Prepreg layer and use thereof

Abstract

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

Description

Technical Field

[0001] The present invention relates to prepregs, their production and use. Background Art

[0002] In particular, components (eg vehicle components, aircraft components, ship components, train interior components, electronic components, etc.) can be produced with fiber-reinforced materials on the basis of fiber-based semi-finished products, the best-known representative of which is "prepreg".

[0003] Prepregs generally contain a fiber material made of one or more types of fibers, such as carbon fibers, glass fibers, aramid fibers, basalt, boron fibers, ceramic fibers, silica fibers, steel fibers, polyester fibers, nylon fibers, polyethylene fibers, organic glass fibers, natural fibers and / or other types of fibers, wherein the fiber material is impregnated with a matrix plastic. The fibers of the fiber material can be present in the prepreg as continuous fibers with a preferred direction (unidirectional layer), as an ordered fabric surface (e.g. woven fabric, knitted fabric, scrim, interlaced knitted fabric...) or as a disordered fabric surface such as wool or a random fiber mat.

[0004] Polymer materials (also called "resin systems") are usually used as matrix plastics for prepregs, such as thermosets (also called duromers; synthetic resins, epoxy resins, phenolic resins, polyester resins), thermoplastics or elastomers. When the prepregs are delivered, thermosets and elastomers have not yet reacted completely and are therefore still plastically deformable. Special storage conditions must be observed here, such as very low storage temperatures. It is well known that thermoplastics can be repeatedly put into a plastically deformable state by heating.

[0005] Prepregs are usually manufactured as layers, sheets, tapes or webs, with the webs usually being delivered in rolls.

[0006] To produce an object or component, a piece large enough is usually separated from the prepreg in order to line the surface of a pressing tool (mold). By pressing the prepreg in a pressing tool under the influence of heat (or more generally by applying a pressure greater than atmospheric pressure to the prepreg), the thermosetting or elastomeric matrix plastic reacts and the object or component is shaped. In the case of a thermoplastic matrix plastic, it acquires plasticity through the action of heat and the shape of the object or component can be achieved by pressing the prepreg under the action of heat and then cooling the shaped prepreg to below the softening temperature of the thermoplastic.

[0007] The requirements for prepregs can be very different, especially with regard to their end use for the production of injection-molded components and / or the preparation of the injection-molding process. In particular, it may be desirable to achieve a particularly uniform, complete and / or strong adhesion of the matrix plastic to the textile surface structure. In particular when considering continuous production, it is necessary to find suitable, cost-effective and fast methods for producing such prepregs.

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

[0009] The object of the present invention is to at least partially overcome the disadvantages described with reference to the prior art and also to produce in a simple manner prepregs of high and variable practical value, in this case ensuring that the composite structure stabilizes the final product as uniformly as possible over the entire planar design of the final product. In particular, a simple possibility of providing prepregs is to be created, wherein the method is suitable for further processing using manufacturing technologies existing on the market that require intensive shaping.

[0010] The objects are solved by the features of the independent claims. Advantageous further developments are specified in detail in the dependent claims. The description, in particular the drawings, illustrate the invention and show further exemplary embodiments. The features listed individually in the claims can be combined with features of other claims and / or the description.

[0011] The prepreg layer contributes to this, the prepreg layer having 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 maximum of 1.0 g / cm 3 Layer density [g per cubic centimeter].

[0012] A "layer" is to be understood as meaning in particular a flat and / or strip-like structure, which can be described, for example, in terms of the dimensions of length and width being significantly greater than the thickness (perpendicular thereto), in particular in a multiple or power manner. The warp (longitudinal) and weft (transverse) threads can be arranged in a (quasi) meandering shape around a common plane and can extend partially or alternately above and below it. The layer preferably has only a single plane with threads, wherein this plane is arranged approximately in the center relative to the thickness of the layer. The layer can be described as a textile. In particular, the layer forms an essentially stable composite material and is distinguished in particular from a loose (massive) collection of fiber elements.

[0013] A large number of threads (also called filaments or (continuous) fibers) can be arranged aligned with each other in a plane or prepreg layer. Threads of different lengths can be used. In particular, the threads form a regular structure, which also leads to a regular, approximately evenly distributed arrangement of the holes formed between the threads.

[0014] The prepreg layer has a large number of holes, i.e. openings extending in particular over the thickness of the layer, in particular extending approximately parallel to the thickness direction. A large number of holes are preferably designed so that they are "transparent" when observing the plane (top and bottom) of the prepreg layer. The prepreg layer (additionally) may also include (a smaller proportion of) holes (or closed cells) extending essentially only within the layer, wherein preferably, the proportion of "transparent" holes extending over the thickness of the layer is clearly dominant (e.g., greater than 95%). Preferably, the holes have substantially the same shape and / or size. The holes may have a substantially non-circular or square shape. The holes may be defined by lines surrounding them, wherein the lines or at least most of the lines preferably do not terminate at the holes but extend around them. Preferably, the holes are not generated into the prepreg layer by a separation method, but for example during the (original) arrangement of the lines to each other, in particular before applying the plastic matrix. A large number of holes may be presented as a regular pattern, so that the prepreg layer is particularly designed as an (open) grid. This has to be distinguished from “cellular” foam, which forms an irregular and / or closed pore system, even though it may contain (short) fibers or particles.

