A green alternative for treating coatings
Light-emitting diodes (LEDs) for UV-curing applications have been commercially available since a long time. However, their unique output characteristics require newly formulated UV chemistries to take advantage of many benefits. The EU-funded project 'Energy efficient UV LED curing without inerting' (UV LED) aimed to develop new formulation components to enable UV LED wood coating curing in air. This coating process may surpass conventional line speeds and eliminates the need for inert atmosphere. The cure quality and quantity varies with formulation composition and lamp system. The project approach was to prepare new, high-efficiency near-UV photoinitiator packages. Photoinitiators are additives, which use energy from UV light to treat coatings. To this end, novel photoinitiators and new chemical methods for overcoming oxygen inhibition and producing tack-free surfaces were developed. Scientists identified photoinitiator combinations suitable for use at LED wavelengths based on acyl phosphine oxides and thioxanthones. In combination with some organic compounds, they obtained coatings with reduced tackiness on their surface when cured with a UV LED array. The coating formulation was successfully sprayed onto a medium-density fibreboard using an air-assisted spray gun. Sufficient cure levels were achieved and air did not have any impact on the cure. Scientists used different UV LED array combinations for determining their effect on the model formulation degree of curing, considering also the array intensity and positioning. Finally, a framework was designed to allow the diode arrays to be mounted on a production line for validation and demonstration trials. UV LED is expected to benefit thousands of small- and medium-sized enterprises that produce wood products as they currently face tremendous competition from non-EU imports.
Keywords
Curing, coating, ultraviolet, light-emitting diode, photoinitiator, oxygen inhibition, acyl phosphine oxides, thioxanthones, spray gun
