VOLUMINATED KNITTED TEXTILE STRUCTURE FOR STRUCTURAL REINFORCEMENT OF A COMPOSITE MATERIAL

Abstract

This bulky knitted textile structure (1) for structural reinforcement of a composite material incorporates biodegradable reinforcing fibers, including natural, plant-based and / or bio-based fibers, obtained by knitting using the drop-stitch technology, notably with a Rachel-type or double-bed hook knitting machine, in which the binding yarns (4) used in its production are monofilamentary. Figure for the abbreviation: Fig 1

Description

Title of the invention: VOLUMINATED KNITTED TEXTILE STRUCTURE FOR REINFORCEMENT STRUCTURE OF A COMPOSITE MATERIAL Scope of the invention

[0001] The invention belongs to the field of composite structures, that is to say complex structures using resins, in particular synthetic resins, generally formed by molding, according to the so-called thermoforming technology.

[0002] Such composite structures have today a great many applications, including, but not limited to, the automotive and aeronautical fields, and more broadly transport (rail, aeronautical, etc.), but also in the field of luggage, pastry molds or more broadly industrial manufacturing (tanks, furniture parts or various machines...) and sports equipment. Prior state of the art

[0003] Composite structures are conventionally mechanically reinforced by means of supports, generally consisting of reinforcements made of carbon fibers or glass fibers. Such reinforcements are obtained by conventional weaving or are made of multidirectional nonwovens.

[0004] Due to the very nature of these reinforcements, in this case woven or non-woven, they have small openings, which may affect the adhesion or impregnation of the synthetic resins used, and consequently the cohesion of the whole thus obtained, risking causing delaminations affecting the mechanical resistance of the finished product.

[0005] Moreover, such woven reinforcement structures are only slightly deformable before molding, consequently limiting the production of large stampings without cutting said supports, and corollarily the possible fields of application.

[0006] Another difficulty lies in the effectiveness of the mechanical reinforcement embedded in the resin. Indeed, the reinforcement structures known to date offer such optimized mechanical resistance within the dimensions of the plane in which they are inscribed. However, some of the forces they are designed to withstand may also occur in a dimension other than that defined by a plane, for example, in the case of a complex shape with a geometry developed by a concave generatrix. The case is even more complex in the case of a non-uniform shape along a generatrix.

[0007] Finally, regardless of how these composite structures are made, the problem of recycling composite products has emerged in recent years. time. Indeed, as part of an eco-environmental approach, the aim is to recycle composite products. Typically, reinforcements made of carbon fibers or glass fibers are not recyclable and constitute waste that is difficult to recover.

[0008] Moreover, and more particularly in the automotive manufacturing sector, a standard has emerged which requires manufacturers to implement a specific percentage of green material, i.e. bio-based, i.e. derived from renewable materials, within said vehicles, de facto reducing the range of materials that can be used to produce these structures.

[0009] The present invention aims to overcome these various difficulties. Description of the invention

[0010] To this end, the invention primarily relates to a bulky knitted textile structure for structural reinforcement of a composite material. This textile structure incorporates reinforcing yarns made from biodegradable fibers, particularly natural, plant-based, and / or bio-based fibers. It is produced by knitting using the drop-stitch technique, notably with a Rachel or crochet-type knitting machine. According to the invention, this structure is obtained on a double-bed knitting machine, and the binding yarns used in its production are monofilament.

[0011] These reinforcing yarns can be made of strands of fibers or cables of flax, hemp or other natural or bio-based material.

[0012] By "voluminized structure" is meant a planar structure but incorporating wires in 3 dimensions, and which has a certain thickness. This structure can deform in three dimensions while maintaining a substantially identical thickness.

[0013] In so doing, such a reinforcing textile structure has a certain thickness, typically between 1 and 10 millimeters, and can even reach 15 to 30 millimeters if necessary, suitable for: - on the one hand, to promote the cohesion of the composite structures in which it is implemented, and therefore, as a corollary, to optimize the mechanical resistance assigned to it; - on the other hand, to improve the impregnation of the resin within this textile structure during the production of the composite structure; - and finally, to give greater conformability to the whole, and therefore open up more possible applications for such composite structures.

[0014] Indeed, the use of knitting to create the reinforcement structure generates openings that promote resin migration and thus impregnation. Typically, the openness ratio of the resulting reinforcement structure The openness rate of the knitting according to the invention is between 10 and 40%. By openness rate, we mean the ratio of the areas free of knitting or binding yarns of each successive plane of the structure to the total surface area of ​​said plane of the structure.

