Methods for manufacturing molded parts

Abstract

Method (10) for producing molded parts (150), each comprising a pre-pressed profile blank (151) which is provided with a surface protection film (152) on at least part of its surface, wherein the blank (151) is produced by cold pressing a mixture of fibrous materials and thermosetting binders (11), and wherein the surface protection film (152) is produced from a carrier layer impregnated with thermosetting resin (12), wherein the profile blank (151) is placed in a tool lower part (120) of a hot pressing device (100) and the surface protection film (152) is placed on the profile blank (151) (13) in order to press both together in a hot pressing operation to connect (14), wherein the surface protection film (152) Before the hot pressing process, the product has a final moisture content of 2-20 wt.%. characterized by that for the hot pressing process, the upper tool part (110) of the hot pressing device (100) is not immediately lowered onto the lower tool part (120) to close the hot pressing device (100), but rather the upper tool part (110) is first held in a partially lowered position at a distance (D1, D2) from the profile body blank (151) and the surface protection film (152) located on it for a dwell time of 1-5 seconds (14a), in order to preheat the surface protection film (152) by heat radiation from the upper tool part (110) before closing (14b) the hot pressing device (100), and that the upper part of the tool (110) is lowered hydraulically by means of a predeterminable pressure build-up in order to ultimately build up a predeterminable pressure of 220-330 bar against the profile body blank (151) located in the lower part of the tool (120) and the surface protection film (152) on it, whereby the residence time is set inversely proportional to the pressure build-up.

Description

[0001] The invention relates to a method for manufacturing molded parts, in particular molded parts comprising a pre-pressed profile body blank consisting of a mixture of fibrous materials and thermosetting binders and provided with a surface protection film at least on parts of its surface.

[0002] Molded parts of the type mentioned above are manufactured in a multi-stage process. The blank is produced by cold-pressing a mixture of fibers and thermosetting binders, and the surface protection film is made from a carrier layer impregnated with thermosetting resin. In a hot-pressing process, the blank is then bonded to the surface protection film and formed into the final shape according to the desired molded part. For this purpose, the profile blank is placed in the lower part of a hot-pressing device, and the surface protection film, which has a final moisture content of 2-20% by weight before the hot-pressing process, is applied to the profile blank.

[0003] DE 42 10 528 A1 discloses a method for producing a surface protection layer on a profile body by applying a pigmented or non-pigmented lacquer layer, in particular in the production of profile bodies pressed from a mixture of lignocellulose-containing chips and a thermosetting synthetic resin, in which a cold-pressed preform is first produced from the mixture, which is then finished by pressing under high pressure and heat input.

[0004] A method for producing molded parts is known, each comprising a pre-pressed profile body blank which is provided with a surface protection film on at least part of its surface, wherein the blank is produced by cold pressing a mixture of fibrous materials and thermosetting binders, and wherein the surface protection film is produced from a carrier layer impregnated with thermosetting resin, wherein the profile body blank is placed in a tool base of a hot pressing device and the surface protection film is applied to the profile body blank in order to join both in a hot pressing process by pressing and simultaneously supplying heat, wherein the surface protection film has a final moisture content of 2-20 wt.% when the surface protection film is applied before the hot pressing process.

[0005] Other known methods are disclosed, for example, in the following documents: EP 0 763 387 B1, US 2015 / 0 115 505 A1, US 5 178 708 A, EP 0 156 926 A1, DE 10 2013 007 532 A1 and DE 42 33 954 A1.

[0006] The applicant has developed advantageous advancements through intensive application of these methods, including the present invention.

[0007] The method according to the invention is characterized in that, for the hot pressing process, the upper part of the hot pressing device is not immediately lowered onto the lower part of the tool to close the hot pressing device, but rather the upper part of the tool is initially held in a partially lowered position for a dwell time of 1-5 seconds, spaced apart from the profile body blank and the surface protection film located on it, in order to preheat the surface protection film before closing the hot pressing device by means of heat radiation from the upper part of the tool.

[0008] Advantages of the invention: Preheating the surface protection film increases its elasticity because the resin's reactivity is stimulated without prior condensation. This allows the surface protection film to conform optimally to the contour of the profile blank. This prevents the film from tearing or breaking at the blank's steep edges. The dwell time, i.e., the time the upper part of the tool is in the partially lowered position, is set inversely proportional to the pressure build-up. With a rapid pressure build-up (high gradient), the dwell time is shortened, and vice versa. The pressure build-up is achieved via a hydraulic system of the controllable drive of the hot pressing device and is controlled accordingly. It has been found that the pressure build-up should preferably be reached within 2-10 seconds.

