Method for producing a prepeg layer, prepeg layers and use thereof

Abstract

The invention relates to a method for producing a prepreg layer (1), at least comprising the following steps: a) providing a yarn structure (2) having a grammage, b) adding a water-polyolefin mixture (3) to the yarn structure (2) so that the grammage is increased by at least 30%, c) dewatering the yarn structure (2) with water-polyolefin mixture (3), d) consolidating the yarn structure (2) with the polyolefin.

Description

[0001] Method for producing a prepreg layer, prepreg layers and their use

[0002] The present invention relates to methods for producing a prepreg layer, prepreg layers and their use.

[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 and, if necessary, also with uniform surface reflection 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, while ensuring that the composite structure stabilizes the final product as evenly as possible across the entire surface of the final product. In particular, a simple method for producing prepregs is to be created, which is suitable for further processing using currently available, possibly highly forming, manufacturing technologies.

[0010] These objects are achieved by the features of the independent claims. Advantageous further developments are specified in the respective dependent claims. The description, particularly with the figures, illustrates the invention and provides further exemplary embodiments. The features listed individually in the claims can be combined with features of other claims and / or the description.

[0011] A method for producing a prepreg layer contributes to this, which comprises at least the following steps: a) providing a thread structure with a basis weight, b) adding a water-polyolefin mixture to the thread structure so that the basis weight is increased by at least 30%, c) dewatering the thread structure with water-polyolefin mixture, d) consolidating the thread structure with the polyolefin.

[0012] Steps a), b), c), and d) can be performed in the order specified here. However, it is also possible for the steps to be performed partially simultaneously or in a superimposed manner. This means, in particular, that the steps are performed (partially) simultaneously but still spatially separately, for example, as in continuous production, where the (endless) thread structure is successively fed to different stations for the execution of steps b), c), and d). These steps are therefore not performed simultaneously on the same section of the thread structure.

[0013] Within the scope of step a), a large number of threads (also called filaments or (continuous) fibers) can be provided. These can be provided individually, in a directed manner and / or (partially) in combination with one another. Alternatively or cumulatively, thread bundles can also be provided, i.e. (separate or separated) strands made up of a large number of threads. The thread bundles can be designed as so-called rovings, i.e. as (multi)filament yarn made up of threads (or filaments) arranged in parallel. It is particularly preferred that all threads and / or thread bundles are provided substantially unidirectionally aligned with one another, in particular in the direction of a common conveying or transport direction. The threads can consist of at least one or more of the fibrous materials mentioned above.

[0014] The threads preferably comprise glass fiber bundles, in particular with a linear density in the range of 300 to 1,200 tex. The threads are preferably formed with or from a plurality of glass fiber filaments that run essentially parallel to one another, thus forming a bundle. The glass fiber bundle can comprise internal pores that can serve as a reservoir for the application of the plastic matrix.

[0015] These threads are arranged in such a way that they provide an (independent) thread structure, for example in the manner of a fleece, woven fabric, knitted fabric, warp-knitted fabric or scrim.

[0016] The thread structure is preferably embodied as a woven fabric. The woven fabric preferably has a regular and / or uniform shape. The woven fabric can be formed essentially only with threads and / or thread bundles. It can be provided in webs and / or panels and / or in single layers. The woven fabric has a very high surface area to material thickness ratio. The woven fabric can be wound and / or stackable and / or (elastically) deformable. The woven fabric can be open, with an open woven fabric having a plurality of (transparent) holes.

[0017] An open or lattice-like thread structure can have holes with an opening width in the range of up to a maximum of 200 mm [millimeters], whereby the opening width is particularly preferably in the range of 1 to 150 mm. The opening width is understood to be the maximum extent of the hole (perpendicular to the thickness of the thread structure), for example, in the case of a square hole, the largest free diagonal. Small opening widths, e.g., in the range of 1 to 10 mm, are preferably produced for processes / components with a high, oriented fiber content. In injection molding reinforcement, these hole sizes are advantageous in order to achieve good embedding in the injection molding compound. Large opening widths, e.g., in the range of 30 to 100 mm, are suitable for large-area applications with lower force absorption, e.g.,In the construction industry, for use with insulation materials for reinforcement or with masonry facings (so-called "bricks"), 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.

