Material for radomes and process for making the same
The invention relates to a material comprising at least one laminate component containing polymeric fibers wherein the material has a loss tangent of less than 8×10 −3 radians as measured at a frequency chosen from the group of frequencies consisting of 1.8 GHz; 3.9 GHz; 10 GHz; 39.5 GHz; and 72 GHz.
1. A material comprising:
at least one laminate component containing a fabric formed of ultrahigh molecular weight polyethylene (UHMWPE) fibers, wherein
the at least one laminate comprises at least two laminae and is substantially free of any binder or matrix, and wherein
the material has an average loss tangent of less than 8×10 −3 radians as measured at frequencies of 1.8 GHz; 3.9 GHz; 10 GHz; 39.5 GHz; and 72 GHz, the average loss tangent being a value of the loss tangent which is an average of loss tangent values obtained by measuring the loss tangent at each of the frequencies.
2. The material of claim 1 , wherein the fabric formed of the UHMWPE fibers is a fabric selected from the group consisting of woven fabrics, knitted fabrics, plaited fabrics, braided fabrics, non-woven fabrics and combinations thereof.
3. The material of claim 1 , wherein the at least one laminate component comprises at least one laminae which comprised of a woven fabric of polymeric fibers or polymeric tapes.
4. The material of claim 1 , wherein the at least one laminate component has a flexural strength of at least 50 MPa.
5. The material of claim 1 , wherein the at least one laminate component comprises an upper surface and a lower surface opposite to the upper surface, and wherein the at least one laminate component includes a polymeric coating on at least the upper surface.
6. The material of claim 5 , wherein the polymeric coating has a thickness of at least 0.5 μm.
7. The material of claim 1 , wherein the material has thickness of at least 100 μm.
8. The material of claim 5 , wherein at least one laminate component includes a polymeric coating on both said upper and lower surfaces.
9. The material of claim 8 , wherein the polymeric coating has a thickness of at least 0.5 μm.
10. A radome wall comprising the material of claim 1 .
11. A radome comprising the material of claim 1 .
12. An electromagnetic window comprising the material of claim 1 .
13. A process for manufacturing the material of claim 1 , comprising the steps of:
(a) providing at least one laminae comprising a fabric formed of ultrahigh molecular weight polyethylene (UHMWPE) fibers;
(b) providing at least one pre-formed polymeric film;
(c) stacking the at least one laminae to obtain a laminae-stack having an upper surface and a lower surface, which is opposite to the upper surface, and placing the at least one pre-formed polymeric film at least on the upper surface to create an assembly containing the laminae-stack and the pre-formed polymeric film;
(d) compressing the assembly of step (c) for a dwell time at a pressure of at least 100 bars and at a temperature of less than a melting temperature of the UHMWPE fibers forming the fabric;
(e) cooling the assembly to below 70° C., followed by releasing the pressure; and
(f) removing the pre-formed polymeric film from the assembly.
14. The process of claim 13 , wherein step (e) is practiced by cooling the assembly to room temperature.
15. The process of claim 13 , wherein the pre-formed polymeric film comprises a polyvinyl-based material.
16. The process of claim 15 , wherein the polyvinyl-based material is a polyvinyl chloride material or a silicone-based material.
17. A compressed laminae-stack obtained by the process of claim 13 .