Wedge seals can be a great way to eliminate the need for an added liner for sealing the package.

The wedge needs to have a slight interference fit into the bottleneck to prevent product leaking. On pressurised packs such as carbonated soft drinks, the single wedge seal may not be sufficient to prevent pressure leaving the pack. These carbonated packs tend to have a complex triple seal on the closure for pressure retention.

For non-pressurised applications, the wedge can prevent products such as oils, dressings, and mayonnaise to leak. They also work well on very lightweight and short skirt closures for still water.

The shape and sizing of the wedge will be critical. Once fully applied to the bottle the wedge contact point to the inner wall of the bottle needs to be approximately 5mm down from the top surface of the bottleneck at a point where the bottle has a high-quality uniform bore.

The wedge will have a pear shaped so that the leading edge is smaller than the bottle bore so that it guides the wedge in without it being damaged when it first comes into contact with the bottle bore.

As the interference fit of the wedge must be for the full 360 degrees any small defect in the bottle bore will cause the sealing system to fail. The required bottle bore finish can only be done by injection-blown process, either PET, PP or HDPE. The nature of extrusion-blown bottles will have a join seam that will allow product to pass by the wedge seal causing the pack to fail. If you fill the pack with water, lay it on its side and apply pressure to the main bottle face you will see if leakage is occurring past the wedge sealing system.