Motorola SE4750, Integration Manual

Page: 27 / 86

Installation 2 - 9
Commercially Available Coatings
Anti-Reflection Coatings
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 can be 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
Table 2-2 .
A Word About Coatings
If using an anti-reflective (AR) coating, the specifications in Table 2-3 apply. When using anti-reflection coating, the
application of additional hard-coating is not recommended. Recess the exit window to minimize scratches and
digs.
Table 2-2
Taber Test Results on Common Exit Window Materials
Sample
Haze 100
cycles
Haze 500
cycles
Abrasion
Resistance
Chemically Tempered Glass 1.20% 1.50% Best
PMMA with Polysiloxane Hardcoat 3% 10%
ADC 5% 30%
PMMA 30% Worst
* All measurements use a 100 gram load and CS-10F Abraser.
Table 2-3
AR Coatings Specifications
Specification Description
Material Both tempered glass and plastic (e.g., CR-39 or hard coated acrylic) exit
windows can be AR coated. Glass is easier to AR coat and more durable due
to better adhesion properties to the glass structure. In addition, it can be more
cost effective to put an AR coating on the glass substrate rather than on the
plastic.
AR Coating Specification •
Single side AR-coating: 92% minimum transmittance within spectrum
range from 420 nm to 730 nm.
•
Double side AR-coating: 97% minimum transmittance within spectrum
range from 420 nm to 730 nm.
•
See Figure 2-9 on page 2-14 for coating reflectivity requirements.