Coating for Digital Print

Posted in Digital Coaters, News

Considerations for Coating Digitally Printed Output

Print service providers (PSPs) often treat digitally printed products with spot or flood coat with either UV or aqueous solutions. It’s important to know the different types of coating because some adversely react to certain substrates. A proper coating can enhance appearance and durability, increasing the digitally printed product’s value.

As digital print grows, new demands affect the process of coating digitally printed output in high-volume production environments. This article focuses on the challenges and considerations of near line and offline coating solutions.

Coating 101
UV coating is popular for digital applications. Vibrant digitally printed applications like posters, book covers, cards, and other paper products with full-coverage images are generally UV coated. This type of coating enhances bright colors and adds value to printed objects while protecting the ink from damage.

While color enhancement makes coating popular, it’s also cost efficient. “UV coating liquid costs about 1.5 cents for a 12×18-inch sheet on both sides,” says Albert Nuno, coating solutions senior advisor, Brandtjen & Kluge.

Like lamination, UV coatings increase product life while enhancing color and vibrancy. Kevin Chen, product manager, Duplo USA, shares that it is popular for direct mail pieces going through the post office system because it protects against smudging.

Before adding coating services, many factors must be considered when looking at equipment. Basic considerations include sheet size, types of coatings, automation, and run lengths. “For some, gloss coating and a handfed machine is enough to handle all of the digital output they want coated, but for others, running the machine inline with another piece of finishing equipment or getting an automated feeder is necessary to keep up with demand,” says Max Allen, dealer manager, Graphic Whizard Inc.

“If you’re looking to just run UV gloss over postcards, then a roller coater may be best. If you’d like to offer high-quality finishes such as high-gloss UV, matte, pearlescent, soft touch, and other coatings with particulates, then a chamber/anilox system would be the right fit,” shares Joshua Bingham, international marketing manager, Harris & Bruno.

Once a PSP has a general idea of what type of a coater is needed, the selection narrows. Some machines offer features where the coating can be changed easily, while others need time to be cleaned. Auto gap features prevent smearing and varnish warm up heaters keep the varnish at an optimal working temperature, points out Chen.

Other considerations include a coater’s lifespan and durability, ease of use, and the ability to apply different types of coating. “The best idea is to pick your preferred coaters, then have each of them run coating over your prints so you can compare,” recommends Bingham.

Considerations and Solutions
In addition to UV, aqueous coatings are available. Aqueous-based coatings typically dry fast and do not require a heating lamp. It’s typically used to protect against smudges, blemishes, and scratches. The coating dries quickly and covers the entire sheet. With a higher gloss, it’s commonly used for direct mail applications. However, aqueous-based coatings may not be suitable for all substrates.

The heavy wax content in some toner-based printers prevents adhesion to the print surface, usually in heavy ink deposit areas. Peter Farmer, international sales director, Kompac Technologies LLC, shares that to provide the correct “keying” to the print, specially developed coatings are available.

For UV coating over digital toners, Nuno says silicone toners are the easiest method and have the widest market for UV coatings. The gloss levels reach from 80 to 90 percent. Wax toners don’t let the silicone-based coatings have a surface retention, so they don’t adhere as well and are a little more difficult to work with, he adds.

Substrate Considerations
Whether a print was produced using electrophotographic or inkjet, as well as the media used in a digital print job plays a large role on which type of coating should be used.

“Inkjet users have to be mindful of aqueous-based coatings, as they can wash out the color intensity. Toner print engines generally require more aggressive formulas to adhere to toner and prevent cracking or peeling,” advises Allen.

It is worth noting that cost-effective, inkjet-optimized coated stocks have limited availability. Slowly, press manufacturers are reformulating their inks to work on standard coated offset papers while more substrate options become available, shares Mike Barisonek, VP of sales and marketing, Epic Products International.

Toner-based output must also be carefully coated. Bingham shares if the wrong type of coating is used, the varnish could rub off and flake because the solution won’t adhere to the toner.

Barisonek adds that substrates used with toner-based inks should be mill coated, otherwise the post printing coating for UV and aqueous dives into the paper fibers. He explains that wax-based toners can also lead to problems for post-printing coating.

When coating inkjet output, also be wary of higher viscosity coatings. Inkjet output paper is generally very porous, which requires higher viscosity coatings to keep the coating from diving into the paper, explains Nuno. Using higher viscosity coatings can cause issues because the thicker coating needs more time to level off and smooth. A UV coater with infrared heating lamps helps speed up the coating flow process.

The substrate used is an essential factor. Farmer shares that non-absorbent stocks obtain the best gloss coating finishes and even some plastics are absorbent.

Synthetic media with low surface tension makes coating difficult, as well as inks and toners found in digital press engines. Bingham explains that corona treating can raise the surface tension of synthetic substrates to aid in adhesion. Glossy and dull-coated paper coat well, but uncoated stock generally dives so that the coating effect is difficult to see.

Allen says universal limitations of substrate types that can pass through a coater, like thin material, can wrap around an applicator roller when it hits the solution. Also, uncoated or overly porous stock will cause the UV solution to dive into the fibers of the page before a UV coating has time to cure. Ultimately, if the characteristics inside the fuser oil, silicone, or ink changes, the formula has to change and the UV varnish needs to follow the characteristics of the ingredient, says Chen.

No matter what substrates need to be coated, there is generally a solution to achieve the best finished look. “With appropriate infrared intensity and the right coating, I have yet to see a coated stock that can’t have a professional, high-quality finish,” admits Allen.

