Thermoplastic Prepreg Containing Continuous and Long Fibers

Abstract

A prepreg that contains a plurality of unidirectionally aligned continuous fibers embedded within a thermoplastic polymer matrix is provided. In addition to continuous fibers, the prepreg also contains a plurality of long fibers that are combined with the continuous fibers so that they are randomly distributed within the thermoplastic matrix. As a result, at least a portion of the long fibers become oriented at an angle (e.g., perpendicular) relative to the direction of the continuous fibers. Through such orientation, the long fibers can substantially increase the mechanical properties of the prepreg in the transverse direction (e.g., strength) and thus achieve a more isotropic material. Although unique isotropic prepregs are one aspect of the present invention, it should be understood that this is not a requirement. In fact, one notable feature of the present invention is the ability to tailor the mechanical properties of the prepreg for an intended application by selectively controlling certain process parameters, such as the type of long fibers employed, the type of continuous fibers employed, the concentration of the long fibers, the concentration of the continuous fibers, the thermoplastic resin(s) employed, etc.

What is claimed is: 
     
         1 - 15 . (canceled) 
     
     
         16 . A method for forming a thermoplastic prepreg, the method comprising:
 supplying continuous fibers and long fibers to an extrusion device;   supplying a thermoplastic feedstock to the extrusion device, wherein the feedstock comprises at least one thermoplastic polymer; and   extruding the continuous fibers, long fibers, and the thermoplastic polymer within an impregnation die to form an extrudate in which the continuous fibers are intermixed with the long fibers and embedded with a matrix of the thermoplastic polymer.   
     
     
         17 . The method of  claim 16 , wherein the feedstock comprises the long fibers. 
     
     
         18 . The method of  claim 16 , further comprising pulling the extrudate through a nip defined between rollers to consolidate the extrudate into the form of a sheet. 
     
     
         19 . The method of  claim 16 , wherein the continuous fibers constitute from about 10 to about 80 wt. % of the prepreg and the long fibers constitute from about 2 to about 35 wt. % of the prepreg. 
     
     
         20 . The method of  claim 16 , wherein the continuous fibers, the long fibers, or both, include glass fibers, carbon fibers, or a combination of glass and carbon fibers. 
     
     
         21 . The method of  claim 16 , wherein the thermoplastic polymer includes a polyolefin, polyether ketone, polyetherimide, polyarylene ketone, liquid crystal polymer, polyarylene sulfide, fluoropolymer, polyacetal, polyurethane, polycarbonate, styrenic polymer, polyester, polyamide, or a combination thereof. 
     
     
         22 . The method of  claim 16 , wherein a manifold assembly supplies the thermoplastic feedstock to the extrusion device, the manifold assembly comprising branched runners through which the thermoplastic feedstock flows. 
     
     
         23 . A method for forming a thermoplastic prepreg, the method comprising:
 supplying continuous fibers to an extrusion device;   supplying a thermoplastic feedstock to the extrusion device, wherein the feedstock comprises at least one thermoplastic polymer; and   extruding the continuous fibers and the feedstock within an impregnation die to form an extrudate in which the continuous fibers are embedded with a matrix of the thermoplastic polymer;   thereafter, applying long fibers to the extrudate to form a composite.   
     
     
         24 . The method of  claim 23 , further comprising pulling the composite through a nip defined between rollers to consolidate the composite into the form of a sheet. 
     
     
         25 . The method of  claim 23 , wherein the continuous fibers constitute from about 10 to about 80 wt. % of the prepreg and the long fibers constitute from about 2 to about 35 wt. % of the prepreg. 
     
     
         26 . The method of  claim 23 , wherein the continuous fibers, the long fibers, or both, include glass fibers, carbon fibers, or a combination of glass and carbon fibers. 
     
     
         27 . The method of  claim 23 , wherein the thermoplastic polymer includes a polyolefin, polyether ketone, polyetherimide, polyarylene ketone, liquid crystal polymer, polyarylene sulfide, fluoropolymer, polyacetal, polyurethane, polycarbonate, styrenic polymer, polyester, polyamide, or a combination thereof. 
     
     
         28 . The method of  claim 23 , wherein a manifold assembly supplies the thermoplastic feedstock to the extrusion device, the manifold assembly comprising branched runners through which the thermoplastic feedstock flows.