Compression molded closure needs no liner for aseptic beverages

Portola (Naperville, IL) is branding these closures with the name Steri-Shield. The linerless plug closures will be marketed as a replacement for the traditionally used closures, which have thermoplastic elastomer (TPE) or foil liners to achieve seal integrity for these beverages. By eliminating the liners, the plug design helps minimize package cost and contribute to material source reduction.

Discussing the development challenge, Robinson commented, "The plug design had to mate with the bottle finish inner surface to create an effective seal. It also had to withstand stringent aseptic filling conditions." Robinson told PlasticsToday that the company has run extensive protocols internally.  "We have found that the closure performs extremely well under the wide range of conditions to which aseptically-filled packages are subjected.  However, because there are a several different types of aseptic filling systems, each individual commercialization still needs its own testing to make sure that specific performance expectations are being met," he explained.

Portola's Steri-Shield closures are compression molded using a proprietary resin blend that includes high-density polyethylene. Portola will not reveal percentages or exact numbers but the closures manufactured in its European facilities are primarily injection molded, while in the United States the company uses both injection and compression molded types. Robinson told PlasticsToday that Portola did the majority of the developmental work for this blend internally, though it also sourced "as much technical information from the resin supplier in advance to make sure the performance specs are thoroughly understood." Portola also an outside lab for some additional testing of the closure, to validate its internal performance findings, he added.   

The end result is a lightweight closure that does not fail during sterilization and distribution. The closures withstand aseptic sterilization up to 140ºF, and are easier for consumers to open because there is no liner to negatively impact torque

Steri-Shield plug closures can be made sized from 38 to 43mm, with or without a tamper-evident band.