Composite material, method for producing the composite material and device comprising such a composite material

Abstract

The invention relates to a composite material (1), in particular a core for a surfboard, a method for producing the composite material, and a device comprising such a composite material. To ensure sufficient stability with the lowest possible weight, a base body (2) of the composite material (1) has at least one groove-shaped recess (7; 8) on an outer side, wherein a thermoplastic material is provided in the recess (7; 8).

Description

[0001] The invention relates to a composite material, in particular a core for a surfboard, according to the preamble of claim 1, a method for producing such a composite material and a device, in particular a surfboard, SUP board or kiteboard, with such a composite material.

[0002] From DE 8201400 U1, a surfboard with a reinforcing element in the form of a so-called surfboard stringer is known. Surfboard stringers are integrated into surfboards and usually consist of a wooden or plastic plate that extends lengthwise along the surfboard. This allows the core of a surfboard, which is otherwise usually made of foamed plastic, to be reinforced, particularly in the longitudinal direction. Without such reinforcements, there is a risk that the surfboard will break during use. However, a disadvantage of using surfboard stringers is the increased weight, which negatively affects the buoyancy and handling of the surfboard. From WO 2011 / 009627 A1, a surfboard is known in which a fabric laminate, among other things made of polyethylene fibers, is arranged in recesses on the outside of a base body.From DE 102 40 606 A1, it is known to shrink a cover layer in the form of a shrink film or shrink tubing, for example made of polyethylene, onto a base body of a surfboard, whereby a hot melt adhesive may be provided for a material-bonded connection. From WO 2018 / 015021 A1, a composite material in the form of a surfboard is known, which comprises a base body and several groove-shaped recesses on the outside of the base body, wherein a reinforcing element designed as a fiber structure is arranged in the recesses. The reinforcing element is material-bonded to the base body by melting an edge region of the base body.

[0003] The object of the invention is therefore to create a composite material, in particular a core for a surfboard, which has sufficient stability at the lowest possible weight.

[0004] The composite material has a base body on the outside of which at least one groove-shaped recess is arranged, wherein, according to the invention, an additional thermoplastic material is provided in the recess. The thermoplastic material can be arranged in the wall of the recess and / or in the free space of the recess, i.e., the recess itself. When the thermoplastic material is heated, a reinforcing element can be attached to the recess particularly easily. The reinforcing element can be, for example, a textile, braid, knit, or net, which in a preferred embodiment can exhibit a certain degree of elasticity. The thermoplastic material can bond materially with the reinforcing element, which is designed, for example, as a fiber structure or textile layer, in its (viscous) liquid, partially molten state and, if necessary,The reinforcing element is also positively engaged / enclosed / impregnated, thereby ensuring secure fastening / consolidation of the reinforcing element.

[0005] Composite materials prepared in this way can be easily stored and fitted with different reinforcing elements depending on the application. The stiffness or flexibility of the base material can be individually adjusted depending on the number, arrangement, and design of the indentations and the selection, number, weight, and arrangement of the reinforcing elements. For example, in a composite material in the form of a surfboard core, the stiffness or flexibility in the longitudinal and / or transverse direction of the surfboard, and possibly locally limited, can be very precisely adjusted by the number, depth, arrangement, and length of the indentations and the selection, type, orientation, quantity, and arrangement of the reinforcing element within the indentation.

[0006] In a preferred embodiment, the thermoplastic material is formed as a surface coating of the base body or as a film that is advantageously applied to the base body. The surface coating or film can be provided only within the groove-shaped recess, i.e., have cutouts, or it can extend into the adjacent areas of the outer surface of the base body, in particular completely over the areas between adjacent recesses. For particularly simple manufacturing, for example, the entire top, bottom, and / or edge areas of the composite material can also be provided with a corresponding surface coating or film made of the thermoplastic material. The base body can consist of a thermoplastic and / or thermoset material, in particular a foamed one.In a particularly preferred embodiment, the base body can consist entirely or at least on one outer surface of a thermoplastic material or comprise a thermoplastic material.

