Field of the invention

The invention relates to a method and a system for manufacturing a product of natural fibre composite. Further, the invention relates to a product of natu- ral fibre composite.

Background of the invention

In industry, recent approaches have been to increasingly replace conven- tional materials, such as plastics, with novel structures of natural fibre composite. For example, various wood fibre composites are used instead of previously applied materials, among other things, in the construction, automotive, transportation, electronics and interior design industries, as well as for furniture applications.

In the prior art, the aim has been to make natural fibre composites, among other things, from a natural fibre composite web in the form of a web or a sheet. However, such solutions of prior art, in which a product comprising three-dimensional shapes is made of a web or sheet of natural fibre composite, involve several drawbacks. Typically, three-dimensional shapes are formed by stretching a sheet to be formed to a desired shape. Normally, the sheet of natural fibre composite is subjected to heat treatment before or during the stretching. Such a sheet of natural fibre composite can be made, for example, by dry forming or wet forming. Natural fibres are typically almost non-stretchable, for which reason it is primarily the binding agent, for example plastic, that is stretched when sheets or webs of natural fibre composites are stretched. Due to the properties of the natural fibre composite, weaker spots are typically formed in areas which require a lot of stretching, when the sheet is stretched to three-dimensional shapes. This is a problem particularly in case there are a lot of natural fibres in relation to the binding agent used, for example plastic and/or plastic fibres. Furthermore,

CORRECTED VERSION cost efficiency is reduced by the amount of waste material from the sheet to be formed, which is normally a large amount. Efficient recycling of said waste material may be difficult, particularly after the melting of the plastic. Making deep shapes by said manufacturing method that utilizes stretching is more successful when pure plastics are used, because the elongation of heated pure plastics is much greater than the elongation of heated natural fibre composites. Due to the poor strain properties caused by the fibres, it is difficult to stretch webs of natural fibre composites, for example, to form such deep, multi-dimensional and large three-dimensional shapes which are typically used in furniture. Consequently, there is a need in industry for an alternative approach to manufacture various three-dimensional products of natural fibre composite. Furthermore, there is a need in industry for materials which combine good mechanical properties, ecological sustainability and low price.

Brief summary of the invention

A purpose of the present invention is to provide a solution to the above-pre- sented problem for forming products of natural fibre composites. For this purpose, a method and a system for manufacturing a product of natural fibre composite are provided. Furthermore, a novel product of natural fibre composite is provided. The invention is based on a novel method for manufacturing a product of natural fibre composite, in which method three-dimensional products of nature fibre composite are made first by forming a blank for the piece to be made of a raw material mixture in a mould that corresponds substantially to the product to be formed, followed by finishing the formed blank to a product of natural fibre composite. The product of natural fibre composite according to the invention is advantageously biodegradable.

It is an aim of the invention to make products of natural fibre composite in a less expensive way than in the prior art, preferably in such a way that so- called deep shapes can also be made by the method. For achieving this aim, in an advantageous embodiment, the raw materials comprise a very large amount of natural fibres, advantageously wood fibres, as well as other fibres and/or fillers, which are bound by a minimum quantity of a binding agent. The binding agent is thus used, among other things, to improve the strength and water resistance of the product.

The method for manufacturing a product of natural fibre composite according to the present invention is primarily characterized in that the method comprises:

forming a mixture of raw materials comprising:

- at least 60 wt-%, preferably at least 80 wt-% of natural fibres, and

1 to 40 wt-%, preferably 10 to 20 wt-% of at least one binding agent;

bringing the mixture of raw materials in a liquid or gaseous medium in connection with a manufacturing mould, the manufacturing mould comprising a first surface and a second surface;

forming a blank of said raw material mixture, substantially having the shape of the product of natural fibre composite to be formed, onto the first surface of said manufacturing mould, the forming of the blank of the raw materials being effected by a pressure difference across the manufacturing mould such that the pressure is substantially greater on the side of the first surface of the manufacturing mould than on the side of the second surface of the manufacturing mould, wherein said medium is transferred by the effect of the pressure difference through the porous manufacturing mould (2); and

finishing the blank as a product of natural fibre composite.

