Method for producing a consolidated sandwich composite

Abstract

The invention relates to a method for producing a consolidated sandwich composite (10), made from at least one core layer (16) and at least one first cover layer (14) and a second cover layer (18) different from the first cover layer (14), comprising the process steps of: providing the sandwich composite (10) in the form of a semi-finished product, made from the core layer (16) and the cover layers (14, 18); heating the sandwich composite (10) in a contact heating press using controllable pressure and / or controllable temperature;and consolidating the cover layers (14, 18) by heating and / or applying pressure, wherein a further layer (20) is applied to the first cover layer (14), and the cover layers (14, 18) are consolidated asymmetrically by introducing a time offset (D) and / or a temperature offset (C) during the heating process, wherein the second cover layer (18) is consolidated more strongly and / or earlier than the first cover layer (14). The invention further relates to a manufacturing system.

Description

[0001] The invention relates to a method for producing a consolidated sandwich composite according to the preamble of claim 1.

[0002] German patent application DE 10 2016 015 465 A1 discloses a method for manufacturing a sandwich component in which a closed-cell foam core is combined with thermoplastic or fiber-reinforced cover layers to create a lightweight, rigid composite.

[0003] DE 10 2015 119 401 A1 discloses the following: A method for manufacturing a sandwich component is presented and described, wherein a sandwich semi-finished product with a first and a second cover layer semi-finished product layer made of a long fiber reinforced pressing compound with a thermoset matrix and between these a core layer semi-finished product layer is extruded in a pressing device.The task of providing a process in which the surface layer semi-finished product layers and the core layer semi-finished product layer can be processed in a single pressing step and in which the greatest possible variety of compositions of the surface layer semi-finished product layers can be processed, is solved by the pressing device having a spacer which, in the closed position, defines the minimum distance between the first and the second tool part, and by the spacer being set such that the pressing pressure in the closed position lies between a minimum processing pressure of the first and / or the second surface layer semi-finished product layer and a maximum permissible limit pressure for the core layer semi-finished product layer.

[0004] DE 2621534 A1 relates to a heat and sound insulating corrugated cardboard panel and to a method for manufacturing such a panel. A method for manufacturing the new panel is disclosed, wherein a flat composite panel is created by forming a thin layer of thermoplastic resin between a sheet of a corrugated paper part and a sheet of a flat paper top, wherein one side of the corrugated paper part is covered by the paper top by the layer of thermoplastic resin adhering both to the respective apex regions of the parallel rib of the corrugated paper part and to the inner surface of the paper top, wherein the composite panel is formed into a desired shape under pressure at a temperature above the softening point of the thermoplastic resin, and wherein the temperature is lowered to cure the thermoplastic layer in the formed panel.

[0005] The object of the invention is to enable targeted material compaction of the cover layers in sandwich composites and thereby increase the flexural stiffness and moisture resistance.

[0006] This problem is solved by means of a method having the features of claim 1. Furthermore, advantageous embodiments of the invention are described by the dependent claims, the following description and the figures.

[0007] A first aspect of the invention relates to a method for producing a consolidated sandwich composite. This sandwich composite comprises a core layer, for example made of closed-cell foam, and in particular two face sheets, which consist, for example, of thermoplastic and / or fiber-reinforced materials. Furthermore, it would be possible to arrange additional face sheets. Production is carried out, in particular, via a semi-finished product that is first treated in a contact heating press under pressure and / or temperature. During this process, the face sheets are compacted by the action of pressure and / or heat. The technical bond between the core and the face sheets thus occurs during consolidation and as a material bond between the foam core and the fibers, in particular the melt fiber and the reinforcing fiber, in which, in particular, air or...Consolidation reduces the air content in the material, thereby creating a homogeneous bond between the layers. It describes, in particular, the ratio of air to fibers in a given volume. Increased consolidation displaces air, resulting in a thinner surface layer and an increased modulus of elasticity. Consequently, for the same component height, the stiffness provided by the surface layers increases.

[0008] To solve the problem of the invention and thus selectively control the material compaction, the invention provides that a further layer (e.g., a decorative layer) is applied to the first top layer, and that the top layers are consolidated asymmetrically. This is necessary to compensate for the uneven mass distribution resulting from, for example, a decorative application or the arrangement of a decorative layer. Furthermore, this is achieved by selectively generating a time and / or temperature offset in the tempering process, the heating process, or the manufacturing process.

[0009] In particular, when the additional layer (decorative layer) is placed on top of the upper first cover layer, the lower second cover layer (e.g., a nonwoven fabric) is consolidated more strongly and / or earlier than the upper first cover layer during the process by controlling the temperature and / or time. The reverse could also be true. This is due to a compensation of the shift of the neutral fiber in the core towards the second cover layer caused by the additional layer (decorative layer). This compensation allows the shift of the neutral fiber back towards the first cover layer. This asymmetrical treatment thus makes it possible to close open foam cells in the core layers and reduce moisture absorption. Technically, this is achieved through essentially precise control of the temperature parameters and / or exposure times, which is provided by the contact heating press.

