UV Curing

Instant photopolymerization for inks, coatings, and adhesives

New to UV? Start here — in plain words

How UV turns a liquid into a solid in a flash

You've heard UV can “cure” or harden coatings, inks and glues. Here's what that actually means — no chemistry degree needed. A couple of minutes, and the detailed engineering version is right below.

What does "curing" even mean?

Curing simply means turning something from a soft liquid into a hard, finished solid. A wet coating, ink or glue goes on as a liquid; a flash of UV light hits it; it comes out dry and solid — often in under a second. Picture instant super-glue setting, but only exactly when you tell it to.
How can light harden a liquid?

The liquid carries tiny “starter” molecules called photoinitiators that stay asleep until the right UV light wakes them. Once lit, they kick off a chain reaction that links the liquid’s molecules into one solid network. Switch the light off and it stops — so you control exactly when and where it sets.
Why use UV instead of heat or just waiting?

Speed and gentleness. Old-style drying needs hot ovens, minutes of time, and often solvents that evaporate into the air. UV sets cold and almost instantly, with no solvents and far less energy — which is why high-speed printing and electronics lines rely on it.
Does "more light" simply mean "better"?

Not quite — it's about getting enough. Like baking, too little “baking” (too little UV) leaves it tacky or weak; the right amount sets it fully through. The amount of light delivered is the dose, and every material has its own target.
What usually goes wrong?

Two classics. First, the lamp’s “colour” (its wavelength) doesn’t match the liquid’s starter, so nothing wakes up. Second, the surface stays sticky because air interferes with the top layer (called oxygen inhibition). Both are fixable — but they’re exactly why a quick simulation before you build pays off.
Is it safe?

Curing light (UV-A, a longer wavelength than the germ-killing UV-C kind) is less harsh than UV-C — but it’s still strong light you don’t look into or expose skin to. Production systems shield it, and operators wear eye protection where needed.

Next: what “dose” really means →

UV Curing in 30 Seconds

Instant hardening of inks, coatings, and adhesives
No solvents, no drying time, no heat damage
UV-A (365nm) or UV-LED (395nm) depending on formulation
Used in printing, electronics, automotive, and medical devices

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How the cure happens

Photoinitiator (~2%) Monomer (liquid) Linked network (solid)

Photoinitiators make up only a few percent of the formulation (typically ~1–5 wt%), yet each one that absorbs a UV photon splits into radicals that start a chain reaction — linking the surrounding monomers into a solid network in a fraction of a second. That is why UV curing is near-instant and needs no heat or solvent evaporation.

Practical Guide

When Is UV Curing the Right Choice?

High-speed production lines, heat-sensitive substrates, VOC-free requirements. Not ideal for: thick pigmented layers (>200µm), shadow areas.

How to Size Your System

Dose = Irradiance × Time. Typical: 500–2000 mJ/cm² for inks, 2000–6000 mJ/cm² for thick coatings. Always match wavelength to photoinitiator.

LED or Mercury Arc?

LED: Single wavelength (365/385/395/405nm), instant on/off, no ozone. Mercury: Broad spectrum, proven for thick layers. Note: UV-curing mercury lamps are not banned in 2027 — their EU RoHS exemption faces a review that year (renewals filed), and Minamata's phase-outs cover consumer lighting, not curing lamps.

Photoinitiator Matching

The photoinitiator absorption spectrum MUST overlap with the lamp emission. LED-optimized formulations use Type I initiators (e.g., TPO, BAPO).

Common Mistakes

Wrong wavelength for formulation. Insufficient dose for full cure. Ignoring oxygen inhibition on surface. Not testing adhesion after cure.

Next Step

Use our UV Simulator to model irradiance distribution and curing dose — optimize lamp placement before building your line.

< 1s

UV curing hardens coatings in under one second — up to 100× faster than thermal drying, with zero VOC emissions.

