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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

Uncoated steel provides a cost-effective substrate (common choices are between 24 and 30 gauge). The biggest disadvantages of uncoated steel are the lack of corrosion resistance, its weight, and the danger associated with sharp edges. Consider the weight of the material with regard to on-press pickup, conveyer, and delivery systems as well as transporting it around the facility. Metal, especially steel, also has thermal conductivity, which will affect curing and handling. The condition of the edge can affect screen life, registration, and handling. Material flatness or deflection can affect registration and press-feed and take-off systems. Metal substrates also require special equipment for cutting, forming, embossing, packing, and shipping.

Cleaning plain, uncoated steel before printing is absolutely necessary. A phosphate wash removes manufacturing salts and lightly etches the surface to promote protective-coating adhesion. Steel is commonly painted or powder coated to protect it from rapidly oxidizing in outdoor applications (the most common place for steel installations).

Painting or coating is accomplished by spraying, dipping, roller coating, or powder coating the metal. Powder coating as the name implies, refers to a thin powder (typically polyester) that covers the metal when it is subjected to an electrical charge. The coating has the opposite electrical charge and when the powder is sprayed onto the steel, it is covered with the powder. The powder coating is then heated to 350-450˚F for 15-20 minutes. The polyester coating melts onto the surface and aggressively adheres as it cools. The result is a hard, durable, and environmentally protected metal surface. Solvent-based thermoset inks are typically used to fuse the ink into the hard surface of the powder coating. UV inks are also used, but working closely with your ink manufacturer is vital in selecting the right ink.

Compared to steel, aluminum provides a better strength-to-weight ratio, has better corrosion resistance, and provides excellent formability. Typical sign materials range from 0.020-0.060 in. thick and are typically 3XXX series aluminum with H12-14 temper, a measure of hardness. Aluminum is often used for jobs that require a lightweight, rust-resistant metal.


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