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

A: Hardness and flexibility often represent competing requirements in UV curing. A highly cross-linked coating can provide good surface hardness and scratch resistance, but excessive cross-linking may make the cured film brittle. A flexible coating can better tolerate bending or impact, but excessive flexibility may reduce hardness, wear resistance, or surface durability.

UV resin is a major film-forming component, so its chemistry and functionality have a significant influence on the final balance. However, resin selection alone does not determine performance. UV monomers, photoinitiators, additives, pigments or fillers, substrate characteristics, film thickness, and curing conditions all contribute to the final result.

Q: Does a higher-functionality UV resin always provide better hardness?

A: Higher functionality can contribute to a denser cross-linked network after curing, which may increase hardness and surface durability. However, functionality should be selected according to the application rather than simply maximized.

Rigid substrates such as glass, metal, and some PVD surfaces may require higher surface hardness, while flexible substrates such as plastics, leather, or flooring materials may require greater elasticity and adhesion. The objective is therefore not simply maximum hardness, but an appropriate balance between hardness, flexibility, adhesion, and durability.

Q: Which UV resin grades can be evaluated for a hardness-flexibility balance?

A: Several grades in the Lencolo UV resin portfolio can be considered as starting points for comparative formulation testing.

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

L-6207 is a two-functional polyurethane acrylate with viscosity of 28,000–38,000 CPS. It combines wear resistance and flexibility with fast curing and documented RCA resistance above 200 times, and is indicated for 3C coatings, glass, plastics, and PVD.

L-6390 is a four-functional polyurethane acrylate offering water and heat resistance, adhesion, and a documented balance of flexibility and hardness. It is used as a candidate material for 3C coatings, SPC flooring, DIY adhesives, nail products, and 3D printing.

Q: Are there options when both high hardness and flexibility are required at higher functionality?

A: L-6601A is a six-functional polyurethane acrylate positioned around high cure speed, high hardness and flexibility, and temperature resistance. Its viscosity is 2,500–5,000 CPS at 60°C, with applications including PVD, gloss varnish, inks, DIY adhesives, 3D printing, and plastics.

L-6601D is a related organotin-free grade with high hardness and flexibility and a viscosity of 20,000–36,000 CPS. It can be included in comparative testing when an organotin-free formulation is required.

For transfer-coating applications, L-8403 is a two-functional polyurethane acrylate characterized by low shrinkage, flexibility, hardness, and good pigment wettability. Its viscosity is 20,000–50,000 CPS, with indicated uses including adhesives, inks, coating-film transfer, and nail gel.

These products should be regarded as candidate materials rather than automatic final selections.

Q: How do curing conditions affect the hardness-flexibility balance?

A: The same UV resin can produce different results under different curing conditions. Mercury UV, UV LED, Excimer + UV, Dual Cure, Moisture + UV, and UV + Thermal/2K systems can differ in curing depth, surface cure, conversion, and final film properties.

Photoinitiator selection, UV wavelength, curing energy, exposure time, and film thickness should therefore be evaluated together with the resin. Incomplete or uneven curing can reduce surface hardness and alter flexibility even when the resin itself has suitable performance characteristics.

Q: What should be checked before choosing the final UV resin?

A: Technical data provides a useful starting point, but final selection should be based on application testing. Key factors include:

• Hardness and scratch resistance

• Flexibility and bending resistance

• Adhesion to the actual substrate

• Abrasion and chemical resistance

• Curing speed and completeness

• Gloss and surface appearance

• Yellowing and weather resistance

• Viscosity and application behavior

• Film thickness and coating method

For example, spray coating, roller coating, curtain coating, screen printing, offset printing, inkjet, and adhesive applications can place different requirements on viscosity and film formation.

The practical approach is to define the substrate, application method, curing system, target hardness and flexibility, and other critical requirements first. Resin candidates can then be compared through controlled formulation trials. Within Lencolo’s catalog of 167 UV resin grades across 16 product families, grades such as L-6113, L-6207, L-6390, L-6601A, L-6601D, and L-8403 provide different starting points for evaluating hardness-flexibility requirements. Final suitability should always be confirmed under the actual formulation and processing conditions.

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

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