The system for manufacturing a product of natural fibre composite according to the present invention is primarily characterized in that the system com- prises:

means for supplying raw material, for bringing the raw material mixture in a liquid or gaseous medium in connection with a porous manufacturing mould, the porous manufacturing mould comprising

a first surface, onto which a blank for a product of natural fibre composite is to be formed, as well as

a second surface, and the raw material mixture comprising

at least 60 wt-%, preferably at least 80 wt-% of natural fibres, and

1 to 40 wt-%, preferably 10 to 20 wt-% of at least one binding agent;

and the system further comprising

means for producing a pressure difference over the manufacturing mould in such a way that the pressure on the side of the first surface of the manufacturing mould is substantially greater than the pressure on the side of the second surface of the manufacturing mould, wherein said medium is transferred through the porous manufacturing mould (2) by the effect of the pressure difference, and a blank is formed of the raw material mixture, substantially in the shape of the product of natural fibre composite to be formed, onto the first surface of the manufacturing mould,

as well as

finishing means for finishing said blank to a product of natural fibre composite. The product of natural fibre composite according to the present invention is primarily characterized in that it is a product made by a method or a system according to any of the claims, preferably an element of interior design, a package, a part of an automobile or a transportation means, an outdoor structure, or an acoustic element.

According to an advantageous embodiment, supplying the raw material mixture in connection with the manufacturing mould comprises a step in which the porous manufacturing mould is immersed in the raw material mixture. Thus, the means for supplying the raw material comprise means for immers- ing said porous manufacturing mould in the raw material mixture.

According to an advantageous example, the system further comprises a wet press for removing the liquid medium from the raw material mixture brought into the shape of the blank. According to an advantageous example, the finishing of said blank comprises applying at least one binding agent, such as latex, resin, polymeric binding agent or inorganic binding agent, onto one or more surfaces of said blank to strengthen the structure of the blank.

According to an advantageous example, the raw material mixture used in the manufacture of the product of natural fibre composite is admixed to a medium. Thus, the dry matter content of said raw material mixture is not more than 6%, preferably not more than 2%, when dosed into the manu- facturing mould.

According to another advantageous example, the natural fibre composite is made of a substantially dry raw material mixture. In other words, the raw materials used in the mixture are mixed with each other when substantially dry, and they are brought as a dry mixture in connection with the manufacturing mould. Thus, the dry matter content of said raw material mixture is at least 50%, advantageously at least 75%, preferably at least 85%, when dosed into the manufacturing mould. According to an advantageous embodiment, the binding agent contains plastic, resin, a polysaccharide derivative, and or latex. Preferably, the binding agent thus comprises a thermoplastic material. The binding agent may be soluble or dispersible in water, or it may be powdered or fibrous. If the binding agent comprises thermoplastic material, the finishing of the blank advan- tageously comprises heating and/or pressing, preferably hot pressing of said blank.

Significant advantages to the prior art are achieved by the product and the method according to the invention. By the solution of the invention, it is pos- sible to reduce waste material that is formed by the manufacturing methods of prior art and that is difficult to recycle. Furthermore, it is possible to avoid typical quality impairments caused by stretching in the approach of prior art, and to produce structures of even layer thickness and uniform quality instead. Also, the manufactured products are typically relatively lightweight and strong. The products made by the method can be, for example, elements for interior design, including furniture, packages, dishes, outdoor structures, and acoustic elements.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows the method for manufacturing a product of natural fibre composite according to an advantageous embodiment of the invention, in a reduced view,

Fig. 2 shows the method for manufacturing a product of natural fibre composite according to another advantageous embodiment of the invention, in a reduced view,

Fig. 3 shows the system according to the embodiment shown in

Fig. 1 , in a reduced flow chart, and Fig. 4 shows the system according to the embodiment shown in

Fig. 2, in a reduced flow chart.

Detailed description of the invention In this application, the term natural fibre refers to various fibres of natural origin. The natural fibre may comprise recycled fibre and/or virgin fibre. The natural fibre may be, for example, mechanically defibrated fibre, dissolving cellulose fibre, sulphite cellulose fibre, sulphate cellulose fibre, or viscose fibre. In an advantageous example, the natural fibre has undergone chemical treatment to reduce the lignin content, because by using lignin-free natural fibres, it is easier to prevent smells which may be harmful in the case of some products. In one application, the natural fibre is selected from the group of wood-based fibres, fibres of plant origin, and their derivatives and mixtures. In one example, the natural fibre is selected from the fibres of wood, sisal, jute, hemp, flax, straw, and other annual plants, as well as mixtures of these. In one application, at least part of the natural fibres may be micro- fibrillated cellulose fibres and/or nanocellulose fibres, which may have the effect of improving the strength of the product.

