Lyophilization stopper (case II)

Lyophilization stopper made of a rubber elastic material and composed of a shank intended for insertion into the container neck to be sealed and of an essentially circular disc shaped flange which is made in one piece with the shank and projects radially beyond it, with the longitudinal axis of the flange being congruent with the longitudinal axis of the shank;

• the shank includes a cavity which surrounds the longitudinal axis of the shank, is open toward the free end face of the shank and extends up to a centrally closed wall portion of the flange;
• over its axial length, the shank includes a first section which extends between a first transverse plane defined by the boundary face of the flange projecting radially outwardly from the shank and a second transverse plane perpendicular to the longitudinal axis of the shank;
• this first section has a closed outer circumferential face whose maximum diameter is slightly larger than the inner diameter of the container neck;
• following the first section, the shank has a second section having an outer enveloping face which has essentially the same diameter as the first section and includes at least one passage communicating with a cavity extending from the end face of the shank to a radial opening disposed in the second section adjacent the second transverse plane;
• a plurality of blocking elements, which can be pushed back by elastic deformation, project outwardly from the second section beyond the enveloping face, with their axially outer boundaries lying on a common third transverse plane perpendicular to the longitudinal axis of the shank and disposed between the second transverse plane and the free end face of the shank perpendicularly to the longitudinal axis of the shank, characterized in that
• the inner wall face (19) laterally defining the cavity (4) lies entirely outside a cone (K) whose axis is the longitudinal axis (A) of the shank, whose tip (K.sub.1) lies in the first transverse plane (Q.sub.1) and whose tip angle (.beta.), in degrees, is larger than a value calculated according to the formula
• -39+75.times.lg (D),
• where "lg" in the formula represents the decimal logarithm and "D" the maximum diameter (D), measured in millimeters, of the first section (Z.sub.1) of the shank (1).