What is Offset printing and its application?
Offset printing is a kind of lithographic printing. Simply speaking, offset printing is a printing method in which the graphics on the printing plate are transferred to the substrate by means of rubber (blanket). It is also the existence of the blanket. This printing method is name. The blanket plays an irreplaceable role in printing, such as: it can make up for the uneven surface of the substrate, so that the ink can be fully transferred, and it can reduce the water on the printing plate (see later for the role of water in printing). ) Transfer to the substrate and so on. The above is just a general concept. We usually say that the scope of offset printing is narrower, that is, the lithographic printing method with three cylinders (plate, blanket, and imprint). In the south of our country, this printing method is called For offset printing.
Incompatible with water and oil
The so-called principle of similarity in chemistry determines that the molecular structure of lightly polar water molecules is different from that of non-polar oil molecules, causing the water and oil to be unable to attract and dissolve. The existence of this rule makes the flat printing plate The idea of using water to distinguish between pictures and texts and blank parts becomes possible.
Select surface adsorption
According to the different surface tension, it can absorb different substances, which also provides the possibility for the separation of images and texts in lithographic offset printing.
Since the printing plate of offset printing is flat, it is impossible to rely on the thickness of the ink to express the level of graphics and text on the printed matter, but by splitting the different levels into tiny dot units that are not noticeable by the naked eye, it can effectively express Come out with rich image levels. In daily life, we have the common sense that on a surface that has been soaked with water, it is not easy to be contaminated by oil, and water and oil always repel each other. Since the printing plates of offset printing are almost in the same plane, it is necessary to find a method that can effectively distinguish the blank part and the graphic part. The role of water in offset printing is called the principle of "water-oil immiscibility". During the printing process, a thin layer of water is evenly coated on the surface of the printing plate (in fact, due to the selective adsorption of the surface of the printing plate, the graphics and text are not wet), and then the printing plate is coated When printing ink, it effectively protects the blank part.