Process for producing a syntactically foamed polymer composition, preferably a pressure-sensitive adhesive composition, apparatus for carrying out the process, extrudate and self-adhesive tape

Process for producing a syntactically foamed polymer composition, where

• a) at least a majority of closed foam voids are achieved by introduction of expandable microspheres into a matrix material and subsequent mixing in a mixing machine (1) and
• b) the expansion of the expandable microspheres is carried out after they have been introduced into the matrix material,
• c) where the temperature distribution in the mixing machine (1) is inhomogeneous in a plane perpendicular to a transport direction of this machine (1),
• wherein
• d) a first surface (3) bounding a mixing space (2) of the mixing machine (1) is, in a plane perpendicular to a transport direction of the mixing machine (1), maintained at a temperature which is sufficiently high for the polymer composition containing the microspheres, insofar as it comes into contact with this first bounding surface (3), to reach a temperature Te which is the minimum temperature that allows for commencement and continuation of expansion,
• e) while in the same plane perpendicular to a transport direction of the mixing machine (1), a second surface (4) bounding the mixing space (2) of the mixing machine (1) is maintained at a temperature which is sufficiently low for polymer composition present in the microspheres, insofar as it comes into contact with this second bounding surface (4), not to reach a temperature Te which is the minimum temperature that allows for commencement and continuation of expansion.