Method and device for melt impregnation of fibers with thermoplastic matrix

Abstract

Method for melt impregnation of plastic fibers (1) with a thermoplastic matrix, wherein the plastic fibers (1) are guided over a bent perforated metal sheet (2) as an impregnation section under application of a contact pressure, wherein the highly viscous, thermoplastic matrix passes through the perforations (3) of the metal sheet in order to subsequently impregnate the plastic fibers (1), characterized in that the metal sheet (2) is sealed off from a carrier tool by means of a hinge pin clamp (5) which presses the metal sheet (2) against the carrier tool (4) with a bent shape.

Description

[0001] The invention relates to a method and a device for melt impregnation of plastic fibers with a thermoplastic matrix, wherein the plastic fibers are guided over a bent, perforated metal sheet as an impregnation section under application of a contact pressure, wherein the highly viscous, thermoplastic matrix passes through the perforations of the metal sheet in order to subsequently impregnate the plastic fibers.

[0002] Numerous processes are known for impregnating plastic fibers with a thermoplastic matrix. These can be divided into the following groups. • Powder impregnation: The fanned-out fibers are brought into contact with a powder (e.g., using a fluidized bed or electrostatic dispersion). The powdered fibers are then passed through a heating section and consolidated into the fiber-matrix semi-finished product using downstream cooling rollers. The main problem with this process is that the grain size of the powder must roughly correspond to the fiber diameter to achieve good impregnation. Obtaining polymers of such fineness is usually associated with high costs and is sometimes technically impossible. • Solvent impregnation: Impregnation occurs by reducing the polymer viscosity with solvents, which diffuse out of the finished semi-finished product after the impregnation process. This process only works for thermoplastics such as PC, PSU, PES, or PEI. • Film impregnation: Fibers and plastic films are pressed together under temperature and pressure. The fiber volume content can be adjusted by varying the number and thickness of the films. This process enables very high-quality fiber impregnation. However, not every plastic is commercially available or producible as a film in any thickness, so this process has limitations regarding its applicability. • Hybrid fiber technology: The reinforcing fibers are spun together with plastic fibers into a mixed roving (also known as a mixed yarn or commingled yarn). During processing of the roving, the plastic fibers are melted, thus ensuring the impregnation of the reinforcing fibers. Similar to film impregnation, here too, it is necessary that the plastic fibers have approximately the same diameter as the reinforcing fibers, otherwise complete impregnation is not possible. • Melt impregnation: The rovings are drawn from a spool holder, spread, and then impregnated with a molten matrix. There are a variety of design solutions for liquefying the matrix and ultimately introducing it into the dry fibers. The most important process parameters for producing high-quality fiber-matrix semi-finished products are the viscosity of the melt and the applied impregnation pressure. Ensuring this functionality usually requires very large systems with corresponding peripherals, which complicates miniaturization (e.g., in the form of a compact winding head).

[0003] A. Lutz and T. Harmia, "Impregnation techniques for fiber bundles or tows," Polypropylene, Vol. 2, J. Karger-Kocsis, Ed. Dordrecht: Springer Netherlands, 1999, pp. 301-306. Doi: 10.1007 / 978-94-011-4421-6_43, describe a melt impregnation system in which the fibers are alternately passed over two impregnation tools made of a metal foam whose pore structure makes it permeable to liquid plastic. With the aid of an extruder, liquid plastic is injected into the core of the metal foam during the ongoing process and transported toward the surface of the metal foam. Impregnation occurs through contact between the dry fibers and the plastic-wetted metal foam. This process has shown promising results in practice.

[0004] From DE 197 57 881 A1 a method and a device for fiber impregnation are known, in which an impregnating agent is introduced into the interstices of the fiber material and envelops and / or impregnates the individual fibers.

[0005] US 5,798,068 A and EP 0 756 537 B1 describe a method for producing a fiber-reinforced polymer material, wherein a fiber bundle slides over an arcuate support surface and a molten or liquid polymer is injected into the bundle through a plurality of slits extending transversely to the bundle.

[0006] All these known solutions have the following disadvantages: • Process control: The fiber impregnation process becomes more complex with increasing matrix viscosity. Precise temperature and pressure control across the impregnation section is crucial. Existing systems do not allow for fine-tuned temperature and pressure control across the impregnation section. Conventional processes only allow for a constant matrix flow across the perimeter. Since the contact pressure of the fibers on the impregnation surface is sinusoidal, there can only be one position in the impregnation channel with ideal conditions for fiber impregnation. This is reflected in the quality of the final product (impregnated semi-finished tape). • Waste: The existing processes generally result in process-related waste, as impregnation cannot be achieved consistently across the entire strip width. A semi-finished fiber product is impregnated over a large area in a continuous process. Edge areas with different cavity conditions and thus different impregnation qualities are usually trimmed off afterward. • Design: Conventional systems do not allow for a compact design and therefore only a limited integration of the technology into existing automation systems (e.g. as an attachment for an industrial robot). • System maintenance: Cleaning conventional systems is usually very laborious. For example, with molten bath impregnation, the entire system must be disassembled and cleaned, which is a complex process. Cleaning during the ongoing process (e.g., using a cleaning agent) is not possible.

