Causes for missing dots
Missing dots are small unprinted dots in screen and solid areas, which fail to transfer from gravure cylinder onto the substrate. This is due to either the cells are previously plugged, already empty before entering the nip or cannot connect properly to the substrate. In lightly screened areas, a steep and strong doctoring can cause the doctor blade to fully empty the cells.
Solutions for missing dots
1. Structured, uneven surfaces of substrate, like paper, hampering a good contact between cell and substrate. Activate Electrostatic Assist (ESA), to pull out the opposite charged ink from the gravure cylinder towards the pressure roller and onto the substrate.
2. Check the doctor blade angle and adjust by reducing the angle or using a more flexible setup.
3. Check if pressure roller is suitable for the substrate and adjust shore hardness accordingly to substrate.
4. Check gravure cylinders for plugged and dried up cells.
TKM recommends to periodically deep clean the gravure cylinder with TKM enpurex, use TKM OptiPrint and TKM PowerPrint.