[0007] According to the invention, a reinforcing element is arranged in the recess, which is bonded to the base body via the thermoplastic material and is designed as a fiber structure or textile layer. The bond is preferably achieved by heating and melting the thermoplastic material, preferably under pressure, so that, as described above, a material-bonded and, if necessary, also form-fit connection is created between the reinforcing element and the base body. A composite material with the corresponding reinforcing element can also be stored particularly easily and kept ready for further processing. The reinforcing element is preferably arranged in the recess adjacent to the base body. The reinforcing element can be provided only in the recesses or also in the adjacent surface sections of the base body.In particular, the reinforcing element can completely cover sections of the surface between adjacent recesses or even the top surface of the base body. The reinforcing element preferably follows the contour of the outer surface of the base body and advantageously rests against it in a continuous surface, even within the recesses. In particularly advantageous embodiments, the reinforcing element is arranged only in the deepest section / bottom of the recess, on the bottom and the adjoining side walls of the recess, only on the side walls of the recess, or on the side walls of the recess and the adjacent edge sections of the recesses on the outer surface of the base body.

[0008] Additionally, a thread / knitted fabric / net / roving can be provided, which corresponds to the recesses and comprises, in particular, natural, glass, carbon, and / or polymer fibers. Advantageously, the thread / roving or the knitted fabric / net can be formed separately and arranged on the thermoplastic element, in particular the thermoplastic film, the reinforcing element, or another carrier material. The fiber orientation of the thread / knitted fabric / net / roving preferably corresponds to the orientation of the recesses along the outside of the base body, and the thread / roving is advantageously woven into the carrier material or bonded to the carrier material or the thermoplastic element. The carrier material allows the thread / roving or the knitted fabric / net to be positioned particularly easily and precisely on the base body. Subsequently, in an advantageous embodiment, the thread / roving can be applied using a heated die.The knitted fabric / net is pressed into the base body and firmly connected to it, resulting in the indentations with the thread / roving or knitted fabric / net arranged in them.

[0009] In a particularly advantageous embodiment, a metallic element, in particular a metal thread, metal wire, metal powder, or metal mesh, is arranged in the recess, preferably following the contours of the recess. The metallic element can be continuous, in particular forming a closed ring along a recess, or it can be provided in sections, with separate elements that are spaced apart from one another or abut each other. In the form of a metal powder, the metallic element can completely or partially line the recess. The metallic element can positively influence the stiffness or flexibility of the composite material. Furthermore, the metallic element facilitates the subsequent application of a laminate consisting of a matrix, for example, polyester resin, epoxy resin, or polyurethane resin, and a fiber material, particularly in injection molding.The infusion process enhances the flowability of the uncured matrix or resin within the depression, ensuring particularly good penetration of the depression by the matrix. A metallic element can be in contact with the base body, the thermoplastic material, and / or the reinforcing element. Alternatively or additionally, a metallic element can be integrated into the thermoplastic material and / or the reinforcing element. A corresponding metallic element can also be used to reinforce a base body without depressions, preferably arranged on the base body in the form of the described depressions, i.e., with a closed pattern, preferably in a honeycomb, rhombic, or triangular shape. Like the thread / roving or knitted fabric / net described above, the metallic element can be mounted on a carrier material or...the thermoplastic element, in particular according to the course of the indentations and possibly together with the thread / roving / knitted fabric / net, is arranged before it is positioned on the base body and connected to the base body by a punch.

[0010] Advantageously, the reinforcing element, designed as a fiber structure or textile layer (as well as the fiber material of the aforementioned laminate), can consist of glass, glass filaments, fiberglass, carbon, aramid, Dyneema, basalt, or renewable raw materials such as hemp, flax, viscose, bamboo, jute, cotton, silk, or sisal, or a mixture thereof. The fiber structure or textile layer can be woven, laid, or nonwoven. The thermoplastic material can be integrated into or adjacent to the reinforcing element and can be provided, in particular, as a fiber, thread, filament, powder, or coating, which forms a matrix by melting, at least in one of the groove-shaped depressions. For example, the reinforcing element can be impregnated with the thermoplastic material before being bonded to the base material; this can also be referred to as a thermoplastic prepreg.For clarification, it should be noted that the prepreg referred to in connection with the invention does not require the presence of a reactive resin in the reinforcing element. Pre-impregnated simply means that a thermoplastic polymer and / or metallic element has been added to it before it is bonded to the base body. A correspondingly pre-impregnated reinforcing element can be prepared in a separate manufacturing process and readily stored.

