Polyvinyl chloride shrink film production process conditions
1) Quenching after biaxial stretching, the molecular orientation of the biaxially stretched PVC film is "frozen" or "memorized", and when heated, shrinks when heated. This process is the key to producing shrink film.

2) Inflation ratio and traction ratio, the inflation ratio is actually the main factor that determines the degree of lateral orientation and the lateral stretch. The traction ratio is actually the main factor determining the degree of longitudinal stretch orientation. Therefore, its size directly affects the shrinkage rate of the shrink film. When the die gap is 0.4-0.7 mm and the inflation ratio is 3.5 to 4.5, a shrink film having a good shrinkage property can be obtained.
3) The height of the frost line. For the upper blowing method, the lateral shrinkage rate increases rapidly with the rise of the frost line. When the longitudinal shrinkage rate is gradually increased to 15 mm, it tends to be gentle, and the excessively high frost line reduces the stability of the tube. Generally controlled at around 150mm.
4) In the die gap, when the film thickness and the bubble diameter are constant, increasing the die gap will inevitably lead to an increase in the traction ratio and an increase in the longitudinal shrinkage. When the die gap is small, the melt rapidly expands from the die and the film becomes thinner, the draw ratio becomes smaller, and the shrinkage rate decreases. Therefore, it is also important to determine the die gap size. When producing 0.02-0.04m film, the die gap is usually taken from 0.6 to 0.8.
5) The relationship between film thickness and shrinkage rate. The general rule is that when the film thickness increases, the longitudinal and transverse shrinkage rate will gradually decrease, while the shrinkage rate will not change much when it is less than 0.02-0.06 mm, so the shrinkage rate is determined as a value. Whenever possible, the film thickness tolerance is within the specified range to maintain a balanced shrinkage.
6) The effect of cooling rate, the faster the cooling rate, the faster the bubble setting, the greater the stress to be frozen, and thus the degree of orientation of the film, so that the shrinkage rate is increased. For this reason, the flow of cooling gas inside and outside the bubble can be adjusted. Change the cooling rate.
7) Process condition control example.
30mm diameter shrink film unit, the temperature control of each section of the extruder is: feeding section 140 ~ 150 ° C; compression section 160-180 ° C; homogenization section 170 ~ 190 ° C; head 170-190 ° C.
Main machine screw speed: 40 ~ 50r / min
Hot stretching temperature: a period of 110 ~ 150 ° C; two sections of 100 ~ 140 ° C.