Press pads with threads featuring a mesh of metal threads

Abstract

The invention relates to a press pad with a fabric comprising threads of a first thread system and threads of a second thread system running perpendicular to the threads of the first thread system, wherein the threads of the first thread system and the threads of the second thread system are interwoven to form a bond, wherein at least a part of the threads of at least one of the two thread systems contains or consists of an elastomeric material at least partially, and wherein at least a part of the threads of at least the other of the two thread systems contains or consists of a metal component.In order to achieve the most uniform heat distribution over the material being pressed and rapid heat transfer through the press pad, it is proposed that the threads containing or consisting of the elastomer material, preferably all of these threads, are sheathed with a braid (6, 6', 6") of metal threads (5, 5', 5"), wherein the metal threads (5, 5', 5") forming the braid (6, 6', 6") - during pressing operation under the influence of a pressing pressure on the press pad - form at least a part of the surface of the press pad that comes into contact with a pressing plate or a heating plate.

Description

Introduction

[0001] The invention relates to a press pad with a fabric made of threads of a first thread system and threads of a second thread system running perpendicular to the threads of the first thread system, wherein the threads of the first thread system and the threads of the second thread system are interwoven to form a bond, wherein at least a part of the threads of at least one of the two thread systems contains or consists of an elastomeric material at least partially, and wherein at least a part of the threads of at least the other of the two thread systems contains or consists of a metal component. State of the art

[0002] A press pad of the aforementioned type is known, for example, from WO 2024 / 141250 A1. To increase the stability and service life of such a pad by reducing metal thread abrasion, both surfaces of the known press pad that come into contact with a press plate or heating plate during pressing operations are made exclusively of a non-metallic material. Specifically, metal threads are wound around threads made of a plastic material in such a way that the metal threads are completely embedded in the outer outline of the plastic thread or double thread (viewed in cross-section). Combined with a high thread density and a relatively strong bend in the threads running perpendicular to the threads containing the embedded metal threads, the metal threads never come into contact with either surface of the press pad.Therefore, no contact occurs between these metal threads and the metal material of the press plate or heating plate. Relative movements between the heating plate or press plate on the one hand and the press pad on the other—these relative movements are caused by the constant temperature changes during the cyclical pressing operation of such press pads—reduce metallic abrasion on the metal threads surrounding the plastic threads and thus reduce wear on the press pad. This reduction in wear comes at the cost of a comparatively poor thermal conductivity of the press pad and therefore a comparatively long cycle time when heating the material being pressed.

[0003] Press pads of the type discussed here are used in hydraulic single- or multi-stage heated presses and serve to equalize pressure within the press during the coating of various wood-based panels with decorative papers impregnated with thermoset resins. Most of these presses are so-called hydraulic single-stage presses and are referred to as short-cycle presses. These presses are operated with heated thermal oil. Depending on the type of coating and the wood-based panel, the specific pressing pressures are approximately 200 N / cm². 2 up to 1000 N / cm 2Wood-based panels, such as plywood, particleboard, MDF, or HDF, are coated with decorative synthetic resin films in these plants. These resin films consist of cross-linkable thermoset resins such as melamine, urea, or mixed resins of both mentioned above, and are highly sensitive to pressure and temperature variations during polycondensation in the presses. If the pressure and temperature distribution is not uniform, various defects appear 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.

[0004] Melamine-urea and phenolic resins belong to the thermosets, which become liquid under pressure and temperature. During this process, they release water and formaldehyde, and in combination with a controlled hardener concentration in the presses, form a solid, irreversible surface. The release products, such as water and formaldehyde, become gaseous during the pressing process and can only diffuse into the wood-based substrate or paper web, as the press plate seals the material gas-tight from above. Since the thermoset resin is initially liquid and then slowly transitions to a gel-like and finally solid state, depending on the hardener concentration and pressing temperature, the vapor diffusion process must occur in the liquid phase; otherwise, the aforementioned surface defects will result. This requires a pressing pressure higher than the vapor pressure of water, as otherwise the water vapor cannot be forced into the receptive layers.Especially in the production of flooring panels (particularly laminate flooring), which consist of MDF or HDF panels with very hard surfaces, uniform and rapid heat transfer and homogeneous pressure distribution are of particular importance. These panels have a density of 800 kg / m³. 3 and 1000 kg / m² 3 and generally possess no inherent spring effect. Many press systems exhibit large pressure and temperature differences, which is why it is particularly important that press cushions can compensate for these differences.

