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The first three articles in this series were specifically related to the use of automatic spraying machines. As stated previously, spraying is the most versatile of automatic application machinery since the surface may be profiled and edges are finished with the same application. While it is true that spraying is the most versatile method, it is not necessarily the most efficient and it is certainly not the “least cost” method of automatic finishing.

If you need to finish a large number of parts that have flat (not profiled) surfaces, the most efficient method of application is by roll coating. Roll coating involves the use of a hard rubber roll to apply the coating directly to the part without the necessity of atomization with spray guns. The several significant advantages of finishing in this manner are as follows:

1) LEAST COST — The coatings cost saving vs. spraying is very significant. We usually consider roll coat finish cost to be only 20 perent of cost by spray. When considering solids content and transfer efficiency issues, spray finishing usually adds up to 25 or 30 cents per square foot. Roll coating cost is commonly calculated to be 4 to 7 cents per square foot.

2) TRANSFER EFFICIENCY — Roll coating transfer efficiency easily approaches 100 percent since the coating is simply recirculated. The coating that is not applied to the part drains down into the original container that then is pumped back to the “nip” of the metering/application rollers. There is no loss of material caused by atomization

3) CLEAR COAT SOLIDS — Almost universally, roll coating clear coats are 100 percent solids UV curable acrylic formulations. Being 100 percent solids, the coatings has zero VOC emissions and UV curing allows for instant total cure. These formulations also have the highest performance characteristics of any industrial coating for wood products. One hundred percent solids UV coatings have the additional benefit of being the “Greenest of the Green” coatings available on the market. They have no VOCs to contribute to outdoor air pollution, nor do they emit free formaldehyde to contribute to indoor air pollution.

4) EQUIPMENT FOOTPRINT — Since UV applications are 100 percent solids, the UV processor (oven) is placed immediately after the roll coater. Coatings are cured within seconds of application since it is not necessary to use ovens to get rid of the solvents (VOC) prior to curing. This allows the use of very small finishing lines.

5) LOW CAPITAL EQUIPMENT COST — Since the roll finishing line is smaller and the machines are considerably simpler than spraying lines, the capital cost for a roll coating line is less than 50 percent that of an equivalent spraying line.

Because of these advantages, it is quite common to see a small roll coat line in the same finishing room with an automatic spraying line since the cost-effectiveness and VOC reduction justifies the additional equipment necessary to roll coat. The usual rule is: “If it can be roll coated – do it!”