[0007] The invention is based on the object of creating a method and a device for impregnating dry plastic fibers with a highly viscous, thermoplastic matrix.

[0008] This object is achieved according to the invention in a generic method in that the metal sheet is sealed against a carrier tool by means of a hinge pin clamp which presses the metal sheet against the carrier tool with a curved shape.

[0009] The metal sheet is not flat, but integrated into the impregnation unit in a curved shape. By deflecting the plastic fibers, which can be in the form of bundles or individual fibers, around the curved metal sheet, the necessary contact pressure between the plastic fibers and the plastic feed is generated. The plastic fibers thus move across the perforated metal sheet under longitudinal tensile stress, creating a sinusoidal contact pressure distribution between the plastic fibers and the metal sheet. The highly viscous, thermoplastic matrix emerges through the perforations and evenly envelops the plastic fibers.

[0010] The advantages of the inventions are the following: • The material and manufacturing costs are very low (for example, the perforation of the metal sheet can be created by laser drilling). • Steel sheets can be obtained inexpensively in very high quality, allowing them to withstand the abrasive effects of the fibers for a long time. Additionally, surface hardening can be applied to extend the service life of the metal sheet. • The surface roughness of the metal sheet can be adapted to the respective fibers and process parameters in order to protect the fibers. • The perforation geometry can be flexibly adapted to the respective fiber-matrix combination depending on the matrix viscosity, for example with the help of numerical flow simulation. • The bent metal sheet requires only a small amount of space and thus enables a compact design of the device.

[0011] A preferred embodiment of the invention is that the perforation pattern of the metal sheet is determined by numerical fluid simulation.

[0012] By adjusting the hole size, hole shape and arrangement of the perforations across the width of the metal sheet depending on the contact pressure, a targeted pressure ratio can be set during the impregnation of the plastic fibers.

[0013] The object of the invention is achieved in a generic device in that a hinged bolt clamp is provided for sealing the metal sheet against a carrier tool, which presses the metal sheet against the carrier tool with a curved shape.

[0014] To seal the metal sheet against the tool, a hinged bolt clamp is provided which presses the metal sheet against a curved support tool.

[0015] This ensures that no plastic can escape radially.

[0016] According to a preferred development of the invention, two or more metal sheets are provided instead of one.

[0017] This makes it possible to create opening contours for the plastic outlet that would otherwise not be possible in terms of manufacturing technology or would only be possible with great effort.

[0018] An advantageous embodiment of the invention is that a lateral limitation of the impregnation section is provided.

[0019] By limiting the impregnation section at the sides, a closed cavity can be created.

[0020] An advantageous embodiment of the invention is that the hinge pin clamp is milled out in the middle.

[0021] The hinged bolt clamp thus simultaneously represents a lateral boundary of the impregnation section. This allows for functional integration of the sheet metal support and the boundary of the impregnation section in one component.

[0022] It is known from injection molding toolmaking that sealing polymer channels is problematic, especially at high operating pressures. This design solves this problem by applying a preload force perpendicular to each contact surface of the impregnation device through which plastic could leak. Furthermore, the impregnation device can be quickly disassembled and is easy to clean. No waste is generated, as impregnation is possible across the entire width of the impregnation zone. This allows for simultaneous width calibration of the product. The width of the impregnation zone is adjustable depending on the spreading capacity of the rovings to be processed. This creates a novel, cost-effective device for producing fiber-thermoplastic semi-finished products with adjustable parameters.

[0023] According to the invention, the carrier tool is designed in two parts.

[0024] This carrier tool serves not only to hold the perforated metal sheet but also to feed the highly viscous, thermoplastic matrix.

[0025] For this purpose, the carrier tool advantageously has a matrix feed and an associated distribution channel on which the bent metal sheet is arranged.

[0026] An embodiment of the invention is explained in more detail below with reference to drawings.

[0027] It shows Fig. 1 a schematic representation of the impregnation process, Fig. 2 the production and operation of the bent metal sheet, Fig. 3 a sectional view (XY plane) of the impregnation device, Fig. 4 a sectional view (ISO view) of the impregnation device, Fig. 5 a sectional view (YZ plane) of the impregnation device.

[0028] Fig. Figure 1a shows a schematic representation of the impregnation process. The dry fibers 1 move continuously in the direction of the image plane (x-direction) on the metal sheet 2 (shown flat here for simplification), while a highly viscous thermoplastic matrix passes through the perforations 3 of the metal sheet 2, with which the fibers 1 are impregnated.

