Coextrusion apparatus, single-layer extrusion apparatus and retrofit kit as well as a method for measuring a layer thickness, for producing a plastic film, and for retrofitting an extrusion apparatus

A coextrusion apparatus for producing a plastic film composite having multiple layers, each having a layer thickness, comprising:

• a first extruder configured for plasticizing a first starting material,
• a second extruder configured for plasticizing a second starting material,
• a coextrusion block, and
• a feed from the extruders to the coextrusion block,
• a detection device disposed in the coextrusion block and/or beyond it, in the machine direction, and being configured for undertaking a measurement of a layer thickness;
• wherein the coextrusion apparatus is set up for producing a film composite having two layers of the same starting material,
• wherein the detection device is set up for undertaking measurement of multiple layer thicknesses, and
• wherein a controller is provided that is data-connected with the detection device, and is actively connected with a layer thickness influencing means, wherein the controller is set up for carrying out regulation by means of the layer thickness influencing means, using a reference value for a layer thickness.

A single-layer extrusion apparatus for producing a plastic film having a layer thickness, comprising:

• an extruder configured for plasticizing a starting material;
• an extrusion tool;
• a feed from the extruder to the extrusion tool;
• a detection agent addition device configured for adding a detection agent for introduction into the plastic film;
• and
• a detection device provided in the coextrusion block and/or beyond it, and beyond the extruder in the machine direction, and being configured for undertaking a measurement of a layer thickness on the basis of detected detection agent.