[0010] In an advantageous embodiment of the invention, the asymmetric consolidation minimizes air content in the second top layer. This particularly improves material density and reduces the risk of material weaknesses.

[0011] In a further advantageous embodiment of the invention, a decorative layer is applied to the upper first face sheet as an additional layer. This layer aesthetically enhances the sandwich composite and also improves mechanical properties such as flexural stiffness. The layer opposite the decorative layer (lower face sheet) is thus selectively densified more strongly through the asymmetric consolidation process. This consolidation of the lower face sheet serves to compensate for the displacement of the neutral axis caused by the decorative layer. The increased density of the lower face sheet improves the load distribution within the sandwich composite, thereby restoring the mechanical properties, particularly the flexural stiffness. This additional layer, or decorative layer, is specifically not heated to prevent its thermal degradation.

[0012] In a further advantageous embodiment of the invention, the asymmetric consolidation leads to a reduction in the air content and / or the sealing of open foam cells in the core layer, thereby increasing the service life of the sandwich composite and improving its moisture resistance.

[0013] In a further advantageous embodiment of the invention, the material density of the second lower cover layer is controlled to a range of, in particular, 90% to 95% of the maximum density. This ensures a more precise adjustment of the mechanical load-bearing capacity.

[0014] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0015] This shows: Fig. 1 a cross-section of an ideal structure of a sandwich composite according to the state of the art; Fig. 2 a cross-section of the sandwich composite to show the effects of a decorative layer of the sandwich composite and to illustrate the resulting displacement; Fig. 3 a cross-section of the sandwich composite in a displacement process through asymmetric consolidation; Fig. 4. A diagram showing the structure of bicomponent fibers; Fig. 5 a diagram to illustrate a temperature offset during a heating process; and Fig. 6 another diagram showing a time offset in the heating process.

[0016] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0017] Fig. Figure 1 shows a schematic diagram of an ideal sandwich composite 10 with a centrally located neutral fiber 12. The sandwich composite 10 consists of an upper face sheet 14, a core layer 16, and a lower face sheet 18. The face sheets 14 and 18 are held apart by the core layer 16 to maximize the flexural stiffness of the sandwich composite 10. The neutral fiber 12 runs through the center of the core layer 16, thus distributing the mechanical load evenly. This corresponds to the theoretical ideal state without a decorative layer or asymmetric consolidation and therefore represents the state of the art.

[0018] Fig. Figure 2 shows a schematic structure of a sandwich composite 10 with a similar structure to that in Fig. 1, consisting of an upper cover layer 14, a core layer 16 and a lower cover layer 18. In contrast to Fig. However, a decorative layer 20 is applied to the upper cover layer 14.

[0019] The additional decorative layer 20 alters the weight distribution and causes the neutral fiber 12 to shift upwards from the center of the core layer 16. This shift is represented by arrow A and means that the mechanical strength of the sandwich composite 10 can no longer be optimally utilized, leading to an unbalanced stress distribution, particularly during bending.

[0020] Accordingly, it is now planned to compensate for the uneven mass distribution resulting from the decorative application or arrangement of the decorative layer 20. In the Fig. Figure 2 shows the neutral fiber 12, which is not located centrally between the cover layers 14 and 16. The plan is therefore to compensate for this neutral fiber 12 and thus correct the displacement.

[0021] Only asymmetric consolidation makes possible the in Fig. 3. The neutral fiber 12 is shifted back to the center of the support, thereby improving the mechanical properties. Fig. 3 shows the one in Fig. Figure 2 shows a sandwich composite 10, in which the neutral fiber 12 is shifted back towards the center of the core layer 16 by an asymmetric consolidation process. This shift is indicated by arrow B. This process is enabled by a time and / or temperature offset in the contact heating press 22. As a result, the lower face layer 18 is consolidated more strongly and / or earlier than the upper face layer 14. The asymmetric consolidation process minimizes air content in the lower face layer 18, seals open foam cells in the core layer 16, and thereby increases moisture resistance.

[0022] This improves, for example, the mechanical properties of the sandwich composite 10 and ensures or enables an improved distribution of the load. This is made possible by a method according to the invention, which achieves the asymmetric consolidation of the face layers 14, 18 by selectively controlling pressure and temperature.

[0023] Fig. Figure 4 shows the detailed structure of the bicomponent fibers 24 used in the cover layers 14, 18. Each bicomponent fiber 24 consists of a core 26 and a sheath 28. The core 26 is a reinforcing fiber, for example made of glass fibers or natural fibers, which provides the mechanical stability of the cover layers 14, 18. The sheath 28 consists of a low-melting-point thermoplastic, for example polypropylene or CoPES, which melts during the consolidation process in the contact heating press 22 and creates a metallurgical bond between the fibers and with the core layer 16. This bond contributes to increasing the strength and minimizing material defects.

