Introduction to ink balance(one)
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Among the four printing methods of flat and concave soft holes, only one way is obviously different from the other three printing methods in the principle of ink transfer. This is lithographic printing, which is what we usually call offset printing.
The most basic printing principle in offset printing is to use two rules of oil-water incompatibility and selective adsorption of printing plates to maintain the balance of ink and water on the printing plate to achieve the transfer of dots, and to achieve clear and full-color print images. Effect. The word ink and water balance comes from this.
First, the understanding of ink and water 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 in the printing area, make the ink bright, saturated, clear and clean, and keep the non-printing area clean and tidy. The balance between the amount of water supplied and the amount of ink supplied is called the ink balance.
Offset ink balance refers to: adjusting the supply amount of dampening solution under a certain printing speed and printing pressure, so that the ratio of dampening liquid contained in the emulsified ink is less than 26%, forming a slight W/O type emulsion ink. With the minimum amount of liquid and the ink on the plate to compete. Offset printing is a natural law that uses oil and water to be incompatible with each other. It forms a graphic and a blank part on the printing plate. It supplies both the ink and the water supply to the printing plate, and absorbs oil against the water through the layout, while the blank part absorbs water and oil. print. If the ideal part of the ink is in equilibrium, the blank part of the printing plate adheres to the dampening solution, and the ink part is attached to the image. Only when the surface tension of the dampening solution and the surface tension of the ink are equal, the diffusion pressure at the interface between the two is Zero, dampening solution and ink remain relatively balanced on the interface, and do not infiltrate each other. In this case, the printing effect is ideal. But in actual printing, the ink-and-wash balance is a dynamic balance that is constantly changing. If the amount of ink supplied to the layout exceeds the balance, the ink expands toward the blank portion after being strongly pressed, and invading the blank surface causes stickiness. On the other hand, if the water supply to the plate exceeds the balance value, when the water roller passes through the surface of the image, it will leave more water on the surface of the image, and then it will be strongly squeezed by the water roller and the ink roller, and attached to the graphic part. The ink layer is deeply emulsified, causing the print to be dull. Moreover, when the water supply amount is too large, the water enters the ink fountain along the inking roller and the squeezing roller, causing a large range of ink emulsification, and finally the printing cannot be carried out.
Ink balance is the basis for lithography. In the offset printing process, the ink balance is just right, and has a very close relationship with the normal transfer of the print, the depth of the ink, the accuracy of the overprint, and the dry state of the print. The correct mastery and control of ink and water balance is the key to ensuring the quality of printed matter.
Second, the conditions for the production of ink and water balance
In the printing process, even if the water delivery device is adjusted and operated correctly, due to the impact of the shutdown, the temperature and humidity of the printing workshop, the running speed of the printing machine, the type of ink, paper, and the blank space of the layout increase with the number of printed copies. The restriction of the hydrophilic property and the like will directly affect the ink and water balance.
1 Plates must have a strong graphic basis and a blank foundation to maintain relative oleophilic and hydrophilic stability. If a certain condition is not available, the ink will be out of balance.
2 The thickness of the sand should be controlled. The sand surface of the printing plate must be kept even and fine, with a certain physical strength, so that the graphic and blank parts have a strong attachment base and good water storage conditions.
3 The temperature and humidity of the workshop should be constant. In principle, the workshop is required to have constant temperature and constant humidity conditions, because the change of temperature causes changes in the viscosity and fluidity of the ink, and the temperature rise causes the water to evaporate, thereby causing the ink to lose balance. Especially resin inks are very 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 production, the machine must be running at a normal speed and at a constant speed. The machine flies quickly and easily, and the ink balance is easily lost.
5 To grasp the characteristics of different types of raw materials such as paper and ink. The performance of inks and paper used in printing varies greatly. Different papers and inks are used, which have different requirements for ink balance. For example, the paper has a texture that is tight and loose, and the water content is divided; the ink has viscosity, fluidity, and pigment particle size. Under the same conditions of printing plate, temperature, humidity, etc., it is necessary to grasp the changes in their properties.
6 The amount of dry oil should be moderate. The drying oil in the ink promotes the drying of the ink to accelerate, but the drying oil causes the ink to stick. Therefore, the discomfort of the dry oil is the main factor that makes the ink balance uncontrolled and dirty.
7 The pH of the dampening solution should not fluctuate. The pH of the fountain solution is also an important condition affecting the balance of ink and water. It must be made constant to avoid large fluctuations.
8 Correctly adjust the pressure. The press must have precise drum pressure, ink roller pressure and water roller pressure, which directly determine the ink balance.
Third, the principle of ensuring ink and water balance
To maintain the balance of ink and water, 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 and odorless transparent liquid. Water is a dipolar substance that dissolves with many other substances. But there are also substances that are incompatible with it. For example, he is incompatible with oils, and the substances that are compatible with them are also intimate, and can be seen from the order of the hydrophilic properties of the metals.
The following arrangement is the order of hydrophilicity from strong to weak: potassium, calcium, sodium, magnesium, aluminum, zinc, chromium, iron, nickel, tin, lead, etc., the plate machine we use is better hydrophilic. Made of aluminum metal.
Offset printing inks generally use inks with good water resistance, bright colors, transparency, saturation and purity. Oil is a non-polar substance that is immiscible with water under normal conditions. Nothing in the world is a purely single elemental substance, as is the water repellency of inks. From 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 has water-repellent and lipophilic properties, called water-repellent group; The oil is hydrophilic and is called a hydrophilic group. These two groups are related to each other and contradict each other. The completely opposite group exists in one molecule. The former is a hydrophobic and oleophilic water-repellent group, which is non-polar, and the latter is an oil-repellent hydrophilic group with polarity. .
