Introduction

Corona treatment is widely used to improve adhesion on plastic films. When applied correctly, it modifies only the outer molecular layer of the substrate, increasing surface energy without affecting bulk properties.

However, when corona treatment is excessive or uncontrolled, it can damage the substrate itself.

This damage is often subtle at first, easily mistaken for ink, adhesive, or material quality issues. Over time, it leads to visual defects, mechanical failure, blocking, and costly rejects.

This article explains what actually happens when corona treatment damages the substrate, how to recognize the warning signs, and how to prevent irreversible material degradation.

How Corona Treatment Is Supposed to Work

Proper corona treatment:

• Modifies only the top molecular layer (nanometers deep)
• Introduces polar functional groups
• Leaves mechanical and optical properties intact
• Improves adhesion without weakening the film

When energy input exceeds the material’s tolerance, this balance is lost.

What “Substrate Damage” Really Means

Substrate damage occurs when corona treatment:

• Breaks polymer chains instead of modifying surface chemistry
• Alters bulk material properties
• Creates permanent defects that cannot be reversed

At this point, increasing or decreasing treatment no longer fixes the problem—the material itself has been compromised.

Common Forms of Corona-Induced Substrate Damage

1. Surface Degradation and Micro-Cracking

Excessive oxidation causes:

• Polymer chain scission
• Micro-cracks at the surface
• Loss of surface integrity

These defects may not be visible to the naked eye but lead to:

• Poor ink anchorage
• Reduced coating uniformity
• Accelerated aging

2. Optical Damage (Haze and Cloudiness)

Over-treatment roughens the surface at a microscopic level:

• Increased light scattering
• Loss of clarity and gloss
• Visible haze, especially in clear films

This is particularly problematic for:

• Food packaging
• Medical packaging
• Display films

Once haze appears, it cannot be removed.

3. Mechanical Property Loss

Corona damage can reduce:

• Tensile strength
• Elongation at break
• Flex resistance

Films may:

• Crack during folding
• Tear during converting
• Fail prematurely in end use

This damage often appears downstream, not at the treater.

4. Blocking and Surface Tackiness

Excessive oxidation creates too many polar groups:

• Film surfaces attract each other
• Rolls block during storage
• Unwinding becomes difficult or impossible

Blocked material is often unsalvageable inventory.

5. Increased Dust and Contamination Attraction

Damaged surfaces:

• Attract airborne particles
• Become electrostatically active
• Show visible contamination after storage

This further degrades print and coating quality.

How to Recognize Corona-Induced Substrate Damage

Visual Inspection

Compare treated vs untreated samples:

• Loss of gloss
• Surface dullness
• Haze under angled light

Use magnification (10×) to detect:

• Micro-cracking
• Pitting
• Texture changes

Simple Mechanical Checks

• Bend or flex the film: brittle behavior is a red flag
• Compare tensile properties before and after treatment
• Acceptable reduction: <5%
• Concerning: >10%

Blocking Test

1. Place two treated surfaces face-to-face
2. Apply moderate pressure
3. Store 24 hours at elevated temperature
4. Attempt separation

Resistance or tearing confirms surface damage.

Why This Damage Is Often Misdiagnosed

Corona-induced substrate damage is frequently blamed on:

• Ink formulation
• Adhesive chemistry
• Supplier material quality
• Operator handling

Because damage occurs at the molecular level, the root cause is often overlooked.

Common Situations That Lead to Substrate Damage

• Using maximum power “to be safe”
• Compensating for uneven treatment
• Treating difficult materials (PP, PET) like PE
• Ignoring upper surface energy limits
• Treating far above application requirements

Safe Operating Principles to Prevent Damage

Define Upper Surface Energy Limits

Treat to:

• Minimum required level
• Plus a 2–4 dyne buffer
• Not the maximum achievable value

Control, Don’t Maximize, Treatment

• Use surface energy testing to verify results
• Avoid “more is better” adjustments
• Fix root causes instead of adding power

Monitor Long-Term Effects

• Test surface energy over time
• Inspect treated material after storage
• Track recurring defects linked to treatment settings

Key Takeaway

Corona treatment is a precision process, not a brute-force operation.

When treatment energy exceeds what the substrate can tolerate, the material itself is damaged—leading to irreversible defects, mechanical failure, and costly waste.

Understanding how and why this damage occurs allows you to:

• Protect material performance
• Maintain adhesion reliability
• Prevent losses that surface testing alone cannot fix

Related Reading

• Can You Over-Treat Plastic with Corona? Signs, Risks, and Safe Limits
• 5 Signs Your Corona Treatment Isn’t Working (And How to Test It)
• Why Corona Treatment Works on PE but Fails on PP and PET