Method and apparatus for the production of thermoplastic caprolactam containing molding compositions

Method for the production of thermoplastic caprolactam containing molding compositions comprising hydrolytically polymerizing caprolactam in a plurality of parallel autocalves at pressures of up to 20 bar and temperatures of 220.degree. to 280.degree. C. in the presence of water and a weak acid to form a crude polycaprolactam containing molten mass, alternatingly feeding the molten mass from one or another of the autoclaves to a vessel under vacuum and therein continuing the polymerization and removing from the molten mass as vapor volatile components including water and monomeric and oligomeric caprolactam, then feeding the molten mass from the vessel under vacuum to a multi-screw extruder having a barrel segmented into sequential zones, independently heating and applying vacuum to the zones to advance the polymerization to the desired degree and to lower the monomer and oligomer contents of the molten mass by removing excesses thereof as vapor, feeding molding composition modifying ingredients selected from the group consisting of lubricants, heat stabilizers, pigments, fillers, reinforcing agents, plasticizers and elasticizers into the molten mass in the extruder, in a zone downstream from the feeding of the molding composition modifying ingredients and adjacent the discharge end of the extruder further heating and applying vacuum to lower further the monomer and oligomer contents of the molten mass by removing the residual excesses thereof as vapor, extruding the molten mass at the discharge end of the extruder and quenching the extrudate to solidify it.