Abstract: An injection molding die for manufacturing a plastic frame on filter cassettes using edge-side plastic extrusion coating of the longitudinal sides of a zigzag-shaped, folded filter material, the die halves of the injection molding die being configured so as to engage each other in a tooth-like manner and forming a receiving space for the filter material and a molding space for the plastic frame, which are separated from each other by a clamping area formed by one of the tool teeth, in the clamping area (31) of the longitudinal sides (4) of the injection molding die (30), the gap dimension (7, 17) between the closed mold halves (1, 2) of the injection molding die (30) in the curved area (32) of the upper and/or lower fold flanks (9, 10) of the filter material (3) being smaller or greater than the gap dimension (8) of the fold flanks (11).