BALLISTIC-RESISTANT HELMET SHELL
The invention relates to a process for producing a ballistic-resistant curved molded article said process comprising forming a stack of a plurality of composite sheets, pressing the stack comprising the composite sheets at a temperature of between 80° C. to 150° C. and a pressure of between 10 and 400 bar for at least 5 minutes to obtain a curved molded article, cooling the compacted stack to a temperature below 80° C. while maintaining the pressure above 10 bar, releasing the pressure from the cooled curved molded article; wherein the composite sheets comprise unidirectionally aligned high tenacity polyethylene fibers and a matrix comprising a polyethylene resin being a homopolymer or copolymer of ethylene having a density of between 870 to 980 kg/m 3 when measured according to ISO1183 and a melt flow index of between 0.5 and 50 g/10 min when measured according to ASTM 1238B-13 at a temperature of 190° C. and a weight of 21.6 kg.
1 . A process for producing a ballistic-resistant curved molded article said process comprising
forming a stack of a plurality of composite sheets
pressing the stack comprising the composite sheets at a temperature of between 80° C. to 150° C. and a pressure of between 10 and 400 bar for at least 5 minutes to obtain a curved molded article,
cooling the compacted stack to a temperature below 80° C. while maintaining the pressure above 10 bar,
releasing the pressure from the cooled curved molded article;
wherein the composite sheets comprise unidirectionally aligned high tenacity polyethylene fibers and a matrix comprising a polyethylene resin being a homopolymer or copolymer of ethylene having a density of between 870 to 980 kg/m 3 when measured according to ISO1183 and a melt flow index of between 0.5 and 50 g/10 min when measured according to ASTM 1238B-13 at a temperature of 190° C. and a weight of 21.6 kg.
2 . The process according to claim 1 wherein the composite sheet comprises from 2 to 25 wt % of the polyethylene resin based on the total weight of the composite sheet.
3 . The process according to claim 1 , wherein the polyethylene resin has a tensile modulus at 25° C. of between 50 MPa and 500 MPa and a tensile modulus at 110° C. of between 0.1 and 10 MPa, determined in accordance with ASTM D5026 at a frequency of 1 Hz at a heating rate of 5° C.
4 . The process according to claim 1 , wherein the polyethylene resin comprises at least 90 mol % of monomeric units derived from ethylene.
5 . The process according to claim 1 , wherein the polyethylene resin is an at least partially neutralized copolymer of ethylene further comprising monomeric units derived from at least one unsaturated carboxylic acid.
6 . A ballistic-resistant curved molded article obtainable by a process as defined in claim 1 .
7 . A ballistic-resistant curved molded article, which article comprises a plurality of molded composite sheets comprising unidirectionally aligned ultra-high molecular weight polyethylene (UHMWPE) fibers and a matrix comprising a polyethylene resin being a homopolymer or copolymer of ethylene having a density of between 870 to 980 kg/m 3 when measured according to ISO1183 and a melt flow index of between 0.5 and 50 g/10 min when measured according to ASTM 1238B-13 at a temperature of 190° C. and a weight of 21.6 kg, which ballistic-resistant curved molded article has an areal density of less than 8.0 kg/m 2 and a V 50 17 grain FSP of greater than 750 m/s according to MIL-STD-662f (1997).
8 . The ballistic-resistant curved molded article according to claim 7 , wherein the ballistic-resistant curved molded article has an average thickness of less than 8 mm.
9 . The ballistic-resistant curved molded article according to claim 7 , wherein the ballistic-resistant curved molded article has a back face signature of less than 20 mm when measured according to NIJ010601 9 mm FMJ RN Remmington threat.
10 . The ballistic-resistant curved molded article according to claim 7 , which further comprises at least one layer comprising carbon fiber.
11 . A ballistic-resistant curved molded article according to claim 7 , which further comprises on the outside surface a coating comprising polyurea.
12 . The ballistic-resistant curved molded article according to claim 7 wherein the ballistic-resistant curved molded article is a ballistic-resistant helmet shell or a radome.
13 . The ballistic-resistant helmet shell of claim 12 having an ear-to-ear stiffness of at most 5 mm measured 24 h after 25 compression cycles at 200 lbs.
14 . The ballistic-resistant helmet shell of claim 12 having a blunt impact performance of less than 110 G when measured according to DOT FMVSS 218.
15 . A ballistic-resistant helmet comprising the ballistic-resistant helmet shell as defined in claim 12 .