The product of natural fibre composite to be made, which may be a finished product of natural fibre composite or a single part of a product of natural fibre composite to be made, comprises at least a binding agent in addition to the natural fibres. In this application, the binding agent refers to either a binding agent consisting of a single binding agent component, or a mixture of two or more binding agent components. The purpose of the binding agent is, among other things, to strengthen the structure of the product being formed, by binding different particles to each other. In an advantageous example, the binding agent is biodegradable. Advantageously, the binding agent is selected from plastics (for example, plastic powder, plastic fibres), latices, resins (for example, resin powders), cellulose derivatives (for example, cel- lulose acetate, cellulose esters, cellulose ethers), as well as inorganic adhe- sives. The binding agent may be not only fibres or powder but also a water soluble or water dispersible binding agent.

In this application, reference is made to Figs. 1 to 4, in which the following reference numerals are used:

1 product of natural fibre composite,

2 manufacturing mould,

2a first surface of the manufacturing mould,

2b second surface of the manufacturing mould,

3 blank for a product of natural fibre composite,

4 raw material mixture,

5 means for supplying the raw material mixture,

6 wet press, and

7 means for finishing the blank.

In an advantageous example, the binding agent or at least part of the binding agent used consists of thermoplastic material. Thus, the method for manufacturing a product of natural fibre composite 1 typically comprises a step in which a blank 3 for the product of natural fibre composite 1 is heated and/or pressed, because the thermoplastic material becomes softer when it is heated and makes the particles, such as natural fibres and other materials used, adhere or glue to each other. As a result of the heating, a compact product is obtained.

The thermoplastic material may be a material that is intrinsically thermo- plastic, or it may be a material that has to be treated to be thermoplastic at the temperatures, to which said material is heated during the manufacture, to soften and/or melt said material. For example, the material may be plasti- cized {i.e. softened) chemically by adding plasticizers to the material, to achieve sufficient thermoplasticity. Various plasticizers are presented in the prior art. For example, glycerol and sorbitol can be used as plasticizers suitable for polysaccharides. Typically, for example several cellulose derivatives, such as cellulose acetate, are not sufficiently thermoplastic to be used as such in the process, but they have to be plasticized to improve the thermoplastic properties.

In an advantageous example, the thermoplastic material comprises thermoplastic plastic. Advantageously, the thermoplastic plastic is selected from polyethylene (PE), polypropylene (PP), ethylene/propylene copolymer, polycarbonate (PC), polystyrene (PS), polyethylene terephthalate (PET), poly- lactic acid (PLA), polyhydroxy butyrate, acrylonitrile/butadiene/styrene copolymer (ABS), styrene/acrylonitrile copolymer (SAN), polyoxymethylene (POM), biodegradable thermosetting plastics, polysaccharide based, e.g. starch based thermosetting plastics, derivatives and mixtures thereof. In an example, the particles of the binding agent, advantageously plastic, used for manufacturing the natural fibre composite have a diameter smaller than 1000 μιη, more advantageously smaller than 500 μηι. In one example, particles of the binding agent, advantageously plastic, are used, which have a diameter smaller than 100 μιη. Thus, they can adhere as a substantially even layer to the surfaces of the fibres. The binding agent particles can be broken to a fine powder, for example by mixing the particles in a medium at a high temperature, or by grinding the particles at a particularly low temperature. In addition to the natural fibres and the binding agent, the product of natural fibre composite may contain, among other things, various fillers and addi- tives. In addition to the natural fibres, the product of natural fibre composite may also comprise other fibres, such as synthetic fibres and/or bicomponent fibres. In the solution according to the invention, the medium, such as air or water, admixed to the raw material mixture, is transferred by the effect of a pressure difference through a porous manufacturing mould 2, such as a wire cloth, wherein part of the raw material mixture is filtered as a blank of natural fibre composite 3 onto the first surface 2a of the porous manufacturing mould. The pressure difference can be produced by devices of prior art.

