Analysis of ink and water balance in offset printi

2022-09-23
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Balance analysis of ink and water in offset printing

in the process of offset printing, the supply of ink and water. 4. The transmission mode of arc tooth synchronization is adopted in the transmission part of the equipment, which is a very key link Offset lithography is based on the lipophilic and water-resistant part of the printing plate pattern, and the hydrophilic part of the blank part accounts for more than 30% of the total resin market demand; The demand for polyvinyl butyral accounts for more than 85% of its total demand, which is based on the principle of water resistance and oil-water immiscibility

printing principle reminds us printers: "Only when there is a very strict boundary between the water film of the blank part of the printing and the ink film of the graphic part, and the oil and water are not saturated with each other, can the water and ink balance of offset printing be achieved.

the water and ink balance is the basis of lithography. In the offset printing process, whether the water and ink balance is right or not is closely related to the normal transfer of imprints, the depth of ink, the accuracy of overprint and the dry state of printed matter. Therefore, whether it is correct or not Mastering and controlling the balance of ink and water is the key to ensure the stability of printing product quality

first, analysis of the phenomenon of ink balance imbalance

how to achieve ink balance, the operator should not only understand and study the organic relationship between ink and water, the constraints between them and the laws of subtle changes between them, but also analyze and explore the adverse consequences caused by ink imbalance

(1) analysis of the phenomenon of less water and less ink: during the printing process, there is a certain water film on the blank part of the printing plate. When the water film can compete with the oil, it will not be stained by the ink on the ink roller. If the water is too small and the amount of the water layer cannot resist the ink's attachment to the blank part, the blank part will be stained with ink, resulting in hanging dirt. A small amount of ink supply will make the print writing Matt, light gray, and the impression is not solid, The footprints are covered with white spots like snowflakes In this state, although the "ink balance" is also achieved, this "ink balance" is not the "ink balance" we want

(2) analysis of the phenomenon of less water and more ink: at this time, it is most likely to produce uneven ink color, dirty hanging, and paste version and word due to water shortage in a certain part or large page At the same time, the imprinted ink color of the print is also relatively deep, making the print dark and unclear, especially affecting the reproduction of fine dots, and the image is not clear

(3) analysis of the phenomenon of large water and little ink: if the water content of the layout is too large, it will gradually spread to the surface of all ink rollers, forming a certain thickness of water layer, which hinders the normal transmission of ink. The emulsification speed of ink is accelerated, the ink color of imprinting is gradually unsaturated, the graphics and texts become shallow, and the handwriting is weak, gray, hairy, flowery, and dim. There is dizziness around the impression, which is not neat, the image is not clear, and there is no hierarchy

(4) analysis of the phenomenon of too much water and too much ink: when there is too much water in the layout, the ink color will become lighter, and it is often blindly believed that the amount of ink supplied is small, so the amount of ink continues to increase. After a long period of cycling, the ink emulsification loses its stability, resulting in a vicious cycle of ink imbalance. The control accuracy will not be poor, resulting in serious emulsification of ink, piling up on the surface of the ink roller, making the printing unable to proceed normally

