Plastic film, which can be produced in various thicknesses and of different polyethylene options, is used in everything from agriculture and printing to clothing and textile manufacturing. This film is widely used in packaging and packing and it is low-cost to produce while still offering a quality, durable material.
The laminate film, packing film or film used for other applications is produced on a specialized piece of equipment known as a film blowing machine. Various sizes and options in thease machines produce different thicknesses and sizes of film that are more suitable for specific types of applications.
Depending on the specific application, blown film may also be called tubular film. This is a complex process that first involves forcing liquid plastic through a die in an extrusion process, then using air to expand the extruded material into a bubble-like shape.
The Method and Process
Different types of film blowing machine models and designs will operate slightly differently, particularly if there are multi-layered films produced. These will use more than one extrusion, but the process itself will still follow the same basic steps.
The process starts with liquid plastic or plastic melt that is pressed through a slit die. This creates a thin walled tube on the other side of the die. At the same time as the plastic melt is moving through the die, a small opening allows a controlled volume of air to move into the extruded tube, causing it to blow up like a balloon.
There is also air blowing on the outside of the film after the extrusion to cool the surface. The tube continually moves through this circulating air up through the chamber and out of the top. At the top, there are rollers that flatten the cooled tube.
Once in this flat shape, it is known as a lay-flat tube and it is moved by rollers from the top of the machine down the sides. It may be left as a tube or the sides may be cut to allow the two sides to be wound onto reels.
With the intact tube, sealing can be done at specific intervals and then cut or adding perforations in the center of the sealed area to create bags.
The thickness of the bags, tubes or film produced by the film blowing machine is a factor of the die used, the amount of air used to inflate the tube and the speed of the process.
