Two Most Popular Ways of PET Bottle Manufacturing

Posted by AcmeDisys on May 23rd, 2017

Out of the various types of bottles used nowadays, PET bottles are the most popular. They are used in everyday life for various purposes. The mineral water, cold beverage, or the simple water bottles available in the market are all examples of PET bottles. As per an estimate, over 100 million PET bottles are used in the world in one day; this is a huge figure indeed. The thought that naturally comes to mind is how these products are produced in such huge quantities.

The most important raw material used for manufacturing PET bottles is polyethylene terephthalate; it is a thermoplastic polymer belonging to the polyester family. These bottles are manufactured in various ways, but two techniques get precedence over the others, viz., Extrusion Stretch Blow Molding, and Injection Stretch Blow Molding. Let’s try to understand what these techniques are all about.

Extrusion Stretch Blow Molding

In this technique, molten plastic is extruded into a hollow tube called parison. Following that, a cooled metal mold is used inside which the parison is clamped to slightly lower down its temperature. Thereafter, the clamped parison is supplied with fresh air, which inflates the parison and transforms it into a bottle. But this newly formed bottle is very delicate as the plastic is still hot, so it’s cooled down inside before releasing it from the mold. The extrusion stretch blow molding technique is generally used for making oil, shampoo, and milk containers, and watering cans.

Injection Stretch Blow Molding

This technique is used quite frequently in the plastic industry for manufacturing PET bottles. This technique can be divided into two divisions: single-stage process and two-stage process. We will first discuss the two-stage and then come to the single-stage process. In the two-stage injection stretch blow molding procedure, plastic preforms are manufactured first through the injection molding technique, which is also a technique that makes use of injection mould and plastic injection mould for bottle production.

The preforms so made have a neck and threads or finish; they are not finished products in themselves, but used for making the finished product. The preforms are also made as separate products by some industries that supply them to manufacturers. These preforms could be reheated later in a separate factory for making PET bottles. The reheating of preforms is usually done by using various types of heaters, mostly infrared heaters. Post heating, fresh air is blown inside the preform, which is covered with a metal mold. This technique is usually preferred for PET bottle production because it offers more flexibility in terms of providing the product with the desired shape, size, pattern, and design. However, one disadvantage could be that this method is capital intensive and thus, suited to mostly big manufacturers and production houses.

Now, let’s come to the single-stage injection stretch blow molding process. In this, the bottle is made out of preform in a single machine, and not another machine; hence, it’s a single-machine production. The advantages offered by this process are cost saving; time-saving; wall-thickness of bottles relatively more, which makes them ideal for storing carbonated drinks. However, the apparent demerit of this process is that it puts a limitation over the design and shape that could be lent to the final product. This method is usually followed by small scale industries.

The above mentioned two techniques are not entirely different from each other; they have something in common. The common characteristic of the two techniques is that both make use of PET preform moulds and dies. No one technique could be said better than the other as both are found suitable in different application areas; both techniques are prevalent in the industry. So the choice regarding which technique to use depends on the manufacturer’s budget and priorities.