[0009] Particularly advantageous, preferred embodiments result from the dependent claims: Preferably, in the partially lowered position, the upper tool part is held at a minimum distance of 2 mm from the surface protection film located on the profile blank, and at a maximum distance of 50 mm from the surface protection film located on the profile blank. The upper tool part is moved and held accordingly by the controllable drive of the hot pressing device. Tests conducted by the applicant have shown that the preheating of the surface protection film, achieved primarily by thermal radiation, is particularly successful when the upper tool part is positioned at a distance of 2–50 mm.

[0010] Regarding the operating temperature of a hot pressing device that performs the process, the operating temperature of the upper tool section is preferably set to an upper temperature between 130 and 180°C; and the operating temperature of the lower tool section is preferably set to a lower temperature between 120 and 180°C. Heating of the tool is carried out by a controllable heating element of the hot pressing device, whereby it is crucial that the operating temperature of the upper tool section is always higher than that of the lower tool section. Preferably, a temperature difference of at least 10°C is maintained between the upper and lower sections, in most applications in the range of 20 to 25°C.

[0011] In many applications, a layer of resin-impregnated paper is first placed at the bottom of the tool base, and the profile blank is then placed on top of this. A crepe layer of resin-impregnated cellulose material is then applied to the profile blank, followed by the surface protection film. This creates a sandwich structure that is particularly mechanically stable, with the (bottom) layer of resin-impregnated paper acting as a mechanical counterweight to the (top) crepe layer.

[0012] The invention is illustrated by reference to the accompanying schematic drawings, which depict the following: Fig. Figure 1 shows a device usable for the inventive method for hot pressing and coating a profile body blank with a surface protection film, wherein the device (hot press) is in the open state; Fig. Figure 2 shows the device (hot press) in a state where the upper tool part is lowered onto the lower tool part to close the hot press, with the upper tool part remaining in a partially lowered position for a dwell time; Fig. Figure 3 shows a cross-sectional view of the structure of the finished molded part; and Fig. Figure 4 shows a flowchart for a method according to the invention.

[0013] The invention will now be described in detail with reference to exemplary embodiments and these drawings.

[0014] Procedure 10 (see Fig. 4) is used for the production of molded parts (see molded part 150 in Fig. 3) and includes the following sequence of steps: Step 11: A profile body blank is pre-pressed, which serves as the core (see 151 in the Fig. 1-3) and is also referred to as a pre-compressed part. Pre-compressed material is produced, for example, by cold pressing a mixture of fibrous materials and thermosetting binders, a process known per se. The applicant has developed and continuously improved a process for this purpose that has proven successful for many years. The pre-compressed part or blank is produced in one piece from a pressing compound containing chip- or fiber-shaped particles and a binder. The pressing compound can, for example, consist of comminuted lignocellulose-containing particles, such as crushed and dried wood chips, bagasse fibers, and the like, to which a thermosetting synthetic resin, such as a melamine-urea-formaldehyde or phenol-formaldehyde resin, is added. Fiber mixtures of various materials can also be used, to which appropriate, preferably organic, binders are added.To produce the blank 151, the mixture is filled into a pre-pressing tool (not shown) with a layer thickness that can be approximately three to seven times that of the finished molded part. By inserting a press ram, the mass is pre-pressed and thereby compacted almost to its final dimensions. The pre-pressed part or blank 151 produced in this way is then subsequently provided with a surface protection layer by means of hot pressing (see step 14) and cured under pressure and temperature. The surface protection layer can also serve decorative purposes and consists of a surface protection film (see 152 in ). Fig. 1-3), which is produced in step 12 from a carrier layer impregnated with thermosetting resin. The carrier layer consists, for example, of resin-impregnated paper. Step 12: This part of the process is also known per se and has been used by the applicant for years. In a plant (not shown here), the carrier film, which may contain a component reactive to the lacquer, is coated with a lacquer. For this purpose, the carrier film is uniformly coated with the lacquer in a continuous casting plant. As mentioned, the carrier film can be, for example, a paper film impregnated with melamine resin. It can also be provided with an adhesion promoter to improve the adhesion of the lacquer layer, for example, an acrylate. In the plant, the lacquer-coated carrier film is dried in a dryer, whereby it should be noted: If the lacquer is a heat-drying lacquer, then only enough heat should be supplied during drying to prevent complete condensation of the carrier film. In this case, the lacquer could be, for example,It is a polyurethane lacquer. However, UV-curing or electron-beam-curing lacquers can also be used.

