Lithographic Offset Balance Control Control (2)

Third, to ensure the principle of ink and water balance

To maintain the balance between water and ink, you should first manage the water. A deep understanding of the nature and role of water is the basis for managing good water. Water is widely distributed in nature. He is a colorless, odorless transparent liquid. Water is a dipole substance that dissolves with many other substances. But there are substances that are incompatible with it. For example, he is immiscible with oils. The substances that are compatible with them are also indistinguishable from each other, and can be seen from the order of the hydrophilic properties of metals.

The following arrangement is the order of the hydrophilic properties from strong to weak: potassium, calcium, sodium, magnesium, aluminum, zinc, chromium, iron, nickel, tin, lead, etc. The plate printing machine we use is hydrophilic. Made of aluminum.

Offset printing inks generally use inks with good water resistance, color, transparency, saturation, and purity. Oils are non-polar substances that are immiscible with water under normal conditions. Nothing in the world is purely a single element of matter, and so is the water repellency of ink. From the perspective of the molecular structure of oil, various types of fats in oil molecules are mainly composed of two parts: Some are very long hydrocarbon chains, have water-repellent and lipophilic properties, and are called water-repellent groups; Oil is hydrophilic and is called hydrophilic group. These two groups are related to each other and contradictory to each other. The completely opposite nature of the group exists in one molecule. The former is a hydrophobic, hydrophobic, water-repellent group that is non-polar. The latter is an oil-and water-repellent hydrophilic group. .

In other words, oil has two properties: it is both non-polar and polar. It has both oil-water incompatibility and oil-water miscibility. However, since the polar and carboxyl groups of the oil-repellent and oil-repellent groups are very few in the entire oil molecule, they are only subordinate to the oil molecules, while the non-polar hydrophobic and oleophilic groups account for an absolute majority of the total oil molecules. The occupies a dominant position in the oil, so the oil is immiscible with oil and water under normal temperature and pressure. Through the analysis and discussion above, we can see that it is impossible for the offset printing process to make the ink not emulsify at all. The key is to master it properly and achieve a balance between ink and water.

Fourth, ensure the ink and water balance measures and control methods

1 During the printing process, the printing plate must have a solid graphic basis and a blank basis to maintain the stability of the lipophilic and hydrophilic.

2 Under the premise of ensuring that the printing plate is not stained, the amount of water supply should be controlled within the smallest possible range (the water supply of the layout should be 26%), and the amount of water supply and the amount of ink should be kept in a relatively stable state. Ink consistency before and after the ink and stable printing operations.

3 Master the principle of less ink and thicker water. There is less water here, assuming that the blank part of the layout is not stained. The so-called ink thickness is also based on less water. Due to the large amount of water caused by ink emulsification, the ink layer cannot be thick. From the process of the transfer of the offset ink, it can be seen that in a single water supply and ink supply, a total of three ink mixing and emulsification occur. It is impossible to maintain a strict boundary between water and oil. . Therefore, the balance of water and ink in offset printing can only be a relative concept, and the perfectly ideal ink-water balance does not exist. As long as the best balance is achieved, the ideal print can be printed.

4 Select the size of the ink according to the material type of the printing plate. The PS version can be smaller and the PVA version can be slightly larger. The smooth paper can be slightly smaller, the rough paper can be slightly larger, and the machine can run faster. The amount of water can be slightly smaller and can be larger at low speeds.

5 Environmental conditions and temperature and humidity cannot be ignored either. As the layout water is distributed in both direct and indirect forms, the layout moisture meets the needs of the ink-and-wash balance during printing, and most of them are distributed to the space. The higher the ambient temperature, the faster the emission will be.

6 The pH of fountain solution must be controlled (typically around 4.5 to 5.5). In addition, since the pH of the surface of the offset printing paper has a great influence on the pH of the fountain solution, it is preferable to measure the pH of the paper. If the pH value of the paper is too low, the pH of the fountain solution should be slightly increased. On the other hand, if the pH of the paper is too high, the pH of the paper should be properly reduced so that it can neutralize the OH- of the paper. Excessive increase in pH of fountain solution. According to relevant data and conclusions drawn from practice, when the pH value of the paper is 9, the pH of the fountain solution is 4; when the pH value of the paper is 8, the pH of the fountain solution is 5 as good.

7 Use scientific instrumentation to control the ink balance. Because the ink obtained under the ink-balanced state is necessarily thick and uniform in density, the change in water-ink balance during the printing process can be detected by continuously measuring the density. When the density value reaches the standard value, it can be concluded that the ink balance is normal.

In addition, in addition to considering the offset transfer process of water and ink, the operator should also consider the different types of raw and auxiliary materials used (paper, ink, plate, blanket, etc.) as well as working environment differences and other related factors. , so that the ink reaches or basically meets the balance required for the printing process.

(to be continued)