In this application, the first surface 2a of the manufacturing mould 2 refers to that surface of the manufacturing mould, from whose side the raw material mixture 4 in the liquid or gaseous medium is transferred by the effect of a pressure difference, for example by suction, through the manufacturing mould. Thus, in a case in which the first surface 2a of the manufacturing mould 2 is the outer surface of the manufacturing mould, when said raw material mixture in a liquid or gaseous medium is sucked by the effect of a pressure difference through said porous manufacturing mould 2, a layer is formed of the raw material mixture 4 onto the outer surface of the manufacturing mould 2, said layer forming the blank 3 for a product of natural fibre composite. In a corresponding way, if the first surface 2a of the manufacturing mould 2 is the inner surface of the manufacturing mould, when said raw material mixture in a liquid or gaseous medium is sucked by the effect of a pressure difference through said porous manufacturing mould 2, a layer of the raw material mixture 4 is formed onto the inner surface of the manufacturing mould 2, said layer constituting the blank 3 for a product of natural fibre composite. In this way, the raw material mixture 4 can be distributed, by the effect of the pressure difference, as a substantially uniform layer onto the first surface 2a of the manufacturing mould 2, forming the blank 3 for a product of natural fibre composite.

In the solution according to the invention, the pressure difference through the manufacturing mould is thus essential in such a way that the pressure is sub- stantially higher on the side of the first surface 2a of the manufacturing mould than on the side of the second surface 2b of the manufacturing mould. Con- sequently, a porous manufacturing mould 2 is used in the solution according to the invention. The manufacturing mould 2 according to the invention, made of a porous material, can be used for manufacturing a product of natural fibre composite by both a dry method and a wet method. The porosity, that is, the mesh size and the density of the apertures, of the manufacturing mould 2 is preferably selected such that the components of the raw material mixture do not substantially penetrate the surface of the manufacturing mould, but the medium can exit through the manufacturing mould. The thickness of the forming layer can be influenced, for example, by adjusting the suction time and/or the pressure difference.

The invention is based on the idea that the structure of natural fibre composite is made by bringing the raw material mixture 4 in connection with the manufacturing mould 2. Advantageously, the raw material particles in said raw material mixture are substantially evenly distributed in the medium. The first surface 2a of the manufacturing mould 2, that is, the mould surface, determines the shape of the product to be made by the manufacturing mould 2. The shape of the first surface 2a is copied in the blank 3 for the product 1 of natural fibre composite to be made, however in such a way that the shape copied in the blank 3 is, in a way, an inverted (negative) shape of the shape of the first surface 2a. Consequently, a recess possibly present in the first surface 2a produces a bulge in the blank 3. Consequently, the surface contour of the blank 3 is substantially uniform to the first surface 2a of the manufacturing mould 2. The product of natural fibre composite 1 according to the invention can be made either from a substantially dry raw material mixture or from a raw material mixture admixed to a liquid medium. In an advantageous example, the structure of natural fibre composite is formed in the manufacturing mould 2 by using a substantially dry raw material mixture, in which case the removal of a liquid medium is not needed.

In a solution according to the invention, the blank 3 for a product of natural fibre composite 1 is preferably formed substantially in the desired shape, wherein the blank 3 is thus substantially equal to said product of natural fibre composite in shape. The blank 3 can further be e.g. softened/melted later on, that is, in the finishing step of the blank 3, for example to improve the strength properties, but such treatments are not necessary as early as in the step of forming the blank 3. In other words, the blank 3 can also be formed, for example, at normal room temperature. Thus, in an advantageous example, the blank 3 for the product of natural fibre composite is formed at a temperature below 110°C or at a temperature below 100°C. In an advantageous example, the blank 3 for the product of natural fibre composite is formed at a temperature below 90 °C or at a temperature below 80 °C. In an advantageous example, the blank 3 for the product of natural fibre composite is formed at a temperature below 70°C or at a temperature below 60°C. The blank 3 for the product of natural fibre composite can also be formed at a temperature lower than 50 °C.

In an advantageous embodiment, supplying the raw material mixture in connection with the first surface 2a of the manufacturing mould comprises a step in which the manufacturing mould 2 is immersed in the raw material mixture. Thus, the means 5 for supplying the raw material comprise means for immersing the manufacturing mould 2 in the raw material mixture 4.

