1. Introduction

UV-curing colorant is a pigment dispersion system that cross-links into a solid film within seconds under ultraviolet radiation, driven by a photoinitiator. As LED-UVA sources and low-VOC regulations advance, understanding its dispersion and curing mechanism is critical for formulators. This article explains the mechanism and the three key factors governing cure.

Fig.1 Tunnel UV curing machine line

2. Technical Features and Mechanism

A UV-curing colorant is defined as a stable dispersion of organic/inorganic pigments in UV-reactive oligomers and monomers, with a matched photoinitiator package. Upon absorption of UVA photons, the photoinitiator generates free radicals (radical cure) or cations (cationic cure), which instantly polymerize the acrylate or epoxy functionality.

DENSON formulates pigment-wetting dispersants that anchor onto pigment surfaces and provide steric stabilization, keeping the fineness below 15 μm (GB/T 1724) and preventing flocculation under UV exposure.

Fig.2 LED UVA lamp curing on conveyor

3. Key Factor 1: Pigment Absorption of UV Light

Pigments can absorb or scatter incident UV, shadowing deep layers. High-absorption colors (black, dark blue) reduce cure depth. Matching pigment loading and using a surface cure/through-cure initiator blend solves this.

4. Key Factor 2: Photoinitiator and Wavelength Matching

The initiator absorption spectrum must match the LED emission (365/385/395 nm). ACS Appl. Electron. Mater. (2026) reports on UV-curable nano-alumina inks where polymeric dispersants improve initiation efficiency under LED-UVA.

5. Key Factor 3: Oxygen Inhibition and Film Thickness

Oxygen inhibits radical polymerization. Nitrogen blanketing or over-cure layers reduce tack-free time; films thicker than 300 μm risk under-cure.

Fig.3 Five colorant sample cups

6. Key Parameters

See more in Literature and DENSON website.

7. Conclusion

UV-curing colorant performance is governed by pigment UV absorption, photoinitiator-wavelength matching, and oxygen inhibition; proper dispersion and initiator selection yield a ≤3 s, high-hardness film.

8. FAQ

Q1: Why does dark UV colorant under-cure?
A: Dark pigments absorb/scatter UV, reducing through-cure; use a through-cure initiator and lower film build.

Q2: Can I use mercury lamp initiators on LED-UVA?
A: Not directly; choose initiators absorbing at 365-395 nm for LED.

Q3: Does oxygen affect cure?
A: Yes, it inhibits radical cure; nitrogen blanketing removes surface tack.

Q4: What fineness is needed?
A: ≤15 μm per GB/T 1724 for high gloss and stable dispersion.

Q5: How to improve adhesion on plastic?
A: Add adhesion promoters and corona-treat the substrate.