By Melissa Donovan
A variety of methods are used to apply coatings to a printed piece. Flood and spot coating practices are two of the most common. While one is seen as more utilitarian and the other attractive, both offer print service providers (PSPs) a chance to enhance the value of applications from direct mail to marketing materials.
Typical coating types include UV and aqueous, both of which are used in flood and spot coating. The print method, substrate, and mechanics of the coating device determine the best fit.
Coatings continue to evolve as digital technologies expand into markets like labels and corrugated board. There is a greater need for UV and aqueous spot and flood coating systems. As more consumers look for eco-friendly, sustainable product packaging, aqueous flood coatings are of particular interest. Similarly, brand owners look to UV spot coating to create an embellished effect.
Above: Kompac Soft Touch spot coating is used to created the textured blanket and puppy in this print.
Flood and spot coating devices are dissimilar in their method of application as well as their purpose. Despite these differences, flood and spot coaters complement each other.
The coating process of each, as conveyed in the actual term “flood” and “spot,” contrasts. “Spot coating is a more advanced technique where a printhead-type application is programmed to put the UV coating on only specified spots whereas flood coating is an even application of the coating on the substrate,” explains Ron Young, product manager, American Ultraviolet.
The purpose of each differs as well. “Flood coating is traditionally used for functional protection of ink from scuffing and to improve the durability of cartons. Spot can be functional, but can also be used for high-end embellishments to create a sensory visual or tactile connection with the audience,” says Sean Tobler, business development manager, Harris-Bruno International.
While flood and spot coating methods are distinctly different, they do complement each other. “Flood coating is used for both aesthetic and protective reasons whereas spot coating is specifically designed for aesthetic purposes. They are complementary because you can flood coat the entire sheet for overall protection and uniformity of gloss and then place a spot coating to further highlight some of the graphic creating a truly embellished print,” shares Moses Nuno, VP of sales, Tec Lighting Inc.
Take direct mail for example. “Every direct mail piece should be flood coated to ensure it arrives to the reader with the same quality it was printed. Flood coating makes the postcard more aesthetically pleasing but also protects it from the mail system. If you wanted to embellish the card further you could add spot coating in a separate process,” suggests Nuno.
Thomas Hayes, president, Kompac, believes “a proper coating not only protects the printed surface from fingerprints, smudges, abrasion, and the outdoor elements, but also enhances the appearance and increases the printed product’s value.”
Each Offers Advantages
Flood and spot coaters each offer specific benefits.
Spot coatings are advantageous for those looking to make a graphic pop. “It is primarily used to embellish specific areas or images on a printed piece. It adds much value and impact when compared to flood coating,” says Anthony Gandara, product manager, Duplo USA Corporation.
For example, Duplo’s DDC-810 Raised Spot UV Coater delivers production output with texture and depth by applying a gloss varnish to defined areas of the substrate. Users upload a raised spot UV layer file in PDF or TIFF format along with an XML file with registration mark data, load the paper in the feeder, and press send.
Flood coatings also have benefits. According to Young, since the flood coat cures the entire output uniformly, this adds a level of color enhancements and durability that PSPs constantly look for.
“Flood coating is a cost effective and efficient way to enhance and protect printed output. Most flood coaters are easy to use. Flood coating does not require any special tool or print plates. The coating is applied to the entire surface of the paper and a variety of varnishes are available for some flood coaters that can also apply textures,” adds Gandara.
Determining which type of coating method to use depends on the business, according to Jim Goff, president, World Wide Graphics Corporation (WWG). “Spot coating is for high-end jobs where you want to pronounce images with gloss on a matte background, while flood coating is a standard for magazine covers and commercial jobs.”
Each method has its own advantages and it’s important to acknowledge the end application and use, agrees Hayes. Considerations include whether the item is mailed, if there is a lot of handling of the finished product, whether it is placed indoors or outdoors, and whether the customer is looking to enhance the visual appeal of the print or protect the surface.
Joining flood and spot coat capabilities together in one device is attractive. Harris-Bruno already offers such an option, its ExcelCoat ZRS. The fully automated flood and spot coater utilizes a flexo-style plate on a quick-change sleeve system. “By switching out the spot coating image plate for a seamless flood plate, the user easily transitions from spot to flood coating in minutes,” shares Tobler.
Kompac also offers a machine with dual flood and spot coating capabilities, the Onyx 30 coating and priming system. Quick changeover technology allows for coating direct mail to marketing materials. A user can also transition between primer, UV, aqueous, and specialty coatings all on the one device.
Admitting that machines exist to offer both flood and spot, Nuno says the devices that perform both are a combination of analog and digital technology, and lean toward analog. “They are overly burdensome for simple flood coating and not very digital when doing spot coating because you have to create a blanket for every spot coating job, which is going in the opposite direction of digital print,” he explains.
Young says future developments may allow for both coating methods in one digital-based device, however there are challenges to overcome including the physical footprint of the coating apparatus and the ability to change between the two modes on the fly.
UV and aqueous coating formulations are available for either flood or spot coaters.
While UV offers a better solution for high gloss, explains Hayes, aqueous provides a soft touch effect. In addition, aqueous is ideal for food-safe solutions whereas UV offers more protection.
In addition, Goff states that “aqueous coatings are a fraction of the cost of UV coatings and have twice square feet coverage per pound.” WWG manufactures an inline web digital inkjet variable data press and offline digital inkjet aqueous coaters that apply aqueous coatings on inexpensive, uncoated digital papers versus coated paper.
With flood coating, both UV and aqueous coatings are commonplace, says Nuno. Spot coating, on the other hand, is UV about 90 percent of the time—especially with inkjet.
