By Cassandra Balentine
The digital print industry is made up of two primary printing methods—inkjet and electrophotographic (EP), which can be further broken down by liquid (LEP) and dry inks/toner. Each comes with advantages and disadvantages, which are typically dependent on a specific print provider’s needs and expectations.
One primary advantage to EP and LEP over inkjet is the fact that it is a mature technology with many media options. These substrates range from paper-based media to vinyl, polyester, and polypropylene films, and specialty offerings like magnetic.
Above: With GPA’s own internal substrate evaluation process, it ensures its products meet client need for ink adhesion, image quality, and overall press performance.
Available for EP
A range of papers, films, and substrates are available for certain EP and LEP presses. Mellissa Campbell, marketing manager, Masterpiece Graphix, points out different options in synthetics are compatible with EP/LEP presses, including static cling, polyester, repositionable vinyl, synthetic paper, and rigid vinyl PVC.
The possibilities are almost limitless. “For example, exotic stocks range from textured pearls to magnets and every imaginable solution in between. EP and LEP presses have proven reliability, broad compatibility, and efficiency—even without exotic media. New and innovative products continue to be added, including fabrics and lower cost synthetics. The EP and LEP product range and reliability emphasizes the fact that these technologies will continue to play a vital role in digital print,” says Craig Surette, business development developer, dry toner market, GPA.
Substrates available for LEP continue to grow. Everyday items, such as coated and uncoated text and cover weight papers have been available for years. “However, the advancement in press and priming technology has opened the door for many new and exciting substrates such as bright silver and holographic foil boards, synthetic substrates like rigid vinyl in both white and clear, wood veneers in both cherry and birch, and also unique fabrics,” offers Mike Blanco, business development director, R&D and technical services, GPA.
Benefits & Limitations
Because EP- and LEP-based printers are a mature technology, media manufacturers and OEMs have worked closely together for decades to grow the list of compatible substrates. Since this is arguably the number one limitation of inkjet, it presents a huge advantage.
“There are more media types proven in this marketplace,” shares Brian Ayers, market development specialist, product identification business team, FLEXcon Company, Inc. He adds that dry toner inks are more flexible than most inkjet ink systems and require less ink deposition.
Surette says that while inkjet brings advantages in speed and lower click charges, the EP and LEP product range and reliability emphasize the fact that these technologies will play a vital, ongoing role in digital print. “If a printer’s business is strictly paper at lighter weights with no requirements for heavy, synthetic, or unique stocks, then aqueous inkjet has advancements to consider. Just like everything in print, it depends on the business and its requirements and the model.”
The ability to print to plastics is one advantage. “The durability and longevity of plastic substrates is unbeatable, offering options for tear-, water-, and chemical-resistance to extend the life of a finished piece,” shares Campbell. Due to the longer lifecycle of synthetic versus paper-based products, reprints are less frequently required. Plastic substrates are less expensive than laminating paper and often result in faster turnaround times since the printer does not need to outsource lamination, she explains.
When printing on plastics, a commercial printer may sometimes encounter challenges including consistent toner transfer, especially on high solids. “However, this is easily solved. Where paper may be plug and play, plastic substrates may require slight setting adjustments to fine tune. Occasionally, post-print static can create challenges for finishing processes,” admits Campbell.
Blanco sees many advantages to EP and LEP devices, such as the variety of substrates available, the ability to quickly move from one job to the other, and the ability to run multiple substrates within the same job due to multi-drawer systems.
Limitations to EP and LEP technologies include limited durability and chemical/solvent resistance. “Liquid toner doesn’t last more than six months outdoors without significant fading, and dry toner doesn’t last more than 12 months outdoors without significant fading. Our testing has shown that dry and liquid toner can be used for outdoor applications when the proper outdoor UV blocking overlaminate is utilized,” shares Ayers.
