Offset printing is a kind of lithographic printing. Simply speaking, offset printing is the printing method that transfers the graphic on the printing plate to the printing material by means of rubber (blanket). It is also the existence of the blanket. name.
Blanket plays an irreplaceable role in printing, such as: it can well make up for the uneven surface of the substrate, so that the ink can be fully transferred, it can reduce the water on the printing plate (the role of water in the printing see later ) Transfer to the substrate and so on. The above is only a general concept. The offset printing that we usually say may be more narrow, that is, there are three lithographic printing methods for printing plates, blankets, and imprints. We call this printing method in the south of our country. Offset printing.
Offset printing in China is an absolutely dominant printing method. Due to its high printing speed, relatively stable printing quality, and short printing cycle, it has many advantages. Books, newspapers, and a considerable part of commercial printing are all using offset printing. When one mentions printing, people immediately think of offset printing. Foreign brands such as Heidelberg, Roland, Mitsubishi and Komori are also familiar to ordinary people.
The three major principles of offset printing are:
First, the principle of water and oil incompatibility
The so-called similar compatibility principle in chemistry determines that there is a slight polarity of the molecular structure of water and non-polarity of the molecular polarity between oil molecules, resulting in the inability to attract and dissolve water and oil, and the existence of this rule makes plane printing plates The idea of using water to distinguish between text and space is made possible.
Second, the surface of the adsorption principle
According to the different surface tension, it can adsorb different substances, which also provides the possibility of lithographic offset printing and graphic separation.
Third, the network structure principle
Since the offset printing plate is flat, it is not possible to rely on the thickness of the ink to express the level of graphics on the printed matter, but by splitting the different levels into tiny tiny dots that are undetectable to the naked eye, the performance can be effectively expressed. Come out with a rich image hierarchy.
In life, we have this common sense: water soaked on the surface is not easily contaminated by oil, water and oil are always mutually exclusive. Since offset printing plates are almost on the same plane, it is necessary to find a method that can effectively distinguish the blank part from the graphic part. The role of water in offset printing is what we call the “water and oil incompatibility” principle. In the printing process, a thin layer of water is uniformly applied on the surface of the printing plate (actually, due to the selective adsorption on the surface of the printing plate, the graphic part is not wetted) and then coated on the printing plate. When ink is used, it effectively protects the blank area.