Slot-Die Application Allows Clean Processing of PSAs

Author: 
Shana Leonard
A slot-die system features a rotating rod lip that enables streak-free application of pressure-sensitive adhesives.

When it comes to people, looks shouldn’t matter. But in the medical device industry, an aesthetically pleasing product can be the differentiating factor in the marketplace. Understanding the importance of clean-looking finished devices to an OEM and end-user alike, Extrusion Dies Industries LLC (EDI) has developed a slot-die system designed to provide consistent, streak-free application of pressure-sensitive adhesives (PSAs).

During conventional roll-coating processes, a series of rollers essentially wipes PSAs, which are employed in medical device applications ranging from product assembly to transdermal patches, onto continuous-web substrates. As a result, adhesive application can be marred by unsightly streaks and lines in the coating, according to William Kays, technical account engineer at EDI. Such aesthetic imperfections, he adds, could negatively affect an end-user’s perception of a product.

A slot die-coating process, in contrast, will typically provide a smooth appearance on the coated substrate—except in the case of hot-melt PSAs. This particular type of PSA, Kays notes, is often plagued by streaks and flaws similar to those associated with roll coating. With slot die-coating of PSAs, though, the defects are caused by gels or unmelted components in the adhesive formulation that become trapped at the coating interface when using a slot die with rigid lips.

To avoid this common problem, EDI has engineered its slot-coating die to include a motorized rotary rod lip. “With our die-coating process, you get a smoother appearance,” Kays states. “[Our system] has this rotary rod lip, and that rod actually rotates at a slow rpm; that frees the particles so you don’t have continuous streaks.” EDI also claims that its system accommodates line speeds up to 2000 ft/min, compared with speeds of less than 1200 ft/min that are reached with roll coating. In addition, the company states that its slot die achieves coat weights as low as 0.5 mil, whereas conventional lower limits for hot melts are typically around 1.0 mil.

When paired with a melt delivery system from ITW Dynatec or incorporated into an existing line, the slot die provides a turnkey coating system to OEMs. Additional capabilities include defining the desired coating width and applying thin, accurate coatings. “The benefit there is that companies can do more with less,” Kays says. “Maybe with a less-precise process, they would have to lay down a certain thickness of coating, but they would have a very large tolerance. Using our [die] that is more specialized to the product they are trying to produce, they can decrease their tolerance and be able to save money on the amount of adhesive they’re using.”

Extrusion Dies Industries LLC
Chippewa Falls, WI
www.extrusiondies.com