Ballistic resistant sheet and use of such a sheet
The invention relates to a ballistic resistant sheet ( 12 ) comprising a three-layer hybrid structure, with a core layer ( 12 - 1 ) and two face layers ( 12 - 2; 12 - 3 ) wherein the core layer comprises at least one first monolayer comprised of first unidirectionally (UD) oriented fibers and a matrix material, and wherein each of the face layers comprise at least one second and at least one third monolayer comprised of second UD oriented fibers and third UD oriented fibers respectively and wherein the stiffness of the face layers is higher than the stiffness of the core layer.
1. A drapable ballistic resistant sheet comprising; a three-layer hybrid structure which comprises an unconsolidated stack of sub-sheets which establish a core layer, a strike face layer and a back face layer, wherein the core layer comprises at least one consolidated first monolayer comprised of first unidirectionally (UD) oriented fibers and a matrix material, and wherein the strike face layer comprises at least one consolidated second monolayer comprised of second UD oriented fibers and a matrix material, and wherein the back face layer comprises at least one consolidated third monolayer comprised of third UD oriented fibers and a matrix material, and wherein each of the strike face layer and the back face layer has a numerical Flexibility Value that is higher than a numerical Flexibility Value of the core layer, wherein the higher numerical Flexibility Value represents increased stiffness.
2. The ballistic resistant sheet according to claim 1 , wherein at least one of the first, second and third UD fibers is formed of organic fibers selected from the group consisting of aromatic polyamide fibers, liquid crystalline polymer fibers, and ladder-like polymer fibers, polyolefin fibers, polyvinyl alcohol fibers, and polyacrylonitriles fibers.
3. The ballistic resistant sheet according to claim 2 , wherein at least one of the first, second and third UD fibers is formed of ultra high molecular weight (UHMW) polyethylene fibers, polybenzimidazole fibers, poly(1,4-phenylene-2,6-benzobisoxazole fibers and poly(2,6-diimidazo[4,5-b-4′,5′-e]pyridinylene-1,4-(2,5-dihydroxy)phenylene) fibers.
4. The ballistic resistant sheet according to claim 1 , wherein the matrix materials of the core layer, the strike face layer and the back face layer are present in an amount of at most 20 mass % of the total mass of the respective core layer, strike face layer and back face layer.
5. The ballistic resistant sheet according to claim 1 , wherein the matrix material is comprised of at least one selected from the group consisting of polybutadiene, polyisoprene, natural rubber, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polysulfide polymers, polyurethane, polyurethane elastomers, modified polyolefins, chlorosulfonated polyethylene, polychloroprene, plasticized polyvinylchloride, butadiene acrylonitrile elastomers, poly(isobutylene-co-isoprene), polyacrylates, polyesters, polyethers, fluoroelastomers, silicone elastomers, thermoplastic elastomers, plastomers, and ethylene copolymers.
6. The ballistic resistant sheet according to claim 1 , wherein the matrix material in the core layer has a tensile modulus of less than 3 MPa.
7. The ballistic resistant sheet according to claim 1 wherein the core layer is present in an amount of 10 to 70 weight % of the total mass of the ballistic resistant article.
8. The ballistic resistant sheet according to claim 1 wherein a weight ratio of the weight of the strike face layer is at least 1.1 times the weight of the back face layer.
9. The ballistic resistant sheet according to claim 1 , wherein at least one polymer film is attached to at least one sub-sheet of the core layer and/or at least one of the strike face layer and the back face layer.
10. The ballistic resistant sheet according to claim 1 wherein the UD-oriented fibers in the strike face and back face layers have a tensile strength of at least 2.0 GPa.
11. The ballistic resistant sheet according to claim 1 , wherein the UD-oriented fibers in the monolayers are formed of ultra high molecular weight polyethylene (UHMWPE).
12. The ballistic resistant sheet according to claim 11 , wherein the UHMWPE has an intrinsic viscosity of at least 6 dl/g.
13. The ballistic resistant sheet according to claim 1 wherein the UD-oriented fibers in the strike face and back face layers have a tensile strength that is at least 1.05 times higher than the tensile strength of the UD-oriented fibers in the core layer.
14. The ballistic resistant sheet according to claim 1 , further comprising a trauma liner.
15. A soft ballistic article which comprises the ballistic resistant sheet according to claim 1 .