[0011] The following items are particularly suitable as pre-impregnated reinforcement elements or prepregs. The fiber structure or textile layer, as well as the optionally usable yarn / knit / net / roving described above, can be powder-coated and / or melt-impregnated with a thermoplastic material. Additionally or alternatively, a hybrid yarn can be used in the reinforcement element, in which, for example, the fibers of the reinforcement element are mixed with thermoplastic fibers, particularly at the filament level. The reinforcement element can be partially or completely made of such a hybrid yarn. Additionally or alternatively, the reinforcement element can also be designed as a hybrid textile, in which reinforcement fibers and thermoplastic fibers are woven into a textile or bonded to form a fiber structure. To potentially...To ensure that the reinforcing element is only applied locally, i.e., inhomogeneously distributed, the powder coating with the thermoplastic material, the melt impregnation, and / or the hybrid yarn or thermoplastic fibers in the hybrid textile can be applied only in specific areas of the reinforcing element. This can be achieved by applying the powder coating only to certain areas of the reinforcing element and / or by weaving / integrating the hybrid yarn or thermoplastic fiber only in certain areas of the reinforcing element. The same applies to the metallic element.These areas of the pre-impregnated reinforcing element, coated with thermoplastic material and / or a metallic element, can, for example, correspond to the shape of the recesses, i.e., form a path that follows the described closed path, in particular in a honeycomb shape with six corners and / or in a rhombus shape with four corners and / or in a triangular shape. The reinforcing element can be impregnated / coated, in particular, with a metallic element in the form of a metal thread, metal wire, metal powder, metal shavings, or metal mesh. The metallic element can be homogeneously distributed throughout the reinforcing element or be locally confined, for example, following the recesses. The metallic element can be continuous throughout the reinforcing element, in particular forming a closed ring following a recess, or it can be applied in sections, with separate elements that are spaced apart from one another or abut each other.Alternatively, the thermoplastic material and / or the metallic element can also be homogeneously distributed, i.e., spread over the entire surface of the reinforcing element and / or on the surface of the base body.

[0012] In the case of a reinforcing element, a homogeneous distribution means that, in a top view of the reinforcing element, which is usually planar, the metallic element and / or the thermoplastic material are uniformly distributed. In a non-homogeneous distribution, areas with a higher proportion of metallic element or thermoplastic material and areas with a lower, preferably non-existent, proportion of metallic element or thermoplastic material exist in the top view. The same applies to the potentially non-homogeneous distribution of the thermoplastic material and / or the metallic element on the surface of the base body. These areas are to be understood macroscopically, not microscopically. Areas that, for example, contain no proportion of metallic element and / or thermoplastic material can be larger than 1 mm², and particularly preferably larger than 25 mm².

[0013] Areas containing metallic elements and / or thermoplastic materials can be arranged in regular patterns as described. Advantageously, metallic elements can be placed only in the areas where thermoplastic materials are used.

[0014] In a particularly preferred embodiment, the recess is further equipped with a filler, preferably pre-impregnated, preferably consisting of microballoons / (hollow) spheres / (glass) beads or fiber scraps / fiber cuts / flakes of the same or different lengths made of glass, carbon, basalt, jute, coconut, sisal, flax, viscose, aramid, cotton, metal, thermoplastic filament or thread, hybrid yarn, etc., and / or of granules or powder of the same or different grain sizes made of glass, wood dust, cork, metallic scraps, thermoplastic material, talc, such as hollow glass spheres, thermoplastic spheres or talc powder, or a mixture thereof.Through a defined selection and / or combination of the aforementioned fillers, the properties of the composite material, and thus of the surfboard, can be precisely adjusted, for example, the mechanical, acoustic, and / or thermal insulation properties and / or the vibration properties, in particular the vibration-reducing or vibration-damping properties. The filler can be placed adjacent to the reinforcing element and / or between the reinforcing element and the base body.

