Process for spinning uhmwpe, uhmwpe multifilament yarns produced thereof and their use

Abstract

The invention relates to a gel-spinning process for producing a high tensile strength ultra high molecular weight polyethylene (UHMWPE) multifilament yarn comprising ultra-low dtex filaments, the process being characterized in that the draw ratio DR fluid applied to fluid filaments obtained by spinning a solution of UHMWPE through a spinneret and into an air gap, is at least 450, wherein DR fluid =DR sp *DR ag , the DR sp and DR ag being the draw ratios in the spinholes and in the air gap, respectively; and provided that DR ag is at least 30. The UHMWPE multifilament yarns produced thereof were characterized by a tensile strength of at least 3.5 GPa and contained filaments having a dtex of at most 0.5. The invention further relates to products comprising said yarns, e.g. fabrics, medical devices and composite and ballistic articles.

1 . A process for gel-spinning high tensile strength UHMWPE yarns comprising ultra-low dtex filaments, the process containing the steps of:
 a) Preparing a solution of an UHMWPE in a solvent;   b) Spinning through a spinneret and into an air gap the solution of step a) to form fluid filaments, the spinneret containing multiple spinholes and wherein each spinhole comprises at least one zone with a gradual decrease in diameter and wherein the downstream diameter of the spinhole from which the solution is issued in the air gap is between 0.1 and 1.5 mm;   c) Drawing the fluid filaments with a fluid draw ratio DR fluid =DR sp ×DR ag , wherein DR sp  and DR ag  are the draw ratios in the spinholes and in the air gap, respectively; and   d) Cooling the fluid filaments to form solvent-containing gel filaments; and   e) Removing at least partly the remaining solvent from the gel filaments to form solid filaments, before, during or after drawing the solid filaments with a draw ratio DR solid  of at least 4;   
       characterized in that the fluid filaments are drawn with a fluid draw ratio DR fluid  of at least 450, provided that DR ag  is at least 30. 
     
     
         2 . The process of  claim 1  wherein DR sp  is between 5 and 20 and DR ag  is chosen to yield a DR fluid  of at least 450. 
     
     
         3 . The process of  claims 1  wherein DR fluid  is at least 500. 
     
     
         4 . The process of  claim 1  wherein DR overall =DR fluid ×DR gel ×DR solid  is at least 9000. 
     
     
         5 . A UHMWPE multifilament yarn having a tensile strength of at least 3.5 GPa and comprising filaments having a dtex of at most 0.5. 
     
     
         6 . The yarn of  claim 5  having a modulus of at least 100 GPa. 
     
     
         7 . A fabric comprising the yarns of  claim 5 . 
     
     
         8 . A medical suture, cable, implantable valve, vascular graft or mesh comprising the yarns of  claim 5 . 
     
     
         9 . Composite articles comprising the yarns of  claim 5 . 
     
     
         10 . Antiballistic articles comprising the yarns of  claim 5 .