Analysis on the causes of inaccurate overprinter in printing
Overprinting is a common printing defect, which will greatly affect the printing color and visual layering. Almost every company has this problem. There are three reasons why printing is not allowed (not including the film itself and printing), so pay attention to it when printing.
First, the plate deformation.
1. Bake the board (to improve the printing resistance of the printing board) to deform,
The temperature must be controlled within 230-250 degrees.
Let it cool naturally within 5-8 minutes.
2. Bending deformation: 4c plates should have the same thickness (for example, Fuji and Xingguang plates can't be mixed when printing), and the padding should not be too thick.
3. Tensile deformation: This is caused by overexertion during plate mounting.
Second, misregister caused by improper adjustment of printing machine.
1. It is caused by different heights of the paper feed suction nozzle or improper adjustment (different speed) of the paper pressure roller. This can be seen from the fluctuation of feida paper feeding.
2. Improper adjustment of rules
1) Improper adjustment of the height and working hours of the front gauge will lead to inaccurate upper and lower gauge groups. The height of the front gauge should be exactly three times the thickness of the paper, and the swing time of the front gauge should be exactly when the paper reaches the front gauge.
2) Improper adjustment of the tension and working time of the side gauge will lead to inaccurate registration of the left and right gauges. At the beginning of machine calibration, you can see it from the waste printed sheets.
3. Improper adjustment of paper delivery teeth and impression cylinder teeth.
This should be adjusted by the dial on the impression cylinder, and experience alone is not enough.
4. Improper lining of the drum (the following are the technical parameters of Heidelberg machine, for Mitsubishi machine's reference only).
The total thickness of the printing plate cylinder lining is generally between 0.6 and 0.8 mm.
The total thickness of rubber roller lining is generally between 3.25 and 3.45 mm.
5. Influence of printing speed
In principle, you should drive at a constant speed, which is generally maintained at about 70% of the maximum speed, except for printing projects with simple difficulty, and the difficulty of printing mainly depends on the draft.
Third, the setting caused by paper deformation is not allowed.
There are mainly paper tensile deformation and curl deformation. In addition to strengthening inspection when collecting white materials, adjusting the temperature and humidity in the workshop is the key (the humidity in the northern printing workshop is often low, so it can be adjusted by sprinkling water on the ground), especially for single-sided printing. After leaving it for too long, the paper turns upside down, and the problem of overprinter is obvious.
Of course, it is also a good practice to print along the grain as far as possible without affecting the printing color (that is, the paper grain is consistent with the ink path), which should be considered when opening the item list;
Another point is to ensure the parallelism between water roller and printing plate, printing plate and blanket, rubber and impression cylinder; And on the premise of ensuring the balance of ink and wash, try to reduce the amount of fountain solution.
Only if you are familiar with the above reasons can you adjust the machine quickly and print stably.