Method for regulatiing the individual layer thicknesses of a coextruded multilayer plastic web

A method for regulating the individual thickness of several layers of a multilayer plastic web produced by coextrusion wherein at least two molten plastic currents are melted separately in one or different extruders and the individual molten currents are brought together in an adapter and superimposed on one another layerwise to form a multilayer stream, the multilayer stream thus formed is fed to a slot die to form the multilayer plastic web, and the flow of the individual molten currents is controlled immediately before the merger of the molten currents in the adapter by changing the flow cross sections of the currents in order to influence both the thickness distribution of a layer formed by each molten current and laid on the multilayer stream when the currents are brought together, as well as the flow rate, which comprises measuring layer thicknesses of individual layers of the multilayer stream corresponding to the various molten currents before the multilayer stream emerges from the slot die;

• evaluating and digitizing resultant measurement data to provide measurement signals;
• comparing values of the measurement signals with digitized predetermined set values for thicknesses of the individual layers;
• and, in the event of deviations in the comparison of the set values versus the actual measured values of the thicknesses of the layers, the resulting deviations are used to change the flow cross sections of the individual molten currents immediately before the molten currents are brought together in the adapter to form the multilayer stream.