Ballistic resistant sheets, articles comprising such sheets and methods of making the same
Ballistic resistant sheets (12), articles (10) comprising such sheets and methods of making the same are provided. The embodiments are especially adapted to facilitate the manufacture of curved ballistic resistant articles (e.g. curved ballistic resistant armor, helmets and the like). In preferred forms, the ballistic resistant sheets are a multi-monolayer construction including a core layer (12-1) formed of at least one first monolayer having first unidirectionally oriented reinforcing fibers and an elastomeric matrix material which is sandwiched between respective face layers (12-2) each formed of at least one second monolayer having second unidirectionally oriented reinforcing fibers and a non-elastomeric matrix material.
1. A ballistic resistant sheet in the form of a three-layer hybrid structure, comprising a core layer and face layers joined to respective opposing surfaces of the core layer, wherein the core layer comprises at least one first monolayer comprised of first unidirectionally (UD) oriented fibers and an elastomeric matrix material, and wherein each of the face layers comprise at least one second monolayer comprised of second UD oriented fibers and a non-elastomeric matrix material.
2. The ballistic resistant sheet according to claim 1 , wherein the first and second UD fibers may be the same or different and are selected from organic fibers and inorganic fibers.
3. The ballistic resistant sheet according to claim 1 , wherein at least one of the first and second UD fibers are formed of inorganic fibers selected from the group consisting of glass fibers, carbon fibers and ceramic fibers.
4. The ballistic resistant sheet according to claim 1 , wherein at least one of the first and second UD fibers are 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.
5. The ballistic resistant sheet according to claim 4 , wherein at least one of the first and second UD fibers are 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.
6. The ballistic resistant sheet according to claim 1 , wherein the matrix materials of the core and face layers are present in an amount of at most 20 mass % of the total mass of the sheet.
7. The ballistic resistant sheet according to claim 1 , wherein the elastomeric matrix material has a tensile modulus of less than 3 MPa.
8. The ballistic resistant sheet according to claim 7 , wherein the elastomeric 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.
9. The ballistic resistant sheet according to claim 8 , wherein the elastomeric matrix comprises a block copolymer of a conjugated diene and a vinyl aromatic monomer.
10. The ballistic resistant sheet according to claim 9 , wherein the conjugated diene is butadiene or isoprene.
11. The ballistic resistant sheet according to claim 1 , wherein the non-elastomeric matrix material has a tensile modulus of at least 3 M Pa or greater.
12. The ballistic resistant sheet according to claim 11 , wherein the non-elastomeric matrix material is at least one selected from the group consisting of acrylates, polyurethanes, modified polyolefins and ethylene vinyl acetate.
13. A ballistic resistant article which comprises at least one sheet according to claim 1 , consolidated at high temperature and pressure.
14. A ballistic resistant article according to claim 13 , which is a three layered ballistic resistant article comprising the core layer and the two face layers, wherein the core layer comprises at least two of the first monolayers comprised of the first unidirectionally (UD) oriented fibers and the elastomeric matrix material, wherein the three layered ballistic resistant article exhibits a V50 of at least about 750 m/s according to Stanag 2920 using a 7.62×39 mm mild steel core bullet.
15. A method of making a ballistic resistant article which comprises consolidating at least one sheet according to claim 1 under an elevated pressure of at least about 16.5 MPa and an elevated temperature below a temperature at which mechanical properties of the first and second UD fibers deteriorate.