A slot die apparatus for the coextrusion of an endless sheet having a thickness of about 0.1-5 mm with an optionally dyed edge strip made from a narrower, optionally colored, melt stream of a width of about 100-500 mm and from a broader melt stream of a width of about 1,000-3,000 mm of a thermoplastic synthetic resin is provided by means of two parallel-operating extruders and associated melt pumps, with merging of the two melt streams. The apparatus is also provided by flanging together, by means of a flange, two dies at their end faces, these dies having identical cross sections and a corresponding width, comprising a spreader block, deckle, bottom lip, and top lip, and a flow channel made up from these components.