By Courtney Saba
Digitally produced fine art prints are revenue generators for many print service providers (PSPs). Customers need prints that withstand challenges such as precipitation and human handling. Liquid coatings aid in achieving this. In addition to protecting, they enhance canvas prints by offering richer colors and different textures to strengthen the artistic intention. When applying liquid coatings, there are several options to consider—brush, roller, spray, or lamination. Each presents its own challenges.
Liquid coatings serve multiple purposes. Physical protection and artistic enhancements are the main reasons a PSP would choose to use them. There is a decreased possibility of UV light degradation, moisture, humidity, handling, and abrasion when a liquid coating is used. In addition to guarding a print, liquid coatings can also prevent the ink set from performing poorly and eliminate the possibility of glare.
“Liquid coating keeps inks from cracking when a canvas print is stretched during the finishing process,” explains Nate Goodman, product manager, Drytac Corporation.
Sarah Perkins, sales and marketing coordinator, Marabu North America, provides an example of when she created a canvas print for a colleague and did one with a liquid coating and the other without. “When I went to stretch the uncoated canvas, the ink immediately cracked at the corners of the piece and started peeling away from the canvas,” she shares. The print that was coated not only provided more saturated colors throughout the graphic, but it was “night and day” how the canvas reacted upon stretching.
Goodman shares that besides physical protection, liquid coatings also help to manage gloss levels and reduce glare and reflections that detract from an image.
While offering protection, liquid coatings provide the added benefit of visual improvements to increase the quality of the canvas print. “It enhances the ‘pop’ factor that makes the colors more rich and vibrant,” explains Michael Clementi, experience center team leader, LexJet Corporation. The color quality that can be achieved after applying a liquid coating is a benefit recommended by multiple companies that manufacture this product.
Greg White, director of sales and marketing, Premier Imaging Products, finds that besides artistic enhancement, different types of coatings improve the end result. “Using a gloss, satin, or matte finish changes the final appearance of the canvas regardless of the initial type of finish.”
White continues by providing the example of beginning with a typically less expensive matte canvas and applying a gloss coating to yield a high-gloss finished product. Another suggestion is applying specialized coatings such as embellishments that provide the appearance of a three-dimensional brush stroke.
Liquid coatings are applied with a brush, roller, spray, or laminator. The size and type of media and intended final appearance determine which method is chosen.
“It is important to consider how compatible a coating is with the inks, media, and application method used. Thicker coatings can be rolled or brushed on, but the coating must be thin enough to run through a spray nozzle if being sprayed on,” recommends Goodman.
Brush application is a popular method. “It is a quick and easy way to coat canvas and you achieve good square footage per gallon. When you use spray, you lose some coating to the atmosphere so square footage is only about 60 percent of what you’d achieve from a brush and roll application,” suggests Perkins.
While a brush is one of the more common and inexpensive ways to apply a liquid coating, it comes with its challenges. “A closed cell brush or roller minimizes the amount of air bubbles during application. But, since the coating is applied in sections with this method, it can result in an uneven or streaky finish. It is also difficult to control the thickness of the coating applied to the media with a brush,” advises Ike Harris, president, Daige.
Rollers are also a low-cost application option. “It is most often a printmaker’s go-to method. It’s simple and low cost to get into, requiring very little ancillary equipment or technical knowhow,” says Will Vermillion, inside sales, Breathing Color.
However, rollers can be difficult to use with larger pieces of art because the coating tends to dry too quickly, causing inconsistencies in the final product. Even with smaller pieces it’s sometimes hard to get the coating to look even and precise.
Spray guns are efficient and easy to use, both White and Clementi point out, but require a bit of technique. Using this method requires the ability to judge how much coating has been applied, as well as the thickness. Another thing to keep in mind with the spray method is the footprint you have to work in. A spray booth is suggested, but will take up a good amount of space.
“Spray applications are nice because they can help avoid paint roller transfer, which is when the coating re-wets the ink and colors transfer from the canvas to the roller. With a spray application the coating settles from above as opposed to disrupting the surface,” shares Perkins.
