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Surface Treatments
There are various kinds of surface treatments that are applied on either
side of the spectacle lenses. In addition to anti-reflection coating which has
already been discussed separately, many other types of surface treatments
are done to enhance optical and / or physical properties of the lens. Optical
properties can be enhanced by tinting, UV coating and mirror coating and
the physical enhancements can be achieved by hard coating, hydrophobic
coating, anti mist coating, anti fog coating and toughening.
HARD COATING
Resin lenses are basically from two families of plastics—thermosetting
materials and thermoplastic materials. A thermosetting material is created
in a mould by chemical reaction, the cross linking of molecules is very
strong to form a rigid structure, and if they are subsequently heated will
not soften. CR and most other high index resin lenses used for spectacle
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Fig. 13.1: Different layers of coating on a lens