In a wet process, the blank 3 usually has to be dried. The drying of the blank 3 made by the wet process can be enhanced by wet pressing the blank in a wet press 6. In an advantageous example, the blank 3 for the product of natural fibre composite can be dried in said porous manufacturing mould. In another advantageous example, the blank for the product of natural fibre composite is dried on top of a separate substrate, such as a separate wire. Preferably, the drying is thus performed by utilizing hot air.

In a dry web machine, when the medium, .e.in this case for example air, is removed through the first surface 2a of the porous manufacturing mould 2 to the second surface 2b, a very bulky blank is typically formed on the first surface of the manufacturing mould 2. The strength properties of such a blank are typically relatively poor. It is even possible that such a blank cannot be removed from the manufacturing mould unless its strength properties are improved. Thus, if the blank contains thermoplastic material, said thermoplastic material can be melted, for example by utilizing hot air or by hot pressing, thereby to improve the strength properties of the blank. In an advantageous example, a blank made by dry forming can also be dried, for example by pressing on a separate substrate, such as a wire. By means of the method of the invention, it is possible to manufacture products of natural fibre composite having a larger content of natural fibres than usually, because the product is made without any separate stretching in the method. Consequently, the product is formed in the same mould during the whole process, all the way to its final shape. In the method of the invention, the (dry) content of natural fibres is advantageously at least 60 wt-%, more advantageously at least 80 wt-%. The (dry) content of the binding agent is advantageously 1 to 40 wt-% or 4 to 30 wt-%, more advantageously 10 to 20 wt-%.

The shape of the first surface 2a of the manufacturing mould 2 is advantageously such that it substantially gives the blank 3 for a product 1 of natural fibre composite to be made the desired shape, that is, a kind of a negative form of the shape of the blank. Said shape of the blank 3 for the product of natural fibre composite may comprise substantially the whole shape of the product to be made, or said shape of the blank 3 for the product (as well as of the product of natural fibre composite to be made of it) can be a single part of the product to be made.

According to an advantageous embodiment of the invention, the raw materials 4 for the product 1 of natural fibre composite to be made are supplied as a mixture onto the first surface 2a of the manufacturing mould 2 by means 5 for supplying the raw material in such a way that a blank 3 for the product 1 of natural fibre composite is formed on the first surface 2a of the manufacturing mould 2. In other words, if the mould comprises recess-like shapes, such as in the situation of Figs. 1 and 2, the raw material mixture preferably does not fill the whole manufacturing mould 2 but only forms a raw material layer (a blank 3) on the first surface 2a of the manufacturing mould 2. In an advantageous embodiment, the thickness of the material layer (blank 3) formed on the first surface is about 1 to 10 mm, more advantageously 1.5 to 5 mm.

In an advantageous example, when thermoplastic material is used as the binding agent, the formed blank 3 for the product 1 of natural fibre composite can be heated to melt the thermoplastic material at least partly, wherein the structure of the blank 3 becomes solid and strong. Thus, the means 7 for finishing the blank comprise means for heating the blank. This can be done, for example, by blowing hot air through the blank 3. Irrespective of whether thermoplastic material is used or nor, it is possible to use binding agents, such as latex or resin, in addition to or instead of the heating, to reinforce the structure of the blank 3. In this way, it may be possible to increase the surface strength and durability of the blank, and/or the strength and/or rigidity of the material. Said binding agent used to reinforce the structure of the blank 3 can be dosed on one surface or both surfaces of the blank 3, for example by spraying.

The means 7 for finishing the blank 3 may also comprise, for example, means for drying the blank and/or for shaping and/or for pressing the blank and/or cooling the blank. Advantageously, the product 1 of natural fibre com- posite receives its final shape and properties during hot pressing of the blank 3, wherein the structure of the blank 3 is solidified when the thermoplastic material melts and reinforces the product of natural fibre composite being manufactured. Thus, the means 7 for finishing the blank comprise means for hot pressing the blank. The means for finishing the blank may also comprise, among other things, means for drying the blank and/or means for heating the blank and/or means for cooling the blank and/or means for shaping the blank and/or means for applying binding agents, for applying a binding agent onto the surface of the blank.

The method for manufacturing a product of natural fibre composite comprises one or more of the following steps:

- Preparing a raw material mixture 4 comprising at least one binding agent and natural fibres.

- Forming a blank 3 for a product 1 of natural fibre composite by bringing said raw material mixture in connection with a mould 2 in such a way that the blank 3 for a product 1 of natural fibre composite is formed by the effect of a pressure difference onto the first surface 2a of the manufacturing mould, substantially conforming to the shape of the blank 3 to be formed.

