PET bottles and jars exhibit superior transparency, gloss and strength and as a result have been replacing many other materials for the packaging of beverages, foodstuffs, pharmaceuticals, cleaning products, personal care products and chemicals.

PET containers are produced in two steps, firstly by injection moulding of test-tube shaped PET preforms from PET granules raw material and secondly by stretch-blow moulding these preforms into bottles or jars.
Resin to Preforms (Injection Moulding). Preforms to Bottles (Stretch Blow Moulding).

There are two distinct processes (types of machines) that are commonly used to produce PET bottles and jars.

Two-stage process: The bottles are produced on machines that implement step 2 by taking ready preforms, heating them and stretch-blow-moulding them into bottles. Two-stage machines are normally used for high production outputs of beverage bottles, using PET preforms with standard neck sizes, which are readily available in the market. About 80% of the PET containers produced globally are made on two-stage, re-heat stretch-blowing machines.

Blowing Stage

Conventional Single-stage process: The bottles are produced on machines that implement BOTH steps 1 and 2 by using PET raw material to mould preforms and then directly stretch-blow-moulding these preforms into the finished bottles or jars. Single-stage machines are well suited to medium production rates as well as for containers with non-standard necks, for which preforms would not be readily available in the market. About 20% of the PET bottles and jars produced globally are made with single-stage machines. Such machines typically have three or four stations (injection, {conditioning,} stretch-blowing and container ejection) with a rotary indexing table for transferring the preforms between stations. There are separate clamping units for opening and closing the injection moulds (vertical clamp) and the blow moulds (horizontal clamp).

Conventional Single-stage Machine

 

Conventional Single-stage vs Two-stage Process Comparison:

Single-stage process advantages:

  • Lower electricity consumption, considering that the moulded preforms do not have to be completely cooled after injection moulding and then re-heated for stretch-blowing.
  • Lower resources requirements, considering that there is no need for packing, storing and transporting preforms.
  • Suitable for all containers irrespective of neck design and weight, considering that there is no restriction to only the preforms available on the market.
  • Superior container clarity and gloss, as there is no preform surface deterioration due to storage and transport.
  • Flexibility to produce a very wide variety of container sizes, shapes and neck diameters on the same machine.

Two-stage process advantages:

  • Substantially higher production outputs per machine are possible.


The new CYPET process retains the advantages of conventional single-stage technologies and provides important additional value-adding benefits.

PET Processing – CYPET Vs Conventional ISBM