Wet package

Over the past few decades, many changes have been made to improve paper quality, Nicasy explains. “An ordinary sheet of paper is actually something pretty special. The complexity starts with the fibers, because every tree is different. Each fiber has its own unique properties; there are hundreds of different ones.  Some fibers are a little longer, others a little sturdier or thicker. And all of them affect the paper very differently.” In addition to the fibers, fillers are added to improve the paper’s properties. The paper may also receive a finishing treatment. “Packages that are delivered to your home increasingly come in paper packaging. But you don’t want a damaged or wet package on your doorstep. That is why packaging paper must be water-resistant, but at the same time, it needs to be printable and recyclable. Much research is therefore being done into multifunctional eco-friendly coatings. Printing ink is also a focus of research: we’re seeing more and more water-based or plant-based inks free of harmful solvents.”

According to Nicasy, knowledge of the behavior of paper fibers is essential for the implementation of sustainable innovations within the paper and printing industry. “There is still a lot of uncertainty about how exactly ink is absorbed by the individual paper fibers, for example. Does it penetrate through the fiber or does it run along the surface? Through fundamental paper fiber research, we aim to provide the paper and printing industry with tools to develop new applications.”

Ultra-fast ink absorption

And so, Nicasy set out to find a method to map ink penetration in detail. But that was easier said than done. “Ink is absorbed very quickly. The latest industrial printers can print more than a hundred pages per minute. It’s a very dynamic process. And besides, the paper is very thin, and opaque.”

The approach he ended up using – he developed an ultra-fast NMR imaging method (UFI-NMR) to track the ink droplet on the paper – is unique, Nicasy reluctantly admits. Nuclear Magnetic Resonance (NMR), known from the medical imaging technique MRI, can say a lot about a material's properties. “The ultra-fast aspect in particular is a breakthrough. We used a special GARField NMR that was developed and built from scratch within our research group. There are only a few of these devices in the whole world. By adjusting the electromagnetic pulse sequence, we can now create an image every 10 milliseconds.”

Pioneering work

This new method immediately yielded some remarkable results. He unabashedly starts talking about penetration depth, swelling phases and latex. “For the first time ever, we were able to distinguish ink absorption in multiple phases. First, we see capillary absorption of the aqueous components – rising moisture – and then the paper fibers swell. The water passes along the fibers, trapping any air present. During the final phase, the trapped air escapes and the ink dries. Our measurements show that swelling has a huge impact on the penetration process in special compressed papers."

In addition, Nicasy spent a lot of time studying latex particles, one of the main components of water-based ink. “By changing the number of latex particles, we were able to modify the ink’s physical properties. The more particles, the further they penetrated. This is an undesirable effect with ink bleeding through to the back of the paper. So we found that we can use latex to control the penetration depth.”

Nicasy’s measurements form a wealth of data that should eventually lead to a predictive model for the printing industry. That way, we can see in advance how an ink will react with a paper, and how we can modify ink and paper to achieve the best print quality. I’m happy that two PhD candidates will be continuing my work. Using UFI-NMR, they will also focus on ink absorption of coated paper and improvements to the ink itself.” So yes, he feels a little proud, he concludes with a twinkle in his eye. Because as a “smooth operator,” he has done a fair share of pioneering work in the field of printing.