Application of viscosity-increasing masterbatch in stretch film

Stretch wrap film, also known as elastic film, can be stretched and wrapped by the self-adhesive elasticity of the film itself, and the product can be tightly wrapped by the viscoelasticity of the film surface and the tensile force used during use to achieve the purpose of protecting the product.

I. Overview

The wrapping film can be used for transportation packaging, such as the wrapping of large pallets; it can also be used for short-distance transportation and sales packaging, such as daily necessities packaging. The raw materials used for stretch wrapping film are PVC (polyvinyl chloride), LDPE (low density polyethylene), LLDPE (linear low density polyethylene), EVA (ethylene-vinyl acetate copolymer) and PB (polybutadiene) Wait. At present, the production of domestic stretch film mainly uses LLDPE and LDPE as raw materials.

II. Tackifier for stretch film

1) The function and type of tackifier

The wrapping film for packaging must have two most basic properties: One is to have good mechanical strength, good extensibility and good resilience; The second is that its surface (single-sided or double-sided) should have strong stickiness. Polyethylene can produce films with good mechanical strength, good extensibility and good resilience, but it is difficult to produce plastic films with sufficient surface tack. Therefore, when producing polyethylene wrapping film, it is often necessary to add tackifier additives to improve the surface tack of the film.

In industrial production, the tackifiers that can be used for polyethylene wrapping films are: Low molecular polyisobutylene (PIB), Ultra low density polyethylene (VLDPE) with density below 0.905, and EVA resin and so on.

l EVA resin is rarely used now due to factors such as possible sour taste, high price and low cost performance;

l Ultra-low-density polyethylene has the characteristics of good flexibility, high viscosity and high puncture resistance, and can be used to make wrapping films, but it also has the problem of low cost performance, and it is rarely used in practice;

l Low molecular weight polyisobutylene, as a tackifier for polyethylene wrapping film, has a large viscosity adjustment range, convenient viscosity adjustment, and relatively low price, with obvious comprehensive advantages of cost performance.

Therefore, low molecular polyisobutylene and its masterbatch are the most commonly used tackifiers in the production of polyethylene wrapping films.

The reason why polyisobutene is an excellent tackifier is not only its inherent viscosity, but also its incompatibility with polyethylene films, which will gradually migrate to the surface, resulting in stickiness.

2) The performance requirements of stretch film for polyisobutene

The "tackiness" required in the use of polyethylene wrapping film actually requires both good peel adhesion and good lap adhesion. The higher the peeling viscosity, the less easy the tray is to be packaged, and the better the sealing performance of the film; The higher the lap viscosity, the less likely the film will be longitudinally displaced. Therefore, in order to obtain strong packaging, especially large-scale integrated packaging of goods such as trays, it is necessary to balance the peel adhesion and lap adhesion of the film.

3) The optimal amount of polyisobutylene added

The self-adhesive performance of the stretch film is positively correlated with the amount of polyisobutylene added. However, when the added amount of polyisobutylene exceeds 3%, with the increase of the added amount of polyisobutylene, the self-adhesion of the wrapping film becomes less obvious. Continuing to increase the amount of polyisobutylene added will cause the precipitated polyisobutylene to agglomerate on the 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 performance of the stretch film, and comprehensively consider the cost of raw materials, the addition of polyisobutylene should be controlled between 1% and 3%.

PIB has an exudation process, and it generally takes about three days for the surface of the film to produce sufficient viscosity; In addition, the migration speed of PIB is related to the storage temperature: Its migration and precipitation rate is faster in summer and slower in winter. Therefore, the proportion of polyisobutylene added in the production of stretch film should be adjusted with seasonal changes, that is, the amount added in winter production is a little more than that in summer.

4) PIB viscosity-increasing masterbatch

Low molecular polyisobutene is a viscous liquid substance, The mixture between PIB and polyethylene pellets will not be smoothly extruded when a general-purpose extruder is used to produce plastic films. Special extrusion equipment is required, such as an extruder with a forced feeder in the hopper, and the mixture of LLDPE and PIB is forced to be fed. Or use a special extruder that can pump viscous liquids, pump in PIB. In order to facilitate production, people have developed high-concentration PIB tackifying masterbatches for the production of polyethylene wrapping films. This masterbatch is made by mixing PIB and polyethylene in a certain proportion. It is similar in shape to various masterbatches often used in the production of plastic products, has good fluidity, is easy to use, and can be used for ordinary film forming units to smoothly produce polyethylene wrapping films.

III. Cling film

Plastic wrap is a commonly used plastic packaging product for fresh food. There are three main types of plastic wrap on the market. The first is polyethylene, which is mainly used for food packaging, such as fruits, vegetables, etc., including semi-finished products purchased in supermarkets; The second is called polyvinyl chloride, which can also be used for food packaging; The third type is polyvinylidene chloride, which is mainly used in the packaging of some cooked foods. Since the plasticizers used in PVC plastic wrap have carcinogenic effects, and the production cost of PVDC is too high, most domestic plastic wraps tend to use PE as a raw material. Cling film is a kind of stretch film, but because it does not need as high self-adhesive properties as stretch film, the amount of polyisobutylene used will be less, and polyisobutylene is mainly used to increase product flexibility and self-adhesion.

Nanjing Haisi Extrusion Equipment Co., Ltd. provides viscosity-increasing masterbatch granulator. Any interest please feel free to contact us!