[China Packaging Network News] There are many factors that affect the transparency of composite films. In actual production, it is necessary to make judgments and solve problems based on the apparent appearance and actual conditions of defective products.
The effect of adhesive color on transparency
In the compounding of flexible packaging, two-component adhesives (alcoholic adhesives, ester-soluble adhesives) or single-component adhesives (aqueous adhesives) are mostly used for processing. The adhesive itself is directly affected The transparency of the composite film. If the adhesive itself has a different color, after compounding, it will leave a corresponding color in the composite film. If the colored composite film is then rolled up to form a film roll, the composite film will be more transparent. The change.
Therefore, in the composite partial transparent or fully transparent composite packaging, the adhesive used should be inspected to confirm that the adhesive itself does not have a different color, and use a yellowish or colorless adhesive.
In addition, there is a method of judging the transparency of the adhesive itself. The main agent and the curing agent are sampled according to a certain ratio, and are put in a transparent cup and matured in an oven at 50° C. for 8 hours for light transmission to verify the adhesiveness. The agent transparency after curing reaction.
Effect of oven temperature on transparency
In dry compounding, the plastic substrate is passed through an oven after drying to dry the residual solvent in the glue solution. The compounding machine oven is generally divided into three sections. The first section includes a constant speed drying section and a part of the lower speed drying section, and evaporates about 85% of the solvent. Generally, the first section of the drying speed cannot be too fast. Because of the entry into the deceleration drying section, the drying rate depends on the rate of diffusion of the solvent from the interior of the coating to the surface.
The second and third stages of the composite oven are in the stage of coating drying and drying. With the decrease of the coating solvent content, the drying rate gradually decreases. The heat of the substrate and the coating absorbing nozzle air flow is higher than the heat consumed by evaporation of the solvent, and the temperature gradually increases until it is close to the hot air. Therefore, the temperature setting of the third drying oven should take into account the shrinkage of the substrate due to the high temperature and the amount of deformation under heat.
The temperature of the three-stage oven must be set from low to high to ensure that the solvent evaporates as clean as possible. If the temperature is not set properly, the temperature will be too high when entering the drying tunnel, and the drying will be too rapid, so that the solvent on the surface of the glue solution will quickly evaporate, resulting in a partial increase of the temperature of the glue on the surface and surface crusting; when the heat penetrates into the interior of the glue layer Gasification of the solvent below the film, breaking the film to form a ring, so that the adhesive layer is not uniform to cause opacity. Therefore, strict low-to-high temperature control should be followed so that the solvent evaporates slowly from the inside to the outside. This avoids ringing and improves transparency.