FR2982283A1 - METHOD FOR MANUFACTURING A CONTINUOUS FIBER SAIL COMPRISING LONG NATURAL FIBERS, INSTALLATION AND SAIL - Google Patents

Abstract

The method comprises the following steps: - bringing in parallel a plurality of ribbons (32) disjoint fibers, at least one ribbon (32) containing natural long fibers; dispersing the adjacent ribbons (32) through a spike field (60) to form a parallel fiber band (62); - tensioning and stretching the strip (62) in the field of points (60) parallel to a scroll axis (B-B '); - Binding the fibers of the stretched strip (62) to form the web (60).

Description

The present invention relates to a method for producing a continuous web of fibers comprising natural long fibers.

Such a sail is intended in particular to be used for the production of parts impregnated with a polymer matrix, for example for the building, for the automobile or for any other application. Natural fibers have many advantages over synthetic fibers.

In particular, natural fibers generally have a low density, a relatively low cost and an ecological character. In addition, natural fibers are renewable and can be produced without depleting natural resources. In this context, flax fibers are widely cultivated and exploited in many fields, and in particular to produce composite materials. The flax fibers are extracted from the stem of the plant "flax" and can be exploited either in the form of bundles of long fibers, or in the form of elementary fibers, or in the form of microfibrils. The bundles of long fibers generally consist of an assembly of elementary fibers connected together by a natural cement and have a length which can be between 2 mm and 1000 mm. These bundles of fibers have interesting mechanical properties, since their Young's modulus is advantageously between 30 GPa and 50 GPa. To use the natural long fibers, it is necessary to produce fiber assemblies to form, for example, sheets, fabrics or relatively thick scrims. These assemblies are the result of a complex and expensive development, but have sufficient mechanical cohesion to lend themselves to subsequent operations of forming parts comprising for example the superposition and the orientation of the assemblies. However, the methods for producing these assemblies are complex and relatively expensive. Therefore in the field of composite materials it is preferred to use flax tow, that is to say a fiber length of 2 cm to 10 cm that can be used in the context of conventional processes called " dry process "comprising the steps of preparation, carding, glazing and possibly needling and which will lead directly to the development of mat without these assembly steps.

FR 2,705,369 describes a process for forming nonwoven webs of flax fibers from natural cements of flax. This method comprises a step of forming a fibrous web, and then binding the fibers of the web with natural cements flax. However, the nonwoven obtained has insufficient mechanical properties for use in producing composite materials. In addition, the materials obtained are thick, not very easy to handle, and have a very variable thickness. An object of the invention is to obtain a method of forming a veil comprising long natural fibers which is simple to implement, and which makes it possible to obtain a veil of very small thickness, of constant weight, at a constant weight. low cost.

