Troubleshooting I Blocking of Printed Sheets

The challenges of blocking

The blocking of printed sheets in the pile is a result of insufficient drying of inks or coating. If inks or coating are still wet, they can set off, i.e. they are transferred to the printed sheet in contact.

The sheets stick together. Especially while using high gloss coatings, blocking may occur. Due to their product characteristics, these coatings dry more slowly than others.

Solving the blocking of printed sheets

S​​tep by Step

1. Increase your dryer performance

The optimal dryer setting is individual (IR and hot air). In the pile, temperature should not be above 35°C. Do provide sufficient exhaust air during the drying process. After a long machine running time, the air contains humidity. If this humidity condenses on the printed sheets, inks and coating may become wet again (laundry effect). Reduce the pressure in the pile.

2. Reduce your fountain solution

If too much fountain solution (>25%) emulsifies into the ink, drying is slowed down. Check your ink/fountain solution balance.

3. Reduce your ink application

A high application of inks slows down the drying process. If possible, reduce your ink application. Also, the ink type affects drying time. Fresh, low odour or migration less inks normally dry more slowly than oxidization drying inks. Choose faster inks if needed.

4. Increase your powder application

Anti-set-off powder provides space between the printed sheets in a pile. Choose the appropriate powder. A high substrate‘s grammage generally requires coarse granularity (attention: scratches). Also compare with: Insufficient scratch and scuff resistance.

5. Use the appropriate anilox roller

If your coating amount is too low, inks are partly exposed and blocking can be the consequence. But be careful: A very high coating application slows down drying. Choose an anilox roller with an appropriate cell volume.

6. Use an appropriate coating

Block resistance is a characteristic of the coating layer. Depending on the coating, this characteristic differs among coatings. Please contact our Technical Services for your consultation.

7. Choose an alternative substrate

We recommend a substrate with a faster penetration behaviour.

Your checklist

Influence factor: Dryer
Measure: Increase performance, provide exhaust air

Influence factor: Pile
Measure: Reduce pressure (pile height)

Influence factor: Fountain solution
Measure: Use less fountain solution

Influence factor: Printing inks
Measure: Reduce ink coverage

Influence factor: Powder
Measure: Increase application

Influence factor: Anilox roller
Measure: Use an appropriate anilox roller

Influence factor: Coating
Measure: Use appropriate coating alternative

Influence factor: Substrate
Measure: Choose a substrate with a faster penetration behaviour

Still have open questions? Contact us and we will support you with the application.

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