Cast Biax Film and Blown Film: A Comprehensive Comparison on Film Extrusion

  • Nik Shah , Process Development Manager
  • Gabriela Martin , Marketing Coordinator

December 12, 2023

Orienting cast biax film and orienting blown film are two popular methods of producing thin plastic films (with a film being any plastic sheet 10 mL thick or under). Both processes involve stretching a film in order to align its polymer chains, which imparts several beneficial properties. However, each method has its own specific set of advantages, causing the two techniques to be most suitable for differing product applications. These distinct benefits of oriented cast biax and blown film are detailed below, along with the products that are best produced by each method.

What are the benefits of oriented cast biax film over oriented blown film?

Low Gauge: Because of the biaxial orientation technique used to stretch the initial plastic sheet into its final oriented film, extremely thin measurements can be achieved, often as low as 4-5 microns. Being able to downgauge a material in this way not only makes it easy to reach the smallest of width requirements in film production, but it also means saving costs by making the starting material last for a longer span of time.

Gauge Uniformity: Cast films tend to have more uniform thickness across their width. This can result in more consistent performance in end-use applications as well as reduced material waste.

Surface Smoothness: Cast film processes generally produce films with smoother surfaces compared to blown film. This is due to the use of a chill roll on, which the molten polymer is quenched in during the casting process.

Optical Clarity: Due to the aforementioned propensity for a uniform thickness and smooth surface finish, oriented cast biax films often have better optical properties, such as clarity and gloss, compared to oriented blown films.

Less Equipment Wear: The cast biax film process can be less abrasive on equipment, leading to potentially longer equipment life and reduced maintenance costs.

Quicker Set-up and Changeover: Cast biax film lines can often be set up and changed over more quickly than blown film lines, leading to increased productivity.

Which products benefit from oriented cast biax film over oriented blown film?

Flexible Packaging with High Clarity Requirements: Given the superior optical properties of oriented cast biax film, products that benefit from clear packaging, such as fresh produce, snacks, or consumer goods, can be improved with the use of cast biax films.

High-Quality Graphics Printing: The smoother surface of oriented cast biax films offers a better substrate for high-resolution graphics printing. Products requiring high-quality branding or graphics, such as premium food products or retail goods, can greatly benefit from this method of film extrusion.

Surface Protective Films: Given the smoother surface and uniform gauge of cast films, they are preferable to be used as protective films for electronics, screens, or other high-end goods.

Medical Packaging: The consistent thickness and smooth surface provided by oriented cast biax film can be critical for certain medical packaging applications where clarity, uniformity, and sterility are key.

Laminating Films: Cast biax films are often used as laminating layers due to their smooth surface, ensuring better adhesion and a more consistent finish than a blown film would.

Adhesive Tapes: For certain types of adhesive tapes, especially those requiring a clear and consistent base, cast biax films are preferred.

Electrical Insulation: For applications requiring precise film thickness and consistent insulating properties, oriented cast films can be the better choice due to their uniformity and consistency over blown film.

Barrier Films: When co-extrusion is used to produce multi-layer barrier films, cast biax film processes achieve better layer adhesion, causing them to be the preferred source of film for these barrier applications.

What are the benefits of oriented blown film over oriented cast film?

Toughness and Strength: Blown films typically exhibit great toughness and often have better balance in biaxial properties, since the film is already oriented both in the machine and transverse directions during the blowing process.

Lower Production Costs: Depending on the scale and specific requirements of the film, blown film lines can have lower capital and operating costs compared to cast biax film lines, even after taking the downgauging of cast film into consideration.

Better Sealability: Blown films possess better heat sealability characteristics, a crucial component for packaging applications in which heat sealing is used.

Ability to Produce Thicker Films: While both processes can produce a range of thicknesses, blown film machinery is more adaptable to producing thicker films.

Flexibility in Resin Choices: The blown film process can be more adaptable to a wider range of polymers, especially when considering specific blends or modified versions of resins.

Environmental Aspects: Depending on its setup, the blown film process is often more energy-efficient than the cast film process, leading to a smaller carbon footprint and a more environmentally friendly production line.

Which products benefit from oriented blown film over oriented cast film?

Heavy Duty Bags: The enhanced toughness and tear resistance of blown films make them suitable for heavy-duty bags used in industrial applications or for waste management.

Shrink Films: Due to their balanced biaxial orientation, blown films can be tailored for excellent shrink properties, making them ideal for shrink wrap applications.

Agricultural Films: Blown films, especially when made to be thicker, are commonly used for mulch films, greenhouse films, and silage covers due to their durability and puncture resistance.

Produce Bags: The strength and slight elasticity of blown films prime them to be produced as bags used for fresh produce.

Barrier Films for Meat and Cheese: Multilayer blown films offer superior barrier properties for the protection of sensitive products such as meat and cheese from unwanted oxygen and moisture.

Construction and Geomembrane Sheeting: The durability, thickness, and resilience of blown films make them more suitable than cast films for construction applications such as vapor barriers, underslab films, or pond liners.

Ultimately, both oriented cast biax film and blown film are quality plastic films produced through two equally viable orientation methods, but they are each best suited for differing applications. While the trademark smoothness and uniformity of cast biax oriented films make them the best fit for products with a more polished surface finish, the strength and flexibility provided by blown films make them the best choice for products requiring greater levels of durability, such as heavy-duty bags or agricultural films. Neither of these film types are better or worse than the other but they are each utilized for different purposes within the plastics industry, a concept that is useful to be aware of before beginning film production with a specific end application in mind.

For more information about our Parkinson Technologies line of plastics orientation equipment, or to find which film extrusion technique is best suited for your specific application, please fill out the form below.