Decoding the Plastic Blown Film Process

The plastic blown film process is an essential step in making plastic bags. In the plastic film manufacturing industry, the blown film process is the most widely used core production technology with the best cost-effectiveness and the most stable forming results. The vast majority of packaging films, industrial protective films, agricultural films, and logistics stretch films on the market are all processed and formed through plastic blown film equipment. Compared with other processes, because the blown film process has stronger production continuity, lower material loss, and stronger product toughness, the blown film process has become one of the core processes in plastic packaging production.

I. What Is Blown Film?

At the very beginning, the raw materials for plastic packaging are made into plastic pellets. Simply put, the blown film process is to heat and melt the plastic pellets, extrude them into a tubular film through an extruder, then use air to blow it upward and inflate it, and after cooling, form a plastic film.

This is the blown film process. Generally speaking, the most commonly used raw material for plastic packaging products is PE. Depending on the intended use of the product, we can adjust the proportion of raw materials to produce products with different functions.

II. The Complete Process Flow of Plastic Blown Film

The main flow of plastic blown film is: plastic raw materials → ingredient mixing → heating and melting → extrusion forming → blowing and inflation → cooling → traction → winding → subsequent processing.

First, we need to select the corresponding plastic raw materials according to the product we need, and then mix them in a certain proportion. After mixing is completed, heating is carried out at a certain temperature. Temperature control is also a key link. If the temperature is too high, the raw materials will age; if the temperature is too low, plasticization will be incomplete and film defects will result. After melting, the material is extruded through a certain die to form a continuous tubular film bubble. At this time, the equipment injects air into the film bubble to make it expand upward. During the rising process, the film bubble is continuously cooled and gradually changes from a molten state into a stable plastic film. After that, the film enters the winding system through the traction device and finally forms a rolled plastic film.

III. What Affects the Quality of the Rolled Film?

The quality of the rolled film is affected not only by the raw materials. The quality of the rolled film is mainly affected by five aspects: the choice of raw materials, temperature control, the stability of the film bubble, the cooling speed, and the traction speed.

1. Choice of raw materials
   Different raw materials have different properties. Before production and manufacturing, we must clearly know the performance of the product we need, and then choose raw materials according to the requirements. Different plastic raw materials have different physical properties. For example, PE material has good flexibility, impact resistance, and processing performance, so it is widely used in shopping bags, garbage bags, express bags, and other plastic packaging products.

2. Temperature control
   During the blown film process, the heating temperature needs to be kept within a reasonable range. If the temperature is too low, the plastic may not melt sufficiently, which can easily lead to unstable extrusion; if the temperature is too high, it may affect the material properties and even cause material degradation. Therefore, during production, it is necessary to reasonably control each heating zone according to the characteristics of different materials.

3. Film bubble stability
   The film bubble formed during the blown film process needs to remain stable. If the film bubble obviously shakes or the thickness distribution is uneven, it may cause inconsistent thickness of the plastic film.

4. Cooling speed
   After the plastic melt is extruded, it needs to be cooled so that it gradually sets. The cooling speed affects the transparency, mechanical properties, and dimensional stability of the film. Therefore, during production, cooling conditions need to be adjusted according to the material and product requirements.

5. Traction speed
   The traction speed also affects the thickness of the final film. If the production speed changes and other parameters are not adjusted in time, the film thickness may fluctuate. Therefore, modern blown film production usually requires comprehensive control of parameters such as extrusion speed, blow-up ratio, and traction speed.

IV. Summary

The blown film process may seem not very technically demanding, but in fact blown film technology is not a simple physical forming technology. It is actually completed by integrating multiple technologies. Moreover, only by precisely controlling each technology is it possible to produce products with stable quality, high cost-effectiveness, and high adaptability. Blown films have fully penetrated major fields such as people's livelihood, industry, agriculture, and logistics, and have become rigid-demand basic materials. In the food industry, food packaging bags, cling film, and vacuum sealing films are all produced by the blown film process, and they are safe, non-toxic, and have good preservation effects; in the logistics industry, stretch wrapping films, express waterproof films, and cargo dust-proof films rely on high toughness to ensure transportation safety.