[0015] The thickness thus imparted to the reinforcement structure results, on the one hand, from the technology used to create the reinforcement structure, in this case on a Rachel double-bed knitting machine, but on the other hand, from the nature of the binding yarns, in this case monofilament, which inherently gives them a certain rigidity that keeps the two knitted faces separated at the two beds. In other words, these binding yarns not only perform their primary function of binding, but also act as spacers for these two faces.

[0016] According to the invention, said binding threads are made of biodegradable materials and in particular of natural materials, of bio-based materials, or of a material of the same nature as the resin of the composite structure in which the reinforcement structure is intended to be integrated or compatible or chemically identical with said resin.

[0017] According to one feature of the invention, the reinforcing structure can also incorporate, between the two faces resulting from the production on a double-bed loom, and during its production, additional reinforcing threads mounted in a capstan configuration and oriented along only one of the directions of the reinforcing structure. In so doing, this provides the structure with additional mechanical strength along the direction of the capstan-mounted threads.

[0018] Such capstan-mounted wires are, for example, made of fiber strands or cables of flax, hemp, or another natural or bio-based material. They are made of biodegradable, natural, or bio-based material. If they are strands, these are loosely twisted. They typically have a diameter between 1 and 7 millimeters, again contributing to the thickness of the reinforcing structure.

[0019] These capstan-mounted reinforcing wires have a count between 300 and 30,000 dtex.

[0020] The invention also relates to a method for producing such a knitted reinforcement structure. This method consists of implementing the dropped stitch technology on a double-bed Rachel knitting machine, in which the yarns constituting the structure are made from biodegradable fibers, in particular natural, plant and / or bio-based fibers, and in which the binding yarns are monofilament type and are made of biodegradable materials, in particular natural or bio-based materials, or of a material of the same nature as the resin of the composite structure into which the reinforcement structure is intended to be integrated, or chemically compatible with the resin.

[0021] According to a variant of the method of the invention, during the knitting phase of the reinforcement structure, yarns are inserted in a capstan between the two bed frames.

[0022] The invention also relates to the composite structure or material incorporating the aforementioned textile reinforcement structure. Preferably, the resin of this composite material is itself biodegradable, or at least has a low carbon footprint throughout its entire life cycle. Brief description of the figures

[0023] The manner in which the invention can be implemented and the resulting advantages will be more apparent from the following embodiment examples, given by way of illustration and not limitation, in support of the attached figures.

[0024] Fig. 1 is a schematic perspective view of the reinforcement structure according to the invention.

[0025] Fig. 2 is a detailed top view of the structure of Fig. 1.

[0026] Figure 3 is a schematic top-view representation of a variant of the reinforcement structure of [Fig.1] and a zoomed-in part of said [Fig.3].

[0027] Figure 4 is a schematic cross-sectional view of the structure of the [Fig.3]. Detailed description of the invention

[0028] A schematic perspective view of the volumetric reinforcement structure (1) conforming to a first embodiment of the invention is shown in [Fig.1].

[0029] In this case, this reinforcement structure is a knitted structure, obtained according to the technology of dropped stitches on a double bed Rachel knitting machine, such as for example marketed by KARL MAYER.

[0030] Typically, this reinforcement structure has a thickness of approximately 4 to 10 millimeters, which can however be greater and reach 15 to 30 millimeters.

[0031] Due to the technology implemented to produce it, by the main use of 2 to 6 bars of wire, it has two faces (2, 3), connected to each other by connecting wires (4) also called in the field concerned, binding wires or hair wires.

[0032] The reinforcing threads appearing on both sides (2, 3). They are fundamentally made from biodegradable fibers. Among these, they may be fibers made from natural materials such as flax or hemp, or even from bio-based or biofragmentable or bioresorbable materials, and for example PLA (polylactic acid) or PBS (polybutylene succinate).

[0033] It may also be weakly twisted strands of natural fibers, in this case flax or hemp or cables.

[0034] The fineness of these wires is between 60 and 100,000 decitex.

[0035] The binding threads (4), for their part, are also biodegradable, whether made of natural or bio-based materials, and are preferably monofilament, in any case exhibiting a certain rigidity. The density of these binding threads is between 50 and 4000 decitex.

[0036] The specific choice of these binding yarns (4) is such that they are relatively rigid, in order to give the reinforcing structure (1) the desired thickness by keeping the two faces (2, 3) resulting from the double-bed knitting apart, and to preserve the volume of the structure during shaping in the composite material

[0037] Furthermore, the binding threads (4) may be of the same chemical composition as the resin used in the composition of the composite material to be produced. In this case, said threads ensure perfect impregnation and homogeneity of the final composite material, thus optimizing both the performance of the composite material and its conformability to the desired shape.

