Certain materials, such as plastics or foils, have inherently low surface energy, which makes adhesion a challenge. The success of a print run will depend on the chemical nature of both the ink and the substrate. If the two technologies are not compatible, ink might smudge–ultimately affecting the final product.
There are industry specialists, however, who have designed corona treaters to handle these challenges. “Corona treatment increases the surface energy of non-absorbent substrates by changing its molecular structure,” explains Kevin McKell, vice president of sales at Vetaphone. “This allows the ink, varnish or other liquid medium to adhere properly to the surface. Corona treatment is essential. If the surface energy of the material is not correct, the ink or varnish will not ‘stick’ and the print will smear or flake off.”
With the label printing landscape affixed to just-in-time printing, fast turnaround times and top quality, omitting corona treatment could lead to delivery delays and costly reprints.
Corona treaters are quite technical by nature. According to Todd Krupa, sales manager at Enercon, a corona treating system, regardless of the type of electrode or roll covering, can be broken down into three major components: the power supply, the high voltage transformer, and the corona station, which includes the electrode and the ground roll. “Corona treaters are basically devices that ionize air,” says Krupa. “Corona treaters form low molecular weight material on the film surface, oxidize the film surface and form positive or negative sites. This activity normally increases the surface energy or dyne level of a non-porous film.”
The amount of surface treatment necessary will vary among materials. Pre-treated engineered films typically benefit the most from corona treatment. These materials encompass PE, PP, BOPP, PET, PVC, and more.
“Some materials are more responsive to corona treatment, such as PS, and require only a small amount of corona to get a very high dyne level,” explains Krupa. “While others–such as polypropylene, with relatively high levels of slip additives–are difficult to treat and may exhibit only moderate increases in surface energy with relatively high power levels. Paper-based materials can benefit from the web cleaning properties of corona treating and are often run to enhance the print quality.”
Films should be pre-treated at the time of extrusion and again inline immediately before printing. The purpose of treatment at the time of extrusion is to ensure the film will be responsive to a second treatment, which Krupa says is often referred to as “bump treating.” Bump treating raises the surface energy to the required levels for successful printing. Krupa adds that it is an industry best practice to bump treat prior to printing to enable adhesion and eliminate surface energy as a printing variable.
While corona treatment might seem like a slam dunk choice for converters, McKell cautions that the decision is not always so simple. “Corona treatment can be used on almost all materials, though you need to be careful when treating top-coated materials,” he says. “Corona treatment is needed most and works best on unsupported filmic materials and foils because they are non-absorbent.”
Evolution of corona
Vetaphone is a pioneer in the corona treatment industry, dating back to 1951. “Fundamentally, the corona process has changed very little since our founder, Verner Eisby, invented it in the 1950s,” explains Vetaphone’s McKell. “But the equipment has evolved significantly in terms of power and controllability. Today’s corona treatment system from Vetaphone uses state of the art computer-controlled technology and is right up to date with the industry’s needs. In fact, we claim to have taken it beyond Industry 4.0.”
Vetaphone offers an extensive range of surface treatment technologies, including corona and plasma systems. These products are capable of treating both sides of the material at any width and at any speed. In addition to narrow web, Vetaphone technology is used worldwide in extrusion, coating and wide web applications from printing to furniture manufacturing.
The company recently debuted the C8 corona treatment station, which is designed for substrates and applications where high corona power is required from a single unit. The new unit is fitted with eight high-power and high-efficiency ceramic electrodes, allowing more corona power to be discharged from a compact modular system suitable for today’s demanding materials. In addition, the iCC7 turns control of the surface treatment system into an intuitive task. Vetaphone promotes a simple display on the front page while also offering optional in-depth sophistication that allows the user to explore more detailed information. The iCC7 logs function and maintenance requirements, with remote analysis via a download tool and USB port.
Meanwhile, Enercon provides converters with corona, plasma and flame treating technologies from narrow web flexo and digital applications to wide web and ultra-wide web converting and extrusion processes. “We have standard offerings for various applications and custom-built treaters to suit various requirements such as material types, line speeds, widths and utilization,” says Enercon’s Krupa. “Most commonly, Enercon offers universal systems that are capable of treating both conductive and non-conductive films without requiring any intervention from an operator. For demanding applications, we combine our high-powered ceramic electrodes with our proprietary ground roll covering to produce high definition corona. This yields greater treatment results with a more powerful and homogenous corona.”
For narrow web applications, Enercon has developed the CoronaFlex, which is designed to be simple to use and ideal for either new presses or for retrofitting into existing lines. It comes equipped with a touchscreen display, with built-in controls and maintenance procedures. The company is also now offering a new power supply for mid to wide web applications, the Compak Pro, which offers a feature set that improves operations’ productivity with maintenance reminders, advanced diagnostics and a USB drive that enables software updates and data downloading.
