PET Bottle – you might have heard this term before. These are the same bottles that you use in your everyday lives. Those mineral water bottles or the cold beverages bottles or the plastic bottles for storing water that you purchase from the market; they all are basically PET bottles.
As a matter of fact, over 100 million PET bottles are used worldwide in a single day. But, do you know how these bottles are manufactured in such large numbers?
The main raw material used for making the PET bottles is called polyethylene terephthalate, which is a thermoplastic polymer resin of the polyester family. There are two primary techniques that are used for manufacturing these bottles, namely: Extrusion Stretch Blow Molding, and Injection Stretch Blow Molding. Let’s discuss both techniques one by one.
Extrusion Stretch Blow Molding
In the extrusion stretch blow molding technique, molten plastic is extruded into a hollow tube, which is usually called a parison. Thereafter, this parison is clamped inside a cooled metal mold. Then, fresh air is blown into the parison, which consequently inflates and assumes the shape of a hollow bottle inside the mold. When this hot plastic bottle cools down to a certain temperature, it is released from the mold. The examples of products that are usually manufactured using this technique are shampoo bottles, milk bottles, and watering cans.
Injection Stretch Blow Molding
The injection stretch blow molding technique is a very popular technique in the plastic industry, especially for making PET bottles. This technique comprises further two methods of production: A single-stage process; and, a two-stage process. Let’s talk about the two-stage process first. In the two-stage injection stretch blow molding process, plastic preforms are made first of all, by employing the injection molding technique (you can learn about this technique in a separate article). The preforms are used for making PET bottles; they are comprised of bottle necks and threads or finish. These preforms serve as separate products, which are reheated later on in a designated facility. Infrared heaters are generally used for this reheating, after which, high-pressure air is introduced in the preforms encompassed by metal molds; they are also stretched here through a core rod. The main advantages of this technique are that it provides more flexibility in terms of deciding bottle design and shape; and, preforms can be sold as separate products to third-party manufacturers. The disadvantage is that it requires comparatively more capital investment.
In the single-stage injection stretch blow molding process, bottle is made out of a preform in the same machine, and not in a separate machine. The advantages offered by this technique are: low costs as the whole process is contracted to a single stage; time-saving process; better wall-thickness of bottles, which make the bottles ideal for carbonated drinks. However, the disadvantage of this production process is that it restricts the bottle design and shape options.
The common thing between the above two techniques of manufacturing PET bottles is that they both make use of PET preform moulds and dies. Both the production techniques are good at their place and both are used in the industry. The choice between the two totally depends on the manufacturer’s budget, requirement, and preferences. But, good quality pet preform moulds are indispensable for making either of the processes successful.