The application of ATR-IR method for distinguishing easy and poor deinkable UV prints

摘要

In recent years, UV-curable ink has been developed and widely used for various printings. However, UV prints can cause dirt troubles when it comes to recovered paper recycling. The new method was developed, which can distinguish UV prints from various printings by means of an attenuated total reflection infrared spectroscopy, hereafter called ATR-IR method. In this paper, the application of this method was tested for efficient use of UV prints as raw materials for paper recycling. First, a mill trial was carried out in the DIP process using UV prints solely as raw materials. Second, model printings were made with four types of UV inks, a kind of conventional UV ink and three kinds of high-sensitive UV inks. Each model printings had four levels of ink coverage patterns (100%, 75%, 50% and 25%). Then, deinkability of those prints were evaluated by lab-experiments. Third, each print was measured by using ATR-IR method, and the relationship between IR spectra and deinkability was investigated. As a result, in the mill trial UV prints caused more than 20 times as much dirt speckles as conventional prints printed with oil-based ink. On the other hand, when some UV prints were taken from bales used for the mill trial and evaluated by lab test, it was revealed that not all UV printings lead to dirt trouble. In order to clarify the factors which affected deinkability of U V prints, model printings were inspected by lab-experiment. Results from lab-experiments, the number of dirt speckles larger than 250 micro-meter in diameter increased as the ink coverage got higher. In addition, according to ATR-IR measurement results, the higher ink coverage area showed stronger intensity of IR spectra which were characteristic of UV-curable ink. These results suggested that deinkability of UV prints could be predicted by ATR-IR method. Finally, the method was applied for assessment of recovered paper from commercial printing presses. It was confirmed that this method made it possible to distinguish easy-deinkable UV prints from other UV printings. Therefore, it is considered that this ATR-IR method is applicable for incoming inspection of recovered paper.