[0015] Alternatively or additionally, pre-impregnated (prepreg) or non-pre-impregnated fibers or rovings made of glass, carbon, basalt, jute, coconut, sisal, flax, viscose, aramid, metal, bamboo, etc. can also be arranged in the depression, which preferably line the depression.

[0016] In a further advantageous embodiment, a cover layer can also be provided, which covers the recess with the filler so that the filler cannot escape from the recess. The cover layer can comprise woven fabric / non-woven material / film / thermoplastic film / prepreg and can be partially or completely bonded to the composite material, either thermoplastically or thermosettingly. Furthermore, the cover layer can have all the features and properties described with respect to the reinforcing element. This allows the composite material with the fillers to be safely stored and transported even before the addition of a matrix or the curing / cooling of an existing matrix prior to further processing. The cover layer can also cover the adjacent surface sections of the base body, in particular the surface sections between the recesses.In cross-section, the cover layer can follow the contours of the depressions or fill them flush, resulting in a smooth surface. Regardless of the use of a filler, a cover layer can also be provided which is firmly bonded to the base body and / or the reinforcing element (with or without fillers) via thermoplastic adhesive bonding, in particular via a thermoplastic polymer, or thermosetting adhesive bonding of the cover layer to the corresponding surfaces, edges / sides of the depressions. The cover layer itself can be made of thermoplastic polymer, as described in relation to the reinforcing element, and / or the thermoplastic polymer in the depression and, if applicable, on the adjacent surface sections can be used for adhesion / attachment / consolidation to secure the cover layer, the reinforcing element, and / or the fillers.In a particularly preferred embodiment, the thermoplastic polymer forms a matrix connecting the base body, the cover layer, the reinforcing element and / or the fillers after possibly multiple melting processes.

[0017] In an advantageous embodiment, the groove-shaped depression has an annular, preferably closed, profile in plan view, particularly in a honeycomb shape with six corners and / or in a rhombus shape with four corners and / or in a triangular shape. In the honeycomb shape, all six sides can be of equal length, or two opposite sides can have identical lengths that are greater than the identical lengths of the other sides. The opposite sides can also have non-identical lengths and be arranged parallel or non-parallel. In particular, several such annular depressions can be formed adjacent to one another, resulting in a corresponding honeycomb pattern in which depressions of one honeycomb shape can also be assigned to the adjacent honeycomb shape.

[0018] For local reinforcement of the outer surface of the base body, a straight indentation can extend from every second corner of the six corners to the center of the honeycomb shape in a subset or all honeycomb shapes, where the indentations merge into one another in a star-like pattern. This divides a six-cornered honeycomb shape into three rhombus shapes, each with four corners. The additional indentations increase stability in this area, while the flowability of a resin during subsequent injection or infusion processes is enhanced by the interlocking nature of the indentations. Additionally or alternatively, straight or curved indentations can be provided, which, in a subset or all rhombus shapes, connect two opposite corners or run independently of existing honeycomb or rhombus patterns.The rhombus shape can therefore be subdivided into two triangular shapes, with the indentations merging into one another. Alternatively or additionally, it can also be provided that at least one honeycomb shape transitions into two smaller honeycomb shapes, as will be described in more detail with reference to the figures. Furthermore, indentations can be provided which, when viewed from above, resemble a spider web on the base body, whereby in areas of higher local pressure, for example in the standing area of ​​a surfboard, the density of indentations—i.e., the number or size of indentations per surface section—is greater than in the adjacent surface sections. Such a pattern of indentations can be the result of pure topology optimization or optimization with regard to the flow properties during the injection or infusion process and the topology.The shape and / or geometry can be partially varied to reinforce load-bearing elements such as fin mounts, attachment points for safety cables, or general inserts (e.g., screw threads). The shape and / or geometry can also be varied to accommodate subsequent compressive, bending, and torsional loads. In plan view, the recesses can be angular and / or have rounded corners.

