Method and apparatus for melt impregnation of fibers with thermoplastic matrix

Abstract

In order to provide a method and a device for impregnating dry fibres with a high-viscosity thermoplastic matrix, the invention proposes that the fibres are guided on a curved perforated metal plate as an impregnation section while applying a contact pressure, in which the high-viscosity thermoplastic matrix passes through the perforations of the metal plate in order to subsequently impregnate the fibres. The metal plate is not flat, but is integrated into the impregnation unit in a curved shape. By deflecting the fiber, which may be a fiber bundle or a single fiber, about a curved metal sheet, the necessary contact pressure may be created between the fiber and the plastic feed. Therefore, the fibers move on the perforated metal plate under the action of longitudinal tensile stress, so that sinusoidal contact pressure distribution is generated between the fibers and the metal plate. A high viscosity thermoplastic matrix appears through the perforations and uniformly coats the fibers.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for melt impregnating fibers with a thermoplastic matrix. Background Art

[0002] Various methods of impregnating fibers with thermoplastic matrices are known. These can be divided into the following groups:

[0003] Powder impregnation: The fan-shaped fibers are contacted with powder (e.g. by fluidized bed or electrostatic dispersion). The powdered fibers are then guided through a heating section and consolidated into a fiber matrix semi-finished product by downstream cooling rollers. The main problem with this method is that the particle size of the powder must roughly correspond to the fiber diameter (e.g. about 6 μm for carbon fibers) to achieve good impregnation. Procuring polymers of this fineness is usually cost-prohibitive and sometimes technically impossible.

[0004] Solvent impregnation: Impregnation is achieved by reducing the viscosity of the polymer using solvents, which diffuse out of the finished semi-finished product after the impregnation process. This method is only suitable for thermoplastics such as PC, PSU, PES or PEI.

[0005] Film impregnation: Fibers and plastic films are pressed together under temperature and pressure. Here, the fiber volume content can be adjusted by varying the number and thickness of the films. This method enables very high quality impregnated fibers. However, not all plastics are commercially available or can be produced as films of any thickness, so this method has limitations in terms of applicability.

[0006] Mixed fiber technology: The reinforcing fibers are spun together with the plastic fibers into a mixed roving (also called mixed yarn or blended yarn). When processing the roving, the plastic fibers are melted and thus impregnate the reinforcing fibers. Here, similar to film impregnation, the plastic fibers must have approximately the same diameter as the reinforcing fibers, otherwise complete impregnation cannot be achieved.

[0007] Melt impregnation: The roving is pulled from a bobbin holder, unrolled and then impregnated with a molten matrix. There are various constructive solutions to liquefy the thermoplastic matrix and ultimately provide dry fibers. Here, the most important process parameters for producing high-quality fiber-matrix semi-finished products are melt viscosity and effective impregnation pressure. To ensure this function, very large systems and corresponding peripheral equipment are usually required, which increases the size of the entire system.

[0008] Therefore, current systems for impregnating fibers with thermoplastics can only be used to a limited extent in combination with other machines (for example production systems for component production), which restricts their areas of application.

[0009] All of these known melt impregnation solutions have the following disadvantages:

[0010] Process regulation: As the viscosity of the matrix increases, the impregnation process of the fibers becomes more complex. In this case, precise temperature and pressure control throughout the impregnation section is essential. In existing systems, fine layered control of the temperature and pressure conditions in the impregnation section is not possible, which negatively affects the quality of the final product (impregnated fiber semi-finished product, also called tape).

[0011] Waste: Existing methods often result in process-related waste, since continuous impregnation over the entire width is not possible. In this case, the fiber semi-finished product is impregnated over a large area in a continuous process. Edge areas with different cavity conditions and impregnation quality are usually cut off afterwards.

[0012] Structure: Conventional systems are not compact, so only limited integration of the technology into existing automation systems is possible (e.g. as an add-on to an industrial robot).

[0013] System maintenance: Cleaning the known systems usually requires great effort. For example, in the case of bath immersion, the entire system must be laboriously disassembled and cleaned. Cleaning the system during production (e.g. using cleaning pellets) is not possible.

