Corona Treatment for Blown Film Extrusion -Tech Extrusion

By /

Table of Contents

Introduction

In the world of blown film extrusion, achieving high-quality
output The film’s performance is often dependent on the successful interaction
of its surface with adhesives, coatings, and inks. This is the point at which
Corona treatment is implemented. By increasing the surface energy of the film,
corona treatment ensures better adhesion and printability, making it a
necessary process in modern packaging and film applications. This article
explores the science, benefits, and practical considerations of corona
treatment in blown film extrusion.

What is Corona Treatment in Blown Film Extrusion?

Corona treatment is a surface modification technique used to
enhance the surface energy of films produced through blown film extrusion. It
involves exposing the film’s surface to a high-voltage electrical discharge,
which modifies its properties to improve adhesion with coatings, inks, and
adhesives.

This treatment is crucial because most polymer films, like
polyethylene and polypropylene, have inherently low surface energy, making them
resistant to adhesives and printing materials unless properly modified.

How Corona Treatment Works for Blown Film Extrusion:

Corona treatment for blown film extrusion is a surface modification process used to improve the printability, coatability, and adhesive bonding properties of plastic films. The gap between the corona treatment electrode and the sleeve roller in blown film extrusion typically ranges from 1.5 to 3 mm.

 
Some factors influencing this gap:
 
Film thickness: Thicker films may require a slightly larger gap to ensure complete treatment.
Line speed: Higher line speeds may require a narrow gap to maintain sufficient treatment intensity.
Treatment intensity: The desired level of surface modification will affect the perfect gap setting 

Maintaining the correct gap is essential for consistent and effective corona treatment, leading to improved product quality and performance.

 
Corona Treatment
Corona treatment for blown film extrusion 

The Science Behind Corona Treatment: How Does It Work?

1. High Voltage:

A high voltage is applied to electrodes near the film surface

2. Ionization of Air:

A high-voltage electrical field is established across the electrodes. It created a strong electric field in the air around the electrodes. The extreme electric field removes electrons from neutral air molecules like oxygen (O₂) and nitrogen (N₂). Positively charged ions and free electrons are formed during this process.

3. Plasma Formation:

The ionized air forms plasma, a partially ionized gas containing charged particles.

4. Surface Modification:

The blown film passes through this plasma field. The surface of the plastic film is bombarded by these charged particles.

5. Increased Surface Energy:

This bombardment modifies the chemical composition of the film surface, introducing polar groups (like hydroxyl groups) that were not present before. This substantially increases the surface energy of the film.

 

Key Components of a Corona Treatment System

A Corona treatment system generally includes

Power Supply: Generates the high voltage
required for Corona discharge.

Electrodes: Deliver the electrical
discharge to the film’s surface.
Dielectric Material: Ensures reliable current
flow and reduces sparking
 

Rollers: Support the film during
treatment, ensuring smooth contact.

Types of Electrode:

In the blown film extrusion, corona treatment generally utilizes the following types of electrodes:
 
a) Wire Electrode: Thin wires, typically made of stainless steel, are arranged across the path of the moving film.
 
How it works: When high voltage is applied, the wire ionizes the surrounding air, creating a plasma field. The ionized air molecules bombard the film surface and transform its chemical composition, increasing surface energy.
 
b) Pin Electrode: Many small pins are arranged in a mesh pattern across the film path.
 
How to work: Each pin acts as a regional source of ionization, creating a more even distribution of the plasma field. This leads to more uniform treatment across the film width compared to wire electrodes. 
 
c) Roller Electrode: Electrodes are integrated within the surface of a rotating roller.
 
How to work: When the film passes over the roller, it is continuously exposed to the plasma field generated by the integrated electrodes. This provides consistent and high-quality treatment across the entire film width.

Conclusion of Electrode:

Wire electrode, pin electrode, and roller electrode—all three electrode types work by generating a high-voltage electrical field that ionizes the surrounding air, creating a plasma that modifies the film’s surface. 
The choice of electrode type depends on factors such as the wanted level of treatment, film width, production speed, and limited funding.

Sleeve roller and sleeve material:

Sleeve roller:

The sleeve roller in blown film extrusion can be made from several materials:
 
1. Hardened steel: a common choice due to its durability, wear resistance, and ability to resist high temperatures.
 
2. Ceramic: highly resistant to wear and tear, capable of enduring significantly higher temperatures compared to steel.
 
3. Chrome-plated steel: delivers a smooth, mirror-like finish, which can be particularly advantageous for films that prioritize visual style and special effects.
 

Sleeve:

Corona treatment sleeves are typically made of silicon rubber.
 
Why silicon rubber is used in sleeves:
 
High Dielectric Strength: Silicon rubber has excellent insulating properties, which are crucial for withstanding the high voltages used in corona treatment.
Chemical Resistance: Silicon rubber is resistant to many chemicals, including ozone, which is generated during corona discharge.
Heat Resistance: It can withstand the high temperatures generated during the treatment process without melting or degrading.
Flexibility and Durability: It’s flexible enough to conform to the roller’s shape and durable enough to withstand the wear and tear of continuous operation. 
 
Silicone rubber sleeves used in corona treatment can typically withstand temperatures ranging from -60 degrees to 230 degrees.

Key Point to Remember:

The gap between the electrodes and the sleeve roller is critical for the most efficient corona treatment performance.

Silicon rubber is the preferred material for sleeves due to its excellent insulating properties and temperature resistance.

Challenges and Maintenance

Common Challenges in Corona Treatment Systems

While Corona treatment is highly effective, certain challenges may arise:
Over-treatment: Can cause film brittleness or a chalky surface.
Uneven Treatment: Results from improper roller alignment or electrode gaps.
Contamination: Dust or oil on the film surface can reduce treatment effectiveness.

Tips for Maintaining Optimal Corona Treatment Performance

Regular Cleaning: Clean electrodes and rollers regularly to remove dust and junk.

Consistent Monitoring: Check surface energy regularly using a dyne test.
System calibration: Ensure electrodes and rollers are properly aligned.

Conclusion

Corona treatment serves a crucial purpose in optimizing the performance of blown film by enhancing its surface energy. This process ensures that films are more suited to adhesives, inks, and coatings, ultimately elevating product quality and market value. By understanding the science, applications, and maintenance of corona treatment, manufacturers can maximize its potential and deliver superior results in blown film extrusion.

Note: Read more about corona treatment.

Related Posts

1 thought on “Corona Treatment for Blown Film Extrusion -Tech Extrusion”

  1. Pingback: Blown Film Extrusion Machine

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top