[0019] To further enhance the flowability of the resin during the subsequent injection or infusion process and to achieve particularly good wetting of the entire top surface of the base body and penetration of the recesses with the matrix, additional, in particular straight or curved, recesses can be provided, which extend along the outside of the base body, preferably over the dimensions of several groove-shaped recesses with an annular shape.

[0020] Furthermore, a method for producing a composite material, in particular a core for a surfboard, is claimed, in which an outer surface of a base body of the composite material is bonded to a reinforcing element in the form of a fiber structure or a textile layer by heating and cooling the thermoplastic polymer in at least one groove-shaped recess. The thermoplastic polymer enables a particularly simple and strong bond between the reinforcing element and the base body. According to a first embodiment of the invention, the thermoplastic polymer is arranged on the base body in the form of a thermoplastic film before heating and bonding. Additionally, the thermoplastic polymer can be provided as a coating on the base body before heating and bonding.To bond the thermoplastic material to the base body, the thermoplastic material can also be heated.

[0021] In a second embodiment of the invention, the thermoplastic material is provided within the reinforcing element prior to heating and bonding with it, for example, in the form of thermoplastic fibers in a fiber structure or a textile layer. The thermoplastic material can be inhomogeneously distributed, i.e., as described above, only in locally limited areas of the reinforcing element. Additionally or alternatively, the base body can consist entirely or at least on one outer surface of a thermoplastic material, or comprise a thermoplastic material, so that no additional thermoplastic material is necessary. Alternatively, in the case of a base body made of a thermoplastic material, the thermoplastic material on the outer surface of the base body can consist of a film or a coating made of a different material and / or a different structure.Furthermore, a thermosetting, curable plastic such as a reaction resin, possibly with a fiber material, can be applied as a matrix to the thermoplastic plastic.

[0022] For a particularly stable connection between the reinforcing element and the base body, the reinforcing element can be pressed into the base body by means of a punch, resulting in at least one depression, preferably with an annular, closed, or open shape. Advantageously, the punch can be heated to heat / thermally deform the thermoplastic material and, if necessary, also the base body. This makes it particularly easy to plastically deform the thermoplastic material and the base body. For this purpose, the punch preferably has a shape corresponding to the shape of the depressions, for example, a honeycomb, rhombic, and / or triangular shape. Advantageously, the punch can be designed so that it only contacts, heats, and / or melts the base body at the depressions to be formed, but not in the intervening areas of the base body's surface.

[0023] In a further advantageous process step, after forming the recess(s) and securing the reinforcing element, a thermosetting matrix, such as a polyester resin, epoxy resin, vinyl ester resin, or polyurethane resin, together with a fiber material, is preferably applied as a top layer to the surface of the base body with the recesses by means of an injection or infusion process. Here, the injection or infusion process of the matrix can be optimized by a defined design of the recesses and / or selection of the reinforcing elements, so that complete wetting of the top surface and penetration of the recesses with the matrix is ​​achieved. Depending on the application, the recesses may eliminate the need for additional flow aids for the resin or matrix during the injection or infusion process.Alternatively or additionally, a cover layer made of a fiber-reinforced material can be attached to the base body via a thermoplastic polymer, preferably the thermoplastic polymer in the recesses and, if necessary, on the adjacent surface sections. This is particularly easy to implement if the base body itself consists entirely of a thermoplastic polymer or at least has a thermoplastic polymer on one of its outer surfaces. For example, it would be possible to provide a thermoset matrix only in the recesses and attach a final cover layer using a thermoplastic polymer.If the cover layer itself has a thermoplastic matrix, for example through the integration of a thermoplastic polymer into the fiber material of the cover layer, it is significantly less sensitive to local pressure loads compared to a brittle thermoset matrix and is also particularly easy to repair. It is also conceivable to cure the thermoplastically bonded reinforcing element and the fillers via a thermoplastic matrix and then apply a thermoset matrix with or without additional reinforcing textiles.

