WO2015005854A1

WO2015005854A1 - A formable composite material and a method for manufacturing a formable composite material

Info

Publication number: WO2015005854A1
Application number: PCT/SE2014/050844
Authority: WO
Inventors: Mats Stading
Original assignee: Sik - Institutet För Livsmedel Och Bioteknik Ab
Priority date: 2013-07-01
Filing date: 2014-07-01
Publication date: 2015-01-15

Abstract

The invention relates to a method for manufacturing a composite material unit (800) comprising a fibre composition, wherein the fibre composition comprises a plurality of conductive fibres and a meltable element. The method comprises the acts of: forming a first flexible layer and a second flexible layer from the fibre composition, assembling a surface of the first flexible layer with a surface of the second flexible layer, shaping the assembled first and second flexible layers, and thereafter putting the conductive fibres in a conductive state so that the meltable element is put in a melting state, and letting the first flexible layer and the second flexible layer assume a rigid structure. The invention also relates to a composite material unit (800) comprising a plurality of conductive fibres and a meltable element.

Description

A FORMABLE COMPOSITE MATERIAL AND A METHOD FOR MANUFACTURING A FORMABLE COMPOSITE MATERIAL

Field of the invention

The present inventive concept generally relates to composite materials. More specifically, the present inventive concept relates to a composite material comprising a fibre composition and a method for manufacturing this composite material.

Background art

Composite material is a broadly defined type of materials which comprise two or more material components and which may be used in a variety of contexts by means of their attractive properties. A composite material often presents physical or chemical properties which are different from the properties that the incorporated material components have by themselves. For example, such a property may be a strength of the material.

A composite material in the form of laminated wood, such as a plywood panel, has a substantially higher strength than that presented by the layers forming the laminated wood. Moreover, a plastic material may be reinforced by adding a reinforcing component, such as a fibre material. Thereby, a reinforced plastic is obtained, whose matrix may consist of a thermoplastic.

There are various field of applications within which a formable composite material is needed. Especially, there is a need for a formable composite material which may assume an essentially arbitrary shape and which may be manufactured in a large quantity.

In WO02/30657 a matrix of fibres comprising at least two materials undergoes a process of heating where at least one of the materials in the matrix is melted. The matrix is compressed in a hot condition and thereafter cooled.

In US1453503 there is described a method for the production of thermoformed sheets from fibres. The method comprises the steps of forming a sheet of vegetable fibres and thermoplastic synthetic polymer fibrils, heating the sheet and shaping the hot sheet under pressure.

In US2006/0105661 there is disclosed a thermoformable panel comprising thermoplastic fibres. There is provided a mat having non-woven fabric layers of these thermoplastic fibres being placed one over the other. The mat is heated up by a heater means and is fed to a forming and compression station. The station comprises a mold in which the mat is molded. It is noted that in US2006/0105661 there no mentioning of

conductive fibres.

However, a problem is that the manufacturing costs of a composite material of this type are too high.

Summary of the invention

In view of the above it is therefore an object of the present inventive concept to provide a method for manufacturing a formable composite material unit which is more cost effective.

In accordance with the inventive concept there is provided a method for manufacturing a composite material unit according to independent claim 1 .

Moreover, there is provided a composite material unit according to

independent claim 15. Preferred embodiments of the present inventive concept are provided in the dependent claims.

Thus, the present inventive concept differs from what is disclosed in

WO02/30657, US1453503 and US2006/0105661 at least in that the layers first are formed, assembled and shaped and thereafter the conductive fibres are put in a conductive state, for heating and joining of the layers, and the layers are fixated by assuming a rigid structure.

An advantage of first forming, assembling and shaping and after that putting the conductive fibres in a conductive state is that the shaping procedure may be better controlled, e.g. since in a non-heated state the flexible layers are more rigid as compared to when they are in a heated state.

Thus, the inventive concept may provide a more cost-effective manufacturing method which at the same time provides for a better controlled shaping procedure. According to a further aspect of the invention there is provided a method for manufacturing a composite material unit comprising a fibre composition. The fibre composition comprises a plurality of conductive fibres and a meltable element. The method comprises the acts of: forming a first flexible layer from the fibre composition, putting the conductive fibres in a conductive state so that the meltable element is put in a melting state, and letting the first flexible layer assume a rigid structure.

