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Induction Sealing Statistics – How You Must Get The Right Cap and Lining Material Combinations

This discussion below is an excerpt of a client discussion we have prior to supplying equipment.

We don’t have to do this; we could be like the ebay or Alibaba or “one stop every machine under the sun supplier” but we are not as we like to think of ourselves as a supplier invited to be a part of your team going forward.

The discussion:

“Hi Team,

I can see there is significant concern over the advice you are receiving about the cap lining material.

The cap lining material specification you sent is the correct “type” of lining material in that it has the correct sealing layer.

We can test seal all the Jars and produce excellent sealing; the sample size is only a dozen or so – this could lead you into a false sense of security if we did not forewarn you the combination of material should have softness in it.

Our knowledge on the matter is significant; beyond most suppliers of induction equipment as we have significant experience in supplying cap lining material to cap manufacturers and even the high ticket equipment that inserts the cap lining material for the cap manufacturers. See our website: https://www.capliningmaterial.com/

I have personally been involved in the selection of induction sealing materials for projects by multibillion dollar companies including Nestle and I have dealt personally with the world’s top 5 cap lining material manufacturers.

The advice below stands:

Hand Torque is part of the equation. Though a poorly applied cap ; even when it has soft lining material or a foam backing can result in unsealed products.

The part I am focussing on is cap and bottle tolerances. I am not sure the cap manufacturer will give a cap tolerance for the flatness of their caps to within +/- 0.2mm.

Similarly the bottle/jar manufacturer may not give a height/flatness tolerance to within +/- 0.2mm with respect to the plain of the top lip of the container. From quality manufacturers, most of the caps/jars may fall within this tolerance though there will be a statistical amount that are outside of this; when tolerances add you can get a case where a 0.25mm thick hard liner will not have enough give to make up for the mismatch of the top plane of the jar neck with the underside plane of the cap. In this case there will be sections of the liner that are not in contact with the jar during the sealing process.

Standard practice is to have some softness behind the liners or very tight control on the capping process and the allowable tolerances on the caps and bottles provided.

For your operations – especially as you are growing it is highly recommended you have either:

a) Softness in one of the layers of the induction lining material

b) A separate foam liner behind the induction liner

Note: for higher volume hand operations we recommend a cap tightener due to the inevitable human error factor

“The purchasing decision to focus on here is the caps and the lining material.

If I was an owner in your business I would suggest the following path.

If time is against you – for your initial launch etc- ; go with what you have and perform a 100% test on what you seal before you send it out. If we are talking about only hundreds of units at a time it is a cumbersome, but, worthwhile task.

First impressions are everything at that stage and a leaking jar of product can be a “game over” at this stage.
Here’s a video of a suggested test that can help you be confident you have a sealed Jar:

New Time Trials - Fused liner test and Circumference Seal Test

2. Going down the track insure you have some softness in your cap/liner combination.”

If your cap supplier can’t do it (maybe because your volumes are too small) you should purchase the caps without liners and source liners from a liner supplier for separate insertion prior to sealing; you will need to source about 10,000 at about 12 cents each (my guess) – We can put you in touch with the supplier to the liners for the SealerOn gallery I showed you for the Nuts.

We want you to move forward with a sound understanding of how you can reduce the statistical probability of sending out products that could leak.

The Poor Man’s Tamper Evident Seal – Pressure Sensitive Cap Sealing

Tamper Evident Seal

When looking into whether to use a pressure sensitive tamper evident seal or an induction seal it is a good idea to understand the core reasons behind applying tamper evident seals and induction seals to bottles and jars.

For induction sealing the key benefits from that type of seal include:

A visual tamper proof barrier showing the client the contents of this product have not been compromised.
An oxygen and moisture barrier, preserving the integrity and shelf life of products. For this reason alone induction seals are often referred to as freshness seals.
Eliminate leaks through caps. Often plastic caps are well tightened after their bottle has been filled, however temperature changes resulting in slight cap expansion and contraction and the vibration of transport result in caps loosening and product leaking, Eg. Often compromising significant portions of product shipment that become very difficult to retail if not impossible.
To provide a professional finish to the product showing the manufacturer cares about the above three major benefits of good product sealing.

