Printing Fairy Water - Fountain Solution

As we all know, the principle of Offset Printing is to print with water and oil resistant to each other. The printed part of the printing plate has the characteristics of lipophilic and water repellent. On the contrary, the non-printed part is hydrophilic and oil-repellent. Therefore, after the printing plate is wetted by fresh water, the non-printed part forms a water film. When the ink passes through the printing plate, only the printed part will be stained with ink, and a piece of printing will be printed out smoothly. However, the water used to moisten the printing plate is not ordinary water. It is actually a chemical substance and a liquid with an electrolyte added to the water. What is added to the water is the fountain solution.

Fountain solution function

In the high-speed printing process, it is unlikely that the non-printed part can maintain hydrophilic and oil-repellent properties and adsorb water film for a long period of time. In fact, the non-printed part is very attractive to water. Limited, if the process of printing, with only ordinary water to wet, it is not easy to form a water film in the blank part of the text. In this way, we can only use the fountain solution to stabilize the hydrophilic and oil-repellent properties of the non-printed part in order to obtain a good printing effect.

Why fountain solution can print quality around? Here, we first talk about what role the fountain solution can play in printing.

(a) Formation of water film on non-printed areas

The formation of a water film is the primary function of the fountain solution. The fountain solution itself has a low surface tension, so adding it to water will allow the clear water to spread out on the non-imprinted surface; on the other hand, the electrolyte of the fountain solution will affect the metal of the printing plate. The chemical reaction produces inorganic salts that allow the water film to adhere tightly to the blank part of the printing plate, preventing the ink from spreading to these parts, otherwise we cannot print the normal picture.

(B) to supplement the damaged hydrophilic layer

During printing, the rollers and ink rollers rotate, causing friction on the printing plate, causing the hydrophilic layer on the printing plate to be worn out; at the same time, the paper is more or less detached from the paper powder and the paper during the printing process. , further deepen the wear and tear, destroy the hydrophilic layer. In this way, if there is no dampening solution in the process, which continuously reacts with the metal layer of the printing plate and forms a new hydrophilic layer again and again, offset printing cannot use the characteristics of water and oil phase rejection.

(three) to reduce the surface temperature of the printing plate

When the ink roller is printing, it runs at a high speed and pulls the ink into a thin film for printing. Since the ink roller moves at an extremely high speed, its temperature rises and the associated ink also changes with temperature. At high temperatures, the viscosity of the ink is reduced and the flowability is increased. In this way, the ink spreads quickly when printing, which can easily cause dots to spread and affect the printing quality. But in the printing process, adding fountain solution, but can effectively reduce the plate temperature, to avoid the above problems.

Appropriate amount of fountain solution

How much fountain solution should I use for each printing to have the best printing effect? This person is not sure, because all kinds of printing factors, every minute changes, regardless of the printing plate, ink, paper, and their slight changes, are enough to affect the fountain solution dose. Therefore, the printer can only determine the correct amount according to the printing environment at that time.

Printing plate

The closest contact with the fountain solution is of course the printing plate. There are many types of offset printing plates. Generally speaking, there are PS plates, paper plates, and silver salt plates. The structure of these printing plates is different, and the adsorptive power of the plates facing the water film is different, so the demand for the fountain solution is also not the same. For example, the absorptive force of the blank part of the paper plate is stronger than that of the PS plate and the silver salt plate. The amount of fountain solution it needs is much less than that of the other two plates. On the other hand, the layout of the picture and type of text, will also affect the amount of fountain solution and PH value. Printed graphics can be roughly divided into three categories: real maps, texts, and dot maps. The amount of fountain solution is directly proportional to the amount of ink needed to print the graphic. When it is a real map, it needs the most fountain solution. The text is the second and the dot is the least.

The PH value is also related to the amount of ink used. The real map is generally printed with more ink and the ink layer is thicker, so a fountain solution with a lower pH is needed to prevent the ink from spreading out from the edge of the field. However, contrary to the real map, it is a dot map because the dot area of ​​the dot map is small. It is easier to emulsify and disappear, so it is not suitable to use the fountain solution with low PH value, otherwise it will accelerate the emulsification. As for the printed text, the pH value of the fountain solution needed is exactly between the real map and the dot map.

Ink

The second important factor is ink. The inks of different types and colors have different viscosity, fluidity, and water resistance. Generally speaking, inks that are difficult to emulsify require a higher concentration of fountain solution, while those that are easier to emulsify do not need to use high inks. Concentration of fountain solution. As for the relationship between the pH and concentration of the fountain solution and the ink, the factors considered are similar to the above: the ink that is not easily emulsified needs to be accompanied by a more acidic, higher concentration fountain solution; the change is easy to emulsify the ink, Only the fountain solution with high pH and low concentration can be used. This middle concentration of acid and alkali is not adjustable.

Paper

As for the impact of paper on the fountain solution, mainly from the paper texture of the paper's PH value in two aspects. A piece of loose texture paper, if its surface strength is low, then paper and paper powder, it is easy to be ink adhesion, piled on the printing tape, increase the degree of wear of the printing plate, and easy to dirt. In this case, it is necessary to increase the amount of fountain solution, or to increase the concentration so as to reduce the damage of deposits to the printing plate. In addition, different printing papers have different PH values, either acidic or alkaline. Therefore, the printer needs to adjust the PH value of the fountain solution by looking at the acidity and alkalinity of the paper.

Knowing the fountain solution as the printed “magic water” is a bit exaggerated, but correct use of fountain solution can effectively control the ink-water balance and improve the quality of printing. With regard to the knowledge of the fountain solution, there are many, the above mentioned, but it is one of the half-claw, to truly understand the fountain solution, have to work hard to study.