What Is Heat Sealing?

Heat sealing is a widely used bonding technology in the packaging and converting industries. It plays a critical role in applications such as food packaging, pharmaceutical blister packs, aluminum foil lids, labels, and laminated films. The performance of a heat-sealed package largely depends on the heat-seal coating and the resins used in its formulation.

Wangqin Resins provides a range of high-performance resins for heat-seal lacquers, including acrylic, polyurethane, and ternary chlorinated acetate resins, helping formulators achieve excellent seal strength, adhesion, and processing stability.

Heat sealing is a process in which two materials are bonded together by applying heat and pressure, sometimes for a short dwell time, allowing a thermoplastic layer to soften or melt and then fuse upon cooling.

In most packaging structures, heat sealing does not rely on mechanical fasteners or liquid adhesives. Instead, a heat-seal coating or resin layer becomes tacky at a specific temperature, forming a strong and durable bond once cooled.

1. Heating
   The heat-seal layer reaches its activation or melting temperature.

2. Pressure Application
   The two substrates (such as aluminum foil and plastic film) are pressed together.

3. Dwell Time
   Heat and pressure are maintained for milliseconds to seconds.

4. Cooling and Bond Formation
   The molten resin solidifies, creating a secure seal.

The quality of the seal depends on temperature, pressure, dwell time, and resin performance.

• Aluminum foil lids (Alu–PVC, Alu–PS, Alu–PET)

• Flexible food packaging

• Pharmaceutical blister packaging

• Cigarette and tobacco packaging

• Paper–plastic and foil–paper laminates

• Medical and hygiene packaging

Each application requires specific resin properties, such as low seal initiation temperature, high seal strength, or food-contact compliance.

An effective heat-seal resin should provide:

• Low seal initiation temperature (SIT)

• High and consistent seal strength

• Good hot tack performance

• Strong adhesion to multiple substrates

• Thermal stability during processing

• Compatibility with other resins and additives

This is where resin selection becomes critical.

Reliable adhesion and versatility

SA-24A is a thermoplastic acrylic resin widely used in heat-seal lacquers and printing applications.

Key advantages:

• Excellent adhesion to aluminum foil and plastic films

• Good film toughness and clarity

• Easy solubility in ketones, esters, and aromatic solvents

• Good compatibility with chlorinated resins and polyurethane resins

SA-24A is often used as a base resin in heat-seal coatings where balanced seal strength and processing stability are required.

Flexibility and enhanced seal strength

WQ-PR888 is a polyurethane resin designed to improve flexibility and bonding performance in heat-seal systems.

Key advantages:

• Excellent flexibility and toughness

• Improved adhesion to plastic substrates such as PVC, PET, and PS

• Enhances hot tack and seal durability

• Good compatibility with acrylic and chlorinated resins

When blended with acrylic resins like SA-24A, WQ-PR888 helps achieve strong, flexible, and reliable heat seals, especially in demanding packaging applications.

Outstanding metal adhesion and chemical resistance

DA60 is a ternary chlorinated acetate resin commonly used in aluminum foil heat-seal lacquers.

Key advantages:

• Excellent adhesion to aluminum and metallized films

• Good chemical resistance and thermal stability

• Strong compatibility with acrylic and polyurethane resins

• Suitable for complex multilayer packaging structures

DA60 is particularly effective in Alu-to-plastic heat-sealing systems, where high seal strength and resistance to storage or transportation conditions are required.

By combining:

• SA-24A acrylic resin (adhesion and film formation),

• WQ-PR888 polyurethane resin (flexibility and toughness),

• DA60 ternary chlorinated acetate resin (metal adhesion and stability),

formulators can design high-performance heat-seal lacquers with:

• Wide sealing windows

• Strong and stable seal strength

• Excellent substrate compatibility

• Reliable performance in food and pharmaceutical packaging

Heat sealing is a critical technology that enables efficient, secure, and hygienic packaging. The success of heat sealing depends not only on equipment and process conditions, but also on the quality and compatibility of the resins used in heat-seal coatings.

With products such as SA-24A solid acrylic resin, WQ-PR888 polyurethane resin, and DA60 ternary chlorinated acetate resin, Wangqin Resins offers proven solutions for formulating reliable, high-performance heat-seal lacquers across a wide range of packaging applications.