What are the common problems that occur in the printing process of aluminum foil bags?

In the process of gravure printing, sometimes there will be failures, which are generally mainly caused by printing plates, inks, substrates and squeegees, etc., mainly in the following aspects.

1) Poor printing fastness. For plastic substrates (such as plastic films), it may be caused by insufficient corona treatment of the film, poor affinity between the printing ink and the printed material, large changes in the temperature and humidity of the printing environment, etc.; For the printing of metal packaging materials (such as aluminum foil), the poor printing fastness is mainly caused by the poor affinity of the ink with the substrate or the surface coating of the substrate, or the large changes in the temperature and humidity of the printing environment.

2) There are scratches on the ink layer of the printed matter. Abrasions on the guide rollers, sand particles mixed in the ink, uneven scrapers, and improper angles between the scraper and the printing plate are the causes of scratches on the printed product. Correct judgment should be made according to the specific situation of the scratch phenomenon, and the specific cause should be found out, and corresponding measures should be taken to solve it.

3) Thin tones. This failure can be caused by the thin color of the ink and the poor reflection performance of color light. When excluding, the performance of the ink should be adjusted.

In addition, for the printing of plastic films, the surface printing is first laid with white ink, and then the color is registered in order; When printing, the hierarchical version is overprinted with three primary colors first, and finally the base color is laid. For the printing of aluminum foil, white ink or white paint can be printed first for priming, and then the color pattern can be printed.

4) Bite the color. In overprinting, the second ink sticks off the first ink, which is the bite color. The reasons for this are:

The ink layer is not completely dried after the first color printing, and the pressure of the second color is large, or the machine speed is too fast, or the cold and hot air is poor, or the substrate has poor printing adaptability. Adding an appropriate amount of quick-drying agent to slow down the speed, reduce the pressure of the imprint cylinder, and increase the volume of cold and hot air are the measures to solve the problem.

5) The print has dull luster, rough ink layer, many blank spots, and textures on the ground. Too much ink solvent, coarse ink particles, excessive ink dilution, and rapid solvent evaporation will cause the above problems. Such ills can be eliminated as long as measures are taken to lower their indicators.

6) Blocking the plate. Due to the unclean cleaning, the ink is dry and fixed in the mesh of the printing plate, or the mesh is blocked by paper wool, paper powder, etc., or the temperature is too high during printing, and the solvent volatilizes too quickly. The methods of exclusion are:

Of course, the imprint paste, uneven ink color of the printed product, and the sticky back of the ink caused by the sticky back of the printed product are also common phenomena encountered in the process of gravure printing, and the key is to adjust the relationship between the printing material, ink, printing equipment, operating environment and printing process, so as to ensure the quality of gravure products to the greatest extent.

The connecting materials used in aluminum foil inks generally include nitrocellulose and polyamide resin, so aluminum foil inks can be divided into nitrocellulose system and polyamide system.

The ink film of nitrocellulose system is hard and brittle, dries quickly, and easily absorbs water. However, the ink is stable, the storage time is long, and the printing machine adaptability is good. Due to the hard ink film, its adhesion to aluminum foil is poor, and sometimes polyamide resin is added to reduce its hardness, increase flexibility, and improve adhesion fastness.

The polyamide system is the opposite of the nitrocellulose system, the ink film is soft and sticky, the drying speed is slow, and the water resistance is better than that of the nitrocellulose system. However, a single polyamide resin can not make its application on aluminum foil perfect, and some phthalate plasticizers need to be added to the ink formula to improve the toughness of its ink film, but the amount added must be controlled, otherwise the phenomenon of back-sticking will occur.