There are several different types of stretch film, intended for different uses. The variety of stretch films are to address common issues such as load size, load weight, load type, etc. There are also other stretch films that address uncommon issues such as UV protection, static reduction, reduced condensation, etc.
Blown stretch film and cast stretch film are the two types of stretch film. Both types of stretch film are manufactured in different ways. They both have different qualities and characteristics. Below is a brief explanation of blown stretch film.
Blown Stretch Film- Blown stretch film is made using the blown extrusion process. The blown extrusion process uses a vertical die that extrudes the plastic melt to form a thin tube. Air is then blown into the center of the tube to form an air bubble with the film. The amount of air blown into the bubble determines the overall width of the finished film. The film is constantly rotating. The speed of the film rotation and how fast the film is being pulled upward determines the thickness of the film.
While traveling upward several feet to the nip rollers, the stretch film begins to cool. Once the bubble hits the rollers it is collapsed into a flat tube. From the rollers, the film moves to another set of rollers. The other set of rollers cut the flat tube into two layers that can each be wound onto their own core. For large width stretch film, one side of the flat tube can be slit to form a large width stretch film.
Cast Stretch Film- Cast stretch film is made using the cast extrusion process. The cast extrusion process uses a horizontal die as opposed to the vertical die used in blown extrusion. The plastic melt is forced through the horizontal die, the slit in the die is flat so the film comes out in a flat film shape. The size of the slit in the die determines the thickness of the film.
After exiting the die, the film passes through chilled nip rollers. These rollers trim the film to a specified width while cooling the film. The film is then passed over more chilled rollers that cool the film. At the end of the rollers is a core that the film will be placed on. Once the film is placed onto the core, it is packaged into cases and prepared for shipping.
Machine Stretch Film- There are some machine rolls that come in smaller 3,000 ft. lengths, but most machine stretch film starts at 5,000 ft. rolls. These machine stretch film rolls are made to fit on a variety of stretch wrap machines. Two common types of stretch wrap machines are semi-automatic and fully automatic stretch wrap machines.
Machine stretch film normally comes in all of the stretch film varieties that have been pointed out earlier in this series. Two commonly used machine stretch film varieties are pre-stretched machine stretch film and opaque machine stretch film. Machine stretch film also comes in what is referred to as wide web machine stretch film rolls. Wide web stretch film rolls generally refer to machine stretch film rolls exceeding 20" in width.
