The first point: oil dirt is mainly due to the induction of ink on the blank part of the printing plate, which makes it appear on the printing plate in a greasy state. It often starts from a small part, and then gradually expands the scope, and the dirty part is relatively fixed and not easy to wipe off, and it is quickly reflected on the printed sheet.
The reasons for oily dirt are: 1. The quality of the printing plate (bad base or recycled version), the blank part of the printing plate is oxidized; 2. The exposure time is insufficient and the developer concentration is too low during printing; 3. The ink 4. The printing pressure is too light or too heavy; 5. The printing plate is not tensioned when the plate is loaded; 6. The pH value of the fountain solution is improper; 7. The surface of the blanket is aging.
The second point: the cause of the floating dirt is mainly due to the emulsification of the ink. One form of the floating dirt is the small particles of the ink, which are often evenly presented on the entire printing plate, and the other form is the ink roller. The emulsified ink with very little viscosity splashes on the printing plate, the blanket, and even directly on the paper.
The main reason for floating dirt is the ink emulsification caused by the imbalance of ink and water. In addition, it is also related to factors such as paper quality, water, and ink roller pressure. In multi-color printing, if each color ink is dirty, it is likely to be a paper problem. If there is only one or two colors of ink floating dirty, it is the problem of ink or printing plate. Dirt often causes a large number of prints to be scrapped, and this kind of printing quality accident must be paid great attention by operators.
Therefore, operators must pay attention to these details before and after printing to avoid the appearance of some problems, but cannot find the reason. Here, everyone must proofread every step, observe carefully, and finally work carefully, so as to complete the pre-printing work of the printed matter.
