What Is Heat Sealing in Packaging?

"What is heat sealing?" is a common question for companies searching for the perfect packaging for their food products. Heat sealing is a widely used packaging technique that involves joining materials, typically plastic films, by applying heat and pressure.

The heat-sealing process is essential in various industries, from food packaging to medical supplies. It ensures product integrity, extends product shelf life, and maintains product freshness.

Heat Sealing Definition

Heat sealing is a process in which two or more thermoplastic materials are joined together by applying heat and pressure over a certain amount of time. Contact equipment like a seal bar or seal band is used to melt the sealant film layer on different types of packaging and fuse the molten surface together. The binding of the different layers creates a seal. The time required to create a seal will depend on the thickness of the materials being bound.

When done correctly, heat sealing creates a strong, airtight, and watertight seal. However, heat sealing that leaves even small leaks can impact the shelf life of the food items held within the packaging (page 2 of the linked PDF).

How Heat Sealing Works

Thermo-reactive polymers like polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) are plastics used to make bags and other packaging containers. They melt when exposed to high temperatures. 

Heat sealing works when two layers of this plastic are subject to heat and pressure by a machine like a sealing bar. A seal is made when the two layers are pressed and melded together.

How Heat Sealing Preserves Food

Heat sealing helps to preserve food by creating an airtight barrier around the food. This prevents the entry of environmental factors that degrade food, like oxygen and moisture. Heat sealing is a great option for flexible packaging for the following reasons:

• Protects product integrity: Airtight seals help to maintain the original condition of the product, preventing damage, spoilage, and leakage.
• Extends product shelf life: The hermetic seal created by heat considerably delays the degradation of food. This extends its shelf life and reduces waste.
• Maintains products' nutritional value: Oxidation can lead to nutrient loss in food products. Heat-sealed packaging preserves the nutritional integrity of the food within.
• Preserves sensory appeal: Heat sealing contributes to maintaining the color, texture, and flavor of food. This keeps it visually appealing for the consumer and boosts customer satisfaction with the product.
• Contributes to food safety: A heat seal provides a barrier against external elements, therefore contributing to the safety of the product. This is especially crucial for fresh produce and perishable prepared meals. 

Other Advantages of Heat Sealing

The other advantages of heat sealing are that it's efficient for high-speed operations and versatile as far as the packaging materials to which it can be applied.

Efficiency and Speed for Manufacturers

Companies with high production levels require an efficient sealing system. Heat sealing achieves this goal in two key ways:

• High-speed production: Heat sealing machines are designed to operate at high speeds, allowing for efficient and rapid packaging processes.
• Consistent sealing: Heat sealing machines provide consistent and reliable seals, minimizing the risk of product damage or contamination.

Versatility

Heat sealing is versatile as it works with different materials and will mold to your product’s specifications. Heat-sealing machines can create custom seals with different shapes, sizes, and patterns.

Remember that an effective heat seal should create airtightness. However, airtight doesn’t always mean smell-proof. Manufacturers that sell strong-smelling products should therefore investigate a range of seal types and materials to keep smells in and air out.

Common Ways to Create Heat Seals

There are various approaches to generating the necessary heat for a seal. The sealing method that companies opt for depends on the type of polymer being sealed, its thickness, and the scale of production. Common methods used to produce heat-sealed bags include:

• Seal bar sealing (direct contact thermal sealing): This method uses a seal bar to create a short burst of heat. This creates a localized seal. This method is suitable for small- or large-scale production. It’s mostly used for sealing multiple individual bags that require the same temperature to seal. Seal bar sealing is a type of constant heat sealing in which the sealing jaws are kept at a high, controlled temperature.

• Impulse sealing: Impulse heat sealers work by applying a short burst of high-voltage electricity to their seal bars. This heats them quickly. The temperature of the seal bar rises and falls rapidly. Impulse sealing is suitable for smaller-scale production and thinner materials.

• Hot wire sealing: Hot wire sealing is a technique used to seal plastic bags or films by using a heated wire to cut and seal the material simultaneously. This method is often used in packaging applications where a clean, precise seal is required.

• Hot air sealing: This method uses a stream of hot air to melt and fuse the edges of the bag. It’s one of the best options for sealing irregular shapes and thicker materials. 

• Induction sealing: This is a non-contact sealing method used on any container that has a cap. Electromagnetic induction is used to heat a metalized liner inside the container's cap. When the liner melts, it bonds with the container's rim. This creates a hermetic seal.

What Temperature Is Needed to Heat Seal a Package?

The temperature needed to heat seal a package depends on which thermo-reactive material is used and the thickness of the plastic. The optimal temperature (as well as the time and pressure) will likely need to be studied for each different food product that goes onto the market.

The following table shows the melting points of different polymers. This is a useful starting point for understanding what kinds of temperatures will be necessary in your heating element:

Polymer Melting Point (ºC/ºF)

Source

Heat Sealing vs Cold Sealing

Cold sealing is a packaging technique that uses pressure-sensitive adhesives rather than heat to seal materials together when pressure is applied. Cold sealing is often chosen to seal heat-sensitive products or for sealing materials that can’t be heat-sealed. 

Vacuum Sealed Jars: An Alternative to Heat and Cold Sealing

Heat and cold sealing are highly effective options for many consumer products. However, both of these seal types become ineffective once the original seal has been broken by the consumer. Vacuum sealed jars bypass this problem with a mechanism that unseals and reseals as needed.

POP VAC jars—a popular vacuum sealed jar option—feature an innovative resealing mechanism that “pops” when it’s opened and closed. This lets the consumer know the seal is firmly closed. Its seal offers a highly effective barrier against air and moisture that degrade product quality. 

POP VAC jars offer unparalleled airtight protection for products that don’t require heat or cold sealing. They’re a highly customizable, eye-catching option for brands that favor a classy, premium-feeling container for their products. Many brands looking for something a little extra opt for premium customization options like raised effects or hologram lettering.

Choose the Most Appropriate Seal for Your Product Type

Heat sealing is a versatile and efficient packaging technique that offers numerous benefits to food and beverage companies. It allows manufacturers to create strong, airtight seals that protect products from contamination, moisture, and other environmental factors. Cold sealing can be used when packaging heat-sensitive products.

Vacuum sealed jars offer an alternative to heat or cold sealing for products that will be opened multiple times. Choose the most appropriate sealing system for the products your company sells to ensure customer satisfaction and the longest possible shelf life.