Process for the production of semi-finished fiber products, semi-finished fiber products and use thereof

Abstract

Method for producing fiber semi-finished products (1) comprising at least two layers of a fiber material (3, 4, 5), comprising the following steps: - Arranging unbound fiber material layers (3, 4, 5) on top of each other to form a fiber layer stack (2), - Applying a binder (6) exclusively locally between the fiber material layers (3, 4, 5) and - Hardening of the binder (6), wherein the method is characterized in that the binder (6) is applied in such areas which are removed during further processing of the fiber semi-finished product (1) by forming processes.

Description

[0001] The present invention relates to a method for producing fiber semi-finished products, a fiber semi-finished product, and a use of the fiber semi-finished product. Furthermore, the invention relates to a die for use in the specified method.

[0002] Fiber-reinforced plastics, due to their high mechanical stability and low weight, are widely used in automotive and aircraft construction, among other applications. According to DE 10 2010 031 639 A1, the production of fiber-reinforced plastics involves stacking layers of fiber material to form a fiber semi-finished product and optionally forming it into a preform in a shaping process. The resulting stack or preform can then be coated with a resin or matrix material and processed into the fiber-reinforced plastic, for example, using a wet pressing or resin transfer molding (RTM) process. In the fiber semi-finished product, the stacked layers of fiber material are coated with a binder on at least one side to stabilize the stack. The binder is also advantageous for fiber-reinforced plastic production using the resin transfer molding process.For the storage of fiber semi-finished products and the production of fiber-reinforced plastics using wet pressing, bonding the fiber layers with a binder is disadvantageous, as the usually thermoplastic binder reacts even to slight increases in temperature and pressure. This leads to deformation of the fiber semi-finished products and / or binder runoff, phenomena that result in a loss of quality in the fiber-reinforced plastic.

[0003] Based on this prior art, the object of the present invention is to provide a method for producing a fiber semi-finished product with at least two layers of fiber material that is easy to store and can be implemented without significant technical effort. Furthermore, the object of the present invention is to provide a die for applying and further simplifying the fiber semi-finished product manufacturing method according to the invention. Finally, the object of the invention is to provide a dimensionally stable and shelf-stable fiber semi-finished product and to specify a use for this fiber semi-finished product.

[0004] The object of a process for producing fiber semi-finished products with at least two layers of a fiber material is, according to the invention, characterized by the steps i) arranging unbound fiber material layers one above the other to form a fiber layer stack – the fiber material layers are therefore free of binder, ii) applying a binder exclusively locally between and, if necessary, also onto the fiber material layers, and iii) curing the binder. Because the binder is introduced exclusively locally between the fiber material layers by the process according to the invention, the layer stack is sufficiently stabilized against displacement of the individual layers. Thus, the layers are stably bonded to one another. The binder can also penetrate individual layers, which further strengthens the layer bond. Slippage or displacement of the layers, even during transport of the fiber semi-finished product, is thus effectively prevented.A local application within the meaning of the invention is an application exclusively to designated, defined areas and not a full-surface application, as is typically the case, for example, with resin injection in the RTM process. Binder is omitted from the remaining areas of the respective layers. The application of the binder between the fiber material layers is solely for the purpose of fixing the layers and preventing translational movement of the layer stack. Thus, those areas of the fiber material layers in which no binder is applied by the inventive method are binder-free, also due to the initial provision of unbindered fiber material layers, and lie more or less loosely on top of one another.The fiber semi-finished product thus exhibits high storage stability with minimal binder usage and very good fixation of the fiber layer stack, which facilitates and simplifies storage and further processing of the fiber semi-finished product, also from a logistical perspective. Due to the production of a fiber layer stack that is only locally bindered, and therefore binder-reduced, the process according to the invention is particularly suitable for producing a fiber semi-finished product for use in a wet pressing process. The layer stack can be very effectively and homogeneously impregnated with resin and formed by pressing. The flow of resin between the layers and around the locally bindered areas is facilitated by the binder-free areas of the fiber layers, thus shortening process times.

[0005] The dependent claims include advantageous further developments and embodiments of the invention.

[0006] According to an advantageous further development of the method, the binder is applied in such a way that it covers a maximum of 25%, and in particular a maximum of 20%, of the total surface area of ​​the fiber material layers. This achieves very good fiber layer stability with minimal binder usage; slippage of the individual fiber layers is effectively prevented.

