How to Reduce Curling in Metallized Paper and Board

Curling is one of those problems that often looks small at first, but quickly turns into a production issue.

Sheets don’t stay flat after slitting.
Stacks become uneven.
Feeding problems start showing up on packing lines.

In cigarette packaging and other high-precision applications, even slight deformation can affect efficiency, alignment, and final product quality.

So why does curling happen so easily in metallized paper and board?

Why Metallized Materials Are More Prone to Curling

Unlike plain paper, metallized structures are not uniform.

They typically combine:

• base paper
• adhesive layer
• metallized layer (aluminum or transfer layer)

Each layer reacts differently to temperature and humidity.
When these reactions are not balanced, internal stress builds up and the material starts to curl.

The Most Common Causes of Curling

1. Moisture Imbalance

Paper is highly sensitive to moisture.

If one side of the material absorbs or loses moisture faster than the other, it creates tension differences across the structure.

This is one of the main reasons why materials curl after:

• storage in humid environments
• transport across different climates
• exposure to open air before processing

2. Structural Tension Between Layers

The metallized layer does not expand or contract the same way as paper.

When bonded together:

• paper tends to expand with moisture
• metal layer remains relatively stable

This mismatch creates internal stress, especially noticeable after slitting or die-cutting.

3. Adhesive Shrinkage

Adhesive systems can shrink during drying or curing.

If the shrinkage is uneven or too strong, it pulls the structure in one direction, leading to:

• edge lifting
• sheet warping
• roll deformation

4. Slitting and Converting Conditions

Curling often becomes more visible after slitting.

Reasons include:

• release of internal stress
• uneven tension during winding
• improper roll hardness

Even if the material looks flat before, converting can trigger deformation.

Why the Problem Gets Worse in Real Production

In controlled conditions, curling may not be obvious.

But in actual production environments:

• humidity fluctuates
• temperature changes throughout the day
• materials stay exposed for longer periods

These factors amplify any imbalance already present in the structure.

That is why curling issues often appear “suddenly” on the shop floor.

Practical Ways to Reduce Curling

Control Moisture Before Processing

• Store materials in a stable environment
• Allow time for acclimatization before use
• Avoid opening packaging too early

Optimize Material Structure

• Use base paper with stable moisture behavior
• Balance coating and metallization on both sides when possible
• Choose adhesive systems with controlled shrinkage

Improve Converting Conditions

• Maintain consistent web tension during slitting
• Avoid over-tight winding
• Monitor roll hardness and alignment

Match Material to Application Environment

Materials that work well in dry regions may not perform the same in humid climates.

Choosing materials designed for your actual operating conditions can significantly reduce risk.

Final

Curling is not caused by a single factor. It is the result of how different materials behave together under changing conditions.

When moisture, structure, and process are aligned, metallized paper and board can remain stable and flat throughout production.

When they are not, even small imbalances can lead to ongoing operational issues.