Pile Blocking (Offset)
Pile blocking is a major print-process problem that results in solidly blocked piles or rolls (web offset). In most cases, pile-blocking will be noticed by the postpress first. Pile blocking normally appears only when sheets are coated using double-sided gloss coating or when printing on plastic stock.
Suspect 1 – Pile temperature too high
Excessive substrate temperature will make the surface of inks and coatings tacky so the may stick on each other
- Reduce the pile/roll temperature to the very minimumUse hot air and hot-air-exhaustion instead of Infrared (IR)
Suspect 2 – Too less or no Anti-Set-Off-Powder
Anti-Set-Off-Powder in between the sheets may prevent the superposed material-layers from sticking to each other. Also, additional air between the layers may improve the drying and cooling-down process.
- Add and adjust applied powder quantity to the maximum applicable level for the given print job
Suspect 3 – Wrong type of Anti-Set-Off-Powder
There are 2 different types of powders available. Silicone-treated powders for use in combination with water-based coatings and untreated ones for non-coating applications and the use of UV-curing inks.
- Apply the correct type of powder and granularity for your application
Suspect 4 – Static Substrate
If the substrate gains electrostatic load while the printing process, temporarily pile blocking is given an advantage
- Let printing stock settle and adjust to pressrooms air-conditions before printing
- Turn ON antistatic devices options of your press (if available )
- Turn OFF static loading devices in the delivery (typically used to keep anti-set-off-powder sticking t the substrate)
- Try a different type of blankets