[0018] According to step a), the thread structure is assigned a predetermined basis weight. The basis weight can be adjusted, for example, by a suitable choice of material and structure of the threads, as well as the arrangement of the threads relative to one another, particularly taking into account the design of the holes. The basis weight is usually expressed in grams per square meter [g / m 2 ] and can, for example, be chosen from a range of 50 to 500 g / m zbe selected or set. The basis weight is considered in particular with a dimension of 10 cm x 10 cm [centimeters], whereby a basis weight value is maintained within such a dimension field. If the fabric is larger than this dimension field, the value of the fabric can preferably be maintained for all dimension fields, especially with the same thickness or structure of the thread structure. After step a), the basis weight is "dry," meaning it contains practically no (separated or unbound) water.

[0019] According to step b), a water-polyolefin mixture is then added to the thread structure so that the basis weight is increased by at least 30%.

[0020] In the water-polyolefin mixture, a polyolefin copolymer is used in particular. Polyolefins (also called "polyalkenes") are polymers made from hydrocarbons of the formula C n H 2nwith a double bond (ethylene, propylene, but-1-ene, isobutene). Polyolefins are semi-crystalline thermoplastics. Polyolefins are currently usually produced from oil or natural gas. The process is called polymerization, whereby short chains of chemicals (monomers) are linked together to form long chains (polymers) using a catalyst. Polyolefin copolymers are therefore polyolefins composed of two different types of monomer units. The polyolefin used is applied using an aqueous solution, for example by spraying or dipping. The water-polyolefin mixture can be added particularly intensively or comprehensively so that the thread structure is completely wetted or even soaked through. This can be assisted by capillary forces, for example due to the selection of the threads and / or the shape of the thread structure.

[0021] After step b), the basis weight is a "wet" one, meaning it particularly comprises a portion of the added water or water-polyolefin mixture, which in particular adheres to and / or in the fabric or is transported with it. The addition is adjusted so that the basis weight is increased by at least 30%. The basis weight after the predefined addition of the water-polyolefin mixture can also be referred to as the "wet basis weight." This increase in basis weight must be adjusted, particularly taking into account the absorbency of the fabric and / or the composition of the polyolefin copolymer and / or the desired properties of the prepreg layer. In particular, the additional layer or the wet basis weight is specifically adjusted and, if necessary, also directly monitored or corrected.For example, during step b), it is possible that more water-polyolefin mixture is initially added than corresponds to the target, with a portion of the coating subsequently being removed, thus setting the target. Obviously, the predetermined increase in area weight is achieved at the end of step b) – no further plastic is added until the end of step d).

[0022] After the water-polyolefin mixture has been added, the (wet) thread structure is dewatered according to step c). In other words, this means in particular that the water content or the water adhering to the thread structure is removed, in particular evaporated. The (dry) basis weight of the thread structure after step c) is therefore generally less than the (wet) basis weight after step b) but also greater than the (dry) basis weight after step a). The basis weight can decrease by at least 9%, in particular in the range from 9 to 27%, when carrying out step c). It is preferred that the basis weight is reduced in the range from 10 to 24%, in particular 13 to 22%, and particularly preferably in the range from 15 to 20% when carrying out step c). The water has the particular function of evenly distributing the polyolefin particles in or on the thread structure, which is supported by its flow properties.It can therefore be assumed that this will be achieved to an acceptable extent at a given time, and that the water can be removed. To largely maintain the distribution of the polyolefin particles in or on the thread structure during this process, evaporation of the water is particularly advantageous. Thus, at the end of step c), a (completely) dry thread structure is obtained.

[0023] It is preferred that step c) is carried out thermally, with a temperature (of the thread structure including the water-polyolefin mixture) being set in the range between 100°C and the melting temperature of the polyolefin. Step c) is preferably carried out by means of electromagnetic radiation in the wavelength range 0.78 pm to 100 pm [micrometers], in particular in the wavelength range 1 pm to 10 pm, or by means of infrared radiation. This obviously stipulates that the support (optionally with the thread structure) is heated to a dewatering temperature that is above the evaporation temperature of the water but (significantly or certainly) below the melting temperature of the polyolefin used. In other words, this means in particular that (significant) melting of the polyolefin used is prevented during step c). The thermal dewatering can more preferably be carried out over a period of 0.2 to 4.0 min [minutes].The predefined time period can be adjusted taking into account the amount of water to be removed per square meter, the exposure distance, the heating power, and / or the feed speed of the yarn structure. For example, if the yarn structure is woven during step a), the feed speed depends significantly on the weft insertion rate (ß / min) and the weft thread density (ß / cm), so the other parameters can be adjusted accordingly.

