2.3.2 The components of optical discs and their stability

The polycarbonate used for optical disc bodies is a transparent polymer with a low thermal expansion factor. It is resistant against deformation by heat at temperatures of up to 130°C. Early discs, especially LV discs, sometime had problems with crazing which made the polymer opaque and unreadable. From experience gained since the introduction of CDs in 1982, it can be expected that modern polycarbonate discs will be stable for several decades.

Apart from gold, all of the metals used to provide the reflective layers are prone to oxidation. Therefore, the protective lacquer layer of CDs plays an important role. It must be resistant against penetration of humidity, a function that often did not work properly with early CDs. Oxidised reflective layers, particularly aluminium, render optical discs unreadable.

The stability of the adhesive that keeps the two polycarbonate parts of a DVD or a BD together is unknown.

The stability of the dyes used in recordable CDs, DVDs and BDs is a factor of great uncertainty. There are three different dyes in use: cyanine, phthalo-cyanine, and azo. All dyes are susceptible to light, specifically uv radiation: an exposure of recordable discs to daylight will render them unreadable within a few weeks. Another uncertainty factor is the decrease in the amount of dye used for discs designed to run at higher recording speeds.

The life expectancy of dyes is often quoted to be between 5 and 100 years, an item of information that is of little practical use. The stability of the semi-transparent layers of DVDRs and BDs is unknown. Finally, the stability of rewritable discs is also unknown, and their potential life expectancy as compared to dye discs is unclear.