First, the status quo

In recent years, there has been a drop in fees in the printing industry, and the period of time required by customers has been continuously shortened. At the same time, it is also necessary to cope with the rapid development of digitalization. The days of the printing industry are indeed not very good. In such a difficult environment, rotary offset printing has won high-speed development relying on its advantages of high production efficiency, and it has grabbed a 65% strong share in the offset printing market demand.

Now, the biggest issue faced by offset printing is speeding up. Under high-speed printing conditions, the print job characteristics of web offset inks, and the adaptability to paper, web, etc., become particularly important. On the other hand, environmental protection initiatives in the printing industry are also moving forward with social responsibility and the promotion of ISO14001. In the world-wide wave of environmental protection, how will rotary offset inks handle VOCs (volatile organic compounds), PCA (polycyclic aromatics), heavy metals, industrial waste, and other resources (recycled paper) and combustion (dioxins) in the future? Environmental issues have become important research topics.

Here, the author will focus on the "high-speed printing conditions" and "environmental issues" to talk about the new trend of rotary offset printing ink.

Composition and Properties of Thermoset Web Offset Printing Ink:
Table 1. Composition and properties of lithographic inks Thermoset web offset inks Non-thermoset web offset inks Leaf ink pigments 15-22 15-22 22-22
Synthetic resin 30-35 20-25 25-30
Vegetable oil 5-10 10-15 10-20
Petroleum series solvent 30-40 30-40 25-25
Additive 1 - 5 1 - 5 4 - 10
Total 100 100 100
Viscosity Medium Low Viscosity Medium-Small Medium-Small Large Shrinkage Medium Film Formation Very Slow Slow

Table 1 compares the composition and properties of thermoset web offset inks, non-thermoset web offset inks, and leaf inks. Among them, the basic composition does not have any difference. It is also a pigment, a synthetic resin, a vegetable oil, a refined oil series solvent, and an additive. The difference in the amount of these ingredients is determined by the difference in drying methods and the paper used. The heat-set web offset printing ink is mainly used in an evaporation-drying method. Therefore, compared with other inks, the refined oil series solvent has a lower boiling point and less vegetable oil. This has a great relationship with the on-board stability of the ink to be described later.


Second, speed up measures

1. High viscosity of ink

On high-speed printers, the ink is greatly affected by high loads and mechanical heating. The increase in the temperature of the printing press causes the ink cohesion force on the ink roller and the blanket to decrease, resulting in a drop in the viscosity of the ink. As a result, problems such as coarse dots, insults, residues on the layout and blanket, ink splashes, and ink flying frequently occur.

The high concentration of ink is an effective means to solve the above problems. High concentration generally brings about an increase in the viscosity of the ink, and an increase in the viscosity of the ink will reduce the range of the applicable paper, so it is also indispensable to control the concentration of the ink as much as possible. This problem is also closely related to the "ink emulsification properties" to be discussed later.

2, stability and drying

The relationship between viscosity and speed (rotation number) and stability is: As the speed increases, the viscosity rises and ΔTV also increases, which will seriously affect the stability of the ink on the machine, and easily lead to the following consequences:

1 limited application of paper;
There are residues on the 2 layout and blanket;
3 poor mobility;
4 ink roller deposition;
5 flying ink and so on.

On high-speed printers, the suppression of the second increase in viscosity, which is the so-called "ΔTV rise", is even more important than the increase in the viscosity of the ink itself.

The choice of resin and solvent and the combination of them are an important part of improving the stability of the ink, but this practice usually results in a decrease in the dryness of the ink. From this we can see that the stability and drying of the machine is inherently a contradiction. Therefore, it is an indispensable condition to grasp the balance between the characteristics of the resin and the solvent.

On the other hand, recently, in order to adapt to the trend of higher speed, dryers with a length of 10 meters or more and 4-color zone drying have become the main force of production, and improvements in the mechanical field are also under way. (to be continued)