Do plastic bags will shrink?

by:Nanxin Print & Packaging     2020-08-26
Material shrinkage rate refers to the plastic bags in the size of the molding temperature and after cooling to room temperature out of the mould size difference between the percentage. It reflects the plastic parts from the mold after cooling the extent of the reduced size. The influencing factors of plastic shrinkage rate are: plastic varieties, forming conditions, the mould structure, and so on and so forth. Different polymer material shrinkage rate each are not identical, also with the shape of the plastic parts of plastic shrinkage rate, the complexity of the internal structure, whether to have insert, etc. A, the molding process of plastic ( Structure: synthetic resin, plasticizer, stabilizer, pigment) The effect of bag shrinkage rate: 1) Forming constant temperature, injection pressure and shrinkage rate decreased; ( 2) Maintain pressure, shrinkage rate decreased; ( 3) Melt temperature, shrinkage rate decreases; ( 4) Mold temperature is high, the shrinkage rate increases; ( 5) The holding time is long, shrinkage rate is reduced, but the gate closed after does not affect the shrinkage rate; ( 6) Mould cooling time is long, the shrinkage rate decreased; ( 7) High speed injection, shrinkage rate slightly increased tendency, smaller effect; ( 8) After the molding shrinkage, shrinking. Plastic bags commonly used food plastic bags are made from polyethylene film, the film non-toxic, it can be used for holding food. There is also a film for PVC, polyvinyl chloride (PVC) itself is non-toxic, but according to the purpose of the thin film additive is often joined by harmful substances to human body, has a certain toxicity. So this kind of film and made of the thin film bag should not be used for holding food. If you want to identify polyvinyl chloride (PVC) and polyethylene plastic bags, plastic bags available to identify the following simple method. Contraction at the start of two days old, after a week or so. Second, the plastic structure on the influence of plastic shrinkage rate, ( 1) Thick wall plastic parts is bigger than thin-walled plastics shrinkage ( But most plastic instead of 1 mm thin wall parts is greater than 2 mm shrinkage rate, and this is due to the melt ( 融化) Within the cavity resistance increase) ; ( 2) Plastic pieces of the embedded with insert than without a little shrinkage; ( 3) Plastics complex shape of shrinkage rate is smaller than simple shape; ( 4) Plastic height direction generally smaller than horizontal shrinkage; ( 5) Thin plastic shrinkage in length direction is small; ( 6) The size of the plastic piece length direction than size shrinkage of small thickness direction; ( 7) Inner hole shrinkage, shrinkage of small shape. Plastic bags is essential items in People's Daily life, are often used to hold other items. Because of its cheap, light weight, large capacity, easy to receive the advantages of widely used, but because of the plastic bag with degradation cycle is very long, difficult faults by some countries ban the production and use. Three, the structure of the mould for plastic ( Structure: synthetic resin, plasticizer, stabilizer, pigment) The effect of bag shrinkage rate: 1) The gate size is big, shrinkage rate decreased; ( 2) Parallel to the vertical direction of the gate of shrinkage rate decreases, and the gate of direction shrinkage rate increases; ( 3) Away from the gate little shrinkage than near gate; ( 4) Plastic mold limitation section shrinkage of small, unlimited plastic part of the shrinkage. Vacuum bag packaging materials commonly used double composite thin film or three-layer aluminum composite membrane made of three seal bag. Vacuum packaging machine commonly used outside the cavity and pump type two kinds of models. Our vacuum packing technology is developed in the early eighty s, and vacuum packaging technology in the early ninety s began to use. Four, the influence of the plastic properties of plastic shrinkage rate: ( 1) Crystalline plastics ( Structure: synthetic resin, plasticizer, stabilizer, pigment) Shrinkage rate is greater than the amorphous plastics; ( 2) Liquid plastic molding shrinkage of small, ( 3) Adding fillers, plastic molding shrinkage rate significantly decreased; ( 4) Different batches of the same plastic molding shrinkage rate is not the same. Food packaging shell can make the food and oxygen, water vapor, stains, such as seepage prevention is also the necessary factors of packaging design. Some packaging include the desiccant or deoxidizer to prolong shelf life. Vacuum packaging or go to the air inside the bag is the main method of food packaging. Save the food within the shelf life of clean, fresh and safety is the first function of packaging. 【 Vacuum bags 】 【 Aluminum foil bag]
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