- Wet pressing 6 said blank 3 to remove the medium. - Heating the blank 3, for example with hot air, to solidify the structure of said blank 3.

- Adding a binding agent, for example latex, to reinforce the structure of the blank 3. The binding agent is applied onto one or more surfaces of the blank.

- Drying the formed blank 3 to reduce the moisture content.

- Hot pressing the blank 3 for the product of natural fibre composite in such a way that the thermoplastic material glues the natural fibres and other production material to form a compact structure.

- Cooling the blank 3 to form the structure of the product.

According to an advantageous example, the preparation of the raw material mixture comprises the following steps:

- disintegrating natural fibres to smaller units, which can be done, for example, by a hammer mill or a corresponding arrangement, and

- mixing the disintegrated natural fibres, the binding agent and other possible raw materials to form the raw material mixture 4.

As mentioned above, if the binding agent comprises thermoplastic material, the formation of the blank 3 is advantageously followed by a heating step. This is advantageously implemented in such a way that the temperature used at the heating stage is, for at least part of the time, higher than the glass transition temperature of said thermoplastic material, advantageously at least 15 or at least 20 degrees higher than said glass transition temperature. Preferably, the temperature applied at the heating step is, for at least part of the time, higher than the melting temperature of said thermoplastic material. In an advantageous example, it is possible to use a temperature of, for exam- pie, about 115°C for polystyrene, a temperature of, for example, about 140°C for polyethylene, and a temperature of, for example, about 170°C for polypropylene. The thermoplastic material should be selected so that the temperature remains sufficiently low for the natural fibre used during the heating, so that the natural fibre used is not damaged. In an advantageous example, the glass transition temperature and the melting temperature of the thermo- plastic material used are not higher than 200 °C, more advantageously not higher than 180°C.

Figure 1 shows a method for manufacturing a product 1 of natural fibre com- posite according to an advantageous embodiment of the invention, and Fig. 3 shows, in turn, a corresponding system for manufacturing a product 1 of natural fibre composite, in a reduced schematic view. In the embodiment of Figs. 1 and 3, said product is formed by the so-called dry method from substantially dry materials in such a way that a gaseous material, preferably air, is used as the medium. The figures show the manufacturing mould 2, the first surface 2a of the manufacturing mould, the second surface 2b of the manufacturing mould, the raw materials 4, the blank 3 for the product of natural fibre composite, and the finished product 1 of natural fibre composite, as well as means 5 for supplying raw material, and means 7 for finishing the blank.

The blank 3 for an advantageous product of natural fibre composite shown in Figs. 1 and 3, to be made according to the example, is formed from a substantially dry raw material mixture 4 by utilizing the dry method. The raw material mixture 4 is contacted with the manufacturing mould 2, whose first surface 2a corresponds substantially to the outer shape of the blank 3 for the product 1 of natural fibre composite to be made. The dry matter content of the raw material mixture 4 is at least 50%, advantageously at least 75%, preferably at least 85%, when supplied into the manufacturing mould 2. The supplying of the raw material in connection with the manufacturing mould 2 by the means 5 for supplying the raw material is advantageously performed by spraying or a corresponding technique. Alternatively, the supplying can also be implemented, for example, in such a way that air flowing and possibly swirling in the mould carries the dry fibres and other components of the raw material mixture 4 to the manufacturing mould 2. In an advantageous exam- pie, the air flow is generated by a separate blower which carries the substantially homogeneous raw material mixture 4 into the mould or to its vicinity. The side of the second surface 2b of the manufacturing mould can also be provided with an underpressure, for example with a suction by suction means, wherein the medium exits through said porous manufacturing mould 2 by the effect of the difference in the pressures prevailing on different sides of the mould. The pressure difference over the manufacturing mould 2 makes the mixture pack onto the first surface 2a of the manufacturing mould 2, to form a blank 3 substantially having a shape conforming to the first surface 2a of the manufacturing mould. The structure of the manufacturing mould 2 is porous, and the pressure on the side of the first surface 2a of the manu- facturing mould is substantially higher than the pressure on the side of the second surface 2b of the manufacturing mould.

