15 June 2010 – Simultaneous coating is always applied when flexible carrier material should be coated on both front and back side, whether with similar or different coating weights. However, the better-known processes such as pan-fed gravure rollers, kiss-roll coating with nip dosing, double-sided wire doctor blade systems or four-roller coaters all hold some risk. Problems such as solvent evaporation and foam development must be reckoned with, and production rates are limited.
Kroenert solved this problem as far back as 1996 with the development of chamber doctor blade coating for gravure roller technology. Since then the process has been under constant further development.
The simultaneous coating station works with hexagonal or trihelical gravure rollers in forward or reverse to the transfer rollers. The closed, pressurised chamber doctor MPG 600 CI applies the coating medium to the gravure surface. The 50mbar to 400mbar regulated chamber pressure determines the filling of the gravure and so enables variation of the coating quantity by the use of the same gravure roll.
The use of trihelical engraved rolls in the simultaneous coating process permits the transfer of the coating compound to the respective rubber rolls by reverse process with higher differential speed. The compound is then transferred to the substrate in forward mode.
Thanks to the continuous further development of this technology at Kroenert’s technology centre, we have been able to improve its efficiency substantially.
Currently, the simultaneous coating of front and back side of substrates in working widths of up to 3,300mm, at speeds of up to 750m/min, is the norm with Kroenert coating machines. After wet coating the substrate is fed into a vertical dryer or by means of a contact-free air turn into a horizontal dryer. This airturn is a contact-less transport system which feeds the material around corners without creasing. The working width and tension parameters of the airturn system are adjustable.
Simultaneous coating technology is flexible and offers a variety of possibilities, such as:
- Use of chromed and ceramic coated rolls
- Use of stainless steel or ceramic doctor blades with specific material thicknesses
- Rubber rolls with sleeve technology
- Cooling or heating of gravure and rubber sleeve rolls
- Mass circulation and pump systems tailored to individual material processing characteristics
Simultaneous coating stations can be assembled in line with paper machines or film producing machines, or off-line in coating machines. They are particularly well-suited to the following coating applications:
- Application of silicone to aqueous emulsions
- Application of silicone to UV-curable, solvent-free silicones
- Application of aqueous, kaolin-containing paints to paper
- Application of wax emulsions for the improvement of abrasive properties of printed paper
- Lay flat control with application of rehumidifiers like water
- Barrier coatings for the reduction of the repellant capacity of kraft paper
- Primer coating
- Anti-inflammatory coating
- Anti-slip coatings for improved stacking ability
- Primer and topcoat (various coating weights per page)
- Primer and release coating (different coating weights on each side)
Simultaneous coating technology is revolutionising machine design and concepts. Machines are not only becoming shorter as they now only consist of a coating head and a floating dryer, but are also substantially less expensive. Contact us for more information.