Corona treatment for plastic films is a core technology addressing the poor adhesion of non-polar films. It enhances the surface energy of films through dual physical and chemical actions, laying a solid foundation for subsequent processes such as printing, lamination, and coating. The entire process requires precise control of surface tension detection, equipment configuration, parameter setting, effect verification, and safety maintenance to ensure stable treatment quality and meet industrial production demands.
Overview of Corona Treatment
Plastic films are mostly non-polar polymers. When untreated, their surface tension is only 29-33 dynes/cm, making it difficult for inks and adhesives to form strong bonds. Corona treatment uses a high-frequency high-voltage electric field to ionize the air, achieving physical roughening and chemical polarity modification on the film surface, significantly increasing the surface tension to 38-52 dynes/cm, perfectly solving the adhesion problem.
The core principle involves a high-frequency high-voltage power supply creating a strong electric field between the electrode and the corona roller, ionizing air molecules into low-temperature plasma. When the plasma bombards the film surface, it forms nanoscale凹凸 structures through electron flow impact, increasing the specific surface area, while simultaneously introducing polar groups such as carbonyl and hydroxyl groups through oxidation reactions, enhancing surface energy. This dual mechanism endows the treated film with both anchoring capability and adsorption capacity.
Compared to flame treatment and chemical treatment, corona treatment offers advantages such as simple operation, controllable effects, low cost, and no pollutant emissions. It is particularly suitable for high-speed continuous production lines and has become a standard process in industries like flexible packaging, electronic films, and printing, covering mainstream film types including LDPE, PP, BOPP, and PET.
Preparation and Surface Tension Detection
Before treatment, it is necessary to determine the initial surface tension of the film and the target value, then prepare the equipment and process to avoid blind treatment leading to poor results or film damage.
Common film surface tension requirements are as follows: LDPE film requires an increase from 29-31 dynes/cm to 38-40 dynes/cm; HDPE film from 30-32 to 39-41 dynes/cm; PP film from 30-32 to 40-42 dynes/cm; BOPP film from 31-33 to 40-42 dynes/cm; PET film from 40-42 to 48-52 dynes/cm.
Surface tension detection methods include the dyne pen test method, which is the most convenient for on-site detection; the standard test mixture method according to DIN ISO 8296, which is accurate and core for laboratory quality judgment; and the BOPP tape peeling method for preliminary qualitative judgment.
Pre-treatment preparations include equipment safety checks, confirming reliable grounding of the high-voltage power supply, no corrosion or foreign objects on the electrode, normal operation of the ozone emission system, and calibrating the film path to ensure smooth and wrinkle-free material travel. Preliminary parameters should be set based on the film type, thickness, and width.
Equipment Configuration and Parameter Setting for Corona Treatment
The effectiveness of corona treatment relies on both equipment hardware and parameter optimization. It is essential to understand the function of each component, accurately set key parameters, and verify and adjust in real-time to ensure uniform and stable treatment.
The equipment consists of several core components: a high-voltage generator, the system core, converting AC power to high-frequency high-voltage output; an electrode system, releasing high-voltage electrical energy; a corona treatment roller, serving as the dielectric; an ozone emission system, installed directly above the electrode; and a film transmission system, ensuring the film passes through the treatment area at a constant speed.
Key process parameters and their setting logic include treatment power, calculated by a specific formula where the power coefficient varies with film type; electrode gap, typically 1-3mm; frequency, mainstream range 18-30kHz; and treatment speed, adjusted in coordination with power.
Reference parameters for different films are as follows: for LDPE film, power coefficient 0.8-1.2, typical frequency 18-22kHz; for HDPE film, 1.0-1.5, 20-24kHz; for PP film, 1.2-1.8, 22-26kHz; for BOPP film, 1.5-2.0, 24-28kHz; for PET film, 2.0-2.5, 26-30kHz.
Real-time verification and adjustment involve online quick verification with a dyne test pen every 30 minutes; precise verification with standard test liquid every 2-4 hours; and intelligent adjustment using an online monitoring system for unmanned precise control.
Treatment Effect Verification and Subsequent Processing Considerations
Post-treatment, multi-dimensional verification is necessary to ensure effectiveness, while avoiding the risk of effect degradation during subsequent processing to guarantee final product quality.
Treatment effect verification methods range from macro to micro: precise measurement of surface tension using the standard test liquid method; chemical structure analysis using ESCA or ATR-FTIR; microscopic morphology observation using SEM; and practical application tests such as printing/laminating tests.
Key considerations for subsequent processing include time control, as the treatment effect degrades over time, requiring completion of subsequent processes within 24 hours; contamination protection, requiring operators to wear powder-free gloves and films to be wrapped with PE film during transport; secondary treatment for films stored beyond 48 hours or contaminated; and tension matching, where different processes require different tension levels.
Prevention and handling of effect degradation can be achieved through formula optimization, in-line corona treatment, and degradation monitoring.
Safety Operation Specifications and Maintenance
Corona treatment involves high voltage and ozone, requiring strict adherence to safety regulations and proper equipment maintenance to ensure long-term stable operation.
Core safety operation requirements include grounding protection, with weekly detection of grounding resistance; ozone protection, with ozone detectors installed in the workshop; high-voltage protection, requiring power disconnection and discharge confirmation before maintenance; fire and explosion prevention, keeping treatment areas away from flammable materials; and personal protection, requiring operators to wear insulated shoes and protective glasses.
Equipment maintenance points include daily wiping of the electrode surface with anhydrous ethanol; weekly inspection of high-voltage cable connections and testing of the cooling system; quarterly cleaning of electrode gaps and inspection of corona roller bearings; and annual replacement of high-voltage cables and detection of ozone emission fan air volume.
Summary and Technology Trends
Corona treatment for plastic films is a process where details determine success. Every step, from surface tension detection to parameter setting, from effect verification to safety maintenance, requires precise control to achieve production goals of high adhesion, low loss, and high efficiency.
Currently, corona treatment technology is developing towards intelligence and energy saving. Intelligent equipment can use AI algorithms to predict parameters, reducing manual adjustment. Energy-saving high-voltage generators reduce energy consumption by 15-20% and ozone generation by 10%, better meeting environmental requirements. Mastering the entire process technology is of great significance for plastic film enterprises to improve product quality and reduce costs.
Hefeng, as a professional China manufacturer, can recommend suitable Plastic Film Corona Treaters or plasma treatment equipment based on customers' printing substrates (such as plastic films, paper, metal foils). Our equipment supports Customized parameter adjustments, with regular models in stock for fast delivery. Before procurement, customers can apply for Free Samples to test treatment effectiveness. We provide clear Pricelists and quotations, and Bulk purchases qualify for buy discounts, helping customers solve insufficient printing adhesion at the lowest cost.