Abstract: The present invention relates to a process for the production of at least two-layer thermoplastic foam sheets via thermal welding of at least two thinner thermoplastic foam sheets. In the process of the invention, at least two heating elements are conducted on mutually offset planes between the surfaces to be welded of the thinner thermoplastic foam sheets, and the foam sheets here do not touch the heating elements. The number of layers of the thermoplastic foam sheet is per se a result of the number of thinner thermoplastic foam sheets that are thermally welded to one another. If by way of example three thinner thermoplastic foam sheets are thermally welded to one another, a three-layer thermoplastic foam sheet is per se obtained, and if there are four thinner thermoplastic foam sheets the result is accordingly per se a four-layer thermoplastic foam sheet.

Abstract: The present invention relates to a process for the production of at least two-layer thermoplastic foam sheets via thermal welding of at least two thinner thermoplastic foam sheets. In the process of the invention, at least two heating elements are conducted on mutually offset planes between the surfaces to be welded of the thinner thermoplastic foam sheets, and the foam sheets here do not touch the heating elements. The number of layers of the thermoplastic foam sheet is per se a result of the number of thinner thermoplastic foam sheets that are thermally welded to one another. If by way of example three thinner thermoplastic foam sheets are thermally welded to one another, a three-layer thermoplastic foam sheet is per se obtained, and if there are four thinner thermoplastic foam sheets the result is accordingly per se a four-layer thermoplastic foam sheet.

Abstract: The invention is directed to extruded foam based on thermoplastic polymers. The foam contains at least one styrene copolymer which contains copolymerized maleic anhydride units or copolymerized maleimide units, and optionally styrene-acrylonitrile copolymers (SAN), and thermoplastic polymers and at least one halogen-containing polymer as flame retardant, and at least one flame retardant synergist selected from antimony trioxide and dicumyl. The invention also relates to a process for producing the foam with introducing carbon dioxide as blowing agent, and acetone as coblowing agent; into the polymer melt in order to form a foamable melt, and extruding the foamable melt into a region of relatively low pressure with foaming to give the extruded foam. The invention also relates to the use of said foam as insulation material and as structural foam.