[0014] A. Lutz and T. Harmia in "Impregnation Technology for Fiber or Filament Bundles" (Polypropylene, Volume 2, J. Karger-Kocsis, ed., Dordrecht, the Netherlands: Springer-Verlag, 1999, pp. 301-306, Doi: 10.1007 / 978-94-011-4421-6_43) propose a known system for melt impregnation, in which the fibers are guided alternately over two impregnation tools, which are made of metal foam, which is permeable to liquid plastic due to its pore structure. During the production process, the liquid plastic is injected into the core of the metal foam by an extruder and conveyed to the surface of the metal foam. Impregnation is achieved by contacting the dry fibers with the plastic-moistened metal foam. The method has achieved good results in practice. The object of the present invention is to provide a method and a device for impregnating dry fibers with a high-viscosity thermoplastic matrix. Summary of the invention

[0015] According to the method of the invention, this object is achieved by guiding the fibers over a curved perforated metal sheet as impregnation section while applying contact pressure, wherein a high-viscosity thermoplastic matrix passes through the perforations of the metal sheet in order to subsequently impregnate the fibers.

[0016] According to the method of the invention, the fibers used are any organic or inorganic fibers suitable for material reinforcement, such as carbon fibers, glass fibers or polyamide fibers.

[0017] The perforated metal sheet is not flat but integrated into the impregnation unit in a curved shape. By deflecting the fibers around the perforated, curved metal sheet, the necessary contact pressure can be generated between the fibers and the plastic feed. The fibers can be in the form of fiber bundles or individual fibers and move on the metal sheet under longitudinal tensile stress. This results in a sinusoidal contact pressure distribution between the fibers and the metal sheet. The highly viscous thermoplastic matrix emerges through the perforations and coats the fibers evenly.

[0018] The advantages of the present invention are as follows:

[0019] The material and manufacturing costs are very low (for example, the perforation of metal sheets can be done by laser drilling).

[0020] Very good quality steel plates can be purchased at low prices so that they can withstand the abrasive effects of the fibers for a long time. In addition, edge hardening can be performed to extend the service life of the metal plates.

[0021] The surface roughness of the metal sheet can be adjusted according to the corresponding fibers and process parameters to protect the fibers.

[0022] The perforation geometry can be flexibly tailored to the respective fiber-matrix combination depending on the matrix viscosity, for example with the aid of numerical flow simulations.

[0023] The bent metal sheet requires only a small amount of installation space, thus enabling a compact design of the device.

[0024] A preferred embodiment of the present invention is to determine the perforation pattern of the metal plate by numerical fluid simulation.

[0025] By coordinating the hole size, hole shape and arrangement of the perforations across the width of the metal sheet with the contact pressure, it is possible to set a precise pressure ratio when impregnating the fibers.

[0026] The object of the present invention can be achieved by the device according to the invention, wherein a bent perforated metal plate is provided as an impregnation section, over which the fibers can be guided while applying contact pressure, wherein a high-viscosity thermoplastic plastic matrix can be guided through the perforations of the metal plate in order to subsequently impregnate the fibers.

[0027] According to a preferred development of the invention, two or more metal plates are provided instead of one metal plate. These can be arranged adjacent to one another or in a stacked form.

[0028] As a result, opening contours of the plastic outlet can be realized which are otherwise not feasible from a production technology perspective or can only be realized with great effort.

[0029] A further development of the invention consists in that the metal plates consist of the same material or of different materials and / or have different rigidities and / or have different wall thicknesses.

[0030] It can be a metal plate made of the same material or a metal plate made of different materials. For example, by using metal plates made of materials of different stiffness, a sealing effect can be produced on the contact surface with the impregnation tool. In addition, the metal plates can also have different wall thicknesses.

[0031] An advantageous embodiment of the invention provides for lateral boundaries of the impregnation section.

