Corona Treatment Explained: How It Improves Surface Energy and Adhesion

Introduction

In modern manufacturing industries such as packaging, printing, and plastics processing, surface adhesion plays a critical role in product quality. Materials such as polyethylene (PE) and polypropylene (PP) are widely used because they are lightweight, durable, and cost-effective. However, these materials have a major limitation: they naturally have very low surface energy.

Low surface energy makes it difficult for inks, coatings, and adhesives to properly bond with the material. Without surface modification, printing ink may peel off, coatings may fail, and adhesive bonds may weaken.

To solve this problem, manufacturers use a process known as corona treatment. This technology increases the surface energy of materials, allowing inks, coatings, and adhesives to spread evenly and adhere properly.

In this article, we will explain what corona treatment is, how it works, and why it is essential for many industrial processes.

What is Corona Treatment?

Corona treatment is a surface modification process used to increase the surface energy of materials such as plastics, films, foils, and polymers.

The process involves exposing the surface of the material to a high-voltage electrical discharge, known as corona discharge. This discharge creates a plasma field that alters the molecular structure of the material’s outer surface layer.

As a result of this treatment:

  • The surface becomes more chemically active
  • Surface energy increases
  • Liquids spread more easily across the material

This improved wettability allows inks, coatings, and adhesives to bond effectively with the material.

Without corona treatment, many plastic materials would be unsuitable for printing, coating, or laminating applications.

Why Plastics Need Corona Treatment

Many commonly used plastics are classified as low surface energy materials. This means liquids tend to bead up on their surfaces rather than spread evenly.

Examples include:

  • Polyethylene (PE)
  • Polypropylene (PP)
  • Polyolefin films

When ink or adhesive is applied to untreated plastic, it often forms droplets instead of forming a smooth layer. This results in poor adhesion and unreliable product performance.

Corona treatment modifies the surface of these materials, making them more receptive to liquids and coatings. After treatment, inks and adhesives can wet the surface properly and form strong bonds.

How Corona Treatment Works

The corona treatment process typically takes place on a production line using a specialized machine called a corona treater.

The process involves several key components:

High Voltage Generator

The system generates a high voltage electrical field, often several thousand volts, which is used to create the corona discharge.

Electrode System

Electrodes positioned near the material surface create an electrical field that ionizes the surrounding air.

Plasma Discharge

The electrical field produces a plasma discharge that interacts with the surface molecules of the material.

This plasma breaks molecular bonds at the surface and introduces oxygen-containing functional groups such as hydroxyl or carbonyl groups. These chemical changes increase the polarity of the surface, which increases its surface energy.

The treatment affects only the very thin outer layer of the material—often only a few nanometers thick—while the bulk properties of the material remain unchanged.

Measuring the Effectiveness of Corona Treatment

After corona treatment, manufacturers must verify that the surface energy has increased to the required level.

One of the most common methods for doing this is dyne testing, which uses testing liquids or pens with known surface tension values.

If the test liquid spreads evenly across the surface, the surface energy is high enough for printing or coating processes. If the liquid beads or retracts, the surface energy is still too low.

This quick test allows operators to ensure that the corona treatment process is working properly and that the material is ready for the next production step.

Many production lines use dyne test pens as part of their routine quality control procedures.

Typical Surface Energy Levels After Corona Treatment

Different applications require different surface energy levels to ensure proper adhesion.

Typical surface energy targets include:

  • Untreated plastics: 30–34 dyne/cm
  • Basic printing applications: 36–38 dyne/cm
  • High-performance coating and lamination: 40–42 dyne/cm

In many flexible packaging applications, a surface energy level of 38 dyne/cm or higher is recommended for reliable ink adhesion.

Industries That Use Corona Treatment

Corona treatment is widely used in many industrial sectors where surface adhesion is critical.

Flexible Packaging

Flexible packaging manufacturers use corona treatment to prepare plastic films for printing and lamination processes.

Printing Industry

Printing companies rely on corona-treated materials to ensure proper ink adhesion on plastic substrates.

Automotive Manufacturing

Plastic components used in vehicles often require painting or adhesive bonding. Surface treatment improves the reliability of these processes.

Electronics Manufacturing

Plastic parts used in electronics often need labels, coatings, or adhesives. Surface treatment ensures consistent adhesion.

Advantages of Corona Treatment

Corona treatment has become the preferred surface modification method for many industries because it offers several advantages.

First, it is a fast and efficient process that can be integrated directly into production lines.

Second, it does not require chemical coatings or additional materials, making it a clean and environmentally friendly solution.

Third, it is highly effective for a wide range of plastic materials, especially polyolefins.

Finally, it significantly improves the quality and durability of printing, coating, and bonding processes.

Limitations of Corona Treatment

Although corona treatment is very effective, it does have some limitations.

One important factor is surface energy decay. Over time, treated surfaces may gradually lose some of their increased surface energy due to molecular rearrangement.

Because of this, printing or coating processes should ideally take place soon after treatment.

In addition, contamination such as dust, oils, or fingerprints can reduce the effectiveness of the treatment.

Proper handling and storage of treated materials is therefore important for maintaining optimal adhesion performance.

Conclusion

Corona treatment is a critical technology used in modern manufacturing to improve the surface energy of plastics and other materials.

By exposing materials to a controlled electrical discharge, this process modifies the outer surface layer and allows inks, coatings, and adhesives to bond more effectively.

When combined with reliable surface energy testing methods such as dyne testing, manufacturers can ensure consistent product quality and prevent costly adhesion failures.

For industries that rely on high-quality printing, coating, and bonding processes, corona treatment remains one of the most important technologies for achieving reliable surface performance.