Analysis: the three principles of offset printing and printing
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One type of flat-panel offset printing is simply that the offset printing is the printing method of transferring the graphic on the printing plate to the printing substrate by means of rubber, which is also the existence of the blanket, which is named after the printing method. The blanket plays an irreplaceable role in printing. For example, it can make up for the unevenness of the surface of the substrate and make the ink transfer fully. It can reduce the water on the printing plate (the role of water in printing is seen later). ) to the substrate and so on. The above is just a general concept. We usually say that the offset printing may be narrower, that is, there are three lithographic printing methods (printing plates, blankets, embossing), which are called in the south of China. For offset printing.
Offset printing in China is an absolutely dominant printing method. Due to the fast printing speed, relatively stable printing quality and short printing cycle, books, newspapers, and quite a part of commercial printing are offset. When it comes to printing, people immediately think of offset printing. Heidelberg, Roland, Mitsubishi, Komori and other foreign brands are also familiar with ordinary people.
The three principles of offset printing are:
First, the principle of water-oil incompatibility, chemically called the principle of similar compatibility, the structure of water molecules with mild polarity and the polarity of molecules between non-polar oil molecules are different, resulting in the inability to attract and dissolve between water and oil. The existence of this rule made it possible for a flat plate to use water for distinguishing between graphics and blanks.
Second, the surface selection adsorption principle,
Depending on the surface tension, it can adsorb different substances, which also provides the possibility of image separation of lithographic offset printing.
Third, the dot structure principle, because the offset printing plate is flat, then you can not rely on the thickness of the ink to express the level of the graphic on the print, but by splitting the different levels into tiny spots that are not visible to the naked eye. Units can effectively express a rich image hierarchy.
In life we have the common sense that water-soaked surfaces are not easily contaminated by oil, and water and oil are always mutually exclusive. Since the offset printing plates are almost in the same plane, it is necessary to find a method for effectively distinguishing the blank portion from the graphic portion. The role of water in offset printing is called the principle of "water-oil incompatibility". During the printing process, a thin layer of water is evenly applied to the surface of the printing plate (actually due to the selective adsorption of the surface of the printing plate, the image is not water-repellent), and then coated on the printing plate. When the ink is in use, the blank portion is effectively protected.