The drying process includes all processes after ink transfer. In these processes, ink curing is the primary condition for post-press processing, and it is also a prerequisite for printed products to be used in daily life.
Depending on the composition of the ink, the drying method can be divided into physical drying, chemical drying, and the comprehensive application of these two methods. Different inks and varnishes require different drying systems, or a combination of several drying systems to get the best drying effect. If you install an infrared and ultraviolet drying system on a printing machine, it can basically meet all the needs of printing, so it is very useful.
Considering its drying performance, the composition of the printing ink must meet the following two conflicting requirements: one is that the ink cannot be dried on the ink roller when the printing machine is printing or is temporarily stopped; the other is that the printing material is printed on the substrate after the printing is completed The ink needs to dry quickly and fix.
The most important factors affecting the drying performance of the ink: ①the composition of the ink (pigment, binder and related additives); ② the performance of the substrate material (such as permeability); ③ the printing conditions (the amount of ink transfer, the receipt Paper stack height, printing speed); ④Climatic conditions (indoor temperature, humidity); ⑤Drying system composition (such as air flow on the ink surface, reaction time, type of energy supplied, etc.). Among them, temperature is a decisive factor. Generally speaking, the higher the temperature, the better. Because the higher the temperature, the faster the ink polymerization speed, the lower the viscosity of the ink, the more conducive to penetration, the faster the solvent evaporation.
Understand the causes of printing static electricity
During the printing process, sometimes the paper or printed matter will stick to each other, as if the paper surface has a strong vacuum suction, it is difficult to separate, this phenomenon is printing static electricity. In the dry climate in winter, the static of the printed paper is particularly prominent, ranging from obstacles to paper feeding, paper collection and flushing, and heavy paper failures such as automatic paper feeding or frequent double sheets, empty sheets, paper delivery disorder, increased loss, etc. As a result, both reduce production efficiency and affect product quality. Therefore, it is of positive significance to correctly understand the printing static electricity and master the countermeasures to promote production.
When the paper contains a high amount of water, it can become a conductor of electricity; on the contrary, when the water content is very low, it is absolute, and the reason why the paper is prone to static electricity: First, the papermaking process is not suitable. That is, during the papermaking process, due to the low content of electrolytes (Ming ?, sodium chloride, etc.) and the excessive content of sizing materials (high areas, etc.), the paper is subjected to high temperature and pressure during the drying and calendering process Make paper with high voltage static electricity. The second is improper storage of paper. For example, when there is a large disparity between the temperature of the paper car and the temperature of the printing workshop, due to the variation of the moisture content, the paper does not even have a stretch to affect the registration, and it is easy to cause static electricity, which causes inconvenience to the brush. In addition, the paper placement time before printing is too short, or the stacking is too high, so that the paper and the printing environment temperature lack of effective balance time, causing static electricity on the paper. The third is printing friction caused by static electricity. When the water content of the paper is obviously too low, the paper will be too dry. During the printing process, due to the friction and pressure of paper feeding and imprinting, the electrons outside the paper nuclei will gain and lose, making the paper static.
The paper is static, and the situation is different. There is a cause, and there are several types of undesirable conditions that are concurrently formed. All kinds of paper, even the same kind of paper, this batch and the previous batch, the size of static electricity is not necessarily the same, that is, the voltage level will be different. Another feature is that the paper is electrostatically charged on both sides, and the front and back sides of the paper are the same when printing, that is, the front side is facing up or the back side is facing up. Therefore, the paper that is in contact with the front and back sides is firmly adsorbed to each other, which is not easy to separate, which brings certain obstacles to printing, conveying, conveying, and aligning paper.
To prevent the occurrence of printed static electricity, we must first control from the source. The paper with static electricity can be used for a while, the storage time should be properly extended, and the temperature and humidity of the paper warehouse should be controlled at 18 ℃ ~ 20 ℃, and the relative humidity of the air should be controlled at 60-65%. It is helpful to reduce or eliminate paper static electricity. Secondly, use paper drying method to remove paper static electricity. When the paper is urgently used, a paper dryer can be used to hang and dry the paper with static electricity. When lifting, you should pay attention to the coordination of the speed and air humidity, that is, when the speed is fast, the relative temperature of the ambient air is controlled at 80-85%, otherwise, when the speed is slow, the air temperature is maintained at 70-80 %. It should be noted that when hanging, the thickness of each stack of paper should be controlled within 10 ?. Third, the emergency drying paper removes static electricity. Static electricity appears when printing on the cut paper. You can use the "steam method" to quickly dry the paper to reduce the static electricity of the paper and complete the printing as soon as possible.
To eliminate paper static electricity, you can also use a comprehensive method of elimination, that is, to increase the paper temperature, moisture content, and the use of static electricity eliminators, the effect will be better. The method is:
1. Install air conditioning equipment in the printing workshop, adjust or maintain the temperature and humidity of the printing workshop according to the strength of the static electricity of the paper. Under normal circumstances, the temperature of the workshop is adjusted between 18 ℃ -20 ℃, and the relative temperature of the air is maintained between 60-65%. If the paper is heavily charged, the relative humidity of the air can be adjusted to between 80-85%.
2. Install a static eliminator on the printing press. Eliminate the static electricity of paper by adjusting the voltage or high frequency. If the static electricity of paper is large, use high voltage or high frequency. If the static electricity is not large, lower the voltage and high frequency.
3. Eliminate printed static electricity with isotope emitters. The principle of isotope emission and static electricity of static eliminator is basically the same, all of which ionize various molecules in the air into ions. Because ions have different electrical properties, they become good conductors of electricity. When paper passes through the ion space, part of the static electricity Being neutralized, the other part is taken away by air ions, so as to achieve the purpose of eliminating static electricity.
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