[0024] Furthermore, a device, in particular a surfboard for stand-up paddleboarding, surfing, kitesurfing, or windsurfing, is claimed, comprising a core and a fiber material firmly bonded to the outside of the core via a matrix, wherein the core is designed as a composite material as described above. Additionally, at least one sandwich layer, for example made of balsa wood or wood veneer, can be applied. With such a surfboard, the stiffness or flexibility in the longitudinal and / or transverse direction can be individually adjusted for each surface section, thereby creating a particularly stable and simultaneously lightweight surfboard with consistently stable flexural properties over the long term.

[0025] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings. These show: Fig. 1 a top view of a composite material in the form of a core for a surfboard; Fig. 2 a detail view of a first alternative embodiment of a composite material; Fig. 3 a detail view of a second alternative embodiment of a composite material; and Fig. 4a-d schematic cross-sections through a recess in the composite material.

[0026] In Figure 1Figure 1 shows a top view of a composite material 1 in the form of a surfboard core. The composite material 1 comprises a base body 2 made of a thermosetting or thermoplastic material, in particular extruded polystyrene (XPS), expanded polystyrene (EPS), polyurethane, or polyethylene, or of a renewable raw material such as wood, cornstarch, rubber, polymers, biopolymers, recycled plastic foams, in particular recycled PU, PET foam, or fungal cultures. For particularly low weight, the material of the base body 2 is preferably foamed with an open-pore or closed-pore structure, in which a gas, preferably air, is arranged in the spaces between the cells. Furthermore, cavities can also be provided within the base body 2, which further reduces the weight.

[0027] The basic body 2 has the shape typical of a surfboard, in which, in top view, a comparatively pointed nose 3 is followed by a front standing area 4, then a rear standing area 5 and finally a tail 6.

[0028] As can be seen from the illustration, the base body 2 has several recesses 7, 8 on its upper surface. In the illustrated embodiment, honeycomb-shaped recesses 7 are arranged in the front base area 4, each individual honeycomb shape being hexagonal with sides of equal length and point-symmetrical about its center point. The recesses of the adjacent honeycomb shapes merge into one another, resulting in the honeycomb pattern shown in the top view.

[0029] In contrast to the front standing area 4, the depressions 8 in the rear standing area 5 run in a rhombus shape, with the individual rhombuses being formed by the honeycomb pattern from the front standing area 4 continuing into the rear standing area 5, but in each hexagonal honeycomb in the rear standing area 5 a straight depression extends from every second corner to the center of the hexagonal honeycomb and there the three depressions merge into each other in a star shape.

[0030] In the illustrated embodiment, the straight indentations within the hexagonal honeycomb shape in the rear standing area 5 extend from the top left, top right, and bottom center corners. However, it is also possible to have the straight indentations within the honeycomb shape of some or all of the honeycombs in the rear standing area 5 extend alternatively from the other corners, i.e., the top center, bottom left, and bottom right corners, to the center point.

[0031] The illustrated design allows the rhombus-shaped recesses 8 to be directly integrated into the honeycomb-shaped recesses 7, enabling a seamless transition. This ensures that, for example, when applying a laminate consisting of a fiber fabric and a matrix, the uncured matrix can flow through the interconnected recesses 7, 8 from one point in a recess to any other point in the recesses via at least one path. This facilitates the flow process and thus complete wetting of the top surface of the base body 2, as well as complete penetration of the recesses 7, 8 by the matrix, particularly during wet lamination or in injection or infusion processes. Furthermore, stress peaks are avoided and the force flow is optimally distributed.

[0032] The depressions 7, 8 can have a constant or varying depth, preferably between 0.01 cm and 3 cm, thereby allowing the flow properties of the uncured matrix within the depressions 7, 8 to be controlled by their design. Similar to the branching of veins in a leaf, depressions with a larger cross-section can be provided, leading into depressions with progressively smaller cross-sections. In this way, the uncured matrix can be supplied via the few depressions with larger cross-sections and distributed throughout the entire depressions. Since the depressions with larger cross-sections also provide greater stability, they can preferably be arranged in areas of higher load, for example, in the support areas 4, 5 and / or in the top view near a center line / line of symmetry of the base body 2.Based on this, the depressions can taper towards the outer edges and / or the nose / tail. In cross-section, the depressions can be square, rectangular, or conical, tapering inwards or outwards towards the base body.

