EP1386723B1 - Press pad - Google Patents

Abstract

The press cushion has a woven fabric where the warps and/or wefts comprise alternating filament types with different degrees of elasticity across their filament axes. Filaments are polymers with a resistance to high temperatures. At least two types of filament have at least one polymer for the mantle surfaces, especially an elastomer. The filament cores are of different metals and polymers. The mantles are of elastomer mixtures. The press cushion has a woven fabric where the warps and/or wefts (1) are composed of alternating filament types (2,3) with different degrees of elasticity across their filament axes. The types of filament are of polymer materials, with a resistance to high temperatures. At least two types of filament have at least one polymer for the mantle surfaces and especially an elastomer. The filament cores (4,6) are of different metals and polymers. The mantles (5,7) are of elastomer mixtures in different proportions.

Description

The invention relates to a press pad with a fabric, the warp and / or weft each having alternating yarn types with transverse to the thread axis of different elasticity.

Press pads are used in hydraulic heating presses, single or multi-day, high-pressure or other presses, for example for plastic coating or lamination of wood-based panels or in the production of printed circuit boards. The press pads lie during pressing on both sides between the pressure plates resting on the press plates and the press plates. Due to their properties, they should ensure a uniform uniform transfer of the pressing pressure with comparatively large tolerances of both the components of the presses and of the pressed material. Convex or concave distortion of the press plates due to different heat radiation or incorrect grinding of the pressed material can thus be compensated. For this purpose, the press pads must on the one hand resist as little resistance as possible to their deformation, but on the other hand have the greatest possible elastic resilience in the case of an intermittent pressure load.

In addition, press cushions must be suitable for use at temperatures above 200 ° C. and in turn enable a uniformly uniform surface and, especially when used in short-cycle presses, a rapid transfer of heat. Press pads are typically made of a fabric, which may still have a one-sided or two-sided coating depending on the purpose. Such fabrics are known in the art in a variety of designs using both metal and polymeric yarns in the thread systems, preferably with warp and weft in linen or twill weave, as well as in other weave and weave styles.

Generic press pads have in the fabric in at least one thread system two different types of yarn with different elasticity transverse to the thread axis. In the context of this document, both the compressibility transverse to the thread axis and the bending stiffness of a thread are termed this term. Both properties characterize each of the elasticity of a press pad, which is also used accordingly as a generic term for its compressibility and flexural rigidity.

Such press pads are, for example, from the brochure "press pad for short cycle presses" of Rheinische Filztuchfabrik GmbH, Stolberg / Germany under the trade name SI-NAS ^® UNIVERSAL known. The fabrics of these press pads have a chain of an aramid multifilament twisted with copper filaments, while the weft alternately consists of stranded copper filaments and an elastomer-coated textile multifilament. The combination of different threads in a thread system - here: in the weft - allows in a particularly simple way, the combination of properties of different threads and the tuning of these properties for certain applications by varying the proportions of one or the other thread type. These generic press pads are characterized by an excellent cushioning effect and high temperature resistance in conjunction with very good heat transfer, which can be even increased by increasing the proportion of copper threads and are used especially for the production of laminated floor panels in modern short-cycle floor presses.

In the highly abrasion-resistant melamine coating of high-density fiber composite panels (also: HDF, High Density Fibreboard) in one-day short-cycle presses increased demands are placed on the press pads used: With the polycondensation of aminoplast resin arise in the coating process microscopic water vapor bubbles that diffuse only slowly into the high-density fiber composite plate. In the otherwise transparent coating, these bubbles can cause visible gray haze or even porosity. This surface defect, which is known as "graying", can only be avoided by applying an especially uniform pressure to the surface of the entire surface over the entire surface. In particular, with delay of the press plates or incorrectly ground HDF plates, the resulting different compression pressures with known press pads can not or only inadequately balanced.

The DE-A-26 50 642 discloses a press pad which can alternately have aramid yarn and rubber yarn both in the warp and weft. This should be combined in the press pad, the heat-permeability of the aramid yarn and the elastic properties of the rubber yarn. The aramid threads take on the strength function whereas the rubber thread is used for improved cushioning properties.

In the US-A-6040253 discloses a press pad according to the preamble of claim 1, which should be characterized by improved press and heat conduction properties. In this case, the press pad consists of a thread system of two threads, wherein the first thread of a group of threads with a metallic portion and the second thread of a group of threads with an elastic portion can be assigned.

Finally, leave the EP 1 167 007 A1 a press pad made of a fabric with longitudinal and transverse threads, of which every second longitudinal thread is replaced by a heating wire to provide an active heating possibility of the press pad. In addition, the fabric is embedded with the heating wires in a so-called matrix of temperature-resistant elastomer.

task

The invention has for its object to propose a press pad, with the compensation of different pressing pressures compared to the known press pads is improved.

solution

The return property of a press pad or the upholstery property results from the type of fabric construction or from the padding material used. For upholstery fabrics with elastomeric threads, the elasticity of the elastomers is determined by their Shore hardness, their density and their compression set (22 h at 175 ° C).

Investigations show that the generic press pads over their entire surface have a uniform restoring property or elasticity.

