Induction sealing

Last updated

Induction sealing is the process of bonding thermoplastic materials by induction heating. This involves controlled heating an electrically conducting object (usually aluminum foil) by electromagnetic induction, through heat generated in the object by eddy currents.

Contents

Induction sealing is used in many types of manufacturing. In packaging, it is used for package fabrication such as forming tubes from flexible materials, attaching plastic closures to package forms, etc. Perhaps the most common use of induction sealing is cap sealing, a non-contact method of heating an inner seal [1] [2] to hermetically seal the top of plastic and glass containers. This sealing process takes place after the container has been filled and capped. [3]

An induction sealed inner seal Induction sealed bottle.jpg
An induction sealed inner seal

Sealing process

An induction sealer with a conveyor Induction sealer conveyor.jpg
An induction sealer with a conveyor

The closure is supplied to the bottler with an aluminum foil layer liner already inserted. Although there are various liners to choose from, a typical induction liner is multi-layered. The top layer is a paper pulp that is generally spot-glued to the cap. The next layer is wax that is used to bond a layer of aluminum foil to the pulp. The bottom layer is a polymer film laminated to the foil. After the cap or closure is applied, the container passes under an induction coil, which emits an oscillating electromagnetic field. As the container passes under the induction coil (sealing head), the conductive aluminum foil liner begins to heat as a result of the eddy currents being induced. The heat melts the wax, which is absorbed into the pulp backing and releases the foil from the cap. The polymer film also heats and flows onto the lip of the container. When cooled, the polymer creates a bond with the container resulting in a hermetically sealed product. Neither the container nor its contents are negatively affected, and the heat generated does not harm the contents. [4]

It is possible to overheat the foil and thereby cause damage to the seal layer and to any protective barriers. This could result in faulty seals, even weeks after the initial sealing process, so proper sizing of the induction sealing is vital to determine the exact system necessary to run a particular product.

Sealing can be done with either a handheld unit or on a conveyor system. A more recent development (which better suits a small number of applications) allows for induction sealing to be used to apply a foil seal to a container without the need for a closure. In this case, foil is supplied pre-cut or in a reel. Where supplied in a reel, it is die cut and transferred onto the container neck. When the foil is in place, it is pressed down by the seal head, the induction cycle is activated, and the seal is bonded to the container. This process is known as direct application or sometimes "capless" induction sealing.

Potential uses

A hand held induction sealer Hand Held induction sealer.jpg
A hand held induction sealer

There are a variety of reasons companies choose to use induction sealing:

Tamper evidence

With the U.S. Food and Drug Administration (FDA) regulations concerning tamper-resistant packaging, pharmaceutical packagers must find ways to comply as outlined in Sec. 450.500 Tamper-Resistant Packaging Requirements for Certain over-the-counter (OTC) Human Drug Products (CPG 7132a.17).

Induction sealing systems meet or exceed these government regulations. As stated in section 6 of Packaging Systems:

"...6. CONTAINER MOUTH INNER SEALS. Paper, thermal plastic, plastic film, foil, or a combination thereof, is sealed to the mouth of a container (e.g., bottle) under the cap. The seal must be torn or broken to open the container and remove the product. The seal cannot be removed and reapplied without leaving visible evidence of entry. Seals applied by heat induction to plastic containers appear to offer a higher degree of tamper-resistance than those that depend on an adhesive to create the bond..."

Leak prevention/protection

A common application for flat sealing heads are to seal containers in the food and beverage industry to prevent leaks and extend shelf life. Induction Sealing Food.jpg
A common application for flat sealing heads are to seal containers in the food and beverage industry to prevent leaks and extend shelf life.

Some shipping companies require liquid chemical products to be sealed prior to shipping to prevent hazardous chemicals from spilling on other shipments.

Freshness

Induction sealing keeps unwanted pollutants from seeping into food products, and may assist in extending shelf life of certain products.

Pilferage protection

Induction-sealed containers help prevent the product from being broken into by leaving a noticeable residue on plastic containers from the liner itself. Pharmaceutical companies purchase liners that will purposely leave liner film/foil residue on bottles. Food companies that use induction seals do not want the liner residue as it could potentially interfere with the product itself upon dispensing. They, in turn, put a notice on the product that it has been induction-sealed for their protection; letting the consumer know it was sealed upon leaving the factory and they should check for an intact seal before using.