To this end, the subject of the invention is a process of the aforementioned type, characterized in that the method comprises the following steps: feeding in parallel a plurality of disjointed ribbons of fibers, at least one ribbon containing long fibers natural; dispersing the adjacent ribbons through a field of points to form a parallel band of fibers; - powering the band in the peak field parallel to a scroll axis; - Binding the fibers of the stretched strip to form the web. The process according to the invention may comprise one or more of the following characteristics, taken alone or in any technically possible combination: the fiber binding step of the strip comprises the spraying of the stretched strip by a solution, impregnating the solution between the fibers of the web and drying the web to form the web; the solution is sprayed by spraying drops, or by forming a foam containing a liquid and a foaming agent, the foam being deposited on the strip; the power-up step is carried out between at least one upstream roller, advantageously having an external metal surface and at least one downstream roller, advantageously made of wood, rubber, or polymer, the belt drive speed downstream of the downstream roll being greater than at least two times, advantageously at least six times the speed of driving the band by the upstream roll; - The field of points comprises a plurality of bars transverse to the axis of travel, each transverse bar having a plurality of points, the transverse bars being advantageously movable together with the band; the method comprises, before the feeding step, a step of forming the plurality of ribbons by doubling several unit ribbons; at least one first unitary ribbon exclusively comprises natural long fibers, at least one second unitary ribbon advantageously comprising additional natural fibers, distinct from the natural long fibers of the first unitary ribbon, and / or synthetic fibers of natural origin and / or synthetic fibers of artificial origin and / or mixtures thereof; - the standard deviation of disjoint tapes is less than 20%; - During the feeding step, the disjointed ribbons are arranged in adjacent chutes opening upstream of the tip field; - The surfacic mass of the web, after the fiber bonding step is less than 500 g / m2, preferably less than 150 g / m2. The invention also relates to an apparatus for manufacturing a continuous web of fibers comprising natural long fibers, characterized in that it comprises: a set of parallel feeds of a plurality of disjointed fiber ribbons, for receiving at least one ribbon containing natural long fibers; a fiber band shaping assembly having a ribbon dispersion assembly having a spike field and a tensioning and stretching system for the web in the spike field; - A binding assembly of the fibers of the web to form the web. The installation according to the invention can comprise one or more of the following characteristics, taken separately or in any technically possible combination: the supply assembly comprises a guide delimiting a plurality of chutes arranged side by side, each trough being intended to receive a ribbon. The invention further relates to a continuous web of fibers comprising at least natural long fibers, characterized in that it comprises a plurality of parallel fibers obtained by dispersion and by tensioning fibers from parallel ribbons, the fibers parallel being interconnected to form the veil, the veil having a uniform thickness over its width. The web according to the invention can comprise one or more of the following characteristics, taken alone or in any technically possible combination: it has a basis weight of less than 500 g / m 2, in particular less than 150 g / m 2 and advantageously a thickness less than 1 mm; - It has a length greater than 100% of its width, the veil being advantageously wound on itself to form a roller; the original long fibers are long flax fibers; the veil comprises more than 50% by mass of natural fibers; - The veil is free of synthetic binder connecting the fibers together. The invention also relates to a web that can be obtained by the method described above. The web of the invention may comprise one or more of the additional features defined above. The invention will be better understood on reading the description which will follow, given solely by way of example, and with reference to the appended drawings, in which: FIG. 1 is a view of a logic diagram illustrating the principal steps of a first method according to the invention; FIG. 2 is a schematic view from above of a first installation intended for implementing the method of FIG. 1; FIG. 3 is a front view of a bar comprising tips, intended to be used in the shaping assembly of the installation of FIG. 2; - Figure 4 is a view similar to Figure 2, during the implementation of the method of Figure 1; - Figure 5 is a cross section taken along the plane V-V of Figure 4; - Figure 6 is a cross section, taken along the vertical plane VI-VI of Figure 4; - Figure 7 is a view of a web obtained by the method according to the invention, packaged in the form of a roller. FIG. 8 is a photograph illustrating the external appearance of a first sail according to the invention; Fig. 9 is a schematic side view of a supply assembly and a supply set of parallel ribbons; FIG. 10 is a schematic side view of a shaping assembly of a band obtained from the ribbons; - Figure 11 is a schematic side view of a binding assembly of the fibers of the web to form a web. In all that follows, the terms "upstream" and "downstream" generally refer to the direction of scrolling of an object manufactured continuously. A first web 10 produced by a method according to the invention is illustrated by FIGS. 7 and 8. In the example of FIG. 7, the web 10 is advantageously wound on itself to form a roll 12.

The web 10 according to the invention comprises natural long fibers, arranged parallel to each other and at least one binder holding the fibers together. In one embodiment, all the fibers of the web 10 are made of natural long fibers. Alternatively, a part of the fibers forming the web 10 is formed by additional natural fibers, distinct from the natural long fibers, by synthetic fibers of natural origin, by synthetic fibers of artificial origin or by a mixture of these fibers. The natural long fibers are advantageously fibers extracted from plants, in particular flax fibers. In a variant, the natural long fibers are sisal, jute, hemp, and kenaf fibers. The additional natural fibers are, for example, chosen from cotton, wool, silk, sisal, hemp fibers or their fibers. mixtures. Synthetic fibers of natural origin are for example chosen from regenerated cellulose fibers, in particular viscose, cupro and / or modal fibers, viscose alginate fibers, lyocell fibers and PLA (poly lactic acid) fibers. and their mixtures. Synthetic fibers are formed from petroleum derivatives or molecules from green chemistry (eg ethylene from bio ethanol). They are selected from polyolefin fibers such as polyethylene fibers and / or polypropylene, polyester, polyamide, polyimide, and mixtures thereof. They can also be bi-component fibers formed of a polymer and a copolymer, the polymer and its copolymer having different melting points Advantageously, the mass proportion of long fibers of natural origin in the web 10 is greater than 50 % of the total mass of the fibers of the web 10.

