Keywords: hydrophobic coating, radome coating, rain attenuation,
rain fade, signal loss, super hydrophobic, improved satellite reception,
Fluorothane.
Note: See Fluorothane
for hydrophobic and super-hydrophobic aircraft, marine and ground radome
coatings. See FluoroPel
for fluoropolymers and FluoroSyl
for flluorosilanes.
UV-Heavy Rain Test for Fluorothane ME and MS Top-Coated SMC Panels and
Reflectors
Description: The UV-Heavy Rain test involves exposing a coated substrate
to ten years of simulated equitorial sunlight followed by 2000 inches of
continuous heavy rain at 10 inches per hour. Evaluation is based on drop
roll-off angle and any physical deterioration of the Fluorothane ME or MS
top coat.
Substrate: SMC panels and SMC Reflectors were painted with white
acrylic paint and allowed to cure. The panels were then spray painted with
Fluorothane ME or MS using gravity feed HVLP spray equipment. Dynamic pressure
was 35 psi, feed was 2, and fan out was set to full width (1/3 turn). HVLP
gun was held 6 inches from substrate, moved at 6 inches per second, with
10% overlap. Reflectors were spray coated with Fluorothane ME or MS using
automated HVLP equipment employing similar parameters. The coated substrates
were allowed to cure at least 48 hours. Drop roll-off angles at 20 locations
on the panel were less than 2 degrees, corresponding to receding contact
angles of 140 to 170 degrees. Reflectors were then cut into sections for
this and other testing.
After curing, one corner of the panels and reflector sections were then
cross-scored with a razor blade through the coating and acrylic paint every
half inch in a 4 inch square pattern. A two inch band along an opposite
edge was also abraided by placing a 2 inch diameter one pound weight on
a paper towel and dragging it across the panel adjacent the edge. Drop roll-off
angles at 5 locations on the abraded area were still less than 2 degrees.
UV-Rain Challenge: The Fluorothane ME and MS coated panels and reflectors
were placed serially in a chamber 8 inches from the focal point of a 400
watt unshielded Hg lamp and aluminum parabolic reflector for 2 hours. The
chamber was air cooled to 140°F. UV exposure in the 280 to 380 nanometer
range during this period was equivalent to 10 years of equitorial sun. The
strong odor of ozone was present near the chamber, but quantitative measurements
were not taken.
The UV exposed Fluorothane ME and MS coated substrates were then placed
at about 45 degrees to a flux of simulated rain at ten inches per hour for
a total of 2000 inches of rain. The simulated rain was produced by jetting
75 psi tap water through a laminar flow molded 1 mm by 5 mm orifice against
a plastic target at about 45 degrees incidence. The resulting spray has
size distribution and velocity parameters similar to very heavy rain in
gusting wind.
Evaluation: Visual inspection indicated no cracking, peeling, blistering
or delamination. The substrates were placed on a variable incline, and 50
microliter drops of water were dispensed from one centimeter above the surface
at 20 locations. The drop roll off angle is the minimum angle from horizontal
where a drop will move at least 3 inches from the drop point.
Drop roll-off angles taken immediately before any period of drying over
20 locations per substrate were all 2 degrees in the non-abraded areas,
indicating advancing and receding contact angles greater than 140 degrees.
Drop roll of angles in the abraded areas were 10 to 15 degrees.
Conclusion: On acrylic painted SMC panels and reflectors Fluorothane
ME and MS showed complete resistance to 280 to 380 nm UV exposure that could
be expected during 10 years at equitorial installations. The drop roll off
angles in the abrasion areas were no better or worse than those observed
using fresh panels that had not been challenged by UV. Scored areas and
unabraded areas showed no evidence of erosion or water penetration.
Cytonix Corporation
8000 Virginia Manor Road
Beltsville, MD 20705
phone: (888) CYTONIX or (301) 470-6267
fax: (301) 470-6269 or email: emailbox@cytonix.com
