Solvent-Based Polyurethane Laminating Adhesive LB 165A / Hardener LB 165B: Properties, Processing, and Packaging Applications

1. Introduction

Flexible packaging plays a crucial role in modern food, pharmaceutical, and consumer goods industries. Multilayer laminated films are widely used because they combine the barrier, mechanical, and sealing properties of different materials into a single structure. Achieving reliable lamination requires high-performance adhesives capable of bonding dissimilar substrates such as polyethylene (PE), polypropylene (PP), polyester (PET), and aluminum foil. Two-component solvent-based polyurethane adhesives remain one of the most widely adopted technologies due to their superior bonding strength, thermal resistance, and chemical durability.

LB 165A combined with Hardener LB 165B is a two-component polyurethane laminating adhesive designed for flexible packaging applications requiring medium-to-high performance. The adhesive system demonstrates strong adhesion, excellent wetting, and resistance to harsh conditions such as boiling and retort sterilization.

2. Chemical Nature and Adhesive System Design

LB 165A is the polyol component, while LB 165B is an isocyanate-based hardener. When mixed, the components react to form a crosslinked polyurethane network. This reaction generates a thermoset adhesive layer with high mechanical integrity and chemical stability. The solvent carrier, primarily ethyl acetate, ensures appropriate viscosity and processability during application, allowing uniform coating and rapid evaporation in drying ovens.

The adhesive contains solids content of approximately 65% for LB 165A and 75% for LB 165B, enabling good coating efficiency while maintaining manageable viscosity during gravure or smooth-roll application.

3. Substrate Compatibility and Lamination Structures

One of the major advantages of LB 165A / LB 165B is its broad compatibility with common packaging substrates. The adhesive provides strong bonding for:

• Aluminum foil
• Pre-treated polyethylene (PE)
• Pre-treated polypropylene (BOPP, CPP)
• Polyester (PET)
• Polyamide (Nylon)
• Metallized films such as met-PET and met-CPP

This versatility makes the adhesive suitable for both duplex and triplex laminate structures, including film/film, film/metallized film, and film/aluminum foil combinations. It is particularly recommended for thicker polyethylene films in the range of 70–130 μm, where strong bonding and good stress distribution are required.

4. Key Performance Characteristics

4.1 Wetting and Initial Tack

The relatively low viscosity of the adhesive system allows excellent surface wetting. Good wetting ensures the adhesive penetrates microscopic surface irregularities, increasing contact area and resulting in higher bond strength. High initial tack further improves lamination efficiency by allowing early handling and reducing the risk of delamination during rewinding.

4.2 Thermal and Sterilization Resistance

A critical requirement in food packaging adhesives is resistance to high-temperature processes such as boiling and retort sterilization. The cured LB 165 adhesive system can withstand:

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

These properties make it suitable for packaging of ready-to-eat meals, sauces, and other heat-processed foods.

4.3 Chemical Resistance and Aging Stability

The crosslinked polyurethane structure provides strong resistance to chemicals, oils, and plasticizers. In addition, the cured adhesive film is odor-free, transparent, elastic, and resistant to aging, ensuring long-term integrity of laminated structures during storage and distribution.

5. Mixing, Dilution, and Pot Life

5.1 Mixing Ratio

The recommended mixing ratio is 20 parts of LB 165A to 3.5 parts of LB 165B by weight. However, the hardener content can be adjusted between 3.0 and 4.0 parts depending on substrate type and metallized film bonding requirements.

5.2 Dilution and Solvent Selection

The adhesive system can be diluted using ethyl acetate, acetone, or methyl ethyl ketone (MEK). Water content in the solvent must remain below 300 ppm to prevent undesirable reactions with isocyanate groups. Aromatic and alcoholic solvents are not suitable because they can interfere with curing and reduce adhesive performance.

5.3 Pot Life Considerations

After mixing, the adhesive has a pot life of approximately 8 hours at standard conditions. In tropical environments where temperature exceeds 28 °C and humidity surpasses 60%, the pot life reduces significantly to about 2 hours. This limitation highlights the sensitivity of polyurethane systems to moisture and temperature, which accelerate crosslinking reactions.

6. Application Process in Dry Lamination

6.1 Coating Methods

LB 165A / LB 165B can be applied using conventional dry lamination machines equipped with gravure or smooth coating rolls. The coating weight typically ranges from 2 to 3.5 g/m² (dry), depending on film type, surface treatment, and end-use conditions. Printed films generally require a slightly higher coating weight to compensate for ink coverage and surface roughness.

6.2 Drying and Solvent Evaporation

Proper drying is essential to remove residual solvents and avoid odor or delamination. A temperature gradient of approximately 55–65 °C, 65–75 °C, and 70–85 °C across successive drying zones is recommended to ensure gradual evaporation without causing bubble formation or surface defects.

6.3 Lamination and Nip Pressure

After drying, the adhesive-coated film is laminated to the second substrate under pressure and elevated temperature. Increasing nip pressure and temperature improves adhesive flow and interfacial contact, thereby enhancing bond strength and optical clarity.

7. Curing Behavior and Laminate Conversion

Although laminated rolls can be handled and slit within one to two days, full curing of the polyurethane adhesive requires 7 to 14 days at room temperature. Complete curing ensures maximum resistance to mechanical stress, chemicals, and high temperatures. Early conversion or insufficient curing may result in poor seal strength or migration issues in food packaging.

8. Regulatory Compliance and Food Safety

For food packaging applications, adhesives must comply with strict migration and compositional regulations. The fully cured LB 165 system meets requirements of:

• U.S. FDA §175.105 for indirect food contact
• German BfR Recommendation XXVIII
• EU plastics directive 2002/72/EC and amendments
• Chinese GB 9685-2016 standard

This regulatory compliance ensures that the adhesive can be used safely in food packaging when applied and cured according to specifications.

9. Storage, Handling, and Safety Considerations

LB 165A and LB 165B have a shelf life of approximately 9 months when stored between –30 °C and +25 °C in unopened containers. Once opened, the hardener should be tightly sealed and consumed quickly to prevent moisture ingress. Polyisocyanates present in the hardener can cause skin irritation, making protective equipment and careful handling essential during use.

10. Advantages and Limitations

Advantages

• Strong adhesion across diverse substrates
• Excellent resistance to boiling and retort conditions
• Good wetting and low viscosity for high-speed coating
• Compliance with major food-contact regulations
• Transparent and odor-free cured film

Limitations

• Presence of solvents requires explosion-proof equipment and solvent recovery systems
• Limited pot life, particularly in humid climates
• Requires careful control of drying to avoid residual solvent

11. Conclusion

LB 165A / Hardener LB 165B represents a versatile and robust solvent-based polyurethane adhesive system tailored for high-performance flexible packaging laminates. Its combination of strong bonding, thermal resistance, and regulatory compliance makes it particularly suitable for food packaging structures subjected to sterilization and harsh storage conditions. Proper control of mixing, drying, and curing parameters is essential to fully realize its performance advantages. As packaging materials continue to evolve toward higher barrier and sustainability requirements, such polyurethane adhesive systems remain indispensable for achieving durable, safe, and functional laminated structures.