Prevention and Diagnosis of Failure in Web Printing (III.1)

The high-quality four-color printing of the paper feeding device should control the paper tension at the time of paper feeding.
1. Tension is not right Before every job, you should reset the tension of the paper.
2. The compensation roller is not moving (pump)
Failure of the compensation roller will result in web breaks (find out by technical service personnel).
3. The accumulation of the residue on the rollers causes the paper to crease, resulting in a web break.
Solution: Wash the rollers frequently to see if they are rotating properly; and check regularly if the mechanical support is flush with the rollers.
4. The pull roller is not installed correctly. If the pull force is uneven, the paper will be misaligned.
Solution: Check whether the two rollers are in parallel and whether the pressure is correct. Check whether the rubber on the surface of the paper-pulling roller is aged and hardened, resulting in unstable tension and paper offset. Use a hardness tester to check the hardness of the rubber.
The paper feeder controls the axial tension of the web to obtain high quality printing.
1. Too much force in the paper feed causes the paper to break when it is fed.
Solution: Check the paper feed, cooling speed, folding tension setting, and the pull roller.
2. The reaction is too fast (pump)
The paper feed force of the web must be continuous and stable. If paper skews, it will cause a change in the paper tension.
3. The accumulation of the residue on the rollers causes the paper to crease, resulting in a web break.
Solution: Wash the rollers frequently to see if they rotate properly. Check regularly if the mechanical support is flush with the rollers.
4. The paper jam is not stable at the platen jam and will cause creases in the web. Excessive paper offset will break the web behind. The cause may be: The installation position of the roll paper is not caused by the instability of the paper tension in the printing drive, or there is a problem with the paper feeding device.
Paper breaks related to ink and wetting Table 2 shows the web breaks associated with ink and wetting. The following analysis is performed in turn.
Table 2 Breaks related to ink and wetting

1. Incompatible ink and paper The paper with poor performance is characterized by a non-smooth surface and loose fibers. Problems often arise when transferring paper with good performance to paper with poor performance (eg from LWC, SC to good newsprint). Printing on high-viscosity inks on uncoated paper can cause paper fluffing, stacking, and web breaks. Therefore, it is required that the viscosity of the ink should match that of the paper, especially when the first color is a black ink (in Europe, the printing ink often changes with the change of the paper. The consistency of the ink paper reduces the amount of ink emulsification, paper nap, pile Ink-induced blanket wear and paper breaks).
2. Over-inking can cause a wrapper at the printing unit and a malfunction at the drying device and the cooling device.
3. Too much fountain solution can cause paper to break at start-up or wrapper at the printing unit. A moderate amount of dampening solution can reduce the paper's tensile strength (the type and amount of fountain solution should be consistent with that of ink and printing). Too much moisture will prevent the ink from drying out. The undried ink accumulates on the chill roll, causing the paper to break. At the same time, the gloss of the ink is reduced, the paper is blistering, and the cooling roller emits smoke when cooling.
4. The viscosity of the ink is too high. It is easy to form wrapping paper on the blanket in the solid printing area. Changes in paper tension can affect overprinting or web breaks at the printing unit.
Possible measures include: lower ink viscosity, increase paper tension, reduce paper roll speed, use a good elasticity blanket. When printing stops, evaporation of the ink solvent increases the viscosity of the ink. When you turn the computer back on, paper may wrap over the blanket. This condition can be exacerbated when the workshop conditions are poor (solvent stabilized inks should be used).
Note: Spraying a small amount of solvent on the roller and blanket can reduce the viscosity of the ink and reduce paper breakage at startup. Newsprint printers often use black ink as the last color sequence to reduce paper fluff.
5. The viscosity of the ink is too high. The cold ink has poor fluidity in the ink fountain, which may cause the ink to be pale, paper fluff, and paper break during printing.
6. Ink fog, flying ink, ink drop equal a. Ink fog (ink roller)
Reason: high speed