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Why does the golden ink turn green after the bag is evacuated?

BOPA/PEThe structure of the vacuum packaging bag, the contents are mung bean, fragrant rice, and one day after vacuuming, the golden ink part of the printed pattern turns green, but this phenomenon does not occur if it is not vacuumed.Analysis of the reasons for vacuum packaging bags: copper and gold powder reacts with carbon dioxide, water and other substances to form patina. Due to the respiration of mung beans and fragrant rice after vacuuming, high carbon dioxide is generated in the vacuum packaging bag, and at the same timePEThe layer has poor gas barrier properties and will penetrate quicklyPEmaterial while accumulating in the printed ink layer whileBOPAIt is a hygroscopic material. The carbon dioxide produced by the action of a higher concentration of carbon dioxide and moisture is caused by the reaction of the copper and gold powder to form a verdigris, so the gold ink has a discoloration phenomenon. However, the golden ink prepared with silver powder by the color contrast mechanism does not have the above-mentioned color change mechanism, so the color and luster will not change greatly after printing the vacuum packaging bag.

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