For pressure sensitive sealing – sometimes called PS22 Wadding the key benefits from that type of seal are reduced:

A visual tamper evident barrier showing the client the contents of this product have probably not been compromised
To provide a professional finish that resembles the level of care used by manufacturers using induction sealing.

Pressure sensitive wadding is susceptible to someone that can come along and carefully peel such a liner partially off the neck of a bottle and then simply tighten the cap again to apply pressure and re-seal the bottle; no equipment or tools is required. In this way bottle sealing with pressure sensitive cap sealing is more visual than practical.

Pressure sensitive cap lining material usually has no foil barrier and therefore has little to no barrier properties to lengthen shelf life or preserve freshness. Being glue based, many liquid contents are not suitable for pressure sensitive or PS22 cap sealing.

So why do companies choose pressure sensitive sealing materials over induction foil sealing?

In some cases it is ignorance of the induction sealing process and in other cases it is the “poor man’s” version of a tamper evident seal.

Induction sealing tamper evidence requires induction sealing machinery. Pressure sensitive sealing requires no machinery.

Safe bench top induction machinery can start at USD$3500.00. Beware there are many hand held induction machines on offer for sub USD$1000 and manufacturers of that level of equipment refuse to provide safety certifications or advise that they do not “yet” have the certification.

An induction machine is not like a toaster or a kettle so beware of anyone offering toaster or kettle prices for induction sealing equipment. An induction machine deals with high currents and produces high levels of magnetic and electrical fields.

If you find a retail product on the shelf with a pressure sensitive seal be aware that while it looks like it is tamper proof it is at best only ‘tamper evident’. The company producing that product is taking the cheapest path to providing you with a look that resembles but in no way performs like an induction seal or a tamper proof seal.

Induction Sealing Bottles with Specialty Caps

Induction Sealing

A Tunnel Induction Sealing Head lets you seal caps where the foil sits a distance greater than say 4 mm from the top surface of the cap; This is often the case with twist top spouts, flip top lids, sports drink caps, sipper caps or shaker caps.

Induction sealing is a process where a coil in the shape of an elongated loop is used to generate a fast oscillating high magnetic field. This magnetic field can change poles as many as 100,000 times every second.

The magnetic field can travel through air and plastic. When the magnetic field meets a metal surface, the magnetic field “induces” a high oscillating current in that metal surface in a plane that is parallel to the coils that generated the magnetic field.

A magnetic field generated from a “point” dissipates with the cube of its distance from that point.

In general, the magnetic field of an induction sealing machine needs to be within 5mm or ¼ inch from the sealing foil to obtain meaningful production speeds.

There are a large range of caps that do not fit the standard flat top profile and present a problem to bring the magnetic field of the heat sealing equipment to within 5mm or ¼ inch from the sealing foil.

These specialty caps need an adaption from a standard flat coil sealing head to a tunnel sealing head. The Coils are shaped to pass around the tunnel. The tunnel allows the protruding feature of the specialty caps to pass through the machine without lifting the plane of the magnetic field further away from the sealing foil within the bottle cap.

On the SealerOn website there is a youtube icon that will link you to videos showing SealerOn™ heat sealing or more accurately induction heat sealing using a tunnel sealing head.

The SealerOn™500 fitted with a sealing tunnel is capable of sealing at sealing speed up to 10 Meters per Minutes or 30 Feet per Minute depending on the cap and foil combination.

For faster induction sealing there is the MeRo adjustable tunnel sealing machines. These machines have the added and unique feature of having an adjustable width sealing head. Having an adjustable width enables higher concentrating and focussing of the induction field allowing for higher speed sealing. A MeRo 2Kw unit is capable of sealing at sealing speed up to 30 Meters per Minutes or 90 Feet per Minute depending on the cap and foil combination.

