Method for producing a continuous web of fibers comprising long natural fibers, and associated apparatus and web

Abstract

The inventive method includes the following steps: bringing a plurality of disjointed ribbons ( 32 ) of fibers into parallel, at least one ribbon ( 32 ) containing long natural fibers; dispersing the adjacent ribbons ( 32 ) through a field of tips ( 60 ) to form a strip ( 62 ) of parallel fibers; tensioning and stretching the strip ( 62 ) in the field of tips ( 60 ) parallel to an axis of travel (B-B′); binding the fibers of the stretched strip ( 62 ) to form the web ( 60 ).

1 . A method for producing a continuous web of fibers comprising long natural fibers, at least part of the long fibers of the web having a length greater than 20 cm, the method comprising the following steps:
 bringing a plurality of disjointed ribbons of fibers into parallel, at least one ribbon containing long natural fibers;   dispersing the adjacent ribbons through a field of tips to form a strip of parallel fibers;   tensioning the strip in the field of tips parallel to an axis of travel;   binding the fibers of the stretched strip to form the web.   
     
     
         2 . The method according to  claim 1 , wherein the step for binding the fibers of the strip includes sprinkling the stretched strip with a solution, impregnating the solution between the fibers of the strip and drying the strip to form the web. 
     
     
         3 . The method according to  claim 2 , wherein the sprinkling of the solution is done by spraying drops, or forming a foam containing a liquid and a foaming agent, the foam being deposited on the strip. 
     
     
         4 . The method according to  claim 1 , wherein the tensioning step is done between at least one upstream roller, and at least one downstream roller, the speed at which the downstream strip of the downstream roller is driven being at least two times, higher than the speed at which the strip is driven by the upstream roller. 
     
     
         5 . The method according to  claim 1 , wherein the field of tips includes a plurality of bars transverse to the axis of travel, each transverse bar including a plurality of tips. 
     
     
         6 . The method according to  claim 1 , including, before the bringing in step, a step for forming the plurality of ribbons by lining with several unitary ribbons. 
     
     
         7 . The method according to  claim 6 , wherein at least one first unitary ribbon comprises exclusively long natural fibers, at least one second unitary ribbon including additional natural fibers, separate from the long natural fibers of the first unitary ribbon, and/or synthetic fibers of natural origin and/or synthetic fibers of artificial origin and/or mixtures thereof. 
     
     
         8 . The method according to  claim 1 , wherein the standard deviation of the disjointed ribbons is less than 20%. 
     
     
         9 . The method according to  claim 1 , wherein, during the bringing in step, the disjointed ribbons are positioned in adjacent chutes emerging upstream from the field of tips. 
     
     
         10 . The method according to  claim 1 , wherein the surface density of the web, after the step for binding the fibers, is less than 500 g/m 2 . 
     
     
         11 . The method according to  claim 1 , wherein the length of the field of tips is greater than or equal to the maximum length of the long natural fibers. 
     
     
         12 . An apparatus for manufacturing a continuous web of fibers comprising long natural fibers, at least part of the long fibers of the web having a length greater than 20 cm including:
 an assembly for bringing a plurality of disjointed ribbons of fibers into parallel, intended to receive at least one ribbon containing long natural fibers;   an assembly for shaping a strip of fibers including an assembly for dispersing ribbons including a field of tips and a system for tensioning and stretching the strip in the field of tips;   an assembly for binding the fibers of the strip to form the web.   
     
     
         13 . The apparatus according to  claim 12 , wherein the assembly for bringing in the plurality of disjointed ribbons of fibers into parallel includes a guide delimiting a plurality of chutes positioned side by side, each chute being designed to receive a ribbon. 
     
     
         14 . A continuous web of fibers comprising at least long natural fibers, including a plurality of parallel fibers obtained by dispersion and by tensioning fibers coming from the parallel ribbons, the parallel fibers being connected to each other to form the web, the web having a uniform thickness over its width, and in that at least part of the long fibers of the web has a length greater than 20 cm. 
     
     
         15 . The web according to  claim 14 , having a surface density below 500 g/m2. 
     
     
         16 . The web according to  claim 15 , having a thickness of less than 1 mm. 
     
     
         17 . The web according to  claim 14 , having a length 100% greater than its width. 
     
     
         18 . The web according to  claim 17 , being wound around itself to form a roll. 
     
     
         19 . The web according to  claim 14 , wherein the long original fibers are long flax fibers. 
     
     
         20 . The web according to  claim 14 , wherein at least part of the long fibers of the web have a length greater than 50 cm.