EP3374172B1 - Pressing tool designed as a press platen - Google Patents

Description

The invention relates to a press tool designed as a press plate for coating wood-based panels in hydraulic press systems.

The coated wooden tool panels are used, for example, as furniture panels or floor panels, the surfaces of which are equipped with synthetic resin films. The synthetic resin films usually consist of printed or plain-colored fine cellulose papers and are soaked in the so-called impregnation plants with the pre-condensed resins and then further condensed in a heated drying zone until they reach a certain moisture content of around 8%. The synthetic resin films consist, for example, of so-called aminoplast resins based on melamine and formaldehyde or also of mixed resins of melamine / urea and formaldehyde. These mixtures are precondensed at a certain condensation temperature and pH in a reaction vessel with an agitator until they have reached the desired viscosity and degree of crosslinking. These so-called pre-condensates are used for paper impregnation. The paper is impregnated using the impregnation process. This is followed by drying in horizontal air ducts at approx. 125 to 155 ° C. This process step initially represents another polycondensation which is interrupted after the drying zone. The synthetic resin films are initially firm and easy to transport, so that they can be processed well in the hydraulic press systems. The coating of the wood-based panels, which are formulated as MDF, HDF, chipboard or plywood, takes place in so-called hydraulic, heated press systems. The heating plates are fixed with appropriate press plates, the surfaces of which are structured or smooth with different degrees of gloss. Press pads made of elastic materials are used between the heating plates and the press plates, which serve to equalize the pressure and to compensate for the thickness tolerances of the press plates and press system. The coating material, which consists of the synthetic resin films and the wood-based panels, is run into the heated press systems, the system closes and is subjected to the required pressure. The precondensed aminoplast resins become liquid again, the condensation of the resins and thus the spatial crosslinking continues. It increases the viscosity of the resins until after a certain time they are converted into the solid and irreversible state. During this process, the surface of the resins is also formed and it takes on the exact structure and gloss level of the corresponding surface of the press plates used. According to the state of the art, metallic press plates are used, which consist of a brass material from the material group MS 64 or chrome steels according to DIN 1.4024 according to AISI 410 or DIN 1.4542 according to AISI 630. Other metallic materials cannot be used as press plates due to their purity, surface formation or their technical data. For example, the purity of the material plays a crucial role in surface processing. The chrome steels used must not have cavities so that there are no flaws in the subsequent surface treatment. The chrome steels listed are vacuum melted and therefore show a uniform and clean metal structure during the rolling process. For the production of the press plates, the rolled raw plates must first be ground in order to achieve a certain thickness tolerance. It should be as small as possible, as a rule tolerances of 0.10 to 0.15 mm are achieved. Further stages of processing are then the stake or very fine sanding in order to eliminate the sanding marks of the tolerance sanding as far as possible. A subsequent polish forms the preparation stage for the surface design. If you want to provide the surface with a structure, it can be produced according to the prior art in a chemical etching process using an etching acid consisting of FeCl ₃ . However, metal removal, which is necessary for structuring, is also possible using a laser. Solid lasers are used for this, the ablation times being very long and therefore currently uneconomical for the large sheet formats. Another theoretical method is the metal application and thus the structure application in the 3D printing process. Neither of the methods listed are currently used. Therefore, the etching method remains the currently productive method. In the chemical etching process, an etching reserve is first applied to the prepared sheet metal surface by means of screen printing, roller printing or digitally using an inkjet printhead. An older method with a photo layer that is then exposed and fixed is hardly used today. After the etching reserve has been applied, the sheet is treated accordingly with FeCl ₃ in an acid bath. The free unprinted areas are attacked by the acid without any etching reserve and metal is removed in accordance with the desired structure depth. In further process steps, the structures can be rounded or designed accordingly. The gloss level setting of the Structured sheet metal surfaces are done in a blasting process with different blasting media and blasting thicknesses, according to the desired degree of gloss.

The final processing stage is the subsequent chrome plating in order to protect the sheet metal surfaces against abrasion and to achieve a good separation effect compared to the aminoplast resins. Structure fabrication using the chemical etching process is a complex and difficult production process, since the structure depths cannot be measured, for example, during the etching process. It is therefore based on the etching time and assumes that the structure depth will then always be the same. In practice, however, it has been shown that this is not the case, because various parameters have a considerable influence on the etching speed and thus on the etching depth of the structure. Acid temperature, acid pressure during spray etching, acid concentration are all factors that influence the etching process. Another disadvantage of FeCl ₃ is that it is harmful to health, it is extremely irritating to the skin and there is a risk of serious damage to eyes.