Efficient cap sealing means that less time is needed under the sealing head and hence higher production speed is possible.

A Flat profile sealing head will allow for a greater range of cap sizes and even allows for that Sealing head to be placed at an angle across the product’s path to achieve sealing of cap diameters that are even wider than the coil winding pattern within the sealing head. It is quite possible to have a Flat profile sealing head that can seal caps from 30mm to 110mm wide. The trade-off for the versatility of this profile sealing head on a heat sealing head is lower speed throughput and an inability to seal specialty caps.

What Shape Sealing Head is Best on an Induction Sealers?

Induction Sealers

To understand this question of the sealing head shape we must first understand how an induction seal is achieved.

The sealing head is the part of the machine that is placed over the path of the product cap/lid. Within the sealing head is usually long oval shaped coils of thick wire that carry high current that changes direction many thousands of times a second. This creates a magnetic field at right angles to the coil that also changes direction many thousands of times a second. The magnetic field can travel through air and plastic but it does get weaker as it travels away from the coils that generated the magnetic field. When the magnetic field comes across metal, it will act to generate current in the metal.

In the case of the heat sealing machine, it waits for a product that has a metal laminated foil in its cap. The magnetic field from the sealing head acts to generate current in the laminated foil and the laminated foil gets hot. Laminated to the foil is a layer that will melt or become “wet” with heat. When the product has completely passed from under the induction machine the foil will begin to cool and the layer that became “wet” will set to bond the laminated foil across the opening of the product.

From the above “theory” it can be understood that the sealing of a bottle or product using induction machines will depend on how long the product is under the magnetic field and how close it gets to that origins of the magnetic field.

There are two distinct shapes of sealing heads for cap sealers being Flat profile and Tunnel profile sealing heads.

The Flat profile sealing head is suitable for “Standard Flat Caps” . A “Flat Cap”, generally speaking, refers to a cap where the plane of the induction liner is within 4.0 mm of the plane of the Cap’s top surface.

The Tunnel profile sealing head is suitable for “Specialty Caps”. A Tunnel Induction Sealing Head lets you seal caps where the foil sits a distance greater than say 4 mm from the top surface of the cap; this is often the case with twist top spouts, flip top lids, sports drink caps, sipper caps or shaker caps.

The Tunnel sealing head concentrates the magnetic field to an area within the tunnel profile and hence provides stronger magnetic fields over a generally smaller width path for the products passing underneath. A Tunnel sealing head also allows the coils within the sealing head to have a path lower than the top of the product caps. This brings the magnetic field closer to the plane of the foil within “specialty caps”. The drawback to this Tunnel profile sealing head is that it is usually not very good for large caps and it does limit the range of cap sizes that can be efficiently sealed. There is a small exception to this rule with the MeRo™ brand induction sealer with an adjustable width tunnel profile. This machine can typically cater for a range of specialty caps with an adjustment of 30mm which would mean a typical cap diameter range of 30mm to 60mm could be very efficiently sealed.

Efficient cap sealing means that less time is needed under the sealing head and hence higher production speed is possible.

Packaging in Glass or PET When Considering Induction Seal

Often there are clients packaging a “pure” product which they are packaging in Glass.

The problem they face is that they are having leaking issues and also want some tamper evidence or freshness seal. In the case of dry products like capsules or powders there are some good options. Take for example coffee which is often packed in glass and has a foil freshness heat seal across the opening of the Jar.

In the case of wet and oily products the Induction Sealing option is not available. The heat sealing process in induction sealing relies on a layer of material laminated to the foil becoming “wet” when it is heated and then setting or drying when the foil cools down. In the case of plastics bottles this sealing layer is usually a plastic based sealing layer that “melts” into the existing plastic of the container. For glass with very high melt temperatures the sealing layer never gets anywhere near hot enough to “melt” into the glass so this sealing layer is usually adhesive based. Wet products and oily products tend to seep into this seal after the sealing process, eventually weakening or neutralising the adhesive and breaking the seal.

