DE102015200875A1 - Process for producing a natural fiber-reinforced plastic component - Google Patents

Abstract

The invention relates to a method for producing a natural-fiber-reinforced plastic component (1), in which at least one semi-finished fiber product (7) made of natural and synthetic fibers (3, 9) is provided, in a heating step the semifinished fiber product (7) above the melting temperature of the synthetic fibers ( 9) is heated, and then in a press-forming step, the heated semifinished fiber product (7) is formed to the plastic component (1) in which the natural fibers (3) are embedded in a plastic matrix (5) formed by the plastic fibers (9). According to the invention, prior to carrying out the heating step, thermoplastic hollow spheres (11) which expand when heated to form a foam structure are combined with a carrier substrate (21). The carrier substrate (21) is then integrated together with the thermoplastic hollow spheres (11) in the semifinished fiber product (7).

Description

The invention relates to a method for producing a natural fiber reinforced plastic component according to the preamble of claim 1 and a semi-finished fiber product according to claim 10.

Natural fiber reinforced plastic components are produced in common practice from a semi-finished fiber made of natural and synthetic fibers. The semi-finished fiber product is first heated in a two-stage compression molding process in a hot press and then pressed in an unheated molding press in the tool-bound form to the plastic component. As a result of the heat, the plastic fibers, for example of polypropylene, melt to form a plastic matrix in which the natural fibers are embedded for reinforcement. From the DE 198 34 048 A1 Such a generic plastic component is known.

A reduction of the component weight of the natural fiber reinforced plastic component can be achieved by the substitution of natural fiber components by foam structures. The foaming agent can be introduced in a wet method as a liquid into the natural fiber mat, that is to say in the semi-finished fiber product consisting of natural and synthetic fibers. A major disadvantage of such a wet process is that the liquid must be dried out of the natural fiber mat following the introduction process.

The object of the invention is to provide a natural-fiber-reinforced plastic component which has a reduced component weight when compared to the prior art constant component stiffness and process technology is easy to produce.

The object is solved by the features of claim 1, 9 or 10. Preferred embodiments of the invention are disclosed in the subclaims.

According to the characterizing part of patent claim 1, prior to carrying out a heating step in which the semifinished fiber product is heated above the melting temperature of the plastic fibers contained therein, thermoplastic hollow spheres are integrated with a propellant gas encapsulated therein in a diffusion-tight manner. The thermoplastic hollow spheres can expand to form a foam structure under heating in the subsequent heating step, without the encapsulated propellant gas can volatilize. For a reliable insertion and as homogeneous as possible distribution of the thermoplastic hollow spheres, a carrier substrate is provided, which is combined with the thermoplastic hollow spheres. The carrier substrate is then integrated together with the thermoplastic hollow spheres (also referred to below as microspheres) into the semi-finished fiber product.

In a first embodiment, the carrier substrate may be a carrier liquid in which the thermoplastic hollow spheres are dispersed to form a dispersion. For integration in the semifinished fiber product, the still-dry semi-finished fiber product can be impregnated with the dispersion. In this way, the microspheres can diffuse into the semifinished fiber product over the entire fiber semifinished product width. Subsequently, a drying step takes place, in which the carrier liquid is dried out of the semifinished fiber product.

In the above method, a homogeneous distribution of the microspheres due to their relatively low mass is only partially possible. In addition, the carrier liquid must again be dried out of the semi-finished fiber process technically consuming. Against this background, in a second embodiment variant, the carrier substrate may be a carrier fiber made of plastic, for example a low-melting PLE (PLE = bioplastic), in which the thermoplastic hollow spheres are embedded. By embedding in the carrier fiber, the microspheres can be uniformly distributed distributed in the natural fiber mat in a homogeneous distribution and are therefore located in all areas of the mat cross-section. In addition, the natural fiber mat remains dry and can then be further processed directly, without intervening drying step.

The above-mentioned carrier fiber having the thermoplastic hollow balls embedded therein can be produced in a continuous process as an endless fiber. The continuous fiber can then be cut into continuous length fiber segments of predetermined length. The continuous fiber segments thus formed can be introduced into the natural fiber mat in a fiber mixing process in a homogeneous distribution, in all areas of the mat cross section. Subsequently, the fiber mixture is deposited on a conveyor belt and connected to one another by means of the needling technique to form a nonwoven.

The carrier fiber or the fiber strand with the microspheres integrated therein can be produced by way of example in a melt spinning or extrusion process. In this embodiment, no contamination of the mixing and transport systems takes place at the manufacturer of natural fiber mats by unbound microspheres particles.

