Analysis and elimination of the cause of the corner of paper
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The corner refers to the phenomenon of inaccurate fitting on the side of the printed paper. In recent years, most corner failures have occurred mostly in multicolor offset printing. The main reasons are:
(1) The front gauge is not on a parallel straight line, causing the paper to reach the front gauge and less paper on one side.
(2) The difference in paper thickness is large
(3) The pressure of each color group is increasing
(4) blanket drum liner is not flat
(5) The difference between the two sides of the impression cylinder
(6) The impression pad is smooth or too low on both sides of the tooth on both sides of the tooth
(7) Due to the large blank area on both sides of the back of the printing plate, the amount of dampening liquid is large in this area, causing the paper to adhere to more dampening liquid, causing the tip to partially expand and contract, forming a corner.
(8) The amount of liquid used in the blank area on both sides of the printing plate is different, and the side will also form a corner.
Similar failures occur in monochrome offset presses.
[case]
A factory uses a four-color offset offset printing machine to print atlases, which are printed on 80g/? offset paper. Some red and blue sleeves are often found at the tip of the trailer, especially some special symbols, such as some urban symbols are blue traps. red. This phenomenon mostly occurs in the latter half of the printing web.
[case analysis]:
The above example is an obvious horn phenomenon. The main reason for this phenomenon is that the printing pressure is not enough, so the printing pressure is re-measured and adjusted. In addition, it is also related to the tightness of the paper and the tightness of the gripper here.
[Case]:
In the process of commissioning CP2000-CD102 machine, a factory carried out color printing test after passing the test of various indicators, and added portraits in different positions of 50% flat net of black, blue, magenta and yellow. The test results show that the coated paper and paperboard above 128g/? are normal, and when testing the 80g/? coated paper of the book, the "corner" phenomenon occurs in the lower right corner of the printed matter, and the angle gauge is not printed.
[case analysis]:
Such "corner" failures are generally independent of the pressure of the various color plates of the paper printing plate and the blanket lining. It may be related to tooth decay, but when checking the tooth decay, the force of the tooth decay is normal, and then the double-diameter impression roller is observed. When the paper is caught, the tooth in the lower right corner is about 4 mm long and the tooth is not caught. The paper is slightly deformed when pressed, resulting in a "corner".
Approach:
Reset the paper side pull gauge position, adjust each related component, and then start the test print, troubleshooting.
[Expert Tips]:
Whether it is a multi-color offset press or a monochrome offset press, do not recklessly change some key parts, pay more attention to the position and range of the crepe paper. For papers with high hardness, such failures are not easy to occur.