Filter manufacturing process and apparatus

The invention relates to a filter manufacturing method and a filter manufacturing device (1) comprising a device (31a-31e) for applying plasticizer (26a-26e) on the filter material (3, 3a-3e), and a filter material conveying device (2, 9, 11, 28). The filter manufacturing method according to the invention comprises the following process steps: - providing a web (3, 3a-3e) of filter material (3, 3a-3e) - applying a softening agent (26a-26e) to the filter material (3, 3a-3e) - forming a strand (32) from the filter material (3, 3a-3e) - separating filters (34) of the strand (32), wherein a at least in the conveying direction (40) of the filter material (3, 3a-3e) on the concentration of the plasticizer (26a-26e) abhangendes signal is generated locally resolved and wherein filters ( 34) with filter material (3, 3a-3e) for which a signal has been generated below a first predefinable threshold value or above a second predetermined threshold value, are discarded. The filter manufacturing apparatus according to the invention is characterized in that a measuring device (36a, 36b, 37, 38a, 38b) (for generating a signal indicative of a at least in the conveying direction (40) of the filter material (3, 3a-3e) spatially resolved Concentration of the plasticizer 25a -26e) (in the filter material 3, 3a-3e) represents.