Prepreg layer and use thereof

Abstract

The invention relates to a prepreg layer (1 ) at least comprising a plurality of filaments (2), a plastic matrix (3) and a plurality of holes (4), wherein the plastic matrix (2) comprises a polyolefin copolymer and the prepreg layer (1) has a layer density up to a maximum of 1.0 g / cm3.

Description

[0001] Prepreg layer and its use

[0002] The present invention relates to prepregs, their production and uses.

[0003] The production of components (such as vehicle components, aircraft components, boat components, interior components of trains, components in electronics, etc.) from fiber-reinforced materials can be carried out, among other things, on the basis of a fiber-matrix semi-finished product, the best known of which is a "prepreg".

[0004] Prepregs typically contain a fibrous material made of one or more fiber types, such as carbon, glass fiber, aramid, basalt, boron, ceramic, silica, steel, polyester, nylon, polyethylene, Plexiglas, natural fiber, and / or another fiber type, with the fibrous material impregnated with a matrix plastic. Within the prepreg, the fibers of the fibrous material can be present as continuous fibers with a preferred direction (unidirectional layer), as an ordered textile surface (e.g., woven, knitted, scrim, etc.), or as a disordered textile surface as a nonwoven or random fiber mat.

[0005] Polymer materials (also called "resin systems"), such as thermosets (also called thermosets; synthetic resins, epoxy resins, phenolic resins, polyester resins), thermoplastics, or elastomers, are generally used as matrix plastics for prepregs. The thermosets and elastomers are not yet fully cured in the prepreg delivery state, meaning they are still plastically deformable. Special storage conditions, such as very low storage temperatures, must be observed. Thermoplastics are known to be repeatedly transformed into a plastically deformable state by applying heat.

[0006] Prepregs are typically manufactured as layered, sheet, tape, or web-like material, with web-like material often being delivered rolled up in rolls. To produce an object or component, a piece of prepreg is conventionally cut off that is large enough to line the surface of a press tool (mold). By pressing the prepreg (or, more generally, by applying pressure to the prepreg at a pressure greater than atmospheric pressure) in the press tool under the influence of heat, the thermosetting or elastomeric matrix plastic reacts, resulting in the shape of the object or component.In the case of a thermoplastic matrix plastic, it acquires plastic properties through the application of heat and the shaping of the object or component can be achieved by pressing the prepreg under the application of heat and then cooling the shaped prepreg below the softening temperature of the thermoplastic plastic.

[0007] The requirements for a prepreg can vary greatly, especially with regard to its final use in the production of an injection-molded component and / or the preparation of the injection molding process. In particular, it may be desirable to achieve particularly uniform, complete, and / or intensive adhesion of the matrix plastic to the textile fabric. Especially with continuous production in mind, suitable, cost-effective, and rapid processes for the production of such prepregs are sought.

[0008] A particular challenge is to provide lightweight prepregs with high deformation and strength properties.

[0009] The object of the present invention is to at least partially overcome the disadvantages described with reference to the prior art and, in addition, to produce prepregs with a high and variable utility value in a simple manner, whereby it should be ensured that the composite structure stabilizes the end product as evenly as possible across the entire planar design of the end product. In particular, a simple method for providing prepregs should be created, which are suitable for further processing using currently available, possibly heavily forming, production technologies. These objects are achieved with the features of the independent claims. Advantageous further developments are specified in the respective dependent claims. The description, in particular also with the figures, illustrates the invention and provides further exemplary embodiments.The features recited individually in the claims may be combined with features of other claims and / or the description.

[0010] This is achieved by a prepreg layer which has at least a plurality of threads, a plastic matrix and a plurality of holes, wherein the plastic matrix comprises a polyolefin copolymer and the prepreg layer has a layer density of up to a maximum of 1.0 g / cm 3 [grams per cubic centimeter].

