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.

　　其实，塑料自封袋保鲜的主要原因是蔬菜和水果是有机食品，含有水溶性营养素和酶。贮藏期间仍有强烈的呼吸活动。有氧气的条件下,糖类在水果和蔬菜或其他有机物质氧化分解,产生二氧化碳和水分,释放大量的成熟的数量,但是,缺乏提高的条件下,糖类不能氧化,可以分解产生酒精,二氧化碳,释放热量。把水果和蔬菜装在塑料袋里，每隔两三天打开塑料袋口，释放二氧化碳和热量，并把塑料袋口扎紧，以减少变质的机会。

　　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，通过上述方法，co2浓度不可能无限上升，只能上升10%。氧气浓度的下降也不能超过5%，因为缺氧呼吸所产生的酒精停留在水果薄，会导致水果薄烂变坏，所以水果蔬菜储存时间内不宜放塑料袋太长。

　　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.

　　阻塞方向的收缩率小于非阻塞方向的收缩率，靠近插入点的收缩率小于远离插入点的收缩率。复杂形状产品的收缩率小于简单形状产品的收缩率。自封闭袋的流动方向与垂直于流动方向的收缩也有显著差异。以下是影响拉链袋收缩的因素的详细描述。

　　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温度，一般缩水率会增加，特别是对于结晶性塑料。可以通过延长保压时间来减小收缩。但是，一旦浇口关闭，延长保压时间将不再影响收缩。

　　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.

　　，增加压力会导致塑料自密封袋的密度增加，导致收缩减小。提高材料温度，可使产品体积膨胀而将压入模腔的材料缩小，使收缩率增加;然而，材料温度的升高会降低粘度，但有利于压力向型腔的传递，并降低收缩率，更终的收缩率取决于上述两种效应的综合影响。一般来说，粘度对塑料的温度变化很敏感，后一种效应影响较大，导致收缩率降低:粘度对塑料的温度变化不敏感，前一种效应影响较大，导致收缩率增大。

　　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.