[0029] The perforations shown do not correspond to the actual dimensions. The diameter of the individual perforations is - depending on the viscosity of the plastic matrix - between 10 and 500 µm, preferably between 15 and 300 µm, and most preferably between 20 and 150 µm.

[0030] Instead of a single metal sheet 2, two or more metal sheets 2 can be stacked on top of each other. This allows opening contours for the plastic outlet to be realized that would otherwise be impossible to achieve in terms of manufacturing technology.

[0031] Fig. 2 shows the production and operation of the bent metal sheet 2. First ( Fig. 2a) a flat perforated metal sheet 2 is produced, whereby the perforation pattern can be adapted to the respective application.

[0032] The opening contours in the metal sheet can be circular, rectangular or any polygonal contour and can have different dimensions and arrangements on the metal sheet according to the sinusoidal contact pressure distribution ( Fig. 2b).

[0033] The impregnation pressure is controlled by the perforation pattern, which is preferably determined by numerical fluid simulation. The metal sheet 2 is then bent into a circular segment ( Fig. 2c), for example by roll bending. Fig. Figure 2d shows a schematic of the fiber impregnation process. The fibers 1 move across the perforated metal sheet 2 under longitudinal tensile stress, creating a sinusoidal contact pressure distribution between the fibers 1 and the metal sheet 2. The liquid plastic flows through the perforations 3. By adjusting the dimensions of the perforations 3 depending on the contact pressure, a specific pressure ratio can be set for the impregnation of the fibers 1.

[0034] The Fig.Figures 3 to 5 show an impregnation device according to the invention. To seal the metal sheet 2 against the support tool 4, a specially developed hinged bolt clamp 5 is used. This clamp presses the metal sheet 2 against the support tool 4, thus ensuring that no plastic can escape radially. The special feature of this solution is that the hinged bolt clamp 5 is additionally milled out in the center, thus simultaneously forming the lateral boundary of the impregnation section. This allows for the functional integration of sheet metal support and the boundary of the impregnation section in a single component.

[0035] The carrier tool 4 is constructed in two parts and, in addition to holding the perforated metal sheet 2, is responsible for feeding the highly viscous, thermoplastic matrix. Through a stepped contour of the matrix feed 6, the highly viscous, thermoplastic matrix is ​​fed from an extruder to the carrier tool 4 and distributed evenly beneath the perforated metal sheet 2 via a distribution channel 7. In addition, the carrier tool 4 serves as a holder for various sensors (e.g., pressure sensor 10, temperature sensor 11) for controlling the process. The dry fibers 1 are guided onto the carrier tool 4 via a deflection roller 8, then run in a semicircle over the perforated metal sheet 2, where they are impregnated with the highly viscous, thermoplastic matrix emerging from the perforations 3, and then leave the carrier tool 4 as an impregnated fiber-matrix semi-finished product 9.

Claims

[1] A method for melt impregnation of plastic fibers (1) with a thermoplastic matrix, wherein the plastic fibers (1) are guided over a bent perforated metal sheet (2) as an impregnation section under application of a contact pressure, wherein the highly viscous, thermoplastic matrix passes through the perforations (3) of the metal sheet in order to subsequently impregnate the plastic fibers (1), characterized by that the metal sheet (2) is sealed against a carrier tool by means of a hinge pin clamp (5) which presses the metal sheet (2) against the carrier tool (4) with a curved shape. [2] Method according to claim 1, characterized by that the perforation pattern of the metal sheet (2) is determined by numerical fluid simulation. [3] Device for melt impregnation of plastic fibers (1) with a thermoplastic matrix, wherein a bent perforated metal sheet (2) is provided as an impregnation section, over which the plastic fibers (1) can be guided under application of a contact pressure, wherein the highly viscous, thermoplastic matrix can be guided through the perforations (3) of the metal sheet (2) in order to subsequently impregnate the plastic fibers (1), characterized by that for sealing the metal sheet (2) against a carrier tool, a hinged bolt clamp (5) is provided which presses the metal sheet (2) against the carrier tool (4) with a curved shape. [4] Device according to claim 3, characterized by that two or more metal sheets (2) are provided. [5] Device according to claim 3 or claim 4, characterized by that a lateral limitation of the impregnation section is provided. [6] Device according to one of claims 3 to 5, characterized bythat the hinge pin clamp (5) is milled out in the middle. [7] Device according to one of claims 3 to 6, characterized by that the carrier tool (4) is made in two parts. [8] Device according to one of claims 3 to 7, characterized by that the carrier tool (4) has a matrix feed (6) and a distribution channel (7) connected thereto, on which the bent metal sheet is arranged.

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