[0024] The dried filamentary structure with the polyolefin is then consolidated in step d). This involves, in particular, thermal consolidation. The (dry) basis weight of the filamentary structure after step d) corresponds (essentially) to the (dry) basis weight after step c). During this step, a permanent bonding or fixing of the polyolefin particles to one another and to the filaments is achieved by melting or melting them onto or onto the filaments and, upon subsequent solidification, bonding them to the filaments or to one another. It is possible for the filamentary structure to be at the dewatering temperature or at a temperature lower than the dewatering temperature at the beginning of step d). Step d) leads to a significant, possibly sudden, increase in the ambient temperature, whereby the greatest possible heating rate of the filamentary structure with the polyolefin can be achieved.In particular, step c) takes place in a first oven, while step d) takes place in a second oven, wherein the thread structure is preferably guided or moved from the first oven directly into the second oven or the ovens merge seamlessly into one another or the oven as such is designed with two different zones.

[0025] Preferably, step d) is carried out thermally, with a temperature (of the thread structure including the water-polyolefin mixture) being set in the range above the melting temperature of the polyolefin. The (thermal) consolidation can more preferably be carried out over a period of 0.2 to 4.0 minutes. The predefined period can be adjusted taking into account the amount of polyolefin to be melted per square meter, the heating power, and / or the feed rate of the thread structure.

[0026] It is preferred that the basis weight in step b) is increased by 35 to 65% by weight. With a 35% by weight water-polyolefin mixture, just enough polyolefin is added to the product to achieve a favorable fiber-to-matrix ratio in the final product. With a loading of 35% by weight or more, it is ensured that the fibers in the final product are sufficiently covered with polyolefin matrix to give the product sufficient dimensional stability so that it can be easily handled with conventional gripper systems and thus easily processed automatically. Furthermore, this sufficient amount of polyolefin matrix ensures good bonding properties during further processing in subsequent processes.Above 65% by weight, the product's economic viability is compromised because there is a significant excess of polyolefin in the product, which is accompanied by large amounts of added water that must be evaporated. Since water evaporation is a highly energy-intensive process, excessive exposure of the product to the water-polyolefin mixture is economically unfavorable.

[0027] It is preferred if a water-polyolefin mixture is added in step b) in which the water content is in the range from 40 to 60 wt. % [percent by weight]. In the range specified here, it can be achieved or guaranteed that the mixture remains stable in the long term and can still be processed economically. The specified lower limit of 40 wt. % can, for example, ensure that the described production process can be operated economically. At lower values, the water content is too high, so that excessive energy would have to be expended for drying. At significantly higher polyolefin weight fractions, e.g. more than 60 wt. %, the mixture can be unstable, i.e. phase separation occurs, so that the polyolefins and water separate, i.e. demix. A uniform distribution of the polyolefins in the thread structure is therefore no longer guaranteed.

[0028] During step b), the thread structure is preferably impregnated in the water-polyolefin mixture. Thus, the thread structure can be fed to a trough, for example, by means of a roller arrangement, so that it dips beneath a surface of the water-polyolefin mixture (so-called "liquor") located in the trough. Rollers can (further) be provided in the region of the trough, over and / or between which the thread structure is guided. The rollers can have a roller surface that adjusts or effects the application or introduction of the water-polyolefin mixture into the thread structure. The viscosity can generally, or for example during impregnation, preferably be below 5,000 mPas, preferably between 500 and 3,000 mPas. In this way, a rapid, uniform, and / or comprehensive addition of the water-polyolefin mixture to the thread structure can be achieved.

[0029] It is possible that during or after this impregnation process, the thread structure impregnated with the water-polyolefin mixture is subjected to a (subsequent) roller squeezing process. During a roller squeezing process, the thread structure is passed between two or more rollers, whereby the pressure between at least two rollers forces the water-polyolefin mixture between the individual threads and their filaments. To adjust the contact weight, the distance between the rollers can be set to a defined gap, or the rollers can be movably supported on one another. The adjustment or setting of the basis weight can be achieved, for example, by at least one of the following measures:

[0030] The contact pressure of the roller(s) is varied, for example by using rollers with higher / lower dead mass, or by varying an external pressure application, e.g. by means of pneumatics, or similar.

