Introduction: EB — Pure Energy Curing of Coatings by Electron Bombardment
The essential difference between EB (Electron Beam) curing and UV curing — UV — requires “photoinitiator” to absorb UV photons → generate free radicals — initiate polymerization
(photoinitiator remains in the coating — residue — possible migration — yellowing). EB high-energy electrons (>150keV) directly bombard coating molecules — “knock out” electrons from molecules to generate free radicals
(no photoinitiator needed — “electrons are the initiator”). EB-cured coating — (1) zero photoinitiator residue
“purest” coating — especially suitable for food packaging (no migration/zero residue)
; (2) extremely deep penetration depth
(>500μm — while UV is only <50μm) — can cure thick coatings (>200μm) + opaque coatings (containing fillers/pigments — UV cannot penetrate)
; (3) curing in inert atmosphere (N₂/zero O₂)
— no oxygen inhibition — uniform and complete curing. EB curing is a more ”fundamental” and more ”pure” energy curing technology than UV curing — but the high equipment cost (>2 million RMB/unit — >10 times that of UV) limits its widespread adoption — currently only used in food packaging/automotive/electronics/coil
and other high-value fields.
I. Comprehensive Comparison of EB Curing vs. UV Curing
| Dimension | EB Curing | UV Curing |
|---|---|---|
| Energy Source | Electron accelerator (>150keV) | UV lamp (mercury lamp/LED/365-405nm) |
| Photoinitiator | Zero (not required) | Essential (>3-8%) |
| Penetration Depth (μm) | >500 (adjustable) | <50 (coating thickness) |
| Inert Atmosphere | Essential (N₂/zero O₂) | Partial (nitrogen protection/optional) |
| Equipment Investment (10k CNY) | >200 | >5-50 |
| Application | Food packaging (zero migration)/automotive/coils/electronics | Woodware/3C/printing/general |
FAQ
Q1: Why is the “penetration depth” of EB more than 10 times that of UV?
UV (photons)——energy 3-5eV——weak penetration (absorbed and scattered by coating——>95% of UV photons absorbed within the first >50μm of the coating)The thicker the coating / the more filler——the shallower the UV curing depth
. EB (electrons)——energy >150keV——collisions between electrons and coating molecules are “random scattering”
——the “range” of electrons in the coating——relationship with electron energy E——R≈0.046×E^1.75/ρ(μm)——150keV electrons in a coating with density 1.2g/cm³——penetrate >200μm——300keV——>500μm——sufficient to cure the full thickness of the vast majority of industrial coatings (>500μm)
.
Q2: Why must EB curing be carried out under N₂ atmosphere—effect of O₂ on EB?
Free radicals generated by EB—are also “consumed” by O₂ (forming peroxy radicals ROO·—no initiation activity)—oxygen inhibition of EB curing is the same as UV
. UV—O₂ concentration at coating surface—air (>21% O₂)—N₂ protection can reduce to 10¹⁸ radicals/cm³·s—>1000 times that of UV)—with such high radical concentration—O₂ “cannot keep up” to consume allEB is less sensitive to oxygen inhibition than UV
—under low O₂ (99.9%) is lower than UV (>99.999%).
Q3: How to determine “insufficient” and “excessive” for the EB curing “dose” (kGy)?
Insufficient dose——coating incompletely cured——surface tacky——MEK wipe——base exposed——poor adhesion
. Excessive dose——(1) coating over-crosslinked embrittled (elongation drop >50%)
; (2) substrate (e.g., paper/plastic) suffers unnecessary radiation damage——degradation/discoloration
. Optimal dose——via DSC——measure residual reaction heat (ΔH) of coating at different doses——the minimum dose where ΔH approaches zero (>95% cured) = optimal dose
. EB curing equipment——dose can be precisely controlled via electron beam current (mA) and line speed (m/min)
“Dose (kGy) = K × beam current (mA) / line speed” controlled within >±5%——this is the controllability advantage of EB over UV.
Related Reading
Summary
EB curing (>150 keV — penetration >500 μm — zero photoinitiator — inert N₂) is the “cleanest” energy-curing technology — irreplaceable in food packaging (zero migration), automotive (thick coatings/opaque), and coil coating (high speed >300 m/min). Equipment investment (>2 million RMB) limits its widespread adoption. Kexin New Materials provides customers with technical support for EB-curable coating formulations and process parameters.