The problem of "white spots" is often encountered in the processing of composite flexible packaging materials. Articles related to "white spots" often appear in relevant newspapers, magazines and websites.
When discussing the issue of "white spots", we usually divide them into two categories
1. When you get off the machine, you can see the "white spots" that may disappear after aging;
2. When you get off the machine, you can see the "white spots" that cannot disappear after aging.
The author thinks: the above classification methods only see the appearance of the problem, but not grasp the essence of the problem.
According to the author's opinion, to analyze the "white spot" problem, we should first explore the causes of the "white spot" problem.
According to the author's observation, the causes of "white spots" are as follows:
1. It is caused by foreign matters in the ambient air. In short, there is no filter cloth (filter) or filter cloth (filter) failure at the air inlet of the combined machine.
2. The old colloid attached on the glue tank, scraper and rubber barrel of the gluing unit is swelled and peeled by the new adhesive solution, which is caused by adhesion to the adhesive film. In short, the cleanliness of the gluing unit is not enough and the circulation filtration system is poor (or not).
3. Second, the "Crystal Point" of the substrate itself.
4. It is caused by the "Crystal Point" of the adhesive. The "Crystal Point" is related to the moisture content of the solvent used and the mixing method of the adhesive.
5. Poor drying conditions and poor drying. This is related to the excessive correlation between the display value of the thermometer and the actual value, the excessive application proportion of the return air of the air supply fan, the insufficient heating capacity of the equipment, and the improper design and installation of the air inlet and exhaust pipe of the composite machine.
6. The distribution of adhesive on the film is not uniform, and there is no adhesive in some areas. This is related to the local blockage of the cots. If there is no smooth roller on the laminating machine, this kind of problem will be more obvious.
7. After compounding, there is air between the second base material and the adhesive layer. This is related to the improper use of the smoothing roller, the "positive pressure" state of the drying box, the insufficient amount of glue, the serious wear of the cot and the application conditions of the scraper.
8. Ink pigment "particles" rough, resulting in "trapped" in the adhesive solvent volatilization is hindered. This situation is related to the state of ink, the ratio of mixed solvent used in printing, the leveling state of adhesive, the air volume and temperature of drying oven, and the pressure and temperature of composite unit.
The problem of "white spots" is mainly reflected in the aluminized composite products. In fact, there are also transparent composite products, but we do not pay enough attention to them. In other words, for transparent or opaque composite products, we have different concerns.
For the composite products with aluminum coating, because of its macro opaque, so we pay special attention to the "white spot" problem;
For transparent composite products, people have become particularly concerned about the so-called "transparency".
In fact, "white dot" and "transparency" are two forms of the same problem.
The author believes that if an enterprise can solve the problem of "transparency" very well, the probability of "white spot" in the enterprise will be quite small.
On the topic of "white spot" classification, the author suggests the following classification methods:
1. The two sides of the composite film present smooth "white spots", which I call "pure white spots";
2. On both sides of the composite film, we can see "white spots" of "bumps" of different sizes, which I call "white bubble points".
The so-called "pure white spot" basically corresponds to the "white spot" which is "when you get off the machine, but not after aging";
The so-called "white bubble point" basically corresponds to the "white spot" which is "when you get off the machine but still after aging".
The causes of "pure white spots" should be 6, 7 and 8 of the above-mentioned 8 reasons; the causes of "white spots" correspond to the five items 1, 2, 3, 4 and 5 of the above-mentioned 8 points.
Only by correctly judging the category of "white spot" phenomenon can we find out the cause and solve the problem as soon as possible.
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, is a research and development, production and marketing