[0032] A further development of the invention consists in that, for sealing the metal sheet to the tool, a hinge pin clamp is provided which presses the metal sheet against the carrier tool having a curved shape.

[0033] This ensures that the plastic cannot escape radially.

[0034] An advantageous embodiment of the invention provides that the center of the hinge pin clamp is milled out.

[0035] The hinge pin clamp thus simultaneously represents the lateral boundary of the impregnation section. This allows the functional integration of the fixing of the sheet metal support to the limiting of the impregnation section in one component.

[0036] It is well known that sealing polymer channels during tool manufacturing for injection molding technology is particularly difficult at high operating pressures. The present design solves this problem by applying a vertical preload on each contact surface of the impregnation device, through which the plastic can flow out. In addition, the impregnation device can be quickly disassembled and easily cleaned. Since impregnation can be carried out over the entire width of the impregnation section, no waste occurs. This allows the width of the product to be calibrated at the same time. Depending on the spreading capacity of the roving to be processed, the width of the impregnation section can be adjusted. This realizes a novel, cost-effective device for the production of fiber thermoplastic semi-finished products with adjustable parameters.

[0037] According to the invention, the carrier is designed in two parts.

[0038] In addition to securing the perforated metal sheet, the carrier tool is also used to convey the highly viscous thermoplastic matrix.

[0039] For this purpose, the carrier tool preferably comprises a substrate supply and an associated distribution channel on which the bent metal sheet is arranged.

[0040] Preferably, a discharge unit is provided at the end of the impregnation section, which is used to calibrate the thickness of the fiber matrix composite material. Thus, the thickness of the fiber matrix composite material can be adjusted. The discharge unit can circulate the matrix before it leaves the impregnation section, thereby additionally improving the impregnation performance and the surface quality.

[0041] In combination with the aforementioned lateral boundaries of the impregnation section, a closed cavity can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Exemplary embodiments of the present invention are described in more detail below with reference to the accompanying drawings.

[0043] In the attached figure:

[0044] Figure 1 A schematic diagram of the impregnation process is shown;

[0045] Figure 2 shows the production and functional principle of bent metal sheets;

[0046] Figure 3 A cross-sectional view (XY plane) of the impregnation device is shown;

[0047] Figure 4 shows a cross-sectional view (ISO view) of the impregnation device;

[0048] Figure 5 shows a cross-sectional view (YZ plane) of the impregnation device; and

[0049] Figure 6 Shown according to Figure 3 Cross-sectional view (XY plane) of an impregnation device with a discharge unit. DETAILED DESCRIPTION

[0050] Figure 1 A schematic diagram of the impregnation process is shown. The dry fiber 1 is continuously moved along the image plane direction (x direction) on the metal plate 2 (shown here in a plane form for simplicity), while the high viscosity thermoplastic matrix passes through the perforations 3 of the metal plate 2, and the fiber 1 is impregnated with the high viscosity thermoplastic matrix.

[0051] The perforations shown in the figures do not correspond to their actual size. Depending on the viscosity of the plastic matrix, the diameter of the individual perforations is between 10 and 500 μm, preferably between 15 and 300 μm and particularly preferably between 20 and 150 μm.

[0052] It is also possible to stack two or more metal plates 2 on top of each other in layers instead of one metal plate 2. This allows opening contours of the plastic outlet to be realized which are otherwise not feasible in terms of production technology.

[0053] FIG2 shows the production and functional principle of a bent metal sheet 2. First ( Figure 2a ), a flat perforated metal sheet 2 is produced, wherein the perforation pattern can be customized according to the respective application.

[0054] The opening profile on the metal plate can be circular, rectangular or any polygonal profile and can have different sizes and arrangements on the metal plate according to the sinusoidal contact pressure distribution ( Figure 2b ).

[0055] The impregnation pressure is controlled by the perforation pattern, which is preferably determined by numerical simulation of the fluid. The metal sheet 2 is then bent (eg by roller bending) into the shape of a circular arc segment ( Figure 2c ). Figure 2d Fiber impregnation is schematically shown. The fiber 1 moves on the perforated metal sheet 2 under the effect of longitudinal tensile stress, resulting in a sinusoidal contact pressure distribution between the fiber 1 and the metal sheet 2. The liquid plastic flows out of the perforations 3. By adjusting the size of the perforations 3 according to the contact pressure, the target pressure ratio when impregnating the fiber 1 can be set.

