According to a study reported in Nonwovens Industry magazine back in January 2012, more than 20 billion diapers are sold in the US each year. Volumes of that magnitude demand high speed manufacturing processes, and adhesive coatings help make that possible.
Diapers, along with many other nonwoven products are assembled from multiple layers. That means joining dissimilar materials, like putting a plastic backing on a nonwoven sheet. While sewing may be the textile joining process that springs to mind first, it produces only an edge joint or seam, and not necessarily one that's waterproof. Furthermore, industrial sewing machines would struggle to keep pace with diaper lines running at 1,000 pieces per minute of more, and their mechanical complexity would challenge any maintenance crew!
That's where adhesive coatings score. Applied to the nonwoven material by spray or contact roller, the delivery rate is matched to the speed of the material web. That results in a uniform coating ensuring consistency of the finished product and reliable in-service performance. From the manufacturers viewpoint, consistency also makes it possible to reduce the adhesive weight per unit area to the minimum necessary for a reliable bond.
The same goes for any product where nonwoven materials must be joined to other components. Adhesive coatings are easily applied by equipment with few moving parts, (compared to a sewing machine,) so downtime and demands on maintenance staff are minimized. Variations in web speed, especially at start-up and shut-down, are monitored and modern process control technology adjusts the application rate to suit.
Adhesive coatings are the cost-effective way of assembling products based around nonwoven materials. Application can be performed in a continuous process with material usage constrained to the minimum necessary for satisfactory product performance.