Adhesives Used in Flexible Packaging: Types, Applications And Selection Guide

Flexible packaging plays a crucial role in today's food, beverage, cosmetics, and industrial markets. It is typically composed of multiple layers of films, metal foils, or paper laminated together to provide barrier properties, structural strength, and visual appeal. Therefore, the adhesives used in the lamination process are critical to ensure the overall integrity, performance, and regulatory compliance of the packaging.

Understanding and selecting the appropriate adhesive can effectively mitigate risks while enhancing production efficiency.

Environmental & Regulatory Pressures

Increasing demand from different brands and laminators for low-VOC, solvent-free, or water-based adhesive systems.

Food Migration Concerns‌

Regulatory scrutiny on chemical migration from adhesives into packaged food, especially for PU adhesives requiring migration testing and simulation.

Speed & Cost requirements‌

Laminators require faster curing adhesives to support higher production speeds while maintaining performance.

Customization Needs‌

Adhesive manufacturers offer tailored chemical systems for specific barrier/film combinations or special applications like microwave, high-pressure sterilization, or freezing.

Main Adhesive Types Used in Flexible Packaging

Adhesives in flexible packaging vary not only in carrier type (solvent-based, solvent-free, waterborne) but also in resin chemistry (e.g., polyurethane, acrylic), resulting in distinct adhesion strength, heat resistance, and barrier properties. Understanding the characteristics, advantages, and limitations of various adhesives is crucial for designing high-performance packaging structures, meeting regulatory requirements, and achieving sustainability goals. The following introduces the main adhesive types commonly used in flexible packaging:

Solvent-Based Adhesives‌

Definition‌: Solvent-based laminating adhesives use organic solvents as carriers for adhesive resin systems. These products have a long history of application and are still widely used in high-demand packaging fields.

Advantages‌

High Initial Adhesion Strength‌: Rapid formation of strong bonds, suitable for high-speed production.

Fast Curing Speed‌: Shortens production cycles and improves efficiency.

Strong Adhesion to Various Films and Metal Foils‌: Excellent adhesion to multiple films (e.g., PET, PE) and metal foils (e.g., aluminum foil).

Superior Heat, Oil, and Durability Resistance‌: Suitable for high-temperature sterilization, hot filling, and oily food packaging.

Disadvantages‌

High VOC Emissions‌: Potential risks to the environment and operator health.

Strict Regulatory Restrictions‌: Must comply with stringent environmental regulations.

High Equipment Requirements‌: Requires drying equipment, increasing initial investment.

High Operational Safety Requirements‌: Requires good ventilation to prevent solvent accumulation.

Typical Applications‌

High-Barrier Composite Packaging‌: Such as PET/AL/PE structure films for food and pharmaceutical packaging.

High-Temperature Sterilization Bags‌: Suitable for food packaging requiring high-temperature sterilization.

Hot Filling Packaging‌: For beverages, sauces, and other hot-filled products.

Oily Food Packaging‌: Such as potato chips and nuts, preventing oil penetration.

Summary‌: Solvent-based adhesives are irreplaceable in high-barrier, heat-resistant, and durable packaging applications but require balancing environmental and regulatory pressures.

Solvent-Free (100% Solids) Adhesives‌

Definition‌: Solvent-free adhesives are nearly 100% active resin components, without water or organic solvents as carriers. This system not only reduces emissions but also saves costs in drying and energy consumption.

Advantages

Excellent Environmental Performance‌ (VOC emissions are extremely low)

High-Performance Performance‌, especially in reactive polyurethane (PU) systems

Energy Saving and Consumption Reduction

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Disadvantages

Coating Equipment Needs to Adapt to Higher Viscosity Systems‌

Curing May Require Longer Time or Specific Conditions‌

Relatively Lower Initial Adhesion Strength‌

Typical Applications‌

Used in high-end flexible packaging, food-contact composite films, and structures requiring high barrier properties and low emissions.

Water-Based Adhesives:‌

Definition‌: Water-based adhesives use water as a dispersing medium instead of organic solvents, aligning with the sustainable development trend.

Advantages‌

Extremely Low VOC Emissions‌

Safer for Operators‌

Easier Equipment Cleaning‌

Disadvantages‌

Longer Drying and Curing Times‌

Higher Requirements for Substrate Surface Conditions‌

Slightly Inferior Performance in High-Barrier, Oily, or High-Temperature Sterilization Packaging Compared to PU Reactive Systems‌

Typical Applications‌

Used in composite packaging for medium to low barrier structures, especially in food packaging fields emphasizing environmental sustainability and regulatory compliance.

Reactive Hot Melt Adhesive

Reactive hot melt adhesive primarily consists of moisture-cured polyurethane (PUR). It fully cross-links through reaction with moisture in the air, forming a heat-resistant, high-molecular network structure after curing.
Composition‌: Includes moisture-cured polyurethane (PUR).

Characteristics‌
Curing Mechanism‌: Fully cross-linked through reaction with moisture, resulting in heat resistance after curing.
Advantages‌: High durability, resistance to boiling water and climate, but higher cost.

Advantages of Hot Melt Adhesives‌:

Environmental Friendliness‌
Solvent-free, extremely low VOC emissions, aligning with environmental trends.
Replaces water-based and solvent-based adhesives, reducing environmental pressure.

Production Efficiency‌
Rapid Curing‌: Immediately solidifies after cooling, eliminating drying steps and improving production speed.
High-Speed Production‌: Line speed can exceed 300 meters/minute, shortening production cycles.

Cost-Effectiveness‌
Low Energy Consumption‌: No drying equipment required, reducing energy costs.
Low Cost‌: In non-high-demand applications, cost is lower than water-based adhesives.
Limitations of Hot Melt Adhesives‌:

Equipment Requirements‌
Requires specialized melting and coating equipment, with higher initial investment.
When changing adhesive types, the entire system must be thoroughly cleaned.

Performance Limitations‌
Reactive Systems‌: Higher cost, requiring a balance between performance and budget.

Typical Applications‌

High-Barrier Composite Packaging‌: Such as PET/AL/PE structure films for food and pharmaceutical packaging.
Hot Filling Packaging‌: Used for beverages, sauces, and other hot-filled products.
Oily Food Packaging‌: Such as potato chips and nuts, preventing oil penetration.

Wood Processing and Furniture Manufacturing
Flat lamination and Bonding‌: PUR adhesive can be used for flat lamination and bonding wood, metal, and plastic, enhancing the stability and strength of furniture.
Edge Banding‌: Due to its waterproof and sealing properties, PUR adhesive is the preferred choice for furniture edge banding, effectively preventing moisture and water vapor from entering the panels through the adhesive joint, especially suitable for humid environments.

Textile Industry:
Fabric Bonding‌: PUR adhesive's water resistance and flexibility make it ideal for fabric to fabric bonding, ensuring durability and comfort of textiles.

Packaging Application Scenarios & Adhesive Matching

Conclusion

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In flexible packaging, selecting the right adhesive means achieving a balance among substrate, performance, process, cost, and sustainability.

Although solvent-based systems still dominate high-performance packaging, solvent-free and water-based adhesives are rapidly gaining popularity due to their environmental benefits. With the growing trend toward sustainable packaging, adhesive technology is continuously innovating, providing the packaging industry with safer, more efficient, and more environmentally friendly solutions.