Another hurdle to get past with glass jars is that more often than not they are designed or supplied with metal caps. The induction sealing process relies on an uninterrupted magnetic field to work on the foil layer of an induction seal to heat that seal. Metal caps or closures interrupt the seal and the metal cap tends to absorb the heat sealing energy before the induction material receives this energy.

While often it is environmental or health based products packed into glass, ironically these manufactures are making a much larger impact on the environment in using glass packaging than their counterparts using PET packaging.

We will not enter into the argument about whether Glass or Plastic is best to package products but rather we will focus on the limitations lifted on induction sealing when using plastic packaging with plastic lids.

There are many products that transition from glass to plastic and are using plastic packs that look like glass yet still have metal lids. These products can be induction sealed using Capless induction sealing. This is a process where the open filled product passed under a sealing head that first cuts a disc of sealing foil, locates that sealing foil over the products opening and then heat seals that foil to the container. After this sealing machine process the package has its metal cap put in place.

More recently plastic packs that look like glass packs are now having screw on sections enabling the development and application of plastic caps. It is the combination of a plastic bottle and a plastic cap that best lend themselves to the induction sealing machine process.

For the pure products market that simply must have their product in glass ,not all hope is lost for induction sealing as development of adhesives for the induction sealing layer that are suitable for glass and resistant to wet and oily products is still taking place. There are definitely some glass sealing foils that perform better than others and the best way to know if your product will suit will be via trials. The longer you can conduct your trials and the more varied conditions, such as temperature ranges and pressure ranges the more certain you can be that the induction sealing process is suited to your application.

What are Cap Liners and What Function Do They Serve?

Cap Liners

Often found yet still rarely realized, inside of many high quality container caps is a material that was placed into the cap prior to the cap being applied on the container or jar.

Sometimes, the end user discover this material.They ask themselves what is the goal of that seal and just how was it put in place? To the astonishment of many, that security seal or freshness seal was put in place with the aid of the cap or lid itself.

Single Piece and two Piece Cap Liners

Individual Piece Cap Liners

Several bottled goods are smaller packs where their contents are required being consumed or used as soon as they are opened. The buyer is not

anticipated to reclose this product or keep product within the container and this kind of product packaging is referred to as one time use packaging. The expected purpose of the lining material or sealing material, in such cases, would be to provide tamper evidence as a protection up until it is opened up. Induction sealing is realized with the aid of single piece materials welded to the peak rim of the jar. Any time you open up a product like this you will observe the aluminium foil across the top of the bottle and when you look into the cap or lid there will not be any other material left from the cap.

2 Piece Cap Liners

Other bottled products and bigger packs usually are not likely to be totally consumed once they are opened. The end user of the product is quite likely going to reclose and store the bottle or container, and thus there is a requirement for a cap the reseals effectively.

As soon as the induction seal has been taken away, there really should still be a material that could result in “friction seal” after the package is closed again. Normally, this is achieved with compressible laminated foam that is around 1 to 2 mm thick.

The soft quality of the foam permit compression as the cap or lid is tightened on the bottle or container. This offers the sort of friction fit tightness which can be kept regardless if the cap or lid is not screwed to its highest possible pressure. Although it is not as effective as a heat induction welded foil, the foam cap inserts supply a resealable seal, permitting the cap or lid can be removed and then replaced and tightened to create a high integrity seal.

Larger sized juice bottles frequently have both a foil lining material and a independent foam lining material. Freshness assurance is justified by the foil while the foam liner provide the resealable capability. For the duration of heat sealing process, the foam element ensures even contact of the foil layer.

When the bottle caps turn loosened while transporting or expand and contract due to temperature or perhaps failed to properly apply, in any case the merchandise integrity and packaging is damaged. With the application of the foil seal on the top of the container, spillage and spoilage are a uncommon occurrence regardless if the caps become loose.