Troubleshooting Guide - Pressroom Coatings
Issue: Coating Foaming
Potential Causes
Excessive heat, moisture & pressure
Solution: Reduce pile temperature, rack loads 8-12", increase exhaust.
Coating is drying too slowly
Solution: Reduce viscocity with 1:1 IPA/water, increase airflow.
Ink not setting in delivery
Solution: Use faster setting inks, reduce water setting, minimize alcohol sub.
Blocking on 2nd pass (re-softening first side of coating)
Solution: Increase time before backup, wind sheets before backup, reduce coating film, reduce load temperature on 2nd pass, rack loads 8-12", increase spray powder.
Potential Causes
Not enough pressure between rollers or blanket
Solution: Adjust rollers and blanket settings, check for low areas in roll blanket and packing.
Not enough pressure between rollers or plate or blanket
Solution: Adjust rollers to plate. Check for low areas in applicator roll or plate or blanket.
Potential Causes
Coater not going on impression soon enough
Solution: Applicator roller should come on prior to or at same time unit goes on impression.
Too much pressure between blanket and impression cylinder
Solution: Adjust blanket from impression, unpack plate or blanket or both.
Not enough coating applied to plate/blanket
Solution: Increase roller speeds to apply more coating or lessen metering screws.
Potential Causes
Level in reservoir too low
Solution: Increase coating level in coating pan.
Air being introduced into circulating systems
Solution: Check pump seals and piping for air leaks.
Recirculating pump running too fast
Solution: Reduce coating pump speed.
Possible water coating problem
Solution: Switch to different water coating lot.
Potential Causes
Uneven pressure between coater rollers
Solution: Adjust coater rollers. Achieve 'kiss contact.'
Uneven pressure between applicator roller and blanket
Solution: Adjust applicator roller to blanket.
Uneven pressure applicator roller to plate
Solution: Adjust applicator roller to plate. Achieve 'kiss contact.'
Uneven pressure between blanket and impression
Solution: Adjust pressure and/or check for low areas/smashes in blanket and packing.
Dried coating within coating system
Solution: Clean rollers, blanket and impression cylinder.
Potential Causes
Ridges in the direction of travel caused by too little coating
Solution: Increase amount of coating. Adjust blanket to back cylinder to achieve 'kiss contact.'
Coating is being 'pushed' into the ink
Solution: Reduce pressure to get uniform application.
Viscocity is too low and is 'soaking into job'
Solution: Specify higher viscocity coating.
Potential Causes
Too little coating to 'seal' ink
Solution: Apply more coating.
Heavy films of inks are setting too slowly to be stable
Solution: Resort to faster setting, stronger or tighter bodied ink. Run as dry as possible to prevent over-emulsification.
Too little spray powder
Solution: Increase spray powder setting.
Excessive pressure from high loads
Solution: Reduce load height or rack loads 8-12".
Too much coating is being applied to lay smoothly
Solution: Reduce coater speed to apply thinner film.
Potential Causes
Stock is absorbing too much water from coating
Solution: Resort to a 'high solids' coating to apply less water.
Excessive heat applied after coating
Solution: Check for proper load temperature. Do not exceed 105 degrees F.
Substrate too light in weight
Solution: Use substrate of 80lbs or higher. Run the coating as near to the edge of the sheet as possible to provide a uniform size change in the sheet.
