About the author: Rong Yongwei, Shililuo Printing Material Co., Ltd. offset printing ink technology director, 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.
Lithographic offset printing is carried out by the principle of incompatibility of oil and water, wetting, adsorption and selective adsorption. Water-ink balance is the most important principle of lithographic offset printing. Reasonable control and use of fountain solution are very important in lithographic offset printing operations. This article takes the current use of alcohol-based fountain solution as an example, starting from the composition and application method of fountain solution, combined with the author's printing work experience, to talk about how to reasonably control the use of fountain solution.
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 0-225uS, and hard water is usually above 450uS. When the water quality is relatively hard (mainly when there is a large amount of Ca +), 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, it will produce something like calcium lemon or Salts such as calcium phosphate. Calcium saponification is oleophilic, which can cause ink to deposit in unnecessary areas such as water roller and ink roller, crystallizing the surface of the rubber roller, resulting in poor water transfer and ink transfer; while calcium salts are hydrophilic and will hinder ink The transfer will cause the ink roller to deink, so the fountain solution additive used when the water quality is hard water should contain the corresponding substance to eliminate the effect caused by excessive calcium ions.
Alcohol or alcohol substitutes: The main role of alcohol in fountain solution is to reduce the surface tension of the aqueous solution. The volatility of alcohol can reduce the emulsification degree of the ink, keep the printing color bright and accelerate the drying of the ink on the substrate. Since isopropyl alcohol evaporates at a slower rate, the ability to reduce the surface tension of water is stronger, while general industrial alcohol has a faster volatility and a lower ability to reduce the surface tension of water. Generally, isopropyl alcohol is used to produce stable printing. At present, the quality and price of alcohol products on the market vary greatly, and products with high purity and better texture should be carefully selected during use. Isopropyl alcohol should be used as much as possible and industrial alcohol should not be used. cost. Generally, the surface tension of tap water is about 72 dynes, and the surface tension of offset printing inks is about 30-36 dynes. The surface tension of the fountain solution must be controlled to the same degree as the surface tension of the ink, so that the two are balanced and stable. To control the degree of emulsification of the ink. Generally, the isopropyl alcohol content of 8-12% can meet the requirements. The alcohol content should not be too high, otherwise it will cause serious emulsification of the ink.
Fountain solution additives: The choice of fountain solution additives should be very cautious. It is necessary to consider whether they contain these ingredients: acidic electrolytes, buffers, hydrophilic colloids, surfactants, preservatives, bactericides, defoamers, etc. A good fountain solution should have the following characteristics: (1) It is weakly acidic, has good buffering capacity and stable PH value; (2) It can react with the non-graphic part of the printing plate to form a water-insoluble hydrophilic inorganic Salt; (3) Can be spread in the non-graphic part of the printing plate, with good wetting performance; (4) Corrosion to the machine, printing plate and other printing materials is weak; (5) The structure of the dampening system of the offset press Adapt, no precipitation, no bubbles? I, do not block the circulation pipeline; (6) Match the printing suitability of ink and substrate, and meet the quality requirements of printed products; (7) The fountain solution is preferably 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 the operator, etc.
The addition amount of fountain solution additives should be kept stable, and standard measuring tools should be equipped for manual addition. The automatic addition device of the water tank should be regularly checked and maintained to ensure that its extraction equipment works normally. Use the test conductivity to control the amount of fountain solution additive. First measure the conductivity of the clean water. In actual application, the conductivity of the clean water should be deducted first. Since alcohol or alcohol substitutes are not conductive, the conductivity will decrease after addition. The conductivity should be measured again after the alcohol is added. Practice shows that the reference standard value of conductivity is generally 800-1200uS higher than that of clean water (after adding alcohol), the PH value is controlled between 4.8-5.3, and the product quality is easy to control.
The use of fountain solution should be based on the machines, water quality, printing materials and other conditions of each printing plant. At present, printing enterprises in the northern and coastal regions and some printing plants that use groundwater have hard water quality, and excessive calcium often occurs. High-quality fountain solution additives should be suitable for modern high-speed printing conditions, and have anti-calcium function for hard water, with excellent buffer capacity, PH value can be stabilized at about 5.1, and effectively prevent calcium from water, paper and ink It accumulates on the rubber roller, keeps the fountain solution clean and free from precipitation and blisters. I is also stable under 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, and often have a multiplier effect. You may wish to give it a try.
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