By a composite material is here meant a material which comprises at least two different material elements, or material components, and which has physical and/or chemical properties which are different from the physical and/or chemical properties of the incorporated material elements. For example, the physical properties may be hardness, elasticity, flexibility, bendability, compliance, electrical conductivity, heat conductivity and magnetic properties. The composite material unit manufactured according to the inventive method comprises at least a plurality of conductive fibres and a meltable element. By a plurality of conductive fibres is here meant a plurality of conductive fibres of the same type. Optionally, however, the fibre composition may comprise a plurality of conductive fibres of different types. Moreover, the composite material unit may comprise reinforcement and a matrix, or base material, which acts as binding medium and which may keep the reinforcement in place.

The composite material unit may comprise renewable or synthetic materials.

A fibre may be a long and narrow material element and may have a filamentous, or threadlike, structure. The fibres may provide reinforcement in the composite material unit. Conductive fibres may be fibres which conduct electrical current or, more specifically, have an electrical conductivity which exceeds a certain minimum value. Conductive fibres which conduct electrical current preferably present an electrical resistance such that a requisite generation of heat and emission of electromagnetic radiation for melting the meltable element is achieved. Conductive fibres may also be fibres which conduct heat, i.e. have a heat conductivity which exceeds a certain minimum value. When the conductive fibres are put in a conductive state, electrical current, heat, or both electrical current and heat, are conducted through them. More specifically, the conductive state may be defined as a state in which an electrical current and/or heat transfer which is exceeding a predetermined threshold value is being conducted through the conductive fibers. In a non- limiting example, the threshold value on the electrical current being conducted through the fibers is 1 Ampere. It is understood that other electrical currents are equally conceivable. In the conductive state, the meltable element may become heated up. Additionally, conductive fibres may be manufactured by adding a conductive material, such as metal, carbon or conductive plastics, to non-conducting fibre components.

A melting state of the meltable element is a state in which at least portions of the meltable element melt. A meltable element which assumes a solid form in a non-melting state may assume a liquid form in the melting state. In the melting state the conductive fibres and the meltable element may at least partially be joined together. This joining may be achieved by mechanical integration of the meltable element and the conductive fibres at a microlevel. For example, the meltable element may abut on a surface of the conductive fibres, in the melting state as well as during a cooling process, for providing a mechanical integration in a subsequent non-melting state. The conductive fibres may have a surface roughness for improving the joining. The joining may also be provided by chemical integration of the meltable element and the conductive fibres.

The meltable element may comprise melt fibres. For example, the meltable element may be thermoplastics, bioplastics or wax, but other meltable elements are equally conceivable. Bioplastics is a thermoplastics which may comprise biological substances, such as polyactides, starch, proteins and wax. Bioplastics may comprise bioplastic fibres. The meltable element is preferably chosen such that it melts in a temperature interval which is suitable for manufacturing of a composite material unit with a given fibre composition. In a non-limiting example, melt fibres which melt below 150 °C may be used.

The meltable element may be a meltable powder, a meltable granulate, a meltable film, a meltable slab, a meltable plate, etc. In one example, the meltable element is such that the resulting fiber composition may be transported along a paper web when forming the first and second flexible layers. In another example, the meltable element is such that the resulting fiber composition is formed into the first and second flexible layers in a stationary, i.e. non-moving, manner.

By way of example, the size of the conductive fibres or the melt fibres may be between 2 and 3 millimetres, but it is understood that other sizes are equally conceivable.

The fibre composition is flexible and may easily be adapted by taking into account durability demands, rate of production, price and end use.

Moreover, the fibre composition may be chosen by taking into account demands regarding biological degradability of the composite material unit. For example, the fibre composition may comprise renewable raw materials. The fibre composition may comprise glass fibres and/or plant fibres.

By putting the conductive fibres in a conductive state, the meltable element may be put in a melting state so that the conductive fibres and the meltable element may mix and join as described in the above. A desired shape of the first flexible layer and the second flexible layer of the composite material unit may be chosen and thereafter be fixed at this shape, whereupon a rigid structure may be assumed. The inventive method allows for a flexible adaptation of the shape of the composite material unit. The fixation may easily be provided, for example by putting the meltable element in a rigid state, or a non-melting state.

