Method for producing a flat semi-finished product from a fiber composite material and flat semi-finished product

Abstract

A method produces a flat semi-finished product from a fiber composite material that contains individual carbon fibers, carbon fiber bundles, or a mixture thereof in a defined anisotropic fiber orientation and a thermoplastic matrix material. The anisotropy of the carbon fibers is created in a carding process using the high orientability of admixed non-carbon textile fibers, at least some of the non-carbon textile fibers being thermoplastic, and the carbon fibers having been isolated from waste or used parts. The flat fibrous web which is produced by a carding process and which has a specific orientation of the carbon fibers in the longitudinal direction is compressed into a sheet material under the effect of heat. This enables the use of carbon fibers, for example from production waste, as reinforcing fibers, whereby a less expensive raw material is provided and the carbon fibers are contained in the waste materials are recycled.

1 . A method for producing a flat semi-finished material of a fiber-reinforced composite plastic having fibers and at least one thermoplastic matrix material, which comprises the steps of:
 isolating the fibers, selected from the group consisting of finite carbon fibers, carbon fiber bundles and a mixture of said finite carbon fibers and said carbon fiber bundles, from waste or used parts containing carbon fibers;   blending the fibers with thermoplastic non-carbon fibers resulting in a mixture being laid down and oriented in a sheet in a carding operation resulting in a fiber web having a targeted orientation of the fibers; and   pressing the fiber web to form a sheet material under an influence of heat.   
     
     
         2 . The method according to  claim 1 , wherein for a high and targeted orientation of the fibers longitudinally in the carding operation, adding the thermoplastic non-carbon fibers in a mixing ratio and/or with a fiber geometry, such that a fiber anisotropy in a range of at least 1:2 is established in the fiber web. 
     
     
         3 . The method according to  claim 1 , which further comprises providing the thermoplastic non-carbon fibers to have fiber lengths in a range of 25 mm to 120 mm. 
     
     
         4 . The method according to  claim 1 , which further comprises:
 aligning the mixture being a largely homogeneous mixture of thermoplastic bonded random fibers and random finite carbon fibers, random carbon fiber bundles or a mixture of the random finite carbon fibers and the random carbon fiber bundles by the carding operation;   laying out the mixture to form a fiber mat;   bringing at least portions of the thermoplastic non-carbon fibers to a tacky state by heat, and then compacted and pressed to form the sheet material; and   cooling the sheet material.   
     
     
         5 . The method according to  claim 1 , wherein the carbon fibers, the carbon fiber bundles or the mixture of the carbon fibers and the carbon fiber bundles have an average fiber length of 10 mm to 150 mm. 
     
     
         6 . The method according to  claim 1 , wherein at least a portion of the carbon fibers originate from reprocessing of textile type carbon waste and/or from physical recycling of CFK components. 
     
     
         7 . The method according to  claim 4 , wherein the mixture of the carbon fibers, the carbon fiber bundles or the mixture of the carbon fibers and the carbon fiber bundles and the thermoplastic non-carbon fibers is produced by a fiber-mixing operation during a formation of the fiber mat. 
     
     
         8 . The method according to  claim 1 , which further comprises producing a targeted degree of orientation of the carbon fibers, the carbon fiber bundles or the mixture of the carbon fibers and the carbon fiber bundles which are initially unoriented as to direction, using a carding machine in such a way that anisotropy of composite strengths and/or the composite stiffnesses in a range of 1:1.5 to 1:10 is achieved in a fiber composite material. 
     
     
         9 . The method according to  claim 8 , wherein in the anisotropy of the composite strengths and/or the composite stiffnesses after a lining operation on the fiber web to yield a web layering is influenced by an additional drawing of an nonwoven. 
     
     
         10 . The method according to  claim 1 , which further comprises providing the thermoplastic non-carbon fibers to have fiber lengths in a range of 40 mm to 100 mm. 
     
     
         11 . The method according to  claim 1 , wherein the carbon fibers, the carbon fiber bundles or the mixture of the carbon fibers and the carbon fiber bundles have an average fiber length of 25 mm to 150 mm. 
     
     
         12 . The method according to  claim 6 , wherein at least a portion of the carbon fibers are cut, new primary fibers. 
     
     
         13 . A flat semi-finished material, comprising:
 a fiber-reinforced composite plastic containing fibers and at least one thermoplastic matrix material by isolating finite carbon fibers, carbon fiber bundles or a mixture of said finite carbon fibers and said carbon fiber bundles from waste or used parts having carbon fibers, laying said fibers flat and orienting them with thermoplastic non-carbon fibers in a carding method, so that a fiber web having a targeted orientation of said fibers being created, and said fiber web then being pressed under an influence of heat to form a sheet material; and   an amount of said thermoplastic matrix material being in a range between 5% and 95%, and said carbon fibers, said carbon fiber bundles or said mixture of said carbon fibers and said carbon fiber bundles have finite lengths and have a fiber length distribution.   
     
     
         14 . The flat semi-finished product according to  claim 13 , wherein said carbon fibers are present in the semi-finished product in such a way that portions of said carbon fibers do not pass through the entire semi-finished product without interruption. 
     
     
         15 . The flat semi-finished product according to  claim 13 ,
 wherein said fibers include at least one of finite carbon fibers, finite carbon fiber bundles or a mixture of said finite carbon fibers and said finite carbon fiber bundles; and   further comprising additional finite reinforcing fibers.   
     
     
         16 . The flat semi-finished product according to  claim 13 , further comprising continuous reinforcing fibers selected from the group consisting of continuous carbon rovings, para-aramid fibers, and glass filament yarns in a form of non-crimp fabrics, woven fabrics or meshes. 
     
     
         17 . The flat semi-finished product according to  claim 13 , wherein said amount of said thermoplastic matrix material being in a range between 30% and 80%. 
     
     
         18 . The flat semi-finished product according to  claim 15 , wherein said additional finite reinforcing fibers are selected from the group consisting of natural fibers, para-aramid fibers and glass fibers.