Process for the manufacture of a shaped part and shaped part obtainable with said process
The invention relates to a process for the manufacture of a shaped part comprising the steps of—forming a stack by stacking (2) or more sheets comprising mono-layers of unidirectional anti-ballistic fibers and a binder followed by placing the stack in a mould, clamping the stack in the mould with a control member closing the mould—consolidating the stack under temperature and pressure into a curved shaped part. The invention furthermore relates to products obtainable with said process, which are very suitable for use in anti-ballistic applications and include e.g. helmets, curved panels, cones and domes.
1. A process for the manufacture of a shaped part comprising the steps of:
forming a stack by stacking 2 or more sheets comprising mono-layers, said mono-layers comprising unidirectional anti-ballistic fibers and a binder which holds the fibers together, wherein the fibers have a tensile strength of at least about 1.2 GPa and a tensile modulus of at least 40 GPa,
whereby in the stack the direction of the anti-ballistic fiber in the sheets comprising mono-layers of unidirectional anti-ballistic fibers and a binder is at an angle α to the fiber direction in an adjacent mono-layer, followed by
placing the stack in a mould,
clamping the stack in the mould with a control member such that the stack can slip and move during the closing of the mould,
closing the mould, and
consolidating the stack under temperature and pressure into a curved shaped part.
2. The process according to claim 1 , wherein the sheets comprising mono-layers of unidirectional anti-ballistic fibers and a binder are rectangular sheets in which the direction of the anti-ballistic fibers is parallel to the diagonal of said rectangular sheets.
3. The process according to claim 2 , wherein between 5 and 60 wt % of the rectangular or square sheets in the stack of mono-layers is interchanged with sheets of a smaller surface area.
4. The process according to claim 1 , wherein the binder is a thermoplastic matrix with a tensile modulus of at least than 250 MPa.
5. The process according to claim 1 , which comprises placing at least one layer of fabric of an anti-ballistic fiber during the forming of the stack on the 2 or more sheets comprising mono-layers of unidirectional anti-ballistic fibers and a binder.
6. The process according to claim 5 , wherein the anti-ballistic fiber in the layer of fabric is embedded in a thermoset matrix.
7. The process according to claim 1 , wherein the anti-ballistic fiber in at least one of the layers closest to a strike face is embedded in a thermoset matrix.
8. The process according to claim 1 , wherein the anti-ballistic fiber is a polyethylene fiber.
9. The process according to claim 1 , wherein the control member fixes the stack in the mould with a clamping force between 50 and 5000N.
10. The process according to claim 1 , wherein the control member fixes the stack in the mould with a clamping force between 100 and 3000N.
11. The process according to claim 1 , wherein the consolidating of the stack into a curved shaped part is done at a pressure of at least 7 MPa.
12. The process according to claim 1 , wherein the consolidating of the stack into a curved shaped part is done at a pressure of at least 13 MPa.
13. The process according to claim 1 , wherein the consolidating of the stack into a curved shaped part at a pressure of at least 7 MPa is preceded by a pre-shaping step by pressing the stack at a pressure between 2 and 5 MPa.
14. The process according to claim 1 , wherein the consolidating of the stack into a curved shaped part is done at a mould temperature of at least 10° C. below the melting respectively softening temperature of the fiber.
15. The process according to claim 1 , wherein the stack includes at least one carbon fibre sheet.
16. The process accordingly to claim 15 , wherein the carbon fibre sheet comprises a plurality of mono-layers of unidirectional carbon fibres and a binder, wherein the direction of the carbon fibers is at an angle α to the fiber direction in an adjacent mono-layer.
17. The process according to claim 15 , wherein the carbon sheet comprises woven carbon fibers.
18. The process according to claim 15 , wherein the carbon sheet is between 20% and 80% of the surface area of the stack.
19. The process according to claim 18 , wherein the carbon sheet forms an annular ring within the mould.
20. A curved shaped part obtained by the process of claim 1 .
21. The curved shaped part according to claim 20 , where in the curved shaped part has a area density of no more than 7.4 kg/m 2 and achieves a V 0 of at least 620 m/s using 1.1 gram fragment simulating projectiles (FSP).
22. The curved shaped part according to claim 20 , wherein the anti-ballistic fibers are selected from the group consisting of glass fibers, carbon fibers, ceramic fibers, aramid fibers, ladder-like polymer fibers, polyacrylonitrile fibers, polyethylene alcohol fibers, linear polyethlene fibers and high performance polyethylene (HPPE) fibers.
23. The curved shaped part according to any one of claims 20 - 22 , comprising 2 or more sheets, each sheet comprising mono-layers of unidirectional anti-ballistic fibers and a binder with the direction of the anti-ballistic fibers in each mono-layer at an angle α to the fiber direction in an adjacent mono-layer, and at least one carbon fiber sheet.
24. The curved shaped part according to claim 23 wherein the anti-ballistic fiber is polyethylene fiber.
25. The curved shaped part according to claim 23 wherein the anti-ballistic fiber is aramid fiber or ladder-like polymer fiber.
26. The curved shaped part according to claim 20 , wherein the part has the shape of a helmet.