[0015] To produce a particularly resistant surface protection film 152 with high weather resistance (step 12), an aqueous condensation resin is preferably used as the impregnating resin, which contains approximately 50 wt.% volatile components during coating, with the impregnated film still containing 8–20 wt.% volatile components before the coating process. The coating is preferably an aqueous system consisting of an OH-group-containing acrylic polymer, polyurethane polymer, or polyester copolymer, to which a crosslinking component has been added. This component crosslinks the coating binder and also mediates a chemical bond with the impregnating resin of the carrier film. Before being applied to the profile body, i.e., before the hot pressing process (step 14), the film is dried to a final moisture content of 2–20 wt.%, preferably 4–10 wt.%.

[0016] Steps 13 and 14 relate to the essential part of the inventive method 10 and relate to the hot pressing of the molded part 150 with the associated coating, which is carried out by the device 100 (this is not part of the invention; see below). Fig. 1-3) is executed:

[0017] Step 13: The profile body blank 151 is placed in or on the tool base 120 of the device 100; the surface protection film 152 is then placed over the blank 151 in order to be formed and cured in the subsequent hot pressing process (step 14) with the press closed under pressure (220-330 bar) and heat (approx. 130-180°C) together with the blank 151 into the final shape to the desired coated molded part 150.

[0018] Step 14: The hot pressing process essentially takes place in two steps 14a and 14b.

[0019] In step 14a, the upper tool part 110 is not fully lowered so that it comes into contact with the lower tool part 120 and the press closes. Instead, the lowering of the upper tool part 110 is temporarily stopped by the controllable drive (not shown), so that the upper tool part 110 remains in a partially lowered position for a predefinable period of approximately 1-5 seconds, preferably about 3 seconds. This situation can be described as a holding state and is described in the Fig. 2 shown: The upper tool part 110 remains in a position spaced apart from the surface protection film 152, maintaining a minimum distance D1 of 2 mm. D2 here denotes a maximum distance resulting from the profile of the blank or the upper tool part 110; it should be less than 50 mm. It is important that the upper tool part 110 and the applied film 152 do not touch when held in place, but also that the distances D1 and D2 are not too large, so that the surface protection film 152 can be preheated by heat radiation from the upper tool part 110 before the hot pressing device 100 is closed.

[0020] Step 14b: Only after the predetermined time of 1-5 seconds has elapsed is the upper tool part 110 fully lowered, thus closing the hot press. Only now does the actual hot pressing into the desired molded part take place. Here, the blank or pre-mold 151 is brought into its final shape under the influence of pressure and heat (e.g., 150-170 °C), hardened, and simultaneously encased with the surface protection film 152. Both sides of the blank can also be covered with a film, e.g., the top with a decorative film and the bottom with a neutral protective film; each film can, for example, have a thickness of approximately 0.1 to 2 mm. The blank can be pre-pressed for a wide variety of molded parts, such as window sills, balcony cladding, or tabletops, which can, for example, have a thickness of approximately 16 mm (6-25 mm) in the center and approximately 30 mm (10-40 mm) at the edges.The molded parts produced in this way (see example 150 in . Fig. 3) These are particularly well-suited for outdoor use, i.e., on balconies, terraces, squares, and in gardens, as they have proven to be highly weather-resistant. In the manufacturing process described, the blank is hot-pressed at temperatures of approximately 150-170 °C, causing the identical resins in the core and surface material to harden, resulting in a composite material that is particularly resistant to heat, moisture, and mechanical stress. The film used only fully hardens during the hot-pressing process, but the preheating in step 14a, just before the actual hot-pressing, optimally preheats it, allowing it to conform better to the profile of the blank and thus further minimizing material stresses in the surface protection layer.

[0021] The operating temperature of the upper tool part 110 should be set to an upper temperature between 130-180°C and the operating temperature of the lower tool part 120 to a lower temperature between 120-180°C, whereby a difference of at least 10°C should be maintained between the upper and lower temperatures, preferably 20-25°C.