[0005] For some time now, compression pads have been widely used, achieving their spring and pressure distribution properties through the use of elastomeric material, particularly elastomeric threads. The elastomeric material possesses high resilience and temperature resistance. For improved weaving properties, the core of the elastomeric threads has high tensile strength to transmit tensile forces without excessive stretching. The core typically consists of metal threads or high-temperature-resistant polymer filaments. The elastomers themselves can be made of cross-linked silicone rubber, fluororubber, fluorosilicone rubber, silicone-fluorosilicone rubber blends, and various other temperature-resistant, elastic materials. In a compression pad fabric, the elastomeric threads can be arranged as warp and / or weft threads.

[0006] The state of the art includes a variety of press pads containing elastomeric material, particularly in thread form. For example, EP 0 735 949 A1 and EP 1 136 248 A1 each 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 elastomeric threads have a metal core.

[0007] EP 1 300 235 B1 describes a press pad consisting of a combined wire mesh made of metal and plastic threads. During the manufacturing process, a flowable silicone coating is applied to this mesh and then scraped off over the entire surface. This scraping process exposes the crimped areas of the metal threads to improve the thermal conductivity of the press pad. Metal powder is added to the silicone rubber used to further increase its thermal conductivity. A disadvantage of adding any additives to an elastomer material, in this case the metal powder, is the increased hardness of the material and the resulting deterioration of the press pad's resilience.

[0008] The prior art also includes a press pad described in DE 20 2012 005 265 U1, which is designed as a woven fabric. This fabric contains high-temperature-resistant elastomeric threads with a core thread, whereby the elastomeric threads can be used as warp and / or weft threads. The elastomeric threads intersect with so-called thermally conductive threads in the other thread system, thereby achieving direct thermally conductive contact on the surfaces of the press pad. The elastomeric threads are equipped with the thermally conductive contact threads before the elastomeric material is cross-linked in such a way that a free, thermally conductive contact surface of the metallic thermally conductive threads is formed, and at the same time, sufficiently firm anchoring of the thermally conductive threads in the elastomeric material is achieved. The thermally conductive threads are embedded in the elastomeric material to approximately 50% of their cross-sectional area.Due to the embedding of the heat-conducting threads, the thermal conductivity and the possibility of introducing heat into the pressed material are limited.

[0009] EP 0 713 762 A1 describes a press pad for high and low pressure presses, which, for example, contains 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.

[0010] Furthermore, DE 20 2007 019 506 U1 discloses a press pad for use in a laminate press. This pad comprises a fabric made of heat-resistant threads, wherein the warp threads and / or the weft threads each comprise a core consisting of several threads and surrounded by a sheath of an elastomeric material. The threads of the other thread system, which does not contain the elastomeric material, include metal threads to increase thermal conductivity.

[0011] EP 0 842 764 A1 describes 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.

[0012] From DE 103 37 403 A1, a compression cushion is known which in turn has a fabric containing threads that are partly made of a high-temperature-resistant polymer material. The special feature in this case is that the threads containing the polymer material contain a proportion of a gas of at least one percent, which is intended to improve the spring properties of the polymer material.

[0013] Furthermore, DE 197 00 371 C1 discloses a method for manufacturing a press pad intended for use in a hot press for producing 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 film is used to bond 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.

[0014] All of the aforementioned press pads can only partially meet the requirements of modern press systems and pressing processes. In particular, the known press pads always represent a compromise between good thermal conductivity on the one hand and good resilience, i.e., good spring action, on the other. Task

[0015] The invention is therefore based on the objective of providing a press cushion that enables both rapid heat transfer from the heating plates of a press system to the material being pressed and possesses high thermal conductivity in order to meet the requirements of extremely short cycle times. Furthermore, the press cushion should be characterized by its ability to achieve a very homogeneous pressure and temperature distribution over the material being pressed. Solution

[0016] Starting from a press pad of the type described above, this problem is solved by sheathing the threads containing or consisting of the elastomer material, preferably all of these threads, with a braid of metal threads, wherein the threads forming the braid - in the pressing operation under the influence of a pressing pressure on the press pad - form at least a part of the surface of the press pad that comes into contact with a pressing plate or a heating plate.