[0011] A "layer" is understood in particular to be a flat and / or band-shaped structure which can be described, for example, by a length and a width whose dimensions are significantly greater, in particular by a multiple or power, than a thickness (perpendicular thereto). Thus, warp threads (lengthwise) and weft threads (crosswise) can be arranged in a meandering pattern around a common plane and extend partially or alternately over and under it. Preferably, the layer has only a single plane with threads, whereby this plane is arranged approximately centrally with respect to the thickness of the layer. The layer can be referred to as a textile. The layer forms, in particular, an intrinsically stable composite and is to be distinguished in particular from a loose (bulk) collection of fiber elements.

[0012] The multitude of threads (also called filaments or (continuous) fibers) can be arranged in a plane or in the prepreg layer, aligned with each other. It is possible to use threads of different lengths. In particular, the threads form a regular structure, which also results in a regular, approximately evenly distributed arrangement of the holes formed between them.

[0013] The prepreg layer has a large number of holes, i.e. in particular openings extending across the thickness of the layer, in particular approximately parallel to the direction of the thickness. The large number of holes is preferably designed such that they are “see-through” when viewed from the plane (top and bottom) of the prepreg layer. It is possible for the prepreg layer to (additionally) also comprise (a smaller proportion) of holes (or closed pores) which extend essentially only within the layer, wherein it is preferred that the proportion of “see-through” holes extending across the thickness of the layer clearly predominates (e.g. greater than 95%). It is preferred that the holes have essentially the same shape and / or size. It is possible for the holes to have a substantially non-round or angular shape. It is possible for the holes to be delimited by threads surrounding them, wherein the threads orAt least the majority of the threads preferably do not end at the holes, but rather encircle them. It is preferable that the holes were not created by a separating process in the prepreg layer, but rather, for example, during the (original) arrangement of the threads relative to one another, particularly prior to the application of the plastic matrix. The multitude of holes can be present in a regular pattern, so that the prepreg layer is designed, in particular, as an (open) grid. This must be distinguished from a "porous" foam, which forms an irregular and / or closed pore system, even if it may contain (short) fibers or particles.

[0014] The plastic matrix comprises or consists of a polyolefin copolymer. Polyolefins (also called "polyalkenes") are polymers made from hydrocarbons of the formula C n H 2nwith a double bond (ethylene, propylene, butene-1, isobutene). Polyolefins are semi-crystalline thermoplastics. Polyolefins are currently typically produced from oil or natural gas. The process is called polymerization, in which short chains of chemicals (monomers) are linked to form long chains (polymers) using a catalyst. Polyolefin copolymers are thus polyolefins composed of two different types of monomer units.

[0015] The composite of threads, holes and plastic matrix is ​​designed in such a way that the prepreg layer has a layer density of up to 1 .0 g / cm 3[grams per cubic centimeter]. The layer density is to be determined in particular by measuring the weight of the layer and setting it in relation to its (enveloping) volume (length x width x thickness of the layer). In other words, this means in particular that the layer density corresponds to the quotient of the basis weight of the prepreg layer and the thickness of the prepreg layer. The thickness of a layer is measured as the distance between a reference plate on which the layer rests and a parallel, circular pressure stamp (preferably with a stamp diameter of approx. 50 mm), which exerts a specified pressure (preferably approx. 1 kPa) on the layers to be measured. The distance between the reference plate and the pressure stamp is measured and recorded. Standard climatic conditions prevail. The thickness measurement should preferably be carried out at various points on the layer and then an average value is calculated from these measurements.The thickness of the layer must be determined in particular according to DIN EN ISO 5084.

[0016] The upper limit value for the layer density of 1 .0 g / cm 3 ensures lightweight prepregs with high deformation and strength properties. The layer density can be achieved in particular through the more open design of the thread arrangement, whereby the provision of the polyolefin copolymer plastic matrix enables a particularly suitable adhesion for this thread arrangement.

[0017] Preferably, the layer density is in a range of 0.45 to 0.9 g / cm 3 , especially in the range of 0.55 to 0.75 g / cm 3 . The range from 0.45 to 0.9 g / cm 3 was identified as particularly advantageous for, for example, grid-like prepreg layers, with the range 0.55 to 0.75 g / cm 3a particularly advantageous application quantity of the polyolefin copolymer plastic matrix, which particularly favors further processing, especially for complex and highly stressed components.

