There are many different types of cap liners available. Selecting the type of cap liner is an important decision. Some liners are more resistant to chemicals whilst other liner types provide a better moisture barrier. Certain liners also provide tamper evidence.
Cap liners provide a number of essential functions which include some or all of the following consumer benefits:
- Preserving freshness
- Authenticating product integrity
- Preventing leakage
- Enhancing consumer confidence
- Preventing product contamination
- Graphic communication and promotion
Neville and More is able to provide over 100 different liner specifications for our closures.
Below is a list and overview of some of the more commonly used liner types.
A poly-vinyl film adhered to a white pulp paper backing. A good liner type for chemical resistance, mild acids, alkalis, solvents, alcohols, oils and aqueous products; not recommended for active hydrocarbons or bleaches.
F217 (commonly known as epe liners)
F217 has a low density foam core sandwiched between two solid layers of low density polyethylene. F217 liners have excellent chemical resistance and low moisture transmission rate. F217 also has good taste and odour resistance.
Pressure Sensitive Liner PS 22
Pressure sensitive liners are loosely fitted into the caps and then adhere to the lip of the container neck when the cap is applied. Pressure sensitive liners can adhere to the container because one side is coated with many small pockets of adhesive. When the closure is applied to the container, the pressure exerted causes the tiny pockets of adhesive to rupture in the contact area between the closure and neck of container, the pressure sensitive liner then sticks to the container and remains in place when the closure is removed. Pressure sensitive liners are available printed (sealed for our protection) or unprinted. Generally used for dry foods and dry pharmaceuticals. Pressure Sensitive Liners do not provide a guarantee of tamper evidence.
Teflon Faced Foamed Polyethylene
A Teflon lined foam polyethylene liner that has the combined excellent chemical resistance of Teflon with the compressibility and sealing properties of polyethylene foam. Typical uses of Teflon faced foamed polyethylene liners include analytical lab samples, high purity chemicals, acids, alkalis, oils, organic solvents.
Pulp Metal Foil
A polyester film laminated to aluminium foil and bonded to pulp board. Pulp metal foil liners have good barrier properties, as well as good resistance to hydrocarbons, chlorinated hydrocarbons, oils, ketones, alcohols and grease. Used for aqueous media where evaporation is critical. Pulp metal foil liners are not recommended for acids or alkalis.
Induction Seal Liners
This type of liner comes in many variations but, fundamentally, all Induction Seal Liners contain a foil laminate (known as an inner-seal) which is welded to the top lip of jars and bottles and creates a hermetic, tamper evident seal. The sealing process takes place after the filling and capping operation. The capped containers pass underneath an induction sealing system which produces an electromagnetic current and the foil laminate generates electrical resistance, heating the foil. The hot foil in turn melts a polymer coating on the inner-seal. The heat, coupled with the pressure of the cap, causes the inner-seal to bond to the lip of the container. The result is a hermetic seal. The FDA recognises induction sealing as an effective means of tamper evidence.
There are several different variations of Induction Seal Liners and materials, depending on the particular application. Single Piece Induction Liners, when bonded to the container lip, leave no residual part of the liner bonded to the closure. Two Piece Induction Liners are initially bonded to the inside of the closure. During the heating process, the hot foil melts an additional wax layer which is holding the two parts of the liner together. These separate and one part of the liner stays bonded to the closure while the other part separates and becomes bonded to the lip of the container. This means that when the container is opened and the seal is removed, there still remains a liner inside the closure to retain a seal.
Before selecting an appropriate Induction Seal Liner, it is important to know the material of the container to be sealed (PET, HDPE, PP, Glass etc). This is because the grade of polymer coating on the foil of the liner, which bonds the liner to the lip of the container, is specified to create the optimum seal for each container material.
Induction Seal Liners may also include custom-printed logos, trademarks, or other messages such as ‘sealed for your protection’.
Induction Seal Liners, when necessary, can also be very tightly welded to the container, forcing the consumer to destroy the seal in order to reach the container’s contents. In other cases, the seals are very easily peeled off (easy-peel).
To facilitate easier opening of the seal, pull tabs can also be incorporated into Induction Seal Liners.
Plastic containers with screw-on plastic caps are easiest to seal. Other applications may take a little more work. It is also possible to seal glass containers and to seal with metal caps but both these applications pose challenges. Glass containers may need to be treated before the lip of the container will accept a seal. And while it is technically feasible, induction sealing with a metal cap requires further consideration. The sealing equipment will heat both the inner-seal foil and the metal cap, and the metal cap will stay hot for a while – presenting a safety problem. Hot metal caps could also melt the plastic threads of the container.
In summary therefore, the Induction Seal Liner which is most suitable for your product depends on many variables. In order to find the right Induction Seal Liner for your product and application, please do not hesitate to contact us for advice and guidance.
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