Hybrid Environments
Environments that include both digital and analog printing equipment have special considerations in terms of finishing. For coating equipment, Chen shares that these environments can be tricky because if the humidity is high and a UV coater is running, the UV varnish will not adhere to the paper as well compared to in a controlled environment.

Quality UV coatings don’t create volatile organic compounds, because they produce 100 percent solids, making them environmentally friendly. Nuno suggests that a good maintenance schedule on a UV dryer is key in hybrid environments so that pollutants aren’t produced.

Allen agrees with the importance of maintenance. “UV systems are economical because they recycle the UV solution ensuring there is no waste. With a larger environment and the introduction of spray powder and more paper dust, operators will need to be a little bit more vigilant about ensuring no foreign particles get into their coating reservoir as it will be recycled and end up back on a job,” he says.

Bingham believes the challenge of a hybrid shop is having jobs that look the same no matter which machine they were printed and coated from. “In this situation, the versatility of a chamber/anilox metering system helps,” he comments.

No matter the challenge, a skilled team can overcome any difficulties. “A good understanding of substrate properties, a solid relationship with a coating supplier, and skilled operators make for successful coating,” suggests Barisonek.

Coating Showcase
A number of coating products targeting high-volume digital production environments are available.

Alliance Technology Corp. (ATC) provides the UV-36HA Cyclone Liquid Coating System. Handling a coating width of up to 36 inches and media up to one-inch thick, the device produces a high-quality finish on a variety of inks, toners, and substrates. It features an adjustable metering system and PLC touchscreen. Its dual doctor blade supports duplex media and an IR pre-heater enables increased coating adhesion to wax-infused toners and inks. The ACT UV-36HA Cyclone is designed to protect and enhance output materials from digital and photo printers as well as offset and lithographic presses.

American Ultraviolet provides its AUV-Coat UV coaters in 20-, 25-, 30-, 36-, and 40-inch models. The devices utilize a three roll roller coating and feature the option of both aqueous and UV coating capabilities.

Brandtjen & Kluge offers the OmniCoat UV roller coater series, available in a wide format series with the ability to coat over 5,000 sheets per hour. It’s capable of one-touch operation. The UV coating protects against humidity, scratching, fading, and scuffing while adding increased detail, vibrancy, and enhancing color. It’s available in matte, gloss, or satin.

Duplo USA carries the Ultra 300Ai, a high-end production UV coater built to connect to the HP Indigo 7000 series of print engines. It is designed for higher volume production and can run offline with a high-capacity stacker and feeder that limits reloading feeder and stacker time. It offers a high-quality gloss, satin, or matte finish while protecting from scratches or scuffs. It features a coating speed of up to 148 feet per minute.

The company previewed the Duplo Digital Spot UV coater at Graph Expo 2016. It is designed to add depth to images and enhance the appeal of printed products.

EMT International offers its Chameleon Coater, available in models UVF20, UVF30, and UVF42 for 20-, 30-, and 42-inch web width applications. The UV coater offers a standard speed of 500 feet per minute.

Epic Products International offers the Epic CT-660 and 750, each targeting high-volume digital production environments. Both products are capable of coating 4,000 sheets per hour and have a quick changeover between UV and aqueous-based coating with a touch pad operator interface. They are fully vented and light shielded for operating and pressroom safety.

Graphic Whizard offers the VividCoater XDC 480/660/750, its largest and most automated UV coaters to accommodate higher run length shops. All coaters have an optional 18-inch deep pile feeder and optional patterned rollers and regular rollers. The regular rollers feature a larger diameter to give troublesome coats a smoother finish.

Harris & Bruno offers the ExcelCoat series of offline/inline UV and aqueous-based coaters. For a high-volume digital production environment, the company suggests the fully automated ZR with a chamber/anilox system that allows printers to prime sheets. It features the Modular Circulation System, which offers separate sets of hoses and pumps, which allow high-throughput shops to have ten minute changeovers between incompatible chemistries. At Drupa 2016, Harris & Bruno featured the Corona Treatment Unit that eases wettability for primers and coatings over difficult adhesive substrates and ink.

Kompac carries coaters with automatic feeders or roll–roll feeds that handle high-volume digital product environments. The Kwik Finish range of coaters can coat over 5,000 sheets per hour and are suitable for flood and spot coating. They also feature the Kwik release blanket bars that make changing jobs a faster process. Additionally, coating change and clean up takes five minutes with the Kompac Vac.

Scodix Ultra Series Digital Enhancement Presses support offset, digital, and laminated print. The heart of these machines is the patent-pending Scodix Ultra Twin-Tray media handling system that conveys the sheets under the fixed array of ink heads in a single pass at a rate of up to 1,250 B2 size sheets per hour.

The company also offers the Scodix S Digital Presses, which produce Scodix SENSE by applying clear polymer to images in variable levels of thickness and texture of up to 250 microns, allowing for easy single or dual-sided printing.

Shark Machinery offers its SUV-18 Smart UV Coater, a low-maintenance, UV curing coating system. It is designed to provide a durable and high-quality finish to printed sheets. The SUV-18 is an 18 inch, hand-fed unit with optional feeding devices available. Its heated UV tank warms you coating to ensure better coating adhesion and a glossier shine. Also available is the company’s 24-inch UV Coater, SUV-24, and SUV-24 PLUS.

TEC Lighting provides a range of UV coaters, including its Tru Mini, which is designed with the short run printer in mind.

Ready to Roll
Coating for digitally printed output can add vibrancy and durability. While the substrate does affect the outcome of the coating, there are methods and coaters that can simplify the process. The coating landscape expands to address demands for attractive finishing for high-volume production environments. 

By Olivia Cahoon | dps magazine | November 2016


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