Sustainability

In some applications, induction sealing can be considered to contribute towards sustainability goals by allowing lower bottle weights as the pack relies on the presence of an induction foil seal for its security, rather than a mechanically strong bottle neck and closure. [5]

Induction heating analysis

Some manufacturers have produced devices which can monitor the magnetic field strength present at the induction head (either directly or indirectly via such mechanisms as pick up coils), dynamically predicting the heating effect in the foil. Such devices provide quantifiable data post-weld in a production environment where uniformity – particularly in parameters such as foil peel-off strength, is important. Analysers may be portable or designed to work in conjunction with conveyor belt systems.

High speed power analysis techniques (voltage and current measurement in near real time) can be used to intercept power delivery from mains to generator or generator to head in order to calculate energy delivered to the foil and the statistical profile of that process. As the thermal capacity of the foil is typically static, such information as true power, apparent power and power factor may be used to predict foil heating with good relevance to final weld parameters and in a dynamic manner.

Many other derivative parameters may be calculated for each weld, yielding confidence in a production environment that is notably more difficult to achieve in conduction transfer systems, where analysis, if present is generally post-weld as relatively large thermal mass of heating and conduction elements combined impair rapid temperature change. Inductive heating with quantitative feedback such as that provided by power analysis techniques further allows for the possibility of dynamic adjustments in energy delivery profile to the target. This opens the possibility of feed-forward systems where the induction generator properties are adjusted in near real-time as the heating process proceeds, allowing for a specific heating profile track and subsequent compliance feedback – something that is not generally practical for conduction heating processes.

Benefits of induction vs. conduction sealing

Conduction sealing requires a hard metal plate to make perfect contact with the container being sealed. Conduction sealing systems delay production time because of required system warm-up time.[ citation needed ] They also have complex temperature sensors and heaters.

Unlike conduction sealing systems, induction sealing systems require very little power resources, deliver instant startup time, and have a sealing head which can conform to "out of specification" containers when sealing.[ citation needed ]

Induction sealing also offers advantages when sealing to glass: Using a conduction sealer to seal a simple foil structure to glass gives no tolerance or compressibility to allow for any irregularity in the glass surface finish. With an induction sealer, the contact face can be of a compressible material, ensuring a perfect bond each time.[ citation needed ]

Real-world applications of induction sealing

Induction sealing is broadly used to preserve the freshness and integrity of various products, such as:

History

Induction Sealing inventor Jack Palmer (circa 1995) Jack Palmer.jpg
Induction Sealing inventor Jack Palmer (circa 1995)

Related Research Articles

A screw cap or closure is a common type of closure for bottles, jars, and tubes.

<span class="mw-page-title-main">Bottle cap</span> Top for holding liquid inside a bottle

A bottle cap or bottle top is a closure for the top opening of a bottle. A cap is sometimes colorfully decorated with the logo of the brand of contents. Plastic caps are used for plastic bottles, while metal with plastic backing is used for glass; plastic caps are commonly made from polyethylene or polypropylene, while metal caps are usually either steel or aluminum. Plastic caps may have a pour spout. Flip-Top caps like Flapper closures provide controlled dispensing of dry products. Caps for plastic bottles are often made of a different type of plastic from the bottle.

<span class="mw-page-title-main">Induction heating</span> Process of heating an electrically conducting object by electromagnetic induction

Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an inductor that creates an electromagnetic field within the coil to heat up and possibly melt steel, copper, brass, graphite, gold, silver, aluminum, or carbide.

<span class="mw-page-title-main">Drum (container)</span> Cylindrical shipping container used for shipping bulk cargo

A drum is a cylindrical shipping container used for shipping bulk cargo. Drums can be made of steel, dense paperboard, or plastic, and are generally used for the transportation and storage of liquids and powders. Drums are often stackable, and have dimensions designed for efficient warehouse and logistics use. This type of packaging is frequently certified for transporting dangerous goods. Proper shipment requires the drum to comply with all applicable regulations.

<span class="mw-page-title-main">Ultrasonic welding</span> Welding process

Ultrasonic welding is an industrial process whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. It is commonly used for plastics and metals, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together. When used to join metals, the temperature stays well below the melting point of the involved materials, preventing any unwanted properties which may arise from high temperature exposure of the metal.

<span class="mw-page-title-main">Plastic welding</span> Welding of semi-finished plastic materials

Plastic welding is welding for semi-finished plastic materials, and is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat. Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semi-finished plastic materials. Based on the mechanism of heat generation at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods, as shown in Fig 1.

<span class="mw-page-title-main">Closure (container)</span> Devices and techniques used to close or seal a bottle, jug, jar, tube, can, etc.

