Packaging box overprint bad, no more than these 5 reasons!

In the production of multi-color printing, sometimes the phenomenon of poor overprinting occurs, making the print ink white, lusterless, appearing “spots”, etc., which seriously affects the quality of the print, thus leading to a decline in the quality of the packaging box, bringing serious economic losses to the packaging box manufacturers.
In this article, based on years of experience, the author summarizes five common factors that cause poor print overlays in multi-color printing production, and proposes corresponding solutions, which hopefully will be of some help to box printers.

Improper printing color sequence
　　Take the overprinting method for multi-color printing, when the latter color ink overprint on the former color ink, after rolling will form a mutual adhesion, separation, if the latter color ink adhesion than the former color ink adhesion is strong, the latter color ink will be the former color ink stick away, thus causing the print overprint bad, resulting in “spot”.

　　Therefore, to rationalize the printing color sequence, generally in accordance with the four-color ink adhesion from large to small, that is, in accordance with the order of black, magenta, blue, yellow.

　　Paper ink absorption improper

　　Multi-color printing, the ink transfer to the paper is in a wet state of wet pressure. If the paper ink absorption is too high, the ink link material will be too much penetration into the paper inside, so that the ink layer in the oil reduction, the ink pigment particles are suspended in the paper surface, resulting in ink film speed slowed down, the lack of glossy prints, and even sometimes the print once rubbed, it will occur flaking phenomenon. Conversely, if the paper is too low ink absorption, ink fixation speed is slow, poor adsorption, after a color ink overprint before a color ink will stick off the previous color ink or overprint on, resulting in poor print overprint.

　　Therefore, try to choose the moderate ink absorption of paper, so that the ink fixation speed moderate, the ink layer on the paper adhesion moderate, and then increase the ink layer on the paper bonding strength.

　　Fountain solution pH value control is not appropriate

　　If the pH value of the fountain solution is too low, the fountain solution will separate the linking material and pigments in the ink, resulting in ink emulsification. When the ink is transferred to the paper, the pigment in the ink will float on the surface of the paper, after a color ink overprint before a color ink, part of the pigment will be stuck away, resulting in poor printing overprint.
Therefore, the pH value of the fountain solution must be controlled. In general, the pH value of the fountain solution should be controlled at 5.0 ~ 5.5.

　　Improper water supply for printing plates

　　The amount of plate water supply is controlled by adjusting the contact pressure between the water bucket roller and the metering roller. When the contact pressure between the water bucket roller and the metering roller is small, the plate water supply is larger, the formation of thicker water film, ink film color will become lighter, resulting in poor print overlay; when the contact pressure between the water bucket roller and the metering roller is larger, the plate water supply is smaller, the formation of water film is thinner, the ink film color will become darker, the overlay effect is better.

　　Therefore, to adjust the contact pressure between the water bucket roller and the measuring roller, so as to control the plate water supply, so that the water film thickness is moderate, so as to avoid poor print overprint.

　　Ink roller surface left crystalline matter

　　Multi-color printing, if some residual paper powder, fountain solution, ink adhering to the surface of the ink roller, it will make the surface of the ink roller crystalline matter, so that the ink roller on the ink film separation is difficult to control, resulting in poor print overlay.

　　Therefore, the ink roller surface should be checked frequently to see if it is smooth, and once the crystalline matter is found, it must be removed in time.