[0007] Advantageously, the binder is applied exclusively to an edge region of the fiber material layer stack. This improves the suitability of the fiber semi-finished product manufactured according to the inventive method for wet pressing. The layer stack can be very effectively and homogeneously impregnated with resin and formed by pressing. The binder-free interior of the fiber layers facilitates resin flow between the layers, thus reducing process times. According to the invention, an edge region is understood to be a region surrounding the fiber material layers, extending from the edges of the fiber material layers approximately 50 mm into the interior or central region of each fiber material layer.The binder can completely cover the edge area of ​​the stack, but partial local application of the binder in designated sections of the edge area is preferred, as this allows more binder material to be saved, which in turn reduces the manufacturing costs of the fiber semi-finished product.

[0008] It is also advantageous to apply the binder to areas that are removed during the further processing of the fiber semi-finished product after the forming process. Such subsequent processes include, for example, cutting, punching, and the like. Areas to be removed can be located at the edge of the fiber layer stack or in its interior. If the binder is applied to an edge area, for example, it is discarded after curing in the mold during wet pressing. By providing and stacking unbound fiber material layers on top of each other and applying the binder only locally to areas that are discarded during further processing, attention must be paid to the chemical nature of the binder to be used and thus to the compatibility of the binder with the fiber semi-finished product and the matrix substances, e.g.,For the wet pressing process, no consideration is given to the binder, as it does not become part of the finished fiber-reinforced plastic or fiber-reinforced composite component and is discarded during the forming process.

[0009] According to an advantageous embodiment of the inventive method, the binder is applied from the uppermost or the lowermost layer of fiber material in the stacking direction of the fiber material layers. Pressure-controlled methods are particularly suitable for this purpose, in which the binder is pressed through the fiber material layers from a surface of the stack. This type of application is particularly easy to automate, since the stack of layers does not need to be specifically held or clamped. The application of the binder can thus be carried out very effectively and, in particular, locally at desired locations. Since the binder penetrates the individual fiber material layers in this application method, a particularly stable layer bond is achieved.

[0010] Alternatively or additionally, the binder can advantageously be applied from at least one side of the fiber layer stack, between the fiber material layers. This allows for precise application of the binder, especially to the outer edge areas of the stack.

[0011] A further cost reduction in the inventive method, through savings in binder, can be achieved by applying the binder only to the corner regions of the fiber material layers. Corner regions are those areas where two edges of the individual fiber material layers meet. If the fiber layers are assumed to be rectangular in shape and the edge region of the fiber layers is considered to be an area extending a maximum of 50 mm from the respective edge of the fiber layer into its interior, then the corner region extends diagonally from the corner point of two edges of the fiber layer by up to approximately 70 mm into the interior of the respective fiber material layer. Further edge regions of the fiber material layer stack preferably remain unbindered.Furthermore, when using the fiber semi-finished product produced in this way in the wet pressing process, it is advantageous to promote the flow of excess matrix material and to produce a fiber composite plastic with a particularly homogeneous layer thickness.

[0012] The binder is advantageously applied with a diameter of 10 to 50 mm, particularly 25 to 40 mm. A binder area of ​​at least 10 mm and at most 50 mm in diameter has proven sufficient for effective stabilization of the layer stack with minimal binder application. Further reduction of the application area to 40 mm or even 25 mm in diameter is possible and significantly reduces the production costs of the fiber semi-finished product.

[0013] Particularly simple, with a very uniform shape and a comparable quantity of binder, is the application of this binder using a punch and the application of pressure. The punch can be guided laterally onto the stack of layers, but preferably from a surface side of the stack, and the binder is applied by applying pressure from an opening in the punch. The pressure causes the binder to flow through the fiber layers, resulting in a uniform binding at the intended location. Advantageously, the punch is placed on the corresponding area of ​​the stack of layers for this purpose. The dispensing of the binder from the punch by pressure can be carried out, for example, mechanically using a slide or automatically with electronic control.

[0014] A further advantageous development involves using an injection needle, flooded with binder, to apply the binder by passing it through the fiber layers. The binder is then applied as the needle is withdrawn from the fiber layer stack. This method is particularly advantageous for fiber layer stacks with a large number of layers, i.e., more than 10 layers, as it promotes precise binder application and effectively prevents binder runoff.

