What Is UV Flexo Ink? Full Guide to Components, Curing, Advantages & Applications

Date: Dec 04 2025   from: StarColor Ink  Views:

UV flexo ink has become a core consumable for modern flexographic printing, thanks to its dual advantages of zero-VOC emissions and ultra-fast UV curing. It is not simply “flexo ink + UV technology,” but a formulation engineered specifically for flexo printing, which requires low viscosity, excellent transfer through anilox rollers, and clean performance at high printing speeds.

The incompatibility of conventional solvent-based inks (slow drying, pollution) and the limitations of water-based inks (weaker weather resistance) have made UV flexo ink the fastest-growing category in the flexographic ink market.

Today, UV flexo ink holds a penetration rate of around 38% in labels, food packaging and flexible packaging, expanding at an average annual growth rate of 12%. This article explains its definition, composition, curing mechanism, key advantages and application guidance.

1. Definition: The Precise Fusion of Flexo Technology and UV Curing

UV flexo ink is a solvent-free flexographic ink that uses ultraviolet light as the curing energy to create a cross-linked polymer film. Its core essence lies in two points: flexo-friendly rheology and UV instant curing. It meets the requirements of anilox-roller ink transfer while eliminating drying dependency on heat or evaporation.

Unlike solvent or water-based flexo inks that rely on evaporation to dry, UV flexo ink forms its ink film through a photo-initiated polymerization reaction. This allows precise control of ink-film thickness (≤0.5 μm deviation) and stable curing at 200–300 m/min. Water-based inks often fail at this speed due to “blocking” and insufficient drying.

Industry Insight: UV flexo ink represents the shift of flexography from solvent-dependent to green and high-speed production.

2. Key Components: A Formula Tailored for Flexo + UV Requirements

2.1 Flexible UV Resin (35%–50%)

UV flexo ink primarily uses polyurethane-acrylate resins with built-in flexible polyether or polyester segments. After curing, the ink film achieves:

• Elongation ≥ 18%
• 100× fold resistance without cracking
• Adhesion compatible with PP/PE films (5B after corona)

The resin’s viscosity (500–1500 mPa·s) becomes flexo-compatible when blended with active diluents, reaching 100–300 mPa·s.

High-end UV flexo inks increasingly use bio-based resins (e.g., soybean-oil acrylates), providing a 40%+ reduction in carbon footprint.

2.2 Flexo-Grade Photoinitiators (3%–5%)

Photoinitiators absorb UV energy and trigger curing. Flexo printing requires fast-response, low-migration grades, such as:

• α-hydroxy ketones (e.g., 1173): respond in ≤0.1 s at 365–395 nm
• Thioxanthones (ITX): improve deep curing and avoid “surface cure only” issues
• Reactive photoinitiators: for food packaging, showing migration ≤0.008 mg/kg

2.3 Active Diluents (20%–30%)

Active diluents replace solvents and fully participate in the polymerization reaction. Common grades include TPGDA and DPGDA, with:

• Viscosity: 20–50 mPa·s
• No VOC emissions
• Enhanced final ink-film strength

2.4 Pigments & Functional Additives

Pigments are dispersed to 100–300 nm to avoid anilox clogging. Additives include:

• Defoamers (0.1%–0.3%)
• Leveling agents (0.5%–1%)
• Adhesion promoters for PP/PE
• UV absorbers, antibacterial agents, anti-static agents

3. Curing Mechanism: Instant Film Formation for High-Speed Flexo

UV flexo ink cures in two stages within 0.2–0.5 seconds:

Stage 1: Pre-Cure & Leveling (0.1–0.2 s)

• The ink smooths due to shear-thinning properties.
• Optional low-energy UV lamp forms a 0.5–1 μm surface gel to prevent abrasion.

Stage 2: Main UV Cross-Linking (0.1–0.3 s)

• Photoinitiators decompose instantly under LED-UV (395 nm).
• Radical polymerization begins at thousands of reactions/s.
• A tight 3D network forms, locking pigments in place.

Typical curing energy requirement:

• PE film: 60–70 mJ/cm²
• Paper: 90–100 mJ/cm²

4. Key Performance Advantages

4.1 Environmental Compliance

• VOC ≤ 10 g/L (far below 100 g/L limit)
• No solvent residue after curing
• Heavy metals ≤ 0.1 mg/kg

4.2 Broad Substrate Compatibility

• PP/PE after corona: adhesion 5B (GB/T 9286)
• PET, aluminum foil: peel strength ≥ 5 N/15 mm
• No smearing on paper or non-wovens

4.3 Durability & Chemical Resistance

• ≥ 1000 abrasion cycles
• 50× alcohol rub resistant
• Stable from –20°C to 70°C

4.4 High-Speed Productivity

• Suitable for 200–300 m/min flexo lines
• No drying tunnel required
• Waste rate ≤ 1%

A label factory example: daily output increased from 200,000 m² to 350,000 m² after switching to UV flexo ink.

5. Applications & Selection Guidelines

• Food packaging: choose low-migration, reactive photoinitiator systems.
• Personal-care labels: prioritize solvent/chemical resistance.
• Flexible packaging: require elongation ≥ 20%.
• Paper packaging: use high-solid systems (50%–60%).

Selection principle: determine substrate (polar/non-polar), printing speed, curing energy and regulatory requirements.

6. Future Trends

• Lower-energy LED curing
• Functional inks (antibacterial, anti-counterfeiting, thermochromic)
• Bio-based resin systems exceeding 50%

Conclusion

UV flexo ink is the result of deep integration between flexographic printing and UV curing. By providing solvent-free formulation, instant curing and wide substrate compatibility, it helps packaging manufacturers achieve higher efficiency, lower emissions and superior print quality. Understanding its mechanism and formulation enables companies to choose the right system and leverage UV flexo technology for competitive advantage.