in fig1 the purpose of which is to remove excess impregnating liquor 16 a from the surface of the material web 12 and or uniformly distribute and or smooth the impregnating liquor 16 a applied to the material web 12 the present invention is not concerned with this partial aspect therefore a detailed description will also be dispensed with in this respect as indicated schematically in fig1 a cooling device 48 is provided in the bottom of the impregnating trough 26 the purpose of which is on the one hand to keep the impregnating liquor 16 a in the third trough section 22 at the desired temperature of approximately 30 u00b0 c but which in the event of a production shut down on the other hand is also used to cool the impregnating liquor 16 a further so as to increase its useful life to such an extent that after a resumption in production it can still be used without loss if necessary it is also possible to provide for this purpose an external cooling device 50 which recirculates and cools the impregnating liquor 16 a from the trough volume 26 a even in normal production operation the impregnating liquor 16 a is recirculated in fact it is removed from the trough volume 26 a via an outlet 52 and conveyed via a line 54 by a pump 56 to the microwave heating device 32 and via the inlet line 30 on to the inlet 34 into the first trough section 18 in this case the pump 56 and the microwave heating device 32 preferably operate under the control of a control unit 58 so that on the one hand it is ensured that the exact amount of impregnating liquor 16 a is always introduced into the first trough.