[0056] Figures 3 to 5 The impregnation device provided by the invention is shown. In order to seal the metal sheet 2 on the carrier 4, a specially developed hinge pin clamp 5 is used. It presses the metal sheet 2 against the carrier 4 and thus ensures that no plastic can flow out radially. The special feature of this solution is that the center of the hinge pin clamp 5 is also milled out and thus represents the lateral boundary of the impregnation section at the same time. This allows the functional integration from the metal sheet support to the limiting impregnation section to be achieved in one component.

[0057] The carrier tool 4 is designed in two parts and, in addition to fixing the perforated metal plate 2, is also responsible for supplying the high-viscosity thermoplastic matrix. The high-viscosity thermoplastic matrix is ​​supplied from the extruder to the carrier tool 4 via the concave profile of the matrix supply part 6 and is evenly distributed under the perforated metal plate 2 via the distribution channel 7. In addition, the carrier tool 4 is also used as a container for various sensors (such as pressure sensor 10, temperature sensor 11) for controlling the process. The dry fibers 1 are guided to the carrier tool 4 via deflection rollers 8 and then run in a semicircle on the perforated metal plate 2, whereby they are impregnated with the high-viscosity thermoplastic matrix emerging from the perforations 3 and then leave the carrier tool 4 as an impregnated fiber matrix semi-finished product 9.

[0058] like Figure 6 As shown, a discharge unit 10 is provided at the end of the impregnation section, which is used to calibrate the thickness of the fiber matrix composite material. Thus, the thickness of the fiber matrix composite material can be adjusted. The discharge unit 10 circulates the matrix before it leaves the impregnation section, thereby additionally improving the impregnation performance and surface quality.

[0059] In combination with the lateral boundaries of the impregnation section, a closed cavity can be formed.

Claims

1. A method for melt impregnating a fiber (1) with a thermoplastic matrix, characterized in that The fibers (1) are guided over a curved perforated metal sheet (2) as an impregnation section while applying contact pressure, wherein a high-viscosity thermoplastic matrix passes through the perforations (3) of the metal sheet in order to subsequently impregnate the fibers (1).

2. The method according to claim 1, characterized in that The perforation pattern of the metal plate (2) is determined by fluid numerical simulation.

3. A device for melt impregnating fibers (1) with a thermoplastic matrix, characterized in that A bent perforated metal sheet (2) is provided as an impregnation section, over which the fibers (1) can be guided while applying contact pressure, wherein a high-viscosity thermoplastic matrix can be guided through the perforations (3) of the metal sheet (2) in order to subsequently impregnate the fibers (1).

4. The device according to claim 3, characterized in that The metal plates (2) are in the form of two or more pieces.

5. The device according to claim 3, characterized in that The metal plates (2) are made of the same material or different materials and / or have different rigidities and / or different wall thicknesses.

6. The device according to any one of claims 3 to 5, characterized in that In order to seal the metal sheet (2) to the tool, a hinge pin clamp (5) is provided, which presses the metal sheet (2) against a carrier tool (4) having a curved shape.

7. The device according to claim 6, characterized in that The center of the hinge pin fixture (5) is milled out.

8. The device according to any one of claims 3 to 7, characterized in that The carrier (4) is designed in two parts.

9. The device according to any one of claims 3 to 8, characterized in that The carrier tool (4) comprises a substrate supply portion (6) and a distribution channel (7) connected to the substrate supply portion (6), and the bent metal plate (2) is arranged on the distribution channel (7).

10. The device according to any one of claims 3 to 9, characterized in that The impregnation section is provided with lateral boundaries.

11. The device according to any one of claims 3 to 10, characterized in that A discharge unit (10) is provided at the end of the impregnation section.

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