This guide explains what corona treatment is, how it changes a surface and why it helps liquids spread more easily. You’ll learn where it is used, what affects the results and how testing helps assess its effectiveness.
It also explains why treatment effects can decline over time, why better wetting does not guarantee stronger adhesion and how corona treatment relates to plasma treatment.
1. What Is Corona Treatment?
Corona treatment is a process that modifies a material’s surface using an electrical discharge in air. Its main purpose is to raise surface energy and improve wettability.
A treated surface can become more receptive to a suitable ink, coating or adhesive. The process does not apply these substances itself.
The term corona-treated therefore describes a surface that has undergone treatment. It does not specify the final bond strength or prove that the surface will work with every formulation.
2. Why Does Surface Energy Matter?
Surface energy describes the energetic state of a solid’s surface. In practical terms, it helps explain why a liquid spreads across one surface but forms beads on another.
Many polymers, including polyethylene and polypropylene, naturally have low surface energy. A liquid may pull back into droplets instead of maintaining broad contact with these surfaces. Corona treatment changes the surface to make wetting easier. See Enercon explains the relationship between surface energy and treatment.
Wetting, Absorption and Adhesion Are Different
These terms describe different events:
A liquid can wet a nonporous surface without being absorbed. Good wetting helps establish contact, but durable adhesion also depends on the materials and the process used to join them.
3. How Does Corona Treatment Work?
An Electrical Discharge Activates the Air
A typical industrial system includes a power supply, a high-voltage electrode and a grounded electrode. An insulating barrier helps control the discharge.
The electrical field energizes and partially ionizes the air in the treatment gap. This produces reactive species that interact with the exposed surface.
Reactive Species Change the Surface Chemistry
On a polymer surface, the discharge can break chemical bonds and enable reactions with oxygen-containing species. These reactions introduce polar chemical groups.
Polar groups are molecular sites that can interact more strongly with suitable polar liquids, helping improve wetting and adhesion. This surface oxidation is central to the explanation given in Pillar Technologies’ corona treatment theory.
The process changes the existing surface. It does not deposit a layer of glue, primer or absorbent material.
4. What Affects the Treatment Result?
The result depends on both the material and the conditions under which it is treated. Identical machine settings do not necessarily produce identical surface properties.
These variables work together. A power setting alone does not describe how much treatment a surface receives.
The aim is a consistent, validated result across the required area. Material trials help establish suitable conditions, as described in Vetaphone’s explanation of treatment variables.
5. What Is Corona Treatment Used For?
Corona treatment prepares a surface for a later process. Its role is to improve conditions at the interface between that surface and the material applied to it.
These uses share a common purpose: improving the interface. They do not require the underlying material to absorb the applied liquid. See TPC Converting describes how corona treatment supports adhesion in converting.
6. How Is Corona Treatment Effectiveness Measured?
Dyne Tests Assess Wetting Behavior
Dyne liquids and pens provide a practical indication of current surface wettability. Their test liquids have specified surface tensions, commonly labeled in dynes/cm. One dyne/cm equals one mN/m.
The test observes whether the liquid remains spread or retracts within the time specified by the method. Follow that method consistently and record the location and time of testing.
The resulting “dyne level” is a practical wetting indicator. It should not be treated as a complete description of the surface’s chemistry.
Contact-angle testing offers another approach: it measures the angle formed where a droplet meets the surface. Under comparable conditions with the same liquid, a smaller angle generally indicates better wetting. See Tantec outlines dyne and contact-angle approaches to surface assessment.
Adhesion Tests Assess the Finished Interface
A wetting test and an adhesion test answer different questions. The first examines liquid behavior on a surface; the second examines how well the resulting interface resists separation.
There is no single dyne value that guarantees success for every ink, coating or adhesive. The target must reflect the actual material combination and processing conditions.
Validation should therefore include the intended formulation and its actual drying or curing conditions. Depending on the application, evaluation may include peel, tape or other suitable adhesion tests.
Two surfaces with similar dyne readings can still produce different bond strengths. Compatibility and processing conditions remain essential, as explained in Enercon’s discussion of why dyne level does not guarantee adhesion.
7. Is Corona Treatment Permanent?
The improved wettability may decline over time. Molecular rearrangement at the surface, additive migration and storage conditions can all influence how the treated surface behaves later.
This does not mean that every material loses treatment at the same rate. There is no universal period after which all treated surfaces become unsuitable.
A measurement describes the surface at the time of testing. An earlier result cannot establish its condition indefinitely.
Treatment may take place during initial manufacturing or closer to the next processing step. If time has passed, reassessment can help determine whether the surface remains suitable. Any decision to retreat should follow current surface measurements, performance tests and confirmation that further treatment is appropriate. See Tantec discusses treatment persistence and the factors affecting it.
8. How Is Corona Treatment Related to Plasma Treatment?
Corona treatment is a form of plasma treatment: it creates a partially ionized gas that interacts with a surface.
In commercial terminology, “corona” often refers to systems using an electrical discharge in surrounding air. “Plasma” may refer to other arrangements, including systems with controlled gas mixtures or different treatment heads. The terminology varies between industries. See Enercon explains these distinctions in its corona-versus-plasma guide.
The useful distinction is how a system delivers treatment and what surface change it produces. The label alone does not establish which approach will work best.
Corona treatment helps create conditions for wetting and bonding. Understanding its chemistry explains the effect; surface measurements and performance tests establish whether that effect meets the needs of a particular process.
