Stretched surface recording disk substrate

Claim 1

A stretched surface recording disk including an annular substrate and an annular or circular film stretched across at least one of the major surfaces of said substrate and adhesively secured thereto, said substrate comprising: a raised annular first ridge adjacent the outer periphery of said substrate, said first ridge projecting above said major surface to define a reference surface upon which said film is supported above said major surface and including a radially outward edge defining a fulcrum around which said film may be drawn downwardly toward said major surface to tension said film; a raised, annular second ridge adjacent the inner diameter of said substrate, said second ridge projecting above said major surface a distance equal to the projection of said first ridge to define a reference surface upon which said film is supported above and parallel to said major surface and including a radially inward edge defining a fulcrum around which said film is drawn downwardly toward said major surface to tension said film; an annular outer film attachment surface located radially outward of said first ridge and sloping from a point adjacent said first ridge fulcrum and intermediate said major surface and said first ridge fulcrum outwardly and downwardly toward the plane of said major surface; an annular inner film attachment surface radially inward of said second ridge fulcrum and curved radially inwardly and downwardly toward said major surface from a point adjacent said second ridge fulcrum and intermediate said second ridge fulcrum and said major surface, said inner film attachment surface having a radius equal to or less than the radius of the contour assumed by said film as said film is drawn around said second ridge fulcrum toward said major surface; and adhesive disposed on said inner and outer film attachment surfaces for securing said film to said substrate.