Introduction to Cast Stretch Film

01 Introduction to Cast Film and Its Production Process

Cast film is a type of plastic film produced through the extrusion casting process, characterized by uniform thickness, flat surface, and excellent optical properties. Its basic production principle involves heating and melting thermoplastic raw materials, extruding the molten material through a flat die to form a film-like melt curtain, which is then rapidly cooled and solidified on cooling rollers, and finally drawn and wound into rolls. This production process enables high-speed continuous production with stable product performance, making it one of the main methods for plastic film production today.
The production process of cast film mainly includes the following key links:
a. Raw material processing: Plastic pellets need to undergo pretreatment such as drying and mixing to ensure their purity and dryness meet production requirements;
b. Extrusion and plasticization: Raw materials are melted and plasticized in the extruder through heating and shearing, with impurities removed via filtration devices;
c. Casting and forming: The molten plastic is extruded through a precision-designed flat die to form a uniform melt curtain;
d. Cooling and solidification: The melt curtain is rapidly cooled and set on cooling rollers, a process that has a decisive impact on the film’s physical properties;
e. Drawing and winding: The film is wound into rolls through a precise tension control system.
Throughout the production process, temperature control, die design, cooling efficiency, and tension control are key factors affecting product quality. The temperature settings of each zone in the extruder need to be precisely adjusted according to material characteristics; the flatness of the die lip and the uniformity of the gap directly affect the film’s thickness distribution; the temperature and surface condition of the cooling rollers determine the film’s transparency and surface gloss; and the stability of winding tension is related to the flatness of the roll and subsequent processing performance. Modern cast film production lines are usually equipped with advanced automated control systems, which can achieve precise monitoring and adjustment of the above parameters to ensure stable product quality.

02 Material Properties and Common Types of Cast Film

Materials used for cast film need to have good melt fluidity, thermal stability, and film-forming properties. From the perspective of material characteristics, resins suitable for cast film production typically have moderate melt flow index, low melt viscosity, and good thermal stability. In addition, the material’s crystallization characteristics, molecular weight distribution, and additive system also significantly affect the casting processability and the final performance of the film. Common raw materials for cast film include general plastics such as polypropylene (PP), polyethylene (PE), polyester (PET), and polyamide (PA), as well as special materials like polyvinylidene fluoride (PVDF) and ethylene-vinyl acetate copolymer (EVA).
Cast films can be divided into various types based on different materials, each with its own characteristics and application fields.
CPP (Cast Polypropylene) film is one of the most common cast films, with excellent transparency, heat-sealing performance, and heat resistance, widely used in food packaging, stationery, and other fields.
CPE (Cast Polyethylene) film is known for its excellent flexibility and impact resistance, often used in heavy packaging and agricultural mulch films.
PVDF (Polyvinylidene Fluoride) cast film has excellent chemical corrosion resistance and weather resistance, mainly used in special fields such as chemical anti-corrosion and photovoltaic backsheets.
PA (Polyamide) cast film, with its outstanding gas barrier properties and mechanical strength, is widely used in meat vacuum packaging and other occasions.
In addition, multi-layer composite cast films can be produced through co-extrusion processes, combining the performance advantages of different materials. For example, a typical three-layer co-extruded cast film with an ABA structure: the middle layer can use low-cost materials to reduce overall costs, while the surface layers use materials with specific functions (such as heat-sealing or printability). With the development of material technology, various functional cast films continue to emerge, such as high-barrier cast films, antibacterial cast films, and breathable cast films, meeting the growing and diversified needs of the packaging material market.

