In the composite process, we often encounter all kinds of small bubbles. In fact, the bubble is just a general concept. It is not necessarily bulging. As long as the two films are not completely bonded, the transparency will be different when the composite is fitted. After that, the glue flow between the film layers is not flat, or the surface energy of the film is not reached, or the amount of glue coating is insufficient, and the bubbles are followed.
First, the bubble generated by insufficient glue
Insufficient amount of glue is a relative concept. If the composite film is not printed, the amount of glue applied is 1.8-2.2g/m2, and the printed composite film is preferably 2.5-2.8g/m2 or more. Of course, it must be used with us. The structure and use of the product are determined. Then, in addition to the influence of the amount of sizing on the peel strength, the leveling property of the coating is an important factor, and the leveling property of the glue coating, in addition to the influence of the amount of sizing, on whether or not the rubber roller is used The surface tension of the substrate and the glue, the viscosity of the glue will have an effect on it, and the comprehensive conditions are good, and the amount of the glue can be appropriately reduced. Therefore, before compound production, we must do a good job in testing the above various compound conditions to avoid the emergence of bubble problems.
Second, the bubbles produced by poor drying
The transparent composite film exhibits a "haze" shape with poor transparency. Adjusting the drying capacity depends first on the drying system of the equipment, and secondly on the amount of glue applied, the greater the amount of glue applied, the higher the drying capacity requirement. According to the film width and the area of â€‹â€‹the printing ink, the gradient design of the drying temperature is also considered, keeping in mind that the first oven temperature is high.
In actual production, sometimes the drying is very sufficient, the amount of glue is also quite a lot, and the composite film just off the machine still has bubbles. In fact, it is impossible to have a little bubble in the newly compounded product, and the small bubbles can be eliminated by ripening. Because the polyurethane glue without solvent but not fully cured has a certain fluidity, the higher the temperature, the greater the fluidity, the larger the molecular weight, the lower the fluidity, the essence of solidification is the process of increasing molecular weight, and the compounding in the curing chamber. Membrane, the binder slowly leveles under the action of temperature, the large bubbles shrink, and the small bubbles disappear until the molecular weight of the binder increases until the glue can not flow, forming a composite network structure, and the experienced operation ability It can be seen how much white spots can disappear. If you are not sure, you can put the sample into the 80 Â°C oven for 15 minutes to check whether the bubbles are removed. The same size of bubbles, low-viscosity glue can be eliminated, and high-viscosity glue may not work. Because the 50% high viscosity glue has a large molecular weight and poor leveling, which is why we promote the use of high solids and low viscosity adhesives.
Third, the bubble generated by blocking
The coating roller was not cleaned with the washing solution for a long time, causing blockage. There are two types of blocking: one is sudden, due to the poor resolubility of the ink and the continuous drop in the transfer rate during the operation. If such a blocking version fails to find out the cause and eliminate it in time, it can only be maintained for a while by stopping the wipe, and it will run out again. Another kind of blocking is a gradual type, which is strictly not a fault, because it is impossible to completely clean the residual glue in the anilox roll after each compounding, and the residual glue is deposited and solidified at the bottom of the mesh day after day. The amount of glue is gradually getting smaller, and the small bubbles are gradually being produced. From small to large, from small to large, the film is required to be particularly high or thicker in one day, and the small bubbles become unbreakable. When cleaning the anilox roller with a special washing solution, the problem is solved, but it is not a good production habit. Because a large number of products between qualified and unqualified products have been produced before, we advocate regular measurement. The amount of sizing, when the amount of sizing is reduced to a predetermined value, the plate roller is cleaned, and it is recommended to clean it twice a week. It is best to use a special washing solution for cleaning, pay attention to safety. It is best to implement it through professional training.
4. Thicker film is brought into the air from the composite heat roller to generate bubbles.
The thicker film has a higher stiffness. If the pressure between the pressure roller and the heat roller is insufficient, it is easy to bring in air. The simplest solution is to increase the coating amount.
5. The composite heat roller and the pressure roller are not flat and generate bubbles.
Uneven areas bring in air, creating bubbles, which periodically appear. Another important but easily overlooked reason is that the bearing parts at both ends of the pressure roller are worn or have tiny bubbles, which cause non-parallelism with the heat roller and also generate air bubbles.
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