Thermofusible yarn leverages the thermoplastic properties of low-melt fibers (e.g., TPU, PA, PET) to form heat-bondable yarns through melting, spinning, and composite processes. The core workflow involves the following key steps:
1. Raw Material Preparation
Low-Melt Polymer Selection: Choose TPU, PA, or modified PET based on application requirements. For example, TPU suits low-temperature bonding, while PA is ideal for high-temperature environments.
Additive Mixing: Incorporate antioxidants, plasticizers (e.g., added to TPU to enhance flowability), or functional agents (flame retardants, antistatic agents).
Drying: Pre-dry hygroscopic materials like PA (e.g., PA6 requires 80–100°C for 4–6 hours) to prevent hydrolysis during melting.
2. Melting and Extrusion
Screw Extruder: Melt polymer pellets at material-specific temperatures:
TPU: 100–150°C (avoid exceeding 160°C to prevent decomposition).
PA: 150–200°C (with nitrogen shielding to minimize oxidation).
PET: 120–170°C (precise temperature control for modified PET).
Melt Filtration: Remove impurities via mesh filters (20–100 mesh) to ensure melt uniformity.
3. Spinning and Fiber Formation
Spinneret Design: Customize nozzle shapes (round, profiled, or multi-hole) for desired fiber cross-sections.
Melt Spinning:
TPU: Low winding speed (800–1,200 m/min) to accommodate high elasticity and prevent breakage.
PA: High-speed spinning (2,000–4,000 m/min) to boost crystallinity and tensile strength.
PET: Apply FDY (Fully Drawn Yarn) technology with multi-stage hot-roller stretching (3–5×) for rigidity.
Cooling and Solidification: Use annular or side-blown air systems to quench fibers. Cooling rates and temperatures influence crystallinity (e.g., rapid cooling for PA reduces spherulite size).
4. Composite Processing (Optional)
Core-Sheath Yarn: Wrap low-melt fibers as a sheath around high-strength cores (e.g., polyester or nylon).
Mixed-Fiber Yarn: Blend with other fibers (cotton, hemp, carbon) and bond via hot pressing for multifunctionality.
Coating: Dip base yarns in low-melt polymer solutions (e.g., TPU) to enhance adhesion.
5. Winding and Post-Treatment
Winding and Shaping: Precision winding machines maintain tension to prevent slack or over-tightening.
Heat Setting: Apply thermal relaxation (e.g., PET at 120°C for 30 minutes) to eliminate internal stress.
Cutting and Packaging: Slit to specifications and seal moisture-proof packaging (critical for PA, often vacuum-packed).
6. Quality Control Benchmarks
Melt Homogeneity: Online viscosity monitoring to prevent gel particles or melt fracture.
Fiber Diameter Consistency: Laser gauging ensures ±5% tolerance.
Melting Point Verification: DSC (Differential Scanning Calorimetry) confirms melt range compliance (e.g., TPU melt range ≤15°C).
Bond Strength Testing: Simulate hot-press conditions (temperature/pressure/duration) and measure peel strength (e.g., ≥5 N/cm for medical textiles).
7. Process Optimization Trends
Energy Efficiency: Twin-screw vented extruders for PA reduce drying energy consumption.
Flexible Production: Modular spinning systems enable rapid switching between TPU/PA/PET lines.
AI-Driven Control: Machine learning predicts melt rheology and auto-adjusts temperature/pressure.
