Elastic Attachment Coating for Nonwovens: High-Speed Rotary Screen Technology
In diaper production, elastic materials (strands or film) are attached to the nonwoven backsheet and leg cuffs to provide fit. The adhesive must bond the elastic (often polyurethane or natural rubber) to the nonwoven while withstanding repeated stretching. Hot melt pattern coating machines apply adhesive in a continuous or intermittent pattern along the elastic path. Rotary screen coaters are preferred because they can apply a fine, controlled dot pattern that remains flexible and does not interfere with elastic elongation. The coat weight is typically 5-15 gsm. The adhesive is a high-elongation SBC-based formula, capable of stretching >500% without breaking.
The rotary screen for elastic attachment has a specific pattern: often a series of dots in a line (e.g., 1 mm dots at 2 mm spacing) or a continuous wavy line. The screen is typically 50-150 mm wide, corresponding to the elastic width. The machine may have multiple screens for multiple elastic strands (e.g., one for each leg elastic). The screen rotates against a backup roll, and the nonwoven passes between them. The hot melt adhesive is forced through the screen by a heated squeegee. The elastic strand is then laid onto the adhesive pattern and laminated by a nip roll. The machine runs at 300-600 m/min, synchronized with the diaper line.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Key machine parameters for elastic attachment: The adhesive temperature is 150-170°C. The viscosity should be 4000-8000 mPa·s. Too low viscosity causes bleeding through the nonwoven; too high causes poor dot formation. The squeegee pressure (0.2-0.6 MPa) affects dot height. The gap between screen and backup roll (0.1-0.3 mm) must be uniform. The screen mesh count is 40-80. The backup roll is typically chrome-plated steel with a release coating. An electrostatic pinning or vacuum can help hold the nonwoven against the roll. The elastic strand is stretched (draw ratio 2-4x) before lamination; the adhesive must hold the stretched elastic in place. After lamination, the composite may be folded and cooled.
Defects specific to elastic attachment: “Elastic pop-out” – the elastic pulls away from the adhesive, especially at the ends. Increase coat weight or use a more aggressive adhesive. “Adhesive stringing” – threads of adhesive between dots; reduce temperature or increase suck-back. “Nonwoven burn” – if the adhesive is too hot, it can melt the polypropylene nonwoven; lower temperature to 140-150°C. “Inconsistent pattern” due to screen clogging; clean screen. “Elastic snap-back” after cutting; ensure adhesive has sufficient cohesive strength. The machine should have a glue pattern inspection system (camera) that verifies dot presence and position relative to elastic. If a missing dot is detected, the line may reject that product.
Maintenance of rotary screen coaters for elastic attachment: The screen is fragile and must be handled carefully. Clean after each shift using hot melt cleaner and compressed air. The squeegee blade (polyurethane) wears every 1000-2000 hours; replace when dot height decreases. The backup roll should be inspected for adhesive buildup; use a scraper. Bearings on the screen drive should be lubricated daily. The gear pump supplying adhesive to the screen must be precise; calibrate flow rate weekly. For high-volume production, a spare screen and squeegee are kept ready.
Future trends: Hot melt coating machines for nonwovens are moving toward lower coat weights (3-5 gsm) to save material and improve softness. New adhesives with lower density and higher bonding efficiency are emerging. Also, smart machines with self-adjusting pattern control using vision feedback are being developed. By mastering rotary screen hot melt coating for elastic attachment, manufacturers produce reliable, comfortable diapers that maintain fit during use.
