Printable View
I just talked to a lady from another lab who was told by a rep that some types of anti glare on certain lenses are considered to be voiding safety rated lenses? I'm not 100% on what types she is talking about as this is the first I have heard of it. Seams like nonsense to me though, an AR coat will do nothing to the integrity of a lens material. Anyone else hear about this mumbo jumbo?
By anti glare are you referring to polarization;which addresses glare or are you referring to anti reflection; which addresses reflections. If you are referring to AR, then yes she is correct in that the AR application with make the lens more brittle. As to voiding a safety warranty that might depend upon the specifics as to the circumstances of it's intended use and the work environment.
Paul Smith is correct.
In the US, If you're talking about safety protectors per ANSI Z87.1, and if your lab is properly complying with the drop ball testing requirements, there should be no worry. Your lab should have tested all material/coating combinations per the applicable performance standard.
Some AR coats also use a primer layer that acts as a cushion coat, that actually improves impact resistance.
Do a search on this board you'll find an great explanation and a graphical example of the science behind the forces where arc reduces the impact resistance.
Just like RT mentioned even with arc on a lens the safety standard does not dictate anything about coatings, just pass the drop ball and the lens is good. It may mean that a lens with arc needs a slight bump in thickness, but that bump is going to be negligable. The effect of a primer layer acts as an absorber to the compression that happens on impact and reduces the tension exerted on the back of the lens.
Another issue can be that a workers employer may place certain restrictions on the safety eyewear. I engaged exclusively in providing on-site safety eyewear for six years and found many employers did not allow metal frames or photochromic lenses or progressive lenses or any lenses with and tint in their facility. I had two accounts which required only glass lenses.
I found out early on not to argue with the plant safety engineer, industrial hygienist or whoever it was that was establishing these policies. They all had their reasons and they were the ones paying the bills.
Trivex is denser and has a higher tensile strength then poly. Would an AR coat really compromise the lens integrity?Quote:
Originally Posted by Paul Smith LDO
Safety lenses are produced in all materials, an AR application will make a lens more brittle. As Dick pointed out some occupations/companies along with the Federal Gov. have very explicit demands and requirements for their employees depending on the type of work that is done. Some occupations require glass lenses whilst others require impact resistant frame and lens materials. This is why we get paid the big bucks, we have to do our research and find out if there are any possible workplace restrictions for safety eyewear.Quote:
Originally Posted by chaoticneutral
Thanks everyone for the good input, and yes I was referring to Anti Reflective coatings. I had no idea that the process can make the lens brittle. I am guessing it apply mostly to CR39? Or would it make a poly or Trivex material brittle as well?
This will depend on the base material, the hard coat, and its reaction to the ionization of the AR process (assuming an inonized and not sputter AR machine) and degassing. Although AR process can make a lens brittle (esp degassing at 1.0 CT), the ionization combined with right hard coat can actually make many materials and lens combo's stronger.
This is one reason I never recommend 1.0 CT anymore, the lenses are damaged by degassing.
Quote:
Originally Posted by Paul Smith LDO
Define "hard" versus "brittle" The harder the material the more brittle it tends to be. By brittle; I mean that is is hard enough not to fail through plasticity but due to cracking.Quote:
Originally Posted by sharpstick777
Just do a drop ball test and you will find out.
The drop ball test is the gold standard. You can fabricate a lens out of anything and tint or coat it with anything and as long as it passes the appropriate drop ball test it is legal to dispense.
Hard and Brittle are sometimes linked, but not always.