Offset printing is a lithographic technique in which the printing ink is first transferred from a plate to a blanket cylinder from where it is printed onto the paper sheet. The printing ink consists of color pigments, modified colophony and alkyds as binding agents, and mineral or vegetable oils as solvents.
As a closely branched, largely aromatic macromolecule with free hydroxy and carboxylic acid groups, lignin is similar in structure to modified colophony. Furthermore, it offers numerous possibilities for chemical modification, enabling its properties to be adapted to the requirements of printing-ink formulations.
We incorporate lignin into alkyd polymers as a substitute for colophony and also test formulations with polyether and polyester polymers. We thereby investigate different lignin types, including kraft lignin, soda lignin and organosolv lignin.
With this project, we are creating a possibility to use the raw material wood more efficiently in the future. Wood is composed mainly of cellulose, hemicellulose and lignin. Every year, paper-manufacturing processes produce around 50 million tonnes of lignin as a waste product. Due to its heterogeneity and low solubility in common organic solvents, there have, however, been hardly any large-scale material applications for lignin up until now. Despite various application tests as adhesives or dispersants, 98 percent of lignin is still burned. Whilst a proportion of the energy generated is used by paper mills and, furthermore, fed into the power grid, a higher-value, material use of lignin would nevertheless be better for the environment and could be economically attractive.
Intermediate results
Lignin has a relatively hydrophilic, i.e. “water-loving” structure. As a very low polarity is essential for good print quality in offset printing, as is the case with oils, one of the main challenges is to reduce the polarity of the lignin.
In a first step, we have therefore developed a method which enables us to quantitatively assess the polarity: by measuring the contact angle of a water droplet on the surface of the lignin binding agent. The higher the angle, the closer we are to our goal of being able to use lignin binders for offset printing.
Through the incorporation of fatty acids into the lignin polymer, we have been able to increase this contact angle by up to 90°. Together with our project partners, we were able to incorporate the lignin binders compounded in this way into a black printing ink and to produce the first print samples. These show very promising results - both in terms of their flow behavior on the printing press and in terms of the finished print image.
Fraunhofer Institute for Wood Research 
