COMPOSITE MATERIAL REINFORCED BY SPRINGLIKE METAL STRUCTURE

Abstract: A composite material (16) comprising a polymer (17) as matrix and a metal structure (10) as a reinforcing element, characterized in that said metal structure (10) comprises two metal springs (12, 14), said springs (12, 14) being wound in opposite directions, said springs having coil parts which alternate with each other along the length of the metal structure, said springs being rolled so as to form a flat shape.

Description: COMPOSITE MATERIAL REINFORCED BY SPRINGLIKE METAL STRUCTURE Field of the invention. The present invention relates to a composite material which comprises a polymer as matrix and a metal structure as a reinforcing element The invention also relates to the use of such a composite material as reinforced canvass, sail cloth, cargo cover or tarpaulin Background of the invention. Composite materials with a polymer as a matrix and a metal structure as a reinforcing element are known in the art An example is WO-A- 97/26146, which discloses a fabric of polyvinylchloπde reinforced by one elongated metal element such as a wire for use as reinforcement of canvasses The disadvantage of this structure is that a wire, in order to provide the required strength and resistance against cutting and against the action of a pair of scissors, must have a diameter which is sufficiently large This large diameter wire then lacks flexibility which may hinder or prevent the canvass from being folded WO-A-98/55682 solves the problem of flexibility by replacing the single steel wire by two or more steel cords in parallel adjacent to each other The steel cords have the advantage of providing sufficient flexibility while still providing the required strength The increased flexibility is obtained by using relatively thin filaments in the steel cords However, in a number of safety applications such as canvasses, these thin filaments often lack the required resistance against the action of a pair of scissors Summary of the invention. It is an object of the present invention to avoid the drawbacks of the prior art It is a further object of the present invention to provide an alternative metal reinforcement for polymer material in safety applications It is also an object of the present invention to provide a metal structure which combines the properties of providing the required strength and resistance against cutting and a sufficient flexibility. It is still another object of the present invention to decrease the weight of composite materials. According to the invention there is provided a composite material which comprises a polymer as matrix and a metal structure as a reinforcing element. The metal structure comprises two metal springs. The springs are wound in opposite directions. The springs have coil parts which alternate with each other along the length of the metal structure. The springs are rolled together so as to form a flat shape and a coherent structure. During this process the individual wires are more or less flattened, taking into account the tensile strength of the wires and the pressure exercised on the rolls. This metal structure has following advantages : (a) The metal structure is flexible in all directions. (b) The metal structure provides an adequate resistance against cutting and against the action of a pair of scissors since each cross-section has at least three, but conveniently four separate cross-sections of metal wires. (c) The metal structure has a great elastic springiness. It allows to a large degree folding and bending without plastic deformation. (d) The metal structure is thin and flat in one direction, so that a minimal amount of polymer is needed to cover it. This reduces the weight of the composite material. A metal structure, as described hereabove, is known as such in the art as corset bones for orthopedical applications. The polymer is preferably a thermoplastic material such as polyvinylchloride (PVC) which can be extruded around the metal structure. Other examples of suitable polymers include polyurethane and thermoplastic elastomers. The term thermoplastic elastomers refers to blends of polyolefins and rubbers in which blends the rubber phase is not cured, blends of polyolefins and rubbers in which blends the rubber phase has been partially or fully cured by a vulcanization process to form thermoplastic vulcanizates, or unvulcanized block-copolymers or blends thereof. The composite material can be in the form of a strip, a sheet or a fabric with a warp and a weft, where at least one of the warp or the weft are a strip. The composite material can be used in applications