Plastic caps for products hot-filled in PET bottles are at the moment almost all made from temperature-resistant polypropylene and are fitted with a separate liner. Corvaglia began the development of a one-piece cap in HDPE four years ago. As well as addressing the tendency to deform when subjected to elevated temperatures, there was first the matter of ensuring a leak-proof seal at ambient temperatures. Immediately after filling there is a slight overpressure in the bottle and as the temperature falls a slight vacuum is created.
Using a newly-developed geometry the two-start 38mm cap, when it has been screwed onto the bottle, has sufficient pre-tension to form a perfect seal, which is actually reinforced by the distortion of the cap under vacuum.
This solution for a one-piece HDPE cap allows considerable cost savings in comparison with the previous PP cap and separate liner.
- Using the one-piece Corvaglia hot-fill cap it is possible to achieve cost savings of over 30 percent - said Romeo Corvaglia, managing director of Corvaglia Holding AG.