UV, UV LED and EB curing technology basics

Definition:

EB : electron beam ➞ accelerated e^-

Benefits:

• No photoinitiators required ➞ minimized migration and low migration
• High degree of conversion
• Very high speed achievable allowing deep penetration for thick coatings
• N₂ atmosphere needed to avoid O₂ inhibition
• High energy radiation
• Improved dot gain control
• No heat for sensitive substrates
• Highest performances : gloss, scuff and abrasion resistance
• Suitable for highly pigmented formulations

Recommended applications:

Principle of technology

Inside an ultra high vacuum chamber,an incandescent filament generates electrons. Then, the electrons are accelerated by a strong electrical field and exit the chamber through a thin titanium window.

Two variables matter particularly, the intensity (number of electrons generated per second) applied to the filament and the tension applied to accelerate these electrons.

The key parameters

With the EB curing technology, there are two key parameters that you can tune separately and independently from each other :

• The dose (kGv) influences the flow of electrons: raising it is equivalent to increasing the  the number of electron hitting a certain surface area
• The energy (kV) influences the penetration depth: increasing the energy is equivalent to amplifying the power of electrons that penetrate into the surface

Interaction with matter

 Let us imagine an electron penetrating an acrylate monomer/oligomer formulation to approach the interaction with matter.

An electron comes from the top, some collisions occur while penetrating the substrate. That the results of energy generation, the electron loses his energy along the trajectory and this energy is deposited in the matter.

Two scenarios:

• The energy is high (or the coating is thin), the electron goes all the way through the substrate
• The energy is low (or the coating is thick), the electron is absorbed by the matter

When the energy is deposited (red crosses), secondary slower electrons (blue circles) may be generated; they are slower than primary electrons.

Initiation mecanism

The low speed secondary electrons produced are solvated by the acrylate and allows the formation of a  radical anion. Then, the protonation (coming from impurities or traces of water) of this radical anion generates a free radical species. A free-radical initiated specie is produced and allow the polymerization start.

Thus, a primary electron generates many free radicals that will initate the polymerization reaction. The higher the primary electron energy is, the more free radicals are generated.  

We believe UV-LED technology to be the future of UV curing, for it is a lower energy-consuming option than traditional Hg-doped lamps. It is also the technology of choice to coat or print on to heat sensitive substrates.

Benefits:

• Very long lifetime and consistent energy output
• No infra-red emission ➞ no heat generated
• No warm-up time required
• Compact and flexible lamp design
• No generation of O₃
• Mercury-free system

Recommended applications:

• Industrial coatings
• Graphic arts
• Food packaging
• Electronics
• Adhesives

Discover our recommendations to improve the performance of your UV-LED curing acrylate systems.