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

Place two treated surfaces face-to-face
Apply moderate pressure
Store 24 hours at elevated temperature
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

What Happens When Corona Treatment Damages the Substrate?

What Happens When Corona Treatment Damages the Substrate?

Introduction

How Corona Treatment Is Supposed to Work

What “Substrate Damage” Really Means

Common Forms of Corona-Induced Substrate Damage