As a flexible packaging substrate that is continuously rolled and easy to slit, the synthesis method of continuous roll film directly determines the film's structural uniformity, mechanical properties, and functional adaptability. Currently, the industry mainly adopts two major process routes: extrusion casting and extrusion blow molding. These can be combined with co-extrusion, stretching modification, and surface treatment to achieve different material combinations and performance customization to meet the diverse needs of food, daily chemicals, logistics, and other scenarios.
Extrusion casting is one of the most common and efficient processes for producing continuous roll film. This method first adds resin granules to an extruder, melts them into a uniform melt under heating and shearing, then extrudes them into thick sheets through a T-die, and rapidly cools and sets them on cooling rollers to form a continuous film substrate. The advantages of casting technology include fast cooling rate, high film transparency, precise thickness control, and high production line speed, making it suitable for mass production of LDPE, LLDPE, and some PP continuous roll films. When multi-layered composite functions are required, multiple extruders can be used with co-extrusion dies for simultaneous feeding, enabling online lamination of the heat-sealing layer, support layer, and barrier layer. This allows for structural integration in a single molding process, reducing secondary processing steps and losses.
The extrusion blow molding process uses a ring die to extrude molten resin into a preform, which is then inflated laterally with compressed air and stretched longitudinally under traction. After cooling and solidification, it is wound into a film. Films formed by this blow molding process possess a certain degree of lateral strength and stiffness due to biaxial stretching, making it particularly suitable for producing roll films with large widths and relatively uniform thickness. This is commonly seen in LLDPE and LDPE single-material or simple blend systems. This process has relatively low equipment investment and good operational flexibility, but it requires high control over thickness uniformity and transparency, necessitating precise adjustment of the blow ratio, traction ratio, and cooling conditions.
After obtaining the base film, post-processing steps can be introduced into the synthesis process to enhance the functionality of the roll film. Biaxial stretching technology is primarily used for PP films. This involves simultaneously stretching the film longitudinally and laterally while it is still in a semi-molten or highly elastic state, causing the molecular chains to orient and crystallize along the direction of force. This significantly improves strength, transparency, and barrier properties, forming BOPP (Boll-in-Place Producing) roll films. Surface treatments, such as corona discharge, can introduce polar groups into the film surface, improving printability and heat-sealing strength. Coating processes can endow the film with special properties such as anti-fogging, antistatic, or gas barrier properties.
In recent years, to align with the trend of green manufacturing, synthesis methods are being optimized towards low energy consumption, low emissions, and recyclability. For example, high-efficiency screws and energy-saving heating systems are used to reduce extrusion energy consumption, online blending of recycled materials reduces raw material waste, and multi-layer co-extrusion formulations with recyclable single materials are being developed to ensure both performance improvement and environmental friendliness.
Overall, the synthesis methods for roll films are centered on extrusion molding, combined with casting or blow molding paths, and expand functional boundaries through processes such as co-extrusion, stretching, and surface treatment. Different methods have their own focuses in terms of production capacity, film structure and performance characteristics. Reasonable selection and process control are the key to achieving high-quality continuous roll film production.