A UV coating can pass a hardness test and still fail during bending, impact, or repeated use. This is why achieving a reliable balance between hardness and flexibility remains an important challenge in UV-curable formulation development. The objective is not simply to maximize one mechanical property, but to develop a cured film that meets the actual requirements of its substrate, application, and service environment.

UV resin plays a central role in determining film formation, crosslinking behavior, adhesion, and mechanical performance. However, the final properties of a coating are shaped by the interaction between the resin, reactive monomers, photoinitiators, additives, pigments, and curing process.

What Determines the Hardness-Flexibility Balance?

The relationship between hardness and flexibility is influenced by resin chemistry and formulation structure. Resin functionality, molecular architecture, and crosslink density can affect the rigidity, toughness, and deformation resistance of a cured film. Higher crosslinking may support surface hardness, while the use of appropriately designed resin structures and reactive components can help address flexibility requirements. These effects are formulation-dependent and should not be interpreted as universal rules for every UV system.

The substrate also plays a significant role. A hard coating for a PVD plastic component, a UV finish for SPC flooring, and a transfer coating applied to a flexible film may require different performance priorities. Scratch resistance, adhesion, elongation, impact resistance, chemical resistance, and water resistance should be considered together rather than evaluated independently.

Lencolo UV Resins for Comparative Formulation Development

Guangdong Lencolo New Material Co., Ltd., operating under the Lencolo brand, supplies UV resins for coatings, inks, adhesives, PVD, and 3D printing. The following grades provide different technical directions for investigating hardness and flexibility in specific application systems.

L-6113 | Modified Epoxy Acrylate

L-6113 is a low-viscosity, four-functional modified epoxy acrylate described as offering fast curing, excellent film formation, soft elasticity, high hardness balance, and scratch resistance. Its viscosity is 800–1,500 CPS, with applications including wood, paper, plastic, and metal coatings, inks, OPV/PVD, and 3D printing.

L-6207 | Two-Functional Polyurethane Acrylate

For applications where wear resistance and flexibility are important, L-6207 is positioned with balanced wear resistance and flexibility, fast curing, and RCA resistance over 200 times. It has a functionality of 2 and viscosity of 28,000–38,000 CPS, and is indicated for 3C coatings, glass, plastic, and PVD.

L-6390 | Four-Functional Polyurethane Acrylate

L-6390 combines documented claims for water resistance, heat resistance, adhesion, and a balance of flexibility and hardness. Its functionality is 4, with viscosity of 4,000–8,000 CPS at 60°C. Application areas include 3C coatings, DIY glue, SPC flooring, nail polish, and 3D printing.

L-6601A and L-6601D | Six-Functional Polyurethane Acrylates

L-6601A is positioned for high curing speed, hardness, flexibility, and temperature resistance. It is indicated for PVD, gloss varnishes, inks, DIY glue, 3D printing, and plastics. L-6601D provides a related organotin-free option with low-viscosity positioning and high hardness and flexibility claims. The applicable grade should be evaluated against the formulation's regulatory and performance requirements.

L-8403 | High-Performance Polyurethane Acrylate

L-8403 is designed for hard-texture transfer coatings and is described as offering low shrinkage, flexibility, hardness, and pigment wettability. With functionality of 2 and viscosity of 20,000–50,000 CPS, it is indicated for transfer films, adhesives, inks, coatings, and nail gel.

How to Compare Resins During Formulation Trials

Product selection becomes more meaningful when each resin is tested under consistent conditions. A comparative evaluation should consider:

• Substrate and adhesion: Whether the cured film remains bonded during bending, impact, or repeated handling.

• Mechanical properties: Hardness, flexibility, abrasion resistance, and resistance to cracking.

• Curing conditions: UV lamp type, LED wavelength, curing dose, line speed, and film thickness.

• Formulation compatibility: Resin viscosity, monomer selection, photoinitiator response, pigment dispersion, and additive effects.

• End-use requirements: Chemical resistance, water resistance, temperature resistance, and weathering performance.

A resin's technical data sheet can help identify suitable starting points, but it cannot establish finished-film performance across all formulations and production conditions.

A More Practical Selection Strategy

When application information is incomplete, it is more appropriate to establish a preliminary comparison plan than to select a definitive resin immediately. Identify the substrate, coating or printing method, curing technology, target viscosity, and required hardness-flexibility range first. These details help narrow the relevant resin families and define the tests needed to compare them.

Lencolo's technical support process includes application information intake, product recommendation, candidate selection, and formulation troubleshooting. Reference formulations and process parameters should be treated as technical guidance for evaluation, with suitability confirmed under the customer's actual conditions.

Conclusion

Hardness and flexibility in UV coatings are influenced by resin structure, formulation composition, substrate compatibility, and curing conditions. Epoxy acrylates and polyurethane acrylates offer different starting points for developing coatings with specific mechanical and application requirements.

Lencolo grades such as L-6113, L-6207, L-6390, L-6601A, L-6601D, and L-8403 can be considered for comparative testing across coatings, inks, PVD, transfer applications, and other UV-curable systems. The most appropriate choice depends on measured performance in the complete formulation rather than a single specification or product description.

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Guangdong Lencolo New Material Co., Ltd.