Preform design

Preform design

SIPA started PET container manufacturing in 1986 with single-stage machines (from resin to finished bottles). This means 30 years of experience in preform and bottle design: a strong competence at customers’ service (bottle optimisation, weight reduction, new shapes, new solutions), under a single roof.
The quality of the finished container lies within the preform, which is therefore an essential aspect every time you need to consider optimisation of a container, reduction in weight, new threads, increase in productivity and cycle time, extension of the process window, ease of filling and new performance.
The most important parameters when designing a preform, in order to achieve the required container specifications with the lowest weight, fastest cycle time, widest process window and ease of filling, are:

  • Wall thickness (WT)
  • Bottom wall thickness (BWT)
  • Total length (TL)
  • Preform overall shape (i.e. straight, bell, reverse taper)
  • Neck finish size and diameter
  • Neck/Thread thickness
  • HUS Height Under Support Ledge
  • Under-ring diameter/thickness/transition area profile
  • Total Weight
  • Injectability
  • Length/wall thickness ratio (L/t)
  • Blowability (stretch ratio)
  • Axial stretch
  • Radial stretch
  • Total stretching ratio

SIPA has developed numerous innovations in preform design:

Sipa applies the most widely used necks to its preforms/bottles; it is also able to develop new necks (thread design and/or light-weighting) thanks to the certification of external bodies or co-operation with cap manufacturers.
Some examples of light-weight neck design innovations we have developed are the HotLight28, a light-weight 28mm PCO thread for hot filled bottles that weighs just 3.8 grams (giving a 40% saving in weight with respect to the standard version), the SUPER, a thread for still or carbonated water weighing 1.9 grams, and an ultra-light version of the 55mm thread for dispenser tanks that allows a 25% reduction compared to standard solutions.

New solutions are always being studied for preforms, not only on the profile but also on the base (the gate is an interchangeable part, even without having to reconstruct the entire cavity). Along with designs from external partners such as Cappello design and Smart base (which allow a reduction in weight of 0.1-0.4g), Sipa is able to offer solutions designed in house, such as the ogive or double curve base.

We have been able to revolutionise the design of preforms, achieving extra-thin walls, particularly under the neck and at the base, to reduce weight where it is not required thanks to two patented processes.
XMOULD. The production of preforms in XMOULD technology injection molds allows a reduction in the friction between the molten PET and the molding surface of the injection moulds, thus allowing the production of preforms with very thin walls and a length/thickness ratio of up to 50. As well as reducing the thickness, this solution also results in faster cycle times, thanks to the ease with which the PET flows over the surfaces of the mold (cavity and core).
XTREME. The new preform production technology with injection-compression allows even more revolutionary preform design that is no longer restricted by the limitations of injection technology.

For technical and specialised containers, such as oval and asymmetrical, large size stackable, heat set containers, development of the container goes hand in hand with preform design: preform thickness, weight, profile, optimised distribution of material, are all important elements to blow a bottle with high performance. Furthermore, the preform must not only be injectable and blowable, but it must be handled by all machines: dimensions suitable for the injection mold in the specific preform production system, dimensions/diameters suitable for transportation and handling in the re-heat stretch-blowing machines. The ratio between preform dimensions and those of the finished bottle are of fundamental importance to understand whether or not a preform is suitable for the container we want to produce, whether it will work or whether it is optimal (radial stretch ratio, i.e. on the diameter, and axial stretch ratio, i.e. on the length/height, biaxially orient the PET in order to reach an optimum distribution of the material).

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