Corona Treatment Decay: Why Surface Energy Decreases Over Time in Plastic Films

What Is Corona Treatment Decay?

Corona treatment decay refers to the gradual loss of surface energy that occurs after a plastic film has been treated with corona discharge. While corona treatment increases the surface energy of polymer substrates to improve ink adhesion, coating performance, and bonding strength, this effect is not permanent.

Over time, the treated surface slowly returns toward its original low-energy state. As a result, the dyne level of the material decreases, which can cause printing, coating, or lamination failures.

This phenomenon is especially common in polyethylene (PE) and polypropylene (PP) films used in packaging and converting industries.

Why Surface Energy Decreases After Corona Treatment

Corona treatment works by exposing the polymer surface to a high-voltage electrical discharge. This process temporarily modifies the surface chemistry by introducing polar functional groups such as:

• hydroxyl groups
• carbonyl groups
• carboxyl groups

These polar groups increase the surface energy of the material, allowing inks, coatings, and adhesives to properly wet the substrate.

However, polymers are mobile materials at the molecular level. Over time, the polar groups introduced by corona treatment migrate back into the bulk of the polymer, reducing the treated surface energy.

This molecular reorientation causes the dyne level to decrease gradually during storage.

Typical Dyne Level Changes Over Time

A freshly treated plastic film may initially show a dyne level of:

40–42 dynes/cm

However, depending on storage conditions, the surface energy may decrease to:

36–38 dynes/cm within a few weeks or months.

This decay rate depends on several factors:

• type of polymer
• treatment intensity
• storage conditions
• film additives
• environmental exposure.

Factors That Accelerate Corona Treatment Decay

Several conditions can accelerate surface energy loss in treated films.

Polymer Structure

Some materials, such as polyethylene and polypropylene, are more prone to treatment decay due to their non-polar molecular structure.

Slip Additives and Processing Aids

Many packaging films contain slip agents, anti-block additives, or lubricants that migrate to the surface over time. These additives can reduce surface energy and interfere with ink adhesion.

Storage Time

The longer a treated film is stored before printing, the more likely the dyne level will decrease.

Environmental Conditions

Heat, humidity, and contamination can also accelerate the loss of surface energy.

How to Measure Corona Treatment Decay

The most common way to monitor surface energy loss is through dyne testing.

Dyne test pens or dyne test solutions are used to verify whether the surface energy of the substrate still meets the required level for printing or coating.

If the dyne level measured during testing is lower than the required value, the film may require re-treatment or additional surface preparation.

Regular testing is especially important in:

• flexographic printing
• gravure printing
• coating operations
• laminating processes.

How to Prevent Adhesion Problems Caused by Treatment Decay

To minimize the impact of corona treatment decay, converters typically follow several best practices:

• print films as soon as possible after treatment
• store films in controlled environments
• test dyne levels before production runs
• avoid contamination during handling
• monitor treatment levels during film extrusion.

Many printing facilities test surface energy at the beginning of every production run to ensure the material still meets the required dyne level.

Why Dyne Testing Is Critical in Production

Because corona treatment decay cannot be visually detected, surface energyhttps://kolorguide.com/iso-8296-dyne-test-pens-accurate-surface-testing/ testing is the only reliable way to confirm whether a treated film is still suitable for printing or coating.

Dyne test pens provide a quick and practical method for verifying surface energy directly on the production floor.

By regularly testing dyne levels, converters can avoid common adhesion problems such as:

• ink rub-off
• coating defects
• lamination failures
• inconsistent print quality.

Conclusion

Corona treatment significantly improves the surface energy of plastic films, making them suitable for printing, coating, and bonding applications. However, this effect gradually decreases over time due to molecular reorientation and additive migration.

Understanding corona treatment decay and monitoring dyne levels during storage and production are essential steps for maintaining consistent adhesion performance in packaging and converting processes.

Regular surface energy testing helps prevent costly printing defects and ensures reliable product quality.