[0015] The plastic matrix comprises a polyolefin copolymer or consists of a polyolefin copolymer. Polyolefins (also called "polyalkene") are compounds of the formula C n H 2n Polyolefins are polymers composed of hydrocarbons (ethylene, propylene, 1-butene, isobutylene). Polyolefins are semi-crystalline thermoplastics. Currently polyolefins are usually produced from petroleum or natural gas. The process is called polymerization, in which catalysts are used to link short chains of chemicals (monomers) into long chains (polymers). Polyolefin copolymers are therefore polyolefins composed of two different types of monomer units.

[0016] The composite material of lines, holes and plastic matrix is ​​designed so that the layer density of the prepreg layer can reach a maximum of 1.0 g / cm 3 [grams per cubic centimeter]. The layer density is determined in this case in particular by measuring the weight of the layer and setting it relative 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 prepreg layer and the thickness of the prepreg layer.

[0017] The thickness of a layer is measured as the distance between a reference plate on which the layer is located and a parallel circular pressure die (preferably a die diameter of about 50 mm) which applies a fixed pressure (preferably about 1 kPa) to the layer to be measured. The distance between the reference plate and the printing die is measured and recorded. The usual climatic conditions apply here. The thickness measurements are preferably made at different points on the layer and an average value is then formed from these measurements. The thickness of the layer must be determined in particular in accordance with DIN EN ISO 5084.

[0018] The upper limit of the layer density specified here is 1.0 g / cm 3 , which ensures high deformation and strength properties of the lightweight prepreg. The layer density can be achieved in particular by a more open shape of the line arrangement, wherein the provision of the polyolefin copolymer plastic matrix enables the line arrangement to have specific adhesive properties.

[0019] The layer density is preferably between 0.45 and 0.9 g / cm 3 In the range of 0.55 to 0.75 g / cm 3 0.45 to 0.9 g / cm 3 The range of 0.55 to 0.75 g / cm is considered to be particularly advantageous for, for example, a grid-like prepreg layer. 3 The range of Å is a particularly advantageous application amount for a polyolefin copolymer plastic matrix, which is particularly advantageous for further processing, in particular for complex and highly stressed components.

[0020] The polyolefin copolymer of the plastic matrix is ​​preferably selected from the group consisting of random copolymers, gradient copolymers, alternating copolymers, block copolymers, polymer mixtures, graft polymers.

[0021] In a random copolymer, the monomers are randomly distributed in the chain, for example as follows:

[0022] AABBABBBBAAAABAABBBAAABBABBAAAABBBABAABBAB….

[0023] Gradient copolymers have a structure similar to random copolymers but have variable monomer ratios along the chain, for example in the following manner:

[0024] AAAAAAAAABAABBBAAABBABBBAABBBBBBABBBBBBBB...

[0025] In an alternating copolymer, the monomers are arranged regularly along the chain, for example in the following manner:

[0026] ABABABABABABABAB...

[0027] Block copolymers are characterized by longer blocks or sequences of each monomer, which may also repeat, for example in one of the following ways:

[0028] AAAAAAAAABBBBBBBBBBBB

[0029] or

[0030] AAAAAAAAABBBBBBBBBBBAAAAAAAAAAAAABBBBBBBBB...

[0031] Mixed polymers are characterized by the presence of different polymers without chemically reactive connections between them, such as the following types:

[0032] AAAAAAA+BBBBBBBB.

[0033] Graft copolymers consist of a backbone composed of a polymer of one monomer onto which are grafted blocks / "side arms" of a polymer of another monomer, such as the following types:

[0034] BBB

[0035] BBBBB

[0036] BBBBB

[0037] AAAAAAAAAAAAAAAAA...

[0038] BBBBB

[0039] BBBB

[0040] B

[0041] B

[0042] In all cases mentioned, the molecular chain may be linear or (slightly) branched.

[0043] This allows the polymeric material to be blended with other substances, in particular for functionalization (e.g. stabilizers, flame retardants, ...) and / or cost reduction (fillers). The copolymers can be selected to provide different properties to different plastics.

