Process and system for producing multi-layer extrudate

DETAILED DESCRIPTION An object of the invention is to make available a coextrusion adapter with an adjustable slide, which can be adjusted without dismantling during the extrusion operation, depending on the unevenness of the extruded cover layer profile occurring in each case.
The above, and other, objects are achieved according to the present invention by a system for producing a multi-layer extrudate of thermoplastically processible plastic, comprising an extrusion adapter block having a main runner through which an extrudate may flow in a flow direction and at least one secondary runner connected to the main runner and through which another extrudate may flow for merger with the extrudate in the main runner to form a multi-layer extrudate.
Means are provided in the adapter block for regulating the thickness of an extrudate flowing through each of the secondary runners, comprising a multi-part slide comprising a plurality of side-by-side slide sections mutually spaced in a direction transverse to the flow direction and slidably fitted in the adapter block for movement to adjustably protrude into the secondary runner.
Control means are provided for separately controlling movement of at least some of the slide sections, the control means comprising at least two independently moveable control elements connected to the slide sections.
A die is provided through which the multi-layer extrudate is extruded, and measuring means are provided for selectably measuring the thickness of individual layers of the extruded multi-layer extrudate at a plurality of places distributed over the width thereof, as well as means for driving the control elements as a function of the thicknesses measured by the measuring means.
The thicknesses of the layers of extruded multi-layer extrudate can thus be controlled during the running operation of the system.
According to another feature of the invention, there is provided a process for producing a multi-layer extrudate of thermoplastically processable plastic, comprising the steps of feeding at least two melted thermoformable plastic extrudates to respective runners of an extrusion adaptor where the extrudates are merged to form a multi-layer extrudate, extruding the multi-layer extrudate through a die to form an extruded multi-layer extrudate, and sensing a thickness of at least one layer of the extruded multi-layer extrudate at a plurality of positions along the width of the extruded multi-layer extrudate during the extruding step