What is ink blocking?
SGIA defines ink blocking as "an undesired adhesion between layers of materials placed in contact under moderate pressure and/or temperature in storage or use, usually occurs in a stack of printed material that is stacked prior to thorough drying." This can occur with single- or double-sided prints.
What causes ink blocking?
Blocking can be caused by a number of factors, and finding a solution to this production issue often requires adjusting more than one variable.
Ink Blocking Causes:
- Heat
- Weight
- Substrate
- Ink Film Rigidity and Gloss
- Cure Levels
Heat and weight are the primary considerations for ink blocking; when temperatures rise in the summer, prints are at higher risk of experiencing ink blocking.
Heavy substrates that absorb and conduct heat easily will increase the primary blocking factors: heat and weight.
Rigid inks are less likely to block than soft, pliable ink films. Fast-curing inks are also less likely to block, as they are less likely to cause heat buildup during the curing process than slow-curing inks. Glossier inks also have a higher chance of leading to ink blocking.
Cure levels can impact blocking by making the ink film softer and more pliable, or increasing the heat during processing.
What can I do to prevent ink blocking?
Ink blocking can be prevented by combating the factors that cause it. Once the issue(s) are identified, several preventative measures can be taken.
Adjustments to Prevent Ink Blocking:
- Reduce Heat: Although heat can be a constant battle in the summer, there are several ways to heat within stacks. Lowering cure levels to a minimum (while ensuring full cure still occurs) lowers the energy level the print is exposed to, reducing heat buildup in each stack. Allowing prints to cool down before stacking also reduces heat.
Blocking caused by pressure points.
- Reduce Weight: Reduce pressure on ink film by arranging smaller stacks with fewer parts, using spacers within a stack, or implement vertical stacking. Stacking in flat and even piles will eliminate pressure points (see photo), decreasing the likelihood of blocking.
- Reduce Ink Gloss: Reducing ink gloss can help with eliminating ink blocking. Flattening additives will give the ink film some “tooth” and prevent 100% ink-to-ink contact; adding a 5% by weight of this product generally does not reduce gloss noticeable, while still reducing the potential for ink blocking. (Consult your Nazdar product’s Technical Data Sheet for compatible ink additives, or browse all Nazdar Ink Additives.)
- Check Cure Levels: Test that ink is fully cured. Particularly with UV products, undercured ink is very soft and significantly more prone to blocking.
If you’re still experiencing problems with ink blocking after following these tips, contact InkAnswers, and a Nazdar Technical Service department representative will help you resolve your ink blocking issues. For more information on flattening products, check out Nazdar Ink Additives.