Flexo inks come in three chemistries: water-based, solvent-based, and energy-curable (UV, LED, and EB). Water-based and solvent-based inks dry by evaporation or absorption. Energy-curable inks cure into a solid film under UV light or an electron beam. The ink system is chosen by the converter, but it also decides which plate material, cleaner, and curve the trade shop should use, so it belongs on the job record.
The three flexo ink types
| Ink type | How it dries | Typical work |
|---|---|---|
| Water-based | Evaporation and absorption | Paper packaging, corrugated, bags, and many narrow-web labels |
| Solvent-based | Evaporation | Wide-web film packaging, overwraps, and pouches |
| Energy-curable (UV, LED, EB) | Cured by UV light or electron beam | UV and LED in narrow-web labels; EB less common, wide and narrow web |
This split follows the Flexographic Technical Association's ink basics article (FTA, 2018). DIC, the parent of Sun Chemical, groups the market the same way: solvent inks mainly for film, water-based for paper and corrugated, and UV for narrow-web labels.
What is in each ink
All three systems carry a colorant in a resin, plus surfactants and additives. The differences that matter on press, per the FTA:
- Water-based: an acrylic resin made soluble with an amine, then thinned with water. This is why pH control matters.
- Solvent-based: a resin dissolved in a solvent, which is also the diluent used to adjust viscosity.
- Energy-curable: oligomers and monomers instead of a solvent. UV and LED inks add a photoinitiator that starts the cure under intense UV light.
The FTA's main rule applies to every type: follow the ink supplier's recommendation for the specific formula.
Why the ink system matters in prepress
Ink chemistry and plate material have to be compatible. DuPont's Cyrel handling guide warns that solvents such as acetates, heptane, or naphtha can swell, shrink, crack, or soften photopolymer plates above certain levels, and that UV inks may contain aggressive monomers that attack the plate in a similar way. DuPont's plate/ink compatibility guide lists the maximum share of each solvent in the ink's solvent portion when blended with n-propanol, for example 20% for ethyl acetate and 5% for acetone.
Swelling changes the printed result. A 2020 study in Coatings measured photopolymer plates swelling up to 5.7% in methoxypropanol, while EPDM rubber plates swelled 0.34%, and linked plate swelling to changes in printed line width.
So the ink system affects:
- Plate material: check the plate supplier's stated compatibility for solvent, water-based, or UV inks before imaging.
- Plate cleaning: DuPont lists alcohol or compatible blends for solvent and UV inks, and mild alkaline detergent for water-based inks.
- Dot gain curves: a curve built for one ink system and print condition does not transfer to another.
- Plate life: an incompatible ink or cleaner shortens the number of reruns a plate survives.
Food packaging needs more than an ink type
No ink type is food-safe by name. The European ink association EuPIA no longer uses the term "low migration ink" and refers to inks designed for food contact materials made under its GMP. Compliance depends on formulation, substrate, drying or curing, and the packaging structure, which the converter verifies. The trade shop should record what the converter specifies, not assume it.
What to keep on the job record
For each approved print condition, record the ink supplier, ink system and series, food-contact requirement if any, plate family and its stated ink compatibility, approved plate cleaner, and the curve built for that combination. When a converter switches from solvent to water-based or UV inks, treat it as a new print condition: check the plate family, rebuild the curve, and quote new plates before the first rerun.
Common questions
What are the main types of flexo ink?
Flexo inks fall into three chemistries: water-based, solvent-based, and energy-curable. Energy-curable inks include UV, LED, and electron beam (EB) systems. Water-based and solvent-based inks dry by evaporation or absorption, while energy-curable inks cure into a solid film under UV light or an electron beam.
Which flexo ink is used for what?
According to the FTA, water-based inks are common on paper packaging, corrugated, bags, and narrow-web labels. Solvent-based inks are used mainly in wide-web film packaging. UV and LED inks are widespread in narrow-web label printing, and EB is used to a lower degree in both wide and narrow web.
Does the ink type affect the flexo plate?
Yes. Solvents such as acetates, heptane, and naphtha, and aggressive monomers in some UV inks, can swell, soften, or crack photopolymer plates above certain levels. Choose a plate family rated for the ink system, use a compatible cleaner, and build the dot gain curve for that ink and print condition.
Are UV flexo inks safe for food packaging?
No ink type is food-safe by name. EuPIA no longer uses the term low migration ink and refers instead to inks designed for food contact materials under its GMP. Compliance depends on the formula, substrate, curing, and packaging structure, which the converter must verify.