DE102011011387B4 - Process for producing a multilayer fiber-plastic composite semifinished product - Google Patents

Abstract

Process for the production of a multi-layer fiber-reinforced plastic semi-finished product (1), which has three or more layers, wherein at least one core layer (3) made of filler bodies (6) connected to one another is arranged between two outer layers (2), the outer layers (2) being connected to the core layer ( 3) are connected, and at least one of the edge layers (2) is an SMC layer (2) made from a fiber arrangement (5) dry-impregnated with a first matrix material (4), the first matrix material (4) being a shrinkage-reduced matrix material (4). and has a composition that is suitable for providing a class A surface, comprising the steps of: - dry impregnating at least one fiber arrangement (5) with the first matrix material (4), which is a powdered matrix material (4) with electrostatically capable particles, in an alternating electric field, - mixing, dry impregnation and/or coating of the filler bodies (6) with a third matrix material (7) and - arranging the filler bodies (6) mixed, dry impregnated and/or coated with the third matrix material (7) between the with the first matrix material (4) dry-impregnated fiber arrangement (5) and a layer forming a second edge layer (2), which is a plastic plate, metal plate or a fiber-reinforced plastic composite plate, in particular a fiber arrangement (5) dry-impregnated with a second matrix material (4), the second Matrix material (4) is the same matrix material (4) as the first matrix material (4) or differs therefrom, - impregnating the fiber arrangement (5) with the first matrix material (4), thereby forming the surface layer designed as an SMC layer (2). (2), and connecting the filling bodies (6) to the third matrix material (7), thereby forming the core layer (3), and connecting the core layer (3) to the surface layers (2) by supplying heat and/or by applying a Pressing pressure, which / the melting of the matrix materials (4, 7) provides.

Description

The invention relates to a production method for a multilayer composite fiber-plastic composite with a core layer arranged between two edge layers.

In the course of lightweight construction, for example in the motor vehicle sector, fiber composite semifinished products, such as sheet molding compounds, SMCs, which are plate-shaped or coil-shaped and can be cut to form the desired component and are reshaped, are increasingly being used as component materials. These components combine the advantages of low weight with excellent mechanical properties.

To produce such fiber-plastic composite and SMC semi-finished products, reinforcing fibers are impregnated in appropriate systems with solvent-containing pastes or resins in the liquid state. This results in dough-like molding compounds of mostly thermosetting reaction resins and reinforcing fibers for the production of fiber-reinforced plastic composite components. In the SMC, all necessary components are ready for use completely pre-mixed. Usual fiber lengths of the reinforcing fibers are between 25 and 50 mm. Further, SMCs with anisotropic fiber structure may have oriented fibers up to 200 mm in length, however, increasing the flow resistance of the SMC.

By adding means for shrinkage reduction SMCs can be produced with low shrinkage, or the shrinkage of the polyester resin can be completely compensated during curing. SMC systems designed to form paintable surfaces with Class A quality have a shrinkage of less than 0.05%.

An SMC composition is composed of reinforcing fibers and a matrix material comprising a crosslinkable plastic material, for example a resin, mineral fillers such as chalk or rock flour, and additives for shrinkage reduction, inhibitors, inert release agents, reaction accelerators, etc. Depending on requirements, the matrix material may also comprise dyes or flame retardants. A typical SMC mass contains about 12% crosslinkable plastic material, 45% mineral fillers, and 30% reinforcing fibers, so it is a resin and filler-rich fiber material.

The SMC semi-finished product can be cut to size and further processed to the finished component using flow or compression molding. However, SMC semi-finished products have so far been characterized by poor mixing quality, air pockets and by the transport and packaging films to be integrated in the process, which are difficult to control and impair the product quality.

For the production of body components for a motor vehicle, a three-layer material composite of two steel cover plates and an intermediate layer of viscoelastic material is also known. Further, for this purpose, multi-layer composite panels of lightweight materials, such as aluminum or fiber composites used. This describes the DE 199 39 513 A1 a multi-layer composite panel with improved rigidity, corrosion protection and vibration and sound damping, the two outer metal or plastic panels as a cover or bottom plate and an intermediate layer of welded together, sintered or glued balls.

Thus, such multilayer composite panels provide maximum weight savings for the manufacture of a body component such as a vehicle roof. Due to the above disadvantages of SMC semi-finished products, these are not used for the construction of such multilayer composite panel.