[0044] The polyolefin copolymer of the plastic matrix may contain or be (in particular) a polymer mixture of polymers with different particle sizes and / or molecular chain lengths. Smaller particles / molecules can penetrate better between the threads or individual filaments and form good bonds between the threads. On the other hand, larger particles / molecules tend to penetrate less and can therefore influence or adjust the surface properties of the prepreg, such as the connection with the subsequent composite material. In addition, by mixing polymers with different melting points, the melting point of the mixture can be easily adjusted to suit the respective application.

[0045] Preferably, the thread content is at least 60% by weight [percent by weight] of the prepreg layer, in particular in the range of 0.75 to 0.85% by weight. The thread proportion can be adjusted significantly by the arrangement of the holes (shape) or threads, the thread fineness used and / or the support of the polyolefin copolymer plastic matrix. In many cases, the thread proportion ensures the required tensile strength of the prepreg layer and a suitable surface and / or a suitable envelope volume for applying a sufficient layer with the polyolefin copolymer plastic matrix.

[0046] The line preferably comprises a glass fiber bundle, particularly a glass fiber bundle with a fineness (tex) in the range of 300 to 1200. The line is preferably formed by a plurality of glass fiber filaments, which extend substantially parallel to each other and thus form a bundle. The glass fiber bundle may comprise built-in holes that can be used as a reservoir of a polyolefin copolymer plastic matrix, or therefore at least a major part or (almost) fully filled. The hole / reservoir can be regulated particularly by selecting the fineness. The provision of these holes / reservoirs and the coordinated selection of the polyolefin copolymer enable the line and the plastic matrix to be very closely combined.

[0047] The opening width of the holes in the prepreg layer can be in the range of up to 200 mm [millimeters], wherein 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 layer), for example the maximum free diagonal in the case of a square hole.

[0048] Small opening widths are preferably produced for processes / components with a high oriented fiber content, for example in the range of 1 to 10 mm. In injection molded reinforcements, these hole sizes are advantageous for achieving good embedding in the injection molding compound.

[0049] However, larger opening widths (e.g. 30 to 100 mm) are suitable for large-area applications with low force absorption, for example in the construction sector with reinforced insulation or masonry facings (so-called "strips") so that the elements form a larger mat, making manual work easier. If square holes are present, edge lengths of about 100 mm (maximum) are preferred for such applications.

[0050] The threads can form a fabric. The fabric preferably has a regular and / or uniform design. The fabric is essentially formed only by threads and / or bundles of threads. This can be provided in the form of a web and / or a sheet and / or a layer. The fabric has a very high ratio of surface area to material thickness. The fabric can be windable and / or stackable and / or (elastic) deformable. The fabric can be open-designed; wherein an open fabric has a large number of (transparent) holes.

[0051] The prepreg layer can have a minimum bending radius of at most 30 mm [millimeters]. The minimum bending radius is understood to be the bending radius at which (under normal room conditions, in particular below room temperature) the plastic matrix does not (significantly) separate and / or kink the threads. In particular, it is in the range of 10 to 20 mm (e.g., a fabric thickness of at most 1.0 mm). The structure of the prepreg layer proposed here therefore allows surprisingly small bending radii without damaging it and / or significantly impairing further use.

[0052] The prepreg layer is designed in particular such that the wires are embedded in the plastic matrix. This means in particular that the plastic matrix surrounds substantially the entire wire. If filament bundles are present, they are also substantially penetrated by the plastic matrix, or the filaments themselves are (mostly) surrounded by the plastic matrix. Thus, there is no (separate) layer structure of wires and plastic matrix. The plastic matrix is ​​formed in particular as the entire surface of the prepreg layer.

[0053] According to another aspect, the use of a plastic matrix having a polyolefin copolymer for producing open prepreg layers with a low layer density is proposed. With regard to the properties of the open prepreg layers and / or their production, full reference may be made to the individual features relating to the prepreg layers themselves.

[0054] Furthermore, it is proposed to use at least one prepreg layer of the type disclosed herein for forming a three-dimensional structural component by means of one of the following manufacturing methods: (injection) casting, lamination (connecting multiple layers using a suitable laminating agent), foaming, pressing, deep drawing, vacuum forming.

[0055] To produce such a prepreg layer, a method comprising at least the following steps may be performed:

[0056] a. providing a wire structure having a specified basis weight,

[0057] b. adding the water-polyolefin mixture to the thread structure to increase the basis weight by at least 30% by weight, in particular 35 to 65% by weight,

[0058] c. dehydrating the thread structure with the water-polyolefin mixture, wherein this is preferably carried out at a temperature in the range of 100° C. to the melting temperature of the polyolefin,

[0059] d. Consolidating the thread structure with the polyolefin, wherein this is preferably done thermally at a temperature above the melting temperature of the polyolefin.

[0060] The interpretation of the prepreg layers can also be used to characterize the manufacturing method and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention and its technical environment are described below in conjunction with the accompanying drawings. It should be noted that the present invention is not limited to the embodiments shown. The features shown in the accompanying drawings can be extracted and, if necessary, combined with other features of the specification or other drawings, unless this is explicitly excluded below.