[0038] In the embodiment described in relation to Figures 1 and 2, the weave used to construct the structure is a simple two-bar weave. However, the RACHEL loom could have three to six bars, in order to generate a more complex weave, and in particular to allow the use of yarns of different types or to adapt the mechanical characteristics or the size of the openings in order to optimize the properties of the composite material.

[0039] According to the embodiment of figures 3 and 4, reinforcing wires (5) mounted in a capstan are further inserted between the two faces (2, 3), suitable for giving the structure greater mechanical resistance in the direction of the extension of such capstan wires, in this case, in the direction of production.

[0040] The introduction of these threads (5) mounted in a capstan between the two bed frames of the Rachel double bed loom, makes it possible to obtain the reinforcement structure in a single operation.

[0041] We then obtain a reinforcement structure with low unidirectional elongation.

[0042] The reinforcement structure thus obtained exhibits a high deformability, in any case much higher than the structures known in the prior art, without affecting its mechanical resistance, whatever the shape one wishes to give it, and therefore whatever the composite structure to be produced, which could not be done effectively until now without affecting the mechanical resistance.

[0043] Moreover, in the more particular context of the embodiment described in connection with figures 3 to 5, the reinforcement structure of the invention offers a great capacity to conform to complex shaped volumes while having the possibility of having reinforcement lines of force due to the presence of the threads mounted in capstan or weft at the places and in the directions requiring the most reinforcement.

[0044] Furthermore, due to the openings within said reinforcement structure, the dimensions of which are adapted by the choice of gauge, i.e., the distance separating the needles of the RACHEL loom, and by the choice of yarn count, particularly for reinforcement, the distribution and impregnation of the resin constituting the composite are optimized, and consequently, its adhesion to said structure is improved. The mechanical properties of the final composite product are thus enhanced.

Claims

Demands

1. Volumetric knitted textile structure (1) for structural reinforcement of a composite material, incorporating biodegradable reinforcing fibers, in particular natural, plant and / or bio-based, obtained by knitting according to the drop stitch technology, in particular using a Rachel type or double bed crochet machine employing binding yarns (4) intended to bind the two faces (2, 3) resulting from the production of the structure on a double bed machine, in which the binding yarns (4) are monofilamentary, and in which the openness rate is between 10 and 40%.

2. Volumetric knitted textile structure (1) for structural reinforcement of a composite material according to claim 1, in which are integrated reinforcing yarns made of fiber strands or cables of flax, hemp or other natural or bio-based material.

3. Volumetric knitted textile structure for structural reinforcement of a composite material according to claim 2, wherein the count of the reinforcing yarns is between 60 and 100,000 dtex.

4. Volumetric knitted textile structure for structural reinforcement of a composite material according to any one of claims 1 to 3, wherein the binding yarns (4) are made of biodegradable materials and in particular of natural materials, bio-based materials, or of a material of the same nature as the resin of the composite material or chemically compatible with said resin.

5. Volumetric knitted textile structure for structural reinforcement of a composite material according to claim 4, wherein the count of the binding yarns (4) is between 50 and 4000 dtex.

6. Volumetric knitted textile structure for structural reinforcement of a composite material according to any one of claims 1 to 5, integrating between the two faces (2, 3) resulting from the production on a double bed loom, additional reinforcing yarns mounted in a capstan (5) and oriented along only one of the directions of said reinforcing structure.

7. Volume-knitted textile structure for structural reinforcement of a composite material according to claim 6, wherein the additional reinforcing yarns mounted in a capstan (5) are made of fiber strands or cables of flax, hemp or made of another natural or bio-based material.

8. Volumetric knitted textile structure for structural reinforcement of a composite material according to any one of claims 6 and 7, wherein the count of the additional capstan-mounted reinforcing yarns (5) is between 300 and 30,000 dtex.

9. Composite material incorporating a volumetric knitted textile structure according to any one of claims 1 to 8.

10. Composite material incorporating a volumetric structure according to claim 9, wherein the resin used for its production is made of a biodegradable material with a low carbon footprint.

11. A method for producing a volumetric knitted textile structure consisting of implementing the dropped stitch technology on a Rachel double bed knitting machine, a method in which the yarns constituting the textile structure are made from biodegradable fibers and in particular natural, plant and / or bio-based fibers, and in which the binding yarns are of the monofilament type and are made from biodegradable materials and in particular natural or bio-based material or from a material of the same nature as the resin of the composite structure into which the volumetric textile reinforcement structure is intended to be integrated or chemically compatible with the resin, and in which, during the knitting phase, yarns are inserted in a capstan between the two beds.

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