troubleshooting tips
AR Expertise
Karlen McLean, ABOC, NCLC
Here, several experts provide answers to some of your recent questions about AR technology.
STACK FACTS
Q: How many coating layers are in a typical AR stack with today's premium coatings, and what are their specific functions?
A: The quality and performance level of an AR coating is determined by a number of components including the underlying hard coating, the AR optical stack (layers) and how they're applied, and the hydrophobic top layer. There's not one optimal combination, but instead various combinations that result in a high-performance AR coating.
The quality is more determined by how well matched each of these components are to the other and the lens substrate as opposed to their individual performance. The actual optical layers of a high-performance AR coating can be as few as four per side or as many as eight depending on the features one is trying to achieve, such as anti-static properties, index matching, residual color hue, or level of light transmission.
— Larry Clarke, president and CEO, Satisloh North America
BURNING QUESTION
Q: Can a hot air blower or a bead pan used for adjusting frames damage lens coatings like AR?
A: It's not recommended to use a hot air blower or bead pan on AR. With use, there's a thermal expansion of the lens that can exceed the thermal expansion of the AR, which can cause it to crack or break. Many times this cracking or breaking may not be visible because of the thinness of the actual AR. [Certain premium] AR technology is less likely to crack because of a flex layer between the lens substrate and the AR. Follow the rule of not exposing AR to a hot air blower or bead pan. If it's necessary to use them, be cautious with time and temperature.
— Bill Markham, technical marketing manager, Essilor of America
| ROUGH AND READY |
|---|
| Q: I've heard that lenses need to be ‘roughed up’ before AR coating is applied. What does that mean and why is it necessary?
A: Lenses need to be etched in order to ensure adhesion of the AR stack. This can be done chemically in an ultrasonic cleaning prior to the lens being coated or it can be done with an ion source in the AR coating chamber that will bombard the lens with a heavy element, usually argon. Again, this etching will rough up the lens' surface just enough to ensure maximum adhesion of the AR coating. The best way is typically by using a combination of both chemical and ion bombardment; that is what most premium AR stacks do to ensure durability. — Kevin Cross, director of sales, North America, Schneider Optical Machines |
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Email: Karlen.McLean@WoltersKluwer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business website at eyecarebusiness.com.
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