From the DE 3126242 A1 is a hot-pressable semi-finished for the production of a molded part in sandwich construction known. The semi-finished product is composed of an upper and a lower fiber layer with oriented fiber orientation, between which there is an intermediate layer of thermosetting plastic and expandable thermoplastic granules.

The DE 19949318 A1 discloses a SMC (Sheet Molding Compound) for producing fiber-reinforced thermoset components consisting of a resin matrix with fiber reinforcement with unidirectional fibers (UD fibers) arranged in an axial orientation and advantageously additionally with cut fibers (random fibers) which are non-directional are arranged in the resin matrix.

The DE 100 59 801 A1 describes a method for producing a fiber composite structure from a blank which can be consolidated by means of extrusion under the influence of heat and which comprises at least one flowable fiber layer impregnated with the matrix system and restructured during extrusion.

The DE 10 2005 039 709 A1 describes a glass fiber fleece with cut glass fibers and resin mats produced therefrom.

From the DE 691 30 111 T2 is a method for producing a shaped composite Item is known by dry impregnation. In this case, a matrix material consisting of individual solid particles is combined with a reinforcing material made of knitted fabric, wherein the matrix material is subjected to a heat treatment in order to bring it into a continuous phase.

Based on this prior art, it is an object of the present invention to provide a production method for an optimized multilayer composite fiber-plastic composite, which is suitable for producing a body component with a paintable surface.

This object is achieved by the manufacturing method with the features of claim 1.

Further developments of the method are carried out in the respective subclaims.

An embodiment which can be produced by the method relates to a multi-layered fiber-plastic composite semifinished product of three or more layers, wherein at least one core layer arranged between two edge layers consists of interconnected fillers and the edge layers are connected to the core layer. At least one of these edge layers is embodied as an SMC layer which is formed from a fiber arrangement dry-impregnated with a first matrix material, this matrix material being a shrink-reduced matrix material having a composition for forming a Class A surface. The SMC edge layer is thus suitable for the formation of a paintable surface, so that the fiber-plastic composite semifinished product can be used to produce a body component.

A method according to the invention for producing a multilayer fiber-plastic composite semifinished product comprises the dry impregnation of at least one fiber arrangement with a first, electrostatically matable powdered matrix material in an alternating electric field. Furthermore, the fillers are mixed with the third, preferably also electrostatically powdered matrix material, dry-impregnated and / or coated. This is followed by arranging the dry-impregnated and / or coated filling bodies mixed with the third matrix material between the fiber arrangement dry-impregnated with the first matrix material and a layer forming a second boundary layer. This can be a plastic plate, a metal plate or a fiber-reinforced plastic composite plate, but it can also be a fiber arrangement dry-impregnated with a second matrix material. The matrix material used for this purpose may be the same matrix material as the first matrix material, so that the second edge layer is likewise an SMC layer, but it is also possible to use a matrix material which differs from the first matrix material.

In this layer arrangement, the actual impregnation of the fiber arrangement with the first matrix material, whereby the SMC layer is formed, and the bonding of the filler bodies to the third matrix material, so that the core layer is formed, takes place by supplying heat and / or by exerting a pressing pressure the bonding of the core layer to the edge layers. If the second boundary layer is a corresponding dry-impregnated fiber arrangement, the layer structure is also produced there by applying heat and / or by exerting the pressure by impregnating the matrix materials and allowing the fibers or fillers to flow around, but not yet harden, or network. After impregnation, the fiber-plastic composite semifinished product can optionally be cooled and the further processing, for example, the production of body parts supplied.

The manufacturing process may include separately preparing the dry-impregnated fiber assemblies that are to form the skin layers and the filler-matrix mixture that will form the core layer, then placing the filler-matrix mixture between the dry-impregnated fiber assemblies, which then be combined and impregnated in a lamination process.

Alternatively, the manufacturing method may combine the steps of dry impregnating and placing and comprising the continuous sequential fabrication of the layers, wherein in a first dry impregnation step a fiber assembly is formed which forms the lower surface layer and onto which the mixture of packing and matrix material optionally incorporated in the alternating electric field is homogenized, is applied to form the core layer. In the last stage, a further dry-impregnated fiber arrangement is applied to form the upper boundary layer on the filler-matrix layer, whereupon the actual impregnation step can follow directly.

The venting of the multi-layer fiber composite plastic semifinished product can be carried out by applying a vacuum during impregnation and / or by additional rolling of the formed multilayer fiber-plastic composite semifinished product at a slightly elevated temperature.

