Blown film and extruded film are both methods of manufacturing plastic films, but they differ in the process by which they are produced. The key distinction lies in the way the plastic is shaped into a film.
Manufacturing Process:
Blown Film: In the blown film extrusion process, a plastic resin is melted and extruded through a circular die. As the plastic exits the die, it is inflated into a bubble using air, and then it is cooled and collapsed to form a flat film. The process results in a tubular structure that is later flattened.
Extruded Film: In extrusion coating or flat film extrusion, the melted plastic is extruded through a flat die, resulting in a flat sheet of plastic. This sheet can then be further processed to create a film through various methods, such as calendaring or stretching.
Structure and Characteristics:
Blown Film: Blown films often have a circular or tubular structure. The bubble shape provides certain advantages, such as better thickness distribution and enhanced mechanical properties in both the machine and transverse directions.
Extruded Film: Extruded films have a flat structure. The flatness of the film can make it suitable for certain applications, and it may exhibit different mechanical properties compared to blown films.
Orientation and Properties:
Blown Film: The blown film process inherently imparts some level of orientation to the molecules in the film, especially in the machine direction (MD) and transverse direction (TD). This orientation can contribute to improved tensile strength and tear resistance.
Extruded Film: Depending on subsequent processing steps, extruded films may or may not have significant molecular orientation. Calendaring, stretching, or other processes can be applied to enhance specific properties.
Applications:
Blown Film: Blown films are commonly used in applications such as packaging (bags, liners, shrink films), agricultural films, and industrial packaging.
Extruded Film: Extruded films find applications in areas like laminating, coating, and flat-sheet products. They may be used in flexible packaging, printing, and other industrial applications.
Thickness Distribution:
Blown Film: The blown film process typically provides better control over thickness distribution, resulting in films with more uniform thickness.
Extruded Film: Achieving uniform thickness across the film width may require additional processing steps in extruded films.