Blanco says some limitations of LEP presses include the maximum thickness and gsm specifications of the press. “These days, customers are always asking for thicker substrates. Packaging is a growing segment in the market, so the desire for thicker and heavier substrates is ever growing. The HP Indigo 30000 press helps in this area with its ability to print up to 24 pt. substrates. However, the press does not duplex like its brother, the 12000 press. So there is a little give and take.”
Surette points out that depending on the level of print quality required, many regard EP and LEP to be superior based on the system and job. However, dry toner or EP technologies have the limitation of sheet width, with most maxing out at about 13 inches. “The technology is currently limited to roughly 150 sheets per minute at the high end, with most platforms achieving around 100 sheets. LEP technology requires stocks to be pretreated in most cases, and the sheets per minute generally have a similar upper range to that of EP. LEP has the advantage of supporting the B2 size platform.”
Pretreatment of media for EP and LEP print engines can be applied at the mill, by a converter, or as part of the production process while printing.
From the mill, materials that are already precoated/treated are ready to be printed via these technologies and can carry approval with industry specifications. However, from the mill, materials that are already pretreated/precoated may not be able to accept additional print technologies, offers Ayers.
Surette says paper-based products require no precoating for dry toner compatibility, which allows for a broad range of product solutions, minimal setup, more uptime, and ease of use. Dry toner synthetics are plug and play with the important distinction that all dry toner presses require pretreated stocks for compatibility. “No dry toner press has an inline treatment capability, so products either work or they do not,” he adds.
Due to the number of dry toner presses in the marketplace, Ayers suggests print providers look into learning more about treatments by speaking with their media supplier to determine the best method.
Steve McLevey, customer service and product manager, Arnold Magnetics, points out that liquid toner inks most generally require a print treatment to be applied to the substrate. Without the treatment, the ink will not adhere or anchor properly to the substrate.
Substrate pretreatment is vital for LEP presses, agrees Blanco. “Advancements in priming technology have given us the ability to bring many specialty substrates to market with outstanding performance, which otherwise would not work at all on the presses. We have many customers who choose to apply post-print UV or aqueous coatings to substrates for added durability protection.”
GPA’s Blanco says its substrates for LEP presses are either primed at the mill or in its production facility in McCook, IL. “This gives us the ability to control the environment in which the primer is applied as well as the process itself,” he explains.
Ayers comments that converters that can apply inline, on-press coatings are able to utilize a media on the floor, eliminating the need for unnecessary SKUs. However, to do this, the converter would need a press that could apply inline or offline. This also presents additional work for the converter.
Blanco points out that some HP Indigo presses have inline priming options. HP offers Digital Indigo Primer (DIP), which is an inline process just like adding another ink. “Although it does have limitations since DIP is not compatible with all substrates, it adds cost to the job by increasing the number of separations being printed, increases in primer cost, and extends the runtime. However, it is an option to consider for substrates that need to add ink adhesion characteristics. HP also has some presses with a separate inline priming unit,” he shares.
To achieve the best performance from synthetic printing materials, Campbell stresses the importance of choosing a supplier that uses set best practices for developing digital media—thorough testing, pristine clean materials, corona testing, and professional drying.
When it comes to the practice of thorough testing, no one digital coating or coating process works on every material. Campbell says each material must be lab tested with a variety of digital coatings and primers, then production coated and thoroughly tested on press to ensure quality.
Digital presses require a very clean environment. “It is essential to use pristine clean materials free of slitter dust—the fine paper shavings that come from dull knives, crush cutting, and the slitting process in general,” says Campbell.
Corona treating can be very effective on many materials in achieving better adhesion of the digital coating. Some materials intrinsically have low surface energy, making it difficult for the coatings to stick. “Digital materials that are not corona treated prior to coating can be less dependable and have poorer print quality than those that are corona treated,” explains Campbell.
The drying process after coating is one of the most critical steps, she adds. “Standard drying units on flexographic presses or other converting units are not adequate. Solvents must be thoroughly dried for proper coat and weight. Without adequate drying, digital materials will have blocking or stitching—the material sticks to itself as it comes off the roll.”
