Liquid coatings can change the durability, look, and feel of all types of printed materials. Different formulations exist to improve the visual appeal or endurance of the hundreds of different products that can be produced with different combinations of inks, toners, and substrates.
For example, different coatings have been developed for coated offset paper, packaging paperboards, canvas, wallpapers, vehicle-wrap vinyls, plastics, aluminum composite boards, and corrugated.
A direct-mail postcard must withstand scuffing from mail-handling equipment, while an outdoor vinyl wall mural needs to endure long-term exposure to sunlight, pollution, and/or graffiti. The coatings applied to inkjet-printed art canvases must remain flexible when the canvas is stretched around the wooden bars in a gallery wrap.
Here is some of the terminology related to different types of post-print coatings, coating techniques, and coating equipment.
Types of Coatings
Aqueous Coatings are low-cost, water-based liquids that are typically designed to protect higher volumes of printed pages on paper. Available in matte or gloss finishes, aqueous coatings protect prints such as business cards, magazine covers, and full-color book pages from fingerprints and scuffing. They also keep metallic inks from tarnishing when exposed to air. Aqueous coatings are typically applied in-line during offset press runs and dried with forced air or infrared systems. Special formulations of aqueous coatings can be overprinted with toner-based addressing systems or written on with a number-two pencil.
A Soft-Touch Coating is a specialized aqueous matte coating that adds a velvety, suede-like feel to the printed piece. Textured coatings use a mix of large and small particles to create the desired effect.
Solvent Coatings were developed to protect fine-art prints output with water-based dye inks or on materials that aren’t resistant to water. The print colors will run if an aqueous coating is applied to aqueous dye inks. Solvent coatings are typically applied with handheld rollers, brushes, aerosol sprays, or spray guns. The work area must be well-ventilated to minimize exposure to VOCs (volatile organic compounds) in solvent coatings.
UV Coatings form a hard film on the print surface when exposed to controlled wavelengths of UV light. Different UV coatings have been developed for output from toner-based presses, inkjet presses, and wide-format printers that use latex, solvent, or UV-curable inks.
Varnish is a clear gloss, matte, or satin ink that is typically used to add shine or visual effects to selected areas of a print. Varnishes can be applied in-line on an offset press or with a digital enhancement press that uses inkjet printheads.
Flood Coating covers the entire printed page with the coating. Flood coating can be used to add a gloss or satin surface to matte papers printed at high speeds on a production inkjet press. The coating helps make digitally printed pages look like offset-printed pages.
Spot Coating changes the look or feel of logos or text on a printed page. On an offset press, an additional plate must be created to apply a spot coating to a specific area of the print. Digital embellishment presses (such as Konica Minolta’s MGI JetVarnish or Scodix presses) use clear UV-curable inks to apply spot coatings to inkjet prints on paper, synthetic papers, and paperboards used for folding cartons. The placement of the spot coating is dictated by data from the digital print file.
Types of Equipment
Web-Fed Coaters are built to handle the rolls of materials printed on offset or digital web presses. They are built to handle different roll widths and sizes. Tec Lighting makes high-speed Web UV coating machines for continuous feed inkjet printers.
Sheet-Fed Coaters are designed to apply coatings to prints on cut sheets. Shops that need to coat a high volume of printed sheets can use a coater that feeds and stacks prints automatically. Manual sheet-fed coaters are available for coating small runs of prints.
Anilox Metering systems use laser-engraved rollers to apply a consistent thickness of coating on every printed sheet.
Some coaters for production inkjet or toner presses can coat both sides of printed papers simultaneously. Other coating machines can also apply pre-print primers to improve ink or toner adhesion to films, plastics, and other super-smooth substrates. Some models can be set up in-line with die-cutting, hot-foiling, creasing, folding, and perforating prints.
Roller Coaters use rollers to feed sheets of thin and thicker rigid materials beneath a series of doctor rollers, scrapers, and application rollers that apply a controlled thickness of the coating. Specialized roller coatings are used to apply coatings to flat sheets of glass, laminated wood, and metals.
Liquid Laminators are wide-format roll-to-roll coaters. Devices such as the Marabu StarLam 1600 and Tec Lighting MegaCoat XL were created as an efficient, low-cost alternative to applying adhesive-backed laminating films to flexible prints from 50 to 63 inches wide. Many wallcovering materials and vehicle wrap graphics are protected with liquid laminates. The Welte AquaSeal 3300 can apply liquid coatings to rolls of flexible materials up to 129 inches wide.