Q: Why does my UV formulation cure well under a mercury lamp but perform poorly with LED UV curing?

A: One possible reason is the difference in emission wavelengths between mercury lamps and LED curing systems. Mercury UV lamps emit a relatively broad spectrum, while UV LEDs typically operate at specific wavelengths, such as 365 nm, 385 nm, 395 nm, or 405 nm.

A photoinitiator must absorb the available LED wavelength effectively to initiate polymerization. However, wavelength compatibility is only the starting point. Resin chemistry, film thickness, pigment loading, photoinitiator concentration, and LED intensity can also affect curing performance.

A photoinitiator system that works under mercury UV may therefore require adjustment when the formulation is transferred to LED curing.

Q: Should I select the photoinitiator first or the UV resin first?

A: In most formulation development projects, these components should be considered together. UV resin is a primary film-forming material that influences viscosity, hardness, flexibility, adhesion, cross-link density, and chemical resistance. Its structure and functionality also affect the curing response of the complete system.

For example, a high-functionality resin designed for hardness and scratch resistance may require a different curing balance from a flexible resin used for films or soft-touch coatings. The monomer system, additives, pigments, and substrate can further change the curing behavior.

Instead of asking whether a photoinitiator is suitable in isolation, it is more useful to evaluate whether it can provide reliable curing with the selected resin under the intended LED conditions.

Q: Are there UV resins that can be used as reference points for LED curing development?

A: Yes. Lencolo offers several UV resin grades positioned for LED-curable applications.

Lencolo L-6240 is an LED-curable polyurethane acrylate positioned for high hardness, high gloss, high cross-link density, and scratch resistance. It is intended for applications such as coatings, inks, adhesives, OPV, plastics, paper, and nail gel.

Lencolo L-6241 is a low-odor LED-curable polyurethane acrylate with a reported viscosity of 20–50 CPS. It is positioned for fast LED curing, low shrinkage, good toughness, and film formation, with potential applications in inkjet, adhesives, OPV, plastics, paper, and nail gel.

For nail polish and nail gel formulations, Lencolo L-8442A is positioned as a color-coat resin with low odor, low LED heat release, fast curing, and good yellowing resistance.

These products have different performance profiles, so the photoinitiator system should be selected according to the resin’s intended application and curing requirements.

Q: Why can the same photoinitiator produce different results in different formulations?

A: The surrounding formulation can significantly influence photoinitiator performance. Pigments and fillers may absorb or scatter UV light, reducing penetration into the coating. Resin and monomer reactivity can affect polymerization speed, while additives may influence compatibility, surface appearance, and curing behavior.

Film thickness is another important variable. A thin, transparent coating may cure differently from a thick or highly pigmented film. In addition, surface dryness does not always indicate complete through-cure.

For this reason, testing should evaluate surface curing, through-cure, hardness, flexibility, adhesion, yellowing, and chemical resistance according to the application.

Q: What information should I collect before selecting a photoinitiator for LED UV curing?

A: The following information can help narrow the selection:

• LED wavelength and equipment intensity

• Exposure time, line speed, and lamp distance

• UV resin type and functionality

• Monomer system and photoinitiator concentration

• Pigment or filler loading

• Coating thickness and application method

• Substrate and required cured-film properties

If an existing formulation is available, the resin, monomers, additives, pigments or fillers, and solvent system should be evaluated together where relevant. This makes it easier to identify whether a curing issue results from wavelength absorption, insufficient light penetration, formulation compatibility, or process conditions.

Q: Can a supplier’s reference formulation be used directly in production?

A: A reference formulation can provide a useful starting point, but it should not be treated as a guaranteed production solution. Changes in raw materials, equipment, substrate, film thickness, or curing conditions may require formulation adjustments.

Lencolo’s technical framework includes product data, application guidance, reference formulations, process parameters, and troubleshooting information. Verified technical references are identified as “Status: Verified” and “Usage: Reference only.” Final suitability depends on the customer’s actual formulation and application conditions.

Q: What is the most practical approach to LED photoinitiator selection?

A: Treat photoinitiator selection as part of a complete formulation development process. Start by matching the photoinitiator’s absorption characteristics with the LED wavelength, then evaluate its compatibility with the UV resin, monomers, additives, pigments, and substrate.

Lencolo‘s LED-curable resin options, including L-6240, L-6241, and L-8442A, can serve as reference points for different application requirements. The final resin–photoinitiator combination should be confirmed through controlled laboratory trials and application-specific testing rather than relying on a single performance claim.

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Guangdong Lencolo New Material Co., Ltd.