A one-piece keyboard housing in a simple but compact manner is provided by using an internal gas pressure injection molding process. The device further includes a support the lower segment of which has a compression chamber cooperating with the extension of the back of case, this extension being able to move axially, and in air-tight fashion, in this chamber. The laptops further include a hinged cover. The carbon-containing layer constitutes a second surface portion formed so as to extend outward from the first surface portion. To gain access to the feed pipe for cleaning during material change, the compaction cylinder is coupled to the compaction ram to form a structural unit which can be raised upwards.