By a rigid structure of a material, such as a layer, a sheet, etc., is here meant that a deformation of the material is small or negligible when the material is exposed to forces or temperature changes which are typical in the contemplated application of the material. In particular, the material may preserve its shape when exposed to forces or temperature changes.

According to the inventive manufacturing method, the first flexible layer, and thence the composite material unit, may be manufactured in a large number. In particular, the inventive manufacturing method may be implemented in an automated production process. In view of the above, the present inventive concept admits a cost-effective manufacturing method of formable composite material units, especially when a large number of formable composite material units are to be manufactured.

Other advantages of the present inventive concept are that the inventive manufacturing method may be used so that the composite material unit becomes a particularly strong rigid material. For example, the method may be used for manufacturing of strong, high-performing composite materials, construction materials, packaging materials which are shaped after the packed product, shells for mobile telephones and other electronic boxes, interior fittings and furniture, as well as for preshaped packaging components such as plates, trays and multiple-product packages. By way of example, the strong, high-performing composite materials may be materials in airplanes, lorries or cars, such as car interior fittings. For example, the construction materials may be wall panels or cable ducts.

Several composite material units may be assembled for forming a composite material element. In one example, the composite material element comprises composite material units of the same type, i.e. essentially comprising the same type of materials. In another example, the composite material element comprises composite material units of different types.

According to one embodiment, the composite material unit comprises a cellulose material. The cellulose material may comprise cellulose fibres, e.g. in conventional form or in the form of nanofibres. By using cellulose material the composite material unit may become more rigid.

According to one embodiment, the first and second flexible layers are formed while the fibre composition is moved along a paper-manufacturing web, or a paper web. Hence, the first and second flexible layers may be sheets of paper comprising the fibre composition. An advantage of this embodiment is that a larger number of flexible layers may be manufactured by means of a method which essentially utilizes conventional paper technology. By conventional paper technology is here meant that the flexible layer may be manufactured by comprising at least one of the steps of stock preparation, shaping, dewatering, pressing, drying and finishing. By way of example, the latter step may comprise that the first and second flexible layers are subjected to glossing, coating, slitting, sheet cutting and wrapping. According to an alternative one embodiment, the first and second flexible layers may be manufactured in another way which is well-known to a person skilled in the art. For example, the first and second flexible layer may be shaped by means of textile engineering. The first and second flexible layer may be a non-woven fabric. Alternatively, the first and second flexible layer may be a woven textile material.

According to one embodiment, the conductive fibres are electrically conducting. In one example, all the conducting fibres in the fibre composition are electrically conducting. In another example, a part of the conducting fibres in the fibre composition are electrically conducting. As described above, an advantage of the present embodiment is that the conductive fibres may emit heat by supplying electric current to them, whereupon the meltable element may be put in a melting state.

According to one embodiment, the conductive fibres are heat conducting. In one example, all the conducting fibres in the fibre composition are heat conducting. In another example, some of the conducting fibres in the fibre composition are heat conducting. By being heat conducting, the conductive fibres may emit heat so that the meltable element may be put in a melting state.

According to one embodiment, the conductive fibres comprise carbon fibres or iron fibres. In one example the conductive fibres comprise carbon fibres as well as iron fibres.

According to one embodiment, the conductive fibres are put in a conductive state by conducting an electrical current exceeding a

predetermined threshold value through the conductive fibers.

According to one embodiment, the conductive fibres are put in a conductive state by conducting heat exceeding a predetermined threshold value through the conductive fibers. The heat may be transported to the meltable element for melting the meltable element.

According to one embodiment, the act of letting the first and second flexible layer assume a rigid structure comprises the act of putting the conductive fibres in a non-conductive state. By putting the conductive fibres in a non-conductive state, so that neither electric current nor heat is transported through them, the conductive fibers may cool, i.e. obtain a lower temperature, which means that the meltable element may be put in a non-melting state. Accordingly, the meltable element, and consequently the first and second flexible layer, may become rigid by the cooling process. More specifically, the non-conductive state may be defined as a state in which a current and/or heat transfer which is falling below a predetermined threshold value is being conducted through the fibers.