Steel or brass sheets are difficult to fix in the press systems due to their weight, especially with the top sheets you need very high clamping pressures. High clamping pressures can also lead to tension in the sheets if they are improperly installed in the systems. Due to the weight of the sheets, there is a large sag. When the press is closed, they are forced into a horizontal position and thereby expand. A further expansion takes place under pressure since the heating plate temperature is significantly higher than the sheet temperature. If the sheets in the clamping devices, which are located outside of the heating plates, cannot expand, the known plastic sheet tensions occur. When cold, the sheets are no longer flat and therefore cannot be reconditioned and must be scrapped. When using steel sheets, it has been shown that the wear of the press pads is very unfavorable. The backs of the steel sheets have a certain roughness, since relative movements occur during the pressing process, the backs of the sheets rub over the press pads, which are equipped with soft metal threads in the form of copper or brass threads. The metal threads are necessary to transfer the heat transfer from the heating plate to the material to be pressed via the press plate. The abrasion then leads to thin metal threads that can no longer absorb the high tensile stresses within the upholstery and tear. The upholstery become unusable. The use of metallic press plates in the coating of wood-based panels is therefore unsatisfactory.

EP 0611 638 A1 discloses a pressing tool according to the preamble of claim 1.

The invention is therefore based on the object of specifying an improved press tool designed as a press plate.

The object of the invention is achieved by a pressing tool for coating wood-based panels in hydraulic heating presses with the features of claim 1.

Polyether ether ketones are relatively light and more convenient to handle. There are several processes available for structuring that are healthier and more reliable, and which can thus eliminate the negative properties of the metal press plates. Surprisingly, the PEEK sheets showed high strength despite a much lower density of 1.31 kg / dm ³ and PEEK with 30% CA of 1.41 kg / dm ³ . A steel sheet of quality DIN 1.4542 or AISI 630 shows a density of 7.8 kg / dm ³ . This means a press plate of the format 6200 × 2400 mm in 5 mm thickness results in a total weight of approx. 580 kg, whereas a PEEK plate of the same size weighs only 97 kg or a PEEK plate with 30% CA 105 kg. You can see that the steel sheet is almost 6 times heavier than a plastic sheet. Therefore, the plastic sheets can be mechanically fixed much easier in the press system and do not lead to the described problems that can occur with the metal press sheets. But it is also possible to fix the plastic sheets in the press system directly with the press pads using a chemical mechanism. Due to the low sag of the sheets and the favorable friction factor, the press pads, especially their metal threads, are protected against abrasion and thus extends the life of the upholstery. Various production processes are available for structuring the surfaces of plastic sheets. Since they are not treated with etching media such as FeCl ₃ , the methods are environmentally friendly and not dangerous to health. One type of structuring is the fused deposition modeling FDM method, also known as fused filament fabrication FFF. In the melt-layer process, a grid of dots is first applied to a surface, similar to a normal printer, the dots being liquefied by heating a wire-shaped plastic, applied by extrusion using a nozzle, and then hardened by cooling to the desired one Position in a grid of the working plane. The structure of the structure is usually done by repeating one working level line by line and then shifting the working level upwards in a stack so that a structure is created in layers. Depending on the desired structure depth, the layer thicknesses are between 25 and 1250 µm. The data transfer is done using CAD technology.

The press plate is made of polyether ether ketone PEEK with at least 10 to 50% with a carbon fiber or with at least 10 to 50% of a graphite powder or with at least 10 to 50% of a thermally conductive material.

In one embodiment, not part of the invention, the press plate can consist of a polyimide PI, a polyamideimide PAI, a polyether ketone PEK, a polyether ketone ether ketone ketone PEKEKK, a polyphenylene sulfide PPS, a polyaryl ether ketone PAEK, a polybenzimidazole PBI or a liquid cristal polymer LCP.

Another technology of structure production is offered by laser technology. In contrast to the production of metallic pressed sheet metal, a CO ₂ laser can be used with the PEEK sheet, which has significantly longer ablation times than with metal removal. When it comes to metal sheet production, according to EP 2 289 708 B1 structuring by means of a laser is proposed, the laser being a pulsed fiber laser. In practice, however, it has been shown that the removal rate is very low with the pulsed fiber laser. Like every laser, the CO ₂ laser is based on the fact that a so-called laser-active medium, in this case carbon dioxide CO ₂ , is pumped by external energy supply. Atomic processes then take place in the medium itself, which take advantage of a complex device structure ultimately cause a chain reaction and thus the emission of laser light. The CO ₂ laser is also known as a gas laser. With the gas laser, it is much easier to realize a larger volume of the laser-active material than, for example, with the fixed laser, simply by dimensioning the container large enough and allowing a corresponding amount of gas to flow in. The volume has a direct influence on the achievable intensity of the laser, which means that high powers can also be achieved. The CO ₂ laser has a long wavelength, which is why it is well absorbed by plastics, while metal surfaces reflect stronger and therefore the removal is less. A power of 200 to 300 watts is sufficient for plastics to achieve good removal rates. By creating digitized data of a 3-D topography of a previously removed structure, the laser is controlled in an x- and a γ-coordinate, the depth determines the z-coordinate of the 3-D topography perpendicular to the surface structure.

