Hot Melt Coating for Nonwoven Fabrics: Breathable and Flexible Bonding Solutions
Nonwoven fabrics are widely used in hygiene (diapers, sanitary napkins), medical (surgical gowns, drapes), and industrial (filters, wipes). Hot melt adhesive coating on nonwovens must provide strong bonding while maintaining fabric softness, breathability, and liquid resistance. Unlike coating on films, nonwovens are porous, so adhesive can penetrate and cause “strike-through” (adhesive visible on the opposite side) or reduce breathability. Therefore, pattern coating (dots, spirals, or random) is preferred over full width coating. Typical coat weight ranges from 2 to 30 gsm. Common hot melt types: SBC-based (styrenic block copolymers) for elastic attachment, and polyolefin-based for lower odor.
The primary coating method for nonwovens is the rotary screen applicator or spiral spray system. Rotary screen applies dots or lines with good control of coverage area (15-40%). Spiral spray uses a nozzle with swirling air to create a fine, open pattern. Both methods require the hot melt coating machine to have a heated head, precise temperature control, and fast on-off valves for intermittent application. For nonwoven lamination (e.g., top sheet to acquisition layer), a full-width pattern coater with 1-2 mm dots spaced 3-4 mm apart is common. The machine must ensure that the adhesive does not migrate to the surface of the top sheet, which would feel sticky. Low coat weight (3-8 gsm) and high viscosity help prevent strike-through.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Adhesive selection: For nonwovens used in diapers, the hot melt must have good flexibility (low modulus) to not stiffen the fabric. The softening point should be high enough (90-110°C) to resist body heat, but not so high as to require excessive temperature that could melt the nonwoven (many nonwovens are polypropylene, melting point ~160°C). The open time must be short (0.5-1 second) because lamination occurs immediately. The adhesive should have no odor. For medical drapes, the adhesive must be breathable (allow water vapor transmission) and not irritate skin. Some machines apply adhesive in a “full coverage but porous” pattern using a special screen that creates a mesh of adhesive.
Machine configuration for nonwoven coating: The hot melt coating machine is typically integrated into a high-speed nonwoven line (200-500 m/min). The coater is positioned after the nonwoven formation and before the winder. It may have multiple applicator heads for multi-layer lamination (e.g., top sheet + acquisition layer + backsheet). Each head has independent temperature and pattern control. The nonwoven web is held flat using a vacuum conveyor or a large backup roll. Because nonwovens have low tensile strength, tension must be kept very low (2-4 N/cm width). Use a dancer roll with light air pressure. The backup roll is often covered with a soft rubber (Shore A 30-40) to prevent damage to the nonwoven.
Defects and solutions: “Strike-through” – adhesive penetrates to the opposite side. Reduce coat weight, increase viscosity (lower temperature), or use a less porous nonwoven. “Fibers sticking to roll” – adhesive may transfer to backup roll; use a release-coated roll or a doctor blade. “Lack of bond” – insufficient adhesive or temperature; increase coat weight or raise adhesive temperature. “Pattern distortion” – web flutter; stabilize with vacuum. “Smoking” – adhesive degradation; lower temperature or improve ventilation. Regular cleaning of the rotary screen or spray nozzles is required. For rotary screen, the screen should be ultrasonically cleaned every 2 weeks. For spray nozzles, daily cleaning with solvent or hot flush.
Quality control: For nonwoven products, bond strength is tested by peeling at 180°, and breathability is measured by air permeability (Gurley). The coated nonwoven should have similar drape and hand feel as uncoated. A common specification: bond strength > 2 N/25mm, air permeability loss < 30%. Online inspection using a camera can detect missing adhesive pattern. Some machines use a radioactive or optical sensor to measure coat weight on the porous web (difficult because of web variability). Process control often relies on pump flow and line speed, with periodic manual sampling. By optimizing the hot melt coating machine for nonwoven fabrics, manufacturers produce comfortable, high-performance hygiene and medical products.
