Water bar refers to the obvious shallow streaks in the axial direction appearing on the printing plate layout and printed parts when printing flat screens or solid printed parts on a metal sheet printing machine, commonly known as "white bars" or "white heads". The water bar is generally caused by the water transport part, the causes and solutions are as follows:
(1) The pressure between the water roller and the main ink distribution is too large, the pressure between them should be readjusted to appropriately reduce some pressure;
(2) Ink emulsification, too much ink on the surface of the water roller;
(3) If the page has too much moisture, reduce the water supply, clean the blanket, and clean the ink roller when it is serious;
(4) The dampening water is too acidic, so the acidity of the dampening water should be reduced.
The pattern refers to the reduction of the dots on the printing plate, the emptiness, the weakening of fat sensitivity, the loss of fine dots, and the dim color. The causes and elimination methods of the pattern are as follows:
(1) The pressure between the water roller and the upper water roller is too small (large water), and the pressure of the water roller and the upper water roller should be properly adjusted;
(2) The dampening water is too acidic, so the dampening water should be diluted to reduce its acidity;
(3) If the water supply is too large, the water supply should be reduced;
(4) If the viscosity of the ink is too high, a certain amount of varnish should be added to the ink to reduce the viscosity of the ink;
(5) The printed version itself has been patterned during the process of plate making and printing, and it should be replaced with a new version.
The causes of the stale version and the elimination methods are as follows:
(1) If the pressure between the plate cylinder and the blanket cylinder is too large, the pressure between the plate cylinder and the blanket cylinder should be reduced;
(2) If the pressure between the plate roller and the printing plate is too light, the pressure should be readjusted (2.5-3mm);
(3) If the pressure of the plate roller and the printing plate is too heavy, the pressure should be reduced;
(4) The dampening water is too acidic, so the acidity of the dampening water should be appropriately reduced;
(5) If the ink is too thin, "0#" oil ink should be added to the ink;
(6) If the ink volume is too large, the ink supply volume should be reduced;
(7) If the desiccant in the ink is excessively added, the ink roller should be cleaned to reduce the amount of desiccant in the ink;
(8) The printed version is too thin and should be replaced with a new version.
Back smearing refers to the phenomenon that the printed sheets just printed by the offset printing press machine are stacked together, and the ink on the lower sheet rubs against the back of the upper sheet, causing the printed sheet to be contaminated.
The reasons for the smearing of the back and the troubleshooting methods are as follows:
(1) If the ink is not dried well or the ink volume is too large, add proper amount of desiccant and anti-sticking agent to the ink or reduce the ink volume;
(2) If the paper stack is too high, the paper stack height should be reduced;
(3) The ink is not dry and the pressing paper is too heavy;
Double image, commonly known as double-printing and ghosting, has two types: axial ghosting, that is, the imprint of the ghosted part is approximately parallel to the axis of the drum; Circumferential double, that is, the imprint of the double part is perpendicular to the axis line of the drum. Causes of axial ghosting are as follows:
(1) The offset machine has poor accuracy and the bearings are worn;
(2) Axial displacement of the plate cylinder or blanket cylinder;
(3) The ink roller moves axially (or the plate roller does not match the original machine);
(4) The causes of the circumferential ghosting of the "lotus leaf" of the paper are as follows:
① The blanket is not tight;
② The roller pressure is not in place;
③ The offset machine has been used for many years, and the roller gears and bearings are worn or the gap between the three rollers is too large.