Heat Seal Coatings: Formulation Play An Important Role In Many Packaging Application

Heat Seal Coatings

Heat Seal Coverings play an important role in many packaging applications by forming strong, reliable seals between films, foils and other substrates. These coatings fuse under application of heat and pressure to create seamless bonds that protect products and extend shelf life. In this article, we will explore the formulation of Heat Seal Coverings and how they are applied.

Composition and Chemistry

Heat Seal Coatings are engineered polymer formulations that typically contain a resin, plasticizer and other additive compounds. The resin, which makes up the largest percentage by weight, provides the structural integrity and adhesion properties. Common resins used include ethylene-vinyl acetate (EVA), polyurethane (PU), polyolefin, and polyester.

Plasticizers are added to the resin to increase flexibility and reduce the melting point, allowing the coating to fuse at lower temperatures. Common plasticizers include esters of phthalic or adipic acid. Additives such as waxes, antioxidants, and slip agents are also included to modify surface characteristics and improve coating performance.

The chemistry of Heat Seal Coverings is designed around generating strong intermolecular attractions between polymer chains upon heating. At elevated temperatures, the polymer chains exhibit increased mobility and Brownian motion, allowing them to become entangled and bond with contacting surfaces through weak van der Waals forces. Upon cooling, the coating develops sufficient rigidity and tensile strength to form a hermetic seal.

Coating Application Methods

There are several techniques used to apply Heat Seal Coatings depending on the substrate material and production requirements. For films and foils, the most common methods are extrusion, lamination, and solution coating.

In extrusion coating, the molten polymer coating is applied directly to the substrate surface through a slot die as it passes between chilled rolls. This results in a uniform layer and tightly controlled coat weight. Lamination involves applying a pre-formed layer of heat seal polymer to the substrate surface under heat and pressure, such as between nip or calender rolls.

Solution coating involves dissolving the sealant polymers into a solvent system and applying the liquid mixture to the substrate. As the solvent evaporates, a uniform solid film is left on the surface. Offline or inline coating variations may be used depending on web handling capabilities. Offline methods are preferred for rigid packaging substrates like paperboard.

Quality Control and Testing

A variety of tests are conducted on Heat Seal Coverings to ensure they meet specification requirements for performance, quality, and compliance. Coating weight is routinely checked through gravimetric analysis to maintain consistency. Seal strength testing determines the sealing temperature window and bond integrity under stress. Heat seal peel and shear tests are commonly used depending on the failure mode of the application.

Seal integrity tests examine the hermetic properties of seals for applications requiring permeability barriers like food or medical packaging. Optical and mechanical coating property measurements evaluate surface qualities like finish, gloss and defects using instruments like micrometers, profilers and goniometers. Additional testing establishes compliance of the final packaging construction to standards like FDA food contact regulations. Comprehensive quality control through every stage of the coating process helps deliver heat seals that reliably perform their function.

Applications

Some common applications that utilize Heat Seal Coatings include:

- Food packaging like pouches, trays, and flow wrap for snack foods, fresh proteins, baked goods. This demands high seal strength and hermetic barriers.

- Medical device packaging such as sterile bags and plastic sterile packaging (pouches). Rigorous validation is required to ensure sterility during shelf life.

- Industrial bags for materials like cement, fertilizer, grains and minerals. Durability against abrasion and environmental stresses is important.

- Paperboard carton seals for liquid and consumer good packaging. Specialty paper and board coatings are required.

- Mailers and envelope construction using facestock like polyester and polypropylene films. Need to perform reliably through distribution channels.

As packaging requirements continue to evolve towards sustainability and new capabilities, Heat Seal Coatings formulations will advance to meet these demands. Bio-based resins, low-temperature fusing polymers, and sealants compatible with compostable substrates enable the shift to renewable and compostable packaging structures. Novel chemistries incorporating antimicrobial components facilitate active packaging functions. Developments in application methods like spray, slot die and micro-extrusion expand opportunities for flexible and digital printing applications as well. Innovation in Heat Seal Coverings technology plays a critical role in delivering high-performance packaging solutions of the future.

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About Author:

Money Singh is a seasoned content writer with over four years of experience in the market research sector. Her expertise spans various industries, including food and beverages, biotechnology, chemical and materials, defense and aerospace, consumer goods, etc. (https://www.linkedin.com/in/money-singh-590844163)