With the development of the printing industry, society has continuously put forward higher and higher requirements for the quality of printed products, from printing equipment, printing materials, printing consumables, to the operating skills of operators have higher requirements. This article will discuss the impact of water quality on printing and the improvement of water from the quality evaluation of offset printing water. 1. Water hardness When the hardness of calcium exceeds 200PPM, it will cause it to form saponified calcium when it comes into contact with the resin in the ink, and when it comes into contact with an acidic solution, it will produce salts like calcium citrate and calcium phosphate. Calcium saponification is oleophilic and will cause the ink to deposit in unwanted areas, such as the surface of the water roller and water gel fleece. The calcium salt has good hydrophilicity, which will hinder ink transfer and cause the ink roller to deink. In addition, if the calcium ion content in the water exceeds the standard, it will directly affect the service life of the rubber roller and will cause the surface of the rubber roller to crystallize. Conclusion 1: Excessively hard water will aggravate the ink emulsification process, will cause the ink to deposit on the waterway, and will aggravate the aging of the rubber roller (surface crystallization). 2. Fluctuation of conductivity when entering water The dynamic surface tension of the fountain solution depends on the concentration of the fountain solution. The higher the concentration, the lower the surface tension. Some commercial automatic conveying devices can control the concentration of fountain solution to achieve a predetermined conductivity. When the conductivity of the incoming water is too large, it will cause the concentration of the fountain solution to change. The result is an imbalance of the oil-water ratio, causing offset printing failure. If the proportion of fountain solution is quantitatively and precisely controlled like other units, the problem may not be great, but when the conductivity of the supplied water changes greatly, it can still cause the imbalance between oil and water. Conclusion 2: When the conductivity of water fluctuates, it will affect the automatic control and detection of fountain solution in the printing process. 3. For large companies with multiple branches Some companies have branches in several cities and need standardized management to achieve a more uniform quality. This also puts forward higher requirements on the water quality used. For example, what is the hardness of the water itself in several cities and what is the impurity rate of water in several cities? These are all issues that must be considered. Conclusion 3: When the water quality is different in different regions, it will have a certain impact on the quality standardization of printed matter. Through the above analysis, we found that the quality of water itself has an impact on the printing process within a certain range, so the treatment of water is not an irrelevant thing. The treatment of printing water by competent enterprises is necessary. Water treatment in bad areas is a must. Water treatment methods: It can be said that the treatment of water can be carried out through a variety of channels, such as: distillation, demineralized water treatment, activated carbon filtration, microfiltration, ultramicrofiltration, reverse osmosis filtration, etc. 1. Demineralized water treatment: Use sodium chloride infiltrated resin to filter the water. When the sodium ions that have been combined with the resin meet the calcium, magnesium and manganese ions in the water, they will be replaced by these ions. , Magnesium plasma is adsorbed on the resin. This treatment can effectively reduce the hardness of the water (that is, reduce the content of calcium and magnesium ions in the water), but it is worth noting that because the concentration of ions contained in the water has not changed, the conductivity of the water itself has not changed. 2. Ion removal This method uses a cationic resin exchanger and an anionic resin exchanger to exchange anions and cations in water separately. When pressurized water passes through the exchange system, the ions in the water will be adsorbed by the resin, the hydrogen ions or hydroxide ions in the resin will be replaced into the water, and the charged resin will also be consumed. When the resin fails, the resin can be reduced with strong acids and bases. There are two main types of equipment for water treatment in this way: ①Double bed type resin exchange equipment. Such equipment generally has two resin containers (yin and yang). 3. Reverse osmosis method: Under normal circumstances, the diffusion of water is from a low-concentration place to a high-concentration place. Reverse osmosis is to reverse this process with certain materials and means to make water from a high-concentration place to a low concentration under pressure. Spread. The reverse osmosis method is a relatively complete impurity removal technology, under normal circumstances can remove 90 to 95% of impurities in our drinking water. The commonly used filter materials are: cellulose acetate membrane, polyamide membrane and composite membrane. ※ Attachment: The measurement of the electrical conductivity of water is a method for characterizing the electrolyte content in water. The unit is S, which is the reciprocal of the water resistance. There are also smaller units of μS. The conductivity of the fountain solution used in the printing process is generally 500 to 1500 μS.
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â‘¡ Mixed type. Use anionic and cationic resins to mix at a certain ratio, and use them at the same time. If the mixing ratio is proper, the water quality after treatment is very good.
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The influence and treatment of the quality of printing water on offset printing