Sheet Fed Hot Melt Coating

The use of hot melt as a bonding adhesive in the industry has been transformed over the past few years and is gradually replacing conventional solvent or water-based systems and flame lamination. Hot melts as bonding adhesives are based on polymers or their compounds, which are formulated to the specific requirement of the application, e.g. melting temperature, initial tack, curing time and crystallization.

The absence of solvents, volatile parts and water, offers an environmentally friendly operating process, and since no additional heating energy is required to evaporate water or solvent and the curing takes place by ambient air temperature or by the humidity of the ambient air, no drying or curing ovens are necessary.

Gravure coating is an old technique whose versatility has been increased by recent technology developments. The gravure coating process relies on an engraved roller running in a coating bath, which fills the engraved dots or lines of the roller with the coating material. The excess coating on the roller is wiped off by the Doctor Blade and the coating is then deposited onto the substrate as it passes between the Engraved roller and a Pressure Roller. This feature is use of conventional gravure. This results in stable bead, which when combined with lamination application gives very good quality and a constant coating weight. A typical configuration is shown in the diagram above.

The gravure coating head consists of a gravure roller and a doctor blade system where the hotmelt adhesive is placed. Both parts are circuit oil heated for an excellent temperature distribution. The gravure of the roller exactly determines the desired uniform add-on and the pattern on the substrate. This is required for minimum coating weights, good bonding strength and soft touch.

Hotmelt adhesives for HYDEN lines are usually melted off-line, in special melting units. For the thermoplastic adhesives an extruder or a tank melter is necessary.

The rotogravure system is the best acceptable coating method, and a must for breathable membranes. Manufacturers of foam/textile laminates for automotive interiors have also recently started using the rotogravure as the best alternative to flame lamination. A tremendous choice of gravures allows an optimal selection of coating patterns and weights. The coating patterns range from regular geometric patterns to random dots and nets and other optical effects.