Induction Cap Sealing Guide

What exactly induction cap sealing is and how to use it for your production line? Take a brief look at our sealing guide page to learn more about the induction sealing process and its upsides of using an induction sealing system.

Induction Sealing Method: What Is It?

The induction sealing process securely bonds an aluminum foil laminate inner seal to the lip of a plastic or glass bottle or jar. After the container has been filled and capped with an induction-lined cap, it passes underneath an induction sealing head. The non-contact heating process welds the cap seal liner to the bottle mouth creating a strong seal.

When properly applied (the proper type of cap seal liner and also a proper application and correct sealing procedure), induction lined caps will provide a strong hermetic, leak proof, and tamper evident seal. It is good to mention that The FDA regards induction sealing to be an effective method of tamper evidence.

Induction sealing will significantly extend product shelf life while it is preserving freshness and preventing costly leaks. Therefore cap sealing enhances your product’s value and greatly increase your clients’ confident that the product they are using is completely intact and safe to use.

 

How Induction Cap Sealing Works?

An induction sealing machine (no matter is it is a hand held sealer or a full automatic sealing system) features two main components: The power supply and sealing head.

 

The power supply

The sealing machine power supply energizes the inductive coil; it produces an electro-magnetic current, called an eddy current. This is what finally leads to the strong sealing.

Sealing head

The sealing head consists of a coiled conductor covered by plastic housing. This part will transmit the electromagnetic current to the container cap. When a container fitted with an induction lined cap passes through this current, the foil from the inner-seal is heated. This melts the polymer coating on the foil, which forms a strong bond with the container lip and seals the bottle.

Choosing the Proper Container, Cap & Sealing Liner

Selecting the best induction seal liner for your product is dependent on so many different items, such as the container’s material, application and the main purpose of sealing.

Induction seal liners are available in 2 major forms, one-piece and two-piece type. The one-piece type consists of a foam-backed or paper-backed foil laminate. After the sealing process, the entire liner will stick to the bottle mouth and nothing will remain in the cap.

A two-piece liner has an additional wax layer and a pulp board layer (a paper or foam layer). The induction heating process will melt the wax, which is absorbed into the pulp board, releasing it from the aluminum foil liner. The pulp board layer remains inside the cap for improved resealing after the foil liner has been removed by consumer. This type of cap seal liner is usually use on products that the consumer won’t use them in a single time and it will take sometimes to consume them. Therefore the pulp-board will act as a secondary sealing liner.

Plastic Cap or Metal Cap, Does It Really Matter?

Plastic containers with continuous thread plastic caps produce the most consistent seal with the least challenges. Some glass containers may need to be treated in order to properly accept an induction seal. Sealing with metal caps is possible, but can pose several problems. As the induction system heats the foil liner, it also heats the metal cap, which can remain hot for a while. This can become a safety hazard and could also melt the threads if used on plastic containers.

Choosing the right power supply strength will depend on the size of your closure and the speed at which the production line will operate. The sealing head design depends on the application. The two most common designs are a flat sealing head or a tunnel head.

Sealing Head Types

Choosing the right power supply strength depends on 2 major factors. Firstly the size of the cap and the secondly the speed at which the production line is operating. The sealing head design depends on the application. The two most common designs are a flat sealing head and tunnel head sealing. Both of these types have their upsides and downsides.

Flat Induction Sealing Head

Flat sealing head will widely disperses the electromagnetic field.

Upsides:

  • Able to seal a large area
  • Accommodates various cap sizes without exchanging sealing head

Downsides:

  • Less concentrated field can cause in inconsistent seals if container is not properly centered

 

Tunnel Induction Sealing Head

Tunnel sealing head will provide concentrated magnetic field on sides and above the bottle cap.

 

Advantages:

  • Uniform field, which results in a more consistent sealing result
  • Deeper field allows for sealing thicker closures (ex. child resistant caps) or closures with recessed liners (ex. spout caps, push/pull caps, flip top caps)

Disadvantages:

  • Cannot accommodate a broad range of neck finishes

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