[0062] Schematically in the accompanying drawings:

[0063] Figure 1 shows a top view of a prepreg layer;

[0064] Figure 2 shows a cross-sectional view of a prepreg layer;

[0065] Figure 3 An overview of the manufacturing method is shown. DETAILED DESCRIPTION

[0066] Figure 1 and Figure 2 By way of example, a prepreg layer 1 is shown having a plurality of threads 2 arranged to form a woven fabric or an open grid. They are embedded in a plastic matrix 3. However, a plurality of holes 4 with a predetermined opening width 5 are provided. The plastic matrix 3 here contains a polyolefin copolymer and the prepreg layer 1 has a maximum of 1.0 g / cm 3 The layer density can be determined by the envelope volume, which can be determined based on the predetermined length 6, width 7 and thickness 8 of the prepreg layer 1.

[0067] With regard to the design of the holes, it should be noted that the prepreg layer 1 (in particular its layer density) is clearly defined by the (at least existing) holes 4, e.g. Figure 1 As shown in the top view of FIG. 1 , they are “transparent” and extend over the thickness 8 of the prepreg layer 1. If necessary, they can also be connected to each other via holes 4, such as Figure 2 However, preferably, Figure 2 As shown, the holes 4 are present only to a small (negligible) extent or (practically) not at all.

[0068] Figure 3 By way of example and schematically a possible manufacturing process of a prepreg layer 1 is shown, wherein from left to right a sequential production is shown and comprises the following steps:

[0069] a. A thread structure made of a thread 2 having a predetermined basis weight is provided, here by means of a weaving machine 10. The produced thread structure is further conveyed along a predetermined feed direction 16.

[0070] b. Adding the water-polyolefin mixture 9 to the thread structure so that the basis weight increases by at least 30%. This step is carried out here in a tank 11 or in a (drum) bath.

[0071] c. Dehydration of the thread structure with the water-polyolefin mixture 9 , this taking place in a first oven 12 .

[0072] d. Consolidation of 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 .

[0073] e. Cooling line structure along cooling section 14.

[0074] f. The prepreg layer 1 and the hardened plastic matrix 3 are wound up in a winding station 15 .

[0075] In conclusion, it should be noted that the solution proposed here at least partially overcomes the disadvantages described with reference to the prior art. The prepreg has a high and variable practical value, enabling the composite structure to stabilize the final product as uniformly as possible over the entire surface design of the final product. In particular, a prepreg is created that is suitable for further processing using manufacturing technologies existing on the market that require intensive shaping.

[0076] Reference numerals list

[0077] 1 Prepreg layer

[0078] 2-wire

[0079] 3 Plastic matrix

[0080] 4 holes

[0081] 5. Opening Width

[0082] 6 Length

[0083] 7 Width

[0084] 8 Thickness

[0085] 9 Water-polyolefin mixture

[0086] 10. Loom

[0087] 11 slots

[0088] 12. First Oven

[0089] 13. Second Oven

[0090] 14 Cooling section

[0091] 15 Winding Station

[0092] 16 Feed direction

Claims

1. A prepreg layer (1) comprising at least a plurality of threads (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 maximum of 1.0 g / cm 3 layer density.

2. The prepreg layer (1) according to claim 1, wherein the layer density is 0.45 to 0.9 g / cm 3 .

3. The prepreg layer (1) according to claim 1 or 2, wherein the polyolefin copolymer of the plastic matrix (3) is selected from the following group: random copolymers, gradient copolymers, alternating copolymers, block copolymers, polymer mixtures, grafted polymers.

4. The prepreg layer (1) according to claim 3, wherein the polyolefin copolymer of the plastic matrix (3) comprises a polymer mixture of polymers having different grain sizes or molecular chain lengths.

5. The prepreg layer (1) according to any one of the preceding claims, wherein the thread content is at least 60% by weight.

6. A prepreg layer (1) according to any one of the preceding claims, wherein the threads (2) comprise glass fibre bundles.

7. 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 150 mm.

8. A prepreg layer (1) according to any one of the preceding claims, wherein the threads (2) form a textile.

9. The prepreg layer (1) according to any one of the preceding claims, wherein the prepreg layer has a minimum bending radius of at most 30 mm.

10. The prepreg layer (1) according to any one of the preceding claims, wherein: The threads (2) are embedded in the plastic matrix (3).

11. Use of a plastic matrix (3) comprising a polyolefin copolymer for producing open prepreg layers (1) having a low layer density.

12. Use of at least one prepreg layer (1) according to any one of claims 1 to 10 for forming a three-dimensional structural component by means of one of the following production methods: casting, lamination, foaming, pressing, deep drawing, vacuum forming.

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