Problems and solutions in the gravure printing process 1

1. White spots on the printing surface

This refers to the irregular distribution of blanks in the graphic part of the substrate. When the surface of the paper or cardboard is not flat enough or the paper is too hard, it is not easy to be flattened, the ink in the ink hole of the printing plate cannot contact the substrate; or the printing pressure is not enough to cause white spots

Solution: You can use a harder printing roller, a solvent with a slower drying speed, reduce the viscosity of the ink, and install an electrostatic ink absorption device. Switch to paper with a flat surface to avoid this problem.

2. Pinhole

Pinholes appear as many small holes in the printed film sheet, especially when printing transparent substrates. This is because the ink cannot completely wet the substrate, resulting in the formation of small round holes in the ink film.

Solution: Switching to another type of solvents and additives can solve this problem to a certain extent. Sometimes air bubbles are mixed into the ink, and the air bubbles entering the ink hole will also cause the appearance of pinholes.

3. The ink is squeezed out

Irregularly distributed ink appeared around a group of ink holes.

Solution: If it is caused by the ink, the viscosity of the ink can be increased; if the printing plate is excessively corroded, if the wall of the ink hole is easily damaged, the ink will overflow from the ink hole.

4. Ashing

Ashing means that there is a thin layer of ink on the surface of the non-graphic part of the printing plate. This layer of ink will be transferred to the printed product. Usually this is because the chrome-plated layer of the printing plate is lipophilic and sucks up the ink. The squeegee failed to completely scrape off these inks. Slight unevenness on the surface of the printing plate can also cause this problem.

Solution: Add some quick-drying solvents to the ink to make the ink layer dry before it touches the printed product: After a few hours, the uneven surface of the printing plate has been polished by the squeegee. You can change it at this time. Use normal solvent. Pigment in ink

Although the content is too high or the pigment is too hard, it will cause the poor dispersion of the pigment in the binder and cause this problem.

5. Crater-like spots

In the ink film, the solvent evaporates too fast, and the solvent suddenly evaporates through the surface of the oil film. There are many small rings on the surface of the ink film. These small rings can be observed with a microscope. This is the sudden solvent between the thick ink layers. The solution to the surface leaving caused by volatilization: reduce the dryness of the ink, reduce the volatilization speed of the solvent in the ink or the temperature of the heating and drying device, and increase the flowability of the ink, which can solve this problem.

6. Spots

Refers to the presence of dark and light spots in the ink printed on the substrate, and uneven prints. The reason is that the solvent in the ink is too slow to dry: or the ink is too diluted and the viscosity is too low. Although it is satisfactory at the high-key area, spots may appear at the low-key area; if the ink is thicker, especially the solid components in the ink (When there are too many pigments and fillers, the thixotropy is too large and it is easy to cause spots: uneven paper surface; poor wettability of the ink to the substrate, etc., may cause spots.

Solution: If the ink is thicker, don’t over-dilute: Increase the amount of ink supply appropriately: Change to paper with better surface quality: Increase the viscosity of the ink appropriately; Use special additives to increase the wettability of the ink; use in the ink Pigments or fillers with relatively low oil absorption can appropriately reduce their rheology; some additives are added to improve the wetting of the ink to the substrate.

7. Printing plate wear

Under normal working conditions, the surface of the printing plate is worn out. This requires that the pigments are well dispersed and the pigment particles should not be too hard。

8. The peeling of the chrome-plated layer on the surface of the printing plate

Some components in some inks have a corrosive effect on the chrome-plated layer on the surface of the printing plate, and eventually cause the chrome-plated layer to be completely peeled off in some areas. Dye-type inks used for aluminum foil printing contain phosphoric acid: inks using chlorinated rubber as the linking material may release chlorine and form hydrochloric acid; these acids will corrode the chrome-plated layer on the surface of the printing plate. In the water-based gravure ink, excessive alkali will also corrode the plate cylinder. It corrodes the copper under the chromium layer through the sand holes on the chromium-plated surface. After the copper is corroded, the chromium will fall off.

Remarks: Reprinted from "Ink Encyclopedia"