While drying, conventional offset inks dry by evaporating volatile components (solvents) into the surrounding air. Also, they dry by absorbing the binders into the printing substrate. Some modern offset ink dries exclusively by setting the binders without having a mentionable amount of volatile components.
The drying process may be disturbed or delayed if some surrounding requirements are not given or application errors apply.
If the drying of the ink is heavily affected, setting ink to the following sheets in the pile is very likely to happen. I major cases, the whole pile may block. Also, additional dirtiness of the press and additional cleaning efforts may follow.
Suspect 1 – Ink/Fountain Solution not working well together
It is a basic requirement in the offset world that all process-related components are tested or approved for prober interaction and compatibility.
- Talk to your consumables supplier or press manufacturer for advice
- Check fountain solution additives for proper concentration
- Check if micro-particle filters do not filter out working ingredients of the fountain solution (bypass for testing)
Suspect 2 – excessive dampening
Over emulsification of the ink will delay the drying process as the water needs to evaporate for complete drying
- Minimize dampening to the lowest threshold to maintain plates free of scumming
Suspect 3 – Air conditioning
The surrounding air needs to be able to accept the additional water exiting the printed stock.
- Make sure, the air is conditioned to a relative humidity not exceeding 70%
Suspect 4 – Deliver-Pile not tempered probably
The pile temperature in the delivery shall be slightly higher than the feeding substrate. If the pile is too cold the humidity may not be released as fast as possible. If the pile temperature is too high, the ink is kept too soft to cure.
- Make sure the stock is climatized to pressroom temperature before processing it.
- Adjust pile temperature using Infrared Emitters (IR) to be at a temperature plus 10-15 Degrees Celsius compared to the feeding pile. In the case of coating with aqueous varnish, use hot air instead of IR to adjust. (See Suspect 5)
- Recommendation: 35 Degrees Celsius (95 Degrees Fahrenheit )
Suspect 5 – Wrong heating system used
Using water-based coatings, the extra humidity from the varnish needs to be released. Otherwise, the drying process might be delayed enormously.
- Use only hot-air dryers and hot air exhaustion, if available.
Suspect 6 – Coating squeezed into the ink
If the coating is smashed into the ink with excessive pressure, the drying process is heavily affected
- Reduce the pressure of the coating form to the substrate to the very minimum possible
Suspect 7 – Too much coating applied
The more coating applied, the more water is held by the pile to release before back-side printed or further processing.
- Reduce the amount of applied coating by selecting an anilox roller with a lower charge
- Check coating chamber doctor blades and renew if worn out
Suspect 8 – Ink film too heavy
If the applied amount of ink is too much for the given substrate, drying delay occurs
- Reduce overall density t te lowest acceptable level
- Re-Calibrate the process using lower densities
Suspect 9 – Total amount o fink too high
The total amount of ink used for every color-separation is controlled by the ICC-profile. An unsuitable simulation profile may cause the use of an unsuitable tota amount of ink for the given substrate. If the substrate is not able to absorb the applied ink, drying may be delayed or prevented at all.
- Deploy an ICC-profile set to a lower Total Amount of Color (TAC)
- Fingerprint the press using lowest solid densities possible and create an individual ICC-profile with a TAC limited to 280%-300%
Suspect 10 – substrate PH too high
If the PH-value of the substrate exceeds 8, drying issues are very likely. Only applicable to papers.
- Try another substrate if possible
- Pre-Coat (Prime) the substrate
- Contact your substrate supplier