How a PET bottle is manufactured

How a PET bottle is manufactured

Plastic bottles are ubiquitous in our daily lives, used for a variety of products including water bottles, soda containers, cooking oil, and food packaging for condiments like mustard and ketchup. Among the various plastics available, manufacturers typically opt for Polyethylene terephthalate (PET) when it comes to creating bottles for food or drinking water. This material is favored due to its ability to produce lightweight, robust, and long-lasting bottles. While the production process may differ slightly among manufacturers due to their unique techniques, the fundamental method for bottle manufacturing remains consistent across the industry.

Raw Materials

Polyethylene terephthalate (PET) is a type of plastic resin that originates from petroleum hydrocarbons. Manufacturers synthesize long chains of plastic molecules through polymerization and then blend this material with various chemical compounds. The resin is then cut into small pellets and shipped to the bottle production facility. At the bottling plant, these PET resin pellets are combined with "regrind," which consists of recycled plastic that has been ground into flakes. Since plastic's physical properties degrade with each reheating, it is essential for manufacturers to restrict the proportion of regrind in their production, generally not exceeding 10% of the overall mixture. Additionally, if the bottles are not intended to be clear, dyes are incorporated into the mixture.

Stretching the Preform

Preforms are introduced into a two-piece mold that clamps around them. The mold's interior is designed to match the final shape of the bottle. Within the mold, a long rod pushes through the preform, which hangs with its screw end pointing downward. This rod elongates the preform towards the mold's upper section, which will become the bottle's base, while also injecting pressurized air into the preform to press it against the mold's walls. The stretch blow molding process must be executed swiftly to ensure the bottle retains its structural integrity and consistent form. Some manufacturers attach a separate bottom piece to the bottle during the blow molding process, while others form the bottom from the preform simultaneously with the rest of the bottle.

Cooling and Trimming

The bottle needs to be cooled rapidly to prevent it from deforming due to gravity when it's still in its soft, heated state. To achieve this, some manufacturers use cold water or liquid nitrogen to cool the bottle through the mold, while others opt for filling it with a burst of room-temperature air. Typically, the mold produces a clean bottle, but occasionally excess material, known as flashing, may form at the seams where the two halves of the mold meet. In such cases, operators remove the surplus material and recycle it into the regrind. This process essentially outlines the manufacturing of a PET bottle.