Influence of water quality on offset printing and treatment
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With the development of the printing industry, the society has continuously raised higher and higher requirements for the quality of printed materials, from printing equipment, printing materials, printing consumables, to the operational skills of operators. This article will examine 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 200 PPM, it causes calcium saponification to form upon contact with the resin in the ink, and when contacted with an acidic solution, salts such as calcium citrate and calcium phosphate are produced.
Saponified calcium is lipophilic, which causes the ink to deposit in undesired areas, such as water rollers and water-foamed surfaces. The calcium salt has good hydrophilicity, which hinders ink transfer and causes the ink roller to be deinked.
In addition, if the calcium ion content in the water exceeds the standard, it will directly affect the service life of the rubber roller, which will cause the surface of the rubber roller to crystallize.
Conclusion 1: Excessive water will aggravate the emulsification process of the ink, which will lead to the deposition of ink on the water path, which will aggravate the aging of the rubber roller (surface crystallization).
2. Fluctuation in conductivity when entering water
The dynamic surface tension of the fountain solution depends on the concentration of the dampening solution. The higher the concentration, the lower the surface tension.
Some commercial automatic conveying devices can control the concentration of the dampening solution to achieve a predetermined conductivity. When the conductivity of the influent water is too large, it will cause a change in the concentration of the dampening solution. The result is an imbalance in the ratio of oil to water, causing an offset failure.
If the proportion of the dampening solution is as quantitative and precise as other units, the problem may be small, but when the conductivity of the supplied water changes greatly, the interaction between the oil and water may still be unbalanced.
Conclusion 2: When the conductivity of water fluctuates, it will affect the automatic control and detection of dampening solution in the printing process.
3. For large companies with multiple branches
Some companies have branches in several cities and need to be standardized to achieve a more uniform quality. This also puts higher demands on the water quality used. For example, the hardness of water in several cities, and the impurity rate of water in several cities. These are all issues that must be considered.
Conclusion 3: When the water quality in different regions is different, 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 ability of enterprises to deal with printing water is necessary for water quality. Water treatment in bad areas is a must.
Water treatment method:
The treatment of water can be said to be carried out in a variety of ways, such as: distillation, softened water treatment, activated carbon filtration, microfiltration, ultrafiltration, reverse osmosis filtration.
1. Softened water treatment:
The water is filtered by using a resin impregnated with sodium chloride. When the sodium ions that have been combined with the resin encounter calcium, magnesium and manganese ions in the water, they are replaced by these ions, that is, the nano ions enter the water while the calcium is Magnesium plasma is adsorbed onto the resin.
This treatment can effectively reduce the hardness of water (ie, reduce the content of calcium and magnesium ions in water), but it is worth noting that the conductivity of water itself does not change because the concentration of ions contained in the water does not change.
2. Ion removal
This method uses a cationic resin exchanger and an anion resin exchanger to exchange the anion and cation in water, respectively. When pressurized water passes through the exchange system, ions in the water are adsorbed by the resin, and hydrogen ions or hydroxide ions in the resin are displaced into the water, and the charged resin is also consumed. When the resin fails, the resin can be reduced with a strong acid and a strong base.
There are two main types of equipment for water treatment in this way:
1 double bed resin exchange equipment. This type of equipment typically has two resin containers (yin and yang).
2 mixed type. The anion-cationic resin is mixed in a certain ratio and used at the same time. If the mixing ratio is proper, the water quality obtained after the treatment is very good.
3. Reverse osmosis method:
Under normal conditions, the diffusion of water is spread from a low concentration to a high concentration. The reverse osmosis method uses a certain material and means to reverse the process. Under pressure, the water has a low concentration from a high concentration. The place spreads. Reverse osmosis is a relatively thorough impurity removal technology that removes 90 to 95% of impurities in our drinking water under normal conditions. The more commonly used filter materials are: cellulose acetate film, polyamide film and composite film.
※ Attachment: The measurement of the conductivity of water is a method for characterizing the electrolyte content in water. The unit is S, which is the reciprocal of water resistance. There are also smaller units used in μS. The conductivity of the dampening solution required during the printing process is generally 500 to 1500 μS.