Engraved roll coating

Different roll coating methods and roll arrangements S = steel roll, R = rubber-covered roll, E = engraved roll. (Courtesy of Faustel Corporation.)... 

Engraved roll Provides accurate control over coating uniformity best for extremely low adhesive weights... 

A major part of film, sheet, coating, pipe, profile, etc. lines involve windup rolls. They include winders, dancer rolls, lip rolls, spreader rolls, textured rolls, engraved rolls, and cooling rolls. All have the common feature that they are required to be extremely precise in all their operations and measurements. Their surface conditions include commercial grade mirror finishes, precision bearings and journals are used, and, most important, controlled variable rotating speed controls to ensure uniform product tension control. 

Different types and materials of the rolls The rolls may be made of metal, generally stainless steel or chromium coated steel, but some rolls may be of steel covered with rubber, for instance to apply water-based glues. The roll surface may be flat or notched, grooved, engraved, in order to hold more adhesive on the surface and calibrate the thickness of the coating. They may even have a special pattern which will be reproduced on the sheets to be coated, for instance to apply a given pattern on the substrate and bond only some areas of the substrate. 

The trial runs were performed on a bare roll corona treatment system as well as on an atmospheric plasma treatment system, resident at the same pilot line. For all runs, two PVdC-coated polyester films were post-treated, one in the APT system with a helium/oxygen plasma, the other by means of a corona treater. Another sample constituted the control reference and was not treated. The samples were then printed at 90 mpm on a PCMC press with aqueous ink (Flint Ink) using a laser-engraved anilox roll to 300 lines per inch (Ipi) and a cell volume of 4.8 billion cubic microns (bcm)/sq.in. The printed image provided solid (100%) ink coverage. The calculated ink transfer (thickness) to the film, based upon this cell volume, was approximately 1.9 microns. The printed web drying temperature occurred at 121 °C, with a web temperature of 77 °C. 

Coating thickness limitations are inherently defined by the flexographic process. When engraved anilox rolls transfer coatings to printing plates and in turn to substrates, the process rarely delivers less than 19% or more than 24% of the cell s wet coating content to the substrate surface [3]. There are therefore clear boundaries as to the amount of coating that can be delivered to a substrate surface. These boundaries are defined in Table 9.2. 

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