Foaming problems in special coated paper for web machines

First, the principle of foaming

Rotary printing presses have the characteristics of high-speed printing, generally 40,000-50,000 sheets per hour (but the fastest lithographic printing is only 10,000 sheets/hour), and the direct folding is performed immediately after the printing is dry, at such a fast speed. In order to prevent the occurrence of printing abnormalities such as ink dripping and back sticking, it is necessary to rapidly dry the printing ink, and the most effective method for rapid drying of the ink is high-temperature heating, so there is an oven in the structure of the rotary machine. The printed paper is heated so that the ink can dry quickly.

Quantitative moisture, while the water is dried at a high temperature (drying temperature is generally around 140 °C), becomes water vapor released outward. However, if full-page printing is performed on both sides of the paper at the same position and the amount of ink is large, water vapor cannot be released to the outside due to the ink covering the entire surface of the paper, resulting in blistering.

Second, several important factors that affect the foaming of the rotary machine:

Based on the above blistering principle, we can summarize three aspects affecting the bubbling of rotary printing: printing conditions, inks, and papers, among which several major factors regarding printing are as follows:

1, the printing press drying temperature and printing speed

Because the speed of rotation is faster, the residence time of the paper in the oven is also shorter. In order to ensure the normal drying of the ink and to prevent backprinting, it is necessary to increase the drying temperature and accelerate the drying of the ink, but according to the gas In the expansion theory, under certain pressure (P1=P2), the higher the temperature (T2>T2), the larger the volume (V2>V1). Therefore, during the printing process, the drying temperature is too high and foaming will occur. However, if the drying temperature is too low, problems such as back-printing may occur because the ink is not dry.

2, the ink drying performance

Rotary printing ink used for special ink. Therefore, the characteristics such as fluidity and drying of the ink have a great influence on the bubbling of the rotary paper. The ink is more likely to be dried. The lower the temperature of the rotary drying, the less likely to blistering, but the ink that dries quickly is printed after printing. Gloss is generally relatively low.

Reprinted from: Printer