[0018] The polyolefin copolymer of the plastic matrix is ​​preferably selected from the following group: random copolymer, gradient copolymer, alternating copolymer, block copolymer, polymer mixture, graft polymer.

[0019] In a statistical copolymer, a random distribution of monomers occurs in the chain, for example, in the following way:

[0020] AABBABBBBAAAABAABBBAAAABBABBAAAABBBABAABBAB.... A gradient copolymer is similar to a random copolymer, but with a variable monomer content along the chain, e.g., in the following way:

[0021] AAAAAAAAABAAABBBAAABBABBBAABBBBBBABBBBBBBB...

[0022] In an alternating copolymer, there is a regular arrangement of the monomers along the chain, e.g. in the following way:

[0023] AB AB ABABABABABABAB ...

[0024] Block copolymers are characterized by longer blocks or sequences of each monomer, which can also be repeated, e.g. in one of the following ways:

[0025] AAAAAAAAABBBBBBBBBBBB or

[0026] AAAAAAAAABBBBBBBBBBBAAAAAAAAAAAAAABBBBBBBBBBB...

[0027] Blend polymers are characterized by the fact that different polymers are present without chemically reactive connection of the polymers, e.g. according to the following type:

[0028] AAAAAAA + BBBBBBBB.

[0029] Graft copolymers consist of a backbone consisting of the polymer of one monomer, onto which blocks / "side arms" of a polymer of another monomer are grafted, e.g. of the following type:

[0030] BBB

[0031] BBBBB

[0032] BBBBB

[0033] AAAAAAAAAAAAAAAAA...

[0034] BBBBB

[0035] BBBB

[0036] B

[0037] B

[0038] In all of the above cases, the molecular chains can be linear or (slightly) branched. This allows polymeric materials to be mixed with other substances, particularly for functionalization (e.g., stabilizers, flame retardants, etc.) and / or cost reduction (fillers). The copolymers can be selected to provide different properties of different plastics.

[0039] The polyolefin copolymer of the plastic matrix can comprise or be a polymer blend (especially) with polymers of different grain sizes and / or molecular chain lengths. Smaller particles / molecules can penetrate better between the threads or individual filaments and create a strong bond between the threads. Larger particles / molecules, on the other hand, tend to penetrate less deeply and can thus influence or adjust the surface properties of the prepreg, e.g., the bond to subsequent material composites. Furthermore, by blending polymers with different melting points, the melting point of the blend can be easily adjusted to the specific application.

[0040] Preferably, the thread content is at least 60 wt.% of the prepreg layer, in particular in a range of 0.75 to 0.85 wt.%. The thread content can be adjusted significantly via the (shape of the) holes or the arrangement of the threads, the thread count(s) used, and / or the coating of the polyolefin copolymer plastic matrix. In many cases, the thread content ensures the desired tensile strength of the prepreg layer and a suitable surface and / or a suitable envelope volume for applying a sufficient coating of the polyolefin copolymer plastic matrix.

[0041] The threads preferably comprise glass fiber bundles, in particular with a linear density (tex) in the range of 300 to 1,200. The threads are preferably formed with a plurality of glass fiber filaments that run essentially parallel to one another and thus form a bundle. The glass fiber bundle can comprise internal pores that can serve as a reservoir for the polyolefin copolymer plastic matrix or are at least predominantly or (almost) completely filled thereby. The pores / reservoirs can be adjusted in particular via the selection of the linear density. The provision of these pores / reservoirs and the coordinated selection of the polyolefin copolymer enables a very intimate bond between threads and plastic matrix.

[0042] The holes in the prepreg layer can have an opening width of up to 200 mm [millimeters], with the opening width particularly preferably being in the range of 1 to 150 mm. The opening width is defined as the maximum dimension of the hole (perpendicular to the thickness of the layer), for example, the largest free diagonal for a square hole.

