1. THE SHIFT TO SOLVENT-FREE SYSTEMS
Why Solvent-Free?
| Driver | Traditional Solvent-Based | Solvent-Free Advantage |
|---|---|---|
| Environmental | VOC emissions (100-300 g/m²) | Near-zero VOCs (<5 g/m²) |
| Regulatory | Air permits, reporting required | Simplified compliance |
| Energy | Drying ovens (60-120°C, 20-40m) | No ovens needed |
| Safety | Flammable solvents, explosion risk | Non-flammable, safer |
| Speed | 24-72 hour curing time | Immediate processing possible |
Comparison of Lamination Technologies:
Technology VOC Emissions Energy Use Cure Time Bond Strength
──────────────────────────────────────────────────────────────────────────────
Dry Lamination 100-300 g/m² High 24-72 hrs Excellent
Extrusion Lamination 5-10 g/m² Medium Immediate Good
Solvent-Free 0-5 g/m² Low Immediate Excellent
UV/EB Curing 0-10 g/m² Low-Medium Immediate Good-Excellent
2. SOLVENT-FREE ADHESIVE TYPES
A. 100% SOLIDS POLYURETHANES
Composition: Two-component systems (polyol + isocyanate)
- No solvents, no water – 100% reactive components
- Mix ratio: Typically 1:1 or specific ratios (e.g., 10:7)
- Viscosity: High (10,000-30,000 cPs at 25°C)
- Application temperature: 40-70°C (heated for proper flow)
B. MOISTURE-CURE POLYURETHANES
Mechanism: Reacts with atmospheric moisture
- Single-component system
- Cure: RH 40-70% optimal, 24-48 hours for full cure
- Advantage: Simpler application (no mixing)
- Challenge: Sensitive to humidity variations
C. HOT MELT ADHESIVES
Thermoplastic systems that melt, apply, then solidify
- EVA, PO, APAO-based formulations
- Application temp: 120-180°C
- Instant bond upon cooling
- Limited heat resistance (typically <60°C)
D. RADIATION-CURABLE ADHESIVES
UV or Electron Beam (EB) curable systems
- Instant cure upon exposure
- Specialized equipment required
- Excellent for clear laminations
3. APPLICATION SYSTEMS & EQUIPMENT
Two-Component Metering & Mixing Systems
Critical Components:
- Precision Pumps: Gear pumps or piston pumps (±0.5% accuracy)
- Static Mixer: 20-40 elements for complete mixing
- Temperature Control: Heated hoses, tanks (40-70°C)
- Degassing System: Removes entrapped air from mixed adhesive
Coating Methods:
| Method | Application | Viscosity Range | Coat Weight |
|---|---|---|---|
| Multi-Roll Coater | Smooth films | 5,000-20,000 cPs | 1.0-3.5 gsm |
| Slot Die Coater | Precision coating | 1,000-50,000 cPs | 0.5-5.0 gsm |
| Gravure Coater | Pattern coating | 500-5,000 cPs | 0.5-3.0 gsm |
| Meyer Rod | Laboratory, low speed | 100-2,000 cPs | 1.0-4.0 gsm |