By means of the method according to the invention, the multilayer can be Semi-finished fiber-plastic composite with a minimum of trapped air and a minimum of transport and packaging, and at the same time improved mixing of the surface layers forming SMCs. Class A surfaces can be realized in lightweight construction.

These and other advantages are set forth by the following description with reference to the accompanying figures. The reference to the figures in the description serves to assist in describing and facilitating the understanding of the subject matter. The figures are merely a schematic representation of an embodiment of the invention.

Showing:

1 a schematic sectional view through the layer structure of an embodiment according to the invention of the fiber-plastic composite semifinished product,

2 a schematic representation of steps of a first embodiment of the manufacturing method according to the invention,

3 a schematic representation of another embodiment of the manufacturing method according to the invention.

The invention relates to a method for producing a multilayer fiber-plastic composite semifinished product 1 as exemplified in 1 outlined. There is the composite semi-finished product 1 from three layers. Unlike shown, the fiber-plastic composite semifinished but also have more layers. In any case, the fiber plastic composite semi-finished 1 one between two outer layers 2 arranged core layer 3 on, made of interconnected packing 6 that exists in 1 are spherical. Edge and core layer 2 . 3 are each connected to each other.

In the present example, both boundary layers 2 designed as SMC layers and are made of one in a first matrix material 4 dry-impregnated fiber arrangement 5 educated. The fiber arrangement 5 may be a non-woven fabric or a fiber mat whose fibers are made of a glass, polymer, ceramic material and / or carbon fibers, or carbon fibers. In order to be able to dry-impregnate a fiber material made of carbon fibers in the alternating electric field, the carbon fibers have an insulating coating. Suitable insulating fillers are known.

With this layer structure, the SMC layers as surface layers 2 has, which form a paintable surface, the semi-finished fiber plastic composite 1 be used for the production of a body component. For this purpose, although generally only a SMC layer formed as a boundary layer 2 necessary, which can form the Class A surface, for easier handling of the fiber-plastic composite semi-finished product 1 however, both marginal layers can 2 As shown, be SMC layers, so that in the arrangement of the fiber-plastic composite semifinished product 1 in a mold not on the side of the surface layer 2 must be respected, ie that both edge layers 2 are suitable for the formation of the class A surface, although for an inwardly facing surface of a body component would not be required due to the later there disguise.

The packing 6 the core layer 3 be through the matrix material 7 connected. Will be a powdery matrix material 7 used, so can the packing 6 be very well mixed with it. Dry impregnation in the alternating electric field also permits a homogeneous mixture of random packings 6 and the matrix material 7 to reach. Optionally, it is also possible to use a granulate which comprises matrix material 7 coated packing 6 consists.

The SMC boundary layer (s) 2 of the fiber-plastic composite semifinished product 1 can have a layer thickness in the range of 0.1 to 0.75 mm, in particular of 0.25 to 0.5 mm, and a density in the range of 1.0 to 3.0 g / cm ³ , in particular of 2, 0 g / cm ³ . The interposed core layer 3 may have a layer thickness in the range of 0.5 to 7.5 mm, in particular of 1 to 5 mm, and a density in the range of 0.3 to 0.7 g / cm ³ , in particular of 0.5 g / cm ³ , An exemplary fiber-plastic composite semifinished product 1 with boundary layers 2 of 0.25 mm each and a density of 2.0 g / cm ³ and a core layer 3 of 2 mm and a density of 0.5 g / cm ³ has a basis weight of 2 kg / m ² , which corresponds to an average density of 0.8 g / cm ³ , resulting in a weight reduction of a manufactured from this body component compared to the state the technique of about 50% results.

To ensure a good bond between layers when using the same matrix materials 2 . 3 to secure the different matrix materials 4 . 7 should be used, matrix materials having the same crosslinkable plastic component. The respective for the different layers 2 . 3 required properties can then be adjusted via varying proportions and various additives. Generally, the matrix material needs 4 the SMC boundary layer 2 a shrink-reduced matrix material 4 be while the matrix material 7 the core layer 3 with regard to an optimal embedding of the packing 6 can be selected. Be different crosslinkable plastic components for the matrix materials of the edge and core layer 2 . 3 used, they should be at least partially miscible with each other and crosslinked during curing in order to achieve a good connection of the layers.

