Order on Demand: Flexographic Print with Gravure Quality

How will buying habits change as a result of COVID-19 and the developing circular packaging economy?

Here is one way: Increased shorter runs without any sacrifice in print quality.

Critical concerns surround the best process and most applicable components for how short-run flexible packaging and multiple SKUs can be profitably printed:

• Central impression (CI) presses became popular because of register accuracy; however, the CI press is not operator-friendly for shorter runs, even with sophisticated setup features
• Mid web CI presses were offered as a short-run solution, but this approach has not gained widespread acceptance because of the need for more versatility over a wider range of packaging requirements
• The inline label press is more operator friendly; however, the long web path increases material waste during setup. Additionally, down gauging of materials increases problems with tension control. By adding sophisticated setup features and tension controls, this has driven up the cost of inline presses

Stack Matches Central Impression

Those production challenges led to the development of an entirely different approach to flexographic printing for short runs—utilization of a 100 percent servo-drive stack press that matches CI in quality, yet offers the advantages of inline converting. Today’s increasingly common belief is that a mid web stack press, in the range of 34-in. to 40-in. with a larger maximum repeat, will provide the capability for a wider range of stand-up pouches and flexible packaging than a 27-in. wide press.

A new, Giave-built, all-servo-drive system promotes register accuracy. State-of-the-art electronics from Siemens are the basis for new integrated process control. Coordination of far more than 60 axes, depending on machine configuration, is done by a high-end motion controller with an integrated register control and Simatic. 

On a CI, the central drum is the master drive and all others follow it. On this stack press example, all drives are master drives that talk to each other with real time communication via Profinet IRT (Isochronous Realtime). Consistently high print quality via the integrated register control with minimal start-up waste is possible—in some cases about 30 feet of setup waste.

Assisting in improving quality is the function Learning Error Compensation (LECo). The self-learning control algorithm uses the drive control behavior to detect cyclic disturbances caused by the typical vibrations of flexographic printing, due to the printing plate gaps (bouncing).

LECo compensates for this automatically, negating its impact on the print. Last, but not least, in order to realize the highest print quality with start of production, the machine builder has developed an innovative pressure control between the cylinders using the standardized interface to the motion control system. This automatically finds the “contact point” between the cylinders electronically. Drive data results in positioning all chosen decks simultaneously.

Listing out the advantages of a mid web, servo-driven stack press tags multiple benefits:

• Low to zero volatile organic content (VOC) and hazardous air pollutants (HAP)
• UV LED between color lamps generate cured resin containing up to 87 percent less carbon dioxide compared to thermal curing water or solvent systems
• No dryers: less energy—estimated 80 percent total energy reduction in BTU, including natural gas and electrical power
• Lower profile: operator friendly
• Less material waste: shorter web path
• Reduced fire and explosion hazard
• No CI drum requiring constant cleaning or causing unsafe UV light bounce back
• Backside print: front and back without turn bars

Executing fast changeovers and processing a wider range of substrates, including combinations of paper, film, foil and thinner-gauge flexible substrates that are extensible in nature in this ever-changing environment, demands a more flexible approach to how these materials are processed.

Narrow web companies benefit from the fact that most manufacturers, especially those operating in the food and drink sectors, have widely embraced controlled inventory costs. The ability to produce both flexible packaging and shrink sleeves on the same press increases the ability to yield a faster payback if volumes require this flexibility.

For wide web printing, this translates into more frequent runs, so converters need to adjust to increase profitability. Converters should consider the best approach to be more profitable in both short and long runs, rather than just stay with the way it has been done in the past.

Hybrid Press

Digital imprint enhancements and personalization are also possible inline and in register to the main press. It can be one to four colors, generally speaking.

Embellishments are a growing opportunity for packaging printers/converters. The ability to produce embellishments on digital devices inline, with analog flexography, will offer additional opportunities—ranging from expanded gamut (EG) printing to application of UV LED drying, and even reverse printing and laminating in a single pass.

Let’s discuss those possibilities.

Inks & Coatings

How flexible packaging materials are printed is an area that needs close scrutiny for the reduction of VOC solvent emissions, lower energy costs and the “Circular Economy.” The versatility of today’s mid web, servo-driven flexographic stack press with sophisticated tension controls opens the way to a new approach to short-run package printing.

Improved UV LED inks are coming on stream every day to meet the demand to eliminate solvent inks:

• They produce extremely high-quality print
• EG colors become easier to use because of the stability of the ink on press throughout the run and consistency from one run to another
• Reduction of spot colors and color matching can lead to a reduction in setup waste
• A reduced environmental footprint, using food packaging-compliant UV LED, inks is possible, if converters can overcome the fears associated with radiation curing inks

Jennifer Heathcote, technical and commercial advisor of UV curing with Eminence UV LLC, states the following: “UV LED-formulated inks, coatings and adhesives, as well as UV LED curing systems and the presses specifically designed to utilize the technology, have advanced tremendously in the last 10 years. Formulators are stepping up to expand UV LED offerings in order to meet growing and diverse print production demands. Lamp head designs have become longer and wider and have been engineered to efficiently emit more UV output.”

She adds, “Presses equipped with UV LED lamp heads are running faster and are better leveraging the technology to solve longstanding integration and process challenges. This includes tighter lamp head form factors that more easily integrate into presses; significantly reducing heat transfer compared to conventional bulb-based systems, which can warp films and damage press components; providing consistent UV output that spans production runs of days, weeks and years; and longer UV LED wavelengths that better penetrate through film constructions and deep into formulations to better cure densely pigmented formulations—especially white inks.

“An increasing number of UV LED system suppliers have recently engineered an incredibly broad range of UV LED designs, in order to meet the diverse needs of curing applications across both printing applications,” Heathcote continues. “In many ways, the industry is now spoiled for choice. Systems intended for one market segment and set of applications are not necessarily suited for another. Properly selecting a UV LED curing system that meets the needs of the print product range for a given press, as well as the intended process conditions, is incredibly important; yet many UV LED system suppliers do not provide enough information regarding how UV LED output potentially impacts cure. This can make it difficult for OEMs and end users to navigate the sourcing process and make informed purchasing and development decisions, unnecessarily stalling printing innovation and UV LED adoption. In cases where the technology is more than viable, an improperly sourced and integrated system can make it appear as if the technology isn’t ready, even though it is.”

Elaborating on points made, she says, “Formulation requirements, working distance and run speed are the primary drivers of the UV lamp head’s spectral output (wavelength), irradiance (intensity) and energy density (dose) that must be delivered to the print surface for suitable polymerization or cure. Consequently, wavelength, peak irradiance at a known location and energy density at a defined line speed should all be specified by UV LED system manufacturers and confirmed by the OEM press manufacturer for each UV LED product being considered for the press.”

According to Heathcote, “OEMs who work closely with formulators and UV LED system suppliers during development—in order to ensure that the correct UV LED system has been matched to the needs of the application and formulation—are the ones who are exceeding customer expectations when it comes to UV LED curing performance. When the correct UV LED system is utilized, cure is consistent, repeatable and reliable.”

So why measure? Because there are no direct, online methods of determining degree of cure. In addition, since there is substantial variation in types of UV lamps, age of the lamps and ink used, the UV exposure conditions must be monitored and correlated with the cure result for the purpose of verifying that the exposure is maintained within predetermined limits.

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