PBT-carbon fiber composites for microwave shielding
Disclosed is a composite comprising: from about 50 wt. % to about 99 wt. % of a thermoplastic resin, wherein the thermoplastic resin comprises a polyester; and from about 0.1 wt. % to 15 wt. % of a carbon fiber filler, wherein the carbon fiber has a bulk density of at least 500 g/l and a volume electrical resistivity of less than 2,000μΩ#cm, with individual filaments that have a length-to-diameter ratio of at least 300, wherein a 3.175 mm thick molded sample of the composite exhibits a Transmission of less than 15% of incident microwave radiation when observed according to a Free Space method, measured at frequencies of 75 to 110 GHz, wherein the combined weight percent value of all components does not exceed 100 wt. %, and all weight percent values are based on the total weight of the composite.
1 . A composite comprising:
from about 50 wt. % to about 99 wt. % of a thermoplastic resin comprising a polyester and a poly(carbonate-siloxane) copolymer; and
from about 0.1 wt. % to 2 wt. % of a carbon fiber filler, wherein the carbon fiber has a bulk density of at least 500 g/l and a volume electrical resistivity of less than 2,000 μΩ·cm, with individual filaments that have a length-to-diameter ratio of at least 300,
wherein
a 3.175 mm thick molded sample of the composite exhibits a Transmission of less than 15% of incident microwave radiation when observed according to a Free Space method, measured at frequencies of 75 to 110 GHz,
a 3.175 mm thick molded sample of the composite exhibits a Percent Reflected Power measured in Transmission mode of at least 15% when observed according to a Free Space method at frequencies from 75 GHz to 110 GHz, and
the combined weight percent value of all components does not exceed 100 wt. %, and all weight percent values are based on the total weight of the composite.
2 . The composite according to claim 1 , wherein the polyester comprises a polyalkylene terephthalate polymer.
3 . The composite according to claim 1 , wherein the polyester comprises polybutylene terephthalate.
4 . The composite according to claim 1 , wherein a 3.175 mm thick molded plaque comprising the composite transmits less than about 5% of incident microwave radiation at frequencies from 75 GHz to 110 GHz.
5 . The composite according to claim 1 , wherein a 3.175 mm thick molded sample of the composite exhibits a Total Shielding Effectiveness of between 40 and 120 dB when measured according to a Free Space method at frequencies from 75 GHz to 110 GHz.
6 . The composite according to claim 1 , wherein a 3.175 mm thick molded sample of the composite exhibits a Total Shielding Effectiveness greater than that of a reference composite comprising the same amount of a carbon powder filler rather than the carbon fiber filler measured according to a Free Space method at frequencies from 75 GHz to 110 GHz.
7 . The composite according to claim 1 , wherein a 3.175 mm thick molded sample of the composite exhibits a higher reflection of microwave radiation than a reference composite comprising the same amount of a carbon powder filler rather than the carbon fiber filler, when observed according to a Free Space method, measured at frequencies of 18 to 26.5 GHz and of 75 to 110 GHz.
8 . The composite according to claim 1 , wherein individual filaments of the carbon fiber filler have a length of from 5 to 10 mm.
9 . The composite according to claim 1 , wherein individual filaments of the carbon fiber filler have a length-to-diameter ratio of at least 500.
10 . The composite according to claim 1 , wherein the composite further comprises from 0.01 wt. % to 0.5 wt. % of a heat stabilizer.
11 . The composite according to claim 10 , wherein the heat stabilizer comprises phosphoric acid.
12 . The composite according to claim 1 , wherein the composite further comprises from 0.01 wt. % to 0.5 wt. % of an antioxidant.
13 . The composite according to claim 1 , wherein the composite is free of or substantially free of carbon nanotubes, carbon platelets, or carbon powder.
14 . The composite according to claim 1 , wherein a 3.175 mm molded sample of the composite exhibits a Percent Absorbed Power of at least 55% measured in Transmission mode of incident microwave radiation when observed according to a Free Space method, measured at frequencies of 75 to 110 GHz.
15 . The composite according to claim 14 , wherein the composite exhibits an un-notched Izod Impact strength at −30° C. of at least 500 J/m, and a notched Izod Impact strength at −30° C. of at least 45 J/m when measured according to ASTM D256.
16 . The composite according to claim 14 , wherein the composite exhibits an un-notched Izod Impact strength at 23° C. of at least 600 J/m, and a notched Izod Impact strength at 23° C. of at least 60 J/m when measured according to ASTM D256.
17 . The composite according to claim 14 , wherein the carbon fiber filler is present in an amount of between about 0.12 wt. % and about 0.98 wt. %, and wherein the Percent Absorbed Power measured in Transmission mode is at least 70% when observed at a frequency of 77 GHz.
18 . The composite according to claim 1 , wherein the poly(carbonate-siloxane) copolymer has a siloxane content of at least 5 wt. % based on the total weight of the poly(carbonate-siloxane) copolymer, and wherein the composite has a total siloxane content of between 1 wt. % and 15 wt. % based on the total weight of the composite.
19 . An article comprising the composite of claim 1 , wherein the article is an autoradar sensor for electromagnetic radiation.