Since our AR chemistries rely heavily on nanoparticles to give them toughness and the right optical properties, they require a little more care than our other materials. To figure out how long they last we did long-term testing here at high, low, and room temperatures. We also thought about what they’d go through in normal storage and shipping. If you use your AR chemistry by the expiration date we expect your lenses to perform just as ours do here. If it’s past the expiration date or was stored incorrectly things aren’t as predictable.
Spending a long time at extreme temperatures or even just sitting around will eventually cause the nanoparticles to stick together. Once that happens their properties change and so do the coatings that are made with them. Expired chemistry can give you hazy coatings or ones that aren’t nearly as tough as they should be. It can also clog up the dispense filters in your nanoCLEAR unit or cause other coating defects like comets.
If we didn’t have to have an expiration date we wouldn’t use one. At this time nanoparticle-based liquid chemistries of all kinds just tend to have shorter shelf lives than those without them. If we figure out a way around it, you can bet we’ll use it. For now though, the expiration date is something we need.