High performance fibers composite sheet
The invention relates to a composite sheet comprising at least two adjacent fibrous monolayers of unidirectionally aligned high tenacity polyethylene fibers, whereby the direction of orientation between the polyethylene fibers of said two fibrous layers differs by at least 80° and up to 90°, the fibers having a tenacity of at least 1.5 N/tex, said fibers being in a matrix comprising a homopolymer or copolymer of ethylene and wherein said homopolymer or copolymer of ethylene has a density as measured according to IS01183 of between 870 to 980 kg/m 3 , said composite sheet having an areal density of between 50 and 500 g/m 2 wherein the composite sheet has an areal density normalized in-plane shear force measured at 25° C. evaluated according to the bias extension test method of at least 0.40 N·m 2 ·g-1 at 10 mm clamp displacement.
1. A composite sheet comprising:
a matrix comprising an at least partially neutralized copolymer of ethylene further comprising monomeric units derived from at least one unsaturated carboxylic acid, wherein the at least partially neutralized copolymer of ethylene has a density as measured according to ISO1183 of between 870 to 980 kg/m 3 , and
at least two adjacent fibrous monolayers of unidirectionally aligned high tenacity polyethylene fibers impregnated with the matrix, wherein a direction of orientation between the polyethylene fibers of the at least two fibrous layers differs by at least 80° and up to 90°, wherein the fibers have a tenacity of at least 1.5 N/tex, and wherein
the composite sheet has an areal density of between 50 and 500 g/m 2 wherein the composite sheet has an areal density normalized in-plane shear force measured at 25° C. evaluated according to a bias extension test method variant of ASTM D3518 of at least 0.40 N·m 2 ·g −1 and lower than 5.0 N·m 2 ·g −1 at 10 mm clamp displacement and an areal density normalized in-plane shear force measured at 110° C. and clamp displacement of 10 mm of at least 0.03 N·m 2 ·g −1 and lower than 0.20 N·m 2 ·g −1 .
2. The composite sheet according to claim 1 , wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 30 N·m 2 ·g −1 and less than 200 N·m 2 ·g −1 , the in-plane shear secant stiffness being measured at 25° C. according to the bias extension test.
3. The composite sheet according to claim 2 1 wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 1.0 N·m 2 ·g −1 and less than 7.0 N·m 2 ·g −1 , the in-plane shear secant stiffness being measured at 110° C. according to the bias extension test.
4. The composite sheet of claim 1 , comprising from 2 to 25 wt % of the at least partially neutralized copolymer of ethylene, based on the total weight of the composite sheet.
5. The composite sheet of claim 4 , wherein the at least partially neutralized copolymer of ethylene comprises at least 90 mol % of monomeric units derived from ethylene.
6. The composite sheet of claim 4 , wherein the at least partially neutralized copolymer of ethylene is an ethylene acrylic acid (EAA) copolymer, an ethylene methacrylic acid (EMA) copolymer or mixtures thereof.
7. The composite sheet of claim 4 , wherein the carboxylic acid comprises as neutralizing ion a cation selected from the group consisting of Na + , K + , Li + , Ag + , Cu + , Cu 2+ , Be + , Mg 2+ , Ca 2+ , Sn 2+ , Sn 4+ , Fe 2+ , Fe 3+ , Zn 2+ , Al 3+ , NH 4+ and combinations thereof.
8. The composite sheet of claim 7 , wherein the carboxylic acid comprises between 1.0 and 30 mol % of NH 4 + as the neutralizing ion.
9. The composite sheet of claim 7 , wherein between 70 and 99.9 mol % of the neutralizing ion is selected from the group consisting of Na + , K + , Li + , Mg 2+ , Ca 2+ , Sn 2+ , Zn 2+ , Al 3+ and mixtures thereof.
10. The composite sheet of claim 4 , wherein the carboxylic acid groups of the at least partially neutralized copolymer of ethylene have a degree of neutralization which is between 50 and 100 mol %.
11. The composite sheet of claim 1 , wherein the at least partially neutralized copolymer of ethylene has 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.
12. The composite sheet according to claim 1 , wherein the at least partially neutralized copolymer of ethylene has a modulus at 25° C. of between 50 MPa and 500 MPa and a modulus at 110° C. of between 0.1 and 10 MPa.
13. A ballistic resistant article comprising at least one composite sheet as defined in claim 1 .
14. The ballistic resistant article of claim 13 , wherein the article is a compression molded panel which comprises at least 10 of the composite sheets.