[0015] Furthermore, the invention describes a punch for use in one of the aforementioned methods, comprising an injection nozzle for applying a binder and a device for hardening the binder. The binder can be selectively dispensed through the injection nozzle by means of pressure and introduced at the designated location between the layers of fiber material. After application, the punch, due to its additional functionality, can simultaneously be used to harden the binder. This is advantageous because the punch is already located in the application area during the binder application, and hardening can be carried out very effectively without repositioning and without damaging surrounding areas. The punch thus offers high functionality and simplifies the production of storage-stable and transport-safe fiber semi-finished products protected against unwanted deformation. It is easy to use and can be implemented with minimal technical effort.

[0016] The advantages, beneficial effects and further developments shown for the method according to the invention also apply to the stamp according to the invention.

[0017] An advantageous further development of the stamp provides that the device for curing the binder includes a radiation source and / or a heat source. By applying energy in the form of heat and / or radiation, such as ultrasound, IR radiation, or UV radiation, in the form of the stamp according to the invention, most common binders can be easily cured without damaging the surrounding fiber structure.

[0018] The invention also describes a fiber semi-finished product comprising at least two superimposed layers of a fiber material. This fiber semi-finished product is characterized in that the layers are bonded together by a hardened binder, which is arranged exclusively locally, preferably in an edge region of the fiber material layers, between the fiber material layers. Surrounding areas, i.e., areas outside the application area, are binder-free. The binder can also be arranged on the fiber material layers. The merely local presence of the binder is due to the use of originally unbindered layers of fiber material. The specific fiber material to be used is not limited. Suitable fiber materials include random fiber mats, nonwovens, knitted fabrics, woven fabrics, and the like, as well as combinations thereof.As described above, the fiber materials used are applied without a binder and are only bonded to each other at a later stage, preferably during or after the production of the layer structure, by introducing the binder exclusively locally, preferably into an edge region of the fiber material layers. The fiber semi-finished product according to the invention is particularly suitable for the production of fiber-reinforced plastics using the wet pressing process, since the resin material to be added can penetrate the layer stack very well due to the exclusively locally applied binder.

[0019] The advantageous further development, whereby the incorporated binder is present exclusively in the edge region of the fiber material layers, allows it to penetrate the fiber material layers at the edges, resulting in a particularly good layer bond. This provides a stable layer stack in which the individual fiber material layers are translationally stable, making storage and further processing particularly easy without any loss of quality.

[0020] Advantageously, the hardened binder is arranged in the corner areas of the fiber material layers. This allows the proportion of binder to be effectively reduced without compromising stability, which has a positive effect on the cost structure of the fiber semi-finished product according to the invention.

[0021] For the reasons already set out above for the inventive method, the hardened binder in the inventive fiber semi-finished product preferably covers a maximum of 25%, in particular a maximum of 20% of a total area of ​​the fiber material layers and / or the binder is applied in such areas that are removed during further processing of the fiber semi-finished product by shaping processes.

[0022] Furthermore, the use of a fiber semi-finished product as described above for the production of a fiber composite material using a wet pressing process is also described. This use is preferred due to the only local application of the binder, since in the wet pressing process the matrix material can penetrate the layer stack particularly uniformly and excess matrix material can flow away unhindered.

[0023] The following advantages result from the solutions according to the invention and their further developments: - The process is simple and can be implemented cost-effectively without high technical effort. - Binder material can be saved. - The fiber semi-finished product is stable during storage and transport. - Further processing of the fiber semi-finished product using the wet pressing process is facilitated. - The stamp reduces the technical effort required for applying the binder and enables precise and targeted application of the binder between the layers of fiber material.

[0024] Further details, features and advantages of the invention will become apparent from the following description and the figures. These show: Fig. 1 a schematic representation of a fiber semi-finished product according to the invention, Fig. 2 a side view of the fiber semi-finished product made of Fig. 1, Fig. 3 a stamp according to a first embodiment of the invention, Fig. 4 a stamp according to a second embodiment of the invention, Fig. 5 a schematic representation of the method according to a first embodiment of the invention and Fig. 6 a schematic representation of the method according to a second embodiment of the invention.

[0025] The present invention is explained in detail with reference to exemplary embodiments. Only those aspects of the present invention relevant here are shown in the figures; all other aspects have been omitted for clarity. Furthermore, identical reference numerals denote identical components.

[0026] Fig. Figure 1 shows a schematic view of a fiber semi-finished product 1 according to an embodiment of the invention. In this embodiment, the fiber semi-finished product 1 comprises, by way of example, three layers of fiber material 3, 4, 5, which are arranged to form a fiber layer stack 2. The number and type of fiber material layers 3-5 are not limited in detail. The fiber material layers 3, 4, 5 can, for example, comprise random fiber mats, non-woven fabrics, knitted fabrics, woven fabrics, braids, and the like, as well as combinations thereof. The fiber material itself is also not limited. Carbon fiber materials are preferably used.