Advantageously, natural long fibers are long flax fibers. Long flax fibers come from the plant called "flax" or "flax plant" of the family "linaceae". These fibers are extracted from the periphery of the stem of the flax plant by mechanical rupture of the stem during a grinding operation, then by separation between the long fibers, the tows which are short and coarse fibers, and the others. flax components. The long fibers thus obtained advantageously have a length of between 2 mm and 1000 mm. By "long fibers" is meant in the sense of the present invention, that the fibers are advantageously constituted by a longitudinal assembly of elementary fibers bonded together by a natural cement.

Long fibers are generally bundles up to a meter long. Part of the natural long fibers of the web 10 has a length greater than 50 cm, and in particular between 50 cm and 80 cm. The bundles of long fibers generally have a diameter of between 10 microns and 100 microns. The binder connecting the different long fibers between them is advantageously made of natural cement of the plant, including natural linseed cements, when the long fibers are long flax fibers. As a variant, the binder is a synthetic binder, such as an adhesive or a resin, in particular a latex, and / or a binder of natural origin, other than linseed cements, for example based on starch. According to the invention, the web 10 has a width much greater than its thickness and much less than its length. Thus, the width of the web is for example greater than 30 mm, and especially between 30 mm and 2000 mm, advantageously between 100 mm and 2000 mm. The thickness is less than 0.1 times its width, and is especially less than 1 mm, advantageously less than 50 / 100th of a mm, advantageously less than 10 / 100th of mm.

The web 10 obtained by the process according to the invention is of uniform thickness. Thus, the standard deviation of the average thickness of each longitudinal strip of web 10 consisting of a longitudinal strip corresponding to 1 / 10th of the width of the web 10 is less than 5%, especially less than 2% relative to the average thickness of the web 10. The average surface density of the web 10 is low, this surface mass is less than 500 g / m 2, in particular less than 150 g / m 2 or even 100 g / m 2, and is advantageously between 30 g / m 2 m2 and 100 g / m2.The mass per unit area is constant by moving along the width of the web.The length of the web 10 is much greater than its width.In particular, the length of the web 10 is greater than 10 m, in particular greater than The web 10 can thus be wound in the form of a roll 12 having a diameter greater than 100 mm, advantageously up to diameters of the order of 600 mm, as illustrated by FIG. according to the invention, the fibers of the web 10 are substantially aligned in a longitudinal direction A-A 'shaping.

Thus, at least 50% of the fibers of the web 10 are parallel to the longitudinal direction A-A ', which is perpendicular to the winding axis of the web 10, when the web 10 is in the form of a roll 12. long fibers of the web 10 are generally arranged parallel to each other and are interconnected by the binder to ensure the mechanical cohesion of the web 10. The web 10 has sufficient mechanical cohesion to allow its handling, especially during later operations impregnation and superposition to form multi directional mats. Thus, the web 10 can be grasped by the hand of a user and by machine manipulators, including manipulators with suction cup (once impregnated otherwise it is porous), without suffering mechanical damage, and maintaining its mechanical strength. The web 10 is self-supporting. The cohesion of the web 10 is such that the average breaking force, taken in the transverse direction perpendicular to the preferential direction AA 'orientation of the fibers as measured by the ISO 13934-1 standard for a test tube of 50 mm width is advantageously greater than 0.1N, especially between 0.2N and 2N, for example around 0.5N. Surprisingly, a web 10 comprising natural long fibers and having both a uniform thickness, and a very marked orientation of the long fibers, while maintaining sufficient cohesion for handling is obtained by the method according to the invention. For this purpose, the web 10 is formed from longitudinal strips of fibers which are fed in parallel and which are dispersed to form a strip of parallel fibers, the fibers of the strip then being bonded. For the purposes of the present invention, the term "ribbon" means a longitudinal element comprising an assembly of fibers, in particular of long fibers. The ribbons are for example obtained by combing or carding, then by energizing individual fibers which are then grouped together to form a longitudinal link. The thickness of the ribbon is generally of the order of its width. It is for example between 0.5 and twice its width. The ribbon may be advantageously obtained from unit ribbons which are doubled by overlapping each other. In the example shown, the width of the ribbons is, for example, less than 30 mm. The thickness of the ribbons is for example greater than 15 mm and between 10 mm and 40 mm. The length of the ribbons is greater than 800 m and in particular between 850 m and 1700 m.

