene-butadiene rubber (SBR), nitrile rubber (NBR), and chloroprene rubber (CR). Ethylene propylene diene monomer (EPDM) rubber can also be used up to 160°C.In practice, however, silicone rubber, fluorosilicone rubber, and copolymers of both have proven effective due to the high temperatures used in the presses. The elastomer threads are first extruded to a specific thickness of approximately 1.5 to 2.0 mm, with a core thread made of metal strands or high-temperature-resistant synthetic fibers, such as para- or meta-aramid, or even melamine resin fibers, being used for reinforcement.

[0016] In many press systems, different temperature zones are sometimes observed, or specific technological requirements are placed on the coatings of the wood-based panels. In such cases, a press pad is necessary to provide appropriate heat equalization. The press pads manufactured according to the invention can meet these requirements and thus represent a significant advancement in further development.

[0017] The described characteristics were tested on a test press pad and showed positive results. A press pad was manufactured, and comparative temperature transfer values ​​were subsequently determined in a press. It was also found that the number of weft strands of the elastomer threads could be significantly reduced with braided steel wires, while simultaneously increasing thermal conductivity. The weft thread was a copolymer of silicone rubber and fluorosilicone rubber with a core thread of triple 0.25 mm thick steel wire, extruded to a diameter of 1.6 mm. The weft thread produced in this way was then braided with six 0.25 mm thick steel wires on an electronically controlled braiding machine. The braiding density was 5 braids / inch.

[0018] The operating principle of a braiding machine is that the braiding threads, which are on spools, are guided through the machine by bobbins. The bobbins are moved in a sinusoidal motion by so-called impellers along tracks milled into the machine bed, causing the braiding threads to interlace and form the braid at the so-called braiding point. The braid is structurally reinforced by the addition of so-called standing threads, in our case elastomer threads. This process is also known as over-braiding or over-braiding.

[0019] Seven 0.20 mm thick brass wires were used as warp threads. The fabric was woven in a plain weave on an electronically controlled loom. Wire twill or loose weaves are also possible. The resulting press pad exhibited good cushioning properties and the desired thermal conductivity. Multiple pressings of the press pad were not necessary, as is common with some press pads before the desired heat transfer is achieved. This has the advantage that the press pad can be used immediately in production.

[0020] Temperature curves were subsequently recorded for this test pad during a pressing process, using various pads already in use by customers as a comparison. The test pad showed a higher heat transfer to the pressed product immediately after the press closed, compared to the other pads, and also exhibited a higher temperature profile at the end of the pressing time. By varying the thickness, number of braided wires, braid density, and type of metal, the thermal conductivity can be adjusted to meet customer requirements and suit existing press systems with varying heat distribution, thus creating a universal pad.

[0021] Further developing the invention, it is provided that the braiding threads around the elastomer thread consist of various metal wires, such as copper with a thermal conductivity of 380, MS 60 with a thermal conductivity of 113, steel with a thermal conductivity of 46, steel with 0.2% carbon with a thermal conductivity of 50, or aluminum with a thermal conductivity of 220. The individual wires can also vary in thickness, with a thickness of 0.20 mm being recommended. The number of bobbins in the braiding machine, which corresponds to the number of wires being braided, can also be selected accordingly, as can the density of the braided elastomer threads. Due to their superior compressive strength, metal threads are preferable as the core in the elastomer threads.

[0022] The invention is described in more detail below with reference to an exemplary embodiment shown in the following drawing. Fig. Figure 1 shows the braiding wires 1 that are braided around the elastomer thread. In the Fig. In 2, the braiding wires 1 are shown in a tighter braid. Fig. Figure 3 shows an elastomeric thread in cross-section 2 with the braided metal wires 1 and the core thread 3. 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

[0005] EP 1 136 248 A1

[0005] EP 1 300 235 B1

[0006] DE 20 2012 005 265 U1

[0007] EP 0 713 762 A2

[0008] DE 20 2007 0195 06 U1

[0009] EP 0 8427 64 A1

[0010] DE 103 37 403 A1

[0011] DE 197 00 371C1

[0012]

Claims

[1] Pressure equalization fabric or press pad for use in hydraulic single- or multi-stage heating presses, consisting of a fabric, characterized by that the fabric consists of a high-temperature resistant elastomeric thread with a metal or high-temperature resistant plastic core as the weft or warp thread and of metal strands as the weft or warp thread, wherein the elastomeric thread Fig. 3 with metal wires Fig. 1 and Fig. 2 is braided. [2] Pressure equalization fabric or compression pad according to claim 1, characterized by that the elastomer consists of fluororubber, silicone rubber, fluorosilicone rubber or of the copolymer of silicone rubber and fluorosilicone rubber. [3] Pressure equalization fabric or compression pad according to claims 1 and 2, characterized by that the elastomer consists of a permanently elastic plastic with a continuous temperature resistance of at least 150 °C. [4] Pressure equalization fabric or compression pad according to claims 1 to 3, characterized by that the metal wires that braid around the elastomer thread are made of steel wire. [5] Pressure equalization fabric or compression pad according to claims 1 to 3, characterized by that the metal wires that braid around the elastomer thread are made of copper wire. [6] Pressure equalization fabric or compression pad according to claims 1 to 3, characterized by that the metal wires that braid around the elastomer thread are made of brass wire. [7] Pressure equalization fabric or compression pad according to claims 1 to 3, characterized by that the metal wires that braid around the elastomer thread are made of aluminum wire. [8] Pressure equalization fabric or compression pad according to claims 1 to 7, characterized by , that the metal wires that braid around the elastomer thread consist of wires with a specific thermal conductivity of 5 to 450 W / m K. [9] Pressure equalization fabric or compression pad according to claims 1 to 7, characterized by that the metal wires that braid around the elastomer thread have a thickness of 0.05 mm to 5.00 mm. [10] Pressure equalization fabric or compression pad according to claims 1 to 8, characterized by , that the number of metal wires that braid around the elastomer consists of at least one and at most 20 threads. [11] Pressure equalization fabric or compression pad according to claims 1 to 9, characterized by , that the number of bobbins of the interlacing metal wires should consist of at least one bobbin and at most 20 bobbins. [12] Pressure equalization fabric or compression pad according to claims 1 to 9, characterized by that the braiding should amount to 1 to 999 braids per inch, depending on the diameter of the braiding wires.

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