In the above manufacturing variant, the microspheres in the melt spinning process can lead to clogging of the nozzles. Before this Background may in a third embodiment variant, the carrier substrate be a carrier film made of plastic, wherein the microspheres are embedded in the material of the film. The microspheres are given by way of example in such a preparation variant in the molten base material of the film. The melt is then rolled through a calender to a thin film. Alternatively, the film can be produced in any Folienherstellverfahren, for example, by an extrusion in which a film strand is produced by a slot die. Subsequently, individual film strands of predetermined cutting length are cut out of the film by a suitable method. The film strands produced in this way can be introduced into the natural fiber mat in a homogeneous distribution, specifically in all areas of the mat cross section, and then interwoven firmly, for example by means of the needling technique, with the semi-finished fiber product (that is, with the natural fiber mat).

As mentioned above, the carrier substrate may be a monofilament. Instead, the carrier substrate may also be an interwoven thread or a multifilament or a fiber bundle. When using a multifilament as the carrier substrate, the microspheres can optionally be arranged between the individual fibers in the fiber bundle, that is not directly in the fiber material itself. In this case, however, there is a risk that the microspheres due to mechanical stresses in the transport of the fibers in the fiber bundle to solve.

With the aid of the above variants, the microspheres can be largely homogeneously introduced into the semi-finished fiber product (natural fiber mat).

In the manufacturing process, the semi-finished fiber product is inserted with the integrated therein thermoplastic hollow spheres in a hot press and heated to the processing temperature at the same time compressing the semifinished fiber product. When opening the hot press, the semi-finished fiber relaxes and foams, that is, expand the thermoplastic hollow spheres. In the further course of the work, the heated semifinished product, which has been pre-compressed in the heating press, is placed in the molding press and the plastic component is formed while cooling down. The pressing process is to be designed so that the foam structure formed by the thermoplastic hemispheres is not damaged.

The microspheres together with the molten thermoplastic form the matrix in which the natural fibers are embedded. The foam structure not only consists of microspheres but is a mixture of the thermoplastic and the microspheres. When foaming, the structure seeks the least resistance and thus preferably reaches the still free areas. The temperature control during the heating step and / or during the compression molding step is to be interpreted as meaning that the melting of the plastic fibers and of the thermoplastic hollow spheres takes place under compression at a temperature level which does not impair the gas diffusion tightness of the thermoplastic hollow spheres. After the melting process and the shaping, the press mold can open while cooling to the desired final dimension with simultaneous foam formation (expansion of the encapsulated gases in the interior of the thermoplastic hollow spheres).

The space for foam formation, ie the expansion of the thermoplastic hollow spheres, is provided by the cavities between the natural and synthetic fibers in the semifinished fiber product. In the case of completely molten plastic fibers, the expansion clearance could optionally be provided by a defined small mold opening of the press tool.

With the help of thermoplastic hollow spheres (so-called microspheres) a production-technically simple foaming of mold components is possible. The thermoplastic hollow spheres can expand by many times their volume when exposed to heat. By way of example, the thermoplastic spheres may be present in a microscopically small powdered form, with a diameter in the range of 10 to 20 μm, before the heating step. After the heating step, the expanded thermoplastic hollow spheres may have a diameter in the range of 30 to 50 μm. The expansion of the thermoplastic hollow spheres takes place during the heating step, in which the semi-finished fiber product is heated to above the melting temperature of the plastic fibers. In this case, both the outer sides of the thermoplastic hollow spheres and the plastic fibers of the semifinished fiber product can plasticize, that is to say melt thermoplastic, and bond to one another in a material-locking manner. Subsequently, the heated semi-finished fiber product is fed to a compression molding process in which the final shaping of the plastic component takes place.

In the microspheres is an alkane (hydrocarbon, e.g., butane) having a low boiling temperature. When heated, the state of the aggregate changes from liquid to gaseous.

By using the thermoplastic hollow spheres according to the invention, a reduction in weight as well as an increase in the bending stiffness of the plastic component are achieved in particular. When constructing a multilayer structure consisting of the above-mentioned cover and core layers, there is the possibility that the microsphere foam contained in the core layer (that is, the thermoplastic Hollow balls formed foam structure) penetrates into free spaces of the outer layers.

The advantageous embodiments and / or further developments of the invention explained above and / or reproduced in the dependent claims can be used individually or else in any desired combination with one another, for example in the case of clear dependencies or incompatible alternatives.

The invention and its advantageous embodiments and further developments and advantages thereof are explained in more detail below with reference to drawings.

