Problems and solutions in the gravure printing process 2

9. Sticky pages

    The printed product that has been printed is glued to another sheet of paper. This is caused by the ink film being wet or being re-softened by the overprinted solvent

Solution: If the ink with a suitable formula is used:; Speed up the drying speed of the remaining solvent in the ink: Improve the drying conditions of the printing machine: Adding a de-tackifier can all reduce this trouble.

10. Dry in the ink hole

    In the gravure printing plate, the ink has dried in the ink hole, especially in the high-gloss area.

Solution: The thinner with slower drying speed can be added: Replace the binder in the ink: Adjust the drying conditions of the printing machine and improve it.

11. Inaccurate overprinting

    Accurate overprinting is one of the most important criteria for beautifully packaged products. Many factors in the printing process can cause inaccurate registration. Inaccurate registration includes two types: inaccurate axial registration and inaccurate radial registration (1) Main causes of inaccurate axial registration

①Inaccurate axial registration caused by uneven film rolls. When the plastic film is blown, there is a phenomenon of uneven winding, which will cause the film to move left and right on the guide roller during printing, causing inaccurate overprinting. If the unevenness of the film is severe, the film can be placed on a photoelectric controlled slitting machine to rewind; for slight misalignment, rubber bands can be added to each guide roller to avoid the axial movement of the film.

②The axial movement of the intaglio plate roller. The axial direction of the plate roller of the multi-color gravure printing machine is positioned by the cooperation of the U-shaped groove at the shaft end and the bearing on the frame. The thickness of the bearing is exactly equal to the width of the U-shaped groove. When the U-shaped groove wears and causes the width to increase, the plate axis may drive the plate roller to move axially, causing inaccurate registration. When the wear amount exceeds 0.2mm, inaccurate registration will result Obviously, the operator should pay attention to frequently adding oil to the bearing fittings and replace them when significant wear occurs.

12. Outlet failure

    Dot failure refers to a dot-like failure in the printed product area. Some dot loss is not printed, and the printing area of some dots has been reduced. This is caused by many reasons, such as ink, printing plate cylinder, and tiller. Pressure systems and paper etc. may cause this problem.

(1) This phenomenon can be caused by the improper flow of oil from the ink hole. In multi-color overprinting, the oil is too mature and dries too quickly: poor fluidity; ink drying in the ink hole: the amount of ink in the ink fountain Insufficiency: Insufficient ink in the ink hole: bubbles in the ink or water in the ink will cause dot failure

(2) Plate cylinder. The corrosion process of the printing plate cylinder has shortcomings: chromium enters the ink hole, causing the ink hole to be shallow and rough; or the cylinder is unbalanced or out of round will cause the failure.

(3) Pressure system. The pressure is not enough and uneven.

(4) Scraper. If the pressure is too light, the ink flows out of the ink hole showing unevenness or the doctor blade angle is incorrect 

(5) Paper. Poor surface smoothness: The coating is too thick: The elastic deformation of the paper is too large. Solution: You can improve the drying performance of the first color ink: This can smoothly overprint without network failure. Reduce the viscosity of the ink: Improve the ink Flowability: add some defoamer: the printing plate cylinder is light and has good corrosion resistance: correctly adjust the angle of the scraper; appropriately and evenly increase the printing pressure and use good paper to solve the problem.

13. The printed product is not resistant to rubbing

    The ink film can be used to finger, wipe (or stick) it off, or lightly wipe the color to fall off. This is because the ink film becomes brittle after drying; the binder in the ink cannot adhere to the surface of the substrate, and the ink binder is not suitable: the paper is too absorbent: the plastic film is improperly handled when printing the plastic film; the solvent selected is improper The solution caused by the poor drying performance of the ink film: plasticizer can be added to the ink, and some anti-contamination additives should be added to avoid the problem of "sticking together": heating can be used when printing cellophane and other materials Method; change to new ink with more binder: change to paper with poor absorbency: treat the film when printing polyolefin film; add wax and other auxiliaries to the ink and other methods to improve.

Remarks: Reposted from "Ink Encyclopedia"