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Troubleshooting in UV offset printing

Time: 2018-11-15

Troubleshooting in UV offset printing

INCIDENTS:

1. Misting (ink splatter)

2. Picking substrate

3. Insufficient drying

4. Poor ink transfer

5. Poor adhesion to the substrate

6. Polymerisation of the inks in their container 

 

1. Misting (ink splatter)

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Too much ink on the rollers.

Reduce the inking.

Rollers incorrectly adjusted.

Check the pressures (reduce if necessary).

Incorrect pH or imbalance in the fount solution.

Check the fount solution and correct if necessary.

Temperature of inking rollers too high.

Lower the temperature of the printing units or renew the ink regularly.

Too much water in the ink.

Reduce the amount of dampening if possible.

Rollers incorrectly adjusted.

Consult the supplier.

 

2. Picking Substrate

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Ink too “sticky” or “tacky” for the substrate used.

Reduce the stickiness or tack of the ink (add UV Tack Reducing Paste or UV Thinner

Paper coating too fragile.

Change the paper.

Unsuitable blanket lining.

Adapt the linings as per the manufacturer’s recommendations.

Substrate temperature too low.

Store the substrate at the same temperature as the print shop and 
follow the recommendations of the substrate manufacturer.

Unsuitable colour sequence.

If possible, do not apply the densest colours on the first printing units

 

 3. Insufficient Drying

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Too much water in the water / ink balance.

Adjust the amount of fount solution.

Unsuitable ink.

Consult the supplier.

Printing speed not adapted to the number and
power rating of the UV lamps.

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.

Unsuitable dryers sequence.

Adapt the sequence to suit the print run.

High inking levels.

Reduce the inking levels or adapt the colour.

The dryer requires maintenance.

Check the condition and efficiency of the lamps, the number of hours used and the reflector cleanliness.

Too much water in the ink.

Reduce the dampening if possible.

Unsuitable ink.

Add Photoinitiator to the ink in the recommended proportions.

Specific cases: Drying of black.

Use iron doped lamps. 
Use 2 printing units to prints blacks with OD above 2.00.

Specific cases: Drying of white.

Use gallium doped lamps.

 

 4. Poor Ink Transfer

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Dirty or badly cleaned rollers.

Clean or deglaze the rollers.

Rollers incompatible with the ink.

Check the rollers are compatible with UV inks.

Temperature of the ink too low.

Store the ink at the temperature of the print shop (or use a mixer).

Viscosity of the ink unsuited to the press

Add UV Thinner or consult the supplier.

 

 5. Poor Adhesion to the Substrate

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Too much water in the water / ink balance.

Adjust the amount of fount solution.

Incorrect surface treatment or surface treatment that is out of date.

Check the surface tension of the substrate or consult the supplier to find out if the treatment is still valid.

Unsuitable ink.

Consult the supplier.

 

 6. Polymerisation of the inks in their container 

Probable Causes & Solutions (back to incidents)

CAUSE

SOLUTION

Inks stored at a too high temperature or in sunlight 
with the containers open. Inks kept for longer than one year.

Check the storage conditions of the UV inks and how stocks are rotated.