Generally, printed patterns are formed by printing with multiple ink colors, and the accuracy of overprinting directly affects the quality of the images and even leads to the scrap of printed products. The printing industry generally requires a precision of no more than ±0.1mm for overprinting of general printed products. The following are the reasons for inaccurate overprinting:
Some thin film pressure-sensitive adhesive materials may shift on the printing equipment due to the unbalanced tension on both sides during the slitting process, and often drift to one direction, resulting in inaccurate overprinting. On the two ends of such substrate materials, one end can be found to be relatively flat while the other end has a scalloped edge.
To solve this problem, the substrate material can be re-rolled, as rolling it again can release the tension and solve the problem. If the problem persists after rolling, a new material needs to be replaced.
Sometimes, uneven self-cutting of the substrate material itself can also lead to inaccurate overprinting. The main manifestation is that the end face of the rolled material is uneven, which can easily cause the overprinting to shift when printing. This phenomenon is especially prone to occur in printing machines without correction devices.
If the width of the substrate material is sufficient, this problem can be solved by secondary slitting, cutting off 2mm on each side. Otherwise, the substrate material needs to be replaced.
The thin film substrate material is relatively sensitive to temperature and is prone to deformation. Therefore, if the UV lamp temperature is too high during printing, the thin film material is susceptible to deformation, affecting the accuracy of overprinting. In this case, decreasing the UV lamp power can help solve the problem, because generally, the higher the power of the UV lamp, the higher the temperature. However, in actual production, we often encounter contradictions. For example, when the UV lamp power is high, the material is warped, resulting in inaccurate overprinting, but if the UV lamp power is too low, the ink cannot be completely solidified.
To solve this problem, comprehensive measures should be taken, such as using bottom coating ink, selecting ink suitable for low surface energy materials, or changing the printing sequence, etc.
The tension value set in the printing machine equipment also directly affects the accuracy of overprinting of thin film materials. If the tension is too small, the substrate material will be too loose, resulting in overprinting errors. Conversely, if the tension is too large, the thin film material will be stretched and deformed, which will also affect the accuracy of overprinting. Therefore, when printing thin film pressure-sensitive adhesive materials, the tension value of the printing equipment should be set to the minimum tension that ensures overprinting accuracy.