[0031] - The wrap angle (angle range of the roll over which the thread structure lies) is adjusted.

[0032] - The roller surface(s) is changed, for example optional use of smooth, (fabric-)covered and / or structured rollers.

[0033] - Adjusting the feed speed of the thread structure.

[0034] - Extension of the residence time below the surface of the fleet.

[0035] During the roll squeezing process, the thread structure can also be patched and / or padded.

[0036] The polyolefin used here is preferably a copolymer selected from the following group: random copolymer, gradient copolymer, alternating copolymer, block copolymer, polymer mixture, graft polymer.

[0037] In a random copolymer, there is a random distribution of monomers in the chain, e.g., in the following manner: AABBABBBBAAAABAABBBAAAABBABBAAAABBBABAABBBAB....

[0038] A gradient copolymer is similar to a random copolymer, but with a variable monomer content along the chain, e.g. in the following way:

[0039] AAAAAAAAABAAABBBAAABBABBBAABBBBBBABBBBBBBB. ...

[0040] In an alternating copolymer, there is a regular arrangement of the monomers along the chain, e.g. in the following way:

[0041] ABABABAB AB AB ABAB ...

[0042] 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:

[0043] AAAAAAAAABBBBBBBBBBBB or

[0044] AAAAAAAAABBBBBBBBBBBAAAAAAAAAAAAAABBBBBBBBBBB...

[0045] 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:

[0046] AAAAAAA + BBBBBBBB.

[0047] 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:

[0048] BBB

[0049] BBBBB

[0050] BBBBB

[0051] AAAAAAAAAAAAAAAAA...

[0052] BBBBB

[0053] BBBBB

[0054] B

[0055] In all of the above cases, the molecular chains can be linear or (slightly) branched.

[0056] 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.

[0057] The polyolefin copolymer is preferably a polymer blend (in particular) 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.

[0058] According to a further aspect, a wet prepreg layer is proposed, comprising a thread structure which is wetted with a water-polyolefin mixture, wherein the water-polyolefin mixture amounts to 35 to 65% of the (wet) layer weight.

[0059] Most preferably, the wet prepreg layer is produced using steps a) and b) of the process proposed here. Independently of this, the stated properties of the "wet" thread structure can also be used individually to characterize the wet prepreg layer, particularly with regard to its subsequent use. Following a further aspect, the use of a wet prepreg layer for thermal post-treatment and production of a prepreg layer with a solid polyolefin matrix is ​​proposed.

[0060] Most preferably, the wet prepreg layer is suitable for thermal post-treatment and production of a prepreg layer according to steps c) and d) of the process proposed here. Independently of this, the specific features of dewatering and / or consolidation can also be used to characterize the wet prepreg layer.

[0061] Finally, a prepreg layer is also proposed, which is produced using a method disclosed here, wherein the smallest bending radius of the prepreg layer is up to a maximum of 30 mm [millimeters]. The smallest bending radius is understood to be the bending radius at which (under normal room conditions, in particular at room temperature) no (significant) detachment of the plastic matrix and / or kinking of the threads occurs. It lies in particular in the range of 10 to 20 mm (for example, with a fabric thickness of a maximum of 1.0 millimeters). The structure of the prepreg layer proposed here therefore allows surprisingly small bending radii without damaging the layer and / or significantly impairing further use.

[0062] The prepreg layer is designed in such a way that the threads are embedded in a polyolefin or plastic matrix. This means, in particular, that the matrix essentially encloses the entire thread. If filament bundles are present, these are essentially also penetrated by the matrix, or the filaments themselves are (largely) surrounded by the matrix. In this way, the matrix forms, in particular, all surfaces of the prepreg layer.

[0063] Most preferably, the prepreg layer is designed with a large number of holes or as an (open) grid, and has a layer density of up to a maximum of 1.0 g / cm 3[grams per cubic centimeter]. The layer density is determined by measuring the weight of the layer and relating it to its (envelope) 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 (consolidated) prepreg layer and the thickness of the (consolidated) prepreg layer.

