MULTIMATERIAL SEMI-COMPONENTS FOR LOAD-BEARING STRUCTURAL COMPONENTS

Description

[0001] The invention relates to a multi-material semi-finished product for load-bearing structural components, in particular for use in the automotive industry.

[0002] In automotive engineering, the trend towards lightweight construction concepts remains unbroken. Beyond the automotive sector, there is also strong interest in manufacturing the lightest possible components, resulting in a final product with a correspondingly low overall weight. In addition to improved fuel consumption in automotive engineering, lightweight construction concepts can offer further benefits. For example, certain lightweight construction concepts can also lead to the substitution of other materials, thus increasing design freedom for both the final product and the associated production processes. Metallic materials, for instance, lead to heavy component structures in motor vehicles, which are associated with high energy and fuel consumption. EU regulations (EU = European Union) No. 443 / 2009 and No.Regulation 333 / 2014 on CO2 reduction in motor vehicles leads to the requirement for weight-optimized vehicle components.

[0003] Natural fiber-reinforced plastics (NFRPs) offer significant lightweight construction potential due to their low density and high weight-to-weight ratio. Current natural fiber-reinforced component structures in motor vehicles often consist of a natural fiber-reinforced thermoplastic (NFT). The natural fibers are processed into a fiber fleece using synthetic polypropylene fibers, which is then pressed into a three-dimensional component by applying heat. The component properties of the pressed natural fiber fleeces are insufficient for load-bearing structures, so component applications have so far been limited to interior trim parts. Applications of natural fiber-reinforced thermoplastics for load-bearing component structures are not currently known.

[0004] The load-bearing structural components currently available on the market are based on thermoplastic semi-finished products known as organosheets. Due to their superior performance, these materials can replace metallic structures and reduce vehicle weight. Organosheets consist of a petrochemical thermoplastic (such as polypropylene or polyamide) and one or more layers of synthetic glass, carbon, or aramid fiber fabric. The reinforcing fibers, which are of unlimited length, impart high mechanical properties to the fiber-reinforced composite, characterized by high strength, stiffness, and impact resistance.

[0005] The use of synthetic glass, carbon, or aramid fibers requires a high energy input and leads to significant CO2 emissions during production. Furthermore, the material density of synthetic reinforcing fibers is higher than that of natural fibers, resulting in a lower lightweighting potential and consequently a higher component weight compared to natural fiber-reinforced organosheets.

[0006] Furthermore, the polymer matrix of current organosheets consists of a petrochemical thermoplastic, which is negative from an ecological perspective and with regard to material recycling according to the EU End-of-Life Vehicles Directive 2000 / 53 / EC. The use of recycled plastics (=recyclates) as the matrix polymer, on the other hand, is considered more positive.

[0007] Several approaches are known from the state of the art, which at least in some areas incorporate the idea of ​​organosheets or technically similar concepts. Common, publicly known solutions or commercially available organosheets consist of a pure glass or natural fiber fabric and an unreinforced petrochemical polymer matrix without the use of PP recyclates (=polypropylene recyclates).

[0008] A fiber-reinforced plastic molded body is disclosed in German patent application DE 198 15 783 A1. This document proposes that the molded body be unidirectionally reinforced with natural fibers, and that these natural fibers be parallelized fibers in strand or ribbon form. Thus, fiber-reinforced plastic molded bodies can be produced using natural fibers of finite length, exhibiting very high strength and stiffness as well as a largely homogeneous fiber distribution, and are therefore suitable for high-quality applications. However, it is not disclosed that a woven structure made from a combination of synthetic and natural fibers is provided.

[0009] German patent application DE 10 2013 017 955 A1 discloses a motor vehicle with a floor element as known. The floor element has at least one cover element, to which a stiffening structure is connected. The cover element is made of a fiber composite material, and the stiffening structure is designed as a honeycomb core or a foam core. The cover element can contain glass fibers and natural fibers and comprise polypropylene as the matrix material. However, it is not disclosed that a woven structure is provided which is made of a combination of synthetic and natural fibers, wherein a natural fiber is arranged between at least two synthetic fibers.

[0010] German patent application DE 10 2014 221 165 A1 discloses a known method for manufacturing a hybrid composite component from organosheets and a metallic reinforcing element. The focus is on how the individual organosheets are joined to the metallic reinforcing element, whereby the injection of a thermoplastic material is provided. However, it is not disclosed that a woven structure is provided, which is made from a combination of synthetic and natural fibers, wherein a natural fiber is arranged between at least two synthetic fibers.

