1. The effect of membrane material

There are dust adsorption, particle impurities, poor plasticization and other crystal points in the film.

The moisture absorption on the film surface of the material and the precipitation of additives in the material will cause composite bubbles.

The thickness of the film should be as uniform as possible, if the distribution is uneven, it is easy to cause the imbalance of the compound pressure, and there will be a gap where the pressure is small, thus forming bubbles.

The way to avoid these effects is to do a good job of raw material inspection and maximize the online corona at the same time of production.

2.The impact of adhesives

A large amount of air was mixed in the preparation of the glue solution due to agitation and circulation, which was not discharged in time during static defoaming and was locked in the composite film to form bubbles. The correct approach is: The adhesive is prepared in strict accordance with the instructions, the main agent is added first, and then the ethyl acetate is added and stirred evenly, and then the curing agent is added while stirring, so that the curing agent is full of activity and evenly dispersed, which is conducive to affinity with the printing substrate and reduce bubbles. In addition, the prepared adhesive should be fully static and degassing, and then poured into the rubber tray for use. Moreover, when pouring glue, it is necessary to fall slowly along the edge of the glue tray, and the glue liquid in the glue tray cannot be violently stirred, so as to avoid the formation of bubbles in the composite film due to the mixture of air.

The viscosity of the adhesive has an important influence on the fluidity, wettability and uniformity of the adhesive. In the dry composite, the viscosity value of the adhesive should be controlled within the appropriate range, if the viscosity of the adhesive is too high, the dispersion and leveling may be poor, affecting the wettability of the surface of the composite substrate, and failures such as coating leakage and bubbles may occur during the coating process. When the two-component two-liquid reaction adhesive is used, it is necessary to dilute the adhesive by adding diluent in order to ensure uniform coating and conducive to infiltration. Diluents include toluene, ethyl acetate, methyl ethyl ketone, etc. Toluene is being phased out because it is not conducive to environmental protection and is easy to cause bubbles. Methyl ethyl ketone is used less because of its high price and not very good affinity with adhesives. At present, the most used diluent is ethyl acetate. Diluent can not contain water, alcohol, amine, etc. If the water content is more than 0.2%, because the volatilization rate of water is much lower than that of ethyl acetate, the volatilization rate of solvent will be greatly reduced, and the spreading and hardening of adhesive will be affected. After the composite of BOPP film and CPP film, the composite product will produce a large bubble, which does not spread outward regularly, and after curing, the peeling strength of the large bubble is very poor, as if there is no glue. Therefore, the purity of the diluent should be above 98%.