A closure is a device used to close or seal a container such as a bottle, jug, jar, tube, or can. A closure may be a cap, cover, lid, plug, liner, or the like. The part of the container to which the closure is applied is called the finish.

<span class="mw-page-title-main">Shrink wrap</span> Polymer used to bundle boxes on a pallet for transport

Shrink wrap, also shrink film, is a material made up of polymer plastic film. When heat is applied, it shrinks tightly over whatever it is covering. Heat can be applied with a handheld heat gun, or the product and film can pass through a heat tunnel on a conveyor.

Tamper-evident describes a device or process that makes unauthorized access to the protected object easily detected. Seals, markings, or other techniques may be tamper indicating.

A hermetic seal is any type of sealing that makes a given object airtight. The term originally applied to airtight glass containers, but as technology advanced it applied to a larger category of materials, including rubber and plastics. Hermetic seals are essential to the correct and safe functionality of many electronic and healthcare products. Used technically, it is stated in conjunction with a specific test method and conditions of use.

<span class="mw-page-title-main">Heat sealer</span> Machine for joining thermoplastic materials using heat

A heat sealer is a machine used to seal products, packaging, and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer.

<span class="mw-page-title-main">Strapping</span> Fastening a strap around item or bundle

Strapping, also known as bundling and banding, is the process of applying a strap to an item to combine, stabilize, hold, reinforce, or fasten it. A strap may also be referred to as strapping. Strapping is most commonly used in the packaging industry.

<span class="mw-page-title-main">Blister pack</span> Type of packaging

A blister pack is any of several types of pre-formed plastic packaging used for small consumer goods, foods, and for pharmaceuticals.

<span class="mw-page-title-main">Vacuum packing</span> Method of removing air from package prior to sealing

Vacuum packing is a method of packaging that removes air from the package prior to sealing. This method involves placing items in a plastic film package, removing air from inside and sealing the package. Shrink film is sometimes used to have a tight fit to the contents. The intent of vacuum packing is usually to remove oxygen from the container to extend the shelf life of foods and, with flexible package forms, to reduce the volume of the contents and package.

Aseptic processing is a processing technique wherein commercially thermally sterilized liquid products are packaged into previously sterilized containers under sterile conditions to produce shelf-stable products that do not need refrigeration. Aseptic processing has almost completely replaced in-container sterilization of liquid foods, including milk, fruit juices and concentrates, cream, yogurt, salad dressing, liquid egg, and ice cream mix. There has been an increasing popularity for foods that contain small discrete particles, such as cottage cheese, baby foods, tomato products, fruit and vegetables, soups, and rice desserts.

<span class="mw-page-title-main">Liquid packaging board</span>

Liquid packaging board is a multi-ply paperboard with high stiffness, strong wet sizing and a high barrier coating, e.g. plastic. Only virgin paper fibers are used. The barrier coating must hold the liquid and prevent migration of air and flavors through the paperboard.

<span class="mw-page-title-main">Tamper-evident band</span>

A tamper-evident band or security ring serves as a tamper resistant or tamper evident function to a screw cap, lid, or closure. The term tamper-proof is sometimes used but is considered a misnomer given that pilfering is still technically possible.

<span class="mw-page-title-main">Drug packaging</span> Packaging for pharmaceutical preparations

Pharmaceutical packaging is the packages and the packaging processes for pharmaceutical preparations. It involves all of the operations from production through drug distribution channels to the end consumer.

<span class="mw-page-title-main">Packaging machinery</span>

Packaging machinery is used throughout all packaging operations, involving primary packages to distribution packs. This includes many packaging processes: fabrication, cleaning, filling, sealing, combining, labeling, overwrapping, palletizing.

Implant induction welding is a joining method used in plastic manufacturing. The welding process uses an induction coil to excite and heat electromagnetically susceptible material at the joint interface and melt the thermoplastic. The susceptible material can be contained in a gasket placed between the welding surface, or within the actual components of a composite material. Its usage is common for large, unusually shaped, or delicate parts that would be difficult to weld through other methods.

References

  1. US 2715474 A,Phillips,"Closure liners and methods",published 1955
  2. US 4778698 A,Ou-Yang,"Innerseal for container for use with liquid contents",published 1988
  3. US 2937481 A,Jack Palmer,"Method of producing a package",published 1958
  4. Evans, Scott (1997), Temperature transfer due to induction sealing, archived from the original on 2 April 2015, retrieved 9 Mar 2015
  5. Company, JSA Packaging. "J.S.A Enterprises". J.S.A Enterprises. Retrieved 2021-03-12.

Further reading