[0033] Further flow assistance for the still uncured matrix can be achieved by the targeted selection of reinforcing elements, which are arranged in the recesses 7 and 8. This allows the flow rate to be increased or decreased locally or throughout the entire component, as required.

[0034] In alternative embodiments not shown, the entire top and / or bottom surface can be partially or completely provided with corresponding recesses. Particularly on the underside, the recesses can be designed to be flush with the fin mounting boxes, thereby providing additional fin stabilization. Furthermore, the hexagonal honeycomb-shaped recesses and the square rhombus-shaped recesses can be freely arranged on the top and / or bottom surface of the base body, depending on the degree to which a specific area requires reinforcement.

[0035] In Figure 2Figure 1 shows a detailed view of a first alternative embodiment of a composite material. As can be seen in the top view of the composite material 1' designed as a surfboard, the honeycomb-shaped depressions 7 transition seamlessly into honeycomb-shaped depressions with smaller dimensions, in particular with a width half that of the honeycomb-shaped depressions 7. In the area of ​​the honeycomb-shaped depressions 7', the density of depressions is higher, resulting in greater stiffness and compressive strength compared to the area with the honeycomb-shaped depressions 7. Consequently, areas of the base body 2 can be provided with such depressions 7' as required. Complete penetration of the depressions 7, 7' with a matrix, particularly by injection or infusion, is readily achievable due to the direct transition between the depressions 7, 7'.

[0036] In Figure 3A detailed view of a second alternative embodiment of a surfboard is shown. Compared to the embodiments of the Figure 1 and 2 Irregular depressions are provided there, which are topologically optimized and thus resemble a Voronoi diagram or Voronoi regions. As with bionic optimization, a load-bearing lightweight structure can be determined using computer-aided calculation methods, from which the course and size of the depressions result. Unlike in Figure 3 As shown, it is advantageous if at least one area with a higher density of depressions is provided near a central axis / axis of symmetry of the base body 2 or the surfboard core, and if areas with a lower density of depressions adjoin this area towards the lateral edges. The [details of the diagram] Figures 1 to 3 The depicted contours of depressions 7, 7', 8 and 9 can easily be combined.

[0037] In the Figures 4a-4d Schematic cross-sections through a recess 10 in the base body 2 of the composite material 1 are shown. Figures 4a-4c Figure 1 shows various arrangements of a reinforcing element 11 in the form of a fiber structure or a textile layer and a metallic element 12 in the form of a metal wire, which are arranged in the recess 10 on the surface of the base body 2. As can be seen from the illustrations, the metallic element 12 can be arranged in the recess 10 between the reinforcing element 11 and the base body 2, in contact with the reinforcing element 11 and / or the base body 2. Figure 4 α). Alternatively, the metallic element 12 can also be arranged on the side of the reinforcing element 11 facing away from the base body 2 and may be in contact with the reinforcing element 11 ( Figure 4b Alternatively, the metallic element 12 can be integrated into the reinforcing element 11 and, if necessary, rest against the base body 2 ( Figure 4c Instead of the metal wire shown, the metallic element can also be formed as a metal powder, which is preferably arranged between the reinforcing element 11 and the base body 2, abutting the reinforcing element 11 and / or the base body 2, and lining the recess / curvature in a wider area. Alternatively or additionally, metal powder can also be arranged on the side of the reinforcing element 11 facing away from the base body 2 and may abut the reinforcing element 11. In all embodiments, a thermoplastic material (not shown) is also present, by means of which the reinforcing element 11 is attached to the base body 2, at least partially, in a material-locking and, if necessary, form-locking manner. For this purpose, the thermoplastic material was melted, at least partially.

