Fibrous tape

Abstract

The invention relates to a fibrous tape made from fibers comprising highly oriented polymer, the tape having a tenacity of at least 1.2 N/tex and an areal density of between 5 and 250 g/m 2 , wherein the tape has a transversal strength of at least 0.5 MPa. The invention also relates to sheets comprising the tape of the invention and antiballistic articles comprising at least two of said sheets. The invention further relates to a process for the preparation of the tapes of the invention.

1 . A fibrous tape made from fibers comprising highly oriented polymer, the tape having a tenacity of at least 1.2 N/tex and an areal density of between 5 and 250 g/m 2 , wherein the tape has a transversal strength of at least 0.5 MPa. 
     
     
         2 . The tape of  claim 1 , wherein the polymer is a polyolefin, preferably a polyethylene and more preferably a high or ultrahigh molecular weight polyethylene (UHMWPE). 
     
     
         3 . The tape of  claim 1  wherein the tape has a cross-sectional aspect ratio thickness to width of at most 1:50, preferably at most 1:100, more preferably at most 1:500. 
     
     
         4 . The tape of  claim 1  wherein the tape has a tenacity of at least 1.5 N/tex, preferably at least 2.0 N/tex, more preferably at least 2.5 N/tex, even more preferably 3.0 N/tex and most preferably 3.5 N/tex. 
     
     
         5 . The tape of  claim 1  wherein the transversal strength is at least 0.6 MPa, more preferably at least 0.7 MPa, even more preferably at least 0.8 MPa, and most preferably at least 0.9 MPa. 
     
     
         6 . The tape of  claim 1  wherein the fibers comprising the polymer comprise at least 10 ppm of a solvent for the polymer. 
     
     
         7 . A sheet comprising at least two monolayers comprising fibrous tape or at least one layer of woven fibrous tapes, wherein the fibrous tapes are selected from  claim 1 . 
     
     
         8 . The sheet according to  claim 7  wherein the direction of the fibrous tape in a monolayer is at an angle α to the direction of a fibrous tape in an adjacent monolayer or wherein the layer of woven fibrous tapes comprises weft and warp woven tapes and the direction of orientation of the weft and the warp woven tapes in the layer of woven fibrous tapes are at an angle β and wherein α or β are between 20 and 90°, more preferably between 45 and 90°, most preferably between 75 and 90°. 
     
     
         9 . An antiballistic article comprising at least 2, preferably at least 4, more preferably at least 8 sheets according to  claim 7 . 
     
     
         10 . The antiballistic article of  claim 9  having an areal density between 0.25 Kg/m 2  and 250 Kg/m 2 , preferably between 0.5 Kg/m 2  and 100 Kg/m 2 , more preferably between 1 Kg/m 2  and 75 kg/m 2  and most preferably between 2 Kg/m 2  and 50 kg/m 2 . 
     
     
         11 . The antiballistic article of  claim 9 , comprising a number of contacts between two tapes separated by an intermediate tape, wherein the number of contacts is less than 20 per unit of width of 1 meter of the intermediate tape, while a contact corresponds to a tape-to-tape interaction of the two tapes separated by an intermediate tape, occurring through a split of the intermediate tape. 
     
     
         12 . A process for the preparation of the fibrous tape of  claim 1 , the process comprising:
 (a) providing fibers comprising a highly oriented polymer, said fibers having a tenacity of at least 1.2 N/tex   (b) forming a layer comprising the fibers;   (c) applying a longitudinal tensile force to the fibers in the layer,   (d) stretching the fiber layer at a draw ratio of at least 1.01 to form a stretched layer;   (e) providing the stretched layer at a processing temperature T p  to compression means;   (f) compressing the stretched layer of fibers by subjecting the layer to a compression by the compression means having a temperature T c  to form a fibrous tape;   (g) optionally stretching the fibrous tape by a draw rate of at most 1.1 and,   (h) cooling the fibrous tape to a temperature of at most 80° C. under a tension sufficient to prevent loss of mechanical properties;   wherein T m  is the melting temperature of the polymer,   wherein T m >T p ≧T m −30 K, and   wherein T c ≦T p −3 K.   
     
     
         13 . The process according to  claim 11   wherein T m >T p ≧T m −15 K, and   wherein T c ≦T p −15 K.   
     
     
         14 . The process according to  claim 11  wherein the polymer is UHMWPE, preferably the UHMWPE has an intrinsic viscosity of between 5 dL/g to 40 dL/g, more preferably between 8 and 30 dL/g. 
     
     
         15 . The process of  claim 11  wherein the filaments are stretched in between the steps (a) and (f) to a draw ratio from 1.02 to 3.0, preferably 1.03 to 2.0.