Cast stretch film and blown stretch film are two common types of stretch wrap used for palletizing and securing goods for transportation or storage.
Manufacturing Process:
Cast Stretch Film: Also known as cast film or extruded stretch film, this type of film is manufactured using a cast extrusion process. In this process, the raw materials (typically LLDPE - Linear Low-Density Polyethylene) are melted and extruded through a flat die onto a chill roll. The film is then cooled and stretched to orient the molecules, resulting in a clear, thin film with consistent thickness.
Blown Stretch Film: Blown film, or blown stretch film, is produced using a blown film extrusion process. In this method, the raw materials are melted and extruded through a circular die. As the extruded tube of molten plastic emerges from the die, it is inflated with air to expand it into a bubble. The bubble is then cooled and collapsed into a flat film through a series of rollers. Blown film tends to have a higher gauge and is typically thicker and more opaque compared to cast film.
Physical Properties:
Cast Stretch Film: Cast film is characterized by its clarity, smoothness, and quiet unwind. It has excellent clarity, allowing for easy barcode scanning and product identification. Cast film is also known for its consistent thickness, good cling properties, and high elongation.
Blown Stretch Film: Blown film tends to be thicker, tougher, and more puncture-resistant compared to cast film. It has a hazier appearance due to the manufacturing process and may have a slightly tackier feel. Blown film offers superior load-holding force and is often preferred for heavy or irregularly shaped loads that require extra strength and protection.
Performance Characteristics:
Cast Stretch Film: Cast film offers excellent optics, making it ideal for retail applications where product visibility is important. It provides good stretchability and cling, making it suitable for wrapping uniform loads with minimal protrusions.
Blown Stretch Film: Blown film excels in demanding applications where puncture resistance and load stability are critical. Its thicker gauge and superior tear resistance make it well-suited for securing heavy or sharp-edged loads, irregularly shaped items, or loads with protrusions.
Cost and Availability:
Cast Stretch Film: Cast film is generally less expensive to produce than blown film, making it more cost-effective for many applications. It is widely available in various widths, thicknesses, and roll lengths.
Blown Stretch Film: Blown film is typically more expensive due to the higher production costs associated with the blown film extrusion process. It may be less readily available in certain sizes or configurations compared to cast film.
