Offset printing is a kind of printing that uses the principle of incompatibility of oil and water. First supply water to the printing plate, and then supply ink to the printing plate, so that the graphic part of the printing plate has ink and no water, and the blank part has water and no ink. However, the water used to wet the printing plate is not ordinary water, but a liquid with chemicals and electrolyte added to the water. This is the fountain solution. From this, the performance of fountain solution is one of the key factors that determine the quality of offset printing products. The performance of the fountain solution can be matched with the printing machine, paper, ink, etc. to print high-quality products, so that the printed graphics are bright in color, clear in layers, smooth in dots, not expanded, not reduced, the blank part is not dirty, and the blot is dry normal.
1. The main function of fountain solution
(1) Form a water film on the blank part of the printing plate
Forming a uniform water film in the blank part of the printing plate, maintaining the ink repellency and hydrophilicity of the blank part of the printing plate is the main role of the fountain solution.
(2) Supplement the hydrophilic layer damaged in the printing process
During printing, the cylinder and the ink roller rotate to produce friction on the printing plate, which causes the hydrophilic layer on the printing plate to be worn away. To further deepen wear and tear and destroy the hydrophilic layer. In this way, if there is no electrolyte in the fountain solution, during the printing process, it will continue to play a chemical role with the metal layer of the printing plate to form a new inorganic salt hydrophilic layer.
(3) Reduce the surface temperature of the printing plate
During printing, because the ink roller moves at a very high speed, its temperature will rise, so that the temperature of the ink will also rise. Under high temperature, the viscosity of the ink decreases and the fluidity increases. In this way, the ink will spread quickly during printing, which will easily cause the dot expansion and affect the printed matter. But in the printing process, the use of fountain solution can effectively reduce the temperature of the printing plate, can reduce the occurrence of such problems.
2. Classification of fountain solution
The fountain solution is generally divided into: â‘ ordinary fountain solution; â‘¡ sprinkle fine fountain solution; â‘¢ non-ionic surfactant fountain solution.
The chemical components added to the ordinary fountain solution are phosphoric acid, phosphate, nitrate and other inorganic compounds, which have the characteristics of high surface tension and poor wettability, but low cost and easy operation.
The alcohol fountain solution is added with ethanol, isopropanol or other alcohols, which has the characteristics of low surface tension and good wettability. It is suitable for lithographic printing machines equipped with an alcohol dampening system.
The characteristics of alcohol are volatile, which can speed up the heat removal from the printing plate and reduce the dirtying of the plate. After adding alcohol to the water, it can reduce the surface tension of the water, so that the water can be quickly and evenly distributed on the plate It is easy to achieve water-ink balance. When printing, the water consumption is small, which improves the accuracy of overprinting. The amount of alcohol is generally controlled between 12% and 20%, too low will make the printing plate dirty, and the temperature of alcohol is generally controlled between 4 and 12 ° C.
Non-ionic surfactant fountain solution is a new fountain solution developed in recent years. It is generally prepared by adding non-ionic surfactant to the fountain solution containing other electrolytes. Non-ionic surfactants commonly used are polyoxyethylene, polyoxypropylene ether, and alkyl alcohol amide. It has the characteristics of low surface tension, good wetting performance and stable chemical performance, and is an ideal fountain solution for high-speed multicolor lithographic printing machines. But poor control is prone to ink emulsification.
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