where an increased resistance against vandalism and robbery is desired. Examples are the reinforcement of canvasses, sail cloths, tarpaulins, tent material, cargo covers. Brief description of the drawings. The invention will now be described into more detail with reference to the accompanying drawings wherein FIGURE 1 illustrates a metal structure used to reinforce a composite material according to the invention ; FIGURE 2 illustrates a cross-section of a composite material in the form of a strip ; - FIGURE 3 illustrates a cross-section of a composite material in the form of a sheet ; FIGURE 4 illustrates a composite material in the form of a fabric. Description of the preferred embodiments of the invention. FIGURE 1 illustrates a metal structure 10 used to reinforce a composite material according to the invention. The metal structure 10 comprises two metal springs 12, 14 which are wound in opposite directions. The springs 12, 14 are so wound in each other that a coil part of spring 12 alternates with a coil part of spring 14, and vice versa. Thereafter the metal structure 10 is rolled so that it forms a coherent and flat structure. The rolling is so that the cross-sections of the individual springs 12 and 14 are also flattened. This flattening increases the resistance against the action of a pair of scissors. The metal springs 12, 14 can be made of hard drawn steel wires with following plain carbon composition : a carbon content between 0.06 % and 1.10 %, a silicon content between 0.10 % and 0.40 % and a manganese content between 0.20 % and 1.20 %. Addition of micro-alloying such as chromium, vanadium, boron ... is not excluded. The use of stainless steel wires is neither excluded. Typical values of the diameter d of the steel wires are 0.40 mm and 0.50 mm (in case of a non-round cross-section, the diameter d equals to the diameter of a round cross-section with the same cross-sectional surface). Generally the wire diameter d ranges from 0.25 mm to 0.80 mm. A typical value of the coil diameter D is 4.0 mm. Generally the coil diameter D ranges from 3.0 mm to 6.0 mm after rolling. The width W of the total metal structure 10 may vary between about 4.0 mm and 11.0 mm after rolling. The pitch p between two coils of the same spring wire varies between the value of a single wire diameter and several times the wire diameter. The steel wire may be coated with a metallic coating such as zinc or a zinc alloy (e.g. a zinc aluminum alloy with 2 % to 10 % Al and 0.1 % to 0.4 % of rare earth elements such as La and/or Ce) in order to provide a good corrosion resistance. Although the undulated and rough surface of the metal structure already guarantees a good mechanical anchoring between the metal structure 10 and the polymer matrix, the individual steel wires or the steel structure as a whole may also be provided with a primer which increases the adhesion to the polymer matrix. A first group of primers that can be used are thermosetting materials. Therefore binding agents are dissolved in an organic solvent or are dispersed with a limited amount of a dispersing agent in water to form an emulsion or a suspension. Suitable binding agents are based on acrylate, alkyd/melamine, epoxy or phenol/epoxy resins. Other binding agents giving a good adhesion to the metal and to the PVC compounds can also be used. Additives such as anticorrosion pigments, wetting agents and/or stabilizing agents can be added. The primer composition is applied to the wires or to the metal structure by immersing the wires or the structure into a solution, an emulsion or a suspension of the primer material. The primer composition can also be applied by spraying. The thickness of the wet primer layer can be calibrated by passing the wire and the primer through the calibrated opening of a die. The thickness of the primer layer can also be calibrated by felt wiping or by air wiping in a controlled air stream. The thickness of the primer layer may be influenced by further diluting the primer composition. In order to allow drying and curing the wire or the metal structure can be heated. Since it is desirable that the weight of the composite is as low as possible, the thickness of the primer layer must be low. The thickness of the dry primer layer is preferably less than 10 μm, more preferably less than 5 μm, for instance less than 1 μm. Radiation curable resins such as ultra violet, electron beam or infra red curable resins are also suitable as primer. A second group of primer layers that can be applied are hot melts, for example ethylene copolymers such as EVA (ethyl vinyl acetate), polyamides or polyesters. In order to