Blown Film Extrusion: Process, Applications, and Innovations

Blown film extrusion is one of the core processes in plastic film forming. With its mature technology, wide range of applicable raw materials, and low production cost, it is widely used in packaging, agriculture, and industry, while continuous innovation and upgrades are being made in material formulation, equipment structure, and green production. The following is a detailed analysis of its process principles, application scenarios, and cutting-edge innovations:

I. Core Process Principles and Flow of Blown Film Extrusion
The essence of blown film extrusion is to heat and plasticize the plastic raw material, then form a tubular film bubble through the extruder die, followed by cooling, traction, and winding to obtain the finished film. The core process consists of 5 key steps:

Raw Material Pretreatment
Dry and dehumidify the granules (such as PE, PP, PLA) (moisture content controlled below 0.01%) to avoid the formation of bubbles during plasticization; additives (such as antistatic agents, toughening agents, and degradation agents) can be added as needed to improve the film's functionality.

Melt Extrusion: The raw material enters the extruder screw through the hopper and undergoes shearing, compression, and heating in the conveying, compression, and metering sections, gradually melting into a homogeneous melt. Screw speed and heating temperature are key parameters and need to be adjusted according to the raw material (e.g., LDPE processing temperature 160-190℃, PP 180-220℃).

Bubble Forming: The melt is extruded through a ring die to form a tubular bubble. Compressed air is introduced above the die to inflate the bubble to the target width (inflation ratio typically 1.5-3:1). The inflation ratio directly affects the transverse strength of the film.

Cooling and Shaping: The outer side of the bubble is cooled by air blown by an air ring, while the inner side can be equipped with an internal cooling system to improve cooling efficiency. The cooling rate determines the crystallinity of the film (the faster the cooling, the lower the crystallinity and the higher the film transparency), which is a key factor in controlling film performance.

Traction and Winding: After cooling, the film bubble is flattened by a herringbone plate and then pulled at a constant speed by traction rollers (the traction ratio is typically 4-6:1, affecting longitudinal strength). Finally, it is wound into a film roll by a winding machine. High-speed production lines are equipped with automatic tension control and online thickness measurement systems to correct film thickness deviations in real time.

Key process control points: Screw speed, heating temperature, blow-up ratio, traction ratio, and cooling airflow must be precisely matched according to the raw material characteristics and film specifications to avoid problems such as unstable film bubbles, uneven thickness, and insufficient tensile strength.