Canning and Fish Packaging Technology

Unit 10 - Manufacture of plastic packages

10.1.1.4.Blow moulding
Containers made by thermoforming and injection moulding should be able to be removed from the mould easily and hence the shape of container should have a wide opening. Blow moulding enables a bottle to be made with a narrower neck than the main part of the body. There are many similarities between making glass bottles and making plastic bottles. A small container with approximate shape of final product made first by injection moulding with complete neck finish which is called parison. The parison (other than the neck portion) is then heated till the plastic becomes soft, and it is taken into a mould and blown till the plastic takes the shape of the mould and then cooled. The two halves of the mould are separated to remove the bottle. Most blow moulded bottle has a distinct visible vertical mark where two halves of the mould meets.

Most blow moulded bottles are made from a single plastic. Recently HDPE is blended with nylon so that Nylon forms platelets with HDPE and reduce the gas permeability. Surface of the plastic bottles are modified using fluorine or sulpher trioxide and even PVDC dispersions to reduce CO₂ loss and O₂ ingress rather to reduce gas permeability.