With the rapid development of packaging industry, users have higher and higher requirements for the quality of corrugated boxes, including the printing quality of sales cartons. If the printing technology is not well mastered, many printing failures will often occur, such as “showing the bottom” and “white spots” when printing on the spot. In view of the fact that there are many variables that produce the above problems, the following only makes a simple analysis from factors such as materials, processes, and plates.
1. Reasons for printing materials
1. Poor smoothness of facial paper and cardboard is the most fundamental reason for the problems of “unrealistic printing”, “showing bottom” and “white spots”.
The smoothness of the facial paper itself is poor, or the cardboard itself is poorly smooth due to the large amount of glue used when the cardboard is compounded, or the light or heavy “washboard” caused by the poor smoothness of the cardboard itself. The binder in the ink cannot completely fill the voids of the paper. When the face paper is printed on white paper, white small holes will appear, resulting in “showing bottom” and “white spots”.
In order to solve this problem, some manufacturers often use the method to increase the printing pressure, but this will produce great side effects: on the one hand, the dots are deformed, and the characters and lines have obvious “edge effects”; on the other hand, the corrugated structure Will be damaged, reducing the strength of the carton.
Therefore, according to the customer’s specific requirements for the cardboard, choosing different smoothness of facial paper, and controlling the process factors of forming the “washboard” during the cardboard production is the fundamental solution to “false imprinting”, “showing bottom” and “white spots”. method.
2. The surface paper coating layer produces paper wool under the combined effect of printing pressure and ink, which often causes “imprinting”, “white spots” and other phenomena.
Solution: For cartons with higher requirements, choose paper with high surface strength; avoid large areas of the field during the day when the layout is designed; according to the surface of the paper, adjust the speed of the printing machine and the viscosity of the ink during printing to prevent the surface The paper has the phenomenon of fuzzing, which avoids the occurrence of “white spots” and so on.
2. Process factors
On the carton production line, the knife is cut from top to bottom when trimming the burr with a single knife, which often results in uneven edges on the cardboard surface. When full-page printing is performed, the edges will not be printed with “open bottom” and “imprints”. Increasing pressure during printing and ensuring sharp edges during trimming can alleviate this phenomenon, but it cannot be completely eliminated.
Three, the factors of the plate
The printing plate of the carton printing machine usually uses rubber plate and flexible resin plate (including domestic or imported), and there is a certain gap between the elasticity and inking ability of the two. Generally, the flexibility and inking ability of the flexible resin plate is higher than that of the rubber plate, and the printing ink layer is relatively thick, and generally there will be no faults such as “false imprinting”, “showing bottom”, and “white spots”.
The surface flatness of the printing plate is poor, which results in the difference in the amount of ink on the plate surface, and the imprints will also appear “underground”, “white spots” and other phenomena.
The flatness of the surface of the flexible resin plate is usually better than that of the rubber plate. Therefore, for cartons with high printing requirements, large area solid or dot printing, flexible resin plate must be selected for printing.