Adhesive bleed through can manifest itself in many ways, with some of the most common being strike through, exposed adhesive and migration. Strike through occurs when the adhesive bleeds through the nonwoven, contaminating machine parts on the line. In this case, the air pressure is oftentimes set too high, resulting in the adhesive being blown through the nonwoven. Exposed adhesive, on the other hand, occurs when nonwoven materials have open areas and the adhesives do not have a surface to bond to. The third type of bleed through that manufacturers may also experience is migration bleed through. This occurs when standard hot melt adhesives continue to move and seep into the nonwoven fibers even after it reaches room temperature, also known as “cold flow”.
Bleed through can also happen as a result of factors outside of adhesives. For example, if the main machine is not set according to the original equipment manufacturer’s (OEM) recommendations, there is a higher risk of bleed through. To prevent this, manufacturers should check the compression to ensure it’s not set too high, and confirm that the web and adhesive coating paths are aligned with the original OEM design. A second example of bleed through that could result from outside factors is related to the hot melt application equipment. If the add-on rates of the equipment have been adjusted improperly, and too much adhesive is applied, this can result in poor patterns or globs of adhesive known as “shot”. The final factor to consider is the nonwoven material. Nonwovens with poor formation, or that have had their surface treatment changed by the manufacturer, may also cause bleed through.
No matter what’s causing bleed through, the challenge in the absorbent product industry cannot be solved without all co-suppliers in the market working together. The nonwoven, the machine equipment, hot melt application equipment, and the adhesive are all different pieces to a puzzle; and in order to put the puzzle together we need to be able to see all the pieces and understand how they fit together. This type of collaboration among suppliers is the best and fastest way to resolve bleed through for the industry.
About the author
Bill Pulcano is the North America hygiene technical service manager at H.B. Fuller, a St. Paul, Minn.-based adhesives company. If you have questions please contact the author directly at firstname.lastname@example.org.