[0027] Layers 3-5 are in Fig. Figure 1 shows the structure in a fanned-out view. It is thus clearly visible that a binder 6 is arranged locally, and as shown here by way of example, in the edge regions, more precisely in the corner regions, of the respective fiber material layers 3-5 and between the fiber material layers 3-5. The corner regions are those areas of the fiber material layers 3-5 or of the fiber layer stack 2 where two edges 7, 8 of a corresponding fiber material layer meet. The remaining areas of the fiber layers 3-5, and in particular their inner or central regions, are unbindered.

[0028] Binder 6 is in Fig. The binder 6 is arranged in a square shape in the corner area, but can alternatively be applied at different locations within the fiber layer stack 2 and in any desired shape. At each edge 7, 8, the binder 6 extends up to approximately 50 mm into the interior of the respective fiber layer. Thus, the binder 6 extends up to approximately 70 mm into the interior of a fiber layer along a diagonal d of the corner areas. The binder 6 therefore advantageously covers a maximum of 25% of the total surface area of ​​the fiber layers 3-5. The binder 6 also penetrates the fiber layers and, after curing, ensures the stability of the fiber layer stack 2. Slippage of the individual fiber layers 3-5 is prevented, and the storage stability and transportability of the fiber layer stack 2 are optimized.

[0029] The fiber semi-finished product 1 is dimensionally stable and stable in storage and is particularly suitable for the production of a fiber composite material using the wet pressing process.

[0030] Fig. Figure 2 is a side view of the fiber semi-finished product 1 made of Fig. 1. Here it can be seen that the fiber material layers 3-5 lie on top of each other and the binder 6 completely penetrates the corner areas of the fiber material layers 3-5. Such an application method can be carried out, for example, using a plunger to apply the binder under pressure or using an injection needle that can be filled with or flooded with binder. The binder is preferably applied from a top surface 9, i.e., either from an exposed top surface of the uppermost fiber material layer 3 or from an exposed underside of the lowermost fiber material layer 5.

[0031] Fig. Figure 3 shows a punch 10 for applying binder according to a first embodiment of the invention. The punch 10 is, by way of example, cylindrical in shape, but can also be shaped differently. The punch 10 comprises an injection nozzle 21 on its underside 23, from which binder can be expelled by means of pressure and applied at the intended location. For this purpose, the punch 10 is preferably placed on a surface of a fiber layer stack. The binder can be stored separately in a tank and conveyed into the punch 10 via a conveying device, or it can be stored within the volume of the punch itself. By applying pressure to the binder 6, it flows out of the injection nozzle 21 and penetrates the fiber layer stack 2 in the stack direction.

[0032] The stamp 10 further comprises a device for curing the binder 22. This device can be, for example, a heat source, such as a heating field, a radiation source, such as a UV lamp, an IR lamp, or an ultrasonic source. The device for curing the binder 22 is selected according to its chemical nature and the curing reaction to be carried out, and can also include combinations of different curing devices.

[0033] The diameter of the injection nozzle 21 is selected such that, when the application pressure is applied to the binder, a desired area and quantity of binder is applied.

[0034] Fig. Figure 4 shows a stamp 20 for applying binder according to a second embodiment of the invention. In contrast to the stamp 10 made of Fig. The stamp indicates 20. Fig. 4 has a rim 24 on its underside 23. This rim 24 limits the application area and prevents the applied binder from flowing away from the application site. In addition, the device for hardening the binder 22 is shielded, which enables particularly safe operation of the stamp 20.

[0035] Fig. Figure 5 shows a schematic representation of the method according to a first embodiment of the invention. A stack of fiber layers 2 is shown, which by way of example comprises three layers of fiber material 3, 4, 5 arranged one above the other. Binder 6 is injected from an injection device 30 via injection needles 31 onto and between the layers of fiber material 3, 4 and 4, 5, in a locally limited manner, and as shown here, into an edge region of the layers of fiber material 3-5, so that an inner region of the layers of fiber material 3-5 remains binder-free.

[0036] The injection device 30 can completely encircle the fiber layer stack 2, thus fully coating the edge areas of the respective fiber material layers 3-5 with binder, or, through interval-like application, deliver the binder only locally. In a subsequent step, the binder is cured.