Ideally, it should be different when using different matrix materials 4 . 7 the shrinkage behavior of the two do not differ too much. Suitable crosslinkable plastic material of the matrix materials are thermoplastic or thermosetting resins. Other constituents of the matrix material may be fillers, in particular mineral fillers such as chalk or rock flour, as well as additives for shrinkage reduction. Other additives such as inhibitors, inert release agents, reaction accelerators, dyes or flame retardants may vary depending on the selected resin.

Over the fiber mat structure, for example over the fiber length, and over the properties of the matrix materials or their compositions, the flow capabilities of edge and core layer can be tuned. The larger the fiber length used, the higher the flow resistance. In general, however, the multi-layer structure of the fiber-plastic composite semi-finished product according to the invention is preferably suitable for molding into components of complex shape, such as a roof outer skin of a motor vehicle body.

Notwithstanding the in 1 shown layer structure, the fiber-plastic composite semifinished product between the surface layers also have other layers. For example, another SMC layer which lies between two random packings or else a layer of a carrier nonwoven or a functional layer is conceivable here. A conductive layer as a functional layer, which is set to a limited conductivity with a surface resistance in a range of 5 to 100 kΩ / cm, can be used for an electrostatic coating of the surface, so that here an arrangement of the functional layer between the SMC surface layer and the Core layer makes sense.

The formation of the core layer 3 used spherical filler 6 give the multilayer semi-finished composite a very good formability. The voltage transition is flowing within the workpiece through the spherical filling body. The spherical or hollow core layer 3 allows a large installation height of the sandwich construction 1 from several millimeters to centimeters at a low specific gravity. Since, as a result of the transmission of the shear stress, this construction height contributes to the overall rigidity with the third power, a high rigidity of the overall composite is achieved on a weight-specific basis. The good formability allows the realization of complex, preformed geometries, such as occur in body parts.

The fiber-plastic composite semifinished product is thus particularly suitable for producing a body component, wherein an edge layer of the fiber-plastic composite semifinished product, which has the class A paintable surface which forms an outer skin of the body component, forms as an SMC layer.

A method according to the invention for producing a multilayered fiber-plastic composite semifinished product comprises the dry impregnation of at least one, an edge layer 2 forming fiber assembly 5 with a first electrostatically controllable powdery and shrink-reduced matrix material 4 in an alternating electric field. This process step is shown in FIG 2 on the left. On the fiber mat 5 , which is supplied continuously, for example from a coil, the powdery matrix material 4 from an application station 10 applied, whereupon the fiber mat 5 with the applied matrix material 4 passes through an electrostatic alternating field, that between the electrodes 11 is built.

This type of introduction of a powdery material into a fiber arrangement is known and is approximately in the EP 1 678 372 B1 described. It describes how organic polymer and mineral powders can be introduced into a fibrous network by means of an applied AC voltage, wherein the organic polymers are thermoplastic or thermally curable polymers. For this purpose, an upper electrode for generating the alternating field there has at least one electrode-like tube and the alternating field used is between 0.1 and 20 kV / mm. In the DE 690 28 550 T2 Also, a dry impregnation process is described with the semis production process for producing sintered composites with a long fiber reinforced composite matrix.

Prerequisite for such a dry impregnation process in the alternating electric field are powders which are movable in the alternating electric field, d. H. Pick up and deliver cargo. Thus, the matrix materials are used in powder form here to form the SMC edge layers according to the invention by dry impregnation and not, as usual in SMC technology, in the form of liquid pastes.

Like the separately dry-impregnated fiber mat 5 , as in 2 illustrated, the other layers for the semifinished fiber plastic composite can be made separately and arranged in a further process step according to the layer structure and merged. The actual impregnation, in which the crosslinkable plastic components of the matrix materials 4 . 7 melted to the fibers of the fiber mat 5 and the fillers of the matrix materials 4 . 7 to flow around, or the packing 6 and the respective layers 2 . 3 to connect with each other takes place under heat and / or by applying a pressing pressure such as by rolling in the device 12 instead of. In the impregnation in the device 12 indeed finds a melting of the matrix materials 4 . 7 but not a crosslinking reaction or the curing of the matrix material 4 instead of.

Other than shown, the second edge layer could possibly consist only of a plastic film, a metal plate or a plastic fiber composite layer, which does not have to meet the requirements of a Class A surface. Preferably, however, the second boundary layer is also used 2 by dry-impregnating a fiber assembly 5 with the first electrostatically powdered matrix material 4 in an alternating electric field 11 formed so that the subsequent handling of the fiber composite preformed composite formed as previously explained is facilitated. However, for example, in the case of incorporation of a functional layer distinguishable edge layers may be advantageous. Optionally, this can also be realized by means of different color additives in the first matrix material.

