Why are there wrinkles in zipper bags?

The zipper bag has the advantages of easy access and repeated use, so it stands out in the domestic and foreign markets, and the market scale continues to expand. But we found that zipper bags are more prone to wrinkles, why? There are two common folds in zipper bags: one is the partial layering or partial folds at both ends of the zipper; the other is the folds at the seal of the zipper and the bag body. Under normal circumstances, the wrinkles at both ends of the zipper bag are related to the melting point of the zipper itself. When the zipper plastic bag is heat-sealed, the zipper and the plastic film are heat-sealed in the same environment. Therefore, it is necessary to pay attention to the melting point and shrinkage rate of the zipper, which should be lower than or equal to the melting point of the composite film and the shrinkage rate of the heat-sealing layer of the composite film. In this way, the probability of wrinkles in the zipper bag can be reduced. In addition, the cooling conditions in bag making are also one of the causes of wrinkles in zipper bags. If the composite film and zipper of the finished zipper bag are still in a viscoelastic state, thermal shrinkage is likely to occur during storage, resulting in wrinkles in the zipper bag. Conversely, if the zipper can be sufficiently cooled before the bag-making process is completed, the probability of wrinkling under normal storage conditions will be greatly reduced. Therefore, before the bag making is completed, the cooling surface temperature of the bag making machine must be strictly controlled to reduce the probability of wrinkles in the zipper bag.