According to one embodiment, the meltable element comprises plastic fibres. An advantage of this embodiment is that plastic fibres may be procured to a low cost. Additionally, a material comprising plastic fibres may alternately be put in a melting state and a non-melting state a plurality of times without destroying the material.

According to yet another to one embodiment, each fibre comprised in the plurality of conductive fibres mentioned above also is a meltable element. For example, this element may comprise electrically conducting plastic fibres.

According to one embodiment, the rigid structure is extended in three space dimensions. By extension in three space dimensions is here meant an extension which is substantially larger than a thickness of the first and/or the second flexible layer. For example, the first and second flexible layers may assume the shape of a thin sheet which is bent in the space. As an example, the shape of the rigid structure may be obtained by placement of the first and second flexible layer in a form and possibly also by pressing it.

The two flexible layers may be assembled since the first, as well as the flexible layer comprise a meltable element. The first and the second flexible layer may melt together at the surfaces which have been assembled. A desired thickness of the composite material unit may be obtained by assembling several flexible layers. Indeed, according to yet another embodiment the method further comprises the act of forming a collection of several flexible layers from the fibre composition, and assembling these flexible layers in analogy with the first and the second flexible layer as described above. The flexible layers may be laminated. According to one embodiment, first flexible layer is assembled with a surface of the second flexible layer by means of pressing. In one example, the pressing and the shaping occur in the same process.

It is clear that the embodiments and examples that have been described above in connection to the first flexible layer also are valid for the second flexible layer as well as for the collection of several flexible layers. For example, the collection of several flexible layers may be assembled by means of pressing.

When a shape of the material is determined and fixated, it may be desirable to change this shape. Therefore, according to one embodiment, the method further comprises the act of, after the first and second layer have assumed a rigid structure, reshaping the rigid structure. This reshaping may occur by putting the conductive fibres in a conductive state again, so that the meltable element melts anew. An advantage of this embodiment is that the flexible layers may be reshaped several times. In addition, recycling of the composite material unit is possible.

According to a further aspect of the invention, there is provided a composite material unit comprising a first fibre element. The first fibre element comprises a plurality of electrically conducting fibres and a meltable element, wherein the first fibre element assumes a three-dimensional rigid structure. The invontivo composite material unit essentially presents those properties and advantages that have been discussed above in relation to the first aspect, whereby reference is made to the above discussion.

According to one embodiment, the first fibre element further comprises a cellulose material.

According to one embodiment, the composite material unit further comprises a second fibre element, which comprises a plurality of electrically conducting fibres and a meltable element, wherein the first fibre element is assembled with the second fibre element so that the first and the second fibre element jointly assume a three-dimensional structure.

Other objects, features and advantages of the present invention will be apparent from the following detailed description, the appended claims and the figures. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps in the methods described herein do not have to be performed exactly in the described order, unless explicitly stated otherwise. Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 illustrates a side view of a manufacturing system according to an embodiment in which the inventive method for manufacturing a composite material unit may be implemented.

Fig. 2 illustrates a block diagram of a method for manufacturing a composite material unit which may be implemented in the manufacturing system according to Fig. 1 .

Fig. 3a is a perspective view of an embodiment of a composite material unit which has been manufactured according to the method which has been described in connection to Fig. 1 and Fig. 2.

Fig. 3b is a view from below of the composite material unit in Fig. 3a.

Detailed description of preferred embodiments

In the following the present inventive concept will be described with reference to Fig. 1 which illustrates a side view of an embodiment of a manufacturing system 100 which is adapted to manufacture a composite material unit.

The manufacturing system 100 comprises a paper device 200, a shaping device 300 and a cutting device 400. The paper device 200 is arranged to receive paper material 500.

Moreover, the paper device 200 comprises a paper web 210 and a paper manufacturing device 220. The paper manufacturing device 220 is adapted to form a plurality of formable sheets 510 from the received paper material 500. The paper web 210 is arranged to transport the paper material 500 by means of a feeding device from an input area 202 to an output area 204, where the paper material 500 has become sheets 510. The transport occurs in a direction which is indicated by the letter R in Fig. 1 .

