How UV Ink Curing Works – Principle and Key Influencing Factors
Principle of UV Ink Curing
The curing of UV ink is a photoinitiated polymerization process. When ultraviolet (UV) light irradiates the ink surface, photoinitiators in the ink absorb the light energy, generating free radicals or cations. These reactive particles bond with monomers and oligomers in the ink, forming a cross-linked polymer network and transforming the ink from a liquid to a solid state.
The curing process consists of four main steps:
Light absorption – The photoinitiator absorbs UV energy.
Free radical generation – The absorbed energy splits the initiator to produce free radicals.
Chain reaction – Free radicals trigger polymerization with monomers and oligomers.
Cross-linking – The polymer chains interconnect, solidifying the ink film.
This reaction occurs in seconds and is an eco-friendly printing process, producing no VOC emissions.
Why Some Materials Are Difficult to Cure
1. Surface Properties of Materials
Smooth or Metallic Surfaces: Materials such as stainless steel, aluminum, and glass have low surface energy, making it difficult for UV ink to adhere. After curing, the ink layer may peel off easily.
Surface Contamination or Coating Residue: Dust, oil, or residual additive films can block UV light exposure or interfere with chemical reactions, resulting in poor curing or weak adhesion.
Solution: Apply surface treatment or primer (e.g., cleaning, flame, or corona treatment) to increase adhesion and ink wetting.
2. Chemical Composition of Materials
High Chemical Stability: Materials such as PTFE, POM, and nylon have highly stable molecular structures, making them less reactive with UV ink.
Reactive Functional Groups: Some plastics contain amines, amine salts, or double bonds, which compete with free radicals during polymerization, thus inhibiting proper curing.
Solution: Use primers or adhesion promoters to improve bonding, or increase UV lamp intensity (e.g., using 365 nm/395 nm wavelength lamps) to enhance curing efficiency.
3. Insufficient Light Conditions
Low or Aged Light Source Power: When the power of UV or LED lamps decreases over time, the emitted energy becomes insufficient.
Incorrect Spectrum Matching: If the photoinitiator’s absorption wavelength does not match the light source, curing efficiency drops.
Improper Curing Speed: If the curing speed is too fast, curing may be incomplete; if too slow, the material may be overheated or scorched.
Solution: Regularly inspect and replace UV lamps, and extend exposure time when needed.
4. Environmental Factors
Oxygen Inhibition Effect: Oxygen in the air reacts with free radicals to form peroxides, which interrupt the polymerization chain reaction.
Abnormal Temperature and Humidity: High humidity reduces ink fluidity, while low temperatures decrease the activity of photoinitiators.
Solution: Maintain an ambient temperature of 20–28 °C and humidity between 40–60%.
Use air circulation or dehumidification equipment when necessary to ensure stable curing conditions.
How to Improve Curing Performance
1. Optimize the UV System
Match ink and lamp wavelength (commonly 365 nm or 395 nm).
2. Surface Pretreatment
Apply flame, plasma, or primer to low-energy materials.
3. Use High-Reactivity UV Ink
Choose formulations containing dual-function photoinitiators or PUA oligomers.
4. Adjust Curing Parameters
Balance power and speed for consistent exposure.
5. Regular Maintenance
Clean the curing system every 500 hours to prevent dust accumulation.
Conclusion
UV ink cures rapidly because photoinitiators trigger a chain polymerization reaction when exposed to ultraviolet light. However, poor curing can occur due to factors such as low surface energy, chemical inertness, insufficient light exposure, or environmental interference. By selecting the right ink, optimizing curing parameters, and applying proper primer treatment, you can greatly enhance adhesion and abrasion resistance, ensuring more stable and reliable printing results.
Contact & Solutions
Want to know how to choose the right UV inks or primers for different materials? Contact us for original UV ink and specialized primer solutions — we’ll provide expert matching advice to help you achieve the best printing results.