According to an advantageous example, the raw materials 4 which comprise at least natural fibres and a binding agent, are mixed with each other to form a mixture such that the dry matter content of the forming mixture is at least 50% as said above. Advantageously, at least part of the binding agents consist of thermoplastic material. After the preparation of the raw material mixture 4, said raw material mixture 4 is transferred by the effect of the pressure difference onto the first surface 2a of the manufacturing mould 2, to form the blank 3.

Preferably, the final shape of the product 1 of natural fibre composite is formed and reinforced by pressing the blank 3 with the finishing means 7. The pressing is advantageously performed by heating, preferably by hot pressing. Thus, the thermoplastic material that is advantageously used as the binding agent glues the other components of the mixture together.

Figure 2 shows a method for manufacturing a natural fibre component according to an advantageous embodiment of the invention, and Fig. 4 shows a corresponding system in a reduced schematic view. In the embodiment of Figs. 2 and 4, the formation of the blank 3 takes place in the presence of a liquid medium, by the so-called wet method. The figures show the manufacturing mould 2, the first surface 2a of the manufacturing mould, the second surface 2b of the manufacturing mould, the raw materials 4, the blank 3 for the product of natural fibre composite, and the finished product 1 of natural fibre composite, as well as means 5 for supplying raw material, a wet press 6, and means 7 for finishing the blank.

In an advantageous example shown in Fig. 2, the product 1 of natural fibre composite is made by the so-called wet forming method. Thus, the blank 3 is formed onto the first surface 2a of the manufacturing mould 2 by utilizing a liquid medium and a pressure difference between the first and second sides of the manufacturing mould. The manufacturing mould 2 is porous, for example a wire conforming to the shape to the manufactured. The raw materials are mixed as a mixture in the presence of a liquid medium, for example water. In one example, an organic solvent is used instead of water as the liquid medium. The raw materials 4 comprise at least natural fibres and one or more binding agents.

Because the raw materials of the product of natural fibre composite made by the wet method are in the liquid medium when transferred to the manufacturing mould 2 by the means 5 for supplying the raw material, the manufacturing method should also include drying of the forming blank 3. Thus, the system may comprise a wet press 6 for removing medium from the blank 3. Further, the means 7 for finishing the blank comprise means for drying the blank. The drying may be slow, particularly in the case of thick material structures. The means 7 for finishing the blank may also comprise, for example, means for shaping the blank, means for heating the blank, means for cooling the blank, and/or means for applying one or more binding agents. In yet another advantageous embodiment of the invention, the wet pressing, drying and hot pressing are carried out in the same process step, wherein the blank 3 made by wet pressing is hot pressed on a kind of a wire mould. It is thus possible to provide the blank 3 with a glossy and substantially smooth top surface, and the lower surface is provided with a pattern made by the wire.

In an advantageous example, when the product 1 of natural fibre composite is made by the wet method, the raw material mixture prepared into the liquid medium is dosed by the means 5 for supplying raw material onto the first surface 2a of the manufacturing mould 2. On the side of the second surface 2b of the manufacturing mould, an underpressure is provided, for example by suction with suction means, or a higher pressure is provided on the side of the first surface 2a, wherein medium is removed through said porous manufacturing mould 2 by the effect of the difference in the pressures prevailing on different sides of the mould, but a substantial quantity of the raw material mixture 4 is left on the first surface 2a of the manufacturing mould. Thus, the raw material mixture forms a layer that constitutes the blank 3 on the first surface 2a of the manufacturing mould 2. After this, the blank 3 formed in this way is dried, which can take place, for example, by the effect of heat. The dry and wet methods according to the invention can also be used to manufacture such structures whose shapes contain considerably large differences in the dimensions. Such a structure is, for example, one in which one part extends in a given direction more than 50% compared with the other parts of the structure. These include, for example, products in which far extending cup-like structures are needed. The manufacture of such products by the techniques of prior art is particularly challenging.

The product made by the method or system according to the invention may be, for example, an element for interior design, such as, for example, a piece of furniture or an acoustic element to be fixed on the wall of a house, or it may be, for example, a package, a part of an electronic device, an outdoor structure, or a part of a vehicle, such as an automobile. The product of natural fibre composite presented can be formed not only in the ways presented in the examples but also in other suitable ways which include the idea of the invention. The invention is thus not limited solely to the examples presented in the above description, but the inventions are characterized in what will be presented in the following claims.