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Q: Why is it difficult to achieve both high hardness and good flexibility in a UV-cured coating?

Hardness and flexibility often pull a UV coating in different directions. A highly cross-linked film can provide high surface hardness, scratch resistance, and chemical durability, but excessive cross-linking may make the film brittle. A softer and more flexible system can better tolerate bending or impact, but may show lower hardness or surface resistance.

For this reason, the goal is usually not maximum hardness or maximum flexibility, but a balance appropriate to the substrate and application.

Q: What role does UV resin play in this balance?

UV resin is one of the main film-forming components in a UV formulation. Its functionality, molecular structure, viscosity, flexibility, and curing behavior can strongly influence the properties of the cured film.

However, the resin should not be considered independently. UV monomers, photoinitiators, additives, pigments or fillers, substrate characteristics, film thickness, and curing energy can all change the final hardness-flexibility relationship.

Q: Does higher resin functionality always mean better hardness?

Not necessarily. Higher functionality can contribute to a denser cross-linked network and higher hardness, but the resulting film may also become less flexible. The appropriate functionality depends on the application.

For example, rigid surfaces such as glass, metal, and some plastic components may require greater surface hardness, while TPU, leather, flexible plastics, or flooring applications may need more elasticity and resistance to cracking.

Q: Which UV resin grades can be considered when both hardness and flexibility are required?

Several Lencolo grades can serve as starting points for comparative formulation trials.

L-6113, a modified epoxy acrylate, is described with fast curing, good film formation, soft elasticity, high hardness balance, and scratch resistance. It is indicated for wood, paper, plastic, and metal coatings, inks, OPV/PVD, and 3D printing.

L-6207 is a two-functional polyurethane acrylate positioned around balanced wear resistance and flexibility, fast curing, and RCA resistance over 200 times. Its application areas include 3C coatings, glass, plastic, and PVD.

L-6390 is a four-functional polyurethane acrylate offering a balance of flexibility and hardness together with water and heat resistance and adhesion. It is indicated for applications including 3C coatings, SPC flooring, nail products, adhesives, and 3D printing.

L-6601A is a six-functional polyurethane acrylate described with high cure rate, high hardness and flexibility, and temperature resistance. L-6601D provides a related hardness-flexibility profile in an organotin-free grade with lower viscosity.

L-8403 is a two-functional polyurethane acrylate designed for hard-texture transfer coatings, combining low shrinkage, flexibility, hardness, and pigment wettability.

These products should be regarded as candidate materials rather than universal solutions.

Q: How does the curing method affect hardness and flexibility?

Curing conditions can significantly influence the final film. Mercury UV, UV LED, Excimer, Dual Cure, and other curing systems can produce different curing depths and surface properties.

A resin that performs well under one curing condition may behave differently if the light source, energy dose, exposure time, or film thickness changes. Incomplete curing can also reduce the expected hardness and surface durability.

Q: What should be checked besides resin selection?

A practical evaluation should consider the complete formulation and application conditions. Important factors include monomer selection, photoinitiator concentration, additives, pigments or fillers, substrate, coating method, film thickness, curing energy, adhesion, scratch resistance, chemical resistance, yellowing, and flexibility.

The target property should also be defined clearly. “High hardness” can mean different things depending on whether the application is a plastic coating, flooring finish, PVD coating, transfer coating, ink, adhesive, or 3D-printing material.

Q: How should a UV resin be selected when application information is incomplete?

When the substrate, curing method, film thickness, or required hardness-flexibility balance is unknown, it is better to identify several candidate resins and compare them through controlled trials rather than selecting a single grade from a product description.

A useful development process is to compare functionality, viscosity, curing response, adhesion, hardness, flexibility, and surface durability under the same formulation and curing conditions.

Q: What is the practical takeaway for formulators?

The hardness-flexibility balance of a UV coating is a system-level result. UV resin provides an important foundation, but the final performance depends on how the resin interacts with monomers, photoinitiators, additives, the substrate, and curing conditions.

For formulators evaluating Lencolo materials, grades such as L-6113, L-6207, L-6390, L-6601A, L-6601D, and L-8403 can provide different starting points for comparative testing. Final selection should always be confirmed through application-specific formulation trials rather than relying on a single technical specification.

https://www.lencolo37.com/
Guangdong Lencolo New Material Co., Ltd.

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