The lack of glue is different from the bubbles produced by poor drying. How to distinguish?
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Insufficient amount of glue is not the same as bubbles produced by poor drying. Will you distinguish when you encounter it? What is the amount of glue applied and the dryness of the compound machine is determined by what?
The difference between the insufficient amount of glue and the bubbles caused by poor drying
The bubbles generated by the coating state are small and the bubbles are small after the aging, but the poorly dried composite film sometimes generates more bubbles after being matured, because the temperature evaporates from the coating after the temperature rises. The solvent accumulates on the surface of the uncured adhesive layer. Of course, the solvent accumulated on the surface of the adhesive layer will also work hard to penetrate the surface film. If the bubble is small enough and the barrier property of the surface film is also poor, the small bubbles can disappear after aging, which occurs in the BOPP/AL mechanism. But the same process used in the PET / AL structure is not so lucky, the bubbles can not disappear.
Factors affecting the amount of glue and its uniformity
The amount of sizing is basically determined by the depth of the gravure roll and the glue concentration. However, when these two factors are fixed, the gluing of the gravure roll is somewhat affected by the softness and hardness of the rubber press roll, the pressure and the blade pressure.
If the pressure of the scraper is too small or even tight, or there is mechanical impurities to cause a gap, the amount of glue is large. The rubber pressure roller is very soft, the elasticity is very good, and the pressure is large, and the amount of glue is small. This is because the rubber will squeeze into the depth of the gauze roll under heavy pressure, and the glue will be driven out a part to reduce the amount of glue transfer.
For dry compounding, uniformity of sizing is the fundamental means to ensure consistent quality. If the mechanical precision is not high, the scraper is not straight, or the left or right mechanical impurities are sandwiched between the plate roll and the knife face, so that the pressure on the left and right sides is different, which will cause unevenness of the glue, and finally make the compound The peel strength was unqualified, resulting in scrapping.
Factors affecting the actual drying capacity of the composite machine
1. The drying tunnel temperature setting is unreasonable
When the temperature of the three sections is not low to high, when the temperature at the entrance of the membrane is high, the drying is too fast, so that the solvent on the surface of the glue layer evaporates rapidly, causing the surface layer to crust. When the heat penetrates into the inner layer of the glue, the solvent under the film vaporizes to form a ring like a volcanic vent, causing opacity and forming bubbles.
2, the drying tunnel temperature is low, the drying capacity is insufficient
Some enterprise compound machine drying tunnel temperature setting is low, or due to a certain heating system damage, the entire drying tunnel system temperature is low, the heat is not enough, the solvent volatilization is not complete, so bubbles will be generated.
3. Insufficient air volume in the drying tunnel
At present, most domestic low-speed composite machines or mini-machine drying tunnels have poor heating and ventilation effects, which are characterized by small air outlets in composite machines. When combined, the air inlet speed is faster than the air outlet speed, and the solvent vapor concentration in heat sealing increases, causing solvents. The volatilization is slowed down, and the film after recombination has more residual solvent and bubbles are formed.
4, the composite line speed is too fast
The speed of the composite line speed indirectly affects the evaporation of the solvent in the adhesive. When the compound line speed is too fast, the time for the film to pass through the drying tunnel is short, the solvent cannot be completely volatilized normally, and the drying is insufficient, resulting in too much solvent involved, thereby causing bubbles in the composite film.