What are the reasons for the poor transparency of food vacuum bags such as rice miscellaneous grains?

January 30, 2023

Feynman yltpacking.com

The transparency of the vacuum bag is an important indicator to determine the visibility and clarity of the packaged goods, and it has a great relationship with the display effect of the goods. Many plastic composite flexible packaging products require high transparency, using a large area of blank base film nylon andPEcompound, but in the dry compound process, sometimes the transparency of plastic compound flexible packaging is poor or reduced, and the quality requirements cannot be met, for example, the finished product is”foggy”, Appear”Little pockmark”, “Wavy fish scales”, “silk pattern”, “mushroom umbrella cloud”, “Dripping and splashing”Phenomena such as this affect the transparency of the composite product, and even make the composite product scrapped in severe cases. What is the reason for this? How to solve it? So for this kind of problem, Xiaobian uses years of experience in bag making to discuss the problem and the reason:

vacuum packaging bags (2)

 

1. The color of the vacuum bag adhesive itself is too dark, dark yellow, yellow red, and sometimes even dark red like soy sauce soup, which is also the corresponding color on the film. Therefore, where high transparency is required, a slightly yellow or even colorless high-transparency adhesive should be selected. Second, the transparency of the vacuum bag substrate. The surface of the inner substrate presents”shark skin”,” runner marks”, crystal point and other apparent quality problems will seriously affect the transparency of composite products. The foggy ink smear transferred to the non-graphic part during printing also significantly affects the transparency of the composite film.

3. Problems with glue matching in vacuum bags. Improper compounding procedures will lead to incomplete mixing of the main agent and curing agent. May produce the “colloidal particles” Phenomenon.

4. The vacuum bag composite product has obvious appearance defects such as glue spots.

5. Improper temperature setting of vacuum bag drying tunnel. When entering the drying tunnel at the beginning, the temperature is too high and the drying is too fast, so that the solvent on the surface of the glue layer evaporates rapidly, resulting in a local increase in the concentration of the glue on the surface, and skinning on the surface. When the heat penetrates into the inside of the glue layer, the skin film The solvent below vaporizes, breaks through the adhesive film, and forms a ring like a volcanic vent. Circle by circle, it also makes the adhesive layer uneven, also known as”orange peel”(Observed closely with the naked eye, it feels that the appearance of the composite film product is uneven like orange peel, hence the name orange peel), resulting in opacity. Therefore, the temperature of the drying tunnel should be gradually increased from the inlet to the outlet, and there is a gradient from low to high, so that the solvent can be evaporated from the inside to the outside in an orderly and continuous manner. In addition, when the amount of glue applied is too large, the above-mentioned glue layer defects are relatively easy to occur in the glue layer during the drying process.

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