PEI Gives Eyewear Frames Lightweight Metallic Look

While style in eyewear frames is always in demand, the comfort level is also key. Nearly 30-yr-old Chinese company Zhengda Optical, has found that it can produce lightweight spectacle frames with novel decorative effects using Ultem PEI from SABIC. The combination of excellent mechanical, thermal and chemical properties is a significant consideration, but Ultem PEI can also be metallized to produce highly attractive designs.

Says Zhengda Optical’s CEP Xia Guangnian, “Spectacle frames made partly or all in metal are very popular with our customers. Being able to offer them frames in Ultem resin that have a metal look, but which are lighter and have design features that are difficult and much more expensive to achieve in solid metal, provides us with a considerable advantage in a very competitive global market.”

Zhengda Optical treats the frames using a PVD (Physical Vapor Deposition) process that applies a very thin layer of metal onto their surface at a temperature of around 150C/302F. This way, Zhengda Optical can combine the design flexibility offered by injection molding—both in terms of shapes and surface textures that can be achieved—with the metal look. Adds Guangnian, “Ultem resin’s resistance to high temperatures enables it to resist the PVD process very easily and the metal also bonds very well to the resin. The metal effects that we can obtain this way are really very impressive. On top of this, the combination of the resin’s high strength and very good flow properties means that we can make high-performance frames that are thin and light, which makes them very comfortable to wear.”

To obtain the same look with solid metal would most likely require the use of extensive and expensive machining, which would result in frames noticeably heavier than the version made of Ultem PEI, which boasts a density of 1.27 g/cm³—at least six times less than that of steel. The resin’s good mechanical properties and high-flow characteristics mean that Zhengda Optical can make its frames with walls as thin as 1.2 mm/0.047 in. A pair of spectacle frames will typically weigh just 7-8 g (0.24-0.28 oz)—around half that of a comparable pair in steel—making them particularly comfortable to wear.