Corona requirements for water-based ink printing BOPP

Date: Oct 15 2024 From: Star Color

Water based ink printed BOPP (biaxially oriented polypropylene) film has a wide range of applications in packaging, labeling, and advertising fields. However, due to the low surface tension value of polypropylene material itself, which is only 31 dynes, the wetting and adhesion of ink during direct printing are not sufficient, which will affect the printing quality.

And corona treatment is a method that can significantly improve the printing adaptability of BOPP film.

1.Basic principles of corona treatment

Corona treatment is achieved by placing a thin film between two electrodes with high voltage, and using the high voltage to ionize the air between the electrodes, forming an electron flow. These electron flows form oxidative polarization groups on the surface of the film, creating polarity on the film surface and improving its wettability and adhesion. The surface tension value of the film after corona treatment is increased to a range suitable for printing, usually 38-42 dynes.

2. The influence of corona treatment on water-based ink printing

1. Improve ink wettability: Corona treatment increases the polarity of the BOPP film surface, allowing water-based ink to better wet the film surface and improve ink spreading and uniformity.
2. Enhance ink adhesion: After corona treatment, a stronger chemical bond is formed between the surface of the film and the ink, making the ink less likely to peel off and improving the durability and aesthetics of the printed material.
3. Reduce printing defects: Corona treatment can effectively reduce defects such as fogging and sticking during the printing process, improving printing accuracy and clarity.

3. Corona requirements for water-based ink printing BOPP

1. Corona treatment strength: The corona treatment strength should be moderate. Excessive treatment strength may lead to excessive oxidation of the film surface, affecting the adhesion of ink and the durability of printed materials; Low processing intensity cannot effectively improve the surface tension of the film and cannot achieve good printing results. The reasonable range of corona value for printed film is between 38-42 dynes.

2. Electrode design: The design of electrodes has a significant impact on the effectiveness of corona treatment. Dual electrodes have higher processing values, lower energy consumption, and better stability compared to single electrodes. The opening degree of the exhaust valve of the electrode also affects the treatment effect. The larger the opening degree, the smaller the surface treatment effect of the film.

3. Film temperature: The temperature of the film has a direct impact on the effectiveness of corona treatment. The set temperature of the preheating roller can control the temperature of the film, thereby affecting the surface tension value after corona treatment.

4. Production line speed: Production line speed is another important factor that affects the effectiveness of corona treatment. The length of time BOPP film stays in the gap between high-voltage electrodes will affect the processing effect.

5. Ink selection: The viscosity, surface tension, and interfacial tension of water-based ink can also affect the printing effect. Choosing ink suitable for BOPP film and corona treatment conditions is crucial. The use of super dispersants and ultra high activity wetting agents with improved substrate wetting properties can further enhance printing adaptability.

The corona requirements for water-based ink printing BOPP involve multiple aspects, including corona treatment strength, electrode design, film temperature, production line speed, and ink selection. By reasonable corona treatment, the printing adaptability and printing quality of BOPP film can be significantly improved.