03 Common Problems and Causes of Cast Film

During the production of cast film, various quality issues often arise, affecting the product’s appearance and performance.
Appearance defects are among the most common problems, including crystal points, fish eyes, and streaks. Crystal points are mainly caused by impurities in the raw materials or incompletely melted resin particles, which may be related to insufficient extrusion temperature or failure of the filtration system; fish eyes usually stem from high molecular weight components or cross-linked substances in the raw materials, reflecting problems with raw material quality or formulation; streaks are often associated with the cleanliness of the die lip, the surface condition of cooling rollers, or fluctuations in process parameters. These appearance defects not only affect the film’s aesthetics but may also have adverse effects on its subsequent processing and usability.
Uneven thickness is another common issue in cast film production, which may manifest as transverse thickness fluctuations or longitudinal thickness changes. Transverse thickness unevenness is usually related to improper adjustment of the die lip gap, uneven temperature distribution of the die, or differences in thermal conductivity of cooling rollers; longitudinal thickness fluctuations are mostly caused by unstable extrusion volume, fluctuations in traction speed, or changes in melt pressure. Thickness unevenness affects the uniformity of the film’s mechanical properties and causes problems in post-processing such as printing and lamination. Modern cast film production lines are usually equipped with online thickness monitoring systems and automatic die lip adjustment devices, which can effectively control the thickness uniformity of the film.
Other common problems include: rough surface or poor gloss of the film, which may be related to insufficient cooling, excessively high cooling roller temperature, or surface contamination; uneven winding of the film roll, usually due to improper tension control or failure of the winding system; failure to meet mechanical performance standards, which may result from inappropriate raw material selection, unsuitable processing temperature, or unreasonable setting of the stretching ratio. To address these issues, it is necessary to establish systematic solutions from multiple aspects such as raw material quality control, equipment maintenance, and process parameter optimization. Regular equipment maintenance, strict raw material inspection, and scientific process management are key factors ensuring the stable quality of cast film.

04 Applications of Cast Film

Cast film is widely used in numerous fields due to its excellent performance.
In the field of food packaging, cast film is an indispensable material. CPP films are commonly used for packaging dry foods such as pastries and biscuits, providing good transparent display and moisture-proof protection; composite cast films are widely used in modified atmosphere packaging for meat, cheese, and other foods, achieving oxygen barrier and fresh-keeping functions through multi-layer structures; high-temperature resistant cast films can be used for microwave food packaging and retort pouches, meeting the requirements of high-temperature sterilization. Food-grade cast films also need to comply with strict hygiene standards to ensure no contamination of food.
In the medical and health field, cast film also plays an important role. Medical-grade cast films can be used for pharmaceutical blister packaging, medical device sterilization packaging, etc., requiring extremely high purity and biocompatibility; breathable cast films are applied to medical dressings and surgical gowns, balancing protection and comfort; in personal care products, cast films are often used for the back layers and packaging of sanitary napkins and diapers, requiring good flexibility and liquid barrier properties. Medical cast films usually undergo strict disinfection and performance testing to ensure their safety and reliability.
Electronic product protection is another important application field of cast film. Anti-static cast films are widely used in the packaging and transportation of electronic components such as integrated circuit boards and liquid crystal displays to prevent electrostatic damage; high-purity cast films are used for temporary protection in semiconductor manufacturing, requiring extremely low particle contamination and chemical release; in addition, there are various functional cast films such as electromagnetic shielding films and thermal conductive films, meeting the special protection and heat dissipation needs of electronic products. As electronic devices develop towards thinner and higher-performance designs, the requirements for protective cast films are increasingly high, driving continuous innovation in related material technologies.

05 Conclusion

As an important plastic film product, cast film has relatively mature production processes and material technologies, but there is still room for continuous improvement and innovation. With the enhancement of environmental awareness and the popularization of sustainable development concepts, environmentally friendly products such as degradable cast films and bio-based cast films will become key development directions in the future. At the same time, the development of functional cast films will continue to deepen, such as intelligent films with self-healing properties and environmental response capabilities, to meet the growing and diversified application needs.
In terms of production processes, digitalization and intelligence will become the development trends of cast film production lines. The introduction of artificial intelligence technology to optimize process parameters and the use of Internet of Things technology to realize real-time monitoring and predictive maintenance of equipment status will further improve production efficiency and product quality stability. In addition, new processing technologies such as supercritical fluid-assisted casting and nano-composite casting are expected to bring breakthrough improvements to cast film performance.
With the continuous expansion of application fields, the cast film industry is facing huge development opportunities and challenges. Continuous investment in raw material innovation, process optimization, equipment upgrading, and application development will drive cast film technology towards higher performance, more environmental protection, and smarter directions, providing better film solutions for various industries.