When applied properly, induction sealing provides a hermetic and air-tight seal that is tamper-evident. The U.S. Food and Drug Administration’s (FDA’s) tamper-resistant packaging requirements even stated that seals applied using heat induction to containers produce more reliable tamper-evident packages. Printing QR codes and promotional materials on the heat induction liner foil is even a trend.
To help you better understand what induction sealing is including induction sealing machines, we have created this guide for you. So keep on reading to know more!
What is Heat Induction Sealing?
Heat induction sealing produces hermetically sealed containers in a non-contact process. These containers have closures that include foil laminates which are heated to create a seal.
Using heat induction sealing is effective in:
- Extending the shelf life of products
- Enhancing the value of your products
- Preserving freshness
- Preventing costly leakage
Typical inner induction seals begin as multi-laminate liners inside a container closure. The liners are composed of four layers:
- A pulpboard layer
- A wax layer
- A layer of aluminum foil
- A polymer layer (heat seal film)
The polymer layer matches the material the container is made from and can be heated to seal the lip of a container.
How Does Induction Sealing Work?
After the containers have undergone the filling and capping processes in the production line, the containers pass underneath an aluminum foil induction sealing machine. These machines have two major components: the sealing head and the power source. The machine’s sealing head is made of a conductor housed in a plastic casing.
- The process of sealing using heat induction involves the application of a current to the multi-laminate liner inside the plastic closure.
- The coiled conductor emits an “eddy” current (electromagnetic current) once the induction sealing machine is turned on. This eddy current disperses into the layer of aluminum foil which results in an electric resistance heating effect.
- When the foil is heated, the layer of wax melts and is absorbed by the pulpboard layer. This process releases the foil layer from the pulpboard.
- Next, the polymer layer melts and hermetically seals the aluminum foil layer to the container’s lip. The thermoplastic polymer layer melts and hermetically seals the aluminum foil layer to the container’s lip. On the other hand, the pulpboard layer stays on the closure’s inner side.
You can obtain high speeds using heat induction sealing making them suitable for high production requirements.
Types of Aluminum Induction Sealing Machine Heads
Choosing the appropriate sealing head for your project depends on your closure’s size and your production line’s operation speed. The two common types of induction sealing machine heads are flat and tunnel heads.
Flat Sealing Heads
Flat induction sealing heads can widely diffuse the electromagnetic field produced by the induction coil. Thus, they are suitable for larger cap sizes.
- It can accommodate a wide variety of cap sizes.
- A change in cap size does not require a change in sealing head.
- The electromagnetic field becomes less concentrated.
- It can cause inconsistent seals if the containers are not properly centered.
Tunnel Sealing Heads
These sealing heads can provide a concentrated electromagnetic field from the top and sides of a closure.
- It applies uniform current to the closure which provides more consistent seals.
- It has a deeper field that can seal thicker closures or those having recessed liners.
- It can only accommodate a few neck finishes.
Tips When Operating A Heat Induction Sealing Machine
- You must apply proper torque on the closures because the right torque will ensure that the induction liner directly contacts the container’s lips. Also, it creates a uniform pressure between the container’s cap circumference and the liner. This torque guide might help you.
- You must properly program the sealing time and power settings of the machine. Insufficient heat will result in weak seals and extreme heat will also burn or deform the induction liners. Start to test under a minimum power then increase it by about 1-2% until you achieve your desired seal.
- Ensure that there is enough distance between the sealing head and the cap. The optimal distance between these two should be ⅛ inch.
- Make sure that your containers are properly centered below the induction sealing head to produce even bonds between the liners and the containers’ lips.
Selecting The Closure and Container
Induction liners work with PVC, PET, PS, LDPE, and HDPE plastic bottles and jars along with glass containers. But plastic containers having plastic closures are the easiest to process and they create the most consistent seals.
As for glass containers, you can seal them using heat induction provided that they have plastic caps. However, you have to treat some glass containers to achieve proper seals.
Induction sealing is among the most effective process in creating tamper-evident packages and is done using induction can sealer machines. We hope that the information we have provided in this guide was able to help you, especially if you are planning on using this type of sealing method. By the way, if you haven’t found your induction sealing machine supplier yet, feel free to check out LPE’s can sealer machines.