Advances in precision and uniformity achieved with a new generation of Ultracoat slot dies enable web converters to apply consistent, distortion-free fluid coatings even at very low coat weights or onto very thin substrates, a leading international supplier of flat dies has said.

Extrusion Dies Inc. (EDI) said the key to the improvements was a new die design.

"As in standard dies, the wet or wiping lip (the lip passed by the substrate after the coating has been applied) is on the upper section of the die: the profile and surface properties of this lip play a critical role in coating quality and consistency. Unlike standard dies, however, EDI's new Ultracoat V die has the flexible lip and lip-adjusting system (used to change the size of the exit gap) on the lower section. This prevents the flexible lip from interfering with wet-lip functions and causing distortions in the coating," EDI said.

"The enhanced coating precision of a fixed wet lip enables converters to improve quality and achieve high throughput rates without sacrificing the versatility of an adjustable flexible lip," said Jeffrey Seckora, EDI product manager for coating dies.

"Because of the improved control over coating application afforded by the Ultracoat V die, some converters will be able to reduce costs by running thinner coatings."

The new-generation die will be particularly valuable for companies running ultra-thin coatings and substrates on high-precision backup rolls, according to Seckora. "For ultra-thin products it is critically important to maintain a consistent distance between the roll and the face of the wiping lip. The new design enables converters to use the flexible lip to tighten the die gap for a very thin coating without affecting the distance between wiping lip and backup roll."

Ultracoat slot coating dies are used for applying hot melts, pressure-sensitive adhesives, photosensitive materials, magnetic media, transdermal patches, inks, waxes, and many other low-viscosity fluids.

"Converters increasingly recognise that slot die coating is a more efficient and controllable alternative to roll coating because it pre-meters coating fluid at a constant rate and is a fully enclosed system that reduces problems with airborne emissions," said Seckora.

The function of the slot die is to maintain coating fluid at the proper temperature for application, distribute it uniformly to the desired width, and apply it to the web. In a typical setup, the die is oriented at 20 to 45 degrees from the horizontal, with the exit slot at the elevated end. The coating substrate moves upward as it passes the lips of the die.

As with previous Ultracoat generations, operators of the Ultracoat V die can use interchangeable inserts on both upper and lower lips to modify the lip profile in accordance with application requirements. They can also adjust the size of a slight setback of the upper lip with respect to the lower lip to accommodate variations in solids content and coating thickness.

To further enhance the precision of Ultracoat dies, EDI supplies these systems: