Choosing Your Lining Material

The liner that you use in your closure can do so many functions. At one end of the spectrum, it can give you tamper evidence by bonding to the container. This is generally done with some form of induction foil that can bond by an electro-magnetic field to the container face. The foil layer can also provide a barrier for product stability and can often leave residue on the container when removed.

At the other end of the spectrum is a simple expanded PE foam that is a form of a gasket that when compressed will seal any imperfections particularly on the bottle face. In between these 2 lining options are a myriad of liners that will depend on the viscosity and chemical strength of your product.

Our experts at TricorBraun understand the ins and outs of the lining material selection process, so here's a breakdown of this potentially complex and important process.

Bottle type and how they are made, ingredients being packed and how the consumer will use the pack are just a few of the considerations you need to examine.

First decision is what will be the bottle material. There is often a different liner for Glass, PE and PET bottles. The next step is knowing what process is being used to make the bottle. The key point is how well formed, flat and repeatable the top surface of the bottle neck will be. The ultimate is a PET injection blow bottle made on a new machine. The worst will be an extrusion blow HDPE bottle made on a very old machine with a nonuniform bottle shape such as a 5 litre bottle with a carry handle.

Will the lined cap be used on just the one bottle or a family of different bottles? Is the product a dry product, a wet product, hot filled and will the bottle face be wet with product when sealed. We generally regard a “Hot Fill Pack” as any product greater than 60 degrees C as it enters the bottle.

Why do you need a liner? We have quite a range of ring seal and bore seal closures that may render a liner unnecessary. Entry level lining is a standard 0.7 mm basic foamed polyethylene wad. For a wider diameter cap or bottle necks with poor trimming and flash, this may need a 1.0 mm thick wad. These liners serve to take up variations on the mouth of the bottle.

If you are looking for tamper evidence by the liner, and/or sterilisation of the head space of a food or beverage, induction foil is a good solution. Induction seal can be a clean peel that leaves no product on the bottle face (so no tamper evidence) or the non-clean peel that leaves fibre evidence that shows the bottle has been open but non clean peel is generally not recommended for beverage bottles as it will feel rough on your consumer’s lips. Some new grades of induction foil include one grade that will do multiple bottle materials (HDPE,PP & PET). We also now have a good grade for use on difficult glass bottles. Wider diameter caps may need a form of foamed backing to provide sufficient rigidity to the wide liner diameter until it is sealed to the bottle.

There can also be versions with a cheaper paper backing. Induction foil provides a second form of Tamper evidence to closures with a tamper band for some markets that want dual tamper evidence. In rare cases we have also had customers experiencing fine powders that escape a simple foam liner due to the very long and rough distribution routes that tend to excite the powder and result in it gradually working its way under the foam seal. Induction foil can be used to hold these powders inside the pack.

Often you may need a secondary seal after the initial liner is removed. This can be foam or paper based. For induction seal and a PE wad, the grade of foam needs to change so that it doesn’t simply bond to the induction foil when it is red hot during the induction sealing. Liners can also be a wax bonded structure. The backing is permanently glued into the closure, with the wax layer holding the induction foil in place. Once applied to the bottle tightly and induction sealed, the heat of the induction process melts most of the wax layer so when the closure is removed it breaks the seal of the backing to the liner. The foil still bonded to the bottle face for the consumer to remove for first use, the backing still glued into the cap for resealing for the life of the pack.

We continue to offer Pressure Seal liners. These have an adhesive face on one side of the foam so bond to the bottle when closed tightly. Whilst widely used in vitamin and tablet packs, the TGA no longer view pressure seal as a form of tamper evidence. Consumers can partially peel back the pressure seal, remove products then reclose that pack tightly so no evidence of previous opening.

For demanding applications where pressure can be building inside the bottle over foam (Bottle bloating) of where a specific breathing rate is required, we do supply a complex vented foam liner that can hold all the liquid within the container but allow a high breathing rate allow the product to vent.

Recently we are seeing increased demands by the EU and FDA on liners due to them being potentially in contact with the product. This can include Migration rates. Some liners are engineered for EU compliance while other will only meet FDA (USA) regulations.

Options on liners include a Lift and peel tab that makes it easy for the consumer to pull open the foil. They can often also be printed with standard messages such as “Sealed for your Protection” or “Sealed for Freshness”. Custom prints can be supplied with very large order quantities and very long initial lead-times.

The most important step in selecting your liner will be performing long term stability testing. This can include holding the pack at elevated temperatures of over 40 degrees C for 30 days to check for any reaction between the liner and the product. As the filler of the product you must always perform this level of testing before ordering a cap with a liner as the result will vary dependant on variables only you can control.

Below is a list of common liners we generally carry in certain slit widths.

We also have an article on Foil Induction Sealing Guidelines that you might find helpful as well.