In a previous GRACE newsletter, we explored solvent-based deinking as a route towards more circular printed products. While these trials demonstrated that inks can be removed from a range of substrates, some materials still required intensive solvent treatment and mechanical action. This raised an important question: instead of removing the ink after use, can printed products be designed from the start to be easier to separate and recycle?
Within GRACE, Centexbel investigated the use of reversible primers as an alternative approach. Rather than focusing on dissolving the printed layer, these primers are placed between the substrate and the ink layer. During use, the primer must provide sufficient adhesion and durability. At end-of-life, however, the same layer should facilitate controlled separation of the printed coating from the substrate, enabling reuse or cleaner recycling.
Two complementary technologies were evaluated
A first approach was based on primers containing expandable microspheres (Expancel®). These materials expand when exposed to elevated temperatures, creating internal stresses that weaken the bond between the surface print and substrate.
The concept was tested on polyester textiles, PVC films and polypropylene films using thin gravure-applied primer layers combined with a coloured PU topcoat.
Second approach
The second approach focused on reversible polyurethane primers containing siloxane building blocks. These primers were specifically developed to create an interface with controlled adhesion behaviour.
By tailoring the chemistry of the primer layer, it becomes possible to maintain adequate performance during use while reducing the force required to separate the coating during recycling. In the case of cotton printed with a pigment ink separation was not possible. Further investigations are being done to improve the deinking
Conclusion
The GRACE results demonstrate that reversible primers can become a valuable addition to the toolbox of circular printing technologies. Together with solvent-based deinking and other recycling strategies, they offer promising pathways to retain material value and durability, while improving recyclability and reduce waste generation in the graphics and signage sector.
