Preformed sheet layers of multiple high-performance polyethylene (HPPE) multifilament yarn monolayers and ballistic-resistant assemblies comprising the same
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 preformed sheet layer comprising at least two monolayers comprised of high-performance polyethylene (HPPE) multifilament yarn and a binder, wherein the multifilament yarn is made from linear ultra-high molar mass polyethylene of IV 8-40 dl/g, contains n filaments and has 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 sheet layer of claim 1 , wherein the mono-layer is a woven and or non-woven fabric.
3. The sheet layer of claim 1 , wherein the fiber direction in each mono-layer is rotated with respect to the fiber direction in an adjacent mono-layer.
4. The sheet layer of claim 1 , wherein the binder has been applied by as a film, as a transverse bonding strip or fibres, or by impregnating and/or embedding the filaments with a matrix, preferably the matrix material is provided as a solution or dispersion in a liquid.
5. The sheet layer of claim 1 , wherein the amount of the binder is less than 30 mass % based on the mass of the layer, more preferably less than 20 or 15 mass %.
6. The sheet layer of claim 1 , wherein the mono-layers further comprise auxiliary components and/or other filaments.
7. The sheet layer of claim 1 , further comprising layers other than the monolayers that have been consolidated or attached to each other.
8. The sheet layer of claim 7 , wherein at least one of the layers other than the monolayers is a polyethylene film.
9. The sheet layer of claim 8 , wherein the sheet layer comprises two or four monolayers of HPPE multifilament yarn and polyethylene sheets on both sides.
10. The sheet layer of claim 1 , wherein f has a value from 6.0 to 10.
11. The sheet layer 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.
12. The sheet layer of claim 1 , wherein the high-performance polyethylene multifilament yarn contains at least 200 filaments.
13. A multi-layer ballistic-resistant assembly comprising at least two preformed sheet layers according to claim 1 .
14. The sheet layer of claim 6 , wherein the mono-layers consist essentially of high-performance polyethylene (HPPE) filaments.
15. The sheet layer of claim 7 , wherein the layers other than the monolayers comprise film or fabric layers.
16. The sheet layer of claim 1 , which comprises polyethylene film layers on both sides.
17. A multilayer ballistic-resistant assembly for soft ballistic applications obtained by stacking at least two preformed sheets according to claim 1 , and securing the stack by stitching the sheets in the stack at the corners or around the edges, or by placing the stack inside an envelope.
18. Body armor which comprises the multilayer ballistic-resistant assembly according to claim 17 .