The dubbing operations consist in superimposing at least two identical, or different, unitary ribbons, then dispersing them in a field of points, keeping them under tension, before reconstituting a single doubled ribbon. The number of dubbing is variable. This number is between 1 and 15 doublings. The linear density of the ribbons intended to be used in the process according to the invention is for example between 10 g / m and 40 g / m. The steps of a first method of manufacturing a web 10 according to the invention are summarized in the flow chart of FIG.

Such a method is implemented, for example, in a sail-making installation 14 shown diagrammatically in FIG. 2 or in FIG. 4. As illustrated in FIGS. 2 and 4, the installation 14 comprises a supply assembly 20 a plurality of fiber ribbons comprising at least one ribbon of natural long fibers, and an assembly 22 for feeding ribbons to arrange them parallel to one another. With reference to FIGS. 2 and 10, the installation 14 further comprises an assembly 24 for shaping a continuous fibrous web from the tapes and a set 26 for binding the fibers of the web to form the web 10 , visible in Figures 2 and 11. The installation 14 further comprises a set 28 of the packaging of the web 10, for the particular storage in the form of a roller 12. As shown in Figure 9, the supply assembly 20 Advantageously, a ribbon storage area 32 is included. The ribbons 32 are for example stored in the form of "tops" or combed ribbons, advantageously in creels.

The tops are obtained by pouring the ribbon 32 contained in a pot, for example of diameter between 30 cm and 1 m, in particular between 40 cm and 60 cm. Once the pot is full, the ribbon 32 is compressed from above, the pot is removed and the ribbon is tied. The top then has the dimensions of the pot with a height of between 30 cm and 80 cm, in particular equal to 40 cm. The mass of the top is for example between 15 kg and 40 kg. For the implementation of the method according to the invention, the ribbons 32 provided in the assembly 20 are advantageously ribbons 32 which have been obtained by doubling unit ribbons, in order to obtain ribbons 32 homogeneous in terms of linear density. Thus, the linear density of the ribbons 32 is advantageously between 10 g / m and 40 g / m. The standard deviation between the linear density of the different ribbons 32 intended to form the same web 10 is less than 20%.

In the case where the web 10 is made of natural long fibers, for example long flax fibers, all the ribbons 32 are natural long fiber ribbons advantageously obtained by doubling unitary ribbons of natural long fibers. In the case where the veil 10 comprises additional natural fibers, synthetic fibers of natural origin or synthetic fibers of artificial origin, at least one ribbon 32 is formed from a unitary ribbon consisting of natural long fibers and from at least one unitary ribbon consisting of additional natural fibers, synthetic fibers of natural origin or synthetic fibers of artificial origin. In all cases, the unit ribbons are each dispersed in a spike field (not shown), then are energized and stacked over each other. The number of dubbing operations is between 1 and 15, advantageously between 2 and 4. The ribbons 32 are then stored in the form of combed ribbons (or "Tops") and are arranged on the floor or on a support. A plurality of ribbons 32 are provided in parallel. As illustrated by FIGS. 2, 9 and 5, the feed assembly 22 comprises a guide 40 for parallel distribution of the ribbons 32, intended to feed the shaping assembly 24 and a mechanism 42 for feeding the guide 40. The feed mechanism 42 includes guide rollers 44 and a pair of feed rollers 80A and 80B for driving each sliver 32 from the spool 30 to the guide 40. As shown in FIGS. and 5, the guide 40 has a plurality of chutes 46 arranged in parallel. The troughs 46 are advantageously arranged adjacent to each other. Each chute 46 is delimited by two side walls 48, at least one of which is common with an adjacent trough 46, and a bottom wall 49. Each trough 46 is intended to receive an individual ribbon, and to distribute it to the set of shaping 24 in the form of rollers parallel to an axis BB 'shaping the web.

Thus, each chute 46 extends longitudinally between an inlet opening 50 and an outlet opening 52 facing the shaping assembly 24. In the example shown in FIGS. 4 and 5, the guide 40 comprises a plurality of convergent chutes 46 from upstream to downstream. The cross section of the chute 46 facing the inlet opening 50 is greater than the cross section of the chute 46 at the outlet opening 52.