UV Curing vs. Thermal Drying

Criteria	UV Curing	Thermal Drying
Cure Time	< 1 second	10–60 minutes
VOC Emissions	Zero (100% solids)	30–70% solvents evaporate
Energy Use	~80% less energy	Large ovens required
Heat-Sensitive Substrates	Minimal heat transfer	Substrate damage risk
Initial Investment	Higher (UV equipment + formulations)	Lower equipment cost
Formulation Flexibility	Requires UV-specific chemistry	Wide material choice

Oxygen Inhibition

Atmospheric oxygen can prevent full surface cure in free-radical systems. Solutions: nitrogen inerting, wax migration additives, or high-intensity LED flood curing.

Deep Dive

How does UV curing work chemically?

UV curing is a photopolymerization process. UV light is absorbed by photoinitiators in the formulation, which generate free radicals or cations. These reactive species trigger chain polymerization of monomers and oligomers, converting the liquid coating to a solid crosslinked polymer network within milliseconds.

Two main mechanisms: Free-radical (most common — acrylates) and cationic (epoxies, vinyl ethers — continues curing after UV exposure).

What wavelengths are used for curing?

UV-A (315–400nm): Most common for curing. Mercury H-bulbs peak at 365nm. LED systems typically operate at 365, 385, 395, or 405nm.

UV-B (280–315nm): Used for surface cure and some specialized initiators.

UV-C (200–280nm): Rarely used for curing — primarily for disinfection. Can cause unwanted degradation of some polymers.

What is the difference between irradiance and dose?

Irradiance (W/cm²) is the instantaneous UV power per unit area at the substrate surface. Dose (J/cm² or mJ/cm²) is irradiance × exposure time — the total energy delivered.

Both matter: high irradiance enables faster line speeds, but sufficient dose is needed for full crosslinking. A common error is achieving the right dose but with too low irradiance, which can lead to incomplete depth cure.

How do I transition from Mercury to LED curing?

Key steps: 1) Reformulate with LED-optimized photoinitiators (TPO, BAPO absorb well at 365–395nm). 2) Adjust dose — LED is narrowband, so efficiency differs from broadband mercury. 3) Test adhesion and cure depth with FTIR or MEK rub tests. 4) Consider nitrogen inerting for surface cure.

Note on regulation: medium-/high-pressure UV-curing mercury lamps are not banned in 2027. Their EU RoHS exemption (Annex III, 4(f)) carries a review deadline of 24 February 2027 — a re-evaluation, not an automatic ban — and renewal requests are filed. Still, the long-term direction favours LED, so an early transition is a sound future-proofing move.

Match the lamp to the chemistry

Lamp

Photoinitiator

Lamp emission Initiator absorption Usable overlap A cure only happens in the overlap — match the initiator's absorption band to your lamp's peak. A long-UV (~380 nm) initiator pairs well with a 385/395 nm LED; the same LED barely reaches a 290 nm benzophenone-type initiator.

Engineering deep-dives

Selecting a material for production? These vendor-neutral, sourced reference articles go beyond this overview into the engineering detail.

Selecting UV-Curable Adhesives & Coatings End-properties-first selection: adhesion, chemical/thermal resistance, shrinkage — and matching the UV source to the job. Read the reference Chemistry Families: Acrylate, Epoxy & Silicone Free-radical vs cationic cure, shrinkage, oxygen sensitivity, dark-cure — the property profile of each family. Read the reference Photoinitiators: Type I / II & Low-Migration Wavelength matching, surface-vs-through cure, yellowing, and food-contact migration limits. Read the reference

Need Expert Guidance?

Our team helps you select the right UV technology for your application — vendor-neutral, data-driven.

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[2] Minamata Convention on Mercury — UNEP (2013, ratified 2017)
[9] IEC 62471: Photobiological Safety of Lamps and Lamp Systems
[10] Kosar (2022): UV Curing: Science and Technology — Photoinitiator Chemistry and Formulation
[11] RadTech International: UV/EB Curing Technology and Applications