ADVANCEMENTS IN FORMULATIONS FOR DIGITAL LABEL PRINTING

Among the various digital technologies, UV and UV-LED inkjet systems have emerged as leading solutions. This is because of their versatility, durability and compatibility with a wide range of substrates. Advancements in printheads, printers and drying systems have elevated the quality and speed of output. These developments have also enabled digital solutions to capture a growing share of the label-printing market. It has, in turn, driven an equally critical innovation – the progression of advanced ink formulations. These are tailored to meet the demands of modern, high-performance printheads.

Sun Chemical works in partnership with leading original equipment manufacturers (OEMs) and partners to develop ink solutions – including inkjet and screen – across a range of technologies and application areas. Together with its partners, the company optimises inks to specifically fit the printhead and hardware configuration. The aim is to deliver output prints that meet all speed and quality requirements. As a result, optimum functional performance for each application and label stock is guaranteed.

“Advanced formulations now achieve open times exceeding 60 minutes”

Inkjet printheads are now capable of delivering resolutions of 1,200dpi at speeds exceeding 100m/min. Many printheads, achieving such performance, require inks with lower viscosities. Lower viscosity ensures reliable jetting through the often smaller nozzles of high-frequency printheads. However, formulating low-viscosity, UV-curable inks is not always straight forward.

To reduce viscosity, ink chemists turn to lower molecular weight. They use smaller monomers to form the building blocks that polymerise under UV light. These monomers often have lower functionality, resulting in fewer reactive sites for cross-linking during curing. While this helps achieve the desired flow characteristics, it introduces several formulation challenges.

Lower functionality monomers tend to reduce the overall reactivity of the ink. This can potentially slow down the curing process. To counteract this, formulators have to carefully select the ideal combination of lower functionality and/or more expensive ‘high solvency’ monomers. Another option is to potentially increase the concentration of photo-initiators. These are compounds that trigger polymerisation under UV exposure. Correctly balancing the chemistry ensures that inks cure rapidly enough for high-speed printing. At the same time, the right balance maintains the low viscosity required by the printheads.

Another potential consequence of using smaller, inherently lower reactivity monomers, is the increased risk of material migration from the ‘cured’ ink film. This is particularly critical in applications such as food, pharma, cosmetic and personal-care packaging and labelling. In these areas, regulatory compliance is essential. Formulators must carefully select and balance ingredients to meet stringent standards such as the Swiss Ordinance and Nestlé compliance guidelines. Safety must be guaranteed without compromising performance.

Low molecular weight monomers can also be more volatile. It can make them more prone to evaporation at the printhead nozzles during idle periods. The result may mean poor ‘open time’. ‘Open time’ is the duration that the ink remains printable without clogging or performance degradation. Advanced formulations now achieve open times exceeding 60 minutes – minimising downtime and improving operational efficiency.

High-frequency, small, drop-size printheads are particularly susceptible to satellite formation. This leads to tiny stray droplets that can accumulate on the printhead faceplate and disrupt jetting. The factors affecting the formation of satellite drops in inkjet printing are complex. Influences come from machine architecture, ink supply system, waveform – used to drive the printhead – as well as ink formulation and quality. 

Ink formulation plays a crucial role in mitigating this issue. It includes selecting high-purity pigments with tightly controlled, narrow particle size distributions. These pigments are essential for the assurance of stable jetting and minimisation of satellite generation. The quality of pigment dispersion is a key determinant of ink performance, especially in high-resolution systems where operating tolerances are tight.

UV curing remains a cornerstone of inkjet digital label printing, offering rapid, on-demand drying that supports high-speed production. Traditionally, mercury vapour lamps have been used to initiate the curing process. However, the industry is increasingly shifting towards UV-LED curing systems, which offer several advantages. Lower energy consumption and heat output make them more compatible with heat-sensitive substrates. UV-LED curing systems also increase operational lifespans and reduce maintenance. In addition, energy efficiency and press uptime is improved with an instant on/off capability. There are also environmental benefits, as UV-LED systems eliminate the need for ozone extraction and mercury disposal.

This transition is supported by ink manufacturers reformulating UV-curable inks to match the narrower emission spectra of UV-LED sources. This move ensures effective curing, without compromising key performance requirements.

In parallel with UV technology, there is growing interest in water-based inkjet formulations. Particularly, for applications where sustainability and regulatory compliance are paramount. These inks may be especially attractive for food and beverage packaging, pharmaceutical labelling and sustainable packaging initiatives.

Water-based inks present their own formulation challenges. Problems include achieving adequate drying speed, substrate adhesion and printhead compatibility. However, advances in pigment dispersion, resin chemistry and drying systems are making water-based, digital label printing a viable and increasingly competitive option.

The rapid advancement of digital label-printing technology owes much to the parallel evolution of ink formulations. As printheads become faster and more precise, ink manufacturers are rising to the challenge. Developments include sophisticated chemistries that balance viscosity, reactivity, stability and compliance. Added momentum comes from UV-LED curing and the emergence of water-based alternatives. As a result, the future of digital label printing is more versatile, sustainable and high performing than ever before.