Choosing Coding Ink for Pharmaceutical Packaging

Coding on pharmaceutical primary and secondary packaging is a small but consequential part of the production process. A missing, illegible, or unreadable code can prevent product release, disrupt distribution, or trigger downstream investigations. The ink chosen for that code — and the process around it — matters more than the code's visual simplicity suggests.

This article outlines the practical decisions involved in choosing a coding ink for pharmaceutical packaging, based on the work Axion Group does with pharmaceutical manufacturers and their coding equipment suppliers.

Coding requirements in pharma

Pharmaceutical coding typically has to satisfy several parallel requirements:

• Legibility for the intended reading method — human, camera, or laser scanner
• Adhesion to the specific packaging substrate under the expected handling conditions
• Durability through any downstream process the coded packaging encounters
• Traceability — the coding equipment and the ink together produce a stable, verifiable mark

A coding ink chosen for one packaging line is not automatically appropriate for another line, even inside the same facility.

Solvent-based vs water-based

Coding inks fall broadly into solvent-based and water-based families. The choice is driven by the substrate and the environment.

• Solvent-based inks — typically use MEK, ethanol, or acetone as the base solvent. They dry quickly on non-porous substrates and can produce durable marks on aluminium foils, PVC, PET, HDPE, and coated cartons. They require appropriate ventilation and handling on the production line.
• Water-based inks — typically used on uncoated paperboard, uncoated labels, and other porous substrates. They are less aggressive on operators and equipment but rely on the substrate's absorbency to dry.

Neither family is intrinsically superior; each is selected for the application.

Cartridge compatibility

Thermal inkjet (TIJ) coders in particular are cartridge-based systems, and the ink and cartridge are engineered together. Using a non-compatible cartridge in a TIJ head can cause code failures, printhead damage, or inconsistent drop formation.

Axion Group supplies solvent-compatible and water-based cartridge references intended for common TIJ platforms. The specific compatibility of a cartridge against a specific coder is confirmed through documentation review and an on-line trial before regular supply.

Substrate considerations

The substrate is the single most important variable in coding ink selection. Practical questions we ask before recommending an ink:

• What is the exact packaging substrate (grade, supplier, coating)?
• Is the print surface pre-treated or coated?
• What downstream processes will the code pass through?
• What is the line speed and code height?
• What reading equipment (camera or scanner) is verifying the code?
• What is the ambient humidity and temperature at the coding station?

A coding ink recommendation that does not account for these variables is a guess.

Trial evaluation

For every new coding ink we recommend a structured trial:

1. Short bench trial on the customer's substrate, at the customer's plant, using the customer's coder.
2. Documented abrasion, solvent, and — where applicable — heat / humidity testing of the coded sample.
3. A limited production run before regular supply.
4. Formal internal review and change control at the customer's quality function.

The trial produces the evidence base a pharmaceutical quality system needs. It is not a bureaucratic step; it is the mechanism by which a new coding ink becomes an approved consumable on a specific line.

Common questions during selection

A few practical points come up repeatedly during coding-ink selection conversations:

• Do we need a fresh trial when the substrate lot changes? In most cases, yes. Even lots from the same substrate supplier can shift in ways that affect adhesion and drying.
• How much sample material should we request? Enough for at least one full bench trial, plus retained samples. A single-cartridge or single-litre sample is often not enough for a meaningful evaluation.
• Is a single successful trial sufficient? Ideally the trial covers at least one shift change and one substrate lot. This surfaces the everyday variability that a one-hour print does not.
• Who signs off the change? The customer's quality function, informed by the trial record. The supplier's role is to provide the ink, technical documentation, and support — not to authorise the change internally.

Talk to Axion Group if you are evaluating a new coding ink, changing coder platform, or trying to consolidate coding consumables across multiple lines — we will work through the trial with you.