Not all polymers lend themselves to blown film-type processing. For these resins, the cast film process is a common alternative. See the schematic of a cast film line below.

Cast film is extruded from a flat slot die onto chilled rolls. The film is rapidly quenched on the chilled roll, which helps produce low haze and high clarity. The rapid chilling minimizes the size of crystal phases in the polymer to reduce light scattering. Key benefits of the cast film process are extremely high line speeds (2000 fpm) and high clarity. 

Cast Film Types and Composition
Cast film is less than 10 mils (250 microns) in thickness—typically between 0.5 to 4 mils (12 – 100 microns). It is generally composed of polypropylene, either a homopolymer or co-polymer. Additives are incorporated to meet specific end-use requirements, including polymer degradation (antioxidants), film blocking (antiblocks), coefficient of friction (COF, slip agents) and melt fracture (polymer process aids PPA). Additive addition levels vary between 500 and 5,000 ppm.

Cast Film Orientation
Downstream film orientation is another reason to use the cast film process. A single orientation can be achieved by using differential roll speed to stretch the film in the machine direction (that is, direction of travel of the film web). Bi-axial orientation can be achieved by using a “Tenter Frame" method; this pulls the film in a direction perpendicular to the machine direction while the film is also being stretched in the machine direction. Bi-axially oriented films offer significantly improved strength and impact/puncture resistance.

 

Learn more:

• Specialty Minerals antiblock talcs for polyolefin films
• What is an antiblock?
• Selecting a talc-based antiblock
• Formulating High Performance LLDPE Blown Films With Optibloc^® High Clarity Antiblocks – Introduction to antiblocks – a downloadable Specialty Minerals publication.
  
  
• Replacing diatomaceous earth with SMI talc-based antiblocks
• Diatomaceous earth replacement study
• Replacing synthetic silica with SMI talc-based antiblocks
• Synthetic silica replacement study: blown film
  
  
• Economical SMI talc antiblocks
  Specialty Minerals antiblocks for low-polymer process aid interaction
• Specialty Minerals antiblocks for low-odor applications
• Reduced slip agent interaction with surface-treated talc antiblocks
  
  
• Blown Film Basics
• Specialty Minerals Antiblock Technical Service Support
  
  
• What is Talc?
  
  
• Download technical data sheets for Specialty Minerals products
• Request a sample
  
  
• Specialty Minerals Publications on talc-based antiblocks – Downloadable papers by Specialty Minerals on talc-based antiblocks and their applications.
  
  
• About Specialty Minerals Inc.
• Specialty Minerals Plant Locations and Profiles
• Quality and ISO at Specialty Minerals