Wire drawing is one of the problems often encountered in gravure printing, which involves gravure printing machine, plate cylinder, Doctor blade, printing environment, ink and many other factors. If not handled properly, production and quality will be affected. There are three common types of wire drawing, and today I will focus on troubleshooting wire drawing faults in shallow mesh positions.
1. Eliminate wire drawing from the source of design and plate making
Fully consider printability during the design and plate making of the original manuscript. Always consider the printing direction and avoid printing from light to deep as much as possible; The black and magenta versions are most prone to shallow online wire drawing. Especially for black printing, due to the coarse carbon particles in the ink, when the black screen is very shallow, it is almost impossible to fit a single carbon particle in a dot, making it more prone to wire drawing. Therefore, a large area of black and light screen should be designated as a special gray version as much as possible to reduce printing difficulty and scrap rate.
2. Use the Doctor blade correctly to avoid wire drawing
Selection of Doctor blade. The surface hardness of the chrome plate cylinder is HV850~1100, and the hardness of the Doctor blade should be lower than that of the printing plate, about HV600. If the hardness is too low, the ink can not scrape clean, and if the hardness is too high, the printing plate will wear faster, and will produce knife marks, which will affect the print quality.
The flatness of the Doctor blade. When installing the Doctor blade, first flatten the blade, and at the same time tighten the screws from the middle to both sides in turn. Do not do it in one step, but repeat it two or three times to ensure that the force on the blade is uniform.
Sharpness of the Doctor blade. Use 600 # water abrasive paper or 2 # metallographic abrasive paper to polish the Doctor blade, or use a special sharpener to grind the back of the Doctor blade into a bevel of about 25 °, even if the knife is new.
Doctor blade angle. The angle of the Doctor blade is smaller than that of normal printing, and the distance between the contact point of the Doctor blade and the printing plate and the embossing point is shortened.
3. Reasonable selection of ink to prevent wire drawing
When there is a large area of shallow screen or layer transition on the layout, high-quality ink should be selected to prevent the ink pigment particles from being too coarse and causing wire drawing. Typically, the fineness of the ink is 15 μ m. Too rough ink particles will cause great damage to the Doctor blade and printing plate.
When mixing ink, on the premise that it does not affect other patterns on the same printing plate, slow drying solvents should be considered, and excessive auxiliary solvents such as ethyl acetate should not be added to prevent changes in ink properties that prevent normal printing.
Ensure moderate and stable ink viscosity. The production of wire drawing is directly related to the viscosity of the ink. Generally speaking, the higher the viscosity of the ink, the easier it is to produce cutting lines in printing. In addition, due to the varying performance of various brands of ink and the varying amount of solvent added, specific data provided by the ink manufacturer can be consulted when mixing ink, and specific operations can be carried out based on one's own printing conditions and the products being printed.