[0043] Small hole sizes, e.g., in the range of 1 to 10 mm, are preferred for processes / components with a high oriented fiber content. In injection molding reinforcement, these hole sizes are advantageous for achieving good embedding in the injection molding compound.

[0044] Larger opening widths, e.g., in the range of 30 to 100 mm, are suitable for large-area applications with lower force absorption, such as in the construction industry for use with insulation materials for reinforcement or with masonry facings (so-called "slips"), for combining individual elements into larger mats and thus facilitating manual work. For a square hole, an edge length of (maximum) approximately 100 mm is preferred for such applications.

[0045] The threads can form a fabric. The fabric preferably has a regular and / or uniform shape. The fabric can be formed essentially only from threads and / or thread bundles. This can be provided in webs and / or panels and / or in a single layer. The fabric has a very high surface area to material thickness ratio. The fabric can be wound and / or stackable and / or (elastically) deformable. The fabric can be open; an open fabric has a plurality of (transparent) holes.

[0046] The prepreg layer can have a minimum bending radius of 30 mm [millimeters]. The minimum bending radius is defined as the bending radius at which (under normal room conditions, especially at room temperature) no (significant) detachment of the plastic matrix and / or kinking of the threads occurs. It is typically in the range of 10 to 20 mm (for example, with a fabric thickness of a maximum of 1.0 millimeters). The prepreg layer structure proposed here therefore allows surprisingly small bending radii without damaging the layer and / or significantly impairing further use.

[0047] The prepreg layer is designed in such a way that the threads are embedded in the plastic matrix. This means, in particular, that the plastic matrix essentially encloses the entire thread. If filament bundles are present, they are essentially also penetrated by the plastic matrix, or the filaments themselves are (largely) surrounded by the plastic matrix. Thus, there is no (separate) layer structure of threads and plastic matrix. The plastic matrix thus forms, in particular, all surfaces of the prepreg layer.

[0048] According to a further aspect, the use of a plastic matrix with polyolefin copolymers is proposed for the production of open prepreg layers with low layer density. Regarding the properties of the open prepreg layer and / or its production, reference can be made in full to the individual features specified in connection with the prepreg layer itself.

[0049] Furthermore, the use of at least one prepreg layer of the type disclosed here for forming three-dimensional structural components by means of one of the following manufacturing processes is also proposed: (injection) molding, laminating (joining several layers with the aid of suitable laminating agents), foaming, pressing, deep drawing, vacuum forming.

[0050] To produce such a prepreg layer, a process can be carried out which comprises at least the following steps: a. Providing a thread structure with a predetermined basis weight, b. Adding a water-polyolefin mixture to the thread structure so that the basis weight is increased by at least 30% by weight, in particular by 35 to 65% by weight, c. Dewatering the thread structure with water-polyolefin mixture, this preferably taking place thermally at a temperature in the range between 100°C and the melting temperature of the polyolefin, d. Consolidating the thread structure with the polyolefin, this preferably taking place thermally at a temperature above the melting temperature of the polyolefin.

[0051] The explanations of the prepreg layer can also be used to characterize the manufacturing process, and vice versa.

[0052] The invention and the technical environment are explained below with reference to figures. It should be noted that the invention is not limited to the embodiments shown. The features illustrated in the figures can be extracted and, if necessary, combined with other features of the description or other figures, unless explicitly excluded below.

[0053] They show schematically:

[0054] Fig. 1 : a plan view of a prepreg layer,

[0055] Fig. 2: a sectional view of a prepreg layer, and

[0056] Fig. 3: an overview of a manufacturing process.

[0057] Figures 1 and 2 illustrate, by way of example, that the prepreg layer 1 comprises a plurality of threads 2 arranged to form a woven or open grid. These threads are embedded in a plastic matrix 3. At the same time, a plurality of holes 4 with a predetermined opening width 5 are provided. The plastic matrix 3 comprises a polyolefin copolymer, and the prepreg layer 1 has a layer density of up to a maximum of 1.0 g / cm 3 . The layer density can be determined by means of the envelope volume, which can be determined based on a given length 6, width 7 and thickness 8 of the prepreg layer 1.

