The transparency of the composite packaging bag is poor. What's wrong?

Many packaging bags require high transparency and use a large area of blank base film for lamination, but sometimes poor transparency occurs. Shunxingyuan Packaging, a professional flexible packaging manufacturer, believes that this is largely related to factors such as adhesives and base films.

1、 The adhesive itself is too dark in color

Dark yellow, yellowish red, sometimes even dark red like soy sauce soup, leaving the corresponding color on the adhesive film.

Therefore, in situations requiring high transparency, a light yellow or even colorless adhesive should be selected.

2、 Dust and other particles are mixed in the adhesive

There is too much dust in the air in the workshop, and the hot air blown in the drying tunnel after gluing also contains dust, which is stuck on the adhesive layer and sandwiched between the two base films during lamination, resulting in many small spots and causing opacity.

The adhesive should be filtered with a 180-mesh metal wire mesh to remove insoluble particles. Workshop cleanliness should also be ensured, with a clean and smooth floor, no fluff, less dust in the air, and the air intake of the drying tunnel should use a high-mesh filter net or other filter materials to remove dust from the hot air.

3、 The surface tension of the base film is not high

The adhesive cannot uniformly wet it, it will shrink, and after drying, it will cause uneven adhesive film, spotty, and poor transparency. Therefore, a film with a surface tension greater than 38 mN/m should be used, or it should be reprocessed and qualified before use.

4、Insufficient fluidity of the adhesive, poor leveling

In this case, an adhesive with good fluidity should be used, or a small amount of solvent that can improve leveling should be used, but care should be taken to prevent too much residual solvent from causing odor problems.

5、 Insufficient amount of adhesive applied

There are blank spaces and small air bubbles, causing mottling or opacity. The amount of adhesive applied should be checked to ensure it is sufficient and uniform.

6、The adhesive itself absorbs moisture, becomes cloudy, and contains insoluble substances

Please prepare the adhesive again and use a solvent that does not contain water, alcohol, acid, amine, or other active groups.

7、 The temperature is too high when entering the drying tunnel

Drying is too fast, causing the solvent on the surface of the adhesive layer to evaporate quickly, resulting in a local increase in the concentration of the surface layer adhesive and surface skin formation.

Then, when the heat penetrates into the interior of the adhesive layer, the solvent below the film vaporizes and breaks through the adhesive film, forming ring-shaped objects like volcanic vents, layer by layer, making the adhesive layer uneven and causing opacity.

Therefore, the drying tunnel temperature should be gradually increased from the inlet to the outlet, from low to high, allowing the solvent to evaporate continuously and orderly from the inside to the outside.

In addition, solvents with different boiling points can be mixed. When heated and evaporated, the high-boiling-point solvent on the surface of the adhesive layer remains for a longer time, preventing the surface film from forming a skin.

However, the amount of residual solvent must also meet the standard, and there should be no odor.

8、 Defects in the rubber rollers during lamination

At a certain point, there is no pressure, resulting in gaps and opacity.

Therefore, regular inspections are necessary. If there are defects, even small ones, they should be replaced with good ones.