According to the present embodiment, the paper device 200 is adapted to receive the paper material 500 which includes a plurality if electrically conducting fibres, a meltable element comprising a plurality of melt fibres, and a cellulose material. For example, the electrically conducting fibres may be carbon fibres or iron fibres and the meltable element may be, for example, thermoplastics, bioplastics, wax, etc. Moreover, the cellulose material may comprise cellulose fibres. The paper material 500 also contains additional material components which are well-known for a skilled person when manufacturing paper. The paper manufacturing device 220 is adapted to dewater and to treat the paper material 500 further for forming a plurality of formable sheets 510 according to methods which are well-known for a skilled person. At the output from the paper device 200 the paper material 500 has become formable sheets 510, wherein each sheet 510 thereby has assumed a structure in the form of a continuous, flexible layer. The sheets 510 thereby assume a given shape which in non-limiting examples may be of a

rectangular shape, a quadratic shape, an oval shape, a circular shape, etc. The sheets 510 assume a specific thickness and preferably have a uniform thickness. It is noted that, for clarity, the thickness of the paper material 500 and the sheets 510 have been exaggerated in Fig. 1 . It is also noted that the thickness of the composite material unit which is to be manufactured easily may be varied by adapting the number of sheets. Hence, after treatment in the paper device 200, the sheets 510 are adapted for further treatment in the shaping device 300.

The shaping device 300 is adapted to receive sheets 510 at an input place 301 from the paper web 210 and to transport them to a pressing area 302 by means of a conveyor 304. According to the present embodiment a plurality of sheets 520 are fed into the shaping device 300 for placement in the pressing area 302. The sheets 520 are placed on top of each other in the pressing area 302. The shaping device 300 comprises a shaping tool 310 and a pressing device 320. The shaping tool 310 comprises a number of wall elements which comprise a cavity. The wall elements make up a receiving surface which defines a shape of the composite material unit which is to be manufactured. The pressing device 320 comprises a pressing tool 322 which is adapted to be received in the shaping tool 310. The shape of the shaping tool 310 corresponds to the shape of the pressing tool 322. According to the present embodiment, the outer surface of the pressing tool 322 assumes the shape of a dome, or half-sphere, whereas the shaping tool 310 is adapted for receiving this pressing tool 322. After the pressing, the sheets 510 may assume a predetermined three-dimensional structure, in the present case the shape of a dome with a certain thickness. The pressing tool 322 is movable in relation to the shaping tool 310 in a vertical direction which is indicated by the letter V in Fig. 1 . The shaping device 300 further comprises a conveyor 306 for feeding out the pressed, fixated material 520 from the pressing area 302 to an output place 303.

The shaping device 300 also comprises an electrical circuit device 330 which comprises electronic components which are needed for supplying current to the pressed sheets 520 via a first 332 and a second 334 electrode. According to the present embodiment, current is supplied to all of the pressed sheets 520. According to an alternative embodiment, current is only supplied to some of the pressed sheets 520. Thus, the electrical circuit device 330 is adapted to melt at least a portion of the meltable element which is comprised in the pressed sheets 520 by conducting current through the sheets.

The shaping device 300 also comprises a cooling unit 340 which is arranged to cool down the pressed sheets 520 after melting the meltable element. During the cooling process the pressed sheets 520 may be fixated at a specific shape. The specific shape is determined by the shape of the pressed sheets 520 during the cooling process. In particular, the specific shape may be determined by the shape of the shaping tool 310 and the pressing tool 322. The cooling unit 340 may be arranged to lower the temperature of the pressed sheets 520 to a predetermined reference temperature. For example, the reference temperature may be determined by an associated desired rigidity of the pressed sheets 520. By way of example, the cooling unit 340 may comprise a cooling fan, a temperature regulator, etc., which is well-known to a person skilled in the art. According to an alternative embodiment, the pressed sheets 520 are cooled down by the ambient air.

