Induction heat sealing – the process of applying a hermetic, tamper-evident foil seal to the neck of a container – has largely been confined to plastic containers, where the low level of heat generated during the induction process is sufficient to bond the foil’s seating lamination reliably to the container rim. Where glass containers are concerned – particularly those with oily, fatty or waxy substances that are likely to infiltrate the seal – achieving reliable induction heat sealing can prove very difficult indeed.
Of course, plastic packaging formats, such as bottles and jars, are widely used to contain oily materials – low weight polyethylene terephthalate (PET), for example, is becoming increasingly popular as a container material for cooking oil, thanks to its superior compatibility with these products compared with other plastic materials. However, glass does remain the preferred packaging medium for high oil/fat content foods, largely as a result of its superior gas impermeability and its ability to store product for far longer than is possible in an equivalent plastic container.
Unfortunately, however, food processors have been unable to guarantee a truly hermetic and airtight seal around the rim of glass containers containing high fat content foodstuffs using induction heated liners because achieving good adhesion between the rim and the foil has traditionally been too much of a problem to solve, posing risks of reputational damages due to product leakage or worse.
The problem is partly due to glass being a difficult substrate to adhere to in the first place – a condition made even more problematical in the presence of fats which have the ability to penetrate and subsequently degrade any adhesive bond created during the induction heating cycle. Instead, it is common practice to seal such high fat/oil content containers with steam-applied metal caps, which, while certainly effective, are difficult to remove by hand – particularly by people with limited dexterity and/or low grip strength who may need to resort to the use of a kitchen utensil to effectively remove the cap.
A foil liner, on the other hand, is a lower-cost alternative to steam-applied metal caps and is much easier to open, thanks to novel designs that provide lifting flaps integrated into the foil structure. It is, however, important to note here that the materials of construction of induction heated foil liners are closely regulated; FCM regulation EC 10/2011 (Annex I, Table 1), for example, states that petroleum based or synthetic hydrocarbon derived waxes (which are frequently used in induction heat sealed liner laminates for glass) must not be used for articles in contact with fatty foods.
OIL BE DAMNED
Induction heat sealing specialists have been working on these problems for some time now and Selig has come up with a new development in induction heat sealed lining materials and construction that holds real promise for the reliable sealing of glass containers subject to oil penetration. Selig’s new proprietary Deltaseal™ 9000 formulation, which was officially launched at Interpack 2017, not only increases adhesion to glass but also improves adhesion in an oil environment. A lower cost alternative to steam-applied metal caps as well as being inherently much easier to open, the liner is also fully compliant with FCM regulation EC 10/2011.
The new lining material consists of an aluminium foil coated with a heat seal polymer layer, laminated to a white lined folding box board. The lining material, when inserted into the closure, is applied to the container and sealed using a conventional induction heat sealing system appropriately configured for line speeds.
The closure retains the liner material behind a retention bead while allowing it to rotate freely. On opening, the seal gives an audible ‘crack’ as the materials separate, leaving a clean, attractive foil on the container and a secondary reseal liner or wad in the cap that ensures no risk of debris contamination of the product, while at the same time leaving no residues on the glass container rim.
SIGNED, SEALED, DELIVERED
With such technical advances opening up new possibilities for glass container sealing, the product integrity of high oil or fat content foods is more easily maintained, and consumers can rest assured that long shelf-life, along with those all-important tamper-proofing and ease-of-removal features are built-in from day one.