Core Issue: Manifestations and Causes of Poor Corona Treatment Effect
Manifestations: Poor printing adhesion, coating peeling, insufficient lamination strength, low surface tension (dyne pen test failure).
Root Cause: Insufficient surface energy of materials. Corona treatment ionizes air via high-frequency and high-voltage discharge to generate ozone and plasma. These high-energy particles bombard material surfaces (e.g., PE, PP, BOPP), causing oxidation and etching, thereby increasing surface energy and enhancing bonding with inks and coatings.
Tuning Tips for Three Core Parameters
1. Power – The "Intensity" of Treatment
Parameter Definition: Output power of the corona treatment machine, usually in kilowatts or watts per centimeter. It directly determines the discharge energy.
Influence Law:
Insufficient Power: Inadequate discharge energy fails to effectively open molecular chains on the material surface, resulting in weak treatment effect and limited surface tension improvement.
Excessive Power: May cause material "breakdown" or "over-treatment". Over-treatment degrades the material surface, breaks molecular chains, reduces strength, even produces odors (ozone decomposing materials), or causes blocking (treated surface adhering to the back of another roll of material).
Tuning Tips:
From Low to High: When tuning a new material for the first time, start with low power and gradually increase it slowly.
Observe Electrodes: The ideal discharge state is a uniform purple corona between the electrode and the roller, accompanied by a stable and continuous "hissing" sound. Bright white arcs (sparking) indicate excessive power or contaminated/damaged electrodes/dielectric layers.
Reference Standard: For common plastic films (e.g., BOPP, CPP, PE), the power density is generally between 1.5~3.0 W/cm². You can start testing from the median of this range (e.g., 2.0 W/cm²).
2. Speed – The "Time" of Treatment
Parameter Definition: Linear speed of the material passing under the corona treatment electrode.
Influence Law:
Excessively High Speed: The material stays in the discharge area for too short a time, resulting in insufficient bombardment by high-energy particles and poor treatment effect.
Excessively Low Speed: Prolonged treatment time easily leads to over-treatment (especially at high power), wasting energy and possibly damaging the material.
Tuning Tips:
Linkage with Power:Power and speed are strongly correlated parameters. Simply put: Treatment Effect ≈ Power / Speed. To improve the effect, either "increase power" or "reduce speed".
Prioritize Speed Fixing and Power Tuning: In production, for efficiency, usually first determine an ideal production speed, then adjust the power to match this speed to achieve the required treatment effect.
Testing Method: Fix power and distance, gradually increase speed, and test with a dyne pen to find the maximum speed that can stably reach the required surface tension (e.g., 38 dynes), which is the point of highest production efficiency.
3. Distance – The "Concentration" of Treatment
Parameter Definition: The gap between the electrode and the corona treatment roller, or the distance from the electrode to the material surface (depending on the machine type).
Influence Law:
Excessively Long Distance: The electric field strength weakens, corona discharge disperses, and energy cannot effectively act on the material surface, reducing treatment effect.
Excessively Short Distance: The electric field strength is too high, easily drawing arcs, breaking down or burning the film, damaging electrodes and dielectric layers, which is very dangerous.
Tuning Tips:
Follow the Equipment Manual:Distance is usually the first parameter to be set and should not be easily changed once set. Different machine types and electrode designs have their recommended optimal gaps (e.g., 1.5-3.0mm).
Ensure Parallelism: When adjusting the distance, it is necessary to ensure that the gap between the entire electrode and the roller is absolutely parallel; otherwise, the treatment effect will be strong on one end and weak on the other.
Fine-Tuning Principle: If adjusting power and speed to the limit still cannot meet the requirements, you can try fine-tuning the distance within the range allowed by the manufacturer. Reducing the distance can significantly enhance the treatment effect, but it must be done very carefully to avoid sparking.
If the test fails after increasing the speed, adjust back to the original speed or slightly increase the power to adapt to the new speed.
Important Note: After each parameter adjustment, wait for at least half a roll of material to pass before testing. Because the corona treatment effect has a certain lag and accumulation, the result of immediate testing is inaccurate.
Other Common Factors Affecting the Effect
Material Itself: Different grades of masterbatches and additives (e.g., slip agents) greatly affect the treatment effect and attenuation rate.
Cleanliness of Electrodes and Dielectric Layers: Electrodes and dielectric covers covered with dust, oil stains, or oxides will seriously hinder discharge and must be regularly cleaned with alcohol, etc.
Ambient Temperature and Humidity: High air humidity affects discharge characteristics; the workshop environment needs to be relatively stable.
Timeliness After Treatment: The corona treatment effect will attenuate over time (especially for films with slip agents), and printing or lamination should be completed within 24 hours after treatment as much as possible.
Summary Rhyme: First fix the distance to ensure parallelism, then fix the speed and tune the power, verify with dyne pen testing, fine-tune the margin to ensure stability.
By scientifically and collaboratively tuning these three core parameters, you can definitely solve the problem of poor corona treatment effect and achieve high-quality and efficient production.