DIRECT GRAVURE ROLL COATING

Direct gravure roll coating has been studied experimentally over a wide range of operating conditions using an infrared gauge to measure the thickness of film transferred onto a substrate. For the three gravure geometries used, the dimensionless film thickness (film thickness/cell volume/cell wetted area) first increases with increasing Reynolds number (substrate speed x descriptive cell size x density/viscosity) but reaches rapidly a constant value of about 1/3. Changes in the speed ratio (substrate/roller) from 0.5 to 2.0 do not affect this limiting value. The results also show the ability of trihelical and pyramidal cell configurations to empty better at low Reynolds number than quadrangular geometries. This work provides a comprehensive set of experimental data describing this important coating operation, usually carried out at large speeds (> 2 m/s) and with low-viscosity liquids, i.e. large Re.