THE ROLE OF INK FORMULATION IN FUTURE-PROOFING PRESS TECHNOLOGY

Ralf Mueller explores how this strategy addresses the distinct safety requirements for both standard and sensitive applications. In this way, a robust framework is provided for future-proofing an original equipment manufacturer’s (OEM’s) technology against shifting market and regulatory demands.

“The ink itself is now viewed as a critical design choice”

As UV-curable inkjet technology matures within the label and packaging sectors, the focus for OEMs is evolving. While machine performance remains paramount, the ink itself is now viewed as a critical design choice. An ink’s formulation directly impacts its successful integration, the system’s regulatory compliance and, ultimately, the future-proof nature of the press technology. This principle of matching safety to application is well-established in conventional printing. However, the unique constraints of inkjet mean that the ink’s chemistry is more deeply intertwined with the hardware’s long-term viability than ever before.

The first level of responsibility in ink formulation is ensuring the safety of personnel handling the liquid ink. This establishes the baseline for all applications, governed by adherence to good manufacturing practices (GMP). GMP ensures rigorous batch-to-batch consistency and the strict exclusion policies set forth by industry bodies such as the European Printing Ink Association (EuPIA).

The primary focus is the elimination of raw materials classified as carcinogenic, mutagenic or toxic for reproduction (CMR). Siegwerk’s standard UV-inkjet ink portfolio – the SICURA Jet range – is formulated in strict accordance with these principles. It provides a robust safety foundation for non-sensitive applications.

However, formulating a compliant ink is only the start. The physical demands of industrial-inkjet printing are exceptionally high. An ink must be precisely tuned to the specific jetting assembly, taking into account factors such as target drop size and jetting frequency. Additionally, the delicate balance between a long open time (to prevent nozzle clogging) and rapid pinning on the substrate (to ensure dot quality) needs to be considered.

To meet these needs, the SICURA Jet portfolio comprises a series of inks, each optimised for the leading industrial printhead technologies. These include those from Kyocera, Fujifilm, Ricoh, Konica Minolta and Seiko. Achieving a stable, reliable and CMR-free ink is a significant formulation challenge. One which needs to satisfy these demanding rheological parameters for each unique printhead family.

When the printed article is intended for sensitive applications in nutrition, pharma and hygiene (NPH), the safety assessment shifts from occupational exposure to consumer protection. The critical technical challenge becomes minimising the migration of substances from the cured ink film into the packaged product.

“The selection of photo-initiators is particularly critical”

Achieving this in an inkjet formulation is significantly more complex than in higher-viscosity conventional inks. The requirement for a very narrow and low viscosity range (typically 5−15 mPas at jetting temperature) severely restricts the available palette of raw materials. Many ideal low-migration components, such as high-molecular-weight photo-initiators and oligomers, are inherently more viscous. As a result, they can easily disrupt the delicate fluid dynamics required for reliable jetting.

“SICURA Jet and SICURA Nutrijet portfolios are engineered for dual-cure capability”

The selection of photo-initiators is particularly critical. Small, mobile photo-initiators such as benzophenone – while effective – are known migration risks and are excluded from these formulations. Instead, development focuses on larger, less mobile alternatives such as polymeric, difunctional or self-initiating monomer/oligomer systems. These molecules are designed to be ‘locked’ into the polymer backbone during the curing process, physically hindering their ability to migrate. 

Similarly, the selection of monomers and oligomers must prioritise not only low intrinsic migratory potential, but also the ability to achieve a very high degree of cure conversion. Any residual, unreacted monomer becomes a potential migrant.

The development of a low-migration ink such as Siegwerk’s SICURA Nutrijet range is therefore a complex task, validated by rigorous analytical testing. This involves migration testing according to established protocols using food simulants (for example, Ethanol 95%, Tenax®). Testing is then followed by analysis using sophisticated equipment including gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS). These methods can quantify migrating substances down to parts-per-billion (ppb) levels. As a result, any potential transfer stays below the specific migration limits (SMLs) defined in regulations such as the Swiss Ordinance or upcoming German Ink Ordinance.

For an OEM, a strategic ink portfolio must de-risk market entry, offer hardware flexibility and future-proof the technology.

A key aspect of this flexibility is curing technology. All ink series within both the SICURA Jet and SICURA Nutrijet portfolios are engineered for dual-cure capability. A highly sophisticated photo-initiator package is required to formulate an ink that cures effectively under both the broad polychromatic spectrum of a mercury-arc lamp and the narrow, monochromatic output of a UV-LED system. 

This photo-initiator package must be sensitive and reactive across different wavelengths to ensure a thorough cure in either system. This empowers OEMs with the freedom to design their press architecture based on market demands for cost, sustainability or substrate versatility, without re-qualifying inks.

Furthermore, this differentiated portfolio serves to de-risk an OEM’s entry into the highly regulated NPH markets. By providing a pre-validated, migration-optimised ink system, such as SICURA Nutrijet, the immense research and development, and toxicological burden is shifted from the press manufacturer to the ink specialist. It provides OEMs with a turnkey solution to confidently offer a machine capable of producing compliant packaging. In turn, this effectively shortens time-to-market.

“Siegwerk is committed to working closely with OEMs at all levels”

This approach transforms the supplier relationship into a deep technical partnership. Siegwerk is committed to working closely with OEMs at all levels. From initial fluid-dynamics testing in the lab and ink chemistry optimisation for new printheads, to on-press validation and end-customer application support. The ink ceases to be a consumable and becomes an integral, co-developed component of the printing system. By building press technology around this collaborative model, OEMs can future-proof their equipment. This ensures that it remains relevant and compliant as safety standards inevitably continue to tighten.