[0011] DE 10 2012 105 500 A1 discloses a fiber composite component and a method for its manufacture. This fiber composite component consists of a fiber semi-finished product and a matrix, wherein this fiber composite component is at least partially based on polymer fibers, in particular bio-based fibers. A first fiber semi-finished product can consist of plastic fibers, and at least one fiber semi-finished product can consist of a composite fabric of plastic fibers and carbon or glass fibers. The composite fabric can consist of bio-based fibers. Further multi-material semi-finished products are disclosed in DE 20 2017 004083 U1.

[0012] The invention is based on the objective of providing a semi-finished product for load-bearing structural components, in particular for use in the automotive industry, which has an improved lightweight potential compared to conventional semi-finished products for load-bearing structural components and which has an improved ecological potential compared to conventional semi-finished products for load-bearing structural components.

[0013] According to the invention, a multi-material semi-finished product for load-bearing structural components, particularly for use in the automotive industry, is provided. Such a semi-finished product comprises at least a woven structure and a plastic matrix surrounding the woven structure, wherein the woven structure is made from a combination of synthetic and natural fibers, with one natural fiber positioned between at least two synthetic fibers. The combination of natural and synthetic fibers protects the less resilient natural fibers with the load-bearing glass fibers, thus preventing premature component failure and enabling the use of natural fiber materials for load-bearing or crash-relevant component structures. If the natural fibers are positioned centrally between the two synthetic fibers, forces occurring within the composite can be dissipated via the two outer synthetic fibers.This allows for the production of a particularly stable semi-finished product, making it suitable for load-bearing structural components, especially in the automotive industry. This approach not only achieves improved lightweight construction potential through the use of lightweight materials, but also offers improved ecological potential, as renewable raw materials are used, among other things. For example, several fabric structures can be incorporated, all embedded within the plastic matrix. Such a composite of fabric structure and matrix can also be described as a hybrid composite. The fabric structure can also be referred to as a hybrid fabric layer. In general, the described combination of different material components leads to optimal ecological, economic, and technical component performance.In natural fiber-reinforced organosheets and semi-finished products, the interwoven natural and synthetic fibers, such as glass fibers, reduce brittle fracture while maintaining virtually the same mechanical properties as pure glass fiber-reinforced organosheets, resulting in robust and crash-optimized component structures. The cost-effective natural and synthetic fibers, such as glass fibers, can be woven into fabrics of unlimited length on industrial weaving machines and further processed into semi-finished products in large quantities using film stacking or direct melting processes. The partial substitution of synthetic fibers, for example, glass fibers with a density of 2.55 g / cm³, with natural fibers with a maximum density of 1.45 g / cm³ results in weight savings of up to 20 to 30 grams in the developed hybrid fabrics and natural fiber-reinforced organosheets.This results in a -% reduction in weight compared to a pure glass fiber reinforced organosheet. This avoids CO2 emissions during the service phase due to the weight reduction, as well as during the production of the semi-finished product.

[0014] Furthermore, the invention provides that the fabric structure is at least partially based on a bidirectional fabric structure with a 3 / 3 Panama weave. The aforementioned advantages can thus be achieved even more effectively.

[0015] The invention also provides that the bidirectional fabric structure contains warp and weft threads that are orthogonally crossed to each other, with the natural fibers arranged as intertwined staple yarns centrally between outer glass fiber filaments. The aforementioned advantages can thus be achieved even more effectively.

[0016] Further preferred embodiments of the invention result from the other features mentioned in the dependent claims.

[0017] In a preferred embodiment of the invention, the polymer matrix comprises at least one low-viscosity thermoplastic material. The presented semi-finished product, or natural fiber-reinforced organosheet, can be considered a fabric-reinforced hybrid composite consisting of a combination of natural and synthetic fibers, for example, glass fibers, and a surrounding low-viscosity thermoplastic polymer matrix. The aforementioned advantages can thus be achieved even more effectively.

[0018] In a preferred embodiment of the invention, the plastic matrix also comprises at least one polypropylene, in particular a low-melting-point polypropylene. Due to the low thermal stability of natural fibers (< 200 °C), low-melting-point polypropylenes are particularly suitable. This ensures that the semi-finished product is stable and reliable for its intended use.

