Recycling: How sustainable is UV-curing?
Commonly used deink technologies tend to have problems with UV-cured printing inks. One of the reasons is the particle size, because too large and too small they don’t stick to soap bubbles that are used in the common alkine pulping.
Too many coloured specks
“The recycled paper has so many coloured specks that it can only be used for low-grade paper/board”, says Dr Stefan Busse from Siegwerk Druckfarben in Germany. Busse, who is working as Regional Director Technology for flexible packaging adds: Studies have shown that the functionality of the binders and monomers or the reactivity of UV-curable ink/coating have little to no influence on particle size.”
“UV resins can be designed to maximize ink removal”, says Scott Auger of Allnex.
On the other hand, Scott Auger who is working as global marketing manager at Allnex, notes that “the problem of detaching and removing UV-cured inks has diminished in scale with the drop in demand for newsprint and magazines.” However, there are new technologies that can get good results. “The latest drum-pulping technology and chemistry can remove UV ink and overprint varnishes at the start of the process using enzymes at relatively low temperatures”, says Auger.
Further breakdown of particles
“Further breakdown of the ink particles would be needed.” says Stefan Busse from Siegwerk Druckfarben.
Stefan Busse from Siegwerk says that the further breakdown of the ink particles and subsequent flotation would be beneficial for the recyclability. “The size and shape of the particles formed can be linked to the hardness and the glass transition temperature of the acrylates and be influenced to a certain degree by the choice of raw materials”, he adds.
A complete and more detailed interview with both experts is published online as of now in European Coatings Journal 5/2017. Furthermore, the Interview discusses future technological trends in UV curing and provides contact data for both experts.