How Do You Manufacture Stretch Film?

tretch film, also known as stretch wrap or pallet wrap, is manufactured using either the cast extrusion process or the blown film extrusion process.
Cast Extrusion Process:
Raw Material Selection: The primary raw material used in stretch film manufacturing is polyethylene resin, typically in the form of Linear Low-Density Polyethylene (LLDPE) or Low-Density Polyethylene (LDPE). Various additives such as tackifiers, slip agents, and UV stabilizers may also be incorporated depending on the desired properties of the film.
Melting and Mixing: The polyethylene resin pellets are melted and mixed with any desired additives in an extruder. The extruder is a machine with a screw conveyor that heats and melts the resin while conveying it through the barrel.
Extrusion and Casting: The molten resin is then extruded through a flat die onto a chilled casting roll. As the molten polymer is deposited onto the roll, it is rapidly cooled, solidifying into a thin sheet of film. The distance between the die and the roll determines the thickness of the film.
Cooling and Orientation: The cast film is cooled further as it travels over the chill roll. At this stage, the film may undergo stretching in both the machine direction (MD) and transverse direction (TD) to orient the polymer molecules and improve mechanical properties such as strength and clarity.
Trimming and Winding: After cooling and stretching, the film is trimmed to the desired width and wound onto large rolls. These rolls can then be slit into smaller rolls of various widths for distribution and use.
Blown Film Extrusion Process:
Raw Material Selection: Similar to the cast extrusion process, the raw material for blown stretch film is polyethylene resin. The choice of resin type and additives depends on the desired film properties.
Melting and Mixing: The resin pellets are melted and mixed with additives in an extruder, similar to the cast extrusion process.
Extrusion and Blowing: The molten polymer is then extruded through a circular die, forming a continuous tube of molten plastic. As the tube exits the die, it is inflated using air, forming a bubble. The bubble expands while the polymer is still in a semi-molten state.
Cooling and Flattening: The inflated bubble is cooled using air or water to solidify the polymer. Once sufficiently cooled, the bubble is collapsed into a flattened film by a series of collapsing frames and nip rollers.
Trimming and Winding: The flattened film is trimmed to the desired width and wound onto large rolls, similar to the cast extrusion process. These rolls can then be slit into smaller rolls for distribution and use.