[0019] Furthermore, in a preferred embodiment of the invention, the at least one polypropylene is an unreinforced, glass-reinforced, or talc-reinforced polypropylene. In particular, a glass-reinforced or talc-reinforced polypropylene can be used as the matrix polymer, thus reducing any fiber anisotropy that may occur. This enables a stable semi-finished product for use in lightweight construction, and in particular facilitates the use of renewable raw materials in the form of natural fibers. When using a glass-fiber-reinforced polypropylene (PP / GF), fiber anisotropy is further reduced because the short glass fibers from the polymer matrix are located in the area of ​​the thread undulation or lifting of the reinforcing fabric. For example, glass-fiber-reinforced polypropylenes can be used in proportions of 0.1 to 35 wt.-% of the low-viscosity polypropylene matrix can be added without significantly increasing the polymer viscosity. During component loading, the shear stresses are distributed evenly across the entire fabric or the natural fiber-reinforced organosheet, thus reducing premature cracking and component failure, and resulting in mechanical composite properties similar to those of a pure glass fiber-reinforced organosheet. Furthermore, the twisted natural fiber yarn or individual natural fibers are reinforced by the short glass fibers within the matrix polymer, enabling the individual natural fibers to better absorb shear stresses and thus improving the overall mechanical properties. A talc-reinforced polypropylene could also be used instead of short glass fibers to reduce fiber anisotropy.In other words, the use of glass- or talc-reinforced polypropylene as a matrix polymer fundamentally reduces anisotropy in the fiber composite system. This effect is particularly pronounced in natural fiber-reinforced organosheets due to the nature of the natural fibers. The anisotropy arises from the fiber lifting or undulation within the fabric structure and results in direction-independent composite properties, for example, in the 0° and 90° directions of the reinforcing fabric.

[0020] Furthermore, in a preferred embodiment of the invention, the plastic matrix comprises at least one recycled polypropylene, wherein the proportion of the at least one recycled polypropylene is 0.1 to 35 wt.% of the plastic matrix. The use of recycled materials is considered positive from an ecological perspective and thus represents an improvement over conventional solutions. Since the component properties are determined by the fiber structure, recycled polypropylenes (= PP recyclate) can also be used as matrix polymers in proportions of 0.1 to 35 wt.%. In this way, at least a partial substitution of petrochemical polypropylene with recycled PP (= PP recyclate) as the matrix polymer can take place, resulting in an environmental improvement compared to conventional solutions.Given that the EU End-of-Life Vehicles Directive 2000 / 53 / EC has required material recycling of at least 85% of the average vehicle weight since 2015, a partial substitution of petrochemical polypropylene with recycled PP (=recyclate) appears positive.

[0021] In a preferred embodiment of the invention, the natural fibers of the fabric structure are selected from flax fibers and / or jute fibers and / or hemp fibers. A significant improvement over conventional solutions can thus be achieved directly, since at least a renewable raw material is used.

[0022] Furthermore, in a preferred embodiment of the invention, the synthetic fibers of the fabric structure are glass fibers. The less resilient natural fibers can thus be protected by the load-bearing glass fibers, thereby preventing premature component failure and allowing the natural fiber materials to be used for load-bearing or crash-relevant component structures.

[0023] Finally, in a preferred embodiment of the invention, the at least one polypropylene is modified by means of at least one additive material in the form of internal release agents and / or lubricants as well as adhesion promoters. This results in improved impregnation and bond strength within the hybrid composite. Furthermore, the optimized low-viscosity polypropylene prevents thermal damage to the natural fibers and ensures a reliable manufacturing temperature of 180 to 190 °C. The impregnated, natural fiber-reinforced organosheet is suitable for further processing by injection molding machines, allowing it to be formed in a one-shot process and back-injected with plastic stiffening and / or joining elements.

[0024] The presented semi-finished products, specifically thermoplastic semi-finished products and organosheets made of hybrid fabric with glass and natural fiber reinforcement, are suitable for load-bearing structural components and can be used in a variety of applications. For example, in addition to the automotive industry, structural applications are possible in the leisure and motorsport sectors, as well as in the aerospace and railway industries. Within a vehicle, for instance, a seat pan reinforced with natural fibers and made of thermoplastic materials could be used. Generally, structural components are conceivable for both interior and exterior applications. These could include door inserts, armrests, map pockets, or seat shells.

[0025] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0026] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Figure 1 is a schematic, perspective view of a multi-material semi-finished product; Figure 2 is a schematic top view of a fabric structure of a multi-material semi-finished product.

