1. Random ink
Phenomenon: random occurrence, no rules to follow, sometimes light sometimes heavy.
Causes: ink roller contact with ink and fountain solution for a long time. Under the action of friction, the surface performance of ink roller decreases and becomes very smooth, and it gradually ages and loses elasticity, resulting in the speed difference between the speed of ink roller and the speed of disk, resulting in sliding friction and ink. In addition, if the offset machine vibration is abnormal, irregular and wide ink will be produced.
Exclusion method: conduct a comprehensive inspection on the ink roller. If it is found that the ink roller is seriously aged, it is necessary to replace it with a new one. On the contrary, it can use pumice powder, grinder and so on to properly grind off the skin on the surface of glass ink roller and increase its friction. In addition, we should also do a good job in the daily maintenance of the offset press, and regularly check whether the bolts of key fasteners are loose and worn. Once found, we must repair them immediately.
2. Equidistant ink
Phenomenon: the plate distribution width is about 25px, the color has dark ink and light ink, the ink spacing is equal to the gear spacing.
Cause: when the drum gear is seriously worn, the gear backlash will expand, the gear engagement will be inaccurate, and the contact between the drum gear will easily generate abnormal vibration, which will cause the contact friction and sliding between the drum gear and the surface, thus forming the ink with equal spacing.
Elimination methods: (1) replace the drum gear with serious wear; (2) if conditions permit, the center distance between rollers can be appropriately reduced to make the gear mesh more closely. In order to avoid the occurrence of top gear accident, the gear side clearance can reach about 0.1mm; (3) replace the soft lining, adjust the pressure between rollers, use fine adjustment, increase 0.02mm each time until the optimal value is reached.
3. floating bar
Phenomenon: floating ink, that is, there are ink particles and ink spots on the ink.
Reasons: (1) the cleaning roller uses cleaning agent and ink to mix, resulting in ink thinning; (2) ink roller aging; (3) using unqualified ink, these ink emulsification, viscosity and other poor performance, easy to produce ink in the printing process.
Exclusion methods: (1) change the ink or add a proper amount of thickener into the original ink. If the printing enterprise uses spot color ink, it is generally not easy to change. This method can adopt the method of adding thickener. (2) if the floating ink is discolored and the water roller is cleaned, it is likely that the residual gasoline or kerosene will mix with the ink, resulting in the change of ink binder structure. Therefore, the water roller should be cleaned again to ensure the cleaning standard before printing. (3) the aging ink roller shall be replaced or grinded in time. (4) when the ink emulsification is serious, the printing plate shall be cleaned again, and the water content of the paper shall be minimized at the beginning of printing.