[0038] In Figure 4dA schematic cross-section through the base body 2 in the area of ​​the recess 10 is shown, without the reinforcing element 11 and the metallic element 12. Various areas of the recess are marked in the illustration where a material-locking and, if necessary, a form-locking connection with the reinforcing element (not shown) can be created via the thermoplastic material (also not shown). The connection can be made, for example, via the base 13 alone or together with the adjacent flanks 14a, 14b. Alternatively, the connection can also be made at the base 13 and at the surface 15a, 15b adjacent to the recess 10. As a further alternative, the connection could be made only at the flanks 14a, 14b.

[0039] In embodiments not shown, the recesses can also be conical or V-shaped in cross-section with a pointed or flattened, in particular horizontal, bottom, U-shaped, segmental circular or rectangular, each with rounded or sharp-edged corners and straight or curved flanks. Reference symbol list:

[0040] 1, 1', 1" Composite material 2 Base body 3 Nose 4 Front base area 5 Rear base area 6 Tail 7, 7' Honeycomb-shaped recesses 8 Rhombus-shaped recesses 9 Topologically optimized recesses 10 Recess 11 Reinforcing element 12 Metallic element 13 Bottom of recess 14a, 14b Sides of recess 15a, 15b Surface adjacent to recess

Claims

1. Composite material (1; 1'; 1''), in particular core for a surfboard, comprising a main body (2) and at least one groove-shaped depression (7; 7'; 8) on the outer face of the main body (2), wherein a reinforcing element in the form of a fibrous structure or, respectively, textile layer is positioned in the depression (7; 7'; 8), characterized in that an additional thermoplastic is provided in the depression (7; 7'; 8) and the reinforcing element is firmly cohesively bonded to the main body (2) via the additional thermoplastic.

2. Composite material (1; 1'; 1'') according to Claim 1, characterized in that the additional thermoplastic is in the form of a film.

3. Composite material (1; 1'; 1'') according to Claim 1 or 2, characterized in that the reinforcing element is in the form of a fibrous structure or, respectively, textile layer of flax and / or viscose.

4. Composite material (1; 1'; 1'') according to any of Claims 1 to 3, characterized in that the additional thermoplastic is integrated in the reinforcing element.

5. Composite material (1; 1'; 1'') according to Claim 4, characterized in that the additional thermoplastic is provided in the form of a fibre, thread, filament, powder or coating, which forms a matrix at least in the groove-shaped depression by melting.

6. Composite material (1; 1'; 1'') according to Claim 4 or 5, characterized in that the additional thermoplastic is distributed inhomogeneously in the reinforcing element.

7. Composite material (1; 1'; 1'') according to any of Claims 1 to 6, characterized in that a metallic element, in particular a metal thread, metal wire, metal turnings or metal knitted fabric, is positioned in the depression.

8. Composite material (1; 1'; 1'') according to Claim 7, characterized in that a metallic element is integrated into or, respectively, adjoins the additional thermoplastic and / or the reinforcing element.

9. Process for producing a composite material (1; 1'; 1''), in particular a core for a surfboard, wherein an outer face of a main body (2) of the composite material (1; 1'; 1''), in at least one groove-shaped depression (7; 7'; 8), is firmly cohesively bonded to a reinforcing element in the form of a fibrous structure or, respectively, in the form of a textile layer by heating and cooling a thermoplastic, characterized in that the thermoplastic is provided on the main body (2) in the form of a thermoplastic film before heating, or in that the thermoplastic is provided in the reinforcing element before heating.

10. Process according to Claim 9, characterized in that the thermoplastic is provided in inhomogeneous distribution in the reinforcing element before heating.

11. Process according to Claim 9 or 10, <b>characterized in that the reinforcing element is pressed by means of a die into the main body (2), so as to obtain at least one depression (7; 7'; 8) with an in particular annular progression, in particular in honeycomb form with six corners and / or in rhombus form with four corners and / or in triangular form.

12. Process according to Claim 11, characterized in that the die is heated in order to heat the thermoplastic.

13. Device, in particular surfboard for stand-up paddling, surfing or windsurfing, having a core and a fibre material firmly bonded to the outer face of the core via a matrix, characterized in that the core is in the form of a composite material (1; 1'; 1'') according to any of Claims 1 to 8.

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