Extrusion of the recycled polymer, formation of the parison, blowing of the bottle and detachment of the sprues

The bottles of products for cleaning the house or for industrial liquids, made from recycled plastic, usually bought in shops, have had a huge spread in recent years, gradually replacing those made of glass and metal.

They are undoubtedly lighter, have a lower production cost and are easily recyclable with a lower environmental impact than other liquid packaging.

A bottle produced with recycled plastic can be produced, used, recycled and reused for a large number of times with a substantial saving of natural raw materials.

But have we ever wondered how a plastic detergent bottle is produced?

The recycling industry has made enormous strides by creating HDPE granules, the main polymer for bottles of liquid household cleaning products, which are increasingly performing and clean, which can be used 100% at least up to a volume of 5 liters of product.

These polymers come mainly from the recycling of the bottles of the same detergents, through a careful selection of the collected waste and a series of operations to improve the secondary raw material, which allows the creation of another bottle with a thickness of a few microns.

In order to produce a bottle in recycled HDPE, in addition to the polymer, we must have an extrusion and blow molding plant for the packaging.

These systems are composed, in a very schematic way, of a feeder in which the HDPE polymer in granules will be placed, an extruder that will have the task of melting the plastic granule creating a moldable melt, a filter that will have the task, especially if a post-consumer recycled HDPE is used, to reduce as much as possible any pollutants present in the polymer and finally a mold in which the bottle is formed.

Looking over the first part of the extrusion process, a topic already covered in a previous article, let's see what happens in the production process downstream of the extrusion.

The HDPE melted by the extruder will be channeled into a plant suitable for the production of a tongue of plastic material, called parison, which will be the raw material for our future bottle.

Once the quantity of material that constitutes the parison has been adjusted, the two parts of the mold will close together, imprisoning it. At this point, air will be blown into the parison, which will inflate the material on the walls of the mold, creating and cooling the bottle.

The force with which the air is introduced is generally not higher than 10 Bar, allowing a correct formation of the product inside the mold, but the blowing duration depends on the volumetric size of the bottle to be made.

Since this process is longer than the previous ones, it is possible to optimize the timing by using, for example, the exchange of blowing air to allow a faster phase cooling of the product inside the mold.

As in all molding operations, even in the production of bottles it is possible that sprues are created around the raw bottle, which were once removed by hand.

Currently the blow molding machines have special cutting edges which, automatically, trim the excess plastic present on the bottles, considerably speeding up the work.

Once the bottle is formed, a conveyor belt will direct it to another automatic blowing system which will have the task, through the insufflation of air inside it, to check that there are no constructive imperfections, such as holes, which would compromise the seal once filled with product.

After this control phase, the bottle can be suitable for the subsequent filling phase with detergents or other liquids to be marketed.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.