Method for producing flame-proofed thermoplastic molding compounds

A process for the preparation of thermoplastic molding materials comprising:

• A) from 40 to 99% by weight of at least one thermoplastic polymer,
• B) from 1 to 60% by weight of a flameproofing component comprising
• B1) an expandable graphite, and
• C) from 0 to 60% by weight of further additives,
• the percentages by weight being based in each case on the total weight of the components A) to C) and together giving 100% by weight,
• by mixing melts of the components A), B) and, if present, C) in a screw extruder, the screw extruder comprising at least one metering zone, one plasticating zone, one homogenization zone, one second metering zone and one discharge zone in this sequence along the conveying direction,
• wherein the metering into the screw extruder having the length L, the length L being defined as the section beginning at the first metering means for the addition of components A, B and/or C and ending, in the conveying direction, at the exit opening, following addition of components A, B and C in the region from 0 L to 0.15 L in a first process step in the absence of component B1) a melt is produced, and in a second process step after addition of the component B1) in the region from 0.5 L to 0.95 L the mixing of component B1) into this melt is carried out.