The cutting device 400 is adapted to cut the pressed, fixated sheets 520. The cutting device 400 may comprise knives, scissors, knife rollers with associated supporting rollers, hole punchers, perforators, stampers, etc. The pressed, fixated sheets 520 may comprise portions which are redundant and which therefore need to be cut in order to obtain a desired shape of the composite material unit. Moreover, the pressed, fixated sheets 520 may give rise to several composite material units by cutting using the cutting device 400.

Next, a method of manufacturing a composite material unit will be described with reference to Fig. 1 and Fig. 2 which illustrate the method in a block diagram. It is realized that the illustrations in Fig. 1 and Fig. 2 are non- limiting and that other ways of implementing the inventive method are equally conceivable.

The method of manufacturing (Box 700) is initiated by forming formable sheets (Box 710) in the paper device 200 which is comprised in the manufacturing system 100. The paper device 200 receives paper material 500 at the input area 202 which then is treated by the paper manufacturing device 220 for formation of a plurality of formable sheets 510 and which thereafter is fed out at the output area 204 in the form of a continuous, flexible layer.

In the next step (Box 720) a plurality of formable sheets 510 are fed to the input place 301 of the shaping device 300 and are then placed on top of each other in the pressing area 302. The sheets 520 are assembled and are shaped at the pressing area 302 by way of pressing (Box 730) by means of the pressing device 320 and thereby assume a predetermined three- dimensional structure.

The pressed sheets 520 are then fixated to the predetermined three- dimensional structure (Box 740). This is accomplished by first supplying current to the pressed sheets 520 by means of the electrical circuit device 330, so that the meltable element melts, whereby the sheets are melted together, and then cooling the pressed sheets 520 by means of the cooling unit 340. Consequently, each flexible sheet becomes a rigid fiber element. The fiber elements are assembled and interlocked.

In order to form the desired composite material unit the pressed sheets

520 are finally cut (Box 750) in the cutting device 400 and the composite material unit is thereafter fed out from the shaping device 300 at the output place 303. It is noted that this cutting procedure may be omitted according to an alternative embodiment.

Optionally, the composite material unit may be aftertreated in an aftertreating device. For example, the aftertreatment may comprise glossing, painting, beveling, sealing, stamping, perforation, hole punching, stacking, wrapping and packing. When packing the composite material unit may partially or completely enclose a product which is to be packed. The composite material unit may be shaped after the product.

Since the fiber elements are rigid the composite material unit thereby keeps its shape over time. However, when needed the composite material unit may be reshaped. This reshaping may occur by a performing a method analogous to the method described above. The reshaping may occur repeatedly.

Fig. 3a and 3b illustrate in a non-limiting example an embodiment of a composite material unit 800 which is manufactured according to the method which has been described above. More particularly, Fig. 3a is a perspective view of the composite material unit 800 as seen obliquely from below and Fig. 3b is a view from below of the same. The composite material unit 800 comprises three half-spherical fiber elements 810, 812, 814 which are assembled by means of pressing according to the method described above. However, it is stressed that any number of fiber elements may be used and that three fiber elements 810, 812, 814 have been chosen only for illuminating purposes. In addition, the thickness of the fiber elements 810, 812, 814 have been exaggerated for the same reason. The shape of the composite material unit 800 is defined by a region between an outer half-sphere 820 and an inner half-sphere 830, wherein the inner half-sphere 830 has a radius which is smaller than a radius of the outer half-sphere 820. The thickness of the composite material unit 800 is determined inter alia by the number of fiber elements 810, 812, 814, the compliance of the fiber elements 810, 812, 814, and the strength of the compression of these during pressing, for example in the pressing device 320. The fiber element 810 and the fiber element 812 are assembled along a contact surface 840. The thickness of the composite material unit 800 is essentially constant along the full half-sphere.

