Wisdom For Polyethylene
The process of making polyethylene bags consists of two main steps
The process of making polyethylene bags consists of two main steps.
1. Inflation process (film formation)
The polyethylene resin is melted to make the film sheet roll.
2. Bag-making process
The film sheet roll is cut to the desired length and thermo-compressed (heat-sealed) with a heat plate.
An overview of each process is given below.
(1) Inflation process
First, polyethylene resin is heated, melted and pressurized at 140°C to 190°C by a screw extruder. Next, air is blown into the tubular film through the cylindrical die (gap in the circular mold) to expand it. Finally, air is blown through an air ring to make the film cool and wind it up as a tube. The desired width and thickness are adjusted by the air volume. The tube is wound around a paper tube like a scroll, and this is the 'film sheet roll'.
(2) Bag-making process
The bag-making process involves heat-sealing polyethylene tubes using a bag-making machine and cutting them into bags of desired dimensions. Heat sealing is a mechanism whereby heat is transferred by applying pressure to the polyethylene tubes on the heat plate of the bag-making machine. These polyethylene tubes are then welded to each other. Mechanically, the process is simple, but because of its simplicity, the heat control, sealing speed and other settings are highly dependent on the 'experience' of the operators, making it difficult to standardize the process. The key points to ensure seal strength are the heat sealing method and the cutting method (the process of cutting the polyethylene tube to the desired size).