PETpla.net Insider 01+02 / 2016

CAPPING / CLOSURES 27 PET planet insider Vol. 17 No. 01+02/16 www.petpla.net CAPPING CLOSURES 27 of the sheet material cannot be used and must be scrapped.  Liners are compression moulded with the cap acting as the cavity. A very small drop of suitable plas- tic is placed directly into the cap and the resulting liner bonds with the cap material. This is the most cost-effective method but leads to a liner that moves with the cap during unscrewing. Small imperfections on the sealing area of the bottle neck may damage the liner and lead to problems.  Liners can also be compression moulded outside the cap and then be inserted into it in the same machine. As a result, the liner can rotate freely inside the cap and eventually become stationary with respect to the bottle neck while still rotating with the caps. This has the advantage that different friction characteristics, as those for glass and PET, have no impact on the opening torque, allowing the use of the same liner for both bottle mate- rials (Fig. 4.13). Advantage • Uniform opening torque • Proofed and well known design • Resistant to smaller inside and out- side preform damages • Resistant to mechanical influences • Easy to sterilise Disadvantage • Sensitive for application torque • Releases pressure after few degree without tamper evidence • High production costs 4.3.2.1 In-shell moulded liner This liner is moulded right inside the cap in such a way that it forms a well into which the bottle neck fits. In a way, this is like the aforementioned triple seal with the majority of the work being done by the outside seal. The open structure poses no obstacles for sterilisation, and this seal is well suited for single-serve juice bottles. As with all liner seals, this design releases pressure after turning the cap only a few degrees and before the tamper-evident band makes it visible. You can easily try this out with a hot-filled product: the bottle expands visibly during turning of the cap as the vacuum inside the bottle is released and well before the tamper-evident band breaks (Fig. 4.13) . 4.3.2.2 Out-shell moulded liner This liner has been molded outside the cap and is inserted in a secondary operation. It sits on a ridge inside the cap and is squeezed against the inside cap surface when the capper screws it onto the bottle. Contamina- tion behind the liner cannot be reached by a sterilization proce- dure. Because the liner is made in a separate process, the cap can be printed inside, and this is the most widely used cap design for promotional initiatives that ask consumers to look behind the liner for a possible prize announcement (Fig. 4.14) . 4.3.2.3 Co-injected liner This design takes the idea of lining the cap one step further. Both cap and liner materials are injected into the same mould via a co-injection process. A smaller, secondary extruder supplies the drop of liner material that is required for each cap. The seal is made in a manner similar to the in-shell design, but the cap construction is somewhat differ- ent. The cost of machinery and tool and the low output have never allowed a breakthrough for this solution (Fig. 4.15) . Advantage • Uniform opening torque • Good seal Disadvantage • Sensitive for application torque • Releases pressure after few degree without tamper evidence • High risk for liner defects • World champion in terms of pro- duction costs Squeezing Drinking Pouring Pumping Meet us at February 24 & 25 Stand A61 NEC Birmingham