There are many reasons that affect the transparency of the composite film of the eight-side sealing bag. In actual production, it is necessary to make judgments and solve them according to the apparent phenomenon and actual situation of the defective products. Adhesive color, substrate transparency, insufficient surface tension of the substrate, insufficient fluidity and poor flatness of the adhesive, insufficient gluing amount, oven temperature, lamination roller, curing temperature and time, film substrate moisture absorption, etc. It affects the transparency of the composite film. In this issue, the editor of the plastic packaging business department of Qiqi Printing, Huiji District, Zhengzhou City, a packaging bag
manufacturer, will tell you about it in detail. 1. Substrate transparency Plastic substrates may have problems in the molding process of casting, biaxial stretching and inflation.“foggy”,“pockmark”,“water pattern”These will seriously affect the transparency of the composite film, even if it is a single film, it will be particularly obvious. Therefore, when selecting a film substrate, a substrate with good transparency should be preferred. In addition, if recycled material is added to the film substrate during the molding process, the surface of the substrate will oxidize and turn yellow after a period of time, which will also seriously affect the transparency of the composite film after winding. In actual production, the composite PE structure is prone to poor transparency. This is because many additives (smoothing agents, antioxidants) are often added during the production and processing of PE, and these additives will migrate and slowly migrate during processing. Precipitation, thus affecting the transparency, this phenomenon will be more obvious for PE with a thickness of more than 70um. 2. The surface tension of the substrate is insufficient. The substrates used for transparent packaging include BOPP, PET, NY, CPP, PE, etc. These substrates have not undergone surface treatment after being processed and formed, so they cannot be directly used for flexible packaging compounding, even PET, Polar materials such as NY have a large surface tension and cannot fully satisfy the use. Under the action of the glue, the glue will shrink, and after curing, there will be problems of uneven film and poor transparency. Therefore, corona treatment on the surface of the plastic substrate can effectively improve the transparency of the composite film after curing and molding. 3. The effect of adhesive color on transparency In the compounding of eight-side sealing bags, two-component adhesives (alcohol-soluble adhesives, ester-soluble adhesives) or single-component adhesives (water-based adhesives) are mostly used. Adhesive) for processing, whether the adhesive itself is transparent directly affects the transparency of the composite film. If the adhesive itself has different colors, the corresponding color will be left in the composite film after compounding. When the composite film is laminated and wound to form a film roll, the change in the transparency of the composite film will be more clearly felt. Therefore, when compounding partially transparent or fully transparent compound packaging, the adhesive used should be checked to confirm that the adhesive itself has no discoloration, and a slightly yellow or colorless adhesive should be selected. In addition, there is a method to judge the transparency of the adhesive itself, that is, to sample the main agent and the curing agent according to a certain ratio, put them in a transparent cup and cure them in an oven at 50 °C for 8 hours for light transmission observation to verify the adhesive. Transparency after curing reaction.
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