Questions about aluminum foil printing

In the current packaging substrate, the barrier property of aluminum foil is the best. Aluminum foil is a high-grade printing and packaging material. In recent years, aluminum foil printing has become an important branch of the gravure printing industry. The application of aluminum foil in packaging is mainly used for trademarks and some high-end food packaging such as beer top label, chocolate packaging, etc. Compared with paper and plastic, aluminum foil is thin, brittle, and easy to wrinkle. It is often used during the printing process. There are some problems.

Taking the top label of beer as an example, in the production of aluminum foil, it is divided into the sales link, the press-punching link, the cut-sheet monolithic link, the flattening link and the die-cutting link. The following is a brief introduction to the problems existing in the printing process and their solutions.

1, ink problem

(1) blurred pattern

That is, during the printing process, the printed pattern is blurred and the color is very light. This is mainly due to the excessive amount of solvent added during the dilution of the ink. The solution is to appropriately increase the speed within the allowable range of printing speed, add ink to the ink tank, and adjust the ratio of solvent and ink appropriately.

(2) Discoloration

That is, after the printing occurs, several colors of ink pull off the phenomenon of the first few colors of ink. By hand-printing the product, the ink will be taken off from the aluminum foil.

This type of problem is caused by poor adhesion of the ink, low viscosity of the printing ink, too slow drying speed, or excessive pressure on the roller.

You can use the ink with excellent adhesion or enhance the flexibility of the ink to improve the adhesion of the ink and solve the phenomenon of impatience. In addition, the ink's printing viscosity should be properly increased, and the proportion of diluted solvents should be properly adjusted. The proportion of solvents can be changed by adding an appropriate amount of quick-drying agent or increasing the amount of hot air (in summer, it is slow-drying, and winter is adjusted to fast).

(3) dirty version

That is, during the printing process, a light layer of mottled color appears on the unpatterned part of the aluminum foil.

Dirty plate problem is a common problem in the gravure printing industry. There are many reasons. We need to deal with ink, printed plate rollers, aluminum foil surface treatment, scraper and plate wear in actual printing, and the angle of the blade. consider.

The solution is to select inks that are more suitable for actual printing; manufacturers of roll production are required to improve the smoothness of the roller surface and improve the wear resistance of the roller; use good quality scrapers and reasonably design the angle of the doctor blade during printing and adjust the blade angle.

(4) Scratches

That is, there is a knife pressure on the aluminum foil, which is caused by the harder impurities in the ink or the scraper.

The solution is to stop → raise the scraper → filter the ink → carefully observe whether there is aluminum foil or other impurities in the ink (if any, remove it). If the scraper is damaged but not serious, it can be ground with fine sandpaper, otherwise the scraper needs to be changed. .

2. Problems between printing presses and aluminum foil

(1) Aluminum foil wrinkle

The factors that arise are tension factors, equipment debugging factors, +preparation maintenance factors, equipment aging factors, and human factors.

Tension factors include the unwinding tension and the tension of the winding tension as well as the balance problem.

If the tension of the unwinding is too small, the aluminum foil will fall off during the printing process; under the pressure of the blanket cylinder and the printing plate cylinder, deformation will occur, forming dead folds, so that the wrinkled portion will not print on the ink.

If the unwinding tension is too large or the rewinding tension is too large, the material may be easily broken. In the winding process of the aluminum foil product with live pleats, if the rewinding tension is too large, jitter may occur, resulting in release.

In the foil printing, the aluminum foil is unwound at the unwinding position, that is, the aluminum foil is wrinkled between the unwinding position and the first color printing drum. This is because the material is unevenly placed on the aluminum foil, that is, between the unwinding reel and the aluminum foil reel. Level or material on both sides of different thickness, this time the material should be adjusted to level, so that it is consistent before and after, and check the guide rollers have bumps or dirt, if any, will be cleaned off dirt; bumps Locally polished with fine sandpaper.

When feeding and discharging, the two sets of printing guide rollers are not horizontal, which will cause wrinkles between the colors in the printing. Adjusting the printing guide rollers to the level can be solved. If there is no wrinkling during feeding (the aluminum foil enters the plate cylinder), and the aluminum foil wrinkles when coming out of the plate cylinder, check whether the rubber roller is clean, whether it is horizontal and whether the rubber roller pressure is too large. If the wrinkle phenomenon still exists after eliminating the influence of the above factors, the solvent may be corrosive during cleaning, and the rubber roller may be deformed.

(2) Aluminium Foil Receipt Rolls

The aluminum foil oscillates left and right during winding, which not only affects the regularity of the collected roll, but also has a great influence on the embossing and die-cutting processes.

The solution is to first determine the process from which the swing starts, and check if there is looseness between the release roll and the discharge roll, and if so, tighten it tightly. Sometimes, because the reel is used for a long time, deep grooves will be worn out, the groove will be leveled with a steel file, and the discharger will be stuck with a spring to solve the problem. If it is found that the discharge shaft rotates in one direction, check all guide rollers, tighten the loosened ones, and replace the bearings with necrosis.

(3) Association between printing objects

Due to the different flexographic materials used in printing, some corresponding values ​​should also be changed. For example: printing 520mm aluminum foil and 360mm aluminum foil, the tension and rubber roller pressure is different, the beer label and chocolate packaging printing method is also different, so depending on the strength of different materials to set different collection and unwinding tension and rubber roller pressure.

(4) Other issues

In the printing process of aluminum foil, ink is not easily printed. This is due to the fact that the time required for the solvent to clean the rubber roller is too long to deform, resulting in unevenness of the surface. The solution is to take it off and re-grind it on the grinder.

In the foil printing process, there will be a phenomenon that the platen roller shakes or the ink is not clean. Check whether the platen roller is installed or whether the platen groove is too large. If the printing plate is not installed, the blade is shaken in a certain part of the plate cylinder due to the friction between the blade and the plate cylinder during high-speed operation of the machine, so that the ink is not scraped and the quality of the printed product is greatly reduced.

3, the operator's technical problems

In the printing process, the operator's skill level is a key factor affecting the entire printing process. Therefore, the trap operator needs not only excellent technical level but also professional ethics and professionalism.

The above is a common problem that arises in the printing of aluminum foil. If you grasp these points, the problem of aluminum foil printing can basically be solved.

Source: China Ink Technology Network