Hygiene products (diapers, sanitary napkins) hot melt coating
Hot melt coating is the dominant bonding technology in the production of disposable hygiene products such as baby diapers, adult incontinence briefs, and feminine sanitary napkins. These products require multiple layers of nonwoven fabrics, absorbent cores, breathable films, and elastic strands to be bonded together with high reliability, softness, and breathability. Hot melt coating machines in this industry operate at extreme line speeds (300–800 m/min) and apply adhesives in various patterns including spiral spray, slot coat, dot, and bead. Typical adhesive applications include construction bonding (holding the core to the topsheet and backsheet), elastic attachment (gluing elastic strands to the nonwoven), core stabilization (spraying adhesive on fluff pulp or superabsorbent polymer), and waistband or leg cuff bonding.
The working principle is integrated into a highly automated converting line. Nonwoven topsheet, acquisition distribution layer, absorbent core, and breathable backsheet are fed from parent rolls. At multiple stations, hot melt adhesive applicators (spray guns, slot dies, or bead guns) apply adhesive to specific zones. For example, a spiral spray applicator applies construction adhesive in an open pattern to bond the topsheet to the core while maintaining liquid permeability. A slot die applies a thin film of elastic attachment adhesive onto elastic strands before they are sandwiched between layers. The components are combined at nip rollers, and the continuous web is then cut and folded into individual products. The entire process is driven by high-speed servo motors and vision systems for quality control.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Specific hygiene applications: 1) Diaper construction adhesive – bonds the top sheet to the absorbent core and the backsheet, typically applied at 2-10 gsm via spiral spray. 2) Elastic attachment – glues Lycra or polyurethane strands to the leg and waist areas; applied at 2-6 gsm with fine bead or slot coat. 3) Core stabilization – sprays adhesive onto the fluff pulp or SAP to prevent shifting; coat weight 1-3 gsm. 4) Fastening tape – applies high-tack adhesive to the front tape pad. 5) Sanitary napkin wing glue – pattern coating on the wing to attach to underwear. 6) Transfer adhesive for the release paper. The adhesives are typically styrenic block copolymer (SBC) based, with viscosities of 500-3000 cP at 150-170°C, formulated for low odor and skin compatibility.
Advantages of hot melt coating in hygiene: Solvent-free and safe for skin contact. Very high speed capability. Allows open pattern coatings that preserve the breathability and softness of the product. Precise placement reduces adhesive waste and product stiffness. The adhesives are also designed to be "non-skinning" to prevent roll jamming. Furthermore, the use of hot melts enables the elimination of mechanical fasteners in many cases, reducing cost and material use.
Critical parameters: The open time of the adhesive is extremely short (0.05-0.2 seconds) because the laminating nip is very close to the applicator (often within 50-200mm). The adhesive must not bleed through the porous nonwoven; thus, the application pattern and viscosity are carefully controlled. The line speed is synchronized with the adhesive pump and valve timing for intermittent patterns (e.g., elastic strands are glued only at certain intervals). Temperature control of the adhesive is critical; a 2°C drop can cause poor spray atomization (resulting in "ropes" rather than a fine pattern). The system must include automatic splice detection to raise applicators during splices to avoid damaging the die or spray heads.
Maintenance and quality: Hygiene lines run 24/7, so the hot melt coating system must have redundant melters and filters. Spray nozzles and slot dies require cleaning every 24-48 hours to prevent char buildup. Online coat weight measurement using infrared or beta gauges is common, with automatic feedback to the pump. The adhesive supply is often from bulk melters (up to 2000 kg capacity) that feed multiple applicators. For feminine hygiene, low-temperature adhesives (melting at 90-110°C) are used to avoid heat damage to thin top sheets. The hygiene industry is also moving toward more sustainable bio-based hot melts and lower coat weights to reduce plastic usage. Hot melt coating is the enabler of modern, high-quality, and affordable disposable hygiene products, with global consumption exceeding one million tons per year.