The substrate options for high-speed digital production in the EP and LEP space have continued to advance over the past ten years.
“When I started running an HP Indigo press in 2003, there were a limited number of substrates available. The following two to three years showed little improvement, and then things started to explode,” recalls Blanco. He says many substrate providers realized how disruptive this technology was and the need for compatible substrates. “The last ten years have brought so many amazing substrates to the market—items I would never have imagined we’d be printing on today,” he adds, noting that many additions are driven by customers asking for items that didn’t exist at the time.
Surette comments that there were previously only one or two solutions in digital fine papers or labels, but today the offerings are vast. The product range is significantly broader and there are new product families for EP and LEP presses. Products that were never before possible are now common, including backlit signage, window and floor graphics, and magnets—just to name a few.
The addition of specially engineered digital print receptive coatings—like those added to Masterpeice Graphix’ synthetic substrates—give print providers the ability to run materials on almost every digital production press, adds Campbell.
Many OEMs have significantly reduced the amount of heat required to fuse dry toner to the surface of the film, says Ayers. This has opened the door to additional options that were not viable in the past. “It has allowed for expansion of additional films such as polypropylenes to be used with dry toner technology, which traditionally would have melted to the fuser’s rollers,” he explains.
“Developments in dry toner technology—such as low-melt toner—are opening up the use of more plastic polymers beyond just traditional polyester. This translates to a broader range of applications for printers, as well as cost reduction,” says Campbell.
While past advancements have paved the way for improved media compatibility, more are on the horizon.
“Innovation drives growth, so expect to see more variety of substrates that drive volume. EP and LEP will continue to be the go-to technologies for solutions beyond lighter weight papers of production inkjet,” says Surette. “That simply reflects the technology limitations for the near- and mid-term horizon. Innovations in point of purchase related substrates, holiday card differentiators, fabric, canvas, and packaging solutions are a few examples of solutions coming to market.”
Ayers points out that advancements in sheet and roll form technologies affect the market. Traditionally, many of these were sheet-type printers. In addition, many printer OEMs now offer roll-form printers, as well as the capability of additional sheet sizes, such as banner widths.
He adds that media options like polypropylene films are popular with the craft beer industry, which can now be printed in roll form. For health and beauty markets, pressure-sensitive films utilize a polyester release liner, providing the ability to have labels dispensed automatically at a high speed onto the container.
Dry Versus Liquid
There are many printer OEMs and model numbers for dry- and liquid-based printers and each are unique. “It’s best to ask specific questions based on your end-use application requirements,” recommends Ayers, when comparing the difference in media requirements between liquid and dry toner printing methods.
Blanco says dry toner presses typically involve high temperatures for fusing ink to the substrate, whereas LEP presses require less heat to cure the ink. “Therefore, some substrates may not be compatible with both LEP and dry toner presses. Specialty polyester substrates work well on both platforms due to their ability to handle high heat,” he adds.
Surette points out that dry toner can support 350 gsm stocks comfortably with many in the market now handling 400 gsm as standard. “That opens up a tremendous range of heavy card, synthetic, tag, and digital light packaging solutions,” he notes. For example, Xerox iGen 5 exceeds that limit with an optional heavy substrate kit to push the limit close to 600 gsm, and the available applications and solutions expand that much more. “Sheet size in this market is perhaps the area of most innovation,” he adds.
Liquid-based toner offers similar support for weight and size as the dry toner market, where 13×19 inches on stocks up to 350 gsm are standard for narrow web digital. “The B2 size changes that, and HP continues to push the boundaries of weight capability, also creating opportunities in heavy card, synthetic, tag, and digital light packaging solutions,” explains Surette.
There are pros and cons to each printing method. The expansive list of substrates suited for EP and LEP technologies is a major benefit, and the options continue to grow as both print engines and media advance.
May2019, DPS Magazine