Meaning and requirements of plastic heat shrinkable film
plastic heat shrinkable film, commonly known as shrinkable film, is a kind of film that can shrink greatly after heating, so it can tightly wrap articles and maintain its shape for a long time. Shrinkable film is made by stretching and quenching process. First stretch the film within the temperature range of high elastic state to make it oriented and arranged, and then quench it, The internal stress caused by stretching in the film is "frozen" and has the "memory" characteristic at room temperature. If the film is heated instantaneously, the external heat energy gives the film internal thermal motion. This "memory" stress elastic recovery part causes the film to shrink.
shrinkage film is widely used in packaging because of its many unique advantages. The main requirements for it are as follows:
1. It has a large shrinkage rate. Shrinkage rate is the main performance of shrink film. It has a large shrinkage rate and good commodity protection effect. Generally, it is required to have a shrinkage rate of more than 30% in the vertical and horizontal directions.
2. The shrinkage temperature should not be too high. The shrink packed articles generally enter the hot air channel to shrink by heating. If the contents are sensitive to heat, the packaging will be damaged.
3. The tensile strength is large. After the film shrinks, there will be a lot of tension, The film should be able to resist this tension without damage.
4. Sufficient heat sealing strength. The strength of the seal is often a weak link, which should be able to withstand the effect of the tensile force after shrinkage.
5. It has a certain impact strength, tear strength, appropriate moisture resistance, oil resistance and other properties to ensure the protective performance of the packaging.
according to its tensile technology, the shrinkage film can be divided into unidirectional stretching and bidirectional stretching. Unidirectional stretching is to stretch the film in one direction of length or width; Biaxial stretching is to stretch the film in both the long and wide directions at the same time, Biaxial stretching is also divided into uniform stretching with equal vertical and horizontal stretching ratio and uneven vertical and horizontal stretching ratio. In addition, the public's awareness of the continuous development of extensibility due to the lack of familiarity with the standard is also increasing. Such films are heated with the original directional arrangement, which completes all the items of uniaxial stretching experiment: 0-0.6fyk-0 (measuring residual deformation) - maximum tension (recording tensile strength) - 0 (measure the total elongation of the maximum force) the sub relaxes and recovers to the state that the incoming tension is fixed forward, so there are unidirectional shrinkage, bidirectional shrinkage, and equal and unequal shrinkage in both vertical and horizontal directions.
declare the compressive strength after freezing, and the average value of MPa is not less than: