Process for making high-performance polyethylene multifilament yarn
Processes for making high-performance polyethylene multi-filament yarn are disclosed which include 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 Dn and length Dn with Ln/Dn 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. High-performance polyethylene multifilament yarn, and semi-finished or end-use products containing said yarn, especially to ropes and ballistic-resistant composites, are also disclosed.
1. A ballistic resistant assembly comprising a plurality of preformed sheets, each preformed sheet comprising 4 layers of filaments from multifilament polyethylene yarn, the polyethylene having an IV of between 8 and 40 dL/g as measured on decalin solutions at 135° C., the plurality of preformed sheets having an areal density of at least 1.5 kg/m 2 and at most 4.3 kg/m 2 , wherein the plurality of preformed sheets has a specific energy absorption of between 280 and 479 J·kg/m 2 as measured against a 9*19 mm FMJ Parabellum FMJ bullet based on Stanag 2920.
2. The ballistic resistant assembly according to claim 1 , wherein the plurality of preformed sheets has a specific energy absorption of between 280 and 391 J·kg/m 2 .
3. The ballistic resistant assembly according to claim 1 , wherein the plurality of preformed sheets has a specific energy absorption of between 300 and 391 J·kg/m 2 .
4. The ballistic resistant assembly according to claim 1 , wherein the plurality of preformed sheets has a specific energy absorption of between 325 and 391 J·kg/m 2 .
5. The ballistic resistant assembly according to claim 1 , wherein the plurality of preformed sheets has an areal density of at least 1.5 kg/m 2 and at most 3.4 kg/m 2 .
6. The ballistic resistant assembly according to claim 1 , wherein the plurality of preformed sheets has an areal density of at least 2.0 kg/m 2 and at most 3.4 kg/m 2 .
7. The ballistic resistant assembly according to claim 1 wherein the filaments in each layer are arranged uni-directionally.
8. The ballistic resistant assembly according to claim 7 wherein the uni-directionally arranged filaments in each layer are rotated with respect to the filaments in an adjacent mono-layer.
9. The ballistic resistant assembly according to claim 1 , wherein the polyethylene has an IV of between 10 and 30 dl/g.
10. The ballistic resistant assembly according to claim 1 , wherein the preformed sheet comprises a binder, wherein the amount of binder is less than 30 mass % based on the mass of the preformed sheet.
11. The ballistic resistant assembly according to claim 10 , wherein the amount of binder is less than 20 mass %.
12. The ballistic resistant assembly according to claim 10 , wherein the amount of binder is less than 15 mass %.
13. The ballistic resistant assembly according to claim 10 , wherein the amount of binder is between 10 and 23 mass %.
14. The ballistic resistant assembly according to claim 1 , wherein the preformed sheet further comprises a film layer.
15. The ballistic resistant assembly according to claim 14 , wherein the film is a polyethylene film.
16. The ballistic resistant assembly according to claim 15 , wherein the polyethylene film has a weight of about 7 g/m 2 .
17. The ballistic resistant assembly according to claim 14 , wherein the preformed sheet comprises a film on both of its sides.
18. The ballistic resistant assembly according to claim 16 , wherein the film is a polyethylene film.
19. The ballistic resistant assembly according to claim 18 , wherein the polyethylene film has a weight of about 7 g/m 2 .
20. The ballistic resistant assembly according to claim 1 , wherein the areal density of each layer of polyethylene filaments is between 20.2 and 40.3 g/m 2 .
21. A ballistic resistant article comprising the ballistic resistant assembly according to claim 1 .
22. A ballistic resistant assembly comprising a plurality of preformed sheets, each preformed sheet comprising 4 layers of filaments from multifilament polyethylene yarn, the polyethylene having an IV of between 8 and 40 dl/g as measured on decalin solutions at 135° C., the plurality of preformed sheets having an areal density of at least 1.5 kg/m 2 and at most 4.3 kg/m 2 , wherein the ballistic resistant assembly has a specific energy absorption of between 280 and 479 J·kg/m 2 as measured against a 9*19 mm FMJ Parabellum FMJ bullet based on Stanag 2920.
23. A preformed sheet comprising four layers, each mono-layer comprising filaments from multifilament polyethylene yarn, wherein the filaments of the multifilament yarn in the four layers are spread uni-directionally; and wherein the direction of the filaments in each layer is rotated with respect to the direction of the filaments in an adjacent layer.
24. A ballistic resistant article comprising the preformed sheet according to claim 23 .