Although the Doctor blade is very inconspicuous, it has a crucial impact on product quality for high-precision ink wash color printing technology. If the Doctor blade is not used well, it is easy to cause defects such as line mark, color difference and blocking on the surface of printed matter. Therefore, it is very important to understand the working principle of the Doctor blade and how to use the Doctor blade correctly.
1、 Selection of polyester plastic Doctor blade
The Doctor blade is mainly used to wipe off the excess ink on the surface of the Anilox, which can better control the amount of ink transferred to the printing plate. The commonly used polyester plastic scrapers range in width from 25mm to 70mm, thickness from 0.5mm to 2.0mm, and blade angles of 30 ° and 45 °.
Before printing, the first thing to consider is the printing layout, whether it is a field version, a line text version, or a multi color overprint dot color version.
A. If 280-380 lines are used for the anilox roll configuration in the factory printing machine, the Doctor blade with a thickness of 1.5mm or 2.0mm and a blade angle of 45 ° can be selected. The reason is that the Anilox of the low screen wire wears the Doctor blade quickly, which results in more ink and darker printing color. When such a Doctor blade is selected, when the ink volume increases with the wear of the blade during use, the printing color change will not be affected too much.
B. If 380-550 lines are used in the configuration of the anilox roll in the factory printing machine, the higher the number of lines of the Anilox, the higher the requirements for the scraping effect. At this time, you can select a Doctor blade with a thickness of 1.5mm and a knife edge angle of 30 °. The reason is that the Anilox of the high screen wire has a good surface finish. At this time, selecting a 30 ° thin blade tip can effectively obtain an ideal ink scraping effect.
2、 Details to be paid attention to when installing polyester plastic Doctor blade
1. Cut the length of the Doctor blade according to the length of the Anilox
When replacing a new Doctor blade or sealing knife, it should be noted that the length after cutting should be slightly 25px longer than the length of the Anilox; Otherwise, ink leakage will occur when the ink on both ends of the Anilox is not wiped off due to the insufficient length of both ends of the Doctor blade and the sealing knife during the printing process.
2. Pay attention to the flatness of the Doctor blade during installation
If the problem requires a new Doctor blade, the mounting screw should be locked from the middle to both ends to ensure the flatness of the Doctor blade. A more practical method is to hold the scraper inward with the thumb of one hand (pay attention to wearing gloves), and hold a wrench in the other hand to lock the screws on the clamping plate.