Some composite packaging bags have high requirements for transparency, but in the composite processing of plastic films, packaging bags often have problems such as poor transparency. So, what are the reasons that affect the transparency of composite packaging bags? Let's interpret the reasons and solutions for the poor transparency of composite packaging bags.

1. Improper choice of adhesive

For example, the adhesive itself has a darker color or lacks fluidity, and the leveling performance is poor, so it cannot be fully spread on the composite base film. Generally, the higher the solid content of the main rubber, the better the fluidity, which is conducive to spreading on the film. Generally speaking, 75% glue is better than 50% transparency, and 50% glue is better than 40% or 35% glue. For laminated films with high transparency requirements, it is difficult to meet the requirements with 50% and 40% glue lamination.

2. Process problems

First, the temperature of the drying tunnel of the composite machine is too high, and the solvent on the surface of the glue that is dry and fast evaporates (evaporated) quickly, and the surface of the glue is skinned prematurely. Then when the heat penetrates into the glue layer, the solvent under the glue film will Gasification, when the gas breaks through the epidermal adhesive film to form rings like volcanic vents, it also makes the adhesive layer not transparent. Secondly, if there is a defect in the fitting pressure rubber roller or scraper, and a certain point is not pressed firmly, forming a gap, it will also cause the film after fitting to be opaque.

There is too much dust in the air that participates in the working environment, and there is also dust in the hot air sucked in the drying tunnel after gluing, which sticks to the surface of the adhesive layer or is sandwiched between the two base films during compounding, and a large amount of dust becomes opaque or poor in transparency.

Solution: Close the gluing part of the compound machine, and use a high-mesh filter at the air inlet of the drying tunnel to block the suction of dust (that is, remove the dust in the hot air of the drying tunnel).

In addition, if there is no stretching roller or the stretching roller is not clean, the laminated film will not be transparent, or the amount of glue applied to the compound will be insufficient, the glue will be unevenly applied, there will be blank spaces, and there will be small air bubbles, forming mottled or opaque.

Solution: Check and adjust the amount of glue applied to make it fully applied and evenly applied, forming a commonly known "hempy face mask".

3. Other issues

It should be noted that the temperature of the composite hot drum is not enough, the hot melt part of the glue cannot be melted, the temperature of the cooling roller is too high, and the temperature of the cooling roller cannot be cooled suddenly, all of which can cause poor transparency of the film.

Solution: The temperature of the hot drum should not be lower than 70 degrees, and the hot-melt part in the colloid will start to melt when the temperature reaches 65 degrees. After melting, not only the transparency will increase, but also the degree of compounding will increase. The cooling roll should be cooled by cooling water or chilled water circulation. The faster the cooling speed, the better the transparency and the flatness of the composite film.