[0024] In other words, it shows Fig. 4 the detailed structure of the bicomponent fibers 24, which are used in the face sheets 14, 18 of the sandwich composite 10. The carrier, designed as a sandwich composite, consists of the face sheet and core sheet, as shown in Fig. Figure 1 shows the basic structure of the layers. This structure is known from the prior art.

[0025] In summary, this results in a structure in which a needle-punched nonwoven fabric forms the cover layers 14 and 18 of the composite. This needle-punched nonwoven fabric consists of a combination of low-melting thermoplastic fibers, for example polypropylene (PP), CoPES, or PET-G, with a melting point of approximately 140 °C to 200 °C, and reinforcing fibers, such as natural fibers, glass fibers, or thermoplastic fibers with a melting point above that of the low-melting fibers.

[0026] During the heating and subsequent shaping process in the manufacturing process, a fiber composite forms in the surface layers 14, 18. This composite consists of reinforcing fibers embedded in a matrix of low-melting thermoplastics, thereby simultaneously creating a material-bonded connection to the foam core or core layer 16. The fibers used can be either a mixture of low-melting fibers and reinforcing fibers or fully formed bicomponent fibers 24. In bicomponent fibers 24, the low-melting component encases the core 26 of the reinforcing fiber, enabling a particularly effective bond within the surface layers.

[0027] After calendering, the nonwoven fabric is consolidated either by mechanical needling or by adhesion resulting from thermal action. The nonwoven fabric has a basis weight of between 200 g / m². 2 and 800 g / m² 2used to ensure the necessary stability and connection to the foam core 16.

[0028] Fig. 5 and Fig. Figure 6 shows schematic diagrams to illustrate the processes during the asymmetric consolidation of the sandwich composite 10. The axes of the graphs represent the temporal and thermal profiles during processing that are responsible for the consolidation of the cover layers 14, 18.

[0029] In Fig. Figure 5 shows time t (in seconds) on the horizontal axis and temperature T (in °C) on the vertical axis. The curve for the upper cover layer 14 and the lower cover layer 18 illustrates the differences in heating rates. While the upper cover layer 14 heats up more slowly, the lower cover layer 18 is heated to a higher temperature more quickly. This temperature difference C causes the lower cover layer 18 to consolidate earlier and more effectively.

[0030] Fig.Figure 6 also shows the time t (in seconds) on the horizontal axis, while the vertical axis shows the temperature T (in °C). This illustrates a time offset D during the process. The curve for the lower top layer 18 begins the heating process earlier, meaning that the lower top layer 18 has already reached a higher temperature than the upper top layer 14 when the contact heating press 22 is closed. This time shift, or time offset D, enables targeted, earlier consolidation of the lower top layer 18 and influences the consolidation process asymmetrically.

[0031] In addition, the graphics illustrate a possible adaptability of the inventive method, in which different consolidation profiles can be generated by varying the heating rate or the pressure applied in the contact heating press 22. The asymmetric consolidation is made possible by the inventive method and ensures that the neutral fiber 12 is displaced back towards the center of the core layer 16. This improves the mechanical properties of the sandwich composite 10.

[0032] In summary, the invention proposes a process for producing an asymmetrically consolidated sandwich composite to compensate for the neutral fiber when applying a decorative layer to increase the mechanical properties.

Claims

[1] Method for producing a consolidated sandwich composite (10) made from at least one core layer (16) and at least one first face layer (14) and a second face layer (18) different from the first face layer (14), comprising the process steps: - Providing the sandwich composite (10) in the form of a semi-finished product, made from the core layer (16) and the cover layers (14, 18); - Heating the sandwich composite (10) in a contact heating press using controllable pressure and / or controllable temperature; and - Consolidation of the surface layers (14, 18) by heating and / or pressure; characterized by, that a further layer (20) is applied to the first cover layer (14), and the cover layers (14, 18) are consolidated asymmetrically by generating a time offset (D) and / or a temperature offset (C) within the heating process, wherein the second cover layer (18) is consolidated more strongly and / or earlier than the first cover layer (14), and wherein a displacement of the neutral fiber (12) caused by the further layer (20) is compensated for by the asymmetric consolidation process. [2] Method according to claim 1, characterized by , that to compact the second cover layer (18), air content in the second cover layer (18) is specifically minimized by asymmetric consolidation. [3] Method according to claim 1 or 2, characterized by , that a decorative layer (20) is applied as the further layer (20) to the first cover layer (14) of the sandwich composite (10). [4] Method according to any one of the preceding claims, characterized by , that through asymmetric consolidation the second cover layer (18) is shaped in such a way that opened foam cells of the core layer (16) are closed again during the process. [5] Method according to any one of the preceding claims, characterized by , that the asymmetric consolidation is controlled such that the material density of the second cover layer (18) is in a range of, in particular, 70% to 95% of the maximum density.

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