The effect of multiple antireflective coatings and center thickness on resistance of polycarbonate spectacle lenses to penetration by pointed missiles.
OBJECTIVE
Previous work has shown that the impact resistance to blunt missiles is affected by coatings applied to either CR-39 or polycarbonate lenses. We investigated the effects of multiple antireflection (minimum angle of resolution [MAR]) coatings on the resistance of polycarbonate lenses to puncture on impact by sharp, high-speed missiles.


METHODS
Four groups of surfaced plano polycarbonate lenses were investigated. Two groups had a scratch-resistant (SR) coating applied to both surfaces. One of these groups had a 2-mm center thickness and the other had a 3-mm center thickness. The other two groups of 2-mm and 3-mm thick lenses had a MAR coating applied over the SR coating. The lenses were impacted by a missile consisting of an industrial sewing machine needle mounted in a cylindrical aluminum carrier.


RESULTS
The sharp missiles were able to pierce the lenses at speeds between 29.6 m/s and 46.2 m/s. Impact resistance was lowest for the thinner lenses and lenses with a MAR coating. The effect of the MAR and lens thickness was subadditive.


CONCLUSIONS
We have confirmed previous observations that polycarbonate lenses are more susceptible to penetration by sharp, high-speed missiles than blunt missiles. We have also found that reducing lens center thickness and applying a MAR coating further reduces the penetration resistance. Therefore, the use of 2-mm center thickness and MAR-coated polycarbonate lenses should be discouraged for industrial eye protectors where sharp missile hazards are possible.
Chou
B Ralph
BR
School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. bchou@uwaterloo.ca
Gupta
Alina
A
Hovis
Jeffery K
JK
D020099:Coated Materials, Biocompatible; D004869:Equipment Safety; D005131:Eye Injuries / Q000517:prevention & control; D005135:Eye Protective Devices; D005139:Eyeglasses / Q000592:standards*; D006801:Humans; D008422:Materials Testing / Q000379:methods*; D011076:Polycarboxylate Cement
D020099:Coated Materials, Biocompatible; D011076:Polycarboxylate Cement; C005506:polycarbonate