Thus, each ribbon 32 inserted into the chute 46 is guided convergently towards the outlet opening 52 to be in contact with the side walls 48 on either side of the ribbon 32, as illustrated in FIG. the opening 52. The angle of inclination of the axis of each chute 46 relative to the axis BB 'increases trough 46 in chute 46 by moving from the axis BB' towards the outside of the guide 40 The width of each trough 46 at the inlet opening 50 is at least 10% greater than the width of the trough 46 at the outlet opening 52. This makes it possible to homogenize the compaction naturally. transverse fibrous bundles .. Out of the troughs ribbons that have been compressed laterally by the converging walls of the troughs will tend to a slight expansion which will cause them to come into contact with each other or to interpenetrate slightly. The maximum width of each chute 46 at the outlet opening 52 is for example between 10 mm and 40 mm.

The thickness of the side walls 48 is less than 5 mm in order to limit the spacing between the various strips 32 when entering the shaping assembly 24. As illustrated by FIGS. 2, 4 and 10, the shaping assembly 24 comprises a point field 60, intended for the dispersion of the ribbon fibers to form a continuous band 62, visible in FIG. 4, and a system 64 for tensioning and stretching the band 62 in the spike field 60. As illustrated by FIGS. 4, 6 and 10, the spike field 60 has a plurality of rows 70 of spikes 72 parallel and transverse to the scroll axis BB '. The rows 70 of spikes 72 advantageously comprise between 2 and 16 spikes per cm, or between 6 and 40 spikes per inch.

The tips 72 have a height greater than the height of the ribbons, and for example between 40 mm and 60 mm. The rows 70 of points 72 are carried by individual transverse bars 74, arranged perpendicularly to the axis B-B '. The assembly formed by each bar 74 and its points 72 is commonly referred to as the "gills".

The bars 74 successive are advantageously placed in contact with each other. Each bar 74 advantageously carries at least one row of tips 70, in particular two rows of tips 70 as can be seen in FIG. 3. The tips 72 of a first row 70 are slightly offset relative to the tips 70 of a second row, transversely with respect to the axis B-B '.

The rows 70 of the point field 60 are advantageously movable along the axis B-B '. Each barette 74 is moved by helical screws and carries a square movement. Thus, the barrettes 74 advance with the band 62 to the end of the field of points 60. They then return to the beginning of the field of points 60. For this purpose, as illustrated by FIG. 10, the field of points 60 comprises a mechanism 75 of longitudinal displacement of the bars 74 along the axis BB 'between an upstream end position and a downstream end position, along a length L1 along the axis B-B'.

The displacement mechanism 75 further comprises return means of each bar 74 from the end downstream position to the upstream end position. For this purpose, each bar 74, when it is located in the upstream end position, is vertically movable between a retracted return position and an active stitching position of the fibers in the plane of the band 62.

In the downstream end position, each bar 74 is movable vertically between the active stitching position and a retracted position. The mechanism 75 moves each bar 74 in the running direction of the band 62 from upstream to downstream by maintaining the bar 74 in its active position, then moves each bar 74 from the downstream position to the upstream position in the opposite direction scrolling the band 62 by maintaining the bar 74 in its retracted position. The length L1 of the point field 60 is greater than 80 cm and is in particular between 100 cm and 80 cm to accommodate the natural long fibers and allow their parallel arrangement to the axis B-B '.

As illustrated by FIGS. 2 and 10, the power-up system 64 comprises at least one upstream roll 80A, 80B and at least one downstream roll 82A, 82B arranged transversely on either side of the field of points 60, respectively between the feed assembly 22 and the spike field 60, and between the spike field 60 and the link assembly 26.

In the example shown in FIG. 10, the energizing system 64 comprises a pair of upstream rollers 80A, 80B arranged vertically one on the other. The upstream rollers 80A, 80B are rotatably mounted about axes perpendicular to the axis B-B '. The upstream rollers 80A, 80B advantageously have a metal outer surface, in particular chrome. They have a gap of height less than the height of the ribbons 32, and especially less than 20 mm, to flatten and pinch the ribbons 32. The gap 84 is advantageously placed horizontally opposite the tips 70 and horizontally facing the outlet openings 52 chutes 46 to allow the packing of the ribbons 32 and the distribution of the fibers from the ribbons 32 in the field of points 60 through the rows 70 of tips 72. In the example shown in Figure 10, the set of bet under voltage 64 has at least two downstream rollers 82A, 82B arranged one on the other. The rollers 82A, 82B are rotatably mounted about axes perpendicular to the axis B-B '. The roller 82A is for example formed of a cylinder of wood, rubber or polymer. It advantageously has a diameter greater than that of the roller 82B. The roller 82B has a metal outer surface, for example a chrome outer surface.

