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Printing on Specialty Substrates

(April 2010) posted on Tue Mar 23, 2010

Managing variables associated with the substrates you use is critical to quality. Find out how to work with some popular, but picky, materials.

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By Gail Flower, Johnny Shell

Aluminum comes in coils or precut sheets with a coated, printable surface on one or two sides. Uncoated is designated as clear/clear. One side coated is designated as white/clear. Aluminum can be found in different colors either through powder coatings or enamel coatings or organic/inorganic coloring agents for anodized aluminum. If it has been coated with enamel, it has usually gone through a process called conversion coating or passivation, which prepares the surface for coating. In many cases a thermoset acrylic enamel designed for exterior applications is used. White-coated aluminum can go through the oven only one time before it yellows. Powder-coated aluminum, as with steel, can be heat processed several times without yellowing.

Anodized aluminum is done through a controlled natural oxidation process when aluminum is exposed to the atmosphere. Electricity and chemicals are used in conjunction to produce a hard, transparent surface that is integral with the base aluminum. The anodizing process includes a cleaning and etching pre-treatment and the buildup of the anodic film that is built on the aluminum itself. The hard, porous film can then be colored by organic and inorganic coloring agents. Later in the process, a hot water bath treatment causes the pores to swell shut, locking in the colorant.

Concerns for steel and aluminum include water stains on the surface of metals from when water condenses or gets trapped between sheets. This can cause white rust in the case of galvanized steel and marks on the anodized aluminum. The metals can stick together when exposed to large amounts of humidity, causing surface damage. Coating softness and excessive heat can also cause blocking, either on the enamel or powder coating when improperly cured. Wear gloves to prevent the transfer of oil from hands. Make sure to square all stock edges before setting up registration for a multicolor job, and keep stock as flat as possible to ensure uniform ink application.

You can print onto hard woods, soft woods, particle board, and veneers that are properly prepared for the application. All woods absorb moisture at different rates. Treating wood with a sanding sealer before printing allows the ink to set on the surface. Softer woods require more sealer applied in multiple coats prior to printing. Most commercial wood-sanding sealers suffice. Apply it by spraying, painting, or roller coating.


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