Analyze the causes of poor ink transfer during offset printing

In the offset printing process, water and ink are two very important substances in the process of ink transfer. Water is a fountain solution and ink is an offset ink. Only when the water and ink can be transferred well, the printed product can be exquisite. However, due to the influence of many uncertainties on the transfer of ink and ink, ink control has become the most difficult problem to control in offset printing. In the offset printing process, various ink transfer failures occur, and one of the failures is that the ink roller may sometimes be powdered, resulting in poor ink transfer.

The so-called "ink roller powder", that is, during the offset printing process, after the printing machine runs for a while, the powdered particulate matter appears on the ink roller, and the ink is deposited in an unnecessary area (such as an ink roller) or the ink roller deinks. Poor transfer of ink, etc. This printing failure occurs mainly because the powdery particles on the ink roller are lipophilic or hydrophilic. What are these powdered particulates? Where did it come from?

In the offset printing process, the substances that continuously enter the printing press from the outside are substrates, inks, and fountain solutions. Therefore, these powdery particulate matter must be brought in directly or indirectly by these three substances.

In general, if the surface of the substrate is of poor quality, it is possible to bring the powdered particulate matter directly into the printing ink system. For example, when the surface of the paper itself carries a large amount of paper powder or other powder, the dirt may be transferred into the ink transfer system through the printing plate as the printing process, resulting in the occurrence of a failure of “ink roller roller”. It is produced by changing the surface of the substrate to print; In addition, the surface of the paper itself is clean, but because of the tightness of the coating on the surface of the paper, powder dropping and hair loss occurs during the printing process, and the ink is transferred to the ink through the printing plate. In the transfer system, the same problem can also be caused by the "ink roller powder" failure, which can be solved by lowering the vehicle speed, lowering the viscosity of the ink, or replacing the paper with better quality.

In addition to the substrate directly introducing the powdered particulate material into the printing system, the chemical reaction between the fountain solution and the ink may cause the possibility of calcium precipitation, thereby indirectly carrying the powdered particulate material into the printing system.

The main component of the fountain solution is water. The hardness of the water is not the same everywhere. The general hardness of the soft water is 0~30ppm, and the total hardness of the hard water is more than 60ppm. When the water quality is too hard (ie when the Ca+ content is high), it usually causes Ca+ to contact with the resin in the ink to form calcium sulphate, and when it comes into contact with the acid in the acid fountain solution, it will produce like lime or calcium phosphate. The calcium salt of the class. Saponified calcium has lipophilic properties, which can cause the ink to deposit in undesired areas, causing the surface of the roller to crystallize, causing water transfer and poor ink transmission. The calcium salt, which is hydrophilic, can hinder ink transfer and cause the ink roller to come off. ink. Therefore, the solution to the problem is to use soft water with low Ca+ content as much as possible to formulate or dilute the fountain solution. At the same time, we should use fountain solutions that can effectively reduce calcium deposition to eliminate the effects of excessive calcium ions.