second, the principle of ensuring the balance of water and ink

to maintain the balance of water and ink, we should first manage the water well. A deep understanding of the nature and function of water is the basis for good water management. Water is widely distributed in nature. It is a colorless and tasteless transparent liquid. Water is a dipolar substance that can dissolve with many other substances. But there are also substances that are incompatible with it. For example, it is incompatible with oils, and it is also different from the substances that can be compatible with it. It can be seen from the order of hydrophilic properties of metals. The following order is from strong to weak hydrophilicity: potassium, calcium, sodium, magnesium, aluminum, zinc, chromium, iron, nickel, tin, lead, etc. the plate printing machine we use is made of aluminum metal with good hydrophilicity. Offset printing inks generally use inks with good water resistance, bright colors, transparency, saturation and purity. Oil is a non-polar substance, which is immiscible with water under normal conditions. Everything in the world is not a pure single element material, so is the water repellency of ink. From the perspective of the molecular structure of oil, all kinds of fats in oil molecules are mainly composed of two parts: one part is a long hydrocarbon chain, which is water repellent and lipophilic, and is called a water repellent group; Another small part has oil repellent hydrophilicity, which is called hydrophilic group. These two groups are interrelated and contradictory. Groups with completely opposite properties exist in a molecule. The former is hydrophobic and lipophilic water repellent group, which is non-polar, and the latter is oil repellent water repellent group, which is polar. In other words, oil has duality, which is both non-polar and polar. There is both immiscibility and possibility of oil-water miscibility. However, because the polar carboxyl groups that are hydrophilic and oil repellent are very few in the whole oil molecule, they are only in a subordinate position in the oil molecule, while the non-polar water repellent lipophilic groups account for the absolute majority and take a dominant position in the whole oil molecule, so the oil is characterized by oil-water immiscibility at room temperature and pressure. Through the above analysis and discussion, it is impossible for offset printing technology to make the ink not emulsified at all. The key is to master it properly and achieve the balance of ink and water

III. measures and control methods to ensure the balance of ink and water

(1) during the printing process, the printing plate must have a solid graphic foundation and blank foundation to maintain the stability of lipophilic and hydrophilic

(2) on the premise of ensuring that the printing plate does not get dirty, control the water supply within the minimum range (the water supply for the printing plate should be 26%), and keep the water supply and the ink volume in a relatively stable state, so as to ensure the consistency of the ink color before and after the printing and the stability of the printing operation

(3) master the principle of less water and thicker ink. This refers to less water, which is based on the premise that the blank part of the page is not stained with dirt. The so-called ink thickness is also based on less water. Large water causes ink emulsification, and the ink layer cannot be thick. From the transfer process of offset ink, it can be seen that in the primary water supply and ink supply, there are three times of ink mixing and emulsification, and it is impossible to maintain a strict dividing line between water and oil. Therefore, ink balance in offset printing can only be a relative concept, and a completely ideal ink balance does not exist. As long as the best balance is achieved, the ideal print can be printed

(4) choose the size of ink according to the material category of the printing plate. The water volume of PS version can be appropriately smaller, and that of PVA version can be slightly larger; The water volume of smooth paper can be slightly smaller, and that of rough paper can be slightly larger. The machine runs faster, and the water volume can be slightly smaller, and it can be larger at low speed

(5) environmental conditions and temperature and humidity cannot be ignored. Because the moisture in the layout is distributed in direct and indirect forms, while meeting the needs of ink and water balance during printing, most of the moisture in the layout is distributed to the space. The higher the ambient temperature is, the faster the moisture will be distributed

(6) the pH value of the fountain solution must be controlled (generally controlled at about 4.5 ~ 5.5). In addition, because the pH value of the offset paper surface has a great impact on the pH value of the fountain solution, it is best to measure the pH value of the paper. If the pH value of the paper is too low, slightly increase the pH value of the fountain solution; On the contrary, if the pH value of the paper is too high, its pH value should be appropriately reduced to neutralize the oh- of the paper, so as to buffer the excessive increase of the pH value of the fountain solution. According to the relevant information and the conclusion drawn from practice, when the pH value of paper is 9, the pH value of fountain solution is 4; When the pH value of the paper is 8, the pH value of the fountain solution is 5

(7) use the method of scientific instrument detection to control the ink balance. Because the printing obtained in the ink balance state must have thick ink color and consistent density, the change of ink balance in the printing process can be detected by continuously measuring the density. When the density value reaches the standard value range, it can be inferred that the ink balance state is normal

in work, in addition to considering the offset printing transmission process of water and ink, the operator should also consider the different types of raw and auxiliary materials used, including computer-aided engineering (CAE) and physical testing materials (paper, ink, plate, blanket, etc.) as well as the differences in working environment and other related factors, so that the water and ink can reach or basically reach the balance suitable for the printing process requirements

source: Interconnection

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