[0064] The thickness of a layer is measured as the distance between a reference plate on which the layer rests and a parallel, circular pressure pad (preferably with a pad diameter of approximately 50 mm), which exerts a specified pressure (preferably approximately 1 kPa) on the layer to be measured. The distance between the reference plate and the pressure pad is measured and recorded. Standard climatic conditions prevail. The thickness measurement should preferably be performed at various points on the layer, and then an average value calculated from these measurements. The determination of the layer thickness must be carried out in accordance with DIN EN ISO 5084.

[0065] The upper limit value for the layer density of 1 .0 g / cm 3ensures 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.

[0066] 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 3 a particularly advantageous application quantity of the polyolefin copolymer plastic matrix, which particularly favors further processing, especially for complex and highly stressed components.

[0067] Preferably, at least a slight gloss is noticeable in the prepreg layer, which is adjusted in particular via consolidation. In particular, the prepreg layer does not have a matte, diffusely reflective surface. With sufficient consolidation, the structural features of the rough surface combine to form a relatively smooth, reflective, glossy film, whereby the structure of the thread material can also influence the surface structure. The invention and the technical field 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 further figures, unless this is explicitly excluded below.

[0068] They show schematically:

[0069] Fig. 1 : a plan view of a prepreg layer,

[0070] Fig. 2: a sectional view of a prepreg layer,

[0071] Fig. 3: an overview of an embodiment of the method disclosed here, and

[0072] Fig. 4: Examples of different implementations of step b).

[0073] Figures 1 and 2 illustrate, by way of example, that the (finished or consolidated) woven prepreg layer 1 comprises a plurality of threads arranged to form a thread structure 2 (woven fabric or open grid). These are embedded in a polyolefin matrix 9. At the same time, a plurality of holes 4 with a predetermined opening width 5 are provided. The polyolefin matrix 9 comprises a polyolefin copolymer, and the prepreg layer 1 has a preferred 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.

[0074] Fig. 3 illustrates, by way of example and schematically, a possible manufacturing process for such a prepreg layer 1, wherein continuous production is shown here from left to right and comprises the following steps: a) Providing a thread structure 2 with a predetermined basis weight, here by means of a weaving machine 10. The produced thread structure 2 is transported further along a predetermined feed direction 16. b) Adding a water-polyolefin mixture 3 to the thread structure 2 such that the basis weight is increased by at least 30%. This step is carried out here in a trough 11, which can in particular be designed according to one of the embodiments from Fig. 4. c) Dewatering the thread structure 2 with water-polyolefin mixture 3, wherein this takes place here in a first oven 12. d) Consolidating the thread structure 2 with the polyolefin, wherein this takes place in a second oven 13.e) Cooling the thread structure 2 along a cooling section 14. f) Winding up the prepreg layer 1 in a winding station 15.

[0075] Fig. 4 discloses, by way of example and schematically, different embodiments of step b), in which the water-polyolefin mixture 3 is added to the thread structure 2 in such a way that the basis weight is increased by at least 30%.

[0076] It is illustrated in various variants (I) to (V) that the thread structure 2 is fed to a trough 11 in which a water-polyolefin mixture 3 is stored. A (lowest) roller 17 is always immersed in the water-polyolefin mixture 3 and is in contact with the thread structure 2 as it is guided past along the feed direction 16. The rollers 17 can have a roller surface that can adjust or effect the application or introduction of the water-polyolefin mixture 3 to the thread structure 2.

[0077] As can be seen from the variants, the rollers used, their number and shape, and / or the contact path or wrap angle of the thread structure 2 can be adapted in various ways to ensure the desired increase in the basis weight in this step. The essential differences between the variants illustrated in Fig. 4 become apparent upon examination and are briefly summarized here: Variant (I): The thread structure 2 is guided (essentially straight) through a gap between two rollers 17, with the lower roller not completely submerged in the bath of water-polyolefin mixture 3.

[0078] Variant (II): The thread structure 2 is passed (essentially straight) through a gap between two (an upper and a middle) rollers 17, with a lower roller not completely submerged in the bath of water-polyolefin mixture 3. The lower roller 17 transfers a portion of the absorbed water-polyolefin mixture 3 to a middle roller 17, which is positioned completely outside the bath of water-polyolefin mixture 3.

