Surface Treatment Methods That Improve Ink Adhesion on BOPP Film

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To improve ink adhesion on BOPP film, a few primary surface treatment methods are commonly used. They all work by modifying the film's inert, non-polar surface to make it more receptive to inks, especially water-based ones.

⚡ Corona Treatment

This is the most widely used and cost-effective method, often integrated directly into the film production or printing line.

How it works: The film is passed through a high-voltage corona discharge, which oxidizes the top layer (about 1 micron deep). This breaks molecular chains and introduces polar oxygen groups onto the surface, raising its surface tension.

Limitations: Its effect can be temporary and degrade over time, particularly on polypropylene, which is notoriously difficult to treat. Performance can also be affected by the film's additives.

A more advanced variation uses Acrylic Acid-Corona treatment, where acrylic acid vapor is introduced during the corona process. This has been shown to create a more durable, hydrophilic surface that can retain good wettability for over 90 days, which is a significant improvement over standard air-corona.

Plasma Treatment

This is an advanced technique that offers a more controlled and effective surface modification.

How it works: The film is exposed to ionized gas (plasma), which introduces specific functional groups (like hydroxyl groups for hydrophilicity) onto the BOPP surface. This method is known for its speed, ease of control, and ability to create a rougher, more adhesive surface.

Application: It is often used as a pre-treatment step before applying functional coatings. For instance, plasma treatment is a crucial first step before grafting polydopamine nanoparticles in advanced nanocomposite coating processes. One study noted that plasma treatment increases surface roughness and introduces polar groups that are essential for subsequent coating adhesion.

Flame Treatment

This method uses a high-temperature flame to activate the PP surface.

How it works: Free radicals from the combustion process (like CH, NO, CO compounds) are grafted onto the PP molecular chain under the influence of high temperature and gas pressure. This treatment creates polar groups on the surface, which are necessary for strong adhesion.

Note: Flame treatment is an older, well-established technique but requires careful control of many parameters (like flame structure, gas mixture, and speed) to achieve consistent, optimal results.

Advanced Coating Technologies

Modern surface treatment goes beyond just activating the film and involves applying specialized chemical layers to create a permanent, print-ready surface.

Primers and Nanocoatings: A key approach is applying a primer (e.g., the Aquasafe Matte BOPP Coating) designed for high-speed gravure printing. More advanced research uses organic/inorganic nanocomposite coatings. For example, one process involves plasma treatment, followed by grafting polydopamine nanoparticles, and finally applying a SiO2@TiO2 coating. This creates a micro-rough, highly adhesive surface that significantly improves the precision and adhesion of water-based inks.

In short, while corona treatment is the industry workhorse for its speed and low cost, its effects can diminish over time. For more demanding applications, particularly with water-based inks, plasma treatment and specialized primers or nanocoatings are used to create a more durable and robust surface for ink adhesion.