Stretch film production

Stretch films have become an integral part of the world of packaging. Thanks to their outstanding properties and versatility, they have been established as the prefered material for pallet securing . High stretching potential and resilience make for a high-performance stretch film – but how does the production work? Here you will find an overview of the two production methods and the characteristics of the films produced using each process.

What is stretch film made of?

All stretch film consists of the raw material polyethylene (PE). Polyethylene is the most widely used plastic worldwide.  It can be produced and modified in many different ways thanks to the high level of development of macromolecular chemistry. For the production of stretch films, various low density polyethylenes (LDPE) are used, which are characterized by a low density and high flexibility . As the production of polyethylene can be adjusted and influenced down to molecular level, the raw material can be precisely adapted to a wide range of applications. Polyethylene is processed in granular form in stretch film production. The LDPE for stretch films can be both virgin material or recycled. When recycled raw material is used, the stretch film does not have the same strength and quality as when produced from pure virgin material.

What production methods are there in stretch film manufacturing?

For the production of stretch film two different production methods are used: The cast method for the production of cast film, and the blowing method for the production of blown film. Due to the very different production processes, cast and blown films have different properties and characteristics. Cast film is produced flat, by running liquid polyethylene through several rollers under high pressure, pressing it into a thin film and cooling it down. As this is a fast and relatively uncomplicated process, cast film is significantly cheaper than blown film. Blown film, on the other hand, does not run flat through rollers, but is blown vertically upwards through a circular nozzle. At the upper end of the resulting tube, the film slowly runs down again over a number of rollers. Due to the air pressure inside the rising tube, the film is not only stretched upwards (in the direction of the machine), but alsotransversely (away from the machine). This so-called biaxial stretching gives the film extreme longitudinal and transverse tear resistance. The main advantage of blown film over cast film is that the adhesion and smoothness of the respective film side are much more pronounced . Due to the excellent adhesion on the inside of blown films, the unwinding noise is higher than that of cast film.

Which film is right for my application?

Which film is suitable for which application depends on many more factors than just the question of the production process. After all, stretch films also differ significantly in their thickness (µ), the number of layers and the stretch capacity. In order to achieve optimum load unit securing with stretch film, other aspects of the load unit must also be considered. Packaging and palletization are also taken into account. You can find more information on our page on load securing. In most cases, it is worth consulting a packaging optimizer or application engineer to take a holistic approach to load unit securing and optimize it. Ideally, a stretch film optimization should be carried out by a packaging expert in order to pack efficiently and sustainably. More information here: > Stretch film optimization from envirogroup