Starting from the generic prior art, the object is achieved according to the invention to the effect that chain and / or weft each contain at least two types of threads with different elasticity, which types of yarn each have a coat of a high temperature resistant elastomeric material and a soul with respect to this higher tensile strength. Investigations show that the fabric of the press pad according to the invention has different Shore hardness and density and significantly improves the balance of different pressing pressures compared to the known press pads.

Under alternating in the sense of the present invention, for example, a sequence of two types of thread A and B in the manner of ... ABAB ... but also ... AABAAB- ... as well as, for example, three types of thread A, B and C sequences like ... ABCABC ...

The elastomeric material used in the threads is preferably a silicone or fluorosilicone elastomer, a blend of the aforementioned or another high temperature resistant elastomeric material. The Shore hardness of the elastomer can be adjusted to the desired value in a manner known to the person skilled in the art, for example by fillers such as quartz flour or metal oxides.

By combining different materials for the coat and the soul of a thread, the deformability can be adjusted individually and longitudinally across the thread.

The core of at least one of the threads preferably consists essentially of metal, on the one hand to ensure the heat conduction through the press pad, on the other hand its good wearability and dimensional stability. This is preferably copper, depending on the application but also brass or stainless steel used. By the sheathing of the metal-containing threads in the tissue of a press pad whose pressure on the other threads of the fabric and thus their wear is reduced in the contact points.

As an alternative or in addition to the sheathing of the metal-containing threads, threads may preferably be used in the same or in another thread system, the core of which consists essentially of polyamide. The in the WO 96/13376 Proposed use of a pure elastomer thread is hardly useful in terms of weaving technology, since loops and warping can arise from distortion of individual fibers in their longitudinal direction from the press pad. Only with a soul higher tensile strength on the one hand, the workability, on the other hand, the dimensional stability during operation guaranteed. The use of the thinnest possible polyamide core hardly influences the Shore hardness and thus the transverse elasticity of the elastomer thread that is essential during operation in comparison to a metallic core. Particularly preferred aromatic polyamide fibers are used, as sold for example by DuPont Inc. under the trade names KEVLAR ^® and NOMEX ^® . In principle, however, any other high temperature resistant fiber having sufficient tensile strength such as that sold under the tradename Basofil ^® melamine resin fiber of the Fa. BASF may be used.

A preferred embodiment comprises threads with a core of stranded or stranded fibers. At high tensile strength of such threads - especially when using non-metallic materials - can still be achieved in this way a high transverse elasticity of the press pad according to the invention. In an alternative embodiment, threads comprise a monofilament core. Thus, particularly with a metal wire, the dimensional stability of the press pad according to the invention can be ensured in a particularly advantageous manner.

Particularly preferred is an inventive, with warp and weft woven press pad whose shot has alternately a thread of different types of yarn. Alternatively, two threads of the one may each be made of a thread of a second type or almost any other numerical combinations.

embodiment

To explain the invention, an embodiment is shown in a drawing. The figure shows a section of a section transverse to the weft direction through the fabric of a press pad according to the invention wherein the warp threads are not shown.

The fabric of the press pad according to the invention has a brass strand of 7 individual wires, each with a diameter of 0.2 mm as a chain. The press pad and its fabric as such, as well as the chain are not shown. In the shot 1, the tissue alternately has a first thread 2 and a second thread 3.

The first thread 2 has a first core 4, which is stranded from symbolically indicated 8 copper wires, each with a diameter of 0.2 mm. The first core 4 is enclosed by a first jacket 5 with a diameter of 1.5 mm made of a blend elastomer of 15% fluorine silicone and 85% pure silicone rubber. The second thread 3 has a 1 mm thick second core 6 of Kevlar filament yarn with 0.168 g / m = 1680 dtex and a 1.5 mm thick second jacket 7 made of another blend elastomer with 10% fluorine silicone and 90% pure silicone rubber. The first jacket 5 has a Shore hardness of 70-75 and a total density of 2.15 g / cm ³ and is thus harder than the second jacket 7 with a Shore hardness of 70-75 and a total density of 1.38 g / cm ³ .

This press pad according to the invention shows over its surface a hydraulic padding effect, which responds to different pressing pressures and compensates accordingly. When used in a hydraulic press line even with some Heizplattenverzug a very good cushioning effect, in particular a very homogeneous pressure distribution over the press pad surface is achieved. An 8 mm thick HDF board, which is coated with an abrasion-resistant melamine resin overlay and a melamine resin decor film, shows a perfectly transparent and closed surface after removal from the press. Under the same conditions, a faulty, not uniformly closed surface with strong graying is achieved with a known prior art press pad.

Claims (5)

1. A press pad, comprising a fabric whose warp and/or weft (1) have alternating types of thread with differing elasticity transverse to the thread axis,
   characterized in that warp and/or weft each contain at least two types of thread with differing elasticity, which types of thread each have a sheath made of a high-temperature-resistant polymer material and a core having higher tensile strength than said sheath.
2. A press pad according to the preceding claim, characterized in that the core is essentially made of metal.
3. A press pad according to claim 1 or 2, characterized in that the core is essentially made of polyamide.
4. A press pad according to one of the claims 1 to 3, characterized in that the core is essentially bunched or stranded from fibers.
5. A press pad according to one of the preceding claims, characterized in that the weft alternately has a first number of threads of a first type of thread and a second number of threads of a second type of thread.

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