Solvent-Free Polyurethane Laminating Adhesive LF 2077 / Hardener LF 2188: Performance, Processing, and Application in Flexible Packaging

The increasing demand for high-performance, food-safe, and environmentally compliant packaging materials has led to rapid adoption of solvent-free polyurethane (PU) laminating adhesives in the flexible packaging industry. The system LF 2077 combined with Hardener LF 2188 represents a two-component, solvent-free polyurethane adhesive designed for high-speed lamination of multi-layer flexible films and foil structures. This article provides a technical overview of the adhesive’s composition, working principles, processing conditions, and advantages in modern lamination applications.

1. Product Overview and Chemical System

LF 2077 / Hardener LF 2188 is a two-component reactive polyurethane adhesive system composed of:

• LF 2077: Isocyanate (ISO) component
• Hardener LF 2188: Hydroxyl-functional polyol component

When mixed, these components react through polyaddition between isocyanate (–NCO) and hydroxyl (–OH) groups, forming a crosslinked polyurethane network. This reaction is solvent-free, which eliminates volatile organic compound (VOC) emissions and reduces environmental impact compared to traditional solvent-based adhesives.

The recommended mixing ratio is 100 : 80 (by weight), although the hardener proportion may be adjusted between 60 and 80 parts to accommodate different lamination structures and performance requirements.

2. Target Applications in Flexible Packaging

The adhesive is engineered for laminating transparent and metallized films used in food packaging. It exhibits strong adhesion across a broad range of substrates commonly used in flexible packaging, including:

• Pre-treated polyethylene (PE)
• Oriented and cast polypropylene (BOPP / CPP)
• Polyester (PET)
• Polyamide (Nylon)
• Metallized films such as metPET and metCPP
• Aluminum foil

This compatibility enables the adhesive to be used in duplex and triplex laminate structures, typically ranging from two to four layers. Such versatility makes it suitable for snack packaging, retort pouches, stand-up pouches, and other high-barrier packaging formats.

3. Performance Characteristics and Functional Benefits

3.1 Excellent Surface Wetting and Coating Behavior

LF 2077 / LF 2188 demonstrates excellent wetting properties, allowing it to uniformly coat film surfaces even at low coating weights. Proper wetting is essential for maximizing interfacial contact and achieving strong adhesive bonds, especially on low-surface-energy polyolefins.

To ensure optimal adhesion, substrates must meet minimum surface energy levels:

• BOPP / PE / CPP ≥ 38 dyne
• PET ≥ 50 dyne
• PA ≥ 52 dyne

These values typically require corona treatment prior to lamination.

3.2 High Bond Strength and Temperature Resistance

The cured polyurethane network provides:

• Strong interlayer bonding
• Elasticity to absorb mechanical stress
• Resistance to delamination during converting operations

Importantly, the adhesive is suitable for thermal processing conditions, including:

• Boiling: 40 minutes at 100 °C
• Retorting: 30 minutes at 121 °C

This makes it suitable for high-temperature sterilized food packaging, where adhesives must maintain integrity without degradation or migration.

3.3 Optical Clarity and Sensory Neutrality

After full curing, the adhesive layer becomes:

• Transparent
• Odorless
• Aging resistant

These properties are critical for clear packaging applications and for compliance with food safety and consumer sensory expectations.

4. Processing and Lamination Conditions

4.1 Coating and Application Equipment

The adhesive is applied using solvent-free laminating machines equipped with multi-roller coating systems. The two components are metered and mixed continuously in a dosing unit and delivered directly to the application nip.

Typical coating weights range from:

1.2 – 3.2 g/m² (dry)

The optimal coating weight depends on:

• Substrate roughness
• Ink coverage in printed laminates
• Final performance requirements

4.2 Pot Life and Viscosity Development

A key processing parameter for reactive PU adhesives is viscosity build-up after mixing. At 40 °C, the viscosity of the mixed adhesive increases rapidly:

• 15 min: ~1,200 mPa·s
• 30 min: ~2,200 mPa·s
• 45 min: ~3,600 mPa·s

This indicates a limited working window, requiring precise process control and continuous dosing to avoid premature gelation or coating defects.

4.3 Web Tension and Winding Control

The technical data emphasizes that accurate web tension and winding programs are essential to prevent:

• Telescoping
• Curling
• Delamination

Because solvent-free adhesives have higher viscosity and lower penetration compared to solvent-based systems, mechanical stresses during winding can significantly influence laminate quality.

5. Curing Behavior and Post-Processing

Curing is achieved through a moisture-independent chemical reaction between the two components. Recommended curing conditions include:

• Temperature: 35 – 45 °C
• Handling time: Rewinding and slitting after 24 hours
• Full cure: 3 – 5 days at room temperature

The ability to proceed with further lamination (e.g., triplex structures) after 24 hours improves production efficiency while ensuring sufficient bond development.

6. Food Contact Compliance and Regulatory Status

The adhesive system is formulated to comply with major international food-contact regulations. Once fully cured, it conforms to:

• FDA 21 CFR §175.105
• BfR Recommendation XXVIII
• EU Plastics Directive 2002/72/EC and amendment 2004/19/EC
• Chinese standard GB 9685-2016

This multi-region compliance makes the product suitable for global packaging supply chains and export-oriented packaging converters.

7. Safety and Handling Considerations

Because the adhesive contains polyisocyanates, strict industrial hygiene practices are required during handling and application. Key safety measures include:

• Installation of efficient exhaust systems at coating units
• Monitoring of airborne isocyanate concentrations
• Use of personal protective equipment to avoid skin contact

Although the product is classified as non-dangerous for transport, improper handling may still pose occupational health risks, particularly respiratory sensitization associated with isocyanates.

8. Storage Stability and Shelf Life

Both components have a shelf life of nine months when stored in unopened containers within the temperature range of –30 °C to 30 °C. Once opened, containers should be resealed immediately to prevent moisture ingress, which can cause premature reaction of the isocyanate component and reduce performance.

9. Process Reliability and Quality Control

The final laminate quality depends on multiple interacting variables, including:

• Ink chemistry and curing level
• Film surface treatment
• Additives and slip agents
• Environmental humidity and temperature

Therefore, the manufacturer recommends compatibility trials and periodic cleaning of the coating unit every 6–8 hours to ensure stable production conditions.

Notably, mixing this adhesive with other grades is discouraged, as uncontrolled chemical interactions may compromise curing behavior and regulatory compliance.

10. Advantages Over Solvent-Based Laminating Adhesives

The LF 2077 / LF 2188 system provides several advantages compared with conventional solvent-based adhesives:

• Zero solvent emissions, supporting environmental regulations and worker safety
• Higher lamination speeds due to absence of drying ovens
• Lower energy consumption and reduced plant footprint
• Improved optical clarity and reduced odor in finished laminates

These characteristics align with the packaging industry’s transition toward sustainable and energy-efficient converting technologies.

Conclusion

LF 2077 / Hardener LF 2188 is a versatile solvent-free polyurethane laminating adhesive designed for high-performance flexible packaging structures. Its strong adhesion to a wide range of polymer films and metalized substrates, combined with excellent thermal resistance and regulatory compliance, makes it particularly suitable for food packaging applications including retort pouches and multilayer barrier films.

By providing fast curing, high clarity, and compatibility with modern high-speed laminators, the system supports both productivity and sustainability goals in packaging converting operations. However, successful implementation requires careful control of mixing ratios, substrate surface energy, and process conditions, as well as strict adherence to safety protocols associated with isocyanate-containing materials.

Overall, this adhesive system represents a technically advanced solution aligned with current industry demands for solvent-free, food-safe, and high-performance lamination technologies.