| || |
The starting point for freeform production is a semi-finished lens, also known as a puck due to its resemblance to an ice hockey puck. These are produced in a casting process that is also used to manufacture stock lenses. The semi-finished lenses are produced in a casting process. Here, liquid monomers are first poured into moulds. Various substances are added to the monomers, e.g. initiators and UV absorbers. The initiator triggers a chemical reaction that leads to hardening or "curing" of the lens, while the UV absorber increases the UV absorption of the lenses and prevents yellowing.
1). Low Weight: Lenses of hard resin have a gravity 1.31/cm3, almost half of that of standard crown glass.The low weight of the lenses give comfort for the spectacle wearers.
2). Safety: Lenses of hard resin have excellent impact resistance lenses with a centrethinkness of 2mm or more comply with the cen lens-strength norm and the FDA balldrop test norm.
3). Optical Quality: Lenses of hard resin have a very high light transmission(among the highest for optical plastics). The Abbe number is high(57) CR-39 monomer gives a sharp defined image for plastic lens wearers.
4). Special Lens Treatment: Monomer allow for special treatment such as rimless frames, color tinting for style or sunglass. UV-protection and photochromic.
5). Lens Curve Stailing: The impact resistance of CR-39 monomer gives plastic lenses the strength to sustain stable curve design.