[0022] The molded part to be produced can also be constructed in a sandwich design: For this purpose, a layer of resin-impregnated paper 154 (see below) is first placed in the lower part of the tool 120. Fig.3) is inserted, and then the profile body blank 151 is placed on top of it. A crepe layer 153 made of resin-impregnated cellulose material is then applied to the profile body blank 151, followed by the surface protection film 152. In the fully pressed state, the resin-impregnated paper layer 154 forms the bottom layer or the mechanically acting counter-layer to the crepe layer 153, which constitutes the top layer. The dimensions of the top layer and bottom layer / counter-layer depend on the contour of the profile body and the required mechanical strength of the finished molded part and primarily serve to prevent material distortion. Reference symbol list 100 hot pressing device (usable for the invention) 110 Tool top 120 Tool base 150 molded part 151 Profile body blank 152 Surface protection film 153 Crepe layer made of resin-impregnated cellulose material (top layer) 154 layers of resin-impregnated paper (underlayer or counterlayer) D1 Minimum distance between tool top and surface protection film D2 Maximum distance between tool top and surface protection film 10. Methods for manufacturing molded parts (invention) A, E Beginning or end of the procedure 11. Step sequence for pre-pressing the profile body blank 12 Steps for manufacturing the surface protection film 14 Step sequence for hot pressing the desired molded part 14a Step with holding the upper part of the tool at a distance Step 14b involves closing the press and completing the molded part.

Claims

[1] A method (10) for producing molded parts (150), each comprising a pre-pressed profile blank (151) which is provided with a surface protection film (152) on at least part of its surface, wherein the blank (151) is produced by cold pressing a mixture of fibrous materials and thermosetting binders (11), and wherein the surface protection film (152) is produced from a carrier layer impregnated with thermosetting resin (12), wherein the profile blank (151) is placed in a tool lower part (120) of a hot pressing device (100) and the surface protection film (152) is placed on the profile blank (151) (13) in order to press both together in a hot pressing operation to connect (14), wherein the surface protection film (152) before the hot pressing process, it has a final moisture content of 2-20 wt.%, characterized by , that for the hot pressing process, the upper tool part (110) of the hot pressing device (100) is not immediately lowered onto the lower tool part (120) to close the hot pressing device (100), but rather the upper tool part (110) is first held in a partially lowered position at a distance (D1, D2) from the profile body blank (151) and the surface protection film (152) located on it for a dwell time of 1-5 seconds (14a), in order to preheat the surface protection film (152) by heat radiation from the upper tool part (110) before closing (14b) the hot pressing device (100), and that the upper part of the tool (110) is lowered hydraulically by means of a predeterminable pressure build-up in order to ultimately build up a predeterminable pressure of 220-330 bar against the profile body blank (151) located in the lower part of the tool (120) and the surface protection film (152) on it, whereby the residence time is set inversely proportional to the pressure build-up. [2] Method (10) according to claim 1, characterized by , that in the partially lowered position the upper part of the tool (110) is held with a minimum distance (D1) of 2 mm to the surface protection film (152) located on the profile body blank (151) and with a maximum distance (D2) of 50 mm to the surface protection film (152) located on the profile body blank (151). [3] Method (10) according to claim 1, characterized by that the pressure build-up is achieved within 2-10 seconds. [4] Method (10) according to any of the preceding claims, characterized by, that the operating temperature of the upper part of the tool (110) is set to an upper temperature between 130-180°C and the operating temperature of the lower part of the tool (120) is set to a lower temperature between 120-180°C, maintaining a difference of at least 10°C between the upper and lower temperatures, preferably 20-25°C. [5] Method (10) according to any of the preceding claims, characterized by , that a layer of resin-impregnated paper (154) is first inserted into the lower part of the tool (120) and then the profile body blank (151) is inserted on top of it. [6] Method (10) according to any of the preceding claims, characterized by , that a crepe layer (153) made of resin-impregnated cellulose material is placed on the profile body blank (151) in the lower part of the tool (120), and then the surface protection film (152) is placed on top of it. [7] Method (10) according to claims 5 and 6, characterized by, that the crepe layer (153) together with the profile body blank (151) and the underlying layer of resin-impregnated paper (154) form a mechanically particularly stable sandwich arrangement, wherein the layer of resin-impregnated paper (154) acts as a mechanically acting counterweight to the crepe layer (153).

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