obtain a sufficient thin layer, it is preferred to use hot melts with a viscosity at 200°C of less than 20 Pa.s, more preferably this viscosity is less than 15 Pa.s. This hot melt can be applied with a variety of different equipment. Very suitable is the melt pot. Also application by extrusion is possible under certain conditions. A method for the application by extrusion is described in the patent specification BE 1006346. Depending on the viscosity and the method of the application of the primer layer, primer layers with a thickness of less than 25 μm, for instance less than 5 μm are obtained. A third group are silane-compounds. These are bifunctional molecules : one functional group is responsible for the binding with the metal(oxides), the other functional group reacts with the polymer. More details about these silane compound can be found in the PCT application with the application number WO-A-99/20682 (PCT/BE98/0015). Usually the silane compounds are diluted in alcohols, although they can be diluted in other solvents or in water as well. With this type of compounds very thin primer layers with a thickness of 20 nm or even less can be achieved. FIGURE 2 shows a cross-section of a composite strip 16. Strip 16 has a PVC matrix 17 which is extruded around a metal structure 10 which has three to four cross-sections of spring wires 12, 14. A typical width of the strip is 6.0 mm and a typical thickness 1.0 mm. Generally, both the width and the thickness depend upon the resp. width and thickness of the metal structure 10. The width may range from 3.0 mm to 25.0 mm and the thickness may range from 0.50 mm to 3.0 mm. FIGURE 3 illustrates a composite sheet 18 at least one direction of which is reinforced by means of a metals structure 10. FIGURE 4 illustrates a fabric 20 where either the warp elements 16' or the weft elements 16" or both are strips reinforced by means of a metal structure 10. Strips 16' are welded to strips 16" so that the PVC material melts and functions as an adhesive between warp and weft. The fabric 20 forms various meshes. The width M of the mesh ranges from 5.0 cm to 20.0 cm. Typical values are 15.0 cm x 15.0 cm and 10.0 cm x 7.5 cm. A fabric 20 may be used as reinforcement for canvasses by bonding or adhering the fabric at the interior side of the canvass so that the external side is still available for publicity or brand names. Canvasses for trucks may be divided into two main categories : canvasses of the curtain type and canvasses of the roll up type. Canvasses of the curtain type are slidingly suspended on horizontal rails and can be horizontally slid to one side to open the canvass. Canvasses of the curtain type require flexibility in the horizontal direction. Canvasses of the roll up type can be rolled up vertically to open the canvass. Canvasses of the roll up type require a flexibility in the vertical direction. Fabrics 20 according to the invention may be realized so that for canvasses of the roll-up type, the flexible metal structure 10 reinforces at least the vertical strips 16' and that for canvasses of the curtain type, the flexible metal structure 10 reinforces at least the horizontal strips 16".

Claims: CLAIMS 1. A composite material comprising a polymer as matrix and a metal structure as a reinforcing element, characterized in that said metal structure comprises two metal springs, said springs being wound in opposite directions, said springs having coil parts which alternate with each other along the length of the metal structure, said springs being rolled so as to form a flat shape. 2. A composite material according to claim 1 wherein said polymer is a thermoplastic material. 3. A composite material according to claim 2 wherein said thermoplastic material is polyvinylchloride. 4. A composite material according to any one of the preceding claims wherein said composite material has the form of a strip. 5. A composite material according to any one of claims 1 to 3 wherein said composite material has the form of a sheet. 6. A fabric comprising a warp and a weft which form meshes, said meshes having a maximum dimension ranging from 5 cm to 25 cm, at least one of the warp or the weft being formed by a strip according to claim 4. 7. A canvass or a sail cloth, said canvass or sail cloth at least partially reinforced by a composite material according to any one of claims 1 to 5.

Inventors: ADRIAENSEN LUDO, VAN LOO GILBERT, ADRIAENSEN, LUDO, VAN LOO, GILBERT
Applicants: ADRIAENSEN LUDO, BEKAERT SA NV, LOO GILBERT VAN, ADRIAENSEN, LUDO, N.V. BEKAERT S.A., VAN LOO, GILBERT
Application year: 2000
Main classification: B29C70
IPC codes: B29C70, D04H3