Analysis: Drying technology used in printing process
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The drying process includes all processes after ink transfer. In these processes, ink curing is the primary condition for post-press processing and the premise that prints can 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 combined application of the two methods. Different inks and varnishes require different drying systems or a combination of several drying systems for optimum drying results. If an infrared and ultraviolet drying system is installed on a printing press, it is basically useful for all printing needs.
Considering its drying performance, the composition of the printing ink needs to meet the following two contradictory requirements: First, the ink can not be dried on the ink roller when printing or short shutdown; first, after printing, on the substrate The ink needs to dry quickly and fix.
Several of the most important factors affecting the drying performance of the ink: 1 the composition of the ink (ink pigment, binder and related additives); 2 the properties of the substrate material (such as permeability); 3 printing conditions (ink transfer amount, income) Paper stack height, printing speed); 4 climatic conditions (indoor temperature, humidity); 5 drying system composition (such as air flow on the ink surface, reaction time, type of energy supplied, etc.). 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 smaller the viscosity of the ink, the better the penetration, and the faster the solvent evaporates.
Know the correct cause of printing static electricity
In the printing process, sometimes paper or prints are adsorbed and adhered to each other, as if the paper surface has a strong vacuum suction and is difficult to separate. This phenomenon is printing static electricity. In the dry climate, the printed paper is particularly sensitive to static electricity. It can cause obstacles to paper feeding, paper delivery and paper-cutting. In addition, it is impossible to automatically feed paper or frequently appear double sheets, empty sheets, paper delivery disorder, and increased loss. Consequences reduce both production efficiency and product quality. Therefore, it is of positive significance to correctly understand the printing static and master the countermeasures to promote production.
When the paper contains a high amount of water, it can become an electric conductor; conversely, when the water content is low, it is absolute, and the paper is prone to static electricity: First, the papermaking process is not suitable. That is, during the paper making process, due to the low content of electrolytes (alum, sodium chloride, etc.), the content of sizing substances (high territory, etc.) is too much, and the paper is subjected to high temperature and pressure during drying and calendering. Paper with high voltage static electricity. Second, the paper is not properly stored. If there is a big disparity between the temperature of the paper car and the temperature of the printing workshop, the paper will not affect the registration due to the variation of the moisture content, and it will easily cause static electricity, which will bring 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 an effective balance time, causing the paper to be electrostatically charged. The third is that printing friction causes static electricity. When the water content of the paper is significantly less, the paper will be excessively dried. During the printing process, due to the friction and pressure of paper feeding, imprinting, etc., the electrons outside the paper nucleus are lost and generated, and the paper is electrostatically charged.
The paper is static and the conditions are different. There are one reason, and there are several unfavorable situations. All kinds of paper, even the same kind of paper, this batch and the previous batch, the size of the static electricity is not necessarily the same, that is, the voltage will be different. Another feature is that the electrical properties of the two sides of the paper are opposite when they are electrostatically charged, and the stacking of the front and back sides of the paper is uniform when printing, that is, the front side or the back side faces upward. Therefore, the papers that are in contact with each other on the front and the back are firmly adhered to each other, and are not easily separated, which brings certain obstacles to printing, conveying, conveying, and aligning paper.
To prevent the occurrence of printing static electricity, we must first control from the source. For paper with static electricity, it can be temporarily suspended, and the stock time should be extended appropriately. The temperature and humidity of the paper library should be controlled at 18 °C–20 °C, and the relative humidity of the air should be between 60-65%. It helps to reduce or eliminate static electricity on the paper. Secondly, the paper is used to remove static electricity from the paper. When using paper urgently, use a paper machine to hang the paper with static electricity. When hanging and drying, pay attention to the coordination between machine speed and air humidity. When the machine speed is faster, the relative air temperature is controlled at 80-85%. Conversely, when the machine speed is slow, the air temperature is kept at 70-80. %. Need to be prompted: when hanging, the thickness of each stack of paper should be within 10mm. Third, emergency air-paper removes static electricity. When static electricity is generated during the printing of the cut paper, the “vapor method” can be used to quickly dry the paper to reduce the static electricity of the paper and complete the printing as soon as possible.
Eliminating static electricity from paper can also be done with a comprehensive elimination method that combines higher paper temperature, water content and the use of a static eliminator. The method is:
1. Install air conditioning equipment in the printing workshop to adjust or maintain the temperature and humidity of the printing workshop according to the static electricity of the paper. In general, the shop temperature is adjusted between 18 ° C and 20 ° C, and the relative air temperature is maintained between 60-65%. If the paper is charged more seriously, adjust the relative humidity of the air to between 80-85%.
2. Install a static eliminator on the press. Eliminate the static electricity of the paper by adjusting the voltage or high frequency. If the paper is static, use high voltage or high frequency. If the static electricity is not large, turn down the voltage and high frequency.
3. Eliminate printing static electricity with an isotope emitter. Isotopic radiation is basically the same as the static electricity of the static eliminator. It is to ionize various molecules in the air into ions. Because the ions have different electrical properties, they become good conductors of electricity. When the paper passes through the ion space, some of the static electricity is charged. It is neutralized and the other part is taken away by air ions, thus achieving the purpose of eliminating static electricity.