Now, in our life, as well as in shopping malls and supermarkets, many users are using plastic bags to keep fruits and vegetables fresh. So, how does plastic bags play a role in keeping fresh? What problems should be paid attention to in use? Here is a detailed introduction of the preservation methods of plastic self sealing bags.

　　其實，塑料自封袋保鮮的主要原因是蔬菜和水果是有機食品，含有水溶性營養素和酶。貯藏期間仍有強烈的呼吸活動。有氧氣的條件下,糖類在水果和蔬菜或其他有機物質氧化分解,產生二氧化碳和水分,釋放大量的成熟的數量,但是,缺乏提高的條件下,糖類不能氧化,可以分解產生酒精,二氧化碳,釋放熱量。把水果和蔬菜裝在塑料袋里，每隔兩三天打開塑料袋口，釋放二氧化碳和熱量，并把塑料袋口扎緊，以減少變質的機會。

　　In fact, the main reason why plastic self sealing bags keep fresh is that vegetables and fruits are organic foods, which contain water-soluble nutrients and enzymes. During storage, there was still strong respiratory activity. Under the condition of oxygen, sugars oxidize and decompose in fruits and vegetables or other organic substances, producing carbon dioxide and water, releasing a large number of mature quantities. However, in the absence of improved conditions, sugars cannot be oxidized, can decompose to produce alcohol, carbon dioxide, and release heat. Put fruits and vegetables in plastic bags, open the plastic bags every two or three days, release carbon dioxide and heat, and tie the plastic bags tightly to reduce the chance of deterioration.

　　但是需要注意的是，通過上述方法，co2濃度不可能無限上升，只能上升10%。氧氣濃度的下降也不能超過5%，因為缺氧呼吸所產生的酒精停留在水果薄，會導致水果薄爛變壞，所以水果蔬菜儲存時間內不宜放塑料袋太長。

　　However, it should be noted that the CO2 concentration can not be increased infinitely, only 10% by the above methods. The decrease of oxygen concentration should not be more than 5%, because the alcohol produced by hypoxia breathing stays in the thin fruit, which will cause the fruit to be thin and rotten, so the storage time of fruits and vegetables should not be too long in plastic bags.

　　阻塞方向的收縮率小于非阻塞方向的收縮率，靠近插入點的收縮率小于遠離插入點的收縮率。復雜形狀產品的收縮率小于簡單形狀產品的收縮率。自封閉袋的流動方向與垂直于流動方向的收縮也有顯著差異。以下是影響拉鏈袋收縮的因素的詳細描述。

　　The shrinkage in the blocking direction is less than that in the non blocking direction, and the shrinkage near the insertion point is less than that far away from the insertion point. The shrinkage of complex shape products is smaller than that of simple shape products. There is also a significant difference between the flow direction of self sealing bag and the contraction perpendicular to the flow direction. The following is a detailed description of the factors that affect the zipper bag shrinkage.

　　二是提高了自封袋模具的溫度，一般縮水率會增加，特別是對于結晶性塑料?？梢酝ㄟ^延長保壓時間來減小收縮。但是，一旦澆口關閉，延長保壓時間將不再影響收縮。

　　The second is to improve the temperature of the self sealing bag mold, the general shrinkage will increase, especially for crystalline plastics. The shrinkage can be reduced by prolonging the holding time. However, once the gate is closed, extending the holding time will no longer affect the shrinkage.

　　，增加壓力會導致塑料自密封袋的密度增加，導致收縮減小。提高材料溫度，可使產品體積膨脹而將壓入模腔的材料縮小，使收縮率增加;然而，材料溫度的升高會降低粘度，但有利于壓力向型腔的傳遞，并降低收縮率，更終的收縮率取決于上述兩種效應的綜合影響。一般來說，粘度對塑料的溫度變化很敏感，后一種效應影響較大，導致收縮率降低:粘度對塑料的溫度變化不敏感，前一種效應影響較大，導致收縮率增大。

　　Finally, increasing the pressure will increase the density of the plastic self sealing bag and reduce the shrinkage. Increasing the material temperature can expand the volume of the product, shrink the material pressed into the mold cavity, and increase the shrinkage; however, the increase of the material temperature will reduce the viscosity, but it is conducive to the transfer of pressure to the mold cavity, and reduce the shrinkage. The final shrinkage depends on the combined effect of the above two effects. Generally speaking, viscosity is very sensitive to the temperature change of plastics, and the latter effect has a greater impact, leading to the reduction of shrinkage: viscosity is not sensitive to the temperature change of plastics, while the former effect has a greater impact, leading to the increase of shrinkage.