[0017] Braiding elastomer threads significantly increases the metallic surface area of ​​these threads, especially compared to the known combination of elastomer and metal threads, where the metal threads are simply wound helically around the outer surface of the elastomer thread. In contrast, a braid is characterized by a (regular) interlacing or entanglement of the metal threads, resulting in a much more homogeneous distribution of the metal threads on the surface of the elastomer threads than simply wrapping an elastomer thread with a single metal thread (even if, for example, the metal thread is a double thread).

[0018] The braid surrounding the elastomer thread can be made very dense if required, forming a nearly closed "shield" around it. Such braids are commonly used, for example, as shielding for data cables. Depending on the requirements for the thermal conductivity of a compression pad on the one hand, or the pad's resilience on the other, braids consisting of only two or three independent, helically wound metal threads can also be used. Further means of adjusting the desired thermal conductivity or spring properties of the compression pad include selecting a suitable braid density, which specifies the number of braids or crossings per unit length, and the diameter ratio between the elastomer threads and the surrounding metal threads. This ratio should be between 3 and 14 braids per 10 mm.Furthermore, the degree of surface coverage of the elastomer threads by the metallic mesh can be varied to influence the properties of the press pad. It is also highly advantageous if the elastomer threads, together with the metal mesh, run between the two opposing surfaces of the press pad and each form part of these surfaces, at least during pressing operations. This improves heat transfer through the press pad.

[0019] In corresponding tests, it was found that, with the aid of the press pad according to the invention, the thermal conductivity could be increased by approximately 5% to 10% compared to press pads in which the elastomer threads are merely wrapped with a helical metal thread, without noticeably impairing the spring properties of the press pad. In pressing tests, such a pad was also characterized by a particularly homogeneous pressure and temperature distribution across the surface of the material being pressed.

[0020] According to a particularly advantageous embodiment of the invention, it has proven particularly advantageous if at least a portion of the threads of at least one of the two thread systems, preferably the threads containing or consisting of the elastomer material, preferably all of these threads, each - a core thread, by means of which a predominant proportion of the tensile force acting on a thread can be transmitted, and - have a sheath enclosing the core thread, made of elastomeric material.

[0021] This significantly facilitates the weaving of the press pad fabric and makes production possible even on high-performance looms.

[0022] Further developing the invention, it is provided that the core threads consist of metal, in particular steel, preferably stainless steel, or copper or brass or bronze, or of a polymer material, in particular an aromatic polyamide or a melamine resin, wherein the aforementioned core threads are preferably composed of a plurality of individual filaments that are twisted, stranded or roped together. By means of twisting, stranding or ropeding, the bending elasticity of the core thread is significantly improved and, at the same time, a high tensile strength is achieved by means of a sufficiently large overall cross-section of the multiple core threads.

[0023] Two advantageous ways to manufacture the elastomer threads are that the thread sheath - is formed by extrusion of an elastomeric material around the core thread and preferably consists of a silicone elastomer or a fluorosilicone elastomer or a blended elastomer made of a silicone elastomer and a fluorosilicone elastomer, or - formed by wrapping or twisting the core thread with at least one sheath thread made of a polymer material, in particular an elastomer material or a high-strength polymer material, preferably an aromatic polyamide or a melamine resin.

[0024] Furthermore, it has proven particularly advantageous for the first thread system to be formed by the weft threads of the fabric and the second thread system by the warp threads of the fabric. Preferably, the fabric should be in plain weave, wire weave, twill weave, rib weave, or Panama weave.

[0025] A further development of the invention consists in the fact that at least part of the threads of only one of the two thread systems, preferably the weft threads, contain an elastomer component, preferably in the form of a thread sheath arranged around a core thread.

[0026] Suitable materials for the metal mesh include steel threads, especially stainless steel threads, and / or brass threads and / or copper threads and / or bronze threads and / or aluminum threads.

