Why is the viscosity of stretch film not enough? To see if it’s the right way to use it.

Table of Contents

stretch film

Stretch film for packaging must have two basic properties, one is to have good mechanical strength extensibility and resilience, and the other is to have a good viscosity of its surface. Polyethylene can provide good mechanical strength, good extensibility and good resilience for the stretch film, but it can not provide enough surface viscosity. Therefore, the polyethylene stretch film needs the help of tackifier additives, to get the surface viscosity of the film.

In industrial production, low molecular weight polyisobutylene (PIB), Low-density polyethylene with a density less than 0.905 and ethylene-vinyl acetate copolymer (Eva) are used as tackifiers for PE stretch films.

Eva because of the acrid sour taste in the processing process, higher prices and low cost-effective reasons, few manufacturers have used it. VLDPE has the characteristics of good softness, high viscosity and puncture resistance, but it is rarely used in practice due to low-cost performance.

Pib, as a tackifier for PE stretch film, has the advantages of a large viscosity adjustment range, convenient adjustment and obvious comprehensive advantage of performance and price. PIB and its masterbatch are the most common tackifier in the production of PE stretch film at present. Because of their incompatibility with PE film, PIB and its masterbatch migrate to the surface of the film and produce viscosity gradually.

The adhesion required by the stretch film should have both good peel adhesion and good lap adhesion. The higher the peel viscosity is, the more difficult the tray is to be loose and the better the film is sealed; the higher the lap adhesion is, the less the film is likely to have longitudinal displacement, so in order to obtain a strong package, it is necessary to achieve a balance between the peel adhesion and lap adhesion of the stretch film.

stretch film

| 1. The influence of molecular weight on the viscosity of stretch film

The adhesive properties of the films vary with the molecular weight of the PIB. The higher the molecular weight of the PIB, the higher the ultimate peel adhesion, but with the increase of the molecular weight of the PIB, the adhesive strength will decrease, because it is more volatile will lead to viscosity retention time is too short. Therefore, it is necessary to select the appropriate molecular weight of PIB in order to get the best performance of the stretch film. The results show that PIB with a molecular weight of about 1300 is suitable for increasing the self-viscosity of the stretch film.


| 2. The effect of the additional amount on the adhesion of the stretch film

The viscosity of the stretch film is positively correlated with the amount of PIB added. However, when the amount of PIB is more than 3%, the enhancement of the self-adhesion of the stretch film is not obvious. If the amount of PIB is further increased, the PIB will precipitate into a mass on the surface of the film, resulting in the uneven self-adhesion of the film, even though the membrane rolls are hard to open. In order to ensure the final performance of the stretch film and to consider the cost of raw materials, the addition of PIB should be controlled between 1% and 3%.

PIB has an exudation process, generally about three days to wrap around the surface of the film to produce enough viscosity.

stretch wrap film

| 3. The effect of the storage temperature of the winding film on the viscosity

The migration velocity of PIB is related to the storage temperature. The environmental temperature increases, the migration velocity of PIB increases and the viscosity increases. Therefore, the film to achieve the required viscosity should be stored at a higher temperature, and should generally prevent a week after the use of requirements. But long-term storage above 30 °C environments, PIB will be a large number of precipitation, easy to produce film roll size head or paper core out of the phenomenon, so in the viscous requirements, should try to store in-15 °C ~ 40 °C environments.

PIB is a viscous liquid material, when the PIB and polyethylene co-extrusion, the material can not be smoothly extruded, the need to use special extrusion equipment, such as a hopper with a forced feeder extruder, a mixture of LLDPE and PIB is fed forcibly, or PIB is pumped using a special extruder that pumps viscous liquids. In order to facilitate production, people have developed a high concentration of PIB tackifying masterbatch for the production of polyethylene winding film, which is made by mixing PIB and polyethylene in a certain proportion, it is similar to all kinds of a masterbatch which are often used in the production of plastic products. It has good fluidity and is easy to use.

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Stretch film the biggest unspoken rule - Reduce 30% purchase amount