Drying coating machines

The paste is coated on both sides of the aluminum metal thin foil by a coating machine. Normally, the thickness of the coated layer has a range of 50-80 tm. The coated foil is dried in a drier at about 150°C to vaporize the NMP solvent. 

Figure 10.15 Semi-automated continuous coating machine for catalyst coating. The procedure is demonstrated here using a microstructured metal foil unwound from a roll. The wash-coat slurry is fed through a slot die onto the metal foil. After coating, the foil is sent through a drying compartment, an infrared calciner (not shown here) and then wound up again (source IMM).

Coating machines are separate machines in which a previously produced dry base paper is unwound, coated, dried, and then reeled again (Fig. 7.24). In contrast to coating appHcators placed on-hne in a paper machine (Section 6.8), they are usually called off-hne coaters or OMC (off-machine coaters). 

As an aqueous dispersion can only dry above 0 °C, the MFFT and white-point temperature are only defined above this value. The control of the polymer layer thickness is crucial for the measurements. Mechanical stress may develop during film formation (particularly when crosslinking is involved) which leads to crack formation above a certain layer thickness. A further point which should be considered is that very short drying times are often used in dispersion processing, for example on coating machines. In this case, the MFFT may well he above the value determined according to ISO 2115. The discrepancy is caused by kinetic limitations in water evaporation and polymer interdiffusion [24]. 

In Europe the ingredients for secondary backing compounds are similar but the filler loads can vary from 0-450 parts per hundred part of dry latex. The configuration of the coating machines determines the compound to be used. On average the viscosity is 5 Pa s. 

Gas impingement from slots, orifices, and nozzles at 10—100 m/s velocities is used for drying sheets, films, coatings (qv), and thin slabs, and as a secondary heat source on dmm dryers and paper (qv) machine cans. The general relationship for convection heat transfer is (13,14) ... 

Paper may also be colored by surface appHcation of dyestuff solutions after the paper has been formed and dried or partially dried by utilizing size-press addition, calendar staining, or coating operations on the paper machine. In addition, paper may be colored in off-machine processes by dip dyeings or absorption of dyestuff solution and subsequent drying, such as for decorative crepe papers. 

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