Lithographic Offset Balance Control Control (1)

Introduction to ink balance

In the four printing methods of plain and concave soft holes, only one way is obviously different from the other three printing methods in the principle of ink transfer. This is lithography, which is what we usually call offset printing.

The basic printing principle in offset printing is to use the two laws of oil and water immiscibility and selective plate adsorption to make ink and water balance each other on the printing plate to realize the transfer of dots, so as to achieve a clear and full color image of the printed matter. Effect. The word "ink balance" comes from this.

I. Understanding of the Ink Balance

The ink and water on the printing plate must be present and balanced at the same time. The purpose is to maintain the maximum amount of ink loaded in the graphic printing area, so that the ink is bright, saturated, and the dots are clear and clean, while keeping the non-printing area highly clean and tidy. The balance between water supply and ink supply is called ink-water balance.

Offset ink balance refers to adjusting the amount of fountain solution at a certain printing speed and printing pressure so that the emulsified ink contains less than 26% of fountain solution, forming a slight W/O emulsion ink. Use a minimum amount of liquid to compete with the ink on the plate. Offset printing is the use of natural laws in which oil and water are incompatible with each other, forming graphic and blank parts on the printing plate. It supplies both ink and water to the printing plate. It absorbs water and resists water while the blank part absorbs water and resists oil. print. If the ideal balance of ink and water, the blank part of the printing plate adheres the fountain solution, and the graphic part is attached with the ink. Only when the surface tension of the fountain solution and the surface tension of the ink are equal, the diffusion pressure at the interface between the two is Zero, the fountain solution and the ink remain relatively balanced at the interface, do not infiltrate each other, in this case the printing effect is ideal. However, in actual printing, the balance of ink and water is a dynamic balance and it is changing all the time. If the amount of ink applied to the layout exceeds equilibrium, the ink will expand toward the blank after being strongly squeezed, and will infiltrate the blank surface causing stickiness. On the other hand, if the water supply to the layout exceeds the equilibrium value, when the water roller passes through the surface of the graphic, it will leave more water on the surface of the graphic, and then it will be strongly pressed by the water roller and the ink roller and attached to the graphic part. The deep emulsification of the ink layer causes the imprint to be dull. When the amount of water supplied is too large, the water enters the ink fountain along the ink fountain roller and the ink fountain roller, causing a large range of ink emulsification, and eventually the printing cannot be continued.

The ink balance is the basis for lithography. In the offset printing process, the balance of ink and ink is just right, and there is a very close relationship with the normal transfer of imprinting, the depth of ink, the accuracy of overprinting, and the dryness of the printed matter. Whether it is possible to correctly control and control the ink-and-wash balance is the key to ensuring the quality of printed matter.

Second, the conditions to produce ink and water balance

In the printing process, even if the water delivery device is adjusted and operated correctly, it is affected by the shutdown, the temperature and humidity of the printing shop, the running speed of the printing machine, the type of ink, the type of paper, and the blank area of ​​the layout with the increase in the number of printed copies. The restriction of the hydrophilic properties, etc. will directly affect the ink-water balance.

1 The plate must have a solid graphic foundation and a blank foundation to keep the oleophilic and hydrophilic properties relatively stable. If a certain condition is not met, ink will lose its balance.

2 The thickness of the sand should be well controlled. The grain of the surface of the printing plate must be kept uniform and dense, with a certain physical strength, so that the graphic and blank parts have a firm attachment base and have good water storage conditions.

3 The workshop temperature and humidity should be constant. In principle, the workshop is required to have a constant temperature and constant humidity, because the change of the temperature will cause the viscosity and fluidity of the ink to change, and the temperature rise will cause the water to evaporate, thus causing the ink to lose its balance. Especially resin inks are sensitive to temperature. It is best to install an air conditioner and control the temperature within the range of 20°C to 25°C.

4 The machine should run at a constant speed. In the production process, the machine must run at a normal speed and at a constant speed. The machine is suddenly fast and slow, and it is easy for the ink and ink balance to lose control.

5 To master the characteristics of different types of paper, ink and other raw materials. The performance of printing inks and papers varies greatly. Different papers and inks are used, which have different requirements for the ink-water balance. If the paper has a close and loose texture, the water content is divided; the ink has the viscosity, fluidity, and the size of the pigment particles. In the same conditions as the printing plate, temperature, humidity, etc., it is necessary to grasp the changes in their properties.

6 The amount of dry oil should be moderate. Putting dry oil in the ink promotes the drying of the ink, but the drying oil promotes ink stickiness. Therefore, the amount of dry oil is not the main factor that causes the ink balance to lose control and become dirty.

7 Fluent dilution pH should not fluctuate. The pH of the fountain solution is also an important condition that affects the ink-water balance. It must be made constant to avoid large-scale fluctuations.

8 Adjust pressure properly. The press must have precise roller pressure, ink roller pressure, and water roller pressure. These three pressures directly determine the ink balance.

(to be continued)