psk@ccice6.UUCP (Paul S. Kopel) (10/11/85)
The reflective, information carrying surface of a CD is covered by a "protective layer" of transparent material through which the scanning beam must pass. Presumably, significant changes over time in the physical and optical properties of the protective layer wil affect a CD's reproducibility (i.e., it may crack, peel, change color, become translucent or opaque, etc.). I am unaware of any discussion of this matter. Should it be a concern, considering the cost of CD's and the claims of CD indestructibility? (If it has been discussed, can someone cite a reference?) Perhaps there are folks on the net with sufficient interest and background in materials/organic chemistry (or friends with same) to address the following: What is the material used for the protective coating; how do its physical and optical properties change over time in a "normal" environment? Are there (non-obvious) storage conditions which would hasten deterioration, either physical or optical? Are there methods of storage which would best prevent possible deterioration?
ark@alice.UucP (Andrew Koenig) (10/15/85)
> What is the material used for the protective coating; > how do its physical and optical properties change over > time in a "normal" environment? > Are there (non-obvious) storage conditions which > would hasten deterioration, either physical or optical? > Are there methods of storage which would best prevent > possible deterioration? I think they use polycarbonate plastic. This is the stuff that is used, among other things, for windshields of light airplanes and food processor work bowls. It is one of the toughest plastics around at any reasonable cost and should last a very long time indeed. The only thing I would think might cause trouble over the long term is UV radiation. In other words, don't leave them out in the sun.