Anti-reflection coatings can be used for stray light control or to achieve maximum working range, and can be applied to the inside and/or outside of the window to reduce the amount of light reflected off the window back into the engine. However, they are expensive and have very poor abrasion and scratch resistance.
Polysiloxane Coating
Polysiloxane type coatings are applied to plastic surfaces to improve the surface resistance to both scratch and abrasion. To apply, dip and air dry in an oven with filtered hot air.
To gauge a window's durability, use ASTM standard D1044, Standard Test Method for Resistance of Transparent Plastics to Surface Abrasion (the Taber Test), which quantifies abrasion resistance as a percent increase in haze after a specified number of cycles and load. Lower values of the increase in haze correspond to better abrasion and scratch resistance. See the following table.
Taber Test Results on Common Exit Window Materials
Sample
Haze 100 cycles
Haze 500 cycles
Abrasion Resistance
Chemically Tempered Glass
1.20%
1.50%
Optimal
PMMA with Polysiloxane Hardcoat
3%
10%
ADC
5%
30%
PMMA
30%
Worst
All measurements use a 100-gram load and CS-10F Abraser.
