Views: 195 Author: Site Editor Publish Time: 2025-06-16 Origin: Site
Flexographic printing, or flexo printing, is a modern and highly versatile printing technique used across numerous industries. The flexo printing machine utilizes flexible relief plates to print on various substrates including paper, plastic films, metallic films, and non-porous materials. Its adaptability makes it an ideal choice for packaging, labels, corrugated containers, and even wallpapers.
One of the critical aspects that determine the success of a flexo printing operation is how well the ink adheres to the substrate. Many synthetic materials like polyethylene or polypropylene have low surface energy, which hinders ink bonding. This is where corona treatment plays a pivotal role. It modifies the surface characteristics of these materials, allowing better ink adhesion and resulting in superior print quality.
Corona treatment is a high-frequency, high-voltage electrical discharge technique that alters the surface properties of plastic and other non-porous materials. In flexo printing, corona treatment is used to increase the surface energy of substrates so that inks, coatings, and adhesives can properly wet and bond to the surface.
When a substrate passes through a corona treater, it is exposed to a plasma field generated between an electrode and a grounded roller. This causes a localized oxidation reaction, effectively "roughening" the molecular surface. As a result, the surface becomes more polar, increasing its receptiveness to ink and enhancing print consistency.
This treatment is typically applied in-line just before the substrate enters the printing section of the flexo machine. It's an invisible but vital step that significantly influences print durability, clarity, and resistance.
In flexo printing, poor ink adhesion leads to smudging, fading, and general print failure. Untreated plastic surfaces often repel water-based or UV-curable inks due to their low surface energy. Corona treatment raises the dyne level of the material, which directly improves ink anchoring and uniform coverage.
By improving the surface characteristics of the substrate, corona treatment enables finer ink distribution and prevents ink bleeding. This results in sharper lines, better color registration, and more vibrant print outcomes—factors that are especially important in high-quality packaging and branding materials.
Since treated surfaces are more receptive to inks, there's a lower risk of printing errors, meaning fewer re-runs and material waste. This not only saves costs but also aligns with environmental sustainability practices.
Corona treatment operates based on an electric field created by a corona discharge. When a high-frequency, high-voltage current (typically 10–20 kHz and 5–10 kV) is passed through an electrode, it ionizes the air gap between the electrode and the substrate, forming a plasma.
Here's a simplified overview in table form:
| Component | Function |
|---|---|
| Electrode | Generates high-voltage electrical field |
| Dielectric Material | Ensures uniform discharge |
| Grounded Roller | Holds the substrate in place |
| Air Gap | Enables plasma formation |
| Treated Substrate | Gains increased surface energy |
The oxidation process breaks down molecular bonds on the surface, adding polar functional groups like hydroxyl and carbonyl. These changes increase surface wettability and improve chemical compatibility with inks and coatings.
Corona treatment is not a one-size-fits-all process. It can be tailored to specific substrate types, such as:
Polyethylene (PE) and Polypropylene (PP): Widely used in flexible packaging.
PET and BOPP films: Common in food and beverage labeling.
Aluminum foils and laminates: Require precise treatment for multilayer adhesion.
In all these applications, the treated substrate demonstrates superior print quality, scratch resistance, and ink durability. For high-speed flexo machines, consistent corona treatment helps maintain production flow and reduces downtime caused by faulty prints.
While corona treatment is the most widely used method in flexo printing, there are alternative methods such as:
| Method | Mechanism | Pros | Cons |
|---|---|---|---|
| Corona | Plasma discharge | Economical, versatile | Not permanent, needs control |
| Flame Treatment | Direct combustion | Strong bonding | Heat-sensitive materials risk |
| Plasma Treatment | Low-pressure gas ionization | Precise, long-lasting | Expensive, complex setup |
Among these, corona treatment remains the most efficient and cost-effective for high-speed flexo printing operations on various plastic films.
In the high-precision world of flexo printing machines, every detail counts—from the anilox roller and photopolymer plate to the chemistry of the ink. Yet, one of the most impactful, albeit invisible, processes is corona treatment.
By enhancing surface energy, corona treatment bridges the gap between substrate and ink, ensuring vibrant, durable, and high-resolution prints. It's a critical step that combines science and practicality, making it an indispensable part of modern flexographic printing workflows.
If you're in the packaging, labeling, or flexible film industry and use a flexo printing machine, integrating a reliable corona treatment system can significantly enhance your production quality and consistency.
For most flexo printing applications, the ideal surface energy level is around 38–42 dynes/cm. However, this can vary depending on ink type and substrate.
Yes. Excessive corona exposure can lead to surface degradation, making it brittle or prone to ink flaking. Modern corona systems are equipped with intensity controls and dyne test pens to monitor and prevent over-treatment.
Corona treatment is not permanent. The surface energy can decay over time, especially if the material is stored in humid or contaminated environments. It's best to print shortly after treatment or use in-line treatment on the press.
Corona treatment is a non-contact, dry process and is considered safe when operated under proper shielding and ventilation systems. Operators must follow safety protocols to avoid electric shock risks.
