Irregular "pull" and inhomogeneous failure analysis of gravure products
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When using the rotary gravure printing machine to print white cardboard products, our company frequently has irregular color strips and uneven ink layers, which directly affects product quality. To this end, the relevant technical personnel of our company have conducted serious observation and analysis.
After observation, we found that the indoor humidity is relatively low when irregular "strips" and uneven ink layers occur. Therefore, our preliminary analysis suggests that the cause of the above-mentioned undesirable phenomenon may be caused by static electricity. The principle of static electricity generation is because the exchange of positive and negative ions in two different substances, that is, the two objects are no longer in the original neutral state due to friction and rapid separation, and some charges will move between the two objects. At this time, static electricity is generated. In the high-speed rotary gravure production process, the static electricity is inevitable due to the large friction between the substrate and the printing equipment itself (such as metal driving roller and colloidal embossing roller).
In addition, because the rotary gravure printing machine has a faster printing speed and is a continuous operation process, in the production process, the substrate and the device itself have a continuous friction process, and an electrostatic field is easily formed around the substrate. The contact between the embossing roller and the plate is more prominent. The detection is performed by an inductive test pencil, and the static electricity between the color groups is up to hundreds of volts. We further analyze that the end of the irregular "strip" phenomenon must point in the opposite direction of the equipment operation due to the existence of the electrostatic field between the color groups and the uniformity of the equipment running direction, and the ink layer is uneven due to the discharge of the electrostatic field. The phenomenon also shows the distribution law related to the electrostatic field. For this reason, we further confirm the irregular "strip" phenomenon and the product sample of the uneven ink layer, which proves that the result of our analysis is correct.
According to the analysis results, we carried out the indoor environmental humidity adjustment test to keep the indoor humidity above 70%, and the irregular "strip" and ink layer unevenness were significantly improved. However, this will cause another quality problem, that is, the product is easily deformed after the indoor humidity is raised, and the paper-based substrate having a strong water absorption is also very susceptible to the effect of the moisture reduction. To this end, we used a static elimination brush for further static elimination test. As a result, the irregular "pull" and the unevenness of the ink layer completely disappeared, and the voltage measurement was performed by the inductive test pencil, and the measured voltage value was close to zero.
To this end, we determined that the irregular "pull" and the unevenness of the ink layer affecting the printing quality are caused by the generation of static electricity. The static elimination brush is used for static elimination, which not only effectively eliminates irregular "strips" and ink layers. Uneven failure, and low input cost, and the effective elimination of printing static electricity can also eliminate some safety hazards caused by static electricity.