Often present yet hardly notices, inside most quality bottle caps is a material that has been inserted into the cap prior to the cap being put in place on the bottle or jar.
Sometimes all or part of the inserted material will be seen by the consumer. How has that seal been inserted and what purpose does it serve? Many people will be surprised to learn that when they open a bottle or jar and see a safety seal or freshness seal across the opening, that seal was put in place with the help of the cap or lid.
Single Piece and two Piece Cap Liners
Single Piece Cap Liners
Many bottled products are small packs where there contents are expected to be consumed or used as soon as they are opened. The consumer is not expected to reclose this product or store the product in the container and this type of packaging is called one time use packaging. In this case the main function of the lining material or sealing material is to protect the goods and provide tamper evidence up until the time the product is opened. This can be achieved with simple single piece materials that are induction welded to the top rim of the container. When you open a product like this you will see the aluminium foil across the top of the container and when you look into the cap or lid there will not be any other material left in the cap.
Two Piece Cap Liners
Other bottled products and larger packs are not expected to be completely used as soon as they are opened. The consumer is expected to reclose the packaging and store the goods. In this case, the bottle or container will need a cap that reseals well.
There needs to be a material left in the cap that will have a “friction seal” when the package is closed again, even after the induction seal has been peeled away. This “friction seal” is often achieved with compressible laminated foam approximately 1 to 2 mm thick.
The foam has a softness that allows it to be compressed as the cap or lid is tightened onto the bottle or container. This provides a kind of friction fit tightness that can be maintained even when the cap or lid is not screwed or pushed on with its maximum force. While not as good as a heat induction welded foil, the foam cap liners provide a resealable seal, allowing the cap or lid can be removed and then replaced and tightened to form a high integrity seal.
Larger fruit Juice bottles often have both a foil lining material and a separate foam lining material.
The foil act as a freshness and product integrity guarantee and the foam liner provides a reseal capability. Actually the foam component plays another role during the packaging process where it helps ensure even contact of the foil layer, all the way around the top surface of the bottle’s neck, during the induction heat sealing process.
Two piece cap liners have an induction sealing foil that is also laminated to a backing board or foam layer. While there are only two obvious pieces to this material there are often seven or more layers of materials sandwiched together to achieve this “Two Piece” cap liner.
A similar result can be achieved by inserting a soft reseal layer into the cap first and then a thin and separate single piece induction foil seal second; this is often the case with fruit juice caps.
The reason for two Piece cap seals is that the caps or lids can be prepared with cap lining material using just one process of cap liner insertion.
The induction seal component of the lining material is critical as it provides a complete moisture barrier and oxygen barrier, customer obvious tamper evidence, extended product shelf life and prevents leaks. The prevention of leaks is an often critical requirement for petroleum seals where petroleum based products such as engine lubricant or additives are being shipped in bottles with caps.
Bottle caps alone can come loose in transport, expand and contract due to temperature or simple fail to be applied properly – in each case the integrity of the product and its packaging is compromised. By applying a foil seal across the top of a container, spillage and spoilage of contents, even when the cap comes loose, becomes a rare occurrence. The lubricants and agrochemical sector want to be very sure they avoid spills as spills can affect entire shipments and cause shipments to be rejected by the larger and more demanding clients and retailers. A foil petroleum seal across the bottle neck of an oily product like a lubricant product insures that even when bottles of oil move through hot and cold climates and the bottle caps and their necks expand and contract at different rates, product will not leak during transport.