[0027] To improve the stability of the threads surrounded by the metal braid, the metal braid can lie close to the outer surface of the associated thread containing the elastomer material or be embedded in the outer surface of the associated thread containing the elastomer material. To prevent thermal conductivity from being excessively embedded in the elastomer material, the braid should be embedded to a maximum of 30% of its diameter, preferably to a maximum of 20%.

[0028] Finally, it is also provided that the number of metal threads forming the mesh, which have a different orientation in the mesh, is between 2 and 20, preferably between 3 and 10. Example of implementation

[0029] The invention is explained in more detail below with reference to threads of a press pad shown in the drawing and their incorporation into a press pad, wherein the figures of the drawing represent the following: Fig. 1: a mesh of three interwoven metal threads, Fig. 2: a mesh of six interwoven metal threads and Fig. 3: a longitudinal section through an elastomeric thread with a core thread and a braid of two interwoven metal threads.

[0030] In many press systems, differing temperature zones are sometimes observed, caused by dimensional or manufacturing tolerances in the production of the press systems, particularly their heating plates, press plates, or machine bed, including the hydraulic cylinders. More recently, however, high technological demands have been placed on the coatings of wood-based panels, making it necessary for the press pad to ensure uniform heat transfer despite the aforementioned geometric deviations within the press system.

[0031] Comparative temperature values ​​were determined in a press system using a press pad according to the invention. It was also found that the number of elastomer threads per unit length of the press pad could be significantly reduced by using the braid of metal threads compared to a known press pad, while simultaneously increasing thermal conductivity.

[0032] A compression pad according to the invention consists of weft threads 1, each with a core thread 2 made of a triple-stranded steel wire 3, each strand 0.25 mm thick. A sheath 4 is extruded onto this core thread 2, which after extrusion has an outer diameter of 1.6 mm. The extruded material consists of a copolymer of silicone rubber and fluorosilicone rubber. Subsequently, the elastomer thread produced in this way is braided on an electronically controlled braiding machine with a selectable number of metal threads, each with a thickness of 0.25 mm. The braid density, i.e., the number of braids per unit length of the braided thread, is 5 braids per inch, i.e., 5 braids per 25.4 mm length of the elastomer thread.

[0033] While according Fig. Figure 3, which shows a longitudinal section through a composite thread used as a weft thread 1, two metal threads 5" form a braid 6" and have a different course, namely offset by 180° in their periodic course to each other, the braid 6 according to Fig. 1 three metal threads 5 with different directions and the braid 6' according to Fig. 2 six metal threads 5' each with a different course.

[0034] The operating principle of a braiding machine consists in the fact that the braiding threads located on spools, in this case the metal threads 5, 5' and 5", are guided in the braiding machine by so-called bobbins. The bobbins are moved sinusoidally by so-called impellers on tracks milled into the machine bed, causing the braiding threads to interlace and form the braid 6, 6' and 6" at the so-called braiding point. By introducing a so-called standing thread running in the center of the thread thus formed, in the case of the press pad according to the invention the weft thread 1, consisting of core thread 2 and the surrounding thread sheath 4, the braid 6, 6', 6" is structurally reinforced. In all three cases according to the Fig. 1 to 3 the metal threads 5, 5', 5" which form the respective braid 6, 6', 6" lie close to the central upright thread (in the Fig. 1 and Fig.(2 not shown for the sake of simplicity). The aforementioned manufacturing process is also known as braiding or overbraiding.

[0035] In the press pad according to the invention, the threads surrounded by the braid 6, 6', 6" are used as weft threads 1. The warp threads, not shown, are made from seven brass wires, each 0.20 mm thick, twisted together. The weft threads 1 and the brass warp threads are woven together on an electronically controlled loom using a plain weave. Other weave types, such as wire weave or twill weave, are also possible. The press pad according to the invention exhibits very good cushioning properties and excellent thermal conductivity. Repeated "pressing" of the press pad, as required for press pads according to the prior art, was not necessary. The desired high thermal conductivity was achieved immediately, which is why production can be started directly after inserting the press pad into the press system.

