Digital printing for packaging

Resources to protect print quality & equipment

Digital printing has been on the rise among commercial printers since the 1990s. And more and more packaging producers are adopting it as well. What are the advantages? And how can you ensure consistent, high print quality and reduce costs with digital printing?

To answer these questions, we look into the evolution of digital printing presses and the various techniques. We will also discuss maintaining consistently high print quality and avoiding premature wear and tear of valuable equipment.

The first commercial digital printing presses were introduced in ‘93 at the IPEX in Birmingham. A revolution, because these presses didn’t require printing plates, but with a printing result that didn’t come close to offset. And because of the high cost per print, the application was limited to printing small runs or proofs.

But the development didn’t stop. Both computer printer manufacturers and large printing press brands threw themselves into innovating and perfecting digital printing technology.

Printheads and the processes that control ink distribution became more sophisticated every year, eliminating many of the limitations of these first digital printing presses.

How does a digital printing press work? What do terms like piezo, binary, DOD, and CIJ mean?

In digital printing, a design or layout is converted to digital data, which is transferred directly – without printing plates – to the substrate. The two most common methods for the actual printing process are laser and inkjet.

1. Laser (LED, electrophotographic) printers

Laser printers use toner, a powder so fine that it appears liquid. A laser or LED projects the digitized image onto an electromagnetic drum. Electrically charged areas on this drum attract the toner particles. Then the drum transfers the toner onto the substrate. To fix the toner, still present as a powder on the substrate, heated cylinders (fusers) melt the toner into the medium.

2. Inkjet printers

Inkjet printers transfer the digitized image by pushing tiny ink droplets from print head nozzles.
But how does the right color of ink get to the right place? That depends on the type of inkjet printer — Continuous Inkjet or Drop on demand.

Continuous Inkjet (CIJ)
A CIJ inkjet printhead produces a continuous stream of ink droplets during printing. The droplets are either sent to the substrate or deflected by an electrostatic charge. Then the unused ink is collected, and can be filtered and reused.

Drop on demand (DOD)
Drop-on-demand, the fastest growing inkjet segment, generates ink drops only when needed. This is done in the print head by either a thermal or a piezoelectric process, the basic principles of which we depict below.

Thermal inkjet printheads

Piezoelectric inkjet printheads

Thermal printheads are fast and provide high image quality, but they are only suitable for heat-resistant, usually water-based inks.
Piezo printheads are expensive but can last a long time under the right conditions (more on this later on) because they are not subject to temperature-induced deterioration. Furthermore, they prevent ink wastage and process a wide range of inks, including heat-sensitive types.

Halftone technology in inkjet presses

Another distinction is how an inkjet printer creates lighter-colored areas, divided into binary and grayscale printhead technology.

Most modern inkjet presses operate with single-pass grayscale printheads because they consume less ink, give better printing results, and are faster than binary inkjet presses.

Offset and flexo are the most used analog printing processes for corrugated and folding carton packaging. For corrugated board displays and boxes, there is a choice between pre-print and post-print.

Pre-print: here the top layer of the corrugated board is printed separately (CMYK offset/litho gravure) and then added in the corrugator as a liner, or label.

Post-print: direct printing of corrugated board, a sheet-fed process. The most commonly used analog post-print method is flexography, used primarily for high print runs due to high setup costs.

Luxury packaging for electronics, jewelry, and perfumes, made of folding carton, cardboard, and virgin fiber paperboard, is usually offset printed.

So there is plenty of choice in tried and tested analog printing techniques. Then why do so many packaging producers and printers invest in digital presses?

In 2014, Smithers Pira predicted digital printing market share to grow from 13.5% to 21% by 2024. A recent report predicts a further increase of 65% by 2029, mainly due to technical improvements and shifts in market demands.

What are these market demands? One trend is the increase in E-commerce and the so-called ‘unboxing experience.’ As more purchases are made online and delivered to people’s s homes, the shipping box plays a significant role.

