Introduction

Corona treatment is essential for improving ink, coating, and adhesive adhesion on plastic films. However, more treatment is not always better.

In many production environments, operators respond to adhesion problems by increasing corona power or slowing the line. While this may temporarily raise surface energy, it can also introduce a different—and often more expensive—set of problems.

This article explains what over-treatment really is, how to recognize it, why it happens, and how to define safe surface energy limits that deliver reliable adhesion without damaging the material.

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

What Over-Treatment Means in Corona Processing

Corona treatment works by oxidizing the polymer surface. When treatment energy exceeds what the material can tolerate, oxidation becomes destructive rather than beneficial.

Over-treatment does not improve adhesion indefinitely. Instead, it leads to surface degradation, mechanical weakness, and downstream converting problems.

Common Signs of Over-Treatment

Over-treated films often exhibit one or more of the following:

• Surface haze or cloudiness
• Micro-pitting or pinholes
• Brittle behavior during flexing
• Reduced tensile strength
• Film sticking to itself during winding (blocking)
• Increased dust attraction

These issues may not appear immediately but often develop during storage or subsequent processing.

Why Over-Treatment Happens

1. “More Is Better” Mentality

When adhesion issues appear, increasing corona power seems logical. Without clear upper limits, operators often push treatment well beyond what the material requires.

2. Compensating for Other Problems

Over-treatment is frequently used to mask:

• Uneven cross-web treatment
• Rapid surface energy decay
• Material-specific response issues
• Contamination

Instead of fixing the root cause, treatment intensity is increased—creating new problems.

3. Lack of Defined Upper Limits

Many plants define minimum surface energy requirements but fail to define maximum safe limits. Without guidance, over-treatment becomes inevitable.

How Over-Treatment Damages Plastic Films

Surface Degradation

Excessive oxidation:

• Breaks polymer chains
• Creates micro-cracks
• Weakens surface integrity

Optical Damage

Surface roughening increases light scattering:

• Loss of clarity
• Visible haze
• Poor appearance in packaging applications

Blocking and Tackiness

Too many polar groups increase surface attraction:

• Films stick during winding or storage
• Rolls become difficult or impossible to unwind
• Inventory becomes unusable

Mechanical Property Loss

Over-treated films may experience:

• Reduced tensile strength
• Lower elongation at break
• Increased brittleness

How to Detect Over-Treatment

Visual Inspection

Compare treated and untreated samples under magnification (10× recommended):

• Look for texture changes
• Identify micro-cracking or pitting
• Observe surface dullness

Blocking Test

1. Treat a film sample under current settings
2. Place two treated surfaces face-to-face
3. Apply a 1 kg weight
4. Store for 24 hours at 40°C
5. Attempt separation

Results:

• Clean separation → Pass
• Resistance or tearing → Blocking (fail)

Mechanical Property Check

Measure tensile strength before and after treatment:

• Acceptable reduction: <5%
• Problematic: >10%

Haze Measurement (If Available)

• Acceptable increase: <2 haze units
• Problematic: >5 haze units

Safe Surface Energy Guidelines

Rule of thumb:
Treat to the minimum requirement + 2–4 dynes buffer, not the maximum achievable value.

How to Fix Over-Treatment

Immediate Actions

1. Reduce corona power by 20–30%
2. Re-test surface energy
3. Confirm adhesion performance
4. Increase power only if necessary

Long-Term Prevention

• Define maximum allowable surface energy by material
• Set upper alarms on corona power (if available)
• Document treatment “recipes” for each material
• Train operators on over-treatment risks
• Use surface energy testing to control—not maximize—treatment

Why Over-Treatment Often Costs More Than Under-Treatment

While under-treatment causes adhesion failure, over-treatment can cause:

• Visual defects
• Blocking and inventory loss
• Mechanical failures during converting
• Customer complaints related to appearance

In many cases, the total cost of over-treatment exceeds the cost of adhesion failure.

Prevention Checklist

• ☐ Define both minimum and maximum surface energy limits
• ☐ Verify treatment settings after material changes
• ☐ Investigate adhesion problems instead of increasing power blindly
• ☐ Monitor for haze, blocking, and brittleness
• ☐ Maintain surface energy within controlled limits

Key Takeaway

Corona treatment is a precision process—not a power contest.

Treating plastic beyond what the application requires introduces unnecessary risk and cost. Controlled, verified surface energy delivers reliable adhesion without sacrificing material performance.

Related Reading

• 5 Signs Your Corona Treatment Isn’t Working (And How to Test It)
• Uneven Corona Treatment Across Web Width: Causes, Testing & Fixes
• Why Corona Treatment Decays Over Time (And How to Measure It Correctly)
• Corona Treater Arcing: What It Means, Why It Happens, and How to Stop It
• Why Corona Treatment Works on PE but Fails on PP and PET