Troubleshooting in UV offset printing

Incidents

Probable causes and remedies

1. Misting (ink splatter) (back to incidents)

Cause	Too much ink on the rollers.
Remedie	Reduce the inking.
Cause	Rollers incorrectly adjusted.
Remedie	Check the pressures (reduce if necessary).
Cause	Incorrect pH or imbalance in the fount solution.
Remedie	Check the fount solution and correct if necessary.
Cause	Temperature of inking rollers too high.
Remedie	Lower the temperature of the printing units or renew the ink regularly.
Cause	Too much water in the ink.
Remedie	Reduce the amount of dampening if possible.
Cause	Unsuitable ink.
Remedie	Consult the supplier.

2. Picking substrate (back to incidents)

Cause	Ink too “sticky” or “tacky” for the substrate used.
Remedie	réduReduce the stickiness or tack of the ink (add UV Tack Reducing Paste or UV Thinner > See « UV Additives ».
Cause	Paper coating too fragile.
Remedie	Change the paper.
Cause	Unsuitable blanket lining.
Remedie	Adapt the linings as per the manufacturer’s recommendations.
Cause	Substrate temperature too low.
Remedie	Store the substrate at the same temperature as the print shop and follow the recommendations of the substrate manufacturer.
Cause	Unsuitable colour sequence.
Remedie	If possible, do not apply the densest colours on the first printing units

3. Insufficient drying (back to incidents)

Cause	Too much water in the water / ink balance.
Remedie	Adjust the amount of fount solution.
Cause	Unsuitable ink.
Remedie	Consult the supplier.
Cause	Printing speed not adapted to the number and power rating of the UV lamps.
Remedie	Reduce the printing speed while maintaining the same output from the lamps, or modify the drying installation in order to increase the overall power output.
Cause	Unsuitable dryers sequence.
Remedie	Adapt the sequence to suit the print run.
Cause	High inking levels.
Remedie	Reduce the inking levels or adapt the colour.
Cause	The dryer requires maintenance.
Remedie	Check the condition and efficiency of the lamps, the number of hours used and the reflector cleanliness.
Cause	Too much water in the ink.
Remedie	Reduce the dampening if possible.
Cause	Unsuitable ink.
Remedie	Add Photoinitiator to the ink in the recommended proportions. > See « UV additives ».
	Specific cases: Drying of black.
Remedie	Use iron doped lamps. Use 2 printing units to prints blacks with OD above 2.00.
	Specific cases: Drying of white.
Remedie	Use gallium doped lamps.

4. Poor ink transfer (back to incidents)

Cause	Dirty or badly cleaned rollers.
Remedie	Clean or deglaze the rollers. > See «UV additives».
Cause	Rollers incompatible with the ink.
Remedie	Check the rollers are compatible with UV inks.
Cause	Temperature of the ink too low.
Remedie	Store the ink at the temperature of the print shop (or use a mixer).
Cause	Viscosity of the ink unsuited to the press
Remedie	Add UV Thinner > See « UV additives » or consult the supplier.

5. Poor adhesion to the substrate (back to incidents)

Cause	Too much water in the water / ink balance.
Remedie	Adjust the amount of fount solution.
Cause	Incorrect surface treatment or surface treatment that is out of date.
Remedie	Check the surface tension of the substrate or consult the supplier to find out if the treatment is still valid.
Cause	Unsuitable ink.
Remedie	Consult the supplier.

6. Polymerisation of the inks in their containers (back to incidents)

Cause	Inks stored at a too high temperature or in sunlight with the containers open. Inks kept for longer than one year.
Remedie	Check the storage conditions of the UV inks and how stocks are rotated.

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