Online videos in which people unpack a purchase and put it to use have an impact on a brand’s popularity. As a result, just adequate but dull packaging no longer suffices.

To help deliver what brands need, digital printing offers the following advantages compared to analog printing:

• There are no plate costs
• Hardly any pre-press costs
• Color changes, as in flexo are not necessary. Therefore, a new printing run with a different design requires hardly any adjustment.
• Beautiful print quality
• Fast turnaround times
• Offer small print runs profitably

Digital printing creates unprecedented opportunities. What about a special edition of a Pepsi six-pack for a soccer tournament? Or custom dog food, tailored to the type and age of your dog, with your hero’s name on the packaging, as Pedigree did? Digital printing makes it possible.

Another application is fast and aesthetic printing of variable data, such as bar codes, expiration dates, and batch numbers.

New developments, digital/flexo hybrid press

Although flexo and offset are the most cost-effective for high-volume printing, many packaging professionals are also looking to offer the benefits of digital.

Manufacturers of inkjet and laser printers, leading printing press manufacturers, and even corrugator brands are putting much effort into developing and improving digital presses for packaging purposes – pre-print as well as post-print.

An interesting development that combines the advantages of analogue and digital printing is the hybrid press. The flexo section prints large solid-color areas; the knocked-out areas can be printed digitally with variable images or data.

Technical innovations have resolved many limitations of the first digital printing presses, for instance:

Print quality: The print quality is no longer inferior to offset due to the innovations of the printheads.

Speed: The multi-pass inkjet technology was slow. The introduction of the single-pass technology made digital printing much faster, thanks to modern printheads that combine grayscale and variable drop formats in one print run.

Limited ink choices: New types of ink replaced inks that were not suitable for food packaging or lacked FDA approval. More and more environmentally friendly, safe inks emerge, including special color and gloss effects options.

However, two factors inherent in paper or cardboard digital printing cause concern. That is the combination of static charge and dust.

The digital printing process utilizes an electrical charge. As a result, the extremely fine print nozzles attract dust. Paper, folding carton and corrugated cardboard are dusty substrates, because of their fibrous nature. In addition, particles from the production environment cling to the material during converting due to static charge.

During printing, these barely visible particles cling to the statically charged print nozzles, which become clogged, splash, or no longer allow any ink to pass through. This results in stains or unprinted areas in the printed material. An additional effect is that clogging reduces the lifespan of the expensive printheads.

Crucial for trouble-free printing: dust-free substrate

For trouble-free digital printing, the substrate — paper, board or corrugated board — must be absolutely clean. This prevents blocked nozzles and premature wear of the printheads. It also avoids hickey’s or bull’s eyes caused by dust, trim remains, or microparticles on the substrate. These are observable as unprinted spots in the printed material and a reason for rejection of the product. A problem that occurs not only in digital printing but also in flexo and offset. (More about the effects of dust in production environments can be found here.)

Solving dust problems is necessary but straightforward. Weducon develops web cleaning solutions that eliminate dust in various production processes – without disturbing highly sensitive manufacturing and printing processes.

A Corrucleaner HE 90, our web cleaning solution for corrugated board, which we integrated into a Quantum corrugator, provided the clean corrugated board for the colorful digitally printed Blue Jay packaging. We also build these web cleaning systems into older corrugators, without disturbing your production schedule and without making changes to your existing configuration.

For dust-free manufacturing and printing of paper and solid board, we equip both existing and new production lines with Weducon HE 90 web cleaning systems, for instance at Kroonpress, and Inpol-Papier.

As we have seen, a clean, dust-free substrate is a #1 condition for good printing results, particularly for digital printing. Solving dust prevents complaints, premature wear and tear, wastage, production stops, and work stress, ensuring a healthy work environment.

Would you like to know more about effective solutions for dust problems in your production process? Contact us; we look forward to hearing from you.