The first pair of rollers 80A, 80B and the second pair of rollers 82A, 82B are driven so that the speed of the web 62 formed in the peak field 60, taken at the output of the downstream rollers 82A, 82B is greater than at least twice, in particular 6 times, advantageously between 6 times and 20 times the speed of the strip 62 at the outlet of the upstream rollers 80A, 80B.

This allows the tape 62 to be tensioned and stretched to adjust its thickness and grammage. As illustrated in FIG. 11, the link assembly 26 comprises a device 90 for spraying the band 62 with a liquid or foaming solution, a space 92 for diffusing the solution on the band 62 and a device 94 for drying the band. the band.

The solution is advantageously formed by an aqueous solution. In a first embodiment, the aqueous solution consists of water. Alternatively, the aqueous solution comprises water and a nonionic surfactant such as a polyvinyl alcohol to form a foam. The proportion of polyvinyl alcohol in the solution is less than 1%.

Alternatively, the liquid solution may comprise a wetting agent. In the example of FIG. 11, the spraying device 90 comprises at least one nozzle 96 intended to eject the solution, in particular in the form of drops, fog or foam, and a transverse box 98 for guiding the solution. Advantageously, the nozzles 96 open into the box 98. The box 98 has a lower opening facing a conveyor belt 100 of the band 62, intended to support and drive the band 62 between the spray device 92 and the drying device 94. The drying device 94 comprises a heating device 102, for example a convector provided with heating plates, and a vapor extraction assembly 104 comprising, for example, a hood 106. The intermediate space 92 is located between the spraying device 90 and the drying device 94. Its length is for example between 0.5 m and 2 m. In this example, the web 10 is packaged in the form of a roll 12. The packaging assembly 28 thus comprises an axis or mandrel 110 for winding the web, and means (not shown) for rotating the web. axis in order to allow the formation of the roll 12. In a variant, the packaging assembly 28 comprises a device for dispensing a separation sheet intended to be wound together with the web 10 to separate two successive layers of web 10 in the roll 12.

The method of manufacturing the web 10 according to the invention will now be described. As illustrated in FIG. 1, this method initially comprises a step 120 for supplying disjointed ribbons 32, then a step 122 for feeding the ribbons 32 in parallel into the supply assembly 22. The method then comprises formatting a continuous strip 62 by dispersion of the tapes 32 in the forming assembly 24, then a step 126 for fixing the band 62 to form a web 10 in a link assembly 26. The method finally comprises a step 128 The process is advantageously carried out continuously, that is to say that the steps 122 to 128 are carried out successively one after the other in a continuous manner, without intermediate stop. In step 120, a plurality of parallel ribbons 32 are provided, for example by being wound in the form of tops of combed ribbons arranged on a support, or on the ground, advantageously in creels. As mentioned above, the ribbons 32 have advantageously been obtained by doubling unitary ribbons, the ribbons 32 for example consisting of unitary ribbons of natural long fibers, or consisting of a mixture of unit ribbons of natural long fibers with at least a unitary ribbon of additional natural fibers, synthetic fibers of natural origin, or synthetic fibers of artificial origin.

The title of the ribbons 32 is substantially constant, so that the standard deviation between the titles of the ribbons 32 is less than 20%.

