Flexible packaging
Beyond nitrocellulose: Why NC-free ink systems demand a whole-process approach to flexo print performance
By Paul Mitchell, regional sales manager – UK & Ireland, Sandon Global
PROCESS INTERDEPENDENCE Flexographic printing operates as a connected system. Ink, anilox, plate, tape, doctor blade and drying all contribute to the result. A change in ink formulation alters that balance.
N
itrocellulose has long been a foundation of solvent-based fl exographic inks. As a polymer binder, it supports pigment wetting, gloss and solvent release
and adhesion, all central to fl exible packaging requirements.
Its position is under increasing pressure. Supply constraints linked to competing demand, including military use, have tightened global availability. At the same time, environmental and regulatory requirements are infl uencing material selection across the packaging value chain. Together, these factors are accelerating the move towards alternative resin systems.
Nitrocellulose (NC)-free inks including those that are polyurethane (PU)-based, are increasingly part of that shift. Their compatibility with polyolefi n recycling streams, supported by industry testing and approvals such as those from RecyClass, aligns with the direction set by the EU’s Packaging and Packaging Waste Regulation. For converters, the transition is moving from evaluation to implementation, often within compressed timeframes.
REFORMULATION AND PRESS PERFORMANCE Changing ink chemistry introduces diff erent performance characteristics on press. NC-free systems, particularly PU-based formulations, can vary in viscosity profi le, fl ow and solvent release. These diff erences infl uence transfer, fi lm formation and drying behaviour. In practice, this aff ects opacity, colour strength and consistency at production speeds. Drying windows may shift, increasing sensitivity to temperature, airfl ow and dwell time. Ink laydown can become less predictable if the system is not aligned with press conditions. In fl exible packaging, where throughput and repeatability are tightly controlled, small variations in transfer or drying can lead to waste, rework or reduced effi ciency.
THE ROLE OF THE ANILOX
The anilox remains central to ink metering and transfer. When ink behaviour changes, its specifi cation becomes a primary control point. NC-free inks can respond diff erently to established cell geometries and volumes. Variations in surface tension and rheology aff ect cell emptying and fi lm consistency. Achieving target opacity can be challenging, particularly at speed.
Increasing cell volume may improve laydown but can introduce extended drying times and higher dot gain. At the same time, interaction with the doctor blade becomes more sensitive, especially where lubrication and viscosity diff er from conventional systems.
Anilox selection therefore requires a clear understanding of how the ink performs in relation to cell geometry, line count and volume. Assumptions based on nitrocellulose systems are unlikely to deliver consistent results.
Surface energy at each interface, anilox condition, blade set-up and drying capacity all infl uence performance. Variability in one area can be amplifi ed when the ink system behaves diff erently under shear and transfer.
This reinforces the need for a whole-process approach. Coordination between ink suppliers, anilox manufacturers, plate providers and press teams supports a more stable outcome and reduces extended trials on press.
TESTING AND QUALIFICATION Structured testing is essential when introducing NC-free ink systems. Controlled trials allow ink and anilox interaction to be assessed under representative conditions, including press speed, substrate and drying parameters. This provides clarity on how diff erent engravings and volumes perform with diff erent resin types and helps defi ne the operating window for consistent production. Without this level of qualifi cation, variability is more likely during live runs. Access to facilities that replicate production conditions, like Sandon Global’s on-site R&D print demo centre, enables informed decision- making. Evaluating transfer, fi lm weight and drying behaviour in advance reduces disruption and shortens the path to stable output.
A PROCESS-LED RESPONSE
The shift towards nitrocellulose-free inks is being driven by supply and regulatory pressures that are unlikely to ease, setting a clear direction for the fl exible packaging industry.
The challenge now lies in execution. Ink reformulation changes the dynamics of transfer and drying, placing greater emphasis on how the entire print process is specifi ed and controlled. Converters that take a structured, system-wide approach, grounded in testing and cross-supplier collaboration, will be best placed to maintain consistency, protect effi ciency and adapt with confi dence as ink technologies continue to change.
C M Y CM MY CY CMY K
20
May/June 2026
www.convertermag.com
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