[0058] With regard to the design of the holes, it should be noted that the prepreg layer 1 (and in particular its layer density) is significantly defined by the (at least present) holes 4, which are shown in the plan view in Fig. 1, which are thus "see-through" and extend across the thickness 8 of the prepreg layer 1. These holes can also be connected to one another via a hole 4, as indicated in Fig. 2. However, it is preferred that holes 4, as indicated in Fig. 2, are present only to a small (negligible) extent or (practically) not at all.

[0059] Fig. 3 illustrates, by way of example and schematically, a possible manufacturing process for a prepreg layer 1, wherein continuous production is shown here from left to right and comprises the following steps: a. Providing a thread structure made of threads 2 with a predetermined basis weight, here by means of a weaving machine 10. The produced thread structure is transported further along a predetermined feed direction 16. b. Adding a water-polyolefin mixture 9 to the thread structure so that the basis weight is increased by at least 30%. This step is carried out here in a trough 11 or a (roller) bath. c. Dewatering the thread structure with water-polyolefin mixture 9, wherein this takes place here in a first oven 12. d. Consolidating the thread structure with the polyolefin, wherein this takes place in a second oven 13, wherein the second oven 13 can also be designed in / on the first oven 12. e. Cooling of the thread structure along a cooling section 14. f.Winding the prepreg layer 1 with the cured plastic matrix 3 in a winding station 15.

[0060] In summary, the solutions proposed here at least partially overcome the disadvantages described with reference to the state of the art. Prepregs with a high and variable utility value were presented, allowing the composite structure to stabilize the final product as evenly as possible across the entire surface of the final product. In particular, prepregs were created that are suitable for further processing using currently available, potentially highly forming, manufacturing technologies.

[0061] 1 prepreg layer

[0062] 2 threads

[0063] 3 Plastic matrix

[0064] 4 holes

[0065] 5 Opening width

[0066] 6 Length

[0067] 7 Width

[0068] 8 thickness

[0069] 9 Water-polyolefin mixture

[0070] 10 weaving machine

[0071] 11 Trough

[0072] 12 first oven

[0073] 13 second oven

[0074] 14 Cooling section

[0075] 15 changing stations

[0076] 16 Feed direction

Claims

Claims Prepreg layer (1) , comprising at least a plurality of filaments (2), a plastic matrix (3) and a plurality of holes (4), wherein the plastic matrix (2) comprises a polyolefin copolymer and the prepreg layer (1) has a layer density of up to a maximum of 1.0 g / cm³ 3 comprising a prepreg layer (1) according to claim 1, wherein the layer density is 0.45 to 0.9 g / cm³. 3A prepreg layer (1) according to claim 1 or 2, wherein the polyolefin copolymer of the polymer matrix (3) is selected from the following group: statistical copolymer, gradient copolymer, alternating copolymer, block copolymer, polymer mixture, graft polymer. A prepreg layer (1) according to claim 3, wherein the polyolefin copolymer of the polymer matrix (3) comprises a polymer mixture with polymers of different particle sizes or molecular chain lengths. A prepreg layer (1) according to any one of the preceding claims, wherein the thread content is at least 60 wt.%. A prepreg layer (1) according to any one of the preceding claims, wherein the threads (2) comprise fiberglass bundles. A prepreg layer (1) according to any one of the preceding claims, wherein the holes (4) have an opening width (5) in the range of up to a maximum of 150 mm. A prepreg layer (1) according to any one of the preceding claims, wherein the threads (2) form a woven fabric.A prepreg layer (1) according to any one of the preceding claims, wherein it has a minimum bending radius of 30 mm. A prepreg layer (1) according to any one of the preceding claims, wherein the threads (2) are embedded in the plastic matrix (3). Use of a plastic matrix (3) with polyolefin copolymers for the production of open prepreg layers (1) with low layer density. Use of at least one prepreg layer (1) according to any one of claims 1 to 10 for forming three-dimensional structural components by means of one of the following manufacturing processes: casting, laminating, foaming, pressing, deep drawing, vacuum forming.

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