“Over recent years, treating has become an integral part of a production line, which has demanded an increase in reliability for the treater components and power supplies,” notes Krupa. “This has put an emphasis on numerous areas, including the ground roll types, such as using ceramic coatings rather than bare rolls or silicon sleeves; the electrode types and ability to access and maintain the cleanliness; and higher powered systems for faster line speeds and difficult-to-treat materials.”
Krupa adds that connectivity of the treater to the press and the facility network has grown significantly, as have enhanced operational efficiencies for reducing downtime and tracking the treatment metrics.
As more information has been released about corona treaters and their benefit to label printing, the practice has become more common. “Customers’ education and understanding of treatment over the years has grown as well and expanded their use of corona throughout facilities,” says Krupa. “Having a treater designed specifically for a client’s application is further growing in demand.”
While education has improved, there is still room for growth. “I’d like to stress the fact that the vast majority of printers and people who use it in everyday commercial production do not fully understand corona,” explains McKell. “They know they need it, and that if they do not have it, their ink does not stick but they don’t know why. Educating printers and converters about the corona process is essential. For example, not all corona systems and treatment are the same. At Vetaphone, we see it time and time again where a customer who does not understand corona buys a system because it is cheap, only to find that it doesn’t work for their process. Vetaphone works hard to educate the industry and help it to understand corona for what it is and what it does – that way, the users can apply the knowledge to their own process and benefit from it. It is not a ‘set and forget’ piece of technology – it needs to be understood to function at its best.”
A digital option?
With demand for digital printing continuing to rise, label converters should recognize the value of corona treatment on their digital press. The process remains relatively the same for digital as for flexo, as both processes use an electrode and ground roll ionizing the air and oxidizing the surface of the film before printing.
“As digital technologies continue to grow, the demand for proper finishing for those labels does as well,” says Enercon’s Krupa. “Understanding your print technologies, either inkjet, EP, toner, etc., will help you in the finishing steps for coatings and laminates. Using a corona treater after printing and prior to applying a varnish or laminate has proven to help clean the substrate, remove any oils or residue, and prepare the inks to accept the decoration.”
According to Vetaphone’s McKell, digital printing generally requires more corona power than flexo. “The process and machinery are basically the same with digital and flexo, but in many cases the corona power–that is the dosage needed to achieve the required surface energy–tends to be higher with digital,” states McKell.
Krupa adds that it’s important to specify the application. “In each case, it’s important to properly define application variables to properly size and configure the corona treating station,” he says. “Variables include types of materials to be treated, including if they are metalized, line speeds and ink types. We have seen significant growth in this section of the market with the proliferation of digital printing and the variety of finishing effects, and we expect this trend to continue.”
Florida-based converting technology manufacturer Karlville has decided to specify Vetaphone corona technology for its range of thermal laminators. The decision to use the Danish manufacturer has allowed Karlville to offer a fully integrated surface treatment solution to its customers that reflects the quality of its own product, according to company president John Price.
The project originally got off the ground when Karlville began its working partnership with HP Indigo on Pack Ready Lamination machines. It was the recommendation of HP, already one of Vetaphone’s top OEM customers, that drew Karlville’s attention to the brand.
“Vetaphone corona systems came with an excellent reputation from HP and a number of other leading manufacturers in the market. They are a highly approachable and innovative company, and their technology fits well with our policy of ‘best TCO.’ We needed a system that we could neatly integrate with our laminator, and Vetaphone responded quickly and within budget. It’s important that every ancillary supplier matches the quality of our brand, and that includes prompt and responsive after-sales support,” says Price.
Each TL-800 laminator requires two corona stations – one in each of the unwind sections, and both need extractor fans and exhaust ducting to work at maximum efficiency. The Vetaphone equipment installed includes VE1H-C(C4)920 corona treater units and iPM200 generator modules. The treaters are single-sided and fitted with four ceramic electrodes with roller faces of 920mm. The generator has a power output of 8kW and gives accurate watt density control by following the line speed automatically. It has a zero-speed switch and automatic start relay that protects the RD62UR standard blower fan that Vetaphone also supplied, along with an OZC-6 ozone eliminator.
Capable of handling rolls up to 762mm wide at speeds of 100 m/m, the TL-800 machine is designed for continuous production in robust commercial environments. It offers a low entry level to flexible packaging, and while it is a good machine for general purpose applications, it is an ideal fit for pouches. At present, Pack Ready laminate compositions can cater for more than 60% of flexible packaging market value by market sector, shared largely between foodstuff (around 80%) and non-food.
“It’s an environmentally friendly machine, with no VOCs, odor or any health issues, making it suitable for the food sector as well as toiletries and medical products. It’s a great fit with HP Indigo technology, offering best time to market with minimal waste. Most of all, it’s reliable, and that’s why we have to choose co-suppliers, like Vetaphone, carefully,” he adds.