Lamination is the final option for applying liquid coating. “By far, a liquid laminator is the quickest, most consistent option,” says Goodman. He explains that certain liquid laminators use a Mayer bar to evenly apply the coating across the image. This is successful in metering the thickness of the coating applied and drying the print before winding it on a core.
Harris outlines three different types of lamination—roll to roll, sheet-fed motorized, and manual. Roll to roll laminators apply the coating to a roll of canvas, dry the coating, then rewind the canvas on a roll. Sheet-fed motorized devices coat individual sheets. Manual laminators apply a smooth, even coating to sheets of canvas.
“Liquid laminators are ideal for those who don’t have the space for a spray booth or brush and roll application—the canvas has to lie flat somewhere and dry in between coats and that can take up a lot of space. They also allow the operator to go do other things while the canvas is running,” recommends Perkins.
Liquid coatings are meant to protect and enhance canvas prints. However, a number of challenges—bubbles, pinholes, ink uptake during rolling, orange peel effect, drips/runs, craters, and unevenness—can occur while using any of the application methods. All are preventable. Additionally, the type of coating and canvas used can present issues.
When spraying liquid coating, a challenge is the liquid running on the canvas. “You’re likely applying too much coating, try increasing your hand speed. Also keep your print at about a 60 degree angle on the easel or spray surface,” suggests Vermillion. He also advises on how to avoid pinholes and bubbling during and after application. After application, if there are pinholes, there is not enough coating being applied during the first coat. If there is bubbling during and after application be sure the liquid is stirred and never shaken.
Clementi adds that for spraying on canvas, “if you have it set too heavy, gravity will cause the coating to coagulate and form drops. This may also cause the spray to form a texture on the surface of the canvas by spitting out too much coating. The quality of the gun and the size of the nozzle also determines how smooth and even the spray applies.”
The biggest challenge for a PSP working with a liquid laminator is keeping the machine running smoothly. To do so, it is important that it regularly undergoes maintenance. Machine settings should also be addressed on a consistent basis to ensure it is working in an optimum environment.
If applying by a roller, ink lifting can occur. This happens when the roller is allowed the time to dry completely. Clementi recommends two coats, one vertically and let dry completely, and then apply the second coat horizontally.
Another common concern is streaking. If there are thicker lines where the edges of the roller applied the coating, go back over them and level them out while still wet. This eliminates any form of streaking.
When using a roller or brush, Perkins cautions against pushing down too hard, the result is bubbling. “Bubbling can also be a result of an incompatibility with the inkjet receptive layer and the coating, causing the air in the pores of the inkjet receptive layer to be pushed to the surface—but nine times out of ten it is just pushing down too hard with the roller or brush.”
Aside from method deficiencies, the coating itself could create some challenges. “Before the liquid coating can be applied, it must be thoroughly mixed. If it is over agitated, bubbles that cannot be popped may appear. To avoid issues like outgassing, reticulation, and streaking, the coating must work well with the print,” explains Goodman.
Coatings should never be mixed with a wood-based product, according to Vermillion. “Never allow wood, cardboard, or newspaper to come in contact with your coating or prints. This can and will likely cause acid contamination and yellow prints.”
Much like a coating can cause difficulties, so too can the canvas. It is important to match the canvas type with the coating. “Water-based liquid laminates are designed for use with water-resistant canvases printed with UV or pigmented inks. If you try to coat a regular canvas with pigmented inks, then the liquid coating will lift the inks,” advises Harris.
“Using a moisture sensitive canvas, as opposed to a matte water-resistant canvas, can cause cracking. It is important to remember that if you are using a moisture-sensitive canvas, you need to use a solvent-based coating as opposed to a water-based coating,” advises Perkins.
Some canvases also have a pre-coat that may cause bubbles. “Although the majority of canvases can be coated properly with the liquid coating, some canvases have a pre-coat that causes excessive bubbles. Instead of the bubbles popping and drying smoothly, they dry into craters,” cautions Harris.
The benefits of using liquid coatings for canvas prints outweigh any challenges. It is important to understand the different application methods before starting a project. When the correct combination is used, the result is a protected canvas print.
Jan2016, Digital Output