[0079] Variant (III): The thread structure 2 is guided under the lower roller 17, which is not completely submerged in the bath of water-polyolefin mixture 3. The thread structure 2 is then guided further around this lower roller 17 and (adjacent to it) through a gap between it and an upper roller 17. The thread structure 2 is then guided further around this upper roller 17 (adjacent to it) and finally transported away again in the original feed direction 16.

[0080] Variant (IV): Here the roller and guide arrangement is as in variant (III), but here a third (uppermost) roller 17 is provided and the thread structure 2 is finally guided through a gap between the two upper rollers 17.

[0081] Variant (V): This illustration illustrates that to set the desired contact weight, the roller spacing can be adjusted to a defined gap or the rollers can be movably supported on one another. The basis weight can be adjusted, for example, by at least one of the measures indicated here: adjusting the contact pressure (+p, -p, 0) with respect to rollers 17; adjusting the wrap angle (+q, -q, 0); adjusting the feed speed (v) of thread structure 2.

[0082] This demonstrates that the solutions proposed here at least partially overcome the disadvantages described with reference to the state of the art. Furthermore, prepregs with a high and variable utility value can be easily produced, ensuring that the composite structure stabilizes the final product as evenly as possible across the entire surface of the final product. In particular, a simple method for providing prepregs has been created, which are suitable for further processing using currently available, potentially highly forming, manufacturing technologies.

[0083] List of reference symbols

[0084] 1 prepreg layer

[0085] 2 thread structures

[0086] 3 Water-polyolefin mixture

[0087] 4 holes

[0088] 5 Opening width

[0089] 6 Length

[0090] 7 Width

[0091] 8 thickness

[0092] 9 Polyolefin matrix

[0093] 10 weaving machine

[0094] 11 Trough

[0095] 12 First oven

[0096] 13 Second oven

[0097] 14 Cooling section

[0098] 15 changing stations

[0099] 16 Feed direction

[0100] 17 roll

Claims

Claims: A method for producing a prepreg layer (1), comprising at least the following steps: a) providing a filament structure (2) with a certain basis weight, b) adding a water-polyolefin mixture (3) to the filament structure (2) such that the basis weight is increased by at least 30%, c) dewatering the filament structure (2) with the water-polyolefin mixture (3), d) consolidating the filament structure (2) with the polyolefin. The method of claim 1, wherein step c) is thermally performed, with a temperature set in the range between 100°C and the melting point of the polyolefin. The method of claim 2, wherein step c) is performed using electromagnetic radiation in the wavelength range of 0.78 pm to 100 pm. The method of any one of the preceding claims, wherein in step d) a temperature is set in the range above the melting point of the polyolefin.A method according to any one of the preceding claims, wherein the basis weight is increased by 35 to 65% in step b). A method according to any one of the preceding claims, wherein a water-polyolefin mixture (3) is added in step b) wherein the water content is in the range of 40 to 60%. A method according to any one of the preceding claims, wherein the filament structure is impregnated in the water-polyolefin mixture (3) in step b). A method according to any one of the preceding claims, wherein the viscosity of the added water-polyolefin mixture is below 5,000 mPas, preferably between 500 and 3,000 mPas. A method according to any one of the preceding claims, wherein the basis weight is reduced by 9 to 27% during step c). A method according to any one of the preceding claims, wherein the polyolefin comprises a copolymer selected from the following group: statistical copolymer, gradient copolymer, alternating copolymer, block copolymer, polymer blend, graft polymer. A method according to claim 10, wherein the polyolefin copolymer comprises a polymer blend with polymers of different particle sizes and / or molecular chain lengths. A wet prepreg layer comprising a filament structure (2) wetted with a water-polyolefin mixture (3), wherein the water-polyolefin mixture (3) constitutes 35 to 65% of the layer weight.A wet prepreg layer according to claim 12, comprising an open or grid-like filament structure (2) having holes with an opening width in the range of 1 to 150 mm. Use of a wet prepreg layer according to claim 12 for thermal post-treatment and production of a prepreg layer (1) with a solid polyolefin matrix (4). A prepreg layer (1) produced by a method according to any one of the preceding claims 1 to 11, wherein it has a minimum bending radius of up to 30 mm.

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