The layers 2 . 3 Alternatively, as in 3 sketched, continuously sequentially constructed. After dry impregnation of a first fiber mat 5 with matrix material 4 in the alternating electric field 11 , are applied directly to this dry-impregnated fiber mat 5 the packing 6 and the matrix material 7 from corresponding devices 13 . 10 applied, and then also by an electrostatic alternating field 11 guided. Other than shown, packing can be 6 and matrix material 7 also mixed in advance, or the filler 6 with the matrix material 7 coated, and together on the bottom dry-impregnated fiber mat 5 be applied. In the third stage is another fiber mat 5 deposited on the packed matrix material layer, with the desired matrix material 4 provided, then when passing through another alternating field 11 in the fiber mat 5 penetrates. Subsequently, the wet impregnation takes place in the device 12 under heat and / or exerting a pressing pressure.

The venting of the multilayer fiber composite plastic semifinished product can by applying a vacuum during the impregnation in device 12 and / or by additional rolling of the formed multilayer fiber-plastic composite semifinished product at slightly elevated temperature. The vent can thus be solved in the simplest case by an applied during the impregnation during SMC pressing vacuum in the press tool.

In both in 2 and 3 outlined variants of the method of the invention, the multi-layer fiber composite plastic semi-finished product with the edge layers 2 and the core layer 3 obtained in a consolidated state for further processing. This can be supported for example by a corresponding cooling during a rolling process.

By means of the method according to the invention, the multilayer fiber composite semifinished product can be produced with a minimum of air inclusions and a minimal amount of transport and packaging, and at the same time improved mixing of the SMCs forming the surface layers. Thus, it is advantageous to realize class A surfaces in lightweight construction.

Claims (3)

Process for producing a multilayer fiber-plastic composite semifinished product ( 1 ) having three or more layers, wherein at least one core layer ( 3 ) of interconnected packing ( 6 ) between two boundary layers ( 2 ), wherein the boundary layers ( 2 ) with the core layer ( 3 ), and at least one of the surface layers ( 2 ) an SMC layer ( 2 ) from one with a first matrix material ( 4 ) dry-impregnated fiber arrangement ( 5 ), the first matrix material ( 4 ) a shrink-reduced matrix material ( 4 ) and having a composition capable of providing a Class A surface, comprising the steps of: - dry-impregnating at least one fiber assembly ( 5 ) with the first matrix material ( 4 ), which is a powdery matrix material ( 4 ) with electrostatically-capable particles, in an alternating electric field, - mixing, dry impregnation and / or coating of the packing ( 6 ) with a third matrix material ( 7 ) and - arranging the with the third matrix material ( 7 ) mixed, dry-impregnated and / or coated filler ( 6 ) between the one with the first matrix material ( 4 ) dry-impregnated fiber arrangement ( 5 ) and a second boundary layer ( 2 ) forming layer comprising a plastic plate, metal plate or a fiber-reinforced plastic composite plate, in particular one with a second matrix material ( 4 ) dry-impregnated fiber arrangement ( 5 ), the second matrix material ( 4 ) the same Matrix material ( 4 ) like the first matrix material ( 4 ) or differs from it, - Impregnating the fiber arrangement ( 5 ) with the first matrix material ( 4 ), thereby forming the SMC layer ( 2 ) formed surface layer ( 2 ), and connecting the packing ( 6 ) with the third matrix material ( 7 ), thereby forming the core layer ( 3 ), and connecting the core layer ( 3 ) with the surface layers ( 2 ) by applying heat and / or by exerting a pressing pressure, the melting of the matrix materials ( 4 . 7 ). The method of claim 1, wherein the core layer ( 3 ), with the third matrix material ( 7 ) mixed filler ( 6 ) and the boundary layers ( 2 ) forming dry-impregnated fiber assemblies ( 5 ) or a lower dry-impregnated fiber assembly ( 5 ) with the third matrix material ( 7 ) mixed filler ( 6 ) and the upper dry-impregnated fiber assembly ( 5 ) are made after and in succession in successive dry impregnation processes. Method according to claim 1 or 2, comprising the step of venting the multilayered fiber-plastic composite semifinished product ( 1 ) by applying a vacuum during the impregnation and / or by rolling the multilayer fiber plastic composite semi-finished product ( 1 ) at elevated temperature.

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