Show it:

1 a sectional view of a natural fiber reinforced plastic component;

2 in a rough schematic representation of process steps for the production of natural fiber reinforced plastic component;

3 in partial sectional views in each case a thermoplastic hollow sphere before the heating step and a thermoplastic hollow sphere after the heating step; and

4 and 5 each views, one compared to 2 illustrate alternative integration step; such as

6 and 7 each views illustrating a further alternative integration step.

The figures are made with a view to a simple understanding of the invention. Therefore, the figures are only roughly simplified representations that do not reflect a realistic construction of a component connection. So is in the 1 a finished natural fiber reinforced plastic component 1 shown. The plastic component 1 For example, it can be used as an interior trim part for a vehicle and is realized as a press molding. In the final state, the plastic component 1 a plastic matrix 5 , such as polypropylene, on, in the natural fibers 3 embedded for reinforcement. The natural fibers 3 may be exemplary flax, hemp, kenaf or other vegetable fibers. In addition, in the plastic matrix 5 a foam structure 4 integrated. The foam structure 4 is due to a variety of thermoplastic hollow spheres 11 (hereinafter also referred to as microspheres) constructed with the plastic matrix 5 are merged.

In the 2 are process steps for the production of natural fiber reinforced plastic component 1 shown. For the production of the plastic component 1 is in accordance with the 2 first a dry semifinished fiber product 7 provided. The semifinished fiber product 7 has the natural fibers 3 as well as plastic fibers 9 on, in the further process run to the already mentioned plastic matrix 5 be melted. The natural and synthetic fibers 3 . 9 are in the semifinished fiber product 7 For example, by means of a needling technique intertwined or knotted to a handling-capable semi-finished fiber 7 to obtain. In the thus provided semi-finished fiber 7 become in an integration step, the thermoplastic hollow spheres 11 introduced, whose properties later on the basis of 3 be explained. For integration in semi-finished fiber products 7 become the microspheres 11 in the 2 first dispersed in a carrier liquid containing a carrier substrate 21 forms. Subsequently, the still dry fiber semi-finished product 7 impregnated with the dispersion. In a subsequent drying step then the carrier liquid 21 from the semifinished fiber product 7 dried out. To reduce the drying time, the dispersion liquid is whipped to a foam. Instead of the liquid, the foam is applied to the mat 7 brought and penetrates this into the fiber structure.

The microspheres 11 according to the 3 a diffusion-tight outer shell 13 on. The outer shell 13 eg consists of PAN. The microspheres 11 are microscopic and are in powder form. Before a heat load in the heating press 15 can the microspheres 11 according to the 3 have a diameter d ₁ in the range of 10 to 20 microns. When exposed to heat, the thermoplastic hollow spheres expand 11 by a multiple of, for example, to a diameter d ₂ in the range 30 to 50 microns. The expansion takes place while reducing the wall thickness of the outer shell.

The thermoplastic hollow spheres 11 depending on the application, either homogeneously or only partially into the semifinished fiber product 7 be introduced. Subsequently, the semifinished fiber product 7 a heating press 15 supplied, in which the semi-finished fiber 7 is subjected to pressure and heat. This allows the expanding microspheres 11 into the fiber free spaces 14 ( 2 ) of the semifinished fiber product 7 diffuse. In addition, the temperature control in the heating press is designed such that the outer edge layer of the thermoplastic hollow spheres 11 melts and with the melting plastic fibers 9 combines. Subsequently, the still heated fiber semi-finished product 7 in a molding press 17 led, in a shaping with subsequent cooling of the semifinished fiber product 7 he follows.

Based on 4 and 5 will be one compared to 2 described alternative integration step, in which the carrier substrate 21 is not a carrier liquid, but rather a carrier fiber made of a plastic. Generally speaking, as plastic a thermoplastic can be used which forms a durable bond with PP and PAN and has a low melting temperature. Like from the 4 the microspheres are 11 in the material of the carrier fiber 21 embedded. The carrier fiber 21 with the microspheres embedded in it 11 can be made in a continuous melt spinning or extrusion process as an endless fiber. The endless fiber 21 becomes continuous fiber segments in the further course of the process 23 ( 3 ) with a predetermined length l. The endless fiber segments 23 are then loose in the semi-finished fiber 7 mixed and firmly using the needling technique with the semi-finished fiber 7 interwoven.