Then, during the feeding step, a plurality of disjointed ribbons 32 are conveyed in parallel from the supply assembly 20 to the shaping assembly 24 through the feed assembly 22. The parallel ribbons 32 is between 2 and 100, and is in particular between 8 and 15 ribbons, to produce sails with a width of between 10 mm and 2000 mm. Then, each ribbon 32 is driven by the feed rollers 44, and is directed towards an inlet opening 50 of a chute 46. The guide 40 thus receives a plurality of parallel ribbons 32, each ribbon 32 being received in a respective chute 46. Then, the ribbons 32 are driven through each chute 46 via the upstream rollers 80A, 80B to the outlet opening 52. During the shaping step 124, the different ribbons 32 are first pinched in the gap 84 between the upstream rollers 80A, 80B to reduce their thickness and disperse them laterally. Then, the fibers from the different adjacent ribbons 32 are introduced into the field of points 60 being stretched by the downstream rollers 82A, 82B. For this purpose, the bar 74 located in the upstream end position moves from its retracted position to its vertically extended position so that its points 72 pass through the parallel fiber alignments and form a regular 62 thick, vertically taken, lower band to the thickness of each strip 32. Then, the bars 74 move longitudinally with the fibers of the strip 62 along the point field 60 to the downstream point. During this passage, the fibers form a band 62 of uniform thickness over its width. On the other hand, in view of the relative speed of rotation of the upstream rollers 80A, 80B and the downstream rollers 82A, 82B, the web 62 is tensioned and is stretched in the spike field 60 to cause a longitudinal alignment of the fibers in a single direction.

The supply of the fibers in the form of disjointed ribbons 32, their dispersion in the upstream rollers 80A, 80B, the passage in the field of tips 60 and the energization by the downstream rollers 82A, 82B make it possible, in synergy, to form a web of substantially uniform thickness, low weight, especially less than 150 g / m2, with a substantially parallel alignment of at least 50% by number of fibers, or even 80% by number of fibers.

At the exit from the point field 60, the band 62 is clamped between the downstream rollers 82A, 82B and is fed to the link assembly 26. Before it passes through the link assembly 26, the stretched band 62 is not cohesive transversely. Thus, the different fibers constituting the stretched strip 62 can be separated from each other by simple manual pressure, when they exit the downstream rollers 82A, 82B upstream of the link assembly 24. The stretched strip 62 thus passes into the connecting assembly 24 to enhance its transverse cohesion. In a first step, the band 62 is sprayed into the spraying device by the solution intended to activate the bond between the fibers. In a first embodiment, the aqueous solution is sprayed in the form of droplets, for example in the form of a mist which is guided through the box 98. In a variant, the solution is in the form of a foam, and the foam is deposited on the strip 62 through the box 98.

Then the band 62 passes into the intermediate space 92, allowing the diffusion of the solution between the fibers by capillarity. In the case where the solution is formed of a foam, the bubbles of the foam break, and the liquid thus formed diffuses through the fibers. This operation has the effect of partially dissolving the natural cements binding the fibers together. Then, the strip 62 impregnated with liquid enters the heating device 94. The strip 62 is heated to a temperature greater than 70 ° C, and in particular between 100 ° C and 180 ° C to allow the evaporation of the portion liquid of the solution. This evaporation is favored by the suction generated by the apparatus 104. The solubilized natural cements resolidify, which reinforces the cohesion between the fibers and ensures in particular transverse cohesion to form the veil 10. In the case where the veil 10 is consisting of less than 50% of long flax fibers, the natural cements of flax are not necessarily sufficient to provide sufficient transversal cohesion to the web 10. In this case, a small percentage of additional binder, as described above can be added to the solution. In the conditioning step, the web 10 is wound on itself to form a roll around the mandrel 110. In a variant, an intermediate sheet is introduced between the various layers of web 10 to avoid damaging it. As mentioned above, all of the preceding steps are carried out continuously, from the parallel feeding of the ribbons 32, to the conditioning of the web 10 after its formation. The speed of movement of the web during all operations is greater than 1 m / minute and is in particular between 1 m / minute and 50 m / minute. When a sufficient length of web 10 has been wound in the form of a roll 12 around the mandrel 110, the roll 12 can be transported easily and economically to its place of use, for example to produce impregnated panels . Thanks to the invention which has just been described, it is therefore possible to form, in a very economical manner, a web 10 comprising a large amount of natural long fibers, especially long flax fibers. This web 10 has a small thickness, and a basis weight less than 500 g / m2, especially less than 150 g / m2, or even between 30 g / m2 and 100 g / m2. It also has a uniform thickness over its width and a very pronounced orientation of the fibers which are substantially aligned and parallel to each other In particular, unlike a fabric of flax fibers, the fibers are not twisted or intersecting. As a result, the web 10 has no relief, which limits its thickness and allows to use a minimum of resin when panels are manufactured. In addition, the manufacturing process does not include the spinning step, it is very simple to implement and therefore has a competitive price. The web 10 obtained after the bonding step is cohesive and self-supporting, so that it can be transported without risk of deterioration, which also has an advantage in terms of cost and handling. In addition, the veil formed 10 being made mainly or exclusively based on natural fibers, especially long flax fibers, it is completely biodegradable and can be achieved without the use of artificial binder, using only the natural cements of natural fibers, for example formed of hemicellulose and lignin.

