The present invention relates to a method and apparatus for use in making stampers used for molding recorded discs. More particularly, the present invention relates to a method and apparatus for separating the stamper from its mold on which it is formed.
Recorded discs are generally formed in a molding apparatus which includes a pair of opposed platens having opposed surfaces which are adapted to form therebetween a mold cavity. At least one of the platens is adapted to move toward and away from the other platen to open and close the mold cavity. On the opposed surface of each mold plate is a separate stamper. Each stamper is a thin sheet of metal, about 0.008 in. (0.2 mm) in thickness, having a surface relief pattern on one surface which is the negative of the information to be formed on the recorded disc. The stampers generally have an opening in the center thereof and are secured to their respective mold plates by a clamping ring around the outer edge of the stamper and a center hold down plate extending through the opening through the stamper and engaging the edge of the center opening in the stamper.
The stampers are generally made by coating a mold, such as by electroplating, with the metal of the stamper until a sheet of the desired thickness is formed. The mold is also a thin metal plate, about 0.019 in. (0.475 mm) in thickness, having on a surface thereof the positive of the surface relief pattern to be formed on the recorded disc. The stamper is electroformed on that one surface of the mold so that the surface relief pattern is formed on the stamper. After the stamper is electroformed on the mold, it must be separated therefrom. Great care must be used to separate the stamper from the mold so as not to damage the surface relief pattern on the surface of either the stamper or the mold. This separation problem is even greater in making stampers for high density recorded discs, such as video discs, because of the high density and fine dimensions of the surface relief pattern on the surface of the stamper. Therefore, it would be desirable to have a method and apparatus which can easily separate the stamper from its mold without damaging either.