Bubbles are common quality problems in soft packaging after coating and laminating with polyurethane laminating adhesive, which are mainly caused by four factors: raw materials, technology, environment and substrate.
On the raw material level, improper preparation of adhesive is easy to cause bubbles. Unbalanced ratio of curing agent and main agent, too fast mixing speed and large amount of air, or glue stored for a long time and mixed with moisture impurities will all form bubbles after coating. At the same time, the viscosity of the glue is on the high side, and the leveling property becomes worse, so that the internal gas cannot be naturally evacuated, and an air gap will remain.
Construction technology is the core inducement, the coating amount is uneven, the glue is too thick, and the gas inside the glue is difficult to exhaust. The pressure of the compound roller is insufficient and the bonding speed is too fast, so the air can not be completely extruded at the moment of film bonding, and it is easy to produce point and strip bubbles. In addition, the temperature setting of the drying tunnel is unreasonable, the temperature rise in the early stage is too fierce, the surface of the glue quickly crusts, the internal solvent and water vapor cannot volatilize, and bubbles are formed between the two films.
The production environment has a significant impact, and the air humidity in the workshop is high.
Polyurethane Glue is easy to absorb moisture and react, and carbon dioxide gas is generated to form bubbles. There is a lot of dust in the environment, and the airflow is unstable, and the impurity gas brought in during bonding will also produce defects.
The problems of the substrate itself can not be ignored, such as insufficient surface tension of the film, wrinkles, oil pollution and water vapor, or uneven surface of aluminum foil and plastic film, and too large bonding gap, which will cause air to stay and form bubbles. In daily production, it is necessary to strictly control the glue mixing process, slow down the stirring speed, reasonably control the drying temperature and compound pressure, and do a good job in dehumidification and substrate pretreatment in the workshop, which can effectively reduce the generation of bubbles.
