Selecting the right chemicals is essential for developing effective ultraviolet (UV)-curing epoxy coatings. UV-curable resins are popular for their versatility, strength, adhesion, and efficiency across various industrial and commercial applications. Curing can take as little as several seconds, supporting even the fastest manufacturing, assembly, finishing, or printing processes.

Oxetane’s Role in UV-Curing Epoxy Coatings

Oxetane is a highly active diluent, making it effective in cationic UV-curable epoxy ring prepolymers. Compared to conventional epoxy or vinyl ether compounds, oxetane monomers exhibit superior adhesion, flexibility, stain resistance, and hydrophobicity when formulated properly in UV-curing epoxy coatings.

As a highly reactive UV photo-cationic monomer, oxetane can cure in seconds via ring-opening polymerization. There are different oxetane UV-curable resin formulations with unique properties and applications, but all of them are known for their low viscosity and fast cure speeds. These advantages make oxetane-based UV-curing epoxy preferred in numerous industries and applications.

Cationic UV Cured Epoxy Coatings

Cationic UV-curing epoxy is primarily made of cycloaliphatic epoxy resin, oxetanes  and a cationic photoinitiator. When exposed to UV rays, the photoinitiator creates a long-lived acidic species that opens an epoxy group, forming a carbocation. The carbocation then begins a chain reaction with other epoxy groups, developing a robust network of cross-linked epoxies.

With a lack of oxygen inhibition, the cross-linked epoxy coating has minimal cure shrinkage or other surface cure issues. The coating also achieves good adhesion, which post-thermal curing can further improve. The strength and versatility of UV-curing epoxy make it an effective choice for many applications, including graphic arts, and its low migration through substrates makes it suitable for food packaging.

Ultimately, the exact formulation and curing process of the cationic UV-cured epoxy coating depend on its exact application.

Guide to UV-Curing Epoxy Formulations

Creating a UV-curing epoxy requires several important considerations and parameters, including:

  • UV Formulation: Depending on how the UV-curing epoxy is formulated, there are several different curing methods available, such as UV or LED  light, electron beams, or free-radical-emitting species (like peroxide)(where was this obtained from?, I know peroxides are used a lot in composite applications with unsaturated polyesters, but don’t know of any examples when used in UV formulations). UV-initiated free-radical curing is the most common type of UV formulation.
  • Curing Process: UV light triggers photoinitiators to produce unpaired electrons or free radicals. The free radicals react with acrylated or methacrylated substances to create a cross-linked polymer matrix pattern. The cationic polymerisation is an acid catalyzed reaction which once initiated continues to cure to completion in the absence of U.V. light, whereas a free-radical reaction which is propagated by free radicals ceases almost immediately after exposure.
  • Formulation Parameters: Numerous parameters must be carefully considered, including the epoxy’s purpose (e.g., coating, adhesive, 3D printing, ink, or photopolymer plate). Application method also matters, as it bears an impact on the following: type of ink (e.g., inkjet, lithography, offset, or screen printing), coating (e.g., roll, flow, or spray coating), adhesive (e.g., microdot or precision dispense), and substrate (e.g., wood, glass, polypropylene, PMMA, PET, aluminum, stainless steel, vinyl, or polycarbonate).
  • Curing Conditions: UV curing conditions can also vary widely. Curing is possible using visible light, metal halide, or broad-spectrum mercury. Some UV-curable resins use LEDs designed to create specific wavelengths, like 365, 385, 395, or 405 nm. It’s also possible to create UV-curing epoxy that only cures from high- or low-intensity light exposure, or for specific application methods, such as conveyor, flood, spot, or roll-to-roll methods. Curing conditions may also affect manufacturing line speed.

UV Curing Epoxy From Toagosei America

Choosing the right formulation and curing method depends on careful analysis of your coating, bonding, or adhesive applications. Toagosei’s Aron Oxetane® chemicals are specifically formulated for UV-curable epoxy resins. We also provide Aronix®, special acrylic monomers and oligomers designed for UV-curable acrylic resins. Toagosei America specializes in providing functional chemical and adhesive technologies that comply with our customers’ unique manufacturing requirements and specifications. These are the UV-curable solutions we provide:

  • UVX-6420 and UVX-6812 (UV adhesives)
  • UVX-5800 (UV curable conformal coatings)
  • UVX-6524 (UV hard coatings)

To learn more about UV-curing epoxy, contact us today.