Q1: Why is it difficult to achieve both high hardness and good flexibility in a UV coating?

Hardness and flexibility often work in opposite directions. A highly cross-linked UV film may provide excellent surface hardness, scratch resistance, and chemical resistance, but excessive cross-link density can make the coating brittle. A softer and more flexible formulation may withstand bending or impact better, but it may be more vulnerable to scratching, abrasion, or surface marking.

UV resin is a major film-forming component, but the final balance depends on the complete formulation. Monomers, photoinitiators, additives, pigments or fillers, substrate properties, film thickness, and curing conditions can all influence the result. Therefore, selecting a resin only because it is described as “high hardness” or “flexible” may not solve the actual application problem.

Q2: Should resin functionality be the first factor to consider?

Functionality is an important starting point because it influences the potential cross-link density after curing. Higher-functionality resins may contribute to increased hardness and surface durability, while lower-functionality or flexible resin structures may provide better elongation and impact resistance.

However, functionality should not be evaluated independently. A high-functionality resin may not be suitable for a flexible substrate if it produces excessive brittleness or shrinkage. Similarly, a low-functionality resin may not provide sufficient surface protection for demanding applications.

The selection should consider the required hardness, flexibility, adhesion, curing speed, and substrate behavior together.

Q3: Are there UV resin grades that can be evaluated for a hardness-flexibility balance?

Yes. Several Lencolo products can be considered as starting points for comparative testing.

L-6113, a modified epoxy acrylate UV resin, is described as offering fast curing, excellent film formation, soft elasticity, high hardness, and good scratch resistance. It has a functionality of 4 and a viscosity of 800–1,500 CPS, with indicated applications including wood, paper, plastic, and metal coatings, inks, OPV, PVD, and 3D printing.

L-6207, a two-functional polyurethane acrylate, is positioned around balanced wear resistance and flexibility, fast curing, and RCA resistance exceeding 200 times. It is indicated for 3C coatings, glass, plastic, and PVD applications.

For applications requiring a combination of hardness, flexibility, and resistance to environmental conditions, L-6390 offers documented water and heat resistance, adhesion, and a balance of flexibility and hardness. Its indicated applications include 3C coatings, DIY adhesives, SPC flooring, nail polish, and 3D printing.

L-6601A is a six-functional polyurethane acrylate described as providing a high curing rate, high hardness and flexibility, and good temperature resistance. L-6601D is a related organotin-free grade with similar hardness-flexibility positioning and a different viscosity profile.

Q4: How do monomers and photoinitiators affect the final result?

The resin cannot be separated from the rest of the formulation. Monomer functionality, type, and concentration can influence cross-link density, shrinkage, hardness, and flexibility. A formulation containing too much highly reactive monomer may cure quickly but become excessively rigid or brittle.

Photoinitiator selection also matters because curing completeness affects the final film properties. The photoinitiator system should be compatible with the curing equipment, wavelength, film thickness, pigments, and resin system. Incomplete curing may reduce hardness and chemical resistance, while an unsuitable curing profile can create an uneven balance between surface hardness and flexibility.

Q5: Does the substrate change the resin selection strategy?

Definitely. A coating for rigid glass or metal may require a different hardness-flexibility balance from a coating applied to leather, TPU, flexible films, or plastic parts.

For example, a hard film on a flexible substrate may crack or lose adhesion during bending. On the other hand, a highly flexible film on a frequently handled plastic surface may show insufficient scratch resistance. Application method, film thickness, surface treatment, and substrate adhesion should therefore be included in the evaluation process.

Q6: How should different candidate resins be compared?

A practical comparison should use the same or carefully controlled formulation conditions. Evaluate hardness and flexibility together with adhesion, scratch resistance, abrasion, impact or bending resistance, shrinkage, chemical resistance, yellowing, and curing completeness.

Lencolo’s technical reference formulations and process parameters are marked “Status: Verified” and “Usage: Reference only.” These references can support preliminary development, but results must be validated under the customer’s actual substrate, application method, film thickness, and curing conditions.

Q7: What is the main principle when balancing hardness and flexibility?

Do not select a UV resin based on one property alone. Start with the substrate and application requirements, then evaluate resin functionality, viscosity, monomer compatibility, photoinitiator selection, and curing conditions as one system.

Lencolo grades such as L-6113, L-6207, L-6390, L-6601A, L-6601D, and L-8403 provide different candidate directions for hardness-flexibility development. The most suitable option should be confirmed through comparative formulation trials rather than assumed from product descriptions alone.

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Guangdong Lencolo New Material Co., Ltd.