Delivering the perfect seal

Induction cap sealing is a non-contact method of fixing a metallic disk onto a container to form an airtight seal, with the potential to offer secure protection for the contents of glass or plastic bottles without allowing leakage or contamination

A variety of closures can be induction sealed

Induction cap sealing technology has moved on since its introduction a few decades ago and now meet the needs of a wide range of applications. Enercon reveals how to get the best results from today’s advanced systems.

Induction cap sealing technology is a non-contact method of fixing a metallic disk onto a container to form an airtight seal, with the potential to offer secure protection for the contents of glass and plastic bottles without allowing leakage or contamination. The process of induction cap sealing has moved on significantly since the early 1990s when low kW water-cooled machines were employed. Today’s cap sealing systems are more advanced, with sophisticated electronics and control devices enabling higher throughput and guaranteed seal integrity.

Diagram of the sealing process

The process of achieving a perfect seal is relatively straightforward. A cap is placed on the bottle with the foil liner inside. The liner is often multi-layered, the nature and number of layers depending upon the application. When the container has been filled and the closure has been fixed into place, the container passes beneath the induction coil, which heats the conductive aluminium foil liner. The heat melts the wax, which is absorbed into the paper, thus releasing the foil from the cap. Meanwhile, the polymer film also heats and melts, creating a bond with the container lip as it cools to form an airtight seal.

A variety of closures can be induction sealed, so whether companies are working with continuous thread caps, child resistant caps or dispensing caps the perfect seal can always be achieved with the right approach. Similarly, a range of container shapes and materials can be used to yield good results, so whether sealing PET, PVC, PE, PP, PS, Gamma (multilayer), glass, Barex, PLA or metal, the perfect seal is always possible.

However, it is not only the material and the type of closure that must be considered; the type of product that is being packaged also dictates the specification of any induction sealing solution. For example, if the product concerned contains potentially aggressive or volatile ingredients, chemicals, acids, solvents, high salt content, alcohol or vinegar, the properties of such liquids need to be entered into the equation.

To prevent such properties from compromising the seal, it may be necessary to provide a protective layer or barrier between the foil and the heat seal film that prevents corrosion.

The liner is the next consideration. For example, when food and beverage products do not require any lining to remain in the closure for resealability after the foil is removed, a single-piece liner can be used. If, however, there is a need for a lining within the closure, a two-piece liner allows a layer of board, pulp or foam to remain. For some products it may be necessary to provide a ‘clean peel’ that leaves no residue, or one that provides evidence of tampering by leaving a residue on the lip of the container when the foil is removed.

Once the product specification is established, Enercon matches the applications to one of its extensive range of induction sealers.

Having specified the best materials and the most appropriate sealer, it is then necessary to define the optimum sealing range by establishing an operating window. This process involves sealing containers under different heat levels, and recording the results to show which of those levels provide no seal, a partial seal, a good seal and an overheated seal.

The perfect seal can always be achieved with the right approach

First, ensure the correct orientation and alignment of the sealing head, with a consistent air gap between the sealing head and the closure. Likewise, containers must follow a controlled path beneath the centre of the sealing head to ensure that all the careful specification defined earlier in the process is not compromised. Variables such as conveyor speed must be considered, together with closure application torque.

Defining the operating window is a task achieved in stages, using one container at a time. With the output of the induction sealer set to minimum, and with all of the other variables fixed, a single container is run through the sealer. If no seal is achieved, the operator increases the output of the induction sealer by 5% and repeats the test with a new container. This process is repeated until a partial seal is achieved. Having established and recorded the output that delivers a partial seal, the operator then repeats the test, this time increasing the output by 1–2% for each new container until a complete seal is achieved. The output level at which a complete seal is attained is termed the minimum set point of the operating window.

To define the maximum set point of the operating window, the sealer is returned to the minimum set point of the operating window and the output of the induction sealer increased by 5%, repeating the test with a series of containers until the liner or cap shows signs of overheating. The output of the induction sealer is then decreased by 1–2% until there are no longer any signs of overheating. This is the maximum set point of the operating window.

Having defined both the minimum and maximum set points of the operating window, the optimum sealing range between the minimum and maximum set points can now be determined.

The results that can be achieved when all of these considerations are taken into account are impressive. A well specified, prepared and managed induction cap sealing system can provide the perfect seal every time, delivering product packaging that does not leak and contents that last longer.

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