Sabic Innovative Plastics is testing six optical-quality grades of its Noryl compound as a potential replacement for polycarbonate in Blu-ray discs.
“Noryl has some advantages because it doesn’t absorb moisture like polycarbonate, and it’s more dimensionally stable,” says Greg Harley, an engineer at Sabic’s Polymer Processing and Development Center in Pittsfield, MA. Noryl is an alloy of polyphenylene oxide (PPO) and polystyrene.
Blu-ray, a very high-capacity storage format, offers opportunities for new materials because it uses a violet laser to read and write data. Conventional DVDs and CDs use red and near-infrared lasers. The Blu-ray data layer is closer to the surface, making it susceptible to scratches, but also creating a wider array of materials choices for the disc.
“With DVDs, the laser is reading through a substrate, so the material has to be transparent,” says Harley. “You can use an opaque material, or any color you want, with a Blu-ray disc.” The cover layer in DVDs typically consists of expensive solvent-casted polycarbonate film that is about 100 microns thick and is bonded with an adhesive to the substrate.
Noryl offers the opportunity to reduce costs for discs. For example, Noryl will not require a moisture-barrier layer and lacquer coating as required for polycarbonate. Because of its superior dimensional stability, a less complicated molding process leads to a higher yield rate.
Another aspect of the technical research at Sabic is development of an improved coating. The new Sabic material is said to combine functionality in one coating, eliminating extra processing steps.
The race to develop improved Blu-ray materials is accelerating because Toshiba has quit development of a competing high-capacity format, called HD DVD.
Watch a video of the Sabic Blu-ray lab in Pittsfield, MA.