The Causes and Countermeasures of Plastic Gravure Cut Line (Part 2)

1. Irregular thickness lines appear on the prints of the first knife line, which extend from the printed pattern part to the unpatterned part. The knife line is longer, and with the squeegee's left and right swings, the knife line also moves, sometimes one, two, and sometimes many. The solution is to adjust the position of the squeegee up and down. At the same time, we should observe whether the color of the squeegee is missing or not.
2. The direction of the second knife line is very regular, appears in the printing pattern part on the same printing plate, and is in the same position, with the squeegee's left and right swing, basically no big change, this is because the ink The coarse particles in the top push up the scraper, and the left and right swing of the scraper cannot drive it at all. If it appears in the middle color, the next color ink will fill the cut lines, that is, the next color ink appears at the cut line.
3. The third knife line is easy to appear in the last color, usually printed on the white plate in the plastic film, such a one or two knife lines will run through the entire print, viewed from the front of the print, if The knife line is not rough, not easy to find, from the back of the printed product can be found through the knife line is always formed by the "mark", this "mark" will appear in the compound, no doubt, especially in the composite aluminum film, more It can be clearly seen.
Whether it is the above kind of knife line, the solution is to stop printing, filter the ink, usually the first and second color used in the ink before filtering on the machine, the filter mesh 140 mesh metal screen, after long-term practice It has achieved initial results and is worthy of learning and learning from peers.
The generation of the knife line and the relationship of the plate cylinder The generation of the knife line is inextricably linked with the smoothness of the plate roll surface and the quality of the coating. Plates are divided into two types: hand-engraved plates and electro-engraved plates. The hand-engraved intaglio plates are not smooth, and the knife lines are easy to appear. The surface of the electric carving and intaglio plates is smooth, and the probability of producing knife lines is much lower than that of hand-carved plates. When printing with hand-engraved gravure, the first time before the machine is used to sand the surface with 1000 # water-resistant sandpaper, the specific approach is: the printing speed faster, empty machine operation, grinding sandpaper back and forth, but can not be used over Big, otherwise it will damage the cell. After polishing, the drum is wiped with a soft cloth and then printed on the machine. The knife line phenomenon is reduced a lot. It should be noted that this work needs to be performed by experienced personnel. If such a knife line appears during printing, the method is as before.
The hardness of the coating is also related to the production of the knife line. The hardness of the coating is not enough. It is easy to damage under the action of the doctor blade, and it will also generate the knife line. Sometimes this knife line is not available, also called the “hidden knife line”, often appears in the printless pattern. This knife line is only easy to find under the reverse side of the fluorescent lamp. There are two solutions to this knife line. First, after this happens, use a 1000# water-resistant sandpaper to gently grind the coating. It will be better, but often after printing for a period of time, it will appear again. Therefore, it is better to carry out the deplating treatment. In severe cases, it is necessary to re-plate; the second is to adjust the squeegee, increase the pressure of the squeegee, and to the layout Hair dryer also received good results.
The generation of the knife line and the relationship with the squeegee The generation of the knife line is closely related to the quality and installation of the squeegee. The squeegee is well-grounded and has a large relationship with the knife line. The squeegee is properly ground and it is not easy to produce a knife line. Otherwise, it is easy to produce a knife line. Grinding, usually using oilstone grinding, and then use 1000 # water-resistant sandpaper plus 6 # oil polished smooth, knife back grinding into a 25 ° oblique mouth, if the blade has a serious gap, you should replace the new blade. At the same time, it should also be noted that if the blade is soft-elastic, it is not easy to produce a blade. If it is a domestic blade, it is easy to produce a blade. The blade must have a certain degree of elasticity. Hard and inelasticity is the main cause of the knife line. There are other reasons, such as scraping dirty ink on the printing plate, and fogging affecting the quality. Generally, the hardness of copper is between 200HV-300HV, the hardness of chromium is between 800HV-900HV, and the hardness of scraper is between 450HV-(900+300)/2. This will not hurt the printing plate and leave no marks. It also reduces the chance of knife cuts. The blade tip of the squeegee should be selected to have a rounded blade tip so that the printing plate can be protected because the plate is circular and the blade is rounded.
Do not destroy the plate, it is easy to scrape the ink. Keep the clean and non-slip ink without pattern at the time of printing. If the blade tip is flat, the scraping ink will not produce a clean cutting line because the flat and very sharp will not only damage the plate but also affect the printing. When installing, the scraper should be protected between 0.5cm -1.2cm between the flat plate in the flatbed under the scraper, the scraper is too prominent, the scraper is easily deformed, has a wavy shape, and affects the scraping effect, resulting in quality accidents. The installation is too short and the ink is easily scratched, but the marks on the plate will be many, and as long as the knife is loose and the printed pattern is thickened or faded, it cannot be used repeatedly. In addition, if the weight of the hammer is too heavy, the blade pressure will produce a knife line too much. The solution is to reduce the weight of the hammer. At the same time, proper hair blowing to the layout will effectively reduce the generation of the knife line.
The generation of knife lines and the environment The generation of knife lines has a lot to do with the environment. If there is dust in the operating environment, dust can enter the ink and cause knife lines. The workshop should first isolate the printing unit to reduce the flow of personnel. The room is equipped with air-conditioning facilities and dust removal equipment. At work, the first color sequence and second-color inks are filtered and printed on the machine before work. There are special health workers to clean the house during work hours. The environment must be kept clean.
The production of knife lines is various and the format is not specific. This requires the operator to develop habits of summing up experience and actively cooperate with the factory management to minimize knife line failures.