– Is the viscosity of the stretched film insufficient? Is there a problem with the method of production?-
Polyethylene can provide outstanding mechanical strength, excellent ductility, and better resilience for stretched films, but it cannot provide satisfactory external viscosity. Therefore, polyethylene stretched films need to rely on tackifier additives to obtain the external viscosity of the film. In industrial production, low molecular weight polyisobutylene (PIB), ultra-low density polyethylene (VLDPE) with a density lower than 0.905 and ethylene-vinyl acetate copolymer (EVA) can be used as the tackifier for polyethylene stretched films.
Stretch film
Due to the sour taste, high price and low cost performance during processing, manufacturers rarely use EVA. VLDPE has the characteristics of good flexibility, high viscosity and high puncture strength, but because of its low cost performance, it is rarely used in practice. As a tackifier for polyethylene stretched film, polyisobutylene has the advantages of large viscosity adjustment range, convenient adjustment, and obvious advantages in terms of sex and price induction. Polyisobutylene and its masterbatch are commonly used tackifiers in the production of polyethylene stretch films. Due to incompatibility with polyethylene film, polyisobutylene and its masterbatch will gradually migrate to the outer surface of the film and become sticky. Stretched films require excellent peel adhesion and excellent lap adhesion. The higher the peel adhesion, the less likely the tray will open and the better the sealing performance of the film. The higher the bonding adhesive, the less likely the film will experience longitudinal displacement. Therefore, in order to obtain a strong package, the peeling adhesive and the adhesive adhesive of the packaging film need to be balanced.
- Effect of molecular weight on adhesion of wrapping film
Different molecular weights will result in different adhesion functions. High molecular weight polyimide will make the film have higher final peel adhesion, but as the molecular weight of polyimide increases, overlapping adhesion will decrease. However, if the molecular weight is too low, the viscosity retention time will be too short due to its easy evaporation. Therefore, only selecting the appropriate molecular weight polyimide can make the wound film have good performance. Studies have shown that polyisoprene with a number average molecular weight of about 1300 is more suitable for adding self-adhesive packaging films.
- The effect of the added amount on the adhesion of the packaging film
The adhesion of the packaging film is positively correlated with the amount of PIB added. However, after PIB participation exceeds 3%, the improvement of the self-adhesion of the wound film becomes insignificant. If the participation of PIB continues to increase, PIB will be separated into fragments on the outer surface of the film, resulting in uneven self-adhesion of the film, and even the film roll is difficult to open. In order to ensure the final function of the packaging film, and considering the cost of raw materials, the amount of PIB added should be controlled between 1% and 3%. PIB has an exudation process, which usually takes about three days to wrap the outer surface of the film to produce Satisfactory adhesion.
- Effect of storage temperature of packaging film on viscosity
The removal speed of PIB is related to the storage temperature. As the ambient temperature increases, the removal speed of PIB increases and the viscosity increases. Therefore, in order to achieve the required viscosity, the wound film should be stored at a higher temperature, and it should generally be avoided to reach the application requirements within one week. However, when stored at a temperature higher than 30 ° C for a long time, PIB will be precipitated in large quantities, and the phenomenon of film roll size head or paper core falling off easily occurs. Therefore, after reaching the viscosity requirements, the PIB should be stored between -15 ° C and 40 ° C as much as possible. Polyisobutylene is a viscous liquid substance. When polyisobutylene and polyethylene are co-extruded, the material cannot be extruded smoothly. Special extrusion equipment is required, such as an extruder with a hopper with a forced feeder, to force feed the mixture of LLDPE and PIB, or a special extruder capable of pumping viscous liquid can be used to pump the PIB. In order to facilitate production, people have developed high-concentration PIB tackifying masterbatch for the production of polyethylene stretch film. This masterbatch is made by mixing polyisobutylene and polyethylene in a certain ratio. It is similar in shape to various masterbatches commonly used in the production of plastic products, has good fluidity and is easy to use.
Shenzhen World Packing Industrial Ltd
Stretch Film & Packing Tape Specialist , Top China manufacturer
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