CD for listening to music is a kind of compact disc, and VCD and DVD for watching video are also a kind of compact disc. The recording surface of almost all discs is shiny. Why?
First, let's understand the structure and composition of the CD. Common CD, VCD and DVD discs are very thin, only about 1.2mm thick, but they include complex structures, which are mainly divided into five layers: substrate, recording layer, reflection layer, protective layer, printing layer, etc.
The substrate is the carrier of various functional structures (such as grooves) of the optical disc, and the materials used are polycarbonate, polymethylmethacrylate and other polymer materials (plastics). It has good impact resistance and toughness, wide temperature range and no toxicity.
The recording layer is the place where the signal is recorded, that is, a special organic dye is coated on the substrate for laser recording information.
The reflective layer is the third layer of the optical disc. It is the area that reflects the laser beam. The data in the optical disc can be read by the reflected laser beam. Its material is pure silver, pure aluminum and other metals. Its function is like a mirror. When the laser beam comes up, it will be reflected back, and the information on the recording layer will be brought out at the same time. Because of this reflective layer, the recording surface of the disc looks shiny. Therefore, we can use the discarded CD to replace the mirror, and some people use it to make desk lamps and reflectors.
The function of the protective layer is to protect the reflective layer and dye layer in the optical disc and prevent the signal from being damaged. The material of the layer is polyacrylic acid polymer. The printing layer is located on the back of the disc and printed with the customer identification, capacity and other relevant information of the disc. At the same time, it can also play a certain role in protecting the disc.