[0037] Fig. Figure 6 shows a schematic representation of the method according to the invention in a second embodiment. In contrast to the one in Fig. In the 5 outlined methods, the binder 6 is applied via a stamp 20, which is, for example, like the stamp made of Fig. 3 or Fig.The punch 20 is placed on the top surface 9 of the fiber layer stack 2, and binder 6 is applied by pressure from an injection nozzle. The pressure distributes the binder 6 between the fiber material layers 3-5 and further penetrates them. A subsequent curing step, which can be performed using a separate device or even by the punch 20 itself, hardens the binder 6 in a designated area, thus permanently and stably bonding the individual layers of the fiber layer stack 2. The punch can be placed at one or more different locations on the fiber layer stack 2 to apply binder 6 to and between the fiber material layers 3, 4, and 5 of the fiber layer stack 2.

[0038] The preceding description of the present invention serves only for illustrative purposes and not to limit the invention. Various changes and modifications are possible within the scope of the invention without departing from the scope of the invention and its equivalents. Reference symbol list: 1 Fiber semi-finished product 2 fiber layer stacks 3 Fiber material layer 4 Fiber material layer 5 Fiber material layer 6 binders 7-edge 8 edge 9 Top side of the fiber layer stack 10 stamps 20 stamps 21 Injection nozzle 22 Device for hardening the binder 23 Underside of the stamp 24 Rand 30 injection devices 31 injection needles

Claims

[1] Method for producing fiber semi-finished products (1) comprising at least two layers of a fiber material (3, 4, 5), comprising the following steps: - Arranging unbound fiber material layers (3, 4, 5) on top of each other to form a fiber layer stack (2), - Applying a binder (6) exclusively locally between the fiber material layers (3, 4, 5) and - Hardening of the binder (6), wherein the process characterized by is that the binder (6) is applied in areas that are removed during the further processing of the fiber semi-finished product (1) by shaping processes. [2] Method according to claim 1, characterized by , that the binder (6) is applied in such a way that it covers a maximum of 25%, in particular a maximum of 20%, of the total area of ​​the fiber material layers (3, 4, 5). [3] Method according to claim 1 or 2, characterized by, that the binder (6) is applied exclusively to an edge area of ​​the fiber material layers (3, 4, 5) between the fiber material layers (3, 4, 5). [4] Method according to any one of the preceding claims, characterized by , that the application of the binder (6) is carried out from the uppermost or the lowermost fiber material layer (3, 4, 5) in the stacking direction of the fiber material layers (3, 4, 5). [5] Method according to any one of the preceding claims, characterized by , that the application of the binder (6) is carried out from at least one side of the fiber layer stack between the fiber material layers (3, 4, 5). [6] Method according to any one of the preceding claims, characterized by , that the binder (6) is applied to corner areas of the fiber material layers (3, 4, 5). [7] Method according to any one of the preceding claims, characterized by , that the binder (6) is applied with a diameter of 10 to 50 mm, in particular of 25 to 40 mm. [8] Method according to any one of the preceding claims, characterized by , that the binder (6) is applied by means of a stamp (10, 20) by applying pressure. [9] Method according to any one of the preceding claims, characterized by , that for the application of the binder (6) an injection needle floodable with binder (6) is passed through the fiber material layers (3, 4, 5) and the binder (6) is applied during the process of withdrawing the injection needle from the fiber layer stack (2). [10] Fiber semi-finished product comprising at least two layers of a fiber material arranged one above the other (3, 4, 5), characterized by , that the fiber material layers (3, 4, 5) are connected to each other by a hardened binder (6) which is arranged exclusively locally, preferably in an edge region of the fiber material layers (3, 4, 5), between the fiber material layers (3, 4, 5), characterized by, that the binder (6) is applied in such areas which are removed during the further processing of the fiber semi-finished product (1) by shaping processes. [11] Fiber semi-finished product according to claim 10, characterized by , that the hardened binder (6) is arranged in corner areas of the fiber material layers (3, 4, 5) and / or that the hardened binder (6) covers a maximum of 25%, in particular a maximum of 20% of a total area of ​​the fiber material layers (3, 4, 5) and / or that the binder (6) is applied in such areas that are removed during the further processing of the fiber semi-finished product (1) by forming processes. [12] Use of a fiber semi-finished product (1) according to claim 10 or 11 for the production of a fiber composite material by wet pressing.

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