According to an alternative embodiment, the fibre composition comprises a dispersion of cellulose fibres, plastic fibres and conducting fibres. The cellulose fibres are provided in the form of paper pulp. The plastic fibres comprises polyethene. The conducting fibres comprises carbon fibres and iron fibres. In non-limiting examples, an amount of paper pulp, X, and an amount of plastic fibres, Y, may be comprised in the intervals 20<X<60 and 40<Y<80, respectively. Here, X and Y are expressed in percentage by weight (wt%) and, moreover, X+Y=100. In a first example, the amount of plastic fibres is X=40 wt% and the amount of paper pulp is Y=60 wt%. In a second example, the amount of plastic fibres is X=80 wt% and the amount of paper pulp is Y=20 wt%. The conducting fibres may be less than 10% of the fibre composition. The paper which is formed from the fibre composition, e.g.

according to the method as described above, is electrically conducting and thereby an electric current may be conducted through the paper. When the conducting paper is put in a conductive state it may reach a temperature of about 170 °C whereby the plastic fibres melt.

According to an alternative embodiment, X and Y as defined above is expressed in percentage by volume (vol%).

According to yet an alternative embodiment, the plastic fibres may be bioplastic fibres, such as polylactic acid or polylactide, PLA. According to yet an alternative embodiment, the meltable element comprises a thermosetting plastic or thermosetting resin. In one example, the meltable element comprises a thermosetting plastic, without any plastic fibres. In another example, the meltable element comprises a thermosetting plastic as well as plastic fibres. According to this embodiment, a conducting paper may be provided, e.g. according to the method described above, whereupon the conducting paper is immerged in a thermosetting plastic which is provided in a liquid form or in a malleable form. In order to cure, the thermosetting plastic needs to be heated. This heating may be accomplished by means of heat from the conducting paper. Thus, by means of the thermosetting plastic or the thermosetting resin, yet a high-performing composite material may be provided.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, the sheets may be assembled after the melting process, the shape of the pressing tool and the shaping tool may be different, etc.

Claims

1 . A method for manufacturing a composite material unit (800) comprising a fibre composition, wherein the fibre composition comprises

a plurality of conductive fibres and

a meltable element,

wherein the method comprises the acts of

forming a first flexible layer and a second flexible layer from the fibre composition,

assembling a surface of said first flexible layer with a surface of said second flexible layer,

shaping the assembled first and second flexible layers, and thereafter putting said conductive fibres in a conductive state so that the meltable element is put in a melting state, and

letting said first flexible layer and said second flexible layer assume a rigid structure.

2. A method according to claim 1 , wherein the composite material unit (800) further comprises a cellulose material.

3. A method according to claim 1 or 2, wherein said first and second flexible layers are formed while the fibre composition is moved along a paper- manufacturing web (210).

4. A method according to any of the preceding claims, wherein the conductive fibres are electrically conducting.

5. A method according to any of the preceding claims, wherein the conductive fibres are heat conducting.

6. A method according to claim 4 or 5, wherein the conductive fibres comprise carbon fibres or iron fibres.

7. A method according to any of the preceding claims, wherein the conductive fibres are put in a conductive state by conducting an electrical current exceeding a predetermined threshold value through the conductive fibers.

8. A method according to any of the preceding claims, wherein the conductive fibres are put in a conductive state by conducting heat exceeding a predetermined threshold value through the conductive fibers.

9. A method according to any of the preceding claims, wherein the act of letting said first and second flexible layer assume a rigid structure comprises the act of putting said conductive fibres in a non-conductive state.

10. A method according to any of the preceding claims, wherein the meltable element comprises plastic fibres.

1 1 . A method according to any of the preceding claims, wherein said rigid structure is extended in three space dimensions.

12. A method according to any of the preceding claims, wherein said first flexible layer is assembled with a surface of said second flexible layer by means of pressing.

13. A method according to any of the preceding claims, further comprising the act of, after the first and second flexible layer have assumed a rigid structure, reshaping said rigid structure.

14. A method according to claim 13, wherein said reshaping comprises putting the conductive fibres in a conductive state so that the meltable element is put in a melting state.

15. Composite material unit (800) comprising a first fibre element (810) and a second fibre element (820), wherein each of said first (810) and second (820) fibre elements comprises

a plurality of electrically conducting fibres and

a meltable element,

wherein the first fibre element (810) is assembled with the second fibre element (820) so that the first (810) and the second (820) fibre element jointly assume a three-dimensional rigid structure.

16. Composite material unit (800) according to claim 15, wherein said first and second fibre elements (810) further comprise a cellulose material.