Optical discs with cover sheets and dynamic pressure stabilization of the enclosed air

An optical disc having a substrate in which data can be written on or read from, said optical disc being adapted to be inserted and clamped onto a spindle in a disc drive and having first and second transparent cover sheets disposed over upper and lower surfaces of the substrate, respectively, comprising:

• a) said optical disc having a perimeter ring on an edge thereof and first and second spacers formed adjacent to a central opening in the optical disc;
• b) said first and second transparent cover sheets spaced from the upper and lower surfaces of the substrate, respectively, the perimeter ring includes a plurality of upper and lower air passages, respectively formed in upper and lower portions of the perimeter ring, that respectively lead from upper and lower spaces, respectively located between the first transparent cover sheet and the upper surface of the substrate and between the second transparent cover sheet and the lower surface of the substrate, to the outside atmosphere, and the first and second spacers being formed with a plurality of air passages leading from the outside atmosphere to the upper and lower spaces, respectively;
• c) filters provided across the air passages in the first and second spacer and the perimeter ring to prevent contaminants from the atmosphere from entering into the upper and lower spaces;
• and
• d) whereby the first and second transparent cover sheets are prevented from deflecting due to pressure differences between the outside atmosphere and the air in the upper and lower spaces by permitting a continuous flow of air through the air passages in the first and second spacers to the upper and lower spaces and out through the upper and lower air passages in the perimeter ring to the outside atmosphere when the optical disc is rotated.