Discussion on rational control and use of fountain

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The technical director of offset printing ink, who has been engaged in the printing industry for many years, is responsible for solving printing technical problems for customers, and has a deep understanding of printing consumables such as ink and fountain solution

offset lithography is based on the principles of oil-water immiscibility, wetting, adsorption and selective adsorption. Water ink balance is the most important principle of offset lithography. Reasonable control and use of fountain solution is very important in offset lithography operation. Taking the alcohol fountain solution which is widely used at present as an example, this paper discusses how to reasonably control the use of fountain solution from the aspects of its composition and application methods, combined with the author's practical experience in printing

water: the main component of fountain solution is water. The water quality conditions and hardness are different everywhere. Generally, the conductivity of soft water is about us, and that of hard water is usually above 450us. When the water quality is hard (mainly when the content of Ca + is high), it usually causes Ca + to contact with the resin in the ink to form calcium saponification. When combined with the acid in the acid fountain solution, salts such as calcium citrate or calcium phosphate will be produced. Calcium saponification is lipophilic, which will lead to the deposition of ink in unwanted areas, such as water roller and inking roller, so that the surface of rubber roller crystallizes, resulting in poor water and ink transfer; Calcium salt is hydrophilic. Inspecting the oil level of the oil tank will hinder the ink transmission and lead to the deinking of the ink roller. Therefore, the expansion of the fountain solution activity used when the water quality is hard water effectively improves the quality awareness of the publishing industry. The additives should contain corresponding substances to eliminate the impact caused by excessive calcium ions

alcohol or alcohol substitutes: the main role of alcohol in the fountain solution is to reduce the surface tension of the aqueous solution. The volatility of alcohol can reduce the emulsification degree of the ink, maintain the bright color of the print and speed up the drying of the ink on the substrate. Because isopropanol volatilizes slowly, it has a strong ability to reduce the surface tension of water, while general industrial alcohol volatilizes faster and has a low ability to reduce the surface tension of water. Usually isopropanol is used for printing, and the production quality is relatively stable. At present, the quality and price of alcohol products in the market vary greatly. When using them, we should carefully choose products with high purity and good texture, try to use isopropanol instead of industrial alcohol, which can reduce the dosage, and put forward the use effect and production quality to reduce the cost. Generally, the surface tension of tap water is about 72 dyne, and the surface tension of offset printing ink is about dyne. It is necessary to control the surface tension of fountain solution to make it the same as the surface tension of ink, so that the two can reach the balance and stability that should be paid attention to in the purchase of testing machine, so as to control the emulsification degree of ink. Usually, the content of isopropanol can meet the requirements when it is% and the alcohol content cannot be too high, otherwise the ink will be seriously emulsified

fountain solution additives: the selection of fountain solution additives should be very careful, considering whether they contain these components: acid electrolyte, buffer, hydrophilic colloid, surfactant, preservative, bactericide, defoamer, etc. A good fountain solution should have the following characteristics: (1) it is weakly acidic, with good buffer capacity and stable pH value; (2) It can react with the non graphic part of the printing plate to produce hydrophilic inorganic salts that are insoluble in water; (3) It can be spread in the non graphic part of the printing plate, with good wetting performance; (4) Weak corrosion to machines, printing plates and other printing materials; (5) It is compatible with the structure of the dampening system of the offset press, without sedimentation, foam and blockage of the circulating pipeline; (6) Match the printability of ink and substrate, and meet the quality requirements of printing products; (7) The fountain solution should be colorless and transparent, which is conducive to the color rendering effect of color printing; (8) No pollution to the environment, no harm to the health of operators, etc

the addition amount of fountain solution additives should be stable. Standard measuring tools should be equipped when adding manually. The automatic adding device of the water tank should be regularly inspected and maintained to ensure the normal operation of its extraction equipment. Test the conductivity to control the amount of additives added to the fountain solution. First measure the conductivity of clean water. In practical application, the conductivity of clean water should be deducted first. Because alcohol or alcohol substitutes are non-conductive, the conductivity will decrease after adding alcohol. After adding alcohol, we should believe that the conductivity can be measured once with the support of 3D printing technology. Practice shows that the reference standard value of conductivity is generally higher than that of clean water (after adding alcohol) us, and the pH value is controlled at 4 3, the product quality is easy to control

the use of fountain solution should be reasonable according to the machine, water quality, printing materials and other conditions of each printing plant. At present, printing enterprises in northern and coastal areas and some printing plants that use groundwater have hard water quality and often have too much calcium. High quality fountain solution additives should be suitable for modern high-speed printing conditions, and have anti calcium function for hard water, excellent buffer capacity, pH value can be stabilized at about 5.1, and effectively prevent calcium from water, paper and ink from accumulating on the cots, so as to keep the fountain solution clean, free of sedimentation, no foam, and stable in hard water conditions

reasonable control of the use of fountain solution in the printing production process can prevent and solve a variety of printing problems, which often results in twice the result with half the effort. You might as well try it

Author: Rong Yongwei, shililo printing materials Co., Ltd

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