Balancing hardness and flexibility is a common challenge in UV-curable coating development. A coating with high hardness may offer better scratch resistance but become brittle under bending or impact, while a flexible film may lack the surface durability required for demanding applications. Selecting the right UV resin is an important step toward achieving both properties, but the final result also depends on monomers, photoinitiators, additives, substrates, film thickness, and curing conditions.

Guangdong Lencolo New Material Co., Ltd., operating under the Lencolo brand, supplies UV-curable resins and related formulation materials for coatings, inks, adhesives, 3D printing, and other industrial applications. Its product portfolio includes epoxy acrylate and polyurethane acrylate resins that can be evaluated for different hardness-flexibility requirements.

1. Why Hardness and Flexibility Must Be Evaluated Together

Hardness, flexibility, scratch resistance, adhesion, and impact resistance are related but distinct performance characteristics. Increasing crosslink density may improve hardness and resistance to certain forms of surface damage, but it can also increase brittleness in some formulations. Conversely, a more flexible resin structure may improve deformation tolerance while changing hardness, chemical resistance, or abrasion performance.

The ideal balance depends on the application. Plastic coatings may require adhesion and flexibility alongside surface hardness. PVD and decorative coatings may prioritize appearance and scratch resistance. SPC flooring, adhesives, and 3D printing materials have different mechanical and processing requirements.

UV resin selection should therefore consider the substrate, application method, curing source, target viscosity, film thickness, and required film properties rather than relying on a single specification.

2. UV Resin Options for Balanced Film Performance

Lencolo offers several UV resin grades with documented properties relevant to hardness and flexibility. These products can serve as candidates for comparative formulation trials, with final selection determined by actual application results.

L-6113: Modified Epoxy Acrylate UV Resin

L-6113 is a four-functional, low-viscosity modified epoxy acrylate. Its listed viscosity is 800–1,500 cP, with an acid value of 4–8. The product is positioned for fast curing, good film formation, scratch resistance, and a balance between softness or elasticity and hardness.

Potential application areas include wood, paper, plastic, and metal coatings, as well as inks, overprint varnishes (OPV), PVD, and 3D printing. It can be evaluated when formulators require efficient curing and surface durability without overlooking film deformation requirements.

L-6207: Difunctional Polyurethane Acrylate

L-6207 is a two-functional polyurethane acrylate with a listed acid value of ≤2 and viscosity of 28,000–38,000 cP. Its stated properties include balanced wear resistance and flexibility, fast curing, and RCA resistance exceeding 200 cycles under the specified test conditions.

The resin is intended for applications including 3C coatings, glass, plastic, and PVD. For projects involving repeated surface contact, the reported RCA result can provide a useful screening reference, but testing conditions and performance on the target substrate should be confirmed before making direct comparisons with other materials.

L-6390: Four-Functional Polyurethane Acrylate

L-6390 is a four-functional polyurethane acrylate with an acid value of ≤1 and a listed viscosity of 4,000–8,000 cP at 60°C. Its stated properties include water and heat resistance, adhesion, and a balance between flexibility and hardness.

Potential applications include 3C coatings, DIY glue, SPC flooring, nail polish, and 3D printing. It may be considered when a formulation needs to combine mechanical balance with resistance to water or heat. Actual performance will depend on the complete formulation and curing conditions.

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

L-6601A is a six-functional polyurethane acrylate with an acid value of ≤5 and a listed viscosity of 2,500–5,000 cP at 60°C. It is positioned for fast curing, high hardness, flexibility, and temperature resistance. Its indicated applications include PVD, gloss varnish, inks, DIY glue, 3D printing, and plastics.

L-6601D is a related organotin-free grade positioned for high hardness and flexibility, with a listed viscosity of 20,000–36,000 cP. It may be worth evaluating where organotin-free material selection is required. Despite their related positioning, the two grades should be compared using current technical data and application-specific tests rather than assumed to perform identically.

L-8403: Polyurethane Acrylate for Transfer Coatings

L-8403 is a two-functional polyurethane acrylate with a listed viscosity of 20,000–50,000 cP. Its stated properties include low shrinkage, good flexibility, good hardness, and good pigment wettability. Potential applications include adhesives, inks, coating-film transfer, and nail gel.

For transfer coating development, these characteristics provide a starting point for assessing film formation and deformation tolerance. Compatibility with the existing formulation and transfer process should be confirmed through trials.

3. Formulation Factors Beyond Resin Chemistry

Even when a resin has the desired hardness-flexibility profile, the complete UV formulation can change the final result. Reactive monomers affect viscosity, crosslinking, and film properties. Photoinitiators influence polymerization under the selected UV source, while additives and pigments can affect dispersion, surface quality, and curing behavior.

Curing methods may include mercury UV lamps, UV LEDs, excimer systems, or suitable dual-cure and UV-plus-thermal processes. The selected resin must be evaluated against the actual equipment, wavelength where applicable, exposure conditions, and coating thickness.

Application method matters as well. Spray coating, roller coating, screen printing, inkjet, and transfer coating impose different requirements on viscosity, flow, film formation, and substrate contact.

4. How to Select and Validate a Candidate Resin

A practical selection process starts by defining the substrate and the most important performance targets. Formulators should then compare resin chemistry, functionality, viscosity, and relevant technical data before preparing trial formulations.

Testing should evaluate hardness, flexibility, adhesion, scratch and abrasion resistance, and any application-specific requirements, such as water resistance, heat resistance, or transfer performance. When an existing formulation is available, the resin should be evaluated alongside the current monomers, photoinitiator, additives, pigments, and other ingredients.

Guangdong Lencolo New Material Co., Ltd. provides UV resin options and technical product information to support this screening process. Its grades L-6113, L-6207, L-6390, L-6601A, L-6601D, and L-8403 offer different starting points for developing UV-curable coatings and related materials. The most suitable choice is the one that meets the project’s mechanical, processing, and surface requirements after testing under actual conditions.

Ultimately, achieving the right balance between hardness and flexibility requires a complete formulation approach. Comparing resin candidates using documented properties and controlled application trials helps manufacturers select UV materials more confidently and develop coatings tailored to their intended use.