In the 5 is a detailed view of the material structure in an already finished plastic component 1 shown. By way of example, here are the continuous fiber segments serving as a carrier substrate 23 made of a polymer whose melting temperature is well below the working temperature (about 200 ° C) of the heating press 15 lies. When Heizpressvorgang thus decompose the continuous fiber segments 23 as it is in the 5 is indicated by the dashed lines. Simultaneously, the microspheres expand 11 and form with the plastic matrix 5 a foam composite. Ideally, the melting temperature of the polymer fibers, that is the carrier fibers 21 , below the expansion start temperature of the microspheres 11 , A low melting point material is thus of particular relevance to prevent the premature expansion of the microspheres in the melt spinning process and to ensure that the microspheres do not react in the press.

Based on 6 and 7 another alternative integration step is described with which the microspheres 11 in the semifinished fiber product 7 can be introduced. As a result, the microspheres become 11 first placed in a molten film base material. Subsequently, the melt by a in the 6 indicated calender 29 rolled into a thin foil, which is the carrier substrate 21 forms. Analogous to that in the 4 shown endless fiber segments 23 will be in the 6 and 7 the carrier film 21 produced as a continuous film and then to individual film strands 25 ( 7 ) with a predetermined length l. The foil strands 25 are then loose and in even distribution in the semi-finished fiber 7 mixed and firmly using the needling technique with the semi-finished fiber 7 interwoven.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19834048 A1 [0002]

Claims (10)

Process for producing a natural-fiber-reinforced plastic component ( 1 ), in which at least one semi-finished fiber product ( 7 ) made of natural and synthetic fibers ( 3 . 9 ), in a heating step, the semi-finished fiber product ( 7 ) above the melting temperature of the plastic fibers ( 9 ) is heated, and then in a press-forming step, the heated semi-finished fiber ( 7 ) to the plastic component ( 1 ), in which the natural fibers ( 3 ) into one of the plastic fibers ( 9 ) formed plastic matrix ( 5 ) are embedded, characterized in that prior to carrying out the heating step thermoplastic hollow spheres ( 11 ), which expand when heated to form a foam structure, with a carrier substrate ( 21 ) and that the carrier substrate ( 21 ) together with the thermoplastic hollow spheres ( 11 ) in the semi-finished fiber product ( 7 ) is integrated. Method according to claim 1, characterized in that the carrier substrate ( 21 ) is a carrier liquid in which, forming a dispersion, the thermoplastic hollow spheres ( 11 ) and that for integration in the semi-finished fiber product ( 7 ) the semi-finished fiber product ( 7 ) is impregnated with the dispersion. A method according to claim 2, characterized in that in a subsequent drying step, the carrier liquid ( 21 ) from the semifinished fiber product ( 7 ) is dried out, and that in particular to reduce the drying time, the carrier liquid is whipped into a foam, which instead of the liquid on the semi-finished fiber ( 7 ) and penetrates into the fiber structure. Method according to claim 1, characterized in that the carrier substrate ( 21 ) is a carrier fiber made of plastic, in particular of low-melting PLE, and that the thermoplastic hollow spheres ( 11 ) in the material of the carrier fiber ( 21 ) are embedded. Method according to claim 4, characterized in that the carrier fiber ( 21 ) with the embedded therein thermoplastic hollow spheres ( 11 ) is produced in a continuous process as an endless fiber, and that for integration in the semifinished fiber product ( 7 ) the continuous fiber to continuous fiber segments ( 23 ) is cut with a predetermined length (l), and that the endless fiber segments ( 23 ) loosely in the semifinished fiber product ( 7 ) are mixed and, in particular by means of the needling technique, fixed. Method according to claim 1, characterized in that the carrier substrate ( 21 ) is a carrier film made of plastic, and that the thermoplastic hollow spheres ( 11 ) in the material of the carrier film ( 21 ) are embedded, and that in particular the carrier film ( 21 ) is produced in an extrusion process. A method according to claim 6, characterized in that for integration in the semifinished fiber product ( 7 ) the carrier foil ( 21 ) to individual foil strands ( 25 ) is cut with a predetermined length (l), and that the film strands ( 25 ) loosely on the semifinished fiber product ( 7 ) and fixed, in particular by means of the needling technique. Method according to claim 1, characterized in that the carrier substrate ( 21 ) is a multifilament, a fiber bundle or a thread, in which the thermoplastic hollow spheres ( 11 ) are integrated. A method according to claim 8, characterized in that for integration in the semifinished fiber product ( 7 ) Loosely apply multifilament segments to the semi-finished fiber 7 ) and, in particular in a needling technique, be fixed. Semifinished fiber product for a process for producing a natural fiber-reinforced plastic component ( 1 ) according to any one of the preceding claims.

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