Beyond the Seal: Unraveling the Uses and Types of Heat Seal Coatings

Heat seal coatings are specialty materials that are applied to the surfaces of packaging materials like films, foils, papers and other substrates to provide the ability to seal via heat. These coatings play a vital role in the food and medical packaging industries by providing safe, tamper-proof and long shelf-life packaging solutions. This article aims to provide an overview of heat seal coatings, their types, properties and applications.

What are Heat Seal Coatings?

Heat seal coatings, also known as heat sealants, are thin polymer films that are coated or laminated onto packaging substrates. When two surfaces with heat seal coatings come in contact under heat, pressure and dwell time, the coatings soften and merge together forming a strong adhesive bond. This seals the package and prevents contents from leaking or escaping.

Heat seal coatings undergo a physical change when exposed to appropriate heat and pressure. They do not undergo a chemical reaction during sealing like adhesive bonding. Common polymers used in heat seal coatings include polyolefins like polyethylene and polypropylene, polyvinyl chloride, polyester and ethylene-vinyl acetate. The coating chemistry and properties are tailored as per the application requirements.

Types of Heat Seal Coatings

There are different types of heat seal coatings used depending on the substrate material and end-use application. Some of the main types are:

- Low density polyethylene (LDPE): LDPE is the most widely used sealant for packaging flexible films like polypropylene and polyethylene. It provides good seals at moderate temperatures and pressures.

- Ethylene-vinyl acetate (EVA): EVA copolymers offer high seal strength over a wide temperature range. They are used for packaging paper, films and rigid plastics.

- Polyvinyl chloride (PVC): PVC coatings require higher heat but provide durable seals for paperboard and rigid plastic packaging. They are often used for meat packaging.

- Polypropylene (PP): Homopolymers and copolymers of PP are suitable for high-temperature food applications like retort pouches.

- Polyester: Polyester sealants like polyethylene terephthalate provide high strength seals for packaging foils and rigid plastic containers.

Properties and Considerations for Heat Seal Coatings

There are several critical properties that determine the effectiveness of a Heat Seal Coating for a particular application. Some of the key properties include:

Seal Strength - The seal peel and seal pull strength parameters determine whether the seal will withstand stresses during distribution, stacking and shelf-life.

Seal Temperature - The softening point or seal initiation temperature of the coating is important. Too high can damage contents and too low can lead to poor seals.

Seal Time - The time required to develop sufficient seal strength is crucial. Very short or long times affect production throughput.

Moisture and Solvent Resistance - Coatings for food and medical packaging must have high resistance to moisture, fats, oils and cleaning agents.

Appearance - Haze, gloss and adhesion properties impact the aesthetic appeal and performance of the packaged product.

Coefficient of Friction - Low slipperiness aids high-speed packaging and prevents blocking or sticking of film rolls.

Barrier Properties - Barrier to gases like oxygen and aromas contributes to product shelf-life extension.

Compliance - Coatings must comply with food contact regulations and be FDA approved for intended application.

Applications of Heat Seal Coatings

Some areas where heat seal coatings are applied include:

Food Packaging
- Pouches for snacks, sugar, coffee, pet food etc.
- Sauces, condiment and liquid cartons
- Reclosable zipper pouches
- Shrink and stretch films for meat

Medical Packaging
- Sterile packaging for medical devices, drugs and implants
- Diagnostic test kits and sample collection bags
- Blood and specimen collection bags

Industrial Applications
- Mailers and security bags
- Desiccants and moisture control sachets
- Trash bags and liners

Emerging Areas
- Composite cardboard/plastic lidding films
- Heat sealing lids for cups and takeaway containers
- Automotive spare parts bags

heat seal coatings are indispensable for developing sustainable and safe packaging solutions across multiple industries. Advances in coating chemistries and application methods continue to expand the capabilities of heat sealing technology. Ongoing research aims to develop bio-based, recyclable and compostable sealants for a greener future. Proper selection and testing of heat seal coatings remain important to fulfill the requirements of diverse packaging applications.