Why Corona Treatment Decays Over Time (And How to Measure It Correctly)

Introduction

Corona treatment is designed to increase the surface energy of plastic films so inks, coatings, and adhesives can bond properly. However, surface energy does not remain constant forever. Some level of decay after treatment is normal.

The real problem occurs when surface energy drops too fast.

In many converting operations, material tests at the correct dyne level immediately after corona treatment but falls below the minimum requirement within hours—or even minutes. Adhesion failures then appear days later, long after the root cause has been forgotten.

This article explains why corona treatment decays over time, how to distinguish normal decay from problematic decay, and how to measure surface energy loss correctly before it causes rejects.

This article is part of our complete guide:
5 Signs Your Corona Treatment Isn’t Working (And How to Test It)

What Surface Energy Decay Looks Like in Production

A common real-world pattern:

• Immediately after treatment: 44 dynes/cm
• After 30–60 minutes: 38–40 dynes/cm
• After 24 hours: 34–36 dynes/cm
• Adhesion failures appear within 24–72 hours

Operators often assume:

• “The material was treated correctly.”
• “The ink or adhesive must be the problem.”

In reality, the surface modification was too shallow or unstable, allowing the surface to revert quickly.

Is Surface Energy Decay Normal?

Yes—some decay is normal.

Corona treatment modifies only the outermost molecular layer of the polymer. Over time, the surface naturally reorients or is affected by environmental exposure.

However, excessive decay is not normal and almost always indicates a process problem.

Commonly Accepted Industry Behavior

Under controlled conditions:

• Treated material should retain at least 90% of its initial surface energy for 48 hours
• Gradual decay over weeks is normal
• Rapid decay within hours or one day is a red flag

Why Corona Treatment Decays Too Quickly

1. Insufficient Initial Treatment

If the initial treatment energy is too low:

• Oxidation depth is shallow
• Functional groups are weakly bonded
• Surface modification disappears quickly

Contributing factors include:

• Low power density
• Excessive line speed
• Large electrode-to-substrate gap
• Worn electrodes reducing effective discharge

2. Surface Contamination

Contamination is one of the most common—and overlooked—causes of rapid decay.

Typical contaminants include:

• Slip agents migrating to the surface
• Anti-block additives
• Residual release coatings
• Handling oils or fingerprints
• Airborne silicone contamination

These materials either prevent proper oxidation or migrate back to the surface shortly after treatment.

3. Environmental Conditions

Environmental exposure accelerates decay:

• High humidity (>70% RH) promotes surface reorientation
• Elevated storage temperatures increase molecular mobility
• UV exposure can degrade surface functional groups
• Poor storage practices allow recontamination

Even well-treated material can lose surface energy rapidly if stored improperly.

How to Measure Corona Treatment Decay Correctly

Equipment Needed

• Dyne test pens (appropriate range for your application)
• Stopwatch or timer
• Controlled storage environment
• Lab notebook or digital log

Time-Series Decay Testing Protocol

1. Treat a test sample under normal production conditions.
2. Measure surface energy immediately after treatment (baseline).
3. Store the sample under controlled conditions:
   • 20–25°C (68–77°F)
   • 40–50% relative humidity
   • Protected from UV and dust
4. Retest surface energy at:
   • 1 hour
   • 4 hours
   • 24 hours
   • 1 week
5. Plot the results to visualize decay behavior.

Normal vs. Abnormal Decay Example

Warning sign:
A drop of more than 4 dynes/cm within 24 hours indicates insufficient or unstable treatment.

Contamination Confirmation Test

To determine whether contamination is driving decay:

1. Clean one section of the film with isopropyl alcohol.
2. Leave an adjacent section uncleaned.
3. Corona-treat both sections identically.
4. Measure surface energy immediately after treatment.

Interpretation:

• If the cleaned section tests 4+ dynes/cm higher, contamination is confirmed.

How to Fix Rapid Surface Energy Decay

For Insufficient Initial Treatment

• Increase power density by 10–20%
• Reduce line speed by 15–20%
• Reduce electrode gap (within safe limits)
• Add a second treatment station if consistently under-treating

(Typical power ranges: ≈10–20 W·min/m² equivalent, depending on material.)

For Contamination Issues

• Implement pre-treatment cleaning
• Review material supplier specifications for additives
• Isolate corona treatment from silicone-containing processes
• Improve material handling practices (gloves, clean surfaces)

For Environmental Causes

• Store treated material in sealed packaging
• Use desiccants where appropriate
• Maintain storage temperature below 25°C
• Limit time between treatment and printing or lamination
• For critical jobs, print within 24 hours

Why This Problem Is Often Missed

Most plants:

• Test surface energy once
• Assume the job is safe
• Discover problems only after conversion or customer use

Without time-based testing, decay-related failures appear random and difficult to trace.

Prevention Checklist

• ☐ Perform time-based surface energy testing on new materials
• ☐ Track decay trends, not just initial dyne values
• ☐ Investigate drops >4 dynes/cm in 24 hours
• ☐ Control storage humidity and temperature
• ☐ Treat as close as possible to printing or lamination

Key Takeaway

Surface energy decay is unavoidable—but rapid decay is not acceptable.

When corona treatment is applied correctly and verified over time, surface energy remains stable long enough for reliable adhesion. Measuring decay correctly transforms a hidden failure mode into a predictable, preventable process variable.

Related Reading

• 5 Signs Your Corona Treatment Isn’t Working (And How to Test It)
• Uneven Corona Treatment Across Web Width: Causes, Testing & Fixes
• Corona Treater Arcing: What It Means and How to Stop It