“UV is used in both flood and spot coating, the result is a super glossy sheen that gives a rich, saturated, dramatic look to printed colors—further enhancing the visual appeal. When it comes to spot coating, UV is the most commonly used to acquire the desired visual affect,” shares Hayes.
According to John P. Vogel, president, Chesapeake Digital Consultants, representative of Alliance Technology Corporation (ATC), UV is the dominate coating in both flood and spot methods.
What a device is equipped with—UV or aqueous coating, or both—is based on the mechanics of a machine’s pumping system, says Tobler. Certain pumps are configured for UV and others for aqueous.
If a machine is designed to run two pumps, and one pump is constructed for UV and the other aqueous, then both formulations can be used on the same machine. For example, the Harris & Bruno ExcelCoat ZRS series of flood and spot coaters feature separate pumps for UV and aqueous.
Another example is Kompac’s coating system lineup, allowing users to switch between UV and aqueous in minutes. “The aim is to provide the capability of duality—switching between UV and aqueous coating at a moment’s notice,” says Hayes.
Tec Lighting also offers a dual-configured device, the TecWeb—a high-speed web UV and aqueous coater that operates at speeds of up to 125 meters per minute. It features a chamber anilox coating system for uniform controlled coating and a double UV lamp system.
Vogel says there are few coaters that can run both UV and aqueous coatings. This is more difficult for flood coaters in particular, because most are considered roller coaters. “Most flood coaters are set for UV and do not have the best recirculation. Aqueous coatings would dry up on the rollers and become hard. That can be almost impossible to clean up and could ruin the roller.”
The ATC UV-13 Cyclone is an offline, sheet-fed liquid coating system that produces a high-quality finish on a variety of inks, toners, and substrates. An adjustable metering system and independent roller speed control allow the operator to regulate coating thickness with ease. This efficient system is ideal for photobook applications as well as finishing brochures and mailers, greeting and trading cards, and decals.
Coating is cured or dried using tools such as UV bulbs or infrared (IR) dryers. For UV, Nuno believes mercury vapor lamps still dominate the market. “Tec Lighting was a pioneer in the design of efficient UV curing systems and they are in all of our UV coating systems,” he adds.
UV LED light is a newer technology. “UV coating has photoinitiators, which when exposed to a specific UV wavelength of light, cause the coating to cure or transform from liquid to solid instantaneously,” explains Hayes.
Light is executed via bulbs offered in specific wattage measurements. For example, Young shares that most UV roll coater technology uses a single-lamp, 300 watt-per-inch UV curing bulb.
For aqueous-based coatings, heat is required to dry the freshly coated piece—and this is not instantaneous, according to Hayes. This is when features like IR dryers are used.
Tobler believes that drying technology is influenced by desired coat weight, type of coating chemistry, and speed. For example, a faster running speed or heavier coat weight requires more drying power.
Inkjet vs. Toner
Whether a piece is printed using inkjet- or toner-based technology, this factor comes into play when choosing a coating type and the method.
“Inkjet- versus toner-based output affects the type of coating used. As digital engines continue to adjust toners so too might the coating need be altered. Many coating OEMs provide uniform types of coating to be effective for different inkjet and toner types,” shares Young.
For example, standard on the conveyor of American Ultraviolet’s AUV-Coat Series of roll coaters are IR units that aid in the adhesion enhancement of wax toner prints. The six different models in the portfolio not only UV coat, but also aqueous coat with the purchase of an additional aqueous rubber roller.
Every ink is different, from how it reacts to the substrate to how it plays with the coating. After printing, some inks require an IR unit to run over the printed sheet to create the proper surface tension, which allows the coating to adhere, shares Vogel.
Other machines may have a corona treatment unit inline “to alter the surface energy of the sheet to get uniform and smooth coating laydown, no matter the print engine used,” adds Tobler.
Trends affecting coatings include sustainability requirements, the move to digital, and demand for spot UV coating.
Eco-friendly, water-based coatings are popular. “These are not only better for the environment, but they help printers save on costs associated with expensive UV coatings. PSPs need to show customers a commitment to sustainability, and using water-based coatings is a great step in that direction,” states Tobler.
The cost of water-based or aqueous coatings also plays into their allure. “The ability to aqueous coat on uncoated paper saves in paper costs compared to coated papers. Aqueous coating also provides a much glossier, smoother professional finish, while providing protection by sealing the inks as well as scuff protection,” shares Goff.
This smoother aesthetic or what Hayes refers to as “soft touch” is another trend. “It is one of the most common specialty coatings requested for both flood and spot coating digital output. It provides silky smooth, velvety textures to the printed surface of the sheet, giving the impression that the item holds a level of prestige and luxury.”
Vogel believes applications like labels and corrugated products are influential in coating trends, especially as they take a strong lead in the transition to digital. “Coatings are designed for those industries that are hitting the market. The transition to digital becomes easier since a number of coating producers are dedicated to the market.”
“The need for coatings is strong and expanding. We see opportunity in single-pass corrugated printing,” agrees Nuno. Although he is quick to point out more traditional applications in the print space like direct mail also benefit from expanded coating offerings. “We see strong market potential in UV coating continuous web inkjet for direct mail and general commercial print.”
Spot UV coating for a tactile effect is a growing trend. “It gives print providers a way to offer something more than just CMYK. By adding spot UV embellishment, they make print more impactful. They add value to printed products and in return can generate more revenue by charging more for them,” recommends Gandara.
The ability to coat digitally printed materials is multi-faceted. There are flood or spot coating devices, and those can either be equipped with UV or aqueous coatings. These technologies combined help improve the durability, functionality, and aesthetics of a digitally printed product.
Nov2019, DPS Magazine