Another structure production variant is die pressing. In contrast to metals, structures can be produced by the action of temperature and pressure. First, a negative structure is used in a steel sheet that serves as a master sample. This master sample serves as a structure generator for all other plastic press plates. Under pressure and temperature that is below the melting point of the plastic, but still above the softening point, the negative structure is embossed into the plastic sheet and thus receives a positive structure. The press material is cooled under pressure until it is just below the softening point of the plastic used and then the press material is removed.

Reproducible structures can be produced using this method. Contrary to the structure production with metallic press plates in the chemical etching process, these structures are all identical and show no deviations. In this way, it is possible to manufacture a structure that is reliable and does not pose a health risk. After structuring, the sheet metal surfaces can also be further processed as with the metallic press sheets. The level of gloss is adjusted using blasting media at a specific jet pressure, depending on the desired level of gloss. The plastic sheets can also be chrome-plated to protect the surfaces, but it is advisable to apply a Cu layer beforehand. This can be done, for example, by reductive copper plating for plastics, or the electroless copper plating of plastics is also used the products Baymetec and Baycoflex. After the copper plating, the usual chrome plating can be carried out in galvanic baths. It has been shown in the tests that not every plastic is suitable for the use of press plates in hydraulic heating presses for plastic coating. The softening point of the plastics must be far above the processing temperature that prevails in the heating presses. This is usually between 190 and 220 ° C. The plastic polyetheretherketone PEEK with an enrichment of approx. 30% carbon fiber or graphite has surprisingly been well suited for the production of press plates. Although plastics have poorer thermal conductivity than metals, these differences could be largely compensated for by an enrichment of carbon fiber or graphite powder. Furthermore, due to their lightness, the plastic sheets show a better and closer fixation to the heating plates, so that the heat loss that occurs with the metallic press sheets due to the large sag does not take place here. These advantages also compensate for the different thermal coefficients.

The different degrees of gloss can also be achieved by different coatings of the surface of the press plate made of a high-temperature-resistant plastic of provenance polyether ether ketone, similar to that in EP 2 060 658 B1 described.

An embodiment of the invention is shown in the attached schematic figure, which shows a press tool designed as a press plate 1.

The press plate 1 consists of a high-temperature-resistant polyether ether ketone plastic and comprises a surface 2 which is structured or smooth with different degrees of gloss.

In the case of the present exemplary embodiment, the press plate 1 is enriched with at least 10 to 50% of a carbon fiber or with at least 10 to 50% of a graphite powder or with at least 10 to 50% of a thermally conductive material.

The press plate 1 can consist, for example, of a polyimide, a polyamideimide, a polyether ketone, a polyether ketone ether ketone ketone, a polyphenylene sulfide, a polyaryl ether ketone, a polybenzimidazole, or a Liquid Cristal Polymer LCP.

The structuring of the surface 2 of the press plate 1 was produced in the case of the present exemplary embodiment by means of a CO ₂ laser 3. In particular, digitized data of a 3-D topography of a previously removed structure assigned to the structuring of the surface 2 were used for controlling the X, Y and Z coordinates of the CO ₂ laser 3.

The structuring of the surface 2 of the press plate 3 can also be carried out by means of a die pressing or produced using the fused deposition modeling method.

Claims (4)

1. A pressing tool for coating wood panels in hydraulic heating presses, which is designed as a pressing plate (1) made from a high-temperature resistant plastic material of polyether ether ketone PEEK provenience and the surface (2) of which is structured or smooth with different degrees of gloss, characterized in that the pressing plate (1) made from polyether ether ketone PEEK is reinforced with at least 10 to 50% of a carbon fiber or with at least 10 to 50% of a graphite powder or with at least 10 to 50% of a thermally conductive material.
2. The pressing tool according to claim 1, wherein the structuring of the surface (2) of the pressing plate (1) is applied by means of a die pressing operation.
3. The pressing tool according to claim 1, wherein the structuring of the surface (2) of the pressing plate (1) is produced according to the fused deposition modeling FDM method.
4. The pressing tool according to claim 1, wherein the structuring of the surface (2) of the pressing plate (1) is produced by means of a CO₂ laser (3) and digitalized data of a 3D topography of a previously recorded structure assigned to the structuring of the surface (2) is used for controlling X-, Y- and Z-coordinates of the CO₂ laser (3).

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