Analysis of Irregular "Brapping" and Inhomogeneous Failure of Gravure Products

When the company used rotary rotogravure printers to print white cardboard products, there were frequent occurrences of irregular “stripe bars” and uneven ink layers at the edges of the color pattern, which directly affected the quality of the product. For this reason, the relevant technical personnel of our company have conducted serious observation and analysis.
After observation, we found that the indoor humidity was relatively low when there were irregular “stretching” and uneven ink layers. Therefore, our preliminary analysis suggests that the above-mentioned unfavorable phenomena may be caused by static electricity. Because the principle of static electricity generation is due to the exchange of positive and negative ions in two different substances, that is, two objects due to friction and rapid separation, so that the positive and negative charges are no longer in the original state of neutralization, some charge will move between the two objects, At this time, static electricity was generated. In the high-speed rotary gravure printing production process, due to the large friction between the substrate and the printing equipment itself (such as: metal transmission roller, gum impression roller), the generation of static electricity becomes inevitable.
In addition, due to the rapid printing speed of the rotary gravure printing machine and the continuous running process, there is a continuous friction process between the substrate and the device itself during the production process, and an electrostatic field is easily formed around the substrate. The contact between the quality embossing roller and the plate will be more prominent. Detected with an inductive pencil, the static electricity between the color groups is as high as hundreds of volts. We further analyze that due to the existence of the electrostatic field between the color groups and the unity of the equipment's running direction, the tail end of the irregular “pulling” phenomenon must point in the opposite direction of the equipment operation, and due to the discharge of the electrostatic field, the ink layer is uneven. The phenomenon also shows the distribution law related to the electrostatic field. To this end, we further confirmed the phenomenon of irregular “pulling bars” and product samples with uneven ink layers, which proved that the results of our analysis were correct.
Based on the analysis results, we conducted an indoor environmental humidity adjustment test, and kept the indoor humidity at 70% or more. Irregular “stripe” and ink layer unevenness were significantly improved. But doing so will cause another kind of quality problem, namely the product is easy to be deformed after the indoor humidity rises, the paperboard type printing material with strong water absorption is very easy to influence the reduction effect because of moisture. For this purpose, we used static elimination brushes for further static elimination tests. As a result, the irregular “stripe” and ink layer unevenness completely disappeared. The voltage measurement was performed with an induction test pencil and the measured voltage value was close to zero.
For this reason, we determined that the irregular “stripe” that affects printing quality and the unevenness of the ink layer are due to the generation of static electricity. Eliminating static electricity using a static elimination brush can effectively eliminate irregular “stripe” and ink layers. Uneven failure, and low input costs, in addition to the effective elimination of printed static electricity, can also eliminate some of the safety hazards caused by static electricity.