That is to say, the oil has duality, which is both non-polar and polar, and there is a possibility that the oil and water are immiscible and that the oil and water are miscible. However, since the polar carboxyl group of the hydrophilic oil-repellent oil is extremely rare in the entire oil molecule, it is only subordinate in the oil molecule, and the non-polar water-repellent lipophilic group accounts for an absolute majority in the entire oil molecule. It takes a dominant position, so the oil is characterized by oil and water being immiscible under normal temperature and pressure. Through the above analysis and discussion, it is known that the offset printing process makes it impossible for the ink to be emulsified at all. The key is to master properly and achieve ink and water balance.
Fourth, measures and control methods to ensure ink and water balance
1 During the printing process, the plate must have a solid graphic foundation and a blank foundation to maintain oleophilic and hydrophilic stability.
2 Under the premise of ensuring that the printing plate is not dirty, the water supply quantity should be controlled to the smallest possible range (the water supply of the layout should be 26%), and the water supply quantity and the ink quantity should be relatively stable, so as to ensure the printed matter. The ink color is consistent before and after and the printing operation is stable.
3 Master the principle of less water and less ink. The amount of water referred to here is based on the premise that the blank part of the layout is not dirty. The so-called thick ink is also based on the lack of water. The water is large and the ink is emulsified. The ink layer cannot be thick. It can be seen from the inkjet ink transfer process that in a single water supply and ink supply, a total of three ink mixing and emulsification occurs. It is impossible to maintain a strict boundary between water and oil. . Therefore, the ink-and-wash balance in offset printing can only be a relative concept, and the perfectly ideal ink-and-wash balance does not exist. As long as the best balance is achieved, the ideal print can be printed.
4 According to the material type of the printing plate, the size of the ink can be selected. The water volume of the PS plate can be appropriately smaller. The water volume of the PVA plate can be slightly larger; the smooth paper can be slightly smaller, the rough paper can be slightly larger, and the machine runs faster. The amount of water can be slightly smaller, and it can be larger at low speeds.
5 Environmental conditions and temperature and humidity can not be ignored. Since the moisture of the layout is distributed in both direct and indirect forms, the moisture of the layout meets the needs of ink balance during printing, and most of it is distributed to the space. The higher the ambient temperature, the faster the emission.
6 The pH of the dampening solution must be controlled (generally controlled from 4.5 to 5.5). In addition, since the pH of the surface of the offset printing paper has a large influence on the pH of the dampening solution, it is preferable to measure the pH of the paper. If the pH of the paper is too low, the pH of the fountain solution should be slightly increased. Conversely, if the pH of the paper is too high, the pH should be appropriately lowered to neutralize the OH- of the paper, thereby buffering The pH of the dampening solution is excessively elevated. According to the conclusions of the relevant data and practice, when the paper PH value is 9, the pH value of the dampening solution is 4; when the PH value of the paper is 8, the pH value of the dampening solution is 5 is better.
7 Scientific instrumentation is used to control ink and water balance. Because the printing obtained under the state of ink balance is inevitably thick and the density is uniform, the change of the 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 addition, in the work, 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 (paper, ink, plate, blanket, etc.) used and the differences in working environment. In order to achieve or achieve a balance that is suitable for the printing process.
Fifth, analysis of the phenomenon of imbalance of ink and water balance
How to achieve the balance of ink and water, operators should not only understand and study the organic relationship between ink and wash, the constraints between each other and the law of subtle changes between them, but also analyze and discuss the adverse consequences caused by the imbalance of ink and wash.
1 Analysis of the phenomenon that there is less water and less ink: During the printing process, the printing plate has a certain water film in the blank part. When the water film and the oil can compete, it will not be stained by the ink on the ink roller. Too small, the amount of water layer can not resist the adsorption of the ink on the blank part, then the blank part will be stained with ink, resulting in hanging dirty. If the amount of ink supply is small, the printed product will be dull, light gray, and the imprint is not real. The imprint is covered with snowflake-like white spots. In this state, although the "ink-ink balance" is reached, this "ink-ink balance" is not the "ink-ink balance" we want.
2 analysis of the phenomenon of less water and more ink: at this time, the most likely to produce uneven printing ink color, hanging dirty, a part or large layout due to lack of water caused by paste, paste. At the same time printed imprinted ink is also deep, The printed matter becomes black and the dots are not clear, especially for the reproduction of fine dots, and the images are indistinguishable.
3 Analysis of the phenomenon of less water and less ink: If the moisture of the layout is too large, it will spread to the surface of all the ink rollers to form a certain thickness of the water layer, which hinders the normal transfer of the ink, and the emulsification speed of the ink is accelerated, and the ink color of the print is gradually unsaturated. The picture is lighter, the writing is imaginary, gray, hairy, hairy, dull and dull. There is dizziness around the imprint, the image is not clear, no level.
4 Analysis of the phenomenon of water and large ink: When the water content of the plate is excessive, the ink color will become lighter, and it will often be blindly considered that the ink supply amount is small, so the ink quantity is continuously increased, and the ink emulsification loses stability after a long period of cycle. The vicious cycle of unbalanced ink and ink causes the ink to be heavily emulsified and accumulates on the surface of the ink roller, making printing impossible.