Hi guys, this is Grace, I’m the sales director of Rainbow Screen Printing Supply Ltd.
From our work experience in plastic printing, a frequently asked question regarding PP ink is how to address poor adhesion issues. Specifically, what are the best adhesion solutions for PP ink? As we know, PP plastic is a non-polar substrate. Due to its molecular structure, it often exhibits poor adhesion characteristics. During the printing or painting process, it can be challenging for plastic printing ink to properly adhere to its surface, leading to undesirable defects like paint peeling, degumming, and flaking.
To enhance the coating power of the plastic surface and improve the bonding force between the paint or plastic printing ink and the base material, it's essential to prepare the top layer of the plastic substrate. Common methods for this include flame treatment, corona treatment, and using a PP treatment primer.
1. PP Flame Treatment
In flame treatment, the plastic surface is pre-treated to initiate an oxidation reaction through high temperatures, which generates polar groups. This increase in polar groups significantly enhances adhesion and forms a robust bond with the ink or paint. However, this method can be unstable due to equipment and control processes, making it easy to burn the substrate.
2. Corona Treatment
Corona treatment is another effective method to improve the adhesion of plastic surfaces. While the equipment can be costly, it effectively increases the dyne value of the plastic surface. However, this value can decay over time, so it’s crucial to ensure timely spraying. This method activates the plastic surface through discharge treatment, rearranging the surface molecular structure and increasing polarity.
3. PP Treatment Primer
A PP treatment primer acts as an intermediate layer between the substrate and the PP plastic ink or paint. It activates the surface of the PP substrate, enhancing its adhesion and wetting properties while chemically bonding with the paint. This results in greater stability and firmness of the coating, as the application of PP primers improves adhesion through a combination of intermolecular forces, chemical bonding, and mechanical bite forces after the primer partially swells and dissolves.
If you're looking for effective adhesion solutions for PP ink or want to resolve poor adhesion issues, feel free to inquire with us. Additionally, if you send your substrate material to us, we can conduct testing to help you find the best plastic printing ink for your needs.
