Process for maing high-performance polyethylene multifilament yarn

Abstract

The invention relates to a process for making high-performance polyethylene multi-filament yarn comprising the steps of a) making a solution of ultra-high molar mass polyethylene in a solvent; b) spinning of the solution through a spinplate containing at least 5 spinholes into an air-gap to form fluid filaments, while applying a draw ratio DR fluid ; c) cooling the fluid filaments to form solvent-containing gel filaments; d) removing at least partly the solvent from the filaments; and e) drawing the filaments in at least one step before, during and/or after said solvent removing, while applying a draw ratio DR solid of at least 4, wherein in step b) each spinhole comprises a contraction zone of specific dimension and a downstream zone of diameter D n and length D n with L n /D n of from 0 to at most 25, to result in a draw ratio DR fluid =DR sp *DR ag of at least 150, wherein DR sp is the draw ratio in the spinholes and DR ag is the draw ratio in the air-gap, with DR sp being greater than 1 and DR ag at least 1. The invention further relates to a high-performance polyethylene multifilament yarn, and to semi-finished or end-use products containing said yarn, especially to ropes and ballistic-resistant composites.

1 . Process for making high-performance polyethylene multifilament yarn comprising the steps of
 a) providing a 3-25 mass % solution of ultra-high molar mass polyethylene having an intrinsic viscosity as measured on solutions in decalin at 135° C. of between about 8 and 40 dl/g, in a solvent;   b) spinning of the solution through a spinplate containing at least 5 spinholes into an air-gap to form fluid filaments, while applying a draw ratio DR fluid  of at least 150, wherein DR fluid =DR sp ×DR ag  where DR sp  is the draw ratio in the spinholes and DR ag  is the draw ratio in the air-gap, with DR sp  being greater than 1 and DR ag  being at least 1;   c) cooling the fluid filaments to form solvent-containing gel filaments;   d) removing at least partly the solvent from the filaments; and   e) drawing the filaments in at least one step before, during and/or after said solvent removing, while applying a draw ratio DR solid  of at least 4.   
     
     
         2 . Process according to  claim 1 , wherein the spinhole has a geometry comprising a contraction zone, with a gradual decrease in diameter from diameter D 0  to D n  with a cone angle in the range 8-75°, and wherein the spinhole comprises a zone of constant diameter D n  with a length/diameter ratio L n /D n  of from 0 to at most 25 downstream of a contraction zone. 
     
     
         3 . Process according to  claim 2 , wherein the cone angle is from 10 to 60°. 
     
     
         4 . Process according to  claim 1 , wherein the draw ratio in the spinholes (DR sp ) is at least 2. 
     
     
         5 . Process according to  claim 4 , wherein the draw ratio in the spinholes (DR sp ) is at least 10. 
     
     
         6 . Process according to  claim 1 , wherein the spinhole further comprises a constant diameter zone downstream of a contraction zone, wherein the constant diameter zone has a constant diameter D n  and a length L n  with a length/diameter ratio L n /D n  of at most 20. 
     
     
         7 . Process according to  claim 6 , wherein the length/diameter ratio L n /D n  is at most 15. 
     
     
         8 . Process according to  claim 1 , wherein the spinhole further comprises an inflow zone having a constant diameter D 0  and a length L 0  with a length/diameter ratio L 0 /D 0  of at least 5. 
     
     
         9 . Process according to  claim 8 , wherein the length/diameter ratio L 0 /D 0  is at least 10. 
     
     
         10 . Process according to  claim 1 , wherein the spinplate comprises at least 10 cylindrical spinholes, wherein each of the cylindrical spinholes has an inflow zone of constant diameter D 0  and a length L 0  with a length/diameter ratio L 0 /D 0  at least 10, a contraction zone with cone angle in the range 10-60°, and a downstream zone having a constant diameter D n  and a length L n  with a length/diameter ratio L n /D n  at most 15. 
     
     
         11 . Process according to  claim 1 , which comprises applying a fluid draw ratio DR fluid  to the fluid filaments of least 250. 
     
     
         12 . Process according to  claim 1 , which comprising spinning a 3-15 mass % solution of linear UHPE of IV 15-25 dl/g through a spinplate containing at least 10 spinholes into the air-gap, wherein the spinholes comprise a contraction zone with a cone angle in the range 10-60° and a zone downstream of the contraction zone, wherein the downstream zone has a constant diameter D n  and a length L n  with a length/diameter ratio L n /D n  smaller than 10, and wherein the process comprises applying a fluid draw ratio DR fluid =DR sp ×DR ag  of at least 200 and a draw ratio DR solid  of between 5 and 30. 
     
     
         13 . Medical implant comprising a High-performance polyethylene multifilament yarn made from linear ultra-high molar mass polyethylene of IV 8-40 dl/g, containing n filaments and having a tensile strength of at least f*(n −0.065 ) GPa, wherein factor f is at least 5.8 and n is at least 5 and containing less than 150 ppm of residual solvent having a boiling point at atmospheric conditions of less than 275° C. 
     
     
         14 . Ballistic-resistant assembly comprising a plurality of mono-layers consisting essentially of high-performance polyethylene multifilament yarn, the assembly having an areal density of at least 1.5 kg/m 2  and a specific energy absorption of at least 300 J.m 2 /kg as measured against a 9*19 mm FMJ Parabellum bullet according to a test procedure based on Stanag 2920. 
     
     
         15 . Ballistic-resistant assembly according to  claim 14 , wherein the mono-layers contain uni-directionally oriented filaments, with the fibre direction in each mono-layer being rotated with respect to the fibre direction in an adjacent mono-layer. 
     
     
         16 . Ballistic-resistant assembly according to  claim 14 , wherein the specific energy absorption of the panel is at least 325 J.m 2 /kg. 
     
     
         17 . Ballistic-resistant moulded panel comprising a plurality of mono-layers consisting essentially of high-performance polyethylene multifilament yarn, the panel having a specific energy absorption of at least 165 J.m 2 /kg as measured against an AK-47 bullet according to a test procedure based on Stanag 2920. 
     
     
         18 . Ballistic-resistant panel according to  claim 17 , wherein the mono-layers contain uni-directionally oriented filaments, with the fibre direction in each mono-layer being rotated with respect to the fibre direction in an adjacent mono-layer.