Claims (16)

CLAIMS 1.- A method of manufacturing a continuous web (10) of fibers comprising natural long fibers, the method comprising the following steps: - bringing in parallel a plurality of ribbons (32) disjoint fibers, at least one ribbon (32) containing natural long fibers; dispersing the adjacent ribbons (32) through a spike field (60) to form a parallel fiber band (62); - energizing the band (62) in the field of points (60) parallel to a scroll axis (B-B '); - Binding the fibers of the stretched strip (62) to form the web (60). 2. A method according to claim 1, characterized in that the fiber binding step of the strip (62) comprises spraying the stretched strip (62) with a solution, the impregnation of the solution between the fibers of the web and drying the web (62) to form the web (60). 3. A process according to claim 2, characterized in that the sprinkling of the solution is carried out by spraying drops, or by forming a foam containing a liquid and a foaming agent, the foam being deposited on the strip (62). ). 4. A method according to any one of the preceding claims, characterized in that the energizing step is performed between at least one upstream roller (80A, 80B), advantageously having a metal outer surface and at least one roller downstream (82A), advantageously made of wood, rubber or polymer, the driving speed of the strip (62) downstream of the downstream roll (82A) being greater than at least two times, advantageously at least six times the driving speed of the web (62) by the upstream roller (80A, 80B). 5. Method according to any one of the preceding claims, characterized in that the field of points (60) comprises a plurality of transverse bars (74) to the scroll axis (B-B '), each transverse bar ( 74) having a plurality of points (72), the transverse webs (74) being preferably displaceable together with the web (62). 6. A method according to any one of the preceding claims, characterized in that it comprises, before the feeding step, a step of forming the plurality of ribbons (32) by doubling several unit ribbons. 7. A process according to claim 6, characterized in that at least a first unitary ribbon comprises exclusively natural long fibers, at least a second unitary ribbon advantageously comprising additional natural fibers, distinct from the natural long fibers of the first unitary ribbon, or / and fibressynthetics of natural origin and / or synthetic fibers of artificial origin and / or their mixtures. 8. A process according to any one of the preceding claims, characterized in that the standard deviation of the title of disjoint tapes (32) is less than 20%. 9.- Method according to any one of the preceding claims, characterized in that, during the feeding step, the disjointed strips (32) are arranged in adjacent troughs (46) opening upstream of the peak field ( 60). 10. A process according to any one of the preceding claims, characterized in that the surfacic weight of the web (10), after the fiber bonding step is less than 500 g / m2, preferably less than 150 g / m2. 11.- Installation (14) for manufacturing a continuous web (10) of fibers comprising natural long fibers, characterized in that it comprises: - a set (22) for feeding in parallel a plurality of ribbons fiber disjoint (32) for receiving at least one ribbon (32) containing natural long fibers; an assembly (24) for shaping a fiber web (62) having a sliver dispersion assembly (32) having a spike field (60) and a power-up and tensioning system (64); stretching the web (62) in the spike field (60); - an assembly (26) for binding the fibers of the strip (62) to form the web (10). 12.- Installation according to claim 11, characterized in that the supply assembly (22) comprises a guide (40) defining a plurality of troughs (46) arranged side by side, each chute (46) being intended to receive a ribbon (32). 13.- continuous web (10) of fibers comprising at least natural long fibers, characterized in that it comprises a plurality of parallel fibers obtained by dispersion and by tensioning fibers from parallel ribbons, the parallel fibers being linked between them to form the web (10), the web (10) having a uniform thickness over its width. 14.- Sail (10) according to claim 13, characterized in that it has a basis weight less than 500 g / m2, especially less than 150 g / m2 and preferably a thickness of less than 1 mm. 15.- Sail (10) according to any one of claims 13 to 14, characterized in that it has a length greater than 100% of its width, the web (10) being advantageously wound on itself to form a roller (12). 16.- Sail (10) according to any one of claims 13 to 15, characterized in that the original long fibers are long flax fibers.