Blown and cast film are two common methods for producing plastic films, each with distinct processes and resulting properties. Here's a detailed comparison:
Blown Film
Process:
Extrusion: Plastic resin is melted and extruded through a circular die to form a thin tube.
Blowing: Air is then blown into the tube, expanding it into a larger diameter bubble. This process creates a thin, continuous film.
Cooling: The film is cooled as it rises and is then flattened.
Winding: The flattened film is wound onto rolls.
Properties:
Thickness Uniformity: The film can have varying thicknesses along its diameter but is usually quite uniform across the width.
Mechanical Properties: Generally offers good strength, impact resistance, and stretching capabilities. The orientation of molecules in the film contributes to these properties.
Surface Finish: Often has a matte finish and can exhibit some optical properties like haze.
Applications: Commonly used for packaging materials, agricultural films, and bags.
Cast Film
Process:
Extrusion: Plastic resin is melted and extruded through a flat die to form a thin, flat sheet.
Cooling: The sheet is rapidly cooled on a large, chilled roller or a cooling belt.
Winding: The cooled film is then wound into rolls.
Properties:
Thickness Uniformity: Generally has very uniform thickness across the width and length.
Mechanical Properties: Offers good clarity, gloss, and can be less strong compared to blown film. The molecular orientation is more uniform, which affects its physical properties.
Surface Finish: Typically has a smooth, glossy surface and excellent optical clarity.
Applications: Often used in applications requiring high clarity and smoothness, such as food packaging, medical films, and consumer goods.