[0027] Figure 1Figure 1 shows a schematic, perspective view of a multi-material semi-finished product 10. Such a semi-finished product 10 can be used, for example, for a structural component, such as those used in the automotive industry. This semi-finished product 10 has a plastic matrix 12, which can be, for example, a thermoplastic matrix. This thermoplastic matrix can be composed of, for example, a single polypropylene (PP) or several different polypropylenes. Furthermore, the use of PP / GF (glass fiber reinforced polypropylene), PP / talc (talc reinforced polypropylene), or even PP recyclate is conceivable. This plastic matrix 12 is in the Figure 1The semi-finished product 10 is shown essentially as a rectangular shape and partially cut off in the foreground relative to the image plane, thus providing a view into its internal structure. The plastic matrix 12 completely surrounds (except for the partial view) several fabric structures 14, which are thus incorporated into the internal structure of the semi-finished product 10. The fabric structures 14 can each also be referred to as textiles. The various fabric structures 14 are stacked on top of each other. In the illustrated embodiment, three fabric structures 14 are stacked on top of each other. This stack 16 of fabric structures 14 is completely surrounded by the plastic matrix 12, with the stack 16 protruding from the plastic matrix 12 in the foreground relative to the image plane. The number of fabric structures 14 shown here is only an example and can vary as desired.It is also conceivable that only one fabric structure 14 is provided. The fabric structure 14 is also essentially depicted as a rectangular shape. The shapes shown are only examples, and any other shapes are conceivable. It is also conceivable that the plastic matrix 12 only partially or at least partially surrounds the fabric structure 14. The individual fabric structures 14 are each composed of individual fibers 18, with seventeen individual fibers 18 protruding from the stack 16 of the lower fabric structure 14 in the front area, for example. The ratio of the seventeen fibers 18 to the width of the fabric structure 14 is shown in the figure. Figure 1The representation is also only exemplary, and any ratio of the number of fibers 18 to the total width of the fabric structure 14 can be imagined. The fibers 18 are not further differentiated and can be, for example, synthetic and natural fibers. The natural fibers could be, for example, flax, jute, or hemp fibers. The synthetic fibers could be, for example, glass fibers or glass fiber filaments. For example, each natural fiber could be surrounded by at least two synthetic fibers. The width of the fibers 18 is also only given as an example. Any different widths and lengths of the various fibers 18 are conceivable. For example, the synthetic fibers could each be twice as wide as the respective natural fibers. The semi-finished product 10 can thus also be described as a natural fiber-reinforced semi-finished product or as an organosheet.Such a semi-finished product could also be described as a thermoplastic hybrid composite.

[0028] Figure 2 shows a schematic top view of a fabric structure 14 of a multi-material semi-finished product 10. The individual fibers 18 are in the Figure 2The diagram is further differentiated. Glass fibers 20 or glass fiber filaments are shown, as well as natural fibers 22 in the form of natural fiber yarn, which can be made, for example, from flax, jute, or hemp fibers. Mixed forms and alternative starting materials for the natural fibers 22 are also conceivable. The fabric structure 14 is shown as a Panama 3 / 3 hybrid fabric, in which each natural fiber 22 is surrounded by two glass fibers 20. The arrangement of the individual fibers 18 or of the glass fibers 20 and the natural fibers 22 is shown only as an example. In addition to the orthogonal arrangement of the individual fibers 18, other arrangements or structures familiar to those skilled in the art are also conceivable, whereby it must be ensured that each natural fiber 22 has at least one glass fiber 20 as an immediately adjacent fiber 18 on each side. Reference symbol list

[0029] 10 Multi-material semi-finished product 12 Plastic matrix 14 Fabric structure 16 Stack 18 Fiber 20 Glass fiber 22 Natural fiber

Claims

1. Multi-material semi-finished product (10) for load-bearing structural components, in particular for use in the automotive industry, said product comprising at least one fabric structure (14) and a plastics matrix (12) surrounding the fabric structure (14), the fabric structure (14) being made of a combination of synthetic fibers and natural fibers (22), characterized in that a natural fiber (22) is arranged between at least two synthetic fibers, the fabric structure (14) being at least partially based on a bidirectional fabric structure which has a 3 / 3 basket weave, and warp threads and weft threads being crossed orthogonally to one another in the bidirectional fabric structure, the natural fibers (22) being arranged as an intertwined staple yarn in the center between outer glass fiber filaments in each case.

2. Semi-finished product (10) according to claim 1, wherein the plastics matrix (12) comprises at least one low-viscosity thermoplastic material.

3. Semi-finished product (10) according to either of the preceding claims, wherein the plastics matrix (12) comprises at least one polypropylene, in particular a low-melting polypropylene.

4. Semi-finished product (10) according to claim 3, wherein the at least one polypropylene is an unreinforced, a glass-reinforced or a talc-reinforced polypropylene.

5. Semi-finished product (10) according to any of the preceding claims, wherein the plastics matrix (12) comprises at least one recycled polypropylene, wherein a proportion of the at least one recycled polypropylene is 0.1 to 35 wt.% of the plastics matrix (12).

6. Semi-finished product (10) according to any of the preceding claims, wherein the natural fibers (22) of the fabric structure (14) are selected from flax fibers and / or jute fibers and / or hemp fibers.

7. Semi-finished product (10) according to any of the preceding claims, wherein the synthetic fibers of the fabric structure (14) are glass fibers (20).

8. Semi-finished product (10) according to any of the preceding claims, wherein the at least one polypropylene is adapted by means of at least one additive material in the form of internal release agents and / or lubricants and adhesion promoters.