The white spot phenomenon of composite aluminum coating can be described in this way. The surface of the composite product has obvious white spots, which can be randomly distributed and uneven in size. It can be divided into two situations: one is that it occurs from time to time when it is off the machine, but it basically disappears after aging; the other is that it does not disappear after aging. The latter is the biggest problem affecting appearance. This type of spot is most likely to appear on a full white or light background. In fact, it should be said that as long as such white spots appear, it is generally full version (except for equipment reasons). It's just that the covering power of white and light background is poor, which is easy to see. There are many reasons for the phenomenon of white spots
1. Ink particle size is large or particle size distribution is too wide, generally white ink particle size has a greater impact. The ethyl ester in the adhesive is a good solvent for ink. The results of different ink particle size infiltration are different, and the color change after drying in the oven will be different, which seems to produce "white spots". In this case, it is obvious when getting off the machine, and the white spot phenomenon will be alleviated or may disappear after aging.
2. The surface tension of adhesive is high and the spreading effect is poor on the aluminized film. This is one of the main reasons for the "white spot phenomenon" of aluminum coating at present. The coating effect of the adhesive is not good. After the printing layer is covered, the color on different parts will change, which will produce the same effect as before, and sometimes large spots will be produced.
3. Equipment process reason. On the one hand, workers do not realize the particularity of aluminized film composite, which has its unique place; on the other hand, the equipment drying, coating, system itself problems can not ensure the full and uniform coating of adhesive or the full volatilization of ethyl ester.
There are other reasons, such as full bottom printing screen roller too shallow, reduce the ink coverage.
The following measures can be taken to eliminate white spots:
1. Increase the particle size test index for different batches of inks, and strictly control them, especially those with full ink varieties and particle size distribution outside the standard range will not be used; select excellent and stable suppliers.
2. Use special adhesive for aluminum coating. The surface tension of special adhesive for aluminizing film is lower, and the spreading effect on the surface of aluminum coating is better than that of general adhesive. It is very easy to control the leveling of the glue solution by using aluminizing glue, and it has ideal coating state. Single from the adhesive coating state, the use of aluminized adhesive can eliminate the possibility of white spots.
3. There is a certain matching relationship between the viscosity of the glue solution and the number of wire rolls. If it goes beyond the matching range, the coating state of the glue will be damaged, resulting in the generation of "white spots" and more serious effects in other aspects. However, it seems that the "white spots" are mainly produced on the aluminum coating, which is more concerned.

4. Aluminum coating is used. The common coating process is printing film (ink surface) coating. Here, a special coating method is used to avoid the uneven penetration of ethyl ester to the ink layer. At the same time, the coated adhesive can cover the aluminum coating surface evenly, which can eliminate the white spots. However, this process has its great limitations. Firstly, it is only limited to the compounding of VMPET, and other aluminum coating films will deform under tension due to the influence of heating in the oven; secondly, certain peeling strength will be sacrificed.

5. Flexible packaging enterprises must adhere to the regular cleaning system of coating roller and master the correct cleaning method of coating roller. In the production of full white or light background printing film, we should pay attention to two points. First, clean the scraper, coating roller and flattening roller thoroughly before production.
6. The adhesive should be dried thoroughly. Due to the good barrier property of aluminum plating, if the adhesion in the composite film is not completely dried, then after the composite film enters the curing chamber, a large amount of residual solvent needs to be released quickly, and under the barrier of aluminum coating, it is bound to form vapor bubbles. There will even be no white spots when off the machine, but white spots will appear after aging.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service. The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries. We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.