Application, Roll Coating

The viscosity of elastomeric adhesives determines their method of application. Typically, solvent-borne rubber compounds require low viscosities for application. Thus, viscosities lower than 0.6 Pas for spray, curtain or dip applications are required, whereas for brush application viscosities lower than 5 Pa s are generally used. Roll- coating technology requires viscosities between 5 and 15 Pa s. 

Roll coating is widely used for uniform, whether flat or cylindrical, surfaces including fiber bundles. In a roll coating process, fibers are coated between two rollers, an applicator roller and a backup roller coating is fed continuously to the applicator roller by a feed roller which runs partially immersed in a coating bath and the backup roller pulls the fibers by rotating in opposite directions. Slow... 

Wire is coated by being passed through a plastic extruder, but most materials are coated with solutions, emulsions, or hot powders. The classic brushing process has been replaced by roll coating, spraying, and hot powder coating. The application of polymers from water dispersions to large objects, such as automobile frames, has been improved by electrode-positon of the polymer onto the metal surface. 

In the past, electron beam radiation was applied to produce PSA exclusively however, recent improvements in UV curing technology (precise UV dose control, suitable photoinitiators) permit UV to be used to produce pressure-sensitive adhesives. PSA formulations can vary in consistency from low-viscosity liquids up to solids melting at 80°C (176°F). Therefore, applications may vary from screen printing to roll coating to melt extrusion. Coat weights for most PSA materials vary from 1 to 10 g/m. ... 

Roller Coaters and Sheet Coaters. These arc often used in coil coating where very large, flat surface areas need to be painted quickly. In these methods, the objects to be painted are passed between a doctor blade and applicator rolls. These methods arc suitable only for coatings that arc to be baked. 

This procedure identifies plastisols that are spread-coated on different substrates such as paper, aluminum foil, wood, and plastic sheet or film. Application is by doctor blade, direct roll, or reverse roll operations (Chapter 10). As an example plastisols are roll coated on adhesively primed metal for house sidings, conveyor belts, cloth fabrics, wood panels, and so on. 

The most common methods of paint applications are brush and roller, air or airless spray, roll coating, electrostatic spraying, electro deposition, and dip coating. Many factors affect the choice of method to be used for a particular application. These include film thickness, appearance requirements, and operating cost. 

Direct roll coating method is used for coating thin-gauge sheets or coil stock. The sheet stock is fed between applicator rollers rotating in the same direction as the moving sheet. The apphcator rollers are fed by smaller pick-up rollers that are partially immersed in trays containing the paint. The coat sheet is subsequently fed into an oven for baking. 

In roll coating arrangements of the sort shown in Figure 1, liquid is carried by the pick-up roll into the nip region between it and the applicator roll. Beyond the nip the liquid is, in effect, stretched and split into two films, each carried off... 

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