[0036] Temperature curves were subsequently recorded during a pressing process using a test cushion. Various cushions constructed according to the prior art, which had previously been used in production, served as comparison cushions. The test cushion according to the invention showed a higher heat transfer to the material being pressed even after the press had closed, and a similarly high temperature profile at the end of the pressing time. By changing the metal threads with regard to their thickness, number of braided wires, braid density, and type of metal, the thermal conductivity can be adapted to the requirements of the respective press system or the product being manufactured. The cushion according to the invention can therefore cover an exceptionally wide range of requirements in a variety of press systems and for a wide variety of pressing tasks and can thus be described, in a sense, as a "universal cushion". Reference symbol list 1 weft thread 2 Soul Threads 3 steel wire 4 thread sheath 5, 5', 5" metal thread 6, 6', 6" braid 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] WO 2024 / 141250 A1

[0002] EP 0 735 949 A1

[0006] EP 1 136 248 A1

[0006] EP 1 300 235 B1

[0007] DE 20 2012 005 265 U1

[0008] EP 0 713 762 A1

[0009] DE 20 2007 019 506 U1

[0010] EP 0 842 764 A1

[0011] DE 103 37 403 A1

[0012] DE 197 00 371 C1

[0013]

Claims

Press pad with a fabric comprising threads of a first thread system and threads of a second thread system running perpendicular to the threads of the first thread system, wherein the threads of the first thread system and the threads of the second thread system are interwoven to form a bond, wherein at least a portion of the threads of at least one of the two thread systems contains or consists of an elastomeric material, and wherein at least a portion of the threads of at least the other of the two thread systems contains or consists of a metal component, characterized in that the threads containing or consisting of the elastomeric material, preferably all of these threads, are sheathed with a braid (6, 6', 6") of metal threads (5, 5', 5"), wherein the metal threads (5, 5', 5") forming the braid (6, 6', 6")5") - in pressing operation under the influence of a pressing pressure on the pressing pad - form at least a part of the surface of the pressing pad that comes into contact with a pressing plate or a heating plate. Press pad according to claim 1, characterized in that at least a part of the threads of at least one of the two thread systems, preferably the threads containing or consisting of the elastomer material, preferably all of these threads, each have a core thread (2) by means of which a predominant proportion of the tensile force acting on a thread can be transmitted, and a thread sheath (4) enclosing the core thread (2), which consists of elastomer material. Press pad according to claim 2, characterized in that the core threads (2) consist of metal, in particular steel, preferably stainless steel, or copper or brass or bronze, or of a polymer material, in particular an aromatic polyamide or a melamine resin, wherein the aforementioned core threads (2) are preferably composed of a plurality of individual filaments which are twisted, stranded or roped together. Press pad according to claim 2 or 3, characterized in that the sheath (4) is formed by extrusion of an elastomer material around the core thread (2) and preferably consists of a silicone elastomer or a fluorosilicone elastomer or a blended elastomer of a silicone elastomer and a fluorosilicone elastomer, or is formed by wrapping or twisting the core thread (2) with at least one sheath thread made of a polymer material, in particular an elastomer material or a high-strength polymer material, preferably an aromatic polyamide or a melamine resin. Press pad according to one of claims 1 to 4, characterized in that the first thread system is formed by weft threads (1) of the fabric and the second thread system is formed by warp threads of the fabric. Press pad according to one of claims 1 to 5, characterized in that the fabric is made in cloth weave, wire weave, twill weave, rib weave or Panama weave. Press pad according to one of claims 1 to 6, characterized in that at least a part of the threads of only one of the two thread systems, preferably the weft threads (1), contain an elastomer component, preferably in the form of a thread sheath (4) arranged around a core thread (2). Press pad according to one of claims 1 to 7, characterized in that the braid (6, 6', 6") consists of metal threads (5, 5', 5") made of steel threads, in particular stainless steel threads, and / or brass threads and / or copper threads and / or bronze threads and / or aluminium threads. Press pad according to one of claims 1 to 8, characterized in that the braid (6, 6', 6") of metal threads (5, 5', 5") lies close to the outer surface of the associated thread containing the elastomer material or is embedded in the outer surface of the associated thread containing the elastomer material. Press pad according to one of claims 1 to 9, characterized in that the number of metal threads (5, 5', 5") forming the braid (6, 6', 6"), which have a different orientation in the braid, is between 2 and 20, preferably between 3 and 10.

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