How to Reduce Bubbles and Foam in UV Coatings: An Engineer’s Approach

Bubbles and foam are common surface defects in UV-curable coatings, but the solution is not always to add more defoamer. The first question should be where the air is introduced and why it remains trapped before the coating cures.

What usually causes bubbles in UV coatings?

Air can enter a UV coating during high-speed mixing, pigment dispersion, pumping, spraying, or other application processes. High viscosity can then make it difficult for the entrained air to escape.

Pigment and substrate wetting can also play a role. Poor wetting may create surface defects that look similar to bubbles, while insufficient leveling can prevent the coating from forming a uniform film and releasing trapped air.

For this reason, bubbles and foam are usually better treated as a formulation and processing issue, rather than as a single-additive problem.

Is a defoamer enough to solve the problem?

Not always.

Defoamers are designed to control foam and entrained air, but other functional additives may also need to be considered. Wetting additives help improve contact between the coating and substrate, leveling additives support uniform film formation, and dispersants help maintain proper pigment distribution.

The balance between these additives is important. Increasing the dosage of one additive too aggressively can change surface tension and potentially affect adhesion, leveling, slip, recoating, or other surface properties.

The resin system should also be evaluated. UV resin and monomer selection influence viscosity and flow, while the overall formulation balance affects how easily air can leave the wet film.

Why do bubbles sometimes appear only after curing?

A wet coating may look acceptable before exposure but develop bubbles or pinholes after UV or LED curing.

One reason is that UV coatings can cure very quickly. If the film begins to gel before entrapped air has escaped, the bubbles can become locked inside the cured coating. Film thickness, resin viscosity, photoinitiator selection, UV/LED wavelength, and curing intensity can therefore influence the final result.

Observing the coating at different stages—mixing, application, leveling, and curing—can help identify when the defect actually develops.

What should be considered for difficult formulations?

For a specific UV coating, useful information includes the resin and monomer system, substrate, coating method, viscosity, film thickness, mixing conditions, and curing equipment.

This is particularly relevant to high-build UV coatings, SPC/PVC flooring coatings, UV transfer coatings, and high-solids spray systems, where viscosity, wetting, leveling, adhesion, hardness, flexibility, and curing speed can interact.

Lencolo supplies UV resins, monomers, photoinitiators, and functional additives, including solutions for wetting, dispersing, leveling, and defoaming. For more complex systems, evaluating the resin and additive combination under actual processing conditions can be more effective than changing the defoamer alone.

In short, effective bubble control starts with identifying where the air enters the coating and what prevents it from escaping. Once the root cause is clear, the appropriate adjustment may involve additives, resin viscosity, formulation balance, application conditions, or UV/LED curing parameters.

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