The lithographic (printed) form of dingy appearance is the appearance of large dots of ink in non-printed areas. The reasons for this are: (1) The printing pressure and the printer's operation damage the sensitive film on the plate to expose the metal, and then it will be immediately caused by trace surface activity, polarity, free fatty acid and other substances. Pollution caused by local ink absorption. (2) Excessive ink layer remaining on the plate during development leaves a dirty plate produced on the plate. (3) The ink is too thin and the oiliness, softness, and viscosity are insufficient, and it is easy to cause the ink roller to slip and then make the water roller dirty. (4) Inadequate sensor processing or gluing is not good. (5) The lack of water on the printing plate and the low acidity of the syrup cause the water roller to absorb the ink. There are also the inherent dirtiness of the PS plate. 
The usual treatment methods are: (1) Adding a varnish (resin solution) to the ink; (2) Minimizing the content of grease and oil in the ink; (3) Increasing the amount of water supply, especially increasing the acid value of the syrup (4) Use a large concentration of ink to make the blotting as thin as possible; (5) Select the syrup with higher surface tension; (6) Adjust the embossing force between the plate and the rubber roller; (7) Reduce the desiccant; (8) Replace the faster dry resin ink.
Third, gravure (gravure) paste version 
In plastic printing, especially for the manufacture of composite inks, small-size or hierarchical layouts do not appear, and even the surface of the substrate forms indistinct ink. Some people think that it is due to poor adhesiveness. Adding adhesion-promoting tackifying (resin) agents without scientific knowledge can overcome the disadvantages of delamination. However, overdosing often results in softening of the ink after film formation. It is impossible to control the paste (staining). The reasons are: (1) the affinity of the surface with the gravure and scraper due to the floating color; (2) the acid value of the composite resin is too low; (3) the wettability of the chrome plating surface on the gravure is strong, resulting in Insufficient ink for scraping blade; (4) Insensitive or angled blade; (5) Rough surface of plate; (6) Ink drying (period) is too slow (e.g. ethyl acetate (fast-drying solvent) in the ink system ) It is preferable that the film be formed on a film within 1 to 3 seconds (7) In a high humidity environment, the charged ink has an affinity for chromium (increase the proportion of antistatic agent).(8) The printing speed is too slow or Bad plate caused by bad plate.
How to troubleshoot this problem. (1) If the chrome-plated surface of the new drum is rough, add a quick-drying solvent to the ink to form a dry thin layer of ink between the scraper and the impression cylinder. After two hours or even hours, polish the surface of the chromium. Replace with normal mixed solvent (such as 7 parts of ethyl acetate, 2 parts of toluene, 1 part of butyl acetate or 8 parts of ethyl acetate, and 2 parts of toluene.) (2) If the ink contains impurities If the pigment particles and paper, plastic crumbs, should increase the solvent, the best way is to filter the ink with a 250 mesh screen (3) change with a new doctor blade, and adjust its angle.(4) if it is slow-drying ink As a result, a quick-drying solvent is added to dilute the ink, whereas if it is caused by a quick-drying ink, a slow-drying solvent or silicone oil may be added to slow down the drying.(5) If the ink is dried due to the blow-drying, Adjust the blowing angle, generally to increase the speed of the printer or re-plate.(6) Add solvent to reduce the viscosity of the ink or add anti-adhesive anti-dirty agent (such as wax, etc.), etc. (7) Adding oil or resin liquid , Or change the non-particle ink.
Fourth, hole version (silk screen) paste version
The ink is often expressed on a silk screen plate. The usual method is to replace the slow-drying ink, or use a slow-drying solvent to adjust the ink.