Process for making high-performance polyethylene multifilament yarn
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 DRfluid; 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 DRsolid 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 Ln with Ln/Dn of from 0 to at most 25, to result in a draw ratio DRfluid=DRsp*DRag of at least 150, wherein DRsp is the draw ratio in the spinholes and DRag is the draw ratio in the air-gap, with DRsp being greater than 1 and DRag 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. A multi-layer ballistic-resistant assembly containing a plurality of mono-layers comprising 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.
2. The assembly of claim 1 wherein the mono-layer is a woven and or non-woven fabric.
3. The assembly of claim 1 , wherein the fibre direction in each mono-layer is rotated with respect to the fibre direction in an adjacent mono-layer.
4. The assembly of claim 1 , wherein the mono-layer further comprises a binder material.
5. The assembly of claim 4 , wherein the binder material has been applied as a film, as a transverse bonding strip or fibres, or by impregnating and/or embedding the filaments with a binder matrix.
6. The assembly of claim 5 , wherein the matrix material is provided as a solution or dispersion in a liquid.
7. The assembly of claim 1 , wherein the amount of binder material is less than 30 mass % based on the mass of the layer, more preferably less than 20 or 15 mass %.
8. The assembly of claim 1 , wherein the mono-layers optionally comprise small amounts of auxiliary components and /or other filaments, preferably the mono-layers essentially consist of HPPE filaments.
9. The assembly of claim 1 , comprising at least two preformed sheet layers, a sheet layer comprising at least two mono-layers comprising high-performance fibres and a binder material, and optionally other layers, like a film or fabric; that have been consolidated or attached to each other.
10. The assembly of claim 1 , being a rigid panel that has been compression-moulded from a plurality of mono-layers containing HPPE yarn.
11. The assembly of claim 1 , being a flexible panel assembled from a plurality of mono-layers containing HPPE yarn, by stacking mono-layers or preformed sheets, preferably the stack has been secured by stitching at the corners or around the edges, or by placing inside an envelope.
12. The assembly of claim 1 , wherein f has a value from 6.0 to 10.
13. The assembly of claim 1 , wherein the multifilament yarn shows a non-reversible peak, as measured by temperature-modulated differential scanning calorimetry, with a maximum at about 152° C. and having an enthalpy of at least 35 J/g.
14. The assembly of claim 1 , wherein the high-performance polyethylene multifilament yarn contains at least 200 filaments.
15. A ballistic-resistant moulded panel which comprises a rigid compression molded panel of a multi-layer ballistic-resistant assembly according to claim 1 , wherein the molded panel has a specific energy absorption (SEA) of at least 165 J·m 2 /kg as measured against an AK-47 bullet according to a test procedure based on Stanag 2920.
16. The ballistic-resistant panel according to claim 15 , wherein the mono-layers of the multi-layer ballistic resistant assembly 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.